publicationDate,title,abstract,id
2008-12-07,Current-induced reversal in magnetic nanopillars passivated by silicon,"We demonstrate that magnetic multilayer nanopillars can be efficiently
protected from oxidation by coating with silicon. Both the protected and the
oxidized nanopillars exhibit an increase of reversal current at cryogenic
temperatures. However the magnetic excitation onset current increases only in
the oxidized samples. We show that oxidized nanopillars exhibit anomalous
switching statistics at low temperature, providing a simple test for the
quality of magnetic nanodevices.",0812.1381v1
2017-12-10,Visible evidence to magnetism of graphene oxide,"Graphene oxide continues to amaze scientific community for multiple
potentials in a broad span of applications such as catalysts, adsorbents,
oxidants, etc., determined by constant unveiling of its fantastic natures. Of
them, magnetism is not ultimately identified and directly observed by naked
eyes. Herein, we report graphene oxide directionally migrated and deposited
together simply under external magnetic field from common Nd-Fe-B magnet,
whereas the ferromagnetism of graphene oxide did not exhibit that strong as
iron. Therefore, we illustrated this interesting pathway to keep close to such
2D carbon materials and potentially promoted magnetic-oriented applications.",1712.03570v4
2007-06-20,Oxide spintronics,"Concomitant with the development of metal-based spintronics in the late
1980's and 1990's, important advances were made on the growth of high-quality
oxide thin films and heterostructures. While this was at first motivated by the
discovery of high-temperature superconductivity in perovskite Cu oxides, this
technological breakthrough was soon applied to other transition metal oxides,
and notably mixed-valence manganites. The discovery of colossal
magnetoresistance in manganite films triggered an intense research activity on
these materials, but the first notable impact of magnetic oxides in the field
of spintronics was the use of such manganites as electrodes in magnetic tunnel
junctions, yielding tunnel magnetoresistance ratios one order of magnitude
larger than what had been obtained with transition metal electrodes. Since
then, the research on oxide spintronics has been intense with the latest
developments focused on diluted magnetic oxides and more recently on
multiferroics. In this paper, we will review the most important results on
oxide spintronics, emphasizing materials physics as well as spin-dependent
transport phenomena, and finally give some perspectives on how the flurry of
new magnetic oxides could be useful for next-generation spintronics devices.",0706.3015v1
2010-11-17,Magnetotransport and spin dynamics in an electron gas formed at oxide interfaces,"We investigate the spin-dependent transport properties of a two-dimensional
electron gas formed at oxides' interface in the presence of a magnetic field.
We consider several scenarios for the oxides' properties, including oxides with
co-linear or spiral magnetic and ferroelectric order. For spiral multiferroic
oxides, the magnetoelectric coupling and the topology of the localized magnetic
moments introduce additional, electric field controlled spin-orbit coupling
that affects the magneto-oscillation of the current. An interplay of this
spin-orbit coupling, the exchange field, and of the applied magnetic field
results in a quantum, gate-controlled spin and charge Hall conductance.",1011.3924v1
2009-06-23,Strain-induced ferroelectricity in simple rocksalt binary oxides,"The alkaline earth binary oxides adopt a simple rocksalt structure and form
an important family of compounds because of their large presence in the earth's
mantle and their potential use in microelectronic devices. In comparison to the
class of multifunctional ferroelectric perovskite oxides, however, their
practical applications remain limited and the emergence of ferroelectricity and
related functional properties in simple binary oxides seems so unlikely that it
was never previously considered. Here, we show using first-principles density
functional calculations that ferroelectricity can be easily induced in simple
alkaline earth binary oxides such as barium oxide (BaO) using appropriate
epitaxial strains. Going beyond the fundamental discovery, we show that the
functional properties (polarization, dielectric constant and piezoelectric
response) of such strained binary oxides are comparable in magnitude to those
of typical ferroelectric perovskite oxides, so making them of direct interest
for applications. Finally, we show that magnetic binary oxides such as EuO,
with the same rocksalt structure, behave similarly to the alkaline earth
oxides, suggesting a route to new multiferroics combining ferroelectric and
magnetic properties.",0906.4235v1
2015-12-06,Magnetic properties of bismuth-cobalt oxides doped by erbium,"We synthesized bismuth - cobalt oxide doped by erbium with general formula
Bi3-xErxCoO3-y. Compound has structure of delta-form bismuth oxide. Magnetic
properties of the compound were measured by Faraday's method using quartz
scales in the temperature range of 80-500 K. The magnetic susceptibility and
effective magnetic moment were calculated.",1512.01782v1
2011-10-27,Magnetically Controlling the Explosion of Dirac Fermions during the Oxidation of Graphene,"The different physical properties of multilayered graphene or graphite
relative to single layer graphene result from the Dirac spins symmetry in
graphene and the Pauli spin symmetry in graphite. The Dirac symmetry in
multilayers of graphene (graphite) is hindered by interlayer interactions.
Different magnetizations, electronics and chemistry of graphite and graphene
follow from absence of interlayer interactions in graphene. The distinct
kinetics and dynamics of graphite and graphene by oxidation by the Hummer's
method in weak external magnetic field are observed in this work. Graphite
manifest enhanced non-explosive oxidation of Pauli spins in weak magnetic field
with background paramagnetic oxygen slowing the magnetic acceleration. Graphene
and graphite oxide manifest explosive oxidation and magnetically decelerated
explosive oxidation of Dirac spins in weak magnetic field for temperatures
below 20 oCelsius. The explosive oxidation of graphene and its deceleration in
weak external magnetic field are interpreted resulting from the giant
nonlocality and spin Hall Effect in the chemically reacting graphene. This is
the first identification, analysis and interpretation of the chemistry of the
Dirac spins and the magnetochemistry of relativistic electrons.",1110.6060v1
2018-07-31,Spin absorption at ferromagnetic-metal/platinum-oxide interface,"We investigate the absorption of a spin current at a
ferromagnetic-metal/Pt-oxide interface by measuring current-induced
ferromagnetic resonance. The spin absorption was characterized by the magnetic
damping of the heterostructure. We show that the magnetic damping of a
Ni$_{81}$Fe$_{19}$ film is clearly enhanced by attaching Pt-oxide on the
Ni$_{81}$Fe$_{19}$ film. The damping enhancement is disappeared by inserting an
ultrathin Cu layer between the Ni$_{81}$Fe$_{19}$ and Pt-oxide layers. These
results demonstrate an essential role of the direct contact between the
Ni$_{81}$Fe$_{19}$ and Pt-oxide to induce sizable interface spin-orbit
coupling. Furthermore, the spin-absorption parameter of the
Ni$_{81}$Fe$_{19}$/Pt-oxide interface is comparable to that of intensively
studied heterostructures with strong spin-orbit coupling, such as an oxide
interface, topological insulators, metallic junctions with Rashba spin-orbit
coupling. This result illustrates strong spin-orbit coupling at the
ferromagnetic-metal/Pt-oxide interface, providing an important piece of
information for quantitative understanding the spin absorption and spin-charge
conversion at the ferromagnetic-metal/metallic-oxide interface.",1807.11806v1
2014-06-24,Atomistic calculation of the thickness and temperature dependence of exchange coupling through a dilute magnetic oxide,"The exchange coupling of two magnetic layers via a diffuse oxide interlayer
is studied with an atomistic spin model. We investigate the effect of magnetic
concentration and oxide layer thickness on the effective exchange coupling
strength and find an exponential dependence of the coupling strength on the
oxide thickness without the need for magnetic pinholes. Furthermore we show
that exchange coupling has a strong temperature dependence which is significant
for the reversal dynamics during heat assisted magnetic recording.",1406.6214v1
2023-06-19,Unveiling the nucleation and growth of Zr oxide precipitates of internally oxidized Nb3Sn superconductors,"We report on atomic-scale analyses of nucleation and growth of Zr oxide
precipitates and the microstructural evolution of internally oxidized Nb3Sn
wires for high-field superconducting magnet applications, utilizing atom probe
tomography (APT), transmission electron microscopy (TEM), and first-principles
calculations. APT analyses reveal that prior to interfacial reactions at
Nb/Nb3Sn interfaces, Zr atoms in an unreacted Nb-1Zr-4Ta (at.%) alloy form
clusters with O atoms owing to their high affinity for oxygen and are
segregated at grain boundaries (GBs) in the Nb grains. Then, nucleation of Zr
oxide precipitates occurs in Nb3Sn and at Nb3Sn/Nb interfaces, driven by the
small solubility of Zr and O in Nb3Sn compared to Nb. Quantitative APT and TEM
analyses of Zr oxide precipitates in Nb3Sn layers demonstrate the nucleation,
growth, and coarsening processes of Zr oxide precipitates in Nb3Sn layers. A
high number density of Zr oxide nanoprecipitates is observed in the Nb3Sn
layers, ~10^23 per m^3, with a mean precipitate diam. <10 nm at 625 oC and 700
oC, which provide pinning centers for grain refinement of Nb3Sn, <100 nm diam.,
and serve as pinning sites for fluxons. First-principles calculations and
classical nucleation theory are employed to describe the nucleation of Zr oxide
precipitates in Nb3Sn: energy barriers and the critical radius for nucleation
of Zr oxide precipitates in Nb3Sn. Our research yields the kinetic pathways for
nucleation and growth of Zr oxide precipitates and the microstructural
evolution of Nb3Sn layers, which helps to improve the fabrication process of
internally oxidized Nb3Sn wires for high-field superconducting magnets.",2306.10866v2
2021-11-10,Dependence of magnetic domain patterns on plasma-induced differential oxidation of CoPd thin films,"We demonstrate the evolution of the micro-patterned magnetic domains in CoPd
thin films pretreated with e-beam lithography and O2 plasma. During the
days-long oxidation, significantly different behaviors of the patterned
magnetic domains under magnetization reversal are observed via magneto-optic
Kerr effect microscopy on different days. The evolution of the magnetic
behaviors indicate critical changes in the local magnetic anisotropy energies
due to the Co oxides that evolve into different oxide forms, which are
characterized by micro-area X-ray absorption spectroscopy and X-ray
photoelectron spectroscopy. The coercive field of the area pre-exposed to
plasma can decrease to a value 10 Oe smaller than that unexposed to plasma,
whereas after a longer duration of oxidation the coercive field can instead
become larger in the area pre-exposed to plasma than that unexposed, leading to
an opposite magnetic pattern. Various forms of oxidation can therefore provide
an additional dimension for magnetic-domain engineering to the current
conventional lithographies.",2111.05767v1
2004-10-29,Magnetic properties of polypyrrole - coated iron oxide nanoparticles,"Iron oxide nanoparticles were prepared by sol -gel process. Insitu
polymerization of pyrrole monomer in the presence of oxygen in iron oxide
ethanol suspension resulted in a iron oxide - polypyrrole nanocomposite. The
structure and magnetic properties were investigated for varying pyrrole
concentrations. The presence of the gamma - iron oxide phase and polypyrrole
were confirmed by XRD and FTIR respectively. Agglomeration was found to be
comparatively much reduced for the coated samples, as shown by TEM. AC
susceptibility measurements confirmed the superparamagnetic behaviour.
Numerical simulations performed for an interacting model system are performed
to estimate the anisotropy and compare favourably with experimental results.",0410760v1
2023-10-03,The effect of surface oxidation and crystal thickness on magnetic properties and magnetic domain structures of Cr2Ge2Te6,"Van der Waals (vdW) magnetic materials such as Cr2Ge2Te6 (CGT) show promise
for novel memory and logic applications. This is due to their broadly tunable
magnetic properties and the presence of topological magnetic features such as
skyrmionic bubbles. A systematic study of thickness and oxidation effects on
magnetic domain structures is important for designing devices and vdW
heterostructures for practical applications. Here, we investigate thickness
effects on magnetic properties, magnetic domains, and bubbles in
oxidation-controlled CGT crystals. We find that CGT exposed to ambient
conditions for 5 days forms an oxide layer approximately 5 nm thick. This
oxidation leads to a significant increase in the oxidation state of the Cr
ions, indicating a change in local magnetic properties. This is supported by
real space magnetic texture imaging through Lorentz transmission electron
microscopy. By comparing the thickness dependent saturation field of oxidized
and pristine crystals, we find that oxidation leads to a non-magnetic surface
layer which is thicker than the oxide layer alone. We also find that the stripe
domain width and skyrmionic bubble size are strongly affected by the crystal
thickness in pristine crystals. These findings underscore the impact of
thickness and surface oxidation on the properties of CGT such as saturation
field and domain/skyrmionic bubble size and suggest a pathway for manipulating
magnetic properties through a controlled oxidation process.",2310.02319v2
2005-04-07,Magnetic oxide semiconductors,"Magnetic oxide semiconductors, oxide semiconductors doped with transition
metal elements, are one of the candidates for a high Curie temperature
ferromagnetic semiconductor that is important to realize semiconductor
spintronics at room temperature. We review in this paper recent progress of
researches on various magnetic oxide semiconductors. The magnetization,
magneto-optical effect, and magneto-transport such as anomalous Hall effect are
examined from viewpoint of feasibility to evaluate the ferromagnetism. The
ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.",0504168v1
2010-11-10,Repair of magnetism in oxidized graphene nanoribbons,"Novel route for the establishing of magnetism in realistic oxidized graphene
nanoribbons is proposed. Modelling of the migration of hydroxyl groups from
central part to the zig-zag edges of graphene nanoribbons passivated by oxygen
are performed with using density functional theory. The presence of hydroxyl
groups near the edges leads formation of dangling bonds there instead saturated
due to oxidation and repairs of magnetism diminished by edges oxidation. The
route of manufacturing and stability of new type of magnetic graphene
nanoribbons are also discussed.",1011.2342v1
2017-03-19,Surface anisotropy of iron oxide nanoparticles and slabs from first principles : influence of coatings and ligands as a test of the Heisenberg model,"We performed ab initio computations of the magnetic properties of simple iron
oxide clusters and slabs. We considered an iron oxide cluster functionalized by
a molecule or glued to a gold cluster of the same size. We also considered a
magnetite slab coated by cobalt oxide or a mixture of iron oxide and cobalt
oxide. The changes in magnetic behavior were explored using constrained
magnetic calculations. A possible value for the surface anisotropy was
estimated from the fit of a classical Heisenberg model on ab initio results.
The value was found to be compatible with estimations obtained by other means,
or inferred from experimental results. The addition of a ligand, coating, or of
a metallic nanoparticle to the systems degraded the quality of the description
by the Heisenberg Hamiltonian. Proposing a change in the anisotropies allowing
for the proportion of each transition atom we could get a much better
description of the magnetism of series of hybrid cobalt and iron oxide systems.",1703.06414v1
2015-09-06,Electrical control of magnetism in oxides,"This review article aims at illustrating the recent progresses in the
electrical control of magnetism in oxides with profound physics and enormous
potential applications. In the first part, we provide a comprehensive summary
of the electrical control of magnetism in the classic multiferroic
heterostructures and clarify their various mechanisms lying behind. The second
part focuses on the novel route of electric double layer gating for driving a
significantly electronic phase transition in magnetic oxides by a small
voltage. The electric field applied on the ordinary dielectric oxide in the
third part is used to control the magnetic phenomenon originated from the
charge transfer and orbital reconstruction at the interface between dissimilar
correlated oxides. At last, we analyze the challenges in electrical control of
magnetism in oxides, both on mechanism and practical application, which would
inspire more in-depth researches and advance the development in this field.",1509.01795v1
2011-12-04,Spintronic oxides grown by laser-MBE,"The recent study of oxides led to the discovery of several new fascinating
physical phenomena. High-temperature superconductivity, colossal
magnetoresistance, dilute magnetic doping, or multiferroicity were discovered
and investigated in transition-metal oxides, representing a prototype class of
strongly correlated electronic systems. This development was accompanied by an
enormous progress regarding thin film fabrication. Within the past two decades,
epitaxial thin films with crystalline quality approaching semiconductor
standards became available using laser molecular beam epitaxy. This evolution
is reviewed, particularly with emphasis on transition-metal oxide thin films,
their versatile physical properties, and their impact on the field of
spintronics. First, the physics of ferromagnetic half-metallic oxides, such as
the doped manganites, the double perovskites and magnetite is presented
together with possible applications based on magnetic tunnel junctions. Second,
the wide bandgap semiconductor zinc oxide is discussed particularly with regard
to the controversy of dilute magnetic doping with transition-metal ions and the
possibility of realizing p-type conductivity. Third, the field of oxide
multiferroics is presented with the recent developments in single-phase
multiferroic thin film perovskites as well as in composite multiferroic
hybrids.",1112.0751v1
2020-04-25,"Effects of Oxidation of Top and Bottom Interfaces on the Electric, Magnetic, and Spin-Orbit Torque Properties of Pt/Co/AlOx Trilayers","Oxidation strongly influences the properties of magnetic layers employed in
spintronic devices. We study the effect of oxidation on the structural,
magnetic, and electrical properties as well as current-induced spin-orbit
torques (SOTs) in Pt/Co/AlOx, Pt/CoOx/Co/AlOx, and PtOx/Co/AlOx layers. We show
how the saturation magnetization, perpendicular magnetic anisotropy, anomalous
Hall resistance, and SOT are systematically affected by the degree of oxidation
of both the Pt/Co and Co/Al interfaces. Oxidation of the Co/Al interface
results in a 21% and 42% variation of the dampinglike and fieldlike SOT
efficiencies, which peak at 0.14 and 0.07, respectively. The insertion of a
paramagnetic CoOx layer between Pt and Co maintains a very strong perpendicular
magnetic anisotropy and improves the dampinglike and fieldlike SOT
efficiencies, up to 0.26 and 0.20, respectively. In contrast with recent
reports, we do not find that the oxidation of Pt leads to a significant
enhancement of the torques. Rather, we find that oxygen migrates from Pt to the
Co and Al layers, leading to a time-dependent oxidation profile and an
effective spin Hall conductivity that decreases with increasing oxygen
concentration. Finally, we study current-induced switching in Pt/Co/AlOx with
different degrees of oxidation and find a linear relationship between the
critical switching current and the effective magnetic anisotropy controlled by
the oxidation of Al. These results highlight the importance of interfaces and
oxidation effects on the SOT and magnetotransport properties of heavy
metal/ferromagnet/oxide trilayers and provide information on how to improve the
SOT efficiency and magnetization-switching characteristics of these systems.",2004.12115v1
2020-11-20,An Investigation of Commercial Iron Oxide Nanoparticles: Advanced Structural and Magnetic Properties Characterization,"Magnetic nanoparticles (MNPs) have been extensively used as tiny heating
sources in magnetic hyperthermia therapy, contrast agents in magnetic resonance
imaging (MRI), tracers in magnetic particle imaging (MPI), carriers for
drug/gene delivery, etc. There have emerged many magnetic
nanoparticle/microbeads suppliers since the last decade, such as Ocean
NanoTech, Nanoprobes, US Research Nanomaterials, Miltenyi Biotec, micromod
Partikeltechnologie GmbH, and nanoComposix, etc. In this paper, we report the
physical and magnetic characterizations on iron oxide nanoparticle products
from Ocean NanoTech. Standard characterization tools such as Vibrating-Sample
Magnetometer (VSM), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS),
Transmission Electron Microscopy (TEM), and Zeta Potential Analyzer are used to
provide magnetic nanoparticle customers and researchers with an overview of
these iron oxide nanoparticle products. In addition, the dynamic magnetic
responses of these iron oxide nanoparticles in aqueous solutions are
investigated under low and high frequency alternating magnetic fields, giving a
standardized operating procedure for characterizing the MNPs from Ocean
NanoTech, thereby yielding the best of magnetic nanoparticles for different
applications.",2011.10215v1
2023-04-01,High-quality NiFe thin films on oxide/non-oxide platforms via pulsed laser deposition at room temperature,"Soft ferromagnetic NiFe thin films are promising for applications in
spintronic devices because of their constituent electrical and magnetic
properties. Electron beam evaporation and sputtering techniques have been used
to deposit NiFe thin films. For in-situ stacking of NiFe with functional
complex oxides, the pulsed laser deposition (PLD) method is highly desirable.
However, the growth of high-quality NiFe (and non-oxide thin films in general)
by PLD remains a formidable task. Here, we report high-quality NiFe thin films
of various thicknesses on oxide/non-oxide substrates with desirable magnetic
properties by PLD at room temperature. The magnetic properties are found to be
strongly dependent on the laser fluence of the deposition process. The laser
fluence of 4 Joule/cm$^2$ produces the highest magnetization of ~547 emu/cc.
The small coercivity (few Oersted) and sharp ferromagnetic switching behaviour
indicate uniaxial anisotropy with an easy axis along the in-plane direction. In
addition, thickness-dependent magnetodynamics characterizations are studied via
ferromagnetic resonance. Our findings indicate the ferromagnetic
characteristics are sensitive to the quality of the oxide/non-oxide substrate
surface. These results offer significant insight into the PLD-based development
of thin metal magnetic films.",2304.00357v1
2010-04-30,Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2,"Single-crystal neutron diffraction has been used to determine the
incommensurate magnetic structure of NaCu2O2, a compound built up of chains of
edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice
symmetry were identified by a group-theoretical analysis, and their magnetic
structure factors were compared to the experimentally observed Bragg
intensities. In conjunction with other experimental data, this analysis yields
an elliptical helix structure in which both the helicity and the polarization
plane alternate among copper-oxide chains. This magnetic ground state is
discussed in the context of the recently reported multiferroic properties of
other copper-oxide chain compounds.",1004.5526v1
2020-04-02,Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide,"Magnetic Weyl fermions, which occur in magnets, have novel transport
phenomena related to pairs of Weyl nodes, and they are, of both, scientific and
technological interest, with the potential for use in high-performance
electronics, spintronics and quantum computing. Although magnetic Weyl fermions
have been predicted to exist in various oxides, evidence for their existence in
oxide materials remains elusive. SrRuO3, a 4d ferromagnetic metal often used as
an epitaxial conducting layer in oxide heterostructures, provides a promising
opportunity to seek for the existence of magnetic Weyl fermions. Advanced oxide
thin film preparation techniques, driven by machine learning technologies, may
allow access to such topological matter. Here we show direct quantum transport
evidence of magnetic Weyl fermions in an epitaxial ferromagnetic oxide SrRuO3:
unsaturated linear positive magnetoresistance (MR), chiral-anomaly-induced
negative MR, Pi Berry phase accumulated along cyclotron orbits, light cyclotron
masses and high quantum mobility of about 10000 cm2/Vs. We employed
machine-learning-assisted molecular beam epitaxy (MBE) to synthesize SrRuO3
films whose quality is sufficiently high to probe their intrinsic quantum
transport properties. We also clarified the disorder dependence of the
transport of the magnetic Weyl fermions, and provided a brand-new diagram for
the Weyl transport, which gives a clear guideline for accessing the
topologically nontrivial transport phenomena. Our results establish SrRuO3 as a
magnetic Weyl semimetal and topological oxide electronics as a new research
field.",2004.00810v2
1997-08-22,Estimation of the Doping Dependence of Antiferromagnetism in the Copper Oxide Material,"Within the $t$-$J$ model, we study the doping dependence of
antiferromagnetism in the copper oxide materials by considering quantum
fluctuations of spinons in the random-phase-approximation. The staggered
magnetization vanishes around doping $\delta=5%$ for a reasonable parameter
value $t/J=5$, which is in agreement with the experiments on copper oxide
materials.",9708176v1
2012-01-26,Superconductivity in the metallic-oxidized magnesium interface,"Metastable superconductivity at 39 - 54 K in the interfaces formed by
metallic and oxidized magnesium (MgO) has been observed by ac magnetic
susceptibility measurements. The superconducting interfaces have been produced
by the surface oxidation of metallic magnesium under special conditions.",1201.5468v1
2003-05-19,Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics,"A review is given for the recent progress of research in the field of
oxide-based diluted magnetic semiconductor (DMS), which was triggered by
combinatorial discovery of transparent ferromagnet. The possible advantages of
oxide semiconductor as a host of DMS are described in comparison with
conventional compound semiconductors. Limits and problems for identifying novel
ferromagnetic DMS are described in view of recent reports in this field.
Several characterization techniques are proposed in order to eliminate
unidentified ferromagnetism of oxide-based DMS (UFO). Perspectives and possible
devices are also given.",0305435v1
2013-02-14,Anamolous reduction of magnetic coercivity of graphene oxide and reduced graphene oxide upon cooling,"In this report we present the temperature evolution of magnetic coercivity of
graphene oxide (GO) and reduced graphene oxide (RGO). We report an anamolous
decrease in coercivity of GO and RGO with decreasing temperature. We could
explain this anamolous behavior invoking the inherent presence of ripple in
graphene. We observe antiferromagnetic and ferromagnetic behavior at room
temperature for GO and RGO respectively, but at low temperatures both shows
paramagnetic behavior.",1302.3336v1
2022-07-13,Boosting spin-orbit torque efficiency in spin-current generator/magnet/oxide superlattices,"Efficient manipulation of magnetic materials is essential for spintronics. In
spin-current generator/magnet bilayers, the efficiency of spin-orbit torques
per magnetic layer thickness scales inversely with the magnetic layer
thickness, leading to considerable power increase in applications with large
magnetic layer thickness. Here, we develop a 3D spin-orbit material scheme in
which the spin torque efficiency can be remarkably boosted up by stacking
[spin-current generator/magnet/oxide]n superlattices, with the oxide layers
breaking the inversion symmetry. In contrast, the spin torque diminishes in
[spin-current generator/magnet]n superlattices lacking inversion symmetry
breaking. These results advances the understanding of spin-orbit torques in
magnetic multilayers and establishes spin-current generator/magnet/oxide
superlattices as advantageous bricks for development of high energy-efficiency,
high-endurance, and high-density spintronic memory and computing.",2207.05968v2
2016-06-28,Termination control of magnetic coupling at a complex oxide interface,"Atomically flat interfaces between ternary oxides have chemically different
variants, depending on the terminating lattice planes of both oxides.
Electronic properties change with the interface termination which affects, for
instance, charge accumulation and magnetic interactions at the interface.
Well-defined terminations have yet rarely been achieved for oxides of ABO3 type
(with metals A, B). Here, we report on a strategy of thin film growth and
interface characterization applied to fabricate the La0.7Sr0.3MnO3-SrRuO3
interface with controlled termination. Ultra-strong antiferromagnetic coupling
between the ferromagnets occurs at the MnO2-SrO interface, but not for the
other termination, in agreement with density functional calculations. X-ray
magnetic circular dichroism measurements reveal coupled reversal of Mn and Ru
magnetic moments at the MnO2-SrO interface. Our results demonstrate termination
control of magnetic coupling across a complex oxide interface and provide a
pathway for theoretical and experimental explorations of novel electronic
interface states with engineered magnetic properties.",1606.08687v1
2018-04-06,Magnetic exchange fields and domain wall superconductivity at an all-oxide superconductor / ferromagnet insulator interface,"At a superconductor-ferromagnet (S/F) interface, the F layer can introduce a
magnetic exchange field within the S layer, which acts to locally spin split
the superconducting density of states. The effect of magnetic exchange fields
on superconductivity has been thoroughly explored at S-ferromagnet insulator
(S/FI) interfaces for isotropic s-wave S and a thickness that is smaller than
the superconducting coherence length. Here we report a magnetic exchange field
effect at an all-oxide S/FI interface involving the anisotropic d-wave high
temperature superconductor praseodymium cerium copper oxide (PCCO) and the FI
praseodymium calcium manganese oxide (PCMO). The magnetic exchange field in
PCCO, detected via magnetotransport measurements through the superconducting
transition, is localized to the PCCO/PCMO interface with an average magnitude
that depends on the presence or absence of magnetic domain walls in PCMO. The
results are promising for the development of all-oxide superconducting
spintronic devices involving unconventional pairing and high temperature
superconductors.",1804.02094v2
2020-01-31,Magnetic properties of rare earth and transition metal based perovskite type high entropy oxides,"High entropy oxides (HEO) are a recently introduced class of oxide materials,
which are characterized by a large number of elements (i.e. five or more)
sharing one lattice site which crystallize in a single phase structure. One
complex example of the rather young HEO family are the rare-earth transition
metal perovskite high entropy oxides. In this comprehensive study, we provide
an overview over the magnetic properties of three perovskite type high entropy
oxides. The compounds have a rare-earth site which is occupied by five
different rare-earth elements, while the transition metal site is occupied by a
single transition metal. In this way a comparison to the parent binary oxides,
namely the orthocobaltites, -chromites and -ferrites is possible. X-ray
absorption near edge spectroscopy (XANES), magnetometry and M\""ossbauer
spectroscopy are employed to characterize these complex materials.
  In general, we find surprising similarities to the magnetic properties of the
binary oxides, despite the chemical disorder on the rare-earth site. However
distinct differences and interesting magnetic properties are also observed such
as noncollinearity, spin reorientation transitions as well as large coercive
fields of up to 2\,T at ambient temperature. Both the chemical disorder on the
RE A-site, and the nature of the TM on the B-site play an important role in the
physical properties of these high entropy oxides.",2002.00026v1
2019-08-06,The complex non-collinear magnetic orderings in Ba2YOsO6: A new approach to tuning spin-lattice interactions and controlling magnetic orderings in frustrated complex oxides,"Frustrated magnets are one class of fascinating materials that host many
intriguing phases such as spin ice, spin liquid and complex long-range magnetic
orderings at low temperatures. In this work we use first-principles
calculations to find that in a wide range of magnetically frustrated oxides, at
zero temperature a number of non-collinear magnetic orderings are more stable
than the type-I collinear ordering that is observed at finite temperatures. The
emergence of non-collinear orderings in those complex oxides is due to
higher-order exchange interactions that originate from second-row and third-row
transition metal elements. This implies a collinear-to-noncollinear spin
transition at sufficiently low temperatures in those frustrated complex oxides.
Furthermore, we find that in a particular oxide Ba$_2$YOsO$_6$, experimentally
feasible uniaxial strain can tune the material between two different
non-collinear magnetic orderings. Our work predicts new non-collinear magnetic
orderings in frustrated complex oxides at very low temperatures and provides a
mechanical route to tuning complex non-collinear magnetic orderings in those
materials.",1908.01916v1
2021-08-30,Magnetic Suboxides as a Source of Two-Level System Losses in Superconducting Niobium,"We identify one potential source of quantum decoherence in three-dimensional
superconducting radio-frequency (SRF) resonators and two-dimensional transmon
qubits that utilize oxidized niobium: magnetic suboxides which drive two-level
system (TLS) losses. By probing the effect of sequential \textit{in situ}
vacuum baking treatments on the RF peformance of bulk Nb SRF resonators and on
the oxide structure of a representative Nb sample within a time-of-flight
secondary ion mass spectrometer (TOF-SIMS), we find a non-monotonic evolution
of cavity quality factor $Q_0$ which correlates with the interplay of
TLS-hosting magnetic suboxide generation and oxide dissolution. We localize
this effect to the oxide itself and present the non-role of diffused
interstitial oxygen in the underlying Nb by regrowing a new oxide \textit{via}
chemistry and wet oxidation which reveals a mitigation of aggravated TLS
losses.",2108.13352v2
2022-08-25,Berry curvature induced anomalous Hall conductivity in magnetic topological oxide double perovskite Sr2FeMoO6,"Oxide materials exhibit several novel structural, magnetic, and electronic
properties. Their stability under ambient conditions, easy synthesis, and high
transition temperatures provide such systems with an ideal ground for realizing
topological properties and real-life technological applications. However,
experimental evidence of topological states in oxide materials is rare. In this
study, we have synthesized single crystals of oxide double perovskite Sr2FeMoO6
and revealed its topological nature by investigating its structural, magnetic,
and electronic properties. We observed that the system crystallized in the
cubic space group Fm-3m, which is a half-metallic ferromagnet. Transport
measurements show an anomalous Hall effect, and it is evident that the Hall
contribution originates from the Berry curvature. Assuming a shift of the Fermi
energy towards the conduction band, the contribution of the anomalous Hall
effect is enhanced owing to the presence of a gaped nodal line. This study can
be used to explore and realize the topological properties of bulk oxide
systems.",2208.11988v1
2022-09-14,Absence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles,"We present a detailed atomistic picture of the oxidation mechanism of Co
nanoparticles and its impact on magnetism by experimentally following the
evolution of the structure, chemical composition, and magnetism of individual,
gas-phase grown Co nanoparticles during controlled oxidation. The early stage
oxidation occurs in a twostep process characterized by (i) the initial
formation of small CoO crystallites randomly distributed across the
nanoparticle surface, until their coalescence leads to structural completion of
the oxide shell and passivation of the metallic core; (ii) progressive
conversion of the CoO shell to Co3O4, accompanied by void formation due to the
nanoscale Kirkendall effect. The Co nanoparticles remain highly reactive toward
oxygen during phase (i), demonstrating the absence of a pressure gap whereby a
low reactivity at low pressures is postulated. Our results provide an important
benchmark for an improved understanding of the magnetism of oxidized cobalt
nanoparticles, with potential implications on their performance in catalytic
reactions.",2209.06949v1
2020-06-11,Embracing defects and disorder in magnetic nanoparticles,"Iron oxide nanoparticles have tremendous scientific and technological
potential in a broad range of technologies, from energy applications to
biomedicine. To improve their performance, single-crystalline and defect-free
nanoparticles have thus far been aspired. However, in several recent studies
defect-rich nanoparticles outperform their defect-free counterparts in magnetic
hyperthermia and magnetic particle imaging. Here, an overview on the
state-of-the-art of design and characterization of defects and resulting spin
disorder in magnetic nanoparticles is presented with a focus on iron oxide
nanoparticles. The beneficial impact of defects and disorder on intracellular
magnetic hyperthermia performance of magnetic nanoparticles for drug delivery
and cancer therapy is emphasized. Defect-engineering in iron oxide
nanoparticles emerges to become an alternative approach to tailor their
magnetic properties for biomedicine, as it is already common practice in
established systems such as semiconductors and emerging fields including
perovskite solar cells. Finally, perspectives and thoughts are given on how to
deliberately induce defects in iron oxide nanoparticles and their potential
implications for magnetic tracers to monitor cell therapy and immunotherapy by
magnetic particle imaging.",2006.06474v1
2019-04-22,Stripe structures in phase separated magnetic oxides,"We investigate the phase separated inhomogeneous charge and spin states in
magnetic oxides. In particular, we study one dimensional harmonic waves and
stripe structures. We show that harmonic spin charge waves are unstable and
inevitably transform into two or three dimensional structures, while the stripe
structures can be stable for certain parameters. Such stripe structures may
allow the control of magnetic state with electric field in a magnetic oxide
thin film.",1904.10053v1
1997-06-06,Charge Fluctuations and Magnetic Inelastic Neutron Scattering in Copper-Oxide high -Tc superconductors,"Spin subsystem of the copper oxides within the polar Jahn-Teller centers
model corresponds to a singlet-triplet magnet where the local boson movement
accompanied by the induced longitudinal spin fluctuations. These fluctuations
determine the features of the magnetic inelastic scattering in the high-Tc
cuprates.",9706054v1
2001-10-15,"Synthesis, Crystal Structure and Magnetic Properties of the Linear-Chain Cobalt Oxide Sr5Pb3CoO12","The novel spin-chain cobalt oxide Sr5Pb3CoO12 [P-62m, a = 10.1093(2) A and c
= 3.562 51(9) A at 295 K] is reported. Polycrystalline sample of the compound
was studied by neutron diffraction (at 6 and 295 K) and magnetic susceptibility
measurements (5 to 390 K). The cobalt oxide was found to be analogous to the
copper oxide Sr5Pb3CoO12, which is comprised of magnetic-linear chains at
inter-chain distance of 10 A. Although the cobalt oxide chains (mu_eff of 3.64
mu_B per Co) are substantially antiferromagnetic (theta_W = -38.8 K), neither
low-dimensional magnetism nor long-range ordering has been found; a
local-structure disorder in the chains might impact on the magnetism. This
compound is highly electrically insulating.",0110292v1
2021-01-19,Tunable Rashba spin-orbit coupling and its interplay with multiorbital effect and magnetic ordering at oxide interfaces,"The complex oxide heterostructures such as LaAlO3/SrTiO3 (LAO/STO) interface
are paradigmatic platforms to explore emerging multi-degrees of freedom
coupling and the associated exotic phenomena. In this study, we reveal the
effects of multiorbital and magnetic ordering on Rashba spin-orbit coupling
(SOC) at the LAO/STO (001) interface. Based on first-principles calculations,
we show that the Rashba spin splitting near the conduction band edge can be
tuned substantially by the interfacial insulator-metal transition due to the
multiorbital effect of the lowest t_2g bands. We further unravel a competition
between Rashba SOC and intrinsic magnetism, in which the Rashba SOC induced
spin polarization is suppressed by the interfacial magnetic ordering. These
results deepen our understanding of intricate electronic and magnetic
reconstruction at the perovskite oxide interfaces and shed light on the
engineering of oxide heterostructures for all-oxides-based spintronic devices.",2101.07586v1
2008-03-25,Superconductivity at 43 K in Samarium-arsenide Oxides $SmFeAsO_{1-x}F_x$,"Since the discovery of high-transition temperature ($T_c$) superconductivity
in layered copper oxides, extensive efforts have been devoted to explore the
higher $T_c$ superconductivity. However, the $T_c$ higher than 40 K can be
obtained only in the copper oxide superconductors so far. The highest reported
value of $T_c$ for non-copper-oxide bulk superconductivity is 39 K in
$MgB_2$.\cite{jun} The $T_c$ of about 40 K is close to or above the theoretical
value predicted from BCS theory.\cite{mcmillan} Therefore, it is very
significant to search for non-copper oxide superconductor with the transition
temperature higher than 40 K to understand the mechanism of high-$T_c$
superconductivity. Here we report the discovery of bulk superconductivity in
samarium-arsenide oxides $SmFeAsO_{1-x}F_x$ with ZrCuAiAs type structure.
Resistivity and magnetization measurements show strong evidences for transition
temperature as high as 43 K. $SmFeAsO_{1-x}F_x$ is the first non-copper oxide
superconductor with $T_c$ higher than 40 K. The $T_c$ higher than 40 K may be a
strong argument to consider $SmFeAsO_{1-x}F_x$ as an unconventional
superconductor.",0803.3603v2
2020-03-09,Chemical instability of free-standing boron monolayers and properties of oxidized borophene sheets,"In this work we report results of step-by-step modeling of the oxidation of
free-standing boron monolayers of different types. Results of the calculations
demonstrate that the process of the oxidation is always exothermic and lead
toward the formation of foam-like boron oxide films with incorporated
non-oxidized small boron clusters. Some of these boron-oxide films demonstrate
the presence of chemically stable magnetic centers. Evaluation of the physical
properties of oxidized boprophene sheets (OBS) demonstrate it possible
application in solar energy, as sensors and coating against leakage of
hydrogen.",2003.03937v1
2024-04-02,Quantum Hall effect in a CVD-grown oxide,"Two-dimensional electron systems (2DES) are promising for investigating
correlated quantum phenomena. In particular, 2D oxides provide a platform that
can host various quantum phases such as quantized Hall effect,
superconductivity, or magnetism. The realization of such quantum phases in 2D
oxides heavily relies on dedicated heterostructure growths. Here we show the
integer quantum Hall effect achieved in chemical vapor deposition grown Bi2O2Se
- a representative member of a more accessible oxide family. A single or few
sub-band 2DES can be prepared in thin films of Bi2O2Se, where the film
thickness acts as the sole design parameter and the sub-band occupation is
determined by the electric field effect. This new oxide platform exhibits
characteristic advantages in structural flexibility due to its layered nature,
making it suitable for scalable growth. The unique small mass distinguishes
Bi2O2Se from other high-mobility oxides, providing a new platform for exploring
quantum Hall physics in 2D oxides.",2404.02104v1
2022-12-29,Magnetic oxides,"In this article we give a general survey of the main properties of magnetic
oxides - mostly the oxides of transition metals, but sometime also containing
rare earths ions. This is a very rich class of materials, among which there are
insulators and metals, systems with insulator-metal transitions, and there are
among them even high-temperature superconductors. One of the main features of
these compounds, which attract to them special attention and which serve as a
basis of many applications, are their rich magnetic properties. In this article
we discuss the main physical effects determining their behaviour, and describe
in detail especially their magnetic properties, but not only. After shortly
discussing the basic structure of isolated magnetic ions, we concentrate on the
collective effects depending on the interaction between sites, especially
exchange interaction, giving rise to different magnetic properties: different
types of magnetic ordering in conventional systems, but also more exotic states
such as spin liquid states in frustrated systems. We also cover related
phenomena in magnetic oxides, such as magnetoelectric and multiferroic
behaviour, and discuss at the end their diverse useful properties serving as a
basis of many applications.",2212.14176v1
2019-12-03,Contact resistivity due to oxide layers between two REBCO tapes,"In a no-insulation (NI) REBCO magnet, the turn-to-turn contact resistivity
(Rc) determines its quench self-protection capability, charging delay time and
the energy loss during field ramps. Therefore it is critically important to be
able to control a range of Rc values suitable for various NI magnet coils. We
used a commercial oxidizing agent Ebonol C to treat the copper surface of REBCO
tapes. The copper oxide layer was characterized by cross-sectional transmission
electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The oxide
layer formed in Ebonol C at 98 {\deg}C for 1 min is Cu2O of about 0.5 um. The
Rc between two oxidized REBCO is in the order of 35 mOhm-cm2 at 4.2 K which
decreases slowly with contact pressure cycles. The Rc increases but only
slightly at 77 K. We also investigated the effect of oxidation of stainless
steel co-wind tape on Rc. The native oxides on 316 stainless steel tape as well
as those heated in air at 200 - 600 {\deg}C were examined by TEM and XPS. The
native oxides layer is about 3 nm thick. After heating at 300 {\deg}C for 8 min
and 600 {\deg}C for 1 min, its thickness increases to about 10 and 30 nm
respectively. For the stainless steel tapes with about 10 nm surface oxides,
pressure cycling for 30,000 cycles decreases Rc by almost 4 orders of
magnitude. Whereas at 77 K, it only changes slightly. For a surface with 30 nm
oxide, the Rc decreases moderately with load cycles. The results suggest that
for an oxidized stainless steel to achieve stable Rc over large number of load
cycles a relatively thick oxide film is needed.",1912.01515v1
2022-08-09,Valence state and lattice incorporation of Ni in Zn/Co-based magnetic oxides,"Ni incorporation has been studied in a comprehensive range of Zn/Co-based
magnetic oxides to elucidate it valence state and lattice incorporation. The
resulting structural and magnetic properties are studied in detail. To the one
end Ni in incorporated by in-diffusion as well as reactive magnetron
co-sputtering in wurtzite ZnO where only the Ni-diffused ZnO exhibits
significant conductivity. This is complemented by Ni and Co codoping of ZnO
leading. To the other end, the ZnCo$_2$O$_4$ spinel is co-doped with varying
amounts of Ni. In the wurtzite oxides Ni is exclusively found on tetrahedral
lattice sites in its formal 2+ oxidation state as deep donor. It behaves as an
anisotropic paramagnet and a limited solubility of Ni about 10\% is found. Due
to its smaller magnetic moment it can induce partial uncompensation of the Co
magnetic moments due to antiferromagnetic coupling. In the spinel Ni is found
to be incorporated in its formal 3+ oxidation state on octahedral sites and
couples antiferromagnetically to the Co moments leading again to magnetic
uncompensation of the otherwise antiferromagnetic ZnCo$_2$O$_4$ spinel and to
ferrimagnetism at higher Ni concentrations. Increasing Ni even further leads to
phase separation of cubic NiO resulting in an exchange-biased composite
magnetic oxide.",2208.11086v1
2007-04-16,Enhanced Half-Metallicity in Edge-Oxidized Zigzag Graphene Nanoribbons,"We present a novel comprehensive first-principles theoretical study of the
electronic properties and relative stabilities of edge-oxidized zigzag graphene
nanoribbons. The oxidation schemes considered include hydroxyl, carboxyl,
ether, and ketone groups. Using screened exchange density functional theory, we
show that these oxidized ribbons are more stable than hydrogen-terminated
nanoribbons except for the case of the etheric groups. The stable oxidized
configurations maintain a spin-polarized ground state with antiferromagnetic
ordering localized at the edges, similar to the fully hydrogenated
counterparts. More important, edge oxidation is found to lower the onset
electric field required to induce half-metallic behavior and extend the overall
field range at which the systems remain half-metallic. Once the half-metallic
state is reached, further increase of the external electric field intensity
produces a rapid decrease in the spin magnetization up to a point where the
magnetization is quenched completely. Finally, we find that oxygen containing
edge groups have a minor effect on the energy difference between the
antiferromagnetic ground state and the above-lying ferromagnetic state.",0704.2043v1
2014-08-14,Emergent properties hidden in plane view: Strong electronic correlations at oxide interfaces,"Finding new collective electronic states in materials is one of the
fundamental goals of condensed matter physics. Atomic-scale superlattices
formed from transition metal oxides are a particularly appealing hunting ground
for new physics. In bulk form, transition metal oxides exhibit a remarkable
range of magnetic, superconducting, and multiferroic phases that are of great
scientific interest and are potentially capable of providing innovative energy,
security, electronics and medical technology platforms. In superlattices new
states may emerge at the interfaces where dissimilar materials meet.
  Here we illustrate the essential features that make transition metal
oxide-based heterostructures an appealing discovery platform for emergent
properties with a few selected examples, showing how charge redistributes,
magnetism and orbital polarization arises and ferroelectric order emerges from
heterostructures comprised of oxide components with nominally contradictory
behavior with the aim providing insight into the creation and control of novel
behavior at oxide interfaces by suitable mechanical, electrical or optical
boundary conditions and excitations.",1408.3173v2
2016-08-03,Moiré-free ultrathin iron oxide film: FeO(111) on Ag(111),"Ultrathin iron oxide films epitaxially grown on the (111)- and
(0001)-oriented metal single crystal supports exhibit unique electronic,
catalytic and magnetic properties not observed for the corresponding bulk
oxides. These properties originate mainly from the presence of Moir\'e
superstructures which, in turn, disqualify ultrathin films as model systems
imitating bulk materials. We present a route for the preparation of a
close-packed Moir\'e-free ultrathin iron oxide film, namely FeO(111) on
Ag(111). Experimental scanning tunneling microscopy (STM), low energy electron
diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) results confirm
perfect structural order in the film. Density functional theory (DFT)-based
calculations suggest full relaxation of the oxide layer that adopts the atomic
lattice of the crystalline support and exhibits properties similar to those of
a free-standing FeO. The results open new pathways for model-type studies of
electronic, catalytic and magnetic properties of fully-relaxed iron oxide films
and related systems.",1608.01376v2
2021-05-20,Magnetic avalanche of non-oxide conductive domain walls,"Atomically sharp domain walls (DWs) in ferroelectrics are considered as an
ideal platform to realize easy-to-reconfigure nanoelectronic building blocks,
created, manipulated and erased by external fields. However, conductive DWs
have been exclusively observed in oxides, where DW mobility and conductivity is
largely influenced by stoichiometry and defects. In contrast, we here report on
conductive DWs in the non-oxide ferroelectric GaV$_4$S$_8$, where charge
carriers are provided intrinsically by multivalent V$_4$ molecular clusters. We
show that this new mechanism gives rise to DWs composed of nanoscale stripes
with alternating electron and hole conduction, unimaginable in oxides. By
exerting magnetic control on these segments we promote the mobile and
effectively 2D DWs into dominating the 3D conductance, triggering abrupt
conductance changes as large as eight orders of magnitude. The flexible
valency, as origin of these novel hybrid DWs with giant conductivity,
demonstrates that non-oxide ferroelectrics can be the source of novel phenomena
beyond the realm of oxide electronics.",2105.09659v1
2006-07-18,Dielectric breakdown in underoxidized magnetic tunnel junctions: Dependence on oxidation time and area,"Magnetic tunnel junctions (MTJs) with partially oxidized 9 \AA
AlO$_x$-barriers were recently shown to have the necessary characteristics to
be used as magnetoresistive sensors in high-density storage devices. Here we
study dielectric breakdown in such underoxidized magnetic tunnel junctions,
focusing on its dependence on tunnel junction area and oxidation time. A clear
relation between breakdown mechanism and junction area is observed for the MTJs
with the highest studied oxidation time: samples with large areas fail usually
due to extrinsic causes (characterized by a smooth resistance decrease at
dielectric breakdown). Small area junctions fail mainly through an intrinsic
mechanism (sharp resistance decrease at breakdown). However, this dependence
changes for lower oxidation times, with extrinsic breakdown becoming dominant.
In fact, in the extremely underoxidized magnetic tunnel junctions, failure is
exclusively related with extrinsic causes, independently of MTJ-area. These
results are related with the presence of defects in the barrier (weak spots
that lead to intrinsic breakdown) and of metallic unoxidized Al
nanoconstrictions (leading to extrinsic breakdown).",0607452v1
2011-02-10,"Hour-glass magnetic spectrum in an insulating, hole-doped antiferromagnet","Superconductivity in layered copper-oxide compounds emerges when charge
carriers are added to antiferromagnetically-ordered CuO2 layers. The carriers
destroy the antiferromagnetic order, but strong spin fluctuations persist
throughout the superconducting phase and are intimately linked to
super-conductivity. Neutron scattering measurements of spin fluctuations in
hole-doped copper oxides have revealed an unusual `hour-glass' feature in the
momentum-resolved magnetic spectrum, present in a wide range of superconducting
and non-superconducting materials. There is no widely-accepted explanation for
this feature. One possibility is that it derives from a pattern of alternating
spin and charge stripes, an idea supported by measurements on stripe-ordered
La1.875Ba0.125CuO4. However, many copper oxides without stripe order also
exhibit an hour-glass spectrum$. Here we report the observation of an
hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the
family of superconducting copper oxides. Our system has stripe correlations and
is an insulator, which means its magnetic dynamics can conclusively be ascribed
to stripes. The results provide compelling evidence that the hour-glass
spectrum in the copper-oxide superconductors arises from fluctuating stripes.",1102.2205v1
2014-11-14,Electronic structure and magnetic properties of graphene/Co composites,"The results of measurements of XPS spectra and magnetic properties of
graphene/Co composites prepared by adding of CoCl$_2$x6H$_2$O diluted in ethyl
alcohol to highly-splitted graphite are presented. XPS Co 2p measurements show
two sets of 2p$_{3/2,1/2}$-lines belonging to oxidized and metallic Co-atoms.
This means that metal in composite is partly oxidized. This conclusion is
confirmed by magnetic measurements which show the presence of the main (from
the metal) and shifted (from the oxide) hysteresis loops. The presence of oxide
layer on the metal surface prevents the metal from the full oxidation and (as
shown by magnetic measurements) provides the preservation of ferromagnetic
properties after long exposure in ambient air which enables the use of
graphene/metal composites in spintronics devices.",1411.3863v1
2022-05-23,Growth of delafossite CuAlO2 single crystals in a reactive crucible,"Delafossite oxide CuAlO2 has engaged great attention as a promising p-type
conducting oxide. In this work, high-quality CuAlO2 single crystals with a size
of several millimeters (mm) are successfully achieved with a reactive crucible
melting method. The crystals are characterized by X-ray diffraction, scanning
electron microscopy with energy-dispersive spectroscopy, transport measurement,
and magnetic susceptibility measurement. The grown single crystals are free of
contamination from a copper oxide flux. This work provides a new approach to
growing high-quality delafossite oxide CuAlO2 with a few mm size.",2205.10979v1
2008-09-11,Ferromagnetic ordering in dilute magnetic dielectrics with and without free carriers,"The state of art in the theoretical and experimental studies of transition
metal doped oxides (dilute magnetic dielectrics) is reviewed. The available
data show that the generic non-equilibrium state of oxide films doped with
magnetic impurities may either favor ferromagnetism with high Curie temperature
or result in highly inhomogeneous state without long-range magnetic order. In
both case concomitant defects (vacancies, interstitial ions play crucial part.",0809.2005v1
2014-12-30,Reversible control of Co magnetism by voltage induced oxidation,"We demonstrate that magnetic properties of ultra-thin Co films adjacent to
Gd2O3 gate oxides can be directly manipulated by voltage. The Co films can be
reversibly changed from an optimally-oxidized state with a strong perpendicular
magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy,
or to an oxidized state with nearly zero magnetization, depending on the
polarity and time duration of the applied electric fields. Consequently, an
unprecedentedly large change of magnetic anisotropy energy up to 0.73 erg/cm2
has been realized in a nonvolatile manner using gate voltages of only a few
volts. These results open a new route to achieve ultra-low energy magnetization
manipulation in spintronic devices.",1412.8668v1
2006-02-18,Anomalous Flux Pinning in ?-Pyrochlore Oxide Superconductor KOs2O6,"The superconducting transition of the ?-pyrochlore oxide KOs2O6 with Tc =
9.60 K is studied by resistivity measurements under various magnetic fields
using a high-quality single crystal. The reentrant behavior of
superconductivity is observed near Tc in low magnetic fields below 2 T. The
recovered resistance probably due to flux flow exhibits an anomalous angle
dependence, indicating that flux pinning is enhanced in magnetic fields along
certain crystallographic directions such as [110], [001] and [112]. It is
suggested that there is an intrinsic pinning mechanism coming from the specific
crystal structure of the ?-pyrochlore oxide.",0602433v1
2009-01-09,Magnetic structure of domain walls confined in a nano-oxide layer,"In the recent years, a spin-valve was developed with a current-confined-path
structure consisting of a non-oxide-layer (NOL). We analyze magnetic structures
of the current-confinedpath in the nano-oxide layer sandwiched between
ferromagnetic electrodes and clarify the dependency of the magnetic structure
on the shape and size of the current-confined-path. Our results of stiffness
energy density and thermal stability shows that we should fabricate a CPP
spin-valve with narrow current-confinedpaths with large aspect ratio and strong
constriction in order to enhance the MR ratio.",0901.1189v1
2009-06-23,Multiferroic oxides-based flash-memory and spin-field-effect transistor,"We propose a modified spin-field-effect transistor fabricated in a two
dimensional electron gas (2DEG) formed at the surface of multiferroic oxides
with a transverse helical magnetic order. The topology of the oxide local
magnetic moments induces a resonant momentum-dependent effective spin-orbit
interaction acting on 2DEG. We show that spin polarization dephasing is
strongly suppressed which is crucial for functionality. The carrier spin
precession phase depend linearly on the magnetic spiral helicity. The latter is
electrically controllable by virtue of the magento-electric effect. We also
suggest a flash-memory device based on this structure.",0906.4210v1
2009-07-17,Electrically controlled persistent spin currents at the interface of multiferroic oxides,"We predict the appearance of a persistent spin current in a two-dimensional
electron gas formed at the interface of multiferroic oxides with a transverse
helical magnetic order. No charge current is generated. This is the result of
an effective spin-orbit coupling generated by the topology of the oxide local
magnetic moments. The effective coupling and the generated spin current depend
linearly on the magnetic spiral helicity which, due to the magneto-electric
coupling, is tunable by a transverse electric field offering thus a new mean
for the generation of electrically controlled persistent spin currents.",0907.3023v1
2017-12-15,"Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered α-, γ-, ε-Fe2O3 and Fe3O4 layers","Hybridization of semiconducting and magnetic materials into a single
heterostructure is believed to be potentially applicable to the design of novel
functional spintronic devices. In the present work we report epitaxial
stabilization of four magnetically ordered iron oxide phases (Fe3O4,
{\gamma}-Fe2O3, {\alpha}-Fe2O3 and most exotic metastable {\epsilon}-Fe2O3) in
the form of nanometer sized single crystalline films on GaN(0001) surface. The
epitaxial growth of as many as four distinctly different iron oxide phases is
demonstrated within the same single-target Laser MBE technological process on a
GaN semiconductor substrate widely used for electronic device fabrication. The
discussed iron oxides belong to a family of simple formula magnetic materials
exhibiting a rich variety of outstanding physical properties including peculiar
Verwey and Morin phase transitions in Fe3O4 and {\alpha}-Fe2O3 and multiferroic
behavior in metastable magnetically hard {\epsilon}-Fe2O3 ferrite. The physical
reasons standing behind the nucleation of a particular phase in an epitaxial
growth process deserve interest from the fundamental point of view. The
practical side of the presented study is to exploit the tunable polymorphism of
iron oxides for creation of ferroic-on-semiconductor heterostructures usable in
novel spintronic devices. By application of a wide range of experimental
techniques the surface morphology, crystalline structure, electronic and
magnetic properties of the single phase iron oxide epitaxial films on GaN have
been studied. A comprehensive comparison has been made to the properties of the
same ferrite materials in the bulk and nanostructured form reported by other
research groups.",1712.05632v1
2013-10-21,"Modifications in the frustrated magnetism, oxidation state of Co and magnetoelectric coupling effects induced by a partial replacement of Ca by Gd in the spin chain compound Ca3Co2O6","We have systematically investigated the influence of gradual replacement of
Ca by Gd on the magnetic and complex dielectric properties of the well-known
geometrically frustrated spin-chain system, Ca3Co2O6 (T_N= 24 K with additional
magnetic transitions below 12K), by studying the series, Ca3-xGdxCo2O6 (x less
than 0.7), down to 1.8K. Heat capacity measurements establish that the
reduction of T_N with Gd substitution is much less as compared to that by Y
substitution. The magnetic moment data reveal that there are changes in the
oxidation state of Co as well, unlike for Y-substitution, beyond x= 0.2. Thus,
despite being isovalent, both these substitutions interestingly differ in
changing these magnetic properties in these oxides. We propose that the valence
electrons of Y and those of R ions play different roles on deciding these
magnetic characteristics of these mixed oxides. It is observed that a small
amount (x= 0.3) of Gd substitution for Ca is enough to suppress glassy ac
magnetic susceptibility behavior for the peak around 12 K. An additional
low-temperature magnetic anomaly close to 5 K gets more prominent with
increasing Gd concentration as revealed by heat-capacity data. Trends in
temperature dependence of complex dielectric behavior were also tracked with
varying composition and a frequency dependence is observed, not only for the
transition in the region around 10 K (for some compositions), but also for the
5 K transition which is well-resolved for a higher concentration of Gd. Thus,
Gd-substituted Ca3Co2O6 series is shown to reveal interesting magnetic and
dielectric behavior of this family of oxides.",1310.5635v1
2002-08-21,Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide,"We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$
270K and ferromagnetic to canted spin glass state at T_f$ $\leq$ 125K is
observed.",0208416v1
2014-11-19,"Elastic, electronic and magnetic properties of new oxide perovskite BaVO3: a first-principles study","The structural, elastic, magnetic properties, as well as electronic structure
and chemical bonding picture of new oxide 3d1-perovskite BaVO3, recently
synthesized, were systematically investigated involving the first-principles
FLAPW-GGA calculations. The obtained results are discussed in comparison with
available experimental data, as well as with those obtained before for
isostructural and isoelectronic SrVO3 perovskite.",1411.5128v1
2013-02-15,A novel magnetic phase prior to a saturation moment in frustrated spinel oxides in ultra-high magnetic fields,"We have investigated the magnetic-field induced phases of a typical
three-dimensional frustrated magnet, CdCr$_2$O$_4$, in magnetic fields of up to
120 T that is generated by the single-turn coil techniques. We focused on
magnetic phase transitions in proximity of a saturated magnetization moment. We
utilized both the electromagnetic induction method using magnetic pick-up coils
and magneto-optical spectroscopies of the $d$-$d$ transitions and the
exciton-magnon-phonon transitions to study the magnetic properties subjected to
ultra-high magnetic fields. Anomalies were observed in magneto-optical
absorption intensity as well as differential magnetization prior to a fully
polarized magnetic phase (a vacuum state in the magnon picture), revealing a
novel magnetic phase associated with changes in both crystal and magnetic
structures accompanied by the first order phase transition. Magnetic superfluid
state such as an umbrella-like magnetic structure or a spin nematic state, is
proposed as a candidate for the novel magnetic phase, which is found universal
in the series of chromium spinel oxides, $A$Cr$_2$O$_4$ ($A$ = Zn, Cd, Hg).",1302.3664v1
2021-11-20,Skyrmionics in correlated oxides,"While chiral magnets, metal-based magnetic multilayers, or Heusler compounds
have been considered as the material workhorses in the field of skyrmionics,
oxides are now emerging as promising alternatives, as they host special
correlations between the spin-orbital-charge-lattice degrees of freedom and/or
coupled ferroic order parameters. These interactions open new possibilities for
practically exploiting skyrmionics. In this article, we review the recent
advances in the observation and control of topological spin textures in various
oxide systems. We start with the discovery of skyrmions and related
quasiparticles in bulk and heterostructure ferromagnetic oxides. Next, we
emphasize the shortcomings of implementing ferromagnetic textures, which have
led to the recent explorations of ferrimagnetic and antiferromagnetic oxide
counterparts, with higher Curie temperatures, stray-field immunity, low Gilbert
damping, ultrafast magnetic dynamics, and/or absence of skyrmion deflection.
Then, we highlight the development of novel pathways to control the stability,
motion, and detection of topological textures using electric fields and
currents. Finally, we present the outstanding challenges that need to be
overcome to achieve all-electrical, nonvolatile, low-power oxide skyrmionic
devices.",2111.10562v2
2023-04-26,Assessment of sol-gel derived iron oxide substituted 45S5 bioglass-ceramics for biomedical applications,"Magnetic bioactive glass ceramic (MGC) powders have been synthesized by sol
gel route by systematically substituting silicon dioxide with iron oxide in the
45S5 glass composition. Powder x-ray diffraction studies revealed a variation
in the percentage of combeite (Ca$_2$Na$_2$Si$_3$O$_9$), magnetite
(Fe$_3$O$_4$), and hematite (Fe$_2$O$_3$) nanocrystalline phases in MGC powders
as a function of composition. Zeta potential measurements showed that MGC
containing up to 10 wt.% iron oxide formed stable suspensions. Saturation
magnetization and heat generation capacity of MGC fluids increased with
increase in iron oxide content. Degradation of MGC powders was investigated in
phosphate buffer saline (PBS). In vitro bioactivity of the MGC powders taken in
pellet form was confirmed by observing the pH variation as well as
hydroxyapatite layer (HAp) formation upon soaking in modified simulated body
fluid. These studies showed a decrement in overall bioactivity in samples with
high iron oxide content due to the proportional decrease in silanol group.
Monitoring the proliferation of MG-63 osteoblast cell in Dulbecco's Modified
Eagle Medium (DMEM) revealed that MGC with up to 10 wt.% iron oxide exhibited
acceptable viability. The systematic study revealed that the MGC with 10 wt.%
iron oxide exhibited optimal cell viability, magnetic properties and induction
heating capacity which were better than those of FluidMag-CT, which is used for
hyperthermia treatment.",2304.13437v1
2003-05-29,Magnetic Interactions in Transition-Metal Oxides,"This a review article, which presents a general framework for the analysis of
interatomic magnetic interactions in the spin-density-functional theory, which
is based on the magnetic force theorem, make a link with the models for
transition-metal oxides, and gives several examples of how this strategy can be
used for the analysis of magnetic properties of colossal-magnetoresistive
perovskite manganites, double perovskite and pyrochlore compounds.",0305668v1
2017-08-16,Copper Tellurium Oxides - A Playground for Magnetism,"A variety of copper tellurium oxide minerals are known, and many of them
exhibit either unusual forms of magnetism, or potentially novel spin liquid
behavior. Here, I review a number of the more interesting materials with a
focus on their crystalline symmetry and, if known, the nature of their
magnetism. Many of these exist (so far) in mineral form only, and most have yet
to have their magnetic properties studied. This means a largely unexplored
space of materials awaits our exploration.",1708.05100v1
2019-09-19,Electronic ferroelectricity and magneto-electric effect in phase separated magnetic oxidesElectronic ferroelectricity and magneto-electric effect in phase separated magnetic oxides,"We consider phase separated states in magnetic oxides (MO) thin films. We
show that these states have a non-zero electric polarization. Moreover, the
polarization is intimately related to a spatial distribution of magnetization
in the film. Polarized states with opposite polarization and opposite magnetic
configuration are degenerate. An external electric field removes the degeneracy
and allows to switch between the two states. So, one can control electric
polarization and magnetic configuration of the phase separated MO thin film
with the external electric field.",1909.09176v1
2015-03-26,Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism,"Understanding the ramifications of reduced crystalline symmetry on magnetic
behavior is a critical step in improving our understanding of nanoscale and
interfacial magnetism. However, investigations of such effects are often
controversial largely due to the challenges inherent in directly correlating
nanoscale stoichiometry and structure to magnetic behavior. Here, we describe
how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic
Circular Dichroism (EMCD) signals as a function of scattering angle to locally
probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0)
surface. Experiments and simulations both reveal a strong dependence of the
magnetic orbital to spin ratio on its scattering vector in reciprocal space. We
exploit this variation to extract the magnetic properties of the oxide cladding
layer, showing that it locally may exhibit an enhanced orbital to spin moment
ratio. This finding is supported here by both spatially and angularly resolved
EMCD measurements, opening up the way for compelling investigations into how
magnetic properties are affected by nanoscale features.",1503.07681v2
2007-07-21,Ferromagnetism as a universal feature of nanoparticles of the otherwise nonmagnetic oxides,"Room-temperature ferromagnetism has been observed in the nanoparticles (7 -
30 nm dia) of nonmagnetic oxides such as CeO2, Al2O3, ZnO, In2O3 and SnO2. The
saturated magnetic moments in CeO_2 and Al_2O_3 nanoparticles are comparable to
those observed in transition metal doped wide band semiconducting oxides. The
other oxide nanoparticles show somewhat lower values of magnetization but with
a clear hysteretic behavior. Conversely, the bulk samples obtained by sintering
the nanoparticles at high temperatures in air or oxygen became diamagnetic. As
there were no magnetic impurities present, we assume that the origin of
ferromagnetism may be due to the exchange interactions between localized
electron spin moments resulting from oxygen vacancies at the surfaces of
nanoparticles. We suggest that ferromagnetism may be a universal characteristic
of nanopartilces of metal oxides",0707.3183v1
1999-03-03,Mass enhancement of two-dimensional electrons in thin-oxide Si-MOSFET's,"We wish to report in this paper a study of the effective mass (m^*) in
thin-oxide Si-metal-oxide-semiconductor field-effect-transistors, using the
temperature dependence of the Shubnikov-de Haas (SdH) effect and following the
methodology developed by J.L. Smith and P.J. Stiles, Phys. Rev. Lett. {\bf 29},
102 (1972). We find that in the thin oxide limit, when the oxide thickness
$d_{ox}$ is smaller than the average two-dimensional electron-electron
separation r, m^* is still enhanced and the enhancement can be described by
$m^*/m_B = 0.815 + 0.23(r/d_{ox})$, where $m_B = 0.195 m_e$ is the bulk
electron mass, $m_e$ the free electron mass. At $n_s = 6 \times 10^{11}/cm^2$,
for example, $m^* \simeq 0.25 m_e$, an enhancement doubles that previously
reported by Smith and Stiles. Our result shows that the interaction between
electrons in the semiconductor and the neutralizing positive charges on the
metallic gate electrode is important for mass enhancement. We also studied the
magnetic-field orientation dependence of the SdH effect and deduced a value of
$3.0 \pm 0.5$ for the effective $g$ factor in our thin oxide samples.",9903058v1
2001-11-14,Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides,"This review is focused on extrinsic magnetotransport effects in ferromagnetic
oxides. It consists of two parts; the second part is devoted to an overview of
experimental data and theoretical models for extrinsic magnetotransport
phenomena. Here a critical discussion of domain-wall scattering is given.
Results on surfacial and interfacial magnetism in oxides are presented.
Spin-polarized tunnelling in ferromagnetic junctions is reviewed and
grain-boundary magnetoresistance is interpreted within a model of
spin-polarized tunnelling through natural oxide barriers. The situation in
ferromagnetic oxides is compared with data and models for conventional
ferromagnets. The first part of the review summarizes basic material
properties, especially data on the spin-polarization and evidence for
half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed.
An outlook on the further development of oxide spin-electronics concludes this
review.",0111263v1
2011-12-26,"Multiferroic and magnetoelectric nature of GaFeO3, AlFeO3 and related oxides","GaFeO3, AlFeO3 and related oxides are ferrimagnetic exhibiting
magnetodielectric effect. There has been no evidence to date for
ferroelectricity and hence multiferroicity in these oxides. We have
investigated these oxides as well as oxides of the composition
Al1-x-yGaxFe1+yO3 (x = 0.2, y = 0.2) for possible ferroelectricity by carrying
out pyroelectric measurements. These measurements establish the occurrence of
ferroelectricity at low temperatures below the N\`eel temperature in these
oxides. They also exhibit significant magnetoelectric effect. We have tried to
understand the origin of ferroelectricity based on non-centrosymmetric magnetic
ordering and disorder by carrying out first-principles calculations.",1112.5848v2
2023-12-27,Correlated Quantum Phenomena of Spin-Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3-Based Artificial Superlattices,"Unexpected, yet useful functionalities emerge when two or more materials
merge coherently. Artificial oxide superlattices realize atomic and crystal
structures that are not available in nature, thus providing controllable
correlated quantum phenomena. This review focuses on 4d and 5d oxide
superlattices, in which the spin-orbit coupling plays a significant role
compared with conventional 3d oxide superlattices. Modulations in crystal
structures with octahedral distortion, phonon engineering, electronic
structures, spin orderings, and dimensionality control are discussed for 4d
oxide superlattices. Atomic and magnetic structures, Jeff = 1/2 pseudospin and
charge fluctuations, and the integration of topology and correlation are
discussed for 5d oxide superlattices. This review provides insights into how
correlated quantum phenomena arise from the deliberate design of superlattice
structures that give birth to novel functionalities.",2312.16748v1
2008-06-18,Selective Heating Mechanism of Magnetic Metal Oxides by Alternating Magnetic Field in Microwave Sintering Process,"The mechanism of rapid and selective heating of magnetic metal oxides under
the magnetic field of microwaves which continues beyond the Curie temperature $
T_{c} $ is identified by using the Heisenberg model. Monte Carlo calculations
based on the energy principle show that such heating is caused by non-resonant
response of electron spins in the unfilled 3d shell to the wave magnetic field.
Small spin reorientation thus generated leads to a large internal energy change
through the exchange interactions between spins, which becomes maximal around $
T_{c} $ for magnetite $ {\rm Fe}_{3}{\rm O}_{4} $. The dissipative spin
dynamics simulation yields the imaginary part of the magnetic susceptibility,
which becomes largest around $ T_{c} $ and for the microwave frequency around 2
GHz. Hematite $ {\rm Fe}_{2}{\rm O}_{3} $ with weak spontaneous magnetization
responds much less to microwaves as observed in experiments. The heating of
titanium oxide by microwave magnetic field only when oxygen defects are present
is also explained by our theory in terms of the absence of spontaneous
magnetization.",0806.3055v3
2020-12-10,Magnetic properties of poly(trimethylene terephthalate-block-poly(tetramethylene oxide) copolymer nanocomposites reinforced by graphene oxide-Fe3O4 hybrid nanoparticles,"Thermoplastic elastomeric nanocomposites based on poly(trimethylene
terephthalate-block-poly(tetramethylene oxide) copolymer (PTT-PTMO) and
graphene oxide-Fe3O4 nanoparticle hybrid were prepared by in situ
polymerization. Superparamagnetic GO-Fe3O4 hybrid nanoparticles before
introducing to elastomeric matrix were characterized by X-ray photoelectron
spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA)
and scanning electron microscopy (SEM). The effect of loading (0.3 and 0.5 wt%)
of GO-Fe3O4 nanoparticle hybrid on the phase structure, tensile and magnetic
properties of synthesized nanocomposites was investigated. The phase structure
of nanocomposites was evaluated by differential scanning calorimetry (DSC) and
dynamic mechanical thermal analysis (DMTA). Dispersion of GO-Fe3O4
nanoparticles in elastomeric matrix was evaluated by transmission electron
microscopy (TEM). Magnetic properties of GO-Fe3O4 nanoparticle hybrid and
nanocomposites with their content were characterized by using two different
techniques: dc SQUID magnetization measurements as a function of temperature
(from 2 to 300 K) and external magnetic field and ferromagnetic resonance (FMR)
at microwave frequency.",2012.05819v1
1997-04-28,Reproducible magnetic fluctuations of microwave absorption in zeolites,"For polycrystalline specimens of zeolites treated to thermal oxidation we
have revealed and studied the weak spectra of reproducible magnetic microwave
absorption fluctuations at a frequency of 9.4 GHz. The investigation was
carried out by the ESR method over the 77-500 K temperature range. The
fluctuation spectra have features typical of mesoscopic phenomena observed
previously in ESR spectra of high temperature superconductors and metals at
temperatures below critical. The similar fluctuation spectra were obtained at
300 K for some oxides, oxidized silver and gold particles. The experiments
performed are, perhaps, the first observation of the phenomenon at unusually
high temperatures which has been observed only in superconducting systems.",9704230v1
2013-06-08,Effect of Spin-Orbit Interaction on (4d)^3- and (5d)^3 -Based Transition-Metal Oxides,"The effects of a spin-orbit interaction on transition-metal ions of (4d)^3-
and (5d)^3 -based oxides in which three electrons occupy t_{2g} orbitals are
studied. The amplitude of the magnetic moment of d electrons on the 5d and 4d
orbitals is estimated by numerical diagonalization. It is found that the
magnetic moment is reduced by the spin-orbit interaction. It is suggested that
(4d)^3- and (5d)^3 -based oxides are located in the middle of the L-S and J-J
coupling schemes.",1306.1880v1
2019-12-08,Thermal Conductivity of Oxide Tunnel Barriers in Magnetic Tunnel Junctions Measured by Ultrafast Thermoreflectance and Magneto-optic Kerr Effect Thermometry,"Spin-dependent charge transport in magnetic tunnel junctions (MTJs) can be
manipulated by a temperature gradient, which can be utilized for spintronic and
spin caloritronic applications. Evaluation of the thermally induced phenomena
requires knowledge of the temperature differences across the oxide tunnel
barrier adjacent to the ferromagnetic (FM) leads. However, it is challenging to
accurately measure thermal properties of an oxide tunnel barrier consisting of
only a few atomic layers. In this work, we experimentally interrogate the
temperature evolutions in Ru/oxide/FM/seed/MgO (oxide=MgO, MgAl2O4; FM=Co,
CoFeB; seed=Pt, Ta) structures having perpendicular magnetic anisotropy using
ultrafast thermometry. The Ru layer is optically thick and heated by ultrafast
laser pulses; the subsequent temperature changes are monitored using
thermoreflectance of Ru and magneto-optic Kerr effect (MOKE) of the FM layers.
We independently measure the response times of Co and CoFeB magnetism using
quadratic MOKE and obtain {\tau}em=0.2 ps for Co and 2 ps for CoFeB. These time
scales are much shorter than the time scale of heat transport through the oxide
tunnel barrier, which occurs at 10-3000 ps. We determine effective thermal
conductivities of MgO and MgAl2O4 tunnel barriers in the range of 0.4-0.6 W m-1
K-1, comparable to an estimate of the series conductance of the Ru/oxide and
oxide/FM interfaces and an order of magnitude smaller than the thermal
conductivity of MgO thin films. We find that the electron-phonon thermal
conductance near the tunnel barrier is only a factor of 5-12 larger than the
thermal conductance of the oxide tunnel barrier. Therefore, the drop in the
electronic temperature is approximately 20-30% larger than the drop in the
phonon temperature across the tunnel barrier.",1912.03588v1
2021-08-25,Kinetics of ion migration in the electric field-driven manipulation of magnetic anisotropy of Pt/Co/oxide multilayers,"Magneto-ionics, by which the magnetic properties of a thin layer can be
modified through the migration of ions within a liquid or solid electrolyte, is
a fast developing research field. This is mainly due to the perspective of
energy efficient magnetic devices, in which the magnetization direction is
controlled not by a magnetic field or an electrical current, as done in
traditional devices, but by an electric field, leading to a considerable
reduction of energy consumption.
  In this work, the interfacial perpendicular magnetic anisotropy (PMA) of a
series of Pt/Co/oxide trilayers covered by a ZrO$_2$ layer, acting as a ionic
conductor, was finely tuned by a gate voltage at room temperature. The
non-volatility and the time evolution of the effect point at oxygen ion
migration across the ZrO$_2$ layer as the driving mechanism. A large variation
of the PMA is obtained by modifying the degree of oxidation of the cobalt layer
with the flux of oxygen ions: the easy magnetization axis can be switched
reversibly from in-plane, with an under-oxidized Co, to in-plane, with an
over-oxidized Co, passing through an out-of-plane magnetization with maximum
PMA. The switching time between the different magnetic states is limited by the
oxygen ion drift velocity through the multilayer structure. This was shown to
depend exponentially on the applied bias voltage, and could be varied by over 5
orders of magnitude, from several minutes to a few ms. On the other hand, for a
fixed gate-voltage, the oxidation of the cobalt layer decreases exponentially
as a function of time. This behavior is in agreement with the theoretical model
developed by Cabrera and Mott (1949) to explain the growth of very thin oxides
at low temperatures. The possibility to explain the observed effect with a
relatively simple theoretical model opens the possibility to engineers
materials with optimized properties.",2108.11263v1
2005-09-22,Magnetism and half-metallicity at the O surfaces of ceramic oxides,"The occurence of spin-polarization at ZrO$_{2}$, Al$_{2}$O$_{3}$ and MgO
surfaces is proved by means of \textit{ab-initio} calculations within the
density functional theory. Large spin moments, as high as 1.56 $\mu_B$, develop
at O-ended polar terminations, transforming the non-magnetic insulator into a
half-metal. The magnetic moments mainly reside in the surface oxygen atoms and
their origin is related to the existence of $2p$ holes of well-defined spin
polarization at the valence band of the ionic oxide. The direct relation
between magnetization and local loss of donor charge makes possible to extend
the magnetization mechanism beyond surface properties.",0509578v1
2006-02-07,Angular dependence of the magnetic-field driven superconductor-insulator transition in thin films of amorphous indium-oxide,"A significant anisotropy of the magnetic-field driven
superconductor-insulator transition is observed in thin films of amorphous
indium-oxide. The anisotropy is largest for more disordered films which have a
lower transition field. At higher magnetic field the anisotropy reduces and
even changes sign beyond a sample specific and temperature independent magnetic
field value. The data are consistent with the existence of more that one
mechanism affecting transport at high magnetic fields.",0602160v1
2009-02-19,Is the nature of magnetic order in copper-oxides and in iron-pnictides different?,"We use the results of first-principles electronic structure calculations and
a strong coupling perturbation approach, together with general theoretical
arguments, to illustrate the differences in super-exchange interactions between
the copper-oxides and iron-pnictides. We show that the two magnetic ground
states can be understood in a simple manner within the same theoretical
foundation. Contrary to the emerging view that magnetic order in the
iron-pnictides is of itinerant nature, we argue that the observed magnetic
moment is small because of frustration introduced by the electrons of the Fe
orbitals as they compete to impose their preferred magnetic ordering.",0902.3450v1
2014-09-15,Ferroelectric Control of Magnetism and Transport in Oxide Heterostructures,"Magnetism and transport are two key functional ingredients in modern
electronic devices. In oxide heterostructures, ferroelectricity can provide a
new route to control these two properties via electrical operations, which is
scientifically interesting and technologically important. In this Brief Review,
we will introduce recent progresses on this fast developing research field.
Several subtopics will be covered. First, the ferroelectric polarization tuning
of interfacial magnetism will be introduced, which includes the tuning of
magnetization, easy axis, magnetic phases, as well as exchange bias. Second,
the ferroelectric polarization tuning of transverse and tunneling transport
will be reviewed.",1409.4125v1
2016-06-09,Nanocomposite RE-Ba-Cu-O bulk superconductors,"Nanocomposite oxide high-temperature bulk superconductors can be used as
quasi-magnets. Thanks to the recent progress of material processing,
quasi-magnet with 26 mm diameter can generate a large field of 17.6 T at 26 K.
These results are highly attractive for applications, involving levitation of
permanent magnets on the bulk superconductors. Indeed, several other
applications such as motors and magnetic resonance microscope using bulk
superconductors have been proposed and demonstrated. In this chapter, we
describe several techniques to improve the magnetic properties for bulk
superconductors together with some basics such as phase diagrams and
solidifications.",1606.02872v1
2019-11-15,Cation spin and superexchange interaction in oxide materials below and above spin crossover under high pressure,"We derived simple rules for the sign of superexchange interaction based on
the multielectron calculations of the superexchange interaction in the
transition metal oxides that are valid both below and above spin crossover
under high pressure. The superexchange interaction between two cations in d$^n$
configurations is given by a sum of individual contributions related to the
electron-hole virtual excitations to the different states of the d$^{n + 1}$
and d$^{n - 1}$ configurations. Using these rules, we have analyzed the sign of
the superexchange interaction of a number of oxides with magnetic cations in
electron configurations from d$^2$ till d$^8$: the iron, cobalt, chromium,
nickel, copper and manganese oxides with increasing pressure. The most
interesting result concerns the magnetic state of cobalt and nickel oxides CoO,
Ni$_2$O$_3$ and also La$_2$CoO$_4$, LaNiO$_3$ isostructural to well-known
high-T$_C$ and colossal magnetoresistance materials. These oxides have a spin
$\frac{1}{2}$ at the high pressure. Change of the interaction from
antiferromagnetic below spin crossover to ferromagnetic above spin crossover is
predicted for oxide materials with cations in d$^5$(FeBO$_3$) and d$^7$(CoO)
configurations, while for materials with the other d$^n$ configurations spin
crossover under high pressure does not change the sign of the superexchange
interaction.",1911.06482v3
2001-06-26,Superconductivity in a pyrochlore oxide Cd2Re2O7,"We make the first report that a metallic pyrochlore oxide \Cd2Re2O7, exhibits
type II superconductivity at 1.1 K. The pyrochlore oxide is known to be a
geometrical frustrated system, which includes the tetrahedral network of
magnetic ions. A large number of compounds are classified in the family of
pyrochlore oxides, and these compounds exhibit a wide variety of physical
properties ranging from insulator through semiconductor and from bad metal to
good metal. Until now, however, no superconductivity has been reported for
frustrated pyrochlore oxides. The bulk superconductivity of this compound is
confirmed by measurements of the resistivity and the a. c. magnetic
susceptibility. The \Hc2, which is extrapolated to 0 K, is estimated as about
0.8 T, using the resistivity measurements under aplied field. The plot of \Hc2
vs $T$ indicates that the Cooper pairs are composed of rather heavy
quasiparticles. This fact suggests that frustrated heavy electrons become
superconducting in this compound.",0106521v1
2002-08-24,"Crystal structure, electronic, and magnetic properties of the bilayered rhodium oxide Sr3Rh2O7","The bilayered rhodium oxide Sr3Rh2O7 was synthesized by high-pressure and
high-temperature heating techniques. The single-phase polycrystalline sample of
Sr3Rh2O7 was characterized by measurements of magnetic susceptibility,
electrical resistivity, specific heat, and thermopower. The structural
characteristics were investigated by powder neutron diffraction study. The
rhodium oxide Sr3Rh2O7 [Bbcb, a = 5.4744(8) A, b = 5.4716(9) A, c = 20.875(2)
A] is isostructural to the metamagnetic metal Sr3Ru2O7, with five 4d electrons
per Rh, which is electronically equivalent to the hypothetic bilayered
ruthenium oxide, where one electron per Ru is doped into the Ru-327 unit. The
present data show the rhodium oxide Sr3Rh2O7 to be metallic with enhanced
paramagnetism, similar to Sr3Ru2O7. However, neither manifest contributions
from spin fluctuations nor any traces of a metamagnetic transition were found
within the studied range from 2 K to 390 K below 70 kOe.",0208467v1
2005-07-18,Anomalous magnetoresistance behavior of CoFe nano-oxide spin valves at low temperatures,"We report magnetoresistance curves of CoFe nano-oxide specular spin valves of
MnIr/CoFe/nano-oxidized CoFe/CoFe/Cu/CoFe/nano-oxidized CoFe/Ta at different
temperatures from 300 to 20 K. We extend the Stoner-Wolfarth model of a common
spin valve to a specular spin valve, introducing the separation of the pinned
layer into two sublayers and their magnetic coupling across the nano-oxide. We
study the effect of different coupling/exchange (between the antiferromagnetic
layer and the bottom sublayer) field ratios on the magnetization and
magnetoresistance, corresponding with the experimentally observed anomalous
bumps in low temperature magnetoresistance curves.",0507423v1
2010-08-09,Detection of bottom ferromagnetic electrode oxidation in magnetic tunnel junctions by magnetometry measurements,"Surface oxidation of the bottom ferromagnetic (FM) electrode, one of the
major detrimental factors to the performance of a Magnetic Tunnel Junction
(MTJ), is difficult to avoid during the fabrication process of the MTJ's tunnel
barrier. Since Co rich alloys are commonly used for the FM electrodes in MTJs,
over-oxidation of the tunnel barrier results in the formation of a CoO
antiferromagnetic (AF) interface layer which couples with the bottom FM
electrode to form a typical AF/FM exchange bias (EB) system. In this work,
surface oxidation of the CoFe and CoFeB bottom electrodes was detected via
magnetometry measurements of exchange-bias characterizations including the EB
field, training effect, uncompensated spin density, and coercivity. Variations
of these parameters were found to be related to the surface oxidation of the
bottom electrode, among them the change of coercivity is most sensitive.
Annealed samples show evidence for an oxygen migration back to the MgO tunnel
barrier by annealing.",1008.1493v1
2019-01-03,Origin of band gaps in 3d perovskite oxides,"With their broad range of magnetic, electronic and structural properties,
transition metal perovskite oxides ABO3 have long served as a platform for
testing condensed matter theories. In particular, their insulating character -
found in most compounds - is often ascribed to dynamical electronic
correlations through the celebrated Mott-Hubbard mechanism where gaping arises
from a uniform, symmetry-preserving electron repulsion mechanism. However,
structural distortions are ubiquitous in perovskites and their relevance with
respect to dynamical correlations in producing this rich array of properties
remains an open question. Here, we address the origin of band gap opening in
the whole family of 3d perovskite oxides. We show that a single-determinant
mean-field approach such as density functional theory (DFT) successfully
describes the structural, magnetic and electronic properties of the whole
series, at low and high temperatures. We find that insulation occurs via
energy-lowering crystal symmetry reduction (octahedral rotations, Jahn-Teller
and bond disproportionation effects), as well as intrinsic electronic
instabilities, all lifting orbital degeneracies. Our work therefore suggests
that whereas ABO3 oxides may be complicated, they are not necessarily strongly
correlated. It also opens the way towards systematic investigations of doping
and defect physics in perovskites, essential for the full realization of
oxide-based electronics.",1901.00829v1
2023-01-10,Anionic nickel and nitrogen effects in the chiral antiferromagnetic antiperovskite Mn$_3$NiN,"Magnetic antiperovskites, holding chiral noncollinear antiferromagnetic
ordering, have shown remarkable properties that cover from negative thermal
expansion to anomalous Hall effect. Nevertheless, details on the electronic
structure related to the oxidation states and the octahedral center's site
effect are still scarce. Here, we show a theoretical study, based on
first-principles calculations in the framework of the density-functional
theory, DFT, on the electronic details associated with the nitrogen site effect
into the structural, electronic, magnetic, and topological degrees of freedom.
Thus, we show that the nitrogen-vacancy increases the values of the anomalous
Hall conductivity and retains the chiral $\Gamma_{4g}$ antiferromagnetic
ordering. Moreover, we reveal, based on the Bader charges and the electronic
structure analysis, the negative and positive oxidation states in the Ni and Mn
sites, respectively. The latter is in agreement with the expected
$A_3^{\alpha+}B^{\beta-}X^{\delta-}$ oxidation states to satisfy the charge
neutrality in the antiperovskites, but rare for transition metals. Finally, we
extrapolate our findings on the oxidation states to several Mn$_3B$N compounds
showing that the antiperovskite structure is an ideal platform to encounter
negative oxidation states in metals sitting at the corner $B$-site.",2301.04242v1
2017-12-18,Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3,"We report the effect of partial substitution of Dy-site by rare-earths (R=Gd,
Er and La)on the magnetic and magnetocaloric behavior of a mixed metal oxide
DyFe0.5Cr0.5O3.Structural studies reveal that substitution of Dy by R has a
minimal influence on the crystal structure. Magnetic and heat capacity studies
show that the magnetic transition around 121 K observed for DyFe0.5Cr0.5O3
remains unchanged with rare-earth substitution, whereas the lower magnetic
transition temperature is suppressed/enhanced by magnetic/non-magnetic
substitution. In all these compounds, the second order nature of magnetic
transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the
values of magnetic entropy change and relative cooling power are increased with
magnetic rare-earth substitution while it decreases with non-magnetic
rare-earth substitution. In all these compounds, magnetic entropy change
follows the power law dependence of magnetic field and the value of the
exponent n indicate the presence of ferromagnetic correlation in an
antiferromagnetic state. A phenomenological universal master curve is also
constructed for all the compounds by normalizing the entropy change with
rescaled temperature using a single reference temperature. This master curve
also reiterates the second order nature of the magnetic phase transition in
such mixed metal oxides.",1712.06396v1
2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2021-09-29,Magnetic interlayer coupling between ferromagnetic SrRuO$_3$ layers through a SrIrO$_3$ spacer,"A key element to tailor the properties of magnetic multilayers is the
coupling between the individual magnetic layers. In case of skyrmion hosting
multilayers, coupling of skyrmions across the magnetic layers is highly
desirable. Here the magnetic interlayer coupling was studied in epitaxial
all-oxide heterostructures of ferromagnetic perovskite SrRuO$_3$ layers
separated by spacers of the strong spin-orbit coupling oxide SrIrO$_3$. This
combination of oxide layers is being discussed as a potential candidate system
to host N\'{e}el skyrmions. First order reversal curve (FORC) measurements were
performed in order to distinguish between magnetic switching processes of the
individual layers and to disentangle the signal of soft magnetic impurities
from the samples$'$ signal. Additionally, FORC investigations enabled to
determine whether the coupling between the magnetic layers is ferromagnetic or
antiferromagnetic. The observed interlayer coupling strength was weak for all
the heterostructures, with SrIrO$_3$ spacers between 2 monolayers and 12
monolayers thick.",2109.14292v2
2016-11-22,Exchange interactions in transition metal oxides: The role of oxygen spin polarization,"Magnetism of transition metal (TM) oxides is usually described in terms of
the Heisenberg model, with orientation-independent interactions between the
spins. However, the applicability of such a model is not fully justified for TM
oxides because spin polarization of oxygen is usually ignored. In the
conventional model based on the Anderson principle, oxygen effects are
considered as a property of the TM ion and only TM interactions are relevant.
Here, we perform a systematic comparison between two approaches for spin
polarization on oxygen in typical TM oxides. To this end, we calculate the
exchange interactions in NiO, MnO, and hematite (Fe2O3) for different magnetic
configurations using the magnetic force theorem. We consider the full spin
Hamiltonian including oxygen sites, and also derive an effective model where
the spin polarization on oxygen renormalizes the exchange interactions between
TM sites. Surprisingly, the exchange interactions in NiO depend on the magnetic
state if spin polarization on oxygen is neglected, resulting in non-Heisenberg
behavior. In contrast, the inclusion of spin polarization in NiO makes the
Heisenberg model more applicable. Just the opposite, MnO behaves as a
Heisenberg magnet when oxygen spin polarization is neglected, but shows strong
non-Heisenberg effects when spin polarization on oxygen is included. In
hematite, both models result in non-Heisenberg behavior. General applicability
of the magnetic force theorem as well as the Heisenberg model to TM oxides is
discussed.",1611.07288v2
2004-01-31,Unprecedented Superconductivity in the beta-Pyrochlore Osmate KOs2O6,"Superconductivity in the potassium osmium oxide KOs2O6 crystallizing in the
beta-pyrochlore structure is studied by means of electrical resistivity,
magnetic susceptibility and specific heat. It is the second superconductor in
the family of pyrochlore oxides, following the alfa-type pyrochlore oxide
Cd2Re2O7 which is believed to be a conventional s-wave superconductor. The
superconducting transition temperature Tc of KOs2O6 is 9.6 K, almost one order
higher than the Tc = 1.0 K of Cd2Re2O7. Moreover, the superconductivity of
KOs2O6 is remarkably robust under high magnetic fields, with a large upper
critical magnetic field Hc2 of about 38 T, which seems to exceed Pauli's limit
expected for conventional superconductivity. This is also in contrast to the
case of Cd2Re2O7, in which the Hc2 is 0.29 T, much smaller than the
corresponding Pauli's limit. These distinct contrasts strongly suggest that the
mechanism of superconductivity is essentially different between the two
pyrochlore oxides.",0402006v3
2012-06-12,Electric field control of magnetic exchange coupling,"Electric control of magnetism is a vision which drives intense research on
magnetic semiconductors and multiferroics. Recently, also ultrathin metallic
films were reported to show magnetoelectric effects at room temperature. Here
we demonstrate much stronger effects by exploiting reduction/oxidation
reactions in a naturally grown oxide layer exchange coupled to an underlying
ferromagnet. For the exemplarily studied FePt/iron oxide composite in an
electrolyte, a large and reversible change of magnetization and anisotropy is
obtained. The principle can be transferred to various metal/oxide combinations.
It represents a novel approach towards multifunctionality.",1206.2467v3
2011-11-25,Growth and electronic and magnetic structure of iron oxide films on Pt(111),"Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111)
single crystal either by the reactive deposition of iron or oxidation of
metallic iron monolayers. These films were characterized using low energy
electron diffraction, scanning tunneling microscopy and conversion electron
Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth
of Fe3O4, in which the electronic and magnetic properties of the bulk material
were modulated by superparamagnetic size effects for thicknesses below 2 nm,
revealing specific surface and interface features. In contrast, the oxide films
with FeO stoichiometry, which could be stabilized as thick as 4 nm under
special preparation conditions, had electronic and magnetic properties that
were very different from their bulk counterpart, w\""ustite. Unusual long range
magnetic order appeared at room temperature for thicknesses between three and
ten monolayers, the appearance of which requires severe structural modification
from the rock-salt structure.",1111.5938v2
2014-06-18,Topological phases in Iridium oxide superlattices: quantized anomalous charge or valley Hall insulators,"We study topological phases in Iridium (Ir) oxide superlattices of
orthorhombic perovskite-type grown along the [001] crystallographic axis. Due
to strong spin-orbit coupling of Ir 5d-orbitals and electronic correlation
effects, Ir oxide bilayer superlattices display topological magnetic insulators
exhibiting quantized anomalous Hall effects. Depending on stacking of two
layers, we also found a valley Hall insulator with counter-propagating edge
currents from two different valleys and a topological crystalline insulator
with edge states protected by the crystal lattice symmetry. In a single layer
Ir oxide superlattice, a topological insulator can be achieved, when a strain
field is applied to break the symmetry of a glide plane protecting the Dirac
points. In the presence of a magnetic ordering or in-plane magnetic field, it
turns into a topological magnetic insulator. We discuss essential ingredients
for these topological phases and experimental signatures to test our
theoretical proposals.",1406.4884v2
2019-02-06,Iron oxide nanoparticles for magnetic hyperthermia,"Assemblies of magnetic nanoparticles show a great potential for application
in biomedicine, in particular, in magnetic hyperthermia. However, to achieve
desired therapeutic effect in magnetic hyperthermia the assembly of
nanoparticles should have a sufficiently high specific absorption rate in
alternating magnetic field of moderate amplitude and frequency.",1902.02220v1
2020-06-25,Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction at an oxide/ferromagnetic metal interface,"We report on the study of both perpendicular magnetic anisotropy (PMA) and
Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM)
interface, i.e. BaTiO3 (BTO)/CoFeB. Thanks to the functional properties of the
BTO film and the capability to precisely control its growth, we are able to
distinguish the dominant role of the oxide termination (TiO2 vs BaO), from the
moderate effect of ferroelectric polarization in the BTO film, on the PMA and
DMI at the oxide/FM interface. We find that the interfacial magnetic anisotropy
energy of the BaO-BTO/CoFeB structure is two times larger than that of the
TiO2-BTO/CoFeB, while the DMI of the TiO2-BTO/CoFeB interface is larger. We
explain the observed phenomena by first-principles calculations, which ascribe
them to the different electronic states around the Fermi level at the
oxide/ferromagnetic metal interfaces and the different spin-flip processes.
This study paves the way for further investigation of the PMA and DMI at
various oxide/FM structures and thus their applications in the promising field
of energy-efficient devices.",2006.14268v1
2023-01-02,Performance of the r$^{2}$SCAN functional in transition metal oxides,"We assess the accuracy and computational efficiency of the recently developed
meta-generalized gradient approximation (metaGGA) functional, the restored
regularized strongly constrained and appropriately normed (r$^2$SCAN), in
transition metal oxide (TMO) systems and compare its performance against SCAN.
Specifically, we benchmark the r$^2$SCAN-calculated oxidation enthalpies,
lattice parameters, on-site magnetic moments, and band gaps of binary
3\textit{d} TMOs against the SCAN-calculated and experimental values.
Additionally, we evaluate the optimal Hubbard \emph{U} correction required for
each transition metal (TM) to improve the accuracy of the r$^2$SCAN functional,
based on experimental oxidation enthalpies, and verify the transferability of
the \emph{U} values by comparing against experimental properties on other
TM-containing oxides. Notably, including the \textit{U}-correction to r$^2$SCAN
increases the lattice parameters, on-site magnetic moments and band gaps of
TMOs, apart from an improved description of the ground state electronic state
in narrow band gap TMOs. The r$^2$SCAN and r$^2$SCAN+\textit{U} calculated
oxidation enthalpies follow the qualitative trends of SCAN and SCAN+\emph{U},
with r$^2$SCAN and r$^2$SCAN+\textit{U} predicting marginally larger lattice
parameters, smaller magnetic moments, and lower band gaps compared to SCAN and
SCAN+\textit{U}, respectively. We observe that the overall computational time
(i.e., for all ionic+electronic steps) required for r$^2$SCAN(+\textit{U}) to
be lower than SCAN(+\textit{U}). Thus, the r$^2$SCAN(+\textit{U}) framework can
offer a reasonably accurate description of the ground state properties of TMOs
with better computational efficiency than SCAN(+\textit{U}).",2301.00535v1
1996-06-05,Hall Resistivity in Ferromagnetic Manganese-Oxide Compounds,"Temperature-dependence and magnetic field-dependence of the Hall effect and
the magnetic property in manganese-oxide thin films are studied. The
spontaneous magnetization and the Hall resistivity are obtained for a various
of magnetic fields over all the temperature. It is shown that the Hall
resistivity in small magnetic field is to exhibit maximum near the Curie point,
and strong magnetic field moves the position of the Hall resistivity peak to
much high temperature and suppresses the peak value. The change of the Hall
resistance in strong magnetic field may be larger than that of the diagonal
ones. The abnormal Hall resistivity in the ferromagnetic manganese-oxide
thin-films is attributed to the spin-correlation fluctuation scattering.",9606030v1
2007-03-01,Magnetic effects at the interface between nonmagnetic oxides,"The electronic reconstruction at the interface between two insulating oxides
can give rise to a highly-conductive interface. In analogy to this remarkable
interface-induced conductivity we show how, additionally, magnetism can be
induced at the interface between the otherwise nonmagnetic insulating
perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the
interface is found, together with a logarithmic temperature dependence of the
sheet resistance. At low temperatures, the sheet resistance reveals magnetic
hysteresis. Magnetic ordering is a key issue in solid-state science and its
underlying mechanisms are still the subject of intense research. In particular,
the interplay between localized magnetic moments and the spin of itinerant
conduction electrons in a solid gives rise to intriguing many-body effects such
as Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, the Kondo effect, and
carrier-induced ferromagnetism in diluted magnetic semiconductors. The
conducting oxide interface now provides a versatile system to induce and
manipulate magnetic moments in otherwise nonmagnetic materials.",0703028v2
2013-07-21,Room-Temperature Electronically-Controlled Ferromagnetism at the LaAlO3/SrTiO3 Interface,"Reports of emergent conductivity, superconductivity, and magnetism at oxide
interfaces have helped to fuel intense interest in their rich physics and
technological potential. Here we employ magnetic force microscopy to search for
room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system. Using
electrical top gating to deplete electrons from the oxide interface, we
directly observe an in-plane ferromagnetic phase with sharply defined domain
walls. Itinerant electrons, introduced by a top gate, align
antiferromagnetically with the magnetization, at first screening and then
destabilizing it as the conductive state is reached. Subsequent depletion of
electrons results in a new, uncorrelated magnetic pattern. This newfound
control over emergent magnetism at the interface between two non-magnetic
oxides portends a number of important technological applications.",1307.5557v2
2014-01-09,Persistent Optically Induced Magnetism in Oxygen-Deficient Strontium Titanate,"Strontium titanate (SrTiO$_3$) is a foundational material in the emerging
field of complex oxide electronics. While its electronic and optical properties
have been studied for decades, SrTiO$_3$ has recently become a renewed
materials research focus catalyzed in part by the discovery of magnetism and
superconductivity at interfaces between SrTiO$_3$ and other oxides. The
formation and distribution of oxygen vacancies may play an essential but
as-yet-incompletely understood role in these effects. Moreover, recent
signatures of magnetization in gated SrTiO$_3$ have further galvanized interest
in the emergent properties of this nominally nonmagnetic material. Here we
observe an optically induced and persistent magnetization in oxygen-deficient
SrTiO$_{3-\delta}$ using magnetic circular dichroism (MCD) spectroscopy and
SQUID magnetometry. This zero-field magnetization appears below ~18K, persists
for hours below 10K, and is tunable via the polarization and wavelength of
sub-bandgap (400-500nm) light. These effects occur only in oxygen-deficient
samples, revealing the detailed interplay between magnetism, lattice defects,
and light in an archetypal oxide material.",1401.1871v1
2019-02-03,Long range antiferromagnetic order in a rocksalt high entropy oxide,"We report for the first time the magnetic structure of the high entropy oxide
$(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})O$ using neutron powder diffraction.
This material exhibits a sluggish magnetic transition but possesses a
long-range ordered antiferromagnetic ground state, as revealed by DC and AC
magnetic susceptibility, elastic and inelastic neutron scattering measurements.
The magnetic propagation wavevector is k=(1/2, 1/2, 1/2) based on the cubic
structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in
the (111) planes with spins antiparallel between two neighboring planes.
Inelastic neutron scattering reveals strong magnetic excitations at 100 K that
survive up to room temperature. This work demonstrates that entropy-stabilized
oxides represent a unique platform to study long range magnetic order with
extreme chemical disorder.",1902.00833v1
2019-02-05,Long-range magnetic ordering in rocksalt-type high-entropy oxides,"We report the magnetic properties of
Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$O, a high-entropy oxide with
rocksalt structure, and the influence of substitutions on these properties.
From the magnetic susceptibility and neutron diffraction measurements, we found
that this compound exhibits long-range magnetic order below 120 K despite the
substantial structuraldisorder. The other rocksalt-type high-entropy oxides
with various chemical substitutions were found to host either an
antiferromagnetic order or spin-glass state depending on the amount of magnetic
ions. The presence of magnetic order for such a disordered material potentially
provide a route to explore novel magnetic properties and functions.",1902.01825v2
2020-08-20,Engineering the magnetic and magnetocaloric properties of PrVO3 epitaxial oxide thin films by strain effects,"Combining multiple degrees of freedom in strongly-correlated materials such
as transition-metal oxides would lead to fascinating magnetic and
magnetocaloric features. Herein, the strain effects are used to markedly tailor
the magnetic and magnetocaloric properties of PrVO3 thin films. The selection
of appropriate thickness and substrate enables us to dramatically decrease the
coercive magnetic field from 2.4 T previously observed in sintered PVO3 bulk to
0.05 T for compressive thin films making from the PrVO3 compound a nearly soft
magnet. This is associated with a marked enhancement of the magnetic moment and
the magnetocaloric effect that reach unusual maximum values of roughly 4.86 uB
and 56.8 J/kg K in the magnetic field change of 6 T applied in the sample plane
at the cryogenic temperature range (3 K), respectively. This work strongly
suggests that taking advantage of different degrees of freedom and the
exploitation of multiple instabilities in a nanoscale regime is a promising
strategy for unveiling unexpected phases accompanied by a large magnetocaloric
effect in oxides.",2008.09193v1
2020-08-28,Tunnel magnetoresistance in scandium nitride magnetic tunnel junctions using first principles,"The magnetic tunnel junction is a cornerstone of spintronic devices and
circuits, providing the main way to convert between magnetic and electrical
information. In state-of-the-art magnetic tunnel junctions, magnesium oxide is
used as the tunnel barrier between magnetic electrodes, providing a uniquely
large tunnel magnetoresistance at room temperature. However, the wide bandgap
and band alignment of magnesium oxide-iron systems increases the
resistance-area product and causes challenges of device-to-device variability
and tunnel barrier degradation under high current. Here, we study using first
principles narrower-bandgap scandium nitride tunneling properties and transport
in magnetic tunnel junctions in comparison to magnesium oxide. These
simulations demonstrate a high tunnel magnetoresistance in Fe/ScN/Fe MTJs via
{\Delta}_1 and {\Delta}_2' symmetry filtering with low wavefunction decay
rates, allowing a low resistance-area product. The results show that scandium
nitride could be a new tunnel barrier material for magnetic tunnel junction
devices to overcome variability and current-injection challenges.",2008.12770v1
2022-02-08,"Electronic, Magnetic and Vibrational Properties of Single Layer Aluminum Oxide","The structural, magnetic, vibrational and electronic properties of single
layer aluminum oxide (AlO2) are investigated by performing state-of-the-art
first-principles calculations. Total energy optimization and phonon
calculations reveal that aluminum oxide forms a distorted octahedral structure
(1T'-AlO2) in its single layer limit. It is also shown that surfaces of
1T'-AlO2 display magnetic behavior originating from the O atoms. While the
ferromagnetic (FM) state is the most favorable magnetic order for 1T'-AlO2,
transformation to a dynamically stable antiferromagnetic (AFM) state upon a
slight distortion in the crystal structure is also possible. It is also shown
that Raman activities (350-400 cm^-1) obtained from the vibrational spectrum
can be utilized to distinguish the possible magnetic phases of the crystal
structure. Electronically, both FM and the AFM phases are semiconductors with
an indirect band gap and they can form a type-III vdW heterojunction with
graphene-like ultra-thin materials. Moreover, it is predicted that presence of
oxygen defects that inevitably occur during synthesis and production do not
alter the magnetic state, even at high vacancy density. Apparently, ultra-thin
1T'-AlO2 with its stable crystal structure, semiconducting nature and robust
magnetic state is a quite promising material for nanoscale device applications.",2202.04144v1
2023-04-01,Magnetic proximity effect at the interface of two-dimensional materials and magnetic oxide insulators,"Two-dimensional (2D) materials provide a platform for developing novel
spintronic devices and circuits for low-power electronics. In particular,
inducing magnetism and injecting spins in graphene have promised the emerging
field of graphene spintronics. This review focuses on the magnetic proximity
effect at the interface of 2D materials and magnetic oxide insulators. We
highlight the unique spin-related phenomena arising from magnetic exchange
interaction and spin-orbital coupling in 2D materials coupled with magnetic
oxides. We also describe the fabrication of multifunctional hybrid devices
based on spin transport. We conclude with a perspective of the field and
highlight challenges for the design and fabrication of 2D spintronic devices
and their potential applications in information storage and logic devices.",2304.00356v1
2024-01-31,Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing,"Tailoring the magnetic properties of iron oxide nanosystems is essential to
expand their biomedical applications. In this study, the 34 nm iron oxide
nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for
2 hours in the presence of O2, N2, He, and Ar to tune the respective phase
volume fractions and control the magnetic properties. X-ray diffraction and
magnetic measurements were carried out post-treatment to evaluate the changes
of the treated samples compared to the as-prepared, which showed an enhancement
of the alpha-Fe2O3 phase in the samples annealed with O2, while the others
indicated Fe3O4 enhancement. Furthermore, the latter samples indicated
enhancements in the crystallinity and saturation magnetization while coercivity
enhancement was most significant in the samples annealed with O2, resulting in
the highest specific absorption rates (up to 1000 W/g) in all the applied
fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia
measurements. The general enhancement in the specific absorption rate
post-annealing underscores the importance of the annealing atmosphere in the
enhancement of the magnetic and structural properties of nanostructures.",2401.18009v1
2005-10-13,Erratum to Three Papers on the beta-Pyrochlore Oxide Superconductors,"The magnitude of magnetic fields given in the three papers that report on the
superconductivity of the beta-pyrochlore oxides is corrected.",0510369v2
2016-07-20,MegaOhm Extraordinary Hall effect in oxidized CoFeB,"We report on development of controllably oxidized CoFeB ferromagnetic films
demonstrating the extraordinary Hall effect (EHE) resistivity exceeding 1 Ohmcm
and magnetic field sensitivity up to 10^6 Ohm/T. Such EHE resistivity is four
orders of magnitude higher than previously observed in ferromagnetic materials,
while sensitivity is two orders larger than the best of semiconductors",1607.05923v1
2012-05-14,Superconductivity in Mg/MgO interface,"Metastable superconductivity at \approx 50 K in the interfaces formed by
metallic and oxidized magnesium (MgO) has been observed by ac magnetic
susceptibility and electrical resistance measurements. The superconducting
interfaces have been produced by the surface oxidation of metallic magnesium
under special conditions.",1205.2981v1
2017-04-25,Characterization of Zinc oxide & Aluminum Ferrite and Simulation studies of M-H plots of Cobalt/Cobaltoxide,"Zinc oxide and Aluminum Ferrite were prepared Chemical route. The samples
were characterized by XRD and VSM. Simulation of M-H plots of Co/CoO thin films
were performed. Effect of parameters was observed on saturation magnetization.",1705.00525v2
2001-09-27,Enhanced paramagnetism of the 4d itinerant electrons in the rhodium oxide perovskite SrRhO3,"Polycrystalline rhodium(IV) oxide perovskite SrRhO3 was obtained by
high-pressure synthesis techniques, followed by measurements of the magnetic
susceptibility, electrical resistivity, and specific heat. The title compound
has five 4d-electrons per perovskite unit and shows Fermi-liquid behavior in
its electrical resistivity. The magnetic susceptibility is large [chi(300K)
\~1.1*10^{-3} emu/mol-Rh] and proportional to 1/T^2 (< 380 K), while there is
no magnetic long-range order above 1.8 K. The specific heat measurements
indicate a probable magnetic contribution below ~ 15 K, which is not predicted
by the self-consistent renormalization theory of spin fluctuations for both
antiferro- and ferromagnetic 3D nearly-ordered metals.",0109522v2
2007-11-02,Origin and control of ferromagnetism in dilute magnetic semiconductors and oxides,"The author reviews the present understanding of the hole-mediated
ferromagnetism in magnetically doped semiconductors and oxides as well as the
origin of high temperature ferromagnetism in materials containing no valence
band holes. It is argued that in these systems spinodal decomposition into
regions with a large and a small concentration of magnetic component takes
place. This self-organized assembling of magnetic nanocrystals can be
controlled by co-doping and growth conditions. Functionalities of these
multicomponent systems are described together with prospects for their
applications in spintronics, nanoelectronics, photonics, plasmonics, and
thermoelectrics.",0711.0343v1
2010-10-26,Giant directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic oxide BaCo$_2$Ge$_2$O$_7$,"We propose that concurrently magnetic and ferroelectric, i.e. multiferroic,
compounds endowed with electrically-active magnetic excitations
(electromagnons) provide a key to produce large directional dichroism for long
wavelengths of light. By exploiting the control of ferroelectric polarization
and magnetization in a multiferroic oxide Ba$_2$CoGe$_2$O$_7$, we demonstrate
the realization of such a directional light-switch function at terahertz
frequecies in resonance with the electromagnon absorption. Our results imply
that this hidden potential is present in a broad variety of multiferroics.",1010.5420v1
2014-12-25,Cu codoping control over magnetic precipitate formation in ZnCoO nanowires,"Using electrodeposition, we have grown nanowires of ZnCoO with Cu codoping
concentrations varying from 4-10 at.%, controlled only by the deposition
potential. We demonstrate control over magnetic Co oxide nano-precipitate
formation in the nanowires via the Cu concentration. The different magnetic
behavior of the Co oxide nano-precipitates indicates the potential of ZnCoO for
magnetic sensor applications.",1412.7792v1
2014-05-11,Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films,"Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface
is a fundamental and intriguing subject. Here we propose an approach to
manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying
MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the
MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and
decreases dramatically due to the onset of crystalline MgO forming with the
increase of MgO thickness. Our work opens an avenue to manipulate the magnetic
anisotropy by the modification of the ferromagnetic metal/oxide interface.",1405.2551v2
2012-05-02,Strain and structure driven complex magnetic ordering of a CoO overlayer on Ir(100),"We have investigated the magnetic ordering in the ultrathin c(10$\times$2)
CoO(111) film supported on Ir(100) on the basis of ab-initio calculations. We
find a close relationship between the local structural properties of the oxide
film and the induced magnetic order, leading to alternating ferromagnetically
and anti-ferromagnetically ordered segments. While the local magnetic order is
directly related to the geometric position of the Co atoms, the mismatch
between the CoO film and the Ir substrate leads to a complex long-range order
of the oxide.",1205.0493v1
2018-03-21,Self-assembly of magnetic iron oxide nanoparticles into cuboidal superstructures,"This chapter describes the synthesis and some characteristics of magnetic
iron oxide nanoparticles, mainly nanocubes, and focus on their self-assembly
into crystalline cuboids in dispersion. The influence of external magnetic
fields, the concentration of particles, and the temperature on the assembly
process is experimentally investigated.",1803.07922v1
2009-06-08,"Enhanced magnetism, memory and aging in Gold-Iron oxide nanoparticle composites","In this report we present systematic magnetic studies of pure iron oxide
nanoparticles and gold iron oxide nanocomposite with increasing Au particle
size/content. For the magnetic studies of these samples we have measured: (1)
zero field cooled (ZFC) and field cooled (FC) magnetization, (2) ac
susceptibility, (3) magnetization vs field at various temperatures, (4)
thermoremanant magnetization relaxation (TRM) and zero field cooled
magnetization relaxation (ZFCM) at fixed temperature for various wait times tw
for studying the aging effect, (5) magnetization memory effect and (6) exchange
bias as a function of cooling field. The detailed magnetic measurement analysis
indicates that the pure Fe3O4 nanoparticles sample behaves like a
superparamagnet and on incorporation of gold (Au) nanoparticles the
nanocomposite system slowly evolves from superparamagnetic to superspin glass
state. The memory and aging effect enhances with the increase of the Au
nanoparticle size/content. The most important observation in this study is the
enhancement of magnetization with the incorporation of Au nanoparticles. The
enhancement increases with the increase in the Au content in the nanocomposite.
We have explained the cause of this enhancement of magnetization as due to
large orbital magnetic moment formation at the Au/magnetic particle interface.",0906.1497v2
2017-03-13,High density nonmagnetic cobalt in thin films,"Recently high density (HD) nonmagnetic (NM) cobalt has been discovered in a
cobalt thin film, grown on Si(111). This cobalt film had a natural cobalt oxide
at the top. The oxide layer forms when the film is taken out of the
electron-beam deposition chamber and exposed to air. Thin HD NM cobalt layers
were found near the cobalt/silicon and the cobalt-oxide/cobalt interfaces,
while the thicker mid-depth region of the film was hcp cobalt with normal
density and normal magnetic moment. If an ultrathin film of gold is grown on
the cobalt layer, before exposing it to air, the oxidation of the cobalt
surface layer is prevented. It is important to investigate whether the growth
of HD NM cobalt layers in the thin film depends on (i) capping of the film by
the gold layer, (ii) the film thickness and (iii) the nature of the substrate.
The results of such investigations, presented here, indicates that for cobalt
films capped with a thin gold layer, and for various film thicknesses, HD NM
cobalt layers are still observed. However, instead of a Si substrate, when the
cobalt films are grown on oxide substrates, such as silicon oxide or cobalt
oxide, HD NM cobalt layers are not observed.",1703.04270v1
2021-10-05,Formation of a stable surface oxide in MnBi$_2$Te$_4$ thin films,"Understanding the air-stability of MnBi$_2$Te$_4$ thin films is crucial for
the development and long-term operation of electronic devices based around
magnetic topological insulators. In the present work, we study MnBi$_2$Te$_4$
thin films upon exposure to atmosphere using a combination of synchrotron-based
photoelectron spectroscopy, room temperature electrical transport and atomic
force microscopy to determine the oxidation process. After 2 days air exposure
a 2 nm thick oxide passivates the surface, corresponding to oxidation of only
the top two surface layers, with the underlying layers preserved. This
protective oxide layer results in samples that still exhibit metallic
conduction even after several days air exposure. Furthermore, the work function
decreases from 4.4 eV for pristine MnBi$_2$Te$_4$ to 4.0 eV after the formation
of the oxide, along with only a small shift in the core levels indicating
minimal doping as a result of air exposure. With the oxide confined to the top
surface layers, and the underlying layers preserved, it may be possible to
explore new avenues in how to handle, prepare and passivate future
MnBi$_2$Te$_4$ devices.",2110.02412v1
2015-11-11,Characterization of Magnetic Ni Clusters on Graphene Scaffold after High Vacuum Annealing,"Magnetic Ni nanoclusters were synthesized by electron beam deposition
utilizing CVD graphene as a scaffold. The subsequent clusters were subjected to
high vacuum (5-8 x10-7 torr) annealing between 300 and 600 0C. The chemical
stability, optical and morphological changes were characterized by X-ray
photoemission microscopy, Raman spectroscopy, atomic force microscopy and
magnetic measurement. Under ambient exposure, nickel nanoparticles was observed
to be oxidized quickly, forming antiferromagnetic nickel oxide. Here, we report
that the majority of the oxidized nickel is in non-stoichiometric form and can
be reduced under high vacuum at temperature as low as 300 0C. Importantly, the
resulting annealed clusters are relatively stable and no further oxidation was
detectable after three weeks of air exposure at room temperature.",1511.03349v1
2016-04-04,Reversibly switchable electromagnetic device with leakage-free electrolyte,"Electrical control of oxygen off-stoichiometry of transition-metal oxides at
room temperature is a desired strategy to simultaneously switch the electrical
conductance and magnetism of the device. Although the use of the
electrochemical redox reaction of transition-metal oxides is the most
reasonable way to achieve the aforementioned switch, such a device has not been
realized because of the lack of a leakage-free liquid electrolyte. Here, we
demonstrate an electromagnetic device that can reversibly switch a
transition-metal oxide from an insulator/non-magnet to a metal/magnet (Tc=275
K) using a newly developed 'leakage-free electrolyte', incorporated in an
amorphous NaTaO3 nanopillar array film. Reversible switching occurs
electrically, obeying Faraday's laws of electrolysis, under a DC voltage of
+(-)3 V within 2-3 s at RT. The present electromagnetic device does not have
the drawback of liquid leakage, and the leakage-free electrolyte provides a
novel design concept for practical electromagnetic devices using
transition-metal oxides.",1604.00824v1
2013-08-06,Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties,"A cluster deposition method was used to produce films of loosely aggregated
nanoclusters (NC) of Fe core-Fe3O4 shell or fully oxidized Fe3O4. Films of
these NC on Si(100) or MgO(100)/Fe3O4(100) were irradiated to 10^16 Si2+/cm2
near room temperature using an ion accelerator. Ion irradiation creates
structural change in the NC film with corresponding chemical and magnetic
changes which depend on the initial oxidation state of the cluster. Films were
characterized using magnetometry (hysteresis, first order reversal curves),
microscopy (transmission electron, helium ion), and x-ray diffraction. In all
cases, the particle sizes increased due to ion irradiation, and when a core of
Fe is present, irradiation reduces the oxide shells to lower valent Fe species.
These results show that ion irradiated behavior of the nanocluster films
depends strongly on the initial nanostructure and chemistry, but in general
saturation magnetization decreases slightly.",1308.1384v1
2017-12-13,Two-dimensional electron system at the magnetically tunable EuO/SrTiO$_3$ interface,"We create a two-dimensional electron system (2DES) at the interface between
EuO, a ferromagnetic insulator, and SrTiO3, a transparent non-magnetic
insulator considered the bedrock of oxide-based electronics. This is achieved
by a controlled in-situ redox reaction between pure metallic Eu deposited at
room temperature on the surface of SrTiO3, an innovative bottom-up approach
that can be easily generalized to other functional oxides and scaled to
applications. Additionally, we find that the resulting EuO capping layer can be
tuned from paramagnetic to ferromagnetic, depending on the layer thickness.
These results demonstrate that the simple, novel technique of creating 2DESs in
oxides by deposition of elementary reducing agents [T. C. R\""odel et al., Adv.
Mater. 28, 1976 (2016)] can be extended to simultaneously produce an active,
e.g. magnetic, capping layer enabling the realization and control of additional
functionalities in such oxide-based 2DESs.",1712.04891v1
2017-09-28,New Approach to Determine the Quality of Graphene,"The reduction of graphene oxide is one of the most facile methods to
fabricate a large amount of graphene and the reduction rate of graphene oxide
is related with the quality of synthesized graphene for its possible
application. The reduction rate is usually determined by using various
spectroscopy measurements such as Raman spectroscopy, Fourier transform
infrared spectroscopy, and X-ray photoelectron spectroscopy. Here we propose
that the magnetic data can be used as a means of determining the quality of
graphene oxide (GO) and reduced graphene oxide (RGO) by the investigation of
close relation between magnetic moment and chemical bonding state. Our
experimental findings and previous theoretical studies suggest that hydroxyl
functional groups in GO mainly contribute to Langevin paramagnetism, carboxyl
functional groups in RGO1 act as the source for Pauli paramagnetism, and sp2
bonding state in RGO2 plays a major role on the diamagnetism. Especially in
terms of mass production, the magnetic data is useful for decomposing the
chemical bonding electronic states in graphene-like samples and judging their
quality.",1709.09879v1
2004-07-23,"High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)","Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found
and we measured the pressure dependence of magnetization up to 1.2 GPa in order
to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is
found that the initial pressure dependence of Tc is positive for all the
compounds. Only KOs2O6 exhibits a saturation in Tc at 0.56 GPa and the downturn
at higher pressure",0407610v1
2005-04-26,Spin filtering through ferromagnetic BiMnO3 tunnel barriers,"We report on experiments of spin filtering through ultra-thin single-crystal
layers of the insulating and ferromagnetic oxide BiMnO3 (BMO). The spin
polarization of the electrons tunneling from a gold electrode through BMO is
analyzed with a counter-electrode of the half-metallic oxide La2/3Sr1/3MnO3
(LSMO). At 3 K we find a 50% change of the tunnel resistances according to
whether the magnetizations of BMO and LSMO are parallel or opposite. This
effect corresponds to a spin filtering effciency of up to 22%. Our results thus
show the potential of complex ferromagnetic insulating oxides for spin
filtering and injection.",0504667v1
2007-02-17,"Metal-insulator Transition in a Pyrochlore-type Ruthenium oxide, Hg2Ru2O7","A new pyrochlore ruthenium oxide, Hg2Ru2O7 was synthesized under a high
pressure of 6 GPa. In contrast to the extensively studied Ru4+ oxides, this
compound possesses a novel Ru5+ valence state, corresponding to a half-filled
t_2g_3 electron configuration. Hg2Ru2O7 exhibits a first order metal-insulator
transition at 107 K, accompanied by a structural transition from cubic to lower
symmetry. The behavior of the magnetic susceptibility suggests the possible
formation of a spin singlet in the insulating low temperature state.",0702411v1
2014-09-16,Tuning ferromagnetism at interfaces between insulating perovskite oxides,"We use density functional theory calculations to show that the LaAlO3|SrTiO3
interface between insulating perovskite oxides is borderline in satisfying the
Stoner criterion for itinerant ferromagnetism and explore other oxide
combinations with a view to satisfying it more amply. The larger lattice
parameter of an LaScO3|BaTiO3 interface is found to be less favorable than the
greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the
latter is predicted to exhibit robust magnetism with a larger saturation moment
and a higher Curie temperature. Our results provide support for a ""two phase""
picture of coexistent superconductivity and ferromagnetism.",1409.4554v1
2015-02-08,Change in sign of the Hall coefficient from Fermi surface curvature in underdoped high Tc copper oxide superconductors,"It has recently been proposed that the Fermi surface of underdoped high Tc
copper oxide materials within the charge-ordered regime consists of a
diamond-shaped electron pocket constructed from arcs connected at vertices. We
show here that on modeling the in-plane magnetotransport of such a Fermi
surface using the Shockley-Chambers tube integral approach and a uniform
scattering time, several key features of the normal state in-plane transport of
the underdoped copper oxide systems can be understood. These include the sign
reversal in the Hall coefficient, the positive magnetoresistance and magnetic
quantum oscillations in the Hall coefficient.",1502.02273v1
2015-03-03,Resolution of SU(2) monopole singularities by oxidation,"We show how ""colored"" SU(2) BPS monopoles (that is: SU(2) monopoles
satisfying the Bogomol'nyi equation whose Higgs field and magnetic charge
vanish at infinity and which are singular at the origin) can be obtained from
the BPST instanton by a singular dimensional reduction, explaining the origin
of the singularity and implying that the singularity can be cured by the
oxidation of the solution. We study the oxidation of other monopole solutions
in this scheme.",1503.01044v1
2015-09-14,Multi-Fields Modulation of Physical Properties of Oxide Thin Films,"Oxide thin films exhibit versatile physical properties such as magnetism,
ferroelectricity, piezoelectricity, metal-insulator transition (MIT),
multiferroicity, colossal magnetoresistivity, switchable resistivity, etc. More
importantly, the exhibited multifunctionality could be tuned by various
external fields, which has enabled demonstration of novel electronic devices.
In this article, recent studies of the multi-fields modulation of physical
properties in oxide thin films have been reviewed. Some of the key issues and
prospects about this field are also addressed.",1509.03939v1
2017-09-26,Spintronic Functionalities in Multiferroic Oxide-based Heterostructures,"The list of materials systems displaying both electric and magnetic long
range order is short. Oxides, however, concentrate numerous examples of
multiferroicity with, in some cases, a large magnetoelectric coupling. As a
result, a fruitful research field has emerged contemporaneously with the
consolidation of spintronic. The synergy between multiferroics and spintronics
was meant to be inevitable and hence the characterization of spintronic
functionalities in multiferroic materials is rather abundant. The aim of the
present chapter is to review the oxide heterostructures where magnetoelectric
coupling is demonstrated by means of spintronic functionalities (i.e.
magnetoresistance, anisotropic magnetoresistance, giant magnetoresistance or
tunnel magnetoresistance).",1709.08918v1
2023-11-10,Observation of the out-of-plane orbital antidamping-like torque,"The out-of-plane antidamping-like orbital torque fosters great hope for
high-efficiency spintronic devices. Here we report experimentally the
observation of out-of-plane antidamping-like torque that could be generated by
z-polarized orbital current in ferromagnetic-metal/oxidized Cu bilayers, which
is presented unambiguously by the magnetic field angle dependence of
spin-torque ferromagnetic resonance signal. The oxidized Cu thickness
dependence of orbital torque ratios highlights the interfacial effect would be
responsible for the generation of orbital current. Besides that, the oxidized
Cu thickness dependence of damping parameter further proves the observation of
antidamping-like torque. This result contributes to enriching the
orbital-related theory of the generation mechanism of the orbital torque.",2311.05868v1
1996-06-05,Transport and magnetic properties in ferromagnetic manganese-oxide thin films,"The transport and magnetic properties in ferromagnetic manganese-oxide thin
films are studied based on the model of the coupling between the mobile
d-electrons and the core spins in Mn ions. The spontaneous magnetization and
the resistivity are obtained for various magnetic fields and temperature. The
resistivity in absence of magnetic field and the magnetoresistance exhibit
maxima near the Curie temperature, the applied magnetic field moves the
position of the resistivity peak to high temperature and suppresses the peak
value, which agree with the experimental results. The Hall resistivity is
predicted to exhibit maximum near the Curie point. The pressure effect of the
magnetoresistance can also be explained qualitatively in this mechanism. The
colossal magnetoresistance in ferromagnetic manganese-oxide thin films is
attributed to the spin-correlation fluctuation scattering and the low
dimensional effect.",9606029v1
2015-09-03,Interfacial Magnetism in Complex Oxide Heterostructures Probed by Neutrons and X-rays,"Magnetic complex-oxide heterostructures are of keen interest because a wealth
of phenomena at the interface of dissimilar materials can give rise to
fundamentally new physics and potentially valuable functionalities. Altered
magnetization, novel magnetic coupling and emergent interfacial magnetism at
the epitaxial layered-oxide interfaces are under intensive investigation, which
shapes our understanding on how to utilize those materials, particularly for
spintronics. Neutron and x-ray based techniques have played a decisive role in
characterizing interfacial magnetic structures and clarifying the underlying
physics in this rapidly developing field. Here we review some recent
experimental results, with an emphasis on those studied via polarized neutron
reflectometery and polarized x-ray absorption spectroscopy. We conclude with
some perspectives.",1509.00912v1
2016-04-28,Incommensurate spin correlations in highly oxidized cobaltates La$_{2-x}$Sr$_{x}$CoO$_{4}$,"We observe quasi-static incommensurate magnetic peaks in neutron scattering
experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states
that have been reported to be paramagnetic. This enables us to measure the
magnetic excitations in this highly hole-doped incommensurate regime and
compare our results with those found in the low-doped incommensurate regime
that exhibit hourglass magnetic spectra. The hourglass shape of magnetic
excitations completely disappears given a high Sr doping. Moreover, broad
low-energy excitations are found, which are not centered at the incommensurate
magnetic peak positions but around the quarter-integer values that are
typically exhibited by excitations in the checkerboard charge ordered phase.
Our findings suggest that the strong inter-site exchange interactions in the
undoped islands are critical for the emergence of hourglass spectra in the
incommensurate magnetic phases of La2-xSrxCoO4.",1604.08389v1
2018-10-23,Absence of a multiglass state in some transition metal doped quantum paraelectrics,"We critically investigate the purported existence of a multiglass state in
the quantum paraelectrics SrTiO${_3}$ and KTaO${_3}$ doped with magnetic 3d
transition metals. We observe that the transition metals have limited
solubility in these hosts, and that traces of impurity magnetic oxides persist
even in the most well processed specimens. Our dielectric measurements indicate
that the polar nano-regions formed as a consequence of doping appear to lack
co-operativity, and the associated relaxation process exhibits a thermally
activated Arrhenius form. At lower temperatures, the dielectric susceptibility
could be fit using the Barrett's formalism, indicating that the
quantum-paraelectric nature of the host lattices are unaltered by the doping of
magnetic transition metal oxides. All these doped quantum paraelectrics exhibit
a crossover from the high temperature Curie-Weiss regime to one dominated by
quantum fluctuations, as evidenced by a $T{^2}$ dependence of the temperature
dependent dielectric susceptibility. The temperature dependence of the magnetic
susceptibility indicate that magnetic signatures observed in some of the
specimens could be solely ascribed to the presence of impurity oxides
corresponding to the magnetic dopants used. Hence, the doped quantum
paraelectrics appear to remain intrinsically paramagnetic down to the lowest
measured temperatures, ruling out the presence of a multiglass state.",1810.09822v1
2013-06-25,Efficient spin injection through a crystalline AlOx tunnel barrier prepared by the oxidation of an ultra-thin Al epitaxial layer on GaAs,"We report that an ultra-thin, post-oxidized aluminum epilayer grown on the
AlGaAs surface works as a high-quality tunnel barrier for spin injection from a
ferromagnetic metal to a semiconductor. One of the key points of the present
oxidation method is the formation of the crystalline AlOx template layer
without oxidizing the AlGaAs region near the Al/AlGaAs interface. The oxidized
Al layer is not amorphous but show well-defined single crystalline feature
reminiscent of the spinel gamma-AlOx phase. A spin-LED consisting of an Fe
layer, a crystalline AlOx barrier layer, and an AlGaAs-InGaAs double
hetero-structure has exhibited circularly polarized electroluminescence with
circular polarization of P_{EL} = 0.145 at the remnant magnetization state of
the Fe layer, indicating the relatively high spin injection efficiency (epsilon
= 2P_{EL} / P_{Fe}) of 0.63.",1306.5847v1
2014-04-09,A high Neel temperature 5$d$ oxide: NaOsO$_3$,"The origin of a high Neel temperature in a 5$d$ oxide, NaOsO$_3$, has been
analyzed within the mean-field limit of a multiband Hubbard model and compared
with the analogous 4$d$ oxide, SrTcO$_3$. Our analysis shows that there are a
lot of similarities in both these oxides on the dependence of the the effective
exchange interaction strength ($J_0$) on the electron-electron interaction
strength ($U$). However, the relevant value of $U$ in each system puts them in
different portions of the parameter space. Although the Neel temperature for
NaOsO$_3$ is less than that for SrTcO$_3$, our results suggest that there could
be examples among other 5$d$ oxides which have a higher Neel temperature. We
have also examined the stability of the G-type antiferromagnetic state found in
NaOsO$_3$ as a function of electron doping within GGA+U calculations and find a
robust G-type antiferromagnetic metallic state stabilized. The most surprising
aspect of the doped results is the rigid band-like evolution of the electronic
structure which indicates that the magnetism in NaOsO$_3$ is not driven by
fermi surface nesting.",1404.2356v1
2015-09-02,The characterization of Co-nanoparticles supported on graphene,"The results of density functional theory calculations and measurements using
X-ray photoelectron spectroscopy of Co-nanoparticles dispersed on graphene/Cu
are presented. It is found that for low cobalt thickness (0.02 nm - 0.06 nm)
the Co forms islands distributed non-homogeneously which are strongly oxidized
under exposure to air to form cobalt oxides. At greater thicknesses up to 2 nm
the upper Co-layers are similarly oxidized whereas the lower layers contacting
the graphene remain metallic. The measurements indicate a Co2+ oxidation state
with no evidence of a 3+ state appearing at any Co thickness, consistent with
CoO and Co[OH]2. The results show that thicker Co (2nm) coverage induces the
formation of a protective oxide layer while providing the magnetic properties
of Co nanoparticles.",1509.00575v1
2015-09-10,Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation,"Ferromagnetic contacts are widely used to inject spin polarized currents into
non-magnetic materials such as semiconductors or 2-dimensional materials like
graphene. In these systems, oxidation of the ferromagnetic materials poses an
intrinsic limitation on device performance. Here we investigate the role of
ex-situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as
an oxidation barrier for nanostructured cobalt and permalloy electrodes. The
chemical state of the ferromagnets was investigated using X-ray photoemission
electron microscopy owing to its high sensitivity and lateral resolution. We
have compared the oxide thickness formed on ferromagnetic nanostructures
covered by hBN to uncovered reference structures. Our results show that hBN
reduces the oxidation rate of ferromagnetic nanostructures suggesting that it
could be used as an ultra-thin protection layer in future spintronic devices.",1509.03087v2
2020-07-15,Structure and Properties of Thermoresponsive Diblock Copolymers Embedded with Metal Oxide Nanoparticles,"Nanostructured polymer-metal oxide composites are a current research area of
great importance due to its highlight applications in sensors, optics,
catalysts and drug delivery. Particularly the use of thermoresponsive polymers
gives more flexibilities and possibilities in the design and construction of
polymer templates. In the present investigation, the structure and magnetic
properties of hybrid metal oxide/DBC films composed of two kinds of
polystyrene-block-poly (N-isopropylacrylamide)(PS-b-PNIPAM) diblock copolymers
(DBCs) with PS and PNIPAM as the major polymer domains respectively, and iron
oxide were investigated. The thermoresponsive PNIPAM has a lower critical
solution temperature (LCST) in aqueous solution at 32{\deg}C, which enables the
controllable volume ratio of PS and PNIPAM in the structure of PS-b-PNIPAM
diblock copolymers (DBCs). Thus, a temperature and humidity controlling cell
was designed and built for precisely tuning the block structure of PS-b-PNIPAM
DBCs, which was investigated by in-situ small-angle X-ray scattering (SAXS) and
grazing-incidence small-angle X-ray scattering (GISAXS) measurements. The
superparamagnetic behavior of the heat-treated hybrid iron oxide/PS-b-PNIPAM
DBC films was investigated using a superconducting quantum interference device
(SQUID) magnetometer.",2007.10111v1
2017-04-17,Structural Distortions At Polar Manganite Interfaces,"Electronic, lattice, and spin interactions at the interfaces between
crystalline complex transition metal oxides can give rise to a wide range of
functional electronic and magnetic phenomena not found in bulk. At
hetero-interfaces, these interactions may be enhanced by combining oxides where
the polarity changes at the interface. The physical structure between non-polar
SrTiO$_3$ and polar La$_{1-x}$Sr$_x$MnO$_3$(x=0.2) is investigated using high
resolution synchrotron x-ray diffraction to directly determine the role of
structure in compensating the polar discontinuity. At both the oxide-oxide
interface and vacuum-oxide interfaces, the lattice is found to expand and
rumple along the growth direction. The SrTiO$_3$/La$_{1-x}$Sr$_x$MnO$_3$
interface also exhibits intermixing of La and Sr over a few unit cells. The
results, hence, demonstrate that polar distortions and ionic intermixing
coexist and both pathways play a significant role at interfaces with polar
discontinuities.",1704.05114v2
2021-02-10,Controlling the oxidation of magnetic and electrically conductive solid-solution iron-rhodium nanoparticles synthesized by Laser Ablation in Liquids,"This study focuses on the synthesis of FeRh nanoparticles via pulsed laser
ablation in liquid and on controlling the oxidation of the synthesized
nanoparticles. Formation of monomodal {\gamma}-FeRh nanoparticles was confirmed
by transmission electron microscopy (TEM) and their composition confirmed by
atom probe tomography (APT). On these particles, three major contributors to
oxidation were analysed: 1) dissolved oxygen in the organic solvents, 2) the
bound oxygen in the solvent and 3) oxygen in the atmosphere above the solvent.
The decrease of oxidation for optimized ablation conditions was confirmed
through energy-dispersive X-ray (EDX) and M\""ossbauer spectroscopy.
Furthermore, the time dependence of oxidation was monitored for dried FeRh
nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By
magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the
solution and characteristic differences of nanostrand formation between
{\gamma}-FeRh and B2-FeRh nanoparticles were observed.",2102.05652v1
2021-04-16,"Structural phase stability, electronic structure, magnetic properties and chemical bonding analysis of transition metal ammine borohydrides with amphoteric hydrogen for hydrogen storage","Usually the ions of a particular element in solids are in positive or
negative oxidation states, depending upon the chemical environment. It is
highly unusual for an atom having both positive as well as negative oxidation
states simultaneously within the same structural framework in a particular
compound. Our structural and chemical bonding analyses show that the hydrogen
ions in the transition metal ammine borohydrides (TMABHs) with the chemical
formula M(BH4)2(NH3)2 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) have both
positive and negative oxidation states. Our detailed analyses confirm the
amphoteric behaviour of hydrogen where hydrogen closer to boron is in negative
oxidation state and that closer to nitrogen is in the positive oxidation state.
From the spin polarised van der Waals interaction included calculation, we
found that TMABHs has antiferromagnetic ordering as ground state. Our nudged
elastic band calculation show that the migration barrier for ammonia diffusion
in these materials are more than 1 eV and hence these compounds may be used for
energy storage applications since they have high weight percentage of hydrogen.
The presence of amphoteric behaviour of hydrogen in TMABHs has implication in
designing volume efficient hydrides for hydrogen storage applications.",2104.08140v1
2022-06-02,Defect Profiling of Oxide-Semiconductor Interfaces Using Low-Energy Muons,"Muon spin rotation with low-energy muons (LE{\mu}SR) is a powerful nuclear
method where electrical and magnetic properties of surface-near regions and
thin films can be studied on a length scale of $\approx$\SI{200}{\nano\meter}.
In this work, we show the potential of utilizing low-energy muons for a
depth-resolved characterization of oxide-semiconductor interfaces, i.e. for
silicon (Si) and silicon carbide (4H-SiC). Silicon dioxide (SiO$_2$) grown by
plasma-enhanced chemical vapor deposition (PECVD) and by thermal oxidation of
the SiO$_2$-semiconductor interface are compared with respect to interface and
defect formation. The nanometer depth resolution of {\mu}allows for a clear
distinction between the oxide and semiconductor layers, while also quantifying
the extension of structural changes caused by the oxidation of both Si and SiC.",2206.00925v1
2022-08-04,Reversible Tuning of Collinear versus Chiral Magnetic Order by Chemical Stimulus,"The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediates collinear
magnetic interactions via the conduction electrons of a non-magnetic spacer,
resulting in a ferro- or antiferromagnetic magnetization in magnetic
multilayers. The resulting spin-polarized charge transport effects have found
numerous applications. Recently it has been discovered that heavy non-magnetic
spacers are able to mediate an indirect magnetic coupling that is non-collinear
and chiral. This Dzyaloshinskii-Moriya-enhanced RKKY (DME-RKKY) interaction
causes the emergence of a variety of interesting magnetic structures, such as
skyrmions and spin spirals. Applications using these magnetic quasi-particles
require a thorough understanding and fine-tuning of the balance between the
Dzyaloshinskii-Moriya interaction and other magnetic interactions, e.g., the
exchange interaction and magnetic anisotropy contributions. Here, we show by
spin-polarized scanning tunneling microscopy that the spin structure of
manganese oxide chains on Ir(001) can reproducibly be switched from chiral to
collinear antiferromagnetic interchain interactions by increasing the oxidation
state of MnO$_2$ while the reverse process can be induced by thermal reduction.
The underlying structural change is revealed by low-energy electron diffraction
intensity data (LEED-IV) analysis. Density functional theory calculations
suggest that the magnetic transition may be caused by a significant increase of
the Heisenberg exchange upon oxidation.",2208.02570v1
2020-04-14,"On the Elastic Anisotropy of the Entropy-Stabilized Oxide (Mg, Co, Ni, Cu, Zn)O","In this paper, we study the elastic properties of the entropy-stabilized
oxide (Mg, Co, Ni, Cu, Zn)O, using experimental and first principles
techniques. Our measurements of the indentation modulus on grains with a wide
range of crystallographic orientations of the entropy-stabilized oxide revealed
a high degree of elastic isotropy at ambient conditions. First principles
calculations predict mild elastic anisotropy for the paramagnetic structure,
which decreases when the system is considered to be non-magnetic. When the
antiferromagnetic state of CoO, CuO and NiO is accounted for in the
calculations, a slight increase in the elastic anisotropy is observed,
suggesting a coupling between magnetic ordering and the orientation dependent
elastic properties. Furthermore, an examination of the local structure reveals
that the isotropy is favored through local ionic distortions of Cu and Zn - due
to their tendency to form tenorite and wurtzite phases. The relationships
between the elastic properties of the multicomponent oxide and those of its
constituent binary oxides are reviewed. These insights open up new avenues for
controlling isotropy for technological applications through tuning composition
and structure in the entropy-stabilized oxide or the high entropy compounds in
general.",2004.06613v1
2012-05-22,Observation of 0 to pi transition in YBCO/Gallium oxide multilayers,"When two superconductors are coupled via an insulator the phase difference
between them is expected to be zero in the ground state and such Josephson
junctions are known as ""0"" type Josephson junctions . But in the presence of
magnetic impurities in the barrier or ferromagnetism, the phase difference in
the ground state could become pi; such Josephson junctions are known as ""pi""
type Josephson junctions1-4. Experimental results have confirmed the
observation of a 0 to pi transition as a function of temperature in Josephson
junctions such as Nb/Cu1-xNix/Nb based on ferromagnetic weak links with low
exchange energy5. Recently, observation of possible magnetic behaviour in
oxides has been reported6,7, and it would, therefore, be interesting to study
the Josephson coupling in YBCO/gallium oxide multilayers. This work reports the
observation of a very anomalous superconducting behaviour in YBCO/gallium oxide
multilayers. A transition to the superconducting state has been observed with
an enhanced superconducting transition temperature of 98 K in the YBCO/gallium
oxide multilayer followed by a second transition temperature at 90 K with the
multilayer losing its superconductivity at intermediate temperatures. This
behaviour is explained by assuming that the Josephson coupling between the
superconducting YBCO layers in the multilayer changes from pi type to 0 type.
This is the first experimental observation of the 0 to pi transition in
HTSC/gallium oxide/HTSC thin film structures.",1205.4869v1
2022-12-04,Explore of exfoliable multifunctional high-k two-dimensional oxides,"As the continuing down-scaling of field-effect transistors (FETs) in
more-than-Moore integrated circuits, finding new functional two-dimensional
(2D) materials with a higher dielectric constant (high-k) serve as gate
dielectrics is critical. Here, we identify dozens of binary 2D oxides by
screening potentially exfoliable bulk metal oxides despite of their non-layered
structures followed by simulation of the exfoliation process. For dynamically
stable materials, we fully characterize their static dielectric constants and
electronic structures, among which GeO2(011)/(101)/(1-11) 2D oxides exhibit
unusually high k values (85-99), being much higher than the k of the currently
highly regarded 2D dielectrics CaF2 (k ~6) and \b{eta}-Bi2SeO5 (k ~22),
together with band gap of 3.3 eV. We further design 2D high-k oxides/2D
semiconductors (such as MoS2) heterostructures, and determine by DFT
calculations whether they can form Van der Waals interfaces to evaluate their
compatibility as gate dielectrics in 2D FETs. In addition to dielectric
properties, we also explore magnetic and mechanical properties of potentially
exfoliable 2D oxides, revealing a number of functional materials that can be
studied experimentally, notably including ferromagnetic half semiconductors,
non-magnetic spintronic materials, flexible high-k 2D oxides, and auxetic
monolayers.",2212.01731v1
2024-03-03,Crystal Structure and Magnetism of Actinide Oxides: A Review,"In actinide systems, the 5f electrons experience a uniquely delicate balance
of effects and interactions having similar energy scales, which are often
difficult to properly disentangle. This interplay of factors such as the dual
nature of 5f-states, strong electronic correlations, and strong spin-orbit
coupling results in electronically unusual and intriguing behavior such as
multi-k antiferromagnetic ordering, multipolar ordering, mott-physics, mixed
valence configurations, and more. Despite the inherent allure of their exotic
properties, the exploratory science of even the more basic, binary systems like
the actinide oxides has been limited due to their toxicity, radioactivity, and
reactivity. In this article, we provide an overview of the available synthesis
techniques for selected binary actinide oxides, including the actinide
dioxides, sesquioxides, and a selection of higher oxides. For these oxides, we
also review and evaluate the current state of knowledge of their crystal
structures and magnetic properties. In many aspects, substantial knowledge gaps
exist in the current body of research on actinide oxides related to
understanding their electronic ground states. Bridging these gaps is vital for
improving not only a fundamental understanding of these systems but also of
future nuclear technologies. To this end, we note the experimental techniques
and necessary future investigations which may aid in better elucidating the
nature of these fascinating systems.",2403.01634v1
1999-02-18,Neutron Scattering from Magnetic Excitations in Bi_2 Sr_2 Ca_2 O_8+delta,"Many physical properties of the copper oxide high temperature superconductors
appear to defy the conventional (one-electron) theory of metals, and the
development of new theories incorporating strong electron correlations is
currently at the forefront of condensed matter physics. Inelastic neutron
scattering provides incisive information about collective magnetic excitations
that is required to guide this effort. Such measurements have thus far proven
possible for only two of the many families of high temperature superconductors,
La_{2-x} Sr_x CuO_4 and YBa_2 Cu_3 O_{6+x},because suitably large single
crystals of other copper oxide compounds could not be grown. While the magnetic
spectra of both materials bear certain similarities, there are also pronounced
differences that have hampered a unified description of the spin dynamics in
the copper oxides. In particular, a sharp resonant spin excitation dominates
the spectrum in the superconducting state of YBa_2 Cu_3 O_{6+x}, but is not
found in La_{2-x} Sr_x CuO_4. Here we report the discovery of a magnetic
resonance peak in the superconducting state of a different copper oxide system,
Bi_2 Sr_2 Ca Cu_2 O_{8+\delta}, made possible by the synthesis of a sizable
single crystal and modern neutron optics. This provides evidence of the
generality of this unusual phenomenon among the copper oxides and greatly
extends the empirical basis for its theoretical description.",9902262v2
2021-09-05,Lateral modulation of magnetic anisotropy in tricolor 3d-5d oxide superlattices,"Manipulating magnetic anisotropy (MA) purposefully in transition metal oxides
(TMOs) enables the development of oxide-based spintronic devices with practical
applications. Here, we report a pathway to reversibly switch the lateral
magnetic easy-axis via interfacial oxygen octahedral coupling (OOC) effects in
3d-5d tricolor superlattices, i.e. [SrIrO3,mRTiO3,SrIrO3,2La0.67Sr0.33MnO3]10
(RTiO3: SrTiO3 and CaTiO3). In the heterostructures, the anisotropy energy
(MAE) is enhanced over one magnitude to ~106 erg/cm3 compared to
La0.67Sr0.33MnO3 films. Moreover, the magnetic easy-axis is reversibly
reoriented between (100)- and (110)-directions by changing the RTiO3. Using
first-principles density functional theory calculations, we find that the
SrIrO3 owns a large single-ion anisotropy due to its strong spin-orbit
interaction. This anisotropy can be reversibly controlled by the OOC, then
reorient the easy-axis of the superlattices. Additionally, it enlarges the MAE
of the films via the cooperation with a robust orbital hybridization between
the Ir and Mn atoms. Our results indicate that the tricolor superlattices
consisting of 3d and 5d oxides provide a powerful platform to study the MA and
develop oxide-based spintronic devices.",2109.02062v1
2005-08-17,Magnetic properties in a partially oxidized nanocomposite of Cu-CuCl,"Magnetism of a very thin antiferromagnetic (AFM) surface CuO has been
investigated with the partially oxidized nanocomposites of Cu-CuCl, ~ 200 nm.
The samples are characterized by X-ray diffraction, X-ray photoelectron
spectroscopy, X-ray-excited Auger electron spectroscopy, transmission electron
microscope and magnetic measurements. The characterizations indicate that the
composites have a core-shell structure. Before the oxidation, it is
(Cu)core/(CuCl)shell, and after the oxidation,
(Cu)core/(Cu2O+CuCl+minuteCuO)shell. The magnetic measurements have revealed
that a ferromagnetic (FM) like open hysteresis exists at the temperature below
the freezing point, TF. In the high field region, a paramagnetic (PM) response
appears without showing a sign of saturation. Also, the field dependent
magnetization (M-H) measurement is PM-like at T > TF. These interesting
magnetic properties are evident to arise from the AFM CuO on the outer surface.
They are attributed to the uncompensated surface spins of Cu2+ and the effect
of surface random potential. More interestingly, the magnetic susceptibility is
greatly enhanced in the presence of Cl- anions at T < TF, according to the
field-cooled/zero-field-cooled (FC/ZFC) measurements. This further supports the
point that the disorder or frustration effect of the impurity would reduce the
AFM ordering of CuO and increase the level of uncompensated spins.",0508387v2
2022-02-08,Tunable Magnetic Anisotropy in Patterned SrRuO3 Quantum Structures: Competition between Lattice Anisotropy and Oxygen Octahedral Rotation,"Artificial perovskite-oxide nanostructures possess intriguing magnetic
properties due to their tailorable electron-electron interactions, which are
extremely sensitive to the oxygen coordination environment. To date,
perovskite-oxide nanodots with sizes below 50 nm have rarely been reported.
Furthermore, the oxygen octahedral distortion and its relation to magnetic
properties in perovskite oxide nanodots remain unexplored yet. Here, we have
studied the magnetic anisotropy in patterned SrRuO3 (SRO) nanodots as small as
30 nm while performing atomic-resolution electron microscopy and spectroscopy
to directly visualize the constituent elements, in particular oxygen ions. We
observe that the magnetic anisotropy and RuO6 octahedra distortion in SRO
nanodots are both nanodots' size-dependent but remain unchanged in the first
3-unit-cell interfacial SRO monolayers regardless of the dots' size. Combined
with the first principle calculations, we unravel a unique structural mechanism
behind the nanodots' size-dependent magnetic anisotropy in SRO nanodots,
sugguesting that the competition between lattice anisotropy and oxygen
octahedral rotation mediates anisotropic exchange interactions in SRO nanodots.
These findings demonstrate a new avenue towards tuning magnetic properties of
correlated perovskite oxides and imply that patterned nanodots could be a
promising playground for engineering emergent functional behaviors.",2202.03820v1
2015-11-14,Magnetic field induced augmented thermal conduction phenomenon in magneto nanocolloids,"Magnetic field induced drastically augmented thermal conductivity of magneto
nanocolloids involving magnetic oxide nanoparticles, viz. Fe2O3, Fe3O4, Nickel
oxide (NiO), Cobalt oxide (Co3O4), dispersed in different base fluids (heat
transfer oil, kerosene, and ethylene glycol) have been reported. Experiments
reveal the augmented thermal transport under the external applied magnetic
field, with kerosene based MNCs showing at relatively low magnetic field
intensities as compared to the heat transfer oil and EG based MNCs. A maximum
thermal conductivity enhancement of 114 % is attained at 7.0 vol. %
concentration and 0.1 T field intensity for Fe3O4/EG magneto nanocolloid.
However, a maximum of 82% thermal conductivity enhancement is observed for
Fe3O4/Kerosene magneto nanocolloid for the same concentration but relatively at
low magnetic field (600 G). Thereby, a strong effect of fluid as well as
particle physical properties on the chain formation propensity, leading to
enhanced conduction, in such systems is observed. Co3O4 nanoparticles show
insignificant effect on the thermal conductivity enhancement of MNCs due to
their minimal magnetic moment. An analytical approach has been proposed to
understand the mechanism and physics behind the thermal conductivity
enhancement under external applied magnetic field, in tune with near field
magnetostatic interactions as well as Neel relaxivity of the magnetic
nanoparticles. Furthermore, the analytical model is able to predict the
phenomenon of enhanced thermal conductivity as a function of physical
parameters such as chain length, size and types of nanoparticles, fluid
characteristics, magnetic field intensity, saturation magnetic moment,
nanoparticle concentration etc. and good agreement with the experimental
results has been observed.",1511.04560v1
2021-02-24,Unusual direction-dependent magnetic orbital moment obtained from X-ray magnetic circular dichroism in a multiferroic oxide system,"The electric-field control of $d$-electron magnetism in multiferroic
transition metal oxides is attracting widespread interest for the underlying
fundamental physics and for next generation spintronic devices. Here, we report
an extensive study of the $3d$ magnetism in magnetoelectric
Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) epitaxial films by polarization dependent x-ray
absorption spectroscopy. We found a non-zero integral of the x-ray magnetic
circular dichroism, with a sign depending upon the relative orientation between
the external magnetic field and the crystallographic axes. %By reliably
enlarging the limit of the spin and orbital sum rules, which usually holds for
materials where the magnetic ions exhibit a unique crystal field symmetry This
finding translates in a sign-reversal between the average Fe magnetic orbital
and spin moments. Large Fe-displacements, among some of the octahedral sites,
lower the symmetry of the system producing anisotropic paths for the Fe-O
bondings giving rise to a large orbital-lattice interaction akin to a
preferential crystallographic direction for the magnetic orbital moment. The
latter may lead to a partial re-orientation of the magnetic orbital moment
under an external magnetic field that, combined to the ferrimagnetic nature of
the GFO, can qualitatively explain the observed sign-reversal of the XMCD
integral. The results suggest that a control over the local symmetry of the
oxygen octahedra in transition metal oxides can offer a suitable leverage over
the manipulation of the effective orbital and spin moments in magnetoelectric
systems.",2102.12118v2
2022-01-21,A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe(3-delta)O4@CoFe2O4@Fe(3-delta)O4 Nanoparticles,"Nanoparticles (NPs) which combine several magnetic phases offer wide
perspectives for cutting edge applications because of the high modularity of
their magnetic properties. Besides the addition of the magnetic characteristics
intrinsic to each phase, the interface that results from core-shell and,
further, from onion structures leads to synergistic properties such as magnetic
exchange coupling. Such a phenomenon is of high interest to overcome the
superparamagnetic limit of iron oxide NPs which hampers potential applications.
In this manuscript, we report on the design of NPs with an onion-like structure
which have been scarcely reported yet. These NPs consist in a Fe(3_delta)O4
core covered by a first shell of CoFe2O4 and a second shell of Fe(3-delta)O4.
They were synthesized by a multi-step seed mediated growth approach. Although
TEM micrographs clearly show the growth of each shell from the iron oxide core,
core sizes and shell thicknesses markedly differ from what is suggested by the
size increase. We investigated very precisely the structure of NPs in
performing high resolution (scanning) TEM imaging and GPA. The chemical
composition and spatial distribution of atoms were studied by EELS. The
chemical environment and oxidation state of cations were investigated by
M\""ossbauer spectrometry, soft XAS and XMCD. These techniques allowed us to
estimate the increase of Fe2+ content in the iron oxide core of the core@shell
structure and the increase of the cobalt ferrite shell thickness in the
core@shell@shell one, while the iron oxide shell appears to be much thinner
than expected. Thus, the modification of the chemical composition as well as
the size of the Fe(3-delta)O4 core and the thickness of the cobalt ferrite
shell have a high impact on the magnetic properties. Furthermore, the growth of
the iron oxide shell also markedly modifies the magnetic properties of the
core-shell NPs.",2201.08923v1
2001-08-20,Magnetic Field Scaling of the Conductance of Epitaxial Cuprate-Manganite Bilayers,"Conductance-voltage characteristics of epitaxial interfaces between oxide
ferromagnets and oxide superconductors have been measured as a function of
temperature and magnetic field. Their functional form is similar to that
predicted by theories of transport across nearly transparent contacts between
highly spin-polarized ferromagnets and d-wave superconductors. However, their
magnetic field dependencies scale in striking and unusual ways, challenging our
current understanding. Existing theories fail to account for apparent
nonequilibium effects that are natural for spin injection in such geometries.",0108313v1
2002-01-25,Magnetic Order in Transition Metal Oxides with Orbital Degrees of Freedom,"We investigate the frustrated magnetic interactions in cubic transition metal
oxides with orbital degeneracy. The $e_g$ orbitals order easier and their
ordering explains the $A$-type antiferromagnetic phase in KCuF$_3$ and
LaMnO$_3$. In $t_{2g}$ systems the magnetic order changes at a transition from
an orbital liquid to orbital ordered states. The fluctuations of $t_{2g}$
orbitals play a prominent role in LaVO$_3$ and YVO$_3$, where they compete with
the Jahn-Teller effect and trigger the C-type antiferromagnetic order.",0201455v1
2004-09-10,Airy-function electron localization in the oxide superlattices,"Oxide superlattices and microstructures hold the promise for creating a new
class of devices with unprecedented functionalities. Density-functional studies
of the recently fabricated superlattices of lattice-matched perovskite
titanates (SrTiO3)n/(LaTiO3)m reveal a classic wedge-shaped potential
originating from the Coulomb potential of a charged sheet of La atoms. The
potential in turn confines the electrons in the vicinity of the sheet, leading
to an Airy-function localization of the electron states. Magnetism is
suppressed for structures with a single LaTiO3 monolayer, while the bulk
antiferromagnetism is recovered in the structures with a thicker LaTiO3, with a
narrow transition region separating the magnetic LaTiO3 and the non-magnetic
SrTiO3.",0409281v1
2006-03-07,Theory of carrier mediated ferromagnetism in dilute magnetic oxides,"We analyze the origin of ferromagnetism as a result of carrier mediation in
diluted magnetic oxide semiconductors in the light of the experimental evidence
reported in the literature. We propose that a combination of percolation of
magnetic polarons at lower temperature and Ruderman-Kittel-Kasuya-Yosida
ferromagnetism at higher temperature may be the reason for the very high
critical temperatures measured (up to ~700 K).",0603182v2
2009-07-24,Unusual non-equilibrium behavior of cupric oxide nanoparticles,"We report studies on temperature, field and time dependence of magnetization
on cupric oxide nanoparticles of sizes 9 nm, 13 nm and 16 nm. The nanoparticles
show unusual features in comparison to other antiferromagnetic nanoparticle
systems. The field cooled (FC) and zero field cooled (ZFC) magnetization curves
bifurcate well above the Neel temperature and the usual peak in the ZFC
magnetization curve is absent.
  The system does not show any memory effects which is in sharp contrast to the
usual behavior shown by other antiferromagnetic nanoparticles. It turns out
that the nature of CuO nanoparticles is very strange and is neither
superparamagnetic nor spin glass-like .",0907.4222v1
2012-07-04,Evidence for Intra-Unit-Cell magnetic order in Bi2Sr2CaCu2O8+d,"Polarized elastic neutron scattering measurements have been performed in the
bilayer copper oxide system Bi2Sr2CaCu2O8+d, providing evidence for an intra
unit cell (IUC) magnetic order inside the pseudo-gap state. That shows time
reversal symmetry breaking in that state as already reported in Bi2Sr2CaCu2O8+d
through dichroism in circularly polarized photoemission experiments. The
magnetic order displays the same characteristic features as the one previously
reported for monolayer HgBa2CuO4+d and bilayer YBa2Cu3O6+x, demonstrating that
this genuine phase is ubiquitous of the pseudo-gap of high temperature copper
oxide materials.",1207.1038v1
2017-04-20,Current-induced effective magnetic field in a half-metallic oxide La0.67Sr0.33MnO3,"We investigated current-induced effective magnetic field Heff in
half-metallic oxide La0.67Sr0.33MnO3 (LSMO) films with various thicknesses by
using the planar Hall effect. Applying in-plane current to the LSMO films
exerted an in-plane Heff orthogonal to the current direction on magnetization.
The Heff magnitude increased with increasing current magnitude, and the
direction reversed when the applied current switched to opposite sign. Assuming
that a 6.5-u.c. insulating layer is created in the LSMO, the values of Heff
observed in devices with three different LSMO thicknesses were almost scaled
with current density, evaluated from the effective LSMO thickness excluding the
insulating layer, suggesting that Heff is induced in the LSMO bulk.",1704.05989v1
2019-01-25,Polarized neutron reflectometry study from iron oxide nanoparticles monolayer,"We report on the polarized neutron reflectometry investigation of monolayer
of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method.
After deposition onto a solid substrate the polarized neutron reflectometry
measurements in the external magnetic field were carried out. Thickness,
density, roughness and in-depth resolved magnetization profile of the resulted
layer were obtained from accurate fitting routine.",1901.08819v1
2009-04-28,Magnetically-induced electric polarization in an organo-metallic magnet,"The coupling between magnetic order and ferroelectricity has been under
intense investigation in a wide range of transition-metal oxides. The strongest
coupling is obtained in so-called magnetically-induced multiferroics where
ferroelectricity arises directly from magnetic order that breaks inversion
symmetry. However, it has been difficult to find non-oxide based materials in
which these effects occur. Here we present a study of copper dimethyl sulfoxide
dichloride (CDC), an organo-metallic quantum magnet containing $S = 1/2$ Cu
spins, in which electric polarization arises from non-collinear magnetic order.
We show that the electric polarization can be switched in a stunning hysteretic
fashion. Because the magnetic order in CDC is mediated by large organic
molecules, our study shows that magnetoelectric interactions can exist in this
important class of materials, opening the road to designing magnetoelectrics
and multiferroics using large molecules as building blocks. Further, we
demonstrate that CDC undergoes a magnetoelectric quantum phase transition where
both ferroelectric and magnetic order emerge simultaneously as a function of
magnetic field at very low temperatures.",0904.4490v1
2020-06-01,High-throughput search for magnetic and topological order in transition metal oxides,"The discovery of intrinsic magnetic topological order in $\rm MnBi_2Te_4$ has
invigorated the search for materials with coexisting magnetic and topological
phases. These multi-order quantum materials are expected to exhibit new
topological phases that can be tuned with magnetic fields, but the search for
such materials is stymied by difficulties in predicting magnetic structure and
stability. Here, we compute over 27,000 unique magnetic orderings for over
3,000 transition metal oxides in the Materials Project database to determine
their magnetic ground states and estimate their effective exchange parameters
and critical temperatures. We perform a high-throughput band topology analysis
of centrosymmetric magnetic materials, calculate topological invariants, and
identify 18 new candidate ferromagnetic topological semimetals, axion
insulators, and antiferromagnetic topological insulators. To accelerate future
efforts, machine learning classifiers are trained to predict both magnetic
ground states and magnetic topological order without requiring first-principles
calculations.",2006.01075v1
2007-12-12,Analysis of anisotropy crossover due to oxygen in Pt/Co/MOx trilayer,"Extraordinary Hall effect and X-ray spectroscopy measurements have been
performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta...) in order to
investigate the role of oxidation in the onset of perpendicular magnetic
anisotropy at the Co/MOx interface. It is observed that varying the oxidation
time modifies the magnetic properties of the Co layer, inducing a magnetic
anisotropy crossover from in-plane to out-of-plane. We focused on the influence
of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The
interfacial electronic structure is analyzed via X-ray photoelectron
spectroscopy measurements. It is shown that the maximum of out-of-plane
magnetic anisotropy corresponds to the appearance of a significant density of
Co-O bondings at the Co/AlOx interface.",0712.1905v1
2014-09-05,Magneto-ionic Control of Interfacial Magnetism,"In metal/oxide heterostructures, rich chemical, electronic, magnetic and
mechanical properties can emerge from interfacial chemistry and structure. The
possibility to dynamically control interface characteristics with an electric
field paves the way towards voltage control of these properties in solid-state
devices. Here we show that electrical switching of the interfacial oxidation
state allows for voltage control of magnetic properties to an extent never
before achieved through conventional magnetoelectric coupling mechanisms. We
directly observe, for the first time, in situ voltage driven O$^{2-}$ migration
in a Co/metal-oxide bilayer, which we use to toggle the interfacial magnetic
anisotropy energy by >0.6 erg/cm$^2$. We exploit the thermally-activated nature
of ion migration to dramatically increase the switching efficiency and to
demonstrate reversible patterning of magnetic properties through local
activation of ionic migration. These results suggest a path towards
voltage-programmable materials based on solid-state switching of interface
oxygen chemistry.",1409.1843v1
2015-04-13,Evidence for Localized Moment Picture in Mn-based Heusler Compounds,"X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism
(XMCD) were used to probe the oxidation state and element specific magnetic
moments of Mn in Heusler compounds with different crystallographic structure.
The results were compared with theoretical calculations, and it was found that
in full Heusler alloys, Mn is metallic (oxidation state near 0) on both
sublattices. The magnetic moment is large and localized when octahedrally
coordinated by the main group element, consistent with previous theoretical
work, and reduced when the main group coordination is tetrahedral. By contrast,
in the half Heusler compounds the magnetic moment of the Mn atoms is large and
the oxidation state is +1 or +2. The magnetic and electronic properties of Mn
in full and half Heusler compounds are strongly dependent on the structure and
sublattice, a fact that can be exploited to design new materials.",1504.03088v1
2015-04-25,Magnetic phase transitions in Ta/CoFeB/MgO multilayers,"We study thin films and magnetic tunnel junction nanopillars based on
Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO multilayers by electrical transport and
magnetometry measurements. These measurements suggest that an ultrathin
magnetic oxide layer forms at the Co$_{20}$Fe$_{60}$B$_{20}$/MgO interface. At
approximately 160 K, the oxide undergoes a phase transition from an insulating
antiferromagnet at low temperatures to a conductive weak ferromagnet at high
temperatures. This interfacial magnetic oxide is expected to have significant
impact on the magnetic properties of CoFeB-based multilayers used in spin
torque memories.",1504.06716v1
2010-05-31,Magnetism in graphite oxide: The role of epoxy groups,"We investigate the magnetism in graphite by controlled oxidation. Our
approach renders graphite an insulator while maintaining its structure. Fourier
transform infrared spectroscopy and X-ray absorption near edge structure
spectra reveal that graphite oxide has epoxy groups on its surface and it is
not thermally stable. Magnetic susceptibility data exhibit negative Curie
temperature, field irreversibility, and slow relaxation. The magnetic
properties diminish after the epoxy groups are destroyed. The overall results
indicate the unexpected magnetism is associated with the presence of epoxy
groups.",1005.5580v2
2016-05-09,Self-heating effects of the surface oxidized FeCo nanoparticles colloid under alternating magnetic field,"To evaluate the self-heating effects of FeCo magnetic nanoparticles, the
surface oxidized FeCo nanoparticles were synthesized by co-precipitation method
with the reduction reaction without any post treatments. As-synthesized FeCo
nanoparticles exhibited the mean diameter of about 39 nm with the oxidized
shell thickness of about 4-5 nm. The saturation magnetization and coercivity
were obtained 172 emu/g and 268 Oe at 300 K, respectively. The heat elevation
of the FeCo magnetic colloid was measured under alternating magnetic fields of
76, 102, and 127 Oe with selectable frequencies of 190, 250 and 355 kHz. The
heat temperature increased up to about 45 oC from initial temperature of 24 oC
under 127 Oe and 355 kHz, which the specific absorption exhibited about 35.7
W/g.",1605.02806v1
2017-06-07,Monte Carlo study of the exchange bias effect in Co/CoO core-shell nanowires,"We study the magnetic properties of cylindrical ferromagnetic core -
antiferromagnetic shell nanowires using Monte Carlo simulations and a classical
Heisenberg Hamiltonian in order to elucidate the impact of the oxidized shell
on the magnetic properties and the magnetization reversal mechanism. We find
that the coupling to the antiferromagnetic shell leads to suppression of the
coercivity and emergence of a weak exchange bias effect. Comparison of the
magnetization reversal mechanism in the bare and the surface-oxidized nanowire
reveals that the domain wall propagation and annihilation remains the dominant
reversal mechanism in surface oxidized nanowires as in their ferromagnetic
counterparts. However, the interface exchange coupling introduces a secondary
reversal mechanism activated in the central part of the wire with
characteristics of coherent rotation, which acts in synergy to wall propagation
leading to enhancement of the wall mobility. This effect is more pronounced in
nanowires with large exchange bias values and is attributed to the
uncompensated interface moments that act as nucleation centers for
magnetization reversal. Our results are in good agreement with recent
measurements in Co and Co/CoO nanowires.",1706.02395v1
2020-02-27,Second Harmonic Generation of cuprous oxide in magnetic fields,"Recently Second Harmonic Generation (SHG) for the yellow exciton series in
cuprous oxide has been demonstrated [J. Mund et al., Phys. Rev. B 98, 085203
(2018)]. Assuming perfect $O_{\mathrm{h}}$ symmetry, SHG is forbidden along
certain high-symmetry axes. Perturbations can break this symmetry and forbidden
transitions may become allowed. We investigate theoretically the effect of
external magnetic fields on the yellow exciton lines of cuprous oxide. We
identify two mechanisms by which an applied magnetic field can induce a second
harmonic signal in a forbidden direction. First of all, a magnetic field by
itself generally lifts the selection rules. In the Voigt configuration, an
additional magneto-Stark electric field appears. This also induces certain SHG
processes differing from those induced by the magnetic field alone.
Complementary to the manuscript by A. Farenbruch et al. [Phys. Rev. B,
submitted], we perform a full numerical diagonalization of the exciton
Hamiltonian including the complex valence band structure. Numerical results are
compared with experimental data.",2002.12064v1
2017-09-21,Current-induced magnetization switching using electrically-insulating spin-torque generator,"Current-induced magnetization switching through spin-orbit torques (SOTs) is
the fundamental building block of spin-orbitronics. The SOTs generally arise
from the spin-orbit coupling of heavy metals. However, even in a
heterostructure where a metallic magnet is sandwiched by two different
insulators, a nonzero current-induced SOT is expected because of the broken
inversion symmetry; an electrical insulator can be a spin-torque generator.
Here, we demonstrate current-induced magnetization switching using an
insulator. We show that oxygen incorporation into the most widely used
spintronic material, Pt, turns the heavy metal into an electrically-insulating
generator of the SOTs, enabling the electrical switching of perpendicular
magnetization in a ferrimagnet sandwiched by electrically-insulating oxides. We
further found that the SOTs generated from the Pt oxide can be controlled
electrically through voltage-driven oxygen migration. These findings open a
route towards energy-efficient, voltage-programmable spin-orbit devices based
on solid-state switching of heavy metal oxidation.",1709.07127v1
2023-02-06,Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide,"Many technologically useful magnetic oxides are ferrimagnetic insulators,
which consist of chemically distinct cations. Here, we examine the spin
dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite
(Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave
excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance
to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice
sites. Our results show that the precessing cation moments retain a rigid,
collinear configuration to within $\approx$2$^\circ$. Moreover, the effective
spin relaxation is identical to within $<$10% for all magnetic cations in the
ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in
resonantly driven ferrimagnetic oxides, where the magnetic moments from
different cations precess as a coherent, collective magnetization.",2302.03100v1
2024-03-08,Design of Magnetic Polar Double-Double Perovskite Oxides through Cation Ordering,"Commencing from the centrosymmetric MnRMnSbO$_6$ compound, we explore the
realm of magnetic polar double-double perovskite oxides characterized by
significant ferroelectric polarization. Employing symmetry operations,
first-principles methodologies, and Monte Carlo simulations, our investigation
delves into the structural, magnetic, ferroelectric, and electronic attributes
of the polar LaFeMnNiO$_6$ and LaTiMnNiO$_6$ compounds. The structural analysis
uncovers that the paraelectric-ferroelectric phase transition is intricately
linked to the Fe/Ti-displacement of square planar Fe/TiO$_4$. Notably, the
magnetic LaFeMnNiO$_6$ and LaTiMnNiO$_6$ compounds demonstrate robust
ferroelectric polarizations, measuring 20.0 $\mu$C/cm$^2$ and 21.8
$\mu$C/cm$^2$, respectively, accompanied by minimalist forbidden energy gaps of
1.40 eV and 1.18 eV using the GGA+U method. Furthermore, we pinpoint elevated
magnetic transition temperatures for these compounds. Additionally, our study
scrutinizes the energies associated with diverse spin configurations and
identifies potential minimum decomposition pathways into stable oxides. This
comprehensive analysis ensures the meticulous formation of the LaFeMnNiO$_6$
and LaTiMnNiO$_6$ compounds.",2403.05498v1
2023-03-28,Hole doping in compositionally complex correlated oxide enables tunable exchange biasing,"Magnetic interfaces and the phenomena arising from them drive both the design
of modern spintronics and fundamental research. Recently, it was revealed that
through designing magnetic frustration in configurationally complex entropy
stabilized oxides, exchange bias can occur in structurally single crystal
films. This eliminates the need for complex heterostructures and nanocomposites
in the design and control of magnetic response phenomena. In this work, we
demonstrate through hole doping of a high entropy perovskite oxide that tuning
of magnetic responses can be achieved. With detailed magnetometry, we show
magnetic coupling exhibiting a variety of magnetic responses including exchange
bias and antiferromagnetic spin reversal in the entropy stabilized ABO3
perovskite oxide La1-xSrx(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 family. We find that
manipulation of the A-site charge state can be used to balance magnetic phase
compositions and coupling responses. This allows for the creation of highly
tunable exchange bias responses. In the low Sr doping regime, a spin frustrated
region arising at the antiferromagnetic phase boundary is shown to directly
couple to the antiferromagnetic moments of the film and emerges as the dominant
mechanism, leading to a vertical shift of magnetization loops in response to
field biasing. At higher concentrations, direct coupling of antiferromagnetic
and ferromagnetic regions is observed. This tunability of magnetic coupling is
discussed within the context of these three competing magnetic phases,
revealing critical features in designing exchange bias through exploiting spin
frustration and disorder in high entropy oxides.",2303.15922v1
2014-11-17,Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices,"Interfaces between correlated complex oxides are promising avenues to realize
new forms of magnetism that arise as a result of charge transfer, proximity
effects and locally broken symmetries. We report upon the discovery of a
non-collinear magnetic structure in superlattices of the ferromagnetic metallic
oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange
interaction between LSMO layers is mediated by the intervening LNO, such that
the angle between the magnetization of neighboring LSMO layers varies in an
oscillatory manner with the thickness of the LNO layer. The magnetic field,
temperature, and spacer thickness dependence of the non-collinear structure are
inconsistent with the bilinear and biquadratic interactions that are used to
model the magnetic structure in conventional metallic multilayers. A model that
couples the LSMO layers to a helical spin state within the LNO fits the
observed behavior. We propose that the spin-helix results from the interaction
between a spatially varying spin susceptibility within the LNO and interfacial
charge transfer that creates localized Ni2+ states. This provides a new
approach to engineering non-collinear spin textures in metallic oxide
heterostructures that can be exploited in devices based on both spin and charge
transport.",1411.4344v1
2015-03-03,Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite,"Magnetic materials have found wide application ranging from electronics and
memories to medicine. Essential to these advances is the control of the
magnetic order. To date, most room-temperature applications have a fixed
magnetic moment whose orientation is manipulated for functionality. Here we
demonstrate an iron-oxide and graphene oxide nanocomposite based device that
acts as a tunable ferromagnet at room temperature. Not only can we tune its
transition temperature in a wide range of temperatures around room temperature,
but the magnetization can also be tuned from zero to 0.011 A.m$^2$/kg through
an initialization process with two readily accessible knobs (magnetic field and
electric current), after which the system retains its magnetic properties
semi-permanently until the next initialization process. We construct a
theoretical model to illustrate that this tunability originates from an
indirect exchange interaction mediated by spin-imbalanced electrons inside the
nanocomposite.",1503.00960v1
2023-03-12,Competing Magnetic Interactions and Field-Induced Metamagnetic Transition in Highly Crystalline Phase-Tunable Iron Oxide Nanorods,"The inherent existence of multi phases in iron oxide nanostructures
highlights the significance of them being investigated deliberately to
understand and possibly control the phases. Here, the effects of annealing at
250 0C with a variable duration on the bulk magnetic and structural properties
of high aspect ratio bi-phase iron oxide nanorods with ferrimagnetic Fe3O4 and
antiferromagnetic alpha-Fe2O3 is explored. Increasing annealing time under a
free flow of oxygen enhanced the alpha-Fe2O3 volume fraction, and improved the
crystallinity of the Fe3O4 phase, identified in changes in the magnetization as
a function of annealing time. A critical annealing time of approximately 3
hours maximized the presence of both phases, as observed via an enhancement in
the magnetization and an interfacial pinning effect. This is attributed to
disordered spins separating the magnetically distinct phases which tend to
align with the application of a magnetic field at high temperatures. The
increased antiferromagnetic phase can be distinguished due to the field-induced
metamagnetic transitions observed in structures annealed for more than 3 hours
and was especially prominent in the 9-hour annealed sample. Our controlled
study in determining the changes in volume fractions with annealing time will
enable precise control over phase tunability in iron oxide nanorods, allowing
custom-made phase volume fractions in different applications ranging from
spintronics to biomedical applications.",2303.06684v1
2002-07-27,The Hydride Anion in an Extended Transition Metal Oxide Array: LaSrCoO_3H_{0.7},"We present the synthesis and structural characterisation of a transition
metal oxide hydride, LaSrCoO_3H_{0.7}, which adopts an unprecedented structure
in which oxide chains are bridged by hydride anions to form a two- dimensional
extended network. The metal centers are strongly coupled by their bonding with
both oxide and hydride ligands to produce magnetic ordering up to at least 350
K. The synthetic route is sufficiently general to allow the prediction of a new
class of transition metal-containing electronic and magnetic materials.",0207660v1
2013-07-24,Sr and Mn co-doped LaCuSO: A wide band gap oxide diluted magnetic semiconductor with TC around 200K,"Here we report the synthesis of a bulk oxide diluted magnetic semiconductor
(DMS) system La1-xSrxCu0.925Mn0.075SO (x=0, 0.025, 0.05, 0.075, and 0.1). As a
wide band gap p-type oxide semiconductor, LaCuSO satisfies all the conditions
forecasted theoretically to be a room temperature DMS. The Curie temperature
(TC) is around 200K as x>0.05, which is among the highest TC record of known
bulk DMS materials up to now. The system provides a rare example of oxide DMS
system with p-type conduction, which is important for formation of high
temperature spintronic devices.",1307.6311v1
2014-05-19,Multiferroic Iron Oxide Thin Films at Room-Temperature,"In spite of being highly relevant for the development of a new generation of
information storage devices, not many single-phase materials displaying
magnetic and ferroelectric orders above room temperature are known. Moreover,
these uncommon materials typically display insignificant values of the remanent
moment in one of the ferroic orders or are complex multicomponent oxides which
will be very challenging to integrate in devices. Here we report on the
strategy to stabilize the metastable epsilon-Fe2O3 in thin film form, and we
show that besides its already known ferrimagnetic nature, the films are also
ferroelectric at 300 K with a remanent polarization of 1 microC/cm2. The film
polarization shows long retention times and can be switched under small applied
voltages. These characteristics make of epsilon-Fe2O3 the first single-ion
transition-metal oxide which is ferro(ferri)magnetic and ferroelectric at room
temperature. The simple composition of this new multiferroic oxide and the
discovery of a robust path for its thin film growth may boost the exploitation
of epsilon-Fe2O3 in novel devices.",1405.4909v1
2020-01-02,Origin of Strong Two-Magnon Scattering in Heavy Metal/Ferromagnet/Oxide Heterostructures,"We experimentally investigate the origin of the two-magnon scattering (TMS)
in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19,
or Fe60Co20B20) by varying the materials located above and below the FM layers.
We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM
interface and increases with the strength of interfacial spin-orbit coupling
and magnetic roughness at this interface. TMS at the FM/oxide interface is
relatively weak, even in systems where spin-orbit coupling at this interface
generates strong interfacial magnetic anisotropy. We also suggest that the
spin-current-induced excitation of non-uniform short-wavelength magnon at the
HM/FM interface may function as a mechanism of spin memory loss for the
spin-orbit torque exerted on the uniform mode.",2001.00300v1
2020-06-10,Hexagonal Perovskites as Quantum Materials,"Hexagonal oxide perovskites, in contrast to the more familiar perovskites,
allow for face-sharing of metal-oxygen octahedra or trigonal prisms within
their structural frameworks. This results in dimers, trimers, tetramers, or
longer fragments of chains of face-sharing octahedra in the crystal structures,
and consequently in much shorter metal-metal distances and lower
metal-oxygen-metal bond angles than are seen in the more familiar perovskites.
The presence of the face-sharing octahedra can have a dramatic impact on
magnetic properties of these compounds, and dimer-based materials, in
particular, have been the subjects of many quantum-materials-directed studies
in materials physics. Hexagonal oxide perovskites are of contemporary interest
due to their potential for geometrical frustration of the ordering of magnetic
moments or orbital occupancies at low temperatures, which is especially
relevant to their significance as quantum materials. As such, several hexagonal
oxide perovskites have been identified as potential candidates for hosting the
quantum spin liquid state at low temperatures. In our view, hexagonal oxide
perovskites are fertile ground for finding new quantum materials. This review
briefly describes the solid state chemistry of many of these materials.",2006.05864v1
2020-10-25,Multifunctional Oxides for Topological Magnetic Textures by Design,"Several challenges in designing an operational Skyrmion racetrack memory are
well-known. Among those challenges, a few contradictions can be identified if
researchers were to rely only on metallic materials. Hence, expanding the
exploration on Skyrmion Physics into oxide materials is essential to bridge the
contradicting gap. In this topical review, we first briefly revise the theories
and criteria involved in stabilizing and manipulating Skymions, followed by
studying the behaviors of dipolar-stabilized magnetic bubbles. Next, we explore
the properties of multiferroic Skyrmions with magnetoelectric coupling, which
can only be stabilized in Cu$_2$OSeO$_3$ thus far, as well as the rare bulk
N\'eel-type Skyrmions in some polar materials. As an interlude section, we
review the theory of Anomalous (AHE) and Topological Hall Effect (THE), before
going through the recent progress of THE in oxide thin films. The debate about
an alternative interpretation is also discussed. Finally, this review ends with
future outlooks about the promising strategies of using interfacial
charge-transfer and (111)-orientation of perovskites to benefit the field of
Skyrmion research.",2010.13012v1
2015-05-13,Optical detection of magnetic orders in HgCr$_2$O$_4$ frustrated spin magnet under pulsed high magnetic fields,"A magneto-optical survey was conducted for HgCr$_2$O$_4$ powder samples under
pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields
observed for the exciton-magnon-phonon optical transition spectra coincide well
with those of magnetization, lattice distortion from X-ray diffraction, and
electron-magnetic resonances. The last-ordered phase was detected prior to the
fully polarized magnetic phase, similarly to the other chromium spinel oxide,
ZnCr$_2$O$_4$ and CdCr$_2$O$_4$.",1505.03216v1
2019-04-16,Oxidation annealing effects on the spin-glass-like magnetism and appearance of superconductivity in T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$ (0.14 $\leq x \leq$ 0.28),"We investigated the magnetism and superconductivity in as-sintered (AS) and
oxidation annealed (OA) T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$ (LESCO)
with 0.14 $\leq x \leq$ 0.28 by the first comprehensive muon spin
rotation/relaxation ($\mu$SR), magnetic susceptibility, and electrical
resistivity measurements. In OA superconducting samples, no evidence of
magnetic order was observed, whereas AS semiconducting samples exhibited
evidence of a disordered magnetic state in the measured temperature range
between $\sim$4 K and $\sim$8 K. Therefore, the ground state in LESCO
drastically varies with oxidation annealing and the magnetic phase
competitively exists with the superconducting (SC) phase. The magnetic phase in
the AS LESCO is quite robust against Sr doping, while the SC phase degrades
with increasing $x$. A monotonous decrease of the SC transition temperature
from 24.5 K in $x$ = 0.14 to 9.0 K in $x$ = 0.28 suggests the disappearance of
the SC phase at $x$ $\sim$ 0.34. Furthermore, we clarified the simultaneous
development of (quasi) static magnetism and the electrical resistivity at a low
temperature in AS samples, suggesting the inducement of magnetism by the
suppression of carrier mobility. The variation in magnetism due to annealing is
discussed from a viewpoint of structural defects, which was previously reported
from neutron diffraction measurements.",1904.07541v2
2011-01-17,Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations,"Iron oxides and oxyhydroxides are challenging to model computationally as
competing phases may differ in formation energies by only several kJ/mol, they
undergo magnetization transitions with temperature, their structures may
contain partially occupied sites or long-range ordering of vacancies, and some
loose structures require proper description of weak interactions such as
hydrogen bonding and dispersive forces. If structures and transformations are
to be reliably predicted under different chemical conditions, each of these
challenges must be overcome simultaneously, while preserving a high level of
numerical accuracy and physical sophistication. Here we present comparative
studies of structure, magnetization, and elasticity properties of iron oxides
and oxyhydroxides using density functional theory calculations with plane-wave
and locally-confined-atomic-orbital basis sets, which are implemented in VASP
and SIESTA packages, respectively. We have selected hematite, maghemite,
goethite, lepidocrocite, and magnetite as model systems from a total of 13
known iron oxides and oxyhydroxides; and use same convergence criteria and
almost equivalent settings in order to make consistent comparisons. Our results
show both basis sets can reproduce the energetic stability and magnetic
ordering, and are in agreement with experimental observations. There are
advantages to choosing one basis set over the other, depending on the intended
focus. In our case, we find the method using PW basis set most appropriate, and
combine our results to construct the first phase diagram of iron oxides and
oxyhydroxides in the space of competing chemical potentials, generated entirely
from first principles",1101.3105v1
2015-04-22,Detection of defect-induced magnetism in low-dimensional ZnO structures by Magnetophotocurrent,"The detection of defect-induced magnetic order in single low-dimensional
oxide structures is in general difficult because of the relatively small yield
of magnetically ordered regions. In this work we have studied the effect of an
external magnetic field on the transient photocurrent measured after light
irradiation on different ZnO samples at room temperature. We found that a
magnetic field produces a change in the relaxation rate of the transient
photocurrent only in magnetically ordered ZnO samples. This rate can decrease
or increase with field depending whether the magnetic order region is in the
bulk or only at the surface of the ZnO sample. The phenomenon reported here is
of importance for the development of magneto-optical low-dimensional oxides
devices and provide a new guideline for the detection of magnetic order in
low-dimensional magnetic semiconductors.",1504.05828v1
2019-04-24,Ultra-low-power orbital-controlled magnetization switching using a ferromagnetic oxide interface,"A major challenge in spin-based electronics is reducing power consumption for
magnetization switching of ferromagnets, which is being implemented by
injecting a large spin-polarized current. The alternative approach is to
control the magnetic anisotropy (MA) of the ferromagnet by an electric field.
However, the voltage-induced MA is too weak to deterministically switch the
magnetization without an assisting magnetic field, and the strategy towards
this goal remains elusive. Here, we demonstrate a new scheme of
orbital-controlled magnetization switching (OCMS): A sharp change in the MA is
induced when the Fermi level is moved between energy bands with different
orbital symmetries. Using a ferromagnetic oxide interface, we show that OCMS
can be used to achieve a deterministic and magnetic-field-free 90
degree-magnetization switching solely by applying an extremely small electric
field of 0.05 V/nm with a negligibly small current density of 10^-2 A/cm^2. Our
results highlight the huge potential of band engineering in ferromagnetic
materials for efficient magnetization control.",1904.10599v1
2021-11-06,Phase transition in the 5d1 double perovskite Ba2CaReO6 induced by high magnetic field,"Magnetic properties of an antiferromagnetic double perovskite oxide
Ba2CaReO6, where Re6+ (5d1) ions with large spin-orbit coupling are arranged on
the face-centered-cubic lattice, are investigated using pulsed high magnetic
field up to 66 T. Magnetization and magnetostriction measurements have revealed
a magnetic field induced phase transition at around 50 T. The phase transition
accompanies a jump of magnetization and longitudinal magnetostriction of
approximately 2 10^(-4) with the change of power law behavior, indicating
sizable coupling between the electronic degrees of freedom and the lattice. The
high field phase exhibits a magnetic moment approximately 0.2 {\mu}B, which is
close to the values observed in 5d1 double perovskite oxides with non-collinear
magnetic structure. We argue that Ba2CaReO6 is an antiferromagnet that sits
close to the phase boundary between the collinear and non-collinear phases,
providing the target material for investigating the interplay between
spin-orbital entangled electrons and magnetic field.",2111.03807v1
2022-02-15,Optically-induced magnetization switching in NiCo2O4 thin films using ultrafast lasers,"Recently, all-optical magnetization control has been garnering considerable
attention in realizing next-generation ultrafast magnetic information devices.
Here, employing a magneto-optical Kerr effect (MOKE) microscope, we observed
the laser-induced magnetization switching of ferrimagnetic oxide NiCo2O4 (NCO)
epitaxial thin films with perpendicular magnetic anisotropy, where the sample
was pumped at 1030-nm laser pulses, and magnetic domain images were acquired
via the MOKE microscope with a white light emitting diode. Laser pulses
irradiated an NCO thin film at various temperatures from 300 K to 400 K while
altering the parameters of pulse interval, fluence, and the number of pulses
with the absence of the external magnetic field. We observed accumulative
all-optical switching at 380 K and above. Our observation of oxide NCO thin
films facilitates the realization of chemically stable magnetization switching
using ultrafast lasers, and without applying a magnetic field.",2202.07257v1
2023-09-11,Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3,"The origin of magnetic anisotropy in magnetic compounds is a longstanding
issue in solid state physics and nonmagnetic ligand ions are considered to
contribute little to magnetic anisotropy. Here, we introduce the concept of
ligand driven magnetic anisotropy in a complex transition-metal oxide. We
conducted X ray absorption and X ray magnetic circular dichroism spectroscopies
at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic
variation of the sample thickness in the range below 10 nm allowed us to
control the localization of Ru 4d t2g states, which affects the magnetic
coupling between the Ru and O ions. We found that the orbital magnetization of
the ligand induced via hybridization with the Ru 4d orbital determines the
magnetic anisotropy in SrRuO3.",2309.05228v2
2020-04-07,Structural Transition in Oxidized Ca$_2$N Electrenes: CaO/CaN 2D heterostructures,"Based on first-principles calculations we show that the oxidation of
ultrathin films of Ca$_2$N electrides, electrenes, drives a
hexagonal$\rightarrow$tetragonal structural transition. The ground state
configuration of the oxidized monolayer (ML) and bilayer (BL) systems can be
viewed as CaO/CaN and CaO/(CaN)$_2$/CaO two dimensional (2D) heterostructures.
In both systems, we found nearly free electron (NFE) states lying near the
vacuum level, and the spatial projection reveals that they are localized above
the oxidized CaO surface. Focusing on the magnetic properties, we find that the
nitrogen atoms of the oxidized Ca$_2$N becomes spin-polarized ($\sim$1
$\mu_{\rm B}$/N-atom); where (i) the ferromagnetic and the anti-ferromagnetic
phases are nearly degenerated in the ML system, CaO/CaN, while (ii) there is an
energetic preference for the ferromagnetic phase in CaO/(CaN)$_2$/CaO. We show
that such a FM preference can be strengthened upon mechanical compression.
Further electronic structure calculations reveal that the FM CaO/Ca$_2$N/CaO
presents half-metallicity, where the metallic channels project (predominantly)
on the N-$2p_{x,y}$ orbitals. In addition to the total energy results,
molecular dynamic and phonon spectra calculations have been done in order to
verify its thermal and structural stabilities. Those findings suggest that
CaO/Ca$_2$N/CaO is a quite interesting, and structurally stable, 2D FM
heterostructure characterized half-metallic bands sandwiched by NFE states
lying on the oxidized surfaces.",2004.03528v2
2016-09-10,Induced ferromagnetic moment at the interface between epitaxial SrRuO$_3$ film and Sr$_2$RuO$_4$ single crystal,"SrRuO$_3$ (SRO113) is an important material for device physics particularly
as one of the best metallic oxide electrodes for ferroelectric devices. This
oxide has moderate electron correlations with novel properties including
ferromagnetic ordering, which can be utilized in future to spintronics and
superconducting spintronics devices. Recently, we observed strongly enhanced
magnetization of SRO113 thin films grown on single crystals of the spin-triplet
superconductor Sr$_2$RuO$_4$ (SRO214). To clarify the origin of such an
enhancement, we conducted systematic investigations of magnetic properties of
SRO113 films deposited on a variety of oxide substrates. We carefully
subtracted the substrate contributions and found that the enhanced 2
magnetization occurs only for SRO113/SRO214 films. We further found that
neither strain nor metallicity of the substrate plays any significant roles in
the enhancement. The X-ray magnetic circular dichroism reveals that the
substrate-induced strain does not switch the Ru4+ state from the low-spin to
high-spin states. The film-thickness dependence of the magnetization of
SRO113/SRO214 films strongly suggest that the additional magnetization arises
due to the induction of magnetic moment into the SRO214 substrate over 20-nm
depth. Our results imply new magnetic functionality that can trigger studies
searching for yet unknown physical phenomena in magnetic ruthenates.",1609.03010v1
2022-05-23,Surface-Driven Evolution of the Anomalous Hall Effect in Magnetic Topological Insulator MnBi2Te4 Thin Films,"Understanding the effects of interfacial modification to the functional
properties of magnetic topological insulator thin films is crucial for
developing novel technological applications from spintronics to quantum
computing. Here, we report that a large electronic and magnetic response is
induced in the intrinsic magnetic topological insulator MnBi2Te4 by controlling
the propagation of surface oxidation. We show that the formation of the surface
oxide layer is confined to the top 1-2 unit cells but drives large changes in
the overall magnetic response. Specifically, we observe a dramatic reversal of
the sign of the anomalous Hall effect driven by finite thickness magnetism,
which indicates that the film splits into distinct magnetic layers each with a
unique electronic signature. These data reveal a delicate dependence of the
overall magnetic and electronic response of MnBi2Te4 on the stoichiometry of
the top layers. Our study suggests that perturbations resulting from surface
oxidation may play a non-trivial role in the stabilization of the quantum
anomalous Hall effect in this system and that understanding targeted
modifications to the surface may open new routes for engineering novel
topological and magnetic responses in this fascinating material.",2205.10991v1
2014-02-04,A polarity-induced defect mechanism for conductivity and magnetism at polar-nonpolar oxide interfaces,"The discovery of conducting two-dimensional electron gas (2DEG) and magnetism
at the interface between insulating nonmagnetic oxides, as exemplified by the
polar LaAlO3 and nonpolar SrTiO3 has raised prospects for attaining interfacial
functionalities absent in the component materials. Yet, the microscopic origin
of such emergent phenomena remains unclear, posing obstacles to design of
improved functionalities. Using first principles defect calculations, we reveal
a unifying polarity-induced defect mechanism for both conductivity and
magnetism at polar-nonpolar interfaces of nonmagnetic insulating oxides. We
demonstrate that the polar-discontinuity across the interface triggers
thermodynamically the spontaneous formation of certain defects that in turn
cancel the polar field induced by the polar discontinuity. It turns out that
the 2DEG originates from those spontaneously formed surface donor defects
(oxygen vacancy), but the density of 2DEG is controlled by the interfacial
anti-site acceptor defects (Al-on-Ti). The interface magnetism is found to
originate from the un-ionized deep Ti-on-Al anti-site donor defects within the
LaAlO3 side near the interface. Our results suggest practical design guidelines
for inducing and controlling both 2DEG and magnetism at polar-nonpolar oxide
interfaces.",1402.0895v3
2020-05-07,Effect of interfacial oxidation layer in spin pumping experiments on Ni$_{80}$Fe$_{20}$/SrIrO$_3$ heterostructures,"SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has
emerged as a potential candidate for efficient spin-orbit torque magnetization
control in spintronic devices. We here report on the influence of an
interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$
(NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have
carried out broadband ferromagnetic resonance (BBFMR) measurements, which
indicate the presence of an interfacial antiferromagnetic oxide layer. We
performed in-plane BBFMR experiments at cryogenic temperatures, which allowed
us to simultaneously study dynamic spin pumping properties (Gilbert damping)
and static magnetic properties (such as the effective magnetization and
magnetic anisotropy). The results for NiFe/SrIrO$_3$ bilayer thin films were
analyzed and compared to those from a NiFe/NbN/SrIrO$_3$ trilayer reference
sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent
oxidation of NiFe. At low temperatures, we observe substantial differences in
the magnetization dynamics parameters of these samples, which can be explained
by an antiferromagnetic interfacial layer in the NiFe/SrIrO$_3$ bilayers.",2005.03727v1
2002-06-06,Current-driven magnetization decrease in single crystalline ferromagnetic manganese oxide,"The electrical and magnetic response to a bias current has been investigated
in a singlecrystalline ferromagnetic manganese oxide
$\Pr_{0.8}$Ca$_{0.2}$MnO$_3$ . A significant decrease of the magnetization is
observed at the same threshold current where a non-linearity of V-I
characteristics appears. Such a behavior cannot be understood in the framework
of the filamentary picture usually invoked for the non linearity of the other
manganese oxides. Instead, an analogy with spintronic features might be useful
and experimental signatures seem to be in agreement with excitations of spin
waves by an electric current. This provides an example of a bulk system in
which the spin polarized current induces a macroscopic change in the
magnetization.",0206073v1
2004-12-14,Nuclear Magnetic Resonance as a probe of nanometre-size orbital textures in magnetic transition metal oxides,"The study of strong electron correlations in transition metal oxides with
modern microscopy and diffraction techniques unveiled a fascinating world of
nanosize textures in the spin, charge, and crystal structure. Examples range
from high $T_c$ superconducting cuprates and nickelates, to hole doped
manganites and cobaltites. However, in many cases the appearance of these
textures is accompanied with ""glassiness"" and multiscale/multiphase effects,
which complicate significantly their experimental verification. Here, we
demonstrate how nuclear magnetic resonance may be uniquely used to probe
nanosize orbital textures in magnetic transition metal oxides. As a convincing
example we show for the first time the detection of nanoscale orbital phase
separation in the ground state of the ferromagnetic insulator
La$_{0.875}$Sr$_{0.125}$MnO$_3$.",0412371v1
2010-11-22,Orbital occupation and magnetic moments of tetrahedrally coordinated iron in CaBaFe4O7,"CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+
ions in tetrahedral coordination. Here we characterize its magnetic properties
by magnetization measurements and investigate its local electronic structure
using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination
with multiplet cluster and spin-resolved band structure calculations. We found
that the Fe2+ ion in the unusual tetrahedral coordination is Jahn-Teller active
with the high-spin e^2 (up) t2^3 (up) e^1 (down) configuration having a
x^2-y^2-like electron for the minority spin. We deduce that there is an
appreciable orbital moment of about L_z=0.36 caused by multiplet interactions,
thereby explaining the observed magnetic anisotropy. CaBaFe4O7, a member of the
'114' oxide family, offers new opportunities to explore charge, orbital and
spin physics in transition metal oxides.",1011.4818v1
2013-01-29,Breathing Pyrochlore Lattice Realized in A-Site Ordered Spinel Oxides LiGaCr4O8 and LiInCr4O8,"A unique type of frustrated lattice is found in two A-site ordered spinel
oxides, LiGaCr4O8 and LiInCr4O8. Because of the large size mismatch between Li+
and Ga3+/In3+ ions at the A site, the pyrochlore lattice, made up of Cr3+ ions
carrying spin 3/2, becomes an alternating array of small and large tetrahedra,
i.e., a ""breathing"" pyrochlore lattice. We introduce a parameter, the breathing
factor Bf, which quantifies the degree of frustration in the pyrochlore
lattice: Bf is defined as J'/J, where J' and J are nearest-neighbor magnetic
interactions in the large and small tetrahedra, respectively. LiGaCr4O8 with Bf
~ 0.6 shows magnetic susceptibility similar to that of conventional Cr spinel
oxides such as ZnCr2O4. In contrast, LiInCr4O8 with a small Bf ~ 0.1 exhibits a
spin-gap behavior in its magnetic susceptibility, suggesting a proximity to an
exotic singlet ground state. Magnetic long-range order occurs at 13.8 and 15.9
K for LiGaCr4O8 and LiInCr4O8, respectively, in both cases likely owing to the
coupling to structural distortions.",1301.6936v1
2016-07-19,Synthesis of strontium ferrite/iron oxide exchange coupled nano-powders with improved energy product for rare earth free permanent magnet applications,"We present a simple, scalable synthesis route for producing exchange coupled
soft/hard magnetic composite powder that outperforms pure soft and hard phase
constituents. Importantly, the composites is iron oxide based (SrFe12O19 and
Fe3O4) and contain no rare earth or precious metal. The two step synthesis
process consists of first precipitating, an Iron oxide/hydroxide precursor
directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing
between the hard and the soft magnetic phases. We then use a second step that
serves to reduce the precursor to create the proper soft magnetic phase and
create the intimate interface necessary for exchange coupling. We establish a
clear processing window; at temperatures below this window the desired soft
phase is not produced, while higher temperatures result in deleterious reaction
at the soft/hard phase interfaces, causing an improper ratio of soft to hard
phases. Improvements of Mr, Ms, and (BH)max are 42%, 29% and 37% respectively
in the SrFe12O19/Fe3O4 composite compared to pure hard phase (SrFe12O19). We
provide evidence of coupling (exchange spring behavior) with hysteresis curves,
first order reversal curve (FORC) analysis and recoil measurements.",1607.05689v1
2016-07-27,Magnetic Collapse and the Behavior of Transition Metal Oxides at High Pressure,"We report a detail theoretical study of the electronic structure and phase
stability of transition metal oxides MnO, FeO, CoO, and NiO in their
paramagnetic cubic B1 structure by employing dynamical mean-field theory of
correlated electrons combined with \emph{ab initio} band structure methods
(DFT+DMFT). Our calculations reveal that under pressure these materials exhibit
a Mott insulator-metal transition (IMT) which is accompanied by a simultaneous
collapse of local magnetic moments and lattice volume, implying a complex
interplay between chemical bonding and electronic correlations. Moreover, our
results for the transition pressure show a monotonous decrease from ~ 145 GPa
to 40 GPa, upon moving from MnO to CoO. In contrast to that, in NiO, magnetic
collapse is found to occur at remarkably higher pressure of ~ 429 GPa. We
provide a unified picture of such a behavior and suggest that it is primary a
localized to itinerant moment behavior transition at the IMT that gives rise to
magnetic collapse in transition metal oxides.",1607.08261v1
2010-05-04,Competition between Ferrimagnetism and Magnetic Frustration in Zinc Substituted YBaFe4O7,"The substitution of zinc for iron in YBaFe4O7 has allowed the oxide series
YBaFe4-xZnxO7, with 0.40 < x < 1.50, belonging to the ""114"" structural family
to be synthesized. These oxides crystallize in the hexagonal symmetry (P63mc),
as opposed to the cubic symmetry (F-43m) of YBaFe4O7. Importantly, the d.c.
magnetization shows that the zinc substitution induces ferrimagnetism, in
contrast to the spin glass behaviour of YBaFe4O7. Moreover, a.c. susceptibility
measurements demonstrate that concomitantly these oxides exhibit a spin glass
or a cluster glass behaviour, which increases at the expense of ferrimagnetism,
as the zinc content is increased. This competition between ferrimagnetism and
magnetic frustration is interpreted in terms of lifting of the geometric
frustration, inducing the magnetic ordering, and of cationic disordering, which
favours the glassy state.",1005.0480v1
2019-06-20,"Crystal structure and the magnetic properties of the 5d transition metal oxide AOsO4 (A = K, Rb, Cs)","We synthesized the 5d1-transition metal oxides AOsO4 (A = K, Rb, Cs) by
solid-state reaction, and performed structure determination and magnetic and
heat capacity measurements. It was found that they crystallize in a scheelite
(A = K and Rb) or a quasi-scheelite structure (A = Cs) comprising of distorted
diamond lattices of septivalent Os (d1) ions tetrahedrally coordinated by four
oxide ions without local inversion symmetry; hence an antisymmetric spin-orbit
coupling is expected in the crystals. The K and Rb compounds have Weiss
temperatures of theta = -66 and -18 K, effective magnetic moments of mu_eff =
1.44 and 1.45 mu_B/Os, and antiferromagnetic transition temperatures of T_N =
36.9 and 21.0 K, respectively. In contrast, the Cs compound has theta = 12 K
and mu_eff = 0.8 mu_B/Os without magnetic transition above 2 K, instead
exhibiting a first-order structural transition at T_s = 152.5 K. The decline of
the Os moment from 1.73 mu_B/Os for the simple d1 spin, particularly for Cs, is
likely to originate from the antiparallel orbital moment, although the
spin-orbit coupling is generally quenched in the low-lying e orbitals.",1906.08519v1
2021-08-10,Metallic nature and site-selective magnetic collapse in iron oxide Fe4O5 at the extreme conditions of Earth's deep interior,"Properties of iron oxides at the extreme conditions are of essential
importance in condensed matter physics and Geophysics. The recent discovery of
a new type of iron oxide, Fe4O5, at high pressure and high temperature of
Earth's deep interior attracts great interests. In this paper, we report the
electronic structure and the magnetic properties of Fe4O5 predicted by the
density functional theory plus dynamic mean field theory (DFT+DMFT) approach.
We find that Fe4O5 stays metallic from ambient pressure to high pressure. The
magnetic moments of iron atoms at the three different crystallographic
positions of Fe4O5 undergo position-dependent collapse as being compressed.
Such site-selective magnetic moment collapse originates from the shift of
energy levels and the consequent charge transfer among the Fe-3d orbits under
compression.",2108.04477v1
2022-08-03,Magnetic biophysical characterization of biomimetic polyeth-ylenimine-coated nanoparticles on in vitro silico model,"Understanding the biophysical and magnetic interactions of nanoparticles
(NPs) with cell mem-branes is critical for developing effective nanocarrier
systems for drug delivery applications and targeted nanophysics applications.
Recent discoveries in nanomedicine can be used to test an in vitro system that
reproduce a similar tumor model. Iron-oxide nanoparticles can be used for
diagnosis, as well as a good carrier of drugs and induced therapeutic for
magnetic hyperthermia. In the present study, we engineered
polyethylenimine-conjugated superparamagnetic iron-oxide nanoparticles (SPIONs)
for the targeted delivery of chemotherapeutics on in vitro silico model.
Doxorubicin is used to treat numerous types of tumors including breast cancer.
The drug-coated mul-ti-functionalized nanoparticles, were assembled stepwise,
with doxorubicin adsorbed to polyeth-ylenimine-iron oxide nanoparticles first,
by electrostatic reaction and allowed for the complexation of doxorubicin.. The
drug-coated particles were able to inhibit growth and proliferation of
resistant cancer cells in vitro, indicating that the system has potential to
act as an antimetastatic chemo-thermotherapeutic agent. Here, we demonstrated a
sophisticated strategy to kill in a precise way only cancer cells by
conjugating a magnetic nanoparticle to chemotherapeutic.",2208.02838v1
2022-10-30,"Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions","The interfacial oxidation level and thermodynamic properties of the MgO-based
perpendicular magnetic tunneling junctions are investigated. The
symmetry-conserved tunneling effect depends sensitively on the MgO adatom
energy during the RF sputtering, as well as the thermal stability of the
structure during the post-growth thermal annealing. Two different failure modes
of the magnetoresistance are highlighted, involving with the decay of
perpendicular magnetic anisotropy and destruction of coherent tunneling
channels, respectively. Through the careful control of interfacial oxidation
level and proper selection of the heavy metal layers, both perpendicular
magnetic anisotropy and tunneling magnetoresistance of the junctions can be
increased.",2210.16734v1
2023-12-21,Magnetic Transparent Conductors for Spintronic Applications,"Transparent Conductors (TCs) exhibit optical transparency and electron
conductivity, and are essential for many opto-electronic and photo-voltaic
devices. The most common TCs are electron-doped oxides, which have few
limitations when transition metals are used as dopants. Non-oxides TCs have the
potential of extending the class of materials to the magnetic realm, bypass
technological bottlenecks, and bring TCs to the field of spintronics. Here we
propose new functional materials that combine transparency and conductivity
with magnetic spin polarization that can be used for spintronic applications,
such as spin filters. By using high-throughput first-principles techniques, we
identified a large number of potential TCs, including non-oxides materials. Our
results indicate that proper doping with transition metals introduces a finite
magnetization that can provide spin filtering up to 90% in the electrical
conductivity, still maintaining a transparency greater than 90%.",2312.13708v1
2003-06-18,Evidence for the coexistence of low-dimensional magnetism and long-range order in Ca3CoRhO6,"We report the results of neutron powder diffraction studies on the spin-chain
compound Ca3CoRhO6 in the temperature range 3 to 293 K. Bragg peaks due to
magnetic ordering start appearing below about 100 K. The most interesting
observation is that there is a diffuse magnetic peak superimposed over the
strongest magnetic Bragg peak. The diffuse magnetic intensity is observed below
as well above 100 K. This finding provides a new insight into the physics of
this compound as though the low-dimensional magnetic interaction coexists with
long range magnetic order - a novel situation among quasi one-dimensional
oxides.",0306481v1
2005-06-20,Monte Carlo study of half-magnetization plateau and magnetic phase diagram in pyrochlore antiferromagnetic Heisenberg model,"The antiferromagnetic Heisenberg model on a pyrochlore lattice under external
magnetic field is studied by classical Monte Carlo simulation. The model
includes bilinear and biquadratic interactions; the latter effectively
describes the coupling to lattice distortions. The magnetization process shows
a half-magnetization plateau at low temperatures, accompanied with strong
suppression of the magnetic susceptibility. Temperature dependence of the
plateau behavior is clarified. Finite-temperature phase diagram under the
magnetic field is determined. The results are compared with recent experimental
results in chromium spinel oxides.",0506500v2
2012-09-17,Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles,"The magnetic properties of densely packed magnetic nanoparticles (MNP)
assemblies are investigated from Monte Carlo simulations. The case of iron
oxide nanoparticles is considered as a typical example of MNP. The main focus
is put on particle size and size polydispersity influences on the magnetization
curve. The particles are modeled as uniformly magnetized spheres isolated one
from each other by a non magnetic layer representing the organic coating. A
comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder
samples differing by their size is given.",1209.3566v1
1996-02-05,"Magnetic and Transport Properties of (La,Sr)MnO$_3$","Magnetic and transport properties of the perovskite-type $3d$
transition-metal oxide (La,Sr)MnO$_3$ are theoretically studied using the
double-exchange model in infinite dimension. Magnetoresistance properties as
well as the magnetic transition temperatures are in good agreement with the
experimental data.",9602016v1
2004-09-03,Helicoidal ordering in iron perovskites,"We consider magnetic ordering in materials with negative charge transfer
energy, such as iron perovskite oxides. We show that for a large weight of
oxygen holes in conduction bands, the double exchange mechanism favors a
helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3
and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic
excitation spectrum and effects of pressure on magnetic ordering in these
materials.",0409068v1
2005-03-17,Signatures of Spin Glass Freezing in NiO Nanoparticles,"We present a detailed study of the magnetic properties of sol-gel prepared
nickel oxide nanoparticles of different sizes. We report various measurements
such as frequency, field and temperature dependence of ac susceptibility,
temperature and field dependence of dc magnetization and time decay of
thermoremanent magnetization. Our results and analysis show that the system
behaves as a spin glass.",0503433v1
2006-02-05,Magnetic properties of vanadium-oxide nanotubes probed by static magnetization and {51}V NMR,"Measurements of the static magnetic susceptibility and of the nuclear
magnetic resonance of multiwalled vanadium-oxide nanotubes are reported. In
this nanoscale magnet the structural low-dimensionality and mixed valency of
vanadium ions yield a complex temperature dependence of the static
magnetization and the nuclear relaxation rates. Analysis of the different
contributions to the magnetism allows to identify individual interlayer
magnetic sites as well as strongly antiferromagnetically coupled vanadium spins
(S = 1/2) in the double layers of the nanotube's wall. In particular, the data
give strong indications that in the structurally well-defined vanadium-spin
chains in the walls, owing to an inhomogeneous charge distribution,
antiferromagnetic dimers and trimers occur. Altogether, about 30% of the
vanadium ions are coupled in dimers, exhibiting a spin gap of the order of 700
K, the other ~ 30% comprise individual spins and trimers, whereas the remaining
\~ 40% are nonmagnetic.",0602114v2
2013-05-09,Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures,"Possible ferromagnetism induced in otherwise non-magnetic materials has been
motivating intense research in complex oxide heterostructures. Here we show
that a confined magnetism is realized at the interface between SrTiO3 and two
insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent
x-ray absorption spectroscopy, we find that in both cases the magnetic order is
stabilized by a negative exchange interaction between the electrons transferred
to the interface and local magnetic moments. These local magnetic moments are
associated to Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+
ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetic
moments are quenched by annealing in oxygen, suggesting a decisive role of
oxygen vacancies in the stabilization of interfacial magnetism.",1305.2226v2
2020-07-16,Crystal and Magnetic Structure of Polar Oxide HoCrWO$_6$,"Polar magnetic oxide HoCrWO$_6$ is synthesized and its crystal structure,
magnetic structure, and thermodynamic properties are investigated. HoCrWO$_6$
forms the polar crystal structure (space group Pna2$_1$ (#33)) due to the
cation ordering of W$^{6+}$ and Cr$^{3+}$. There is an antiferromagnetic
transition at TN = 24.5 K along with the magnetic entropy change (~5
J.Kg.$^{-1}$K$^{-1}$ at 70 kOe). Neutron diffraction measurement indicates that
both Cr and Ho sublattices are ordered with the moment of 2.32(5)$\mu_B$ and
8.7(4)$\mu_B$ at 2 K, respectively. While Cr forms A-type collinear
antiferromagnetic (AFM) structure with magnetic moment along the $b$ axis, Ho
sublattice orders in a non-coplanar AFM arrangement. A comparison with
isostructural DyFeWO$_6$ and DyCrWO$_6$ indicates that the magnetic structure
of this family of compounds is controlled by the presence or absence of eg
electrons in the transition metal sublattice.",2007.08581v1
2012-05-09,Magnetically ordered state at correlated oxide interfaces: the role of random oxygen defects,"Using an effective one-band Hubbard model with disorder, we consider magnetic
states of the correlated oxide interfaces, where effective hole self-doping and
a magnetially ordered state emerge due to electronic and ionic reconstructions.
By employing the coherent potential approximation, we analyze the effect of
random oxygen vacancies on the two-dimensional magnetism. We find that the
random vacancies enhance the ferromagnetically ordered state and stabilize a
robust magnetization above a critical vacancy concentration of about c=0.1. In
the strong-correlated regime, we also obtain a nonmonotonic increase of the
magnetization upon an increase of vacancy concentration and a substantial
increase of the magnetic moments, which can be realized at oxygen reduced
high-Tc cuprate interfaces.",1205.1981v1
2023-02-03,Defect-induced magnetism in TiO$_2$: An example of quasi 2D magnetic order with perpendicular anisotropy,"Magnetic order at room temperature induced by atomic lattice defects, like
vacancies, interstitials or pairs of them, has been observed in a large number
of different nonmagnetic hosts, such as pure graphite, oxides and silicon-based
materials. High Curie temperatures and time independent magnetic response at
room temperature indicate the extraordinary robustness of this new phenomenon
in solid state magnetism. In this work, we review experimental and theoretical
results in pure TiO$_2$ (anatase), which magnetic order can be triggered by
low-energy ion irradiation. In particular, we discuss the systematic
observation of an ultrathin magnetic layer with perpendicular magnetic
anisotropy at the surface of this oxide.",2302.01803v1
2012-08-02,Strong electronic correlation and strain effects at the interfaces between polar and nonpolar complex oxides,"The interface between the polar LaAlO$_3$ and nonpolar SrTiO$_3$ layers has
been shown to exhibit various electronic and magnetic phases such as two
dimensional electron gas, superconductivity, magnetism and electronic phase
separation. These rich phases are expected due to the strong interplay between
charge, spin and orbital degree of freedom at the interface between these
complex oxides, leading to the electronic reconstruction in this system.
However, until now all of these new properties have been studied extensively
based on the interfaces which involve a polar LaAlO$_3$ layer. To investigate
the role of the A and B cationic sites of the ABO$_3$ polar layer, here we
study various combinations of polar/nonpolar oxide (NdAlO$_3$/SrTiO$_3$,
PrAlO$_3$/SrTiO$_3$ and NdGaO$_3$/SrTiO$_3$) interfaces which are similar in
nature to LaAlO$_3$/SrTiO$_3$ interface. Our results show that all of these new
interfaces can also produce 2DEG at their interfaces, supporting the idea that
the electronic reconstruction is the driving mechanism for the creation of the
2DEG at these oxide interfaces. Furthermore, the electrical properties of these
interfaces are shown to be strongly governed by the interface strain and strong
correlation effects provided by the polar layers. Our observations may provide
a novel approach to further tune the properties of the 2DEG at the selected
polar/nonpolar oxide interfaces.",1208.0410v1
2020-09-17,Anodic Oxidation of Epitaxial Superconductor-Semiconductor Hybrids,"We demonstrate a new fabrication process for hybrid
semiconductor-superconductor heterostructures based on anodic oxidation (AO),
allowing controlled thinning of epitaxial Al films. Structural and transport
studies of oxidized epitaxial Al films grown on insulating GaAs substrates
reveal spatial non-uniformity and enhanced critical temperature and magnetic
fields. Oxidation of epitaxial Al on hybrid InAs heterostructures with a
conducting quantum well show similarly enhanced superconducting properties
transferred to the two-dimensional electron gas (2DEG) by proximity effect,
with critical perpendicular magnetic fields up to 3.5 T. An insulating AlOx
film, that passivates the heterostructure from exposure to air, is obtained by
complete oxidation of the Al. It simultaneously removes the need to strip Al
which damages the underlying semiconductor. AO passivation yielded 2DEG
mobilities two times higher than similar devices with Al removed by wet
etching. An AO-passivated Hall bar showed quantum Hall features emerging at a
transverse field of 2.5 T, below the critical transverse field of thinned
films, eventually allowing transparent coupling of quantum Hall effect and
superconductivity. AO thinning and passivation are compatible with standard
lithographic techniques, giving lateral resolution below <50 nm. We demonstrate
local patterning of AO by realizing a semiconductor-based Josephson junction
operating up to 0.3 T perpendicular.",2009.08190v1
2021-05-02,Tunable Néel-Bloch magnetic twists in Fe3GeTe2 with van der Waals structure,"The advent of ferromagnetism in two-dimensional (2D) van der Waals (vdW)
magnets has stimulated high interest in exploring topological magnetic
textures, such as skyrmions for use in future skyrmion-based spintronic
devices. To engineer skyrmions in vdW magnets by transforming Bloch-type
magnetic bubbles into N\'eel-type skyrmions, the heterostructure of heavy
metal/vdW magnetic thin film has been made to induce interfacial
Dzyaloshinskii-Moriya interaction (DMI). However, the unambiguous
identification of the magnetic textures inherent to vdW magnets, e.g., whether
the magnetic twists (skyrmions/domain walls) are N\'eel- or Bloch-type, is
unclear. Here we demonstrate that the N\'eel- or Bloch-type magnetic twists can
be tuned in the vdW magnet Fe3GeTe2 (FGT) with/without interfacial DMI. We use
an in-plane magnetic field to align the modulation wavevector q of the
magnetizations in order to distinguish the N\'eel- or Bloch-type magnetic
twists. We observe that q is perpendicular to the in-plane field in the
heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated
angle with respect to the field direction in the thin plate by thinning bulk
FGT. We find that the aligned domain wall twists hold fan-like modulations,
coinciding qualitatively with our computational results.",2105.00468v1
1998-09-05,Coexistence of the Electron Cooper Pair and Antiferromagnetic Short-Range Correlation in Copper Oxide Materials,"Within the fermion-spin theory, the physical properties of the electron
pairing state in the copper oxide materials are discussed. According to the
common form of the electron Cooper pair, it is shown that there is a
coexistence of the electron Cooper pair and magnetic short-range correlation,
and hence the antiferromagnetic short-range correlation can persist into the
superconducting state. Moreover, the mean-field results indicate that the
electron pairing state originating from the pure magnetic interaction in the
two-dimensional t-J model is the local state, and then does not reveal the true
superconducting ground-state.",9809098v2
2003-03-06,Orbital Ordering and Orbital Fluctuations in Transition Metal Oxides,"We summarize some characteristic features of the frustrated magnetic
interactions in spin-orbital models adequate for cubic transition metal oxides
with orbital degeneracy. A generic tendency towards dimerization, found already
in the degenerate Hubbard model, is confirmed for $t_{2g}$ but not for $e_g$
systems. In the $t_{2g}$ case the quantum orbital fluctuations are more
pronounced and contribute to a stronger competition between different magnetic
and orbital states. Therefore the orbital liquid states exist in some undoped
$t_{2g}$ systems, while in the manganites such states can be triggered only by
doping.",0303113v1
2004-07-27,Composition dependent magnetic properties of iron oxide - polyaniline nanoclusters,"Gamma - Iron Oxide prepared by sol -gel process was used to produce
nanocomposites with polyaniline of varying aniline concentrations. TEM shows
the presence of chain like structure for lower polyaniline concentration. The
room temperature hysteresis curves show finite coercivity of 160 Oe for all the
composites while the saturation magnetization was found to decrease with
increasing polymer content. ZFC - FC magnetisation measurements indicate high
blocking temperatures. It is believed that this indicates a strongly
interacting system, which is also shown by our TEM results. Monte Carlo
simulations performed on a random anisotropy model with dipolar and exchange
inteactions match well with experimental results.",0407693v1
2006-11-29,Room temperature tunneling anisotropic and collinear magnetoresistance,"We report a room temperature tunneling anisotropic magnetoresistance in
Co/Al2O3/NiFe junctions containing magnetic electrodes oxidized prior to
forming the Al2O3 layer. A significant change in a tunnel magnetoresistance is
observed when the layer magnetizations are rotated collinearly in the junction
plane by an applied external field. The angular dependence of the tunneling
anisotropic magnetoresistance could be explained by the presence of an
antiferromagnetic oxide layer formed within the barrier.",0611751v1
2010-06-30,Control of the structural and magnetic properties of perovskite oxide ultrathin films through the substrate symmetry effect,"Perovskite transition-metal oxides are networks of corner-sharing octahedra
whose tilts and distortions are known to affect their electronic and magnetic
properties. We report calculations on a model interfacial structure to avoid
chemical influences and show that the symmetry mismatch imposes an interfacial
layer with distortion modes that do not exist in either bulk material, creating
new interface properties driven by symmetry alone. Depending on the resistance
of the octahedra to deformation, the interface layer can be as small as one
unit cell or extend deep into the thin film.",1006.5758v1
2011-06-28,Oxygen adsorption effect on magnetic properties of graphite,"Both experimental and theoretical studies of the magnetic properties of
micrographite and nanographite indicate a crucial role of the partial oxidation
of graphitic zigzag edges in ferromagnetism. In contrast to total and partial
hydrogenation, the oxidation of half of the carbon atoms on the graphite edges
transforms the antiferromagnetic exchange interaction between graphite planes
and over graphite ribbons to the ferromagnetic interaction. The stability of
the ferromagnetism is discussed.",1106.5565v1
2013-08-19,Spirals and skyrmions in two dimensional oxide heterostructures,"We construct the general free energy governing long-wavelength magnetism in
two-dimensional oxide heterostructures, which applies irrespective of the
microscopic mechanism for magnetism. This leads, in the relevant regime of weak
but non-negligible spin-orbit coupling, to a rich phase diagram containing
in-plane ferromagnetic, spiral, cone, and skyrmion lattice phases, as well as a
nematic state stabilized by thermal fluctuations. The general conclusions are
vetted by a microscopic derivation for a simple model with Rashba spin-orbit
coupling.",1308.4179v2
2017-06-16,Electronic and magnetic properties of epitaxial SrRhO3 films,"Strong interplay of fundamental order parameters in complex oxides are known
to give rise to exotic physical phenomena. The 4d transition metal oxide SrRhO3
has generated much interest, but advances have been hindered by difficulties in
preparing single crystalline phases. Here, we have epitaxially stabilized high
quality single crystalline SrRhO3 films and investigated their structural,
electronic, and magnetic properties. We determine that their properties
significantly differ from the paramagnetic metallic ground state that governs
bulk samples and are strongly related to rotations of the RhO6 octahedra.",1706.05409v1
2017-07-26,Magnetism from intermetallics and perovskite oxides,"This work has been presented by RJCV to obtain his PhD degree at Fluminense
Federal University, in March of 2017. We focused on the synthesis of compounds
and then on their magneto-strucutral characterization; mainly due to the
interplay of these physical properties. We have prepared intermetallic alloys
(including Heusler alloys) and perovskite oxides (manganites and cobaltites);
in bulk and nanoparticles. A thorough analysis of the influence of the
morphology and crystal structure on the magnetic properties of these compounds
is addressed.",1707.09868v2
2019-10-09,Electric-field control of magnetism in iron oxide nanoparticle / BaTiO3 film composites,"We study composites of monodisperse ferrimagnetic nanoparticles (NPs)
embedded into ferroelectric barium titanate (BTO) films. The BTO films were
prepared by pulsed laser deposition. The composite consists of a stack of two
BTO films sandwiching one monolayer of iron oxide NPs. We observe a
magnetoelectric coupling due to strain and interface charge co-mediation
between the BTO and the NPs. This is demonstrated by measurements of the
magnetization as function of DC and AC electric fields.",1910.04127v1
2019-02-17,Redox-controlled epitaxy and magnetism of oxide heterointerfaces: EuO/SrTiO$_3$,"We demonstrate a novel route to prepare thin films of the ferromagnetic
insulator Europium monoxide. Key is a redox-controlled interface reaction
between metallic Eu and the substrate SrTiO$_3$ as the supplier of oxygen. The
process allows tuning the electronic, magnetic and structural properties of the
EuO films. Furthermore, we apply this technique to various oxidic substrates
and demonstrate the universality and limits of a redox-controlled EuO film
synthesis.",1902.06301v1
2019-12-23,Electronic and magnetic properties of structural defects in SrTiO$_3$(Co),"The synthesis conditions of SrTiO$_3$(Co) samples in which cobalt
predominantly enters the $A$ or $B$ sites of the perovskite $AB$O$_3$ structure
are found. EXAFS studies show that the Co impurity at the $A$ site is
off-center and is displaced from the site by 1.0 {\AA}. XANES studies reveal
two predominant oxidation states of Co: Co$^{2+}$ at the $A$ site and Co$^{3+}$
at the $B$ site. First-principles calculations of a number of possible
cobalt-containing structural defects reveal defects whose properties are
compatible with the experimentally observed Co oxidation state, its local
structure, magnetic, electrical, and optical properties.",1912.10711v1
2020-03-12,Superconductor-Insulator Transition and the Crossover to Non Equilibrium in two-dimensional Indium - Indium-Oxide composite,"Magnetic-field tuned superconductor to insulator transition was observed in a
novel hybrid system of granular superconducting indium, deposited on indium
oxide thin film, which exhibits global superconductivity at low magnetic
fields. We have used annealing to tune the coupling to lie just at the
borderline where superconductivity in the underlying InOx is suppressed, which
is also close to the metal-insulator transition of the InOx. The hybrid system
exhibits a ""giant"" magnetoresistance above the H-SIT, with critical behavior
that manifests the duality between Cooper pairs and vortices.",2003.05723v2
2024-02-28,Harnessing the Duality of Magnetism and Conductivity: A Review of Oxide based Dilute Magnetic Semiconductors,"Over the last two decades, the new branch of spintronics, i.e., semiconductor
spintronics, has gained more attention because it integrates the
characteristics of conventional semiconductors, such as optical bandgap and
charge carriers, helpful for processing and computing pieces of information
combined with magnets for data storage applications in a single device.
Likewise, substituting transition metal (TM) ions to induce magnetic qualities
into semiconductors or oxides creates dilute magnetic semiconductors (DMSs) or
oxides (DMOs) with high electronic, photonic, and magnetic functionality. This
review article discusses the historical outline of magnetic semiconductors with
their origin and mechanism. It also includes a concise overview of various DMO
systems based on their conductivity (p-type and n-type) to elucidate the
synthesis, origin, and control mechanisms and further evoke the prepared
spintronics devices. The occurrence of RTFM with transparency and conductivity
can be helpful in spintronics device fabrications, which was assumed to be
governed by the formation of intrinsic defects, charge carriers, morphology,
and the induced exchange interactions between ions. The DMOs-based spintronics
devices, such as magneto-optical devices, transparent ferromagnets, and
spin-based solar cells, exploit both semiconducting and magnetic properties,
which have also been discussed in this review article with outlook and
perspectives.",2402.18173v1
2021-12-13,Mechanism of Spin-Orbit Torques in Platinum Oxide Systems,"Spin-Orbit Torque (SOT) Magnetic Random-Access Memories (MRAM) have shown
promising results towards the realization of fast, non-volatile memory systems.
Oxidation of the heavy-metal (HM) layer of the SOT-MRAM has been proposed as a
method to increase its energy efficiency. But the results are widely divergent
due to the difficulty in controlling the HM oxidation because of its low
enthalpy of formation. Here, we reconcile these differences by performing a
gradual oxidation procedure, which allows correlating the chemical structure to
the physical properties of the stack. As an HM layer, we chose Pt because of
the strong SOT and the low enthalpy of formation of its oxides. We find
evidence of an oxide inversion layer at the FM/HM interface: the oxygen is
drawn into the FM, while the HM remains metallic near the interface. We further
demonstrate that the oxygen migrates in the volume of the FM layer rather than
being concentrated at the interface. Consequently, we find that the intrinsic
magnitude of the SOT is unchanged compared to the fully metallic structure. The
previously reported apparent increase of SOTs is not intrinsic to platinum
oxide and instead arises from systemic changes produced by oxidation.",2112.07034v1
2023-07-05,Heterophased grain boundary-rich superparamagnetic Iron Oxides/carbon composite for Cationic and Anionic Dye Removal,"Iron oxide-based nanostructures receive significant attention as an efficient
adsorbent for organic dyes removal. The removal properties have strong
dependency on the stoichiometry, phases, reactive edges, defect states etc
present in the iron-oxides nanostructures. Herein, iron oxide/carbon composite
with well-defined heterophased grain boundaries is synthesized by simple
precipitation method and followed by calcination. The local structure, spin
dynamics and magnetic properties of heterophased iron oxides/carbon composite
are thoroughly investigated to explore its cationic and anionic dye removal
capability. To validate the effectivity of the presence of heterogeneous grain
boundaries, iron oxide/carbon nanocomposite with homogeneous grain boundaries
is also examined. It was found that the hetero-phased iron oxide/carbon showed
removal capacity of 35.45 mg g-1 and 45.84 mg g-1 for cationic (Crystal Violet)
and anionic (Congo Red) dyes, respectively as compared to that of
as-synthesised imidazole-capped superparamagnetic {\alpha}-Fe2O3 (25.11 mg g-1
and 40.44 mg g-1, respectively) and homophased iron oxide/carbon nanocomposite
(9.41 mg g-1 and 5.43 mg g-1, respectively). The plausible mechanism on the
local structural evolution of the heterophase in the course of calcination and
increase of the removal capacity is discussed. A detailed dye adsorption
investigation is presented including the adsorption kinetic study. The
pseudo-second order kinetic model is found to be an appropriate one and
suggests that the chemisorption is dominant factor leading to adsorption of
dyes. Whereas Weber-Morris model indicate the strong influence of boundary
layers of nanocomposite on the adsorption process.",2307.02142v1
2008-04-04,Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems,"In high-transition temperature (high-Tc) copper oxides, it is generally
believed that antiferromagnetism plays a fundamental role in the
superconducting mechanism because superconductivity occurs when mobile
electrons or holes are doped into the antiferromagnetic parent compounds. The
recent discovery of superconductivity in the rare-earth (R) iron-based oxide
systems [RO1-xFxFeAs] has generated enormous interest because these materials
are the first noncopper oxide superconductors with Tc exceeding 50 K. The
parent (nonsuperconducting) LaOFeAs material is metallic but shows anomalies
near 150 K in both resistivity and dc magnetic susceptibility. While optical
conductivity and theoretical calculations suggest that LaOFeAs exhibits a
spin-density-wave (SDW) instability that is suppressed with doping electrons to
form superconductivity, there has been no direct evidence of the SDW order.
Here we use neutron scattering to demonstrate that LaOFeAs undergoes an abrupt
structural distortion below ~150 K, changing the symmetry from tetragonal
(space group P4/nmm) to monoclinic (space group P112/n) at low temperatures,
and then followed with the development of long range SDW-type antiferromagnetic
order at ~134 K with a small moment but simple magnetic structure. Doping the
system with flourine suppresses both the magnetic order and structural
distortion in favor of superconductivity. Therefore, much like high-Tc copper
oxides, the superconducting regime in these Fe-based materials occurs in close
proximity to a long-range ordered antiferromagnetic ground state. Since the
discovery of long",0804.0795v1
2017-10-31,Electric-field control of oxygen vacancy and magnetic phase transition in cobaltite/manganite bilayer,"Manipulation of oxygen vacancies (V_O) in single oxide layers by varying the
electric field can result in significant modulation of the ground state.
However, in many oxide multilayers with strong application potentials, e.g.
ferroelectric tunnel junctions and solid-oxide fuel cells, understanding V_O
behaviour in various layers under an applied electric field remains a
challenge, owing to complex V_O transport between different layers. By sweeping
the external voltage, a reversible manipulation of V_O and a corresponding
fixed magnetic phase transition sequence in cobaltite/manganite
(SrCoO3-x/La0.45Sr0.55MnO3-y) heterostructures are reported. The magnetic phase
transition sequence confirms that the priority of electric-field-induced V_O
formation/annihilation in the complex bilayer system is mainly determined by
the V_O formation energies and Gibbs free energy differences, which is
supported by theoretical analysis. We not only realize a reversible
manipulation of the magnetic phase transition in an oxide bilayer, but also
provide insight into the electric field control of V_O engineering in
heterostructures.",1712.01355v1
2021-10-06,"Stacking-order effect on spin-orbit torque, spin-Hall magnetoresistance, and magnetic anisotropy in Ni$_{81}$Fe$_{19}$-IrO$_2$ bilayers","The 5d transition-metal oxides have been an intriguing platform to
demonstrate efficient charge to spin current conversion due to a unique
electronic structure dominated by strong spin-orbit coupling. Here, we report
on stacking-order effect of spin-orbit torque (SOT), spin-Hall
magnetoresistance, and magnetic anisotropy in bilayer Ni$_{81}$Fe$_{19}$-5d
iridium oxide, IrO$_2$. While all the IrO$_2$ and Pt control samples exhibit
large dampinglike-SOT generation stemming from the efficient charge to spin
current conversion, the magnitude of the SOT is larger in the IrO$_2$
(Pt)-bottom sample than in the IrO$_2$ (Pt)-top one. The fieldlike-SOT has even
more significant stack order effect, resulting in an opposite sign in the
IrO$_2$ samples in contrast to the same sign in the Pt samples. Furthermore, we
observe that the magnetic anisotropy energy density and the anomalous Hall
effect are increased in the IrO$_2$ (Pt)-bottom sample, suggesting enhanced
interfacial perpendicular magnetic anisotropy. Our findings highlight the
significant influence of the stack order on spin transport and magnetotransport
properties of Ir oxide/ferromagnet systems, providing useful information on
design of SOT devices including 5d transition-metal oxides.",2110.02517v1
2001-06-19,The oxidation state at tunnel junction interfaces,"We demonstrate that at the usual 1E-7 torr range of base pressures in the
sputtering chamber, X-ray photoelectron spectroscopy shows the existence of a
thin AlOx layer at the Nb/Al interface in both Nb/Al-AlOx/Pb tunnel junctions
and Nb/Al bilayers. This is due to the time elapsed between the deposition of
the Nb and Al bottom layers, even at times as short as 100 s. We also give some
direct evidence of the oxidation of the top Pb electrode on the Nb electrode
surface. Such oxidation probably occurs at the pinholes of the intermediate
Al-AlOx layer of the junctions, as a consequence of the oxidation state at the
Nb/Al interface. We therefore suggest that both the base pressure and the time
lapse between layer depositions should be carefully controlled in magnetic
tunnel junctions.",0106376v1
2005-01-31,Specific Heat of the beta-Pyrochlore Oxide Superconductors CsOs2O6 and RbOs2O6,"Two beta-pyrochlore oxide superconductors, CsOs2O6 and RbOs2O6, are studied
thermodynamically by measuring specific heat on polycrystalline samples. It is
found that a Sommerfeld coefficient ? is nearly equal, 20 mJ/K2 mol Os, in the
two oxides with different superconducting transition temperatures; Tc = 3.3 K
and 6.3 K, respectively. This suggests that the density of states at the Fermi
level is not a crucial parameter to determine the Tc of the beta-pyrochlore
oxide superconductors, which is incompatible with the general expectation for a
conventional BCS-type superconductor. Anomalous lattice contributions to
specific heat at low temperature are also reported, which may come from nearly
localized phonon modes associated with the rattling of the alkali metal ions
weakly bound in an oversized cage formed by OsO6 octahedra.",0501736v3
2005-04-13,Growth Mechanisms and Oxidation-Resistance of Gold-Coated Iron Nanoparticles,"We report the chemical synthesis of Fe-core/Au-shell nanoparticles by a
reverse micelle method, and the investigation of their growth mechanisms and
oxidation-resistant characteristics. The core-shell structure and the presence
of the Fe & Au phases have been confirmed by transmission electron microscopy,
energy dispersive spectroscopy, X-ray diffraction, Mossbauer spectroscopy, and
inductively coupled plasma techniques. Additionally, atomic-resolution
Z-contrast imaging and electron energy loss spectroscopy (EELS) in a scanning
transmission electron microscope (STEM) have been used to study details of the
growth processes. The Au-shell grows by nucleating on the Fe-core surface
before coalescing. The magnetic moments of such nanoparticles, in the loose
powder form, decrease over time due to oxidation. The less than ideal
oxidation-resistance of the Au shell may have been caused by the rough Au
surfaces. However, in the pressed pellet form, electrical transport
measurements show that the particles are fairly stable, as the resistance of
the pellet does not change appreciably over time.",0504314v1
2014-01-08,Nanoscale Phenomena in Oxide Heterostructures,"Recent advances in creating complex oxide heterostructures, interfaces formed
between two different transition metal oxides, have heralded a new era of
materials and physics research, enabling a uniquely diverse set of coexisting
physical properties to be combined with an ever- increasing degree of
experimental control. Already, these systems have exhibited such varied
phenomena as superconductivity, magnetism, and ferroelasticity, all of which
are gate-tunable, demonstrating their promise for fundamental discovery and
technological innovation alike. To fully exploit this richness, it is necessary
to understand and control the physics on the smallest scales, making the use of
nanoscale probes essential. Using the prototypical LaAlO$_3$/SrTiO$_3$
interface as a guide, we explore the exciting developments in the physics of
oxide-based heterostructures, with a focus on nanostructures and the nanoscale
probes employed to unravel their complex behavior.",1401.1772v1
2020-07-03,Ferroelectric Exchange Bias Affects Interfacial Electronic States,"In polar oxide interfaces phenomena such as conductivity, superconductivity,
magnetism, one-dimensional conductivity and Quantum Hall states can emerge at
the polar discontinuity. Combining controllable ferroelectricity at such
interfaces can affect the superconducting properties and shed light on the
mutual effects between the polar oxide and the ferroelectric oxide. Here we
study the interface between the polar oxide LaAlO3 and the ferroelectric
Ca-doped SrTiO3 by means of electrical transport combined with local imaging of
the current flow with the use of scanning Superconducting Quantum Interference
Device (SQUID). Anomalous behavior of the interface resistivity is observed at
low temperatures. The scanning SQUID maps of the current flow suggest that this
behavior originates from an intrinsic bias induced by the polar LaAlO3 layer.
Our data imply that the intrinsic bias combined with ferroelectricity constrain
the possible structural domain tiling near the interface. We recommend the use
of this intrinsic bias as a method of controlling and tuning the initial state
of ferroelectric materials by design of the polar structure. The hysteretic
dependence of the normal and the superconducting state properties on gate
voltage can be utilized in multifaceted controllable memory devices.",2007.01785v1
2016-11-26,Band alignment and charge transfer in complex oxide interfaces,"The synthesis of transition metal heterostructures is currently one of the
most vivid fields in the design of novel functional materials. In this paper we
propose a simple scheme to predict \emph{band alignment }and \emph{charge
transfer} in complex oxide interfaces. For semiconductor heterostructures band
alignment rules like the well known Anderson or Schottky-Mott rule are based on
comparison of the work function or electron affinity of the bulk components.
This scheme breaks down for oxides due to the invalidity of a single
workfunction approximation as recently shown (Phys. Rev. B 93, 235116; Adv.
Funct. Mater. 26, 5471). Here we propose a new scheme which is built on a
continuity condition of valence states originating in the compounds' shared
network of oxygen. It allows for the prediction of sign and relative amplitude
of the intrinsic charge transfer, taking as input only information about the
bulk properties of the components. We support our claims by numerical density
functional theory simulations as well as (where available) experimental
evidence. Specific applications include i) controlled doping of SrTiO$_3$
layers with the use of 4$d$ and 5$d$ transition metal oxides and ii) the
control of magnetic ordering in manganites through tuned charge transfer.",1611.08689v1
2016-05-23,Direct evidence for charge stripes in a layered cobalt oxide,"Recent experiments indicate that static stripe-like charge order is generic
to the hole-doped copper oxide superconductors and competes with
superconductivity. Here we show that a similar type of charge order is present
in La$_{5/3}$Sr$_{1/3}$CoO$_4$, an insulating analogue of the copper oxide
superconductors containing cobalt in place of copper. The stripe phase we have
detected is accompanied by short-range, quasi-one-dimensional,
antiferromagnetic order, and provides a natural explanation for the distinctive
hourglass shape of the magnetic spectrum previously observed in neutron
scattering measurements of La$_{5/3}$Sr$_{1/3}$CoO$_4$ and many hole-doped
copper oxide superconductors. The results establish a solid empirical basis for
theories of the hourglass spectrum built on short-range, quasi-static, stripe
correlations.",1605.07087v1
2017-06-07,"Effect of oxygen vacancy on structural, electronic and magnetic properties of La-based oxide interfaces","Disorder, primarily in the form of oxygen vacancies, cation stoichiometry and
atomic inter-diffusion, appear to play vital roles in the electronic and
transport properties of the metallic electron liquid at the oxide
hetero-interfaces. Antisite disorder is also understood to be a key player in
this context. In order to delineate the roles of two of these key factors,
oxygen vacancy and antisite disorder, we have investigated the effect of oxygen
vacancy on the antisite disorder at a number of interfaces separating two
La-based transition metal oxides using density functional theory. Oxygen
vacancy is found to suppress the antisite disorder in some heterostructures and
thereby stabilizes the ordered structure, while in some other systems it tends
to drive the disorder. Thus by controlling the oxygen partial pressure during
the growth, it is possible to engineer the antisite disorder in many oxide
heretostructures.",1706.02210v2
2017-05-08,Origin of the crossover from polarons to Fermi liquids in transition metal oxides,"Transition metal oxides (TMOs) host a wealth of exotic phenomena ranging from
charge, orbital, and magnetic order to nontrivial topological phases and
superconductivity. In order to translate these unique materials properties into
novel device functionalities, TMOs must be doped. However, the nature of
carriers in doped oxides and their conduction mechanism at the atomic scale
remain unclear. Recent angle-resolved photoelectron spectroscopy (ARPES)
investigations provided new insight into these questions, revealing that the
carriers of prototypical metal oxides undergo a transition from a polaronic
liquid to a Fermi liquid regime with increasing doping. Here, by performing
\textit{ab initio} many-body calculations of the ARPES spectra of TiO$_2$, we
show that this transition originates from non-adiabatic polar electron-phonon
coupling, and occurs when the frequency of plasma oscillations exceeds that of
longitudinal-optical phonons. This finding suggests that a universal mechanism
may underlie polaron formation in TMOs, and provides a new paradigm for
engineering emergent properties in quantum matter.",1705.02967v1
2018-03-08,Topological Properties and Functionalities in Oxide Thin Films and Interfaces,"As symbolized by the Nobel Prize in Physics 2016, ""topology"" has been
recognized as an essential standpoint to understand and control the physics of
condensed matter. This concept may be spreading even into application areas
such as novel electronics. In this trend, there has been reported a number of
study for the oxide films and heterostructures with topologically non-trivial
electronic or magnetic states. In this review, we overview the trends of new
topological properties and functionalities in oxide materials with sorting out
a number of examples. The technological advances in oxide film growth achieved
over the last few decades are now opening the door for harnessing novel
topological properties.",1803.03050v1
2018-08-17,Universal superconducting precursor in perovskite-based oxides,"A pivotal challenge posed by unconventional superconductors is to unravel how
superconductivity emerges upon cooling from the generally complex normal state.
Some of the most prominent unconventional superconductors are oxides: strontium
titanate, strontium ruthenate, and the cuprates exhibit greatly different
superconducting transition temperatures $T_c$, and although their respective
superconducting pairing mechanisms remain unknown, they are thought to differ
as well. Here we use nonlinear magnetic response, a probe that is uniquely
sensitive to the superconducting precursor, to uncover remarkable universal
behavior in these three distinct classes of superconductors. We find unusual
exponential temperature dependence of the diamagnetic response above the
transition temperature $T_c$, with a characteristic temperature scale that
strongly varies with $T_c$. We correlate this scale with the sensitivity of
$T_c$ to local stress, and show that it is influenced by intentionally-induced
structural disorder. The universal behavior is therefore caused by intrinsic,
self-organized structural inhomogeneity, inherent to the oxides
perovskite-based structure. The prevalence of such inhomogeneity has
far-reaching implications for the interpretation of electronic properties of
perovskite-related oxides in general.",1808.05763v2
2020-09-21,Characterizing oxygen atoms in perovskite and pyrochlore oxides using ADF-STEM at a resolution of a few tens of picometers,"We present an aberration corrected scanning transmission electron microscopy
(ac-STEM) analysis of the perovskite (LaFeO3) and pyrochlore (Yb2Ti2O7 and
Pr2Zr2O7) oxides and demonstrate that both the shape and contrast of visible
atomic columns in annular dark-field (ADF) images are sensitive to the presence
of nearby atoms of low atomic number (e.g. oxygen). We show that point defects
(e.g. oxygen vacancies), which are invisible - or difficult to observe due to
limited sensitivity - in X-ray and neutron diffraction measurements, are the
origin of the complex magnetic ground state of pyrochlore oxides. In addition,
we present, for the first time, a method by which light atoms can be resolved
in quantitative ADF-STEM images. Using this method, we resolved oxygen atoms in
perovskite and pyrochlore oxides.",2009.10037v1
2022-04-25,Ab-initio study of magneto-ionic mechanisms in ferromagnet/oxide multilayers,"The application of gate voltages in heavy metal/ferromagnet/Oxide multilayer
stacks has been identified as one possible candidate to manipulate their
anisotropy at will. However, this method has proven to show a wide variety of
behaviours in terms of reversibility, depending on the nature of the
metal/oxide interface and its degree of oxidation. In order to shed light on
the microscopic mechanism governing the complex magneto-ionic behaviour in
$\text{Ta/CoFeB/}\text{HfO}_2$, we perform ab-initio simulations on various
setups comprising $\text{Fe/O, Fe/HfO}_2$ interfaces with different oxygen atom
interfacial geometries. After the determination of the more stable interfacial
configurations, we calculate the magnetic anisotropy energy on the different
unit cell configurations and formulate a possible mechanism that well describes
the recent experimental observations in $\text{Ta/CoFeB/}\text{HfO}_2$.",2204.11699v1
2023-11-17,Observation of superconductivity and enhanced upper critical field of $η$-carbide-type oxide Zr${_\mathrm{4}}$Pd$_{\mathrm{2}}$O,"We report the first observation of bulk superconductivity of a
${\eta}$-carbide-type oxide Zr$_{4}$Pd$_{2}$O. The crystal structure and the
superconducting properties were studied through synchrotron X-ray diffraction,
magnetization, electrical resistivity, and specific heat measurement. The
superconducting transition was observed at $T_{\mathrm{c}}$ = 2.73 K. Our
measurement revealed that the ${\eta}$-carbide-type oxide superconductor
Zr$_{4}$Pd$_{2}$O shows an enhanced upper critical field
${\mu_{\mathrm{0}}H_{\mathrm{c2}}\mathrm{(0)}}$ = 6.72 T, which violates the
Pauli-Clogston limit ${\mu_{\mathrm{0}}H_{\mathrm{P}}}$ = 5.29 T. On the other
hand, we found that the enhanced upper critical field is absent in a Rh
analogue Zr$_{4}$Rh$_{2}$O. The large
${\mu_{\mathrm{0}}H_{\mathrm{c2}}\mathrm{(0)}}$ of Zr$_{4}$Pd$_{2}$O would be
raised from strong spin-orbit coupling with Pd-4$d$ electrons. The discovery of
new superconducting properties for Zr$_{4}$Pd$_{2}$O would shed light on the
further development of ${\eta}$-carbide-type oxide superconductors.",2311.10338v1
2023-12-09,Large nonlinear Hall effect and Berry curvature in KTaO3 based two-dimensional electron gas,"The two-dimensional electron gas (2DEG) at oxide interfaces exhibits various
exotic properties stemming from interfacial inversion symmetry breaking. In
this work, we report the emergence of large nonlinear Hall effects (NHE) in the
LaAlO3/KTaO3(111) interface 2DEG under zero magnetic field. Skew scattering was
identified as the dominant origin based on the cubic scaling of nonlinear Hall
conductivity with longitudinal conductivity and the threefold symmetry.
Moreover, a gate-tunable NHE with pronounced peak and dip was observed and
reproduced by our theoretical calculation. These results indicate the presence
of Berry curvature hotspots and thus a large Berry curvature triple at the
oxide interface. Our theoretical calculations confirm the existence of large
Berry curvatures from the avoided crossing of multiple 5d-orbit bands, orders
of magnitude larger than that in transition-metal dichalcogenides. NHE offers a
new pathway to probe the Berry curvature at oxide interfaces, and facilitates
new applications in oxide nonlinear electronics.",2312.05578v1
2023-10-19,Coupling of strain and magnetism in manganite-based complex oxide heterostructures,"Complex oxide thin films and heterostructures offer a wide range of
properties originating from the intrinsic coupling between lattice strain and
magnetic/electronic ordering. This article reviews experimental,
phenomenological, and theoretical analyses of the coupling of strain with
electronic and magnetic properties of mixed valence manganite heterostructures.
The influence of epitaxial strain on the magnetic properties of manganite films
is measured using macroscopic magnetization measurements and shown mixed
reports suggesting, both, an increase and decrease in ferromagnetic phases on
the application of the strain. Using polarized neutron reflectivity (PNR), a
simultaneous measurement of transport and magnetic properties of manganite thin
films showed direct evidence of modification in the magnetic properties on the
application of bending strain. The coupling coefficient of strain and magnetism
of manganite heterostructures was estimated using PNR, which not only helped to
understand the correlation of elastic strain with magnetism but also explained
the condition of magnetic phase order change in the phase-separated systems
within a phenomenological Ginzburg Landau theory. An overview is also provided
of the current perspectives and existing studies on the influence of strain on
structure, electronic, magnetic, magnetic anisotropy, phase coexistence and
magnetocaloric properties of mixed valence manganite heterostructures. Based on
the understanding of a diverse range of perovskite functionalities, detailed
perspectives on how the coupling of strain and magnetism open up pathways
toward the emergence of novel device design features including the different
ways of applying uniform strain, are discussed.",2310.12573v1
2010-08-02,First-Principles Prediction of Novel Magnetic Materials Based on ZrCuSiAs-like Semiconducting Pnictide-Oxides,"We assumed that significant enlargement of the functional properties of the
family of quaternary ZrCuSiAs-like pnictide-oxides, often called also as 1111
phases, which are known now first of all as parent phases for new FeAs
superconductors, may be achieved by replacement of nonmagnetic ions by magnetic
ions in semiconducting ZrCuSiAs-like phases. We checked this assumption by
means of first-principles FLAPW-GGA calculations using a wide-band-gap
semiconductor YZnAsO doped with Mn, Fe, and Co as an example. Our main finding
is that substitution of Mn, Fe, and Co for Zn leads to drastic transformations
of electronic and magnetic properties of the parent material: as distinct from
the non-magnetic YZnAsO, the examined doped phases YZn0.89Mn0.11AsO,
YZn0.89Fe0.11AsO, and YZn0.89Co0.11AsO behave as a magnetic semiconductor, a
magnetic half-metal or as a magnetic gapless semi-metal, respectively.",1008.0250v1
2010-08-23,Magnetic field dependent specific heat and enhanced Wilson ratio in strongly correlated layered cobalt oxide,"We have investigated the low temperature specific heat properties as a
function of magnetic field in the strongly correlated layered cobalt oxide
[BiBa$_{0.66}$K$_{0.36}$O$_2$]CoO$_2$. These measurements reveal two kinds of
magnetic field dependent contributions in qualitative agreement with the
presence of a previously inferred magnetic Quantum Critical Point (QCP). First,
the coefficient of the low temperature T$^3$ behavior of the specific heat
turns out to sizeably decrease near a magnetic field consistent with the
critical value reported in a recent paper. In addition, a moderate but
significant enhancement of the Sommerfeld coefficient is found in the vicinity
of the QCP suggesting a slight increase of the electronic effective mass. This
result contrasts with the divergent behavior of the previously reported Pauli
susceptibility. Thus, a strongly enhanced Wilson ratio is deduced, suggesting
efficient ferromagnetic fluctuations in the Fermi liquid regime which could
explain the unusual magnetic field dependent specific heat. As a strong check,
the high magnetic field Wilson ratio asymptotically recovers the universal
limit of the local Fermi liquid against ferromagnetism.",1008.3799v1
2018-11-08,Magnetically-driven orbital-selective insulator-metal transition in double perovskite oxides,"Interaction-driven metal-insulator transitions or Mott transitions
  are widely observed in condensed-matter systems. In multi-orbital
  systems, many-body physics is richer in which an orbital-selective
  metal-insulator transition is an intriguing and unique
  phenomenon. Here we use first-principles calculations to show that a
  magnetic transition (from paramagnetic to long-range magnetically
  ordered) can simultaneously induce an orbital-selective
  insulator-metal transition in rock-salt ordered double perovskite
  oxides $A_2BB'$O$_6$ where $B$ is a non-magnetic ion (Y$^{3+}$ and
  Sc$^{3+}$) and $B'$ a
  magnetic ion with a $d^3$ electronic configuration (Ru$^{5+}$ and
  Os$^{5+}$). The orbital selectivity originates from
  geometrical frustration of a face-centered-cubic lattice on which
  the magnetic ions $B'$ reside. Including realistic structural
  distortions and spin-orbit interaction do
  not affect the transition. The predicted orbital-selective transition
  naturally explains the anomaly observed in the electric resistivity
  of Sr$_2$YRuO$_6$. Implications of other available experimental data
  are also discussed. Our work shows that by exploiting
  geometrical frustration on non-bipartite lattices, novel
  electronic/magnetic/orbital-coupled phase transitions can occur in
  correlated materials that are in the vicinity of metal-insulator phase
  boundary.",1811.03465v1
2017-04-26,Magnetic Force Microscopy Characterization of Superparamagnetic Iron Oxide Nanoparticles (SPIONs),"Superparamagnetic iron oxide nanoparticles (SPIONs), due to their
controllable sizes, relatively long in vivo half-life and limited
agglomeration, are ideal for biomedical applications such as magnetic labeling,
hyperthermia cancer treatment, targeted drug delivery and for magnetic
resonance imaging (MRI) as contrast enhancement agents. In order to understand
how SPIONs interact with cells and cellular membranes it would be of interest
to characterize individual SPIONs at the nanoscale in physiologically relevant
conditions without labeling them. We demonstrate that Magnetic Force Microscopy
(MFM) can be used to image SPIONs in air as well as in liquid. The magnetic
properties of bare and SiO2 coated SPIONs are compared using MFM. We report
that surface modification using (3-mercaptopropyl)-trimethoxysilane
significantly improves adsorption and distribution of SPIONs on gold surfaces.
To obtain proof of principle that SPIONS can be imaged with MFM inside the cell
we imaged SPIONs buried in thin polymer films (polystyrene (PS) and poly
methyl-methacrylate (PMMA)). This opens the possibility of visualizing SPIONs
inside the cell without any labeling or modifications and present MFM as a
potential magnetic analogue for fluorescence microscopy. The results of these
studies may have a valuable impact for characterization and further development
of biomedical applications of SPIONs and other magnetic nanoparticles.",1704.08316v1
2018-10-03,Possible origin of the absence of magnetic order in LiOsO$_3$: Spin-orbit coupling controlled ground state,"LiOsO$_3$ is the first experimentally confirmed polar metal with
ferroelectric-like distortion. One puzzling experimental fact is its
paramagnetic state down to very low temperature with negligible magnetic
moment, which is anomalous considering its $5d^3$ electron configuration since
other osmium oxides (e.g. NaOsO$_3$) with $5d^3$ Os ions are magnetic. Here the
magnetic and electronic properties of LiOsO$_3$ are re-investigated carefully
using the first-principles density functional theory. Our calculations reveal
that the magnetic state of LiOsO$_3$ can be completely suppressed by the
spin-orbit coupling. The subtle balance between significant spin-orbit coupling
and weak Hubbard $U$ of $5d$ electrons can explain both the nonmagnetic
LiOsO$_3$ and magnetic NaOsO$_3$. Our work provides a reasonable understanding
of the long-standing puzzle of magnetism in some osmium oxides.",1810.01639v1
2022-02-07,Chern Number Tunable Quantum Anomalous Hall Effect in Monolayer Transitional Metal Oxides via Manipulating Magnetization Orientation,"Although much effort has been made to explore quantum anomalous Hall effect
(QAHE) in both theory and experiment, the QAHE systems with tunable Chern
numbers are yet limited. Here, we theoretically propose that NiAsO$_3$ and
PdSbO$_3$, monolayer transitional metal oxides, can realize QAHE with tunable
Chern numbers via manipulating their magnetization orientations. When the
magnetization lies in the \textit{x-y} plane and all mirror symmetries are
broken, the low-Chern-number (i.e., $\mathcal{C}=\pm1$) phase emerges. When the
magnetization exhibits non-zero \textit{z}-direction component, the system
enters the high-Chern-number (i.e., $\mathcal{C}=\pm3$) phase, even in the
presence of canted magnetization. The global band gap can approach the
room-temperature energy scale in monolayer PdSbO$_3$ (23.4 meV), when the
magnetization is aligned to \textit{z}-direction. By using Wannier-based
tight-binding model, we establish the phase diagram of magnetization induced
topological phase transition. Our work provides a high-temperature QAHE system
with tunable Chern number for the practical electronic application.",2202.02945v2
2004-06-07,"Electronic self-doping of Mo-states in A2FeMoO6 (A=Ca, Sr and Ba) half-metallic ferromagnets - a Nuclear Magnetic Resonance study","A systematic study of (A,A')2FeMoO6 (A,A'=Ca, Sr, Ba) ferromagnetic oxides
with double perovskite structure has been performed using 95,97Mo and 57Fe NMR
spectroscopy. These oxides are isoelectronic but have substantially different
Curie temperatures. The NMR analysis provides clear evidence that the magnetic
moment at Mo sites is not constant but varies sensitively with the ionic size
of the alkaline ions. The 95,97Mo frequency, and thus the electronic charge at
Mo ions, is found to be smaller in Ba and Ca than in Sr-based oxides. The
charge release from Mo sites is accompanied by an uptake at Fe sites, and thus
a self-doping Fe-Mo process is observed. This process is controlled by relevant
structural parameters: the Fe-O-Mo bond length and bending. A clear
relationship between the Curie temperature and the magnetic moment and thus
electron density at Mo sites has been disclosed. The relevance of these
findings for the understanding of ferromagnetic coupling in double perovskites
is discussed.",0406161v1
2006-02-01,Giant Magnetoresistance in an all-oxide spacerless junction,"We report the fabrication of an oxide-specific type of magnetoresistive
junction, which is a ferromagnetic bilayer. Both electrodes are high
spin-polarization oxides: magnetite (Fe3O4) and manganite (La0.7Sr0.3MnO3).
Negligible magnetic coupling between both ferromagnetic electrodes is realised,
which allows to obtain parallel and antiparallel magnetic configurations of the
electrodes when sweeping the applied magnetic field. The structure exhibits
negative giant magnetoresistance (GMR) at low temperatures. This negative MR
shows that both electrodes stay spin-polarized at the interface and have
opposite spin polarizations, i.e. the Fe3O4 layer has a negative spin
polarization at low temperature. Maximum GMR (-5%) is obtained at 55K.",0602017v2
2007-01-29,Parameters of the Dzyaloshinsky-Moriya type weak ferromagnetism for some perovskite compounds,"Compounds with distorted perovskite structure of the 4-f and 3-d transition
metals with the common formula LnTO3 (where Ln is rare-earth element, T is an
element from the Fe group) are the most multifold binary oxides of these two
groups elements. Wide range of stability for this structure allows the
realization of combinations of the Lanthanides with all the transition metals
except the Nickel. Quite interesting physical phenomena take place in these
oxides like charge and orbital ordering; relatively independent magnetic
lattices of the both metals; particular magnetic structures; high optical
indicators; giant magneto-resistance; peculiar dielectric and ferroelectric
properties etc. We have investigated the magnetic properties of pure ferrites
and chromium-based materials as well as of some mixed type oxides like
HoxTb1-xO3, HoMnxFe1-xO3, HoMnxCr1-xO3 and DyFexCr1-xO3.",0701708v1
2008-10-02,Structural phase stability and Magnetism in Co2FeO4 spinel oxide,"We report a correlation between structural phase stability and magnetic
properties of Co2FeO4 spinel oxide. We employed mechanical alloying and
subsequent annealing to obtain the desired samples. The particle size of the
samples changes from 25 nm to 45 nm. The structural phase separation of
samples, except sample annealed at 9000C, into Co rich and Fe rich spinel phase
has been examined from XRD spectrum, SEM picture, along with EDAX spectrum, and
magnetic measurements. The present study indicated the ferrimagnetic character
of Co2FeO4, irrespective of structural phase stability. The observation of
mixed ferrimagnetic phases, associated with two Curie temperatures at TC1 and
TC2 (>TC1), respectively, provides the additional support of the splitting of
single cubic spinel phase in Co2FeO4 spinel oxide.",0810.0449v1
2009-05-26,Compensated magnetism by design in double perovskite oxides,"Taking into account Goodenough's superexchange rules, including both full
structural relaxation and spin-orbit coupling, and checking strong correlation
effects, we look for compensated half metals within the class of oxide double
perovskites materials. Identifying likely half metallic (or half semimetallic)
antiferromagnets, the full complications including orbital magnetism are
included in order to arrive at realistic predictions of designed magnetic
compounds with (near) vanishing net moment. After sorting through several
candidates that have not been considered previously, two materials,
K$_2$MnRhO$_6$ and La$_2$CrWO$_6$, remain as viable candidates. An important
factor is obtaining compounds either with very small induced orbital moment
(helped by closed subshells) or with an orbital moment that compensates the
spin-orbit driven degradation of half metallic character. While thermodynamic
stability of these materials cannot be ensured, the development of
layer-by-layer oxide deposition techniques does not require that materials be
thermodynamically stable to be synthesized.",0905.4199v1
2009-06-18,Magnetic Pyrochlore Oxides,"Within the past 20 years or so, there has occurred an explosion of interest
in the magnetic behavior of pyrochlore oxides of the type
$A_{2}^{3+}$$B_{2}^{4+}$O$_{7}$ where $A$ is a rare-earth ion and $B$ is
usually a transition metal. Both the $A$ and $B$ sites form a network of
corner-sharing tetrahedra which is the quintessential framework for a
geometrically frustrated magnet. In these systems the natural tendency to form
long range ordered ground states in accord with the Third Law is frustrated,
resulting in some novel short range ordered alternatives such as spin glasses,
spin ices and spin liquids and much new physics. This article attempts to
review the myriad of properties found in pyrochlore oxides, mainly from a
materials perspective, but with an appropriate theoretical context.",0906.3661v1
2010-10-05,Large bias-dependent magnetoresistance in all-oxide magnetic tunnel junctions with a ferroelectric barrier,"All-oxide magnetic tunnel junctions (MTJs) incorporating functional materials
as insulating barriers have the potential of becoming the founding technology
for novel multi-functional devices. We investigate, by first-principles density
functional theory, the bias-dependent transport properties of an all-oxide
SrRuO3/BaTiO3/SrRuO3 MTJ. This incorporates a BaTiO3 barrier which can be found
either in a non-ferroic or in a ferroelectric state. In such an MTJ not only
can the tunneling magnetoresistance reach enormous values, but also, for
certain voltages, its sign can be changed by altering the barrier electric
state. These findings pave the way for a new generation of
electrically-controlled magnetic sensors.",1010.0902v1
2011-04-22,Electronic structure and bonding properties of cobalt oxide in the spinel structure,"The spinel cobalt oxide Co3O4 is a magnetic semiconductor containing cobalt
ions in Co2+ and Co3+ oxidation states. We have studied the electronic,
magnetic and bonding properties of Co3O4 using density functional theory (DFT)
at the Generalized Gradient Approximation (GGA), GGA+U, and PBE0 hybrid
functional levels. The GGA correctly predicts Co3O4 to be a semiconductor, but
severely underestimates the band gap. The GGA+U band gap (1.96 eV) agrees well
with the available experimental value (~ 1.6 eV), whereas the band gap obtained
using the PBE0 hybrid functional (3.42 eV) is strongly overestimated. All the
employed exchange-correlation functionals predict 3 unpaired d electrons on the
Co2+ ions, in agreement with crystal field theory, but the values of the
magnetic moments given by GGA+U and PBE0 are in closer agreement with the
experiment than the GGA value, indicating a better description of the cobalt
localized d states. Bonding properties are studied by means of Maximally
Localized Wannier Functions (MLWFs). We find d-type MLWFs on the cobalt ions,
as well as Wannier functions with the character of sp3d bonds between cobalt
and oxygen ions. Such hybridized bonding states indicate the presence of a
small covalent component in the primarily ionic bonding mechanism of this
compound.",1104.4383v1
2011-05-06,The interplay between dopants and oxygen vacancies in the magnetism of V-doped TiO2,"Density functional theory calculations indicate that the incorporation of V
into Ti lattice positions of rutile TiO2 leads to magnetic V4+ species, but the
extension and sign of the coupling between dopant moments confirm that
ferromagnetic order cannot be reached via low-concentration doping in the
non-defective oxide. Oxygen vacancies can introduce additional magnetic
centres, and we show here that one of the effects of vanadium doping is to
reduce the formation energies of these defects. In the presence of both V
dopants and O vacancies all the spins tend to align with the same orientation.
We conclude that V doping favours the ferromagnetic behaviour of TiO2 not only
by introducing spins associated with the dopant centres but also by increasing
the concentration of oxygen vacancies with respect to the pure oxide.",1105.1289v1
2013-02-22,Gigantic magnetic field polarization and magnetoelectric coupling in a ferrimagnetic oxide CaBaCo4O7,"The single crystal study of CaBaCo4O7, a non collinear ferrimagnet (TC=64K),
with a polar orthorhombic space group (Pbn21) between 4 K and 293 K, shows the
appearance below TC of a large electric polarization along its c axis, reaching
17mC.m-2 at 10K. At 62.5K, a magnetic field driven giant variation of
polarization, P(9T)-P(0T)=8mC.m-2, is observed. Moreover, the present
magnetoelectric measurements, are fully consistent with the m'm2' magnetic
point group, strongly supporting that this oxide is also ferrotoroidic. This
ferrimagnetic oxide, which belongs to the '114' structural family, opens an
avenue for the search of new magnetoelectrics.",1302.5541v2
2014-11-24,Plasma cleaning of ITER first mirrors in magnetic field,"To avoid reflectivity losses in ITER optical diagnostic systems, plasma
sputtering of metallic First Mirrors is foreseen in order to remove deposits
coming from the main wall (mainly beryllium and tungsten). Therefore plasma
cleaning has to work on large mirrors (up to a size of 200*300 mm) and under
the influence of strong magnetic fields (several Tesla). This work presents the
results of plasma cleaning of aluminium and aluminium oxide (used as beryllium
proxy) deposited on molybdenum mirrors. Using radio frequency (13.56 MHz) argon
plasma, the removal of a 260 nm mixed aluminium/aluminium oxide film deposited
by magnetron sputtering on a mirror (98 mm diameter) was demonstrated. 50 nm of
pure aluminium oxide were removed from test mirrors (25 mm diameter) in a
magnetic field of 0.35 T for various angles between the field lines and the
mirrors surfaces. The cleaning efficiency was evaluated by performing
reflectivity measurements, Scanning Electron Microscopy and X-ray Photoelectron
Spectroscopy.",1411.6659v1
2015-01-22,Coexistence and interconvertibility of ferromagnetic and antiferromagnetic phases in the single crystal of Mn$_3$ single-molecule magnet,"We report the coexistence of ferromagnetic and antiferromagnetic phases in
the single crystal of Mn$_3$ single-molecule magnet. The coexistent state
appears within a certain period of time in the progress of either oxidation or
reduction during a reversible oxidation-reduction process, when the sample is
exposed in the air (oxygen) or the methyl vapor. We noticed an apparent change
in the molecular structure, which is also reversible in terms of that the
methyl group is dropped or added to the molecules during the oxidation or
reduction. The absence or presence of the methyl group in the molecules exert
an essential impact upon the intermolecular exchange interaction, and the
ferromagnetic phase comes from the heterogenous intermolecular bonds between
pairs of molecules of which one molecule has a methyl group whereas the other
has lost the methyl group. The reversible change in molecular structure
suggests the magnetic structure of Mn$_3$ might be designed and modulated at
molecular scale, which implies Mn$_3$ has a great application potential.",1501.05484v1
2016-10-21,Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance,"Thin films of perovskite oxides offer the possibility of combining emerging
concepts of strongly correlated electron phenomena and spin current in magnetic
devices. However, spin transport and magnetization dynamics in these complex
oxide materials are not well understood. Here, we experimentally quantify spin
transport parameters and magnetization damping in epitaxial perovskite
ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
thickness dependence of Gilbert damping, we estimate a short spin diffusion
length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
that anisotropic non-Gilbert damping due to two-magnon scattering also
increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
spin-source/spin-sink system that may be a foundation for examining
spin-current transport in various perovskite heterostructures.",1610.06661v1
2017-03-22,Coexistence of Interfacial Stress and Charge Transfer in Graphene Oxide based Magnetic Nanocomposites,"In this paper, we establish the existence of both compressive stress and
charge transfer process in hydrothermally synthesized cobalt ferrite-graphene
oxide (CoFe2O4/GO) nanocomposites. Transmission electron microscopy (TEM)
results reveal the decoration of CoFe2O4 nanoparticles on GO sheets. Magnetic
response of nanocomposites was confirme from superconducting quantum
interference device (SQUID) magnetometer measurement. Optical properties of
these nanocomposites were investigated by Raman spectroscopy. Interfacial
compressive stress involved in this system is evaluated from observed blue
shift of characteristic G peak of graphene oxide. Increase in full width
half-maximum ( FWHM) as well as up shift in D and G peaks are clear indicator
of involvement of charge transfer process between GO sheets and dispersed
magnetic nanoparticles. The effect of charge transfer process is quantified in
terms of shifting of Fermi level of these nanocomposites. This is evaluated
from variation in contact surface potential difference (CPD) using Scanning
Kelvin probe microscopy (SKPM). XRD spectra of CoFe2O4/GO confirm the
polycrystalline nature of CoFe2O4 nanoparticles. Lattice strain estimated from
XRD peaks are correlated to the observed Raman shift.",1703.07545v1
2009-12-07,High temperature ferromagnetism of Li-doped vanadium oxide nanotubes,"The nature of a puzzling high temperature ferromagnetism of doped
mixed-valent vanadium oxide nanotubes reported earlier by Krusin-Elbaum et al.,
Nature 431 (2004) 672, has been addressed by static magnetization, muon spin
relaxation, nuclear magnetic and electron spin resonance spectroscopy
techniques. A precise control of the charge doping was achieved by
electrochemical Li intercalation. We find that it provides excess electrons,
thereby increasing the number of interacting magnetic vanadium sites, and, at a
certain doping level, yields a ferromagnetic-like response persisting up to
room temperature. Thus we confirm the surprising previous results on the
samples prepared by a completely different intercalation method. Moreover our
spectroscopic data provide first ample evidence for the bulk nature of the
effect. In particular, they enable a conclusion that the Li nucleates
superparamagnetic nanosize spin clusters around the intercalation site which
are responsible for the unusual high temperature ferromagnetism of vanadium
oxide nanotubes.",0912.1237v1
2017-05-08,"Re-entrant spin-glass freezing and magneto-dielectric behavior of Li3NiRuO6, a layered rock-salt related oxide","We report the results of neutron diffraction, ac and dc magnetization,
heat-capacity, complex permittivity, and pyrocurrent measurements on an oxide,
Li3NiRuO5, hitherto not paid much attention in the literature, except for a
previous report on its promising electrochemical performance. We emphasize on
the following findings: (i) Observation of re-entrant spin-glass behavior; that
is, this oxide undergoes ferrilmagnetic ordering below 8- K, entering
spin-glass regime around 12 K. (ii) There is no prominent feature in the
complex dielectric permittivity (in particular, at the magnetic transitions) in
the absence of external magnetic field, indicative of the absence of
ferroelectricity. However, there is a distinct evidence for magneto-dielectric
(MDE) coupling. The sign of MDE coupling also changes as the sample is cooled
from ferrimagnetic state to spin-glass regime. (iii) There are pyroelectric
anomalies in the vicinity of 30-70 K, presumably from thermally stimulated
depolarization current.",1705.02868v1
2022-05-12,Electron paramagnetic resonance of alkali metal atoms and dimers on ultrathin MgO,"Electron paramagnetic resonance (EPR) can provide unique insight into the
chemical structure and magnetic properties of dopants in oxide and
semiconducting materials that are of interest for applications in electronics,
catalysis, and quantum sensing. Here, we demonstrate that EPR in combination
with scanning tunneling microscopy (STM) allows for probing the bonding and
charge state of alkali metal atoms on an ultrathin magnesium oxide layer on a
Ag substrate. We observe a magnetic moment of $1\mu_\mathrm{B}$ for Li$_2$,
LiNa, and Na$_2$ dimers corresponding to spin radicals with a charge state of
$+1e$. Single alkali atoms have the same charge state and no magnetic moment.
The ionization of the adsorbates is attributed to charge transfer through the
oxide to the metal substrate. Our work highlights the potential of EPR-STM to
provide insight into dopant atoms that are relevant for the control of the
electrical properties of surfaces and nanodevices.",2205.05998v1
2023-05-16,Unconventional anomalous Hall effect in epitaxially stabilized orthorhombic Ru$^{3+}$ perovskite thin films,"Complex oxides are mesmerizing material systems to realize multiple physical
properties and functionalities by integrating different elements in a single
compound. However, owing to the chemical instability, not all the combinations
of elements can be materialized despite the intriguing potential expected from
their magnetic and electronic properties. In this study, we demonstrate an
epitaxial stabilization of orthorhombic Ru$^{3+}$ perovskite oxides: LaRuO$_3$
and NdRuO$_3$, and their magnetotransport properties that reflect the
difference between non-magnetic La$^{3+}$ and magnetic Nd$^{3+}$. Above all, an
unconventional anomalous Hall effect accompanied by an inflection point in
magnetoresistance is observed around 1.3 T below 1 K for NdRuO$_3$, which is
ascribed to topological Hall effect possibly due to a non-coplanar spin texture
on Nd$^{3+}$ sublattice. These studies not only serve a new testbed for the
interplay between spin-orbit coupling and Coulomb interaction but also open a
new avenue to explore topological emergent phenomena in well-studied perovskite
oxides.",2305.09201v1
2023-06-02,Copper-based charge transfer multiferroics with a $d^9$ configuration,"Multiferroics are materials with a coexistence of magnetic and ferroelectric
order allowing the manipulation of magnetism by applications of an electric
field through magnetoelectric coupling effects. Here we propose an idea to
design a class of multiferroics with a $d^9$ configuration using the magnetic
order in copper-oxygen layers appearing in copper oxide high-temperature
superconductors by inducing ferroelectricity. Copper-based charge transfer
multiferroics SnCuO2 and PbCuO2 having the inversion symmetry breaking $P4mm$
polar space group are predicted to be such materials. The active inner s
electrons in Sn and Pb hybridize with O $2p$ states leading the buckling in
copper-oxygen layers and thus induces ferroelectricity, which is known as the
lone pair mechanism. As a result of the $d^9$ configuration, SnCuO2 and PbCuO2
are charge transfer insulators with the antiferromagnetic ground state of the
moment on Cu retaining some strongly correlated physical properties of parent
compounds of copper oxide high-temperature superconductors. Our work reveals
the possibility of designing multiferroics based on copper oxide
high-temperature superconductors.",2306.01361v1
2023-07-23,Ru doping induced spin frustration and enhancement of the room-temperature anomalous Hall effect in La2/3Sr1/3MnO3 films,"In transition-metal-oxide heterostructures, the anomalous Hall effect (AHE)
is a powerful tool for detecting the magnetic state and revealing intriguing
interfacial magnetic orderings. However, achieving a larger AHE at room
temperature in oxide heterostructures is still challenging due to the dilemma
of mutually strong spin-orbit coupling and magnetic exchange interactions.
Here, we exploit the Ru doping-enhanced AHE in LSMRO epitaxial films. As the
B-site Ru doping level increases up to 20 percent, the anomalous Hall
resistivity at room temperature can be enhanced from nOhmcm to uOhmcm scale. Ru
doping leads to strong competition between ferromagnetic double-exchange
interaction and antiferromagnetic super-exchange interaction. The resultant
spin frustration and spin-glass state facilitate a strong skew-scattering
process, thus significantly enhancing the extrinsic AHE. Our findings could
pave a feasible approach for boosting the controllability and reliability of
oxide-based spintronic devices.",2307.12253v1
2010-03-29,Ferromagnetism in defect-ridden oxides and related materials,"The existence of high-temperature ferromagnetism in thin films and
nanoparticles of oxides containing small quantities of magnetic dopants remains
controversial. Some regard these materials as dilute magnetic semiconductors,
while others think they are ferromagnetic only because the magnetic dopants
form secondary ferromagnetic impurity phases such as cobalt metal or magnetite.
There are also reports in d0 systems and other defective oxides that contain no
magnetic ions. Here, we investigate TiO2 (rutile) containing 1 - 5% of iron
cations and find that the room-temperature ferromagnetism of films prepared by
pulsed-laser deposition is not due to magnetic ordering of the iron. The films
are neither dilute magnetic semiconductors nor hosts to an iron-based
ferromagnetic impurity phase. A new model is developed for defect-related
ferromagnetism which involves a spin-split defect band populated by charge
transfer from a proximate charge reservoir in the present case a mixture Fe2+
and Fe3+ ions in the oxide lattice. The phase diagram for the model shows how
inhomogeneous Stoner ferromagnetism depends on the total number of electrons
Ntot, the Stoner exchange integral I and the defect bandwidth W; the band
occupancy is governed by the d-d Coulomb interaction U. There are regions of
ferromagnetic metal, half-metal and insulator as well as nonmagnetic metal and
insulator. A characteristic feature of the high-temperature Stoner magnetism is
an an anhysteretic magnetization curve which is practically temperature
independent below room temperature. This is related to a wandering
ferromagnetic axis which is determined by local dipole fields. The
magnetization is limited by the defect concentration, not by the 3d doping.
Only 1-2 % of the volume of the films is magnetically ordered.",1003.5558v1
2018-05-25,Room Temperature Magnetic Order in Air-Stable Ultra-Thin Iron Oxide,"Certain two-dimensional (2D) materials exhibit intriguing properties such as
valley polarization, ferroelectricity, superconductivity and charge-density
waves. Many of these materials can be manually assembled into atomic-scale
multilayer devices under ambient conditions, owing to their exceptional
chemical stability. Efforts have been made to add a magnetic degree of freedom
to these 2D materials via defects, but only local magnetism has been achieved.
Only with the recent discoveries of 2D materials supporting intrinsic
ferromagnetism have stacked spintronic devices become realistic. Assembling 2D
multilayer devices with these ferromagnets under ambient conditions remains
challenging due to their sensitivity to environmental degradation, and magnetic
order at room temperature is rare in van der Waals materials. Here, we report
the growth of air-stable ultra-thin epsilon-phase iron oxide crystals that
exhibit magnetic order at room temperature. These crystals require no
passivation and can be prepared in large quantity by cost-effective chemical
vapor deposition (CVD). We find that the epsilon phase, which is energetically
unfavorable and does not form in bulk, can be easily made in 2D down to a seven
unit-cell thickness. Magneto-optical Kerr effect (MOKE) magnetometry of
individual crystals shows that even at this ultrathin limit the epsilon phase
exhibits robust magnetism with coercive fields of hundreds of mT. These
measurements highlight the advantages of ultrathin iron oxide as a promising
candidate towards air-stable 2D magnetism and integration into 2D spintronic
devices.",1805.10372v1
2024-02-06,Ultrafast terahertz field control of the emergent magnetic and electronic interactions at oxide interfaces,"Ultrafast electric-field control of emergent electronic and magnetic states
at oxide interfaces offers exciting prospects for the development of new
generations of energy-efficient devices. Here, we demonstrate that the
electronic structure and emergent ferromagnetic interfacial state in epitaxial
LaNiO3/CaMnO3 superlattices can be effectively controlled using intense
single-cycle THz electric-field pulses. We employ a combination of
polarization-dependent X-ray absorption spectroscopy with magnetic circular
dichroism and X-ray resonant magnetic reflectivity to measure a detailed
magneto-optical profile and thickness of the ferromagnetic interfacial layer.
Then, we use time-resolved and temperature-dependent magneto-optical Kerr
effect, along with transient optical reflectivity and transmissivity
measurements, to disentangle multiple correlated electronic and magnetic
processes driven by ultrafast high-field (~1 MV/cm) THz pulses. These processes
include an initial sub-picosecond electronic response, consistent with
non-equilibrium Joule heating; a rapid (~270 fs) demagnetization of the
ferromagnetic interfacial layer, driven by THz-field-induced nonequilibrium
spin-polarized currents; and subsequent multi-picosecond dynamics, possibly
indicative of a change in the magnetic state of the superlattice due to the
transfer of spin angular momentum to the lattice. Our findings shed light on
the intricate interplay of electronic and magnetic phenomena in this strongly
correlated material system, suggesting a promising avenue for efficient control
of two-dimensional ferromagnetic states at oxide interfaces using ultrafast
electric-field pulses.",2402.04302v1
2004-08-18,Half-magnetization plateau stabilized by structural distortion in the antiferromagnetic Heisenberg model on a pyrochlore lattice,"Magnetization plateaus, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. We show how
an extremely robust half-magnetization plateau can arise from coupling between
spin and lattice degrees of freedom in a pyrochlore antiferromagnet, and
develop a detailed symmetry of analysis of the simplest possible scenario for
such a plateau state. The application of this theory to the spinel oxides
CdCr2O4 and HgCr2O4, where a robust half magnetization plateau has been
observed, is discussed.",0408397v1
2006-09-19,Half-magnetization plateaux in Cr spinels,"Magnetization plateaux, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. An
extremely robust half-magnetization plateau is observed in the spinel oxides
CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice
distortion. We give an overview of the present state experiment for CdCr2O4 and
HgCr2O4, and show how such a half-magnetization plateau arises quite naturally
in a simple model of these systems, once coupling to the lattice is taken into
account.",0609470v1
2012-12-01,Ab initio calculation of the local magnetic moment in titanium doped zinc oxide with a corrected-band-gap scheme,"The local magnetic moment of Ti:ZnO is calculated from first principles by
using the corrected-band-gap scheme (CBGS). The results shows that the system
is magnetic with the magnetization of 0.699 $\mu_B$ per dopant. The origin of
the local magnetic moment is considered to be the impurity band partially
occupied by the donor electrons in the conduction band. Further, the impacts of
applying Hubbard U to Ti-d orbital on the magnetic moment have been
investigated.",1212.0066v1
2006-09-20,Elastic and magnetic properties on field-induced Metal-Insulator transition of bilayer manganese oxide $(La_{1-z} Pr_z)_{1.2} Sr_{1.8} Mn_2 O_7$ ($z$=0.6),"The elastic and magnetic properties of a single crystal of 327 bilayer
manganese oxide $(La_{1-z} Pr_z)_{1.2} Sr_{1.8} Mn_2 O_7$ with $z$=0.6 have
been investigated by ultrasonic and high-field magnetization measurements. A
distinct elastic anomaly was observed at low temperatures and in high magnetic
fields when crossing the phase boundary. A pronounced elastic softening as a
function of magnetic field ($H$) appears across the boundary of the
low-temperature magnetic phase below around 40 K, accompanied by a distinct
hysteresis. In the high field region, however, these elastic constants exhibit
an increase with increasing a magnetic field in the high-field region. The
high-field magnetization measurement characterizing the magnetic state
clarified a strong connection between elastic strains and magnetic moments. The
new metamagnetic transition was found in the high-field region above 40 K,
accompanied with no hysteresis. The present results of elastic constants are
discussed in terms of a coupling effect between elastic strains associated with
sound waves and relevant magnetic moments, and relevant conduction bands. They
are explained reasonably in terms of a strong coupling between elastic strains
and magnetic susceptibility $chi$$_{m}$=$partial$$M$/$partial$$H$.",0609498v1
2022-11-28,Entropy engineering and tunable magnetic order in the spinel high entropy oxide,"Spinel oxides are an ideal setting to explore the interplay between
configurational entropy, site selectivity, and magnetism in high entropy
oxides. In this work we characterize the magnetic properties of the spinel
(Cr,Mn,Fe,Co,Ni)$_3$O$_4$ and study the evolution of its magnetism as a
function of non-magnetic gallium substitution. Across the range of compositions
studied here, from 0% to 40% Ga, magnetic susceptibility and powder neutron
diffraction measurements show that ferrimagnetic order is robust in the spinel
HEO. However, we also find that the ferrimagnetic order is highly tunable, with
the ordering temperature, saturated and sublattice moments, and magnetic
hardness all varying significantly as a function of Ga concentration. Through
x-ray absorption and magnetic circular dichroism, we are able to correlate this
magnetic tunability with strong site selectivity between the various cations
and the tetrahedral and octahedral sites in the spinel structure. In
particular, we find that while Ni and Cr are largely unaffected by the
substitution with Ga, the occupancies of Mn, Co, and Fe are each significantly
redistributed. Ga substitution also requires an overall reduction in the
transition metal valence, and this is entirely accommodated by Mn. Finally, we
show that while site selectivity has an overall suppressing effect on the
configurational entropy, over a certain range of compositions, Ga substitution
yields a striking increase in the configurational entropy and may confer
additional stabilization. Spinel oxides can be tuned seamlessly from the
low-entropy to the high-entropy regime, making this an ideal platform for
entropy engineering.",2211.15798v1
2012-10-05,Rapid Microwave-Assisted Synthesis of Dextran-Coated Iron Oxide Nanoparticles for Magnetic Resonance Imaging,"Currently, magnetic iron oxide nanoparticles are the only nano-sized magnetic
resonance imaging (MRI) contrast agents approved for clinical use, yet
commercial manufacturing of these agents has been limited or discontinued.
Though there is still widespread demand for these particles both for clinical
use and research, they are difficult to obtain commercially, and complicated
syntheses make in-house preparation infeasible for most biological research
labs or clinics. To make commercial production viable and increase
accessibility of these products, it is crucial to develop simple, rapid, and
reproducible preparations of biocompatible iron oxide nanoparticles. Here, we
report a rapid, straightforward microwave-assisted synthesis of
superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles
were produced in two hydrodynamic sizes with differing core morphologies by
varying the synthetic method as either a two-step or single step process. A
striking benefit of these methods is the ability to obtain swift and consistent
results without the necessity for air, pH, or temperature sensitive techniques;
therefore, reaction times and complex manufacturing processes are greatly
reduced as compared to conventional synthetic methods. This is a great benefit
for cost-effective translation to commercial production. The nanoparticles are
found to be superparamagnetic and exhibit properties consistent for use in MRI.
In addition, the dextran coating imparts the water-solubility and
biocompatibility necessary for in vivo utilization.",1210.1827v1
2014-11-19,Internally Oxidized Nb3Sn Strands with Fine Grain Size and High Critical Current Density,"Nb3Sn superconducting strands are the most practical conductors to generate
high magnetic fields (12-16 T), and thus have significant applications in
nuclear magnetic resonance (NMR), and great potential for fusion reactors and
particle accelerator magnets. High critical current density (Jc) is a key
parameter for such applications. Significant efforts towards optimization of
various factors led to an 80% improvement in Jc from the early 1990s to 2003,
when the 4.2 K, 12 T non-matrix Jc reached 3000 A/mm2 (corresponding to 5000
A/mm2 in Nb3Sn layer Jc). However, further efforts over the past decade have
failed to bring about further increase beyond this level, leading some
researchers to conclude that the Jc of conventional Nb3Sn strands had reached
its maximum. Here, however, by applying an internal oxidation method, we reduce
the grain size by a factor of three and nearly double the 12 T Jc. In this
method, a Nb3Sn strand is fabricated with Nb-Zr alloy as starting material;
with oxygen supplied properly via an oxide powder, the Zr atoms in the Nb-Zr
alloy are internally oxidized, forming fine intra-granular and inter-granular
ZrO2 particles in Nb3Sn layer, which effectively refine Nb3Sn grain size. At a
reaction temperature of 625 {\deg}C, grain size down to 20-50 nm (36 nm on
average) has been achieved. For this sample the 4.2 K, 12 T Nb3Sn layer Jc
reached 9600 A/mm2.",1411.5397v1
2017-02-22,Interfacial Multiferroics of TiO2/PbTiO3 Heterostructure Driven by Ferroelectric Polarization Discontinuity,"Novel phenomena appear when two different oxide materials are combined
together to form an interface. For example, at the interface of LaAlO3/SrTiO3,
two dimensional conductive states form to avoid the polar discontinuity and
magnetic properties are found at such interface. In this work, we propose a new
type of interface between two nonmagnetic and nonpolar oxides that could host a
conductive state with magnetic properties, where it is the ferroelectric
polarization discontinuity instead of the polar discontinuity that leads to the
charge transfer, forming the interfacial conductive or magnetic states. As a
concrete example, we investigate by first-principles calculations the
heterostructures made of ferroelectric perovskite oxide PbTiO3 and
non-ferroelectric polarized oxides TiO2. We show that charge is transferred to
the interfacial layer forming an interfacial conductive state with
ferromagnetic ordering that may persist up to room temperature. Especially, the
strong coupling between bulk ferroelectric polarization and interface
ferromagnetism represents a new type of magnetoelectric effect, which provides
an ideal platform for exploring the intriguing interfacial multiferroics. The
findings here are important not only for fundamental science but also for
promising applications in nanoscale electronics and spintronics.",1702.06656v1
2017-04-28,Ferromagnetism and spin-dependent transport at a complex oxide interface,"Complex oxide interfaces are a promising platform for studying a wide array
of correlated electron phenomena in low-dimensions, including magnetism and
superconductivity. The microscopic origin of these phenomena in complex oxide
interfaces remains an open question. Here we investigate for the first time the
magnetic properties of semi-insulating NdTiO$_3$/SrTiO$_3$ (NTO/STO) interfaces
and present the first milli-Kelvin study of NTO/STO. The magnetoresistance (MR)
reveals signatures of local ferromagnetic order and of spin-dependent
thermally-activated transport, which are described quantitatively by a simple
phenomenological model. We discuss possible origins of the interfacial
ferromagnetism. In addition, the MR also shows transient hysteretic features on
a timescale of ~10-100 seconds. We demonstrate that these are consistent with
an extrinsic magneto-thermal origin, which may have been misinterpreted in
previous reports of magnetism in STO-based oxide interfaces. The existence of
these two MR regimes (steady-state and transient) highlights the importance of
time-dependent measurements for distinguishing signatures of ferromagnetism
from other effects that can produce hysteresis at low temperatures.",1704.08828v3
2017-11-07,Mixing of $t_{2g}$-$e_g$ orbitals in 4d and 5d transition metal oxides,"Using exact diagonalization, we study the spin-orbit coupling and
interaction-induced mixing between $t_{2g}$ and $e_g$ $d$-orbital states in a
cubic crystalline environment, as commonly occurs in transition metal oxides.
We make a direct comparison with the widely used $t_{2g}$ only or $e_g$ only
model, depending on electronic filling. We consider all electron fillings of
the $d$-shell and compute the total magnetic moment, the spin, the occupancy of
each orbital, and the effective spin-orbit coupling strength (renormalized
through interaction effects) in terms of the bare interaction parameters,
spin-orbit coupling, and crystal field splitting, focusing on the parameter
ranges relevant to 4d and 5d transition metal oxides. In various limits we
provide perturbative results consistent with our numerical calculations. We
find that the $t_{2g}$-$e_g$ mixing can be large, with up to 20\% occupation of
orbitals that are nominally ""empty"", which has experimental implications for
the interpretation of the branching ratio in experiments, and can impact the
effective local moment Hamiltonian used to study magnetic phases and magnetic
excitations in transition metal oxides. Our results can aid the theoretical
interpretation of experiments on these materials, which often fall in a regime
of intermediate coupling with respect to electron-electron interactions.",1711.02328v2
2019-01-08,High entropy oxides: An emerging prospect for magnetic rare earth - transition metal perovskites,"It has been shown that oxide ceramics containing multiple transition and/or
rare-earth elements in equimolar ratios have a strong tendency to crystallize
in simple single phase structures, stabilized by the high configurational
entropy. In analogy to the metallic alloy systems, these oxides are denoted
high entropy oxides (HEOs). The HEO concept allows to access hitherto uncharted
areas in the multi-element phase diagram. Among the already realized structures
there is the highly complex class of rare earth - transition element
perovskites. This fascinating class of materials generated by applying the
innovative concept of high entropy stabilization provides a new and manyfold
research space with promise of discoveries of unprecedented properties and
phenomena. The present study provides a first investigation of the magnetic
properties of selected compounds of this novel class of materials.
Comprehensive studies by DC and AC magnetometry are combined with element
specific spectroscopy in order to understand the interplay between magnetic
exchange and the high degree of chemical disorder in the systems. We observe a
predominant antiferromagnetic behavior in the single phase materials, combined
with a small ferromagnetic contribution possibly stemming from small
ferromagnetic clusters or configurations in the antiferromagnetic matrix. In
the long term perspective it is proposed to screen the properties of this
family of compounds with high throughput methods, including combined
experimental and theoretical approaches.",1901.02395v2
2019-04-06,Solution Processed Large-scale Multiferroic Complex Oxide Epitaxy with Magnetically Switched Polarization,"Complex oxides with tunable structures have many fascinating properties,
though high-quality complex oxide epitaxy with precisely controlled composition
is still out of reach. Here we have successfully developed solution-based
single crystalline epitaxy for multiferroic
(1-x)BiTi(1-y)/2FeyMg(1-y)/2O3-(x)CaTiO3 (BTFM-CTO) solid solution in large
area, confirming its ferroelectricity at atomic-scale with a spontaneous
polarization of 79~89uC/cm2. Careful compositional tuning leads to a bulk
magnetization of ~0.07uB/Fe at room temperature, enabling magnetically induced
polarization switching exhibiting a large magnetoelectric coefficient of
2.7-3.0X10-7s/m. This work demonstrates the great potential of solution
processing in large-scale complex oxide epitaxy and establishes novel
room-temperature magnetoelectric coupling in epitaxial BTFM-CTO film, making it
possible to explore a much wider space of composition, phase, and structure
that can be easily scaled up for industrial applications.",1904.03370v1
2022-03-02,Emergence of insulating ferrimagnetism and perpendicular magnetic anisotropy in 3d-5d perovskite oxide composite films for insulator spintronic,"Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play
a key role in exploring pure spin current phenomena and developing
ultralow-dissipation spintronic devices, thereby it is highly desirable to
develop new material platforms. Here we report epitaxial growth of
La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different
crystalline orientations fabricated by sequential two-target ablation process
using pulsed laser deposition. The LSMIO films exhibit high crystalline quality
with homogeneous mixture of LSMO and SIO at atomic level. Ferrimagnetic and
insulating transport characteristics are observed, with the
temperature-dependent electric resistivity well fitted by Mott
variable-range-hopping model. Moreover, the LSMIO films show strong PMA.
Through further constructing all perovskite oxide heterostructures of the
ferrimagnetic insulator LSMIO and a strong spin-orbital coupled SIO layer,
pronounced spin Hall magnetoresistance (SMR) and spin Hall-like anomalous Hall
effect (SH-AHE) were observed. These results illustrate the potential
application of the ferrimagnetic insulator LSMIO in developing all-oxide
ultralow-dissipation spintronic devices.",2203.00818v1
2022-06-07,Non-volatile electric control of spin-orbit torques in an oxide two-dimensional electron gas,"Spin-orbit torques (SOTs) have opened a novel way to manipulate the
magnetization using in-plane current, with a great potential for the
development of fast and low power information technologies. It has been
recently shown that two-dimensional electron gases (2DEGs) appearing at oxide
interfaces provide a highly efficient spin-to-charge current interconversion.
The ability to manipulate 2DEGs using gate voltages could offer a degree of
freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for
spin-orbitronics, in which the sign and amplitude of SOTs at a given current
are fixed by the stack structure. Here, we report the non-volatile
electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We
demonstrate that the 2DEG is controlled using a back-gate electric-field,
providing two remanent and switchable states, with a large resistance contrast
of 1064%. The SOTs can then be controlled electrically in a non-volatile way,
both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO
heterostructures with large perpendicular magnetization further validates the
compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving
the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT
oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.",2206.03068v1
2023-07-10,Unconventional quantum oscillations and evidence of non-trivial electronic states in quasi-two-dimensional electron system at complex oxide interfaces,"The simultaneous occurrence of electric-field controlled superconductivity
and spin-orbit interaction makes two-dimensional electron systems (2DES)
constructed from perovskite transition metal oxides promising candidates for
the next generation of spintronics and quantum computing. It is, however,
essential to understand the electronic bands thoroughly and verify the
predicted electronic states experimentally in these 2DES to advance
technological applications. Here, we present novel insights into the electronic
states of the 2DES at oxide interfaces through comprehensive investigations of
Shubnikov-de Haas oscillations in two different systems: EuO/KTaO$_3$ (EuO/KTO)
and LaAlO$_3$/SrTiO$_3$ (LAO/STO). To accurately resolve these oscillations, we
conducted transport measurements in high magnetic fields up to 60 T and low
temperatures down to 100 mK. For 2D confined electrons at both interfaces, we
observed a progressive increase of oscillations frequency and cyclotron mass
with the magnetic field. We interpret these intriguing findings by considering
the existence of non-trivial electronic bands, for which the $E-k$ dispersion
incorporates both linear and parabolic dispersion relations. In addition to
providing experimental evidence for topological-like electronic states in
KTO-2DES and STO-2DES, the unconventional oscillations presented in this study
establish a new paradigm for quantum oscillations in 2DES based on perovskite
transition metal oxides, where the oscillations frequency exhibits quadratic
dependence on the magnetic field.",2307.04854v2
2023-11-01,Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies,"In magnetic tunnel junctions based on iron oxide nanoparticles the disorder
and the oxidation state of the surface spin as well as the nanoparticles
functionalization play a crucial role in the magnetotransport properties. In
this work, we report a systematic study of the effects of vacuum annealing on
the structural, magnetic and transport properties of self-assembled ~10 nm
Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K)
decomposes the organic coating into amorphous carbon, reducing the electrical
resistivity of the assemblies by 4 orders of magnitude. At the same time, the
3Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing
temperature of the sample increases from 573 to 873 K, indicating an important
surface oxidation. Although the 2 nm physical gap remains unchanged with the
thermal treatment, a monotonous decrease of tunnel barrier width was obtained
from the electron transport measurements when the annealing temperature
increases, indicating an increment in the number of defects and hot-spots in
the gap between the nanoparticles. This is reflected in the reduction of the
spin dependent tunneling, which reduces the interparticle magnetoresistance.
This work shows new insights about influence of the nanoparticle interfacial
composition, as well their the spatial arrangement, on the tunnel transport of
self-assemblies, and evidence the importance of optimizing the nanostructure
fabrication for increasing the tunneling current without degrading the spin
polarized current.",2311.00700v1
2006-01-30,59Co Nuclear Quadrupole Resonance Studies of Superconducting and Non-superconducting Bilayer Water Intercalated Sodium Cobalt Oxides NaxCoO2.yH2O,"We report 59Co nuclear quadrupole resonance (NQR) studies of bilayer water
intercalated sodium cobalt oxides NaxCoO2.yH2O (BLH) with the superconducting
transition temperatures, 2 K < T_c <= 4.6 K, as well as a magnetic BLH sample
without superconductivity. We obtained a magnetic phase diagram of T_c and the
magnetic ordering temperature T_M against the peak frequency nu_3 59Co NQR
transition I_z = +- 5/2 <=> +-7/2 and found a dome shape superconducting phase.
The 59Co NQR spectrum of the non-superconducting BLH shows a broadening below
T_M without the critical divergence of 1/T_1 and 1/T_2, suggesting an
unconventional magnetic ordering. The degree of the enhancement of 1/T_1T at
low temperatures increases with the increase of nu_3 though the optimal
nu_3~12.30 MHz. In the NaxCoO2.yH2O system, the optimal-T_c superconductivity
emerges close to the magnetic instability. T_c is suppressed near the phase
boundary at nu_3~12.50 MHz, which is not a conventional magnetic quantum
critical point.",0601659v1
2007-09-17,X-Ray Analysis of Oxygen-induced Perpendicular Magnetic Anisotropy in Pt/Co/AlOx trilayer,"X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx
trilayers to investigate the role of Co oxidation in the perpendicular magnetic
anisotropy of the Co/AlOx interface. It is observed that high temperature
annealing modifies the magnetic properties of the Co layer, inducing an
enhancement of the perpendicular magnetic anisotropy. The microscopic
structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray
Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements.
It is shown that annealing enhances the amount of interfacial oxide, which may
be at the origin of a strong perpendicular magnetic anisotropy.",0709.2581v2
2007-11-02,Origin of ferromagnetic response in diluted magnetic semiconductors and oxides,"This paper reviews the present understanding of the origin of ferromagnetic
response of diluted magnetic semiconductors and diluted magnetic oxides as well
as in some nominally magnetically undoped materials. It is argued that these
systems can be grouped into four classes. To the first belong composite
materials in which precipitations of a known ferromagnetic, ferrimagnetic or
antiferromagnetic compound account for magnetic characteristics at high
temperatures. The second class forms alloys showing chemical nano-scale phase
separation into the regions with small and large concentrations of the magnetic
constituent. To the third class belong (Ga,Mn)As, heavily doped p-(Zn,Mn)Te,
and related semiconductors. In these solid solutions the theory built on p-d
Zener's model of hole-mediated ferromagnetism and on either the Kohn-Luttinger
kp theory or the multi-orbital tight-binding approach describes qualitatively,
and often quantitatively many relevant properties. Finally, in a number of
carrier-doped DMS and DMO a competition between long-range ferromagnetic and
short-range antiferromagnetic interactions and/or the proximity of the
localisation boundary lead to an electronic nano-scale phase separation.",0711.0340v1
2010-01-15,On Using Magnetic and optical methods to determine the size and characteristics of nanoparticles embedded in oxide semiconductors,"Films of oxides doped with transition metals are frequently believed to have
magnetic inclusions. Magnetic methods to determine the amount of nanophases and
their magnetic characteristics are described. The amount of the sample that is
paramagnetic may also be measured. Optical methods are described and shown to
be very powerful to determine which defects are also magnetic.",1001.2674v1
2010-07-27,Magnetic interaction at an interface between manganite and other transition metal oxides,"A general consideration is presented for the magnetic interaction at an
interface between a perovskite manganite and other transition metal oxides. The
latter is specified by the electron number $n$ in the $d_{3z^2-r^2}$ level as
$(d_{3z^2-r^2})^n$. Based on the molecular orbitals formed at the interface and
the generalized Hund's rule, the sign of the magnetic interaction is rather
uniquely determined. The exception is when the $d_{3z^2-r^2}$ orbital is
stabilized in the interfacial manganite layer neighboring to a
$(d_{3z^2-r^2})^1$ or $(d_{3z^2-r^2})^2$ system. In this case, the magnetic
interaction is sensitive to the occupancy of the Mn $d_{3z^2-r2}$ orbital. It
is also shown that the magnetic interaction between the interfacial Mn layer
and the bulk region can be changed. Manganite-based heterostructures thus show
a rich magnetic behavior. We also present how to generalize the argument
including $t_{2g}$ orbitals.",1007.4763v1
2013-03-14,Magnetic hysteresis loop as a probe to distinguish single layer from many layer graphitic structure,"In this report we have pointed out that magnetic hysteresis loop can be used
as a probe to distinguish a single layer from a many layer graphitic structure.
Chemically we have synthesized graphitic oxide (GO) and reduced graphitic oxide
(RGO) for this investigation. We observe ferromagnetic like hysteresis loops
for both GO and RGO below a certain applied critical magnetic field and above
this critical field we observe cross-over of the positive magnetization to
negative magnetization leading to diamagnetic behaviour. This cross-over is
more dominant for the case of many layer graphitic structure. Upon annealing of
GO in air the critical cross-over field decreases and the magnetization
increases for multilayer graphitic structure. Possible reasons for all these
observations and phenomena is presented here.",1303.3433v1
2017-03-29,Thickness dependence and dimensionality effects of charge and magnetic orderings in La1/3Sr2/3FeO3 thin films,"We investigate the thickness effects on charge and magnetic orderings in Fe
perovskite oxide La1/3Sr2/3FeO3/SrTiO3 thin films by hard x-ray and resonant
soft x-ray scattering (RSXS) with changing thin film thickness systematically.
We found that the correlation lengths of the magnetic ordering along the
in-plane and out-of-plane directions are comparable and proportional to the
thickness, and shows stronger thickness dependence than those of charge orderg.
%the thickness dependence of correlation length of charge ordering is smaller
than that of magnetic orderings. The magnetic ordered states disappear when the
correlation length of magnetic ordering decreases to that of charge ordering
through the intrinsic thickness effects. Surface sensitive grazing-incident
RSXS revealed that the orderings exist even in the surface region, which
indicates that the observed orderings is not affected by surface effect like
oxygen vacancies. Critical thickness is in 5-15 nm, which corresponds to 4-11
antiferromagnetic ordering period. This critical value seems to be common to
other ferromagnetic oxide thin films.",1703.09995v1
2017-04-11,Role of polar compensation in interfacial ferromagnetism of LaNiO$_3$/CaMnO$_3$ superlattices,"Polar compensation can play an important role in the determination of
interfacial electronic and magnetic properties in oxide heterostructures. Using
x-ray absorption spectroscopy, x-ray magnetic circular dichroism, bulk
magnetometry, and transport measurements, we find that interfacial charge
redistribution via polar compensation is essential for explaining the evolution
of interfacial ferromagnetism in LaNiO$_3$/CaMnO$_3$ superlattices as a
function of LaNiO$_3$ layer thickness. In insulating superlattices (4 unit
cells or less of LaNiO$_3$), magnetism is dominated by Ni-Mn superexchange,
while itinerant electron-based Mn-Mn double-exchange plays a role in thicker
metallic superlattices. X-ray magnetic circular dichroism and resonant x-ray
scattering show that Ni-Mn superexchange contributes to the magnetization even
in metallic superlattices. This Ni-Mn superexchange interaction can be
explained in terms of polar compensation at the LaNiO$_3$-CaMnO$_3$ interface.
These results highlight the different mechanisms responsible for interfacial
ferromagnetism and the importance of understanding compensation due to polar
mismatch at oxide-based interfaces when engineering magnetic properties.",1704.03163v1
2019-11-07,Limited role of vortices in transport in highly disordered superconductors near $B_{c2}$,"At finite temperatures and magnetic fields, type-II superconductors in the
mixed state have a non-zero resistance that is overwhelmingly associated with
vortex motion. In this work we study amorphous indium oxide films, which are
thicker than the superconducting coherence length, and show that near $B_{c2}$
their resistance in the presence of perpendicular and in-plane magnetic fields
becomes almost isotropic. Up to a linear rescaling of the magnetic fields both
the equilibrium resistance as well as the non-equilibrium current-voltage
characteristics are insensitive to magnetic field orientation suggesting that,
for our superconductors, there is no fundamental difference in transport
between perpendicular and in-plane magnetic fields. Additionally we show that
this near-isotropic behavior extends to the insulating phase of amorphous
indium oxide films of larger disorder strength that undergo a magnetic field
driven superconductor-insulator transition. This near-isotropic behavior raises
questions regarding the role of vortices in transport and the origin of
resistance in thin-film superconductors.",1911.02818v1
2022-01-06,Large Magnetic-Field-Induced Strain at the Spin-Reorientation Transition in the A-Site Ordered Spinel Oxide LiFeCr4O8,"Sintered samples of a spinel oxide LiFeCr4O8, where Cr3+ and Fe3+ ions have
localized moments, were found to show a large magnetic-field-induced volume
increase approaching 500 ppm by applying a magnetic field of 9 T. This large
volume increase appeared only at around 30 K. At 30 K, a spin-reorientation
transition from ferrimagnetic to conical order occurs, giving rise to this
large volume increase. The coexistence of ferrimagnetic and conical phases at
this transition was found to be important, suggesting that such a large
magnetic-field-induced volume change can be realized at various magnetic
transitions in localized magnets with strong spin-lattice coupling.",2201.01897v1
2023-07-26,Highly Tunable Perpendicular Magnetic Anisotropy and Anisotropic Magnetoresistance in Ru-doped La0.67Sr0.33MnO3 Epitaxial Films,"As a prototypical half-metallic ferromagnet, La0.67Sr0.33MnO3 (LSMO) has been
extensively studied due to its versatile physical properties and great
potential in spintronic applications. However, the weak perpendicular magnetic
anisotropy (PMA) limits the controllability and detection of magnetism in LSMO,
thus hindering the realization of oxide-based spintronic devices with low
energy consumption and high integration level. Motivated by this challenge, we
develop an experimental approach to enhance the PMA of LSMO epitaxial films. By
cooperatively introducing 4d Ru doping and a moderate compressive strain, the
maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach 3.0 to 1E5 J/m3
at 10 K. Furthermore, we find a significant anisotropic magnetoresistance
effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our
findings offer an effective pathway to harness and detect the orientations of
magnetic moments in LSMO films, thus promoting the feasibility of oxide-based
spintronic devices, such as spin valves and magnetic tunnel junctions.",2307.13881v1
2016-06-30,Surface magnetism of strontium titanate,"SrTiO3 plays a central role in oxide electronics. It is the substrate of
choice for functional oxide heterostructures based on perovskite-structure
thin-film stacks, and its surface or interface with a polar oxide such as
LaAlO3 can become a two-dimensional conductor because of electronic
reconstruction or the presence of oxygen defects. Inconsistent reports of
magnetic order in SrTiO3 abound in the literature. Here we report a systematic
experimental study aimed at establishing how and when SrTiO3 can develop a
magnetic moment at room temperature. Polished 100, 110 or 111 crystal slices
from four different suppliers are characterized before and after vacuum
annealing at 750 {\deg}C, both in single-crystal and powdered form. Impurity
content is analysed at the surface and in the bulk. Besides the underlying
intrinsic diamagnetism of SrTiO3, magnetic signals are of three types-a Curie
law susceptibility due to dilute magnetic impurities at the ppm level, a
hysteretic, temperature-dependent ferromagnetic impurity contribution, and a
practically-anhysteretic, defect-related temperature-independent component that
saturates in about 200 mT. The latter component is intrinsic. It is often the
largest, reaching 10 Bohr magnetons per nm2 of surface area or more and
dominating the magnetic response in low fields at room temperature. It is
associated with defects near the surface, and can be destroyed by treatment
with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong
complex with titanium at the surface. The origin of this unusual
high-temperature ferromagnetic-like response is discussed.",1606.09422v1
2018-04-21,The effect of adding magnetic oxide as grain boundary for HAMR,"Grain-to-grain Curie temperature (Tc) variation in the media reduces
signal-to-noise ratio due to its contribution in transition jitter noise,
especially when average grain size is pushing down to increase the area storage
capacity. A thermally insulating magnetic grain boundary may suppress such
grain-to-grain Tc variation, especially at small grain size. Here we present an
experimental study on the effect of adding thermally-insulating magnetic oxide,
in particular BaFexOy, as part of the grain boundary materials in granular
FePt-C HAMR media. It is found that the BaFexOy is chemically inert to FePt and
the chemical ordering of FePt-BaFexOy-C media are similar to that of FePt-C
meida. By tuning the volume fraction of BaFexOy and C, well-separated FePt
grains (average grain size = 6.8 nm) surrounded by BaFexOy shell with
perpendicular Hc above 35 kOe can be obtained. Transmission electron microscopy
study with chemical analysis shows that the magnetic oxide appears to be
crystalline and surround the FePt grains with immediate full enclosure.
Magnetic measurements indicate an effective increase of magnetic grain size at
temperatures below FePt Curie temperature. Pulsed laser pump-probe measurement
indicates a measurable reduction of Curie temperature variation for the
FePt-BaFexOy-C media with carefully comparison with the reference FePt-C media.",1804.07892v1
2020-04-02,Tunable and Enhanced Rashba Spin-Orbit Coupling in Iridate-Manganite Heterostructures,"Tailoring spin-orbit interactions and Coulomb repulsion are the key features
to observe exotic physical phenomena such as magnetic anisotropy and
topological spin texture at oxide interfaces. Our study proposes a novel
platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3
(3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls
the lattice displacement and spin-correlated interfacial coupling through
charge transfer. We report on a tunable and enhanced interface-induced Rashba
spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3
bilayer with change in the underlying magnetic order of LaMnO3. We also
observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to
previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals
the quantitative valence of Mn and their impact on charge transfer. Further, we
performed angle-dependent magnetoresistance measurements, which show signatures
of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of
LaMnO3. Our work thus demonstrates a new route to engineer the interface
induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide
interfaces which makes SrIrO3 an ideal candidate for spintronics applications.",2004.00800v1
2018-08-07,Enhanced magnetic properties in ZnCoAlO caused by exchangecoupling to Co nanoparticles,"Wereport the results of a sequence of magnetisation and magneto-optical
studies on laser ablated thin films of ZnCoAlO and ZnCoO that contain a small
amount of metallic cobalt. The results are compared to those expected when all
the magnetization is due to isolated metallic clusters of cobalt and with an
oxide sample that is almost free from metallic inclusions. Using a variety of
direct magnetic measurements and also magnetic circular dichroism we find that
there is ferromagnetism within both the oxide and the metallic inclusions, and
furthermore that these magnetic components are exchange-coupled when aluminium
is included. This enhances both the coercive field and the remanence. Hence the
presence of a controlled quantity of metallic nanoparticles in ZnAlO can
improve the magnetic response of the oxide, thus giving great advantages for
applications in spintronics.",1808.02269v1
2022-03-15,Free-spin dominated magnetocaloric effect in dense Gd$^{3+}$ double perovskites,"Frustrated lanthanide oxides with dense magnetic lattices are of fundamental
interest for their potential in cryogenic refrigeration due to a large ground
state entropy and suppressed ordering temperatures, but can often be limited by
short-range correlations. Here, we present examples of frustrated fcc oxides,
Ba$_2$GdSbO$_6$ and Sr$_2$GdSbO$_6$ and the new site-disordered analog
Ca$_2$GdSbO$_6$ ([CaGd]$_A$[CaSb]$_B$O$_6$), in which the magnetocaloric effect
is influenced by minimal superexchange ($J_1 \sim 10$ mK). We report on the
crystal structures using powder x-ray diffraction and the bulk magnetic
properties through low-field susceptibility and isothermal magnetization
measurements. The Gd compounds exhibit a magnetic entropy change of up to -15.8
J/K/mol$_\textrm{Gd}$ in a field of 7 T at 2 K, a 20 % excess compared to the
value of -13.0 J/K/mol$_\textrm{Gd}$ for a standard in magnetic refrigeration,
Gd$_3$Ga$_5$O$_{12}$. Heat capacity measurements indicate a lack of magnetic
ordering down to 0.4 K for Ba$_2$GdSbO$_6$ and Sr$_2$GdSbO$_6$, suggesting
cooling down through the liquid 4-He regime. A mean-field model is used to
elucidate the role of primarily free spin behavior in the magnetocaloric
performance of these compounds in comparison to other top-performing Gd-based
oxides. The chemical flexibility of the double perovskites raises the
possibility of further enhancement of the magnetocaloric effect in the
Gd$^{3+}$ fcc lattices.",2203.08214v1
2022-05-31,Engineering of Heterostructure Pt/Co/AlOx for the enhancement of Dyzaloshinskii-Moria interaction,"The interfacial Dyzaloshinskii-Moria interaction (DMI) helps to stabilize
chiral domain walls and magnetic skyrmions, which will facilitate new magnetic
memories and spintronics logic devices. The study of interfacial DMI in
perpendicularly magnetized structurally asymmetric heavy metal (HM) /
ferromagnetic (FM) multilayer systems is of high importance due to the
formation of chiral magnetic textures in the presence of DMI. Here, we report
the impact of the cobalt oxidation at the cobalt -aluminum oxide interface in
Pt/Co/AlOx trilayer structure on the DMI by varying the post-growth annealing
time and Aluminum thickness. For quantifying DMI, we employed magneto-optical
imaging of asymmetric domain wall expansion, hysteresis loop shift, and
spin-wave spectroscopy techniques. We further correlated the Cobalt oxidation
with low-temperature Hall effect measurements and X-ray photoelectron
spectroscopy. Our results emphasize the characterization of magnetic films for
MRAM technologies semiconductor temperature process window, where magnetic
interaction will be critical for device performance.",2205.15940v1
2022-08-29,Room temperature spin-orbit torque efficiency and magnetization switching in SrRuO3-based heterostructures,"Spin-orbit torques (SOTs) from transition metal oxides (TMOs) in conjunction
with magnetic materials have recently attracted tremendous attention for
realizing high-efficient spintronic devices. SrRuO3 is a promising candidate
among TMOs due to its large and tunable SOT-efficiency as well as high
conductivity and chemical stability. However, a further study for benchmarking
the SOT-efficiency and realizing SOT-driven magnetization switching in SrRuO3
is still highly desired so far. Here, we systematically study the SOT
properties of high-quality SrRuO3 thin film heterostructuring with different
magnetic alloys of both IMA and PMA configuration by the harmonic Hall voltage
technique. Our results indicate that SrRuO3 possesses pronounced SOT-efficiency
of about 0.2 at room temperature regardless of the magnetic alloys, which is
comparable to typical heavy metals (HMs). Furthermore, we achieve SOT-driven
magnetization switching with a low threshold current density of 3.8x10^10
A/m^2, demonstrating the promising potential of SrRuO3 for practical devices.
By making a comprehensive comparison with HMs, our work unambiguously
benchmarks the SOT properties and concludes the advantages of SrRuO3, which may
bring more diverse choices for SOT applications by utilizing hybrid-oxide/metal
and all-oxide systems.",2208.13574v1
2023-07-10,Spin transport properties of spinel vanadate-based heterostructures,"Spin-orbit coupling and breaking of inversion symmetry are necessary
ingredients to enable a pure spin current-based manipulation of the
magnetization via the spin-orbit torque effect. Currently, magnetic insulator
oxides with non-dissipative characteristics are being explored. When combined
with non-magnetic heavy metals, known for their large spin-orbit coupling, they
offer promising potential for energy-efficient spin-orbitronics applications.
The intrinsic electronic correlations characterizing those strongly correlated
oxides hold the promises to add extra control-knobs to the desired efficient
spin-wave propagation and abrupt magnetization switching phenomena. Spinel
vanadate FeV2O4 (FVO) exhibits several structural phase transitions which are
accompanied by an intricate interplay of magnetic, charge and orbital
orderings. When grown as a thin film onto SrTiO3, the compressive strain state
induces a perpendicular magnetic anisotropy, making FVO-based heterostructures
desirable for spin-orbitronics applications. In this study, we have optimised
the deposition of stoichiometric and epitaxial Pt/FVO heterostructures by
Pulsed Laser Deposition and examined their spin-related phenomena. From
angle-dependent magnetotransport measurements, we observed both Anisotropic
Magnetoresistance (AMR) and Spin Hall Magnetoresistance (SMR) effects. Our
findings show the SMR component as the primary contributor to the overall
magnetoresistance, whose high value of 0.12% is only comparable to properly
optimized oxide-based systems.",2307.04389v1
2007-05-03,Electron Doping of Cuprates via Interfaces with Manganites,"The electron doping of undoped high-$T_c$ cuprates via the transfer of charge
from manganites (or other oxides) using heterostructure geometries is here
theoretically discussed. This possibility is mainly addressed via a detailed
analysis of photoemission and diffusion voltage experiments, which locate the
Fermi level of manganites above the bottom of the upper Hubbard band of some
cuprate parent compounds. A diagram with the relative location of Fermi levels
and gaps for several oxides is presented. The procedure discussed here is
generic, allowing for the qualitative prediction of the charge flow direction
at several oxide interfaces. The addition of electrons to antiferromagnetic Cu
oxides may lead to a superconducting state at the interface with minimal
quenched disorder. Model calculations using static and dynamical mean-field
theory, supplemented by a Poisson equation formalism to address charge
redistribution at the interface, support this view. The magnetic state of the
manganites could be antiferromagnetic or ferromagnetic. The former is better to
induce superconductivity than the latter, since the spin-polarized charge
transfer will be detrimental to singlet superconductivity. It is concluded that
in spite of the robust Hubbard gaps, the electron doping of undoped cuprates at
interfaces appears possible, and its realization may open an exciting area of
research in oxide heterostructures.",0705.0498v1
2013-07-04,Quantum many-body interactions in digital oxide superlattices,"Controlling the electronic properties of interfaces has enormous scientific
and technological implications and has been recently extended from
semiconductors to complex oxides which host emergent ground states not present
in the parent materials. These oxide interfaces present a fundamentally new
opportunity where, instead of conventional bandgap engineering, the electronic
and magnetic properties can be optimized by engineering quantum many-body
interactions. We utilize an integrated oxide molecular-beam epitaxy and
angle-resolved photoemission spectroscopy system to synthesize and investigate
the electronic structure of superlattices of the Mott insulator LaMnO3 and the
band insulator SrMnO3. By digitally varying the separation between interfaces
in (LaMnO3)2n/(SrMnO3)n superlattices with atomic-layer precision, we
demonstrate that quantum many-body interactions are enhanced, driving the
electronic states from a ferromagnetic polaronic metal to a pseudogapped
insulating ground state. This work demonstrates how many-body interactions can
be engineered at correlated oxide interfaces, an important prerequisite to
exploiting such effects in novel electronics.",1307.1475v1
2013-11-19,Tunneling Electroresistance Induced by Interfacial Phase Transitions in Ultrathin Oxide Heterostructures,"The ferroelectric (FE) control of electronic transport is one of the emerging
technologies in oxide heterostructures. Many previous studies in FE tunnel
junctions (FTJs) exploited solely the differences in the electrostatic
potential across the FTJs that are induced by changes in the FE polarization
direction. Here, we show that in practice the junction current ratios between
the two polarization states can be further enhanced by the electrostatic
modification in the correlated electron oxide electrodes, and that FTJs with
nanometer thin layers can effectively produce a considerably large
electroresistance ratio at room temperature. To understand these surprising
results, we employed an additional control parameter, which is related to the
crossing of electronic and magnetic phase boundaries of the correlated electron
oxide. The FE-induced phase modulation at the heterointerface ultimately
results in an enhanced electroresistance effect. Our study highlights that the
strong coupling between degrees of freedom across heterointerfaces could yield
versatile and novel applications in oxide electronics.",1311.4874v1
2016-02-25,Colossal dielectric constant in high entropy oxides,"Entropic contributions to the stability of solids are very well understood
and the mixing entropy has been used for forming various solids, for instance
such as inverse spinels. A particular development was related to high entropy
alloys in which the configurational disorder is responsible for forming simple
solid solutions and which are thoroughly studied for various applications
especially due to their mechanical properties but also electrical properties,
hydrogen storage, magnetic properties. Many unexplored compositions and
properties still remain for this class of materials due to their large phase
space. In a recent report it has been shown that the configurational disorder
can be used for stabilizing simple solid solutions of oxides, which should
normally not form solid solutions, these new materials were called
""entropy-stabilized oxides"". In this pioneering report, it was shown that
mixing five equimolar binary oxides yielded, after heating at high temperature
and quenching, an unexpected rock salt structure compound with statistical
distribution of the cations in a face centered cubic lattice. Following this
seminal study, we show here that these high entropy oxides (named HEOx
hereafter) can be substituted by aliovalent elements with a charge compensation
mechanism. This possibility largely increases the potential development of new
materials by widening their (already complex) phase space. As a first example,
we report here that at least one HEOx composition exhibits colossal dielectric
constants, which could make it very promising for applications as large-k
dielectric materials.",1602.07842v1
2016-04-07,Phase transitions via selective elemental vacancy engineering in complex oxide thin films,"Defect engineering has brought about a unique level of control for Si-based
semiconductors, leading to the optimization of various opto-electronic
properties and devices. With regard to perovskite transition metal oxides,
oxygen vacancies have been a key ingredient in defect engineering, as they play
a central role in determining the crystal field and consequent electronic
structure, leading to important electronic and magnetic phase transitions.
Therefore, experimental approaches toward understanding the role of defects in
complex oxides have been largely limited to controlling oxygen vacancies. In
this study, we report on the selective formation of different types of
elemental vacancies and their individual roles in determining the atomic and
electronic structure of perovskite SrTiO3 (STO) homoepitaxial thin films
fabricated by pulsed laser epitaxy. Structural and electronic transitions have
been achieved via selective control of the Sr and oxygen vacancy
concentrations, respectively, indicating a decoupling between the two phase
transitions. In particular, oxygen vacancies were responsible for
metal-insulator transitions, but did not influence the Sr vacancy induced
cubic-to-tetragonal structural transition in epitaxial STO thin film. The
independent control of multiple phase transitions in complex oxides by
exploiting selective vacancy engineering opens up an unprecedented opportunity
toward understanding and customizing complex oxide thin films.",1604.01875v1
2021-07-07,Coupling charge and topological reconstructions at polar oxide interfaces,"In oxide heterostructures, different materials are integrated into a single
artificial crystal, resulting in a breaking of inversion-symmetry across the
heterointerfaces. A notable example is the interface between polar and
non-polar materials, where valence discontinuities lead to otherwise
inaccessible charge and spin states. This approach paved the way to the
discovery of numerous unconventional properties absent in the bulk
constituents. However, control of the geometric structure of the electronic
wavefunctions in correlated oxides remains an open challenge. Here, we create
heterostructures consisting of ultrathin SrRuO$_3$, an itinerant ferromagnet
hosting momentum-space sources of Berry curvature, and LaAlO$_3$, a polar
wide-bandgap insulator. Transmission electron microscopy reveals an atomically
sharp LaO/RuO$_2$/SrO interface configuration, leading to excess charge being
pinned near the LaAlO$_3$/SrRuO$_3$ interface. We demonstrate through
magneto-optical characterization, theoretical calculations and transport
measurements that the real-space charge reconstruction modifies the
momentum-space Berry curvature in SrRuO$_3$, driving a reorganization of the
topological charges in the band structure. Our results illustrate how the
topological and magnetic features of oxides can be manipulated by engineering
charge discontinuities at oxide interfaces.",2107.03359v1
2022-04-13,Oxygen Octahedral Tilt Controlled Topological Hall Effect in Epitaxial and Freestanding SrRuO3/SrIrO3 Heterostructures,"The fabrication technique of freestanding oxide flakes by epitaxial lift-off
has made significant contributions to the multifunctional oxide thin film
research. Several highly impactful work have recently demonstrated the
robustness of freestanding oxide flakes retaining their desirable properties
after detachment from the substrate by dissolving away the water-soluble
Sr3Al2O6 buffer layer. Firstly, in epitaxial SrRuO3/SrIrO3 systems showing
Hall-humps reminiescence of Topological Hall Effect, first-principle
calculations revealed that octahedral tilts can modify the sign of
Dzyaloshinskii-Moriya interaction and avoid cancellation in a symmetric
trilayer structure. Secondly, freestanding flakes of the trilayer is also able
to retain the Hall-humps across a wide temperature range. The behaviour of
humps' peak field does not vary with field direction rotation away from surface
normal, consistent to a micromagnetic simulation result of N\'eel-type magnetic
Skyrmions. The layer-resolved octahedral tilts in the freestanding
heterostructures also crucially controls the occurrence of Hall-humps,
consistent to the insight from the epitaxial ones. This work offers a new
perspective to understanding Hall-humps in perovskite oxides, as well as
demonstrates the fabrication of oxide heterostructure membranes with high
interfacial quality.",2204.06174v2
2022-11-16,Characterisation of Gamma-irradiated MCz-Silicon Detectors with a High-$K$ Negative Oxide as Field Insulator,"The high-luminosity operation of the Tracker in the Compact Muon Solenid
(CMS) detector at the Large Hadron Collider (LHC) experiment calls for the
development of silicon-based sensors. This involves implementation of
AC-coupling to micro-scale pixel sensor areas to provide enhanced isolation of
radiation-induced leakage currents. The motivation of this study is the
development of AC-pixel sensors with negative oxides (such as aluminium oxide -
Al$_2$O$_3$ and hafnium oxide - HfO$_2$) as field insulators that possess good
dielectric strength and provide radiation hardness. Thin films of Al$_2$O$_3$
and HfO$_2$ grown by atomic layer deposition (ALD) method were used as
dielectrics for capacitive coupling. A comparison study based on dielectric
material used in MOS capacitors indicate HfO$_2$ as a better candidate since it
provides higher sensitivity (where, the term sensitivity is defined as the
ratio of the change in flat-band voltage to dose) to negative charge
accumulation with gamma irradiation.
  Further, space charge sign inversion was observed for sensors processed on
high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates that
were irradiated with gamma rays up to a dose of 1 MGy. The inter-pixel
resistance values of heavily gamma irradiated AC-coupled pixel sensors suggest
that high-$K$ negative oxides as field insulators provide a good electrical
isolation between the pixels.",2211.09158v2
2023-01-06,APC Nb$_3$Sn superconductors based on internal oxidation of Nb-Ta-Hf alloys,"In the last few years, a new type of Nb$_3$Sn superconducting composite,
containing a high density of artificial pinning centers (APC) generated via an
internal oxidation approach, has demonstrated a significantly superior
performance relative to present, state-of-the-art commercial Nb$_3$Sn
conductors. This was achieved via the internal oxidation of Nb-4at.%Ta-1at.%Zr
alloy. On the other hand, our recent studies have shown that internal oxidation
of Nb-Ta-Hf alloys can also lead to dramatic improvements in Nb$_3$Sn
performance. In this work we follow up this latter approach, fabricating a
61-stack APC wire based on the internal oxidation of Nb-4at.%Ta-1at.%Hf alloy,
and compare its critical current density (Jc) and irreversibility field (Birr)
with APC wires made using Nb-4at.%Ta-1at.%Zr. A second goal of this work was to
improve the filamentary design of APC wires in order to improve their wire
quality and electromagnetic stability. Our new modifications have led to
significantly improved RRR and stability in the conductors, while still keeping
non-Cu Jc at or above the FCC Jc specification. Further improvement via
optimization of the wire recipe and design is ongoing. Finally, additional work
needed to make APC conductors ready for applications in magnets is discussed.",2301.02571v2
2023-04-08,Novel entropy-stabilized fluorite oxides with multifunctional properties,"Development of new high-entropy oxides having configurational entropy
dominating the phase stability has become a hot topic since the discovery of
rock salt structure entropy-stabilized (ES)(MgCoNiCuZn)O in 2015. Herein, we
report a set of novel entropy-stabilized fluorite oxides:
Zr0.2Hf0.2Ce0.2Sn0.2Mn0.2O2-{\delta}, Zr0.2Hf0.2Ti0.2Mn0.2Ce0.2O2-{\delta},
Zr0.225Hf0.225Ti0.225Mn0.225Ce0.1O2-{\delta}, and
Zr0.2Hf0.2Ti0.2Mn0.2Ce0.1Ta0.05Fe0.05O2-{\delta} synthesized using standard
solid-state reaction. These compounds have been investigated using X-ray
diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy
techniques to discern their structural, microstructural, and chemical
properties. The configurational-entropy dominated phase stability and hence the
entropy stabilization of the compounds is confirmed by cyclic heat treatments.
The mismatch in the ionic radii and oxidation state of the cations are the key
factors in achieving a single-phase fluorite structure. Further, screening of
physical properties including thermal conductivity, optical band gap, magnetic
properties, and impedance spectroscopy is discussed. Thermal conductivity of
1.4-1.7 Wm-1K-1 is observed at 300 K and remains mostly invariant across a wide
temperature range (300K-1073K), favorable for thermal barrier coating
applications. These ES samples have an optical band gap of 1.6-1.8 eV, enabling
light absorption across the visible spectrum and hence could be promising for
photocatalytic applications. The impedance spectroscopy data of the
entropy-stabilized samples reveal the presence of electronic contributions with
small activation energy (0.3-0.4 eV) across a temperature range of 298K-423K.
These observations in ES fluorite systems show potential for their
multifunctional applications via further optimization and confirm the great
chemical versatility of entropy-stabilized oxides.",2304.04084v2
2016-03-14,Magnetic properties of restacked 2D spin $\frac{1}{2}$ honeycomb RuCl$_3$ nanosheets,"Spin $\frac{1}{2}$ honeycomb materials have gained substantial interest due
to their exotic magnetism and possible application in quantum computing.
However, in all current materials out-of-plane interactions are interfering
with the in-plane order, hence a true 2D magnetic honeycomb system is still of
demand. Here, we report the exfoliation of the magnetic semiconductor
$\alpha$-RuCl$_3$ into the first halide monolayers and the magnetic
characterization of the spin $\frac{1}{2}$ honeycomb arrangement of
turbostratically stacked RuCl$_3$ monolayers. The exfoliation is based on a
reductive lithiation/hydration approach, which gives rise to a loss of
cooperative magnetism due to the disruption of the spin $\frac{1}{2}$ state by
electron injection into the layers. After an oxidative treatment, cooperative
magnetism similar to the bulk is restored. The oxidized pellets of restacked
single layers feature a magnetic transition at T$_N$ = 7 K in the in-plane
direction, while the magnetic properties in the out-of-plane direction vastly
differ from bulk $\alpha$-RuCl$_3$. The macroscopic pellets of RuCl$_3$
therefore behave like a stack of monolayers without any symmetry relation in
the stacking direction. The deliberate introduction of turbostratic disorder to
manipulate the spin structure of RuCl$_3$ is of interest for research in
frustrated magnetism and complex magnetic order as predicted by the
Kitaev-Heisenberg model.",1603.04463v2
2022-10-04,Bragg diffraction by a magnetic all-in-all-out configuration with application to a cubic cerium pyrochlore oxide,"The Bragg diffraction of neutrons and x-rays are well-suited to the task of
determining the distribution of magnetization in crystals. Applications of the
two techniques proceed by contrasting observed intensities with intensities
calculated with a specific model, and changing the model as need be to achieve
satisfactory agreement. An all-in-all-out (AIAO) magnetic configuration of
magnetic dipoles on a cubic face-centred lattice with networks of
corner-sharing tetrahedra is often mentioned in the context of pyrochlore
oxides, for example, but the corresponding neutron and x-ray diffraction
patterns appear not have been calculated. Our results for patterns of Bragg
spots from an AIAO magnetic configuration defined by a magnetic space group are
symmetry informed and yield exact reflection conditions. Specifically, a
long-range order of magnetic dipoles is forbidden in our model. Bulk properties
arise from higher-order multipoles that include quadrupoles and octupoles.
Bragg spots that exclude all magnetic multipoles other than an octupole have
been discovered, and they can be observed by both neutron diffraction and
resonant x-ray diffraction. All magnetic multipoles allowed in diffraction by
cerium ions (4f1) are presented in terms of coefficients in a well-documented
and unusual magnetic ground state. Symmetry of the cerium site in the cubic
structure constrains the coefficients. Our scattering amplitudes have an
application in both neutron and x-ray diffraction experiments on Ce2Zr2O7, for
example, and searches for the sought-after cerium octupole. Also presented for
future use is a result for the total, energy-integrated magnetic neutron
scattering intensity by a powder sample.",2210.01449v2
2023-03-23,Harnessing van der Waals CrPS4 and Surface Oxides for non-monotonic pre-set field induced Exchange Bias in Fe3GeTe2,"Two-dimensional van der Waals (vdW) heterostructures are an attractive
platform for studying exchange bias due to their defect free and atomically
flat interfaces. Chromium thiophosphate (CrPS4), an antiferromagnetic material,
possesses uncompensated magnetic spins in a single layer, rendering it a
promising candidate for exploring exchange bias phenomena. Recent findings have
highlighted that naturally oxidized vdW ferromagnetic Fe3GeTe2 exhibits
exchange bias, attributed to the antiferromagnetic coupling of its ultrathin
surface oxide layer (O-FGT) with the underlying unoxidized Fe3GeTe2. Anomalous
Hall measurements are employed to scrutinize the exchange bias within the
CrPS4/(O-FGT)/Fe3GeTe2 heterostructure. This analysis takes into account the
contributions from both the perfectly uncompensated interfacial CrPS4 layer and
the interfacial oxide layer. Intriguingly, a distinct and non-monotonic
exchange bias trend is observed as a function of temperature below 140 K. The
occurrence of exchange bias induced by a 'pre-set field' implies that the
prevailing phase in the polycrystalline surface oxide is ferrimagnetic Fe3O4.
Moreover, the exchange bias induced by the ferrimagnetic Fe3O4 is significantly
modulated by the presence of the van der Waals antiferromagnetic CrPS4 layer,
forming a heterostructure, along with additional iron oxide phases within the
oxide layer. These findings underscore the intricate and complex nature of
exchange bias in van der Waals heterostructures, highlighting their potential
for tailored manipulation and control.",2303.13167v3
2004-08-26,Further Evidences for Spin Glass like behavior in NiO nanoparticles,"Nickel oxide nanoparticles are prepared by a sol gel method and characterized
by x-ray diffraction and transmission electron microscope. Here we present
measurements on temperature and field dependence of magnetization and time
dependence of thermoremanent magnetization. Our conclusion based on these
measurements is that the system shows spin glass like behavior.",0408579v1
2016-04-23,M(H) dependence and size distribution of SPIONs measured by atomic magnetometry,"We demonstrate that the quasistatic recording of the magnetic excitation
function M(H) of superparamagnetic iron oxide magnetic nanoparticle (SPION)
suspensions by an atomic magnetometer allows a precise determination of the
sample's iron mass content mFe and the particle size distribution.",1604.06882v1
2020-04-24,"Antiferromagnetism in a nanocrystalline high entropy oxide (Co,Cu,Mg,Ni,Zn)O : Magnetic constituents and surface anisotropy leading to lattice distortion","For the first time, this study shows that distortion in a crystal structure
due to magnetic effect is possible in a lattice with extreme chemical disorder.
The multicomponent equimolar transition metal oxide (ME TMO),
(Co,Cu,Mg,Ni,Zn)O, which is a high entropy oxide, has been attracting a lot of
attention due to its unique application potential in many fields including
electrochemical energy storage. In the present investigation, nanocrystalline
ME TMO was synthesised by three bottom up methods. The presence of distortion
in the rocksalt crystal structure, revealed by X ray diffraction and Raman
spectroscopy, and correlated with magnetic measurements from SQUID and EPR
studies could be attributed to the additive effects of exchange striction (from
the magnetic constituents) and magnetic anisotropy (from the decreased
crystallite size). For the first time, iron has been doped into ME TMO, to show
that a higher amount of magnetic constituent increases the distortion in the
lattice. Nanocrystalline ME TMO also showed a core shell magnetic behavior
below the bifurcation temperature arising from the uncompensated or canted spin
at the surface. Neel temperature of the nanocrystalline ME TMO is reported for
first time to be as high as 700 K. This study helps unravel the structure and
magnetic properties of such high entropy materials, and augurs a definite scope
for better understanding of the factors influencing the crystal structure in
high entropy oxides.",2004.11684v1
1997-09-03,Polar Jahn-Teller centers and magnetic neutron scattering cross-section in copper oxides,"In the framework of the model of the polar singlet-triplet Jahn-Teller
centers the cross-section is obtained for magnetic neutron scattering in
high-$T_{c}$ cuprates. Multi-mode character of the $CuO_{4}$ cluster ground
manifold in the new phase of polar centers determines the dependence of
magnetic form-factor on the local structure and charge state of the center. It
is shown that magnetic inelastic neutron scattering in the system of the polar
singlet-triplet Jahn-Teller centers permits to investigate the non-magnetic
charge and structure excitations.",9709033v1
2006-08-22,The magnetic orders induced ferroelectricity,"We studied the ferroelectricity of magnetic oxides in which its emergence
coincides with the onset of a second incommensurate magnetic order. We solved
for the wave function of e_{g} electrons in the presence of magnetic orders.
The coupling between the magnetic and electric orders is provided by the
spin-orbit interaction. It was found that the net electric dipole moment of the
system came from the bond between the transition metal and oxygen atoms. The
anisotropy of d-orbitals also played an important role. Finally, the form of
the coupling leads us to the conclusion that it is an improper
ferroelectricity.",0608470v1
2006-09-01,Calculations of Magnetic Exchange Interactions in Mott--Hubbard Systems,"An efficient method to compute magnetic exchange interactions in systems with
strong correlations is introduced. It is based on a magnetic force theorem
which evaluates linear response due to rotations of magnetic moments and uses a
novel spectral density functional framework combining our exact diagonalization
based dynamical mean field and local density functional theories. Applications
to spin waves and magnetic transition temperatures of 3d metal mono--oxides as
well as high--T_{c} superconductors are in good agreement with experiment.",0609006v1
2006-11-26,Strong magnetic scattering from TiO$_{x}$ adhesion layers,"Electronic phase coherence in normal metals is incredibly sensitive to
magnetic scattering. As a result, the weak localization magnetoresistance and
time-dependent universal conductance fluctuations are powerful probes of
magnetic impurities. We report measurements of these effects in Au and Ag
nanowires with a 1.5 nm thick Ti adhesion layer underneath the deposited metal.
The results indicate an anomalously large magnetic impurity concentration due
to the Ti layer. Results suggest that this magnetic scattering and its
evolution are related to the oxidation state of the Ti.",0611633v1
2013-10-30,Investigation of MoS2 and Graphene Nanosheets by Magnetic Force Microscopy,"For the first time, the magnetic force microscopy (MFM) is used to
characterize the mechanically-exfoliated single- and few-layer MoS2 and
graphene nanosheets. By analysis of the phase and amplitude shifts, the
magnetic response of MoS2 and graphene nanosheets exhibits the dependence on
their layer number. However, the solution-processed single-layer MoS2 nanosheet
shows the reverse magnetic signal to the mechanically-exfoliated one, and the
graphene oxide nanosheet has not shown any detectable magnetic signal.
Importantly, graphene and MoS2 flakes become nonmagnetic when they exceed a
certain thickness.",1310.8172v1
2014-03-04,Low-temperature magnetism in the honeycomb systems SrLn2O4,"Recent progress in the understanding of the complex magnetic properties of
the family of rare-earth strontium oxides, SrLn2O4, is reviewed. These
compounds consisting of hexagons and triangles are affected by geometrical
frustration and therefore exhibit its characteristic features, such as a
significant reduction of magnetic ordering temperatures and complex phase
diagrams in an applied field. Some of the observed features appear to be rather
remarkable even in the context of the unusual behavior associated with
geometrically frustrated magnetic systems. Of particular interest is the
coexistence at the lowest temperature of different magnetic structures
(exhibiting either long or short-range order) characterized by different
propagation vectors in materials without significant chemical or structural
disorder.",1403.0877v1
2012-04-27,Spin-dependent electron grating effect from helical magnetization in multiferroic tunnel junctions,"In multiferroic oxides with a transverse helical magnetic order, the
magnetization exchange coupling is sinusoidally space-dependent. We
theoretically investigate the spin-dependent electron grating effect in
normal-metal/helical-multiferroic/ferromagnettic heterojunctions. The spin wave
vector of the spiral can be added or subtracted from the electron spacial wave
vector inducing spin-conserved and spin-flipped diffracted transmission and
reflection. The predicted grating effect can be controlled by magnetization
exchange coupling strength, the helicity spatial period, and the magnetization
of the ferromagnetic layer.",1204.6095v1
2019-06-02,Structural and Magnetic Properties of Er3Fe5-xAlxO12 Garnets,"Er3Fe5-xAlxO12 (0.0 < x < 0.8) garnets were prepared by ball milling and
sintering at 1300 C. Rietveld refinement of the samples revealed a garnet
structure with Ia3d symmetry. The lattice parameter, cell volume, X-ray density
and magnetization of the prepared garnets decreased with the increase of Al
content (x). The coercivity of the garnets increased with x, but remained
generally low, being below 20 Oe. Low temperature magnetic measurements versus
temperature indicated that the magnetization of x = 0.0 exhibited a
compensation temperature at -186 C, however, x = 0.8 exhibited a minimum at a
higher temperature of -134 C.",1906.00405v1
1998-07-24,Magnetoresistance of metallic perovskite oxide LaNiO$_{3-δ}$,"We report a study of the magnetoresistance (MR) of the metallic perovskite
oxide LaNiO$_{3-\delta}$ as a function of the oxygen stoichiometry $\delta$
($\delta \leq$ 0.14), magnetic field (H $\leq 6T$) and temperature (1.5K $\leq
$ T $\leq $ 25K). We find a strong dependence of the nature of MR on the oxygen
stoichiometry. The MR at low temperatures change from positive to negative as
the sample becomes more oxygen deficient (i.e, $\delta$ increases). Some of the
samples which are more resistive, show a resistivity minima at $T_{min}$
$\approx$ 20K. We find that in these samples the MR is positive at T >
$T_{min}$ and negative for T < $T_{min}$. We conclude that in the absence of
strong magnetic interaction, the negative MR in these oxides can arise from
weak localisation effects.",9807330v1
2002-11-19,Fermi-liquid ground state in n-type copper-oxide superconductor Pr0.91Ce0.09LaCuO4-y,"We report nuclear magnetic resonance studies on the low-doped n-type
copper-oxide Pr_{0.91}LaCe_{0.09}CuO_{4-y} (T_c=24 K) in the superconducting
state and in the normal state uncovered by the application of a strong magnetic
field. We find that when the superconductivity is removed, the underlying
ground state is the Fermi liquid state. This result is at variance with that
inferred from previous thermal conductivity measurement and contrast with that
in p-type copper-oxides with a similar doping level where high-T_c
superconductivity sets in within the pseudogap phase. The data in the
superconducting state are consistent with the line-nodes gap model.",0211400v2
2004-06-29,Ferromagnetism in substituted zinc oxide,"Room-temperature ferromagnetism is observed in (110) oriented ZnO films
containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There
are large moments, 1.9 and 0.5 muB/atom for Co- and Ti-substituted oxides,
respectively. Sc-substituted ZnO shows also a moment of 0.3 muB/Sc.
Magnetization is very anisotropic, with variations of up to a factor three
depending on the orientation of the applied field relative to the R-cut
sapphire substrates. Results are interpreted in terms of a spin-split donor
impurity band model, which can account for ferromagnetism in insulating or
conducting high-k oxides with concentrations of magnetic ions that lie far
below the percolation threshold. The variation of the ferromagnetism with
oxygen pressure used during film growth is evidence of a link between
ferromagnetism and defect concentration.",0406719v1
2005-02-02,Second Anomaly in the Specific Heat of beta-Pyrochlore Oxide Superconductor KOs2O6,"Resistivity and specific heat have been measured on a single crystalline
sample of the beta-pyrochlore oxide superconductor, KOs2O6. It is found that a
second peak in specific heat, which may evidence an unknown phase transition,
appears around Tp ~ 7.5 K below the superconducting transition temperature Tc =
9.53 K. Applying magnetic fields up to 14 T, Tc is reduced gradually down to
7.1 K, while Tp is raised a little and becomes even higher than Tc at 14 T,
which implies that the second anomaly is not associated directly with the
superconductivity. It is demonstrated, however, that there is significant
communication between the two anomalies, suggesting that they come from the
same electrons. It is also reported that the Sommerfeld coefficient ? in KOs2O6
is possibly much larger than in other members of beta-pyrochlore oxide
superconductors, RbOs2O6 (Tc = 6.3 K) and CsOs2O6 (Tc = 3.3 K).",0502043v2
2005-09-01,Exceptional type-I superconductivity of the layered silver oxide Ag$_5$Pb$_2$O$_6$,"We report zero-resistivity transition and the details of magnetic transition
of a layered silver oxide Ag$_5$Pb$_2$O$_6$ single crystal, which make
definitive evidence of superconductivity in this compound. In the AC
susceptibility of a mono-crystal, we observed large supercooling, as well as
positive peaks in the real part of the susceptibility indicating the
reversibility of magnetic process. These observations reveal that
Ag$_5$Pb$_2$O$_6$ is probably the first oxide that shows type-I
superconductivity. Evaluation of the superconducting parameters not only gives
confirming evidence of type-I superconductivity, but also indicates that it is
a dirty-limit superconductor. We also analyze supercooling to determine the
upper limit of the Ginzburg-Landau parameter.",0509018v2
2006-07-03,A second phase transition and superconductivity in the beta-pyrochlore oxide KOs2O6,"Another phase transition that is probably of first order is found in the
beta-pyrochlore oxide superconductor KOs2O6 with a superconducting transition
temperature Tc of 9.6 K. It takes place at Tp=7.5 K in the superconducting
state in a zero magnetic field. By applying magnetic fields of up to 140 kOe,
the Tc gradually decreased to 5.2 K, while Tp changed little, eventually
breaking through the Hc2 line at approximately 65 kOe in the H-T diagram. Both
the normal-state resistivity and Hc2 change slightly but significantly across
the second phase transition. It is suggested that the transition is associated
with the rattling of potassium ions located in an oversized cage of osmium and
oxide ions.",0607064v2
2007-10-09,Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation,"The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated
by means of X-ray powder diffraction, electron diffraction, magnetic
susceptibility measurements and band structure calculations. Its structure is
similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin
system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements
reveal a spin gap-like behavior with \Delta ~ 270 K and a spin singlet ground
state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a
system of weakly coupled dimers in perfect agreement with the experimental
data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the
spin system in layered vanadium oxides by cation substitution. Simple
correlations between the cation size, geometrical parameters and exchange
integrals for the MV(2)O(5)-type oxides are established and discussed.",0710.1806v1
2009-04-28,Oxide layer boron leads to reduced symmetry spin filtering magnetic tunnel junctions,"Experimental studies of FeCoB/MgO/FeCoB tunnel junctions indicate that boron
diffuses into MgO during rf-sputtering and forms polycrystalline Mg-B-O
regions. These tunnel junctions provide high tunneling magnetoresistance values
and low RA products. However the crystal structure of the Mg-B-O region remains
unknown. Using density functional techniques, I examine three potential Mg(B)
oxides including Mg$_{2}$B$_{2}$O$_{5}$ (monoclinic and triclinic) and the
orthorhombic mineral Kotoite (Mg$_3$B$_2$O$_6$). Kotoite is the best candidate
for formation in magnetic tunnel junctions. The (100) surface of Kotoite has a
good lattice match with (001) MgO and could template neighboring FeCo into bcc
layers during annealing. Complex band structure analysis of Kotoite shows that
the C$_{2v}$ $\tilde{\Delta}_1$ band has a much smaller imaginary k component
than the C$_{2v}$ $\tilde{\Delta}_4$ band. Based on symmetry analysis, the
majority spin $\Delta_1$ band in FeCo should couple well with the Kotoite
$\tilde{\Delta}_1$ band, while the minority FeCo $\Delta_5$ will couple
partially with the $\tilde{\Delta}_4$ band. Kotoite provides a new route to
high tunneling magnetoresistance based on spin filtering by a lower symmetry
oxide region.",0904.4475v1
2009-08-05,"Synthesis and characterization of ferromagnetic cobalt nanospheres, nanodiscs and nanocubes","We report the synthesis of cobalt nanoparticles with different shapes and
sizes by rapid pyrolysis of cobalt carbonyl in the presence of various
surfactants. The size and shape of the nanoparticles were influenced by
reaction conditions, such as type of the surfactant, molar ratio of surfactant
to precursor, reflux temperature and reaction time. The shapes that we have
achieved include spherical, nearly spherical, disc and cube. The presence of
linear amine yielded nanodiscs and they spontaneously self-assembled into long
ribbons. The effect of shape anisotropy on magnetic nanoparticles has been
investigated. Spherical nanoparticles of diameter 14.5 nm show strong
ferromagnetic behavior at low temperature and superparamagnetism at room
temperature. On the other hand the cubic nanoparticles of 45 nm sides showed
negligible coercive field at T = 10 K and ferromagnetism that persisted above T
= 300 K. The cobalt nanospheres were oxidized to grow cobalt oxide shell of
varying thickness to study exchange bias effect. A pronounced exchange bias and
a strong temperature dependant magnetization were observed in oxidized cobalt
nanospheres.",0908.0665v1
2009-08-06,Control of magnetism in cobalt nanoparticles by oxygen passivation,"We report on the preparation of ferromagnetic cobalt nanospheres with
antiferromagnetic oxide capping layer and its implication for the variation in
magnetic property. The hcp cobalt nanospheres were prepared by thermal
decomposition of cobalt carbonyl in the presence of organic surfactants. The
spherical nanoparticles thus prepared were oxidized to grow antiferromagnetic
layers of varying composition and thickness on top of cobalt spheres. High
resolution transmission electron microscopy confirmed growth of Co3O4 in one
case and CoO in another case. Strong exchange anisotropy and enhanced coercive
field was observed due to the core-shell structure in Co-CoO system. On the
other hand only a marginal improvement was seen in Co-Co3O4 system. A low
temperature paramagnetic behavior was also observed that is interpreted in the
framework of crystal defects in the oxide shell.",0908.0791v1
2010-08-17,Exchange bias in GeMn nanocolumns: the role of surface oxidation,"We report on the exchange biasing of self-assembled ferromagnetic GeMn
nanocolumns by GeMn-oxide caps. The x-ray absorption spectroscopy analysis of
this surface oxide shows a multiplet fine structure that is typical of the Mn2+
valence state in MnO. A magnetization hysteresis shift |HE|~100 Oe and a
coercivity enhancement of about 70 Oe have been obtained upon cooling (300-5 K)
in a magnetic field as low as 0.25 T. This exchange bias is attributed to the
interface coupling between the ferromagnetic nanocolumns and the
antiferromagnetic MnO-like caps. The effect enhancement is achieved by
depositing a MnO layer on the GeMn nanocolumns.",1008.2872v1
2010-11-23,NaIrO3 - A pentavalent post-perovskite,"Sodium iridium(V) oxide, NaIrO3, was synthesized by a high pressure solid
state method and recovered to ambient conditions. It is found to be
isostructural with CaIrO3, the much-studied structural analogue of the
high-pressure post-perovskite phase of MgSiO3. Among the oxide
post-perovskites, NaIrO3 is the first example with a pentavalent cation. The
structure consists of layers of corner- and edge-sharing IrO6 octahedra
separated by layers of NaO8 bicapped trigonal prisms. NaIrO3 shows no magnetic
ordering and resistivity measurements show non-metallic behavior. The crystal
structure, electrical and magnetic properties are discussed and compared to
known post-perovskites and pentavalent perovskite metal oxides.",1011.5125v2
2011-05-01,Symmetry and Nonstoichiometry as Possible Origin of Ferromagnetism in Nanoscale oxides,"We show through density functional theory calculations that extended magnetic
states can inherently occur in oxides as the size of the crystals is reduced
down to the nanometer scale even when they do not explicitly include intrinsic
defects. This is because in nanoscale systems crystallographically perfect
crystallites paradoxically result in nonstoichiometric compositions owing to
the finite number of constituting atoms. In these structurally perfect but
stoichiometrically imperfect nanocrystallites, the spin-triplet state is found
to be more stable than the spin-singlet state, giving rise to an extended spin
distribution that expands over the entire crystal. According to this picture,
long-range magnetic order arises from the combined effect of crystal symmetry
and nonstoichiometry that can coexist exclusively in nanoscale systems. The
idea can also give reasonable explanations for the unprecedented ferromagnetic
features observed commonly in nanoscale oxides, including ubiquity, anisotropy,
and diluteness.",1105.0171v1
2011-10-31,Spin-dependent recombination in Czochralski silicon containing oxide precipitates,"Electrically detected magnetic resonance is used to identify recombination
centers in a set of Czochralski grown silicon samples processed to contain
strained oxide precipitates with a wide range of densities (~ 1e9 cm-3 to ~
7e10 cm-3). Measurements reveal that photo-excited charge carriers recombine
through Pb0 and Pb1 dangling bonds and comparison to precipitate-free material
indicates that these are present at both the sample surface and the oxide
precipitates. The electronic recombination rates vary approximately linearly
with precipitate density. Additional resonance lines arising from iron-boron
and interstitial iron are observed and discussed. Our observations are
inconsistent with bolometric heating and interpreted in terms of spin-dependent
recombination. Electrically detected magnetic resonance is thus a very powerful
and sensitive spectroscopic technique to selectively probe recombination
centers in modern photovoltaic device materials.",1110.6727v1
2013-12-03,Reconsidering the possibility of room temperature ferromagnetism in Mn doped Zirconium oxide,"The possibility to induce long range ferromagnetic order by doping oxides
with transition metal ions has become a very exciting challenge in the last
decade. Theoretically, it has been claimed that Mn doped ZrO$_2$ could be a
very promising spintronic candidate and that high critical temperatures could
be already achieved even for a low Mn concentration. Some experiments have
reported room temperature ferromagnetism (RT-FM) whilst some others only
paramagnetism. When observed, the nature of RT-FM appears to be controversial
and not clearly understood. In this study, we propose to clarify and shed light
on some of theses existing issues. A detailed study of the critical
temperatures and low energy magnetic excitations in Mn doped ZrO$_2$ is
performed. We show that the Curie temperatures were largely overestimated
previously, due to the inadequate treatment of both thermal and transverse
fluctuations, and disorder. It appears that the Mn-Mn couplings can not explain
the observed RT-FM. We argue, that this can be attributed to the interaction
between large moments induced in the vicinity of the manganese. This is similar
to the non-magnetic defect induced ferromagnetism reported in oxides,
semiconductors and graphene/graphite.",1312.0808v1
2014-02-06,Bi containing multiferroic perovskite oxide thin films,"In this work multiferroic thin films of Bi containing perovskite oxides are
discussed, where the driving force for ferroelectricity are the Bi3+ lone-pair
electrons. First, a brief introduction of Bi containing multiferroic perovskite
oxides will be presented to describe the mechanisms for establishing magnetic
and ferroelectric order in these compounds and some recent developments in this
field of research are reported. The second section addresses experimental
aspects of epitaxial thin film growth of BiMnO3, (Bi0.9La0.1)2NiMnO6 (BLNMO)
and BiFeO3 thin films by pulsed laser deposition. The third section is
dedicated to the physical properties of such films in terms of structural
characterization and the magnetic and ferroelectric properties and their
correlations in form of magnetoelectric coupling (MEC).",1402.1442v2
2015-01-16,"Spectroscopic Studies of Iron-based Superconductors, Multi-ferroic Oxides and Double-perovskite: Phonons, Electronic and Spin Excitations","Raman spectroscopy is a very powerful probe to study the nature of
quasi-particle excitations in condensed matter physics. The work presented in
this thesis is focused on two different families of novel materials, namely the
iron-based superconductors (FeBS), multiferroic oxides and double perovskite.
Although the properties of these two systems are quite different, some
comparison can still be drawn between them. For instance, in both of these
systems magnetism plays a crucial role and intricate coupling between phononic,
magnetic and orbital degrees of freedom is crucial to understand their
underlying physics responsible for their various exotic physical properties.
Understanding the microscopic origin of quasi-particle excitations, such as
phonons, magnons, orbitons, plasmons etc., and coupling between them in these
complex materials, has been an intense field of research because it is believed
that these excitations hold the key for explaining their rich physics. The
systems studied in the thesis include (A) FeBS - (i) FeSe0.82 (ii)
Ce1-zYzFeAsO1-xFx (z = 0, 0.4; x = 0.1, 0.2) (iii) Ca4Al2O5.7Fe2As2 (iv)
Ca(Fe1-xCox)2As2 (x = 0.03, 0.05). (B) Multiferroic oxides - (i) AlFeO3 (ii)
TbMnO3 and double perovskite (iii) La2NiMnO6.",1501.04055v1
2015-05-19,Pair breaking in multi-orbital superconductors: an application to oxide interfaces,"We investigate the impact of impurity scattering on superconductivity in an
anisotropic multi-orbital model with spin-orbit coupling which describes the
electron fluid at two-dimensional oxide interfaces. As the pairing mechanism is
under debate, both conventional and unconventional superconducting states are
analyzed. We consider magnetic and nonmagnetic spin-dependent intra- and
interorbital scattering and discuss possible microscopic realizations leading
to these processes. It is found that, for magnetic disorder, the unconventional
superconductor is protected against interband scattering and, thus, more robust
than the conventional condensate. In case of nonmagnetic impurities, the
conventional superconductor is protected as expected from the Anderson theorem
and the critical scattering rate of the unconventional state is enhanced by a
factor of four due to the spin-orbit coupling and anisotropic masses in oxide
interfaces.",1505.04919v1
2015-11-23,Structure and ferromagnetic instability of the oxygen-deficient SrTiO$_3$ surface,"SrTiO$_3$ (STO) is the substrate of choice to grow oxide thin-films and oxide
heterojunctions, which can form quasi-two-dimensional electronic phases that
exhibit a wealth of phenomena, and, thus, a workhorse in the emerging field of
metal-oxide electronics. Hence, it is of great importance to know the exact
character of the STO surface itself under various oxygen environments. Using
density functional theory within the spin generalized gradient approximation we
have investigated the structural, electronic and magnetic properties of the
oxygen-deficient STO surface. We find that the surface oxygen vacancies order
in periodic arrays giving rise to surface magnetic moments and a quasi
two-dimensional electron gas in the occupied Ti 3-d orbitals. The surface
confinement, the oxygen-vacancy ordering, and the octahedra distortions give
rise to spin-polarized $t_{2g}$ dispersive sub-bands; their energy split near
the Brillouin zone center acts as an effective Zeeman term, which, when we turn
on a Rashba interaction, produces bands with momentum-spin correlations similar
to those recently discovered on oxygen deficient STO surface.",1511.07495v1
2016-06-30,Tunneling into a quantum confinement created by a single-step nano-lithography of conducting oxide interfaces,"A new nano-lithography technique compatible with conducting oxide interfaces,
which requires a single lithographic step with no additional amorphous layer
deposition or etching, is presented. It is demonstrated on SrTiO3/LaAlO3
interface where a constriction is patterned in the electron liquid. We find
that an additional back-gating can further confine the electron liquid into an
isolated island. Conductance and differential conductance measurements show
resonant tunneling through the island. The data at various temperatures and
magnetic fields are analyzed and the effective island size is found to be of
the order of 10nm. The magnetic field dependence suggests absence of spin
degeneracy in the island. Our method is suitable for creating superconducting
and oxide-interface based electronic devices.",1606.09340v1
2017-01-23,"Time-reversal symmetry breaking hidden order in Sr$_2$(Ir,Rh)O$_4$","Layered 5$d$ transition iridium oxides, Sr$_2$(Ir,Rh)O$_4$, are described as
unconventional Mott insulators with strong spin-orbit coupling. The undoped
compound, Sr$_2$IrO$_4$, is a nearly ideal two-dimensional pseudospin-$1/2$
Heisenberg antiferromagnet, similarly to the insulating parent compound of
high-temperature superconducting copper oxides. Using polarized neutron
diffraction, we here report a hidden magnetic order in pure and doped
Sr$_2$(Ir,Rh)O$_4$, distinct from the usual antiferromagnetic pseudo-spin
ordering. We find that time-reversal symmetry is broken while the lattice
translation invariance is preserved in the hidden order phase. The onset
temperature matches that of the odd-parity hidden order recently highlighted
using optical second harmonic generation experiments. The novel magnetic order
and broken symmetries can be explained by the loop-current model, previously
predicted for the copper oxide superconductors.",1701.06485v1
2012-04-13,NO-assisted molecular-beam epitaxial growth of nitrogen substituted EuO,"We have investigated a method for substituting oxygen with nitrogen in EuO
thin films, which is based on molecular beam epitaxy distillation with NO gas
as the oxidizer. By varying the NO gas pressure, we produce crystalline,
epitaxial EuO_(1-x)N_x films with good control over the films' nitrogen
concentration. In-situ x-ray photoemission spectroscopy reveals that nitrogen
substitution is connected to the formation Eu3+ 4f6 and a corresponding
decrease in the number of Eu2+ 4f7, indicating that nitrogen is being
incorporated in its 3- oxidation state. While small amounts of Eu3+ in
over-oxidized Eu_(1-delta)O thin films lead to a drastic suppression of the
ferromagnetism, the formation of Eu3+ in EuO_(1-x)N_x still allows the
ferromagnetic phase to exist with an unaffected Tc, thus providing an ideal
model system to study the interplay between the magnetic f7 (J=7/2) and the
non-magnetic f6 (J=0) states close to the Fermi level.",1204.2861v1
2015-12-19,Structural evolution of epitaxial SrCoOx films near topotactic phase transition,"Control of oxygen stoichiometry in complex oxides via topotactic phase
transition is an interesting avenue to not only modifying the physical
properties, but utilizing in many energy technologies, such as energy storage
and catalysts. However, detailed structural evolution in the close proximity of
the topotactic phase transition in multivalent oxides has not been much
studied. In this work, we used strontium cobaltites (SrCoOx) epitaxially grown
by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven
evolution of the structure, electronic, and magnetic properties. We grew
coherently strained SrCoO2.5 thin films and performed post-annealing at various
temperatures for topotactic conversion into the perovskite phase
(SrCoO3-{\delta}). We clearly observed significant changes in electronic
transport, magnetism, and microstructure near the critical temperature for the
topotactic transformation from the brownmillerite to the perovskite phase.
Nevertheless, the overall crystallinity was well maintained without much
structural degradation, indicating that topotactic phase control can be a
useful tool to control the physical properties repeatedly via redox reactions.",1512.06167v1
2015-12-21,"Novel synthesis method of nonstoichiometric Na2-xIrO3. Crystal structure, transport and magnetic properties","Transition metal oxides with 4d or 5d metals are of great interest due to the
competing interactions, of the Coulomb repulsion and the itineracy of the
d-electrons, opening a possibility of building new quantum ground states.
Particularly the 5d metal oxides containing Iridium have received significant
attention within the last years, due to their unexpected physical properties,
caused by a strong spin orbit coupling observed in Ir(IV). A prominent example
is the Mott-insulator Sr2IrO4. Another member of this family, the honeycomb
lattice compound Na2IrO3, also being a Mott-insulator having, most probably, a
Kitaev spin liquid ground state. By deintercalating sodium from Na2IrO3, we
were able to synthesize a new honeycomb lattice compound with more than 50%
reduced sodium content. The reduction of the sodium content in this layered
compound leads to a change of the oxidation state of iridium from +IV to +V/+VI
and a symmetry change from C2/c to P-3. This goes along with significant
changes of the physical properties. Besides the vanishing magnetic ordering at
15K, also the transport properties changes and instead insulating
semiconducting properties are observed.",1512.06627v1
2016-04-30,Thermal stimulated current response in cupric oxide single crystal thin films over a wide temperature range,"Cupric oxide single crystal thin films were grown by plasma-assisted
molecular beam epitaxy. X-ray diffraction, Raman spectrum and in situ
reflection high-energy electron diffraction show that the thin films are 2x2
reconstructed with an in-plane compression and out-of-plane stretching. Thermal
stimulated current measurement indicates that the electric polarization
response presents in the special 2D cupric oxide single crystal thin film over
a wide temperature range from 130 K to near-room temperature. We infer that the
abnormal electric response involves the changing of phase transition
temperature induced by structure distortion, the spin frustration and magnetic
fluctuation effect of short-range magnetic order, or the combined action of
both two factors mentioned above. This work suggests a promising clue for
finding new room temperature single phase multiferroics or tuning phase
transition temperature.",1605.00109v1
2016-12-30,Exchange Bias Effects in Iron Oxide-Based Nanoparticle Systems,"The exploration of exchange bias (EB) on the nanoscale provides a novel
approach to improving the anisotropic properties of magnetic nanoparticles for
prospective applications in nanospintronics and nanomedicine. However, the
physical origin of EB is not fully understood. Recent advances in chemical
synthesis provide a unique opportunity to explore EB in a variety of iron
oxide-based nanostructures ranging from core/shell to hollow and hybrid
composite nanoparticles. Experimental and atomistic Monte Carlo studies have
shed light on the roles of interface and surface spins in these nanosystems.
This review paper aims to provide a thorough understanding of the EB and
related phenomena in iron oxide-based nanoparticle systems, knowledge of which
is essential to tune the anisotropic magnetic properties of exchange-coupled
nanoparticle systems for potential applications.",1612.09455v1
2017-11-11,Spin-orbital polarons in electron doped copper oxides,"Present work demonstrates the formation of spin-orbital polarons in electron
doped copper oxides, that arise due to doping-induced polarisation of the
oxygen orbitals in the CuO$_2$ planes. The concept of such polarons is
fundamentally different from previous interpretations. The novel aspect of
spin-orbit polarons is best described by electrons becoming self-trapped in
one-dimensional channels created by polarisation of the oxygen orbitals. The
one-dimensional channels form elongated filaments with two possible
orientations, along the diagonals of the elementary CuO$_2$ square plaquette.
As the density of doped electrons increases multiple filaments are formed.
These may condense into a single percollating filamentary phase. Alternatively,
the filaments may cross perpendicularly to create an interconnected conducting
quasi-one-dimensional web. At low electron doping the antiferromagnetic (AFM)
state and the polaron web coexist. As the doping is increased the web of
filaments modifies and transforms the AFM correlations leading to a series of
quantum phase transitions - which affect the normal and superconducting state
properties.",1711.04164v1
2017-11-30,Complementary logic operation based on electric-field controlled spin-orbit torques,"Spintronic devices as alternatives to traditional semiconductor-based
electronic devices attract considerable interest as they offer zero quiescent
power, built-in memory, scalability, and reconfigurability. To realize
spintronic logic gates for practical use, a complementary logic operation is
essential but still missing despite a recent progress in spin-based logic
devices. Here, we report the development of a complementary spin logic device
using electric-field controlled spin-orbit torque (SOT) switching. In heavy
metal/ferromagnet/oxide structures, the critical current for SOT-induced
switching of perpendicular magnetization is efficiently modulated by an
electric field via voltage-controlled magnetic anisotropy (VCMA) effect in a
non-volatile manner. Moreover, the polarity of the VCMA is tuned by the
modification of oxidation state at the ferromagnet/oxide interface. This allows
us to fabricate both n-type and p-type spin logic devices and to enable a
complementary logic operation, paving the way for the development of
non-volatile and reconfigurable logic devices.",1711.11172v1
2019-02-26,"Magnetic, electrochemical and thermoelectric properties of $P2 - Na_x(Co_{7/8}Sb_{1/8})O_2$","We theoretically investigated the electronic, electrochemical and magnetic
properties of Sb doped $Na_xCoO_2$ ($x = 1, 0.75$ and $0.50$). $Sb_{Co}$
dopants adopt +5 oxidation state in $Na_xCoO_2$ host lattice for all Na
concentrations ($x$). Due to high oxidation states, $Sb^{5+}$ strongly repels
Na ions and therefore it decreases the electrochemical potential (vs.
Na/Na$^+$). The electrons introduced by $Sb^{5+}$ localize on nearby Co ions
creating $Co^{2+}$ species which are absent in undoped $Na_xCoO_2$. $Co^{2+}$
ions reduce the spin entropy flow decreasing the Seebeck coefficient in the Sb
doped compounds. The results can be generalized to other dopants with high
oxidation state.",1902.09760v1
2019-08-23,Damping enhancement in coherent ferrite/insulating-paramagnet bilayers,"High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are
promising nanoscale building blocks for all-oxide heterostructures driven by
pure spin current. However, the impact of oxide interfaces on spin dynamics in
such heterostructures remains an open question. Here, we investigate the spin
dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO
coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of
paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO
without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a
factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this
damping enhancement to spin scattering at the $\sim$1-nm-thick chemically
disordered layer at the MAFO/CCO interface, rather than spin pumping or
proximity-induced magnetism. Our results indicate that damping in ferrite-based
heterostructures is strongly influenced by interfacial chemical disorder, even
if the thickness of the disordered layer is a small fraction of the ferrite
thickness.",1908.08629v2
2020-03-27,Perspective: Strongly correlated and topological states in [111] grown transition metal oxide thin films and heterostructures,"We highlight recent advances in the theory, materials fabrication, and
experimental characterization of strongly correlated and topological states in
[111] oriented transition metal oxide thin films and heterostructures, which
are notoriously difficult to realize compared to their [001] oriented
counterparts. We focus on two classes of complex oxides, with the chemical
formula ABO3 and A2B2O7, where the B sites are occupied by an open-shell
transition metal ion with a local moment, and the A sites are typically a rare
earth. The [111] oriented quasi-two-dimensional lattices derived from these
parent compound lattices can exhibit peculiar geometries and symmetries,
namely, a buckled honeycomb lattice, as well as kagome and triangular lattices.
These lattice motifs form the basis for emergent strongly correlated and
topological states expressed in exotic magnetism, various forms of orbital
ordering, topological insulators, topological semimetals, quantum anomalous
Hall insulators, and quantum spin liquids. For transition metal ions with high
atomic number, spin-orbit coupling plays a significant role and may give rise
to additional topological features in the electronic band structure and in the
spectrum of magnetic excitations. We conclude the Perspective by articulating
open challenges and opportunities in this actively developing field.",2003.12211v1
2021-12-22,Neutron Scattering Studies of the Breathing Pyrochlore Antiferromagnet LiGaCr$_{4}$O$_{8}$,"We report neutron scattering measurements of the spinel oxide
LiGaCr$_{4}$O$_{8}$, in which magnetic ions Cr$^{3+}$ form a breathing
pyrochlore lattice. Our experiments reveal the coexistence of a nearly
dispersionless resonance mode and dispersive spin wave excitations in the
magnetically ordered state, which can be quantitatively described by a quantum
spin model of hexagonal loops and linear spin wave theory with the same set of
exchange parameters, respectively. Comparison to other Cr spinel oxides reveals
a linear relationship between the resonance energy and lattice constant across
all these materials, which is in agreement with our hexagonal loop
calculations. Our results suggest a unified picture for spin resonances in Cr
spinel oxides.",2112.11709v1
2022-12-23,Surface ferromagnetism in a chiral topological semimetal CoSi,"Despite the chiral topological semimetal CoSi is known as bulk diamagnetic,
it shows unusual surface ferromagnetism of debatable origin. The ferromagnetic
ordering has been attributed to the distorted bonds, the superlattice of
ordered vacancies, or even to topological surface textures due to the spin
polarization in the neighboring Fermi arcs. We experimentally compare
magnetization reversal curves for initially oxidized CoSi single crystals and
cleaved samples with a fresh, oxide-free surface. While the oxidized CoSi
samples do not show sizable ferromagnetism, the fresh CoSi surface gives a
strong ferromagnetic response, which is accompanied by the pronounced
modulation of the angle dependence of magnetization, as it can be expected for
easy and hard axes in a ferromagnet. In addition to the first order reversal
curves analysis, this observation allows us to distinguish between different
mechanisms of the ferromagnetic ordering in CoSi single crystals. We conclude
that the surface states-induced RKKY interaction between distorted bonds near
the sample surface is responsible for the strong ferromagnetic multi-domain
behavior for freshly cleaved samples.",2212.12383v2
2023-11-15,Thermal Magnetoelectrics in all Inorganic Quasi-Two-Dimensional Halide Perovskites,"From lithium-ion batteries to high-temperature superconductors, oxide
materials have been widely used in electronic devices. However, demands of
future technologies require materials beyond oxides, as anion chemistries
distinct from oxygen can expand the palette of mechanisms and phenomena, to
achieve superior functionalities. Examples include nitride-based wide bandgap
semiconductors and halide perovskite solar cells, with MAPbBr3 being a
representation revolutionizing photovoltaics research. Here, we demonstrate
magnetoelectric behaviour in quasi-two-dimensional halides (K,Rb)3Mn2Cl7
through simultaneous thermal control of electric and magnetic polarizations by
exploiting a polar-to-antipolar displacive transition. Additionally, our
calculations indicate a possible polarization switching path including a strong
magnetoelectric coupling, indicating halides can be excellent platforms to
design future multiferroic and ferroelectric devices. We expect our findings to
broaden the exploration of multiferroics to non-oxide materials and open access
to novel mechanisms, beyond conventional electric/magnetic control, for
coupling ferroic orders.",2311.09324v1
2023-12-11,Phase transitions of LaMnO$_3$ and SrRuO$_3$ from DFT + U based machine learning force fields simulations,"Perovskite oxides are known to exhibit many magnetic, electronic and
structural phases as function of doping and temperature. These materials are
theoretically frequently investigated by the DFT+U method, typically in their
ground state structure at $T=0$. We show that by combining machine learning
force fields (MLFFs) and DFT+U based molecular dynamics, it becomes possible to
investigate the crystal structure of complex oxides as function of temperature
and $U$. Here, we apply this method to the magnetic transition metal compounds
LaMnO$_3$ and SrRuO$_3$. We show that the structural phase transition from
orthorhombic to cubic in LaMnO$_3$, which is accompanied by the suppression of
a Jahn-Teller distortion, can be simulated with an appropriate choice of $U$.
For SrRuO$_3$, we show that the sequence of orthorhombic to tetragonal to cubic
crystal phase transitions can be described with great accuracy. We propose that
the $U$ values that correctly capture the temperature-dependent structures of
these complex oxides, can be identified by comparison of the MLFF simulated and
experimentally determined structures.",2312.06492v1
2019-04-12,The magnetic structure factor of correlated moments in small-angle neutron scattering,"The interplay between structural and magnetic properties of nanostructured
magnetic materials allows to realize unconventional magnetic effects, which
results in a demand for experimental techniques to determine the magnetization
profile with nanoscale resolution. Magnetic small-angle neutron scattering
(SANS) probes both the chemical and magnetic nanostructure and is thus a
powerful technique e.g. for the characterization of magnetic nanoparticles.
Here, we show that the conventionally used particle-matrix approach to describe
SANS of magnetic particle assemblies, however, leads to a flawed
interpretation. As remedy, we provide general expressions for the
field-dependent 2D magnetic SANS cross-section of correlated moments. It is
shown that for structurally disordered ensembles the magnetic structure factor
is in general, and contrary to common assumptions, (i) anisotropic also in zero
field, and (ii) that even in saturation the magnetic structure factor deviates
from the nuclear one. These theoretical predictions explain qualitatively the
intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled
iron oxide nanoparticles.",1904.06243v3
2023-09-24,FeCo Nanowire-Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products,"Due to the issues associated with rare-earth elements, there arises a strong
need for magnets with properties between those of ferrites and rare-earth
magnets that could substitute the latter in selected applications. Here, we
produce a high remanent magnetization composite bonded magnet by mixing FeCo
nanowire powders with hexaferrite particles. In the first step, metallic
nanowires with diameters between 30 and 100 nm and length of at least 2 {\mu}m
are fabricated by electrodeposition. The oriented as-synthesized nanowires show
remanence ratios above 0.76 and coercivities above 199 kA/m and resist core
oxidation up to 300 {\deg}C due to the existence of a > 8 nm thin oxide
passivating shell. In the second step, a composite powder is fabricated by
mixing the nanowires with hexaferrite particles. After the optimal nanowire
diameter and composite composition are selected, a bonded magnet is produced.
The resulting magnet presents a 20% increase in remanence and an enhancement of
the energy product of 48% with respect to a pure hexaferrite (strontium
ferrite) magnet. These results put nanowire-ferrite composites at the forefront
as candidate materials for alternative magnets for substitution of rare earths
in applications that operate with moderate magnet performance.",2309.13724v1
1996-06-12,Temperature and Pressure Effects on the Resistivity of the Manganese Oxides,"The temperature and pressure effects on the resistivity of the manganese
oxides are studied analytically via the Kondo lattice model with a strong
Hund's coupling. We obtain analytically the single-particle density of states
on the Bethe lattice in the large connectivity limit using the analytical
variant of the dynamic Lanczos method. From the density of states for the doped
system, we obtain resistivity and show resistivity drop when temperature
crosses the magnetic transition point. We also demonstrate the effect of
pressure both below and above the transition temperature.",9606079v1
1996-08-23,NMR in copper-Oxide Metals,"The anomalous part of the NMR relaxation rate of coppernuclei in the normal
state of copper-oxide metals is calculated using the orbital magnetic parts of
the fluctuations derived in a recent theory to explain the long wavelength
transport anomalies. Oxygen and Yttrium reside on lattice sites at which the
anomalous contribution is absent at all hole densities. The frequency, momentum
dependence, and the form-factor of the fluctuations is predicted,which is
verifiable by inelastic neutron scattering experiments.",9608109v1
1997-10-22,X-Ray Resonant Scattering as a Direct Probe of Orbital Ordering in Transition-Metal Oxides,"X-ray resonant scattering at the K-edge of transition metal oxides is shown
to measure the orbital order parameter, supposed to accompany magnetic ordering
in some cases. Virtual transitions to the 3d-orbitals are quadrupolar in
general. In cases with no inversion symmetry, such as V$_2$O$_3$, treated in
detail here, a dipole component enhances the resonance. Hence, we argue that
the detailed structure of orbital order in V$_2$O$_3$ is experimentally
accessible.",9710232v1
2001-03-21,Spin-Peierls transition with strong structural fluctuations in the vanadium oxide VOSb$_{2}$O$_{4}$,"We report on the magnetic susceptibility and electron spin resonance
measurements on polycrystalline samples of the vanadium oxide
VOSb$_{2}$O$_{4}$, a quasi-one dimensional S=1/2 Heisenberg system. We show
that the susceptibility vanishes at zero temperature, as in a gapped system,
and we argue that this is due to a spin-Peierls transition with strong
structural fluctuations.",0103441v1
2001-09-04,Structural Phase Transition in the Superconducting Pyrochlore Oxide Cd2Re2O7,"We report a structural phase transition found at Ts = 200 K in a pyrochlore
oxide Cd2Re2O7 which shows superconductivity at Tc = 1.0 K. X-ray
diffractionexperiments indicate that the phase transition is of the second
order, from a high-temperature phase with the ideal cubic pyrochlore structure
(space group Fd-3m) to a low-temperature phase with another cubic structure
(space group F-43m). It is accompanied by a dramatic change in the resistivity
and magnetic susceptibility and thus must induce a significant change in the
electronic structure of Cd2Re2O7.",0109050v1
2001-11-08,Superconducting properties of the pyrochlore oxide Cd2Re2O7,"We report the superconducting properties of the pyrochlore oxide Cd2Re2O7.
The bulk superconducting transition temperature Tc is about 1.0 K, and the
upper critical field Hc2 determined by the measurement of specific heat under
magnetic fields is 0.29 T. The superconducting coherence length is estimated to
be 34 nm. Specific heat data measured on single crystals suggest that the
superconducting gap of Cd2Re2O7 is nodeless.",0111126v2
2003-06-27,Kagomé in triangular lattice: electronic state of CoO_2 layer with hexagonal structure,"The electronic state in layered cobalt oxides with hexagonal structure is
examined. We find that the electronic structure reflects the nature of the
Kagom\'e lattice hidden in the CoO_2 layer which consists of stacked triangular
lattices of oxygen ions and of cobalt ions. A fundamental model for the
electron system is proposed and the mechanism of the unique transport and
magnetic properties of the cobalt oxides are discussed in the light of the
model.",0306696v1
2004-03-24,New Pyrochlore Oxide Superconductor RbOs2O6,"We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The
compound crystallizes in the same beta-pyrochlore structure as the recently
discovered superconductor KOs2O6, where Os atoms form a corner-sharing
tetrahedral network called the pyrochlore lattice with Rb or K atoms in the
cage. Resistivity, magnetic susceptibility and specific heat measurements on
polycrystalline samples evidence a bulk superconductivity with Tc = 6.3 K.",0403601v2
2007-01-25,Spin-polarization coupling in multiferroic transition-metal oxides,"A systematic microscopic theory of magnetically induced ferroelectricity and
lattice modulation is presented for all electron configurations of
Mott-insulating transition-metal oxides. Various mechanisms of polarization are
identified in terms of a strong-coupling perturbation theory. Especially, the
spin-orbit interaction acting on the ligand p orbitals is shown to give the
ferroelectric polarization of the spin-current form, which plays a crucial role
particularly in eg systems. Semiquantitative agreements with the multiferroic
TbMnO3 are obtained. Predictions for X-ray and neutron scattering experiments
are proposed to clarify the microscopic mechanism of the spin-polarization
coupling in different materials.",0701614v1
2007-02-05,"Theory of Layered Iron Oxide on Frustrated Geometry: Electric Polarization, Magnetoelectric Effect and Orbital State","A layered iron oxide \rfeo ($R$: rare-earth elements) is an exotic dielectric
material with charge-order (CO) driven electric polarization and
magnetoelectric effect caused by spin-charge coupling. In this paper, a theory
of electronic structure and dielectric property in \rfeo is presented. Charge
frustration in paired-triangular lattices allows a charge imbalance without
inversion symmetry. Spin frustration induces reinforcement of this polar CO by
a magnetic ordering. We also analyze an orbital model for the Fe ion which does
not show a conventional long-range order.",0702087v2
2007-10-19,Paramagnonlike excitations and spin diffusion in magnetic resonance studies of copper oxide superconductors,"The relaxation function theory for a doped two-dimensional Heisenberg
antiferromagnetic system in the paramagnetic state for all wave vectors through
the Brillouin zone is presented in view of low frequency response of high-$T_c$
copper oxide superconductors. We deduced the regions of long lifetime [$T
\lesssim 400(1-4x)$ K] and ""overdamped"" [$T \gtrsim 700(1-4x)$ K]
paramagnonlike excitations in the temperature ($T$)-doping index ($x$) phase
diagram from plane oxygen nuclear spin-lattice relaxation rate $^{17}(1/T_1)$
data in up to optimally doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ thus providing the
regimes for the spin wave concept and the ''overdamped'' mode.",0710.3615v1
2007-10-25,The ground state phases of orbitally degenerate spinel oxides,"I review the microscopic spin-orbital Hamiltonian and ground state properties
of spin one-half spinel oxides with threefold $t_{2g}$ orbital degeneracy. It
is shown that for any orbital configuration a ground state of corresponding
spin only Hamiltonian is infinitely degenerate in the classical limit. The
extensive classical degeneracy is lifted by the quantum nature of the spins, an
effect similar to order-out-of-disorder phenomenon by quantum fluctuations.
This drives the system to a non-magnetic spin-singlet dimer manifold with a
residual degeneracy due to relative orientation of dimers. The magneto-elastic
mechanism of lifting the ``orientational'' degeneracy is also briefly reviewed.",0710.4773v1
2008-11-04,Dual electronic states in thermoelectric cobalt oxide,"We investigate the low temperature magnetic field dependence of the
resistivity in the thermoelectric misfit cobalt oxide [Bi1.7Ca2O4]0.59CoO2 from
60 K down to 3 K. The scaling of the negative magnetoresistance demonstrates a
spin dependent transport mechanism due to a strong Hund's coupling. The
inferred microscopic description implies dual electronic states which explain
the coexistence between localized and itinerant electrons both contributing to
the thermopower. By shedding a new light on the electronic states which lead to
a high thermopower, this result likely provides a new potential way to optimize
the thermoelectric properties.",0811.0498v1
2009-02-27,Modulation of superconductivity by spin canting in a hybrid antiferromagnet/superconductor oxide,"The proximity effect of a C-type antiferromagnet (C-AFM) with the spin
canting at low temperature is investigated in the hybrid
Nd0.35Sr0.65MnO3(NSCO)/YBa2Cu3O7(YBCO) oxide system through magnetic and
transport measurements. It is found that the onset of a spin-canted state
destroys partially the superconducting order parameter. Interestingly, due to
the instability of this spin-canted state, zero-resistivity recovers at the
offset of spin canting. Our result demonstrates clearly the high sensitivity of
superconducting order parameter to a modulation of internal field.",0902.4737v1
2011-02-18,Electron spin diffusion at the interface of multiferroic oxides,"We study the spin diffusion in a two-dimensional electron gas at the
interface of oxide heterostructure LaAlO$_3$/SrTiO$_3$ grown on multiferroic
TbMnO$_3$ at 15 K by means of the kinetic spin Bloch equation approach. The
spiral magnetic moments of Mn$^{3+}$ in TbMnO$_3$ interact with the diffusing
spins at the LaAlO$_3$/SrTiO$_3$ interface via the Heisenberg exchange
interaction. It is demonstrated that the spin diffusion length is always
finite, despite the polarization direction of the injected spins. Our study
also reveals the important role played by the Coulomb scattering, which can
effectively suppress the spin diffusion.",1102.3757v1
2011-09-06,Topological insulators from complex orbital order in transition-metal oxides heterostructures,"Topological band insulators which are dynamically generated by
electron-electron interactions have been the- oretically proposed in two and
three dimensional lattice models. We present evidence that the two-dimensional
version can be stabilized in digital (111) heterostructures of transition-metal
oxides as a result of purely local interactions. The topological phases are
accompanied by spontaneous ordering of complex orbitals and we discuss their
stability with respect to the Hund's rule coupling, Jahn-Teller interaction and
inversion symmetry breaking terms. As main competitors we identify spin-nematic
and magnetic phases.",1109.1297v2
2015-03-25,All-oxide spin Seebeck effects,"We report the observation of longitudinal spin Seebeck effects (LSSE) in an
all-oxide bilayer system comprising an IrO$_2$ film and an Y$_3$Fe$_5$O$_{12}$
film. Spin currents generated by a temperature gradient across the
IrO$_2$/Y$_3$Fe$_5$O$_{12}$ interface were detected as electric voltage via the
inverse spin Hall effect in the conductive IrO$_2$ layer. This electric voltage
is proportional to the magnitude of the temperature gradient and its magnetic
field dependence is well consistent with the characteristic of the LSSE. This
demonstration may lead to the realization of low-cost, stable, and transparent
spin-current-driven thermoelectric devices.",1503.07378v1
2017-03-04,"Specific Cation Diffusion across the (La,Sr)MnO3 (Ce,Gd)O2 interface in SOFCs","Oxide interfaces play very important roles for the physical and chemical
properties of nanostructured materials, such as an ionic conductivity,
superconductivity, and magnetism. Gadolinia-doped Ceria (GDC) is commonly
selected as the interlayer between (La,Sr)MnO3 and Y2O3-stabilized ZrO2 in fuel
cells. The chemical expansions across the oxide interlayer were carefully
examined at the atomic resolution in order to understand the cation diffusion
and existence of oxygen deficiency at the interfaces.",1703.01373v1
2016-08-09,Search for the magnetocaloric effect in multiferroics oxides,"In this paper, we report on the magnetocaloric properties of some selected
multiferroic oxides, namely HoMn2O5 and La2(Ni,Co)MnO6 compounds which exhibit
transition points from 10K up to almost room temperature. In order to avoid
grain boundary effects and structural inhomogeneity observed frequently in
polycrystalline samples, only single crystals were considered for this study.",1608.02809v1
2016-12-16,Relaxation mechanism driven by spin angular momentum absorption throughout antiferromagnetic phase transition in NiFe surface oxides,"We report an alternative mechanism for the physical origin of the
temperature-dependent ferromagnetic relaxation of Permalloy (NiFe) thin films.
Through spin-pumping experiments, we demonstrate that the peak in the
temperature-dependence of NiFe damping can be understood in terms of enhanced
spin angular momentum absorption at the magnetic phase transition in
antiferromagnetic surface-oxidized layers. These results suggest new avenues
for the investigation of an incompletely-understood phenomenon in physics.",1612.05556v1
2017-11-08,Micromagnetic simulation study of a disordered model for one-dimensional granular perovskite manganite oxide nanostructures,"Chemical techniques are an efficient method to synthesize one-dimensional
perovskite manganite oxide nanostructures with a granular morphology, that is,
formed by arrays of monodomain magnetic nanoparticles. Integrating the
stochastic Landau-Lifshitz-Gilbert equation, we simulate the dynamics of a
simple disordered model for such materials that only takes into account the
morphological characteristics of their nanograins. We show that it is possible
to describe reasonably well experimental hysteresis loops reported in the
literature for single La_0.67Ca_0.33MnO_3 nanotubes and powders of these
nanostructures, simulating small systems consisting of only 100 nanoparticles.",1711.03159v2
2017-11-21,Current-induced spin polarization in isotropic k-cubed Rashba model: Theoretical study for p-doped semiconductor heterostructures and perovskite oxides interfaces,"Using the Matsubara Green's function formalism we calculate the temperature
dependence of the nonequilibrium spin polarization induced by an external
electric field in the presence of spin-orbit coupling. The model Hamiltonian
includes an isotropic k-cubed form of the Rashba spin-orbit interaction. Such a
Hamiltonian captures the electronic and spin properties of two-dimensional
electron (hole) gas at the surfaces or interfaces of transition metal oxides or
in p-doped semiconductor heterostructures. The induced spin polarization is
calculated for the nonmagnetic as well as magnetic electron/hole gas. Relation
of the spin polarization to the Berry curvature is also discussed.",1711.07707v1
2020-10-09,Tunable Magnetism and Insulator-Metal Transition in Bilayer Perovskites,"Two-dimensional (2D) transition-metal oxide perovskites greatly expand the
field of available 2D multifunctional material systems. Here, based on density
functional theory calculations, we predicted the presence of ferromagnetism
orders accompanying with an insulator-metal phase transition in bilayer
$KNbO_{3}$ and $KTaO_{3}$ by applying strain engineering and/or external
electric field. Our results will contribute to the applications of few-layer
transition metal oxide perovskites in the emerging spintronics and
straintronics.",2010.04766v1
2018-02-12,Canted ferrimagnetism and giant coercivity in the non-stoichiometric double perovskite La2Ni1.19Os0.81O6,"The non-stoichiometric double perovskite oxide La2Ni1.19Os0.81O6 was
synthesized by solid state reaction and its crystal and magnetic structures
were investigated by powder x-ray and neutron diffraction. La2Ni1.19Os0.81O6
crystallizes in the monoclinic double perovskite structure (general formula
A2BB'O6) with space group P21/n, where the B site is fully occupied by Ni and
the B' site by 19 % Ni and 81 % Os atoms. Using x-ray absorption spectroscopy
an Os4.5+ oxidation state was established, suggesting presence of about 50 %
paramagnetic Os5+ (5d3, S = 3/2) and 50 % non-magnetic Os4+ (5d4, Jeff = 0)
ions at the B' sites. Magnetization and neutron diffraction measurements on
La2Ni1.19Os0.81O6 provide evidence for a ferrimagnetic transition at 125 K. The
analysis of the neutron data suggests a canted ferrimagnetic spin structure
with collinear Ni2+ spin chains extending along the c axis but a non-collinear
spin alignment within the ab plane. The magnetization curve of
La2Ni1.19Os0.81O6 features a hysteresis with a very high coercive field, HC =
41 kOe, at T = 5 K, which is explained in terms of large magnetocrystalline
anisotropy due to the presence of Os ions together with atomic disorder. Our
results are encouraging to search for rare earth free hard magnets in the class
of double perovskite oxides.",1802.03874v1
2019-03-04,Structural and magnetic properties in sputtered iron oxide epitaxial thin films -- Magnetite Fe$_3$O$_4$ and epsilon ferrite e-Fe$_2$O$_3$,"Epitaxial thin film fabrication of iron oxides including magnetite Fe3O4 and
epsilon-ferrite epsilon-Fe2O3 with the potential for advancing electromagnetic
devices has been investigated, which led to the first ever epsilon-ferrite
epitaxial layer being synthesized in the conventional sputtering process.
Concerning Fe3O4 (100) / MgO (100) films, a cube-on-cube epitaxial relationship
and sharp rocking curves with FWHM of 50 - 350 arcsec were confirmed regardless
of the small amount of Ge additions. Sputtering Ar gas pressure PAr heavily
influenced their magnetic and transport properties. High PAr = 15 mTorr caused
a high magnetization of 6.52 kG for the Ge added sample and the clear Verwey
transition at 122 K for the non Ge addition case. Conversion electron Mossbauer
spectroscopy (CEMS) measurements revealed that low PAr < 10 mTorr causes Fe/O
off-stoichiometry on the oxidizing side for the non Ge addition case and the
reductive side for the Ge addition case, respectively. Regarding the
epsilon-Fe2O3 (001) / SrTiO3(111) epilayer synthesis, bilayer microstructure
composed of an approximately 5nm thick initially grown epsilon-Fe2O3 (001)
epilayer and subsequently grown e-Fe2O3 (001) epilayer was confirmed from
cross-sectional TEM observations. The coexistence of magnetically hard and soft
phases was confirmed from the magnetization measurements. As a possible
application of the single nm thick epsilon-Fe2O3 layer, 4-resistive-state
multiferroic tunnel junction (MFTJ) is considered.",1903.01022v1
2019-03-12,Zero Field Assembly of Long Magnetic Dipolar Chains in 2D Polymer Nanocomposite Films,"The existence of magnetic dipolar nanoparticle chains at zero field has been
predicted theoretically for decades, but these structures are rarely observed
experimentally. A prerequisite is a permanent magnetic moment on the particles
forming the chain. Here we report on the observation of magnetic dipolar chains
of spherical iron oxide nanoparticles with a diameter of
\SI{12.8}{\nano\meter}. The nanoparticles are embedded in an ultrathin polymer
film. Due to the high viscosity of the polymer matrix, the dominating
aggregation mechanism is driven by dipolar interactions. Smaller iron oxide
nanoparticles (\SI{9.4}{\nano\meter}) show no permanent magnetic moment and do
not form chains but compact aggregates. Mixed monolayers of different iron
oxide nanoparticles and polymer at the air-water interface are characterized by
Langmuir isotherms and in-situ X-ray reflectometry (XRR). The combination of
the particles with a polymer leads to a stable polymer nanocomposite film at
the air-water interface. XRR experiments show that nanoparticles are immersed
in a thin polymer matrix of \SI{3}{\nano\meter}. Using atomic force microscopy
(AFM) on Langmuir-Blodgett films, we measure the lateral distribution of
particles in the film. An analysis of single structures within transferred
films results in fractal dimensions that are in excellent agreement with 2D
simulations.",1903.04877v1
2021-06-07,High-mobility two-dimensional carriers from surface Fermi arcs in magnetic Weyl semimetal films,"High-mobility two-dimensional carriers originating from surface Fermi arcs in
magnetic Weyl semimetals are highly desired for accessing exotic quantum
transport phenomena and for topological electronics applications. Here, we
demonstrate high-mobility two-dimensional carriers that show quantum
oscillations in magnetic Weyl semimetal SrRuO3 epitaxial films by systematic
angle-dependent, high-magnetic field magnetotransport experiments. The
exceptionally high-quality SrRuO3 films were grown by state-of-the-art oxide
thin film growth technologies driven by machine learning algorithm. The quantum
oscillations for the 10-nm SrRuO3 film show a high quantum mobility of 3500
cm2/Vs, a light cyclotron mass, and two-dimensional angular dependence, which
can be attributed to the surface Fermi arcs. The linear thickness dependence of
the phase shift of the quantum oscillations provides evidence for the
non-trivial nature of the quantum oscillations mediated by the surface Fermi
arcs. In addition, at low temperatures and under magnetic fields of up to 52 T,
the quantum limit of SrRuO3 manifests the chiral anomaly of the Weyl nodes.
Emergence of the hitherto hidden two-dimensional Weyl states in a ferromagnetic
oxide pave the way to explore novel quantum transport phenomena for topological
oxide electronics.",2106.03292v2
2021-10-24,$^{139}$La-NMR study of spin-dynamics coupled with hole mobility in $T$*-type La$_{0.86}$Eu$_{0.86}$Sr$_{0.28}$CuO$_{4-δ}$,"In $T$*-type cuprate oxides with five oxygen coordination, little is known
about the relationship between the spin correlations and dope carriers. We
performed $^{139}$La-nuclear magnetic resonance (NMR) and electrical
resistivity measurements on an as-sintered (AS) and oxidation annealed (OA)
polycrystalline $T$*-type La$_{0.86}$Eu$_{0.86}$S$_{0.28}$CuO$_4$ (LESCO) to
investigate its magnetic and superconducting (SC) properties. Upon cooling, the
NMR spectrum of AS LESCO broadened below 3 K, at which the nuclear spin-lattice
relaxation rate $1/T_1$ against the temperature exhibited a maximum, thereby
indicating the appearance of static magnetism. The temperature dependence of
$1/T_1$ between 3 K and 20 K was similar to that of the resistivity displaying
the semiconducting behavior. Furthermore, the energy scale of the transport gap
and spin-dynamics estimated was found to be comparable. These results suggest a
close connection between the mobility of the doped carriers and low-energy
spin-dynamics, as reported for lightly doped $T$-type La$_{2-x}$Sr$_x$CuO$_4$.
In the OA SC sample, we confirmed the absence of a magnetic order and the
Korringa relation above 10 K. Therefore, in the $T$*-type LESCO with $x$ =
0.28, the magnetic state coupled with holes drastically turns to the weakly
correlated metallic state by oxidation annealing.",2110.12333v1
2022-12-21,"Large anomalous Hall, Nernst effect and topological phases in the 3d-4d/5d based oxide double perovskites","Magnetic topological quantum materials are attracting considerable attention
owing to their potential technological applications. However, only a small
number of these materials have been experimentally realized, thereby giving
rise to the need for new stable magnetic topological quantum materials.
Magnetism and spin-orbit coupling, two essential ingredients of the oxide
materials, lead to various topological transport phenomena such as the
anomalous Hall and anomalous Nernst effects, which can be significantly
enhanced by designing an electronic structure with a large Berry curvature. In
that respect, double perovskites with the general formula A$_2$BB'O$_6$ with an
alternating ordered arrangement of two transition metal sites, B(3d) and
B'(4d/5d), present attractive possibilities as they are robustly stable against
oxidation under ambient conditions and versatile. These double perovskites also
offer a high energy scale for magnetism as well as strong spin-orbit coupling
with a high magnetic ordering temperature. Here, using first-principles density
functional theory calculations, we present a comprehensive study of the
intrinsic anomalous transport for 3d-4d/5d based cubic and tetragonal stable
double perovskite (DP) compounds. A few of the DPs exhibit a very large
anomalous Hall effect with a distinct topological band crossing in the vicinity
of the Fermi energy. Our results show the importance of symmetries,
particularly the mirror planes, as well as the clean topological band crossing
near the Fermi energy, which is primarily contributed by the 5d-t$_{2g}$ for
large anomalous Hall and Nernst effects.",2212.11324v1
1997-08-29,Electronic States and Magnetic Propertis of Edge-sharing Cu-O Chains,"The electronic states and magnetic properties for the copper oxides
containing edge-sharing Cu-O chains such as Li$_2$CuO$_2$,
La$_6$Ca$_8$Cu$_{24}$O$_{41}$ and CuGeO$_3$ are systematically studied. The
optical conductivity $\sigma(\omega)$ and the temperature dependence of the
magnetic susceptibility $\chi(T)$ for single crystalline samples Li$_2$CuO$_2$
are measured as a reference system and analyzed by using the exact
diagonalization method for small Cu-O clusters. It is shown that the spectral
distribution of $\sigma(\omega)$ is different between edge-sharing and
corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is
larger than that of high-$T_{c}$ cuprates. The exchange interaction between
nearest-neighbor copper ions in edge-sharing chains $J_1$ depends sensitively
on the Cu-O-Cu bond angles. In addition to $J_1$, the exchange interaction
between next-nearest-neighbor copper ions $J_2$ has sufficient contribution to
the magnetic properties. We calculate $J_1$ and $J_2$ for all the copper oxides
containing edge-sharing Cu-O chains and discuss the magnetic properties.",9708232v2
2003-06-17,"Magnetic behaviour of quasi-one-dimensional oxides, Ca$_3$Co$_(1+x)$Mn$_{1-x}$O$_6$","The results of ac and dc magnetization and heat capacity measurements on the
oxides, Ca$_3$Co$_{1+x}$Mn$_{1-x}$O$_6$, forming in a K$_4$CdCl$_6$-derived
rhombohedral quasi-one-dimensional crystal structure, are reported. As far as
Ca$_3$Co$_2$O$_6$ is concerned, the results reveal truly complex nature of the
two magnetic transitions, identified to set in at 24 and 12 K in the previous
literature. However, partial replacement of Co by Mn apparently results in a
long magnetic ordering of an antiferromagnetic type (below 13 and 18 K for x=
0.0 and 0.25 respectively), instead of spin-glass freezing in spite of the fact
that there is Co-Mn disorder; in addition, interestingly there are hysteretic
spin reorientation effects as revealed by isothermal magnetization behavior.",0306426v1
2005-10-14,Crossover between local-moment magnetism and itinerant-electron magnetism in the t-J model,"A Kondo-lattice theory is applied to the crossover between local-moment
magnetism for almost half fillings of electrons and itinerant-electron
magnetism away from the half filling. In clean systems with no disorder, the
bandwidth W^* of quasiparticles is non-zero and of the order of |J| at T=0K
even in the limit of the half filling, with J the superexchange interaction
constant between nearest neighbors. The so called Gutzwiller's term also
contributes to W^* away from the half filling; it is approximately proportional
to doping concentrations measured from the half filling. Magnetism is enhanced
by disorder because the renormalization of W^* by J is reduced by disorder. The
asymmetry of disorder between electron-doped and hole-doped cuprate oxide
superconductors must be, at least partly, responsible for that of
antiferromagnetic phases between them. The so called Kumagai phase is
characterized as an SDW state in a disordered system rather than a spin glass.
The Neel temperature T_N about 300K of non-doped cuprate oxides can be
explained by the reduction of T_N by critical thermal antiferromagnetic
fluctuations in quasi-two dimensions.",0510377v1
2009-03-16,Spin Ice,"Geometric frustration usually arises in systems that comprise magnetic
moments (spins) which reside on the sites of a lattice made up of elementary
triangular or tetrahedral units and which interact via antiferromagnetic
nearest-neighbor exchange. Albeit much less common, geometric frustration can
also arise in systems with strong non-collinear single-ion easy-axis
(Ising-like) anisotropy and ferromagnetically} coupled spins. This is what
happens in some pyrochlore oxide materials where Ising-like magnetic rare earth
moments (Ho$^{3+}$, Dy$^{3+}$) sit on a lattice of corner-shared tetrahedra and
are coupled via effectively ferromagnetic (dipolar) interactions. These systems
possess a macroscopic number of quasi-degenerate classical ground states and
display an extensive low-temperature entropy closely related to the extensive
proton disorder entropy in common water ice. For this reason, these magnetic
systems are called {\it spin ice}. This chapter reviews the essential
ingredients of spin ice phenomenology in magnetic pyrochlore oxides.",0903.2772v1
2010-07-22,Strong reduction of V4+ amount in vanadium oxide/hexadecylamine nanotubes by doping with Co2+ and Ni2+ ions: EPR and magnetic studies,"In this work we present a complete characterization and magnetic study of
vanadium oxide/hexadecylamine nanotubes (VOx/Hexa NT's) doped with Co2+ and
Ni2+ ions. The morphology of the NT's has been characterized by Transmission
Electron Microscopy (TEM) while the metallic elements have been quantified by
Instrumental Neutron Activation Analysis (INAA) technique. The static and
dynamic magnetic properties were studied collecting data of magnetization as a
function of magnetic field and temperature and by Electron Paramagnetic
Resonance (EPR). We observed that the incorporation of metallic ions (Co2+,
S=3/2 and Ni2+, S=1) decrease notably the amount of V4+ ions in the system,
from 14-16% (non-doped case) to 2-4%, with respect to the total vanadium atoms
into the tubular nanostructure, improving considerably their potential
technological applications as Li-ion batteries cathodes.",1007.3968v1
2011-04-08,Magnetic nanocomposites at microwave frequencies,"Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.",1104.1535v1
2011-05-09,Unconventional Magnetism in a Nitrogen-Based Analogue of Cupric Oxide,"We have investigated the magnetic properties of CuNCN, the first
nitrogen-based analogue of cupric oxide, CuO. Our muon spin relaxation, nuclear
magnetic resonance and electron spin resonance studies reveal that classical
magnetic ordering is absent down to lowest temperatures. However, large
enhancement of spin correlations and unexpected inhomogeneous magnetism have
been observed below 80 K. We attribute this to a peculiar fragility of the
electronic state against weak perturbations due to geometrical frustration,
which selects between competing spin-liquid and more conventional frozen
states.",1105.1691v2
2012-12-26,Epitaxial strain induced magnetic transitions and phonon instabilities of the tetragonal SrRuO3,"Using density-functional theory calculations, we investigate the magnetic as
well as the dynamical properties of tetragonal SrRuO3 (SRO) under the influence
of epitaxial strain. It is found that both the tensile and compressive strain
in the xy-plane could induce the abrupt change in the magnetic moment of Ru
atom. In particular, under the in-plane ~4% compressive strain, a ferromagnetic
to nonmagnetic transition is induced. Whereas for the tensile strain larger
than 3%, the Ru magnetic moment drops gradually with the increase of the
strain, exhibiting a weak ferromagnetic state. We find that such magnetic
transitions could be qualitatively explained by the Stoner model. In addition,
frozen phonon calculations at {\Gamma} point reveal structural instabilities
could occur under both compressive and tensile strains. Such instabilities are
very similar to those of the ferroelectric perovskite oxides, even though SRO
remains to be metallic in the range we studied. These might have influence on
the physical properties of oxide supercells taking SRO as constituent.",1212.6132v1
2014-01-06,Engineering spin-orbital magnetic insulator by tailoring superlattices,"Novel interplay of spin-orbit coupling and electron correlations in complex
Ir oxides recently emerged as a new paradigm for correlated electron physics.
Because of a large spin-orbit coupling of ~0.5 eV, which is comparable to the
transfer energy t and the crystal field splitting $\Delta$ and Coulomb U, a
variety of ground states including magnetic insulator, band insulator,
semimetal and metal, shows up in a narrow materials phase space. Utilizing such
subtle competition of the ground states, we successfully tailor a spin-orbital
magnetic insulator out of a semimetal SrIrO$_3$ by controlling dimensionality
using superlattice of [(SrIrO$_3$)$_m$, SrTiO$_3$] and show that a magnetic
ordering triggers the transition to magnetic insulator. Those results can be
described well by a first-principles calculation. This study is an important
step towards the design and the realization of topological phases in complex Ir
oxides with very strong spin-orbit coupling.",1401.1066v1
2015-02-01,Lifshitz metal-insulator transition induced by the all-in/all-out magnetic order in the pyrochlore oxide Cd2Os2O7,"We investigate the metal-insulator transition (MIT) of the osmium pyrochlore
oxide Cd2Os2O7 through transport and magnetization measurements. The MIT and a
magnetic transition to the all-in/all-out (AIAO) order occur simultaneously at
227 K. We propose a mechanism based on a Lifshitz transition induced by the
AIAO magnetic order probably via strong spin-orbit couplings in the specific
semimetallic band structure. It is suggested, moreover, that two observed
puzzles, a finite conductivity near T = 0 and an emergence of weak
ferromagnetic moments, are not bulk properties but originate at magnetic domain
walls between two kinds of AIAO domains.",1502.00191v1
2015-11-30,Spin-orbit driven magnetic insulating state with ${J}_{\mathrm{eff}}\mathbf{=}1/2$ character in a 4d oxide,"The unusual magnetic and electronic ground states of 5d iridates has been
shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The
influence of appreciable but reduced SOC in creating the manifested magnetic
insulating states in 4d oxides is less clear, with one hurdle being the
existence of such compounds. Here we present experimental and theoretical
results on Sr$_4$RhO$_6$ that reveal SOC dominated behavior. Neutron
measurements show the octahedra are both spatially separated and locally ideal,
making the electronic ground state susceptible to alterations by SOC. Magnetic
ordering is observed with a similar structure to an analogous
${J}_{\mathrm{eff}}\mathbf{=}1/2$ Mott iridate. We consider the underlying role
of SOC in this rhodate with density functional theory and x-ray absorption
spectroscopy and find a magnetic insulating ground state with
${J}_{\mathrm{eff}}\mathbf{=}1/2$ character.",1511.09431v1
2018-02-26,Evolution of ferromagnetism in two-dimensional electron gas of LaTiO3/SrTiO3,"Understanding, creating, and manipulating spin polarization of
two-dimensional electron gases at complex oxide interfaces presents an
experimental challenge. For example, despite almost a decade long research
effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3
heterojunction is still an open question. Here, by using a prototypical
two-dimensional electron gas (2DEG) which emerges at the interface between band
insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3 , the experiment
reveals the evidence for magnetic phase separation in hole-doped Ti d1 t2g
system resulting in spin-polarized 2DEG. The details of electronic and magnetic
properties of the 2DEG were investigated by temperature-dependent d.c.
transport, angle-dependent X-ray photoemission spectroscopy, and
temperature-dependent magnetoresistance. The observation of clear hysteresis in
magnetotransport at low magnetic fields implies spin-polarization from magnetic
islands in the hole rich LaTiO3 near the interface. These findings emphasize
the role of magnetic instabilities in doped Mott insulators thus providing
another path for designing all-oxide structures relevant to spintronics
applications.",1802.09614v1
2014-03-16,Theory of the Magnetic Resonance for the High-$T_C$ Copper-Oxide Superconductors,"The magnetic response expected from a state characterized by rotating
antiferromagnetism in a neutron-scattering experiment is calculated. We predict
the occurrence of a peak at the frequency of the rotation of the rotating
antiferromagnetic order parameter. The doping dependence of this frequency is
very similar to that of the frequency of the magnetic resonance observed in the
neutron-scattering experiments for the hole-doped high-$T_C$ cuprates. This
leads us to propose the rotating antiferromagnetism as a possible mechanism for
this magnetic resonance. We conclude that while the magnitude of the rotating
antiferromagnetic order parameter was previously proposed to be responsible for
the pseudogap and the unusual thermodynamic and transport properties, the phase
of the rotating order parameter is proposed here to be responsible for the
unusual magnetic properties of the high-$T_C$ copper-oxide superconductors.",1403.3968v2
2016-08-10,Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3,"We report a detailed investigation of magnetization, magnetocaloric effect
and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to
perovskite family. Our results reveal that the compound is in canted magnetic
state (CMS) where ferromagnetic correlations are present in an
antiferromagnetic state. Magnetic entropy change of this compound follows a
power law (deltaS_M ~ H^m) dependence of magnetic field. In this compound,
inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional
magnetocaloric effect (CMCE) above it. The exponent m is found to be
independent of temperature and field only in the IMCE region. Investigation of
temperature and magnetic field dependence studies of exchange bias, reveal a
competition between effective Zeeman energy of the ferromagnetic regions and
anisotropic exchange energy at the interface between ferromagnetic and
antiferromagnetic regions. Variation of exchange bias due to temperature and
field cycling is also investigated.",1608.03223v1
2017-06-08,Characterization of physicochemical and colloidal properties of hydrogel chitosan-coated iron-oxide nanoparticles for cancer therapy,"Superparamagnetic iron oxide nanoparticles have recently been investigated
for their potential to kill cancer cells with promising results, owing to their
ability to be targeted and heated by magnetic fields. In this study, novel
hydrogel, chitosan Fe3O4 magnetic nanoparticles were synthesized to induce
magnetic hyperthermia, and targeted delivering of chemotherapeutics in the
cancer microenvironment. The characteristic properties of synthesized bare and
CS-MNPs were analyzed by various analytical methods: X-ray diffraction, Fourier
transformed infrared spectroscopy, Scanning electron microscopy and
Thermo-gravimetric analysis/differential thermal analysis. Magnetic
nanoparticles were successfully synthesized using the co-precipitation method.
This synthesis technique resulted in nanoparticles with an average particle
size of 16 nm. The pure obtained nanoparticles were then successfully
encapsulated with 4-nm-thick chitosan coating. The formation of chitosan on the
surface of nanoparticles was confirmed by physicochemical analyses. Heating
experiments at safe magnetic field (f = 100 kHz, H =10-20 kA m-1) revealed that
the maximum achieved temperature of water stable chitosan-coated nanoparticles
(50 mg ml-1) is fully in agreement with cancer therapy and biomedical
applications.",1706.02590v1
2017-06-20,Hidden peculiar magnetic anisotropy at the interface in a ferromagnetic perovskite-oxide heterostructure,"Understanding and controlling the interfacial magnetic properties of
ferromagnetic thin films are crucial for spintronic device applications.
However, using conventional magnetometry, it is difficult to detect them
separately from the bulk properties. Here, by utilizing tunneling anisotropic
magnetoresistance in a single-barrier heterostructure composed of
La0.6Sr0.4MnO3 (LSMO)/ LaAlO3 (LAO)/ Nb-doped SrTiO3 (001), we reveal the
presence of a peculiar strong two-fold magnetic anisotropy (MA) along the
[110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO.
This MA shows unknown behavior that the easy magnetization axis rotates by
90{\deg} at an energy of 0.2 eV below the Fermi level in LSMO. We attribute
this phenomenon to the transition between the eg and t2g bands at the LSMO
interface. Our finding and approach to understanding the energy dependence of
the MA demonstrate a new possibility of efficient control of the interfacial
magnetic properties by controlling the band structures of oxide
heterostructures.",1706.06300v1
2017-07-15,Structural and magnetic properties of lightly doped M-type hexaferrites,"Vanadium substituted SrM hexaferrites (SrFe12-xVxO19 with x = 0.2, 0.4) and
Eu-substituted BaM hexaferrite (Ba0.8Eu0.2Fe12O19) were prepared by high energy
ball milling and sintering at 1200{\deg} C. X-ray diffraction measurements
revealed that the V-substituted SrM samples exhibited phase separation
resulting in the coexistence of the pure SrM magnetic phase with nonmagnetic
Sr3(VO4)2 vanadate and {\alpha}-Fe2O3 iron oxide phase. Also, the
Eu-substituted BaM hexaferrite revealed the formation of the pure BaM phase
coexisting with {\alpha}-Fe2O3 secondary phase, and Eu-garnet minor phase.
Although the magnetic properties of the samples deteriorated with respect to
pure hexaferrite properties, the magnetic parameters of the substituted samples
were found to be of potential importance for practical applications. Further,
the results of the study suggest methods for the preparation of high quality
SrM hexaferrites, and hexaferrite/garnet composites.",1707.04709v1
2018-01-16,3D Crystallographic Alignment of Alumina Ceramics by Application of Low Magnetic Fields,"Non-cubic crystals exhibit anisotropic physical and functional properties.
Microscopic crystallites as constituents of polycrystalline materials are
randomly oriented, thus polycrystalline ceramics lack the anisotropic
properties of their monocrystalline counterparts. We propose a technology that
exploits the synergy between magnetic alignment and colloidal ceramics
processing, and enables to independently tune the orientation of grains in
different sample regions by infinitesimal magnetic fields (<10 millitesla). The
grain pivot mechanism enables the emulation of single crystals, as well as the
creation of large complex-shaped ceramic elements with designed
crystallographic landscapes and spatially and directionally tuned properties.
Ultra-high magnetic response arises from magnetic shape anisotropy of
platelet-shaped seed crystallites coated with small amounts of iron oxide
nanoparticles. To control crystallographic growth directions during subsequent
annealing procedures, the seeds are dispersed and aligned in a matrix of
chemically identical, but much finer spherical particles. The degree of
crystalline orientation in accordingly prepared aluminum oxide exceeds 99%.
This technology opens an avenue to remarkably improve structural and functional
properties of ceramic elements employed in numerous industrial applications.",1801.05102v3
2020-12-18,Frustrated Magnetism in Fluoride and Chalcogenide Pyrochlore Lattice Materials,"Pyrochlore lattices, which are found in two important classes of materials --
the $A_2B_2X_7$ pyrochlore family and the $AB_2X_4$ spinel family -- are the
quintessential 3-dimensional frustrated lattice architecture. While
historically oxides ($X =$~O) have played the starring role in this field, the
past decade has seen materials synthesis breakthroughs that have lead to the
emergence of fluoride ($X =$~F) and chalcogenide ($X =$~S, Se) pyrochlore
lattice materials. In this Research Update, we summarize recent progress in
understanding the magnetically frustrated ground states in three families of
non-oxide pyrochlore lattice materials: (i) $3d$-transition metal fluoride
pyrochlores, (ii) rare earth chalcogenide spinels, and (iii) chromium
chalcogenide spinels with a breathing pyrochlore lattice. We highlight how the
change of anion can modify the single ion spin anisotropy due to crystal
electric field effects, stabilize the incorporation of new magnetic elements,
and dramatically alter the exchange pathways and thereby lead to new magnetic
ground states. We also consider a range of future directions -- materials with
the potential to define the next decade of research in frustrated magnetism.",2012.10060v2
2021-03-11,Stimuli-responsive assembly of iron oxide nanoparticles into magnetic flexible filaments,"The combination of multiple functionalities in a single material is an
appealing strategy for the de-velopment of smart materials with unique
features. In this work, we present the preparation of thermoresponsive magnetic
nanoparticles and their one-dimensional assembly into transient
micro-filaments. The material is based on 9.4 nm iron oxide nanoparticles
grafted with poly(N-n-propylacrylamide) via multiphosphonic acid anchoring
sites. The hybrid nanoparticles present a low critical solution temperature
(LCST) transition between 21 {\deg}C and 28 {\deg}C, depending on the pH and
the ionic strength. When heated above the LCST in defined conditions, the
nanoparticles ag-gregate and respond to an external magnetic field. An
intrinsic characteristic of the thermorespon-sive particles is an asymmetric
transition between cooling and heating cycles, that was favorably exploited to
build one-dimensional permanent microstructures, such as magnetic
microfilaments and cilia. In summary, we present the development of a
nanoplatform responsive to multiple stimu-li, including temperature, magnetic
field, pH and ionic strength and its transformation into magneti-cally active
microfilaments that could find potential applications in remotely controlled
devices.",2103.06837v1
2021-07-16,Defect engineering of magnetic ground state in EuTiO$_3$ epitaxial thin films,"Atomistic defect engineering through the pulsed laser epitaxy of perovskite
transition metal oxides offers facile control of their emergent
opto-electromagnetic and energy properties. Among the various perovskite
oxides, EuTiO3 exhibits a strong coupling between the lattice, electronic, and
magnetic degrees of freedom. This coupling is highly susceptible to atomistic
defects. In this study, we investigated the magnetic phase of EuTiO$_3$
epitaxial thin films via systematic defect engineering. A magnetic phase
transition from an antiferromagnet to a ferromagnet was observed when the unit
cell volume of EuTiO3 expanded due to the introduction of Eu-O vacancies.
Optical spectroscopy and density functional theory calculations show that the
change in the electronic structure as the ferromagnetic phase emerges can be
attributed to the weakened Eu-Ti-Eu super-exchange interaction and the
developed ferromagnetic Eu-O-Eu interaction. Facile defect engineering in
EuTiO$_3$ thin films facilitates understanding and tailoring of their magnetic
ground state.",2107.07711v1
2022-05-22,Rashba spin-orbit interaction induced modulation of magnetic anisotropy,"In past few decades, Rashba spin-orbit coupling (SOC) has been successfully
employed for the emergence of exotic phenomena at the quantum oxide interfaces.
In these systems, the combined effect of charge transfer, broken symmetries and
SOC yields intriguing interfacial magnetism and transport properties. Here, we
provide an insight to control and tune interfacial phenomena in CaMnO3/CaIrO3
based 3d-5d oxide heterostructures by the charge transfer driven Rashba SOC.
Anomalous Hall effect in these canted antiferromagnetic heterostructures
originates from the intrinsic contribution associated with the topology of the
electronic band structure and it is mostly confined to the interface. Rashba
SOC reconstructs the Berry curvature and enhances the anomalous Hall
conductivity by two orders of magnitude. From the anisotropy magnetoresistance
measurements we demonstrate that Rashba SOC is instrumental in tailoring
magnetic anisotropy where magnetization easy-axis rotates from the out-of-plane
direction to the in-plane direction. The ability to tune Rashba SOC and
resulting competing magnetic anisotropy provides a route to manipulate
electronic band structure for the origin of non-trivial spin texture useful for
spin-orbitronics applications.",2205.10859v1
2022-06-06,Strain-induced magnetization control in an oxide multiferroic heterostructure,"Controlling magnetism by using electric fields is a goal of research towards
novel spintronic devices and future nano-electronics. For this reason,
multiferroic heterostructures attract much interest. Here we provide
experimental evidence, and supporting DFT analysis, of a transition in
La0.65Sr0.35MnO3 (LSMO) thin film to a stable ferromagnetic phase, that is
induced by the structural and strain properties of the ferroelectric BaTiO3
(BTO) substrate, which can be modified by applying external electric fields.
X-ray Magnetic Circular Dichroism (XMCD) measurements on Mn L edges with a
synchrotron radiation show, in fact two magnetic transitions as a function of
temperature that correspond to structural changes of the BTO substrate. We also
show that ferromagnetism, absent in the pristine condition at room temperature,
can be established by electrically switching the BTO ferroelectric domains in
the out-of-plane direction. The present results confirm that electrically
induced strain can be exploited to control magnetism in multiferroic oxide
heterostructures.",2206.02864v1
2023-01-12,Cryogenic temperature deposition of high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions on 300 mm wafers,"We developed a cryogenic temperature deposition process for high-performance
CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on 300 mm thermally oxidized
silicon wafers. The effect of the deposition temperature of the CoFeB layers on
the nanostructure, magnetic and magneto-transport properties of the MTJs were
investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a
perpendicular magnetic anisotropy (PMA) of 214 uJ/m2 and a voltage-controlled
magnetic anisotropy (VCMA) coefficient of -45 fJ/Vm, corresponding to 1.4- and
1.7-fold enhancements in PMA and VCMA, respectively, compared to the case of
room-temperature deposition of CoFeB. The improvement in the MTJ properties was
not simply due to the morphology of the MTJ films. The interface-sensitive
magneto-transport properties indicated that interfacial qualities such as
intermixing and oxidation states at the MgO/CoFeB interfaces were improved by
the cryogenic temperature deposition. Cryogenic-temperature sputtering
deposition is expected to be a standard manufacturing process for
next-generation magnetoresistive random-access memory.",2301.04823v1
2023-09-24,A Platform for Addressing Individual Magnetite Islands Grown Epitaxially on Ru(0001) and Manipulating Their Magnetic Domains,"We have grown high-quality magnetite micrometric islands on ruthenium stripes
on sapphire through a combination of magnetron sputtering (Ru film),
high-temperature molecular beam epitaxy (oxide islands), and optical
lithography. The samples have been characterized by atomic force microscopy,
Raman spectroscopy, X-ray absorption and magnetic circular dichroism in a
photoemission microscope. The magnetic domains on the magnetite islands can be
modified by the application of current pulses through the Ru stripes in
combination with magnetic fields. The modification of the magnetic domains is
explained by the Oersted field generated by the electrical current flowing
through the stripes underneath the magnetite nanostructures. The fabrication
method is applicable to a wide variety of rock salt and spinel oxides.",2309.14376v1
2008-02-14,"Enhanced annealing, high Curie temperature and low-voltage gating in (Ga,Mn)As: A surface oxide control study","(Ga,Mn)As and related diluted magnetic semiconductors play a major role in
spintronics research because of their potential to combine ferromagnetism and
semiconducting properties in one physical system. Ferromagnetism requires
~1-10% of substitutional Mn_Ga. Unintentional defects formed during growth at
these high dopings significantly suppress the Curie temperature. We present
experiments in which by etching the (Ga,Mn)As surface oxide we achieve a
dramatic reduction of annealing times necessary to optimize the ferromagnetic
film after growth, and report Curie temperature of 180 K at approximately 8% of
Mn_Ga. Our study elucidates the mechanism controlling the removal of the most
detrimental, interstitial Mn defect. The limits and utility of electrical
gating of the highly-doped (Ga,Mn)As semiconductor are not yet established; so
far electric-field effects have been demonstrated on magnetization with tens of
Volts applied on a top-gate, field effect transistor structure. In the second
part of the paper we present a back-gate, n-GaAs/AlAs/GaMnAs transistor
operating at a few Volts. Inspired by the etching study of (Ga,Mn)As films we
apply the oxide-etching/re-oxidation procedure to reduce the thickness (arial
density of carriers) of the (Ga,Mn)As and observe a large enhancement of the
gating efficiency. We report gatable spintronic characteristics on a series of
anisotropic magnetoresistance measurements.",0802.2080v1
2015-11-09,Proximity driven commensurate pinning in YBa2Cu3O7 through all-oxide magnetic nanostructures,"The design of artificial vortex pinning landscapes is a major goal towards
large scale applications of cuprate superconductors. While disordered
nanometric inclusions have shown to modify their vortex phase diagram and to
produce enhancements of the critical current1,2, the effect of ordered oxide
nanostructures remains essentially unexplored. This is due to the very small
nanostructure size imposed by the short coherence length, and to the
technological difficulties in the nanofabrication process. Yet, the novel
phenomena occurring at oxide interfaces open a wide spectrum of technological
opportunities to interplay with the superconductivity in cuprates. Here we show
that the unusual long range suppression of the superconductivity occurring at
the interface between manganites and cuprates affects vortex nucleation and
provides a novel vortex pinning mechanism. In particular, we show evidence of
commensurate pinning in YBCO films with ordered arrays of LCMO ferromagnetic
nanodots. Vortex pinning results from the proximity induced reduction of the
condensation energy at the vicinity of the magnetic nanodots, and yields an
enhanced friction between the nanodot array and the moving vortex lattice in
the liquid phase. This result shows that all-oxide ordered nanostructures
constitute a powerful, new route for the artificial manipulation of vortex
matter in cuprates.",1511.02750v1
2016-03-06,"Controlling Dzyaloshinskii-Moriya Interaction via Chirality Dependent Layer Stacking, Insulator Capping and Electric Field","Using first-principle calculations, we demonstrate several approaches to
manipulate Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin magnetic films.
First, we find that DMI is significantly enhanced when the ferromagnetic (FM)
layer is sandwiched between nonmagnetic (NM) layers inducing additive DMI in
NM/FM/NM structures. For instance, as Pt and Ir below Co induce DMI of opposite
chirality, inserting Co between Pt (below) and Ir (above) in Ir/Co/Pt trilayers
enhances the DMI of Co/Pt bilayers by 15\%. Furthermore, in case of Pb/Co/Pt
trilayers (Ir/Fe/Co/Pt multilayers), DMI can be enhanced by 50\% (almost
doubled) compared to Co/Pt bilayers reaching a very large DMI amplitude of 2.7
(3.2) meV/atom. Our second approach for enhancing DMI is to use oxide capping
layer. We show that DMI is enhanced by 60\% in Oxide/Co/Pt structures compared
to Co/Pt bilayers. Moreover, we unveiled the DMI mechanism at Oxide/Co inerface
due to interfacial electric field effect, which is different to Fert-Levy DMI
at FM/NM interfaces. Finally, we demonstrate that DMI amplitude can be
modulated using an electric field with efficiency factor comparable to that of
the electric field control of perpendicular magnetic anisotropy in transition
metal/oxide interfaces. These approaches of DMI controlling pave the way for
skyrmions and domain wall motion-based spintronic applications.",1603.01847v2
2017-09-05,Charge Localization and Ordering in A$_2$Mn$_8$O$_{16}$ Hollandite Group Oxides: Impact of Density Functional Theory Approaches,"The phases of A$_2$Mn$_8$O$_{16}$ hollandite group oxides emerge from the
competition between ionic interactions, Jahn-Teller effects, charge ordering,
and magnetic interactions. Their balanced treatment with feasible computational
approaches can be challenging for commonly used approximations in Density
Functional Theory. Three examples (A = Ag, Li and K) are studied with a
sequence of different approximate exchange-correlation functionals. Starting
from a generalized gradient approximation (GGA), an extension to include van
der Waals interactions and a recently proposed meta-GGA are considered. Then
local Coulomb interactions for the Mn $3d$ electrons are more explicitly
considered with the DFT+$U$ approach. Finally selected results from a hybrid
functional approach provide a reference. Results for the binding energy of the
A species in the parent oxide highlight the role of van der Waals interactions.
Relatively accurate results for insertion energies can be achieved with a low
$U$ and a high $U$ approach. In the low $U$ case, the materials are described
as band metals with a high symmetry, tetragonal crystal structure. In the high
$U$ case, the electrons donated by A result in formation of local Mn$^{3+}$
centers and corresponding Jahn-Teller distortions characterized by a local
order parameter. The resulting degree of monoclinic distortion depends on
charge ordering and magnetic interactions in the phase formed. The reference
hybrid functional results show charge localization and ordering. Comparison to
low temperature experiments of related compounds suggests that charge
localization is the physically correct result for the hollandite group oxides
studied here. . . .",1709.01390v1
2019-11-13,Superparamagnetic iron oxide nanoparticles conjugated with doxorubicin for targeting breast cancer,"Development of the next generations of cancer therapy modalities is currently
a crucial requirement of oncology. Advances in nanotechnology are bringing us
closer to the development of dual and multifunctional nanoparticles that are
challenging the traditional distinction between diagnostic and treatment
agents. The chase of innovative, multifunctional, more efficient, and safer
treatments is a major challenge in preclinical nanoparticle-mediated
thermotherapeutic research for breast cancer. Here, we report that iron oxide
nanoparticles have the dual capacity to act as both magnetic and drug delivery
agents. The aim of this work was to investigate the in vitro effect of the
loading of doxorubicin (DOX) on negatively charged polycarboxylic iron-oxide
nanoparticles (SPIONs) and Rhodamine B functionalized SPIONs on breast
carcinoma cell lines. For proper analysis and understanding of cell behavior
after administration of DOX-SPIONs compared with free DOX, a complex set of in
vitro tests, including production of MTT assay, cell cycle determination, and
cellular uptake, were utilized. In summary, we have developed a magnetic
nanoparticle-based drug delivery system that sequentially delivers the
cytotoxic drug doxorubicin to breast cancer cells (MCF-7 and MDA-MB-231). The
drug-coated nanoparticles, DOX-NPs, were assembled stepwise, with doxorubicin
adsorbed to bare iron oxide nanoparticles first, by electrostatic reaction and
allowed for the complexation of doxorubicin. In contrast, they were
internalized to a much greater extent in MCF-7 and MDA-MB-231 cells and were
cytotoxic due to the synergistic action of the two drugs and the effects of
hyperthermia. The drug-coated particles were able to inhibit growth and
proliferation of breast cancer cells in vitro, indicating that the system has
potential to act as an antimetastatic chemothermotherapeutic agent.",1911.05378v1
2023-10-10,"Soft-Chemical Synthesis, Structure Evolution, and Insulator-to-Metal Transition in a Prototypical Metal Oxide, λ-RhO$_2$","${\lambda}$-RhO$_2$, a prototype 4d transition metal oxide, has been prepared
by oxidative delithiation of spinel LiRh$_2$O$_4$ using ceric ammonium nitrate.
Average-structure studies of this RhO$_2$ polytype, including synchrotron
powder X-ray diffraction and electron diffraction, indicate the room
temperature structure to be tetragonal, in the space group I41/amd, with a
first-order structural transition to cubic Fd-3m at T = 345 K on warming.
Synchrotron X-ray pair distribution function analysis and $^7$Li solid state
nuclear magnetic resonance measurements suggest that the room temperature
structure displays local Rh-Rh bonding. The formation of these local dimers
appears to be associated with a metal-to insulator transition with a
non-magnetic ground state, as also supported by density functional theory-based
electronic structure calculations. This contribution demonstrates the power of
soft chemistry to kinetically stabilize a surprisingly simple binary oxide
compound.",2310.07053v1
2015-10-16,Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy,"We have studied the magnetic layer thickness dependence of the orbital
magnetic moment in magnetic heterostructures to identify contributions from
interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and
Pt/Co/Pt, which possess significant interface contribution to the perpendicular
magnetic anisotropy, are studied as model systems. X-ray magnetic circular
dichroism spectroscopy is used to evaluate the relative orbital moment, i.e.
the ratio of the orbital to spin moments, of the magnetic elements constituting
the heterostructures. We find that the relative orbital moment of Co in
Pt/Co/Pt remains constant against its thickness whereas the moment increases
with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a
non-zero interface orbital moment exists for the latter system. For
Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray
absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$,
absent in other heterosturctures, may give rise to the interface orbital moment
in this system. These results show element specific contributions to the
interface orbital magnetic moments in ultrathin magnetic heterostructures.",1510.04756v1
2017-01-16,Dynamics of magnetic nano particles in a viscous fluid driven by rotating magnetic fields,"The rotational dynamics of magnetic nano particles in rotating magnetic
fields in the presence of thermal noise is studied both theoretically and by
performing numerical calculations. Kinetic equations for the dynamics of
particles with uniaxial magnetic anisotropy are studied and the phase lag
between the rotating magnetic moment and the driving field is obtained. It is
shown that for large enough anisotropy energy the magnetic moment is locked to
the anisotropy axis so that the particle behaves like a rotating magnetic
dipole. The corresponding rigid dipole model is analyzed both numerically by
solving the appropriate Fokker-Planck equation and analytically by applying an
effective field method. In the special case of a rotating magnetic field
applied analytic results are obtained in perfect agreement with numerical
results based on the Fokker-Planck equation. The analytic formulas derived are
not restricted to small magnetic fields or low frequencies and are therefore
important for applications. The illustrative numerical calculations presented
are performed for magnetic parameters typical for iron oxide.",1702.04673v1
2021-01-26,Understanding Magnetism in Double Double Perovskites: A Complex Multiple Magnetic Sublattice System,"Understanding magnetism in multiple magnetic sublattice system, driven by the
interplay of varied nature of magnetic exchanges, is on one hand challenging
and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6
double double perovskites with multiple magnetic ions both at A- and B-sites,
we investigate the mechanism of magnetic behavior in these interesting class of
compounds. We find that the magnetism in such multiple sublattice compounds is
governed by the interplay and delicate balance between two distinct mechanisms,
a) kinetic energy-driven multiple sublattice double exchange mechanism and b)
the conventional super-exchange mechanism. The derived spin Hamiltonian based
on first-principles calculations is solved by the classical Monte Carlo
technique which reproduces the observed magnetic properties. Finally, the
influence of off-stoichiometry, as in experimental samples, is discussed. Some
of these double double perovskite compounds are found to possess large total
magnetic moment and also are found to be half-metallic, which raises the hope
of future applications of these large magnetic moment half-metallic oxides in
spintronics and memory devices.",2101.10822v1
2024-04-01,"Harnessing Interlayer Magnetic Coupling for Efficient, Field-Free Current-Induced Magnetization Switching in a Magnetic Insulator","Owing to the unique features of low Gilbert damping, long spin-diffusion
lengths and zero Ohmic losses, magnetic insulators are promising candidate
materials for next-generation spintronic applications. However, due to the
localized magnetic moments and the complex metal-oxide interface between
magnetic insulators and heavy metals, spin-functional Dzyaloshinskii-Moriya
interactions or spin Hall and Edelstein effects are weak, which diminishes the
performance of these typical building blocks for spintronic devices. Here, we
exploit the exchange coupling between metallic and insulating magnets for
efficient electrical manipulation of heavy metal/magnetic insulator
heterostructures. By inserting a thin Co layer, we enhance the spin-orbit
torque efficiency by more than 20 times, which significantly reduces the
switching current density. Moreover, we demonstrate field-free current-induced
magnetization switching caused by a symmetry-breaking non-collinear magnetic
texture. Our work launches magnetic insulators as an alternative platform for
low-power spintronic devices.",2404.00845v1
2011-07-21,Short-range spin order and frustrated magnetism in Mn2InSbO6 and Mn2ScSbO6,"The complex metal oxides Mn2ASbO6 (A=In, Sc) with a corundum-related
structure A3BO6 have been prepared as polycrystalline powders by a solid state
reaction route. The crystal structure and magnetic properties have been
investigated using a combination of X-ray and neutron powder diffraction,
electron microscopy, calorimetric and magnetic measurements. At room
temperature these compounds adopt a trigonal structure, space group R-3 with a
= 8.9313(1) {\AA}, c = 10.7071(2) {\AA} (for In) and a = 8.8836(1) {\AA}, c =
10.6168(2) {\AA} (for Sc) which persists down to 1.6 K. The Mn and A cations
were found to be randomly distributed over the A-sites. The overall behavior of
the magnetization of Mn2InSbO6 and Mn2ScSbO6 is quite similar. In spite of the
relatively large amount of Mn ions on the A-site, only short-ranged magnetism
is observed. Neutron diffraction patterns of Mn2InSbO6 showed no evidence of a
long-range magnetic ordering at 1.6 K, instead only a weak diffuse magnetic
peak was observed at low temperatures. The factors governing the observed
structural and magnetic properties of Mn2ASbO6 are discussed and compared with
those of other Mn-containing complex metal oxides with a corundum-related
structure. The influence of the A-cation sublattice on magnetic properties is
also considered.",1107.4206v1
2023-06-27,Permanent magnet systems to study the interaction between magnetic nanoparticles and cells in microslide channels,"We optimized designs of permanent magnet systems to study the effect of
magnetic nanoparticles on cell cultures in microslide channels. This produced
two designs, one of which is based on a large cylindrical magnet that applies a
uniform force density of 6 MN/m$^3$ on soft magnetic iron-oxide spherical
nanoparticles at a field strength of over 300 mT. We achieved a force
uniformity of better than 14% over the channel area leading to a concentration
variation that was below our measurement resolution. The second design was
aimed at maximizing the force by using a Halbach array. We indeed increased the
force by more than one order of magnitude at force density values over 400
MN/m$^3$, but at the cost of uniformity. However, the latter system can be used
to trap magnetic nanoparticles efficiently and to create concentration
gradients. We demonstrated both designs by analyzing the effect of magnetic
forces on the cell viability of human hepatoma HepG2 cells in the presence of
bare Fe$_2$O$_3$ and cross-linked dextran iron-oxide cluster-type particles
(MicroMod). Python scripts for magnetic force calculations and particle
trajectory modeling as well as source files for 3D prints have been made
available so these designs can be easily adapted and optimized for other
geometries.",2306.15459v2
2023-11-22,Effects of magnetic fields and orbital angular momentum on excitonic condensation in two-orbital Hubbard model,"We investigate the magnetic-field effects on a two-orbital Hubbard model that
describes multiple spin states. Cobalt oxides have been investigated as
materials possessing spin-state degrees of freedom due to the interplay between
the Hund coupling interaction and crystalline field effect. In the competing
region, quantum hybridizations between distinct spin states are expected to
emerge, corresponding to excitonic condensation. Applied magnetic fields could
also induce such a competition. To understand magnetic-field effects on
excitonic condensation in multi-orbital systems, it is crucial to account for
contributions from both spin and orbital degrees of freedom to magnetic
properties. Here, we study field-induced phenomena in the two-orbital Hubbard
model by focusing on the role of the orbital angular momentum. We
comprehensively analyze this model on a square lattice employing the
Hartree-Fock approximation. Omitting contributions from the orbital moment, we
find that an applied magnetic field gives rise to two excitonic phases, besides
the spin-state ordered phase, between the nonmagnetic low-spin and
spin-polarized high-spin phases. One of these excitonic phases manifests a
staggered-type spin-state order, interpreted as an excitonic supersolid state.
Conversely, the other phase is not accompanied by it and exhibits only a spin
polarization due to the applied magnetic field. When spin-orbit coupling is
present, this phase displays a ferrimagnetic spin alignment attributed to spin
anisotropy. Our analysis also reveals that incorporating the contribution of
the orbital magnetic moment to the Zeeman term significantly alters the overall
structure of the phase diagram. Notably, the orbital magnetization destabilizes
the excitonic phase in contrast to scenarios without this contribution. We also
discuss the relevance of our findings to real materials, such as cobalt oxides.",2311.13191v1
2024-03-06,The role of interfacial interactions and oxygen vacancies in tuning magnetic anisotropy in LaCrO$_{3}$/LaMnO$_{3}$ heterostructures,"The interplay of lattice, electronic, and spin degrees of freedom at
epitaxial complex oxide interfaces provides a route to tune their magnetic
ground states. Unraveling the competing contributions is critical for tuning
their functional properties. We investigate the relationship between magnetic
ordering and magnetic anisotropy and the lattice symmetry, oxygen content, and
film thickness in compressively strained LaMnO$_3$/LaCrO$_3$ superlattices.
Mn-O-Cr antiferromagnetic superexchange interactions across the heterointerface
resulting in a net ferrimagnetic magnetic structure. Bulk magnetometry
measurements reveal isotropic in-plane magnetism for as-grown oxygen-deficient
thinner thin samples due to equal fractions of orthorhombic a+a-c-, and a-a+c-
twin domains. As the superlattice thickness is increased, in-plane magnetic
anisotropy emerges as the fraction of the a+a-c- domain increases. On annealing
in oxygen, the suppression of oxygen vacancies results in a contraction of the
lattice volume, and an orthorhombic to rhombohedral transition leads to
isotropic magnetism independent of the film thickness. The complex interactions
are investigated using high-resolution synchrotron diffraction and X-ray
absorption spectroscopy. These results highlight the role of the evolution of
structural domains with film thickness, interfacial spin interactions, and
oxygen-vacancy-induced structural phase transitions in tuning the magnetic
properties of complex oxide heterostructures.",2403.03764v1
2020-01-08,Non-equilibrium spin dynamics in the temperature and magnetic field dependence of magnetization curves of ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ and its composite with BaTiO$_3$,"A comparative study of the non-equilibrium magnetic phenomena (magnetic
blocking, memory, exchange bias and aging effect) has been presented for
ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with
non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have
confirmed coexistence of CFO and BTO structures in composite, but magnetic spin
dynamics have been remarkably modified. The blocking phenomenon of
ferrimagnetic domains below the room temperature has been studied by different
modes of (zero field cooled and field cooled) magnetic measurements in
collaboration with magnetic fields ON and OFF modes and time dependent
magnetization. The applications of unconventional protocols during time
dependent magnetization measurement at different stages of the temperature and
field dependence of the magnetization curves have been useful to reveal the
non-equilibrium dynamics of magnetic spin order. The applying of off-field
relaxation experiments has made possible to tune the magnetic state and
coercivity of the systems. The role of interfacial coupling between magnetic
and non-magnetic particles has been understood on different magnetic phenomena
(meta-stable magnetic state, exchange bias and memory effect) by comparing the
experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its
composite with BaTiO$_3$ particles.",2001.02602v2
2022-05-13,Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films,"Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too.",2205.06563v1
2023-06-16,Tailoring defects and nanocrystal transformation for optimal heating power in bimagnetic $Co_yFe_{1-y}O@Co_xFe_{3-x}O_4$ particles,"The effects of cobalt incorporation in spherical heterostructured iron oxide
nanocrystals (NCs) of sub-critical size have been explored by colloidal
chemistry methods. Synchrotron X-ray total scattering methods suggest that
cobalt (Co) substitution in rock salt iron oxide NCs tends to remedy its vacant
iron sites, offering a higher degree of resistance to oxidative conversion.
Self-passivation still creates a spinel-like shell, but with higher volume
fraction of the rock salt Co-containing phase in the core. The higher divalent
metal stoichiometry in the rock salt phase, with increasing Co content, results
in a population of unoccupied tetrahedral metal sites in the spinel part,
likely through oxidative shell creation, involving an ordered defect-clustering
mechanism, directly correlated to the core stabilization. To shed light on the
effects of Co-substitution and atomic-scale defects (vacant sites), Monte Carlo
simulations suggest that designed NCs, with desirable, enhanced magnetic
properties (cf. exchange bias and coercivity), are developed with
magnetocrystalline anisotropy raised at relatively low content of Co ions in
the lattice. Growth of optimally performing candidates combines also a strongly
exchange-coupled system, secured through a high volumetric ratio rock salt
phase, interfaced by a not so defective spinel shell. In view of these
requirements, Specific Absorption Rate (SAR) calculations demonstrate that the
sufficiently protected from oxidation rock salt core and preserved over time
heterostructure, play a key role in magnetically-mediated heating efficacies,
for potential use of such NCs in magnetic hyperthermia applications.",2306.09684v1
2018-03-20,Direct demonstration of the emergent magnetism resulting from the multivalence Mn in a LaMnO3 epitaxial thin film system,"Atomically engineered oxide heterostructures provide a fertile ground for
creating novel states. For example, a two-dimensional electron gas at the
interface between two oxide insulators, giant thermoelectric Seebeck
coefficient, emergent ferromagnetism from otherwise nonmagnetic components, and
colossal ionic conductivity. Extensive research efforts reveal that oxygen
deficiency or lattice strain play an important role in determining these
unexpected properties. Herein, by studying the abrupt presence of robust
ferromagnetism (up to 1.5 uB/Mn) in LaMnO3-based heterostructures, we find the
multivalence states of Mn that play a decisive role in the emergence of
ferromagnetism in the otherwise antiferromagnetic LaMnO3 thin films. Combining
spatially resolved electron energy-loss spectroscopy, X-ray absorption
spectroscopy and X-ray magnetic circular dichroism techniques, we determine
unambiguously that the ferromagnetism results from a conventional Mn3+-O-Mn4+
double-exchange mechanism rather than an interfacial effect. In contrast, the
magnetic dead layer of 5 unit cell in proximity to the interface is found to be
accompanied with the accumulation of Mn2+ induced by electronic reconstruction.
These findings provide a hitherto-unexplored multivalence state of Mn on the
emergent magnetism in undoped manganite epitaxial thin films, such as LaMnO3
and BiMnO3, and shed new light on all-oxide spintronic devices.",1803.07402v1
2022-12-20,Chemical Design of Electronic and Magnetic Energy Scales in Tetravalent Praseodymium,"Lanthanides in the trivalent oxidation state are typically described using an
ionic picture that leads to localized magnetic moments. The hierarchical energy
scales associated with trivalent lanthanides produce desirable properties for
e.g., molecular magnetism, quantum materials, and quantum transduction. Here,
we show that this traditional ionic paradigm breaks down for praseodymium in
the 4+ oxidation state. Synthetic, spectroscopic, and theoretical tools
deployed on several solid-state Pr4+ oxides uncover the unusual participation
of 4f orbitals in bonding and the anomalous hybridization of the 4f1
configuration with ligand valence electrons, analogous to transition metals.
The resulting competition between crystal-field and spin-orbit-coupling
interactions fundamentally transforms the spin-orbital magnetism of Pr4+, which
departs from the Jeff =1/2 limit and resembles that of high-valent actinides.
Our results show that Pr4+ ions are in a class on their own, where the
hierarchy of single-ion energy scales can be tailored to explore new correlated
phenomena in quantum materials.",2212.10401v1
2023-06-11,Visualizing magnetic field-induced rotational electronic symmetry breaking in a spinel oxide superconductor,"The spinel oxide superconductor LiTi2O4 (LTO) is an intriguing material
platform where the electronic structure near the Fermi energy (EF) is derived
from 3d elections on the geometrically frustrated Ti pyrochlore network. A
recent angle-resolved photoemission spectroscopy (ARPES) study has revealed the
existence of an exotic quasiparticle state arising from the competition between
instability towards orbital ordering and geometrical frustration below 150 K.
An intriguing remaining challenge is the imaging of Abrikosov vortices, which
generally inherits the symmetry of the Fermi surface at k_z=0. Here, we observe
surprising triangular-shaped Abrikosov vortices on an LTO(111) film, deviating
from the conventional expectations of the six-fold symmetric Fermi surface at
k_z=0. In combination with the experimentally observed isotropic pairing, we
propose magnetic field-driven rotational electronic symmetry breaking of the
underlying Fermi surface. Consequently, we observe Josephson vortices along the
crystalline domain boundary, across which quasiparticle hopping is suppressed
due to the symmetry-broken Fermi surface in each domain. Our discoveries point
to the existence of unique physics of magnetic field-induced electronic
rotational symmetry breaking in the spinel oxide superconductor LTO. This
picture is in stark contrast to the other exotic superconductors with partial
gap opening or long-range ordering with broken symmetry above the
superconducting critical temperature at zero magnetic field.",2306.06711v1
2002-11-09,Magnetic order and superconductivity in LSCO: a review,"High-Tc copper oxides of the LSCO family show a very clear case of
competition between antiferromagnetic (AF) order and superconductivity.
Magnetic order can, however, coexist with superconductivity, and the
experimental evidence for frozen magnetic moments in superconducting samples is
reviewed here. The primary characteristics of the magnetic order are summarized
and some open questions are outlined, particularly concerning the intrinsic or
extrinsic nature of this order around x=0.12.",0211178v1
2002-12-17,Unconventional magnetic transition and transport behavior in Na0.75CoO2,"Here we report an unconventional magnetic and transport phenomenon in a
layered cobalt oxide, NaxCoO2. Only for x = 0.75, a magnetic transition of the
second order was clearly detected at Tm ~ 22 K where an apparent specific-heat
jump, an onset of extremely small spontaneous magnetization, and a kink in
resistivity came in. Moreover large positive magnetoresistance effect was
observed below Tm. These features of the transition strongly indicate the
appearance of an unusual electronic state that may be attributed to the
strongly-correlated electrons in Na0.75CoO2.",0212395v1
2003-07-12,"Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures","Structural, magnetic and ferromagnetic resonance characterization studies
have been performed on lay-ered ferromagnetic-ferroelectric oxides that show
strong magnetoelectric coupling. The samples contained thick films of ferrites
or substituted lanthanum manganites for the ferromagnetic phase and lead
zirconate titanate for the ferroelectric phase, and were sintered high
temperatures. Results indicate defect free ferrites, but deterioration of
manganite parameters due to diffusion at the interface and accounts for poor
magnetoelectric coupling in manganite-PZT samples.",0307302v1
2003-07-17,"Specific heat and magnetization study on single crystals of a frustrated, quasi one-dimensional oxide: Ca3Co2O6","Specific heat and magnetization measurements have been carried out under a
range of magnetic fields on single crystals of Ca3Co2O6. This compound is
composed of Ising magnetic chains that are arranged on a triangular lattice.
The intrachain and interchain couplings are ferromagnetic and
antiferromagnetic, respectively. This situation gives rise to geometrical
frustration, that bears some similarity to the classical problem of a
two-dimensional Ising triangular antiferromagnet. This paper reports on the
ordering process at low-T and the possibility of one-dimensional features at
high-T.",0307429v1
2003-09-16,Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario,"Field-induced magnetization jumps with similar characteristics are observed
at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent
manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even
the existence- of these jumps depends critically on the magnetic field sweep
rate used to record the data. It is proposed that, for both compounds, the
martensitic character of their antiferromagnetic-to-ferromagnetic transitions
is at the origin of the magnetization steps.",0309389v1
2004-03-16,Rashba Effect at Magnetic Metal Surfaces,"We give experimental and theoretical evidence of the Rashba effect at the
magnetic rare-earth metal surface Gd(0001). The Rashba effect is substantially
enhanced and the Rashba parameter changes its sign when a metal-oxide surface
layer is formed. The experimental observations are quantitatively described by
ab initio calculations that give a detailed account of the near-surface charge
density gradients causing the Rashba effect. Since the sign of the Rashba
splitting depends on the magnetization direction, the findings open up new
opportunities for the study of surface and interface magnetism.",0403405v2
2004-03-29,"Ground state, electronic structure and magnetism of LaMnO3","We have calculated the discrete low-energy electronic structure in LaMnO3
originating from the atomic-like states of the strongly correlated 3d4
electronic system occurring in the Mn3+ ion. We take into account very strong
intra-atomic correlations, crystal field interactions and the intra-atomic
spin-orbit coupling. We calculated magnetic and paramagnetic state of LaMnO3
within the consistent description given by Quantum Atomistic Solid State Theory
(QUASST). Our studies indicate that the intra-atomic spin-orbit coupling and
the orbital magnetism are indispensable for the physically adequate description
of electronic and magnetic properties of LaMnO3.
  Keywords: 3d oxides, crystal field, spin-orbit coupling, LaMnO3
  PACS: 71.70Ej, 75.10Dg",0403714v1
2006-08-23,A New Multiferroic Material: MnWO4,"We report the multiferroic behaviour of MnWO$_4$, a magnetic oxide with
monoclinic crystal structure and spiral long-range magnetic order. Based upon
recent theoretical predictions MnWO$_4$ should exhibit ferroelectric
polarization coexisting with the proper magnetic structure. We have confirmed
the multiferroic state below 13 K by observing a finite electrical polarization
in the magnetically ordered state via pyroelectric current measurements.",0608498v1
2007-11-05,Magnetic excitations in vanadium spinels,"We study magnetic excitations in vanadium spinel oxides AV$_2$O$_4$ (A=Zn,
Mg, Cd) using two models: first one is a superexchange model for vanadium S=1
spins, second one includes in addition spin-orbit coupling, and crystal
anisotropy. We show that the experimentally observed magnetic ordering can be
obtained in both models, however the orbital ordering is different with and
without spin-orbit coupling and crystal anisotropy. We demonstrate that this
difference strongly affects the spin-wave excitation spectrum above the
magnetically ordered state, and argue that the neutron measurement of such
dispersion is a way to distinguish between the two possible orbital orderings
in AV$_2$O$_4$.",0711.0732v1
2008-04-21,Unusual magnetic behavior in ferrite hollow nanospheres,"We report unusual magnetic behavior in iron oxide hollow nanospheres of 9.3
$nm$ in diameter. The large fraction of atoms existing at the inner and outer
surfaces gives rise to a high magnetic disorder. The overall magnetic behavior
can be explained considering the coexistence of a soft superparamagnetic phase
and a hard phase corresponding to the highly frustrated cluster-glass like
phase at the surface regions.",0804.3292v1
2009-11-10,Anomalous magnetic behavior of CuO nanoparticles,"We report studies on temperature, field and time dependence of magnetization
on cupric oxide nanoparticles of sizes 9 nm, 13 nm and 16 nm. The nanoparticles
show unusual features in comparison to other antiferromagnetic nanoparticle
systems. The field cooled (FC) and zero field cooled (ZFC) magnetization curves
bifurcate well above the N\'eel temperature and the usual peak in the ZFC
magnetization curve is absent.
  The system does not show any memory effects which is in sharp contrast to the
usual behavior shown by other antiferromagnetic nanoparticles. It turns out
that the non-equilibrium behavior of CuO nanoparticles is very strange and is
neither superparamagnetic nor spin glass-like.",0911.1838v2
2011-03-09,Antiferromagnetic Heisenberg S=5/2 spin chain compound SrMn$_2$V$_2$O$_8$,"Large single crystals of the new compound SrMn$_2$V$_2$O$_8$ have been grown
by the floating-zone method. This transition-metal based oxide is isostructural
to SrNi$_2$V$_2$O$_8$, described by the tetragonal space group $I4_1cd$.
Magnetic properties were investigated by means of susceptibility,
magnetization, and specific heat measurements. The title compound behaves like
a one-dimensional magnetic system above the ordering temperature ($T_N$ = 43
K). The magnetic ground state can be described as a classical long-range
ordered antiferromagnet with weak anisotropy.",1103.1830v1
2011-06-16,Thermomagnonic spin transfer and Peltier effects in insulating magnets,"We study the coupled magnon energy transport and collective magnetization
dynamics in ferromagnets with magnetic textures. By constructing a
phenomenological theory based on irreversible thermodynamics, we describe
motion of domain walls by thermal gradients and generation of heat flows by
magnetization dynamics. From microscopic description based on magnon kinetics,
we estimate the transport coefficients and analyze the feasibility of
energy-related applications in insulating ferromagnets, such as yttrium iron
garnet and europium oxide.",1106.3135v2
2011-12-16,"Comment on ""Unconventional Magnetism in a Nitrogen-Containing Analog of Cupric Oxide""","In a recent Letter [PRL, 107, 047208 (2011)], Zorko et al. report on an
""unexpected inhomogeneous magnetism"" related to ""a peculiar fragility"" of the
resonating-valence-bond (RVB) electronic state in the spin-1/2 quantum magnet
CuNCN. Here, we show that: i) the spin model of the anisotropic triangular
lattice (ATL), as proposed by Zorko et al., does not apply to CuNCN; ii) this
model does not support the proclaimed RVB ground state in the relevant
parameter range; iii) the magnetic state of CuNCN is not necessarily
inhomogeneous.",1112.3894v1
2012-09-14,Magnetic Order and Charge Disproportionation in a Spin-ice type Kondo Lattice Model: Large Scale Monte Carlo Study,"Phase diagram of a spin-ice type Kondo lattice model, potentially relevant to
metallic pyrochlore oxides, is obtained by the Monte Carlo simulation
implementing the polynomial expansion technique up to the system size with 2048
sites. We identified a new 32-sublattice magnetic phase with concomitant charge
disproportionation, along with other phases such as two-in two-out and
all-in/all-out orders. The spin and charge pattern can be switched by external
magnetic field to a different one accompanied by a half magnetization plateau.",1209.3134v1
2016-04-15,Electron magnetic resonance in magnetic nanoparticles: dependence on the particle size and applicability of the modified giant spin model,"Superparamagnetic nanoparticles containing hundreds and thousands of coupled
electron spins are on the boundary between classical and quantum behavior, and
demonstrate features which are typical for paramagnetic spins and absent in
macroscopic ferromagnetic systems. In order to better understand the evolution
of magnetization dynamics from quantum to classical behavior with the increase
in the system size, we study the electron magnetic resonance signal in
suspensions of iron oxide nanoparticles as the function of the particle size.
The experimental data are compared with numerical simulations based on the
giant spin approach.",1604.04594v2
2001-02-23,Holes in a Quantum Spin Liquid,"Magnetic neutron scattering provides evidence for nucleation of
antiferromagnetic droplets around impurities in a doped nickel-oxide based
quantum magnet. The undoped parent compound contains a spin liquid with a
cooperative singlet ground state and a gap in the magnetic excitation spectrum.
Calcium doping creates excitations below the gap with an incommensurate
structure factor. We show that weakly interacting antiferromagnetic droplets
with a central phase shift of $\pi$ and a size controlled by the correlation
length of the quantum liquid can account for the data. The experiment provides
a first quantitative impression of the magnetic polarization cloud associated
with holes in a doped transition metal oxide.",0102445v2
2001-10-12,Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12,"The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.",0110262v1
2001-10-22,Commensurate and Incommensurate Phases of a Spin-Peierls System,"The interest in the study of spin-Peierls phenomenon has increased with the
discovery of copper germanium oxide (CuGeO_3) as an example of spin-Peierls
systems. The availability of this inorganic compound as large, high quality
single crystals, allow experimental measurements which aid in understanding the
spin-Peierls phenomenon. This report details the numerical and analytical work
done on the various magnetic phases that occur in a quasi-one-dimensional
spin-Peierls system (like that of copper germanium oxide). Taking the system to
be finite, the bond displacements, single particle energies, energy
eigenfunctions, spin densities and phonon frequencies are calculated
numerically for all possible magnetizations, which includes both the
commensurate and incommensurate phases, at zero temperature. Solitons of
fractional spin are found to be present in the system for appropriate
magnetizations. The uniform to dimerized phase transition occurring in this
system is also modelled numerically. The single particle and ground-state
energies are later obtained theoretically for the uniform and dimerized phases.
In addition, the lattice spin displacements are analytically modelled for a
particular magnetization of the system.",0110446v1
2003-07-17,Specific heat investigation of the magnetic ordering in two frustrated spin-chain oxides: Ca3Co2O6 and Ca3CoRhO6,"Specific heat measurements were carried out on the closely related spin-chain
oxides Ca3Co2O6 and Ca3CoRhO6. Both compounds consist of Ising magnetic chains
that are arranged on a triangular lattice. The spin coupling along and between
the chains are ferromagnetic and antiferromagnetic, respectively. Geometrical
frustration is expected from the combination of these magnetic features. The
present study reports that the specific heat data of these compounds exhibit
similarities in the spin-freezing process at low T, whereas striking
differences exist in the antiferromagnetic interchain ordering at higher T.
These results are discussed in connection with previous magnetization and
neutron diffraction data.",0307433v1
2004-06-21,"Orbital ordering and one-dimensional magnetic correlation in vanadium spinel oxides AV2O4 (A = Zn, Mg, or Cd)","We present our theoretical results on the mechanism of two transitions in
vanadium spinel oxides $A$V$_2$O$_4$ ($A$=Zn, Mg, or Cd) in which magnetic V
cations constitute a geometrically-frustrated pyrochlore structure. We have
derived an effective spin-orbital-lattice coupled model in the strong
correlation limit of the multiorbital Hubbard model, and applied Monte Carlo
simulation to the model. The results reveal that the higher-temperature
transition is a layered antiferro-type orbital ordering accompanied by
tetragonal Jahn-Teller distortion, and the lower-temperature transition is an
antiferromagnetic spin ordering. The orbital order lifts the magnetic
frustration partially, and induces spatial anisotropy in magnetic exchange
interactions. In the intermediate phase, the system can be considered to
consist of weakly-coupled antiferromagnetic chains lying in the perpendicular
planes to the tetragonal distortion.",0406462v1
2004-09-10,Novel Reconfigurable Logic Gates Using Spin Metal-Oxide-Semiconductor Field-Effect Transistors,"We propose and numerically simulate novel reconfigurable logic gates
employing spin metal-oxide-semiconductor field-effect transistors (spin
MOSFETs). The output characteristics of the spin MOSFETs depend on the relative
magnetization configuration of the ferromagnetic contacts for the source and
drain, that is, high current-drive capability in the parallel magnetization and
low current-drive capability in the antiparallel magnetization [S. Sugahara and
M. Tanaka: Appl. Phys. Lett. 84 (2004) 2307]. A reconfigurable NAND/NOR logic
gate can be realized by using a spin MOSFET as a driver or an active load of a
complimentary MOS (CMOS) inverter with a neuron MOS input stage. Its logic
function can be switched by changing the relative magnetization configuration
of the ferromagnetic source and drain of the spin MOSFET. A reconfigurable
logic gate for all symmetric Boolean functions can be configured using only
five CMOS inverters including four spin MOSFETs. The operation of these
reconfigurable logic gates was confirmed by numerical simulations using a
simple device model for the spin MOSFETs",0409262v1
2008-02-25,Onset of Magnetic Order in Strongly-Correlated Systems from ab initio Electronic Structure Calculations: Application to Transition Metal Oxides,"We describe an ab initio theory of finite temperature magnetism in
strongly-correlated electron systems. The formalism is based on spin density
functional theory, with a self-interaction corrected local spin density
approximation (SIC-LSDA). The self-interaction correction is implemented
locally, within the KKR multiple-scattering method. Thermally induced magnetic
fluctuations are treated using a mean-field `disordered local moment' (DLM)
approach and at no stage is there a fitting to an effective Heisenberg model.
We apply the theory to the 3d transition metal oxides, where our calculations
reproduce the experimental ordering tendencies, as well as the qualitative
trend in ordering temperatures. We find a large insulating gap in the
paramagnetic state which hardly changes with the onset of magnetic order.",0802.3660v2
2009-04-03,A radical approach to promote multiferroic coupling in double perovskites,"Double perovskites provide a unique opportunity to induce and control
multiferroic behaviors in oxide systems. The appealing possibility to design
materials with a strong coupling between the magnetization and the polarization
fields may be achieved in this family since these magnetic insulators can
present structural self-ordering in the appropriate growth conditions. We have
studied the functional properties of La2CoMnO6 and Bi2CoMnO6 epitaxial thin
films grown by pulsed laser deposition. Cation-ordered La2CoMnO6 films display
a magnetic Curie temperature of 250 K while cation-disordered Bi2CoMnO6 films
present ferromagnetism up to ~ 800 K. Such high transition temperature for
magnetic ordering can be further tuned by varying the strain in the films
indicating an important contribution from the structural characteristics of the
materials. Our approach might be generalized for other oxide systems. At this
end, our results are compared with other multiferroic systems. The roles of
various cations, their arrangements and structural effects are further
discussed.",0904.0615v1
2010-06-29,Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study,"Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometry",1006.5598v1
2010-07-19,High-Tc ferrolectricity emerging from magnetic degeneracy in cupric oxide,"Cupric oxide is multiferroic at unusual high temperatures. From density
functional calculations we find that the low-T magnetic phase is paraelectric
and the higher-T one ferroelectric, with a size and direction of polarization
in good agreement with experiment. By mapping of the ab initio results on an
effective spin model we find with Monte Carlo that in the high-T magnetic state
non-collinearity and inversion symmetry breaking stabilize each other via the
Dzyaloshinskii Moriya interaction. This leads to a novel mechanism for
multiferroicity, with the particular property that non-magnetic impurities
enhance the effect.",1007.3220v2
2010-09-20,Sr$_6$Co$_5$0{$_1$$_5$}: non-one-dimensional behavior of a charge ordered structurally quasi-one-dimensional oxide,"We have synthesized Sr$_6$Co$_5$O$_{15}$, a quasi-one-dimensional oxide,
measured its magnetic properties and calculated its electronic structure by ab
initio techniques. We have found strong evidence for its electronic and
magnetic behavior not to follow the trend of its structural series. The
magnetic coupling inside the CoO$_3$ chains is not purely ferromagnetic, the
long-range coupling inside them is very weak. The Co moments are slightly
canted due to their large orbital angular momenta being oriented along each
particular quantization axis, that is different for each Co$^{4+}$ atom in the
structure. Our thermopower calculations are in agreement with the experiment,
supporting our model of the magnetic ground state of the compound.",1009.3736v2
2010-10-05,Structural and magnetic characterization of self-assembled iron oxide nanoparticle arrays,"We report about a combined structural and magnetometric characterization of
self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide
nanoparticles with a diameter of 20 nm were synthesized by thermal
decomposition. The nanoparticle suspension was spin-coated on Si substrates to
achieve self-organized arrays of particles and subsequently annealed at various
conditions. The samples were characterized by x-ray diffraction, bright and
dark field high resolution transmission electron microscopy (HRTEM). The
structural analysis is compared to the magnetic behavior investigated by
superconducting interference device (SQUID) magnetometry. We can identify
either multi-phase FeO/g-Fe2O3 or multi-phase FeO/Fe3O4 nanoparticles. The
FeO/g-Fe2O3 system shows a pronounced exchange bias effect which explains the
peculiar magnetization data obtained for this system.",1010.0938v1
2011-01-10,Novel magnetic order in pseudogap state of high Tc copper oxides superconductors,"One of the leading issues in high-$\rm T_c$ copper oxide superconductors is
the origin of the pseudogap phase in the underdoped regime of their phase
diagram. Using polarized neutron diffraction, a novel magnetic order has been
identified as an hidden order parameter of the pseudogap as the transition
temperature corresponds to what is expected for the pseudogap. The observed
magnetic order preserves translational symmetry as predicted for orbital
moments in the circulating current theory. Being now reported in three
different cuprates familles, it appears as a universal phenomenon whatever the
crystal structure (with single CuO$_2$ layer or bilayer per unit cell). To
date, it is the first direct evidence of an hidden order parameter
characterizing the pseudogap phase of high-$\rm T_c$ cuprates.",1101.1786v2
2011-06-14,Crossover between two different magnetization reversal modes in arrays of iron oxide nanotubes,"The magnetization reversal in ordered arrays of iron oxide nanotubes of 50 nm
outer diameter grown by atomic layer deposition is investigated theoretically
as a function of the tube wall thickness, $d_{w}$. In thin tubes ($d_{w}<13$
nm) the reversal of magnetization is achieved by the propagation of a vortex
domain boundary, while in thick tubes ($d_{w}>13$ nm) the reversal is driven by
the propagation of a transverse domain boundary. Magnetostatic interactions
between the tubes are responsible for a decrease of the coercive field in the
array. Our calculations are in agreement with recently reported experimental
results. We predict that the crossover between the vortex and transverse modes
of magnetization reversal is a general phenomenon on the length scale
considered.",1106.2833v1
2011-08-25,Fabrication of magnetic clusters and rods using electrostatic co-assembly,"Using a novel protocol for mixing oppositely charged colloids and
macromolecules, magnetic clusters and rods are fabricated using 10 nm-iron
oxide nanoparticles and polymers. Here, we show that as the dispersions undergo
the so-called desalting transition, spherical clusters in the range 100 nm - 1
{\mu}m form spontaneously upon dialysis or dilution. With a magnetic field
applied during the dialysis, a one-dimensional growth of the aggregates is
initiated, resulting in the formation of 1 - 100 {\mu}m rods of average
diameter 200 nm. In this paper, we demonstrate that the nanostructured rods
have inherited the properties of the iron oxide particles, namely to be
superparamagnetic. We also discuss the dependence of the magnetic properties as
a function of the nanoparticle diameter.",1108.5023v1
2011-10-10,Magnetic order and frustrated dynamics in Li(Ni0.8Co0.1Mn0.1)O2: a study by μ+SR and SQUID magnetometry,"Recently, the mixed transition metal oxides of the form Li(Ni1-y-zCoyMnz)O2,
have become the center of attention as promising candidates for novel battery
material. These materials have also revealed very interesting magnetic
properties due to the alternate stacking of planes of metal oxides on a 2D
triangular lattice and the Li-layers. The title compound,
Li(Ni0.8Co0.1Mn0.1)O2, has been investigated by both magnetometry and
measurements and {\mu}+SR. We find the evolution of localized magnetic moments
with decreasing temperature below 70 K. The magnetic ground state (T = 2 K) is,
however, shown to be a frustrated system in 3D, followed by a transition into a
possible 2D spinglass above 22 K. With further increasing temperature the
compound show the presence of remaining correlations with increasing effective
dimensionality all the way up to the ferrimagnetic transition at TC = 70 K.",1110.2071v1
2015-07-07,Spectrum for non-magnetic Mott insulators from power functional within Reduced Density Matrix Functional Theory,"A fully first principles theory capable of treating strongly correlated
solids remains the outstanding challenge of modern day materials science. This
is exemplified by the transition metal oxides, prototypical Mott insulators,
that remain insulating even in the absence of long range magnetic order.
Capturing the non-magnetic insulating state of these materials presents a
difficult challenge for any modern electronic structure theory. In this paper
we demonstrate that reduced density matrix functional theory, in conjunction
with the power functional, can successfully treat the non-magnetic insulating
state of the transition metal oxides NiO and MnO. We show that the electronic
spectrum retains a gap even in the absence of spin order. We further discuss
the detailed way in which RDMFT performs for Mott insulators and band
insulators, finding that for the latter occupation number minimization alone is
required, but for the former full minimization over both occupation numbers and
natural orbitals is essential.",1507.01754v1
2015-08-14,Antiferromagnetism at T > 500 K in the Layered Hexagonal Ruthenate SrRu2O6,"We report an experimental and computational study of magnetic and electronic
properties of the layered Ru(V) oxide SrRu2O6 (hexagonal, P-3 1m), which shows
antiferromagnetic order with a N\'eel temperature of 563(2) K, among the
highest for 4d oxides. Magnetic order occurs both within edge-shared octahedral
sheets and between layers and is accompanied by anisotropic thermal expansivity
that implies strong magnetoelastic coupling of Ru(V) centers. Electrical
transport measurements using focused ion beam induced deposited contacts on a
micron-scale crystallite as a function of temperature show p-type
semiconductivity. The calculated electronic structure using hybrid density
functional theory successfully accounts for the experimentally observed
magnetic and electronic structure and Monte Carlo simulations reveals how
strong intralayer as well as weaker interlayer interactions are a defining
feature of the high temperature magnetic order in the material.",1508.03609v2
2015-11-09,Mechanism responsible for initiating room temperature ferromagnetism and spin polarized current in diluted magnetic oxides,"The main obstacles in realizing diluted magnetic oxide (DMO) in spintronics
are the unknown electronic structures associated with its high TC
ferromagnetism and spin polarized current and how to manipulate desired
electronic structures by fabrication techniques. We demonstrate that fine-tuned
electronic structures and band structures can be modified to initiate DMO
properties. Interestingly, in the semiconducting state, the doped Co ions and
oxygen vacancies contribute non-negligible magnetic moments; and the magnetic
coupling between these moments is mediated by the localized carriers via highly
spin polarized hopping transport. These results unravel the myth of the origin
of spintronic characteristics with desirable electronic states; thereby
reopening the door for future applications.",1511.02632v1
2015-11-26,Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3,"With large spin-orbit coupling, the $t_{2g}^5$ electron configuration in
$d$-metal oxides is prone to highly anisotropic exchange interactions and
exotic magnetic properties. In $5d^5$ iridates, given the existing variety of
crystal structures, the magnetic anisotropy can be tuned from antisymmetric to
symmetric Kitaev-type, with interaction strengths that outsize the isotropic
terms. By many-body electronic-structure calculations we here address the
nature of the magnetic exchange and the intriguing spin-glass behavior of
Li$_2$RhO$_3$, a $4d^5$ honeycomb oxide. For pristine crystals without Rh-Li
site inversion, we predict a dimerized ground state as in the isostructural
$5d^5$ iridate Li$_2$IrO$_3$, with triplet spin dimers effectively placed on a
frustrated triangular lattice. With Rh-Li anti-site disorder, we explain the
observed spin-glass phase as a superposition of different, nearly degenerate
symmetry-broken configurations.",1511.08333v1
2016-10-03,Orbital driven impurity spin effect on the magnetic order of quasi-three dimensional cupric oxide,"Density functional calculations are performed to study the magnetic order of
the severely distorted square planar cupric oxide (CuO) and local spin disorder
in it in the presence of the transition metal impurities M (= Cr, Mn, Fe, Co
and Ni). The distortion in the crystal structure, arisen to reduce the band
energy by minimizing the covalent interaction, creates two crisscrossing zigzag
spin-1/2 chains. From the spin dimer analysis we find that while the spin chain
along [10$\bar 1$] has strong Heisenberg type antiferromagnetic coupling (J ~
127 meV), along [101] it exhibits weak, but robust, ferromagnetic coupling (J ~
9 meV) mediated by reminiscent p-d covalent interactions. The impurity effect
on the magnetic ordering is independent of M and purely orbital driven. If the
given spin-state of M is such that the d$_{x^2-y^2}$ orbital is spin-polarized,
then the original long-range ordering is maintained. However, if d$_{x^2-y^2}$
orbital is unoccupied, the absence of corresponding covalent interaction breaks
the weak ferromagnetic coupling and a spin-flip takes place at the impurity
site leading to breakdown of the long range magnetic ordering.",1610.00458v1
2011-11-28,Noncollinear magnetism and spin-orbit coupling in 5d pyrochlore oxide Cd2Os2O7,"We investigated the electronic and magnetic properties of the pyrochlore
oxide Cd$_2$Os$_2$O$_7$ using the density-functional theory plus on-site
repulsion ($U$) method, and depict the ground-state phase diagram with respect
to $U$. We conclude that the all-in/all-out non-collinear magnetic order is
stable in a wide range of $U$. We also show that the easy-axis anisotropy
arising from the spin-orbit (SO) coupling plays a significant role in
stabilizing the all-in/all-out magnetic order. A \textit{pseudo gap} was
observed near the transition between the antiferromagnetic metallic and
insulating phases. Finally, we discuss possible origins of the peculiar
low-temperature($T$) properties observed in experiments.",1111.6347v2
2018-09-04,Formation and Control of Twin Domains in the Pyrochlore Oxide Cd2Re2O7,"The successive phase transitions of the pyrochlore oxide Cd2Re2O7 are studied
by polarizing microscopy and magnetic susceptibility measurements. The
formation of twin domains is visualized in the polarizing images of a pristine
(111) crystal surface upon cooling through the cubic-to-tetragonal transition
at Ts1 ~ 200 K. Moreover, a dramatic change in the twinning pattern is observed
at Ts2 ~120 K, which suggests that the tetragonal c axis flips as the strain
changes its direction at the tetragonal-to-tetragonal transition. Magnetic
susceptibility measurements reveal significant domain alignment upon cooling
across Ts1 and Ts2 in a magnetic field of 7 T, which are due to ~10% anisotropy
in the magnetic susceptibility for the low-temperature phases. Interestingly,
the anisotropy is reversed at Ts2: \c{hi}c < \c{hi}a above Ts2 and vice versa
below Ts2.",1809.00771v2
2018-10-10,Spin-Orbital Entangled Liquid State in the Copper Oxide Ba$_3$CuSb$_2$O$_9$,"Structure with orbital degeneracy is unstable toward spontaneous distortion.
Such orbital correlation usually has a much higher energy scale than spins, and
therefore, magnetic transition takes place at a much lower temperature, almost
independently from orbital ordering. However, when the energy scales of
orbitals and spins meet, there is a possibility of spin-orbital entanglement
that would stabilize novel ground state such as spin-orbital liquid and random
singlet state. Here we review on such a novel spin-orbital magnetism found in
the hexagonal perovskite oxide Ba$_3$CuSb$_2$O$_9$, which hosts a
self-organized honeycomblike short-range order of a strong Jahn-Teller ion
Cu$^{2+}$. Comprehensive structural and magnetic measurements have revealed
that the system has neither magnetic nor Jahn-Teller transition down to the
lowest temperatures, and Cu spins and orbitals retain the hexagonal symmetry
and paramagnetic state. Various macroscopic and microscopic measurements all
indicate that spins and orbitals remain fluctuating down to low temperatures
without freezing, forming a spin-orbital entangled liquid state.",1810.04346v1
2019-07-23,Magnetotransport properties of granular oxide-segregated CoPtCr films for applications in future magnetic memory technology,"Magnetotransport properties of granular oxide-segregated CoPtCr films were
studied on both macroscopic and microscopic length scales by performing bulk
and point-contact magnetoresistance measurements, respectively. Such a
perpendicular magnetic medium is used in state-of-the-art hard disc drives and
if combined with magnetoresistive phenomena (for read/write operations) may
lead to a novel concept for magnetic recording with high areal density. While
the bulk measurements on the films showed only small variations in dc
resistance as a function of applied magnetic field (magnetoresistance of less
than 0.02 %), the point-contact measurements revealed
giant-magnetoresistance-like changes in resistance with up to 50,000 % ratios.
The observed magnetorestive effect could be attributed to a tunnel
magnetoresistance between CoPtCr grains with different coercivity. The
tunneling picture of electronic transport in our granular medium was confirmed
by the observation of tunneling-like current-voltage characteristics and bias
dependence of magnetoresistance; both the point-contact resistance and
magnetoresistance were found to decrease with the applied dc bias.",1907.09675v1
2020-01-09,"High temperature thermal cycling effect on the irreversible responses of lattice structure, magnetic properties and electrical conductivity in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide","We report high temperature synchrotron X-ray diffraction (SXRD), dc
magnetization and current-voltage (I-V) characteristics for the samples of
Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical
reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing
at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by
cycling the temperature from 300 K to high temperature (warming mode) and
return back to 300 K (cooling mode). The SXRD patterns indicated a fine
bi-phased cubic spinel structure in the highly Co rich spinel oxide.
Magnetization curves showed intrinsic ferrimagnetic features and defect induced
additional ferromagnetic phase at higher temperatures. Electrical conductivity
showed thermal hysteresis loop between warming and cooling modes of temperature
variation. The samples exhibited new information on the irreversibility
phenomena of lattice structure, magnetization and electrical conductivity on
cycling the measurement temperatures.",2001.02829v2
2021-07-11,Hysteretic Magnetoresistance in a Non-Magnetic SrSnO3 Film via Thermal Coupling to Dynamic Substrate Behavior,"Hysteretic magnetoresistance (MR) is often used as a signature of
ferromagnetism in conducting oxide thin films and heterostructures. Here,
magnetotransport is investigated in a non-magnetic uniformly La-doped SrSnO3
film grown using hybrid molecular beam epitaxy. A 12 nm La:SrSnO3/2 nm
SrSnO3/GdScO3 (110) film with insulating behavior exhibited a robust hysteresis
loop in the MR at T < 5 K accompanied by an anomaly at ~ +/- 3 T at T < 2.5 K.
Furthermore, MR with the field in-plane yielded a value exceeded 100% at 1.8 K.
Using detailed temperature-, angle- and magnetic field-dependent resistance
measurements, we illustrate the origin of hysteresis is not due to magnetism in
the film but rather is associated with the magnetocaloric effect of the GdScO3
substrate. Given GdScO3 and similar substrates are commonly used in complex
oxide research, this work highlights the importance of thermal coupling to
processes in the substrates which must be carefully accounted for in the data
interpretation for thin films and heterostructures utilizing these substrates.",2107.04965v1
2022-05-02,Novel quantum phase of the chromium spinel oxide HgCr$_{\rm 2}$O$_{\rm 4}$ in high magnetic fields,"In this study, we have performed the magnetocaloric effect and the specific
heat measurements of chromium spinel oxide HgCr$_2$O$_4$, wherein the magnetic
Cr$^{3+}$ ions form a highly frustrated pyrochlore lattice with significant
spin-lattice coupling. In addition to the known magnetic-field-induced phases,
our thermodynamic measurements detect a novel quantum phase just before the
saturation of the magnetization, which has not been expected from the classical
theories of the pyrochlore lattice antiferromagnet with spin-lattice coupling.
Based on recent theoretical model calculation, we discuss the possibility of a
spin nematic state appearing for this quantum phase.",2205.00810v1
2023-03-20,Electronic and magnetic properties of Lu and LuH$_2$,"Clarifying the electronic and magnetic properties of lutetium, lutetium
dihydride, and lutetium oxide is very helpful to understand the emergent
phenomena in lutetium-based compounds (such as room-temperature
superconductivity). However, this kind of study is still scarce at present.
Here, we report on the electronic and magnetic properties of lutetium metals,
lutetium dihydride powders, and lutetium oxide powders. Crystal structures and
chemical compositions of these samples were characterized by X-ray diffraction
and X-ray photoemission spectroscopy, respectively. Electrical transport
measurements show that the resistance of lutetium has a linear behavior
depending on temperature, whereas the resistance of lutetium dihydride powders
is independent of temperature. More interestingly,
paramagnetism-ferromagnetism-spin glass transitions were observed at near 240
and 200 K, respectively, in lutetium metals. Our work uncovered the complex
magnetic properties of Lu-based compounds.",2303.11063v2
2023-07-18,Room-temperature magnetism and controlled cation distribution in vanadium ferrite thin films,"Spinel oxides demonstrate significant technological promise due to the vast
array of interrelated physical properties that their unique structure supports.
Specifically, the Fe1+xV2-xO4 spinel system garners extensive interest due to
the presence of orbitally ordered states and multiferroism. This study focuses
on the elaboration of high-quality Fe2VO4 (x = 1) thin films on MgO substrates
via pulsed laser deposition. Structural analyses confirm the epitaxial growth
of the films, their high crystallinity and fully strained nature. The cationic
distribution and stoichiometry were investigated using Resonant Elastic X-ray
Scattering experiments, in conjunction with comprehensive characterization of
the films' physical and electrical properties. The films exhibit
room-temperature magnetism, with a magnetization consistent with the
(Fe3+)Td[Fe2+V3+2]OhO4 inverse spinel structure unveiled by anomalous
diffraction. This work represents the inaugural successful deposition of Fe2VO4
thin films, thereby expanding the family of spinel vanadium oxide thin films
with a new member that demonstrates room-temperature magnetic properties.",2307.09598v1
2004-03-29,Quantum Tunneling of the Magnetization in the Ising Chain Compound Ca3Co2O6,"The magnetic behavior of the Ca3Co2O6 spin chain compound is characterized by
a large Ising-like character of its ferromagnetic chains, set on triangular
lattice, that are antiferromagnetically coupled. At low temperature, T < 7K,
the 3D antiferromagnetic state evolves towards a spin frozen state. In this
temperature range, magnetic field driven magnetization of single crystals
(H//chains) exhibits stepped variations. The occurrence of these steps at
regular intervals of the applied magnetic field, Hstep=1.2T, is reminiscent of
the quantum tunneling of the magnetization (QTM) of molecular based magnets.
Magnetization relaxation experiments also strongly support the occurrence of
this quantum phenomenon. This first observation of QTM in a magnetic oxide
belonging to the large family of the A3BBO6 compounds opens new opportunities
to study a quantum effect in a very different class of materials from molecular
magnets.",0403695v1
2018-11-09,Giant Exchange Bias in the Single-layered Ruddlesden-Popper Perovskite SrLaCo0.5Mn0.5O4,"Exchange bias (EB) as large as ~5.5 kOe is observed in SrLaCo0.5Mn0.5O4 which
is the highest ever found in any layered transition metal oxides including
Ruddlesden-Popper series. Neutron diffraction measurement rules out long-range
magnetic ordering and together with dc magnetic measurements suggest formation
of short-range magnetic domains. AC magnetic susceptibility, magnetic memory
effect and magnetic training effect confirm the system to be a cluster spin
glass. By carrying out density functional calculations on several model
configurations, we propose that EB is originated at the boundary between
Mn-rich antiferromagnetic and Co-rich ferromagnetic domains at the
sub-nanoscale. Reversal of magnetization axis on the Co-side alters the
magnetic coupling between the interfacial Mn and Co spins which leads to EB.
Our analysis infers that the presence of competing magnetic interactions is
sufficient to induce exchange bias and thereby a wide range of materials
exhibiting giant EB can be engineered for designing novel magnetic memory
devices.",1811.03960v1
2017-12-05,Inducing and Manipulating Magnetization in Two-Dimensional ZnO by Strain and External Gating,"Two-dimensional structures that exhibit intriguing magnetic phenomena such as
perpendicular magnetic anisotropy and switchable magnetization are of great
interests in spintronics research. Herein, the density-functional theory
studies reveal the critical impacts of strain and external gating on
vacancy-induced magnetism and its spin direction in a graphene-like single
layer of zinc oxide (ZnO). In contrast to the pristine and defective ZnO with
an O-vacancy, the presence of a Zn-vacancy induces significant magnetic moments
to its first neighboring O and Zn atoms due to the charge deficit. We further
predict that the direction of magnetization easy axis reverses from an in-plane
to perpendicular orientation under a practically achieved biaxial compressive
strain of $\sim$1--2\% or applying an electric-field by means of the charge
density modulation. This magnetization reversal is driven by the strain- and
electric-field-induced changes in the spin-orbit coupled \emph{d} states of the
first-neighbor Zn atom to the Zn-vacancy. These findings open interesting
prospects for exploiting strain and electric-field engineering to manipulate
magnetism and magnetization orientation of two-dimensional materials.",1712.01578v1
2019-03-01,A quantum pathway to overcome the trilemma of magnetic data storage,"The three essential pillars of magnetic data storage devices are readability,
writeability, and stability. However, these requirements compete as magnetic
domain sizes reach the fundamental limit of single atoms and molecules. The
proven magnetic bistability of individual holmium atoms on magnesium oxide
appeared to operate within this magnetic trilemma, sacrificing writeability for
unprecedented stability. Using the magnetic stray field created by the tip of a
spin-polarized scanning tunneling microscope (SP-STM), we controllably move the
Ho state into the quantum regime, allowing us to write its state via the
quantum tunneling of magnetization (QTM). We find that the hyperfine
interaction causes both the excellent magnetic bistability, even at zero
applied magnetic field, and the avoided level crossings which we use to control
the magnetic state via QTM. We explore how to use such a system to realize a
high-fidelity single atom NOT gate (inverter). Our approach reveals the
prospect of combining the best traits of the classical and quantum worlds for
next generation data storage.",1903.00242v1
2023-06-11,Jahn-Teller magnets,"A wide class of materials with different crystal and electronic structures
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO$_4$), 3D systems as
manganites RMnO$_3$, ferrates (CaSr)FeO$_3$, nickelates RNiO$_3$, to silver
oxide AgO are based on Jahn-Teller $3d$ and $4d$ ions. These unusual materials
called Jahn-Teller (JT) magnets are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states. The unconventional properties of the JT-magnets can
be related to the instability of their highly symmetric Jahn-Teller
""progenitors"" with the ground orbital $E$-state to charge transfer with
anti-Jahn-Teller $d$-$d$ disproportionation and the formation of a system of
effective local composite spin-singlet or spin-triplet, electronic or hole
$S$-type bosons moving in a non-magnetic or magnetic lattice. We consider
specific features of the anti-JT-disproportionation reaction, properties of the
electron-hole dimers, possible phase states of JT-magnets, effective
Hamiltonians for single- and two-band JT-magnets, and present a short overview
of physical properties for actual JT-magnets.",2306.06612v1
2010-01-06,Proximity effect and electron transport in the oxide hybrid heterostructures with superconducting/magnetic interfaces,"We report on the study of electron transport in the oxide heterostructures
with superconductor/magnetic matter (S/M) interfaces where anomaly large
penetration of superconducting correlations in magnetic matter (proximity
effect) is realized. The developed theoretical model based on multilayer
magnetic structure of M-interlayer and experiment show presence of the
long-range proximity effect at S/M-interface with antiferromagnetic (AF)
ordering of the interlayer magnetization. The investigated hybrid
heterostructures include cuprate superconductor, the AF-cuprate interlayer and
conventional superconductor, Nb. The superconducting critical current with
density 1-10A/cm2 and the characteristic voltage, 0.1-0.2 mV, are observed at
liquid helium temperature for 15-50 nm thick M-interlayer made of AF film
CaSrCuO. These heterostructures demonstrate deviation from sin-type
superconducting current-phase relation and had the critical current of the
second harmonic of 10-20% of the first harmonic one. The hybrid
heterostructures with S/AF interface show high sensitivity to the external
magnetic field that is possibly caused by the influence of an external magnetic
field on the canting of magnetic moments of individual layers of AF
-interlayer. Substituting the AF cuprate by a manganite film, no critical
current was observed, although the M- interlayer was made very thin, down to 5
nm.",1001.0963v1
2018-11-24,The interfacial spin modulation of graphene on Fe(111),"When Fe, which is a typical ferromagnet using d- or f-orbital states, is
combined with 2D materials such as graphene, it offers many opportunities for
spintronics. The origin of 2D magnetism is from magnetic insulating behaviors,
which could result in magnetic excitations and also proximity effects. However,
the phenomena were only observed at extremely low temperatures. Fe and graphene
interfaces could control spin structures in which they show a unique atomic
spin modulation and magnetic coupling through the interface. Another reason for
covering graphene on Fe is to prevent oxidation under ambient conditions. We
investigated the engineering of spin configurations by growing monolayer
graphene on an Fe(111) single crystal surface and observed the presence of
sharply branched, 3D tree-like domain structures. Magnetization by a sweeping
magnetic field (m-H) revealed that the interface showed canted magnetization in
the in-plane (IP) orientation. Moreover, graphene could completely prevent the
oxidation of the Fe surface. The results indicate possible control of the spin
structures at the atomic scale and the interface phenomena in the 2D structure.
The study introduces a new approach for room temperature 2D magnetism.",1811.09773v1
2018-10-09,"Magnetic behavior, Griffiths phase and magneto-transport study in 3$d$ based nano-crystalline double perovskite Pr$_2$CoMnO$_6$","Double perovskite (DP) oxide material receive extensive research interest due
to exciting physical properties with potential technological application. 3$d$
based DP oxides are promising for exciting physics like magnetodielectric,
ferroelectric, Griffith phase etc., specially Co/Mn DPs are gaining much
research interest. In this paper we present the study of magnetic phase and
transport properties in nano-crystalline Pr$_2$CoMnO$_6$ a 3$d$ based double
perovskite compound. This material shows a paramagnetic (PM) to ferromagnetic
(FM) phase transition below 173 K marked by a rapid increase in magnetic moment
due to spin ordering. We found divergence in inverse magnetic susceptibility
($\chi$$^{-1}$) from Curie weiss behavior around 206 K which indicates the
evolution of Griffiths phase before actual PM-FM transition. We found that the
Griffiths phase suppressed with increasing applied magnetic filed. For the
understanding of charge transport in this material we have measured temperature
dependent electrical resistivity. Pr$_2$CoMnO$_6$ is a strong insulator where
resistivity increase abruptly below magnetic phase transition. To understand
the effect of magnetic field on transport behavior we have also measured the
magnetoresistance (MR) at different temperatures. Sample shows the negative MR
with maximum value $\sim$22 $\%$ under applied magnetic field of 50 kOe at 125
K. MR follows quadratic field dependency above $T_c$ however below $T_c$ the MR
shows deviation from this field dependency at low field.",1810.03895v1
2019-02-14,High-speed domain wall racetracks in a magnetic insulator,"Recent reports of current-induced switching of ferrimagnetic oxides coupled
to a heavy metal layer have opened realistic prospects for implementing
magnetic insulators into electrically addressable spintronic devices. However,
key aspects such as the configuration and dynamics of magnetic domain walls
driven by electrical currents in insulating oxides remain unexplored. Here, we
investigate the internal structure of the domain walls in Tm3Fe5O12 (TmIG) and
TmIG/Pt bilayers and demonstrate their efficient manipulation by spin-orbit
torques with velocities of up to 400 m s$^{-1}$ and minimal current threshold
for domain wall flow of 5 x 10$^{6}$ A cm$^{-2}$. Domain wall racetracks
embedded in TmIG are defined by the deposition of Pt current lines, which allow
us to control the domain propagation and magnetization switching in selected
regions of an extended magnetic layer. Scanning nitrogen-vacancy magnetometry
reveals that the domain walls of thin TmIG films are N\'eel walls with
left-handed chirality, with the domain wall magnetization rotating towards an
intermediate N\'eel-Bloch configuration upon deposition of Pt. These results
indicate the presence of a sizable interfacial Dzyaloshinskii-Moriya
interaction in TmIG, which leads to novel possibilities to control the
formation of chiral spin textures in magnetic insulators. Ultimately, domain
wall racetracks provide an efficient scheme to pattern the magnetic landscape
of TmIG in a fast and reversible way",1902.05639v1
2022-10-18,Spin re-orientation induced anisotropic magnetoresistance switching in LaCo$_{0.5}$Ni$_{0.5}$O$_{3-δ}$ thin films,"Realization of novel functionalities by tuning magnetic interactions in rare
earth perovskite oxide thin films opens up exciting technological prospects.
Strain-induced tuning of magnetic interactions in rare earth cobaltates and
nickelates is of central importance due to their versatility in electronic
transport properties. Here we reported the spin re-orientation induced
switching of anisotropic magnetoresistance (AMR) and its tunability with strain
in epitaxial LaCo$_{0.5}$Ni$_{0.5}$O$_{3-\delta}$ thin films across the
ferromagnetic transition. Moreover, with strain tuning, we could observe a
two-fold to four-fold symmetry crossover in AMR across the magnetic transition
temperature. The magnetization measurements revealed an onset of ferromagnetic
transition around 50 K, and a further reduction in temperature showed a subtle
change in the magnetization dynamics, which reduced the ferromagnetic
long-range ordering and introduced glassiness in the system. X-ray absorption
and X-ray magnetic circular dichroism spectroscopy measurements over Co and Ni
L edges revealed the Co spin state transition below the magnetic transition
temperature leading to the AMR switching and also the presence of Ni$^{2+}$ and
Co$^{4+}$ ions evidencing the charge transfer from Ni to Co ions. Our work
demonstrated the tunability of magnetic interactions mediated electronic
transport in cobaltate-nickelate thin films, which is relevant in understanding
Ni-Co interactions in oxides for their technological applications such as in
AMR sensors.",2210.09608v3
2021-10-21,Heat Capacity of oxide scale in the range from 0 C to 1300 C: Generalized estimates with account for movability of phase transitions,"The known data on the heat capacity of magnetite (Fe3O4), hematite (Fe2O3)
and iron (Fe) at different temperatures are approximated by formulas containing
phase transition temperatures as varying parameters. This allows to take into
account the effect of phase transition shifts, for example, due to impurities,
lattice defects, grain sizes or high cooling rates. For this purpose, the
entire target temperature range from 0 C to 1300 C is divided by phase
transition temperatures into separate intervals. The conjugation of the
approximating functions between the intervals at the magnetic transition point
is performed without a gap, and at the point of polymorphic transformation
(alpha Fe - gamma Fe) with a finite gap of heat capacity values. For wustite
Fe1-xO which does not experience phase transformations, the temperature
dependence of the heat capacity is approximated by a single smooth function. In
combination with previously obtained formulas for the density of iron oxides
and iron the proposed approximations allow us to estimate the specific mass
heat capacity of oxide scale depending of its structural composition and
temperature. By model calculations it is shown that at temperatures of 200 C
and 900 C specific mass heat capacity of oxide scale practically does not
depend on the percentage of its individual components and is approximately 750
and 850 J/(kg K) respectively. At a temperature of about 575 C, on contrary,
actually possible variations in the composition of oxide scale can lead to a
change in its specific heat capacity from 850 to 1150 J/(kg K). The obtained
dependencies are recommended for use in mathematical modeling of production and
processing of steel products in the presence of oxide scale on their surface",2110.11101v1
2011-01-04,"Density functional theory analysis of the interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction and spin-orbit coupling in Ca3CoMO6 (M = Co, Rh, Ir)","In the isostructural oxides Ca3CoMO6 (M = Co, Rh, Ir), the CoMO6 chains made
up of face-sharing CoO6 trigonal prisms and MO6 octahedra are separated by Ca
atoms. We analyzed the magnetic and electronic properties of these oxides on
the basis of density functional theory calculations including on-site repulsion
and spin-orbit coupling, and examined the essential one-electron pictures
hidden behind results of these calculations. Our analysis reveals an intimate
interplay between Jahn-Teller instability, uniaxial magnetism, spin
arrangement, metal-metal interaction, and spin-orbit coupling in governing the
magnetic and electronic properties of these oxides. These oxides undergo a
Jahn-Teller distortion but their distortions are weak, so that their
trigonal-prism Con+ (n = 2, 3) ions still give rise to strong easy-axis
anisotropy along the chain direction. As for the d-state split pattern of these
ions, the electronic and magnetic properties of Ca3CoMO6 (M = Co, Rh, Ir) are
consistent with d0 < (d2, d-2) < (d1, d-1), but not with (d2, d-2) < d0 < (d1,
d-1). The trigonal-prism Co3+ ion in Ca3Co2O6 has the L = 2 configuration
(d0)1(d2, d-2)3(d1, d-1)2 because of the metal-metal interaction between
adjacent Co3+ ions in each Co2O6 chain, which is mediated by their z2 orbitals,
and the spin-orbit coupling of the trigonal-prism Co3+ ion. The spins in each
CoMO6 chain of Ca3CoMO6 prefer the ferromagnetic arrangement for M = Co and Rh,
but the antiferromagnetic arrangement for M = Ir. The octahedral M4+ ion of
Ca3CoMO6 has the (1a)1(1e)4 configuration for M = Rh but the (1a)2(1e)3
configuration for M = Ir, which arises from the difference in the spin-orbit
coupling of the M4+ ions and the Co...M metal-metal interactions.",1101.0644v1
2019-07-26,Stabilization of $\varepsilon$-Fe$_2$O$_3$ epitaxial layer on MgO(111)/GaN via an intermediate $γ$-Fe$_2$O$_3$-phase,"In the present study we have demonstrated epitaxial stabilization of the
metastable magnetically-hard $\varepsilon$-Fe$_2$O$_3$ phase on top of a thin
MgO(111) buffer layer grown onto the GaN (0001) surface. The primary purpose to
introduce a 4\,nm-thick buffer layer of MgO in between Fe$_2$O$_3$ and GaN was
to stop thermal migration of Ga into the iron oxide layer. Though such
migration and successive formation of the orthorhombic GaFeO$_3$ was supposed
earlier to be a potential trigger of the nucleation of the isostructural
$\varepsilon$-Fe$_2$O$_3$, the present work demonstrates that the growth of
single crystalline uniform films of epsilon ferrite by pulsed laser deposition
is possible even on the MgO capped GaN. The structural properties of the 60\,nm
thick Fe$_2$O$_3$ layer on MgO / GaN were probed by electron and x-ray
diffraction, both suggesting that the growth of $\varepsilon$-Fe$_2$O$_3$ is
preceded by formation of a thin layer of $\gamma$-Fe$_2$O$_3$. The presence of
the magnetically hard epsilon ferrite was independently confirmed by
temperature dependent magnetometry measurements. The depth-resolved x-ray and
polarized neutron reflectometry reveal that the 10\,nm iron oxide layer at the
interface has a lower density and a higher magnetization than the main volume
of the $\varepsilon$-Fe$_2$O$_3$ film. The density and magnetic moment depth
profiles derived from fitting the reflectometry data are in a good agreement
with the presence of the magnetically degraded $\gamma$-Fe$_2$O$_3$ transition
layer between MgO and $\varepsilon$-Fe$_2$O$_3$. The natural occurrence of the
interface between magnetoelectric $\varepsilon$- and spin caloritronic
$\gamma$- iron oxide phases can enable further opportunities to design novel
all-oxide-on-semiconductor devices.",1907.11611v2
1998-01-20,Electronic States and Excitation Spectra of Copper Oxides with Ladder and/or Chain,"Recently the superconductivity has been reported in the copper oxides
(Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$ with ladders and edge-sharing chains under
pressure. In order to understand the mechanism of the superconductivity, it is
crucial to clarify the distribution of self-doped holes. From the analysis of
the optical conductivity by ionic model and exact diagonalization method, we
confirm that with substituting Ca for Sr, the self-doped holes are transferred
from the chains to the ladders. We also examine the electronic states of
edge-sharing chain in a variety of copper oxides, and derive the effective
Hamiltonian. The dependences of the magnetic interactions between Cu ions and
of the hopping energies of the Zhang-Rice singlet on the bond angle of Cu-O-Cu
are discussed.",9801195v1
2000-10-20,Geometric frustration in the mixed layer pnictide oxides,"We present results from a Monte Carlo investigation of a simple bilayer model
with geometrically frustrated interactions similar to those found in the mixed
layer pnictide oxides $(Sr_{2}Mn_{3}Pn_{2}O_{2}, Pn=As,Sb).$ Our model is
composed of two inequivalent square lattices with nearest neighbor intra- and
interlayer interactions. We find a ground state composed of two independent
N\'{e}el ordered layers when the interlayer exchange is an order of magnitude
weaker than the intralayer exchange, as suggested by experiment. We observe
this result independent of the number of layers in our model. We find evidence
for local orthogonal order between the layers, but it occurs in regions of
parameter space that are not experimentally realized. We conclude that
frustration caused by nearest neighbor interactions in the mixed layer pnictide
oxides is not sufficient to explain the long--range orthogonal order that is
observed experimentally, and that it is likely that other terms (e.g., local
anisotropies) in the Hamiltonian are required to explain the magnetic behavior.",0010303v1
2002-01-15,Magnetic Resonant Mode in the Single-Layer High Temperature Superconductor Tl$_2$Ba$_2$Cu$_{6+δ}$,"An unusual spin excitation mode observed by neutron scattering has inspired
numerous theoretical studies of the interplay between charged quasiparticles
and collective spin excitations in the copper oxide high temperature
superconductors. The mode has thus far only been observed in materials with
crystal structures consisting of copper oxide bilayers, and it is notably
absent in the single-layer compound La$_{2-x}$Sr$_{x}$CuO$_{4+\delta}$. Neutron
scattering data now show that the mode is present in
Tl$_2$Ba$_2$Cu$_{6+\delta}$, a single-layer compound with T$_c$ $\sim$ 90 K,
thus demonstrating that it is a generic feature of the copper oxide
superconductors, independent of the layer sequence. This restricts the
theoretical models for the origin of the resonant mode and its role in the
mechanism of high temperature superconductivity.",0201252v1
2006-08-11,Scaling behavior in thermoelectric misfit cobalt oxides,"We investigate both thermoelectric and thermodynamic properties of the misfit
cobalt oxide [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$. A
large negative magnetothermopower is found to scale with both magnetic field
and temperature revealing a significant spin entropy contribution to
thermoelectric properties giving rise to a constant S$_0\approx$ 60 $\mu$V
K$^{-1}$ equal to the high temperature asymptotic value of the spin 1/2
entropy. Low temperature specific heat measurements allow us to determine an
enhanced electronic part with $\gamma\approx$ 50 mJ (mol K$^{2}$)$^{-1}$
attesting of strong correlations. Thereby, a critical comparison between
[Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$, other cobaltites
as well as other materials reveals a universal behavior of the thermopower low
temperature slope as a function of $\gamma$ testifying thus a purely electronic
origin. This potentially generic scaling behavior suggests here that the high
room temperature value of the thermopower in misfit cobalt oxides results from
the addition of a spin entropy contribution to an enlarged electronic one.",0608264v1
2008-09-05,Structure-Property Relation of SrTiO3-LaAlO3 Interfaces,"A large variety of transport properties have been observed at the interface
between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D
interface metallicity, 3D bulk metallicity, Kondo scattering, magnetism and
superconductivity. The relation between the structure and the properties of the
SrTiO3-LaAlO3 interface can be explained in a meaningful way by taking into
account the relative contribution of three structural aspects: oxygen
vacancies, structural deformations (including cation disorder) and electronic
interface reconstruction. The emerging phase diagram is much richer than for
related bulk oxides due to the occurrence of interface electronic
reconstruction. The observation of this interface phenomenon is a display of
recent advances in thin film deposition and characterization techniques, and
provides an extension to the range of exceptional electronic properties of
complex oxides.",0809.1068v1
2008-12-20,Distinct transport behaviors of LaFe1-yCoyAsO1-xFx (x=0.11) between the superconducting and nonsuperconducting metallic y regions divided by y ~ 0.05,"Electrical resistivities, Hall coefficients and thermoelectric powers have
been measured for polycrystalline samples of LaFe1-yCoyAsO1-xFx (x=0.11) with
various values of y. The results show that there exists clear distinction of
these transport behaviors between the superconducting and nonsuperconducting
metallic regions of y divided by the boundary value yc~0.05. We have found that
the behaviors in both regions are very similar to those of high-Tc Cu oxides in
the corresponding phases. If they reflect, as in the case of Cu oxides, effects
of strong magnetic fluctuations, the energy scale of the fluctuations is
considered to be smaller than that of the high Cu oxides by a factor of ~1/2.
Arguments on the electronic nature and superconducting symmetry are presented
on the basis of the observed small rate of the Tc suppression rate by the Co
doping.",0812.3949v1
2009-03-19,Superconductivity at 17 K in (Fe2P2)(Sr4Sc2O6): a new superconducting layered pnictide oxide with a thick perovskite oxide layer,"A new layered oxypnictide (Fe2P2)(Sr4Sc2O6) have been synthesized by
solid-state reaction. This material has an alternating layer stacking structure
of anti-fluorite Fe2P2 and perovskite-based Sr4Sc2O6 oxide layers. Space group
of the material is P4/nmm and lattice constants a and c are 4.016 A and 15.543
A, respectively. The interlayer Fe-Fe distance corresponding to the c-axis
length is the longest ever reported in the iron-based oxypnictide systems. In
both magnetization and resistivity measurements, the present compound exhibited
superconductivity below 17 K, which is much higher than that of LaFePO and the
highest in arsenic-free iron-based oxypnictide systems under ambient pressure.",0903.3314v3
2009-07-19,Hyperthermia HeLa cell treatment with silica coated manganese oxide nanoparticles,"The effect of a high frequency alternating magnetic field on HeLa tumour
cells incubated with ferromagnetic nanoparticles of manganese oxide perovskite
La0.56(SrCa)0.22MnO3 have been studied. The particles were subjected to a size
selection process and coated with silica to improve their biocompatibility. The
control assays made with HeLa tumour cells showed that cell survival and growth
rate were not affected by the particle internalization in cells, or by the
electromagnetic field on cells without nanoparticles. However, the application
of an alternating electromagnetic field to cells incubated with this silica
coated manganese oxide induced a significant cellular damage that finally lead
to cell death by an apoptotic mechanism. Cell death is triggered even thought
the temperature increase in the cell culture during the hyperthermia treatment
is lower than 0.5 C.",0907.3278v2
2009-08-19,Supercell band calculations and correlation for high-$T_C$ copper oxide superconductors,"First principle band calculations based on local versions of density
functional theory (DFT), together with results from nearly free-electron
models, can describe many typical but unusual properties of the high-$T_C$
copper oxides. The methods and a few of the most important results are
reviewed. Some additional calculations are presented and the problems with the
commonly used approximate versions of DFT for oxides are discussed with a few
ideas for corrections. It is concluded that rather modest corrections to the
approximate DFT, without particular assumptions about strong correlation, can
push the ground state towards anti-ferro magnetic (AFM) order. Spin
fluctuations interacting with phonons are crucial for the mechanism of
superconductivity in this scenario.",0908.2767v1
2009-11-16,Doping graphene by adsorption of polar molecules at the oxidized zigzag edges,"We have theoretically investigated the electronic and magnetic properties of
graphene whose zigzag edges are oxidized. The alteration of these properties by
adsorption of $\mathrm{H_{2}O}$ and $\mathrm{NH_3}$ molecules have been
considered. It was found that the adsorbed molecules form a cluster along the
oxidized zigzag edges of graphene due to interaction with the electro-negative
oxygen. Graphene tends to donate a charge to the adsorbates through the oxygen
atoms and the efficiency of donation depends on the intermolecular distance and
on the location of the adsorbed molecules relative to the plane of graphene. It
was found that by appropriate selection of the adsorbates, a controllable and
gradual growth of $p$-doping in graphene with a variety of adsorbed molecules
can be achieved.",0911.3046v2
2010-03-16,All Magnesium diboride Josephson Junctions with MgO and native oxide barriers,"We present results on all-MgB2 tunnel junctions, where the tunnel barrier is
deposited MgO or native-oxide of base electrode. For the junctions with MgO,
the hysteretic I-V curve resembles a conventional underdamped Josephson
junction characteristic with critical current-resistance product nearly
independent of the junction area. The dependence of the critical current with
temperature up to 20 K agrees with the [Ambegaokar and Baratoff, Phys. Rev.
Lett. 10, 486 (1963)] expression. For the junctions with native-oxide,
conductance at low bias exhibits subgap features while at high bias reveals
thick barriers. As a result no supercurrent was observed in the latter, despite
the presence of superconducting-gaps to over 30 K.",1003.3158v1
2010-04-02,First Principles NMR Signatures of Graphene Oxide,"Nuclear magnetic resonance (NMR) has been widely used in the graphene oxide
(GO) structure study. However, the detailed relationship between its
spectroscopic features and the GO structural configuration has remained
elusive. Based on first principles $^{13}$C chemical shift calculations using
the gauge including projector augmented waves (GIPAW) method, we provide a
spectrum-structure connection. Chemical shift of carbon is found to be very
sensitive to atomic environment, even with an identical oxidation group.
Factors determining the chemical shifts for epoxy and hydroxy groups have been
discussed. GO structures previously reported in the literature have been
checked from the NMR point of view. The energetically favorable hydroxy chain
structure is not expected to be widely existed in real GO samples according to
our NMR simulations. The epoxy pair we proposed previously is also supported by
chemical shift calculations.",1004.0333v1
2010-11-21,Localized vs. delocalized character of charge carriers in LaAlO3/ SrTiO3 superlattices,"Understanding the nature of electrical conductivity, superconductivity and
magnetism between layers of oxides is of immense importance for the design of
electronic devices employing oxide heterostructures. We demonstrate that
resonant inelastic X-ray scattering can be applied to directly probe the
carriers in oxide heterostructures. Our investigation on epitaxially grown
LaAlO3/SrTiO3 superlattices unambiguously reveals the presence of both
localized and delocalized Ti 3d carriers. These two types of carriers are
caused by oxygen vacancies and electron transfer due to the polar discontinuity
at the interface. This result allows explaining the reported discrepancy
between theoretically calculated and experimentally measured carrier density
values in LaAlO3/SrTiO3 heterostructures.",1011.4674v1
2011-10-19,Synthesis of novel rare earth - iron oxide chalcogenides with the La2Fe2O3Se2 structure,"Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and
Zn resulted in preparation of two new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 which
are isostructural to La2Fe2O3Se2 and Sm2Ti2O3Sb2. Crystal structures of the new
compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 were determined from powder X-ray
diffraction data. Magnetic measurements were performed for Ce2Fe2O3S2 and
revealed behavior very similar to that of isostructural oxide chalcogenides of
iron and pnictides of titanium. In particular, no superconductivity was
observed down to 4 K. Crystal chemical factors determining the stability of the
La2Fe2O3Se2 structure type are discussed.",1110.4234v1
2012-02-04,Phonon anomalies and dynamic stripes,"Stripe order where electrons self-organize into alternating periodic
charge-rich and magnetically-ordered charge-poor parallel lines was proposed as
a way of optimizing the kinetic energy of holes in a doped Mott insulator.
Static stripes detected as extra peaks in diffraction patterns, appear in a
number of oxide perovskites as well as some other systems. The more
controversial dynamic stripes, which are not detectable by diffraction, may be
universally present in copper oxide superconductors. Thus it is important to
learn how to detect dynamic stripes as well as to understand their influence on
electronic properties. This review article focuses on lattice vibrations
(phonons) that might show signatures of the charge component of dynamic
stripes. The first part of the article describes recent progress in learning
about how the phonon signatures of different types of electronic charge
fluctuations including stripes can be distinguished from purely structural
instabilities and from each other. Then I will focus on the evidence for
dynamic stripes in the phonon spectra of copper oxide superconductors.",1202.0852v2
2012-03-30,Preventing the reconstruction of the polar discontinuity at oxide heterointerfaces,"Perovskite oxide heteroepitaxy receives much attention because of the
possibility to com- bine the diverse functionalities of perovskite oxide
building blocks. A general boundary con- dition for the epitaxy is the presence
of polar discontinuities at heterointerfaces. These polar discontinuities
result in reconstructions, often creating new functionalities at the interface.
However, for a significant number of materials these reconstructions are
unwanted as they alter the intrinsic materials properties at the interface.
Therefore, a strategy to eliminate this reconstruction of the polar
discontinuity at the interfaces is required. We show that the use of
compositional interface engineering can prevent the reconstruction at the
La0.67Sr0.33MnO3/SrTiO3 (LSMO/STO) interface. The polar discontinuity at this
interface can be removed by the insertion of a single La0.33Sr0.67O layer,
resulting in improved interface magnetization and electrical conductivity.",1203.6729v1
2012-07-19,Strongly coupled phase transition in ferroelectric/correlated electron oxide heterostructures,"We fabricated ultrathin ferroelectric/correlated electron oxide
heterostructures composed of the ferroelectric Pb(Zr0.2Ti0.8)O3 and the
correlated electron oxide (CEO) La0.8Sr0.2MnO3 on SrTiO3 substrates by pulsed
laser epitaxy. The hole accumulation in the ultrathin CEO layer was
substantially modified by heterostructuring with the ferroelectric layer,
resulting in an insulator-metal transition. In particular, our thickness
dependent study showed that drastic changes in transport and magnetic
properties were strongly coupled to the modulation of charge carriers by
ferroelectric field effect, which was confined to the vicinity of the
interface. Thus, our results provide crucial evidence that strong ferroelectric
field effect control can be achieved in ultrathin (10 nm) heterostructures,
yielding at least a 100,000-fold change in resistivity.",1207.4723v1
2013-10-31,Origin of two-dimensional electron gases at oxide interfaces: insights from theory,"The response of oxide thin films to polar discontinuities at interfaces and
surfaces has generated an enormous activity due to the variety of interesting
effects it gives rise to. A case in point is the discovery of the electron gas
at the interface between LaAlO3 and SrTiO3, which has since been shown to be
quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite
these findings, the origin of the two-dimensional electron gas is highly
debated and several possible mechanisms remain. Here we review the main
proposed mechanisms and attempt to model expected effects in a quantitative way
with the ambition of better constraining what effects can/cannot explain the
observed phenomenology. We do it in the framework of a phenomenological model
for understanding electronic and/or redox screening of the chemical charge in
oxide heterostructures. We also discuss the effect of intermixing, both
conserving and non-conserving the total stoichiometry.",1310.8427v2
2013-12-30,Correlation effects in (111) bilayers of perovskite transition-metal oxides,"We investigate the correlation-induced Mott, magnetic, and topological phase
transitions in artificial (111) bilayers of perovskite transition-metal oxides
LaAuO$_3$ and SrIrO$_3$ for which the previous density-functional theory
calculations predicted topological insulating states. Using the
dynamical-mean-field theory with realistic band structures and Coulomb
interactions, LaAuO$_3$ bilayer is shown to be far away from a Mott insulating
regime, and a topological-insulating state is robust. On the other hand,
SrIrO$_3$ bilayer is on the verge of an orbital-selective topological Mott
transition and turns to a trivial insulator by an antiferromagnetic ordering.
Oxide bilayers thus provide a novel class of topological materials for which
the interplay between the spin-orbit coupling and electron-electron
interactions is a fundamental ingredient.",1401.0009v2
2014-12-16,Terahertz spectroscopy of N$^{18}$O and isotopic invariant fit of several nitric oxide isotopologs,"A tunable far-infrared laser sideband spectrometer was used to investigate a
nitric oxide sample enriched in 18O between 0.99 and 4.75 THz. Regular,
electric dipole transitions were recorded between 0.99 and 2.52 THz, while
magnetic dipole transitions between the 2Pi(1/2) and 2Pi(3/2) spin-ladders were
recorded between 3.71 and 4.75 THz. These data were combined with lower
frequency data of N(18)$O (unlabeled atoms refer to (14)N and (16)O,
respectively), with rotational data of NO, (15)NO, N(17)O, and (15)N(18)O, and
with heterodyne infrared data of NO to be subjected to one isotopic invariant
fit. Rotational, fine and hyperfine structure parameters were determined along
with vibrational, rotational, and Born-Oppenheimer breakdown corrections. The
resulting spectroscopic parameters permit prediction of rotational spectra
suitable for the identification of various nitric oxide isotopologs especially
in the interstellar medium by means of rotational spectroscopy.",1412.4974v1
2015-11-19,Spin-density functional theories and their $+U$ and $+J$ extensions: a comparative study of transition metals and transition metal oxides,"Previous work on the physical content of exchange correlation functionals
that depend on both charge and spin densities is extended to elemental
transition metals and a wider range of perovskite transition metal oxides. A
comparison of spectra and magnetic moments calculated using exchange
correlation functionals depending on charge density only or on both charge and
spin densities, as well as the $+U$ and $+J$ extensions of these methods
confirms previous conclusions that the spin-dependent part of the exchange
correlation functional provides an effective Hund's interaction acting on the
transition metal $d$ orbitals. For the local spin density approximation and
spin-dependent Perdew-Burke-Ernzerhof generalized gradient approximation, the
effective Hund's exchange is found to be larger than 1 eV. The results indicate
that at least as far as applications to transition metals and their oxides are
concerned, $+U$, $+J$ and +dynamical mean field theory extensions of density
functional theory should be based on exchange-correlation functionals of charge
density only.",1511.06042v1
2016-04-19,Dirac topological insulator in the d$_{z^2}$ manifold of a honeycomb oxide,"We show by means of ab initio calculations and tight-binding modeling that an
oxide system based on a honeycomb lattice can sustain topologically non-trivial
states if a single orbital dominates the spectrum close to the Fermi level. In
such situation, the low energy spectra is described by two Dirac equations that
become non-trivially gapped when spin-orbit coupling (SOC) is switched on. We
provide one specific example for this but the recipe is general. We discuss a
realization of this starting from a conventional spin-a-half honeycomb
antiferromagnet whose states close to the Fermi energy are d$_{z^2}$ orbitals.
Switching off magnetism by atomic substitution and ensuring that the electronic
structure becomes two-dimensional is sufficient for topologicality to arise in
such a system. We show that the gap in such model scales linearly with SOC,
opposed to other oxide-based topological insulators, where smaller gaps tend to
appear by construction of the lattice. We also provide a study of the quantum
Hall effect in such system, showing the close connections with the physics of
graphene but in a d-electron system.",1604.05554v2
2017-01-30,Effect of iron oxide loading on magnetoferritin structure in solution as revealed by SAXS and SANS,"Synthetic biological macromolecule of magnetoferritin containing an iron
oxide core inside a protein shell (apoferritin) is prepared with different
content of iron. Its structure in aqueous solution is analyzed by small-angle
synchrotron X-ray (SAXS) and neutron (SANS) scattering. The loading factor (LF)
defined as the average number of iron atoms per protein is varied up to LF=800.
With an increase of the LF, the scattering curves exhibit a relative increase
in the total scattered intensity, a partial smearing and a shift of the match
point in the SANS contrast variation data. The analysis shows an increase in
the polydispersity of the proteins and a corresponding effective increase in
the relative content of magnetic material against the protein moiety of the
shell with the LF growth. At LFs above ~150, the apoferritin shell undergoes
structural changes, which is strongly indicative of the fact that the shell
stability is affected by iron oxide presence.",1702.00350v1
2017-03-11,Competing weak localization and weak antilocalization in amorphous indium-gallium-zinc-oxide thin-film transistors,"We have investigated the gate-voltage dependence and the temperature
dependence of the magnetoconductivity of amorphous indium-gallium-zinc-oxide
thin-film transistors. A weak-localization feature is observed at small
magnetic fields on top of an overall negative magnetoconductivity at higher
fields. An intriguing controllable competition between weak localization and
weak antilocalization is observed by tuning the gate voltage or varying the
temperature. Our findings reflect controllable quantum interference competition
in the electron systems in amorphous indium-gallium-zinc-oxide thin-film
transistors.",1703.04007v1
2017-08-01,Ultrafast Modification of the Polarity at LaAlO$_3$/SrTiO$_3$ Interfaces,"Oxide growth with semiconductor-like accuracy has led to atomically precise
thin films and interfaces that exhibit a plethora of phases and functionalities
not found in the oxide bulk material. This yielded spectacular discoveries such
as the conducting, magnetic or even superconducting LaAlO$_3$/SrTiO$_3$
interfaces separating two prototypical insulating perovskite materials. All
these investigations, however, consider the static state at the interface,
although studies on fast oxide interface dynamics would introduce a powerful
degree of freedom to understanding the nature of the LaAlO$_3$/SrTiO$_3$
interface state. Here we show that the polarization state at the
LaAlO$_3$/SrTiO$_3$ interface can be optically enhanced or attenuated within
picoseconds. Our observations are explained by a model based on charge
propagation effects in the interfacial vicinity and transient polarization
buildup at the interface.",1708.00198v1
2017-08-15,Polarizing oxygen vacancies in insulating metal oxides under high electric field,"We demonstrate a thermodynamic formulation to quantify defect formation
energetics in an insulator under high electric field. As a model system, we
analyzed neutral oxygen vacancies (color centers) in alkaline-earth-metal
binary oxides using density functional theory, Berry phase calculations, and
maximally localized Wannier functions. Work of polarization lowers the field
dependent electric Gibbs energy of formation of this defect. This is attributed
mainly to the ease of polarizing the two electrons trapped in the vacant site,
and secondarily to the defect induced reduction in bond stiffness and softening
of phonon modes. The formulation and analysis have implications for
understanding the behavior of insulating oxides in electronic, magnetic,
catalytic, and electrocaloric devices under high electric field.",1708.04598v1
2017-08-30,Depth profiling charge accumulation from a ferroelectric into a doped Mott insulator,"The electric field control of functional properties is a crucial goal in
oxide-based electronics. Non-volatile switching between different resistivity
or magnetic states in an oxide channel can be achieved through charge
accumulation or depletion from an adjacent ferroelectric. However, the way in
which charge distributes near the interface between the ferroelectric and the
oxide remains poorly known, which limits our understanding of such switching
effects. Here we use a first-of-a-kind combination of scanning transmission
electron microscopy with electron energy loss spectroscopy,
near-total-reflection hard X-ray photoemission spectroscopy, and ab-initio
theory to address this issue. We achieve a direct, quantitative, atomic-scale
characterization of the polarization-induced charge density changes at the
interface between the ferroelectric BiFeO3 and the doped Mott insulator
Ca1-xCexMnO3, thus providing insight on how interface-engineering can enhance
these switching effects.",1708.09160v1
2018-05-01,Averievite: a copper oxide kagome antiferromagnet,"Averievite, Cu$_5$V$_2$O$_{10}$(CsCl), is an oxide mineral composed of
Cu$^{2+}$ kagome layers sandwiched by Cu$^{2+}$-V$^{5+}$ honeycomb layers. We
have synthesized this oxide and investigated its properties from ab initio
calculations along with susceptibility and specific heat measurements. The data
indicate a Curie-Weiss temperature of 185 K as well as long-range magnetic
order at 24 K due to the significant interlayer coupling from the honeycomb
copper ions. This order is suppressed by substituting these coppers by
isoelectronic zinc, suggesting that Zn-substituted averievite is a promising
spin liquid candidate. A further proposed substitution that replaces V$^{5+}$
by Ti$^{4+}$ not only dopes the material, but is predicted to give rise to a
two-dimensional electronic structure featuring Dirac crossings. As such,
averievite is an attractive platform for S=1/2 kagome physics with the
potential for realizing novel electronic states.",1805.00561v2
2014-05-13,Real structure of lattice matched GaAs-Fe3Si core-shell nanowires,"GaAs nanowires and GaAs-Fe3Si core-shell nanowire structures were grown by
molecular-beam epitaxy on oxidized Si(111) substrates and characterized by
transmission electron microscopy (TEM) and X-ray diffraction (XRD). Ga droplets
were formed on the oxide surface, and the semiconducting GaAs nanowires grew
epitaxially via the vapor-liquid-solid mechanism as single-crystals from holes
in the oxide film. We observed two stages of growth of the GaAs nanowires,
first the regular growth and second the residual growth after the Ga supply was
finished. The magnetic Fe3Si shells were deposited in an As-free chamber. They
completely cover the GaAs cores although they consist of small grains.
High-resolution TEM micrographs depict the differently oriented grains in the
Fe3Si shells. Selected area diffraction of electrons and XRD gave further
evidence that the shells are textured and not single crystals. Facetting of the
shells was observed, which lead to thickness inhomogeneities of the shells.",1405.3143v2
2015-12-17,New Honeycomb Iridium (V) Oxides: NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$,"We report the structures and physical properties of two new iridates,
NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$, both of which contain continuous
two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature
oxidative deintercalation of sodium from Na$_2$IrO$_3$, and contains
edge-sharing IrO6 octahedra that form a planar honeycomb lattice.
Sr$_3$CaIr$_2$O$_9$, produced via conventional solid-state synthesis, hosts a
buckled honeycomb lattice with novel corner-sharing connectivity between IrO6
octahedra. Both of these new compounds are comprised of Ir$^{5+}$ (5$d^4$) and
exhibit negligible magnetic susceptibility. They are thus platforms to
investigate the origin of the nonmagnetic behavior exhibited by Ir$^{5+}$
oxides, and provide the first examples of a $J$ = 0 state on a honeycomb
lattice.",1512.05804v1
2017-10-02,Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-layer- induced Octahedral Distortion,"With reduced dimensionality, it is often easier to modify the properties of
ultra-thin films than their bulk counterparts. Strain engineering, usually
achieved by choosing appropriate substrates, has been proven effective in
controlling the properties of perovskite oxide films. An emerging alternative
route for developing new multifunctional perovskite is by modification of the
oxygen octahedral structure. Here we report the control of structural oxygen
octahedral rotation in ultra-thin perovskite SrRuO3 films by the deposition of
a SrTiO3 capping layer, which can be lithographically patterned to achieve
local control. Using a scanning Sagnac magnetic microscope, we show increase in
the Curie temperature of SrRuO3 due to the suppression octahedral rotations
revealed by the synchrotron x-ray diffraction. This capping-layer-based
technique may open new possibilities for developing functional oxide materials.",1710.00729v1
2017-10-24,La interstitial defect-induced insulator-metal transition in oxide heterostructures LaAlO3/SrTiO3,"Perovskite oxide interfaces have attracted tremendous research interest for
their fundamental physics and promising all-oxide electronics applications.
Here, based on first-principles calculations, we propose a novel surface La
interstitial promoted interface insulator-metal transition in LaAlO3/SrTiO3
(110). Compared with surface oxygen vacancies, which play a determining role on
the insulator-metal transition of LaAlO3/SrTiO3 (001) interfaces, we find that
surface La interstitials can be more experimentally realistic and accessible
for manipulation and more stable in ambient atmospheric environment.
Interestingly, these surface La interstitials also induce significant
spin-splitting states with Ti dyz/dxz character at conducting LaAlO3/SrTiO3
(110) interface. On the other hand, for insulating LaAlO3/SrTiO3 (110) (<4 unit
cells LaAlO3 thickness), a distortion between La (Al) and O atoms is found at
the LaAlO3 side, partially compensating the polarization divergence. Our
results reveal the origin of metal-insulator transition in LaAlO3/SrTiO3 (110)
heterostructures, and also shed light on the manipulation of the superior
properties of LaAlO3/SrTiO3 (110) for new possibilities of electronic and
magnetic applications.",1710.08652v1
2018-01-12,Control of oxidation and spin state in a single-molecule junction,"The oxidation and spin state of a metal-organic molecule determine its
chemical reactivity and magnetic properties. Here, we demonstrate the
reversible control of the oxidation and spin state in a single Fe-porphyrin
molecule in the force field of the tip of a scanning tunneling microscope.
Within the regimes of half-integer and integer spin state, we can further track
the evolution of the magnetocrystalline anisotropy. Our experimental results
are corroborated by density functional theory and wave function theory. This
combined analysis allows us to draw a complete picture of the molecular states
over a large range of intramolecular deformations.",1801.04162v1
2019-09-27,Enhancement of spin mixing conductance in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/LaNiO$_{3}$/SrRuO$_{3}$ heterostructures,"We investigate spin pumping and the effective spin mixing conductance in
heterostructures based on magnetic oxide trilayers composed of
La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO), LaNiO$_3$ (LNO), and SrRuO$_3$ (SRO). The
heterostructures serve as a model system for an estimation of the effective
spin mixing conductance at the different interfaces. Our results show that by
introducing a LNO interlayer between LSMO and SRO, the total effective spin
mixing conductance increases due to the much more favourable interface of
LSMO/LNO with respect to the LSMO/SRO interface. Neverheless, the spin current
into the SRO does not decrease because of the spin diffusion length of
$\lambda_\text{LNO}\approx$3.3 nm in the LNO. This value is two times higher
than that of SRO. Our results show the potential of using oxide interfaces to
tune the effective spin mixing conductance in heterostructures and to bring
novel functionalities into spintronics by implementing complex oxides.",1909.12766v1
2020-04-21,Electrical and acoustic self-oscillations in an epitaxial oxide for neuromorphic applications,"Developing materials that can lead to compact versions of artificial neurons
(neuristors) and synapses (memristors) is the main aspiration of the nascent
neuromorphic materials research field. Oscillating circuits are interesting as
neuristors, emulating the firing of action potentials. We present
room-temperature self-oscillating devices fabricated from epitaxial thin films
of semiconducting TbMnO3. We show that these electrical oscillations induce
concomitant mechanical oscillations that produce audible sound waves, offering
an additional degree of freedom to interface with other devices. The intrinsic
nature of the mechanism governing the oscillations gives rise to a high degree
of control and repeatability. Obtaining such properties in an epitaxial
perovskite oxide, opens the way towards combining self-oscillating properties
with those of other piezoelectric, ferroelectric, or magnetic perovskite oxides
to achieve hybrid neuristor-memristor functionality in compact heterostuctures.",2004.09903v2
2017-04-29,Improved electronic structure and magnetic exchange interactions in transition metal oxides,"We discuss the application of the Agapito Curtarolo and Buongiorno Nardelli
(ACBN0) pseudo-hybrid Hubbard density functional to several transition metal
oxides. ACBN0 is a fast, accurate and parameter-free alternative to traditional
DFT+$U$ and hybrid exact exchange methods. In ACBN0, the Hubbard energy of
DFT+$U$ is calculated via the direct evaluation of the local Coulomb and
exchange integrals in which the screening of the bare Coulomb potential is
accounted for by a renormalization of the density matrix. We demonstrate the
success of the ACBN0 approach for the electronic properties of a series
technologically relevant mono-oxides (MnO, CoO, NiO, FeO, both at equilibrium
and under pressure). We also present results on two mixed valence compounds,
Co$_3$O$_4$ and Mn$_3$O$_4$. Our results, obtained at the computational cost of
a standard LDA/PBE calculation, are in excellent agreement with hybrid
functionals, the GW approximation and experimental measurements.",1705.00194v1
2017-09-22,Universality in the Electronic Structure of 3d Transition Metal Oxides,"Electronic structure of strongly correlated transition metal oxides (TMOs) is
a complex phenomenon due to competing interaction among the charge, spin,
orbital and lattice degrees of freedom. Often individual compounds are examined
to explain certain properties associated with these compounds or in rare cases
few members of a family are investigated to define a particular trend exhibited
by that family. Here, with the objective of generalization, we have
investigated the electronic structure of three families of compounds, namely,
highly symmetric cubic mono-oxides, symmetry-lowered spinels and asymmetric
olivine phosphates, through density functional calculations. From the results
we have developed empirical hypotheses involving electron hopping,
electron-lattice coupling, Hund's rule coupling, strong correlation and d-band
filling. These hypotheses, classified through the point group symmetry of the
transition metal - oxygen complexes, can be useful to understand and predict
the electronic and magnetic structure of 3d TMOs.",1709.07868v1
2018-12-12,Room-temperature ferromagnetic insulating state in highly cation-ordered epitaxial oxide double perovskite,"Ferromagnetic insulators (FMIs) are one of the most important components in
developing dissipationless electronic and spintronic devices. However, since
ferromagnetism generally accompanies metallicity, FMIs are innately rare to
find in nature. Here, novel room-temperature FMI films are epitaxially
synthesized by deliberate control of the ratio of two B-site cations in the
double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic
phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature
(Tc~400 K) and a large saturation magnetization (MS~1.8 {\mu}B/f.u.) is found
in highly cation-ordered Fe-rich phases. The stabilization of the FMI state is
attributed to the formation of extra Fe3+-Fe3+ and Fe3+-Re6+ bonding states,
which originate from the excess Fe. The emerging FMI state by controlling
cations in the epitaxial oxide perovskites opens the door to developing novel
oxide quantum materials & heterostructures.",1812.04953v1
2020-06-02,Spin pumping and inverse spin Hall effect in iridium oxide,"Large charge-to-spin conversion (spin Hall angle) and spin Hall conductivity
are prerequisites for development of next generation power efficient spintronic
devices. In this context, heavy metals (e.g. Pt, W etc.), topological
insulators, antiferromagnets are usually considered because they exhibit high
spin-orbit coupling (SOC). In addition to the above materials, 5d transition
metal oxide e.g. Iridium Oxide (IrO 2 ) is a potential candidate which exhibits
high SOC strength. Here we report a study of spin pumping and inverse spin Hall
effect (ISHE), via ferromagnetic resonance (FMR), in IrO 2 /CoFeB system. We
identify the individual contribution of spin pumping and other spin
rectification effects in the magnetic layer, by investigating the in-plane
angular dependence of ISHE signal. Our analysis shows significant contribution
of spin pumping effect to the ISHE signal. We show that polycrystalline IrO 2
thin film exhibits high spin Hall conductivity and spin Hall angle which are
comparable to the values of Pt.",2006.01865v2
2020-06-06,Controlling Metal-Insulator Transitions in Vanadium Oxide Thin Films by Modifying Oxygen Stoichiometry,"Vanadium oxides are strongly correlated materials which display
metal-insulator transitions as well as various structural and magnetic
properties that depend heavily on oxygen stoichiometry. Therefore, it is
crucial to precisely control oxygen stoichiometry in these materials,
especially in thin films. This work demonstrates a high-vacuum gas evolution
technique which allows for the modification of oxygen concentration in VOX thin
films by carefully tuning thermodynamic conditions. We were able to control the
evolution between VO2, V3O5, and V2O3 phases on sapphire substrates, overcoming
the narrow phase stability of adjacent Magn\'eli phases. A variety of annealing
routes were found to achieve the desired phases and eventually to control the
metal-insulator transition (MIT). The pronounced MIT of the transformed films
along with the detailed structural investigations based on x-ray diffraction
measurements and reciprocal space mapping show that optimal stoichiometry is
obtained and stabilized. Using this technique, we find that the thin film V-O
phase diagram differs from that of the bulk material due to strain and finite
size effects. Our study demonstrates new pathways to strategically tune the
oxygen stoichiometry in complex oxides and provides a roadmap for understanding
the phase stability of VOX thin films.",2006.03998v1
2020-08-06,Crossover between Photochemical and Photothermal Oxidations of Atomically Thin Magnetic Semiconductor CrPS4,"Many two-dimensional (2D) semiconductors represented by transition metal
dichalcogenides have tunable optical bandgaps in the visible or near IR-range
standing as a promising candidate for optoelectronic devices. Despite this
potential, however, their photoreactions are not well understood or
controversial in the mechanistic details. In this work, we report a unique
thickness-dependent photoreaction sensitivity and a switchover between two
competing reaction mechanisms in atomically thin chromium thiophosphate
(CrPS4), a two-dimensional antiferromagnetic semiconductor. CrPS4 showed a
threshold power density 2 orders of magnitude smaller than that for MoS2
obeying a photothermal reaction route. In addition, reaction cross section
quantified with Raman spectroscopy revealed distinctive power dependences in
the low and high power regimes. On the basis of optical in situ thermometric
measurements and control experiments against O2, water, and photon energy, we
proposed a photochemical oxidation mechanism involving singlet O2 in the low
power regime with a photothermal route for the other. We also demonstrated a
highly effective encapsulation with Al2O3 as a protection against the
destructive photoinduced and ambient oxidations.",2008.02468v1
2021-02-08,"Schottky Barrier Heights of Defect-free Metal/ZnO, CdO, MgO and SrO Interfaces","The Schottky barrier heights (SBHs) of defect-free interfaces of ZnO, CdO,
MgO and SrO with various metals and different terminations are investigated by
density functional supercell calculations. The oxide bands are corrected for
their density functional band gap error by applying U-type treatment to their
metal-d and O-p states where necessary. The p-type SBHs are found to decrease
linearly with increasing metal work function. The pinning factor S of the
non-polar and polar interfaces are similar for each oxide. S is found to be
0.26, 0.56, 0.74 and 0.96 for CdO, ZnO, MgO and SrO, respectively, with S
increasing for increased oxide ionicity. The calculated pinning factors are
generally consistent with the metal-induced gap states (MIGS) model in terms of
variation with ionicity and dielectric constant. A significant shift of SBHs
from the non-polar to the polar interfaces of 0.4 eV, 1 eV and 0.5 eV for ZnO,
MgO and SrO, respectively, can be explained by an interfacial dipole. Our
results are also useful to describe Co,Fe|MgO interfaces in magnetic tunnel
junctions.",2102.04482v1
2021-10-26,Evidence for unconventional superconductivity in a spinel oxide,"The charge frustration with the mixed-valence state inherent to
LiTi$_2$O$_4$, which is found to be a unique spinel oxide superconductor, is
the impetus for paying special attention to reveal the existence of intriguing
superconducting properties. Here, we report a pronounced fourfold rotational
symmetry of the superconductivity in high-quality single-crystalline
LiTi$_2$O$_4$ (001) thin films. Both the magnetoresistivity and upper critical
field under an applied magnetic field manifest striking fourfold oscillations
deep inside the superconducting state, whereas the anisotropy vanishes in the
normal state, demonstrating that it is an intrinsic property of the
superconducting phase. We attribute this behavior to the unconventional
$d$-wave superconducting Cooper pairs with the irreducible representation of
$E_g$ protected by $O_h$ point group in LiTi$_2$O$_4$. Our findings demonstrate
the unconventional character of the pairing interaction in a three-dimensional
spinel oxide superconductor and shed new light on the pairing mechanism of
unconventional superconductivity.",2110.13397v2
2023-06-21,Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion,"The conditions whereby epitaxy is achieved are commonly believed to be mostly
governed by misfit strain. We report on a systematic investigation of growth
and interface structure of single crystalline tungsten thin films on two
different metal oxide substrates, Al$_{2}$O$_{3}$ ($11\bar{2}0$) and MgO
($001$). We demonstrate that despite a significant mismatch, enhanced crystal
quality is observed for tungsten grown on the sapphire substrates. This is
promoted by stronger adhesion and chemical bonding with sapphire compared to
magnesium oxide, along with the restructuring of the tungsten layers close to
the interface. The latter is supported by ab initio calculations using density
functional theory. Finally, we demonstrate the growth of magnetic
heterostructures consisting of high-quality tungsten layers in combination with
ferromagnetic CoFe layers, which are relevant for spintronic applications.",2306.12233v2
2004-04-29,Strongly-correlated crystal-field approach to 3d oxides - the orbital magnetism in 3d-ion compounds,"We have developed the crystal-field approach with strong electron
correlations, extended to the Quantum Atomistic Solid-State theory (QUASST), as
a physically relevant theoretical model for the description of electronic and
magnetic properties of 3d-atom compounds. Its applicability has been
illustrated for LaCoO3, FeBr2 and Na2V3O7. According to the QUASST theory in
compounds containing open 3d-/4f-/5f-shell atoms the discrete atomic-like
low-energy electronic structure survives also when the 3d atom becomes the full
part of a solid matter. This low-energy atomic-like electronic structure, being
determined by local crystal-field interactions and the intra-atomic spin-orbit
coupling, predominantly determines electronic and magnetic properties of the
whole compound.
  We understand our theoretical research as a continuation of the Van Vleck's
studies on the localized magnetism. We point out, however, the importance of
the orbital magnetism and the intra-atomic spin-orbit coupling for the
physically adequate description of real 3d-ion compounds and 3d magnetism. Our
studies clearly indicate that it is the highest time to ''unquench'' the
orbital moment in solid-state physics in description of 3d-atom containing
compounds.
  PACS No: 75.10.D; 71.70.E
  Keywords: magnetism, transition-metal compounds, 3d magnetism, crystal field,
spin-orbit coupling, orbital magnetism",0404713v1
2012-10-16,Magnetic dichroism in angular resolved hard X-ray photoelectron spectroscopy from buried magnetic layers,"This work reports on the measurement of magnetic dichroism in
angular-resolved photoelectron spectroscopy from in-plane magnetized buried
thin films. The high bulk sensitivity of hard X-ray photoelectron spectroscopy
(HAXPES) in combination with circularly polarized radiation enables the
investigation of the magnetic properties of buried layers. Angular
distributions of high kinetic energy (7 to 8 keV) photoelectrons in a range of
about 60 deg were recorded in parallel to the energy distribution. Depending on
purpose, energy and angular resolutions of 150 to 250 meV and 0.17 to 2 deg can
be accomplished simultaneously in such experiments. Experiments were performed
on exchange-biased magnetic layers covered by thin oxide films. More
specifically, the angular distribution of photoelectrons from the ferromagnetic
layer Co2FeAl layer grown on MnIr exchange-biasing layer was investigated where
the magnetic structure is buried beneath a MgO layer. Pronounced magnetic
dichroism is found in the Co and Fe 2p states for all angles of emission. A
slightly increased magnetic dichroism was observed for normal emission in
agreement with theoretical considerations.",1210.4374v1
2013-10-22,Evidence for Multiferroic Characteristics in NdCrTiO5,"We report NdCrTiO5 to be an unusual multiferroic material with large magnetic
field dependent electric polarization. While magneto-electric coupling in this
two magnetic sub-lattice oxide is well established, the purpose of this study
is to look for spontaneous symmetry breaking at the magnetic transition. The
conclusions are based on extensive magnetization, dielectric and polarization
measurements around its antiferromagnetic ordering temperature of 18K. Room
temperature X-ray diffraction pattern of NdCrTiO5 reveals that the sample is
single phase with an orthorhombic crystal structure that allows linear
magneto-electric coupling. DC magnetization measurement shows magnetization
downturn at 11K together with a small kink corresponding to the Co+3
sub-lattice ordering at ~18K. An anomaly in dielectric constant is observed
around the magnetic ordering temperature that increases substantially with
increasing magnetic field. Through detailed pyroelectric current measurements
at zero magnetic field, particularly as a function of thermal cycling, we
establish that NdCrTiO5 is a genuine multiferroic material that is possibly
driven by collinear magneto-striction.",1310.5803v1
2017-04-10,Magnetic Transitions under Ultrahigh Magnetic Fields of up to 130 T in the Breathing Pyrochlore Antiferromagnet LiInCr4O8,"The magnetization processes of the spin-3/2 antiferromagnet LiInCr4O8
comprising a ""breathing"" pyrochlore lattice, which is an alternating array of
small and large tetrahedra, are studied under ultrahigh magnetic fields of up
to 130 T using state-of-the-art pulsed magnets. A half magnetization plateau is
observed above 90 T to 130 T, suggesting that LiInCr4O8 has a strong
spin-lattice coupling, similar to conventional chromium spinel oxides. The
magnetization of LiGa0.125In0.875Cr4O8, in which the structural and magnetic
transitions at low temperatures have been completely suppressed, shows a sudden
increase above 13 T, indicating that a spin gap of 2.2 meV exists between a
tetramer singlet ground state and an excited state with total spin 1, with the
latter being stabilized by the application of a magnetic field. The breathing
pyrochlore antiferromagnet is found to be a unique frustrated system with
strong spin-lattice coupling and bond alternation.",1704.02784v1
2011-11-26,DC and AC Magnetization Study of Complex Ilmenite Oxides (Ni1-xCox)TiO3 (0.05 < x < 0.8),"Ilmenite solid-solutions, (Ni1-xCox)TiO3 (0.05 < x < 0.8), were synthesized
at ambient atmosphere through solid-state reaction and were studied by energy
dispersive spectroscopy of X-rays, X-ray diffraction, and DC and AC
magnetometry. Temperature dependent DC magnetic measurements revealed two
transitions. The first took place at around 27 K and the second at 63 K. The
low-temperature phase was antiferromagnetic. The phase observed between 27 and
63 K is characteristic to the solid-solution and is not found in either of the
constituent members. A fit of the data to the Curie-Weiss law gave magnetic
moment values which were significantly larger than the values based on the
quenched orbital momentum assumption. Zero-field-cooled magnetization
measurements with weak magnetic field revealed unexpected negative
magnetization at low temperatures. Below 63 K the DC magnetization exhibited
time dependent behavior. Frequency and magnetic field dependent AC
magnetization is also addressed.",1111.6140v1
2018-06-12,Emergent c-axis magnetic helix in manganite-nickelate superlattices,"The nature of the magnetic order in (La2/3Sr1/3MnO3)9/(LaNiO3)3 superlattices
is investigated using x-ray resonant magnetic reflectometry. We observe a new
c-axis magnetic helix state in the (LaNiO3)3 layers that had never been
reported in nickelates, and which mediates the ~130deg magnetic coupling
between the ferromagnetic (La2/3Sr1/3MnO3)9 layers, illustrating the power of
x-rays for discovering the magnetic state of complex oxide interfaces. Resonant
inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O
ligand hole states from bulk LaNiO3 are mostly filled due to interfacial
electron transfer from Mn, driving the Ni orbitals closer to an atomic-like 3d8
configuration. We discuss the constraints imposed by this electronic
configuration to the microscopic origin of the observed magnetic structure. The
presence of a magnetic helix in (La2/3Sr1/3MnO3)9/(LaNiO3)3 is crucial for
modeling the potential spintronic functionality of this system and may be
important for designing emergent magnetism in novel devices in general.",1806.04775v1
2019-11-05,Foucault imaging and small-angle electron diffraction in controlled external magnetic fields,"We report a method for acquiring Foucault images and small-angle electron
diffraction patterns in external magnetic fields using a conventional
transmission electron microscope without any modification. In the electron
optical system that we have constructed, external magnetic fields parallel to
the optical axis can be controlled using the objective lens pole piece under
weak excitation conditions in the Foucault mode and the diffraction mode. We
observe two ferromagnetic perovskite-type manganese oxides,
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ and Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$, in order to
visualize magnetic domains and their magnetic responses to external magnetic
fields. In rhombohedral-structured La$_{0.7}$Sr$_{0.3}$MnO$_{3}$, pinning of
magnetic domain walls at crystallographic twin boundaries was found to have a
strong influence on the generation of new magnetic domains in external applied
magnetic fields.",1911.01683v1
2022-05-11,Violation of the Rule of Parsimony: Mixed Local Moment and Itinerant Fe Magnetism in Fe$_{3}$GeN,"Ternary iron nitrides are of considerable interest due to their diverse
magnetic properties. We find, based on first principles calculations, that the
relatively minor structural distortion from the cubic antiperovskite structure
in Fe$_3$GeN leads to unusual magnetic behavior. In particular, there is a
separation into Fe sites with very different magnetic behaviors, specifically a
site with Fe atoms having a stable local moment and a site where the Fe shows
characteristics of much more itinerant behavior. This shows a remarkable
flexibility of the Fe magnetic behavior in these nitrides and points towards
the possibility of systems where minor structural and chemical changes can lead
to dramatic changes in magnetic properties. The results suggest that,
analogously to oxide perovskite materials, modulation of magnetic properties
via chemical or strain control of octahedral rotation may be feasible. This may
then lead to approaches for tuning magnetism to realize properties of interest,
for example tuning magnetic transitions to quantum critical regimes or to
proximity to metamagnetic transitions of interest for devices.",2205.05506v2
2006-08-08,Multi-vanadium substituted polyoxometalates as efficient electrocatalysts for the oxidation of l-cysteine at low potential on glassy carbon electrodes,"The electrochemical behaviours of the sandwich-type complex
[As2W18(VO)3O66]11- were studied in a pH 7 medium and compared with those of
the three following Dawson-type vanadium-substituted complexes: [P2V2W16O62]8-
(P2V2W16), [P2MoV2W15O62]8- (P2MoV2W15) and [P2V3W15O62]9- (P2V3W15).
Electrochemistry shows that the sandwich-type POM contains 2 VIV centers and
one VV center and must be formulated As2V2IVVW18, in agreement with titration,
elemental analysis and magnetic measurements on this element.. All the POMs of
this work proved efficient for the oxidation of L-cysteine. Comparison of the
present results with those of mono-Vanadium substituted POMs indicates that
accumulation of vanadium atoms in the POM framework is beneficial in the
electrocatalytic process. In addition, the present work highlights the
important influence of the POM structure in the electrocatalytic oxidation of
L-cysteine. The remarkable outcome of this work is that the potential for the
oxidation of L-cysteine in the presence of the selected POMs has been
substantially driven in the negative direction compared to the case of glassy
carbon alone, a feature which is associated with faster kinetics. The stability
of the systems must also be pointed out.",0608085v1
2008-01-08,Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor,"Despite twenty years of research, the phase diagram of high transition-
temperature superconductors remains enigmatic. A central issue is the origin of
the differences in the physical properties of these copper oxides doped to
opposite sides of the superconducting region. In the overdoped regime, the
material behaves as a reasonably conventional metal, with a large Fermi
surface. The underdoped regime, however, is highly anomalous and appears to
have no coherent Fermi surface, but only disconnected ""Fermi arcs"". The
fundamental question, then, is whether underdoped copper oxides have a Fermi
surface, and if so, whether it is topologically different from that seen in the
overdoped regime. Here we report the observation of quantum oscillations in the
electrical resistance of the oxygen-ordered copper oxide YBa2Cu3O6.5,
establishing the existence of a well-defined Fermi surface in the ground state
of underdoped copper oxides, once superconductivity is suppressed by a magnetic
field. The low oscillation frequency reveals a Fermi surface made of small
pockets, in contrast to the large cylinder characteristic of the overdoped
regime. Two possible interpretations are discussed: either a small pocket is
part of the band structure specific to YBa2Cu3O6.5 or small pockets arise from
a topological change at a critical point in the phase diagram. Our
understanding of high-transition temperature (high-Tc) superconductors will
depend critically on which of these two interpretations proves to be correct.",0801.1281v1
2009-10-30,Resonant x-ray scattering in 3d-transition-metal oxides: Anisotropy and charge orderings,"The structural, magnetic and electronic properties of transition metal oxides
reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray
scattering (RXS) allows us to perform an accurate investigation of all these
electronic degrees. RXS combines high-Q resolution x-ray diffraction with the
properties of the resonance providing information similar to that obtained by
atomic spectroscopy (element selectivity and a large enhancement of scattering
amplitude for this particular element and sensitivity to the symmetry of the
electronic levels through the multipole electric transitions). Since electronic
states are coupled to the local symmetry, RXS reveals the occurrence of
symmetry breaking effects such as lattice distortions, onset of electronic
orbital ordering or ordering of electronic charge distributions. We shall
discuss the strength of RXS at the K absorption edge of 3d transition-metal
oxides by describing various applications in the observation of local
anisotropy and charge disproportionation. Examples of these resonant effects
are (I) charge ordering transitions in manganites, Fe3O4 and ferrites and (II)
forbidden reflections and anisotropy in Mn3+ perovskites, spinel ferrites and
cobalt oxides. In all the studied cases, the electronic (charge and/or
anisotropy) orderings are determined by the structural distortions.",0910.5789v1
2017-08-29,Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces,"At interfaces between conventional materials, band bending and alignment are
classically controlled by differences in electrochemical potential. Applying
this concept to oxides in which interfaces can be polar and cations may adopt a
mixed valence has led to the discovery of novel two-dimensional states between
simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a
more complex electronic structure, with charge, orbital and/or spin orders
arising from correlations between transition metal and oxygen ions. Strong
correlations thus offer a rich playground to engineer functional interfaces but
their compatibility with the classical band alignment picture remains an open
question. Here we show that beyond differences in electron affinities and polar
effects, a key parameter determining charge transfer at correlated oxide
interfaces is the energy required to alter the covalence of the metaloxygen
bond. Using the perovskite nickelate (RNiO3) family as a template, we probe
charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray
absorption spectroscopy shows that the charge transfer is thwarted by
hybridization effects tuned by the rare-earth (R) size. Charge transfer results
in an induced ferromagnetic-like state in the nickelate, exemplifying the
potential of correlated interfaces to design novel phases. Further, our work
clarifies strategies to engineer two-dimensional systems through the control of
both doping and covalence.",1708.08823v1
2017-12-27,Controlled synthesis of the antiperovskite oxide superconductor Sr$_{3-x}$SnO,"A large variety of perovskite oxide superconductors are known, including some
of the most prominent high-temperature and unconventional superconductors.
However, superconductivity among the oxidation state inverted material class,
the antiperovskite oxides, was reported just recently for the first time. In
this superconductor, Sr$_{3-x}$SnO, the unconventional ionic state Sn$^{4-}$ is
realized and possible unconventional superconductivity due to a band inversion
has been discussed. Here, we discuss an improved facile synthesis method,
making it possible to control the strontium deficiency in Sr$_{3-x}$SnO.
Additionally, a synthesis method above the melting point of Sr$_{3}$SnO is
presented. We show temperature dependence of magnetization and electrical
resistivity for superconducting strontium deficient Sr$_{3-x}$SnO
($T_{\mathrm{c}}$ ~ 5 K) and for Sr$_{3}$SnO without a superconducting
transition down to 0.15 K. Further, we reveal a significant effect of strontium
raw material purity on the superconductivity and achieve 40% increased
superconducting volume fraction (~100%) compared to the highest value reported
so far. More detailed characterisation utilising powder X-ray diffraction and
energy-dispersive X-ray spectroscopy show that a minor cubic phase, previously
suggested to be a Sr$_{3-x}$SnO, is SrO. The improved characterization and
controlled synthesis reported herein enable detailed investigations on the
superconducting nature and its dependency on the strontium deficiency in
Sr$_{3-x}$SnO.",1712.09484v1
2019-04-03,Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides,"Here we systematically explore the use of pulsed laser deposition technique
(PLD) to grow three basic oxides that have rocksalt structure but different
chemical stability in the ambient atmosphere: NiO (stable), MnO (metastable)
and EuO (unstable). By tuning laser fluence, an epitaxial single-phase nickel
oxide thin-film growth can be achieved in a wide range of temperatures from 10
to 750 {\deg}C. At the lowest growth temperature, the out-of-plane strain
raises to 1.5%, which is five times bigger than that in a NiO film grown at 750
{\deg}C. MnO thin films that had long-range ordered were successfully deposited
on the MgO substrates after appropriate tuning of deposition parameters. The
growth of MnO phase was strongly influenced by substrate temperature and laser
fluence. EuO films with satisfactory quality were deposited by PLD after oxygen
availability had been minimized. Synthesis of EuO thin films at rather low
growth temperature prevented thermally-driven lattice relaxation and allowed
growth of strained films. Overall, PLD was a quick and reliable method to grow
binary oxides with rocksalt structure in high quality that can satisfy
requirements for applications and for basic research.",1904.01780v2
2021-10-30,Atomic-scale 3D imaging of individual dopant atoms in a complex oxide,"A small percentage of dopant atoms can completely change the physical
properties of the host material. For example, chemical doping controls the
electronic transport behavior of semiconductors and gives rise to a wide range
of emergent electric and magnetic phenomena in oxides. Imaging of individual
dopant atoms in lightly doped systems, however, remains a major challenge,
hindering characterization of the site-specific effects and local dopant
concentrations that determine the atomic-scale physics. Here, we apply
atom-probe tomography (APT) to resolve individual Ti atoms in the narrow band
gap semiconductor ErMnO3 with a nominal proportion of 0.04 atomic percent. Our
3D imaging measures the Ti concentration at the unit cell level, providing
quantitative information about the dopant distribution within the ErMnO3
crystal lattice. High-resolution APT maps reveal the 3D lattice position of
individual Ti atoms, showing that they are located within the Mn layers with no
signs of clustering or other chemical inhomogeneities. The 3D atomic-scale
visualization of individual dopant atoms provides new opportunities for the
study of local structure-property relations in complex oxides, representing an
important step toward controlling dopant-driven quantum phenomena in
next-generation oxide electronics.",2111.00317v1
2022-09-26,Ionic modulation at the LaAlO$_3$/KTaO$_3$ interface for extreme high-mobility two-dimensional electron gas,"Due to the coexistence of many emergent phenomena, including 2D
superconductivity and a large Rashba spin-orbit coupling, 5d transition metal
oxides based two-dimensional electron systems (2DESs) have been prospected as
one of the potential intrants for modern electronics. However, despite the
lighter electron mass, the mobility of carriers, a key requisite for
high-performance devices, in 5d-oxides devices remains far behind their
3d-oxides analogs. The carriers mobility in these oxides is significantly
hampered by the inevitable presence of defects generated during the growth
process. Here, we report very high mobility ($\sim$ 22650
cm$^2$V$^{-1}$s$^{-1}$) of 5d-2DES confined at the LaAlO$_3$/KTaO$_3$
interface. The high mobility, which is beyond the values observed in
LaAlO$_3$/SrTiO$_3$ and $\gamma$-Al$_2$O$_3$/SrTiO$_3$ systems in the same
carrier-density range, is achieved using the ionic-liquid gating at room
temperature. We postulate that the ionic-liquid gating affects the oxygen
vacancies and efficiently reduces any disorder at the interface. Investigating
density and mobility in a broad range of back-gate voltage, we reveal that the
mobility follows the power-law $\mu \propto n^{1.2}$, indicating the very high
quality of ionic-liquid-gated LaAlO$_3$/KTaO$_3$ devices, consistent with our
postulate. Further, the analysis of the quantum oscillations measured in high
magnetic fields confirms that the high-mobility electrons occupy the electronic
sub-bands emerging from the Ta:5d orbitals of KTaO$_3$.",2209.12390v1
2022-11-09,Charge ordering as the driving mechanism for superconductivity in rare-earth nickel oxides,"Superconductivity is one of the most intriguing properties of matter
described by an attractive interaction that bounds electrons into Cooper pairs.
To date, the highest critical temperature at ambient conditions is achieved in
copper oxides. While layered nickel oxides were long proposed to be analogous
to cuprates, superconductivity was only demonstrated in 2019 albeit without
clarifying the pairing mechanism. Here we use Density Functional Theory (DFT)
to show that superconductivity in nickelates is driven by an electron-phonon
coupling originating from a charge ordering. Due to an intrinsic electronic
instability in half-doped compounds, Ni$^{1.5+}$ cations dismutate into more
stable Ni$^+$ and Ni$^{2+}$ cations, which is accompanied by a bond
disproportionation of NiO$_4$ complexes producing an insulating charge ordered
state. Once doping suppresses the instability, the bond disproportionation
vibration is sufficient to reproduce the key characteristic of nickelates
observed experimentally, notably the dome of T$_c$ as a function of doping
content. These phenomena are identified if relevant degrees of freedom as well
as an exchange correlation functional that sufficiently amends self-interaction
errors are involved in the simulations. Finally, despite the presence of
correlation effects inherent to $3d$ elements, nickelates superconductors
appear similar to non-magnetic bismuth oxide superconductors.",2211.04870v2
2022-11-16,Emergence of large spin-charge interconversion at an oxidized Cu/W interface,"Spin-orbitronic devices can integrate memory and logic by exploiting
spin-charge interconversion (SCI), which is optimized by design and materials
selection. In these devices, such as the magnetoelectric spin-orbit (MESO)
logic, interfaces are crucial elements as they can prohibit or promote spin
flow in a device as well as possess spin-orbit coupling resulting in
interfacial SCI. Here, we study the origin of SCI in a Py/Cu/W lateral spin
valve and quantify its efficiency. An exhaustive characterization of the
interface between Cu and W electrodes uncovers the presence of an oxidized
layer (WO$_x$). We determine that the SCI occurs at the Cu/WO$_x$ interface
with a temperature-independent interfacial spin-loss conductance of $G_{||}
\approx$ 20 $\times$ 10$^{13} \Omega^{-1}m^{-2}$ and an interfacial spin-charge
conductivity $\sigma_{SC}=-$1610 $\Omega^{-1}cm^{-1}$ at 10 K ($-$830
$\Omega^{-1}cm^{-1}$ at 300 K). This corresponds to an efficiency given by the
inverse Edelstein length $\lambda_{IEE}=-$0.76 nm at 10 K ($-$0.4 nm at 300 K),
which is remarkably larger than in metal/metal and metal/oxide interfaces and
bulk heavy metals. The large SCI efficiency at such an oxidized interface is a
promising candidate for the magnetic readout in MESO logic devices.",2211.09250v1
2002-07-03,Magnetic enhancement of Co$_{0.2}$Zn$_{0.8}$Fe$_2$O$_4$ spinel oxide by mechanical milling,"We report the magnetic properties of mechanically milled
Co$_{0.2}$Zn$_{0.8}$Fe$_2$O$_4$ spinel oxide. After 24 hours milling of the
bulk sample, the XRD spectra show nanostructure with average particle size
$\approx$ 20 nm. The as milled sample shows an enhancement in magnetization and
ordering temperature compared to the bulk sample. If the as milled sample is
annealed at different temperatures for the same duration, recrystallization
process occurs and approaches to the bulk structure on increasing the annealing
temperatures. The magnetization of the annealed samples first increases and
then decreases. At higher annealing temperature ($\sim$ 1000$^{0}$C) the system
shows two coexisting magnetic phases {\it i.e.}, spin glass state and
ferrimagnetic state, similar to the as prepared bulk sample. The room
temperature M\""{o}ssbauer spectra of the as milled sample, annealed at
300$^{0}$C for different durations (upto 575 hours), suggest that the observed
change in magnetic behaviour is strongly related with cations redistribution
between tetrahedral (A) and octahedral (O) sites in the spinel structure. Apart
from the cation redistribution, we suggest that the enhancement of
magnetization and ordering temperature is related with the reduction of B site
spin canting and increase of strain induced anisotropic energy during
mechanical milling.",0207095v1
2020-07-19,A geometric approach to separate the effects of magnetic susceptibility and chemical shift/exchange in a phantom with isotropic magnetic susceptibility,"Purpose: To separate the effects of magnetic susceptibility and chemical
shift/exchange in a phantom with isotropic magnetic susceptibility. To generate
a chemical shift/exchange-corrected quantitative susceptibility mapping (QSM)
result.
  Theory and Methods: Magnetic susceptibility and chemical shift/exchange are
the properties of a material. Both are known to induce the resonance frequency
shift in MRI. In current QSM, the susceptibility is reconstructed from the
frequency shift, ignoring the contribution of the chemical shift/exchange. In
this work, a simple geometric approach, which averages the frequency shift maps
from three orthogonal B0 directions to generate a chemical shift/exchange map,
is developed using the fact that the average nullifies the (isotropic)
susceptibility effects. The resulting chemical shift/exchange map is subtracted
from the total frequency shift, producing a frequency shift map solely from
susceptibility. Finally, this frequency shift map is reconstructed to a
susceptibility map using a QSM algorithm. The proposed method is validated in
numerical simulations and applied to phantom experiments with olive oil, bovine
serum albumin, ferritin, and iron oxide solutions.
  Results: Both simulations and experiments confirm that the method
successfully separates the contributions of the susceptibility and chemical
shift/exchange, reporting the susceptibility and chemical shift/exchange of
olive oil (susceptibility: 0.62 ppm, chemical shift: -3.60 ppm), bovine serum
albumin (susceptibility: -0.059 ppm, chemical shift: 0.008 ppm), ferritin
(susceptibility: 0.125 ppm, chemical shift: -0.005 ppm), and iron oxide
(susceptibility: 0.30 ppm, chemical shift: -0.039 ppm) solutions.
  Conclusion: The proposed method successfully separates the susceptibility and
chemical shift/exchange in phantoms with isotropic magnetic susceptibility.",2007.09614v1
2009-12-01,"Electronic structure, magnetic and dielectric properties of the edge-sharing copper-oxide chain compound NaCu$_{2}$O$_{2}$","We report an experimental study of \nco, a Mott insulator containing chains
of edge-sharing CuO$_4$ plaquettes, by polarized x-ray absorption spectroscopy
(XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and
pyroelectric current measurements. The XAS data show that the valence holes
reside exclusively on the Cu$^{2+}$ sites within the copper-oxide spin chains
and populate a $d$-orbital polarized within the CuO$_4$ plaquettes. The RMXS
measurements confirm the presence of incommensurate magnetic order below a
N\'eel temperature of $T_N = 11.5$ K, which was previously inferred from
neutron powder diffraction and nuclear magnetic resonance data. In conjunction
with the magnetic susceptibility and XAS data, they also demonstrate a new
""orbital"" selection rule for RMXS that is of general relevance for magnetic
structure determinations by this technique. Dielectric property measurements
reveal the absence of significant ferroelectric polarization below $T_N$, which
is in striking contrast to corresponding observations on the isostructural
compound \lco. The results are discussed in the context of current theories of
multiferroicity.",0912.0168v1
2012-04-19,Ferromagnetism in graphene nanoribbons: split versus oxidative unzipped ribbons,"Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons
(GNRs), and (b) oxidative unzipped and chemically converted graphene
nanoribbons (CCGNRs) were investigated for their magnetic properties using the
combination of static magnetization and electron spin resonance measurements.
The two types of ribbons possess remarkably different magnetic properties.
While the low temperature ferromagnet-like feature is observed in both types of
ribbons, such room temperature feature persists only in potassium-split
ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a
'positive exchange bias'. Electron spin resonance measurements infer that the
carbon related defects may responsible for the observed magnetic behaviour in
both types of ribbons. Furthermore, proton hyperfine coupling strength has been
obtained from hyperfine sublevel correlation experiments performed on the GNRs.
Electron spin resonance provides no indications for the presence of potassium
(cluster) related signals, emphasizing the intrinsic magnetic nature of the
ribbons. Our combined experimental results may infer the coexistence of
ferromagnetic clusters with anti-ferromagnetic regions leading to disordered
magnetic phase. We discuss the origin of the observed contrast in the magnetic
behaviours of these two types of ribbons.",1204.4401v1
2019-06-03,An XMCD study of magnetism and valence state in iron-substituted strontium titanate,"Room temperature ferromagnetism was characterized for thin films of
SrTi$_{0.6}$Fe$_{0.4}$O$_{3-{\delta}}$ grown by pulsed laser deposition on
SrTiO$_{3}$ and Si substrates under different oxygen pressures and after
annealing under oxygen and vacuum conditions. X-ray magnetic circular dichroism
demonstrated that the magnetization originated from Fe$^{2+}$ cations, whereas
Fe$^{3+}$ and Ti$^{4+}$ did not contribute. Films with the highest magnetic
moment (0.8 {\mu}B per Fe) had the highest measured Fe$^{2+}$:Fe${^3+}$ ratio
of 0.1 corresponding to the largest concentration of oxygen vacancies ({\delta}
= 0.19). Post-growth annealing treatments under oxidizing and reducing
conditions demonstrated quenching and partial recovery of magnetism
respectively, and a change in Fe valence states. The study elucidates the
microscopic origin of magnetism in highly Fe-substituted
SrTi$_{1-x}$Fe$_x$O$_{3-{\delta}}$ perovskite oxides and demonstrates that the
magnetic moment, which correlates with the relative content of Fe$^{2+}$ and
Fe$^{3+}$, can be controlled via the oxygen content, either during growth or by
post-growth annealing.",1906.00509v1
2004-01-30,Quantum Magnetic Excitations from Stripes in Copper-Oxide Superconductors,"In the copper-oxide parent compounds of the high-transition-temperature
superconductors, the valence electrons are localized, one per copper site, due
to strong intraatomic Coulomb repulsion. A symptom of the localization is
antiferromagnetism, where the spins of localized electrons alternate between up
and down. The superconductivity appears when mobile 'holes' are doped into this
insulating state, and it coexists with antiferromagnetic fluctuations. In one
approach to the coexistence, the holes are believed to self-organize into
'stripes' that alternate with antiferromagnetic (insulating) regions within
copper-oxide planes. Such an unusual electronic state would necessitate an
unconventional mechanism of superconductivity. There is an apparent problem
with this picture, however: measurements of magnetic excitations in
superconducting YBa(2)Cu(3)O(6+x) near optimum doping are incompatible with the
naive expectations for a material with stripes. Here we report neutron
scattering measurements on stripe-ordered La(1.875)Ba(0.125)CuO(4). We show
that the measured excitations are, surprisingly, quite similar to those in
YBa(2)Cu(3)O(6+x) (i.e., the predicted spectrum of magnetic excitations is
wrong). We find instead that the observed spectrum can be understood within a
stripe model by taking account of quantum excitations. Our results support the
concept that stripe correlations are essential to high-transition-temperature
superconductivity.",0401621v2
2012-11-27,"Structural Phase Transitions of the Metal Oxide Perovskites SrTiO3, LaAlO3 and LaTiO3 Studied with a Screened Hybrid Functional","We have investigated the structural phase transitions of the transition metal
oxide perovskites SrTiO$_{3}$, LaAlO$_{3}$ and LaTiO$_{3}$ using the screened
hybrid density functional of Heyd, Scuseria and Ernzerhof (HSE06). We show that
HSE06-computed lattice parameters, octahedral tilts and rotations, as well as
electronic properties, are significantly improved over semilocal functionals.
We predict the crystal field splitting ($\Delta_{CF}$) resulting from the
structural phase transition in SrTiO$_{3}$ and LaAlO$_{3}$ to be 3 meV and 10
meV, respectively, in excellent agreement with experimental results. HSE06
identifies correctly LaTiO$_{3}$ in the magnetic sates as a Mott insulator.
Also, it predicts that the GdFeO$_{3}$-type distortion in non-magnetic
LaTiO$_{3}$ will induce a large $\Delta_{CF}$ of 410 meV. This large
crystal-field splitting associated with the large magnetic moment found in the
G-type antiferromagnetic state suggest that LaTiO$_{3}$ has an induced orbital
order, which is confirmed by the visualisation of the highest occupied
orbitals. These results strongly indicate that HSE06 is capable of efficiently
and accurately modeling perovskite oxides, and promises to efficiently capture
the physics at their heterointerfaces.",1211.6371v1
2016-09-14,Magnetoexcitons in cuprous oxide,"Two of the most striking experimental findings when investigating exciton
spectra in cuprous oxide using high-resolution spectroscopy are the
observability and the fine structure splitting of $F$ excitons reported by J.
Thewes et al. [Phys. Rev. Lett. 115, 027402 (2015)]. These findings show that
it is indispensable to account for the complex valence band structure and the
cubic symmetry of the solid in the theory of excitons. This is all the more
important for magnetoexcitons, where the external magnetic field reduces the
symmetry of the system even further. We present the theory of excitons in
$\mathrm{Cu_{2}O}$ in an external magnetic field and especially discuss the
dependence of the spectra on the direction of the external magnetic field,
which cannot be understood from a simple hydrogen-like model. Using
high-resolution spectroscopy, we also present the corresponding experimental
spectra for cuprous oxide in Faraday configuration. The theoretical results and
experimental spectra are in excellent agreement as regards not only the
energies but also the relative oscillator strengths. Furthermore, this
comparison allows for the determination of the fourth Luttinger parameter
$\kappa$ of this semiconductor.",1609.04275v3
2016-10-26,Doping of Ga in antiferromagnetic semiconductor alpha-Cr2O3oxide and its effects on modified magnetic and electronic properties,"The samples of Ga doped Cr2O3 oxide have been prepared using chemical
co-precipitation route. X-ray diffraction pattern and Raman spectra have
confirmed rhombohedral crystal structure with space group R3-C. Magnetic
measurement has indicated the dilution of antiferromagnetic (AFM) spin order in
Ga doped alpha-Cr2O3 system oxide, where the AFM transition temperature of bulk
alpha-Cr2O3 oxide at about 320 K has been suppressed and ferrimagnetic behavior
is observed from the analysis of the temperature dependence of magnetization
data below 350 K. Apart from Ga doping effect, the spin freezing (50 K-70 K)
and superparamagnetic behavior of the surface spins at lower temperatures,
typically below 50 K, have been exhibited due to nano-sized grains of the
samples. All the samples showed non-linear current-voltage (I-V)
characteristics. However, I-V characteristics of the Ga doped samples are
remarkably different from alpha-Cr2O3 sample. The I-V curves of Ga doped
samples have exhibited many unique electronic properties, e.g., bi-stable (low
resistance- LR and high resistance-HR) electronic states and negative
differential resistance (NDR). Optical absorption spectra revealed three
electronic transitions in the samples associated with band gap energy at about
2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively.",1610.08426v1
2017-01-26,Magnetic and electronic properties of La$_3M$O$_7$ and possible polaron formation in hole-doped La$_3M$O$_7$ ($M$=Ru and Os),"Oxides with $4d$/$5d$ transition metal ions are physically interesting for
their particular crystalline structures as well as the spin-orbit coupled
electronic structures. Recent experiments revealed a series of $4d$/$5d$
transition metal oxides $R_3M$O$_7$ ($R$: rare earth; $M$: $4d$/$5d$ transition
metal) with unique quasi-one-dimensional $M$ chains. Here first-principles
calculations have been performed to study the electronic structures of
La$_3$OsO$_7$ and La$_3$RuO$_7$. Our study confirm both of them to be Mott
insulating antiferromagnets with identical magnetic order. The reduced magnetic
moments, which are much smaller than the expected value for ideal high-spin
state ($3$ $t_{2g}$ orbitals occupied), are attributed to the strong $p-d$
hybridization with oxygen ions, instead of the spin-orbit coupling. The
Ca-doping to La$_3$OsO$_7$ and La$_3$RuO$_7$ can not only modulate the nominal
carrier density but also affect the orbital order as well as the local
distortions. The Coulombic attraction and particular orbital order would prefer
to form polarons, which might explain the puzzling insulating behavior of doped
$5d$ transition metal oxides. In addition, our calculation predict that the
Ca-doping can trigger ferromagnetism in La$_3$RuO$_7$ but not in La$_3$OsO$_7$.",1701.07655v1
2019-11-17,Soft X-ray Absorption Spectroscopy and Magnetic Circular Dichroism as Operando Probes of Complex Oxide Electrolyte Gate Transistors,"Electrolyte-based transistors utilizing ionic liquids/gels have been highly
successful in the study of charge-density-controlled phenomena, particularly in
oxides. Experimental probes beyond transport have played a significant role,
despite challenges to their application in electric double-layer transistors.
Here, we demonstrate application of synchrotron soft X-ray absorption
spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) as operando
probes of the charge state and magnetism in ion-gel-gated ferromagnetic
perovskite films. Electrochemical response via oxygen vacancies at positive
gate bias in LaAlO$_3$(001)/La$_{0.5}$Sr$_{0.5}$CoO$_{3-{\delta}}$ is used as a
test case. XAS/XMCD measurements of 4-25 unit-cell-thick films first probe the
evolution of hole doping (from the O K-edge pre-peak) and ferromagnetism (at
the Co L-edges), to establish a baseline. Operando soft XAS/XMCD of
electrolyte-gated films is then demonstrated, using optimized spin-coated gels
with thickness $\sim$1 ${\mu}$m, and specific composition. Application of gate
voltages up to +4 V is shown to dramatically suppress the O $K$-edge XAS
pre-peak intensity and Co $L$-edge XMCD, thus enabling the Co valence and
ferromagnetism to be tracked upon gate-induced reduction. Soft XAS and XMCD,
with appropriate electrolyte design, are thus established as viable for the
operando characterization of electrolyte-gated oxides.",1911.07139v1
2021-03-18,An antisite defect mechanism for room temperature ferroelectricity in orthoferrites,"Single-phase multiferroic materials that allow the coexistence of
ferroelectric and magnetic ordering above room temperature are highly
desirable, motivating an ongoing search for mechanisms for unconventional
ferroelectricity in magnetic oxides. Here, we report an antisite defect
mechanism for room temperature ferroelectricity in epitaxial thin films of
yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A
combination of piezoresponse force microscopy, atomically resolved elemental
mapping with aberration corrected scanning transmission electron microscopy and
density functional theory calculations reveals that the presence of YFe
antisite defects facilitates a non-centrosymmetric distortion promoting
ferroelectricity. This mechanism is predicted to work analogously for other
rare earth orthoferrites, with a dependence of the polarization on the radius
of the rare earth cation. Furthermore, a vertically aligned nanocomposite
consisting of pillars of a magnetoelastic oxide CoFe2O4 embedded epitaxially in
the YFeO3 matrix exhibits both robust ferroelectricity and ferrimagnetism at
room temperature, as well as a noticeable strain-mediated magnetoelectric
coupling effect. Our work uncovers the distinctive role of antisite defects in
providing a novel mechanism for ferroelectricity in a range of magnetic
orthoferrites and further augments the functionality of this family of complex
oxides for multiferroic applications.",2103.10338v1
2023-11-15,Orbital degree of freedom in high entropy oxides,"The spin, charge, and lattice degrees of freedom and their interplay in high
entropy oxides were intensively investigated in recent years. However, how the
orbital degree of freedom is affected by the extreme disorder in high entropy
oxides hasn't been studied. In this work, using perovskite structured
\textit{R}VO$_3$ as a materials playground, we report how the disorder arising
from mixing different rare earth ions at the rare earth site affects the
orbital ordering of V$^{3+}$ t$_{2g}$-electrons. Since each member of
\textit{R}VO$_3$ crystallizes into the same orthorhombic \textit{Pbnm}
structure, the configurational entropy should not be critical for the success
synthesis of (\textit{R}$_1$,...,\textit{R}$_n$)VO$_3$. The spin and orbital
ordering was studied by measuring magnetic properties and specific heat of
single crystals. Rather than the number and type of rare earth ions, the
average ionic radius and size variance are the key factors determining the spin
and orbital order in (\textit{R}$_1$,...,\textit{R}$_n$)VO$_3$. When the size
variance is small, the average ionic radius takes precedence in dictating spin
and orbital order. Increasing size variance suppresses the G-type orbital order
and C-type magnetic order but favors the C-OO/G-AF state and the spin-orbital
entanglement. These findings suggest that the extreme disorder introduced by
mixing multiple rare earth ions in high entropy perovskites might be employed
to preserve the orbital degree of freedom to near the magnetic ordering
temperature, which is necessary for the electronic driven orbital ordering in a
Kugel-Khomskii compound.",2311.09087v2
2024-03-30,Ferromagnetic state with large magnetic moments realized in epitaxially strained Sr3Ru2O7 films,"Technical advancement of oxide molecular beam epitaxy (MBE) has opened new
avenues for studying various quantum transport phenomena in correlated
transition-metal oxides, as exemplified by the exotic superconductivity of
Sr$_2$RuO$_4$ and quantum oscillations of SrRuO$_3$. On the other hand, film
research of another Ruddlesden-Popper strontium ruthenate Sr$_3$Ru$_2$O$_7$
which exhibits a unique quantum phase related to metamagnetism in bulk systems
did not progress well. Here we report the fabrication of high-quality
Sr$_3$Ru$_2$O$_7$ thin films by oxide MBE and the observation of a
strain-induced ferromagnetic ground state. The change in magnetic exchange
coupling evaluated by first-principles calculations indicates a systematic
relation between the compression of the $c$-axis length and induced
ferromagnetism. Giant epitaxial strain in high-quality films will be a key to a
comprehensive understanding of the magnetism in Ruddlesden-Popper strontium
ruthenates Sr$_{n+1}$Ru$_n$O$_{3n+1}$, which sensitively depends on the ratio
of in-plane to out-of-plane Ru-Ru distances.",2404.00214v1
2008-08-27,Magnetic phase evolution in the spinel compounds Zn$_{1-x}$Co$_x$Cr$_2$O$_4$,"We present the magnetic properties of complete solid solutions of
ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very
different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$
cations occupying the A site and magnetic $d^3$ cations on the B site, is a
highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations
(three unpaired electrons) on the A site as well, exhibits both N\'eel
ferrimagnetism as well as commensurate and incommensurate non-collinear
magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for
its polar behavior which arises from conical magnetic ordering. Gradually
introducing magnetism on the A site of ZnCr$_2$O$_4$ results in a transition
from frustrated antiferromagnetism to glassy magnetism at low concentrations of
Co, and eventually to ferrimagnetic and conical ground states at higher
concentrations. Real-space Monte-Carlo simulations of the magnetic
susceptibility suggest that the first magnetic ordering transition and features
of the susceptibility across $x$ are captured by near-neighbor self- and
cross-couplings between the magnetic A and B atoms. We present as a part of
this study, a method for displaying the temperature dependence of magnetic
susceptibility in a manner which helps distinguish between compounds possessing
purely antiferromagnetic interactions from compounds where other kinds of
ordering are present.",0808.3789v3
2024-01-24,Magnetic nanoparticles: from the nanostructure to the physical properties,"Some of the synthesis methods and physical properties of iron-oxide based
magnetic nanoparticles such as Fe3-xO4 and CoxFe3-xO4 are reviewed because of
their interest in health, environmental applications, and ultra-high-density
magnetic recording. Unlike high crystalline quality nanoparticles larger than a
few nanometers that show bulk-like magnetic and electronic properties,
nanostructures with increasing structural defects yield a progressive worsening
of their general performance due to frozen magnetic disorder and local breaking
of their crystalline symmetry. Thus, it is shown that single-crystal,
monophasic nanoparticles do not exhibit significant surface or finite-size
effects, such as spin canting, reduced saturation magnetization, high closure
magnetic fields, hysteresis-loop shift or dead magnetic layer features which
are mostly associated with crystallographic defective systems. Besides, the key
role of the nanoparticle coating, surface anisotropy, and inter-particle
interactions are discussed. Finally, the results of some single particle
techniques -- magnetic force microscopy, X-ray photoemission electron
microscopy, and electron magnetic chiral dichroism -- that allow studying
individual nanoparticles down to sub-nanometer resolution with element, valence
and magnetic selectivity, are presented. All in all, the intimate, fundamental
correlation of the nanostructure (crystalline, chemical, magnetic) to the
physical properties of the nanoparticles is ascertained.",2401.13422v1
2004-04-07,Absence of room temperature ferromagnetism in bulk Mn-doped ZnO,"Structural and magnetic properties have been studied for polycrystalline
Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves
unreacted starting ZnO and manganese oxides. Contrary to a recent report, no
bulk ferromagnetism was observed for single-phase materials synthesized in air
at temperatures above 900 oC. Single-phase samples show paramagnetic
Curie-Weiss behavior.",0404186v1
2004-08-19,Magnetic Susceptibility of NiO Nanoparticles,"Nickel oxide nanoparticles of different sizes are prepared and characterized
by x-ray diffraction and transmission electron microscopy. A.C. susceptibility
measurements as a function of temperature are carried out for various particle
sizes and frequencies. We find that the behavior of the system is spin glass
like.",0408427v1
2008-01-20,The Kondo effect of surface excitons,"A recombination radiation line of real excitons in dense two-dimensional
electron gas at the [100] silicon surface is observed in luminescence spectra
of metal-oxide-semiconductor (MOS) structures. A new effect of anisotropic
paramagnetic reduction of the luminescence line indicates a strong influence of
the Kondo correlations on electron paramagnetism of the excitons.",0801.3055v1
2014-05-13,Magneto-electric operators in neutron scattering,"We succeed in deriving an exact expression for the magnetic interaction of
neutrons and electrons including magneto-electric operators, allowed in the
absence of a centre of inversion symmetry. Central characters are a spin
anapole and an orbital (toroidal) analogue, in addition to familiar parity-even
operators. A simulation of neutron diffraction by antiferromagnetic copper
oxide makes full use of information inferred from a thorough investigation with
resonant x-ray Bragg diffraction.",1405.3060v1
2020-08-13,On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation,"Exchange bias effects linked to surface spin freezing (SSF) are commonly
found in iron oxide nanoparticles, while signatures of SSF in low-field
temperature-dependent magnetization curves have been much less frequently
reported. Here, we present magnetic properties of dense assemblies of
similar-sized (~ 8 nm diameter) particles synthesized by a magnetite (sample
S1) and a maghemite (sample S2) method, and the influence of long-term (4-year)
sample aging under ambient conditions on these properties. The size of the
exchange bias field of the different sample (fresh or aged) states is found to
correlate with (a) whether a low-temperature hump feature signaling the SSF
transition is detected in out-of-phase ac susceptibility or zero-field-cooled
(ZFC) dc magnetization recorded at low field and with (b) the prominence of
irreversibility between FC and ZFC curves recorded at high field. Sample S1
displays a lower magnetization than S2, and it is in S1 where the largest SSF
effects are found. These effects are significantly weakened by aging but remain
larger than the SSF effects in S2, where the influence of aging is considerably
smaller. A non-saturating component due to spin disorder in S1 also weakens
with aging, accompanied by, we infer, an increase in the superspin and the
radius of the ordered nanoparticle cores. X-ray diffraction and M\""ossbauer
spectroscopy provide indication of maghemite-like stoichiometry in both aged
samples as well as thicker disordered particle shells in aged-S1 relative to
aged-S2 (crystallographically-disordered and spin-disordered according to
diffraction and M\""ossbauer, respectively). The pronounced diminution in SSF
effects with aging in S1 is attributed to a (long-term) transition, caused by
ambient oxidation, from magnetite-like to maghemite-like stoichiometry, and a
concomitant softening of the spin-disordered shell anisotropy...",2008.05874v1
1999-07-27,Cooperative Jahn-Teller Effect on the Magnetic Structure of Manganese Oxides,"The magnetic structure of LaMnO$_3$ is investigated on three-dimensional
clusters of MnO$_6$ octahedra by using a combination of relaxation and Monte
Carlo techniques. It is found that the cooperative Jahn-Teller phonons lead to
the stabilization of A-type antiferromagnetic and C-type orbital structures in
the physically relevant region of parameter space for LaMnO$_3$ with small
corrections due to tilting effects. The results suggest that strong Coulomb
interactions are not necessary for a qualitative description of undoped
manganites. In fact, it is shown that the present result is not essentially
changed even if the Coulomb interaction is explicitly included.",9907430v1
2003-10-27,A spin metal-oxide-semiconductor field-effect transistor using half-metallic-ferromagnet contacts for the source and drain,"We propose and theoretically analyze a novel metal-oxide-semiconductor
field-effect-transistor (MOSFET) type of spin transistor (hereafter referred to
as a spin MOSFET) consisting of a MOS gate structure and
half-metallic-ferromagnet (HMF) contacts for the source and drain. When the
magnetization configuration between the HMF source and drain is parallel
(antiparallel), highly spin-polarized carriers injected from the HMF source to
the channel are transported into (blocked by) the HMF drain, resulting in the
magnetization-configuration-dependent output characteristics. Our
two-dimensional numerical analysis indicates that the spin MOSFET exhibits high
(low) current drive capability in the parallel (antiparallel) magnetization,
and that extremely large magnetocurrent ratios can be obtained. Furthermore,
the spin MOSFET satisfies other important requirements for ""spintronic""
integrated circuits, such as high amplification capability, low power-delay
product, and low off-current.",0310623v1
2004-02-13,Superconducting Properties under Magnetic Field in Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O Single Crystal,"We report the in-plane resistivity and magnetic susceptibility of the layered
cobalt oxide Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O single crystal. The
temperature dependence of the resistivity shows metallic behavior from room
temperature to the superconducting transition temperature $T_{c}$ of 4.5 K.
Sharp resistive transition, zero resistivity and almost perfect superconducting
volume fraction below $T_{c}$ indicate the good quality and the bulk
superconductivity of the single crystal. The upper critical field $H_{c2}$ and
the coherence length $\xi$ are obtained from the resistive transitions in
magnetic field parallel to the c-axis and the $ab$-plane. The anisotropy of
$\xi$, $\xi_{ab} / \xi_{c} =$ 12 nm/1.3 nm $\simeq$ 9.2, suggests that this
material is considered to be an anisotropic three dimensional superconductor.
In the field parallel to the $ab$-plane, $H_{c2}$ seems to be suppressed to the
value of Pauli paramagnetic limit. It may indicate the spin singlet
superconductivity in the cobalt oxide.",0402355v1
2005-05-10,Percolative Ferromagnetism in Anatase Co:TiO2,"We revisit the most widely investigated and controversial oxide diluted
magnetic semiconductor (DMS), Co:TiO2, with a new high temperature film growth,
and show that the corresponding material is not only an intrinsic DMS
ferromagnet, but also supports a percolative mechanism of ferromagnetism. We
establish the uniformity of dopant distribution across the film cross section
by Z-contrast imaging via scanning transmission electron microscopy (STEM) and
electron energy loss spectroscopy (EELS) at spatial resolution of 0.4 nm and
the oxidized 2+ valence state of cobalt by x-ray absorption spectroscopy (XAS).
The dependence of magnetic properties on cobalt concentration is consistent
with the defect polaron percolation model. The peculiar increase in the
transport activation energy above a specific cobalt concentration further
emphasizes the polaron contribution to magnetic order.",0505265v1
2005-08-11,"Co-doped (La,Sr)TiO3-d: a high-Curie temperature diluted magnetic system with large spin-polarization","We report on tunneling magnetoresistance (TMR) experiments that demonstrate
the existence of a significant spin polarization in Co-doped (La,Sr)TiO3-d
(Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie
temperature. These TMR experiments have been performed on magnetic tunnel
junctions associating Co-LSTO and Co electrodes. Extensive structural analysis
of Co-LSTO combining high-resolution transmission electron microscopy and Auger
electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer
and thus, the measured ferromagnetism and high spin polarization are intrinsic
properties of this DMOS. Our results argue for the DMOS approach with complex
oxide materials in spintronics.",0508289v1
2005-12-14,Anomalous Magnetic and Thermal Behavior in Some RMn2O5 Oxides,"The RMn2O5 (R=Pr, Nd, Sm, and Eu) oxides showing magnetoelectric (ME)
behavior have been prepared in polycrystalline form by a standard citrate
route. The lattice parameters, obtained from the powder XRD analysis, follow
the rare-earth contraction indicating the trivalent character of the R ions.
Cusp-like anomalies in the magnetic susceptibility curve and sharp peaks in the
specific heat were reported at the corresponding temperatures in RMn2O5 (R=Pr,
Nd, Sm, and Eu) indicating the magnetic or electric ordering transitions.",0512293v1
2006-12-07,Metal-ligand interplay in strongly-correlated oxides: a parametrized phase diagram for pressure induced spin transitions,"We investigate the magnetic properties of archetypal transition-metal oxides
MnO, FeO, CoO and NiO under very high pressure by x-ray emission spectroscopy
at the K\beta line. We observe a strong modification of the magnetism in the
megabar range in all the samples except NiO. The results are analyzed within a
multiplet approach including charge-transfer effects. The pressure dependence
of the emission line is well accounted for by changes of the ligand field
acting on the d electrons and allows us to extract parameters like local
d-hybridization strength, O-2p bandwidth and ionic crystal field across the
magnetic transition. This approach allows a first-hand insight into the
mechanism of the pressure induced spin transition.",0612179v1
2008-02-08,Magnetodielectric coupling in a triangular Ising lattice,"Dielectric constant measurement under magnetic field is an efficient
technique to study the coupling between charges and spins in insulating
materials. For magnetic oxides, the geometric frustration is known to be a key
ingredient to observe such a coupling. Measurements for the triangular
Ising-like cobaltite Ca3Co2O6 have been made. Single crystals of Ca3Co2O6 are
found to exhibit a magnetodielectric effect below TN=25K with a peak in the
e(H) curve at the ferri to ferromagnetic transition. This relation between e
and magnetization has been modelized by using two order parameters in an energy
expansion derived from the Landau formalism and the fluctuation-dissipation
theorem. This result emphasizes the great potential of insulating transition
metal oxides for the search of magnetodielectric effect.",0802.1136v1
2008-04-07,CaCrO3: an anomalous antiferromagnetic metallic oxide,"Combining infrared reflectivity, transport, susceptibility and several
diffraction techniques, we find compelling evidence that CaCrO3 is a rare case
of a metallic and antiferromagnetic transition-metal oxide with a
three-dimensional electronic structure. LSDA calculations correctly describe
the metallic behavior as well as the anisotropic magnetic ordering pattern of C
type: The high Cr valence state induces via sizeable pd hybridization
remarkably strong next-nearest neighbor interactions stabilizing this ordering.
The subtle balance of magnetic interactions gives rise to magneto-elastic
coupling, explaining pronounced structural anomalies observed at the magnetic
ordering transition.",0804.1071v1
2008-08-18,Magnetic and charge transport properties of the Na-based Os oxide pyrochlore,"Na-based osmium oxide pyrochlore was synthesized for the first time by an
ion-exchange method. KOs2O6 was used as a host compound. Elelectron probe
micro-analysis, synchrotron x-ray diffraction analysis, and thermo-gravimetric
analysis confirmed its structure not as the beta-type but as the defect-type
pyrochlore. The composition was identified as Na1.4Os2O6.H2O. Electrical
resistivity, heat capacity, and magnetization measurements of the
polycrystalline Na1.4Os2O6.H2O clarified absence of superconductivity above 2
K, being in contrast to what were found for the beta-pyrochlore AOs2O6 (A = Cs,
Rb, K). Sommerfeld coefficient of 22 mJ K-2 mol-1 of Na1.4Os2O6.H2O was
smallest among those of AOs2O6. A magnetic anomaly at ~57 K and possible
associated magnetoresistance (+3.7 % at 2 K in 70 kOe) were found.",0808.2331v1
2008-12-15,"Synthesis and structure of new pyrochlore-type oxides Ln2ScNbO7 (Ln = Pr, Nd, Eu, Gd, Dy)","We report the synthesis and structural study of mixed oxides in the Ln2ScNbO7
series. New phases with Ln = Pr, Eu, Gd and Dy are obtained. All crystallize in
the cubic pyrochlore structure type, space group F-d3m, with no Sc-Nb ordering
on the B-site. The structures are determined by Rietveld refinement. The
evolution of cell parameters, interatomic distances and angles as a function of
lanthanide cation size is discussed. Magnetic measurements show the absence of
ordering down to 2 K, in agreement with the presence of strong geometric
frustration in the lanthanide sublattice. The europium phase shows a peculiar
magnetic behaviour; its magnetic susceptibility becomes constant below ca 50 K.
This feature confirms the behaviour observed previously on Eu2Ti2O7 and is
ascribed to crystal field effects.",0812.2758v1
2010-07-09,From quantum criticality to enhanced thermopower in strongly correlated layered cobalt oxide,"We report on susceptibility measurements in the strongly correlated layered
cobalt oxide [BiBa0.66K0.36O2]CoO2, which demonstrate the existence of a
magnetic quantum critical point (QCP) governing the electronic properties. The
investigated low frequency susceptibility displays a scaling behavior with both
the temperature T and the magnetic field B ranging from the high-T non-Fermi
liquid down to the low-T Fermi liquid. Whereas the inferred scaling form can be
discussed within the standard framework of the quantum critical phenomena, the
determined critical exponents suggest an unconventional magnetic QCP of a
potentially generic type. Accordingly, these quantum critical fluctuations
account for the anomalous logarithmic temperature dependence of the
thermopower. This result allows us to conjecture that quantum criticality can
be an efficient source of enhanced thermopower.",1007.1606v1
2010-08-15,Charge and orbital order in transition metal oxides,"A short introduction to the complex phenomena encountered in transition metal
oxides with either charge or orbital or joint charge-and-orbital order, usually
accompanied by magnetic order, is presented. It is argued that all the types of
above ordered phases in these systems follow from strong Coulomb interactions
as a result of certain compromise between competing instabilities towards
various types of magnetic order and optimize the gain of kinetic energy in
doped systems. This competition provides a natural explanation of the stripe
order observed in doped cuprates, nickelates and manganites. In the undoped
correlated insulators with orbital degrees of freedom the orbital order
stabilizes particular types of anisotropic magnetic phases, and we contrast the
case of decoupled spin and orbital degrees of freedom in the manganites with
entangled spin-orbital states which decide about certain rather exotic
phenomena observed in the perovskite vanadates at finite temperature. Examples
of successful concepts in the theoretical approaches to these complex systems
are given and some open problems of current interest are indicated.",1008.2515v1
2010-10-26,Rods of Neutron Scattering Intensity in Yb2Ti2O7: Compelling Evidence for Significant Anisotropic Exchange in a Magnetic Pyrochlore Oxide,"Paramagnetic correlations in the magnetic material Yb2Ti2O7 have been
investigated via neutron scattering, revealing a [111] rod of scattering
intensity. Assuming interactions between the Yb^{3+} ions composed of all
symmetry-allowed nearest neighbor exchange interactions and long-range dipolar
interactions, we construct a model Hamiltonian that allows for an excellent
description of the neutron scattering data. Our results provide compelling
evidence for significant anisotropic exchange interactions in an insulating
magnetic pyrochlore oxide. We also compute the real space correlations leading
to the [111] rod of scattering.",1010.5476v2
2011-01-22,Unconventional Multiferroicity in Cupric Oxide,"The magnetic phase transitions reported below 230 K in cupric oxide are
analyzed theoretically at the macroscopic and microscopic levels. The
incommensurate multiferroic and lock-in commensurate phases are shown to
realize an inverted sequence of symmetry-breaking mechanisms with respect to
the usual sequence occurring in low temperature multiferroic compounds. The
higher temperature spin-spiral phase results from coupled order-parameters
which decouple at the lock-in transition to the commensurate ground state
phase. Expressing the order-parameters in function of the magnetic spins allows
determining the symmetries and magnetic structures of the equilibrium phases
and the microscopic interactions which give rise to the polarization.",1101.4284v1
2012-12-18,Magnetoelasticity in ACr2O4 spinel oxides,"Dynamical properties of the lattice structure was studied by optical
spectroscopy in ACr2O4 chromium spinel oxide magnetic semiconductors over a
broad temperature region of T=10-335K. The systematic change of the A-site ions
(A=Mn, Fe, Co, Ni and Cu) showed that the occupancy of 3d orbitals on the
A-site, has strong impact on the lattice dynamics. For compounds with orbital
degeneracy (FeCr2O4, NiCr2O4 and CuCr2O4), clear splitting of infrared-active
phonon modes and/or activation of silent vibrational modes have been observed
upon the Jahn-Teller transition and at the onset of the subsequent long-range
magnetic order. Although MnCr2O4 and CoCr2O4 show multiferroic and
magnetoelectric character, no considerable magnetoelasticity was found in
spinel compounds without orbital degeneracy as they closely preserve the
high-temperature cubic spinel structure even in their magnetic ground state.
Besides lattice vibrations, intra-atomic 3d-3d transitions of the A$^{2+}$ ions
were also investigated to determine the crystal field and Racah parameters and
the strength of the spin-orbit coupling.",1212.4301v1
2013-03-29,Formation of double ring patterns on Co2MnSi Heusler alloy thin film by anodic oxidation under scanning probe microscope,"Double ring formation on Co2MnSi (CMS) films is observed at electrical
breakdown voltage during local anodic oxidation (LAO) using atomic force
microscope (AFM). Corona effect and segregation of cobalt in the vicinity of
the rings is studied using magnetic force microscopy and energy dispersive
spectroscopy. Double ring forma-tion is attributed to the interaction of
ablated material with the induced magnetic field during LAO. Steepness of
forward bias transport characteristics from the unperturbed region of the CMS
film suggest a non equilibrium spin contribution. Such mesoscopic textures in
magnetic films by AFM tip can be potentially used for memory storage
applications.",1303.7470v2
2014-08-14,Effect of Diffused Hydrogen on the Conductance of Fe/Mgo/Fe Magnetic Tunnel Junctions: Atomistic Simulation,"In this work we have analysed the deterimental effect on conductance caused
by diffusion of hydrogen atoms in interstitial voids during fabrication process
of magnesium oxide barrier of an Fe MgO Fe magnetic tunnel junction, using
first principle calculations. This diffusion of hydrogen atoms in interstitial
voids in barrier disturbs a certain kind of symmetry possessed by magnesium
oxide often termed as delta 1 state symmetry. Distortion in delta 1 state
symmetry tempers the condutance through the magnetic tunnel junction specially
in parallel configuration, which in turn reduces the Tunnelling Magneto
Resistance TMR to large extent. Improved methods of fabrication can be used to
counter such kind of problems which affect device operation.",1408.3199v1
2014-09-10,Torque magnetometry of an amorphous-alumina/strontium-titanate interface,"We report torque magnetometry measurements of an oxide heterostructure
consisting of an amorphous Al$_2$O$_3$ thin film grown on a crystalline
SrTiO$_3$ substrate ($a$-AO/STO) by atomic layer deposition. We find a torque
response that resembles previous studies of crystalline LaAlO$_3$/SrTiO$_3$
(LAO/STO) heterointerfaces, consistent with strongly anisotropic magnetic
ordering in the plane of the interface. Unlike crystalline LAO, amorphous
Al$_2$O$_3$ is nonpolar, indicating that planar magnetism at an oxide interface
is possible without the strong internal electric fields generated within the
polarization catastrophe model. We discuss our results in the context of
current theoretical efforts to explain magnetism in crystalline LAO/STO.",1409.3194v4
2015-03-08,Antiferromagnetic order and spin dynamics in iron-based superconductors,"High-transition temperature (high-$T_c$) superconductivity in the iron
pnictides/chalcogenides emerges from the suppression of the static
antiferromagnetic order in their parent compounds, similar to copper oxides
superconductors. This raises a fundamental question concerning the role of
magnetism in the superconductivity of these materials. Neutron scattering, a
powerful probe to study the magnetic order and spin dynamics, plays an
essential role in determining the relationship between magnetism and
superconductivity in high-$T_c$ superconductors. The rapid development of
modern neutron time-of-flight spectrometers allows a direct determination of
the spin dynamical properties of iron-based superconductors throughout the
entire Brillouin zone. In this review, we present an overview of the neutron
scattering results on iron-based superconductors, focusing on the evolution of
spin excitation spectra as a function of electron/hole-doping and isoelectronic
substitution. We compare spin dynamical properties of iron-based
superconductors with those of copper oxide and heavy fermion superconductors,
and discuss the common features of spin excitations in these three families of
unconventional superconductors and their relationship with superconductivity.",1503.02340v2
2015-05-20,"Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO_4(OH) (A = Na, K)","A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO_4(OH) is prepared
by the hydrothermal method. The crystal structures of KCuMoO_4(OH) and the
already-known Na-analogue, NaCuMoO_4(OH), are isotypic, comprising chains of
Cu^{2+} ions in edge-sharing CuO_4(OH)_2 octahedra. Despite the structural
similarity, their magnetic properties are quite different because of the
different arrangements of d_{x2-y2} orbitals carrying spins. For NaCuMoO_4(OH),
d_{x2-y2} orbitals are linked by superexchange couplings via two bridging oxide
ions, which gives a ferromagnetic nearest-neighbor interaction J_1 of -51 K and
an antiferromagnetic next-nearest-neighbor interaction J_2 of 36 K in the
chain. In contrast, a staggered d_{x2-y2} orbital arrangement in KCuMoO_4(OH)
results in superexchange couplings via only one bridging oxide ion, which makes
J_1 antiferromagnetic as large as 238 K and J_2 negligible. This comparison
between the two isotypic compounds demonstrates an important role of orbital
arrangements in determining the magnetic properties of cuprates.",1505.05332v1
2015-05-27,Selective Interface Control of Order Parameters in Complex Oxides,"In complex materials observed electronic phases and transitions between them
often involves coupling between many degrees of freedom whose entanglement
convolutes understanding of the instigating mechanism. Metal-insulator
transitions are one such problem where coupling to the structural, orbital,
charge, and magnetic order parameters frequently obscures the underlying
physics. Here, we demonstrate a way to unravel this conundrum by
heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra
thin geometry, which preserves the metal-to-insulator transition and bulk-like
magnetic order parameter, but entirely suppresses the symmetry lowering and
charge order parameter. These findings illustrate the utility of
heterointerfaces as a powerful method for removing competing order parameters
to gain greater insight into the nature of the transition, here revealing that
the magnetic order generates the transition independently, leading to a purely
electronic Mott metal-insulator transition.",1505.07451v4
2015-07-15,Modulated Helical Metals at Magnetic Domain Walls of Pyrochlore Iridium Oxides,"Spontaneous symmetry breakings, metal-insulator transitions, and transport
properties of magnetic-domain-wall states in pyrochlore iridium oxides are
studied by employing a symmetry adapted effective hamiltonian with a slab
perpendicular to the (111) direction of the pyrochlore lattice. Emergent
metallic domain wall, which has unconventional topological nature with a
controllable and mobile metallic layer, is shown to host Fermi surfaces with
modulated helical spin textures resembling Rashba metals. The helical nature of
the domain-wall Fermi surfaces is experimentally detectable by anomalous Hall
conductivity, circular dichroism, and optical Hall conductivity under external
magnetic fields. Possible applications of the domain-wall metals to
spin-current generation and ""half-metallic"" conduction are also discussed.",1507.04153v1
2015-07-22,Fragile charge order in the non-superconducting ground state of the underdoped high temperature superconductors,"The normal state in the hole underdoped copper oxide superconductors has
proven to be a source of mystery for decades. The measurement of a small Fermi
surface by quantum oscillations on suppression of superconductivity by high
applied magnetic fields, together with complementary spectroscopic measurements
in the hole underdoped copper oxide superconductors, point to a nodal electron
pocket from charge order in YBa2Cu3O6+x. Here we report quantum oscillation
measurements in the closely related stoichiometric material YBa2Cu4O8, which
reveal similar Fermi surface properties to YBa2Cu3O6+x, despite an absence of
charge order signatures in the same spectroscopic techniques such as x-ray
diffraction that revealed signatures of charge order in YBa2Cu3O6+x. Fermi
surface reconstruction in YBa2Cu4O8 is suggested to occur from magnetic field
enhancement of charge order that is rendered fragile in zero magnetic fields
because of its potential unconventional symmetry, and/or its occurrence as a
subsidiary to more robust underlying electronic correlations.",1507.06109v1
2015-10-11,The ferroelectric polarization of Y2CoMnO6 aligns along the b-axis: the first-principles calculations,"Double-perovskite A2BB'O6 oxides with magnetic B and B' ions and E*-type
antiferromagnetic order (E*-AFM, i.e. the ++-- structure) are believed to
exhibit promising multiferroic properties, and Y2CoMnO6 (YCMO) is one candidate
in this category. However, the microscopic origins for magnetically induced
ferroelectricity in YCMO remain unclear. In this work, we perform detailed
symmetry analysis on the exchange striction effect and lattice distortion, plus
the first-principles calculations on YCMO. The E*-AFM state as the ground state
with other competing states such as ferromagnetic and A-antiferromagnetic
orders is confirmed. It is revealed that the ferroelectricity is generated by
the exchange striction associated with the E*-AFM order and chemically rdered
Mn/Co occupation. Both the lattice symmetry consideration and first-principles
calculations predict that the electric polarization aligns along the b-axis.
The calculated polarization reaches up to 0.4682 uC/cm2, mainly from the ionic
displacement contribution. The present work presents a comprehensive
understanding of the multiferroic mechanisms in YCMO and is of general
significance for predicting emergent multiferroicity in other double-perovskite
magnetic oxides.",1510.03039v1
2015-11-15,Oxidation and magnetic states of chalcopyrite CuFeS$_{2}$: a first principles calculation,"The ground state band structure, magnetic moments, charges and population
numbers of electronic shells of Cu and Fe atoms have been calculated for
chalcopyrite CuFeS2 using density functional theory. The comparison between our
calculation results and experimental data (X-ray photoemission, X-ray
absorption and neutron diffraction spectroscopy) has been made. Our
calculations predict a formal oxidation state for chalcopyrite as
Cu$^{1+}$Fe$^{3+}$S$_{2}$$^{2-}$. However, the assignment of formal valence
state to transition metal atoms appears to be oversimplified. It is anticipated
that the valence state can be confirmed experimentally by nuclear magnetic and
nuclear quadrupole resonance and M\""ossbauer spectroscopy methods.",1511.04753v1
2016-09-09,On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films,"Very high magnetic anisotropies have been theoretically predicted for
strained Fe-Co(-X) and indeed several experiments on epitaxial thin films
seemed to confirm strain induced anisotropy enhancement. This study presents a
critical analysis of the different contributions to perpendicular anisotropy:
volume, interface and surface anisotropies. Tracing these contributions,
thickness series of single layer films as well as multilayers with Au-Cu
buffers/interlayers of different lattice parameters have been prepared. The
analysis of their magnetic anisotropy reveals a negligible influence of the
lattice parameter of the buffer. Electronic effects, originating from both, the
Au-Cu interface and the film surface, outrange the elastic effects. Surface
anisotropy, however, exceeds the interface anisotropy by more than a factor of
three. A comparison with results from Density Functional Theory suggests, that
the experimentally observed strong perpendicular surface anisotropy originates
from a deviation from an ideal oxide-free surface. Accordingly, tailored
Fe-Co-X/oxide interfaces may open a route towards high anisotropy in rare-earth
free materials.",1609.02903v2
2017-08-26,Magneto-thermopower in the Weak Ferromagnetic Oxide CaRu0.8Sc0.2O3: An Experimental Test for the Kelvin Formula in a Magnetic Material,"We have measured the resistivity, the thermopower, and the specific heat of
the weak ferromagnetic oxide CaRu0.8Sc0.2O3 in external magnetic fields up to
140 kOe below 80 K. We have observed that the thermopower Q is significantly
suppressed by magnetic fields at around the ferromagnetic transition
temperature of 30 K, and have further found that the magneto-thermopower
{\Delta}Q(H, T) = Q(H, T) - Q(0, T) is roughly proportional to the
magneto-entropy {\Delta}S(H, T) = S(H, T)-S(0, T).We discuss this relationship
between the two quantities in terms of the Kelvin formula, and find that the
observed {\Delta}Q is quantitatively consistent with the values expected from
the Kelvin formula, a possible physical meaning of which is discussed.",1708.07992v1
2020-07-24,Reversible vs. irreversible voltage manipulation of interfacial magnetic anisotropy in Pt/Co/oxide multilayers,"The perpendicular magnetic anisotropy at the Co/oxide interface in Pt/Co/MOx
(MOx = MgOx, AlOx, TbOx) was modified by an electric field using a 10 nm-thick
ZrO2 as a solid electrolyte. The large voltage-driven modification of
interfacial magnetic anisotropy and the non-volatility of the effect is
explained in terms of the migration of oxygen ions towards/away from the Co/MOx
interface. While the effect is reversible in Pt/Co/AlOx and Pt/Co/TbOx, where
the Co layer can be oxidised or reduced, in Pt/Co/MgOx the effect has been
found to be irreversible. We propose that these differences may be related to
the different nature of the ionic conduction within the MOx layers.",2007.12570v1
2014-03-13,Hyper-honeycomb iridate $β$-Li2IrO3 as a platform for Kitaev magnetism,"The realization of Kitaev spin liquid, where spins on a honeycomb lattice are
coupled ferromagnetically by bond-dependent anisotropic interactions, has been
a sought-after dream. 5d iridium oxides $\alpha$-Li2IrO3 and $\alpha$-Na2IrO3
with a honeycomb lattice of Jeff = 1/2 moments recently emerged as a possible
materialization. Strong signature of Kitaev physics, however, was not captured.
Here we report the discovery of a complex iridium oxide $\beta$-Li2IrO3 with
Jeff = 1/2 moments on ""hyper-honeycomb"" lattice, a three-dimensional analogue
of honeycomb lattice. A positive Curie-Weiss temperature $\theta_{CW}$ ~ 40 K
indicated dominant ferromagnetic interactions among Jeff = 1/2 moments in
$\beta$-Li2IrO3. A magnetic ordering with a small entropy change was observed
at Tc = 38 K, which, with the application of magnetic field of only 3 T,
changed to a fully polarized state of Jeff = 1/2 moments. Those results imply
that hyper-honeycomb beta-Li2IrO3 is located in the vicinity to a Kitaev spin
liquid.",1403.3296v1
2016-08-08,"Spin-glass behavior and pyroelectric anomalies in a new lithium-based oxide, Li3FeRuO5","The results of dc and ac magnetization, heat-capacity, 57Fe Moessbauer
spectroscopy, dielectric, pyroelectric current and isothermal
magneto-capacitance measurements on a recently reported lithium-based oxide,
Li3FeRuO6, related to LiCoO2-type rhombohedral structure (space group, R-3m)
are presented. The results reveal that the compound undergoes spin-glass
freezing below 15 K. There is a peak around 34 K in pyroelectric data, which
can not be attributed to ferroelectricity, but to the phenomenon of thermally
stimulated depolarization current. As revealed by magnetocapacitance data above
and below magnetic ordering temperature, magnetic and electric dipoles appear
to be coupled, thereby offering evidence for magnetodielectric coupling.",1608.02304v1
2019-10-30,Rydberg excitons in electric and magnetic fields obtained with the complex-coordinate-rotation method,"The complete theoretical description of experimentally observed
magnetoexcitons in cuprous oxide has been achieved by F. Schweiner et al [Phys.
Rev. B 95, 035202 (2017)], using a complete basis set and taking into account
the valence band structure and the cubic symmetry of the solid. Here, we extend
these calculations by investigating numerically the autoionising resonances of
cuprous oxide in electric fields and in parallel electric and magnetic fields
oriented in [001] direction. To this aim we apply the
complex-coordinate-rotation method. Complex resonance energies are computed by
solving a non-Hermitian generalised eigenvalue problem, and absorption spectra
are simulated by using relative oscillator strengths. The method allows us to
investigate the influence of different electric and magnetic field strengths on
the position, the lifetime, and the shape of resonances.",1910.13941v1
2017-05-18,Enhanced Ferromagnetism in Lacey Reduced Graphene Oxide Nano-ribbon,"Incorporation of magnetism in graphene based compounds holds great promise
for potential spintronic applications. By optimizing point defects and high
edge density of defects, we report many-fold increase in the ferromagnetic
saturation moment in lacey reduced graphene oxide nanoribbons (LRGONR) as
compared to other graphene derivatives. The samples were synthesized using
chemical unzipping methodology. Detailed structural and morphological
characterizations are discussed that include XRD, Raman, SEM, HRTEM and XPS
measurements. Brilluoin function analysis to magnetization data reflects best
fit for J = 7/2 with a saturation moment of 1.1 emu/g. The microscopic origin
of magnetization in LRGONR is assigned to high edge defect density which has
also been correlated to microstructure.",1705.06531v1
2017-05-30,Magnetic and nematic orders of the 2DEG at oxide (111) surfaces and interfaces,"Recent experiments have explored two-dimensional electron gases (2DEGs) at
oxide (111) surfaces and interfaces, finding evidence for hexagonal symmetry
breaking in SrTiO$_3$ at low temperature. We discuss many-body instabilities of
such (111) 2DEGs, incorporating multiorbital interactions in the $t_{2g}$
manifold which can induce diverse magnetic and orbital orders. Such broken
symmetries may partly account for the observed nematicity, cooperating or
competing with phonon mechanisms. We present an effective field theory for the
interplay of magnetism and nematic charge order, and discuss implications of
the nematicity for transport and superconductivity in (111) 2DEGs.",1705.10795v3
2019-01-27,The distribution of oxygen at the Ni81Fe19/Ta interface,"The knowledge of how oxygen atoms are distributed at a magnetic-metal /
oxide, or magnetic-metal / non-magnetic-metal interface, can be an useful tool
to optimize device production. Multilayered Ni81Fe19 / Ta samples consisting of
15 bilayers of 2.5 nm each, grown onto glass substrates by magnetron sputtering
from Ni81Fe19 and Ta targets, have been investigated. X-ray absorption near
edge structure, extended X-Ray absorption fine structure, small angle X-ray
diffraction, and simulations, were used to characterize the samples. Oxygen
atoms incorporated onto Ni81Fe19 films during O2 exposition are mainly bonded
to Fe atoms. This partial oxidation of the Ni81Fe19 surface works as a barrier
to arriving Ta atoms, preventing intermixing at the Ni81Fe19 / Ta interface.
The reduction of the Ni81Fe19 surface by the formation of TaO x is observed.",1901.09368v1
2019-04-23,Offset fields in perpendicularly magnetized tunnel junctions,"We study the offset fields affecting the free layer of perpendicularly
magnetized tunnel junctions. In extended films, the free layer offset field
results from interlayer exchange coupling with the reference layer through the
MgO tunnel oxide. The free layer offset field is thus accompanied with a shift
of the free layer and reference layer ferromagnetic resonance frequencies. The
shifts depend on the mutual orientation of the two magnetizations. The offset
field decreases with the resistance area product of the tunnel oxide.
Patterning the tunnel junction into an STT-MRAM disk-shaped cell changes
substantially the offset field, as the reduction of the lateral dimension comes
with the generation of stray fields by the reference and the hard layer. The
experimental offset field compares best with the spatial average of the sum of
these stray fields, thereby providing guidelines for the offset field
engineering.",1904.10170v1
2019-11-13,Perpendicular Magnetic Anisotropy in Conducting NiCo2O4 Films from Spin-Lattice Coupling,"High perpendicular magnetic anisotropy (PMA), a property needed for nanoscale
spintronic applications, is rare in oxide conductors. We report the observation
of a PMA up to 0.23 MJ/m3 in modestly strained epitaxial NiCo2O4 (NCO) films
which are room-temperature ferrimagnetic conductors. Spin-lattice coupling
manifested as magnetoelastic effect was found as the origin of the PMA. The
in-plane xx-yy states of Co on tetrahedral sites play crucial role in the
magnetic anisotropy and spin-lattice coupling with an energy scale of 1
meV/f.u. The elucidation of the microscopic origin paves a way for engineering
oxide conductors for PMA using metal/oxygen hybridizations.",1911.05322v1
2020-11-02,Simulating Spin Waves in Entropy Stabilized Oxides,"The entropy stabilized oxide
Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$O exhibits antiferromagnetic
order and magnetic excitations, as revealed by recent neutron scattering
experiments. This observation raises the question of the nature of spin wave
excitations in such disordered systems. Here, we investigate theoretically the
magnetic ground state and the spin-wave excitations using linear spin-wave
theory in combination with the supercell approximation to take into account the
extreme disorder in this magnetic system. We find that the experimentally
observed antiferromagnetic structure can be stabilized by a rhombohedral
distortion together with large second nearest neighbor interactions. Our
calculations show that the spin-wave spectrum consists of a well-defined
low-energy coherent spectrum in the background of an incoherent continuum that
extends to higher energies.",2011.01288v1
2021-09-23,Giant magnetostriction and nonsaturating electric polarization up to 60 T in the polar magnet CaBaCo4O7,"Giant magnetostriction in insulating magnetic materials is highly required
for applications but is rarely observed. Here we show that giant
magnetostriction (> 1500 ppm) can be achieved in an insulating transition metal
oxide CaBaCo4O7 where the ferrimagnetic ordering at TC ~ 62 K is associated
with a huge change in the lattice. Moreover, because this material is
pyroelectric with a non-switchable electric polarization (P), the giant
magnetostriction results in a record-breaking magnetoelectric effect - a
gigantic change of electric polarization (deltaP ~ 1.6 {\mu}C/cm2) in response
to the applied magnetic field up to 60 T. Geometric frustration as well as the
orbital instability of Co2+/Co3+ ions is believed to play a crucial role in the
giant magnetostriction. Our study provides new insights on how to achieve both
giant magnetostriction and pronounced magnetoelectric effect in insulating
transition metal oxides.",2109.11149v1
2021-12-13,Induction of Large Magnetic Anisotropy Energy and Formation of Multiple Dirac States in SrIrO$_3$ Films: Role of correlation and spin-orbit coupling,"The 5$d$ transition metal oxides, in particular iridates, host novel
electronic and magnetic phases due to the interplay between onsite Coulomb
repulsion ($U$) and spin-orbit coupling (SOC). The reduced dimensionality
brings another degree of freedom to increase the functionality of these
systems. By taking the example of ultrathin films of SrIrO$_3$,theoretically,
we demonstrate that confinement led localization can introduce large magnetic
anisotropy energy (MAE) in the range 2-7 meV/Ir which is one to two orders
higher than that of the traditional MAE compounds formed out of transition
metals and their multilayers. Furthermore, in the weak correlation limit,
tailored terminations can yield multiple Dirac states across a large energy
window of 2 eV around the Fermi energy which is a rare phenomena in correlated
oxides and upon experimental realization it will give rise to unique transport
properties with excitation and doping.",2112.06813v2
2023-01-04,Atomic-scale Modulation of Synthetic Magnetic Order in Oxide Superlattices,"Atomic-scale precision control of magnetic interactions facilitates a
synthetic spin order useful for spintronics, including advanced memory and
quantum logic devices. Conventional modulation of synthetic spin order has been
limited to metallic heterostructures that exploit RKKY interaction through a
nonmagnetic metallic spacer; however, they face problems arising from Joule
heating and/or electric breakdown. The practical realization and observation of
a synthetic spin order across a nonmagnetic insulating spacer would lead to the
development of spin-related devices with a completely different concept.
Herein, we report the atomic-scale modulation of the synthetic spiral spin
order in oxide superlattices composed of ferromagnetic metal and nonmagnetic
insulator layers. The atomically controlled superlattice exhibit an oscillatory
magnetic behavior, representing the existence of a spiral spin structure.
Depth-sensitive polarized neutron reflectometry evidences modulated spiral spin
structures as a function of the nonmagnetic insulator layer thickness.
Atomic-scale customization of the spin state could lead the field one step
further to actual spintronic applications.",2301.01403v1
2023-06-30,Orbital-selective altermagnetism and correlation-enhanced spin-splitting in transition metal oxides,"We investigate the altermagnetic properties of strongly-correlated transition
metal oxides considering the family of the quasi two-dimensional A2BO4 and
three-dimensional ABO3. As a test study, we analyze the Mott insulators Ca2RuO4
and YVO3. In both cases, the orbital physics is extremely relevant in the t2g
subsector with the presence of an orbital-selective Mott physics in the first
case and of a robust orbital-order in the second case. Using first-principles
calculations, we show the presence of an orbital-selective altermagnetism in
the case of Ca2RuO4. In the case of YVO3, we study the altermagnetism as a
function of the magnetic ordering and of the Coulomb repulsion U. We find that
the altermagnetism is present in all magnetic orders with the symmetries of the
Brillouin zone depending on the magnetic order. Finally, the Coulomb repulsion
enhances the non-relativistic spin-splitting making the strongly-correlated
systems an exciting playground for the study of the altermagnetism.",2306.17497v1
2023-07-31,Persistent spin dynamics in magnetically ordered honeycomb cobalt oxides,"In the quest to find quantum spin liquids, layered cobalt oxides Na2Co2TeO6
and Na3Co2SbO6 have been proposed as promising candidates for approximating the
Kitaev honeycomb model. Yet, their suitability has been thrown into question
due to observed long-range magnetic order at low temperatures and indications
of easy-plane, rather than Kitaev-type, spin anisotropy. Here we use muon spin
relaxation to reveal an unexpected picture: contrary to the anticipated static
nature of the long-range order, the systems show prevalent spin dynamics with
spatially uneven distribution and varied correlation times. This underlines
that the magnetic ground states cannot be solely described by the long-range
order, suggesting a significant role of quantum fluctuations. Our findings not
only shed new light on the complex physics of these systems but also underscore
the need for a refined approach in the search for realizable quantum spin
liquids.",2307.16451v1
2024-01-22,The origin of magnetism in a supposedly nonmagnetic osmium oxide,"A supposedly nonmagnetic 5d$^1$ double perosvkite oxide is investigated by a
combination of spectroscopic and theoretical methods, namely resonant inelastic
X-ray scattering, X-ray absorption spectroscopy, magnetic circular dichroism,
and multiplet ligand field calculations. We found that the large spin-orbit
coupling admixes the 5d $t_{2g}$ and $e_g$ orbitals, covalency raises the 5d
population well above the nominal value, and the local symmetry is lower than
$O_h$. The obtained electronic interactions account for the finite magnetic
moment of Os in this compound and, in general, of 5d$^1$ ions. Our results
provide direct evidence of elusive Jahn-Teller distortions, hinting at a strong
electron-lattice coupling.",2401.12035v1
2024-03-29,Synthesis and Characterization of Superparamagnetic Iron Oxide Nanoparticles: A Series of Laboratory Experiments,"The following laboratory procedure provides students with a hands-on
experience in nanomaterials chemistry and characterization. This three-day
protocol is easy to follow for undergraduates with basic chemistry or materials
science backgrounds and is suitable for inclusion in upper division courses in
inorganic chemistry or materials science. Students use air-free chemistry
procedures to synthesize and separate iron oxide magnetic nanoparticles and
subsequently modify the nanoparticle surface using a chemical stripping agent.
The morphology and chemical composition of the nanoparticles are characterized
using electron microscopy and dynamic light scattering measurements.
Additionally, magnetic characterization of the particles is performed using an
open-source (3D-printed), inexpensive magnetophotometer. Possible modifications
to the synthesis procedure including the incorporation of dopants to modify the
magnetic response and alternative characterization techniques are discussed.
The three-day synthesis, purification, and characterization laboratory will
prepare students with crucial skills for advanced technology industries such as
semiconductor manufacturing, nanomedicine, and green chemistry.",2403.19970v1
1994-03-03,Effect of a magnetic field on Mott-Hubbard systems,"The effect of a magnetic field on Mott-Hubbard systems is investigated by
studying the half-filled Hubbard model in the limit of infinite dimensions. A
first-order metamagnetic transition between the strongly correlated metal and
the Mott insulator is found for a critical value of the applied field. The
field and temperature dependence of the magnetization, one-particle properties
and susceptibility are studied and compared to the Gutzwiller approximation.
The experimental relevance for transition-metal oxides and liquid $^{3}He$ is
discussed.",9403016v1
1994-09-19,Motion of a Single Hole in a Disordered Magnetic Background,"The spectrum of a single hole is calculated within the spin-hole model using
a variational method. This calculation is done for any rotational invariant
magnetic background. We have found that when the magnetic background changes
from a disordered to a locally ordered state, the spectrum changes
qualitatively. We have also found that the spin pattern around the hole is
polarized. This problem is related to the study of copper oxide planes $CuO_2$
doped with a small number of holes.",9409077v1
1996-11-13,Dramatic Switching of Magnetic Exchange in a Classic Transition Metal Oxide: Evidence for Orbital Ordering,"Spin correlations in metallic and insulating phases of $V_2O_3$ and its
derivatives are investigated using magnetic neutron scattering. Metallic
samples have incommensurate spin correlations varying little with hole doping.
Paramagnetic insulating samples have spin correlations only among near
neighbors. The transition from either of these phases into the low temperature
insulating antiferromagnetic phase is accompanied by an abrupt change of
dynamic magnetic short range order. Our results support the idea that the
transition into the antiferromagnetic insulator is also an orbital ordering
transition.",9611109v1
1999-10-25,Heavy Fermion Behaviors in LiV_{2}O_{4},"Experiments of various types on the metallic transition metal oxide compound
LiV_{2}O_{4} with the fcc normal-spinel structure are reviewed. The
low-temperature T < 10 K data consistently indicate heavy fermion (HF)
behaviors characteristic of those of the heaviest-mass f-electron HF compounds.
A crossover is observed above about 50 K in the magnetic susceptibility, ^{7}Li
spin-lattice relaxation rate and neutron magnetic scattering function to a
magnetic state variously described as an antiferromagnetically-coupled
local-moment metal or, at the opposite extreme, as an itinerant
nearly-ferromagnetic metal. Recent theoretical investigations to understand
these properties of LiV_{2}O_{4} are discussed.",9910404v1
2000-11-24,"Jahn-Teller, Charge and Magnetic Ordering in half-doped Manganese Oxides","The phase diagram of half-doped manganite systems of formula
A_{0.5}A'_{0.5}MnO_3 is investigated within a single-orbital model
incorporating magnetic double-exchange and superexchange, together with
intersite Coulomb and electron-lattice interactions. Strong Jahn-Teller and
breathing mode deformations compete together and result in shear lattice
deformations. The latters stabilize the charge-ordered CE-type phase, which
undergo first-order transitions with temperature or magnetic field to either
Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in
the ferromagnetic phase.",0011419v1
2001-05-09,Thermodynamics of the interplay between magnetism and high-temperature superconductivity,"The copper-oxide based high temperature superconductors have complex phase
diagrams with multiple ordered phases. It even appears that the highest
superconducting transition temperatures for certain cuprates are found in
samples which display simultaneous onset of magnetism and superconductivity. We
show here how the thermodynamics of fluid mixtures - a touchstone for chemists
as well as hard and soft condensed matter physics - accounts for this startling
observation, as well as many other properties of the cuprates in the vicinity
of the instability towards ``striped'' magnetism.",0105200v3
2001-06-06,Low Voltage I-V Characteristics in Magnetic Tunnel Junctions,"We show that elastic currents that take into account variations of the tunnel
transmitivity with voltage and a large ratio of majority to minority spin
densities of states of the $s$ band, can account for the low voltage current
anomalies observed in magnet-oxide-magnet junctions. The anomalies can be
positive, negative or have a mixed form, depending of the position of the Fermi
level in the $s$ band, in agreement with observations. Magnon contribution is
negligible small to account for the sharp drop of the magnetoresistance with
the voltage bias.",0106123v1
2002-01-14,Magnetic and superconducting properties of Cd2Re2O7: Cd NMR and Re NQR,"We report Cd NMR and Re NQR studies on Cd2Re2O7, the first superconductor
among pyrochlore oxides Tc=1 K. Re NQR spectrum at zero magnetic field below
100 K rules out any magnetic or charge order. The spin-lattice relaxation rate
below Tc exhibits a pronounced coherence peak and behaves within the
weak-coupling BCS theory with nearly isotropic energy gap. Cd NMR results point
to moderate ferromagnetic enhancement at high temperatures followed by rapid
decrease of the density of states below the structural transition temperature
of 200 K.",0201215v1
2002-04-21,Magnetic effect from non-magnetic impurity in superconducting CuO_{2} plane,"We propose a new model for impurity center formed by a cathion substitute for
Cu, like Zn, in CuO_{2} planes. Its main effect on superconducting electrons is
due to the non-zero exchange field on O sites, neighbors to the (non-magnetic)
impurity. We discuss a strong suppression of d-wave order parameter, a zero-
energy resonance in local density of states, and spin polarization of charge
carriers, which can be related to the experimentally observed effects in
Zn-doped copper oxides. These results are obtained \emph{without} using the
unitary scattering limit.",0204454v1
2004-01-16,Ferromagnetism in Fe-doped SnO2 thin films,"Thin films grown by pulsed-laser deposition from targets of Sn0.95Fe0.05O2
are transparent ferromagnets with Curie temperature and spontaneous
magnetization of 610 K and 2.2 Am2kg-1, respectively. The 57Fe Mossbauer
spectra show the iron is all high-spin Fe3+ but the films are magnetically
inhomogeneous on an atomic scale, with only 23 % of the iron ordering
magnetically. The net ferromagnetic moment per ordered iron ion, 1.8 Bohr
magnetons, is greater than for any simple iron oxide. Ferromagnetic coupling of
ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is
proposed to explain the high Curie temperature",0401293v1
2004-10-12,Evidence for magnetic clusters in BaCoO$_3$,"Magnetic properties of the transition metal oxide BaCoO$_3$ are analyzed on
the basis of the experimental and theoretical literature available via ab inito
calculations. These can be explained by assuming the material to be formed by
noninteracting ferromagnetic clusters of about 1.2 nm in diameter separated by
about 3 diameters. Above about 50 K, the so-called blocking temperature,
superparamagnetic behavior of the magnetic clusters occurs and, above 250 K,
paramagnetism sets in.",0410303v1
2004-12-17,The low-energy electronic structure and the orbital magnetism in NiO,"The orbital and spin moment of the Ni2+ ion in NiO has been calculated within
the quasi-atomic approach. The orbital moment of 0.46 mu_B amounts at 0 K, in
the magnetically-ordered state, to about 20% of the total moment (2.45 mu_B).
For this outcome, being in nice agreement with the recent experimental finding
of the orbital moment, taking into account the intra-atomic spin-orbit coupling
is indispensable.
  PACS: 75.25.+z, 75.10.Dg
  Keywords: Crystalline Electric Field, 3d oxides, magnetism, NiO",0412484v1
2004-12-23,Why the magnetic interactions in Na$_{x}$CoO$_{2}$ are 3D,"The puzzle of 3D magnetic interactions in the structurally 2D layered oxide
Na$_{x}$CoO$_2$ is addressed using first principles calculations and analysis
of the exchange mechanisms. The calculations agree with recent neutron results,
favoring AFM stacking of FM planes. Superexchange via direct O-O hopping and
through intermediate Na $sp^2$ hybrids couples each Co to its nearest and six
\textit{next}-nearest interplanar neighbors equally. The individual exchange
constants are rather 2D, like the lattice itself, but due to multiple c-axis
exchange paths, the magnetism becomes effectively 3D.",0412663v1
2005-09-26,Interplay between mesoscopic phase separation and bulk magnetism in the layered NaxCoO2,"Specific heat of the layered NaxCoO2 (x=0.65, 0.70 and 0.75) oxides has been
measured in the temperature range of 3-360 K and magnetic field of 0 and 9 T.
The analysis of data, assuming the combined effect of inter-layer superexchange
and the phase separation into mesoscopic magnetic domains with localized spins
embedded in a matrix with itinerant electronic character, suggests that the
dominant contribution to the specific heat in the region of short-range
ordering is mediated by quasi-2D antiferromagnetic clusters, perpendicular to
the CoO2 layers.",0509655v1
2005-11-25,"Comment on a Phys. Rev. Lett. paper: ""All-Electron Self-Consistent GW Approximation: Application to Si, MnO, and NiO"". Magnetic moment of NiO","We claim that any approach neglecting the spin-orbit coupling and the orbital
magnetism is not physically adequate for 3d oxides, including NiO, and that in
reaching ""excellent agreement"" in a Phys. Rev. Lett. 93, 126406 (2004) paper
too small experimental value of 1.9 muB has been taken for the Ni magnetic
moment despite publication of a new experimental value of 2.2 muB, at 300 K
yielding 2.6 muB at T = 0 K, already in a year of 1998.",0511624v1
2006-02-24,Magnetic field-assisted manipulation and entanglement of Si spin qubits,"Architectures of donor-electron based qubits in silicon near an oxide
interface are considered theoretically. We find that the precondition for
reliable logic and read-out operations, namely the individual identification of
each donor-bound electron near the interface, may be accomplished by
fine-tuning electric and magnetic fields, both applied perpendicularly to the
interface. We argue that such magnetic fields may also be valuable in
controlling two-qubit entanglement via donor electron pairs near the interface.",0602597v2
2006-08-28,Stripeless incommensurate magnetism in a doped strongly correlated oxide,"We studied the nano-scale structure of the short-range incommensurate
magnetic order in La1.5Sr0.5CoO4 by elastic neutron scattering. We find that
magnetic diffuse scattering is isotropic in the a-b plane, in contrast with the
naive expectation based on the popular stripe model. Indeed, charge segregation
into lines favoring certain lattice direction(s) would facilitate linear
stacking faults in an otherwise robust antiferromagnetism of un-doped material,
leading to anisotropic disorder, with a characteristic symmetry pattern present
in the neutron scattering data.",0608575v3
2007-02-26,Impurity Conduction and Magnetic Polarons in Antiferromagnetic Oxides,"Low-temperature transport and magnetization measurements for the
antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile
states separated by energy E from electrons bound in Coulombic potentials. Very
weak electric fields are sufficient to excite bound electrons to the impurity
band, increasing the mobile carrier concentration by more than three orders of
magnitude. The data argue against the formation of self-trapped magnetic
polarons (MPs) predicted by theory, and rather imply that bound MPs become
stable only for kT<<E.",0702608v1
2007-03-11,Hole states in wide band-gap diluted magnetic semiconductors and oxides,"Puzzling disagreement between photoemission and optical findings in
magnetically doped GaN and ZnO is explained within a generalized alloy theory.
The obtained results show that the strong coupling between valence-band holes
and localized spins gives rise to a mid-gap Zhang-Rice-like state, to a sign
reversal of the apparent p-d exchange integral, and to an increase of the
band-gap with the magnetic ion concentration.",0703278v1
2007-07-05,Anomalous exchange coupling in transition-metal-oxide based superlattices with antiferromagnetic spacer layers,"A direct correlation is seen between the coercive field (HC) and the
magnetic-field-dependent resistivity (MR) in SrMnO3/SrRuO3 superlattices of
perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at
Hc for in-plane current and the out-of-plane magnetic field. Both HC and
high-field MR also oscillate with the thickness of the SrMnO3 spacer layers
separating the metallic ruthenate. Since the spacer in these superlattices has
no mobile carriers to facilitate an oscillatory coupling, we attribute the
observed behavior to the spin-polarized quantum tunneling of electrons between
the ferromagnetic layers and antiferromagnetically ordered t2g spins of SrMnO3.",0707.0768v1
2008-05-24,Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2,"Electric and magnetic properties of a high temperature ferromagnetic oxide
semiconductor, cobalt-doped rutile TiO2, are summarized. The cobalt-doped
rutile TiO2 epitaxial thin films with different electron densities and cobalt
contents were grown on r-sapphire substrates with laser molecular beam epitaxy.
Results of magnetization, magnetic circular dichroism, and anomalous Hall
effect measurements were examined for samples with systematically varied
electron densities and cobalt contents. The samples with high electron
densities and cobalt contents show the high temperature ferromagnetism,
suggesting that charge carriers induce the ferromagnetism.",0805.3748v1
2008-08-07,Incommensurate spin density modulation in a copper-oxide chain compound with commensurate charge order,"Neutron diffraction has been used to determine the magnetic structure of
Na$_8$Cu$_5$O$_{10}$, a stoichiometric compound containing chains based on
edge-sharing CuO$_4$ plaquettes. The chains are doped with 2/5 hole per Cu site
and exhibit long-range commensurate charge order with an onset well above room
temperature. Below $T_N = 23$ K, the neutron data indicate long-range collinear
magnetic order with a spin density modulation whose propagation vector is
commensurate along and incommensurate perpendicular to the chains. Competing
interchain exchange interactions are discussed as a possible origin of the
incommensurate magnetic order.",0808.1009v1
2011-04-03,Dynamical magnetoelectric effects in multiferroic oxides,"Multiferroics with coexistent ferroelectric and magnetic orders can provide
an interesting laboratory to test unprecedented magnetoelectric responses and
their possible applications. One such example is the dynamical and/or resonant
coupling between magnetic and electric dipoles in a solid. As the examples of
such dynamical magnetoelectric effects, (1) the multiferroic domain wall
dynamics and (2) the electric-dipole active magnetic responses are discussed
with the overview of recent experimental observations.",1104.0357v1
2011-07-03,Terahertz magnetoelectric response via electromagnons in magnetic oxides,"Terahertz magnetic resonance driven by the light electric field, now referred
to as electromagnon, has stimulated interest due to its strong candidate for
future spin-electronics. One unique characteristic of electromagnons is the
terahertz magnetochromism, a color change by external magnetic field, as
recently demonstrated in the hexaferrite. By taking perovskite manganites and
hexaferrite as model cases, the current understating of the electromagnon
activity is discussed in terms of the symmetric exchange mechanism.",1107.0428v1
2012-09-23,On the Origin of Zigzag Magnetic Order in Iridium Oxide Na2IrO3,"We explore the phase diagram of spin-orbit Mott insulators on a honeycomb
lattice, within the Kitaev-Heisenberg model extended to its full parameter
space. Zigzag-type magnetic order is found to occupy a large part of the phase
diagram of the model, and its physical origin is explained as due to
interorbital t2g-eg hopping. Magnetic susceptibility and spin wave spectra are
calculated and compared to the experimental data, obtaining thereby the spin
coupling constants in Na2IrO3 and Li2IrO3.",1209.5100v1
2012-11-15,Spin-Droplet State of an Interacting 2D Electron System,"We report thermodynamic magnetization measurements of two-dimensional
electrons in several high mobility Si metal-oxide-semiconductor field-effect
transistors. We provide evidence for an easily polarizable electron state in a
wide density range from insulating to deep into the metallic phase. The
temperature and magnetic field dependence of the magnetization is consistent
with the formation of large-spin droplets in the insulating phase. These
droplets melt in the metallic phase with increasing density and temperature,
although they survive up to large densities.",1211.3536v1
2012-11-30,Ab initio study of magnetic anisotropy in cobalt doped zinc oxide with electron-filling,"Based on first-principles calculation, it has been predicted that the
magnetic anisotropy energy (MAE) in Co-doped ZnO (Co:ZnO) depends on
electron-filling. Results show that the charge neutral Co:ZnO presents a ""easy
plane"" magnetic state. While modifying the total number of electrons, the easy
axis rotates from in-plane to out-of-plane. The alternation of the MAE is
considered to be the change of the ground state of Co ion, resulting from the
relocating of electrons on Co d-orbitals with electron-filling.",1211.7287v2
2013-05-22,Electric control of the magnetization in BiFeO$_3$/LaFeO$_3$ superlattices,"First-principles techniques are used to investigate the behavior of
BiFeO$_{3}$/LaFeO$_{3}$ perovskite oxide superlattices epitaxially grown on a
(001)-SrTiO$_3$ substrate. The calculations show that 1/1 superlattices exhibit
a $Pmc2_1$ ground state combining a trilinear coupling of one polar and two
oxygen rotational lattice modes, and weak ferromagnetism. The microscopic
mechanism allowing one to manipulate the magnetization with an electric field
in such systems is presented and its dependence on strain and chemical
substitution is discussed. BiFeO$_{3}$/LaFeO$_{3}$ artificial superlattices
appear to be good candidates to achieve electric switching of magnetization at
room temperature.",1305.5093v1
2016-03-23,Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts,"We report magnetoresistance for current flow through iron/topological
insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is
used to initially orient the magnetic alignment of the incorporated
ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature.
This magnetoresistance is associated with the relative orientation of the Fe
bar magnetization and spin-polarization of electrons moving on the surface of
the TI with helical spin-momentum locking. The magnitude of the observed
magnetoresistance is relatively large compared to that observed in prior work.",1603.07283v1
2017-08-09,Can Nitric Oxide be Evaporatively Cooled in its Ground State?,"Cold collisions of $^{14}$N$^{16}$O molecules in the $^{2}\Pi_{1/2}$ ground
state, subject to electric and magnetic fields, are investigated. It is found
that elastic collision rates significantly exceed state-changing inelastic
rates only at temperatures above 0.5 K at laboratory strength fields. It is
found, however, that in very large fields $> 10^{4}$ V/cm, inelastic rates can
be somewhat suppressed. Magnetic fields have negligible influence on scattering
for this nearly non-magnetic state.",1708.02875v1
2013-09-12,Structural control of magnetic anisotropy in a strain driven multiferroic EuTiO3 thin film,"Octahedral distortion plays a key role in engineering the physical properties
of heterostructures composed of perovskite oxides. We observe a strong in-plane
uniaxial magnetic anisotropy in a strain-enabled multiferroic EuTiO3 thin film
epitaxially grown on a (110)o DyScO3 substrate. First principles calculations
show that the magnetic anisotropy is closely correlated with the uniaxial TiO6
octahedral tilting and the ferroelectric polarization of the film, indicating
potential strong magnetoelectric coupling in the strain-engineered multiferroic
system.",1309.3185v1
2017-09-08,Room temperature ferromagnetism in transparent and conducting Mn-doped $SnO_{2}$ thin films,"The magnetization as a function of magnetic field showed hysteretic behavior
at room temperature. According to the temperature dependence of the
magnetization, the Curie temperature $(T_{C})$ is higher than 350 K.
Ferromagnetic Mn-doped tin oxide thin films exhibited low electrical
resistivity and high optical transmittance in the visible region (400-800 nm).
The coexistence of ferromagnetism, high visible transparency and high
electrical conductivity in the Mn-doped $SnO_{2}$ films is expected to be a
desirable trait for spintronics devices.",1709.05930v1
2019-02-24,Spin interactions and magnetic order in the iron oxychalcogenides BaFe2Q2O,"The ability to tune the iron chalcogenides BaFe2Q3 from Mott insulators, to
metals and then superconductors with applied pressure has renewed interest in
low-dimensional iron chalcogenides and oxychalcogenides. We report here a
combined experimental and theoretical study on the iron oxychalcogenides
BaFe2Q2O (Q=S, Se) and show that their magnetic behaviour results from
nearest-neighbour magnetic exchange interactions via oxide and selenide anions
of similar strength, with properties consistent with more localised electronic
structures than those of BaFe2Q3 systems.",1902.09035v2
2021-09-21,Ferromagnetic Double Perovskite Semiconductors with Tunable Properties,"We successfully dope the magnetically silent double perovskite semiconductor
Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially
substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering
with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double
perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and
has tunable ferromagnetic ordering temperature and band gap, suggests that
magnetic ion doping of double perovskites is a productive avenue towards
obtaining materials for application in next-generation oxide-based spintronic
devices.",2109.10405v1
2023-11-30,Spin-Dependent Capture Mechanism for Magnetic Field Effects on Interface Recombination Current in Semiconductor Devices,"Electrically detected magnetic resonance (EDMR) and near-zero field
magnetoresistance (NZFMR) are techniques that probe defect states at dielectric
interfaces critical for metal-oxide-semiconductor (MOS) electronic devices such
as the Si/SiO$_2$ MOS field effect transistor (MOSFET). A comprehensive theory,
adapted from the trap-assisted recombination theory of Shockley, Read, and
Hall, is introduced to include the spin-dependent recombination effects that
provide the mechanism for magnetic field sensitivity.",2312.14933v1
2017-12-11,"Electronic structure, magnetism and exchange integrals in transition metal oxides: role of the spin polarization of the functional in DFT+$U$ calculations","Density functional theory augmented with Hubbard-$U$ corrections (DFT+$U$) is
currently one of the widely used methods for first-principles electronic
structure modeling of insulating transition metal oxides (TMOs). Since $U$ is
relatively large compared to band widths, the magnetic excitations in TMOs are
expected to be well described by a Heisenberg model. However, in practice the
calculated exchange parameters $J_{ij}$ depend on the magnetic configuration
from which they are extracted and on the functional used to compute them. In
this work we investigate how the spin polarization dependence of the underlying
exchange-correlation functional influences the calculated magnetic exchange
constants of TMOs. We perform a systematic study of the predictions of
calculations based on the local density approximation plus $U$ (LDA+$U$) and
the local spin density approximation plus $U$ (LSDA+$U$) for the electronic
structures, total energies and magnetic exchange interactions $J_{ij}$'s
extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of
several transition metal oxide materials. We report that, for realistic choices
of Hubbard $U$ and Hund's $J$ parameters, LSDA+$U$ and LDA+$U$ calculations
result in different values of the magnetic exchange constants and band gap. The
dependence of the band gap on the magnetic configuration is stronger in LDA+$U$
than in LSDA+$U$ and we argue that this is the main reason why the
configuration dependence of the $J_{ij}$'s is found to be systematically more
pronounced in LDA+$U$ than in LSDA+$U$ calculations. We report a very good
correspondence between the computed total energies and the parameterized
Heisenberg model for LDA+$U$ calculations, but not for LSDA+$U$, suggesting
that LDA+$U$ is a more appropriate method for estimating exchange interactions.",1712.03907v3
2021-03-14,Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates,"Perpendicularly magnetized films showing small saturation magnetization,
$M_\mathrm{s}$, are essential for spin-transfer-torque writing type
magnetoresistive random access memories, STT-MRAMs. An intermetallic compound,
{(Mn-Cr)AlGe} of the Cu$_2$Sb-type crystal structure was investigated, in this
study, as a material showing the low $M_\mathrm{s}$ ($\sim 300$ kA/m) and
high-perpendicular magnetic anisotropy, $K_\mathrm{u}$. The layer thickness
dependence of $K_\mathrm{u}$ and effects of Mg-insertion layers at top and
bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated
onto thermally oxidized silicon substrates to realize high-$K_\mathrm{u}$ in
the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were
1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were
relatively thick compared to results in similar insertion effect investigations
on magnetic tunnel junctions reported in previous studies. The cross-sectional
transmission electron microscope images revealed that the Mg-insertion layers
acted as barriers to interdiffusion of Al-atoms as well as oxidization from the
MgO layers. The values of $K_\mathrm{u}$ were about $7 \times 10^5$ and $2
\times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe
films, respectively, with the optimum Mg-insertion thicknesses. The
$K_\mathrm{u}$ at a few nanometer thicknesses is comparable or higher than
those reported in perpendicularly magnetized CoFeB films which are
conventionally used in MRAMs, while the $M_\mathrm{s}$ value is one third or
less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are
promising from the viewpoint of not only the magnetic properties, but also the
compatibility to the silicon process in the film fabrication.",2103.07847v2
2010-11-30,Neutron diffraction studies and the magnetism of an ordered perovskite: Ba2CoTeO6,"The complex perovskite Ba2CoTeO6 (BCTO) has been synthesised, and the crystal
structure and magnetic properties have been investigated using a combination of
X-ray and neutron powder diffraction, electron microscopy and dielectric,
calorimetric and magnetic measurements. It was shown that at room temperature
this compound adopts the 6L-trigonal perovskite structure, space group P-3m (N
164) (a= 5.7996(1){\AA}, c=14.2658(3){\AA}). The structure comprises dimers of
face-sharing octahedra as well as octahedra which share only vertices with
their neighbours. A long-range antiferromagnetically ordered state has been
identified from neutron diffraction and magnetic studies. The magnetic
diffraction peaks were registered below the magnetic transition at about 15 K
and a possible model for the magnetic structure is proposed. The structural and
magnetic features of this compound are discussed and compared with those of
other Co-based quaternary oxides adopting the perovskite structure.",1011.6637v1
2017-02-03,"Evolution of structure, magnetism and electronic transport in doped pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$","The interplay between spin-orbit coupling (SOC) and electron correlation
($U$) is considered for many exotic phenomena in iridium oxides. We have
investigated the evolution of structural, magnetic and electronic properties in
pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$ where the substitution of Ru
has been aimed to tune this interplay. The Ru substitution does not introduce
any structural phase transition, however, we do observe an evolution of lattice
parameters with the doping level $x$. X-ray photoemission spectroscopy (XPS)
study indicates Ru adopts charge state of Ru$^{4+}$ and replaces the Ir$^{4+}$
accordingly. Magnetization data reveal both the onset of magnetic
irreversibility and the magnetic moment decreases with progressive substitution
of Ru. These materials show non-equilibrium low temperature magnetic state as
revealed by magnetic relaxation data. Interestingly, we find magnetic
relaxation rate increases with substitution of Ru. The electrical resistivity
shows an insulating behavior in whole temperature range, however, resistivity
decreases with substitution of Ru. Nature of electronic conduction has been
found to follow power-law behavior for all the materials.",1702.01023v1
2015-12-04,Magnetic proximity effect at interface between a cuprate superconductor and an oxide spin valve,"Heterostructures consisting of a cuprate superconductor YBa2Cu3O7x and a
ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve have been studied by
SQUID magnetometry, ferromagnetic resonances and neutron reflectometry. It was
shown that due to the influence of magnetic proximity effect a magnetic moment
is induced in the superconducting part of heterostructure and at the same time
the magnetic moment is suppressed in the ferromagnetic spin valve. The
experimental value of magnetization induced in the superconductor has the same
order of magnitude with the calculations based on the induced magnetic moment
of Cu atoms due to orbital reconstruction at the superconductor-ferromagnetic
interface. It corresponds also to the model that takes into account the change
in the density of states at a distance of order of the coherence length in the
superconductor. The experimentally obtained characteristic length of
penetration of the magnetic moment into superconductor exceeds the coherence
length for cuprate superconductor. This fact points on the dominance of the
mechanism of the induced magnetic moment of Cu atoms due to orbital
reconstruction.",1512.01336v1
2016-11-30,Temperature-dependent magnetic anisotropy from directional-dependent interactions,"Magnetic anisotropy of spin models with directional-dependent interactions in
the high-temperature paramagnetic phase is theoretically studied. Using a high
temperature expansion, we show that the Ising type directional-dependent
interaction gives rise to magnetic anisotropy which depends on the temperature
as $\propto T^{-5}$. This phenomenon arises from the anisotropic exchange
interaction, and is distinct from the orbital effect, such as van Vleck
susceptibility. It is shown that while the quadratic term in the magnetization
favors to point the spins along the bond, the fourth order term in
magnetization prefers to point spins to the perpendicular direction. The theory
is applied to the Heisenberg-Kitaev model on the honeycomb lattice and a cubic
lattice model that is potentially relevant to perovskite iridates. We show
that, in these models, the anisotropic terms in quadratic order cancels out,
and the leading order for the magnetic anisotropy arises from the fourth order
contribution. The result shows that the anisotropy from the
directional-dependent interaction gives rise to $\langle100\rangle$ magnetic
anisotropy. These results are potentially relevant to heavy transition metal
oxides such as iridates. Experimental observation of the magnitude of
anisotropic interactions using magnetic torque measurement is also discussed.",1612.00057v1
2017-12-21,Thermal and magnetic field stability of holmium single atom magnets,"We use spin-polarized scanning tunneling microscopy to demonstrate that Ho
atoms on magnesium oxide exhibit a coercive field of more than 8 T and magnetic
bistability for many minutes, both at 35 K. The first spontaneous magnetization
reversal events are recorded at 45 K for which the metastable state relaxes in
an external field of 8 T. The transverse magnetic anisotropy energy is
estimated from magnetic field and bias voltage dependent switching rates at 4.3
K. Our measurements constrain the possible ground state of Ho single atom
magnets to either Jz = 7 or 8, both compatible with magnetic bistability at
fields larger than 10 mT.",1712.07871v1
2019-10-03,Magnetization process of the breathing pyrochlore magnet CuInCr$_4$S$_8$ in ultra-high magnetic fields up to 150 T,"The magnetization process of the breathing pyrochlore magnet CuInCr4S8 has
been investigated in ultra-high magnetic fields up to 150 T. Successive phase
transitions characterized with a substantially wide 1/2-plateau from 55 T to
110 T are observed in this system, resembling those reported in chromium spinel
oxides. In addition to the 1/2-plateau phase, the magnetization is found to
exhibit two inherent behaviors: a slight change in the slope of the M-H curve
at ~ 85 T and a shoulder-like shape at ~ 130 T prior to the saturation. Both of
them are accompanied by a hysteresis, suggesting first-order transitions. The
theoretical calculation applicable to CuInCr4S8 is also shown, based on the
microscopic model with the spin-lattice coupling. The calculation fairly well
reproduces the main features of the experimentally observed magnetization
process, including a relatively wide cant 2:1:1 phase clearly observed in the
previous work [Y. Okamoto et al., J. Phys. Soc. Jpn. 87, 034709 (2018)]. The
robust 1/2-plateau on CuInCr4S8 seems to be originated from the dominant
antiferromagnetic interactions and the strong spin-lattice coupling.",1910.01315v1
2018-06-26,Ultrahigh Magnetic Fields Produced by Shearing Carbon Nanotubes,"In laboratories, ultrahigh magnetic fields are usually produced with very
large currents through superconducting, resistive or hybrid magnets, which
require extreme conditions, such as low temperature, huge cooling water or tens
of megawatts of power. In this work we report that when single walled carbon
nanotubes (SWNTs) are cut, there are magnetic moments at the shearing end of
SWNTs. The average magnetic moment is found to be 41.5+-9.8uB per carbon atom
in the end states with a width of 1 nm at temperature of 300.0K, suggesting
ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of
the carbon atoms at the shearing ends play important roles for this
unexpectedly high magnetic moments because the oxidation temperature of cut
SWNTs is found to be as low as 312 in dry air. Producing ultrahigh magnetic
field with SWNTs has the advantage of working at higher working temperature and
with low energy consumption, suggesting great potentials of applications.",1806.09891v1
2019-11-30,Phono-magnetic analogs to opto-magnetic effects,"The magneto-optical and opto-magnetic effects describe the interaction of
light with a magnetic medium. The most prominent examples are the Faraday and
Cotton-Mouton effects that modify the transmission of light through a medium,
and the inverse Faraday and inverse Cotton-Mouton effects that produce
effective magnetic fields for the spin in the material. Here, we introduce the
phenomenology of the analogous magneto-phononic and phono-magnetic effects, in
which vibrational quanta take the place of the light quanta. We show, using a
combination of first-principles calculations and phenomenological modeling,
that the effective magnetic fields exerted by the phonon analogs of the inverse
Faraday and inverse Cotton-Mouton effects on the spins of antiferromagnetic
nickel oxide yield magnitudes comparable to and potentially larger than those
of the opto-magnetic originals.",1912.00129v2
2023-06-20,Giant effective magnetic moments of chiral phonons from orbit-lattice coupling,"Circularly polarized lattice vibrations carry angular momentum and lead to
magnetic responses in applied magnetic fields or when resonantly driven with
ultrashort laser pulses. Recent measurements have found responses that are
orders of magnitude larger than those calculated in prior theoretical studies.
Here, we present a microscopic model for the effective magnetic moments of
chiral phonons in magnetic materials that is able to reproduce the
experimentally measured magnitudes and that allows us to make quantitative
predictions for materials with giant magnetic responses using microscopic
parameters. Our model is based on orbit-lattice couplings that hybridize
optical phonons with orbital electronic transitions. We apply our model to two
types of materials: $4f$ rare-earth halide paramagnets and $3d$
transition-metal oxide magnets. In both cases, we find that chiral phonons can
carry giant effective magnetic moments of the order of a Bohr magneton, orders
of magnitude larger than previous predictions.",2306.11630v1
2011-03-22,Dipolar Interactions between Iron-Oxide Nanoparticles in Frozen Ferrofluids and Ferronematics,"We present a detailed study of the magnetic behavior of iron-oxide
(gamma-Fe2O3 and Fe3O4) nanoparticles constituents of ferrofluids (FF's) with
average particle sizes <d> = 2.5 and 10 nm. The particles were dispersed in the
frozen liquid carrier (pure FF) and in a frozen lyotropic liquid crystalline
matrix in the nematic phase or ferronematic (FN) (ferrolyomesophase). Both FF
and FN phases displayed superparamagnetic (SPM) behaviour at room temperature,
with blocking temperatures T_B ~ 10 and 100 K for <d> = 2.5 and 10 nm,
respectively. Dynamic ac susceptibility measurements showed a thermally
activated N\'eel-Brown dependence of the blocking temperature with applied
frequency. Our results show that dipolar interactions are small, but
non-negligible, as compared to the single-particle energy barriers from
magnetic anisotropy. From the fit of ac susceptibility we calculated the
effective magnetic anisotropy constant K_{eff} for 2.5 nm maghemite particles.
Although interparticle interactions present in highly diluted samples do not
appreciably modify the dynamic magnetic behavior of isolated particles, the
calculated magnetic anisotropy were abut one order of magnitude larger that the
bulk materials, suggesting the existence of large surface anisotropy. Using the
thermally activated model to fit the dynamic data yielded effective energy
barriers Ea = 3.5x10^{-21} J. From these data, we obtained K_{eff} = 422 kJ/m^3
for the single-particle effective magnetic anisotropy.",1103.4403v1
2012-02-13,Nature of magnetic excitations in superconducting BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$,"Since the discovery of the metallic antiferromagnetic (AF) ground state near
superconductivity in iron-pnictide superconductors, a central question has been
whether magnetism in these materials arises from weakly correlated electrons,
as in the case of spin-density-wave in pure chromium, requires strong electron
correlations, or can even be described in terms of localized electrons such as
the AF insulating state of copper oxides. Here we use inelastic neutron
scattering to determine the absolute intensity of the magnetic excitations
throughout the Brillouin zone in electron-doped superconducting
BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ ($T_c=20$ K), which allows us to obtain the size
of the fluctuating magnetic moment $<m^2>$, and its energy distribution. We
find that superconducting BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ and AF BaFe$_2$As$_2$
both have fluctuating magnetic moments $<m^2>\approx3.2\ \mu_B^2$ per Fe(Ni),
which are similar to those found in the AF insulating copper oxides. The common
theme in both classes of high temperature superconductors is that magnetic
excitations have partly localized character, thus showing the importance of
strong correlations for high temperature superconductivity.",1202.2827v1
2013-04-04,Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications,"The performance of magnetic nanoparticles is intimately entwined with their
structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique
way of engineering the magnetic response by modifying the strength of the
dipolar interactions between particles. Here we report on an experimental and
theoretical analysis of magnetic hyperthermia, a rapidly developing technique
in medical research and oncology. Experimentally, we demonstrate that
single-domain cubic iron oxide particles resembling bacterial magnetosomes have
superior magnetic heating efficiency compared to spherical particles of similar
sizes. Monte Carlo simulations at the atomic level corroborate the larger
anisotropy of the cubic particles in comparison with the spherical ones, thus
evidencing the beneficial role of surface anisotropy in the improved heating
power. Moreover we establish a quantitative link between the particle
assembling, the interactions and the heating properties. This knowledge opens
new perspectives for improved hyperthermia, an alternative to conventional
cancer therapies.",1304.1298v1
2014-12-22,Inverse magneto-refraction as a mechanism for laser modification of spin-spin exchange parameters and subsequent terahertz emission from iron oxides,"Ultrafast non-thermal manipulation of magnetization by light relies on either
indirect coupling of the electric field component of the light with spins via
spin-orbit interaction or direct coupling between the magnetic field component
and spins. Here we propose a novel scenario for coupling between the electric
field of light and spins via optical modification of the exchange interaction,
one of the strongest quantum effects, the strength of which can reach 1000
Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be
called the inverse magneto-refraction, is allowed in a material of any
symmetry. Its existence is corroborated by the experimental observation of THz
emission by magnetic-dipole active spin resonances optically excited in a broad
class of iron oxides with a canted spin configuration. From its strength we
estimate that a sub-picosecond laser pulse with a moderate fluence of ~ 1
mJ/cm^2 acts as a pulsed effective magnetic field of 0.01 Tesla, arising from
the optically perturbed balance between the exchange parameters. Our findings
are supported by a low-energy theory for the microscopic magnetic interactions
between non-equilibrium electrons subjected to an optical field which suggests
a possibility to modify the exchange interactions by light over 1 %.",1412.7094v1
2016-03-31,"Theory of multiple--phase competition in pyrochlore magnets with anisotropic exchange, with application to Yb2Ti2O7, Er2Ti2O7 and Er2Sn2O7","The family of magnetic rare-earth pyrochlore oxides R2M2O7 plays host to a
diverse array of exotic phenomena, driven by the interplay between geometrical
frustration and spin-orbit interaction, which leads to anisotropy in both
magnetic moments and their interactions. In this article we establish a
general, symmetry--based theory of pyrochlore magnets with anisotropic exchange
interactions. Starting from a very general model of nearest-neighbour exchange
between Kramers ions, we find four distinct classical ordered states, all with
q=0, competing with a variety of spin-liquids and unconventional forms of
magnetic order. The finite-temperature phase diagram of this model is
determined by Monte Carlo simulation, supported by classical spin-wave
calculations. We pay particular attention to the region of parameter space
relevant to the widely studied materials Er2Ti2O7, Yb2Ti2O7, and Er2Sn2O7. We
find that many of the most interesting properties of these materials can be
traced back to the ""accidental"" degeneracies where phases with different
symmetries meet. These include the ordered ground state selection by
fluctuations in Er2Ti2O7, the dimensional-reduction observed in Yb2Ti2O7, and
the lack of reported magnetic order in Er2Sn2O7. We also discuss the
application of this theory to other pyrochlore oxides.",1603.09466v2
2010-05-07,Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation,"Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose
electronic properties within a localized ion picture are characterized by
non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical
frustration, has been investigated by muon spin rotation/relaxation (muSR)
technique. The A cation (mostly divalent) was varied to examine the effect of
covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg
that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is
associated with a weak structural transition), a nearly commensurate magnetic
order is observed to develop in accordance with the MI transition. Meanwhile,
in the case of A = Cd where the MI transition is suppressed to the level of
small anomaly in the resistivity, the local field distribution probed by muon
indicates emergence of a certain magnetic inhomogeneity below {\guillemotright}
30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly
inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru
moments and thus described as a ""frozen spin liquid"" state. The systematic
trend of increasing randomness and itinerant character with decreasing
covalency suggests close relationship between these two characters. As a
reference for the effect of orbital degeneracy and associated Jahn-Teller
instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+,
4d4), where the result of muSR indicates a non-magnetic ground state that is
consistent with the formation of the Haldane chains suggested by neutron
diffraction experiment.",1005.1133v2
2014-06-28,Disorder in a Quantum Critical Superconductor,"In four classes of materials, the layered copper-oxides, organics,
iron-pnictides and heavy-fermion compounds, an unconventional superconducting
state emerges as a magnetic transition is tuned toward absolute zero
temperature, that is, toward a magnetic quantum-critical point (QCP). In most
materials, the QCP is accessed by chemical substitutions or applied pressure.
CeCoIn5 is one of the few materials that are born as a quantum-critical
superconductor and, therefore, offers the opportunity to explore the
consequences of chemical disorder. Cadmium-doped crystals of CeCoIn5 are a
particularly interesting case where Cd substitution induces long-range magnetic
order, as in Zn-doped copper-oxides. Applied pressure globally supresses the
Cd-induced magnetic order and restores bulk superconductivity. Here we show,
however, that local magnetic correlations, whose spatial extent decreases with
applied pressure, persist at the extrapolated QCP. The residual droplets of
impurity-induced magnetic moments prevent the reappearance of conventional
signatures of quantum criticality, but induce a heterogeneous electronic state.
These discoveries show that spin droplets can be a source of electronic
heterogeneity in classes of strongly correlated electron systems and emphasize
the need for caution when interpreting the effects of tuning a correlated
system by chemical substitution.",1406.7370v1
2015-12-01,Magnetization reversal of an individual exchange biased permalloy nanotube,"We investigate the magnetization reversal mechanism in an individual
permalloy (Py) nanotube (NT) using a hybrid magnetometer consisting of a
nanometer-scale SQUID (nanoSQUID) and a cantilever torque sensor. The Py NT is
affixed to the tip of a Si cantilever and positioned in order to optimally
couple its stray flux into a Nb nanoSQUID. We are thus able to measure both the
NT's volume magnetization by dynamic cantilever magnetometry and its stray flux
using the nanoSQUID. We observe a training effect and temperature dependence in
the magnetic hysteresis, suggesting an exchange bias. We find a low blocking
temperature $T_B = 18 \pm 2$ K, indicating the presence of a thin
antiferromagnetic native oxide, as confirmed by X-ray absorption spectroscopy
on similar samples. Furthermore, we measure changes in the shape of the
magnetic hysteresis as a function of temperature and increased training. These
observations show that the presence of a thin exchange-coupled native oxide
modifies the magnetization reversal process at low temperatures. Complementary
information obtained via cantilever and nanoSQUID magnetometry allows us to
conclude that, in the absence of exchange coupling, this reversal process is
nucleated at the NT's ends and propagates along its length as predicted by
theory.",1512.00199v1
2021-10-13,Nonmonotonic magnetic field dependence of remanent ferroelectric polarization in reduced-graphene-oxide-BiFeO$_3$ nanocomposite,"In a nanocomposite of reduced graphene oxide (RGO) and BiFeO$_3$ (BFO), the
remanent ferroelectric polarization is found to follow nonmonotonic magnetic
field dependence at room temperature as the applied magnetic field is swept
across 0-20 kOe on a pristine sample. The remanent ferroelectric polarization
is determined both from direct electrical measurements on an assembly of
nanoparticles and powder neutron diffraction patterns recorded under 0-20 kOe
field. The nanosized ($\sim$20 nm) particles of BFO are anchored onto the
graphene sheets of RGO via Fe-C bonds with concomitant rise in covalency in the
Fe-O bonds. The field-dependent competition between the positive and negative
magnetoelectric coupling arising from magnetostriction due to, respectively,
interface and bulk magnetization appears to be giving rise to the observed
nonmonotonic field dependence of polarization. The emergence of Fe-C bonds and
consequent change in the magnetic and electronic structure of the interface
region has influenced the coupling between ferroelectric and magnetic
properties remarkably and thus creates a new way of tuning the magnetoelectric
properties via reconstruction of interfaces in nanocomposites or
heterostructures of graphene/single-phase-multiferroic systems.",2110.06519v1
2021-11-20,Exchange coupling in synthetic anion-engineered chromia heterostructures,"Control of magnetic states by external factors has garnered a mainstream
status in spintronic research for designing low power consumption and
fast-response information storage and processing devices. Previously,
magnetic-cation substitution is the conventional means to induce ferromagnetism
in an intrinsic antiferromagnet. Theoretically, the anion-doping is proposed to
be another effect means to change magnetic ground states. Here we demonstrate
the synthesis of high-quality single-phase chromium oxynitride thin films using
in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide
and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and
insulating state, as demonstrated by the combination of multiple magnetization
probes and theoretical calculations. With increasing the nitrogen content, the
crystal structure of chromium oxynitride transits from trigonal (R3c) to
tetragonal (4mm) phase and its saturation magnetization reduces significantly.
Furthermore, we achieve a large and controllable exchange bias field in the
chromia heterostructures by synthetic anion engineering. This work reflects the
anion engineering in functional oxides towards the potential applications in
giant magnetoresistance and tunnelling junctions of modern magnetic sensors and
read heads.",2111.10564v1
2022-07-31,Interface Engineering Enabled Low Temperature Growth of Magnetic Insulator on Topological Insulator,"Combining topological insulators (TIs) and magnetic materials in
heterostructures is crucial for advancing spin-based electronics. Magnetic
insulators (MIs) can be deposited on TIs using the spin-spray process, which is
a unique non-vacuum, low-temperature growth process. TIs have highly reactive
surfaces that oxidize upon exposure to atmosphere, making it challenging to
grow spin-spray ferrites on TIs. In this work, it is demonstrated that a thin
titanium capping layer on TI, followed by oxidation in atmosphere to produce a
thin TiOx interfacial layer, protects the TI surface, without significantly
compromising spin transport from the magnetic material across the TiOx to the
TI surface states. First, it was demonstrated that in Bi2Te3/TiOx/Ni80Fe20
heterostructures that TiOx provided an excellent barrier against diffusion of
magnetic species, yet maintained a large spin-pumping effect. Second, the TiOx
was also used as a protective capping layer on Bi2Te3, followed by the
spin-spray growth of the MI, NixZnyFe2O4 (NZFO). For the thinnest TiOx
barriers, Bi2Te3/TiOx/NZFO samples had AFM disordered interfacial layer because
of diffusion. With increasing TiOx barrier thickness, the diffusion was
reduced, but still maintained strong interfacial spin-pumping interaction.
These experimental results demonstrate a novel method of low-temperature growth
of magnetic insulators on TIs enabled by interface engineering.",2208.00499v1
2013-11-23,Universal Scaling Law to Predict the Efficiency of Magnetic Nanoparticles as MRI T2-Contrast Agents,"Magnetic particles are very efficient Magnetic Resonance Imaging (MRI)
contrast agents. In the recent years, chemists have unleashed their imagination
to design multi-functional nanoprobes for biomedical applications including MRI
contrast enhancement. This study is focused on the direct relationship between
the size and magnetization of the particles and their nuclear magnetic
resonance relaxation properties, which condition their efficiency. Experimental
relaxation results with maghemite particles exhibiting a wide range of sizes
and magnetizations are compared to previously published data and to
well-established relaxation theories with a good agreement. This allows
deriving the experimental master curve of the transverse relaxivity versus
particle size and to predict the MRI contrast efficiency of any type of
magnetic nanoparticles. This prediction only requires the knowledge of the size
of the particles impermeable to water protons and the saturation magnetization
of the corresponding volume. To predict the T2 relaxation efficiency of
magnetic single crystals, the crystal size and magnetization obtained through a
single Langevin fit of a magnetization curve is the only information needed.
For contrast agents made of several magnetic cores assembled into various
geometries (dilute fractal aggregates, dense spherical clusters, core-shell
micelles, hollow vesicles), one needs to know a third parameter, namely the
intra-aggregate volume fraction occupied by the magnetic materials relatively
to the whole (hydrodynamic) sphere. Finally a calculation of the maximum
achievable relaxation effect and the size needed to reach this maximum is
performed for different cases: maghemite single crystals and dense clusters,
core-shell particles (oxide layer around a metallic core) and zinc manganese
ferrite crystals.",1311.6022v1
2022-03-22,Co-loading of doxorubicin and iron oxide nanocubes in polycaprolactone fibers for combining Magneto-Thermal and chemotherapeutic effects on cancer cells,"Among the strategies to fight cancer, multi-therapeutic approaches are
considered as a wise choice to put in place multiple weapons to suppress
tumors. In this work, to combine chemotherapeutic effects to magnetic
hyperthermia when using biocompatible scaffolds, we have established an
electrospinning method to produce nanofibers of polycaprolactone loaded with
magnetic nanoparticles as heat mediators to be selectively activated under
alternating magnetic field and doxorubicin as a chemotherapeutic drug.
Production of the fibers was investigated with iron oxide nanoparticles of
peculiar cubic shape (at 15 and 23 nm in cube edges) as they provide benchmark
heat performance under clinical magnetic hyperthermia conditions. With 23 nm
nanocubes when included into the fibers, an arrangement in chains was obtained.
This linear configuration of magnetic nanoparticles resemble that of the
magnetosomes, produced by magnetotactic bacteria, and our magnetic fibers
exhibited remarkable heating effects as the magnetosomes. Magnetic fiber
scaffolds showed excellent biocompatibility on fibroblast cells when missing
the chemotherapeutic agent and when not exposed to magnetic hyperthermia as
shown by viability assays. On the contrary, the fibers containing both magnetic
nanocubes and doxorubicin showed significant cytotoxic effects on cervical
cancer cells following the exposure to magnetic hyperthermia. Notably, these
tests were conducted at magnetic hyperthermia field conditions of clinical use.
As here shown, on the doxorubicin sensitive cervical cancer cells, the
combination of heat damage by magnetic hyperthermia with enhanced diffusion of
doxorubicin at therapeutic temperature are responsible for a more effective
oncotherapy.",2203.12380v1
2016-07-05,Delayed hepatic uptake of multi-phosphonic acid poly(ethylene glycol) coated iron oxide measured by real-time Magnetic Resonance Imaging,"We report on the synthesis, characterization, stability and pharmacokinetics
of novel iron based contrast agents for magnetic resonance imaging (MRI).
Statistical copolymers combining multiple phosphonic acid groups and
poly(ethylene glycol) (PEG) were synthesized and used as coating agents for 10
nm iron oxide nanocrystals. In vitro, protein corona and stability assays show
that phosphonic acid PEG copolymers outperform all other coating types
examined, including low molecular weight anionic ligands and polymers. In vivo,
the particle pharmacokinetics is investigated by monitoring the MRI signal
intensity from mouse liver, spleen and arteries as a function of the time,
between one minute and seven days after injection. Iron oxide particles coated
with multi-phosphonic acid PEG polymers are shown to have a blood circulation
lifetime of 250 minutes, i.e. 10 to 50 times greater than that of recently
published PEGylated probes and benchmarks. The clearance from the liver takes
in average 2 to 3 days and is independent of the core size, coating and
particle stability. By comparing identical core particles with different
coatings, we are able to determine the optimum conditions for stealth MRI
probes.",1607.01656v1
2008-07-20,"Nearly Isotropic superconductivity in (Ba,K)Fe2As2","Superconductivity was recently observed in the iron-arsenic-based compounds
with a superconducting transition temperature (Tc) as high as 56K [1-7],
naturally raising comparisons with the high Tc copper oxides. The copper oxides
have layered crystal structures with quasi-two-dimensional electronic
properties, which led to speculations that reduced dimensionality (that is,
extreme anisotropy) is a necessary prerequisite for superconductivity at
temperatures above 40 K [8,9]. Early work on the iron-arsenic compounds seemed
to support this view [7,10]. Here we report measurements of the electrical
resistivity in single crystals of (Ba,K)Fe2As2 in a magnetic field up to 60 T.
We find that the superconducting properties are in fact quite isotropic, being
rather independent of the direction of the applied magnetic fields at low
temperature. Such behaviour is strikingly different from all previously-known
layered superconductors [9,11], and indicates that reduced dimensionality in
these compounds is not a prerequisite for high-temperature superconductivity.
We suggest that this situation arises because of the underlying electronic
structure of the iron-arsenide compounds, which appears to be much more three
dimensional than that of the copper oxides. Extrapolations of low-field
single-crystal data incorrectly suggest a high anisotropy and a greatly
exaggerated zero-temperature upper critical field.",0807.3137v4
2018-01-24,Interplay between superconductivity and magnetism in one-unit-cell LaAlO3 capped with SrTiO3,"To form a conducting layer at the interface between the oxide insulators
LaAlO3 and SrTiO3, the LaAlO3 layer on the SrTiO3 substrate must be at least
four unit-cells-thick. The LaAlO3 SrTiO3 heterointerface thus formed exhibits
various intriguing phenomena such as ferromagnetism and superconductivity. It
has been widely studied for being a low-dimensional ferromagnetic oxide
superconducting system with a strong gate-tunable spin-orbit interaction.
However, its lack of stability and environmental susceptiveness have been an
obstacle to its further experimental investigations and applications. Here, we
demonstrate that capping the bilayer with SrTiO3 relieves this thickness limit,
while enhancing the stability and controllability of the interface. In
addition, the SrTiO3-capped LaAlO3 exhibits unconventional superconductivity;
the critical current dramatically increases under a parallel magnetic field,
and shows a reversed hysteresis contrary to the conventional hysteresis of
magnetoresistance. Its superconducting energy gap of $\Delta \sim 1.31k_BT_c$
also deviates from conventional BCS-type superconductivity. The oxide trilayer
could be a robust platform for studying the extraordinary interplay of
superconductivity and ferromagnetism at the interface electron system between
LaAlO3 and SrTiO3.",1801.08022v1
2021-11-23,Elucidating the local atomic and electronic structure of amorphous oxidized superconducting niobium films,"Qubits made from superconducting materials are a mature platform for quantum
information science application such as quantum computing. However,
materials-based losses are now a limiting factor in reaching the coherence
times needed for applications. In particular, knowledge of the atomistic
structure and properties of the circuit materials is needed to identify,
understand, and mitigate materials-based decoherence channels. In this work we
characterize the atomic structure of the native oxide film formed on Nb
resonators by comparing fluctuation electron microscopy experiments to density
functional theory calculations, finding that an amorphous layer consistent with
an Nb$_2$O$_5$ stoichiometry. Comparing X-ray absorption measurements at the
Oxygen K edge with first-principles calculations, we find evidence of d-type
magnetic impurities in our sample, known to cause impedance in proximal
superconductors. This work identifies the structural and chemical composition
of the oxide layer grown on Nb superconductors, and shows that soft X-ray
absorption can fingerprint magnetic impurities in these superconducting
systems.",2111.11590v1
2022-01-11,High-throughput determination of Hubbard U and Hund J values for transition metal oxides via linear response formalism,"DFT+U provides a convenient, cost-effective correction for the
self-interaction error (SIE) that arises when describing correlated electronic
states using conventional approximate density functional theory (DFT). The
success of a DFT+U(+J) calculation hinges on the accurate determination of its
Hubbard U and Hund's J parameters, and the linear response (LR) methodology has
proven to be computationally effective and accurate for calculating these
parameters. This study provides a high-throughput computational analysis of the
U and J values for transition metal d-electron states in a representative set
of over 2000 magnetic transition metal oxides (TMOs), providing a frame of
reference for researchers who use DFT+U to study transition metal oxides. In
order to perform this high-throughput study, an atomate workflow is developed
for calculating U and J values automatically on massively parallel
supercomputing architectures. To demonstrate an application of this workflow,
the spin-canting magnetic structure and unit cell parameters of the
multiferroic olivine LiNiPO4 are calculated using the computed Hubbard U and
Hund J values for Ni-d and O-p states, and are compared with experiment. Both
the Ni-d U and J corrections have a strong effect on the Ni-moment canting
angle. Additionally, including a O-p U value results in a significantly
improved agreement between the computed lattice parameters and experiment.",2201.04213v2
2022-02-22,Multiplet Effects in the Electronic Correlation of One-Dimensional Magnetic Transition-Metal Oxides on Metals,"We use the constrained random phase approximation (cRPA) method to calculate
the Hubbard $U$ parameter in four one-dimensional magnetic transition metal
atom oxides of composition XO$_2$ (X = Mn, Fe, Co, Ni) on Ir(100). In addition
to the expected screening of the oxide, i.e., a significant reduction of the
$U$ value by the presence of the metal substrate, we find a strong dependence
on the electronic configuration (multiplet) of the X($d$) orbital. Each
particular electronic configuration attained by atom X is dictated by the O
ligands, as well as by the charge transfer and hybridization with the Ir(100)
substrate. We find that MnO$_2$ and NiO$_2$ chains exhibit two different
screening regimes, while the case of CoO$_2$ is somewhere in between. The
electronic structure of the MnO$_2$ chain remains almost unchanged upon
adsorption. Therefore, in this regime, the additional screening is
predominantly generated by the electrons of the neighboring metal surface
atoms. The screening strength for NiO$_2$/Ir(100) is found to depend on the
Ni($d$) configuration in the adsorbed state. The case of FeO$_2$ shows an
exceptional behavior, as it is the only insulating system in the absence of
metallic substrate and, thus, it has the largest $U$ value. However, this value
is significantly reduced by the two mentioned screening effects after
adsorption.",2202.10805v1
2011-10-07,Evolution of magnetic properties in the normal spinel solid solution Mg(1-x)Cu(x)Cr2O4,"We examine the evolution of magnetic properties in the normal spinel oxides
Mg(1-x)Cu(x)Cr2O4 using magnetization and heat capacity measurements. The
end-member compounds of the solid solution series have been studied in some
detail because of their very interesting magnetic behavior. MgCr2O4 is a highly
frustrated system that undergoes a first order structural transition at its
antiferromagnetic ordering temperature. CuCr2O4 is tetragonal at room
temperature as a result of Jahn-Teller active tetrahedral Cu^2+ and undergoes a
magnetic transition at 135 K. Substitution of magnetic cations for diamagnetic
Mg^2+ on the tetrahedral A site in the compositional series Mg(1-x)Cu(x)Cr2O4
dramatically affects magnetic behavior. In the composition range 0 < x < 0.3,
the compounds are antiferromagnetic. A sharp peak observed at 12.5K in the heat
capacity of MgCr2O4 corresponding to a magnetically driven first order
structural transition is suppressed even for small x suggesting glassy
disorder. Uncompensated magnetism - with open magnetization loops - develops
for samples in the x range 0.43 < x < 1. Multiple magnetic ordering
temperatures and large coercive fields emerge in the intermediate composition
range 0.43 < x < 0.47. The Neel temperature increases with increasing x across
the series while the value of the Curie-Weiss Theta decreases. A magnetic
temperature-composition phase diagram of the solid solution series is
presented.",1110.1662v1
2016-01-19,Collective magnetic response of CeO2 nanoparticles,"The magnetism of nanoparticles and thin films of wide-bandgap oxides that
include no magnetic cations is an unsolved puzzle. Progress has been hampered
both by the irreproducibility of much of the experimental data, and the lack of
any generally-accepted theoretical explanation. The characteristic signature is
a virtually anhysteretic, temperature-independent magnetization curve which
saturates in an applied field that is several orders of magnitude greater than
the magnetization. It appears as if a tiny volume fraction, < 0.1%, of the
samples is magnetic and that the energy scale of the problem is unusually high
for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2
nanoparticles with powders of gamma-Al2O3, sugar or latex microspheres. The
saturation magnetization, Ms ~ 60 A/m for compact samples, is maximized by 1
wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic
moment by up to an order of magnitude. There is a characteristic length scale
of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The
phenomenon is explained in terms of a giant orbital paramagnetism that appears
in coherent mesoscopic domains due to resonant interaction with zero-point
fluctuations of the vacuum electromagnetic field. The theory explains the
observed temperature-independent magnetization curve and its doping and
dispersion dependence, based on a length scale of 300 nm that corresponds to
the wavelength of a maximum in the UV absorption spectrum of the magnetic CeO2
nanoparticles. The coherent domains occupy roughly ten percent of the sample
volume.",1601.04933v1
2016-12-19,Evidence of room temperature magnetoelectric properties in α-Fe1.6Ga0.4O3 oxide by magnetic field controlled electric properties and electric field controlled magnetism,"We have stabilized the {\alpha}-Fe1.6Ga0.4O3 (Ga doped {\alpha}-Fe2O3) system
in rhombohedral structure. The system has shown magnetically canted
ferromagnetic state and ferroelectric properties at room temperature. In first
time, we confirm the existence of magneto-electric coupling and
multiferro-electric properties at room temperature in the Ga doped
{\alpha}-Fe2O3 system based on the experimental observation of magnetic field
controlled electric polarization and electric field controlled magnetization.
The {\alpha}-Fe2O3 system does not exhibit electric field controlled magnetic
exchange bias effect, where as Ga doped {\alpha}-Fe2O3 showed exchange bias
shift up to the value of 370 Oe. We have recorded the response of
current-voltage characteristics and in-field magnetic relaxation of the system
under the simultaneous application of magnetic and electric fields. The
magnetization of the system is found highly sensitive to the ON and OFF modes,
as well as change of the polarity of external electric field. The system is a
new addition in the list of non-traditional
magneto-electrics/multi-ferroelectrics so far reported in literature. Such
novel materials, where magnetization and electric polarization can be
controlled by simultaneous application of magnetic and electric fields, is in
the increasing demand for potential applications in the field of next
generation magnetic sensor, switching, non-volatile memory and spintronic
devices.",1612.06049v1
2019-07-12,New method for characterization of magnetic nanoparticles by scanning magnetic microscopy,"In this paper, we present a new method for the magnetic characterization of
bulk materials, microstructures, and nanostructures. We investigated the
magnetic and morphological properties of two colloidal dispersions of iron
oxide (Fe3O4) magnetic nanoparticles (MNPs), synthesized by chemical
precipitation (co-precipitation) and pulsed laser ablation (PLA) in liquid, by
scanning magnetic microscopy (SMM) applied to a small sample with mass on the
order of tens of {\mu}g. We evaluated the performance of this technique by
comparing magnetization curves and measurements obtained with commercial
magnetometers, considered standard. The errors obtained for the saturation and
remanent magnetization were approximately 0.18 Am2/kg and 0.6 Am2/kg,
respectively. The average size distribution of the NPs estimated from the
magnetization curve measurements is consistent with the results obtained by
traditional transmission electron microscopy (TEM). The technique can be
extended to measure and analyze magnetization curves (hysteresis loops), thus
enabling an even more accurate estimation of overall NP sizes.",1907.05908v1
2023-09-28,On-Command Disassembly of Microrobotic Superstructures for Transport and Delivery of Magnetic Micromachines,"Magnetic microrobots have been developed for navigating microscale
environments by means of remote magnetic fields. However, limited propulsion
speeds at small scales remain an issue in the maneuverability of these devices
as magnetic force and torque are proportional to their magnetic volume. Here,
we propose a microrobotic superstructure, which, as analogous to a
supramolecular system, consists of two or more microrobotic units that are
interconnected and organized through a physical (transient) component (a
polymeric frame or a thread). Our superstructures consist of microfabricated
magnetic helical micromachines interlocked by a magnetic gelatin nanocomposite
containing iron oxide nanoparticles (IONPs). While the microhelices enable the
motion of the superstructure, the IONPs serve as heating transducers for
dissolving the gelatin chassis via magnetic hyperthermia. In a practical
demonstration, we showcase the superstructure's motion with a gradient magnetic
field in a large channel, the disassembly of the superstructure and release of
the helical micromachines by a high-frequency alternating magnetic field, and
the corkscrew locomotion of the released helices through a small channel via a
rotating magnetic field. This adaptable microrobotic superstructure reacts to
different magnetic inputs, which could be used to perform complex delivery
procedures within intricate regions of the human body.",2310.04433v1
2006-06-20,"Terrestrial planetary dynamics: a view from U, Th geochemistry","The migration of U and Th inside a planet is controlled by its oxidation
state imposed by the volatile composition. In the deep interior of a planet, an
absence of oxidative volatiles will cause U and Th to stay in a state of metal
or low valance compounds with a big density. Consequently, they migrate to the
bottom of its mantle first, and then are gradually sequestered to its liquid
metal core. Earth is rich in oxidative volatiles including water, therefore, U
and Th in the core can be moved up by an internal circulation system consisting
of the outer core, hot super plumes, asthenosphere and subduction zone (or cold
super plumes). This internal circulation system is the key for the formation of
plate tectonics, the geodynamo and the consequent geomagnetic field. Moreover,
plentiful oxidative volatiles and water within Earth is the precondition to
form such a circulation system. In the early stage (> 4 Ga), Mars developed an
Earth-like internal circulation system due to relatively large amount of
oxidative volatile compositions coming from its building material. This would
have produced a dynamo and correspondingly an Earth-like magnetic field.
However, this internal circulation system was destroyed by one or several giant
impact events in the early stage, which drove off these volatile compositions.
These events also shaped the striking hemispheric dichotomy structure on the
Martian surface. The other result is that its dynamo and geomagnetic field have
also disappeared. Since then, Mars has been the same as Mercury and Venus in
that the heat release from the U and Th in their cores can not be moved by an
internal circulation system gently, but by sporadically catastrophic
resurfacing events (Venus), or super plumes (Mars) or gradual heat conduction
(Mercury).",0606468v4
2014-12-19,Contact-induced charge contributions to non-local spin transport measurements in Co/MgO/graphene devices,"Recently, it has been shown that oxide barriers in graphene-based non-local
spin-valve structures can be the bottleneck for spin transport. The barriers
may cause spin dephasing during or right after electrical spin injection which
limit spin transport parameters such as the spin lifetime of the whole device.
An important task is to evaluate the quality of the oxide barriers of both spin
injection and detection contacts in a fabricated device. To address this issue,
we discuss the influence of spatially inhomogeneous oxide barriers and
especially conducting pinholes within the barrier on the background signal in
non-local measurements of graphene/MgO/Co spin-valve devices. By both
simulations and reference measurements on devices with non-ferromagnetic
electrodes, we demonstrate that the background signal can be caused by
inhomogeneous current flow through the oxide barriers. As a main result, we
demonstrate the existence of charge accumulation next to the actual spin
accumulation signal in non-local voltage measurements, which can be explained
by a redistribution of charge carriers by a perpendicular magnetic field
similar to the classical Hall effect. Furthermore, we present systematic
studies on the phase of the low frequency non-local ac voltage signal which is
measured in non-local spin measurements when applying ac lock-in techniques.
This phase has so far widely been neglected in the analysis of non-local spin
transport. We demonstrate that this phase is another hallmark of the
homogeneity of the MgO spin injection and detection barriers. We link backgate
dependent changes of the phase to the interplay between the capacitance of the
oxide barrier to the quantum capacitance of graphene.",1412.6224v1
2018-02-02,Energetics of oxygen-octahedra rotations in perovskite oxides from first principles,"We use first-principles methods to study oxygen-octahedra rotations in ABO3
perovskite oxides. We focus on the short-period, perfectly antiphase or
in-phase, tilt patterns that characterize most compounds and control their
physical (e.g., conductive, magnetic) properties. Based on an analytical form
of the relevant potential energy surface, we discuss the conditions for the
stability of polymorphs presenting different tilt patterns, and obtain
numerical results for a collection of thirty-five representative materials. Our
results reveal the mechanisms responsible for the frequent occurrence of a
particular structure that combines antiphase and in-phase rotations, i.e., the
orthorhombic Pbnm phase displayed by about half of all perovskite oxides and by
many non-oxidic perovskites. The Pbnm phase benefits from the simultaneous
occurrence of antiphase and in-phase tilt patterns that compete with each
other, but not as strongly as to be mutually exclusive. We also find that
secondary antipolar modes, involving the A cations, contribute to weaken the
competition between different tilts and play a key role in their coexistence.
Our results thus confirm and better explain previous observations for
particular compounds. Interestingly, we also find that strain effects, which
are known to be a major factor governing phase competition in related (e.g.,
ferroelectric) perovskite oxides, play no essential role as regards the
relative stability of different rotational polymorphs. Further, we discuss why
the Pbnm structure stops being the ground state in two opposite limits, for
large and small A cations, showing that very different effects become relevant
in each case. Our work thus provides a comprehensive discussion on these
all-important and abundant materials, which will be useful to better understand
existing compounds as well as to identify new strategies for materials
engineering.",1802.00784v1
2020-09-28,Control of skyrmion chirality in Ta/FeCoB/TaOx trilayers by TaOx oxidation and FeCoB thickness,"Skyrmions are magnetic bubbles with nontrivial topology envisioned as data
bits for ultrafast and power-efficient spintronic memory and logic devices.
They may be stabilized in heavy-metal/ferromagnetic/oxide trilayer systems. The
skyrmion chirality is then determined by the sign of the interfacial
Dzyaloshinskii-Moriya interaction (DMI). Nevertheless, for apparently identical
systems, there is some controversy about the DMI sign. Here, we show that the
degree of oxidation of the top interface and the thickness of the ferromagnetic
layer play a major role. Using Brillouin light-scattering measurements in
Ta/Fe-Co-B/TaOx trilayers, we demonstrate a sign change of the DMI with the
degree of oxidation of the Fe-Co-B/TaOx interface. Using polar magneto-optical
Kerr effect microscopy, we consistently observe a reversal of the direction of
current-induced motion of skyrmions with the oxidation level of TaOx; this is
attributed to their chirality reversal. In addition, a second chirality
reversal is observed when changing the Fe-Co-B thickness, probably due to the
proximity of the two Fe-Co-B interfaces in the ultrathin case. By properly
tuning the chirality of the skyrmion, spin-transfer and spin-orbit torques
combine constructively to enhance the skyrmion velocity. These observations
thus allow us to envision an optimization of the material parameters to produce
highly mobile skyrmions. Moreover, this chirality control enables a versatile
manipulation of skyrmions and paves the way towards multidirectional devices.",2009.13136v3
2021-10-16,Generalized estimates for thermal expansion of oxide scale in the range from 0C to 1300C with account for movability of phase transitions in its components,"The thermophysical properties of oxide scale, in the general case, are
affected by the variation of the temperature of phase transitions (either
magnetic or polymorphic) in its components due to impurities, lattice defects,
grain sizes, etc. In this case, since the phase transition is usually
accompanied by a sharp change in properties, even a small shift of such a
critical temperature can lead to large changes in properties in its vicinity.
In order to account for this effect, data known from various sources on the
true coefficient of linear thermal expansion (CLTE) of w\""ustite , magnetite ,
hematite , and metallic iron are generalized by approximating functions that
include critical temperatures as variable parameters. It is shown that the true
CLTE of magnetite at the same rated temperature can differ by up to 30%
depending on the position of the Curie point within the limits of its possible
""movability"". The proposed methods allow to take into account the critical
temperatures as adaptation parameters in engineering calculations of thermal
expansion of oxide scale. Generalized formulas for each scale component are
also given in a particular form for fixed (basic) values of critical
temperatures. The dependence of the true CLTE of oxide scale as a whole
({\alpha}sc) on the volume fraction of each component is proposed. It is shown
by model computations that there are temperatures at which {\alpha}sc is almost
independent of the scale composition, as well as areas of instability, where
{\alpha}sc depends significantly on the percentage of components. The results
of the work are recommended to be used when mathematical modeling of production
and processing of steel products in the presence of oxide scale on their
surface.",2110.08528v1
2023-09-22,Ultrathin Magnesium-based Coating as an Efficient Oxygen Barrier for Superconducting Circuit Materials,"Scaling up superconducting quantum circuits based on transmon qubits
necessitates substantial enhancements in qubit coherence time. Among the
materials considered for transmon qubits, tantalum (Ta) has emerged as a
promising candidate, surpassing conventional counterparts in terms of coherence
time. However, the presence of an amorphous surface Ta oxide layer introduces
dielectric loss, ultimately placing a limit on the coherence time. In this
study, we present a novel approach for suppressing the formation of tantalum
oxide using an ultrathin magnesium (Mg) capping layer deposited on top of
tantalum. Synchrotron-based X-ray photoelectron spectroscopy (XPS) studies
demonstrate that oxide is confined to an extremely thin region directly beneath
the Mg/Ta interface. Additionally, we demonstrate that the superconducting
properties of thin Ta films are improved following the Mg capping, exhibiting
sharper and higher-temperature transitions to superconductive and magnetically
ordered states. Based on the experimental data and computational modeling, we
establish an atomic-scale mechanistic understanding of the role of the capping
layer in protecting Ta from oxidation. This work provides valuable insights
into the formation mechanism and functionality of surface tantalum oxide, as
well as a new materials design principle with the potential to reduce
dielectric loss in superconducting quantum materials. Ultimately, our findings
pave the way for the realization of large-scale, high-performance quantum
computing systems.",2309.12603v2
2020-10-16,Sudden collapse of magnetic order in oxygen deficient nickelate films,"Oxygen vacancies play a crucial role in the control of the electronic,
magnetic, ionic, and transport properties of functional oxide perovskites. Rare
earth nickelates (RENiO$_{3-x}$) have emerged over the years as a rich platform
to study the interplay between the lattice, the electronic structure, and
ordered magnetism. In this study, we investigate the evolution of the
electronic and magnetic structure in thin films of RENiO$_{3-x}$, using a
combination of X-ray absorption spectroscopy and imaging, resonant X-ray
scattering, and extended multiplet ligand field theory modeling. We find that
oxygen vacancies modify the electronic configuration within the Ni-O orbital
manifolds, leading to a dramatic evolution of long-range electronic transport
pathways despite the absence of nanoscale phase separation. Remarkably,
magnetism is robust to substantial levels of carrier doping, and only a
moderate weakening of the $(1/4, 1/4, 1/4)_{pc}$ antiferromagnetic order
parameter is observed, whereas the magnetic transition temperature is largely
unchanged. Only at a certain point long-range magnetism is abruptly erased
without an accompanying structural transition. We propose the progressive
disruption of the 3D magnetic superexchange pathways upon introduction of point
defects as the mechanism behind the sudden collapse of magnetic order in
oxygen-deficient nickelates. Our work demonstrates that, unlike most other
oxides, ordered magnetism in RENiO$_{3-x}$ is mostly insensitive to carrier
doping. The sudden collapse of ordered magnetism upon oxygen removal may
provide a new mechanism for solid-state magneto-ionic switching and new
applications in antiferromagnetic spintronics.",2010.08545v1
2006-02-28,Magnetic field dependence of the magnetic phase separation in Pr1-xCaxMnO3 manganites studied by small-angle neutron scattering,"Transport properties of manganese oxides suggest that their colossal
magnetoresistance (CMR) is due to percolation between ferromagnetic metallic
(FM) clusters in an antiferromagnetic insulating (AFI) matrix. We have studied
small-angle neutron scattering under applied magnetic field in CMR Pr1-xCaxMnO3
crystals for x around 0.33. Quantitative analysis of the small-angle magnetic
neutron scattering shows that the magnetic heterogeneities take place at
different scales. At the mesoscopic scale (200nm), the inhomogeneities
correspond to the percolation of the conducting ferromagnetic phase into the
insulating phases. It is at the origin of the colossal magnetoresistance of the
compound. The other inhomogeneities are nanoscopic: inside the
antiferromagnetic phase (AFI), there exist small ferromagnetic clusters. Inside
the ferromagnetic phase which exists in absence of magnetic field in some
compounds and is in fact insulating (FI), there also exist small non
ferromagnetic objects. No evolution of this nanostructure is observed when the
magnetic field is applied. The existence of such nanoscale objects is discussed
in relation to the cationic disorder of these compounds.",0602668v1
2006-08-14,Nitrogen based magnetic semiconductors,"We describe a possible pathway to new magnetic materials with no conventional
magnetic elements present. The substitution of Nitrogen for Oxygen in simple
non magnetic oxides leads to holes in N 2$p$ states which form local magnetic
moments. Because of the very large Hund's rule coupling of Nitrogen and O 2$p$
electrons and the rather extended spatial extend of the wave functions these
materials are predicted to be ferromagnetic metals or small band gap
insulators. Experimental studies support the theoretical calculations with
regard to the basic electronic structure and the formation of local magnetic
moments. It remains to be seen if these materials are magnetically ordered and
if so below what temperature.",0608313v1
2006-11-19,Magnetic coupling in CoCr_2O_4 and MnCr_2O_4: an LSDA+U study,"We present a first principles LSDA+U study of the magnetic coupling constants
in the spinel magnets CoCr_2O_4 and MnCr_2O_4. Our calculated coupling
constants highlight the possible importance of AA interactions in spinel
systems with magnetic ions on both A and B sites. Furthermore, we show that a
careful analysis of the dependence of the magnetic coupling constants on the
LSDA+U parameters provides valuable insights in the underlying coupling
mechanisms, and allows to obtain a quantitative estimate of the magnetic
coupling constants. We discuss in detail the capabilities and possible pitfalls
of the LSDA+U method in determining magnetic coupling constants in complex
transition metal oxides.",0611502v3
2008-01-31,Impurity-Ion pair induced high-temperature ferromagnetism in Co-doped ZnO,"Magnetic 3d-ions doped into wide-gap oxides show signatures of room
temperature ferromagnetism, although their concentration is two orders of
magnitude smaller than that in conventional magnets. The prototype of these
exceptional materials is Co-doped ZnO, for which an explanation of the room
temperature ferromagnetism is still elusive. Here we demonstrate that magnetism
originates from Co2+ oxygen-vacancy pairs with a partially filled level close
to the ZnO conduction band minimum. The magnetic interaction between these
pairs is sufficiently long-ranged to cause percolation at moderate
concentrations. However, magnetically correlated clusters large enough to show
hysteresis at room temperature already form below the percolation threshold and
explain the current experimental findings. Our work demonstrates that the
magnetism in ZnO:Co is entirely governed by intrinsic defects and a phase
diagram is presented. This suggests a recipe for tailoring the magnetic
properties of spintronics materials by controlling their intrinsic defects.",0801.4945v1
2010-03-12,Magnetic interaction of Co ions near the {10\bar{1}0} ZnO surface,"Co-doped ZnO is the prototypical dilute magnetic oxide showing many of the
characteristics of ferromagnetism. The microscopic origin of the long range
order however remains elusive, since the conventional mechanisms for the
magnetic interaction, such as super-exchange and double exchange, fail either
at the fundamental or at a quantitative level. Intriguingly, there is a growing
evidence that defects both in point-like or extended form play a fundamental
role in driving the magnetic order. Here we explore one of such possibilities
by performing {\it ab initio} density functional theory calculations for the
magnetic interaction of Co ions at or near a ZnO \{10$\bar{1}$0\} surface. We
find that extended surface states can hybridize with the $e$-levels of Co and
efficiently mediate the magnetic order, although such a mechanism is effective
only for ions placed in the first few atomic planes near the surface. We also
find that the magnetic anisotropy changes at the surface from an hard-axis
easy-plane to an easy axis, with an associated increase of its magnitude. We
then conclude that clusters with high densities of surfacial Co ions may
display blocking temperatures much higher than in the bulk.",1003.2576v1
2010-04-13,Incommensurate magnetic order and dynamics induced by spinless impurities in YBa$_2$Cu$_3$O$_{6.6}$,"We report an inelastic-neutron-scattering and muon-spin-relaxation study of
the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of
YBa$_2$Cu$_3$O$_{6.6}$, an underdoped high-temperature superconductor that
exhibits a prominent spin-pseudogap in its normal state. Zn substitution
induces static magnetic order at low temperatures and triggers a large-scale
spectral-weight redistribution from the magnetic resonant mode at 38 meV into
uniaxial, incommensurate spin excitations with energies well below the
spin-pseudogap. These observations indicate a competition between
incommensurate magnetic order and superconductivity close to a quantum critical
point. Comparison to prior data on La$_{2-x}$Sr$_x$CuO$_{4}$ suggests that this
behavior is universal for the layered copper oxides and analogous to
impurity-induced magnetic order in one-dimensional quantum magnets.",1004.2139v1
2011-04-29,New type of incommensurate magnetic ordering in Mn3TeO6,"The complex metal oxide Mn3TeO6 exhibits a corundum related structure and has
been prepared both in forms of single crystals by chemical transport reactions
and of polycrystalline powders by a solid state reaction route. The crystal
structure and magnetic properties have been investigated using a combination of
X-ray and neutron powder diffraction, electron microscopy, calorimetric and
magnetic measurements. At room temperature this compound adopts a trigonal
structure, space group R3 with a = 8.8679(1) {\AA}, c = 10.6727(2) {\AA}. A
long-range magnetically ordered state is identified below 23 K. An unexpected
feature of this magnetic structure is several types of Mn-chains. Under the
action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)]
the unique Mn site is split into two magnetically different orbits. One orbit
forms a perfect helix with the spiral axis along the c-axis while the other
orbit has a sine wave character along the c-axis.",1104.5560v1
2011-05-23,Novel Magnetic Phases Revealed by Ultra-High Magnetic Field in the Frustrated Magnet ZnCr2O4,"The Faraday rotation technique is used to map out the finite-temperature
phase diagram of the prototypical frustrated magnet ZnCr2O4, in magnetic fields
of up to 190 T generated by the single-turn coil method. We find evidence for a
number of magnetic phase transitions, which are well-described by the theory
based on spin-lattice coupling. In addition to the 1/2 plateau and a 3:1 canted
phase, a 2:1:1 canted phase is found for the first time in chromium spinel
oxides, which has been predicted by a theory of Penc et al. to realize in a
small spin-lattice coupling limit. Both the new 2:1:1 and the 3:1 phase are
regarded as the supersolid phases according to a magnetic analogy of Matsuda
and Tsuneto, and Liu and Fisher.",1105.4412v1
2011-05-26,Magneto-structural transitions in a frustrated magnet at high fields,"Ultrasound and magnetization studies of bond-frustrated ZnCr2S4 spinel are
performed in static magnetic fields up to 18 T and in pulsed fields up to 62 T.
At temperatures below the antiferromagnetic transition at T_N1 14 K the sound
velocity as function of magnetic field reveals a sequence of steps followed by
plateaus indicating a succession of crystallographic structures with constant
stiffness. At the same time, the magnetization evolves continuously with field
up to full magnetic polarization without any plateaus in contrast to
geometrically frustrated chromium oxide spinels. The observed high-field
magneto-structural states are discussed within a H-T phase diagram taking into
account the field and temperature evolution of three coexisting spin structures
and subsequent lattice transformations induced by magnetic field.",1105.5220v1
2014-07-02,Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface,"Depth-sensitive magnetic, structural and chemical characterization is
important in the understanding and optimization of novel physical phenomena
emerging at interfaces of transition metal oxide heterostructures. In a
simultaneous approach we have used polarized neutron and resonant X-ray
reflectometry to determine the magnetic profile across atomically sharp
interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers
with sub-nanometer resolution. In particular, the X-ray resonant magnetic
reflectivity measurements at the Fe and Mn resonance edges allowed us to
determine the element specific depth profile of the ferromagnetic moments in
both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a
magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in
contrast to previous observations on inversely deposited layers. Additional
resonant X-ray reflection measurements indicate a region of an altered Mn- and
O-content at the interface, with a thickness matching that of the magnetic
diluted layer, as origin of the reduction of the magnetic moment.",1407.0737v1
2015-02-05,Domain structure and perpendicular magnetic anisotropy in CoFe/Pd multilayers using off-axis electron holography,"Multilayers of Co90Fe10/Pd with different bilayer thicknesses, have been
deposited by dc-magnetron sputtering on thermally oxidized Si wafers.
Transmission electron microscopy showed that the highly textured crystalline
films had columnar structure, while scanning transmission electron microscopy
and atomic force microscopy respectively indicated some layer waviness and
surface roughness. The magnetic domain structure and perpendicular magnetic
anisotropy (PMA) of the Co90Fe10/Pd multilayers were investigated by off-axis
electron holography and magnetic force microscopy. The Co90Fe10 layer thickness
was the primary factor determining the magnetic domain size and the
perpendicular magnetization: both decreased as the thickness increased. The
strongest PMA was observed in the sample with the thinnest magnetic layer of
0.45 nm.",1502.01422v1
2015-02-19,Plentiful magnetic moments in oxygen deficient SrTiO3,"Correlated band theory is employed to investigate the magnetic and electronic
properties of different arrangements of oxygen di- and tri-vacancy clusters in
SrTiO$_3$. Hole and electron doping of oxygen deficient SrTiO$_3$ yields
various degrees of magnetization as a result of the interaction between
localized magnetic moments at the defected sites. Different kinds of Ti atomic
orbital hybridization are described as a function of the doping level and
defect geometry. We find that magnetism in SrTiO$_{3-\delta}$ is sensitive to
the arrangement of neighbouring vacancy sites, charge carrier density, and
vacancy-vacancy interaction. Permanent magnetic moments in the absence of
vacancy doping electrons are observed. Our description of the charged clusters
of oxygen vacancies widens the previous descriptions of mono and
multi-vacancies and points out the importance of the controled formation at the
atomic level of defects for the realization of transition metal oxide based
devices with a desirable magnetic performance.",1502.05749v1
2015-05-27,Microscopic analysis of the magnetic form factor in low-dimensional cuprates,"We analyze the magnetic form factor of Cu$^{2+}$ in low-dimensional quantum
magnets by taking the metal-ligand hybridization into account explicitly. In
this analysis we use the form of magnetic Wannier orbitals, derived from the
first-principles calculations, and identify the contributions of different
atomic sites. Having performed local density approximation calculations for
cuprates with different types of ligand atoms, we discuss the influence of the
on-site Coulomb correlations on the structure of the magnetic orbital. The
typical composition of Wannier functions for copper oxides, chlorides and
bromides is defined and related to features of the magnetic form factor. We
propose easy-to-use approximations of the partial orbital contributions to the
magnetic form factor in order to give a microscopic explanation for the results
obtained in previous first-principles studies.",1505.07288v1
2015-09-17,Dynamics of magnetic single domain particles embedded in a viscous liquid,"Kinetic equations for magnetic nano particles dispersed in a viscous liquid
are developed and analyzed numerically. Depending on the amplitude of an
applied oscillatory magnetic field the particles orient their time averaged
anisotropy axis perpendicular to the applied field for low magnetic field
amplitudes and nearly parallel to the direction of the field for high
amplitudes. The transition between these regions takes place in a narrow field
interval. In the low field region the magnetic moment is locked to some crystal
axis and the energy absorption in an oscillatory driving field is dominated by
viscous losses associated with particle rotation in the liquid. In the opposite
limit the magnetic moment rotates within the particle while its easy axis being
nearly parallel to the external field direction oscillates. The kinetic
equations are generalized to include thermal fluctuations. This leads to a
significant increase of the power absorption in the low and intermediate field
region with a pronounced absorption peak as function of particle size. In the
high field region, on the other hand, the inclusion of thermal fluctuations
reduces the power absorption. The illustrative numerical calculations presented
are performed for magnetic parameters typical for iron oxide.",1509.05233v1
2017-02-28,Magnetic ground state of SrRuO$_3$ thin film and applicability of standard first-principles approximations to metallic magnetism,"A systematic first-principles study has been performed to understand the
magnetism of thin film SrRuO$_3$ which lots of research efforts have been
devoted to but no clear consensus has been reached about its ground state
properties. The relative t$_{2g}$ level difference, lattice distortion as well
as the layer thickness play together in determining the spin order. In
particular, it is important to understand the difference between two standard
approximations, namely LDA and GGA, in describing this metallic magnetism.
Landau free energy analysis and the magnetization-energy-ratio plot clearly
show the different tendency of favoring the magnetic moment formation, and it
is magnified when applied to the thin film limit where the experimental
information is severely limited. As a result, LDA gives a qualitatively
different prediction from GGA in the experimentally relevant region of strain
whereas both approximations give reasonable results for the bulk phase. We
discuss the origin of this difference and the applicability of standard methods
to the correlated oxide and the metallic magnetic systems.",1702.08647v2
2017-03-06,Magnetically induced Ferroelectricity in Bi$_2$CuO$_4$,"The tetragonal copper oxide Bi$_2$CuO$_4$ has an unusual crystal structure
with a three-dimensional network of well separated CuO$_4$ plaquettes. This
material was recently predicted to host electronic excitations with an
unconventional spectrum and the spin structure of its magnetically ordered
state appearing at T$_N$ $\sim$43 K remains controversial. Here we present the
results of detailed studies of specific heat, magnetic and dielectric
properties of Bi$_2$CuO$_4$ single crystals grown by the floating zone
technique, combined with the polarized neutron scattering and high-resolution
X-ray measurements. Our polarized neutron scattering data show Cu spins are
parallel to the $ab$ plane. Below the onset of the long range antiferromagnetic
ordering we observe an electric polarization induced by an applied magnetic
field, which indicates inversion symmetry breaking by the ordered state of Cu
spins. For the magnetic field applied perpendicular to the tetragonal axis, the
spin-induced ferroelectricity is explained in terms of the linear
magnetoelectric effect that occurs in a metastable magnetic state. A relatively
small electric polarization induced by the field parallel to the tetragonal
axis may indicate a more complex magnetic ordering in Bi$_2$CuO$_4$.",1703.02069v1
2018-02-27,Low lying magnetic states of the mixed valence cobalt ludwigite,"There are two interpretations offered for the different structural and
magnetic properties of the mixed valence homo-metallic ludwigites, Co3O2BO3 and
Fe3O2BO3. One of them associates the physical behavior to charge ordering
processes among the cations, as is well known in simpler oxides. The other
attributes the effects to local pairwise magnetic interactions. Recently first
principles calculations in the iron ludwigite have shown that the structural
cation dimerization is due to the formation of strong magnetic dyads supporting
the second model. Here we confirm the dominance of magnetic interactions to
explain the absence of dimerization in the cobalt compound. Density functional
non-collinear spin calculations are carried out on Co3O2BO3 to determine its
low temperature magnetic order. Low spin is found on tri-valent cobalt sites,
thus preventing the formation of the ferromagnetic dyad, the mechanism which
favors dimerization in Fe3O2BO3. We conclude that the difference between high
spin Fe3+ and low spin Co3+ pairwise interactions is responsible for the
observed differences between the two compounds. The pairwise magnetic
interactions also explain the difference between the existence of low
temperature bulk AF state in the Fe ludwigite and its absence in the Co
material.",1802.10063v2
2018-11-12,Site selective spin and orbital excitations in Fe3O4,"$Fe_3O_4$ is a mixed-valence strongly correlated transition metal oxide which
displays the intriguing metal to insulator Verwey transition. Here we
investigate the electronic and magnetic structure of $Fe_3O_4$ by a unique
combination of high-resolution Fe 2p3d resonant inelastic scattering magnetic
circular (RIXS-MCD) and magnetic linear (RIXS-MLD) dichroism. We show that by
coupling the site selectivity of RIXS with the magnetic selectivity imposed by
the incident polarization handedness, we can unambiguously identify spin-flip
excitations and quantify the exchange interaction of the different sublattices.
Furthermore, our RIXS-MLD measurements show spin-orbital excitations that
exhibit strong polarization and magnetic field dependence. Guided by
theoretical simulations, we reveal that the angular dependence arises from a
strong interplay between trigonal crystal-field, magnetic exchange and
spin-orbit interaction at the nominal $Fe^{2+}$ sites. Our results highlight
the capabilities of RIXS magnetic dichroism studies to investigate the ground
state of complex systems where in-equivalent sites and bonds are simultaneously
present.",1811.04836v1
2019-05-07,Modulation of magnetism via electric field in MgO nanoribbons,"We report on a theoretical study of electromagnetic properties of zigzag
magnesium oxides nanoribbons (Z-MgONRs). We propose that the polar charges and
the spin polarization are the two key factors for edge magnetism. Based on
first-principle calculations, we demonstrate that both O- and Mg-edges are
magnetic and their magnetic moments all can be efficiently modulated via
external electric field.And the edge magnetism is further studied in the
framework of effective tight-binding model, which provides a starting point for
the calculation of one particle Green's function and the determination of
exchange interactions. Utilizing the linear response model, we find that
Z-MgONRs exhibit two kinds of exchange interaction with extremely different
natures. The magnetism in O-edge is strongly localized with ferromagnetic order
while the magnetism in Mg-edge is itinerant with Ruderman-Kittel-Kasuya-Yosida
(RKKY) like interactions. And these two couplings can also be modulated by
electric field, giving rise to the electrical modulations of spin-density-wave
(SDW) and the modulation of Curie temperature in O-edge. All these suggest that
Z-MgONRs are ideal platforms for ME coupling and appealing candidates for
manifold applications.",1905.02328v1
2017-04-24,Interface magnetism and electronic structure: ZnO(0001)/Co3O4(111),"We have studied the structural, electronic and magnetic properties of spinel
$\rm Co_3O_4$(111) surfaces and their interfaces with ZnO (0001) using density
functional theory (DFT) within the Generalized Gradient Approximation with
on-site Coulomb repulsion term (GGA+U). Two possible forms of spinel surface,
containing $\rm Co^{2+} $ and $\rm Co^{3+} $ ions and terminated with either
cobalt or oxygen ions were considered, as well as their interface with zinc
oxide. Our calculations demonstrate that $\rm Co^{3+} $ ions attain non-zero
magnetic moments at the surface and interface, in contrast to the bulk, where
they are not magnetic, leading to the ferromagnetic ordering. Since heavily
Co-doped ZnO samples can contain $\rm Co_3O_4 $ secondary phase, such a
magnetic ordering at the interface might explain the origin of the magnetism in
these diluted magnetic semiconductors (DMS).",1704.07148v4
2017-04-26,Magnetic Force Microscopy for Nanoparticle Characterization,"Since the invention of the atomic force microscope (AFM) in 1986, there has
been a drive to apply this scanning probe technique or a form of this technique
to various disciplines in nanoscale science. Magnetic force microscopy (MFM) is
a member of a growing family of scanning probe methods and has been widely used
for the study of magnetic materials. In MFM a magnetic probe is used to
raster-scan the surface of the sample, of which its magnetic field interacts
with the magnetic tip to offer insight into its magnetic properties. This
review will focus on the use of MFM in relation to nanoparticle
characterization, including superparamagnetic iron oxide nanoparticles,
covering MFM imaging in air and in liquid environments.",1704.08289v1
2015-12-01,Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping,"Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component.",1512.00286v1
2015-12-08,Development of magnetic liquid metal suspensions for magnetohydrodynamics,"A new class of materials is developed that is a liquid with both high
conductivity and magnetic susceptibility for magnetohydrodynamic (MHD)
applications. We develop a general method for making such suspensions and
demonstrate that various magnetic and non-magnetic metal particles, from 40 nm
- 500 microns in diameter, can be suspended in liquid gallium and its alloys.
The method uses an acid solution to prevent oxidation of the liquid metal and
metallic particles, which allows wetting and thus suspending. We can increase
the magnetic permeability by a factor of 5.0 by controlling the packing
fraction of magnetic particles, which gives these materials the potential to
exhibit strong MHD effects on the laboratory scale that are usually only
observable in the cores of planets and stars. We can independently tune the
viscosity by a factor of 230 by adding non-magnetic particles, which would
allow independent control of MHD effects from turbulence.",1512.02575v4
2020-01-07,Growth-sequence-dependent interface magnetism of SrIrO$_3$ - La$_{0.7}$Sr$_{0.3}$MnO$_3$ bilayers,"Bilayers of the oxide 3d ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) and
the 5d paramagnet SrIrO$_{3}$ (SIO) with large spin-orbit coupling (SOC) have
been investigated regarding the impact of interfacial SOC on magnetic order.
For the growth sequence of LSMO on SIO, ferromagnetism is strongly altered and
large out-of-plane-canted anisotropy associated with lacking magnetic
saturation up to 4 T has been observed. Thin bilayer films have been grown
coherently in both growth sequences on SrTiO$_3$ (001) by pulsed laser
deposition and structurally characterized by scanning transmission electron
microscopy (STEM) and x-ray diffraction (XRD). Measurements of magnetization
and field-dependent Mn L$_{2,3}$ edge x-ray magnetic circular dichroism (XMCD)
reveal changes of LSMO magnetic order which are strong in LSMO on SIO and weak
in LSMO underneath of SIO. We attribute the impact of the growth sequence to
the interfacial lattice structure/symmetry which is known to influence the
interfacial magnetic coupling.",2001.02083v1
2017-09-25,"The structural, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure","The magnetic transition-metal (TM) @ oxide nanoparticles have been of great
interest due to their wide range of applications, from medical sensors in
magnetic resonance imaging to photo-catalysis. Although several studies on
small clusters of TM@oxide have been reported, the understanding of the
physical electronic properties of TMn@(ZnO)42 is far from sufficient. In this
work, the electronic, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe,
Co and Ni) hetero-nanostructure are investigated using the density functional
theory (DFT). It has been found that the core-shell nanostructure Fe13@(ZnO)42,
Co15@(ZnO)42 and Ni15@(ZnO)42 are the most stable structures. Moreover, it is
also predicted that the variation of the magnetic moment and magnetism of Fe,
Co and Ni in TMn@ZnO42 hetero-nanostructure mainly stems from effective
hybridization between core TM-3d orbitals and shell O-2p orbitals, and a
magnetic moment inversion for Fe15@(ZnO)42 is investigated. Finally, optical
properties studied by calculations show a red shift phenomenon in the
absorption spectrum compared with the case of (ZnO)48.",1709.08502v1
2019-04-18,Suppression of long range magnetic ordering and electrical conduction in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$ thin film,"We find that the long-range magnetic ordering is absent and electrical
conduction suppressed in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$/YSZ(100) thin film
prepared by pulsed laser deposition. The sharp down-turn of inverse magnetic
susceptibility X-1(T) from the conventional Curie-Weiss behaviour below T* ~
168K suggests an inhomogeneous ferromagnetic Griffiths like phase. The
transport and magnetic properties are explained on the basis of the coexistence
of mixed oxidation states of Ir, (i.e. Ir4+ and Ir3+) leading to non-magnetic
defects and reduction in t2g density of states at the Fermi level.",1904.08615v1
2020-10-14,Interface-driven magnetic anisotropy in relaxed La$_{0.7}$Sr$_{0.3}$CrO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructures on MgO,"We investigate the structural and magnetic properties of
La$_{0.7}$Sr$_{0.3}$CrO$_3$ (LSCO)/La$_{0.7}$Sr$_{0.3}$MnO$_3$(LSMO)
heterostructures grown on (001)-oriented MgO by molecular beam epitaxy. Due to
the large film-substrate lattice mismatch, strain relaxation is found to occur
within the first 2-3 unit cells (uc) of the film as evidenced by reflection
high energy electron diffraction and high-resolution synchrotron X-ray
reciprocal space mapping. We find that the presence of the LSCO spacer and
capping layers leads to ferromagnetism in ultra-thin LSMO layers with
thicknesses on the order of 2 uc with the magnetic easy axis oriented in the
film plane. Net magnetic moments of 1.4 and 2.4 $\mu_B$/Mn are measured for [2
uc LSCO/ 2 uc LSMO] and [2 uc LSCO/ 4 uc LSMO] superlattices, respectively by
SQUID magnetometry. The effective magnetic anisotropy of the relaxed [2 uc
LSCO/ 4 uc LSMO] heterostructure is found to be an order of magnitude higher
than bulk LSMO highlighting the critical role of interfacial magnetic exchange
interactions in tuning magnetic anisotropy at complex oxide interfaces.",2010.07180v1
2021-05-25,Dynamics of particles with cubic magnetic anisotropy in a viscous liquid,"The specific absorption rate (SAR) of a dilute assembly of spherical iron
nanoparticles with cubic anisotropy distributed in a viscous liquid is
calculated using the solution of stochastic Landau - Lifshitz equation for unit
magnetization vector and stochastic equations for multiple particle directors
that specify the spatial orientation of the nanoparticle in a liquid. The
viscous and magnetic magnetization reversal modes of particles are revealed at
low and sufficiently high amplitudes of alternating magnetic field,
respectively. The SAR of iron nanoparticle assembly is shown to exceed
significantly that of iron oxide nanoparticles with uniaxial anisotropy at the
same amplitudes and frequencies of applied magnetic field. The linear response
theory is shown to be valid only at small magnetic field amplitudes, H0 < 50 -
70 Oe.",2105.11916v1
2021-07-21,Radical pairs can explain magnetic field and lithium effects on the circadian clock,"Drosophila's circadian clock can be perturbed by magnetic fields, as well as
by lithium administration. Cryptochromes are critical for the circadian clock.
Further, the radical pairs in cryptochrome also can explain magnetoreception in
animals. Based on a simple radical pair mechanism model of the animal magnetic
compass, we show that both magnetic fields and lithium can influence the spin
dynamics of the naturally occurring radical pairs and hence modulate the
circadian clock's rhythms. Using a simple chemical oscillator model for the
circadian clock, we show that the spin dynamics influence a rate in the
chemical oscillator model, which translates into a change in the circadian
period. Our model can reproduce the results of two independent experiments,
magnetic fields and lithium effects on the circadian clock. Our model predicts
that stronger magnetic fields would shorten the clock's period. We also predict
that lithium influences the clock in an isotope-dependent manner. Furthermore,
our model also predicts that magnetic fields and hyperfine interactions
modulate oxidative stress. The findings of this work suggest that quantum
nature and entanglement of radical pairs might play roles in the brain, as
another piece of evidence in addition to recent results on xenon anesthesia and
lithium effects on hyperactivity.",2107.10677v1
2021-08-14,Voltage-controlled magnetism enabled by resistive switching,"The discovery of new mechanisms of controlling magnetic properties by
electric fields or currents furthers the fundamental understanding of magnetism
and has important implications for practical use. Here, we present a novel
approach of utilizing resistive switching to control magnetic anisotropy. We
study a ferromagnetic oxide that exhibits an electrically triggered
metal-to-insulator phase transition producing a volatile resistive switching.
This switching occurs in a characteristic spatial pattern: the formation of a
transverse insulating barrier inside a metallic matrix resulting in an unusual
ferromagnetic/paramagnetic/ferromagnetic configuration. We found that the
formation of this voltage-driven paramagnetic insulating barrier is accompanied
by the emergence of a strong uniaxial magnetic anisotropy that overpowers the
intrinsic material anisotropy. Our results demonstrate that resistive switching
is an effective tool for manipulating magnetic properties. Because resistive
switching can be induced in a very broad range of materials, our findings could
enable a new class of voltage-controlled magnetism systems.",2108.06445v1
2021-09-16,Oxygen vacancy-induced anomalous Hall effect in a nominally non-magnetic oxide,"The anomalous Hall effect, a hallmark of broken time-reversal symmetry and
spin-orbit coupling, is frequently observed in magnetically polarized systems.
Its realization in non-magnetic systems, however, remains elusive. Here, we
report on the observation of anomalous Hall effect in nominally non-magnetic
KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to
intrinsic crossover. A paramagnetic behavior is observed in reduced samples
using first principles calculations and quantitative magnetometry. The observed
anomalous Hall effect follows the oxygen vacancy-induced magnetization
response, suggesting that the localized magnetic moments of the oxygen
vacancies scatter conduction electrons asymmetrically and give rise to
anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to
scattering rate in the low temperature limit (T<5 K), implying that the Berry
curvature of the electrons on the Fermi surface controls the anomalous Hall
effect. Our observations describe a detailed picture of many-body interactions,
triggering anomalous Hall effect in a non-magnetic system.",2109.08073v2
2022-05-10,"Structural, electronic and magnetic properties of La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$ double perovskite","In this work, we report the synthesis and investigation of structural,
electronic, and magnetic properties of
La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$. Our polycrystalline sample
forms as a single-phase double perovskite in monoclinic $P2_{1}/n$ space group.
Co and Ir are most likely in bivalent and tetravalent oxidation states,
respectively, while Mossbauer spectroscopy indicates that Fe is in a trivalent
state. The ac and dc magnetization data suggest a ferrimagnetic behavior
resulting from the presence of two antiferromagnetic sublattices at Co/Fe and
Ir sites. The large coercive field H_C $\simeq$ 32 kOe observed at 10 K,
comparable to that of other double perovskites of interest for hard magnets, is
discussed in terms of the structural distortion and the spin and orbital
magnetic moments of the transition metal ions.",2205.04778v1
2022-06-30,Strain engineering of the magnetic anisotropy and magnetic moment in NdFeO3 epitaxial thin films,"Strain engineering is a powerful mean for tuning the various functionalities
of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials
such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic
properties as well as their technological potential applications especially as
thin films. Here, using a large set of complementary and advanced techniques,
we show that NFO epitaxial thin films, successfully grown by pulsed laser
deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical
thickness tc of 54 nm, associated with the occurrence of structural
modifications related to symmetry and domain pattern changes. By varying the
tensile misfit strain through the decrease of film thickness below tc, the
amplitudes of in and out-of-plane magnetization can be continuously tuned while
their ratio stays constant. Furthermore, different low-temperature magnetic
behaviors are evidenced for strained and relaxed films, suggesting that the
strain-induced structural state impacts the magnetic phase stability.",2206.15071v1
2023-03-29,Magnetic Anisotropy and Its Structural Origins in Ru-Substituted Manganite Films,"Controlling magnetic anisotropy (MA) is important in a variety of
applications including magnetic memories, spintronic sensors, and
skyrmion-based data distribution. The perovskite manganite family provides a
fertile playground for complex, intricate, and potentially useful
structure-magnetism relations. Here we report on the MA that emerges in 10% Ru
substituted $La_{0.7}Sr_{0.3}MnO_{3}$ (Ru-LSMO) films for which strong
perpendicular magnetization and anisotropic in-plane magnetization are found.
These moderately compressively strained films possess a rich microstructure,
consisting of coherently strained phase which evolves into a one dimensional
(1D) periodically-modulated structure above a critical thickness. We illustrate
how 10% Ru substitution plays a crucial role behind the observed MA, and how
the structural distortion and 1D periodic structural modulation produce the
anisotropic in-plane magnetization. We highlight the practical significance of
the observed MA, which could pave the way towards the realization of
cutting-edge oxide-based room temperature spintronic memory devices.",2303.17008v2
2023-04-27,"Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO$_4$","Geometrically frustrated structures combined with competing exchange
interactions that have different magnitudes are known ingredients for achieving
exotic properties. Herein, we studied detailed structural, magnetic, thermal
(specific heat), magneto-dielectric, and magnetic exchange bias properties of a
mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed
magnetization, heat capacity, and neutron powder diffraction studies (NPD)
highlight long-range ferrimagnetic ordering with an onset at 355 K. The
magnetic structure is established using a ferrimagnetic model (collinear-type)
that has a propagation vector k = 0, 0, 0. The magneto-dielectric effect
appears below the magnetic ordering temperature, and the exchange bias (EB)
effect is observed in field cooled (FC) conditions below 355 K. The
magneto-dielectric coupling in CoFeRhO$_4$ originates due to the frustration in
the structure, collinear ferrimagnetic ordering, and uncompensated magnetic
moments. The unidirectional anisotropy resulting from the uncompensated
magnetic moments causes the room-temperature exchange bias effect. Remarkably,
the appearance of technologically important properties (ferromagnetism,
magnetodielectric effect, and EB) at room temperature in CoFeRhO$_4$ indicates
its potential use in sensors or spintronics.",2304.13983v1
2023-09-12,Probing spatial variation of magnetic order in strained SrMnO$_3$ thin films using Spin Hall Magnetoresistance,"SrMnO$_{3}$ (SMO) is a magnetic insulator and predicted to exhibit a
multiferroic phase upon straining. Strained films of SMO display a wide range
of magnetic orders, ranging from G-type to C-and A-type, indicative of
competing magnetic interactions. The potential of spin Hall magnetoresistance
(SMR) is exploited as an electrical probe for detecting surface magnetic order,
to read surface magnetic moments in SMO and its spatial variation, by designing
and positioning electrodes of different sizes on the film. The findings
demonstrate antiferromagnetic domains with different magnetocrystalline
anisotropies along with a ferromagnetic order, where the magnetization arises
from double exchange mediated ferromagnetic order and canted antiferromagnetic
moments. Further, from a complete analysis of the SMR, a predominance of
antiferromagnetic domain sizes of 3.5 $\mu$m$^2$ is extracted. This work
enhances the applicability of SMR in unraveling the richness of correlation
effects in complex oxides, as manifested by the detection of coexisting and
competing ground states and lays the foundation for the study of magnon
transport for different magnetoelectric based computing applications.",2309.06279v1
2023-10-02,Adiabatic demagnetization refrigeration to mK temperatures with the distorted square lattice magnet NaYbGeO$_{4}$,"We report the synthesis, characterization, low-temperature magnetic, and
thermodynamic measurements of the novel milli-Kelvin adiabatic demagnetization
refrigeration (mK-ADR) candidate material NaYbGeO$_4$ which exhibits a
distorted square lattice arrangement of YbO$_{6}$ magnetic units. Magnetization
and specific heat indicate weakly interacting effective spin-1/2 moments below
10~K, with a Curie-Weiss temperature of only 15~mK, that can be polarized by
magnetic fields of order 1~T. For the ADR performance test, we start the
demagnetization from 5~T at a temperature of $\sim 2$~K and reach a minimum
temperature of 150~mK at zero field. The warming curve indicates a sharp
magnetic transition in the heat capacity at 210~mK, implying only weak magnetic
frustration. The entropy density of $S_{\rm GS}\simeq 101$ mJ K$
^{-1}$cm$^{-3}$ and hold time below 2~K of 220~min are competitive while the
minimal temperature is higher compared to frustrated Ytterbium-oxide ADR
materials studied under similar conditions.",2310.00961v1
2023-12-17,Magnetic Fluctuations in Niobium Pentoxide,"Using a spin-polarized muon beam we were able to capture magnetic dynamics in
an amorphous niobium pentoxide thin film. Muons are used to probe internal
magnetic fields produced by defects. Magnetic fluctuations could be described
by the dynamical Kubo-Toyabe model considering a time-dependent local magnetic
field. We state that observed fluctuations result from the correlated motion of
electron spins. We expect that oxygen vacancies play a significant role in
these films and lead to a complex magnetic field distribution which is
non-stationary. The characteristic average rate of magnetic field change is on
the order of 100~MHz. The observed dynamics may provide insight into potential
noise sources in Nb-based superconducting devices, while also highlighting the
limitations imposed by amorphous oxides.",2312.10697v1
2024-03-01,Cooperatively Modulating Magnetic Anisotropy and Colossal Magnetoresistance via Atomic-Scale Buffer Layers in Highly Strained La0.7Sr0.3MnO3 Films,"Simultaneous control of magnetic anisotropy and magnetoresistance, especially
with atomic scale precision, remains a pivotal challenge for realizing advanced
spintronic functionalities. Here we demonstrate cooperative continuous control
over both magnetoresistance and magnetic anisotropy in highly strained
La0.7Sr0.3MnO3 (LSMO) thin films. By inserting varying perovskite buffer
layers, compressively strained LSMO films transition from a ferromagnetic
insulator with out-of-plane magnetic anisotropy to a metallic state with
in-plane anisotropy. Atomic-scale buffer layer insertion enables remarkably
acute, precise control to sharply modulate this magnetic phase transformation.
A gigantic 10,000% modulation of the colossal magnetoresistance (CMR) and an
exceptionally sharp transition from out-of-plane to in-plane magnetic
anisotropy are attained in just a few contiguous layers. These atomic-scale
correlations among electronic, magnetic, and structural order parameters yield
flexible multifunctional control promising for next-generation oxide
spintronics.",2403.00361v1
1998-12-01,"Synthesis, Characterization and Magnetic Susceptibility of the Heavy Fermion Transition Metal Oxide LiV_{2}O_{4}","The preparative method, characterization and magnetic susceptibility \chi
measurements versus temperature T of the heavy fermion transition metal oxide
LiV_{2}O_{4} are reported in detail. The intrinsic \chi(T) shows a nearly
T-independent behavior below ~ 30 K with a shallow broad maximum at about 16 K,
whereas Curie-Weiss-like behavior is observed above 50-100 K. Field-cooled and
zero-field-cooled magnetization M measurements in applied magnetic fields H =
10 to 100 G from 1.8 to 50 K showed no evidence for spin-glass ordering.
Crystalline electric field theory for an assumed cubic V point group symmetry
is found insufficient to describe the observed temperature variation of the
effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not
describe the magnitude and T dependence of \chi with realistic parameters. In
the high T range, fits of \chi(T) by the predictions of high temperature series
expansion calculations provide estimates of the V-V antiferromagnetic exchange
coupling constant J/k_{B} ~ 20 K, g-factor g ~ 2 and the T-independent
susceptibility. Other possible models to describe the \chi(T) are discussed.
The paramagnetic impurities in the samples were characterized using isothermal
M(H) measurements with 0 < H <= 5.5 Tesla at 2 to 6 K. These impurities are
inferred to have spin S_{imp} ~ 3/2 to 4, g_{imp} ~ 2 and molar concentrations
of 0.01 to 0.8 %, depending on the sample.",9812020v1
2006-01-17,Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights,"The temperature dependence and anisotropy of optical spectral weights
associated with different multiplet transitions is determined by the spin and
orbital correlations. To provide a systematic basis to exploit this close
relationship between magnetism and optical spectra, we present and analyze the
spin-orbital superexchange models for a series of representative
orbital-degenerate transition metal oxides with different multiplet structure.
For each case we derive the magnetic exchange constants, which determine the
spin wave dispersions, as well as the partial optical sum rules. The magnetic
and optical properties of early transition metal oxides with degenerate
$t_{2g}$ orbitals (titanates and vanadates with perovskite structure) are shown
to depend only on two parameters, viz. the superexchange energy $J$ and the
ratio $\eta$ of Hund's exchange to the intraorbital Coulomb interaction, and on
the actual orbital state. In $e_g$ systems important corrections follow from
charge transfer excitations, and we show that KCuF$_3$ can be classified as a
charge transfer insulator, while LaMnO$_3$ is a Mott insulator with moderate
charge transfer contributions. In some cases orbital fluctuations are quenched
and decoupling of spin and orbital degrees of freedom with static orbital order
gives satisfactory results for the optical weights. On the example of cubic
vanadates we describe a case where the full quantum spin-orbital physics must
be considered. Thus information on optical excitations, their energies,
temperature dependence and anisotropy, combined with the results of magnetic
neutron scattering experiments, provides an important consistency test of the
spin-orbital models, and indicates whether orbital and/or spin fluctuations are
important in a given compound.",0601381v1
2010-09-03,Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2Co_{1-x}Rh_xO_{3-δ},"We report measurements and analysis of magnetization, resistivity and
thermopower of polycrystalline samples of the perovskite-type Co/Rh oxide
La$_{0.8}$Sr$_{0.2}$Co$_{1-x}$Rh$_x$O$_{3-\delta}$. This system constitutes a
solid solution for a full range of $x$,in which the crystal structure changes
from rhombohedral to orthorhombic symmetry with increasing Rh content $x$. The
magnetization data reveal that the magnetic ground state immediately changes
upon Rh substitution from ferromagnetic to paramagnetic with increasing $x$
near 0.25, which is close to the structural phase boundary. We find that one
substituted Rh ion diminishes the saturation moment by 9 $\mu_B$, which implies
that one Rh$^{3+}$ ion makes a few magnetic Co$^{3+}$ ions nonmagnetic (the low
spin state), and causes disorder in the spin state and the highest occupied
orbital. In this disordered composition ($0.05\le x \le 0.75$), we find that
the thermopower is anomalously enhanced below 50 K. In particular, the
thermopower of $x$=0.5 is larger by a factor of 10 than those of $x$=0 and 1,
and the temperature coefficient reaches 4 $\mu$V/K$^2$ which is as large as
that of heavy-fermion materials such as CeRu$_2$Si$_2$.",1009.0728v2
2010-11-23,Quantum fluctuations in the effective pseudospin-1/2 model for magnetic pyrochlore oxides,"The effective quantum pseudospin-1/2 model for interacting rare-earth
magnetic moments, which are locally described with atomic doublets, is studied
theoretically for magnetic pyrochlore oxides. It is derived microscopically for
localized Pr^{3+} 4f moments in Pr_2TM_2O_7 (TM = Zr, Sn, Hf, and Ir) by
starting from the atomic non-Kramers magnetic doublets and performing the
strong-coupling perturbation expansion of the virtual electron transfer between
the Pr 4f and O 2p electrons. The most generic form of the nearest-neighbor
anisotropic superexchange pseudospin-1/2 Hamiltonian is also constructed from
the symmetry properties, which is applicable to Kramers ions Nd^{3+}, Sm^{3+},
and Yb^{3+} potentially showing large quantum effects. The effective model is
then studied by means of a classical mean-field theory and the exact
diagonalization on a single tetrahedron and on a 16-site cluster. These
calculations reveal appreciable quantum fluctuations leading to quantum phase
transitions to a quadrupolar state as a melting of spin ice for the Pr^{3+}
case. The model also shows a formation of cooperative quadrupole moment and
pseudospin chirality on tetrahedrons. A sign of a singlet quantum spin ice is
also found in a finite region in the space of coupling constants. The relevance
to the experiments is discussed.",1011.4981v2
2012-12-07,Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol-Gel method,"Bulk monolithic samples of {\gamma}-Fe2O3/SiO2 composites with different iron
oxide/silica ratios have been prepared by the sol-gel technique. Iron oxide
nanoparticles are obtained in-situ during heat treatment of samples and silica
matrix consolidation. Preparation method was previously optimized to minimize
the percentage of antiferromagnetic {\alpha}-Fe2O3 and parallelepipeds of
roughly 2x5x12 mm3, with good mechanical stability, are obtained. RT
magnetization curves show a non-hysteretic behavior. Thus, magnetization
measurements have been well fitted to an expression that combines the Langevin
equation with an additional linear term, indicating that some of the
nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and
electron microscopy measurements. Zero field cooled /field cooled experiments
show curves with slightly different shapes, depending on the size and shape
distribution of nanoparticles for a given composition. Magneto-optical Faraday
effect measurements show that the Faraday rotation is proportional to
magnetization of the samples, as expected. As a demonstration of their sensing
possibilities, the relative intensity of polarized light, measured at 5{\deg}
from the extinction angle, was plotted versus applied magnetic field.",1212.1690v1
2012-12-20,The Mott State and Superconductivity in Face-Centred Cubic Structured Cs3C60: A 133Cs-Nuclear Magnetic Resonance Study under Pressure,"Over the past 20 years, fullerides have been studied as the source of
high-transition-temperature (Tc) superconductivity except for copper oxides.
The recent finding of the Mott insulating state right beside superconductivity
in Cs3C60 has suggested that magnetism helps raise Tc even in fullerides as in
heavy-fermion compounds, high-Tc copper oxides, two-dimensional organic
conductors, and iron pnictides. Namely, one tends to think that the link
between Mott insulator and superconductivity takes place in fullerides, which
can give rise to the mechanism beyond the Bardeen-Cooper-Schrieffer framework.
However, the relationship between the Mott state and the superconductivity in
Cs3C60 is still under debate. By nuclear magnetic resonance measurements under
pressure, we find that the magnetism and superconductivity in Cs3C60 are
competing orders. Different from previous reports, the phase separation of
Cs3C60 crystals into the Mott and metallic states allows us to systematically
study the evolution of the ground state under pressure. Our careful experiments
have found that the prevention of a magnetic order is rather essential for the
superconductivity in face-centred cubic Cs3C60, which presents a basic strategy
for finding still higher Tc in this system.",1212.4937v1
2013-06-21,Evidence for Intra-Unit-Cell magnetic order in the pseudo-gap state of high-Tc cuprates,"The existence of the mysterious pseudo-gap state in the phase diagram of
copper oxide superconductors and its interplay with unconventional {\it d-wave}
superconductivity has been a long standing issue for more than a decade. There
is now a growing number of experimental indications that the pseudo-gap phase
actually corresponds to a symmetry breaking state. In his theory for cuprates,
C. M. Varma proposes that the pseudo-gap is a new state of matter associated
with the spontaneous appearance of circulating current loops within $\rm CuO_2$
unit cell. This intra-unit-cell order breaks time reversal symmetry, but
preserves lattice translation invariance. Polarized elastic neutron scattering
measurements provide evidence for an intra-unit-cell magnetic order inside the
pseudo-gap state. This order could be produced by the orbital-like magnetic
moments induced by the circulating current loops. The magnetic order displays
the same characteristic features in $\rm HgBa_2CuO_{4+\delta}$, $\rm
YBa_2Cu_3O_{6+x}$ and $\rm Bi_2Sr_2CaCu_2O_{8+\delta}$ demonstrating that this
genuine phase is ubiquitous of the pseudo-gap of high temperature copper oxide
materials. We review the main properties characterizing this intra-unit-cell
magnetic order and discuss its interplay or competition with other spin and
charge instabilities.",1306.5124v1
2015-05-04,Spatially resolved ultrafast magnetic dynamics launched at a complex-oxide hetero-interface,"Static strain in complex oxide heterostructures has been extensively used to
engineer electronic and magnetic properties at equilibrium. In the same spirit,
deformations of the crystal lattice with light may be used to achieve
functional control across hetero-interfaces dynamically. Here, by exciting
large amplitude infrared-active vibrations in a LaAlO3 substrate we induce
magnetic order melting in a NdNiO3 film across a hetero-interface. Femtosecond
Resonant Soft X-ray Diffraction is used to determine the spatial and temporal
evolution of the magnetic disordering. We observe a magnetic melt front that
grows from the substrate interface into the film, at a speed that suggests
electronically driven propagation. Light control and ultrafast phase front
propagation at hetero-interfaces may lead to new opportunities in
optomagnetism, for example by driving domain wall motion to transport
information across suitably designed devices.",1505.00601v1
2015-05-29,Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties of BaFeO$_{3-δ},"We studied structural, electronic and magnetic properties of a cubic
perovskite BaFeO$_{3-\delta}$ ($0 \le \delta \le 0.5$) within the density
functional theory using a generalized gradient approximation and a GGA+U
method. According to our calculations, BaFeO$_3$ in its stoichiometric cubic
structure should be half-metallic and strongly ferromagnetic, with extremely
high Curie temperature ($T_C$) of 700 - 900 K. However, a such estimate of
$T_C$ disagrees with all available experiments, which report that $T_C$ of the
BaFeO$_3$ and undoped BaFeO$_{3-\delta}$ films varies between 111 K and 235 K
or, alternatively, that no ferromagnetic order was detected there. Fitting the
calculated x-ray magnetic circular dichroism spectra to the experimental
features seen for BaFeO$_3$, we concluded that the presence of oxygen vacancies
in our model enables a good agreement. Thus, the relatively low $T_C$ measured
in BaFeO$_3$ can be explained by oxygen vacancies intrinsically presented in
the material. Since iron species near the O vacancy change their oxidation
state from $4+$ to $3+$, the interaction between Fe$^{4+}$ and Fe$^{3+}$, which
is antiferromagnetic, weakens the effective magnetic interaction in the system,
which is predominantly ferromagnetic. With increasing $\delta$ in
BaFeO$_{3-\delta}$, its $T_C$ decreases down to the critical value when the
magnetic order becomes antiferromagnetic. Our calculations of the electronic
structure of BaFeO$_{3-\delta}$ illustrate how the ferromagnetism originates
and also how one can keep this cubic perovskite robustly ferromagnetic far
above the room temperature.",1505.07942v1
2019-05-24,Contrasting magnetism in isovalent layered LaSr3NiRuO4H4 and LaSrNiRuO4 due to distinct spin-orbital states,"The recently synthesized first 4d transition-metal oxide-hydride
LaSr3NiRuO4H4 with the unusual high H:O ratio surprisingly displays no magnetic
order down to 1.8 K. This is in sharp contrast to the similar unusual
low-valent Ni+ - Ru2+ layered oxide LaSrNiRuO4 which has a rather high
ferromagnetic (FM) ordering Curie temperature TC about 250 K. In this work,
using density functional calculations with aid of crystal field level diagrams
and superexchange pictures, we find that the contrasting magnetism is due to
the distinct spin-orbital states of the Ru2+ ions (in addition to the common
Ni+ S=1/2 state but with a different orbital state): the Ru2+ S=0 state in
LaSr3NiRuO4H4, but the Ru2+ S=1 state in LaSrNiRuO4. The Ru2+ S=0 state has the
(xy)2(xz; yz)4 occupation due to the RuH4O2 octahedral coordination, and then
the nonmagnetic Ru2+ ions dilute the S=1/2 Ni+ sublattice which consequently
has a very weak antiferromagnetic (AF) superexchange and thus accounts for no
presence of magnetic order down to 1.8 K in LaSr3NiRuO4H4. In strong contrast,
the Ru2+ S=1 state in LaSrNiRuO4 has the (3z2-r2)2(xz; yz)3(xy)1 occupation due
to the planar square RuO4 coordination, and then the multi-orbital FM
superexchange between the S=1/2 Ni+ and S=1 Ru2+ ions gives rise to the high TC
in LaSrNiRuO4. This work highlights the importance of spin-orbital states in
determining the distinct magnetism.",1905.10055v1
2017-07-12,Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces,"Complex oxide systems have attracted considerable attention because of their
fascinating properties, including the magnetic ordering at the conducting
interface between two band insulators, such as LaAlO3 (LAO) and SrTiO3 (STO).
However, the manipulation of the spin degree of freedom at the LAO/STO
heterointerface has remained elusive. Here, we have fabricated hybrid magnetic
tunnel junctions consisting of Co and LAO/STO ferromagnets with the insertion
of a Ti layer in between, which clearly exhibit magnetic switching and the
tunnelling magnetoresistance (TMR) effect below 10 K. The magnitude and the of
the TMR are strongly dependent on the direction of the rotational magnetic
field parallel to the LAO/STO plane, which is attributed to a strong
Rashba-type spin orbit coupling in the LAO/STO heterostructure. Our study
provides a further support for the existence of the macroscopic ferromagnetism
at LAO/STO heterointerfaces and opens a novel route to realize interfacial
spintronics devices.",1707.03509v1
2019-06-28,Mapping different skyrmion phases in double wedges of Ta/FeCoB(tFeCoB)/Ta(tTa)Ox,"Skyrmions are chiral magnetic textures that have immense potential for
applications in spintronic devices. However, their formation is quite
challenging and necessitates a subtle balance of the magnetic interactions at
play. Here, we study Ta/FeCoB/TaOx trilayer using crossed double wedges i.e.
thickness gradients of FeCoB and of top Ta, which is subsequently oxidized
leading to an oxidation gradient. This enabled us to observe micron-sized
skyrmions in the vicinity of different transition regions of the sample: from
perpendicular magnetic anisotropy to paramagnetic phase and also from
perpendicular to in-plane magnetic anisotropy. These observations can be
explained by the isolated bubble model taking into account the different energy
contributions at play namely anisotropy, exchange, Dzyaloshinskii-Moriya,
dipolar and Zeeman. We also qualitatively compare the current-induced motion of
skyrmions obtained in different transition regions. Our study not only provides
an effective means to form skyrmions by tuning the interfacial magnetic
properties but also highlights the differences pertaining to the skyrmions
observed in different transition zones, which is extremely crucial for any
envisaged application.",1906.12271v2
2020-01-09,"Tuning of structural phase, magnetic spin order and electrical conductivity in mechanical alloyed material of alpha-Fe2O3 and alpha-Cr2O3 oxides","Alpha-Fe2O3 and alpha-Cr2O3 has been mechanical alloyed to prepare Fe1-xCrxO3
oxides for x = 0.2-0.8. Synchrotron X-ray diffraction and Raman spectra have
shown inhomogeneous structure of {\alpha}-Fe2O3 and {\alpha}-Cr2O3 phases in
as-alloyed samples. The as-alloyed samples have shown soft ferromagnetic
properties with signature of two Morin transitions. The heat treatment of
as-alloyed samples has homogenized structure and successfully incorporated the
Cr atoms into the lattice sites of Fe atoms in {\alpha}-Fe2O3. The magnetic and
electrical properties have been modified in the heat treated samples. For
example, canted antiferromagnetic order has been appeared as an effect of heat
treatment, irrespective of the Cr content in Fe1-xCrxO3. The magnetic field
induced spin flop transition has been observed at a critical magnetic field
that depends on Cr content in the system. The M\""ossbauer spectrum at room
temperature has been fitted with two sextets. The variation of M\""ossbauer
parameters suggest a distribution of magnetic spin order between Fe and Cr ions
in the rhombohedral structure of Fe1-xCrxO3. The electrical conductivity,
derived from current-voltage characteristics of the heat treated samples, has
been enhanced by increasing Cr content in alpha-Fe2O3 structure. The
experimental results have been explained based on the theoretical models
available in literature.",2001.02831v1
2017-05-25,Topological Weyl and Node-Line Semimetals in Ferromagnetic Vanadium-Phosphorous-Oxide $β$-V$_2$OPO$_4$ Compound,"We propose that the topological semimetal features can co-exist with
ferromagnetic ground state in vanadium-phosphorous-oxide $\beta$-V$_2$OPO$_4$
compound from first-principles calculations. In this magnetic system with
inversion symmetry, the direction of magnetization is able to manipulate the
symmetric protected band structures from a node-line type to a Weyl one in the
presence of spin-orbital-coupling. The node-line semimetal phase is protected
by the mirror symmetry with the reflection-invariant plane perpendicular to
magnetic order. Within mirror symmetry breaking due to the magnetization along
other directions, the gapless node-line loop will degenerate to only one pair
of Weyl points protected by the rotational symmetry along the magnetic axis,
which are largely separated in momentum space. Such Weyl semimetal phase
provides a nice candidate with the minimum number of Weyl points in a condensed
matter system. The results of surface band calculations confirm the non-trivial
topology of this proposed compound. This findings provide a realistic candidate
for the investigation of topological semimetals with time-reversal symmetry
breaking, particularly towards the realization of quantum anomalous Hall effect
in Weyl semimetals.",1705.09234v1
2020-03-11,A two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO$_{3}$(001),"Studies on oxide quasi-two dimensional electron gas (q2DEG) have been a
playground for the discovery of novel and sometimes unexpected phenomena, like
the reported magnetism at the surface and at the interface between LaAlO$_{3}$
and SrTiO$_{3}$ non-magnetic materials. However, magnetism in this system is
weak and there are evidences of a not intrinsic origin. Here, by using in-situ
high-resolution angle resolved photoemission we demonstrate that ferromagnetic
EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$ in the bulk, hosts a q2DEG
at its (001) surface. This is confirmed by density functional theory
calculations with Hubbard U terms in the presence of oxygen divacancies in
various configurations, all of them leading to a spin-polarized q2DEG related
to the ferromagnetic order of Eu-4f magnetic moments. The results suggest
EuTiO$_{3}$(001) as a new material platform for oxide q2DEGs, characterized by
broken inversion and time reversal symmetries.",2003.05494v2
2020-05-05,Fast magneto-ionic switching of interface anisotropy using yttria-stabilized zirconia gate oxide,"Voltage control of interfacial magnetism has been greatly highlighted in
spintronics research for many years, as it might enable ultra-low power
technologies. Among few suggested approaches, magneto-ionic control of
magnetism has demonstrated large modulation of magnetic anisotropy. Moreover,
the recent demonstration of magneto-ionic devices using hydrogen ions presented
relatively fast magnetization toggle switching, tsw ~ 100 ms, at room
temperature. However, the operation speed may need to be significantly improved
to be used for modern electronic devices. Here, we demonstrate that the speed
of proton-induced magnetization toggle switching largely depends on
proton-conducting oxides. We achieve ~1 ms reliable (> 103 cycles) switching
using yttria-stabilized zirconia (YSZ), which is ~ 100 times faster than the
state-of-the-art magneto-ionic devices reported to date at room temperature.
Our results suggest further engineering of the proton-conducting materials
could bring substantial improvement that may enable new low-power computing
scheme based on magneto-ionics.",2005.02005v1
2021-05-10,Spin reorientation in tetragonally distorted spinel oxide NiCo$_2$O$_4$ epitaxial films,"We experimentally investigated the magnetic properties of NiCo$_2$O$_4$
epitaxial films known to be conductive oxides with perpendicular magnetic
anisotropy (PMA) at room temperature. Both magneto-torque and magnetization
measurements at various temperatures provide clear experimental evidence of the
spin reorientation transition at which the MA changes from PMA to easy-cone
magnetic anisotropy (ECMA) at a certain temperature ($T_{\rm{SR}}$). ECMA was
commonly observed in films grown by pulsed laser deposition and reactive radio
frequency magnetron sputtering, although $T_{\mathrm{SR}}$ is dependent on the
growth method as well as the conditions. The cone angles measured from the
$c$-axis increased successively at $T_{\mathrm{SR}}$ and approached a maximum
of 45-50 degrees at the lowest measurement temperature of 5 K. Calculation with
the cluster model suggests that the Ni$^{3+}$ ions occupying the $T_d$ site
could be the origin of the ECMA. Both the magnetic properties and the results
of the calculation based on the cluster model indicate that the ECMA is
attributable to the cation anti-site distribution of Ni$^{3+}$, which is
possibly formed during the growth process of the thin films.",2105.04115v1
2021-06-09,Intriguing Magnetoelectric Effect in Two-dimensional Ferromagnetic/Perovskite Oxide Ferroelectric Heterostructure,"Two-dimensional (2D) magnets have broad application prospects in the
spintronics, but how to effectively control them with a small electric field is
still an issue. Here we propose that 2D magnets can be efficiently controlled
in a multiferroic heterostructure composed of 2D magnetic material and
perovskite oxide ferroelectric (POF) whose dielectric polarization is easily
flipped under a small electric field. We illustrate the feasibility of such
strategy in the bilayer CrI3/BiFeO3(001) heterostructure by using the
first-principles calculations. Different from the traditional POF multiferroic
heterostructures which have strong interface interactions, we find that the
interface interaction between CrI3 and BiFeO3(001) is van der Waals type.
Whereas, the heterostructure has particular strong magnetoelectric coupling
where the bilayer CrI3 can be efficiently switched between ferromagnetic and
antiferromagnetic types by the polarized states of BiFeO3(001). We also
discover the competing effect between electron doping and the additional
electric field on the interlayer exchange coupling interaction of CrI3, which
is responsible to the magnetic phase transition. Our results provide a new
avenue for the tuning of 2D magnets with a small electric field.",2106.04998v2
2022-10-19,"Fluorite-related iridate Pr$_3$IrO$_7$: Crystal growth, structure, magnetism, thermodynamic, and optical properties","Spin-orbit coupling in heavy 5$d$ metal oxides, in particular, iridates have
received tremendous interest in recent years due to the realization of exotic
electronic and magnetic phases. Here, we report the synthesis, structural,
magnetic, thermodynamic, and optical properties of the ternary iridate
Pr$_3$IrO$_7$. Single crystals of Pr$_3$IrO$_7$ have been grown by the KF flux
method. Structural analysis shows that Pr$_3$IrO$_7$ crystallizes in an
orthorhombic phase with $Cmcm$ symmetry. The electron energy loss spectroscopy
study indicates that Pr is in a 3+ valence state, which implies a 5+ oxidation
state of Ir. Magnetization data measured at high and low magnetic fields do not
exhibit any bifurcation between $M_{ZFC}$ and $M_{FC}$, however, a weak hump in
$M(T)$ is observed at $T^*$$\sim$10.4~K. The specific heat data reveal two
maxima at $\sim$253 K and $\sim$4.8 K. The optical conductivity
$\sigma_1(\omega)$ spectrum shows 24 infrared-active phonon modes and reveals
an insulating behavior with an optical gap $\Delta_{OP}$ of size $\sim$500~meV.
During cooling down, the temperature-dependent reflectivity spectrum reveals
eight extra phonon modes below the structural phase transition ($\sim$ 253 K).
An anomaly is observed at around $T^*$ in the temperature evolution of
infrared-active mode frequencies suggesting the presence of significant
spin-phonon coupling in the system.",2210.10496v1
2023-03-27,Measuring Magnetic 1/f Noise in Superconducting Microstructures and the Fluctuation-Dissipation Theorem,"The performance of superconducting devices like qubits, SQUIDs, and particle
detectors is often limited by finite coherence times and 1/f noise. Various
types of slow fluctuators in the Josephson junctions and the passive parts of
these superconducting circuits can be the cause, and devices usually suffer
from a combination of different noise sources, which are hard to disentangle
and therefore hard to eliminate. One contribution is magnetic 1/f noise caused
by fluctuating magnetic moments of magnetic impurities or dangling bonds in
superconducting inductances, surface oxides, insulating oxide layers, and
adsorbates. In an effort to further analyze such sources of noise, we have
developed an experimental set-up to measure both the complex impedance of
superconducting microstructures, and the overall noise picked up by these
structures. This allows for important sanity checks by connecting both
quantities via the fluctuation-dissipation theorem. Since these two
measurements are sensitive to different types of noise, we are able to identify
and quantify individual noise sources. The superconducting inductances under
investigation form a Wheatstone-like bridge, read out by two independent
cross-correlated dc-SQUID read-out chains. The resulting noise resolution lies
beneath the quantum limit of the front-end SQUIDs and lets us measure noise
caused by just a few ppm of impurities in close-by materials. We present
measurements of the insulating SiO2 layers of our devices, and magnetically
doped noble metal layers in the vicinity of the pickup coils at T = 40 mK - 800
mK and f = 1 Hz - 100 kHz.",2303.15257v2
2023-07-25,Emergent magnetism with continuous control in the ultrahigh conductivity layered oxide PdCoO2,"The current challenge to realizing continuously tunable magnetism lies in our
inability to systematically change properties such as valence, spin, and
orbital degrees of freedom as well as crystallographic geometry. Here, we
demonstrate that ferromagnetism can be externally turned on with the
application of low-energy helium implantation and subsequently erased and
returned to the pristine state via annealing. This high level of continuous
control is made possible by targeting magnetic metastability in the ultra-high
conductivity, non-magnetic layered oxide PdCoO2 where local lattice distortions
generated by helium implantation induce emergence of a net moment on the
surrounding transition metal octahedral sites. These highly-localized moments
communicate through the itinerant metal states which triggers the onset of
percolated long-range ferromagnetism. The ability to continuously tune
competing interactions enables tailoring precise magnetic and magnetotransport
responses in an ultra-high conductivity film and will be critical to
applications across spintronics.",2307.13490v2
2023-08-12,Antisymmetric Planar Hall Effect in Rutile Oxide Films Induced by the Lorentz Force,"The conventional Hall effect is linearly proportional to the field component
or magnetization component perpendicular to a film. Despite the increasing
theoretical proposals on the Hall effect to the in-plane field or magnetization
in various special systems induced by the Berry curvature, such an
unconventional Hall effect has only been experimentally reported in Weyl
semimetals and in a heterodimensional superlattice. Here, we report an
unambiguous experimental observation of the antisymmetric planar Hall effect
(APHE) with respect to the in-plane magnetic field in centrosymmetric rutile
RuO2 and IrO2 single-crystal films. The measured Hall resistivity is found to
be linearly proportional to the component of the applied in-plane magnetic
field along a particular crystal axis and to be independent of the current
direction or temperature. Both the experimental observations and theoretical
calculations confirm that the APHE in rutile oxide films is induced by the
Lorentz force. Our findings can be generalized to ferromagnetic materials for
the discovery of anomalous Hall effects and quantum anomalous Hall effects
induced by in-plane magnetization. In addition to significantly expanding
knowledge of the Hall effect, this work opens the door to explore new members
in the Hall effect family.",2308.06651v2
2024-01-08,Microwave-assisted synthesis of LaMnO3+d: Tuning physical properties with microwave power,"Synthesis of transition metal oxides by microwave irradiation is a faster and
energy-saving method compared to conventional heating in an electrical furnace
because microwave energy is directly converted into heat within precursors.
However, not much is known about how the physical properties are modified by
the power of microwaves. We synthesized LaMnO3+d by irradiating oxide
precursors with microwaves and studied the impact of microwave power (P = 1000
W, 1200 W, 1400 W and 1600 W) on magnetism, resistivity, magnetoresistance,
thermopower, magnetic entropy change, magnetostriction, and electron spin
resonance. It is found that paramagnetic to ferromagnetic transition becomes
sharper, saturation magnetization increases, and electrical resistivity at low
temperatures dramatically decreases as P increases. While the resistivity of
samples irradiated with MW power of P less than or equal to 1400 W show
insulating-like behavior down to 50 K, an insulator-metal transition occurs in
the sample exposed to P = 1600 W and this sample also shows a maximum
magnetoresistance (= -55%), magneto-thermopower (=-87%), magnetostriction (-180
x10-6) for H = 50 kOe and magnetic entropy change of 4.78 J/kg. K for H = 30
kOe around the Curie temperature. The intensity of electron spin resonance
spectra at 300 K increases with P. We postulate that the much enhanced physical
properties observed for the P = 1600 W sample arise from the creation of higher
hole density, chemical homogeneity, and increased grain size. Our study shows
that microwave power can be used as a knob to tune magnetism and other physical
properties to our advantage.",2401.04087v1
2024-02-14,Structure and magnetic properties of a La$_{0.75}$Sr$_{0.25}$Cr$_{0.90}$O$_{3-δ}$ single crystal,"We have successfully grown large and good-quality single crystals of the
La$_{0.75}$Sr$_{0.25}$Cr$_{0.90}$O$_{3-\delta}$ compound using the
floating-zone method with laser diodes. We investigated the crystal quality,
crystallography, chemical composition, magnetic properties and the oxidation
state of Cr in the grown single crystals by employing a combination of
techniques, including X-ray Laue and powder diffraction, scanning electron
microscopy, magnetization measurements, X-ray photoelectron spectroscopy and
light absorption. The La$_{0.75}$Sr$_{0.25}$Cr$_{0.90}$O$_{3-\delta}$ single
crystal exhibits a single-phase composition, crystallizing in a trigonal
structure with the space group $R\bar{3}c$ at room temperature. The chemical
composition was determined as La$_{0.75}$Sr$_{0.25}$Cr$_{0.90}$O$_{3-\delta}$,
indicating a significant chromium deficiency. Upon warming, we observed five
distinctive characteristic temperatures, namely $T_1 =$ 21.50(1) K, $T_2 =$
34.98(1) K, $T_3 =$ 117.94(1) K, $T_4 =$ 155.01(1) K, and $T_{\textrm{N}} =$
271.80(1) K, revealing five distinct magnetic anomalies. Our magnetization
study allows us to explore the nature of these anomalies. Remarkably, the
oxidation state of chromium in the single-crystal
La$_{0.75}$Sr$_{0.25}$Cr$_{0.90}$O$_{3-\delta}$, characterized by a band gap of
1.630(8) eV, is exclusively attributed to Cr$^{3+}$ ions, making a departure
from the findings of previous studies on polycrystalline materials.",2402.08940v2
1995-03-08,Screening effect of interlayer coupling on electronic transport properties of layered high-$T_c$ oxides,"We have investigated the effect of thermal fluctuation on the interlayer
coupling of three-dimensional Josephson-junction arrays with anisotropic
interactions as a model of layered high-$T_c$ oxides, focusing on non-Ohmic
current-voltage characteristics. Langevin dynamic simulations were performed
for various Josephson-coupling anisotropies and for various temperatures in
both zero and finite magnetic fields. We find that, in the highly anisotropic
region, the interlayer coupling, which causes the non-vanishing critical
current ($I_{c}$), is suppressed by thermal fluctuations, and tends to push up
the Kosterlitz-Thouless transition temperature ($T_{KT}$) of the
two-dimensional (2D) regime. In this highly anisotropic region, $I_c$ begins to
decrease drastically near $T_{KT}$. This suggests that interlayer coupling is
screened by thermally excited 2D small vortex-antivortex pairs as well as the
intralayer logarithmic part of vortex-antivortex interactions. Moreover, weak
magnetic fields parallel to the $c$-axis affect only the
logarithmic-interaction part between the 2D pancake vortices.",9503039v1
1998-08-25,P-wave Pairing and Colossal Magnetoresistance in Manganese Oxides,"We point out that the existing experimental data of most manganese oxides
show the {\sl frustrated} p-wave superconducting condensation in the
ferromagnetic phase in the sense that the superconducting coherence is not long
enough to cover the whole system. The superconducting state is similar to the
$A_{1}$ state in superfluid He-3. The sharp drop of resistivity, the steep jump
of specific heat, and the gap opening in tunneling are well understood in terms
of the p-wave pairing. In addition, colossal magnetoresistance (CMR) is
naturally explained by the superconducting fluctuations with increasing
magnetic fields. The finite resistivity may be due to some magnetic
inhomogeneities. This study leads to the possibility of room temperature
superconductivity.",9808275v1
1999-05-06,Role of Orbitals in Manganese Oxides - Ordering and Fluctuation,"We study the manganese oxides from the viewpoint of the strongly correlated
doped Mott insulator. The magnetic ordering and the charge transport are
governed by the orbital degrees of freedom, and their dimensionality is
controlled by the anisotropic transfer integrals between the $e_g$ orbitals. As
x increases the magnetic structure is predicted to change as $A \to F \to A \to
C \to G$ (F: ferromagnet, A: layered antiferromagnet, C: rod-type
antiferromagnet, G: usual antiferromagnet), in agreement with experiments.
Especially the orbital is aligned as $d_{x^2-y^2}$ in the metallic A state,
which explains the quasi 2D transport and no canting of the spin observed
experimentally. Next we discuss the ferromagnetic state without the orbital
ordering due to the quantum fluctuation. Here the interplay between the
electron repulsion U and the Jahn-Teller electron-phonon interation $E_{LR}$ is
studied with a large d model. In addition to this strong correlation, we
propose that the dynamical phase separation could explain the specific heat as
well as the various anomalous physical properties, e.g., resistivity,
photo-emission, etc.",9905072v1
2000-04-24,Magnetic Phase Transition of the Perovskite-type Ti Oxides,"Properties and mechanism of the magnetic phase transition of the
perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle
distortion, are studied theoretically by using the effective spin and
pseudo-spin Hamiltonian with strong Coulomb repulsion. It is shown that the
A-type antiferromagnetic(AFM(A)) to ferromagnetic(FM) phase transition occurs
as the Ti-O-Ti bond angle is decreased. Through this phase transition, the
orbital state is hardly changed so that the spin-exchange coupling along the
c-axis changes nearly continuously from positive to negative and takes
approximately zero at the phase boundary. The resultant strong
two-dimensionality in the spin coupling causes a rapid suppression of the
critical temperature as is observed experimentally.",0004389v1
2001-02-13,Magnetic and Orbital States and Their Phase Transition of the Perovskite-Type Ti Oxides: Strong Coupling Approach,"The properties and mechanism of the magnetic phase transition of the
perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle
distortion, are studied theoretically by using the effective spin and
pseudospin Hamiltonian with strong Coulomb repulsion. It is shown that the
A-type antiferromagnetic (AFM(A)) to ferromagnetic (FM) phase transition occurs
as the Ti-O-Ti bond angle is decreased. Through this phase transition, the
orbital state changes only little whereas the spin-exchange coupling along the
c-axis is expected to change from positive to negative nearly continuously and
approaches zero at the phase boundary. The resultant strong two-dimensionality
in the spin coupling causes rapid suppression of the critical temperature, as
observed experimentally. It may induce large quantum fluctuations in this
region.",0102223v1
2002-09-11,Co-doped LaLa1-xSrxTiO3-d : A Diluted Magnetic Oxide System with High Curie Temperature,"Ferromagnetism is observed at and above room temperature in pulsed laser
deposited epitaxial films of Co-doped Ti-based oxide perovskite
(La1-xSrxTiO3-d). The system has the characteristics of an intrinsic diluted
magnetic semiconductor (metal) at low concentrations (<~ 2 %), but develops
inhomogeneity at higher cobalt concentrations. The films range from being
opaque metallic to transparent semiconducting depending on the oxygen pressure
during growth and are yet ferromagnetic.",0209267v3
2002-11-27,Effect of FET geometry on charge ordering of transition metal oxides,"We examine the effect of an FET geometry on the charge ordering phase diagram
of transition metal oxides using numerical simulations of a semiclassical model
including long-range Coulomb fields, resulting in nanoscale pattern formation.
We find that the phase diagram is unchanged for insulating layers thicker than
approximately twice the magnetic correlation length. For very thin insulating
layers, the onset of a charge clump phase is shifted to lower values of the
strength of the magnetic dipolar interaction, and intermediate diagonal stripe
and geometric phases can be suppressed. Our results indicate that, for
sufficiently thick insulating layers, charge injection in an FET geometry can
be used to experimentally probe the intrinsic charge ordering phases in these
materials.",0211611v1
2003-08-18,Contrasting Pathways to Mott Gap Collapse in Electron and Hole Doped Cuprates,"Recent ARPES measurements on the electron-doped cuprate Nd_{2-x}Ce_xCuO_4 can
be interpreted in a mean field model of uniform doping of an antiferromagnet,
with the Mott gap closing near optimal doping. Mode coupling calculations
confirm the mean field results, while clarifying the relation between the Mott
gap and short-range magnetic order. The same calculations find that hole doped
cuprates should follow a strikingly different doping dependence, involving
instability toward spiral phases or stripes. Nevertheless, the magnetic order
(now associated with stripes) again collapses near optimal doping.",0308361v1
2003-08-20,Two resonant magnetic modes in an overdoped high-$\bf T_c$ superconductor,"A detailed inelastic neutron scattering study of the overdoped high
temperature copper oxide superconductor ${Y_{0.9}Ca_{0.1}Ba_{2}Cu_3O_{7}}$
reveals two distinct magnetic resonant modes in the superconducting state. The
modes differ in their symmetry with respect to exchange between adjacent copper
oxide layers. Counterparts of the mode with odd symmetry, but not the one with
even symmetry, had been observed before at lower doping levels. The observation
of the even mode resolves a long-standing puzzle, and the spectral weight ratio
of both modes yields an estimate of the onset of particle-hole spin-flip
excitations.",0308394v1
2004-06-09,Superconductivity in the insulating phase above the field-tuned superconductor-insulator transition in disordered indium oxide films,"We study the insulating phase of disordered indium oxide films that undergo a
field-tuned superconductor-insulator transition. The transport measurements in
a perpendicular magnetic field show distinct regimes of strongly fluctuating
order-parameter amplitude and phase, and reveal a wide range of insulator
strength in samples with differing disorder, despite the similarity in behavior
near the SIT. We characterize the strength of the insulating phase and compare
it to the superconducting strength. We find that the films do not return to the
expected normal state even at high perpendicular magnetic fields where all
pairs should be broken, suggesting the remaining presence of superconductivity
at high fields.",0406227v3
2004-08-14,Structural and Magnetic Studies on La2-xDyxCa2xBa2Cu4+2xOz Type Superconducting Oxides,"The La-2125 type La2-xDyxCa2xBa2Cu4+2xOz (0.1 < x < 0.5; LDBO) compounds have
been synthesized and studied for their structural and superconducting
properties by room temperature neutron diffraction, high field dc
magnetization, four-probe resistivity and iodometric double titration. The
Rietveld analysis of the neutron diffraction data reveals tetragonal structure
for all the samples, which crystallizes into La-123 type tetragonal structure
in P4/mmm space group. Iodometric double titrations were performed to determine
the oxygen content values and calculate mobile charge carrier (holes) density.
The superconducting transition temperatures (Tc) increases from ~ 20 K for x =
0.1 to a maximum of 75 K for x = 0.5. Flux pinning force (Fp) and critical
current density (Jc), calculated from the low temperature hysteresis loops,
also increases with increasing dopant concentration. The paper presents the
studies on structure and superconducting properties of all LDBO compounds in
light of the role of calcium in inducing superconductivity in the tetragonal
non-superconducting oxide.",0408334v1
2004-09-28,Enhanced annealing effect in an oxygen atmosphere on GaMnAs,"We report on in-situ resistivity measurements on GaMnAs during post-growth
annealing in different atmospheres. A drop in the resistivity is observed when
the GaMnAs is exposed to oxygen, which indicates that the passivation of Mn
interstitials (Mn_I) at the free surface occurs through oxidation. The presence
of oxygen can therefore be an important annealing condition for the
optimization of GaMnAs thin films, all the more since the oxidation appears to
be limited to the sample surface. Annealing in an oxygen-free atmosphere leads
to an increase in the resistivity indicating a second annealing mechanism
besides the out-diffusion of Mn_I. According to our magnetization and Hall
effect data, this mechanism reduces the amount of magnetically and electrically
active Mn atoms.",0409720v1
2004-12-29,"Dilute Metals: Superconductivity, Critical Currents, Magnetic Properties","Properties of oxides are interpreted as a result of existence of the virtual
sublattices formed by the atomic quantum states. An infinite cluster with the
superconductivity of the Bose-Einstein condensate kind can be formed in the
ground state sublattice at certain oxigen atoms concentration in the
effectively diluted system of metal atoms (above the percolation threshold).
Then the electron pairs concentration n/2 can be much less than the metal atoms
concentration N in the oxide. The similar situation takes place in metals with
superconductivity of the BCS type. Above the percolation threshold the
superconductivity Tc may be limited by the magnetic properties of the oxigen
2p4quantum state sublattice. Data on the critical current density allow us to
estimate the electronic pair density n/2 and to obtain an information
concerning the superconductivity nature.",0412740v2
2005-12-21,Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2,"A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by
means of resistivity, magnetic susceptibility, specific heat and X-ray
diffraction. The crystal structure is characterized by alternating stacking of
a Ni3+O2 layer and a (Ag2)+ layer, the former realizing a spin-1/2 triangular
lattice with eg orbital degeneracy and the latter providing itinerant
electrons. It is found that the NiO2 layer exhibits orbital ordering at Ts =
260 K and antiferromagnetic spin ordering at TN = 56 K. Moreover, a moderately
large mass enhancement is found for the itinerant electrons, suggesting a
significant contribution from the nearly localized Ni 3d state to the Ag 5s
state that forms a broad band.",0512524v1
2006-10-04,"Intermediate phase in the oxidative hydrothermal synthesis of potassium jarosite, a model kagome antiferromagnet","The jarosite family of minerals contain antiferromagnetically coupled Fe3+
ions that make up the kagome network. This geometric arrangement of the Fe3+
ions causes magnetic frustration that results in exotic electronic ground
states, e.g. spin glasses and spin liquids. Synthesic research into jarosites
has focused on producing near perfect stoichiometry to eliminate possible
magnetic disorder. An new oxidative synthesis method has been devel-oped for
the potassium, sodium, rubidium and ammonium jarosites that leads to high Fe
coverage. We show through the identification of a meta-stable intermediate,
using powder X-ray diffraction, how near perfect Fe coverage arises using this
method. Understanding this new mechanism for jarosite formation suggests that
is it possible to synthesis hydronium jarosite, an unconventional spin glass,
with a very high Fe coverage.",0610119v1
2007-01-26,Use of Superparamagnetic Nanoparticle/Block Copolymer Electrostatic Complexes as Contrast Agents in Magnetic Resonance Imaging,"During the past years we have investigated the complexation between
nanocolloids and oppositely charged polymers. The nanocolloids examined were
ionic surfactant micelles and inorganic oxide nanoparticles. For the polymers,
we used homopolyelectrolytes and block copolymers with linear and comb
architectures. In general, the attractive interactions between oppositely
charged species are strong and as such, the simple mixing of solutions
containing dispersed constituents yield to a precipitation, or to a phase
separation. We have developed means to control the electrostatically-driven
attractions and to preserve the stability of the mixed solution. With these
approaches, we designed novel core-shell nanostructures, e.g. as those obtained
with polymers and iron oxide superparamagnetic nanoparticles. In this
presentation, we show that electrostatic complexation can be used to tailor new
functionalized nanoparticles and we provide examples related to biomedical
applications in the domain of contrast agents for Magnetic Resonance Imaging.",0701663v1
2007-02-07,Anomalous magnetic phase in an undistorted pyrochlore oxide Cd2Os2O7 induced by geometrical frustration,"We report on the muon spin rotation/relaxation study of a pyrochlore oxide,
Cd2Os2O7, which exhibits a metal-insulator (MI) transition at T_{MI}~225 K
without structural phase transition. It reveals strong spin fluctuation
(>10^8/s) below the MI transition, suggesting a predominant role of geometrical
spin frustration amongst Os^{5+} ions. Meanwhile, upon further cooling, a
static spin density wave discontinuously develops below T_{SDW}~150 K. These
observations strongly suggest the occurrence of an anomalous magnetic
transition and associated change in the local spin dynamics in undistorted
pyrochlore antiferromagnet.",0702164v2
2007-11-28,"Chemical Tuning of Positive and Negative Magnetoresistances, and Superconductivity in 1222-type Ruthenocuprates","High critical-temperature superconductivity and large (colossal)
magnetoresistances are two important electronic conducting phenomena found in
transition metal oxides. High-Tc materials have applications such as
superconducting magnets for MRI and NMR, and magnetoresistive materials may
find use in magnetic sensors and spintronic devices. Here we report chemical
doping studies of RuSr2(R2-xCex)Cu2O10-d ruthenocuprates which show that a
single oxide system can be tuned between superconductivity at high hole dopings
and varied magnetoresistive properties at low doping levels. A robust variation
of negative magnetoresistance with hole concentration is found in the
RuSr2R1.8-xY0.2CexCu2O10-d series, while RuSr2R1.1Ce0.9Cu2O10-d materials show
an unprecedented crossover from negative to positive magnetoresistance with
rare earth (R) ion radius.",0711.4611v1
2008-08-16,All Oxide Ferromagnet/Semiconductor Epitaxial Heterostructures,"Oxide based ferromagnet/semiconductor heterostructures offer substantial
advantages for spin electronics. We have grown (111) oriented Fe3O4 thin films
and Fe3O4/ZnO heterostructures on ZnO(0001) and Al2O3(0001) substrates by
pulsed laser deposition. High quality crystalline films with mosaic spread as
small as 0.03 degree, sharp interfaces, and rms surface roughness of 0.3 nm
were achieved. Magnetization measurements show clear ferromagnetic behavior of
the magnetite layers with a saturation magnetization of 3.2 muB/f.u. at 300 K.
Our results demonstrate that the Fe3O4/ZnO system is an intriguing and
promising candidate for the realization of multi-functional heterostructures.",0808.2245v1
2008-12-30,Structure and magnetism in ultrathin iron oxides characterized by low energy electron microscopy,"We have grown epitaxial films a few atomic layers thick of iron oxides on
ruthenium. We characterize the growth by low energy electron microscopy. Using
selected area diffraction and intensity vs. voltage spectroscopy, we detect two
distinct phases which are assigned to wustite and magnetite. Spin polarized low
energy electron microscopy shows magnetic domain patterns in the magnetite
phase at room temperature.",0812.5049v2
2009-08-05,Non-DMS related ferromagnetism in transition metal doped zinc oxide,"We review pitfalls in recent efforts to make a conventional semiconductor,
namely ZnO, ferromagnetic by means of doping with transition metal ions. Since
the solubility of those elements is rather low, formation of secondary phases
and the creation of defects upon low temperature processing can lead to
unwanted magnetic effects. Among others, ion implantation is a method of
doping, which is highly suited for the investigation of those effects. By
focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that
there are manifold sources for ferromagnetism in this material which can easily
be confused with the formation of a ferromagnetic diluted magnetic
semiconductor (DMS). We will focus on metallic as well as oxide precipitates
and the difficulties of their identification.",0908.0645v1
2010-02-04,Realistic Modeling of Complex Oxide Materials,"Since electronic and magnetic properties of many transition-metal oxides can
be efficiently controlled by external factors such as the temperature,
pressure, electric or magnetic field, they are regarded as promising materials
for various applications. From the viewpoint of electronic structure, these
phenomena are frequently related to the behavior of a small group of states
close to the Fermi level. The basic idea of this project is to construct a
low-energy model for the states near the Fermi level on the basis of
first-principles density functional theory, and to study this model by modern
many-body techniques. After a brief review of the method, the abilities of this
approach will be illustrated on a number of examples, including multiferroic
manganites and spin-orbital-lattice coupled phenomena in RVO3 (R being the
three-valent element).",1002.0905v1
2010-09-17,"Role of oxygen-oxygen hopping in the three-band copper-oxide model: quasiparticle weight, metal insulator and magnetic phase boundaries, gap values and optical conductivity","We investigate the effect of oxygen-oxygen hopping on the three-band
copper-oxide model relevant to high-$T_c$ cuprates, finding that the physics is
changed only slightly as the oxygen-oxygen hopping is varied. The location of
the metal-insulator phase boundary in the plane of interaction strength and
charge transfer energy shifts by $\sim 0.5$eV or less along the charge transfer
axis, the quasiparticle weight has approximately the same magnitude and doping
dependence and the qualitative characteristics of the electron-doped and
hole-doped sides of the phase diagram do not change. The results confirm the
identification of La$_2$CuO$_4$ as a material with intermediate correlation
strength. However, the magnetic phase boundary as well as higher-energy
features of the optical spectrum are found to depend on the magnitude of the
oxygen-oxygen hopping. We compare our results to previously published one-band
and three-band model calculations.",1009.3490v2
2010-10-30,Metal-Insulator Transition and Magnetic Order in the Pyrochlore Oxide Hg2Ru2O7,"We report results of NMR experiments on the ruthenium oxide Hg2Ru2O7 with the
pyrochlore structure, which exhibits a metal-insulator transition at TMI = 107
K. In the metallic phase above TMI, the nuclear spin-lattice relaxation rate
1/T1 and the Knight shift at the Hg sites follow the Korringa relation,
indicating the absence of substantial spatial spin correlation. At low
temperatures in the insulating phase, 99,101Ru-NMR signals are observed at zero
magnetic field, providing evidence for a commensurate antiferromagnetic order.
The estimated ordered moment is about 1 muB per Ru, much smaller than 3 muB
expected for the ionic (4d)3plus configuration of Ru5plus. Thus the localized
spin models are not appropriate for the insulating phase of Hg2Ru2O7. We also
discuss possible antiferromagnetic spin structures.",1011.0049v2
2010-12-11,Magnetism in C or N-doped MgO and ZnO: density-functional study of impurity pairs,"It is shown that substitution of C or N for O recently proposed as a way to
create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by
formation of impurity pairs, and the resultant C2 spin=1 dimers as well as the
isoelectronic N2^{2+} interact antiferromagneticallly in p-type MgO. For
C-doped ZnO, however, we demonstrate using the HSE hybrid functional that a
resonance of the spin-polarized C2 pp\pi* states with the host conduction band
results in a long-range ferromagnetic interaction. Magnetism of open-shell
impurity molecules is proposed as a possible route to d0-ferromagnetism in
oxide spintronic materials.",1012.2439v1
2011-04-11,The High Temperature Superconductivity in Cuprates,"We discuss the high-temperature superconductivity in copper oxide ceramics.
We propose an effective Hamiltonian to describe the dynamics of electrons or
holes injected into the copper oxide layers. We show that our approach is able
to account for both the pseudogap and the superconductivity gap. For the
hole-doped cuprates we discuss in details the underdoped, optimal doped, and
overdoped regions of the phase diagram. In the underdoped region we determine
the doping dependence of the upper critical magnetic field, the vortex region,
and the discrete states bounded to the core of isolated vortices. We explain
the origin of the Fermi arcs and Fermi pockets. Moreover, we discuss the
recently reported peculiar dependence of the specific heat on the applied
magnetic field. We determine the critical doping where the pseudogap vanishes.
We find that in the overdoped region the superconducting transition is
described by the conventional d-wave BCS theory. We discuss the optimal doping
region and the crossover between the underdoped region and the overdoped
region. We also discuss briefly the electron-doped cuprate superconductors.",1104.1857v3
2011-05-13,Room temperature p-induced surface ferromagnetism,"We prove a spontaneous magnetization of the oxygen-terminated ZnO (0001)
surface by utilizing a multi-code, SIESTA and KKR, first-principles approach,
involving both LSDA+U and selfinteraction corrections (SIC) to treat electron
correlation effects. Critical temperatures are estimated from Monte Carlo
simulations, showing that at and above 300 K the surface is thermodynamically
stable and ferromagnetic. The observed half-metallicity and long-range magnetic
order originate from the presence of p-holes in the valence band of the oxide.
The mechanism is universal in ionic oxides and points to a new route for the
design of ferromagnetic low dimensional systems.",1105.2777v1
2011-06-29,A variational pseudo-self-interaction correction approach: ab-initio description of correlated oxides and molecules,"We present a fully variational generalization of the pseudo self-interaction
correction (VPSIC) approach previously presented in two implementations based
on plane-waves and atomic orbital basis set, known as PSIC and ASIC,
respectively. The new method is essentially equivalent to the previous version
for what concern the electronic properties, but it can be exploited to
calculate total-energy derived properties as well, such as forces and
structural optimization. We apply the method to a variety of test cases
including both non-magnetic and magnetic correlated oxides and molecules,
showing a generally good accuracy in the description of both structural and
electronic properties.",1106.5993v1
2013-03-05,Suppression of Magnetic Phase Separation in Epitaxial SrCoOx Films,"Using pulsed laser deposition and a unique fast quenching method, we have
prepared SrCoOx epitaxial films on SiTiO3 substrates. As electrochemical
oxidation increases the oxygen content from x = 2.75 to 3.0, the films tend to
favor the discrete magnetic phases seen in bulk samples for the homologous
series SrCoO(3-n/8) (n = 0, 1, 2). Unlike bulk samples, 200nm thick films
remain single phase throughout the oxidation cycle. 300 nm films can show two
simultaneous phases during deoxidation. These results are attributed to finite
thickness effects and imply the formation of ordered regions larger than
approximately 300 nm.",1303.1149v1
2013-04-08,Spin states of iron impurities in magnesium oxide under pressure: A possible intermediate state,"Ferropericlase (Mg,Fe)O is a major lower mantle mineral, and studying its
properties is a fundamental step toward understanding the Earth's interior.
Here, we performed a first-principles investigation on the properties of iron
as an isolated impurity in magnesium oxide, which is the condition of
ferropericlase under which iron-iron interactions could be neglected. The
calculations were carried using the all-electron full-potential linearized
augmented plane wave method within the density functional theory in the
generalized gradient approximation plus the on-site Hubbard correction. We
present the electronic and magnetic properties, electric and magnetic hyperfine
splitting of this impurity in high and low spin states for several charge
states at zero pressure, which were then extended to high pressures. For the
impurity in the neutral charge state, our results indicated that there is a
metastable intermediate spin state (S=1), in addition to the high (S=2) and low
(S=0) spin states. Those results were discussed in the context of an
intermediate spin state, experimentally identified in ferrosilicate perovskite.",1304.2227v1
2013-07-20,Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling,"We propose a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures that includes a Rashba spin-orbit coupling
proportional to an electric field oriented perpendicularly to the interface.
Taking into account the electron density dependence of this electric field
confining the electron gas at the interface, we report the occurrence of a
phase separation instability (signaled by a negative compressibility) for
realistic values of the spin-orbit coupling and of the electronic
band-structure parameters at zero temperature. We extend the analysis to finite
temperatures and in the presence of an in-plane magnetic field, thereby
obtaining two phase diagrams which exhibit a phase separation dome. By varying
the gating potential the phase separation dome may shrink and vanish at zero
temperature into a quantum critical point where the charge fluctuates
dynamically. Similarly the phase separation may be spoiled by a planar magnetic
field even at zero temperature leading to a line of quantum critical points.",1307.5427v3
2014-02-15,Quantifying and controlling the magnetic dipole contribution to 1.5 $μ$m light emission in erbium-doped yttrium oxide,"We experimentally quantify the contribution of magnetic dipole (MD)
transitions to the near-infrared light emission from trivalent erbium-doped
yttrium oxide (Er$^{3+}$:Y$_2$O$_3$). Using energy-momentum spectroscopy, we
demonstrate that the $^4$I$_{13/2}{\to}^4$I$_{15/2}$ emission near 1.5 $\mu$m
originates from nearly equal contributions of electric dipole (ED) and MD
transitions that exhibit distinct emission spectra. We then show how these
distinct spectra, together with the differing local density of optical states
(LDOS) for ED and MD transitions, can be leveraged to control Er$^{3+}$
emission in structured environments. We demonstrate that far-field emission
spectra can be tuned to resemble almost pure emission from either ED or MD
transitions, and show that the observed spectral modifications can be
accurately predicted from the measured ED and MD intrinsic emission rates.",1402.3717v1
2014-08-07,Magneto-transport properties of oriented Mn2CoAl films sputtered on thermally oxidized Si substrates,"Spin gapless semiconductors are interesting novel class of materials by
embracing both magnetism and semiconducting. Its potential application in
future spintronics requires realization in thin film form. In this letter, we
report a successful growth of spin gapless Mn2CoAl films on thermally oxidized
Si substrates by magnetron sputtering deposition. The films deposited at 673K
are well oriented to (001) direction and display a uniform-crystalline surface.
Magnetotransport measurements on the oriented films reveal a
semiconducting-like resistivity, small anomalous Hall conductivity and linear
magnetoresistance (MR) representative of the transport signatures of spin
gapless semiconductors. The magnetic properties of the films have also been
investigated and compared to that of bulk Mn2CoAl, with small discrepancy
induced by the composition deviation.",1408.1547v1
2015-01-09,Giant spin-phonon-electronic coupling in a 5d oxide,"Enhanced coupling of material properties offers new fundamental insights and
routes to multifunctional devices. In this context 5d oxides provide new
paradigms of cooperative interactions driving novel emergent behavior. This is
exemplified in 5d osmates that host a metal-insulator transition (MIT) driven
by magnetic order. Here we consider the most robust case, the 5d perovskite
NaOsO3, and reveal a giant coupling between spin and phonon through a frequency
shift of {\Delta}{\omega}=40 cm-1, the largest measured in any material. We
identify the dominant octahedral breathing mode and show isosymmetry with spin
ordering which induces dynamic charge disproportionation that sheds new light
on the MIT. The occurrence of the dramatic spin-phonon-electronic coupling in
NaOsO3 is due to a property common to all 5d materials: the large spatial
extent of the 5d ion. This allows magnetism to couple to phonons on an
unprecedented scale and consequently offers multiple new routes to enhanced
coupled phenomena.",1501.02290v1
2015-06-23,Interface exchange processes in LaAlO$_3$/SrTiO$_3$ induced by oxygen vacancies,"Understanding the role of defects in oxide heterostructures is crucial for
future materials control and functionalization. We hence study the impact of
oxygen vacancies (OVs) at variable concentrations on orbital- and spin exchange
in the LaAlO$_3$/SrTiO$_3$ interface by first principles many-body theory and
real-space model-Hamiltonian techniques. Intricate interplay between Hubbard
$U$ and Hund's coupling $J_{\rm H}$ for OV-induced correlated states is
demonstrated. Orbital polarization towards an effective $e_g$ state with
predominant local antiferromagnetic alignment on Ti sites near OVs is
contrasted with $t_{2g}(xy)$ states with ferromagnetic tendencies in the
defect-free regions. Different magnetic phases are identified, giving rise to
distinct net-moment behavior at low and high OV concentrations. This provides a
theoretical basis for prospective tailored magnetism by defect manipulation in
oxide interfaces.",1506.07066v3
2016-01-15,Analysis of electronic and structural properties of surfaces and interfaces based on LaAlO3 and SrTiO3,"Recently, it was established that a two-dimensional electron system can arise
at the interface between two oxide insulators LaAlO3 and SrTiO3. This
paradigmatic example exhibits metallic behaviour and magnetic properties
between non-magnetic and insulating oxides. Despite a huge amount of
theoretical and experimental work a thorough understanding has yet to be
achieved. We analyzed the structural deformations of a LaAlO3 (001) slab
induced by hydrogen ad-atoms and oxygen vacancies at its surface by means of
density functional theory. Moreover, we investigated the influence of surface
reconstruction on the density of states and determined the change of the local
density of states at the Fermi level with increasing distance from the surface
for bare LaAlO3 and for a conducting LaAlO3/SrTiO3 interface. In addition, the
Al-atom displacements and distortions of the TiO6-octahedra were estimated.",1601.04009v1
2016-07-24,Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces,"We have observed a super-giant (~10,000,000%) negative magnetoresistance at
39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires,
potential barriers form at the two Cu/Au interfaces because of Cu oxidation
that results in an ultrathin copper oxide layer forming between Cu and Au.
Current flows when electrons tunnel through, and/or thermionically emit over,
these barriers. A magnetic field applied transverse to the direction of current
flow along the wire deflects electrons toward one edge of the wire because of
the Lorentz force, causing electron accumulation at that edge and depletion at
the other. This lowers the potential barrier at the accumulated edge and raises
it at the depleted edge, causing a super-giant magnetoresistance at room
temperature.",1607.07091v1
2016-09-16,Interface Engineering in La0.67Sr0.33MnO3-SrTiO3 Heterostructures,"Interface engineering is an extremely useful tool for systematically
investigating materials and the various ways materials interact with each
other. We describe different interface engineering strategies designed to
reveal the origin of the electric and magnetic dead-layer at La0.67Sr0.33MnO3
interfaces. La0.67Sr0.33MnO3 is a key example of a strongly correlated
peroskite oxide material in which a subtle balance of competing interactions
gives rise to a ferromagnetic metallic groundstate. This balance, however, is
easily disrupted at interfaces. We systematically vary the dopant profile, the
disorder and the oxygen octahedra rotations at the interface to investigate
which mechanism is responsible for the dead layer. We find that the magnetic
dead layer can be completely eliminated by compositional interface engineering
such that the polar discontinuity at the interface is removed. This, however,
leaves the electrical dead-layer largely intact. We find that deformations in
the oxygen octahedra network at the interface are the dominant cause for the
electrical dead layer.",1609.04976v1
2018-02-05,Intrinsic spin-orbit torque arising from Berry curvature in metallic-magnet/Cu-oxide interface,"We report the observation of the intrinsic damping-like spin-orbit torque
(SOT) arising from the Berry curvature in metallic-magnet/CuO$_x$
heterostructures. We show that a robust damping-like SOT, an order of magnitude
larger than a field-like SOT, is generated in the heterostructure despite the
absence of the bulk spin-orbit effect in the CuO$_x$ layer. Furthermore, by
tuning the interface oxidation level, we demonstrate that the field-like SOT
changes drastically and even switches its sign, which originates from oxygen
modulated spin-dependent disorder. These results provide an important
information for fundamental understanding of the physics of the SOTs.",1802.01285v2
2018-11-13,Nanoscale ordered Layered-Segregation of Cobalt and Iron in the Perovskite SmFe0.5Co0.5O3,"The possibility to segregate cobalt and iron in a single perovskite, at a
nanoscale in the form of layers has been investigated, using sol gel technic
synthesis. Quite remarkably, it is shown that such a nanoscale ordering, which
can only be detected by a combined HAADF-STEM and EELS study, has a significant
impact upon the magnetic properties of this SmFe0.5Co0.5O3 oxide. This suggests
that careful nanoscale characterization of oxides will be necessary in the
future before proceeding to a viable interpretation of their physical
properties, at least in the field of magnetism.",1811.05221v1
2019-05-23,Topological Hall Effect and Emergent Skyrmion Crystal in Manganite-Iridate Oxide Interfaces,"Scalar spin chirality is expected to induce a finite contribution to the Hall
response at low temperatures. We study this spin-chirality-driven Hall effect,
known as the topological Hall effect, at the manganite side of the interface
between La$_{1-x}$Sr$_{x}$MnO$_{3}$ and SrIrO$_3$. The ferromagnetic
double-exchange hopping at the manganite layer, in conjunction with the
Dzyaloshinskii-Moriya (DM) interaction which arises at the interface due to
broken inversion symmetry and strong spin-orbit coupling from the iridate
layer, could produce a skyrmion-crystal (SkX) phase in the presence of an
external magnetic field. Using the Monte Carlo technique and a two-orbital
spin-fermion model for manganites, supplemented by an in-plane DM interaction,
we obtain phase diagrams which reveal at low temperatures a clear SkX phase and
also a low-field spin-spiral phase. Increasing temperature, a skyrmion-gas
phase, precursor of the SkX phase upon cooling, was identified. The topological
Hall effect primarily appears in the SkX phase, as observed before in oxide
heterostructures. We conclude that the manganite-iridate superlattices provide
another useful platform to explore a plethora of unconventional magnetic and
transport properties.",1905.09887v2
2013-08-02,Termination control of electronic phases in oxide thin films and interfaces: LaAlO3/SrTiO3(001),"A wealth of intriguing properties emerge in the seemingly simple system
composed of the band insulators LaAlO3 and SrTiO3 such as a two-dimensional
electron gas, superconductivity and magnetism. In this paper we review the
current insight obtained from first principles calculations on the mechanisms
governing the behavior of thin LaAlO3 films on SrTiO3(001). In particular, we
explore the strong dependence of the electronic properties on the surface and
interface termination, the finite film thickness, lattice polarization and
defects. A further aspect that is addressed is how the electronic behavior and
functionality can be tuned by a SrTiO3 capping layer, adsorbates and metallic
contacts. Lastly, we discuss recent reports on the coexistence of magnetism and
superconductivity in this system for what they might imply about the electronic
structure of this system.",1308.0481v1
2016-11-11,MgGa2O4 spinel barrier for magnetic tunnel junctions: coherent tunneling and low barrier height,"Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel
junctions (MTJs) were fabricated by magnetron sputtering. Tunnel
magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was
observed, suggesting a TMR enhancement by the coherent tunneling effect in the
MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good
lattice matching with the Fe layers owing to slight tetragonal lattice
distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance
and current-voltage characteristics revealed that the barrier height of the
MgGa2O4 barrier is much lower than that in an MgAl2O4 barrier. This study
demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a
large TMR ratio at a low resistance area product.",1611.03606v1
2009-12-17,Surface magnetism in ZnO/Co3O4 mixtures,"We recently reported the observation of room temperature ferromagnetism in
mixtures of ZnO and Co3O4 despite the diamagnetic and antiferromagnetic
character of these oxides respectively. Here we present a detailed study on the
electronic structure of this material in order to account for this unexpected
ferromagnetism. Electrostatic interactions between both oxides lead to a
dispersion of Co3O4 particles over the surface of ZnO larger ones. As a
consequence, the reduction of Co+3 to Co2+ at the particle surface takes place
as evidenced by XAS measurements and optical spectrocopy. This reduction allows
to xplain the observed ferromagnetic signal within the well established
theories of magnetism.",0912.3458v1
2013-09-01,High-pressure cupric oxide: a room-temperature multiferroic,"Multiferroic materials, in which ferroelectric and magnetic ordering coexist,
are of fundamental interest for the development of multi-state memory devices
that allow for electrical writing and non-destructive magnetic read-out
operation. The great challenge is to create multiferroic materials that operate
at room-temperature and have a large ferroelectric polarization P. Cupric
oxide, CuO, is promising because of its large P ~ 10^{2} {\mu}C.m^{-2}, but is
unfortunately only multiferroic in a temperature range of 20 K, from 210 to 230
K. Here, using a combination of density functional theory and Monte Carlo
calculations, we establish that pressure-driven phase competition induces a
giant stabilization of the multiferroic phase of CuO, which at 20-40 GPa
becomes stable in a domain larger than 300 K, from 0 to T > 300 K. Thus, under
high-pressure, CuO is predicted to be a room-temperature multiferroic with
large polarization.",1309.0246v1
2014-05-06,Magnetic and transport signatures of Rashba spin-orbit coupling on the ferromagnetic Kondo lattice model in two dimensions,"Motivated by emergent phenomena at oxide surfaces and interfaces,
particularly those involving transition metal oxides with perovskite crystal
structure such as LaTiO3/SrTiO3, we examine the ferromagnetic Kondo lattice
model (FKLM) in the presence of a Rashba spin-orbit coupling (RSOC). Using
numerical techniques, under the assumption that the electrons on localized
orbitals may be treated as classical continuum spins, we compute various
charge, spin and transport properties on square clusters at zero temperature.
We find that the main effect of the RSOC is the destruction of the
ferromagnetic state present in the FKLM at low electron fillings, with the
consequent suppression of conductivity. In addition, near half-filling the RSOC
leads to a departure of the antiferromagnetic state of the FKLM with a
consequent reduction to the intrinsic tendency to electronic phase separation.
The interplay between phase separation on one side, and magnetic and transport
properties on the other, is carefully analyzed as a function of the
RSOC/hopping ratio.",1405.1240v2
2014-05-13,From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores,"We present new magnetic heat capacity and neutron scattering results for two
magnetically frustrated molybdate pyrochlores: $S=1$ oxide Lu$_2$Mo$_2$O$_7$
and $S={\frac{1}{2}}$ oxynitride Lu$_2$Mo$_2$O$_5$N$_2$. Lu$_2$Mo$_2$O$_7$
undergoes a transition to an unconventional spin glass ground state at $T_f
{\sim} 16$ K. However, the preparation of the corresponding oxynitride tunes
the nature of the ground state from spin glass to quantum spin liquid. The
comparison of the static and dynamic spin correlations within the oxide and
oxynitride phases presented here reveals the crucial role played by quantum
fluctuations in the selection of a ground state. Furthermore, we estimate an
upper limit for a gap in the spin excitation spectrum of the quantum spin
liquid state of the oxynitride of ${\Delta} {\sim} 0.05$ meV or
${\frac{\Delta}{|\theta|}}\sim0.004$, in units of its antiferromagnetic Weiss
constant ${\theta} {\sim}-121$ K.",1405.3172v1
2014-05-24,Triclinic Ni0.6Co0.4TiO3 Ilmenite Oxide,"Forming a solid-solution of NiTiO3 and CoTiO3, two isostructural (ilmenite)
and isosymmetrical (space group R-3) compounds, result in a single-phase
compound with a remarkably low crystal symmetry. By neutron and X-ray
synchrotron powder diffraction techniques, the space group symmetry of the
Ni0.6Co0.4TiO3 sample was found to be triclinic P-1 at room temperature, far
above the magnetic transition temperature. Ni and Co ions were found to prefer
positions close to the octahedron center, whereas Ti ions took off-center
positions. This structural distortion is the first known case in ilmenites and
opens up ways to modify functional properties of magnetic oxides. Origin of the
symmetry lowering is discussed.",1405.6330v1
2016-08-18,Exotic Spin-Orbital Physics in Hybrid Oxides,"We compare the effective spin-orbital super\-exchange triggered by magnetic
$3d$ impurities with $d^3$ and $d^2$ configurations and either no orbital
degree of freedom (orbital dilution) or hole replacing a doublon (charge
dilution) in a $4d^4$ Mott insulator with $S=1$ spins. Impurities causing
orbital dilution act either as spin defects decoupled from the surrounding
ions, or generate orbital polarons along $d^3$-$d^4$ hybrid bonds. The exchange
on these bonds determines which orbital is occupied by a doublon on the host
site. In case of charge dilution by $3d^2$ impurities additional $\propto
T_i^+T_j^+$ terms arise which enhance orbital fluctuations. We show that such
terms may radically change orbital pattern at relatively low doping by $x=1/8$
hole defects. Our findings provide new perspective for future theoretical and
experimental studies of doped transition metal oxides.",1608.05330v1
2016-12-13,Multiple structural transitions driven by spin-phonon couplings in a perovskite oxide,"Spin-phonon interactions are central to many interesting phenomena, ranging
from superconductivity to magnetoelectric effects. Yet, they are believed to
have a negligible influence on the structural behavior of most materials. For
example, magnetic perovskite oxides often undergo structural transitions
accompanied by magnetic signatures whose minuteness suggests that the
underlying spin-phonon couplings are largely irrelevant. Here we present an
exception to this rule, showing that novel effects can occur as a consequence.
Our first-principles calculations reveal that spin-phonon interactions are
essential to reproduce the experimental observations on the phase diagram of
magnetoelectric multiferroic BiCoO$_{3}$. Moreover, we predict that, under
compression, these couplings lead to an unprecedented temperature-driven
double-reentrant sequence of ferroelectric transitions. We propose how to
modify BiCoO$_{3}$ via chemical doping to reproduce such striking effects at
ambient conditions, thereby yielding useful multifunctionality.",1612.04356v1
2018-01-19,Electric-field control of anomalous and topological Hall effects in oxide bilayer thin films,"One of the key technologies in spintronics is to tame spin-orbit coupling
(SOC) that links spin and motion of electrons, giving rise to intriguing
magneto-transport properties in itinerant magnets. Prominent examples of such
SOC-based phenomena are anomalous and topological Hall effects. However,
controlling them by electric field has remained unachieved since electric field
tends to be screened in itinerant magnets. Here we demonstrate that both
anomalous and topological Hall effects can be modulated by electric field in
oxide heterostructures consisting of ferromagnetic SrRuO$_{3}$ and nonmagnetic
SrIrO$_{3}$. We observed clear electric-field effect only when SrIrO$_{3}$ is
inserted between SrRuO$_{3}$ and a gate dielectric. Our results establish that
strong SOC of nonmagnetic materials such as SrIrO$_{3}$ is essential in
electrical tuning of these Hall effects and possibly other SOC-related
phenomena.",1801.06272v1
2019-09-13,Tunable perpendicular exchange bias in oxide heterostructures,"The exchange bias effect is an essential component of magnetic memory and
spintronic devices. Whereas recent research has shown that anisotropies
perpendicular to the device plane provide superior stability against thermal
noise, it has proven remarkably difficult to realize perpendicular exchange
bias in thin-film structures. Here we demonstrate a strong perpendicular
exchange bias effect in heterostructures of the quasi-two-dimensional canted
antiferromagnet La$_2$CuO$_4$ and ferromagnetic (La,Sr)MnO$_3$ synthesized by
ozone-assisted molecular beam epitaxy. The magnitude of this effect can be
controlled via the doping level of the cuprate layers. Canted
antiferromagnetism of layered oxides is thus a new and potentially powerful
source of uniaxial anisotropy in magnetic devices.",1909.06152v1
2019-09-19,Influence of magnetic ordering on the spectral properties of binary transition metal oxides,"Using the ab initio embedded DMFT (eDMFT) approach, we study the effect of
long-range magnetic ordering on the spectral properties in the binary
transition metal oxides, and find that the most significant changes appear in
the momentum resolved spectral functions, which sharpen into quite well-defined
bands in the antiferromagnetic (AFM) phase. The strongest change across the
transition is found at the topmost valence band edge (VBE), which is commonly
associated with the Zhang-Rice bound state. This VBE state strengthens in the
AFM phase, but only for the minority spin component, which is subject to
stronger fluctuations. A similar hybridized VBE state also appears in the DFT
single-particle description of the AFM phase, but gets much stronger and
acquires a well-defined energy in the eDMFT description.",1909.09189v1
2020-12-02,Ballistic transport through quantum point contacts of multi-orbital oxides,"Linear and non-linear transport properties through an atomic-size point
contact based on oxides two-dimensional electron gas is examined using the
tight-binding method and the $\mathbf{k\cdot p}$ approach. The ballistic
transport is analyzed in contacts realized at the (001) interface between band
insulators $LaAlO_3$ and $SrTiO_3$ by using the Landauer-B\""uttiker method for
many sub-bands derived from three Ti 3d orbitals ($d_{yz}$, $d_{zx}$ and
$d_{xy}$) in the presence of an out-of-plane magnetic field. We focus
especially on the role played by the atomic spin-orbit coupling and the
inversion symmetry breaking term pointing out three transport regimes: the
first, at low energies, involving the first $d_{xy}$-like sub-bands, where the
conductance quantization is robust; a second one, at intermediate energies,
entailing further $d_{xy}$-like sub-bands, where the sub-band splitting induced
by the magnetic field is quenched; the third one, where the mixing between
light $d_{xy}$-like, heavy $d_{yz}$-like and $d_{zx}$-like sub-bands is so
strong that the conductance plateaus turn out to be very narrow. Very good
agreement is found with recent experiments exploring the transport properties
at low energies.",2012.01395v1
2017-05-31,Tuning of Magnetic and Electrical Properties in Complex oxide Thin Films Deposited By Pulsed Laser Deposition,"Lanthanum manganite, LaMnO (LMO) is the parent compound for a class of hole
doped(e.g. La1-xCaxMnO3, La1-xSrxMnO3) and electron doped (e.g. . La1-xCexMnO3,
La1-xSnxMnO3) perovskite complex oxide materials. Strong correlation between
the spin,lattice, charge and orbital degrees of freedom is a hallmark of these
class of materials (popularly known as manganites). Competition and interplay
of these degrees of freedom lead to a wide range of interesting electronic
behavior including half-metallicity, colossal magneto-resistivity, etc.
Although a lot of experimental research has been carried out on the hole doped
and the electron doped counterparts, the parent system LMO remains less
investigated. This could be attributed to the difficulty in making
stoichiometric LMO (whether in bulk polycrystalline, single crystals or thin
films). There exists phenomenon like double-exchange (DE) and
anti-ferromagnetic super-exchange (SE) interactions which leads to
ferromagnetism in LMO thin films. This project work is aimed at the fabrication
and characterization of thin films of stoichiometric LMO and their structural,
magnetic and electrical studies.",1705.11003v1
2018-03-19,Clear variation of spin splitting by changing electron distribution at non-magnetic metal/Bi2O3 interfaces,"Large spin splitting at Rashba interface, giving rise to strong spin-momentum
locking, is essential for efficient spin-to-charge conversion. Recently, a
Cu/Bismuth oxide (Bi2O3) interface has been found to exhibit an efficient
spin-to-charge conversion similar to a Ag/Bi interface with large Rashba spin
splitting. However, the guiding principle of designing the metal/oxide
interface for the efficient conversion has not been clarified yet. Here we
report strong non-magnetic (NM) material dependence of spin splitting at
NM/Bi2O3 interfaces. We employed spin pumping technique to inject spin current
into the interface and evaluated the magnitude of interfacial spin-to-charge
conversion. We observed large modulation and sign change in conversion
coefficient which corresponds to the variation of spin splitting. Our
experimental results together with first-principles calculations indicate that
such large variation is caused by material dependent electron distribution near
the interface. The results suggest that control of interfacial electron
distribution by tuning the difference in work function across the interface may
be an effective way to tune the magnitude and sign of spin-to-charge conversion
and Rashba parameter at interface.",1803.06789v1
2018-08-07,"Development of Ferromagnetic Fluctuations in Heavily Overdoped (Bi,Pb)_2_Sr_2_CuO_6+delta_ Copper Oxides","We demonstrate the presence of ferromagnetic (FM) fluctuations in the
superconducting and non-superconducting heavily overdoped regimes of
high-temperature superconducting copper oxides, using
(Bi,Pb)_2_Sr_2_CuO_6+delta_ (Bi-2201) single crystals. Magnetization curves
exhibit a tendency to be saturated in high magnetic fields at low temperatures
in the heavily overdoped crystals, which is probably a precursor phenomenon of
a FM transition at a lower temperature. Muon spin relaxation detects the
enhancement of spin fluctuations at high temperatures below 200 K.
Correspondingly, the ab-plane resistivity follows a 4/3 power law in a wide
temperature range, which is characteristic of metals with two-dimensional FM
fluctuations due to itinerant electrons. As the Wilson ratio evidences the
enhancement of spin fluctuations with hole doping in the heavily overdoped
regime, it is concluded that two-dimensional FM fluctuations reside in the
heavily overdoped Bi-2201 cuprates, which is probably related to the decrease
in the superconducting transition temperature in the heavily overdoped
cuprates.",1808.02317v1
2018-08-17,Electromagnon excitation in cupric oxide measured by Fabry-Pérot enhanced terahertz Mueller matrix ellipsometry,"Here we present the use of Fabry-P\'erot enhanced terahertz (THz) Mueller
matrix ellipsometry to measure an electromagnon excitation in monoclinic cupric
oxide (CuO). As a magnetically induced ferroelectric multiferroic, CuO exhibits
coupling between electric and magnetic order. This gives rise to special
quasiparticle excitations at THz frequencies called electromagnons. In order to
measure the electromagnons in CuO, we exploit single-crystal CuO as a THz
Fabry-P\'erot cavity to resonantly enhance the excitation's signature. This
enhancement technique enables the complex index of refraction to be extracted.
We observe a peak in the absorption coefficient near 0.705 THz and 215 K, which
corresponds to the electromagnon excitation. This absorption peak is observed
along only one major polarizability axis in the monoclinic a-c plane. We show
the excitation can be represented using the Lorentz oscillator model, and
discuss how these Lorentz parameters evolve with temperature. Our findings are
in excellent agreement with previous characterizations by THz time-domain
spectroscopy (THz-TDS), which demonstrates the validity of this enhancement
technique.",1808.06005v1
2019-02-19,Superexchange interactions between spin-orbit-coupled $j\!\approx\!1/2$ ions in oxides with face-sharing ligand octahedra,"Using ab initio wave-function-based calculations, we provide valuable
insights with regard to the magnetic exchange in 5$d$ and 4$d$ oxides with
face-sharing ligand octahedra, BaIrO$_3$ and BaRhO$_3$. Surprisingly strong
antiferromagnetic Heisenberg interactions as large as 400 meV are computed for
idealized iridate structures with 90$^{\circ}$ Ir-O-Ir bond angles and in the
range of 125 meV for angles of 80$^{\circ}$ as measured experimentally in
BaIrO$_3$. These estimates exceed the values derived so far for corner-sharing
and edge-sharing systems and motivate more detailed experimental investigations
of quantum magnets with extended 5$d$/4$d$ orbitals and networks of
face-sharing ligand cages. The strong electron-lattice couplings evidenced by
our calculations suggest rich phase diagrams as function of strain and
pressure, a research direction with much potential for materials of this type.",1902.07269v2
2019-04-07,Polarity and spin-orbit coupling induced large interfacial exchange coupling an asymmetric charge transfer in iridate-manganite heterostructure,"Charge transfer is of particular importance in manipulating the interface
physics in transition-metal oxide heterostructures. In this work, we have
fabricated epitaxial bilayers composed of polar 3d LaMnO3 and nonpolar 5d
SrIrO3. Systematic magnetic measurements reveal an unexpectedly large exchange
bias effect in the bilayer, together with a dramatic enhancement of the
coercivity of LaMnO3. Based on first-principles calculations and x-ray
absorption spectroscopy measurements, such a strong interfacial magnetic
coupling is found closely associated with the polar nature of LaMnO3 and the
strong spin-orbit interaction in SrIrO3, which collectively drives an
asymmetric interfacial charge transfer and leads to the emergence of an
interfacial spin glass state. Our study provides new insight into the charge
transfer in transition-metal oxide heterostructures and offers a novel means to
tune the interfacial exchange coupling for a variety of device applications.",1904.03613v2
2019-12-17,Tuning Crystal Field Potential by Orbital Dilution in $d^4$ Oxides,"We investigate the interplay between Coulomb driven orbital order and
octahedral distortions in strongly correlated Mott insulators due to orbital
dilution, i.e., doping by metal ions without an orbital degree of freedom. In
particular, we focus on layered transition metal oxides and study the effective
spin-orbital exchange due to $d^3$ substitution at $d^4$ sites. The structure
of the $d^3-d^4$ spin-orbital coupling between the impurity and the host in the
presence of octahedral rotations favors a distinct type of orbital polarization
pointing towards the impurity and outside the impurity--host plane. This yields
an effective lattice potential that generally competes with that associated
with flat octahedra and, in turn, can drive an inversion of the crystal field
interaction.",1912.07975v1
2020-06-26,Spin and orbital Edelstein effect in an oxide two-dimensional electron gas: theory and application to AlO$_x$/SrTiO$_{3}$,"The Edelstein effect provides the purely electrical generation and control of
a homogeneous magnetization in primarily nonmagnetic materials with broken
inversion symmetry. Usually, only the spin density response to an external
electric field is discussed. Here, we report on the electrically induced
magnetization containing spin as well as orbital contributions in the
topological oxide two-dimensional electron gas at the interface between
SrTiO$_3$ and AlO. We find that in this particular system the orbital Edelstein
effect exceeds the spin Edelstein effect by more than one order of magnitude.
The main reason are orbital moments of different magnitude in the
Rashba-like-split band pairs.",2006.14958v1
2020-08-12,Stabilization of a honeycomb lattice of IrO$_6$ octahedra in superlattices with ilmenite-type MnTiO$_3$,"In the quest for quantum spin liquids, thin films are expected to open the
way for the control of intricate magnetic interactions in actual materials by
exploiting epitaxial strain and two-dimensionality. However, materials
compatible with conventional thin-film growth methods have largely remained
undeveloped. As a promising candidate towards the materialization of quantum
spin liquids in thin films, we here present a robust ilmenite-type oxide with a
honeycomb lattice of edge-sharing IrO$_6$ octahedra artificially stabilized by
superlattice formation with an ilmenite-type antiferromagnetic oxide MnTiO$_3$.
The stabilized sub-unit-cell-thick Mn-Ir-O layer is isostructural to MnTiO$_3$,
having the atomic arrangement corresponding to ilmenite-type MnTiO$_3$ not
discovered yet. By spin Hall magnetoresistance measurements, we found that
antiferromagnetic ordering in the ilmenite Mn sublattice is suppressed by
modified magnetic interactions in the MnO$_6$ planes via the IrO$_6$ planes.
These findings lay the foundation for the creation of two-dimensional Kitaev
candidate materials, accelerating the discovery of exotic physics and
applications specific to quantum spin liquids.",2008.05236v2
2021-07-30,Emergence of Ferromagnetism Through the Metal-Insulator Transition in Undoped Indium Tin Oxide Films,"We present a detailed study of the emergence of bulk ferromagnetism in low
carrier density samples of undoped indium tin oxide (ITO). We used annealing to
increase the density of oxygen vacancies and change sample morphology without
introducing impurities through the metal insulator transition (MIT). We
utilized a novel and highly sensitive ""Corbino-disk torque magnetometry""
technique to simultaneously measure the thermodynamic and transport effects of
magnetism on the same sample after successive annealing. With increased sample
granularity, carrier density increased, the sample became more metallic, and
ferromagnetism appeared as resistance approached the MIT. Ferromagnetism was
observed through the detection of magnetization hysteresis, anomalous Hall
effect (AHE), and hysteretic magnetoresistance. A sign change of the AHE as the
MIT is approached may elucidate the interplay between the impurity band and the
conduction band in the weakly insulating side of the MIT.",2107.14463v1
2021-08-17,Importance of the many-body effects for structural properties of the novel iron oxide: Fe$_2$O,"The importance of many-body effects on electronic and magnetic properties and
stability of different structural phases was studied in novel iron oxide -
Fe$_2$O. It was found that while Hubbard repulsion hardly affects the
electronic spectrum of this material ($m^*/m \sim 1.2$), but it strongly
changes its phase diagram shifting critical pressures of structural transitions
to much lower values. Moreover, one of the previously obtained in the density
functional theory (DFT) structures (P$\bar 3$m1) becomes energetically unstable
if many-body effects are taken into consideration. It is shown that this is an
account of magnetic moment fluctuations in the DFT+DMFT approach, which
strongly contributes to modification of the phase diagram of Fe$_2$O.",2108.07645v1
2021-12-21,Pyrochlore Oxide Hg2Os2O7 on Verge of Metal-Insulator Boundary,"Semimetallic osmium pyrochlore oxide Cd2Os2O7 undergoes a magnetic transition
to an all-in-all-out (AIAO)-type order at 227 K, followed by a crossover to an
AIAO insulator at around 210 K. Here, we studied the isostructural and
isoelectronic compound Hg2Os2O7 through thermodynamic measurements, muSR
spectroscopy and neutron diffraction experiments. A similar magnetic
transition, probably to an AIAO-type order, was observed at 88 K, while the
resistivity showed a decrease at the transition and remained metallic down to 2
K. Thus, the ground state of Hg2Os2O7 is most likely an AIAO semimetal, which
is analogous to the intermediate-temperature state of Cd2Os2O7. Hg2Os2O7 exists
on the verge of the metal-insulator boundary on the metal side and provides an
excellent platform for studying the electronic instability of 5d electrons with
moderate electron correlations and strong spin-orbit interactions.",2112.11558v1
2022-02-03,Synthesis of Core/Shell Ti/TiOx Photocatalyst via Single-Mode Magnetic Microwave Assisted Direct Oxidation of TiH2,"Submicron core/shell Ti/TiOx photocatalyst is successfully synthesized via
single-mode magnetic microwave (SMMW) assisted direct oxidation of planetary
ball-milled TiH2. The thickness of TiOx shell including highly concentrated
defects such as Ti3+ and/or oxygen vacancies is controllable in the range from
6 to over 18 nm by varying the treatment time in the SMMW assisted reaction. In
addition to its quite narrow optical bandgap (1.34-2.69 eV) and efficient
visible-light absorption capacity, the submicron Ti/TiOx particle exhibits
superior photocatalytic performance towards H2 production from water under both
UV and visible-light irradiation to compare with a commercial TiO2
photocatalyst (P-25). Such excellent performance can be achieved by the
synergetic effect of enhancement in visible light absorption capacity and
photo-excited carrier separation because of the highly concentrated surface
defects and the specific Ti/TiOx core/shell structure, respectively.",2202.01363v1
2022-03-07,Understanding the growth of high-aspect-ratio grains in granular L10-FePt thin-film magnetic media,"A systematic investigation has been performed to optimize the microstructure
of $\mathrm{L1_0-FePt-SiO_x}$ granular thin film as recording media for
heat-assisted magnetic recording. The FePt-BN nucleation layer, which is stable
even at $700^\circ \text{C}$, is used to control the grain sizes and
microstructure during high-temperature processing. The study finds that films
of high-aspect-ratio FePt grains with well-formed silicon oxide (SiOx) grain
boundaries require the grading of the deposition temperature during film growth
as well as the grading of the silicon oxide concentration. Well-isolated
columnar grains of $\mathrm{L1_0-FePt}$ with an average height greater than 11
nm and diameters less than 7 nm have been achieved. Transmission electron
microscopy (TEM) analysis of the microstructures of samples produced under a
variety of non-optimal conditions is presented to show how the microstructure
of the films depends on each of the sputtering parameters.",2203.03496v1
2022-04-04,Strain Effect on Air-Stability of Monolayer CrSe2,"The discovery of two dimensional (2D) magnetic materials has brought great
research value for spintronics and data storage devices. However, their
air-stability as well as the oxidation mechanism has not been unveiled, which
limits their further applications. Here, by first-principles calculations, we
carried out a detailed study on the oxidation process of monolayer CrSe2 and
biaxial tensile strain effect. We found dissociation process of O2 on pristine
CrSe2 sheet is an endothermic reaction with a reaction energy barrier of 0.53
eV, indicating its thermodynamics stability. However, such a process becomes
exothermic under a biaxial tensile strain reaching 1%, accompanying with a
decreased reaction barrier, leading to reduced stability. These results
manifest that in-plane strain plays a significant role in modifying
air-stability in CrSe2 and shed considerable light on searching appropriate
substrate to stabilize 2D magnetic materials.",2204.01400v2
2022-09-29,Evaluation of Neel temperatures from fully self-consistent broken-symmetry GW and high-temperature expansion: application to cubic transition-metal oxides,"Using fully self-consistent thermal broken-symmetry GW we construct effective
magnetic Heisenberg Hamiltonians for a series of transition metal oxides (NiO,
CoO, FeO, MnO), capturing a rigorous but condensed description of the magnetic
states. Then applying high-temperature expansion, we find the decomposition
coefficients for spin susceptibility and specific heat. The radius of
convergence of the found series determine the Neel temperature. The NiO, CoO,
and FeO contain a small ferromagnetic interaction between the nearest neighbors
(NN) and the dominant antiferromagnetic interaction between the next-nearest
neighbors (NNN). For them the derived Neel temperatures are in a good agreement
with experiment. The case of MnO is different because both NN and NNN couplings
are antiferromagnetic and comparable in magnitude, for which the error in the
estimated Neel temperature is larger, which is a signature of additional
effects not captured by electronic structure calculations.",2209.14904v2
2022-10-28,Electron-hole asymmetry of quantum collective excitations in high-$T_c$ copper oxides,"We carry out a systematic study of collective spin- and charge excitations
for the canonical single-band Hubbard, $t$-$J$-$U$, and $t$-$J$ models of
high-temperature copper-oxide superconductors, both on electron- and hole-doped
side of the phase diagram. Recently developed variational wave function
approach, combined with the expansion in inverse number of fermionic flavors,
is employed. All three models exhibit a substantial electron-hole asymmetry of
magnetic excitations, with a robust paramagnon emerging for hole-doping, in
agreement with available resonant inelastic $x$-ray scattering data for the
cuprates. The $t$-$J$ model yields additional high-energy peak in the magnetic
spectrum that is not unambiguously identified in spectroscopy. For all
considered Hamiltonians, the dynamical charge susceptibility contains a
coherent mode for both hole- and electron doping, with overall bandwidth
renormalization controlled by the on-site Coulomb repulsion. Away from the
strong-coupling limit, the antiferromagnetic ordering tendency is more
pronounced on electron-doped side of the phase diagram.",2210.16109v3
2022-11-28,Hallmarks of non-trivial topology in Josephson junctions based on oxide nanochannels,"We investigate the topological properties of a Josephson junction obtained by
constraining a two-dimensional electron gas at oxide interface to form a
quasi-1D conductor. We reveal an anomalous critical current behaviour with a
magnetic field applied perpendicular to the Rashba spin-orbit one. We relate
the observed critical current enhancement at small magnetic fields with a
non-trivial topology, accompanied by Majorana bound states (MBSs) pinned at the
edges of the superconducting leads. Signatures of MBSs also include a sawtooth
profile in the current-phase relation. Our findings allow to recognize
fingerprints of topological superconductivity in non-centrosymmetric materials
and confined systems with Rashba spin-orbit interaction, and to explain recent
experimental observations for which a microscopic description is still lacking.",2211.15433v1
2023-05-06,Giant magnetostriction in La2CoMnO6 synthesized by microwave irradiation,"Polycrystalline insulating ferromagnetic double perovskite La2CoMnO6
possessing monoclinic structure and a high ferromagnetic Curie temperature (TC
= 222 K) was rapidly synthesized ( 30 min) by irradiating stoichiometric
mixture of oxides with the microwave. The sample exhibits negative
magnetostriction, i.e., contraction of length along the magnetic field
direction in the ferromagnetic state. At 10 K, the parallel magnetostriction
does not show saturation up to a magnetic field of 50 kOe where it reaches 610
ppm which is one of the highest values of magnetostriction found so far among
perovskite oxides with 3d ions. The magnitude of magnetostriction decreases
monotonically as the temperature increases and becomes negligible above TC. The
giant magnetostriction in this double perovskite is suggested to originate from
large spin-orbit coupling associated with Co2+ (d7) cation. The obtained
magnetostriction value is comparable to 630 ppm in an identical composition
obtained through solid-state reaction over several days in a conventional
furnace which indicates the advantages of microwave-assisted synthesis in
saving reaction time and electric power without deteriorating physical
properties.",2305.03886v1
2023-07-10,Porous CrO$_2$: a ferromagnetic half-metallic member in sparse hollandite oxide family,"A stable polymorph of CrO$_2$ is predicted using PBE+U method. The porous
material is isostructural with $\alpha$-MnO$_2$ making it the second transition
metal oxide in sparse hollandite group of materials. However, unlike the
anti-ferromagnetic semiconducting character of the $\alpha$-MnO$_2$, it is
found to be a ferromagnetic half-metal. At Fermi level, the hole pocket has
ample contribution from O-2$p$ orbital, though, the electron pocket is mostly
contributed by Cr-3$d_{xy}$ and Cr-3d$_{x^2-y^2}$. A combination of negative
charge transfer through orbital mixing and extended anti-bonding state near
Fermi level is responsible for the half-metallic ferromagnetic character of the
structure. A comparative study of rutile and hollandite CrO$_2$ and hollandite
MnO$_2$ structures delineate the interplay between structural, electronic and
magnetic properties. The material shows a robust magnetic character under
hydrothermal pressure, as well as, the band topology is conserved under
uniaxial strain. Moderate magneto-crystalline anisotropy is observed and it
shows a correspondence with the anisotropy of elastic constants.",2307.04584v1
2023-08-13,The impact of the near-surface region on the interpretation of x-ray absorption spectroscopy,"Transition metal oxides (TMOs) exhibit a broad spectrum of electronic,
magnetic, and optical properties, making them intriguing materials for various
technological applications. Soft x-ray absorption spectroscopy (XAS) is widely
used to study TMOs, shedding light on their chemical state, electronic
structure, orbital polarization, element-specific magnetism, and more.
Different XAS acquisition modes feature different information depth regimes in
the sample. Here, we employ two XAS acquisition modes, having surface-sensitive
versus bulk probing depths, on the prototypical TMO SrVO3. We illustrate and
elucidate a strong apparent discrepancy between the different modes,
emphasizing the impact of the near-surface region on the interpretation of XAS
data. These findings highlight the importance of the acquisition mode selection
in XAS analysis. Moreover, the results highlight the role of the near-surface
region not only in the characterization of TMOs, but also in the design of
future nanoscale oxide electronics.",2308.06724v1
2023-11-14,Spin-phonon coupling suppressing the structural transition in perovskite-like oxide,"Multifunctional properties in quantum systems require the interaction between
different degrees of freedom. As such, spin-phonon coupling emerges as an ideal
mechanism to tune multiferroicity, magnetism, and magnetoelectric response. In
this letter, we demonstrate and explain, based on theoretical and experimental
analyses, an unusual manifestation of spin-phonon coupling, i.e., prevention of
a ferroelastic structural transition, and locking of high-temperature R-3m
phase in a magnetically frustrated perovskite-like oxide Ba2NiTeO6. We present
Ba2NiTeO6 as a prototype example among its family where long-range
antiferromagnetic structure couples with a low-frequency Eg mode (at 55 cm-1)
that exhibits a large anharmonicity. Our findings establish that spin-phonon
coupling clearly suppresses the phonon anharmonicity preventing the structural
phase transition from the R-3m to the C2/m phase in Ba2NiTeO6.",2311.08028v1
2024-02-09,Copper phosphate micro-flowers coated with indocyanine green and iron oxide nanoparticles for in vivo localization optoacoustic tomography and magnetic actuation,"Efficient drug delivery is a major challenge in modern medicine and
pharmaceutical research. Micrometer-scale robots have recently been proposed as
a promising venue to amplify precision of drug administration. Remotely
controlled microrobots sufficiently small to navigate through microvascular
networks can reach any part of the human body, yet real-time tracking is
crucial for providing precise guidance and verifying successful arrival at the
target. In vivo deep-tissue monitoring of individual microrobots is currently
hampered by the lack of sensitivity and/or spatio-temporal resolution of
commonly used clinical imaging modalities. We synthesized biocompatible and
biodegradable copper phosphate micro-flowers loaded with indocyanine green and
iron oxide nanoparticles to enable in vivo individual detection with
localization optoacoustic tomography. We demonstrate magnetic actuation and
optoacoustic tracking of these decorated micro-flowers at a per-particle level.
Functional super-resolution imaging achieved via tracking intravenously
injected particles provides a means of identifying microvascular targets and
quantifying blood flow, while the versatile carrying capacity can be further
exploited for transporting multiple types of drug formulations.",2402.06749v1
2009-05-20,Measuring magnetic profiles at manganite surfaces with monolayer resolution,"The performance of manganite-based magnetic tunnel junctions (MTJs) has
suffered from reduced magnetization present at the junction interfaces that is
ultimately responsible for the spin polarization of injected currents; this
behavior has been attributed to a magnetic ""dead layer"" that typically extends
a few unit cells into the manganite. X-ray magnetic scattering in resonant
conditions (XRMS) is one of the most innovative and effective techniques to
extract surface or interfacial magnetization profiles with subnanometer
resolution, and has only recently been applied to oxide heterostructures. Here
we present our approach to characterizing the surface and interfacial
magnetization of such heterostructures using the XRMS technique, conducted at
the BEAR beamline (Elettra synchrotron, Trieste). Measurements were carried out
in specular reflectivity geometry, switching the left/right elliptical
polarization of light as well the magnetization direction in the scattering
plane. Spectra were collected across the Mn L2,3 edge for at least four
different grazing angles in order to better analyse the interference phenomena.
The resulting reflectivity spectra have been carefully fit to obtain the
magnetization profiles, minimizing the number of free parameters as much as
possible. Optical constants of the samples (real and imaginary part of the
refractive index) in the interested frequency range are obtained through
absorption measurements in two magnetization states and subsequent
Kramers-Kronig transformation, allowing quantitative fits of the magnetization
profile at different temperatures. We apply this method to the study of
air-exposed surfaces of epitaxial La2/3Sr1/3MnO3 (001) films grown on SrTiO3
(001) substrates.",0905.3204v1
2016-09-17,Magnetic-anisotropy induced spin blockade in a single-molecule transistor,"We present a new mechanism for a spin blockade effect associated with a
change in the type of magnetic anisotropy over oxidation state in a single
molecule transistor, by taking an example of an individual
Eu$_{2}$(C$_{8}$H$_{8}$)$_{3}$ molecule weakly coupled to non-magnetic
electrodes without linker groups. The molecule switches its magnetization
direction from in-plane to out-of-plane when it is charged. In other words, the
magnetic anisotropy of the molecule changes from easy plane to easy axis when
the molecule is charged. By solving the master equation based on model
Hamiltonian, we find that current through the molecule is highly suppressed at
low bias independently of gate voltage due to the interplay between spin
selection rules and the change in the type of magnetic anisotropy. Transitions
between the lowest magnetic levels in successive charge states are forbidden
because the magnetic levels differ by $|\Delta M| > 1/2$ due to the change in
the type of magnetic anisotropy, although the total spins differ by $|\Delta
S|=1/2$. This current suppression can be lifted by significant B field, and the
threshold B field varies as a function of the field direction and the strength
of magnetic anisotropy. The spin blockade effect shed light on switching the
magnetization direction by non-spin-polarized current and on exploring effects
of this property coupled to other molecular degrees of freedom.",1609.05269v1
2017-07-13,Electric field controlled magnetic exchange bias and magnetic state switching at room temperature in Ga doped α-Fe2O3 oxide,"We have developed a new magnetoelectric material based on Ga doped
{\alpha}-Fe2O3 in rhombohedral phase. The material is a canted ferromagnet at
room temperature and showing magneto-electric properties. The experimental
results of electric field controlled magnetic state provided a direct evidence
of room temperature magnetoelectric coupling in Ga doped {\alpha}-Fe2O3 system.
Interestingly, (un-doped) {\alpha}-Fe2O3 system does not exhibit any electric
field controlled magnetic exchange bias shift, but Ga doped {\alpha}-Fe2O3
system has shown an extremely high electric field induced magnetic exchange
bias shift up to the value of 1120 Oe (positive). On the other hand, in a first
time, we report the electric field controlled magnetic state switching both in
{\alpha}-Fe2O3 and in Ga doped {\alpha}-Fe2O3 systems. The switching of
magnetic state is highly sensitive to ON and OFF modes, as well as to the
change of polarity of applied electric voltage during in-field magnetic
relaxation experiments. The switching of magnetic state to upper level for
positive electric field and to down level for negative electric field indicates
that electric and magnetic orders are coupled in the Ga doped hematite system.
Such material is of increasing demand in today for multifunctional applications
in next generation magnetic sensor, switching, non-volatile memory and
spintronic devices.",1707.04496v1
2020-01-16,Tailoring magnetic order via atomically stacking 3d/5d electrons,"The ability to tune magnetic orders, such as magnetic anisotropy and
topological spin texture, is desired in order to achieve high-performance
spintronic devices. A recent strategy has been to employ interfacial
engineering techniques, such as the introduction of spin-correlated interfacial
coupling, to tailor magnetic orders and achieve novel magnetic properties. We
chose a unique polar-nonpolar LaMnO3/SrIrO3 superlattice because Mn (3d)/Ir
(5d) oxides exhibit rich magnetic behaviors and strong spin-orbit coupling
through the entanglement of their 3d and 5d electrons. Through magnetization
and magnetotransport measurements, we found that the magnetic order is
interface-dominated as the superlattice period is decreased. We were able to
then effectively modify the magnetization, tilt of the ferromagnetic easy axis,
and symmetry transition of the anisotropic magnetoresistance of the
LaMnO3/SrIrO3 superlattice by introducing additional Mn (3d) and Ir (5d)
interfaces. Further investigations using in-depth first-principles calculations
and numerical simulations revealed that these magnetic behaviors could be
understood by the 3d/5d electron correlation and Rashba spin-orbit coupling.
The results reported here demonstrate a new route to synchronously engineer
magnetic properties through the atomic stacking of different electrons,
contributing to future applications.",2001.05821v2
2021-03-30,Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films,"Magnetic insulators are important materials for a range of next generation
memory and spintronic applications. Structural constraints in this class of
devices generally require a clean heterointerface that allows effective
magnetic coupling between the insulating layer and the conducting layer.
However, there are relatively few examples of magnetic insulators which can be
synthesized with surface qualities that would allow these smooth interfaces and
precisely tuned interfacial magnetic exchange coupling which might be
applicable at room temperature. In this work, we demonstrate an example of how
the configurational complexity in the magnetic insulator layer can be used to
realize these properties. The entropy-assisted synthesis is used to create
single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a
range of strain states. These films show smooth surfaces, high resistivity, and
strong magnetic responses at room temperature. Local and global magnetic
measurements further demonstrate how strain can be used to manipulate magnetic
texture and anisotropy. These findings provide insight into how precise
magnetic responses can be designed using compositionally complex materials that
may find application in next generation magnetic devices.",2103.16722v1
2023-10-09,Super-resolution diamond magnetic microscopy of superparamagnetic nanoparticles,"Scanning-probe and wide-field magnetic microscopes based on Nitrogen-Vacancy
(NV) centers in diamond have enabled remarkable advances in the study of
biology and materials, but each method has drawbacks. Here, we implement an
alternative method for nanoscale magnetic microscopy based on optical control
of the charge state of NV centers in a dense layer near the diamond surface. By
combining a donut-beam super-resolution technique with optically detected
magnetic resonance spectroscopy, we imaged the magnetic fields produced by
single 30-nm iron-oxide nanoparticles. The magnetic microscope has a lateral
spatial resolution of ~100 nm, and it resolves the individual magnetic dipole
features from clusters of nanoparticles with interparticle spacings down to
~190 nm. The magnetic feature amplitudes are more than an order of magnitude
larger than those obtained by confocal magnetic microscopy due to the smaller
characteristic NV-nanoparticle distance within nearby sensing voxels. We
analyze the magnetic point-spread function and sensitivity as a function of the
microscope's spatial resolution and identify sources of background fluorescence
that limit the present performance, including diamond second-order Raman
emission and imperfect NV charge-state control. Our method, which uses less
than 10 mW laser power and can be parallelized by patterned illumination,
introduces a new format for nanoscale magnetic imaging.",2310.05436v1
2023-06-19,Onion-like Fe3O4/MgO/CoFe2O4 magnetic nanoparticles: new ways to control magnetic coupling between soft/hard phases,"The control of the magnetization inversion dynamics is one of the main
challenges driving the design of new nanostructured magnetic materials for
magnetoelectronic applications. Nanoparticles with onion-like architecture
offer a unique opportunity to expand the possibilities allowing to combine
different phases at the nanoscale and also modulate the coupling between
magnetic phases by introducing spacers in the same structure. Here we report
the fabrication, by a three-step high temperature decomposition method, of
Fe3O4/MgO/CoFe2O4 onio-like nanoparticles and their detailed structural
analysis, elemental compositional maps and magnetic response. The
core/shell/shell nanoparticles present epitaxial growth and cubic shape with
overall size of (29+-6) nm. These nanoparticles are formed by cubic iron oxide
core of (22+-4) nm covered by two shells, the inner of magnesium oxide and the
outer of cobalt ferrite of ~1 and ~2.5 nm of thickness, respectively. The
magnetization measurements show a single reversion magnetization curve and the
enhancement of the coercivity field, from HC~608 Oe for the Fe3O4/MgO to
HC~5890 Oe to the Fe3O4/MgO/CoFe2O4 nanoparticles at T=5 K, ascribed to the
coupling between both ferrimagnetic phases with a coupling constant of =2
erg/cm2. The system also exhibits exchange bias effect, where the exchange bias
field increases up to HEB~2850 Oe at 5 K accompanied with the broadening of the
magnetization loop of HC~6650 Oe. This exchange bias effect originates from the
freezing of the surface spins below the freezing temperature TF=32 K that
pinned the magnetic moment of the cobalt ferrite shell.",2306.13108v1
2017-01-28,Spin glass behavior in frustrated quantum spin system CuAl2O4 with a possible orbital liquid state,"CuAl2O4 is a normal spinel oxide having quantum spin, S=1/2 for Cu2+. It is a
rather unique feature that the Cu2+ ions of CuAl2O4 sit at a tetrahedral
position, not like the usual octahedral position for many oxides. At low
temperatures, it exhibits all the thermodynamic evidence of a quantum spin
glass. For example, the polycrystalline CuAl2O4 shows a cusp centered at ~2 K
in the low-field dc magnetization data and a clear frequency dependence in the
ac magnetic susceptibility while it displays logarithmic relaxation behavior in
a time dependence of the magnetization. At the same time, there is a peak at
~2.3 K in the heat capacity, which shifts towards higher temperature with
magnetic fields. On the other hand, there is no evidence of new superlattice
peaks in the high-resolution neutron powder diffraction data when cooled from
40 to 0.4 K. This implies that there is no long-ranged magnetic order down to
0.4 K, thus confirming a spin glass-like ground state for CuAl2O4.
Interestingly, there is no sign of structural distortion either although Cu2+
is a Jahn-Teller active ion. Thus, we claim that an orbital liquid state is the
most likely ground state in CuAl2O4. Of further interest, it also exhibits a
large frustration parameter, f = Theta_CW/Tm ~67, one of the largest values
reported for spinel oxides. Our observations suggest that CuAl2O4 should be a
rare example of a frustrated quantum spin glass with a good candidate for an
orbital liquid state.",1701.08272v1
2020-02-19,Ion-Irradiation-Induced Cobalt/Cobalt Oxide Heterostructures: Printing 3D Interfaces,"Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers
offer unique properties due to spin-orbit coupling and symmetry breaking,
yielding effects such as exchange bias, perpendicular magnetic anisotropy,
spin-pumping, spin-transfer torques, conversion between charge and spin
currents and vice-versa. These interfacial phenomena play crucial roles for
magnetic data storage and transfer applications, which require forming FM
nano-structures embedded in non-ferromagnetic matrices. Here, we investigate
the possiblity of creating such nano-structures by ion-irradiation. We study
the effect of lateral confinement on the ion-irradiation-induced reduction of
non-magnetic metal oxides (e.g., antiferro- or paramagnetic) to form
ferromagnetic metals. Our findings are later exploited to form 3-dimensional
magnetic interfaces between Co, CoO and Pt by spatially-selective irradiation
of CoO/Pt multilayers. We demonstrate that the mechanical displacement of the O
atoms plays a crucial role during the reduction from insulating,
non-ferromagnetic cobalt oxides to metallic cobalt. Metallic cobalt yields both
perpendicular magnetic anisotropy in the generated Co/Pt nano-structures, and,
at low temperatures, exchange bias at vertical interfaces between Co and CoO.
If pushed to the limit of ion-irradiation technology, this approach could, in
principle, enable the creation of densely-packed, atomic scale ferromagnetic
point-contact spin-torque oscillator (STO) networks, or conductive channels for
current-confined-path based current perpendicular-to-plane giant
magnetoresistance read-heads.",2002.08090v1
2020-04-01,Perovskite-type cobalt oxide at the multiferroic Co/Pb Zr$_{0.2}$Ti$_{0.8}$O$_{3}$ interface,"Magnetic Tunnel Junctions whose basic element consists of two ferromagnetic
electrodes separated by an insulating non-magnetic barrier have become
intensely studied and used in non-volatile spintronic devices. Since ballistic
tunnel of spin-polarized electrons sensitively depends on the chemical
composition and the atomic geometry of the lead/barrier interfaces their proper
design is a key issue for achieving the required functionality of the devices
such as e.g. a high tunnel magneto resistance. An important leap in the
development of novel spintronic devices is to replace the insulating barrier by
a ferroelectric which adds new additional functionality induced by the
polarization direction in the barrier giving rise to the tunnel electro
resistance (TER). The multiferroic tunnel junction
Co/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$/La$_{2/3}$Sr$_{1/3}$MnO$_3$ (Co/PZT/LSMO)
represents an archetype system for which - despite intense studies - no
consensus exists for the interface geometry and their effect on transport
properties. Here we provide the first analysis of the Co/PZT interface at the
atomic scale using complementary techniques, namely x-ray diffraction and
extended x-ray absorption fine structure in combination with x-ray magnetic
circular dichroism and ab-initio calculations. The Co/PZT interface consists of
one perovskite-type cobalt oxide unit cell [CoO$_{2}$/CoO/Ti(Zr)O$_{2}$] on
which a locally ordered cobalt film grows. Magnetic moments (m) of cobalt lie
in the range between m=2.3 and m=2.7$\mu_{B}$, while for the interfacial
titanium atoms they are small (m=+0.005 $\mu_{B}$) and parallel to cobalt which
is attributed to the presence of the cobalt-oxide interface layers. These
insights into the atomistic relation between interface and magnetic properties
is expected to pave the way for future high TER devices.",2004.00489v1
2007-03-20,Real-time observation of oxidation and photo-oxidation of rubrene thin films by spectroscopic ellipsometry,"We follow in real-time and under controlled conditions the oxidation of the
organic semiconductor rubrene grown on SiO_2 using spectroscopic ellipsometry.
We derive the complex dielectric function epsilon_1 + i epsilon_2 for pristine
and oxidized rubrene showing that the oxidation is accompanied by a significant
change of the optical properties, namely the absorption. We observe that
photo-oxidation of rubrene is orders of magnitude faster than oxidation without
illumination. By following different absorption bands (around 2.5eV and 4.0eV
for pristine rubrene and around 4.9eV for oxidized rubrene) we infer that the
observed photo-oxidation of these films involves non-Fickian diffusion
mechanisms.",0703522v1
2020-01-29,A Hybrid Density Functional Theory Benchmark Study on Lithium Manganese Oxides,"The lithium manganese oxide spinel Li$_x$Mn$_2$O$_4$, with $0\leq x\leq 2$,
is an important example for cathode materials in lithium ion batteries.
However, an accurate description of Li$_x$Mn$_2$O$_4$ by first-principles
methods like density functional theory is far from trivial due to its complex
electronic structure, with a variety of energetically close electronic and
magnetic states. It was found that the local density approximation as well as
the generalized gradient approximation (GGA) are unable to describe
Li$_x$Mn$_2$O$_4$ correctly. Here, we report an extensive benchmark for
different Li$_x$Mn$_y$O$_z$ systems using the hybrid functionals PBE0 and
HSE06, as well as the recently introduced local hybrid functional PBE0r. We
find that all of these functionals yield energetic, structural, electronic, and
magnetic properties in good agreement with experimental data. The notable
benefit of the PBE0r functional, which relies on on-site Hartree-Fock exchange
only, is a much reduced computational effort that is comparable to GGA
functionals. Furthermore, the Hartree-Fock mixing factors in PBE0r are smaller
than in PBE0, which improves the results for (lithium) manganese oxides. The
investigation of Li$_x$Mn$_2$O$_4$ shows that two Mn oxidation states, +III and
+IV, coexist. The Mn$^\text{III}$ ions are in the high-spin state and the
corresponding MnO$_6$ octahedra are Jahn-Teller distorted. The ratio between
Mn$^\text{III}$ and Mn$^\text{IV}$ and thus the electronic structure changes
with the Li content while no major structural changes occur in the range from
$x=0$ to $1$. This work demonstrates that the PBE0r functional provides an
equally accurate and efficient description of the investigated
Li$_x$Mn$_y$O$_z$ systems.",2001.10975v2
1995-05-03,"Magnetic Transition Temperature of (La,Sr)MnO$_3$","Using the Kondo lattice model with classical spins in infinite dimension,
  magnetic phase transition in the perovskite-type $3d$ transition-metal oxide
(La,Sr)MnO$_3$ is theoretically studied. On the Bethe lattice, the
self-consistency equations are solved exactly. Curie temperatures at the region
of double-exchange ferromagnetism $0.1 < x < 0.25$ as well as the Neel
temperature at $x=0$ are well reproduced quantitatively. Pressure effect on the
Curie temperature is also discussed.",9505009v2
1995-05-25,"Temperature Dependence of the Conductivity in (La,Sr)MnO$_3$","Using the Kondo lattice model with classical spins in infinite dimension,
conductivity in the perovskite-type $3d$ transition-metal oxide (La,Sr)MnO$_3$
is theoretically studied. Green's functions as well as spontaneous
magnetization are obtained exactly on the Bethe lattice as a function of
temperature. Conductivity is calculated from the Kubo formula. Below the Curie
temperature, resistivity as a function of magnetization is in a good agreement
with the experimental data. Anomalous behaviour in the temperature dependence
of the optical conductivity observed in (La,Sr)MnO$_3$ is also explained.",9505117v1
1996-05-21,Conductance through a Magnetic Domain Wall in Double Exchange System,"The conductance through a magnetic domain wall is calculated for the double
exchange system as a function of energy and the width of the domain wall. It is
shown that when the carrier density is low enough, the blockade is almost
complete even for the smoothly varying spin configuration, i.e., large width of
the domain wall. This result is applied to the manganese oxides.",9605130v1
1997-12-10,Pseudo-gap behavior in dynamical properties of high-Tc cuprates,"Dynamical properties of 2D antiferromagnets with hole doping are investigated
to see the effects of short range local magnetic order on the temperature
dependence of the dynamical magnetic susceptibility. We show the pseudo-gap
like behavior of the temperature dependence of the NMR relaxation rate. We also
discuss implications of the results in relations to the observed spin gap like
behavior of low-doped copper oxide high-$T_c$ superconductors.",9712104v2
1998-09-21,First Principles Investigation of Ferromagnetism and Ferroelectricity in Bismuth Manganite,"We present results of local spin density approximation (LSDA) pseudopotential
calculations for the perovskite structure oxide, bismuth manganite (BiMnO3).
The origin of the differences between bismuth manganite and other perovskite
manganites is determined by first calculating total energies and band
structures of the high symmetry cubic phase, then sequentially lowering the
magnetic and structural symmetry. Our results indicate that covalent bonding
between bismuth cations and oxygen anions stabilizes different magnetic and
structural phases compared with the rare earth manganites. This is consistent
with recent experimental results showing enhancement of charge ordering in
doped bismuth manganite.",9809282v1
1999-06-03,Microwave Absorption Peaks : Signatures of Spin Dynamics in Cuprates,"We show that a common feature of temperature-dependent microwave absorption
is the presence of absorption peaks. $ac$ loss peaks can arise when the
internal $T$-dependent magnetic relaxation time crosses the measurement
frequency. These features are observed in the \QTR{em}{insulating}
($Sr_{x}Ca_{14-x}Cu_{24}O_{41}$, $La_{5/3}Sr_{1/3}NiO_{4}$ and
$YBa_{2}Cu_{3}O_{6.0}$), \QTR{em}{pseudo-gap} ($T>T_{c}$ in underdoped
$YBa_{2}Cu_{3}O_{7-\delta}$, $Hg:1223$ and $Hg:1201$) and
\QTR{em}{superconducting} ($T<T_{c}$) states of the oxides. The commonality of
these features suggests a magnetic (spin) mechanism, rather than a
quasiparticle origin, for the so-called ``conductivity'' peaks observed in the
cuprate superconductors.",9906053v2
2000-01-20,Destruction of long-range antiferromagnetic order by hole doping,"We study the renormalization of the staggered magnetization of a
two-dimensional antiferromagnet as a function of hole doping, in the framework
of the t-J model. It is shown that the motion of holes generates decay of spin
waves into ''particle-hole'' pairs, which causes the destruction of the
long-range magnetic order at a small hole concentration. This effect is mainly
determined by the coherent motion of holes. The value obtained for the critical
hole concentration, of a few percent, is consistent with experimental data for
the doped copper oxide high-Tc superconductors.",0001289v1
2000-12-01,Theory for Phase Transitions in Insulating Vanadium Oxide,"We show that the recently proposed S=2 bond model with orbital degrees of
freedom for insulating V$_{2}$O$_{3}$ not only explains the anomalous magnetic
ordering, but also other mysteries of the magnetic phase transition. The model
contains an additional orbital degree of freedom that exhibits a zero
temperature quantum phase transtion in the Ising universality class.",0012019v3
2001-01-18,C-axis Optical Sum Rule in Josephson Coupled Vortex State,"Observed violations of the $c$-axis optical sum rule can give important
information on deviations from in-plane Fermi liquid behavior and on the nature
of interlayer coupling between adjacent copper oxide planes. Application of a
magnetic field perpendicular to these planes is another way to probe in-plane
dynamics. We find that the optical sum rule is considerably modified in the
presence of the $c$-axis magnetic field. Interlayer correlation of pancake
vortices is involved in the sum rule modification; however, details of the
vortex distribution in the plane are less important.",0101288v2
2001-10-30,Localization corrections and small-q phonon-mediated unconventional superconductivity in the cuprates,"Taking into account the first localization corrections in the
electron-impurity self-energy we study the effect of non-magnetic impurities on
unconventional superconductivity (SC) mediated by small-q electron-phonon
scattering. We show that when van Hove singularities are close to the Fermi
level making the electronic system anisotropic as in the high-$T_c$ oxides,
both the d-wave and s-wave states are sensitive to non-magnetic impurities and
beyond a critical impurity concentration SC disappears in {\it both gap
symmetry channels}. Impurity doping may induce a first order transition from
d-wave to s-wave SC, but no saturation of the impuruty effect is reported due
to the intrinsically anisotropic character of the localization corrections in
this context.",0110637v1
2002-05-27,"Polaron Effects on Superexchange Interaction: Isotope Shifts of $T_N$, $T_C$, and $T^*$ in Layered Copper Oxides","A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures ($T_N$), critical temperatures of
transitions to a superconducting state ($T_C$), and characteristic temperatures
of the pseudogap in the normal state ($T^*$).",0205558v1
2003-01-21,"Structure, Magnetic Properties and Spin-glass Behavior in La$sub{0.9}Tesub{0.1}MnOsub{3}$","In this study we report the structure, magnetic and electrical transport
properties of pervoskite oxide La$sub{0.9}Tesub{0.1}MnOsub{3}$. This is a novel
material with the space group R-3c, which shows the spin-glass-like feature at
low temperature and has a good colossal magnetoresistance behavior. The
magnetoresistance ratio is about 51% at 200 K in a field of 4 T. The XPS
measurement suggests that Te ions are in the Te$up{4+}$ state, while Mn ions
may be in the 2+ and 3+ valence state.",0301384v1
2003-01-22,Magnetic light scattering in low-dimensional quantum spin systems,"An overview of one- and two-dimensional quantum spin systems based on
transition-metal oxides and halides of current interest is given, such as
spin-Peierls, spin-dimer, geometrically frustrated and ladder systems. The most
significant and outstanding contributions of magnetic light scattering to the
understanding of these materials are discussed and compared to results of other
spectroscopies and thermodynamic measurements.",0301413v1
2004-01-05,Enhancement of flux-line pinning in all-oxide superconductor/ferromagnet heterostructures,"We have studied the local critical current density, jc, in the superconductor
thin film of bilayer structures consisting of YBa2Cu3O7 and the ferromagnets
La2/3Ca1/3MnO3 and SrRuO3, respectively, by means of quantitative
magneto-optics. A pronounced hysteresis of jc was observed which is ascribed to
the magnetization state of the ferromagnetic layer. The results are discussed
within the frame of magnetic vortex - wall interactions.",0401033v1
2004-01-19,Magnetic Resonant excitations in High-{$\rm T_c$} superconductors,"The observation of an unusual spin resonant excitation in the superconducting
state of various High-Tc ~copper oxides by inelastic neutron scattering
measurements is reviewed. This magnetic mode % (that does not exist in
conventional superconductors) is discussed in light of a few theoretical models
and likely corresponds to a spin-1 collective mode.",0401328v2
2004-02-12,Interpreting Stone's model of Berry Phases,"We show that a simple quantum-mechanical model, put forward by Stone sometime
ago, affords description of site magnetoelectricity, a phenomenon which takes
place in crystals (and molecular systems) when space inversion is locally
broken and coexistence of electric and magnetic moments is permitted by the
site point group. We demonstrate this by identifying a local order parameter,
which is odd under both space inversion and time reversal. This order parameter
(a magnetic quadrupole) characterises Stone's ground state. Our results
indicate that the model, extended to a lattice of sites, could be relevant to
the study of electronic properties of transition-metal oxides. A generalisation
of Stone's hamiltonian to cover cases of different symmetry is also discussed.",0402339v1
2004-04-07,Electric Field Effect in Diluted Magnetic Insulator Anatase Co:TiO2,"An external electric field induced reversible modulation of room temperature
magnetic moment is achieved in an epitaxial and insulating thin film of
dilutely cobalt-doped anatase TiO2. This first demonstration of electric field
effect in any oxide based diluted ferromagnet is realized in a high quality
epitaxial heterostructure of PbZr0.2Ti0.8O3/Co:TiO2/SrRuO3 grown on (001)
LaAlO3. The observed effect, which is about 15% in strength in a given
heterostructure, can be modulated over several cycles. Possible mechanisms for
electric field induced modulation of insulating ferromagnetism are discussed.",0404172v1
2004-09-15,Evidence for charged critical behavior in the pyrochlore superconductor RbOs2O6,"We analyze magnetic penetration depth data of the recently discovered
superconducting pyrochlore oxide RbOs2O6. Our results strongly suggest that in
RbOs2O6 charged critical fuctuations dominate the temperature dependence of the
magnetic penetration depth near Tc. This is in contrast to the mean-field
behavior observed in conventional superconductors and the uncharged critical
behavior found in nearly optimally doped cuprate superconductors. However, this
finding agrees with the theoretical predictions for charged criticality and the
charged criticality observed in underdoped YBa2Cu3O6.59.",0409398v1
2004-10-28,Power law resistivity behavior in 2D superconductors across the magnetic-field tuned superconductor-insulator transition,"We present the results of a systematic study of thin-films of amorphous
indium-oxide near the superconductor-insulator transition. We show that the
film's resistivity follows a simple, well-defined, power-law dependence on the
perpendicular magnetic field. This dependence holds well into the insulating
state. Our results indicate that vortices play a central role in the transport
of our films in the superconducting as well as insulating phases.",0410724v2
2005-02-06,Interplay of orbitally polarized and magnetically ordered phases in doped transition metal oxides,"We investigate the magnetic instabilities of the two-dimensional model of
interacting e_g electrons for hole doping away from two electrons per site in
the mean-field approximation. In particular, we address the occurrence of
orbitally polarized states due to the inequivalent orbitals, and their
interplay with ferromagnetic and antiferromagnetic spin order. The role played
by the Hund's exchange coupling J_H and by the crystal field orbital splitting
E_z in stabilizing one of the competing phases is discussed in detail.",0502158v1
2005-07-06,A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction,"A magnetic tunnel junctions composed of room temperature ferromagnetic
semiconductor rutile Ti1-xCoxO2-d and ferromagnetic metal Fe0.1Co0.9 separated
by AlOx barrier showed positive tunneling magnetoresistance (TMR) with a ratio
of ~11 % at 15 K, indicating that Ti1-xCoxO2-d can be used as a spin injection
electrode. The TMR decreased with increasing temperature and vanished above 180
K. TMR action at high temperature is likely prohibited by the inelastic
tunneling conduction due to the low quality of the amorphous barrier layer
and/or the junction interface.",0507137v1
2005-07-12,Epitaxial magnetic perovskite nanostructures,"Precise arrays of sub-100 nm diameter nanodots are fabricated from magnetic
oxide perovskites with the total coverage area up to 5 mm2. Epitaxial single
crystal structure of the nanodots is demonstrated by cross-sectional TEM. Low
temperature MFM study confirmed the ferromagnetism of the produced particles.",0507280v1
2005-12-29,Effect of the Triplet State on the Random Telegraph Signal in Si n-MOSFETs,"We report on the static magnetic field dependence of the random telegraph
signal (RTS) in a submicrometer silicon n-metal-oxide-semiconductor
field-effect transistor. Using intense magnetic fields and $^{3}$He
temperatures, we find that the characteristic time ratio changes by 3 orders of
magnitude when the field increases from 0 to 12 T. Similar behaviour is found
when the static field is either in-plane or perpendicular to the two
dimensional electron gas. The experimental data can be explained by considering
a model which includes the triplet state of the trapping center and the
polarization of the channel electron gas.",0512692v1
2007-06-05,Room-temperature ferromagnetism in nanoparticles of superconducting materials,"Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.",0706.0634v1
2007-06-22,Orbital and Spin Excitations in Cobalt Oxide,"By means of neutron scattering we have determined new branches of magnetic
excitations in orbitally active CoO (TN=290 K) up to 15 THz and for
temperatures from 6 K to 450 K. Data were taken in the (111) direction in six
single-crystal zones. From the dependence on temperature and Q we have
identified several branches of magnetic excitation. We describe a model for the
coupled orbital and spin states of Co2+ subject to a crystal field and
tetragonal distortion.",0706.3345v1
2007-07-17,"How Large is the Intrinsic Flux Noise of a Magnetic Flux Quantum, of Half a Flux Quantum and of a Vortex-Free Superconductor?","This article addresses the question whether the magnetic flux of stationary
vortices or of half flux quanta generated by frustrated superconducting rings
is noisy. It is found that the flux noise generated intrinsically by a
superconductor is, in good approximation, not enhanced by stationary vortices.
Half flux quanta generated by $\pi$-rings are characterized by considerably
larger noise.",0707.2550v1
2007-08-24,"Observation of strong-coupling effects in a diluted magnetic semiconductor (Ga,Fe)N","A direct observation of the giant Zeeman splitting of the free excitons in
(Ga,Fe)N is reported. The magnetooptical and magnetization data imply the
ferromagnetic sign and a reduced magnitude of the effective p-d exchange energy
governing the interaction between Fe^{3+} ions and holes in GaN, N_0 beta^(app)
= +0.5 +/- 0.2 eV. This finding corroborates the recent suggestion that the
strong p-d hybridization specific to nitrides and oxides leads to significant
renormalization of the valence band exchange splitting.",0708.3296v1
2008-11-20,Interlayer exchange coupling in Co2FeAl0.5Si0.5/Cr/Co2FeAl0.5Si0.5 trilayers,"Interlayer exchange couplings were examined for Co2FeAl0.5Si0.5(CFAS)/Cr/CFAS
trilayered films grown on MgO (001) single crystal and thermally oxidized Si
substrates. The films were (001) epitaxial on MgO and (110) textured
polycrystalline on SiO2. Strong exchange couplings were observed for the films
with the 1.5 nm thick Cr spacer layer. A 90 degree coupling is dominant in the
(001) epitaxial film. In contrast, an antiparallel coupling exists in the
polycrystalline one. The relationship of interlayer couplings with the
structure is discussed.",0811.3278v1
2009-07-25,Short-range magnetic order and temperature-dependent properties of cupric oxide,"The temperature dependence of the optical and magnetic properties of CuO were
examined by means of hybrid density functional theory calculations. Our work
shows that the spin exchange interactions in CuO are neither fully
one-dimensional nor fully three-dimensional. The large temperature dependence
of the optical band gap and the 63Cu nuclear quadrupole resonance frequency of
CuO originate from the combined effect of a strong coupling between the spin
order and the electronic structure and the progressive appearance of
short-range order with temperature.",0907.4415v1
2010-06-03,Relaxor characteristics at the interfaces of [NdMnO3/SrMnO3/LaMnO3] superlattices,"We have investigated the magnetic properties of transition metal oxide
superlattices with broken inversion symmetry composed of three different
antiferromagnetic insulators, [NdMnO3/SrMnO3/LaMnO3]. In the superlattices
studied here, we identify the emergence of a relaxor, glassy-like behavior
below spin glass temperature, T=36K. Our results offer the possibility to study
and utilize magnetically metastable devices confined in nano-scale interfaces.",1006.0602v3
2010-12-15,Giant Tunneling Electroresistance Effect Driven by an Electrically Controlled Spin Valve at a Complex Oxide Interface,"A giant tunneling electroresistance effect may be achieved in a ferroelectric
tunnel junction by exploiting the magnetoelectric effect at the interface
between a ferroelectric barrier and magnetic La1-xSrxMnO3 electrode. Using
first-principles density functional theory we demonstrate that a few magnetic
monolayers of La1-xSrxMnO3 near the interface act, in response to ferroelectric
polarization reversal, as an atomic scale spin-valve by filtering
spin-dependent current. This effect produces more than an order of magnitude
change in conductance, and thus constitutes a giant resistive switching effect.",1012.3421v2
2011-05-06,Radio frequency readout of electrically detected magnetic resonance in phosphorus-doped silicon MOSFETs,"We demonstrate radio frequency (RF) readout of electrically detected magnetic
resonance in phosphorus-doped silicon metal-oxide field-effecttransistors
(MOSFETs), operated at liquid helium temperatures. For the first time, the Si:P
hyperfine lines have been observed using radio frequency reflectometry, which
is promising for high-bandwidth operation and possibly time-resolved detection
of spin resonance in donor-based semiconductor devices. Here we present the
effect of microwave (MW) power and MOSFET biasing conditions on the EDMR
signals.",1105.1235v1
2012-07-30,Strain engineering magnetic frustration in perovskite oxide thin films,"Our first-principles results show that geometric frustration can be induced
in thin films of multiferroic BiFeO3. We find that competing magnetic
interactions occur in the so-called super-tetragonal phase of this material,
which can be grown on strongly-compressive substrates. We show that the
frustration level can be tuned by appropriately choosing the substrate; in
fact, the three-dimensional spin order gets totally annihilated in a narrow
range of epitaxial strains. We argue that the effects revealed here are not
exclusive to BiFeO3, and predict that they also occur in multiferroic BiCoO3.",1207.6859v1
2014-07-07,"Multiferroic hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu): an experimental review","Hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu) have recently been identified as
a new family of multiferroic complex oxides.
  The coexisting spontaneous electric and magnetic polarizations make
h-RFeO$_3$ rare-case ferroelectric ferromagnets at low temperature.
  Plus the room-temperature multiferroicity and predicted magnetoelectric
effect, h-RFeO$_3$ are promising materials for multiferroic applications.
  Here we review the structural, ferroelectric, magnetic, and magnetoelectric
properties of h-RFeO$_3$.
  The thin film growth is also discussed because it is critical in making high
quality single crystalline materials for studying intrinsic properties.",1407.1798v1
2015-07-11,Insulator/metal phase transition and colossal magnetoresistance in holographic model,"Within massive gravity, we construct a gravity dual for insulator/metal phase
transition and colossal magnetoresistance (CMR) effect found in some manganese
oxides materials. In heavy graviton limit, a remarkable
magnetic-field-sensitive DC resistivity peak appears at the Curie temperature,
where an insulator/metal phase transition happens and the magnetoresistance is
scaled with the square of field-induced magnetization. We find that metallic
and insulating phases coexist below the Curie point and the relation with the
electronic phase separation is discussed.",1507.03105v2
2016-03-29,Effect of delithiation on the dimer transition of the honeycomb-lattice ruthenate Li$_{2-x}$RuO$_3$,"The honeycomb-lattice ruthenate Li$_2$RuO$_3$ is made heavily Li-deficient by
chemical oxidation by iodine. The delithiation triggers a different phase
Li$_{2-x}$RuO$_3$, the ""D-phase"", with superlattice. For the first time we
disclose the magnetic and structural properties of the D-phase in the
dimer-solid state. The low temperature magnetic susceptibility and the bond
lengths indicate a bonding configuration consisting of both Ru$^{4+}$-Ru$^{4+}$
and Ru$^{5+}$-Ru$^{5+}$ dimers.",1603.08764v1
2016-09-13,Spin-dependent transport and current modulation in a current-in-plane field-effect transistor,"We propose a current-in-plane spin-valve field-effect transistor
(CIP-SV-FET), which is composed of a ferromagnet / nonferromagnet / ferromagnet
trilayer structure and a gate electrode. This is a promising device alternative
to spin metal-oxide-semiconductor field-effect transistors. Here, we fabricate
a ferromagnetic-semiconductor GaMnAs-based CIP-SV-FET and demonstrate its basic
operation of the resistance modulation both by the magnetization configuration
and by the gate electric field. Furthermore, we present the
electric-field-assisted magnetization reversal in this device.",1609.05859v1
2020-07-04,Synthesis of FeNi tetrataenite phase by means of chemical precipitation,"FeNi L10 (tetrataenite) phase has great perspectives for hard magnetic
materials production. In this paper it was synthesized in chemically
co-precipitated FeNi nanopowder by means of thermal treating included cycling
of oxidation and reduction processes at 320 {\deg}C. The presence of FeNi L10
phase in the samples was confirmed by magnetic measurements and DSC analysis.",2007.02177v2
2013-08-05,Sub-Piconewton Force Detection using Micron-Size Wire Deflections,"The mechanical properties of nanostructured wires obtained by co-assembly of
iron oxide particles are studied. The intrinsic magnetic properties of the
wires are used to induce and quantify the bending of the one-dimensional
objects. From the relationship between the deflection and the magnitude of the
magnetic field, the elastic rigidity and Young modulus of the wires are
determined. Young moduli in the megapascal range are obtained and are
consistent with sub-piconewton force detection.",1308.0893v1
2012-01-16,Electric field control of chiral magnetic domains in the high-temperature multiferroic CuO,"We have studied the high temperature multiferroic cupric oxide using
polarized neutron diffraction as a function of temperature and applied electric
field. We find that the chiral domain population can be varied using an
external electric field applied along the b axis. Using representation analysis
we derive the incommensurate magnetic structure in the multiferroic phase. The
origin of the magnetoelectric coupling is consistent with models based on the
inverse Dzyaloshinskii-Moriya interaction, but is different from the simple
cycloidal mechanism.",1201.3309v1
2018-07-02,Enhanced thermopower via spin-state modification,"We investigated the effect of pressure on the magnetic and thermoelectric
properties of Sr$_{3.1}$Y$_{0.9}$Co$_{4}$O$_{10+\delta }$. The magnetization is
reduced with the application of pressure, reflecting the spin-state
modification of the Co$^{3+}$ ions into the nonmagnetic low-spin state.
Accordingly, with increasing pressure, the Seebeck coefficient is enhanced,
especially at low temperatures, at which the effect of pressure on the spin
state becomes significant. These results indicate that the spin-orbital entropy
is a key valuable for the thermoelectric properties of the strongly correlated
cobalt oxides.",1807.00551v1
2019-11-06,Disclosing antiferromagnetism in tetragonal Cr2O3 by electrical measurements,"The tetragonal phase of chromium (III) oxide, although unstable in the bulk,
can be synthesized in epitaxial heterostructures. The theoretical investigation
by density functional theory predicts an antiferromagnetic ground state for
this compound. We demonstrate experimentally antiferromagnetism up to 40 K in
ultrathin films of t-Cr2O3 by electrical measurements exploiting interface
effect within a neighboring ultrathin Pt layer. We show that magnetotransport
in Pt is affected by both spin-Hall magnetoresistance and magnetic proximity
effect while we exclude any role of magnetism for the low-temperature
resistance anomaly observed in Pt.",1911.02596v1
2020-06-22,Magnetic excitations of Sr$_3$Ir$_2$O$_7$ observed by inelastic neutron scattering measurement,"In this short note, we report on the first inelastic neutron scattering (INS)
study on high-energy magnetic excitations in Sr$_3$Ir$_2$O$_7$. We observed
excitations between $\sim$80 meV and $\sim$180 meV. The peak position of the
excitations is consistent with the dispersion of a single magnon determined by
resonant inelastic X-ray scattering (RIXS) measurement. Thus, our results
demonstrate that INS and RIXS observe identical excitations in iridate oxides,
as in La$_2$CuO$_4$.",2006.12074v2
2021-07-07,Origin of nonlinear magnetoelectric response in rare-earth orthoferrite perovskite oxides,"We report a theoretical study of the non-linear magnetoelectric response of
GdFeO$_3$ through an analytical approach combined with a Heisenberg model which
is fitted against first-principles calculations. Our theory reproduces the
non-linear change of polarization under applied magnetic field reported
experimentally such that it allows to analyze the origin of the large responses
in the different directions. We show that the non-linear character of the
response in these materials originates from the fact that the antiferromagnetic
order of Gd atoms changes non-linearly with respect to the applied magnetic
field. Our model can be generalized to other materials in which the
antiferromagnetic ordering breaks inversion symmetry.",2107.03228v1
2022-02-03,TiO2 with Super Narrow Bandgap Achieved in One-Step Single-Mode Magnetic Microwave Induced Plasma Treatment,"TiO2 with super narrow bandgap (1.1 eV~) are successfully synthesized via a
facile and novel one-step single-mode magnetic microwave induced plasma
treatment. The selectively surface Ti3+-doping on obtained TiO2 as trapping
centers which significantly restrain the photo-excited carrier recombination
and achieve the enhancement of visible-light photocatalytic performance. In
addition, the surface chemical composition of TiOx is precisely controlled in a
wide region of 1.19 < x < 1.92 during one-step reaction. A detailed XPS
analysis reveals that the surface formed Ti3+ shows highly thermal/chemical
stability even through high-temperature treatment (~800 oC) in oxidative
atmosphere and photocatalytic reaction.",2202.01368v1
2022-07-25,Broken-symmetry self-consistent GW approach: degree of spin contamination and evaluation of effective exchange couplings in solid antiferromagnets,"We adopt a broken-symmetry strategy for evaluating effective magnetic
constants $J$ within the fully self-consistent GW method. To understand the
degree of spin contamination present in broken-symmetry periodic solutions, we
propose several size-extensive quantities that demonstrate that the
unrestricted self-consistent GW preserves well the broken-symmetry character of
the unrestricted Hartree--Fock solutions. The extracted $J$ are close to the
ones obtained from multireference wave-function calculations. In this paper, we
establish a robust computational procedure for finding magnetic coupling
constants from self-consistent GW calculations and apply it to solid
antiferromagnetic nickel and manganese oxides.",2207.12064v1
2023-06-12,Wide Range Thin-FIlm Ceramic Metal-Alloy Thermometers with Low Magnetoresistance,"Many thermal measurements in high magnetic fields require thermometers that
are sensitive over a wide temperature range, are low mass, have a rapid thermal
response, and have a minimal, easily correctable magnetoresistance. Here we
report the development of a new granular-metal oxide ceramic composite (cermet)
for this purpose formed by co-sputtering of the metallic alloy nichrome
Ni$_{0.8}$Cr$_{0.2}$ and the insulator silcon dioxide SiO$_2$. The resulting
thin films are sensitive enough to be used from room temperature down to below
100 mK in magnetic fields up to at least 35 tesla.",2306.06950v2
2023-03-06,Pressure-Dependent Layer-by-Layer Oxidation of ZrS2(001) Surface,"Understanding oxidation mechanisms of layered semiconducting transition-metal
dichalcogenide (TMDC) is important not only for controlling native oxide
formation but also for synthesis of oxide and oxysulfide products. Here,
reactive molecular dynamics simulations show that oxygen partial pressure
controls not only the ZrS2 oxidation rate but also the oxide morphology and
quality. We find a transition from layer-by-layer oxidation to
amorphous-oxide-mediated continuous oxidation as the oxidation progresses,
where different pressures selectively expose different oxidation stages within
a given time window. While the kinetics of the fast continuous oxidation stage
is well described by the conventional Deal-Grove model, the layer-by-layer
oxidation stage is dictated by reactive bond-switching mechanisms. This work
provides atomistic details and a potential foundation for rational
pressure-controlled oxidation of broad TMDC materials.",2303.03220v1
2000-02-16,"Magnetic pair-breaking in superconducting (Ba,K)BiO_3 investigated by magnetotunneling","The de Gennes and Maki theory of gapless superconductivity for dirty
superconductors is used to interpret the tunneling measurements on the strongly
type-II high-Tc oxide-superconductor Ba1-xKxBiO3 in high magnetic fields up to
30 Tesla. We show that this theory is applicable at all temperatures and in a
wide range of magnetic fields starting from 50 percent of the upper critical
field Bc2. In this magnetic field range the measured superconducting density of
states (DOS) has the simple energy dependence as predicted by de Gennes from
which the temperature dependence of the pair-breaking parameter alpha(T), or
Bc2(T), has been obtained. The deduced temperature dependence of Bc2(T) follows
the Werthamer-Helfand-Hohenberg prediction for classical type-II
superconductors in agreement with our previous direct determination. The
amplitudes of the deviations in the DOS depend on the magnetic field via the
spatially averaged superconducting order parameter which has a square-root
dependence on the magnetic field. Finally, the second Ginzburg-Landau parameter
kappa2(T) has been determined from the experimental data.",0002241v1
2000-03-14,"Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0)","We have investigated the magnetic and electrical resistance behaviour of
  Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from
Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic
  Curie temperature ($\theta$$_p$) is negative indicative of antiferromagnetic
ordering, the large magnitude (-250 K) of $\theta$$_p$ reveals complex nature
of the magnetism in this compound. Ru ions appear to be in the pentavalent
state. We note that the N\'eel temperature undergoes only a marginal reduction
by Y substitution. All these compositions are found to be insulators and thus
the electron doping does not result in metallicity. Thus the overall magnetic
and transport behaviour are found to be essentially insensitive to Y
substitution for Ca, a finding which may favour the idea of
quasi-one-dimensional magnetism in these compounds.",0003227v1
2002-09-17,Sr2V3O9 and Ba2V3O9: quasi one-dimensional spin-systems with an anomalous low temperature susceptibility,"The magnetic behaviour of the low-dimensional Vanadium-oxides Sr2V3O9 and
Ba2V3O9 was investigated by means of magnetic susceptibility and specific heat
measurements. In both compounds, the results can be very well described by an
S=1/2 Heisenberg antiferromagnetic chain with an intrachain exchange of J = 82
K and J = 94 K in Sr2V3O9 and Ba2V3O9, respectively. In Sr2V3O9,
antiferromagnetic ordering at T_N = 5.3 K indicate a weak interchain exchange
of the order of J_perp ~ 2 K. In contrast, no evidence for magnetic order was
found in Ba2V3O9 down to 0.5 K, pointing to an even smaller interchain
coupling. In both compounds, we observe a pronounced Curie-like increase of the
susceptibility below 30 K, which we tentatively attribute to a staggered field
effect induced by the applied magnetic field. Results of LDA calculations
support the quasi one-dimensional character and indicate that in Sr2V3O9, the
magnetic chain is perpendicular to the structural one with the magnetic
exchange being transferred through VO4 tetrahedra.",0209409v1
2003-06-25,Static magnetic response of clusters in Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel oxide,"Earlier investigation of Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel has
shown the existence of ""super-ferromagnetic "" clusters containing Fe^{3+} and
Ho^{3+} ions along with small size clusters of Fe^{3+} ions (Bhowmik et al, J.
Magn. Magn. Mater. {247}, 83 (2002)). Here, We report the static magnetic
response of these clusters. The experimental data suggests some interesting
magnetic features, such as, enhancement of magnetization; re-entrant magnetic
transitions with paramagnetic to ferromagnetic state below 225 K and
ferromagnetic to spin glass state below 120 K; appearance of field induced
ferromagnetism. We also observe an unusual maximum in the thermoremanent
magnetization (TRM) vs temperature data. Our measurements suggest that this
unusuality in TRM is related to the blocking of ""super-ferromagnetic"" clusters
,out of the ferromagnetic state, along their local anisotropy axis.",0306653v1
2004-06-18,Magnetic Superconducting Heterostructures,"Heterogeneous magnetic superconducting systems (HMSS) represent a new class
of nanostructures. They are made of ferromagnetic (FM) and superconducting (SC)
pieces separated by thin layers of insulating oxides. In contrast to the case
of a homogeneous ferromagnetic superconductor studied during the last two
decades, the two order parameters, the magnetization and the SC electron
density do not suppress each other. In HMSS, the interaction between the two
order parameters is due to the magnetic field created by the magnetic and SC
textures. Strong interaction of the FM and SC systems not only gives rise to a
new class of novel phenomena and physical effects, but also shows the important
technological promise of devices whose transport properties can be easily tuned
by comparatively weak magnetic fields.",0406443v1
2005-03-16,The atomic-start description of NiO,"We have calculated magnetic properties and the electronic structure of NiO
both in the paramagnetic and in magnetically-ordered state as well as
zero-temperature properties and thermodynamics within the strongly-correlated
crystal-field approach. It is in agreement with a Mott's suggestion that NiO is
an insulator due to strong electron correlations. We have quantified
crystal-field, spin-orbit and magnetic interactions of the Ni2+ ion in NiO. We
have obtained that E_dd >> E_CF(=2.0 eV) >> E_{s-o}(=0.29 eV) > E_mag(=0.07
eV). The orbital moment of 0.54 mu_B amounts at 0 K, in the
magnetically-ordered state, to about 20% of the total moment (2.53 mu_B). Our
studies indicate that it is the highest time to ""unquench"" orbital magnetic
moment in 3d solid-state physics and the necessity to take always into account
strong intra-atomic correlations among d electrons and the intra-atomic
spin-orbit coupling.
  Pacs: 75.25.+z, 75.10.Dg
  Keywords: Crystalline Electric Field, 3d oxides, magnetism, spin-orbit
coupling NiO",0503407v1
2007-02-05,Existence of two electronic states in Sr4Ru3O10 at low temperatures,"We report measurements on in-plane resistivity, thermopower, and
magnetization as a function of temperature and magnetic fields on single
crystalline Sr4Ru3O10 grown by the floating zone method. As the temperature was
lowered to below around 30 K, the in-plane and c-axis resistivities and the
thermopower were found to exhibit a step feature accompanied by hysteresis
behavior when the in-plane field was swept up and down from below 10 kOe to
above 20 kOe. The sharp increase in the thermopower with increasing in-plane
magnetic field at low temperatures has not been observed previously in layered
transition metal oxides. Comparing with magnetization data, we propose that the
step feature marks the transition between the two different electronic states
in Sr4Ru3O10. We propose that the alignment of domains by the in-plane magnetic
field is responsible to the emergence of the new electronic states in high
applied in-plane magnetic field.",0702093v1
2007-11-02,Magnetism without magnetic impurities in oxides ZrO2 and TiO2,"We perform a theoretical study of the magnetism induced in transition metal
dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an
impurity from the groups 1A or 2A of the periodic table, where the impurity is
either K or Ca. In the present study both supercell and embedded cluster
methods are used. It is demonstrated that the vacancy and the K-impurity leads
to a robust induced magnetic moment on the surrounding O-atoms for both the
cubic ZrO2 and rutile TiO2 host crystals. On the other hand it is shown that
Ca-impurity leads to a non magnetic state. The native O-vacancy does not induce
a magnetic moment in the host dioxide crystal.",0711.0280v1
2007-12-18,Observation of electromagnon excitations in the BiFe0$_3$ spiral magnet,"Recently, oxide multiferroics have attracted much attention due to their
large magnetoelectric effect which allows the tuning of magnetic properties
with electric field and vice versa and open new venues for future spintronic
applications such as multiple-state memory devices with dual magnetic and
electric control. BiFeO$_3$ (BFO) belongs to this new class of materials and
shows both ferroelectric and antiferromagnetic orders at room temperature with
a large electric polarizationassociated with a cycloidal spiral magnetic
ordering. The incommensurate magnetic order induces magnon zone folding and
allows investigations by optical probes of unusual spin waves which couples to
optical phonons, the so called ""`electromagnons""'. Here, we unravel for the
first time the electromagnon spectra of BFO by means low energy inelastic light
scattering technique. We show the existence of two species of electromagnons
corresponding to spin wave excitations in and out of the cycloidal plane. The
present observations present an unique opportunity to study the interplay
between ferroelectric and magnetic orders.",0712.3044v1
2008-01-09,Magnetic coupling in highly-ordered NiO/Fe3O4(110): Ultrasharp magnetic interfaces vs. long-range magnetoelastic interactions,"We present a laterally resolved X-ray magnetic dichroism study of the
magnetic proximity effect in a highly ordered oxide system, i.e. NiO films on
Fe3O4(110). We found that the magnetic interface shows an ultrasharp
electronic, magnetic and structural transition from the ferrimagnet to the
antiferromagnet. The monolayer which forms the interface reconstructs to
NiFe2O4 and exhibits an enhanced Fe and Ni orbital moment, possibly caused by
bonding anisotropy or electronic interaction between Fe and Ni cations. The
absence of spin-flop coupling for this crystallographic orientation can be
explained by a structurally uncompensated interface and additional
magnetoelastic effects.",0801.1468v1
2009-07-23,Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes,"We report on the magnetic hyperthermia properties of chemically synthesized
ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the
saturation magnetization of bulk iron. The specific absorption rate measured on
16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to
specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in
other systems. A way to quantify the degree of optimization of any system with
respect to hyperthermia applications is proposed. Applied here, this method
shows that our nanoparticles are not fully optimized, probably due to the
strong influence of magnetic interactions on their magnetic response. Once
protected from oxidation and further optimized, such nano-objects could
constitute efficient magnetic cores for biomedical applications requiring very
large heating power.",0907.4063v3
2009-09-24,"Magnetic, Thermal, and Transport Properties of the Mixed Valent Vanadium Oxides LuV4O8 and YV4O8","LV4O8 (L = Yb, Y, Lu) compounds are reported to crystallize in a structure
similar to that of the orthorhombic CaFe2O4 structure-type, and contain four
inequivalent V sites arranged in zigzag chains. We confirm the structure and
report the magnetic, thermal, and transport properties of polycrystalline YV4O8
and LuV4O8. A first-order like phase transition is observed at 50 K in both
YV4O8 and LuV4O8. The symmetry remains the same with the lattice parameters
changing discontinously. The structural transition in YV4O8 leads to partial
dimerization of the V atoms resulting in a sudden sharp drop in the magnetic
susceptibility. The V spins that do not form dimers order in a canted
antiferromagnetic state. The magnetic susceptibility of LuV4O8 shows a sharp
peak at ~ 50 K. The magnetic entropies calculated from heat capacity versus
temperature measurements indicate bulk magnetic transitions below 90 K for both
YV4O8 and LuV4O8.",0909.4572v2
2010-08-25,"Carrier-Concentration Dependence of the Pseudogap Ground State of Superconducting Bi2Sr2-xLaxCuO6+delta Revealed by 63,65Cu-Nuclear Magnetic Resonance in Very High Magnetic Fields","We report the results of the Knight shift by 63,65Cu-nuclear-magnetic
resonance (NMR) measurements on single-layered copper-oxide
Bi2Sr2-xLaxCuO6+delta conducted under very high magnetic fields up to 44 T. The
magnetic field suppresses superconductivity completely and the pseudogap ground
state is revealed. The 63Cu-NMR Knight shift shows that there remains a finite
density of states (DOS) at the Fermi level in the zero-temperature limit, which
indicates that the pseudogap ground state is a metallic state with a finite
volume of Fermi surface. The residual DOS in the pseudogap ground state
decreases with decreasing doping (increasing x) but remains quite large even at
the vicinity of the magnetically ordered phase of x > 0.8, which suggests that
the DOS plunges to zero upon approaching the Mott insulating phase.",1008.4277v1
2011-06-29,Hysteretic magnetoresistance and thermal bistability in a magnetic two-dimensional hole system,"Colossal negative magnetoresistance and the associated field-induced
insulator-to-metal transition, the most characteristic features of magnetic
semiconductors, are observed in n-type rare earth oxides and chalcogenides,
p-type manganites, n-type and p-type diluted magnetic semiconductors (DMS) as
well as in quantum wells of n-type DMS. Here, we report on magnetostransport
studies of Mn modulation-doped InAs quantum wells, which reveal a magnetic
field driven and bias voltage dependent insulator-to-metal transition with
abrupt and hysteretic changes of resistance over several orders of magnitude.
These phenomena coexist with the quantised Hall effect in high magnetic fields.
We show that the exchange coupling between a hole and the parent Mn acceptor
produces a magnetic anisotropy barrier that shifts the spin relaxation time of
the bound hole to a 100 s range in compressively strained quantum wells. This
bistability of the individual Mn acceptors explains the hysteretic behaviour
while opening prospects for information storing and processing. At high bias
voltage another bistability, caused by the overheating of electrons10, gives
rise to abrupt resistance jumps.",1106.5832v1
2012-03-21,High-field magnetization and magnetoresistance of the $A$-site ordered perovskite oxide CaCu$_{3}$Ti$_{4-x}$Ru$_{x}$O$_{12}$~($0 \le x \le 4$),"We have measured high-field magnetization and magnetoresistance of
polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0
- 4) utilizing a non-destructive pulsed magnet. We find that the magnetization
for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This
is highly nontrivial because the magnetization for x=0 and 4 is linear in
external field up to the highest one. We have analyzed this field dependence
based on the thermodynamics of magnetic materials, and propose that the
external fields delocalize the holes on the Cu2+ ions in order to maximize the
entropy. This scenario is qualitatively consistent with a large
magnetoresistance of -70% observed at 4.2 K at 52 T for x=1.5.",1203.4660v1
2013-01-23,Electric-field-induced magnetization changes in Co/Al2O3 granular multilayers,"We study experimentally the effect of electric field on the magnetization of
Co/Al2O3 granular multilayers. We observe two distinct regimes: (a) low-field
regime when the net magnetization of the system changes in a reversible way
with the applied electric field and (b) high-field regime when the
magnetization decreases irreversibly. The former is attributed to the changes
in the relative 3d-orbital occupation of the minority and majority bands in the
Co granules. A theoretical model has been developed to explain the electric
field induced changes in the band structure of the granular system and hence
the magnetic moment. The latter result may be understood assuming the electric
field induces oxygen migration from Al2O3 to the Co granules, since an increase
in oxidation state of the Co granules is shown, through ab-initio calculations,
to give rise to a reduced magnetization of the system.",1301.5396v1
2013-03-19,X-ray absorption spectroscopy and magnetic circular dichroism studies of L1_0-Mn-Ga thin films,"Tetragonally distorted \(\rm{Mn}_{3-x}\rm{Ga}_x\) thin films with \(0.1< x <
2\) show a strong perpendicular magnetic anisotropy and low magnetization and
thus have the potential to serve as electrodes in spin transfer torque magnetic
random access memory. Because a direct capping of these films with MgO is
problematic due to oxide formation, we examined the influence of a CoFeB
interlayer, and of two different deposition methods for the MgO barrier on the
formation of interfacial MnO for \(\rm{Mn}_{62}\rm{Ga}_{38}\) by element
specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism
(XMCD). A highly textured L1\(_0\) crystal structure of the Mn-Ga films was
verified by X-ray diffraction (XRD) measurements. For samples with e-beam
evaporated MgO barrier no evidence for MnO was found, whereas in samples with
magnetron sputtered MgO MnO was detected, even for the thickest interlayer
thickness. Both XAS and XMCD measurements showed an increasing interfacial MnO
amount with decreasing CoFeB interlayer thickness. Additional element specific
full hysteresis loops determined an out-of-plane magnetization axis for the Mn
and Co, respectively.",1303.4648v2
2014-10-10,"Two dimensional magnetic correlation in the unconventional corrugated layered oxides (Ba,Sr)$_4$Mn$_3$O$_{10}$","Both Ba$_4$Mn$_3$O$_{10}$ and Sr$_4$Mn$_3$O$_{10}$ crystallize in an
orthorhombic crystal structure consisting of corrugated layers containing
Mn$_3$O$_{12}$ polydedra. The thermal variation of magnetic susceptibility of
the compositions consists of a broad hump like feature indicating the presence
of low dimensional magnetic correlation. We have systematically investigated
the magnetic data of these compounds and found that the experimental results
match quite well with the two dimensional Heisenberg model of spin-spin
interaction. The two dimensional nature of the magnetic spin-spin interaction
is supported by the low temperature heat capacity data of Ba$_4$Mn$_3$O$_{10}$.
Interestingly, both the samples show dielectric anomaly near the magnetic
ordering temperature indicating multiferroic behavior.",1410.2715v1
2015-04-06,Quantifying the complex permittivity and permeability of magnetic nanoparticles,"The complex permittivity and permeability of superparamagnetic iron-oxide
nanoparticles has been quantified using a circular waveguide assembly with a
static magnetic field to align the nanoparticle's magnetization. The high
sensitivity of the measurement provides the precise resonant feature of
nanoparticles. The complex permeability in the vicinity of ferromagnetic
resonance (FMR) is in agreement with the nanoparticle's measured magnetization
via conventional magnetometry. A rigorous and self-consistent measure of
complex permittivities and permeabilities of nanoparticles is crucial to
ascertain accurately the dielectric behaviour as well as the frequency response
of nanoparticle magnetization, necessary ingredients when designing and
optimizing magnetic nanoparticles for biomedical applications.",1504.01404v1
2015-05-18,Magnetic state dependent transient lateral photovoltaic effect in patterned ferromagnetic metal-oxide-semiconductor films,"We investigate the influence of an external magnetic field on the magnitude
and dephasing of the transient lateral photovoltaic effect (T-LPE) in
lithographically patterned Co lines of widths of a few microns grown over
naturally passivated p-type Si(100). The T-LPE peak-to-peak magnitude and
dephasing, measured by lock-in or through the characteristic time of laser OFF
exponential relaxation, exhibit a notable influence of the magnetization
direction of the ferromagnetic overlayer. We show experimentally and by
numerical simulations that the T-LPE magnitude is determined by the Co
anisotropic magnetoresistance. On the other hand, the magnetic field dependence
of the dephasing could be described by the influence of the Lorentz force
acting perpendiculary to both the Co magnetization and the photocarrier drift
directions. Our findings could stimulate the development of fast position
sensitive detectors with magnetically tuned magnitude and phase responses.",1505.04580v1
2015-09-16,Charge-Induced Spin Torque in Anomalous Hall Ferromagnets,"We demonstrate that spin-orbit coupled electrons in a magnetically doped
system exert a spin torque on the local magnetization, without a flowing
current, when the chemical potential is modulated in a magnetic field. The spin
torque is proportional to the anomalous Hall conductivity, and its effective
field strength may overcome the Zeeman field. Using this effect, the direction
of the local magnetization is switched by gate control in a thin film. This
charge-induced spin torque is essentially an equilibrium effect, in contrast to
the conventional current-induced spin-orbit torque, and, thus, devices using
this operating principle possibly have higher efficiency than the conventional
ones. In addition to a comprehensive phenomenological derivation, we present a
physical understanding based on a model of a Dirac-Weyl semimetal, possibly
realized in a magnetically doped topological insulator. The effect might be
realized also in nanoscale transition materials, complex oxide ferromagnets,
and dilute magnetic semiconductors.",1509.04799v1
2020-07-03,From Weak Antilocalization to Kondo Scattering in a Magnetic Complex Oxide Interface,"Quantum corrections to electrical resistance can serve as sensitive probes of
the magnetic landscape of a material. For example, interference between
time-reversed electron paths gives rise to weak localization effects, which can
provide information about the coupling between spins and orbital motion, while
the Kondo effect is sensitive to the presence of spin impurities. Here we use
low-temperature magnetotransport measurements to reveal a transition from weak
antilocalization (WAL) to Kondo scattering in the quasi-two-dimensional
electron gas formed at the interface between SrTiO$_3$ and the Mott insulator
NdTiO$_3$. This transition occurs as the thickness of the NdTiO$_3$ layer is
increased. Analysis of the Kondo scattering and WAL points to the presence of
atomic-scale magnetic impurities coexisting with extended magnetic regions that
affect transport via a strong magnetic exchange interaction. This leads to
distinct magnetoresistance behaviors that can serve as a sensitive probe of
magnetic properties in two dimensions.",2007.01853v1
2013-08-24,Emerging magnetism and electronic phase separation at titanate interfaces,"The emergence of magnetism in otherwise nonmagnetic compounds and its
underlying mechanisms have become the subject of intense research. Here we
demonstrate that the nonmagnetic oxygen vacancies are responsible for an
unconventional magnetic state common for titanate interfaces and surfaces.
Using an effective multiorbital modelling, we find that the presence of
localized vacancies leads to an interplay of ferromagnetic order in the
itinerant t2g band and complex magnetic oscillations in the
orbitally-reconstructed eg-band, which can be tuned by gate fields at oxide
interfaces. The magnetic phase diagram includes highly fragmented regions of
stable and phase-separated magnetic states forming beyond nonzero critical
defect concentrations.",1308.5319v1
2012-04-11,Frustrated magnets and quantum paramagnetic phases at finite temperature,"We develop a general framework, which combines exact diagonalization in small
clusters with a density matrix variational principle, to study frustrated
magnets at finite temperature. This thermodynamic hierarchical mean-field
technique is used to determine the phase diagram and magnetization process of
the three-dimensional spin-1/2 $J_1$-$J_2$ antiferromagnet on a stacked square
lattice. Its non-magnetic phase exhibits a thermal crossover from a quantum to
a classical paramagnet at a temperature $T=T_0$ which can be extracted from
thermodynamic measurements. At low temperature an applied magnetic field
stabilizes, through order-by-disorder, a variety of phases with non-trivial
spin textures and a magnetization plateau at half-saturation which continuously
disappears at $T\sim T_0$. Our results are relevant for frustrated vanadium
oxides.",1204.2559v2
2014-05-05,A single crystal high-temperature pyrochlore antiferromagnet,"We report the magnetic characterization of the frustrated transition metal
pyrochlore NaCaCo$_2$F$_7$. This material has high spin Co$^{2+}$ in CoF$_6$
octahedra in a pyrochlore lattice, and disordered non-magnetic Na and Ca on the
large-atom sites in the structure. Large crystals grown by the floating zone
method were studied. The magnetic susceptibility is isotropic, the Co moment is
larger than the spin-only value, and in spite of the large Curie Weiss theta
(-140 K), freezing of the spin system, as characterized by peaks in the ac and
dc susceptibility and specific heat, does not occur until around 2.4 K. This
yields a frustration index of f = $-\theta_{CW}$/$T_f$ $\approx$ 56, an
indication that the system is highly frustrated. The observed entropy loss at
the freezing transition is low, indicating that magnetic entropy remains
present in the system at 0.6 K. The compound may be the realization of a
frustrated pyrochlore antiferromagnet with weak bond disorder. The high
magnetic interaction strength, strong frustration, and the availability of
large single crystals makes NaCaCo$_2$F$_7$ an interesting alternative to rare
earth oxide pyrochlores for the study of geometric magnetic frustration in
pyrochlore lattices.",1405.0956v1
2015-12-19,Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and \textit{ab initio} theory,"We present temperature-dependent atomic and magnetic pair distribution
function (PDF) analysis of neutron total scattering measurements of
antiferromagnetic MnO, an archetypal strongly correlated transition-metal
oxide. The known antiferromagnetic ground-state structure fits the
low-temperature data closely with refined parameters that agree with
conventional techniques, confirming the reliability of the newly developed
magnetic PDF method. The measurements performed in the paramagnetic phase
reveal significant short-range magnetic correlations on a $\sim$1~nm length
scale that differ substantially from the low-temperature long-range spin
arrangement. \textit{Ab initio} calculations using a self-interaction-corrected
local spin density approximation of density functional theory predict magnetic
interactions dominated by Anderson superexchange and reproduce the measured
short-range magnetic correlations to a high degree of accuracy. Further
calculations simulating an additional contribution from a direct exchange
interaction show much worse agreement with the data. The Anderson superexchange
model for MnO is thus verified by experiment and confirmed by \textit{ab
initio} theory.",1512.06270v2
2017-07-03,Heavy-mass magnetic modes in pyrochlore iridates due to dominant Dzyaloshinskii-Moriya interaction,"Materials with strong spin-orbit interactions are presently a main target in
the search for systems with novel magnetic properties. Magnetic anisotropies
can be very large in such compounds, ranging from strongly frustrated Kitaev
exchange in honeycomb iridates and the associated spin-liquid states to robust
antisymmetric couplings in square-lattice Sr_2IrO_4 . Here we predict from ab
initio quantum chemistry calculations that another highly unusual regime is
realized in pyrochlore iridium oxides: the nearest-neighbor Heisenberg
interaction can vanish whilst the antisymmetric Dzyaloshinskii- Moriya exchange
reaches values as large as 5 meV, a result which challenges common notions and
existing phenomenological models of magnetic superexchange. The resulting spin
excitation spectra reveal a very flat magnon dispersion in the Nd- and Tb-based
pyrochlore iridates, suggesting the possibility of using these modes to store
magnetic information. Indeed the magnetization dynamics indicates that these
modes are unable to propagate out of the excitation region.",1707.00500v1
2017-12-06,Dynamic quantum kagome ice,"The search for two dimensional quantum spin liquids, exotic magnetic states
with an entangled ground state remaining disordered down to zero temperature,
has been a great challenge in frustrated magnetism during the last decades.
Recently, fractionalized excitations, called spinons, emerging from these
states, have been evidenced in kagome and triangular antiferromagnets. In
contrast, quantum ferromagnetic spin liquids in two dimensions, namely quantum
kagome ices, have been less investigated, yet their classical counterparts
exhibit amazing properties, magnetic monopole crystals as well as magnetic
fragmentation. Here we show that, by applying a magnetic field on the
pyrochlore oxide Nd$_2$Zr$_2$O$_7$, which has been shown to develop three
dimensional quantum magnetic fragmentation in zero field, we are able to reduce
the dimension of the system and to create a dynamic kagome ice state. Our
results open the way to the observation of the quantum kagome ice state which
was recently investigated theoretically.",1712.02418v2
2018-10-30,Magnetic field sensing with the kinetic inductance of a high-$T_\mathrm{c}$ superconductor,"We carry out an experimental feasibility study of a magnetic field sensor
based on the kinetic inductance of the high-$T_\mathrm{c}$ superconductor
yttrium barium copper oxide. We pattern thin superconducting films into
radio-frequency resonators that feature a magnetic field pick-up loop. At 77 K
and for film thicknesses down to 75 nm, we observe the persistence of screening
currents that modulate the loop kinetic inductance. According to the
experimental results the device concept appears attractive for sensing
applications in ambient magnetic field environments. We report on a device with
a magnetic field sensitivity of 4 pT/Hz${}^{1/2}$, an instantaneous dynamic
range of 11 $\mu$T, and operability in magnetic fields up to 28 $\mu$T.",1810.12725v1
2020-04-01,Suppression of magnetic phase transition at high magnetic field and non-Debye's nature of nano-crystalline Gd$_2$CoMnO$_6$: a detail study of physical properties,"Structural, magnetization, phonon behavior, and dielectric response of
nano-crystalline Gd$_2$CoMnO$_6$ have been presented in this paper. The study
shows that the material crystallizes in $\textit{P2$_1$/n}$ phase group of the
monoclinic crystal structure. XPS measurement shows Co$^{2+}$ and Mn$^{4+}$
oxidation states are present in the sample. Magnetization study reveals that
the sample undergoes a ferromagnetic ordering of Co$^{2+}$ and Mn$^{4+}$
magnetic ions around $T_c$ $\sim$132 K. However we have seen that with the
application of external magnetic field the phase transition is largely
suppressed. Raman study reveals the presence spin-phonon coupling in
Gd$_2$CoMnO$_6$. Dielectric study reveals that the sample shows large
dielectric constant and strong dispersion in mid frequency range. The
dielectric loss shows there are two relaxation processes present in the
material with different relaxation time and which are driven by thermally
activated relaxation mechanics. Further, the Nyquist plot and AC conductivity
study show that this sample is non-Debye's in nature.",2004.00737v1
2018-06-14,Magnetic inhomogeneity in the copper pseudochalcogenide CuNCN,"Copper carbodiimide, CuNCN, is a geometrically frustrated nitrogen-based
analogue of cupric oxide, whose magnetism remains ambiguous. Here, we employ a
combination of local-probe techniques, including $^{63,\, 65}$Cu nuclear
quadrupole resonance, $^{13}$C nuclear magnetic resonance and muon spin
rotation to show that the magnetic ground state of the Cu$^{2+}$ ($S=1/2$)
spins is frozen and disordered. Moreover, these complementary experiments
unequivocally establish an onset of intrinsically inhomogeneous magnetic state
at $T_h=80$ K. Below $T_h$, the low-temperature frozen component coexist with
the remnant high-temperature dynamical component down to $T_l = 20$ K, where
the latter finally ceases to exist. Based on a scaling of internal magnetic
fields of both components we conclude that the two components coexist on a
microscopic level.",1806.05486v2
2018-07-24,Forced- and Self-Rotation of Magnetic Nanorods Assembly at the Cell Membrane: A Biomagnetic Torsion Pendulum,"In order to give insights into how anisotropic nano-objects interact with
living cell membranes, and possibly self-assemble, we designed magnetic
nanorods with average size around 100 nm x 1$\mu$m by assembling iron oxide
nanocubes within a polymeric matrix under a magnetic field. We then explored
the nano-bio interface at the cell membrane under the influence of a rotating
magnetic field. We observed a complex structuration of the nanorods intertwined
with the membranes. Unexpectedly, after a magnetic rotating stimulation, the
resulting macrorods were able to rotate freely for multiple rotations,
revealing the creation of a bio-magnetic torsion pendulum.",1807.08994v1
2019-03-01,Temperature dependence of the magnetization of La$_{0.67}$Sr$_{0.33}$MnO$_3$ thin films on LaAlO$_3$,"The authors report on the interplay between magnetically ordered phases with
temperature and magnetic field across compressively strained interfaces of thin
La0.67Sr0.33MnO3 films on LaAlO3 substrates. From the temperature dependence of
the magnetization and resistivity studies, they find two distinct temperature
regimes, where this interplay is clearly exhibited. They ascribe this to the
strain induced Jahn-Teller-like distortion that favors the stabilization of the
d3z2-r2 orbitals and enhances superexchange between adjoining Mn atoms. The
temperature and field sweep of the magnetization and electronic transport lead
to a hybridization between the closely spaced energy levels of d3z2-r2 and
dx2-y2 orbitals leading to the coexistence of ferromagnetic and
antiferromagnetic phases. Such an observation, not reported earlier, offers new
routes for the design and study of magnetic textures in variously strained
interfaces between perovskite oxides.",1903.00319v1
2019-03-26,"Magnetic and magnetoelectric properties of $A$FeF$_5$ ($A$ = Ca, Sr) spin-chain compounds","Fluorides in general are characterized by big variety of crystal structures,
whereas those containing transition metals also often show sizable magnetic
properties. The tendency of fluorine to form linear chain structures in many
cases results in low-dimensional magnetism. Despite the plethora of magnetic
phenomena in fluorides, their magnetoelectric properties are less studied than
those of oxides. In the present work we theoretically study the magnetic and
magnetoelectric properties of spin-chain compounds CaFeF$_5$ and SrFeF$_5$. The
density functional theory is employed for determination of magnetic exchange
constants, which are then used in Monte Carlo calculations. The symmetry
analysis reveals that CaFeF$_5$ does not show magnetoelectric properties,
whereas SrFeF$_5$ is a multiferroic.",1903.10828v2
2019-04-01,Experimental creation and annihilation of nonvolatile magnetic skyrmions using voltage control of magnetic anisotropy without an external magnetic field,"In this work, we utilize voltage controlled magnetic anisotropy (VCMA) to
manipulate magnetic skyrmions that are fixed in space. Memory devices based on
this strategy can potentially be of smaller footprint and better energy
efficiency than current-controlled motion-based skyrmionic devices. To
demonstrate VCMA induced manipulation of skyrmions, we fabricate
antiferromagnet/ferromagnet/oxide heterostructure films where skyrmions can be
stabilized without any external magnetic field due to the presence of exchange
bias. These isolated skyrmions were annihilated by applying a voltage pulse
that increased PMA. On the other hand, decreasing PMA promoted formation of
more skyrmions. Furthermore, skyrmions can be created from chiral domains by
increasing PMA of the system. To corroborate our experimental observations, we
performed micromagnetic simulation. The proposed method could potentially lead
to novel skyrmion-based memory devices.",1904.00701v1
2020-03-21,Magnetic Particle Spectroscopy: A Short Review of Applications,"Magnetic particle spectroscopy (MPS), also called magnetization response
spectroscopy, is a novel measurement tool derived from magnetic particle
imaging (MPI). It can be interpreted as a zero-dimensional version of MPI
scanner. MPS was primarily designed for characterizing superparamagnetic iron
oxide nanoparticles (SPIONs) regarding their applicability for MPI. In recent
years, it has evolved into an independent, versatile, highly sensitive,
inexpensive platform for biological and biomedical assays, cell labeling and
tracking, and blood analysis. MPS has also developed into an auxiliary tool for
magnetic imaging and hyperthermia by providing high spatial and temporal
mappings of temperature and viscosity. Furthermore, other MPS-based
applications are being explored such as magnetic fingerprints for product
tracking and identification in supply chains. There are a variety of novel
MPS-based applications being reported and demonstrated by many groups. In this
short review, we highlighted some of the representative applications based on
MPS platform, thereby providing a roadmap of this technology and our insights
for researchers in this area.",2003.09577v1
2020-05-29,Plasma-induced magnetic patterning of FePd thin films without and with exchange bias,"We demonstrate control of magnetic domain structures in continuous FePd thin
films by patterning their surfaces with plasma treatment. The Fe-oxide layer
formed on the surface upon ambient exposure of the FePd alloy thin film grown
on an Al$_2$O$_3$(0001) substrate was patterned into microstructures by e-beam
lithography followed by O$_2$- or Ar-plasma treatment. Microscopic pinning of
magnetic domain walls in the thin films is then observed by magneto-optic Kerr
effect microscopy, with the magnetic field needed to reverse the magnetization
of the plasma-treated areas being larger than that for the untreated areas. An
intriguing competition between the uniaxial anisotropy and the exchange bias is
also observed in the system. This study demonstrates that patterning of the
film surface with plasma treatment can be an easy and efficient method for
sophisticated engineering of magnetic structures in thin films, and therefore
has potential application in developing future data-storage and spintronic
devices.",2005.14497v1
2020-10-21,Strong tuning of magnetism and electronic structure by spin orientation,"To efficiently manipulate magnetism is a key physical issue for modern
condensed matter physics, which is also crucial for magnetic functional
applications. Most previous relevant studies rely on the tuning of spin
texture, while the spin orientation is often negligible. As an exception,
spin-orbit coupled $J_{\rm eff}$ states of $4d$/$5d$ electrons provide an ideal
platform for emergent quantum effects. However, many expectations have not been
realized due to the complexities of real materials. Thus the pursuit for more
ideal $J_{\rm eff}$ states remains ongoing. Here a near-ideal $J_{\rm
eff}$=$3/2$ Mott insulating phase is predicted in the family of hexachloro
niobates, which avoid some common drawbacks of perovskite oxides. The local
magnetic moment is nearly compensated between spin and orbital components,
rendering exotic recessive magnetism. More interestingly, the electronic
structure and magnetism can be strongly tuned by rotating spin axis, which is
rare but crucial for spintronic applications.",2010.10741v1
2021-10-26,"Structure and magnetic studies of geometrically frustrated disordered pyrochlores A$_{2}$Zr$_{2}$O$_{7}$: (A = Eu, Gd, Er)","The spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$ exhibits strong
frequency-dependent spin-freezing at $\sim$ 16 K temperature. Although it has
been a matter of discussion for years, the origin of this unusual spin freezing
is still unknown. The replacement of Ti with isovalent Zr leads to the dynamic
magnetic ground state at low temperatures in Dy$_{2}$Zr$_{2}$O$_{7}$ and
prevents the formation of high-temperature spin freezing. Interestingly the
high-temperature spin freezing re-emerges in the presence of the magnetic
field. In this direction, we have studied a series of disordered pyrochlore
oxides A$_{2}$Zr$_{2}$O$_{7}$ (A = Eu, Gd, Er) and compared their crystal
structure, magnetic, and heat capacity behavior with that of
Dy$_{2}$Zr$_{2}$O$_{7}$ and Ho$_{2}$Zr$_{2}$O$_{7}$ systems. Our study shows
that depending on the disordered parameter, the spin-freezing behavior can be
retained by slowing down the spin dynamic with a suitable choice of the
magnetic field. We observe that unlike titanates, modification at the rare
earth site does not make considerable change in the magnetic ground state of
these zirconates compounds.",2110.13573v1
2022-03-19,Spin wave excitation and directional propagation in presence of magnetic charges in square artificial spin ice,"Artificial spin ice is a special class of engineered lattice of highly shape
anisotropic single domain magnetic nanostructures which is used as one of the
model systems to study the spin ice behavior observed in pyrochlore oxides. The
nanomagnets interact via dipolar interaction which results in correlated
magnetization dynamics exhibiting macroscopic spin configuration states. Here,
we exploit the interplay of underlying magnetic state and external bias field
orientation to study controlled spin wave propagation in square Artificial Spin
Ice (sASI) by performing detailed micromagnetic simulations. We report that
careful selection of vertices with local magnetic charges can effectively
direct the anisotropic spin wave in presence of an external field. Further, we
explore the influence of local charges due to the excited state in
even-coordinated vertices as well as uncompensated charges due to
odd-coordinated vertices on spin wave behavior. Our studies suggest that there
is no perceptible difference on spin wave dynamical behavior due to the origin
of local magnetic charge in sASI. Our results of controlled and directional
spin wave propagation in sASI system may be useful for low-power consumption
based all magnonic on-chip devices.",2203.10345v1
2022-12-28,First-principles study of spin orbit coupling contribution to anisotropic magnetic interaction,"Anisotropic magnetic exchange interactions lead to a surprisingly rich
variety of the magnetic properties. Considering the spin orbit coupling (SOC)
as perturbation, we extract the general expression of a bilinear spin
Hamiltonian, including isotropic exchange interaction, antisymmetric
Dzyaloshinskii-Moriya (DM) interaction and symmetric $\Gamma $ term. Though it
is commonly believed that the magnitude of the DM and $\Gamma $ interaction
correspond to the first and second order of SOC strength $% \lambda $
respectively, we clarify that the term proportional to $\lambda ^{2}$ also has
contribution to DM interaction. Based on combining magnetic force theorem and
linear-response approach, we have presented the method of calculating
anisotropic magnetic interactions, which now has been implemented in the open
source software WienJ. Furthermore, we introduce another method which could
calculate the first and second order SOC contribution to the DM interaction
separately, and overcome some shortcomings of previous methods. Our methods are
successfully applied to several typical weak ferromagnets for $3d$, $4d$ and
$5d$ transition metal oxides. We also predict the conditions where the DM
interactions proportional to $\lambda $ are symmetrically forbidden while the
DM interactions proportional to $\lambda ^{2}$ are nonzero, and believe that it
is widespread in certain magnetic materials.",2212.13963v1
2023-01-25,Discovery of spin glass in maple-leaf lattice Na2Mn3O7,"Geometrically frustrated magnetism is commonly studied in triangular and
Kagome lattices. A rare lattice which exhibits frustration is obtained by
depleting 1/7 of the sites from a triangular lattice and is called a maple-leaf
lattice. We report the magnetic properties of an oxide material with a
maple-leaf lattice: Na2Mn3O7. Structural studies suggest slight lattice
distortion and density functional theory predicts energetic near-degeneracy
between ferromagnetism and antiferromagnetic phases which points towards
competing magnetic orderings at low temperatures. In addition, from our
magnetic studies, we discovered a non-equilibrium spin state below ~50 K. The
bifurcation of field-cooled and zero-field-cooled magnetization curves,
hysteresis of ~16 kOe at 2 K, and time-dependent magnetization response is
consistent with a spin glass state. To our knowledge this is the first report
of such a state in materials with a MLL. This is a promising discovery towards
using spin glass to transport angular momentum or spins for applications low
power spintronics.",2301.10399v1
2023-02-26,Emergence of net magnetization by magnetic-field-biased diffusion in antiferromagnetic L1$_0$ NiMn,"NiMn is a collinear antiferromagnet with high magneto crystalline anisotropy
($K_2=-9.7\times10^5\;\text{J m}^{-3}$). Through magnetic annealing of NiMn
with excess Ni, strongly pinned magnetic moments emerge due to an imbalance in
the distribution of Ni in the antiferromagnetic Mn-sublattices. The results are
explained with a model of magnetic-field-biased diffusion, supported by ab
initio calculations. Another observation is the oxidation of Mn at the surface,
causing an enrichment of Ni in the sub-surface region. This leads to an
additional ferromagnetic response appearing in the magnetization measurements,
which can be removed by surface polishing.",2302.13387v1
2023-12-04,Negative Magnetization and Magnetic Ordering of Rare Earth and Transition Metal Sublattices in NdFe0.5Cr0.5O3,"We investigate the effect of alloying at the 3d transition metal site of a
rare-earth-transition metal oxide, by considering NdFe0.5Cr0.5O3 alloy with two
equal and random distribution of 3d ions, Cr and Fe, interacting with an early
4f rare earth ion, Nd. Employing temperature- and field-dependent magnetization
measurements, temperature-dependent x-ray diffraction, neutron powder
diffraction, and Raman spectroscopy, we characterize its structural and
magnetic properties. Our study reveals bipolar magnetic switching (arising from
negative magnetization) and magnetocaloric effect which underline the potential
of the studied alloy in device application. The neutron diffraction study shows
the absence of spin reorientation transition over the entire temperature range
of 1.5-320 K, although both parent compounds exhibit spin orientation
transition. We discuss the microscopic origin of this curious behavior. The
neutron diffraction results also reveal the ordering of Nd spins at an
unusually high temperature of about 40 K, which is corroborated by Raman
measurements.",2312.01595v1
2024-01-26,Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface,"Magnetization dynamics, which determine the speed of magnetization switching
and spin information propagation, play a central role in modern spintronics.
Gaining its control will satisfy the different needs of various spintronic
devices. In this work, we demonstrate that the surface oxidized Cu
(CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics
of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$
layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in
comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower
than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of
anti-damping phenomena. Further, the reduction in damping is accompanied by a
very small reduction in the spin pumping-induced output DC voltage in the
CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping
and spin-to-charge conversion can be attributed to the orbital Rashba effect
observed at the HM/CuO$_\text{x}$ interface. Our experimental findings
illustrate that the cost-effective CuO$_\text{x}$ can be employed as an
integral part of modern spintronics devices owing to its rich underneath
spin-orbital physics.",2401.14708v1
1997-11-13,The singlet-triplet magnetism and induced spin fluctuations in the high-$T_c$ copper oxides,"High-$T_c$ cuprates like $La_{2-x}Sr_{x}CuO_{4}$ and $YBa_{2-x}Cu_{3}O_{6+x}$
are considered as a system of the electron and hole polar pseudo-Jahn-Teller
$CuO_{4}$ centers $[{CuO}_{4}^{7-}]_{JT}$ and $[CuO_{4}^{5-}]_{JT}$,
respectively, or a system of the local bosons moving in a lattice of the hole
centers. Ground manifold of the polar centers includes three terms $^{1}A_{1g}$
(Zhang-Rice singlet), $^{1}E_{u}$, $^{3}E_{u}$ with different spin
multiplicity, orbital degeneracy and parity that provides an unconventional
multi-mode behaviour of the cuprates. The spin subsystem of the copper oxides
within the polar Jahn-Teller $CuO_{4}$ centers model is a two-component spin
liquid and corresponds to a singlet-triplet magnet with possible noncollinear
spin configurations. In the framework of a modified mean field approximation
some kinds of spin ordering are discussed including as a trivial singlet or
triplet states as a pure quantum singlet-triplet mixed state. A local boson
movement is accompanied by a modulation of the spin density on the site
resulting in the so called induced spin fluctuations. Some unconventional
features of the induced spin fluctuations are considered including an
appearance of the induced longitudinal ferrimagnetism with an appropriate
contribution to the spin susceptibility, a possibility to observe and examine
the charge fluctuations with the help of the traditional magnetic methods such
as the magnetic inelastic neutron scattering and the spin lattice relaxation
experiments. The suggested model, in comparison with the nearly
antiferromagnetic Fermi-liquid model, represents new approach to the
description of the spin system of the high-$T_c$ cuprates.",9711116v1
2006-02-02,Lattice Distortion and Magnetism of 3d-$t_{2g}$ Perovskite Oxides,"Several puzzling aspects of interplay of the experimental lattice distortion
and the the magnetic properties of four narrow $t_{2g}$-band perovskite oxides
(YTiO$_3$, LaTiO$_3$, YVO$_3$, and LaVO$_3$) are clarified using results of
first-principles electronic structure calculations. First, we derive parameters
of the effective Hubbard-type Hamiltonian for the isolated $t_{2g}$ bands using
newly developed downfolding method for the kinetic-energy part and a hybrid
approach, based on the combination of the random-phase approximation and the
constraint local-density approximation, for the screened Coulomb interaction
part. Then, we solve the obtained Hamiltonian using a number of techniques,
including the mean-field Hartree-Fock (HF) approximation, the second-order
perturbation theory for the correlation energy, and a variational superexchange
theory. Even though the crystal-field splitting is not particularly large to
quench the orbital degrees of freedom, the crystal distortion imposes a severe
constraint on the form of the possible orbital states, which favor the
formation of the experimentally observed magnetic structures in YTiO$_3$,
YVO$_$, and LaVO$_3$ even at the HF level. Beyond the HF approximation, the
correlations effects systematically improve the agreement with the experimental
data. Using the same type of approximations we could not reproduce the correct
magnetic ground state of LaTiO$_3$. However, we expect that the situation may
change by systematically improving the level of approximations for dealing with
the correlation effects.",0602035v1
2009-04-02,The layered iron arsenides Sr2CrO3FeAs and Ba2ScO3FeAs,"Polycrystalline samples of the layered iron arsenides Sr2CrO3FeAs and
Ba2ScO3FeAs were synthesized by high temperature solid state reactions and
their crystal structures determined by the X-ray powder diffraction. Their
structures are tetragonal (P4/nmm; Sr2CrO3FeAs: a = 391.12(1) pm, c =
1579.05(3) pm; Ba2ScO3FeAs: a = 412.66(5) pm, c = 1680.0(2) pm, Z = 2) and
isotypic to Sr2ScO3CuS. Iron arsenide layers are sandwiched between
perowskite-like oxide blocks and separated by ~1600 pm, which is much larger
compared to the 1111 iron arsenide superconductors. The bond length and angles
within the FeAs layers are adapted to the space requirements of the oxide
blocks. Measurements of the magnetic susceptibility and electrical resistivity
show no hint for a SDW-like anomaly in both compounds. Sr2CrO3FeAs shows
Curie-Weiss paramagnetism above 160 K with an effective magnetic moment of
3.83(3) muB in good agreement with the theoretical value of 3.87 muB for Cr3+.
Antiferromagnetic ordering was detected below TN ~ 31 K. 57Fe Moessbauer
spectra of Sr2CrO3FeAs show a single signal that broadens below the magnetic
ordering temperature due to a small transferred hyperfine field induced by the
magnetic ordering of the chromium atoms. 57Fe-Moessbauer spectra of Ba2ScO3FeAs
show single signals at 298, 77, and 4.2 K which are only subject to weak
quadrupole splitting.",0904.0479v2
2009-09-19,"Electronic phase diagram of the layered cobalt oxide system, LixCoO2 (0.0 <= x <= 1.0)","Here we report the magnetic properties of the layered cobalt oxide system,
LixCoO2, in the whole range of Li composition, 0 <= x <= 1. Based on
dc-magnetic susceptibility data, combined with results of 59Co-NMR/NQR
observations, the electronic phase diagram of LixCoO2 has been established. As
in the related material NaxCoO2, a magnetic critical point is found to exist
between x = 0.35 and 0.40, which separates a Pauli-paramagnetic and a
Curie-Weiss metals. In the Pauli-paramagnetic regime (x <= 0.35), the
antiferromagnetic spin correlations systematically increase with decreasing x.
Nevertheless, CoO2, the x = 0 end member is a non-correlated metal in the whole
temperature range studied. In the Curie-Weiss regime (x >= 0.40), on the other
hand, various phase transitions are observed. For x = 0.40, a susceptibility
hump is seen at 30 K, suggesting the onset of static AF order. A magnetic jump,
which is likely to be triggered by charge ordering, is clearly observed at Tt =
175 K in samples with x = 0.50 (= 1/2) and 0.67 (= 2/3), while only a tiny kink
appears at T = 210 K in the sample with an intermediate Li composition, x =
0.60. Thus, the phase diagram of the LixCoO2 system is complex, and the
electronic properties are sensitively influenced by the Li content (x).",0909.3556v2
2009-11-02,Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Nonsuperconducting Copper Oxide,"The doping of charge carriers into the CuO2 planes of copper oxide Mott
insulators causes a gradual destruction of antiferromagnetism and the emergence
of high-temperature superconductivity. Optimal superconductivity is achieved at
a doping concentration p beyond which further increases in doping cause a
weakening and eventual disappearance of superconductivity. A potential
explanation for this demise is that ferromagnetic fluctuations compete with
superconductivity in the overdoped regime. In this case a ferromagnetic phase
at very low temperatures is predicted to exist beyond the doping concentration
at which superconductivity disappears. Here we report on a direct examination
of this scenario in overdoped La2-xSrxCuO4 using the technique of muon spin
relaxation. We detect the onset of static magnetic moments of electronic origin
at low temperature in the heavily overdoped nonsuperconducting region. However,
the magnetism does not exist in a commensurate long-range ordered state.
Instead it appears as a dilute concentration of static magnetic moments. This
finding places severe restrictions on the form of ferromagnetism that may exist
in the overdoped regime. Although an extrinsic impurity cannot be absolutely
ruled out as the source of the magnetism that does occur, the results presented
here lend support to electronic band calculations that predict the occurrence
of weak localized ferromagnetism at high doping.",0911.0407v3
2011-03-05,"Measurement of the internal magnetic field in the correlated iridates Ca$_4$IrO$_6$, Ca$_5$Ir$_3$O$_{12}$, Sr$_3$Ir$_2$O$_7$ and Sr$_2$IrO$_4$","Oxides containing iridium ions display a range of magnetic and conducting
properties that depend on the delicate balance between interactions and are
controlled, at least in part, by the details of the crystal architecture. We
have used muon-spin rotation ($\mu$SR) to study the local field in four iridium
oxides, Ca$_4$IrO$_6$, Ca$_5$Ir$_3$O$_{12}$, Sr$_3$Ir$_2$O$_7$ and
Sr$_2$IrO$_4$, which show contrasting behavior. Our $\mu$SR data on
Ca$_4$IrO$_6$ and Ca$_5$Ir$_3$O$_{12}$ are consistent with conventional
antiferromagnetism where quasistatic magnetic order develops below $T_{\rm
N}=13.85(6)$ K and 7.84(7) K respectively. A lower internal field is observed
for Ca$_5$Ir$_3$O$_{12}$, as compared to Ca$_4$IrO$_6$ reflecting the presence
of both Ir$^{4+}$ and Ir$^{5+}$ ions, resulting in a more magnetically dilute
structure. Muon precession is only observed over a restricted range of
temperature in Sr$_3$Ir$_2$O$_7$, while the Mott insulator Sr$_2$IrO$_4$
displays more complex behavior, with the $\mu$SR signal containing a single,
well-resolved precession signal below $T_{\rm N}=230$\,K, which splits into two
precession signals at low temperature following a reorientation of the spins in
the ordered state.",1103.1036v1
2012-07-09,Unusual magnetic phases in the strong interaction limit of two-dimensional topological band insulators in transition metal oxides,"The expected phenomenology of non-interacting topological band insulators
(TBI) is now largely theoretically understood. However, the fate of TBIs in the
presence of interactions remains an active area of research with novel,
interaction-driven topological states possible, as well as new exotic magnetic
states. In this work we study the magnetic phases of an exchange Hamiltonian
arising in the strong interaction limit of a Hubbard model on the honeycomb
lattice whose non-interacting limit is a two-dimensional TBI recently proposed
for the layered heavy transition metal oxide compound, (Li,Na)$_2$IrO$_3$. By a
combination of analytical methods and exact diagonalization studies on finite
size clusters, we map out the magnetic phase diagram of the model. We find that
strong spin-orbit coupling can lead to a phase transition from an
antiferromagnetic Ne\'el state to a spiral or stripy ordered state. We also
discuss the conditions under which a quantum spin liquid may appear in our
model, and we compare our results with the different but related
Kitaev-Heisenberg-$J_2$-$J_3$ model which has recently been studied in a
similar context.",1207.2156v2
2013-11-27,Engineered spatial inversion symmetry breaking in an oxide heterostructure built from isosymmetric room-temperature magnetically ordered components,"The oxide heterostructure [(YFeO$_3$)$_5$(LaFeO$_3$)$_5$]$_{40}$, which is
magnetically ordered and piezoelectric at room temperature, has been
constructed from two weak ferromagnetic AFeO$_3$ perovskites with different A
cations using RHEED-monitored pulsed laser deposition. The polarisation arises
through the removal of inversion centres present within the individual AFeO$_3$
components. This symmetry reduction is a result of combining ordering on the A
site, imposed by the periodicity of the grown structure, with appropriate
orientations of the octahedral tilting characteristic of the perovskite units
themselves, according to simple symmetry-controlled rules. The polarisation is
robust against A site interdiffusion between the two layers which produces a
sinusoidally modulated occupancy that retains the coupling of translational and
point symmetries required to produce a polar structure. Magnetization and
magneto-optical Kerr rotation measurements show that the heterostructure's
magnetic structure is similar to that of the individual components. Evidence of
the polarity was obtained from second harmonic generation and piezoelectric
force microscopy measurements. Modeling of the piezoresponse allows extraction
of $d_{33}$ (approximately 10 pC/N) of the heterostructure, which is in
agreement with DFT calculations.",1311.7032v1
2015-06-05,Ground-state selection and spin-liquid behaviour in the classical Heisenberg model on the breathing pyrochlore lattice,"Magnetic pyrochlore oxides, including the spin ice materials, have proved to
be a rich field for the study of geometrical frustration in 3 dimensions.
Recently, a new family of magnetic oxides has been synthesised in which the
half of the tetrahedra in the pyrochlore lattice are inflated relative to the
other half, making an alternating array of small and large tetrahedra. These
""breathing pyrochlore"" materials such as LiGaCr4O8, LiInCr4O8 and Ba3Yb2Zn5O11
provide new opportunities in the study of frustrated magnetism. Here we provide
an analytic theory for the ground state phase diagram and spin correlations for
the minimal model of magnetism in breathing pyrochlores: a classical nearest
neighbour Heisenberg model with different exchange coefficients for the two
species of tetrahedra. We find that the phase diagram comprises a Coulombic
spin liquid phase, a conventional ferromagnetic phase and an unusual
antiferromagnetic phase with lines of soft modes in reciprocal space,
stabilised by an order-by-disorder mechanism. We obtain a theory of the spin
correlations in this model using the Self Consistent Gaussian Approximation
(SCGA) which enables us to discuss the development of correlations in breathing
pyrochlores as a function of temperature, and we quantitatively characterise
the thermal crossover from the limit of isolated tetrahedra to the strongly
correlated limit of the problem. We compare the results of our analysis with
the results of recent neutron scattering experiments on LiInCr4O8.",1506.01822v1
2015-09-07,Emergent nanoscale superparamagnetism at oxide interfaces,"Atomically sharp oxide heterostructures exhibit a range of novel physical
phenomena that do not occur in the parent bulk compounds. The most prominent
example is the appearance of highly conducting and superconducting states at
the interface between the band insulators LaAlO3 and SrTiO3. Here we report a
new emergent phenomenon at the LaMnO3/SrTiO3 interface in which an
antiferromagnetic insulator abruptly transforms into a magnetic state that
exhibits unexpected nanoscale superparamagnetic dynamics. Upon increasing the
thickness of LaMnO3 above five unit cells, our scanning nanoSQUID-on-tip
microscopy shows spontaneous formation of isolated magnetic islands of 10 to 50
nm diameter, which display random moment reversals by thermal activation or in
response to an in-plane magnetic field. Our charge reconstruction model of the
polar LaMnO3/SrTiO3 heterostructure describes the sharp emergence of
thermodynamic phase separation leading to nucleation of metallic ferromagnetic
islands in an insulating antiferromagnetic matrix. The model further suggests
that the nearby superparamagnetic-ferromagnetic transition can be gate tuned,
holding potential for applications in magnetic storage and spintronics.",1509.01895v1
2017-01-20,"Tuning sizes, morphologies, and magnetic properties of mono- vs. multi-core iron oxide nanoparticles through control of added water in the polyol synthesis","The polyol route is a versatile and up-scalable method to produce large
batches of iron oxide nanoparticles with well-defined structure and magnetic
properties. Controlling parameters such as temperature and duration of
reaction, heating profile, nature of polyol solvent or of organometallic
precursors were reported in previous studies of literature, but none of them
described yet the crucial role of water in the forced hydrolysis pathway, whose
presence is mandatory for nanoparticle production. This communication
investigates the influence of the water amount and temperature at which it is
injected in the reflux system for either pure polyol or mixture with a
poly(hydroxy) amine. Distinct morphologies of nanoparticles were thereby
obtained, from ultra-ultra-small smooth spheres down to 4 nm in diameter to
large ones up to 37 nm in diameter. Nanoflowers were also synthesized, which
are well-defined multi-core assemblies with narrow grain size dispersity. A
diverse and large library of samples was obtained by playing on the nature of
solvents and amount of water traces while keeping all the other parameters
fixed. The varied morphologies lead to magnetic nanoparticles well-fitting to
required applications among magnetic hyperthermia and MRI contrast agent, or
both.",1701.05858v3
2020-04-08,Spin dynamics and a nearly continuous magnetic phase transition in an entropy-stabilized oxide antiferromagnet,"The magnetic order and the spin dynamics in the antiferromagnetic
entropy-stabilized oxide (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O
(MgO-ESO) have been studied using muon spin relaxation ($\mu$SR) and inelastic
neutron scattering. We find that antiferromagnetic order develops gradually in
the sample volume as it is cooled below 140 K, becoming fully ordered around
100 K. The spin dynamics show a critical slowing down in the vicinity of the
transition, and the magnetic order parameter grows continuously in the ordered
state. These results indicate that the antiferromagnetic transition is
continuous but proceeds with a Gaussian distribution of ordering temperatures.
The magnetic contribution to the specific heat determined from inelastic
neutron scattering likewise shows a broad feature centered around 120 K.
High-resolution inelastic neutron scattering further reveals an initially
gapped spectrum at low temperature which sees an increase in a quasielastic
contribution upon heating until the ordering temperature.",2004.04218v2
2019-02-21,Effects of the removal of Ta capping layer on the magnetization dynamics of Permalloy thin films,"We have investigated the spin wave dynamics of Permalloy (Py) thin films with
and without a Ta capping layer for varying Py thickness (15 nm, 20 nm and 30
nm) using all optical time-resolved magneto-optical Kerr effect measurements.
XPS measurements confirm the oxidation of the originally-prepared samples and
also that the removal of the Ta capping layer is achievable by a few sputtering
cycles. The magnetic field strength dependencies of the spin wave modes with
the variation of the Py film thickness for the samples are studied. We observe
that the presence of the Ta capping layer reduces the precessional frequencies
of the samples while the samples without a Ta capping layer enhance the role of
Py thickness. We also observe that the decay time of spin waves is highly
dependent on the top layer of the samples. The decay time increases with
increasing Py thicknesses for Ta/Py/Ta samples implying that the enhancement of
decay time is caused by the Ta/Py/Ta interfaces. Whereas, for Ta/Py samples the
decay time decreases with increasing Py thickness. The results of this work
extend the knowledge on the magnetization dynamics of Py thin films giving
information on how to resume and even enhance the spin mobility after a
deleterious oxidation process. This can open new scenarios on the building
process and on the maintenance of fast magnetic switching devices.",1902.07832v1
2019-04-19,Magnetization density distribution of Sr$_2$IrO$_4$: Deviation from a local $j_\text{eff}=1/2$ picture,"$5d$ iridium oxides are of huge interest due to the potential for new quantum
states driven by strong spin-orbit coupling. The strontium iridate
Sr$_2$IrO$_4$ is particularly in the spotlight because of the so-called
$j_\text{eff}=1/2$ state consisting of a quantum superposition of the three
local $t_{2g}$ orbitals with -- in its most simple version -- nearly equal
population, which stabilizes an unconventional Mott insulating state. Here, we
report an anisotropic and aspherical magnetization density distribution
measured by polarized neutron diffraction in a magnetic field up to 5~T at 4~K,
which strongly deviates from a local \jeffHalf picture even when
distortion-induced deviations from the equal weights of the orbital populations
are taken into account. Once reconstructed by the maximum entropy method and
multipole expansion model refinement, the magnetization density shows
cross-shaped positive four lobes along the crystallographic tetragonal axes
with a large spatial extent, showing that the $xy$ orbital contribution is
dominant. The analogy to the superconducting copper oxide systems might then be
weaker than commonly thought.",1904.09139v4
2020-05-19,Controlling the electrical and magnetic ground states by doping in the complete phase diagram of titanate Eu1-xLaxTiO3 thin films,"EuTiO3, a band insulator, and LaTiO3, a Mott insulator, are both
antiferromagnetic with transition temperatures ~ 5.5 K and ~ 160 K,
respectively. Here, we report the synthesis of Eu1-xLaxTiO3 thin films with x =
0 to 1 by oxide molecular beam epitaxy. The films in the full range have high
crystalline quality and show no phase segregation, allowing us carry out
transport measurements to study their electrical and magnetic properties. From
x = 0.03 to 0.95, Eu1-xLaxTiO3 films show conduction by electrons as charge
carriers, with differences in carrier densities and mobilities, contrary to the
insulating nature of pure EuTiO3 and LaTiO3. Following a rich phase diagram,
the magnetic ground states of the films vary with increasing La-doping level,
changing Eu1-xLaxTiO3 from an antiferromagnetic insulator to an
antiferromagnetic metal, a ferromagnetic metal, a paramagnetic metal, and back
to an antiferromagnetic insulator. These emergent properties reflect the
evolutions of the band structure, mainly at the Ti t2g bands near the Fermi
level, when Eu2+ are gradually replaced by La3+. This work sheds light on this
method for designing the electrical and magnetic properties in
strongly-correlated oxides and completes the phase diagram of the titanate
Eu1-xLaxTiO3.",2005.09581v1
2020-05-29,Large magnetoelectric coupling in multiferroic oxide heterostructures assembled via epitaxial lift-off,"The strain dependent functional properties of epitaxial transition metal
oxide films can be significantly modified via substrate selection. However,
large lattice mismatches preclude dislocation-free epitaxial growth on
ferroelectric substrates, whose strain states are modified by applied electric
fields. Here we overcome this mismatch problem by depositing an epitaxial film
of ferromagnetic La0.7Sr0.3MnO3 on a single crystal substrate of well lattice
matched SrTiO3 via a film of SrRuO3 that we subsequently dissolved, permitting
the transfer of unstrained La0.7Sr0.3MnO3 to a ferroelectric substrate of
0.68Pb(Mg1/3Nb2/3)O3 0.32PbTiO3 in a different crystallographic orientation.
Ferroelectric domain switching, and a concomitant ferroelectric phase
transition, produced large non volatile changes of magnetization that were
mediated by magnetic domain rotations at locations defined by the
microstructure - as revealed via high resolution vector maps of magnetization
constructed from photoemission electron microscopy data, with contrast from
x-ray magnetic circular dichroism. In future, our method may be exploited to
control functional properties in dislocation free epitaxial films of any
composition.",2006.00034v2
2021-03-16,Emergent Magnetic Phenomenon with Unconventional Structure in Epitaxial Manganate Thin Films,"A variety of emergent phenomena has been enabled by interface engineering in
the complex oxides heterostructures. While extensive attention has been
attracted to LaMnO3 (LMO) thin films for observing the control of
functionalities at its interface with substrate, the nature of the magnetic
phases in the thin film is, however,controversial. Here, it is reported that
the ferromagnetism in 2 and 5 unit cells thick LMO films epitaxially deposited
(001)-SrTiO3 substrates ferromagnetic/ferromagnetic coupling in 8 and
10-unit-cell ones, and a striking ferromagnetic/antiferromagnetic pinning
effect with apparent positive exchange bias in 15 and 20-unit-cell ones are
observed. This novel phenomenon in both 15 and 20-unit-cell films indicates a
coexistence of three magnetic orderings in a single LMO film.The
high-resolution scanning transmission electron microscopy suggests a P21/n to
Pbnm symmetry transition from interface to surface, with the spatial
stratification of MnO6 octahedral morphology, corresponding to different
magnetic orderings. These results should shed some new lights on manipulating
the functionality of oxides by interface engineering.",2103.09133v1
2021-08-10,Site-selective magnetic moment collapse in compressed Fe5O6,"Iron oxide is one of the most important components in Earth's mantle. Recent
discovery of the stable presence of Fe5O6 at Earth's mantle environment
stimulates significant interests in the understanding of this new category of
iron oxides. In this paper, we report the electronic structure and magnetic
properties of Fe5O6 calculated by the density functional theory plus dynamic
mean field theory (DFT+DMFT) approach. Our calculations indicate that Fe5O6 is
a conductor at the ambient pressure with dominant Fe-3d density of states at
the Fermi level. The magnetic moments of iron atoms at three non-equivalent
crystallographic sites in Fe5O6 collapse at significantly different rate under
pressure. Such site-selective collapse of magnetic moments originates from the
shifting of energy levels and the consequent charge transfer among the Fe-3d
orbits when Fe5O6 is being compressed. Our simulations suggest that there could
be high conductivity and volume contraction in Fe5O6 at high pressure, which
may induce anomalous features in seismic velocity, energy exchange, and mass
distribution at the deep interior of Earth.",2108.04473v1
2021-12-22,Low temperature magnetic and dielectric properties correlation in Fe-doped copper (ii) oxide ceramics for potential device application,"The bulk samples of CuO and Fe-doped CuO were synthesized by ceramics
methods. Structural and compositional analyses were performed by using X-ray
diffraction, SEM, and EDAX. Through this manuscript, we are going to report the
effect of trivalent iron doping (Fe$^{3+}$) in copper (II) oxide
(Cu$_{0.95}$Fe$_{0.05}$O) bulk samples on magnetic and dielectric behavior. The
paramagnetic phase has been established in CuO as a result of Fe$^{3+}$ doping.
The strong correlation between magnetic and dielectric properties indicated
spin-polaron interaction at the transition temperature. Bulk CuO and also
Cu$_{0.95}$Fe$_{0.05}$O exhibit the multiferroic phase in a narrow temperature
range (190 K to 230 K). Two transitions happened from a
paramagnetic-paraelectric phase to incommensurate or asymmetrical
antiferromagnetic (AF) and ferroelectric state near highest Neel temperature
(TN1) ~230 K and another second phase transition, the order of AF phase
transformed to commensurate AF phase and ferroelectricity disappeared at around
the Neel temperature (TN2) ~210 K in all samples. This Cu$_{0.95}$Fe$_{0.05}$O
would show its potential in the spintronic application for a high dielectric
constant with low loss and high magnetic susceptibility.",2112.11874v1
2022-10-25,Engineered Kondo screening and nonzero Berry phase in SrTiO3/LaTiO3/SrTiO3 heterostructures,"Controlling the interplay between localized spins and itinerant electrons at
the oxide interfaces can lead to exotic magnetic states. Here we devise
SrTiO3/LaTiO3/SrTiO3 heterostructures with varied thickness of the LaTiO3 layer
(n monolayers) to investigate the magnetic interactions in the two-dimensional
electron gas system. The heterostructures exhibit significant Kondo effect when
the LaTiO3 layer is rather thin (n = 2, 10), manifesting the strong interaction
between the itinerant electrons and the localized magnetic moments at the
interfaces, while the Kondo effect is greatly inhibited when n = 20. Notably,
distinct Shubnikov-de Haas oscillations are observed and a nonzero Berry phase
of {\pi} is extracted when the LaTiO3 layer is rather thin (n = 2, 10), which
is absent in the heterostructure with thicker LaTiO3 layer (n = 20). The
observed phenomena are consistently interpreted as a result of sub-band
splitting and symmetry breaking due to the interplay between the interfacial
Rashba spin-orbit coupling and the magnetic orderings in the heterostructures.
Our findings provide a route for exploring and manipulating nontrivial
electronic band structures at complex oxide interfaces.",2210.13951v1
2023-07-15,"Controlling electronic, magnetic, thermal, and optical properties of boron-nitrogen codoped strontium oxide monolayer: Activation of optical transitions in the VL region","The electronic, thermal, magnetic and optical properties of BN-codoped
strontium oxide (SrO) monolayers are studied taking into account the
interaction effects between the B and the N dopant atoms. The indirect band gap
of a pure two dimensional SrO is modified to a narrow direct band gap by tuning
the B-N attractive interaction. The B or N separately doped SrO leads to a
metallic behavior, while a BN-codoped SrO has a semiconductor character. The
strong B-N attractive interaction changes a non-magnetic SrO to a magnetic
system and reduces its heat capacity. An ab initio molecular dynamics, AIMD,
calculations are also utilized to check the thermodynamic stability of the pure
and BN-codoped SrO monolayers. The band gap reduction of SrO increases the
optical conductivity shifting the most intense peak from the Deep-UV to the
visible light region. The red shifted optical conductivity emerges due to the
B-N attractive interaction. In addition, both iso- and anisotropic characters
are seen in the optical properties depending on the strength of the B-N
attractive interaction. It can thus be confirmed that the interaction effects
of the BN-codopants can be used to control the properties of SrO monolayers for
thermo- and opto-electronic devices.",2307.09173v1
2023-12-10,Stability and Character of Zero Field Skyrmionic States in Hybrid Magnetic Multilayer Nanodots,"Ambient magnetic skyrmions stabilized in multilayer nanostructures are of
immense interest due to their relevance to magnetic tunnel junction (MTJ)
devices for memory and unconventional computing applications. However, existing
skyrmionic nanostructures built using conventional metallic or oxide multilayer
nanodots are unable to concurrently fulfill the requirements of nanoscale
skyrmion stability and feasibility of all-electrical readout and manipulation.
Here, we develop a few-repeat hybrid multilayer platform consisting of metallic
[Pt/CoB/Ir]3 and oxide [Pt/CoB/MgO] components that are coupled to evolve
together as a single, composite stack. Zero-field (ZF) skyrmions with sizes as
small as 50 nm are stabilized in the hybrid multilayer nanodots, which are
smoothly modulated by up to 2.5x by varying CoB thickness and dot sizes.
Meanwhile, skyrmion multiplets are also stabilized by small bias fields.
Crucially, we observe higher order 'target' skyrmions with varying
magnetization rotations in moderately-sized, low anisotropy nanodots. These
results provide a viable route to realize long-sought skyrmionic MTJ devices
and new possibilities for multi-state skyrmionic device concepts.",2312.05801v1
2016-06-16,"Magnetic Properties from the Viewpoints of Electronic Hamiltonian: Spin Exchange Parameters, Spin Orientation and Spin-Half Misconception","In this chapter we review the quantitative and qualitative aspects of
describing the properties of magnetic solids on the basis of electronic
Hamiltonian. We show that a spin Hamiltonian approach becomes consistent with
an electronic Hamiltonian approach if the spin lattice and its associated spin
exchange parameters, to be used for the spin Hamiltonian, are determined by the
energy-mapping analysis based on DFT calculations. The preferred spin
orientation (i.e., the magnetic anisotropy) of a magnetic ion is not predicted
by a spin Hamiltonian because it does not include the orbital degree of freedom
explicitly. In contrast, the magnetic anisotropy is readily predicted by
electronic structure theories employing both orbital and spin degrees of
freedom, if one takes into consideration the spin-orbit coupling (SOC). It was
shown that the preferred spin orientation of a magnetic ion can be predicted
and understood in terms of the HOMO-LUMO interactions of the magnetic ion by
taking SOC as perturbation. A spin Hamiltonian gives rise to the spin-half
misconception, namely, the blind belief that spin-half magnetic ions do not
possess magnetic anisotropy that arise from SOC. This misconception is a direct
consequence from the limitedness of a spin Hamiltonian that it lacks the
orbital degree of freedom. We show that the magnetic properties of 5d ion
oxides are better explained by the LS-coupling than by the jj-coupling scheme
of SOC, that the spin-orbital entanglement of 5d ions is not as strong as has
been assumed.",1606.05220v1
2016-07-14,Reading and Writing Single-Atom Magnets,"The highest-density magnetic storage media will code data in single-atom
bits. To date, the smallest individually addressable bistable magnetic bits on
surfaces consist of 5-12 atoms. Long magnetic relaxation times were
demonstrated in molecular magnets containing one lanthanide atom, and recently
in ensembles of single holmium (Ho) atoms supported on magnesium oxide (MgO).
Those experiments indicated the possibility for data storage at the fundamental
limit, but it remained unclear how to access the individual magnetic centers.
Here we demonstrate the reading and writing of individual Ho atoms on MgO, and
show that they independently retain their magnetic information over many hours.
We read the Ho states by tunnel magnetoresistance and write with current pulses
using a scanning tunneling microscope. The magnetic origin of the long-lived
states is confirmed by single-atom electron paramagnetic resonance (EPR) on a
nearby Fe sensor atom, which shows that Ho has a large out-of-plane moment of
$(10.1 \pm 0.1)$ $\mu_{\rm B}$ on this surface. In order to demonstrate
independent reading and writing, we built an atomic scale structure with two Ho
bits to which we write the four possible states and which we read out remotely
by EPR. The high magnetic stability combined with electrical reading and
writing shows that single-atom magnetic memory is possible.",1607.03977v1
2016-09-13,Enhancing interfacial magnetization with a ferroelectric,"Ferroelectric control of interfacial magnetism has attracted much attention.
However, the coupling of these two functionalities has not been understood well
at the atomic scale. The lack of scientific progress is mainly due to the
limited characterization methods by which the interface's magnetic properties
can be probed at an atomic level. Here, we use polarized neutron reflectometry
(PNR) to probe the evolution of the magnetic moment at interfaces in
ferroelectric/strongly correlated oxide [PbZr0.2Ti0.8O3/La0.8Sr0.2MnO3
(PZT/LSMO)] heterostructures. We find that there is always suppressed
magnetization at the surface and interface of LSMO and such magnetic
deterioration can be strongly improved by interfacing with a strongly polar PZT
film. The magnetoelectric coupling of magnetism and ferroelectric polarization
occurs within a couple of nanometers of the interface as demonstrated by the
enhanced interfacial magnetization beyond the bulk value by 5% depending on the
polarization of PZT. The latter value is 70% higher than the surface
magnetization of a LSMO film without interfacing with a ferroelectric layer.
These compelling results not only probe the presence of nanoscale magnetic
suppression and its control by ferroelectrics, but also emphasize the
importance of utilizing probing techniques that can distinguish between bulk
and interfacial phenomena.",1609.03983v1
2018-04-02,Collective Coordinate Descriptions of Magnetic Domain Wall Motion in Perpendicularly Magnetized Nanostructures under the Application of In-plane Fields,"Manipulation of magnetic domain walls can be used to improve the capabilities
of the next generation of memory and sensing devices. Materials of recent
interest for such devices include heterostructures of ultrathin ferromagnets
sandwiched between a heavy metal and an oxide, where spin-orbit coupling and
broken inversion symmetry give rise to the Dzyaloshinskii-Moriya interaction
(DMI), stabilizing chiral domain walls. The efficiency of the motion of these
chiral domain walls may be controlled using in-plane magnetic fields. This
property has been used for measurement of DMI strength. While micromagnetic
simulations are able to accurately predict domain wall motion under in-plane
fields in these materials, collective coordinate models such as the $q-\phi$
and $q-\phi-\chi$ models fail to reproduce the micromagnetic results. In this
theoretical work, we present a set of extended collective coordinate models
including canting in the domains, which better reproduce micromagnetic results,
and helps us better understand the effect of in-plane fields on magnetic domain
walls. These models are used in conjunction with micromagnetic simulations to
identify critical points observed in the motion of the domain walls driven by
out-of-plane magnetic fields, and electric current under magnetic in-plane
fields. Our new models and results help in the development of future domain
wall based devices based on perpendicularly magnetized materials.",1804.00569v3
2019-01-05,Investigating the Effect of Magnetic Dipole-Dipole Interaction on Magnetic Particle Spectroscopy (MPS): Implications for Magnetic Nanoparticle-based Bioassays and Magnetic Particle Imaging (MPI),"Superparamagnetic iron oxide nanoparticles (SPIONs), with comparable size to
biomolecules (such as proteins, nucleic acids, etc.) and unique magnetic
properties, good biocompatibility, low toxicity, potent catalytic behavior, are
promising candidates for many biomedical applications. There is one property
present in most SPION systems, yet it has not been fully exploited, which is
the dipole-dipole interaction (also called dipolar interaction) between the
SPIONs. It is known that the magnetic dynamics of an ensemble of SPIONs are
substantially influenced by the dipolar interactions. However, the exact way it
affects the performance of magnetic particle-based bioassays and magnetic
particle imaging (MPI) is still an open question. The purpose of this paper is
to give a partial answer to this question. This is accomplished by numerical
simulations on the dipolar interactions between two nearby SPIONs and
experimental measurements on an ensemble of SPIONs using our lab-based magnetic
particle spectroscopy (MPS) system. Our results show that even moderate changes
in the SPION concentration may have substantial effects on the magnetic
dynamics of the SPION system and the harmonic signal magnitudes can be
increased or decreased by 60%, depending on the values of MPS system
parameters.",1901.01355v1
2019-08-29,Tuning Single-Atom Electron Spin Resonance in a Vector-Magnetic Field,"Spin resonance of single spin centers bears great potential for chemical
structure analysis, quantum sensing and quantum coherent manipulation.
Essential for these experiments is the presence of a two-level spin system
whose energy splitting can be chosen by applying a magnetic field. In recent
years, a combination of electron spin resonance (ESR) and scanning tunneling
microscopy (STM) has been demonstrated as a technique to detect magnetic
properties of single atoms on surfaces and to achieve sub-${\mu}$eV energy
resolution. Nevertheless, up to now the role of the required magnetic fields
has not been elucidated. Here, we perform single-atom ESR on individual Fe
atoms adsorbed on magnesium oxide (MgO), using a 2D vector magnetic field as
well as the local field of the magnetic STM tip in a commercially available
STM. We show how the ESR amplitude can be greatly improved by optimizing the
magnetic fields, revealing in particular an enhanced signal at large in-plane
magnetic fields. Moreover, we demonstrate that the stray field from the
magnetic STM tip is a versatile tool. We use it here to drive the electron spin
more efficiently and to perform ESR measurements at constant frequency by
employing tip-field sweeps. Lastly, we show that it is possible to perform ESR
using only the tip field, under zero external magnetic field, which promises to
make this technique available in many existing STM systems.",1908.11061v1
2021-03-24,Structural and Magnetic Transitions in the Planar Antiferromagnet Ba$_4$Ir$_3$O$_{10}$,"We report the structural and magnetic ground state properties of the
monoclinic compound barium iridium oxide Ba$_4$Ir$_3$O$_{10}$ using a
combination of resonant x-ray scattering, magnetometry, and thermodynamic
techniques. Magnetic susceptibility exhibits a pronounced antiferromagnetic
transition at $T_{\text{N}}$ $\approx$ 25K, a weaker anomaly at $T_{\text{S}}$
$\approx$ 142K, and strong magnetic anisotropy at all temperatures. Resonant
elastic x-ray scattering experiments reveal a second order structural phase
transition at $T_{\text{S}}$ and a magnetic transition at $T_{\text{N}}$. Both
structural and magnetic superlattice peaks are observed at $L$ = half integer
values. The magnetization anomaly at $T_{\text{S}}$ implies the presence of
magneto-elastic coupling, which conceivably facilitates the symmetry lowering.
Mean field critical scattering is observed above $T_{\text{S}}$. The magnetic
structure of the antiferromagnetic ground state is discussed based on the
measured magnetic superlattice peak intensity. Our study not only presents
essential information for understanding the intertwined structural and magnetic
properties in Ba$_4$Ir$_3$O$_{10}$, but also highlights the necessary
ingredients for exploring novel ground states with octahedra trimers.",2103.12979v1
2012-10-30,Electronic structure of TiO2 thin films and LaAlO3-SrTiO3 heterostructures: the role of titanium 3d1 states in magnetic and transport properties,"In this Thesis, a study of the electronic structure of two Ti-based oxide
systems, TiO2 thin films and the ultra-thin LaAlO3-SrTiO3 (LAO-STO)
heterojunctions, is given. A weak room-temperature ferromagnetism (FM) has been
detected in slightly reduced TiO2 thin film and in other oxides; as these
materials are insulating closed-shell systems, this phenomenon has been
classified as ""d0 magnetism"". Since this magnetism could be related to the
growth process and to the presence of defects (oxygen vacancies, VO), an
analysis of Ti electronic states (especially of Ti3+ energy levels) is
mandatory. The first part of this work is devoted to the magnetic
characterization of a set of TiO2 and N-doped TiO2 samples, together with the
analysis of Ti 3d-related states carried out with X-ray photoemission (XPS) and
resonant photoemission (ResPES). The hypothesis of clustered VO as the source
of FM is then discussed in the light of the experimental and theoretical
results. Another interesting oxide system in which the stoichiometry of Ti ions
play a fundamental role is the LAO-STO interface. In fact, while LAO and STO
separately are two band insulators, the interface created by growing LAO on the
top of STO (001) has found to become metallic, hosting a 2D electron gas. The
second part of this Thesis is devoted to the study of conductive and insulating
LAO-STO interfaces, carried out by XPS, X-ray absorption (XAS) and with ResPES.
The sample stoichiometry is evaluated through a comparison with LAO and STO
single crystals. A resonance enhancement of the conductive Ti states,
associated to Ti3+ ions, is reported and compared to theoretical calculations.
On the basis of these results, the origin of metallic states in ultra-thin
LAO-STO interfaces is properly addressed. In addition, a characterization of
the structural disorder at the interface is shown, carried out with
angle-resolved XPS.",1210.8000v1
2019-11-29,"Role of Ni substitution on structural, magnetic and electronic properties of epitaxial CoCr2O4 spinel thin films","Cubic spinel CoCr2O4 has attained recent attention due to its multiferroic
properties. However, the Co site substitution effect on the structural and
magnetic properties has rarely been studied in thin film form. In this work,
the structural and magnetic properties of Co1-xNixCr2O4 (x = 0, 0.5) epitaxial
thin films deposited on MgAl2O4 (100) and MgO (100) substrates to manipulate
the nature of strain in the films using pulsed laser deposition (PLD) technique
are presented. The epitaxial nature of the films was confirmed through X-ray
diffraction (XRD) and Rutherford backscattering spectrometry (RBS)
measurements. Raman measurements revealed a disappearance of characteristic A1g
and F2g modes of the CoCr2O4 with increase in the Ni content. Atomic force
microscopy (AFM) studies show a modification of the surface morphology upon Ni
substitution. Magnetic measurements disclose that the ferrimagnetic Curie
temperature (Tc) of the CoCr2O4 in thin film grown on MgAl2O4 (100) and MgO
(100) substrates were found to be 100.6 +/- 0.5 K and 93.8 +/- 0.2 K,
respectively. With Ni substitution the transition temperatures significantly
get enhanced from that of CoCr2O4. X-ray photoelectron spectroscopy (XPS)
suggests Cr3+ oxidation states in the films, while Co ions are present in a
mixed Co2+/Co3+ oxidation state. The substitution of Ni at Co site
significantly modifies the line shape of the core level as well as the valence
band. Ni ions are also found to be in a mixed 2+/3+ oxidation state. O 1s core
level display asymmetry related to possible defects like oxygen vacancies in
the films.",1912.00051v1
2020-03-12,Magnetism and Ion Diffusion in Honeycomb Layered Oxide K$_2$Ni$_2$TeO$_6$: First Time Study by Muon Spin Rotation & Neutron Scattering,"In the quest of finding novel and efficient batteries, a great interest has
raised in K-based honeycomb layer oxide materials both for their fundamental
properties and potential applications. A key issue in the realization of
efficient batteries based on such compounds, is to understand the K-ion
diffusion mechanism. However, investigation of potassium-ion (K$^+$) dynamics
in materials using magneto-spin properties has so far been challenging, due to
its inherently weak nuclear magnetic moment, in contrast to other alkali ions
such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic
ratio, make the muon spin rotation and relaxation ($\mu$+SR) technique ideal
for probing ions dynamics in weak magneto-spin moment materials. Here we report
the magnetic properties and K+ dynamics in honeycomb layered oxide material of
the K$_2$Ni$_2$TeO$_6$ using $\mu$+SR measurements. Our low-temperature
$\mu$+SR results together with, with complementary magnetic susceptibility,
find an antiferromagnetic transition at 26 K. Further $\mu$+SR studies
performed at higher temperatures reveal that potassium ions (K$^+$) become
mobile above 250 K and the activation energy for the diffusion process is Ea =
121(13) meV. This is the first time that K+ dynamics in potassium-based battery
materials has been measured using $\mu$+SR. Finally our results also indicate
an interesting possibility that K-ion self diffusion occurs predominantly at
the surface of the powder particles. This opens future possibilities for
improving ion diffusion and device performance using nano-structuring.",2003.05805v2
2004-04-30,"Orbital and spin interplay in spin-gap formation in pyroxene titanium oxides ATiSi2O6 (A=Na, Li)","Interplay between orbital and spin degrees of freedom is theoretically
studied for the phase transition to the spin-singlet state with lattice
dimerization in pyroxene titanium oxides ATiSi2O6 (A=Na, Li). For the quasi
one-dimensional spin-1/2 systems, we derive an effective spin-orbital-lattice
coupled model in the strong correlation limit with explicitly taking account of
the t_2g orbital degeneracy, and investigate the model by numerical simulation
as well as the mean-field analysis. We find a nontrivial feedback effect
between orbital and spin degrees of freedom; as temperature decreases,
development of antiferromagnetic spin correlations changes the sign of orbital
correlations from antiferro to ferro type, and finally the ferro-type orbital
correlations induce the dimerization and the spin-singlet formation. As a
result of this interplay, the system undergoes a finite-temperature transition
to the spin-dimer and orbital-ferro ordered phase concomitant with the
Jahn-Teller lattice distortion. The numerical results for the magnetic
susceptibility show a deviation from the Curie-Weiss behavior, and well
reproduce the experimental data. The results reveal that the Jahn-Teller energy
scale is considerably small and the orbital and spin exchange interactions play
a decisive role in the pyroxene titanium oxides.",0404730v2
2006-03-16,Low energy physical properties of high-Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments,"In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed
out that an early resonating valence bond (RVB) theory is able to explain a
number of unusual properties of high temperature superconducting (SC)
Cu-oxides. Here we extend previous calculations \cite{anderson87,FC
Zhang,Randeria} to study more systematically low energy physical properties of
the plain vanilla d-wave RVB state, and to compare results with the available
experiments. We use a renormalized mean field theory combined with variational
Monte Carlo and power Lanczos methods to study the RVB state of an extended
$t-J$ model in a square lattice with parameters suitable for the hole doped
Cu-oxides. The physical observable quantities we study include the specific
heat, the linear residual thermal conductivity, the in-plane magnetic
penetration depth, the quasiparticle energy at the antinode $(\pi, 0)$, the
superconducting energy gap, the quasiparticle spectra and the Drude weight. The
traits of nodes (including $k_{F}$, the Fermi velocity $v_{F}$ and the velocity
along Fermi surface $v_{2}$), as well as the SC order parameter are also
studied. Comparisons of the theory and the experiments in cuprates show an
overall qualitative agreement, especially on their doping dependences.",0603423v5
2011-12-21,Anisotropic conductance at improper ferroelectric domain walls,"Transition metal oxides hold great potential for the development of new
device paradigms because of the field-tunable functionalities driven by their
strong electronic correlations, combined with their earth abundance and
environmental friendliness. Recently, the interfaces between transition-metal
oxides have revealed striking phenomena such as insulator-metal transitions,
magnetism, magnetoresistance, and superconductivity. Such oxide interfaces are
usually produced by sophisticated layer-by-layer growth techniques, which can
yield high quality, epitaxial interfaces with almost monolayer control of
atomic positions. The resulting interfaces, however, are fixed in space by the
arrangement of the atoms. Here we demonstrate a route to overcoming this
geometric limitation. We show that the electrical conductance at the
interfacial ferroelectric domain walls in hexagonal ErMnO3 is a continuous
function of the domain wall orientation, with a range of an order of magnitude.
We explain the observed behaviour using first-principles density functional and
phenomenological theories, and relate it to the unexpected stability of
head-to-head and tail-to-tail domain walls in ErMnO3 and related hexagonal
manganites. Since the domain wall orientation in ferroelectrics is tunable
using modest external electric fields, our finding opens a degree of freedom
that is not accessible to spatially fixed interfaces.",1112.5194v1
2012-06-06,Irreversibility and time relaxation in electrostatic doping of oxide interfaces,"Two-dimensional electron gas (2DEG) confined in quantum wells at insulating
oxide interfaces have attracted much attention as their electronic properties
display a rich physics with various electronics orders such as
superconductivity and magnetism. A particularly exciting features of these
hetero-structures lies in the possibility to control their electronic
properties by electrostatic gating, opening up new opportunities for the
development of oxide based electronics. However, unexplained gating hysteresis
and time relaxation of the 2DEG resistivity have been reported in some bias
range, raising the question of the precise role of the gate voltage. Here we
show that in LaTiO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures, above a filling
threshold, electrons irreversibly escape out of the well. This mechanism, which
is directly responsible for the hysteresis and time relaxation, can be entirely
described by a simple analytical model derived in this letter. Our results
highlight the crucial role of the gate voltage both on the shape and the
filling of the quantum well. They also demonstrate that it is possible to
achieve a low-carrier density regime in a semiconductor limit, whereas the
high-carrier density regime is intrinsically limited.",1206.1198v1
2012-08-30,Unexpected Anisotropic Two Dimensional Electron Gas at the LaAlO3/SrTiO3 (110) Interface,"The observation of a two dimensional electron gas (2DEG) (1, 2),
superconductivity (3, 4), magnetic effects (5) and electronic phase separation
(6-8) at the interfaces of insulating oxides, especially LaAlO3/SrTiO3, has
further enhanced the potential of complex oxides for novel electronics. The
occurrence of the 2DEG is strongly believed to be driven by the polarization
discontinuity (9) at the interface between the two oxides. In this scenario,
the crystal orientation plays an important role and no conductivity would be
expected for e.g., the interface between LaAlO3 and (110)-oriented SrTiO3,
which should not have a polarization discontinuity (10, 11). Here, we report
the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface
prepared on (110)-oriented SrTiO3. The conductivity was further found to be
strongly anisotropic, with the ratio of the conductance along the different
directions parallel to the substrate surface showing a remarkable dependence on
the oxygen pressure during deposition. The conductance and its anisotropy are
discussed based on the atomic structure at the interface, as revealed by
Scanning Transmission Electron Microscopy (STEM) and further supported by
density functional theory (DFT) calculations.",1208.6135v1
2012-10-05,"Rapid Size-Controlled Synthesis of Dextran-Coated, 64Cu-Doped Iron Oxide Nanoparticles","Research into developing dual modality probes enabled for magnetic resonance
imaging (MRI) and positron emission tomography (PET) has been on the rise
recently due to the potential to combine the high resolution of MRI and the
high sensitivity of PET. Current synthesis techniques for developing multimodal
probes is largely hindered in part by prolonged reaction times during
radioisotope incorporation - leading to a weakening of the radioactivity. Along
with a time-efficient synthesis, the resulting products must fit within a
critical size range (between 20-100nm) to increase blood retention time. In
this work, we describe a novel, rapid, microwave-based synthesis technique to
grow dextran-coated iron oxide nanoparticles doped with copper (DIO/Cu).
Traditional methods for coprecipitation of dextran-coated iron oxide
nanoparticles require refluxing for 2 hours and result in approximately 50 nm
diameter particles. We demonstrate that microwave synthesis can produce 50 nm
nanoparticles with 5 minutes of heating. We discuss the various parameters used
in the microwave synthesis protocol to vary the size distribution of DIO/Cu,
and demonstrate the successful incorporation of 64Cu into these particles with
the aim of future use for dual-mode MR/PET imaging.",1210.1823v1
2015-05-04,Vacancy Formation and Oxidation Characteristics of Single Layer TiS3,"The structural, electronic, and magnetic properties of pristine, defective,
and oxidized monolayer TiS3 are investigated using first-principles
calculations in the framework of density functional theory. We found that a
single layer of TiS3 is a direct band gap semiconductor, and the bonding nature
of the crystal is fundamentally different from other transition metal
chalcogenides. The negatively charged surfaces of single layer TiS3 makes this
crystal a promising material for lubrication applications. The formation
energies of possible vacancies, i.e. S, Ti, TiS, and double S, are investigated
via total energy optimization calculations. We found that the formation of a
single S vacancy was the most likely one among the considered vacancy types.
While a single S vacancy results in a nonmagnetic, semiconducting character
with an enhanced band gap, other vacancy types induce metallic behavior with
spin polarization of 0.3-0.8 {\mu}B. The reactivity of pristine and defective
TiS3 crystals against oxidation was investigated using conjugate gradient
calculations where we considered the interaction with atomic O, O2, and O3.
While O2 has the lowest binding energy with 0.05-0.07 eV, O3 forms strong bonds
stable even at moderate temperatures. The strong interaction (3.9-4.0 eV)
between atomic O and TiS3 results in dissociative adsorption of some
O-containing molecules. In addition, the presence of S-vacancies enhances the
reactivity of the surface with atomic O, whereas it had a negative effect on
the reactivity with O2 and O3 molecules.",1505.00827v1
2015-10-15,"Mott transitions and Novel Orders in Multi-Orbital Models: The Relevance of Structural ""Double Exchange""","In real transition-metal oxides, the so-called GdFeO3 octahedral tilt is long
known to be a relevant control parameter influencing the range of orbital and
magnetic ordered states found across families of cubic perovskite families.
Their precise role in the interplay between itinerance and localisation, long
known to underpin Mottness in d-band oxides, has however received much less
attention. We analyse the relevance of the GdFeO3 tilt in detail in a
representative setting of a partially-filled e g orbital system. We identify a
new generalised principle of broad relevance, namely, that this tilt acts like
a structural ""double exchange"" and acts contrary to the well-known
Anderson-Hasegawa double exchange. As a function of this tilt, therefore, a
phase transition from a Mott-Hubbard insulator to an incoherent bad-metal
occurs as an effective band-width-controlled Mott transition. We analyse the
incoherent metal in detail by studying one- and two-particle spectral responses
and propose that this selective-metal is a novel orbital analogue of the FL*
state with fractionalised orbitons. Finally, we apply these ideas to
qualitatively discuss the effect of strain on thin films of such d-band oxides
on suitable substrates, and discuss the exciting possibility of engineering
novel ordered phases, such as unconventional circulating currents, nematics and
superconductors, by suitable strain engineering in TMO thin films.",1510.04475v1
2016-03-09,Origin of the kink in the band dispersion of the ferromagnetic perovskite SrRuO3: Electron-phonon coupling,"Perovskite SrRuO3, a prototypical conductive ferromagnetic oxide, exhibits a
kink in its band dispersion signalling the unusual electron dynamics therein.
However, the origin of this kink remains elusive. By taking advantage of the
combo of reactive molecular beam epitaxy and in situ angle-resolved
photoemission spectroscopy, we systematically studied the evolution of the
low-energy electronic structure of SrRuO3 films with thickness thinning down to
nearly two-dimensional limit in a well-controlled way. The kink structure
persists even in the 4-unit-cell-thick film. Moreover, through quantitative
self-energy analysis, we observed the negligible thickness dependence of the
binding energy of the kink, which is in sharp contrast to the downward trend of
the Curie temperature with reducing the film thickness. Together with
previously reported transport and Raman studies, this finding suggests that the
kink of perovskite SrRuO3 should originate from the electron-phonon coupling
rather than magnetic collective modes, and the in-plane phonons may play a
dominant role. Considering such a kink structure of SrRuO3 is similar to these
of many other correlated oxides, we suggest the possible ubiquity of the
coupling of electrons to oxygen-related phonons in correlated oxides.",1603.03066v1
2016-10-15,A conducting nano-filament (CNF) network as a precursor to the origin of superconductivity in electron-doped copper oxides,"Emergency of superconductivity at the instabilities of antiferromagnetism has
been widely recognized in unconventional superconductors. In copper-oxide
superconductors, spin fluctuations play a predominant role in electron pairing
with electron dopants yet composite orders veil the nature of superconductivity
for hole-doped family. However, in electron-doped copper oxide superconductors
(cuprates) the AFM critical end point is still in controversy for different
probes, demonstrating high sensitivity to oxygen content. Here, by carefully
tuning the oxygen content, a systematic study of the Hall signal and
magnetoresistivity up to 58 Tesla on LCCO thin films identifies two
characteristic temperatures. The former is quite robust, whereas the latter
becomes flexible with increasing magnetic field, thereby linking respectively
to two- and three-dimensional AFM, evident from the multidimensional phase
diagram as a function of oxygen and Ce dopants. A rigorous theoretical analysis
of the presented data suggest the existence of conductive nano-filamentary
structures that effectively corroborate all previously reported field studies.
The new findings provide a uniquely consistent alternative picture in
understanding the interactions between AFM and superconductivity in
electron-doped cuprates and offer a consolidating interpretation to the
pioneering scaling law in cuprates recently established by Bozovic et al.
(Nature, 2016)",1610.04788v1
2017-04-21,Enhancement of electron mobility at oxide interfaces induced by WO3 overlayers,"Interfaces between complex oxides constitute a unique playground for 2D
electron systems (2DES), where superconductivity and magnetism can arise from
combinations of bulk insulators. The 2DES at the LaAlO3/SrTiO3 interface is one
of the most studied in this regard, and its origin is determined by both the
presence of a polar field in LaAlO3 and the insurgence of point defects, such
as oxygen vacancies and intermixed cations. These defects usually reside in the
conduction channel and are responsible for a decreased electronic mobility. In
this work we use an amorphous WO3 overlayer to control the defect formation and
obtain an increased electron mobility and effective mass in WO3/LaAlO3/SrTiO3
heterostructures. The studied system shows a sharp insulator-to-metal
transition as a function of both LaAlO3 and WO3 layer thickness.
Low-temperature magnetotransport reveals a strong magnetoresistance reaching
900% at 10 T and 1.5 K, the presence of multiple conduction channels with
carrier mobility up to 80 000 cm2/Vs and an unusually high effective mass of
5.6 me. The amorphous character of the WO3 overlayer makes this a versatile
approach for defect control at oxide interfaces, which could be applied to
other heterestrostures disregarding the constraints imposed by crystal
symmetry.",1704.06522v1
2018-05-08,Tuning the probability of defect formation via substrate strains in Sr$_2$FeMoO$_6$ films,"Since oxide materials like Sr$_2$FeMoO$_6$ are usually applied as thin films,
we studied the effect of biaxial strain, resulting from the substrate, on the
electronic and magnetic properties and, in particular, on the formation energy
of point defects. From our first-principles calculations, we determined that
the probability of forming point defects - like vacancies or substitutions - in
Sr$_2$FeMoO$_6$ could be adjusted by choosing a proper substrate. For example,
the amount of anti-site disorder can be reduced with compressive strain in
order to obtain purer Sr$_2$FeMoO$_6$ as needed for spintronic applications,
while the formation of oxygen vacancies is more likely for tensile strain,
which improves the functionality of Sr$_2$FeMoO$_6$ as a basis material of
solid oxide fuel cells. In addition, we were also be able to include the oxygen
partial pressure in our study by using its thermodynamic connection with the
chemical potential. Strontium vacancies become for example more likely than
oxygen vacancies at a pressure of 1$\,$bar. Hence, this degree of freedom might
offer in general another potential method for defect engineering in oxides
besides, e.g., experimental growth conditions like temperature or gas pressure.",1805.02969v2
2012-01-13,High-Tc Superconductivity and Antiferromagnetism in Multilayered Copper Oxides - A New Paradigm of Superconducting Mechanism -,"High-temperature superconductivity (HTSC) in copper oxides emerges on a
layered CuO2 plane when an antiferromagnetic Mott insulator is doped with
mobile hole carriers. We review extensive studies of multilayered copper oxides
by site-selective nuclear magnetic resonance (NMR), which have uncovered the
intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a
disorder-free CuO2 plane with hole carriers. We present our experimental
findings such as the existence of the AFM metallic state in doped Mott
insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of
d-wave SC with a maximum Tc just outside a critical carrier density, at which
the AFM moment on a CuO2 plane disappears. These results can be accounted for
by the Mott physics based on the t-J model. The superexchange interaction J_in
among spins plays a vital role as a glue for Cooper pairs or mobile
spin-singlet pairs, in contrast to the phonon-mediated attractive interaction
among electrons established in the Bardeen-Cooper-Schrieffer (BCS) theory. We
remark that the attractive interaction for raising the $T_c$ of HTSC up to
temperatures as high as 160 K is the large J_in (~0.12 eV), which binds
electrons of opposite spins to be on neighboring sites, and that there are no
bosonic glues. It is the Coulomb repulsive interaction U(> 6 eV) among Cu-3d
electrons that plays a central role in the physics behind high-Tc phenomena. A
new paradigm of the SC mechanism opens to strongly correlated electron matter.",1201.2726v1
2017-06-08,Emergence of quantum critical behavior in metallic quantum-well states of strongly correlated oxides,"Controlling quantum critical phenomena in strongly correlated electron
systems, which emerge in the neighborhood of a quantum phase transition, is a
major challenge in modern condensed matter physics. Quantum critical phenomena
are generated from the delicate balance between long-range order and its
quantum fluctuation. So far, the nature of quantum phase transitions has been
investigated by changing a limited number of external parameters such as
pressure and magnetic field. We propose a new approach for investigating
quantum criticality by changing the strength of quantum fluctuation that is
controlled by the dimensional crossover in metallic quantum well (QW)
structures of strongly correlated oxides. With reducing layer thickness to the
critical thickness of metal-insulator transition, crossover from a Fermi liquid
to a non-Fermi liquid has clearly been observed in the metallic QW of SrVO$_3$
by \textit{in situ} angle-resolved photoemission spectroscopy. Non-Fermi liquid
behavior with the critical exponent ${\alpha} = 1$ is found to emerge in the
two-dimensional limit of the metallic QW states, indicating that a quantum
critical point exists in the neighborhood of the thickness-dependent Mott
transition. These results suggest that artificial QW structures provide a
unique platform for investigating novel quantum phenomena in strongly
correlated oxides in a controllable fashion.",1706.02433v1
2017-07-02,Ramp Reversal Memory and Phase-Boundary Scarring in Transition Metal Oxides,"Transition metal oxides (TMOs) are complex electronic systems which exhibit a
multitude of collective phenomena. Two archetypal examples are VO2 and NdNiO3,
which undergo a metal-insulator phase-transition (MIT), the origin of which is
still under debate. Here we report the discovery of a memory effect in both
systems, manifest through an increase of resistance at a specific temperature,
which is set by reversing the temperature-ramp from heating to cooling during
the MIT. The characteristics of this ramp-reversal memory effect do not
coincide with any previously reported history or memory effects in manganites,
electron-glass or magnetic systems. From a broad range of experimental
features, supported by theoretical modelling, we find that the main ingredients
for the effect to arise are the spatial phase-separation of metallic and
insulating regions during the MIT and the coupling of lattice strain to the
local critical temperature of the phase transition. We conclude that the
emergent memory effect originates from phase boundaries at the
reversal-temperature leaving `scars` in the underlying lattice structure,
giving rise to a local increase in the transition temperature. The universality
and robustness of the effect shed new light on the MIT in complex oxides.",1707.00303v1
2018-10-25,"Exceptionally high, strongly temperature dependent, spin Hall conductivity of SrRuO3","Spin-orbit torques (SOT) in thin film heterostructures originate from strong
spin-orbit interactions (SOI) that, in the bulk, generate a spin current as the
result of extrinsic spin-dependent, skew or/and side-jump, scattering, or in
the intrinsic case due to Berry curvature in the conduction band. While most
SOT studies have focused on materials with heavy metal components, the oxide
perovskite SrRuO3 has been predicted to have a pronounced Berry curvature.
Through quantification of its spin current by the SOT exerted on an adjacent Co
ferromagnetic layer, we determine that SrRuO3 has a strongly temperature (T)
dependent spin Hall conductivity which becomes particularly high at low T, e.g.
\sigma_{SH} \geqslant (\hbar/2e)3x10^{5} \Omega^{-1}m^{-1} at 60 K. Below the
SrRuO3 ferromagnetic transition, non-standard SOT components develop associated
with the magnetic characteristics of the oxide, but these do not dominate as
with spin currents from a conventional ferromagnet. Our results establish a new
approach for the study of SOI in epitaxial conducting oxide heterostructures
and confirm SrRuO3 as a promising candidate material for achieving new and
enhanced spintronics functionalities.",1810.11136v1
2019-09-18,Optical Absorption Induced by Small Polaron Formation in Transition Metal Oxides -- The Case of Co$_3$O$_4$,"Small polarons (SPs) are known to exist in most important transition metal
oxides (TMOs); however, the nature of small polaron formation remains
enigmatic, and a fundamental understanding of how SPs impact the intrinsic
electronic structure and optical properties of these materials is largely
lacking. In this work, we employ first-principles calculations to investigate
SP formation in Co$_{3}$O$_{4}$, a highly promising material for a wide range
of emerging energy applications, and we resolve the conflicting findings that
have been reported on the electronic structure of the system. We confirm that
the intrinsic band gap of Co$_{3}$O$_{4}$ is 1.6 eV, and we show that the
formation of hole small polarons significantly influences the optical
absorption spectra, leading to a 0.8 eV transition that is often misinterpreted
as the band edge that defines the fundamental gap. In addition, we discuss how
uniaxial strain can be utilized to probe the Jahn-Teller distortion of SP
states and in turn, effect their optical transitions. Beyond Co$_{3}$O$_{4}$,
our study suggests a general roadmap for establishing a first-principles
computational approach that can simultaneously achieve an accurate description
of SP states, electronic band structure and optical transitions of polaronic
magnetic oxides.",1909.08653v1
2019-10-01,Study of second and third harmonic generation from an indium tin oxide nanolayer: influence of nonlocal effects and hot electrons,"We report comparative experimental and theoretical studies of second and
third harmonic generation from a 20nm-thick indium tin oxide layer in proximity
of the epsilon-near-zero condition. Using a tunable OPA laser we record both
spectral and angular dependence of the generated harmonic signals close to this
particular point. In addition to the enhancement of the second harmonic
efficiency close to the epsilon-near-zero wavelength, at oblique incidence
third harmonic generation displays unusual behavior, predicted but not observed
before. We implement a comprehensive, first-principles hydrodynamic approach
able to simulate our experimental conditions. The model is unique, flexible,
and able to capture all major physical mechanisms that drive the electrodynamic
behavior of conductive oxide layers: nonlocal effects, which blueshift the
epsilon-near-zero resonance by tens of nanometers; plasma frequency redshift
due to variations of the effective mass of hot carriers; charge density
distribution inside the layer, which determines nonlinear surface and magnetic
interactions; and the nonlinearity of the background medium triggered by bound
electrons. We show that by taking these contributions into account our
theoretical predictions are in very good qualitative and quantitative agreement
with our experimental results. We show that by taking these contributions into
account our theoretical predictions are in very good qualitative and
quantitative agreement with our experimental results. We expect that our
results can be extended to other geometries where ENZ nonlinearity plays an
important role.",1910.00313v1
2020-02-25,Emergent electric field control of phase transformation in oxide superlattices,"Electric fields can transform materials with respect to their structure and
properties, enabling various applications ranging from batteries to
spintronics. Recently electrolytic gating, which can generate large electric
fields and voltage-driven ion transfer, has been identified as a powerful means
to achieve electric-field-controlled phase transformations. The class of
transition metal oxides (TMOs) provide many potential candidates that present a
strong response under electrolytic gating. However, very few show a reversible
structural transformation at room-temperature. Here, we report the realization
of a digitally synthesized TMO that shows a reversible,
electric-field-controlled transformation between distinct crystalline phases at
room-temperature. In superlattices comprised of alternating one-unit-cell of
SrIrO3 and La0.2Sr0.8MnO3, we find a reversible phase transformation with a 7%
lattice change and dramatic modulation in chemical, electronic, magnetic and
optical properties, mediated by the reversible transfer of oxygen and hydrogen
ions. Strikingly, this phase transformation is absent in the constituent
oxides, solid solutions and larger period superlattices. Our findings open up a
new class of materials for voltage-controlled functionality.",2002.10872v1
2021-01-17,"Comparative analysis for meaningful interpretation of rare-earth oxide M$_{4,5}$ energy loss edges","The magnetic, electronic, and optical properties of rare earth-oxides are
directly influenced by the valency of the metallic cation. With the development
of next generation electron energy-loss spectrometers, high-energy lanthanide
fine structure can be studied with improved signal-to-noise for quantitative
analysis. Unfortunately, the behavior of rare-earth $4f$ orbital electrons is
not well understood. To establish best practices for analysis of energy-loss
spectra from lanthanide oxides, we have performed a comparative study of the
four traditional white line analysis methods extended to lanthanide $M_{4,5}$
edges resulting from $3d \rightarrow 4f$ orbital transitions using data from
Gatan's EELS Atlas. The ${M_4}/{M_5}$ spectral feature ratios were examined as
a function of $4f$ occupancy. The ${M_4}/{M_5}$ spectral feature ratio
decreases exponentially as $4f$ occupancy increases, except for a plateau
between S$\text{m}^{3+}$ and D$\text{y}^{3+}$. The full-width at half the
maximum intensity of the $M_4$ edges shows increased broadening for
S$\text{m}^{3+}$ through D$\text{y}^{3+}$. We suggest that the plateau results
from $4f$ orbital half-filling and is explained through the relationship
between electron transition probability and transition lifetime as expressed
through Fermi's Golden Rule. Of the four spectral analysis methods described,
only the integrated area method can be ascribed a quantitative physical
interpretation.",2101.06794v1
2018-07-04,Anomalies Of Phase Diagrams And Physical Properties Of Antiferrodistortive Perovskide Oxides,"The influence of rotomagnetic (RM), rotoelectric (RE) and magnetoelectric
(ME) coupling on phase diagram and properties of antiferrodistortive (AFD)
perovskite oxides was reviewed. The main examples we consider in the review are
typical AFD perovkites, such as incipient ferroelectrics EuTiO3, SrTiO3,
EuxSr1-xTiO3, multiferroic BiFeO3 and Bi1-xRxFeO3 (x = La, Nd). The strong
influence of RM, RE and ME couplings on the physical properties and phase
diagrams including antiferromagnetic (AFM), ferroelectric (FE) and structural
AFD phases has been revealed in the framework of Landau-Ginzburg-Devonshire
(LGD) theory, as well as the prediction of novel (double and triple)
multiferroic phases has been demonstrated.
  In the review we are especially focused on (a) the possibility to induce FM
(FE) phase in EuTiO3 (as well as in other paraelectric AFM oxides) by the
application of an electric (magnetic) field due to the ME coupling; (b) the
analysis of the size effects and novel phases in EuxSr1-xTiO3 nanosystems,
where the LGD predicts the presence of the triple AFD-FE-FM(AFM) phase at low
temperatures; (c) the appearance of improper spontaneous polarization and
pyroelectricity in the vicinity of antiphase domain boundaries, structural twin
walls, surfaces and interphases in the AFD phase of non-ferroelectric SrTiO3
induced by the flexoelectricity and rotostriction; (d) the occurrence of low
symmetry monoclinic phase with in-plane FE polarization in thin strained
EuxSr1-xTiO3 films and its stabilization over wide temperature range by AFD
oxygen octahedron tilts due to flexoelectric and rotostriction coupling; (e)
discussion of a surprisingly strong size-induced increase of AFM transition
temperature caused by the joint action of RM coupling with elastic stress
accumulated in the intergrain spaces of BiFeO3 dense ceramics.",1807.01743v1
2018-08-14,Impurities and Defects in Mott Systems,"Disorder has intriguing consequences for correlated electronic materials,
which include several families of high-temperature superconductors and
resistive switching systems. We address the question of why strongly correlated
d-wave superconductors, such as the cuprates, prove to be surprisingly robust
against the introduction of non-magnetic impurities. We show that, very
generally, both the pair-breaking and the normal state transport scattering
rates are significantly suppressed by strong correlations effects arising in
the proximity to a Mott insulating state. We also show that the
correlation-renormalized scattering amplitude is generically enhanced in the
forward direction, an effect which was previously often ascribed to the
specific scattering by charged impurities outside the copper-oxide planes. We
provide the theoretical insights for resistive switching systems and show how
impurities and underlying correlations can play significant roles in practical
devices. We report the striking result of a connection between the resistive
switching and shock wave formation, a classic topic of non-linear dynamics. We
argue that the profile of oxygen vacancies that migrate during the commutation
forms a shock wave that propagates through a highly resistive region of the
device. We validate the scenario by means of model simulations and experiments
in a manganese-oxide based memristor device and we extend our theory to the
case of binary oxides. The shock wave scenario brings unprecedented physical
insight and enables to rationalize the process of oxygen-vacancy-driven
resistive change with direct implications for a key technological aspect- the
commutation speed.",1808.04767v1
2018-08-21,Two-dimensional Peierls instability via zone boundary Dirac line nodes in layered perovskite oxides,"Interplay of Fermi surface topology and electron correlation is the
quintessential ingredient underlying spontaneous symmetry breaking in itinerant
electronic systems. In one-dimensional (1D) systems at half-filling, the
inherent Fermi surface nesting makes the translationally invariant metallic
state unstable, which is known as Peierls instability. Extending the scope of
Peierls instability to two (2D) or three dimensions (3D), however, is not
straightforward, since the Fermi surface in higher dimensions is generally not
nested. In this work, we show that a perfectly nested Fermi surface can be
realized in a class of 2D perovskite oxides, giving rise to 2D Peierls
instability. Here the central role is played by the zone boundary Dirac line
node (DLN) protected by two orthogonal glide mirrors induced by the rotation of
oxygen octahedra. Especially, at a critical angle of the octahedron rotation,
the zone-boundary DLN flattens, leading to logarithmically diverging
susceptibility. We propose the 2D Peierls instability driven by dispersionless
DLN as a principle mechanism for spontaneous symmetry breaking in various
layered perovskite oxides including the antiferromagnetism of Sr$_2$IrO$_4$. As
a clear signature of the 2D Peierls instability, we predict that the magnetic
domain wall in Sr$_2$IrO$_4$ hosts localized soliton modes.",1808.06830v2
2019-02-05,Chromium Oxide Formation on Nanosecond and Femtosecond Laser Irradiated Thin Chromium Films,"Thin coatings of Chromium oxide have been used for applications as absorbing
material in solar cells, as protections for magnetic data recording devices and
as shields in flexible solar cells. Thin coatings of pure chromium were vacuum
deposited on a glass substrate using hot electrons from tungsten filament.
These coatings were then treated with a nanosecond and femtosecond laser in
ambient conditions. The microstructure, morphology and the color of the
coatings treated with laser sources were modified and there was a formation of
an oxide layer due to the heat dissipation on the chromium coating from the
energetic photons. High-resolution scanning electron microscope studies showed
the morphological evolution that are directly correlated with the laser fluence
of both the nanosecond and femtosecond lasers. This morphological evolution was
accompanied by the microstructural change as observed from the x-ray
diffraction patterns, the chromaticity response of the coating was studied by
UV-Vis spectrometer and the response of the coating in the visible region
evolved with the laser fluences. The Rutherford backscattering depth profiling
of the laser treated coatings revealed the diffusion of oxygen atoms in the
coating as a result of laser treatment fluence.",1902.01851v4
2020-08-31,Atomic-scale mechanisms for magnetostriction in CoFe$_2$O$_4$ and La$_{0.5}$Sr$_{0.5}$CoO$_3$ oxides determined by differential x-ray absorption spectroscopy,"The atomic environments involved in the magnetostriction effect in
CoFe$_2$O$_4$ and La$_{0.5}$Sr$_{0.5}$CoO$_3$ polycrystalline samples have been
identified by differential extended x-ray absorption fine structure (DiffEXAFS)
spectroscopy. We demonstrate that cobalt atoms at octahedral sites are
responsible for their magnetostriction. The analysis of DiffEXAFS data
indicates that the local-site magnetostrictive strains of Co atoms are reversed
in these two oxides, in agreement with the macroscopic magnetostriction. For
the CoFe$_2$O$_4$ spinel, a large negative strain along the (100) direction has
been determined for the CoO$_6$ octahedron causing a tetragonal contraction in
contrast with the La$_{0.5}$Sr$_{0.5}$CoO$_3$ perovskite, where a positive
moderate strain along the (100) direction was found resulting in a tetragonal
expansion. The different local-site magnetostriction is understood in terms of
the different valence and spin state of the Co atoms for the two oxides. The
macroscopicmagnetostriction would be explained then by the relative change in
volume, either contraction in CoFe$_2$O$_4$ or expansion in
La$_{0.5}$Sr$_{0.5}$CoO$_3$, when the tetragonal axis of the Co site is
reoriented under an externally applied magnetic field.",2008.13658v1
2020-10-23,Maximizing spin-orbit torque efficiency of Ta(O)/Py via modulating oxygen-induced interface orbital hybridization,"Spin-orbit torques due to interfacial Rashba and spin Hall effects have been
widely considered as a potentially more efficient approach than the
conventional spin-transfer torque to control the magnetization of ferromagnets.
We report a comprehensive study of spin-orbit torque efficiency in
Ta(O)/Ni81Fe19 bilayers by tuning low-oxidation of \b{eta}-phase tantalum, and
find that the spin Hall angle {\theta}DL increases from ~ -0.18 of the pure
Ta/Py to the maximum value ~ -0.30 of Ta(O)/Py with 7.8% oxidation.
Furthermore, we distinguish the efficiency of the spin-orbit torque generated
by the bulk spin Hall effect and by interfacial Rashba effect, respectively,
via a series of Py/Cu(0-2 nm)/Ta(O) control experiments. The latter has more
than twofold enhancement, and even more significant than that of the former at
the optimum oxidation level. Our results indicate that 65% enhancement of the
efficiency should be related to the modulation of the interfacial Rashba-like
spin-orbit torque due to oxygen-induced orbital hybridization cross the
interface. Our results suggest that the modulation of interfacial coupling via
oxygen-induced orbital hybridization can be an alternative method to boost the
change-spin conversion rate.",2010.12253v1
2021-10-05,Spin-orbit torque generation in NiFe/IrO2 bilayers,"The 5d transition-metal oxides have a unique electronic structure dominated
by strong spin-orbit coupling and hence they can be an intriguing platform to
explore spin-current physics. Here, we report on room-temperature generation of
spin-orbit torque (SOT) from a conductive 5d iridium oxide, IrO2. By measuring
second-harmonic Hall resistance of Ni81Fe19/IrO2 bilayers, we find both
dampinglike and fieldlike SOTs. The former is larger than the latter, enabling
easier control of magnetization. We also observe that the dampinglike SOT
efficiency has a significant dependence on IrO2 thickness, which is well
described by the drift-diffusion model based on the bulk spin Hall effect. We
deduce the effective spin Hall angle of +0.093 +- 0.003 and the spin-diffusion
length of 1.7 +- 0.2 nm. By comparison with control samples Pt and Ir, we show
that the effective spin Hall angle of IrO2 is comparable to that of Pt and
seven times higher than that of Ir. The fieldlike SOT efficiency has a negative
sign without appreciable dependence on the thickness, in contrast to the
dampinglike SOT. This suggests that the fieldlike SOT likely stems from the
interface. These experimental findings suggest that the uniqueness of the
electronic structure of 5d transition-metal oxides is crucial for highly
efficient charge to spin-current conversion.",2110.01801v1
2021-11-26,Room-temperature ferromagnetism at an oxide/nitride interface,"Heterointerfaces have led to the discovery of novel electronic and magnetic
states because of their strongly entangled electronic degrees of freedom.
Single-phase chromium compounds always exhibit antiferromagnetism following the
prediction of Goodenough-Kanamori rules. So far, exchange coupling between
chromium ions via hetero-anions has not been explored and the associated
quantum states is unknown. Here we report the successful epitaxial synthesis
and characterizations of chromium oxide (Cr2O3)-chromium nitride (CrN)
superlattices. Room-temperature ferromagnetic spin ordering is achieved at the
interfaces between these two antiferromagnets, and the magnitude of the effect
decays with increasing layer thickness. First-principles calculations indicate
that robust ferromagnetic spin interaction between Cr3+ ions via
anion-hybridizations across the interface yields the lowest total energy. This
work opens the door to fundamental understanding of the unexpected and
exceptional properties of oxide-nitride interfaces and provides access to
hidden phases at low-dimensional quantum heterostructures.",2111.13278v1
2022-03-06,Two-Dimensional Electron Gas with High Mobility Forming at BaO/SrTiO3 Interface,"Two-dimensional electron gas (2DEG) formed at the interface between two
insulating oxides offers an opportunity for fundamental research and device
applications. Binary alkaline earth metal oxides possess compatible lattice
constants with both silicon and perovskite oxides, exhibiting an enormous
potential to bridging those two materials classes for multifunctionalities.
Here we report the formation of 2DEG at the interface between the rock-salt BaO
and SrTiO3. The highest electron mobility reaches 69000 cm^2 V.S^-1 at 2 K,
leading to the typical Shubniko de Haas (SdH) oscillations under the high
magnetic fields. The presence of SdH oscillations at different field-angles
reveals a quasi-two-dimensional character of the Fermi surface. The
first-principles calculations suggest that the effective charge transfer from
the BaO to Ti 3dxy orbital at the interfaces is responsible to the observed
high carrier mobility. Our results demonstrate that the BaO/STO heterointerface
is a platform for exploring the correlated quantum phases, opening a door to
the low-power and mesoscopic electronic devices.",2203.02934v1
2022-07-14,Braiding lateral morphotropic grain boundary in homogeneitic oxides,"Interfaces formed by correlated oxides offer a critical avenue for
discovering emergent phenomena and quantum states. However, the fabrication of
oxide interfaces with variable crystallographic orientations and strain states
integrated along a film plane is extremely challenge by conventional
layer-by-layer stacking or self-assembling. Here, we report the creation of
morphotropic grain boundaries (GBs) in laterally interconnected cobaltite
homostructures. Single-crystalline substrates and suspended ultrathin
freestanding membranes provide independent templates for coherent epitaxy and
constraint on the growth orientation, resulting in seamless and atomically
sharp GBs. Electronic states and magnetic behavior in hybrid structures are
laterally modulated and isolated by GBs, enabling artificially engineered
functionalities in the planar matrix. Our work offers a simple and scalable
method for fabricating unprecedented innovative interfaces through controlled
synthesis routes as well as provides a platform for exploring potential
applications in neuromorphics, solid state batteries, and catalysis.",2207.06566v1
2023-02-13,Performance of high impedance resonators in dirty dielectric environments,"High-impedance resonators are a promising contender for realizing
long-distance entangling gates between spin qubits. Often, the fabrication of
spin qubits relies on the use of gate dielectrics which are detrimental to the
quality of the resonator. Here, we investigate loss mechanisms of
high-impedance NbTiN resonators in the vicinity of thermally grown
SiO\textsubscript{2} and Al\textsubscript{2}O\textsubscript{3} fabricated by
atomic layer deposition. We benchmark the resonator performance in elevated
magnetic fields and at elevated temperatures and find that the internal quality
factors are limited by the coupling between the resonator and two-level systems
of the employed oxides. Nonetheless, the internal quality factors of
high-impedance resonators exceed $10^3$ in all investigated oxide
configurations which implies that the dielectric configuration would not limit
the performance of resonators integrated in a spin-qubit device. Because these
oxides are commonly used for spin qubit device fabrication, our results allow
for straightforward integration of high-impedance resonators into spin-based
quantum processors. Hence, these experiments pave the way for large-scale,
spin-based quantum computers.",2302.06303v2
2023-04-10,"Spin-phonon interactions and magnetoelectric coupling in Co$_4$$B_2$O$_9$ ($B$ = Nb, Ta)","In order to explore the consequences of spin-orbit coupling on spin-phonon
interactions in a set of chemically-similar mixed metal oxides, we measured the
infrared vibrational properties of Co$_4B_2$O$_9$ ($B$ = Nb, Ta) as a function
of temperature and compared our findings with lattice dynamics calculations and
several different models of spin-phonon coupling. Frequency vs. temperature
trends for the Co$^{2+}$ shearing mode near 150 cm$^{-1}$ reveal significant
shifts across the magnetic ordering temperature that are especially large in
relative terms. Bringing these results together and accounting for
noncollinearity, we obtain spin-phonon coupling constants of -3.4 and -4.3
cm$^{-1}$ for Co$_4$Nb$_2$O$_9$ and the Ta analog, respectively. Analysis
reveals that these coupling constants derive from interlayer (rather than
intralayer) exchange interactions and that the interlayer interactions contain
competing antiferromagnetic and ferromagnetic contributions. At the same time,
beyond-Heisenberg terms are minimized due to fortuitous symmetry
considerations, different than most other 4$d$- and 5$d$-containing oxides.
Comparison with other contemporary oxides shows that spin-phonon coupling in
this family of materials is among the strongest ever reported, suggesting an
origin for magnetoelectric coupling.",2304.04865v1
2023-06-30,3D oxygen vacancy order and defect-property relations in multiferroic (LuFeO$_3$)$_9$/(LuFe$_2$O$_4$)$_1$ superlattices,"Oxide heterostructures exhibit a vast variety of unique physical properties.
Examples are unconventional superconductivity in layered nickelates and
topological polar order in (PbTiO$_3$)$_n$/(SrTiO$_3$)$_n$ superlattices.
Although it is clear that variations in oxygen content are crucial for the
electronic correlation phenomena in oxides, it remains a major challenge to
quantify their impact. Here, we measure the chemical composition in
multiferroic (LuFeO$_3$)$_9$/(LuFe$_2$O$_4$)$_1$ superlattices, revealing a
one-to-one correlation between the distribution of oxygen vacancies and the
electric and magnetic properties. Using atom probe tomography, we observe
oxygen vacancies arranging in a layered three-dimensional structure with a
local density on the order of 10$^{14}$ cm$^{-2}$, congruent with the
formula-unit-thick ferrimagnetic LuFe$_2$O$_4$ layers. The vacancy order is
promoted by the locally reduced formation energy and plays a key role in
stabilizing the ferroelectric domains and ferrimagnetism in the LuFeO$_3$ and
LuFe$_2$O$_4$ layers, respectively. The results demonstrate the importance of
oxygen vacancies for the room-temperature multiferroicity in this system and
establish an approach for quantifying the oxygen defects with atomic-scale
precision in 3D, giving new opportunities for deterministic defect-enabled
property control in oxide heterostructures.",2307.00139v1
2015-08-08,Emergent excitation at the magnetic metal-insulator transition in the pyrochlore osmate Cd2Os2O7,"The rich physics manifested by 5d oxides falls outside the Mott-Hubbard
paradigm used to successfully explain the electronic and magnetic properties of
3d oxides. Much consideration has been given to the extent to which strong
spin-orbit coupling (SOC), in the limit of increased bandwidth and reduced
electron correlation, drives the formation of novel electronic states, as
manifested through the existence of metal-insulator transitions (MITs). SOC is
believed to play a dominant role in 5d5 systems such as iridates (Ir4+),
undergoing MITs which may or may not be intimately connected to magnetic order,
with pyrochlore and perovksite systems being examples of the former and latter,
respectively. However, the role of SOC for other 5d configurations is less
clear. For example, 5d3 (e.g Os5+) systems are expected to have an orbital
singlet and consequently a reduced effect of SOC in the groundstate. The
pyrochlore osmate Cd2Os2O7 nonetheless exhibits a MIT intimately entwined with
magnetic order with phenomena similar to pyrochlore iridates. Here we report
the first resonant inelastic X-ray scattering (RIXS) measurements on an osmium
compound, allowing us to determine the salient electronic and magnetic energy
scales controlling the MIT in Cd2Os2O7, which we benchmark against detailed
quantum chemistry calculations. In particular, we reveal the emergence at the
MIT of a magnetic excitation corresponding to a superposition of multiple
spin-flip processes from an Ising-like all-in/all-out magnetic groundstate. We
discuss our results with respect to the role of SOC in magnetically mediated
MITs in 5d systems",1508.01848v1
2019-06-18,Multi-analytical characterization of Fe-rich magnetic inclusions in diamonds,"Magnetic mineral inclusions, as iron oxides or sulfides, occur quite rarely
in natural diamonds. Nonetheless, they represent a key tool not only to unveil
the conditions of formation of host diamonds, but also to get hints about the
paleointensity of the geomagnetic field present at times of the Earth's history
otherwise not accessible. This possibility is related to their capability to
carry a remanent magnetization dependent on their magnetic history. However,
comprehensive experimental studies on magnetic inclusions in diamonds have been
rarely reported so far. Here we exploit X-ray diffraction, Synchrotron-based
X-ray Tomographic Microscopy and Alternating Field Magnetometry to determine
the crystallographic, morphological and magnetic properties of ferrimagnetic
Fe-oxides entrapped in diamonds coming from Akwatia (Ghana). We exploit the
methodology to estimate the natural remanence of the inclusions, associated to
the Earth's magnetic field they experienced, and to get insights on the
relative time of formation between host and inclusion systems. Furthermore,
from the hysteresis loops and First Order Reversal Curves we determine
qualitatively the anisotropy, size and domain state configuration of the
magnetic grains constituting the inclusions.",1906.07641v3
2001-08-17,Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple SDW and CDW,"A theory of Kondo lattices is applied to studying possible magnetic and
charge structures of itinerant-electron antiferromagnets. Even helical spin
structures can be stabilized when the nesting of the Fermi surface is not sharp
and the superexchange interaction, which arises from the virtual exchange of
pair excitations across the Mott-Hubbard gap, is mainly responsible for
magnetic instability. Sinusoidal spin structures or spin density waves (SDW)
are only stabilized when the nesting of the Fermi surface is sharp enough and a
novel exchange interaction arising from that of pair excitations of
quasi-particles is mainly responsible for magnetic instability. In particular,
multiple SDW are stabilized when their incommensurate ordering wave-numbers
$\pm{\bf Q}$ are multiple; magnetizations of different $\pm{\bf Q}$ components
are orthogonal to each other in double and triple SDW when magnetic anisotropy
is weak enough. Unless $\pm 2{\bf Q}$ are commensurate, charge density waves
(CDW) with $\pm 2{\bf Q}$ coexist with SDW with $\pm{\bf Q}$. Because the
quenching of magnetic moments by the Kondo effect depends on local numbers of
electrons, the phase of CDW or electron densities is such that magnetic moments
are large where the quenching is weak. It is proposed that the so called stipe
order in cuprate-oxide high-temperature superconductors must be the coexisting
state of double incommensurate SDW and CDW.",0108270v1
2008-12-30,Covalent bonding and magnetism in cuprates,"The importance of covalent bonding for the magnetism of 3d metal complexes
was first noted by Pauling in 1931. His point became moot, however, with the
success of the ionic picture of Van Vleck, where ligands influence magnetic
electrons of 3d ions mainly through electrostatic fields. Anderson's theory of
spin superexchange later established that covalency is at the heart of
cooperative magnetism in insulators, but its energy scale was believed to be
small compared to other inter-ionic interactions and therefore it was
considered a small perturbation of the ionic picture. This assertion fails
dramatically in copper oxides, which came to prominence following the discovery
of high critical temperature superconductors (HTSC). Magnetic interactions in
cuprates are remarkably strong and are often considered the origin of the
unusually high superconducting transition temperature, Tc. Here we report a
detailed survey of magnetic excitations in the one-dimensional cuprate Sr2CuO3
using inelastic neutron scattering (INS). We show that although the
experimental dynamical spin structure factor is well described by the model
S=1/2 nearest-neighbour Heisenberg Hamiltonian typically used for cuprates, the
magnetic intensity is modified dramatically by strong hybridization of Cu 3d
states with O p states, showing that the ionic picture of localized 3d
Heisenberg spin magnetism is grossly inadequate. Our findings provide a natural
explanation for the puzzle of the missing INS magnetic intensity in cuprates
and have profound implications for understanding current and future
experimental data on these materials.",0812.5007v1
2019-05-13,Electronic structure of Fe and magnetism in the $3d/5d$ double perovskites Ca$_2$FeReO$_6$ and Ba$_2$FeReO$_6$,"The Fe electronic structure and magnetism in (i) monoclinic Ca$_2$FeReO$_6$
with a metal-insulator transition at $T_{MI} \sim 140$ K and (ii) quasi-cubic
half-metallic Ba$_2$FeReO$_6$ ceramic double perovskites are probed by soft
x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD).
These materials show distinct Fe $L_{2,3}$ XAS and XMCD spectra, which are
primarily associated with their different average Fe oxidation states (close to
Fe$^{3+}$ for Ca$_2$FeReO$_6$ and intermediate between Fe$^{2+}$ and Fe$^{3+}$
for Ba$_2$FeReO$_6$) despite being related by an isoelectronic
(Ca$^{2+}$/Ba$^{2+}$) substitution. For Ca$_2$FeReO$_6$, the powder-averaged Fe
spin moment along the field direction ($B = 5$ T), as probed by the XMCD
experiment, is strongly reduced in comparison with the spontaneous Fe moment
previously obtained by neutron diffraction, consistent with a scenario where
the magnetic moments are constrained to remain within an easy plane. For $B=1$
T, the unsaturated XMCD signal is reduced below $T_{MI}$ consistent with a
magnetic transition to an easy-axis state that further reduces the
powder-averaged magnetization in the field direction. For Ba$_2$FeReO$_6$, the
field-aligned Fe spins are larger than for Ca$_2$FeReO$_6$ ($B=5$ T) and the
temperature dependence of the Fe magnetic moment is consistent with the
magnetic ordering transition at $T_C^{Ba} = 305$ K. Our results illustrate the
dramatic influence of the specific spin-orbital configuration of Re $5d$
electrons on the Fe $3d$ local magnetism of these Fe/Re double perovskites.",1905.04988v1
2020-07-08,"Probing low temperature non-equilibrium magnetic state in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments","The low temperature lattice structure and magnetic properties of
Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite have been investigated using experimental
results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac
susceptibility, neutron diffraction and neutron depolarization techniques. The
samples have been prepared by chemical co-precipitation of the Fe and Co
nitrates solution in high alkaline medium and subsequent thermal annealing of
the precipitates in the temperature range of 200- 900 $^\circ$C. Rietveld
refinement of the SXRD patterns at room temperature indicated two-phased cubic
spinel structure for the samples annealed at temperatures 200-600 $^\circ$C.
The samples annealed at temperatures 700 $^\circ$C and 900 $^\circ$C (CF90)
have been best fitted with single phased lattice structure. Refinement of the
neutron diffraction patterns in the temperature range of 5-300 K confirmed
antiferromagnetic (AFM) Co$_3$O$_4$ and ferrimagnetic (FIM)
Co$_{2.75}$Fe$_{0.25}$O$_4$ phases for the sample annealed at 600 $^\circ$C and
single FIM phase of Co$_{2.75}$Fe$_{0.25}$O$_4$ for the CF90 sample. Magnetic
measurements have shown a non-equilibrium magnetic structure, consisting of the
high temperature FIM phase and low temperature AFM phase. The magnetic phases
are sensitive to magnetic fields, where high temperature phase is suppressed at
higher magnetic fields by enhancing the low temperature AFM phase, irrespective
of annealing temperature of the samples.",2007.03906v1
2016-05-17,"Magnetism of a rhombohedral-type pyrochlore-derived Kagome series, Mn2R3Sb3O14 (R= Rare-earths)","The results of magnetic investigations on a new series of compounds,
Mn2R3Sb3O14, containing 2-dimensional Kagome lattice of R ions and belonging to
pyrochlore series, are presented. Crystallographic features of light R members
(R= La, Pr and Nd) of this family, as established in the recent literature,
have been reported to be novel in many respects, in particular, the rhomohedral
nature of the structure which is rare among pyrochlores. It was also reported
that, as the R becomes heavier, beyond R= Sm, the fraction of well-known cubic
pyrochlore phase tends to gradually dominate. Here, we report that we are able
to form the Gd member in the rhombohedral form without noticeable admixture
from the cubic phase. With respect to magnetic behavior, our magnetization
measurements on the La member reveal that Mn exists in divalent state without
any evidence for long range magnetic ordering down to 2 K (that is, suppressed
magnetism), which is not so common for Mn based oxides, though
antiferromagnerism below 2 K is not ruled out. Nd and Gd members, are however,
found to show distinct features above 2 K in magnetic susceptibility and
heat-capacity, attributable to long-range magnetic ordering from respective
rare-earth sublattice. The experimental results with respect to magnetism are
found to be consistent with the results from ab initio band structure
calculations performed for the La case. The calculations imply that electron
correlation is important to describe insulating behavior.",1605.05027v1
2021-05-01,Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors,"Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons",2105.00269v1
2021-08-25,Magnetic properties of BiFeO$_3$-BaTiO$_3$ ceramics in the morphotropic phase boundary: a role of crystal structure and structural parameters,"A correlation between the crystal structure and magnetic properties of system
(1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase
boundary was studied using X-ray and neutron diffraction, magnetometry, and
Mossbauer spectroscopy measurements. Increase in the dopants content leads to
the structural transition from the rhombohedral phase to the cubic phase via a
formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic
structure changes from the modulated G-type antiferromagnetic to the collinear
antiferromagnetic via a stabilization of the non-collinear antiferromagnetic
phase with non-zero remanent magnetization. The value of magnetic moment
calculated per iron ion based on the Mossbauer and neutron diffraction data
decreases from m = 4.4 mB for the compound with x=0.25 to m=3.2 mB for the
compound with x=0.35 testifying a dominance of 3+ oxidation state of the iron
ions. Increase in the amount of the cubic phase leads to a reduction in the
remanent magnetization from 0.02 emu.g for the compounds with the dominant
rhombohedral phase (x < 0.27) down to about 0.001 emu/g for the compounds with
dominant cubic structure (x >= 0.27). Rapid decrease in the remanent
magnetization observed in the compounds across the phase coexistence region
points at no direct correlation between the type of structural distortion and
non-zero remanent magnetization, while the oxygen octahedra tilting is the key
factor determining the presence of non-zero remanent magnetization.",2108.11447v1
2023-02-23,First-principles based Monte Carlo modeling of oxygen deficient Fe-substituted SrTiO$_3$ experimental magnetization,"Ferroics based on transition-metal (TM) substituted SrTiO$_{3}$ have called
much attention as magnetism and/or ferroelectricity can be tuned by using
cations substitution and defects, strain and/or oxygen deficiency. C. A. Ross
et al. [Phys. Rev. Applied 7, 024006 (2017)] demonstrated the
SrTi$_{1-x}$Fe$_{x}$O$_{3-\delta}$ (STF) magnetization behavior for different
deposition oxygen-pressures, substrates and magnetic fields. The relation
between oxygen deficiency and ferroic orders is yet to be well understood, for
which the full potential of oxygen-stoichiometry engineered materials remain an
open question. Here, we use hybrid-DFT to calculate different oxygen vacancy
($v_{o}$) states in STF with a variety of TM distributions. The resulting
cations' magnetic states and alignments associated to the $v_{o}$ ground-states
for $x=\{0.125,0.25\}$ are used within a Monte Carlo scope for collinear
magnetism to simulate the spontaneous magnetization. Our model captures several
experimental STF features i.e., display a maximum of the magnetization at
intermediate number of vacancies, a monotonous quenching from
$\sim{0.35}\mu{_{B}}$ for small ${\delta}$, and a slower decreasing of such
saturation for larger number of vacancies. Moreover, our approach gives a
further insight into the relations between defects stabilization and
magnetization, vacancy density and the oxygen pressure required to maximize
such ferroic order, and sets guidelines for future Machine Learning based
computational synthesis of multiferroic oxides.",2302.12174v1
1996-11-30,Slow antiferromagnetic dynamics in the low temperature tetragonal phase of La_{2-x}Sr_xCuO_4 as revealed by ESR of Gd spin probes,"Measuring the ESR of Gd spin probes we have studied the magnetic properties
of the copper oxide planes in the low temperature tetragonal (LTT) phase of Eu
doped La_{2-x}Sr_xCuO_4. The data give evidence that at particular levels of Sr
and Eu doping the frequency of the antiferromagnetic fluctuations in the LTT
phase dramatically decreases at low temperatures by almost three orders of
magnitude. However, no static magnetic order has been found for T>8K in
contrast to the observation by neutron scattering of stripe ordering of spins
below 50K in a Nd doped La_{2-x}Sr_xCuO_4 single crystal. To our opinion static
order in the Nd doped compound is induced due to the interaction between the Cu
spins with the rare earth magnetic moments. Therefore, a really characteristic
property of the magnetism in the LTT structural phase may be not static
magnetic order at elevated temperatures but rather extremely slow
antiferromagnetic dynamics.",9612011v1
1999-02-16,Dependence of Magnetic Anisotropy and Magnetoresistance of Ni81Fe19-Films on Annealing,"Permalloy (Py:Ni81Fe19) exhibits an anisotropic magnetoresistance (AMR) which
is very often used to read magnetic signals from storage devices. Py-films of
thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field
onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to
1000K in order to investigate the dependence of the magnetic anisotropy and the
AMR on heat treatments. The films exhibit an uniaxial anisotropy after
preparation which changes during annealing above 520K. The AMR along the former
magnetically easy axis as well as the corresponding field sensitivity are
increased by a heat treatment around 700K reaching maxima of about 8% and a
maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for
the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of
the local atomic order.",9902222v1
2001-10-01,"Importance of Magnetism in Phase Stability, Equations of State, and Elasticity","The effects of magnetism on high pressure properties of transition metals and
transition metal compounds can be quite important. In the case of Fe, magnetism
is responsible for stability of the body-centered cubic (bcc) phase at ambient
conditions, and the large thermal expansivity in face-centered cubic (fcc)
iron, and also has large effects on the equation of state and elasticity of
hexagonal close-packed (hcp) iron. In transition metal oxides, local magnetic
moments are responsible for their insulating behavior. LDA+U results are
presented for CoO and FeO, and predictions are made for high pressure
metallization. The inclusion of a local Coulomb repulsion, U, greatly inhibits
the high-spin low-spin transitions found with conventional exchange-correlation
functionals (i.e. generalized gradient corrections, GGA). We discuss theory and
computations for the effects of magnetism on high pressure cohesive properties.",0110025v5
2004-12-22,Role of Point Defects on the Properties of Manganites,"La1-xCaxMnO3+delta and La1-xNaxMnO3+delta samples with well defined cation
molecularity and oxygen contents are analyzed with XRPD, electrical
conductivity, electron paramagnetic resonance and static magnetization
measurements. Point defects are introduced in the structure by: i) aliovalent
cation doping (substitutional defects), ii) oxygen over-stoichiometry (cation
vacancies) and iii) oxygen under-stoichiometry (oxygen vacancies). The cation
doping mainly influences the material by affecting the tolerance factor and the
oxidation of the Mn ions; the cation vacancies affect the magnetic properties
by interrupting the interaction paths between Mn4+-Mn3+ ions whereas the oxygen
vacancies have a stronger influence on the structural and electrical properties
and act on the magnetic properties by the overall decrease on the Mn4+ amount
and by the creation of sample regions with different magnetic features. We can
state that the basic magnetic and electrical behaviors of the Ca- and Na-doped
lanthanum manganite compounds are driven from the Mn4+-Mn3+ ratio and all the
peculiar behaviors are indeed caused by defects, concentration gradient and,
more generally, by lattice disorder.",0412606v1
2005-04-08,On the crystal field in the modern solid-state theory,"We point out the high physical correctness of the use and the concept of the
crystal-field approach, even if is used to metallic magnetic materials of
transition-metal 3d/4f/5f compounds. We discuss the place of the crystal-field
theory in modern solid-state physics and we point out the necessity to consider
the crystal-field approach with the spin-orbit coupling and strong electron
correlations, as a contrast to the single-electron version of the crystal field
customarily used for 3d electrons. We have extended the strongly-correlated
crystal-field theory to a Quantum Atomistic Solid-State Theory (QUASST) to
account for the translational symmetry and inter-site spin-dependent
interactions indispensable for formation of magnetically-ordered state. We have
correlated macroscopic magnetic and electronic properties with the atomic-scale
electronic structure for ErNi5, UPd2Al3, FeBr2, LaCoO3 and LaMnO3. In QUASST we
have made unification of 3d and rare-earth compounds in description of the
low-energy electronic structures and magnetism of open 3d-/4f-/5f-shell
electrons. QUASST offers consistent description of zero-temperature properties
and thermodynamic properties of 4f-/5f-/3d-atom containing compounds. Our
studies indicate that it is the highest time to unquench the orbital magnetism
in 3d oxides.",0504199v1
2006-01-19,Enhancement of giant magnetoresistance effect in the Ruddlesden-Popper phase Sr3Fe2-xCoxO7-d: Predominant role of oxygen nonstoichiometry and magnetic phase separation,"The magnetic and magnetotransport properties of the Sr3Fe2-xCoxO7-d system
(0.2 <= x <= 1.0) were systematically investigated. This oxide system exhibits
a giant magnetoresistance (GMR) effect at low temperatures, reaching up to 80%
in 7 T at 5 K. Ac-susceptibility measurements show that there exists a strong
competition between ferromagnetic (F) and spin glass states, and the balance
between these two magnetic states can be controlled by varying cobalt (x)
and/or oxygen contents (d). Importantly, the MR effect is closely related to
the magnetic property: the development of magnetic disordering leads to
enhancement in the negative MR effect. It is suggested that the compound
segregates into F clusters embedded in a non-F matrix, being a naturally
occurring analog of the artificial granular-GMR materials, as in the doped
perovskite cobaltites, La1-xSrxCoO3 (x < 0.18).",0601428v1
2006-01-22,GHz sandwich strip inductors based on Fe-N Films,"Planar strip inductors consisting of two Fe-N films enclosing a conducting
film made of Cu, were fabricated on oxidized Si substrates. The inductors were
1mm long, 2 to 100 um wide, with layers of thickness ~0.1 um for the magnetic
films and ~0.5 um for the conductor. The soft (Hc=4-8 Oe) magnetic layers were
biased during impedance measurement by applying an external field along the
strip length thereby facilitating the transverse susceptibility configuration.
Biased strips exhibited 70 to 100% inductance enhancement at 1GHz with quality
factors Q=4.5 to 3, respectively. The magnetic contribution to the total flux
in the narrow devices was less than predicted theoretically, which was
attributed to hardening of the magnetic material at the edges of the strip,
where the deposition was close to 60 degree incidence. Test films were
fabricated on tilted substrates and found to develop a very high anisotropy (up
to 1 kOe) for deposition angles larger than 30 degrees. Optimizing the flux
closure at the strip edges and using thicker conductor layers is essential for
further improving the performance of sandwich strip inductors.",0601497v1
2007-08-13,On the absence of a spiral magnetic order in Li2CuO2 with one-dimensional CuO2 ribbon chains,"On the basis of first principles density functional theory electronic
structure calculations as well as classical spin analysis, we explored why the
magnetic oxide Li2CuO2, consisting of CuO2 ribbon chains made up of
edge-sharing CuO4 squares, does not exhibit a spiral-magnetic order. Our work
shows that, due to the next-nearest-neighbor interchain interactions, the
observed collinear magnetic structure becomes only slightly less stable than
the spin-spiral ground state, and many states become nearly degenerate in
energy with the observed collinear structure. This suggests that the collinear
magnetic structure of Li2CuO2 is a consequence of order-by-disorder induced by
next-nearest-neighbor interchain interactions.",0708.1708v1
2007-09-21,"Self-assembly of polymers or copolymers and ferrofluids leading to either 1-d, 2-d or 3-d aggregates decorated with magnetic nanoparticles","A novel type of hybrid colloids is presented, based on the association of
several polymeric systems and ferrofluids. On the one hand, we use inorganic
nanoparticles made of magnetic iron oxide prepared at the LI2C, which response
to a magnetic field of low intensity. On the other hand the organic part is
made either of long linear polyacrylamide chains or of mesoscopic structures
(vesicles and micelles) self-assembled from amphiphile
polybutadiene-b-poly(glutamic acid) di-block copolymers, which conformation is
pH-sensitive.",0709.3514v1
2008-04-24,Magnetic states at the Oxygen surfaces of ZnO and Co-doped ZnO,"First principles calculations of the O surfaces of Co-ZnO show that
substitutional Co ions develop large magnetic moments which long-range coupling
depends on their mutual distance. The local spin polarization induced at the O
atoms is three times larger at the surface than in the bulk, and the surface
stability is considerably reinforced by Co. Moreover, a robust ferromagnetic
state is predicted at the Oxygen (0001) surface even in the absence of magnetic
atoms. The occurrence of surface magnetic moments correlates with the number of
{\it p}-holes in the valence band of the oxide, and the distribution of the
magnetic charge is, even in the absence of spin-orbit interaction, highly
anisotropic.",0804.3937v1
2008-05-06,"Decisive Influence of Cation Size on the Magnetic Groundstate and Non-Fermi Liquid Behavior of ARuO3 (A = Ca, Sr)","We report calorimetric, magnetic and electric transport properties of
single-crystal CaRuO3 and SrRuO3 as a function of temperature T and applied
magnetic field B. We find that CaRuO3 is a non-Fermi-liquid metal near a
magnetic instability, as characterized by the following properties: (1) the
heat capacity C(T,B) ~ -T log T is readily enhanced in low applied fields, and
exhibits a Schottky peak at 2.3 K that exhibits field dependence when T is
reduced; (2) the magnetic susceptibility diverges as T^-x at low temperatures
with 1/2 < x < 1, depending on the applied field; and (3) the electrical
resistivity exhibits a T3/2 dependence over the range 1.7 < T < 24 K. No
Shubnikov-de Haas oscillations are discerned at T = 0.65 K for applied fields
up to 45 T. These properties, which sharply contrast those of the itinerant
ferromagnet SrRuO3, indicate CaRuO3 is a rare example of a stoichiometric oxide
compound that exhibits non-Fermi-liquid behavior near a quantum critical point.",0805.0741v1
2008-11-13,Magnetism in a TiO2/LaAlO3 heterostructure: an ab initio study about the role of oxygen vacancies,"In this work we study the electronic structure and magnetism of a TiO2 film
grown on another non-magnetic oxide such as a LaAlO3 (001) substrate,
concentrating on the role played by structural relaxation and oxygen vacancies.
Using Density Functional Theory ab-initio methods, we study the free-standing
anatase film as well as the interfaces with either the LaO or AlO2 planes of
LaAlO3, focusing on the possibility of magnetic solutions. Our results show
that the interface LaO/TiO2 is favored against the AlO2/TiO2 one if no oxygen
vacancies are present in the interface whereas the contrary happens when there
are oxygen vacancies. In both cases, the cohesive energy is of the same order
of magnitude but only the AlO2/TiO2 interface presents an stable magnetic
solution.",0811.2172v1
2009-07-23,Electrostatic co-assembly of magnetic nanoparticles and fluorescent nanospheres: a versatile approach toward bimodal nanorods,"The elaboration of multimodal nanoparticles stimulates tremendous interest
owing to their numerous potentialities in many applicative fields like
optoelectronics, photonics and especially bioimaging. The concomitant
association of various properties (optical, electrochemical, magnetic) allows
for the use of complementary stimuli in order to probe the interactions between
the nanoparticles and their surroundings.Nanoparticles (NPs) have thus become
highly praised tools to image cells and tissues with a large contrast
compatible with the dimensions of biological materials and the existence of
quantum confinement effects induced by the reduced dimensions. In this context,
the combination of magnetism and emissive properties such as fluorescence
appears particularly attractive for non-invasive investigations, cell sorting
or drug vectorization. Therefore, combining both fluorescence and magnetism
requires the delicate construction of hybrid assemblies. Most of the magnetic
nanoparticles are made of metallic oxides or alloys, e.g. gamma-Fe2O3, Fe3O4,
FePt, while the target fluorescent entities are often organic dyes or quantum
dots (QDs).",0907.3979v1
2009-11-09,Role of dipole-dipole interactions in multiple quantum transitions in magnetic nanoparticles,"In order to better understand the origin of multiple quantum transitions
observed in superparamagnetic nanoparticles, electron magnetic resonance (EMR)
studies have been performed on iron oxide nanoparticles assembled inside the
anodic alumina membrane. The positions of both the main resonance and
""forbidden"" (double-quantum, 2Q) transitions observed at the half-field
demonstrate the characteristic angular dependence with the line shifts
proportional to 3cos2q-1, where q is the angle between the channel axis and
external magnetic field B. This result can be attributed to the interparticle
dipole-dipole interactions within elongated aggregates inside the channels. The
angular dependence of the 2Q intensity is found to be proportional to
sin2qcos2q, that is consistent with the predictions of quantum-mechanical
calculations with the account for the mixing of states by non-secular
inter-particle dipole-dipole interactions. Good agreement is demonstrated
between different kinds of measurements (magnetization curves, line shifts and
2Q intensity), evidencing applicability of the quantum approach to the
magnetization dynamics of superparamagnetic objects.",0911.1752v1
2011-01-12,Multiferroic Properties of CaMn$_7$O$_{12}$,"We report that CaMn$_7$O$_{12}$ is a new magnetic multiferroic material. The
appearance of a ferroelectric polarization coinciding with the magnetic phase
transition ($\sim90$ K) suggests the presence of ferroelectricity induced by
magnetism, further confirmed by its strong magnetoelectric response. With
respect to other known magnetic multiferroics, CaMn$_7$O$_{12}$ displays
attractive multiferroic properties, such as a high ferroelectric critical
temperature and large polarization. More importantly, these results open a new
avenue to search for magnetic multiferroics in the catalogue of doped oxides.",1101.2276v4
2011-02-24,The role of magnetic anisotropy in spin filter junctions,"We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.",1102.4978v1
2011-05-10,Multiferroic behavior in the new double-perovskite Lu$_2$MnCoO$_6$,"We present a new member of the multiferroic oxides, Lu$_2$MnCoO$_6$, which we
have investigated using X-ray diffraction, neutron diffraction, specific heat,
magnetization, electric polarization, and dielectric constant measurements.
This material possesses an electric polarization strongly coupled to a net
magnetization below 35 K, despite the antiferromagnetic ordering of the $S =
3/2$ Mn$^{4+}$ and Co$^{2+}$ spins in an $\uparrow \uparrow \downarrow
\downarrow$ configuration along the c-direction. We discuss the magnetic order
in terms of a condensation of domain boundaries between $\uparrow \uparrow$ and
$\downarrow \downarrow$ ferromagnetic domains, with each domain boundary
producing a net electric polarization due to spatial inversion symmetry
breaking. In an applied magnetic field the domain boundaries slide, controlling
the size of the net magnetization, electric polarization, and magnetoelectric
coupling.",1105.2058v1
2012-07-13,Magneto-absorption spectra of hydrogen-like yellow exciton series in cuprous oxide: excitons in strong magnetic fields,"We study the absorption spectra of the yellow excitons in Cu$_2$O in high
magnetic fields using polarization-resolved optical absorption measurements
with a high frequency resolution. We show that the symmetry of the yellow
exciton results in unusual selection rules for the optical absorption of
polarized light and that the mixing of ortho- and para- excitons in magnetic
field is important. Our calculation of the energies of the yellow exciton
series in an arbitrary magnetic field gives an excellent fit to experimental
data and allows us to understand the complex structure of excitonic levels and
their magnetic field dependence, which resolves the old-standing disagreement
between the results of optical absorption and cyclotron resonance measurements.",1207.3372v1
2012-08-17,Interface induced perpendicular magnetic anisotropy in Co/CoO/Co thin film structure: An in-situ MOKE investigation,"Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic
properties have been investigated using in-situ magneto-optic Kerr effect
during growth of the sample. Magnetic anisotropy with easy axis perpendicular
to the film surface has been observed in top Co layer, whereas bottom layer was
found to be soft with in-plane magnetization without any influence of top
layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that
the growth of Co on oxidized interface takes place with preferential
orientation of c-axis perpendicular to the film plane, which results in the
observed perpendicular magnetic anisotropy. Texturing of the c-axis is expected
to be a result of minimization of the interface energy due to hybridization
between Co and oxygen at the interface.",1208.3673v1
2012-10-18,Measurement of Magnetic Exchange in Ferromagnet-Superconductor La2/3Ca1/3MnO3/YBa2Cu3O7 Bilayers,"The existence of coherent magnetic correlations in the normal phase of
cuprate high-temperature superconductors has proven difficult to measure
directly. Here we report on a study of ferromagnetic-superconductor bilayers of
La2/3Ca1/3MnO3/YBa2Cu3O7 (LCMO/YBCO) with varying YBCO layer thicknesses. Using
x-ray magnetic circular dichroism, we demonstrate that the ferromagnetic layer
induces a Cu magnetic moment in the adjacent high-temperature superconductor.
For thin samples, this moment exists at all temperatures below the Curie
temperature of the LCMO layer. However, for a YBCO layer thicker than 12 unit
cells, the Cu moment is suppressed for temperatures above the superconducting
transition, suggesting this to be a direct measurement of magnetic coherence in
the normal state of a superconducting oxide.",1210.5049v1
2013-02-11,Quantum-Confinement-Induced Magnetism in LaNiO$_3$-LaMnO$_3$ Superlattices,"The emergence of magnetic reconstructions at the interfaces of oxide
heterostructures are often explained via subtle modifications in the electronic
densities, exchange couplings, or strain. Here an additional possible route for
induced magnetism is studied in the context of the
(LaNiO$_3$)$_n$/(LaMnO$_3$)$_n$ superlattices using a hybrid tight-binding
model. In the LaNiO$_3$ region, the induced magnetizations decouple from the
intensity of charge leakage from Mn to Ni, but originate from the spin-filtered
quantum confinement present in these nanostructures. In general, the induced
magnetization is the largest for the (111)-stacking and the weakest for the
(001)-stacking superlattices, results compatible with the exchange bias effects
reported by Gibert et al. Nat. Mater. 11, 195 (2012).",1302.3253v2
2013-02-27,When metal organic frameworks turn into linear magnets,"We investigate the existence of linear magnetism in the metal organic
framework materials MOF-74-Fe, MOF-74-Co, and MOF-74-Ni, using first-principles
density functional theory. MOF-74 displays regular quasi-linear chains of
open-shell transition metal atoms, which are well separated. Our results show
that within these chains-for all three materials-ferromagnetic coupling of
significant strength occurs. In addition, the coupling in-between chains is at
least one order of magnitude smaller, making these materials almost perfect 1D
magnets at low temperature. The inter-chain coupling is found to be
anti-ferromagnetic, in agreement with experiments. While some quasi-1D
materials exist that exhibit linear magnetism-mostly complex oxides, polymers,
and a few other rare material-they are typically very difficult to synthesize.
The significance of our finding is that MOF-74 is very easy to synthesize and
it is likely the simplest realization of the 1D Ising model in nature. MOF-74
could thus be used in future experiments to study 1D magnetism at low
temperature.",1302.6886v1
2013-03-14,Thermal Stability and Electrical Control of Magnetization of Heusler/Oxide Interface and Non-collinear Spin Transport of Its Junction,"Towards next-generation spintronics devices, such as computer memories and
logic chips, it is necessary to satisfy high thermal stability, low-power
consumption and high spin-polarization simultaneously. Here, from
first-principles, we investigate thermal stability (both structure and
magnetization) and the electric field control of magnetic anisotropy on Co2FeAl
(CFA)/MgO. A phase diagram of structural thermal stability of the CFA/MgO
interface is illustrated. An interfacial perpendicular-anisotropy, coming from
the Fe-O orbital hybridization, provides high magnetic thermal stability and a
low stray field. We find an electric-field-induced giant modification of such
perpendicular-anisotropy via a great magnetoelectric effect (the anisotropy
energy coefficient beta~10-7 erg/V cm). Our spin electronic-structure and
non-collinear transport calculations indicate high spin-polarized interfacial
states and good magnetoresistance properties of CFA/MgO/CFA perpendicular
magnetic tunnel junctions.",1303.3473v2
2013-06-17,MnSb2O6: A polar magnet with a chiral crystal structure,"Structural and magnetic chiralities are found to coexist in a small group of
materials in which they produce intriguing phenomenologies such as the recently
discovered skyrmion phases. Here, we describe a previously unknown
manifestation of this interplay in MnSb2O6, a trigonal oxide with a chiral
crystal structure. Unlike all other known cases, the MnSb2O6 magnetic structure
is based on co-rotating cycloids rather than helices. The coupling to the
structural chirality is provided by a magnetic axial vector, related to the
so-called vector chirality. We show that this unique arrangement is the
magnetic ground state of the symmetric-exchange Hamiltonian, based on ab-initio
theoretical calculations of the Heisenberg exchange interactions, and is
stabilised by out-of-plane anisotropy. MnSb2O6 is predicted to be multiferroic
with a unique ferroelectric switching mechanism.",1306.3854v1
2014-01-15,Chiral magnetization textures stabilized by the Dzyaloshinskii-Moriya interaction during spin-orbit torque switching,"We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on
current-induced magnetic switching of a perpendicularly magnetized
heavy-metal/ferromagnet/oxide trilayer both experimentally and through
micromagnetic simulations. We report the generation of stable helical
magnetization stripes for a sufficiently large DMI strength in the switching
region, giving rise to intermediate states in the magnetization confirming the
essential role of the DMI on switching processes. We compare the simulation and
experimental results to a macrospin model, showing the need for a micromagnetic
approach. The influence of the temperature on the switching is also discussed.",1401.3526v2
2014-07-30,Synthetic magnetoelectric coupling in a nanocomposite multiferroic,"Given the paucity of single phase multiferroic materials (with large
ferromagnetic moment), composite systems seem an attractive solution in the
quest to realize magnetoelectric cou-pling between ferromagnetic and
ferroelectric order parameters. Despite having antiferro-magnetic order, BiFeO3
(BFO) has nevertheless been a key material in this quest due to excel-lent
ferroelectric properties at room temperature. We studied a superlattice
composed of 8 repetitions of 6 unit cells of La0.7Sr0.3MnO3 (LSMO) grown on 5
unit cells of BFO. Significant net uncompensated magnetization in BFO is
demonstrated using polarized neutron reflectometry in an insulating
superlattice. Remarkably, the magnetization enables magnetic field to change
the dielectric properties of the superlattice, which we cite as an example of
synthetic magnetoelectric coupling. Importantly, this controlled creation of
magnetic moment in BFO suggests a much needed path forward for the design and
implementation of integrated oxide devices for next generation magnetoelectric
data storage platforms.",1407.8157v2
2014-10-23,Magnetic structure determination from the magnetic pair distribution function (mPDF): ground state of MnO,"An experimental determination of the magnetic pair distribution function
(mPDF) defined in an earlier paper (Frandsen, Yang, and Billinge. (2014) Acta
Crystallogr. A, 70(1), 3-11) is presented for the first time. The mPDF was
determined from neutron powder diffraction data from a reactor and a neutron
time-of-flight total scattering source on a powder sample of the
antiferromagnetic oxide MnO. A description of the data treatment that allowed
the measured mPDF to be extracted and then modelled is provided and utilized to
investigate the low-temperature structure of MnO. Atomic and magnetic
co-refinements support the scenario of a locally monoclinic ground-state atomic
structure, despite the average structure being rhombohedral, with the magnetic
PDF analysis successfully recovering the known antiferromagnetic spin
configuration. The total scattering data suggest a preference for the spin axis
to lie along the pseudocubic [10$\bar{1}$] direction. Finally, $r$-dependent
PDF refinements indicate that the local monoclinic structure tends toward the
average rhombohedral $R\overline{3}m$ symmetry over a length scale of
approximately 100~\AA.",1410.6377v2
2014-10-27,Hysteretic Magnetotransport in SmB6 at Low Magnetic Fields,"Utilizing Corbino disc structures, we have examined the magnetic field
response of resistivity for the surface states of SmB6 on different crystalline
surfaces at low temperatures. Our results reveal a hysteretic behavior whose
magnitude depends on the magnetic field sweep rate and temperature. Although
this feature becomes smaller when the field sweep is slower, a complete
elimination or saturation is not observed in our slowest sweep-rate
measurements, which is much slower than a typical magnetotransport trace. These
observations cannot be explained by quantum interference corrections such as
weak anti-localization. Instead, they are consistent with behaviors of glassy
surface magnetic ordering, whose magnetic origin is most likely from samarium
oxide (Sm2O3) forming on the surface during exposure to ambient conditions.",1410.7430v1
2015-01-08,X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO (100),"The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film
synthesized by plasma assisted simultaneous oxidization on MgO(100) have been
studied with X-ray magnetic circular dichroism (XMCD). The ultrathin film
retains a rather large total magnetic moment, i.e. (2.7+-0.15) uB/f.u., which
is ~ 70% of that for the bulk-like Fe3O4. A significant unquenched orbital
moment up to (0.54+-0.05) uB/f.u. was observed, which could come from the
symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will
add capacities to the Fe3O4-based spintronics devices in the magnetization
reversal by the electric field.",1501.01803v3
2015-02-20,"Preparation, structural and magnetic studies on BiFe1-xCrxO3 (x=0.0, 0.05 and 0.1) multiferroic nanoparticles","BiFe1-xCrxO3 (x=0.0, 0.05 and 0.1) nanoparticles are prepared by a combustion
method without using any solvent. All the synthesized nanoparticles are single
phase in nature, nearly spherical in shape and crystallize in distorted
perovskite structure and space group R3c with an average crystallite size of
the order of 40 nm. The room temperature magnetization observed in BiFeO3
nanoparticles is larger than that in the bulk. Increasing Cr doping leads to
increase in the magnetization and coercivity. Strong superexchange interaction
between Fe3+ and Cr3+ atoms is likely to give rise to such increase in
magnetization with Cr-doping. M\""ossbauer data of these nanoparticles show
ordered magnetic state in which Fe atoms are in 3+ oxidation states.",1502.05921v1
2015-03-12,A single crystal Co2+ fluoride pyrochlore antiferromagnet,"We report the crystal growth, crystal structure and basic magnetic properties
of a new cobalt-based pyrochlore, NaSrCo$_2$F$_7$. Na and Sr are completely
disordered on the non-magnetic large atom A sites, while magnetic S=3/2
Co$^{2+}$ fully occupies the pyrochlore lattice B sites. This system exhibits
an isotropic magnetic susceptibility with strong antiferromagnetic interactions
(${\theta}_{CW}$ = -127(1)), a large effective moment (${\rho_{eff}}$ = 5.9(1)
${\mu_B}$/Co) and no spin freezing until 3 K. Thus NaSrCo$_2$F$_7$ is a
geometrically frustrated antiferromagnet with a frustration index f =
-${\theta_{CW}}$/T$_f$ = 42. AC susceptibility, DC susceptibility, and heat
capacity are utilized to characterize the spin freezing at low temperatures. We
propose that NaSrCo$_2$F$_7$, compared here to the related material
NaCaCo$_2$F$_7$, may be the realization of a frustrated pyrochlore
antiferromagnet with weak bond disorder. The strong magnetic frustration at an
easily accessible temperature and the availability of large single crystals
make this one of the potentially interesting alternatives to the more commonly
studied rare earth oxide pyrochlores.",1503.03751v1
2015-04-07,Evolution of Magnetism in Single-Crystal Ca2Ru1-xIrxO4 (0< x <0.65),"We report structural, magnetic, transport and thermal properties of
single-crystal Ca2Ru1-xIrxO4 (0 < x< 0.65). Ca2RuO4 is a structurally-driven
Mott insulator with a metal-insulator transition at TMI = 357 K, which is well
separated from antiferromagnetic order at TN = 110 K. Substitution of 5d
element, Ir, for Ru enhances spin-orbit coupling (SOC) and locking between the
structural distortions and magnetic moment canting. In particular, Ir doping
intensifies the distortion or rotation of Ru/IrO6 octahedra and induces weak
ferromagnetic behavior along the c-axis. Moreover, the magnetic ordering
temperature TN increases from 110 K at x = 0 to 215 K with enhanced magnetic
anisotropy at x = 0.65. The effect of Ir doping sharply contrasts with that of
3d-element doping such as Cr, Mn and Fe, which suppresses TN and induces
unusual negative volume thermal expansion. The stark difference between 3d- and
5d-element doping underlines a strong magnetoelastic coupling inherent in the
Ir-rich oxides.",1504.01750v1
2015-04-27,Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$,"Magnetic fluctuations in transition metal oxides are a subject of intensive
research because of the key role they are expected to play in the transition
from the Mott insulator to the unconventional metallic phase of these
materials, and also as drivers of superconductivity. Despite much effort, a
clear link between magnetic fluctuations and the insulator-to-metal transition
has not yet been established. Here we report the discovery of a compelling link
between magnetic fluctuations and the insulator-to-metal transition in
Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$ perovskites as a function of the doping
coefficient x. We show that when the material turns from insulator to metal, at
a critical value of x$\sim$ 0.3, magnetic fluctuations change their character
from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant
electron state with Hund's orbital coupling. These results are expected to have
wide-ranging implications for our understanding of the unconventional
properties of strongly correlated electrons systems",1504.06901v1
2015-06-09,"Synthesis, Crystal Structure and Magnetism of Eu3Sc2O5Fe2As2","The iron arsenide Eu3Fe2O5Fe2As2 was synthesized at 1173-1373 K in a
resistance furnace and characterized by X-ray powder diffraction with Rietveld
analysis: Sr3Fe2O5Cu2S2-type, I4/mmm, a = 406.40(1) pm, c = 2646.9(1) pm.
Layers of edge-sharing FeAs4/4 tetrahedra are separated by perovskite-like
oxide blocks. No structural transition occurs in the temperature range from 10
to 300 K. Magnetic measurements have revealed Curie-Weiss behavior with an
effective magnetic moment of 7.79 muB per europium atom in agreement with the
theoretical value of 7.94 muB for Eu2+. A drop in the magnetic susceptibility
at 5 K indicates possible antiferromagnetic ordering. 151Eu and 57Fe
M\""ossbauer spectroscopic measurements have confirmed a beginning cooperative
magnetic phenomenon by showing significantly broadened spectra at 4.8 K
compared to those at 78 K.",1506.02925v1
2015-08-07,Magnetic and spectral properties of multi-sublattice oxides SrY2O4:Er3+ and SrEr2O4,"SrEr2O4 is a geometrically frustrated magnet which demonstrates rather
unusual properties at low temperatures including a coexistence of long- and
short-range magnetic order, characterized by two different propagation vectors.
In the present work, the effects of crystal fields (CF) in this compound
containing four magnetically inequivalent erbium sublattices are investigated
experimentally and theoretically. We combine the measurements of the CF levels
of the Er3+ ions made on a powder sample of SrEr2O4 using neutron spectroscopy
with site-selective optical and electron paramagnetic resonance measurements
performed on single crystal samples of the lightly Er-doped nonmagnetic
analogue, SrY2O4. Two sets of CF parameters corresponding to the Er3+ ions at
the crystallographically inequivalent lattice sites are derived which fit all
the available experimental data well, including the magnetization and dc
susceptibility data for both lightly doped and concentrated samples.",1508.01638v1
2015-08-12,Ferroelectricity driven magnetism at domain walls in LaAlO$_3$/PbTiO$_3$ superlattices,"Charge dipole moment and spin moment rarely coexist in single-phase bulk
materials except in some multiferroics. Despite the progress in the past
decade, for most multiferroics their magnetoelectric performance remains poor
due to the intrinsic exclusion between charge dipole and spin moment. As an
alternative approach, the oxide heterostructures may evade the intrinsic limits
in bulk materials and provide more attractive potential to realize the
magnetoelectric functions. Here we perform a first-principles study on
LaAlO$_3$/PbTiO$_3$ superlattices. Although neither of the components is
magnetic, magnetic moments emerge at the ferroelectric domain walls of
PbTiO$_3$ in these superlattices. Such a twist between ferroelectric domain and
local magnetic moment, not only manifests an interesting type of
multiferroicity, but also is possible useful to pursuit the electrical-control
of magnetism in nanoscale heterostructures.",1508.02889v1
2016-03-11,Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices,"Magnetic anisotropy (MA) is one of the most important material properties for
modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e.
magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry.
Extrinsic control over the MA is usually achieved by introducing shape
anisotropy or exchange bias from another magnetically ordered material. Here we
demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by
digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling
(SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3
(LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control
of thickness at atomic scale. Magnetic easy axis reorientation is observed by
controlling the dimensionality of SIO, mediated through the emergence of a
novel spin-orbit state within the nominally paramagnetic SIO.",1603.03794v2
2016-06-14,Chiral Ordering Spin Associated Glass like State in SrRuO3SrIrO3 Superlattice,"Heterostructure interface provides a powerful platform to observe rich
emergent phenomena, such as interfacial superconductivity, nontrivial
topological surface state. Here SrRuO3/SrIrO3 superlattices were epitaxially
synthesized. The magnetic and electrical properties of these superlattices were
characterized. Broad cusps in the zero field cooling magnetization curves and
near stable residual magnetization below the broad cusps, as well as two steps
magnetization hysteresis loops are observed. The magnetization relaxes
following a modified Stretched function model indicating coexistence of spin
glass and ferromagnetic ordering in the superlattices. Topological Hall effect
was demonstrated at low temperature and weakened with the increase of SrIrO3
layer thickness. These results suggest that chiral ordering spin texture were
generated at the interfaces due to the interfacial Dzyaloshinskii-Moriya (DM)
interaction, which generates the spin glass behaviors. The present work
demonstrates that SrIrO3 can effectively induce interface DM interactions in
heterostructures, it would pave light on the new research directions of strong
spin orbit interaction oxides, from the viewpoints of both basic science and
prospective spintronics devices applications.",1606.04313v2
2016-09-29,Proposal for a Leaky-Integrate-Fire Spiking Neuron based on Magneto-Electric Switching of Ferro-magnets,"The efficiency of the human brain in performing classification tasks has
attracted considerable research interest in brain-inspired neuromorphic
computing. Hardware implementations of a neuromorphic system aims to mimic the
computations in the brain through interconnection of neurons and synaptic
weights. A leaky-integrate-fire (LIF) spiking model is widely used to emulate
the dynamics of neuronal action potentials. In this work, we propose a spin
based LIF spiking neuron using the magneto-electric (ME) switching of
ferro-magnets. The voltage across the ME oxide exhibits a typical
leaky-integrate behavior, which in turn switches an underlying ferro-magnet.
Due to the effect of thermal noise, the ferro-magnet exhibits probabilistic
switching dynamics, which is reminiscent of the stochasticity exhibited by
biological neurons. The energy-efficiency of the ME switching mechanism coupled
with the intrinsic non-volatility of ferro-magnets result in lower energy
consumption, when compared to a CMOS LIF neuron. A device to system-level
simulation framework has been developed to investigate the feasibility of the
proposed LIF neuron for a hand-written digit recognition problem",1609.09158v1
2018-02-14,Collective Coordinate Models of Domain Wall Motion in Perpendicularly Magnetized Systems under the Spin Hall Effect and Longitudinal Fields,"Recent studies on heterostructures of ultrathin ferromagnets sandwiched
between a heavy metal layer and an oxide have highlighted the importance of
spin-orbit coupling (SOC) and broken inversion symmetry in domain wall (DW)
motion. Specifically, chiral DWs are stabilized in these systems due to the
Dzyaloshinskii-Moriya interaction (DMI). SOC can also lead to enhanced current
induced DW motion, with the spin Hall effect (SHE) suggested as the dominant
mechanism for this observation. The efficiency of SHE driven DW motion depends
on the internal magnetic structure of the DW, which could be controlled using
externally applied longitudinal in-plane fields. In this work, micromagnetic
simulations and collective coordinate models are used to study current-driven
DW motion under longitudinal in-plane fields in perpendicularly magnetized
samples with strong DMI. Several extended collective coordinate models are
developed to reproduce the micromagnetic results. While these extended models
show improvements over traditional models of this kind, there are still
discrepancies between them and micromagnetic simulations which require further
work.",1802.04917v1
2018-04-02,Gapped ground state in the zigzag pseudospin-1/2 quantum antiferromagnetic chain compound PrTiNbO6,"We report a single-crystal study on the magnetism of the rare-earth compound
PrTiNbO$_6$ that experimentally realizes the zigzag pseudospin-$\frac{1}{2}$
quantum antiferromagnetic chain model. Random crystal electric field caused by
the site mixing between non-magnetic Ti$^{4+}$ and Nb$^{5+}$, results in the
non-Kramers ground state quasi-doublet of Pr$^{3+}$ with the effective
pseudospin-$\frac{1}{2}$ Ising moment. Despite the antiferromagnetic intersite
coupling of about 4 K, no magnetic freezing is detected down to 0.1 K, whilst
the system approaches its ground state with almost zero residual spin entropy.
At low temperatures, a sizable gap of about 1 K is observed in zero field. We
ascribe this gap to off-diagonal anisotropy terms in the pseudospin
Hamiltonian, and argue that rare-earth oxides open an interesting venue for
studying magnetism of quantum spin chains.",1804.00687v1
2018-11-03,Ferromagnetic resonance in the complex permeability of an Fe$_3$O$_4$ nanosuspension at radio and microwave frequencies,"The complex permeability of an iron-oxide nanosuspension has been measured as
a function of magnetic field strength at RF and microwave frequencies using a
loop-gap resonator. The particles were suspended in water and had an 8-nm
diameter Fe$_3$O$_4$ core that was coated by Dextran. The real part of the
permeability increased sharply beyond a frequency-dependent threshold value of
the static magnetic field before saturating. Just beyond this threshold field,
there was a peak in the imaginary part of the permeability. The permeability
measurements, which exhibited features associated with ferromagnetic resonance,
were used to determine the dependence of the microwave absorption on static
magnetic field strength. Using the absorption data, the $g$-factor of the
nanosuspension was found to be $1.86\pm 0.07$.",1811.01168v1
2019-05-28,Emergent magnetic state in (111)-oriented quasi-two-dimensional spinel oxides,"We report on the emergent magnetic state of (111)-oriented CoCr2O4 ultrathin
films sandwiched by Al2O3 in the quantum confined geometry. At the
two-dimensional crossover, polarized neutron reflectometry reveals an anomalous
enhancement of the total magnetization compared to the bulk value. Synchrotron
x-ray magnetic circular dichroism (XMCD) demonstrates the appearance of
long-range ferromagnetic ordering of spins on both Co and Cr sublattices.
Brillouin function analyses further corroborates that the observed phenomena
are due to the strongly altered magnetic frustration, manifested by the onset
of a Yafet-Kittel type ordering as the new ground state in the ultrathin limit,
which is unattainable in the bulk.",1905.12024v1
2016-11-02,DFT modelling of the effect of strong magnetic field on Aniline molecule,"Aniline is an organic compound with the stoichiometric expression
$C_{6}H_{5}NH_{2}$; consisting of a phenyl structure attached to an amino
group. It is colorless, but it slowly oxidizes and resinifies in air, giving a
red-brown tint to aged samples. Until now, there are only few researches on
Aniline considering low magnetic fields. In this work, we study Aniline
molecule under different high magnetic fields using density functional theory
methods including independent particle and interacting particle approaches. We
obtain charge density distrubitions, energy dispersions, dipol moments and
forces as functions of position and magnetic field. Our numerical results show
that magnetic field affects electron density of the considered molecule. As a
result, it is observed that there are strong fluctuations in energy dispersion.",1611.00552v1
2017-04-26,Transfer of magnetic order and anisotropy through epitaxial integration of 3$d$ and 4$f$ spin systems,"Resonant x-ray scattering at the Dy $M_5$ and Ni $L_3$ absorption edges was
used to probe the temperature and magnetic field dependence of magnetic order
in epitaxial LaNiO$_3$-DyScO$_3$ superlattices. For superlattices with 2 unit
cell thick LaNiO$_3$ layers, a commensurate spiral state develops in the Ni
spin system below 100 K. Upon cooling below $T_{ind} = 18$ K, Dy-Ni exchange
interactions across the LaNiO$_3$-DyScO$_3$ interfaces induce collinear
magnetic order of interfacial Dy moments as well as a reorientation of the Ni
spins to a direction dictated by the strong magneto-crystalline anisotropy of
Dy. This transition is reversible by an external magnetic field of 3 T.
Tailored exchange interactions between rare-earth and transition-metal ions
thus open up new perspectives for the manipulation of spin structures in
metal-oxide heterostructures and devices.",1704.07967v1
2012-01-11,Neutron scattering studies on stripe phases in non-cuprate materials,"Several non-cuprates layered transition-metal oxides exhibit clear evidence
for stripe ordering of charges and magnetic moments. Therefore, stripe order
should be considered as the typical consequence of doping a Mott insulator, but
only in cuprates stripe order or fluctuating stripes coexist with metallic
properties. A linear relationship between the charge concentration and the
incommensurate structural and magnetic modulations can be considered as the
finger print of stripe ordering with localized degrees of freedom. In
nickelates and in cobaltates with K2NiF4 structure, doping suppresses the
nearest-neighbor antiferromagnetism and induces stripe order. The higher amount
of doping needed to induce stripe phases in these non-cuprates series can be
attributed to reduced charge mobility. Also manganites exhibit clear evidence
for stripe phases with further enhanced complexity, because orbital degrees of
freedom are involved. Orbital ordering is the key element of stripe order in
manganites since it is associated with the strongest structural distortion and
with the perfectly fulfilled relation between doping and incommensurability.
Magnetic excitations in insulating stripe phases exhibit strong similarity with
those in the cuprates, but only for sufficiently short magnetic correlation
lengths reflecting well-defined magnetic stripes that are only loosely coupled.",1201.2356v1
2014-06-16,An air-cooled Litz wire coil for measuring the high frequency hysteresis loops of magnetic samples : a useful setup for magnetic hyperthermia applications,"A low-cost and simple setup for measuring the high-frequency hysteresis loops
of magnetic samples is described. An AMF in the range 6-100 kHz with amplitude
up to 80 mT is produced by a Litz wire coil. The latter is air-cooled using a
forced-air approach so no water flow is required to run the setup.
High-frequency hysteresis loops are measured using a system of pick-up coils
and numerical integration of signals. Reproducible measurements are obtained in
the frequency range of 6-56 kHz. Measurement examples on ferrite cylinders and
on iron oxide nanoparticle ferrofluids are shown. Comparison with other
measurement methods of the hysteresis loop area (complex susceptibility,
quasi-static hysteresis loops and calorific measurements) is provided and shows
the coherency of the results obtained with this setup. This setup is well
adapted to the magnetic characterization of colloidal solutions of MNPs for
magnetic hyperthermia applications.",1406.4013v1
2016-08-26,Magnetic properties of the honeycomb oxide Na$_2$Co$_2$TeO$_6$,"We have studied the magnetic properties of Na$_2$Co$_2$TeO$_6$, which
features a honeycomb lattice of magnetic Co$^{2+}$ ions, through macroscopic
characterization and neutron diffraction on a powder sample. We have shown that
this material orders in a zig-zag antiferromagnetic structure. In addition to
allowing a linear magnetoelectric coupling, this magnetic arrangement displays
very peculiar spatial magnetic correlations, larger in the honeycomb planes
than between the planes, which do not evolve with the temperature. We have
investigated this behavior by Monte Carlo calculations using the
$J_1$-$J_2$-$J_3$ model on a honeycomb lattice with a small interplane
interaction. Our model reproduces the experimental neutron structure factor,
although its absence of temperature evolution must be due to additional
ingredients, such as chemical disorder or quantum fluctuations enhanced by the
proximity to a phase boundary.",1608.07593v2
2017-10-20,Confinement of magnetism in atomically-thin $La_{0.7}Sr_{0.3}CrO_3$/$La_{0.7}Sr_{0.3}MnO_3$ heterostructures,"At crystalline interfaces where a valence mismatch exists, electronic and
structural interactions may occur to relieve the polar mismatch leading to the
stabilization of non-bulklike phases. We show that spontaneous reconstructions
at polar $La_{0.7}Sr_{0.3}MnO_3$ interfaces are correlated with suppressed
ferromagnetism for film thicknesses on the order of a unit cell. We investigate
the structural and magnetic properties of valence-matched
$La_{0.7}Sr_{0.3}CrO_3$ - $La_{0.7}Sr_{0.3}MnO_3$ interfaces using a
combination of high-resolution electron microscopy, first principles theory,
synchrotron X-ray scattering and magnetic spectroscopy and
temperature-dependent magnetometry. A combination of an antiferromagnetic
coupling between the $La_{0.7}Sr_{0.3}CrO_3$ and $La_{0.7}Sr_{0.3}MnO_3$ layers
and a suppression of interfacial polar distortions are found to result in
robust long range ferromagnetic ordering for ultra-thin
$La_{0.7}Sr_{0.3}MnO_3$. These results underscore the critical importance of
interfacial structural and magnetic interactions in the design of devices based
on two-dimensional oxide magnetic systems.",1710.07592v2
2017-12-04,Surface magnetism of gallium arsenide nanofilms,"Gallium arsenide (GaAs) is the widest used second generation semiconductor
with a direct band gap and increasingly used as nanofilms. However, the
magnetic properties of GaAs nanofilms have never been studied. Here we find by
comprehensive density functional theory calculations that GaAs nanofilms
cleaved along the <111> and <100> directions become intrinsically metallic
films with strong surface magnetism and magnetoelectric (ME) effect. The
surface magnetism and electrical conductivity are realized via a combined
effect of transferring charge induced by spontaneous electric-polarization
through the film thickness and spin-polarized surface states. The surface
magnetism of <111> nanofilms can be significantly and linearly tuned by
vertically applied electric field, endowing the nanofilms unexpectedly high ME
coefficients, which are tens of times higher than those of ferromagnetic metals
and transition metal oxides.",1712.00990v1
2019-06-18,Discovery of room temperature ferromagnetism in metal-free organic semiconductors,"Creating magnetic semiconductors that work at warm circumstance is still a
great challenge in the physical sciences. Here, we report the discovery of
ferromagnetism in the metal-free perylene diimide semiconductor, whose Curie
temperature is higher than 400 Kelvin. A solvothermal approach is used to
reduce and dissolve the rigid-backbone perylene diimide crystallites, and
radical anion aggregates were fabricated by the subsequent self-assembly and
oxidation process. Magnetic measurements exhibit the ferromagnetic ordering
with the saturated magnetization of 0.48 $\mu_{\rm B}$ per molecule and the
appreciable magnetic anisotropy. X-ray magnetic circular dichroism spectra
suggest the ferromagnetism stems from $\pi$ orbitals of radicals. Our findings
unambitiously demonstrate the long-range ferromagnetic ordering can survive at
room temperature in organic semiconductors, although which are intuitively
regarded to be nonmagnetic.",1906.07531v2
2019-07-05,Supraferromagnetic correlations in clusters of magnetic nanoflowers,"Magnetic nanoflowers are densely packed aggregates of superferromagnetically
coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia
experiments. Here, we investigate the nature of the moment coupling within a
powder of such nanoflowers using spin-resolved small-angle neutron scattering.
Within the powder the nanoparticles are agglomerated to clusters, and we can
show that the moments of neighboring nanoflowers tend to align parallel to each
other. Thus, the whole system resembles a hierarchical magnetic nanostructure
consisting of three distinct levels, i.e. (i) the ferrimagnetic
nanocrystallites as building blocks, (ii) the superferromagnetic nanoflowers,
and (iii) the \textit{supra}ferromagnetic clusters of nanoflowers. We surmise
that such a supraferromagnetic coupling explains the enhanced magnetic
hyperthermia performance in case of interacting nanoflowers.",1907.02752v2
2019-09-30,Highly frustrated magnetism in relativistic $\boldsymbol{d}^\mathbf{4}$ Mott insulators: Bosonic analog of Kitaev honeycomb model,"We study the orbitally frustrated singlet-triplet models that emerge in the
context of spin-orbit coupled Mott insulators with $t_{2g}^4$ electronic
configuration. In these compounds, low-energy magnetic degrees of freedom can
be cast in terms of three-flavor ""triplon"" operators describing the transitions
between spin-orbit entangled $J=0$ ionic ground state and excited $J=1$ levels.
In contrast to a conventional, flavor-isotropic O(3) singlet-triplet models,
spin-orbit entangled triplon interactions are flavor-and-bond selective and
thus highly frustrated. In a honeycomb lattice, we find close analogies with
the Kitaev spin model -- an infinite number of conserved quantities, no
magnetic condensation, and spin correlations being strictly short-ranged.
However, due to the bosonic nature of triplons, there are no emergent gapless
excitations within the spin gap, and ground state is a strongly correlated
paramagnet of dense triplon pairs with no long-range entanglement. Using exact
diagonalization, we study the bosonic Kitaev model and its various extensions,
which break exact symmetries of the model and allow magnetic condensation of
triplons. Possible implications for magnetism of ruthenium oxides are
discussed.",1910.00074v2
2019-10-03,Shaping Magnetite Nanoparticles from First-principles,"Iron oxide magnetic nanoparticles (NPs) are stimuli-responsive materials at
the forefront of nanomedicine. Their realistic finite temperature simulations
are a formidable challenge for first-principles methods. Here, we use density
functional tight binding to open up the required time and length scales and
obtain global minimum structures of Fe3O4 NPs of realistic size (1400 atoms,
2.5 nm) and of different shapes, which we then refine with hybrid density
functional theory methods to accomplish proper electronic and magnetic
properties, which have never been accurately described in simulations. On this
basis, we develop a general empirical formula and prove its predictive power
for the evaluation of the total magnetic moment of Fe3O4 NPs. By converting the
total magnetic moment into the macroscopic saturation magnetization, we
rationalize the experimentally observed dependence with shape. We also reveal
interesting reconstruction mechanisms and unexpected patterns of charge
ordering.",1910.01704v2
2021-01-22,"Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-d (M = Fe, Co, Ni)","The discovery of superconductivity in copper oxide compounds has attracted
considerable attention over the past three decades. The high transition
temperature in these compounds, exhibiting proximity to an antiferromagnetic
order in their phase diagrams, remains one of the main areas of research. The
present study attempts to introduce Fe, Co and Ni magnetic impurities into the
superconducting Y-123 with the aim of exploring the transition temperature
behavior. The solid-state synthesis is exploited to prepare fully oxygenated
Y1-xMxBa2Cu3O7 (M = Co, Fe, Ni) samples with low levels of doping (0< x <
0.03). Systematic measurements are then employed to assess the synthesized
samples using AC magnetic susceptibility, electrical resistivity and X-ray
diffraction. The measurements revealed an increase in Tc as a result of
magnetic substitution for Y. However, the study of non-magnetic dopings on the
fully oxygenated Y1-xM'xBa2Cu3O7 (M' = Ca, Sr) samples showed a decrease in Tc.
Quantitative XRD analysis further suggested that the internal pressure could
have minor effects on the increase in Tc. The normal state resistivity vs
temperature showed a linear profile, confirming that the samples are at an
optimal doping of the carrier concentration.",2101.09292v1
2017-05-11,"First principles investigations of electronic, magnetic and bonding peculiarities of uranium nitride-fluoride UNF","Based on geometry optimization and magnetic structure investigations within
density functional theory, unique uranium nitride fluoride UNF, isoelectronic
with UO2, is shown to present peculiar differentiated physical properties. Such
specificities versus the oxide are related with the mixed anionic sublattices
and the layered-like tetragonal structure characterized by covalent like
[U2N2]2+motifs interlayered by ionic like [F2]2- ones and illustrated herein
with electron localization function graphs. Particularly the ionocovalent
chemical picture shows, based on overlap population analyses, stronger U-N
bonding versus N-F and d(U-N) < d(U-F) distances. Based on LDA+U calculations
the ground state magnetic structure is insulating antiferromagnet with 2 Bohr
Magnetons magnetization per magnetic subcell and ~2 eV band gap.",1705.04068v1
2019-02-08,Magnetization beyond the Ising limit of Ho$_2$Ti$_2$O$_7$,"We report that the local Ising anisotropy in pyrochlore oxides - the crucial
requirement for realizing the spin-ice state - can be broken by means of high
magnetic fields. For the case of the well-established classical spin-ice
compound Ho$_2$Ti$_2$O$_7$ the magnetization exceeds the angle-dependent
saturation value of the Ising limit using ultra-high fields up to 120 T.
However, even under such extreme magnetic fields full saturation cannot be
achieved. Crystal-electric-field calculations reveal that a level crossing for
two of the four ion positions leads to magnetization steps at 55 and 100 T. In
addition, we show that by using a field sweep rate in the range of the
spin-relaxation time the dynamics of the spin system can be probed. Exclusively
at 25 ns/T a new peak of the susceptibility appears around 2 T. We argue, this
signals the cross-over between spin-ice and polarized correlations.",1902.02990v1
2019-02-24,Magnetic Nanoparticle Relaxation Dynamics-based Magnetic Particle Spectroscopy (MPS) for Rapid and Wash-free Molecular Sensing,"Magnetic nanoparticles (MNPs) have been extensively used as contrasts and
tracers for bioimaging, heating sources for tumor therapy, carriers for
controlled drug delivery, and labels for magnetic immunoassays. Here, we
describe a MNP relaxation dynamics-based magnetic particle spectroscopy (MPS)
method for the quantitative detection of molecular biomarkers. In MPS
measurements, the harmonics of oscillating MNPs are recorded and used as a
metric for the freedom of rotational motion, which indicates the bound states
of the MNPs. These harmonics can be collected from microgram quantities of iron
oxide nanoparticles within 10 seconds. Using a streptavidin-biotin binding
system, we demonstrate the feasibility of using MPS to sense these molecular
interactions, showing this method is able to achieve rapid, wash-free
bioassays, and is suitable for future point-of-care (POC), sensitive, and
versatile diagnosis.",1902.08867v2
2019-03-06,Anomalous Magnetic Behavior in Ba2CoO4 with Isolated CoO4 Tetrahedra,"The dimensionality of the electronic and magnetic structure of a given
material is generally predetermined by its crystal structure. Here, using
elastic and inelastic neutron scattering combined with magnetization
measurements, we find unusual magnetic behavior in three-dimensional (3D)
Ba2CoO4. In spite of isolated CoO4 tetrahedra, the system exhibits a 3D
noncollinear antiferromagnetic order in the ground state with an anomalously
large Curie-Weiss temperature of 110 K compared to TN = 26 K. More
unexpectedly, spin dynamics displays quasi-2D spin wave dispersion with an
unusually large spin gap, and 1D magnetoelastic coupling. Our results indicate
that Ba2CoO4 is a unique system for exploring the interplay between isolated
polyhedra, low-dimensional magnetism, and novel spin states in oxides.",1903.02490v1
2021-04-29,High-Dimensional Neural Network Potentials for Magnetic Systems Using Spin-Dependent Atom-Centered Symmetry Functions,"Machine learning potentials have emerged as a powerful tool to extend the
time and length scales of first principles-quality simulations. Still, most
machine learning potentials cannot distinguish different electronic spin
orientations and thus are not applicable to materials in different magnetic
states. Here, we propose spin-dependent atom-centered symmetry functions as a
new type of descriptor taking the atomic spin degrees of freedom into account.
When used as input for a high-dimensional neural network potential (HDNNP),
accurate potential energy surfaces of multicomponent systems describing
multiple magnetic states can be constructed. We demonstrate the performance of
these magnetic HDNNPs for the case of manganese oxide, MnO. We show that the
method predicts the magnetically distorted rhombohedral structure in excellent
agreement with density functional theory and experiment. Its efficiency allows
to determine the N\'{e}el temperature considering structural fluctuations,
entropic effects, and defects. The method is general and is expected to be
useful also for other types of systems like oligonuclear transition metal
complexes.",2104.14439v1
2021-06-09,Nearly itinerant electronic groundstate in the intercalated honeycomb iridate Ag$_3$LiIr$_2$O$_6$,"We use x-ray spectroscopy at Ir L$_3$/L$_2$ absorption edge to study powder
samples of the intercalated honeycomb magnet Ag$_3$LiIr$_2$O$_6$. Based on
x-ray absorption and resonant inelastic x-ray scattering measurements, and
exact diagonalization calculations including next-neighbour Ir-Ir electron
hoping integrals, we argue that the intercalation of Ag atoms results in a
nearly itinerant electronic structure with enhanced Ir-O hybridization. As a
result of the departure from the local relativistic $j_{\rm eff}\! = \!1/2$
state, we find that the relative orbital contribution to the magnetic moment is
increased, and the magnetization density is spatially extended and asymmetric.
Our results confirm the importance of metal - ligand hybridazation in the
magnetism of transition metal oxides and provide empirical guidance for
understanding the collective magnetism in intercalated honeycomb iridates.",2106.05309v1
2021-07-16,Dependence of band gaps in d-electron perovskite oxides on magnetism,"Understanding the controlling principles of band gaps trends in d electron
perovskites is needed both for gauging metal-insulator transitions, as well as
their application in catalysis and doping. The magnitude of this band gap is
rather different for different magnetic spin configurations. We find via
electronic structure theory that the factors that connect gapping magnitudes to
magnetism depend on the nature of the band edge orbital character (BEOC) and
surprisingly scale with the number of antiferromagnetic contacts z$_i$ between
neighboring transition metal ions. The dependence is weak when the BEOC are
(d,d)-like (""Mott insulators""), whereas this dependence is rather strong in
(p,d)-like (""charge transfer"" insulators). These unexpected rules are traced to
the reduced orbital interactions through the increase in the number of
antiferromagnetic contacts between transition metal ions. The impact of
magnetic order is not limited to the band gap magnitude and includes also the
magnitude of lattice distortions connected to the electronic structure. These
results highlight the importance of establishing in electronic structure theory
of gap-related phenomena (doping, transport, metal-insulator transitions,
conductive interfaces) the appropriate magnetic order.",2107.07794v1
2021-11-01,Sr$_3$LiIrO$_6$: a potential quantum spin liquid candidate in the one dimensional $d^4$ iridate family,"Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary
magnetic and electronic properties in otherwise `ordinary pool' of heavy ion
oxides. Here we present a detailed study on an apparently isolated hexagonal
2$H$ spin-chain $d^4$ iridate Sr$_3$LiIrO$_6$ (SLIO) with geometric
frustration. Our structural studies clearly reveal perfect Li-Ir chemical order
in this compound. Our combined experimental and {\it ab-initio} electronic
structure investigations establish a magnetic ground state with finite
Ir$^{5+}$ magnetic moments in this compound, contrary to the anticipated
nonmagnetic $J$=0 state. Furthermore, the dc magnetic susceptibility ($\chi$),
heat capacity ($C_p$) and spin-polarized density functional theory (DFT)
studies unravel that despite having noticeable antiferromagnetic correlation
among the Ir$^{5+}$ local moments, this SLIO system evades any kind of magnetic
ordering down to at least 2 K due to geometrical frustration, arising from the
comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence
promoting SLIO as a potential quantum spin liquid candidate.",2111.00925v1
2021-11-18,Quantum magnetic properties and metal-to-insulator transition in chemically doped calcium ruthenate perovskite,"Ruthenates provide comprehensive platform to study a plethora of novel
properties, such as quantum magnetism, superconductivity and magnetic
fluctuation mediated metal-insulator transition. In this article, we provide an
overview of quantum mechanical phenomenology in calcium ruthenium oxide with
varying compositions. While the stochiometric composition of CaRuO$_{3}$
exhibits non-Fermi liquid behavior with quasi-criticality, chemically doped
compounds depict prominent signatures of quantum magnetic fluctuations at low
temperature that in some cases are argued to mediate in metal-insulator
transition. In the case of cobalt doped- CaRuO$_{3}$, an unusual continuum
fluctuation is found to persist deep inside the glassy phase of the material.
These observations reflect the richness of ruthenate research platform in the
study of quantum magnetic phenomena of fundamental importance.",2111.09738v1
2021-11-23,Magnetic-cations doped into a Double Perovskite Semiconductor,"We report two solid solutions based on magnetic ion doping of the double
perovskite oxide Sr2GaSbO6: Sr2Ga1-xCrxSbO6 (0.1 < x < 0.4) and Sr2Ga1-xFexSbO6
(0.1 < x < 0.4). All compositions crystallize in the same space group (I4/m) as
their undoped parent phase Sr2GaSbO6, with the trivalent magnetic cations Cr3+
or Fe3+ partially substituting for non-magnetic Ga3+ in one of the B-cation
sites. The Cr- and Fe-doped phases display dominant antiferromagnetic coupling
among the dopant magnetic moments, and exhibit decreasing band gaps with
increasing substitution level.",2111.12015v1
2022-04-26,Chirality-Induced Noncollinear Magnetization and Asymmetric Domain-Wall Propagation in Hydrogenated CoPd Thin Films,"Array-patterned CoPd-based heterostructures are created through e-beam
lithography and plasma pretreatment that induces oxidation with depth gradient
in the CoPd alloy films, breaking the central symmetry of the structure.
Effects on the magnetic properties of the follow-up hydrogenation of the thin
film are observed via magneto-optic Kerr effect microscopy. The system exhibits
strong vertical and lateral antiferromagnetic coupling in the perpendicular
component between the areas with and without plasma pretreatment, and
asymmetric domain-wall propagation in the plasma-pretreated areas during
magnetization reversal. These phenomenon exhibit evident magnetic chirality and
can be interpreted with the Ruderman-Kittel-Kasuya-Yosida coupling and the
Dzyaloshinskii-Moriya interaction (DMI). The sample processing demonstrated in
this study allows easy incorporation of lithography techniques that can define
areas with or without DMI to create intricate magnetic patterns on the sample,
which provides an avenue towards more sophisticate control of canted spin
textures in future spintronic devices.",2204.12428v1
2022-12-08,Impact of a ferromagnetic insulating barrier in magnetic tunnel junctions,"We investigate spin-dependent conductance across a magnetic tunnel junction
(MTJ) including a ferromagnetic insulating barrier. The MTJ consists of two
half-metallic ferromagnetic La2/3Sr1/3MnO3 (LSMO) manganites as electrodes and
La2NiMnO6 (LNMO) double perovskite as a ferromagnetic insulating barrier. The
resistance of the junction is strongly dependent not only on the orientation of
the magnetic moments in LSMO electrodes, but also on the direction of the
magnetization of the LNMO barrier with respect to that of LSMO. The ratio of
tunnel magnetoresistance reaches a maximum value of 24% at 10 K, and it
decreases with temperature until it completely disappears above the critical
temperature of LNMO at 280 K. The tunneling process is described using a
mechanism which involves both empty and filled eg states of the LNMO barrier
acting as a spin-filter. A magnetic insulating barrier is an interesting path
for achieving room temperature magnetoresistance in oxide-based
heterostructures.",2212.04416v1
2023-06-13,Unraveling Magnetic Anisotropy Energy in Ferromagnetic Monolayer on Ferroelectric ABO$_3$ via DFT and Machine Learning,"Spin-based devices have attracted attention as an alternative to CMOS-based
technology. However, one of the challenges in spintronics devices is reducing
the spin-switching energy in ferromagnetic (FM) materials. To address this, we
considered ferroelectric (FE) materials, which may affect the magnetic
properties of FM materials. We explored various oxide perovskites ABO$_3$ as FE
materials, onto which a Fe monolayer was placed as the FM material. We
evaluated the magnetic anisotropy energy (MAE) of the Fe monolayer while
varying the polarization of ABO$_3$. Our analysis showed that the MAE depends
on the magnetic dipole moment induced in the FE material at the interface
between the FE and FM materials due to structural modifications. Machine
learning techniques were also employed to identify universal behaviors of the
MAE in the presence of FE layers, confirming the importance of magnetic moments
near the interface in explaining the dependence of the MAE on FE materials.",2306.07953v1
2023-10-13,Emerging interfacial magnetization in isovalent manganite heterostructures driven by octahedral coupling,"The distortion of corner-sharing octahedra in isovalent perovskite
transition-metal oxide interfaces is proven to be an excellent way to tailor
the electronic and magnetic properties of their heterostructures. Combining
depth-dependent magnetic characterization technique; (polarized neutron
reflectivity, PNR); and theoretical calculation (density functional theory), we
report interface-driven magnetic exchange interactions due to a modification in
the octahedral rotations at the interfaces in an isovalent La0.67Ca0.33MnO3
(LCMO)/La0.67Sr0.33MnO3 (LSMO) heterostructures. PNR results determined a
length scale of ~ 8 unit cells at the interface, which demonstrated a
modification in magnetic properties. The results also predicted a
low-temperature exchange bias for these ferromagnetic heterostructures with a
maximum exchange bias for the heterostructure, which showed an enhanced
antiferromagnetic coupling at the interfaces.",2310.09059v1
2023-11-11,Single-Phase L1$_{0}$-Ordered High Entropy Thin Films with High Magnetic Anisotropy,"The vast high entropy alloy (HEA) composition space is promising for
discovery of new material phases with unique properties. We explore the
potential to achieve rare-earth-free high magnetic anisotropy materials in
single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally
oxidized Si/SiO$_{2}$ substrates at room temperature are magnetically soft,
with a coercivity on the order of 10 Oe. After post-deposition rapid thermal
annealing (RTA), the films exhibit a single face-centered-cubic (fcc) phase,
with an almost 40-fold increase in coercivity. Inclusion of 50 at.% Pt in the
film leads to ordering of a single L1$_{0}$ high entropy intermetallic phase
after RTA, along with high magnetic anisotropy and a 3 orders of magnitude
coercivity increase. These results demonstrate a promising HEA approach to
achieve high magnetic anisotropy materials using RTA.",2311.06618v2
2024-01-19,Anti-Jahn-Teller disproportionation and prospects for spin-triplet superconductivity in d-element compounds,"We argue that the unusual properties of a wide class of materials based on
Jahn-Teller 3d and 4d ions with different crystal and electronic structures,
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO4), manganites with
local superconductivity to 3D ferrates (CaSr)FeO3, nickelates RNiO3 and silver
oxide AgO with unusual charge and magnetic order can be explained within a
single scenario. The properties of these materials are related to the
instability of their highly symmetric Jahn-Teller ""progenitors"" with the ground
orbital E-state to charge transfer with anti-Jahn-Teller disproportionation and
the formation of a system of effective local composite spin-singlet or
spin-triplet, electronic or hole bosons moving in a non-magnetic or magnetic
lattice. These unusual systems are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states.",2401.11028v1
2005-12-16,A Magnetic and Moessbauer Spectral Study of Core/Shell Structured Fe/Au Nanoparticles,"Fe/Au nanoparticles have been chemically synthesized through a reverse
micelle reaction and investigated by both conventional and synchrotron based
x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder
x-ray diffraction patterns reveal both the presence of crystalline alpha-iron
and gold and the absence of any crystalline iron oxides or other crystalline
products. First-order reversal curves, along with the major hysteresis loops of
the Fe/Au nanoparticles have been measured as a function of time in order to
investigate the evolution of their magnetic properties. The iron-57 Moessbauer
spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have
been measured at 78 and 295 K and indicate that two major iron containing
components are present, namely the expected alpha-iron and the unexpected
amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide
components as well as paramagnetic iron(II) and iron(III) components are also
observed. These results indicate that the Fe-core/Au-shell nanoparticles
synthesized through reverse micelles are far more complex that had been
believed.",0512413v1
2007-05-28,Dangling-bond spin relaxation and magnetic 1/f noise from the amorphous-semiconductor/oxide interface: Theory,"We propose a model for magnetic noise based on spin-flips (not
electron-trapping) of paramagnetic dangling-bonds at the
amorphous-semiconductor/oxide interface. A wide distribution of spin-flip times
is derived from the single-phonon cross-relaxation mechanism for a
dangling-bond interacting with the tunneling two-level systems of the amorphous
interface. The temperature and frequency dependence is sensitive to three
energy scales: The dangling-bond spin Zeeman energy delta, as well as the
minimum (E_min) and maximum (E_max) values for the energy splittings of the
tunneling two-level systems. We compare and fit our model parameters to a
recent experiment probing spin coherence of antimony donors implanted in
nuclear-spin-free silicon [T. Schenkel {\it et al.}, Appl. Phys. Lett. 88,
112101 (2006)], and conclude that a dangling-bond area density of the order of
10^{14}cm^{-2} is consistent with the data. This enables the prediction of
single spin qubit coherence times as a function of the distance from the
interface and the dangling-bond area density in a real device structure. We
apply our theory to calculations of magnetic flux noise affecting SQUID devices
due to their Si/SiO_2 substrate. Our explicit estimates of flux noise in SQUIDs
lead to a noise spectral density of the order of 10^{-12}Phi_{0}^{2} {Hz}^{-1}
at f=1Hz. This value might explain the origin of flux noise in some SQUID
devices. Finally, we consider the suppression of these effects using surface
passivation with hydrogen, and the residual nuclear-spin noise resulting from a
perfect silicon-hydride surface.",0705.4088v3
2009-10-11,Uniform spin chain physics arising from NCN bridges in CuNCN: surprises on the way from copper oxides to their nitride analogs,"We report on the unexpected uniform spin chain physics in CuNCN, the
insulating nitride analog of copper oxides. Based on full-potential band
structure calculations, we derive the relevant microscopic parameters, estimate
individual exchange couplings, and establish a realistic spin model of this
compound. The structure of CuNCN contains chains of edge-sharing CuN(4)
squares. As a surprise, in contrast to analogous [CuO(2)] chains in
""edge-sharing"" cuprates, the leading magnetic interactions J ~ 2500 K run
perpendicular to the structural [CuN(2)] chains via bridging NCN groups. The
resulting spin model of a uniform chain is in agreement with the experimentally
observed temperature-independent magnetic susceptibility below 300 K. The
nearest-neighbor and next-nearest-neighbor interactions along the structural
[CuN(2)] chains are J(1) ~ -500 K and J(2) ~ 100 K, respectively. Despite the
frustrating nature of J(1) and J(2), we assign the anomaly at 70 K to
long-range magnetic ordering, which is likely collinear with antiparallel and
parallel arrangement of spins along the 'c' and 'a' directions, respectively.
The pronounced one-dimensionality of the spin system should lead to a reduction
in the ordered moment and to a suppression of the transition anomaly in the
specific heat, thus impeding the experimental observation of the long-range
ordering. Our results suggest CuNCN as a promising material for ballistic heat
transport within spin chains, while the sizable bandwidth W ~ 3 eV may lead to
a metal-insulator transition and other exotic properties under high pressure.",0910.2056v1
2010-04-07,Iron oxide doped boron nitride nanotubes: structural and magnetic properties,"A first-principles formalism is employed to investigate the interaction of
iron oxide (FeO) with a boron nitride (BN) nanotube. The stable structure of
the FeO-nanotube has Fe atoms binding N atoms, with bond length of roughly
$\sim$2.1 \AA, and binding between O and B atoms, with bond length of 1.55 \AA.
In case of small FeO concentrations, the total magnetic moment is
(4$\mu_{Bohr}$) times the number of Fe atoms in the unit cell and it is
energetically favorable to FeO units to aggregate rather than randomly bind to
the tube. As a larger FeO concentration case, we study a BN nanotube fully
covered by a single layer of FeO. We found that such a structure has square FeO
lattice with Fe-O bond length of 2.11 \AA, similar to that of FeO bulk, and
total magnetic moment of 3.94$\mu_{Bohr}$ per Fe atom. Consistently with
experimental results, the FeO covered nanotube is a semi-half-metal which can
become a half-metal if a small change in the Fermi level is induced. Such a
structure may be important in the spintronics context.",1004.1151v2
2010-07-13,Modeling of complex oxide materials from the first principles: systematic applications to vanadates RVO3 with distorted perovskite structure,"""Realistic modeling"" is a new direction of electronic structure calculations,
where the main emphasis is made on the construction of some effective
low-energy model entirely within a first-principle framework. Ideally, it is a
model in form, but with all the parameters derived rigorously, on the basis of
first-principles electronic structure calculations. The method is especially
suit for transition-metal oxides and other strongly correlated systems, whose
electronic and magnetic properties are predetermined by the behavior of some
limited number of states located near the Fermi level. After reviewing general
ideas of realistic modeling, we will illustrate abilities of this approach on
the wide series of vanadates RVO3 (R= La, Ce, Pr, Nd, Sm, Gd, Tb, Yb, and Y)
with distorted perovskite structure. Particular attention will be paid to
computational tools, which can be used for microscopic analysis of different
spin and orbital states in the partially filled t2g-band. We will explicitly
show how the lifting of the orbital degeneracy by the monoclinic distortion
stabilizes C-type antiferromagnetic (AFM) state, which can be further
transformed to the G-type AFM state by changing the crystal distortion from
monoclinic to orthorhombic one. Two microscopic mechanisms of such a
stabilization, associated with the one-electron crystal field and electron
correlation interactions, are discussed. The flexibility of the orbital degrees
of freedom is analyzed in terms of the magnetic-state dependence of interatomic
magnetic interactions.",1007.2058v1
2011-10-21,Exchange-spring behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite,"In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2
nanocomposites. The latter compound is a good system to study hard
ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to
synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation
of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second
reduction reaction of cobalt ferrite nanoparticles using activated charcoal in
inert atmosphere and high temperature. The phase structures, particle sizes,
morphology, and magnetic properties of CoFe2O4 nanoparticles have been
investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS),
transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM)
with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter
of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for
Fe3+. One site is related to Fe in an octahedral coordination and the other one
to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal
structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a
thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles
increase to about 100 nm. The magnetization of nanocomposite showed hysteresis
loop that is characteristic of the exchange spring systems. A maximum energy
product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2
nanocomposites, which is about 115% higher than the value obtained for CoFe2O4
precursor. The exchange-spring interaction and the enhancement of product
(BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.",1110.4905v1
2013-05-13,Jumps in entropy and magnetic susceptibility at the valence and spin-state transition in a cobalt oxide,"A wide family of cobalt oxides of formulation (Pr,Ln,Ca)CoO3 (Ln being a
lanthanide) exhibits a coupled valence and spin-state transition (VSST) at a
temperature T*, which involves two concomitant modifications: (i) a change in
the spin state of Co3+ from low-spin (T < T*) to a higher spin-state (T > T*),
and (ii) a change in the valence state of Pr, from a mixed Pr4+/Pr3+ state (T <
T*) to a purely trivalent state (T > T*), accompanied by an equivalent charge
transfer within the Co3+/Co4+ subsystem. In the present paper, the VSST taking
place in (Pr0.7Sm0.3)0.7Ca0.3CoO3 at T* = about 90 K is investigated by
magnetization and heat capacity measurements. First, we quantitatively
characterized the jumps in magnetic susceptibility (khi) and entropy (S) around
T*. Then, these values were compared to those calculated as a function of the
variations in the population of the different cationic species involved in the
VSST. X-ray absorption spectroscopy experiments recently showed that the higher
spin state above T* should be regarded as an inhomogeneous mixture between
low-spin (LS) and high-spin (HS) states. In the frame of this description, we
demonstrate that the jumps in both khi and S can be associated to the same
change in the Co3+ HS content around T*. This result lends further support to
the relevance of the LS/HS picture for the VSST, challenging the currently
dominant interpretation based on the occurrence of an intermediate-spin (IS)
state of Co3+ above T*.",1305.2829v1
2014-09-11,Anisotropic magnetoresistance in antiferromagnetic Sr2IrO4,"We report point-contact measurements of anisotropic magnetoresistance (AMR)
in a single crystal of antiferromagnetic (AFM) Mott insulator Sr2IrO4. The
point-contact technique is used here as a local probe of magnetotransport
properties on the nanoscale. The measurements at liquid nitrogen temperature
revealed negative magnetoresistances (MRs) (up to 28%) for modest magnetic
fields (250 mT) applied within the IrO2 a-b plane and electric currents flowing
perpendicular to the plane. The angular dependence of MR shows a crossover from
four-fold to two-fold symmetry in response to an increasing magnetic field with
angular variations in resistance from 1-14%. We tentatively attribute the
four-fold symmetry to the crystalline component of AMR and the field-induced
transition to the effects of applied field on the canting of AFM-coupled
moments in Sr2IrO4. The observed AMR is very large compared to the crystalline
AMRs in 3d transition metal alloys/oxides (0.1-0.5%) and can be associated with
the large spin-orbit interactions in this 5d oxide while the transition
provides evidence of correlations between electronic transport, magnetic order
and orbital states. The finding of this work opens an entirely new avenue to
not only gain a new insight into physics associated with spin-orbit coupling
but also better harness the power of spintronics in a more technically
favorable fashion.",1409.3491v2
2018-11-27,Self-consistent site-dependent DFT+$U$ study of stoichiometric and defective SrMnO$_3$,"We propose a self-consistent site-dependent Hubbard $U$ approach for DFT+$U$
calculations of defects in complex transition-metal oxides, using Hubbard
parameters computed via linear-response theory. The formation of a defect
locally perturbs the chemical environment of Hubbard sites in its vicinity,
resulting in different Hubbard $U$ parameters for different sites. Using oxygen
vacancies in SrMnO$_3$ as a model system, we investigate the dependence of $U$
on the chemical environment and study its influence on the structural,
electronic, and magnetic properties of defective bulk and strained thin-film
structures. Our results show that a self-consistent $U$ improves the
description of stoichiometric bulk SrMnO$_3$ with respect to GGA or GGA+$U$
calculations using an empirical $U$. For defective systems, $U$ changes as a
function of the distance of the Hubbard site from the defect, its oxidation
state and the magnetic phase of the bulk structure. Taking into account this
dependence, in turn, affects the computed defect formation energies and the
predicted strain- and/or defect-induced magnetic phase transitions, especially
when occupied localized states appear in the band gap of the material upon
defect creation.",1811.10858v2
2016-05-01,Development of a method for measuring blood coagulation using superparamagnetic iron oxide nanoparticles and an alternating magnetic field,"We developed a method for measuring blood coagulation using superparamagnetic
iron oxide nanoparticles (SPIONs) and an alternating magnetic field (AMF). The
3rd and 5th harmonic signals from SPIONs mixed with blood induced by AMF were
detected using a gradiometer coil. Blood coagulation was induced artificially
by adding CaCl2 solution to whole blood of sheep at various temperatures and
hematocrits. We calculated the coagulation rate (k) and normalized signal
intensity at infinite time (Sinf) by fitting the time course of the normalized
3rd harmonic signal to S(t)=(1-Sinf)exp(-kt)+Sinf. The k values increased
significantly with increasing temperature and decreased significantly with
increasing hematocrit. The Sinf values decreased significantly with increasing
temperature and tended to increase with increasing hematocrit. Blood
anticoagulation was induced by adding heparin to the whole blood sampled from
mice. There were significant differences in both the 3rd and 5th harmonic
signals between groups with and without heparin at 25 min or more after adding
heparin. We also calculated the 3rd and 5th harmonic signals for viscosities
ranging from 0.001 to 1 kg/m/s, with an assumption that the magnetization and
particle size distribution of SPIONs obey the Langevin theory of paramagnetism
and log-normal distribution, respectively. The 3rd and 5th harmonic signals
increased slowly with increasing viscosity and had peaks at approximately 0.015
and 0.025 kg/m/s, respectively. After these peaks, they decreased monotonically
with increasing viscosity. These results confirm the rationale of our method.
In conclusion, our method will be useful for measuring blood coagulation and
anticoagulation and for studying their processes.",1605.00255v2
2016-05-19,Hydration induced spin glass state in a frustrated Na-Mn-O triangular lattice,"Birnessite compounds are stable across a wide range of compositions that
produces a remarkable diversity in their physical, electrochemical and
functional properties. These are hydrated analogues of the magnetically
frustrated, mixed-valent manganese oxide structures, with general formula,
NaxMnO2. Here we demonstrate that the direct hydration of layered rock-salt
type a-NaMnO2, with the geometrically frustrated triangular lattice topology,
yields the birnessite type oxide, Na0.36MnO2 0.2H2O, transforming its magnetic
properties. This compound has a much-expanded interlayer spacing compared to
its parent a-NaMnO2 compound. We show that while the parent a-NaMnO2 possesses
a Neel temperature of 45 K as a result of broken symmetry in the Mn3+
sub-lattice, the hydrated derivative undergoes collective spin-freezing at 29 K
within the Mn3+/Mn4+ sub-lattice. Scaling-law analysis of the frequency
dispersion of the AC susceptibility, as well as the temperature-dependent,
low-field DC magnetization confirm a cooperative spin-glass state of strongly
interacting spins. This is supported by complementary spectroscopic analysis
(HAADF-STEM, EDS, EELS) as well as by a structural investigation
(high-resolution TEM, X-ray and neutron powder diffraction) that yield insights
into the chemical and atomic structure modifications. We conclude that the
spin-glass state in birnessite is driven by the spin-frustration imposed by the
underlying triangular lattice topology that is further enhanced by the in-plane
bond-disorder generated by the mixed-valent character of manganese in the
layers.",1605.06067v1
2018-10-25,Superdislocations and point defects in pyrochlore Yb2Ti2O7 single crystals and implication on magnetic ground states,"This study reports atomic-scale characterization of structural defects in
Yb2Ti2O7, a pyrochlore oxide whose subtle magnetic interactions is prone to
small perturbations. Due to discrepancies in the reported magnetic ground
states, it has become a pressing issue to determine the nature of defects in
this system. In the present study, we use atomic resolution scanning
transmission electron microscopy techniques to identify the type of defects in
the ytterbium titanate single crystals grown by the conventional optical
floating zone (FZ) method. In addition to the known point defects of
substitution Yb on Ti B-sites, extended defects such as dissociated
superdislocations and anti-phase boundaries were discovered for the first time
in this material. Such defects were prevalently observed in the FZ grown single
crystals (of a darker color), in contrast to the stoichiometric white
polycrystalline powders or high quality colorless single crystals grown by the
traveling solvent floating zone (TSFZ) technique. The lattice strains from
these extended defects result in distortions of Yb-tetrahedron. A change of Ti
valance was not detected at the defects. Our findings provide new insights into
understanding the nature of defects that are of great importance for the
physical property studies of geometrically frustrated compounds. Furthermore,
this work sheds light on the complicated core structure of superdislocations
that have large Burgers vectors in oxides with complex unit cells.",1810.11055v1
2020-04-07,Probing electronic and magnetic transitions of short periodic nickelate superlattices using synchrotron x-ray,"Transition metal based oxide heterostructures exhibit diverse emergent
phenomena e.g. two dimensional electron gas, superconductivity, non-collinear
magnetic phase, ferroelectricity, polar vortices, topological Hall effect etc.,
which are absent in the constituent bulk oxides. The microscopic understandings
of these properties in such nanometer thick materials are extremely
challenging. Synchrotron x-ray based techniques such as x-ray diffraction,
x-ray absorption spectroscopy (XAS), resonant x-ray scattering (RXS), resonant
inelastic x-ray scattering (RIXS), x-ray photoemission spectroscopy, etc. are
essential to elucidating the response of lattice, charge, orbital, and spin
degrees of freedoms to the heterostructuring. As a prototypical case of complex
behavior, rare-earth nickelates (RENiO3 with RE=La, Pr, Nd, Sm, Eu, Lu) based
thin films and heterostructures have been investigated quite extensively in
recent years. An extensive body of literature about these systems exists and
for an overview of the field, we refer the interested readers to the recent
reviews Annual Review of Materials Research 46, 305 (2016) and Reports on
Progress in Physics 81, 046501 (2018). In the present article, we give a brief
review that concentrates on the use of synchrotron based techniques to
investigate a specific set of EuNiO3/LaNiO3 superlattices, specifically
designed to solve a long-standing puzzle about the origin of simultaneous
electronic, magnetic and structural transitions of the RENiO3 series.",2004.03100v1
2017-09-22,Tuning electromagnetic properties of SrRuO3 epitaxial thin films via atomic control of cation vacancies,"Elemental defects in transition metal oxides is an important and intriguing
subject that result in modifications in variety of physical properties
including atomic and electronic structure, optical and magnetic properties.
Understanding the formation of elemental vacancies and their influence on
different physical properties is essential in studying the complex oxide thin
films. In this study, we investigated the physical properties of epitaxial
SrRuO3 thin films by systematically manipulating cation and/or oxygen
vacancies, via changing the oxygen partial pressure (P(O2)) during the pulsed
laser epitaxy (PLE) growth. Ru vacancies in the low-P(O2)-grown SrRuO3 thin
films induce lattice expansion with the suppression of the ferromagnetic TC
down to ~120 K. Sr vacancies also disturb the ferromagnetic ordering, even
though Sr is not a magnetic element. Our results indicate that both A and B
cation vacancies in an ABO3 perovskite can be systematically engineered via
PLE, and the structural, electrical, and magnetic properties can be tailored
accordingly.",1709.07600v1
2018-08-20,Unconventional exchange bias coupling at perovskite/brownmillerite interface in spontaneously stabilized SrCoO3-δ/SrCoO2.5 bi-layer,"Interface effect in complex oxide thin film heterostructures lies at the
vanguard of current research to design technologically relevant functionality
and explore emergent physical phenomena. While most of the previous works focus
on the perovskite/perovskite heterostructures, the study on
perovskite/brownmillerite interfaces remain at its infancy. Here, we
investigate spontaneously stabilized perovskite-ferromagnet
(SrCoO3-{\delta})/brownmillertite-antiferromagnet (SrCoO2.5) bi-layer with TN >
TC and discover an unconventional interfacial magnetic exchange bias effect.
From magnetometry investigations, it is rationalized that the observed effect
stems from the interfacial ferromagnet/antiferromagnet coupling. The
possibility for coupled ferromagnet/spinglass interface engendering such effect
is ruled out. Strikingly, a finite coercive field persists in the paramagnetic
state of SrCoO3-{\delta} whereas the exchange bias field vanishes at TC. We
conjecture the observed effect to be due to the effective external quenched
staggered field provided by the antiferromagtic layer for the ferromagnetic
spins at the interface. Our results not only unveil a new paradigm to tailor
the interfacial magnetic properties in oxide heterostructures without altering
the cations at the interface, but also provide a purview to delve into the
fundamental aspects of exchange bias in such unusual systems paving a big step
forward in thin film magnetism.",1808.06321v1
2019-03-08,Spin stripe order in a square planar trilayer nickelate,"Trilayer nickelates, which exhibit a high degree of orbital polarization
combined with an electron count (d8.67) corresponding to overdoped cuprates,
have been identified as a promising candidate platform for achieving high-Tc
superconductivity. One such material, La4Ni3O8, undergoes a
semiconductor-insulator transition at ~105 K, which was recently shown to arise
from the formation of charge stripes. However, an outstanding issue has been
the origin of an anomaly in the magnetic susceptibility at the transition and
whether it signifies formation of spin stripes akin to single layer nickelates.
Here we report single crystal neutron diffraction measurements (both polarized
and unpolarized) that establish that the ground state is indeed magnetic. The
ordering is modeled as antiferromagnetic spin stripes that are commensurate
with the charge stripes, the magnetic ordering occurring in individual
trilayers that are essentially uncorrelated along the crystallographic c-axis.
Comparison of the charge and spin stripe order parameters reveals that, in
contrast to single-layer nickelates such as La2-xSrxNiO4 as well as related
quasi-2D oxides including manganites, cobaltates, and cuprates, these orders
uniquely appear simultaneously, thus demonstrating a stronger coupling between
spin and charge than in these related low-dimensional correlated oxides.",1903.03246v2
2019-08-09,Lattice small polarons and magnetic interactions drive preferential nanocrystal growth in silicon doped hematite,"Understanding the interplay between the structural, chemical and physical
properties of nanomaterials is crucial for designing new devices with enhanced
performance. In this regards, doping of metal oxides is a general strategy to
tune size, morphology, charge, lattice, orbital and spin degrees of freedoms
and has been shown to affect nanomaterials properties for photoelectrochemical
water splitting, batteries, catalysis, magnetic applications and optics. Here
we report the role of lattice small polaron in driving the morphological
transition from nearly isotropic to nanowire crystals in Si doped hematite
($\alpha-Fe_2O_3$). Lattice small polaron formation is well evidenced by the
increase of hexagonal strain and degree of distortion of $FeO_6$ showing a
hyperbolic trend with increasing Si content. Local analysis via pair
distribution function highlights an unreported crossover from small to large
polarons, which affects the correlation length of the polaronic distortion from
short to average scales. Ferromagnetic double exchange interactions between
$Fe^{2+}/Fe^{3+}$ species is found to be the driving force of the crossover,
constraining the chaining of chemical bonds along the [110] crystallographic
direction. This promotes the increase in the reticular density of Fe atoms
along the hematite basal plane only, which boosts the anisotropic growth of
nanocrystals with more extended [110] facets. Our results show that magnetic
and electronic interactions drive preferential crystallographic growth in doped
metal oxides, thus providing a new route to design their functional properties.",1908.03377v1
2020-11-16,Ferroelectric tunnel junctions,"My research is dedicated to the electronic properties of functional oxides.
My activity specifically focuses on ferroelectric tunnel junctions in which an
ultrathin layer of ferroelectric material is intercalated between two metallic
electrodes. In these devices, polarization reversal induces large modifications
of the tunnel resistance, leading to a non-destructive readout of the
information. After a demonstration of the concept with scanning probe
microscopy techniques, I have been exploring the properties of ferroelectric
tunnel junctions with various ferroelectric materials (BaTiO3, BiFeO3, and
PVDF). I showed that these devices possess attractive properties for
applications as non-volatile binary memories. In addition, exploring the fact
that polarization usually reverses by the nucleation and propagation of
domains, I demonstrated a memristive behavior in the junctions associated to
non-uniform configurations of ferroelectric domains. Such ferroelectric
memristors can be used as artificial synapses in neuromorphic architectures.
Coupled to magnetic electrodes, the resulting multiferroic tunnel junctions
enable a non-volatile control of magnetism at the ferroelectric/electrode
interface and of the spin-polarized current associated. Besides this main
activity on tunnel devices, I explored the influence of ferroelectricity on
magnetic orders and on the properties of functional oxides.",2011.07864v1
2021-09-13,Orbital selective switching of ferromagnetism in an oxide quasi two-dimensional electron gas,"Multi-orbital physics in quasi-two-dimensional electron gases (q2DEGs)
triggers unique phenomena not observed in bulk materials, such as
unconventional superconductivity and magnetism. Here, we investigate the
mechanism of orbital selective switching of the spin-polarization in the oxide
q2DEG formed at the (001) interface between the LaAlO$_{3}$, EuTiO$_{3}$ and
SrTiO$_{3}$ band insulators. By using density functional theory calculations,
transport, magnetic and x-ray spectroscopy measurements, we find that the
filling of titanium-bands with 3d$_{xz,yz}$ orbital character in the EuTiO3
layer and at the interface with SrTiO$_{3}$ induces an antiferromagnetic to
ferromagnetic switching of the exchange interaction between Eu-4f$^{7}$
magnetic moments. The results explain the observation of the carrier density
dependent ferromagnetic correlations and anomalous Hall effect in this q2DEG,
and demonstrate how combined theoretical and experimental approaches can lead
to a deeper understanding of novel electronic phases and serve as a guide for
the materials design for advanced electronic applications.",2109.06138v1
2021-11-23,Microscopic Theory of Magnetic Disorder-Induced Decoherence in Superconducting Nb Films,"The performance of superconducting qubits is orders of magnitude below what
is expected from theoretical estimates based on the loss tangents of the
constituent bulk materials. This has been attributed to the presence of
uncontrolled surface oxides formed during fabrication which can introduce
defects and impurities that create decoherence channels. Here, we develop an ab
initio Shiba theory to investigate the microscopic origin of magnetic-induced
decoherence in niobium thin film superconductors and the formation of native
oxides. Our ab initio calculations encompass the roles of structural disorder,
stoichiometry, and strain on the formation of decoherence-inducing local spin
moments. With parameters derived from these first-principles calculations we
develop an effective quasi-classical model of magnetic-induced losses in the
superconductor. We identify d-channel losses (associated with oxygen vacancies)
as especially parasitic, resulting in a residual zero temperature surface
impedance. This work provides a route to connecting atomic scale properties of
superconducting materials and macroscopic decoherence channels affecting
quantum systems.",2111.11684v1
2023-04-26,Tunable Magnetic Properties in Sr$_2$FeReO$_6$ Double-Perovskite,"Double-perovskite oxides have attracted recent attention due to their
attractive functionalities and application potential. In this paper, we
demonstrate the effect of dual controls, i.e., the deposition pressure of
oxygen (P$_O2$) and lattice mismatch ($\epsilon$), on tuning magnetic
properties in epitaxial double-perovskite Sr$_2$FeReO$_6$ films. In a
nearly-lattice-matched Sr$_2$FeReO$_6$/SrTiO$_3$ film, the
ferrimagnetic-to-paramagnetic phase transition occurs when P$_O2$ is reduced to
30 mTorr, probably due to the formation of Re$^{4+}$ ions that replace the
stoichiometric Re$^{5+}$ to cause disorders of $B$-site ions. On the other
hand, a large compressive strain or tensile strain shifts this critical P$_O2$
to below 1 mTorr or above 40 mTorr, respectively. The observations could be
attributed to the modulation of $B$-site ordering by epitaxial strain through
affecting elemental valence. Our results provide a feasible way to expand the
functional tunability of magnetic double-perovskite oxides that hold great
promise for spintronic devices.",2304.13288v1
2023-05-22,First-principles design of ferromagnetic monolayer MnO$_2$ at the complex interface,"Rapidly increasing interest in low-dimensional materials is driven by the
emerging requirement to develop nanoscale
  solid-state devices with novel functional properties that are not available
in three-dimensional bulk phases.
  Among the well-known low-dimensional systems, complex transition metal oxide
interface holds promise for broad
  applications in electronic and spintronics devices. Herein, intriguing
metal-insulator and
  ferromagnetic-antiferromagnetic transitions are achieved in monolayer MnO$_2$
that is sandwiched into
  SrTiO$_3$-based heterointerface systems through interface engineering.
  By using first-principles calculations, we modeled three types of
SrTiO$_3$-based heterointerface systems with different interface terminations
and performed a comparative study on the spin-dependent magnetic and electronic
properties that are established in the confined MnO$_2$ monolayer.
First-principles study predicts that metal-insulator transition and magnetic
transition in the monolayer MnO$_2$ are independent on the thickness of capping
layers. Moreover, 100$\%$ spin-polarized two-dimensional electron gases
accompanied by robust room temperature magnetism are uncovered in the monolayer
MnO$_2$. Not only is the buried MnO$_2$ monolayer a new interface phase of
fundamental physical interest, but it is also a promising candidate material
for nanoscale spintronics applications. Our study suggests interface
engineering at complex oxide interfaces is an alternative approach to designing
high-performance two-dimensional materials.",2305.13549v1
2023-06-26,Magnetic ground states and excitations in Zn-doped averieite -- a family of oxide-based $S=1/2$ kagome antiferromagnets,"Spin-1/2 kagome materials have recently attracted a resurgence of interest as
they are considered an ideal host of the quantum spin liquid (QSL) state, which
can underpin functionality such as superconductivity. Here we report the first
synthesis and characterization of a new oxide-based distorted $S=1/2$ kagome
antiferromagnet (KAFM) in the Zn$_x$Cu$_{5-x}$(VO$_4$)$_{2}$O$_2$CsCl (termed
Zn$\mathbf {_x}$) series, namely Zn$_2$-averievite, Zn$\mathbf {_2}$ ($x=2$).
Using magnetometry, synchrotron diffraction and neutron scattering we
demonstrate an evolution of ground states with $x$ in Zn$\mathbf {_x}$; from
long-range magnetic order in averievite ($x=0$), via a spin-glass-like ground
state in Zn$\mathbf {_1}$, to a quantum spin liquid (QSL) in Zn$\mathbf {_2}$
for which inelastic neutron scattering reveals a gapless continuum of
excitations. Similar to archetypal $S = 1/2$ KAFMs herbertsmithite and
SrCr$_{8.19}$Ga$_{3.81}$O$_{19}$ (SCGO), the dynamic magnetic susceptibility of
Zn$\mathbf {_2}$ shows scaling behavior consistent with proximity to a quantum
critical point. The results demonstrate that the new Zn$\mathbf {_2}$ material
is an excellent test bed for achieving the elusive goal of charge carrier
doping in QSL states of $S = 1/2$ KAFMs, in-line with previous theoretical
studies.",2306.14739v1
2012-05-29,Compositional Analysis of the High Molecular Weight Ethylene Oxide Propylene Oxide Copolymer by MALDI Mass Spectrometry,"The composition of narrow distribution poly ethylene oxide-propylene oxide
copolymer (Mw ~ 8700 Da) was studied using matrix assisted laser desorption
ionization (MALDI) mass spectrometry. The ethylene oxide-propylene oxide
copolymer produced oligomers separated by 14 Da. The average resolving power
over the entire spectrum was 28,000. Approximately 448 isotopically resolved
peaks representing about 56 oligomers are identified. Although agreement
between experimental and calculated isotopic distributions was strong, the
compositional assignment was difficult. This is due to the large number of
possible isobaric components. The purpose of this research is to resolve and
study the composition of high mass copolymer such as ethylene oxide-propylene
oxide.",1205.6421v1
1998-06-01,Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides,"A new mechanism is proposed to explain the colossal magnetoresistance and
related phenomena. Moving electrons accompanied by Jahn-Teller phonon and
spin-wave clouds may form composite polarons in ferromagnetic narrow-band
manganites. The ground-state and finite-temperature properties of such
composite polarons are studied in the present paper. By using a variational
method, it is shown that the energy of the system at zero temperature decreases
with the formation of composite polaron; the energy spectrum and effective mass
of the composite polaron at finite temperature is found to be strongly
renormalized by the temperature and the magnetic field. It is suggested that
the composite polaron contribute significantly to the transport and the
thermodynamic properties in ferromagnetic narrow-band metallic manganese
oxides.",9806017v1
2001-01-11,"Unusual valence, negative charge-transfer gaps and self-doping in transition-metal compounds","In this paper I discuss the electronic structure and properties of a
specific, rather unconventional class of transition metal (TM) compounds, e.g.
TM oxides, which formally have unusually high values of the oxidation state, or
valence, of TM. In contrast to the typical situation, in this case the
charge-transfer gap (excitation energy for the transfer of electrons from the
ligands to the TM) is very small and may even become negative. As a result a
profound modification of an electronic structure and of all the properties may
take place: there appear holes in the oxygen p-bands (``self-doping''); the
material may become the metal of a specific type; there may occur
insulator--metal transitions of a specific type; magnetic properties may be
quite different from the ones expected normally; the character of elementary
excitations may change drastically. I give general discussion of such situation
and consider several examples of corresponding systems and their specific
properties.",0101164v1
2001-07-12,Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films,"We present a method for fabricating Josephson junctions and superconducting
quantum interference devices (SQUIDs) which is based on the local anodization
of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an
Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained
either by partial or total oxidation of the niobium layer. Two types of weak
link geometries are fabricated : lateral constriction (Dayem bridges) and
variable thickness bridges. SQUIDs based on both geometries show a modulation
of the maximum Josephson current with a magnetic flux periodic with respect to
the superconducting flux quantum h/2e. They persist up to 4K. The modulation
shape and depth for SQUIDs based on variable thickness bridges indicate that
the weak link size becomes comparable to the superconducting film coherence
length which is of the order of 10nm.",0107273v1
2001-10-12,Large Thermopower in Metallic Oxides: Misfit Cobaltites and Mangano-Ruthenates,"Two different kinds of metal transition oxides have been studied for their
large thermopower values. The first one corresponds to the Tl-based misfit
cobaltite which is a hole-doped metal. We demonstrate that the partial
Bi-substitution for Tl in this phase induces an increase of the room
temperature (RT) thermopower (TEP) value. Same result is obtained with the new
Pb_{1/3}SrCoO_{3+delta} misfit corresponding to the Tl complete replacement by
lead. Simultaneously, the T dependence of their resistivity exhibits a
re-entrance below 70-90K where a large negative magnetoresistance is observed.
Magnetic measurements reveal a strong interplay between spins and charges for
this class of materials. Electron-doped (n-type) perovskite manganites are a
second class of potential candidates for applications. In particular, the
Ru^{4+/5+} substitution for Mn in the CaMnO_3 semi-conductor induces a drastic
drop of the resistivity values. Metals with large RT TEP values and not too
large thermal conductivities are generated. A comparison with best known
materials, Bi_2Te_3 and NaCo_2O_4 is made.",0110270v1
2002-02-06,Impurity-induced transition and impurity-enhanced thermopower in the thermoelectric oxide NaCo_{2-x}Cu_x$O_4,"Various physical quantities are measured and analysed for the Cu-substituted
thermoelectric oxide NaCo_{2-x}Cu_xO_4. As was previously known, the
substituted Cu enhances the thermoelectric power, while it does not increase
the resistivity significantly. The susceptibility and the electron
specific-heat are substantially decreased with increasing x, which implies that
the substituted Cu decreases the effective-mass enhancement. Through a
quantitative comparison with the heavy fermion compounds and the valence
fluctuation systems, we have found that the Cu substitution effectively
increases the coupling between the conduction electron and the magnetic
fluctuation. The Cu substitution induces a phase transition at 22 K that is
very similar to a spin-density-wave transition.",0202089v1
2002-07-23,Study of Percolative Transitions with First-Order Characteristics in the Context of CMR Manganites,"The unusual magneto-transport properties of manganites are widely believed to
be caused by mixed-phase tendencies and concomitant percolative processes.
However, dramatic deviations from ""standard"" percolation have been unveiled
experimentally. Here, a semi-phenomenological description of Mn oxides is
proposed based on coexisting clusters with smooth surfaces, as suggested by
Monte Carlo simulations of realistic models for manganites, also briefly
discussed here. The present approach produces fairly abrupt percolative
transitions and even first-order discontinuities, in agreement with
experiments. These transitions may describe the percolation that occurs after
magnetic fields align the randomly oriented ferromagnetic clusters believed to
exist above the Curie temperature in Mn oxides. In this respect, part of the
manganite phenomenology could belong to a new class of percolative processes
triggered by phase competition and correlations.",0207560v2
2003-02-13,Growth of Single Unit-Cell Superconducting La$_{2-x}$Sr$_x$CuO$_{4}$ Films,"We have developed an approach to grow high quality ultrathin films of
La$_{2-x}$Sr$_x$CuO$_{4}$ with molecular beam epitaxy, by adding a
homoepitaxial buffer layer in order to minimize the degradation of the film
structure at the interface. The advantage of this method is to enable a further
reduction of the minimal thickness of a superconducting
La$_{1.9}$Sr$_{0.1}$CuO$_{4}$ film. The main result of our work is that a
single unit cell (only two copper oxide planes) grown on a SrLaAlO$_4$
substrate exhibits a superconducting transition at 12.5 K (zero resistance) and
an in-plane magnetic penetration depth $\lambda_{ab}(0)$ = 535 nm.",0302261v1
2003-12-31,Spinons in the strongly correlated copper oxide chains in SrCuO2,"We have investigated the spin dynamics in the strongly correlated chain
copper oxide SrCuO$_2$ for energies up to $\gtrsim 0.6$ eV using inelastic
neutron scattering. We observe an acoustic band of magnetic excitations which
is well described by the ""Muller-ansatz"" for the two-spinon continuum in the
S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the
continuum extends up to $\approx 360$ meV, which corresponds to an exchange
constant $J = 226(12)$ meV. Our finding that an effective Heisenberg spin
Hamlitonian adequately describes the spin sector of this 1D electron system,
even though its energy scale is comparable to that of charge excitations,
provides compelling experimental evidence for spin-charge separation.",0312724v2
2004-07-28,Room temperature tunneling magnetoresistance in magnetite based junctions: Influence of tunneling barrier,"Magnetite (Fe3O4) based tunnel junctions with turret/mesa structure have been
investigated for different barrier materials (SrTiO3, NdGaO3, MgO, SiO2, and
Al2O(3-x)). Junctions with a Ni counter electrode and an aluminium oxide
barrier showed reproducibly a tunneling magnetoresistance (TMR) effect at room
temperature of up to 5% with almost ideal switching behavior. This number only
partially reflects the intrinsic high spin polarization of Fe3O4. It is
considerably decreased due to an additional series resistance within the
junction. Only SiO2 and Al2O(3-x) barriers provide magnetically decoupled
electrodes as necessary for sharp switching. The observed decrease of the TMR
effect as a function of increasing temperature is due to a decrease in spin
polarization and an increase in spin-scattering in the barrier. Among the oxide
half-metals magnetite has the potential to enhance the performance of TMR based
devices.",0407725v1
2004-09-07,Evidence for s-wave superconductivity in the new beta-pyrochlore oxide RbOs2O6,"We report the results of 87Rb NMR measurements on RbOs2O6, a new member of
the family of the superconducting pyrochlore-type oxides with a critical
temperature Tc = 6.4 K. In the normal state, the nuclear spin-lattice
relaxation time T1 obeys the Korringa-type relation T1T = constant and the
Knight shift is independent of temperature, indicating the absence of strong
magnetic correlations. In the superconducting state, T1^{-1}(T) exhibits a tiny
coherence enhancement just below Tc, and decreases exponentially with further
decreasing temperatures. The value of the corresponding energy gap is close to
that predicted by the conventional weak-coupling BCS theory. Our results
indicate that RbOs2O6 is a conventional s-wave-type superconductor.",0409169v1
2004-10-16,Phase transitions in spin-orbital coupled model for pyroxene titanium oxides,"We study the competing phases and the phase transition phenomena in an
effective spin-orbital coupled model derived for pyroxene titanium oxides
ATiSi2O6 (A=Na, Li). Using the mean-field-type analysis and the numerical
quantum transfer matrix method, we show that the model exhibits two different
ordered states, the spin-dimer and orbital-ferro state and the spin-ferro and
orbital-antiferro state. The transition between two phases is driven by the
relative strength of the Hund's-rule coupling to the onsite Coulomb repulsion
and/or by the external magnetic field. The ground-state phase diagram is
determined. There is a keen competition between orbital and spin degrees of
freedom in the multicritical regime, which causes large fluctuations and
significantly affects finite-temperature properties in the paramagnetic phase.",0410411v1
2005-04-22,Characterizing the Hexagonality of Anodic Aluminium Oxide Nanoporous Arrays,"Nanoporous anodized alumina oxide have been used as templates for obtaining
nanomaterials such as nanowires, which exhibit interesting electronic, magnetic
and optical properties. This article presents how the regularity of the spatial
distribution of pores in such templates, which affects several of the physical
properties of the obtained nanomaterials, has been objectively quantified. The
method uses adaptive thresholding, wave propagation image analysis methods, as
well as an hexagonality measurement which was found to be particularly suitable
because of its locality and invariance to translation, rotation and scaling. A
comparison between commercial and laboratory-made samples is presented in order
to test the method, resulting higher hexagonality for the latter type of
templates.",0504573v1
2005-05-09,Spin and orbital degrees of freedom in transition metal oxides and oxide thin films studied by soft x-ray absorption spectroscopy,"The class of transition metal compounds shows an enormous richness of
physical properties, such as metal-insulator transitions, colossal
magneto-resistance, super-conductivity, magneto-optics and spin-depend
transport. It now becomes more and more clear that in order to describe
transition metal compounds the charge, orbital, spin and lattice degrees of
freedom should all be taken into account. With the recognition that the local
orbital occupation plays an important role in many of the transition metal
compounds there is a need for experimental techniques that can measure the
orbital occupation. This technique is soft x-ray absorption spectroscopy.
Within this PhD. Thesis we will illustrate the usefulness of this technique by
some examples: 1) Magnetic versus crystal-field linear dichroism in NiO thin
films. 2) The importance of spin-orbit coupling in CoO bulk and CoO thin films.
3) Aligning spins in anti ferromagneticfilms using antiferromagnets. 4) The
spin-state puzzle in the cobaltates. 5) Determination of the orbital momentum
and crystal-field splitting in LaTiO3. 6) Orbital-assisted metal-insulator
transition in VO2.",0505214v1
2006-05-01,Ground State Properties and Optical Conductivity of the Transition Metal Oxide ${\rm Sr_{2}VO_{4}}$,"Combining first-principles calculations with a technique for many-body
problems, we investigate properties of the transition metal oxide ${\rm
Sr_{2}VO_{4}}$ from the microscopic point of view. By using the local density
approximation (LDA), the high-energy band structure is obtained, while screened
Coulomb interactions are derived from the constrained LDA and the GW method.
The renormalization of the kinetic energy is determined from the GW method. By
these downfolding procedures, an effective Hamiltonian at low energies is
derived. Applying the path integral renormalization group method to this
Hamiltonian, we obtain ground state properties such as the magnetic and orbital
orders. Obtained results are consistent with experiments within available data.
We find that ${\rm Sr_{2}VO_{4}}$ is close to the metal-insulator transition.
Furthermore, because of the coexistence and competition of ferromagnetic and
antiferromgnetic exchange interactions in this system, an antiferromagnetic and
orbital-ordered state with a nontrivial and large unit cell structure is
predicted in the ground state. The calculated optical conductivity shows
characteristic shoulder structure in agreement with the experimental results.
This suggests an orbital selective reduction of the Mott gap.",0605027v1
2006-05-02,Spin Singlet State in Heptamers Emerging in Spinel Oxide AlV$_2$O$_4$,"We present our theoretical results on the electronic state in vanadium spinel
oxide AlV$_2$O$_4$. The material is a mixed-valent system with the average
valence V$^{2.5+}$, and V cations constitute a frustrated pyrochlore structure.
It shows a structural transition at $\sim 700$ K, leading to the formation of
seven V-sites clusters -- heptamers. We study the electronic state of the
heptamer by explicitly taking account of orbital degree of freedom as well as
electron correlations. We show that the ground state of the heptamer for
realistic parameters becomes spin-singlet because of strong $\sigma$-type
bonding states of $t_{2g}$ orbitals. The temperature dependence of the magnetic
susceptibility in experiments is naturally understood by this singlet formation
in heptamers. Our results indicate that in AlV$_2$O$_4$ orbital physics is
relevant to stabilize a cluster-type singlet state instead of a previously
proposed charge-ordered state with valence skipping.",0605046v2
2006-10-25,High quality Fe3-deltaO4/InAs hybrid structure for electrical spin injection,"Single Crystalline Fe3-deltaO4 (0<=delta<=0.33) films have been epitaxially
grown on InAs (001) substrates by molecular beam epitaxy using O2 as source of
active oxygen. Under optimum growth conditions in-situ real time reflection
high-energy electron diffraction patterns along with ex-situ atomic force
microscopy indicated the (001) Fe3-deltaO4 to be grown under step-flow-growth
mode with a characteristic surface reconstruction. X-ray photoelectron
spectroscopy demonstrate the possibility to obtain iron oxides with
compositions ranging from Fe3O4 to gamma-Fe2O3. Superconducting quantum
interference device magnetometer at 300K shows well behaved magnetic properties
giving therefore credibility to the promise of iron based oxides for spintronic
applications.",0610697v1
2007-02-20,Anomalous electric conductions in KSbO3-type metallic rhenium oxides,"Single crystals of KSbO3-type rhenium oxides, La4Re6O$19, Pb6Re6O19, Sr2Re3O9
and Bi3Re3O11, were synthesized by a hydrothermal method. Their crystal
structures can be regarded as a network of three-dimensional orthogonal-dimer
lattice of edge-shared ReO6 octahedra. All of them exhibit small magnitude of
Pauli paramagnetism, indicating metallic electronic states without strong
electron correlations. The resistivity of these rhenates, except Bi3Re3O11,
have a temperature dependence of $rho(T)=\rho_{0}+AT^{n}$ $(n \approx 1.6)$ in
a wide temperature range between 5 K and 300 K, which is extraordinary for
three-dimensional metals without strong electron correlations. The resistivity
of Bi3Re3O11 shows an anomaly around at 50 K, where the magnetic susceptibility
also detects a deviation from ordinary Pauli paramagnetism.",0702451v1
2007-07-14,Influence of oxygen vacancy on the electronic structure of HfO$_2$ film,"We investigated the unoccupied part of the electronic structure of the
oxygen-deficient hafnium oxide (HfO$_{\sim1.8}$) using soft x-ray absorption
spectroscopy at O $K$ and Hf $N_3$ edges. Band-tail states beneath the
unoccupied Hf 5$d$ band are observed in the O $K$-edge spectra; combined with
ultraviolet photoemission spectrum, this indicates the non-negligible
occupation of Hf 5$d$ state. However, Hf $N_3$-edge magnetic circular dichroism
spectrum reveals the absence of a long-range ferromagnetic spin order in the
oxide. Thus the small amount of $d$ electron gained by the vacancy formation
does not show inter-site correlation, contrary to a recent report [M.
Venkatesan {\it et al.}, Nature {\bf 430}, 630 (2004)].",0707.2127v1
2007-09-13,Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors,"II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light
elements are investigated as potential dilute magnetic semiconductors (DMS).
Based on our first-principle calculations, nitrogen doped ZnO, carbon doped
ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism
of such DMS materials can be attributed to a p-d exchange-like p-p coupling
interaction which is derived from the similar symmetry and wave function
between the impurity (p-like t_2) and valence (p) states. We also propose a
co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance
the ferromagnetic coupling and to increase the solubility and activity.",0709.2059v1
2007-10-04,Structure and dynamics of Oxide Melts and Glasses : a view from multinuclear and high temperature NMR,"Solid State Nuclear Magnetic Resonance (NMR) experiments allow characterizing
the local structure and dynamics of oxide glasses and melts. Thanks to the
development of new experiments, it now becomes possible to evidence not only
the details of the coordination state of the network formers of glasses but
also to characterize the nature of polyatomic molecular motifs extending over
several chemical bonds. We present results involving 31P homonuclear
experiments that allow description of groups of up to three phosphate units and
27Al/17O heteronuclear that allows evidencing &#956;3 oxygen bridges in
aluminate glasses and rediscussion of the structure of high temperature melts.",0710.1003v1
2008-04-02,Origin and control of high-temperature ferromagnetism in semiconductors,"The extensive experimental and computational search for multifunctional
materials has resulted in the development of semiconductor and oxide systems,
such as (Ga,Mn)N, (Zn,Cr)Te, and HfO2, which exhibit surprisingly stable
ferromagnetic signatures despite having a small or nominally zero concentration
of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and
the associated magnetooptical and magnetotransport functionalities, are
dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded
in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these
nanocrystals can be controlled by manipulating the charge state of Cr ions
during the epitaxy. The findings provide insight into the origin of
ferromagnetism in a broad range of semiconductors and oxides, and indicate
possible functionalities of these composite systems. Furthermore, they
demonstrate a bottom-up method for self-organized nanostructure fabrication
that is applicable to any system in which the charge state of a constituent
depends on the Fermi-level position in the host semiconductor.",0804.0322v1
2008-08-22,Ferromagnetism in transparent Mn(II)-doped indium tin oxide films prepared by sol-gel process,"We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr
Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO)
films. The nanocrystalline films with average grain size 10-22 nm and thickness
150-350 nm are prepared by sol-gel coating technique on sodalime silica glass
substrate. The ferromagnetic property is, of course, weak for films deposited
on pure silica glass substrate. The structural parameters of the films appear
to be governing the magnetic property strongly which vary appreciably depending
on the substrate. The observation of room temperature ferromagnetism in
transparent conducting ITO films may find a plethora of applications in the
area of magneto-optics.",0808.3063v1
2008-09-17,The effect of Coulomb interaction at ferromagnetic-paramagnetic metallic perovskite junctions,"We study the effect of Coulomb interactions in transition metal oxides
junctions. In this paper we analyze charge transfer at the interface of a three
layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose
a charge model considering a few atomic planes within each layer and obtain
results for the magnetic coupling between the ferromagnetic layers. For large
number of planes in the paramagnetic spacer we find that the coupling
oscillates with the same period as in RKKY but the amplitude is sensitive to
the Coulomb energy. At small spacer thickness however, large differences may
appear as function of : the number of electrons per atom in the ferromagnetics
and paramagnetics materials, the dielectric constant at each component, and the
charge defects at the interface plane emphasizing the effects of charge
transfer.",0809.2984v1
2009-03-29,Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba_0.7K_0.3Fe_2As_2: NMR in a single crystal,"We report the first ^{75}As-NMR study on a single crystal of the hole-doped
iron-pnictide superconductor Ba_{0.7}K_{0.3}Fe_2As_{2} (T_c = 31.5 K). We find
that the Fe antiferromagnetic spin fluctuations are anisotropic and are weaker
compared to underdoped copper-oxides or cobalt-oxide superconductors. The spin
lattice relaxation rate 1/T_1 decreases below T_c with no coherence peak and
shows a step-wise variation at low temperatures, which is indicative of
multiple superconducting gaps, as in the electron-doped
Pr(La)FeAsO$_{1-x}$F$_{x}$. Furthermore, no evidence was obtained for a
microscopic coexistence of a long-range magnetic and superconductivity.",0903.5098v2
2009-07-27,Evidence of kinetically arrested supercooled phases in the pervoskite oxide NdNiO$_3$,"We report the time and temperature dependent response of thermopower in the
non-magnetic perovskite oxide NdNiO$_3$. We find that on cooling below the
metal-insulator transition temperature the system evolves into a phase
separated state which consists of supercooled metallic and insulating phases.
This phase separated state exhibits out of equilibrium features such as cooling
rate dependence and time dependence. The existence of these dynamical features
is attributed to the transformation of supercooled metallic phases to the
insulating state. On cooling a small fraction of supercooled phases gets
kinetically arrested in a glassy state and these supercooled phases remain in
that state down to low temperature. In the heating cycle the arrested states
dearrest above 150 K and this results in the reappearance of time dependent
features.",0907.4512v1
2009-09-16,"Superconductivity at 39 K in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6)","We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr), which was found in our previous study. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs and perovskite-type blocking layers. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). In both
magnetization and resistivity measurements, this compound exhibits
superconductivity below 10 K. Moreover, ratio of Mg and Ti in this compound can
be changed toward Ti-rich composition. (Fe2As2)(Sr4Mg1-xTi1+xO6) phase is
obtained at 0 < x as a main phase, and Tc and superconducting volume fraction
increase with increasing x. The highest Tc(onset) was confirmed at 39 K for x =
0.6 in resistivity measurement.",0909.2945v3
2009-10-27,Optically induced softening of the charge-transfer gap in Sr2CuO2Cl2,"Energy- and time-resolved spectroscopy reveals a photoinduced softening of
the charge-transfer gap in the insulating copper oxide Sr2CuO2Cl2 that
indicates rapid and efficient photoproduction of optical phonons. By relating
the pump-probe signal amplitude to the thermal difference spectrum, we estimate
that eleven to twenty optical phonons are created for every one 3 eV photon.
Assuming relaxation to the optical absorption edge at 1.5 eV, this corresponds
to 70-130 meV per boson. While the lower limit is consistent with relaxation
exclusively through optical phonons, the upper limit suggests a significant
role for magnetic excitations. We observe a photoinduced bleaching of the gap
excitation that we associate with phase space filling, and estimate the
excluded area of the photoexcited state to be about nine copper oxide
plaquettes. The temporal decay of the pump-probe signal is consistent with
anharmonic phonon decay.",0910.5048v1
2010-06-18,Tunable magnetic interaction at the atomic scale in oxide heterostructures,"We report on a systematic study of a number of structurally identical but
chemically distinct transition metal oxides in order to determine how the
material-specific properties such as the composition and the strain affect the
properties at the interface of heterostructures. Our study considers a series
of structures containing two layers of ferromagnetic SrRuO3, with
antiferromagnetic insulating manganites sandwiched in between. The results
demonstrate how to control the strength and relative orientation of interfacial
ferromagnetism in correlated electron materials by means of valence state
variation and substrate-induced strain, respectively.",1006.3603v2
2010-06-18,"A New Iron Pnictide Oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and a New Phase in Fe-As-Ca-Mg-Ti-O system","A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and its structural
derivative were found in the Fe-As-Ca-Mg-Ti-O system. The crystal structure of
(Fe2As2)(Ca5(Mg,Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc,Ti)4Oy), which
was reported in our previous study. The lattice constants of this compound are
a = 3.86(4) A and c = 41.05(2) A. In addition, another phase with a thicker
blocking layer was found. The structure of the compound and its derivative was
tentatively assigned through STEM observation as (Fe2As2)(Ca8(Mg,Ti)6Oy) with
sextuple perovskite-type sheets divided by a rock salt layer. The interlayer
Fe-Fe distance of this compound is ~30 A. The compound and its derivative
exhibited bulk superconductivity, as found from magnetization and resistivity
measurements.",1006.3769v4
2010-08-31,"Total scattering descriptions of local and cooperative distortions in the oxide spinel (Mg,Cu)Cr2O4 with dilute Jahn-Teller ions","The normal spinel oxide MgCr2O4 is cubic at room temperature while the normal
spinel CuCr2O4 is tetragonal as a consequence of the Jahn-Teller nature of Cu2+
on the tetrahedral sites. Despite different end-member structures, complete
solid solutions of Mg_{1-x}Cu_xCr2O4 can be prepared that display a first-order
structural transition with composition x = 0.43 at room temperature. Reverse
Monte Carlo analysis of total neutron scattering on data acquired between 300 K
and 15 K on samples with x = 0.10, 0.20, and 0.43 provides unbiased local and
average structure descriptions of the samples, including an understanding of
the transition from local Jahn-Teller distortions in the cubic phase to
cooperative distortions that result in a tetragonal structure. Distributions of
continuous symmetry measures help to understand and distinguish distorted and
undistorted coordination around the tetrahedral site in the solid solutions.
Magnetic exchange bias is observed in field-cooled hysteresis loops of samples
with dilute Cu2+ concentration and in samples with tetragonal--cubic phase
coexistence around 300 K.",1008.5363v4
2011-02-18,Structure of graphene oxide: thermodynamics versus kinetics,"Graphene oxide (GO) is an important intermediate to prepare graphene and it
is also a versatile material with various applications. However, despite its
importance, the detailed structure of GO is still unclear. For example,
previous theoretical studies based on energetics have suggested that hydroxyl
chain is an important structural motif of GO, which, however, is found to be
contrary to nuclear magnetic resonance (NMR) experiment. In this study, we
check both thermodynamic and kinetic aspects missed previously. First
principles thermodynamics gives a free energy based stability ordering similar
to that based on energetics, and hydroxyl chain is thus thermodynamically still
favorable. At the same time, by checking the calculated vibrational
frequencies, we note that hydroxyl chain structure is also inconsistent with
infrared experiment. Therefore, kinetics during GO synthesis is expected to
make an important role in GO structure. Transition state calculations predict
large energy barriers between local minima, which suggests that experimentally
obtained GO has a kinetically constrained structure.",1102.3797v1
2011-07-21,Superconductivity and Ferromagnetism in Oxide Interface Structures: Possibility of Finite Momentum Pairing,"We introduce a model to explain the observed ferromagnetism and
superconductivity in LAO/STO oxide interface structures. Due to the polar
catastrophe mechanism, 1/2 charge per unit cell is transferred to the interface
layer. We argue that this charge localizes and orders ferromagnetically via
exchange with the conduction electrons. Ordinarily this ferromagnetism would
destroy superconductivity, but due to strong spin-orbit coupling near the
interface, the magnetism and superconductivity can coexist by forming an
FFLO-type condensate of Cooper pairs at finite momentum, which is surprisingly
robust in the presence of strong disorder.",1107.4352v3
2011-10-31,Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier,"We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds.",1110.6810v1
2012-02-07,Universal conductance fluctuations in indium tin oxide nanowires,"Magnetic field dependent universal conductance fluctuations (UCF's) are
observed in weakly disordered indium tin oxide nanowires from 0.26 K up to
$\sim 25$ K. The fluctuation magnitudes increase with decreasing temperature,
reaching a fraction of $e^2/h$ at $T \lesssim 1$ K. The shape of the UCF
patterns is found to be very sensitive to thermal cycling of the sample to room
temperatures, which induces irreversible impurity reconfigurations. On the
other hand, the UCF magnitudes are insensitive to thermal cycling. Our measured
temperature dependence of the root-mean-square UCF magnitudes are compared with
the existing theory [C. W. J. Beenakker and H. van Houten, Phys. Rev. B
\textbf{37}, 6544 (1988)]. A notable discrepancy is found, which seems to imply
that the experimental UCF's are not cut off by the thermal diffusion length
$L_T$, as would be expected by the theoretical prediction when $L_T <
L_\varphi$, where $L_\varphi$ is the electron dephasing length. The approximate
electron dephasing length is inferred from the UCF magnitudes and compared with
that extracted from the weak-localization magnetoresistance studies. A
reasonable semiquantitative agreement is observed.",1202.1329v1
2012-02-22,Coexistance of giant tunneling electroresistance and magnetoresistance in an all-oxide magnetic tunnel junction,"We demonstrate with first-principles electron transport calculations that
large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER)
effects can coexist in an all-oxide device. The TMR originates from the
symmetry-driven spin filtering provided by the insulating BaTiO3 barrier to the
electrons injected from SrRuO3. In contrast the TER is possible only when a
thin SrTiO3 layer is intercalated at one of the SrRuO3/BaTiO3 interfaces. As
the complex band-structure of SrTiO3 has the same symmetry than that of BaTiO3,
the inclusion of such an intercalated layer does not negatively alter the TMR
and in fact increases it. Crucially, the magnitude of the TER also scales with
the thickness of the SrTiO3 layer. The SrTiO3 thickness becomes then a single
control parameter for both the TMR and the TER effect. This protocol offers a
practical way to the fabrication of four-state memory cells.",1202.4919v1
2012-06-28,Competing misfit relaxation mechanisms in epitaxial correlated oxides,"Strain engineering of functional properties in epitaxial thin films of
strongly correlated oxides exhibiting octahedral-framework structures is
hindered by the lack of adequate misfit relaxation models. Here we present
unreported experimental evidences of a four-stage hierarchical development of
octahedral-framework perturbations resulting from a progressive imbalance
between electronic, elastic and octahedral tilting energies in La0.7Sr0.3MnO3
epitaxial thin films grown on SrTiO3 substrates. Electronic softening of the Mn
- O bonds near the substrate leads to the formation of an interfacial layer
clamped to the substrate with strongly degraded magnetotransport properties,
i.e. the so-called dead layer, while rigid octahedral tilts become relevant at
advanced growth stages without significant effects on charge transport and
magnetic ordering.",1206.6680v2
2012-07-20,The Magnetoelectric Effect in Transition Metal Oxides: Insights and the Rational Design of New Materials from First Principles,"The search for materials displaying a large magnetoelectric effect has
occupied researchers for many decades. The rewards could include not only
advanced electronics technologies, but also fundamental insights concerning the
dielectric and magnetic properties of condensed matter. In this article, we
focus on the magnetoelectric effect in transition metal oxides and review the
manner in which first-principles calculations have helped guide the search for
(and increasingly, predicted) new materials and shed light on the microscopic
mechanisms responsible for magnetoelectric phenomena.",1207.5026v2
2012-09-24,Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33): A Layered Titanium-based Pnictide Oxide Superconductor,"A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 <=
x <= 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal
CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm;
a=4.1196(1){\AA}; c=8.0951(2){\AA}), exhibits a CDW/SDW transition at 54K. Upon
chemical doping with Na, the CDW/SDW transition is systematically suppressed
and super-conductivity arises with the critical temperatures, Tc, increasing to
5.5 K. Bulk superconductivity is confirmed by resistivity, magnetic and heat
capacity measurements. Like the high-Tc cuprates and the iron pnictides,
superconductivity in BaTi2Sb2O arises from an ordered state. Similarities and
differences to the cuprate and iron pnictide supercon-ductors are discussed.",1209.5447v2
2013-01-17,Giant Magnetoresistance Effect in the Metal-Insulator Transition of Pyrochlore Oxide Nd2Ir2O7,"We investigated the magnetoresistance (MR) effect of the pyrochlore oxide
Nd2Ir2O7, which shows a metal-insulator transition at T_MI =33 K. A small
positive MR effect was observed in the metallic state above T_MI, while a large
negative MR effect was observed in the insulating state below T_MI . MR effects
exceeding 3000% were found at 1 K at a field of 9 T. As a result, we confirmed
the crossover from the insulating state to a state with a small or partial band
gap in a field up to 56 T. Furthermore, from the MR effect in Eu2Ir2O7 (T_MI =
120 K) and Gd$_2$Ir$_2$O$_7$ (T_MI = 127 K), we revealed that the large
negative MR effect of the pyrochlore iridate Ln2Ir2O7 depends on the magnetism
of the lanthanide Ln^{3+} ion. The d-f interaction plays a significant role in
the large negative MR effect in the insulating state.",1301.3969v1
2013-03-05,Interplay of octahedral rotations and breathing distortions in charge ordering perovskite oxides,"We investigate the structure--property relationships in $AB$O$_3$ perovskites
exhibiting octahedral rotations and cooperative octahedral breathing
distortions (CBD) using group theoretical methods. Rotations of octahedra are
ubiquitous in the perovskite family, while the appearance of breathing
distortions -- oxygen displacement patterns that lead to approximately uniform
dilation and contraction of the $B$O$_6$ octahedra -- are rarer in compositions
with a single, chemically unique $B$-site. The presence of a CBD relies on
electronic instabilities of the $B$-site cations, either orbital degeneracies
or valence-state fluctuations, and often appear concomitant with charge order
metal--insulator transitions or $B$-site cation ordering. We enumerate the
structural variants obtained from rotational and breathing lattice modes and
formulate a general Landau functional describing their interaction. We use this
information and combine it with statistical correlation techniques to evaluate
the role of atomic scale distortions on the critical temperatures in
representative charge ordering nickelate and bismuthate perovskites. Our
results provide new microscopic insights into the underlying
structure--property interactions across electronic and magnetic phase
boundaries, suggesting plausible routes to tailor the behavior of functional
oxides by design.",1303.0903v2
2013-07-25,Reentrant Superconductivity and Superconducting Critical Temperature Oscillations in F/S/F trilayers of Cu41Ni59/Nb/Cu41Ni59 Grown on Cobalt Oxide,"Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core
of a superconducting spin valve. The switching effect of the spin valve is
based on interference phenomena occurring due to the proximity effect at the
S/F interfaces. A remarkable effect is only expected if the core structure
exhibits strong critical temperature oscillations, or most favorable, reentrant
superconductivity, when the thickness of the ferromagnetic layer is increased.
The core structure has to be grown on an antiferromagnetic oxide layer (or such
layer to be placed on top) to pin by exchange bias the
magnetization-orientation of one of the ferromagnetic layers. In the present
paper we demonstrate that this is possible, keeping the superconducting
behavior of the core structure undisturbed.",1307.6737v1
2013-10-29,Theory of Antiferromagnetic Order in High-Tc Oxides: An Approach Based on Ginzburg-Landau Expansion,"The mean-field phase diagram of antiferromagnetic order in t-J model has been
examined, using the free energy obtained by Ginzburg-Landau (GL) expansion. We
extended the usual GL theory in two ways: First, we have included higher order
terms with respect to the spatial derivative (or wave number) to incorporate
the incommensurate antiferromagnetic order. Second, we have also included
higher order terms with respect to the order parameter amplitude, in order to
treat the first order phase transition between paramagnetic and
antiferromagnetic phase, which appears at some doping rates. We found the
possibility of tricritical point and critical endpoint in the magnetic phase
diagram of the high-Tc oxides associated with the commensurate and
incommensurate antiferromagnetic order. The possible effects of thermal
fluctuations and randomness (spin glass) are also discussed qualitatively based
on the GL free energy.",1310.7777v1
2014-01-16,Active silicon integrated nanophotonics: ferroelectric BaTiO3 devices,"The integration of complex oxides on silicon presents opportunities to extend
and enhance silicon technology with novel electronic, magnetic, and photonic
properties. Among these materials, barium titanate (BaTiO3) is a particularly
strong ferroelectric perovskite oxide with attractive dielectric and
electro-optic properties. Here we demonstrate nanophotonic circuits
incorporating ferroelectric BaTiO3 thin films on the ubiquitous
silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline
BaTiO3 directly on SOI and engineer integrated waveguide structures that
simultaneously confine light and an RF electric field in the BaTiO3 layer.
Using on-chip photonic interferometers, we extract a large effective Pockels
coefficient of 213 plus minus 49 pm/V, a value more than six times larger than
found in commercial optical modulators based on lithium niobate. The
monolithically integrated BaTiO3 optical modulators show modulation bandwidth
in the gigahertz regime, which is promising for broadband applications.",1401.4184v2
2014-02-22,Ab initio quantum Monte Carlo calculations of spin superexchange in cuprates: the benchmarking case of Ca$_2$CuO$_3$,"In view of the continuous theoretical efforts aimed at an accurate
microscopic description of the strongly correlated transition metal oxides and
related materials, we show that with continuum quantum Monte Carlo (QMC)
calculations it is possible to obtain the value of the spin superexchange
coupling constant of a copper oxide in a quantitatively excellent agreement
with experiment. The variational nature of the QMC total energy allows us to
identify the best trial wave function out of the available pool of wave
functions, which makes the approach essentially free from adjustable parameters
and thus truly ab initio. The present results on magnetic interactions suggest
that QMC is capable of accurately describing ground state properties of
strongly correlated materials.",1402.5561v2
2014-02-25,"Double perovskite heterostructures: Magnetism, Chern bands, and Chern insulators","Experiments demonstrating the controlled growth of oxide heterostructures
have raised the prospect of realizing topologically nontrivial states of
correlated electrons in low dimensions. Here, we study heterostructures
consisting of {111}-bilayers of double perovskites separated by inert band
insulators. In bulk, these double perovskites have well-defined local moments
interacting with itinerant electrons leading to high temperature
ferromagnetism. Incorporating spin-orbit coupling in the two-dimensional
honeycomb geometry of a {111}-bilayer, we find a rich phase diagram with
tunable ferromagnetic order, topological Chern bands, and a C=2 Chern insulator
regime. An effective two-band model of Zeeman-split j=3/2 states captures this
nontrivial band topology. Our results are of broad relevance to oxide materials
such as Sr2FeMoO6, Ba2FeReO6, and Sr2CrWO6.",1402.6347v4
2014-04-21,Wide-angle energy-momentum spectroscopy,"Light emission is defined by its distribution in energy, momentum, and
polarization. Here, we demonstrate a method that resolves these distributions
by means of wide-angle energy-momentum spectroscopy. Specifically, we image the
back focal plane of a microscope objective through a Wollaston prism to obtain
polarized Fourier-space momentum distributions, and disperse these
two-dimensional radiation patterns through an imaging spectrograph without an
entrance slit. The resulting measurements represent a convolution of individual
radiation patterns at adjacent wavelengths, which can be readily deconvolved
using any well-defined basis for light emission. As an illustrative example, we
use this technique with the multipole basis to quantify the intrinsic emission
rates for electric and magnetic dipole transitions in europium-doped yttrium
oxide (Eu$^{3+}$:Y$_{2}$O$_{3}$) and chromium-doped magnesium oxide
(Cr$^{3+}$:MgO). Once extracted, these rates allow us to reconstruct the full,
polarized, two-dimensional radiation patterns at each wavelength.",1404.5109v1
2014-09-01,Imaging and Control of Ferromagnetism in a Polar Antiferromagnet,"Atomically sharp oxide heterostructures often exhibit unusual physical
properties that are absent in the constituent bulk materials. The interplay
between electrostatic boundary conditions, strain and dimensionality in
ultrathin epitaxial films can result in monolayer-scale transitions in
electronic or magnetic properties. Here we report an atomically sharp
antiferromagnetic-to-ferromagnetic phase transition when atomically growing
polar antiferromagnetic LaMnO3 (001) films on SrTiO3 substrates. For a
thickness of five unit cells or less, the films are antiferromagnetic, but for
six unit cells or more, the LaMnO3 film undergoes a phase transition to a
ferromagnetic state over its entire area, which is visualized by scanning
superconducting quantum interference device microscopy. The transition is
explained in terms of electronic reconstruction originating from the polar
nature of the LaMnO3 (001) films. Our results demonstrate how new emergent
functionalities can be visualized and engineered in atomically thick oxide
films at the atomic level.",1409.0520v1
2014-09-18,Electronic and magnetic properties of Ti4O7 predicted by self-interaction corrected density functional theory,"Understanding electronic properties of sub-stoichiometric phases of titanium
oxide such as Magn\'eli phase Ti4O7 is crucial in designing and modeling
resistive switching devices. Here we present our study on Magn\'eli phase Ti4O7
together with rutile TiO2 and Ti2O3 using density functional theory methods
with atomic-orbital-based self-interaction correction (ASIC). We predict a new
antiferromagnetic ground state in the low temperature phase (or LT phase), and
we explain energy difference with a competing antiferromagnetic state using a
Heisenberg model. The predicted energy ordering of these states in the LT phase
is calculated to be robust in a wide range of modeled isotropic strain. We have
also investigated the dependence of the electronic structures of the Ti-O
phases on stoichiometry. The splitting of titanium t2g orbitals is enhanced
with increasing oxygen deficiency as Ti-O is reduced. The electronic properties
of all these phases can be reasonably well described by applying ASIC with a
standard value for transition metal oxides of the empirical parameter {\alpha}
of 0.5 representing the magnitude of the applied self-interaction correction.",1409.5331v2
2014-10-08,Transport properties of beta-Ga2O3 Nanoparticles embedded in Nb thin films,"The origin of ferromagnetism in nanoparticles of nonmagnetic oxides is an
interesting area of research. In the present work, transport properties of
niobium thin films, with beta-Ga2O3 nanoparticles embedded within them, are
presented. Nanoparticles of beta-Ga2O3 embedded in a Nb matrix were prepared at
room temperature by radio frequency co-sputtering technique on Si (100) and
glass substrates held at room temperature. The thin films deposited on Si
substrates were subjected to Ar annealing at a temperature range of 600-650 C
for 1 hour. Films were characterized by X-ray diffraction (XRD), Micro-Raman
and elemental identification was performed with an Energy Dispersive X-ray
Spectroscopy (EDS). Transport measurements were performed down to liquid helium
temperatures by four-probe contact technique, showed characteristics analogous
to those observed in the context of a Kondo system. A comparison of the
experimental data with the theoretical formalism of Kondo and Hamann is
presented. It is suggested that this behavior arises from the existence of
magnetic moments associated with the oxygen vacancy defects in the
nanoparticles of the nonmagnetic oxide Ga2O3.",1410.2047v1
2014-11-22,Large voltage-induced modification of spin-orbit torques in Pt/Co/GdOx,"We report on large modifications of current-induced spin-orbit torques in a
gated Pt/Co/Gd-oxide microstrip due to voltage-driven O$^{2-}$ migration. The
Slonczewski-like and field-like torques are quantified using a low-frequency
harmonic technique based on the polar magneto-optical Kerr effect.
Voltage-induced oxidation of Co enhances the Slonczewski-like torque by as much
as an order of magnitude, and simultaneously reduces the anisotropy energy
barrier by a factor of ~5. Such magneto-ionic tuning of interfacial spin-orbit
effects may significantly enhance the efficiency of magnetization switching and
provide additional degrees of freedom in spintronic devices.",1411.6153v1
2014-11-24,Kitaev magnetism in honeycomb RuCl3 with intermediate spin-orbit coupling,"Intensive studies of the interplay between spin-orbit coupling (SOC) and
electronic correlations in transition metal compounds have recently been
undertaken. In particular, $j_{\rm eff}$ = 1/2 bands on a honeycomb lattice
provide a pathway to realize Kitaev's exactly solvable spin model. However,
since current wisdom requires strong atomic SOC to make $j_{\rm eff}=1/2$
bands, studies have been limited to iridium oxides. Contrary to this
expectation, we demonstrate how Kitaev interactions arise in 4$d$-orbital
honeycomb $\alpha$-RuCl$_3$, despite having significantly weaker SOC than the
iridium oxides, via assistance from electron correlations. A strong coupling
spin model for these correlation-assisted $j_{\rm eff}$ = 1/2 bands is derived,
in which large antiferromagnetic Kitaev interactions emerge along with
ferromagnetic Heisenberg interactions. Our analyses suggest that the ground
state is a zigzag-ordered phase lying close to the antiferromagnetic Kitaev
spin liquid. Experimental implications for angle resolved photoemission
spectroscopy, neutron scattering, and optical conductivities are discussed.",1411.6623v3
2015-01-08,Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure,"A new approach to all-optical detection and control of the coupling between
electric and magnetic order on ultrafast timescales is achieved using
time-resolved second harmonic generation (SHG) to study a ferroelectric
(FE)/ferromagnet (FM) oxide heterostructure. We use femtosecond optical pulses
to modify the spin alignment in a
Ba$_{0.1}$Sr$_{0.9}$TiO$_{3}$(BSTO)/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO)
heterostructure and selectively probe the ferroelectric response using SHG. In
this heterostructure, the pump pulses photoexcite non-equilibrium
quasiparticles in LCMO, which rapidly interact with phonons before undergoing
spin-lattice relaxation on a timescale of tens of picoseconds. This reduces the
spin-spin interactions in LCMO, applying stress on BSTO through
magnetostriction. This then modifies the FE polarization through the
piezoelectric effect, on a timescale much faster than laser-induced heat
diffusion from LCMO to BSTO. We have thus demonstrated an ultrafast indirect
magnetoelectric effect in a FE/FM heterostructure mediated through elastic
coupling, with a timescale primarily governed by spin-lattice relaxation in the
FM layer.",1501.01753v1
2015-02-26,Possible mechanisms of electronic phase separation in oxide interfaces,"LaAlO3/SrTiO3 ad LaTiO3/SrTiO3 interfaces are known to host a strongly
inhomogeneous (nearly) two-dimensional electron gas (2DEG). In this work we
present three unconventional electronic mechanisms of electronic phase
separation (EPS) in a 2DEG as a possible source of inhomogeneity in oxide
interfaces. Common to all three mechanisms is the dependence of some
(interaction) potential on the 2DEG's density. We first consider a mechanism
resulting from a sizable density-dependent Rashba spin-orbit coupling. Next, we
point out that an EPS may also occur in the case of a density-dependent
superconducting pairing interaction. Finally, we show that the confinement of
the 2DEG to the interface by a density-dependent, self-consistent electrostatic
potential can by itself cause an EPS.",1502.07561v1
2015-03-02,Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by TEM and EELS,"Nanoscale defect structure within the magnetic penetration depth of ~100nm is
key to the performance limitations of niobium superconducting radio frequency
(SRF) cavities. Using a unique combination of advanced thermometry during
cavity RF measurements, and TEM structural and compositional characterization
of the samples extracted from cavity walls, we discover the existence of
nanoscale hydrides in electropolished cavities limited by the high field Q
slope, and show the decreased hydride formation in the electropolished cavity
after 120C baking. Furthermore, we demonstrate that adding 800C hydrogen
degassing followed by light buffered chemical polishing restores the hydride
formation to the pre-120C bake level. We also show absence of niobium oxides
along the grain boundaries and the modifications of the surface oxide upon 120C
bake.",1503.02046v2
2015-06-01,Negative Magnetoresistance in Amorphous Indium Oxide Wires,"We study magneto-transport properties of several amorphous Indium oxide
nanowires of different widths. The wires show superconducting transition at
zero magnetic field, but, there exist a finite resistance at the lowest
temperature. The $R(T)$ broadening was explained by available phase slip
models. At low field, and far below the superconducting critical temperature,
the wires with diameter equal to or less than 100 nm, show negative
magnetoresistance (nMR). The magnitude of nMR and the crossover field are found
to be dependent on both temperature and the cross-sectional area. We find that
this intriguing behavior originates from the interplay between two field
dependent contributions.",1506.00459v3
2015-06-08,A compact plasmonic MOS-based 2x2 electro-optic switch,"We report on a three-waveguide electro-optic switch for compact photonic
integrated circuits and data routing applications. The device features a
plasmonic metal-oxide-semiconductor (MOS) mode for enhanced
light-matter-interactions. The switching mechanism originates from a
capacitor-like design where the refractive index of the active medium,
Indium-Tin-Oxide, is altered via shifting the plasma frequency due to carrier
accumulation inside the waveguide-based MOS structure. This light manipulation
mechanism controls the transmission direction of transverse magnetic polarized
light into either a CROSS or BAR waveguide port. The extinction ratio of 18 dB
(7) dB for the CROSS (BAR) state, respectively, is achieved via a gating
voltage bias. The ultrafast broadband fJ/bit device allows for seamless
integration with Siliconon- Insulator platforms to for low-cost manufacturing.",1506.02337v1
2015-07-10,Jahn-Teller distortions as a novel source of multiferroicity,"The Jahn-Teller effect is a fascinating and ubiquitous phenomenon in modern
quantum physics and chemistry. We propose a class of oxides with melilite
structure Ba$_2$TGe$_2$O$_7$ (T=V,Ni) where Jahn-Teller distortions are the
main responsibles for the appearance of electric polarization. At the hearth of
the proposed mechanism lies the lack of inversion symmetry displayed by
tetrahedrally coordinated transition-metal ions, which allows for the
condensation of polar Jahn-Teller distortions, at odds with octahedral
coordination typical of conventional ferroelectric oxides with perovskite
structure. Since the noncentrosymmetric local environment of transition-metal
ions also activates the proposed spin-dependent hybridization mechanism for
magnetically-induced electric polarization, proper multiferroic phases with
intrinsic magnetoelectric interaction could be realized in this class of
low-symmetry materials.",1507.02810v1
2015-07-18,Two step solid state synthesis and Synchrotron X-ray characterizations of ceramic Co3TeO6; an improper multiferroic,"A two step solid state reaction route has been presented to synthesize
monophasic cobalt tellurate (Co3TeO6, CTO) using Co3O4 and TeO2 as starting
reagents. During synthesis, initial ingredient Co3O4 is found better than CoO
in circumventing the intermediate Co5TeO8 or CoTeO3 phases. High resolution
Synchrotron X-ray Diffraction has been used to probe different phases present
in synthesized CTO and to achieve its single phase. Further, XANES studies near
Co K and Te L-edge reveal mixed oxidation states of Co (i.e. Co2+ and Co3+) and
+VI valence state of Te respectively, which is also confirmed with XPS. Charge
imbalance due to different oxidation states of the Co-ions has been observed to
be compensated by plausible Te-cations vacancy. Enhanced multiferroic
properties like effective magnetic moment (JAP 116, (2014)) have been
correlated with the present synthesis route.",1507.05190v1
2016-03-11,Novel Charge Ordering in the Trimer Iridium Oxide BaIrO3,"We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with
face-shared Ir3O12 trimers, and have investigated the origin of the phase
transition at 182 K by measuring resistivity, thermopower, magnetization and
synchrotron x-ray diffraction. We propose a possible electronic model and
transition mechanism, starting from a localized electron picture on the basis
of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded
as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or
one lattice site. The transition can be viewed as a transition from the Mott
insulator phase to a kind of charge ordered insulator phase.",1603.03525v1
2016-03-17,Reconciling the ionic and covalent pictures in rare-earth nickelates,"The properties of AMO3 perovskite oxides, where M is a 3d transition metal,
depend strongly on the level of covalency between the metal d and oxygen p
orbitals. With their complex spin orders and metal-insulator transition,
rare-earth nickelates verge between dominantly ionic and covalent characters.
Accordingly, the nature of their ground state is highly debated. Here, we
reconcile the ionic and covalent visions of the insulating state of nickelates.
Through first-principles calculations, we show that it is reminiscent of the
ionic charge disproportionation picture (with strictly low-spin 4+ and
high-spin 2+ Ni sites) while exhibiting strong covalence effects with oxygen
electrons shifted toward the depleted Ni cations, mimicking a configuration
with identical Ni sites. Our results further hint at strategies to control
electronic and magnetic phases of transition metal oxide perovskites.",1603.05480v1
2016-09-07,Emerging magnetism and anomalous Hall effect in iridate-manganite heterostructures,"Strong Coulomb repulsion and spin-orbit coupling are known to give rise to
exotic physical phenomena in transition metal oxides. Initial attempts to
investigate systems where both of these fundamental interactions are comparably
strong, such as 3d and 5d complex oxide superlattices, have revealed properties
that only slightly differ from the bulk ones of the constituent materials.
Here, we observe that the interfacial coupling between the 3d antiferromagnetic
insulator SrMnO3 and the 5d paramagnetic metal SrIrO3 is enormously strong,
yielding an anomalous Hall response as the result of charge transfer driven
interfacial ferromagnetism. These findings show that low dimensional spin-orbit
entangled 3d-5d interfaces provide an avenue to uncover technologically
relevant physical phenomena unattainable in bulk materials.",1609.01973v1
2016-09-12,Estimation of spin relaxation lengths in spin valves of In and In2O3 nanostructures,"We report the electrical injection and detection of spin polarized current in
lateral ferromagnet-nonmagnet-ferromagnet spin valve devices, ferromagnet being
cobalt and nonmagnet being indium (In) or indium oxide (In2O3) nanostructures.
The In nanostructures were grown by depositing pure In on lithographically
pre-patterned structures. In2O3 nanostructures were obtained by oxidation of In
nanostructures. Spin valve devices were fabricated by depositing micro magnets
over the nanostructures with connecting nonmagnetic electrodes via two steps of
e-beam lithography. Clear spin switching behavior was observed in the both
types of spin valve devices measured at 10 K. From the measured spin signal,
the spin relaxation length ({\lambda}N) of In and In2O3 nanostructures were
estimated to be 449.6 nm and 788.6 nm respectively.",1609.03609v1
2016-09-20,Observation of Inverse Edelstein Effect in Rashba-Split 2DEG between SrTiO3 and LaAlO3 at Room Temperature,"The Rashba physics has been intensively studied in the field of spin
orbitronics, for the purpose of searching novel physical properties and the FM
magnetization switching for technology applications. Here, we report the
observation of the inverse Edelstein effect up to room temperature in the
Rashba-split 2DEG between two insulating oxides SrTiO3 and LaAlO3 with the
LaAlO3 layer thickness from 3 to 40 unit cells (UC). We further demonstrate
that the spin voltage could be dramatically manipulated by electric field
effect for the 2DEG between SrTiO3 and 3 UC LaAlO3. These results demonstrate
that the Rashba-split 2DEG at the complex oxide interface can be used for room
temperature efficient charge-and-spin conversion for the generation and
detection of spin current.",1609.06207v2
2016-09-23,Emergent ultrafast phenomena in correlated oxides and heterostructures,"The possibility of investigating the dynamics of solids on timescales faster
than the thermalization of the internal degrees of freedom has disclosed novel
non-equilibrium phenomena that have no counterpart at equilibrium. Transition
metal oxides (TMOs) provide an interesting playground in which the correlations
among the charges in the metal $d$-orbitals give rise to a wealth of intriguing
electronic and thermodynamic properties involving the spin, charge, lattice and
orbital orders. Furthermore, the physical properties of TMOs can be engineered
at the atomic level, thus providing the platform to investigate the transport
phenomena on timescales of the order of the intrinsic decoherence time of the
charge excitations.
  Here, we review and discuss three paradigmatic examples of transient emerging
properties that are expected to open new fields of research: i) the creation of
non-thermal magnetic states in spin-orbit Mott insulators; ii) the possible
exploitation of quantum paths for the transport and collection of charge
excitations in TMO-based few-monolayers devices; iii) the transient wave-like
behavior of the temperature field in strongly anisotropic TMOs.",1609.07394v1
2017-03-03,A high-temperature superconducting weak-link defined by ferroelectric field-effect,"In all-oxide ferroelectric (FE) - superconductor (S) bilayers, due to the low
carrier concentration of oxides compared to transition metals, the FE
interfacial polarization charges induce an accumulation (or depletion) of
charge carriers in the S. This leads either to an enhancement or a depression
of its critical temperature depending on FE polarization direction.Here we
exploit this effect at a local scale to define planar weak-links in
high-temperature superconducting wires. This is realized in
BiFeO3(FE)/YBa2Cu3O7(S)bilayers in which the remnant FE domain structure is
written at will by locally applying voltage pulses with a conductive-tip atomic
force microscope. In this fashion, the FE domain pattern defines a spatial
modulation of superconductivity. This allows us to write a device whose
electrical transport shows different temperature regimes and magnetic field
matching effects that are characteristic of Josephson coupled weak-links. This
illustrates the potential of the ferroelectric approach for the realization of
high-temperature superconducting devices.",1703.01219v1
2017-08-21,Spin-orbit coupling in three-orbital Kanamori impurity model and its relevance for transition-metal oxides,"We investigate the effects of the spin-orbit coupling (SOC) in a
three-orbital impurity model with Kanamori interaction using the numerical
renormalization group method. We focus on the impurity occupancy $N_d=2$
relevant to the dynamical mean-field theory studies of Hund's metals. Depending
on the strength of SOC $\lambda$ we identify three regimes: usual Hund's
impurity for $|\lambda|<\lambda_c$, van-Vleck non-magnetic impurity for
$\lambda > \lambda_c$, and a $J=2$ impurity for $\lambda < -\lambda_c$. They
all correspond to a Fermi liquid but with very different quasiparticle phase
shifts and different physical properties. The crossover between these regimes
is controlled by an emergent scale, the orbital Kondo temperature, $\lambda_c
=T_K^\mathrm{orb}$ that drops with increasing interaction strength. This
implies that oxides with strong electronic correlations are more prone to the
effects of the spin-orbit coupling.",1708.06089v1
2017-08-28,Dependence of Dzyaloshinskii-Moriya interaction on the oxygen coverage in Pt/Co/MOx trilayers,"We have studied the interfacial Dzyaloshinskii-Moriya interaction (DMI) in a
series of Pt/Co/MOx (M=Al, Gd) trilayers in which the degree of oxidation of
the top Co interface is varied. To access to reliable values of the DMI
strength, we have used a method based on the measurement of the saturation
velocity of field driven chiral N\'eel domain walls. We show that the effective
DMI strength in the Pt/Co/MOx trilayers varies with the oxidation degree of the
Co/MOx interface. This strongly suggests that the Co/MOx interface gives a
distinct contribution to the total DMI, adding to that of the Pt/Co interface.
The DMI presents a maximum for the oxygen coverage maximizing also the
interface magnetic anisotropy energy Ks. This calls for common microscopic
origins for the contributions of the Co/MOx interface to DMI and Ks.",1708.08516v1
2018-04-11,Computational study on the half-metallicity in transition metal-oxide-incorporated 2D g-C3N4 nanosheets,"In this study, based on the first-principles calculations, we systematically
investigated the electronic and magnetic properties of the transition
metal-oxide-incorporated 2D g-C3N4 nanosheet (labeled C3N4-TM-O, TM = Sc-Mn).
The results suggest that the TM-O binds to g-C3N4 nanosheets strongly for all
systems. We found that the 2D C3N4-TM-O framework is ferromagnetic for TM = Sc,
Ti, V, Cr, while it is antiferromagnetic for TM = Mn. All the ferromagnetic
systems exhibit the half-metallic property. Furthermore, Monte Carlo
simulations based on the Heisenberg model suggest that the Curie temperatures
(T_c) of the C3N4-TM-O (TM = Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K,
and 190 K, respectively. Based on Bader charge analysis, we found that the
origin of the half-metallicity at Fermi energy can be partially attributed to
the transfer of electrons from TM atoms to the g-C3N4 nanosheet. In addition,
we found that not only electrons but also holes can induce half-metallicity for
2D g-C3N4 nanosheets, which may help to understand the origin of
half-metallicity for graphitic carbon nitride.",1804.03779v1
2018-04-30,Magneto-Stark-effect of yellow excitons in cuprous oxide,"We investigate and compare experimental and numerical excitonic spectra of
the yellow series in cuprous oxide Cu$_2$O in the Voigt configuration and thus
partially extend the results from Schweiner et al. [Phys. Rev. B 95, 035202
(2017)], who only considered the Faraday configuration. The main difference
between the configurations is given by an additional effective electric field
in the Voigt configuration, caused by the motion of the exciton through the
magnetic field. This Magneto-Stark effect was already postulated by Gross et
al. and Thomas et al. in 1961 [Sov. Phys. Solid State 3, 221 (1961); Phys. Rev.
124, 657 (1961)]. Group theoretical considerations show that the field most of
all significantly increases the number of allowed lines by decreasing the
symmetry of the system. This conclusion is supported by both the experimental
and numerical data.",1804.11093v3
2019-05-23,Interface ferromagnetism and anomalous Hall effect of CdO/ferromagnetic insulator heterostructures,"The experimental observation of quantum anomalous Hall effect (QAHE) in
magnetic topological insulators has stimulated enormous interest in
condensed-matter physics and materials science. For the purpose of realizing
high-temperature QAHE, several material candidates have been proposed, among
which the interface states in the CdO/ferromagnetic insulator heterostructures
are particularly interesting and favorable for technological applications.
Here, we report the experimental observation of the interfacial ferromagnetism
and anomalous Hall effect in the Fe3O4/CdO/Fe3O4 heterostructures grown via
oxide molecular-beam epitaxy. Systematical variation of the CdO thickness
reveals the interface ferromagnetism as the major cause for the observed planar
magnetoresistance and anomalous Hall effect. Our results might pave the way to
engineer oxide interface states for the exploration of QAHE towards exotic
quantum-physical phenomena and potential applications.",1905.09425v1
2010-05-04,NMR evidence for antiferromagnetic order in a planar 3d9/3d8 nickelate,"We report La-139 Nuclear Magnetic Resonance (NMR) data in La4Ni3O8 which
reveals the presence of antiferromagnetic order below T_N ~ 105 K. This
compound contains two-dimensional layers of NiO2 that are isostructural to the
copper oxide planes of the high temperature superconductors. This compound is
remarkable because the average Ni valence of 1.33+ for formally 2Ni1+ + Ni2+
indicates a 3d9/3d8 electronic configuration. Nickel oxides with Ni1+ valence
are rare and unstable, yet may provide new routes to high temperature
superconductivity. La4Ni3O8, with antiferromagnetic order of S=1/2 Ni1+ spins,
is analogous to the parent compounds of the cuprate superconductors. Our data
clearly reveal dramatic spectral changes and low energy antiferromagnetic
correlations associated with the onset of long range order below T_N.",1005.0435v1
2010-05-18,Apical oxygens and correlation strength in electron and hole doped copper oxides,"We use the Local Density Approximation in combination with the Dynamical Mean
Field Theory to carry out a comparative investigation of a typical electron
doped and a typical hole doped copper oxide, NCCO and LSCO respectively. The
parent compounds of both materials are strongly correlated electron systems in
the vicinity of the metal to charge transfer insulator transition. In NCCO the
magnetic long range order is essential to open a charge transfer gap, while
Mott physics is responsible for the gap in LSCO. We highlights the role of the
apical oxygens in determining the strength of the correlations and obtaining
overall good agreement between theory and several experimentally determined
quantities. Results for optical conductivity, polarized X-ray absorption and
angle resolved photoemission are presented and compared with experiments.",1005.3100v1
2017-01-27,Thickness dependent properties in oxide heterostructures driven by structurally induced metal-oxygen hybridization variations,"Thickness driven electronic phase transitions are broadly observed in
different types of functional perovskite heterostructures. However, uncertainty
remains whether these effects are solely due to spatial confinement, broken
symmetry or rather to a change of structure with varying film thickness. Here,
we present direct evidence for the relaxation of oxygen 2p and Mn 3d orbital
(p-d) hybridization coupled to the layer dependent octahedral tilts within a
La2/3Sr1/3MnO3 film driven by interfacial octahedral coupling. An enhanced
Curie temperature is achieved by reducing the octahedral tilting via interface
structure engineering. Atomically resolved lattice, electronic and magnetic
structures together with X-ray absorption spectroscopy demonstrate the central
role of thickness dependent p-d hybridization in the widely observed
dimensionality effects present in correlated oxide heterostructures.",1701.07930v1
2017-01-27,Low-energy excitation spectra in the excitonic phase of cobalt oxides,"We study the excitonic phase and low-energy excitation spectra of perovskite
cobalt oxides. Constructing the five-orbital Hubbard model defined on the
three-dimensional cubic lattice for the $3d$ bands of
Pr$_{0.5}$Ca$_{0.5}$CoO$_3$, we calculate the excitonic susceptibility in the
normal state in the random-phase approximation (RPA) to show the presence of
the instability toward excitonic condensation. Based on the excitonic ground
state with a magnetic multipole obtained in the mean-field approximation, we
calculate the dynamical susceptibility of the excitonic phase in the RPA and
find that there appear the gapless collective excitation in the spin-transverse
mode (Goldstone mode) and the gapful collective excitation in the
spin-longitudinal mode (Higgs mode). Experimental relevance is discussed.",1701.07943v3
2018-05-08,Understanding LiOH Chemistry in a Ruthenium Catalyzed Li-O2 Battery,"Non-aqueous Li-O2 batteries are promising for next generation energy storage.
New battery chemistries based on LiOH, rather than Li2O2, have recently been
reported in systems with added water, one using a soluble additive LiI and the
other using solid Ru catalysts. Here, we focus on the mechanism of Ru-catalyzed
LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical
pressure measurements and mass spectrometry, we show that on discharging LiOH
forms via a 4 e- oxygen reduction reaction, the H in LiOH coming solely from
added H2O and the O from both O2 and H2O. On charging, quantitative LiOH
oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone
in the electrolyte. Compared to Li2O2, LiOH formation over Ru incurs hardly any
side reactions, a critical advantage for developing a long-lived battery. An
optimized metal catalyst-electrolyte couple needs to be sought that aids LiOH
oxidation and is able stable towards attack by hydroxyl radicals.",1805.03268v1
2018-05-16,Quantum well structure of a double perovskite superlattice and formation of a spin-polarized two-dimensional electron gas,"Layered oxide heterostructures are the new routes to tailor desired
electronic and magnetic phases emerging from competing interactions involving
strong correlation, orbital hopping, tunnelling and lattice coupling phenomena.
Here, we propose a half-metal/insulator superlattice that intrinsically forms
spin-polarized two-dimensional electron gas (2DEG) following a mechanism very
different from the widely reported 2DEG at the single perovskite polar
interfaces. From DFT$+U$ study on Sr$_2$FeMoO$_6$/La$_2$CoMnO$_6$ (001)
superlattice, we find that a periodic quantum well is created along [001] which
breaks the three-fold $t_{2g}$ degeneracy to separate the doubly degenerate
$xz$ and $yz$ states from the planar $xy$ state. In the spin-down channel, the
dual effect of quantum confinement and strong correlation localizes the
degenerate states, whereas the dispersive $xy$ state forms the 2DEG which is
robust against perturbations to the superlattice symmetry. The spin-up channel
retains the bulk insulating. Both spin polarization and orbital polarization
make the superlattice ideal for spintronic and orbitronic applications. The
suggested 2DEG mechanism widens the scope of fabricating next generation of
oxide heterostructures.",1805.06128v2
2018-05-06,Alkoxide-intercalated NiFe-layered double hydroxides magnetic nanosheets as efficient water oxidation electrocatalysts,"Alkoxide-intercalated NiFe-layered double hydroxides were synthesized via the
nonaqueous methanolic route. These nanoplatelets exhibit high crystalline
quality as demonstrated by atomic resolution scanning transmission electron
microscopy combined with electron energy-loss spectroscopy. Moreover, the
presence of the alkoxide moieties has been unambiguously demonstrated by means
of thermogravimetric analysis coupled to a mass spectrometer. These NiFe-LDHs
can be exfoliated in water or organic solvents and processed into homogeneous
ultra-thin films (< 3nm thick) with the assistance of O2-plasma. The study of
their behaviour as water oxidation electrocatalysts has shown an outstanding
performance at basic pHs (small overpotential of ca. 249 mV and Tafel slopes in
the range of 52-55 mV per decade).",1805.11668v1
2009-12-23,The effect of anomalous adsorption of H2O and CO2 by pre-hydrated YBa_2Cu_3O_{6.53},"The results of a comprehensive study on the YBa_2Cu_3O_{6.53} oxide subjected
to ""mild"" hydration (exposure at small values of pH2O) by a special technique
have been reported. The material modified in this way acquires an interesting
property; namely, in natural conditions it intensively absorbs large quantities
of components (H2O and CO2) comprising the gas atmosphere. Arguments have been
adduced that at least the water enters the crystal lattice of the
yttrium-barium cuprate. This lattice is in the two-phase (tetragonal and
orthorhombic) state: testing of the magnetic properties of the oxide has
revealed the presence of antiferromagnetic and diamagnetic regions in this
material.",0912.4601v1
2012-04-11,The structural and electronic properties of tin oxide nanowires: an {\it ab initio} investigation,"We performed an {\it ab initio} investigation on the properties of rutile tin
oxide (SnO$_{x}$) nanowires. We computed the wire properties determining the
equilibrium geometries, binding energies and electronic band structures for
several wire dimensions and surface facet configurations. The results allowed
to establish scaling laws for the structural properties, in terms of the
nanowire perimeters. The results also showed that the surface states control
most of the electronic properties of the nanowires. Oxygen incorporation in the
nanowire surfaces passivated the surface-related electronic states, and the
resulting quantum properties and scaling laws were fully consistent with
electrons confined inside the nanowire. Additionally, oxygen incorporation in
the wire surfaces generated an unbalanced concentration of spin up and down
electrons, leading to magnetic states for the nanowires.",1204.2534v1
2015-12-01,Erosion behaviour of composite Al-Cr cathodes in cathodic arc plasmas in inert and reactive atmospheres,"Al$_{x}$Cr$_{1-x}$ composite cathodes with Al contents of x = 0.75, 0.5 and
0.25 were exposed to cathodic arc plasmas in Ar, N$_2$ and O$_2$ atmospheres
and their erosion behaviour was studied. Cross-sectional analysis of the
elemental distribution of the near-surface zone in the cathodes by scanning
electron microscopy revealed the formation of a modified layer for all cathodes
and atmospheres. Due to intermixing of Al and Cr in the heat-affected zone,
intermetallic Al-Cr phases formed as evidenced by X-ray diffraction analysis.
Cathode poisoning effects in the reactive N$_2$ and O$_2$ atmospheres were
non-uniform as a result of the applied magnetic field configuration. With the
exception of oxide islands on Al-rich cathodes, reactive layers were absent in
the circular erosion zone, while nitrides and oxides formed in the less eroded
centre region of the cathodes.",1512.00332v2
2018-10-24,Electronic landscape of the P-cluster of nitrogenase as revealed through many-electron quantum wavefunctions,"The electronic structure of the nitrogenase metal cofactors is central to
nitrogen fixation. However, the P-cluster and iron molybdenum cofactor, each
containing eight irons, have resisted detailed characterization of their
electronic properties. Through exhaustive many-electron wavefunction
simulations enabled by new theoretical methods, we report on the low-energy
electronic states of the P-cluster in three oxidation states. The energy scales
of orbital and spin excitations overlap, yielding a dense spectrum with
features we trace to the underlying atomic states and recouplings. The clusters
exist in superpositions of spin configurations with non-classical spin
correlations, complicating interpretation of magnetic spectroscopies, while the
charges are mostly localized from reorganization of the cluster and its
surroundings. Upon oxidation, the opening of the P-cluster significantly
increases the density of states, which is intriguing given its proposed role in
electron transfer. These results demonstrate that many-electron simulations
stand to provide new insights into the electronic structure of the nitrogenase
cofactors.",1810.10196v2
2018-10-24,A systematic study of the local minima in L(S)DA+U,"We have performed a systematic study of the emergence of meta-stable states
in density functional theory plus Hubbard U (DFT+U ) simulations of NiO, CoO,
FeO. Particular attention is given to the spin-polarization of the
exchange-correlation functional and the double counting term, and the role of
the spin-orbit coupling. The method of occupation matrix control is extended to
use constrained random density matrices to map out the local minima in the
total energy landscape. The extended scheme, random density matrix control, is
successfully benchmarked against UO2, one of the most investigated systems in
the field. When applied to the transition metal oxides it yields several meta-
stable states which are well-characterized by their local spin and orbital
moments. We find that the addition of spin-orbit coupling helps the simulations
to converge to the global high-spin energy minimum. The random density matrix
control scheme combined with LDA+U yields accurate magnetic moments for all the
studied AFM transition metal oxides.",1810.10393v1
2021-01-24,Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films,"High-entropy perovskite thin films, as the prototypical representative of the
high-entropy oxides with novel electrical and magnetic features, have recently
attracted great attention. Here, we reported the electronic structure and
charge transport properties of sol-gel-derived high-entropy
Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films annealed at various temperatures. By
means of X-ray photoelectron spectroscopy and absorption spectrum, it is found
that the conduction-band-minimum shifts downward and the valence-band-maximum
shifts upward with the increase of annealing temperature, leading to the
narrowed band gap. Electrical resistance measurements confirmed a
semiconductor-like behavior for all the thin films. Two charge transport
mechanisms, i.e., the thermally-activated transport mechanism at high
temperatures and the activation-less transport mechanism at low temperatures,
are identified by a self-consistent analysis method. These findings provide a
critical insight into the electronic band structure and charge transport
behavior of Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, validating it as a compelling
high-entropy oxide material for future electronic/energy-related technologies.",2101.09633v2
2017-09-11,Tuning electrical properties of silicon dioxide through intrinsic nano-patterns,"The inherent network of nanopores and voids in silicon dioxide (SiO2) is
generally undesirable for aspects of film quality, electrical insulation and
dielectric performance. However, if we view these pores as natural
nano-patterns embedded in a dielectric matrix then that opens up new vistas for
exploration. The nano-pattern platform can be used to tailor electrical,
optical, magnetic and mechanical properties of the carrier film. In this
article we report the tunable electrical properties of thermal SiO2 thin-film
achieved through utilization of the metal-nanopore network where the pores are
filled with metallic Titanium (Ti). Without any intentional chemical doping, we
have shown that the electrical resistivity of the oxide film can be controlled
through physical filling up of the intrinsic oxide nanopores with Ti. The
electrical resistance of the composite film remains constant even after
complete removal of the metal from the film surface except the pores. Careful
morphological, electrical and structural analyses are carried out to establish
that the presence of Ti in the nanopores play a crucial role in the observed
conductive nature of the nanoporous film.",1709.03259v1
2017-11-07,Epitaxial stabilization of pulsed laser deposited Sr$_{n+1}$Ir$_n$O$_{3n+1}$ thin films: entangled effect of growth dynamics and strain,"The subtle balance of electronic correlations, crystal field splitting and
spin--orbit coupling in layered Ir$^{4+}$ oxides can give rise to novel
electronic and magnetic phases. Experimental progress in this field relies on
the synthesis of epitaxial films of these oxides. However, the growth of
layered iridates with excellent structural quality is a great experimental
challenge. Here we selectively grow high quality single--phase films of
Sr$_2$IrO$_4$, Sr$_3$Ir$_2$O$_7$, and SrIrO$_3$ on various substrates from a
single Sr$_3$Ir$_2$O$_7$ target by tuning background oxygen pressure and
epitaxial strain. We demonstrate a complex interplay between growth dynamics
and strain during thin film deposition. Such interplay leads to the
stabilization of different phases in films grown on different substrates under
identical growth conditions, which cannot be explained by a simple kinetic
model. We further investigate the thermoelectric properties of the three phases
and propose that weak localization is responsible for the low temperature
activated resistivity observed in SrIrO$_3$ under compressive strain.",1711.02767v3
2018-12-21,Influence of spin-orbit and spin-Hall effects on the spin Seebeck current beyond linear response,"We study the spin transport theoretically in heterostructures consisting of a
ferromagnetic metallic thin film sandwiched between heavy-metal and oxide
layers. The spin current in the heavy metal layer is generated via the spin
Hall effect, while the oxide layer induces at the interface with the
ferromagnetic layer a spin-orbital coupling of the Rashba type. Impact of the
spin Hall effect and Rashba spin-orbit coupling on the spin Seebeck current is
explored with a particular emphasis on nonlinear effects. Technically, we
employ the Fokker-Planck approach and contrast the analytical expressions with
full numerical micromagnetic simulations. We show that when an external
magnetic field is aligned parallel (antiparallel) to the Rashba field, the
spin-orbit coupling enhances (reduces) the spin pumping current. In turn, the
spin Hall effect and the Dzyaloshinskii-Moriya interaction are shown to
increase the spin pumping current.",1812.09270v1
2019-01-28,X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate,"In the present study we compare a structure of a Langmuir film assembled from
magnetic iron oxide nanoparticles on water surface and a structure of the same
film after its transfer to a solid substrate by the Langmuir-Schaefer method.
In contrast to most of related studies, where different techniques are used to
characterize the films before and after the deposition, we use the same
combination of X-ray reflectometry and Grazing Incidence Small-Angle X-ray
scattering. In both cases -- on a liquid and on a solid substrate -- the film
was identified as a well-ordered monolayer of the nanoparticles laterally
organized in a two-dimensional hexagonal lattice. However parameters of the
lattice were found to be slightly different depending on the type of the
substrate. It is also demonstrated that Langmuir-Schaefer technique is the
right way for deposition of such kind of the particles on a solid substrate.",1901.09636v1
2019-02-09,Revealing the Hidden Heavy Fermi Liquid in CaRuO3,"The perovskite ruthenate has attracted considerable interest due to reports
of possible non-Fermi-liquid behavior and its proximity to a magnetic quantum
critical point, yet its ground state and electronic structure remain enigmatic.
Here we report the first measurements of the Fermi surface and quasiparticle
dispersion in CaRuO3 through a combination of oxide molecular beam epitaxy and
in situ angle-resolved photoemission spectroscopy. Our results reveal a complex
and anisotropic Fermi surface consisting of small electron pockets and straight
segments, consistent with the bulk orthorhombic crystal structure with large
octahedral rotations. We observe a strongly band-dependent mass
renormalization, with prominent heavy quasiparticle bands which lie close to
the Fermi energy and exhibit strong temperature dependence. These results are
consistent with a heavy Fermi liquid with a complex Fermiology and small
hybridization gaps near the Fermi energy. Our results provide a unified
framework for explaining previous experimental results on CaRuO3, such as its
unusual optical conductivity, and demonstrate the importance of octahedral
rotations in determining the quasiparticle band structure, and electron
correlations in complex transition metal oxides.",1902.03359v1
2019-03-01,Engineering Transport in Manganites by Tuning Local Non-Stoichiometry in Grain Boundaries,"Interface-dominated materials such as nanocrystalline thin films have emerged
as an enthralling class of materials able to engineer functional properties of
transition metal oxides widely used in energy and information technologies. In
particular, it has been proved that strain-induced defects in grain boundaries
of manganites deeply impact their functional properties by boosting their
oxygen mass transport while abating their electronic and magnetic order. In
this work, the origin of these dramatic changes is correlated for the first
time with strong modifications of the anionic and cationic composition in the
vicinity of strained grain boundary regions. We are also able to alter the
grain boundary composition by tuning the overall cationic content in the films,
which represents a new and powerful tool, beyond the classical space charge
layer effect, for engineering electronic and mass transport properties of metal
oxide thin films useful for a collection of relevant solid state devices.",1903.00225v1
2019-03-12,Magnetism tailored by mechanical strain engineering in PrVO$_3$ thin films,"Transition-metal oxides with an ABO$_3$ perovskite structure exhibit strongly
entangled structural and electronic degrees of freedom and thus, one expects to
unveil exotic phases and properties by acting on the lattice through various
external stimuli. Using the Jahn-Teller active praseodymium vanadate
Pr$^{3+}$V$^{3+}$O$_3$ compound as a model system, we show that PrVO$_3$ N\'eel
temperature T$_N$ can be raised by 40 K with respect to the bulk when grown as
thin films. Using advanced experimental techniques, this enhancement is
unambiguously ascribed to a tetragonality resulting from the epitaxial
compressive strain experienced by the films. First-principles simulations not
only confirm experimental results, but they also reveal that the strain
promotes an unprecedented orbital-ordering of the V$^{3+}$ d electrons,
strongly favouring antiferromagnetic interactions. These results show that an
accurate control of structural aspects is the key for unveiling unexpected
phases in oxides.",1903.04791v1
2020-08-24,Dependence of the Nonlinear-Optical Response of Materials on their Linear $ε$ and $μ$,"We investigate, theoretically and numerically, the dependence of a material's
nonlinear-optical response on the linear relative electric permittivity
$\epsilon$ and magnetic permeability $\mu$. The conversion efficiency of
low-order harmonic-generation processes, as well as the increase rate of
Kerr-effect nonlinear phase shift and nonlinear losses from two-photon
absorption (TPA), are seen to increase with decreasing $\epsilon$ and/or
increasing $\mu$. We also discuss the rationale and physical insights behind
this nonlinear response, particularly its enhancement in $\epsilon$-near-zero
(ENZ) media. This behavior is consistent with the experimental observation of
intriguingly high effective nonlinear refractive index in degenerate
semiconductors such as indium tin oxide [\textit{Alam et al., Science 352
(795), 2016}] (where the nonlinearity is attributed to a modification of the
energy distribution of conduction-band electrons due to laser-induced electron
heating) and aluminum zinc oxide [\textit{Caspani et al., Phys. Rev. Lett. 116
(233901), 2016}] at frequencies with vanishing real part of the linear
permittivity. Such strong nonlinear response can pave the way for a new
paradigm in nonlinear optics with much higher conversion efficiencies and
therefore better miniaturization capabilities and power requirements for
next-generation integrated nanophotonics.",2008.10512v1
2020-08-27,Particle-hole asymmetric lifetimes promoted by spin and orbital fluctuations in SrVO$_3$ monolayers,"The two-dimensional nature of engineered transition-metal ultra-thin oxide
films offers a large playground of yet to be fully understood physics. Here, we
study pristine SrVO$_3$ monolayers that have recently been predicted to display
a variety of magnetic and orbital orders. Above all ordering temperatures, we
find that the associated non-local fluctuations lead to a momentum
differentiation in the self-energy, particularly in the scattering rate. In the
one-band 2D Hubbard model, momentum-selectivity on the Fermi surface
(""$k=k_F$"") is known to lead to pseudogap physics. Here instead, in the
multi-orbital case, we evidence a differentiation between momenta on the
occupied (""$k<k_F$"") and the unoccupied side (""$k>k_F$"") of the Fermi surface.
Our work, based on the dynamical vertex approximation, complements the
understanding of spectral signatures of non-local fluctuations, calls to
(re)examine other ultra-thin oxide films and interfaces with methods beyond
dynamical mean-field theory, and may point to correlation-enhanced
thermoelectric effects.",2008.12227v2
2021-02-01,"Strong magneto-optical effects in ACr2O4 A=Fe, Co spinel oxides generated by tetrahedrally coordinated transition metal ions","Magneto-optical effects have been investigated over the infrared{visible
spectral range in ACr2O4 (A = Fe, Co) spinel oxides with non-collinear spin
orders in their ground states. We found large magneto-optical Kerr rotation and
ellipticity at the on-site d-d transitions of the A2+ ions located within the
charge gap. The magneto-optical Kerr rotation of 12 deg observed in CoCr2O4 is
unprecedentedly large among magnetic semiconductors and points towards the
uniqueness of tetrahedrally coordinated Co2+ ions in generating a strong
magneto-optical response. Criteria of strong magneto-optical effects emerging
at on-site d-d transitions of transition metal ions are discussed.",2102.00956v1
2021-03-03,Near-Room Temperature Ferromagnetic Insulating State in Highly Distorted LaCoO2.5 with CoO5 Square Pyramids,"Dedicated control of oxygen vacancies is an important route to
functionalizing complex oxide films. It is well-known that tensile strain
significantly lowers the oxygen vacancy formation energy, whereas compressive
strain plays a minor role. Thus, atomically reconstruction by extracting oxygen
from a compressive-strained film is challenging. Here we report an unexpected
LaCoO2.5 phase with a zigzag-like oxygen vacancy ordering through annealing a
compressive-strained LaCoO3 in vacuum. The synergetic tilt and distortion of
CoO5 square pyramids with large La and Co shifts are quantified using scanning
transmission electron microscopy. The large in-plane expansion of CoO5 square
pyramids weaken the crystal-field splitting and facilitated the ordered
high-spin state of Co2+, which produces an insulating ferromagnetic state with
a Curie temperature of ~284 K and a saturation magnetization of ~0.25
{\mu}B/Co. These results demonstrate that extracting targeted oxygen from a
compressive-strained oxide provides an opportunity for creating unexpected
crystal structures and novel functionalities.",2103.02100v1
2021-04-15,Magnetotransport of Functional Oxide Heterostructures Affected by Spin-Orbit Coupling: A Tale of Two-Dimensional Systems,"Oxide heterostructures allow for detailed studies of 2D electronic transport
phenomena. Herein, different facets of magnetotransport in selected
spin-orbit-coupled systems are analyzed and characterized by their single-band
and multiband behavior, respectively. Experimentally, temperature- and magnetic
field-dependent measurements in the single-band system BaPbO$_3$/SrTiO$_3$
reveal strong interplay of weak antilocalization (WAL) and electron-electron
interaction (EEI). Within a scheme which treats both, WAL and EEI, on an equal
footing a strong contribution of EEI at low temperatures is found which
suggests the emergence of a strongly correlated ground state. Furthermore, now
considering multiband effects as they appear, e.g., in the model system
LaAlO$_3$/SrTiO$_3$, theoretical investigations predict a huge impact of
filling on the topological Hall effect in systems with intermingled bands.
Already weak band coupling produces striking deviations from the well-known
Hall conductivity that are explainable in a fully quantum mechanical treatment
which builds upon the hybridization of intersecting Hofstadter bands.",2104.07270v2
2021-04-28,Visualizing quantum phenomena at complex oxide interfaces: an atomic view from scanning transmission electron microscopy,"Complex oxide interfaces have been one of the central focuses in condensed
matter physics and material science. Over the past decade, aberration corrected
scanning transmission electron microscopy and spectroscopy has proven to be
invaluable to visualize and understand the emerging quantum phenomena at an
interface. In this paper, we briefly review some recent progress in the
utilization of electron microscopy to probe interfaces. Specifically, we
discuss several important challenges for electron microscopy to advance our
understanding on interface phenomena, from the perspective of variable
temperature, magnetism, electron energy loss spectroscopy analysis, electronic
symmetry, and defects probing.",2104.13587v1
2021-04-28,From Slater to Mott physics: epitaxial engineering of electronic correlations in oxide interfaces,"Using spin-assisted ab-initio random structure searches, we explore an
exhaustive quantum phase diagram of archetypal interfaced Mott insulators, i.e.
lanthanum-iron and lanthanum-titanium oxides. In particular, we report that the
charge transfer induced by the interfacial electronic reconstruction stabilises
a high spin ferrous Fe2+ state. We provide a pathway to control the strength of
correlation in this electronic state by tuning the epitaxial strain, yielding a
manifold of quantum electronic phases, i.e. Mott-Hubbard, charge transfer and
Slater insulating states. Furthermore we report that the electronic
correlations are closely related to the structural oxygen octahedral rotations,
whose control is able to stabilise the low spin state of Fe2+ at low pressure
previously observed only under the extreme high pressure conditions in the
Earth's lower mantle. Thus we provide avenues for magnetic switching via THz
radiations which have crucial implications for next generation of spintronics
technologies.",2104.13723v1
2021-06-25,"Interplay between polarization, strain and defect-pairs in Fe-doped SrMnO$_{3-δ}$","Defect chemistry, strain, and structural, magnetic and electronic degrees of
freedom constitute a rich space for the design of functional properties in
transition metal oxides. Here, we show that it is possible to engineer polarity
and ferroelectricity in non-polar perovskite oxides via polar defect pairs
formed by anion vacancies coupled to substitutional cations. We use a
self-consistent site-dependent DFT+$U$ approach that accounts for local
structural and chemical changes upon defect creation and which is crucial to
reconcile predictions with the available experimental data. Our results for
Fe-doped oxygen-deficient SrMnO$_3$ show that substitutional Fe and oxygen
vacancies can promote polarity due to an off-center displacement of the defect
charge resulting in a net electric dipole moment, which polarizes the lattice
in the defect neighborhood. The formation of these defects and the resulting
polarization can be tuned by epitaxial strain, resulting in enhanced
polarization also for strain values lower than the ones necessary to induce a
polar phase transition in undoped SrMnO$_3$. For high enough defect
concentrations, these defect dipoles couple in a parallel fashion, thus
enabling defect- and strain-based engineering of ferroelectricity in SrMnO$_3$.",2106.13854v1
2021-06-28,Optical and excitonic properties of transition metal oxide perovskites by the Bethe-Salpeter equation,"We present a systematic investigation of the role and importance of excitonic
effects on the optical properties of transitions metal oxide perovskites. A
representative set of fourteen compounds has been selected, including 3$d$
(SrTiO$_3$, LaScO$_3$, LaTiO$_3$, LaVO$_3$, LaCrO$_3$, LaMnO$_3$, LaFeO$_3$ and
SrMnO$_3$), 4$d$ (SrZrO$_3$, SrTcO$_3$ and Ca$_2$RuO$_4$) and 5$d$ (SrHfO$_3$,
KTaO$_3$ and NaOsO$_3$) perovskites, covering a band gap ranging from 0.1 eV to
6.1 eV and exhibiting different electronic, structural and magnetic properties.
Optical conductivities and optical transitions including electron-hole
interactions are calculated through the solution of the Bethe-Salpeter equation
(BSE) with quasi-particle energies evaluated by single-shot $G_0W_0$
approximation. The exciton binding energies are computed by means of a
model-BSE (mBSE), carefully benchmarked against the full BSE method, in order
to obtain well-converged results in terms of k-point sampling. The predicted
results are compared with available measured data, with an overall satisfactory
agreement between theory and experiment.",2106.14632v1
2021-08-01,Cobalt in strontium titanate as a new off-center magnetic impurity,"The local structure and oxidation state of the cobalt impurity in SrTiO$_3$
is studied by X-ray absorption fine structure (XAFS) spectroscopy. The
synthesis conditions, under which cobalt predominantly (up to 76%) substitutes
the atoms at the $A$ site of the perovskite structure, is found for
SrTiO$_3$(Co) samples. By varying the synthesis conditions, it is possible to
appreciably change the ratio between the concentrations of cobalt atoms
incorporated into the $A$ and $B$ sites. It is established that the oxidation
state of cobalt is +2 at the $A$ site and +3 at the $B$ site. It is revealed
that the Co impurity at the $A$ site is off-center, and its displacement from
the lattice site is $\sim$1.0 {\AA}. First-principles calculations show that an
isolated Co$^{3+}$ ion at the $B$ site is diamagnetic, whereas the Co$^{2+}$
ion at the $A$ site is in a high-spin state ($S = 3/2$).",2108.00481v1
2021-09-22,"Design, Fabrication, Characterization and Reliability Study of CMOS-MEMS Lorentz-Force Magnetometers","This article presents several design techniques to fabricate
micro-electro-mechanical systems (MEMS) using standard complementary
metal-oxide semiconductor (CMOS) processes. They were applied to fabricate high
yield CMOS-MEMS shielded Lorentz-force magnetometers (LFM). The multilayered
metals and oxides of the back-end-of-line (BEOL), normally used for electronic
routing, comprise the structural part of the MEMS. The most important
fabrication challenges, modeling approaches and design solutions are discussed.
Equations that predict the Q factor, sensitivity, Brownian noise and resonant
frequency as a function of temperature, gas pressure and design parameters are
presented and validated in characterization tests. A number of the fabricated
magnetometers were packaged into Quad Flat No-leads (QFN) packages. We show
this process can achieve yields above 95 % when the proper design techniques
are adopted. Despite CMOS not being a process for MEMS manufacturing, estimated
performance (sensitivity and noise level) is similar or superior to current
commercial magnetometers and others built with MEMS processes. Additionally,
typical offsets present in Lorentz-force magnetometers were prevented with a
shielding electrode, whose efficiency is quantified. Finally, several
reliability test results are presented, which demonstrate the robustness
against high temperatures, magnetic fields and acceleration shocks.",2109.10980v1
2022-02-03,A Novel Single-Mode Microwave Assisted Synthesis of Metal Oxide as Visible-light Photocatalyst,"Visible-light photocatalyst titanium dioxide (TiO2) was successfully prepared
via a novel and facile single-mode microwave assisted synthesis process. In
this one-step synthesis, Ti as target material selectively oxides in magnetic
field throughout rapid heating, whose process requires less energy consumption
and short time. In obtained TiO2, self-doping of Ti3+ was confirmed, which
makes TiO2 performed sufficient light absorption in visible region with
wavelength above 400 nm. Such Ti3+ self-doped TiO2 exhibits much narrower
optical bandgap (2.14 eV) to compare with stoichiometric TiO2 (3.0-3.2 eV). The
synthesized TiO2 also shows superior photocatalytic activity to commercially
available TiO2 towards the degradation of Rhodamine B under visible light
irradiation.",2202.01360v1
2022-02-04,Engineering multifunctionality at oxide interfaces by multimode coupling,"We employed first-principles density functional theory calculations guided by
group-theoretical analysis and demonstrated the control of
insulator-metal-insulator transition, polarization and two sublattice
magnetization in (LaFeO$_3$)$_1$/(CaFeO$_3$)$_1$ superlattice via. multi
structural mode coupling i.e., 'multimode coupling'. We have discovered a polar
A-type charge disproportionation mode, Q$_{ACD}$ (analogous to the A-type
antiferromagnetic ordering), and found that it couples with the trilinear
coupling, $Q_{Tri}$ mode (common in $Pnma$ perovskite oxides and involves three
structural modes), and lowers the symmetry further. By tuning the strength of
the coupling between the participating modes, the polar metallic phase, polar
zero bandgap semiconducting, and polar insulating phases can be obtained. Here,
$Q_{Tri}$ switches the polarization direction, whereas, Q$_{ACD}$ can trigger
insulator-metal-insulator transition along with the polarization switching. The
mechanism is true for any transition metal superlattices constituted with
$Pnma$ building blocks and with partially filled $e_g$ or $t_{2g}$ electron(s)
at the transition metal sites.",2202.02027v1
2022-09-04,Spin-Polarisation measurement using NbN-Insulator-Ferromagnet Tunnel Junction with oxidized barrier,"We report a two-step process for the fabrication of
superconductor-insulator-normal metal tunnel junctions using NbN as the
superconducting electrode and its surface oxide as the insulating tunnel
barrier, and investigate its efficacy in measuring spin-polarisation of
ferromagnets using the Meservey-Tedrow technique. We observe that for NbN film
thickness below 10 nm, under the application of parallel magnetic field, the
superconducting density of states show clear ""Zeeman"" splitting into spin-up
and spin-down sub-bands. Tunnelling measurements on devices where ferromagnetic
Co is used as the normal electrode shows that these devices can be used to
reliably measure spin polarisation of a ferromagnet at temperatures up to 1.6
K. The simplicity of our fabrication process, and the ability to perform
spin-polarisation measurements at 4He temperatures makes NbN a very attractive
candidate for spin polarisation measurements.",2209.01626v1
2022-10-18,Strain sensitive flexible magnetoelectric ceramic nanocomposites,"Advanced flexible electronics and soft robotics require the development and
implementation of flexible functional materials. Magnetoelectric (ME) oxide
materials can convert magnetic input into electric output and vice versa,
making them excellent candidates for advanced sensing, actuating, data storage,
and communication. However, their application has been limited to rigid devices
due to their brittle nature. Here, we report flexible ME oxide composite
(BaTiO3/CoFe2O4) thin film nanostructures that can be transferred onto a
stretchable substrate such as polydimethylsiloxane (PDMS). In contrast to rigid
bulk counterparts, these ceramic nanostructures display a flexible behavior and
exhibit reversibly tunable ME coupling via mechanical stretching. We believe
our study can open up new avenues for integrating ceramic ME composites into
flexible electronics and soft robotic devices.",2210.09679v1
2022-10-26,Oxygen vacancies at the origin of pinned moments in oxide interfaces: the example of tetragonal CuO/SrTiO$_3$,"Obtaining an accurate theoretical description of the emergent phenomena in
oxide heterostructures is a major challenge. Recently, intriguing paramagnetic
spin and pinned orbital moments have been discovered by x-ray magnetic circular
dichro\""ism measurements at the Cu $L_{2,3}$-edge of a tetragonal CuO/SrTiO$_3$
heterostructure. Using first principles calculations, we propose a scenario
that explains both types of moments, based on the formation of oxygen vacancies
in the TiO$_2$ interface layer. We show the emergence of a paramagnetic 2D
electron gas hosted in the interface CuO layer. It is invisible at the Ti
$L_{2,3}$-edge since the valence of the Ti atoms remains unchanged. Strong
structural distortions breaking both the local and global fourfold rotation
$C_4$ symmetries at the interface lead to the in-plane pinning of the Cu
orbital moment close to the vacancy. Our results, and in particular the pinning
of the orbital moment, may have implications for other systems, especially
monoxide/dioxide interfaces with similar metal-oxygen bond length and weak
spin-orbit coupling.",2210.15084v1
2023-01-04,Atomic and Electronic Structures of Correlated SrRuO3/SrTiO3 Superlattices,"Atomic-scale precision epitaxy of perovskite oxide superlattices provides
unique opportunities for controlling the correlated electronic structures,
activating effective control knobs for intriguing functionalities including
electromagnetic, thermoelectric, and electrocatalytic behaviors. In this study,
we investigated the close interplay between the atomic and electronic
structures of correlated superlattices synthesized by atomic-scale precision
epitaxy. In particular, we employ superlattices composed of correlated magnetic
SrRuO3 (SRO) and quantum paraelectric SrTiO3 (STO) layers. In those
superlattices, RuO6 octahedral distortion is systematically controlled from 167
to 175 degrees depending on the thickness of the STO layers, also affecting the
TiO6 octahedral distortion within the STO layer. Customized octahedral
distortion within SRO/STO superlattices in turn modifies the electronic
structures of both the Ti and Ru compounds, observed by X-ray absorption
spectroscopy. Our results identify the close correlation between atomic lattice
and electronic structures enabled by the facile controllability of atomic-scale
epitaxy, which would be useful for designing future correlated oxide devices.",2301.01406v1
2023-04-24,Electronic Correlation-driven Exotic Quantum Phase Transitions in Infinite-layer Manganese Oxide,"Despite the intensive interest in copper- and nickel-based superconductivity
in infinite-layer structures, the physical properties of many other
infinite-layer transition-metal oxides remain largely unknown. Here we unveil,
by the first-principles calculations, the electronic correlation-driven quantum
phase transitions in infinite-layer SrMnO2, where spin and charge orders are
strongly interwoven. At weak electronic correlation region, SrMnO2 is a
ferromagnetic metal with anisotropic spin transportation, as a promising spin
valve under room-temperature. At middle electronic correlation region, a
structural transition accompanied by charge/bond disproportion occurs as a
consequence of Fermi surface nesting, resulting in a ferromagnetic insulator
with reduced Curie temperature. At strong electronic correlation region,
another structural transition occurs that drives the system into degenerately
antiferromagnetic insulators with tunable magnetic order by piezoelectricity, a
new type of multiferroics. Therefore, infinite-layer SrMnO2 is possibly a
unique system on the quantum critical point, where electronic correlation can
induce noticeable Fermi surface evolutions and small perturbations can realize
remarkable quantum phase transitions.",2304.11777v1
2023-05-20,Magnetostriction-Driven Muon Localization in an Antiferromagnetic Oxide,"Magnetostriction drives a rhombohedral distortion in the cubic rock salt
antiferromagnet MnO at the N\'eel temperature $T_{N}=118$ K. As an unexpected
consequence we show that this distortion acts to localize the site of an
implanted muon due to the accompanying redistribution of electron density. This
lifts the degeneracy between equivalent sites, resulting in a single observed
muon precession frequency. Above $T_{N}$, the muon instead becomes delocalized
around a network of equivalent sites. Our first-principles simulations based on
Hubbard-corrected density-functional theory and molecular dynamics are
consistent with our experimental data and help to resolve a long-standing
puzzle regarding muon data on MnO, as well as having wider applicability to
other magnetic oxides.",2305.12237v3
2023-05-29,Zeeman dependence of the quasiparticle scattering rate and ARPES in copper oxides and related materials,"Within a strongly interacting Fermi liquid framework, we calculate the
effects of the Zeeman energy $\omega_H$ for a finite magnetic field, in a
metallic system with a van Hove peak in the density of states, located close to
and below the Fermi surface. We find that the chemical potential increases with
the square of $\omega_H$. We obtain a characteristic quasiparticle scattering
rate linear in the maximum of $\omega_H$ and temperature, both in the normal
and the d-wave superconducting state. We predict that ARPES experiments in
copper oxides, and related compounds, should be able to elucidate this behavior
of the scattering rate, and in particular, the difference between spin up and
down electrons.",2305.18083v2
2023-08-16,Dynamic motion of polar skyrmions in oxide heterostructures,"Polar skyrmions have been widely investigated in oxide heterostructure
recently, due to their exotic properties and intriguing physical insights.
Meanwhile, so far, the external field-driven motion of the polar skyrmion, akin
to the magnetic counterpart, has yet to be discovered. Here, using phase-field
simulations, we demonstrate the dynamic motion of the polar skyrmions with
integrated external thermal, electrical, and mechanical stimuli. The external
heating reduces the spontaneous polarization hence the skyrmion motion barrier,
while the skyrmions shrink under the electric field, which could weaken the
lattice pinning and interactions between the skyrmions. The mechanical force
transforms the skyrmions into c-domain in the vicinity of the indenter center
under the electric field, providing the space and driving force needed for the
skyrmions to move. This study confirmed that the skyrmions are quasi-particles
that can move collectively, while also providing concrete guidance for the
further design of polar skyrmion-based electronic devices.",2308.08219v1
2023-10-09,Pressure-Driven Transitions in La2CoTiO6: Antiferromagnetic Insulator to Nonmagnetic Metal via Antiferromagnetic Metal in a Double Perovskite Oxide,"La$_2$CoTiO$6$ (LCTO), a double perovskite oxide, transitions from an
antiferromagnetic insulator (AFM-I) to an antiferromagnetic metal (AFM-M) and
eventually to a nonmagnetic metal (NM-M) under external hydrostatic pressure.
This pressure-driven sequence is accompanied by a shift in spin states, with a
remarkable spin-state transition from high-spin (HS) to low-spin (LS) at $\sim$
42 GPa. Monoclinic distortion induced by pressure plays a key role in this
transition. Even under ambient conditions, the LS state persists in a highly
symmetric theoretical structure, highlighting the role of distortion in
facilitating the HS to LS transition. In the LS state, LCTO becomes metallic,
even with a strong local correlation (Hubbard $U$) on Co. This transition is
elucidated through an energy level diagram, revealing a substantial
modification in the crystal field splitting between Co-$t{2g}$ and -$e_g$
levels due to strong Co-$d$ and O-$p$ orbital hybridization. Beyond 130 GPa,
the system enters the NM-M phase, completely quenching the magnetic moment on
Co.",2310.05523v1
2022-06-17,The Open Catalyst 2022 (OC22) Dataset and Challenges for Oxide Electrocatalysts,"The development of machine learning models for electrocatalysts requires a
broad set of training data to enable their use across a wide variety of
materials. One class of materials that currently lacks sufficient training data
is oxides, which are critical for the development of OER catalysts. To address
this, we developed the OC22 dataset, consisting of 62,331 DFT relaxations
(~9,854,504 single point calculations) across a range of oxide materials,
coverages, and adsorbates. We define generalized total energy tasks that enable
property prediction beyond adsorption energies; we test baseline performance of
several graph neural networks; and we provide pre-defined dataset splits to
establish clear benchmarks for future efforts. In the most general task,
GemNet-OC sees a ~36% improvement in energy predictions when combining the
chemically dissimilar OC20 and OC22 datasets via fine-tuning. Similarly, we
achieved a ~19% improvement in total energy predictions on OC20 and a ~9%
improvement in force predictions in OC22 when using joint training. We
demonstrate the practical utility of a top performing model by capturing
literature adsorption energies and important OER scaling relationships. We
expect OC22 to provide an important benchmark for models seeking to incorporate
intricate long-range electrostatic and magnetic interactions in oxide surfaces.
Dataset and baseline models are open sourced, and a public leaderboard is
available to encourage continued community developments on the total energy
tasks and data.",2206.08917v3
2020-02-13,"Multipolar magnetism in d-orbital systems: Crystal field levels, octupolar order, and orbital loop currents","Quantum magnets with spin $J=2$, which arise in spin-orbit coupled Mott
insulators, can potentially display multipolar orders. We carry out an exact
diagonalization study of a simple octahedral crystal field Hamiltonian for two
electrons, incorporating spin-orbit coupling (SOC) and interactions, finding
that either explicitly including the $e_g$ orbitals, or going beyond the
rotationally invariant Coulomb interaction within the $t_{2g}$ sector, causes a
degeneracy breaking of the $J\!=\!2$ level degeneracy. This can lead to a
low-lying non-Kramers doublet carrying quadrupolar and octupolar moments and an
excited triplet which supports magnetic dipole moments, bolstering our previous
phenomenological proposal for the stabilization of ferro-octupolar order in
heavy transition metal oxides. We show that the spontaneous time-reversal
symmetry breaking due to ferro-octupolar ordering within the non-Kramers
doublet leads to electronic orbital loop currents. The resulting internal
magnetic fields can potentially explain the small fields inferred from
muon-spin relaxation ($\mu$SR) experiments on cubic $5d^2$ osmate double
perovskites Ba$_2$ZnOsO$_6$, Ba$_2$CaOsO$_6$, and Ba$_2$MgOsO$_6$, which were
previously attributed to weak dipolar magnetism. We make further predictions
for oxygen NMR experiments on these materials. We also study the reversed level
scheme, where the $J\!=\!2$ multiplet splits into a low-lying magnetic triplet
and excited non-Kramers doublet, presenting single-ion results for the magnetic
susceptibility in this case, and pointing out its possible relevance for the
rhenate Ba$_2$YReO$_6$. Our work highlights the intimate connection between the
physics of heavy transition metal oxides and that of $f$-electron based heavy
fermion compounds.",2002.05737v2
2022-02-16,"Spin Seebeck effect in iron oxide thin films: Effects of phase transition, phase coexistence, and surface magnetism","Understanding impacts of phase transition, phase coexistence, and surface
magnetism on the longitudinal spin Seebeck effect (LSSE) in a magnetic system
is essential to manipulate the spin to charge current conversion efficiency for
spincaloritronic applications. We aim to elucidate these effects by performing
a comprehensive study of the temperature dependence of LSSE in biphase iron
oxide (BPIO = alpha-Fe2O3 + Fe3O4) thin films grown on Si (100) and Al2O3 (111)
substrates. A combination of temperature-dependent anomalous Nernst effect
(ANE) and electrical resistivity measurements show that the contribution of ANE
from the BPIO layer is negligible compared to the intrinsic LSSE in the
Si/BPIO/Pt heterostructure even at room temperature. Below the Verwey
transition of the Fe3O4 phase, the total signal across BPIO/Pt is dominated by
the LSSE. Noticeable changes in the intrinsic LSSE signal for both Si/BPIO/Pt
and Al2O3/BPIO/Pt heterostructures around the Verwey transition of the Fe3O4
phase and the antiferromagnetic (AFM) Morin transition of the alpha-Fe2O3 phase
are observed. The LSSE signal for Si/BPIO/Pt is found to be almost two times
greater than that for Al2O3/BPIO/Pt, an opposite trend is observed for the
saturation magnetization though. Magnetic force microscopy reveals the higher
density of surface magnetic moments of the Si/BPIO film compared to the
Al2O3/BPIO film, which underscores a dominant role of interfacial magnetism on
the LSSE signal and thereby explains the larger LSSE for Si/BPIO/Pt.",2202.07910v1
2018-12-11,First-Principles Study of Localised and Delocalised Electronic States in Crystallographic Shear Phases of Niobium Oxide,"Crystallographic shear phases of niobium oxide form an interesting family of
compounds that have received attention both for their unusual electronic and
magnetic properties, as well as their performance as intercalation electrode
materials for lithium-ion batteries. Here, we present a first-principles
density-functional theory study of the electronic structure and magnetism of
H-Nb$_2$O$_5$, Nb$_{25}$O$_{62}$, Nb$_{47}$O$_{116}$, Nb$_{22}$O$_{54}$, and
Nb$_{12}$O$_{29}$. These compounds feature blocks of niobium-oxygen octahedra
as structural units, and we show that this block structure leads to a
coexistence of flat and dispersive energy bands, corresponding to localised and
delocalised electronic states. Electrons localise in orbitals spanning multiple
niobium sites in the plane of the blocks. Localised and delocalised electronic
states are both effectively one-dimensional and are partitioned between
different types of niobium sites. Flat bands associated with localised
electrons are present even at the GGA level, but a correct description of the
localisation requires the use of GGA+U or hybrid functionals. We discuss the
experimentally observed electrical and magnetic properties of niobium suboxides
in light of our results, and argue that their behaviour is similar to that of
$n$-doped semiconductors, but with a limited capacity for localised electrons.
When a threshold of one electron per block is exceeded, metallic electrons are
added to existing localised electrons. We propose that this behaviour of shear
phases is general for any type of $n$-doping, and should transfer to doping by
alkali metal (lithium) ions during operation of niobium oxide-based battery
electrodes. Future directions for theory and experiment on mixed-metal shear
phases are suggested.",1812.04632v2
2021-11-16,DFT+U+J with linear response parameters predicts non-magnetic oxide band gaps with hybrid-functional accuracy,"First-principles Hubbard-corrected approximate density-functional theory
(DFT+U) is a low-cost, potentially high throughput method of simulating
materials, but it has been hampered by empiricism and inconsistent band-gap
correction in transition-metal oxides. DFT+U property prediction of
non-magnetic systems such as d0 and d10 transition-metal oxides is typically
faced with excessively large calculated Hubbard U values, and with difficulty
in obtaining acceptable band-gaps and lattice volumes. Meanwhile, Hund's
exchange coupling J is an important but often neglected component of DFT+U, and
the J parameter has proven challenging to directly calculate by means of linear
response. In this work, we provide a revised formula for computing Hund's J
using established self-consistent field DFT+U codes. For non-magnetic systems,
we introduce a non-approximate technique for calculating U and J simultaneously
in such codes, at no additional cost. Using unmodified Quantum ESPRESSO, we
assess the resulting values using two different DFT+U functionals incorporating
J, namely the widely used DFT+(U-J) and the readily available DFT+U+J. We
assess a test set comprising TiO2, ZrO2, HfO2, Cu2O and ZnO, and apply the
corrections both to metal and oxygen centered pseudoatomic subspaces. Starting
from the PBE functional, we find that DFT+(U-J) is significantly out-performed
in band-gap accuracy by DFT+U+J, the RMS band-gap error of which matches that
of the hybrid functional HSE06. ZnO, a long-standing challenge case for DFT+U,
is addressed by means of Zn 4s instead of Zn 3d correction, in which case the
first-principles DFT+U+J band-gap error is half of that reported for HSE06.",2111.08487v1
2022-07-28,Symmetry protected 1D chains in mixed-valence iron oxides,"During the last decade of high-pressure research a whole new series of iron
oxides was discovered, like Fe$_4$O$_5$, Fe$_5$O$_6$, Fe$_7$O$_9$ etc.,
featuring closely related structures with arrays of one-dimensional (1D) chains
of trigonal prisms embedded between slabs of octahedra. Here, we develop a
unified approach to the series based on a specific crystallographic generation
mechanism which predicts the structures of these oxides and naturally
classifies them in terms of the slab cycle. When including magnetic
interactions, we show that the 1D chains have a symmetry protection against
magnetic perturbations from the iron ions in the slabs, and that the slab size
determines the type of magnetic order, which is either ferromagnetic or
antiferromagnetic. Dynamical mean-field theory calculations reveal the
orbitally selective Mott state of the Fe ions and tendency of conductivity to
low-dimensional behavior with particular enhancement along the 1D chains.
Across the series, the decoupling of the chains increases, and so with the
inherent charge ordering of the slabs, these structures have the potential to
allow experimental realization of the model system of coupled 1D wires. We
point out the possibility to stabilize these compounds in the thin-film form
that, together with a wide range of possible ionic substitutions and fact that
these compounds are recoverable at ambient pressure, makes them a very
promising platform to engineer physical systems with interesting
magnetotransport phenomena, as corroborated by the recent discovery of quantum
Hall effect in ZrTe$_5$.",2207.14111v1
2006-08-11,Magnetic Excitations and their energy change available to Superconducting Condensation in Optimally Doped YBa$_2$Cu$_3$O$_{6.95}$,"Understanding the magnetic excitations in high-transition temperature
(high-$T_c$) copper oxides is important because they may mediate the electron
pairing for superconductivity. By determining the wavevector ({\bf Q}) and
energy ($\hbar\omega$) dependence of the magnetic excitations, one can
calculate the change in the exchange energy available to the superconducting
condensation energy. For the high-$T_c$ superconductor YBa$_2$Cu$_3$O$_{6+x}$,
the most prominent feature in the magnetic excitations is the resonance.
Although the resonance has been suggested to contribute a major part of the
superconducting condensation, the accuracy of such an estimation has been in
doubt because the resonance is only a small portion of the total magnetic
scattering. Here we report an extensive mapping of magnetic excitations for
YBa$_2$Cu$_3$O$_{6.95}$ ($T_c\approx 93$ K). Using the absolute intensity
measurements of the full spectra, we estimate the change in the magnetic
exchange energy between the normal and superconducting states and find it to be
about 15 times larger than the superconducting condensation energy. Our results
thus indicate that the change in the magnetic exchange energy is large enough
to provide the driving force for high-$T_c$ superconductivity in
YBa$_2$Cu$_3$O$_{6.95}$.",0608280v1
2006-12-07,"Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N - relation between structural, electronic, and magnetic properties","We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and
(Ga,Fe)N layers on c-sapphire substrates and their thorough characterization
via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy
(TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS),
secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect,
electron-paramagnetic resonance (EPR), and magnetometry employing a
superconducting quantum interference device (SQUID). A combination of TEM and
EDS reveals the presence of coherent nanocrystals presumably FexN with the
composition and lattice parameter imposed by the host. From both TEM and SIMS
studies, it is stated that the density of nanocrystals and, thus the Fe
concentration increases towards the surface. In layers with iron content x<0.4%
the presence of ferromagnetic signatures, such as magnetization hysteresis and
spontaneous magnetization, have been detected. We link the presence of
ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced
by TEM and EDS studies. This interpretation is supported by magnetization
measurements after cooling in- and without an external magnetic field, pointing
to superparamagnetic properties of the system. It is argued that the high
temperature ferromagnetic response due to spinodal decomposition into regions
with small and large concentration of the magnetic component is a generic
property of diluted magnetic semiconductors and diluted magnetic oxides showing
high apparent Curie temperature.",0612200v2
2011-06-24,Magnetic dichroism in angular-resolved hard X-ray photoelectron spectroscopy from buried layers,"This work reports the measurement of magnetic dichroism in angular-resolved
photoemission from in-plane magnetized buried thin films. The high bulk
sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination
with circularly polarized radiation enables the investigation of the magnetic
properties of buried layers. HAXPES experiments with an excitation energy of 8
keV were performed on exchange-biased magnetic layers covered by thin oxide
films. Two types of structures were investigated with the IrMn exchange-biasing
layer either above or below the ferromagnetic layer: one with a CoFe layer on
top and another with a Co$_2$FeAl layer buried beneath the IrMn layer. A
pronounced magnetic dichroism is found in the Co and Fe $2p$ states of both
materials. The localization of the magnetic moments at the Fe site conditioning
the peculiar characteristics of the Co$_2$FeAl Heusler compound, predicted to
be a half-metallic ferromagnet, is revealed from the magnetic dichroism
detected in the Fe $2p$ states.",1106.4976v1
2012-06-29,Laser spectroscopy of finite size and covering effects in magnetite nanoparticles,"The experiments on the impact of the size of magnetite clusters on various
magnetic properties (magnetic moment, Curie temperature, blocking temperature
etc.) have been carried out. The methods of magnetic separation, centrifuging
of water suspensions of biocompatible iron oxide nanoparticles (NPs) allow
producing fractions with diameter of nanoparticles in the range of 4{\div}22
nm. The size of NPs are controlled by the methods of dynamic light scattering
(DLS), transmission electron microscopy (TEM) and atomic force microscopy
(AFM). For the first time the DLS method is applied in real time to control the
size during the process of the separation of the NPs in aqueous suspensions.
The changes of the size of NPs cause a shift in the Curie temperature and in
the changes in the specific magnetic properties of the iron NPs. The
experimental data is interpreted on the basis of Monte Carlo simulations for
the classical Heisenberg model with different bulk and surface magnetic
moments. It is demonstrated experimentally and by theoretical modeling that
magnetic properties of magnetite NPs are determined not only by their sizes,
but also by the their surface spin states, while both growing and falling
dependences of the magnetic moment (per Fe3O4 formula unit) being possible,
depending on the number of magnetic atoms in the nanoparticle. Both NPs clean
and covered with a bioresorbable layer clusters have been investigated.",1206.6985v5
2014-08-12,Magnetic properties of geometrically frustrated SrGd2O4,"A study of the magnetic properties of the frustrated rare earth oxide SrGd2O4
has been completed using bulk property measurements of magnetization,
susceptibility and specific heat on single crystal samples. Two zero-field
phase transitions have been identified at 2.73 and 0.48 K. For the field, H,
applied along the a and b axes, a single boundary is identified that delineates
the transition from a low field, low temperature magnetically ordered regime to
a high field, high temperature paramagnetic phase. Several field-induced
transitions, however, have been observed with H || c. The measurements have
been used to map out the magnetic phase diagram of SrGd2O4, suggesting that it
is a complex system with several competing magnetic interactions. The
low-temperature magnetic behavior of SrGd2O4 is very different compared to the
other SrLn2O4 (Ln = Lanthanide) compounds, even though all of the SrLn2O4
compounds are isostructural, with the magnetic ions forming a low-dimensional
lattice of zigzag chains that run along the c axis. The differences are likely
to be due to the fact that in the ground state Gd3+ has zero orbital angular
momentum and therefore the spin-orbit interactions, which are crucial for other
SrLn2O4 compounds, can largely be neglected. Instead, given the relatively
short Gd3+-Gd3+ distances in SrGd2O4, dipolar interactions must be taken into
account for this antiferromagnet alongside the Heisenberg exchange terms.",1408.2771v1
2015-01-13,Strain-Induced Extrinsic High-Temperature Ferromagnetism in the Fe-Doped Hexagonal Barium Titanate,"Diluted magnetic semiconductors possessing intrinsic static magnetism at high
temperatures represent a promising class of multifunctional materials with high
application potential in spintronics and magneto-optics. In the hexagonal
Fe-doped diluted magnetic oxide, 6H-BaTiO$_{3-\delta}$, room-temperature
ferromagnetism has been previously reported. Ferromagnetism is broadly accepted
as an intrinsic property of this material, despite its unusual dependence on
doping concentration and processing conditions. However, the here reported
combination of bulk magnetization and complementary in-depth local-probe
electron spin resonance and muon spin relaxation measurements, challenges this
conjecture. While a ferromagnetic transition occurs around 700 K, it does so
only in additionally annealed samples and is accompanied by an extremely small
average value of the ordered magnetic moment. Furthermore, several additional
magnetic instabilities are detected at lower temperatures. These coincide with
electronic instabilities of the Fe-doped 3C-BaTiO$_{3-\delta}$ pseudocubic
polymorph. Moreover, the distribution of iron dopants with frozen magnetic
moments is found to be non-uniform. Our results demonstrate that the intricate
static magnetism of the hexagonal phase is not intrinsic, but rather stems from
sparse strain-induced pseudocubic regions. We point out the vital role of
internal strain in establishing defect ferromagnetism in systems with competing
structural phases.",1501.02938v1
2015-07-07,Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides La$_{2-x}$Sr$_x$CoO$_4$,"The magnetic excitations in the cuprate superconductors might be essential
for an understanding of high-temperature superconductivity. In these cuprate
superconductors the magnetic excitation spectrum resembles an hour-glass and
certain resonant magnetic excitations within are believed to be connected to
the pairing mechanism which is corroborated by the observation of a universal
linear scaling of superconducting gap and magnetic resonance energy. So far,
charge stripes are widely believed to be involved in the physics of hour-glass
spectra. Here we study an isostructural cobaltate that also exhibits an
hour-glass magnetic spectrum. Instead of the expected charge stripe order we
observe nano phase separation and unravel a microscopically split origin of
hour-glass spectra on the nano scale pointing to a connection between the
magnetic resonance peak and the spin gap originating in islands of the
antiferromagnetic parent insulator. Our findings open new ways to theories of
magnetic excitations and superconductivity in cuprate superconductors.",1507.01783v1
2019-05-25,Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets,"We investigate how different chemical environment influences magnetic
properties of terbium(III) (Tb)-based single-molecule magnets (SMMs), using
first-principles relativistic multireference methods. Recent experiments showed
that Tb-based SMMs can have exceptionally large magnetic anisotropy and that
they can be used for experimental realization of quantum information
applications, with a judicious choice of chemical environment. Here, we perform
complete active space self-consistent field (CASSCF) calculations including
relativistic spin-orbit interaction (SOI) for representative Tb-based SMMs such
as TbPc$_2$ and TbPcNc in three charge states. We calculate low-energy
electronic structure from which we compute the Tb crystal-field parameters and
construct an effective pseudospin Hamiltonian. Our calculations show that
ligand type and fine points of molecular geometry do not affect the zero-field
splitting, while the latter varies weakly with oxidation number. On the other
hand, higher-energy levels have a strong dependence on all these
characteristics. For neutral TbPc$_2$ and TbPcNc molecules, the Tb magnetic
moment and the ligand spin are parallel to each other and the coupling strength
between them does not depend much on ligand type and details of atomic
structure. However, ligand distortion and molecular symmetry play a crucial
role in transverse crystal-field parameters which lead to tunnel splitting. The
tunnel splitting induces quantum tunneling of magnetization by itself or by
combining with other processes. Our results provide insight into mechanisms of
magnetization relaxation in the representative Tb-based SMMs.",1905.10635v1
2018-06-22,"Magnetic clustering, half-moons, and shadow pinch points as signals of a proximate Coulomb phase in frustrated Heisenberg magnets","We study the formation of magnetic clusters in frustrated magnets in their
cooperative paramagnetic regime. For this purpose, we consider the
$J_1$-$J_2$-$J_3$ classical Heisenberg model on kagome and pyrochlore lattices
with $J_2 = J_3=J$. In the absence of farther-neighbor couplings, $J=0$, the
system is in the Coulomb phase with magnetic correlations well characterized by
pinch-point singularities. Farther-neighbor couplings lead to the formation of
magnetic clusters, which can be interpreted as a counterpart of
topological-charge clusters in Ising frustrated magnets [T. Mizoguchi, L. D. C.
Jaubert and M. Udagawa, Phys. Rev. Lett. {\bf 119}, 077207 (2017)]. The
concomitant static and dynamical magnetic structure factors, respectively
$\mathcal{S}({\bm{q}})$ and $\mathcal{S}({\bm{q}},\omega)$, develop half-moon
patterns. As $J$ increases, the continuous nature of the Heisenberg spins
enables the half-moons to coalesce into connected `star' structures spreading
across multiple Brillouin zones. These characteristic patterns are a dispersive
complement of the pinch point singularities, and signal the proximity to a
Coulomb phase. Shadows of the pinch points remain visible at finite energy,
$\omega$. This opens the way to observe these clusters through (in)elastic
neutron scattering experiments. The origin of these features are clarified by
complementary methods: large-$N$ calculations, semi-classical dynamics of the
Landau-Lifshitz equation, and Monte Carlo simulations. As promising candidates
to observe the clustering states, we revisit the origin of ""spin molecules""
observed in a family of spinel oxides $AB_2$O$_4$ ($A=$ Zn, Hg, Mg, $B=$ Cr,
Fe).",1806.08534v2
2018-07-04,Critical behavior in itinerant ferromagnet SrRu$_{1-x}$Ti$_x$O$_3$,"SrRuO$_3$ presents a rare example of ferromagnetism among the 4$d$ based
oxides. While the nature of magnetic state in SrRuO$_3$ is mostly believed to
be of itinerant type, recent studies suggest a coexistence of both itinerant
and localized model of magnetism in this material. Here, we have investigated
the evolution of magnetic state in doped SrRu$_{1-x}$Ti$_x$O$_3$ through
studying the critical behavior using standard techniques such as, modified
Arrott plot, Kouvel-Fisher plot and critical isotherm analysis across the
magnetic transition temperature $T_c$. The substitution of nonmagnetic
Ti$^{4+}$ (3$d^{0}$) for Ru$^{4+}$ (4$d^4$) would simply dilute the magnetic
system apart from modifying the electron correlation effect and the density of
states at Fermi level. Surprisingly, $T_c$ does not change with $x$. Moreover,
our analysis show the exponent $\beta$ related to spontaneous magnetization
increases while the exponents $\gamma$ and $\delta$ related to initial inverse
susceptibility and critical magnetization, respectively decrease with Ti
substitution. The estimated exponents do not match with any established
theoretical models for universality classes, however, the exponent obey the
Widom relation and the scaling behavior. Interestingly, this particular
evolution of exponents in present series has similarity with that in
isoelectronic doped Sr$_{1-x}$Ca$_x$RuO$_3$. We believe that site dilution by
Ti leads to formation magnetic clusters which causes this specific changes in
critical exponents.",1807.01445v1
2021-05-11,Spin-dependent magnetism and superparamagnetic contribution to the magnetocaloric effect of non-stoichiometric manganite nanoparticles,"Despite extensive researches on manganites owing to widespread use in modern
electronics, this class of metal oxides does not cease to surprise with its
unique properties and new phenomena. Here we have studied structural and
magnetic properties of non-Heisenberg manganite nanoparticles with a strong
spin-electron coupling. During transition from low temperature ferromagnetic to
high temperature paramagnetic state, the change in charge, valence and spin
(magnetic moment) with the localization of eg-electrons on the manganese ions
have been detected. With decrease in a temperature, the overstated effective
magnetic moment of Mn ions in paramagnetic phase is reduced dramatically
testifying to spin-dependent magnetism. The critical behavior of magnetization
with determination of critical parameters near second-order phase transition
has been studied comprehensively. Based on unusual behavior of temperature and
field dependences of magnetic entropy change under different magnetic field, an
additional influence of superparamagnetism of nanoparticles on the
magnetocaloric effect has been found.",2105.04831v1
2021-07-23,Intermixing Induced Anisotropy Variations in CoB-based Chiral Multilayer Films,"We examine the atomic intermixing phenomenon in three distinct amorphous
CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO
- which are shown to stabilise room-temperature chiral magnetic textures.
Intermixing occurs predominantly between adjacent metallic layers. Notably, it
is stack-order dependent, and particularly extensive when Ir sits atop CoB.
Intermixing induced variations in magnetic properties are ascribed to the
formation of magnetic dead layer arising from CoIr alloying in the metallic
stacks. It also produces systematic variations in saturation magnetization, by
as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness
for the transition from perpendicular to in-plane magnetic anisotropy differs
by more than 2x across the stacks. Finally, with thermal annealing treatment
over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy
increases monotonically across all stacks, coupled with discernibly larger Hc
for the metallic stacks. These are attributed to thermally induced CoPt
alloying and MgO crystallization in the metallic and oxide stacks,
respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its
amorphous nature after annealing. Our results set the stage for harnessing the
collective attributes of amorphous CoB-based material platforms and associated
annealing processes for modulating magnetic interactions, enabling the tuning
of chiral magnetic texture properties in ambient conditions.",2107.11034v1
2014-04-21,"Unconventional magnetism in the spin-orbit driven Mott insulators Ba3MIr2O9 (M=Sc,Y)","We have carried out detailed bulk and local probe studies on the hexagonal
oxides Ba3MIr2O9 (M=Sc,Y) where Ir is expected to have a fractional oxidation
state of +4.5. In the structure, Ir-Ir dimers are arranged in an edge shared
triangular network parallel to the ab plane. Whereas only weak anomalies are
evident in the susceptibility data, clearer anomalies are present in the heat
capacity data. Our 45Sc nuclear magnetic resonance (NMR) lineshape (first order
quadrupole split) is symmetric at room temperature but becomes progressively
asymmetric with decreasing temperatures. This is suggestive of distortions in
the structure which could arise from progressive tilt/rotation of the IrO6
octahedra with a decrease in temperature T. The 45Sc NMR spectral weight shifts
near the reference frequency with decreasing T indicating the development of
magnetic singlet regions. Around 10K, a significant change in the spectrum
takes place with a large intensity appearing near the reference frequency but
with the spectrum remaining multi-peak. It appears from our 45Sc NMR data that
in Ba3ScIr2O9 significant disorder is still present below 10K. In the case of
Ba3YIr2O9, the 89Y NMR spectral lines are asymmetric at high temperatures but
become nearly symmetric (single magnetic environment) below T~70K. Our 89Y
spectra and T1 measurements confirm the onset of long range ordering (LRO) from
a bulk of the sample at 4K in this compound. Our results suggest that Ba3YIr2O9
might be structurally distorted at room temperature (via, for example,
tilt/rotations of the IrO6 octahedra) but becomes progressively a regular
triangular lattice with decreasing T. The effective magnetic moments and
magnetic entropy changes are strongly reduced in Ba3YIr2O9 as compared to those
expected for a S=1/2 system. Similar effects have been found in other iridates
which naturally have strong spin-orbit coupling (SOC).",1404.5262v1
2019-10-07,Structural and magnetic properties of 3d transition metal oxide chains on the (001) surfaces of Ir and Pt,"We present a survey of the structural and magnetic properties of submonolayer
transition metal dioxides on the (001) surfaces of the heavy face-centered
cubic (fcc) noble metals Ir and Pt performed by spin-averaged scanning
tunneling microscopy (STM) and spin-polarized (SP-)STM. Our STM results confirm
that deposition of Co, Fe, Mn, and Cr on the (2 {\times} 1)
oxygen-reconstructed Ir(001) surface leads to the formation of quasi
one-dimensional chains with a (3 {\times} 1) unit cell. As recently predicted
by density functional theory [Ferstl et al., Phys. Rev. Lett. 117, 046101
(2016)], our SP-STM images of FeO2 and MnO2 on Ir(001) show a two-fold
periodicity along the chains which is characteristic for an antiferromagnetic
coupling along the chains. In addition, these two materials also exhibit
spontaneous, permanent, and long-range magnetic coupling across the chains.
Whereas we find a ferromagnetic inter-chain coupling for FeO2/Ir(001), the
magnetic coupling of MnO2 on Ir(001) appears to be a non-collinear 120{\deg}
spin spiral, resulting in a (9 {\times} 2) magnetic unit cell. On Pt(001)
patches of (3 {\times} 1)-reconstructed oxide chains could only be prepared by
transition metal (Co, Fe, and Mn) deposition onto the cold substrate and
subsequent annealing in an oxygen atmosphere. Again SP-STM on MnO2/Pt(001)
reveals a very large, (15 {\times} 2) magnetic unit cell which can tentatively
be explained by a commensurate 72{\deg} spin spiral. Large scale SP-STM images
reveal a long wavelength spin rotation along the MnO2 chain.",1910.02707v1
2021-04-12,Designer Magnetism in High Entropy Oxides,"Disorder can have a dominating influence on correlated and quantum materials
leading to novel behaviors which have no clean limit counterparts. In magnetic
systems, spin and exchange disorder can provide access to quantum criticality,
frustration, and spin dynamics, but broad tunability of these responses and a
deeper understanding of strong limit disorder is lacking. In this work, we
demonstrate that high entropy oxides present an unexplored route to designing
quantum materials in which the presence of strong local compositional disorder
hosted on a positionally ordered lattice can be used to generate highly tunable
emergent magnetic behavior--from macroscopically ordered states to
frustration-driven dynamic spin interactions. Single crystal
La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films are used as a structurally uniform model
system hosting a magnetic sublattice with massive microstate disorder in the
form of site-to-site spin and exchange type inhomogeneity. A classical
Heisenberg model is found to be sufficient to describe how compositionally
disordered systems can paradoxically host long-range magnetic uniformity and
demonstrates that balancing the populating elements based on their discrete
quantum parameters can be used to give continuous control over ordering types
and critical temperatures. Theory-guided experiments show that composite
exchange values derived from the complex mix of microstate interactions can be
used to design the required compositional parameters for a desired response.
These predicted materials are synthesized and found to possess an incipient
quantum critical point when magnetic ordering types are designed to be in
direct competition; this leads to highly controllable exchange bias sensitivity
in the monolithic single crystal films previously accessible only in
intentionally designed bilayer heterojunctions.",2104.05552v2
2021-05-26,Magnetic Particle Spectroscopy (MPS) with One-stage Lock-in Implementation for Magnetic Bioassays with Improved Sensitivities,"In recent years, magnetic particle spectroscopy (MPS) has become a highly
sensitive and versatile sensing technique for quantitative bioassays. It relies
on the dynamic magnetic responses of magnetic nanoparticles (MNPs) for the
detection of target analytes in liquid phase. There are many research studies
reporting the application of MPS for detecting a variety of analytes including
viruses, toxins, and nucleic acids, etc. Herein, we report a modified version
of MPS platform with the addition of a one-stage lock-in design to remove the
feedthrough signals induced by external driving magnetic fields, thus capturing
only MNP responses for improved system sensitivity. This one-stage lock-in MPS
system is able to detect as low as 781 ng multi-core Nanomag50 iron oxide MNPs
(micromod Partikeltechnologie GmbH) and 78 ng single-core SHB30 iron oxide MNPs
(Ocean NanoTech). In addition, using a streptavidin-biotin binding system as a
proof-of-concept, we show that these single-core SHB30 MNPs can be used for
Brownian relaxation-based bioassays while the multi-core Nanomag50 cannot be
used. The effects of MNP amount on the concentration dependent response
profiles for detecting streptavidin was also investigated. Results show that by
using lower concentration/amount of MNPs, concentration-response curves shift
to lower concentration/amount of target analytes. This lower
concentrationresponse indicates the possibility of improved bioassay
sensitivities by using lower amounts of MNPs.",2105.12718v1
2021-09-10,Giant shifts of crystal-field excitations with temperature as consequence of internal magnetic exchange fields,"Crystal-field excitations, for example in transition-metal oxides where a
rare-earth element is used as a spacer between the transition-metal-oxide
tetrahedra and octahedra, are assumed to be extremely robust with respect to
external perturbations such as temperature. Using inelastic neutron scattering
experiments, a giant shift of the energy of the lowest crystal-field excitation
of Er3+ (4I15/2) in ErFeO3 from 0.30(2) meV to 0.75(2) meV was measured below
the magnetic-ordering temperature of erbium at 4.1 K. Quantum-mechanical
point-charge calculations of the crystal-field levels indicate that the shift
is caused by the internal magnetic field created by the erbium spins
themselves, which causes a Zeeman splitting of the erbium 4f electronic levels,
and therefore a change in the energies of crystal-field transitions. To verify
this explanation, the effect of an external magnetic field on the crystal-field
excitations was measured by inelastic neutron scattering and compared to the
field-dependent point-charge calculations. The existence of an internal
magnetic exchange interaction will have implications for a deeper understanding
of a broader group of phenomena such as multiferroic properties or spin
frustration, which are a consequence of various competing electronic and
magnetic exchange interactions.",2109.04610v2
1996-03-07,Electronic and Magnetic Structure of LaCuO$_{2.5}$,"The recently-discovered ``ladder'' compound LaCuO$_{2.5}$ has been found to
admit hole doping without altering its structure of coupled copper oxide
ladders. While susceptibility measurements on the parent compound suggest a
spin gap and a spin-liquid state, NMR results indicate magnetic order at low
temperatures. These seemingly contradictory results may be reconciled if in
fact the magnetic state is near the crossover from spin liquid to
antiferromagnet, and we investigate this possibility. From a tight-binding fit
to the valence LDA bandstructure, we deduce that the strength of the
interladder hopping term is approximately half that of intraladder hopping,
showing that the material is three-dimensional in character. A mean-field
treatment of the insulating magnetic state gives a spin-liquid phase whose spin
gap decreases with increasing interladder coupling, vanishing (signalling a
transition to the ordered phase) at a value somewhat below that obtained for
LaCuO$_{2.5}$. The introduction of an on-site repulsion term, $U$, to the band
scheme causes a transition to an antiferromagnetic insulator for rather small
but finite values of $U$, reflecting the predominance of (one-dimensional)
ladder behavior, and an absence of any special nesting features.",9603054v2
1996-11-20,Spin-dependent tunneling in metal-insulator-narrow gap semiconductor structures in a magnetic field,"We present results of tunneling studies of p-Hg_{1-x}Cd_{x}Te-oxide-Al
structures with 0.165<x<0.2 in a magnetic field up to 6 T. The tunneling
conductivity oscillations resulting from the Landau quantization of the energy
spectrum in the semiconductor volume are investigated. Under an in-plane
magnetic field the amplitudes of tunneling conductivity maxima connected with
the tunneling into `a' and `b' spin sublevels are found to differ
substantionally from one another, and the amplitude ratio varying from
structure to structure. To understand the cause of this behavior, the tunneling
conductivity for this magnetic field orientation is calculated taking into
consideration the multi-band energy spectrum. It is shown that the
contributions of the different spin-sublevels to the tunneling conductivity are
dissimilar and the relationship between them depends strongly on the value of
surface potential.",9611149v1
1999-01-08,Anisotropy and magnetism of high temperature oxides superconductors,"Phonon or electron mediated weak BCS attraction is enough to have high
critical temperature if a van Hove anomaly is at work. This could apply to
electron doped compounds and also to compounds with CuO$_2$ planes overdoped in
holes, where $T_c$ decreases with increasing doping. If phonons dominate, it
should lead to an anisotropic but mainly $s$ superconductive gap, as observed
recently in overdoped LaSrCuO, and probably also in electron doped compounds.
If electrons dominate, a $d$ gap should develop as observed in a number of
cases. In the underdoped range, the observed decrease of $T_c$ with hole doping
can be related in all cases to the development of antiferromagnetic
fluctuations which produces a magnetic pseudogap, thus lowering the density of
states at the Fermi level. The observed mainly $d$ superconductive gap then can
be due to a prevalent superconductive coupling through antiferromagnetic
fluctuations; it could also possibly be attributed to the same phonon coupling
as in the overdoped range, now acting on Bloch functions scattered in the
magnetic pseudogap. More systematic studies of superconductive gap anisotropy
and of magnetic fluctuations would be in order.",9901065v2
2000-04-10,Combined Paramagnetic and Diamagnetic Response of YBCO,"It has been predicted that the zero frequency density of states of YBCO in
the superconducting phase can display interesting anisotropy effects when a
magnetic field is applied parallel to the copper-oxide planes, due to the
diamagnetic response of the quasi-particles. In this paper we incorporate
paramagnetism into the theory and show that it lessens the anisotropy and can
even eliminate it altogether. At the same time paramagnetism also changes the
scaling with the square root of the magnetic field first deduced by Volovik
leading to an experimentally testable prediction. We also map out the analytic
structure of the zero frequency density of states as a function of the
diamagnetic and paramagnetic energies. At certain critical magnetic field
values we predict kinks as we vary the magnetic field. However these probably
lie beyond currently accessible field strengths.",0004152v1
2000-07-06,Non-Langevin behaviour of the uncompensated magnetisation in nanoparticles of artificial ferritin,"The magnetic behaviour of nanoparticles of antiferromagnetic ferritin has
been investigated by 57Fe Mossbauer absorption spectroscopy and magnetisation
measurements, in the temperature range 2.5K-250K and with magnetic fields up to
7T. Samples containing nanoparticles with an average number of Fe atoms ranging
from 400 to 2500 were studied. The value of the anisotropy energy per unit
volume was determined and found to be in the range 3-6 10**5 ergs/cm3, which is
a value typical for ferric oxides. By comparing the results of the two
experimental methods at large field, we show that, contratry to what is
currently assumed, the uncompensated magnetisation of the feritin cores in the
superparamagnetic regime does not follow a Langevin law. For magnetic fields
below the spin-flop field, we propose an approximate law for the field and
temperature variation of the uncompensated magnetisation which has so far never
been applied in antiferromagnetic systems. This approach should more generally
hold for randomly oriented antiferro- magnetic nanoparticles systems with weak
uncompensated moments.",0007087v2
2000-11-06,Thermodynamics of d-wave superconductors in a magnetic field,"We investigate the thermodynamic properties of a two-dimensional d-wave
superconductor in the vortex state using a semiclassical approach, and argue
that such an approach is valid for the analysis of the experimental data on
high-temperature superconductors. We develop a formalism where the spatial
average of a physical quantity is written as an integral over the probability
density of the Doppler shift, and evaluate this probability density for several
model cases. The approach is then used to analyse the behavior of the specific
heat and the NMR spin-lattice relaxation rate in a magnetic field. We compare
our results with the experimental measurements, and explain the origin of the
discrepancy between the results from different groups. We also address the
observability of the recently predicted fourfold oscillations of the specific
heat for the magnetic field parallel to the copper oxide planes. We consider
both the orbital and the Zeeman effects, and conclude that at experimentally
relevant temperatures Zeeman splitting does not appreciably reduce the
anisotropy, although it does change the field dependence of the anisotropic
specific heat. We predict a scaling law for the non-exponentially decaying NMR
magnetization, and discuss different approaches to the effective relaxation
rate.",0011091v1
2001-02-27,A new class of magnetic materials: Sr2FeMoO6 and related compounds,"Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. It is now believed
that the origin of magnetism in this class of compounds is based on a novel
kinetically-driven mechanism. This new mechanism is also likely to be
responsible for the unusually high temperature ferromagnetism in several other
systems, such as dilute magnetic semiconductors, as well as in various
half-metallic ferromagnetic systems, such as Heussler alloys.",0102502v1
2003-03-11,Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability,"Hydrostatic pressure effects on the temperature- and magnetic field
dependencies of the in-plane and out-of-plane magnetization of the bi-layered
perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under
a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature
value of the paramagnetic susceptibility has been found to systematically
decrease with increasing pressure. The effect is accompanied by an increase of
the temperature Tmax of a pronounced peak of susceptibility. Thus,
magnetization measurements under hydrostatic pressure reveal that the lattice
contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not
ferromagnetism, contrary to the previous beliefs. The effects can be explained
by the enhancement of the inter-bi-layer antiferromagnetic spin coupling,
driven by the shortening of the superexchange path, and suppression, due to the
band-broadening effect, of competing itinerant ferromagnetic correlations.",0303199v1
2003-04-18,Magnetic field-induced Landau Fermi Liquid in high-T_c metals,"We consider the behavior of strongly correlated electron liquid in
high-temperature superconductors within the framework of the fermion
condensation model. We show that at low temperatures the normal state recovered
by the application of a magnetic field larger than the critical field can be
viewed as the Landau Fermi liquid induced by the magnetic field. In this state,
the Wiedemann-Franz law and the Korringa law are held and the elementary
excitations are the Landau Fermi Liquid quasiparticles. Contrary to what might
be expected from the Landau theory, the effective mass of quasiparticles
depends on the magnetic field. The recent experimental verifications of the
Wiedemann-Franz law in heavily hole-overdoped, overdoped and optimally doped
cuprates and the verification of the Korringa law in the electron-doped
copper-oxide superconductor strongly support the existence of fermion
condensate in high-T_c metals.",0304432v2
2003-08-28,Spurious magnetism in high-Tc superconductor,"One challenge in condensed-matter physics is to unravel the interplay between
magnetism and superconductivity in copper oxides with a high critical
temperature (Tc). Kang et al. claim to have revealed a quantum phase transition
from the superconducting to an antiferromagnetic state in the electron-doped
material Nd2-xCexCuO4 (NCCO) based on the observation of magnetic-field-induced
neutron scattering intensity at (1/2,1/2,0), (1/2,0,0), and related
reflections. Here we argue that the observed magnetic intensity is due to a
secondary phase of (Nd,Ce)2O3. We therefore contend that the effect is spurious
and not intrinsic to superconducting NCCO.",0308607v2
2003-09-10,Diagonal Antiferromagnetic Easy Axis in Lightly Hole Doped Y_{1-x}Ca_xBa_2Cu_3O_6,"Hole induced changes in the antiferromagnetic structure of a lightly Ca doped
Gd:Y_{1-x}Ca_xBa_2Cu_3O_6 copper oxide single crystal with x~0.008 is
investigated by Gd3+ electron spin resonance. Holes do not localize to Ca2+
ions above 2.5 K since the charge distribution and spin susceptibility next to
the Ca2+ are independent of temperature. Both hole doped and pristine crystals
are magnetically twinned with an external magnetic field dependent
antiferromagnetic domain structure. Unlike the undoped crystal, where the easy
magnetic axis is along [100] at all temperatures, the easy direction in the
hole doped crystal is along the [110] diagonal at low temperatures and changes
gradually to the [100] direction between 10 K and 100 K. The transition is
tentatively attributed to a magnetic anisotropy introduced by hole ordering.",0309258v1
2004-03-17,Universal Dispersive Excitations in the High-Temperature Superconductors,"High-resolution neutron scattering experiments on optimally doped
La$_{2-x}$Sr$_x$CuO$_4$ have been performed which reveal that the magnetic
excitations are dispersive. The dispersion is found to be the same as in the
YBa$_2$Cu$_3$O$_{6+x}$ family, and is quantitatively related to that observed
with charge sensitive probes. The excitations are also found to broaden rapidly
with increasing energy, forming a continuum at higher energy, and bear a
remarkable resemblance to multi-particle excitations observed in
low-dimensional antiferromagnets and some magnetic metals. The magnetic
correlations are two dimensional, and so rule out the simplest scenarios where
the copper oxide planes are subdivided into weakly interacting one-dimensional
magnets.",0403439v2
2004-03-19,Charge dynamics and Kondo effect in single electron traps in field effect transistors,"We study magneto-electric properties of single electron traps in
metal-oxide-semiconductor field effect transistors. Using a microscopic
description of the system based on the single-site Anderson-Holstein model, we
derive an effective low energy action for the system. The behavior of the
system is characterized by simultaneous polaron tunneling (corresponding to the
charging and discharging of the trap) and Kondo screening of the trap spin in
the singly occupied state. Hence, the obtained state of the system is a hybrid
between the Kondo regime, typically associated with single electron occupancy,
and the mixed valence regime, associated with large charge fluctuations. In the
presence of a strong magnetic field, we demonstrate that the system is
equivalent to a two level-level system coupled to an Ohmic bath, with a bias
controlled by the applied magnetic field. Due to the Kondo screening, the
effect of the magnetic field is significantly suppressed in the singly occupied
state. We claim that this suppression can be responsible for the experimentally
observed anomalous magnetic field dependence of the average trap occupancy in
${\rm Si-Si0_2}$ field effect transistors.",0403491v1
2004-11-27,Spin-Charge Coupling in lightly doped Nd$_{2-x}$Ce$_{x}$CuO$_4$,"We use neutron scattering to study the influence of a magnetic field on spin
structures of Nd$_2$CuO$_4$. On cooling from room temperature, Nd$_2$CuO$_4$
goes through a series of antiferromagnetic (AF) phase transitions with
different noncollinear spin structures. While a c-axis aligned magnetic field
does not alter the basic zero-field noncollinear spin structures, a field
parallel to the CuO$_2$ plane can transform the noncollinear structure to a
collinear one (""spin-flop"" transition), induce magnetic disorder along the
c-axis, and cause hysteresis in the AF phase transitions. By comparing these
results directly to the magnetoresistance (MR) measurements of
Nd$_{1.975}$Ce$_{0.025}$CuO$_4$, which has essentially the same AF structures
as Nd$_2$CuO$_4$, we find that a magnetic-field-induced spin-flop transition,
AF phase hysteresis, and spin c-axis disorder all affect the transport
properties of the material. Our results thus provide direct evidence for the
existence of a strong spin-charge coupling in electron-doped copper oxides.",0411694v1
2005-01-29,Magnetic structural effect in nonequilibrium defective solids,"Scientific study of the effect of structural memory of nonequilibrium
defective solids about the processing in magnetic field (the magnetic
structural effect (MSE) was continued in this paper. The study was aimed to
reveal the universal nature of the MSE, which was investigated in several new
nonequilibrium defective solids. The results of investigation of the processing
in the vortical magnetic field (PVMF) and its effect on the structure of the
natural magnetite Fe3O4 and the SnO2 films were presented. The methods of
M&#246;ssbauer and X-ray spectroscopy were used. The PVMF reduction of a
defectiveness of Fe3O4 structure in the magnetite was detected. The MSE was
also observed in the M&#246;ssbauer spectra of diamagnetic tin oxide SnO2 films
after the PVMF. One of the possible explanations of the MSE was given in the
paper.",0501727v1
2005-02-23,Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films,"Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial
growth of spinel NiFe2O4 ultrathin films onto SrTiO3 single-crystals. We will
show that - under appropriate growth conditions - epitaxial stabilization leads
to the formation of a spinel phase with magnetic and electrical properties that
radically differ from those of the bulk material : an enhanced magnetic moment
(Ms) - about 250% larger - and a metallic character. A systematic study of the
thickness dependence of Ms allows to conclude that its enhanced value is due to
an anomalous distribution of the Fe and Ni cations among the A and B sites of
the spinel structure resulting from the off-equilibrium growth conditions and
to interface effects. The relevance of these findings for spinel- and, more
generally, oxide-based heterostructures is discussed. We will argue that this
novel material could be an alternative ferromagetic-metallic electrode in
magnetic tunnel junctions.",0502558v1
2005-04-18,Geometrical Magnetic Frustration in Rare Earth Chalcogenide Spinels,"We have characterized the magnetic and structural properties of the CdLn2Se4
(Ln = Dy, Ho), and CdLn2S4 (Ln = Ho, Er, Tm, Yb) spinels. We observe all
compounds to be normal spinels, possessing a geometrically frustrated
sublattice of lanthanide atoms with no observable structural disorder. Fits to
the high temperature magnetic susceptibilities indicate these materials to have
effective antiferromagnetic interactions, with Curie-Weiss temperatures theta ~
-10 K, except CdYb2S4 for which theta ~ -40 K. The absence of magnetic long
range order or glassiness above T = 1.8 K strongly suggests that these
materials are a new venue in which to study the effects of strong geometrical
frustration, potentially as rich in new physical phenomena as that of the
pyrochlore oxides.",0504422v2
2005-04-29,Non-invasive detection of charge-rearrangement in a quantum dot in high magnetic fields,"We demonstrate electron redistribution caused by magnetic field on a single
quantum dot measured by means of a quantum point contact as non-invasive
detector. Our device which is fabricated by local anodic oxidation allows to
control independently the quantum point contact and all tunnelling barriers of
the quantum dot. Thus we are able to measure both the change of the quantum dot
charge and also changes of the electron configuration at constant number of
electrons on the quantum dot. We use these features to exploit the quantum dot
in a high magnetic field where transport through the quantum dot displays the
effects of Landau shells and spin blockade. We confirm the internal
rearrangement of electrons as function of the magnetic field for a fixed number
of electrons on the quantum dot.",0504777v1
2005-05-12,"Influence of Ru-doping on structure, defect chemistry, magnetic interaction and carrier motion of the La1-xNaxMnO3+delta manganite","In this work we report a structural, electrical and magnetic characterization
of the La1-xNaxMn1-yRuyO3+d (LNMRO) system with x = 0.05, 0.15 and y = 0, 0.05,
0.15, also comprising an investigation of the role of the oxygen content on the
related redox properties. The experimental investigation has been realized with
the aid of X-ray powder diffraction, electron microprobe analysis,
thermogravimetry, electrical resistivity and magnetization measurements, and
electron paramagnetic resonance. We demonstrate that the effect of ruthenium
doping on the studied LNMRO compounds is not only directly related to the Ru/Mn
substitution and to the Ru oxidation state but also indirectly connected to the
oxygen content in the sample. Our data show that ruthenium addition can improve
electrical and magnetic properties of non-optimally (low) cation doped
manganites, causing an increase of the TC value and the insurgence of MR
effect, as observed for the x = 0.05 and y = 0.05 sample.",0505309v1
2005-11-12,Universal properties of modulated antiferromagnetic systems,"Magnetism and superconductivity are physical phenomena whose foundations are
rooted in quantum mechanics and whose technological applications do not cease
to surprise us. In this article we describe a class of magnetic materials, we
call modulated antiferromagnetic systems (MAS), that has a prominent
representative in the copper-oxide high-temperature superconductors. The class,
however, is not exclusive to these superconductors. Indeed, several materials
that belong to that class are insulators. The magnetic spectral weight of MAS
displays the following universal properties: a local intensity maximum
(resonance peak) at the commensurate antiferromagnetic wave vector; peaks at
the nearly-antiferromagnetic wave vectors for excitation energies well below
the resonance, and at wave vectors rotated by 45 degrees for energies above
resonance. Moreover, we predict an observable rotation by 45 degrees of the
peaks immediately below the resonance. All these universal signatures,
condensed in a twisted hour-glass-like spectrum, are merely consequences of the
unique topological characteristics of the single-particle magnetic dispersion
relation. We thus provide a unifying scenario that explains the phenomenology
that has been observed in inelastic neutron scattering experiments of the
high-temperature superconductors.",0511303v1
2006-05-04,Magnetic anisotropy of $Co_x Pt_{1-x}$ clusters embedded in matrix: Influences of the cluster chemical composition and the matrix nature,"We report on the magnetic properties of Co$\_x$Pt$\_{1-x}$ clusters embedded
in various matrices. Using a careful analysis of magnetization curves and ZFC
susceptibility measurements, we determine the clusters magnetic anisotropy
energy (MAE) and separate the surface and volume contributions. By comparing
different chemical compositions, we show that a small amount of Pt (15%)
induces an important increase in the volume anisotropy with respect to pure Co
clusters, even in chemically disordered fcc clusters. Comparing the
measurements of clusters embedded in Nb and MgO matrices, we show that the
oxide matrix induces an important increase of the surface MAE attributed to the
formation of an antiferromagnetic CoO shell around the clusters.",0605107v1
2006-06-09,The magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3 superlattices grown by pulsed laser deposition technique,"We have investigated the magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3
superlattices, grown on SrTiO3 substrate by pulsed laser deposition technique,
both with current-in-plane and current-perpendicular-to-the-plane directions.
Several features indicate the presence of magnetic inhomogeneities at the
interfaces which is independent of BaTiO3 layer thickness variation. First, the
magnetic property in the superlattices decreases. Second, a hysteresis in
magnetoresistance due to the relaxation of the resistive state is observed.
Third, a threshold under an applied magnetic field in the magnetoresistance is
seen. Such behaviors are in agreement with the phase separation scenario which
could be the possible reason for these magnetic inhomogeneities at the
interfaces. On the contrary, the magnetoresistance with the
current-perpendicular-to-the-plane direction is mostly attributed to the
tunneling effect along with the ordering of the spin at the interface. This
study confirms the importance of the interfaces in superlattices that can be
used to control novel physical properties in oxide materials.",0606232v1
2006-07-14,Electric field control of exchange bias in multiferroic epitaxial heterostructures,"The magnetic exchange bias between epitaxial thin films of the multiferroic
(antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft
ferromagnetic (FM) layer is used to couple the magnetic response of the
ferromagnetic layer to the magnetic state of the antiferromagnetic one. We will
show that biasing the ferroelectric YMnO3 layer by an appropriate electric
field allows modifying and controlling the magnetic exchange bias and
subsequently the magnetotransport properties of the FM layer. This finding may
contribute to pave the way towards a new generation of electric-field
controlled spintronics devices.",0607381v1
2006-11-14,Re-entrant ferromagnetism in a generic class of diluted magnetic semiconductors,"Considering a general situation where a semiconductor is doped by magnetic
impurities leading to a carrier-induced ferromagnetic exchange coupling between
the impurity moments, we show theoretically the possible generic existence of
three ferromagnetic transition temperatures, T_1 > T_2 > T_3, with two distinct
ferromagnetic regimes existing for T_1 > T > T_2 and T < T_3. Such an
intriguing re-entrant ferromagnetism, with a paramagnetic phase (T_2 > T > T_3)
between two ferromagnetic phases, arises from a subtle competition between
indirect exchange induced by thermally activated carriers in an otherwise empty
conduction band versus the exchange coupling existing in the impurity band due
to the bound carriers themselves. We comment on the possibility of observing
such a re-entrance phenomenon in diluted magnetic semiconductors and magnetic
oxides.",0611384v1
2007-01-16,Magnetoelectric coupling in epitaxial orthorhombic YMnO3 thin films,"We have grown epitaxial thin-films of the orthorhombic phase of YMnO3 oxide
on Nb:SrTiO3(001) substrates and their structure, magnetic and dielectric
response have been measured. We have found that a substrate-induced strain
produces an in-plane compression of the YMnO3 unit cell. The
temperature-dependent magnetization curves display a significant ZFC-FC
hysteresis at temperatures below the Neel temperature (TN around 40K). The
dielectric constant increases gradually (up to 26%) below TN and mimics the ZFC
magnetization curve. We argue that these effects are a manifestation of
magnetoelectric coupling in thin films and that the magnetic structure of YMnO3
can be controlled by substrate selection.",0701387v1
2007-05-19,Spin-Liquid State in the S = 1/2 Hyperkagome Antiferromagnet Na4Ir3O8,"A spinel related oxide, Na4Ir3O8, was found to have a three dimensional
network of corner shared Ir4+ (t2g^5) triangles. This gives rise to an
antiferromagnetically coupled S = 1/2 spin system formed on a geometrically
frustrated hyperkagome lattice. Magnetization M and magnetic specific heat Cm
data showed the absence of long range magnetic ordering at least down to 2 K.
The large Cm at low temperatures is independent of applied magnetic field up to
12 T, in striking parallel to the behavior seen in triangular and kagome
antiferromagnets reported to have a spin-liquid ground state. These results
strongly suggest that the ground state of Na4Ir3O8 is a three dimensional
manifestation of a spin liquid.",0705.2821v2
2007-05-21,Room temperature spin polarized magnetic semiconductor,"Alternating layers of granular Iron (Fe) and Titanium dioxide
(TiO$_{2-\delta}$) were deposited on (100) Lanthanum aluminate (LaAlO$_3$)
substrates in low oxygen chamber pressure using a controlled pulsed laser
ablation deposition technique. The total thickness of the film was about 200
nm. The films show ferromagnetic behavior for temperatures ranging from 4 to
$400 ^oK$. The layered film structure was characterized as p-type magnetic
semiconductor at $300 ^oK$ with a carrier density of the order of $10^{20}
/cm^3$. The undoped pure TiO$_{2-\delta}$ film was characterized as an n-type
magnetic semiconductor. The hole carriers were excited at the interface between
the granular Fe and TiO$_{2-\delta}$ layers similar to holes excited in the
metal/n-type semiconductor interface commonly observed in
Metal-Oxide-Semiconductor (MOS) devices. The holes at the interface were
polarized in an applied magnetic field raising the possibility that these
granular MOS structures can be utilized for practical spintronic device
applications.",0705.2993v1
2007-05-30,Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order,"Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser
deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed
X-ray diffraction and cross-section transmission electron microscopy analysis
revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films
very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+
cation ordering along the [111] direction. The films contain no detectable
magnetic iron oxide impurities and have the correct cationic average
stoichiometry throughout their thickness. They however exhibit a slight
modulation in the Fe and Cr compositions forming complementary stripe patterns,
suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO
films exhibit good ferroelectric and piezoelectric properties, in addition to
magnetic properties at room temperature, as well as an unexpected
crystallographic orientation dependence of their room temperature magnetic
properties. Our results qualitatively confirm the predictions made using the
ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films
exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along
with the unpredicted existence of magnetic ordering at room temperature.",0705.4390v1
2007-06-19,Probing the Role of the Barrier Layer in Magnetic Tunnel Junction Transport,"Magnetic tunnel junctions with a ferrimagnetic barrier layer have been
studied to understand the role of the barrier layer in the tunneling process -
a factor that has been largely overlooked until recently. Epitaxial oxide
junctions of highly spin polarized La0.7Sr0.3MnO3 and Fe3O4 electrodes with
magnetic NiMn2O4 (NMO) insulating barrier layers provide a magnetic tunnel
junction system in which we can probe the effect of the barrier by comparing
junction behavior above and below the Curie temperature of the barrier layer.
When the barrier is paramagnetic, the spin polarized transport is dominated by
interface scattering and surface spin waves; however, when the barrier is
ferrimagnetic, spin flip scattering due to spin waves within the NMO barrier
dominates the transport.",0706.2726v2
2007-08-15,Insulator to semiconductor transition and magnetic properties of the one-dimensional S = 1/2 system In_2VO_5,"We report structural, magnetization, electrical resistivity and nuclear- and
electron spin resonance data of the complex transition metal oxide In_2VO_5 in
which structurally well-defined V-O chains are realized. An itinerant character
of the vanadium d-electrons and ferromagnetic correlations, revealed at high
temperatures, are contrasted with the insulating behavior and predominantly
antiferromagnetic exchange between the localized V^{4+} S = 1/2-magnetic
moments which develop below a certain characteristic temperature T* ~ 120 K.
Eventually the compound exhibits short-range magnetic order at $T_SRO ~ 20 K.
We attribute this crossover occurring around T* to the unusual anisotropic
thermal contraction of the lattice which changes significantly the overlap
integrals and the character of magnetic intra- and interchain interactions.",0708.2088v1
2007-09-11,Magnetically asymmetric interfaces in a (LaMnO$_3$)/(SrMnO$_3$) superlattice due to structural asymmetries,"Polarized neutron reflectivity measurements of a ferromagnetic
[(LaMnO$_3$)$_{11.8}$/(SrMnO$_3$)$_{4.4}$]$_6$ superlattice reveal a modulated
magnetic structure with an enhanced magnetization at the interfaces where
LaMnO$_3$ was deposited on SrMnO$_3$ (LMO/SMO). However, the opposite
interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The
magnetic asymmetry arises from the difference in lateral structural roughness
of the two interfaces observed via electron microscopy, with strong
ferromagnetism present at the interfaces that are atomically smooth over tens
of nanometers. This result demonstrates that atomic-scale roughness can
destabilize interfacial phases in complex oxide heterostructures.",0709.1715v2
2008-10-02,Magnetic Modulation in Mechanical Alloyed Cr1.4fe0.6o3 Oxide,"We have synthesized Cr1.4Fe0.6O3 compound through mechanical alloying of
Cr2O3 and Fe2O3 powders and subsequent thermal annealing. The XRD spectrum, SEM
picture and microanalysis of EDAX spectrum have been used to understand the
structural evolution in the alloyed compound. The alloyed samples are matching
to rhombohedral structure with R3C space group. The observation of a modulated
magnetic order confirmed a systematic diffusion of Fe atoms into the Cr sites
of lattice structure. A field induced magnetic behaviour is seen in the field
dependence of magnetization data of the annealed samples. The behaviour is
significantly different from the mechanical alloyed samples. The experimental
results provided the indications of considering the present material as a
potential candidate for opto-electronic applications.",0810.0439v1
2009-04-14,Optimizing the flux coupling between a nanoSQUID and a magnetic particle using atomic force microscope nanolithography,"We present results of Niobium based SQUID magnetometers for which the
weak-links are engineered by the local oxidation of thin films using an Atomic
Force Microscope (AFM). Firstly, we show that this technique allows the
creation of variable thickness bridges with 10 nm lateral resolution. Precise
control of the weak-link milling is offered by the possibility to realtime
monitor weak-link conductance. Such a process is shown to enhance the magnetic
field modulation hence the sensitivity of the magnetometer. Secondly, AFM
lithography is used to provide a precise alignment of NanoSQUID weak-links with
respect to a ferromagnetic iron dot. The magnetization switching of the
near-field coupled particle is studied as a junction of the applied magnetic
field direction.",0904.2100v1
2009-05-01,Huge ac magnetoresistance in La0.7Sr0.3MnO3 in sub- kilo gauss magnetic fields,"We report dynamical magnetotransport in a ferromagnetic metallic oxide,
La0.7Sr0.3MnO3 using the ac impedance technique. The temperature dependence of
the ac resistance(R) and the inductive reactance (X) of the complex impedance
(Z = R+jX) under different dc bias magnetic fields (Hdc = 0-1 kOe) were studied
for different frequencies f = 0.1 to 5 MHz of alternating current. The zero
field R, which decreases smoothly around the Curie temperature TC for f = 100
kHz, transforms into a peak for f = 0.5-5 MHz. The peak decreases in amplitude,
broadens and shifts downward in temperature as the bias field increases. A huge
ac magnetoresistance (= 45 % at f = 2 MHz) in a field of Hdc = 1 kOe is found
and we attribute it to the magnetic field- induced enhancement in the skin
depth and concomitant suppression of magnetic fluctuations near TC. Our study
suggests that radio frequency magnetotransport provides an alternative strategy
to enhance the magnetoresistance and probe the spin-charge coupling in
manganites.",0905.0090v1
2009-07-23,Nature of the Magnetic Order in BaMn2As2,"Neutron diffraction measurements have been performed on a powder sample of
BaMn2As2 over the temperature T range from 10 K to 675 K. These measurements
demonstrate that this compound exhibits collinear antiferromagnetic ordering
below the Neel temperature T_N = 625(1) K. The ordered moment mu = 3.88(4)
mu_B/Mn at T = 10 K is oriented along the c axis and the magnetic structure is
G-type, with all nearest-neighbor Mn moments antiferromagnetically aligned. The
value of the ordered moment indicates that the oxidation state of Mn is Mn^{2+}
with a high spin S = 5/2. The T dependence of mu suggests that the magnetic
transition is second-order in nature. In contrast to the closely related
AFe2As2 (A = Ca, Sr, Ba, Eu) compounds, no structural distortion is observed in
the magnetically ordered state of BaMn2As2.",0907.4094v2
2010-03-22,Magnetic excitations of spin and orbital moments in cobalt oxide,"Magnetic and phonon excitations in the antiferromagnet CoO with an unquenched
orbital angular momentum are studied by neutron scattering. Results of energy
scans in several Brillouin zones in the (HHL) plane for energy transfers up to
16 THz are presented. The measurements were performed in the antiferromagnetic
ordered state at 6 K (well below TN~290 K) as well as in the paramagnetic state
at 450 K. Several magnetic excitation modes are identified from the dependence
of their intensity on wavevector and temperature. Within a Hund's rule model
the excitations correspond to fluctuations of coupled orbital and spin degrees
of freedom whose bandwidth is controlled by interionic superexchange. The
different <111> ordering domains give rise to several magnetic peaks at each
wavevector transfer.",1003.4166v1
2010-09-23,Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders,"Oxide based diluted magnetic semiconductor (DMS) materials have been a
subject of increasing interest due to reports of room temperature
ferromagnetism in several systems and their potential use in the development of
spintronic devices. However, concerns on the stability of the magnetic
properties of different DMS systems have been raised. Their magnetic moment is
often unstable, vanishing with a characteristic decay time of weeks or months,
which precludes the development of real applications. This paper reports on the
ferromagnetic properties of two-year-aged Ti1-xCoxO2-{\delta} reduced anatase
nanopowders with different Co contents (0.03<x<0.10). Aged samples retain
rather high values of magnetization, remanence and coercivity which provide
strong evidence for a quite preserved long-range ferromagnetic order. In what
concern Co segregation, some degree of metastability of the diluted Co doped
anatase structure could be inferred in the case of the sample with the higher
Co content.",1009.4671v1
2010-11-15,Light-induced size changes in BiFeO3 crystals,"Multifunctional oxides are promising materials because of their fundamental
physical properties as well as their potential in applications1. Among these
materials, multiferroics exhibiting ferroelectricity and magnetism are good
candidates for spin electronic applications using the magnetoelectric effect,
which couples magnetism and ferroelecticity. Furthermore, because
ferroelectrics are insulators with a reasonable bandgap, photons can
efficiently interact with electrons leading to photoconduction or photovoltaic
effects. However, until now, coupling of light with mechanical degrees of
freedom has been elusive, although ferroelasticity is a well-known property of
these materials. Here, we report on the observation, for the first time, of a
substantial visiblelight- induced change in the dimensions of BiFeO3 crystals
at room temperature. The relative light-induced photostrictive effect is of the
order of 10e-5 with response times below 0.1s. It depends on the polarization
of incident light as well as applied magnetic fields. This opens the
perspective of combining mechanical, magnetic, electric and optical
functionalities in future generations of remote switchable devices.",1011.3398v1
2010-11-25,First-principles investigation of the very large Perpendicular Magnetic Anisotropy at Fe|MgO Interfaces,"The perpendicular magnetic anisotropy (PMA) arising at the interface between
ferromagnetic transition metals and metallic oxides are investigated via
first-principles calculations. In this work very large values of PMA up to 3
erg/cm$^2$ at Fe$|$MgO interfaces are reported in agreement with recent
experiments. The origin of PMA is attributed to overlap between O-$p_z$ and
transition metal $d_{z^2}$ orbitals hybridized with $d_{xz(yz)}$ orbitals with
stronger spin-orbit coupling induced splitting around the Fermi level for
perpendicular magnetization orientation. Furthemore, it is shown that the PMA
value weakens in case of over- or underoxidation when oxygen $p_z$ and
transition metal $d_{z^2}$ orbitals overlap is strongly affected by disorder,
in agreement with experimental observations in magnetic tunnel junctions.",1011.5667v1
2011-04-07,Integer spin-chain antiferromagnetism of the 4d oxide CaRuO3 with post-perovskite structure,"A quasi-one dimensional magnetism was discovered in the post-perovskite
CaRuO3 (Ru4+: 4d4, Cmcm), which is iso-compositional with the perovskite CaRuO3
(Pbnm). An antiferromagnetic spin-chain function with -J/kB = 350 K well
reproduces the experimental curve of the magnetic susceptibility vs.
temperature, suggesting long-range antiferromagnetic correlations. The
anisotropic magnetism is probably owing to the dyz - 2p- dzx and dzx - 2p- dyz
superexchange bonds along a-axis. The Sommerfeld coefficient of the specific
heat is fairly small, 0.16(2) mJ mol-1 K-2, indicating that the magnetism
reflects localized nature of the 4d electrons. As far as we know, this is the
first observation of an integer (S = 1) spin-chain antiferromagnetism in the 4d
electron system.",1104.1461v1
2011-04-25,"Spin canted magnetism, decoupling of charge and spin ordering in NdNiO$_3$","We report detailed magnetization measurements on the perovskite oxide
NdNiO$_3$. This system has a first order metal-insulator (M-I) transition at
about 200 K which is associated with charge ordering. There is also a
concurrent paramagnetic to antiferromagnetic spin ordering transition in the
system. We show that the antiferromagnetic state of the nickel sublattice is
spin canted. We also show that the concurrency of the charge ordering and spin
ordering transitions is seen only while warming up the system from low
temperature. The transitions are not concurrent while cooling the system
through the M-I transition temperature. This is explained based on the fact
that the charge ordering transition is first order while the spin ordering
transition is continuous. In the magnetically ordered state the system exhibits
ZFC-FC irreversibilities, as well as history-dependent magnetization and aging.
Our analysis rules out the possibility of spin-glass or superparamagnetism and
suggests that the irreversibilities originate from magnetocrystalline
anisotropy and domain wall pinning.",1104.4766v2
2011-04-30,Magnetic hydrogels derived from polysaccharides with improved specific power absorption: potential devices for remotely triggered drug delivery,"We report on novel ferrogels derived from polysaccharides (sodium alginate
and chitosan) with embedded iron oxide nanoparticles synthesized in situ and
their combination with thermally responsive poly (N-isopropylacrylamide) for
externally-driven drug release using AC magnetic fields. Samples were
characterized by Raman spectroscopy, transmission electron microscopy (TEM) and
magnetic measurements. The obtained nanoparticles were found to be of ca. 10 nm
average size, showing magnetic properties very close to those of the bulk
material. The thermal response was measured by power absorption experiments,
finding specific power absorption (SPA) values between 100-300 W/g, which was
enough for attaining the lower critical solution temperature (LCST) of the
polymeric matrix within few minutes. This fast response makes these materials
good candidates for externally controlled drug release.",1105.0075v1
2011-09-19,Magnetic field-induced novel insulating phase in 2D superconductors,"DC and finite frequency transport measurements of thin films of amorphous
indium oxide that were driven through the critical point of
superconductor-insulator transition by the application of perpendicular
magnetic field are presented. The observation of non-monotonic dependence of
resistance on magnetic field in the insulating phase, novel transport
characteristics near the resistance peak and finite superfluid stiffness in the
insulating phase are all discussed from the point of view that suggests a
possible relation between the conduction mechanisms in the superconducting and
insulating phases. The results are summarized in the form of an experimental
phase diagram for disordered superconductors in the disorder-magnetic field
plane.",1109.4087v1
2012-06-08,Superconductivity with Rashba Spin-Orbit Coupling and Magnetic Field,"Two dimensional electron systems at oxide interfaces are often influenced by
a Rashba type spin- orbit coupling (SOC), which is tunable by a transverse
electric field. Ferromagnetism at the interface can simultaneously induce
strong local magnetic fields. This combination of SOC and magnetism leads to
asymmetric two-sheeted Fermi surfaces, on which either intra- or inter-band
pairing is favored. The superconducting order parameters are derived within a
microscopic pairing model realizing both, the Bardeen-Cooper-Schrieffer
superconductor with inter-band pairing in the regime of dominating magnetic
field, and a mixed-parity intra-band pairing state with finite-momentum pairing
in the regime of dominating SOC. We present a phase diagram for the
superconducting groundstates and analyze the density of states of the different
phases. The results are discussed in the context of superconductivity and
ferromagnetism at LaAlO3-SrTiO3 interfaces.",1206.1816v2
2013-01-02,Spin-orbital locked magnetic excitations in a half-metallic double perovskite Ba2FeReO6,"We present a powder inelastic neutron scattering study of magnetic
excitations in Ba$_2$FeReO$_6$, a member of the double perovskite family of
materials which exhibit half-metallic behavior and high Curie temperatures. We
find clear evidence of two well-defined dispersing magnetic modes in its low
temperature ferrimagnetic state. We develop a local moment model, which
incorporates the interaction of Fe spins with spin-orbit locked magnetic
moments on Re, and show that this captures our experimental observations. Our
study further opens up double perovskites as model systems to explore the
interplay of strong correlations and spin-orbit coupling in 5d transition metal
oxides.",1301.0327v1
2013-01-09,High coercivity induced by mechanical milling in cobalt ferrite powders,"In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 treated by mechanical milling with different grinding balls. The
cobalt ferrite nanoparticles were prepared using a simple hydrothermal method
and annealed at 500oC. The non-milled sample presented coercivity of about 1.9
kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42.
After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and
saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence
ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To
investigate the influence of the microstructure on the magnetic behavior of
these samples, we used X-ray powder diffraction (XPD), transmission electron
microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by
the Williamson-Hall plot was used to estimate the average crystallite size and
strain induced by mechanical milling in the samples.",1301.1945v1
2013-02-26,R-M interactions in R2BaMO5 (R=Y or Gd and M=Cu or Zn),"R2BaMO5 (R = Gd, Y and M = Cu, Zn) oxides have been studied by specific heat,
dc magnetic susceptibility, and electron paramagnetic resonance (EPR). For one
member of the series without magnetic moment at M, namely Gd2BaZnO5,
measurements reveal long range antiferromagnetic order at TN(Gd2BaZnO5) =
2.3(0.1)K, much lower than the Curie Weiss temperature of {\Theta}=15.9(0.3)K.
This indicates the existence of competing interactions that introduce a large
degree of magnetic frustration in the system. For Y2BaCuO5 the Cu Cu
interactions are responsible for the broad maximum in the magnetic contribution
to the specific heat centered at 18.5(0.01)K that stretches beyond the
instrumental limit of 25K. The strong Cu Cu interactions also present in
Gd2BaCuO5, combined with the Gd-Cu interaction, polarize the Gd sublattice
giving measurable contributions to the specific heat in the same temperature
range. In addition, they broaden the Gd EPR line and saturate its integrated
intensity. The ordering temperature of Gd ions is raised to
TN(Gd2BaCuO5)=12.0(0.1)K.",1302.6327v1
2013-06-09,Metallic Interface Emerging at Magnetic Domain Wall of Antiferromagnetic Insulator---Fate of Extinct Weyl Electrons,"Topological insulators, in contrast to ordinary semiconductors, accompany
protected metallic surfaces described by Dirac-type fermions. Here, we
theoretically show another emergent two-dimensional metal embedded in the bulk
insulator is realized at a magnetic domain wall. The domain wall has long been
studied as ingredients of both old-fashioned and leading-edge spintronics. The
domain wall here, as an interface of seemingly trivial antiferromagnetic
insulators, emergently realizes a functional interface preserved by zero modes
with robust two-dimensional Fermi surfaces, where pyrochlore iridium oxides
proposed to host condensed-matter realization of Weyl fermions offer such
examples at low temperatures. The existence of ingap states pinned at domain
walls, theoretically resembling spin/charge solitons in polyacetylene, and
protected as the edge of hidden one-dimensional weak Chern insulators
characterized by a zero-dimensional class A topological invariant, solves
experimental puzzles observed in R2Ir2O7 with rare earth elements R. The domain
wall realizes a novel quantum confinement of electrons and embosses a net
uniform magnetization, which enables magnetic control of electronic interface
transports beyond semiconductor paradigm.",1306.2022v3
2013-10-02,Full Control of Magnetism in Manganite Bilayer by Ferroelectric Polarization,"An oxide heterostructure made of manganite bilayers and ferroelectric
perovskites is predicted to lead to the full control of magnetism when
switching the ferroelectric polarizations. By using asymmetric polar interfaces
in the superlattices, more electrons occupy the Mn layer at the $n$-type
interface side than at the $p$-type side. This charge disproportionation can be
enhanced or suppressed by the ferroelectric polarization. Quantum model and
density functional theory calculations reach the same conclusion: a
ferromagnetic-ferrimagnetic phase transition with maximal change $>90%$ of the
total magnetization can be achieved by switching the polarization's direction.
This function is robust and provides full control of the magnetization's
magnitude, not only its direction, via electrical methods.",1310.0811v1
2013-12-31,Magnetic quantum ratchet effect in Si-MOSFETs,"We report on the observation of magnetic quantum ratchet effect in
metal-oxide-semiconductor field-effect-transistors on silicon surface
(Si-MOSFETs). We show that the excitation of an unbiased transistor by ac
electric field of terahertz radiation at normal incidence leads to a direct
electric current between the source and drain contacts if the transistor is
subjected to an in-plane magnetic field. The current rises linearly with the
magnetic field strength and quadratically with the ac electric field amplitude.
It depends on the polarization state of the ac field and can be induced by both
linearly and circularly polarized radiation. We present the quasi-classical and
quantum theories of the observed effect and show that the current originates
from the Lorentz force acting upon carriers in asymmetric inversion channels of
the transistors.",1401.0135v1
2014-01-05,Phase-coexistence and glass-like behavior in magnetic and dielectric solids with long range order,"Phase-coexistence in the manganese-oxide compounds or manganites with
colossal magneto-resistance (CMR) has been generally considered to be an
inhomogeneous ground state. An alternative explanation of phase-coexistence as
the manifestation of a disorder-broadened first order magnetic phase transition
being interrupted by the glasslike arrest of kinetics is now gradually gaining
ground. This kinetic arrest of a first order phase transitions, between two
states with long-range magnetic order, has actually been observed in various
other classes of magnetic materials in addition to the CMR manganites. The
underlying common features of this kinetic arrest of a first order phase
transition are discussed in terms of the phenomenology of glasses. The possible
manifestations of such glass-like arrested states across disorder-influenced
first order phase transitions in dielectric solids and in multiferroic
materials, are also discussed.",1401.0891v2
2014-04-04,Angular and temperature dependence of current induced spin-orbit effective fields in Ta/CoFeB/MgO nanowires,"Current induced spin-orbit effective magnetic fields in
metal/ferromagnet/oxide trilayers provide a new way to manipulate the
magnetization, which is an alternative to the conventional current induced spin
transfer torque arising from noncollinear magnetization. Ta/CoFeB/MgO
structures are expected to be useful for non-volatile memories and logic
devices due to its perpendicular anisotropy and large current induced
spin-orbit effective fields. However many aspects such as the angular and
temperature dependent phenomena of the effective fields are little understood.
Here, we evaluate the angular and temperature dependence of the current-induced
spin-orbit effective fields considering contributions from both the anomalous
and planar Hall effects. The longitudinal and transverse components of
effective fields are found to have strong angular dependence on the
magnetization direction at 300 K. The transverse field decreases significantly
with decreasing temperature, whereas the longitudinal field shows weaker
temperature dependence. Our results reveal important features and provide an
opportunity for a more comprehensive understanding of current induced
spin-orbit effective fields.",1404.1130v1
2014-07-02,Induced Ferromagnetism at BiFeO3/YBa2Cu3O7 Interfaces,"Transition metal oxides (TMOs) exhibit many emergent phenomena ranging from
high-temperature superconductivity and giant magnetoresistance to magnetism and
ferroelectricity. In addition, when TMOs are interfaced with each other, new
functionalities can arise, which are absent in individual components. Here, we
report results from first-principles calculations on the magnetism at the
BiFeO3/YBa2Cu3O7 interfaces. By comparing the total energy for various magnetic
spin configurations inside BiFeO3, we are able to show that a metallic
ferromagnetism is induced near the interface. We further develop an interface
exchange-coupling model and place the extracted exchange coupling interaction
strengths, from the first-principles calculations, into a resultant generic
phase diagram. Our conclusion of interfacial ferromagnetism is confirmed by the
presence of a hysteresis loop in field-dependent magnetization data. The
emergence of interfacial ferromagnetism should have implications to electronic
and transport properties.",1407.0722v1
2014-11-26,Electrical manipulation of orbital occupancy and magnetic anisotropy in manganites,"Electrical manipulation of lattice, charge, and spin has been realized
respectively by the piezoelectric effect, field-effect transistor, and electric
field control of ferromagnetism, bringing about dramatic promotions both in
fundamental research and industrial production. However, it is generally
accepted that the orbital of materials are impossible to be altered once they
have been made. Here we use electric-field to dynamically tune the electronic
phase transition in (La,Sr)MnO3 films with different Mn^4+/(Mn^3+ + Mn^4+)
ratios. The orbital occupancy and corresponding magnetic anisotropy of these
thin films are manipulated by gate voltage in a reversible and quantitative
manner. Positive gate voltage increases the proportion of occupancy of the
orbital and magnetic anisotropy that were initially favored by strain
(irrespective of tensile and compressive), while negative gate voltage reduces
the concomitant preferential orbital occupancy and magnetic anisotropy. Besides
its fundamental significance in orbital physics, our findings might advance the
process towards practical oxide-electronics based on orbital.",1411.7128v1
2014-12-08,The Phase Diagram in Electron-Doped LCCO,"Superconductors are a striking example of a quantum phenomenon in which
electrons move coherently over macroscopic distances without scattering. The
high-temperature superconducting oxides(cuprates) are the most studied class of
superconductors, composed of two-dimensional CuO2 planes separated by other
layers which control the electron concentration in the planes. A key unresolved
issue in cuprates is the relationship between superconductivity and magnetism.
In this paper, we report a sharp phase boundary of static three-dimensional
magnetic order in the electron-doped superconductor La2-xCexCuO4-d where small
changes in doping or depth from the surface switch the material from
superconducting to magnetic. Using low-energy spin polarized muons, we find
static magnetism disappears close to where superconductivity begins and well
below the doping where dramatic changes in the transport properties are
reported. These results indicate a higher degree of symmetry between the
electron and hole-doped cuprates than previously thought.",1412.2775v1
2015-02-06,"First-principles insights into f magnetism, a case study on some magnetic pyrochlores","First-principles calculations are performed to investigate f magnetism in
A$_2$Ti$_2$O$_7$ (A=Eu, Gd, Tb, Dy, Ho, Er, Yb) magnetic pyrochlore oxides. The
Hubbard U parameter and the relativistic spin orbit correction is applied for
more accurate description of the electronic structure of the systems. It is
argued that the main obstacle for first-principles study of these systems is
the multi-minima solutions of their electronic configuration. Among the studied
pyrochlores, Gd$_2$Ti$_2$O$_7$ shows the least multi-minima problem. The
crystal electric field theory is applied for phenomenological comparison of the
calculated spin and orbital moments with the experimental data.",1502.01814v1
2015-03-03,Magnetic Fields of Uranus and Neptune: Metallic Fluid Hydrogen,"The magnetic fields of the Ice Giant Planets Uranus and Neptune (U/N) are
unique in the solar system. Based on a substantial database measured on Earth
for representative planetary fluids at representative dynamic pressures up to
200 GPa (2 Mbar) and a few 1000 K, the complex magnetic fields of U/N are (i)
probably made primarily by degenerate metallic fluid H (MFH) at or near the
crossover from the H-He envelopes to Ice cores at ~100 GPa (Mbar) pressures and
normalized radii of ~90% of the radii of U/N; (ii) because those magnetic
fields are made relatively close to the surfaces of U/N, non-dipolar fields can
be expected; (iii) the Ice cores are most probably a heterogeneous fluid
mixture of H, N, O, C, Fe/Ni and silicate-oxides and their mutual reaction
products at high pressures and temperatures,as discussed elsewhere. Ironically,
there is probably little nebular Ice in the Ice Giant Planets.",1503.01042v2
2015-03-31,Magnetic Phase Diagram of the Breathing Pyrochlore Antiferromagnet LiGa1-xInxCr4O8,"The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore
lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation.
We show here that the solid solutions LiGa1-xInxCr4O8 between these two
'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and
structural transitions upon doping the end members, (ii) spin-glass-like
freezing above 2 K in the range 0.1 $\lesssim$ x $\lesssim$ 0.6, and (iii)
apparent spin-gap behavior for x $\gtrsim$ 0.7. Furthermore, no transitions are
observed above 2 K at x ~ 0.9, where magnetic susceptibility remains finite at
2 K and magnetic heat capacity shows a quadratic temperature dependence at 1-5
K. Our work shows that breathing pyrochlore compounds provide a unique
opportunity for studying both geometrical frustration and bond alternation.",1503.08902v1
2015-04-10,Variation of magnetic properties of Sr$_2$FeMoO$_6$ due to oxygen vacancies,"Oxygen vacancies can be of utmost importance for improving or deteriorating
physical properties of oxide materials. Here, we studied from first-principles
the electronic and magnetic properties of oxygen vacancies in the double
perovskite Sr$_2$FeMoO$_6$ (SFMO). We show that oxygen vacancies can increase
the Curie temperature in SFMO, although the total magnetic moment is reduced at
the same time. We found also that the experimentally observed valence change of
the Fe ions from $3+$ to $2+$ in the x-ray magnetic circular dichroism (XMCD)
measurements is better explained by oxygen vacancies than by the assumed mixed
valence state. The agreement of the calculated x-ray absorption spectra and
XMCD results with experimental data is considerably improved by inclusion of
oxygen vacancies.",1504.02629v6
2015-05-04,Composite spin and quadrupole wave in the ordered phase of Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$,"The hidden ordered state of the frustrated pyrochlore oxide
Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ is possibly one of the two electric multipolar,
or quadrupolar, states of the effective pseudospin-1/2 Hamiltonian derived from
crystal-field ground state doublets of non-Kramers Tb$^{3+}$ ions. These
long-range orders are antiparallel or parallel alignments of transverse
pseudospin components representing electric quadrupole moments, which cannot be
observed as magnetic Bragg reflections by neutron scattering. However
pseudospin waves of these states are composite waves of the magnetic-dipole and
electric-quadrupole moments, and can be partly observed by inelastic magnetic
neutron scattering. We calculate these spin-quadrupole waves using linear
spin-wave theory and discuss previously observed low-energy magnetic excitation
spectra of a polycrystalline sample with $x = 0.005$ ($T_{\text{c}} = 0.5 $ K).",1505.00503v5
2015-09-03,Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures,"We measure the dissipation and frequency shift of a magnetically coupled
cantilever in the vicinity of a silicon chip, down to $25$ mK. The dissipation
and frequency shift originates from the interaction with the unpaired
electrons, associated with the dangling bonds in the native oxide layer of the
silicon, which form a two dimensional system of electron spins. We approach the
sample with a $3.43$ $\mu$m-diameter magnetic particle attached to an ultrasoft
cantilever, and measure the frequency shift and quality factor as a function of
temperature and the distance. Using a recent theoretical analysis [J. M. de
Voogd et al., arXiv:1508.07972 (2015)] of the dynamics of a system consisting
of a spin and a magnetic resonator, we are able to fit the data and extract the
relaxation time $T_1=0.39\pm0.08$ ms and spin density $\sigma=0.14\pm0.01$
spins per nm$^2$. Our analysis shows that at temperatures $\leq500$ mK magnetic
dissipation is an important source of non-contact friction.",1509.01251v2
2016-04-16,"Spin-orbit excitation energies, anisotropic exchange, and magnetic phases of honeycomb RuCl3","Using quantum chemistry calculations we shed fresh light on the electronic
structure and magnetic properties of RuCl3, a proposed realization of the
honeycomb Kitaev spin model. It is found that the nearest-neighbor Kitaev
exchange K is weaker than in 5d5 Ir oxides but still larger than other
effective spin couplings. The electronic-structure computations also indicate a
ferromagnetic K in the halide, which is supported by a detailed analysis of the
field-dependent magnetization. From exact-diagonalization calculations for
extended Kitaev-Heisenberg Hamiltonians we additionally find that a transition
from zigzag order to a spin-liquid ground state can be induced in RuCl3 with
external magnetic field.",1604.04755v1
2016-06-13,Electronic and magnetic structures and bonding properties of Ce2CrN3 and U2CrN3 from first principles,"The electronic and magnetic structures of A2CrN3 (A = Ce, U) ternary
compounds calculated based on band magnetism within DFT exhibit different
behaviors of the nf elements (n = 4, 5 resp.). Charge analysis allows to
formally express the two compounds as A2Cr 5+ N3 5- thus classifying them as
covalent nitrides, i.e. far from formal exchange of +- 9 electrons. From
establishing the energy-volume equations of state, the two compounds are found
with hardness magnitudes: B0(A=Ce) =192 GPa and B0(A=U) = 243 GPa, within range
of oxides due to covalent metal-nitrogen bonding shown as based on overlap
matrix analysis. The uranium compound is harder due to a smaller volume and
less compressible U versus Ce metals. Ce2CrN3 exhibits large magnetization on
Cr (1.94BM) and a very small moment develops on cerium (0.14 BM) pointing out
to an intermediate valence state while in U2CrN3, M(Cr) = 0.49 BM and M(U) =
0.97BM. These results are stressed by broad band-like density of states (DOS)
behavior for A=U and localized DOS for A=Ce. Both compounds are found
ferromagnetic in the ground state",1606.04066v1
2017-03-29,Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Films,"Magnetic skyrmions are topological spin structures having immense potential
for energy efficient spintronic devices. However, observations of skyrmions at
room temperature are limited to patterned nanostructures. Here, we report the
observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film
heterostructures at room temperature and in zero external magnetic field
employing magnetic force microscopy. The skyrmions are observed in a trilayer
structure comprised of heavy metal (HM)/ferromagnet (FM)/Oxide interfaces which
result in strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as
evidenced by Brillouin light scattering measurements, in agreement with the
results of micromagnetic simulations. We also emphasize on room temperature
observation of multiple skyrmions which can be stabilized for suitable choices
of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These
results open up a new paradigm for designing room temperature spintronic
devices based on skyrmions in FM continuous thin films.",1703.10224v1
2017-08-09,Bubble Magnetometry of Nanoparticle Heterogeneity and Interaction,"Bubbles have a rich history as transducers in particle-physics experiments.
In a solid-state analogue, we use bubble domains in nanomagnetic films to
measure magnetic nanoparticles. This technique can determine the magnetic
orientation of a single nanoparticle in a fraction of a second, and generate a
full hysteresis loop in a few seconds, which is much faster than any other
reported technique. We achieve this unprecedented speed by tuning the
nanomagnetic properties of the films, including the Dzyaloshinskii-Moriya
interaction, in the first application of topological protection from the
skyrmion state to a nanoparticle sensor. We demonstrate the technique on
iron/nickel nanorods and iron oxide nanoparticles, which delineate a wide range
of properties and applications. Bubble magnetometry enables the first
measurement with high throughput for statistical analysis of the magnetic
hysteresis of dispersed nanoparticles, and the first direct measurement of a
transition from superparamagnetic behavior as single nanoparticles to
collective behavior in nanoscale agglomerates. These results demonstrate a
breakthrough capability for measuring the heterogeneity and interaction of
magnetic nanoparticles.",1708.02706v2
2018-02-16,Carrier driven antiferromagnetism and exchange-bias in SrRuO3/CaRuO3 heterostructures,"Oxide heterostructures exhibit a rich variety of magnetic and transport
properties which arise due to contact at an interface. This can lead to
surprising effects that are very different from the bulk properties of the
materials involved. We report the magnetic properties of bilayers of SrRuO3, a
well known ferromagnet, and CaRuO3, which is nominally a paramagnet. We find
intriguing features that are consistent with CaRuO3 developing dual magnetic
character, with both a net moment as well as antiferromagnetic order. We argue
the ordered SrRuO3 layer induces an undulating polarization profile in the
conduction electrons of CaRuO3, by a mechanism akin to Friedel oscillations. At
low temperatures, this oscillating polarization is inherited by rigid local
moments within CaRuO3, leading to a robust exchange bias. We present ab initio
simulations in support of this picture. Our results demonstrate a new ordering
mechanism and throw light on the magnetic character of CaRuO3 .",1802.05869v1
2018-04-25,Spin precession in anisotropic media,"We generalize the diffusive model for spin injection and detection in
nonlocal spin structures to account for spin precession under an applied
magnetic field in an anisotropic medium, for which the spin lifetime is not
unique and depends on the spin orientation.We demonstrate that the spin
precession (Hanle) line shape is strongly dependent on the degree of anisotropy
and on the orientation of the magnetic field. In particular, we show that the
anisotropy of the spin lifetime can be extracted from the measured spin signal,
after dephasing in an oblique magnetic field, by using an analytical formula
with a single fitting parameter. Alternatively, after identifying the
fingerprints associated with the anisotropy, we propose a simple scaling of the
Hanle line shapes at specific magnetic field orientations that results in a
universal curve only in the isotropic case. The deviation from the universal
curve can be used as a complementary means of quantifying the anisotropy by
direct comparison with the solution of our generalized model. Finally, we
applied our model to graphene devices and find that the spin relaxation for
graphene on silicon oxide is isotropic within our experimental resolution.",1804.09426v1
2010-05-19,2D orbital-like magnetic order in ${\rm La_{2-x}Sr_xCuO_4}$,"In high temperature copper oxides superconductors, a novel magnetic order
associated with the pseudogap phase has been identified in two different
cuprate families over a wide region of temperature and doping. We here report
the observation below 120 K of a similar magnetic ordering in the archetypal
cuprate ${\rm La_{2-x}Sr_xCuO_4}$ (LSCO) system for x=0.085. In contrast to the
previous reports, the magnetic ordering in LSCO is {\it\bf only} short range
with an in-plane correlation length of $\sim$ 10 \AA\ and is bidimensional
(2D). Such a less pronounced order suggests an interaction with other
electronic instabilities. In particular, LSCO also exhibits a strong tendency
towards stripes ordering at the expense of the superconducting state.",1005.3406v1
2013-08-05,Spin and Orbital Contributions to Magnetically Ordered Moments in 5d Layered Perovskite Sr2IrO4,"The ratio of orbital (L) and spin (S) contributions to the magnetically
ordered moments of a 5d transition metal oxide, Sr2IrO4 was evaluated by
non-resonant magnetic x-ray diffraction. We applied a new experimental setting
to minimize the error in which we varied only the linear-polarization of
incident x-ray at a fixed scattering angle. Strong polarization dependence of
the intensity of magnetic diffraction was observed, from which we conclude that
the ordered moments contain substantial contribution from the orbital degree of
freedom with the ratio of <L>/<S> ~5.0, evidencing the pronounce effect of
spin-orbit coupling. The obtained ratio is close to but slightly larger than
the expected value for the ideal J_eff = 1/2 moment of a spin-orbital Mott
insulator, |<J_1/2|L_z|J_1/2>|/|<J_1/2|S_z|J_1/2>| = 4, which cannot be
accounted by the redistribution of orbital components within the t_2g bands
associated with the elongation of the IrO6 octahedra.",1308.0923v1
2013-08-15,Magnetic Phase Diagram of a Five-Orbital Hubbard Model in the Real-Space Hartree Fock Approximation Varying the Electronic Density,"Using the real-space Hartree Fock approximation, the magnetic phase diagram
of a five-orbital Hubbard model for the iron-based superconductors is studied
varying the electronic density $n$ in the range from 5 to 7 electrons per
transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed
Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing
magnetic states are observed. At $n$=5, a robust G-type antiferromagnetic
insulator is found, in agreement with experimental results for BaMn$_2$As$_2$.
As $n$ increases away from 5, magnetic states with an increasing number of
nearest-neighbors ferromagnetic links become energetically stable. This
includes the well-known C-type antiferromagnetic state at $n$=6, the E-phase
known to exist in FeTe, and also a variety of novel states not found yet
experimentally, some of them involving blocks of ferromagnetically oriented
spins. Regions of phase separation, as in Mn-oxides, have also been detected.
Comparison with previous theoretical investigations indicate that these
qualitative trends may be generic characteristics of phase diagrams of
multiorbital Hubbard models.",1308.3426v1
2014-03-19,Nature of Structural Changes Near the Magnetic Ordering Temperature in Small-Ion Rare Earth Perovskites RMnO3,"Detailed structural measurements were conducted on a new perovskite, ScMnO3,
and on orthorhombic LuMnO3. Complementary density functional theory (DFT)
calculations were carried out, and predict that ScMnO3 possesses E-phase
magnetic order at low temperature with displacements of the Mn sites (relative
to the high temperature state) of ~0.07 {\AA}, compared to ~ 0.04 {\AA}
predicted for LuMnO3. However, detailed local, intermediate and long-range
structural measurements by x-ray pair distribution function analysis, single
crystal x-ray diffraction and x-ray absorption spectroscopy, find no local or
long- range distortions on crossing into the low temperature E-phase of the
magnetically ordered state. The measurements place upper limits on any
structural changes to be at most one order of magnitude lower than density
functional theory predictions and suggest that this theoretical approach does
not properly account for the spin-lattice coupling in these oxides and may
possibly predict the incorrect magnetic order at low temperatures. The results
suggest that the electronic contribution to the electrical polarization
dominates and should be properly treated in theoretical models.",1403.4807v1
2016-11-08,Thermal and Magnetic Properties of Nanostructured Ferrimagnetic Composites with Graphene - Graphite Fillers,"We report the results of an experimental study of thermal and magnetic
properties of nanostructured ferrimagnetic iron oxide composites with graphene
and graphite fillers synthesized via the current activated pressure assisted
densification. The thermal conductivity was measured using the laser-flash and
transient plane source techniques. It was demonstrated that addition of 5 wt. %
of equal mixture of graphene and graphite flakes to the composite results in a
factor of x2.6 enhancement of the thermal conductivity without significant
degradation of the saturation magnetization. The microscopy and spectroscopic
characterization reveal that sp2 carbon fillers preserve their crystal
structure and morphology during the composite processing. The strong increase
in the thermal conductivity was attributed to the excellent phonon heat
conduction properties of graphene and graphite. The results are important for
energy and electronic applications of the nanostructured permanent magnets.",1611.02359v1
2017-01-09,Absence of magnetic long range order in Ba$_3$ZnRu$_2$O$_9$: A spin-liquid candidate in the $S=3/2$ dimer lattice,"We have discovered a novel candidate for a spin liquid state in a ruthenium
oxide composed of dimers of $S = $ 3/2 spins of Ru$^{5+}$,Ba$_3$ZnRu$_2$O$_9$.
This compound lacks a long range order down to 37 mK, which is a temperature
5000-times lower than the magnetic interaction scale of around 200 K. Partial
substitution for Zn can continuously vary the magnetic ground state from an
antiferromagnetic order to a spin-gapped state through the liquid state. This
indicates that the spin-liquid state emerges from a delicate balance of inter-
and intra-dimer interactions, and the spin state of the dimer plays a vital
role. This unique feature should realize a new type of quantum magnetism.",1701.02257v2
2017-01-14,Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces,"We report on the perpendicular magnetic anisotropy (PMA) behavior of heavy
metal (HM)/ Fe alloy/MgO thin film heterostructures after an ultrathin HfO2
passivation layer is inserted between the Fe alloy and the MgO. This is
accomplished by depositing one to two atomic layers of Hf onto the Fe alloy
before the subsequent rf sputter deposition of the MgO layer. This Hf layer is
fully oxidized during the subsequent deposition of the MgO layer, as confirmed
by X-ray photoelectron spectroscopy measurements. As the result a strong
interfacial perpendicular anisotropy energy density can be achieved without any
post-fabrication annealing treatment, for example 1.7 erg/cm^2 for the
Ta/Fe60Co20B20/HfO2/MgO heterostructure. Depending on the HM, further
enhancements of the PMA can be realized by thermal annealing to at least 400C.
We show that ultra-thin HfO2 layers offer a range of options for enhancing the
magnetic properties of magnetic heterostructures for spintronics applications.",1701.03933v1
2017-01-24,Spin mediated enhanced negative magnetoresistance in Ni80Fe20 and p-silicon bilayer,"In this work, we present an experimental study of spin mediated enhanced
negative magnetoresistance in Ni80Fe20 (50 nm)/p-Si (350 nm) bilayer. The
resistance measurement shows a reduction of ~2.5% for the bilayer specimen as
compared to 1.3% for Ni80Fe20 (50 nm) on oxide specimen for an out-of-plane
applied magnetic field of 3T. In the Ni80Fe20-only film, the negative
magnetoresistance behavior is attributed to anisotropic magnetoresistance. We
propose that spin polarization due to spin-Hall effect is the underlying cause
of the enhanced negative magnetoresistance observed in the bilayer. Silicon has
weak spin orbit coupling so spin Hall magnetoresistance measurement is not
feasible. We use V2{\omega} and V3{\omega} measurement as a function of
magnetic field and angular rotation of magnetic field in direction normal to
electric current to elucidate the spin-Hall effect. The angular rotation of
magnetic field shows a sinusoidal behavior for both V2{\omega} and V3{\omega},
which is attributed to the spin phonon interactions resulting from the
spin-Hall effect mediated spin polarization. We propose that the spin
polarization leads to a decrease in hole-phonon scattering resulting in
enhanced negative magnetoresistance.",1701.07049v1
2012-04-10,Observation of spin-glass behavior in nickel adsorbed few layer graphene,"Nickel-adsorbed graphene was prepared by first synthesizing graphite oxide
(GO) by modified Hummers' method and then reducing a solution containing both
GO and $Ni^{2+}$. EDX analysis showed 31 atomic percent nickel was present.
Magnetization measurements under both dc and ac magnetic fields were carried
out in the temperature range 2 K to 300 K. The zero field cooled and field
cooled magnetization data showed a pronounced irreversibility at a temperature
around 20 K. The analysis of the ac susceptibility data were carried out by
both Vogel-Fulcher as well as power law. From dynamic scaling analysis the
microscopic flipping time $\tau_{0}\sim 10^{-13} s$ and critical exponent
$z\nu=5.9\pm0.1$ were found, indicating presence of conventional spin glass in
the system. The spin glass transition temperature was estimated as 19.5 K.
  Decay of thermoremanent magnetization (TRM) was explained by stretched
exponential function with a value of the exponent as 0.6 .
  From the results it is concluded that nickel adsorbed graphene behaves like a
spin-glass.",1204.2123v2
2012-04-27,"Disorder, cluster spin glass, and hour-glass spectra in striped magnetic insulators","Hour-glass-shaped magnetic excitation spectra have been detected in a variety
of doped transition-metal oxides with stripe-like charge order. Compared to the
predictions of spin-wave theory, these spectra display a different intensity
distribution and anomalous broadening. Here we show, based on a comprehensive
modelling of these phenomena for La5/3Sr1/3CoO4, how quenched disorder in the
charge sector causes frustration, and consequently cluster-glass behavior at
low temperatures, in the spin sector. This spin-glass physics, which is
insensitive to the detailed nature of the charge disorder, but sensitive to the
relative strength of the magnetic inter-stripe coupling, ultimately determines
the distribution of magnetic spectral weight and thus causes the hour-glass
spectrum.",1204.6323v2
2016-08-10,Effect of rare-earth (Er and Gd) substitution on the magnetic and multiferroic properties of DyFe0.5Cr0.5O3,"We report the results of our investigations on the influence of partial
substitution of Er and Gd for Dy on the magnetic and magnetoelectric properties
of DyFe0.5Cr0.5O3, which is known to be a multiferroic system. Magnetic
susceptibility and heat capacity data, apart from confirming the occurrence of
magnetic transitions at ~ 121 and 13 K in DyFe0.5Cr0.5O3, bring out that the
lower transition temperature only is suppressed by rare-earth substitution.
Multiferroic behavior is found to persist in Dy0.4Ln0.6Fe0.5Cr0.5O3 (Ln= Er and
Gd). There is an evidence for magnetoelectric coupling in all these materials
with qualitative differences in its behavior as the temperature is changed
across these two transitions. Remnant electric polarization is observed for all
the compounds. The most notable observation is that electric polarization is
seen to get enhanced as a result of rare-earth substitution with respect to
that in DyFe0.5Cr0.5O3. Interestingly, similar trend is seen in magnetocaloric
effect, consistent with the existence of magnetoelectric coupling. The results
thus provide evidence for the tuning of magnetoelectric coupling by rare-earth
substitution in this family of oxides.",1608.03228v1
2018-09-19,Incorporation of magnetic nanoparticles into lamellar polystyrene-b-poly(n-butyl methacrylate) diblock copolymer films: influence of the chain end-groups on nanostructuration,"In this article, we present new samples of lamellar magnetic nanocomposites
based on the self-assembly of a polystyrene-b-poly(n-butyl methacrylate)
diblock copolymer synthesized by atom transfer radical polymerization. The
polymer films were loaded with magnetic iron oxide nanoparticles covered with
polystyrene chains grown by surface initiated-ATRP. The nanostructuration of
the pure and magnetically loaded copolymer films on silicon was studied by
atomic force microscopy, ellipsometry, neutron reflectivity and contact angle
measurement. The present study highlights the strong influence of the copolymer
extremity - driven itself by the choice of the ATRP chemical route - on the
order of the repetition sequences of the blocks in the multi-lamellar films. In
addition, a narrower distribution of the nanoparticles' sizes was examined as a
control parameter of the SI-ATRP reaction.",1809.07063v1
2018-09-27,"$\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ Alloy Nanoparticles Encapsulated inside Carbon Nanotubes: Controlled Synthesis, Structure and Magnetic Properties","In the present work, different synthesis procedures have been demonstrated to
fill carbon nanotubes (CNTs) with $\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ alloy
nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of
magnetic nanoparticles, and provide a protective shield against oxidation as
well as prevent nanoparticles agglomeration. By variation of the reaction
parameters, the purity of the samples, degree of filling, the composition and
size of filling nanoparticles have been tailored and therefore the magnetic
properties. The samples were analyzed by scanning electron microscopy (SEM),
transmission electron microscopy (TEM), Bright-field (BF) TEM tomography, X-ray
powder diffraction, superconducting quantum interference device (SQUID) and
thermogravimetric analysis (TGA). The Fe1-xNix-filled CNTs show a huge
enhancement in the coercive fields compared to the corresponding bulk
materials, which make them excellent candidates for several applications such
as magnetic storage devices.",1809.10500v1
2018-09-28,Defect-induced exchange bias in a single SrRuO3 layer,"Exchange bias stems from the interaction between different magnetic phases
and therefore it generally occurs in magnetic multilayers. Here we present a
large exchange bias in a single SrRuO3 layer induced by helium ion irradiation.
When the fluence increases, the induced defects not only suppress the
magnetization and the Curie temperature, but also drive a metal-insulator
transition at a low temperature. In particular, a large exchange bias field up
to around 0.36 T can be created by the irradiation. This large exchange bias is
related to the coexistence of different magnetic and structural phases that are
introduced by embedded defects. Our work demonstrates that spintronic
properties in complex oxides can be created and enhanced by applying ion
irradiation.",1809.11035v1
2019-09-05,Large off diagonal exchange couplings and spin liquid states in $\mathbf{C_3}$ symmetric iridates,"Iridate oxides on a honeycomb lattice are considered promising candidates for
realization of quantum spin liquid states. We investigate the magnetic
couplings in a structural model for a honeycomb iridate K$_2$IrO$_3$, with
$C_3$ point group symmetry at the Ir sites, which is an end member of the
recently synthesized iridate family K$_x$Ir$_y$O$_2$. Using \textit{ab-initio}
quantum chemical methods, we elucidate the subtle relationship between the real
space symmetry and magnetic anisotropy and show that the higher point group
symmetry leads to high frustration with strong magnetic anisotropy driven by
the unusually large off-diagonal exchange couplings ($\Gamma$'s) as opposed to
other spin-liquid candidates considered so far. Consequently, large quantum
fluctuations imply lack of magnetic ordering consistent with the experiments.
Exact diagonalization calculations for the fully anisotropic $K$-$J$-$\Gamma$
Hamiltonian reveal the importance of the off-diagonal anisotropic exchange
couplings in stabilizing a spin liquid state and highlight an alternative route
to stabilize spin liquid states for ferromagnetic $K$.",1909.02277v1
2017-11-28,Interplay of spin-orbit coupling and hybridization in Ca3LiOsO6 and Ca3LiRuO6,"The electronic ground state of Ca3LiOsO6 was recently considered within an
intermediate coupling regime that revealed J=3/2 spin-orbit entangled magnetic
moments. Through inelastic neutron scattering and density functional theory we
investigate the magnetic interactions and probe how the magnetism is influenced
by the change in hierarchy of interactions as we move from Ca3LiOsO6 (5d3) to
Ca3LiRuO6 (4d3). An alteration of the spin-gap and ordered local moment is
observed, however the magnetic structure, Neel temperature and exchange
interactions are unaltered. To explain this behavior it is necessary to include
both spin-orbit coupling and hybridization, indicating the importance of an
intermediate coupling approach when describing 5$d$ oxides.",1711.10393v1
2018-06-18,Impurity-induced vector spin chirality and anomalous Hall effect in ferromagnetic metals,"Scattering by multiple scatterers sometimes gives rise to nontrivial
consequences such as anomalous Hall effect. We here study a mechanism for
anomalous Hall effect which originates from the correlation of nonmagnetic
impurities and localized moments; a Hall effect induced by vector spin
chirality. Using a scattering theory approach, we study the skew scattering
induced by the scattering processes that involve two magnetic moments and a
non-magnetic impurity, which is proportional to the vector spin chirality of
the spins in the vicinity of the non-magnetic impurity. Furthermore, we show
that a finite vector spin chirality naturally exists around an impurity in the
usual ferromagnetic metals at finite temperature due to the local
inversion-symmetry breaking by the impurity. The result is potentially relevant
to magnetic oxides which the anomalous Hall effect is enhanced at finite
temperatures.",1806.06833v1
2018-06-25,Ferromagnetism above 1000 K in highly cation-ordered double-perovskite insulator Sr3OsO6,"Magnetic insulators have been intensively studied for over 100 years, and
they, in particular ferrites, are considered to be the cradle of magnetic
exchange interactions in solids. Their wide range of applications include
microwave devices and permanent magnets . They are also suitable for spintronic
devices owing to their high resistivity, low magnetic damping, and
spin-dependent tunneling probabilities. The Curie temperature is the crucial
factor determining the temperature range in which any ferri/ferromagnetic
system remains stable. However, the record Curie temperature has stood for over
eight decades in insulators and oxides (943 K for spinel ferrite LiFe5O8). Here
we show that a highly B-site ordered double-perovskite, Sr2(SrOs)O6 (Sr3OsO6),
surpasses this long standing Curie temperature record by more than 100 K. We
revealed this B-site ordering by atomic-resolution scanning transmission
electron microscopy. The density functional theory (DFT) calculations suggest
that the large spin-orbit coupling (SOC) of Os6+ 5d2 orbitals drives the system
toward a Jeff = 3/2 ferromagnetic (FM) insulating state. Moreover, the Sr3OsO6
is the first epitaxially grown osmate, which means it is highly compatible with
device fabrication processes and thus promising for spintronic applications.",1806.09308v1
2018-08-11,Role of Ce 4f hybridization in the origin of magnetism in nanoceria,"Nanoscale CeO2 (nanoceria) is a prototypical system that presents d0
ferromagnetism. Using a combination of x-ray absorption spectroscopy, x-ray
magnetic circular dichroism and modelling, we show that nanostructure, defects
and disorder, and non-stoichiometry create magnetically polarized Ce 4f and O
2p hybridized states captured by the vacancy orbitals (Vorb) that are vital to
ferromagnetism. Further, we demonstrate that foreign ions (Fe and Co) enhance
the moment at Ce 4f sites while the number of Vorb is unchanged, pointing
clearly to the mechanism of orbital hybridization being key missing ingredient
to understanding the unexpected ferromagnetism in many nanoscale dilute
magnetic oxides and semiconductors.",1808.03758v3
2019-01-30,Tuning the Magnetic Ordering Temperature of Hexagonal Ferrites by Structural Distortion Control,"To tune the magnetic properties of hexagonal ferrites, a family of
magnetoelectric multiferroic materials, by atomic-scale structural engineering,
we studied the effect of structural distortion on the magnetic ordering
temperature (TN). Using the symmetry analysis, we show that unlike most
antiferromagnetic rare-earth transition-metal perovskites, a larger structural
distortion leads to a higher TN in hexagonal ferrites and manganites, because
the K3 structural distortion induces the three-dimensional magnetic ordering,
which is forbidden in the undistorted structure by symmetry. We also revealed a
near-linear relation between TN and the tolerance factor and a power-law
relation between TN and the K3 distortion amplitude. Following the analysis, a
record-high TN (185 K) among hexagonal ferrites was predicted in hexagonal
ScFeO3 and experimentally verified in epitaxially stabilized films. These
results add to the paradigm of spin-lattice coupling in antiferromagnetic
oxides and suggests further tunability of hexagonal ferrites if more lattice
distortion can be achieved.",1901.11118v1
2019-02-12,Magnetically driven loss of centrosymmetry in metallic Pb2CoOsO6,"We report magnetic, transport, neutron diffraction, and muon spin rotation
data showing that Pb$_2$CoOsO$_6$, a newly synthesized metallic
double-perovskite with a centrosymmetric space group at room temperature,
exhibits a continuous second-order phase transition at 45 K to a magnetically
ordered state with a non-centrosymmetric space group. The absence of inversion
symmetry is very uncommon in metals, particularly metallic oxides. In contrast
to the recently reported ferroelectric-like structural transition in LiOsO$_3$,
the phase transition in Pb$_2$CoOsO$_6$ is driven by a long-range collinear
antiferromagnetic order, with propagation vector $\textbf{k} =
(\frac{1}{2},0,\frac{1}{2})$, which relieves the frustration associated with
the symmetry of themagnetic exchanges. This magnetically-driven loss of
inversion symmetry represents a new frontier in the search for novel metallic
behavior.",1902.04482v2
2019-02-20,Electron states and magnetic phase diagrams of strongly correlated systems,"Various auxiliary-particle approaches to treat electron correlations in
many-electron models are analyzed. Applications to copper-oxide layered systems
are discussed. The ground-state magnetic phase diagrams are considered within
the Hubbard and $s$-$d$ exchange (Kondo) models for square and simple cubic
lattices vs. band filling and interaction parameter. A generalized Hartree-Fock
approximation is employed to treat commensurate ferro-, antiferromagnetic, and
incommensurate (spiral) magnetic phases, and also magnetic phase separation.
The correlations are taken into account within the Hubbard model by using the
slave-boson approach. The main advantage of this approach is correct estimating
the contribution of doubly occupied states number and therefore the
paramagnetic phase energy.",1902.07431v1
2019-03-12,Superconductivity behavior in epitaxial TiN films points at surface magnetic disorder,"We analyze the evolution of the normal and superconducting electronic
properties in epitaxial TiN films, characterized by high Ioffe-Regel parameter
values, as a function of the film thickness. As the film thickness decreases,
we observe an increase of in the residual resistivity, which becomes dominated
by diffusive surface scattering for $d\leq20\,$nm. At the same time, a
substantial thickness-dependent reduction of the superconducting critical
temperature is observed compared to the bulk TiN value. In such a high quality
material films, this effect can be explained by a weak magnetic disorder
residing in the surface layer with a characteristic magnetic defect density of
$\sim10^{12}\,\mathrm{cm}^{-2}$. Our results suggest that surface magnetic
disorder is generally present in oxidized TiN films.",1903.05009v3
2019-04-08,"YBa2Cu3O7/LaXMnO3 (X: Ca, Sr) based Superconductor/Ferromagnet/Superconductor junctions with memory functionality","Complex oxides exhibit a variety of unusual physical properties, which can be
used for designing novel electronic devices. Here we fabricate and study
experimentally nano-scale Superconductor/ Ferromagnet/Superconductor junctions
with the high-Tc cuprate superconductor YBa2Cu3O7 and the colossal
magnetoresistive (CMR) manganite ferromagnets LaXMnO3 (X: Ca or Sr). We
demonstrate that in a broad temperature range the magnetization of a manganite
nanoparticle, forming the junction interface, switches abruptly in a
mono-domain manner. The CMR phenomenon translates the magnetization loop into a
hysteretic magnetoresistance loop. The latter facilitates a memory
functionality of such a junction with just a single CMR ferromagnetic layer.
The orientation of the magnetization (stored information) can be read out by
simply measuring the junction resistance in an applied magnetic field. The CMR
facilitates a large read-out signal in a small applied field. We argue that
such a simple single layer CMR junction can operate as a memory cell both in
the superconducting state at cryogenic temperatures and in the normal state up
to room temperature.",1904.03951v1
2020-09-30,Electronic structure and finite temperature magnetism of yttrium iron garnet,"Yttrium iron garnet is a complex ferrimagnetic insulator with 20 magnon modes
which is used extensively in fundamental experimental studies of magnetisation
dynamics. As a transition metal oxide with moderate gap (2.8 eV), yttrium iron
garnet requires a careful treatment of electronic correlation. We have applied
quasiparticle self-consistent GW to provide a fully ab initio description of
the electronic structure and resulting magnetic properties, including the
parameterisation of a Heisenberg model for magnetic exchange interactions.
Subsequent spin dynamical modelling with quantum statistics extends our
description to the magnon spectrum and thermodynamic properties such as the
Curie temperature, finding favourable agreement with experimental measurements.
This work provides a snapshot of the state-of-the art in modelling of complex
magnetic insulators.",2009.14601v1
2020-11-27,d0 Ferromagnetism in Mg-doped Rutile TiO2 Nanoparticles,"In a quest of enriching the area of d0 magnetism in oxide materials, we have
undertaken to study Mg-doped TiO2 compounds. The Ti1-xMgxO2 (x=0, 0.02, 0.04
and 0.06) nanoparticles were prepared by solid-state reaction route. The X-ray
diffractions (XRD) patterns of these samples indicate single phase of
tetragonal rutile-structure of TiO2. The refinement of the XRD patterns reveals
no change in the crystallographic lattice parameters in comparison to pure TiO2
upon Mg doping and it indicates that Mg2+ ions do not enter core grains and
form core/shell structure. SEM observations reveal the uniform morphology with
nanometric grains in the range of 150-200 nm. The measurement of magnetic
properties of these compounds indicates that pure TiO2 and Ti0.98Mg0.02
compounds exhibit paramagnetic behavior and Ti0.96Mg0.04 compound exhibits
ferromagnetic (FM) phase superimposed with the dominating paramagnetic phase.
However, Ti0.94Mg0.06 compound exhibits ferromagnetic to paramagnetic
transition with FM transition temperature of 180.2 K. The measurements of zero
field and field cooled magnetization data indicate low temperature magnetic
irreversibility for x=0.06 sample and it was attributed to the competing AFM
(core) and the FM (shell) interactions. The measurement of hysteresis curves at
various temperatures indicates domain wall pinning and an exchange-bias
behavior.",2011.13718v1
2021-03-20,Importance of anisotropic Coulomb interactions in the electronic and magnetic properties of Mn$_3$O$_4$,"We report the importance of anisotropic Coulomb interactions in DFT+U
calculations of the electronic and magnetic properties of Mn$_3$O$_4$. The
effects of anisotropic interactions in Mn$^{2+}$ and Mn$^{3+}$ are separately
examined by defining two different sets of Hubbard parameters: $U^{2+}$ and
$J^{2+}$ for Mn$^{2+}$ and $U^{3+}$ and $J^{3+}$ for Mn$^{3+}$. The anisotropic
interactions in Mn$^{3+}$ have a significant impact on the physical properties
of Mn$_3$O$_4$ including local magnetic moments, canted angle, spontaneous
magnetic moment, and superexchange coupling, but those in Mn$^{2+}$ do not make
any noticeable difference. Weak ferromagnetic interchain superexchange,
observed in experiments, is predicted only if a sizable anisotropic interaction
is considered in Mn$^{3+}$. By analyzing the eigenoccupations of the on-site Mn
density matrix, we found that the spin channel involving Mn$^{3+}$
$d_{x^2-y^2}$ orbitals, which governs the 90$^\circ$ correlation superexchange,
is directly controlled by the anisotropic interactions. These findings
demostrate that the exchange correction $J$ for the intraorbital Coulomb
potential is of critical importance for first-principles description of reduced
Mn oxides containing Mn$^{3+}$ or Mn$^{4+}$.",2103.11082v1
2021-04-16,Electronic and magnetic properties of VOCl/FeOCl antiferromagnetic heterobilayers,"We study the electronic properties of the heterobilayer of vanadium and iron
oxychlorides, VOCl and FeOCl, two layered air stable van der Waals insulating
oxides with different types of antiferromagnetic order in bulk: VOCl monolayers
are ferromagnetic (FM) whereas the FeOCl monolayers are antiferromagnetic (AF).
We use density functional theory (DFT) calculations, with Hubbard correction
that is found to be needed to describe correctly the insulating nature of these
compounds. We compute the magnetic anisotropy and propose a spin model
Hamiltonian. Our calculations show that interlayer coupling in weak and
ferromagnetic so that magnetic order of the monolayers is preserved in the
heterobilayers providing thereby a van der Waals heterostructure that combines
two monolayers with different magnetic order. Interlayer exchange should lead
both to exchange bias and to the emergence of hybrid collective modes that that
combine FM and AF magnons. The energy band of the heterobilayer show a type II
band alignment, and feature spin-splitting of the states of the AF layer due to
the breaking of the inversion symmetry.",2104.08214v1
2021-05-28,Exceptional sign changes of the non-local spin Seebeck effect in antiferromagnetic hematite,"Low power spintronic devices based on the propagation of pure magnonic spin
currents in antiferromagnetic insulator materials offer several distinct
advantages over ferromagnetic components including higher frequency magnons and
a stability against disturbing external magnetic fields. In this work, we make
use of the insulating antiferromagnetic phase of iron oxide, the mineral
hematite $\alpha$-Fe$_2$O$_3$ to investigate the long distance transport of
thermally generated magnonic spin currents. We report on the excitation of
magnons generated by the spin Seebeck effect, transported both parallel and
perpendicular to the antiferromagnetic easy-axis under an applied magnetic
field. Making use of an atomistic hematite toy model, we calculate the
transport characteristics from the deviation of the antiferromagnetic ordering
from equilibrium under an applied field. We resolve the role of the magnetic
order parameters in the transport, and experimentally we find significant
thermal spin transport without the need for a net magnetization.",2105.13653v1
2021-07-13,Exploration of trivial and non-trivial electronic phases and of collinear and non-collinear magnetic phases in low-spin d$^5$ perovskites,"The $4d$ and $5d$ transition metal oxides have become important members of
the emerging quantum materials family due to competition between onsite Coulomb
repulsion ($U$) and spin-orbit coupling (SOC). Specifically, the systems with
$d^5$ electronic configuration in an octahedral environment are found to be
capable of posessing invariant semimetallic state and perturbations can lead to
diverse magnetic phases. In this work, by formulating a multi-band Hubbard
model and performing SOC tunable DFT+$U$ calculations on a prototype SrIrO$_3$
and extending the analysis to other iso-structural and isovalent compounds, we
present eight possible electronic and magnetic configurations in the $U$-SOC
phase diagram that can be observed in the family of low-spin $d^5$ perovskites.
They include the protected Dirac semimetal state, metal and insulator regimes,
collinear and noncollinear spin ordering. The latter is explained through
connecting hopping interactions to the rotation and tilting of the octahedra as
observed in GdFeO$_3$. Presence of several soft phase boundaries makes the
family of $d^5$ perovskites an ideal platform to study electronic and magnetic
phase transitions under external stimuli.",2107.06016v2
2021-10-21,Micromagnetic simulations of clusters of nanoparticles with internal structure: Application to magnetic hyperthermia,"Micromagnetic simulation results on dynamic hysteresis loops of clusters of
iron oxide nanoparticles (NPs) with internal structure composed of nanorods are
compared with the widely used macrospin approximation. Such calculations
allowing for nanorod-composed NPs is facilitated by a previously developed
coarse-graining method based on the renormalization group approach. With a
focus on applications to magnetic hyperthermia, we show that magnetostatic
interactions improve the heating performance of NPs in chains and triangles,
and reduce heating performance in fcc arrangements. Hysteresis loops of
triangular and fcc systems of complex NPs are not recovered within the
macrospin approximation, especially at smaller interparticle distances. For
triangular arrangements, the macrospin approximation predicts that
magnetostatic interactions reduce loop area, in contrast to the complex NP
case. An investigation of the local hysteresis loops of individual NPs and
macrospins in clusters reveals the impact of the geometry of their neighbours
on individual versus collective magnetic response, inhomogenous heating within
clusters, and further differences between simulating NPs with internal
structure and the use of the macrospin approximation. Capturing the internal
physical and magnetic structure of NPs is thus important for some applications.",2110.11178v2
2022-01-27,Edge and Width Dependent Electronic Properties of Nanoribbons of Manganese Oxide,"In the present work, the structural, magnetic, and electronic properties of
the two- and one-dimensional honeycomb structures of recently synthesized MnO
[Zhang et al. Nat. Commun., 20, 1073-1078 (2021)] are investigated by using
first principles calculations. Our calculations show that the single layer 2D
MnO crystal has a degenerate antiferromagnetic (AFM) ground state and a
relatively less favorable ferromagnetic (FM) state. In addition, magnetic
anisotropy calculations unveil that the easy-axis direction for magnetism
originating from unpaired electron states in manganese atoms is normal to the
crystal plane. Electronically, while the FM-MnO is a direct semiconductor with
a narrow bandgap, AFM phases display large indirect bandgap semiconducting
behavior. Moreover, calculations on nanoribbons of MnO reveal that zigzag edged
ribbons display metallic bahavior, whereas armchair edged nanoribbons are
semiconductors. Magnetically, for both zigzag- or armchair-edged nanoribbons,
AFM order perpendicular to the nanoribbon growth direction is found to be
favorable over the other AFM and FM orders. Moreover, depending on the edge
symmetry and ribbon width, forbidden band gap values of nanoribbons display
distinct family behaviors.",2201.11698v1
2022-08-11,"A versatile platform for graphene nanoribbon synthesis, electronic decoupling, and spin polarized measurements","The on-surface synthesis of nano-graphenes has led the charge in prototyping
structures with perspectives beyond silicon-based technology. Following reports
of open-shell systems in graphene-nanoribbons (GNR), a flurry of research
activities is directed at investigating their magnetic properties with a keen
eye for spintronic applications. Although the synthesis of nano-graphenes is
usually straightforward on gold, it is difficult to use it for electronic
decoupling and spin-polarized measurements. Using a binary alloy Cu3Au(111), we
show how to combine the efficient gold-like nano-graphene formation with spin
polarization and electronic decoupling known from copper. We prepare copper
oxide layers, demonstrate thermally and tip-assisted synthesis of GNR and grow
thermally stable magnetic Co islands. We functionalize the tip of a scanning
tunneling microscope with carbon-monoxide, nickelocene, or attach Co clusters
for high-resolution imaging, magnetic sensing, or spin-polarized measurements.
This versatile platform will be a valuable tool in the advanced study of
magnetic nano-graphenes.",2208.05760v1
2022-09-22,Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgO$\text{/}$Fe$\text{/}$MgO films,"Broadband ferromagnetic resonance is measured in single crystalline Fe films
of varying thickness sandwiched between MgO layers. An exhaustive magnetic
characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first
perpendicular standing spin wave modes as a function of applied magnetic field
and film thickness. Additional measurements of non-reciprocal spin wave
propagation allow us to separate each of the two interface contributions to the
total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom
interfaces, a difference ascribed to different oxidation states.",2209.10906v2
2022-12-01,Weyl Metal Phase in Delafossite Oxide PtNiO$_2$,"On the basis of density functional theory calculations we predict Weyl points
in rhombohedral structure of PtNiO$_2$ having symmorphic symmetry. From the
formation energy and phonon calculations, PtNiO$_2$ is found to be structurally
stable. The magnetic ground state is ferromagnetic with an effective magnetic
moment of 1.01 $\mu_B$ per unit cell. The electronic structure shows major
contributions from Pt-$5d$, Ni-$3d$ and O-$2p$ orbitals with band crossing
close to the Fermi level. The orbital contribution around 8 eV above the Fermi
level are from the Pt-$s,p$ orbitals forming a kagome like electronic structure
confirmed by surface Fermi surface spectral function. We found 20 pairs of
confirmed Weyl nodes along the magnetic easy axis [100]. These results are
expected to provide a useful and exciting platform for exploring and
understanding the magnetic Weyl physics in delafossites.",2212.00579v2
2022-12-03,Magnetoplasmonics: current challenges and future opportunities,"Plasmonics represents a unique approach to confine and enhance
electromagnetic radiation well below the diffraction limit, bringing a huge
potential for novel applications, for instance in energy harvesting,
optoelectronics, and nanoscale biochemistry. To achieve novel functionalities,
the combination of plasmonic properties with other material functions has
become increasingly attractive. In this Perspective, we review the current
state of the art, challenges, and future opportunities in nanoscale
magnetoplasmonics, an emerging area aiming to merge magnetism and plasmonics in
confined geometries to control either plasmons, electromagnetic-induced
collective electronic excitations, using magnetic properties, or magnetic
phenomena with plasmons. We begin by highlighting the cornerstones of the
history and principles of this research field. We then provide our vision of
its future development by showcasing raising research directions in
mid-infrared light-driven spintronics and novel materials for
magnetoplasmonics, such as transparent conductive oxides and hyperbolic
metamaterials. As well, we provide an overview of recent developments in
plasmon-driven magnetization dynamics, nanoscale optomagnetism and
acousto-magnetoplasmonics. We conclude by giving our personal vision of the
future of this thriving research field.",2212.01684v1
2023-01-29,Anisotropic magnetic and magnetotransport properties in morphologically distinct Nd0.6Sr0.4MnO3 thin films,"We investigate the magnetic and magnetotransport properties of nanostructured
Nd0.6Sr0.4MnO3 (NSMO) thin films grown on (100) oriented SrTiO3 (STO)
substrates. The thin films fabricated using the pulsed laser deposition
technique have been found to possess two distinct surface morphologies:
granular and nano rod type. Magnetization measurements have revealed that the
films with rod-type morphology exhibit improved in-plane magnetic anisotropy.
Magnetotransport studies have revealed that the granular thin films display a
characteristic butterfly-shaped low-field magneto-resistive (LFMR) behavior.
Furthermore, we investigate the anisotropic magneto-resistive (AMR) phenomenon
in the samples and we find that morphology greatly affects AMR. Thin films with
rod-type morphology show an enhanced AMR %. Such morphology dependent
tunability in magnetoresistance properties over a wide temperature range is
potentially interesting for developing oxide-based sensors and devices.",2301.12406v1
2023-02-20,Magnetic properties of ferromagnetic Gd$_5$Si$_4$-Fe$_3$O$_4$ bilayer thin film heterostructure,"Magnetic properties of thin films differs from that of the corresponding bulk
materials and show novel physics as a result of their reduced size and
dimensionality. Profound changes in magnetic properties can also result with
exchange bias between the interface of the thin films of different materials.
Here we present Fe$_3$O$_4$, Gd$_5$Si$_4$ and Fe$_3$O$_4$-Gd$_5$Si$_4$ bilayer
thin films of varying thicknesses were prepared by RF Magnetron sputtering of
Fe$_3$O$_4$ and Gd$_5$Si$_4$ targets on silicon substrates in high vacuum.
Their magnetization was measured at room temperature in fields of 3T and
between 50 K to 400 K temperatures. Gd5Si4 films resulted in oxidation due to
the exposure to the air. Deposited film thickness of all the specimens are
larger than 50nm and show ferromagnetic behavior.",2302.09774v1
2023-03-26,Strong lateral exchange coupling and current-induced switching in single-layer ferrimagnetic films with patterned compensation temperature,"Strong, adjustable magnetic couplings are of great importance to all devices
based on magnetic materials. Controlling the coupling between adjacent regions
of a single magnetic layer, however, is challenging. In this work, we
demonstrate strong exchange-based coupling between arbitrarily shaped regions
of a single ferrimagnetic layer. This is achieved by spatially patterning the
compensation temperature of the ferrimagnet by either oxidation or He+
irradiation. The coupling originates at the lateral interface between regions
with different compensation temperature and scales inversely with their width.
We show that this coupling generates large lateral exchange coupling fields and
we demonstrate its application to control the switching of magnetically
compensated dots with an electric current.",2303.14809v1
2023-04-09,Competing spin-glass and spin-fluctuation states in NdxPr4-xNi3O8,"Neodymium nickelates have attracted research interest due to their strongly
correlated behaviour and remarkable magnetic properties. More importantly,
superconductivity has recently been confirmed in thin-film samples of Sr-doped
NdNiO2, bringing the layered rare earth nickel oxides into the research
spotlight. In this report, we present results on a series of NdNiO2 analogues,
NdxPr4-xNi3O8 (x = 0.1, 0.25, 1, 2, and 4) obtained by topotactic reduction, in
which we observe systematic changes in the magnetic behaviour. As the Nd3+
content increases, the initially large spin-freezing region with magnetic
frustration becomes smaller and gradually shifts to low temperatures, while the
magnetic response gradually increases. The muon-spin spectroscopy measurements
on Nd4Ni3O8 show that this phenomenon is likely due to the enhancement of spin
fluctuations in NdxPr4-xNi3O8, which weakens the spin frustration behaviour for
high Nd3+ contents and at low temperatures. These spin fluctuations can be
caused by both Nd and Ni ions and could be one of the factors determining the
occurrence of possible superconductivity.",2304.04263v1
2023-04-27,Enhanced Critical Field of Superconductivity at an Oxide Interface,"The nature of superconductivity and its interplay with strong spin-orbit
coupling at the KTaO3(111) interfaces remains a subject of debate. To address
this problem, we grew epitaxial LaMnO3/KTaO3(111) heterostructures. We show
that superconductivity is robust against the in-plane magnetic field, with the
critical field of superconductivity reaching 25 T in optimally doped
heterostructures. The superconducting order parameter is highly sensitive to
carrier density. We argue that spin-orbit coupling drives the formation of
anomalous quasiparticles with vanishing magnetic moment, providing the
condensate significant immunity against magnetic fields beyond the Pauli
paramagnetic limit. These results offer design opportunities for
superconductors with extreme resilience against magnetic field.",2304.14426v1
2023-09-05,Ruthenium dioxide RuO$_{2}$: effect of the altermagnetism on the physical properties,"Ruthenium oxide with the rutile structure is one of example of altermagnets.
These systems are characterized by compensated magnetic moments (typical for
antiferromagnets) and strong time reversal symmetry breaking (typical for
ferromagnets). However, in such cases, the electronic band structure exhibit
strong spin splitting along some directions in the momentum space. Occurrence
of the compensated magnetic textures allows for realization of surfaces with
specific magnetization, which dependent on the surface orientation and/or its
termination. Here, we study interplay between the electronic surface states and
the surface magnetization. We show that the spin-resolved spectra strongly
depends on a direction in reciprocal space. Such properties can be used for the
experimental confirmation of the altermagnetism in RuO$_{2}$ within the
spectroscopic techniques. Additionally, we show that the most modified orbitals
in the system are $d_{z^{2}}$ and $d_{xy}$ orbitals of Ru. Similarly, the Ru
$e_{g}$ states are most sensitive on epitaxial strain, what can suggest some
link between altermagnetism and strain.",2309.02421v1
2023-12-18,Incommensurate magnetic order: a fingerprint for electronic correlations in hole-doped cuprates,"Intertwined charge and magnetic fluctuations in high-$T_\text{c}$ copper
oxide superconductors (cuprates) are hypothesized to be a consequence of their
correlated electronic nature. Among other observables, this is apparent in the
doping dependence of incommensurate magnetic order, known as the Yamada
relation (YR). We analyze the Hubbard model to challenge the universality of YR
as a function of interaction strength $U$ through Kotliar-Ruckenstein
slave-boson (SB) mean-field theory and truncated unity functional
renormalization group (TUFRG). While TUFRG tends to lock in to a doping
dependence of the incommensurate magnetic ordering vector obtained for the
perturbative weak-coupling limit, SB not only exhibits an enhanced sensitivity
upon a variation of $U$ from weak to strong coupling, but also shows good
agreement with experimental data. It supports the placement of weakly
hole-doped cuprates in the intermediate-to-strong coupling regime.",2312.11628v1
2024-03-08,3d-oxide molecules to tailor large magnetic anisotropy energies on MgO films,"Designing systems with large magnetic anisotropy energy (MAE) is desirable
and critical for nanoscale magnetic devices. A recent breakthrough achieved the
theoretical limit of the MAE for 3$d$ transition metal atoms by placing a
single Co atom on a MgO(100) surface, a result not replicated by standard
first-principles simulations. Our study, incorporating Hubbard-$U$ correction
and spin-orbit coupling, successfully reproduces and explains the high MAE of a
Co adatom on a MgO (001) surface. We go further by exploring ways to enhance
MAE in 3d transition metal adatoms through different structural geometries of
3d--O molecules on MgO. One promising structure, with molecules perpendicular
to the surface, enhances MAE while reducing substrate interaction, minimizing
spin fluctuations, and boosting magnetic stability. Additionally, we
demonstrate significant control over MAE by precisely placing 3d--O molecules
on the substrate at the atomic level.",2403.05432v1
2023-08-31,Beyond domain alignment: Revealing the effect of intrinsic magnetic order on electrochemical water splitting,"To reach a long term viable green hydrogen economy, rational design of active
oxygen evolution reaction (OER) catalysts is critical. An important hurdle in
this reaction originates from the fact that the reactants are singlet
molecules, whereas the oxygen molecule has a triplet ground state with parallel
spin alignment, implying that magnetic order in the catalyst is essential.
Accordingly, multiple experimentalists reported a positive effect of external
magnetic fields on OER activity of ferromagnetic catalysts. However, it remains
a challenge to investigate the influence of the intrinsic magnetic order on
catalytic activity. Here, we tuned the intrinsic magnetic order of epitaxial
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ thin film model catalysts from ferro- to
paramagnetic by changing the temperature in-situ during water electrolysis.
Using this strategy, we show that ferromagnetic ordering below the Curie
temperature enhances OER activity. Moreover, we show a slight current density
enhancement upon application of an external magnetic field and find that the
dependence of magnetic field direction correlates with the magnetic anisotropy
in the catalyst film. Our work thus suggests that both the intrinsic magnetic
order in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films and magnetic domain alignment
increase their catalytic activity. We observe no long-range magnetic order at
the catalytic surface, implying that the OER enhancement is connected to the
magnetic order of the bulk catalyst. Combining the effects found with existing
literature, we propose a unifying picture for the spin-polarized enhancement in
magnetic oxide catalysts.",2308.16654v1
2004-05-06,Application of Kondo-lattice theory to Mott-Hubbard metal-insulator crossover in disordered cuprate-oxide superconductors,"A theory of Kondo lattices is applied to the crossover between local-moment
magnetism and itinerant-electron magnetism in the t-J model on a quasi-two
dimensional lattice. The Kondo temperature T_K is defined as a characteristic
temperature or energy scale of local quantum spin fluctuations. Magnetism with
T_N >> T_K, where T_N is the N\eel temperature, is characterized as
local-moment one, while magnetism with T_N << T_K is characterized as
itinerant-electron one. The Kondo temperature, which also gives a measure of
the strength of the quenching of magnetic moments, is renormalized by the Fock
term of the superexchange interaction. Because the renormalization depends on
life-time widths \gamma of quasiparticles in such a way that T_K is higher for
smaller \gamma, T_N can be controlled by disorder. The asymmetry of T_N between
electron-doped and hole-doped cuprates must mainly arise from that of disorder;
an almost symmetric behavior of T_N must be restored if we can prepare
hole-doped and electron-doped cuprates with similar degree of disorder to each
other. Because effective disorder is enhanced by magnetic fields in Kondo
lattices, antiferromagnetic ordering must be induced by magnetic fields in
cuprates that exhibit large magnetoresistance.",0405101v2
2007-01-22,New Consideration on Composed Nonextensive Magnetic Systems,"In this paper a composed A+B magnetic system, with spins J_A=2 and J_B=3/2,
is considered within the mean-field approximation, in the framework of Tsallis
nonextensive statistics. Our motivation is twofold: (1) to approach the
existing experimental data of manganese oxides (manganites), where Mn^{3+} and
Mn^{4+} form two magnetic sublattices, and (2) to investigate the structure of
nonextensive density matrices of composed systems. By imposing that
thermodynamic quantities, such as the magnetization of sublattices A and B,
must be invariant weather the calculation is taken over the total Hilbert space
or over partial subspaces, we found that the expression for the nonextensive
entropy must be adapted. Our argument is supported by calculation of
sublattices magnetization M_A and M_B, internal energy, U_A and U_B, and
magnetic specific heat, CA and CB. It is shown that only with the modified
entropy the two methods of calculation agree to each other. Internal energy and
magnetization are additive, but no clear relationship was found between S_A,
S_B and the total entropy S_{A+B} for q \neq 1. It is shown that the reason for
the failure of the standard way of calculation is the assumption of statistical
independence between the two subsystems, which however does not affect the
density matrix in the full Hilbert space.",0701495v3
2010-11-30,Structural and magnetic properties of the ordered perovskite Pb2CoTeO6,"The complex perovskite Pb2CoTeO6 (PCTO) has been prepared as polycrystalline
powders by solid state reaction route, and the crystal structure and magnetic
properties have been investigated using a combination of X-ray and neutron
powder diffraction, electron microscopy, dielectric, calorimetric and magnetic
measurements. It was shown that at room temperature this compound adopts a
trigonal perovskite structure, space group R-3 (a= 5.6782(1){\AA}, c=
13.8552(3){\AA}). The compound undergoes a number of temperature-induced phase
transitions and adopts four different structures in the temperature range 5-500
K: monoclinic in P21/n(5<T<125K, tilt system (a+b-b-)), monoclinic in I2/m
(125<T<210 K, tilt system (a0b-b-)), rhombohedral in R-3 (210<T<370K, tilt
system (a-a-a-)), and finally cubic in Fm-3m (above 370K without any tilting).
These structural phase transitions are coupled to a change in the dielectric
constant and the heat capacity around 210 and 370K. A long-range
antiferromagnetically ordered state has been identified from neutron powder
diffraction and magnetic studies at different temperatures. Magnetic
diffraction peaks were registered below the transition at about 16 K and a
possible model for the magnetic structure is proposed. Possible coexistence of
long-range ordering of electrical dipoles and magnetic moments at low
temperatures making PCTO a multiferroic candidate is discussed and compared
with those of other Co-based quaternary oxides adopting the perovskite
structure.",1011.6638v1
2011-06-30,Formation of magnetic glass in calcium doped YBaCo2O5.5 cobaltites,"The d.c. magnetization and magnetic relaxation studies of the calcium doped
samples, Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5, show the existence of a
magnetic glass like behaviour in the family of cobaltites for the first time.
Our investigations reveal glass-like arrest of kinetics at low temperature
which prevents the system from reaching its magnetic ground state. We show that
the low temperature state of these calcium doped phases, which consists of
coexisting antiferromagnetic and ferro (or ferri) magnetic phase fractions, can
be tuned in a number of ways. Our observations establish that the low
temperature state of this oxide is not in thermal equilibrium. The glassy state
is formed with the assistance of an external magnetic field, which makes it
distinctly different from the more well known metastable state, the spin glass
state. The cooling field can tune the fractions of the coexisting phases, and
the glass-like state formed at low temperature can also be devitrified by
warming the sample. The role of Ca doping in the appearance of these phenomena
is discussed in terms of phase separation, involving Co3+ disproportionation
into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters.",1106.6253v1
2012-09-25,Strong magnetic field effect on above-barrier transport in Pb-p-HgCdTe Schottky barriers,"Due to large difference in effective masses of light and heavy holes it is
usually supposed that the above-barrier current in Schottky barriers on p-type
semiconductor is controlled only by the heavy holes. However, in real
structures, there is an additional potential barrier caused by a oxide layer at
interface. For typical values of thickness and height of a barrier its tunnel
transparency for light holes can be higher by three order of magnitude than
that for heavy holes. Due to such separative role of insulator layer one can
expect that the current is manly a contribution of light holes. To clear up
this problem the investigation of transport in a magnetic field is used as a
key experiment in this work. The pronounced magnetic field effect for heavy
holes in investigated Pb-p-HgCdTe Schottky barriers is expected only at
extremely strong magnetic fields B>10 T within the framework of both diode and
diffusion mechanism of transport. At the same time experimentally more than
twofold decrease in saturation current is observed even at B=0.5 T at any
orientation of magnetic field. The studies performed for HgCdTe with different
Kane's gap and at different temperatures show that the magnitude of magnetic
field effect is uniquely determined by the ratio of light hole cyclotron energy
to a thermal energy. However the magnitude of effect exceeds considerably the
prediction of the simple theory and the experimental magnetic field
dependencies of a saturation current do not follow the simple exponential
falling predicted for thermionic current. The reason of this discrepancy
remains a mystery.",1209.5528v1
2012-11-15,Electrical Investigation of the Oblique Hanle Effect in Ferromagnet/Oxide/Semiconductor Contacts,"We have investigated the electrical Hanle effect with magnetic fields applied
at an oblique angle ({\theta}) to the spin direction (the oblique Hanle effect,
OHE) in CoFe/MgO/semiconductor (SC) contacts by employing a three-terminal
measurement scheme. The electrical oblique Hanle signals obtained in
CoFe/MgO/Si and CoFe/MgO/Ge contacts show clearly different line shapes
depending on the spin lifetime of the host SC. Notably, at moderate magnetic
fields, the asymptotic values of the oblique Hanle signals (in both contacts)
are consistently reduced by a factor of cos^2({\theta}) irrespective of the
bias current and temperature. These results are in good agreement with
predictions of the spin precession and relaxation model for the electrical
oblique Hanle effect. At high magnetic fields where the magnetization of CoFe
is significantly tilted from the film plane to the magnetic field direction, we
find that the observed angular dependence of voltage signals in the CoFe/MgO/Si
and CoFe/MgO/Ge contacts are well explained by the OHE, considering the
misalignment angle between the external magnetic field and the magnetization of
CoFe.",1211.3486v4
2013-11-04,Interplay of many-body and single-particle interactions in iridates and rhodates,"Motivated by recent experiments exploring the spin-orbit-coupled magnetism in
$4d$- and $5d$-band transition metal oxides, we study magnetic interactions in
Ir- and Rh-based compounds. In these systems, the comparable strength of
spin-orbit coupling (SOC), crystal field splitting (CF) and Coulomb and Hund's
coupling leads to a rich variety of magnetic exchange interactions, leading to
new types of ground states. Using a strong coupling approach, we derive
effective low-energy super-exchange Hamiltonians from the multi-orbital Hubbard
model by taking full account of the Coulomb and Hund's interactions in the
intermediate states. We find that in the presence of strong SOC and lattice
distortions the super-exchange Hamiltonian contains various kinds of magnetic
anisotropies.
  Here we are primarily interested in the magnetic properties of Sr$_2$IrO$_4$
and Sr$_2$Ir$_{1-x}$Rh$_x$O$_4$ compounds. We perform a systematic study of how
magnetic interactions in these systems depend on the microscopic parameters and
provide a thorough analysis of the resulting magnetic phase diagram. Comparison
of our results with experimental data shows good agreement. Finally, we discuss
the parameter space in which the spin-flop transition in Sr$_2$IrO$_4$,
experimentally observed under pressure, can be realized.",1311.0852v2
2014-12-23,Field-induced inter-planar correlations in the high-temperature superconductor La1.88Sr0.12CuO4,"We present neutron scattering studies of the inter-planar correlations in the
high-temperature superconductor La1.88Sr0.12CuO4 (T_c=27 K). The correlations
are studied both in a magnetic field applied perpendicular to the CuO2 planes,
and in zero field under different cooling conditions. We find that the effect
of the magnetic field is to increase the magnetic scattering signal at all
values of the out-of-plane wave vector L, indicating an overall increase of the
magnetic moments. In addition, weak correlations between the copper oxide
planes develop in the presence of a magnetic field. This effect is not taken
into account in previous reports on the field effect of magnetic scattering,
since usually only L~0 is probed. Interestingly, the results of quench-cooling
the sample are similar to those obtained by applying a magnetic field. Finally,
a small variation of the incommensurate peak position as a function of L
provides evidence that the incommensurate signal is twinned with the dominating
and sub-dominant twin displaying peaks at even or odd L, respectively.",1412.7329v1
2015-05-05,Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures,"The spin-orbit interaction in heavy metal/ferromagnet/oxide structures has
been extensively investigated because it can be employed in manipulation of the
magnetization direction by in-plane current. This implies the existence of an
inverse effect, in which the conductivity in such structures should depend on
the magnetization orientation. In this work, we report a systematic study of
the magnetoresistance (MR) of the W/CoFeB/MgO structures and its correlation to
the current-induced torque to the magnetization. We observe that the MR is
independent of the angle between magnetization and current direction, but is
determined by the relative magnetization orientation with respect to the spin
direction accumulated by spin Hall effect, which is the same symmetry of
so-called spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is
considerably larger than those in other structures of Ta/CoFeB/MgO or
Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the
similar W thickness dependence of the MR and the current-induced magnetization
switching efficiency demonstrates that they share the same underlying physics,
which allows one to utilize the MR in non-magnet/ferromagnet structure in order
to understand closely related other spin-orbit coupling effects such as inverse
spin Hall effect, spin-orbit spin transfer torques, etc.",1505.00899v1
2015-09-25,Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3,"Fe3PO4O3 forms a non-centrosymmetric lattice structure (space group R3m)
comprising triangular motifs of Fe^{3+} coupled by strong antiferromagnetic
interactions (|\Theta_{CW}| > 900 K). Neutron diffraction from polycrystalline
samples shows that strong frustration eventually gives way to an ordered
helical incommensurate structure below T_N = 163 K, with the helical axis in
the hexagonal ab plane and a modulation length of ~ 86 \AA. The magnetic
structure consists of an unusual needle-like correlation volume that extends
past 900 \AA along the hexagonal c-axis but is limited to ~ 70 \AA in the ab
plane, despite the three-dimensional nature of the magnetic sublattice
topology. The small in-plane correlation length, which persists to at least T =
T_N/40, indicates a robust blocking of long-range order of the helical magnetic
structure, and therefore stable domain walls, or other defect spin textures,
must be abundant in Fe3PO7. Temperature dependent neutron powder diffraction
reveals small negative thermal expansion below T_N. No change in lattice
symmetry is observed on cooling through T_N, as revealed by high resolution
synchrotron X-ray diffraction. The previously reported reduced moment of the
Fe^{3+} ions (S=5/2), \mu ~ 4.2 \mu_B, is confirmed here through magnetization
studies of a magnetically diluted solid solution series of compounds,
Fe3-xGaxPO4O3, and is consistent with the refined magnetic moment from neutron
diffraction 4.14(2) \mu_B. We attribute the reduced moment to a modified spin
density distribution arising from ligand charge transfer in this insulating
oxide.",1509.07846v2
2016-02-20,Covalent bonds against magnetism in transition metal compounds,"Magnetism in transition metal compounds is usually considered starting from a
description of isolated ions, as exact as possible, and treating their
(exchange) interaction at a later stage. We show that this standard approach
may break down in many cases, especially in $4d$ and $5d$ compounds. We argue
that there is an important intersite effect -- an orbital-selective formation
of covalent metal-metal bonds, which leads to an ""exclusion"" of corresponding
electrons from the magnetic subsystem, and thus strongly affects magnetic
properties of the system. This effect is especially prominent for noninteger
electron number, when it results in suppression of the famous double exchange,
the main mechanism of ferromagnetism in transition metal compounds. We study
this novel mechanism analytically and numerically and show that it explains
magnetic properties of not only several $4d-5d$ materials, including
Nb$_2$O$_2$F$_3$ and Ba$_5$AlIr$_2$O$_{11}$, but can also be operative in $3d$
transition metal oxides, e.g. in CrO$_2$ under pressure. We also discuss the
role of spin-orbit coupling on the competition between covalency and magnetism.
Our results demonstrate that strong intersite coupling may invalidate the
standard single-site starting point for considering magnetism, and can lead to
a qualitatively new behaviour.",1602.06425v2
2013-09-07,High temperature non-collinear magnetism in a classical bilinear-biquadratic Heisenberg model,"Motivated by the magnetically-driven high-temperature ferroelectric behavior
of CuO and the subsequent theoretical efforts to understand this intriguing
phenomenon, we study a spin model on a two-dimensional square lattice which
possesses some of the key features of the models proposed for CuO. The model
consists of Heisenberg couplings between nearest and next-nearest neighbor
spins, and biquadratic couplings between nearest neighbors. We use a
combination of variational calculations and classical Monte Carlo simulations
to study this model at zero and finite temperatures. We show that even an
arbitrarily weak biquadratic coupling plays a crucial role in selecting the
magnetic ground state. More importantly, a non-collinear magnetic state,
characterized by a finite spin current, is stable at finite temperatures. The
interesting aspect is that the present model neither includes an
inversion-symmetry-breaking term nor the effects of lattice distortions in the
Hamiltonian. We conclude that non-collinear magnetism at high temperatures, as
observed in CuO, can be explained via pure spin Hamiltonians. We find that the
spiral phase is inhomogeneous, and is stabilized by entropic effects. Our study
demonstrates that higher order interaction terms are of crucial importance if
the stronger interactions together with the lattice geometry contemplate to
generate a near degeneracy of magnetic states. The conclusions presented in
this work are of particular relevance to the non-collinear magnetism and
ferroelectricity observed at high temperatures in cupric oxide.",1309.1874v1
2017-07-16,First Principles Study of the Giant Magnetic Anisotropy Energy in Bulk Na4IrO4,"In 5d transition metal oxides, novel properties arise from the interplay of
electron correlations and spin--orbit interactions. Na4IrO4, where 5d
transition-metal Ir atom occupies the center of the square-planar coordination
environment, is synthesized. Based on density functional theory, we calculate
its electronic and magnetic properties. Our numerical results show that the
Ir-5d bands are quite narrow, and the bands around the Fermi level are mainly
contributed by d_{xy},d_{yz} and d_{zx} orbitals. The magnetic easy-axis is
perpendicular to the IrO4 plane, and the magnetic anisotropy energy (MAE) of
Na4IrO4 is found to be very giant. We estimate the magnetic parameters by
mapping the calculated total energy for different spin configurations onto a
spin model. The next nearest neighbor exchange interaction J2 is much larger
than other intersite exchange interactions and results in the magnetic ground
state configuration. Our study clearly demonstrates that the huge MAE comes
from the single-ion anisotropy rather than the anisotropic interatomic spin
exchange. This compound has a large spin gap but very narrow spin-wave
dispersion, due to the large single-ion anisotropy and relatively small
exchange couplings. Noticing this remarkable magnetic feature originated from
its highly isolated IrO4 moiety, we also explore the possiblity to further
enhance the MAE.",1707.04865v1
2017-10-09,Huge magnetoresistance and ultra-sharp metamagnetic transition in polycrystalline ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$,"Large magnetoresistive materials are of immense interest for a number of
spintronic applications by developing high density magnetic memory devices,
magnetic sensors and magnetic switches. Colossal magnetoresistance, for which
resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external
magnetic field, occurs mainly in phase separated oxide materials, namely
manganites, due to the phase competition between the ferromagnetic metallic and
the antiferromagnetic insulating regions. Can one further enhance the
magnetoresistance by tuning the volume fraction of the two phases? In this
work, we report a huge colossal magnetoresistance along with the ultra-sharp
metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$
manganite compound by suitably tuning the volume fraction of the competing
phases. The obtained magnetoresistance value at 10 K is as large as
$\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90
kOe external magnetic field and is several orders of magnitude higher than any
other observed magnetoresistance value reported so far. Using model Hamiltonian
calculations we have shown that the inhomogeneous disorder, deduced from
tunneling electron microscopy, suppresses the CE-type phase and seeds the
ferromagnetic metal in an external magnetic field.",1710.03007v2
2019-07-13,"Detection of Influenza A Virus Nucleoprotein Through the Self-Assembly of Nanoparticles in Magnetic Particle Spectroscopy-Based Bioassays: A Method for Rapid, Sensitive, and Wash-free Magnetic Immunoassays","Magnetic nanoparticles (MNPs) with proper surface functionalization have been
extensively applied as labels for magnetic immunoassays, carriers for
controlled drug/gene delivery, tracers and contrasts for magnetic imaging, etc.
Here, we introduce a new biosensing scheme based on magnetic particle
spectroscopy (MPS) and the self-assembly of MNPs to quantitatively detect H1N1
nucleoprotein molecules. MPS monitors the harmonics of oscillating MNPs as a
metric for the freedom of rotational motion, thus indicating the bound states
of MNPs. These harmonics can be readily collected from nanogram quantities of
iron oxide nanoparticles within 10 s. H1N1 nucleoprotein molecule hosts
multiple different epitopes that forms binding sites for many IgG polyclonal
antibodies. Anchoring IgG polyclonal antibodies onto MNPs triggers the
cross-linking between MNPs and H1N1 nucleoprotein molecules, thereby forming
MNP self-assemblies. Using MPS and the self-assembly of MNPs, we achieved the
sensitivity of 44 nM (442 pmole) for detecting H1N1 nucleoprotein. In addition,
the morphologies and the hydrodynamic sizes of the MNP self-assemblies are
characterized to verify the MPS results. Different MNP self-assembly models
such as classical cluster, open ring tetramer, chain model as well as multimers
(from dimer to pentamer) are proposed in this paper. Herein, we claim the
feasibility of using MPS and the self-assembly of MNPs as a new biosensing
scheme for detecting ultralow concentrations of target biomolecules, which can
be employed as rapid, sensitive, and wash-free magnetic immunoassays.",1907.06000v1
2020-12-21,Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba2MnTeO6,"Oxide double perovskites wherein octahedra formed by both 3d elements and
sp-based heavy elements give rise to unconventional magnetic ordering and
correlated quantum phenomena crucial for futuristic applications. Here, by
carrying out experimental and first principles investigations, we present the
electronic structure and magnetic phases of Ba2MnTeO6, where Mn^2+ ions with S
= 5/2 spins constitute a perfect triangular lattice. The magnetic
susceptibility reveals a large Curie- Weiss temperature -152 K suggesting the
presence of strong antiferromagnetic interactions between Mn^2+ moments in the
spin lattice. A phase transition at 20 K is revealed by magnetic susceptibility
and specific heat which is attributed to the presence of a sizeable inter-plane
interactions. Below the transition temperature, the specific heat data show
antiferromagnetic magnon excitations with a gap of 1.4 K. Furthermore, muon
spin-relaxation reveals the presence of static internal fields in the ordered
state and provides strong evidence of short-range spin correlations for T > TN.
The DFT+U calculations and spin-dimer analysis infer that Heisenberg
interactions govern the inter and intra-layer spin-frustrations in this
perovskite. The inter and intra-layer exchange interactions are of comparable
strengths (J1 = 4.6 K, J2 = 0.92 J1). However, a weak third nearest-neighbor
ferromagnetic inter-layer interaction exists (J3=-0.04 J1) due to
double-exchange interaction via the linear path Mn-O-Te-O-Mn. The combined
effect of J2 and J3 interactions stabilizes a three dimensional long-range
magnetic ordering in this frustrated magnet.",2012.11292v1
2018-05-31,Resonate and Fire Neuron with Fixed Magnetic Skyrmions,"In the brain, the membrane potential of many neurons oscillates in a
subthreshold damped fashion and fire when excited by an input frequency that
nearly equals their eigen frequency. In this work, we investigate theoretically
the artificial implementation of such ""resonate-and-fire"" neurons by utilizing
the magnetization dynamics of a fixed magnetic skyrmion in the free layer of a
magnetic tunnel junction (MTJ). To realize firing of this nanomagnetic
implementation of an artificial neuron, we propose to employ voltage control of
magnetic anisotropy or voltage generated strain as an input (spike or
sinusoidal) signal, which modulates the perpendicular magnetic anisotropy
(PMA). This results in continual expansion and shrinking (i.e. breathing) of a
skyrmion core that mimics the subthreshold oscillation. Any subsequent input
pulse having an interval close to the breathing period or a sinusoidal input
close to the eigen frequency drives the magnetization dynamics of the fixed
skyrmion in a resonant manner. The time varying electrical resistance of the
MTJ layer due to this resonant oscillation of the skyrmion core is used to
drive a Complementary Metal Oxide Semiconductor (CMOS) buffer circuit, which
produces spike outputs. By rigorous micromagnetic simulation, we investigate
the interspike timing dependence and response to different excitatory and
inhibitory incoming input pulses. Finally, we show that such resonate and fire
neurons have potential application in coupled nanomagnetic oscillator based
associative memory arrays.",1806.00076v1
2021-05-05,Superconductivity assisted change of the perpendicular magnetic anisotropy in V/MgO/Fe junctions,"Controlling the perpendicular magnetic anisotropy (PMA) in thin films has
received considerable attention in recent years due to its technological
importance. PMA based devices usually involve heavy-metal
(oxide)/ferromagnetic-metal bilayers, where, thanks to interfacial spin-orbit
coupling (SOC), the in-plane (IP) stability of the magnetization is broken.
Here we show that in V/MgO/Fe(001) epitaxial junctions with competing in-plane
and out-of-plane (OOP) magnetic anisotropies, the SOC mediated interaction
between a ferromagnet (FM) and a superconductor (SC) enhances the effective PMA
below the superconducting transition. This produces a partial magnetization
reorientation without any applied field for all but the largest junctions,
where the IP anisotropy is more robust; for the smallest junctions there is a
reduction of the field required to induce a complete OOP transition
($H_\text{OOP}$) due to the stronger competition between the IP and OOP
anisotropies. Our results suggest that the degree of effective PMA could be
controlled by the junction lateral size in the presence of superconductivity
and an applied electric field. We also discuss how the $H_\text{OOP}$ field
could be affected by the interaction between magnetic stray fields and
superconducting vortices. Our experimental findings, supported by numerical
modelling of the ferromagnet-superconductor interaction, open pathways to
active control of magnetic anisotropy in the emerging dissipation-free
superconducting spin electronics.",2105.02050v4
2021-06-09,Magnetic properties of the quasi two-dimensional centered honeycomb antiferromagnet GdInO$_3$,"The crystal structure and magnetic property of the single crystalline
hexagonal rare-earth indium oxides GdInO$_3$ have been studied by combing
experiments and model calculations. The two inequivalent Gd$^{3+}$ ions form
the centered honeycomb lattice, which consists of honeycomb and triangular
sublattices. The dc magnetic susceptibility and specific heat measurements
suggest two antiferromagnetic phase transitions at $T_\textrm{N1}$ = 2.3 K and
$T_\textrm{N2}$ = 1.02 K. An inflection point is observed in the isothermal
magnetization curve, which implies an up-up-down phase with a 1/3 magnetization
plateau. We also observe a large magnetic entropy change originated from the
magnetic frustration in GdInO$_3$. By considering a classical spin Hamiltonian,
we establish the ground state phase diagram, which suggests that GdInO$_3$ has
a weak easy-axis anisotropy and is close to the equilateral triangular-lattice
system. The theoretical ground-state phase diagram may be used as a reference
in NMR, ESR, or $\mu$SR experiments in future.",2106.05071v2
2021-07-13,Investigation of spin-phonon coupling and local magnetic properties in magnetoelectric Fe2TeO6,"Spin-phonon coupling originated from spin-lattice correlation depends upon
different exchange interactions in transition metal oxides containing 3d
magnetic ions. Spin-lattice coupling can influence the coupling mechanism in
magnetoelectric material. To understand the spin-lattice correlation in inverse
trirutile Fe2TeO6 (FTO), magnetic properties and phonon spectra are studied.
Signature of short-range magnetic correlation induced by 5/2-5/2 dimeric
interaction and magnetic anomaly at 150 K is perceived apart from the familiar
sharp transition (TN~210K) corresponding to long-range order by magnetization
and heat capacity measurement. The magnetic transitions and the spin dynamics
are further locally probed by muon spin resonance ({\mu}SR) measurement in both
zero fields (ZF) and longitudinal field (LF) mode. Three dynamically distinct
temperature regimes; (i) T >TN, (ii) TN>T>150 K, and (iii) T<150 K, are
observed. A swift change in spin dynamics is realized at 150K by {\mu}SR,
though previous studies suggest long-range antiferromagnetic order. The
observation of renormalization of different Raman modes below 210K suggests the
existence of spin-phonon coupling in the material. The coupling strength is
quantified as in the range 0.1-1.2 cm-1 following the two-spin cluster
approximation. We propose that the spin-phonon coupling is mediated by the
Fe-O2-Fe interbilayer exchange play a significant role in ME coupling observed
in the material.",2107.06269v2
2021-09-16,Highly Tunable Magnetic and Magnetotransport Properties of Exchange Coupled Ferromagnet/Antiferromagnet-based Heterostructures,"Antiferromagnets (AFMs) with zero net magnetization are proposed as active
elements in future spintronic devices. Depending on the critical thickness of
the AFM thin films and the measurement temperature, bimetallic Mn-based alloys
and transition metal oxide-based AFMs can host various coexisting ordered,
disordered, and frustrated AFM phases. Such coexisting phases in the exchange
coupled ferromagnetic (FM)/AFM-based heterostructures can result in unusual
magnetic and magnetotransport phenomena. Here, we integrate chemically
disordered AFM IrMn3 thin films with coexisting AFM phases into complex
exchange coupled MgO(001)/Ni3Fe/IrMn3/Ni3Fe/CoO heterostructures and study the
structural, magnetic, and magnetotransport properties in various magnetic field
cooling states. In particular, we unveil the impact of rotating the relative
orientation of the disordered and reversible AFM moments with respect to the
irreversible AFM moments on the magnetic and magnetoresistance properties of
the exchange coupled heterostructures. We further found that the persistence of
AFM grains with thermally disordered and reversible AFM order is crucial for
achieving highly tunable magnetic properties and multi-level magnetoresistance
states. We anticipate that the introduced approach and the heterostructure
architecture can be utilized in future spintronic devices to manipulate the
thermally disordered and reversible AFM order at the nanoscale.",2109.08136v1
2022-01-15,Tailoring epitaxial growth and magnetism in La1-xSrxMnO3 / SrTiO3 heterostructures via temperature-driven defect engineering,"Among the class of strongly-correlated oxides, La1-xSrxMnO3 $-$ a half
metallic ferromagnet with a Curie temperature above room temperature $-$ has
sparked a huge interest as a functional building block for memory storage and
spintronic applications. In this respect, defect engineering has been in the
focus of a long-standing quest for fabricating LSMO thin films with highest
quality in terms of both structural and magnetic properties. Here, we discuss
the correlation between structural defects, such as oxygen vacancies and
impurity islands, and magnetism in La0.74Sr0.26MnO3/SrTiO3 (LSMO/STO) epitaxial
heterostructures by systematic control of the growth temperature and
post-deposition annealing conditions. Upon increasing the growth temperature
within the 500 $-$ 700 $^{\circ}$C range, the epitaxial LSMO films experience a
progressive improvement in oxygen stoichiometry, leading to enhanced magnetic
characteristics. Concurrently, however, the use of a high growth temperature
triggers the diffusion of impurities from the bulk of STO, which cause the
creation of off-stoichiometric, dendritic-like SrMoOx islands at the
film/substrate interface. As a valuable workaround, post-deposition annealing
of the LSMO films grown at a relatively-low temperature of about 500
$^{\circ}$C permits to obtain high-quality epitaxy, atomically-flat surface as
well as a sharp magnetic transition above room temperature and robust
ferromagnetism. Furthermore, under such optimized fabrication conditions
possible scenarios for the formation of the magnetic dead layer as a function
of LSMO film thickness are discussed. Our findings offer effective routes to
finely tailor the complex interplay between structural and magnetic properties
of LSMO thin films via temperature-controlled defect engineering.",2201.05873v1
2022-02-09,"Ferromagnetism induced by hybridization of Fe 3d orbitals with ligand InSb bands in n-type ferromagnetic semiconductor (In,Fe)Sb","Fe-doped III-V ferromagnetic semiconductor (FMS) (In,Fe)Sb is a promising
material for spintronic device applications because of the n-type carrier
conduction and the ferromagnetism with high Curie temperature (TC > 300 K). To
clarify the mechanism of the high-TC ferromagnetism, we have investigated the
electronic structure and magnetic properties of an (In,Fe)Sb thin film by
performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD) measurements at the Fe L2,3 edges. The magnetic-field
dependence of the XMCD spectra reveals that there are ferromagnetic-like Fe and
paramagnetic-like Fe components in the (In,Fe)Sb thin film. The XAS and XMCD
spectra of the ferromagnetic-like and paramagnetic-like Fe components resemble
those of other Fe-doped FMSs and extrinsic oxides, respectively. The finite
value of the ratio between the orbital and spin magnetic moments estimated by
applying the XMCD sum rules indicates that the valence state of the Fe ions
substituting for the In sites in (In,Fe)Sb is not purely ionic Fe3+, but
intermediate between Fe3+ and Fe2+. The qualitative correspondence between the
magnetic-field dependence of the visible-light magnetic circular dichroism
intensity and that of the XMCD intensity demonstrates that the Zeeman splitting
of the InSb band is proportional to the net magnetization of the doped Fe.
These results suggest that the ferromagnetism of (In,Fe)Sb originates from the
Fe 3d orbitals hybridized with the host InSb bands.",2202.04286v1
2023-05-30,Aging and passivation of magnetic properties in Co/Gd bilayers,"Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging
the gap between volatile information in the photonic domain and non-volatile
information in the magnetic domain, without the need for any intermediary
electronic conversion. Specifically, these systems exhibit strong spin-orbit
torque effects, fast domain wall motion and single-pulse all-optical switching
of the magnetization. An important open challenge to bring these materials to
the brink of applications is to achieve long-term stability of their magnetic
properties. In this work, we address the time-evolution of the magnetic moment
and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with
various capping layers. Over the course of three months, the net magnetic
moment and compensation temperature change significantly, which we attribute to
quenching of the Gd magnetization. We identify that intermixing of the capping
layer and Gd is primarily responsible for this effect, which can be alleviated
by choosing nitrides for capping as long as reduction of nitride to oxide is
properly addressed. In short, this work provides an overview of the relevant
aging effects that should be taken into account when designing synthetic
ferrimagnets based on Co and Gd for spintronic applications.",2305.18984v1
2023-08-08,Room temperature reversible colossal volto-magnetic effect in all-oxide metallicmagnet/topotactic-phase-transition material heterostructures,"Multiferroic materials have undergone extensive research in the past two
decades in an effort to produce a sizable room-temperature magneto-electric
(ME) effect in either exclusive or composite materials for use in a variety of
electronic or spintronic devices. These studies have looked into the ME effect
by switching the electric polarization by the magnetic field or switching the
magnetism by the electric field. Here, an innovative way is developed to knot
the functional properties based on the tremendous modulation of electronics and
magnetization by the electric field of the topotactic phase transitions (TPT)
in heterostructures composed of metallic-magnet/TPT-material. It is divulged
that application of a nominal potential difference of 2-3 Volts induces
gigantic changes in magnetization by 100-250% leading to colossal Voltomagnetic
effect, which would be tremendously beneficial for low-power consumption
applications in spintronics. Switching electronics and magnetism by inducing
TPT through applying an electric field requires much less energy, making such
TPT-based systems promising for energy-efficient memory and logic applications
as well as opening a plethora of tremendous opportunities for applications in
different domains.",2308.04324v1
1994-07-12,Transport Properties of the Kondo Lattice Model in the Limit $S=\infty$ and $D=\infty$,"The Kondo lattice model with Hund's ferromagnetic spin coupling is
investigated as a microscopic model of the perovskite-type 3d transition-metal
oxide La$_{1-x}$Sr$_x$MnO$_3$. In the classical spin limit $S=\infty$ and the
infinite-dimensional limit $D=\infty$, the one-body Green's function is
calculated exactly. Transport properties of the system in the presence of
magnetic fields are calculated. The giant magnetoresistance of this model,
which is in a good agreement with the experimental data of
La$_{1-x}$Sr$_x$MnO$_3$, is explained by the spin disorder scattering process.",9407052v1
1997-03-24,A Quantum Chemical Approach to Cohesive Properties of NiO,"We apply ab-initio quantum chemical methods to calculate correlation effects
on cohesive properties of NiO, thereby extending a recently proposed scheme to
transition metal oxides with partially filled $d$-bands. We obtain good
agreement with experiment for the cohesive energy and show that the deviation
of the lattice constant at the Hartree-Fock level is mainly due to van der
Waals-like interactions. Correlations enhance the stability of the magnetic
ground state found at the Hartree-Fock level.",9703201v1
1997-04-07,Charge ordering in doped manganese oxides: lattice dynamics and magnetic structure,"Based on the Hamiltonian of small polarons with the strong nearest neighbor
repulsion, we have investigated the charge ordering phenomena observed in
half-doped manganites R_{1/2}A_{1/2}MnO_3. We have explored possible
consequences of the charge ordering phase in the half-doped manganites. First,
we have studied the renormalization of the sound velocity around $T_{CO}$,
considering the acoustic phonons coupled to the electrons participating in the
charge ordering. Second, we have found a new antiferromagnetic phase induced by
the charge ordering, and discussed its role in connection with the specific
CE-type antiferromagnetic structure observed in half-doped manganites.",9704052v1
1997-05-09,CrO2: a self-doped double exchange ferromagnet,"Band structure calculations of CrO2 carried out in the LSDA+U approach reveal
a clear picture of the physics behind the metallic ferromagnetic properties.
Arguments are presented that the metallic ferromagnetic oxide CrO2 belongs to a
class of materials in which magnetic ordering exists due to double exchange (in
this respect CrO2 turns out to be similar to the CMR manganates). It is
concluded that CrO2 has small or even negative charge transfer gap which can
result in self-doping. Certain experiments to check the proposed picture are
suggested.",9705091v1
1997-08-01,Double exchange magnets: Spin-dynamics in the paramagnetic phase,"The electronic structure of perovskite manganese oxides is investigated in
terms of a Kondo lattice model with ferromagnetic Hund coupling and
antiferromagnetic exchange between $t_{2g}$-spins using a finite temperature
diagonalization technique. Results for the dynamic structure factor are
consistent with recent neutron scattering experiments for the bilayer manganite
La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ . The susceptibility shows Curie-Weiss
behaviour and is used to derive a phase diagram. In the paramagnetic phase
carriers are characterized as ferromagnetic polarons in an antiferromagnetic
spin liquid.",9708007v1
1998-06-06,Percolation of finite-sized objects on a lattice,"We study the percolation of FINITE-SIZED objects on two- and
three-dimensional lattices. Our motivation stems, on one hand from some recent
interesting experimental results on transport properties of impurity-doped
oxide perovskites and on the other hand from the theoretical appeal that this
problem presents. Our system exhibits a well-defined percolation threshold. We
estimate the size of magnetic polarons, believed to be the carriers of the
abovementioned transport. We have also obtained two critical exponents for our
model, which characterize its universality class.",9806086v1
1999-09-02,Orbital Polarization and Fluctuation in Manganese Oxides,"In a form which include the mother compound, we studied the extended
Hubbard-type model with the orbital degeneracy for any doping concentration.
Meanfield phase diagram and the spin wave excitation in RPA are calculated. It
turned out that a large orbital polarization is essential to reproduce the
magnetic phases depending on the doping concentration. Base on this result, we
discuss the spin canting, the spin wave dispersion, and spin wave stiffness
from the standing point of the large orbital polarization. We also discuss the
orbital fluctuation which turned out to be important in the ferromagnetic
metallic region where the CMR is observed. Spin wave softening near the zone
boundary is also discussed in this context.",9909023v1
1999-09-24,Biquadratic interactions and spin-Peierls transition in the spin 1 chain LiVGe2O6,"The magnetic susceptibility of a new one-dimensional, S=1 system, the
vanadium oxide LiVGe2O6, has been measured. Contrary to previous S=1 chains, it
exhibits an abrupt drop at 22 K typical of a spin-Peierls transition, and it is
consistent with a gapless spectrum above this temperature. We propose that this
behaviour is due to the presence of a significant biquadratic exchange
interaction, a suggestion supported by quantum chemistry calculations that take
into account the quasi-degeneracy of the t2g levels.",9909357v1
2000-07-28,Resistivity of Mixed-Phase Manganites,"The resistivity $\rho_{dc}$ of manganites is studied using a
random-resistor-network, based on phase-separation between metallic and
insulating domains. When percolation occurs, both as chemical composition and
temperature vary, results in good agreement with experiments are obtained.
Similar conclusions are reached using quantum calculations and microscopic
considerations. Above the Curie temperature, it is argued that ferromagnetic
clusters should exist in Mn-oxides. Small magnetic fields induce large
$\rho_{dc}$ changes and a bad-metal state with (disconnected) insulating
domains.",0007480v1
2000-09-08,Charge Ordering and Polaron Formation in the Magnetoresistive Oxide La0.7Ca0.3MnO3,"Neutron scattering has been used to study the nature of the ferromagnetic
transition in a single crystal of the perovskite La0.7Ca0.3MnO3. Diffuse
scattering from lattice polarons develops as the Curie temperature is
approached from below, along with short range polaron correlations that are
consistent with stripe formation. Both the scattering due to the polaron
correlations and the anomalous quasielastic component in the magnetic
fluctuation spectrum maximize very close to T_C, in a manner remarkably similar
to the resistivity, indicating that they have a common origin.",0009132v1
2001-05-11,Temperature dependence of the structural parameters of the non-oxide perovskite superconductor MgCNi3,"We report the structural parameters of superconducting MgCxNi3 (x=0.96,
TC=7.3 K) as a function of temperature, from 2 K to 295 K, determined by
neutron powder diffraction profile refinement. The compound has the perovskite
structure over the whole temperature range, with symmetry Pm3m and a=3.81221(5)
A at 295 K: no structural or long range magnetic ordering transitions were
observed. The lattice parameter a and the Debye-Waller factors for the
individual atoms decrease smoothly with decreasing temperature. There are no
unusual changes of the structural parameters near TC.",0105240v1
2001-06-21,Superconductivity at 1 K in Cd2Re2O7,"We report the first pyrochlore oxide superconductor Cd2Re2O7.
Resistivity,magnetic susceptibility,and specific heat measurements on single
crystals evidence a bulk superconductivity at 1 K. Another phase transition
found at 200 K suggests that a peculiar electronic structure lies behind the
superconductivity.",0106421v4
2001-07-11,Antiferromagnetic ordering in a 90 K copper oxide superconductor,"Using elastic neutron scattering, we evidence a commensurate
antiferromagnetic Cu(2) order (AF) in the superconducting (SC) high-$\rm T_c$
cuprate $\rm YBa_2(Cu_{1-y}Co_y)_3O_{7+\delta}$ (y=0.013, $\rm T_c$=93 K). As
in the Co-free system, the spin excitation spectrum is dominated by a magnetic
resonance peak at 41 meV but with a reduced spectral weight. The substitution
of Co thus leads to a state where AF and SC cohabit showing that the CuO$_2$
plane is a highly antiferromagnetically polarizable medium even for a sample
where T$_c$ remains optimum.",0107218v2
2001-08-30,Electronic properties of antidot lattices fabricated by atomic force lithography,"Antidot lattices were fabricated by atomic force lithography using local
oxidation. High quality finite 20 x20 lattices are demonstrated with periods of
300 nm. The low temperature magnetoresistance shows well developed
commensurability oscillations as well as a quenching of the Hall effect around
zero magnetic field. In addition, we find B periodic oscillations superimposed
on the classical commensurability peaks at temperatures as high as 1.7 K. These
observations indicate the high electronic quality of our samples.",0108520v1
2002-07-04,Formation Mechanisms of Single-Pulse and Secondary Echoes in Systems with a Large Inhomogeneous Broadening of NMR Lines,"In the frames of Mims transformation matrix method the equation for nuclear
magnetization are obtained describing the dynamics of nuclear spin-systems with
a strong Larmor and Rabi inhomogeneous broadenings of NMR line in conditions of
their unequlibrium earlier obtained by the statistical tensors method. As
example, properties of proton single-pulse echo and its secondary signals in
probe material (silicon oil) coated on the surface of high-Tc
superconducting-oxides powder and in metallic hydride are presented.",0207124v1
2002-08-30,Electronic properties of the novel 4d metallic oxide SrRhO3,"The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping
studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and
20%, respectively. Although SrRhO3 was chemically compressed, approximately
5.7% by the Ca doping, no significant influence was observed on the magnetic
and electrical properties.",0208591v1
2002-11-08,Nearly total spin polarization in La2/3Sr1/3MnO3 from tunneling experiments,"We have performed magnetotransport measurements on La2/3Sr1/3MnO3 / SrTiO3 /
La2/3Sr1/3MnO3 magnetic tunnel junctions. A magnetoresistance ratio of more
than 1800 % is obtained at 4K, from which we infer an electrode spin
polarization of at least 95 %. This result strongly underscores the
half-metallic nature of mixed-valence manganites and demonstrates its
capability as a spin analyzer. The magnetoresistance extends up to temperatures
of more than 270K. We argue that these improvements over most previous works
may result from optimizing the patterning process for oxide heterostructures.",0211158v1
2003-08-22,Relevance of Cooperative Lattice Effects and Correlated Disorder in Phase-Separation Theories for CMR Manganites,"Previous theoretical investigations of colossal magnetoresistance (CMR)
materials explain this effect using a ``clustered'' state with preformed
ferromagnetic islands that rapidly align their moments with increasing external
magnetic fields. While qualitatively successful, explicit calculations indicate
drastically different typical resistivity values in two- and three-dimensional
lattices, contrary to experimental observations. This conceptual bottleneck in
the phase-separated CMR scenario is resolved here considering the cooperative
nature of the Mn-oxide lattice distortions. This induces power-law correlations
in the quenched random fields used in toy models with phase competition. When
these effects are incorporated, resistor-network calculations reveal very
similar results in two and three dimensions, solving the puzzle.",0308456v1
2003-09-30,"Spin glass anomalies in stoichiometric spin-chain oxides, Ca3CoXO6 (X = Rh, Ir and Co)","The results of ac susceptibility (chi) measurements for Ca3CoXO6 (X = Rh, Ir
and Co) compounds, containing spin-chains separated by Ca ions, are presented.
All these compounds exhibit an unusually large frequency dependence of ac chi,
in the vicinity of respective magnetic ordering temperatures, which is normally
not encountered in conventional spin-glasses. The frequency dependence of ac
chi, peak temperature is however found to obey Vogel-Fulcher relationship. The
results thus establish that these compounds are unusual spin-glasses, that too
among stoichiometric compounds presumably due to geometrical frustration.",0309702v1
2003-10-20,Spin Blockade in Capacitively Coupled Quantum Dots,"We present transport measurements on a lateral double dot produced by
combining local anodic oxidation and electron beam lithography. We investigate
the tunability of our device and demonstrate, that we can switch between
capacitive and tunnel coupling. In the regime of capacitive coupling we observe
the phenomenon of spin blockade in a magnetic field and analyze the influence
of capacitive interdot coupling on this effect.",0310469v1
2004-03-18,Theory of optical spectral weights in Mott insulators with orbital degrees of freedom,"Introducing partial sum rules for the optical multiplet transitions, we
outline a unified approach to magnetic and optical properties of strongly
correlated transition metal oxides. On the example of LaVO$_3$ we demonstrate
how the temperature and polarization dependences of different components of the
optical multiplet are determined by the underlying spin and orbital
correlations dictated by the low-energy superexchange Hamiltonian. Thereby the
optical data provides deep insight into the complex spin-orbital physics and
the role played by orbital fluctuations.",0403459v2
2004-03-30,Valence-electron transfer and a metal-insulator transition in a strongly correlated perovskite oxide,"We present transport and thermal data for the quadruple-perovskites
MCu3(Ti1-xRux)4O12 where 0 < x < 1. A metal-insulator transition (MIT) occurs
for Ru concentrations x~0.75. At the same time, the Cu2+ antiferromagnetic
state is destroyed and it's magnetic entropy suppressed by Ru on a 1:1 basis.
This implies that each Ru transfers an electron to a Cu ion and thus the MIT
correlates with filling the Cu 3d shell. The Cu spin entropy in this strongly
correlated electron material provides a unique probe among MIT systems.",0403742v1
2004-05-26,An Inhomogeneous Josephson Phase Near the (Super) Conductor-Insulator Transition,"In many cases inhomogeneities are known to exist near the metal (or
superconductor)- insulator transition, as follows from well-known domain-wall
arguments. If the conducting regions are large enough, and if they have
superconducting correlations, it becomes energetically favorable for the system
to go into a Josephson- coupled zero-resistance state before (i.e. at higher
resistance than) the material becomes a real metal. We show that this is
plausible by a simple comparison of the relevant coupling constants. We also
illustrate using data in the literature on oxide materials as well as
ultra-thin films, that when this proposed Josephson state is quenched by a
magnetic field, an insulating, rather then a metallic, state indeed appears.",0405625v1
2004-11-16,An Interesting Magnetoresistive System: Sr2FeMoO6,"Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. In this small
review, we present few theoretical and experimental results, describing mainly
the effects of Fe/Mo antisite defects on the properties of this compound and
also briefly discuss few other puzzling facts about this fascinating compound",0411400v1
2005-01-17,"Jahn-Teller stabilization of a ""polar"" metal oxide surface: Fe3O4(001)","Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.",0501402v1
2005-02-03,Charge order in the incommensurate compounds $Sr\_{14-x}Ca\_xCu\_{24}O\_{41}$,"The present paper studies, using ab-initio calculations, the influence of the
incommensurate structural modulations on the low energy physics of the
$Sr\_{14-x}Ca\_xCu\_{24}O\_{41}$ oxides. On-site, nearest-neighbor and
next-nearest-neighbor effective parameters were computed within a $t-J+V$ model
based on the copper magnetic orbitals. The structural modulations appear to be
the key degree of freedom, responsible for the low energy properties such as
the electron localization, the formation of dimers in the $x=0$ compound or the
anti-ferromagnetic order in the $x=13.6$ compound.",0502105v1
2005-03-04,Orbital excitations in titanates,"Raman scattering is used to observe pronounced electronic excitations around
230 meV - well above the two-phonon range - in the Mott insulators LaTiO$_3$
and YTiO$_3$. Based on the temperature, polarization, and photon energy
dependence, the modes are identified as orbital excitations. The observed
profiles bear a striking resemblance to magnetic Raman modes in the insulating
parent compounds of the superconducting cuprates, indicating an unanticipated
universality of the electronic excitations in transition metal oxides.",0503106v1
2005-04-11,Atom-optical elements on micro chips,"We describe the realization of atom-optical elements as magnetic waveguide
potentials, beam splitters and gravitational traps on a microchip. The
microchip was produced by electroplating gold conductors on an aluminium-oxide
substrate. The conductors are 30-150 $\mu$m wide and allow for the generation
of waveguides at large distances to the chip surface, where surface effects are
negligible. We show that these elements can be integrated on a single chip to
achieve complex atom-optical circuits.",0504242v2
2005-05-24,Nanowire Acting as a Superconducting Quantum Interference Device,"We present the results from an experimental study of the magneto-transport of
superconducting wires of amorphous Indium-Oxide, having widths in the range 40
- 120 nm. We find that, below the superconducting transition temperature, the
wires exhibit clear, reproducible, oscillations in their resistance as a
function of magnetic field. The oscillations are reminiscent of those which
underlie the operation of a superconducting quantum interference device.",0505577v1
2005-08-08,23Na NMR Studies of Non-superconducting and Superconducting Na0.35CoO2-1.3H2O (Tc < 1.8 and ~ 4.5 K),"We report 23Na NMR studies of the polycrystalline samples of bilayer hydrated
cobalt oxides Na0.35CoO2-1.3H2O with the superconducting transition
temperatures Tc < 1.8 and ~ 4.5 K. The magnitude of the 23Na nuclear
spin-lattice relaxation rate 23(1/T1) significantly decreased from non-hydrated
Na0.7CoO2 to the bilayer hydrates. We found that the temperature dependence of
23(1/T1) of the non-superconducting bilayer hydrate is similar to that of the
non-hydrated Na0.7CoO2, the spin dynamics of which is understood by A-type
(intra-layer ferromagnetic and inter-layer antiferromagnetic) spin
fluctuations. The superconducting phase is located close to the A-type magnetic
instability.",0508197v1
2005-10-24,Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors,"A close link between the charge transfer electronic structures and polarity
dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is
demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs
predicted from their charge transfer energies reproduce experimental trends
well. These results provide a unified basis for understanding both n- and
p-type ferromagnetic oxide DMSs.",0510644v1
2006-12-27,Strong Aharonov-Bohm oscillations in GaAs two-dimensional holes,"We measured Aharonov-Bohm resistance oscillations in a shallow
two-dimensional GaAs hole ring structure, defined by local anodic surface
oxidation. The amplitude of the oscillations is about 10% of the ring
resistance, the strongest seen in a hole system. In addition we observe
resistance oscillations as a function of front gate bias at zero magnetic
field. We discuss the results in light of spin interference in the ring and
possible applications to spintronics.",0612638v2
2007-02-18,Phase coherent transport in a side-gated mesoscopic graphite wire,"We investigate the magnetotransport properties of a thin graphite wire
resting on a silicon oxide substrate. The electric field effect is demonstrated
with back and side gate electrodes. We study the conductance fluctuations as a
function of gate voltage, magnetic field and temperature. The phase coherence
length extracted from weak localization is larger than the wire width even at
the lowest carrier densities making the system effectively one-dimensional. We
find that the phase coherence length increases linearly with the conductivity
suggesting that at 1.7 K dephasing originates mainly from electron-electron
interactions.",0702401v1
1999-08-27,Delocalized Supergravity Solutions for Brane/Anti-brane Systems and their Bound States,"We obtain various solutions for D=4 dipoles and their bound states whose U(1)
fields originate from various form fields in the effective string theories. We
oxidize such dipole solutions to D=10 to obtain delocalized supergravity
solutions for the brane/anti-brane pairs and their bound states. We speculate
on generalized harmonic superposition rules for supergravity solutions for
(intersecting) brane/anti-brane pairs.",9908182v2
2007-05-10,A Josephson Junction Microscope for Low-frequency Fluctuators,"The high-Q harmonic oscillator mode of a Josephson junction can be used as a
novel probe of spurious two-level systems (TLSs) inside the amorphous oxide
tunnel barriers of the junction. In particular, we show that spectroscopic
transmission measurements of the junction resonator mode can reveal how the
coupling magnitude between the junction and the TLSs varies with an external
magnetic field applied in the plane of the tunnel barrier. The proposed
experiments offer the possibility of clearly resolving the underlying coupling
mechanism for these spurious TLSs, an important decoherence source limiting the
quality of superconducting quantum devices.",0705.1380v1
2007-11-08,Ferroelectrically induced weak-ferromagnetism in a single-phase multiferroic by design,"We present a strategy to design structures for which a polar lattice
distortion induces weak ferromagnetism. We identify a large class of
multiferroic oxides as potential realizations and use density-functional theory
to screen several promising candidates. By elucidating the interplay between
the polarization and the Dzyaloshinskii-Moriya vector, we show how the
direction of the magnetization can be switched between 180$^{\circ}$ symmetry
equivalent states with an applied electric field.",0711.1331v2
2008-02-15,Non-intrinsic superconductivity in InN epilayers: role of Indium Oxide,"In recent years there have been reports of anomalous electrical resistivity
and the presence of superconductivity in semiconducting InN layers. By a
careful correlation of the temperature dependence of resistivity and magnetic
susceptibility with structural information from highresolution x-ray
diffraction measurements we show that superconductivity is not intrinsic to InN
and is seen only in samples that show traces of oxygen impurity. We hence
believe that InN is not intrinsically a superconducting semiconductor.",0802.2126v1
2008-04-24,Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces,"The formation of a novel spin-polarized 2D electron gas at the LaMnO$_3$
monolayer embedded in SrMnO$_3$ is predicted from the first-principles
density-functional calculations. The La (d) electrons become confined in the
direction normal to the interface in the potential well of the La layer,
serving as a positively-charged layer of electron donors. These electrons
mediate a ferromagnetic alignment of the Mn t$_{2g}$ spins near the interface
via the Anderson-Hasegawa double exchange and become, in turn, spin-polarized
due to the internal magnetic fields of the Mn moments.",0804.4023v1
2008-10-06,Spin polarized current and Andreev transmission in planar superconducting/ferromagnetic Nb/Ni junctions,"We have measured the tunnelling current in Nb/Nb$_x$O$_y$/Ni planar tunnel
junctions at different temperatures. The junctions are in the intermediate
transparency regime. We have extracted the current polarization of the
metal/ferromagnet junction without applying a magnetic field. We have used a
simple theoretical model, that provides consistent fitting parameters for the
whole range of temperatures analyzed. We have also been able to gain insight
into the microscopic structure of the oxide barriers of our junctions.%",0810.0929v1
2009-01-28,Depth dependent local structures in thin films unraveled by grazing incidence x-ray absorption spectroscopy,"A method of using X-ray absorption spectroscopy (XAS) together with resolved
grazing incidence geometry for depth profiling atomic, electronic, chemical or
magnetic local structures in thin films is presented. The quantitative
deconvolution of thickness-dependent spectral features is performed by fully
considering both scattering and absorption formalisms. Surface oxidation and
local structural depth profiles in nanometric FePt films are determined,
exemplifying the application of the method.",0901.4542v1
2009-04-27,Accurate evaluation of magnetic coupling between atoms with numerous open-shells : an ab-initio method,"We propose a new ab initio method designed for the accurate calculation of
effective exchange integrals between atoms with numerous open-shells. This
method applies to ferromagnetic as well as antiferromagnetic exchange, direct
or ligand-mediated exchange. Test calculations on high spin transition metal
oxides such as KNiF3, Ba2CoS3 or YMnO3 exhibit a very good accuracy compared
either to the best ab initio calculations --when those are feasible-- and with
experimental evaluations.",0904.4231v2
2009-05-02,Implications and consequences of ferromagnetism universally exhibited by inorganic nanoparticles,"Occurrence of surface ferromagnetism in inorganic nanoprticles as a universal
property not only explains many of the unusual magnetic features of oxidic thin
films, but also suggests its possible use in creating new materials, as
exemplified by multiferroic BaTiO3 nanoparticles. While the use of Mn-doped ZnO
and such materials in spintronics appears doubtful, it is possible to have
materials exhibiting coexistence of (bulk) superconductivity with (surface)
ferromagnetism.",0905.0183v1
2010-01-29,Conversion of neutral nitrogen-vacancy centers to negatively-charged nitrogen-vacancy centers through selective oxidation,"The conversion of neutral nitrogen-vacancy centers to negatively charged
nitrogen-vacancy centers is demonstrated for centers created by ion
implantation and annealing in high-purity diamond. Conversion occurs with
surface exposure to an oxygen atmosphere at 465 C. The spectral properties of
the charge-converted centers are investigated. Charge state control of
nitrogen-vacancy centers close to the diamond surface is an important step
toward the integration of these centers into devices for quantum information
and magnetic sensing applications.",1001.5449v1
2010-01-30,Magnetoresistance of a spin MOSFET with ferromagnetic MnAs source and drain contacts,"Spin-dependent transport was investigated in a spin metal-oxide-semiconductor
field-effect transistors (spin MOSFET) with ferromagnetic MnAs source and drain
(S/D) contacts. The spin MOSFET of bottom-gate type was fabricated by
photolithography using an epitaxial MnAs film grown on a silicon-on-insulator
(SOI) substrate. In-plane magnetoresistance showed spin-valve-type hysteretic
behavior, when the measurements were performed with constant source-drain and
source-gate biases. By comparing with the magnetization-related resistance
change resulting from the MnAs contacts, we conclude that the spin-polarized
electrons are injected from the MnAs source into the Si MOS inversion channel,
and detected by the MnAs drain.",1002.0057v1
2010-12-27,Disorder induced superconducting ratchet effect in nanowires,"A dc voltage drop develops along amorphous indium oxide nanowires that are
exposed to an ac bias source. This voltage is anti-symmetric with magnetic
field and is characterized by sample specific quasi-periodic magneto-voltage
oscillations. The voltage magnitude increases with decreasing temperature below
$T_{C}$ but saturates at low T. As the disorder of the sample is decreased, the
dc voltage is suppressed. We suggest that this rectification is a manifestation
of the superconducting ratchet effect in which disorder and geometrical
confinement play the role of asymmetric pinning centers. This effect
demonstrates the importance of inherent inhomogeneity and vortex motion in the
superconductor-insulator transition of disordered superconductors.",1012.5609v1
2011-01-06,Effective quantum pseudospin-1/2 model for Yb pyrochlore oxides,"An effective quantum pseudospin-1/2 Hamiltonian for Yb_2TM_2O_7 (TM = Ti and
Sn) is obtained in terms of the atomic Kramers ground doublet of the LS
coupling and the crystalline electric field, which is almost described with
J^z=\pm 1/2. It is calculated microscopically as the sum of Anderson's
superexchange interaction and the magnetic dipole interaction. It is found that
it shows a strong exchange anisotropy.",1101.1230v1
2011-03-15,Quantum transport in oxide nanostructures,"We describe magnetotransport experiments performed on Hall crosses made from
quantum wires at LaAlO3/SrTiO3 interfaces. Shubnikov-de Haas oscillations
measured in a 14-nm wide structure exhibit modulations that are consistent with
spin-orbit coupling or valley degeneracies. Hall measurements performed on the
6 nm-wide Hall cross reveal dissipative coupling to magnetic phases. Hall
plateaus are observed that deviate significantly from two-dimensional quantum
Hall counterparts. Non-monotonic dips in the Hall resistance are attributed to
one-dimensional confinement and spin-orbit coupling.",1103.3036v1
2011-04-12,Non-monotonic temperature dependence of thermopower in strongly correlated electron systems,"We examine the temperature dependence of thermopower in the single band
Hubbard model using dynamical mean-field theory. The strong Coulomb interaction
brings about the coherent-to-incoherent crossover as temperature increases. As
a result, the thermopower exhibits non-monotonic temperature dependence and
asymptotically approaches values given by the Mott-Heikes formula. In the light
of our theoretical result, we discuss the thermopower in some transition metal
oxides. The magnetic field dependence of the thermopower is also discussed.",1104.2119v4
2011-04-15,Quantized Landau level spectrum and its density dependence,"Scanning tunneling microscopy and spectroscopy in magnetic field was used to
study Landau quantization in graphene and its dependence on charge carrier
density. Measurements were carried out on exfoliated graphene samples deposited
on a chlorinated SiO2 thermal oxide which allowed observing the Landau level
sequences characteristic of single layer graphene while tuning the density
through the Si backgate. Upon changing the carrier density we find abrupt jumps
in the Fermi level after each Landau level is filled. Moreover, the Landau
level spacing shows a marked increase at low doping levels, consistent with an
interaction-induced renormalization of the Dirac cone.",1104.2947v1
2011-04-25,"Metallic characteristics in superlattices composed of insulators, NdMnO3/SrMnO3/LaMnO3","We report on the electronic properties of superlattices composed of three
different antiferromagnetic insulators, NdMnO3/SrMnO3/LaMnO3 grown on SrTiO3
substrates. Photoemission spectra obtained by tuning the x-ray energy at the Mn
2p -> 3d edge show a Fermi cut-off, indicating metallic behavior mainly
originating from Mn e_g electrons. Furthermore, the density of states near the
Fermi energy and the magnetization obey a similar temperature dependence,
suggesting a correlation between the spin and charge degrees of freedom at the
interfaces of these oxides.",1104.4694v1
2011-05-05,Understanding interface effects in perovskite thin films,"The control of matter properties (transport, magnetic, dielectric,...) using
synthesis as thin films is strongly hindered by the lack of reliable theories,
able to guide the design of new systems, through the understanding of the
interface effects and of the way the substrate constraints are imposed to the
material. The present paper analyses the energetic contributions at the
interfaces, and proposes a model describing the microscopic mechanisms
governing the interactions at an epitaxial interface between a manganite and
another transition metal oxide in perovskite structure (as for instance $\rm
SrTiO_3$). The model is checked against experimental results and literature
analysis.",1105.0986v1
2011-05-25,Interface study of FeMgOFe magnetic tunnel junctions using 3D Atom Probe,"A detailed interface study was conducted on a Fe/MgO/Fe system using laser
assisted 3D atom probe. It exhibits an additional oxide formation at the second
interface of the multilayer structure independent of laser wavelength, laser
fluence and the thickness of the tunnel barrier. We have shown with the help of
simulation that this phenomena is caused by the field evaporation of two layers
having two different evaporation",1105.5099v1
2011-12-04,A Superconducting Gap in an Insulator,"We present tunneling spectroscopy and transport measurements on disordered
indium oxide films that reveal the existence of a superconducting gap in an
insulating state. Two films on both sides of the disorder induced
superconductor to insulator transition (SIT) show the same energy gap scale at
low temperatures. This energy gap persists up to relatively high magnetic
fields and is observed across the magnetoresistance peak typical of disordered
superconductors. The results provide useful information for understanding the
nature of the insulating state in the disorder induced SIT.",1112.0776v1
2012-03-23,Charge dynamics of a single donor coupled to a few electrons quantum dot in silicon,"We study the charge transfer dynamics between a silicon quantum dot and an
individual phosphorous donor using the conduction through the quantum dot as a
probe for the donor ionization state. We use a silicon n-MOSFET (metal oxide
field effect transistor) biased near threshold in the SET regime with two side
gates to control both the device conductance and the donor charge. Temperature
and magnetic field independent tunneling time is measured. We measure the
statistics of the transfer of electrons observed when the ground state D0 of
the donor is aligned with the SET states.",1203.5264v1
2012-03-30,Determining the Curie temperature of La0.67Sr0.33MnO3 thin films,"When comparing a set of La0.67Sr0.33MnO3 (LSMO) samples, the Curie
temperature (TC) of the samples is an important figure of merit for the sample
quality. Therefore, a reliable method to determine TC is required. Here, a
method based on the analysis of the magnetization loops is proposed.",1203.6730v1
2012-09-12,Coherent spin control by electrical manipulation of the magnetic anisotropy,"High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide
exhibit a simple almost axial anisotropy and phase coherence times of the order
of a millisecond at low temperatures. The anisotropy energy is tunable using an
externally applied electric field. This can be used to control electrically the
phase of spin superpositions and to drive spin transitions with resonant
microwave electric fields.",1209.2745v2
2012-10-17,Tunneling Spectroscopy of Graphene using Planar Pb Probes,"We show that evaporating lead (Pb) directly on graphene can create
high-yield, high-quality tunnel probes, and we demonstrate high magnetic
field/low temperature spectroscopy using these probes. Comparisons of Pb, Al
and Ti/Au probes shows that after oxidation a well-formed self-limited tunnel
barrier is created only between the Pb and the graphene. Tunneling spectroscopy
using the Pb probes manifests energy-dependent features such as scattering
resonances and localization behavior, and can thus be used to probe the
microscopic electronics of graphene.",1210.4987v1
2013-01-24,Pressure effects in hollow and solid iron oxide nanoparticles,"We report a study on the pressure response of the anisotropy energy of hollow
and solid maghemite nanoparticles. The differences between the maghemite
samples are understood in terms of size, magnetic anisotropy and shape of the
particles. In particular, the differences between hollow and solid samples are
due to the different shape of the nanoparticles and by comparing both pressure
responses it is possible to conclude that the shell has a larger pressure
response when compared to the core.",1301.5708v1
2013-03-28,Superconductivity of Mg/MgO interface formed by shock-wave pressure,"A mixture of Mg and MgO has been subjected to a shock-wave pressure of 170
kbar. The ac susceptibility measurements of the product has revealed a
metastable superconductivity with Tc=30 K, characterized by glassy dynamics of
the shielding currents below Tc. Comparison of the ac susceptibility and the dc
magnetization measurements infers that the superconductivity arises within the
interfacial layer formed between metallic Mg and its oxide due to the
shock-wave treatment.",1303.7141v1
2013-05-30,Origin of giant spin-lattice coupling and the suppression of ferroelectricity in EuTiO3 from first principles,"We elucidate the microscopic mechanism that causes a suppression of
ferroelectricity and an enhancement of octahedral rotations in EuTiO3 from
first principles. We find that the hybridization of the rare-earth Eu 4f states
with the B-site Ti cation drives the system away from ferroelectricity. We also
show that the magnetic order dependence of this hybridization is the dominant
source of spin-phonon coupling in this material. Our results underline the
importance of rare-earth f electrons on the lattice dynamics and stability of
these transition metal oxides.",1305.7201v2
2013-07-15,Cobalt spin state above the valence and spin-state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3,"(Pr0.7Sm0.3)0.7Ca0.3CoO3 belongs to a class of cobalt oxides undergoing a
first-order transition (T* close to 90 K) associated to a coupled change in the
valence and spin-state degrees of freedom. The Curie-Weiss regime present
around room temperature (T >> T*) was analysed in detail to address the
controversial issue of the cobalt spin states above the transition. This
magnetic investigation indicates that the Co4+ are in an intermediate
spin-state, while the Co3+ are in a mixed state combining low-spin and
high-spin states. These results are discussed with respect to the literature on
related compounds and recent results of x-ray absorption spectroscopy.",1307.3966v1
2013-10-30,Geometrical origin of ferrimagnetism and superparamagnetism in Fe-based double perovskite multiferroics,"We show that a superstructure of antiferromagnetically interacting Fe$^{3+}$
($S=5/2$) ions in double perovskites AFe$_{1/2}$M$_{1/2}$O$_{3}$ exhibits a
ferrimagnetic ordering below $T_{fe} \approx 5.6J_1$ ($J_1/k_B \sim 50$~K),
which is close to room temperature. Small clusters of the same structure
exhibit a superparamagnetic behavior at $T \lesssim T_{fe}$. The possibility of
formation of such clusters explains the room-temperature (superpara)magnetism
in 3$d$-metal based oxides.",1310.8079v2
2013-12-09,Nanoscale nuclear magnetic resonance with a 1.9-nm-deep nitrogen-vacancy sensor,"We present nanoscale NMR measurements performed with nitrogen-vacancy (NV)
centers located down to about 2 nm from the diamond surface. NV centers were
created by shallow ion implantation followed by a slow, nanometer-by-nanometer
removal of diamond material using oxidative etching in air. The close proximity
of NV centers to the surface yielded large 1H NMR signals of up to 3.4 uT-rms,
corresponding to ~330 statistically polarized or ~10 fully polarized proton
spins in a ~(1.8 nm)^3 detection volume.",1312.2394v2
2015-02-10,Mechanisms and origin of multiferroicity,"Motivated by the potential applications of their intrinsic cross-coupling
properties, the interest in multiferroic materials has constantly increased
recently, leading to significant experimental and theoretical advancements.
From the theoretical point of view, recent progresses have allowed to identify
different mechanisms responsible for the appearence of ferroelectric
polarization coexisting with -- and coupled to -- magnetic properties. This
chapter aims at reviewing the fundamental mechanisms devised so far, mainly in
transition-metal oxides, which lie at the origin of multiferroicity.",1502.02897v1
2015-05-22,Oxygen-annealing effects on superconductivity in polycrystalline Fe1-xTe1-ySey,"Superconductivity in anti-PbO-type iron chalcogenides Fe1-xTe1-ySey (x = 0,
0.1, y = 0.1 0.4) depends on the amount (x) of interstitial iron atoms located
between the FeTe1-ySey layers. Non-superconducting samples of nominal
Fe1.1Te1-ySey convert to superconductors with critical temperatures up to 14 K
after annealing at 300{\deg}C in an oxygen atmosphere. The process is
irreversible upon subsequent hydrogen annealing. Magnetic measurements are
consistent with the formation of iron oxides suggesting that oxygen annealing
preferably extracts interstitial iron from Fe1-xTe1-ySey which interfere with
superconductivity.",1505.06066v1
2015-10-08,Nematic ordering in pyrochlore antiferromagnets: high-field phase of chromium spinel oxides,"Motivated by recent observation of a new high field phase near saturation in
chromium spinels $A$Cr$_2$O$_4$ ($A=$ Zn, Cd, Hg), we study the $S = 3/2$
pyrochlore Heisenberg antiferromagnet with biquadratic interactions. Magnon
instability analysis at the saturation field reveals that a very small
biquadratic interaction can induce magnon pairing in pyrochlore
antiferromagnets, which leads to the emergence of a ferro-quadrupolar phase, or
equivalently a spin nematic phase, below the saturation field. We present the
magnetic phase diagram in an applied field, studying both $S=3/2$ and $S=1$
spin systems. The relevance of our result to chromium spinels is discussed.",1510.02373v1
2015-10-28,Strong correlations generically protect d-wave superconductivity against disorder,"We address the question of why strongly correlated d-wave superconductors,
such as the cuprates, prove to be surprisingly robust against the introduction
of non-magnetic impurities. We show that, very generally, both the
pair-breaking and the normal state transport scattering rates are significantly
suppressed by strong correlations effects arising in the proximity to a Mott
insulating state. We also show that the correlation-renormalized scattering
amplitude is generically enhanced in the forward direction, an effect which was
previously often ascribed to the specific scattering by charged impurities
outside the copper-oxide planes.",1510.08152v2
2017-02-01,Structural characterization of magnetoferritin,"The physicochemical characterization of the magnetoferritin biomacromolecule
in terms of morphology, structural and magnetic properties shows that iron
oxides can be efficiently loaded into apoferritin molecules, preserving their
native biocompatible structure and affecting the morphology of the protein
shell.",1702.00138v1
2017-03-20,Why only hole conductors can be superconductors,"The conventional theory of superconductivity says that charge carriers in a
metal that becomes superconducting can be either electrons or holes. I argue
that this is incorrect. In order to satisfy conservation of mechanical momentum
and of entropy of the universe in the superconductor to normal transition in
the presence of a magnetic field it is necessary that the normal state charge
carriers are holes. I will also review the empirical evidence in favor of the
hypothesis that all superconductors are hole superconductors, and discuss the
implications of this for the search for higher $T_c$ superconductors.",1703.09777v1
2018-04-04,Theoretical prediction of two-dimensional CrOF sheet as a ferromagnetic semiconductor or a half-metal,"Two-dimensional chromium oxide fluoride CrOF sheet was studied based on
density functional theory. The investigation indicates that the CrOF sheet is
an intrinsic ferromagnetic semiconductor. The calculated low cleavage energy
implies that the ferromagnetic semiconductor can be exfoliated from its bulk
form. The corresponding Curie temperature is 150 K. In particular, the Curie
temperature increases up to 410 K under hole doping and the CrOF sheet becomes
a half-metal. The versatile electronic and magnetic properties indicate that
the two-dimensional CrOF sheet can be a promising candidate for next-generation
spintronic devices.",1804.01621v1
2013-08-26,"Enhancement of antiferromagnetic interaction and transition temperature in M3TeO6 systems (M = Mn, Co, Ni, Cu)","Several M3 TeO6 (M = Mn, Co, Ni, Cu) oxides order antiferromagnetically at
low temperatures (near or below 60 K), while displaying interesting dielectric
properties at high temperatures (ferroelectricity below 1000 K in M = Ni case).
We have investigated and analyzed the structural and magnetic properties of
Mn-doped Co3 TeO6 and Ni3 TeO6, which order antiferromagnetically at
temperatures higher than their undoped counterparts.",1308.5505v1
2016-11-17,Colossal enhancement of electrical conductivity in Y2Ir2O7 nanoparticles,"We present a comparative study of the magnetic and electrical properties of
polycrystalline and nanocrystalline Y2Ir2O7, the latter prepared using a new
chemical route. We find that reduction in particle size leads to enhanced
ferromagnetism and orders of magnitude enhancement of electrical conductivity
in the nanocrystalline sample. Based on x ray photoelectron spectroscopy and x
ray absorption near edge structure spectroscopy results, the phenomenon is
attributed to the increased fraction of pentavalent oxidation state of Iridium
and the resulting increase in double exchange interaction along with the
weakening of spin orbit coupling strength in the nanocrystalline sample
compared to the bulk.",1611.05661v1
2018-05-02,"Accurate Cathode Properties of LiNiO2, LiCoO2, and LiMnO2 Using the SCAN Meta-GGA Density Functional","Layered lithium intercalating transition metal (TM) oxides are promising
cathode materials for Li-ion batteries. Here we scrutinize the recently
developed strongly constrained and appropriately normed (SCAN) density
functional method to study structural, magnetic and electrochemical properties
of prototype cathode materials LiNiO2, LiCoO2, and LiMnO2 at different
Li-intercalation limits. We show that SCAN outperforms earlier popular
functional combinations, providing results in considerably better agreement
with experiment without use of Hubbard parameters, and dispersion corrections
are found to have a small effect. In particular, SCAN provides a good
description of the electronic structures, electron densities, band gaps,
predicted cell parameters, and voltage profiles.",1805.00642v1
2008-07-29,Thermally activated Peierls dimerization in ferromagnetic spin chains,"We demonstrate that a Peierls dimerization can occur in ferromagnetic spin
chains activated by thermal fluctuations. The dimer order parameter and
entanglement measures are studied as functions of the modulation of the
magnetic exchange interaction and temperature, using a spin-wave theory and the
density-matrix renormalization group. We discuss the case where a periodic
modulation is caused by spin-phonon coupling and the case where electronic
states effectively induce such a modulation. The importance of the latter for a
number of transition metal oxides is highlighted.",0807.4693v1
2017-12-28,A survey of TiOλ567 nm absorption in solar-type stars,"Molecular absorption bands are estimators of stellar activity and spot cycles
on magnetically active stars. We have previously introduced a new color index
that compare absorption strength of the titanium oxide (TiO) at 567 nm with
nearby continuum. In this paper we implement this index to measure long-term
activity variations and the statistical properties of the index in a sample of
302 solar-type stars from the HARPS planet search program. The results indicate
a pattern of change in star's activity, covers a range of periods from 2 years
up to 17 years.",1712.09882v1
2018-01-25,Optical frequency comb Faraday rotation spectroscopy,"We demonstrate optical frequency comb Faraday rotation spectroscopy (OFC-FRS)
for broadband interference-free detection of paramagnetic species. The system
is based on a femtosecond doubly resonant optical parametric oscillator and a
fast-scanning Fourier transform spectrometer (FTS). The sample is placed in a
DC magnetic field parallel to the light propagation. Efficient background
suppression is implemented via switching the direction of the field on
consecutive FTS scans and subtracting the consecutive spectra, which enables
long term averaging. In this first demonstration, we measure the entire Q- and
R-branches of the fundamental band of nitric oxide in the 5.2-5.4 {\mu}m range
and achieve good agreement with a theoretical model.",1801.08399v1
2019-10-31,Valence bond phases of herbertsmithite and related copper kagome materials,"Recent evidence from magnetic torque, electron spin resonance, and second
harmonic generation indicate that the prototypical quantum spin liquid
candidate, herbertsmithite, has a symmetry lower than its x-ray refined
trigonal space group. Here, we consider known and possible distortions of this
mineral class, along with related copper kagome oxides and fluorides, relate
these to possible valence bond patterns, and comment on their relevance to the
physics of these interesting materials.",1910.14196v2
2000-06-02,Dzyaloshinskii-Moriya interaction in NaV$_2$O$_5$: a microscopic study,"We present a unified account of magnetic exchange and Raman scattering in the
quasi-one-dimensional transition-metal oxide NaV$_2$O$_5$. Based on a
cluster-model approach explicit expressions for the exchange integral and the
Raman-operator are given. It is demonstrated that a combination of the
electronic-structure and the Dzyaloshinskii-Moriya interaction, allowed by
symmetry in this material, are responsible for the finite Raman cross-section
giving rise to both, one- and two-magnon scattering amplitudes.",0006036v1
2018-06-19,Consequences of the CMR effect on EELS in TEM,"Double perovskite oxides have gained in importance and exhibit negative
magnetoresistance, which is known as colossal magnetoresistance (CMR) effect.
Using a La$_2$CoMnO$_6$ (LCM) thin film we prove that the physical consequences
of the CMR effect do also influence the electron energy loss spectrometry
(EELS) signal. We observe a change of the band gap at low energy losses and are
able to study the magnetisation with chemical sensitivity by employing energy
loss magnetic chiral dichroism (EMCD) below the Curie temperature T$_C$ where
the CMR effect becomes significant.",1806.07118v1
2018-12-21,Electric field tuning of the anomalous Hall effect at oxide interfaces,"We show that the anomalous Hall effect (AHE) at a magnetic interface with
strong spin-orbit coupling can be tuned with an external electric field. By
altering the strength of the inversion symmetry breaking, the electric field
changes the Rashba interaction, which in turn modifies the magnitude of the
Berry curvature, the central quantity in determining the anomalous Hall
conductivity (AHC). The effect is illustrated with a square lattice model,
which yields a quadratic dependence of the AHC for small electric fields.
Explicit density-functional calculations were performed for the recently grown
iridate interface, viz., the (SrIrO$_3$)$_1$/(SrMnO$_3$)$_1$ (001) structure,
both with and without an electric field. The effect may be potentially useful
in spintronics applications.",1812.08950v1
2023-12-07,Oxidation tuning of ferroic transitions in Gd$_2$C monolayer,"Tuning of ferroic phases provides great opportunities for material
functionalities, especially in two-dimensional materials. Here, a $4f$
rare-earth carbide Gd$_2$C monolayer is predicted to be ferromagnetic metal
with large magnetization, inherited from its bulk property. Based on
first-principles calculations, we propose a strategy that the surface
passivation can effectively tune its ferroicity, namely switching among
ferromagnetic, antiferromagnetic, and ferroelectric phases. Metal-insulator
transition also occurs accompanying these ferroic transitions. Our calculation
also suggests that the magneto-optic Kerr effect and second harmonic generation
are effective methods to monitor these phase transitions.",2312.04011v1
1993-07-19,Evolution of Magnetic Properties of Lightly Doped Copper Oxides,"We study how doping destroys the AF order in the layered cuprates within the
framework of the charge--transfer insulator concept. We use the criterion of
stability of the AF background to show that the stability problem is one of the
main issues in any correspondence between results for the $t-J$ model and, say,
the three--band model for the lightly--doped layered oxides. Provided a
phenomenological conduction band is chosen to satisfy the criterion of
stability, a detailed picture of how dopants influence the spin wave spectrum
at $T=0$ is presented. The critical concentration $x_c$ for the destruction of
the AF long range order is due to the Cherenkov effect when the Fermi velocity
first exceeds the spin wave velocity. We then discuss the overall spectrum of
spin excitations and find that the spin wave attenuation for $x < x_c$, $T=0$
due to Landau damping appears in the range of magnon momenta $k(x) = 2 m^* s
\pm \alpha \sqrt{x}$. We also argue that in the presence of superconductivity,
the Cherenkov effect is eliminated due to the gap in the spectrum. This may
restore the role of the AF fluctuations as the main source of dissipation at
the lowest temperatures.",9307040v1
1997-12-15,Spin Tunneling in Conducting Oxides,"Direct tunneling in ferromagnetic junctions is compared with
impurity-assisted, surface state assisted, and inelastic contributions to a
tunneling magnetoresistance (TMR). Theoretically calculated direct tunneling in
iron group systems leads to about a 30% change in resistance, which is close to
experimentally observed values. It is shown that the larger observed values of
the TMR might be a result of tunneling involving surface polarized states. We
find that tunneling via resonant defect states in the barrier radically
decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel
diode structure would give a TMR of about 8%. With regards to inelastic
tunneling, magnons and phonons exhibit opposite effects: one-magnon emission
generally results in spin mixing and, consequently, reduces the TMR, whereas
phonons are shown to enhance the TMR. The inclusion of both magnons and phonons
reasonably explains an unusual bias dependence of the TMR.
  The model presented here is applied qualitatively to half-metallics with 100%
spin polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO$_2$/TiO$_2$ and CrO$_2$/RuO$_2$, and an account of their peculiar band
structures is presented. The implications and relation of these systems to CMR
materials which are nearly half-metallic, are discussed.",9712170v2
2001-11-01,"To the problem of electron-phonon interaction and ""d-wave pairing"" in high-Tc oxides","It is supported a recent proposal by Maksimov that electron-phonon
interaction (EPI) (Gruneisen-Bloch formulae) determines the linearity of
temperature dependence of resistivity for both HTSC-cuprates and most of metals
at T near above 0.2 of their characteristic Debye temperature (normal state for
HTSC). However, it is emphasized here that in this T-region the resistivity is
not proportional to T but is only linear in T. This fact indicates to
T-independent contribution to normal-state resistivity in HTSC-cuprates
(magnetic contribution, in our treatment) which behavior, in its turn,
indicates to possible magnetic (SDW-like) phase transition before SC transition
in HTSC-system. SDW-gap (measured as pseudogap with d-wave symmetry, in our
treatment) is formed at the symmetrical parts of the Fermi surface above Tc and
persists in SC state. The magnitude of SDW-gap is essentially larger than that
for SC-gap. So, SDW formed can mimic d-wave symmetry of the order parameter
measured below Tc (which is now attributed to d-wave pairing). On the other
hand, since the Gruneisen-Bloch curve appears to be (in approach used) a
geometric locus for the Tc(onset)(H) (as in LTSC) this fact evidents about
EPI-nature (BCS) of SC transition (s-wave) in high-Tc oxides. The proposal to
increase Tc using above (SDW/CDW/SC) model (and possible realization) is
presented.",0111015v1
2002-02-14,Spin and Orbital States and Their Phase Transitions of the Perovskite-Type Ti Oxides: Weak coupling Approach,"The magnetic phase diagram of the perovskite-type Ti oxides as a function of
the GdFeO3-type distortion is examined by using the Hartree-Fock analysis of a
multiband d-p Hamiltonian from a viewpoint of competitions of the spin-orbit
interaction, the Jahn-Teller (JT) level-splitting and spin-orbital
superexchange interactions. Near the antiferromagnetic (AFM)-to-ferromagnetic
(FM) phase boundary, A-type AFM [AFM(A)] and FM states accompanied by a certain
type of orbital ordering are lowered in energy at large JT distortion, which is
in agreement with the previous strong coupling study. With increasing the
GdFeO3-type distortion, their phase transition occurs. Through this magnetic
phase transition, the orbital state hardly changes, which induces nearly
continuous change in the spin coupling along the c-axis from negative to
positive. The resultant strong two-dimensionality in the spin coupling near the
phase boundary is attributed to the strong suppression of T_N and T_C, which is
experimentally observed. On the other hand, at small GdFeO3-type without JT
distortions, which correspond to LaTiO3, the most stable solution is not G-type
AFM [AFM(G)] but FM. Although the spin-orbit interaction has been considered to
be relevant at the small or no JT distortion of LaTiO3 in the literature, our
analysis indicates that the spin-orbit interaction is irrelevant to the AFM(G)
state in LaTiO3 and superexchange-type interaction dominates. On the basis of
further investigations on the nature of this FM state and other solutions, this
discrepancy is discussed in detail.",0202242v1
2003-09-10,First principles electronic structure of spinel LiCr2O4: A possible half-metal?,"We have employed first-principles electronic structure calculations to
examine the hypothetical (but plausible) oxide spinel, LiCr2O4 with the d^{2.5}
electronic configuration. The cell (cubic) and internal (oxygen position)
structural parameters have been obtained for this compound through structural
relaxation in the first-principles framework. Within the one-electron band
picture, we find that LiCr2O4 is magnetic, and a candidate half-metal. The
electronic structure is substantially different from the closely related and
well known rutile half-metal CrO2. In particular, we find a smaller conduction
band width in the spinel compound, perhaps as a result of the distinct topology
of the spinel crystal structure, and the reduced oxidation state. The magnetism
and half-metallicity of LiCr2O4 has been mapped in the parameter space of its
cubic crystal structure. Comparisons with superconducting LiTi2O4 (d^{0.5}),
heavy-fermion LiV2O4 (d^{1.5}) and charge-ordering LiMn2O4 (d^{3.5}) suggest
the effectiveness of a nearly-rigid band picture involving simple shifts of the
position of E_F in these very different materials. Comparisons are also made
with the electronic structure of ZnV2O4 (d^{2}), a correlated insulator that
undergoes a structural and antiferromagnetic phase transition.",0309246v2
2004-07-27,Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi_2O_4,"Magnetic field dependence of low temperature specific heat of spinel oxide
superconductor LiTi_2O_4 has been elaborately investigated. In the normal
state, the obtained electronic coefficient of specific heat gamma_n = 19.15
mJ/mol K2, the Debye temperature is 657 K and some other parameters are
compared with those reported earlier. The superconducting transition at Tc ~
11.4 K is very sharp (DeltaTc ~ 0.3 K) and the estimated delataC/gamma_nTc is ~
1.78. In the superconducting state, the best fit of data leads to the
electronic specific heat C_es/Gamma_nTc = 9.87 exp (-1.58 Tc/T) without field
and gamma(H) ~ H^0.95 with fields. In addition, Hc2(0) ~ 11.7 T, Hc(0) ~ 0.32
T, xi_GL(0) ~ 5.5 nm, lambda_GL(0) ~ 160 nm, and Hc1(0) ~ 26 mT are estimated
from Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All
results from the present study indicate that LiTi2O4 can be well described by a
typical type-II, BCS-like, moderate coupling, and fully gapped superconductor
in the dirty limit. It is further suggested that LiTi2O4 is a moderately
electron-electron correlated system.",0407695v1
2005-01-11,Two dimensionality in quasi one-dimensional cobalt oxides,"By means of muon spin rotation and relaxation ($\mu^+$SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
$AE_{n+2}$Co$_{n+1}$O$_{3n+3}$ ($AE$=Ca, Sr and Ba, $n$=1, 2, 3, 5 and
$\infty$), in which the 1D CoO$_3$ chain is surrounded by six equally spaced
chains forming a triangular lattice in the $ab$-plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with $n$=1 - 5,
transverse field $\mu^+$SR experiments showed the existence of a magnetic
transition below $\sim$100 K. The onset temperature of the transition ($T_{\rm
c}^{\rm on}$) was found to decrease with $n$; from 100 K for $n$=1 to 60 K for
$n$=5. A damped muon spin oscillation was observed only in the sample with
$n$=1 (Ca$_3$Co$_2$O$_6$), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below $T_{\rm c}^{\rm on}$ for all
compounds with $n$=1 - 5; but quasi-static long-range AF order formed only in
Ca$_3$Co$_2$O$_6$, below 25 K. For BaCoO$_3$ ($n$=$\infty$), as $T$ decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.",0501232v1
2005-06-27,Strong-coupling theory of high-temperature superconductivity and colossal magnetoresistance,"We argue that the extension of the BCS theory to the strong-coupling regime
describes the high-temperature superconductivity of cuprates and the colossal
magnetoresistance (CMR) of ferromagnetic oxides if the phonon dressing of
carriers and strong attractive correlations are taken into account. The
long-range Froehlich electron-phonon interaction has been identified as the
most essential in cuprates providing ""superlight"" lattice polarons and
bipolarons. Here some kinetic, magnetic, and more recent thermomagnetic normal
state measurements are interpreted in the framework of the strong-coupling
theory, including the Nernst effect and normal state diamagnetism. Remarkably,
a similar strong-coupling approach offers a simple explanation of CMR in
ferromagnetic oxides. The pairing of oxygen holes into heavy bipolarons in the
paramagnetic phase and their magnetic pair-breaking in the ferromagnetic phase
account for the first-order ferromagnetic phase transition, CMR, isotope
effects, and pseudogaps in doped manganites. Here we propose an explanation of
the phase coexistence and describe the shape of resistivity of manganites near
the transition in the framework of the strong-coupling approach.",0506706v3
2005-08-31,Spinel ferrites: old materials bring new opportunities for spintronics,"Over the past few years, intensive studies of ultrathin epitaxial films of
perovskite oxides have often revealed exciting properties like giant
magnetoresistive tunnelling and electric field effects. Spinel oxides appear as
even more versatile due to their more complex structure and the resulting many
degrees of freedom. Here we show that the epitaxial growth of nanometric
NiFe2O4 films onto perovskite substrates allows the stabilization of novel
ferrite phases with properties dramatically differing from bulk ones. Indeed,
NiFe2O4 films few nanometres thick have a saturation magnetization at least
twice that of the bulk compound and their resistivity can be tuned by orders of
magnitude, depending on the growth conditions. By integrating such thin NiFe2O4
layers into spin-dependent tunnelling heterostructures, we demonstrate that
this versatile material can be useful for spintronics, either as a conductive
electrode in magnetic tunnel junctions or as a spin-filtering insulating
barrier in the little explored type of tunnel junction called spin-filter. Our
findings are thus opening the way for the realisation of monolithic spintronics
architectures integrating several layers of a single material, where the layers
are functionalised in a controlled manner.",0508764v1
2005-10-03,New Misfit-Layered Cobalt Oxide (CaOH)1.14CoO2,"We found a new cobalt oxide (CaOH)1.14CoO2 by utilizing the high-pressure
technique. X-ray and electron diffraction studies revealed that the compound
has layer structure which consists of CdI2-type CoO2 layers and rock-salt-type
double CaOH atomic layers. The two subcells have incommensurate periodicity
along the a-axis, resulting in modulated crystal structure due to the
inter-subcell interaction. The structural modulation affects carrier conduction
through the potential randomness. We found that the two-dimensional (2-D)
variable-range hopping (VRH) regime with hole conduction is dominant at low
temperature for this compound, and that the conduction mechanism undergoes
crossover from the 2-D VRH regime to thermal activation-energy type one with
increasing temperature. Based on the experimental results of resistivity,
thermoelectric power, magnetic susceptibility and specific heat measurements,
we suggested a possible electronic-band structure model to explain these
results. The cobalt t2g-derivative band crosses Fermi energy level near the
band edge, yielding small finite density of localized states at the Fermi level
in the band. The observed resistivity, Seebeck coefficient, large Pauli
paramagnetic component in the magnetic susceptibility and comparatively small
Sommerfeld constant in the specific heat are principally attributed to the
holes in the t2g-derivative band. We estimated the Wilson ratio to be about
2.8, suggesting the strong electron correlation realized in this compound.",0510031v1
2006-07-05,Resonance in the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO(4-delta),"In conventional superconductors, the interaction that pairs the electrons to
form the superconducting state is mediated by lattice vibrations (phonons). In
high-transition temperature (high-Tc) copper oxides, it is generally believed
that magnetic excitations play a fundamental role in the superconducting
mechanism because superconductivity occurs when mobile 'electrons' or 'holes'
are doped into the antiferromagnetic parent compounds. Indeed, a sharp magnetic
excitation termed ""resonance"" has been observed by neutron scattering in a
number of hole-doped materials. The resonance is intimately related to
superconductivity, and its interaction with charged quasi-particles observed by
photoemission, optical conductivity, and tunneling suggests that it plays a
similar role as phonons in conventional superconductors. However, the relevance
of the resonance to high-Tc superconductivity has been in doubt because so far
it has been found only in hole-doped materials. Here we report the discovery of
the resonance in electron-doped superconducting Pr0.88LaCe0.12CuO(4-delta) (Tc
= 24 K). We find that the resonance energy (Er) is proportional to Tc via Er =
5.8kBTc (kB is the Boltzmann's constant) for all high-Tc superconductors
irrespective of electron- or hole-doping (Fig. 1e). Our results demonstrate
that the resonance is a fundamental property of the superconducting copper
oxides and therefore must play an essential role in the mechanism of
superconductivity.",0607134v1
2006-10-07,"Synthesis of nanocrystalline (Co,Ni)Al2O4 spinel powder by mechanical milling of quasicrystalline material","The (Co,Ni)Al2O4 is an aluminum transition metals oxide which falls into the
category of aluminate spinels. The synthesis of nano-crystalline spinels has
been investigated extensively due to their potential applications such as a
high-density magnetic recording, microwave devices magnetic fluids, ceramic
pigment as well as a heterogeneous catalytic material. In the present study,
attempts have been made to synthesise the nano-crystalline (Co,Ni)Al2O4 spinel
powders by ball milling and subsequent annealing. An alloy of Al70 Ni15 Co15,
exhibiting the formation of a complex intermetallic compound known as decagonal
quasicrystals in the as-solidified condition, is selected as the starting
material for mechanical milling. It is interesting to note that this alloy is
close to the stoichiometry of aluminum and transition metal atoms required to
form of the aluminate spinel. The milling was carried out in an attritor mill
at 400 rpm for 40 hours with ball to powder ratio of 20:1 in hexane medium and
the annealing was performed for 10, 20 and 40 h at 600 0 C in air in side the
furnace in order to oxidize the decagonal phase and finally to form the spinel
structures. The X-ray diffraction (XRD) and transmission electron microscopy
(TEM) confirmed the formation of nano-sized decagonal phase after milling and
then (Co,Ni)Al2O4 spinel type structure from the nano-size decagonal phase
during annealing. The average crystallite size has been found to be ~40 nm by
XRD and TEM studies, the lattice strain is 0.6 %, and the lattice parameter is
8.0756 A . The ferromagnetic behaviour is also observed in the milled and the
annealed samples.",0610203v1
2007-08-27,The nanoscale phase separation in hole-doped manganites,"A macroscopic phase separation, in which ferromagnetic clusters are observed
in an insulating matrix, is sometimes observed, and believed to be essential to
the colossal magnetoresistive (CMR) properties of manganese oxides. The
application of a magnetic field may indeed trigger large magnetoresistance
effects due to the percolation between clusters allowing the movement of the
charge carriers. However, this macroscopic phase separation is mainly related
to extrinsic defects or impurities, which hinder the long-ranged charge-orbital
order of the system. We show in the present article that rather than the
macroscopic phase separation, an homogeneous short-ranged charge-orbital order
accompanied by a spin glass state occurs, as an intrinsic result of the
uniformity of the random potential perturbation induced by the solid solution
of the cations on the $A$-sites of the structure of these materials. Hence the
phase separation does occur, but in a more subtle and interesting nanoscopic
form, here referred as ``homogeneous''. Remarkably, this ``nanoscale phase
separation'' alone is able to bring forth the colossal magnetoresistance in the
perovskite manganites, and is potentially relevant to a wide variety of other
magnetic and/or electrical properties of manganites, as well as many other
transition metal oxides, in bulk or thin film form as we exemplify throughout
the article.",0708.3524v2
2009-03-16,Spin Waves and Magnetic Exchange Interactions in CaFe2As2,"Antiferromagnetism is relevant to high temperature (high-Tc)
superconductivity because copper oxide and iron arsenide high-Tc
superconductors arise from electron- or hole-doping of their antiferromagnetic
(AF) ordered parent compounds. There are two broad classes of explanation for
the phenomenon of antiferromagnetism: in the local moment picture, appropriate
for the insulating copper oxides, AF interactions are well described by a
Heisenberg Hamiltonian; while in the itinerant model, suitable for metallic
chromium, AF order arises from quasiparticle excitations of a nested Fermi
surface. There has been contradictory evidence regarding the microscopic origin
of the AF order in iron arsenide materials, with some favoring a localized
picture while others supporting an itinerant point of view. More importantly,
there has not even been agreement about the simplest effective ground state
Hamiltonian necessary to describe the AF order. Here we report inelastic
neutron scattering mapping of spin-wave excitations in CaFe2As2, a parent
compound of the iron arsenide family of superconductors. We find that the spin
waves in the entire Brillouin zone can be described by an effective
three-dimensional local moment Heisenberg Hamiltonian, but the large in-plane
anisotropy cannot. Therefore, magnetism in the parent compounds of iron
arsenide superconductors is neither purely local nor purely itinerant; rather
it is a complicated mix of the two.",0903.2686v1
2012-08-16,Strain-Induced Spin States in Atomically Ordered Cobaltites,"Epitaxial strain imposed in complex oxide thin films by heteroepitaxy is
recognized as a powerful tool for identifying new properties and exploring the
vast potential of materials performance. A particular example is LaCoO3, a zero
spin, nonmagnetic material in the bulk, whose strong ferromagnetism in a thin
film remains enigmatic despite a decade of intense research. Here, we use
scanning transmission electron microscopy complemented by X-ray and optical
spectroscopy to study LaCoO3 epitaxial thin films under different strain
states. We observed an unconventional strain relaxation behavior resulting in
stripe-like, lattice modulated patterns, which did not involve uncontrolled
misfit dislocations or other defects. The modulation entails the formation of
ferromagnetically ordered sheets comprising intermediate or high spin Co3+,
thus offering an unambiguous description for the exotic magnetism found in
epitaxially strained LaCoO3 films. This observation provides a novel route to
tailoring the electronic and magnetic properties of functional oxide
heterostructures.",1208.3479v1
2012-11-06,Inhomogeneous superconductivity induced by interstitial Fe deintercalation in oxidizing-agent-annealed and HNO3-treated Fe1+y(Te1-xSex),"We have systematically investigated the annealing effect on the
superconductivity of iron chalcogenide Fe1+y(Te1-xSex). The atmospheres used
for annealing include O2, N2, I2 vapor, air and vacuum. We observed that
annealing in O2, I2 and air could enhance superconductivity for the underdoped
samples, consistent with the results reported in literatures. Interestingly, we
found that annealing in N2 also leads to superconductivity enhancement, similar
to the annealing effects of O2, I2 and air. However, vacuum annealing does not
enhance superconductivity, which indicates that the enhanced superconductivity
in O2-, N2-, I2- and air-annealed samples is not due to improved homogeneity.
In addition, we have treated the underdoped samples with nitric acid, which is
found to enhance superconductivity as well. Our analyses of these results
support the argument that the superconductivity enhancement, caused either by
annealing or nitric acid treatment, originates from the variation of
interstitial Fe. The interstitial Fe, which is destructive to superconducting
pairing, can be reduced by annealing in oxidation agents or nitric acid
treatment. We also find that although N2-, O2- and air-annealed samples exhibit
strong superconducting diamagnetism with -4pichi ~1 (chi, dc magnetic
susceptibility) for some samples, their actual superconducting volume fraction
probed by specific heat is low, ranging from 10% to 30% for 0.09 < x < 0.3,
indicating that the superconductivity suppression remains significant even in
annealed samples. The strong diamagnetism is associated with the
superconducting shielding effect on the non-superconducting phase. We have also
established the phase diagram of the annealed samples and compared it with that
of the as-grown samples. The effect of annealing on the interplay between
magnetism and superconductivity is discussed.",1211.1292v1
2013-11-26,Spatial Correlations and the Insulating Phase of the High-$T_c$ Cuprates: Insights from a Configuration-Interaction-Based Solver for Dynamical Mean Field Theory,"A recently proposed configuration-interaction based impurity solver is used
in combination with the single-site and four-site cluster dynamical mean field
approximations to investigate the three-band copper oxide model believed to
describe the electronic structure of high transition temperature copper-oxide
superconductors. Use of the configuration interaction solver enables
verification of the convergence of results with respect to the number of bath
orbitals. The spatial correlations included in the cluster approximation
substantially shift the metal-insulator phase boundary relative to the
prediction of the single-site approximation and increase the predicted energy
gap of the insulating phase by about 1 eV above the single-site result. Vertex
corrections occurring in the four-site approximation act to dramatically
increase the value of the optical conductivity near the gap edge, resulting in
a better agreement with the data. The calculations reveal two distinct
correlated insulating states: the `magnetically correlated insulator', in which
nontrivial intersite correlations play an essential role in stabilizing the
insulating state, and the strongly correlated insulator, in which local physics
suffices. Comparison of the calculations to the data place the cuprates in the
magnetically correlated Mott insulator regime.",1311.6819v3
2013-12-28,Kitaev interactions between j=1/2 moments in honeycomb Na2IrO3 are large and ferromagnetic: insights from ab initio quantum chemistry calculations,"Na$_2$IrO$_3$, a honeycomb 5$d^5$ oxide, has been recently identified as a
potential realization of the Kitaev spin lattice. The basic feature of this
spin model is that for each of the three metal-metal links emerging out of a
metal site, the Kitaev interaction connects only spin components perpendicular
to the plaquette defined by the magnetic ions and two bridging ligands. The
fact that reciprocally orthogonal spin components are coupled along the three
different links leads to strong frustration effects and nontrivial physics.
While the experiments indicate zigzag antiferromagnetic order in Na$_2$IrO$_3$,
the signs and relative strengths of the Kitaev and Heisenberg interactions are
still under debate. Herein we report results of ab initio many-body electronic
structure calculations and establish that the nearest-neighbor exchange is
strongly anisotropic with a dominant ferromagnetic Kitaev part, whereas the
Heisenberg contribution is significantly weaker and antiferromagnetic. The
calculations further reveal a strong sensitivity to tiny structural details
such as the bond angles. In addition to the large spin-orbit interactions, this
strong dependence on distortions of the Ir$_2$O$_2$ plaquettes singles out the
honeycomb 5$d^5$ oxides as a new playground for the realization of
unconventional magnetic ground states and excitations in extended systems.",1312.7437v2
2014-04-28,Bandgap Controlling of the Oxygen-Vacancy-Induced Two-Dimensional Electron Gas in SrTiO3,"We report very large bandgap enhancement in SrTiO3 (STO) films (fabricated by
pulsed laser deposition below 800 {\deg}C), which can be up to 20% greater than
the bulk value, depending on the deposition temperature. The origin is
comprehensively investigated and finally attributed to Sr/Ti antisite point
defects, supported by density functional theory calculations. More importantly,
the bandgap enhancement can be utilized to tailor the electronic and magnetic
phases of the two-dimensional electron gas (2DEG) in STO-based interface
systems. For example, the oxygen-vacancy-induced 2DEG (2DEG-V) at the interface
between amorphous LaAlO3 and STO films is more localized and the ferromagnetic
order in the STO-film-based 2DEG-V can be clearly seen from low-temperature
magnetotransport measurements. This opens an attractive path to tailor
electronic, magnetic and optical properties of STO-based oxide interface
systems under intensive focus in the oxide electronics community. Meanwhile,
our study provides key insight into the origin of the fundamental issue that
STO films are difficult to be doped into the fully metallic state by oxygen
vacancies.",1404.6863v2
2015-04-30,Self Duality and a possible Hall-insulator phase near the superconductor-to-insulator transition in two-dimensional indium-oxide films,"We combine measurements of the longitudinal ($\rho_{xx}$) and Hall
($\rho_{xy}$) resistivities of disordered two dimensional amorphous
indium-oxide films to study the magnetic-field tuned superconductor to
insulator transition (H-SIT) in the $T \to 0$ limit. At the critical field,
$H_c$, the full resistivity tensor is $T$ independent with $\rho_{xx}(H_c) =
h/4e^2$ and $\rho_{xy}(H_c)=0$ within experimental uncertainty in all films
(i.e. these appear to be ""universal"" values), this is strongly suggestive that
there is a particle-vortex self-duality at $H=H_c$. The transition separates
the (presumably) superconducting state at $H<H_c$ from a ""Hall-insulator"" phase
in which $\rho_{xx}\to \infty$ as $T\to 0$ while $\rho_{xy}$ approaches a
non-zero value smaller than its ""classical value"" $H/nec$, i.e.
$0<\rho_{xy}<H/nec$. A still higher characteristic magnetic field, $H_c^*>
H_c$, at which the Hall resistance is $T$ independent and roughly equal to its
classical value, $\rho_{xy}\approx H/nec$, marks an additional crossover to a
highfield regime (probably to a Fermi-insulator) in which $\rho_{xy} > H/nec$
and possibly diverges as $T\to 0$. We also highlight a profound analogy between
the H-SIT and quantum-Hall liquid to insulator transitions (QHIT).",1504.08115v3
2015-09-07,Finite Size Effect in Amorphous Indium oxide,"We study the low temperature magneto-transport properties of several highly
disordered amorphous Indium oxide(a:InO) samples. Simultaneously fabricated
devices comprising a 2-dimensional (2D) film and 10 $\mu$m long wires of
different widths were measured to investigate the effect of size as we approach
the 1D limit, which is around 4 times the correlation length, and happens to be
around 100 nm for a:InO. The film and the wires showed magnetic field ({\it B})
induced superconductor to insulator transition (SIT). In the superconducting
side, the resistance increased with decrease in wire width, whereas, an
opposite trend is observed in the insulating side. We find that this effect can
be explained in light of charge-vortex duality picture of the SIT. Resistance
of the 2D film follows an activated behavior over the temperature ($T$),
whereas, the wires show a crossover from the high-$T$ activated to a
$T$-independent behavior. At high temperature regime the wires' resistance
follow the film's until they deviate and became independent of $T$. We find
that temperature at which this deviation occurs evolve with magnetic field and
the width of the wire, which show the effect of finite size on the transport.",1509.02033v2
2015-11-09,Origin and Enhancement of Spin Polarization Current in Diluted Magnetic Oxides by Oxygen Vacancies and Nano Grain Size,"Spin polarized current is the main ingredient of diluted magnetic oxides due
to its potential manipulation in spintronic devices. However, most research has
focused on ferromagnetic properties rather than polarization of electric
current, because direct measurements were difficult and the origin of spin
polarized currents has yet to be fully understood. The method to increase the
spin polarized current percentage is beyond practical consideration at the
present status. To target this problem, we focus on the role of oxygen
vacancies and nano grain size on the spin polarized current, which are
controlled by growing the Co-doped ZnO thin-films at room temperature in a
reducing atmosphere [Ar + (1% ~ 30%) H2]. We found that the conductivity
increases with an increase in oxygen vacancies via two independent channels:
the variable range hopping (VRH) within localized states and the itinerant
transport in the conduction band. The Andreev Reflection measurements prove
that the VRH conduction is equivalent to spin polarized current. Transport
measurements show that the best way to increase the VRH content, or the
percentage of spin polarized current, is to increase oxygen vacancy
concentration and to reduce grain size and lattice constants of the films.",1511.02630v1
2016-06-17,Long-range charge density wave proximity effect at cuprate-manganate interfaces,"The interplay between charge density waves (CDWs) and high-temperature
superconductivity is currently under intense investigation. Experimental
research on this issue is difficult because CDW formation in bulk copper-oxides
is strongly influenced by random disorder, and a long-range-ordered CDW state
in high magnetic fields is difficult to access with spectroscopic and
diffraction probes. Here we use resonant x-ray scattering in zero magnetic
field to show that interfaces with the metallic ferromagnet
La$_{2/3}$Ca$_{1/3}$MnO$_3$ greatly enhance CDW formation in the optimally
doped high-temperature superconductor YBa$_2$Cu$_3$O$_{6+\delta}$ ($\bf \delta
\sim 1$), and that this effect persists over several tens of nm. The wavevector
of the incommensurate CDW serves as an internal calibration standard of the
charge carrier concentration, which allows us to rule out any significant
influence of oxygen non-stoichiometry, and to attribute the observed phenomenon
to a genuine electronic proximity effect. Long-range proximity effects induced
by heterointerfaces thus offer a powerful method to stabilize the charge
density wave state in the cuprates, and more generally, to manipulate the
interplay between different collective phenomena in metal oxides.",1606.05531v2
2016-09-23,Quantum Anomalous Hall and Half-metallic Phases in Ferromagnetic (111) Bilayers of 4d and 5d Transition Metal Perovskites,"Extraordinary electronic phases can form in artificial oxide
heterostructures, which will provide a fertile ground for new physics and also
give rise to novel device functions. Based on a systematic first-principles
density functional theory study of the magnetic and electronic properties of
the (111) superlattices (ABO3)2/(AB'O3)10 of 4d and 5d transition metal
perovskite (B = Ru, Rh, Ag, Re, Os, Ir, Au; AB'O3 = LaAlO3, SrTiO3), we
demonstrate that due to quantum confinement, bilayers (LaBO3)2 (B = Ru, Re, Os)
and (SrBO3)2 (B = Rh, Os, Ir) are ferromagnetic with ordering temperatures up
to room temperature. In particular, bilayer (LaOsO3)2 is an exotic
spin-polarized quantum anomalous Hall insulator, while the other ferromagnetic
bilayers are metallic with large Hall conductances comparable to the
conductance quantum. Furthermore, bilayers (LaRuO3)2 and (SrRhO3)2 are
half-metallic, while bilayer (SrIrO3)2 exhibits peculiar colossal magnetic
anisotropy. Our findings thus show that 4d and 5d metal perovskite (111)
bilayers are a class of quasi-two-dimensional materials for exploring exotic
quantum phases and also for advanced applications such as low-power
nanoelectronics and oxide spintronics.",1609.07383v1
2018-03-31,Understanding current-driven dynamics of magnetic Néel walls in heavy metal/ferromagnetic metal/oxide trilayers,"We consider analytically current-driven dynamics of magnetic N\'{e}el walls
in heavy metal/ferromagnetic metal/oxide trilayers where strong spin-orbit
coupling and interfacial Dzyaloshinskii-Moriya interaction (i-DMI) coexist. We
show that field-like spin-orbit torque (FL-SOT) with effective field along
$\mathbf{n}\times\hat{\mathbf{J}}$ ($\mathbf{n}$ being the interface normal and
$\hat{\mathbf{J}}$ being the charge current direction) and i-DMI induced torque
can both lead to Walker breakdown suppression meanwhile leaving the wall
mobility (velocity versus current density) unchanged. However, i-DMI itself can
not induce the ""universal absence of Walker breakdown"" (UAWB) while FL-SOT
exceeding a certain threshold can. Finitely-enlarged Walker limits before UAWB
are theoretically calculated and well explain existing data. In addition,
change in wall mobility and even its sign-inversion can be understood only if
the anti-damping-like (ADL) SOT is appended. For N\'{e}el walls in
ferromagnetic-metal layer with both perpendicular and in-plane anisotropies, we
have calculated the respective modifications of wall mobility under the
coexistence of spin-transfer torque, SOTs and i-DMI. Analytics shows that in
trilayers with perpendicular anisotropy strong enough spin Hall angle and
appropriate sign of i-DMI parameter can lead to sign-inversion in wall mobility
even under small enough current density, while in those with in-plane
anisotropy this only occurs for current density in a specific range.",1804.00127v4
2017-01-11,Carrier driven coupling in ferromagnetic oxide heterostructures,"Transition metal oxides are well known for their complex magnetic and
electrical properties. When brought together in heterostructure geometries,
they show particular promise for spintronics and colossal magnetoresistance
applications. In this letter, we propose a new mechanism for the coupling
between layers of itinerant ferromagnetic materials in heterostructures. The
coupling is mediated by charge carriers that strive to maximally delocalize
through the heterostructure to gain kinetic energy. In doing so, they force a
ferromagnetic or antiferromagnetic coupling between the constituent layers. To
illustrate this, we focus on heterostructures composed of SrRuO$_3$ and
La$_{1-x}$A$_{x}$MnO$_3$ (A=Ca/Sr). Our mechanism is consistent with
antiferromagnetic alignment that is known to occur in multilayers of
SrRuO$_3$-La$_{1-x}$A$_{x}$MnO$_3$. To support our assertion, we present a
minimal Kondo-lattice model which reproduces the known magnetization properties
of such multilayers. In addition, we discuss a quantum well model for
heterostructures and argue that the spin-dependent density of states determines
the nature of the coupling. As a smoking gun signature, we propose that
bilayers with the same constituents will oscillate between ferromagnetic and
antiferromagnetic coupling upon tuning the relative thicknesses of the layers.",1701.03117v1
2018-05-22,FMR-related phenomena in spintronic devices,"Spintronic devices, such as non-volatile magnetic random access memories and
logic devices, have attracted considerable attention as potential candidates
for future high efficient data storage and computing technology. In a heavy
metal or other emerging material with strong spin-orbit coupling (SOC), the
charge currents induce spin currents or spin accumulations via SOC. The
generated spin currents can exert spin-orbit torques (SOTs) on an adjacent
ferromagnet, which opens up a new way to realize magnetization dynamics and
switching of the ferromagnetic layer for spintronic devices. In the SOT scheme,
the charge-to-spin interconversion efficiency (SOT efficiency) is an important
figure of merit for applications. For the effective characterization of this
efficiency, the ferromagnetic resonance (FMR) based methods, such as the spin
transfer torque ferromagnetic resonance (ST-FMR) and the spin pumping, are
common utilized in addition to low frequency harmonic or dc measurements. In
this review, we focus on the ST-FMR measurements for the evaluation of the SOT
efficiency. We provide a brief summary of the different ST-FMR setups and data
analysis methods. We then discuss ST-FMR and SOT studies in various materials,
including heavy metals and alloys, topological insulators, two dimensional (2D)
materials, interfaces with strong Rashba effect, antiferromagnetic materials,
two dimensional electron gas (2DEG) in oxide materials and oxidized nonmagnetic
materials.",1805.08496v1
2008-07-10,Modeling of Spin Metal-Oxide-Semiconductor Field-Effect-Transistor: A Non-Equilibrium Green's Function Approach with Spin Relaxation,"A spin metal-oxide-semiconductor field-effect-transistor (spin MOSFET), which
combines a Schottky-barrier MOSFET with ferromagnetic source and drain
contacts, is a promising device for spintronic logic. Previous simulation
studies predict that this device should display a very high magnetoresistance
(MR) ratio (between the cases of parallel and anti-parallel magnetizations) for
the case of half-metal ferromagnets (HMF). We use the non-equilibrium Green's
function (NEGF) formalism to describe tunneling and carrier transport in this
device and to incorporate spin relaxation at the HMF-semiconductor interfaces.
Spin relaxation at interfaces results in non-ideal spin injection. Minority
spin currents arise and dominate the leakage current for anti-parallel
magnetizations. This reduces the MR ratio and sets a practical limit for spin
MOSFET performance. We found that MR saturates at a lower value for smaller
source-to-drain bias. In addition, spin relaxation at the detector side is
found to be more detrimental to MR than that at the injector side, for drain
bias less than the energy difference of the minority spin edge and the Fermi
level.",0807.1709v2
2016-05-11,Percolation via combined electrostatic and chemical doping in complex oxide films,"Stimulated by experimental advances in electrolyte gating methods, we
investigate theoretically percolation in thin films of inhomogenous complex
oxides, such as La$_{1-x}$Sr$_{x}$CoO$_{3}$ (LSCO), induced by a combination of
bulk chemical and surface electrostatic doping. Using numerical and analytical
methods, we identify two mechanisms that describe how bulk dopants reduce the
amount of electrostatic surface charge required to reach percolation: (i)
bulk-assisted surface percolation, and (ii) surface-assisted bulk percolation.
We show that the critical surface charge strongly depends on the film thickness
when the film is close to the chemical percolation threshold. In particular,
thin films can be driven across the percolation transition by modest surface
charge densities \emph{via} surface-assisted bulk percolation. If percolation
is associated with the onset of ferromagnetism, as in LSCO, we further
demonstrate that the presence of critical magnetic clusters extending from the
film surface into the bulk results in considerable volume enhancement of the
saturation magnetization, with pronounced experimental consequences. These
results should significantly guide experimental work seeking to verify
gate-induced percolation transitions in such materials.",1605.03463v1
2017-10-06,3d Transition Metals and Oxides within Carbon Nanotubes by Co-Pyrolysis of Metallocene & Camphor: High Filling Efficiency and Self-Organized Structures,"We demonstrate that a single zone furnace with a modified synthesis chamber
design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes
(CNT) with high filling efficiency and controlled morphology. Samples are
formed by pyrolysis of metallocenes, a synthesis technique that otherwise
requires a dual zone furnace. Respective metallocene in all three cases are
sublimed in powder form, a crucial factor for obtaining high filling
efficiency. While Fe@CNT is routinely produced using this technique,
well-formed Ni@CNT or Co@CNT samples are reported for the first time. This is
achieved by sublimation of nickelocene (or cobaltocene) in combination with
'camphor'. These samples exhibit some of the highest saturation magnetization
(Ms) values, at least an order of magnitude higher than that reported for Ni or
Co filled CNT, by aerosol assisted pyrolysis. The results also elucidate on why
Ni or Co@CNT are relatively difficult to obtain by pyrolyzing powder
metallocene alone. Overall, a systematic variation of synthesis parameters
provides insights for obtaining narrow length and diameter distribution and
reduced residue particles outside filled CNT - factors which are important for
device related applications. Finally, the utility of this technique is
demonstrated by obtaining highly aligned forest of Fe2O3@CNT, wherein Fe2O3 is
a functional magnetic oxide relevant to spintronics and battery applications.",1710.02413v1
2018-01-05,Large current modulation and tunneling magnetoresistance change by a side-gate electric field in a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor,"A vertical spin metal-oxide-semiconductor field-effect transistor (spin
MOSFET) is a promising low-power device for the post scaling era. Here, using a
ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs
channel layer, we demonstrate a large drain-source current IDS modulation by a
gate-source voltage VGS with a modulation ratio up to 130%, which is the
largest value that has ever been reported for vertical spin field-effect
transistors thus far. We find that the electric field effect on indirect
tunneling via defect states in the GaAs channel layer is responsible for the
large IDS modulation. This device shows a tunneling magnetoresistance (TMR)
ratio up to ~7%, which is larger than that of the planar-type spin MOSFETs,
indicating that IDS can be controlled by the magnetization configuration.
Furthermore, we find that the TMR ratio can be modulated by VGS. This result
mainly originates from the electric field modulation of the magnetic anisotropy
of the GaMnAs ferromagnetic electrodes as well as the potential modulation of
the nonmagnetic semiconductor GaAs channel layer. Our findings provide
important progress towards high-performance vertical spin MOSFETs.",1801.01670v1
2018-10-24,Radiation Damage and Thermal Recovery of Perovskite Superconductor Yttrium Barium Copper Oxide,"High temperature superconducting materials are being considered to generate
the magnetic fields required for the confinement of plasma in fusion reactors.
The present study aims to assess the microstructural degradation resulting from
ion implantation at room temperature under two implantation conditions in
Yttrium Barium Copper Oxide (YBCO) tapes. Xray Diffraction (XRD) and high
resolution characterisation techniques including Atom Probe Tomography (APT)
and Transmission Electron Microscopy (TEM) analyses were used to correlate
alterations in superconducting behaviour measured using a Magnetic Properties
Measurement System (MPMS) to amorphization and recovery caused by ion
implantation. TEM analysis was performed to depth profile the degree of
crystallinity (or lack thereof) on irradiated samples. SRIM predicted the
damage depth at 900 nm below the sample surface of the 2 MeV Xe implanted
sample and 450 nm beneath the surface of the 0.6 MeV Xe implanted sample. 2 MeV
Xe implantation caused the superconducting temperature to decrease by 10 K and
the critical current density to display a 10 fold reduction. Post irradiation
heat treatments up to 600C caused recrystallisation of the irradiated layer,
but also oxygen loss and alterations in grain size. The recrystallised grain
orientation was random in TEM lamellae, however, bulk samples re-grew along the
original crystal orientation provided that some of the original material was
not amorphized (ie if they nucleated on crystalline YBCO). This is extremely
promising for the thermal recovery of tokamak components.",1810.10477v3
2019-10-15,Integration of the Noncollinear Antiferromagnetic Metal Mn3Sn onto Ferroelectric Oxides for Electric-Field Control,"Non-collinear antiferromagnetic materials have received dramatically
increasing attention in the field of spintronics as their exotic topological
features such as the Berry-curvature-induced anomalous Hall effect and possible
magnetic Weyl states could be utilized in future topological antiferromagnetic
spintronic devices. In this work, we report the successful integration of the
antiferromagnetic metal Mn3Sn thin films onto ferroelectric oxide PMN-PT. By
optimizing growth, we realized the large anomalous Hall effect with small
switching magnetic fields of several tens mT fully comparable to those of bulk
Mn3Sn single crystals, anisotropic magnetoresistance and negative parallel
magnetoresistance in Mn3Sn thin films with antiferromagnetic order, which are
similar to the signatures of the Weyl state in bulk Mn3Sn single crystals. More
importantly, we found that the anomalous Hall effect in antiferromagnetic Mn3Sn
thin films can be manipulated by electric fields applied onto the ferroelectric
materials, thus demonstrating the feasibility of Mn3Sn-based topological
spintronic devices operated in an ultralow power manner.",1910.06555v1
2020-04-16,Intertwined density waves in a metallic nickelate,"Nickelates are a rich class of materials, ranging from insulating magnets to
superconductors. But for stoichiometric materials, insulating behavior is the
norm, as for most late transition metal oxides. Notable exceptions are the 3D
perovskite LaNiO$_3$, an unconventional paramagnetic metal, and the layered
Ruddlesden-Popper phases R$_4$Ni$_3$O$_{10}$, (R=La, Pr, Nd). The latter are
particularly intriguing because they exhibit an unusual metal-to-metal
transition. Here, we demonstrate that this transition results from an
incommensurate density wave with both charge and magnetic character that lies
intermediate in behavior between the metallic density wave seen in chromium
metal and the insulating stripes typically found in layered nickelates. As
such, R$_4$Ni$_3$O$_{10}$, which appears to be the first known example of an
itinerant spin density wave in a 3d transition metal oxide, represents an
important bridge between the paramagnetism of 3D metallic LaNiO$_3$ at higher
nickel valence and the polaronic behavior of quasi-2D R$_{2-x}$Sr$_x$NiO$_4$ at
lower nickel valence.",2004.07897v1
2021-01-12,Persistence of Flare-Driven Atmospheric Chemistry on Rocky Habitable Zone Worlds,"Low-mass stars show evidence of vigorous magnetic activity in the form of
large flares and coronal mass ejections. Such space weather events may have
important ramifications for the habitability and observational fingerprints of
exoplanetary atmospheres. Here, using a suite of three-dimensional coupled
chemistry-climate model (CCM) simulations, we explore effects of time-dependent
stellar activity on rocky planet atmospheres orbiting G-, K-, and M-dwarf
stars. We employ observed data from the MUSCLES campaign and Transiting
Exoplanet Satellite Survey and test a range of rotation period, magnetic field
strength, and flare frequency assumptions. We find that recurring flares drive
K- and M-dwarf planet atmospheres into chemical equilibria that substantially
deviate from their pre-flare regimes, whereas G-dwarf planet atmospheres
quickly return to their baseline states. Interestingly, simulated O$_2$-poor
and O$_2$-rich atmospheres experiencing flares produce similar mesospheric
nitric oxide abundances, suggesting that stellar flares can highlight otherwise
undetectable chemical species. Applying a radiative transfer model to our CCM
results, we find that flare-driven transmission features of bio-indicating
species, such as nitrogen dioxide, nitrous oxide, and nitric acid, show
particular promise for detection by future instruments.",2101.04507v3
2017-09-07,Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures,"Emergent phenomena at polar-nonpolar oxide interfaces have been studied
intensely in pursuit of next-generation oxide electronics and spintronics. Here
we report the disentanglement of critical thicknesses for electron
reconstruction and the emergence of ferromagnetism in polar-mismatched
LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific
X-ray absorption spectroscopy and dichroism, and first-principles calculations,
interfacial electron accumulation and ferromagnetism have been observed within
the polar, antiferromagnetic insulator LaMnO3. Our results show that the
critical thickness for the onset of electron accumulation is as thin as 2 unit
cells (UC), significantly thinner than the observed critical thickness for
ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely
induced by electron over-accumulation. In turn, by controlling the doping of
the LaMnO3, we are able to neutralize the excessive electrons from the polar
mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as
thin as 3 UC, extending the limits of our ability to synthesize and tailor
emergent phenomena at interfaces and demonstrating manipulation of the
electronic and magnetic structures of materials at the shortest length scales.",1709.02035v1
2019-08-07,Evolution of topological superconductivity by orbital selective confinement in oxide nanowires,"We determine the optimal conditions to achieve topological superconducting
phases having spin-singlet pairing for a planar nanowire with finite lateral
width in the presence of an in-plane external magnetic field. We employ a
microscopic description that is based on a three-band electronic model
including both the atomic spin-orbit coupling and the inversion asymmetric
potential at the interface between oxide band-gap insulators. We consider
amplitudes of the pairing gap, spin-orbit interactions and electronic
parameters that are directly applicable to nanowires of LaAlO$_3$-SrTiO$_3$.
The lateral confinement introduces a splitting of the $d$-orbitals that alters
the orbital energy hierarchy and significantly affects the electron filling
dependence of the topological phase diagram. Due to the orbital directionality
of the $t_{2g}$-states, we find that in the regime of strong confinement the
onset of topological phases is pinned at electron filling where the quasi flat
heavy bands start to get populated. The increase of the nanowire thickness
leads to a changeover from sparse-to-dense distribution of topologically
non-trivial domains which occurs at the cross-over associated to the orbital
population inversion. These findings are corroborated by a detailed analysis of
the most favorable topological superconducting phases in the electron
doping-magnetic field plane highlighting the role of orbital selective
confinement.",1908.02857v1
2021-08-16,Neutron Scattering Signature of Phonon Renormalization in Nickel (II) Oxide,"The physics of mutual interaction of phonon quasiparticles with electronic
spin degrees of freedom, leading to unusual transport phenomena of spin and
heat, has been a subject of continuing interests for decades. Despite its
pivotal role in transport processes, the effect of spin-phonon coupling on the
phonon system, especially acoustic phonon properties, has so far been elusive.
By means of inelastic neutron scattering and first-principles calculations,
anomalous scattering spectral intensity from acoustic phonons was identified in
the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong
spin-lattice correlations that renormalize the polarization of acoustic phonon.
In particular, a clear magnetic scattering signature of the measured neutron
scattering intensity from acoustic phonons is demonstrated by its momentum
transfer and temperature dependences. The anomalous scattering intensity is
successfully modeled with a modified magneto-vibrational scattering cross
section, suggesting the presence of spin precession driven by phonon. The
renormalization of phonon eigenvector is indicated by the observed
""geometry-forbidden"" neutron scattering intensity from transverse acoustic
phonon. Importantly, the eigenvector renormalization cannot be explained by
magnetostriction but instead, it could result from the coupling between phonon
and local magnetization of ions.",2108.07363v3
2021-10-14,Superconductor-insulator transitions in three-dimensional indium-oxide at high pressures,"Experiments investigating magnetic-field-tuned superconductor-insulator
transition (HSIT) mostly focus on two-dimensional material systems where the
transition and its proximate ground-state phases, often exhibit features that
are seemingly at odds with the expected behavior. Here we present a
complementary study of a three-dimensional pressure-packed amorphous
indium-oxide (InOx) powder where granularity controls the HSIT. Above a low
threshold pressure of ~0.2 GPa, vestiges of superconductivity are detected,
although neither a true superconducting transition nor insulating behavior are
observed. Instead, a saturation at very high resistivity at low pressure is
followed by saturation at very low resistivity at higher pressure. We identify
both as different manifestations of anomalous metallic phases dominated by
superconducting fluctuations. By analogy with previous identification of the
low resistance saturation as a ""failed superconductor"", our data suggests that
the very high resistance saturation is a manifestation of a ""failed insulator"".
Above a threshold pressure of ~6 GPa, the sample becomes fully packed, and
superconductivity is robust, with TC tunable with pressure. A quantum critical
point at PC~25 GPa marks the complete suppression of superconductivity. For a
finite pressure below PC, a magnetic field is shown to induce a HSIT from a
true zero-resistance superconducting state to a weakly insulating behavior.
Determining the critical field, HC, we show that similar to the 2D behavior,
the insulating-like state maintains a superconducting character, which is
quenched at higher field, above which the magnetoresistance decreases to its
fermionic normal state value.",2110.07251v3
2023-10-27,Spin Selective Evolution of Zhang-Rice State in Binary Transition Metal Oxide,"The Zhang-Rice (ZR) state is a strongly hybridized bound state formed by the
transition metal and oxygen atoms. The spin-fluctuations within the ZR state
are known to play an important role in high-$T_\mathrm{c}$ superconductivity in
cuprates. Here, we employ a combination of angle-resolved photoemission
spectroscopy (ARPES), X-ray photoemission spectroscopy (XPS), and {\it ab
initio} embedded dynamical mean-field theory (eDMFT) to investigate the
influence of magnetic ordering on the spectral characteristics of the valence
band and Mn 2$p$ core-level in MnO (001) ultrathin films. Our results
demonstrate that a complex spin-selective evolution of Mn 3$d$$-$O 2$p$
hybridization develops due to the long-range antiferromagnetic (AFM) ordering.
This hybridization significantly alters the spectral shape and weight of the ZR
state. Specifically, in the AFM phase, we observed the sharpening of the ZR
state and band folding with the periodicity of the AFM unit cell of MnO(001).
We also demonstrated a strong connection between the spectral evolution of the
ZR state and the non-local screening channels of the photoexcited core holes.
Further, our detailed temperature-dependent study reveals the presence of
short-range antiferromagnetic correlations that exist at much higher
temperatures than $T_\mathrm{N}$. Such comprehensive studies showing the
evolution of the ZR state across the magnetic transitions and its implication
to the core-hole screening have never been reported in any 3$d$ binary
transition metal oxides.",2310.17833v1
2023-11-10,Provoking topology by octahedral tilting in strained SrNbO$_3$,"Transition metal oxides with a wide variety of electronic and magnetic
properties offer an extraordinary possibility to be a platform for developing
future electronics based on unconventional quantum phenomena, for instance, the
topology. The formation of topologically non-trivial states is related to
crystalline symmetry, spin-orbit coupling, and magnetic ordering. Here, we
demonstrate how lattice distortions and octahedral rotation in SrNbO$_3$ films
induce the band topology. By employing angle-resolved photoemission
spectroscopy (ARPES) and density functional theory (DFT) calculations, we
verify the presence of in-phase $a^0a^0c^+$ octahedral rotation in ultra-thin
SrNbO$_3$ films, which causes the formation of topologically-protected Dirac
band crossings. Our study illustrates that octahedral engineering can be
effectively exploited for implanting and controlling quantum topological phases
in transition metal oxides.",2311.06072v1
2014-08-08,Spin-Orbital Order Modified by Orbital Dilution in Transition Metal Oxides: From Spin Defects to Frustrated Spins Polarizing Host Orbitals,"We study the $3d$ substitution in $4d$ transition metal oxides in the cases
of $3d^3$ doping at either $3d^2$ or $4d^4$ sites which realize orbital
dilution. We derive the effective $3d-4d$ (or $3d-3d$) superexchange in a Mott
insulator with different ionic valencies, underlining the emerging structure of
the spin-orbital coupling between the impurity and the host sites and
demonstrate that it is qualitatively different from that encountered in the
host itself. This derivation shows that the interaction between the host and
the impurity depends in a crucial way on the type of doubly occupied $t_{2g}$
orbital. One finds that in some cases, due to the quench of the orbital degree
of freedom at the $3d$ impurity, the spin and orbital order within the host is
drastically modified by doping. The impurity acts either as a spin defect
accompanied by an orbital vacancy in the spin-orbital structure when the
host-impurity coupling is weak, or it favors doubly occupied active orbitals
(orbital polarons) along the $3d-4d$ bond leading to antiferromagnetic or
ferromagnetic spin coupling. This competition between different magnetic
couplings leads to quite different ground states. We find that magnetic
frustration and spin degeneracy can be lifted by the quantum orbital flips of
the host but they are robust in special regions of the incommensurate phase
diagram. The spin-orbit coupling can lead to anisotropic spin and orbital
patterns along the symmetry directions and cause a radical modification of the
order imposed by the spin-orbital superexchange. Our findings are expected to
be of importance for future theoretical understanding of experimental results
for doped $4d$ transition metal oxides doped with $3d^3$ ions. We suggest how
the local or global changes of the spin-orbital order induced by such
impurities could be detected experimentally.",1408.1838v3
2012-05-24,Turning ABO$_3$ antiferroelectrics into ferroelectrics: Design rules for practical rotation-driven ferroelectricity in double perovskites and A$_3$B$_2$O$_7$ Ruddlesden-Popper compounds,"Ferroic transition metal oxides, which exhibit spontaneous elastic,
electrical, magnetic or toroidal order, exhibit functional properties that find
use in ultrastable solid-state memories to sensors and medical imaging
technologies. To realize multifunctional behavior, where one order parameter
can be coupled to the conjugate field of another order parameter, however,
requires a common microscopic origin for the long-range order. Here, we
formulate a complete theory for a novel form of ferroelectricity, whereby a
spontaneous and switchable polarization emerges from the destruction of an
antiferroelectric state due to octahedral rotations and ordered cation
sublattices. We then construct a materials design framework based on
crystal-chemistry descriptors rooted in group theory, which enables the facile
design of artificial oxides with large electric polarizations, P, simultaneous
with small energetic switching barriers between +P and -P. We validate the
theory with first principles density functional calculations on more than 16
perovskite-structured oxides, illustrating it could be operative in any
materials classes exhibiting two- or three-dimensional corner-connected
octahedral frameworks. We show the principles governing materials selection of
the ""layered"" systems originate in the lattice dynamics of the A cation
displacements stabilized by the pervasive BO$_6$ rotations of single phase
ABO$_3$ materials, whereby the latter distortions govern the optical band gaps,
magnetic order and critical transition temperatures. Our approach provides the
elusive route to the ultimate multifunctionality property control by an
external electric field.",1205.5526v3
2019-12-22,Two-dimensional electron systems in perovskite oxide heterostructures: Role of the polarity-induced substitutional defects,"The discovery of a two-dimensional electron system (2DES) at the interfaces
of perovskite oxides such as LaAlO3 and SrTiO3 has motivated enormous efforts
in engineering interfacial functionalities with this type of oxide
heterostructures. However, its fundamental origins are still not understood,
e.g. the microscopic mechanisms of coexisting interface conductivity and
magnetism. Here we report a comprehensive spectroscopic investigation of the
depth profile of 2DES-relevant Ti 3d interface carriers using depth- and
element-specific techniques, standing-wave excited photoemission and resonant
inelastic scattering. We found that one type of Ti 3d interface carriers, which
give rise to the 2DES are located within 3 unit cells from the n-type interface
in the SrTiO3 layer. Unexpectedly, another type of interface carriers, which
are polarity-induced Ti-on-Al antisite defects, reside in the first 3 unit
cells of the opposing LaAlO3 layer (~10 {\AA}). Our findings provide a
microscopic picture of how the localized and mobile Ti 3d interface carriers
distribute across the interface and suggest that the 2DES and 2D magnetism at
the LaAlO3/SrTiO3 interface have disparate explanations as originating from
different types of interface carriers.",1912.10384v3
2020-10-20,Strong Ferromagnetism Achieved via Breathing Lattices in Atomically Thin Cobaltites,"Low-dimensional quantum materials that remain strongly ferromagnetic down to
mono layer thickness are highly desired for spintronic applications. Although
oxide materials are important candidates for next generation of spintronic,
ferromagnetism decays severely when the thickness is scaled to the nano meter
regime, leading to deterioration of device performance. Here we report a
methodology for maintaining strong ferromagnetism in insulating LaCoO3 (LCO)
layers down to the thickness of a single unit cell. We find that the magnetic
and electronic states of LCO are linked intimately to the structural parameters
of adjacent ""breathing lattice"" SrCuO2 (SCO). As the dimensionality of SCO is
reduced, the lattice constant elongates over 10% along the growth direction,
leading to a significant distortion of the CoO6 octahedra, and promoting a
higher spin state and long-range spin ordering. For atomically thin LCO layers,
we observe surprisingly large magnetic moment (0.5 uB/Co) and Curie temperature
(75 K), values larger than previously reported for any mono layer oxide. Our
results demonstrate a strategy for creating ultra thin ferromagnetic oxides by
exploiting atomic hetero interface engineering,confinement-driven structural
transformation, and spin-lattice entanglement in strongly correlated materials.",2010.09998v1
2014-04-14,Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields,"When a micron-sized magnetizable particle is introduced into a suspension of
nanosized magnetic particles, the nanoparticles accumulate around the
microparticle and form thick anisotropic clouds extended in the direction of
the applied magnetic field. This phenomenon promotes colloidal stabilization of
bimodal magnetic suspensions and allows efficient magnetic separation of
nanoparticles used in bioanalysis and water purification. In the present work,
size and shape of nanoparticle clouds under the simultaneous action of an
external uniform magnetic field and the flow have been studied in details. In
experiments, dilute suspension of iron oxide nanoclusters (of a mean diameter
of 60 nm) was pushed through a thin slit channel with the nickel microspheres
(of a mean diameter of 50$\mu$m) attached to the channel wall. The behavior of
nanocluster clouds was observed in the steady state using an optical
microscope. In the presence of strong enough flow, the size of the clouds
monotonically decreases with increasing flow speed in both longitudinal and
transverse magnetic fields. This is qualitatively explained by enhancement of
hydrodynamic forces washing the nanoclusters away from the clouds. In the
longitudinal field, the flow induces asymmetry of the front and the back
clouds. To explain the flow and the field effects on the clouds, we have
developed a simple model based on the balance of the stresses and particle
fluxes on the cloud surface. This model, applied to the case of the magnetic
field parallel to the flow, captures reasonably well the flow effect on the
size and shape of the cloud and reveals that the only dimensionless parameter
governing the cloud size is the ratio of hydrodynamic-to-magnetic forces - the
Mason number. At strong magnetic interactions considered in the present work
(dipolar coupling parameter $\alpha \geq 2$), the Brownian motion seems not to
affect the cloud behavior.",1404.3927v1
2020-11-04,Unveiling temperature dependence mechanisms of perpendicular magnetic anisotropy at Fe/MgO interfaces,"The perpendicular magnetic anisotropy (PMA) at magnetic transition
metal/oxide interfaces is a key element in building out-of-plane magnetized
magnetic tunnel junctions for spin-transfer-torque magnetic random access
memory (STT-MRAM). Size downscaling renders magnetic properties more sensitive
to thermal effects. Thus, understanding the temperature dependence of the
magnetic anisotropy is crucial. In this work, we theoretically address the
correlation between temperature dependence of PMA and magnetization in typical
Fe/MgO-based structures. In particular, the possible mechanisms behind the
experiments reporting deviations from the Callen and Callen scaling power law
are analyzed. At ideal interfaces, first-principles calculations reveal (i)
small high-order anisotropy constants compared to first order and (ii) enhanced
exchange constants. Considering these two intrinsic effects in the atomistic
simulations, the temperature-dependence of the total and layer-resolved
anisotropy are found to follow the Callen and Callen scaling power law, thus
ruling out an intrinsic microscopic mechanism underlying deviations from this
law. Besides, two possible extrinsic macroscopic mechanisms are unveiled namely
the influence of the dead layer, often present in the storage layer of STT-MRAM
cells, and the spatial inhomogeneities of the interfacial magnetic anisotropy.
About the first mechanism, we show that the presence of a dead layer tends to
reduce the scaling exponents. In the second mechanism, increasing the
percentage of inhomogeneity in the interfacial PMA is revealed to decrease the
scaling exponent. These results allow us to explain the difference in scaling
exponents relating anisotropy and magnetization thermal variations reported in
earlier experiments. This is crucial for the understanding of the thermal
stability of the storage layer magnetization in STT-MRAM applications.",2011.02220v3
2022-05-06,Tuning the dynamics of chiral domain walls of ferrimagnetic films with the magneto-ionic effect,"The manipulation of magnetism with a gate voltage is expected to lead the way
towards the realization of energy-efficient spintronics devices and
high-performance magnetic memories. Exploiting magneto-ionic effects under
micro-patterned electrodes in solid-state devices adds the possibility to
modify magnetic properties locally, in a non-volatile and reversible way.
Tuning magnetic anisotropy, magnetization and Dzyaloshinskii-Moriya interaction
allows modifying at will the dynamics of non trivial magnetic textures such as
skyrmions and chiral domain walls in magnetic race tracks. In this work, we
illustrate efficient magneto-ionic effects in a ferrimagnetic Pt/Co/Tb stack
using a ZrO2 thin layer as a solid state ionic conductor. When a thin layer of
terbium is deposited on top of cobalt, it acquires a magnetic moment that
aligns antiparallel to that of cobalt, reducing the effective magnetization.
Below the micro-patterned electrodes, the voltage-driven migration of oxygen
ions in a ZrO2 towards the ferrimagnetic stack partially oxidizes the Tb layer,
leading to the local variation not only of the spontaneous magnetization, but
also of the effective magnetic anisotropy and of the Dzyaloshinskii-Moriya
interaction. This leads to a huge increase of the domain wall velocity, which
varies from 10 m/s in the pristine state to 250 m/s after gating. This
non-volatile and reversible tuning of the domain wall dynamics may lead to
applications to reprogrammable magnetic memories or other spintronic devices.",2205.03158v1
2023-10-02,Control of the magnetic anisotropy in multi-repeat Pt/Co/Al heterostructures using magneto-ionic gating,"Controlling magnetic properties through the application of an electric field
is a significant challenge in modern nanomagnetism. In this study, we
investigate the magneto-ionic control of magnetic anisotropy in the topmost Co
layer in Ta/Pt/[Co/Al/Pt]$_n$/Co/Al/AlO$_\text{x}$ multilayer stacks comprising
$n +1$ Co layers and its impact on the magnetic properties of the multilayers.
We demonstrate that the perpendicular magnetic anisotropy can be reversibly
quenched through gate-driven oxidation of the intermediary Al layer between Co
and AlO$_\text{x}$, enabling dynamic control of the magnetic layers
contributing to the out-of-plane remanence - varying between $n$ and $n +1$.
For multilayer configurations with $n = 2$ and $n = 4$, we observe reversible
and non-volatile additions of 1/3 and 1/5, respectively, to the anomalous Hall
effect amplitude based on the applied gate voltage. Magnetic imaging reveals
that the gate-induced spin-reorientation transition occurs through the
propagation of a single 90$^{\circ}$ magnetic domain wall separating the
perpendicular and in-plane anisotropy states. In the 5-repetition multilayer,
the modification leads to a doubling of the period of the magnetic domains at
remanence. These results demonstrate that the magneto-ionic control of the
anisotropy of a single magnetic layer can be used to control the magnetic
properties of coupled multilayer systems, extending beyond the gating effects
on a single magnetic layer.",2310.01623v1
2008-02-05,CO oxidation on Pd(100) at technologically relevant pressure conditions: A first-principles kinetic Monte Carlo study,"The possible importance of oxide formation for the catalytic activity of
transition metals in heterogenous oxidation catalysis has evoked a lively
discussion over the recent years. On the more noble transition metals (like Pd,
Pt or Ag) the low stability of the common bulk oxides suggests primarily
sub-nanometer thin oxide films, so-called surface oxides, as potential
candidates that may be stabilized under gas phase conditions representative of
technological oxidation catalysis. We address this issue for the Pd(100) model
catalyst surface with first-principles kinetic Monte Carlo (kMC) simulations
that assess the stability of the well-characterized (sqrt{5} x sqrt{5})R27
surface oxide during steady-state CO oxidation. Our results show that at
ambient pressure conditions the surface oxide is stabilized at the surface up
to CO:O2 partial pressure ratios just around the catalytically most relevant
stoichiometric feeds (p(CO):p(O2) = 2:1). The precise value depends sensitively
on temperature, so that both local pressure and temperature fluctuations may
induce a continuous formation and decomposition of oxidic phases during
steady-state operation under ambient stoichiometric conditions.",0802.0553v1
2011-04-06,"Sr flux stability against oxidation in oxide-MBE environment: flux, geometry, and pressure dependence","Maintaining stable fluxes for multiple source elements is a challenging task
when the source materials have significantly different oxygen affinities in a
complex-oxide molecular-beam-epitaxy (MBE) environment. Considering that Sr is
one of the most easily oxidized and widely used element in various complex
oxides, we took Sr as a probe to investigate the flux stability problem in a
number of different conditions. Source oxidation was less for higher flux,
extended port geometry, and un-melted source shape. The extended port geometry
also eliminated the flux transient after opening a source shutter as observed
in the standard port. We also found that the source oxidation occurred more
easily on the crucible wall than on the surface of the source material. Atomic
oxygen, in spite of its stronger oxidation effectiveness, did not make any
difference in source oxidation as compared to molecular oxygen in this
geometry. Our results may provide a guide for solutions to the source oxidation
problem in oxide-MBE system.",1104.1117v1
2013-01-10,Research on Interpore Distance of Anodic Aluminum Oxide Template,"The relationship between the interpore of anodic aluminum oxide (AAO)
template and the influencing factors of electrolyte, temperature and oxidation
voltage etc. was researched and summarized in this paper. It was pointed out
that the interpore was influenced mostly by electrolyte type and oxidation
voltage, and least by the electrolyte concentration and oxidation temperature.
The interpore of AAO template increases with the oxidation voltage increases.
By adjusting the electrolyte and oxidation voltage, a desired interpore of
template can be acquired. To acquire a large interpore template can use
electrolyte of phosphoric acid or chromic acid under a comparatively higher
oxidation voltage. To acquire a small interpore template (with interpore within
10nm) can use sulfate electrolyte under a comparatively lower oxidation voltage
or pulse voltage. Alternatively, oxidizing with lower oxidation voltage in a
mixed electrolyte of H2SO4 and Al2 (SO4)3, whereafter immersion in the mixture
of HCl and CuCl2 to corrode the template for some time, until the angles of
cell appear six holes with small pore diameter, the interpore of AAO template
decrease to about 0.6 times of the original.",1301.2058v1
2012-03-13,Understanding of the Retarded Oxidation Effects in Silicon Nanostructures,"In-depth understanding of the retarded oxidation phenomenon observed during
the oxidation of silicon nanostructures is proposed. The wet thermal oxidation
of various silicon nanostructures such as nanobeams, concave/convex nanorings
and nanowires exhibits an extremely different and complex behavior. Such
effects have been investigated by the modeling of the mechanical stress
generated during the oxidation process explaining the retarded regime. The
model describes the oxidation kinetics of silicon nanowires down to a few
nanometers while predicting reasonable and physical stress levels at the
Si/SiO$_{2}$ interface by correctly taking into account the relaxation effects
in silicon oxide through plastic flow.",1203.2803v1
2012-10-30,Competing Atomic and Molecular Mechanisms of Thermal Oxidation,"The oxidation of SiC and Si provide a unique opportunity for studying
oxidation mechanisms because the product is the same, SiO2. Silicon oxidation
follows a linear-parabolic law, with molecular oxygen identified as the
oxidant. SiC oxidation obeys the same linear-parabolic law but has different
rates and activation energies and exhibits much stronger face-dependence. Using
results from first-principles calculations, we show that atomic and molecular
oxygen are the oxidant for Si- and C-face SiC respectively. Comparing SiC with
Si, we elucidate how the interface controls the competition between atomic and
molecular mechanisms.",1210.7899v2
2021-03-31,Effects of point defects on oxidation of 3C-SiC,"The influence of implantation-induced point defects (PDs) on SiC oxidation is
investigated via molecular dynamics simulations. PDs generally increase the
oxidation rate of crystalline grains. Particularly, accelerations caused by Si
antisites and vacancies are comparable, and followed by Si interstitials, which
are higher than those by C antisites and C interstitials. However, in the grain
boundary (GB) region, defect contribution to oxidation is more complex, with C
antisites decelerating oxidation. The underlying reason is the formation of a
C-rich region along the oxygen diffusion pathway that blocks the access of O to
Si and thus reduces the oxidation rate, as compared to the oxidation along a GB
without defects.",2103.16742v1
2013-11-18,Orbital magnetization of insulating perovskite transition-metal oxides with the net ferromagnetic moment in the ground state,"Modern theory of the orbital magnetization is applied to the series of
insulating perovskite transition metal oxides (orthorhombic YTiO$_3$,
LaMnO$_3$, and YVO$_3$, as well as monoclinic YVO$_3$), carrying a net
ferromagnetic (FM) moment in the ground state. For these purposes, we use an
effective Hubbard-type model, derived from the first-principles
electronic-structure calculations and describing the behavior of magnetically
active states near the Fermi level. The solution of this model in the
mean-field Hartree-Fock approximation with the relativistic spin-orbit coupling
typically gives us a distribution of the local orbital magnetic moments, which
are related to the site-diagonal part of the density matrix $\hat{\cal D}$ by
the ""standard"" expression $\boldsymbol{\mu}^0 = - \mu_{\rm B} \mathrm{Tr} \{
\hat{\textbf{L}} \hat{\cal D} \}$ and which are usually well quenched by the
crystal field. In this work, we evaluate ""itinerant"" corrections $\Delta
\boldsymbol{\cal M}$ to the net FM moment, suggested by the modern theory. We
show that these corrections are small and in most cases can be neglected.
Nevertheless, the most interesting aspect of our analysis is that, even for
these compounds, which are typically regarded as normal Mott insulators, the
""itinerant"" corrections reveal a strong $\textbf{k}$-dependence in the
reciprocal space, following the behavior of Chern invariants. Therefore, the
small value of $\Delta \boldsymbol{\cal M}$ is the result of strong cancelation
of relatively large contributions, coming from different parts of the Brillouin
zone. We discuss details as well as possible implications of this cancelation,
which depends on the crystal structure as well as the type of the magnetic
ground state.",1311.4263v1
2018-03-22,Direct observation of electron density reconstruction at the metal-insulator transition in NaOsO3,"5d transition metal oxides offer new opportunities to test our understanding
of the interplay of correlation effects and spin-orbit interactions in
materials in the absence of a single dominant interaction. The subtle balance
between solid-state interactions can result in new mechanisms that minimize the
interaction energy, and in material properties of potential use for
applications. We focus here on the 5d transition metal oxide NaOsO3, a strong
candidate for the realization of a magnetically driven transition from a
metallic to an insulating state exploiting the so-called Slater mechanism.
Experimental results are derived from non-resonant and resonant x-ray single
crystal diffraction at the Os L-edges. A change in the crystallographic
symmetry does not accompany the metal-insulator transition in the Slater
mechanism and, indeed, we find no evidence of such a change in NaOsO3. An
equally important experimental observation is the emergence of the (300) Bragg
peak in the resonant condition with the onset of magnetic order. The intensity
of this space-group forbidden Bragg peak continuously increases with decreasing
temperature in line with the square of intensity observed for an allowed
magnetic Bragg peak. Our main experimental results, the absence of crystal
symmetry breaking and the emergence of a space-group forbidden Bragg peak with
developing magnetic order, support the use of the Slater mechanism to interpret
the metal-insulator transition in NaOsO3. We successfully describe our
experimental results with simulations of the electronic structure and, also,
with an atomic model based on the established symmetry of the crystal and
magnetic structure.",1803.08271v5
2019-04-02,Relationship between charge redistribution and ferromagnetism at the heterointerface between perovskite oxides LaNiO$_3$ and LaMnO$_3$,"To investigate the relationship between the charge redistribution and
ferromagnetism at the heterointerface between perovskite transition-metal
oxides LaNiO$_3$ (LNO) and LaMnO$_3$ (LMO), we performed x-ray absorption
spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements. In the
LNO/LMO heterostructures with asymmetric charge redistribution, the electrons
donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the
interface, whereas holes are distributed over 3-4 ML on the LMO side. A
detailed analysis of the Ni-$L_{2,3}$ and Mn-$L_{2,3}$ XMCD spectra reveals
that Ni magnetization is induced only by the Ni$^{2+}$ ions in the 1 ML LNO
adjacent to the interface, while the magnetization of Mn ions is increased in
the 3-4 ML LMO of the interfacial region. The characteristic length scale of
the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is
in good agreement with that of the charge distribution across the interface,
indicating a close relationship between the charge redistribution due to the
interfacial charge transfer and the ferromagnetism of the LNO/LMO interface.
Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced
magnetization of both ions are aligned ferromagnetically, suggesting that the
delicate balance between the exchange interactions occurring inside each layer
and across the interface may induce the canted ferromagnetism of Ni$^{2+}$
ions, resulting in weak magnetization in the 1 ML LNO adjacent to the
interface.",1904.01335v1
2021-07-02,Interplay between singlet and triplet pairings in multi-band two-dimensional oxide superconductors,"We theoretically study the superconducting properties of multi-band
two-dimensional transition metal oxide superconductors by analyzing not only
the role played by conventional singlet pairings, but also by the triplet order
parameters, favored by the spin-orbit couplings present in these ma- terials.
In particular, we focus on the two-dimensional electron gas at the (001)
interface between LaAlO3 and SrTiO3 band insulators where the low electron
densities and the sizeable spin-orbit couplings affect the superconducting
features. Our theoretical study is based on an extended su- perconducting
mean-field analysis of the typical multi-band tight-binding Hamiltonian, as
well as on a parallel analysis of the effective electronic bands in the
low-momentum limit, including static on-site and inter-site intra-band
attractive potentials under applied magnetic fields. The presence of triplet
pairings is able to strongly reduce the singlet order parameters which, as a
result, are no longer a monotonic function of the charge density. The interplay
between the singlet and the triplet pairings affects the dispersion of
quasi-particle excitations in the Brillouin zone and also induces anisotropy in
the superconducting behavior under the action of an in-plane and of an out-
of-plane magnetic fields. Finally, non-trivial topological superconducting
states become stable as a function of the charge density, as well as of the
magnitude and of the orientation of the magnetic field. In addition to the
chiral, time-reversal breaking, topological superconducting phase, favored by
the linear Rashba couplings and by the on-site attractive potentials in the
presence of an out- of-plane magnetic field, we find that a time-reversal
invariant topological helical superconducting phase is promoted by not-linear
spin-orbit couplings and by the inter-site attractive interactions in the
absence of magnetic field.",2107.01100v2
2015-08-05,Atomistic details of oxide surfaces and surface oxidation: the example of copper and its oxides,"The oxidation and corrosion of metals are fundamental problems in materials
science and technology that have been studied using a large variety of
experimental and computational techniques. Here we review some of the recent
studies that have led to significant advances in our atomic-level understanding
of copper oxide, one of the most studied and best understood metal oxides. We
show that a good atomistic understanding of the physical characteristics of
cuprous (Cu$_2$O) and cupric (CuO) oxide and of some key processes of their
formation has been obtained. Indeed, the growth of the oxide has been shown to
be epitaxial with the surface and to proceed, in most cases, through the
formation of oxide nano-islands which, with continuous oxygen exposure, grow
and eventually coalesce. We also show how electronic structure calculations
have become increasingly useful in helping to characterise the structures and
energetics of various Cu oxide surfaces. However a number of challenges remain.
For example, it is not clear under which conditions the oxidation of copper in
air at room temperature (known as native oxidation) leads to the formation of a
cuprous oxide film only, or also of a cupric overlayer. Moreover, the atomistic
details of the nucleation of the oxide islands are still unknown. We close our
review with a brief perspective on future work and discuss how recent advances
in experimental techniques, bringing greater temporal and spatial resolution,
along with improvements in the accuracy, realism and timescales achievable with
computational approaches make it possible for these questions to be answered in
the near future.",1508.01005v1
2007-10-18,"Growth, Structure and Properties of BiFeO3-BiCrO3 Films obtained by Dual Cross Beam PLD","The properties of epitaxial Bi2FeCrO6 thin films, recently synthesized by
pulsed laser deposition, have partially confirmed the theoretical predictions
(i.e. a magnetic moment of 2 muB per formula unit and a polarization of ~80
microC/cm2 at 0K). The existence of magnetic ordering at room temperature for
this material is an unexpected but very promising result that needs to be
further investigated. Since magnetism is assumed to arise from the exchange
interaction between the Fe and Cr cations, the magnetic behaviour is strongly
dependent on both their ordering and the distance between them. We present here
the successful synthesis of epitaxial Bi2FexCryO6 (BFCO x/y) films grown on
SrTiO3 substrates using dual crossed beam pulsed laser deposition. The crystal
structure of the films has different types of (111)-oriented superstructures
depending on the deposition conditions. The multiferroic character of BFCO
(x/y) films is proven by the presence of both ferroelectric and magnetic
hysteresis at room temperature. The oxidation state of Fe and Cr ions in the
films is shown to be 3+ only and the difference in macroscopic magnetization
with Fe/Cr ratio composition could only be due to ordering of the Cr3+ and Fe3+
cations therefore to the modification of the exchange interaction between them.",0710.3424v1
2007-11-08,Spin Frustration and Magnetic Exchange in Cobalt Aluminum Oxide Spinels,"We report on x-ray diffraction, magnetic susceptibility, electron- spin
resonance and heat- capacity studies of Co[Al_1-xCo_x]_2O_4 for Co
concentrations 0<x<1. In this spinel system only the A-site Co^2+ cation is
magnetic, while the non-magnetic B-site Al^3+ is substituted by the low-spin
non-magnetic Co^3+, and it is possible to investigate the complete phase
diagram from Co^2+Al^3+_2O_4 to Co^2+Co^3+_2O_4. All samples reveal large
negative Curie-Weiss temperatures Theta_CW of the order of -110 K independent
of concentration, which is attributed to a high multiplicity of the
superexchange interactions between the A-site Co^2+ cations. A pure
antiferromagnetic state is found for x = 1.0 and 0.9 with Neel temperatures T_N
= 29.5 K and 21.2 K, respectively, as evidenced by lambda-like anomalies in the
specific heat. Compositions with 0.3<x<0.75 show smeared out strongly reduced
magnetic ordering temperatures. At low temperatures, a T^2.5 dependence of the
specific heat is indicative of a spin-liquid state. For x < 0.2 a T^2
dependence of the specific heat and a spin-glass like behavior of the
susceptibility below T_f = 4.7 K are observed. The high value of the
frustration parameter f = |Theta_CW|/T_f > 10 indicates the presence of strong
spin frustration at least for x < 0.6. The frustration mechanism is attributed
to competing nearest neighbor and next-nearest neighbor superexchange
interactions between the A-site Co^2+ ions.",0711.1301v1
2007-11-26,Quantum fluctuations in high field magnetization of 2D square lattice J1-J2 antiferromagnets,"The J1-J2 square lattice Heisenberg model with spin S=1/2 has three phases
with long-range magnetic order and two unconventionally ordered phases
depending on the ratio of exchange constants. It describes a number of recently
found layered vanadium oxide compounds. A simple means of investigating the
ground state is the study of the magnetization curve and high-field
susceptibility. We discuss these quantities by using the spin-wave theory and
the exact diagonalization in the whole J1-J2 plane. We compare both results and
find good overall agreement in the sectors of the phase diagram with magnetic
order. Close to the disordered regions the magnetization curve shows strong
deviations from the classical linear behaviour caused by large quantum
fluctuations and spin-wave approximation breaks down. On the FM side (J1<0)
where one approaches the quantum gapless spin nematic ground state this region
is surprisingly large. We find that inclusion of second order spin-wave
corrections does not lead to fundamental improvement. Quantum corrections to
the tilting angle of the ordered moments are also calculated. They may have
both signs, contrary to the always negative first order quantum corrections to
the magnetization. Finally we investigate the effect of the interlayer coupling
and find that the quasi-2D picture remains valid up to |J_\perp/J1| ~ 0.3.",0711.4054v1
2009-03-09,Interacting Superparamagnetism in La0.7Sr0.3MnO3 Nanoparticles,"The magnetic order of La0.7Sr0.3MnO3 nanoparticles (NPs) fabricated in a SPEX
D8000 mill was systematically studied. The La0.7Sr0.3MnO3 nanocrystals grow
from the milled constituent oxides during the milling processes. The
magnetization data obtained by using a SQUID magnetometer show the NPs as a
superparamagnet in terms of anhysteretic curves near room temperature.
Unoverlaping of the scaled M(H-ext, T)/M-s vs. H-ext, T plots and the dc
susceptibility obeying the Curie-Weiss behavior rather than the Curie law at
high temperatures provide evidence that the NPs are interacting
superparamagnetic ensembles. A mean-field correction to the Langevin function L
([H-ext + alpha M]/k(B)T) worked well for the magnetic ordering of the NPs. By
means of the Langevin fitting, the diameter of the NP was estimated to be lower
than 15 nm, depending oil the milling time. The saturation magnetization of NPs
varied from 48.5 em/g to 19 emu/g, with the higher value corresponding to a
larger particle size. A core-shell structure of the NP was adopted, with the NP
having the core-shell magnetically-effective mass density. This is applicable
to the variation of the saturation magnetization with particle size.",0903.1565v1
2009-04-28,Exotic magnetism in the alkali sesquoxides Rb4O6 and Cs4O6,"Among the various alkali oxides the sesquioxides Rb4O6 and Cs4O6 are of
special interest. Electronic structure calculations using the local
spin-density approximation predicted that Rb4O6 should be a half-metallic
ferromagnet, which was later contradicted when an experimental investigation of
the temperature dependent magnetization of Rb4O6 showed a low-temperature
magnetic transition and differences between zero-field-cooled (ZFC) and
field-cooled (FC) measurements. Such behavior is known from spin glasses and
frustrated systems. Rb4O6 and Cs4O6 comprise two different types of dioxygen
anions, the hyperoxide and the peroxide anions. The nonmagnetic peroxide anions
do not contain unpaired electrons while the hyperoxide anions contain unpaired
electrons in antibonding pi*-orbitals. High electron localization (narrow
bands) suggests that electronic correlations are of major importance in these
open shell p-electron systems. Correlations and charge ordering due to the
mixed valency render p-electron-based anionogenic magnetic order possible in
the sesquioxides. In this work we present an experimental comparison of Rb4O6
and the related Cs4O6. The crystal structures are verified using powder x-ray
diffraction. The mixed valency of both compounds is confirmed using Raman
spectroscopy, and time-dependent magnetization experiments indicate that both
compounds show magnetic frustration, a feature only previously known from d-
and f-electron systems.",0904.4338v1
2010-01-26,Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation,"The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles
decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2 of
adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG)
pulse-echo sequence. This effect is commonly used to measure the concentrations
of a variety of small molecules. We perform extensive Monte Carlo simulations
of water diffusing around SPIO nanoparticle aggregates to determine the
relationship between T2 and details of the aggregate. We find that in the
motional averaging regime T2 scales as a power law with the number N of
nanoparticles in an aggregate. The specific scaling is dependent on the fractal
dimension d of the aggregates. We find T2 N^{-0.44} for aggregates with d=2.2,
a value typical of diffusion limited aggregation. We also find that in
two-nanoparticle systems, T2 is strongly dependent on the orientation of the
two nanoparticles relative to the external magnetic field, which implies that
it may be possible to sense the orientation of a two-nanoparticle aggregate. To
optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is
best to have aggregates with few nanoparticles, close together, measured with
long pulse-echo times.",1001.4768v2
2010-11-20,Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers,"Large area arrays of through-thickness nanoscale pores have been milled into
superconducting Nb thin films via a process utilizing anodized aluminum oxide
thin film templates. These pores act as artificial flux pinning centers,
increasing the superconducting critical current, Jc, of the Nb films. By
optimizing the process conditions including anodization time, pore size and
milling time, Jc values approaching and in some cases matching the
Ginzburg-Landau depairing current of 30 MA/cm^2 at 5 K have been achieved - a
Jc enhancement over as-deposited films of more than 50 times. In the field
dependence of Jc, a matching field corresponding to the areal pore density has
also been clearly observed. The effect of back-filling the pores with magnetic
material has then been investigated. While back-filling with Co has been
successfully achieved, the effect of the magnetic material on Jc has been found
to be largely detrimental compared to voids, although a distinct influence of
the magnetic material in producing a hysteretic Jc versus applied field
behavior has been observed. This behavior has been tested for compatibility
with currently proposed models of magnetic pinning and found to be most closely
explained by a model describing the magnetic attraction between the flux
vortices and the magnetic inclusions.",1011.4599v2
2011-06-22,Spin correlations in the extended kagome system YBaCo3FeO7,"The transition metal based oxide YBaCo3FeO7 is structurally related to the
mineral Swedenborgite SbNaBe4O7, a polar non-centrosymmetric crystal system.
The magnetic Co3Fe sublattice consists of a tetrahedral network containing
kagome-like layers with trigonal interlayer sites. This geometry causes
frustration effects for magnetic ordering, which were investigated by
magnetization measurements, M\""ossbauer spectroscopy, polarized neutron
diffraction, and neutron spectroscopy. Magnetization measurement and neutron
diffraction do not show long range ordering even at low temperature (1 K)
although a strong antiferromagnetic coupling (~2000 K) is deduced from the
magnetic susceptibility. Below 590 K, we observe two features, a spontaneous
weak anisotropic magnetization hysteresis along the polar crystallographic axis
and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the
interlayer sites remain idle. Below ~50 K, the onset of a hyperfine field shows
the development of moments static on the M\""ossbauer time scale also for the Fe
interlayer sites. Simultaneously, an increase of spin correlations is found by
polarized neutron diffraction. The relaxation part of the dynamic response has
been further investigated by high-resolution neutron spectroscopy, which
reveals that the spin correlations start to freeze in below ~50 K. Monte Carlo
simulations show that the neutron scattering results at lower temperatures are
compatible with a recent proposal that the particular geometric frustration in
the Swedenborgite structure promotes quasi one dimensional partial order.",1106.4465v1
2014-02-27,Enhanced Stability of Skyrmions in Two-Dimensional Chiral Magnets with Rashba Spin-Orbit Coupling,"Recent developments have led to an explosion of activity on skyrmions in
three-dimensional (3D) chiral magnets. Experiments have directly probed these
topological spin textures, revealed their nontrivial properties, and led to
suggestions for novel applications. However, in 3D the skyrmion crystal phase
is observed only in a narrow region of the temperature-field phase diagram. We
show here, using a general analysis based on symmetry, that skyrmions are much
more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit
coupling. This enhanced stability arises from the competition between field and
easy-plane magnetic anisotropy and results in a nontrivial structure in the
topological charge density in the core of the skyrmions. We further show that,
in a variety of microscopic models for magnetic exchange, the required
easy-plane anisotropy naturally arises from the same spin-orbit coupling that
is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results
are of particular interest for 2D materials like thin films, surfaces, and
oxide interfaces, where broken surface-inversion symmetry and Rashba spin-orbit
coupling naturally lead to chiral exchange and easy-plane compass anisotropy.
Our theory gives a clear direction for experimental studies of 2D magnetic
materials to stabilize skyrmions over a large range of magnetic fields down to
T=0.",1402.7082v2
2014-09-19,X-ray spectroscopic study of BaFeO$_{3}$ thin films; an Fe$ ^{4+}$ ferromagnetic insulator,"We investigated the electronic and magnetic properties of fully oxidized
BaFeO3 thin films, which show ferromagnetic-insulating properties with cubic
crystal structure, by hard x-ray photoemission spectroscopy (HAXPES), x-ray
absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism
(XMCD). We analyzed the results with configuration-interaction (CI)
cluster-model calculations for Fe4+, which showed good agreement with the
experimental results. We also studied SrFeO3 thin films, which have an Fe4+ ion
helical magnetism in cubic crystal structure, but are metallic at all
temperatures. We found that BaFeO3 thin films are insulating with large
magnetization (2.1muB/formula unit) under ~ 1 T, using valence-band HAXPES and
Fe 2p XMCD, which is consistent with the previously reported resistivity and
magnetization measurements. Although Fe 2p core-level HAXPES and Fe 2p XAS
spectra of BaFeO3 and SrFeO3 thin films are quite similar, we compared the
insulating BaFeO3 to metallic SrFeO3 thin films with valence-band HAXPES. The
CI cluster-model analysis indicates that the ground state of BaFeO3 is
dominated by d5L (L: ligand hole) configuration due to the negative charge
transfer energy, and that the band gap has significant O 2p character. We
revealed that the differences of the electronic and magnetic properties between
BaFeO3 and SrFeO3 arise from the differences in their lattice constants,
through affecting the strength of hybridization and bandwidth.",1409.5538v1
2016-07-04,First-principles investigations into the thermodynamics of cation disorder and it's impact on electronic structure and magnetic properties of spinel $Co\left(Cr_{1-x}Mn_{x} \right)_{2}O_{4}$,"Recent experiments on Mn doped multiferroic $CoCr_{2}O_{4}$ indicate that a
possible distribution of Mn atoms among tetrahedrally and octahedrally
coordinated sites in the spinel lattice give rise to different variations in
the structural parameters and saturation magnetisations in different
concentration regimes of Mn atoms substituting the Cr. A composition dependent
magnetic compensation behaviour points to the role conversions of the magnetic
constituents. In this work, we have investigated the thermodynamics of cation
disorder in $Co\left(Cr_{1-x}Mn_{x}\right)_{2}O_{4}$ system and it's
consequences on the structural, electronic and magnetic properties, using
results from first-principles electronic structure calculations. We have
computed the variations in the cation-disorder as a function of Mn
concentration and the temperature and found that at the annealing temperature
of the experiment many of the systems exhibit cation disorder. Our results
support the interpretations of the experimental results regarding the
qualitative variations in the sub-lattice occupancies and the associated
magnetisation behaviour, with composition. We have analysed the variations in
structural, magnetic and electronic properties of this system with variations
in the compositions and the degree of cation disorder from the variations in
their electronic structures and by using the ideas from crystal field theory.
Our study provides a complete microscopic picture of the effects that are
responsible for composition dependent behavioural differences of the properties
of this system. This work lays down a general framework, based upon results
from first-principles calculations, to understand and analyse the
substitutional magnetic spinel oxides $A\left(B_{1-x}C_{x} \right)_{2}O_{4}$ in
presence of cation disorder.",1607.00742v1
2016-07-29,"A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers","The area of research to discover new Li containing materials and to
understand their physical properties has been of constant interest due to
applications potential for rechargeable batteries. Here, we present the results
of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to
be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal
magnetization (M) data support ferrimagnetism, more detailed magnetic studies
establish that this ferrimagnetic phase exhibits some features similar to
spin-glasses. In addition, we find another broad magnetic anomaly around 40-55
K in magnetic susceptibility, attributable to cluster spin-glass phenomenon.
Gradual dominance of cluster spin-glass dynamics with a decrease of temperature
(T) and the apparent spread in freezing temperature suggest that the
ferrimagnetism of this compound is a chaotic one. The absence of a unique
freezing temperature for a crystalline material is interesting. In addition,
pyroelectric current data reveals a feature in the range 40-50 K, attributable
to thermally stimulated depolarization current. We hope this finding motivates
future work to explore whether there is any intriguing correlation of such a
feature with spin-glass dynamics. We attribute these magnetic and electric
dipole anomalies to the crystallographic disorder intrinsic to this compound.",1607.08689v1
2016-10-27,Coulomb spin liquid in anion-disordered pyrochlore Tb$_2$Hf$_2$O$_7$,"The charge ordered structure of ions and vacancies characterizing rare-earth
pyrochlore oxides serves as a model for the study of geometrically frustrated
magnetism. The organization of magnetic ions into networks of corner-sharing
tetrahedra gives rise to highly correlated magnetic phases with strong
fluctuations, including spin liquids and spin ices. It is an open question how
these ground states governed by local rules are affected by disorder. In the
pyrochlore Tb$_2$Hf$_2$O$_7$, we demonstrate that the vicinity of the
disordering transition towards a defective fluorite structure translates into a
tunable density of anion Frenkel disorder while cations remain ordered.
Quenched random crystal fields and disordered exchange interactions can
therefore be introduced into otherwise perfect pyrochlore lattices of magnetic
ions. We show that disorder can play a crucial role in preventing long-range
magnetic order at low temperatures, and instead induces a strongly-fluctuating
Coulomb spin liquid with defect-induced frozen magnetic degrees of freedom.",1610.08714v3
2018-04-06,Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0.65Zn0.35Fe2O4 (NZFO) Thin Films,"Varying the substrate temperature changes structural and magnetic properties
of spinel ferrite NZFO thin films. XRD of films grown at different temperature
display only 004 reflections, without any secondary peaks, showing growth
orientation along the c axis. We find an increase in crystalline quality of
these thin films with the rise of substrate temperature. The surface topography
of the thin films grown on various growth temperatures conditions reveal that
these films are smooth with low roughness, however the thin films grown at 800
C exhibit lowest average and rms roughness among all thin films. We find iron
and nickel to be more oxidized i,e greater Fe and Ni content in films grown and
annealed at 700 C and 800 C, compared to those grown at lower temperatures. The
magnetic moment is observed to increase with an increase of substrate
temperature and all thin films possess high saturation magnetization and low
coercive field at room temperature. Films grown at 800 C exhibit a
ferrimagnetic paramagnetic phase transition well above room temperature. The
observed large magnetizations with soft magnetic behavior in NZFO thin films
above room temperature suggest potential application in memory, spintronics,
and multifunctional devices.",1804.02458v2
2008-07-30,Coexistence of static magnetism and superconductivity in SmFeAsO1-xFx as revealed by muon spin rotation,"The recent observation of superconductivity with critical temperatures up to
55 K in the FeAs based pnictide compounds marks the first discovery of a non
copper-oxide based layered high-Tc superconductor (HTSC) [1-3]. It has raised
the suspicion that these new materials share a similar pairing mechanism to the
cuprates, since both exhibit superconductivity following charge doping of a
magnetic parent material. Here we present a muon spin rotation study on
SmFeAsO1-xFx (x=0-0.30), which shows that static magnetism persists well into
the superconducting regime. The analogy with the cuprates is quite surprising
since the parent compounds appear to have different magnetic ground states:
itinerant spin density wave for the pnictides contrasted with the Mott-Hubbard
insulator in the cuprates. Our findings suggest that proximity to magnetic
order and associated soft magnetic fluctuations, rather than the strong
electronic correlations in the vicinity of a Mott-Hubbard-metal-to-insulator
transition, may be the key ingredients of HTSC.",0807.4876v2
2012-01-03,Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals,"The search for oxide-based room-temperature ferromagnetism has been one of
the holy grails in condensed matter physics. Room-temperature ferromagnetism
observed in Nb-doped SrTiO3 single crystals is reported in this Rapid
Communication. The ferromagnetism can be eliminated by air annealing (making
the samples predominantly diamagnetic) and can be recovered by subsequent
vacuum annealing. The temperature dependence of magnetic moment resembles the
temperature dependence of carrier density, indicating that the magnetism is
closely related to the free carriers. Our results suggest that the
ferromagnetism is induced by oxygen vacancies. In addition, hysteretic
magnetoresistance was observed for magnetic field parallel to current,
indicating that the magnetic moments are in the plane of the samples. The x-ray
photoemission spectroscopy, the static time-of-flight and the dynamic secondary
ion mass spectroscopy and proton induced x-ray emission measurements were
performed to examine magnetic impurities, showing that the observed
ferromagnetism is unlikely due to any magnetic contaminant.",1201.0579v4
2016-05-23,Beyond the Interface Limit: Structural and Magnetic Depth Profiles of Voltage-Controlled Magneto-Ionic Heterostructures,"Electric-field control of magnetism provides a promising route towards
ultralow power information storage and sensor technologies. The effects of
magneto-ionic motion have so far been prominently featured in the direct
modification of interface chemical and physical characteristics. Here we
demonstrate magnetoelectric coupling moderated by voltage-driven oxygen
migration beyond the interface limit in relatively thick AlOx/GdOx/Co (15 nm)
films. Oxygen migration and its ramifications on the Co magnetization are
quantitatively mapped with polarized neutron reflectometry under thermal and
electro-thermal conditionings. The depth-resolved profiles uniquely identify
interfacial and bulk behaviors and a semi-reversible suppression and recovery
of the magnetization. Magnetometry measurements show that the conditioning
changes the microstructure so as to disrupt long-range ferromagnetic ordering,
resulting in an additional magnetically soft phase. X-ray spectroscopy confirms
electric field induced changes in the Co oxidation state but not in the Gd,
suggesting that the GdOx transmits oxygen but does not source or sink it. These
results together provide crucial insight into controlling magnetic
heterostructures via magneto-ionic motion, not only at the interface, but also
throughout the bulk of the films.",1605.07209v1
2017-10-17,Nature of Lattice Distortions in Cubic Double-Perovskite Ba$_2$NaOsO$_6$,"We present detailed calculations of the electric field gradient (EFG) using a
point charge approximation in Ba$_2$NaOsO$_6$, a Mott insulator with strong
spin-orbit interaction. Recent $^{23}$Na nuclear magnetic resonance (NMR)
measurements found that the onset of local point symmetry breaking, likely
caused by the formation of quadrupolar order, precedes the formation of long
range magnetic order in this compound. An extension of the static $^{23}$Na NMR
measurements as a function of the orientation of a 15 T applied magnetic field
at 8 K in the magnetically ordered phase is reported. Broken local cubic
symmetry induces a non-spherical electronic charge distribution around the Na
site and thus finite EFG, affecting the NMR spectral shape. We combine the
spectral analysis as a function of the orientation of the magnetic field with
calculations of the EFG to determine the exact microscopic nature of the
lattice distortions present in low temperature phases of this material. We
establish that orthorhombic distortions, constrained along the cubic axes of
the perovskite reference unit cell, of oxygen octahedra surrounding Na nuclei
are present in the magnetic phase.
  Other common types of distortions often observed in oxide structures are
considered as well.",1710.06052v1
2019-09-20,Field-free spin-orbit torque switching through domain wall motion,"Deterministic current-induced spin-orbit torque (SOT) switching of
magnetization in a heavy transition metal/ferromagnetic metal/oxide magnetic
heterostructure with the ferromagnetic layer being perpendicularly-magnetized
typically requires an externally-applied in-plane field to break the switching
symmetry. We show that by inserting an in-plane magnetized ferromagnetic layer
CoFeB underneath the conventional W/CoFeB/MgO SOT heterostructure,
deterministic SOT switching of the perpendicularly-magnetized top CoFeB layer
can be realized without the need of in-plane bias field. Kerr imaging study
further unveils that the observed switching is mainly dominated by domain
nucleation and domain wall motion, which might limit the potentiality of using
this type of multilayer stack design for nanoscale SOT-MRAM application.
Comparison of the experimental switching behavior with micromagnetic
simulations reveals that the deterministic switching in our devices cannot be
explained by the stray field contribution of the in-plane magnetized layer, and
the roughness-caused N\'eel coupling effect might play a more important role in
achieving the observed field-free deterministic switching.",1909.09604v1
2019-10-05,"Enhancement of magnetodielectric coupling in 6H-perovskites Ba3RRu2O9 for heavier rare earth cations (R=Ho,Tb)","The role of rare-earth (R) ions on the magnetodielectric (MD) coupling is
always intriguing and markedly different for different systems. Although many
reports are available concerning this aspect in frustrated 3d-transition metal
oxides, no such reports exist on higher d (4d/5d)-orbital based systems due to
the rare availability of highly insulating 4d/5d-systems. Here, we
systematically investigated the magnetic, dielectric, ferroelectric and
magnetodielectric behavior of the 6H-perovskites Ba3RRu2O9 for different
R-ions, namely, R= Sm, Tb and Ho, which magnetically order at 12, 9.5 and 10.2
K respectively. For R=Tb and Ho, the temperature and magnetic-field dependent
complex dielectric constant traces the magnetic features, which manifests MD
coupling in this system. A weak magnetic-field (H) induced transition is
observed for ~30 kOe, which is clearly captured in H-dependent dielectric
measurements. No MD coupling is observed for Ba3SmRu2O9. The MD coupling is
enhanced by a factor of 3 and 20 times for R=Tb and Ho, respectively, when
compared to that of the Nd-counterpart. These results evidence the gradual
enhancement of MD coupling with the introduction of heavier R-ions in this
series, which is attributed to their larger moment values. A weak improper
ferroelectricity is documented for Ho-member, which is absent for Nd. Our
investigation establishes dominating 4d(Ru)-4f(R) magnetic correlation in this
series for the heavier R-members.",1910.02204v1
2020-01-17,Single-layer graphene on epitaxial FeRh thin films,"Graphene is a 2D material that displays excellent electronic transport
properties with prospective applications in many fields. Inducing and
controlling magnetism in the graphene layer, for instance by proximity of
magnetic materials, may enable its utilization in spintronic devices. This
paper presents fabrication and detailed characterization of single-layer
graphene formed on the surface of epitaxial FeRh thin films. The magnetic state
of the FeRh surface can be controlled by temperature, magnetic field or strain
due to interconnected order parameters. Characterization of graphene layers by
X-ray Photoemission and X-ray Absorption Spectroscopy, Low-Energy Ion
Scattering, Scanning Tunneling Microscopy, and Low-Energy Electron Microscopy
shows that graphene is single-layer, polycrystalline and covers more than 97%
of the substrate. Graphene displays several preferential orientations on the
FeRh(001) surface with unit vectors of graphene rotated by 30{\deg}, 15{\deg},
11{\deg}, and 19{\deg} with respect to FeRh substrate unit vectors. In
addition, the graphene layer is capable to protect the films from oxidation
when exposed to air for several months. Therefore, it can be also used as a
protective layer during fabrication of magnetic elements or as an atomically
thin spacer, which enables incorporation of switchable magnetic layers within
stacks of 2D materials in advanced devices.",2001.06559v1
2020-04-23,Correlation-driven eightfold magnetic anisotropy in a two-dimensional oxide monolayer,"Engineering magnetic anisotropy in two-dimensional systems has enormous
scientific and technological implications. The uniaxial anisotropy universally
exhibited by two-dimensional magnets has only two stable spin directions,
demanding 180 degrees spin switching between states. We demonstrate a novel
eightfold anisotropy in magnetic SrRuO3 monolayers by inducing a spin
reorientation in (SrRuO3)1/(SrTiO3)N superlattices, in which the magnetic easy
axis of Ru spins is transformed from uniaxial <001> direction (N = 1 and 2) to
eightfold <111> directions (N = 3, 4 and 5). This eightfold anisotropy enables
71 and 109 degrees spin switching in SrRuO3 monolayers, analogous to 71 and 109
degrees polarization switching in ferroelectric BiFeO3. First-principle
calculations reveal that increasing the SrTiO3 layer thickness induces an
emergent correlation-driven orbital ordering, tuning spin-orbit interactions
and reorienting the SrRuO3 monolayer easy axis. Our work demonstrates that
correlation effects can be exploited to substantially change spin-orbit
interactions, stabilizing unprecedented properties in two-dimensional magnets
and opening rich opportunities for low-power, multi-state device applications.",2004.10939v1
2020-12-21,Electronic correlations and magnetic interactions in infinite-layer NdNiO$_2$,"The large antiferromagnetic exchange coupling in the parent high-$T_{\rm c}$
cuprate superconductors is believed to play a crucial role in pairing the
superconducting carriers. The recent observation of superconductivity in
hole-doped infinite-layer (IL-) NdNiO$_2$ brings to the fore the relevance of
magnetic coupling in high-$T_{\rm c}$ superconductors, particularly because no
magnetic ordering is observed in the undoped IL-NdNiO$_2$ unlike in parent
copper oxides. Here, we investigate the electronic structure and the nature of
magnetic exchange in IL-NdNiO$_2$ using state-of-the-art many-body quantum
chemistry methods. From a systematic comparison of the electronic and magnetic
properties with isostructural cuprate IL-CaCuO$_2$, we find that the on-site
dynamical correlations are significantly stronger in IL-NdNiO$_2$ compared to
the cuprate analog. These dynamical correlations play a critical role in the
magnetic exchange resulting in an unexpectedly large antiferromagnetic nearest
neighbor isotropic $J$ of 77 meV between the Ni$^{1+}$ ions within the
$ab$-plane. While we find many similarities in the electronic structure between
the nickelate and the cuprate, the role of electronic correlations is
profoundly different in the two. We further discuss the implications of our
findings in understanding the origin of superconductivity in nickelates.",2012.11179v1
2018-03-05,Dipolar-coupled moment correlations in clusters of magnetic nanoparticles,"Here, we investigate the nature of the moment coupling between 10-nm
DMSA-coated magnetic nanoparticles, in both colloidal dispersion and in powder
form. The individual iron oxide cores were composed of > 95% maghemite and
agglomerated to clusters. At room temperature the ensemble behaved as a
superparamagnet according to M\""ossbauer and magnetization measurements,
however, with clear signs of dipolar interactions at low temperatures. Analysis
of temperature-dependent AC susceptibility data in the superparamagnetic regime
indicates a tendency for dipolar coupled anticorrelations of the core moments
within the clusters. To resolve the directional correlations between the
particle moments we performed polarized small-angle neutron scattering and
determined the magnetic spin-flip cross-section of the powder in low magnetic
field at 300 K. We extract the underlying pair distance distribution function
of the magnetization vector field by an indirect Fourier transform of the
cross-section, and which suggests positive as well as negative correlations
between nearest neighbor moments, with anticorrelations clearly dominating for
next-nearest moments. These tendencies are confirmed by Monte Carlo simulations
of such core-clusters.",1803.01747v2
2018-07-03,Electronic structure depiction of magnetic origin in BaTiO$_{3-δ}$ thin film: A combined experimental and first-principles based investigation,"With the motive of unraveling the origin of native vacancy induced
magnetization in ferroelectric perovskite oxide systems, here we explore the
consequences of electronic structure modification in magnetic ordering of
oxygen deficient epitaxial BaTiO$_{3-\delta}$ thin films. Our adapted
methodology employs state-of-the-art experimental approaches viz.
photo-emission, photo-absorption spectroscopies, magnetometric measurements
duly combined with first principles based theoretical methods within the frame
work of density functional theory (DFT and DFT+\textit{U}) calculations. Oxygen
vacancy (O$ _{V} $) is observed leading partial population of Ti 3\textit{d}
(t$_{2g}$), which induces defect state in electronic structure near the Fermi
level and reduces the band gap. The oxygen deficient BaTiO$_{2.75} $ film
reveals Mott-Hubbard insulator characteristic, in contrast to the band gap
insulating nature of the stoichiometric BaTiO$ _{3}$. The observed magnetic
ordering is attributed to the asymmetric distribution of spin polarized charge
density in the vicinity of O$ _{V} $ site which originates unequal magnetic
moment values at first and second nearest neighboring Ti sites, respectively.
Hereby, we present an exclusive method for maneuvering the band gap and on-site
electron correlation energy with consequences on magnetic properties of
BaTiO$_{3-\delta}$ system, which can open a gateway for designing novel single
phase multiferroic system.",1807.01214v2
2019-02-12,High Quality Factor High-Temperature Superconducting Microwave Cavity Development for the Dark Matter Axion Search in a Strong Magnetic Field,"We demonstrate a superconducting (SC) microwave (mw) cavity that can
accelerate the dark matter search by maintaining superconductivity in a high DC
magnetic field. We used high-temperature superconductor (HTSC) yttrium barium
copper oxide (YBCO) with a phase transition temperature of 90K to prevent SC
failure by the magnetic field. Since the direct deposition of HTSC film on the
metallic mw cavity is very difficult, we used the commercial HTSC tapes which
are flexible metallic tapes coated with HTSC thin films. We fabricated
resonating cavity ($f_{TM010}$ ~ 6.89 GHz) with a third of the inner wall
covered by YBCO tapes and measured the quality factor (Q factor) at 4K
temperature, varying the DC magnetic field from 0 to 8 tesla. There was no
significant quality (Q) factor drop and the superconductivity was well
maintained even in 8 tesla magnetic field. This implies the possibility of good
performance of HTSC mw resonant cavity under a strong magnetic field for axion
detection.",1902.04551v3
2019-11-08,Effect of strain on magnetic and orbital ordering of LaSrCrO$_3$/LaSrMnO$_3$ heterostructures,"We investigate the effect of strain and film thickness on the orbital and
magnetic properties of LaSrCrO$_3$ (LSCO)/LaSrMnO$_3$ (LSMO) heterostructures
using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles
density functional theory, high-resolution electron microscopy and X-ray
diffraction. We observe an anti-parallel ordering of the magnetic moments
between the ferromagnetic LSMO layers and the LSCO spacers leading to a
strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures
for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a
net ferromagnetic state is maintained, however, the average magnetic moment per
Mn is found to be dependent on the magnitude of the substrate-induced strain.
The differences in the magnetic responses are related to preferential
occupation of the Mn $x^2-y^2$ (in-plane) d-orbitals for tensile strain and
$3z^2-r^2$ (out-of-plane) orbitals under compressive strain leading to
competing ferromagnetic and anti-ferromagnetic exchange interactions within the
LSMO layers. These results underscore the relative contributions of orbital,
structural and spin degree of freedom and their tunability in atomically-thin
crystalline complex oxide layers.",1911.03007v2
2020-11-13,Cell dynamics simulations of coupled charge and magnetic phase transformation in correlated oxides,"We present a comprehensive numerical study on the kinetics of phase
transition that is characterized by two non-conserved scalar order parameters
coupled by a special linear-quadratic interaction. This particular
Ginzburg-Landau theory has been proposed to describe the coupled charge- and
magnetic transition in nickelates and the collinear stripe phase in cuprates.
The inhomogeneous state of such systems at low temperatures consists of
magnetic domains separated by quasi-metallic domain-walls where the
charge-order is reduced. By performing large-scale cell dynamics simulations,
we find a two-stage phase-ordering process in which a short period of
independent evolution of the two order parameters is followed by a correlated
coarsening process. The long-time growth and coarsening of magnetic domains is
shown to follow the Allen-Cahn power law. We further show that the
nucleation-and-growth dynamics during phase transformation to the ordered
states is well described by the Kolmogorov-Johnson-Mehl-Avrami theory in two
dimensions. On the other hand, the presence of quasi-metallic magnetic domain
walls in the ordered states gives rise to a very different kinetics for phase
transition to the high temperature paramagnetic phase. In this new scenario,
the phase transformation is initiated by the decay of magnetic domain walls
into two insulator-metal boundaries, which subsequently move away from each
other. Implications of our findings to recent nano-imaging experiments on
nickelates are also discussed.",2011.07045v2
2021-02-22,Single Harmonic-based Narrowband Magnetic Particle Imaging,"Visualization of the in vivo spatial distribution of superparamagnetic iron
oxide nanoparticles (SPIONs) is crucial to biomedicine. Magnetic particle
imaging (MPI) is one of the most promising approaches for direct measurements
of the SPION distribution. In this paper, we systematically investigate a
single-harmonic-based narrowband MPI approach. Herein, only the 3rd harmonic at
15 kHz of the SPION signal induced in an excitation magnetic field of 5 kHz is
measured via a narrowband detection system for imaging during scanning a
field-free-point in a field of view. Experiments on spot and line phantoms are
performed to evaluate the spatial distribution by the assessment of the full
width at half maximum and modulation transfer function at different excitation
magnetic fields from 4 to 10 mT. Experimental results demonstrate that
reconstructed images have a spatial resolution of 1.6 and 1.5 mm for a gradient
field of 2.2 T/m and 4.4 T/m in x- and z-direction, respectively, at an
excitation magnetic field of 4 mT. In terms of line gap, two lines with a gap
of 0.5 mm are resolved. With increasing the excitation magnetic field to 10 mT,
the spatial resolution gets worse to 2.4 and 2.0 mm in x- and z-direction,
respectively. Moreover, the custom-built MPI scanner allows a limit of
detection of 53 microgram (Fe)/mL (500 ng Fe weight) using perimag SPIONs. In
addition, the excellent performance is demonstrated by imaging experiments on
an ""emg"" logo phantom. We believe that the proposed narrowband MPI approach is
a promising approach for SPION imaging.",2102.10954v1
2021-03-10,Finite transverse conductance and anisotropic magnetoconductance under an applied in-plane magnetic field in two-dimensional electron gases with strong spin-orbit coupling,"The current in response to a bias in certain two-dimensional electron gas
(2DEG), can have a nonzero transverse component under a finite magnetic field
applied in the plane where electrons are confined. This phenomenon known as
planar Hall effect is accompanied by dependencies of both the longitudinal and
the transverse components of the current on the angle $\phi$ between the bias
direction and the magnetic field. In 2DEG with spin orbit coupling (SOC) such
as oxide interfaces, this effect has been experimentally witnessed. Further, a
fourfold oscillation in longitudinal resistance as a function of $\phi$ has
also been observed. Motivated by these, we perform scattering theory
calculations on a 2DEG with SOC in presence of an in-plane magnetic field
connected to two dimensional leads on either sides to obtain longitudinal and
transverse conductances. We find that the longitudinal conductance is
$\pi$-periodic and the transverse conductance is $2\pi$-periodic in $\phi$. The
magnitude of oscillation in transverse conductance with $\phi$ is enhanced in
certain patches in $(\alpha,b)$-plane where $\alpha$ is the strength of SOC and
$b$ is Zeeman energy due to magnetic field. The oscillation in transverse
conductance with $\phi$ can be highly multi-fold for large values of $\alpha$
and $b$. The highly multi-fold oscillations of transverse conductance are due
to Fabry-P\'erot type interference between the modes in the central region as
backed by its length dependent features. Our study establishes that SOC in a
material is sufficient to observe planar Hall effect without the need for
anisotropic magnetic ordering or nontrivial topology of the bandstructure.",2103.05901v2
2021-04-05,Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A3ReO5Cl2 (A = Ba and Sr),"We report the synthesis, crystal structure, and magnetic properties of two
new quantum antiferromagnets A3ReO5Cl2 (A = Sr and Ba). The crystal structure
is isostructural with the mineral pinalite Pb3WO5Cl2, in which the Re6+ ion is
square-pyramidally coordinated by five oxide atoms, and forms an anisotropic
triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and
J' in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9)
and 9.2 (19.3) K, respectively, with J'/J = 0.47 (0.43) for A = Ba (Sr). For
each compound, heat capacity at low temperatures shows a large T-linear
component with no signature of long-range magnetic order above 2 K, which
suggests a gapless spin liquid state of one-dimensional character of the J
chains in spite of the significantly large J' couplings. This is a consequence
of one-dimensionalization by geometrical frustration in the ATL magnet; a
similar phenomenon has been observed in two compounds with slightly smaller
J'/J values: Cs2CuCl4 (J'/J = 0.3) and the related compound Ca3ReO5Cl2 (0.32).
Our findings demonstrate that 5d mixed-anion compounds provide a unique
opportunity to explore novel quantum magnetism.",2104.01838v1
2021-07-24,Anomalous Nernst thermopower and giant magnetostriction in microwave synthesized La0.5Sr0.5CoO3,"Ferromagnetic metallic oxides have potential applications in spincaloric
devices which utilize the spin property of charge carriers for interconversion
of heat and electricity through the spin Seebeck or the anomalous Nernst effect
or both. In this work, we synthesized polycrystalline La0.5S0.5CoO3 by
microwave irradiation method and studied its transverse thermoelectric voltage
(Nernst thermopower) and change in the linear dimension of the sample (Joule
magnetostriction) in response to external magnetic fields. In addition,
magnetization, temperature dependences of electrical resistivity, and
longitudinal Seebeck coefficient (Sxx) in absence of an external magnetic field
were also measured. The sample is ferromagnetic with a Curie temperature of TC
= 247 K and shows a metal-like resistivity above and below TC with a negative
sign of Sxx suggesting charge transport due to electrons. Magnetic field
dependence of the Nernst thermopower (Sxy) at a fixed temperature shows a rapid
increase at low fields and a tendency to saturate at high fields as like the
magnetization. Anomalous contribution to Sxy was extracted from total Sxy
measured and it exhibits a maximum value of ~ 0.21 microV/K at 180 K for H = 50
kOe, which is comparable to the value found in a single crystal for a lower Sr
content. The Joule magnetostriction is positive, i.e., the length of the sample
expands along the direction of the magnetic field and it does not saturate even
at 50 kOe. The magnetostriction increases with decreasing temperature below TC
and reaches a maximum value of 500 ppm at T = 40 K and below. Coexistence of
the anomalous Nernst thermopower and giant magnetostriction in a single
compound has potential applications for thermal energy harvesting and
low-temperature actuators, respectively.",2107.11535v1
2021-09-05,Cooperative control of perpendicular magnetic anisotropy via crystal structure and orientation in single-crystal flexible SrRuO3 membranes,"Flexible magnetic materials with robust and controllable perpendicular
magnetic anisotropy (PMA) are highly desirable for developing flexible
high-performance spintronic devices. However, it is still challenge to
fabricate PMA films through current techniques of direct deposition on
polymers. Here, we report a facile method for synthesizing single-crystal
freestanding SrRuO3 (SRO) membranes with controlled crystal structure and
orientation using water-soluble Ca3-xSrxAl2O6 sacrificial layers. Through
cooperative effect of crystal structure and orientation engineering, flexible
SrRuO3 membranes reveal highly tunable magnetic anisotropy from in-plane to
our-of-plane with a remarkable PMA energy of 7.34*106 erg/cm3. Based on the
first-principles calculations, it reveals that the underlying mechanism of PMA
modulation is intimately correlated with structure-controlled Ru 4d-orbital
occupation, as well as the spin-orbital matrix element differences, dependent
on the crystal orientation. In addition, there are no obvious changes of the
magnetism after 10,000 bending cycles, indicating an excellent magnetism
reliability in the prepared films. This work provides a feasible approach to
prepare the flexible oxide films with strong and controllable PMA.",2109.02061v1
2022-09-24,Magnetic nature of wolframite MgReO$_4$,"Rhenium oxides belonging to the family $A$ReO$_4$ where $A$ is a metal
cation, exhibit interesting electronic and magnetic properties. In this study
we have utilized the muon spin rotation/relaxation ($\mu^+$SR) technique to
study the magnetic properties of the MgReO$_4$ compound. To the best of our
knowledge, this is the first investigation reported on this interesting
material, that is stabilized in a wolframite crystal structure using a special
high-pressure synthesis technique. Bulk magnetic studies show the onset of an
antiferromagnetic (AF) long range order, or a possible singlet spin state at
$T_{\rm C1}\approx90$~K, with a subtle second high-temperature transition at
$T_{\rm C2}\approx280$~K. Both transitions are also confirmed by heat capacity
($C_p$) measurements. From our $\mu^+$SR measurements, it is clear that the
sample enters an AF order below $T_{\rm C1}=T_{\rm N}\approx85$~K. We find no
evidence of magnetic signal above $T_{\rm N}$, which indicates that $T_{\rm
C2}$ is likely linked to a structural transition. Further, via sensitive zero
field (ZF) $\mu^+$SR measurements we find evidence of a spin reorientation at
$T_{\rm Cant}\approx65$~K. This points towards a transition from a collinear AF
into a canted AF order at low temperature, which is proposed to be driven by
competing magnetic interactions.",2209.11966v1
2023-03-25,Type-II antiferromagnetic ordering in double perovskite oxide Sr$_2$NiWO$_6$,"Magnetic double perovskite compounds provide a fertile playground to explore
interesting electronic and magnetic properties. By complementary macroscopic
characterizations, neutron powder diffraction measurements and first-principles
calculations, we have performed comprehensive studies on the magnetic ordering
in the double perovskite compound Sr$_2$NiWO$_6$. It is found by neutron
diffraction to order magnetically in a collinear type-II antiferromagnetic
structure in a tetragonal lattice with $k$ = (0.5, 0, 0.5) below $T\rm_N$ = 56
K. In the ground state, the ordered moment of the spin-1 Ni$^{2+}$ ions is
determined to be 1.9(2) $\mu\rm_{B}$, indicating a significant quenching of the
orbital moment. The Ni$^{2+}$ moments in Sr$_2$NiWO$_6$ are revealed to cant
off the $c$ axis by 29.2$^{\circ}$, which is well supported by the
first-principles magnetic anisotropy energy calculations. Furthermore, the
in-plane and out-of-plane next-nearest-neighbor superexchange couplings
($J\rm_2$ and $J\rm_{2c}$) are found to play a dominant role in the spin
Hamiltonian of Sr$_2$NiWO$_6$, which accounts for the stabilization of the
type-II AFM structure as its magnetic ground state.",2303.14370v2
2023-07-26,Establishing Magnetic Coupling in Spin-crossover-2D Hybrid Nanostructures via Interfacial Charge-transfer Interaction,"Despite a clear demonstration of bistability in spin-crossover (SCO)
materials, the absence of long-range magnetic order and poor electrical
conductivity limit their prospect in spintronic and nanoelectronic
applications. Intending to create hybrid devices made of spin-crossover
(SCO)-2D architecture, here, we report an easily processable Fe-based SCO
nanostructures grown on 2D reduced graphene oxide (rGO). The heterostructure
shows enhanced cooperativity due to formation of interfacial charge transfer
induced inter-molecular interaction. The spin transition temperature is
controlled by tuning the coverage area of SCO nanostructured networks over the
2D surfaces, thus manipulating hysteresis (aka memory) of the heterostructure.
The enhanced magnetic coupling of the heterostructure leads to the spontaneous
magnetization states with a large coercive field of $\sim$ 3000 Oe.
Additionally, the low conductivity of the pristine SCO nanostructures is
addressed by encapsulating them on suitable 2D rGO template, enabling detection
of magnetic bistable spin states during high-spin/low-spin conductance change.
This adds spin functionality in conductance switching for realizing hybrid 2D
spintronic devices. Ab-inito calculations, on the experimentally proposed
nanostructures, corroborate the enhanced magnetic interaction in the proposed
architecture facilitated by interfacial charge transfer and provide insights on
the microscopic mechanism.",2307.14135v1
2023-11-22,Engineering magnetic domain wall energies in multiferroic BiFeO$_3$ via epitaxial strain,"Epitaxial strain has emerged as a powerful tool to tune magnetic and
ferroelectric properties in functional materials such as in multiferroic
perovskite oxides. Here, we use first-principles calculations to explore the
evolution of magnetic interactions in the antiferromagnetic multiferroic
BiFeO$_3$ (BFO), one of the most promising multiferroics for future technology.
The epitaxial strain in BFO(001) oriented film is varied between
$\varepsilon_{xx,yy}$ $\in$ $[-2\%, +2\%]$. We find that both strengths of the
exchange interaction and Dzyaloshinskii-Moriya interaction (DMI) decrease
linearly from compressive to tensile strain whereas the uniaxial
magnetocrystalline anisotropy follows a parabolic behavior which lifts the
energy degeneracy of the (111) easy plane of bulk BFO. From the trends of the
magnetic interactions we can explain the destruction of cycloidal order in
compressive strain as observed in experiments due to the increasing anisotropy
energy. For tensile strain, we predict that the ground state remains unchanged
as a function of strain. By using the domain wall (DW) energy, we envision the
region where isolated chiral magnetic texture might occur as function of strain
i.e. where the DW and the spin spiral energy are equal. This transition between
$-1.5\%$ and $-0.5\%$ of strain should allow topologically stable magnetic
states such as antiferromagnetic skyrmions and merons to occur. Hence, our work
should trigger experimental and theoretical investigations in this range of
strain.",2311.13215v1
1995-05-26,Specific Heat of YBa$_2$Cu$_3$O$_{7 - {\rm δ}}$ Single Crystals: Implications for the Vortex Structure,"The anisotropy of the magnetic field dependence of the specific heat of
YBa$_2$Cu$_3$O$_{7 - {\rm \delta}}$ can be used to identify different
low-energy excitations, which include phonons, spin-$ \frac{1}{2}$ particles,
and electronic contributions. With a magnetic field H applied perpendicular to
the copper oxide planes, we find that the specific heat includes a linear-T
term proportional to $\sqrt{H}$. The nonlinear field dependence of the density
of states at the Fermi level suggests that there are quasiparticle excitations
throughout the entire vortex, not just in the vortex core. The $\sqrt{H} T$
term agrees quantitatively with G. Volovik's prediction for a superconductor
with lines of nodes in the gap. A similar, but much smaller, effect is
predicted for fields parallel to the planes, and sensitive measurements of the
in-plane anisotropic magnetic field dependence of the specific heat could be
used to map out the nodes.",9505129v1
1996-03-15,Effect of non-magnetic impurities on the gap of a $d_{x^2-y^2}$ superconductor as seen by angle-resolved photoemission,"An analysis of angle-resolved photoemission (ARPES) experiments in the
superconducting state of the high \tc copper-oxides is presented. It is based
on a phenomenological weak-coupling BCS model which incorporates the
experimental normal state dispersion extracted from ARPES, and non-magnetic
impurity scattering in the presence of a $d_{x^2-y^2}$ order parameter (OP). It
is shown, that already in the pure case, the broadening by finite momentum
resolution of the analyzer leads to a finite region of apparent `gaplessness'
around the true node of the OP. Non-magnetic impurities further amplify this
effect by introducing additional spectral weight around zero frequency. At
sufficiently large impurity concentrations $n_i\approx 0.02-0.05$, this results
in an extended region of `gaplessness' up to $\delta\phi=\pm7$ ($\phi$ the
angle on the Fermi surface) around the true node for a large range of moderate
to strong impurity potential strengths. Different ways to identify the presence
of impurity scattering in the ARPES spectra are proposed.",9603117v1
1998-11-25,Quantum Oscillations and Overcritical Torque Interaction in Sr2RuO4,"Sr2RuO4 is the only known layered perovskite oxide superconductor without
copper; there is strong evidence for an unconventional (""p-wave"") pairing
mechanism, and it has recently been shown to possess a cylindrical,
""quasi-two-dimensional"" Fermi surface. Using Sr2RuO4 as a test case for the
detection of quantum oscillations with piezoresistive microcantilevers, the
piezolever torque magnetometry technique was successfully implemented on a
dilution refrigerator. It was possible to reproduce the quantum-oscillatory
magnetization data on all three Fermi surface sheets, in a crystal of microgram
mass. Moreover, an absolute estimate of the amplitude of the oscillation is
provided. We also investigated the phenomenon of torque interaction which
distorts the magnetization signal and introduces harmonics and sidebands to the
dHvA spectrum. As the torque interaction effect grows in strength,
overcriticality is shown to lead to discrete magnetization jumps and to a
near-asymptotically damped ""sproing"" effect.",9811364v1
2000-03-18,Inhomogeneity-Induced Superconductivity?,"A t-J-like model for inhomogeneous superconductivity of cuprate oxides is
presented, in which local anisotropic magnetic terms are essential. We show
that this model predicts pairing, consistent with experiments, and argue how
the macroscopic phase-coherent state gradually grows upon lowering of the
temperature. We show that appropriate inhomogeneities are essential in order to
have significant pair binding in the thermodynamic limit. Particularly, {\it
local} breaking of SU(2) spin symmetry is an efficient mechanism for inducing
pairing of two holes, as well as explaining the magnetic scattering properties.
We also discuss the connection of the resulting inhomogeneity-induced
superconductivity to recent experimental evidence for a linear relation between
magnetic incommensurability and the superconducting transition temperature, as
a function of doping.",0003321v1
2000-03-29,Static and dynamic spin correlations in the spin-glass phase of slightly-doped La_{2-x}Sr_xCuO_4,"Neutron scattering experiments reveal that a diagonal spin modulation, which
is a one-dimensional modulation rotated away by 45$^\circ$ from that in the
superconducting phase, occurs universally across the insulating spin-glass
phase in La$_{2-x}$Sr$_x$CuO$_4$ (0.02$\le x\le$0.055). This establishes an
intimate relation between the magnetism and the transport properties in the
high-temperature copper oxide superconductors. Furthermore, it is found that
the charge density per unit length estimated using a charge stripe model is
almost constant throughout the phase diagram, even when the modulation rotates
away by 45$^\circ$ at the superconducting boundary. However, at the lowest
values for $x$ the density changes approaching 1 hole/Cu as in
La$_{2-x}$Sr$_x$NiO$_4$. Magnetic excitation spectra suggest that magnetic
correlations change from incommensurate to commensurate at $\omega\sim$7 meV
and $T\sim$70 K, indicating a characteristic energy for the incommensurate
structure of 6-7 meV.",0003466v2
2000-09-07,Coulomb interaction in oxygen \textit{p}-shell in LDA+U method and its influence on calculated spectral and magnetic properties of transition metal oxides,"Coulomb interaction between electrons on p-orbitals of oxygen atom in
strongly correlated compounds is not negligible, since its value (U_p) has
comparable order of magnitude with the value of Coulomb interaction on
d-orbitals of transition metal atom (U_d). We investigate the effect of taking
into account Coulomb correlations in oxygen p-shell in addition to the
correlations in the transition metal d-shell in frame of the LDA+U method. Our
calculations for NiO, MnO and La2CuO4 show that this additional correction in
general improves the agreement with experimental data for the spectral (energy
gap values, relative position of the main peaks in X-ray photoemission
spectroscopy (XPS) and Bremsstrahlung isohromate spectroscopy (BIS)) and
magnetic properties (magnetic moment values and intersite exchange interaction
parameters values).",0009107v1
2002-02-15,Non-volatile magnetoresistive memory in phase separated La$_{0.325}$Pr$_{0.300}$Ca$_{0.375}$MnO$_3$,"We have measured magnetic and transport response on the polycrystalline
La$_{5/8-y}$Pr$_y$Ca$_{3/8}$MnO$_3$ ($y=0.30$, average grain size 2 microns)
compound. In the temperature range where ferromagnetic metallic and insulating
regions coexist we observed a persistent memory of low magnetic fields ($<$ 1
T) which is determined by the actual amount of the ferromagnetic phase. The
possibility to manipulate this fraction with relatively small external
perturbations is related to the phase separated nature of these manganese oxide
based compounds. The colossal magnetoresistance figures obtained (about 80%)
are determined by the fraction enlargement mechanism. Self-shielding of the
memory to external fields is found under certain described circumstances. We
show that this non-volatile memory has multilevel capability associated with
different applied low magnetic field values.",0202261v1
2002-07-16,High-T_{c} Superconductors with AF Order: Limitations on Spin-Fluctuation Pairing Mechanism,"The very intriguing antagonistic interplay of antiferromagnetism (AF) and
superconductivity (SC), recently discovered in high-temperature
superconductors, is studied in the framework of a microscopic theory. We
explain the surprisingly large increase of the magnetic Bragg peak intensity
$I_{Q}$ at $Q\sim (\pi ,\pi)$ in the magnetic field $H\ll H_{c2}$ at low
temperatures $0<T\ll T_{c},T_{AF}$ in $La_{2-x}Sr_{x}CuO_{4}$. Good agreement
with experimental results is found. The theory predicts large anisotropy of the
relative intensity $R_{Q}(H)=(I_{Q}(H)-I_{Q}(0))/I_{Q}(0)$%, i.e.
$R_{Q}(H\parallel c-axis)\gg R_{Q}(H\perp c-axis)$. The quantum (T=0) phase
diagram at H=0 is constructed. The theory also predicts: (i) the magnetic field
induced AF order in the SC state; (ii) small value for the spin-fluctuation
coupling constant $g<(0.025-0.05)$ $eV$. The latter gives very small SC
critical temperature $T_{c}(\ll 40$ $K)$, thus questioning the spin-fluctuation
mechanism of pairing in HTS oxides.",0207400v2
2002-10-28,"Structure, electric and magnetic properties of the electron-doped manganese oxide: La{sub(1-x)}Te{sub(x)}MnO{sub(3)}(x=0.1, 0.15)","In this letter, the electrical and magnetic properties of
La{sub(1-x)}Te{sub(x)}MnO{sub(3)}(x=0.1, 0.15), which is a new material and
shows good colossal magnetoresistance (CMR) behavior, have been investigated.
These compounds have rhombohedral structure. In this materical, Te replaced a
part of La ions, which induced the lattice cell constriction and Mn-O-Mn bond
angle widening. X-ray photoemission spectroscopy (XPS) measurement revealed
that the Te ions were in the tetravalent state and the manganese ions could be
considered as in a mixture state of Mn{sup(2+)} and Mn{Sup(3+)}. Thus the
material could be viewed as an electron-doped compound. The Curie temperature
(Tc) was about 240 K and 255 K for x=0.1, 0.15, respectively. The maximum
magnetoresistance ratio MR=[r(0)-r(H)]/r(0) was about 51% at 200 K and in the
applied magnetic field of 40 kOe.",0210609v2
2003-09-30,"Structural and magnetic anomalies among the spin-chain compounds, Ca3Co1+xIr1-xO6","The results of x-ray diffraction, and ac and dc magnetization as a function
of temperature are reported for a new class of spin-chain oxides,
Ca3Co1+xIr1-xO6. While the x= 0.0, 0.3, 0.5 and 1.0 are found to form in the
K4CdCl6-derived rhombhohedral (space group R-3c) structure, the x= 0.7
composition is found to undergo a monoclinic distortion in contrast to a
literature report. Apparently, the change in the crystal symmetry with x
manifests itself as a change in the sign of paramagnetic Curie temperature for
this composition as though magnetic coupling sensitively depends on such
crystallographic distortions. All the compositions exhibit spin-glass anomalies
with an unusually large frequency dependence of the peak temperature in ac
susceptibility in a temperature range below 50 K, interestingly obeying
Voger-Fulcher relationship even for the stoichiometric compounds.",0309700v1
2004-02-25,High-transition-temperature superconductivity in the absence of the magnetic-resonance mode,"The fundamental mechanism that gives rise to high-transition-temperature
(high-Tc) superconductivity in the copper oxide materials has been debated
since the discovery of the phenomenon. Recent work has focussed on a sharp
'kink' in the kinetic energy spectra of the electrons as a possible signature
of the force that creates the superconducting state. The kink has been related
to a magnetic resonance and also to phonons. Here we report that infrared
spectra of Bi2Sr2CaCu2O(8+d), (Bi-2212) show that this sharp feature can be
separated from a broad background and, interestingly, weakens with doping
before disappearing completely at a critical doping level of 0.23 holes per
copper atom. Superconductivity is still strong in terms of the transition
temperature (Tc approx 55 K), so our results rule out both the magnetic
resonance peak and phonons as the principal cause of high-Tc superconductivity.
The broad background, on the other hand, is a universal property of the copper
oxygen plane and a good candidate for the 'glue' that binds the electrons.",0402612v1
2004-03-01,Mass-Enhanced Fermi Liquid Ground State in Na$_{1.5}$Co$_2$O$_4$,"Magnetic, transport, and specific heat measurements have been performed on
layered metallic oxide Na$_{1.5}$Co$_2$O$_4$ as a function of temperature $T$.
Below a characteristic temperature $T^*$=30$-$40 K, electrical resistivity
shows a metallic conductivity with a $T^2$ behavior and magnetic susceptibility
deviates from the Curie-Weiss behavior showing a broad peak at $\sim$14 K. The
electronic specific heat coefficient $\gamma$ is $\sim$60 mJ/molK$^2$ at 2 K.
No evidence for magnetic ordering is found. These behaviors suggest the
formation of mass-enhanced Fermi liquid ground state analogous to that in
$d$-electron heavy fermion compound LiV$_2$O$_4$.",0403028v1
2004-03-10,Structural and magnetic properties of a series of low doped Zn$_{1-x}$Co$_x$O thin films deposited from Zn and Co metal targets on (0001) Al$_2$O$_3$ substrates,"We report on the synthesis of low doping Zn$_{1-x}$Co$_x$O ($0<x<0.1$) thin
films on (0001)-Al$_2$O$_3$ substrates. The films were prepared in an oxidizing
atmosphere, using the pulsed laser deposition technique starting from Zn and Co
metallic targets. We first studied the influence of the strains of ZnO and
their stuctural properties. Second, we have investigated the structural and the
magnetic properties of the Zn$_{1-x}$Co$_x$O films. We show that at low doping,
the lattice parameters and the magnetization of the Zn$_{1-x}$Co$_x$O films
depend strongly on the Co concentration.",0403281v1
2004-03-12,Decoupling of orbital and spin degrees of freedom in Li1-xNaxNiO2,"In the Li1-xNaxNiO2 solid solutions three different single phase regions
exist: for x > 0.9, forx = 0.7 and for x < 0.3. Although the intermediate
compound does not show the cooperative Jahn-Teller transition of NaNiO2, its
magnetic properties remain very similar with, in particular, the low
temperature 3D magnetic ordering. Therefore, the strong coupling between
orbital and spindegrees of freedom, characteristic of other oxides like
perovskites, and usually invoked to explainthe absence of both long-range
orbital and magnetic ordering in LiNiO2, seems not to take placein these
layered compounds with 90-degree bonds. We also discuss the relevance of the O
crystal fieldsplitting induced by the trigonal distortion, in generating AFM
Ni-Ni in-plane interactions.",0403329v2
2004-06-22,A-site Randomness Effect on Structural and Physical Properties of Ba-based Perovskite Manganites,"The discovery of novel structural and physical properties in the $A$-site
ordered manganite $R$BaMn$_{2}$O$_{6}$ ($R$ = Y and rare earth elements) has
demanded new comprehension about perovskite manganese oxides. In the present
study, the $A$-site disordered form, $R_{0.5}$Ba$_{0.5}$MnO$_{3}$, has been
investigated and compared with both $R$BaMn$_{2}$O$_{6}$ and
$R_{0.5}A_{0.5}$MnO$_{3}$ ($A$: Sr, Ca) in the structures and electromagnetic
properties. $R_{0.5}$Ba$_{0.5}$MnO$_{3}$ has a primitive cubic perovskite cell
in the structure and magnetic glassy states are dominant as its ground state,
in contrast to the ordinary disordered $R_{0.5}A_{0.5}$MnO$_{3}$ ($A$: Sr, Ca).
In Pr-compounds with various degrees of Pr/Ba randomness at the $A$-sites, the
$A$-site disorder gradually suppresses both ferromagnetic and A-type
antiferromagnetic transitions and finally leads to a magnetic glassy state in
Pr$_{0.5}$Ba$_{0.5}$MnO$_{3}$. A peculiar behavior, multi-step magnetization
and resistivity change, has been observed in Pr$_{0.5}$Ba$_{0.5}$MnO$_{3}$.
These properties could be closely related to any spatial heterogeneity caused
by the random distribution of Ba$^{2 +}$ and $R^{3 +}$ with much different
ionic radius.",0406505v1
2004-07-16,Strong Room-Temperature Ferromagnetism in Co2+-Doped TiO2 made from Colloidal Nanocrystals,"Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and
studied by electronic absorption, magnetic circular dichroism, transmission
electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption
spectroscopy, and extended X-ray absorption fine structure measurements. The
nanocrystals were paramagnetic when isolated by surface-passivating ligands,
weakly ferromagnetic (Ms = 1.5 x 10-3 mB/Co2+ at 300 K) when aggregated, and
strongly ferromagnetic (up to Ms = 1.9 mB/Co2+ at 300 K) when spin-coated into
nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co2+
oxidation state in all samples. In addition to providing strong experimental
support for the existence of intrinsic ferromagnetism in cobalt-doped TiO2,
these results demonstrate the possibility of using colloidal TiO2 diluted
magnetic semiconductor nanocrystals as building blocks for assembly of
ferromagnetic semiconductor nanostructures with potential spintronics
applications.",0407451v1
2004-08-13,Insulator-metal transition and the magnetic phase diagram of La1-xTexMnO3,"The structural, electrical transport and magnetic properties of perovskite
oxides La1-xTexMnO3 have been investigated and thus the magnetic phase diagram
of La1-xTexMnO3 compounds as a function of temperature and the doping level x
has been obtained. All samples have rhombohedral structure and undergo
paramagnetic-ferromagnetic (PM-FM) transition accompanied with metal-insulator
transition (MIT). Whereas a charge ordering (CO) transition begins to appear at
for the sample with x=0.60. Moreover, the variation of the Curie temperature
and the MIT temperature is quite complex and the results are discussed in terms
of three factors including the average A-site cation radius <rA>, the size
mismatch and the Te content. In addition, there has an evident
magnetoresistance (MR) at low temperatures for all samples.",0408307v1
2004-11-26,Electronic band structure of alfa-(Per)2M(mnt)2 compounds,"The band structure of alfa-(Per)2M(mnt)2, leads to a description of these
materials as nearly perfectly one dimensional conductors. The conduction is
mainly along the stacking direction of the partially oxidized perylene
molecules, (Per)1/2+, with virtually no interchain bandwidth. However, recent
high magnetic field experiments suggest orbital coupling of the magnetic field
to the electronic structure, indicating a finite interchain bandwidth. The
details of the band structure and the possible variances, at low energies, from
a perfect one dimensional system are examined. In particular, multiple
quasi-one dimensional Fermi surface sheets, which would become important at low
temperatures, may lead to an explanation for the experimental finding of a
magnetic field induced high field charge density wave ground state.
Experimental tests to observe the effects of the finite interchain bandwidth
are proposed.",0411676v2
2005-04-15,"Competition between ferromagnetism and spin glass: the key for large magnetoresistance in oxygen deficient perovskites SrCo1-xMxO3-d (M = Nb, Ru)","The magnetic and magnetotransport properties of the oxygen deficient
perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and
Ru-substituted cobaltites are weak ferromagnets, with transition temperatures
Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass
behavior at temperatures below Tf = 80-90 K. It is demonstrated that there
exists a strong competition between ferromagnetism and spin glass state, where
Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites
induces magnetic disorder, and this particular magnetic behavior is the origin
of large negative magnetoresistance of these oxides, reaching up to 30% at 5 K
in 7 T. The differences between Nb- and Ru-substituted cobaltites are discussed
on the basis of the different electronic configuration of niobium and ruthenium
cations.",0504379v1
2005-09-05,Magnetoelectric Coupling in epsilon-Fe2O3,"Nanoparticles of the ferrimagnetic epsilon-Fe2O3 oxide have been synthesized
by sol-gel method. Here, we report on the measurements of the dielectric
permittivity as a function of temperature, frequency and magnetic field. It is
found that, coinciding with the transition from collinear ferrimagnetic
ordering to an incommensurate magnetic state occurring at about 100 K, there is
an abrupt change (about 30 %) of permittivity suggesting the existence of a
magnetoelectric coupling in this material. Indeed, magnetic field dependent
measurements at 100 K have revealed an increase of the permittivity by about
0.3 % in 6 T. Prospective advantages of epsilon-Fe2O3 as multiferroic material
are discussed.",0509104v1
2005-10-02,Orbital order and fluctuations in Mott insulators,"Basic mechanisms controlling orbital order and orbital fluctuations in
transition metal oxides are discussed. The lattice driven classical orbital
picture, e.g. like in manganites LaMnO$_3$, is contrasted to the quantum
behavior of orbitals in frustrated superexchange models as realised in
pseudocubic titanites ATiO$_3$ and vanadates AVO$_3$. In YVO$_3$, the lattice
and superexchange effects strongly compete -- this explains the extreme
sensitivity of magnetic states to temperature and doping. Lifting the $t_{2g}$
orbital degeneracy by a relativistic spin-orbital coupling is considered on
example of the layered cobaltates. We find that the spin-orbital mixing of
low-energy states leads to unusual magnetic correlations in a triangular
lattice of the CoO$_2$ parent compound. Finally, the magnetism of sodium-rich
compounds Na$_{1-x}$CoO$_2$ is discussed in terms of a spin/orbital polaronic
liquid.",0510025v2
2006-01-24,Magnetic and Metal-Insulator Transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 -NMR and Neutron Diffraction Studies-,"Co-oxides beta-Na0.5CoO2 and gamma-K0.5CoO2 have been prepared by the Na
de-intercalation from alpha-NaCoO2 and by the floating-zone method,
respectively. It has been found that successive phase transitions take place at
temperatures Tc1 and Tc2 in both systems. The appearance of the internal
magnetic field at Tc1 with decreasing temperature T indicates that the
antiferromagnetic order exists at T < Tc1, as in gamma-Na0.5CoO2. For
beta-Na0.5CoO2, the transition temperatures and the NMR parameters determined
from the data taken for magnetically ordered state are similar to those of
gamma-Na0.5CoO2, indicating that the difference of the stacking ways of the
CoO2 layers between these systems do not significantly affect their physical
properties. For gamma-K0.5CoO2, the quantitative difference of the physical
quantities are found from those of beta- and gamma-Na0.5CoO2. The difference
between the values of Tci (i = 1 and 2) of these systems might be explained by
considering the distance between CoO2 layers.",0601538v1
2006-02-27,"Relating supercooling and glass-like arrest of kinetics for phase separated systems: studies on doped CeFe$_2$ and (La,Pr,Ca)MnO$_3$","Coexisting ferromagnetic and antiferromagnetic phases over a range of
temperature as well as magnetic field have been reported in many materials of
current interest, showing disorder-broadened 1st order transitions. Anomalous
history effects observed in magnetization and resistivity are being explained
invoking the concepts of kinetic arrest akin to glass transitions. From
magnetization measurements traversing novel paths in field-temperature space,
we obtain the intriguing result that the regions of the sample which can be
supercooled to lower temperatures undergo kinetic-arrest at higher
temperatures, and vice versa. Our results are for two diverse systems viz. the
inter-metallic doped CeFe$_2$ which has an antiferromagnetic ground state, and
the oxide La-Pr-Ca-Mn-O which has a ferromagnetic ground state, indicating the
possible universality of this effect of disorder on the widely encountered
phenomenon of glass-like arrest of kinetics.",0602627v1
2006-03-24,Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films,"We investigate the structure and magneto-transport properties of thin films
of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a
half-metal by first-principles theoretical calculations. Thin films are
deposited by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized Si
substrates to highly textured and even epitaxial on MgO(001) substrates,
respectively. Our Heusler films are magnetically very soft and ferromagnetic
with Curie temperatures up to 630 K. The total magnetic moment is reduced
compared to the theoretical bulk value, but still comparable to values reported
for films grown at elevated temperature. Polycrystalline Heusler films combined
with MgO barriers are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature.",0603649v1
2006-03-31,Pinhole and tunneling conduction channels superimposed in magnetic tunnel junction: results and inferences,"The influence of ballistic channels superimposed on tunneling conduction
channels in magnetic tunnel junctions has been studied in a manganese oxide
based tunneling device. Inversion of magnetoresistance has been observed in
magnetic tunnel junctions with pinhole nanocontacts over a broad temperature
range. The tunnel magnetoresistance undergoes a change of sign at higher bias
and temperature. This phenomenon is attributed to the parallel conduction
channels consisting of spin conserved ballistic transport through the pinhole
contact where the transmission probability is close to unity and spin polarized
tunneling across the insulating spacer with weak transmittivity. The results
seem to resolve a controversy regarding ballistic magnetoresistance in
ferromagnetic nanocontacts and establishes that ballistic magnetoresistance do
exist even if the previous results are attributed to magnetostriction and
magnetostatic force related artifacts.",0603843v1
2006-06-16,Unravelling the origin of the controversial magnetic properties of BiFeO3 thin films,"Single phase (001)-oriented BiFeO3 (BFO) thin films grown by pulsed laser
deposition can only be obtained in a narrow window of deposition pressure and
temperature and have a low magnetic moment. Out of the stability window Fe- or
Bi-rich impurity phases form, which has a strong impact on the physical and
structural properties of the films, even for impurity concentrations hardly
detectable by standard X-ray diffraction measurements. By using more sensitive
tools such as X-Ray absorption spectroscopy and X-ray magnetic circular
dichroism and performing advanced X-ray diffraction characterization, we show
that in non-optimal conditions Fe forms ferrimagnetic gamma-Fe2O3 precipitates
that are responsible for virtually all the ferromagnetic signal measured on
such BFO films by standard magnetometry. This confirms that the BFO phase has a
very low intrinsic moment that does not depend on strain. We also study the
influence of film thickness on the nucleation of parasitic phases and find that
epitaxial strain can stabilize the pure BFO phase in slightly over-oxidizing
growth conditions.",0606441v1
2006-12-18,Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO,"In this paper, a correlation between structural and magnetic properties of Fe
implanted ZnO is presented. High fluence Fe^+ implantation into ZnO leads to
the formation of superparamagnetic alpha-Fe nanoparticles. High vacuum
annealing at 823 K results in the growth of alpha-Fe particles, but the
annealing at 1073 K oxidized the majority of the Fe nanoparticles. After a long
term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles
were formed inside ZnO with the orientation relationship of
ZnFe2O4(111)[110]//ZnO(0001)[1120]. These ZnFe2O4 nanoparticles show a
hysteretic behavior upon magnetization reversal at 5 K.",0612444v1
2006-10-23,Integrated Cell Manipulation Systems,"A new type of microfluidic system for biological cell manipulation, a
CMOS/microfluidic hybrid, is demonstrated. The hybrid system starts with a
custom-designed CMOS (complementary metal-oxide semiconductor) chip fabricated
in a semiconductor foundry using standard integration circuit technology. A
microfluidic channel is post-fabricated on top of the CMOS chip to provide
biocompatible environment. The motion of individual biological cells that are
tagged with magnetic beads is directly controlled by the CMOS chip that
generates localized magnetic filed patterns using an on-chip array of
micro-electromagnets. The speed and the programmability of the CMOS chip
further allow for the dynamic reconfiguration of the magnetic fields,
substantially increasing the manipulation capability of the hybrid system. The
concept of a hybrid system is verified by simultaneously manipulating
individual biological cells with microscopic resolution. A new operation
protocol that exploits the fast speed of electronics to trap and move a large
number of cells with less power consumption is also demonstrated. Combining the
advantages of microelectronics, the CMOS/microfluidic hybrid approach presents
a new model for a multifunctional lab-on-a chip for biological and medical
applications.",0610043v1
2007-04-10,Coupling between magnetic ordering and structural instabilities in perovskite biferroics: A first-principles study,"We use first-principles density functional theory-based calculations to
investigate structural instabilities in the high symmetry cubic perovskite
structure of rare-earth (R $=$ La, Y, Lu) and Bi-based biferroic chromites,
focusing on $\Gamma$ and $R$ point phonons of states with para-, ferro-, and
antiferromagnetic ordering. We find that (a) the structure with G-type
antiferromagnetic ordering is most stable, (b) the most dominant structural
instabilities in these oxides are the ones associated with rotations of oxygen
octahedra, and (c) structural instabilities involving changes in Cr-O-Cr bond
angle depend sensitively on the changes in magnetic ordering. The dependence of
structural instabilities on magnetic ordering can be understood in terms of how
super-exchange interactions depend on the Cr-O-Cr bond angles and Cr-O bond
lengths. We demonstrate how adequate buckling of Cr-O-Cr chains can favour
ferromagnetism. Born effective charges (BEC) calculated using the Berry phase
expression are found to be anomalously large for the A-cations, indicating
their chemical relevance to ferroelectric distortions.",0704.1251v1
2007-04-14,Evidence for nonmonotonic magnetic field penetration in a type-I superconductor,"Polarized neutron reflectometry (PNR) provides evidence that nonlocal
electrodynamics governs the magnetic field penetration in an extreme low-k
superconductor. The sample is an indium film with a large elastic mean free
path (11 mkm) deposited on a silicon oxide wafer. It is shown that PNR can
resolve the difference between the reflected neutron spin asymmetries predicted
by the local and nonlocal theories of superconductivity. The experimental data
support the nonlocal theory, which predicts a nonmonotonic decay of the
magnetic field.",0704.1872v2
2007-06-14,Carrier-mediated magnetoelectricity in complex oxide heterostructures,"While tremendous success has been achieved to date in creating both single
phase and composite magnetoelectric materials, the quintessential
electric-field control of magnetism remains elusive. In this work, we
demonstrate a linear magnetoelectric effect which arises from a novel
carrier-mediated mechanism, and is a universal feature of the interface between
a dielectric and a spin-polarized metal. Using first-principles density
functional calculations, we illustrate this effect at the SrRuO$_3$/SrTiO$_3$
interface and describe its origin. To formally quantify the magnetic response
of such an interface to an applied electric field, we introduce and define the
concept of spin capacitance. In addition to its magnetoelectric and spin
capacitive behavior, the interface displays a spatial coexistence of magnetism
and dielectric polarization suggesting a route to a new type of interfacial
multiferroic.",0706.2199v1
2007-06-19,Tunneling spectroscopy of persistent currents in superconducting microrings,"It is shown that in a structure consisting of a superconducting ring-shaped
electrode overlapped by a normal metal contact through a thin oxide barrier,
measurements of the tunnel current in magnetic field can probe persistent
currents in the ring. The effect manifests itself as periodic oscillations of
the tunnel current through the junction at a fixed bias voltage as function of
perpendicular magnetic field. The magnitude of oscillations depends on bias
point. It reaches maximum at energy eV which is close to the superconducting
gap and decreases with increase of temperature. The period of oscillations dF
in units of magnetic flux is equal neither to h/e nor to h/2e, but
significantly exceeds these values for larger loop circumferences. The
phenomenon is explained by formation of metastable states with large vorticity.
The pairing potential and the superconducting density of states are
periodically modulated by the persistent currents at sub-critical values
resulting in corresponding variations of the measured tunnel current.",0706.2776v1
2007-10-12,First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6,"First principles calculations based on the density functional theory within
the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral
Bi$_2$FeTiO$_6$ is a potential multiferroic in which the magnetism and
ferroelectricity coexist . A ferromagnetic configuration with magnetic moment
of 4 $\mu_B$ per formula unit have been reported with respect to the minimum
total energy. Spontaneous polarization of 27.3 $\mu$ C/cm$^2$, caused mainly by
the ferroelectric distortions of Ti, was evaluated using the berry phase
approach in the modern theory of polarization. The Bi-6s stereochemical
activity of long-pair and the `d$^0$-ness' criterion in off-centring of Ti were
coexisting in the predicted new system. In view of the oxidation state of
Bi$^{3+}$,Fe$^{2+}$,Ti$^{4+}$, and O$^{2-}$ from the orbital-resolved density
of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of
Bi$_2$FeTiO$_6$ in the rhombohedral phase was found to be
Bi$_2$$^{3+}$Fe$^{2+}$Ti$^{4+}$O$_6$.",0710.2391v1
2007-10-19,Magnetism and structure of LixCoO2 and comparison to NaxCoO2,"The magnetic properties and structure of LixCoO2 for x between 0.5 and 1.0
are reported. Co4+ is found to be high-spin in LixCoO2 for x between 0.94 and
1.0 and low-spin for x between 0.50 and 0.78. Weak antiferromagnetic coupling
is observed, increasing in strength as more Co4+ is introduced. At an x value
of about 0.65, the temperature-independent contribution to the magnetic
susceptibility and the electronic contribution to the specific heat are
largest. Neutron diffraction analysis reveals that the lithium oxide layer
expands perpendicular to the basal plane and the Li ions displace from their
ideal octahedral sites with decreasing x. A comparison of the structures of the
NaxCoO2 and LixCoO2 systems reveals that the CoO2 layer changes substantially
with alkali content in the former but is relatively rigid in the latter.
Further, the CoO6 octahedra in LixCoO2 are less distorted than those in
NaxCoO2. We postulate that these structural differences strongly influence the
physical properties in the two systems.",0710.3767v1
2008-06-10,Image charge screening: a new approach to enhance magnetic ordering temperatures,"We have tested the concept of image charge screening as a new approach to
enhance magnetic ordering temperatures and superexchange interactions in ultra
thin films. Using a 3 monolayer NiO(100) film grown on Ag(100) and an
identically thin film on MgO(100) as model systems, we observed that the Neel
temperature of the NiO film on the highly polarizable metal substrate is 390 K
while that of the film on the poorly polarizable insulator substrate is below
40 K. This demonstrates that screening by highly polarizable media may point to
a practical way towards designing strongly correlated oxide nanostructures with
greatly improved magnetic properties.",0806.1710v1
2008-10-05,Structural and magnetic properties of an InGaAs/Fe$_3$Si superlattice in cylindrical geometry,"The structure and the magnetic properties of an InGaAs/Fe3Si superlattice in
a cylindrical geometry are investigated by electron microscopy techniques,
x-ray diffraction and magnetometry. To form a radial superlattice, a
pseudomorphic InGaAs/Fe3As bilayer has been released from its substrate
self-forming into a rolled-up microtube. Oxide-free interfaces as well as areas
of crystalline bonding are observed and an overall lattice mismatch between
succeeding layers is determined. The cylindrical symmetry of the final radial
superlattice shows a significant effect on the magnetization behavior of the
rolled-up layers.",0810.0835v2
2008-10-13,"Synthesis, crystal structure and spin-density-wave anomaly of the iron arsenide-fluoride SrFeAsF","The new quaternary iron arsenide-fluoride SrFeAsF with the tetragonal
ZrCuSiAs-type structure was synthesized and the crystal structure was
determined by X-ray powder diffraction (P4/nmm, a = 399.30(1), c = 895.46(1)
pm). SrFeAsF undergoes a structural and magnetic phase transition at 175 K,
accompanied by strong anomalies in the specific heat, electrical resistance and
magnetic susceptibility. In the course of this transition, the space group
symmetry changes from tetragonal (P4/nmm) to orthorhombic (Cmme). 57Fe
Moessbauer spectroscopy experiments show a single signal at room temperature at
an isomer shift of 0.30(1) mm/s and magnetic hyperfine-field splitting below
the phase transition temperature. Our results clearly show that SrFeAsF
exhibits a spin density wave (SDW) anomaly at 175 K very similar to LaFeAsO,
the parent compound of the iron arsenide-oxide superconductors and thus SrFeAsF
may serve as a further parent compound for oxygen-free iron arsenide
superconductors.",0810.2120v1
2009-02-06,Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2,"We report $^{23}$Na and $^{59}$Co nuclear magnetic (NMR) and quadrupolar
resonance (NQR) studies for the $x=2/3$ phase of the lamellar oxide
Na$_{x}$CoO$_{2}$, which allowed us to establish reliably the atomic order of
the Na layers and their stacking between the CoO$_{2}$ slabs. We evidence that
the Na$^{+}$ order stabilizes filled non magnetic Co$^{3+}$ ions on 25% of the
cobalt sites arranged in a triangular sublattice. The transferred holes are
delocalized on the 75% complementary cobalt sites which unexpectedly display a
planar cobalt kagom\'{e} structure. These experimental results resolve a
puzzling issue by precluding localized moments pictures for the magnetic
properties. They establish that the quasi ferromagnetic properties result from
a narrow band connecting a frustrated arrangement of atomic orbitals, and open
the route to unravel through similar studies the electronic properties of the
diverse ordered phases of sodium cobaltates.",0902.1108v1
2009-05-12,Considerations on the symmetry of loop order in cuprates,"The loop-current state discovered in the pseudogap phase of cuprates breaks
time reversal symmetry and lowers the point group symmetry of the crystal. The
order parameter and the magnetic structure within each unit cell which is
associated with it can be described by a toroidal moment parallel to the
copper-oxide planes. We discuss lattice point group symmetry of the magnetic
structure. As an application, we discuss a few effects that necessarily
accompany order parameter in the pseudogap phase. The magnitude estimated for
these specific effects makes them hard to observe because they rely on the
small magnetic fields associated with the order parameter. Effects, associated
with the electronic energies are much larger. Some of them have already been
discussed.",0905.1987v3
2009-11-10,Co-doped Ceria: Tendency towards ferromagnetism driven by oxygen vacancies,"We perform an electronic structure study for cerium oxide homogeneously-doped
with cobalt impurities, focusing on the role played by oxygen vacancies and
structural relaxation. By means of full-potential ab-initio methods, we explore
the possibility of ferromagnetism as observed in recent experiments. Our
results indicate that oxygen vacancies seem to be crucial for the appearance of
a ferromagnetic alignment among Co impurities, obtaining an increasing tendency
towards ferromagnetism with growing vacancy concentration. The estimated
couplings cannot explain though, the experimentally observed room-temperature
ferromagnetism. In this systematic study, we draw relevant conclusions
regarding the location of the oxygen vacancies and the magnetic couplings
involved. In particular, we find that oxygen vacancies tend to nucleate in the
neighborhood of Co impurities and we get a remarkably strong ferromagnetic
coupling between Co atoms and the Ce^{3+} neighboring ions. The calculated
magnetic moments per cell depend on the degree of reduction which could explain
the wide spread in the magnetization values observed in the experiments.",0911.1959v1
2010-03-11,"Magnetic and Electrical Properties of Ordered 112-type Perovskite LnBaCoMnO5+δ(Ln = Nd, Eu)","Investigation of the oxygen-deficient 112-type ordered oxides of the type
LnBaCoMnO5+\delta (Ln = Nd, Eu) evidences certain unusual magnetic behavior at
low temperatures, compared to the LnBaCo2O5+\delta cobaltites. One observes
that the substitution of manganese for cobalt suppresses the ferromagnetic
state and induces strong antiferromagnetic interactions. Importantly,
NdBaCoMnO5.9 depicts a clear paramagnetic to antiferromagnetic type transition
around 220 K, whereas for EuBaCoMnO5.7 one observes an unusual magnetic
behavior below 177 K which consists of ferromagnetic regions embedded in an
antiferromagnetic matrix. The existence of two sorts of crystallographic sites
for Co/Mn and their mixed valence states favor the ferromagnetic interaction
whereas antiferromagnetism originates from the Co3+-O-Co3+ and Mn4+-O-Mn4+
interactions. Unlike the parent compounds, the present Mn-substituted phases do
not exhibit prominent magnetoresistance effects in the temperature range
75-400K.",1003.2262v1
2010-06-04,Low-temperature ferromagnetism in a weakly doped Hubbard magnet,"In the framework of the diagrammatic method with self-consistent field, the
maximum on the temperature dependence of the susceptibility of a weakly doped
narrow-band Hubbard magnet below the Curie temperature $T_{\rm C}$ is
predicted. By numerical calculations, it is proved that it appears at small
hole concentrations $n_{h}$. In this case, the temperature dependence of the
magnetization $M$($T$) has a typical Fermi-like shape with the point of
inflection at a temperature $T_{\rm inf}$. The approximate solution of the
system of equations for the mean spin and the chemical potential gives the
Schottky susceptibility typical of a two-level system with a gap of order of
$n_{h}(1-n_{h})W$, where W is the bandwidth. This behavior reflects the
existence of two subbands with up- and down-spins. It may be observed
experimentally in the surface layers of oxide metal nanoparticles with narrow
bands and a weak oxygen nonstoichiometry.",1006.0907v1
2010-07-01,ZnO:Co Diluted Magnetic Semiconductor or Hybrid Nanostructure for Spintronics?,"We have studied the influence of intrinsic and extrinsic defects in the
magnetic and electrical transport properties of Co-doped ZnO thin films. X ray
absorption measurements show that Co substitute Zn in the ZnO structure and it
is in the 2+ oxidation state. Magnetization (M) measurements show that doped
samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found
that the values of the orbital L and spin S numbers are between 1 and 1.3 for L
and S = 3/2, in agreement with the representative values for isolated Co 2+.
The obtained negative values of the Curie-Weiss temperatures indicate the
existence of antiferromagnetic interactions between transition metal atoms.",1007.0269v1
2010-08-10,On the resistivity at low temperatures in electron-doped cuprate superconductors,"We measured the magnetoresistance as a function of temperature down to 20mK
and magnetic field for a set of underdoped PrCeCuO (x=0.12) thin films with
controlled oxygen content. This allows us to access the edge of the
superconducting dome on the underdoped side. The sheet resistance increases
with increasing oxygen content whereas the superconducting transition
temperature is steadily decreasing down to zero. Upon applying various magnetic
fields to suppress superconductivity we found that the sheet resistance
increases when the temperature is lowered. It saturates at very low
temperatures. These results, along with the magnetoresistance, cannot be
described in the context of zero temperature two dimensional
superconductor-to-insulator transition nor as a simple Kondo effect due to
scattering off spins in the copper-oxide planes. We conjecture that due to the
proximity to an antiferromagnetic phase magnetic droplets are induced. This
results in negative magnetoresistance and in an upturn in the resistivity.",1008.1682v1
2010-12-02,Electronic structure and magnetism of transition metal doped Zn12O12 clusters: Role of defects,"We present a comprehensive study of the energetics and magnetic properties of
ZnO clusters doped with 3d transition metals (TM) using ab initio density
functional calculations in the framework of generalized gradient approximation
+ Hubbard U (GGA+U) method. Our results within GGA+U for all 3d dopants except
Ti indicate that antiferromagnetic interaction dominates in a neutral,
defect-free cluster. Formation energies are calculated to identify the stable
defects in the ZnO cluster. We have analyzed in details the role of these
defects to stabilize ferromagnetism when the cluster is doped with Mn, Fe, and
Co. Our calculations reveal that in the presence of charged defects the
transition metal atoms residing at the surface of the cluster may have an
unusual oxidation state, that plays an important role to render the cluster
ferromagnetic. Defect induced magnetism in ZnO clusters without any TM dopants
is also analyzed. These results on ZnO clusters may have significant
contributions in the nanoengineering of defects to achieve desired
ferromagnetic properties for spintronic applications.",1012.0430v1
2010-12-14,Scaling behavior of the spin pumping effect in ferromagnet/platinum bilayers,"We systematically measured the DC voltage V_ISH induced by spin pumping
together with the inverse spin Hall effect in ferromagnet/platinum bilayer
films. In all our samples, comprising ferromagnetic 3d transition metals,
Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V_ISH
invariably has the same polarity. V_ISH furthermore scales with the
magnetization precession cone angle with a universal prefactor, irrespective of
the magnetic properties, the charge carrier transport mechanism or type. These
findings quantitatively corroborate the present theoretical understanding of
spin pumping in combination with the inverse spin Hall effect.",1012.3017v2
2011-01-05,"Non-thermal laser induced precession of magnetization in ferromagnetic semiconductor (Ga,Mn)As","Non-thermal laser induced spin excitations, recently discovered in
conventional oxide and metal ferromagnets, open unprecedented opportunities for
research and applications of ultrafast optical manipulation of magnetic
systems. Ferromagnetic semiconductors, and (Ga,Mn)As in particular, should
represent ideal systems for exploring this new field. Remarkably, the presence
of non-thermal effects has remained one of the outstanding unresolved problems
in the research of ferromagnetic semiconductors to date. Here we demonstrate
that coherent magnetization dynamics can be excited in (Ga,Mn)As non-thermally
by a transfer of angular momentum from circularly polarized femtosecond laser
pulses and by a combination of non-thermal and thermal effects due to a
transfer of energy from laser pulses. The thermal effects can be completely
suppressed in piezo-electrically controlled samples. Our work is based on
pump-and-probe measurements in a large set of (Ga,Mn)As epilayers and on
systematic analysis of circular and linear magneto-optical coefficients. We
provide microscopic theoretical interpretation of the experimental results.",1101.1049v1
2011-01-10,A story of high-temperature ferromagnetism in semiconductors,"The comprehensive search for multifunctional materials has resulted in the
discovery of semiconductors and oxides showing ferromagnetic features
persisting to room temperature. In this tutorial review the methods of
synthesis of these materials, as well as the application of element-specific
nano-analytic tools, particularly involving synchrotron radiation and electron
microscopy, are described and shown to reveal the presence of nano-scale phase
separations. Various means to control the aggregation of magnetic cations are
discussed together with the mechanisms accounting for ferromagnetism of either
condensed or diluted magnetic semiconductors. Finally, the question of whether
high temperature ferromagnetism is possible in semiconductors not containing
magnetic ions is touched upon.",1101.1981v1
2011-01-31,Template assisted self-assembly of individual and clusters of magnetic nanoparticles,"The deliberate control over the spatial arrangement of nanostructures is the
desired goal for many applications as e.g. in data storage, plasmonics or
sensor arrays. Here we present a novel method to assist the self-assembly
process of magnetic nanoparticles. The method makes use of nanostructured
aluminum templates obtained after anodization of aluminum disks and the
subsequent growth and removal of the newly formed alumina layer, resulting in a
regular honeycomb type array of hexagonally shaped valleys. The iron oxide
nanoparticles, 20 nm in diameter, are spin coated onto the nanostructured
templates. Depending on the size, each hexagon site can host up to 30
nanoparticles. These nanoparticles form clusters of different arrangements
within the valleys, such as collars, chains, and hexagonally closed islands.
Ultimately, it is possible to isolate individual nanoparticles. The strengths
of magnetic interaction between particles in a cluster is probed using the
memory effect known from the coupled state in superspin glass systems.",1101.5899v1
2011-06-29,Highly spin-polarized conducting state at the interface between non-magnetic band insulators: LaAlO3/FeS2 (001),"First-principles density functional calculations demonstrate that a
spin-polarized two-dimensional conducting state can be realized at the
interface between two non-magnetic band insulators. The (001) surface of the
diamagnetic insulator FeS2 (pyrite) supports a localized surface state deriving
from Fe d-orbitals near the conduction band minimum. The deposition of a few
unit cells of the polar perovskite oxide LaAlO3 leads to electron transfer into
these surface bands, thereby creating a conducting interface. The occupation of
these narrow bands leads to an exchange splitting between the spin sub-bands,
yielding a highly spin-polarized conducting state distinct from the rest of the
non-magnetic, insulating bulk. Such an interface presents intriguing
possibilities for spintronics applications.",1106.6010v1
2011-08-23,Resonant X-Ray Diffraction Study of Strongly Spin-Orbit-Coupled Mott Insulator CaIrO3,"We performed resonant x-ray diffraction experiments at the $L$ absorption
edges for the post-perovskite-type compound CaIrO$_{3}$ with $(t_{2g})^5$
electronic configuration. By observing the magnetic signals, we could clearly
see that the magnetic structure was a striped order with an antiferromagnetic
moment along the c-axis and that the wavefunction of a $t_{2g}$ hole is
strongly spin-orbit entangled, the $J_{\rm eff} =1/2$ state. The observed spin
arrangement is consistent with theoretical work predicting a unique
superexchange interaction in the $J_{\rm eff} =1/2$ state and points to the
universal importance of the spin-orbit coupling in Ir oxides, irrespective of
the local coordination and lattice topology. We also propose that the
non-magnetic resonant scattering is a powerful tool for unraveling an orbital
state even in a metallic iridate.",1108.4523v1
2011-08-24,In vitro toxicity and uptake of magnetic nanorods,"In this paper we investigate the internalization and cytotoxicity of
nanostructured materials having the form of elongated rods, with diameter of
200 nm and lengths 1 - 10 {\mu}m. The rods were made from the controlled
aggregation of sub-10 nm iron oxide nanoparticles. Recently, we have shown that
the nanorods inherited the superparamagnetic property of the particles. These
rods can actually be moved by the application of an external magnetic field.
Here we evaluate the in vitro toxicity of the magnetic nanorods by using MTT
assays on NIH/3T3 mouse fibroblasts. The toxicity assays revealed that the
nanorods are biocompatible, as exposed cells remained 100% viable relative to
controls over a period of a few days. Optical microscopy allow to visualize the
rods inside the cells and to determine their number per cell. Roughly 1/3 of
the total incubated rods were uptaken by the fibroblasts.",1108.4773v1
2012-02-07,Magnetically driven metal-insulator transition in NaOsO3,"The metal-insulator transition (MIT) is one of the most dramatic
manifestations of electron correlations in materials. Various mechanisms
producing MITs have been extensively considered, including the Mott (electron
localization via Coulomb repulsion), Anderson (localization via disorder) and
Peierls (localization via distortion of a periodic 1D lattice). One additional
route to a MIT proposed by Slater, in which long-range magnetic order in a
three dimensional system drives the MIT, has received relatively little
attention. Using neutron and X-ray scattering we show that the MIT in NaOsO3 is
coincident with the onset of long-range commensurate three dimensional magnetic
order. Whilst candidate materials have been suggested, our experimental
methodology allows the first definitive demonstration of the long predicted
Slater MIT. We discuss our results in the light of recent reports of a Mott
spin-orbit insulating state in other 5d oxides.",1202.1482v1
2012-02-09,Observation of Huge Magnetoresistance and Multiferroic-like Behavior of Co Nanoparticles in a C60 matrix,"Tunneling magnetoresistance (TMR) via oxides or molecules includes fruitful
physics, such as spin filtering and hybridized interface states, in addition to
various practical applications using large TMR ratio at room temperature. Then,
a larger TMR effect with a new fundamental physics is awaited because further
progress on spintronics can be realized. Here we report a discovery of a
gigantic TMR ratio of 1,400,000% in a C60-Co nanocomposite spin device. The
observed effect is induced by a combination of a Coulomb blockade effect and a
novel magnetic switching effect. Theoretical investigation reveals that an
electric field and a magnetic field control the magnetization and the
electronic charging state, respectively, of the Co nanoparticles as in physics
of multiferroicity.",1202.1920v3
2012-08-10,Magnetic structural change of Sr2IrO4 upon Mn doping,"The layered 5d transition metal oxide Sr2IrO4 has been shown to host a novel
Jeff=1/2 Mott spin orbit insulating state with antiferromagnetic ordering,
leading to comparisons with the layered cuprates. Here we study the effect of
substituting Mn for Ir in single crystals of Sr2Ir0.9Mn0.1O4 through an
investigation involving bulk measurements and resonant x-ray and neutron
scattering. We observe a new long range magnetic structure emerge upon doping
through a reordering of the spins from the basal plane to the c-axis with a
reduced ordering temperature compared to Sr2IrO4. The strong enhancement of the
magnetic x-ray scattering intensity at the L3 edge relative to the L2 edge
indicates that the Jeff=1/2 state is robust and capable of hosting a variety of
ground states.",1208.2229v2
2012-11-27,Magnetic Insulator-Induced Proximity Effects in Graphene: Spin Filtering and Exchange Splitting Gaps,"We report on first-principles calculations of spin-dependent properties in
graphene induced by its interaction with a nearby magnetic insulator (Europium
oxide, EuO). The magnetic proximity effect results in spin polarization of
graphene $\pi$ orbitals by up to 24 %, together with large exchange splitting
bandgap of about 36 meV. The position of the Dirac cone is further shown to
depend strongly on the graphene-EuO interlayer. These findings point towards
the possible engineering of spin gating by proximity effect at relatively high
temperature, which stands as a hallmark for future all-spin information
processing technologies.",1211.6377v1
2012-12-24,Robustness of basal-plane antiferromagnetic order and the $J_{eff}=1/2$ state in single-layer iridate spin-orbit Mott insulators,"The magnetic structure and electronic groundstate of the layered perovskite
Ba2IrO4 have been investigated using x-ray resonant magnetic scattering (XRMS).
Our results are compared with those for Sr2IrO4, for which we provide
supplementary data on its magnetic structure. We find that the dominant,
long-range antiferromagnetic order is remarkably similar in the two compounds,
and that the electronic groundstate in Ba2IrO4, deduced from an investigation
of the XRMS $L_3/L_2$ intensity ratio, is consistent with a $J_{eff}=1/2$
description. The robustness of these two key electronic properties to the
considerable structural differences between the Ba and Sr analogues is
discussed in terms of the enhanced role of the spin-orbit interaction in 5d
transition metal oxides.",1212.5912v1
2013-02-07,Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3d-5d Transition-Metal Compound Sr3CuIrO6,"We report a combined experimental and theoretical study of the unusual
ferromagnetism in the one-dimensional copper-iridium oxide Sr$_3$CuIrO$_6$.
Utilizing Ir $L_3$ edge resonant inelastic x-ray scattering, we reveal a large
gap magnetic excitation spectrum. We find that it is caused by an unusual
exchange anisotropy generating mechanism, namely, strong ferromagnetic
anisotropy arising from antiferromagnetic superexchange, driven by the
alternating strong and weak spin-orbit coupling on the $5d$ Ir and 3d Cu
magnetic ions, respectively. From symmetry consideration, this novel mechanism
is generally present in systems with edge-sharing Cu$^{2+}$O$_4$ plaquettes and
Ir$^{4+}$O$_6$ octahedra. Our results point to unusual magnetic behavior to be
expected in mixed 3d-5d transition-metal compounds via exchange pathways that
are absent in pure 3d or 5d compounds.",1302.1818v2
2013-02-23,Crystal structures of spin-Jahn-Teller ordered MgCr_2O_4 and ZnCr_2O_4,"Magnetic ordering in the geometrically frustrated magnetic oxide spinels
MgCr_2O_4 and ZnCr_2O_4 is accompanied by a structural change that helps
relieve the frustration. Analysis of high-resolution synchrotron X-ray
scattering reveals that the low-temperature structures are well described by a
two-phase model of tetragonal I4_1/amd and orthorhombic Fddd symmetries. The
Cr_4 tetrahedra of the pyrochlore lattice are distorted at these
low-temperatures, with the Fddd phase displaying larger distortions than the
I4_1/amd phase. The spin-Jahn-Teller distortion is approximately one order of
magnitude smaller than is observed in first-order Jahn-Teller spinels such as
NiCr_2O_4 and CuCr_2O_4. In analogy with NiCr_2O_4 and CuCr_2O_4, we further
suggest that the precise nature of magnetic ordering can itself provide a
second driving force for structural change.",1302.5746v2
2013-03-13,"Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO_3/SrTiO_3 interface","The electronic properties of the polar interface between insulating oxides is
a subject of great current interest. An exciting new development is the
observation of robust magnetism at the interface of two non-magnetic materials
LaAlO_3 (LAO) and SrTiO_3 (STO). Here we present a microscopic theory for the
formation and interaction of local moments, which depends on essential features
of the LAO/STO interface. We show that correlation-induced moments arise due to
interfacial splitting of orbital degeneracy. We find that gate-tunable Rashba
spin-orbit coupling at the interface influences the exchange interaction
mediated by conduction electrons. We predict that the zero-field ground state
is a long-wavelength spiral and show that its evolution in an external field
accounts semi-quantitatively for torque magnetometry data. Our theory describes
qualitative aspects of the scanning SQUID measurements and makes several
testable predictions for future experiments.",1303.3275v2
2013-03-22,Ultralow-current-density and bias-field-free spin-transfer nano-oscillator,"The spin-transfer nano-oscillator (STNO) offers the possibility of using the
transfer of spin angular momentum via spin-polarized currents to generate
microwave signals. However, at present STNO microwave emission mainly relies on
both large drive currents and external magnetic fields. These issues hinder the
implementation of STNOs for practical applications in terms of power
dissipation and size. Here, we report microwave measurements on STNOs built
with MgO-based magnetic tunnel junctions having a planar polarizer and a
perpendicular free layer, where microwave emission with large output power,
excited at ultralow current densities, and in the absence of any bias magnetic
fields is observed. The measured critical current density is over one order of
magnitude smaller than previously reported. These results suggest the
possibility of improved integration of STNOs with complementary
metal-oxide-semiconductor technology, and could represent a new route for the
development of the next-generation of on-chip oscillators.",1303.5562v1
2013-03-24,Self-energy effects in electronic Raman spectra of doped cuprates due to magnetic fluctuations,"We present results for magnetic excitations in doped copper oxides using the
random phase approximation and itinerant electrons. In the [1,0] direction the
observed excitations resemble dispersive quasi-particles both in the normal and
superconducting state similar as in recent resonant inelastic X-ray scattering
(RIXS) experiments. In the [1,1] direction the excitations form, except for the
critical region near the antiferromagnetic wave vector ${\bf Q}=(\pi,\pi)$,
only very broad continua. Using the obtained spin propagators we calculate
electron self-energies and their effects on electronic Raman spectra. We show
that the recently observed additional peak at about twice the pair breaking in
B$_{1g}$ symmetry below T$_c$ in HgBa$_2$CuO$_{4+\delta}$ can be explained as a
self-energy effect where a broken Cooper pair and a magnetic excitation appear
as final states. The absence of this peak in B$_{2g}$ symmetry, which probes
mainly electrons near the nodal direction, is explained by their small
self-energies compared to those in the antinodal direction.",1303.5975v1
2013-04-06,Theoretical study on copper's energetics and magnetism in TiO2 polymorphs,"We carried out density functional theory calculations to model the electronic
structure and the magnetic interactions in copper doped anatase and rutile
titanium dioxide in order to shed light on the potential of these systems as
magnetic oxides using different density functional schemes. In both polymorphs
copper dopant was found to be most stable in substitutional lattice positions.
Ferromagnetism is predicted to be stable well above room temperature with long
range interactions prevailing in the anatase phase while the rutile phase
exhibits only short range superexchange interaction among nearest neighbouring
Cu ions. Additionally, energetic evaluation of dopants in scattered and compact
configurations reveals a dopant clustering tendency in anatase TiO2.",1304.1854v2
2013-07-20,Emergent Spin-Filter at the interface between Ferromagnetic and Insulating Layered Oxides,"We report a strong effect of interface-induced magnetization on the transport
properties of magnetic tunnel junctions consisting of ferromagnetic manganite
La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ and insulating cuprate PrBa$_{2}$Cu$_{3}$O$_{7}$.
Contrary to the typically observed steady increase of the tunnel
magnetoresistance with decreasing temperature, this system exhibits a sudden
anomalous decrease at low temperatures. Interestingly, this anomalous behavior
can be attributed to the competition between the positive spin polarization of
the manganite contacts and the negative spin-filter effect from the
interface-induced Cu magnetization.",1307.5475v2
2013-10-05,"Effect of ""dipolar-biasing"" on the tunability of tunneling magnetoresistance in transition metal oxide systems","We observe an unusual tunneling magnetoresistance (TMR) phenomenon in a
composite of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ with CoFe$_{2}$O$_{4}$ where the TMR
versus applied magnetic field loop suggests a ""negative coercive field"".
Tracing its origin back to a ""dipolar-biasing"" of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$
by CoFe$_{2}$O$_{4}$, we show that the TMR of even a single composite can be
tuned continuously so that the resistance peak or the highest sensitivity of
the TMR can be positioned anywhere on the magnetic field axis with a suitable
magnetic history of the sample. This phenomenon of an unprecedented tunability
of the TMR should be present in general in all such composites.",1310.1466v1
2013-10-22,Conduction of spin currents through insulating oxides,"Spintronics is a field of electronics based on using the electron spin
instead of its charge. The recent advance in the manipulation of pure spin
currents, i.e. angular momentum transfer not associated to conventional charge
currents, has opened new opportunities to build spin based devices with low
energy consumption. It has also allowed to integrate ferromagnetic insulators
in spintronic devices, either as spin sources or spin conductors using their
magnetic excitations to propagate a spin signal. Antiferromagnetic insulators
belong to another class of materials that can also sustain magnetic
excitations, even with a higher group velocity. Hence, they have potential as
angular momentum conductors, possibly making faster spin devices. At the
opposite end, angular momentum insulators are also required in spintronic
circuits. The present letter underlines some essential features relevant for
spin current conduction, based on measurements of angular momentum transmission
in antiferromagnetic NiO and in the non-magnetic light element insulator
SiO$_2$.",1310.6000v1
2013-11-03,Probing the Electromagnetic Local Density of States with a Strongly Mixed Electric and Magnetic Dipole Emitter,"We identify a solid-state quantum emitter whose room-temperature radiative
decay is mediated by a nearly equal mixture of isotropic electric dipole (ED)
and magnetic dipole (MD) transitions. Using energy-momentum spectroscopy, we
experimentally show that the near-infrared $^3$T$_2{\rightarrow}^3$A$_2$
emission from divalent-nickel-doped magnesium oxide (Ni$^{2+}$:MgO) is composed
of $\sim$50% MD and $\sim$50% ED transitions. We then demonstrate that the
spontaneous emission rate of these ions near planar interfaces is determined by
the combined electric and magnetic local density of optical states (LDOS). This
electromagnetic LDOS probes the total mode density, and thus similar to thermal
emission, these unique electronic emitters effectively excite all polarizations
and orientations of the electromagnetic field.",1311.0516v1
2013-11-19,Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide,"An hour-glass shaped magnetic excitation spectrum appears to be an universal
characteristic of the high-temperature superconducting cuprates. Fluctuating
charge stripes or alternative band structure approaches are able to explain the
origin of these spectra. Recently, an hour- glass spectrum has been observed in
an insulating cobaltate, thus, favouring the charge stripe scenario. Here we
show that neither charge stripes nor band structure effects are responsible for
the hour-glass dispersion in a cobaltate within the checkerboard charge ordered
regime of La2-xSrxCoO4. The search for charge stripe ordering reflections
yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by
our phonon studies. With the observation of an hour-glass-shaped excitation
spectrum in this stripe-less insulating cobaltate, we provide experimental
evidence that the hour-glass spectrum is neither necessarily connected to
charge stripes nor to band structure effects, but instead, probably intimately
coupled to frustration and arising chiral or non-collinear magnetic
correlations.",1311.4757v2
2014-01-03,Intrinsic paramagnetism and aggregation of manganese dopants in SrTiO$_3$,"Using local-probe magnetic-characterization techniques of muon spin
relaxation ($\mu$SR) and electron spin resonance (ESR) we have investigated the
Mn-induced magnetism of the wide-bandgap perovskite SrTiO$_3$. Our results
clearly demonstrate that this diluted magnetic oxide (DMO) remains paramagnetic
down to low temperatures for both doping cases, i.e., when Mn substitutes for
Sr or Ti. In addition, both experimental techniques have unveiled that the
distribution of individual Mn$^{2+}$ and Mn$^{4+}$ ions is nonrandom, as these
ions partially aggregate into nanosized clusters.",1401.0607v2
2014-10-29,Large time-dependent coercivity and resistivity modification under sustained voltage application in a Pt/Co/AlOx/Pt junction,"The coercivity and resistivity of a Pt/Co/AlOx/Pt junction are measured under
sustained voltage application. High bias voltages of either polarity are
determined to cause a strongly enhanced, reversible coercivity modification
compared to low voltages. Time-resolved measurements show a logarithmic
development of the coercive field in this regime, which continues over a period
as long as thirty minutes. Furthermore, the resistance of the dielectric
barrier is found to change strongly and reversibly on the same time scale,
suggesting an electrochemical process is taking place within the dielectric. It
is argued that the migration of oxygen vacancies at the magnet/oxide interface
could explain both the resistance variation and the enhanced electric field
effect at high voltages. A thermal fluctuation aftereffect model is applied to
account for the observed logarithmic dependence.",1410.8018v1
2014-10-31,Enhanced ferrimagnetism in auxetic NiFe2O4 in the crossover to the ultrathin film limit,"We investigate the sensitive interplay between magnetic, electronic and
structural properties in the ferrimagnetic oxide NiFe2O4. Emphasis is placed on
the impact of reduced dimensionality in the crossover from bulk-like to
ultrathin films. We observed an enhanced saturation magnetization $M_S$ for
ultrathin NiFe2O4 films on Nb-SrTiO3 (001) substrates that co-occurs with a
reduced out-of-plane lattice constant under compressive in-plane epitaxial
strain. We found a bulk-like cationic coordination of the inverse spinel
lattice independent of the NiFe2O4 film thickness -- thus ruling out a cationic
inversion that nominally could account for an enhanced $M_S$. Our study instead
uncovers a reduction of the unit cell volume, i.e. an auxetic behavior in
ultrathin NiFe2O4 films, which may result in an enhanced magnetic exchange
caused by an increased interatomic electronic localization.",1410.8782v1
2014-11-11,Mechanism of spin crossover in LaCoO3 resolved by shape magnetostriction in pulsed magnetic fields,"In the scientific description of unconventional transport properties of
oxides (spin-dependent transport, superconductivity etc.), the spin-state
degree of freedom plays a fundamental role. Because of this, temperature- or
magnetic field-induced spin-state transitions are in the focus of solid-state
physics. Cobaltites, e.g. LaCoO3, are prominent examples showing these spin
transitions. However, the microscopic nature of the spontaneous spin crossover
in LaCoO3 is still controversial. Here we report magnetostriction measurements
on LaCoO3 in magnetic fields up to 70 T to study the sharp, field-induced
transition at Hc ~ 60 T. Measurements of both longitudinal and transversal
magnetostriction allow us to separate magnetovolume and magnetodistortive
changes. We find a large increase in volume, but only a very small increase in
tetragonal distortion at Hc. The results, supported by electronic energy
calculations by the configuration interaction cluster method, provide
compelling evidence that above Hc LaCoO3 adopts a correlated low spin/high spin
state.",1411.2757v1
2014-11-12,Observation of transient superconductivity at the LaAlO$_3$/SrTiO$_3$ interface,"We report the observation of a magnetic field assisted transient
superconducting state in the two dimensional electron gas existing at the
interface of LaAlO$_3$/SrTiO$_3$ heterostructures. This metastable state
depends critically on the density of charge carriers in the system. It appears
concomitantly with a Lifshitz transition as a consequence of the interplay
between ferromagnetism and superconductivity and the finite relaxation time of
the in-plane magnetization. Our results clearly demonstrate the inherently
metastable nature of the superconducting state competing with a magnetic order
in these systems. The co-existence of superconductivity and ferromagnetism in
the conducting electronic layer formed at the interface of insulating oxides
has thrown up several intriguing and as yet unanswered questions. An open
question in this field is the energetics of the interplay between these two
competing orders and the present observation goes a long way in understanding
the underlying mechanism.",1411.3103v2
2015-04-11,Magnetic Nanorods Confined in a Lamellar Lyotropic Phase,"The dilute lamellar phase of the nonionic surfactant C$_{12}$EO$_5$ was doped
with goethite (iron oxide) nanorods up to a fraction of 5 vol. %. The
interaction between the inclusions and the host phase was studied by polarized
optical microscopy (with or without an applied magnetic field) and by
small-angle X-ray scattering. We find that, when the orientation of the
nanorods is modified using the magnetic field, the texture of the lamellar
phase changes accordingly; one can thus induce a homeotropic-planar
reorientation transition. On the other hand, the lamellar phase induces an
attractive interaction between the nanorods. In more concentrated lamellar
phases (under stronger confinement) the particles form aggregates. This
behavior is not encountered for a similar system doped with spherical
particles, emphasizing the role of particle shape in the interaction between
doping particles and the host phase.",1504.02879v1
2015-06-25,Multi-band theory of superconductivity at the LaAlO$_3$/SrTiO$_3$ interface,"We present a multi-band model for superconductivity at the metallic interface
between insulating oxides LaAlO$_3$ and SrTiO$_3$ (001). Using a
self-consistent Bogoliubov-de Gennes theory, formulated with the realistic
bands at the interface, we investigate the spin-singlet and spin-triplet
pairings in intra-band and inter-band channels. We find that the Rashba and
atomic spin-orbit interactions at the interface induce singlet pairing in the
inter-band channel and triplet pairing in both the intra-band and inter-band
channels when the pairing amplitude in the singlet intra-band channel is
finite. The gate-voltage variation of superconductivity is resolved in
different pairing channels, compared with experimental results and found to
match quite well. Interestingly, an enhancement of the superconducting
transition temperature by external in-plane magnetic field is found revealing
the existence of a hidden superconducting state above the observed one. As the
interface is known to possess high level of inhomogeneity, we explore the role
of non-magnetic disorder incorporating thermal phase fluctuations by using a
Monte-Carlo method. We show that even after the transition to the
non-superconducting phase, driven by temperature or magnetic field, the
interface possesses localized Cooper pairs whose signature was observed in
previous experiments.",1506.07841v1
2015-08-06,Odd-parity magnetoresistance in pyrochlore iridate thin films with broken time-reversal symmetry,"A new class of materials termed topological insulators have been intensively
investigated due to their unique Dirac surface state carrying dissipationless
edge spin currents. Recently, it has been theoretically proposed that the three
dimensional analogue of this type of band structure, the Weyl Semimetal phase,
is materialized in pyrochlore oxides with strong spin-orbit coupling,
accompanied by all-in-all-out spin ordering. Here, we report on the fabrication
and magnetotransport of Eu2Ir2O7 single crystalline thin films. We reveal that
one of the two degenerate all-in-all-out domain structures, which are connected
by time-reversal operation, can be selectively formed by the polarity of the
cooling magnetic field. Once formed, the domain is robust against an oppositely
polarised magnetic field, as evidenced by an unusual odd field dependent term
in the magnetoresistance and an anomalous term in the Hall resistance. Our
findings pave the way for exploring the predicted novel quantum transport
phenomenon at the surfaces/interfaces or magnetic domain walls of pyrochlore
iridates.",1508.01318v1
2015-09-10,Ultrafast cooling and heating scenarios for the laser induced phase transition in CuO,"The multiferroic compound CuO exhibits low temperature magnetic properties
similar to antiferromagnetic iron oxides, while the electronic properties have
much more in common with the high $T_c$ cuprate superconductors. This suggests
novel possibilities for the ultrafast optical excitation of magnetism. On the
basis on atomistic spin dynamics simulations, we study the effect of
phonon-assisted multimagnon absorption and photodoping on the spin dynamics in
the vicinity of the first-order phase transition from collinear to spin-spiral
magnetic order. Similar as in recent experiments, we find that for both
excitations the phase transition can proceed on the picosecond timescale.
Interestingly, however, these excitation mechanisms display very distinct
dynamics. Following photodoping, the spin system first cools down on sub-ps
timescales, which we explain as an ultrafast magnetocaloric effect. Opposed to
this, following phonon-assisted multimagnon excitation the spin systems rapidly
heats up and subsequently evolves to the noncollinear phase even under the
influence of isotropic exchange interactions alone.",1509.03202v2
2015-11-01,Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review,"Spin Hall effect and its inverse provide essential means to convert charge to
spin currents and vice versa, which serve as a primary function for spintronic
phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck
effect. These effects can oscillate magnetization or detect a thermally
generated spin splitting in the chemical potential. Importantly this conversion
process occurs via the spin-orbit interaction, and requires neither magnetic
materials nor external magnetic fields. However, the spin Hall angle, i.e., the
conversion yield between the charge and spin currents, depends severely on the
experimental methods. Here we discuss the spin Hall angle and the spin
diffusion length for a variety of materials including pure metals such as Pt
and Ta, alloys and oxides determined by the spin absorption method in a lateral
spin valve structure.",1511.00332v1
2015-11-05,Interface control of electronic transport across the magnetic phase transition in SrRuO_3/SrTiO_3 heterointerface,"The emerging material class of complex-oxides, where manipulation of physical
properties lead to new functionalities at their heterointerfaces, is expected
to open new frontiers in Spintronics. For example, SrRuO_3 is a promising
material where external stimuli like strain, temperature and structural
distortions control the stability of electronic and magnetic states, across its
magnetic phase transition, useful for Spintronics. Despite this, not much has
been studied to understand such correlations in SrRuO_3. Here we explore the
influence of electron-lattice correlation to electron-transport, at interfaces
between SrRuO_3 and Nb:SrTiO_3 across its ferromagnetic transition, using a
nanoscale transport probe and first-principles calculations. We find that the
geometrical reconstructions at the interface and hence modifications in
electronic structures dominate the transmission across its ferromagnetic
transition, eventually flipping the charge-transport length-scale in SrRuO_3.
This approach can be easily extended to other devices where competing ground
states can lead to different functional properties across their
heterointerfaces.",1511.01933v1
2016-01-22,Micrometer-scale ballistic transport of electron pairs in LaAlO3/SrTiO3 nanowires,"High-mobility complex-oxide heterostructures and nanostructures offer new
opportunities for extending the paradigm of quantum transport beyond the realm
of traditional III-V or carbon-based materials. Recent quantum transport
investigations with LaAlO$_3$/SrTiO$_3$-based quantum dots have revealed the
existence of a strongly correlated phase in which electrons form spin-singlet
pairs without becoming superconducting. Here we report evidence for
micrometer-scale ballistic transport of electron pairs in quasi-one-dimensional
(quasi-1D) LaAlO$_3$/SrTiO$_3$ nanowire cavities. In the paired phase,
Fabry-Perot-like quantum interference is observed, in sync with conductance
oscillations observed in the superconducting regime (at zero magnetic field).
Above a critical magnetic field $B_p$, electron pairs unbind and conductance
oscillations shift with magnetic field. These experimental observations extend
the regime of ballistic electronic transport to strongly correlated phases.",1601.06053v1
2016-02-01,All-in-all-out magnetic domain wall conduction in pyrochlore iridate heterointerface,"Pyrochlore oxides possessing ""all-in-all-out"" spin ordering have attracted
burgeoning interest as a rich ground of emergent states. This ordering has two
distinct types of magnetic domains (all-in-all-out or all-out-all-in) with
broken time-reversal symmetry, and a non-trivial metallic surface state has
been theoretically demonstrated to appear at their domain wall. Here, we report
on observation of this metallic conduction at the single
all-in-all-out/all-out-all-in magnetic domain wall formed at the
heterointerface of two pyrochlore iridates. By utilizing different
magnetoresponses of them with different lanthanide ions, the domain wall is
controllably inserted at the heterointerface, the surface state being detected
as anomalous conduction enhancement with a ferroic hysteresis. Our
establishment paves the way for further investigation and manipulation of this
new type of surface transport.",1602.00450v1
2016-02-20,Effect of disorder on the dimer transition of the honeycomb-lattice compound Li$_{2}$RuO$_3$,"We report the dependence of magnetic properties on the crystalline disorder
in Li$_{2}$RuO$_3$ with Ru honeycomb lattice. This oxide exhibits
unconventional Ru-dimer transition below $T_\text{d} \sim$ 540 K. We
demonstrate that the cell parameters, related to the coherence of the dimer
formation, are strongly dependent on the synthesis procedure. We show that the
magnetic behavior at the dimer transition is closely related to the lattice
parameters. In particular, we revealed that samples with well-ordered dimers
exhibit a first-order magnetic transition with the onset exceeding 550~K,
higher than that reported previously. We discuss possible dimer configurations
leading to this magneto-lattice coupling.",1602.06396v1
2016-02-27,Quantum topological Hall effect and noncoplanar antiferromagnetism in K$_{0.5}$RhO$_2$,"Quantum anomalous Hall (QAH) phase is a two-dimensional bulk ferromagnetic
insulator with a nonzero Chern number in presence of spin-orbit coupling (SOC)
but absence of applied magnetic fields. Associated metallic chiral edge states
host dissipationless current transport in electronic devices. This intriguing
QAH phase has recently been observed in magnetic impurity-doped topological
insulators, {\it albeit}, at extremely low temperatures. Based on
first-principles density functional calculations, here we predict that layered
rhodium oxide K$_{0.5}$RhO$_2$ in noncoplanar chiral antiferromagnetic state is
an unconventional three-dimensional QAH insulator with a large band gap and a
Neel temperature of a few tens Kelvins. Furthermore, this unconventional QAH
phase is revealed to be the exotic quantum topological Hall effect caused by
nonzero scalar spin chirality due to the topological spin structure in the
system and without the need of net magnetization and SOC.",1602.08553v1
2016-02-27,Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites,"We investigate a series of manganese oxides, the
La0.225Pr0.4(Ca1-xSrx)0.375MnO3 system. The x = 0 sample is a prototype
compound for the study of phase separation in manganites, where ferromagnetic
and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+
gradually turns the system into a homogeneous ferromagnet. Our results show
that the material structure plays a major role in the observed magnetic
properties. On cooling, at temperatures below 100 K, a strong contraction of
the lattice is followed by an increase in the magnetization. This is observed
both through thermal expansion and magnetostriction measurements, providing
distinct evidence of magneto-elastic coupling in these phase separated
compounds.",1602.08597v3
2016-03-21,Ferrimagnetic ordering and spin entropy of field-dependent intermediate spins in Na0.82CoO2,"The peculiar field-dependent magnetism of Na0.82CoO2 has been investigated
through an analysis of its DC and AC spin susceptibilities. To account for the
easily activated narrow b2g-a1g gap of the crystal field for Co in the cobalt
oxide layer, the spin-state transition of Co3+ (3d6) between the low spin (LS)
state b2g^2-a1g^0 of S=0 and the intermediate spin (IS) state b2g^1-a1g^1 of
S=1 is thus seen as thermally activated and exhibits a Boltzmann distribution.
The IS state of Co3+ within each sqrt(13a) hexagonal superlattice formed by the
S=1/2 state of the Co4+ ions appears randomly within each supercell and shows
significant temperature and field dependence. The magnetic field is found to
assist in pinning down the thermally activated state of Co3+ and swings the
Boltzmann distribution weight toward a higher fraction of the IS state. The
field dependence of the in-plane magnetic moment from the added number of S=1
spins is used to explain the origin of A-type antiferromagnetic (AF) ordering,
particularly that the ferromagnetic (FM)-like behavior below TN at low field is
actually a ferrimagnetic IS spin ordering of Co3+.",1603.06451v1
2016-04-12,High field magneto-transport in two-dimensional electron gas LaAlO3/SrTiO3,"Transport properties of the complex oxide LaAlO3/SrTiO3 interface are
investigated under high magnetic field (55T). By rotating the sample with
respect to the magnetic field, the two-dimensional nature of charge transport
is clearly established. Small oscillations of the agnetoresistance with altered
periodicity are observed when plotted versus inverse magnetic field. We
attribute this effect to Rashba spin-orbit coupling which remains consistent
with large negative magnetoresistance when the field is parallel to the sample
plane. A large inconsistency between the carrier density extracted from
Shubnikov-de Haas analysis and from the Hall effect is explained by the
contribution to transport of at least two bands with different mobility.",1604.03451v1
2017-02-17,An ultra-sensitive and wideband magnetometer based on a superconducting quantum interference device,"The magnetic field noise in superconducting quantum interference devices
(SQUIDs) used for biomagnetic research such as magnetoencephalography or
ultra-low-field nuclear magnetic resonance is usually limited by instrumental
dewar noise. We constructed a wideband, ultra-low noise system with a 45 mm
diameter superconducting pick-up coil inductively coupled to a current sensor
SQUID. Thermal noise in the liquid helium dewar is minimized by using
aluminized polyester fabric as superinsulation and aluminum oxide strips as
heat shields, respectively. With a magnetometer pick-up coil in the center of
the Berlin magneti- cally shielded room 2 (BMSR2) a noise level of around 150
aT Hz$^{-1/2}$ is achieved in the white noise regime between about 20 kHz and
the system bandwidth of about 2.5 MHz. At lower frequencies, the resolution is
limited by magnetic field noise arising from the walls of the shielded room.
Modeling the BMSR2 as a closed cube with continuous \mu-metal walls we can
quantitatively reproduce its measured field noise.",1702.05428v1
2017-08-29,"Structural, magnetic, and electronic properties of GdTiO3 Mott insulator thin films grown by pulsed laser deposition","We report on the optimization process to synthesize epitaxial thin films of
GdTiO3 on SrLaGaO4 substrates by pulsed laser deposition. Optimized films are
free of impurity phases and are fully strained. They possess a magnetic Curie
temperature TC = 31.8 K with a saturation magnetization of 4.2 muB per formula
unit at 10 K. Transport measurements reveal an insulating response, as
expected. Optical spectroscopy indicates a band gap of 0.7 eV, comparable to
the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of
perovskite materials for the design of emergent strongly correlated states at
oxide interfaces using a versatile growth technique such as pulsed laser
deposition.",1708.08785v1
2018-04-17,Emergent Magnetism at the 3$d$-5$d$ Interface: SrMnO$_3/$SrIrO$_3$,"Recent experiments have found new magnetic behaviors, which are different
from the parent bulk materials, at the interfaces between 3$d$ and 5$d$ oxides
such as SrMnO$_3$ (SMO) and SrIrO$_3$ (SIO). The system is of considerable
interest due to the strong spin-orbit coupling in the 5$d$ materials on one
hand and the double exchange physics in SMO on the other, which belongs to the
class of the colossal magnetoresistive (CMR) manganites. In order to gain
insight into the physics of the system, we have performed density-functional
studies on a selected interface structure, viz., the (SMO)$_1$(SIO)$_1$
superlattice, which has been experimentally grown and studied. Our
density-functional results show that the interfacial magnetism is controlled by
a net charge transfer at the interface from the SIO to the SMO side, turning
both of them into ferromagnetic metal from the original antiferromagnetic
insulating state in the bulk. The transferred electrons to the SMO side make it
ferromagnetic through the Anderson-Hasegawa double exchange interaction, while
the SIO part becomes ferromagnetic due to the doping of the half-filled
Mott-Hubbard insulator as suggested by the Nagaoka Theorem. Our results are
discussed in the context of the experiments for the same structure.",1804.06381v1
2018-11-06,Skew scattering dominated anomalous Nernst effect in monovalent cation doped bulk La1-xNaxMnO3,"We report the anomalous Nernst effect (ANE), i.e. creation of electrical
voltage transverse to the direction of applied temperature gradient and
magnetic field in bulk samples of La1-xNaxMnO3 (x = 0.02, 0.05, 0.1 and 0.3)
whose ferromagnetic Cure temperature(TC) varies from 251 K for x = 0.02 to 310
K for x = 0.3. We measured both the magnetic field and temperature dependences
of ANE. While ANE is negligible much above TC, it increases rapidly at TC and
exhibits a peak just below it. The field dependence of ANE closely follows
magnetization. The maximum value of ANE at TC increases from x = 0.02 to 0.1,
but decreases significantly for x = 0.3. Besides ANE, we also measured dc
resistivity and longitudinal Seebeck coefficient as a function of temperature
and used these data to analyze our results. Our data analysis indicates that
skew scattering is the main source of the ANE in these oxides.",1811.02432v1
2018-11-14,Intercalated Rare-Earth Metals under Graphene on SiC,"Intercalation of rare earth metals ($RE$ = Eu, Dy, and Gd) is achieved by
depositing the $RE$ metal on graphene that is grown on silicon-carbide (SiC)
and by subsequent annealing at high temperatures to promote intercalation. STM
images of the films reveal that the graphene layer is defect free and that each
of the intercalated metals has a distinct nucleation pattern. Intercalated Eu
forms nano-clusters that are situated on the vertices of a Moir{\`e} pattern,
while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic
circular dichroism (XMCD) measurements of intercalated films reveal the
magnetic properties of these $RE$'s nano-clusters. Furthermore, field
dependence and temperature dependence of the magnetic moments extracted from
the XMCD show paramagnetic-like behaviors with moments that are generally
smaller than those predicted by the Brillouin function. XMCD measurements of
$RE$-oxides compared with those of the intercalated $RE$'s under graphene after
exposure to air for months indicate that the graphene membranes protect these
intercalants against oxidation.",1811.06111v1
2014-03-03,High-energy spin and charge excitations in electron-doped copper oxide superconductors,"The evolution of electronic (spin and charge) excitations upon carrier doping
is an extremely important issue in superconducting layered cuprates and the
knowledge of its asymmetry between electron- and hole-dopings is still
fragmentary. Here we combine x-ray and neutron inelastic scattering
measurements to track the doping dependence of both spin and charge excitations
in electron-doped materials. Copper L3 resonant inelastic x-ray scattering
spectra show that magnetic excitations shift to higher energy upon doping.
Their dispersion becomes steeper near the magnetic zone center and deeply mix
with charge excitations, indicating that electrons acquire a highly itinerant
character in the doped metallic state. Moreover, above the magnetic
excitations, an additional dispersing feature is observed near the
{\Gamma}-point, and we ascribe it to particle-hole charge excitations. These
properties are in stark contrast with the more localized spin-excitations
(paramagnons) recently observed in hole-doped compounds even at high
doping-levels.",1403.0283v1
2016-11-04,The skyrmion switch: turning magnetic skyrmion bubbles on and off with an electric field,"Nanoscale magnetic skyrmions are considered as potential information carriers
for future spintronics memory and logic devices. Such applications will require
the control of their local creation and annihilation, which involves so far
solutions that are either energy consuming or difficult to integrate. Here we
demonstrate the control of skyrmion bubbles nucleation and annihilation using
electric field gating, an easily integrable and potentially energetically
efficient solution. We present a detailed stability diagram of the skyrmion
bubbles in a Pt/Co/oxide trilayer and show that their stability can be
controlled via an applied electric field. An analytical bubble model, with the
Dzyaloshinskii-Moriya interaction imbedded in the domain wall energy, account
for the observed electrical skyrmion switching effect. This allows us to unveil
the origin of the electrical control of skyrmions stability and to show that
both magnetic dipolar interaction and the Dzyaloshinskii-Moriya interaction
play an important role in the skyrmion bubble stabilization.",1611.01453v4
2016-11-29,Cluster superconductivity in the magnetoelectric Pb(Fe1/2Sb1/2)O3 ceramics,"We report the observation of cluster (local) superconductivity in the
magnetoelectric Pb(Fe1/2Sb1/2)O3 ceramics prepared at a hydrostatic pressure of
6 GPa and temperatures 1200-1800 K to stabilize the perovskite phase. The
superconductivity is manifested by an abrupt drop of the magnetic
susceptibility at the critical temperature TC 7 K. Both the magnitude of this
drop and TC decrease with magnetic field increase. Similarly, the low-field
paramagnetic absorption measured by EPR spectrometer drops significantly below
TC as well. The observed effects and their critical magnetic field dependence
are interpreted as manifestation of the superconductivity and Meissner effect
in metallic Pb nanoclusters existing in the ceramics. Their volume fraction and
average size were estimated as 0.1-0.2% and 140-150 nm, respectively. The
superconductivity related effects disappear after oxidizing annealing of the
ceramics.",1611.09895v1
2017-01-31,SANS contrast variation study of magnetoferritin structure at various iron loading,"Magnetoferritin, a synthetic derivate of iron storage protein - ferritin, has
been synthesized with different iron oxide loading values. Small-angle neutron
scattering experiments were applied to study the structure of magnetoferritin
solutions using contrast variation method by varying the light to heavy water
ratio of the solvent. Higher iron loading leads to increasing of the neutron
scattering length density of magnetoferritin and also to the increase of the
polydispersity of complexes. The formation of the magnetic core and the
variation of the protein shell structure upon iron loading are concluded.",1701.09174v1
2008-07-24,Chemical functionalization of graphene with defects,"Defects change essentially not only electronic but also chemical properties
of graphene being centers of its chemical activity. Their functionalization is
a way to modify electronic and crystal structure of graphene which may be
important for graphene-based nanoelectronics. Using hydrogen as an example, we
have simulated a chemistry of imperfect graphene for a broad class of defects
(Stone-Wales defects, bivacancy, nitrogen substitution impurity, and zigzag
edges) by density functional calculations. We have studied also an effect of
finite width of graphene nanoribbons on their chemical properties. It is shown
that magnetism at graphene edges is fragile with respect to oxidation and,
therefore, a chemical protection of the graphene edges may be required for
application of graphene in spintronics. At the same time, hydrogenation of the
Stone-Wales defects may be a perspective way to create magnetic carbon.",0807.3855v2
2011-11-15,Origin of ferroelectricity in high-$T_c$ magnetic ferroelectric CuO,"Cupric oxide is a unique magnetic ferroelectric material with a transition
temperature significantly higher than the boiling point of liquid nitrogen.
However, the mechanism of high-T$_c$ multiferroicity in CuO remains puzzling.
In this paper, we clarify the mechanism of high-T$_c$ multiferroicity in CuO,
using combined first-principles calculations and an effective Hamiltonian
model. We find that CuO contains two magnetic sublattices, with strong
intrasublattice interactions and weakly frustrated intersublattice
interactions, which may represent one of the main reasons for the high ordering
temperature of the compound. The weak spin frustration leads to incommensurate
spin excitations that dramatically enhance the entropy of the mutliferroic
phase and eventually stabilize that phase in CuO.",1111.3414v2
2014-06-20,Evidence for spin-triplet superconducting correlations in metal-oxide heterostructures with non-collinear magnetization,"Heterostructures composed of ferromagnetic La0.7Sr0.3MnO3, ferromagnetic
SrRuO3, and superconducting YBa2Cu3Ox were studied experimentally. Structures
of composition Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3Ox were prepared by pulsed laser
deposition, and their high quality was confirmed by X-ray diffraction and
reflectometry. A non-collinear magnetic state of the heterostructures was
revealed by means of SQUID magnetometry and polarized neutron reflectometry. We
have further observed superconducting currents in mesa-structures fabricated by
deposition of a second superconducting Nb layer on top of the heterostructure,
followed by patterning with photolithography and ion-beam etching. Josephson
effects observed in these mesa-structures can be explained by the penetration
of a triplet component of the superconducting order parameter into the magnetic
layers.",1406.5442v1
2015-12-01,Nonequilibrium low temperature phase in pyrochlore iridate Y$_2$Ir$_2$O$_7$: Possibility of glass-like dynamics,"Geometrical frustration and spin-orbit coupling effect together play vital
role to influence properties in pyrochlore based iridium oxides. Here we have
investigated detailed structural, magnetic, thermodynamic and transport
properties of pyrochlore iridate Y$_2$Ir$_2$O$_7$. Magnetization data show
onset of magnetic irreversibility around temperature $T_{irr}$ $\sim$ 160 K,
however, no sign of long-range type ferromagnetic ordering is observed below
$T_{irr}$. Specific heat data show no visible anomaly across $T_{irr}$, and the
analysis of data indicate sizable density of states across Fermi level.
Temperature dependent x-ray diffraction measurements show no change in
structural symmetry down to low temperature. The material, on the other hand,
shows significant relaxation and aging behavior similar to glassy dynamics. The
electronic charge transport in this highly insulating system is found to follow
power law dependence with temperature. The material shows negative
magnetoresistance which is explained with quantum interference effect.",1512.00233v1
2015-12-18,Exchange Bias and Bistable Magneto-Resistance States in Amorphous TbFeCo thin Films,"Amorphous TbFeCo thin films sputter deposited at room temperature on
thermally oxidized Si substrate are found to exhibit strong perpendicular
magnetic anisotropy (PMA). Atom probe tomography (APT), scanning transmission
electron microscopy (STEM), and energy dispersive spectroscopy (EDS) mapping
have revealed two nanoscale amorphous phases with different Tb atomic
percentages distributed within the amorphous film. Exchange bias accompanied by
bistable magneto-resistance states has been uncovered near room temperature by
magnetization and magneto-transport measurements. The exchange anisotropy
originates from the exchange interaction between the ferrimagnetic and
ferromagnetic components corresponding to the two amorphous phases. This study
provides a platform for exchange bias and magneto-resistance switching using
single-layer amorphous ferrimagnetic thin films that require no epitaxial
growth.",1512.06103v1
2017-06-07,PbTi1-xPdxO3: A New Room-temperature Magnetoelectric Multiferroic Device Material,"There have been a large number of papers on bismuth ferrite (BiFeO3) over the
past few years, trying to exploit its room-temperature magnetoelectric
multiferroic properties. Although these are attractive, BiFeO3 is not the ideal
multiferroic, due to weak magnetization and the difficulty in limiting leakage
currents. Thus there is an ongoing search for alternatives, including such
materials as gallium ferrite (GaFeO3). In the present work we report a
comprehensive study of the perovskite PbTi1-xPdxO3 with 0 < x < 0.3. Our study
includes dielectric, impedance and magnetization measurements, conductivity
analysis and study of crystallographic phases present in the samples with
special attention paid to minor phases, identified as PdO, PbPdO2, and Pd3Pb.
The work is remarkable in two ways: Pd is difficult to substitute into ABO3
perovskite oxides (where it might be useful for catalysis), and Pd is magnetic
under only unusual conditions (under strain or internal electric fields). The
new material, as a PZT derivative, is expected to have much stronger
piezoelectric properties than BiFeO3.",1706.02194v1
2017-06-19,Spin Hall effect from hybridized 3$d$-4$p$ orbitals,"Electrical manipulation of magnetization by spin-orbit torque (SOT) has shown
promise for realizing reliable magnetic memories and oscillators. To date, the
generation of transverse spin current and SOT, whether it is of spin Hall
effect (SHE), Rashba-Edelstein effect or spin-momentum locking origin, relies
primarily on materials or heterostructures containing 5$d$ or 6$p$ heavy
elements with strong spin-orbit coupling. Here we show that a paramagnetic CoGa
compound possesses large enough spin Hall angle to allow robust SOT switching
of perpendicularly-magnetized ferrimagnetic MnGa films in CoGa/MnGa/Oxide
heterostructures. The spin Hall efficiency estimated via spin Hall
magnetoresistance and harmonic Hall measurements is +0.05$\pm$0.01, which is
surprisingly large for a system that does not contain any heavy metal element.
First-principles calculations corroborate our experimental observations and
suggest that the hybridized Co 3$d$ - Ga 4$p$ orbitals along R-X in the
Brillouin zone is responsible for the intrinsic SHE. Our results suggest that
efficient spin current generation can be realized in intermetallic by alloying
a transition metal with a $p$-orbital element and by Fermi level tuning.",1706.05846v1
2017-10-19,"Structural, Electrical, and Magnetic Properties of La2Ni1.5Mn0.5O6 double perovskites","Among multifunctional double perovskite oxides, La2NiMnO6 has recently drawn
significant attention due to its importance both in terms of understanding of
fundamental physics and potential for device applications. The relative
alteration in Ni:Mn ratio strongly influences the structural, magnetic and
electrical properties of La2NiMnO6. In the present study, La2Ni1.5Mn0.5O6
sample with Ni:Mn = 3:1 ratio has been prepared using sol-gel method and
modifications of the above physical properties from that of a stiochiometric
sample of La2NiMnO6 are discussed. Rietveld analysis of X-ray diffraction data
shows that La2Ni1.5Mn0.5O6 samples belong to a major monoclinic structural
phase (P21/n), with partially disordered arrangement of Ni and Mn ions.
Magnetic characterization and X-ray absorption near edge structure analysis
reveal ferromagnetic ordering around 260 K between Ni2+ and Mn4+ ions while
spin glass like behavior is revealed at ~45 K. Semiconducting nature of the
sample was confirmed from temperature dependent resistivity measurements as
well as from the I-V characteristics measured at room temperature.",1710.07091v2
2018-10-15,Realizing Magnetoelectric Coupling with Hydroxide as a Knob,"Materials with a coexistence of magnetic and ferroelectric order (i.e.,
multiferroics) provide an efficient route for the control of magnetism by
electric fields. Unfortunately, a long-sought room temperature multiferroic
with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic)
orderings is still lacking. Here, we propose that hydrogen intercalation in
antiferromagnetic transition metal oxides is a promising way to realize
multiferroics with strong magnetoelectric coupling. Taking brownmillerite
SrCoO2.5 as an example, we show that hydrogen intercalated SrCoO2.5 displays
strong ferrimagnetism and large electric polarization in which the hydroxide
acts as a new knob to simultaneously control the magnetization and polarization
at room temperature. We expect that ion intercalation will become a general way
to design magnetoelectric and spintronic functional materials.",1810.06357v1
2018-10-20,Evidence for Intra-Unit Cell Magnetism in Superconducting Cuprates: a Technical Assessment,"Intra unit cell (IUC) magnetic order observed by polarized neutron
diffraction (PND) is one of the hallmarks of the pseudogap state of
high-temperature copper oxide superconductors. This experimental observation,
usually interpreted as a result of loop currents, has been recently challenged
based on lower statistics data. We here address the crucial issue of
polarization inhomogeneities in the neutron beams showing that the original
data had a much better reproducibilty. Within these technical limitations, we
here propose a self-consistent analysis that potentially solves the
controversy. We show that all the reported PND experiments in superconducting
cuprates are actually compatible with the existence of an IUC magnetism.",1810.08779v1
2019-06-18,Indirect Chiral Magnetic Exchange through Dzyaloshinskii-Moriya--Enhanced RKKY Interactions in Manganese Oxide Chains on Ir(100),"Ruderman-Kittel-Kasuya-Yosida interaction even if their wave functions lack
direct overlap. Theory predicts that spin-orbit scattering leads to a
Dzyaloshinskii-Moriya type enhancement of this indirect exchange interaction,
giving rise to chiral exchange terms. Here we present a combined spin-polarized
scanning tunneling microscopy, angle-resolved photoemission, and density
functional theory study of MnO$_2$ chains on Ir(100). Whereas we find
antiferromagnetic Mn--Mn coupling along the chain, the inter-chain coupling
across the non-magnetic Ir substrate turns out to be chiral with a
$120^{\circ}$ rotation between adjacent MnO$_2$ chains. Calculations reveal
that the Dzyaloshinskii-Moriya interaction results in spin spirals with a
periodicity in agreement with experiment. Our findings confirm the existence of
indirect chiral magnetic exchange, potentially giving rise to exotic phenomena,
such as chiral spin-liquid states in spin ice systems or the emergence of new
quasiparticles.",1906.07703v1
2019-07-23,FeTe$_{0.55}$Se$_{0.45}$ van der Waals Tunneling Devices,"We report on fabrication of devices integrating FeTe$_{0.55}$Se$_{0.45}$ with
other van-der-Waals materials, measuring transport properties as well as
tunneling spectra at variable magnetic fields and temperatures down to 35 mK.
Transport measurements are reliable and repeatable, revealing temperature and
magnetic field dependence in agreement with prior results, confirming that
fabrication processing does not alter bulk properties. However, cross-section
scanning transmission microscopy reveals oxidation of the surface, which may
explain a lower yield of tunneling device fabrication. We nonetheless observe
hard-gap planar tunneling into FeTe$_{0.55}$Se$_{0.45}$ through a MoS$_2$
barrier. Notably, a minimal hard gap of 0.5 meV persists up to a magnetic field
of 9 T in the $ab$ plane and 3 T out of plane. This may be the result of very
small junction dimensions, or a quantum-limit minimal energy spacing between
vortex bound states. We also observed defect assisted tunneling, exhibiting
bias-symmetric resonant states which may arise due to resonant Andreev
processes.",1907.09758v1
2019-09-10,Spin Pumping from Permalloy into Uncompensated Antiferromagnetic Co doped Zinc Oxide,"Heterostructures of Co-doped ZnO and Permalloy were investigated for their
static and dynamic magnetic interaction. The highly Co-doped ZnO is
paramagentic at room temperature and becomes an uncompensated antiferromagnet
at low temperatures, showing a narrowly opened hysteresis and a vertical
exchange bias shift even in the absence of any ferromagnetic layer. At low
temperatures in combination with Permalloy an exchange bias is found causing a
horizontal as well as vertical shift of the hysteresis of the heterostructure
together with an increase in coercive field. Furthermore, an increase in the
Gilbert damping parameter at room temperature was found by multifrequency FMR
evidencing spin pumping. Temperature dependent FMR shows a maximum in magnetic
damping close to the magnetic phase transition. These measurements also
evidence the exchange bias interaction of Permalloy and long-range ordered
Co-O-Co structures in ZnO, that are barely detectable by SQUID due to the
shorter probing times in FMR.",1909.04362v3
2019-09-12,Temperature and field evolution of site-dependent magnetism in $ε$-Fe$_2$O$_3$ nanoparticles,"8~nm epsilon-Fe2O3 nanoparticles exhibit a spin reorientation transition that
begins at 150 K which is a hallmark of this unique iron-oxide polymorph. We
find that the change from the high to low temperature magnetic structures has
been suppressed by ~50 K. At the spin reorientation temperature, a change of
the field-dependent response of the tetrahedral sites in intermediate field
strengths (0.25 - 1.5 T) indicates that a collective tetrahedral distortion
occurs to which the octahedral sites adjust, altering the magnetic anisotropy.
An abrupt step in the hyperfine parameters' temperature dependencies,
especially at 125 K for the hyperfine field associated with the Fe4 tetrahedral
sites, suggests strongly a change in the superexchange pathways are responsible
for the spin reorientation.",1909.05763v1
2020-12-14,Correlation-Induced Octahedral Rotations in SrMoO$_3$,"Distortions of the oxygen octahedra influence the fundamental electronic
structure of perovskite oxides, such as their bandwidth and exchange
interactions. Utilizing a fully ab-initio methodology based on density
functional theory plus dynamical mean field theory (DFT+DMFT), we study the
crystal and magnetic structure of SrMoO$_3$. Comparing our results with DFT+$U$
performed on the same footing, we find that DFT+$U$ overestimates the
propensity for magnetic ordering, as well as the octahedral rotations, leading
to a different ground state structure. This demonstrates that structural
distortions can be highly sensitive to electronic correlation effects, and to
the considered magnetic state, even in a moderately correlated metal such as
SrMoO$_3$. Moreover, by comparing different downfolding schemes, we demonstrate
the robustness of the DFT+DMFT method for obtaining structural properties,
highlighting its versatility for applications to a broad range of materials.",2012.07871v2
2020-12-15,Advanced materials for magnetic cooling:fundamentals and practical aspects,"Over the last two decades, the research activities on magnetocalorics have
been exponentially increased leading to the discovery of a wide category of
materials including intermetallics and oxides. Even though the reported
materials were found to show excellent magnetocaloric properties on laboratory
scale, only a restricted family among them could be upscaled toward industrial
levels and implemented as refrigerants in magnetic cooling devices. On the
other hand, in the most of reported reviews, the magnetocaloric materials are
usually discussed in terms of their adiabatic temperature and entropy changes,
which is not enough to get more insight about their large scale applicability.
In this review, not only the fundamental properties of recently reported
magnetocaloric materials are discussed but also their thermodynamic performance
in functional devices. The reviewed families particularly include Gd1-xRx
alloys, LaFe13-xSix, MnFeP1-xAsx and R1-xAxMnO3 based compounds. Other relevant
practical aspects such as mechanical stability, synthesis and corrosion issues
are discussed. In addition, the intrinsic and extrinsic parameters that play a
crucial role in the control of magnetic and magnetocaloric properties are
regarded. In order to reproduce the needed magnetocaloric parameters, some
practical models are proposed. Finally, the concepts of the rotating
magnetocaloric effect and multilayered magnetocalorics are introduced.",2012.08176v1
2020-12-18,Competing magnetic orders and multipolar Weyl fermions in 227 pyrochlore iridates,"Owing to comparably strong spin-orbit coupling and Hubbard interaction,
iridium based 227 pyrochlore oxides harbor a rich confluence of competing
magnetic orders and emergent multipolar Weyl quasiparticles. Here we show that
this family of materials is predominantly susceptible toward the nucleation of
electronic noncoplanar all-in all-out (AIAO) and three-in one-out (3I1O)
orders, respectively transforming under the singlet $A_{2u}$ and triplet
$T_{1u}$ representations, supporting octupolar and dipolar Weyl fermions, and
favored by strong on-site Hubbard and nearest-neighbor ferromagnetic
interaction. Furthermore, a coplanar magnetic order generically appears as an
intermediate phase between them. This order transforms under the triplet
$T_{2u}$ representation and also hosts octupolar Weyl fermions. With the AIAO
and 3I1O phases possibly being realized in (Nd$_{1-x}$Pr$_{x}$)$_2$Ir$_2$O$_7$
when $x=0$ and 1, respectively, the intervening $T_{2u}$ order can in principle
be found at an intermediate doping ($0<x<1$) or in pressured (hydrostatic)
Nd$_2$Ir$_2$O$_7$.",2012.10442v2
2017-09-21,Structurally Triggered Metal-Insulator Transition in Rare-Earth Nickelates,"Rare-earth nickelates form an intriguing series of correlated perovskite
oxides. Apart from LaNiO3, they exhibit on cooling a sharp metal-insulator
electronic phase transition, a concurrent structural phase transition and a
magnetic phase transition toward an unusual antiferromagnetic spin order.
Appealing for various applications, full exploitation of these compounds is
still hampered by the lack of global understanding of the interplay between
their electronic, structural and magnetic properties. Here, we show from
first-principles calculations that the metal-insulator transition of nickelates
arises from the softening of an oxygen breathing distortion, structurally
triggered by oxygen-octahedra rotation motions. The origin of such a rare
triggered mechanism is traced back in their electronic and magnetic properties,
providing a united picture. We further develop a Landau model accounting for
the evolution of the metal-insulator transition in terms of the $R cations and
rationalising how to tune this transition by acting on oxygen rotation motions.",1709.07240v1
2018-03-06,Effect of charge ordering on the electrical properties and magnetoresistance of manganites,"The Monte Carlo Ferromagnetic Ising model was used to study the electrical
properties of manganese oxides due to the charge ordering phase occurring at
doping, x = 0.5. The half-doped manganites have an insulator antiferromagnetic
ground state. We calculated the internal energy, specific heat, resistivity and
the magneto-resistance, MR, with parallel and anti-parallel applied magnetic
fields. Our simulation reveals that the resistivity decreases exponentially and
the electric current increases with increasing temperature according the free
charge increase, to transport from an insulator to conductor phase. The
magnetoresistance has negative small values with parallel magnetic field but
has positive high values with unti-parallel magnetic field. The obtained
semiconductor-metal transition behavior candidates the half-doped manganites to
be very good semiconductors diode junctions.",1803.02283v1
2018-03-27,Magneto-Electric Effect in a Spin-State Transition System,"Magnetic, dielectric, and magnetoelectric properties in a spin-state
transition system are examined, motivated by the recent discovery of a
multiferroic behavior in a cobalt oxide. We construct an effective model
Hamiltonian based on the two-orbital Hubbard model, in which the spin-state
degrees of freedom in magnetic ions couple with ferroelectric-type lattice
distortions. A phase transition occurs from the high-temperature low-spin phase
to the low-temperature high-spin ferroelectric phase with accompanying an
increase of the spin entropy. The calculated results are consistent with the
experimental pressure-temperature phase diagram. We predict the magnetic-field
induced electric polarization in the low-spin paraelectric phase near the
ferroelectric phase boundary.",1803.09881v1
2018-06-06,Anomalous Antiferromagnetism in Metallic RuO$_2$ Determined by Resonant X-ray Scattering,"We studied the magnetic ordering of thin films and bulk crystals of rutile
RuO$_2$ using resonant X-ray scattering across the Ru L$_2$ absorption edge.
Combining polarization analysis and azimuthal-angle dependence of the magnetic
Bragg signal, we have established the presence of G-type antiferromagnetism in
RuO$_2$ with T$_N$ $>$ 300 K. In addition to revealing a spin-ordered ground
state in the simplest ruthenium oxide compound, the persistence of magnetic
order even in nanometer-thick films lays the ground for potential applications
of RuO$_2$ in antiferromagnetic spintronics.",1806.02036v3
2018-06-11,Giant perpendicular magnetic anisotropy in Fe/III-V nitride thin films,"Large perpendicular magnetic anisotropy (PMA) in transition metal thin films
provides a pathway for enabling the intriguing physics of nanomagnetism and
developing broad spintronics applications. After decades of searches for
promising materials, the energy scale of PMA of transition metal thin films,
unfortunately, remains only about 1 meV. This limitation has become a major
bottleneck in the development of ultradense storage and memory devices. We
discovered unprecedented PMA in Fe thin-film growth on the $(000\bar{1})$
N-terminated surface of III-V nitrides from first-principles calculations. PMA
ranges from 24.1 meV/u.c. in Fe/BN to 53.7 meV/u.c. in Fe/InN.
Symmetry-protected degeneracy between $x^2-y^2$ and $xy$ orbitals and its lift
by the spin-orbit coupling play a dominant role. As a consequence, PMA in
Fe/III-V nitride thin films is dominated by first-order perturbation of the
spin-orbit coupling, instead of second-order in conventional transition
metal/oxide thin films. This game-changing scenario would also open a new field
of magnetism on transition metal/nitride interfaces.",1806.04162v1
2018-07-25,Role of interfaces in the biased composition of TbFe(Co) thin films,"Ferrimagnetic TbFe or TbFeCo amorphous alloy thin films have been grown by
co-evaporation in ultra-high vacuum. They exhibit an out-of-plane magnetic
anisotropy up to their Curie temperature with a nucleation and propagation
reversal mechanism suitable for current induced domain wall motion. Rutherford
back scattering experiments confirmed a fine control of the Tb depth-integrated
composition within the evaporation process. However, a large set of
experimental techniques were used to evidence an interface related contribution
in such thin films as compared to much thicker samples. In particular, scanning
transmission electron microscopy experiments evidence a depth dependent
composition and perturbed top and bottom interfaces with preferential oxidation
and diffusion of terbium. Despite of that, amorphous and homogeneous alloy film
remains in a bulk-like part. The composition of that bulk-like part of the
magnetic layer, labeled as effective composition, is biased when compared with
the depth-integrated composition. The magnetic properties of the film are
mostly dictated by this effective composition, which we show changes with
different top and bottom interfaces.",1807.09570v1
2019-08-06,Spectral properties of spin-orbital polarons as a fingerprint of orbital order,"Transition metal oxides are a rich group of materials with very interesting
physical properties that arise from the interplay of the charge, spin, orbital,
and lattice degrees of freedom. One interesting consequence of this,
encountered in systems with orbital degeneracy, is the coexistence of long
range magnetic and orbital order, and the coupling between them. In this paper
we develop and study an effective spin-orbital superexchange model for $e_g^3$
systems and use it to investigate the spectral properties of a charge (hole)
injected into the system, which is relevant for photoemission spectroscopy.
Using an accurate, semi-analytical, magnon expansion method, we gain insight
into various physical aspects of these systems and demonstrate a number of
subtle effects, such as orbital to magnetic polaron crossover, the coupling
between orbital and magnetic order, as well as the orbital order driving the
system towards one-dimensional quantum spin liquid behavior. Our calculations
also suggest a potentially simple experimental verification of the character of
the orbital order in the system, something that is not easily accessible
through most experimental techniques.",1908.02232v1
2020-03-24,Electric-field-controllable high-spin SrRuO3 driven by a solid ionic junction,"Controlling magnetism and spin structures in strongly correlated systems by
using electric field is of fundamental importance but challenging. Here, a
high-spin ruthenate phase is achieved via a solid ionic chemical junction at
SrRuO3/SrTiO3 interface with distinct formation energies and diffusion barriers
of oxygen vacancies, analogue to electronic band alignment in semiconductor
heterojunction. Oxygen vacancies trapped within this interfacial SrRuO3
reconstruct Ru-4d electronic structure and orbital occupancy, leading to an
enhanced magnetic moment. Furthermore, an interfacial magnetic phase can be
switched reversibly by electric-field-rectifying oxygen migration in a
solid-state ionic gating device, providing a framework for atomic design of
functionalities in strongly correlated oxides using a way of solid chemistry.",2003.11050v1
2020-03-30,Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting,"Spin-reorientation phase transitions that involve the rotation of a
crystal$'$s magnetization have been well characterized in distorted-perovskite
oxides such as the orthoferrites. In these systems spin reorientation occurs
due to competing rare-earth and transition metal anisotropies coupled via
$f$-$d$ exchange. Here, we demonstrate an alternative paradigm for spin
reorientation in distorted perovskites. We show that the
$R_2\mathrm{CuMnMn_4O_{12}}$ (R = Y or Dy) triple A-site columnar-ordered
quadruple perovskites have three ordered magnetic phases and up to two
spin-reorientation phase transitions. Unlike the spin-reorientation phenomena
in other distorted perovskites, these transitions are independent of rare-earth
magnetism, but are instead driven by an instability towards antiferromagnetic
spin canting likely originating in frustrated Heisenberg exchange interactions,
and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.",2003.13774v1
2020-08-21,Robust anomalous metallic states and vestiges of self duality in two-dimensional granular In-InOx composites,"Many experiments investigating magnetic field tuned superconductor-insulator
transition (H-SIT), often exhibit low-temperature resistance saturation, which
is interpreted as an anomalous metallic phase emerging from a ""failed
superconductor,"" thus challenging conventional theory. Here we study a random
granular array of indium islands grown on a gateable layer of indium-oxide. By
tuning the intergrain couplings, we reveal a wide range of magnetic fields
where resistance saturation is observed, under conditions of careful
electromagnetic filtering and within a wide range of linear response. Exposure
to external broadband noise or microwave radiation is shown to strengthen the
tendency of superconductivity, where at low field a global superconducting
phase is restored. Increasing magnetic field unveils an ""avoided H-SIT,"" that
exhibits granularity-induced logarithmic divergence of the
resistance/conductance above/below that transition, pointing to possible
vestiges of the original emergent duality observed in a true H-SIT. We conclude
that anomalous metallic phase is intimately associated with inherent
inhomogeneities, exhibiting robust behavior at attainable temperatures for
strongly granular two-dimensional systems.",2008.09325v2
2020-11-06,Electrical conduction of Ti/TiOx/Ti structures at low temperatures and high magnetic fields,"We present results of electrical conduction studies of Ti/TiOx/Ti planar
structures prepared by tip-induced local anodic oxidation (LAO) of titanium
thin films. The prepared structures have shown almost linear I-V curves at
temperatures between 300 K and 30 K, and only slight deviation from linear
behaviour at lower temperatures. Electrical conductance of the structures can
be adequately explained by a two-channel model where variable range hopping
channels and metallic ones coexist in parallel, while a crossover from Mott to
Efros-Shklovskii variable-range-hopping conductivity has been observed at
decreasing temperature. The magnetoresistance of the studied structures is very
small even in magnetic fields up to 9 T. The reported electrical properties of
the structures indicate their promising applications as very low heat capacity
temperature sensors for cryogenic region and high magnetic fields.",2011.03253v1
2020-11-30,Monopole matter from magnetoelastic coupling in the Ising pyrochlore,"Ising models on a pyrochlore oxide lattice are usually associated with spin
ice materials and ""magnetic monopoles"". Ever more often effects connecting
magnetic and elastic degrees of freedom are reported on these and other related
frustrated materials. Here we extend a spin-ice Hamiltonian to include coupling
between spins and the O$^{-2}$ ions mediating superexchange; we call it the
Magnetoelastic Spin Ice model (MeSI). There has been a long search for a model
in which monopoles would spontaneously become the building blocks of new
ground-states: the MeSI Hamiltonian is such a model. In spite of its simplicity
and classical approach, it describes (both spin and oxygen lattice) the
double-layered monopole crystal observed in Tb$_2$Ti$_2$O$_7$. Remarkably, the
dipolar electric moment of single monopoles emerges as a probe for magnetism.
As an example we show that, in principle, pinch points related to Coulomb
phases could be detected in association with the O$^{-2}$-ion displacements.",2011.15017v1
2021-02-02,First-principles characterization of the magnetic properties of Cu$_2$(OH)$_3$Br,"Low dimensional spin-1/2 transition metal oxides and oxyhalides continue to
be at the forefront of research investigating nonclassical phases such as
quantum spin liquids. In this study, we examine the magnetic properties of the
oxyhalide $\text{Cu}_2\text{(OH)}_3\text{Br}$ in the botallackite structure
using first-principles density functional theory, linear spin-wave theory, and
exact diagonalization calculations. This quasi-2D system consists of
$\text{Cu}^{2+}$ $\mathrm{S} = 1/2$ moments arranged on a distorted triangular
lattice. Our exact diagonalization calculations, which rely on a
first-principles-based magnetic model, generate spectral functions consistent
with inelastic neutron scattering (INS) data. By performing computational
experiments to disentangle the chemical and steric effects of the halide ions,
we find that the dominant effect of the halogen ions is steric in the
$\text{Cu}_2\text{(OH)}_3\text{X}$ series of compounds.",2102.01542v1
2021-02-16,Magnetic phase diagram of rare-earth orthorhombic perovskite oxides,"Spin reorientation and magnetisation reversal are two important features of
the rare-earth orthorhombic provskites ($RM$O$_{3}$'s) that have attracted a
lot of attention, though their exact microscopic origin has eluded researchers.
Here, using density functional theory and classical atomistic spin dynamics we
build a general Heisenberg magnetic model that allows to explore the whole
phase diagram of the chromite and ferrite compounds and to scrutinize the
microscopic mechanism responsible for spin reorientations and magnetisation
reversals. We show that the occurrence of a magnetization reversal transition
depends on the relative strength and sign of two interactions between
rare-earth and transition-metal atoms: superexchange and Dzyaloshinsky-Moriya.
We also conclude that the presence of a smooth spin reorientation transition
between the so-called $\Gamma_4$ and the $\Gamma_2$ phases through a coexisting
region, and the temperature range in which it occurs, depends on subtle balance
of metal--metal (superexchange and Dzyaloshinsky-Moriya) and metal--rare-earth
(Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate
coexistence region occurs because the spin sublattices rotate at different
rates.",2102.08152v1
2021-03-16,Large Enhancement of Ferro-Magnetism under Collective Strong Coupling of YBCO Nanoparticles,"Light-matter strong coupling in the vacuum limit has been shown to enhance
material properties over the past decade. Oxide nanoparticles are known to
exhibit weak ferromagnetism due to vacancies in the lattice. Here we report the
700-fold enhancement of the ferromagnetism of YBa$_2$Cu$_3$O$_{7-x}$
nanoparticles under cooperative strong coupling at room temperature. The
magnetic moment reaches 0.90 $\mu_{\rm B}$/mol, and with such a high value, it
competes with YBa$_2$Cu$_3$O$_{7-x}$ superconductivity at low temperature. This
strong ferromagnetism at room temperature suggest that strong coupling is a new
tool for the development of next generations of magnetic and spintronic
nanodevices.",2103.09331v2
2021-05-19,Structural and Morphological Effect of Ti underlayer on Pt/Co/Pt Magnetic Ultra-Thin Film,"Pt(x{\AA})/Co(5{\AA})/Pt(10{\AA}) trilayer films were deposited on naturally
oxidized Si(111) substrate to investigate Ti underlayer effect on PMA. A small
amount of Ti underlayer promoted the magnetic anisotropy to a perpendicular
direction for x=8{\AA} and 10{\AA}. Both GI XRD and STM results showed that the
Ti underlayer manipulated the growth of trilayer film. The Pt particles
preferably grow the neighborhood of the Ti cluster, giving rise to a relatively
smooth layer with a fiber texture fcc (111) structure. By contrast, the absence
of Ti underlayer leads to clustered, relatively rough, and randomly oriented
nano-crystalline growth. Differences in the growth mode, especially roughness,
also appeared as intensity loss in XPS spectra due to shadowing effects. Our
results indicate that a traceable amount of underlayer can change the magnetic
anisotropy of the film by manipulating film growth.",2105.09355v1
2021-06-02,Ultrafast demagnetization in NiCo2O4 thin films probed by time-resolved microscopy,"Using a time-resolved magneto-optical Kerr effect (TR-MOKE) microscope, we
observed ultrafast demagnetization of inverse-spinel-type NiCo2O4 (NCO)
epitaxial thin films of the inverse spinel type ferrimagnet NCO with
perpendicular magnetic anisotropy. This microscope uses a pump-probe method,
where the sample is pumped at 1030 nm, and magnetic domain images are acquired
via MOKE microscopy at 515 nm (the second harmonic). We successfully observed
the dynamics of the magnetic domain of the NCO thin film via laser irradiation,
and obtained a demagnetization time constant of approximately 0.4 ps. This time
constant was significantly smaller than the large time constants reported for
other half-metallic oxides. These results, combined with the results of our
x-ray photoemission spectroscopy study, indicate that this NCO thin film is a
ferrimagnetic metal whose electronic structure deviates from the theoretically
predicted half-metallic one.",2106.01026v2
2021-06-24,Magnon Transport in the Presence of Antisymmetric Exchange in a Weak Antiferromagnet,"The Dzyaloshinskii-Moriya interaction (DMI) is at the heart of many modern
developments in the research field of spintronics. DMI is known to generate
noncollinear magnetic textures, and can take two forms in antiferromagnets:
homogeneous or inter-sublattice, leading to small, canted moments and
inhomogeneous or intra-sublattice, leading to formation of chiral structures.
In this work, we first determine the strength of the effective field created by
the DMI, using SQUID based magnetometry and transport measurements, in thin
films of the antiferromagnetic iron oxide hematite, $\alpha$-Fe$_2$O$_3$. We
demonstrate that DMI additionally introduces reconfigurability in the long
distance magnon transport in these films under different orientations of a
magnetic field. This arises as a hysteresis centred around the easy-axis
direction for an external field rotated in opposing directions whose width
decreases with increasing magnetic field as the Zeeman energy competes with the
effective field created by the DMI.",2106.12853v2
2021-09-01,Epitaxial Integration of a Perpendicularly Magnetized Ferrimagnetic Metal on a Ferroelectric oxide for Electric-Field Control,"Ferrimagnets, which contain the advantages of both ferromagnets (detectable
moments) and antiferromagnets (ultrafast spin dynamics), have recently
attracted great attention. Here we report the optimization of epitaxial growth
of a tetragonal perpendicularly magnetized ferrimagnet Mn2Ga on MgO. Electrical
transport, magnetic properties and the anomalous Hall effect (AHE) were
systematically studied. Furthermore, we successfully integrated high-quality
epitaxial ferrimagnetic Mn2Ga thin films onto ferroelectric PMN-PT single
crystals with a MgO buffer layer. It was found that the AHE of such a
ferrimagnet can be effectively modulated by a small electric field over a large
temperature range in a nonvolatile manner. This work thus demonstrates the
great potential of ferrimagnets for developing high-density and low-power
spintronic devices.",2109.00169v1
2021-10-09,Field induced spin freezing and low temperature heat capacity of disordered pyrochlore oxide Ho$_{2}$Zr$_{2}$O$_{7}$,"Spin ice materials are the model systems that have a zero-point entropy as
\textit{T} $\rightarrow$ 0 K, owing to the frozen disordered states. Here, we
chemically alter the well-known spin ice Ho$_{2}$Ti$_{2}$O$_{7}$ by replacing
Ti sites with isovalent but larger Zr ion. Unlike the Ho$_{2}$Ti$_{2}$O$_{7}$
which is a pyrochlore material, Ho$_{2}$Zr$_{2}$O$_{7}$ crystallizes in
disordered pyrochlore structure. We have performed detailed structural, ac
magnetic susceptibility and heat capacity studies on Ho$_{2}$Zr$_{2}$O$_{7}$ to
investigate the interplay of structural disorder and frustrated interactions.
The zero-field ground state exhibits large magnetic susceptibility and remains
dynamic down to 30 mK without showing Pauling's residual entropy. The dynamic
state is suppressed continuously with the magnetic field and freezing
transition evolves ($\sim$ 10 K) at a field of $\sim$ 10 kOe. These results
suggest that the alteration of chemical order and local strain in
Ho$_{2}$Ti$_{2}$O$_{7}$ prevents the development of spin ice state and provides
a new material to study the geometrical frustration based on the structure.",2110.04555v1
2021-10-25,Phonon Anomaly In 9R-Ba0.9Sr0.1MnO3,"Materials which possess coupling between different degrees of freedom such as
charge, spin, orbital and lattice are of tremendous interest due to their
potential for device applications. It has been recently realized that some of
manganite perovskite oxides show structural and ferroelectric instabilities
which may be tuned by imposing internal or external strain. Among manganite
perovskites, AMnO3 (A = Ca, Sr and Ba) are reported to be good candidates to
show spin-phonon coupling driven multiferroicity. Here, we have probed the
correlation between vibrational and magnetic properties in the 9R-type
hexagonal Ba0.9Sr0.1MnO3 (BSM10). Nine Raman active modes are observed which
are characteristic phonon modes for 9R phase. The frequency ({omega}) of an Eg
(344 cm-1) mode which is related to Mn vibrations shows anomaly with
temperature (T) manifested as a change in slope of {omega} vs T at 260 K. The
temperature-dependent magnetization of BSM10 suggests a possible
antiferromagnetic ordering at ~ 260 K. We, therefore, attribute the phonon
anomaly to spin-phonon coupling arising due to the magnetic ordering.",2110.13808v1
2021-12-18,Enhanced Tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) Magnetic Tunnel Junctions,"Spinel MgAl2O4 and family oxides are emerging barrier materials useful for
magnetic tunnel junctions (MTJs). We report large tunnel magnetoresistance
(TMR) ratios up to 429% at room temperature (RT) and 1,034% at 10 K in a
Fe/MgAl2O4/Fe(001)-based MTJ prepared using electron-beam evaporation of
Mg4Al-Ox. Resistance oscillations with a MTJ barrier thickness of 0.3-nm were
significantly enhanced compared to those of a Fe/MgO/Fe(001) MTJ, resulting in
a large TMR oscillation peak-to-valley difference of 125% at RT. The
differential conductance spectra were symmetric with bias polarity, and the
spectrum in the parallel magnetization state at low temperature demonstrate
significant peaks within broad local minima at |0.2-0.6| V, indicating improved
barrier interfaces by the Mg4Al-Ox barrier. This study demonstrates that TMR
ratios in Fe(001)-MTJs can still be improved.",2112.09910v1
2021-12-22,The Preliminary design of DC Magnet Power Supply System for ITER Static Magnetic Field Test facility,"ITER (International Thermonuclear Experimental Reactor) static magnetic field
(SMF) test facility requires a DC power supply with low voltage, high current,
and high stability. Due to the limitation ofswitching loss, there is a
contradiction between the output current capability and the output ripple.
Large output current usually leads to low switching frequency, and low
switching frequency will generate a large number of harmonics. To solve the
problems, a topology based on the interleaving parallel buck converter is used
and tested in this paper. Moreover, the topology is realized with only a small
number of switching metal-oxide-semiconductor field effect transistors
(MOSFETs). This article introduces the system design scheme and control method
in detail. The analysis of harmonic and simulation are carried out. The
validity of proposed scheme and control strategy were confirmed by experiments,
the power supply system can supply large current of 15kA and has ability of low
ripple.",2112.13669v2
2022-02-03,Unconventional interlayer exchange coupling via chiral phonons in synthetic magnetic oxide heterostructures,"Chiral symmetry breaking of phonons plays an essential role in emergent
quantum phenomena owing to its strong coupling to spin degree of freedom.
However, direct experimental evidence of the chiral phonon-spin coupling is
lacking. In this study, we report a chiral phonon-mediated interlayer exchange
interaction in atomically controlled ferromagnetic metal (SrRuO3)-nonmagnetic
insulator (SrTiO3) heterostructures. Owing to the unconventional interlayer
exchange interaction, we have observed rotation of magnetic moments as a
function of nonmagnetic insulating spacer thickness, resulting in a spin spiral
state. The chiral phonon-spin coupling is further confirmed by phonon Zeeman
effects. The existence of the chiral phonons and their interplay with spins
along with our atomic-scale heterostructure approach open a window to unveil
the crucial roles of chiral phonons in magnetic materials.",2202.01447v1
2022-03-04,Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom,"Optical trapping of magnetic Fe-oxide particles is notoriously difficult due
to their high refractive indices, not to mention high absorptivity at the
trapping infra-red wavelengths. We synthesize Fe co-doped NaYF4:Yb,Er
ferromagnetic upconversion particles that not only have refractive indices
conducive for optical trapping, but also heat less than Haematite particles at
off-resonant wavelengths. These particles are hexagonal shaped with dimensions
of the order of 3 micrometer and also bear high coercivity of 20 mT and
saturation magnetisation of 1 Am^2/kg. This enables simultaneous use of optical
trapping and magnetic forces to generate micro-manipulation in all the six
degrees of freedom of a rigid body. We also show that these particles heat
significantly when illuminated on absorption resonance at 975 nm while emitting
visible light with possible implications for fluorescence microscopy and
photothermal therapy of cancer cells.",2203.02152v2
2022-04-04,Hole-doping induced ferromagnetism in 2D materials,"Two-dimensional (2D) ferromagnetic materials are considered as promising
candidates for the future generations of spintronic devices. Yet, 2D materials
with intrinsic ferromagnetism are scarce. High-throughput first-principles
simulations are performed in order to screen 2D materials that present a
non-magnetic to a ferromagnetic transition upon hole doping. A global
evolutionary search is subsequently performed, in order to identify alternative
possible atomic structures of the eligible candidates, and 122 materials
exhibiting a hole-doping induced ferromagnetism are identified. Their energetic
and dynamic stability, as well as their magnetic properties under hole doping
are investigated systematically. Half of these 2D materials are metal halides,
followed by chalcogenides, oxides and nitrides, some of them having predicted
Curie temperatures above 300 K. The exchange interactions responsible for the
ferromagnetic order in these 2D materials are also discussed. This work not
only provides theoretical insights into hole-doped 2D ferromagnetic materials,
but also enriches the family of 2D magnetic materials for possible spintronic
applications.",2204.01551v2
2022-04-27,Magnetic molecule tunnel heterojunctions,"We characterize molecular magnet heterojunctions in which sublimated CoPc
films as thin as 5 nm are sandwiched between transparent conducting
bottom-layer indium tin oxide and top-layer soft-landing eutectic GaIn (EGaIn)
electrodes. The roughness of the cobalt phthalocyanine (CoPc) films was
determined by atomic force microscopy to be on the order of several nanometers,
and crystalline ordering of lying-down planar molecules was confirmed by X-ray
diffraction. The current-voltage (I-V) characteristics reveal the onset of a
superconducting gap at Tc = 6 K, which together with higher temperature fits to
a modified Simmons' model, provide incontrovertible evidence for direct quantum
mechanical tunneling processes through the magnetic molecules in our
heterojunctions. The voltage dependent features in the differential conductance
measurements relate to spin states of single molecules or aggregates of
molecules and should prove to be important for quantum information device
development.",2204.13152v1
2022-05-07,Interplay between the extended s-wave symmetry of the gap and the spin-orbit coupling in the low-electron concentration regime of quasi-two-dimensional superconductors,"We analyze the real-space paired state with the $\mathbf{k}$-dependent
superconducting gap in the presence of Rashba type spin-orbit coupling and
external magnetic field. We show that the $extended$ $s$-$wave$ pairing
symmetry is the most probable scenario to appear in the low-electron
concentration regime. According to our study, the van Hove singularity induced
by the spin-orbit coupling may lead to a significant enhancement of the
superconducting gap, critical temperature and critical magnetic field.
Moreover, the combined effect of the spin-orbit coupling and the external
magnetic field results in a non-zero total momentum of the Cooper pairs, which
is a characteristic feature of the so-called helical state. In such situation,
due to the C$_4$ symmetry breaking, a small $d$-$wave$ and $p$-$wave$
contributions to the pairing appear, which significantly change the character
of the helical state. The obtained results are discussed in the context of the
experimental data related with the unconventional superconducting features of
the transition metal oxide interfaces as well as the recently reported
supercurrent diode effect.",2205.03632v3
2022-06-03,Development of Ni doped SnO$_2$ Dilute magnetic oxides for electronics and spintronics applications,"We used a solid-state reaction method to prepare Sn$_{1-x}$Ni$_x$O$_2$ with
$x$ = 0, 0.05, 0.1, 0.15 polycrystalline compounds. A rutile phase with
tetragonal crystal structure was confirmed by X-ray diffraction. At room
temperature, the magnetisation study shows that the saturation magnetization
increases with Ni doping content whereas the coercive field decreases after
$x$=0.1. The spin number increases as the Ni doping concentration increases,
indicating that the incorporation of Ni into the Sn sites increases the number
of spins interacting to improve the ferromagnetic phase , which is like
saturation magnetization and coercive field.",2206.01525v1
2022-06-08,A multiferroic two-dimensional electron gas,"Multiferroics are compounds in which at least two ferroic orders coexist -
typically (anti)ferromagnetism and ferroelectricity. While magnetic order can
arise in both insulating and conducting compounds, ferroelectricity is in
principle not allowed in metals although a few two-dimensional (semi)metals
were reported to behave as ferroelectrics. Yet, the combination with magnetic
order to realize multiferroic metals remains elusive. Here, by combining x-ray
spectroscopy and magnetotransport, we show the coexistence of ferroelectricity
and magnetism in an oxide-based two-dimensional electron gas (2DEG). The data
evidence a non-volatile switching of the polar displacements and of the
anomalous Hall effect by the polarization direction, demonstrating a
magnetoelectric coupling. Our findings provide new opportunities in quantum
matter stemming from the interplay between ferroelectricity, ferromagnetism and
Rashba spin-orbit coupling in a 2DEG.",2206.03843v1
2022-10-12,Critical role of magnetic moments on lattice dynamics in YBa${}_{2}$Cu${}_{3}$O${}_{6}$,"The role of lattice dynamics in unconventional high-temperature
superconductivity is still vigorously debated. Theoretical insights into this
problem have long been prevented by the absence of an accurate first-principles
description of the combined electronic, magnetic, and lattice degrees of
freedom. Utilizing the recently constructed r$^2$SCAN density functional that
stabilizes the antiferromagnetic (AFM) state of the pristine oxide
YBa$_2$Cu$_3$O$_6$, we faithfully reproduce the experimental dispersion of key
phonon modes. We further find significant magnetoelastic coupling in numerous
high energy Cu-O bond stretching optical branches, where the AFM results
improve over the soft non-magnetic phonon bands.",2210.06569v2
2022-11-04,Tunable magnetocaloric effect and enhanced refrigerant capacity in composite-like oxide heterostructures,"We report a detailed study of the magnetocaloric effect in heterostructures
of La2NiMnO6 and La2/3Sr1/3MnO3. The shape, width and magnitude of the
temperature dependence of the magnetic entropy change ($\Delta S_{m}$) for
these multilayer samples can be tuned and controlled by changing their layout.
A large $\Delta S_{m}$ over a wide temperature range which goes beyond room
temperature is observed in all samples. We observe a temperature-independent
table-top-like $\Delta S_{m}$ over a temperature range as large as 100 K in the
trilayer samples. La2NiMnO6 double perovskite with multiple magnetic phase
transitions is the key to tuning and shaping the temperature dependence of the
magnetic entropy changes to suit the requirements of several cooling cycles.",2211.02715v1
2022-12-01,"Tuning Structural, Transport and Magnetic Properties of Epitaxial SrRuO3 through Ba-Substitution","The perovskite ruthenates (ARuO3, A = Ca, Ba, or Sr) exhibit unique
properties owing to a subtle interplay of crystal structure and electronic-spin
degrees of freedom. Here, we demonstrate an intriguing continuous tuning of
crystal symmetry from orthorhombic to tetragonal (no octahedral rotations)
phases in epitaxial SrRuO3 achieved via Ba-substitution (Sr1-xBaxRuO3 with 0 <
x < 0.7). An initial Ba-substitution to SrRuO3 not only changes the
ferromagnetic properties, but also tunes the perpendicular magnetic anisotropy
via flattening the Ru-O-Ru bond angle (to 180{\deg}), resulting in the maximum
Curie temperature and an extinction of RuO6 rotational distortions at x = 0.20.
For x > 0.2, the suppression of RuO6 octahedral rotational distortion
dominantly enhances the ferromagnetism in the system, though competing with the
impact of the RuO6 tetragonal distortion. Further increasing x > 0.2 gradually
enhances the tetragonal-type distortion, resulting in the tuning of Ru-4d
orbital occupancy and suppression of ferromagnetism. Our results demonstrate
that isovalent substitution of the A-site cations significantly and
controllably impacts both electronic and magnetic properties of perovskite
oxides.",2212.00267v2
2022-12-23,Thickness Dependent Itinerant Ferromagnetism in Ultrathin Ba-Doped SrRuO3 films,"The electronic and magnetic properties in ABO3 perovskite oxides are
extremely sensitive to lattice structure but also the dimensionality, such as
the thickness in thin film form. Here, we report the thickness-dependent
electro-magnetic properties of ultrathin epitaxially stabilized Sr1-xBaxRuO3 (x
= 0.08, 0.2) thin films on SrTiO3 (001) substrate. The results reveal that the
Ba-doping (0.08 < x < 0.20) reduces RuO6 orthorhombic distortions existing in
SrRuO3 and induces a tetragonal distortion as evidenced by out-of-plane lattice
expansion. A metal-to-insulator transition, accompanied by a ferromagnetic to
non-magnetic transition occurs with reducing film thickness from 10 to 3
unit-cell (u.c.) for both x = 0.08 and 0.2, regardless of the doping level. The
results suggest that the effects of compositional vacancies and
surface/interface contributions introduced via dimensional confinement are more
dominant than A-site chemical disorder or structural distortion for the loss of
metallicity and ferromagnetism in ultra-thin epitaxial films.",2212.12120v1
2023-02-14,MICROSTRUCTURE OF Glidcop AL-60,"Glidcop is an oxide-particle-dispersion strengthened copper composite that
has a combination of high mechanical strength and high electrical conductivity.
It has been used as a conductor for 100 T ultrahigh field pulsed magnets by the
National High Magnetic Field Laboratory, USA. In the quest for even higher
field pulsed magnets, material development is crucial. Since the mechanical
properties of a material are often determined by its micro-structure, full
characterization of the microstructure of Glidcop is necessary. In this work,
we studied the microstructure of Glidcop AL-60 using both transmission electron
microscopy (TEM) and scanning transmission electron microscopy (STEM). We
identified both alpha-Al2O3 and cubic eta-Al2O3 nanoparticles in AL-60 and
investigated their size and density distribution. The small alumina particles
eta-Al2O3 nanoparticles with typical size of 5 to 30 nm are of triangular
shape. They have had well defined crystal orientation relation-ship with the Cu
matrix. We observed dislocations pinned by the alumina nanoparticles in
cold-drawn wires. We believed that dislocation bypassing alumina particles via
Orowan looping was the main strengthening mechanism. We observed microcracks
near large particles, demonstrating the detrimental effect of large particles
in AL-60.",2302.08978v1
2023-02-22,Switchable-magnetisation planar probe MFM sensor,"We present an alternative switching-magnetization magnetic force microscopy
(SM- MFM) method using planar tip-on-chip probes. Unlike traditional
needle-like tips, the planar probe approach integrates a microdevice near the
tip apex with dedicated functionality. Its 1 mm x 1 mm planar surface paves the
way for freedom in ultra thin-film engineering and micro-/nano-tailoring for
application-oriented tip functionalization. Here, we form a microscale current
pathway near the tip end to control tip magnetisation. The chip like probe or
planar probe, was applied to study the complex magnetic behaviour of epitaxial
transition metal oxide perovskite LaMnO3, which was previously shown to behave
as complex material with domains associated with superpara-, antiferro- and
ferromagnetism. To this end we successfully imaged an inhomogeneous
distribution of weak ferromagnetic islands with a resolution better than 10 nm.",2302.11387v1
2023-03-22,Magnetic nanorods for quantitative viscosity imaging using heterodyne holography,"Many processes in microfluidics and biology are driven or affected by
viscosity. While several methods are able to measure this parameter globally
(AFM, surface acoustic waves, DLS, ...), very few can provide high resolution
viscosity images, particularly in living cells. Here, we propose to use
sub-micrometer magnetic rods to perform high resolution viscosity imaging. An
external magnetic field forces the oscillation of superparamagnetic iron oxide
nanorods. Under linearly polarized illumination, the rotation of these highly
anisotropic optical scatterers induces a blinking which is analyzed by
heterodyne holography. The spectral analysis of the rotation dynamics yields a
regime transition frequency f t from which the local viscosity is deduced.
Holography provides 3D image reconstruction and 3D superlocalization of the
nanorods, which allows super-resolved viscosity measurements. Relying on the
fast Brownian rotation of nanorods instead of their slower translation
therefore allows faster measurements and, crucially, smaller effective voxels
for viscosity determination. Viscosity imaging is demonstrated with a 0.5
{\mu}m 3 3D resolution.",2303.12545v1
2023-03-25,Muon spin relaxation and emergence of disorder-induced unconventional dynamic magnetic fluctuations in Dy$_{2}$Zr$_{2}$O$_{7}$,"The disordered pyrochlore oxide Dy$_{2}$Zr$_{2}$O$_{7}$ shows the signatures
of field-induced spin freezing with remnant zero-point spin-ice entropy at 5
kOe magnetic field. We have performed zero-field and longitudinal field Muon
spin relaxation ($\mu$SR) studies on Dy$_{2}$Zr$_{2}$O$_{7}$. Our zero field
studies reveal the absence of both long-range ordering and spin freezing down
to 62 mK. The $\mu$SR relaxation rate exhibits a temperature-independent
plateau below 4 K, indicating a dynamic ground state of fluctuating spins
similar to the well-known spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$. The
low-temperature spin fluctuations persist in the longitudinal field of 20 kOe
as well and show unusual field dependence of the relaxation rate, which is
uncommon for a spin-liquid system. Our results, combined with the previous
studies do not show any evidence of spin ice or spin glass ground state, rather
point to a disorder-induced dynamic magnetic ground state in the
Dy$_{2}$Zr$_{2}$O$_{7}$ material.",2303.14426v1
2023-03-31,Tailoring the interfacial magnetic interaction in epitaxial La$_{0.7}$Sr$_{0.3}$MnO$_3$/Sm$_{0.5}$Ca$_{0.5}$MnO$_3$ heterostructures,"Interface engineering in complex oxide heterostructures has developed into a
flourishing field as various intriguing physical phenomena can be demonstrated
which are otherwise absent in their constituent bulk compounds. Here we present
La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) / Sm$_{0.5}$Ca$_{0.5}$MnO$_3$ (SCMO) based
heterostructures showcasing the dominance of antiferromagnetic interaction with
increasing interfaces. In particular, we demonstrate that exchange bias can be
tuned by increasing the number of interfaces; while, on the other hand,
electronic phase separation can be mimicked by creating epitaxial multilayers
of such robust charge ordered antiferromagnetic (CO-AF) and ferromagnetic (FM)
manganites with increased AF nature, which otherwise would require
intrinsically disordered mixed phase materials. The origin of these phenomena
is discussed in terms of magnetic interactions between the interfacial layers
of the LSMO/SCMO. A theoretical model has been utilized to account for the
experimentally observed magnetization curves in order to draw out the complex
interplay between FM and AF spins at interfaces with the onset of charge
ordering.",2303.18054v1
2023-06-23,Electronic structure of RE1-xAxMnO3 manganite films investigated by magnetic circular dichroism spectroscopy,"Magnetic circular dichroism (MCD) spectroscopy was used to study the features
of the electronic structure of an epitaxial La0.7Ca0.3MnO3 film in the range of
1.2 - 4 eV. The study of the temperature behavior of the MCD spectra made it
possible to establish a correlation between the magnetooptical and transport
properties of the sample. The data obtained were analyzed in comparison with
MCD data for polycrystalline manganite films of various RE1-xAxMnO3
compositions. The MCD spectra of the films were compared with the spectra of
the off-diagonal component of the permittivity tensor calculated from the data
of the magneto-optical Kerr effect for films of the same composition. A unified
set of ground and excited electronic states characteristic of RE1-xAxMnO3
manganites in the visible and near infrared ranges has been identified. These
results are important for a qualitative theoretical description of the
electronic structure of strongly correlated magnetic oxides.",2306.13510v1
2024-03-13,Geometric and electronic properties of two kinds of CrO2 magnetic monolayers: D3d and D2h phases,"Due to the high magnetic coupling strength between the Cr elements, the bulk
phase CrO2 is one of several ferromagnetic oxides known to have the highest
Curie temperature. When the dimensionality of the material is reduced from 3D
to 2D, the 2D CrO2 system material is expected to maintain a high Curie
temperature. In this work, we predict two new phases of CrO2 monolayer (D3d and
D2h) by using first-principles calculations. We have found that the Curie
temperature of 2D CrO2 is much lower than that of its bulk phase, but still
remains as high as 191K, which is comparable to that of Fe2Cr2Ge6. In addition,
1L D3d-CrO2 is in the ferromagnetic state, while 1L D2h-CrO2 is in the
antiferromagnetic state. Also, the different geometric structure affects its
electrical properties: the 1L D3d-CrO2 is a half-metal while 1L D2h-CrO2 is a
semiconductor. Our studies have shown that there is a wealth of electrical and
magnetic properties in CrO2.",2403.08357v1
2020-08-31,"Structural, magnetic and electronic properties of CaBaCo4-xMxO7 (M= Fe, Zn)","The effect of substituting iron and zinc for cobalt in CaBaCo$_4$O$_7$ has
been investigated using neutron diffraction and x-ray absorption spectroscopy.
The orthorhombic distortion present in the parent compound CaBaCo$_4$O$_7$
decreases with increasing the content of either Fe or Zn. The samples
CaBaCo$_3$ZnO$_7$ and CaBaCo$_{4-x}$Fe$_x$O$_7$ with $x \leq 1.5$ are
metrically hexagonal but much better refinements in the neutron diffraction
patterns are obtained using an orthorhombic unit cell. The two types of
substitution have opposite effects on the structural and magnetic properties.
Fe atoms preferentially occupy the sites at the triangular layer. Thus, the
replacement of Co by Fe supresses the ferrimagnetic ordering and
CaBaCo$_{4-x}$Fe$_x$O$_7$ samples are antiferromagnetically ordered with a new
propagation vector k=(1/3,0,0). However, the Zn atoms prefer occupying the
Kagome layer, which is very detrimental for the long range magnetic
interactions giving rise to a magnetic glass. The oxidation state of iron and
zinc is found to be 3+ and 2+, respectively, independently of the content.
Therefore, the average Co oxidation state changes accordingly with the
Fe$^{3+}$ or Zn$^{2+}$ doping. Also, x-ray absorption spectroscopy data
confirms the different preferential occupation for both Fe and Zn cations. The
combined information obtained by neutron diffraction and x-ray absorption
spectroscopy indicates that cobalt atoms can be either in a fluctuating
Co$^{2+}$/Co$^{3+}$ valence state or, alternatively, Co$^{2+}$ and Co$^{3+}$
ions being randomly distributed in the lattice. These results explain the
occurrence of local disorder in the CoO$_4$ tetrahedra obtained by EXAFS. An
anomaly in the lattice parameters and an increase in the local disorder is
observed only at the ferrimagnetic transition for CaBaCo$_4$O$_7$ revealing the
occurrence of local magneto-elastic coupling.",2008.13649v1
2021-04-15,Active Magnetoplasmonics with Transparent Conductive Oxide Nanocrystals,"Magnetoplasmonics is highly promising to devise active optical elements:
modulating the plasmon resonance condition with magnetic field can boost the
performance of refractometric sensors and nanophotonic optical devices.
Nevertheless, real life applications are hampered by the magnetoplasmonic
trilemma: 1) a good plasmonic metal has sharp optical resonances but low
magneto-optical response; 2) a magnetic metal has strong magneto-optical
response but a very broad plasmonic resonance; 3) mixing the two components
degrades the quality of both features. To overcome the trilemma, we use a
different class of materials, transparent conductive oxide nanocrystals (NCs)
with plasmonic response in the near infrared. Although non-magnetic, they
combine a large cyclotron frequency (due to small electron effective mass) with
sharp plasmonic resonances. We benchmark the concept with F- and In- doped CdO
(FICO) and Sn-doped In2O3 (ITO) NCs to boost the magneto-optical Faraday
rotation and ellipticity, reaching the highest magneto-optical response for a
non-magnetic plasmonic material, and exceeding the performance of
state-of-the-art ferromagnetic nanostructures. The magnetoplasmonic response of
these NCs was rationalized with analytical model based on the excitation of
circular magnetoplasmonic modes. Finally, proof of concept experiments
demonstrated the superior performance of FICO NCs with respect to current state
of the art in magnetoplasmonic refractometric sensing, approaching the
sensitivity of leading localized plasmon refractometric methods with the
advantage of not requiring complex curve fitting.",2104.07772v1
2021-06-15,Low-energy spin dynamics in rare-earth perovskite oxides,"We review recent studies of spin dynamics in rare-earth orthorhombic
perovskite oxides of the type $RM$O$_3$, where $R$ is a rare-earth ion and $M$
is a transition-metal ion, using single-crystal inelastic neutron scattering
(INS). After a short introduction to the magnetic INS technique in general, the
results of INS experiments on both transition-metal and rare-earth subsystems
for four selected compounds (YbFeO$_3$, TmFeO$_3$, YFeO$_3$, YbAlO$_3$) are
presented. We show that the spectrum of magnetic excitations consists of two
types of collective modes that are well separated in energy: gapped magnons
with a typical bandwidth of $<$70 meV, associated with the
antiferromagnetically (AFM) ordered transition-metal subsystem, and AFM
fluctuations of $<$5 meV within the rare-earth subsystem, with no hybridization
of those modes. We discuss the high-energy conventional magnon excitations of
the 3$d$ subsystem only briefly, and focus in more detail on the spectacular
dynamics of the rare-earth sublattice in these materials. We observe that the
nature of the ground state and the low-energy excitation strongly depends on
the identity of the rare-earth ion. In the case of non-Kramers ions, the
low-symmetry crystal field completely eliminates the degeneracy of the
multiplet state, creating a rich magnetic field-temperature phase diagram. In
the case of Kramers ions, the resulting ground state is at least a doublet,
which can be viewed as an effective quantum spin-1/2. Equally important is the
fact that in Yb-based materials the nearest-neighbor exchange interaction
dominates in one direction, despite the three-dimensional nature of the
orthoperovskite crystal structure. The observation of a fractional spinon
continuum and quantum criticality in YbAlO$_3$ demonstrates that Kramers
rare-earth based magnets can provide realizations of various aspects of quantum
low-dimensional physics.",2106.08378v1
2022-03-22,Discovery of charge density wave in a correlated kagome lattice antiferromagnet,"A hallmark of strongly correlated quantum materials is the rich phase diagram
resulting from competing and intertwined phases with nearly degenerate ground
state energies. A well-known example is the copper oxides, where a charge
density wave (CDW) is ordered well above and strongly coupled to the magnetic
order to form spin-charge separated stripes that compete with
superconductivity. Recently, such rich phase diagrams have also been revealed
in correlated topological materials. In two-dimensional kagome lattice metals
consisting of corner-sharing triangles, the geometry of the lattice can produce
flat bands with localized electrons, non-trivial topology, chiral magnetic
order, superconductivity and CDW order. While CDW has been found in weakly
electron correlated nonmagnetic AV3Sb5 (A = K, Rb, Cs), it has not yet been
observed in correlated magnetic ordered kagome lattice metals. Here we report
the discovery of CDW within the antiferromagnetic (AFM) ordered phase of kagome
lattice FeGe. The CDW in FeGe occurs at wavevectors identical to that of
AV3Sb5, enhances the AFM ordered moment, and induces an emergent anomalous Hall
effect. Our findings suggest that CDW in FeGe arises from the combination of
electron correlations-driven AFM order and van Hove singularities-driven
instability possibly associated with a chiral flux phase, in stark contrast to
strongly correlated copper oxides and nickelates, where the CDW precedes or
accompanies the magnetic order.",2203.11467v1
2010-07-16,Magnetism and Charge Dynamics in Iron Pnictides,"In a wide variety of materials, such as copper oxides, heavy fermions,
organic salts, and the recently discovered iron pnictides, superconductivity is
found in close proximity to a magnetically ordered state. The character of the
proximate magnetic phase is thus believed to be crucial for understanding the
differences between the various families of unconventional superconductors and
the mechanism of superconductivity. Unlike the AFM order in cuprates, the
nature of the magnetism and of the underlying electronic state in the iron
pnictide superconductors is not well understood. Neither density functional
theory nor models based on atomic physics and superexchange, account for the
small size of the magnetic moment. Many low energy probes such as transport,
STM and ARPES measured strong anisotropy of the electronic states akin to the
nematic order in a liquid crystal, but there is no consensus on its physical
origin, and a three dimensional picture of electronic states and its relations
to the optical conductivity in the magnetic state is lacking. Using a first
principles approach, we obtained the experimentally observed magnetic moment,
optical conductivity, and the anisotropy of the electronic states. The theory
connects ARPES, which measures one particle electronic states, optical
spectroscopy, probing the particle hole excitations of the solid and neutron
scattering which measures the magnetic moment. We predict a manifestation of
the anisotropy in the optical conductivity, and we show that the magnetic phase
arises from the paramagnetic phase by a large gain of the Hund's rule coupling
energy and a smaller loss of kinetic energy, indicating that iron pnictides
represent a new class of compounds where the nature of magnetism is
intermediate between the spin density wave of almost independent particles, and
the antiferromagnetic state of local moments.",1007.2867v1
2019-05-06,"Nonmagnetic substitution in pyrochlore iridate Y$_2$(Ir$_{1-x}$Ti$_{x}$)$_2$O$_7$: Structure, magnetism and electronic properties","Tuning of spin-orbit coupling and electron correlation effects in pyrochlore
iridates is considered for many interesting phenomena. We have investigated the
temperature evolution of structural, magnetic and electronic properties in
doped Y$_2$(Ir$_{1-x}$Ti$_{x}$)$_2$O$_7$ ($x$ = 0.0, 0.02, 0.05, 0.10 and 0.15)
where the substitution of nonmagnetic Ti$^{4+}$ (3$d^0$) for Ir$^{4+}$ (5$d^5$)
amounts to dilution of magnetic network and tuning of these parameters in
opposite way. The system retains its original structural symmetry but local
structural parameters show an evolution with Ti content. While the magnetic
transition temperature is not largely influenced, both magnetic moment and
magnetic frustration decreases with Ti doping. Magnetic relaxation measurement
shows the parent compound Y$_2$Ir$_2$O$_7$ as well as its Ti doped analogues
are in nonequilibrium magnetic state where the magnetic relaxation rate
increases with Ti. Temperature dependent Raman measurements indicate no changes
in structural symmetry, however, across the magnetic transition temperature an
anomaly in A$_{1g}$ Raman mode is observed. Temperature dependent x-ray
diffraction data also support the Raman spectroscopy data, however, an
evolution of lattice parameters with temperature is observed. The electrical
resistivity data of Y$_2$(Ir$_{1-x}$Ti$_{x}$)$_2$O$_7$ series exhibits
insulating behavior throughout the temperature range, however, the resistivity
decreases with Ti doping. The nature of charge conduction is found to follow
power-law behavior in whole series but the validity of this model varies with
temperature. A negative magnetoresistance has been observed at low temperature
in present series which is explained with weak localized mechanism. Similar to
other Ir based oxides, a crossover from negative to positive MR has been
observed in present system.",1905.01951v1
2011-11-22,Observation of spin glass state in weakly ferromagnetic Sr$_2$FeCoO$_6$ double perovskite,"We report the observation of spin glass state in the double perovskite oxide
Sr$_{2}$FeCoO$_{6}$ prepared through sol-gel technique. Initial structural
studies using x rays reveal that the compound crystallizes in tetragonal $I
4/m$ structure with lattice parameters, $a$ = 5.4609(2) \AA and $c$ = 7.7113(7)
\AA. The temperature dependent powder x ray studies reveal no structural phase
transition in the temperature range 10 -- 300 K. However, the unit cell volume
shows an anomaly coinciding with the magnetic transition temperature thereby
suggesting a close connection between lattice and magnetism. Neutron
diffraction studies and subsequent bond valence sums analysis show that in
Sr$_{2}$FeCoO$_{6}$, the $B$ site is randomly occupied by Fe and Co in the
mixed valence states of Fe$^{3+}$/Fe$^{4+}$ and Co$^{3+}$/Co$^{4+}$. The random
occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange
interactions and in turn, for the spin glass like state in this double
perovskite which is observed as an irreversibility in temperature dependent dc
magnetization at $T_f\sim$ 75 K. Thermal hysteresis observed in the
magnetization profile of Sr$_{2}$FeCoO$_{6}$ is indicative of the mixed
magnetic phases present. The dynamic magnetic susceptibility displays
characteristic frequency dependence and confirms the spin glass nature of this
material. Dynamical scaling analysis of $\chi'(T)$ yields a critical
temperature $T_{ct}$ = 75.14(8) K and an exponent $z\nu$ = 6.2(2) typical for
spin glasses. The signature of presence of mixed magnetic interactions is
obtained from the thermal hysteresis in magnetization of Sr$_{2}$FeCoO$_{6}$.
Combining the neutron and magnetization results of Sr$_2$FeCoO$_6$, we deduce
the spin states of Fe to be in low spin while that of Co to be in low spin and
intermediate spin.",1111.5136v1
2023-03-19,Quasi One-Dimensional Ising-like Antiferromagnetism in the Rare-earth Perovskite Oxide TbScO$_3$,"The rare-earth perovskite TbScO$_3$ has been widely used as a substrate for
the growth of epitaxial ferroelectric and multiferroic thin films, while its
detailed low-temperature magnetic properties were rarely reported. In this
paper, we performed detailed magnetization, specific heat and single crystal
neutron scattering measurements, along with the crystalline electric field
calculations to study the low-temperature magnetic properties of TbScO$_3$. All
our results suggest the magnetic Tb$^{3+}$ has an Ising-like pseudo-doublet
ground state at low temperatures. Due to the constrain of local point symmetry,
these Tb$^{3+}$ Ising moments are confined in the $ab$ plane with a tilt angle
of $\varphi = \pm48^{\mathrm{o}}$ to the $a$ axis. In zero field, the system
undergoes an antiferromagnetic phase transition at $T_{\mathrm{N}}=2.53$ K, and
forms a $G_xA_y$ noncollinear magnetic structure below $T_{\mathrm{N}}$. We
find the dipole-dipole interactions play an important role to determine the
magnetic ground state, which are also responsible for the quasi-one-dimensional
magnetism in TbScO$_3$. The significant anisotropic diffuse scatterings further
confirm the quasi-one-dimensional magnetism along the $c$ axis. The magnetic
phase diagram with the field along the easy $b$ axis is well established. In
addition to the $G_xA_y$ antiferromagnetic state, there is an exotic
field-induced phase emerged near the critical field $B_{\mathrm{c}}\simeq0.7$
T, where three-dimensional magnetic order is suppressed but strong
one-dimensional correlations may still exist.",2303.10578v1
2004-07-13,Surface oxidation of liquid Sn,"We report the results of an x-ray scattering study that reveals oxidation
kinetics and formation of a previously unreported crystalline phase of SnO at
the liquid-vapour interface of Sn. Our experiments reveal that the pure liquid
Sn surface does not react with molecular oxygen below an activation pressure of
\~5.0*10-6 Torr. Above that pressure a rough solid Sn oxide grows over the
liquid metal surface. Once the activation pressure has been exceeded the
oxidation proceeds at pressures below the oxidation pressure threshold. The
observed diffraction pattern associated with the surface oxidation does not
match any of the known Sn oxide phases. The data have an explicit signature of
the face-centred cubic structure, however it requires lattice parameters that
are about 9% smaller than those reported for cubic structures of high-pressure
phases of Sn oxides.
  Keywords: X-ray scattering, diffraction, and reflection; Oxidation; Surface
chemical reaction; Surface structure, morphology, roughness, and topography;
Tin; Tin oxides; Liquid surfaces; Polycrystalline thin films",0407313v1
2010-03-22,Dissociative adsorption of methane on surface oxide structures of Pd-Pt alloys,"The dissociative adsorption of methane on variously oxidized Pd, Pt and Pd-Pt
surfaces is investigated using density-functional theory, as a step towards
understanding the combustion of methane on these materials. For Pd-Pt alloys,
models of surface oxide structures are built on the basis of known oxides on Pd
and Pt. The methane adsorption energy presents large variations depending on
the oxide structure and composition. Adsorption is endothermic on the bare
Pd(111) metal surface as well as on stable thin layer oxide structures such as
the ($\sqrt{5}\times\sqrt{5}$) surface oxide on Pd(100) and the PtO$_2$-like
oxide on Pt(111). Instead, large adsorption energies are obtained for the (100)
surface of bulk PdO, for metastable mixed Pd$_{1-x}$Pt$_x$O$_{4/3}$ oxide
layers on Pt(100), and for Pd-Pt(111) surfaces covered with one oxygen
monolayer. In the latter case, we find a net thermodynamic preference for a
direct conversion of methane to methanol, which remains adsorbed on the
oxidized metal substrates via weak hydrogen-bond interactions.",1003.4114v1
2011-06-03,Simple self-gettering differential-pump for minimizing source oxidation in oxide-MBE environment,"Source oxidation of easily oxidizing elements such as Ca, Sr, Ba, and Ti in
an oxidizing ambient leads to their flux instability and is one of the biggest
problems in the multi-elemental oxide Molecular Beam Epitaxy technique. Here we
report a new scheme that can completely eliminate the source oxidation problem:
a self-gettering differential pump using the source itself as the pumping
medium. The pump simply comprises a long collimator mounted in front of the
source in extended port geometry. With this arrangement, the oxygen partial
pressure near the source was easily maintained well below the source oxidation
regime, resulting in a stabilized flux, comparable to that of an
ultra-high-vacuum environment. Moreover, this pump has a self-feedback
mechanism that allows a stronger pumping effectiveness for more easily
oxidizing elements, which is a desired property for eliminating the source
oxidation problem.",1106.0677v1
2013-01-08,Shot-Peening of Pre-Oxidized Plates of Zirconium: Influence of Residual Stress on Oxidation,"The present study deals with oxidation behavior under residual stress of
shot-peened plates of ""commercially pure"" zirconium exposed for 30 min at 650
C. The influence of the shot-peening on a pre-oxidized material is presented.
The results have been used to determine the influences of these chemical
(preoxidation) and mechanical (shot-peening) treatments on the high temperature
oxidation of zirconium. The oxygen profile was revealed using micro-hardness
techniques and confirmed by SEM-EDS techniques. After pre-oxidation the samples
were first resurfaced then shot-peened in order to introduce residual stress. A
significant increase of the hardness of about 400 HV was observed on
pre-oxidized shot-peened samples. Thermogravimetric analysis for 30 min at 650
C under 200 mbar O2 showed a significantly slower oxidation rate for
shot-peened samples. A comparison with our computations points out the role of
the residual stresses on the diffusion and, consequently, on the oxidation.",1301.1635v2
2019-09-30,"The effect of surface preparation on high temperature oxidation of Ni, Cu and Ni-Cu alloy","In the present paper, the analysis of polishing, grinding and sand-blasting
processes on oxidation behavior of nickel, copper and nickel-copper alloy has
been investigated. Surface roughness has been measured using two methods: by
contact profilometer and by fractal analysis. It has been proved that
sand-blasting process influences the surface roughness the most but also
contaminates the surface with alumina particles. The oxidation tests were
performed in thermogravimetrical furnace. The obtained mass gain plots, SEM
microphotographs of cross-sections and SEM EDS analysis of the samples prove
that surface preparation changes oxidation kinetics morphology of the polished
and ground samples does not vary significantly after oxidation at investigated
temperatures, but differences in oxide layer thicknesses and mass gains were
observed. Oxidized sandblasted samples reveal that increased surface roughness
and alumina intrusions change the oxidation process mixed Al (Ni, Cu or Ni-Cu)
oxide is formed and separate Al2O3 particles are visible. The results prove
that surface preparation influence high temperature oxidation of the samples by
promoting new diffusion mechanism.",1909.13659v2
2021-05-24,Manganese oxide coated TiO2 nanotube-based electrode for efficient and selective electrocatalytic sulfide oxidation to colloidal sulfur,"Manganese oxide-coated TiO2 nanotube array (NTA) was synthesized and applied
for the (electro)catalytic oxidation of sulfide. By setting the
electrodeposition parameters and calcination temperature, the coating obtained
was MnO2 or Mn2O3, with rod or needle like morphology. Excellent catalytic
activity of the Ti/TiO2 NTA/MnxOy anodes resulted in robust and selective
oxidation of sulfide to elemental sulfur via an inner sphere complex between
the sulfide ion and Mn-oxide. The penetration of the MnxOy inside the NTA
improved adhesion and enhanced the electron transfer, thus enabling complete
and rapid electrocatalytic re-oxidation of the Mn-oxide coating. At pH 8, the
final product of sulfide oxidation was colloidal sulfur, S8, which prevented
anode passivation and enabled a stable (electro)catalytic activity in the
subsequent applications. This was observed in both synthetic electrolyte and
real sewage, thus demonstrating the efficiency of the Ti/TiO2 NTA/MnxOy anode
for sulfide oxidation in complex waste streams.",2105.11191v1
2023-11-26,On the special oxidation mechanism of a Mg-Y-Al alloy contained LPSO phase at high temperatures,"This work investigated the oxidation of Mg-11Y-1Al alloy in Ar-20%O2 at
500{\deg}through multiscale characterization. The results show that the
network-like long-period stacking ordered(LPSO) phase decomposed into a
needle-like LPSO phase and a polygonal Mg24Y5 phase. The needle-like LPSO phase
resulted in the formation of a high-dense of needle-like oxide at the oxidation
front of the area initially occupied by the network-like LPSO phase. The
further inward oxygen would diffuse along the needle-like oxide-matrix
interfaces and react with Y in the surrounding Mg matrix, resulting in the
lateral growth of these needle-like oxides. Finally, the discrete needle-like
oxides were interconnected to form a thicker and continuous oxide scale which
could be more effective in hindering the elemental diffusion. Meanwhile, Al
could partially enter the Y2O3 oxide scale and formed a strengthened (Y,Al)O
oxide scale which could show a greater resistance to cracking and debonding.",2311.15182v1
2014-11-28,Growth control of the oxidation state in vanadium oxide thin films,"Precise control of the chemical valence or oxidation state of vanadium in
vanadium oxide thin films is highly desirable for not only fundamental
research, but also technological applications that utilize the subtle change in
the physical properties originating from the metal- insulator transition (MIT)
near room temperature. However, due to the multivalent nature of vanadium and
the lack of a good understanding on growth control of the oxidation state,
stabilization of phase pure vanadium oxides with a single oxidation state is
extremely challenging. Here, we systematically varied the growth conditions to
clearly map out the growth window for preparing phase pure epitaxial vanadium
oxides by pulsed laser deposition for providing a guideline to grow high
quality thin films with well-defined oxidation states of V2(+3)O3, V(+4)O2, and
V2(+5)O5. A well pronounced MIT was only observed in VO2 films grown in a very
narrow range of oxygen partial pressure P(O2). The films grown either in lower
(< 10 mTorr) or higher P(O2) (> 25 mTorr) result in V2O3 and V2O5 phases,
respectively, thereby suppressing the MIT for both cases. We have also found
that the resistivity ratio before and after the MIT of VO2 thin films can be
further enhanced by one order of magnitude when the films are further oxidized
by post-annealing at a well-controlled oxidizing ambient. This result indicates
that stabilizing vanadium into a single valence state has to compromise with
insufficient oxidation of an as grown thin film and, thereby, a subsequent
oxidation is required for an improved MIT behavior.",1411.7922v1
2020-06-19,High-Temperature Oxidation Kinetics of Additively Manufactured NiTiHf,"NiTi-based high-temperature shape memory alloys (HTSMAs) such as NiTiHf have
been utilized in a broad range of applications due to their high strength and
work output, as well as, their ability to increase the transformation
temperatures (TTs). Recently, additive manufacturing techniques (AM) have been
widely used to fabricate complex shape memory alloy components without any
major modifications or tooling and has paved the way to tailor the
manufacturing and fabrications of microstructure and critical properties of
their final parts. NiTi alloys properties such as transformation temperatures
can be significantly altered due to oxidation, which can occur during the
manufacturing process or post-processing. In this work, the oxidation behavior
of Ni-rich NiTi20Hf shape memory alloys, which was fabricated by the selective
laser melting (SLM) method, is evaluated. Thermogravimetric analysis (TGA) is
used to assess the kinetic behavior of the oxidation at different temperature
ranges of 500, 700, and 900 C for 20 hours in the air. After oxidation, to
evaluate the microstructure and chemical composition X-ray diffraction (XRD),
scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy
(EDS) was conducted. The isothermal oxidation kinetics of conventional NiTi20Hf
alloys were studied, and the results were compared to AM samples. Results show
a two-stage oxidation rate at which oxidation increased with the high rate at
the initial stage. As the oxidation time increased, the oxidation rate
gradually decreased. The oxidation behavior of NiTiHf alloys initially obeyed
logarithmic rate law and then followed by parabolic rate law. SEM results
showed the formation of a multi-layered oxide scale, including TiO2, NiTiO3,
and Hf oxide.",2006.11114v1
2021-07-03,Effect of Vanadium Thickness and Deposition Temperature on VO2 Synthesis using Atmospheric Pressure Thermal Oxidation,"Vanadium dioxide (VO2) is a phase transition material that undergoes a
reversible insulator-metal phase transition at ~ 68 C. Atmospheric pressure
thermal oxidation (APTO) of vanadium (V) is a simple VO2 synthesis method in
which V thin film is oxidized in open air. For an optimum oxidation duration,
VO2 films are obtained with good phase transition properties. We recently
reported a modified APTO process using a step temperature profile for oxidation
(Thin Solid Films 706, 138003 (2020)). We demonstrated an ultra-low thermal
budget synthesis of VO2 thin films with good electrical and optical phase
transition properties. For a 130 nm room-temperature RF sputtered V thin film,
an optimum oxidation duration of ~ 30 s was obtained. In this work, we study
how the starting V film thickness and deposition temperature affects the
optimum oxidation duration. V thin films of varying thickness (15-212 nm) and
120 nm thick V films with varying deposition temperature (~27-450 C) are
prepared using RF magnetron sputtering. These films are oxidized for different
oxidation durations and characterized using Raman and four-probe measurements
to find the optimum oxidation duration for each deposition condition. We find
that the optimum oxidation duration increases with the increase in V film
thickness and V deposition temperature. We model the effect of V film thickness
and deposition temperature on the optimal oxidation time using a parabolic law
which can be used to obtain the optimal oxidation times for intermediate V
thicknesses/deposition temperatures.",2107.01413v1
2022-11-30,Kinetic control for planar oxidation of MoS$_2$,"Layered transition metal dichalcogenide (TMD) semiconductors oxidize readily
in a variety of conditions, and a thorough understanding of this oxide
formation is required for the advancement of TMD-based microelectronics. Here,
we combine scanning transmission electron microscopy (STEM) with spectroscopic
ellipsometry (SE) to investigate oxide formation at the atomic scale of the
most widely-studied TMD, MoS$_2$. We find that aggressive thermal oxidation
results in $\alpha$-phase plate-like crystalline MoO$_3$ with sharp interfaces,
voids, and a textured alignment with the underlying MoS$_2$. Experiments with
remote substrates and patterned MoS$_2$ prove that thermal oxidation proceeds
via vapor-phase mass transport and redeposition - a challenge to forming thin,
conformal planar oxide films. We accelerate the kinetics of oxidation relative
to the kinetics of mass transport using a non-thermal oxygen plasma process, to
form a smooth and conformal amorphous oxide. The resulting amorphous MoO$_3$
films can be grown several nanometers thick, and we calibrate the oxidation
rate for varying plasma processing conditions. Our results illustrate how TMD
semiconductor oxidation differs significantly from oxidation of legacy
semiconductors, most notably silicon, and provide quantitative guidance for
managing both the atomic scale structure and thin film morphology of oxides in
the design and processing of MoS$_2$ semiconductor devices.",2211.16789v1
2000-04-12,Resonant Spin-Dependent Tunneling in Spin-Valve Junctions in the Presence of Paramagnetic Impurities,"The tunnel magnetoresistance (TMR) of F/O/F magnetic junctions, (F's are
ferromagnetic layers and O is an oxide spacer) in the presence of magnetic
impurities within the barrier, is investigated. We assume that magnetic
couplings exist both between the spin of impurity and the bulk magnetization of
the neighboring magnetic electrode, and between the spin of impurity and the
spin of tunneling electron. Consequently, the resonance levels of the system
formed by a tunneling electron and a paramagnetic impurity with spin S=1, are a
sextet. As a result the resonant tunneling depends on the direction of the
tunneling electron spin. At low temperatures and zero bias voltage the TMR of
the considered system may be larger than TMR of the same structure without
paramagnetic impurities. It is calculated that an increase in temperature leads
to a decrease in the TMR amplitude due to excitation of spin-flip processes
resulting in mixing of spin up and down channels. It is also shown that
asymmetry in the location of the impurities within the barrier can lead to
asymmetry in $I(V)$ characteristics of impurity assisted current and two
mechanisms responsible for the origin of this effect are established. The first
one is due to the excitation of spin-flip processes at low voltages and the
second one arises from the shift of resonant levels inside the insulator layer
under high applied voltages.",0004198v2
2002-08-09,Persistent magnetoresistive memory in phase separated manganites,"We have studied magnetic and transport properties on different manganese
oxide based compounds exhibiting phase separation: polycrystalline
La5/8-yPryCa3/8MnO3 (y=0.3) and La1/2Ca1/2Mn1-zFezO3 (z = 0.05), and single
crystals of La5/8-yPryCa3/8MnO3 (y=0.35). Time dependent effects indicate that
the fractions of the coexisting phases are dynamically changing in a definite
temperature range. We found that in this range the ferromagnetic fraction f can
be easily tuned by application of low magnetic fields (< 1 T). The effect is
persistent after the field is turned off, thus the field remains imprinted in
the actual value of f and can be recovered through transport measurements. This
effect is due both to the existence of a true phase separated equilibrium state
with definite equilibrium fraction f0, and to the slow growth dynamics. The
fact that the same global features were found on different compounds and in
polycrystalline and single crystalline samples, suggests that the effect is a
general feature of some phase separated media.",0208199v1
2003-02-21,"Transport and Magnetic Properties of R1-xAxCoO3 (R=La, Pr and Nd; A=Ba, Sr and Ca)","Transport and magnetic measurements have been carried out on perovskite
Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of
the R and A species except Nd1-xBaxCoO3 have been studied.). With increasing
the Sr- or Ba-concentration x, the system becomes metallic ferromagnet with
rather large magnetic moments. For R=Pr and Nd and A=Ca, the system approaches
the metal- insulator phase boundary but does not become metallic. The magnetic
moments of the Ca-doped systems measured with the magnetic field H=0.1 T are
much smaller than those of the Ba- and Sr-doped systems. The thermoelectric
powers of the Ba- and Sr-doped systems decrease from large positive values of
lightly doped samples to negative ones with increasing doping level, while
those of Ca-doped systems remain positive. These results can be understood by
considering the relationship between the average ionic radius of R1-xAx and the
energy difference between the low spin and intermediate spin states. We have
found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under
pressure in the wide region of x, which indicates the existence of a phase
transition different from the one reported in the very restricted region of
x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No
indication of this kind of transition has been observed in other species of R.",0302435v1
2005-09-12,Pressure dependence of magnetic and superconducting transitions in sodium cobalt oxides NaxCoO2,"The results of DC magnetization measurements under hydrostatic (helium-gas)
pressure are reported for an ambient pressure superconductor Na0.35CoO2.1.4D2O
and its precursor compound, the gamma-phase Na0.75CoO2 that is known to combine
a metallic conductivity with an unusual magnetic state below ~22K. The obtained
data allowed us to present for the first time the pressure dependence of the
magnetic transition in a metallic sodium cobaltate system. This dependence
appears to be positive, with the magnetic transition rapidly shifting towards
higher temperatures when an applied pressure increases. We ascribe the observed
effect to the pressure-induced enhancement of the out-of-plane
antiferromagnetic coupling mediated by localized spins interactions (of either
superexchange or RKKY type), the scenario consistent with the A-type
antiferromagnetic state suggested by recent neutron-scattering data. As for the
pressure effect on the superconductivity in Na0.35CoO2.1.4D2O, our measurements
established negative and linear for the entire pressure range from 1 bar to 8.3
kbar pressure dependence of Tc, the behavior quite different from the reported
by previous workers strong non-linearity of the Tc (P) dependence. (Dated
September 12, 2005)
  PACS numbers: 74.62.Fj, 74.70.-b, 75.20. En, 75.50 Ee, 75.30 Kz.",0509308v1
2010-04-28,"Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers","Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were
synthesized. Their temperature- and applied magnetic field-dependent
structural, transport, thermal, and magnetic properties were characterized by
means of x-ray and neutron diffraction, electrical resistivity rho, heat
capacity, magnetization and magnetic susceptibility measurements. These
compounds have a body-centered-tetragonal crystal structure (space group
I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the
CuO2 layers in high superconducting transition temperature Tc cuprate
superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the
FeAs layers in high-Tc pnictides. These two types of layers alternate along the
crystallographic c-axis and are separated by Sr atoms. The site occupancies of
Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron
powder diffraction data. The temperature dependences of rho suggest metallic
character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and
Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie
temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state
structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to
an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each
layer are ferromagnetically aligned, but are antiferromagnetically aligned
between layers.",1004.5038v1
2011-07-27,Magnetic frustration in the context of pseudo-dipolar ionic disorder,"We consider an alternative to the usual spin glass paradigm for disordered
magnetism, consisting of the previously unstudied combination of frustrated
magnetic interactions and pseudo-dipolar disorder in spin positions. We argue
that this model represents a general limiting case for real systems as well as
a realistic model for certain binary fluorides and oxides. Furthermore, it is
of great relevance to the highly topical subjects of the Coulomb phase and
`charge ice'. We derive an analytical solution for the ground state phase
diagram of a model system constructed in this paradigm and identify magnetic
phases that remain either disordered or partially ordered even at zero
temperature. These phases are of a hitherto unobserved type, but may be broadly
classified as either `spin liquids' or `semi-spin liquids' in contrast to the
usual spin glass or semi-spin glass. Numerical simulations are used to show
that the spin liquid phase exhibits no spin glass transition at finite
temperature, despite the combination of frustration and disorder. By mapping
onto a model of uncoupled loops of Ising spins, we show that the magnetic
structure factor of this phase acts, in the limit $T\rightarrow0$, as a
sensitive probe of the positional disorder correlations. We suggest that this
result can be generalized to more complex systems, including experimental
realizations of canonical spin glass models.",1107.5411v2
2011-08-16,Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface,"LaAlO3 and SrTiO3 are insulating, nonmagnetic oxides, yet the interface
between them exhibits a two-dimensional electron system with high electron
mobility,1 superconductivity at low temperatures,2-6 and electric-field-tuned
metal-insulator and superconductorinsulator phase transitions.3,6-8 Bulk
magnetization and magnetoresistance measurements also suggest some form of
magnetism depending on preparation conditions5,9-11 and suggest a tendency
towards nanoscale electronic phase separation.10 Here we use local imaging of
the magnetization and magnetic susceptibility to directly observe a landscape
of ferromagnetism, paramagnetism, and superconductivity. We find submicron
patches of ferromagnetism in a uniform background of paramagnetism, with a
nonuniform, weak diamagnetic superconducting susceptibility at low temperature.
These results demonstrate the existence of nanoscale phase separation as
suggested by theoretical predictions based on nearly degenerate interface
sub-bands associated with the Ti orbitals.12,13 The magnitude and temperature
dependence of the paramagnetic response suggests that the vast majority of the
electrons at the interface are localized, and do not contribute to transport
measurements.3,6,7 In addition to the implications for magnetism, the existence
of a 2D superconductor at an interface with highly broken inversion symmetry
and a ferromagnetic landscape in the background suggests the potential for
exotic superconducting phenomena.",1108.3150v1
2012-06-25,Interplay between spin-orbit coupling and Hubbard interaction in SrIrO3 and related Pbnm perovskites,"There has been a rapidly growing interest on the interplay between spin-orbit
coupling (SOC) and Hubbard interaction U in correlated materials. A current
consensus is that the stronger the SOC, the smaller is the critical interaction
Uc required for a spin-orbit Mott insulator, because the atomic SOC splits a
band into different total angular momentum bands narrowing the effective
bandwidth. It was further claimed that at large enough SOC, the stronger the
SOC, the weaker the Uc because in general the effective SOC is enhanced with
increasing electron-electron interaction strength. Contrary to this
expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the
stronger the SOC, the bigger the Uc. This is originated from a line of Dirac
node in Jeff=1/2 bands near the Fermi level inherited from a combination of the
lattice structure and a large SOC. Due to this protected line of nodes, there
are small hole and electron pockets in SrIrO3, and such a small density of
states makes Hubbard interaction less efficient in building a magnetic
insulator. The full phase diagram in U vs. SOC is obtained, where non-magnetic
semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering
patterns beyond Uc are also presented. We further discuss implications of our
finding in relation to other perovskites such as SrRhO3 and SrRuO3.",1206.5836v2
2013-04-01,Spin and Dipole Ordering in Ni_2InSbO_6 and Ni_2ScSbO_6 with corundum-related structure,"The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been
prepared in form of polycrystalline powders by a solid state reaction route.
The crystal structure and magnetic properties of the compounds were
investigated using a combination of X-ray and neutron powder diffraction,
electron microscopy, calorimetric and magnetic measurements. The compounds
adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6
(NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO
structure was found to be occupied by In (Sc). NTO has non-centrosymmetric
structure and is ferroelectric below 1000 K, dielectric and second harmonic
measurements suggest that also NISO and NSSO are correspondingly ferroelectric.
Magnetization measurements signified antiferromagnetic ordering below TN=60 K
(NSSO) and 76 K (NISO). The magnetic structure is formed by two
antiferromagnetically coupled incommensurate helices with the spiral axis along
the b-axis and propagation vector k = [0, ky,0] with ky= 0.036(1) (NSSO) and
ky= 0.029(1) (NISO). The observed structural and magnetic properties of NISO
and NSSO are discussed and compared with those of NTO.",1304.0474v1
2013-04-17,Magnetism and electronic structure of La2ZnIrO6 and La2MgIrO6: candidate Jeff =1/2 Mott insulators,"We study experimentally and theoretically the electronic and magnetic
properties of two insulating double perovskites that show similar atomic and
electronic structure, but different magnetic properties. In magnetization
measurements, La2ZnIrO6 displays weak ferromagnetic behavior below 7.5 K
whereas La2MgIrO6 shows antiferromagnetic behavior (AFM) below TN = 12 K.
Electronic structure calculations find that the weak ferromagnetic behavior
observed in La2ZnIrO6 is in fact due to canted antiferromagnetism. The
calculations also predict canted antiferromagnetic behavior in La2MgIrO6, but
intriguingly this was not observed. Neutron diffraction measurements confirm
the essentially antiferromagnetic behavior of both systems, but lack the
sensitivity to resolve the small (0.22 {\mu}B/Ir) ferromagnetic component in
La2ZnIrO6. Overall, the results presented here indicate the crucial role of
spin-orbit coupling (SOC) and the on-site Coulomb repulsion on the magnetic,
transport, and thermodynamic properties of both compounds. The electronic
structure calculations show that both compounds, like Sr2IrO4, are Jeff = 1/2
Mott insulators. Our present findings suggest that La2ZnIrO6 and La2MgIrO6
provide a new playground to study the interplay between SOC and on-site Coulomb
repulsion in a 5d transition metal oxide.",1304.4769v1
2014-01-09,FMR Study of Co/Ti Bilayer Thin Films,". We focused on the interaction between two ferromagnetic cobalt layers
through a non-magnetic titanium layer. The magnetic properties of the structure
were characterized by ferromagnetic resonance technique (FMR). The data were
collected as a function of non-magnetic titanium layer thickness. Co/Ti
multilayer (Ti (50 {\AA})/Co(45 {\AA})/Ti(2-40 {\AA})/Co(40 {\AA})/Ti(100
{\AA}))films were grown onto naturally oxidized p-type single crystal Si (100)
substrate at UHV condition with magnetron sputtering system at room
temperature. The thickness of Ti spacer layer ranges from 2 to 40 {\AA} with 2
{\AA} steps. We did not observe usual optic and acoustic modes; instead we had
two broad overlapped peaks for the films ranged from 6 {\AA} to 40 {\AA}. One
interesting result was the high anisotropic resonance field values for these
films. Exchange coupling between ferromagnetic layers causes shift on resonance
field values but these shifts in our samples were much larger than expected.
This large anisotropic behavior is not clear at the moment. Our theoretical
model was not able to determine a value for the exchange coupling parameter.
One reason can be the close thickness values for Co sublayers. The other reason
can be the Ti non-magnetic layer. If titanium did not grow layer by layer on
cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a
result one cannot observe exchange interaction between ferromagnetic layers
through non-magnetic spacer.",1401.1924v1
2014-02-05,Size and shape control of magnetite nanoparticles with a nonselective binding surfactants,"A Martian meteorite, magnetic inks, drug targeting, batteries, contrasts for
MRI, data storage or even clinical thermo-therapy seem to have no connection,
but all have in common a dark mineral called magnetite. However, in each of
these applications this iron oxide shows up with different forms because their
optical, electrical and magnetic properties are strongly dependent on size,
shape and kind of surfactant. In this sense the control of this characteristics
has long been of scientific and technological interest. In an AC magnetic
field-assisted cancer therapy, \textit{e.g.}, from a biological point of view,
the interaction of the nanoparticles with cells is critically determined by the
surface properties which control their fate in biological environments. Besides
the size, factors as the shape also seems to affect the cellular uptake. On the
other hand, the specific absorption rate (SAR) at a fixed frequency and
magnetic field, is hugely dependent on average and distribution of size, shape,
crystalline anisotropy, and degree of aggregation or agglomeration of the
nanoparticles. Each of these factors contributes to an independent energy loss
mechanism: N\'eel relaxation, Brown relaxation or magnetic hysteresis loss.
Thus, the key for improving the efficiency of a given application is the
knowledge about the morphological control.",1402.1134v1
2014-09-29,Unconventional magnetism in the layered oxide LaSrRhO$_4$,"We have prepared polycrystalline samples of LaSrRh$_{1-x}$Ga$_x$O$_4$ and
LaSr$_{1-x}$Ca$_x$RhO$_4$,and have measured the x-ray diffraction, resistivity,
Seebeck coefficient, magnetization and electron spin resonance in order to
evaluate their electronic states. The energy gap evaluated from the resistivity
and the Seebeck coefficient systematically changes with the Ga concentration,
and suggests that the system changes from a small polaron insulator to a band
insulator. We find that all the samples show Curie-Weiss-like susceptibility
with a small Weiss temperature of the order of 1 K, which is seriously
incompatible with the collective wisdom that a trivalent rhodium ion is
nonmagnetic. We have determined the $g$ factor to be $g$=2.3 from the electron
spin resonance, and the spin number to be $S$=1 from the magnetization-field
curves by fitting with a modified Brillouin function. The fraction of the $S$=1
spins is 2--5%, which depends on the degree of disorder in the La/Sr/Ca-site,
which implies that disorder near the apical oxygen is related to the magnetism
of this system. A possible origin for the magnetic Rh$^{3+}$ ions is discussed.",1409.8092v1
2014-11-03,Sign problem free quantum Monte-Carlo study on thermodynamic properties and magnetic phase transitions in orbital-active itinerant ferromagnets,"The microscopic mechanism of itinerant ferromagnetism is a long-standing
problem due to the lack of non-perturbative methods to handle strong magnetic
fluctuations of itinerant electrons. We have non-pertubatively studied
thermodynamic properties and magnetic phase transitions of a two-dimensional
multi-orbital Hubbard model exhibiting ferromagnetic ground states. Quantum
Monte-Carlo simulations are employed, which are proved in a wide density region
free of the sign problem usually suffered by simulations for fermions. Both
Hund's coupling and electron itinerancy are essential for establishing the
ferromagnetic coherence. No local magnetic moments exist in the system as a
priori, nevertheless, the spin channel remains incoherent showing the
Curie-Weiss type spin magnetic susceptibility down to very low temperatures at
which the charge channel is already coherent exhibiting a weakly
temperature-dependent compressibility. For the SU(2) invariant systems, the
spin susceptibility further grows exponentially as approaching zero temperature
in two dimensions. In the paramagnetic phase close to the Curie temperature,
the momentum space Fermi distributions exhibit strong resemblance to those in
the fully polarized state. The long-range ferromagnetic ordering appears when
the symmetry is reduced to the Ising class, and the Curie temperature is
accurately determined. These simulations provide helpful guidance to searching
for novel ferromagnetic materials in both strongly correlated $d$-orbital
transition metal oxide layers and the $p$-orbital ultra-cold atom optical
lattice systems.",1411.0340v2
2014-12-12,Magnetoresistance from broken spin helicity,"The propensity of some materials and multilayers to have a magnetic field
dependent resistance, called magnetoresistance, has found commercial
applications such as giant magnetoresistance harddisk read heads. But
magnetoresistance can also be a powerful probe of electronic and magnetic
interactions in matter. For example, magnetoresistance can be used to analyze
multiband conductivity, conduction inhomogeneity, localized magnetic moments,
and (fractional) Landau level structure. For materials with strong spin-orbit
interaction, magnetoresistance can be used as a probe for weak antilocalization
or a nontrivial Berry phase, such as in topological insulator surface states.
For the three dimensional topological insulators a large and linear
magnetoresistance is often used as indication for underlying non-trivial
topology, although the origin of this effect has not yet been established.
Here, we observe a large magnetoresistance in the conducting bulk state of
Bi$_2$Te$_3$. We show that this type of large magnetoresistance is due to the
competition between helical spin-momentum locking (i.e. spin rotates with
momentum direction) and the unidirectional spin alignment by an applied
magnetic field. Warping effects are found to provide the (quasi) linear
dependence on magnetic field. We provide a quantitative model for the helicity
breaking induced magnetoresistance that can be applied to a vast range of
materials, surfaces or interfaces with weak to strong spin-orbit interactions,
such as the contemporary oxide interfaces, bulk Rashba systems, and topological
insulator surface states.",1412.4065v1
2015-07-15,Structural anomalies and short-range magnetic correlations in the orbitally degenerated system Sr$_2$VO$_4$,"We report on the electronic ground state of a layered perovskite vanadium
oxide Sr$_2$VO$_4$ studied by the combined use of synchrotron radiation x-ray
diffraction (SR-XRD) and muon spin rotation/relaxation ($\mu$SR) techniques,
where $\mu$SR measurements were extended down to 30 mK. We found an
intermediate orthorhombic phase between $T_{\rm c2} \sim$~130 K and $T_{\rm c1}
\sim$~100 K, whereas a tetragonal phase appears for $T > T_{\rm c2}$ and $T <
T_{\rm c1}$. The absence of long-range magnetic order was confirmed by $\mu$SR
at the reentrant tetragonal phase below $T_{\rm c1}$, where the relative
enhancement in the $c$-axis length versus that of the $a$-axis length was
observed. However, no clear indication of the lowering of the tetragonal
lattice symmetry with superlattice modulation, which is expected in the orbital
order state with superstructure of $d_{yz}$ and $d_{zx}$ orbitals, was observed
by SR-XRD below $T_{\rm c1}$. Instead, it was inferred from $\mu$SR that a
magnetic state developed below $T_{\rm c0} \sim$~10 K, which was characterized
by the highly inhomogeneous and fluctuating local magnetic fields down to 30
mK. We argue that the anomalous magnetic ground state below $T_{\rm c0}$
originates from the coexistence of ferromagnetic and antiferromagnetic
correlations.",1507.04139v1
2016-07-21,Possibility of an unconventional spin state of Ir$^{4+}$ in Ba$_{21}$Ir$_9$O$_{43}$ single crystal,"We report the synthesis of single crystals of a novel layered iridate
Ba$_{21}$Ir$_9$O$_{43}$, and present the crystallographic, transport and
magnetic properties of this material. The compound has a hexagonal structure
with two iridium oxide layers stacked along the $c$ direction. One layer
consists of a triangular arrangement of Ir$_2$O$_9$ dimers while the other
layer comprises two regular octahedra and one triangular pyramid, forming
inter-penetrated triangular lattices. The resistivity as a function of
temperature exhibits an insulating behavior, with a peculiar $T^{-3}$ behavior.
Magnetic susceptibility shows antiferromagnetic Curie-Weiss behavior with
$\Theta_\mathrm{CW} \simeq -$90 K while a magnetic transition occurs at
substantially lower temperature of 9 K. We discuss possible valence states and
effective magnetic moments on Ir ions in different local environments, and
argue that the Ir ions in a unique triangular-pyramidal configuration likely
carry unusually large magnetic moments.",1607.06441v2
2018-11-19,Room-temperature Low-field Colossal Magneto-resistance in Double-perovskite Manganite,"The gigantic decrease of resistance by an applied magnetic field, which is
often referred to as colossal magnetoresistance (CMR), has been an attracting
phenomenon in strongly correlated electron systems. The discovery of CMR in
manganese oxide compounds has developed the science of strong coupling among
charge, orbital, and spin degrees of freedom. CMR is also attracting scientists
from the viewpoint of possible applications to sensors, memories, and so on.
However, no application using CMR effect has been achieved so far, partly
because the CMR materials which satisfy all of the required conditions for the
application, namely, high operating temperature, low operating magnetic field,
and sharp resistive change, have not been discovered. Here we report a
resistance change of more than two-orders of magnitude at a magnetic field
lower than 2 T near 300 K in an A-site ordered NdBaMn_2_O_6_ crystal. When
temperature and a magnetic field sweep from insulating (metallic) phase to
metallic (insulating) phase, the insulating (metallic) conduction changes to
the metallic (insulating) conduction within 1 K and 0.5 T, respectively. The
CMR is ascribed to the melting of the charge ordering. The entropy change which
is estimated from the B-T phase diagram is smaller than what is expected for
the charge and orbital ordering. The suppression of the entropy change is
attributable to the loss of the short range ferromagnetic fluctuation of Mn
spin moments, which an important key of the high temperature and low magnetic
field CMR effect.",1811.07596v1
2018-11-29,Structural and Magnetic Study of Metallo-Organic YIG Powder Using 2-ethylhexanoate Carboxylate Based Precursors,"The crystallization and magnetic behavior of yttrium iron garnet (YIG)
prepared by metallo-organic decomposition (MOD) method are discussed. The
chemistry and physics related to synthesis of iron and yttrium carboxylates
based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found
which elucidates synthesis of metallo-organic precursor of YIG in spite of the
literatures of doped YIG samples such as Bi-YIG. Typically, the metal
carboxylates used in preparation of ceramic oxide materials are
2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and
solubility of yttrium and iron 2EH used in synthesis of YIG powder by MOD are
reported. The crystallization and magnetic parameters, including saturation
magnetization and coercivity of these samples, smoothly change as a function of
the annealing temperature. It is observed that high sintering temperature of
1300 to 1400 {\deg}C promotes the diffraction peaks of YIG, therefore, we can
conclude that the formation of YIG in MOD method increases the crystallization
temperature. The maximum value of saturation magnetization and minimum value of
coercivity and remanence are observed for the sample sintered at 1200{\deg}C
which are 13.7 emu/g, 10.38 Oe and 1.5 emu/g, respectively. This study cites
the drawbacks in chemical synthesis of metallo-organic based YIG production.",1811.12514v1
2016-11-16,Switching based Spin Transfer Torque Oscillator with zero-bias field and large tuning-ratio,"We propose a novel concept of obtaining oscillations with frequencies in
very-high frequency (VHF) and ultra-high frequency (UHF) bands. A traditional
spin torque nano-oscillator (STNO) consists of at least one pinned layer (PL)
and one free layer (FL) which precesses in a fixed orbit, defined by a
precession angle, which results in magneto-resistance (MR) oscillations. In
STNO, with aligned or even orthogonal easy-axis of the magnetic layers and with
or without external bias magnetic field, it is not possible to attain full MR
swing. The constringed MR swing jeopardizes the extracted output power.
Furthermore, the orbit is strongly disturbed by the thermal fluctuations
resulting in strong magnetic noise. In stark contrast to the operation
principle of a STNO, we theoretically demonstrate, with the practical
parameters from the experiments, that with a unidirectional current in a dual
asymmetric free-layers (with no pinned layer) based perpendicular magnetic
tunnel junction (pMTJ), both of the free layers can attain a complete and
out-of-phase self-sustained switching without the aid of any external magnetic
field. This design facilitates a switching based spin torque oscillator
(SW-STO) with a full MR swing, and hence a larger output power, for stable and
more thermally robust free-running oscillations. Furthermore, the integration
with the n-type metal-oxide-semiconductor (NMOS) field-effect transistors at
130, 65 and 14 nm node is appraised to expound its effect on the oscillator
performance, controllability with DC bias and the design constraints, to
demonstrate the viability of the design as a dynamically controllable
oscillator for practical on-chip implementation.",1611.05169v3
2017-01-16,High-field transport properties of a P-doped BaFe2As2 film on technical substrate,"High temperature (high-Tc) superconductors like cuprates have superior
critical current properties in magnetic fields over other superconductors.
However, superconducting wires for high-field-magnet applications are still
dominated by low-Tc Nb3Sn due probably to cost and processing issues. The
recent discovery of a second class of high-Tc materials, Fe-based
superconductors, may provide another option for high-field-magnet wires. In
particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best
candidates for high-field-magnet applications because of its high upper
critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we
report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films
grown on technical substrates (i.e., biaxially textured oxides templates on
metal tapes) by pulsed laser deposition. The P-doped Ba-122 coated conductor
sample exceeds a transport Jc of 10^5 A/cm^2 at 15 T for both major
crystallographic directions of the applied magnetic field, which is favourable
for practical applications. Our P-doped Ba-122 coated conductors show a
superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above
20 T. By analysing the E-J curves for determining Jc, a non-Ohmic linear
differential signature is observed at low field due to flux flow along the
grain boundaries. However, grain boundaries work as flux pinning centres as
demonstrated by the pinning force analysis.",1701.04154v1
2018-05-07,Electrically controlled long-distance spin transport through an antiferromagnetic insulator,"Spintronics uses spins, the intrinsic angular momentum of electrons, as an
alternative for the electron charge. Its long-term goal is in the development
of beyond-Moore low dissipation technology devices. Recent progress
demonstrated the long-distance transport of spin signals across ferromagnetic
insulators. Antiferromagnetically ordered materials are however the most common
class of magnetic materials with several crucial advantages over ferromagnetic
systems. In contrast to the latter, antiferromagnets exhibit no net magnetic
moment, which renders them stable and impervious to external fields. In
addition, they can be operated at THz frequencies. While fundamentally their
properties bode well for spin transport, previous indirect observations
indicate that spin transmission through antiferromagnets is limited to short
distances of a few nanometers. Here we demonstrate the long-distance, over tens
of micrometers, propagation of spin currents through hematite (\alpha-Fe2O3),
the most common antiferromagnetic iron oxide, exploiting the spin Hall effect
for spin injection. We control the spin current flow by the interfacial
spin-bias and by tuning the antiferromagnetic resonance frequency with an
external magnetic field. This simple antiferromagnetic insulator is shown to
convey spin information parallel to the compensated moment (N\'eel order) over
distances exceeding tens of micrometers. This newly-discovered mechanism
transports spin as efficiently as the net magnetic moments in the best-suited
complex ferromagnets. Our results pave the way to ultra-fast, low-power
antiferromagnet-insulator-based spin-logic devices that operate at room
temperature and in the absence of magnetic fields.",1805.02451v1
2016-12-08,Elucidating the Voltage Controlled Magnetic Anisotropy,"Voltage controlled magnetic anisotropy (VCMA) is an efficient way to
manipulate the magnetization states in nanomagnets, promising for low-power
spintronic applications. The underlying physical mechanism for VCMA is known to
involve a change in the d-orbital occupation on the transition metal interface
atoms with an applied electric field. However, a simple qualitative picture of
how this occupation controls the magnetocrystalline anisotropy (MCA) and even
why in certain cases the MCA has opposite sign still remains elusive. In this
paper, we exploit a simple model of orbital populations to elucidate a number
of features typical for the interface MCA and the effect of electric field on
it, for 3d transition metal thin films used in magnetic tunnel junctions. We
find that in all considered cases including the Fe (001) surface, clean
Fe1-xCox(001)/MgO interface and oxidized Fe(001)/MgO interface, the effects of
alloying and electric field enhance the MCA energy with electron depletion
which is largely explained by the occupancy of the minority-spin dxz,yz
orbitals. On the other hand, the hole doped Fe(001) exhibits an inverse VCMA,
where the MCA enhancement is achieved when electrons are accumulated at the Fe
(001)/MgO interface with applied electric field. In this regime we predict a
significantly enhanced VCMA which exceeds 1pJ/Vm. Realizing this regime
experimentally may be favorable for a practical purpose of voltage driven
magnetization reversal.",1612.02724v1
2018-01-29,Observation of the Meissner effect at room temperature in single-layer graphene brought into contact with alkanes,"There are claims of synthesis of a room temperature superconductor. However,
these claims have not been officially accepted by scientific communities.
Currently, the highest transition temperature (Tc) recognized in scientific
articles is 135 K at 1 atm of Hg-Ba-Ca-Cu-O system which is a copper oxide
superconductor. We packed graphite flakes into a ring-shaped
polytetrafluoroethylene (PTFE) tube and further injected heptane or octane.
Then we generated circulating current in this ring tube by electromagnetic
induction and showed that this circulating current continues to flow
continuously at room temperature for 50 days. This experiment suggests that
bringing alkane into contact with graphite may result in a material with zero
resistance at room temperature. In addition, we showed by means of AC
resistance measurements using the two-terminal method that the resistances of
graphite fibers brought into contact with various alkanes suddenly change at
specific critical temperatures between 363 and 504 K. In this study, we show
that after a magnetic field is applied to a single-layer graphene at room
temperature, alkane is brought into contact with the single-layer graphene,
then the graphene excludes the magnetic field immediately. This phenomenon
demonstrates that the alkane-wetted single-layer graphene shows Meissner effect
at room temperature. Furthermore, we applied a magnetic field perpendicularly
to the annular single-layer graphene brought into contact with n-hexane and
immediately removed the magnetic field. After that we observed that a constant
magnetic field generates from this annular graphene for some time. In
conclusion, the single-layer graphene brought into contact with alkane shows
Meissner effect at room temperature, which provides definitive evidence for
room temperature superconductivity.",1801.09376v1
2019-06-24,"Itinerancy-dependent non-collinear spin textures in SrFeO3, CaFeO3, and CaFeO3/SrFeO3 heterostructures probed via resonant x-ray scattering","Non-collinear, multi-q spin textures can give rise to exotic, topologically
protected spin structures such as skyrmions, but the reason for their formation
over simple single-q structures is not well understood. While lattice
frustration and the Dzyaloshinskii-Moriya interaction are known to produce
non-collinear spin textures, the role of electron itinerancy in multi-q
formation is much less studied. Here we investigated the non-collinear, helical
spin structures in epitaxial films of the perovskite oxides SrFeO3 and CaFeO3
using magnetotransport and resonant soft x-ray magnetic diffraction. Metallic
SrFeO3 exhibits features in its magnetoresistance that are consistent with its
recently proposed multi-q structure. Additionally, the magnetic Bragg peak of
SrFeO3 measured at the Fe L edge resonance energy asymmetrically broadens with
decreasing temperature in its multi-q state. In contrast, insulating CaFeO3 has
a symmetric scattering peak with an intensity 10x weaker than SrFeO3. Enhanced
magnetic scattering at O K edge prepeak energies demonstrates the role of a
negative charge transfer energy and the resulting oxygen ligand holes in the
magnetic ordering of these ferrates. By measuring magnetic diffraction of
CaFeO3/SrFeO3 superlattices with thick CaFeO3 layers, we find that the CaFeO3
helical ordering is coherent across 1 unit cell-thick SrFeO3 layers but not 6
unit cell-thick layers. We conclude that insulating CaFeO3 supports only a
simple single-q helical structure in contrast to metallic SrFeO3 that hosts
multi-q structures. Our results provide important insight into the role of
electron itinerancy in the formation of multi-q spin structures.",1906.09998v1
2019-09-30,Switching the Optical Chirality in Magneto-plasmonic Metasurfaces Using Applied Magnetic Fields,"Chiral nanophotonic devices are promising candidates for chiral molecules
sensing, polarization diverse nanophotonics and display technologies. Active
chiral nanophotonic devices, where the optical chirality can be controlled by
an external stimulus has triggered great research interest. However, efficient
modulation of the optical chirality has been challenging. Here, we demonstrate
switching of the extrinsic chirality by applied magnetic fields in a
magneto-plasmonic metasurface device based on a magneto-optical oxide material,
Ce1Y2Fe5O12 (Ce:YIG). Thanks to the low optical loss and strong magneto-optical
effect of Ce:YIG, we experimentally demonstrated a giant and continuous
far-field circular dichroism (CD) modulation by applied magnetic fields from
-0.65{\deg} to +1.9{\deg} at 950 nm wavelength under glancing incident
conditions. The far field CD modulation is due to both magneto-optical circular
dichroism and near-field modulation of the superchiral fields by applied
magnetic fields. Finally, we demonstrate magnetic field tunable chiral imaging
in millimeter-scale magneto-plasmonic metasurfaces fabricated using
self-assembly. Our results provide a new way for achieving planar integrated,
large-scale and active chiral metasurfaces for polarization diverse
nanophotonics.",1909.13605v1
2019-10-03,"Correlating the nanoscale structural, magnetic and magneto-transport properties in SrRuO3-based perovskite oxide ultra-thin films","We investigated the structural and magnetic properties of bare SrRuO$_3$
(SRO) ultra-thin films and SrRuO$_3$/SrIrO$_3$/SrZrO$_3$ (SRO/SIO/SZO: RIZ)
trilayer heterostructures between 10 K and 80 K, by comparing macroscopic data
using magneto-optical Kerr effect (MOKE) and magneto-transport (anomalous Hall
effect: AHE), with nanoscale fingerprints when applying non-contact scanning
force microscopy (nc-SFM) and magnetic force microscopy (MFM). SRO and RIZ
ultra-thin films were epitaxially grown at 650C onto vicinal SrTiO$_3$ (100)
single-crystalline substrates to a nominal thickness of 4 and 4/2/2 unit cells
(uc), respectively. Our correlated analysis allows associating topographic
sample features of overgrown individual layers to their residual magnetization,
as is shown here to be relevant for interpreting the macroscopic AHE data.
Although the hump-like features in the AHE suggest a magnetically extured
skyrmion phase to exist around 55 K associated to the topological Hall effect
(THE), both our MOKE and MFM data cannot support this theory. In contrast, our
SFM/MFM local-scale analysis finds the local coercive field to be strongly
dependent on the effective layer thickness and stoichiometry in both the SRO
and RIZ samples, with huge impact on the local band-structure. In fact, it is
these variations that in turn mimic a potential THE through anomalies in the
AHE resistivity loops.",1910.01474v1
2019-10-04,Scale-invariant magnetic textures in the strongly correlated oxide NdNiO$_3$,"Strongly correlated quantum solids are characterized by an inherently
granular electronic fabric, with spatial patterns that can span multiple length
scales in proximity to a critical point. Here, we used a resonant magnetic
X-ray scattering nanoprobe with sub-100 nm spatial resolution to directly
visualize the texture of antiferromagnetic domains in NdNiO$_3$. Surprisingly,
our measurements revealed a highly textured magnetic fabric, which is shown to
be robust and nonvolatile even after thermal erasure across its ordering
($T_{N\acute{e}el}$) temperature. The scale-free distribution of
antiferromagnetic domains and its non-integral dimensionality point to a
hitherto-unobserved magnetic fractal geometry in this system. These
scale-invariant textures directly reflect the continuous nature of the magnetic
transition and the proximity of this system to a critical point. The present
study not only exposes the near-critical behavior in rare earth nickelates but
also underscores the potential for novel X-ray scattering nanoprobes to image
the multiscale signatures of criticality near a critical point.",1910.02072v1
2020-04-21,Silica anchored colloidal suspension of magnetite nanorods,"This study focuses on the interaction of colloidal silica nanoparticles with
the magnetite (Fe3O4) magnetic fluids (MF), which eventually forms nanorod like
structure. The aqueous magnetic fluid consists of magnetite nanoparticles
having double layers of lauric acid surfactants. This surfactant provides
stability towards short-range van der Waals attractive and steric repulsive
forces, as well as long-range dipole-dipole interactive force. Whereas, in the
colloidal silica, the sodium ions provide stability to the silica
nanoparticles. The colloidal silica and magnetic fluid both were mixed in
different proportions to understand the interaction between the silica and
magnetite nanoparticles. Thus, the interaction present in the system is studied
using FTIR, TGA, and magnetic field induced microscopy. The FTIR and TGA data
reveal that silica interacts with the outer layer of lauric acid through the
Si-O bond and eventually provides stability to the system. The length of the
lauric acid sheath varies with the concentration of silica nanoparticles. The
SEM images indicate nanorod formation, and its structure dimensions vary with
the silica concentrations, which is also reflected in the magnetic
field-induced structure formations. The structure observed using microscopy
correlated with the interaction derived from FTIR and TGA data analysis. XRD
data of iron oxide (magnetite) nanoparticles are present here again for
completion.",2004.09944v2
2000-06-28,The connection between superconducting phase correlations and spin excitations in YBa$_2$Cu$_3$O$_{6.6}$: A magnetic field study,"One of the most striking universal properties of the
high-transition-temperature (high-$T_c$) superconductors is that they are all
derived from the hole-doping of their insulating antiferromagnetic (AF) parent
compounds. From the outset, the intimate relationship between magnetism and
superconductivity in these copper-oxides has intrigued researchers. Evidence
for this link comes from neutron scattering experiments that show the
unambiguous presence of short-range AF correlations (excitations) in cuprate
superconductors. Even so, the role of such excitations in the pairing mechanism
and superconductivity is still a subject of controversy. For
YBa$_2$Cu$_3$O$_{6+x}$, where $x$ controls the hole-doping level, the most
prominent feature in the magnetic excitations spectra is the ``resonance''.
Here we show that for underdoped YBa$_2$Cu$_3$O$_{6.6}$, where $x$ and $T_c$
are below the optimal values, modest magnetic fields suppress the resonance
significantly, much more so for fields approximately perpendicular rather than
parallel to the CuO$_2$ planes. Our results indicate that the resonance
measures pairing and phase coherence, suggesting that magnetism plays an
important role in the superconductivity of cuprates. The persistence of a field
effect above $T_c$ favors mechanisms with preformed pairs in the normal state
of underdoped cuprates.",0006433v1
2019-01-04,Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe,"We demonstrate that we can determine the antiferromagnetic anisotropies and
the bulk Dzyaloshinskii-Moriya fields of the insulating iron oxide hematite,
{\alpha}-Fe2O3, using a surface sensitive spin-Hall magnetoresistance (SMR)
technique. We develop an analytical model that in combination with SMR
measurements, allow for the identification of the material parameters of this
prototypical antiferromagnet over a wide range of temperatures and magnetic
field values. Using devices with different orientations, we demonstrate that
the SMR response strongly depends on the direction of the charge current with
respect to the magneto-crystalline anisotropies axis. We show that we can
extract the anisotropies over a wide temperature range including across the
Morin phase transition. We observe that the electrical response is dominated by
the orientation of the antiferromagnetic N\'eel order parameter, rather than by
the emergent weak magnetic moment. Our results highlight that the surface
sensitivity of the SMR allows accessing the magnetic anisotropies of
antiferromagnetic crystals and in particular thin films where other methods to
determine anisotropies such as bulk-sensitive magnetic susceptibility
measurements do not provide sufficient sensitivity.",1901.01213v1
2019-04-02,Magnetoelectrically driven catalytic degradation of organics,"Here, we report the catalytic degradation of organic compounds by exploiting
the magnetoelectric (ME) nature of cobalt ferrite-bismuth ferrite (CFO-BFO)
core-shell nanoparticles. The combination of magnetostrictive CFO with the
multiferroic BFO gives rise to a magnetoelectric engine that purifies water
under wireless magnetic fields via advanced oxidation processes, without
involvement of any sacrificial molecules or co-catalysts. Magnetostrictive
CoFe2O4 nanoparticles are fabricated using hydrothermal synthesis, followed by
sol-gel synthesis to create the multiferroic BiFeO3 shell. We perform
theoretical modeling to study the magnetic field induced polarization on the
surface of magnetoelectric nanoparticles. The results obtained from these
simulations are consistent with the experimental findings of the piezo-force
microscopy analysis, where we observe changes in the piezoresponse of the
nanoparticles under magnetic fields. Next, we investigate the magnetoelectric
effect induced catalytic degradation of organic pollutants under AC magnetic
fields and obtained 97% removal efficiency for synthetic dyes and over 85%
removal efficiency for routinely used pharmaceuticals. Additionally, we perform
trapping experiments to elucidate the mechanism behind the magnetic field
induced catalytic degradation of organic pollutants by using scavengers for
each of the reactive species. Our results indicate that hydroxyl and superoxide
radicals are the main reactive species in the magnetoelectrically induced
catalytic degradation of organic compounds.",1904.01271v1
2019-11-01,Electric-Field Control of the Interlayer Exchange Coupling for Magnetization Switching,"We propose an electric-field-controlled mechanism for magnetization switching
assisted solely by the interlayer-exchange coupling (IEC) between the fixed and
the free magnets, which are separated by two oxide barriers sandwiching a
spacer material known for exhibiting large IEC. The basic idea relies on the
formation of a quantum-well (QW) within the spacer material and controlling the
transmission coefficient across the structure with an electric-field via the
resonant tunneling phenomena. Using non-equilibrium Green's function (NEGF)
method, we show that the structure can exhibit a bias-dependent oscillatory IEC
that can switch the free magnet to have either a parallel or an antiparallel
configuration with respect to the fixed magnet, depending on the sign of the
IEC. Such bi-directional switching can be achieved with the same voltage
polarity but different magnitudes. With proper choice of the spacer material,
the current in the structure can be significantly reduced. Due to the
conservative nature of the exerted torque by the IEC, the switching threshold
of the proposed mechanism is decoupled from the switching speed, while the
conventional spin-torque devices exhibit a trade-off due to the
non-conservative nature of the exerted torque.",1911.00183v1
2020-03-10,Room-temperature ferrimagnetism of anti-site-disordered Ca2MnOsO6,"Room-temperature ferrimagnetism was discovered for the anti-site-disordered
perovskite Ca2MnOsO6 with Tc = 305 K. Ca2MnOsO6 crystallizes into an
orthorhombic structure with a space group of Pnma, in which Mn and Os share the
oxygen-coordinated-octahedral site at an equal ratio without a noticeable
ordered arrangement. The material is electrically semiconducting with
variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the
trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic
circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are
aligned antiferromagnetically, thereby classifying the material as a
ferrimagnet which is in accordance with band structure calculations. It is
intriguing that the magnetic signal of the Os is very weak, and that the
observed total magnetic moment is primarily due to the Mn. The Tc = 305 K is
the second highest in the material category of so-called disordered
ferromagnets such as CaRu1-xMnxO3, SrRu1-xCrxO3, and CaIr1-xMnxO3, and hence,
may support the development of spintronic oxides with relaxed requirements
concerning the anti-site disorder of the magnetic ions.",2003.04608v1
2020-05-17,Salt-Driven Assembly of Magnetic Silica Microbeads with Tunable Porosity,"Porous magnetic silica beads are promising materials for biological and
environmental applications due to their enhanced adsorption and ease of
recovery. This work aims to develop a new, inexpensive and environmentally
friendly approach based on agglomeration of nanoparticles in aqueous droplets.
The use of an emulsion as a geometrical constraint is expected to result in the
formation of spherical beads with tunable composition depending on the aqueous
phase content. Magnetic silica beads are produced at room temperature by
colloidal destabilization induced by addition of calcium chloride to a
water-in-oil emulsion containing silica and iron oxide nanoparticles. The
impact of the salt concentration, emulsification method, concentration of
hydrophobic surfactant as well as silica content is presented in this paper.
This method enables the production of spherical beads with diameters between 1
and 9 micrometers. The incorporation of magnetic nanoparticles inside the beads
structure is confirmed using Energy Dispersive X-ray spectrometry and Scanning
Transmission Electron Microscopy and results in the production of magnetic
responsive beads with a preparation yield up to 84 percent. By incorporating
the surfactant Span 80 in the oil phase it is possible to tune the roughness
and porosity of the beads.",2005.08192v1
2021-08-09,Spin-orbit effects in pentavalent Iridates: Models and materials,"Spin-orbit effects in heavy 5$d$ transition metal oxides, in particular,
iridates, have received enormous current interest due to the prediction as well
as the realization of a plethora of exotic and unconventional magnetic
properties. While a bulk of these works are based on tetravalent iridates
($d^5$), where the counter-intuitive insulating state of the rather extended
5$d$ orbitals are explained by invoking strong spin-orbit coupling, the recent
quest in iridate research has shifted to the other valencies of Ir, of which
pentavalent iridates constitute a notable representative. In contrast to the
tetravalent iridates, spin-orbit entangled electrons in $d^4$ systems are
expected to be confined to the $J = 0$ singlet state without any resultant
moment or magnetic response. However, it has been recently predicted that,
magnetism in $d^4$ systems may occur via magnetic condensation of excitations
across spin-orbit-coupled states. In reality, the magnetism in Ir$^{5+}$
systems are often quite debatable both from theoretical as well as experimental
point of view. Here we provide a comprehensive overview of the spin-orbit
coupled $d^4$ model systems and its implications in the studied pentavalent
iridates. In particular, we review here the current experimental and
theoretical understanding of the double perovskite ($A_2B$YIrO$_6$, $A =$ Sr,
Ba, $B =$Y, Sc, Gd), 6H-perovskite (Ba$_3M$Ir$_2$O$_9$, $M =$ Zn, Mg, Sr, Ca),
post-perovskite (NaIrO$_3$), and Hexagonal (Sr$_3$MIrO$_6$) iridates, along
with a number of open questions that require future investigation.",2108.04158v1
2021-09-16,Giant shifts of crystal-field excitations in ErFeO3 driven by internal magnetic fields,"Due to the complex interactions between rare-earth elements and transition
metals, as well as/or themselves, rare-earth transition-metal oxides are likely
to exhibit highly intriguing and novel magnetic structures and dynamic
behaviours. Rare-earth elements in these compounds frequently demonstrate
unusual behaviours in their crystal-field (CF) excitations, which necessitate
thorough research for in-depth comprehensions. When cooling from 10 K to 1.5 K
via the magnetic ordering temperature of Er3+ at 4.1 K, we observed a
significant energy shift of the low-lying CF excitation of Er3+ in ErFeO3 from
0.35 meV to 0.75 meV utilizing the inelastic neutron-scattering technique. A
sound CF model was proposed for Er3+ in ErFeO3 by fitting to the observed CF
excitation peaks, which enables to explain all the observed experimental
results in a very consistent manner. According to the model, the ground crystal
field level of Er3+, which corresponds to the lowest Kramers doublet supposed
to be at zero energy, has been shifted by the internal magnetic fields induced
by both Er3+ and Fe3+ spin orders below and above the Er3+ ordering
temperature, respectively. Additional measurements in various magnetic fields
offer compelling evidence in favour of this hypothesis. The measured external
field dependence of the CF excitation energy led to the derivation of the
internal field of Er3+ as 0.33 meV, which is strongly corroborated by
theoretical modelling. Additionally, the effective g-factor for Er3+ in ErFeO3
showed an exceptionally significant anisotropy.",2109.07667v2
2022-05-23,Direct Determination of Spin-Splitting Energy in Magnetic Graphene by Landau Fan Shifts,"Spin-polarized two-dimensional materials with large and tunable
spin-splitting energy promise the field of 2D spintronics. While graphene has
been a canonical 2D material, its spin properties and tunability are limited.
Here, we demonstrate the emergence of robust spin-polarization in graphene with
large and tunable spin-splitting energy of up to 132 meV at zero applied
magnetic fields. The spin polarization is induced through a magnetic exchange
interaction between graphene and the underlying ferrimagnetic oxide insulating
layer, Tm3Fe5O12, as confirmed by its X-ray magnetic circular dichroism. The
spin-splitting energies are directly measured and visualized by the shift in
their landau fan diagram mapped by analyzing the measured subnikov-de-Haas
oscillations as a function of applied electric fields, showing consistent fit
with our first-principles and machine learning calculations. Further, the
observed spin-splitting energies can be tuned over a broad range between 98 and
166 meV by cooling fields. Our methods and results are applicable to other
two-dimensional (magnetic) materials and heterostructures, and offer great
potential for developing next-generation spin logic and memory devices.",2205.11042v2
2022-06-06,Quantitative theory of magnetic interactions in solids,"In this report we review the method of explicit calculations of interatomic
exchange interactions of magnetic materials. This involves exchange mechanisms
normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction
and anisotropic symmetric exchange. The connection between microscopic theories
of the electronic structure, such as density functional theory or dynamical
mean field theory, and interatomic exchange, is given in detail. The different
aspects of extracting information for an effective spin Hamiltonian that
involves thousands of atoms, from electronic structure calculations considering
significantly fewer atoms (1-50) is highlighted. Examples of exchange
interactions of a large group of materials is presented, which involves heavy
elements of the 3d period, alloys between transition metals, Heusler compounds,
multilayer systems as well as overlayers and adatoms on a substrate, transition
metal oxides, 4f elements, magnetic materials in two dimensions and molecular
magnets. Where possible, a comparison to experimental data is made, that
naturally becomes focused on the magnon dispersion. The influence of relativity
is reviewed for a few cases, as is the importance of dynamical correlations.
Development to theories that handle out of equilibrium conditions is also
described here. The review ends with a short description of extensions of the
theories behind explicit calculations of interatomic exchange, to non-magnetic
situations, e.g. that describe chemical (charge) order and superconductivity.",2206.02415v2
2022-06-16,Nodal superconducting exchange coupling,"The superconducting equivalent of giant magnetoresistance, involves placing a
thin-film superconductor between two ferromagnetic layers. A change of
magnetization-alignment in such a superconducting spin-valve from parallel (P)
to antiparallel (AP) creates a positive shift in the superconducting transition
temperature ({\Delta}Tc) due to an interplay of the magnetic exchange energy
and the superconducting condensate. The magnitude of {\Delta}Tc scales
inversely with the superconductor thickness (dS) and is zero when dS exceeds
the superconducting coherence length ({\xi}) as predicted by de Gennes. Here,
we report a superconducting spin-valve effect involving a different underlying
mechanism that goes beyond de Gennes in which magnetization-alignment and
{\Delta}Tc are determined by the nodal quasiparticle-excitation states on the
Fermi surface of the d-wave superconductor YBa2Cu3O7-{\delta} (YBCO) grown
between insulating layers of ferromagnetic Pr0.8Ca0.2MnO3. We observe
{\Delta}Tc values that approach 2 K with {\Delta}Tc oscillating with dS over a
length scale exceeding 100 {\xi} and, for particular values of dS, we find that
the superconducting state reinforces an antiparallel magnetization-alignment.
These results pave the way for all-oxide superconducting memory in which
superconductivity modulates the magnetic state.",2206.07911v1
2022-06-24,Traversing the pyrochlore stability diagram; microwave-assisted synthesis and discovery of mixed B-site Ln$_2$InSbO$_7$ family,"The lanthanide pyrochlore oxides Ln$_2$B$_2$O$_7$ are one of the most
intensely studied classes of materials within condensed matter physics, firmly
centered as one of the pillars of frustrated magnetism. The extensive chemical
diversity of the pyrochlores, coupled with their innate geometric frustration,
enables realization of a wide array of exotic and complex magnetic ground
states. Thus, the discovery of new pyrochlore compositions has been a
persistent theme that continues to drive the field in exciting directions. The
recent focus on the mixed B-site pyrochlores offers a unique route towards
tuning both local coordination chemistry and sterics, while maintaining a
nominally pristine magnetic sublattice. Here, we present a broad overview of
the pyrochlore stability field, integrating recent synthetic efforts in mixed
B-site systems with the historically established Ln$_2$B$_2$O$_7$ families. In
parallel, we present the discovery and synthesis of the entire Ln$_2$InSbO$_7$
family (Ln: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) located near
the boundary of the pyrochlore stability field using a rapid, hybrid
mechanicochemical/microwave-assisted synthesis technique. Magnetic
characterization on the entire class of compounds draws striking parallels to
the stannate analogs, suggesting that these compounds may host a breadth of
exotic magnetic ground states.",2206.12022v1
2022-09-21,Dynamics of photo-induced ferromagnetism in oxides with orbital degeneracy,"By using intense coherent electromagnetic radiation, it may be possible to
manipulate the properties of quantum materials very quickly, or even induce new
and potentially useful phases that are absent in equilibrium. For instance,
ultrafast control of magnetic dynamics is crucial for a number of proposed
spintronic devices and can also shed light on the possible dynamics of
correlated phases out of equilibrium. Inspired by recent experiments on
spin-orbital ferromagnet YTiO$_3$ we consider the nonequilibrium dynamics of
Heisenberg ferromagnetic insulator with low-lying orbital excitations. We model
the dynamics of the magnon excitations in this system following an optical
pulse which resonantly excites infrared-active phonon modes. As the phonons
ring down they can dynamically couple the orbitals with the low-lying magnons,
leading to a dramatically modified effective bath for the magnons. We show this
transient coupling can lead to a dynamical acceleration of the magnetization
dynamics, which is otherwise bottlenecked by small anisotropy. Exploring the
parameter space more we find that the magnon dynamics can also even completely
reverse, leading to a negative relaxation rate when the pump is blue-detuned
with respect to the orbital bath resonance. We therefore show that by using
specially targeted optical pulses, one can exert a much greater degree of
control over the magnetization dynamics, allowing one to optically steer
magnetic order in this system. We conclude by discussing interesting parallels
between the magnetization dynamics we find here and recent experiments on
photo-induced superconductivity, where it is similarly observed that depending
on the initial pump frequency, an apparent metastable superconducting phase
emerges.",2209.10567v1
2023-02-07,What can one learn about Fe-Cr alloys using Mössbauer spectroscopy?,"Applications of the M\""ossbauer spectroscopy (MS) in the investigation of
Fe-Cr alloys are reviewed. A high sensitivity of the hyperfine magnetic field
to the presence of Cr atoms in the vicinity of the probe Fe atoms permits
quantitative investigation of various aspects related both to the
crystallographic as well as to the magnetic phase diagram of this alloy system.
Concerning the former, presented is the relevance of MS for determining borders
of the miscibility gap and kinetics of the phase decomposition, distinguishing
between nucleation and growth and spinodal decomposition, identifying the
sigma-phase and studying kinetics of its precipitation. Regarding the magnetic
phase diagram, MS is useful for determining the Curie, the N\'eel and the
spin-freezing temperature, hence studying paramagnetic-ferromagnetic,
paramagnetic-antiferromagnetic and paramagnetic-spin-glass transitions. An
effect of different heat treatments, strain and irradiation with various
particles on a distribution of Cr atoms in the Fe matrix is demonstrated, too.
For bcc-FeCr alloys relevance of MS for determining changes in spin and charge
densities at Fe-sites induced by neighboring Cr atoms is illustrated, as well
as its usefulness in studying changes caused by a high-temperature sulphidation
and oxidation. Concerning properties of sigma-FeCr alloys the application of MS
for determining the Curie and Debye temperature is reviewed. Application of MS
to study an effect of magnetism on the lattice dynamics of Fe atoms in
sigma-FeCr is also exemplified. Last but not least, determining a magnetic
texture and mechanical alloying is addressed.",2302.03436v1
2023-03-14,The unusual distribution of spin-triplet supercurrents in disk-shaped Josephson junctions,"The phenomenon of s-wave spin triplet Cooper pairs induced in ferromagnetic
metals has been researched now for more than a decade, and its main aspects are
well understood. Crucial in converting s-wave singlet pairs in the
superconductor to s-wave triplets in the ferromagnet is the engineering of
well-defined magnetic inhomogeneity (the 'generator') at the interface with the
superconductor. Vertical layer stacks are typically used as such, where two
separate thin ferromagnetic layers with homogeneous but non-collinear
magnetizations, provide the inhomogeneity. Alternatively, magnetic textures,
like ferromagnetic domain walls and vortices, are possible triplet generators,
although they are far less studied. In this paper we review our experiments on
lateral disk-shaped Josephson junctions where a ferromagnetic bottom layer
provides a weak link with a vortex magnetization imposed by the shape of the
disk. We present three different junction configurations, exhibiting their own
generator mechanism. In the first, we utilize the non-collinearity with a
second ferromagnetic layer to produce the triplet correlations. The second
configuration consists of only the bottom ferromagnet and the superconducting
contacts; it relies on the vortex magnetization itself to generate the
spin-polarized supercurrents. In the third case we exploit an intrinsic
generator by combining a conventional superconductor (NbTi) and a half-metallic
ferromagnetic oxide (La$_{0.7}$Sr$_{0.3}$MnO$_3$). We find strong supercurrents
in all cases. A particularly interesting finding is that the supercurrents are
strongly confined at the rims of the device, independent of the generating
mechanism, but directly related to their triplet nature. What causes these rim
currents remains an open question.",2303.07993v1
2023-03-29,Light induced decoupling of electronic and magnetic properties in manganites,"The strongly correlated material La0.7Sr0.3MnO3 (LSMO) exhibits
metal-to-insulator and magnetic transition near room temperature. Although the
physical properties of LSMO can be manipulated by strain, chemical doping,
temperature, or magnetic field, they often require large external stimuli. To
include additional flexibility and tunability, we developed a hybrid
optoelectronic heterostructure that uses photocarrier injection from cadmium
sulfide (CdS) to an LSMO layer to change its electrical conductivity. LSMO
exhibits no significant optical response, however, the CdS/LSMO
heterostructures show an enhanced conductivity, with ~ 37 % resistance drop, at
the transition temperature under light stimuli. This enhanced conductivity in
response to light is comparable to the effect of a 9 T magnetic field in pure
LSMO. Surprisingly, the optical and magnetic responses of CdS/LSMO
heterostructures are decoupled and exhibit different effects when both stimuli
are applied. This unexpected behavior shows that heterostructuring strongly
correlated oxides may require a new understanding of the coupling of physical
properties across the transitions and provide the means to implement new
functionalities.",2303.17049v1
2023-04-11,Syntropic spin alignment at the interface between ferromagnetic and superconducting nitrides,"The magnetic correlations at the superconductor/ferromagnet (S/F) interfaces
play a crucial role in realizing dissipation-less spin-based logic and memory
technologies, such as triplet-supercurrent spin-valves and ""{\pi}"" Josephson
junctions. Here we report the coexistence of an induced large magnetic moment
and a crypto ferromagnetic state at high-quality nitride S/F interfaces. Using
polarized neutron reflectometry and d. c. SQUID measurements, we quantitatively
determined the magnetization profile of S/F bilayer and confirmed the induced
magnetic moment in the adjacent superconductor only exists below TC.
Interestingly, the direction of the induced moment in the superconductors was
unexpectedly parallel to that in the ferromagnet, which contrasts with earlier
findings in S/F heterostructures based on metals or oxides. The
first-principles calculations verify the observed unusual interfacial spin
texture is caused by the Heisenberg direct exchange coupling through d orbital
overlapping and severe charge transfer across the interfaces. Our work
establishes an incisive experimental probe for understanding the magnetic
proximity behavior at S/F interfaces and provides a prototype epitaxial
building block for superconducting spintronics.",2304.05234v1
2023-04-11,Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts,"Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as
magnetocaloric effect during the magneto-structural phase transition, making
this material interesting for solid-state cooling application. Material
processing by additive manufacturing can overcome difficulties related to
machinability of the alloys, caused by their intrinsic brittleness. Since the
magnetic properties and transition temperature are highly sensitive to the
chemical composition, it is essential to understand and monitoring these
properties over the entire processing chain. In the present work the
microstructural and magnetic properties from gas-atomized powder to
post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was
used for processing, promoting the evolution of a polycrystalline
microstructure being characterized by elongated grains along the building
direction. A complete and sharp martensitic transformation can be achieved
after applying a subsequent heat treatment at 1173 K for 24 h. The
Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing
lead to an increase of the transition temperature of 45 K and a decrease of
magnetization, clearly pointing at the necessity of controlling the
composition, oxygen partial pressure and magnetic properties over the entire
processing chain.",2304.05383v1
2023-06-08,Influence of native defects on magneto-optoelectronic properties of $α$-MoO$_{3}$,"Semiconducting oxides possess a variety of intriguing electronic, optical,
and magnetic properties, and native defects play a crucial role in these
systems. In this study, we study the influence of native defects on these
properties of $\alpha$-MoO$_{3}$ using the first-principles density functional
theory (DFT) calculations. From the formation energy calculations, it is
concluded that Mo vacancies are difficult to form in the system, while O and
Mo-O co-vacancies are energetically quite favorable. We further find that
vacancies give rise to mid-gap states (trap states) that remarkably affect the
magneto-optoelectronic properties of the material. Our calculations indicate
that a single Mo vacancy leads to half-metallic behavior, and also induces a
large magnetic moment of 5.98 $\mu_{B}$. On the other hand, for the single O
vacancy case, the band gap disappears completely, but the system remains in a
non-magnetic state. For Mo-O co-vacancies of two types considered in this work,
a reduced band gap is found, along with an induced magnetic moment of 2.0
$\mu_{B}$. Furthermore, a few finite peaks below the main band edge are
observed in the absorption spectra of configurations with Mo and O vacancies,
while they are absent in the Mo-O co-vacancies of both types, just like in the
pristine state. From the ab-initio molecular dynamics simulations, stability
and sustainability of induced magnetic moment at room temperate is verified.
Our findings will enable the development of defect strategies that maximize the
functionality of the system, and further help in designing highly efficient
magneto-optoelectronic and spintronic devices.",2306.04978v1
2023-11-01,Large Energy Shifts of Crystal-field Excitations in Erbium Orthoferrite Driven by Internal Magnetic Fields,"Due to the complex interactions between rare-earth elements and transition
metals, as well as between themselves, rare-earth transition-metal oxides are
likely to exhibit highly intriguing and novel magnetic structures and dynamic
behaviours. Rare-earth elements in these compounds frequently demonstrate
unusual behaviours in their crystal-field (CF) excitations, which necessitate
thorough studies for in-depth comprehensions. When cooling from 10 K to 1.5 K
through the magnetic ordering temperature of $Er^{3+}$ at 4.1 K, we observed a
significant energy shift of the low-lying CF excitation of $Er^{3+}$ in erbium
orthoferrite ($ErFeO_3$) from 0.32 meV to 0.75 meV utilizing the inelastic
neutron-scattering technique. A sound CF model was proposed for $Er^{3+}$ in
$ErFeO_3$ by fitting to the observed CF excitation peaks, which enables to
explain all the observed experimental results in a very consistent manner.
According to the model, the ground crystal field level of $Er^{3+}$, which
corresponds to the lowest Kramers doublet supposed to be at zero energy
transfer, has been shifted by the internal magnetic fields induced by both
$Er^{3+}$ and $Fe^{3+}$ spin orders below and above the $Er^{3+}$ ordering
temperature, respectively. Additional measurements in various magnetic fields
offer compelling evidence in favour of this hypothesis. The measured external
field dependence of the CF excitation energy led to a derivation of the
internal field of $Er^{3+}$ as 0.54 T, which is strongly corroborated by
theoretical modelling. Additionally, the g-factor for the $Er^{3+}$ ground
state in $ErFeO_3$ shows an exceptionally significant anisotropy.",2311.00478v1
2015-06-18,Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating,"Since the discovery of n-type copper oxide superconductors, the evolution of
electron- and hole-bands and its relation to the superconductivity have been
seen as a key factor in unveiling the mechanism of high-Tc superconductors. So
far, the occurrence of electrons and holes in n-type copper oxides has been
achieved by chemical doping, pressure, and/or deoxygenation. However, the
observed electronic properties are blurred by the concomitant effects such as
change of lattice structure, disorder, etc. Here, we report on successful
tuning the electronic band structure of n-type Pr2-xCexCuO4 (x = 0.15)
ultrathin films, via the electric double layer transistor technique. Abnormal
transport properties, such as multiple sign reversals of Hall resistivity in
normal and mixed states, have been revealed within an electrostatic field in
range of -2 V to +2 V, as well as varying the temperature and magnetic field.
In the mixed state, the intrinsic anomalous Hall conductivity invokes the
contribution of both electron and hole-bands as well as the energy dependent
density of states near the Fermi level. The two-band model can also describe
the normal state transport properties well, whereas the carrier concentrations
of electrons and holes are always enhanced or depressed simultaneously in
electric fields. This is in contrast to the scenario of Fermi surface
reconstruction by antiferromagnetism, where an anti-correlation between
electrons and holes is commonly expected. Our findings paint the picture where
Coulomb repulsion plays an important role in the evolution of the electronic
states in n-type cuprate superconductors.",1506.05727v1
2018-02-23,Tuning the electronic and chemisorption properties of hexagonal MgO nanotubes by doping - Theoretical study,"Oxide materials offer a wide range of interesting physical and chemical
properties. Even more versatile behavior of oxides is seen at the nanoscale,
qualifying these materials for a number of applications. In this study we used
DFT calculations to investigate the physical and chemical properties of small
hexagonal MgO nanotubes of different length. We analyzed the effect of Li, B,
C, N, and F doping on the properties of the nanotubes. We find that all dopants
favor the edge positions when, incorporated into the nanotubes. Doping results
in the net magnetization whose value depends on the type of the impurity. Using
the CO molecule as a probe, we studied the adsorption properties of pristine
and doped MgO nanotubes. Our results show that the dopant sites are also the
centers of significantly altered chemical reactivity. While pristine MgO
nanotubes adsorb CO weakly, very strong adsorption at the dopant sites (B-, C-,
and N-doped nanotubes) or neighboring edge atoms (F- and Li-doped nanotubes) is
observed. Our results suggest that impurity engineering in oxide materials can
be a promising strategy for the development of novel materials with possible
use as selective adsorbents or catalysts.",1802.08440v2
2018-11-22,Oxygen-Octahedral-Tilting-Driven Topological Hall Effect in Ultrathin SrRuO3 Films,"Topological spin textures as an emerging class of topological matter offer a
medium for information storage and processing. The recently discovered
topological Hall effect (THE) is considered as a fingerprint for electrically
probing non-trivial spin-textures. But the origin of THE in oxides has remained
elusive. Here we report an observation of the THE in ultrathin (unit cells.
u.c.) 4d ferromagnetic SrRuO3 films grown on SrTiO3(001) substrates, which can
be attributed to the chiral ordering of spin structure (i.e., skyrmion-like) in
the single SrRuO3 layer without contacting 5d oxide SrIrO3 layer. It is
revealed that the RuO6 octahedral tilting induced by local
orthorhombic-to-tetragonal structural phase transition exists across the
SrRuO3/SrTiO3 interface, which naturally breaks the inversion symmetry. Our
theoretical calculations demonstrate that the Dzyaloshinskii-Moriya (DM)
interaction arises owing to the broken inversion symmetry and strong spin-orbit
interaction of 4d SrRuO3. This DM interaction can stabilize the N\'eel-type
magnetic skyrmions, which in turn accounts for the observed THE in transport.
The RuO6 octahedral tilting-induced DM interaction provides a pathway toward
the electrical control of the topological spin textures and resultant THE,
which is confirmed both experimentally and theoretically. Besides the
fundamental significance, the understanding of THE in oxides and its electrical
manipulation presented in this work could advance the low power cost
topological electronic and spintronic applications.",1811.09075v1
2017-11-02,Converged GW quasiparticle energies for transition metal oxide perovskites,"The ab initio calculation of quasiparticle (QP) energies is a technically and
computationally challenging problem. In condensed matter physics the most
widely used approach to determine QP energies is the GW approximation. Although
the GW method has been widely applied to many typical semiconductors and
insulators, its application to more complex compounds such as transition metal
oxide perovskites has been comparatively rare, and its proper use is not well
established from a technical point of view. In this work, we have applied the
single-shot G0W0 method to a representative set of transition metal oxide
perovskites including 3d (SrTiO3, LaScO3, SrMnO3, LaTiO3, LaVO3, LaCrO3,
LaMnO3, and LaFeO3), 4d (SrZrO3, SrTcO3, and Ca2RuO4) and 5d (SrHfO3, KTaO3 and
NaOsO3) compounds with different electronic configurations, magnetic orderings,
structural characteristics and bandgaps ranging from 0.1 to 6.1 eV. We discuss
the proper procedure to obtain well converged QP energies and accurate bandgaps
within single-shot G0W0 by comparing the conventional approach based on an
incremental variation of a specific set of parameters (number of bands, energy
cutoff for the plane-wave expansion and number of k-points and the basis-set
extrapolation scheme [Phys. Rev. B 90, 075125 (2014)]. In addition, we have
inspected the difference between the adoption of norm-conserving and ultrasoft
potentials in GW calculations. A minimal statistical analysis indicates that
the correlation of the GW data with the DFT gap is more robust than the
correlation with the experimental gaps; moreover we identify the static
dielectric constant as alternative useful parameter for the approximation of GW
gap in high-throughput automatic procedures. Finally, we compute the QP band
structure and spectra within the random phase approximation and compare the
results with available experimental data.",1711.00916v3
2021-08-17,Spin-charge interconversion in KTaO$_3$ two-dimensional electron gases,"Oxide interfaces exhibit a broad range of physical effects stemming from
broken inversion symmetry. In particular, they can display non-reciprocal
phenomena when time reversal symmetry is also broken, e.g., by the application
of a magnetic field. Examples include the direct and inverse Edelstein effects
(DEE, IEE) that allow the interconversion between spin currents and charge
currents. The DEE and IEE have been investigated in interfaces based on the
perovskite SrTiO$_3$ (STO), albeit in separate studies focusing on one or the
other. The demonstration of these effects remains mostly elusive in other oxide
interface systems despite their blossoming in the last decade. Here, we report
the observation of both the DEE and IEE in a new interfacial two-dimensional
electron gas (2DEG) based on the perovskite oxide KTaO$_3$. We generate 2DEGs
by the simple deposition of Al metal onto KTaO$_3$ single crystals,
characterize them by angle-resolved photoemission spectroscopy and
magnetotransport, and demonstrate the DEE through unidirectional
magnetoresistance and the IEE by spin-pumping experiments. We compare the
spin-charge interconversion efficiency with that of STO-based interfaces,
relate it to the 2DEG electronic structure, and give perspectives for the
implementation of KTaO$_3$ 2DEGs into spin-orbitronic devices.",2108.07479v1
2023-02-20,Observation of near room temperature thin film superconductivity of atmospherically stable Ag-Au mesoscopic thin film,"An environmentally stable mesoscopic thin film of Au of certain thickness has
been deposited thermally on top of a Ag+ implanted oxide substrate to develop a
close to room temperature superconductor. This thin film has been deposited in
two different stages. Initially, a sol-gel derived ion conducting metal oxide
(ICMO) thin film has been deposited by spin coating. Afterward, Ag+ has been
introduced inside ICMO thin film by a chemical method. Following this, a thin
layer of Au has been deposited on top of that Ag ion-implanted oxide via
thermal evaporation. The temperature dependent resistivity (R-T) has been
studied by four probe method. During high-to-low temperature sweep, around 240
K this thin film sample shows a sudden drop of resistance from 0.7 Ohm to 0.1
micro-Ohm. This 6-7 orders drop of resistance has been observed instantly
within <0.1 K temperature variation of the sample. This transition temperature
(TC) has been shifted toward the higher temperature by 5-6 degrees when
temperature has been increased from low to the higher side. During 2nd and 3rd
temperature cycling, both these transitions have been shifted by ~10 K towards
room temperature w.r.t the earlier. However, after three successive temperature
cycles, TC becomes stable and transitions occur close to 0 oC repeatedly. At
the low resistance phase, current level has been varied from +100 mA to -100 mA
which shows a random fluctuation of voltage drop within 10 nV range, indicating
resistance under such circumstance is too low to measure by Delta mode
electrical measurement (0.1 micro-Ohm). Besides, transition temperature reduces
to lower temperature by 4 K, after applying 1 tesla magnetic field
perpendicular to the thin film. Few YouTube video links of temperature
dependent electrical characterization of such a thin film is given next to the
acknowledgement section.",2302.09974v3
1999-11-23,Charge ordering and long-range interactions in layered transition metal oxides: a quasiclassical continuum study,"The competition between long-range and short-range interactions among holes
moving in an antiferromagnet (AF), is studied within a model derived from the
spin density wave picture of layered transition metal oxides. A novel numerical
approach is developed which allows one to solve the problem at finite hole
densities in very large systems (of order hundreds of lattice spacings), albeit
in a quasiclassical limit, and to correctly incorporate the long-range part of
the Coulomb interaction. The focus is on the problem of charge ordering and the
charge phase diagram: at low temperatures four different phases are found,
depending on the strength of the magnetic (dipolar) interaction generated by
the spin-wave exchange, and the density of holes. The four phases are the
Wigner crystal, diagonal stripes, a grid phase (horizontal-vertical stripe
loops) and a glassy-clumped phase. In the presence of both in-plane and
out-of-plane charged impurities the stripe ordering is suppressed, although
finite stripe segments persist. At finite temperatures multiscale
(intermittency) dynamics is found, reminiscent of that in glasses. The dynamics
of stripe melting and its implications for experiments is discussed.",9911380v2
2004-10-26,Orbital Physics in the Perovskite Ti Oxides,"In the perovskite Ti oxide RTiO3 (R=rare-earth ions), the Ti t2g orbitals and
spins in the 3d^1 state couple each other through the strong electron
correlations, resulting in a rich variety of orbital-spin phases. The origin
and nature of orbital-spin states of these Mott insulators have been
intensively studied. In this article, we review the studies on orbital physics
in the perovskite titanates. We focus on the following three topics: (1) the
origin and nature of the ferromagnetism as well as the orbital ordering in the
compounds with relatively small R ions such as GdTiO3 and YTiO3, (2) the origin
of the G-type antiferromagnetism and the orbital state in LaTiO3, and (3) the
orbital-spin structures in other AFM(G) compounds with relatively large R ions
(R=Ce, Pr, Nd and Sm). On the basis of these discussions, we discuss the whole
phase diagram together with mechanisms of the magnetic phase transition. We
also show that the Ti t2g degeneracy is inherently lifted in the titanates,
which allows the single-band descriptions of the ground-state and low-energy
electronic structures as a good starting point. Our analyses indicate that
these compounds offer touchstone materials described by the single-band Hubbard
model on the cubic lattice. From this insight, we also reanalyze the hole-doped
titanates. Experimentally revealed filling-dependent and bandwidth-dependent
properties and the critical behavior of the metal-insulator transitions are
discussed in the light of theories based on the single-band Hubbard models.",0410650v1
2005-11-05,Polarons and confinement of electronic motion to two dimensions in a layered transition metal oxide,"A very remarkable feature of the layered transition metal oxides (TMOs),
whose most famous members are the high-temperature superconductors (HTSs), is
that even though they are prepared as bulk three-dimensional single crystals,
they display hugely anisotropic electrical and optical properties, seeming to
be insulating perpendicular to the layers and metallic within them. This is the
phenomenon of confinement, a concept at odds with the conventional theory of
solids and recognized as due to magnetic and electron-lattice interactions in
the layers which must be overcome at a substantial energy cost if electrons are
to be transferred between layers. The associated energy gap or 'pseudogap' is
particularly obvious in experiments where charge is moved perpendicular to the
planes, most notably scanning tunneling microscopy (STM) and polarized infrared
spectroscopy. Here, using the same experimental tools, we show that there is a
second family of TMOs - the layered manganites La2-2xSr1+2xMn2O7 (LSMO) - with
even more extreme confinement and pseudogap effects. The data, which are the
first to resolve atoms in any metallic manganite, demonstrate quantitatively
that because they are attached to polarons - lattice and spin textures within
the planes -, it is equally difficult to remove carriers from the planes via
vacuum tunneling into a conventional metallic tip, as it is for them to move
between Mn-rich layers within the material itself.",0511138v1
2006-08-29,Correlation Energies in Distorted 3d-$t_{2g}$ Perovskite Oxides,"Using an effective low-energy Hamiltonian derived from the first-principles
electronic structure calculations for the narrow $t_{2g}$ bands of YTiO$_3$,
LaTiO$_3$, YVO$_3$, and LaVO$_3$, we evaluate the contributions of the
correlation energy ($E_C$) to the stability of different magnetic structures,
which can be realized in these distorted perovskite oxides. We consider two
approximations for $E_C$, which are based on the regular perturbation theory
expansion around a nondegenerate Hartree-Fock ground state. One is the second
order of perturbation theory, which allows us to compare the effects of local
and nonlocal correlations. Another one is the local $t$-matrix approach, which
allows us to treat some higher-order contributions to $E_C$. The correlation
effects systematically improve the agreement with the experimental data and
additionally stabilize the experimentally observed $G$- and $C$-type
antiferromagnetic (AFM) structures in YVO$_3$ and LaVO$_3$, though the absolute
magnitude of the stabilization energy is sensitive to the level of
approximations and somewhat smaller in the $t$-matrix method. The nonlocal
correlations additionally stabilize the ferromagnetic ground state in YTiO$_3$
and the $C$-type AFM ground state in LaVO$_3$. Amongst two inequivalent
transition-metal sites in the monoclinic structure, the local correlations are
stronger at the sites with the least distorted environment. Limitations of the
regular perturbation-theory expansion for LaTiO$_3$ are also discussed.",0608625v1
2008-01-15,Exchange Interaction and $T_c$ in Alkaline-earth-metal-oxide-based DMS without Magnetic Impurities: First Principle Pseudo-SIC and Monte Carlo Calculation,"The prospects of half-metallic ferromagnetism being induced by the
incorporation of C atoms into alkaline-earth-metal-oxides are investigated by
the first principle calculation. The origin of the ferromagnetism is discussed
through the calculation of the electronic structure and exchange coupling
constant by using the pseudo-potential-like self-interaction-corrected local
spin density method. The Curie temperature ($T_c$) is also predicted by
employing the Monte Carlo simulation. It is shown that by taking the electron
self-interaction into account, the half-metallic ferromagnetism induced by C in
the host materials is more stabilized in comparison with the standard LDA case,
and the C's $2p$ electron states in the bandgap become more localized resulting
in the predominance of the short-ranged exchange interaction. While the
ferromagnetism in MgO$_{1-x}$C$_x$ is stabilized due to the exchange
interaction of the $1st$-nearest neighbor pairs and might be suppressed by the
anti-ferromagnetic super-exchange interaction at higher $x$, the ferromagnetism
in CaO$_{1-x}$C$_x$, SrO$_{1-x}$C$_x$, and BaO$_{1-x}$C$_x$ is stabilized by
both the $1st$- and $2nd$-nearest neighbor pairs, and $T_c$ monotonously
increases with the C concentration.",0801.2249v1
2008-06-02,Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs,"Since the discovery of high transition-temperature (Tc) superconductivity in
copper oxides two decades ago, continuous efforts have been devoted to
searching for similar phenomenon in other compounds. With the exception of MgB2
(Tc =39 K), however, Tc is generally far lower than desired. Recently,
breakthrough has been made in a new class of oxypnictide compounds. Following
the initial discovery of superconductivity in LaO1-x FxFeAs (Tc =26 K), Tc
onset has been raised to 55 K in ReO1-xFxFeAs (Re: Ce, Pr, Nd, Sm). Meanwhile,
unravelling the nature of the energy associated with the formation of
current-carrying pairs (Cooper pairs), referred to as the superconducting
energy gap, is the first and vital step towards understanding why the
superconductivity occurs at such high temperature and is also important for
finding superconductors with still higher Tc. Here we show that, on the basis
of the nuclear magnetic resonance (NMR) measurements in PrO0.89F0.11FeAs (Tc
=45 K), the Cooper pair is in the spin-singlet state (two spins are
anti-paralleled), with two energy gaps opening below Tc. The results strongly
suggest the existence of nodes (zeros) in the gap. None of superconductors
known to date has such unique gap features, although copper-oxides and MgB2
share part of them.",0806.0249v1
2009-01-17,Electrostatic co-assembly of iron oxide nanoparticles and polymers : towards the generation of highly persistent superparamagnetic nanorods,"A paradigm proposed recently by Boal et al. (A.K. Boal et al., Nature 404,
746-748, 2000) deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of colloidal and supracolloidal
assemblies. It is anticipated that these constructs could be made of different
shapes, patterns and functionalities and could constitute the components of
future nanodevices including sensors, actuators or nanocircuits. Here we report
a protocol that allowed us to fabricate such nanoparticle aggregates. The
building blocks of the constructs were anionically coated iron oxide
nanocrytals (superparamagnetic, size 7 nm) and cationic-neutral block
copolymers. We have shown that the electrostatic interactions between charged
species can be controlled by tuning the ionic strength of the dispersion. Under
appropriate conditions, the control of electrostatics resulted in the
elaboration of spherical or elongated aggregates at the micrometer length
scale. The elongated aggregates were found to be rod-like, with diameters of a
few hundred nanometers and lengths between 1 and 50 micrometers. In addition to
their remarkable stiffness, the nanostructured rods were found to reorient
along with an externally applied magnetic field, in agreement with the laws of
superparamagnetism.",0901.2667v1
2009-04-12,Long Range Coulomb Interactions and Nanoscale Electronic Inhomogeneities in Correlated Oxides,"Electronic, magnetic or structural inhomogeneities ranging in size from
nanoscopic to mesoscopic scales seem endemic, and are possibly generic, to
colossal magnetoresistance manganites and other transition metal oxides. We
show here that an extension, to include long range Coulomb interactions, of a
quantum two-fluid $\ell-b$ model proposed recently for manganites [Phys. Rev.
Lett., {\bf 92}, 157203 (2004)] leads to an excellent description of such
inhomogeneities. In the $\ell-b$ model two very different kinds of electronic
states, one localized and polaronic ($\ell$), and the other extended or broad
band ($b$) co-exist. For model parameters appropriate to manganites, and even
within a simple dynamical mean-filed theory (DMFT) framework, it describes many
of the unusual phenomena seen in manganites, including colossal
magnetoresistance (CMR), qualitatively and quantitatively. However, in the
absence of long ranged Coulomb interaction, a system described by such a model
would actually phase separate, into macroscopic regions of $l$ and $b$
electrons respectively. As we show in this paper, in the presence of Coulomb
interactions, the {\em macroscopic} phase separation gets suppressed, and
instead nanometer scale regions of polarons interspersed with band electron
puddles appear, constituting a new kind of quantum Coulomb glass. Our work
points to an interplay of strong correlations, long range Coulomb interaction
and dopant ion disorder as the origin of nanoscale inhomogeneities, rather than
disorder frustrated phase competition as is generally believed. Based on this,
we argue that the observed micrometer(meso)-scale inhomogeneities owe their
existence to extrinsic causes, eg. strain due to cracks and defects. We suggest
possible experiments to validate our speculation.",0904.1886v1
2010-08-16,"Second Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]","We have discovered a new homologous series of iron pnictide oxides
(Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]. These compounds have perovskite-like
blocking layers between Fe2As2 layers. The structure of new compounds are
tetragonal with space groups of P4/nmm for n = 2 and 4 and P4mm for n = 3,
which are similar to those of (Fe2As2)(Can+1(Sc,Ti)nOy)[n = 3,4,5] found in our
previous study. Compounds with n = 3 and 4 have new crystal structures with 3
and 4 sheets of perovskite layers, respectively, including a rock salt layer in
each blocking layer. The a-axis lengths of the three compounds are
approximately 3.8 A, which are close to those of FeSe and LiFeAs.
(Fe2As2)(Ca6(Al,Ti)4Oy) exhibited bulk superconductivity in magnetization
measurement with Tc(onset)~36 K and resistivity drop was observed at ~39 K.
(Fe2As2)(Ca5(Al,Ti)3Oy) also showed large diamagnetism at low temperatures.
These new compounds indicate considerable rooms are still remaining for new
superconductors in layered iron pnictides.",1008.2582v4
2011-08-03,Link between spin fluctuations and Cooper pairing in copper oxide superconductors,"Although it is generally accepted that superconductivity (SC) is
unconventional in the high- transition temperature copper oxides (high-Tc
cuprates), the relative importance of phenomena such as spin and charge
(stripe) order, SC fluctuations, proximity to a Mott insulator, a pseudogap
phase, and quantum criticality are still a matter of great debate1. In
electron-doped cuprates, the absence of an anomalous pseudogap phase in the
underdoped region of the phase diagram2 and weaker electron correlations3,4,
suggest that Mott physics and other unidentified competing orders are less
relevant and that antiferromagnetic (AFM) spin fluctuations are the dominant
feature. Here we demonstrate that a linear-temperature (T-linear) scattering
rate - a key feature of the anomalous normal state properties of the cuprates -
is correlated with the Cooper pairing (SC). Through a study of magnetotransport
in thin films of the electron-doped cuprate La2 xCexCuO4 (LCCO), we show that
an envelope of T-linear scattering surrounds the SC phase, and survives to zero
temperature when superconductivity is suppressed by magnetic fields. Comparison
with similar behavior found in organic superconductors5 strongly suggests that
the T-linear resistivity is caused by spin-fluctuation scattering. Our results
establish a fundamental connection between AFM spin fluctuations and the
pairing mechanism of high temperature superconductivity in the cuprates.",1108.0940v1
2012-06-06,The role of oxygen vacancies on the structure and the density of states of iron doped zirconia,"In this paper we study, both with theoretical and experimental approach, the
effect of iron doping in zirconia. Combining density functional theory (DFT)
simulations with the experimental characterization of thin films, we show that
iron is in the Fe3+ oxidation state and accordingly that the films are rich in
oxygen vacancies (VO). VO favor the formation of the tetragonal phase in doped
zirconia (ZrO2:Fe) and affect the density of state at the Fermi level as well
as the local magnetization of Fe atoms. We also show that the Fe(2p) and Fe(3p)
energy levels can be used as a marker for the presence of vacancies in the
doped system. In particular the computed position of the Fe(3p) peak is
strongly sensitive to the VO to Fe atoms ratio. A comparison of the theoretical
and experimental Fe(3p) peak position suggests that in our films this ratio is
close to 0.5. Besides the interest in the material by itself, ZrO2:Fe
constitutes a test case for the application of DFT on transition metals
embedded in oxides. In ZrO2:Fe the inclusion of the Hubbard U correction
significantly changes the electronic properties of the system. However the
inclusion of this correction, at least for the value U = 3.3 eV chosen in the
present work, worsen the agreement with the measured photo-emission valence
band spectra.",1206.1197v4
2012-07-12,Fingerprints of spin-orbital entanglement in transition metal oxides,"The concept of spin-orbital entanglement on superexchange bonds in transition
metal oxides is introduced and explained on several examples. It is shown that
spin-orbital entanglement in superexchange models destabilizes the long-range
(spin and orbital) order and may lead either to a disordered spin-liquid state
or to novel phases at low temperature which arise from strongly frustrated
interactions. Such novel ground states cannot be described within the
conventionally used mean field theory which separates spin and orbital degrees
of freedom. Even in cases where the ground states are disentangled,
spin-orbital entanglement occurs in excited states and may become crucial for a
correct description of physical properties at finite temperature. As an
important example of this behaviour we present spin-orbital entanglement in the
$R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature
properties of these compounds can be understood only using entangled states:
($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence
of transition temperatures for the onset of orbital and magnetic order on the
ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$)
dimerization observed in the magnon spectra for the $C$-type antiferromagnetic
phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in
an ordered phase with coexisting antiferromagnetic and alternating orbital
order introduces topological constraints for the hole propagation and will thus
radically modify transport properties in doped Mott insulators where hole
motion implies simultaneous spin and orbital excitations.",1207.3010v1
2012-11-02,Topological phases in layered pyrochlore oxide thin films along the [111] direction,"We theoretically study a multi-band Hubbard model of pyrochlore oxides of the
form A$_2$B$_2$O$_7$, where B is a heavy transition metal ion with strong
spin-orbit coupling, in a thin film geometry orientated along the [111]
direction. Along this direction, the pyrochlore lattice consists of alternating
kagome and triangular lattice planes of B ions. We consider a single kagome
layer, a bilayer, and the two different trilayers. As a function of the
strength of the spin-orbit coupling, the direct and indirect $d$-orbital
hopping, and the band filling, we identify a number of scenarios where a
non-interacting time-reversal invariant Z$_2$ topological phase is expected and
we suggest some candidate materials. We study the interactions in the
half-filled $d$-shell within Hatree-Fock theory and identify parameter regimes
where a zero magnetic field Chern insulator with Chern number $\pm1$ can be
found. The most promising geometries for topological phases appear to be the
bilayer which supports both a Z$_2$ topological insulator and a Chern
insulator, and the triangular-kagome-triangular trilayer which supports a
relatively robust Chern insulator phase.",1211.0562v2
2013-03-06,ARPES: A probe of electronic correlations,"Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. Among the various classes of complex systems, of
great interest are the transition metal oxides, which have been at the center
stage in condensed matter physics for the last four decades. Following a
general introduction to the topic, we will lay the theoretical basis needed to
understand the pivotal role of ARPES in the study of such systems. After a
brief overview on the state-of-the-art capabilities of the technique, we will
review some of the most interesting and relevant case studies of the novel
physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.",1303.1438v1
2014-08-18,Anomalous magnetoresistance in the spinel superconductor LiTi2O4,"Transition-metal oxides offer an opportunity to explore unconventional
superconductors, where the superconductivity (SC) is often interrelated with
novel phenomena such as spin/charge order, fluctuations, and Fermi surface
instability (1-3). LiTi2O4 (LTO) is a unique compound in that it is the only
known spinel oxide superconductor. In addition to electron-phonon coupling,
electron-electron and spin fluctuation contributions have been suggested as
playing important roles in the microscopic mechanism for its superconductivity
(4-8). However, the lack of high quality single crystals has thus far prevented
systematic investigation of their transport properties (9). Here, we report a
careful study of transport and tunneling spectroscopy in epitaxial LTO thin
films. In the superconducting state, the energy gap was found to decrease as a
quadratic function of magnetic field. In the normal state, an unusual
magnetoresistance (MR) was observed where it changes from anisotropic positive
to isotropic negative as the temperature is increased. A constant charge
carrier concentration without any abrupt change in lattice parameters as a
function of temperature suggests that the isotropic MR stems from the
suppression of spin scattering/fluctuations, while the anisotropic term
originates from an orbital contribution. These observations point to an
important role strong correlations play in this unique superconductor.",1408.3894v1
2014-09-22,Analysis of charge states in the mixed valent ionic insulator AgO,"The doubly ionized $d^9$ copper ion provides, originally in La$_2$CuO$_4$ and
later in many more compounds, the platform for high temperature
superconductivity when it is forced toward higher levels of oxidation. The
nearest chemical equivalent is Ag$^{2+}$, which is almost entirely avoided in
nature. AgO is an illustrative example, being an unusual nonmagnetic insulating
compound with an open $4d$ shell on one site. This compound has been
interpreted in terms of one Ag$^{3+}$ ion at the fourfold site and one Ag$^{+}$
ion that is twofold coordinated. We analyze more aspects of this compound,
finding that indeed the Ag$^{3+}$ ion supports only four occupied $4d$-based
Wannier functions per spin, while Ag$^+$ supports five, yet their physical
charges are nearly equal. The oxygen $2p$ Wannier functions display two
distinct types of behavior, one type of which includes conspicuous Ag $4d$
tails. Calculation of the Born effective charge tensor shows that the mean
effective charges of the Ag ions differ by about a factor of two, roughly
consistent with the assigned formal charges. We analyze the $4d$ charge density
and discuss it in terms of recent insights into charge states of insulating
(and usually magnetic) transition metal oxides. What might be expected in
electron- and hole-doped AgO is discussed briefly.",1409.6371v1
2014-09-29,Convergence of quasiparticle self-consistent GW calculations of transition metal monoxides,"Finding an accurate ab initio approach for calculating the electronic
properties of transition metal oxides has been a problem for several decades.
In this paper, we investigate the electronic structure of the transition metal
monoxides MnO, CoO, and NiO in their undistorted rock-salt structure within a
fully iterated quasiparticle self-consistent GW (QPscGW) scheme. We study the
convergence of the QPscGW method, i.e., how the quasiparticle energy
eigenvalues and wavefunctions converge as a function of the QPscGW iterations,
and we compare the converged outputs obtained from different starting
wavefunctions. We find that the convergence is slow and that a one-shot
G$_0$W$_0$ calculation does not significantly improve the initial eigenvalues
and states. It is important to notice that in some cases the ""path"" to
convergence may go through energy band reordering which cannot be captured by
the simple initial unperturbed Hamiltonian. When we reach a fully iterated
solution, the converged density of states, band-gaps and magnetic moments of
these oxides are found to be only weakly dependent on the choice of the
starting wavefunctions and in reasonably good agreement with the experiment.
Finally, this approach provides a clear picture of the interplay between the
various orbitals near the Fermi level of these simple transition metal
monoxides. The results of these accurate {\it ab initio} calculations can
provide input for models aiming at describing the low energy physics in these
materials.",1409.8312v2
2015-01-13,Weyl semimetal from spontaneous inversion symmetry breaking in pyrochlore oxides,"We study the electronic properties of strongly spin-orbit coupled electrons
on the elastic pyrochlore lattice. Akin to the Peierls transition in
one-dimensional systems, the coupling of the lattice to the electronic degrees
of freedom can stabilize a spontaneous deformation of the crystal. This
deformation corresponds to a breathing mode, which breaks the inversion
symmetry. We find that for intermediate values of the staggered strain, the
inversion-symmetry broken phase realizes a topological Weyl semimetal. In the
temperature-elasticity phase diagram, the Weyl semimetal shows a reentrant
phase behavior: it can be reached from a symmetric phase realized both at
higher and at lower temperatures. The symmetric phase is a Dirac semimetal,
which is protected by the non-symmorphic space group of the pyrochlore lattice.
Beyond a critical value of the staggered strain, the symmetry-broken phase is a
fully gapped trivial insulator. The surface states of the Weyl semimetal form
open Fermi arcs and we observe that their connectivity depends on the
termination of the crystal. In particular, for the $\{111\}$ films, the
semiclassical closed electronic orbits of the surface states in a magnetic
field cross the bulk either twice, four, six or twelve times. We demonstrate
how one can tune the number of bulk crossings through a Lifshitz-like
transition of the Fermi arcs, which we call Weyl-Lifshitz transition, by
applying a surface potential. Our results offer a route to a topological Weyl
semimetal in nonmagnetic materials and might be relevant for pyrochlore oxides
with heavy transition-metal ions such as alloys of iridates.",1501.03029v1
2015-02-27,Electrically Tunable Band Gap in Antiferromagnetic Mott Insulator Sr2IrO4,"The electronic band gap in conventional semiconductor materials, such as
silicon, is fixed by the material's crystal structure and chemical composition.
The gap defines the material's transport and optical properties and is of great
importance for performance of semiconductor devices like diodes, transistors
and lasers. The ability to tune its value would allow enhanced functionality
and flexibility of future electronic and optical devices. Recently, an
electrically tunable band gap was realized in a 2D material - electronically
gated bilayer graphene [1-3]. Here we demonstrate the realization of an
electrically tunable band gap in a 3D antiferromagnetic Mott insulator Sr2IrO4.
Using nano-scale contacts between a sharpened Cu tip and a single crystal of
Sr2IrO4, we apply a variable external electric field up to a few MV/m and
demonstrate a continuous reduction in the band gap of Sr2IrO4 by as much as
16%. We further demonstrate the feasibility of reversible resistive switching
and electrically tunable anisotropic magnetoresistance,which provide evidence
of correlations between electronic transport, magnetic order, and orbital
states in this 5d oxide. Our findings suggest a promising path towards band gap
engineering in 5d transition-metal oxides that could potentially lead to
appealing technical solutions for next-generation electronic devices.",1502.07982v1
2015-05-11,Impact of low-dose electron irradiation on n+p silicon strip sensors,"The response of n+p silicon strip sensors to electrons from a Sr-90 source
was measured using a multi-channel read-out system with 25 ns sampling time.
The measurements were performed over a period of several weeks, during which
the operating conditions were varied. The sensors were fabricated by Hamamatsu
Photonics K.K. on 200 micrometer thick float-zone and magnetic-Czochralski
silicon. Their pitch was 80 micrometer, and both p-stop and p-spray isolation
of the n+ strips were studied. The electrons from the Sr-90 source were
collimated to a spot with a full-width-at-half-maximum of 2 mm at the sensor
surface, and the dose rate in the SiO2 at the maximum was about 50 Gy/d.
  After only a few hours of making measurements, significant changes in charge
collection and charge sharing were observed. Annealing studies, with
temperatures up to 80{\deg}C and annealing times of 18 hours, showed that the
changes can only be partially annealed. The observations can be qualitatively
explained by the increase of the positive oxide-charge density due to the
ionization of the SiO2 by the radiation from the {\ss} source. TCAD simulations
of the electric field in the sensor for different oxide-charge densities and
different boundary conditions at the sensor surface support this explanation.
  The relevance of the measurements for the design of p+n strip sensors is
discussed.",1505.02672v1
2015-04-29,"Comparative Study of Optical and Magneto-Optical Properties of Normal, Disordered and Inverse Spinel Type Oxides","Co$_3$O$_4$, ZnFe$_2$O$_4$, CoFe$_2$O$_4$, ZnCo$_2$O$_4$, and Fe$_3$O$_4$
thin films were fabricated by pulsed laser deposition at high and low
temperatures resulting in crystalline single-phase normal, inverse, as well as
disordered spinel oxide thin films with smooth surface morphology. The
dielectric function, determined by spectroscopic ellipsometry in a wide
spectral range from 0.5 eV to 8.5 eV, is compared with the magneto-optical
response of the dielectric tensor, investigated by magneto-optical Kerr effect
(MOKE) spectroscopy in the spectral range from 1.7 eV to 5.5 eV with an applied
magnetic field of 1.7 T. Crystal field, inter-valence and inter-sublattice
charge transfer transitions, and transitions from O$_{2p}$ to metal cation 3d
or 4s bands are identified in both the principal diagonal elements and the
magneto-optically active off-diagonal elements of the dielectric tensor.
Depending on the degree of cation disorder, resulting in local symmetry
distortion, the magneto-optical response is found to be strongest for high
crystal quality inverse spinels and for disordered normal spinel structure,
contrary to the first principle studies of CoFe$_2$O$_4$ and ZnFe$_2$O$_4$. The
results presented provide a basis for deeper understanding of light-matter
interaction in this material system that is of vital importance for
device-related phenomena and engineering.",1505.04664v3
2015-07-05,Normal-state nodal electronic structure in underdoped high-Tc copper oxides,"An outstanding problem in the field of high-transition-temperature (high Tc)
superconductivity is the identification of the normal state out of which
superconductivity emerges in the mysterious underdoped regime. The normal state
uncomplicated by thermal fluctuations is effectively accessed by the use of
applied magnetic fields sufficiently strong to suppress long-range
superconductivity at low temperatures. Proposals in which the normal ground
state is characterised by small Fermi surface pockets that exist in the absence
of symmetry breaking have been superseded by models based on the existence of a
superlattice that breaks the translational symmetry of the underlying lattice.
Recently, a charge superlattice model that positions a small electron-like
Fermi pocket in the vicinity of the nodes (where the superconducting gap is
minimum) has been proposed a replacement for the prevalent superlattice models
that position the Fermi pocket in the vicinity of the pseudogap at the
antinodes (where the superconducting gap is maximum). Although some ingredients
of symmetry breaking have been recently revealed by crystallographic studies,
their relevance to the electronic structure remains unresolved. Here we report
angle-resolved quantum oscillation measurements in the underdoped copper oxide
YBa2Cu3O6+x. These measurements reveal a normal ground state comprising
electron-like Fermi surface pockets located in the vicinity of the
superconducting gap minima (or nodes), and further point to an underlying
superlattice structure of low frequency and long wavelength with features in
common with the charge order identified recently by complementary spectroscopic
techniques.",1507.01195v1
2015-10-26,A close look at antiferromagnetism in multidimensional phase diagram of electron-doped copper oxide,"Emergency of superconductivity at the instabilities of antiferromagnetism
(AFM), spin/charge density waves has been widely recognized in unconventional
superconductors. In copper-oxide superconductors, spin fluctuations play a
predominant role in electron pairing with electron dopants yet composite orders
veil the nature of superconductivity for hole-doped family. However, in
electron-doped ones the ending point of AFM is still in controversy for
different probes or its sensitivity to oxygen content. Here, by carefully
tuning the oxygen content, a systematic study of Hall signal and
magnetoresistivity up to 58 Tesla on optimally doped La2-xCexCuO4+-{\delta} (x
= 0.10) thin films identifies two characteristic temperatures at 62.5+-7.5 K
and 25+-5 K. The former is quite robust whereas the latter becomes flexible
with increasing magnetic field, thereby linked to two- and three-dimensional
AFM, evident from the multidimensional phase diagram as a function of oxygen as
well as Ce dopants. Consequently, the observation of extended AFM phase in
contrast to {\mu}SR probe corroborates an elevated critical doping in field,
providing an unambiguous picture to understand the interactions between AFM and
superconductivity.",1510.07388v1
2016-03-24,Unconventional Magnetism and Band Gap Formation in LiFePO4: Consequence of Polyanion Induced Non-planarity,"Oxygen plays a critical role in strongly correlated transition metal oxides
as crystal field effect is one of the key factors that determine the degree of
localization of the valence d/f states. Based on the localization, a set of
conventional mechanisms such as Mott-Hubbard, Charge-transfer and Slater were
formulated to explain the antiferromagnetic and insulating (AFI) phenomena in
many of these correlated systems. From the case study on LiFePO4, through
density-functional calculations, we demonstrate that none of these mechanisms
are strictly applicable to explain the AFI behavior when the transition metal
oxides have polyanions such as (PO4)3-. The symmetry-lowering of the
metal-oxygen complex, to stabilize the polyanion, creates an asymmetric crystal
field for d/f states. In LiFePO4 this field creates completely non-degenerate
Fe-d states which, with negligible p-d and d-d covalent interactions, become
atomically localized to ensure a gap at the Fermi level. Due to large exchange
splitting, high spin state is favored and an antiferromagnetic configuration is
stabilized. For the prototype LiFePO4, independent electron approximation is
good enough to obtain the AFI ground state. Inclusion of additional correlation
measures like Hubbard U simply amplifies the gap and therefore LiFePO4 can be
preferably called as weakly coupled Mott insulator.",1603.08403v1
2017-02-19,Correlative cellular ptychography with functionalized nanoparticles at the Fe L-edge,"Precise localization of nanoparticles within a cell is crucial to the
understanding of cell-particle interactions and has broad applications in
nanomedicine. Here, we report a proof-of-principle experiment for imaging
individual functionalized nanoparticles within a mammalian cell by correlative
microscopy. Using a chemically-fixed, HeLa cell labeled with fluorescent
core-shell nanoparticles as a model system, we implemented a graphene-oxide
layer as a substrate to significantly reduce background scattering. We
identified cellular features of interest by fluorescence microscopy, followed
by scanning transmission X-ray tomography to localize the particles in 3D, and
ptychographic coherent diffractive imaging of the fine features in the region
at high resolution. By tuning the X-ray energy to the Fe L-edge, we
demonstrated sensitive detection of nanoparticles composed of a 22 nm magnetic
Fe3O4 core encased by a 25-nm-thick fluorescent silica (SiO2) shell. These
fluorescent core-shell nanoparticles act as landmarks and offer clarity in a
cellular context. Our correlative microscopy results confirmed a subset of
particles to be fully internalized, and high-contrast ptychographic images
showed two oxidation states of individual nanoparticles with a resolution of
~16.5 nm. The ability to precisely localize individual fluorescent
nanoparticles within mammalian cells will expand our understanding of the
structure/function relationships for functionalized nanoparticles.",1702.05680v1
2017-08-06,Electrical transport and optical band gap of NiFe$_\textrm{2}$O$_\textrm{x}$ thin films,"We fabricated NiFe$_\textrm{2}$O$_\textrm{x}$ thin films on
MgAl$_2$O$_4$(001) substrates by reactive dc magnetron co-sputtering varying
the oxygen partial pressure during deposition. The fabrication of a variable
material with oxygen deficiency leads to controllable electrical and optical
properties which would be beneficial for the investigations of the transport
phenomena and would, therefore, promote the use of such materials in spintronic
and spin caloritronic applications. We used several characterization techniques
in order to investigate the film properties, focusing on their structural,
magnetic, electrical, and optical properties. From the electrical resistivity
measurements we obtained the conduction mechanisms that govern the systems in
high and low temperature regimes, extracting low thermal activation energies
which unveil extrinsic transport mechanisms. The thermal activation energy
decreases in the less oxidized samples revealing the pronounced contribution of
a large amount of electronic states localized in the band gap to the electrical
conductivity. Hall effect measurements showed the mixed-type semiconducting
character of our films. The optical band gaps were determined via
ultraviolet-visible spectroscopy. They follow a similar trend as the thermal
activation energy, with lower band gap values in the less oxidized samples.",1708.01937v1
2018-04-07,Bare and Polymer Coated Iron Oxide Superparamagnetic Nanoparticles for Effective Removal of U (VI) from Acidic and Neutral Aqueous Medium,"Superparamagnetic {\gamma}-Fe2O3 nanoparticles (5 nm diameter) were
synthesized in water. The bare particles exhibit good colloidal stability at ~
pH 2 because of the strong electrostatic repulsion with a surface charge of +25
mV. The polyacrylic acid (PAA)-coated particles exhibit remarkable colloidal
stability at ~ pH 7 with abundant free carboxyl groups as reactive sites for
subsequent functionalization. In this work, we used zeta potential analysis,
transmission electron microscopy, small angle X-ray scattering, and Inductively
coupled plasma mass spectrometry to investigate the adsorption behavior of U
(VI) on bare and coated colloidal superparamagnetic nanoparticles at pH 2 and
pH 7. At pH 2, uranyl ion (UO22+) absorbed on the surface of the bare particles
with decreasing particle surface charge. This induced particle agglomeration.
At pH 7, uranyl ion (UO22+) hydrolyzed and formed plate-like particles of
uranium hydroxide that were ~ 50 nm in diameter. The PAA-coated iron oxide
nanoparticles absorbed on the surface of these U (VI) hydroxide plates to form
large aggregates that precipitate to the bottom of the dispersion. At both pH 2
and pH 7, the resulting U (VI)/nanoparticle complex can be easily collected and
extracted from the aqueous environment via an external magnetic field. The
results show that both bare and polymer-coated superparamagnetic {\gamma}-Fe2O3
nanoparticles are potential absorbents for removing U (VI) from water.",1804.02522v1
2013-08-26,Superconductivity in Ba1-xKxTi2Sb2O (0 < x < 1) controlled by charge doping,"The solid solution of antimonide-oxides Ba1-xKxTi2Sb2O (0 < x < 1) has been
synthesized by solid-state reactions and characterized by X-ray powder
diffraction (CeCr2Si2C-type structure; P4/mmm, Z = 1). The crystal structure
consists of Ti2Sb2O-layers that are stacked with layers of barium atoms along
the c-axis. BaTi2Sb2O is a known superconductor with a critical temperature
(Tc) of 1.2 K. Substitution of barium through potassium raises Tc up to 6.1 K
at 12 % potassium, while no superconductivity emerges with concentrations
higher than 20 %. Anomalies in electrical transport and magnetic susceptibility
indicate charge density wave (CDW) instabilities. The CDW transition
temperatures (Ta) decrease from 50 K in the parent compound to 28 K at 10 %
potassium substitution. No CDW transition was detected at higher
concentrations, and no evidence for a reduction of the lattice symmetry below
Ta was found. The lattice parameters vary linearly while the unit cell volume
increases with higher potassium concentrations. The phase diagrams Tc(x) and
Ta(x) of Ba1-xKxTi2Sb2O are remarkably similar to the known series
Ba1-xNaxTi2Sb2O (0 < x < 0.33) in spite of the reverse volume effect. From this
we conclude that the charge and not the volume determines the phase diagrams of
these superconducting antimony oxides.",1308.5660v1
2017-04-06,Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil,"Superparamagnetic iron-oxide nanoparticles can be used in a variety of
medical applications like vascular or targeted imaging. Magnetic particle
imaging (MPI) is a promising tomographic imaging technique that allows
visualizing the 3D nanoparticle distribution concentration in a non-invasive
manner. The two main strengths of MPI are high temporal resolution and high
sensitivity. While the first has been proven in the assessment of dynamic
processes like cardiac imaging, it is unknown how far the detection limit of
MPI can be lowered. Within this work, we will present a highly sensitive
gradiometric receive-coil unit combined with a noise-matching network tailored
for the measurement of mice. The setup is capable of detecting 5 ng of iron in
vitro at 2.14 sec acquisition time. In terms of iron concentration we are able
to detect 156 {\mu}g/L marking the lowest value that has been reported for an
MPI scanner so far. In vivo MPI mouse images of a 512 ng bolus at 21.5 ms
acquisition time allow for capturing the flow of an intravenously injected
tracer through the heart of a mouse. Since it has been rather difficult to
compare detection limits across MPI publications we propose guidelines
improving the comparability of future MPI studies.",1704.01789v2
2012-01-14,Effect of lattice geometry on magnon Hall effect in ferromagnetic insulators,"We have investigated the thermal Hall effect of magnons for various
ferromagnetic insulators. For pyrochlore ferromagnetic insulators
Lu$_2$V$_2$O$_7$, Ho$_2$V$_2$O$_7$, and In$_2$Mn$_2$O$_7$, finite thermal Hall
conductivities have been observed below the Curie temperature $T_C$ . From the
temperature and magnetic field dependences, it is concluded that magnons are
responsible for the thermal Hall effect. The Hall effect of magnons can be well
explained by the theory based on the Berry curvature in momentum space induced
by the Dzyaloshinskii-Moriya (DM) interaction. The analysis has been extended
to the transition metal (TM) oxides with perovskite structure. The thermal Hall
signal was absent or far smaller in La$_2$NiMnO$_6$ and YTiO$_3$, which have
the distorted perovskite structure with four TM ions in the unit cell. On the
other hand, a finite thermal Hall response is discernible below $T_C$ in
another ferromagentic perovskite oxide BiMnO$_3$, which shows orbital ordering
with a larger unit cell. The presence or absence of the thermal Hall effect in
insulating pyrochlore and perovskite systems reflect the geometric and
topological aspect of DM-induced magnon Hall effect.",1201.3002v2
2016-12-13,Multiple supersonic phase fronts launched at a complex-oxide hetero-interface,"Selective optical excitation of a substrate lattice can drive phase changes
across hetero-interfaces. This phenomenon is a non-equilibrium analogue of
static strain control in heterostructures and may lead to new applications in
optically controlled phase change devices. Here, we make use of time-resolved
non-resonant and resonant x-ray diffraction to clarify the underlying physics,
and to separate different microscopic degrees of freedom in space and time. We
measure the dynamics of the lattice and that of the charge disproportionation
in NdNiO3, when an insulator-metal transition is driven by coherent lattice
distortions in the LaAlO3 substrate. We find that charge redistribution
propagates at supersonic speeds from the interface into the NdNiO3 film,
followed by a sonic lattice wave. When combined with measurements of magnetic
disordering and of the metal-insulator transition, these results establish a
hierarchy of events for ultrafast control at complex oxide hetero-interfaces.",1612.04089v1
2018-01-16,Atmospheric Beacons of Life from Exoplanets Around G and K Stars,"The current explosion in detection and characterization of thousands of
extrasolar planets from the Kepler mission, the Hubble Space Telescope, and
large ground-based telescopes opens a new era in searches for Earth-analog
exoplanets with conditions suitable for sustaining life. As more Earth-sized
exoplanets are detected in the near future, we will soon have an opportunity to
identify habitable worlds. Which atmospheric biosignature gases from habitable
planets can be detected with our current capabilities? The detection of the
common biosignatures from nitrogen-oxygen rich terrestrial-type exoplanets
including molecular oxygen (O2), ozone (O3), water vapor (H2O), carbon dioxide
(CO2), nitrous oxide (N2O), and methane (CH4) requires days of integration time
with largest space telescopes, and thus are very challenging for current
instruments. In this paper we propose to use the powerful emission from
rotational-vibrational bands of nitric oxide, hydroxyl and molecular oxygen as
signatures of nitrogen, oxygen, and water rich atmospheres of terrestrial type
exoplanets highlighted by the magnetic activity from young G and K
main-sequence stars. The signals from these fundamental chemical prerequisites
of life we call atmospheric beacons of life create a unique opportunity to
perform direct imaging observations of Earth-sized exoplanets with high
signal-to-noise and low spectral resolution with the upcoming NASA missions.",1801.05341v1
2018-09-07,Infinite-randomness fixed point of the quantum superconductor-metal transitions in amorphous thin films,"The magnetic-field-tuned quantum superconductor-insulator transitions of
disordered amorphous indium oxide films are a paradigm in the study of quantum
phase transitions, and exhibit power-law scaling behavior. For superconducting
indium oxide films with low disorder, such as the ones reported on here, the
high-field state appears to be a quantum-corrected metal. Resistance data
across the superconductor-metal transition in these films are shown here to
obey an activated scaling form appropriate to a quantum phase transition
controlled by an infinite randomness fixed point in the universality class of
the random transverse-field Ising model. Collapse of the field-dependent
resistance vs. temperature data is obtained using an activated scaling form
appropriate to this universality class, using values determined through a
modified form of power-law scaling analysis. This exotic behavior of films
exhibiting a superconductor-metal transition is caused by the dissipative
dynamics of superconducting rare regions immersed in a metallic matrix, as
predicted by a recent renormalization group theory. The smeared crossing points
of isotherms observed are due to corrections to scaling which are expected near
an infinite randomness critical point, where the inverse disorder strength acts
as an irrelevant scaling variable.",1809.02672v3
2018-09-12,Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces,"Polar discontinuities occurring at interfaces between two different materials
constitute both a challenge and an opportunity in the study and application of
a variety of devices. In order to cure the large electric field occurring in
such structures, a reconfiguration of the charge landscape sets in at the
interface via chemical modifications, adsorbates or charge transfer. In the
latter case, one may expect a local electronic doping of one material: one
sparkling example is the two-dimensional electron liquid (2DEL) appearing in
SrTiO$_3$ once covered by a polar LaAlO$_3$ layer. Here we show that tuning the
formal polarisation of a (La,Al)$_{1-x}$(Sr,Ti)$_x$O$_3$ (LASTO:$x$) overlayer
through chemical composition modifies the quantum confinement of the 2DEL in
SrTiO$_3$ and its electronic band structure. The analysis of the behaviour in
magnetic field of superconducting field-effect devices reveals, in agreement
with $ab\ initio$ calculations and self-consistent Poisson-Schr\""odinger
modelling, that quantum confinement and energy splitting between electronic
bands of different symmetries strongly depend on interface charge densities.
These results not only strongly support the polar discontinuity mechanisms with
a full charge transfer to explain the origin of the 2DEL at the celebrated
LaAlO$_3$/SrTiO$_3$ interface, but also demonstrate an effective tool for
tailoring the electronic structure at oxide interfaces.",1809.04246v1
2019-06-24,Conductivity of Dirac-like surface states in correlated honeycomb transition metal oxide Mott insulators,"The search for materials with novel and unusual electronic properties is at
the heart of condensed matter physics as well as the basis to develop
conceptual new technologies. In this context, the correlated honeycomb
transition metal oxides attract large attention for both, being a possible
experimental realization of the theoretically predicted magnetic Kitaev
exchange and the theoretical prospect of topological nontriviality. The Mott
insulating sodium iridate is prototypical among these materials with the
promising prospect to bridge the field of strongly correlated systems with
topology, finally opening a path to a wide band gap material with exotic
surface properties. Here, we report a profound study of the electronic
properties of ultra-high-vacuum cleaved surfaces combining transport
measurements with scanning tunneling techniques, showing that multiple
conductive channels with differing nature are simultaneously apparent in this
material. Most importantly, a V-shaped density of states and a low sheet
resistance, in spite of a large defect concentration, point towards a
topologically protected surface conductivity contribution. By incorporating the
issue of the addressability of electronic states in the tunneling process, we
develop a framework connecting previous experimental results as well as
theoretical considerations.",1906.09809v2
2020-04-06,Unexpected crystalline homogeneity from the disordered bond network in La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films,"Designing and understanding functional electronic and magnetic properties in
perovskite oxides requires controlling and tuning the underlying crystal
lattice. Here we report the structure, including oxygen and cation positions,
of a single-crystal, entropy stabilized perovskite oxide film of
La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 grown on SrTiO3 (001). The parent materials
range from orthorhombic (LaCrO3, LaMnO3 and LaFeO3) to rhombohedral (LaCoO3 and
LaNiO3), and first principles calculations indicate that these structural
motifs are nearly degenerate in energy and should be highly distorted
site-to-site. Despite this extraordinary local configurational disorder on the
B-site sublattice, we find a structure with unexpected macroscopic crystalline
homogeneity with a clear orthorhombic unit cell, whose orientation is
demonstrated to be controlled by the strain and crystal structure of the
substrate for films grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) and NdGaO3
(110). Furthermore, quantification of the atom positions within the unit cell
reveal that the orthorhombic distortions are small, close to LaCrO3, which may
be driven by a combination of disorder averaging and the average ionic radii.
This is the first step towards understanding the rules for designing new
crystal motifs and tuning functional properties through controlled
configurational complexity.",2004.02985v1
2020-12-14,Universal quantum transition from superconducting to insulating states in pressurized Bi2Sr2CaCu2O8+δ superconductors,"Copper oxide superconductors have continually fascinated the communities of
condensed matter physics and material sciences because they host the highest
ambient-pressure superconducting transition temperature (Tc) and mysterious
physics. Searching for the universal correlation between the superconducting
state and its normal state or neighboring ground state is believed to be an
effective way for finding clues to elucidate the underlying mechanism of the
superconductivity. One of the common pictures for the copper oxide
superconductors is that a well-behaved metallic phase will present after the
superconductivity is entirely suppressed by chemical doping or application of
the magnetic field. Here, we report a different observation of universal
quantum transition from superconducting state to insulating-like state under
pressure in the under-, optimally- and over-doped Bi2212 superconductors with
two CuO2 planes in a unit cell. The same phenomenon has been also found in the
Bi2201 superconductor with one CuO2 plane and the Bi2223 superconductor with
three CuO2 planes in a unit cell. These results not only provide fresh
information but also pose a new challenge for achieving a unified understanding
on the underlying physics of the high-Tc superconductivity.",2012.07523v3
2017-05-07,Antiferromagnetic correlations in the metallic strongly correlated transition metal oxide LaNiO$_3$,"The material class of rare earth nickelates with high Ni$^{3+}$ oxidation
state is generating continued interest due to the occurrence of a
metal-insulator transition with charge order and the appearance of
non-collinear magnetic phases within this insulating regime. The recent
theoretical prediction for superconductivity in LaNiO$_3$ thin films has also
triggered intensive research efforts. LaNiO$_3$ seems to be the only rare earth
nickelate that stays metallic and paramagnetic down to lowest temperatures. So
far, centimetre-sized impurity-free single crystal growth has not been reported
for the rare earth nickelates material class since elevated oxygen pressures
are required for their synthesis. Here, we report on the successful growth of
centimetre-sized LaNiO$_3$ single crystals by the floating zone technique at
oxygen pressures of up to 150 bar. Our crystals are essentially free from
Ni$^{2+}$ impurities and exhibit metallic properties together with an
unexpected but clear antiferromagnetic transition.",1705.02589v2
2017-11-27,"Emergent odd-parity multipoles and magnetoelectric effects on a diamond structure: implication to 5$d$ transition metal oxides $A$OsO$_4$ ($A=$ K, Rb, and Cs)","We report our theoretical predictions on the linear magnetoelectric (ME)
effects originating from odd-parity multipoles associated with spontaneous spin
and orbital ordering on a diamond structure. We derive a two-orbital model for
$d$ electrons in $e_g$ orbitals by including the effective spin-orbit coupling
which arises from the mixing between $e_g$ and $t_{2g}$ orbitals. We show that
the model acquires a net antisymmetric spin-orbit coupling once staggered spin
and orbital orders occur spontaneously. The staggered orders are accompanied by
odd-parity multipoles: magnetic monopole, quadrupoles, and toroidal dipoles. We
classify the types of the odd-parity multipoles according to the symmetry of
the spin and orbital orders. Furthermore, by computing the ME tensor using the
linear response theory, we show that the staggered orders induce a variety of
the linear ME responses. We elaborate all possible ME responses for each
staggered order, which are useful to identify the order parameter and to detect
the odd-parity multipoles by measuring the ME effects. We also elucidate the
effect of lowering symmetry by a tetragonal distortion, which leads to richer
ME responses. The implications of our results are discussed for $5d$ transition
metal oxides, $A$OsO$_4$ ($A=$ K, Rb, and Cs), in which the order parameters
are not fully identified.",1711.09507v1
2018-06-04,Towards a systematically improvable many-body description of antiferromagnetic iron oxide,"We report variational and fixed-node diffusion quantum Monte Carlo (QMC)
calculations of anti-ferromagnetic iron oxide (FeO) in the ground state B1
crystal structure. The goal of this study was a systematic investigation of the
sensitivity of several ground state properties to a variety of QMC wave
function generation techniques including advanced wave functions such as
multi-determinant expansions and backflow transformations. We found that the
predicted lattice distortion was largely controlled by the choice of single
particle orbitals used to construct the wave function, rather than by
subsequent wave function optimization techniques within QMC. However, the
absolute magnetic moment was remarkably insensitive to the method of wave
function construction. QMC estimates of total spin density indicate that in
addition to strong electronic correlation of the Fe $3d$ states, charge
transfer may be an important but challenging piece of physics to accurately
capture within existing QMC methods. Finally, we highlight the need for
advanced and systematically improvable many-body wave functions suitable for
accurately describing challenging real systems.",1806.01383v2
2019-01-12,Probing single unit-cell resolved electronic structure modulations in oxide superlattices with standing-wave photoemission,"Control of structural couplings at the complex-oxide interfaces is a powerful
platform for creating new ultrathin layers with electronic and magnetic
properties unattainable in the bulk. However, with the capability to design and
control the electronic structure of such buried layers and interfaces at a
unit-cell level, a new challenge emerges to be able to probe these engineered
emergent phenomena with depth-dependent atomic resolution as well as element-
and orbital selectivity. Here, we utilize a combination of core-level and
valence-band soft x-ray standing-wave photoemission spectroscopy, in
conjunction with scanning transmission electron microscopy, to probe the
depth-dependent and single-unit-cell resolved electronic structure of an
isovalent manganite superlattice [Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3]x15 wherein the
electronic-structural properties are intentionally modulated with depth via
engineered oxygen octahedra rotations/tilts and A-site displacements. Our
unit-cell resolved measurements reveal significant transformations in the local
chemical and electronic valence-band states, which are consistent with the
layer-resolved first-principles theoretical calculations, thus opening the door
for future depth-resolved studies of a wide variety of hetero-engineered
material systems.",1901.03778v1
2019-04-26,"Spin, orbital and topological order in models of strongly correlated electrons","Different types of order are discussed in the context of strongly correlated
transition metal oxides, involving pure compounds and $3d^{3}-4d^{4}$ and
$3d^{2}-4d^{4}$ hybrids. Apart from standard, long-range spin and orbital
orders we observe also exotic non-colinear spin patterns. Such patters can
arise in presence of atomic spin-orbit coupling, which is a typical case, or
due to spin-orbital entanglement at the bonds in its absence, being much less
trivial. Within a special interacting one-dimensional spin-orbital model it is
also possible to find a rigorous topological magnetic order in a gapless phase
that goes beyond any classification tables of topological states of matter.
This is an exotic example of a strongly correlated topological state. Finally,
in the less correlated limit of $4d^{4}$ oxides, when orbital selective Mott
localization can occur it is possible to stabilize by a $3d^{3}$ doping
one-dimensional zigzag antiferromagnetic phases. Such phases have exhibit
nonsymmorphic spatial symmetries that can lead to various topological
phenomena, like single and mutliple Dirac points that can turn into nodal rings
or multiple topological charges protecting single Dirac points. Finally, by
creating a one-dimensional $3d^{2}-4d^{4}$ hybrid system that involves orbital
pairing terms, it is possible to obtain an insulating spin-orbital model where
the orbital part after fermionization maps to a non-uniform Kitaev model. Such
model is proved to have topological phases in a wide parameter range even in
the case of completely disordered $3d^{2}$ impurities. What more, it exhibits
hidden Lorentz-like symmetries of the topological phase, that live in the
parameters space of the model.",1904.11772v1
2019-11-18,Bivalent nature of Fe and W ions in the antiferromagnetic Sr2FeWO6 material produced by the combustion technique,"The synthesis of the double perovskite Sr2FeWO6 through the direct combustion
technique is reported. A complete characterization of the crystalline structure
is performed from Synchrotron X-ray measurements and subsequent Rietveld
analysis. The results evidence that this material crystallizes in a monoclinic
structure, P21/n space group, with strong distortions in the Fe-O6 and W-O6
octahedra, which is consistent with Glazer's notation a-b+a-. A superficial
morphological study through scanning electron microscopy images reveals that
this synthesis technique allows obtaining nanometric grains with 160 nm mean
size. The semiquantitative compositional analysis through spectroscopy of X-ray
energy dispersion by electrons shows that the produced material does not
contain other chemical elements besides those expected form the stoichiometric
formula. Results of analyzes of spectroscopy of photoelectrons emitted by
X-rays suggest that there is 66.9% of the material with oxidation states Fe2+
and W6+ and 33.1% with oxidation states Fe3+ and W5+. This bivalence of Fe and
W cations is corroborated by means the M\""ossbauer spectroscopy technique.
Finally, the magnetic response in AC susceptibility curves allows us to affirm
that at low temperatures the material adopts an antiferromagnetic behavior with
TN=32 K, with a tendency to the ferromagnetic state above T=150 K mostly due to
the presence of Fe3+ ions in the high spin configuration 3d5, S = 5/2.",1911.07610v1
2020-06-26,Propagation control of octahedral tilt in SrRuO3 via artificial heterostructuring,"Bonding geometry engineering of metal-oxygen octahedra is a facile way of
tailoring various functional properties of transition metal oxides. Several
approaches, including epitaxial strain, thickness, and stoichiometry control,
have been proposed to efficiently tune the rotation and tilting of the
octahedra, but these approaches are inevitably accompanied by unnecessary
structural modifications such as changes in thin-film lattice parameters. In
this study, we propose a method to selectively engineer the octahedral bonding
geometries, while maintaining other parameters that might implicitly influence
the functional properties. A concept of octahedral tilt propagation engineering
has been developed using atomically designed SrRuO3/SrTiO3 superlattices. In
particular, the propagation of RuO6 octahedral tilting within the SrRuO3 layers
having identical thicknesses was systematically controlled by varying the
thickness of adjacent SrTiO3 layers. This led to a substantial modification in
the electromagnetic properties of the SrRuO3 layer, significantly enhancing the
magnetic moment of Ru. Our approach provides a method to selectively manipulate
the bonding geometry of strongly correlated oxides, thereby enabling a better
understanding and greater controllability of their functional properties.",2006.14740v1
2020-09-17,Probing the Meta-Stability of Oxide Core/Shell Nanoparticle Systems at Atomic Resolution,"Hybrid nanoparticles allow exploiting the interplay of confinement, proximity
between different materials and interfacial effects. However, to harness their
properties an in-depth understanding of their (meta)stability and interfacial
characteristics is crucial. This is especially the case of nanosystems based on
functional oxides working under reducing conditions, which may severely impact
their properties. In this work, the in-situ electron-induced selective
reduction of Mn3O4 to MnO is studied in magnetic Fe3O4/Mn3O4 and Mn3O4/Fe3O4
core/shell nanoparticles by means of high-resolution scanning transmission
electron microscopy combined with electron energy-loss spectroscopy. Such
in-situ transformation allows mimicking the actual processes in operando
environments. A multi-stage image analysis using geometric phase analysis
combined with particle image velocity enables direct monitoring of the
relationship between structure, chemical composition and strain relaxation
during the Mn3O4 reduction. In the case of Fe3O4/Mn3O4 core/shell the
transformation occurs smoothly without the formation of defects. However, for
the inverse Mn3O4/Fe3O4 core/shell configuration the electron beam-induced
transformation occurs in different stages that include redox reactions and void
formation followed by strain field relaxation via formation of defects. This
study highlights the relevance of understanding the local dynamics responsible
for changes in the particle composition in order to control stability and,
ultimately, macroscopic functionality.",2009.08133v1
2021-04-21,Establishing quasi-linear quadrupole functional topology by oxygen-vacancy engineering at a ferroelectric domain wall,"Oxygen vacancies in two-dimensional metal-oxide structures garner much
attention due to unique conductive, magnetic and even superconductive
functionalities they induce. Ferroelectric domain walls have been a prominent
recent example because they serve as a hub for topological defects that enable
unusual symmetries and are relevant for low-energy switching technologies.
However, owing to the light weight of oxygen atoms and localized effects of
their vacancies, the atomic-scale electrical and mechanical influence of oxygen
vacancies has remained elusive. Here, stable individual oxygen vacancies were
found and engineered in situ at domain walls of seminal titanate perovskite
ferroics. The atomic-scale strain, electric-field, charge and dipole-moment
distribution around these vacancies were characterized by combining advanced
transmission electron microscopy and first-principle methodologies. 3-5 %
tensile strain was observed at the immediate surrounding unit cells of the
vacancies. The dipole-moment distribution around the vacancy was found to be an
alternating head-to-head $-$ tail-to-tail $-$ head-to-head structure, giving
rise to a quasi-linear quadrupole topology. Reduction of the nearby Ti ion as
well as enhanced charging and electric-field concentration near the vacancy
confirmed the quadrupole structure and illustrated its local effects on the
electrical and structural properties. Significant intra-band states were found
in the unit cell of the vacancies, proposing a meaningful domain-wall
conductivity. Oxygen-vacancy engineering and controllable quadrupoles that
enable pre-determining both atomic-scale and global functional properties offer
a promising platform of electro-mechanical topological solitons and device
miniaturization in metal oxides.",2104.10445v1
2021-06-22,Intrinsic versus extrinsic orbital and electronic reconstructions at complex oxide interfaces,"The interface between the insulators LaAlO$_3$ and SrTiO$_3$ accommodates a
two-dimensional electron liquid (2DEL) -- a high mobility electron system
exhibiting superconductivity as well as indications of magnetism and
correlations. While this flagship oxide heterostructure shows promise for
electronics applications, the origin and microscopic properties of the 2DEL
remain unclear. The uncertainty remains in part because the electronic
structures of such nanoscale buried interfaces are difficult to probe, and is
compounded by the variable presence of oxygen vacancies and coexistence of both
localized and delocalized charges. These various complications have precluded
decisive tests of intrinsic electronic and orbital reconstruction at this
interface. Here we overcome prior difficulties by developing an interface
analysis based on the inherently interface-sensitive resonant x-ray
reflectometry. We discover a high charge density of 0.5 electrons per
interfacial unit cell for samples above the critical LaAlO$_3$ thickness, and
extract the depth dependence of both the orbital and electronic reconstructions
near the buried interface. We find that the majority of the reconstruction
phenomena are confined to within 2 unit cells of the interface, and we quantify
how oxygen vacancies significantly affect the electronic system. Our results
provide strong support for the existence of polarity induced electronic
reconstruction, clearly separating its effects from those of oxygen vacancies.",2106.12061v1
2021-10-04,Data-driven quest for two-dimensional non-van der Waals materials,"Two-dimensional (2D) materials are frequently associated with the sheets
which form bulk layered compounds bonded by van der Waals (vdW) forces. The
anisotropy and weak interaction between the sheets have also been the main
criteria in the computational search for new 2D systems, which predicted about
2000 exfoliable compounds. However, several representatives of a new type of
non-vdW 2D systems, such as hematene or ilmenene, which have no layered 3D
analogues, and which, unlike, e.g. silicene, do not need to strongly interact
with the substrate to be stable, were recently manufactured. The family of
non-vdW 2D materials is an attractive playground for data-driven
high-throughput approaches as computational design principles are still
missing. Here, we outline a new set of 8 binary and 20 ternary candidates by
filtering the AFLOW-ICSD database according to the structural prototype of the
first two template systems realized in experiment. All materials show a strong
structural relaxation upon confinement to 2D which is essential to correctly
estimate the bonding strength between facets. The oxidation state of the
cations at the surface of the sheets is demonstrated to regulate the
inter-facet binding energy with low oxidation states leading to weak bonding.
We anticipate this descriptor to be highly useful to obtain novel 2D materials,
providing clear guidelines for experiments. Our calculations further indicate
that the materials exhibit a vast range of appealing electronic, optical and
magnetic properties, which is expected to also make them attractive for
potential applications particularly in spintronics.",2110.01366v1
2021-12-06,CaCu$_3$Ru$_4$O$_{12}$: a high Kondo-temperature transition metal oxide,"We present a comprehensive study of CaCu$_3$Ru$_4$O$_{12}$ using bulk
sensitive hard and soft x-ray spectroscopy combined with local-density
approximation (LDA) + dynamical mean-field theory (DMFT) calculations.
Correlation effects on both the Cu and Ru ions can be observed. From the Cu
$2p$ core level spectra we deduce the presence of magnetic Cu$^{2+}$ ions
hybridized with a reservoir of itinerant electrons. The strong photon energy
dependence of the valence band allows us to disentangle the Ru, Cu, and O
contributions and thus to optimize the DMFT calculations. The calculated spin
and charge susceptibilities show that the transition metal oxide
CaCu$_3$Ru$_4$O$_{12}$ must be classified as a Kondo system and that the Kondo
temperature is in the range of 500-1000 K.",2112.02898v1
2022-01-20,Stabilization of CeGe$_3$ with Ti and O featuring tetravalent Ce ions: (Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$,"Sub-oxides with the anti-perovskite structure constitute a large part of the
interstitial stabilized compounds with novel chemical and physical properties,
especially in the systems containing rare earth elements and/or early
transition metal elements. A new sub-oxide compound,
(Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$, is synthesized by flux growth. The
compound crystallizes in a cubic structure which can be considered as an
ordered vacancy variant of anti-perovskite-structure or an ordered interstitial
variant of the Cu$_3$Au type, with a space group of Fm-3m (225). The structure
is refined from X-ray single crystal methods. The compound may be considered as
a compound stabilized by chemical pressure generated by the substitution and
the interstitials atoms. The stability of the compounds in RTr$_3$ systems (R =
rare earth elements except Pm and Sc, Tr = tetrel elements such as Si, Ge, Sn,
Pb) seem to be highly correlated to the ratio of the rare earth elements' radii
to the main group elements' atomic radii. The magnetic property of the compound
confirms the 4$^+$ valence of the Ce atoms. The resistivity measurement of the
compound shows that it is metallic.",2201.08449v1
2022-02-02,Stabilization of three-dimensional charge order through interplanar orbital hybridization in Pr$_x$Y$_{1-x}$Ba$_2$Cu$_3$O$_{6+δ}$,"The shape of 3$d$-orbitals often governs the electronic and magnetic
properties of correlated transition metal oxides. In the superconducting
cuprates, the planar confinement of the $d_{x^2-y^2}$ orbital dictates the
two-dimensional nature of the unconventional superconductivity and a competing
charge order. Achieving orbital-specific control of the electronic structure to
allow coupling pathways across adjacent planes would enable direct assessment
of the role of dimensionality in the intertwined orders. Using Cu-$L_3$ and
Pr-$M_5$ resonant x-ray scattering and first-principles calculations, we report
a highly correlated three-dimensional charge order in Pr-substituted
YBa$_2$Cu$_3$O$_{7}$, where the Pr $f$-electrons create a direct orbital bridge
between CuO$_2$ planes. With this, we demonstrate that interplanar orbital
engineering can be used to surgically control electronic phases in correlated
oxides and other layered materials.",2202.00852v1
2022-03-16,Resource estimations for the Hamiltonian simulation in correlated electron materials,"Correlated electron materials, such as superconductors and magnetic
materials, are regarded as fascinating targets in quantum computing. However,
the quantitative resources, specifically the number of quantum gates and
qubits, required to perform a quantum algorithm to simulate correlated electron
materials remain unclear. In this study, we estimate the resources required for
the Hamiltonian simulation algorithm for correlated electron materials,
specifically for organic superconductors, iron-based superconductors, binary
transition metal oxides, and perovskite oxides, using the fermionic swap
network. The effective Hamiltonian derived using the $ab~initio$ downfolding
method is adopted for the Hamiltonian simulation, and a procedure for the
resource estimation by using the fermionic swap network for the effective
Hamiltonians including the exchange interactions is proposed. For example, in
the system for the $10^2$ unit cells, the estimated number of gates per Trotter
step and qubits are approximately $10^7$ and $10^3$, respectively, on average
for the correlated electron materials. Furthermore, our results show that the
number of interaction terms in the effective Hamiltonian, especially for the
Coulomb interaction terms, is dominant in the gate resources when the number of
unit cells constituting the whole system is up to $10^2$, whereas the number of
fermionic swap operations is dominant when the number of unit cells is more
than $10^3$.",2203.08446v3
2022-04-01,High-resolution Compton spectroscopy using X-ray microcalorimeters,"X-ray Compton spectroscopy is one of the few direct probes of the electron
momentum distribution of bulk materials in ambient and operando environments.
We report high-resolution inelastic X-ray scattering experiments with high
momentum and energy transfer performed at a storage-ring-based high-energy
X-ray light source facility using an X-ray microcalorimeter detector. Compton
profiles were measured for lithium and cobalt oxide powders relevant to
lithium-ion battery research. Spectroscopic analysis of the measured Compton
profiles shows high-sensitivity to the low-Z elements and oxidation states. The
lineshape analysis of the measured Compton profiles in comparison with computed
Hartree-Fock profiles is limited by the resolution of the energy-resolving
semiconductor detector. We have characterized an X-ray transition-edge sensor
microcalorimeter detector for high-resolution Compton scattering experiments
using a bending magnet source at the Advanced Photon Source (APS) with a double
crystal monochromator providing monochromatic photon energies near 27.5 keV.
The momentum resolution below 0.16 atomic units was measured yielding an
improvement of more than a factor of 7 over a state-of-the-art silicon drift
detector for the same scattering geometry. Furthermore, the lineshapes of
narrow valence and broad core electron profiles of sealed lithium metal were
clearly resolved using an X-ray microcalorimeter detector compared to smeared
and broadened lineshapes observed when using a silicon drift detector.
High-resolution Compton scattering using the energy-resolving detector shown
here presents new opportunities for spatial imaging of electron momentum
distributions for a wide class of materials with applications ranging from
electrochemistry to condensed matter physics.",2204.00568v1
2022-05-12,Pivotal Role of Intersite Hubbard Interactions in Fe-doped $α$-MnO$_2$,"We present a first-principles investigation of the structural, electronic,
and magnetic properties of the pristine and Fe-doped $\alpha$-MnO$_2$ using
density-functional theory with extended Hubbard functionals. The onsite $U$ and
intersite $V$ Hubbard parameters are determined from first principles and
self-consistently using density-functional perturbation theory in the basis of
L\""owdin-orthogonalized atomic orbitals. For the pristine $\alpha$-MnO$_2$ we
find that the so-called C2-AFM spin configuration is the most energetically
favorable, in agreement with the experimentally observed antiferromagnetic
ground state. For the Fe-doped $\alpha$-MnO$_2$ two types of doping are
considered: Fe insertion in the $2 \times 2$ tunnels and partial substitution
of Fe for Mn. We find that the interstitial doping preserves the C2-AFM spin
configuration of the host lattice only when both onsite $U$ and intersite $V$
Hubbard corrections are included, while for the substitutional doping the
onsite Hubbard $U$ correction alone is able to preserve the C2-AFM spin
configuration of the host lattice. The oxidation state of Fe is found to be
$+2$ and $+4$ in the case of the interstitial and substitutional doping,
respectively, while the oxidation state of Mn is $+4$ in both cases. This work
paves the way for accurate studies of other MnO$_2$ polymorphs and complex
transition-metal compounds when the localization of $3d$ electrons occurs in
the presence of strong covalent interactions with ligands.",2205.05977v2
2022-09-05,Surface-phase superconductivity in Mg-deficient V-doped MgTi$_2$O$_4$ spinel,"Around fifty years ago, LiTi$_2$O$_4$ was reported to be first spinel oxide
to exhibit a superconducting transition with highest T$_c$ $\approx$ 13.7 K.
Recently, MgTi$_2$O$_4$ has been found to be the only other spinel oxide to
reveal a superconducting transition with a T$_c$ $\approx$ 3 K, however, its
superconducting state is realized only in thin film superlattices involving
SrTiO$_3$. We find that a V-doped Mg$_{1-x}$Ti$_2$O$_4$ phase, which gets
stabilized as a thin surface layer on top of stoichiometric and insulating
V-doped MgTi$_2$O$_4$ bulk sample, exhibits high-temperature superconductivity
with T$_c$ $\approx$ 16 K. The superconducting transition is also confirmed
through a concomitant sharp diamagnetic transition immediately below T$_c$. The
spinel phase of the superconducting surface layer is elucidated through
grazing-incidence X-ray diffraction and Micro-Raman spectroscopy. A small shift
of the sharp superconducting transition temperature ($\sim$ 4 K) with
application of a high magnetic field (upto 9 Tesla) suggests a very high
critical field for the system, $\sim$ 25 Tesla. Thus, V-doped
Mg$_{1-x}$Ti$_2$O$_4$ exhibits the highest T$_c$ among spinel superconductors
and also possesses a very high critical field.",2209.02053v2
2022-09-29,The importance of electronic correlations in exploring the exotic phase diagram of layered Li$_x$MnO$_2$,"Using ab initio dynamical mean-field theory we explore the electronic and
magnetic states of layered Li$_x$MnO$_2$ as a function of $x$, the state of
charge. Constructing real-space Wannier projections of Kohn-Sham orbitals based
on the low-energy subspace of Mn $3d$ states and solving a multi-impurity
problem, our approach focuses on local correlations at Mn sites. The
antiferromagnetic insulating state in LiMnO$_2$ has a moderate N\'{e}el
temperature of $T_N=296\,K$ in agreement with experimental studies. Upon
delithiation the system proceeds through a number of states: ferrimagnetic
correlated metals at $x$=0.92, 0.83; multiple charge disproportionated
ferromagnetic correlated metals with large quasiparticle weights at $x$=0.67,
0.50, 0.33; ferromagnetic metals with small quasiparticle weights at $x$=0.17,
0.08 and an antiferromagnetic insulator for the fully delithiated state,
$x=0.0$. At moderate states of charge, $x=0.67-0.33$, a mix of +3/+4 formal
oxidation states of Mn is observed, while the overall nominal oxidation of Mn
state changes from +3 in LiMnO$_2$ to +4 in MnO$_2$. In all these cases the
high-spin state emerges as the most likely state in our calculations
considering the full $d$~manifold of Mn based on the proximity of $e_g$ levels
in energy to $t_{2g}$. The quasiparticle peaks in the correlated metallic
states were attributed to polaronic states based on previous literature for
similar isoelectronic JT driven materials, arising due to non-Fermi liquid type
behaviour of the strongly correlated system.",2209.14682v3
2022-10-19,Evolution of local atomic structure accompanying devitrification of amorphous Ni-Zr alloy thin films,"Thin film metallic glasses undergoing devitrification can form partially
crystallized or fully crystallized materials with novel structural and magnetic
properties. The development of desired and tunable properties of such systems
drives the need to understand the mechanism of their thermal evolution at the
atomic level. Co-sputtered amorphous Ni-Zr alloy thin films which were
thermally annealed in steps of 200 deg C from room temperature up to 800 deg C,
were observed to undergo an amorphous-to-crystalline transformation. Evolutions
in local atomic structure, including oxide formation and depletion during this
devitrification process, were determined using a combination of X-ray
reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and Extended
X-ray Absorption Fine Structure (EXAFS) techniques. The most probable phase of
the alloy was determined as Ni7Zr2; undergoing a polymorphous transformation.
The slight oxide content in the films was also noted to decrease rapidly as
annealing proceeded; leaving the crystallization pathway unhindered. Modelling
and analyses of XRR and GIXRD data showed that film thickness decreased with
annealing while long range order increased. Pair distribution function peak
widths were observed to decrease with annealing, indicating a control over
structural disorder in the system as it transitioned from the amorphous to
crystalline state. Partial atomic distribution in the environment of each
constituent was examined at every stage of annealing through EXAFS
measurements, which gave proper insight into atomic scale changes to the order
present. Detailed analyses through these techniques gave coherent results, thus
providing a true picture of the thermal evolution process of devitrification in
this technologically useful material.",2210.10399v1
2022-11-10,Honeycomb oxide heterostructure: a new platform for Kitaev quantum spin liquid,"Kitaev quantum spin liquid, massively quantum entangled states, is so scarce
in nature that searching for new candidate systems remains a great challenge.
Honeycomb heterostructure could be a promising route to realize and utilize
such an exotic quantum phase by providing additional controllability of
Hamiltonian and device compatibility, respectively. Here, we provide epitaxial
honeycomb oxide thin film Na3Co2SbO6, a candidate of Kitaev quantum spin liquid
proposed recently. We found a spin glass and antiferromagnetic ground states
depending on Na stoichiometry, signifying not only the importance of Na vacancy
control but also strong frustration in Na3Co2SbO6. Despite its classical ground
state, the field-dependent magnetic susceptibility shows remarkable scaling
collapse with a single critical exponent, which can be interpreted as evidence
of quantum criticality. Its electronic ground state and derived spin
Hamiltonian from spectroscopies are consistent with the predicted Kitaev model.
Our work provides a unique route to the realization and utilization of Kitaev
quantum spin liquid.",2211.05376v3
2023-02-09,Structural changes induced by electric currents in a single crystal of Pr$_2$CuO$_4$,"We demonstrate a novel approach to the structural and electronic property
modification of perovskites, focusing on Pr$_2$CuO$_4$, an undoped parent
compound of a class of electron-doped copper-oxide superconductors. Currents
were passed parallel or perpendicular to the copper-oxygen layers with the
voltage ramped up until a rapid drop in the resistivity was achieved, a process
referred to as ""flash"". The current was then further increased tenfold in
current-control mode. This state was quenched by immersion into liquid
nitrogen. Flash can drive many compounds into different atomic structures with
new properties, whereas the quench freezes them into a long-lived state.
Single-crystal neutron diffraction of as-grown and modified Pr$_2$CuO$_4$
revealed a $\sqrt{10}$x$\sqrt{10}$ superlattice due to oxygen-vacancy order.
The diffraction peak intensities of the superlattice of the modified sample
were significantly enhanced relative to the pristine sample. Raman-active
phonons in the modified sample were considerably sharper. Measurements of
electrical resistivity, magnetization and two-magnon Raman scattering indicate
that the modification affected only the Pr-O layers, but not the Cu-O planes.
These results point to enhanced oxygen-vacancy order in the modified samples
well beyond what can be achieved without passing electrical current. Our work
opens a new avenue toward electric field/quench control of structure and
properties of layered perovskite oxides.",2302.04385v2
2023-03-09,Materials challenges for SrRuO3: from conventional to quantum electronics,"The need for faster and more miniaturised electronics is challenging
scientists to develop novel forms of electronics based on quantum degrees of
freedom different from electron charge. In this fast-developing field, often
referred to as quantum electronics, the metal-oxide perovskite SrRuO3 can play
an important role thanks to its diverse physical properties, which have been
intensively investigated, mostly for conventional electronics. In addition to
being chemically stable, easy to fabricate with high quality and to grow
epitaxially onto many oxides - these are all desirable properties also for
conventional electronics - SrRuO3 has interesting properties for quantum
electronics like itinerant ferromagnetism and metallic behaviour, strong
correlation between magnetic anisotropy and spin-orbit coupling,
strain-tuneable magnetisation, anomalous Hall and Berry effects. In this
Research Update, after describing the main phenomena emerging from the
interplay between spin, orbital, lattice and topological quantum degrees of
freedom in SrRuO3, we discuss the challenges still open to achieve control over
these phenomena. We then provide our perspectives on the most promising
applications of SrRuO3 for devices for conventional and quantum electronics. We
suggest new device configurations and discuss the materials challenges for
their realisation. For conventional electronics, we single out applications
where SrRuO3 devices can bring competitive advantages over existing ones. For
quantum electronics, we propose devices that can help gain a deeper
understanding of quantum effects in SrRuO3 to exploit them for quantum
technologies. We finally give an outlook about properties of SrRuO3 still
waiting for discovery and applications that may stem from them.",2303.05114v1
2023-10-07,Giant 2D Skyrmion Topological Hall Effect with Ultrawide Temperature Window and Low-Current Manipulation in 2D Room-Temperature Ferromagnetic Crystals,"The discovery and manipulation of topological Hall effect (THE), an abnormal
magnetoelectric response mostly related to the Dzyaloshinskii-Moriya
interaction (DMI), are promising for next-generation spintronic devices based
on topological spin textures such as magnetic skyrmions. However, most
skyrmions and THE are stabilized in a narrow temperature window either below or
over room temperature with high critical current manipulation. It is still
elusive and challenging to achieve large THE with both wide temperature window
till room temperature and low critical current manipulation. Here, by using
controllable, naturally-oxidized, sub-20 and sub-10 nm 2D van der Waals
room-temperature ferromagnetic Fe3GaTe2-x crystals, robust 2D THE with
ultrawide temperature window ranging in three orders of magnitude from 2 to 300
K is reported, combining with giant THE of ~5.4 micro-ohm cm at 10 K and ~0.15
micro-ohm cm at 300 K which is 1-3 orders of magnitude larger than that of all
known room-temperature 2D skyrmion systems. Moreover, room-temperature
current-controlled THE is also realized with a low critical current density of
~6.2*10^5 A cm^-2. First-principles calculations unveil natural
oxidation-induced highly-enhanced 2D interfacial DMI reasonable for robust
giant THE. This work paves the way to room-temperature, electrically-controlled
2D THE-based practical spintronic devices.",2310.04663v1
2023-10-11,Multifunctional magnetic oxide-MoS$_2$ heterostructures on silicon,"Correlated oxides and related heterostructures are intriguing for developing
future multifunctional devices by exploiting their exotic properties, but their
integration with other materials, especially on Si-based platforms, is
challenging. Here, van der Waals heterostructures of
La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO), a correlated manganite perovskite, and
MoS$_2$ are demonstrated on Si substrates with multiple functions. To overcome
the problems due to the incompatible growth process, technologies involving
freestanding LSMO membranes and van der Waals force-mediated transfer are used
to fabricate the LSMO-MoS$_2$ heterostructures. The LSMO-MoS$_2$
heterostructures exhibit a gate-tunable rectifying behavior, based on which
metal-semiconductor field-effect transistors (MESFETs) with on-off ratios of
over 104 can be achieved. The LSMO-MoS$_2$ heterostructures can function as
photodiodes displaying considerable open-circuit voltages and photocurrents. In
addition, the colossal magnetoresistance of LSMO endows the LSMO-MoS$_2$
heterostructures with an electrically tunable magnetoresponse at room
temperature. This work not only proves the applicability of the LSMO-MoS$_2$
heterostructure devices on Si-based platform but also demonstrates a paradigm
to create multifunctional heterostructures from materials with disparate
properties.",2310.07783v1
2024-01-23,Integration of High-Tc Superconductors with High Q Factor Oxide Mechanical Resonators,"Micro-mechanical resonators are building blocks of a variety of applications
in basic science and applied electronics. This device technology is mainly
based on well-established and reproducible silicon-based fabrication processes
with outstanding performances in term of mechanical Q factor and sensitivity to
external perturbations. Broadening the functionalities of MEMS by the
integration of functional materials is a key step for both applied and
fundamental science. However, combining functional materials and silicon-based
compounds is challenging. An alternative approach is fabricating MEMS based on
complex heterostructures made of materials inherently showing a variety of
physical properties such as transition metal oxides. Here, we report on the
integration of a high-Tc superconductor YBa2Cu3O7 (YBCO) with high Q factor
micro-bridge resonator made of a single-crystal LaAlO3 (LAO) thin film. LAO
resonators are tensile strained, with a stress of 345 MPa, show Q factor in the
range of tens of thousands, and have low roughness. The topmost YBCO layer
deposited by Pulse Laser Deposition shows a superconducting transition starting
at 90 K with zero resistance below 78 K. This result opens new possibilities
towards the development of advanced transducers, such as bolometers or magnetic
field detectors, as well as basic science experiments in solid state physics,
material science, and quantum opto-mechanics.",2401.12758v1
2024-02-05,Tracing d-d transitions in FePS$_{3}$ on ultrafast time scales,"Excitations between localized 3d states of transition metal ions within
crystalline solids, commonly known as d-d transitions, play a pivotal role in
diverse phenomena across solid state physics, materials science, and chemistry.
These transitions contribute to the coloration in transition metal oxides,
catalytic processes on oxide surfaces, and high-temperature superconductivity.
They also couple optical excitation to quantized collective phenomena such as
phonons and magnons in magnetic systems. Until now, an experimental method to
unravel the complex quasiparticle dynamics associated with d-d transitions has
remained elusive. We bridge this gap by demonstrating that d-d transitions can
be distinctly traced in momentum space and time using time- and angle-resolved
photoelectron spectroscopy (trARPES). Through this approach, we can assign
specific momentum-dependent characteristics and elucidate the decay mechanisms
of specific d-d transitions in FePS$_{3}$, a two-dimensional van der Waals
antiferromagnet with a rich array of quantum phenomena stemming from d-d
transitions. This study pioneers the use of ARPES in probing the dynamics of
d-d transitions across a wide spectrum of solid-state systems.",2402.03018v1
2024-03-11,Bulk and interface spin-orbit torques in Pt/Co/MgO thin film structures,"We investigate the origin of spin-orbit torques (SOTs) in archetypical
Pt/Co/MgO thin films structures by performing harmonic Hall measurements. The
behaviour of the damping like (DL) effective field ($h_{DL}$) with varying the
Pt layer thickness and the Co layer thickness indicates that bulk spin-Hall
effect (SHE) in Pt is mainly responsible for DL-SOT. The insertion of a Pd
ultrathin layer at the Pt/Co interface leads to a step decrease in $h_{DL}$,
attributed to the modification of interfacial spin transparency. Further
increase in Pd thickness led to a reduction of the interfacial spin-orbit
coupling (iSOC) quantified by the decrease in the surface magnetic anisotropy.
The consistent insensitivity of $h_{DL}$ to variations in iSOC at the bottom
Pt/Co interface and oxidation at the top Co/MgO interface provides additional
evidence for the bulk SHE origin of DL-SOT. The strong reduction in the
field-like (FL) torque effective field ($h_{FL}$) with decreasing iSOC at the
Pt/Co interface points to the interfacial nature of FL-SOT, either due to iSOC
induced interfacial spin-currents or to the Rashba-Edelstein effect at the
Pt/Co interface. Furthermore, we demonstrate that a FL-SOT develops at the top
Co/MgO interface opposing the one generated at the bottom Pt/Co interface,
whose strength increases with Co/MgO interfacial oxidation, and attributed to
the Rashba-Edelstein effect.",2403.06627v1
2012-03-17,Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field,"We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.",1203.3873v1
2016-07-02,Interface-Induced Phenomena in Magnetism,"This article reviews static and dynamic interfacial effects in magnetism,
focusing on interfacially-driven magnetic effects and phenomena associated with
spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides
a historical background and literature survey, but focuses on recent progress,
identifying the most exciting new scientific results and pointing to promising
future research directions. It starts with an introduction and overview of how
basic magnetic properties are affected by interfaces, then turns to a
discussion of charge and spin transport through and near interfaces and how
these can be used to control the properties of the magnetic layer. Important
concepts include spin accumulation, spin currents, spin transfer torque, and
spin pumping. An overview is provided to the current state of knowledge and
existing review literature on interfacial effects such as exchange bias,
exchange spring magnets, spin Hall effect, oxide heterostructures, and
topological insulators. The article highlights recent discoveries of
interface-induced magnetism and non-collinear spin textures, non-linear
dynamics including spin torque transfer and magnetization reversal induced by
interfaces, and interfacial effects in ultrafast magnetization processes.",1607.00439v4
2020-07-18,Giant magneto-birefringence effect and tuneable colouration of 2D crystals' suspensions,"One of the long sought-after goals in manipulation of light through
light-matter interactions is the realization of magnetic-field-tuneable
colouration, so-called magneto-chromatic effect, which holds great promise for
optical, biochemical and medical applications due to its contactless and
non-invasive nature. This goal can be achieved by magnetic-field controlled
birefringence, where colours are produced by the interference between
phase-retarded components of transmitted polarised light. Thus far
birefringence-tuneable coloration has been demonstrated using electric field,
material chirality and mechanical strain but magnetic field control remained
elusive due to either weak magneto-optical response of transparent media or low
transmittance to visible light of magnetically responsive media, such as
ferrofluids. Here we demonstrate magnetically tuneable colouration of aqueous
suspensions of two-dimensional cobalt-doped titanium oxide which exhibit an
anomalously large magneto-birefringence effect. The colour of the suspensions
can be tuned over more than two wavelength cycles in the visible range by
moderate magnetic fields below 0.8 T. We show that such giant magneto-chromatic
response is due to particularly large phase retardation (>3 pi) of the
polarised light, which in its turn is a combined result of a large
Cotton-Mouton coefficient (three orders of magnitude larger than for known
liquid crystals), relatively high saturation birefringence (delta n = 2 x
10^-4) and high transparency of our suspensions to visible light. The work
opens a new avenue to achieve tuneable colouration through engineered magnetic
birefringence and can readily be extended to other magnetic 2D nanocrystals.
The demonstrated effect can be used in a variety of magneto-optical
applications, including magnetic field sensors, wavelength-tuneable optical
filters and see-through printing.",2007.09388v1
2020-01-15,"Emergence of weak pyrochlore phase and signature of field induced spin ice ground state in Dy$_{2-x}$La$_{x}$Zr$_{2}$O$_{7}$; x = 0, 0.15, 0.3","The pyrochlore oxides Dy$_{2}$Ti$_{2}$O$_{7}$ and Ho$_{2}$Ti$_{2}$O$_{7}$ are
well studied spin ice systems and have shown the evidences of magnetic monopole
excitations. Unlike these, Dy$_{2}$Zr$_{2}$O$_{7}$ is reported to crystallize
in a distorted fluorite structure. We present here the magnetic and heat
capacity studies of La substituted Dy$_{2}$Zr$_{2}$O$_{7}$. Our findings
suggest the absence of spin ice state in Dy$_{2}$Zr$_{2}$O$_{7}$ but the
emergence of the magnetic field induced spin freezing near T $\approx$ 10 K in
ac susceptibility measurements which is similar to Dy$_{2}$Ti$_{2}$O$_{7}$. The
magnetic heat capacity of Dy$_{2}$Zr$_{2}$O$_{7}$ shows a shift in the peak
position from 1.2 K in zero field to higher temperatures in the magnetic field,
with the corresponding decrease in the magnetic entropy. The low temperature
magnetic entropy at 5 kOe field is Rln2 - (1/2)Rln(3/2) which is same as for
the spin ice state. Substitution of non-magnetic, isovalent La$^{3+}$ for
Dy$^{3+}$ gradually induces the structural change from highly disordered
fluorite to weakly ordered pyrochlore phase. The La$^{3+}$ substituted
compounds with less distorted pyrochlore phase show the spin freezing at lower
field which strengthens further on the application of magnetic field. Our
results suggest that the spin ice state can be stabilized in
Dy$_{2}$Zr$_{2}$O$_{7}$ either by slowing down of the spin dynamics or by
strengthening the pyrochlore phase by suitable substitution in the system.",2001.05244v2
2023-02-03,Universality of the {\bf q}=1/2 Orbital Magnetism in the Pseudogap Phase of the High-$T_c$ superconductor $\rm YBa_{2}Cu_{3}O_{6+x}$,"Several decades of debate have centered around the nature of the enigmatic
pseudo-gap state in high temperature superconducting copper oxides. Recently,
we reported polarized neutron diffraction measurements that suggested the
existence of a magnetic texture bound to the pseudo-gap phase [Bounoua, {\it et
al}. Communications Physics 5, 268 (2022)]. Such a magnetic texture is likely
to involve the spontaneous appearance of loop currents within the CuO$_2$ unit
cells, which give birth to complex correlated patterns. In the underdoped ${\rm
YBa_{2}Cu_{3}O_{6.6}}$, the magnetic structure factor of such an orbital
magnetic texture gives rise to two distinct magnetic responses at {\bf q}=0 and
{\bf q}=1/2. As this pattern alters the lattice translation invariance, such a
state of matter could contribute to an instability of the Fermi surface. Here,
we report polarized neutron scattering measurements on a nearly optimally doped
high quality single crystal of ${\rm YBa_{2}Cu_{3}O_{6.9}}$ that exhibits the
same {\bf q}=1/2 magnetism and a weakly overdoped ${\rm YBa_{2}Cu_{3}O_{7}}$
sample where this signal is no longer sizeable. The in-plane and out-of-plane
magnetic neutron scattering intensities in ${\rm YBa_{2}Cu_{3}O_{6.9}}$ (at
{\bf q}=1/2) and ${\rm YBa_{2}Cu_{3}O_{6.85}}$ (at {\bf q}=0), reported
previously, display the same temperature dependent hallmarks. The magnitudes of
both {\bf q}=0 and {\bf q}=1/2 magnetic signals further exhibit the same trends
upon doping in ${\rm YBa_{2}Cu_{3}O_{6+x}}$, confirming that they are likely
intertwined.",2302.01870v2
2023-03-12,Emergence of a Non-van der Waals Magnetic Phase in a van der Waals Ferromagnet,"Manipulation of long-range order in two-dimensional (2D) van der Waals (vdW)
magnetic materials (e.g., CrI$_3$, CrSiTe$_3$ etc.), exfoliated in few-atomic
layer, can be achieved via application of electric field,
mechanical-constraint, interface engineering, or even by chemical
substitution/doping. Usually, active surface oxidation due to the exposure in
the ambient condition and hydrolysis in the presence of water/moisture causes
degradation in magnetic nanosheets which, in turn, affects the
nanoelectronic/spintronic device performance. Counterintuitively, our current
study reveals that exposure to the air at ambient atmosphere results in advent
of a stable nonlayered secondary ferromagnetic phase in the form of
Cr$_2$Te$_3$ (T$_{C2}$ ~ 160 K) in the parent vdW magnetic semiconductor
Cr$_2$Ge$_2$Te$_6$ (T$_{C1}$ ~ 69 K). In addition, the magnetic anisotropy
energy (MAE) enhances in the hybrid by an order from the weakly anisotropic
pristine Cr$_2$Ge$_2$Te$_6$ crystal, increasing the stability of the FM ground
state with time. Comparing with the freshly prepared Cr$_2$Ge$_2$Te$_6$, the
coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is
confirmed through systematic investigation of crystal structure along with
detailed dc/ac magnetic susceptibility, specific heat, and magnetotransport
measurement. To capture the concurrence of the two ferromagnetic phases in a
single material, Ginzburg-Landau theory with two independent order parameters
(as magnetization) with a coupling term can be introduced. In contrast to
rather common poor environmental stability of the vdW magnets, our results open
possibilities of finding air-stable novel materials having multiple magnetic
phases.",2303.06732v1
2024-01-09,2024 Roadmap on Magnetic Microscopy Techniques and Their Applications in Materials Science,"Considering the growing interest in magnetic materials for unconventional
computing, data storage, and sensor applications, there is active research not
only on material synthesis but also characterisation of their properties. In
addition to structural and integral magnetic characterisations, imaging of
magnetization patterns, current distributions and magnetic fields at nano- and
microscale is of major importance to understand the material responses and
qualify them for specific applications. In this roadmap, we aim to cover a
broad portfolio of techniques to perform nano- and microscale magnetic imaging
using SQUIDs, spin center and Hall effect magnetometries, scanning probe
microscopies, x-ray- and electron-based methods as well as magnetooptics and
nanoMRI. The roadmap is aimed as a single access point of information for
experts in the field as well as the young generation of students outlining
prospects of the development of magnetic imaging technologies for the upcoming
decade with a focus on physics, materials science, and chemistry of planar, 3D
and geometrically curved objects of different material classes including 2D
materials, complex oxides, semi-metals, multiferroics, skyrmions,
antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic
conductors, superconductors, spintronic and spinorbitronic materials.",2401.04793v1
2013-11-30,Electronic Transport in Composites of Graphite Oxide with Carbon Nanotubes,"We show that the presence of electrically insulating graphite oxide (GO)
within a single wall carbon nanotube network strongly enhances electrical
conductivity, whereas reduced graphite oxide, even though electrically
conductive, suppresses electrical conductivity within a composite network with
single wall carbon nanotubes. Measurements of Young modulus and of Raman
spectra strongly support our interpretation of the indirect role of the oxide
groups, present in graphite oxide within the single wall carbon
nanotubes/graphite oxide composite, through electronic doping of metallic
single wall carbon nanotubes.",1312.0152v1
2008-07-07,Oxidative stress response: a proteomic view,"The oxidative stress response is characterized by various effects on a range
of biologic molecules. When examined at the protein level, both expression
levels and protein modifications are altered by oxidative stress. While these
effects have been studied in the past by classic biochemical methods, the
recent onset of proteomics methods has allowed the oxidative stress response to
be studied on a much wider scale. The input of proteomics in the study of
oxidative stress response and in the evidence of an oxidative stress component
in biologic phenomena is reviewed in this paper.",0807.1041v1
2000-01-11,Magnetic Susceptibilities of Spin-1/2 Antiferromagnetic Heisenberg Ladders and Applications to Ladder Oxide Compounds,"A comprehensive theoretical and experimental study is presented of the
magnetic susceptibility versus temperature \chi(T) of spin S = 1/2 two- and
three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum
Monte Carlo simulations of \chi(T) were carried out for both isolated and
coupled two-leg ladders with spatially anisotropic intraladder exchange.
Accurate fits to these and related literature QMC data were obtained. We have
also calculated the one- and two-magnon dispersion relations and the dynamical
spin structure factor for anisotropic isolated 2 x 12 ladders. The exchange
constants in the two-leg ladder compound SrCu2O3 are estimated from LDA+U
calculations. We report the detailed crystal structure of SrCu2O3 and of the
three-leg ladder compound Sr2Cu3O5. New experimental \chi(T) data are reported
for the two-leg ladder cuprates SrCu2O3 and LaCuO_{2.5}, and for the
(nominally) two-leg ladder vanadates CaV2O5 and MgV2O5. The new and literature
\chi(T) data for these compounds and for Sr2Cu3O5 are modeled using our QMC
\chi(T) simulation fits, and the exchange coupling constants between the
spins-1/2 are thereby estimated for each material. The surpisingly strong
spatial anisotropy of the bilinear intraladder exchange constants in the
cuprate compounds is discussed together with the results of other experiments
sensitive to this anisotropy. Recent theoretical predictions are discussed
including those which indicate that a four-spin cyclic exchange interaction
within a Cu4 plaquette is important to determining the magnetic properties and
which can significantly influence the exchange interactions estimated from
\chi(T) data assuming the presence of only bilinear exchange.",0001147v1
2012-11-19,Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium,"The magnitude of spin accumulation created in semiconductors by electrical
injection of spin-polarized electrons from a ferromagnetic tunnel contact is
investigated, focusing on how the spin signal detected in a Hanle measurement
varies with the thickness of the tunnel oxide. An extensive set of
spin-transport data for Si and Ge magnetic tunnel devices reveals a scaling
with the tunnel resistance that violates the core feature of available
theories, namely, the linear proportionality of the spin voltage to the
injected spin current density. Instead, an anomalous scaling of the spin signal
with the tunnel resistance is observed, following a power-law with an exponent
between 0.75 and 1 over 6 decades. The scaling extends to tunnel resistance
values larger than 10$^{9}$ $\Omega\mu m^2$, far beyond the regime where the
classical impedance mismatch plays a role. This scaling is incompatible with
existing theory for direct tunnel injection of spins into the semiconductor. It
also demonstrates conclusively that the large spin signal does not originate
from two-step tunneling via localized states near the oxide/semiconductor
interface. Control experiments on devices with a non-magnetic metal (Ru)
electrode, instead of the semiconductor, exhibit no Hanle spin signal, showing
that spin accumulation in localized states within the tunnel barrier is also
not responsible. Control devices in which the spin current is removed by
inserting a non-magnetic interlayer exhibit no Hanle signals either, proving
that the spin signals observed in the standard devices are genuine and
originate from spin-polarized tunneling and the resulting spin accumulation.
Altogether, the scaling results suggest that the spin signal is proportional to
the applied bias voltage, rather than the (spin) current.",1211.4460v1
2015-05-13,Multiferroic crossover in perovskite oxides,"Recently, the perovskite BiCoO$_3$ has been shown experimentally to be
isostructural with PbTiO$_3$, while simultaneously the $d^6$ Co$^{3+}$ ion has
a high spin ground state with $C$-type antiferromagnetic ordering. Using hybrid
density functional calculations, we investigate the atomic, electronic and
magnetic structure of BiCoO$_3$ to elucidate the origin of the multiferroic
state. To begin with, we perform a qualitative trend sudy of the role of $d$
electrons in affecting the tendency for perovskite materials to exhibit a
ferroelectric distortion; this work initially explores a qualitative trend
study in artificial cubic and tetragonal LaBO$_3$ perovskites. We choose La as
the A-cation so as to remove the effects of Bi $6s$ hybridization. Through
first-principles calculations of the LaBO$_3$ series, where B is a $d^0 - d^8$
cation from the $3d$-block, the trend study reveals that increasing the $d$
orbital occupation initially removes the tendency for a polar distortion, as
expected. However, for high spin $d^5-d^7$ and $d^8$ cations a strong
ferroelectric instability is recovered. We explained this effect in terms of
the pseudo Jahn-Teller theory for ferroelectricity. It is shown that, in some
cases, unpaired electron spins actually drive ferroelectricity, rather than
inhibit it, which represents a shift in the understanding of how
ferroelectricity and magnetism interact in perovskite oxides. It follows, that
for the case of BiCoO$_3$, the Co$^{3+}$ ion plays a major role in the
ferroelectric lattice instability. Importantly, the ferroelectric polarization
is greatly enhanced when the Co$^{3+}$ ion is in the high spin state, when
compared to the nonmagnetic, low spin state, and a large coupling of the
electrical and magnetic polarization is present. Importantly, it is
demonstrated that the ground spin state is switched by reducing the internal
ferroelectric polarization.",1505.03249v4
2018-02-27,Depth-resolved resonant inelastic x-ray scattering at a superconductor/half-metallic ferromagnet interface through standing-wave excitation,"We demonstrate that combining standing-wave (SW) excitation with resonant
inelastic x-ray scattering (RIXS) can lead to depth resolution and interface
sensitivity for studying orbital and magnetic excitations in correlated oxide
heterostructures. SW-RIXS has been applied to multilayer heterostructures
consisting of a superconductor La$_{1.85}$Sr$_{0.15}$CuO$_{4}$(LSCO) and a
half-metallic ferromagnet La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO). Easily
observable SW effects on the RIXS excitations were found in these LSCO/LSMO
multilayers. In addition, we observe different depth distribution of the RIXS
excitations. The magnetic excitations are found to arise from the LSCO/LSMO
interfaces, and there is also a suggestion that one of the dd excitations comes
from the interfaces. SW-RIXS measurements of correlated-oxide and other
multilayer heterostructures should provide unique layer-resolved insights
concerning their orbital and magnetic excitations, as well as a challenge for
RIXS theory to specifically deal with interface effects.",1802.09743v5
2012-04-27,Effect of Boron substitution on the superconductivity of non-oxide perovskite MgCNi3,"We report synthesis, structural and magnetic (DC and AC) properties of Boron
substituted MgCNi3 superconductor. A series of polycrystalline bulk samples
Mg1.2C1.6-xBxNi3 (x = 0.0, 0.08 and 0.16) is synthesized through standard
solid-state reaction route, which are found to crystallize in cubic perovskite
structure with space group Pm3m. Rietveld analysis of observed XRD data show
that lattice parameters expand from a = 3.8106 (4) {\AA} for pure, to 3.8164
(2) {\AA} and 3.8173 (5) {\AA} for 5% and 10% Boron substituted samples
respectively. DC magnetization exhibited superconducting transition (Tc) at
around 7.3 K for pure sample, and the same decreases slightly with Boron
substitution. The lower critical field (Hc1) at 2 K is around 150 Oe for pure
sample, which increases slightly with Boron substitution. For pure sample the
upper critical field (Hc2) being determined from AC susceptibility measurements
is 11.6 kOe and 91.70 kOe with 50% and 90% diamagnetism criteria respectively,
which decreases to 5.57 kOe and 42.5 kOe respectively for 10% Boron substituted
sample. 10% Boron substitution at Carbon site has decreased both the Hc2 and
Tc. On the other hand lower critical field (Hc1) at 2 K is slightly increased
from around 150 Oe for pure sample, to 200 Oe for 10% Boron substituted sample.
Seemingly, the Carbon site Boron substitution induced disorder though has
increased slightly the Hc1 but with simultaneous decrease in superconducting
transition temperature (Tc) and upper critical field (Hc2). The high relative
proportion of Ni in studied MgCNi3 suggests that magnetic interactions are
important and non-oxide perovskite structure make it interesting.",1204.6175v3
2017-11-14,Strong spin-orbit coupling and magnetism in (111) (La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35})$/SrTiO$_3$,"Strong correlations, multiple lattice degrees of freedom, and the ease of
doping make complex oxides a source of great research interest. Complex oxide
heterointerfaces break inversion symmetry and can host a two dimensional
carrier gas, which can display a variety of coexisting and competing phenomena.
In the case of heterointerfaces based on SrTiO$_3$, many of these phenomena can
be effectively tuned by using an electric gate, due to the large dielectric
constant of SrTiO$_3$. Most studies so far have focused on (001) oriented
heterostructures; however, (111) oriented heterostructures have recently gained
attention due to the possibility of finding exotic physics in these systems due
their hexagonal surface crystal symmetry. In this work, we use
magnetoresistance to study the evolution of spin-orbit interaction and
magnetism in a new system, (111) oriented
(La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35}$)/SrTiO$_3$. At more positive
values of the gate voltage, which correspond to high carrier densities, we find
that transport is multiband, and dominated by high mobility carriers with a
tendency towards weak localization. At more negative gate voltages, the carrier
density is reduced, the high mobility bands are depopulated, and weak
antilocalization effects begin to dominate, indicating that spin-orbit
interaction becomes stronger. At millikelvin temperatures, and gate voltages
corresponding to the strong spin-orbit regime, we observe hysteresis in
magnetoresistance, indicative of ferromagnetism in the system. Our results
suggest that in the (111)
(La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35}$)/SrTiO$_3$ system, low mobility
carriers which experience strong spin-orbit interactions participate in
creating magnetic order in the system.",1711.05322v2
2018-03-20,Unravelling Dzyaloshinskii-Moriya interaction and chiral nature of Graphene/Cobalt interface,"A major challenge for future spintronics is to develop suitable spin
transport channels with long spin lifetime and propagation length. Graphene can
meet these requirements, even at room temperature. On the other side, taking
advantage of the fast motion of chiral textures, i.e., N\'eel-type domain walls
and magnetic skyrmions, can satisfy the demands for high-density data storage,
low power consumption and high processing speed. We have engineered epitaxial
structures where an epitaxial ferromagnetic Co layer is sandwiched between an
epitaxial Pt(111) buffer grown in turn onto MgO(111) substrates and a graphene
layer. We provide evidence of a graphene-induced enhancement of the
perpendicular magnetic anisotropy up to 4 nm thick Co films, and of the
existence of chiral left-handed N\'eel-type domain walls stabilized by the
effective Dzyaloshinskii-Moriya interaction (DMI) in the stack. The experiments
show evidence of a sizeable DMI at the gr/Co interface, which is described in
terms of a conduction electron mediated Rashba-DMI mechanism and points
opposite to the Spin Orbit Coupling-induced DMI at the Co/Pt interface. In
addition, the presence of graphene results in: i) a surfactant action for the
Co growth, producing an intercalated, flat, highly perfect fcc film,
pseudomorphic with Pt and ii) an efficient protection from oxidation. The
magnetic chiral texture is stable at room temperature and grown on insulating
substrate. Our findings open new routes to control chiral spin structures using
interfacial engineering in graphene-based systems for future spin-orbitronics
devices fully integrated on oxide substrates.",1803.07443v3
2020-10-20,Origin of the Magnetic and Orbital ordering in $α$-Sr$_2$CrO$_4$,"Motivated by recent experimental progress in transition metal oxides with the
K$_2$NiF$_4$ structure, we investigate the magnetic and orbital ordering in
$\alpha$-Sr$_2$CrO$_4$. Using first principles calculations, first we derive a
three-orbital Hubbard model, which reproduces the {\it ab initio} band
structure near the Fermi level. The unique reverse splitting of $t_{2g}$
orbitals in $\alpha$-Sr$_2$CrO$_4$, with the $3d^2$ electronic configuration
for the Cr$^{4+}$ oxidation state, opens up the possibility of orbital ordering
in this material. Using real-space Hartree-Fock for multi-orbital systems, we
constructed the ground-state phase diagram for the two-dimensional compound
$\alpha$-Sr$_2$CrO$_4$. We found stable ferromagnetic, antiferromagnetic,
antiferro-orbital, and staggered orbital stripe ordering in robust regions of
the phase diagram. Furthermore, using the density matrix renormalization group
method for two-leg ladders with the realistic hopping parameters of
$\alpha$-Sr$_2$CrO$_4$, we explore magnetic and orbital ordering for
experimentally relevant interaction parameters. Again, we find a clear
signature of antiferromagnetic spin ordering along with antiferro-orbital
ordering at moderate to large Hubbard interaction strength. We also explore the
orbital-resolved density of states with Lanczos, predicting insulating behavior
for the compound $\alpha$-Sr$_2$CrO$_4$, in agreement with experiments.
Finally, an intuitive understanding of the results is provided based on a
hierarchy between orbitals, with $d_{xy}$ driving the spin order, while
electronic repulsion and the effective one dimensionality of the movement
within the $d_{xz}$ and $d_{yz}$ orbitals driving the orbital order.",2010.10342v1
2021-07-09,"Complete crystallographic, spin-electronic and magnetic structure of (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4: Unraveling the suppression of entropy in high entropy oxides","High entropy oxides (HEOs) are a rapidly emerging class of functional
materials consisting of multiple principal cations. The original paradigm of
HEOs assumes cationic occupations with the highest possible configurational
entropy allowed by the composition and crystallographic structure. However, the
fundamental question remains on the actual degree of configurational disorder
in HEOs, especially, in systems with a low enthalpy barriers for cation
anti-site mixing. Considering the experimental limitations due to the presence
of multiple principal cations in HEOs, here we utilize a robust and
cross-referenced characterization approach using soft X-ray magnetic circular
dichroism, hard X-ray absorption spectroscopy, M\""ossbauer spectroscopy,
neutron powder diffraction and SQUID magnetometry to study the competition
between crystal field stabilization energy and configurational entropy
governing the cation occupation in a spinel HEO (S-HEO),
(Co$_{0.2}$Cr$_{0.2}$Fe$_{0.2}$Mn$_{0.2}$Ni$_{0.2}$)$_3$O$_4$. In contrast to
the previous studies, the derived complete structural and spin-electronic
model,
(Co$_{0.6}$Fe$_{0.4}$)(Cr$_{0.3}$Fe$_{0.1}$Mn$_{0.3}$Ni$_{0.3}$)$_2$O$_4$,
highlights a significant deviation from the hitherto assumed paradigm of
entropy-driven non-preferential distribution of cations in HEOs. An immediate
correlation of this result can be drawn with bulk as well as the local element
specific magnetic properties, which are intrinsically dictated by cationic
occupations in spinels. The real local lattice picture presented here provides
an alternate viewpoint on ionic arrangement in HEOs, which is of fundamental
interest for predicting and designing their structure-dependent
functionalities.",2107.04274v2
2022-05-02,Evidence for charge and spin order in single crystals of La$_3$Ni$_2$O$_7$ and La$_3$Ni$_2$O$_6$,"Charge and spin order is intimately related to superconductivity in copper
oxide superconductors. To elucidate the competing orders in various nickel
oxide compounds are crucial given the fact that superconductivity has been
discovered in Nd$_{0.8}$Sr$_{0.2}$NiO$_2$ films. Herein, we report structural,
electronic transport, magnetic, and thermodynamic characterizations on single
crystals of La$_3$Ni$_2$O$_7$ and La$_3$Ni$_2$O$_6$. La$_3$Ni$_2$O$_7$ is
metallic with mixed Ni$^{2+}$ and Ni$^{3+}$ valent states. Resistivity
measurements yield two transition-like kinks at $\sim$110 and 153 K,
respectively. The kink at 153 K is further revealed from magnetization and
specific heat measurements, indicative of the formation of charge and spin
order. La$_3$Ni$_2$O$_6$ single crystals obtained from topochemical reduction
of La$_3$Ni$_2$O$_7$ are insulating and show an anomaly at $\sim$176 K on
magnetic susceptibility. The transition-like behaviors of La$_3$Ni$_2$O$_7$ and
La$_3$Ni$_2$O$_6$ are analogous to the charge and spin order observed in
La$_4$Ni$_3$O$_{10}$ and La$_4$Ni$_3$O$_8$, suggesting charge and spin order is
a common feature in the ternary La-Ni-O system with mixed-valent states of
nickel.",2205.00950v1
2004-09-29,Nanometer and sub-nanometer thin oxide films at surfaces of late transition metals,"If metal surfaces are exposed to sufficiently oxygen-rich environments,
oxides start to form. Important steps in this process are the dissociative
adsorption of oxygen at the surface, the incorporation of O atoms into the
surface, the formation of a thin oxidic overlayer and the growth of the once
formed oxide film. For the oxidation process of late transition metals (TM),
recent experimental and theoretical studies provided a quite intriguing
atomic-scale insight: The formed initial oxidic overlayers are not merely few
atomic-layer thin versions of the known bulk oxides, but can exhibit structural
and electronic properties that are quite distinct to the surfaces of both the
corresponding bulk metals and bulk oxides. If such nanometer or even
sub-nanometer surface oxide films are stabilized in applications, new
functionalities not scalable from the known bulk materials could
correspondingly arise. This can be particularly important for oxidation
catalysis, where technologically relevant gas phase conditions are typically
quite oxygen-rich. In such environments surface oxides may even form naturally
in the induction period, and actuate then the reactive steady-state behavior
that has traditionally been ascribed to the metal substrates. Corresponding
aspects are reviewed by focusing on recent progress in the modeling and
understanding of the oxidation behavior of late TMs, using particularly the
late 4d series from Ru to Ag to discuss trends.",0409743v1
2005-06-04,"Book Chapter 1: Theory of size, confinement and oxidation effect on oxide nanomaterials","Introduction bond-band-barrier (BOLS) correlation for the effect of
electronic process of oxidation and the bond order-length-strengtrh (BOLS)
correlation for the behaviour of nanostructures.",0506106v1
2019-05-20,Effect of the degree of oxidation of graphene oxide on As(III) adsorption,"The study of the interaction between graphene oxide and arsenic is of great
relevance towards the development of adsorbent materials and as a way to
understand how these two materials interact in the environment. In this work we
show that As(III) adsorption, primarily H3AsO3, by graphene oxide is dependent
on its degree of oxidation. Variations in the concentration of potassium
permanganate resulted in an increase on the C/O ratio from 1.98 to 1.35 with
C-OH and C-O-C concentrations of 18 and 32%, respectively. Three oxidation
degrees were studied, the less oxidized material reached a maximum As(III)
adsorption capacity of 124 mg/g, whereas the graphene with the highest degree
of oxidation reached a value of 288 mg/g at pH 7, to the authors knowledge, the
highest reported in the literature. The interaction between graphene oxide and
As(III) was also studied by Density Functional Theory (DFT) computer models
showing that graphene oxide interacts with As(III) primarily through hydrogen
bonds, having interaction energies with the hydroxyl and epoxide groups of 378
and 361 kcal/mol, respectively. Finally, cytotoxicity tests showed that the
graphene oxide had a cellular viability of 57% with 50 {\mu}g/ml, regardless of
its degree of oxidation.",1905.12168v1
2020-05-14,Simulating the fabrication of aluminium oxide tunnel junctions,"Aluminium oxide (AlO$_\mathrm{x}$) tunnel junctions are important components
in a range of nanoelectric devices including superconducting qubits where they
can be used as Josephson junctions. While many improvements in the
reproducibility and reliability of qubits have been made possible through new
circuit designs, there are still knowledge gaps in the relevant materials
science. A better understanding of how fabrication conditions affect the
density, uniformity, and elemental composition of the oxide barrier may lead to
the development of lower noise and more reliable nanoelectronics and quantum
computers. In this paper we use molecular dynamics to develop models of
Al-AlO$_\mathrm{x}$-Al junctions by iteratively growing the structures with
sequential calculations. With this approach we can see how the surface oxide
grows and changes during the oxidation simulation. Dynamic processes such as
the evolution of a charge gradient across the oxide, the formation of holes in
the oxide layer, and changes between amorphous and semi-crystalline phases are
observed. Our results are widely in agreement with previous work including
reported oxide densities, self-limiting of the oxidation, and increased
crystallinity as the simulation temperature is raised. The encapsulation of the
oxide with metal evaporation is also studied atom by atom. Low density regions
at the metal-oxide interfaces are a common feature in the final junction
structures which persists for different oxidation parameters, empirical
potentials, and crystal orientations of the aluminium substrate.",2005.06687v2
2021-03-08,Understanding the role of exchange and correlations in complex oxides under strain and oxide heterostructures,"The study of complex oxides and oxide heterostructures have dominated the
field of experimental and theoretical condensed matter research for the better
part of the last few decades. Powerful experimental techniques like molecular
beam epitaxy and pulsed laser deposition have made fabrication of oxide
heterostructures with atomically sharp interfaces possible, while more and more
sophisticated handling of exchange and correlations within first principles
methods including density functional theory (DFT) supplemented with Hubbard U
corrections and hybrid functionals, and beyond DFT techniques like dynamical
mean field theory (DMFT) have made understanding of such correlated oxides and
oxide interfaces easier. The emergence of the high mobility two dimensional
electron gas with fascinating properties like giant photoconductance, large
negative magnetoresistance, superconductivity, ferromagnetism, and the
mysterious coexistence of the latter two have indeed caught the attention of
condensed matter community at large. Similarly strain tuning of oxides have
generated considerable interest particularly after the recent discovery of
piezoelectric methods of strain generation. Theoretical understanding and
prediction of the possible exotic phases emerging in such complex oxides both
under strain and in heterostructures will eventually lead to better design of
device applications in this new emerging field of oxide electronics, along with
possible discovery of exotic physics in condensed matter systems which may be
of wider significance! In this review we briefly look at theoretical studies of
novel phenomena in oxides under strain and oxide heterostructures, and try to
understand the role of exchange and particularly correlation in giving rise to
such exotic electronic states.",2103.04943v1
2021-05-21,Vanadium Dioxide Thin Films Synthesized Using Low Thermal Budget Atmospheric Oxidation,"Vanadium dioxide is a complex oxide material, which shows large resistivity
and optical reflectance change while transitioning from the insulator to metal
phase at ~68 {\deg}C. In this work, we use a modified atmospheric thermal
oxidation method to oxidize RF-sputtered Vanadium films. Structural,
surface-morphology and phase-transition properties of the oxidized films as a
function of oxidation duration are presented. Phase-pure VO2 films are obtained
by oxidizing ~130 nm Vanadium films in short oxidation duration of ~30 seconds.
Compared to previous reports on VO2 synthesis using atmospheric oxidation of
Vanadium films of similar thickness, we obtain a reduction in oxidation
duration by more than one order. Synthesized VO2 thin film shows resistance
switching of ~3 orders of magnitude. We demonstrate optical reflectance
switching in long-wave infrared wavelengths in VO2 films synthesized using
atmospheric oxidation of Vanadium. The extracted refractive index of VO2 in the
insulating and in the metallic phase is in good agreement with VO2 synthesized
using other methods. The considerable reduction in oxidation time of VO2
synthesis while retaining good resistance and optical switching properties will
help in integration of VO2 in limited thermal budget processes, enabling
further applications of this phase-transition material.",2105.10264v1
2021-07-15,Color of Copper/Copper oxide,"Stochastic inhomogeneous oxidation is an inherent characteristic of copper
(Cu), often hindering color tuning and bandgap engineering of oxides. Coherent
control of the interface between metal and metal oxide remains unresolved. We
demonstrate coherent propagation of an oxidation front in single-crystal Cu
thin film to achieve a full-color spectrum for Cu by precisely controlling its
oxide-layer thickness. Grain boundary-free and atomically flat films prepared
by atomic-sputtering epitaxy allow tailoring of the oxide layer with an abrupt
interface via heat treatment with a suppressed temperature gradient. Color
tuning of nearly full-color RGB indices is realized by precise control of
oxide-layer thickness; our samples covered ~50.4% of the sRGB color space. The
color of copper/copper oxide is realized by the reconstruction of the
quantitative yield color from oxide pigment (complex dielectric functions of
Cu2O) and light-layer interference (reflectance spectra obtained from the
Fresnel equations) to produce structural color. We further demonstrate
laser-oxide lithography with micron-scale linewidth and depth through local
phase transformation to oxides embedded in the metal, providing spacing
necessary for semiconducting transport and optoelectronics functionality.",2107.07175v1
2021-10-14,Three regimes in the tribo-oxidation of high purity copper at temperatures of up to 150 $^\circ$C,"Surface oxidation of high-purity copper is accelerated under tribological
loading. Tribo-oxide formation at room temperature is associated with diffusion
processes along defects, such as dislocations or grain boundaries. Here, we
embark on investigating the additional influence of temperature on the
tribo-oxidation of copper. Dry, reciprocating sliding tests were performed with
a variation of the sample temperature between 21 - 150 $^\circ$C.
Microstructural changes were monitored and analyzed with state-of-the-art
electron microscopy techniques. Oxide layer formation through thermal oxidation
was observed for 150 $^\circ$C, but not for lower temperatures. As the
temperature increases from room temperature up to 100 $^\circ$C, a
significantly stronger tribo-oxidation into deeper material layers and an
increase in the amount of formed pores and oxides was detected. Up to 75
$^\circ$C, diffusional processes along grain boundaries and dislocation pipes
were identified. Starting at 100 $^\circ$C, CuO was detected. Hence,
tribological loading significantly alters the CuO formation in comparison with
static oxidation. Along with the CuO formation at temperatures >= 90 $^\circ$C,
the oxide layer thickness decreased while the friction coefficient increased.
The observations broaden our understanding of the elementary mechanisms of
tribo-oxidation in high-purity copper. Eventually, this will allow to
systematically customize surfaces showing tribo-oxidation for specific
tribological applications.",2110.07260v1
2022-10-09,Probing the microscopic structure and flexibility of oxidized DNA by molecular simulations,"The oxidative damage of DNA is a compelling issue in molecular biophysics as
it plays a vital role in the epigenetic control of gene expression and is
believed to be associated with mutagenesis, carcinogenesis, and ageing. To
understand the microscopic structural changes in physical properties of DNA and
the resulting influence on its function due to oxidative damage of its
nucleotide bases, we have conducted all-atom molecular dynamic simulations of
double-stranded DNA (dsDNA) with its guanine bases being oxidized. The guanine
bases are more prone to oxidative damage due to the lowest value of redox
potential among all nucleobases. We have analyzed the local as well as global
mechanical properties of native and oxidized dsDNA and explained those results
by microscopic structural parameters and thermodynamic calculations. Our
results show that the oxidative damage of dsDNA does not deform the
Watson-Crick geometry; instead, the oxidized DNA structures are found to be
better stabilized through electrostatic interactions. Moreover, oxidative
damage changes the mechanical, helical, and groove parameters of dsDNA. The
persistence length, stretch modulus, and torsional stiffness are found to be
48.87 nm, 1239.26 pN, and 477.30 pN.nm^2, respectively, for native dsDNA, and
these values are 61.31 nm, 659.91 pN, and 407.79 pN.nm^2, respectively, when
all the guanine bases of the dsDNA are oxidized. Compared to the global
mechanical properties, the changes in helical and groove properties are found
to be more prominent, concentrated locally at the oxidation sites, and causing
the transition of the backbone conformations from BI to BII at the regions of
oxidative damage.",2210.04235v1
2014-09-01,Phosphorene Oxide: Stability and electronic properties of a novel 2D material,"Phosphorene, the monolayer form of the (black) phosphorus, was recently
exfoliated from its bulk counterpart. Phosphorene oxide, by analogy to graphene
oxide, is expected to have novel chemical and electronic properties, and may
provide an alternative route to synthesis of phosphorene. In this letter, we
investigate physical and chemical properties of the phosphorene oxide including
its formation by the oxygen adsorption on the bare phosphorene. Analysis of the
phonon dispersion curves finds stoichiometric and non-stoichiometric oxide
configurations to be stable at ambient conditions, thus suggesting that the
oxygen absorption may not degrade the phosphorene. The nature of the band gap
of the oxides depends on the degree of the functionalization of phosphorene;
indirect gap is predicted for the non-stoichiometric configurations whereas a
direct gap is predicted for the stoichiometric oxide. Application of the
mechanical strain and external electric field leads to tunability of the band
gap of the phosphorene oxide. In contrast to the case of the bare phosphorene,
dependence of the diode-like asymmetric current-voltage response on the degree
of stoichiometry is predicted for the phosphorene oxide.",1409.0459v2
2014-10-15,Phosphorene oxides: bandgap engineering of phosphorene by oxidation,"We show that oxidation of phosphorene can lead to the formation of a new
family of planar (2D) and tubular (1D) oxides and sub-oxides, most of them
insulating. This confers to black phosphorus a native oxide that can be used as
barrier material and protective layer. Further, the bandgap of phosphorene
oxides depends on the oxygen concentration, suggesting that controlled
oxidation can be used as a means to engineer the bandgap. For the oxygen
saturated composition, P$_2$O$_5$, both the planar and tubular phases have a
large bandgap energy of about 8.5eV, and are transparent in the near UV. These
two forms of phosphorene oxides are predicted to have the same formation
enthalpy as o$^\prime$-P$_2$O$_5$, the most stable of the previously known
forms of phosphorus pentoxide.",1410.3906v1
2014-11-05,Oxidation of graphite surface: the role of water,"Based on density functional calculations, we demonstrate a significant
difference in oxidation patterns between graphene and graphite and the
formation of defects after oxidation. Step-by-step modeling demonstrates that
oxidation of 80% of the graphite surface is favorable. Oxidation above half of
the graphite surface significantly decreases the energy costs of vacancy
formation with CO2 production. The presence of water is crucial in the
transformation of epoxy groups to hydroxyl, the intercalation with further
bundle and exfoliation. In water-rich conditions, water intercalates graphite
at the initial stages of oxidation and oxidation, which is similar to the
oxidation process of free-standing graphene; in contrast, in water-free
conditions, large molecules intercalate graphite only after oxidation occurs on
more than half of the surface.",1411.1143v1
2019-09-30,Mechanically prepared copper surface in oxidizing and non-oxidizing conditions,"In the present work surface roughness of copper samples after mechanical
surface preparation processes (polishing, grinding, sand-blasting) and after
exposure in non-oxidizing (high purity argon) and oxidizing (air) conditions at
700 and 750{\deg}C have been evaluated by contact profilometer and by fractal
analysis. Quantitative description of surfaces that are hidden from the sight
of conventional methods is possible by fractal analysis, e.g. in the present
work, the roughness of Cu2O/Cu boundary has been evaluated under oxide layer.
It has been pointed out, that in both oxidizing and non-oxidizing conditions
initial surface roughness of copper is affected by annealing at high
temperature: at 700{\deg}C surface roughness of polished and ground samples
increased but at 750{\deg}C decreased in comparison to surface roughness prior
to heat treatment. For sand-blasted samples in both oxidizing and non-oxidizing
conditions the lowest values of surface roughness parameters were obtained at
750{\deg}C. It is then concluded that two phenomena are responsible for such
effect: chemical reaction between copper and oxygen and surface diffusion of
copper due to high temperature of annealing.",1909.13645v2
2020-01-24,Passivation mechanisms and pre-oxidation effects on model surfaces of FeCrNi austenitic stainless steel,"Passivation mechanisms were investigated on (100)-oriented Fe-18Cr-13Ni
surfaces with direct transfer between surface preparation and analysis by X-ray
photoelectron spectroscopy and scanning tunneling microscopy and
electrochemical characterization. Starting from oxide-free surfaces,
pre-oxidation at saturation under ultra-low pressure (ULP) oxygen markedly
promotes the oxide film Cr(III) enrichment and hinders/delays subsequent iron
oxidation in water-containing environment. Exposure to sulfuric acid at open
circuit potential causes preferential dissolution of oxidized iron species.
Anodic passivation forces oxide film re-growth, Cr(III) dehydroxylation and
further enrichment. ULP pre-oxidation promotes Cr(III) hydroxide formation at
open circuit potential, compactness of the nanogranular oxide film and
corrosion protection.",2001.09025v1
2017-05-07,Remarkably strong chemisorption of nitric oxide on insulating oxide films promoted by hybrid structure,"The remarkably strong chemical adsorption behaviors of nitric oxide on
magnesia (001) film deposited on metal substrate have been investigated by
employing periodic density functional calculations with Van der Waals
corrections. The molybdenum supported magnesia (001) show significantly
enhanced adsorption properties and the nitric oxide is chemisorbed strongly and
preferably trapped in flat adsorption configuration on metal supported oxide
film, due to the substantially large adsorption energies and transformation
barriers. The analysis of Bader charges, projected density of states,
differential charge densities, electron localization function, highest occupied
orbital and particular orbital with largest Mg-NO-Mg bonding coefficients, are
applied to reveal the electronic adsorption properties and characteristics of
bonding between nitric oxide and surface as well as the bonding within the
hybrid structure. The strong chemical binding of nitric oxide on magnesia
deposited on molybdenum slab offers new opportunities for toxic gas detection
and treatment. We anticipate that hybrid structure promoted remarkable chemical
adsorption of nitric oxide on magnesia in this study will provide versatile
strategy for enhancing chemical reactivity and properties of insulating oxide.",1705.02590v1
2018-08-02,A Generalized Mathematical Framework for Thermal Oxidation Kinetics,"We present a generalized mathematical model for thermal oxidation and the
growth kinetics of oxide films. The model expands long-standing classical
models by taking into account the reaction occurring at the interface as well
as transport processes in greater details. The standard Deal-Grove model (the
linear-parabolic rate law) relies on the assumption of quasi-static diffusion
that results in a linear concentration profile of, for example, oxidant species
in the oxide layer. By relaxing this assumption and resolving the entire
problem, three regimes can be clearly identified corresponding to different
stages of oxidation. Namely, the oxidation starts with the reaction-controlled
regime (described by a linear rate law), is followed by a transitional regime
(described by a logarithmic or power law depending on the stoichiometry
coefficient m), and ends with the well known diffusion-controlled regime
(described by a parabolic rate law). Deal-Grove's theory is shown to be the
lower order approximation of the proposed model. Various oxidation rate laws
are unified into a single model to describe the entire oxidation process.",1808.00916v1
2020-10-11,Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic,"The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic
(LBE) at 200 oC is studied using electrochemical impedance spectroscopy. The
structures and resistance of oxide grown on iron oxidized in air at different
temperatures and durations are compared. The results show that the resistance
of the oxide film increases with increasing oxidizing temperature, due to the
formation of a thicker scale and fewer defects. At the same temperature (600
oC), increasing the oxidation time can also reduce the defect concentration in
the oxide film and improve the impedance of the oxide scale in LBE.",2010.05372v1
2020-11-17,Effect of Surface Treatment on High-Temperature Oxidation Behavior of IN 713C,"The effects of surface preparations on oxidation kinetics and oxide scale
morphology for the commercially available Ni-based superalloy IN 713C have been
investigated. The ground and polished samples were exposed in air at 800-1100C.
The ground specimens were found to demonstrate lower oxidation kinetics
compared to those after polishing. The grinding also affected the oxide scale
morphology, resulting in a protective alumina scale, while the polished samples
developed Ni-/Cr-rich mixed oxides on the surface. Better oxidation resistance
of the ground surfaces is related to a higher concentration of defects in the
nearsurface region introduced by cold working. These defects facilitate the
outward transport of the scaleforming element Al and thus are beneficial for
protective oxidation. The oxidation mechanism at lower temperatures was
introduced. The model based on the generalized Darken method and multiphase
approximation was proposed.",2011.08910v1
2022-01-11,Oxide-stabilized microstructure of severe plastically deformed CuCo alloys,"Nanocrystalline materials are well known for their beneficial mechanical and
physical properties. However, it is of utmost importance to stabilize the
microstructure at elevated temperatures to broaden the window of application
e.g. by pinning grain boundaries through impurities or oxides. CuCo alloys,
severe plastically deformed using high-pressure torsion, were used to
investigate the evolution of oxides upon annealing. These investigations were
performed using electron microscopy, synchrotron high-energy X-ray scattering
and atom probe tomography. Monitoring the evolution of oxides by in-situ small
angle scattering investigations indicates the growth of primary oxides as well
as the formation of another species of oxide at elevated temperatures. Slightly
different coarsening can be observed in heat-treated samples, which can be
traced back to the influence of different oxide amounts. The initially
supersaturated CuCo matrix changes by the decomposition process as well as Co-
and Cu-based oxides formation and growth. It has been found that the major
number of oxides which are present after annealing, can already be found in the
starting materials.",2201.03900v1
1995-05-03,Magnetic and Transport Properties of the Kondo Lattice Model with Ferromagnetic Exchange Coupling,"The Kondo lattice model with Hund's ferromagnetic spin coupling is
investigated as a microscopic model of the perovskite-type $3d$ manganese oxide
(R,A)MnO$_3$ where $R$ and $A$ are rare earth element and alkaline earth
element, respectively. We take the classical spin limit $S=\infty$ for the
simplicity of the calculation, since the quantum exchange process seems to be
irrelevant in the high temperature paramagnetic phase. Magnetic and transport
properties of the system are calculated. In the hole doped systems,
ferromagnetic instabilities are observed as the temperature is lowered. The
giant magnetoresistance of this model is in excellent agreement with the
experimental data of (La,Sr)MnO$_3$.",9505011v3
1998-02-03,Magnetic properties of the coupled ladder system MgV$_2$O$_5$,"We present magnetic susceptibility measurements on MgV$_2$O$_5$, a compound
in which the vanadium oxide planes have the same topology as in CaV$_2$O$_5$.
The most striking property is that there is an energy gap of about 15 K, much
smaller than in CaV$_2$O$_5$, where the values reported are of the order of 500
K. We show that this may be understood naturally in terms of the phase diagram
of the frustrated, coupled ladder system. This analysis leads to the prediction
that MgV$_2$O$_5$ should have incommensurate dynamic spin fluctuations.",9802029v1
1998-04-17,High-Tc superconductivity through a charge pairing mechanism in a strongly coupled disordered phase,"We present a lattice field theory of spins coupled to Dirac fermions, as a
model for the doped copper oxide compounds. Both the fermionic and spin degrees
of freedom are treated dynamically. The influence of the charge carriers on the
magnetic ordering follows automatically. The magnetic phase diagram at zero
temperature is studied numerically and with Mean-Field methods. The Hybrid
Monte Carlo algorithm is adapted to the O(3) non-linear sigma model constraint.
The charged excitations in the various phases are studied at the Mean-Field
level. Bound states of two charged fermions are found in a strongly coupled
paramagnetic phase, without requiring a Fermi sea. We acquire a qualitative
understanding of high-T$_c$ superconductivity through Bose-Einstein
condensation of those dynamically bound pairs. The model also implies
insulating behaviour at low doping, and Fermi liquid behaviour at large doping.
We predict the possibility of reentrant superconductivity and the absence of
superconductivity in spin-1 and spin-3/2 materials.",9804184v1
1998-07-24,Destruction of localized electron pairs above the magnetic-field-driven superconductor-insulator transition in amorphous InO films,"We have investigated the field-induced superconductivity-destroying quantum
transition in amorphous indium oxide films at low temperatures down to 30 mK.
It has been found that, on the high-field side of the transition, the
magnetoresistance reaches a maximum and the phase can be insulating as well as
metallic. With further increasing magnetic field the film resistance drops and
approaches in the high-field limit the resistance value at transition point so
that at high fields the metallic phase occurs for both cases. We give a
qualitative account of this behavior in terms of field-induced destruction of
localized electron pairs.",9807332v2
1999-02-11,Neutron Scattering Study of Spin Density Wave Order in the Superconducting State of Excess-Oxygen-Doped La2CuO4+y,"We report neutron scattering measurements of spin density wave order within
the superconducting state of a single crystal of predominately stage-4
La2CuO4+y with a Tc(onset) of 42 K. The low temperature elastic magnetic
scattering is incommensurate with the lattice and is characterized by
long-range order in the copper-oxide plane with the spin direction identical to
that in the insulator. Between neighboring planes, the spins exhibit
short-range correlations with a stacking arrangement reminiscent of that in the
undoped antiferromagnetic insulator. The elastic magnetic peak intensity
appears at the same temperature within the errors as the superconductivity,
suggesting that the two phenomena are strongly correlated. These observations
directly reveal the persistent influence of the antiferromagnetic order as the
doping level increases from the insulator to the superconductor. In addition,
our results confirm that spin density wave order for incommensurabilities near
1/8 is a robust feature of the La2CuO4-based superconductors.",9902157v2
1999-05-12,Phase diagram of an extended Kondo lattice model for manganites: the Schwinger-boson mean-field approach,"We investigate the phase diagram of an extended Kondo lattice model for doped
manganese oxides in the presence of strong but finite Hund's coupling and
on-site Coulomb interaction. By means of the Schwinger-boson mean-field
approach, it is found that, besides magnetic ordering, there will be
non-uniform charge distributions, such as charge ordering and phase separation,
if the interaction between electrons prevails over the hybridization. Which of
the charge ordering and phase separation appears is determined by a competition
between effective repulsive and attractive interactions due to virtual
processes of electron hopping. Calculated results show that strong electron
correlations caused by the on-site Coulomb interaction as well as the finite
Hund's coupling play an important role in the magnetic ordering and charge
distribution at low temperatures.",9905152v1
1999-10-28,Magnetic Properties of Weakly Doped Antiferromagnets,"We study the spin excitations and the transverse susceptibility of a
two-dimensional antiferromagnet doped with a small concentration of holes in
the t-J model. The motion of holes generates a renormalization of the magnetic
properties. The Green's functions are calculated in the self-consistent Born
approximation. It is shown that the long-wavelength spin waves are
significantly softened and the shorter-wavelength spin waves become strongly
damped as the doping increases. The spin wave velocity is reduced by the
coherent motion of holes, and not increased as has been claimed elsewhere. The
transverse susceptibility is found to increase considerably with doping, also
as a result of coherent hole motion. Our results are in agreement with
experimental data for the doped copper oxide superconductors.",9910474v1
2000-03-17,Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3,"Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a
macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been
observed at various temperatures ranging from 4K to 170K, well below the Curie
temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF)
vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the
TLF to gain insight into the microscopic electronic and magnetic state of this
manganite. At low temperature (below 30K) The TLF is well described by a
thermally activated two-level model. An estimate of the energy difference
between the two states is inferred. At higher temperature (between 60K and
170K) we observed critical effects of the temperature on the life-times of the
TLF. We discuss this peculiar temperature dependence in terms of a sharp change
in the free energy functional of the fluctuators. We attribute the origin of
the RTN to be a dynamic mixed-phase percolative conduction process, where
manganese clusters switch back and forth between two phases that differ in
their conductivity and magnetization.",0003313v1
2000-08-25,Random Berry Phase Magnetoresistance as a Probe of Interface Roughness in Si MOSFETs,"The effect of silicon-oxide interface roughness on the weak-localization
magnetoconductance of a silicon MOSFET in a magnetic field, tilted with respect
to the interface, is studied. It is shown that an electron picks up a random
Berry's phase as it traverses a closed orbit. Effectively, due to roughness,
the electron sees an uniform field parallel to the interface as a random
perpendicular field. At zero parallel field the dependence of the conductance
on the perpendicular field has a well known form, the weak-localization
lineshape. Here the effect of applying a fixed parallel field on the lineshape
is analyzed. Many types of behavior are found including homogeneous broadening,
inhomogeneous broadening and a remarkable regime in which the change in
lineshape depends only on the magnetic field, the two length scales that
characterize the interface roughness and fundamental constants. Good agreement
is obtained with experiments that are in the homogeneous broadening limit. The
implications for using weak-localization magnetoconductance as a probe of
interface roughness, as proposed by Wheeler and coworkers, are discussed.",0008375v1
2001-06-04,Dzyaloshinski-Moriya Interaction in the 2D Spin Gap System SrCu2(BO3)2,"The Dzyaloshinski-Moriya interaction partially lifts the magnetic frustration
of the spin-1/2 oxide SrCu2(BO3)2. It explains the fine structure of the
excited triplet state and its unusual magnetic field dependence, as observed in
previous ESR and new neutron inelastic scattering experiments. We claim that it
is mainly responsible for the dispersion. We propose also a new mechanism for
the observed ESR transitions forbidden by standard selection rules, that relies
on an instantaneous Dzyaloshinski-Moriya interaction induced by spin-phonon
couplings.",0106036v3
2001-07-30,Martensitic accommodation strain and the metal-insulator transition in manganites,"In this paper, we report polarized optical microscopy and electrical
transport studies of manganese oxides that reveal that the charge ordering
transition in these compounds exhibits typical signatures of a martensitic
transformation. We demonstrate that specific electronic properties of
charge-ordered manganites stem from a combination of martensitic accommodation
strain and effects of strong electron correlations. This intrinsic strain is
strongly affected by the grain boundaries in ceramic samples. Consistently, our
studies show a remarkable enhancement of low field magnetoresistance and the
grain size effect on the resistivity in polycrystalline samples and suggest
that the transport properties of this class of manganites are governed by the
charge-disordered insulating phase stabilized at low temperature by virtue of
martensitic accommodation strain. High sensitivity of this phase to strains and
magnetic field leads to a variety of striking phenomena, such as unusually high
magnetoresistance (10^10 %) in low magnetic fields.",0107609v1
2001-11-05,Microscopic Magnetic Properties of (V$_{1-x}$Ti$_{x}$)$_2$O$_3$ near the Phase Boundary of the Metal-Insulator Transition,"Magnetic susceptibility (chi) and $^{51}$V NMR have been measured in
(V$_{1-x}$Ti$_{x}$)$_2$O$_3$ near the phase boundary of the metal-insulator
transition. It is established that the transition from antiferromagnetic
insulating (AFI) to antiferromagnetic metallic phases near $x_{\rm c}\approx
0.05$ is not quantum critical but is discontinuous with a jump of the
transition temperature. In the AFI phase at 4.2 K, we observed the satellite in
the zero-field $^{51}$V NMR spectrum around 181 MHz in addition to the ``host''
resonance around 203 MHz. The satellite is also observable in the paramagnetic
metallic phase of the x = 0.055 sample. We associated the satellite with the V
sites near Ti which are in the V$^{3+}$-like oxidation state but has different
temperature dependence of the NMR shift from that of the host V site. The host
d-spin susceptibility for x = 0.055 decreases below $\sim$60 K but remains
finite in the low-temperature limit.",0111059v2
2001-11-10,"Temperature Dependence of the Magnetic Penetration Depth in the Vortex State of the Pyrochlore Superconductor, Cd2Re2O7","We report transverse field and zero field muon spin rotation studies of the
superconducting rhenium oxide pyrochlore, Cd2Re2O7. Transverse field
measurements (H=0.007 T) show line broadening below Tc, which is characteristic
of a vortex state, demonstrating conclusively the type-II nature of this
superconductor. The penetration depth is seen to level off below about 400 mK
(T/Tc~0.4), with a rather large value of lambda (T=0)~7500A. The temperature
independent behavior below ~ 400 mK is consistent with a nodeless
superconducting energy gap. Zero-field measurements indicate no static magnetic
fields developing below the transition temperature.",0111187v1
2001-11-10,Detailed Structure of the Magnetic Excitation Spectra of YBa2Cu3Oy and Its Implication on the Physical Characteristics of the Electron System,"Detailed structure of the magnetic excitation spectra x""(q,w) of the
superconducting oxide YBa2Cu3O6.5(the transition temperature Tc ~ 52 K) in the
wave vector (q)- and the energy(w)-space, and its temperature (T) dependence
have been studied. By adopting an effective energy dispersion of the quasi
particles which can reproduce the shape of the Fermi surface and by introducing
the exchange interaction between the Cu spins, a rather satisfactory agreement
between the calculation and the experimentally observed data can be obtained.
In the study, it has been found that the effects of the quasi particle- energy
broadening on the excitation spectra x""(q,w) is important. The sharp resonance
peak observed at w ~ 40 meV for the optimally doped system of YBa2Cu3Oy can be
naturally reproduced by the present model",0111190v3
2002-01-15,Structural and Magnetic Instabilities of La$_{2-x}$Sr$_x$CaCu$_2$O$_6$,"A neutron scattering study of nonsuperconducting
La$_{2-x}$Sr$_x$CaCu$_2$O$_6$ (x=0 and 0.2), a bilayer copper oxide without CuO
chains, has revealed an unexpected tetragonal-to-orthorhombic transition with a
doping dependent transition temperature. The predominant structural
modification below the transition is an in-plane shift of the apical oxygen. In
the doped sample, the orthorhombic superstructure is strongly disordered, and a
glassy state involving both magnetic and structural degrees of freedom develops
at low temperature. The spin correlations are commensurate.",0201253v2
2002-03-11,Pressure dependence of phase transitions in the quasi one-dimensional metal-insulator transition system beta-Na1/3V2O5,"The pressure dependence of phase transitions in the quasi one-dimensional
vanadium oxide $\beta$-Na$_{1/3}$V$_2$O$_5$ has been studied by magnetic
susceptibility and electrical resistivity measurements. The pressure dependence
of the various transition temperatures is quite differently. The transition at
T=240 K, previously reported and attributed to ordering on Na sites, and a
second transition at $T \approx 222$ K, reported here for the first time and
attributed to a further increase of order on Na sites, are almost independent
of pressure. On the other hand, the metal-insulator (MI) transition at
$T_{MI}=130$ K shifts to lower temperatures, while the magnetic transition at
$T_N=24$ K shifts to higher temperatures with increasing pressure. We discuss
the different pressure dependencies of $T_{MI}$ and $T_N$ in terms of
increasing interchain coupling and the MI transition to be of Peierls type.",0203234v1
2002-08-09,"On the nature of ferromagnetism in diluted magnetic semiconductors: GaAs:Mn, GaP:Mn","A microscopic Hamiltonian for interacting manganese impurities in diluted
magnetic semiconductors (DMS) is derived. It is shown that in p -type III-V DMS
the indirect exchange between Mn impurities has similarities with the Zener
mechanism in transition metal oxides. Here the mobile holes and localized
states near the top of the valence band play the role of unoccupied oxygen
orbitals which induce ferromagnetism. The Curie temperature estimated from the
proposed kinematic exchange agrees with recent experiments on GaAs:Mn. The
model is also applicable to the GaP:Mn system.",0208188v1
2002-08-28,Orbital state and magnetic properties of LiV_2 O_4,"LiV_2 O_4 is one of the most puzzling compounds among transition metal oxides
because of its heavy fermion like behavior at low temperatures. In this paper
we present results for the orbital state and magnetic properties of LiV_2 O_4
obtained from a combination of density functional theory within the local
density approximation and dynamical mean-field theory (DMFT). The DMFT
equations are solved by quantum Monte Carlo simulations. The trigonal crystal
field splits the V 3d orbitals such that the a_{1g} and e_{g}^{pi} orbitals
cross the Fermi level, with the former being slightly lower in energy and
narrower in bandwidth. In this situation, the d-d Coulomb interaction leads to
an almost localization of one electron per V ion in the a_{1g} orbital, while
the e_{g}^{pi} orbitals form relatively broad bands with 1/8 filling. 2The
theoretical high-temperature paramagnetic susceptibility chi(T) follows a
Curie-Weiss law with an effective paramagnetic moment p_{eff}=1.65 in agreement
with the experimental results.",0208547v1
2002-08-30,Nickel Antidot Arrays on Anodic Alumina Substrates,"Large area nickel antidot arrays with density up to 10^10 /cm^2 have been
fabricated by depositing nickel onto anodic aluminum oxide membranes that
contain lattices of nanopores. Electron microscopy images show a high degree of
order of the antidot arrays. Various sizes and shapes of the antidots were
observed with increasing thickness of the deposited nickel. New features appear
in the antidot arrays in both magnetization and transport measurements when the
external magnetic field is parallel to the current direction, including an
enhancement and a nonmonotonous field dependence of the magnetoresistance,
larger values of the coercive field and remanence moment, and smaller
saturation field.",0208608v2
2002-11-15,Specific Heat of Kagome Ice in the Pyrochlore Oxide Dy2Ti2O7,"A novel macroscopically degenerate state called kagome ice, which was
recently found in a spin ice compound Dy2Ti2O7 in a magnetic field applied
along the [111] direction of the cubic unit cell, is studied by specific heat
measurements. The residual entropy of the kagome ice is estimated to be 0.65
J/K mol Dy, which is nearly 40 % of that for the tetrahedral spin ice obtained
in a zero field (1.68 J/K mol Dy) and is in good agreement with a theoretical
prediction. It is also reported that the kagom ice state, which is stabilized
at a range of magnetic field of 0.3 ~ 0.6 T, is a 'gas' phase and condenses
into a 'liquid' phase with nearly zero entropy at a critical field of 1 T.",0211326v1
2002-11-27,Theory of dopants and defects in Co-doped TiO2 anatase,"We report first-principles microscopic calculations of the formation energy,
electrical activity, and magnetic moment of Co dopants and a variety of native
defects in TiO2 anatase. Using these results, we use equilibrium thermodynamics
to predict the resulting carrier concentration, the average magnetic moment per
Co, and the dominant oxidation state of Co. The predicted values are in good
agreement with experiment under the assumption of O-poor growth conditions. In
this regime, a substantial fraction of Co dopants occupy interstitial sites as
donors. The incomplete compensation of these donors by substitutional Co
acceptors then leads to n-type behavior, as observed experimentally.",0211614v2
2003-01-14,Griffiths singularities and magnetoresistive manganites,"The large, so-called colossal, magnetoresistivity of doped manganese oxides
based on LaMnO3 has attracted considerable attention, but only one unusual
feature of the ferromagnetic transition in these compounds. We examine in this
paper the progression of magnetic and thermodynamic behavior as the transition
temperature is made to vary from 360 K to 218 K by changing the divalent
dopant. Single crystals of La_{0.7}Sr_{0.3}MnO3, as is well known, show modest
magnetoresistivity and conventional critical behavior. La$_{0.7}$Pb$_{0.3}$
Mn$O_3$, and to an even greater extent, La$_{0.7}$Ca$_{0.3}$MnO$_3$, have
unusual magnetic properties extending more than 100 K above the transition. We
treat the properties of the latter samples in the context of a Griffiths phase
in which the transition temperature is depressed from its maximum value T_{G}
by random bond-angle bending.",0301243v1
2003-02-21,Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7,"Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been
studied. The magnetizations M measured under the conditions of the
zero-field-cooling(ZFC) and the field-cooling(FC) have different values below
the temperature T=TG. The anomalous T-dependence of the electrical
resistivities r and the thermoelectric powers S observed at around TG indicates
that the behavior of the magnetization is due to the transition to the state
with the spin freezing. In this spin-frozen state, the Hall resistivities rH
measured with the ZFC and FC conditions are found to have different values,
too, in the low temperature phase (T<TG). Possible mechanisms which induce such
the hysteretic behavior are discussed.",0302437v1
2003-07-18,Structures and electromagnetic properties of the A-site ordered/disordered manganites; RBaMn2O6/R0.5Ba0.5MnO3 (R = Y and rare earth elements),"The discovery of novel structural and physical properties in the $A$-site
ordered manganite $R$BaMn$_2$O$_6$ ($R$ = Y and rare earth elements) has
demanded new comprehension about perovskite manganese oxides. In the present
study, the $A$-site disordered form $R$$_{0.5}$Ba$_{0.5}$MnO$_3$ was
successfully synthesized and compared with $R$BaMn$_2$O$_6$ in the structures
and electromagnetic properties. $R$$_{0.5}$Ba$_{0.5}$MnO$_3$ has a primitive
cubic perovskite cell. Unexpectedly the magnetic glassy states are dominant as
the ground state for $R$$_{0.5}$Ba$_{0.5}$MnO$_3$. A peculiar behavior, the
steplike ultrasharp magnetization and resistivity change, has been observed in
Pr$_{0.5}$Ba$_{0.5}$MnO$_3$.",0307456v1
2003-08-19,Unconventional Charge Ordering in Na0.70CoO2 below 300 K,"We present the results of measurements of the dc-magnetic susceptibility
chi(T) and the 23Na-NMR response of Na_{0.70}CoO_{2} at temperatures between 50
and 340 K. The chi(T) data suggest that for T > 75 K, the Co ions adopt an
effective configuration of Co^{3.4+}. The 23Na-NMR response reveals pronounced
anomalies near 250 and 295 K, but no evidence for magnetic phase transitions is
found in chi(T). Our data suggest the onset of a dramatic change in the Co
3d-electron spin dynamics at 295 K. This process is completed at 230 K. Our
results maybe interpreted as evidence for either a tendency to electron
localization or an unconventional charge-density wave phenomenon within the
cobalt oxide layer, CoO_2, 3d electron system near room temperature.",0308383v2
2003-12-16,Magnetoresistive study of antiferromagnetic--weak ferromagnetic transition in single-crystal La$_{2}$CuO$_{4+δ}$,"The resistive measurements were made to study the magnetic field-induced
antiferromagnetic (AF) - weak ferromagnetic (WF) transition in La$_2$CuO$_4$
single-crystal. The magnetic field (DC or pulsed) was applied normally to the
CuO$_2$ layers. The transition manifested itself in a drastic decrease of the
resistance in critical fields of ~5-7 T. The study is the first to display the
effect of the AF -WF transition on the conductivity of the La$_2$CuO$_4$
single-crystal in the parallel - to - CuO$_2$ layers direction. The results
provide support for the 3-dimensional nature of the hopping conduction of this
layered oxide.",0312409v1
2004-01-08,Orbital degeneracy as a source of frustration in LiNiO$_2$,"Motivated by the absence of cooperative Jahn-Teller effect and of magnetic
ordering in LiNiO$_2$, a layered oxide with triangular planes, we study a
general spin-orbital model on the triangular lattice. A mean-field approach
reveals the presence of several singlet phases between the SU(4) symmetric
point and a ferromagnetic phase, a conclusion supported by exact
diagonalizations of finite clusters. We argue that one of the phases,
characterized by a large number of low-lying singlets associated to dimer
coverings of the triangular lattice, could explain the properties of LiNiO$_2$,
while a ferro-orbital phase that lies nearby in parameter space leads to a new
prediction for the magnetic properties of NaNiO$_2$.",0401122v2
2004-01-30,Magnetoelectric Effects in Ferromagnetic Metal-Piezoelectric Oxide Layered Structures,"Frequency dependence of magnetoelectric (ME) coupling is investigated in
trilayers of ferromagnetic alloy and piezoelectric lead zirconate titanate
(PZT). The ferromagnetic phases studied include permendur, a soft magnet with
high magnetostriction, iron, nickel, and cobalt. Low frequency data on ME
voltage coefficient versus bias magnetic field indicate strong coupling only
for trilayers with permendure or Ni. Measurements of frequency dependence of ME
voltage reveal a giant ME coupling at electromechanical resonance. The ME
interactions for transverse fields is an order of magnitude stronger than for
longitudinal fields. The maximum voltage coefficient of 90 V/cm Oe at resonance
is measured for samples with nickel or permendure and is three orders of
magnitude higher than low-frequency values.",0401648v1
2004-03-01,Unconventional superconductivity in Na$_{0.35}$CoO$_{2}\cdot$1.3D$_{2}$O and proximity to a magnetically ordered phase,"Muon spin relaxation ($\mu$SR) measurements on the new layered cobalt oxide
superconductor Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O and its parent,
non-superconducting compounds, have revealed unconventional nature of
superconductivity through: (1) a small superfluid energy which implies a
surprisingly high effective mass of the charge carriers, approximately 100
times the bare electron mass; (2) the superconducting transition temperature
$T_{c}$ scaling with the superfluid energy following the correlations found in
high-$T_{c}$ cuprate and some other two-dimensional superconductors; (3) an
anisotropic pairing without broken time-reversal symmetry; and (4) the
proximity of a magnetically ordered insulating phase at Na$_{0.5}$CoO$_{2}$
below $T_{N}$ = 53 K.",0403031v1
2004-08-17,Two-Dimensional Geometry of Spin Excitations in the High Temperature Superconductor YBa2Cu3O6+x,"The fundamental building block of the copper oxide superconductors is a Cu4O4
square plaquette. In most of these materials, the plaquettes are slightly
distorted and form a rectangular lattice. An influential theory predicts that
high-temperature superconductivity is nucleated in ""stripes"" aligned along one
of the axes of this lattice. This theory had received strong support from
experiments that appeared to indicate a one-dimensional character of the
magnetic excitations in the high temperature superconductor YBa2Cu3O6.6. Here
we report neutron scattering data on ""untwinned"" YBa2Cu3O6+x crystals, in which
the orientation of the rectangular lattice is maintained throughout the entire
volume. Contrary to the earlier claim, we demonstrate that the geometry of the
magnetic fluctuations is two-dimensional. Rigid stripe arrays therefore appear
to be ruled out over a wide range of doping levels in YBa2Cu3O6+x, but the data
may be consistent with liquid-crystalline stripe order.",0408379v1
2004-08-24,Interfacial strain measurements in $SrRuO_3/SrMnO_3$ magnetic multilayers,"Magnetic multilayers of $(SrRuO_3)_m(SrMnO_3)_n$ were grown artificially
using the pulsed laser deposition technique on (001)-oriented $SrTiO_3$
substrates. The state of strain at the interfaces and the structural coherency
are studied in details utilizing asymmetrical $X$-ray diffraction and the $\sin
^2\psi $ method. First, the evolution of the lattice parameters, the
crystallinity and the epitaxy of the films are evaluated as a function of the
number of $SrMnO_3$ unit cells using $X$-rays diffraction and transmission
electron microscopy. Second, our results on the stress indicate that the
$SrRuO_3/SrMnO_3$ superlattices show a larger residual strain as compared to
the single layer film of $SrRuO_3$. This suggests that the lattice stiffening
from interfacial strain and inhibiting the dislocation by composition
modulation. Finally, these results bring insights on the interfacial stress
measurements of oxide multilayers that can be used to control the physical
properties at the level of the atomic scale.",0408513v1
2004-10-27,Matrix Assisted Formation of Ferrihydrite Nanoparticles in a Siloxane/Poly(Oxyethylene) Nanohybrid,"Matrix-assisted formation of ferrihydrite, an iron oxide hydroxide analogue
of the protein ferritin-core, in a sol-gel derived organic-inorganic hybrid is
reported. The hybrid network (named di-ureasil) is composed of
poly(oxyethylene) chains of different average polymer molecular weights grafted
to siloxane domains by means of urea cross-linkages and accommodates
ferrihydrite nanoparticles. Magnetic measurements, Fourier transform infrared
and nuclear magnetic resonance spectroscopy reveal that the controlled
modification of the polymer molecular weight allows the fine-tuning of the
ability of the hybrid matrix to assist and promote iron coordination at the
organic-inorganic interface and subsequent nucleation and growth of the
ferrihydrite nanoparticles whose core size (2-4 nm) is tuned by the amount of
iron incorporated. The polymer chain length, its arrangement and crystallinity,
are key factors on the anchoring and formation of the ferrihydrite particles.",0410695v1
2004-10-28,"High-pressure synthesis, crystal structure determination, and a Ca substitution study of the metallic rhodium oxide NaRh2O4","The sodium rhodate NaRh2O4 was synthesized for the first time and
characterized by neutron and x-ray diffraction studies, measurements of
magnetic susceptibility, specific heat, electrical resistivity, and the Seebeck
coefficient. NaRh2O4 crystallizes in the CaFe2O4-type structure, which is
comprised of a characteristic RhO6 octahedra network. The compound is metallic
in nature, probably reflecting the 1 to 1 mixed valence character of Rh(III)
and Rh(IV) in the network. For further studies of the compound, the Rh valence
was varied significantly by means of an aliovalent substitution: the full range
solid solution between NaRh2O4 and CaRh2O4 was achieved and characterized as
well. The metallic state was dramatically altered, and a peculiar magnetism
developed in the low Na concentration range.",0410742v1
2004-11-26,Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25),"We have measured magnetic susceptibility and resistivity of
Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ ($x=$ 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 $\leq x\leq$ 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for $x=$
0.225 is 0.25 $\mu_B$/Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.",0411671v3
2004-11-30,Helicoidal magnetic order in a clean copper oxide spin chain compound,"We report susceptibility, specific heat, and neutron diffraction measurements
on NaCu$_2$O$_2$, a spin-1/2 chain compound isostructural to LiCu$_2$O$_2$,
which has been extensively investigated. Below 13 K, we find a long-range
ordered, incommensurate magnetic helix state with a propagation vector similar
to that of LiCu$_2$O$_2$. In contrast to the Li analogue, substitutional
disorder is negligible in NaCu$_2$O$_2$. We can thus rule out that the helix is
induced by impurities, as was claimed on the basis of prior work on
LiCu$_2$O$_2$. A spin Hamiltonian with frustrated longer-range exchange
interactions provides a good description of both the ordered state and the
paramagnetic susceptibility.",0411753v2
2005-02-24,Spin-related magnetoresistance of n-type ZnO:Al and Zn_{1-x}Mn_{x}O:Al thin films,"Effects of spin-orbit coupling and s-d exchange interaction are probed by
magnetoresistance measurements carried out down to 50 mK on ZnO and
Zn_{1-x}Mn_{x}O with x = 3 and 7%. The films were obtained by laser ablation
and doped with Al to electron concentration ~10^{20} cm^{-3}. A quantitative
description of the data for ZnO:Al in terms of weak-localization theory makes
it possible to determine the coupling constant \lambda_{so} = (4.4 +-
0.4)*10^{-11} eVcm of the kp hamiltonian for the wurzite structure, H_{so} =
\lambda_{so}*c(s x k). A complex and large magnetoresistance of
Zn_{1-x}Mn_{x}O:Al is interpreted in terms of the influence of the s-d
spin-splitting and magnetic polaron formation on the disorder-modified
electron-electron interactions. It is suggested that the proposed model
explains the origin of magnetoresistance observed recently in many magnetic
oxide systems.",0502574v1
2005-04-22,Possible Localization Behavior of the Inherent Conducting Polymer (CH$_3$)$_{0.9}$ReO$_3$,"Polymeric methyltrioxorhenium (poly-MTO) represents the first example of an
inherent conducting organometallic oxide. It adopts the structural motives and
transport properties of some classical perovskites in two dimensions. In this
study we present resistivity data down to 30 mK which exhibit a crossover from
a metallic (d$\rho$/d$T >$ 0) to an insulating (d$\rho$/d$T <$ 0) behavior at
about 30 K. Below 30 K an unusual resistivity behavior, similar to that of some
doped cuprate systems, is observed: initially the resistivity increases
approximately as $\rho \sim$ log$(1/T$) before it starts to saturate below 2 K.
Furthermore, a linear positive magnetoresistance is found (up to 7 T).
Temperature dependent magnetization and specific heat measurements in various
magnetic fields indicate that the unusual resistivity behavior may be driven by
spatial localization of the d$^1$ moments at the Re atoms.",0504585v1
2005-04-25,Influence of parasitic phases on the properties of BiFeO3 epitaxial thin films,"We have explored the influence of deposition pressure and temperature on the
growth of BiFeO3 thin films by pulsed laser deposition onto (001)-oriented
SrTiO3 substrates. Single-phase BiFeO3 films are obtained in a region close to
10-2 mbar and 580C. In non-optimal conditions, X-ray diffraction reveals the
presence of Fe oxides or of Bi2O3. We address the influence of these parasitic
phases on the magnetic and electrical properties of the films and show that
films with Fe2O3 systematically exhibit a ferromagnetic behaviour, while
single-phase films have a low bulk-like magnetic moment. Conductive-tip atomic
force microscopy mappings also indicate that Bi2O3 conductive outgrowths create
shortcuts through the BiFeO3 films, thus preventing their practical use as
ferroelectric elements in functional heterostructures.",0504631v1
2005-05-01,"Exchange Biasing of the Ferromagnetic Semiconductor (Ga,Mn)As by MnO","We provide an overview of progress on the exchange biasing of a ferromagnetic
semiconductor (Ga1-xMnxAs) by proximity to an antiferromagnetic oxide layer
(MnO). We present a detailed characterization study of the antiferromagnetic
layer using Rutherford backscattering spectrometry, x-ray photoelectron
spectroscopy, transmission electron microscopy, and x-ray reflection. In
addition, we describe the variation of the exchange and coercive fields with
temperature and cooling field for multiple samples.",0505015v1
2005-05-30,Magnetism and superconductivity of heavy fermion matter,"The interplay of magnetism and unconventional superconductivity (d singlet
wave or p triplet wave) in strongly correlated electronic system (SCES) is
discussed with recent examples found in heavy fermion compounds. A short
presentation is given on the formation of the heavy quasiparticle with the two
sources of a local and intersite enhancement for the effective mass. Two cases
of the coexistence or repulsion of antiferromagnetism and superconductivity are
given with CeIn3 and CeCoIn5. A spectacular example is the emergence of
superconductivity in relatively strong itinerant ferromagnets UGe2 and URhGe.
The impact of heavy fermion matter among other SCES as organic conductor or
high Tc oxide is briefly pointed out.",0505713v2
2005-06-23,"Interplay among Spin, Orbital and Lattice Degrees of Freedom in $t_{2g}$ Electron Systems with Edge-Sharing Network of Octahedra","Transition metal oxides whose lattice structure has edge-sharing network of
octahedra constitute a diverse group of intriguing materials besides compounds
with corner-sharing octahedra such as perovskites. We present a theoretical
investigation of the interplay among spin, orbital and lattice degrees of
freedom in these materials. We focus on $t_{2g}$ electron systems where a keen
competition among those degrees of freedom is expected to emerge under a
relatively weak Jahn-Teller coupling. We study the interplay between spin and
orbital degrees of freedom in vanadium spinels and titanium pyroxenes. We
clarify the important role of the strong anisotropy in the orbital interactions
due to the edge-sharing geometry. We also discuss the interplay between spin
and lattice in chromium spinels focusing on the magnetization process under the
external magnetic field.",0506598v1
2005-10-06,Ca_25Co_22O_56(OH)_28: a layered misfit compound,"The high pressure synthesis, structure and magnetic properties of
Ca_25Co_22O_56(OH)_28 are reported. The compound has a misfit structure,
consisting of double, square calcium oxide hydroxide rock-salt-like layers
between hexagonal CoO_2 layers. The misfit compound crystallizes in the
monoclinic space group C2/m, and can be characterized by the coexistence of two
subsystems with common a=4.893(5)A, c=8.825(9)A and b=95.745(8) parameters, and
different b parameters: b_RS=4.894(5)A, and b_HEX=2.809(3)A, for the rock-salt
and hexagonal type planes respectively. The compound shows Curie-Weiss
paramagnetism with an antiferromagnetic Weiss temperature of -43K and a reduced
Co moment. Substantial deviations from Curie-Weiss behavior are seen below 50K
with no indication of magnetic ordering. No superconductivity was observed down
to a temperature of 2K.",0510137v2
2005-11-18,Spin Correlations and Magnetic Susceptibilities of Lightly Doped Antiferromagnets,"We calculate the spin correlation function and the magnetic longitudinal and
transverse susceptibilities of a two-dimensional antiferromagnet doped with a
small concentration of holes, in the t-J model. We find that the motion of
holes generates spin fluctuations which add to the quantum fluctuations, the
spin correlations decaying with the inverse of the spin distance, while
increasing with doping as the critical hole concentration, where the long-range
order disappears, is approached. Moreover, the longitudinal susceptibility
becomes finite in the presence of doping, due to the strong damping effects
induced by the hole motion, while the transverse susceptibility is renormalized
by softening effects. Both the longitudinal and the transverse susceptibilities
increase with doping, the former more significantly than the latter. Our
results imply that doping destroys the long-range order while local
antiferromagnetic spin correlations persist. This is consistent with
experiments on the doped copper oxide superconductors.",0511459v1
2005-12-17,Stripe phases - possible ground state of the high-Tc superconductors,"Based on the mean-field method applied either to the extended single-band
Hubbard model or to the single-band Peierls-Hubbard Hamiltonian we study the
stability of both site-centered and bond-centered charge domain walls. The
difference in energy between these phases is found to be small. Therefore,
moderate perturbations to the pure Hubbard model, such as next nearest hopping,
lattice anisotropy, or coupling to the lattice, induce phase transitions, shown
in the corresponding phase diagrams. In addition, we determine for stable
phases charge and magnetization densities, double occupancy, kinetic and
magnetic energies, and investigate the role of a finite electron-lattice
coupling. We also review experimental signatures of stripes in the
superconducting copper oxides.",0512420v1
2006-02-07,Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study,"In order to gain insights into the origin of colossal magneto-resistance
(CMR) in manganese oxides, we performed a ^{139}La NMR study in the
double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie
temperature T_C=126 K, applying a magnetic field induces a long-range
ferromagnetic order that persists up to T=330 K. The critical field at which
the induced magnetic moment is saturated coincides with the field at which the
CMR effect reaches to a maximum. Our results therefore indicate that the CMR
observed above T_C in this compound is due to the field-induced ferromagnetism
that produces a metallic state via the double exchange interaction.",0602161v1
2006-03-01,Model for vacancy-induced d$^0$ ferromagnetism in oxide compounds,"We propose a model with few parameters, for vacancy-induced ferromagnetism
based on a correlated model for anions (oxygen orbitals) with random potentials
that represent cation vacancies. There is a range of potential strength for
which moments appear on oxygen sites neighboring the vacancies. By using
techniques which allow us to treat the randomness exactly, we calculate the
magnetic couplings between the total moment around each vacancy, the Curie
temperature and dynamical correlations as a function of the effective stren gth
of the vacancy potential and doping properties, the density of vacancies, as
well as the correlation and band width of the host. For physically reasonable
parameters this predicts Curie temperatures well above room temperature for
small concentrations of vacancies and appropriate parameters. We disc uss our
results in relation to questions of stability and reproducibility raised in
experiments. To circumvent the difficulties of controlling intrinsic defects,
we propose specific non-magnetic host doping that could be, for example,
substituted for cations in HfO$_2$ or ZrO$_2$.",0603022v2
2006-04-13,Angle-dependence of the Hall effect in HgBa2CaCu2O6 thin films,"Superconducting compounds of the family Hg-Ba-Ca-Cu-O have been the subject
of intense study since the current record-holder for the highest critical
temperature of a superconductor belongs to this class of materials. Thin films
of the compound with two adjacent copper-oxide layers and a critical
temperature of about 120 K were prepared by a two-step process that consists of
the pulsed-laser deposition of precursor films and the subsequent annealing in
mercury-vapor atmosphere. Like some other high-temperature superconductors,
Hg-Ba-Ca-Cu-O exhibits a specific anomaly of the Hall effect, a double-sign
change of the Hall coefficient close to the superconducting transition. We have
investigated this phenomenon by measurements of the Hall effect at different
angles between the magnetic field direction and the crystallographic c-axis.
The results concerning the upper part of the transition, where the first sign
change occurs, are discussed in terms of the renormalized fluctuation model for
the Hall conductivity, adapted through the field rescaling procedure in order
to take into account the arbitrary orientation of the magnetic field.",0604352v1
2006-05-11,Multifilament YBa2Cu3O6+x -coated conductors with minimized coupling losses,"We report an experimental approach to making multifilament coated conductors
with low losses in applied time-varying magnetic field. Previously, the
multifilament conductors obtained for that purpose by laser ablation suffered
from high coupling losses. Here we report how this problem can be solved. When
the substrate metal in the grooves segregating the filaments is exposed to
oxygen, it forms high resistivity oxides that electrically insulate the stripes
from each other and from the substrate. As the result, the coupling loss has
become negligible over the entire range of tested parameters (magnetic field
amplitudes B and frequencies f) available to us.",0605313v1
2006-11-09,New ultrasmall iron-oxide nanoparticles with high magnetisation as potential T1-MRI contrast agents for Molecular Imaging,"Here we report on the synthesis of very small gamma-Fe2O3 nanoparticles (5
nm) presenting very narrow particle size distribution and exceptionally high
saturation magnetisation. The synthesis has been carried out in an organic
medium with subsequent transfer to an aqueous solution at physiological pH. The
structural and magnetic properties were kept unaltered after the solvent
exchange. NMR relaxometric measurements show the potential of these particles
as specific reporters for magnetic resonance molecular imaging.",0611243v1
2006-11-20,Spin correlation in kagomé ice state: neutron scattering study of the dipolar spin ice Dy_{2}Ti_{2}O_{7} under magnetic field along [111],"We have investigated the kagom\'{e} ice state in the frustrated pyrochlore
oxide Dy_{2}Ti_{2}O_{7} under magnetic field along a [111] axis. Spin
correlations have been measured by neutron scattering and analyzed by
Monte-Carlo simulation. The kagom\'{e} ice state, which has a non-vanishing
residual entropy well established for the nearest-neighbor spin ice model by
the exact solution, has been proved to be realized in the dipolar-interacting
spin ice Dy_{2}Ti_{2}O_{7} by observing the characteristic spin correlations.
The simulation shows that the long-range interaction gives rise to only weak
lifting of the ground state degeneracy and that the system freezes within the
degenerate kagom\'{e} ice manifold .",0611527v2
2007-04-23,Two-Staged Magnetoresistance Driven by Ising-like Spin Sublattice in SrCo6O11,"A two-staged, uniaxial magnetoresistive effect has been discovered in
SrCo6O11 having a layered hexagonal structure. Conduction electrons and
localized Ising spins are in different sublattices but their interpenetration
makes the conduction electrons sensitively pick up the stepwise
field-dependence of magnetization. The stepwise field-dependence suggests two
competitive interlayer interactions between ferromagnetic Ising-spin layers,
i.e., a ferromagnetic nearest-layer interaction and an antiferromagnetic
next-nearest-layer interaction. This oxide offers a unique opportunity to study
nontrivial interplay between conduction electrons and Ising spins, the coupling
of which can be finely controlled by a magnetic field of a few Tesla.",0704.3025v2
2007-05-17,Incoherent non-Fermi liquid scattering in a Kondo lattice,"One of the most notorious non-Fermi liquid properties of both archetypal
heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is
an electrical resistivity that evolves linearly with temperature, T. In the
heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the
first indications of the presence of a zero-temperature instability, or quantum
critical point. Here, we report the observation of a unique control parameter
of T-linear scattering in CeCoIn5, found through systematic chemical
substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce
sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5
is strongly dependent on the f-electron configuration of the R ion, whereas two
other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are
not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature
of incoherent scattering centers in the Kondo lattice, which provides insight
into the anomalous scattering rate synonymous with quantum criticality [7].",0705.2592v2
2007-06-05,Structure-Property Relationship in the Ordered-Perovskite- Related Oxide Sr3.12Er0.88Co4O10.5,"Synchrotron X-ray diffraction patterns were measured and analyzed for a
polycrystalline sample of the room-temperature ferromagnet Sr3.12Er0.88Co4O10.5
from 300 to 650 K, from which two structural phase transitions were found to
occur successively. The higher-temperature transition at 509 K is driven by
ordering of the oxygen vacancies, which is closely related to the metallic
state at high temperatures. The lower-temperature transition at 360 K is of
first order, at which the ferromagnetic state suddenly appears with exhibiting
a jump in magnetization and resistivity. Based on the refined structure,
possible spin and orbital models for the magnetic order are proposed.",0706.0605v2
2007-06-28,Non-Fermi-liquid behavior in nearly ferromagnetic metallic SrIrO3 single crystals,"We report transport and thermodynamic properties of single-crystal SrIrO3 as
a function of temperature T and applied magnetic field H. We find that SrIrO3
is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized
by the following properties: (1) small ordered moment but no evidence for
long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility
that diverges as T or T1/2 at low temperatures, depending on the applied field;
(3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied
fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence
of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based
on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound
that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0
and H = 0.23 T).",0706.4319v1
2007-07-20,The Ba2LnFeNb4O15 Tetragonal Tungsten Bronze: towards RT composite multiferroics,"Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd)
with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by
conventional solid-state methods. The Neodymium, Samarium and Europium
compounds are ferroelectric with Curie temperature ranging from 320 to 440K.
The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300
K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium
compounds exhibit magnetic hysteresis loops at room temperature originating
from traces of a barium ferrite secondary phase. The presence of both
ferroelectric and magnetic hysteresis loops at room temperature allows
considering these materials as composites multiferroic. Based on
crystal-chemical analysis we propose some relationships between the
introduction of Ln3+ ions in the TTB framework and the chemical, structural and
physical properties of these materials.",0707.3112v2
2007-07-24,Role of magnetism and electron-lattice interactions in STM spectra of cuprates,"The study of bosonic modes that couple to the charge carriers is a key
element in understanding superconductivity. Lee et al. have used
atomic-resolution scanning tunneling spectroscopy (STM) in an attempt to
extract the spectrum of of these modes in the high temperature superconductor
Bi2Sr2CaCu2O8+d and they found a mode whose frequency did not depend on doping
but changed on 16O to 18O isotopic substitution leading them to suggest a role
for lattice modes (phonons). A careful examination of their published data
reveals a weaker but distinct feature that has all the characteristics of the
magnetic excitation identified as the bosonic mode in other competing
experiments. We suggest the lattice mode seen by Lee et al. is not relevant to
superconductivity and is due to inelastic tunneling through the insulating
oxide layer.",0707.3623v1
2007-10-16,Formation of collective spins in frustrated clusters,"Using magnetization, specific heat and neutron scattering measurements, as
well as exact calculations on realistic models, the magnetic properties of the
\lacuvo compound are characterized on a wide temperature range. At high
temperature, this oxide is well described by strongly correlated atomic $S$=1/2
spins while decreasing the temperature it switches to a set of weakly
interacting and randomly distributed entangled pseudo spins $\tilde S=1/2$ and
$\tilde S=0$. These pseudo-spins are built over frustrated clusters, similar to
the kagom\'e building block, at the vertices of a triangular superlattice, the
geometrical frustration intervening then at different scales.",0710.3025v2
2007-11-01,Magnetic resonance in iron oxide nanoparticles: quantum features and effect of size,"In order to better understand the transition from quantum to classical
behavior in spin system, electron magnetic resonance (EMR) is studied in
suspensions of superparamagnetic magnetite nanoparticles with an average
diameter of ~ 9 nm and analyzed in comparison with the results obtained in the
maghemite particles of smaller size (~ 5 nm). It is shown that both types of
particles demonstrate common EMR behavior, including special features such as
the temperature-dependent narrow spectral component and multiple-quantum
transitions. These features are common for small quantum systems and not
expected in classical case. The relative intensity of these signals rapidly
decreases with cooling or increase of particle size, marking gradual transition
to the classical FMR behavior.",0711.0168v1
2007-12-14,Magnetic properties of HO2 thin films,"We report on the magnetic and transport studies of hafnium oxide thin films
grown by pulsed-laser deposition on sapphire substrates under different oxygen
pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these
thin films appear to depend on the oxygen pressure during growth: the film
grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is
conducting, with a positive Hall signal, while those grown under higher oxygen
pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic
ferromagnetic signal could be attributed to the HfO2 films, irrespective of the
oxygen pressure during the deposition.",0712.2410v1
2008-05-30,Doped orbitally-ordered systems: another case of phase separation,"A possible mechanism of electronic phase separation in the systems with
orbital ordering is analyzed. We suggest a simple model taking into account an
interplay between the delocalization of charge carriers introduced by doping
and the cooperative ordering of local lattice distortions. The proposed
mechanism is quite similar to the double exchange usually invoked for
interpretation of phase separation in doped magnetic oxides like manganites,
but can be efficient even in the absence of any magnetic ordering. It is
demonstrated that the delocalized charge carriers favor the formation of
nanoscale inhomogeneities with the orbital structure different from that in the
undoped material. The directional character of orbitals leads to
inhomogeneities of different shapes and sizes.",0805.4806v1
2008-06-16,Structural and magnetic phase diagram of CeFeAsO1-xFx and its relationship to high-temperature superconductivity,"We use neutron scattering to study the structural and magnetic phase
transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a
semimetal to a high-transition-temperature (high-Tc) superconductor through
Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural
lattice distortion followed by a stripe like commensurate antiferromagnetic
order with decreasing temperature. With increasing Fluorine doping, the
structural phase transition decreases gradually while the antiferromagnetic
order is suppressed before the appearance of superconductivity, resulting an
electronic phase diagram remarkably similar to that of the high-Tc copper
oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other
Fe-based superconductors reveals that the effective electronic band width
decreases systematically for materials with higher Tc. The results suggest that
electron correlation effects are important for the mechanism of high-Tc
superconductivity in these Fe pnictides.",0806.2528v1
2008-06-20,Destruction of Neel order and appearance of superconductivity in electron-doped cuprates by oxygen annealing process,"We use thermodynamic and neutron scattering measurements to study the effect
of oxygen annealing on the superconductivity and magnetism in
Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$. Although the transition temperature
$T_c$ measured by susceptibility and superconducting coherence length increase
smoothly with gradual oxygen removal from the annealing process, bulk
superconductivity, marked by a specific heat anomaly at $T_c$ and the presence
of a neutron magnetic resonance, only appears abruptly when $T_c$ is close to
the largest value. These results suggest that the effect of oxygen annealing
must be first determined in order to establish a Ce-doping dependence of
antiferromagnetism and superconductivity phase diagram for electron-doped
copper oxides.",0806.3426v1
2008-06-26,A Multiferroic Ceramic with Perovskite Structure: La0.5Bi0.5Mn0.5Fe0.5O3.09,"ABO3 perovskite multiferroic La0.5Bi0.5Mn0.5Fe0.5O3.09 where the B-site
cations is responsible for the magnetic properties and the A-site cation with
lone pair electron is responsible for the ferroelectric properties was
synthesized at normal conditions. This oxide exhibits a ferromagnetic
transition around 240 K with a well defined hysteresis loop, and a significant
reversible remnant polarization below 67K similar to ferroelectric behavior.
The magnetic interaction is interpreted by the ferromagnetic Fe3+-O-Mn3+ and
antiferromagnetic Fe3+(Mn3+)-O-Fe3+(Mn3+) interactions competed each other,
whereas the ferroelectricity is predominantly due to the polar nature
introduced by the 6s2 lone pair of Bi3+ cations",0806.4274v1
2008-10-07,Interface Ferromagnetism in (110)-Oriented La0.7Sr0.3MnO3/SrTiO3 Ultrathin Superlattices,"We explore manganite interface magnetism in epitaxially grown
La0.7Sr0.3MnO3(LSMO)/SrTiO3 ultrathin superlattices (SL) along (110)
orientation. we show that robust ferromagnetism persists down to four
monolayers LSMO(MLs) (~1.1 nm in thickness), of which 50% Mn is at the
interface state. Above eight MLs, the magnetic moment is nearly saturated to
the theoretical value of 3.7u_B, with an estimated interface moment of 3.2u_B.
In comparison to (100)-oriented SLs which were previously shown to have a spin
canted ground state, (110)-oriented SLs exhibit stronger low-dimensional
ferromagnetism and better metallicity, suggesting a ferromagnetic interface
spin state well suited for all-oxide spintronic devices. The underlining
mechanism is qualitatively discussed.",0810.1309v2
2008-10-31,Quantum electric dipole glass and frustrated magnetism near a critical point in Li2ZrCuO4,"We report a new peculiar effect of the interaction between a sublattice of
frustrated quantum spin-1/2 chains and a sublattice of pseudospin-1/2 centers
(quantum electric dipoles) uniquely co-existing in the complex oxide Li2ZrCuO4.
7Li nuclear magnetic-, Cu2+ electron spin resonance and a complex dielectric
constant data reveal that the sublattice of Li+-derived electric dipoles orders
glass like at Tg ~ 70 K yielding a spin site nonequivalency in the CuO2 chains.
We suggest that such a remarkable interplay between electrical and spin degrees
of freedom might strongly influence the properties of the spiral spin state in
Li2ZrCuO4 that is close to a quantum ferromagnetic critical point. In
particular that strong quantum fluctuations and/or the glassy behavior of
electric dipoles might renormalize the exchange integrals affecting this way
the pitch angle of the spiral as well as be responsible for the missing
multiferroicity present in other helicoidal magnets.",0810.5754v3
2009-01-20,Nonvolatile SRAM architecture using MOSFET-based spin-transistors,"The authors proposed and computationally analyzed nonvolatile static random
access memory (NV-SRAM) architecture using metal-oxide-semiconductor
field-effect transistor (MOSFET) type of spin-transistors referred to as
pseudo-spin-MOSFET (PS-MOSFET). PS-MOSFET is a new circuit approach to
reproduce the functions of spin-transistors, based on recently progressed
magnetoresistive random access memory (MRAM) technology. The proposed NV-SRAM
cell can be simply configured by connecting two PS-MOSFETs to the storage nodes
of a standard SRAM cell. The logic information of the storage nodes can be
electrically stored into the magnetic tunnel junctions (MTJs) of the PS-MOSFETs
by current-induced magnetization switching (CIMS), and the stored information
is automatically restored when the inverter loop circuit wakes up. In addition,
the proposed NV-SRAM cell has no influence on the performance of normal SRAM
operations. Low power dissipation and high degree of freedom of MTJ design are
also remarkable features for NV-SRAM using PS-MOSFETs.",0901.2980v1
2009-02-28,Magneto-optical readout of dark exciton distribution in cuprous oxide,"An experimental study of the yellow exciton series in Cu2O in strong magnetic
fields up to 32 T shows the optical activation of direct and phonon-assisted
paraexciton luminescence due to mixing with the quadruple allowed orthoexciton
state. The observed phonon-assisted luminescence yields information on the
statistical distribution of occupied states. Additional time-resolved
experiments provide a unique opportunity to directly determine the time
evolution of the thermodynamical properties of the paraexciton gas. Because the
lifetime of paraexciton is hardly affected by the optical activation in a
strong magnetic field, this opens new possibilities for studies aiming at
Bose-Einstein condensation of excitons in bulk semiconductors.",0903.0072v1
2009-03-31,Gigantic Impact of Magnetic Impurity on Stripe Order in La$_{2-x}$Sr$_{x}$CuO$_4$ ($x$$\sim$1/8),"Precise neutron-scattering experiments on
La$_{1.88-y}$Sr$_{0.12+y}$Cu$_{0.99}$R$_{0.01}$O$_4$ ($y$=0 for R=Cu, Zn and
$y$=0.01 for R=Ga, Fe) were performed to examine the stability of stripe order
in cuprate oxides through impurity substitution effects. For all the
impurity-substituted samples a static charge-density-wave order similar to that
reported in the low-temperature-tetragonal phase (LTT) was discovered in the
low-temperature-orthorhombic (LTO) phase for the first time. Fe substitution
significantly enhanced both the charge- and spin-density-wave orders. These
results indicate that dynamical charge stripes can be stabilized into static
ones around the Cu-site defects regardless of the type of crystal structure.
Additionally, large magnetic moments at the Cu-site may induce a decrease in
the Cu spin fluctuations around the defects, which in turn, enhances the static
charge-density-wave order.",0903.5391v1
2009-04-27,Role of Oxygen Electrons in the Metal-Insulator Transition in the Magnetoresistive Oxide La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ Probed by Compton Scattering,"We have studied the [100]-[110] anisotropy of the Compton profile in the
bilayer manganite. Quantitative agreement is found between theory and
experiment with respect to the anisotropy in the two metallic phases (i.e. the
low temperature ferromagnetic and the colossal magnetoresistant phase under a
magnetic field of 7 T). Robust signatures of the metal-insulator transition are
identified in the momentum density for the paramagnetic phase above the Curie
temperature. We interpret our results as providing direct evidence for the
transition from the metallic-like to the admixed ionic-covalent bonding
accompanying the magnetic transition. The number of electrons involved in this
phase transition is estimated from the area enclosed by the Compton profile
anisotropy differences. Our study demonstrates the sensitivity of the Compton
scattering technique for identifying the number and type of electrons involved
in the metal-insulator transition.",0904.4255v1
2009-05-04,Ferromagnetism in Carbon doped Zinc Oxide Systems,"We report spin polarized density functional calculations of ferromagnetic
properties of a series of ZnO clusters and solid containing one or two
substitutional carbon impurities. We analyze the eigen value spectra, spin
densities and molecular orbitals, and induced magnetic moments for ZnC,
Zn$_{2}$C, Zn$_{2}$OC, carbon substituted clusters Zn$_{n}$O$_{n}$ (n=3--10,
12) and ZnO solid. The results show that the doping induces magnetic moment of
the $\sim$2 $\mu_{B}$ in all the cases. All the systems with two carbon
impurities show ferromagnetic interaction except when the carbon atoms share
the same Zn atom as the nearest neighbor. This ferromagnetic interaction is
predominantly mediated via $\pi$ bonds in ring structures and through $\pi$ and
$\sigma$ bonds in three dimensional structure. The calculations also show that
the interaction is significantly enhanced in solid, bringing out the role of
dimensionality of Zn-O network connecting two carbon atoms.",0905.0366v1
2009-05-11,Flux dynamics in NdO1-xFxFeAs bulk sample,"We present data of multi harmonic magneto-dynamic experiments. In particular,
we performed ac magnetic susceptibility experiments on layered pnictide-oxide
quaternary compound NdOFeAs doped with fluorine. The experiments allow measure
the critical temperature and probe the flux dynamic behavior using the third
harmonic component of the ac susceptibility of a NdF0.16FeAsO0.84 bulk sample
as a function of temperature and frequency of the applied ac magnetic fields.
Measured signals are connected with the non-linear superconducting flux dynamic
behavior and are characterized by a flux critical states sustaining a
superconducting critical current. In this framework the irreversibility line
that describes the stable superconducting state has been extracted from the
onset of the third harmonic signal vs. frequency. Finally we present also the
analysis of the flux dynamic dimensionality in the investigated sample.",0905.1633v1
2009-06-11,Spin polarized electron transport near the Si/SiO2 interface,"Using long-distance lateral devices, spin transport near the interface of Si
and its native oxide (SiO2) is studied by spin-valve measurements in an
in-plane magnetic field and spin precession measurements in a perpendicular
magnetic field at 60K. As electrons are attracted to the interface by an
electrostatic gate, we observe shorter average spin transit times and an
increase in spin coherence, despite a reduction in total spin polarization.
This behavior, which is in contrast to the expected exponential depolarization
seen in bulk transport devices, is explained using a transform method to
recover the empirical spin transit-time distribution and a simple two-stage
drift-diffusion model. We identify strong interface-induced spin depolarization
(reducing the spin lifetime by over two orders of magnitude from its bulk
transport value) as the consistent cause of these phenomena.",0906.2146v2
2009-07-09,Spin-lattice coupling in frustrated antiferromagnets,"We review the mechanism of spin-lattice coupling in relieving the geometrical
frustration of pyrochlore antiferromagnets, in particular spinel oxides. The
tetrahedral unit, which is the building block of the pyrochlore lattice,
undergoes a spin-driven Jahn-Teller instability when lattice degrees of freedom
are coupled to the antiferromagnetism. By restricting our considerations to
distortions which preserve the translational symmetries of the lattice, we
present a general theory of the collective spin-Jahn-Teller effect in the
pyrochlore lattice. One of the predicted lattice distortions breaks the
inversion symmetry and gives rise to a chiral pyrochlore lattice, in which
frustrated bonds form helices with a definite handedness. The chirality is
transferred to the spin system through spin-orbit coupling, resulting in a
long-period spiral state, as observed in spinel CdCr2O4. We discuss explicit
models of spin-lattice coupling using local phonon modes, and their
applications in other frustrated magnets.",0907.1693v1
2009-09-08,Magnetism and orbital-ordering in an interacting three band model: a dynamical mean field study,"Single-site dynamical mean field theory is used to determine the magnetic and
orbital-ordering phase diagram for a model of electrons moving on a lattice
with three orbital states per site and with the fully rotationally invariant
Slater-Kanamori on-site interactions. The model captures important aspects of
the physics of transition metal oxides with partially filled $t_{2g}$ shells,
and of electron-doped C$_{60}$. We introduce an unbiased, computationally
simple and inexpensive method for estimating the presence of two sublattice
order, determine the regimes in which spatially uniform and two-sublattice spin
and orbital orderings are present and give physical arguments for the origins
of the different phases. Guidelines are determined for optimizing the presence
of ferromagnetism, which may be desirable in applications",0909.1499v1
2010-07-19,Electronic Structure of Weakly Correlated Antiferromagnetic Metal SrCrO3: First-principles calculations,"By systematic first-principles calculations, we study the electronic
structure and magnetic property of SrCrO$_3$. Our results suggest that
SrCrO$_3$ is a weakly correlated antiferromagnetic (AF) metal, a very rare
situation in transition-metal oxides. Among various possible AF states, the
C-type spin ordering with small amount of orbital polarization (dxy orbital is
more occupied than the d_{yz/zx} orbital) is favored. The detailed mechanism to
stabilize the C-type AF state is analyzed based on the competition between the
itinerant Stoner instability and superexchange, and our results suggest that
the magnetic instability rather than the orbital or lattice instabilities plays
an important role in this system. The experimentally observed compressive
tetragonal distortion can be naturally explained from the C-type AF state. By
applying the LDA+$U$ method to study this system, we show that wrong ground
state will be obtained if $U$ is large.",1007.3156v1
2010-08-16,Topological Magnetic Insulators with Corundum Structure,"Topological insulators are new states of quantum matter in which surface
states residing in the bulk insulating gap are protected by time-reversal
symmetry. When a proper kind of antiferromagnetic long range order is
established in a topological insulator, the system supports axionic
excitations. In this paper, we study theoretically the electronic states in a
transition metal oxide of corundum structure, in which both spin-orbit
interaction and electron-electron interaction play crucial roles. A
tight-binding model analysis predicts that materials with this structure can be
strong topological insulator. Because of the electron correlation, an
antiferromagnetic order may develop, giving rise to a topological magnetic
insulator phase with axionic excitations.",1008.2666v1
2010-08-19,Electronic and magnetic properties of SrTiO3/LaAlO3 interfaces from first principles,"A number of intriguing properties emerge upon the formation of the epitaxial
interface between the insulating oxides LaAlO3 and SrTiO3. These properties,
which include a quasi two-dimensional conducting electron gas, low temperature
superconductivity, and magnetism, are not present in the bulk materials,
generating a great deal of interest in the fundamental physics of their
origins. While it is generally accepted that the novel behavior arises as a
result of a combination of electronic and atomic reconstructions and
growth-induced defects, the complex interplay between these effects remains
unclear. In this report, we review the progress that has been made towards
unraveling the complete picture of the SrTiO3/LaAlO3 interface, focusing
primarily on present ab initio theoretical work and its relation to the
experimental data. In the process, we highlight some key unresolved issues and
discuss how they might be addressed by future experimental and theoretical
studies.",1008.3379v1
2010-10-26,Suppression of the Néel temperature in hydrothermally synthesized alpha-Fe2O3 nanoparticles,"Magnetic measurements up to 1000 K have been performed on hydrothermally
synthesized $\alpha$-Fe$_{2}$O$_{3}$ nanoparticles (60 nm) using a Quantum
Design vibrating sample magnetometer. A high vacuum environment
(1$\times$10$^{-5}$ torr) during the magnetic measurement up to 1000 K leads to
a complete reduction of $\alpha$-Fe$_{2}$O$_{3}$ to Fe$_{3}$O$_{4}$. This
precludes the determination of the N\'eel temperature for the
$\alpha$-Fe$_{2}$O$_{3}$ nanoparticles. In contrast, coating
$\alpha$-Fe$_{2}$O$_{3}$ nanoparticles with SiO$_{2}$ stabilizes the
$\alpha$-Fe$_{2}$O$_{3}$ phase up to 930 K, which allows us to determine the
N\'eel temperature of the $\alpha$-Fe$_{2}$O$_{3}$ nanoparticles for the first
time. The N\'eel temperature of the 60-nm $\alpha$-Fe$_{2}$O$_{3}$
nanoparticles is found to be 945 K, about 15 K below the bulk value. The small
reduction of the N\'eel temperature of the $\alpha$-Fe$_{2}$O$_{3}$
nanoparticles is consistent with a finite-size scaling theory. Our current
results also show that coating nanoparticles with SiO$_{2}$ can effectively
protect nanoparticles from oxidation or reduction, which is important to
technological applications.",1010.5294v1
2010-12-10,The Curie temperature and exchange energy between two sublattices in half-metallic greigite Fe3S4,"High-temperature magnetic measurements have been carried out in
hydrothermally synthesized greigite (Fe3S4). We show that the Curie temperature
of greigite is significantly lower than that for its iron oxide counterpart
Fe3O4. The lower TC value (about 677 K) of greigite is in quantitative
agreement with that calculated using the exchange energy (3.25 meV) and the
spin values of the two sublattices, which are inferred from the neutron and
magnetization data of high-quality pure greigite samples. We further show that,
with an effective on-site Hubbard energy Ueff = 1.16 eV, the lattice constant
and two sublattice spins predicted from ab initio density-function theory are
in nearly perfect agreement with the measured values. The parameter Ueff = 1.16
eV ensures Fe3S4 to be an excellent half-metallic material for spintronic
applications.",1012.2364v1
2010-12-13,Magnetocaloric effect and improved relative cooling power in (La0.7Sr0.3MnO3/SrRuO3) superlattices,"Magnetic properties of a series of (La0.7Sr0.3MnO3/SrRuO3) superlattices,
where the SrRuO3 layer thickness is varying, are examined. A room-temperature
magnetocaloric effect is obtained owing to the finite size effect which reduces
the TC of La0.7Sr0.3MnO3 layers. While the working temperature ranges are
enlarged,, -DeltaSmax values remains similar to the values in polycrystalline
La0.7Sr0.3MnO3. Consequently, the relative cooling powers are significantly
improved, the microscopic mechanism of which is related to the effect of the
interfaces at La0.7Sr0.3MnO3/SrRuO3 and higher nanostructural disorder. This
study indicates that artificial oxide superlattices/multilayers might provide
an alternative pathway in searching for efficient room-temperature magnetic
refrigerators for (nano)microscale systems.",1012.2675v1
2011-01-14,Magnetic Frustration in a Mn Honeycomb Lattice Induced by Mn-O-O-Mn Pathways,"We investigated the electronic structure of layered Mn oxide Bi3Mn4O12(NO3)
with a Mn honeycomb lattice by x-ray absorption spectroscopy. The valence of Mn
was determined to be 4+ with a small charge-transfer energy. We estimated the
values of superexchange interactions up to the fourth nearest neighbors (J1,
J2, J3, and J4) by unrestricted Hartree-Fock calculations and a perturbation
method. We found that the absolute values of J1 through J4 are similar with
positive (antiferromagnetic) J1 and J4, and negative (ferromagnetic) J2 and J3,
due to Mn-O-O-Mn pathways activated by the smallness of charge-transfer energy.
The negative J3 provides magnetic frustration in the honeycomb lattice to
prevent long-range ordering.",1101.2847v1
2011-01-28,Sr3Co2O6: a possible frustrated spin-chain material,"A dense phase of a post-layered perovskite Sr3Co2O6 was created by a
high-pressure and high-temperature synthetic route and quenched to ambient
conditions. The structure of Sr3Co2O6 was determined by synchrotron X-ray
powder diffraction. Sr3Co2O6 crystallizes in the K4CdCl6-type structure (an
infinite chain-type structure), which is 6% denser than the known,
iso-compositional layered perovskite Sr3Co2O7-d (d~1). The K4CdCl6-type
Sr3Co2O6 shows complex magnetic behavior reflecting the spin-chain nature as
well as the analogue oxides Ca3Co2O6 and Ca3CoRhO6, whose microscopic magnetic
origin is still highly debated.",1101.5457v1
2011-04-15,Structural and Magnetic Phase Transitions in NdCoAsO under High Pressures,"We have investigated structural and magnetic phase transitions under high
pressures in a quaternary rare earth transition metal arsenide oxide NdCoAsO
compound that is isostructural to high temperature superconductor NdFeAsO.
Four-probe electrical resistance measurements carried out in a designer diamond
anvil cell show that the ferromagnetic Curie temperature and anti-ferromagnetic
Neel temperature increase with an increase in pressure. High pressure x-ray
diffraction studies using a synchrotron source show a structural phase
transition from a tetragonal phase to a new crystallographic phase at a
pressure of 23 GPa at 300 K. The NdCoAsO sample remained anti-ferromagnetic and
non-superconducting to temperatures down to 10 K and to the highest pressure
achieved in this experiment of 53 GPa. A P-T phase diagram for NdCoAsO is
presented to a pressure of 53 GPa and low temperatures of 10 K.",1104.3172v1
2011-05-03,Exchange interactions and magnetic phases of transition metal oxides: benchmarking advanced ab initio methods,"The magnetic properties of the transition metal monoxides MnO and NiO are
investigated at equilibrium and under pressure via several advanced
first-principles methods coupled with Heisenberg Hamiltonian MonteCarlo. The
comparative first-principles analysis involves two promising beyond-local
density functionals approaches, namely the hybrid density functional theory and
the recently developed variational pseudo-self-interaction correction method,
implemented with both plane-wave and atomic-orbital basis sets. The advanced
functionals deliver a very satisfying rendition, curing the main drawbacks of
the local functionals and improving over many other previous theoretical
predictions. Furthermore, and most importantly, they convincingly demonstrate a
degree of internal consistency, despite differences emerging due to
methodological details (e.g. plane waves vs. atomic orbitals)",1105.0647v3
2011-05-16,Isotope effects in high-Tc cuprate superconductors: Ultimate proof for bipolaron theory of superconductivity,"Developing a theory of high-temperature superconductivity in copper oxides is
one of the outstanding problems in physics. Twenty-five years after its
discovery, no consensus on the microscopic theory has been reached despite
tremendous theoretical and experimental efforts. Attempts to understand this
problem are hindered by the subtle interplay among a few mechanisms and the
presence of several nearly degenerate and competing phases in these systems.
Here we provide unified parameter-free explanation of the observed
oxygen-isotope effects on the critical temperature, the magnetic-field
penetration depth, and on the normal-state pseudogap for underdoped cuprate
superconductors within the framework of the bipolaron theory compatible with
the strong Coulomb and Froehlich interactions, and with many other independent
observations in these highly polarizable doped insulators. Remarkably, we also
quantitatively explain measured critical temperatures and magnitudes of the
magnetic-field penetration depth. The present work thus represents an ultimate
proof of the bipolaron theory of high-temperature superconductivity, which
takes into account essential Coulomb and electron-phonon interactions.",1105.3124v1
2011-08-12,A model of the T-dependent pseudogap and its competition with superconductivity in copp er oxides,"Results for pseudogaps are obtained from a band model, where the stability of
the gap depends on the amplitudes of vibrational displacements, or magnetic
moments, and their coupling to electrons. A one-particle gap is favored by
normal thermal excitations of phonons or spin waves. Another gap can be
generated by spontaneous waves at lower temperature, if the electronic energy
gain overcomes the elastic/magnetic energy needed for increased amplitudes of
the oscillations. This state is characterized by charge or spin density waves.
The pseudogap has many features in common with the superconducting gap, and the
model lends support to the interpretation that the pseudogap is a precursor of,
and competes with, superconducting pairing.",1108.2626v1
2011-08-15,Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3,"We report long-range ordered antiferromagnetism concomitant with local iron
displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic
correlations, present at room temperature, develop into long-range
antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to
1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state
correlates with local displacements of the Fe atoms. These iron displacements
imply significant magnetoelastic coupling in FeX$_4$-based materials, an
ingredient hypothesized to be important in the emergence of superconductivity.
This result also suggests that knowledge of these local displacements is
essential for properly understanding the electronic structure of these systems.
As with the copper oxide superconductors two decades ago, our results highlight
the importance of reduced dimensionality spin ladder compounds in the study of
the coupling of spin, charge, and atom positions in superconducting materials.",1108.2928v2
2011-09-09,"Magnetisation Studies of Geometrically Frustrated Antiferromagnets SrLn2O4, with Ln = Er, Dy and Ho","We present the results of susceptibility \chi(T) and magnetisation M(H)
measurements performed on single crystal samples of the rare-earth oxides
SrLn2O4 (Ln = Er, Dy and Ho). The measurements reveal the presence of magnetic
ordering transition in SrHo2O4 at 0.62 K and confirm that SrEr2O4 orders
magnetically at 0.73 K, while in SrDy2O4 such a transition is absent down to at
least 0.5 K. The observed ordering temperatures are significantly lower than
the Curie-Weiss temperatures, \theta_{CW}, obtained from the high-temperature
linear fits to the 1/\chi(T) curves, which implies that these materials are
subject to geometric frustration. Strong anisotropy found in the \chi(T) curves
for a field applied along the different crystallographic directions is also
evident in the M(H) curves measured both above and below the ordering
temperatures. For all three compounds the magnetisation plateaux at
approximately one third of the magnetisation saturation values can be seen for
certain directions of applied field, which is indicative of field-induced
stabilisation of a collinear {\it two-up one-down} structure.",1109.2094v1
2011-10-04,Isospin Dynamics in Sr2IrO4 : Forging Links to Cuprate Superconductivity,"We used resonant inelastic x-ray scattering to reveal the nature of magnetic
interactions in Sr2IrO4, a 5d transition-metal oxide with a spin-orbit
entangled ground state and Jeff=1/2 magnetic momemts, referred to as
'isospins'. The magnon dispersion in Sr2IrO4 is well described by an
antiferromagnetic Heisenberg model with isospin one-half moments on a square
lattice, which renders the low-energy effective physics of Sr2IrO4 much akin to
that in superconducting cuprates. This is further supported by the observation
of exciton modes in Sr2IrO4 whose dispersion is strongly renormalized by
magnons, which can be understood by analogy to the hole propagation in the
background of antiferromagnetically ordered spins in the cuprates.",1110.0759v1
2012-02-20,Near room-temperature colossal magnetodielectricity and multiglass properties in partially-disordered La2NiMnO6,"We report magnetic, dielectric and magnetodielectric responses of pure
monoclinic bulk phase of partially-disordered La2NiMnO6, exhibiting a spectrum
of unusual properties and establish that this system intrinsically is a true
multiglass with a large magnetodielectric coupling (8-20%) over a wide range of
temperatures (150 - 300 K). Specifically, our results establish a unique way to
obtain colossal magnetodielectricity, independent of any striction effects, by
engineering the asymmetric hopping contribution to the dielectric constant via
the tuning of the relative spin orientations between neighboring magnetic ions
in a transition metal oxide system. We discuss the role of anti-site (Ni-Mn)
disorder in emergence of these unusual properties.",1202.4319v2
2012-03-14,Oxygen vacancy enhanced room temperature ferromagnetism in Al-doped MgO nanoparticles,"We have investigated the room temperature ferromagnetic order that develops
in Al-substituted magnesium oxide, Mg(Al)O, nanoparticles with Al fractions of
up to 5 at.%. All samples, including undoped MgO nanoparticles, exhibit room
temperature ferromagnetism, with the saturation magnetization reaching a
maximum of 0.023 emu/g at 2 at.% of Al. X-ray photoelectron spectroscopy
identifies the presence of oxygen vacancies in both doped and undoped MgO
nanoparticles, with the vacancy concentration increasing upon vacuum annealing
of Mg(Al)O, resulting in two-fold enhancement of the saturation magnetization
for 2 at.% Al-doped MgO. Our results suggest that the oxygen vacancies are
largely responsible for room temperature ferromagnetism in MgO.",1203.2991v3
2012-06-05,Spin ordering and electronic texture in the bilayer iridate Sr$_3$Ir$_2$O$_7$,"Through a neutron scattering, charge transport, and magnetization study, the
correlated ground state in the bilayer iridium oxide Sr$_3$Ir$_2$O$_7$ is
explored. Our combined results resolve scattering consistent with a high
temperature magnetic phase that persists above 600 K, reorients at the
previously defined $T_{AF}=280$ K, and coexists with an electronic ground state
whose phase behavior suggests the formation of a fluctuating charge or orbital
phase that freezes below $T^{*}\approx70$ K. Our study provides a window into
the emergence of multiple electronic order parameters near the boundary of the
metal to insulator phase transition of the 5d $J_{eff}=1/2$ Mott phase.",1206.1006v2
2012-06-25,Spin-induced symmetry breaking in orbitally ordered NiCr_2O_4 and CuCr_2O_4,"At room temperature, the normal oxide spinels NiCr_2O_4 and CuCr_2O_4 are
tetragonally distorted and crystallize in the I4_1/amd space group due to
cooperative Jahn-Teller ordering driven by the orbital degeneracy of
tetrahedral Ni$^{2+}$ ($t_2^4$) and Cu$^{2+}$ ($t_2^5$). Upon cooling, these
compounds undergo magnetic ordering transitions; interactions being somewhat
frustrated for NiCr_2O_4 but not for CuCr_2O_4. We employ variable-temperature
high-resolution synchrotron X-ray powder diffraction to establish that at the
magnetic ordering temperatures there are further structural changes, which
result in both compounds distorting to an orthorhombic structure consistent
with the Fddd space group. NiCr_2O_4 exhibits additional distortion, likely
within the same space group, at a yet-lower transition temperature of $T$ = 30
K. The tetragonal to orthorhombic structural transition in these compounds
appears to primarily involve changes in NiO_4 and CuO_4 tetrahedra.",1206.5760v1
2012-07-25,Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding,"Within the broad class of multiferroics (compounds showing a coexistence of
magnetism and ferroelectricity), we focus on the subclass of ""improper
electronic ferroelectrics"", i.e. correlated materials where electronic degrees
of freedom (such as spin, charge or orbital) drive ferroelectricity. In
particular, in spin-induced ferroelectrics, there is not only a {\em
coexistence} of the two intriguing magnetic and dipolar orders; rather, there
is such an intimate link that one drives the other, suggesting a giant
magnetoelectric coupling. Via first-principles approaches based on density
functional theory, we review the microscopic mechanisms at the basis of
multiferroicity in several compounds, ranging from transition metal oxides to
organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic
frameworks, MOFs)",1207.5918v1
2012-08-30,Spin-Polarized Ground States and Ferromagnetic Order Induced by Low-Coordinated Surface Atoms and Defects in Nanoscale Magnesium Oxide,"We investigate the effect of low-coordinated surface atoms on the
defect-induced magnetism in MgO nanocrystallites using hybrid density
functional theory calculations. It has been demonstrated that when Mg vacancies
are introduced at the corners of cube-like MgO clusters, a magnetic state
becomes lower in total energy than the nonmagnetic singlet state by 1-2 eV,
resulting in the spin-polarized ground state. The spin density is not only
located at the surrounding O atoms neighbor to the corner Mg vacancy site but
is also extended to the distant (1 nm or longer) low-coordinated surface O
atoms along the <110> directions. This directional spin delocalization allows a
remote Mg vacancy-Mg vacancyinteraction, eventually leading to a spontaneous
long-range ferromagnetic interaction.",1208.6097v1
2012-10-24,Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered structures,"A slave rotor-Hartree Fock formalism is presented for studying the properties
of the p-d model describing perovskite transition metal oxides, and a flexible
and efficient numerical formalism is developed for its solution. The
methodology is shown to yield, within an unified formulation, the significant
aspects of the rare earth nickelate phase diagram, including the paramagnetic
metal state observed for the LaNiO3 and the correct ground-state magnetic order
of insulating compounds. It is then used to elucidate ground state changes
occurring as morphology is varied from bulk to strained and un-strained
thin-film form. For ultrathin films, epitaxial strain and charge-transfer to
the apical out-of-plane oxygen sites are shown to have significant impact on
the phase diagram.",1210.6693v1
2012-11-15,Long-range order and spin-liquid states of polycrystalline Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$,"Low-temperature states of polycrystalline samples of a frustrated pyrochlore
oxide Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ have been investigated by specific heat,
magnetic susceptibility, and neutron scattering experiments. We have found that
this system can be tuned by a minute change of $x$ from a spin-liquid state ($x
< x_{\text{c}}$) to a partly ordered state with a small antiferromagnetic
ordering of the order of $0.1 \mu_{\text{B}}$. Specific heat shows a sharp peak
at a phase transition at $T_{\text{c}}= 0.5$ K for $x=0.005$. Magnetic
excitation spectra for this sample change from a quasielastic to a gapped type
through $T_{\text{c}}$. The possibility of a Jahn-Teller transition is
discussed.",1211.3529v3
2012-11-27,Theoretical spectroscopy of realistic condensed matter systems,"This thesis is devoted to ab initio calculations of ground and excited state
properties of different systems within density functional theory and time
dependent density functional theory. From the numerical point of view we
implemented an original method in the DP code to calculate the independent
particle response function. Moreover, we generalized the DP code to the spin
degree of freedom in order to study the magnetic properties of realistic
condensed matter systems. We studied reflectance anisotropy and energy loss
spectra of a clean and oxidized surface, and we performed an analysis of the
origin of the main spectral features. Thanks to the comparison between
experimental and theoretical energy loss spectra, we roule out the p(2x1)
reconstruction for the Si(100) surface. Moreover, in the case of a simple BeH
molecule we evidenced the problem of correctly describing the excitation
spectra for open shell systems within the TDDFT framework. In the second part
of the thesis, we presented the study of the optical properties of magnetic
systems such as FeS2, CoS2 or NiS2, interesting materials for possible
technological applications in the growing field of spintronics. Within this
context we calculated ground state properties and optical condictivity of BCC
bulk iron, for which we found a nice agreement with available experimental
data.",1211.6270v1
2012-12-20,First-Order Superconducting Transition of Sr2RuO4,"By means of the magnetocaloric effect, we examine the nature of the
superconducting-normal (S-N) transition of Sr2RuO4, a most promising candidate
for a spin-triplet superconductor. We provide thermodynamic evidence that the
S-N transition of this oxide is of first order below approximately 0.8 K and
only for magnetic field directions very close to the conducting plane, in clear
contrast to the ordinary type-II superconductors exhibiting second-order S-N
transitions. The entropy release across the transition at 0.2 K is 10% of the
normal-state entropy. Our result urges an introduction of a new mechanism to
break superconductivity by magnetic field.",1212.4954v1
2013-02-09,Current-driven dynamics of chiral ferromagnetic domain walls,"In most ferromagnets the magnetization rotates from one domain to the next
with no preferred handedness. However, broken inversion symmetry can lift the
chiral degeneracy, leading to topologically-rich spin textures such as
spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI).
Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy
metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin
texture enables extremely efficient current-driven motion. We show that spin
torque from the spin Hall effect drives DWs in opposite directions in
Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a
N\'eel configuration with left-handed chirality. We directly confirm the DW
chirality and rigidity by examining current-driven DW dynamics with magnetic
fields applied perpendicular and parallel to the spin spiral. This work
resolves the origin of controversial experimental results and highlights a new
path towards interfacial design of spintronic devices.",1302.2257v1
2013-02-19,High critical current density and low anisotropy in textured Sr1-xKxFe2As2 tapes for high field applications,"From the application point of view, large critical current densities Jc (H)
for superconducting wires are required, preferably for magnetic fields higher
than 5 T. Here we show that strong c-axis textured Sr1-xKxFe2As2 tapes with
nearly isotropic transport Jc were fabricated by an ex-situ powder-in-tube
(PIT) process. At 4.2 K, the Jc values show extremely weak magnetic field
dependence and reach high values of 1.7x10^4 A/cm^2 at 10 T and 1.4x10^4 A/cm^2
at 14 T, respectively, these values are by far the highest ever reported for
iron based wires and approach the Jc level desired for practical applications.
Transmission electron microscopy investigations revealed that amorphous oxide
layers at grain boundaries were significantly reduced by Sn addition which
resulted in greatly improved intergranular connectivity. Our results
demonstrated the strong potential of using iron based superconductors for high
field applications.",1302.4583v1
2013-03-19,Electronic structure of relativistic Mott insulator Li$_2$RhO$_3$,"Motivated by studies of coexisting electron correlation and spin-orbit
coupling effect in Na$_2$IrO$_3$ and a recent experiment of its 4d analogue
Li$_2$RhO$_3$, we performed first-principles calculations of the rhodium oxide
compound. The experimentally observed ground state of Li$_2$RhO$_3$ can be
recovered only if both spin-orbit coupling and on-site Coulomb interaction are
taken into consideration. Within the proper $U$ range for 4d-orbitals
($2\leqslant U\leqslant 4$ eV), the ground state of Li$_2$RhO$_3$ could be
either zigzag-AFM or stripy-AFM, both yielding energy gap close to experimental
observation. Furthermore, the total energy differences between the competing
magnetic phases are $\leqslant 3$ meV/Rh within $2\leqslant U\leqslant 4$ eV,
manifesting strong magnetic frustration in the compound. Finally, the phase
energy of Li$_2$RhO$_3$ cannot be fitted with the two-dimensional
Heisenberg-Kitaev model involving only the nearest neighbor interactions, and
we propose that inter-layer interactions may be responsible for the
discrepancy.",1303.4675v1
2013-03-28,k.p subband structure of the LaAlO3/SrTiO3 interface,"Heterostructures made of transition metal oxides are new tailor-made
materials which are attracting much attention. We have constructed a 6-band k.p
Hamiltonian and used it within the envelope function method to calculate the
subband structure of a variety of LaAlO3/SrTiO3 heterostructures. By use of
density functional calculations, we determine the k.p parameters describing the
conduction band edge of SrTiO3: the three effective mass parameters, L=0.6104
eV AA^2, M=9.73 eV AA^2, N=-1.616 eV AA^2, the spin orbit splitting
Delta_SO=28.5 meV and the low temperature tetragonal distortion energy
splitting Delta_T=2.1 meV. For confined systems we find strongly anisotropic
non-parabolic subbands. As an application we calculate bands, density of states
and magnetic energy levels and compare the results to Shubnikov-de Haas quantum
oscillations observed in high magnetic fields. For typical heterostructures we
find that electric field strength at the interface of F = 0.1 meV/AA for a
carrier density of 7.2 10^{12} cm^-2 results in a subband structure that is
similar to experimental results.",1303.7095v2
2013-04-04,Ab-initio prediction of magnetoelectricity in infinite-layer CaFeO2 and MgFeO2,"Density functional based simulations are employed to explore magnetoelectric
effects in iron-based oxides, showing a unique layered structure. We
theoretically predict CaFeO2 to be a promising magnetoelectric, showing
magnetically-controlled large electric polarization, possibly even above room
temperature. The cross coupling between magnetic and dipolar degrees of freedom
needs, as main ingredients, Fe-site spin-orbit coupling and a spin-dependent O
p - Fe d hybridization, along with structural constraints related to the
non-centrosymmetric point group and the peculiar geometry characterized by
""flattened"" FeO4 tetrahedrons. In order to enhance magnetoelectric effects, we
performed a materials-design leading to a novel and optimized system, MgFeO2,
where the larger O4 tetrahedral distortion leads to a stronger polarization.",1304.1228v2
2013-04-17,Stability and metastability of clusters in a reactive atmosphere: theoretical evidence for unexpected stoichiometries of MgMOx,"By applying a genetic algorithm in a cascade approach of increasing accuracy,
we calculate the composition and structure of MgMOx clusters at realistic
temperatures and oxygen pressures. The stable and metastable systems are
identified by ab initio atomistic thermodynamics. We find that small clusters
(M <= 5) are in thermodynamic equilibrium when x > M. The non-stoichiometric
clusters exhibit peculiar magnetic behavior, suggesting the possibility of
tuning magnetic properties by changing environmental pressure and temperature
conditions. Furthermore, we show that density-functional theory (DFT) with a
hybrid exchange-correlation (xc) functional is needed for predicting accurate
phase diagrams of metal-oxide clusters. Neither a (sophisticated) force field
nor DFT with (semi)local xc functionals are sufficient for even a qualitative
prediction.",1304.4803v2
2013-04-24,"Low temperature ferromagnetism, surface paramagnetism and exchange bias effect in nano-grained alpha-Fe1.4Ga0.6O3 oxide","The compound alpha-Fe1.4Ga0.6O3 has been prepared by mechanical alloying of
alpha-Fe2O3 and Ga2O3 and subsequent heating of the mechanical alloyed samples
in vacuum condition. Magnetic ordering of alpha-Fe2O3 has been modified by
substitution of non-magnetic Ga atoms. The ferromagnetism in alpha-Fe1.4Ga0.6O3
is more soft and enhanced in comparison to alpha-Fe2O3. M\""ossbauer
spectroscopy also confirmed enhanced ferromagnetic order in alpha-Fe1.4Ga0.6O3.
The room temperature soft ferromagnetism by Ga substitution is interesting for
designing alpha-Fe2O3 based unconventional ferromagnet, which is a great
challenge to the materials scientists. The alpha-Fe1.4Ga0.6O3 samples also
exhibited features of exchange bias, low temperature surface paramagnetism, and
suppression of Morin transition. These features have been affected up to
certain extent by the nano-sized grains of the samples.",1304.6512v1
2013-05-27,Collinear and non-collinear spin ground state of wurtzite CoO,"Collinear and non-collinear spin structures of wurtzite phase CoO often
appearing in nano-sized samples are investigated using first-principles density
functional theory calculations. We examined the total energy of several
different spin configurations, electronic structure and the effective magnetic
coupling strengths. It is shown that the AF3-type antiferromagnetic ordering is
energetically most stable among possible collinear configurations. Further, we
found that a novel spiral spin order can be stabilized by including the
relativistic spin-orbit coupling and the non-collinearity of spin direction.
Our result suggests that a non-collinear spin ground state can be observed in
the transition-metal-oxide nanostructures which adds an interesting new aspect
to the nano-magnetism study.",1305.6496v1
2013-06-08,Quantum Hall Effects with High Spin-Chern Numbers in Buckled Honeycomb Structure with Magnetic Order,"As a topological insulator, the quantum Hall (QH) effect is indexed by the
Chern and spin-Chern numbers $\mathcal{C}$ and $\mathcal{C}_{\text{spin}}$. We
have only $\mathcal{C}_{\text{spin}}=0$ or $\pm \frac{1}{2}$ in conventional QH
systems. We investigate QH effects in generic monolayer honeycomb systems. We
search for spin-resolved characteristic patterns by exploring Hofstadter's
butterfly diagrams in the lattice theory and fan diagrams in the low-energy
Dirac theory. The Chern and spin-Chern numbers are calculated based on the
bulk-edge correspondence in the lattice theory and on the Kubo formula in the
Dirac theory. It is shown that the spin-Chern number can takes an arbitrary
high value for certain QH systems in coexistence with buckled structure and
magnetic order. This is a new type of topological insulators. Samples may be
provided by silicene with ferromagnetic order and transition-metal oxide with
antiferromagnetic order.",1306.1859v1
2013-07-09,"Synthesis, Crystal Structure and Physical Properties of Sr2FeOsO6","In the exploration of new osmium based double perovskites, Sr2FeOsO6 is a new
insertion in the existing family. The polycrystalline compound has been
prepared by solid state synthesis from the respective binary oxides. PXRD
analysis shows the structure is pseudo-cubic at room temperature, whereas
low-temperature synchrotron data refinements reveal the structure to be
tetragonal, space group I4/m. Heat capacity and magnetic measurements of
Sr2FeOsO6 indicated the presence of two magnetic phase transitions at T1 = 140
K and T2 = 67 K. Band structure calculations showed the compound as a narrow
energy gap semiconductor, which supports the experimental results obtained from
the resistivity measurements. The present study documents significant
structural and electronic effects of substituting Fe3+ for Cr3+ ion in
Sr2CrOsO6.",1307.2586v1
2013-10-16,Evidence for skyrmions in the high-temperature superconductors,"We claim that the charge density wave recently found by resonant soft x-ray
scattering in layered copper oxides is the tetragonal symmetry defined by the
distance between neighbor Cu$^{3+}$ ions in the CuO$_2$ layer that determines
the critical temperature. We find evidence that this tetragonal symmetry is a
skyrmionic state, which is responsible for an unusual magnetic order and charge
flow in the layers that leads to the breaking of the time reversal symmetry
below the pseudogap line. The core of the skyrmions form pockets of local
magnetic field piercing the superconducting layers in opposite direction to the
rest of the unit cell.",1310.4472v1
2013-11-17,Giant magnetocaloric effect in magnetoelectric Eu1-xBaxTiO3,"We report the magnetic entropy change (Delta Sm) in magnetoelectric
Eu1-xBaxTiO3 for x = 0.1- 0.9. We find - delta Sm = 11 (40) J/kg.K in x = 0.1
for a field change of 1 (5) Tesla respectively, which is the largest value
among all Eu-based oxides. Delta Sm arises from the field-induced suppression
of the spin entropy of Eu2+:4f7 localized moments. While -delta Sm decreases
with increasing x, -DeltaSm = 6.58 J/kg.K observed in the high spin diluted
composition x = 0.9 is larger than that in many manganites. Our results
indicate that these magnetoelectrics are potential candidates for cryogenic
magnetic refrigeration.",1311.4161v1
2013-11-28,"Effect of La Doping on the Crystal Structure, Electric, Magnetic and Morphologic Properties of the BSCCO System","Studies of the doping process can provide a better understanding of the
superconducting mechanisms in cuprous oxide materials. In this work, we studied
the doping effects on the crystal structure, electric, morphologic and magnetic
properties of the BSCCO system with the nominal composition
$Bi_{1.6}Pb_{0.4}Sr_{(2-x)}RE_xCa_2Cu_3O_{(10-{\delta})}$. Here, the rare earth
element (RE) was replaced by La in the sites of Sr. The x was ranged from 0.0
to 2.0, in steps of 0.5. The samples were prepared based on Pechini's method.
The resulting powder was pressed at room temperature and the pellets were
submitted to several heat treatments. The characterizations confirm the La in
the sites of Sr however, the superconducting properties of the sample were not
improved.",1311.7353v2
2013-12-04,Magnetic excitation in resonant inelastic x-ray scattering of Sr$_2$IrO$_4$: A localized spin picture,"We study the magnetic excitations in 5d transition-metal oxide Sr$_2$IrO$_4$
on the basis of the Heisenberg model with small anisotropic terms on a square
lattice. We calculate the correlation functions by using the Green's functions
in the spin-wave approximation. The spin waves are split into two modes with
slightly different energies due to the anisotropic terms. It is shown that the
spin correlation functions of the y and z components are composed of a single
peak corresponding to each mode. We analyze the process of resonant inelastic
x-ray scattering (RIXS) without relying on the fast collision approximation to
obtain the local scattering operator. The RIXS intensity is derived as a sum of
the correlation functions of the y and z spin components. We demonstrate that
the RIXS intensity as a function of energy shows two-peak structure brought
about by the two modes, which could be observed in the RIXS experiment.",1312.1071v2
2013-12-05,The Chemical Instability of Na2IrO3 in Air,"We report that Na2IrO3, which has a layered honeycomb iridium oxide
sublattice interleaved by Na planes, decomposes in laboratory air while
maintaining the same basic crystal structure. The decomposition reaction was
monitored by time-dependent powder x-ray diffraction under different ambient
atmospheres, through which it was determined that it occurs only in the
simultaneous presence of both CO2 and H2O. A hydrated sodium carbonate is the
primary decomposition product along with altered Na2IrO3. The diffraction
signature of the altered Na2IrO3 is quite similar to that of the pristine
material, which makes the detection of decomposition difficult in a sample
handled under ordinary laboratory conditions. The decomposed samples show a
significantly decreased magnetic susceptibility and the disappearance of the
low temperature antiferromagnetic transition considered to be characteristic of
the phase. Samples that have never been exposed to air after synthesis display
a previously unreported magnetic transition at 5K.",1312.1637v1
2014-02-05,Superconductivity of Cu/CuOx interface formed by shock-wave pressure,"A mixture of powdered Cu and CuO has been subjected to a shock-wave pressure
of 350 kbar with following quenching of the vacuum-encapsulated product to 77
K. The ac magnetic susceptibility measurements of the samples have revealed
metastable superconductivity with Tc = 19.5 K, characterized by glassy dynamics
of the shielding currents below Tc . Comparison of the ac susceptibility and
the dc magnetization measurements infers that the superconductivity arises
within the granular interfacial layer formed between metallic Cu and its oxides
due to the shock-wave treatment.",1402.0960v1
2014-02-19,A site-selective antiferromagnetic ground state in layered pnictide-oxide BaTi2As2O,"The electronic and magnetic properties of BaTi$_{2}$As$_{2}$O have been
investigated using both the first-principles and analytical methods. The
full-potential linearized augmented plane-wave calculations show that the most
stable state is a site-selective antiferromagnetic (AFM) metal with a
$\text{2}\times \text{1}\times \text{1}$ magnetic unit cell containing two
nonmagnetic Ti atoms and two other Ti atoms with antiparallel moments. Further
analysis to Fermi surface and spin susceptibility shows that the site-selective
AFM ground state is driven by the Fermi surface nesting and the Coulomb
correlation. Meanwhile, the charge density distribution remains uniform,
suggesting that the phase transition at $200$ K in experiment is a
spin-density-wave (SDW) transition.",1402.4723v1
2014-04-24,Large-amplitude spin oscillations triggered by nonequilibrium strongly correlated $t_{2g}$ electrons,"Laser-induced ultrafast (fs) magnetization experiments in antiferromagnets
have recently attracted large attention, paving the road for inherently fast
spin dynamics in the THz regime without invoking stray fields. The technical
importance is emphasized by the rising new research field of antiferromagnetic
(AFM) spintronics, where superexchange-dominated strongly correlated compounds
provide an interesting materials playground. An intriguing question is whether
the Coulomb interaction may be a key to control AFM order on ultrafast time
scales. Therefore, we study (de)magnetization processes in a time-dependent
multiorbital Hubbard model, focusing on $t_{2g}$ electrons in a wider doping
range. Depending on filling, we reveal large-amplitude spin oscillations via
interaction quenches from the antiferromagnetic or paramagnetic state.
Nonequilibrium ultrafast spin-orientation effects in prominent correlated
transition-metal oxides are therefrom predicted.",1404.6118v4
2014-10-14,The magneto-structural relationship in the tetrahedral spin chain oxide CsCoO$_2$,"We have investigated the structural and magnetic transitions in CsCoO$_2$
using calorimetric measurements, neutron powder diffraction (NPD), density
functional theory (DFT) calculations and muon-spin relaxation ($\mu$SR)
measurements. CsCoO$_2$ exhibits three-dimensional long-range antiferromagnetic
(AFM) order at 424~K, resulting in antiferromagnetic alignment of chains of
ferromagnetically ordered Co-Co spin dimers. Although there is no change in
magnetic structure around a structural transition at $T^{*}=100$~K, the
resulting bifurcation of corner-shared Co--O--Co bond angles causes a weakening
of the AFM interaction for one set of bonds along the chains. Consequently, the
system undergoes a complex freezing out of relaxation processes on cooling.",1410.3686v1
2014-11-19,Universal domain wall dynamics under electric field in Ta/CoFeB/MgO devices with perpendicular anisotropy,"Electric field effects in ferromagnetic/oxide dielectric structures provide a
new route to control domain wall (DW) dynamics with low power dissipation.
However, electric field effects on DW velocities have only been observed so far
in the creep regime where DW velocities are low due to strong interactions with
pinning sites. Here, we show gate voltage modulation of DW velocities ranging
from the creep to the flow regime in Ta/Co40Fe40B20/MgO/TiO2 structures with
perpendicular magnetic anisotropy. We demonstrate a universal description of
the role of applied electric fields in the various pinning dependent regimes by
taking into account an effective magnetic field being linear with the electric
field. In addition, the electric field effect is found to change sign in the
Walker regime. Our work opens new opportunities for the study and optimization
of electric field effect at ferromagnetic metal/insulator interfaces.",1411.5267v2
2014-12-02,Two-stage magnetic-field-tuned superconductor-insulator transition in underdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$,"In the underdoped pseudogap regime of cuprate superconductors, the normal
state is commonly probed by applying a magnetic field ($H$). However, the
nature of the $H$-induced resistive state has been the subject of a long-term
debate, and clear evidence for a zero-temperature ($T=0$) $H$-tuned
superconductor-insulator transition (SIT) has proved elusive. Here we report
magnetoresistance measurements in underdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$,
providing striking evidence for quantum critical behavior of the resistivity --
the signature of a $H$-driven SIT. The transition is not direct: it is
accompanied by the emergence of an intermediate state, which is a
superconductor only at $T=0$. Our finding of a two-stage $H$-driven SIT goes
beyond the conventional scenario in which a single quantum critical point
separates the superconductor and the insulator in the presence of a
perpendicular $H$. Similar two-stage $H$-driven SIT, in which both disorder and
quantum phase fluctuations play an important role, may also be expected in
other copper-oxide high-temperature superconductors.",1412.1134v1
2015-04-02,High field termination of a Cooper-pair insulator,"We conducted a systematic study of the disorder dependence of the termination
of superconductivity, at high magnetic fields (B), of amorphous indium oxide
films. Our lower disorder films show conventional behavior where
superconductivity is terminated with a transition to a metallic state at a
well-defined critical field, Bc2. Our higher disorder samples undergo a
B-induced transition into a strongly insulating state, which terminates at
higher B's forming an insulating peak. We demonstrate that the B terminating
this peak coincides with Bc2 of the lower disorder samples. Additionally we
show that, beyond this field, these samples enter a different insulating state
in which the magnetic field dependence of the resistance is weak. These results
provide crucial evidence for the importance of Cooper-pairing in the insulating
peak regime.",1504.00528v2
2015-05-22,Charge transfer and hybrid ferroelectricity in (YFeO$_{3}$)$_{n}$/(YTiO$_{3}$)$_{n}$ magnetic superlattices,"Interfaces in oxide heterostructures always provide a fertile ground for
emergent properties. Charge transfer from a high energy band to a low energy
opponent is naturally expected, as occurring in semiconductor $p$-$n$
junctions. In this study, several exceptional physical phenomena have been
predicted in (YFeO$_3$)$_n$/(YTiO$_3$)$_n$ superlattices. First, the charge
transfer between these Mott insulators is in opposite to the intuitive band
alignment scenario. Second, hybrid ferroelectricity with a moderate
polarization is generated in the $n=2$ magnetic superlattice. Furthermore, the
ferroelectric-type distortion can persist even if the
($AB$O$_3$)$_2$/($AB$'O$_3$)$_2$ system turns to be metallic, rending possible
metallic ferroelectricity.",1505.05978v1
2015-06-02,Effects of frustration and cyclic exchange on the spin-1/2 Heisenberg antiferromagnet within the self-consistent spin-wave theory,"The relevance of the quasi-two-dimensional spin-1/2 frustrated quantum
antiferromagnet due to its possibility of modelling the high-temperature
superconducting parent compounds has resulted in numerous theoretical and
experimental studies. This paper presents a detailed research of the influence
of the varying exchange interactions on the model magnetic properties within
the framework of self-consistent spin-wave theory based on Dyson-Maleev
representation. Beside the nearest neighbour interaction within the plane, the
planar frustration up to the third nearest neighbours, cyclic interaction and
the interlayer coupling are taken into account. The detailed description of the
elementary spin excitations, staggered magnetization, spin-wave velocity
renormalization factor and ground-state energy is given. The results are
compared to the predictions of the linear spin-wave theory and when possible
also to the second-order perturbative spin-wave expansion results. Finally,
having at our disposal improved experimental results for the in-plane spin-wave
dispersion in high-$T_c$ copper oxide $\mbox{La}_2\mbox{CuO}_4$, the
self-consistent spin-wave theory is applied to that compound in order to
correct earlier obtained set of exchange parameters and high temperature
spin-wave dispersion.",1506.00773v1
2015-06-20,"Common effect of chemical and external pressures on the magnetic properties of $R$CoPO ($R$ = La, Pr, Nd, Sm). II","The direct correspondence between Co band ferromagnetism and structural
parameters is investigated in the pnictide oxides $R$CoPO for different
rare-earth ions ($R$ = La, Pr, Nd, Sm) by means of muon-spin spectroscopy and
{\it ab-initio} calculations, complementing our results published previously
[G. Prando {\it et al.}, {\it Phys. Rev. B} {\bf 87}, 064401 (2013)]. Both the
transition temperature to the ferromagnetic phase $T_{_{\textrm{C}}}$ and the
volume of the crystallographic unit cell $V$ are found to be conveniently tuned
by the $R$ ionic radius and/or external pressure. A linear correlation between
$T_{_{\textrm{C}}}$ and $V$ is reported and {\it ab-initio} calculations
unambiguously demonstrate a full equivalence of chemical and external
pressures. As such, $R$ ions are shown to be influencing the ferromagnetic
phase only via the induced structural shrinkage without involving any active
role from the electronic $f$ degrees of freedom, which are only giving a
sizeable magnetic contribution at much lower temperatures.",1506.06211v1
2015-06-23,Novel Spin-Orbital Phases Induced by Orbital Dilution,"We demonstrate that magnetic $3d$ impurities with $S=3/2$ spins and no
orbital degree of freedom induce changes of spin-orbital order in a $4d^4$ Mott
insulator with $S=1$ spins. Impurities act either as spin defects which
decouple from the surrounding ions, or trigger orbital polarons along $3d$-$4d$
bonds. The $4d$-$4d$ superexchange in the host $J_{\rm host}$ competes with
$3d$-$4d$ superexchange $J_{\rm imp}$ --- it depends on which orbital is doubly
occupied. The spin-orbital order within the host is totally modified at doping
$x=1/4$. Our findings provide new perspective for future theoretical and
experimental studies of doped transition-metal oxides.",1506.07048v1
2015-06-24,Direct writing of CoFe alloy nanostructures by focused electron beam induced deposition from a heteronuclear precursor,"Recently, focused electron beam induced deposition has been employed to
prepare functional magnetic nanostructures with potential in nanomagnetic logic
and sensing applications by using homonuclear precursor gases like Fe(CO)5 or
Co2(CO)8. Here we show that an extension towards the fabrication of bi-metallic
compounds is possible by using a single-source heteronuclear precursor gas. We
have grown CoFe alloy magnetic nanostructures from the HFeCo3(CO)12 metal
carbonyl precursor. The compositional analysis indicate that the samples
contain about 80 at% of metal and 10 at% of carbon and oxygen. Four-probe
magnetotransport measurements are carried out on nanowires of various sizes
down to a width of 50 nm, for which the room temperature resistivity of
43~$\mu\Omega$cm is found. Micro-Hall magnetometry reveals that
50~nm$\times$250~nm nanobars of the material are ferromagnetic up to the
highest measured temperature of 250 K. Finally, the TEM microstructural
investigation shows that the deposits consist of a bcc Co-Fe phase mixed with a
FeCo2O4 spinel oxide phase with nanograins of about 5 nm diameter.",1506.07311v1
2015-07-10,New synthesis route and magnetic structure of Tm2Mn2O7 - pyrochlore,"In this work we present a new chemical route to synthesize Tm2Mn2O7
pyrochlore, a compound which is thermodynamically unstable at ambient pressure.
Differently from the reported in the past high pressure synthesis of the same
compound applying oxides as starting materials, we have obtained a pure phase
Tm2Mn2O7 by a converting TmMnO3 at 1100 C and 1300 bar oxygen pressure. The
studies of Tm2Mn2O7 performed by a high resolution neutron powder diffraction
have shown, that a pure pyrochlore cubic phase Tm2Mn2O7 (space group Fd-3m)
have been obtained. On cooling below 25K there is a transition to a
ferromagnetically (FM) ordered phase observed with an additional
antiferromagnetic (AFM) canting suggesting a lowering of the initial cubic
crystal symmetry. The magnetic transition is accompanied by small but well
visible magnetostrsiction effect. Using symmetry analysis we have found a
solution for the AFM structure in the maximal Shubnikov subgroup I41/am'd'.",1507.02830v1
2015-08-31,Partial spin polarization of conductance in vertical bi-layer nanowire with rectangular and smooth lateral confinement potential,"We simulate the electron transport in vertical bi-layer nanowire which can be
fabricated in molecular beam epitaxy process with lateral confinement potential
formed by means of cleaved overgrowth or surface oxidization methods giving
rectangular and smooth side confinement, respectively. In calculations we take
into account interaction between charge carriers using DFT within local spin
density approximation. If magnetic field is perpendicular to the wire axis,
pseudogaps are opened in energy dispersion relation E(k) what in conjunction
with spin Zeeman shift of spin-up and spin-down subbands allows for quite high
spin polarization of conductance. We find that in nanowire with rectangular
lateral confinement potential, electron density has two maximums localized at
wire edges in each layers. This modificates strongly all magnetosubbands giving
up to four energy minimums in lowest subband and considerably diminishes widths
of pseudogaps what translates into low maximal spin polarization of
conductance, not exceeding $40\%$. This drawback is absent in wire with smooth
lateral confinement. However, in order to gain a large spin polarization
simultaneous tuning of magnetic field as well as the Fermi energies in both
layers of nanowire are required.",1508.07963v1
2015-09-02,Pauli Spin Blockade of Heavy Holes in a Silicon Double Quantum Dot,"In this work, we study hole transport in a planar silicon
metal-oxide-semiconductor based double quantum dot. We demonstrate Pauli spin
blockade in the few hole regime and map the spin relaxation induced leakage
current as a function of inter-dot level spacing and magnetic field. With
varied inter-dot tunnel coupling we can identify different dominant spin
relaxation mechanisms. Applying a strong out-of-plane magnetic field causes an
avoided singlet-triplet level crossing, from which the heavy hole g-factor
$\sim$ 0.93, and the strength of spin-orbit interaction $\sim$ 110 $\mu$eV, can
be obtained. The demonstrated strong spin-orbit interaction of heavy hole
promises fast local spin manipulation using only electrical fields, which is of
great interest for quantum information processing.",1509.00553v1
2015-10-07,Polar domain walls trigger magnetoelectric coupling,"Interface physics in oxide heterostructures is pivotal in material's science.
Domain walls (DWs) in ferroic systems are examples of naturally occurring
interfaces, where order parameter of neighboring domains is modified and
emerging properties may develop. Here we show that electric tuning of
ferroelastic domain walls in SrTiO3 leads to dramatic changes of the magnetic
domain structure of a neighboring magnetic layer (La1/2Sr1/2MnO3) epitaxially
clamped on a SrTiO3 substrate. We show that by exploiting the resposiveness of
DWs nanoregions to external stimuli, even in absence of any domain
contribution, prominent and adjustable macroscopic reactions of neighboring
layers can be obtained. We conclude that polar DWs, known to exist in other
materials, can be used to trigger tunable responses and may lead to new ways
for manipulation of interfacial emerging properties.",1510.02039v1
2015-10-16,Adjacent Fe-Vacancy Interactions as the Origin of Room Temperature Ferromagnetism in (In$_{1-x}$Fe$_x$)$_2$O$_3$,"Dilute magnetic semiconductors (DMSs) show great promise for applications in
spin-based electronics, but in most cases continue to elude explanations of
their magnetic behavior. Here, we combine quantitative x-ray spectroscopy and
Anderson impurity model calculations to study ferromagnetic Fe-substituted
In$_2$O$_3$ films, and we identify a subset of Fe atoms adjacent to oxygen
vacancies in the crystal lattice which are responsible for the observed room
temperature ferromagnetism. Using resonant inelastic x-ray scattering, we map
out the near gap electronic structure and provide further support for this
conclusion. Serving as a concrete verification of recent theoretical results
and indirect experimental evidence, these results solidify the role of
impurity-vacancy coupling in oxide-based DMSs.",1510.05030v1
2015-11-09,Investigation of the magnetic structure and crystal field states of pyrochlore antiferromagnet Nd2Zr2O7,"We present synchrotron x-ray diffraction, neutron powder diffraction and
time-of-flight inelastic neutron scattering measurements on the rare earth
pyrochlore oxide Nd2Zr2O7 to study the ordered state magnetic structure and
cystal field states. The structural characterization by high-resolution
synchrotron x-ray diffraction confirms that the pyrochlore structure has no
detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals
long range all-in/all-out antiferromagnetic order below T_N ~ 0.4 K with
propagation vector k = (0 0 0) and an ordered moment of 1.26(2) \mu_B/Nd at 0.1
K. The ordered moment is much smaller than the estimated moment of 2.65
\mu_B/Nd for the local <111> Ising ground state of Nd3+ (J=9/2) suggesting that
the ordering is partially suppressed by quantum fluctuations. The strong Ising
anisotropy is further confirmed by the inelastic neutron scattering data which
reveals a well-isolated dipolar-octupolar type Kramers doublet ground state.
The crystal field level scheme and ground state wavefunction have been
determined.",1511.02749v1
2015-11-28,Spin-orbit torque engineering via oxygen manipulation,"Spin transfer torques allow the electrical manipulation of the magnetization
at room temperature, which is desirable in spintronic devices such as spin
transfer torque memories. When combined with spin-orbit coupling, they give
rise to spin-orbit torques which are a more powerful tool for magnetization
control and can enrich device functionalities. The engineering of spin-orbit
torques, based mostly on the spin Hall effect, is being intensely pursued. Here
we report that the oxidation of spin-orbit torque devices triggers a new
mechanism of spin-orbit torque, which is about two times stronger than that
based on the spin Hall effect. We thus introduce a way to engineer spin-orbit
torques via oxygen manipulation. Combined with electrical gating of the oxygen
level, our findings may also pave the way towards reconfigurable logic devices.",1511.08868v1
2016-02-24,Critical behavior of sputter-deposited magnetoelectric antiferromagnetic Cr$_2$O$_3$ films near Néel temperature,"Chromium(III) oxide is a classical collinear antiferromagnet with a linear
magnetoelectric effect. We are presenting the measurements of the
magnetoelectric susceptibility $\alpha$ of a sputter-deposited 500-nm film and
a bulk single-crystal of Cr$_\mathrm{2}$O$_\mathrm{3}$. We investigated the
magnetic phase-transition and the critical exponent $\beta$ of the sublattice
magnetization near N\'eel temperature. For the films, an exponent of 0.49(1)
was found below 293 K, and changed to 1.06(4) near the N\'eel temperature of
298 K. For the single-crystal, the exponent was constant at 0.324(4). We
investigated the reversal probability of antiferromagnetic domains during
magnetoelectric field cooling. For the sputtered films, reversal probability
was zero above 298 K and stabilized only below 293 K. We attribute this
behavior to formation of grains during film growth, which gives different
intergrain and intragrain exchange-coupling energies. For the single-crystal,
reversal probability was stabilized immediately at the N\'eel temperature of
307.6 K.",1602.07547v2
2016-03-10,Local charge variation enhanced spin canting of BiFeO3/La0.7Sr0.3MnO3 heterostructure,"Transition-metal oxides (TMOs) exhibit many emergent phenomena ranging from
high-temperature super- conductivity and giant magnetoresistance to magnetism
and ferroelectricity. When TMOs are interfaced with each other, new
multi-functionalities can arise, which are absent in individual components. In
this work, we have systematically studied, within a unified double-exchange
model, the interfacial magnetic response in layered BiFeO3 (BFO) and
La0.7Sr0.3MnO3 (LSMO) heterostructures. The ferromagnetic/antiferromagnetic
canting is shown to be enhanced on the interface of BFO by the influence of
local charge variation. More interestingly, it is found that the spin canting
in BFO can be further enhanced with deeper penetration depth to the bulk when a
local oxygen vacancy is placed around the interface.",1603.03107v2
2016-03-14,Probing the Nuclear Spin-Lattice Relaxation Time at the Nanoscale,"Nuclear spin-lattice relaxation times are measured on copper using magnetic
resonance force microscopy performed at temperatures down to 42 mK. The low
temperature is verified by comparison with the Korringa relation. Measuring
spin-lattice relaxation times locally at very low temperatures opens up the
possibility to measure the magnetic properties of inhomogeneous electron
systems realized in oxide interfaces, topological insulators and other strongly
correlated electron systems such as high-Tc superconductors.",1603.04238v2
2016-04-22,Multiband behavior and non-metallic low-temperature state of K$_{0.50}$Na$_{0.24}$Fe$_{1.52}$Se$_{2}$,"We report evidence for multiband transport and an insulating low-temperature
normal state in superconducting K$_{0.50}$Na$_{0.24}$Fe$_{1.52}$Se$_{2}$ with
$T_{c}\approx 20$ K. The temperature-dependent upper critical field, $H_{c2}$,
is well described by a two-band BCS model. The normal-state resistance,
accessible at low temperatures only in pulsed magnetic fields, shows an
insulating logarithmic temperature dependence as $T \rightarrow 0$ after
superconductivity is suppressed. This is similar as for high-$T_{c}$ copper
oxides and granular type-I superconductors, suggesting that the
superconductor-insulator transition observed in high magnetic fields is related
to intrinsic nanoscale phase separation.",1604.06793v1
2016-06-16,Template-Assisted Direct Growth of 1Td/in$^2$ Bit Patterned Media,"We present a method for growing bit patterned magnetic recording media using
directed growth of sputtered granular perpendicular magnetic recording media.
The grain nucleation is templated using an epitaxial seed layer which contains
Pt pillars separated by amorphous metal oxide. The scheme enables the creation
of both templated data and servo regions suitable for high density hard disk
drive operation. We illustrate the importance of using a process that is both
topographically and chemically driven to achieve high quality media.",1606.05370v1
2016-09-06,How to measure the local Dzyaloshinskii Moriya Interaction in Skyrmion Thin Film Multilayers,"The current driven motion of skyrmions in MnSi and FeGe thinned single
crystals could be initiated at current densities of the order of $10^6$ A/m,
five orders of magnitude smaller than for magnetic domain walls. The
technologically crucial step of replicating these results in thin films has not
been successful to date, but the reasons are not clear. Elucidating them
requires analyzing system characteristics at scales of few nm where the key
Dzyaloshinskii Moriya (DM) interactions vary, and doing so in near application
conditions, i.e. oxidation protected systems at room temperature. In this
work's magnetic force microscopy (MFM) studies of magnetron sputtered Ir/Co/Pt
multilayers we show skyrmions that are smaller than previously observed, are
not circularly symmetric, and are pinned to 50 nm wide areas of 75 percent
higher than average DM interaction. This finding matches our measurement of Co
layer thickness inhomogeneity of the order of $\pm$1.2 atomic monolayers per
0.6 nm layer, and indicates that layer flatness must be controlled with greater
precision to preclude skyrmion pinning.",1609.01615v1
2017-02-27,Determination of oxygen vacancy limit in Mn substituted YSZ ceramics,"The series of Mnx(Y0.148Zr0.852)1-xO2-{\delta} ceramics was systematically
studied by means of X-ray absorption and emission spectroscopy and DC magnetic
susceptibility. XAS and XES results show changes in manganese oxidation state
and a gradual evolution of the local atomic environment around Mn ions upon
increasing dopants content, which is due to structural relaxation caused by
growing amount of oxygen vacancies. Magnetic susceptibility measurements reveal
that Mn3O4 precipitates are formed for x greater than or equal to 0.1 and
enable independent determination of actual quantity of Mn ions dissolved in YSZ
solid solution. We show that amount of oxygen vacancies generated by manganese
doping into YSZ is limited to 0.19 per formula unit.",1702.08361v1
2017-03-31,(LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ as a model system for unconventional charge transfer and polar metallicity,"At interfaces between oxide materials, lattice and electronic reconstructions
always play important roles in exotic phenomena. In this study, the density
functional theory and maximally localized Wannier functions are employed to
investigate the (LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ magnetic superlattices. The
electron transfer from Ti$^{3+}$ to V$^{3+}$ is predicted, which violates the
intuitive band alignment based on the electronic structures of LaTiO$_3$ and
LaVO$_3$. Such unconventional charge transfer quenches the magnetism of
LaTiO$_3$ layer mostly and leads to metal-insulator transition in the $n=1$
superlattice when the stacking orientation is altered. In addition, the
compatibility among the polar structure, ferrimagnetism, and metallicity is
predicted in the $n=2$ superlattice.",1703.10748v1
2018-02-23,Probing the $J_{eff}=0$ ground state and the Van Vleck paramagnetism of the Ir$^{5+}$ ions in the layered Sr$_2$Co$_{0.5}$Ir$_{0.5}$O$_4$,"We report a combined experimental and theoretical x-ray magnetic circular
dichroism (XMCD) spectroscopy study at the Ir-$L_{2,3}$ edges on the Ir$^{5+}$
ions of the layered hybrid solid state oxide Sr$_2$Co$_{0.5}$Ir$_{0.5}$O$_4$
with the K$_2$NiF$_4$ structure. From theoretical simulation of the
experimental Ir-$L_{2,3}$ XMCD spectrum, we found a deviation from a pure
$J_{eff}=0$ ground state with an anisotropic orbital-to-spin moment ratio
($L_x/2S_x$ = 0.43 and $L_z/2S_z$ = 0.78). This deviation is mainly due to
multiplet interactions being not small compared to the cubic crystal field and
due to the presence of a large tetragonal crystal field associated with the
crystal structure. Nevertheless, our calculations show that the energy gap
between the singlet ground state and the triplet excited state is still large
and that the magnetic properties of the Ir$^{5+}$ ions can be well described in
terms of singlet Van Vleck paramagnetism.",1802.08752v1
2018-04-04,Direct magnetization-polarization coupling in BaCuF$_4$ fluoride,"Despite oxides and some fluorides perovskites have emerged as prototypes of
multiferroic and magnetoelectric materials, they have not impacted real
devices. Unfortunately, their working temperatures are very low and the
magnetoelectric coupling has been reported to be rather small. Herewith, we
report from first-principles calculations an ideal magnetization reversal
through polarization switching in BaCuF$_4$ which, according to our results,
could be achieved close to room temperature. We also show that this ideal
coupling is driven by a soft mode that combines both, polarization and
octahedral rotation. The later being directly coupled to the weak
ferromagnetism of BaCuF$_4$. This, added to its strong Jahn-Teller distortion
and its orbital ordering, makes this material as a very appealing prototype for
crystals in the $ABX_4$ family in multifunctional applications.",1804.01476v1
2019-05-09,A Novel ground state in a new dimer iridate Ba13Ir6O30 with Ir6+(5d3) Ions,"We have synthesized and studied a new iridate, Ba13Ir6O30, with unusual Ir
oxidation states: 2/3 Ir6+(5d3) ions and 1/3 Ir5+(5d4) ions. Its crystal
structure features dimers of face-sharing IrO6 octahedra, and IrO6 monomers,
that are linked via long, zigzag Ir-O-Ba-O-Ir pathways. Nevertheless,
Ba13Ir6O30 exhibits two transitions at TN1 = 4.7 K and TN2 = 1.6 K. This
magnetic order is accompanied by a huge Sommerfeld coefficient 200 mJ/mole K
below TN2, signaling a coexisting frustrated/disordered state persisting down
to at least 0.05 K. This iridate hosts unusually large Jeff=3/2 degrees of
freedom, which is enabled by strong spin-orbit interactions (SOI) in the
monomers with Ir6+ ions and a joint effect of molecular orbitals and SOI in the
dimers occupied by Ir5+ and Ir6+ ions. Features displayed by the magnetization
and heat capacity suggest that the combination of covalency, SOI and large
effective spins leads to highly frustrated ferrimagnetic ordering, possibly
into a skyrmion crystal, a novelty of this new high-spin iridate.",1905.03891v1
2020-07-13,Spin polarized STM imaging of nanoscale Néel skyrmions in an SrIrO3/SrRuO3 Perovskite Bilayer,"Spin-polarized scanning tunneling microscopy (SPSTM) was used to directly
image nanoscale N\'eel skyrmions in a SrIrO3 / SrRuO3 bilayer system that are
among the smallest reported to date in any system. Off-axis magnetron
sputtering was used to cap epitaxial films of the oxide ferromagnet SRO with 2
unit cells of SrIrO3, intended to provide interfacial spin orbit coupling.
Atomic resolution STM imaging and tunneling spectroscopy were used to identify
island-like SrIrO3 grains and small regions of bare SrRuO3. Isolated skyrmions
were only observed in SrIrO3-covered regions of the film, and exhibited a
distribution of sizes and shapes with an average diameter of 3 nm. We found
that skyrmions must be fully contained within, but may be smaller than, any
given SrIrO3 region. Additionally, skyrmions were observed on SrIrO3 islands of
varying thickness without loss of SPSTM contrast, suggesting the magnetic
texture lies within the SrIrO3 island rather than the underlying ferromagnetic
SrRuO3. Density functional theory calculations suggest this could be due to a
small induced magnetic moment associated with IrO layers in the SrIrO3 film.",2007.06139v1
2010-05-18,Strength of Correlations in electron and hole doped cuprates,"High temperature superconductivity was achieved by introducing holes in a
parent compound consisting of copper oxide layers separated by spacer layers.
It is possible to dope some of the parent compounds with electrons, and their
physical properties are bearing some similarities but also significant
differences from the hole doped counterparts. Here, we use a recently developed
first principles method, to study the electron doped cuprates and elucidate the
deep physical reasons why their behavior is so different than the hole doped
materials. We find that electron doped compounds are Slater insulators, e.g. a
material where the insulating behavior is the result of the presence of
magnetic long range order. This is in sharp contrast with the hole doped
materials, where the parent compound is a Mott charge transfer insulator,
namely a material which is insulating due to the strong electronic correlations
but not due to the magnetic order.",1005.3095v1
2013-08-02,"Control of Spin in La(Mn,Zn)AsO Alloy by Carrier Doping","The control of spin without magnetic field is one of challenges in developing
spintronic devices. In an attempt to solve this problem, we proposed a novel
hypothetic LaMn0.5Zn0.5AsO alloy from two experimentally synthesized rare earth
element transition metal arsenide oxides, i.e. LaMnAsO and LaZnAsO. On the
basis of the first-principles calculations with strong-correlated correction,
we found that the LaMn0.5Zn0.5AsO alloy is an antiferromagnetic semiconductor
at ground state, while bipolar magnetic semiconductor at ferromagnetic state.
Both electron and hole doping in the LaMn0.5Zn0.5AsO alloy induces the
transition from antiferromagnetic to ferromagnetic, as well as semiconductor to
half metal. In particular, the spin-polarization direction is switchable
depending on the doped carrier's type. As carrier doping can be realized easily
in experiment by applying a gate voltage, the LaMn0.5Zn0.5AsO alloy stands for
a promising spintronic material to generate and control the spin-polarized
carriers with electric field.",1308.0439v1
2013-08-02,Temperature-dependent exchange bias properties of polycrystalline PtxCo1-x/CoO bilayers,"Temperature and PtCo composition dependence of exchange bias in PtxCo1-x/CoO
bilayers is investigated. It is observed that exchange bias properties,
blocking temperature and magnetic anisotropy of the PtxCo1-x/CoO thin films are
strongly affected by the concentration of Pt at the common interface. A
detailed structural analysis of antiferromagnetic CoO has been done by x-ray
photoelectron spectroscopy (XPS). The XPS data revealed that CoO layer grows
with non-stoichiometric behavior which results in other cobalt oxide phases and
thus lowers blocking temperature for the exchange biased systems. Increase of
Pt concentration in PtCo layer strengths the exchange bias and thus decreases
training of the system. It also results in enhancement of growth-induced
uniaxial magnetic anisotropy and onset of exchange bias at higher temperatures.
The role of Pt concentration on the interfacial interactions between
ferromagnetic and antiferromagnetic layers, and the effect of
superstoichiometric CoO on blocking temperature are also discussed.",1308.0483v1
2013-08-06,NMR evidence for spin fluctuations in the bilayer nickelate La3Ni2O6,"We report nuclear magnetic resonance data in the bilayer nickelate La3Ni2O6.
This material belongs to a family of low valence nickel oxides with square
planar coordination of the Ni ions and is isoelectronic to the high temperature
superconducting cuprates. Although the three layer nickelate compound exhibits
a spin-state transition accompanied by antiferromagnetic order, the bilayer
material shows no phase transition. The NMR data in the bilayer La3Ni2O6 reveal
the presence of antiferromagnetic spin fluctuations down to 5K that are
surprisingly similar to those present in the magnetically ordered trilayer
La4Ni3O8, suggesting a similar electronic structure in the paramagnetic phase
of both compounds.",1308.1322v1
2013-08-06,"Superlattice origin of incommensurable density waves in La_{2-x}Ae_xCuO4 (Ae = Ba, Sr)","In line with the Coulomb-oscillator model of superconductivity, loop currents
of excited 3s electrons from O^2- ions, passing in the CuO2 plane through
nuclei of nearest-neighbor oxygen quartets, create the antiferromagnetic phase
of undoped copper oxides. Holes, introduced by alkaline-earth doping of
La2CuO4, destroy the loop currents, thereby weakening antiferromagnetism until
it disappears at doping x = 0.02. Further doping of La_2-xAe_xCuO4 gives rise
to incommensurate free-hole density waves whose wavelength is determined by the
spacing of a doping superlattice. Modulating the ordering of the ions' magnetic
moments, the charge-density wave, of incommensurability 2 delta, causes a
magnetic density wave of incommensurability delta. The formula derived for
delta(x) is in excellent agreement with data from X-ray diffraction and neutron
scattering.",1308.1396v2
2017-01-03,Magnetite nano-islands on silicon-carbide with graphene,"X-ray magnetic circular dichroism (XMCD) measurements of iron nano-islands
grown on graphene and covered with a Au film for passivation reveal that the
oxidation through defects in the Au film spontaneously leads to the formation
of magnetite nano-particles (i.e, $Fe_3$$O_4$). The Fe nano-islands (20 and 75
monolayers; MLs) are grown on epitaxial graphene formed by thermally annealing
6H-SiC(0001) and subsequently covered, in the growth chamber, with nominal 20
layers of Au. Our X-ray absorption spectroscopy and XMCD measurements at
applied magnetic fields show that the thin film (20 ML) is totally converted to
magnetite whereas the thicker film (75 ML) exhibits properties of magnetite but
also those of pure metallic iron. Temperature dependence of the XMCD signal (of
both samples) shows a clear transition at $T_{\rm V}\approx 120$ K consistent
with the Verwey transition of bulk magnetite. These results have implications
on the synthesis of magnetite nano-crystals and also on their regular
arrangements on functional substrates such as graphene.",1701.00861v1
2018-05-15,Spin accumulation at nonmagnetic interface induced by direct Rashba Edelstein effect,"Rashba effect describes how electrons moving in an electric field experience
a momentum dependent magnetic field that couples to the electron angular
momentum (spin). This physical phenomenon permits the generation of spin
polarization from charge current (Edelstein effect), which leads to the buildup
of spin accumulation. Spin accumulation due to Rashba Edelstein effect has been
recently reported to be uniform and oriented in plane, which has been suggested
for applications as spin filter device and efficient driving force for
magnetization switching. Here, we report the X-ray spectroscopy
characterization Rashba interface formed between nonmagnetic metal (Cu, Ag) and
oxide (Bi$_{2}$O$_{3}$) at grazing incidence angles. We further discuss the
generation of spin accumulation by injection of electrical current at these
Rashba interfaces, and its optical detection by time resolved magneto optical
Kerr effect. We provide details of our characterization which can be extended
to other Rashba type systems beyond those reported here.",1805.05523v1
2012-01-31,Principles of the Field Theory of High Temperature Superconductivity in Underdoped Copper-Oxides,"Here I extend my last work about the origin of the pseudo-gaps in underdoped
cuprates (arXiv: cond-mat. 1011.3206), to include the mechanism of
superconductivity. This is done by adapting the formalism of the double
correlations in systems with nested Fermi surfaces to the semi one dimensional
system of strings of holes. It is proposed that magnetic interaction is crucial
for the establishment of the pseudogap and the high temperature
superconductivity. It is shown that superconductivity disturbs the completeness
of the strings of holes, and creates fluctuations in their shapes. This, in
turn, reduces the magnetic interaction and the pseudogap order.",1201.6494v11
2013-09-12,One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6,"Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.",1309.3222v2
2013-09-17,Strongly Correlated Materials,"Strongly correlated materials are profoundly affected by the repulsive
electron-electron interaction. This stands in contrast to many commonly used
materials such as silicon and aluminum, whose properties are comparatively
unaffected by the Coulomb repulsion. Correlated materials often have remarkable
properties and transitions between distinct, competing phases with dramatically
different electronic and magnetic orders. These rich phenomena are fascinating
from the basic science perspective and offer possibilities for technological
applications. This article looks at these materials through the lens of
research performed at Rice University. Topics examined include: Quantum phase
transitions and quantum criticality in ""heavy fermion"" materials and the iron
pnictide high temperature superconductors; computational ab initio methods to
examine strongly correlated materials and their interface with analytical
theory techniques; layered dichalcogenides as example correlated materials with
rich phases (charge density waves, superconductivity, hard ferromagnetism) that
may be tuned by composition, pressure, and magnetic field; and nanostructure
methods applied to the correlated oxides VO2 and Fe3O4, where metal-insulator
transitions can be manipulated by doping at the nanoscale or driving the system
out of equilibrium. We conclude with a discussion of the exciting prospects for
this class of materials.",1309.4473v1
2013-09-20,Steadfast perpendicular exchange coupling in an ultrathin CoO/PtFe double-layer: strain and spin orientation,"We report on the exchange coupling and magnetic properties of a strained
ultrathin CoO/PtFe double-layer with perpendicular magnetic anisotropy. The
cobalt oxide growth by reactive molecular beam epitaxy on a Pt-terminated
PtFe/Pt(001) surface gives rise to an hexagonal surface and a monoclinic
distorted CoO 3nm film at room temperature. This distorted ultrathin CoO layer
couples with the PtFe(001) layer establishing a robust perpendicular exchange
bias shift. Soft x-ray absorption spectroscopy provides a full description of
the spin orientations in the CoO/PtFe doublelayer. The exchange bias shift is
preserved up to the Neel antiferromagnetic ordering temperature of TN=293 K.
This unique example of selfsame value for blocking and ordering temperatures,
yet identical to the bulk ordering temperature, is likely related to the
original strain induced distortion and strengthened interaction between the two
well-ordered spin layers.",1309.5288v1
2014-05-27,"Non-d$^0$ Electric Dipole in FeO$_5$ bipyramid: a New Resource for Quantum Paraelectrics, Ferroelectrics and Multiferroics","Electric polarization in conventional ferroelectric oxides usually involves
nonmagnetic transition-metal ions with an empty d shell (the d$^0$ rule). Here
we unravel a new mechanism for local electric dipoles based on magnetic
Fe$^{3+}$ (3d$^5$) ion violating the d$^0$ rule. The competition between the
long-range Coulomb interaction and short-range Pauli repulsion in a FeO$_5$
bipyramid with proper lattice parameters would favor an off-center displacement
of Fe$^{3+}$ that induces a local electric dipole. The manipulation of this
kind of non-d$^0$ electric dipoles opens up a new route for generating
unconventional dielectrics, ferroelectrics, and multiferroics. As a prototype
example, we show that the non-d$^0$ electric dipoles in ferrimagnetic
hexaferrites (Ba,Sr)Fe$_{12}$O$_{19}$ lead to a new family of magnetic quantum
paraelectrics.",1405.6806v1
2014-06-10,Multiferroic interfaces composed of d0 perovskites oxides,"We investigate the electronic, ferroelectric and magnetic properties of
KTaO3/PbTiO3 interfaces by using conventional density functional theory (DFT)
and advanced DFT such as hybrid functional HSE06. We show that doped holes in
valence bands or electrons in conduction bands give rise to ferromagnetism at
the interfaces. The ferromagnetic states are ground states for both hole-doped
(p-type) and electron-doped (n-type) interfaces by comparison with their
corresponding nonmagnetic and antiferromagnetic states. Carriers (holes or
electrons) concentrate near the interface to screen the polarization charge and
thus the concentration of carrier varies with the ferroelectric polarization.
Furthermore, the interface magnetization, which is nearly proportional to the
concentration of carrier, can be tuned by ferroelectric polarization reversal,
leading to strong intrinsic magnetoelectric effects at the interface of
originally nonmagnetic KTaO3 and PbTiO3. Interestingly, a
ferromagnetic-nonmagnetic transition tuned by an applied electric field can be
realized at the p-type interface. This suggests an illuminating approach to
multiferroic materials beyond conventional single-phase multiferroics and
multi-phase multiferroics such as ferroelectric/ferromagnet heterostructures.
The KTaO3/PbTiO3 interfaces may be promising in future multiferroic devices
applications.",1406.2595v2
2014-06-16,Infrared dichroism of gold nanorods controlled using a magnetically addressable mesophase,"Gold nanorods have unique optical properties, which make them promising
candidates for building nano-structured materials using a ""bottom-up"" strategy.
We formulate stable bulk materials with anisotropic optical properties by
inserting gold and iron oxide nanorods within a lamellar mesophase.
Quantitative measurements of the order parameter by modelling the absorbance
spectra show that the medium is macroscopically aligned in a direction defined
by an external magnetic field. Under field, the system exhibits significant
absorption dichroism in the infrared range, at the position of the longitudinal
plasmon peak of the gold nanorods (about 1200 nm), indicating strong
confinement of these particles within the water layers of the lamellar phase.
This approach can yield soft and addressable optical elements.",1406.4014v1
2016-08-09,High-temperature large-gap quantum anomalous Hall insulator in ultrathin double perovskite films,"Motivated by the goal of realizing topological phases in thin films and
heterostructures of correlated oxides, we propose here a quantum anomalous Hall
insulator (QAHI) in ultrathin films of double perovskites based on mixed 3d-5d
or 3d-4d transition metal ions, grown along the [111] direction. Considering
the specific case of ultrathin Ba2FeReO6, we present a theoretical analysis of
an effective Hamiltonian derived from first-principles. We establish that a
strong spin-orbit coupling at Re site, t2g symmetry of the low-energy d-bands,
polarity of its [111] orientation of perovskite structure, and mixed 3d-5d
chemistry results in room temperature magnetism with a robust QAHI state of
Chern number C=1 and a large band-gap. We uncover and highlight a
non-relativistic orbital-Rashba-type effect in addition to the spin-orbit
coupling, that governs this QAHI state. Our prediction of a large topological
band-gap of ~100 meV in electronic structure, and a magnetic transition
temperature Tc~300K estimated by Monte Carlo simulations, is expected to
stimulate experimental efforts at synthesis of such films and enable possible
practical applications of its dissipationless edge currents.",1608.02950v1
2017-06-12,Non-equilibrium restoration of duality symmetry in the vicinity of the superconductor-insulator transition,"The magnetic field driven superconductor to insulator transition in thin
films was theoretically analyzed via a vortex-charge duality transformation
applied to the Hamiltonian. Vortices condensation was conjectured as the
underline physical mechanism of the insulating phase. Experimental evidence
supported duality symmetry across the magnetic-field driven superconductor to
insulator transition in amorphous Indium Oxide films. Counterintuitively,
duality symmetry is broken at low temperatures where the insulating phase
develops strongly non linear current-voltage characteristics. Here, we follow
the breakdown of duality symmetry down to very low temperatures and demonstrate
the restoration of duality symmetry out of equilibrium.",1706.03511v2
2017-10-15,Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO$_2$,"We study the electronic structure of the Pd-terminated surface of the
non-magnetic delafossite oxide metal PdCoO$_2$. Combining angle-resolved
photoemission spectroscopy and density-functional theory, we show how an
electronic reconstruction driven by surface polarity mediates a Stoner-like
magnetic instability towards itinerant surface ferromagnetism. Our results
reveal how this leads to a rich multi-band surface electronic structure, and
provide spectroscopic evidence for an intriguing sample-dependent coupling of
the surface electrons to a bosonic mode which we attribute to electron-magnon
interactions. Moreover, we find similar surface state dispersions in PdCrO$_2$,
suggesting surface ferromagnetism persists in this sister compound despite its
bulk antiferromagnetic order.",1710.05392v1
2017-10-16,Positive-Negative Birefringence in Multiferroic Layered Metasurfaces,"We uncover and identify the regime for a magnetically and ferroelectrically
controllable negative refraction of light traversing multiferroic, oxide-based
metastructure consisting of alternating nanoscopic ferroelectric (SrTiO$_2$)
and ferromagnetic (Y$_3$Fe$_2$(FeO$_4$)$_3$, YIG) layers. We perform analytical
and numerical simulations based on discretized, coupled equations for the
self-consistent Maxwell/ferroelectric/ferromagnetic dynamics and obtain a
biquadratic relation for the refractive index. Various scenarios of ordinary
and negative refraction in different frequency ranges are analyzed and
quantified by simple analytical formula that are confirmed by full-fledge
numerical simulations. Electromagnetic-waves injected at the edges of the
sample are propagated exactly numerically. We discovered that for particular
GHz frequencies, waves with different polarizations are characterized by
different signs of the refractive index giving rise to novel types of phenomena
such as a positive-negative birefringence effect, and magnetically controlled
light trapping and accelerations.",1710.05995v1
2017-10-20,Intercalated europium metal in epitaxial graphene on SiC,"X-ray magnetic circular dichroism (XMCD) reveal the magnetic properties of
intercalated europium metal under graphene on SiC(0001). Intercalation of Eu
nano-clusters (average size 2.5 nm) between graphene and SiC substate are
formed by deposition of Eu on epitaxially grown graphene that is subsequently
annealed at various temperatures while keeping the integrity of the graphene
layer. Using sum-rules analysis of the XMCD of Eu M$_{4,5}$ edges at $T = 15$
K, our samples show paramagnetic-like behavior with distinct anomaly at T
$\approx$ 90 K which may be related to the N{\`e}el transition, T$_N$ = 91 K,
of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or
antiferromagnetism due to Eu$_2$O$_3$ indicating that the graphene layer
protects the intercalated metallic Eu against oxidation over months of exposure
to atmospheric environment.",1710.07396v1
2017-12-26,Electro-optic and magneto-optic photonic devices based on multilayers photonic structures,"In this work we describe different types of photonic structures that allow
tunability of the photonic band gap upon the application of external stimuli,
as the electric or magnetic field. We review and compare two porous 1D photonic
crystals: in the first one a liquid crystal has been infiltrated in the pores
of the nanoparticle network, while in the second one the optical response to
the electric field of metallic nanoparticles has been exploited. Then, we
present a 1D photonic crystal made with indium tin oxide (ITO) nanoparticles,
and we propose this system for electro-optic tuning. Finally, we describe a
microcavity with a defect mode that is tuned in the near infrared by the
magnetic field, envisaging a contact-less magneto-optic switch. These optical
switches can find applications in ICT and electrochromic windows.",1712.09453v1
2018-01-04,Tunable magnetic and transport properties of Mn3Ga thin films on Ta/Ru seedlayer,"Hexagonal D019-type Mn3Z alloys that possess large anomalous and
topological-like Hall effects have attracted much attention due to their great
potential in the antiferromagnetic spintronic devices. Here, we report the
preparation of Mn3Ga film in both tetragonal and hexagonal phases with a tuned
Ta/Ru seed layer on the thermally oxidized Si substrate. A large coercivity
together with a large anomalous Hall resistivity is found in the Ta-only sample
with mixed tetragonal phase. By increasing the thickness of Ru layer, the
tetragonal phase gradually disappears and a relatively pure hexagonal phase is
obtained in the Ta(5)/Ru(30) buffered sample. Further magnetic and transport
measurements revealed that the anomalous Hall conductivity nearly vanishes in
the pure hexagonal sample, while an abnormal asymmetric hump structure emerges
in the low field region. The extracted additional Hall term is robust in a
large temperature range and presents a sign reversal above 200K. The abnormal
Hall properties are proposed to be closely related with the frustrated spin
structure of D019 Mn3Ga.",1801.01233v1
2018-01-17,Interference induced enhancement of magneto-optical Kerr effect in ultrathin magnetic films,"We have studied the magneto-optical spectra of ultrathin magnetic films
deposited on Si substrates coated with an oxide layer (SiOx). We find that the
Kerr rotation angle and the ellipticity of ~1 nm thick CoFeB thin films, almost
transparent to visible light, show a strong dependence on the thickness of the
SiOx layer. The Kerr signal from the 1 nm CoFeB thin film can be larger than
that of ~100 nm thick CoFeB films for a given SiOx thickness and light
wavelength. The enhancement of the Kerr signal occurs when optical interference
takes place within the SiOx layer. Interestingly, under such resonance
condition, the measured Kerr signal is in some cases larger than the estimation
despite the good agreement of the measured and calculated reflection amplitude.
We infer the discrepancy originates from interface states that are distinct
from the bulk characteristics. These results show that optical interference
effect can be utilized to study the magneto-optical properties of ultrathin
films.",1801.05539v1
2018-09-12,Atomic-Scale Interface Engineering of Majorana Edge Modes in a 2D Magnet-Superconductor Hybrid System,"Topological superconductors are predicted to harbor exotic boundary states -
Majorana zero-energy modes - whose non-Abelian braiding statistics present a
new paradigm for the realization of topological quantum computing. Using
low-temperature scanning tunneling spectroscopy (STS), we here report on the
direct real-space visualization of chiral Majorana edge states in a monolayer
topological superconductor, a prototypical magnet-superconductor hybrid system
comprised of nano-scale Fe islands of monoatomic height on a
Re(0001)-O(2$\times$1) surface. In particular, we demonstrate that interface
engineering by an atomically thin oxide layer is crucial for driving the hybrid
system into a topologically non-trivial state as confirmed by theoretical
calculations of the topological invariant, the Chern number.",1809.04503v1
2018-09-21,Electronic correlations and competing orders in multiorbital dimers: a cluster DMFT study,"We investigate the violation of the first Hund's rule in 4$d$ and 5$d$
transition metal oxides that form solids of dimers. Bonding states within these
dimers reduce the magnetization of such materials. We parametrize the dimer
formation with realistic hopping parameters and find not only regimes, where
the system behaves as a Fermi liquid or as a Peierls insulator, but also
strongly correlated regions due to Hund's coupling and its competition with the
dimer formation. The electronic structure is investigated using the cluster
dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two
orbitals per site and $3/8$-filling, that is three electrons per dimer. It
reveals dimer-antiferromagnetic order of a high-spin (double exchange) state
and a low-spin (molecular orbital) state. At the crossover region we observe
the suppression of long-range magnetic order, fluctuation enhancement and
renormalization of electron masses. At certain interaction strengths the system
becomes an incoherent antiferromagnetic metal with well defined local moments.",1809.07989v1
2018-09-26,Eigenenergies of excitonic giant-dipole states in cuprous oxide,"In this work we present the eigenspectra of a novel species of Wannier
excitons when exposed to crossed electric and magnetic fields. In particular,
we compute the eigenenergies of giant-dipole excitons in
$\textrm{Cu}_2\textrm{O}$ in crossed fields. In our theoretical approach, we
calculate the excitonic spectra within both an approximate as well as a
numerically exact approach for arbitrary field configurations. We verify that
stable bound excitonic giant-dipole states are only possible in the strong
magnetic field limit, as this is the only regime providing sufficiently deep
potential wells for their existence. Comparing both analytic as well as
numerical calculations, we obtain excitonic giant-dipole spectra with level
spacings in the range of $0.6\ldots100\, \mu \textrm{eV}$.",1809.10039v1
2018-08-31,The Changed Crystal Filed of Gd3+ in Natural Zircon with Heat Treatment in Oxidizing and Reducing Atmosphere Monitor by ESR Spectroscopy,"The main purpose of this research is dedicated to the ESR study of the
impurity ions such as Gd3+ in the natural zircon crystal because the presence
of the impurity ions in the crystal usually causes color in crystal. The Zeeman
interaction, the weak hyperfine interaction and the crystal field interaction
due to the environments of the impurity ions will be calculated. Furthermore,
the relation between the resonance magnetic field positions in the ESR spectra
and the applied magnetic field directions will reflect the impurity ion site
symmetry. The change in the crystal field parameters of heat-treated zircon at
different atmospheres were related to the change in the color of zircon.",1810.00941v1
2018-10-24,Tuning from failed superconductor to failed insulator with magnetic field,"Do charge modulations compete with electron pairing in high-temperature
copper-oxide superconductors? We investigated this question by suppressing
superconductivity in a stripe-ordered cuprate compound at low temperature with
high magnetic fields. With increasing field, loss of three-dimensional
superconducting order is followed by reentrant two-dimensional
superconductivity and then an ultra-quantum metal phase. Circumstantial
evidence suggests that the latter state is bosonic and associated with the
charge stripes. These results provide experimental support to the theoretical
perspective that local segregation of doped holes and antiferromagnetic spin
correlations underlies the electron-pairing mechanism in cuprates.",1810.10646v2
2018-10-30,Discovery of Ordered Vortex Phase in Multiferroic Oxide Superlattices,"Ferroics, characterized by a broken symmetry state with nonzero elastic,
polar, or magnetic order parameters $\vec{u}$, are recognized platforms for
staging and manipulating topologically-protected structures as well as for
detecting unconventional topological phenomena. The unrealized possibility of
producing ordered topological phases in magnetoelectric multiferroics,
exhibiting coupled magnetic and polar order parameters, is anticipated to
engender novel functionality and open avenues for manipulating topological
features. Here, we report the discovery of an ordered $\pi_1$-$S_\infty$ vortex
phase within single-phase magnetoelectric multiferroic BiFeO$_3$. The phase,
characterized by positive topological charge and chiral staggering, is realized
in coherent TbScO$_3$ and BiFeO$_3$ superlattices and established via the
combination of direct- and Fourier-space analyses. Observed order-parameter
morphologies are reproduced with a field model describing the local
order-parameter stiffness and competing non-local dipole-dipole interactions.
Anisotropies canting the order parameter towards $\left<100\right>$ suppress
chiral staggering and produced a competing $\pi_1$-$C_{\infty v}$ vortex phase
in which cores are centered.",1810.12895v1
2019-06-26,k-Resolved electronic structure of buried heterostructure and impurity systems by soft-X-ray ARPES,"Angle-resolved photoelectron spectroscopy (ARPES) is the main experimental
tool to explore electronic structure of solids resolved in the electron
momentum k . Soft-X-ray ARPES (SX-ARPES), operating in a photon energy range
around 1 keV, benefits from enhanced probing depth compared to the conventional
VUV-range ARPES, and elemental/chemical state specificity achieved with
resonant photoemission. These advantages make SX-ARPES ideally suited for
buried heterostructure and impurity systems, which are at the heart of current
and future electronics. These applications are illustrated here with a few
pioneering results, including buried quantum-well states in semiconductor and
oxide heterostructures, their bosonic coupling critically affecting electron
transport, magnetic impurities in diluted magnetic semiconductors and
topological materials, etc. High photon flux and detection efficiency are
crucial for pushing the SX-ARPES experiment to these most photon-hungry cases.",1906.11025v1
2019-06-28,Anomalous Hall and Nernst effects in a two-dimensional electron gas with an anisotropic cubic Rashba spin-orbit interaction,"The anomalous Hall and Nernst effects are considered theoretically within
Matsubara-Green's function formalism. The effective Hamiltonian of a magnetized
two-dimensional electron gas with cubic Rashba spin-orbit interaction may
describe transport properties of electronic states at the interfaces or
surfaces of perovskite oxides or another type of heterostructures that, due to
symmetry, may be described by the same effective model. In the quasi-ballistic
limit, both effects are determined by the topological (Fermi sea) contribution
whereas the states at the Fermi level gives a negligibly small response. For a
wide range of parameters describing the considered system, the anomalous Nernst
conductivity reveals a change of the sign before the magnetic phase transition.",1906.12190v1
2019-06-28,"Exploring the structural , electronic and magnetic properties of cation ordered 3d-5d double perovskite Bi$_2$FeReO$_6$ and Bi$_2$FeIrO$_6$ thin-films from first-principles","We report a first-principles study of Bi-based 3$d$-5$d$ ordered double
perovskite oxides (A$_2$BB$^\prime$O$_6$) with a 3$d$ atom (Fe) at the B-site
and 5$d$ atoms (Re,Ir) at the B$^\prime$-site while keeping highly polarizable
ions (Bi$^{3+}$) at the A-site. We find that, under coherent heteroepitaxy,
Bi$_2$FeReO$_6$} exhibits a strain-driven anti-ferromagnetic insulator to
ferrimagnetic semi-metal transition, while Bi$_2$FeIrO$_6$ shows correlation
driven ferromagnetic insulator to ferrimagnetic half-metal transition with
calculated magnetic moments of 5 $\mu_B$/f.u. and 3 $\mu_B$/f.u., respectively.
These properties along with the low band gaps in the insulating phases make the
compounds appealing for spintronics applications. Furthermore, in
Bi$_2$FeIrO$_6$, the conduction and valence states are localized on different
transition metal sublattices implying more efficient electron-hole separation
upon photoexcitation, a desirable feature for photovoltaic applications.",1907.00041v1
2019-09-16,Two-dimensional transition metal oxides Mn2O3 realized quantum anomalous Hall effect,"The quantum anomalous Hall effect is a intriguing topological nontrivial
phase arising from spontaneous magnetization and spin-orbit coupling. However,
the tremendously harsh realizing requirements of the quantum anomalous Hall
effects in magnetic topological insulators of Cr or V-doped (Bi,Sb)2Te3 film,
hinder its practical applications. Here, we use first principles calculations
to predict that the three Mn2O3 structure is an intrinsic ferromagnetic Chern
insulator. Remarkably, a quantum anomalous Hall phase of Chern number C = -2 is
found, and there are two corresponding gapless chiral edge states appearing
inside the bulk gap. More interestingly, only a small tensile strain is needed
to induce the phase transition from Cmm2 and C222 phase to P6/mmm phase.
Meanwhile, a topological quantum phase transition between a quantum anomalous
Hall phase and a trivial insulating phase can be realize. The combination of
these novel properties renders the two-dimensional ferromagnet a promising
platform for high effciency electronic and spintronic applications.",1909.07019v3
2019-09-24,"Magnetism of (LaCoO$_3$)$_n$+(LaTiO$_3$)$_n$ superlattices with $n=1,2$","LaCoO$_3$ provides a poignant example of a transition metal oxide where the
cobalt cations display multiple spin states and spin transitions and which
continues to garner substantial attention. In this work, we describe first
principles studies, based on DFT+$U$ theory, of superlattices containing
LaCoO$_3$, specifically (LaCoO$_3$)$_n$+(LaTiO$_3$)$_n$ for $n=1,2$. The
superlattices show strong electron transfer from Ti to Co resulting in
Co$^{2+}$, significant structural distortions and a robust orbital polarization
of Co$^{2+}$. We predict high-spin Co$^{2+}$ and a checkerboard or G-type
antiferromagnetic (AFM) ground state. We provide a detailed analysis of the
magnetic interactions and phases in the superlattices. We predict that
ferromagnetic order on the Co${2+}$ can be stabilized by hole doping (e.g.,
replacing La by Sr) which is rather unusual for Co$^{2+}$ cations.",1909.11007v1
2019-10-30,"Emergence of Griffiths phase, re-entrant cluster glass,metamagnetic transition and field induced unusual spin dynamics in Tb2CoMnO6","The structural and magnetic properties of double perovskiteTb2CoMnO6 have
been investigated. Electronic structure analysis by XPS study reveals the
presence of mixed oxidation state (Mn4+/Mn3+ and Co2+/Co3+) of B-site ions. The
dc and ac magnetization measurements reveal different interesting phases such
as Griffith phase, re-entrant spin glass, metamagnetic steps, Hopkinson like
peak and also unusual slow relaxation. The M-H curve indicates the presence of
competing AFM/FM interactions. The disorder in Tb2CoMnO6 leads to spin
frustration at low temperature giving rise to the re-entrant spin glass.
Moreover, the field-dependent ac susceptibility studies unraveled the presence
of Hopkinson like peak associated with the domain wall motion and the large
anisotropy field. The further study yielded that the relaxation associated with
this peak is unusually slow.",1910.13734v1
2020-02-26,Gate-tuned Anomalous Hall Effect Driven by Rashba Splitting in Intermixed LaAlO3/GdTiO3/SrTiO3,"The Anomalous Hall Effect (AHE) is an important quantity in determining the
properties and understanding the behavior of the two-dimensional electron
system forming at the interface of SrTiO3-based oxide heterostructures. The
occurrence of AHE is often interpreted as a signature of ferromagnetism, but it
is becoming more and more clear that also paramagnets may contribute to AHE. We
studied the influence of magnetic ions by measuring intermixed
LaAlO3/GdTiO3/SrTiO3 at temperatures below 10 K. We find that, as function of
gate voltage, the system undergoes a Lifshitz transition, while at the same
time an onset of AHE is observed. However, we do not observe clear signs of
ferromagnetism. We argue the AHE to be due to the change in Rashba spin-orbit
coupling at the Lifshitz transition and conclude that also paramagnetic moments
which are easily polarizable at low temperatures and high magnetic filds lead
to the presence of AHE, which needs to be taken into account when extracting
carrier densities and mobilities.",2002.11408v1
2020-12-18,Spin and charge order in doped spin-orbit coupled Mott insulators,"We study a two-dimensional single band Hubbard Hamiltonian with antisymmetric
spin-orbit coupling. We argue that this is the minimal model to understand the
electronic properties of locally non-centrosymmetric transition-metal (TM)
oxides such as Sr$_2$IrO$_4$. Based on exact diagonalizations of small clusters
and the random phase approximation, we investigate the correlation effects on
charge and magnetic order as a function of doping and of the TM-oxygen-TM bond
angle $\theta$. For small doping and $\theta$ $\lesssim$ $15^\circ$ we find
dominant commensurate in-plane antiferromagnetic fluctuations while
ferromagnetic fluctuations dominate for $\theta$ $\gtrsim$ $25^\circ$.
Moderately strong nearest-neighbor Hubbard interactions can also stabilize a
charge density wave order. Furthermore, we compare the dispersion of magnetic
excitations for the hole-doped case to resonant inelastic X-ray scattering data
and find good qualitative agreement.",2012.10479v1
2012-05-22,"Thickness dependence of magnetic properties of (Ga,Mn)As","We report on a monotonic reduction of Curie temperature in dilute
ferromagnetic semiconductor (Ga,Mn)As upon a well controlled
chemical-etching/oxidizing thinning from 15 nm down to complete removal of the
ferro- magnetic response. The effect already starts at the very beginning of
the thinning process and is accompanied by the spin reorientation transition of
the in-plane uniaxial anisotropy. We postulate that a negative gradient along
the growth direction of self-compensating defects (Mn interstitial) and the
presence of surface donor traps gives quantitative account on these effects
within the p-d mean field Zener model with adequate mod- ifications to take a
nonuniform distribution of holes and Mn cations into account. The described
here effects are of practical importance for employing thin and ultrathin
layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like
resonant tunneling devices in particular.",1205.4824v1
2017-05-12,Intricacies of the Co$^{3+}$ spin state in Sr$_2$Co$_{0.5}$Ir$_{0.5}$O$_4$: an x-ray absorption and magnetic circular dichroism study,"We report on a combined soft x-ray absorption and magnetic circular dichroism
(XMCD) study at the Co-$L_{3,2}$ on the hybrid 3$d$/5$d$ solid state oxide
Sr$_2$Co$_{0.5}$Ir$_{0.5}$O$_4$ with the K$_2$NiF$_4$ structure. Our data
indicate unambiguously a pure high spin state $(S=2)$ for the Co$^{3+}$
(3$d^6$) ions with a significant unquenched orbital moment $L_z/2S_z=0.25$
despite the sizeable elongation of the CoO$_6$ octahedra. Using quantitative
model calculations based on parameters consistent with our spectra, we have
investigated the stability of this high spin state with respect to the
competing low spin and intermediate spin states.",1705.04550v1
2017-05-23,"Unexpected 3+ valence of iron in FeO$_2$, a geologically important material lying ""in between"" oxides and peroxides","Recent discovery of pyrite FeO$_2$, which can be an important ingredient of
the Earth's lower mantle and which in particular may serve as an extra source
of water in the Earth's interior, opens new perspectives for geophysics and
geochemistry, but this is also an extremely interesting material from physical
point of view. We found that in contrast to naive expectations Fe is nearly 3+
in this material, which strongly affects its magnetic properties and makes it
qualitatively different from well known sulfide analogue - FeS$_2$. Doping,
which is most likely to occur in the Earth's mantle, makes FeO$_2$ much more
magnetic. In addition we show that unique electronic structure places FeO$_2$
""in between"" the usual dioxides and peroxides making this system interesting
both for physics and solid state chemistry.",1705.08085v2
2017-09-11,"The effect of double counting, spin density, and Hund interaction in the different DFT+$U$ functionals","A systematic comparative study has been performed to better understand
DFT$+U$ (density functional theory + $U$) method. We examine the effect of
choosing different double counting and exchange-correlation functionals. The
calculated energy distribution and the Hund-$J$ dependence of potential profile
for representative configurations clearly show the different behaviors of each
DFT$+U$ formalism. In particular, adopting spin-dependent exchange-correlation
functionals likely leads to undesirable magnetic solution. Our analyses are
further highlighted by real material examples ranging from insulating oxides
(MnO and NiO) to metallic magnetic systems (SrRuO$_3$ and BaFe$_2$As$_2$). The
current work sheds new light on understanding DFT$+U$ and provides a guideline
to use the related methods.",1709.03214v2
2017-09-13,Vortex Variable Range Hopping in a Conventional Superconducting Film,"The behavior of a disordered amorphous thin film of superconducting Indium
Oxide has been studied as a function of temperature and magnetic field applied
perpendicular to its plane. A superconductor-insulator transition has been
observed, though the isotherms do not cross at a single point. The curves of
resistance vs. temperature on the putative superconducting side of this
transition, where the resistance decreases with decreasing temperature, obey
two-dimensional Mott variable-range hopping of vortices over wide ranges of
temperature and resistance. To estimate the parameters of hopping, the film is
modeled as a granular system and the hopping of vortices is treated in a manner
analogous to hopping of charges. The reason the long range interaction between
vortices over the range of magnetic fields investigated does not lead to a
stronger variation of resistance with temperature than that of two-dimensional
Mott variable-range hopping remains unresolved.",1709.04128v2
2017-09-25,Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2,"Ferromagnetic van der Waals (vdW) materials are in demand for spintronic
devices with all-two-dimensional-materials heterostructures. Here, we
demonstrate mechanical exfoliation of magnetic-atom-intercalated transition
metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such
intercalated materials were thought difficult to exfoliate. Magnetotransport in
exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering
below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic
anisotropy; these are identical to its bulk properties. Further, van der Waals
heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet
Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated
heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide
tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing
possible spin injection and detection with these exfoliatable ferromagnetic
materials through the vdW junction.",1709.08313v1
2017-09-25,Electrically detected magnetic resonance of carbon dangling bonds at the Si-face 4H-SiC/SiO$_2$ interface,"SiC based metal-oxide-semiconductor field-effect transistors (MOSFETs) have
gained a significant importance in power electronics applications. However,
electrically active defects at the SiC/SiO$_2$ interface degrade the ideal
behavior of the devices. The relevant microscopic defects can be identified by
electron paramagnetic resonance (EPR) or electrically detected magnetic
resonance (EDMR). This helps to decide which changes to the fabrication process
will likely lead to further increases of device performance and reliability.
EDMR measurements have shown very similar dominant hyperfine (HF) spectra in
differently processed MOSFETs although some discrepancies were observed in the
measured $g$-factors. Here, the HF spectra measured of different SiC MOSFETs
are compared and it is argued that the same dominant defect is present in all
devices. A comparison of the data with simulated spectra of the C dangling bond
(P$_\textrm{bC}$) center and the silicon vacancy (V$_\textrm{Si}$) demonstrates
that the P$_\textrm{bC}$ center is a more suitable candidate to explain the
observed HF spectra.",1709.08664v1
2018-08-14,Engineering the spin couplings in atomically crafted spin chains on an elemental superconductor,"Magnetic atoms on a superconductor give rise to Yu-Shiba-Rusinov (YSR) states
within the superconducting energy gap. A spin chain of magnetic adatoms on an
s-wave superconductor may lead to topological superconductivity accompanied by
the emergence of Majorana modes at the chain ends. For their usage in quantum
computation, it is a prerequisite to artificially assemble the chains and
control the exchange couplings between the spins in the chain and in the
substrate. Here, using a scanning tunneling microscope tip, we demonstrate
engineering of the energy levels of the YSR states by placing interstitial Fe
atoms in close proximity to adsorbed Fe atoms on an oxidized Ta surface. Based
on this prototype platform, we show that the interaction within a long chain
can be strengthened by linking the adsorbed Fe atoms with the interstitial
ones. Our work adds an important step towards the controlled design and
manipulation of Majorana end states.",1808.04641v1
2019-02-12,Ultra-low damping in lift-off structured yttrium iron garnet thin films,"We show that using maskless photolithography and the lift-off technique,
patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
high crystalline quality, low surface roughness, and the effective
magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
5x10-4. The obtained structures have well-defined sharp edges which along with
good structural and magnetic film properties pave a path in the fabrication of
high-quality magnonic circuits and oxide-based spintronic devices.",1902.04605v1
2019-04-03,"Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4","Using density-functional theory calculations and experimental investigations
on structural, magnetic and dielectric properties, we have elucidated a unique
tetragonal ground state for MnTi2O4, a Ti^{3+} (3d^1)-ion containing
spinel-oxide. With lowering of temperature around 164 K, cubic MnTi2O4
undergoes a structural transition into a polar P4_1 tetragonal structure and at
further lower temperatures, around 45 K, the system undergoes a paramagnetic to
ferrimagnetic transition. Magnetic superexchange interactions involving Mn and
Ti spins and minimization of strain energy associated with co-operative
Jahn-Teller distortions plays a critical role in stabilization of the unique
tetramer-orbital ordered ground state which further gives rise to lattice
chirality through subtle Ti-Ti bond-length modulations.",1904.01792v1
2019-04-11,Triangular array of iron-oxide nanoparticles: A simulation study of intra- and inter-particle magnetism,"A study of spherical maghemite nanoparticles on a two dimensional triangular
array was carried out using a stochastic Landau-Lifshitz-Gilbert (sLLG)
approach. The simulation method was first validated with a triangular array of
simple dipoles, where results show the expected phase transition to a
ferromagnetic state at a finite temperature. The ground state exhibited a
continuous degeneracy that was lifted by an order-from-disorder mechanism at
infinitesimal temperatures with the appearance of a six-fold planar anisotropy.
The nanoparticle array consisted of 7.5 nm diameter maghemite spheres with
bulk-like superexchange interactions between Fe-ions in the core, and weaker
exchange between surface Fe-ions and a radial anisotropy. The triangular
nanoparticle array ordered at the same reduced temperature as the simple dipole
array, but exhibited different behaviour at low temperatures due to the surface
anisotropy. We find that the vacancies on the octahedral sites in the
nanoparticles combine with the surface anisotropy to produce an effective
random temperature-dependent anisotropy for each particle. This leads to a
reduction in the net magnetization of the nanoparticle array at zero
temperature compared to the simple dipole array.",1904.05515v1
2019-04-11,Study of soft/hard bimagnetic CoFe2/CoFe2O4 nanocomposite,"We report an experimental study of the bimagnetic nanocomposites
CoFe2/CoFe2O4.The precursor material, CoFe2O4 was prepared using the
conventional stoichiometric combustion method. The nanocomposite CoFe2/CoFe2O4
was obtained by total reduction of CoFe2O4 using a thermal treatment at 350oC
in H2 atmospheres following a partial oxidation in O2 atmospheres at 380oC
during 120; 30; 15, 10, and 5 min. The X-ray diffraction and Mossbauer
spectroscopy confirmed the formation the material CoFe2/CoFe2O4 The magnetic
hysteresis with different saturation magnetization confirms the formation of
the CoFe2/CoFe2O4 with different content of CoFe2O4. The high energy milling to
the precursor material increase the coercivity from 1.0 to 3.3 kOe, however the
same effect was not observed to the CoFe2/CoFe2O4 material.",1904.05984v1
2019-07-31,Perspective: Heusler interfaces -- opportunities beyond spintronics?,"Heusler compounds, in both cubic and hexagonal polymorphs, exhibit a
remarkable range of electronic, magnetic, elastic, and topological properties,
rivaling that of the transition metal oxides. To date, research on these
quantum materials has focused primarily on bulk magnetic and thermoelectric
properties or on applications in spintronics. More broadly, however, Heuslers
provide a platform for discovery and manipulation of emergent properties at
well-defined crystalline interfaces. Here, motivated by advances in the
epitaxial growth of layered Heusler heterostructures, I present a vision for
Heusler interfaces, focusing on the frontiers and challenges that lie beyond
spintronics. The ability to grow these materials epitaxially on technologically
important semiconductor substrates, such as GaAs, Ge, and Si, provides a direct
path for their integration with modern electronics. Further advances will
require new methods to control the stoichiometry and defects to ""electronic
grade"" quality, and to control the interface abruptness and ordering at the
atomic scale.",1908.00101v1
2019-08-14,Spin-orbital glass transition in a model of a frustrated pyrochlore magnet without quenched disorder,"We show theoretically that spin and orbital degrees of freedom in the
pyrochlore oxide Y2Mo2O7, which is free of quenched disorder, can exhibit a
simultaneous glass transition, working as dynamical randomness to each other.
The interplay of spins and orbitals is mediated by the Jahn-Teller lattice
distortion that selects the choice of orbitals, which then generates variant
spin exchange interactions ranging from ferromagnetic to antiferromagnetic
ones. Our Monte Carlo simulations detect the power-law divergence of the
relaxation times and the negative divergence of both the magnetic and
dielectric non-linear susceptibilities, resolving the long-standing puzzle on
the origin of the disorder-free spin glass.",1908.05070v3
2019-08-16,Metallic liquid H3O in a thin-shell zone inside Uranus and Neptune,"The Solar System harbors deep unresolved mysteries despite centuries-long
study. A highly intriguing case concerns anomalous non-dipolar and
non-axisymmetric magnetic fields of Uranus and Neptune that have long eluded
explanation by the prevailing theory. A thin-shell dynamo conjecture captures
observed phenomena but leaves unexplained fundamental material basis and
underlying mechanism. Here, we report the discovery of trihydrogen oxide (H3O)
in metallic liquid state stabilized at extreme pressure and temperature
conditions inside these icy planets. Calculated stability pressure field
compared to known pressure-radius relation for Uranus and Neptune places
metallic liquid H3O in a thin-shell zone near planetary cores. These findings
from accurate quantum mechanical calculations rationalize the empirically
conjectured thin-shell dynamo model and establish key physical benchmarks that
are essential to elucidating the enigmatic magnetic-field anomaly of Uranus and
Neptune, resolving a major mystery in planetary science.",1908.05821v1
2019-08-18,Conductivity noise across temperature driven transitions of rare-earth nickelate heterostructures,"The metal-insulator transition (MIT) of bulk rare-earth nickelates is
accompanied by a simultaneous charge ordering (CO) transition. We have
investigated low-frequency resistance fluctuations (noise) across the MIT and
magnetic transition of [EuNiO$_3$/LaNiO$_3$] superlattices, where selective
suppression of charge ordering has been achieved by mismatching the
superlattice periodicity with the periodicity of charge ordering. We have
observed that irrespective of the presence/absence of long-range CO, the noise
magnitude is enhanced by several orders with strong non-1/$f$ ($f$ = frequency)
component when the system undergoes MIT and magnetic transition. The higher
order statistics of resistance fluctuations reveal the presence of strong
non-Gaussian components in both cases, further indicating inhomogeneous
electrical transport arising from the electronic phase separation.
Specifically, we find almost three orders of magnitude smaller noise in the
insulating phase of the sample without long-range CO compared to the sample
with CO. These findings suggest that digital synthesis can be a potential route
to implement electronic transitions of complex oxides for device application.",1908.06413v1
2019-08-28,A Cantilever Torque Magnetometry Method for the Measurement of Hall Conductivity of Highly Resistive Samples,"We present the first measurements of Hall conductivity utilizing a new torque
magnetometry method designed for insulators. A Corbino disk exhibits a magnetic
dipole moment proportional to Hall conductivity when voltage is applied across
a test material. This magnetic dipole moment can be measured through torque
magnetometry. The symmetry of this contactless technique allows for the
measurement of Hall conductivity in previously inaccessible materials. Finally,
a low-temperature noise bound, the lack of systematic errors on dummy devices,
and a measurement of the Hall conductivity of sputtered indium tin oxide
demonstrate the efficacy of the technique.",1908.10857v3
2019-12-01,Coarse-graining in micromagnetic simulations of dynamic hysteresis loops,"Micromagnetic simulations based on the stochastic Landau-Lifshitz-Gilbert
equation are used to calculate dynamic magnetic hysteresis loops relevant to
magnetic hyperthermia. With the goal to effectively simulate room-temperature
loops for large iron-oxide-based systems at relatively slow sweep rates on the
order of 1 Oe/ns or less, a previously derived renormalization group approach
for coarse-graining (Grinstein and Koch, Phys. Rev. Lett. 20, 207201, 2003) is
modified and applied to calculating loops for a magnetite nanorod. The nanorod
modelled is the building block for larger nanoparticles that were employed in
preclinical studies (Dennis et al., Nanotechnology 20, 395103, 2009). The
scaling algorithm is shown to produce nearly identical loops over several
decades in the model grain size. Sweep-rate scaling involving the Gilbert
damping parameter is also demonstrated to allow orders of magnitude speed-up of
the loop calculations.",1912.00310v3
2020-02-29,Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films,"We investigate the transfer and control of nonreciprocity through magnons
themselves in permalloy thin films deposited on surface oxide silicon
substrate. Evidences of nonreciprocal emergence of hybridized dipole exchange
magnons (spin waves) at two permalloy surfaces are provided by studying magnon
transmission and asymmetry, via Brillouin light scattering measurements. The
dipole dominated spin wave and exchange dominated spin wave are found to be
localized near the top and bottom surfaces, respectively, and traveling along
opposite directions. The nonreciprocity and the localization are intertwined
and ca n be tuned by an in plane magnetic field. The effects are well explained
by the magnetostatic theory and can be quantitatively reproduced by the
micromagnetic simulations. Our findings provide a simple and flexible approach
to nonreciprocal all magnon logi c devices with highly compatible with silicon
based integrated circuit technology.",2003.00230v4
2020-03-20,Spin-orbit-coupled metal candidate PbRe2O6,"We study the lead rhenium oxide PbRe2O6 as a candidate spin-orbit-coupled
metal (SOCM), which has attracted much attention as a testing ground for
studying unconventional Fermi liquid instability associated with a large
spin-orbit interaction. The compound comprises a stack of modulated honeycomb
lattices made of Re5+ (5d2) ions in a centrosymmetric R-3m structure at room
temperature. Resistivity, magnetic susceptibility, and heat capacity
measurements using single crystals reveal two successive first-order phase
transitions at Ts1 = 265 K and Ts2 = 123 K. At Ts1, the magnetic susceptibility
is enormously reduced and a structural transition to a monoclinic structure
takes place, while relatively small changes are observed at Ts2. Surprisingly,
PbRe2O6 bears a close resemblance to another SOCM candidate Cd2Re2O7 despite
crucial differences in the crystal structure and probably in the electronic
structure, suggesting that PbRe2O6 is an SOCM.",2003.09051v1
2020-08-05,Spin filtering in germanium/silicon core/shell nanowires with pseudo-helical gap,"Semiconductors with strong spin-orbit interactions can exhibit a helical gap
with spin-momentum locking opened by a magnetic field. Such a gap is highly
spin selective as a result of a topologically protected spin-momentum locking,
which can be used for spin filtering. We experimentally demonstrate such a spin
filtering effect in a quasi-ballistic p-type germanium/silicon core/shell
nanowire (NW), which possesses a pseudo-helical gap without the application of
magnetic field. Polarized hole spin injection to the NW is achieved using
cobalt ferromagnetic contacts with controlled natural surface oxide on the NW
as a tunnel barrier. Local and nonlocal spin valve effects are measured as the
verification of polarized spin transport in the NW outside the helical gap. We
electrically tune the NW into the helical gap by scanning its chemical
potential with a gate. A hysteresis loop with three resistance states is
observed in the local spin valve geometry, as an evidence of spin filtering in
the helical gap.",2008.01952v1
2020-08-18,Near-Zero-Field Spin-Dependent Recombination Current and Electrically Detected Magnetic Resonance from the Si/SiO$_2$ interface,"Dielectric interfaces critical for metal-oxide-semiconductor (MOS) electronic
devices, such as the Si/SiO$_2$ MOS field effect transistor (MOSFET), possess
trap states that can be visualized with electrically-detected spin resonance
techniques, however the interpretation of such measurements has been hampered
by the lack of a general theory of the phenomena. This article presents such a
theory for two electrical spin-resonance techniques, electrically detected
magnetic resonance (EDMR) and the recently observed near-zero field
magnetoresistance (NZFMR), by generalizing Shockley Read Hall trap-assisted
recombination current calculations via stochastic Liouville equations. Spin
mixing at this dielectric interface occurs via the hyperfine interaction, which
we show can be treated either quantum mechanically or semiclassically, yielding
distinctive differences in the current across the interface. By analyzing the
bias dependence of NZFMR and EDMR, we find that the recombination in a
Si/SiO$_2$ MOSFET is well understood within a semiclassical approach.",2008.08121v1
2020-08-28,Novel Copper Fluoride Analogs of Cuprates,"On the basis of the first-principles evolutionary crystal structure
prediction of stable compounds in the Cu-F system, we predict two
experimentally unknown stable phases -- Cu2F5 and CuF3. Cu2F5 comprises two
interacting magnetic subsystems with the Cu atoms in the oxidation states +2
and +3. CuF3 contains magnetic Cu 3+ ions forming a lattice with the
antiferromagnetic coupling. We showed that some or all of Cu 3+ ions can be
reduced to Cu 2+ by electron doping, as in the well known KCuF3. Significant
similarities between the electronic structures calculated in the framework of
DFT+U suggest that doped CuF3 and Cu2F5 may exhibit high-temperature
superconductivity with the same mechanism as in cuprates.",2008.12491v1
2020-10-21,Interface combinatorial pulsed laser deposition to enhance heterostructures functional properties,"In this chapter we will describe a new development of combinatorial pulsed
laser deposition (CPLD) which targets the exploration of interface libraries.
The idea is to modulate continuously the composition of interfaces on a few
atomic layers in order to alter their functional properties. This unique
combinatorial synthesis of interfaces is possible due to very specific PLD
characteristics. The first one is its well-known ability for complex oxide
stoichiometry transfer from the target to the film. The second one is the layer
by layer control of thin film growth at the atomic level using in-situ RHEED
characterization. The third one relates to the directionality of the ablated
plume which allows for selective area deposition on the substrate using a
mobile shadow-mask. However PLD also has some limitations and important PLD
aspects to be considered for reliable CPLD are reviewed. Multiple examples
regarding the control of interface magnetism in magnetic tunnel junctions and
energy band and Schottky barrier height tuning in ferroelectric tunable
capacitors are presented.",2010.10773v2
2020-10-27,"Predicting the Structural, Electronic and Magnetic Properties of Few Atomic-layer Polar Perovskite","Density functional theory (DFT) calculations are performed to predict the
structural, electronic and magnetic properties of electrically neutral or
charged few-atomic-layer (AL) oxides whose parent systems are based on polar
perovskite $KTaO_{3}$. Their properties vary greatly with the number of ALs
($n_{AL}$) and the stoichiometric ratio. In the few-AL limit ($n_{AL}\leqslant
14$), the even AL (EL) systems with chemical formula $(KTaO_{3})_{n}$ are
semiconductors, while the odd AL (OL) systems with formula
($K_{n+1}Ta_{n}O_{3n+1}$ or $K_{n}Ta_{n+1}O_{3n+2}$) are half-metal except for
the unique $KTa_{2}O_{5}$ case which is a semiconductor due to the large
Peierls distortions. After reaching certain critical thickness ($n_{AL}>14$),
the EL systems show ferromagnetic surface states, while ferromagnetism
disappears in the OL systems. These predictions from fundamental complexity of
polar perovskite when approaching the two-dimensional (2D) limit may be helpful
for interpreting experimental observations later.",2010.13977v1
2020-10-28,Complete phase diagram of Sr$_{1-x}$La$_x$FeO$_3$ with versatile magnetic and charge ordering,"A detailed electronic phase diagram of perovskite-type oxides
Sr$_{1-x}$La$_x$FeO$_3$ $(0\leq x \leq 0.5)$ was established by synchrotron
X-ray diffraction, magnetization, and transport measurements for
polycrystalline samples synthesized by a high-pressure technique. Among three
kinds of helimagnetic phases in SrFeO$_3$ at zero field, two of them showing
multiple-${\it q}$ helimagnetic spin textures tend to rapidly disappear in
cubic symmetry upon the La substitution with $x$ less than 0.1, which
accompanies the loss of metallic nature. On the other hand, the third
helimagnetic phase apparently remains robustly in Sr$_{1-x}$La$_x$FeO$_3$ with
$x$ higher than 0.1, followed by merging to the spin/charge ordered phase with
$x\sim 1/3$. We propose an important role of itinerant ligand holes on the
emergence of multiple-${\it q}$ states and a possible link between the third
(putative single-${\it q}$) helimagnetic phase in SrFeO$_3$ and the spin/charge
ordered phase in Sr$_{2/3}$La$_{1/3}$FeO$_3$.",2010.14966v1
2020-11-06,Template-Free Preparation of Thermoresponsive Mag-netic Cilia Compatible with Biological Conditions,"Bio-inspired materials are commonly used in the development of functional
devices. The fabrication of artificial cilia mimicking the biological functions
has emerged as a promising strategy for fluid manipulation in miniaturized
systems. In this study, we propose a different physicochemical insight for the
preparation of magnetic cilia based on the temperature-triggered reversible
assembly of coated iron oxide nanoparticles in a bio-compatible template-free
approach. The length of the prepared cilia could be tuned between 10 and 100
microns reaching aspect ratios up to 100 in a very dense array of flexible
structures with persistence lengths around 8 microns. Magnetic actuation of the
cilia revealed robust structures (over several hours of actuation) with a wide
range of bending amplitudes resulting from high susceptibility of the
filaments. The results demonstrate that the proposed strategy is an efficient
and versatile alternative for templated fabrication methods and producing cilia
with remarkable characteristics and dimensions within the template-free
approaches.",2011.03347v1
2020-11-14,Fabrication Of Economical Signal Amplified Vibrating Sample Magnetometer With Spiral Designed Detector,"The design and fabrication of a cost-effective vibrating sample magnetometer
are explained. Improvement in the detected signal can be obtained using an
operational amplifier circuit. The fabricated spiral detection coil design
enhances the induced voltage obtained as shielding flux is reduced. A homemade
setup is obtained by taking a woofer as an actuator and plexiglass as the
vibrating medium. Lock-in amplifier analyzed the booster enhanced induced
voltage signal by the principle of phase detection. Study of amplified and non
amplified signals from the Nickel (99% purity) sample was done. Conversion of
induced voltage to magnetization was done by calibration incorporating the
coercivity and retentivity measurement. Magnetic oxide can be analyzed using
this cost-effective designed Vibrating sample magnetometer. The data obtained
from the VSM can conclude the successful operation of the designed
magnetometer.",2011.07253v1
2020-11-16,"First-principles study of the electronic, magnetic, and crystal structure of perovskite molybdates","The molybdate oxides SrMoO$_3$, PbMoO$_3$, and LaMoO$_3$ are a class of
metallic perovskites that exhibit interesting properties including high
mobility, and unusual resistivity behavior. We use first-principles methods
based on density functional theory to explore the electronic, crystal, and
magnetic structure of these materials. In order to account for the electron
correlations in the partially-filled Mo $4d$ shell, a local Hubbard $U$
interaction is included. The value of $U$ is estimated via the constrained
random-phase approximation approach, and the dependence of the results on the
choice of $U$ are explored. For all materials, GGA+$U$ predicts a metal with an
orthorhombic, antiferromagnetic structure. For LaMoO$_3$, the $Pnma$ space
group is the most stable, while for SrMoO$_3$ and PbMoO$_3$, the $Imma$ and
$Pnma$ structures are close in energy. The $R_4^+$ octahedral rotations for
SrMoO$_3$ and PbMoO$_3$ are found to be overestimated compared to the
experimental low-temperature structure.",2011.08323v2
2020-11-24,Uniaxial Néel Vector Control in Perovskite Oxide Thin Films by Anisotropic Strain Engineering,"Antiferromagnetic thin films typically exhibit a multi-domain state, and
control of the antiferromagnetic N\'eel vector is challenging as
antiferromagnetic materials are robust to magnetic perturbations. By relying on
anisotropic in-plane strain engineering of epitaxial thin films of the
prototypical antiferromagnetic material LaFeO3, uniaxial N\'eel vector control
is demonstrated. Orthorhombic (011)- and (101)-oriented DyScO3, GdScO3 and
NdGaO3 substrates are used to engineer different anisotropic in-plane strain
states. The anisotropic in-plane strain stabilises structurally monodomain
monoclinic LaFeO3 thin films. The uniaxial N\'eel vector is found along the
tensile strained b axis, contrary to bulk LaFeO3 having the N\'eel vector along
the shorter a axis, and no magnetic domains are found. Hence, anisotropic
strain engineering is a viable tool for designing unique functional responses,
further enabling antiferromagnetic materials for mesoscopic device technology.",2011.12056v1
2020-11-27,Understanding doping of quantum materials,"Doping mobile carriers into ordinary semiconductors such as Si, GaAs, and ZnO
was the enabling step in the electronic and optoelectronic revolutions. The
recent emergence of a class of ""Quantum Materials"", where uniquely quantum
interactions between the components produce specific behaviors such as
topological insulation, unusual magnetism, superconductivity,
spin-orbit-induced and magnetically-induced spin splitting, polaron formation,
and transparency of electrical conductors, pointed attention to a range of
doping-related phenomena associated with chemical classes that differ from the
traditional semiconductors. These include wide-gap oxides, compounds containing
open-shell d electrons, and compounds made of heavy elements yet having
significant band gaps. The atomistic electronic structure theory of doping that
has been developed over the past two decades in the sub-field of semiconductor
physics has recently been extended and applied to quantum materials. The
present review focuses on explaining the main concepts needed for a basic
understanding of the doping phenomenology and indeed peculiarities in quantum
materials from the perspective of condensed matter theory, with the hope of
forging bridges to the chemists that have enabled the synthesis of some of the
most interesting compounds in this field.",2011.13521v1
2020-11-27,d0 Ferromagnetism in Ag-doped Monoclinic ZrO2 Compounds,"Recently d0 or intrinsic ferromagnetism was believed to provide an
alternative pathway to transition metal induced ferromagnetism in oxide. In
pursuit of augmenting the area of d0 ferromagnetism; we have undertaken to
study the crystal structure and magnetic properties of Ag-doped ZrO2 compounds.
Polycrystalline samples of Zr1-xAgxO2 (with x=0, 0.02, 0.04, 0.06 and 0.08)
were prepared by solid-state reaction route. All the prepared compounds are
found to crystallize in monoclinic symmetry of ZrO2. In our study, pure ZrO2
compound exhibits paramagnetic behavior. However, the Ag-doped ZrO2 compounds
exhibit ferromagnetic to paramagnetic transition. The Curie temperature was
found to increase from 28.7 K for x=0.02 to 173.2 K for x= 0.08 doped ZrO2.
Thus, the introduction of Ag in ZrO2 induces ferromagnetism with a large
ThetaC. The measurements of hysteresis curves indicate that Ag doped ZrO2
compounds exhibit hysteresis loops with a coercivity of around 1350 Oe.
Moreover, increase in Ag concentration resulted increase in the value of
saturation magnetization (MS); the maximum value of MS was recorded as 0.01
{\mu}B/Ag ion for x= 0.06 sample. The sintering of sample at high temperature
(13500C) diminishes the ferromagnetism and it leads to paramagnetic behaviour.",2011.13727v1
2021-03-10,Crystal Growth of a New 8H Perovskite Sr8Os6.3O24 Exhibiting High TC Ferromagnetism,"Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24
have been synthesized, and structural and magnetic properties have been
determined. The compound crystallizes in a hexagonal cell with lattice
parameters a = 9.6988(3) {\AA} and c = 18.1657(5) {\AA}. The structure is an
eight-layered hexagonal B-site deficient perovskite with the layer sequence
(ccch)2 and represents the first example of a hexagonal structure among 5d
oxides adopting a twin option. The sample shows spontaneous ferromagnetic
magnetization below 430 K with a small saturation moment of 0.11 {\mu}B/Os ion.
This is the highest Curie temperature (TC) reported for any bulk perovskite
containing only 5d ions at the B site.",2103.06305v1
2021-05-21,Photo-induced Antiferromagnetic-ferromagnetic Transition and Electronic Structure Modulation in GdBaCo$_2$O$_{5.5}$ Thin Film,"We investigate both the ferromagnetic (FM) and antiferromagnetic (AFM)
ultrafast dynamics of a strongly correlated oxide system, GdBaCo$_2$O$_{5.5}$
thin film, by time-resolved x-ray magnetic circular dichroism in reflectivity
(XMCDR) and resonant magnetic x-ray diffraction (RMXD). A photo-induced AFM-FM
transition characterized by an increase of the transient XMCDR beyond the
unpumped value and a decay of RMXD was observed. The photon-energy dependence
of the transient XMCDR and reflectivity can likely be interpreted as a
concomitant photo-induced spinstate transition.",2105.10083v1
2021-06-18,Abrupt orthorhombic relaxation in compressively strained ultra-thin SrRuO3 films,"Lattice structure can dictate electronic and magnetic properties of a
material. Especially, reconstruction at a surface or heterointerface can create
properties that are fundamentally different from those of the corresponding
bulk material. We have investigated the lattice structure on the surface and in
the thin films of epitaxial SrRuO3 with the film thickness up to 22
pseudo-cubic unit cells (u.c.), using the combination of surface sensitive low
energy electron diffraction and bulk sensitive scanning transmission electron
microscopy. Our analysis indicates that, in contrast to many perovskite oxides,
the RuO6 tilt and rotational distortions appear even in single unit cell SrRuO3
thin films on cubic SrTiO3, while the full relaxation to the bulk-like
orthorhombic structure takes 3-4 u.c. from the interface for thicker films. Yet
the TiO6 octahedra of the substrate near the interface with SrRuO3 films show
no sign of distortion, unlike those near the interface with CaRuO3 films. Two
orthogonal in-plane rotated structural domains are identified. These structural
distortions are essential for the nature of the thickness dependent transport
and magnetism in ultrathin films.",2106.10204v1
2021-07-05,Collective spin and charge excitations in the $t$-$J$-$U$ model of high-$T_c$ cuprates,"The $t$-$J$-$U$ model of high-$T_c$ copper-oxide superconductors incorporates
both the on-site Coulomb repulsion and kinetic exchange interaction and yields
a semi-quantitative description of the static properties of those materials. We
extend this analysis to dynamic quantities and address collective spin- and
charge excitations in the correlated metallic state of the $t$-$J$-$U$ model.
We employ VWF+$1/\mathcal{N}_f$ approach that combines the variational wave
function (VWF) approach with the expansion in the inverse number of fermionic
flavors ($1/\mathcal{N}_f$). It is shown that the resonant (paramagnon)
contribution to the dynamic magnetic susceptibility remains robust as one
interpolates between the Hubbard- and $t$-$J$-model limits, whereas the
incoherent continuum undergoes substantial renormalization. Energy of the
collective charge mode diminishes as the strong-coupling limit is approached.
We also introduce the concept of effective kinetic exchange interaction that
allows for a unified interpretation of magnetic dynamics in the Hubbard,
$t$-$J$, and $t$-$J$-$U$ models. The results are discussed in the context of
recent resonant inelastic $x$-ray scattering experiments for the high-$T_c$
cuprates.",2107.02152v1
2021-07-26,Engineering of Ferroic Orders in Thin Films by Anionic Substitution,"Multiferroics are a unique class of materials where magnetic and
ferroelectric orders coexist. The research on multiferroics contributes
significantly to the fundamental understanding of the strong correlations
between different material degrees of freedom and provides an energy-efficient
route toward the electrical control of magnetism. While multiple ABO3 oxide
perovskites have been identified as being multiferroic, their magnetoelectric
coupling strength is often weak, necessitating the material search in different
compounds. Here, we report the observation of room-temperature multiferroic
orders in multi-anion SrNbO3-xNx thin films. In these samples, the multi-anion
state enables the room-temperature ferromagnetic ordering of the Nb
d-electrons. Simultaneously, we find ferroelectric responses that originate
from the structural symmetry breaking associated with both the off-center
displacements of Nb and the geometric displacements of Sr, depending on the
relative O-N arrangements within the Nb-centered octahedra. Our findings not
only diversify the available multiferroic material pool but also demonstrate a
new multiferroism design strategy via multi-anion engineering.",2107.12509v1
2021-08-07,Space-based weather observatory at Earth-Moon Lagrange point L1 to monitor earth's magnetotail effects on the Moon,"Lunar hematite is formed by the oxidation of iron on the surface of the Moon
by oxygen from the Earth's upper atmosphere. The Moon's surface is continuously
affected by solar particles from the sun. However, Earth's magnetic tail blocks
99 % of the solar wind and provides windows of opportunity to transport oxygen
from Earth's upper atmosphere to the Moon through magnetotail when it is in its
full moon phase. Here, we propose to place a space weather observatory at the
Earth-Moon L1 Lagrange point carrying a crucial payload onboard to study how
Earth's magnetotail causes the Moon's surface to rust. The space weather
observatory monitors the effect of Earth's magnetic field on the Moon using
advanced spectroscopic sensors from Lagrange-based stations. Earth-moon L1
Lagrange point is the key location for space-weather observation as spacecraft
near this point obtains a nearly unobstructed view of the moon. Numerical
methods needed for a high-order analytical approximation have been implemented
for more accurate predictions.",2108.03522v2
2021-10-25,Large Phonon Thermal Hall Conductivity in a Simple Antiferromagnetic Insulator,"Phonons are known to generate a thermal Hall effect in certain insulators,
including oxides with rare-earth impurities, quantum paraelectrics,
multiferroic materials and cuprate Mott insulators. In each case, a special
feature of the material is presumed relevant for the underlying mechanism that
confers chirality to phonons in a magnetic field. The question is whether a
phonon Hall effect is an unusual occurrence - linked to special characteristics
such as skew scattering off rare-earth impurities, structural domains,
ferroelectricity, ferromagnetism - or a much more common property of insulators
than hitherto believed. To help answer this question, we have turned to a
simple insulator, with none of the previously encountered special features: the
cubic antiferromagnet Cu$_3$TeO$_6$. We find that it has the largest thermal
Hall conductivity $\kappa_{\rm{xy}}$ of any insulator so far. We show that this
record-high $\kappa_{\rm{xy}}$ signal is due to phonons and it does not require
the presence of magnetic order, as it persists above the ordering temperature.
We conclude that the phonon Hall effect is likely to be a fairly common
property of solids.",2110.13277v1
2021-10-30,"Excitonic Correlations, Spin-State Ordering, and Magnetic-Field Effects in One-Dimensional Two-Orbital Hubbard Model for Spin-Crossover Region","The electronic properties of excitonic insulators have been examined
precisely in recent years. Pictures of exciton condensation may be applied to
the spin-state transition observed in perovskite cobalt oxides. We examine the
crystal-field and magnetic-field dependences of spatial spin structures on the
basis of the density matrix renormalization group method using an effective
model for the one-dimensional two-orbital Hubbard model in strong-coupling
limit. We find an excitonic insulating (EI) phase and a spin-state ordering
(SSO) phase in the intermediate region between low-spin and high-spin phases.
In the EI phase, spin-triplet excitons are spatially fluctuating due to quantum
effects, and an incommensurate spin correlation realizes. The analyses of a
spin gap and degeneracy of entanglement spectra suggest the realization of the
Haldane-like edge state in the EI phase. In the SSO phase, 3-fold or
incommensurate SSO structures realize depending on the crystal-field splitting.
These structures are stabilized as a result of the competition of exchange
interactions between spin states.",2111.00209v4
2021-12-09,Tuneable electron-magnon coupling of ferromagnetic surface states in PdCoO$_2$,"Controlling spin wave excitations in magnetic materials underpins the
burgeoning field of magnonics. Yet, little is known about how magnons interact
with the conduction electrons of itinerant magnets, or how this interplay can
be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a
strong and highly-tuneable electron-magnon coupling at the Pd-terminated
surface of the delafossite oxide PdCoO$_2$, where a polar surface charge
mediates a Stoner transition to itinerant surface ferromagnetism. We show how
the coupling can be enhanced 7-fold with increasing surface disorder, and
concomitant charge carrier doping, becoming sufficiently strong to drive the
system into a polaronic regime, accompanied by a significant quasiparticle mass
enhancement. Our study thus sheds new light on electron-magnon interactions in
solid-state materials, and the ways in which these can be controlled.",2112.04869v1
2022-01-11,Giant Valley-Polarized Spin Splittings in Magnetized Janus Pt Dichalcogenides,"We reveal giant proximity-induced magnetism and valley-polarization effects
in Janus Pt dichalcogenides (such as SPtSe), when bound to the Europium oxide
(EuO) substrate. Using first-principles simulations, it is surprisingly found
that the charge redistribution, resulting from proximity with EuO, leads to the
formation of two K and K$^{'}$valleys in the conduction bands. Each of these
valleys displays its own spin polarization and a specific spin-texture dictated
by broken inversion and time-reversal symmetries, and valley-exchange and
Rashba splittings as large as hundreds of meV. This provides a platform for
exploring novel spin-valley physics in low-dimensional semiconductors, with
potential spin transport mechanisms such as spin-orbit torques much more
resilient to disorder and temperature effects.",2201.04106v1
2022-01-18,"Characterization of the Magnetism and Conformation of Single Porphyrin Molecules Adsorbed on Surfaces, and Artificial Graphene Nanoflakes","My thesis mostly focusses on the systems of porphyrin molecules adsorbed on
single-crystalline metallic surfaces. Cyclic tetrapyrrole porphyrins play key
roles in many important chemical and biological processes, such as oxygen
transport in heme (iron porphyrin), electron transfer and oxidation reactions
in photosynthetic chlorophyll (magnesium porphyrin). Comprehensive
understanding of the magnetic and conformational properties of single porphyrin
molecules adsorbed on metallic substrates attracts intensive research interest.
In my thesis, I have studied the structural and electronics properties of
porphyrin molecules by Low-temperature scanning tunneling spectroscopy (LT-STM)
and scanning tunneling spectroscopy (STS) and theoretical methods. Owing to the
high resolution of LT-STM, both geometric and electronic properties at the
atomic level were probed. Moreover, the experimental results were understood by
comprehensive theoretical methods, i.e. density functional theory, molecular
dynamics, tight-binding and plane-wave expansion calculations.",2201.07085v2
2022-01-21,Electron Spin Resonance Scanning Tunneling Microscope of Non-Magnetic Molecules,"Electron Spin Resonance-Scanning Tunneling Microscopy (ESR-STM) of C60
radical ion on graphene is a first demonstration on radical ions. ESR-STM
signal at g=2.00 was measured in accordance with macroscopic ESR of fullerene
radical ion. The ESR-STM signal was bias voltage dependent, as it reflects the
charge state of the molecule. The signal appears in the bias voltage which
enables the ionization of the lowest unoccupied molecular orbital (LUMO)
(creation of radical anion) and the highest occupied molecular orbital (HOMO
(creation of a radical cation) of the C60 molecule when it deposited on
graphene.
  The linewidth provides information on the lifetime of the free radical. In
several experiments, a 13C hyperfine splitting was observed, and a change in
the phase of the ESR-STM peak as a function of the speed of the magnetic field
sweep was changed. This might be used to provide information on the relaxation
times of the molecules. In parallel, ESR-STM signal at g=1.6 was ascribed to
Tungsten oxide (W5+) at the tip apex, which is not bias voltage dependent.
  The ability of ESR-STM to explore non paramagnetic molecules, significantly
broadens the scope of this technique.",2201.08608v1
2022-01-31,Nuclear spin-lattice relaxation studies of Cu$_{2}$O,"We report the $^{63}$Cu and $^{65}$Cu nuclear spin-lattice relaxation rate
measurements of cuprous oxide Cu$_2$O in a zero field Cu nuclear quadrupole
resonance at $T$ = 77$-$325 K. From the detailed isotopic measurements of the
relaxation rates, we successfully estimated a finite magnetic relaxation rate
$^{63}W_M$ and a predominant nuclear quadrupole relaxation rate $^{63}W_Q$.
$^{63}W_Q$ changed as $T^{2.1}$, while $^{63}W_M$ changed as $T^{1.6}$ or
$T^{\beta}\mathrm{exp}(-\it\Delta/T)$ with $\beta$ = 0.6(3) and $\it\Delta$ =
190(62) K. The nuclear spin scattering process due to a non-degenerate Fermi
gas was discussed as a possible candidate of the magnetic relaxation.",2201.13074v3
2022-05-02,Suppression of Motion Artifacts Caused by Temporally Recurring Tracer Distributions in Multi-Patch Magnetic Particle Imaging,"Magnetic particle imaging is a tracer based imaging technique to determine
the spatial distribution of superparamagnetic iron oxide nanoparticles with a
high spatial and temporal resolution. Due to physiological constraints, the
imaging volume is restricted in size and larger volumes are covered by shifting
object and imaging volume relative to each other. This results in reduced
temporal resolution, which can lead to motion artifacts when imaging dynamic
tracer distributions. A common source of such dynamic distributions are cardiac
and respiratory motion in in-vivo experiments, which are in good approximation
periodic. We present a raw data processing technique that combines data
snippets into virtual frames corresponding to a specific state of the dynamic
motion. The technique is evaluated on the basis of measurement data obtained
from a rotational phantom at two different rotational frequencies. These
frequencies are determined from the raw data without reconstruction and without
an additional navigator signal. The reconstructed images give reasonable
representations of the rotational phantom frozen in several different states of
motion while motion artifacts are suppressed.",2205.01085v1
2022-07-15,Tunable spin and orbital Edelstein effect at (111) LaAlO$_3$/SrTiO$_3$ interface,"Converting charge current into spin current is one of the main mechanisms
exploited in spintronics. One prominent example is the Edelstein effect, namely
the generation of a magnetization in response to an external electric field,
which can be realized in systems with lack of inversion symmetry. If a system
has electrons with an orbital angular momentum character, an orbital
magnetization can be generated by the applied electric field giving rise to the
so-called orbital Edelstein effect. Oxide heterostructures are the ideal
platform for these effects due to the strong spin-orbit coupling and the lack
of inversion symmetries. Beyond a gate-tunable spin Edelstein effect, we
predict an orbital Edelstein effect an order of magnitude larger then the spin
one at the (111) LaAlO$_3$/SrTiO$_3$ interface. We model the material as a
bilayer of $t_{2g}$ orbitals using a tight-binding approach, while transport
properties are obtained in the Boltzmann approach. We give an effective model
at low filling which explains the non-trivial behaviour of the Edelstein
response, showing that the hybridization between the electronic bands crucially
impacts the Edelstein susceptibility.",2207.07663v1
2022-11-25,Possible helimagnetic order in Co4+-containing perovskites Sr1-xCaxCoO3,"We systematically synthesized perovskite-type oxides Sr1-xCaxCoO3 containing
unusually high valence Co4+ ions by a high pressure technique, and investigated
the effect of systematic lattice change on the magnetic and electronic
properties. As the Ca content x exceeds about 0.6, the structure changes from
cubic to orthorhombic, which is supported by the first-principles calculations
of enthalpy. Upon the orthorhombic distortion, the ground state remains to be
apparently ferromagnetic with a slight drop of the Curie temperature.
Importantly, the compounds with x larger than 0.8 show antiferromagnetic
behavior with positive Weiss temperatures and nonlinear magnetization curves at
lowest temperature, implying that the ground state is noncollinear
antiferromagnetic or helimagnetic. Considering the incoherent metallic behavior
and the suppression of the electronic specific heat at high x region, the
possible emergence of a helimagnetic state in Sr1-xCaxCoO3 is discussed in
terms of the band-width narrowing and the double-exchange mechanism with the
negative charge transfer energy as well as the spin frustration owing to the
next-nearest neighbor interaction.",2211.13903v1
2023-02-04,"Calculating spin-lattice interactions in ferro- and antiferromagnets: the role of symmetry, dimension and frustration","Recently, the interplay between spin and lattice degrees of freedom has
gained a lot of attention due to its importance for various fundamental
phenomena as well as for spintronic and magnonic applications. Examples are
ultrafast angular momentum transfer between the spin and lattice subsystems
during ultrafast demagnetization, frustration driven by structural distortions
in transition metal oxides, or in acoustically driven spin-wave resonances. In
this work, we provide a systematic analysis of spin-lattice interactions for
ferro- and antiferromagnetic materials and focus on the role of lattice
symmetries and dimensions, magnetic order, and the relevance of spin-lattice
interactions for angular momentum transfer as well as magnetic frustration. For
this purpose, we use a recently developed scheme which allows an efficient
calculation of spin-lattice interaction tensors from first principles. In
addition to that, we provide a more accurate and self consistent scheme to
calculate ab initio spin lattice interactions by using embedded clusters which
allows to benchmark the performance of the scheme introduced previously.",2302.02066v2
2023-03-21,Inducing or suppressing the anisotropy in multilayers based on CoFeB,"Controlling the uniaxial magnetic anisotropy is of practical interest to a
wide variety of applications. We study Co$_{40}$Fe$_{40}$B$_{20}$ single films
grown on various crystalline orientations of LiNbO$_3$ substrates and on
oxidized silicon. We identify the annealing conditions that are appropriate to
induce or suppress uniaxial anisotropy. Anisotropy fields can be increased by
annealing up to 11 mT when using substrates with anisotropic surfaces. They can
be decreased to below 1 mT when using isotropic surfaces. In the first case,
the observed increase of the anisotropy originates from the biaxial strain in
the film caused by the anisotropic thermal contraction of the substrate when
back at room temperature after strain relaxation during annealing. In the
second case, anisotropy is progressively removed by applying successive
orthogonal fields that are assumed to progressively suppress any chemical
ordering within the magnetic film. The method can be applied to CoFeB/Ru/CoFeB
synthetic antiferromagnets but the tuning of the anisotropy comes with a
decrease of the interlayer exchange coupling and a drastic change of the
exchange stiffness.",2303.11718v1
2023-03-22,Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO$_2$,"We report crystal structure and magnetic behavior of the triangular
antiferromagnet KYbO$_2$, the A-site substituted version of the quantum spin
liquid candidate NaYbO$_2$. The replacement of Na by K introduces an
anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice
expansion. Compared to NaYbO$_2$, both Curie-Weiss temperature and saturation
field are reduced by about 20% as the result of the increased Yb--O--Yb angles,
whereas the $g$-tensor of Yb$^{3+}$ becomes isotropic with $g=3.08(3)$.
Field-dependent magnetization shows the plateau at 1/2 of the saturated value
and suggests the formation of the up-up-up-down field-induced order in the
triangular AYbO$_2$ oxides (A = alkali metal), in contrast to the isostructural
selenides that exhibit the 1/3 plateau and the up-up-down field-induced order.",2303.12448v2
2023-05-12,Control of ternary alloy composition during remote epitaxy on graphene,"Understanding the sticking coefficient $\sigma$, i.e., the probability of an
adatom sticking to a surface, is essential for controlling the stoichiometry
during epitaxial film growth. However, $\sigma$ on monolayer graphene-covered
surfaces and its impact on remote epitaxy are not understood. Here, using
molecular-beam epitaxial (MBE) growth of the magnetic shape memory alloy
Ni$_2$MnGa, we show that the sticking coefficients for metals on
graphene-covered MgO (001) are less than one and are temperature and element
dependent, as revealed by ion backscattering spectrometry (IBS) and energy
dispersive x-ray spectroscopy (EDS). This lies in stark contrast with most
transition metals sticking on semiconductor and oxide substrates, for which
$\sigma$ is near unity at typical growth temperatures ($T<800\degree$C). By
initiating growth below $400 \degree$ C, where the sticking coefficients are
closer to unity and wetting on the graphene surface is improved, we demonstrate
epitaxy of Ni$_2$MnGa films with controlled stoichiometry that can be
exfoliated to produce freestanding membranes. Straining these membranes tunes
the magnetic coercive field. Our results provide a route to synthesize
membranes with complex stoichiometries whose properties can be manipulated via
strain.",2305.07793v1
2023-07-24,Enhanced Magnetism and Phase Transitions in Ultrathin Quantum Spin Liquid Na2IrO3 Flakes,"The quest for quantum spin liquids has garnered significant attention due to
their rich physics and disruptive prospects in quantum communication and
computation. Spin-orbit coupling, electron correlation, and structural
distortion play critical roles in the candidate materials that eventually order
antiferromagnetically at low temperatures. We introduce quantum electron
confinement to the existing complexity and explore the interplay between
Heisenberg and Kitaev interactions in ultrathin \ce{Na2IrO3} layers using
first-principles calculations. The zigzag antiferromagnetic state in the
monolayer is reinforced and pushed further away from the Kitaev spin liquid
state due to the increased strength of Heisenberg and off-diagonal exchange
interactions. In contrast, the carrier-doped flakes undergo a Mott
insulator-to-metal transition accompanied by an antiferromagnetic to
ferromagnetic transition. These findings present exciting prospects for
comprehending magnetism in a novel two-dimensional framework of non-van der
Waals correlated oxide flakes.",2307.12554v1
2023-08-18,Pressure-induced softening in bulk modulus due to magneto-elastic coupling in Nd$_2$CoFeO$_6$ double Perovskite,"Double perovskite oxide materials have garnered tremendous interest due to
their strong spin-lattice-charge coupling. Interesting in their own right,
rare-earth-based DPOs have yet to be subjected to high-pressure studies. In
this paper, we have investigated the structural response of Nd$_2$CoFeO$_6$ to
pressure by XRD and Raman spectroscopic measurements. From XRD data, we have
observed pressure-induced structural transition from the orthorhombic phase to
the monoclinic phase at about 13.8~\si{\giga\pascal}. An anomalous increase in
compressibility at a much lower pressure($\sim$1.1~\si{\giga\pascal}) is seen
where no structural transition occurs. At about the same pressure, a sudden
drop in the slope of Raman modes is observed. Further investigation at low
temperatures reveals that the B$_g$ Raman mode is strongly affected by magnetic
interactions. Additional high-pressure Raman experiments with the application
of a magnetic field indicated that the mentioned anomaly around
1.1~\si{\giga\pascal} can be explained by a high-spin to low-spin transition of
Co$^{3+}$.",2308.09651v2
2023-09-21,Development of Transient $μ$SR Method for High-Flux Pulsed Muons,"In order to expand the applicability of muon spin rotation, relaxation, and
resonance ($\mu$SR) experiments with pulsed muons and to make effective use of
the high-flux beam, we have developed a new experimental method ``transient
$\mu$SR''. In this method, $\mu$SR data for each muon pulse are tagged with
external parameters such as temperature and magnetic field in real time,
allowing the sample environment to be changed without interrupting data
collection. As a result, continuous $\mu$SR measurements under sample
conditions that vary on a time scale longer than the beam pulse interval (40
ms) are realized, and efficient beam utilization is achieved by eliminating the
lag time associated with moving between discrete measurement points. The
transient $\mu$SR method was applied to the study of the magnetic properties of
cupric oxide (CuO) and the observation of level-crossing resonance relaxation
in copper, and the method was successfully established by confirming that the
results reproduce those in the previous reports.",2309.11757v1
2023-09-30,Quantum Materials Group Annual Report 2022,"The Quantum Materials group at Indian Institute of Technology Patna is
working on a range of topics relating to nanoelectronics, spintronics, clean
energy and memory design etc. The PI has past experiences of working
extensively with superconducting systems like cuprates [1, 2], ruthanate [3],
pnictide [4, 5], thin film heterostructures [6, 7] etc and magnetic recording
media [8, 9] etc. In this report, we have summarised the ongoing works in our
group. We explored a range of functional materials like two-dimensional
materials, oxides. topological insulators, organic materials etc. using a
combination of experimnetal and computational tools. Some of the useful
highlights are as follows: (a) tuning and control of the magnetic and
electronic state of 2D magentic materials with rapid enhancement in the Curie
temperature, (b) Design and detection of single electron transistor based
nanosensors for the detection of biological species with single molecular
resolution, (c) Observation of non-volatile memory behaviour in the hybrid
structures made of perovskite materials and 2D hybrids. The results offer
useful insight in the design of nanoelectronic architecrures for diverse
applications.",2310.00456v2
2023-10-02,Gate-voltage switching of non-reciprocal transport in oxide-based Rashba interfaces,"The linear magnetoelectric effect (ME) is the phenomenon by which an electric
field produces a magnetization. Its observation requires both time-reversal and
space-inversion symmetries to be broken, as in multiferroics. While the ME
effect has only been studied in insulating materials, it can actually exist in
non-centrosymmetric conductors such as two-dimensional electron gases (2DEGs)
with Rashba spin-orbit coupling. It is then coined the Edelstein effect (EE),
by which a bias voltage -- generating a charge current -- produces a transverse
spin density, i.e. a magnetization. Interestingly, 2D systems are sensitive to
voltage gating, which provides an extra handle to control the EE. Here, we show
that the sign of the EE in a SrTiO$_3$ 2DEG can be controlled by a gate
voltage. We propose various logic devices harnessing the dual control of the
spin density by current and gate voltages and discuss the potential of our
findings for gate-tunable non-reciprocal electronics.",2310.01598v1
2023-09-09,Investigation into the nature behind the interesting half levitation behavior of claimed superconductor LK-99,"A recent article published by Lee et.al. claimed to have successfully
achieved superconductivity at room temperature (RT) has become a topical issue.
Besides the research paper, Lee and his team provided a demonstration video of
LK-99 half levitating (HL) on a magnet. Such interesting HL appearance has
drawn tremendous sensation both in academia and the network. However, the true
identity of LK-99 still remains unclear, i.e., whether the HL behavior can
necessarily indicate the diamagnetism behavior of the sample. Here, we
fabricated our own LK-99 samples following the procedures reported by Lee et
al. We found quite a few sample pieces showing the typical HL that is similar
to those reported. Meanwhile, oxidation during the sample preparation was found
to deleterious to acquiring HL in the sample, while furnace cooling or water
quenching in the last step revealed little effect. However, our careful
observations indicated that those HL pieces are more likely simple
ferromagnetic. Then we conducted a comprehensive study on the behavior patterns
of typical diamagnetism and ferromagnetic substances interacting with a
Nd2Fe14B magnet, and provided instructions to distinguish the characteristics
between ferromagnetic and diamagnetic to prevent misunderstanding of LK-99 like
levitation behavior.",2310.08594v1
2023-10-15,A singlet-triplet hole-spin qubit in MOS silicon,"Holes in silicon quantum dots are promising for spin qubit applications due
to the strong intrinsic spin-orbit coupling. The spin-orbit coupling produces
complex hole-spin dynamics, providing opportunities to further optimize spin
qubits. Here, we demonstrate a singlet-triplet qubit using hole states in a
planar metal-oxide-semiconductor double quantum dot. We observe rapid qubit
control with singlet-triplet oscillations up to 400 MHz. The qubit exhibits
promising coherence, with a maximum dephasing time of 600 ns, which is enhanced
to 1.3 us using refocusing techniques. We investigate the magnetic field
anisotropy of the eigenstates, and determine a magnetic field orientation to
improve the qubit initialisation fidelity. These results present a step forward
for spin qubit technology, by implementing a high quality singlet-triplet
hole-spin qubit in planar architecture suitable for scaling up to 2D arrays of
coupled qubits.",2310.09722v1
2023-12-06,Fingerprints of the Jahn-Teller and superexchange physics in optical spectra of manganites,"Transition metal oxides incorporating Jahn-Teller (JT) ions Mn3+ (3d4) in
manganites and Cu2+ (3d9) in cuprates exhibit outstanding magnetic and
electronic properties, including colossal magnetoresistance (CMR) and
high-temperature superconductivity (HTSC). The physics of these compounds is
associated with the orbitally-degenerate electronic states of JT ions, leading
to the linear electron-lattice interaction, complemented by the entirely
electronic superexchange (SE) interaction. Here, we discuss the fingerprints of
the JT and SE physics in the temperature-dependent complex dielectric function
spectra and multi-order Raman scattering spectra measured in a detwinned LaMnO3
crystal, which is a famous compound exhibiting cooperative JT effect, being
also a progenitor of magnetic materials exhibiting CMR effect. In accordance
with the obtained experimental evidence, the associated effective parameters
characterizing the JT and SE physics in manganites are presented.",2312.03677v1
2023-12-18,Impact of Oxidation State on the Valence-bond-glass Physics in the lithium-intercalated Mo$_3$O$_8$ Cluster Mott Insulators,"We have successfully synthesized four Mo$_3$O$_8$-type cluster Mott
insulators (CMI) by intercalating lithium into nonmagnetic precursors to
regulate the Mo$_3$ cluster valence. The resulting materials are
Li$_{1+x}$$R$Mo$_3$O$_8$ ($R$ = Sc, Y, Lu) and Li$_x$Zn$_2$Mo$_3$O$_8$. Our
magnetic susceptibility measurements revealed that these materials display
characteristics akin to a valence bond glass state and suggest the presence of
short-range ordering when the Mo$_3$ cluster valence approximates its ideal
value. These findings challenge the prevailing belief that the plaquette charge
ordering state is an inherent feature of Mo$_3$O$_8$-type CMI. Instead, they
underscore the importance of Mo$_3$ cluster valence in determining the physical
properties of these systems. These insights furnish a fresh understanding of
the Mo$_3$O$_8$-type CMI and open new research opportunities in highly
frustrated magnetism.",2312.11342v1
2024-01-02,High entropy ceramics for applications in extreme environments,"Compositionally complex materials have demonstrated extraordinary promise for
structural robustness in extreme environments. Of these, the most commonly
thought of are high entropy alloys, where chemical complexity grants uncommon
combinations of hardness, ductility, and thermal resilience. In contrast to
these metal-metal bonded systems, the addition of ionic and covalent bonding
has led to the discovery of high entropy ceramics. These materials also possess
outstanding structural, thermal, and chemical robustness but with a far greater
variety of functional properties which enable access to continuously
controllable magnetic, electronic, and optical phenomena. In this perspective,
we outline the potential for high entropy ceramics in functional applications
under extreme environments, where intrinsic stability may provide a new path
toward inherently hardened device design. Current works on high entropy
carbides, actinide bearing ceramics, and high entropy oxides are reviewed in
the areas of radiation, high temperature, and corrosion tolerance where the
role of local disorder is shown to create pathways toward self-healing and
structural robustness. In this context, new strategies for creating future
electronic, magnetic, and optical devices to be operated in harsh environments
are outlined.",2401.01418v1
2024-02-02,Mechanism of ferromagnetism enhancement in a La$_{2/3}$ Sr$_{1/3}$ MnO$_3$ membrane released from epitaxial strain,"Recent studies have shown that the magnetic properties of the ferromagnetic
perovskite oxide La$_{2/3}$ Sr$_{1/3}$ MnO$_3$ (LSMO) grown on an SrTiO3 (STO)
substrate, such as its magnetic moment and Curie temperature, can be improved
by releasing the film from the substrate. However, the microscopic origin of
this enhancement is not yet well understood. In this study, we use synchrotron
radiation measurements to investigate the mechanism of ferromagnetism
enhancement in an LSMO membrane released from an STO substrate by dissolving a
water-soluble Sr$_4$Al$_2$O$_7$ buffer layer. Using resonant photoemission
spectroscopy on the as-grown LSMO film and LSMO membrane, we elucidate that the
strain release from the STO substrate enhances the itineracy of the Mn-3d
electrons via p-d hybridization, and this strengthens the double-exchange
interaction. The reinforcement of the double-exchange interaction, in turn,
improves the ferromagnetism of LSMO.",2402.01179v1
2024-02-13,Tracking topological defect motion and incommensurate charge order melting in a perovskite manganite,"Charge order pervades the phase diagrams of many quantum materials where it
competes with superconducting and magnetic phases, hosts electronic phase
transitions and topological defects, and couples to the lattice generating
intricate structural distortions. Incommensurate charge order is readily
stabilized in manganese oxides where it is associated with anomalous electronic
and magnetic properties, but its nanoscale structural inhomogeneity complicates
precise characterization and understanding of these phases. Leveraging
atomic-resolution variable temperature cryogenic scanning transmission electron
microscopy (cryo-STEM), we characterize the thermal evolution of charge order
in a model manganite system, finding that mobile networks of topological
defects generate phase inhomogeneity and induce incommensuration in an
otherwise lattice-locked modulation. The melting of charge order at high
temperatures is accompanied by generation of additional defects which decouple
large areas of the order from the lattice.",2402.08580v1
2024-02-22,Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface,"We investigate the structural and electronic origin of antiferromagnetic
coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at
the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in
samples prepared with surface ion milling, indicative of antiferromagnetic
exchange coupling at the YIG/Py interface. Using scanning transmission electron
microscopy (STEM), we highlight significant interfacial differences introduced
by ion-milling. The observations suggests that the antiferromagnetic coupling
in YIG/Py bilayers is predominantly driven by an oxygen-mediated super-exchange
coupling mechanism on the tetrahedral Fe terminated YIG surface, which is
supported by density functional theory (DFT) calculations. This research
provides critical insight into the fundamental mechanisms governing the
efficiency of coupling in magnetic bilayers and underscores the pivotal role of
oxide surface termination in modulating magnetic interfacial dynamics.",2402.14553v2
2024-03-29,Synthesis of $c$-axis textured CaKFe$_4$As$_4$ superconducting bulk via spark plasma texturing technique,"Grain alignment is a key factor that determines the performance of a
superconducting bulk. In this study, the spark plasma texturing (SPT) technique
was used to fabricate a CaKFe$_4$As$_4$ superconducting bulk. X-ray diffraction
and electron backscatter diffraction revealed that the $c$-axes of the
CaKFe$_4$As$_4$ grains in the SPT bulk are aligned, demonstrating that the SPT
technique is effective in achieving $c$-axis texture. In addition, chemical
composition analysis showed that oxide impurities, which affect the grain
boundary characteristics that determine the inter-grain critical current
density ($J_c$), are randomly distributed in the SPT bulk. Magnetization
measurements showed high $J_c$ values of the SPT bulk, reaching 127 kA
cm$^{-2}$ and 26 kA cm$^{-2}$ at 4.2 K under a self-field and magnetic field of
5 T, respectively. These results suggest that the SPT technique is a promising
approach for obtaining a high-performance superconducting bulk material for
high-field applications.",2403.19984v1
2015-01-22,A Measure of Monopole Inertia in the Quantum Spin Ice Yb$_2$Ti$_2$O$_7$,"An important and continuing theme of modern solid state physics is the
realization of exotic excitations in materials (e.g. quasiparticles) that have
no analogy (or have not yet been observed) in the actual physical vacuum of
free space. Although they are not fundamental particles, such quasiparticles do
constitute the most basic description of the excited states of the ""vacuum"" in
which they reside. In this regard the magnetic textures of the excited states
of spin ices, magnetic pyrochlore oxides with dominant Ising interactions, are
proposed to be modeled as effective magnetic charge monopoles. Recent inelastic
neutron scattering experiments have established the pyrochlore material
Yb$_2$Ti$_2$O$_7$ (YbTO) as a quantum spin ice, where in addition to the Ising
interactions there are substantial transverse terms that may induce quantum
dynamics and - in principle - coherent monopole motion. Here we report a
combined time domain terahertz spectroscopy (TDTS) and microwave cavity study
of YbTO to probe its complex dynamic magnetic susceptibility. We find that the
form of the susceptibility is consistent with monopole motion and a magnetic
monopole conductivity can be defined and measured. Using the unique phase
sensitive capabilities of these techniques, we observe a sign change in the
reactive part of the magnetic response. In generic models of monopole motion
this is only possible through introducing inertial effects, e.g. a mass
dependent term, to the equations of motion. Analogous to conventional electric
charge systems, measurement of the conductivity's spectral weight allows us to
derive a value for the magnetic monopole mass, which we find to be
approximately 1800 electron masses. Our results establish the magnetic
monopoles of quantum spin ice as true coherently propagating quasiparticles of
this system.",1501.05638v1
2019-05-10,Complex magnetic order in nickelate slabs,"Magnetic ordering phenomena have a profound influence on the macroscopic
properties of correlated-electron materials, but their realistic prediction
remains a formidable challenge. An archetypical example is the ternary nickel
oxide system RNiO3 (R = rare earth), where the period-four magnetic order with
proposals of collinear and non-collinear structures and the amplitude of
magnetic moments on different Ni sublattices have been subjects of debate for
decades. Here we introduce an elementary model system - NdNiO3 slabs embedded
in a non-magnetic NdGaO3 matrix - and use polarized resonant x-ray scattering
(RXS) to show that both collinear and non-collinear magnetic structures can be
realized, depending on the slab thickness. The crossover between both spin
structures is correctly predicted by density functional theory and can be
qualitatively understood in a low-energy spin model. We further demonstrate
that the amplitude ratio of magnetic moments in neighboring NiO6 octahedra can
be accurately determined by RXS in combination with a correlated double cluster
model. Targeted synthesis of model systems with controlled thickness and
synergistic application of polarized RXS and ab-initio theory thus provide new
perspectives for research on complex magnetism, in analogy to two-dimensional
materials created by exfoliation.",1905.04160v1
2020-12-02,Synthesis and Characterization of Sodium Iron Antimonate Na2FeSbO5 One-Dimensional Antiferromagnetic Chain Compound with a Spin Glass Ground State,"A new oxide, sodium iron antimonate, Na2FeSbO5, was synthesized and
structurally characterized, and its static and dynamic magnetic properties were
comprehensively studied both experimentally by dc and ac magnetic
susceptibility, magnetization, specific heat, electron spin resonance (ESR) and
Moessbauer measurements, and theoretically by density functional calculations.
The resulting single-crystal structure (a = 15.6991(9) A; b = 5.3323 (4) A; c =
10.8875(6) A; S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which
alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The
57Fe Moessbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in
a distorted tetrahedral oxygen coordination. The magnetic susceptibility and
specific heat data show the absence of a long-range magnetic ordering in
Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates
spin-glass-type behavior with a unique two-step freezing at Tf1 about 80 K and
Tf2 about 35 K. Magnetic hyperfine splitting of 57Fe Moessbauer spectra was
observed below T* about 104 K (Tf1 < T*). The spectra just below T* (Tf1 < T <
T*) exhibit a relaxation behavior caused by critical spin fluctuations,
indicating the existence of short-range correlations. The stochastic model of
ionic spin relaxation was used to account for the shape of the Moessbauer
spectra below the freezing temperature. A complex slow dynamics is further
supported by ESR data revealing two different absorption modes presumably
related to ordered and disordered segments of spin chains. The data imply a
spin-cluster ground state for Na2FeSbO5.",2012.01106v1
2020-12-30,Properties of Assembly of Superparamagnetic Nanoparticles in Viscous Liquid,"Detailed calculations of the specific absorption rate (SAR) of a dilute
assembly of iron oxide nanoparticles with effective uniaxial anisotropy
dispersed in a liquid are performed depending on the particle diameters, the
alternating (ac) magnetic field amplitude and the liquid viscosity. For small
and moderate ac magnetic field amplitudes H0 with respect to particle
anisotropy field Hk the SAR of the assembly as a function of the particle
diameter passes through a characteristic maximum and then reaches a plateau,
whereas for sufficiently large amplitudes, H0 ~ Hk, the SAR increases
monotonically as a function of particle diameter. This difference is a
consequence of realization of viscous and magnetic oscillation modes for
particle unit magnetization vector and director for moderate and sufficiently
large H0 values, respectively. It is found that the SAR of the assembly changes
inversely with the viscosity only in a viscous mode, for nanoparticles of
sufficiently large diameters. In the developed magnetic mode the SAR of the
assembly is practically independent of the viscosity, since in this case the
nanoparticle director only weakly oscillates around the ac magnetic field
direction. At moderate amplitudes of the ac magnetic field the SAR values of
the assembly in the liquid and in the solid matrix are found to be close,
except of the range of large particle diameters and sufficiently low viscosity.
However, at large field amplitudes the SAR of randomly oriented assembly of
nanoparticles in a solid matrix is approximately two times less than that in a
liquid, because a significant fraction of nanoparticles of the assembly in the
solid matrix is not optimally oriented with respect to the ac magnetic field
direction. The conditions for the validity of the linear response theory have
been clarified by comparison with the numerical simulation data.",2012.15179v1
2021-05-13,Near-Room-Temperature Ferromagnetic Behavior of Single-Atom-Thick 2D Iron in Nanolaminated Ternary MAX Phases,"Two dimensional (2D) ferromagnetic materials have attracted much attention in
the fields of condensed matter physics and materials science, but their
synthesis is still a challenge given their limitations on structural stability
and susceptibility to oxidization. MAX phases nanolaminated ternary carbides or
nitrides possess a unique crystal structure in which single-atom-thick A
sublayers are interleaved by two dimensional MX slabs, providing nanostructured
templates for designing 2D ferromagnetic materials if the non-magnetic A
sublayers can be substituted replaced by magnetic elements. Here, we report
three new ternary magnetic MAX phases (Ta2FeC, Ti2FeN and Nb2FeC) with A
sublayers of single-atom-thick 2D iron through an isomorphous replacement
reaction of MAX precursors (Ta2AlC, Ti2AlN and Nb2AlC) with a Lewis acid salts
(FeCl2). All these MAX phases exhibit ferromagnetic (FM) behavior. The Curie
temperature (Tc) of Ta2FeC and Nb2FeC MAX phase are 281 K and 291 K,
respectively, i.e. close to room temperature. The saturation magnetization of
these ternary magnetic MAX phases is almost two orders of magnitude higher than
that of V2(Sn,Fe)C MAX phase whose A-site is partial substituted by Fe.
Theoretical calculations on magnetic orderings of spin moments of Fe atoms in
these nanolaminated magnetic MAX phases reveal that the magnetism can be mainly
ascribed to intralayer exchange interaction of the 2D Fe atomic layers. Owning
to the richness in composition of MAX phases, there is a large compositional
space for constructing functional single-atom-thick 2D layers in materials
using these nanolaminated templates.",2105.06139v1
2022-06-17,Strain and electric field control of magnetic and electrical transport properties in a magneto-elastically coupled Fe3O4/BaTiO3(001) heterostructure,"We present a study of the control of electric field induced strain on the
magnetic and electrical transport properties in a magneto-elastically coupled
artificial multiferroic Fe3O4/BaTiO3 heterostructure. In this Fe3O4/BaTiO3
heterostructure, the Fe3O4 thin film is epitaxially grown in the form of
bilateral domains, analogous to a-c stripe domains of the underlying
BaTiO3(001) substrate. By in-situ electric field dependent magnetization
measurements, we demonstrate the extrinsic control of the magnetic anisotropy
and the characteristic Verwey metal-insulator transition of the epitaxial Fe3O4
thin film in a wide temperature range between 20-300 K, via strain mediated
converse magnetoelectric coupling. In addition, we observe strain induced
modulations in the magnetic and electrical transport properties of the Fe3O4
thin film across the thermally driven intrinsic ferroelectric and structural
phase transitions of the BaTiO3 substrate. In-situ electric field dependent
Raman measurements reveal that the electric field does not significantly modify
the anti-phase boundary defects in the Fe3O4 thin film once it is
thermodynamically stable after deposition and that the modification of the
magnetic properties is mainly caused by strain induced lattice distortions and
magnetic anisotropy. These results provide a framework to realize electrical
control of the magnetization in a classical highly correlated transition metal
oxide.",2206.08664v1
2023-03-16,Nitrogen-vacancy magnetometry of individual Fe-triazole spin crossover nanorods,"[Fe(Htrz)2(trz)](BF4) (Fe-triazole) spin crossover molecules show thermal,
electrical, and optical switching between high spin (HS) and low spin (LS)
states, making them promising candidates for molecular spintronics. The LS and
HS transitions originate from the electronic configurations of Fe(II), and are
considered to be diamagnetic and paramagnetic respectively. The Fe(II) LS state
has six paired electrons in the ground states with no interaction with the
magnetic field and a diamagnetic behavior is usually observed. While the bulk
magnetic properties of Fe-triazole compounds are widely studied by standard
magnetometry techniques their properties at the individual level are missing.
Here we use nitrogen vacancy (NV) based magnetometry to study the magnetic
properties of the Fe-triazole LS state of nanoparticle clusters and individual
nanorods of size varying from 20 to 1000 nm. Scanning electron microscopy (SEM)
and Raman spectroscopy are performed to determine the size of the
nanoparticles/nanorods and to confirm their respective spin state. The magnetic
field patterns produced by the nanoparticles/nanorods are imaged by NV magnetic
microscopy as a function of applied magnetic field (up to 350 mT) and
correlated with SEM and Raman. We found that in most of the nanorods the LS
state is slightly paramagnetic, possibly originating from the surface oxidation
and/or the greater Fe(III) presence along the nanorod edges. NV measurements on
the Fe-triazole LS state nanoparticle clusters revealed both diamagnetic and
paramagnetic behavior. Our results highlight the potential of NV quantum
sensors to study the magnetic properties of spin crossover molecules and
molecular magnets.",2303.09636v4
2024-03-27,Hydroflux-Controlled Growth of Magnetic K-Cu-Te-O(H) Phases,"Innovative synthetic approaches can yield new phases containing novel
structural and magnetic motifs. In this work, we show the synthesis and
magnetic characterization of three new and one previously reported layered
phase in the K-Cu-Te-O(H) phase space using a tunable hydroflux technique. The
hydroflux, with a roughly equal molar ratio of water and alkali hydroxide, is a
highly oxidizing, low melting solvent which can be used to isolate metastable
phases unattainable through traditional solid state or flux techniques. The
newly synthesized phases, K$_{2}$Cu$_{2}$TeO$_{6}$, K$_{2}$Cu$_{2}$TeO$_{6}$
$\cdot$ H$_{2}$O, and K$_{6}$Cu$_{9}$Te$_{4}$O$_{24}$ $\cdot$ 2 H$_{2}$O,
contain Cu$^{2+}$ within CuO$_{4}$ square planar plaquettes and TeO$_{6}$
octahedra ordering to form structural honeycomb layers isolated by interlayer
K$^{+}$ ions and H$_{2}$O molecules. We find the synthesized structures display
varying tilt sequences of the CuO$_{4}$ plaquettes, leading to distinct
Cu$^{2+}$ magnetic motifs on the structural honeycomb lattice and a range of
effective magnetic dimensionalities. We find that K$_{2}$Cu$_{2}$TeO$_{6}$
$\cdot$ H$_{2}$O does not order and displays alternating chain Heisenberg
antiferromagnetic (AFM) behavior, while K$_{2}$Cu$_{2}$TeO$_{6}$ and
K$_{6}$Cu$_{9}$Te$_{4}$O$_{24}$ $\cdot$ 2 H$_{2}$O order antiferromagnetically
(T$_{N}$ = 100 K and T$_{N}$ = 6.5 K respectively). The previously known phase,
K$_{2}$CuTeO$_{4}$(OH)$_{2}$ $\cdot$ H$_{2}$O, we find contains structurally
and magnetically one-dimensional CuO$_{4}$ plaquettes leading to uniform chain
Heisenberg AFM behavior and shows no magnetic order down to T = 0.4 K. We
discuss and highlight the usefulness of the hydroflux technique in novel
syntheses and the interesting magnetic motifs that arise in these particular
phases.",2403.18726v1
2003-06-02,Possible Spin-triplet Superconductivity in NaxCoO2yH2O - 59Co NMR Study,"We report 59Co NMR studies on the magnetically oriented powder samples of
Co-oxide superconductors NaxCoO2yH2O with Tc ~ 4.7 K. From two-dimensional
powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal
state was estimated by the magnetic field dependence of second-order quadrupole
shifts at various temperatures. Below 50 K, the Knight shift shows a
Curie-Weiss-like temperature dependence, similarly to the bulk magnetic
susceptibility chi. From the analysis of so-called K-chi plot, the spin and the
orbital components of K and the positive hyperfine coupling constant were
estimated. The onset temperature of superconducting transition in the Knight
shift does not change so much in an applied magnetic field up to 7 T, which is
consistent with the reported high upper critical field Hc2. The Knight shift at
7 T shows an invariant behavior below Tc. No coherence peak just below Tc was
observed in the temperature dependence of the nuclear spin-lattice relaxation
rate 1/T1 in both cases of NMR and NQR. We conclude that the invariant behavior
of the Knight shift below Tc and unconventional behaviors of 1/T possibly
indicate the spin-triplet superconductivity with p- or f-wave symmetry.",0306036v4
2004-03-19,Quantum spin fluctuations in the dipolar Heisenberg-like rare earth pyrochlores,"The magnetic pyrochlore oxide materials of general chemical formula R2Ti2O7
and R2Sn2O7 (R = rare earth) display a host of interesting physical behaviours
depending on the flavour of rare earth ion. These properties depend on the
value of the total magnetic moment, the crystal field interactions at each rare
earth site and the complex interplay between magnetic exchange and long-range
dipole-dipole interactions. This work focuses on the low temperature physics of
the dipolar isotropic frustrated antiferromagnetic pyrochlore materials.
Candidate magnetic ground states are numerically determined at zero temperature
and the role of quantum spin fluctuations around these states are studied using
a Holstein-Primakoff spin wave expansion to order 1/S. The results indicate the
strong stability of the proposed classical ground states against quantum
fluctuations. The inclusion of long range dipole interactions causes a
restoration of symmetry and a suppression of the observed anisotropy gap
leading to an increase in quantum fluctuations in the ground state when
compared to a model with truncated dipole interactions. The system retains most
of its classical character and there is little deviation from the fully ordered
moment at zero temperature.",0403494v1
2004-06-02,Orbital and magnetic transitions in geometrically-frustrated vanadium spinels -- Monte Carlo study of an effective spin-orbital-lattice coupled model --,"We present our theoretical and numerical results on thermodynamic properties
and the microscopic mechanism of two successive transitions in vanadium spinel
oxides $A$V$_2$O$_4$ ($A$=Zn, Mg, or Cd) obtained by Monte Carlo calculations
of an effective spin-orbital-lattice model in the strong correlation limit.
Geometrical frustration in the pyrochlore lattice structure of V cations
suppresses development of spin and orbital correlations, however, we find that
the model exhibits two transitions at low temperatures. First, a discontinuous
transition occurs with an orbital ordering assisted by the tetragonal
Jahn-Teller distortion. The orbital order reduces the frustration in spin
exchange interactions, and induces antiferromagnetic correlations in
one-dimensional chains lying in the perpendicular planes to the tetragonal
distortion. Secondly, at a lower temperature, a three-dimensional
antiferromagnetic order sets in continuously, which is stabilized by the
third-neighbor interaction among the one-dimensional antiferromagnetic chains.
Thermal fluctuations are crucial to stabilize the collinear magnetic state by
the order-by-disorder mechanism. The results well reproduce the experimental
data such as transition temperatures, temperature dependence of the magnetic
susceptibility, changes of the entropy at the transitions, and the magnetic
ordering structure at low temperatures. Quantum fluctuation effect is also
examined by the linear spin wave theory at zero temperature. The staggered
moment in the ground state is found to be considerably reduced from saturated
value, and reasonably agrees with the experimental data.",0406039v1
2006-03-27,Jahn-Teller distortions and phase separation in doped manganites,"A ""minimal model"" of the Kondo-lattice type is used to describe a competition
between the localization and metallicity in doped manganites and related
magnetic oxides with Jahn-Teller ions. It is shown that the number of itinerant
charge carriers can be significantly lower than that implied by the doping
level x. A strong tendency to the phase separation is demonstrated for a wide
range of intermediate doping concentrations vanishing at low and high doping.
The phase diagram of the model in the x-T plane is constructed. At low
temperatures, the system is in a state with a long-range magnetic order:
antiferromagnetic (AF), ferromagnetic (FM), or AF-FM phase separated (PS)
state. At high temperatures, there can exist two types of the paramagnetic (PM)
state with zero and nonzero density of the itinerant electrons. In the
intermediate temperature range, the phase diagram includes different kinds of
the PS states: AF-FM, FM-PM, and PM with different content of itinerant
electrons. The applied magnetic field changes the phase diagram favoring the FM
ordering. It is shown that the variation of temperature or magnetic field can
induce the metal-insulator transition in a certain range of doping levels.",0603711v3
2006-09-15,Magnetic properties of iron nanoparticles prepared by exploding wire technique,"Nanoparticles of iron were prepared in distilled water using very thin iron
wires and sheets, by the electro-exploding wire technique. Transmission
electron microscopy reveals the size of the nanoparticles to be in the range 10
to 50 nm. However, particles of different sizes can be segregated by using
ultrahigh centrifuge. X-ray diffraction studies confirm the presence of the
cubic phase of iron. These iron nanoparticles were found to exhibit
fluorescence in the visible region in contrast to the normal bulk material. The
room temperature hysteresis measurements upto a field of 1.0 tesla were
performed on a suspension of iron particles in the solution as well as in the
powders obtained by filtration. The hysteresis loops indicate that the
particles are superparamagnetic in nature. The saturation magnetizations was ~
60 emu / gm. As these iron particles are very sensitive to oxygen a coating of
non-magnetic iron oxide tends to form around the particles giving it a core -
shell structure. The core particle size is estimated theoretically from the
magnetization measurements. Suspensions of iron nanoparticles in water have
been proposed to be used as an effective decontaminant for ground water.",0609370v1
2007-01-30,Influence of chemical and magnetic interface properties of Co-Fe-B / MgO / Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance,"The knowledge of chemical and magnetic conditions at the Co40Fe40B20 / MgO
interface is important to interpret the strong annealing temperature dependence
of tunnel magnetoresistance of Co-Fe-B / MgO / Co-Fe-B magnetic tunnel
junctions, which increases with annealing temperature from 20% after annealing
at 200C up to a maximum value of 112% after annealing at 350C. While the well
defined nearest neighbor ordering indicating crystallinity of the MgO barrier
does not change by the annealing, a small amount of interfacial Fe-O at the
lower Co-Fe-B / MgO interface is found in the as grown samples, which is
completely reduced after annealing at 275C. This is accompanied by a
simultaneous increase of the Fe magnetic moment and the tunnel
magnetoresistance. However, the TMR of the MgO based junctions increases
further for higher annealing temperature which can not be caused by Fe-O
reduction. The occurrence of an x-ray absorption near-edge structure above the
Fe and Co L-edges after annealing at 350C indicates the recrystallization of
the Co-Fe-B electrode. This is prerequisite for coherent tunneling and has been
suggested to be responsible for the further increase of the TMR above 275C.
Simultaneously, the B concentration in the Co-Fe-B decreases with increasing
annealing temperature, at least some of the B diffuses towards or into the MgO
barrier and forms a B2O3 oxide.",0701749v1
2007-08-07,Spin and charge orders and their hole-doping dependence in single layered cobaltate La2-xCaxCoO4(0.3<x<0.8),"Neutron scattering experiments were performed on single crystals of layered
cobalt-oxides La2-xCaxCoO4 (LCCO) to characterize the charge and spin orders in
a wide hole-doping range of 0.3<x<0.8. For a commensurate value of x=0.5 in
(H,0,L) plane, two types of superlattice reflections concomitantly appear at
low temperature; one corresponds to a checkerboard charge ordered pattern of
Co2+/Co3+ ions and the other is magnetic in origin. Further, the latter
magnetic-superlattice peaks show two types of symmetry in the reflections,
suggesting antiferromagnetic-stacking (AF-S) and ferromagnetic-stacking (F-S)
patterns of spins along the c direction. From the hole-doping dependence, the
in-plane correlation lengths of both charge and spin orders are found to give a
maximum at x=0.5. These features are the same with those of x=0.5 in
La1-xSr1+xMnO4 (LSMO), a typical checkerboard and spin ordered compound.
However, in (H,H,L) plane, we found a magnetic scattering peak at
Q=(1/4,1/4,1/2) position below TN. This magnetic peak can not be understood by
considering the Co2+ spin configuration, suggesting that this peak is
originated from Co3+ spin order. By analyzing these superlattice reflections,
we found that they are originated from high-spin state of Co3+ spin order.",0708.0939v1
2008-01-08,"Nano granular metallic Fe - oxygen deficient TiO$_{2-δ}$ composite films: A room temperature, highly carrier polarized magnetic semiconductor","Nano granular metallic iron (Fe) and titanium dioxide (TiO$_{2-\delta}$) were
co-deposited on (100) lanthanum aluminate (LaAlO$_3$) substrates in a low
oxygen chamber pressure using a pulsed laser ablation deposition (PLD)
technique. The co-deposition of Fe and TiO$_2$ resulted in $\approx$ 10 nm
metallic Fe spherical grains suspended within a TiO$_{2-\delta}$ matrix. The
films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss
at room temperature. Our estimate of the saturation magnetization based on the
size and distribution of the Fe spheres agreed well with the measured value.
The film composite structure was characterized as p-type magnetic semiconductor
at 300 K with a carrier density of the order of $ 10^{22} /{\rm cm^3}$. The
hole carriers were excited at the interface between the nano granular Fe and
TiO$_{2-\delta}$ matrix similar to holes excited in the metal/n-type
semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS)
devices. From the large anomalous Hall effect directly observed in these films
it follows that the holes at the interface were strongly spin polarized.
Structure and magneto transport properties suggested that these PLD films have
potential nano spintronics applications.",0801.1285v1
2008-03-04,"59Co, 23Na, and 1H NMR Studies of Double-Layer Hydrated Superconductors NaxCoO2-yH2O","We present our NMR studies of double-layer hydrated cobalt oxides
NaxCoO2-yH2O (x ~ 0.35, y ~ 1.3) with various Tc = 0 - 4.8 K and magnetic
transition temperatures. High-resolution $^{1}$H NMR spectrum served as an
evidence for the existence of H$_{3}$O$^{+}$ oxonium ions. $^{23}$Na nuclear
spin-lattice relaxation rates served to detect local field fluctuations
sensitive to Tc. $^{59}$Co nuclear quadrupole resonance (NQR) spectra served to
classify the various Tc samples. From the classification by $^{59}$Co NQR
frequency, the double-layer hydrated compounds were found to have two
superconducting phases closely located to a magnetic phase. In the normal state
and at a magnetic field in the $ab$-plane, two $^{59}$Co NMR signals with
different Knight shifts and different $^{59}$Co nuclear spin-lattice relaxation
times $^{59}T_{1}$ were observed. The two $^{59}$Co NMR signals suggest
magnetic disproportionation of two Co sites or in-plane (XY) anisotropy of a
single Co site. Non Korringa behavior and power law behavior in zero-field NQR
1/$^{59}T_{1}$ above and below Tc suggest non-Fermi liquid and unconventional
superconductivity.",0803.0366v1
2008-04-24,Modelling Magnetic Fluctuations in the Stripe Ordered State,"The nature of the interplay between superconductivity and magnetism in the
cuprates remains one of the fundamental unsolved problems in high temperature
superconductivity. Whether and how these two phenomena are interdependent is
perhaps most sharply seen in the stripe phases of various copper-oxide
materials. These phases, involving a mixture of spin and charge density waves,
do not yet admit a complete, overarching theoretical treatment. However aspects
of this problem can be analyzed. In this work, we focus on the magnetic side of
stripe physics. To this end, we study a simple model of a stripe-ordered phase
consisting of an array of alternating coupled doped and undoped two-leg
Hubbard-like ladders. To obtain the magnetic response, we employ already
available dynamical susceptibilities of the individual two-leg ladders and
treat the interladder coupling in a random phase approximation. Strikingly, we
find two possible scenarios for the ordered state induced by the coupling
between ladders: the spin modulation can occur either along or perpendicular to
the direction of the stripes. These two scenarios are differentiated according
to different microscopic realizations of the component doped ladders. However
inelastic neutron scattering experiments on the two stripe ordered cuprates,
La_{1.875}Ba_{0.125}CuO_4 and La_{2-x}Sr_xCuO_4, do not readily distinguish
between these two scenarios due to manner in which stripes form in these
materials.",0804.3832v1
2008-10-21,A novel approach towards selective bulk synthesis of delaminated graphenes in an electric arc,"Here we demonstrate the selective bulk scale synthesis of delaminated
graphene sheets by a proper choice of magnetic field modulating an
electric-arc. An ultra-high purity glassy graphite anode was sublimated in an
argon atmosphere. Carbon nanotubes, as well as graphene sheets were found
inside the deposit formed on the cathode. Both the high purity carbon nanotubes
as well as graphene sheets, with minimal structural defects, were synthesized
separately by varying the strength and orientation of the external magnetic
field generated by arrays of permanent magnets. The as-synthesized carbonaceous
samples were characterized with the help of transmission electron microscopy,
selected area electron diffraction, Raman spectroscopy and thermogravimetry for
optimizing the highest selective production of delaminated graphenes. This
optimization was done by varying the strength and orientation of the external
magnetic field.
  The as-synthesized graphene sheets exhibited relatively high degree of
graphitization and low structural defect density as confirmed by RS. They were
found to exhibit higher oxidation temperature than that of the carbon
nanocrystalline particles as inferred from the thermogravimatric analysis.
Moreover, they were found to form scroll-like carbon nanotubes at their edges
on account of their surface energy minimization. This was confirmed by the
selected area electron diffraction analysis. With this new technique, we could
successfully synthesize delaminated graphenes at a rate of few grams per hour.",0810.3907v1
2008-10-23,Electron spin blockade and singlet-triplet transition in a silicon single electron transistor,"We investigate a silicon single-electron transistor (SET) in a
metal-oxide-semiconductor (MOS) structure by applying a magnetic field
perpendicular to the sample surface. The quantum dot is defined
electrostatically in a point contact channel and by the potential barriers from
negatively charged interface traps. The magnetic field dependence of the
excitation spectrum is primarily driven by the Zeeman effect. In the
two-electron singlet-triplet (ST) transition, electron-electron Coulomb
interaction plays a significant role. The evolution of Coulomb blockade peaks
with magnetic field B is also owing to the Zeeman splitting with no obvious
orbital effect up to 9 T. The filling pattern shows an alternate
spin-up-spin-down sequence. The amplitude spectroscopy allows for the
observation of the spin blockade effect, where the two-electron system forms a
singlet state at low fields, and the spin polarized injection from the lead
reduces the tunneling conductance by a factor of 8. At a higher magnetic field,
due to the ST transition, the spin blockade effect is lifted and the
conductance is fully recovered.",0810.4268v3
2009-05-03,Exchange bias in Co/CoO core-shell nanowires: Role of the antiferromagnetic superparamagnetic fluctuations,"The magnetic properties of Co (<D>=15 nm, <L>=130nm) nanowires are reported.
In oxidized wires, we measure large exchange bias fields of the order of 0.1 T
below T ~ 100 K. The onset of the exchange bias, between the ferromagnetic core
and the anti-ferromagnetic CoO shell, is accompanied by a coercivity drop of
0.2 T which leads to a minimum in coercivity at $\sim100$ K. Magnetization
relaxation measurements show a temperature dependence of the magnetic viscosity
S which is consistent with a volume distribution of the CoO grains at the
surface. We propose that the superparamagnetic fluctuations of the
anti-ferromagnetic CoO shell play a key role in the flipping of the nanowire
magnetization and explain the coercivity drop. This is supported by
micromagnetic simulations. This behavior is specific to the geometry of a 1D
system which possesses a large shape anisotropy and was not previously observed
in 0D (spheres) or 2D (thin films) systems which have a high degree of symmetry
and low coercivities. This study underlines the importance of the AFM
super-paramagnetic fluctuations in the exchange bias mechanism.",0905.0268v4
2009-06-16,Microwave Technologies-- Determination of Magnetic and Dielectric Materials Microwave Properties,"In this study, four different techniques are presented. 1 Rectangular
waveguide measurement technique for normal microwave materials microwave
properties such as permeability and permittivity. This technique removed guess
parameter and dispersive effect issues of the old waveguide measurement
techniques. It projects a new route for determination of any microwave
materials magnetic and dielectric properties without using any guesses. 2
Coaxial probe measurement technique for the liquid and biological tissues
dielectric permittivity. This coaxial probe technique has an advantage which is
to attain the highest reflected signal from the coaxial probe tip, so that it
is a fast and very sensitive technique to differentiate lossy materials
dielectric permittivity. This technique could be useful non destructive
detections for tumors in hospital and non destructive detections for chemical
liquids as well. 3 A microstripline measurement technique for oxides microwave
measurement at low frequency spectra where the waveguide technique becomes
robot and cumbersome. 4 A new methodology is presented for the rectangular
waveguide technique to determine microwave metamaterials refractive index,
permeability and permittivity using the rectangular waveguide. In summary, the
presented techniques are capable enough to determine magnetic and non magnetic
solid state materials, liquids, powders and biological tissues microwave
properties from the broad microwave frequencies spectra between 1 GHz to 50
GHz. Lastly, a special ferrites microwave properties are also presented since
the negative refractive index from the insulator ferrite could be an
interesting subject.",0906.2928v1
2010-06-30,Electronic Structure of Pyrochlore Iridates: From Topological Dirac Metal to Mott Insulator,"In 5d transition metal oxides such as the iridates, novel properties arise
from the interplay of electron correlations and spin-orbit interactions. We
investigate the electronic structure of the pyrochlore iridates, (such as
Y$_{2}$Ir$_{2}$O$_{7}$) using density functional theory, LDA+U method, and
effective low energy models. A remarkably rich phase diagram emerges on tuning
the correlation strength U. The Ir magnetic moment are always found to be
non-collinearly ordered. However, the ground state changes from a magnetic
metal at weak U, to a Mott insulator at large U. Most interestingly, the
intermediate U regime is found to be a Dirac semi-metal, with vanishing density
of states at the Fermi energy. It also exhibits topological properties -
manifested by special surface states in the form of Fermi arcs, that connect
the bulk Dirac points. This Dirac phase, a three dimensional analog of
graphene, is proposed as the ground state of Y$_{2}$Ir$_{2}$O$_{7}$ and related
compounds. A narrow window of magnetic `axion' insulator, with axion parameter
$\theta=\pi$, may also be present at intermediate U. An applied magnetic field
induces ferromagnetic order and a metallic ground state.",1007.0016v1
2011-09-04,Resonant soft x-ray scattering from La(1-x)Sr(x)MnO(3) quantum wire arrays,"We describe a strategy for using resonant soft x-ray scattering (RSXS) to
study the electronic structure of transition metal oxide quantum wires. Using
electron beam lithography and ion milling, we have produced periodic, patterned
arrays of colossal magnetoresistance (CMR) phase La(1-x)Sr(x)MnO(3) consisting
of ~ 5000 wires, each of which is 80 nm in width. The scattered intensity
exhibits a series of peaks that can be interpreted as Bragg reflections from
the periodic structure or, equivalently, diffraction orders from the
grating-like structure. RSXS measurements at the Mn L(2,3) edge, which has a
large magnetic cross section, show clear evidence for a magnetic superstructure
with a commensurate period of five wires, which we interpret as commensurately
modulated antiferromagnetism. This superstructure, which is accompanied by
non-trivial reorganization of the magnetization within each wire, likely
results from classical dipole interactions among the wires. We introduce a
simple, exactly soluble, analytic model of the scattering that captures,
semi-quantitatively, the primary features in the RSXS data; this model will act
as a foundation for forthcoming, detailed studies of the magnetic structure in
these systems.",1109.0734v1
2011-09-09,Magnetic-field-induced charge-stripe order in the high temperature superconductor YBa2Cu3Oy,"Electronic charges introduced in copper-oxide planes generate high-transition
temperature superconductivity but, under special circumstances, they can also
order into filaments called stripes. Whether an underlying tendency of charges
to order is present in all cuprates and whether this has any relationship with
superconductivity are, however, two highly controversial issues. In order to
uncover underlying electronic orders, magnetic fields strong enough to
destabilise superconductivity can be used. Such experiments, including quantum
oscillations in YBa2Cu3Oy (a notoriously clean cuprate where charge order is
not observed) have suggested that superconductivity competes with spin, rather
than charge, order. Here, using nuclear magnetic resonance, we demonstrate that
high magnetic fields actually induce charge order, without spin order, in the
CuO2 planes of YBa2Cu3Oy. The observed static, unidirectional, modulation of
the charge density breaks translational symmetry, thus explaining quantum
oscillation results, and we argue that it is most likely the same 4a-periodic
modulation as in stripe-ordered cuprates. The discovery that it develops only
when superconductivity fades away and near the same 1/8th hole doping as in
La2-xBaxCuO4 suggests that charge order, although visibly pinned by CuO chains
in YBa2Cu3Oy, is an intrinsic propensity of the superconducting planes of high
Tc cuprates.",1109.2011v1
2011-09-15,Surface impedance of superconductors with magnetic impurities,"Motivated by the problem of the residual surface resistance of the
superconducting radio-frequency (SRF) cavities, we develop a microscopic theory
of the surface impedance of s-wave superconductors with magnetic impurities. We
analytically calculate the current response function and surface impedance for
a sample with spatially uniform distribution of impurities, treating magnetic
impurities in the framework of the Shiba theory. The obtained general
expressions hold in a wide range of parameter values, such as temperature,
frequency, mean free path, and exchange coupling strength. This generality, on
the one hand, allows for direct numerical implementation of our results to
describe experimental systems (SRF cavities, superconducting qubits) under
various practically relevant conditions. On the other hand, explicit analytical
expressions can be obtained in a number of limiting cases, which makes possible
further theoretical investigation of certain regimes. As a feature of key
relevance to SRF cavities, we show that in the regime of ""gapless
superconductivity"" the surface resistance exhibits saturation at zero
temperature. Our theory thus explicitly demonstrates that magnetic impurities,
presumably contained in the oxide surface layer of the SRF cavities, provide a
microscopic mechanism for the residual resistance.",1109.3395v2
2012-03-28,"Geometric and disorder -- type magnetic frustration in ferrimagnetic ""114"" Ferrites: Role of diamagnetic Li+ and Zn2+ cation substitution","The comparative study of the substitution of zinc and lithium for iron in the
""114"" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations
play a major role in tuning the competition between ferrimagnetism and magnetic
frustration in these oxides. The substitution of Li or Zn for Fe in the cubic
phase YBaFe4O7 leads to a structural transition to a hexagonal phase
YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It
is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for
Zn), these diamagnetic cations induce a strong ferrimagnetic component in the
samples, in contrast to the spin glass behaviour of the cubic phase. In all the
hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen
that in the low doping regime (x ~ 0.3 to 0.5), the competition between
ferrimagnetism and 2 D magnetic frustration is dominated by the average valency
of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a
spin glass is controlled by the high degree of cationic disorder, irrespective
of the iron valency.",1203.6220v1
2012-08-21,High temperature structural and magnetic properties of cobalt nanowires,"We present in this paper the structural and magnetic properties of high
aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in
situ X ray diffraction (XRD) and SQUID characterizations. We show that the
anisotropic shapes, the structural and texture properties are preserved up to
500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the
magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant
and Ms the saturation magnetization. Hc decreases linearly when the temperature
is increased due to the loss of the Co magnetocrystalline anisotropy
contribution. At 500K, 50% of the room temperature coercivity is preserved
corresponding to the shape anisotropy contribution only. We show that the
coercivity drop is reversible in the range 300 - 500 K in good agreement with
the absence of particle alteration. Above 525 K, the magnetic properties are
irreversibly altered either by sintering or by oxidation.",1208.4403v2
2012-10-04,"Spin-state transition, magnetism and local crystal structure in Eu_{1-x}Ca_xCoO_{3-d}","The doping series Eu1-xCaxCoO3-d provides a rather peculiar way to study the
spin-state transition in cobalt-based complex oxides since partial substitution
of Eu3+ ions by Ca2+ ions does not increase the mean valence state of cobalt
but is accompanied by appearance of oxygen vacancies in the ratio d \sim x/2.
In the parent compound EuCoO3, the low spin (LS)-high spin (HS) transition
takes place at temperatures so high that the chemical decomposition prevents
its direct observation. The substitution of Eu3+ for Ca2+ in this system shifts
the LS-HS transition to lower temperatures. The energy gap associated with this
transition in octahedrally-coordinated Co3+ ions changes from 1940 K in EuCoO3
to 1540 K in Eu0.9Ca0.1CoO2.95 and 1050 K in Eu0.8Ca0.2CoO2.9. Besides, each
O2- vacancy reduces the local coordination of two neighboring Co3+ ions from
octahedral to pyramidal thereby locally creating magnetically active sites
which couple into dimers. These dimers at low temperatures form another gapped
magnetic system with very different energy scale, D~3 K, on the background of
intrinsically non-magnetic lattice of octahedrally-coordinated low-spin Co3+
ions.",1210.1289v1
2015-03-09,Dual gate control of bulk transport and magnetism in the spin-orbit insulator Sr2IrO4,"The 5d iridates have been the subject of much recent attention due to the
predictions of a large array of novel electronic phases driven by twisting
strong spin-orbit coupling and Hubbard correlation. As a prototype, the single
layered perovskite Sr2IrO4 was first revealed to host a Jeff=1/2 Mott
insulating state. In this material, the approximate energy scale of a variety
of interactions, involving spin-orbit coupling, magnetic exchange interaction,
and the Mott gap, allows close coupling among the corresponding physical
excitations, opening the possibility of cross control of the physical
properties. Here, we experimentally demonstrate the effective gate control of
both the transport and magnetism in a Sr2IrO4-based field effect transistor
using an ionic liquid dielectric. This approach could go beyond the
surface-limited field effect seen in conventional transistors, reflecting the
unique aspect of the Jeff=1/2 state. The simultaneous modulation of conduction
and magnetism confirms the proposed intimate coupling of charge, orbital, and
spin degrees of freedom in this oxide. These phenomena are probably related to
an enhanced deviation from the ideal Jeff=1/2 state due to the gate-promoted
conduction. The present work would have important implications in modelling the
unusual physics enabled by strong spin-orbit coupling, and provides a new route
to explore those emergent quantum phases in iridates.",1503.02513v1
2015-05-14,Morphology control of the magnetization reversal mechanism in Co80Ni20 nanomagnets,"Nanowires with very different size, shape, morphology and crystal symmetry
can give rise to a wide ensemble of magnetic behaviors whose optimization
determines their applications in nanomagnets. We present here an experimental
work on the shape and morphological dependence of the magnetization reversal
mechanism in weakly interacting Co80Ni20 hexagonal-close-packed nanowires.
Non-agglomerated nanowires (with length L and diameter d) with a controlled
shape going from quasi perfect cylinders to diabolos, have been studied inside
their polyol solution in order to avoid any oxidation process. The coercive
field HC was found to follow a standard behavior and to be optimized for an
aspect ratio L/d > 15. Interestingly, an unexpected behavior was observed as
function of the head morphology leading to the strange situation where a
diabolo shaped nanowire is a better nanomagnet than a cylinder. This
paradoxical behavior can be ascribed to the growth-competition between the
aspect ratio L/d and the head morphology ratio d/D (D being the head width).
Our experimental results clearly show the importance of the independent
parameter (t = head thickness) that needs to be considered in addition to the
shape aspect ratio (L/d) in order to fully describe the nanomagnets magnetic
behavior. Micromagnetic simulations well support the experimental results and
bring important insights for future optimization of the nanomagnets morphology",1505.03890v1
2015-06-08,Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO,"We investigate the structural and magnetic origins of the unusual ultrafast
second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel
oxide (NiO) previously attributed to oscillatory reorientation dynamics of the
magnetic structure induced by d-d excitations. Using time-resolved x-ray
diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the
magnitude of the magnetic structure factor following ultrafast optical
excitation are limited to $\Delta<F_m>/<F_m>$ = 1.5% in the first 30 ps. An
extended investigation of the ultrafast SHG response reveals a strong
dependence on wavelength as well as characteristic echoes, both of which give
evidence for an acoustic origin of the dynamics. We therefore propose an
alternative mechanism for the SHG response based on perturbations of the
nonlinear susceptibility via optically induced strain in a spatially confined
medium. In this model, the two observed oscillation periods can be understood
as the times required for an acoustic strain wave to traverse one coherence
length of the SHG process in either the collinear or anti-collinear geometries.",1506.02679v1
2015-08-14,Magnetic fields facilitate DNA-mediated charge transport,"Exaggerate radical-induced DNA damage under magnetic fields is of great
concerns to medical biosafety and to bio-molecular device based upon DNA
electronic conductivity. In this report, the effect of applying an external
magnetic field (MF) on DNA-mediated charge transport (CT) was investigated by
studying guanine oxidation by a kinetics trap (8CPG) via photoirradiation of
anthraquinone (AQ) in the presence of an external MF. Positive enhancement in
CT efficiencies was observed in both the proximal and distal 8CPG after
applying a static MF of 300 mT. MF assisted CT has shown sensitivities to
magnetic field strength, duplex structures, and the integrity of base pair
stacking. MF effects on spin evolution of charge injection upon AQ irradiation
and alignment of base pairs to CT-active conformation during radical
propagation were proposed to be the two major factors that MF attributed to
facilitate DNA-mediated CT. Herein, our results suggested that the electronic
conductivity of duplex DNA can be enhanced by applying an external MF. MF
effects on DNA-mediated CT may offer a new avenue for designing DNA-based
electronic device, and unraveled MF effects on redox and radical relevant
biological processes.",1508.03512v1
2016-07-26,Interface-driven topological Hall effect in SrRuO$_3$-SrIrO$_3$ bilayer,"Electron transport coupled with magnetism has attracted attention over the
years as exemplified in anomalous Hall effect due to a Berry phase in momentum
space. Another type of unconventional Hall effect -- topological Hall effect,
originating from the real-space Berry phase, has recently become of great
importance in the context of magnetic skyrmions. We have observed topological
Hall effect in bilayers consisting of ferromagnetic SrRuO$_3$ and paramagnetic
SrIrO$_3$ over a wide region of both temperature and magnetic field. The
topological term rapidly decreases with the thickness of SrRuO$_3$, ending up
with the complete disappearance at 7 unit cells of SrRuO$_3$. Combined with
model calculation, we concluded that the topological Hall effect is driven by
interface Dzyaloshinskii-Moriya interaction, which is caused by both the broken
inversion symmetry and the strong spin-orbit coupling of SrIrO$_3$. Such
interaction is expected to realize the N\'{e}el-type magnetic skyrmion, of
which size is estimated to be $\sim$10 nm from the magnitude of topological
Hall resistivity. The results established that the high-quality oxide interface
enables us to tune the chirality of the system; this can be a step towards the
future topological electronics.",1607.07536v1
2018-04-25,Determination of the spin-lifetime anisotropy in graphene using oblique spin precession,"We determine the spin-lifetime anisotropy of spin-polarized carriers in
graphene. In contrast to prior approaches, our method does not require large
out-of-plane magnetic fields and thus it is reliable for both low- and
high-carrier densities. We first determine the in-plane spin lifetime by
conventional spin precession measurements with magnetic fields perpendicular to
the graphene plane. Then, to evaluate the out-of-plane spin lifetime, we
implement spin precession measurements under oblique magnetic fields that
generate an out-of-plane spin population. We find that the spin-lifetime
anisotropy of graphene on silicon oxide is independent of carrier density and
temperature down to 150 K, and much weaker than previously reported. Indeed,
within the experimental uncertainty, the spin relaxation is isotropic.
Altogether with the gate dependence of the spin lifetime, this indicates that
the spin relaxation is driven by magnetic impurities or random spin-orbit or
gauge fields.",1804.09556v1
2020-07-28,Defect Induced Room Temperature Ferromagnetism in High Quality Co-doped ZnO Bulk Samples,"The nature of the often reported room temperature ferromagnetism in
transition metal doped oxides is still a matter of huge debate. Herein we
report on room temperature ferromagnetism in high quality Co-doped ZnO
(Zn1-xCoxO) bulk samples synthesized via standard solid-state reaction route.
Reference paramagnetic Co-doped ZnO samples with low level of structural
defects are subjected to heat treatments in a reductive atmosphere in order to
introduce defects in the samples in a controlled way. A detailed structural
analysis is carried out in order to characterize the induced defects and their
concentration. The magnetometry revealed the coexistence of a paramagnetic and
a ferromagnetic phase at room temperature in straight correlation with the
structural properties. The saturation magnetization is found to increase with
the intensification of the heat treatment, and, therefore, with the increase of
the density of induced defects. The magnetic behavior is fully explained in
terms of the bound magnetic polaron model. Based on the experimental findings,
supported by theoretical calculations, we attribute the origin of the observed
defect-induced-ferromagnetism to the ferromagnetic coupling between the Co ions
mediated by magnetic polarons due to zinc interstitial defects.",2007.14140v1
2013-08-05,Physics picture from neutron scattering study on Fe-based superconductors,"Neutron scattering, with its ability to measure the crystal structure, the
magnetic order, and the structural and magnetic excitations, plays an active
role in investigating various families of Fe-based high-Tc superconductors.
Three different types of antiferromag- netic orders have been discovered in the
Fe plane, but two of them cannot be explained by the spin-density-wave (SDW)
mechanism of nesting Fermi surfaces. Noticing the close relation between
antiferromagnetic order and lattice distortion in orbital ordering from
previous studies on manganites and other oxides, we have advocated orbital or-
dering as the underlying common mechanism for the structural and
antiferromagnetic transitions in the 1111, 122 and 11 parent compounds. We
observe the coexistence of antiferromagnetic order and superconductivity in the
(Ba,K)Fe2 As2 system, when its phase separation is generally accepted. Optimal
Tc is proposed to be controlled by the local FeAs4 tetrahedron from our
investigation on the 1111 materials. The Bloch phase coherence of the Fermi
liquid is found crucial to the occurrence of bulk superconductiv- ity in iron
chalcogenides of both the 11 and the 245 families. Iron chalcogenides carry a
larger staggered magnetic moment (> 2{\mu}B /Fe) than that in iron pnictides (<
1{\mu}B /Fe) in the antiferromagnetic order. Normal state magnetic excitations
in the 11 supercon- ductor are of the itinerant nature while in the 245
superconductor the spin-waves of localized moments. The observation of
superconducting resonance peak provides a cru- cial piece of information in
current deliberation of the pairing symmetry in Fe-based superconductors.",1308.1040v1
2014-06-13,Low Energy Electrodynamics of Novel Spin Excitations in the Quantum Spin Ice Yb$_2$Ti$_2$O$_7$,"In condensed matter systems, the formation of long range order (LRO) with
broken symmetry is often accompanied by new types of excitations. However, in
many magnetic pyrochlore oxides, geometrical frustration suppresses
conventional LRO while at the same time non-trivial spin correlations are
observed. For such materials, a natural question to ask then is what is the
nature of the excitations in this highly correlated state without broken
symmetry? Frequently the application of a symmetry breaking field can stabilize
excitations whose properties still reflect certain aspects of the anomalous
state without long-range order. Here we report evidence of novel magnetic
excitations in the quantum spin ice material Yb$_2$Ti$_2$O$_7$, obtained from
time-domain terahertz spectroscopy (TDTS). At large fields, both magnon and
two-magnon-like excitations are observed in a $<$001$>$ directed magnetic field
illustrating the stabilization of a field induced LRO state. The unique ability
of TDTS to measure complex response functions allows a direct study of magnetic
responses in different polarization channels, revealing the existence of an
unusual left-hand polarized magnon. The g-factors of these excitations are
dramatically enhanced in the low-field limit, showing a cross-over of these
one- and two-magnon states into features consistent with quantum string-like
excitations proposed to exist in quantum spin ice in a small $<$001$>$ applied
field.",1406.3576v1
2016-12-15,Ba2NiOsO6: A Dirac-Mott insulator with ferromagnetism near 100 K,"The ferromagnetic semiconductor Ba2NiOsO6 (Tmag ~100 K) was synthesized at 6
GPa and 1500 {\deg}C. It crystallizes into a double perovskite structure
[Fm-3m; a = 8.0428(1) {\AA}], where the Ni2+ and Os6+ ions are perfectly
ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+
plays an essential role in opening the charge gap. The magnetic state was
investigated by density functional theory calculations and powder neutron
diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe
magnetic field at 5 K. The ferromagnetic gapped state is fundamentally
different from that of known dilute magnetic semiconductors such as (Ga,Mn)As
and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2CoAl (Tmag ~720
K), and the ferromagnetic insulators EuO (Tmag ~70 K) and Bi3Cr3O11 (Tmag ~220
K). It is also qualitatively different from known ferrimagnetic
insulator/semiconductors, which are characterized by an antiparallel spin
arrangement. Our finding of the ferromagnetic semiconductivity of Ba2NiOsO6
should increase interest in the platinum group oxides, because this new class
of materials should be useful in the development of spintronic, quantum
magnetic, and related devices.",1612.05041v1
2016-12-15,Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic,"For 4$d^1$ and 5$d^1$ spin-orbit-coupled electron configurations, the notion
of nonmagnetic j=3/2 quartet ground state discussed in classical textbooks is
at odds with the observed variety of magnetic properties. Here we throw fresh
light on the electronic structure of 4$d^1$ and 5$d^1$ ions in molybdenum- and
osmium-based double-perovskite systems and reveal different kinds of on-site
many-body physics in the two families of compounds: while the sizable magnetic
moments and $g$ factors measured experimentally are due to both metal
$d$-ligand $p$ hybridization and dynamic Jahn-Teller interactions for 4$d$
electrons, it is essentially $d$-$p$ covalency for the 5$d^1$ configuration.
These results highlight the subtle interplay of spin-orbit interactions,
covalency and electron-lattice couplings as the major factor in deciding the
nature of the magnetic ground states of 4$d$ and 5$d$ quantum materials. Cation
charge imbalance in the double-perovskite structure is further shown to allow a
fine tuning of the gap between the $t_{2g}$ and $e_g$ levels, an effect of much
potential in the context of orbital engineering in oxide electronics.",1612.05158v1
2017-06-25,Frustration-driven C4 symmetric orders in a hetero-structured iron-based superconductor,"A subtle balance between competing interactions in strongly correlated
systems can be easily tipped by additional interfacial interactions in a
heterostructure. This often induces exotic phases with unprecedented
properties, as recently exemplified by high-Tc superconductivity in FeSe
monolayer on the nonmagnetic SrTiO3. When the proximity-coupled layer is
magnetically active, even richer phase diagrams are expected in iron-based
superconductors (FeSCs), which however has not been explored due to the lack of
a proper material system. One promising candidate is Sr2VO3FeAs, a
naturally-assembled heterostructure of a FeSC and a Mott-insulating vanadium
oxide. Here, using high-quality single crystals and high-accuracy 75As and 51V
nuclear magnetic resonance (NMR) measurements, we show that a novel electronic
phase is emerging in the FeAs layer below T0 ~ 155 K without either static
magnetism or a crystal symmetry change, which has never been observed in other
FeSCs. We find that frustration of the otherwise dominant Fe stripe and V Neel
fluctuations via interfacial coupling induces a charge/orbital order with
C4-symmetry in the FeAs layers, while suppressing the Neel antiferromagnetism
in the SrVO3 layers. These findings demonstrate that the magnetic proximity
coupling is effective to stabilize a hidden order in FeSCs and, more generally,
in strongly correlated heterostructures.",1706.08157v1
2018-01-30,"Crystalline structure and XMCD studies of Co40Fe40B20 grown on Bi2Te3, BiTeI and Bi2Se3","Epitaxial films of Co40Fe40B20 (further - CoFeB) were grown on Bi2Te3(001)
and Bi2Se3(001) substrates by laser molecular beam epitaxy (LMBE) technique at
200-400C. Bcc-type crystalline structure of CoFeB with (111) plane parallel to
(001) plane of Bi2Te3 was observed, in contrast to polycrystalline CoFeB film
formed on Bi2Se3(001) at RT using high-temperature seeding layer. Therefore,
structurally ordered ferromagnetic thin films were obtained on the topological
insulator surface for the first time. Using high energy electron diffraction
(RHEED) 3D reciprocal space mapping, epitaxial relations of main
crystallographic axes for the CoFeB/ Bi2Te3 heterostructure were revealed. MOKE
and AFM measurements showed the isotropic azimuthal in-plane behavior of
magnetization vector in CoFeB/ Bi2Te3, in contrast to 2nd order magnetic
anisotropy seen in CoFeB/Bi2Se3. XPS measurements showed more stable behavior
of CoFeB grown on Bi2Te3 to the oxidation, in compare to CoFeB grown on Bi2Se3.
XAS and XMCD measurements of both concerned nanostructures allowed calculation
of spin and orbital magnetic moments for Co and Fe. Additionally, crystalline
structure and XMCD response of the CoFeB/BiTeI and Co55Fe45/BiTeI systems were
studied, epitaxial relations of main crystallographic axes were found, and spin
and orbital magnetic moments were calculated.",1801.10061v1
2018-10-03,Stable hump-like Hall effect and non-coplanar spin textures in SrRuO$_3$ ultrathin film,"We observed a hump-like feature in Hall effects of SrRuO$_3$ ultrathin films,
and systematically investigated it with controlling thicknesses, temperatures
and magnetic fields. The hump-like feature is extremely stable, even surviving
as a magnetic field is tilted by as much as 85$^\circ$. Based on the
atomic-level structural analysis of a SrRuO$_3$ ultrathin film with a
theoretical calculation, we reveal that atomic rumplings at the thin-film
surface enhance Dzyaloshinskii-Moriya interaction, which can generate stable
chiral spin textures and a hump-like Hall effect. Moreover, temperature
dependent resonant X-ray measurements at Ru L-edge under a magnetic field
showed that the intensity modulation of unexpected peaks was correlated with
the hump region in the Hall effect. We verify that the two-dimensional property
of ultrathin films generates stable non-coplanar spin textures having a
magnetic order in a ferromagnetic oxide material.",1810.01615v2
2019-06-10,Anomalous electron transport in epitaxial NdNiO$_3$ films,"The origin of simultaneous electronic, structural and magnetic transitions in
bulk rare-earth nickelates ($RE$NiO$_3$) remains puzzling with multiple
conflicting reports on the nature of these entangled phase transitions.
Heterostructure engineering of these materials offers unique opportunity to
decouple metal-insulator transition (MIT) from the magnetic transition.
However, the evolution of underlying electronic properties across these
decoupled transitions remains largely unexplored. In order to address this, we
have measured Hall effect on a series of epitaxial NdNiO$_3$ films, spanning a
variety of electronic and magnetic phases. We find that the MIT results in only
partially gapped Fermi surface, whereas full insulating phase forms below the
magnetic transition. In addition, we also find a systematic reduction of the
Hall coefficient ($R_H$) in the metallic phase of these films with epitaxial
strain and also a surprising transition to negative value at large compressive
strain. Partially gapped weakly insulating, paramagnetic phase is reminiscence
of pseudogap behavior of high $T_c$ cuprates. The precursor metallic phase,
which undergoes transition to insulating phase is a non-Fermi liquid with the
temperature exponent ($n$) of resistivity of 1, whereas the exponent increases
to 4/3 in the non-insulating samples. Such nickelate phase diagram with
sign-reversal of $R_H$, pseudo-gap phase and non Fermi liquid behavior are
intriguingly similar to high $T_c$ cuprates, giving important guideline to
engineer unconventional superconductivity in oxide heterostructure.",1906.03809v1
2019-09-06,Octupolar order in d-orbital Mott insulators,"Motivated by experimental and theoretical interest in realizing multipolar
orders in $d$-orbital materials, we discuss the quantum magnetism of $J\!=\!2$
ions which can be realized in spin-orbit coupled oxides with $5d^2$ transition
metal ions. Based on the crystal field environment, we argue for a splitting of
the $J\!=\!2$ multiplet, leading to a low lying non-Kramers doublet which hosts
quadrupolar and octupolar moments. We discuss a microscopic mechanism whereby
the combined perturbative effects of orbital repulsion and antiferromagnetic
Heisenberg spin interactions leads to ferro-octupolar coupling between
neighboring sites, and stabilizes ferro-octupolar order for a face-centered
cubic lattice. This same mechanism is also shown to disfavor quadrupolar
ordering. We show that studying crystal field levels via Raman scattering in a
magnetic field provides a probe of octupolar order. We study spin dynamics in
the ferro-octupolar state using a slave-boson approach, uncovering a gapped and
dispersive magnetic exciton. For sufficiently strong magnetic exchange, the
dispersive exciton can condense, leading to conventional type-I
antiferromagnetic (AFM) order which can preempt octupolar order. Our proposal
for ferrooctupolar order, with specific results in the context of a model
Hamiltonian, provides a comprehensive understanding of thermodynamics, $\mu$SR,
X-ray diffraction, and inelastic neutron scattering measurements on a range of
cubic $5d^2$ double perovskite materials including Ba$_2$ZnOsO$_6$,
Ba$_2$CaOsO$_6$, and Ba$_2$MgOsO$_6$. Our proposal for exciton condensation
leading to type-I AFM order may be relevant to materials such as
Sr$_2$MgOsO$_6$.",1909.03089v3
2019-09-11,Giant pressure-enhancement of multiferroicity in CuBr2,"Type-II multiferroic materials, in which ferroelectric polarization is
induced by inversion non-symmetric magnetic order, promise new and highly
efficient multifunctional applications based on the mutual control of magnetic
and electric properties. Although this phenomenon has to date been limited to
low temperatures, here we report a giant pressure-dependence of the
multiferroic critical temperature in CuBr$_2$. At 4.5 GPa, $T_\mathrm{C}$ is
enhanced from 73.5 to 162 K, to our knowledge the highest value yet reported
for a non-oxide type-II multiferroic. This growth shows no sign of saturating
and the dielectric loss remains small under these high pressures. We establish
the structure under pressure and demonstrate a 60\% increase in the two-magnon
Raman energy scale up to 3.6 GPa. First-principles structural and magnetic
energy calculations provide a quantitative explanation in terms of dramatically
pressure-enhanced interactions between CuBr$_2$ chains. These large,
pressure-tuned magnetic interactions motivate structural control in cuprous
halides as a route to applied high-temperature multiferroicity.",1909.04989v2
2019-10-09,Controlling magnetisation's reversal mechanism and hyperthermia efficiency in core/shell magnetic nanoparticles by tuning the interphase coupling,"Magnetic particle hyperthermia, in which colloidal nanostructures are exposed
to an alternating magnetic field, is a promising approach to cancer therapy.
Unfortunately, the clinical efficacy of hyperthermia has not yet been
optimized. Consequently, routes to improve magnetic particle hyperthermia such
as designing hybrid structures comprised from different phase materials are
actively pursued. Here we demonstrate enhanced hyperthermia efficiency in
relative large spherical Fe/Fe-oxide core/shell nanoparticles through the
manipulation of interactions between the core and shell phases. Experimental
results on exemplary samples with diameters in the range 30-80 nm indicated a
direct correlation of hysteresis losses to the observed temperature elevation
rate with a maximum efficiency of around 0.9 kW/g. The absolute particle size,
the core/shell ratio, and the interposition of a thin w\""ustite interlayer, are
shown to have powerful effects on the specific absorption rate. By comparing
our measurements to micromagnetic calculations we have unveiled topologically
non-trivial magnetisation reversal modes under which interparticle interactions
become negligible, aggregates formation is minimized, and the energy that is
converted into heat is increased. This information has been overlooked till
date and is in stark contrast to the existing knowledge on homogeneous
particles.",1910.03914v1
2019-10-23,Multi-messenger nano-probes of hidden magnetism in a strained manganite,"The ground state properties of correlated electron systems can be
extraordinarily sensitive to external stimuli, such as temperature, strain, and
electromagnetic fields, offering abundant platforms for functional materials.
We present a metastable and reversible photoinduced ferromagnetic transition in
strained films of the doped manganite La(2/3)Ca(1/3)MnO3. Using the novel
multi-messenger combination of atomic force microscopy, cryogenic scanning
near-field optical microscopy, magnetic force microscopy, and ultrafast laser
excitation, we demonstrate both ""writing"" and ""erasing"" of a metastable
ferromagnetic metal phase with nanometer-resolved finesse. By tracking both
optical conductivity and magnetism at the nano-scale, we reveal how spontaneous
strain underlies the thermal stability, persistence, and reversal of this
photoinduced metal. Our first-principles electronic structure calculations
reveal how an epitaxially engineered Jahn-Teller distortion can stabilize
nearly degenerate antiferromagnetic insulator and ferromagnetic metal phases.
We propose a Ginzburg-Landau description to rationalize the co-active interplay
of strain, lattice distortion, and magnetism we resolve in strained LCMO, thus
guiding future functional engineering of epitaxial oxides like manganites into
the regime of phase-programmable materials.",1910.10361v1
2020-04-20,Current-induced torque originating from orbital current,"The electrical manipulation of magnetization by current-induced spin torques
has given access to realize a plethora of ultralow power and fast spintronic
devices such as non-volatile magnetic memories, spin-torque nano-oscillators,
and neuromorphic computing devices. Recent advances have led to the notion that
relativistic spin-orbit coupling is an efficient source for current-induced
torques, opening the field of spin-orbitronics. Despite the significant
progress, however, the fundamental mechanism of magnetization manipulation, the
requirement of spin currents in generating current-induced torques, has
remained unchanged. Here, we demonstrate the generation of current-induced
torques without the use of spin currents. By measuring the current-induced
torque for naturally-oxidized-Cu/ferromagnetic-metal bilayers, we observed an
exceptionally high effective spin Hall conductivity at low temperatures despite
the absence of strong spin-orbit coupling. Furthermore, we found that the
direction of the torque depends on the choice of the ferromagnetic layer, which
counters the conventional understanding of the current-induced torque. These
unconventional features are best interpreted in terms of an orbital counterpart
of the spin torque, an orbital torque, which arises from the orbital Rashba
effect and orbital current. These findings will shed light on the underlying
physics of current-induced magnetization manipulation, potentially altering the
landscape of spin-orbitronics.",2004.09165v1
2017-05-08,"Relaxor ferroelectric behavior and intrinsic magnetodielectric behavior near room temperature in Li2Ni2Mo3O12, a compound with distorted honeycomb and spin-chains","Keeping current interests to identify materials with intrinsic
magnetodielectric behavior near room temperature and with novel pyroelectric
current anomalies, we report temperature and magnetic-field dependent behavior
of complex dielectric permittivity and pyroelectric current for an oxide,
Li2Ni2Mo3O12, containing magnetic ions with (distorted) honey-comb and chain
arrangement and ordering magnetically below 8 K. The dielectric data reveal the
existence of relaxor ferroelectricity behavior in the range 160-240 K and there
are corresponding Raman mode anomalies as well in that temperature range.
Pyrocurrent behavior is also consistent with this interpretation, with the
pyrocurrent peak-temperature interestingly correlating with the poling
temperature. 7Li NMR offer an evidence for crystallographic disorder intrinsic
to this compound and we therefore conclude that such a disorder is apparently
responsible for the randomness of local electric field leading to relaxor
ferroelectric property. Another observation of emphasis is that there is a
notable decrease in the dielectric constant with the application of magnetic
field to the tune of about -2.4% at 300 K, with the magnitude varying
mariginally with temperature. Small loss factor values validate intrinsic
behavior of the magnetodielectric effect at room temperature.",1705.02855v1
2017-09-12,Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice,"The asymmetry of chemical nature at the hetero-structural interface offers an
unique opportunity to design desirable electronic structure by controlling
charge transfer and orbital hybridization across the interface. However, the
control of hetero-interface remains a daunting task. Here, we report the
modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n
superlattices by manipulating the periodic thickness with n unit cells of
SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy
rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K.
Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with
breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n
interface, and electronic charge transfer from Mn to Ti 3d orbitals across the
interface. Orbital hybridization accompanying the charge transfer results in
preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a
stronger electronic hopping integral along the out-of-plane direction and
corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that
interfacial orbital hybridization in superlattices of strongly correlated
oxides may be a promising approach to tailor electronic and magnetic properties
in device applications.",1709.03903v1
2018-07-04,"Spin-orbit coupling driven insulating state in hexagonal iridates Sr3MIrO6 (M = Sr, Na and Li)","The spin-orbit coupling (SOC) interactions, electron correlation effects and
Hund coupling cooperate and compete with each other, leading to novel
properties, quantum phase and non-trivial topological electronic behavior in
iridium oxides. Because of the well separated IrO6 octahedra approaching cubic
crystal-field limit, the hexagonal iridates Sr3MIrO6 (M = Sr, Na and Li) serves
as a canonical model system to investigate the underlying physical properties
that arises from the novel Jeff state. Based on density functional theory
calculations complemented by Green's function methods, we systematically
explore the critical role of SOC on the electronic structure and magnetic
properties of Sr3MIrO6. The crystal-field splitting combined with correlation
effects are insufficient to account for the insulating nature, but the SOC
interactions is the intrinsic source to trigger the insulating ground states in
these hexagonal iridates. The decreasing geometry connectivity of IrO6
octahedra gives rise to the increasing of effective electronic correlations and
SOC interactions, tuning the hexagonal iridates from low-spin Jeff = 1/2 states
with large local magnetic moments for the Ir4+ (5d5) ions in Sr4IrO6 to
nonmagnetic singlet Jeff = 0 states without magnetic moments for the Ir5+ (5d4)
ions in Sr3NaIrO6 and Sr3LiIrO6. The theoretical calculated results are in good
agreement with available experimental data, and explain the magnetic properties
of Sr3MIrO6 well.",1807.01807v1
2019-03-19,Kitaev quantum spin liquid - concept and materialization,"A decade ago, Alexei Kitaev proposed an exactly solvable $S$ = 1/2 model on a
two-dimensional honeycomb lattice, where the spins fractionalize into Majorana
fermions and form a topological quantum spin liquid (QSL) in the ground state.
It was soon recognized that a family of complex iridium oxides, as well as
ruthenium chloride, with honeycomb structure are magnetic insulators and
accommodate essential ingredients of the Kitaev model, due to the interplay of
electron correlation and spin-orbit coupling. This initiated a race to
materialize the Kitaev QSL and to capture the signature of Majorana fermions.
In this review, we provide a wide perspective of this rapidly growing field,
including theory, materials and experiment. We first summarize the theoretical
background of the Kitaev QSL ground state and its materialization using
spin-orbital-entangled $J_{\rm eff}$ = 1/2 moments. This is followed by an
overview of candidate materials and their magnetic properties, including
Na$_2$IrO$_3$, $\alpha$, $\beta$, $\gamma$-Li$_2$IrO$_3$,$\alpha$-RuCl$_3$ and
H$_3$LiIr$_2$O$_6$. Finally, we review the latest exciting progress in the
search for the Kitaev QSL. In particular, H$_3$LiIr$_2$O$_6$ and
$\alpha$-RuCl$_3$ in applied magnetic field show signatures of the QSL state,
and $\alpha$-RuCl$_3$ has unusual magnetic excitations and thermal transport
properties that are consistent with spin fractionalization.",1903.08081v1
2019-08-18,Electron g-factor engineering for non-reciprocal spin photonics,"We study the interplay of electron and photon spin in non-reciprocal
materials. Traditionally, the primary mechanism to design non-reciprocal
photonic devices has been magnetic fields in conjunction with magnetic oxides,
such as iron garnets. In this work, we present an alternative paradigm that
allows tunability and reconfigurability of the non-reciprocity through
spintronic approaches. The proposed design uses the high-spin-orbit coupling of
a narrow-band gap semiconductor (InSb) with ferromagnetic dopants. A
combination of the intrinsic and a gate-applied electric field gives rise to a
strong external Rashba spin-orbit coupling (RSOC) in a magnetically doped InSb
film. The RSOC which is gate alterable is shown to adjust the magnetic
permeability tensor via the electron g-factor of the medium. We use electronic
band structure calculations (k$\cdot$p theory) to show the gate-adjustable RSOC
manifest itself in the non-reciprocal coefficient of photon fields via shifts
in the Kerr and Faraday rotations. In addition, we show that photon spin
properties of dipolar emitters placed in the vicinity of a non-reciprocal
electromagnetic environment is distinct from reciprocal counterparts. The
Purcell factor (F$_{p}$) of a spin-polarized emitter (right-handed circular
dipole) is significantly enhanced due to a larger g-factor while a left-handed
dipole remains essentially unaffected. Our work can lead to electron spin
controlled reconfigurable non-reciprocal photonic devices.",1908.06393v2
2019-11-11,Atomic Origin of Spin-Valve Magnetoresistance at the SrRuO3 Grain Boundary,"Defects ubiquitously exist in crystal materials and usually exhibit a very
different nature than the bulk matrix, and hence, their presence can have
significant impacts on the properties of devices. Although it is well accepted
that the properties of defects are determined by their unique atomic
environments, the precise knowledge of such relationships is far from clear for
most oxides due to the complexity of defects and difficulties in
characterization. Here, we fabricate a 36.8{\deg} SrRuO3 grain boundary of
which the transport measurements show a spin-valve magnetoresistance. We
identify its atomic arrangement, including oxygen, using scanning transmission
electron microscopy and spectroscopy. Based on the as-obtained atomic
structure, the density functional theory calculations suggest that the
spin-valve magnetoresistance is because of the dramatically reduced magnetic
moments at the boundary. The ability to manipulate magnetic properties at the
nanometer scale via defect control allows new strategies to design
magnetic/electronic devices with low-dimensional magnetic order.",1911.04108v1
2020-05-21,Enhancement of perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction in thin ferromagnetic films by atomic-scale modulation of interfaces,"To stabilize the non-trivial spin textures, e.g., skyrmions or chiral domain
walls in ultrathin magnetic films, an additional degree of freedom such as the
interfacial Dzyaloshinskii-Moriya interaction (IDMI) must be induced by the
strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However,
advanced approaches to simultaneously control IDMI and perpendicular magnetic
anisotropy (PMA) are needed for future spin-orbitronic device implementations.
Here, we show an effect of atomic-scale surface modulation on the magnetic
properties and IDMI in ultrathin films composed of 5d heavy
metal/ferromagnet/4d(5d) heavy metal or oxide interfaces, such as
Pt/CoFeSiB/Ru, Pt/CoFeSiB/Ta, and Pt/CoFeSiB/MgO. The maximum IDMI value
corresponds to the correlated roughness of the bottom and top interfaces of the
ferromagnetic layer. The proposed approach for significant enhancement of PMA
and IDMI through the interface roughness engineering at the atomic scale offers
a powerful tool for the development of the spin-orbitronic devices with the
precise and reliable controllability of their functionality.",2005.10584v1
2020-09-23,Magnetodielectric coupling and multi-blocking effect in the Ising-chain magnet Sr2Ca2CoMn2O9,"We have demonstrated magnetodielectric (MD) coupling in an Ising-chain magnet
Sr2Ca2CoMn2O9, via detailed investigation of ac susceptibility and dielectric
constant as a function of temperature, magnetic field and frequency.
Sr2Ca2CoMn2O9 consists of spin-chains, made of the regular stacking of one CoO6
trigonal prism with two MnO6 octahedra. The (Co2+ Mn4+ Mn4+) unit stabilizes a
(up-down-up) spin-state along the chains which are distributed on a triangular
lattice. This compound undergoes a partially disordered antiferromagnetic
transition at TN ~ 28 K. The dielectric constant exhibits a clear peak at TN
only in presence of an external magnetic field (above 5 kOe), evidencing the
presence of MD coupling, which is further confirmed by field-dependent
dielectric measurements. We argue that spatial inversion symmetry can be broken
as a result of exchange-striction along each spin chain, inducing uncompensated
local dipoles. At low temperatures, a dipolar relaxation phenomenon is
observed, bearing strong similarities with the blocking effect typical of the
spin dynamics in this compound. Such a spin-dipole relationship is referred to
as a multi-blocking effect, in relation with the concept of magnetodielectric
multiglass previously introduced for related materials.",2009.10969v2
2020-09-26,"Electroferrofluids with non-equilibrium voltage-controlled magnetism, interfaces, and patterns","Materials with continuous dissipation can exhibit responses and
functionalities that are not possible in thermodynamic equilibrium. While this
concept is well-known, a major challenge has been the implementation: how to
rationally design materials with functional non-equilibrium states and quantify
the dissipation? Here we address these questions for the widely used colloidal
nanoparticles that convey several functionalities. We propose that useful
non-equilibrium states can be realised by creating and maintaining steady-state
nanoparticle concentration gradients by continuous injection and dissipation of
energy. We experimentally demonstrate this with superparamagnetic iron oxide
nanoparticles that in thermodynamic equilibrium form a homogeneous functional
fluid with a strong magnetic response (a ferrofluid). To create non-equilibrium
functionalities, we charge the nanoparticles with anionic charge control agents
to create electroferrofluids where nanoparticles act as charge carriers that
can be driven with electric fields and current to non-homogeneous dissipative
steady-states. The dissipative steady-states exhibit voltage-controlled
magnetic properties and emergent diffuse interfaces. The diffuse interfaces
respond strongly to external magnetic fields, leading to dissipative patterns
that are not possible in the equilibrium state. We identify the closest
non-dissipative analogues of these dissipative patterns, discuss the
differences, and highlight how pattern formation in electroferrofluids is
linked to dissipation that can be directly quantified. Beyond electrically
controlled ferrofluids and patterns, we foresee that the concept can be
generalized to other functional nanoparticles to create various scientifically
and technologically relevant non-equilibrium states with optical, electrical,
catalytic, and mechanical responses that are not possible in thermodynamic
equilibrium.",2009.12563v1
2020-10-11,Stripes in oxygen-enriched cuprates,"Charge-order stripes of different types occur when copper oxides are doped
with either heterovalent metal, like $La_{2-x}Sr_xCuO_4$, or oxygen, like
$YBa_2Cu_3O_{6+y}$. The difference shows up in the doping dependence of their
incommensurability: $q_c(x) \propto \sqrt{x-\check{p}}$ but $q_c(y) \approx
0.3$. The square-root dependence in the former compound family results from
Coulomb repulsion between doped holes (or electrons), residing pairwise in
lattice-site $O$ (or $Cu$) atoms of the $CuO_2$ planes. The almost constant
$q_c(y)$ value in the second family results from the aggregation of ozone-like
molecules, formed from $O^{2-}$ ions of the host with embedded oxygen atoms,
$O_i$, at interstitial sites in the $CuO_2$ planes. The magnetic moments,
$\mathbf{m}(O)$, of the lattice-defect $O$ atoms in the first family arrange
antiferromagnetically, which gives rise to accompanying magnetization stripes
of incommensurability $q_m(x) = q_c(x)/2$. The ozone complexes have a vanishing
magnetic moment, $\mathbf{m}=0$, which explains the absence of accompanying
magnetization stripes in the second family. Embedding excess oxygen as $O_i$
atoms in $CuO_2$ planes is likewise assumed for $HgBa_2CuO_{4+\delta}$ and
oxygen-enriched bismuth cuprates. A combination of characteristics from both
families is present in oxygen-enriched $La_2CuO_{4+y}$. The validity of
determining the hole density in oxygen-enriched cuprates with the
universal-dome method is independently confirmed. Besides causing different
types of stripes, the two types of lattice-defect oxygen may also cause
different types of superconductivity. This could explain the much higher
$T_{c,max}$ in oxygen-enriched than $Sr$-doped cuprates, as well as the cusped
cooling-curves of X-ray intensity diffracted by stripes in the former family.",2010.06388v2
2020-11-12,Effective Magnetic Hamiltonian at Finite Temperatures for Rare Earth Chalcogenides,"Alkali metal rare-earth chalcogenide $ARECh2$ (A=alkali or monovalent metal,
RE=rare earth, Ch=O, S, Se, Te), is a large family of quantum spin liquid (QSL)
candidates we discovered recently. Unlike $YbMgGaO4$, most members in the
family except for the oxide ones, have relatively small crystalline
electric-field (CEF) excitation levels, particularly the first ones. This makes
the conventional Curie-Weiss analysis at finite temperatures inapplicable and
CEF excitations may play an essential role in understanding the low-energy spin
physics. Here we considered an effective magnetic Hamiltonian incorporating CEF
excitations and spin-spin interactions, to accurately describe thermodynamics
in such a system. By taking $NaYbSe2$ as an example, we were able to analyze
magnetic susceptibility, magnetization under pulsed high fields and heat
capacity in a systematic and comprehensive way. The analysis allows us to
produce accurate anisotropic exchange coupling energies and unambiguously
determine a crossover temperature ($\sim$25 K in the case of $NaYbSe2$), below
which CEF effects fade away and pure spin-spin interactions stand out. We
further validated the effective picture by successfully explaining the
anomalous temperature dependence of electron spin resonance (ESR) spectral
width. The effective scenario in principle can be generalized to other
rare-earth spin systems with small CEF excitations.",2011.06274v2
2021-08-18,"Charge Order and Fluctuations in Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ Revealed by $^{63,65}$Cu-Nuclear Magnetic Resonance","The discovery of a magnetic-field-induced charge-density-wave (CDW) order in
the pseudogap state via nuclear magnetic resonance (NMR) studies has
highlighted the importance of ""charge"" in the physics of high
transition-temperature ($T_{\rm c}$) superconductivity in copper oxides
(cuprates). Herein, after briefly reviewing the progress achieved in the last
few years, we report new results of $^{63,65}$Cu-NMR measurements on the CDW
order and its fluctuation in the single-layered cuprate
Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$. The NMR spectrum under both in- and
out-of-plane magnetic fields above $ H $ = 10 T indicates that the CDW replaces
the antiferromagnetic order before superconductivity appears, but disappears
before superconductivity is optimized. We found that the CDW onset temperature
$T_{\rm CDW}$ scales with the pseudogap temperature $T^{\rm *}$. Comparison
between $^{63}$Cu and $^{65}$Cu NMR indicates that the spin-lattice relaxation
process is dominated by charge fluctuations in the doping regions where the CDW
appears as well as at the pseudogap end point ($T^*$ = 0). These results
suggest that charge orders and fluctuations exist in multiple doping regions
and over a quite wide temperature range.",2108.08150v1
2021-12-08,Manipulation of spin orientation via ferroelectric switching in Fe-doped Bi2WO6 from first principles,"Atomic-scale control of spins by electric fields is highly desirable for
future technological applications. Magnetically-doped Aurivillius-phase oxides
present one route to achieve this, with magnetic ions substituted into the
ferroelectric structure at dilute concentrations, resulting in spin-charge
coupling. However, there has been minimal exploration of the ferroelectric
switching pathways in this materials class, limiting predictions of the
influence of an electric field on the magnetic spins in the structure. Here, we
determine the ferroelectric switching pathways of the end member of the
Aurivilius phase family, Bi2WO6, using a combination of group theoretic
analysis and density functional theory calculations. We find that in the ground
state P21ab phase, a two-step switching pathway via C2 and Cm intermediate
phases provides the lowest energy barrier. Considering iron substitutions on
the W-site in Bi2WO6, we determine the spin easy axis. By tracking the change
in spin directionality during ferroelectric switching, we find that a 90 degree
switch in the polarization direction leads to a 112 degree reorientation of the
spin easy axis. The low symmetry crystal-field environment of Bi2WO6 and
magnetoelastic coupling on the magnetic dopant provide a route to spin control
via and applied electric field.",2112.04055v1
2022-01-21,Spin Hall magnetoresistance in paramagnetic NdGaO3,"In recent years, spin Hall magnetoresistance (SMR) has emerged as an
efficient way to probe the spontaneous magnetization state in ordered magnetic
systems, by electrical current. Less known is its versatility as a probe of
materials that do not possess spontaneous magnetization such as in paramagnets.
In this work, SMR is used to probe paramagnetic NdGaO3 (NGO), a rare earth
oxide, possessing a sizable spin orbit interaction (L=6). NGO has not been
investigated earlier for its efficiency in propagating spins. We have performed
extensive temperature and angle dependent-magnetoresistance (ADMR) studies
along dissimilar crystallographic axes in NGO, using platinum (Pt) as spin
injector and detector and utilizing (inverse) spin Hall effect. We find a close
correlation between the temperature dependence of the ADMR response with
magnetization in NGO and a linear current bias dependence of the ADMR
amplitudes. These are chacteristics of SMR effect in Pt/NGO, arising from the
torque acting on localized moments in NGO and considering crystal field induced
intermultiplet transitions with temperature. Control experiments on Pt/SrTiO3
and Pt/SiO2 devices were also carried out in order to validate the observed SMR
response in Pt/NGO bilayer and to rule out magnetoresistive contributions from
Pt.",2201.08685v1
2022-02-28,Strongly anisotropic electronic and magnetic structures in oxide dichlorides RuOCl$_2$ and OsOCl$_2$,"Here, using density functional theory and density matrix renormalization
group methods, we investigate the electronic and magnetic properties of
RuOCl$_2$ and OsOCl$_2$ with $d^4$ electronic configurations. Different from a
previous study using VOI$_2$ with $d^1$ configuration, these systems with
$4d^4$ or $5d^4$ do not exhibit a ferroelectric instability along the $a$-axis.
Due to the fully-occupied $d_{xy}$ orbital in RuOCl$_2$ and OsOCl$_2$, the
Peierls instability distortion disappears along the $b$-axis, leading to an
undistorted I${\rm mmm}$ phase (No. 71). Furthermore, we observe strongly
anisotropic electronic and magnetic structures along the $a$-axis. The large
crystal-field splitting energy (between $d_{xz/yz}$ and $d_{xy}$ orbitals) and
large hopping between nearest-neighbor Ru and Os atoms suppresses the
spin-orbital effect in $M$OCl$_2$ ($M$ = Ru or Os) with electronic density $n =
4$, resulting in a spin-1 system instead of a $J = 0$ singlet ground state.
Moreover, we find staggered antiferromagnetic order with $\pi$ wavevector along
the $M$-O chain direction ($a$-axis) while the magnetic coupling along the
$b$-axis is weak. Based on Wannier functions from first-principles
calculations, we calculated the relevant hopping amplitudes and crystal-field
splitting energies of the $t_{2g}$ orbitals for the Os atoms to construct a
multi-orbital Hubbard model for the $M$-O chains. Staggered AFM with
$\uparrow$-$\downarrow$-$\uparrow$-$\downarrow$ spin structure dominates in our
DMRG calculations, in agreement with DFT calculations.",2203.00060v2
2022-05-08,Spin interaction and magnetism in cobaltate Kitaev candidate materials: an $ab$ $initio$ and model Hamiltonian approach,"In the quest for materials hosting Kitaev spin liquids, much of the efforts
have been focused on the fourth- and fifth-row transition metal compounds,
which are spin-orbit coupling assisted Mott insulators. Here, we study the
structural and magnetic properties of 3$d$ transition metal oxides,
Na$_2$Co$_2$TeO$_6$ and Na$_3$Co$_2$SbO$_6$. The partial occupancy of sodium in
former compound is addressed using a cluster expansion, and a honeycomb lattice
of sodiums is found to be energetically favored. Starting from the \textit{ab
initio} band structures, a many-body second order perturbation theory leads to
a pseudospin-$\frac{1}{2}$ Hamiltonian with estimated magnetic interactions. We
show that the experimentally observed zigzag magnetic state is stabilized only
when the first neighbor Kitaev coupling dominates over the Heisenberg term,
both of which are highly suppressed due to presence of $e_g$ orbitals. A third
neighbor Heisenberg interaction is found dominant in both these compounds. We
also present a phase diagram for Na$_2$Co$_2$TeO$_6$ by varying the
electron-electron and spin-orbit interactions. The computed spin excitation
spectra are found to capture essential features of recent experimental magnon
spectrum, lending support to our results.",2205.03836v2
2022-10-17,"Long-range order, bosonic fluctuations, and pseudogap in strongly correlated electron systems","This thesis deals with the Hubbard model as prototypical model to describe
the physics of electrons in the two-dimensional copper-oxide planes of
high-$T_c$ cuprates. To get approximate solutions, we employ functional
renormalization group (fRG) and dynamical mean-field theory (DMFT) methods.
  We deal with the problem of identifying bosonic fluctuations in the vertex
function, exhibiting an intricate dependence on momenta and frequencies already
at moderate coupling. In the normal, paramagnetic phase, the goal is achieved
by employing the recently introduced single-boson exchange decomposition. In
the symmetry-broken phases, we reformulate the previously introduced
combination of fRG with mean-field theory by explicitly introducing a bosonic
field.
  A widely discussed and challenging problem is the emergence of a pseudogap in
the Hubbard model. In this thesis we assume this phase to be characterized by
strong magnetic fluctuations. Following previous works, we fractionalize the
electron in a chargon, carrying the electron's charge, and a charge neutral
spinon, which represents local fluctuations of the spin orientation. The
chargons undergo N\'eel or spiral magnetic order below a density-dependent
transition temperature $T^*$. We compute DC charge transport coefficients for
the chargons, and obtain a pronounced drop in the charge carrier density across
the magnetic-to-paramagnetic transition. Directional fluctuations of the spin
orientation are described by a non-linear sigma model and prevent long-range
ordering of the electrons at any finite temperature. The phase where the
chargon degrees of freedom are magnetically ordered shares many features with
the pseudogap regime observed in high-$T_c$ cuprates: a strong reduction of the
charge carrier density, a spin gap, Fermi arcs, and electronic nematicity.",2210.08889v1
2022-10-17,"A comprehensive review on the ferroelectric orthochromates: Synthesis, property, and application","Multiferroics represent a class of advanced materials for promising
applications and stand at the forefront of modern science for the special
feature possessing both charge polar and magnetic order. Previous studies
indicate that the family of RECrO3 (RE = rare earth) compounds is likely
another rare candidate system holding both ferroelectricity and magnetism.
However, many issues remain unsolved, casting hot disputes about whether RECrO3
is multiferroic or not. For example, an incompatibility exists between reported
structural models and observed ferroelectric behaviors, and it is not easy to
determine the spin canting degree. To address these questions, one key step is
to grow single crystals because they can provide more reliable information than
other forms of matter do. In this review, the parent and doped ferroelectric
YCrO3 compounds are comprehensively reviewed based on scientific and patent
literatures from 1954 to 2022. The materials syntheses with different methods,
including poly-, nano-, and single-crystalline samples and thin films, are
summarized. The structural, magnetic, ferroelectric and dielectric, optical,
and chemical-pressure (on Y and Cr sites by doping) dependent chemical and
physical properties and the corresponding phase diagrams, are discussed.
Diverse (potential) applications, including anti-corrosion, magnetohydrodynamic
electrode, catalyst, negative-temperature-coefficient thermistor, magnetic
refrigeration, protective coating, and solid oxide fuel cell, are present. To
conclude, we summarize general results, reached consensuses, and existing
controversies of the past nearly 69 years of intensive studies and highlight
future research opportunities and emerging challenges to address existing
issues.",2210.09170v1
2023-04-13,"In situ theranostic platform uniting highly localized magnetic fluid hyperthermia, magnetic particle imaging, and thermometry in 3D","In all of medical profession a broad field of research is dedicated to seek
less invasive and low-risk forms of therapy with the ultimate goal of
non-invasive therapy, particularly in neoplasmic diseases. Theranostic
platforms, combining diagnostic and therapeutic approaches within one system,
have thus garnered interest to augment invasive surgical, chemical, and
ionizing interventions. Magnetic particle imaging (MPI) offers, with its
versatile tracer material (superparamagnetic iron oxide nanoparticles, SPIOs),
a quite recent alternative to established radiation based diagnostic
modalities. In addition, MPI lends a bimodal theranostic frame allowing to
combine tomographic imaging with therapy techniques using the very same SPIOs.
In this work, we show for the first time the interleaved combination of
MPI-based imaging, therapy (highly localized magnetic fluid hyperthermia) and
therapy safety control (MPI-based thermometry) within one theranostic platform
in all three spatial dimensions.",2304.06554v2
2023-04-23,Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator,"The scanning superconducting quantum interference device (SQUID) fabricated
on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile
tool for nanoscale imaging of magnetic, thermal, and transport properties of
microscopic devices of quantum materials. We present the design and performance
of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free
dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight
cell mounted at the bottom of the probe and is suspended by springs to suppress
vibrations caused by the pulse tube cryocooler. Two capillaries allow in-situ
control of helium exchange gas pressure in the cell that is required for
thermal imaging. A nanoscale heater is used to create local temperature
gradients in the sample, which enables quantitative characterization of the
relative vibrations between the tip and the sample. The spectrum of the
vibrations shows distinct resonant peaks with maximal power density of about 27
nm/Hz$^{1/2}$ in the in-plane direction. The performance of the SQUID-on-tip
microscope is demonstrated by magnetic imaging of the MnBi$_2$Te$_4$ magnetic
topological insulator, magnetization and current distribution imaging in a
SrRuO$_3$ ferromagnetic oxide thin film, and by thermal imaging of dissipation
in graphene.",2304.11667v1
2024-01-10,Observation of correlation induced metal to half-metal phase transition and large orbital moment in $\mathrm{Sr_2CoO_4}$,"We present a detailed mean-field study to address the fundamental discrepancy
in the ground state magnetization of $\mathrm{Sr_{2}CoO_{4}}$ (SCO). In
contrast to the ferromagnetic metallic ground state obtained from density
functional theory (DFT), DFT+$U$ gives three ferromagnetic solutions converging
to integer moment values (1, 2 \& 3 $\mu_B$/f.u) over a range of $U$.
Interestingly, two of the solutions are found to exhibit half-metallicity with
correspondingly $S$=1/2 and S=3/2 spin states. The half-metallic ferromagnetic
state with $S$=3/2 is found to be the ground state solution for SCO. Co atoms
show a large deviation from the formal +4 oxidation state indicating the
presence of strong covalency effects. Our results suggest a plausible metal to
half-metal phase transition around $U$($J$)=4.4(1.16) eV. The Fermi surface
study shows gradual collapse in states leading to half-metallicity suggesting
\textit{\textbf{k}}-dependence of effective $U$ around the critical region.
Surprisingly, in the presence of spin-orbit coupling (SOC), unexpectedly large
orbital moment ($L_{z}$=0.6) is noted in SCO putting it among the class of 3$d$
based transition metal compounds exhibiting pronounced orbital magnetization.
The calculations give large magnetocrystalline anisotropy energy (MAE) of
$\sim$48 meV. Large values of orbital magnetic moment contribution and MAE, in
the presence of strong correlation effects, provide a better interpretation of
experimental magnetization observed in SCO.",2401.05149v1
2024-02-25,Superconducting stripes induced by ferromagnetic proximity in an oxide heterostructure,"The intimate connection between magnetism and superconducting pairing
routinely plays a central role in determining the occurrence of unconventional
superconducting states. In high-transition-temperature (high-Tc) stripe-ordered
cuprate superconductors and a magnetically ordered iron-based superconductor,
the coupling between magnetism and superconductivity gives birth to novel
phases of matter with modulation of the superconducting pairing in the real
space. Further exploration of these phases can shed light on the mechanism of
unconventional superconductivity. Here we report on the discovery of a peculiar
spatially-varying superconducting state residing at the interface between
(110)-oriented KTaO3 and ferromagnetic EuO. Electrical transport measurements
reveal different Tc and upper critical fields (Hc2) with current applied along
the two orthogonal in-plane directions. Such anisotropy persistently occurs in
the low-carrier-density samples that are characterized by strong coupling
between Ta 5d and Eu 4f electrons, whereas in the high-carrier-density samples
the coupling is weakened and Tc and Hc2 becomes isotropic. Complemented by
local imaging of diamagnetism and theoretical analysis, our observations imply
an unprecedented emergence of superconducting stripes wherein the phase
coherence is established ahead of the rest of the interface, arising from a
band-filling-dependent ferromagnetic proximity. The realization of such exotic
superconducting states provides impetus for the study of novel physics in
heterostructures possessing both magnetism and superconductivity.",2402.16022v1
2024-03-13,Antiferromagnetic ordering and glassy nature in NASICON type NaFe$_2$PO$_4$(SO$_4$)$_2$,"We investigate crystal structure and magnetic properties including spin
relaxation and magnetocaloric effect in NASICON type NaFe$_2$PO$_4$(SO$_4$)$_2$
sample. The Rietveld refinement of x-ray and neutron diffraction patterns show
a rhombohedral crystal structure with the R$\bar{3}$c space group. The
core-level spectra confirm the desired oxidation state of constituent elements.
The {\it dc}--magnetic susceptibility ($\chi$) behavior in zero field-cooled
(ZFC) and field-cooled (FC) modes show the ordering temperature $\approx$50~K.
Interestingly, the analysis of temperature dependent neutron diffraction
patterns reveal an A-type antiferromagnetic (AFM) structure with the ordered
moment of 3.8 $\mu_{B}$/Fe$^{3+}$ at 5~K, and a magnetostriction below $T_{\rm
N}=$ 50~K. Further, the peak position in the {\it ac}--$\chi$ is found to be
invariant with the excitation frequency supporting the notion of dominating AFM
transition. Also, the unsaturated isothermal magnetization curve supports the
AFM ordering of the moments; however, the observed coercivity suggests the
presence of weak ferromagnetic (FM) correlations at 5~K. On the other hand, a
clear bifurcation between ZFC and FC curves of {\it dc}--$\chi$ and the
observed decrease in peak height of {\it ac}--$\chi$ with frequency suggest for
the complex magnetic interactions. The spin relaxation behavior in
thermo-remanent magnetization and aging measurements indicate the glassy states
at 5~K. Moreover, the Arrott plots and magnetocaloric analysis reveal the
AFM--FM interactions in the sample at lower temperatures.",2403.08679v1
2020-07-14,High-resolution neutron imaging: a new approach to characterize water in anodic aluminum oxides,"During the growth of anodic Al oxide layers water incorporates in the film
and therefore influences the intrinsic properties of the oxide formed. In this
study, we propose a new approach, based on the use of high-resolution neutron
imaging, to visualize and quantify the water content in porous Al oxides as a
function of anodizing conditions. Water in these porous films is either
incorporated directly in the oxide structure (structural) and/or fills the
pores (morphological). This preliminary study demonstrates that the differences
in water content of porous anodic Al oxide layers are strongly related to the
oxide growth parameters but interestingly cannot be directly correlated to a
specific change in the amorphous oxide structure or in the pore morphology. Due
to the high sensitivity of high-resolution neutron imaging to small changes in
the water content, we furthermore show that the morphological water content in
Al oxides formed in sulfuric acid as well as in phosphoric acid is partially
reversible upon heat treatment and immersion. High-resolution neutron imaging
is also found to be highly sensitive to structural disorder and
crystallographic orientations, allowing to identify different crystalline Al
oxide samples based on their structural and morphological defect content. This
offers new perspectives to study the effect of the hydrogen and/or water
incorporation as well as oxide-related structural modifications on Al
oxihydroxides in relation to growth parameters, stability, functionalization as
well as properties tuning, highly relevant to surface protection and their use
as templates.",2007.07118v1
2014-03-18,"Film structure of epitaxial graphene oxide on SiC: Insight on the relationship between interlayer spacing, water content, and intralayer structure","Chemical oxidation of multilayer graphene grown on silicon carbide yields
films exhibiting reproducible characteristics, lateral uniformity, smoothness
over large areas, and manageable chemical complexity, thereby opening
opportunities to accelerate both fundamental understanding and technological
applications of this form of graphene oxide films. Here, we investigate the
vertical inter-layer structure of these ultra-thin oxide films. X-ray
diffraction, atomic force microscopy, and IR experiments show that the
multilayer films exhibit excellent inter-layer registry, little amount (<10%)
of intercalated water, and unexpectedly large interlayer separations of about
9.35 {\AA}. Density functional theory calculations show that the apparent
contradiction of ""little water but large interlayer spacing in the graphene
oxide films"" can be explained by considering a multilayer film formed by carbon
layers presenting, at the nanoscale, a non-homogenous oxidation, where
non-oxidized and highly oxidized nano-domains coexist and where a few water
molecules trapped between oxidized regions of the stacked layers are sufficient
to account for the observed large inter-layer separations. This work sheds
light on both the vertical and intra-layer structure of graphene oxide films
grown on silicon carbide, and more in general, it provides novel insight on the
relationship between inter-layer spacing, water content, and structure of
graphene/graphite oxide materials.",1403.4633v1
2016-11-22,Alpha-tocopherol inhibits pore formation in the oxidized bilayers,"In biological membranes, alpha-tocopherols ({\alpha}-toc; vitamin E) protect
polyunsaturated lipids from free radicals. Although the interactions of
{\alpha}-toc with non-oxidized lipid bilayers have been studied, their on
oxidized bilayers remain unknown. In this study, atomistic molecular dynamics
(MD) simulations of oxidized lipid bilayers were performed with varying
concentrations of {\alpha}-toc. Bilayers with
1-palmitoyl-2-lauroyl-sn-glycero-3-phosphocholine (PLPC) lipids and its
aldehyde derivatives at 1:1 ratio were studied. Our simulations show that
oxidized lipids self-assemble into aggregates with a water pore rapidly
developing across the lipid bilayer. The free energy of transporting an
{\alpha}-toc molecule in a lipid bilayer suggests that {\alpha}-tocs can
passively adsorb into the bilayer. When {\alpha}-toc molecules were present at
low concentrations in bilayers containing oxidized lipids, the formation of
water pores was slowed down. At high {\alpha}-toc concentra-tions, no pores
were observed. Based on the simulations, we propose that the mechanism of how
{\alpha}-toc inhibits pore formation in bilayers with oxidized lipids is the
follow-ing: {\alpha}-tocs trap the polar groups of the oxidized lipids at the
membrane-water interface resulting in a decreased probability for the oxidized
lipids to reach contact with the two leaflets and initiate pore formation. This
demon-strates that {\alpha}-toc molecules not only protect the bilayer from
oxidation but also help to stabilize the bilayer after lipid peroxidation
occurs. These results will help in de-signing more efficient molecules to
protect membranes from oxidative stress.",1611.07264v1
2017-05-17,Visualizing the Cu and Cu2O Interface Transition in Nanoparticles with Environmental Scanning Transmission Electron Microscopy,"Understanding the oxidation and reduction mechanisms of catalytically active
transition metal nanoparticles is important to improve their application in a
variety of chemical processes. In nanocatalysis the nanoparticles can undergo
oxidation or reduction in situ, and thus the redox species are not what are
observed before and after reactions. We have used the novel environmental
scanning transmission electron microscope (ESTEM) with 0.1 nm resolution in
systematic studies of complex dynamic oxidation and reduction mechanisms of
copper nanoparticles. The oxidation of copper has previously been reported to
be dependent on its crystallography and its interaction with the substrate. By
following the dynamic oxidation process in situ, in real time, with high-angle
annular dark-field imaging in the ESTEM, we use conditions ideal to track the
oxidation front as it progresses across a copper nanoparticle by following the
changes in the atomic number (z) contrast with time. The oxidation occurs via
the nucleation of the oxide phase (Cu2O) from one area of the nanoparticle
which then progresses unidirectionally across the particle, with the Cu-to-Cu2O
interface having a relationship of Cu{111} parallel to Cu2O{111}. The oxidation
kinetics are related to the temperature and oxygen pressure. When the process
is reversed in hydrogen, the reduction process is observed to be similar to the
oxidation, with the same crystallographic relationship between the two phases.
The dynamic observations provide unique insights into redox mechanisms which
are important to understanding and controlling the oxidation and reduction of
copper-based nanoparticles.",1705.06065v1
2018-06-18,"Copper Doped Zinc Oxide Nanocrystalline Thin Film: Growth, Characterization, Effect of annealing on Photocatalytic activity and electrical properties of irradiated film","The problem of detecting the ability of some metal oxides as photocatalysts
is receiving considerable attention in the world. The studied zinc oxide is
considered as one of the most utilized semiconductors, due to its direct band
gap of 3.37 eV and a large exciton binding energy of 60 meV at room
temperature. The characteristic formulation of Copper doped zinc oxide is
implemented to obtain an improved adsorption kinetics and photocatalytic
activity of zinc oxide photocatalyst capable of evolving estimated
photoluminescence (PL) spectra of zinc oxide nanoparticles to explore the
effect of Copper doping and annealing temperature on its optical properties.
using Solgel spin coating technique, Zinc oxide and copper doped zinc oxide
thin films were deposited on borosilicate substrate and all films was annealed
at 500 C for 5- hours. Optical properties of the films have been studied using
spectrophotometer in the wavelength range 300-800nm and structure of zinc oxide
films is investigated and included reported, also the effect of the doping
concentration of Copper. Further the characteristic formulation to treat the
photocatalytic performance of pure zinc oxide and Copper Doped zinc oxide
samples were investigated through the degradation of Malachite Green (MG), as a
model of organic pollutants, under UV light irradiation. Mainly, these films
exhibited a good transparency in the visible region. It was observed that when
the doping concentration increased, the transmittance also increased.
irradiation for different times.",1806.06494v1
2022-07-06,Detecting chiral asymmetry in the interstellar medium using propylene-oxide,"(Abridged) Life is distinctly homochiral. The origins of this homochirality
are under active debate. Recently, propylene-oxide has been detected in the
gas-phase interstellar medium (ISM) (McGuire et al. 2016). The enantiomeric
composition of ISM propylene-oxide may be probed through circular polarization
measurements, but accurate estimates of the circular dichroism properties of
the microwave transitions of propylene-oxide are not available. We develop a
model of the circular dichroic activity in torsion-rotation transitions of
closed-shell chiral molecules, such as propylene-oxide. With this model, we
estimate the viability, and optimize observation strategies, of enantiomeric
excess detection in ISM propylene-oxide. We present estimates for the dichroic
activity of the torsion-rotation transitions of propylene-oxide, where we
predict that the circular polarization fractions of emission lines of
enantiopure propylene-oxide relevant to astronomical detection of
propylene-oxide are on the order of 10^(-6). Due to the low predicted circular
polarization fractions, we conclude that enantiomeric characterization of
propylene-oxide in the gas phase of the ISM is impossible with current
astronomical observation techniques. We suggest that only chiral radical
species may be viably employed for enantiomeric excess detection. We estimate
that laboratory experiments may be successful in detecting the enantiomeric
composition of a mixture of propylene-oxide through microwave dichroism
spectroscopy. The theory we present in this paper provides a solid theoretical
underpinning for such laboratory circular dichroism measurements in microwave
transitions.",2207.02888v1
2023-08-10,Predictions and correlation analyses of Ellingham diagrams in binary oxides,"Knowing oxide-forming ability is vital to gain desired or avoid deleterious
oxides formation through tuning oxidizing environment and materials chemistry.
Here, we have conducted a comprehensive thermodynamic analysis of 137 binary
oxides using the presently predicted Ellingham diagrams. It is found that the
active elements to form oxides easily are the f-block elements (lanthanides and
actinides), elements in the groups II, III, and IV (alkaline earth, Sc, Y, Ti,
Zr, and Hf), and Al and Li; while the noble elements with their oxides
nonstable and easily reduced are coinage metals (Cu, Ag, and especially Au),
Pt-group elements, and Hg and Se. Machine learning based sequential feature
selection indicates that oxide-forming ability can be represented by electronic
structures of pure elements, for example, their d- and s-valence electrons,
Mendeleev numbers, and the groups, making the periodic table a useful tool to
tailor oxide-forming ability. The other key elemental features to correlate
oxide-forming ability are thermochemical properties such as melting points and
standard entropy at 298 K of pure elements. It further shows that the present
Ellingham diagrams enable qualitatively understanding and even predicting
oxides formed in multicomponent materials, such as the Fe-20Cr-20Ni alloy (in
wt.%) and the equimolar high entropy alloy of AlCoCrFeNi, which are in
accordance with thermodynamic calculations using the CALPHAD approach and
experimental observations in the literature.",2308.05837v1
2020-07-30,The effect of structural and magnetic disorder on the 3$d$-5$d$ exchange interactions of La$_{2-x}$Ca$_{x}$CoIrO$_{6}$,"The delicate balance between spin-orbit coupling, Coulomb repulsion and
crystalline electric field interactions observed in Ir-based oxides is usually
manifested as exotic magnetic behavior. Here we investigate the evolution of
the exchange coupling between Co and Ir for partial La substitution by Ca in
La$_{2}$CoIrO$_6$. A great advantage of the use of Ca$^{2+}$ as replacement for
La$^{3+}$ is the similarity of its ionic radii. Thus, the observed magnetic
changes can more easily be associated to electronic variations. A thorough
investigation of the structural, electronic and magnetic properties of the
La$_{2-x}$Ca$_{x}$CoIrO$_6$ system was carried out by means of synchrotron
x-ray powder diffraction, muon spin rotation and relaxation ($\mu$SR), AC and
DC magnetization, XAS, XMCD, Raman spectroscopy, electrical resistivity and
dielectric permittivity. Our XAS results show that up to 25% of Ca substitution
at the La site results in the emergence of Co$^{3+}$, possibly in high spin
state, while the introduction of larger amount of Ca leads to the increase of
Ir valence. The competing magnetic interactions resulting from the mixed
valences lead to a coexistence of a magnetically ordered and an emerging spin
glass (SG) state for the doped samples. Our $\mu$SR results indicate that for
La$_{2}$CoIrO$_6$ a nearly constant fraction of a paramagnetic (PM) phase
persists down to low temperature, possibly related to the presence of a small
amount of Ir$^{3+}$ and to the anti-site disorder at Co/Ir sites. For the doped
compounds the PM phase freezes below 30 K, but there is still some dynamics
associated with the SG. The dielectric data obtained for the parent compound
and the one with 25% of Ca-doping indicate a possible magnetodielectric effect,
which is discussed in terms of the electron hopping between the TM ions, the
anti-site disorder and the distorted crystalline structure.",2007.15318v1
2018-05-31,Hydrogen Decrepitation and Spark Plasma Sintering to Produce Recycled SmCo5 Magnets With High Coercivity,"Spark plasma sintering (SPS) technique is applied in combination with
hydrogen decrepitation process for the recycling of SmCo5 magnets. The SmCo5
magnets for recycling were first decrepitated by hydrogen gas of a pressure of
4 bar for 3 hours to produce decrepitated powder. This powder was then used to
prepare isotropic sintered magnets using the SPS technique, by sintering at
800-1000 oC for 1 minute. Full densification of the SPS-ed magnets was possible
at a temperature of 1000 oC. The sample sintered at 900 oC showed the best
internal coercivity (jHc) of higher than 1500 kA/m with high remanence (Br)
value of 0.47 T and energy product (BH(max)) of 43.4 kJ/m3. The properties of
the SPS-ed sample sintered at 900 oC were compared with conventionally sintered
(CVS-ed) sample prepared by using fresh SmCo5 powder. The results showed the
improvement of the magnetic properties of the SPS-ed sample in comparison to
the CVS-ed sample at room temperature, and the possibility to use the SPS-ed
sample at high temperature of 180 oC, where the sample showed good magnetic
properties of jHc of 1502 kA/m, Br of 0.44 T and BH(max) of 36.4 kJ/m3. The
microstructure and X-ray diffraction patterns of the SPS-ed and the CVS-ed
samples were studied; where the samples showed to basically consist of SmCo5
matrix phase with Sm2Co7 and Sm-oxides.",1805.12347v1
2020-12-16,Observation of anti-damping spin-orbit torques generated by in-plane and out-of-plane spin polarizations in MnPd3,"High spin-orbit torques (SOTs) generated by topological materials and heavy
metals interfaced with a ferromagnetic layer show promise for next generation
magnetic memory and logic devices. SOTs generated from the in-plane spin
polarization along y-axis originated by the spin Hall and Edelstein effects can
switch magnetization collinear with the spin polarization in the absence of
external magnetic fields. However, an external magnetic field is required to
switch the magnetization along x and z-axes via SOT generated by y-spin
polarization. Here, we present that the above limitation can be circumvented by
unconventional SOT in magnetron-sputtered thin film MnPd3. In addition to the
conventional in-plane anti-damping-like torque due to the y-spin polarization,
out-of-plane and in-plane anti-damping-like torques originating from z-spin and
x-spin polarizations, respectively have been observed at room temperature. The
spin torque efficiency corresponding to the y-spin polarization from MnPd3 thin
films grown on thermally oxidized silicon substrate and post annealed at 400
Deg C is 0.34 - 0.44. Remarkably, we have demonstrated complete external
magnetic field-free switching of perpendicular Co layer via unconventional
out-of-plane anti-damping-like torque from z-spin polarization. Based on the
density functional theory calculations, we determine that the observed x- and
z- spin polarizations with the in-plane charge current are due to the low
symmetry of the (114) oriented MnPd3 thin films. Taken together, the new
material reported here provides a path to realize a practical spin channel in
ultrafast magnetic memory and logic devices.",2012.09315v1
2021-09-03,Anomalous magnetic exchange in a dimerized quantum-magnet composed of unlike spin species,"We present here a study of the magnetic properties of the antiferromagnetic
dimer material CuVOF$_4$(H$_2$O)$_6\cdot$H$_2$O, in which the dimer unit is
composed of two different $S = 1/2$ species, Cu(II) and V(IV). An applied
magnetic field of $\mu_0H_{\rm c1} = 13.1(1)~\rm T$ is found to close the
singlet-triplet energy gap, the magnitude of which is governed by the
antiferromagnetic intradimer, $J_0 \approx 21~\rm K$, and interdimer, $J'
\approx 1~\rm K$, exchange energies, determined from magnetometry and
electron-spin resonance measurements. The results of density functional theory
(DFT) calculations are consistent with the experimental results and predicts
antiferromagnetic coupling along all nearest-neighbor bonds, with the magnetic
ground state comprising spins of different species aligning antiparallel to one
another, while spins of the same species are aligned parallel. The magnetism in
this system cannot be accurately described by the overlap between localized V
orbitals and magnetic Cu orbitals lying in the Jahn-Teller (JT) plane, with a
tight-binding model based on such a set of orbitals incorrectly predicting that
interdimer exchange should be dominant. DFT calculations indicate significant
spin density on the bridging oxide, suggesting instead an unusual mechanism in
which intradimer exchange is mediated through the O atom on the Cu(II) JT axis.",2109.01529v2
2023-08-05,$μ$SR Study of the Dipole-Octupole Quantum Spin Ice Candidate Ce$_2$Zr$_2$O$_7$,"The Ce$^{3+}$ pseudospin-1/2 degrees of freedom in Ce$_2$Zr$_2$O$_7$ possess
both dipolar and octupolar character which enables the possibility of novel
quantum spin liquid ground states in this material. Here we report new muon
spin relaxation and rotation ($\mu$SR) measurements on single crystal samples
of Ce$_2$Zr$_2$O$_7$ in zero magnetic field and in magnetic fields directed
along the $[1,\bar{1},0]$ and $[1,1,1]$ crystallographic directions, and for
magnetic fields directed both longitudinal and transverse to the direction of
muon polarization. Our zero-field results show no signs of magnetic ordering or
spin freezing, consistent with earlier zero-field $\mu$SR measurements on a
powder sample of Ce$_2$Zr$_2$O$_7$, and also with the expectations for a
quantum spin ice. However, we measure a more gentle relaxation rate for
Ce$_2$Zr$_2$O$_7$ in zero-field at low temperatures than was previously
reported. This difference in relaxation rate is likely due to the low
oxidation, and correspondingly, the high stoichiometry of our single crystal
samples. Longitudinal field measurements confirm that the magnetic dipole
moments in Ce$_2$Zr$_2$O$_7$ remain dynamic at $T = 0.1$ $\mathrm{K}$. For both
$[1,\bar{1},0]$ and $[1,1,1]$ magnetic fields, our $\mu$SR Knight shift
measurements show a field-induced leveling off of the magnetic susceptibility
at low temperature which is qualitatively consistent with corresponding
calculations using the numerical-linked-cluster method in combination with
recent estimates for the nearest-neighbour exchange parameters of
Ce$_2$Zr$_2$O$_7$.",2308.02800v3
2013-10-25,Quantum magnons of the intermediate phase of half-doped manganite oxides,"At half doping, the ground state of three-dimensional manganite perovskite
oxides like R$_{1-x}$Ca$_x$MnO$_3$, where R is a trivalent ion such as La, Pr,
etc, is still unclear. Many experimental findings agree better with the
combined magnetic, charge, and orbital order characteristic of the
""intermediate phase"", introduced by Efremov et al. in 2004 [Nature Mats. 3,
853]. This phase consists of spin dimers (thus incorporating aspects of the
Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine et al. [Phys. Rev.
Lett. 89, 097205]), though formed by a pair of parallel Mn spins of different
magnitude, in principle (thereby allowing for a degree of Mn charge
disproportionation: not necessarily as large as that of Mn$^{3+}$-Mn$^{4+}$ in
Goodenough's original CE phase [Phys. Rev. 100, 564 (1955)]). In the
intermediate phase, consecutive spin dimers localed along the planar zig-zag
chains are oriented at a constant relative angle $\Phi$ between them. Varying
Mn-charge disproportionation and $\Phi$, the intermediate phase should allow to
continuously interpolate between the two limiting cases of the CE phase and the
dimer phase denoted as ""orthogonal intermediate $\pi/2-$phase"". It is not easy
to find a microscopic model able to describe the phenomenological intermediate
phase adequately for the spin, charge, and orbital degrees of freedom
simultaneously. Here, we study the quantum spin excitations of a planar model
of interacting localized spins, which we found can stabilize the intermediate
phase classically. We compare the quantum magnons of the intermediate phase
with those of the CE and orthogonal $\pi/2$ phases, in the context of recent
experimental results.",1310.6954v1
2015-06-16,Evidence of quantum dimer excitations in Sr$_3$Ir$_2$O$_7$,"The magnetic excitation spectrum in the bilayer iridate Sr$_3$Ir$_2$O$_7$ has
been investigated using high-resolution resonant inelastic x-ray scattering
(RIXS) performed at the iridium L$_3$ edge and theoretical techniques. A study
of the systematic dependence of the RIXS spectrum on the orientation of the
wavevector transfer, $\mathbf{Q}$, with respect to the iridium-oxide bilayer
has revealed that the magnon dispersion is comprised of two branches well
separated in energy and gapped across the entire Brillouin zone. Our results
contrast with those of an earlier study which reported the existence of a
single dominant branch. While these earlier results were interpreted as two
overlapping modes within a spin-wave model of weakly coupled iridium-oxide
planes, our results are more reminiscent of those expected for a system of
weakly coupled dimers. In this latter approach the lower and higher energy
modes find a natural explanation as those corresponding to transverse and
longitudinal fluctuations, respectively. We have therefore developed a
bond-operator theory which describes the magnetic dispersion in
Sr$_3$Ir$_2$O$_7$ in terms of quantum dimer excitations. In our model
dimerisation is produced by the leading Heisenberg exchange, $J_c$, which
couples iridium ions in adjacent planes of the bilayer. The Hamiltonian also
includes in plane exchange, $J$, as well as further neighbour couplings and
relevant anisotropies. The bond-operator theory provides an excellent account
of the dispersion of both modes, while the measured $\mathbf{Q}$ dependence of
the RIXS intensities is in reasonable qualitative accord with the spin-spin
correlation function calculated from the theory. We discuss our results in the
context of the quantum criticality of bilayer dimer systems in the presence of
anisotropic interactions derived from strong spin-orbit coupling.",1506.04877v1
2016-04-18,The High Temperature Superconductivity in Cuprates: Physics of the Pseudogap Region,"We discuss the physics of the high temperature superconductivity in hole
doped copper oxide ceramics in the pseudogap region. Starting from an effective
reduced Hamiltonian relevant to the dynamics of holes injected into the copper
oxide layers proposed in a previous paper, we determine the superconductive
condensate wavefunction. We show that the low-lying elementary condensate
excitations are analogous to the rotons in superfluid $^4He$. We argue that the
rotons-like excitations account for the specific heat anomaly at the critical
temperature. We discuss and compare with experimental observations the London
penetration length, the Abrikosov vortices, the upper and lower critical
magnetic fields, and the critical current density. We give arguments to explain
the origin of the Fermi arcs and Fermi pockets. We investigate the nodal gap in
the cuprate superconductors and discuss both the doping and temperature
dependence of the nodal gap. We suggest that the nodal gap is responsible for
the doping dependence of the so-called nodal Fermi velocity detected in angle
resolved photoemission spectroscopy studies. We discuss the thermodynamics of
the nodal quasielectron liquid and their role in the low temperature specific
heat. We propose that the ubiquitous presence of charge density wave in hole
doped cuprate superconductors in the pseudogap region originates from
instabilities of the nodal quasielectrons driven by the interaction with the
planar $CuO_2$ lattice. We investigate the doping dependence of the charge
density wave gap and the competition between charge order and
superconductivity. We discuss the effects of external magnetic fields on the
charge density wave gap and elucidate the interplay between charge density wave
and Abrikosov vortices. Finally, we examine the physics underlying quantum
oscillations in the pseudogap region.",1604.05059v3
2018-04-05,"Spin-orbit coupled systems in the ""atomic"" limit: rhenates, osmates, iridates","Motivated by RIXS experiments on a wide range of complex heavy oxides,
including rhenates, osmates, and iridates, we discuss the theory of RIXS for
site-localized $t_{2g}$ orbital systems with strong spin-orbit coupling. For
such systems, we present exact diagonalization results for the spectrum at
different electron fillings, showing that it accesses ""single-particle"" and
""multi-particle"" excitations. This leads to a simple picture for the energies
and intensities of the RIXS spectra in Mott insulators such as double
perovskites which feature highly localized electrons, and yields estimates of
the spin-orbit coupling and Hund's coupling in correlated $5d$ oxides. We
present new higher resolution RIXS data at the Re-L$_3$ edge in Ba$_2$YReO$_6$
which finds a previously unresolved peak splitting, providing further
confirmation of our theoretical predictions. Using ab initio electronic
structure calculations on Ba$_2$${\cal M}$ReO$_6$ (with ${\cal M}$=Re, Os, Ir)
we show that while the atomic limit yields a reasonable effective Hamiltonian
description of the experimental observations, effects such as $t_{2g}$-$e_g$
interactions and hybridization with oxygen are important. Our ab initio
estimate for the strength of the intersite exchange coupling shows that,
compared to the osmates, the exchange is one or two orders of magnitude weaker
in the rhenates and iridates, which may partly explain the suppression of
long-range magnetic order in the latter compounds. As a way to interpolate
between the site-localized picture and our electronic structure band
calculations, we discuss the spin-orbital levels of the ${\cal M}$O$_6$
cluster. This suggests a possible role for non-dispersive intra-cluster
excitons in Ba$_2$YIrO$_6$ which may lead to a weak breakdown of the atomic
$J_{\rm eff}=0$ picture and to small magnetic moments.",1804.02006v2
2014-06-19,AC loss and coupling currents in YBCO coated conductors with varying number of filaments,"Striation of HTS coated conductors (CCs) as a way to reduce their
magnetization AC losses has been the subject of intense research in the past
years by several groups. While the principle of this approach is well
understood, its practical application on commercial material to be used in
power application is still far to be implemented due to manufacturing and
technological constraints. Recent advances in tape quality and striation
technology are now enabling systematic investigations of the influence of the
number of filaments on AC loss reduction with a consistency that was not
available in the past. In this work we demonstrate the technological
feasibility of reducing the magnetization losses of commercially available CC
by striating them into a high number of filaments (up to 120). The loss
reduction exceeds one order of magnitude and does not come at the expense of
current-carrying capability: samples with 10 and 20 filaments are unaffected by
the striation process, while samples with 80 and 120 filaments still retain 80
and 70% of the current-carrying potential, respectively. We also investigate
the transverse resistivity in order to understand the paths followed by the
coupling currents: we found that the coupling current prevalently flows in the
metallic substrate, rather than in and out of the filaments. Finally, we use
oxidation as a method to reduce the coupling currents and losses. The
contribution of this work is three-fold: 1) It describes the know-how to
produce a large number of high quality striations in commercially available
CCs, greatly reducing their losses without extensively degrading their
transport properties; 2) It provides a comprehensive characterization of said
samples (e.g. measurements in a wide frequency range, transverse resistance
profiles, influence of oxidation on DC and AC behavior); 3) It provides new
insight on the patterns of the coupling currents.",1406.4990v2
2018-12-17,Electron spin relaxation of single phosphorus donors in metal-oxide-semiconductor nanoscale devices,"We analyze the electron spin relaxation rate $1/T_1$ of individual
ion-implanted $^{31}$P donors, in a large set of metal-oxide-semiconductor
(MOS) silicon nanoscale devices, with the aim of identifying spin relaxation
mechanisms peculiar to the environment of the spins. The measurements are
conducted at low temperatures ($T\approx 100$~mK), as a function of external
magnetic field $B_0$ and donor electrochemical potential $\mu_{\rm D}$. We
observe a magnetic field dependence of the form $1/T_1\propto B_0^5$ for
$B_0\gtrsim 3\,$ T, corresponding to the phonon-induced relaxation typical of
donors in the bulk. However, the relaxation rate varies by up to two orders of
magnitude between different devices. We attribute these differences to
variations in lattice strain at the location of the donor. For $B_0\lesssim
3\,$T, the relaxation rate changes to $1/T_1\propto B_0$ for two devices. This
is consistent with relaxation induced by evanescent-wave Johnson noise created
by the metal structures fabricated above the donors. At such low fields, where
$T_1>1\,$s, we also observe and quantify the spurious increase of $1/T_1$ when
the electrochemical potential of the spin excited state $|\uparrow\rangle$
comes in proximity to empty states in the charge reservoir, leading to
spin-dependent tunneling that resets the spin to $|\downarrow\rangle$. These
results give precious insights into the microscopic phenomena that affect spin
relaxation in MOS nanoscale devices, and provide strategies for engineering
spin qubits with improved spin lifetimes.",1812.06644v2
2019-03-01,Coexistence of metallic and nonmetallic properties in the pyrochlore Lu$_2$Rh$_2$O$_7$,"Transition metal oxides of the $4d$ and $5d$ block have recently become the
targets of materials discovery, largely due to their strong spin-orbit coupling
that can generate exotic magnetic and electronic states. Here we report the
high pressure synthesis of Lu$_2$Rh$_2$O$_7$, a new cubic pyrochlore oxide
based on $4d^5$ Rh$^{4+}$ and characterizations via thermodynamic, electrical
transport, and muon spin relaxation measurements. Magnetic susceptibility
measurements reveal a large temperature-independent Pauli paramagnetic
contribution, while heat capacity shows an enhanced Sommerfeld coefficient,
$\gamma$ = 21.8(1) mJ/mol-Rh K$^2$. Muon spin relaxation measurements confirm
that Lu$_2$Rh$_2$O$_7$ remains paramagnetic down to 2 K. Taken in combination,
these three measurements suggest that Lu$_2$Rh$_2$O$_7$ is a correlated
paramagnetic metal with a Wilson ratio of $R_W = 2.5$. However, electric
transport measurements present a striking contradiction as the resistivity of
Lu$_2$Rh$_2$O$_7$ is observed to monotonically increase with decreasing
temperature, indicative of a nonmetallic state. Furthermore, although the
magnitude of the resistivity is that of a semiconductor, the temperature
dependence does not obey any conventional form. Thus, we propose that
Lu$_2$Rh$_2$O$_7$ may belong to the same novel class of non-Fermi liquids as
the nonmetallic metal FeCrAs.",1903.00399v1
2019-12-10,Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite oxide thin films,"Magnetism and spin-orbit coupling (SOC) are two quintessential ingredients
underlying novel topological transport phenomena in itinerant ferromagnets.
When spin-polarized bands support nodal points/lines with band degeneracy that
can be lifted by SOC, the nodal structures become a source of Berry curvature;
this leads to a large anomalous Hall effect (AHE). Contrary to
three-dimensional systems that naturally host nodal points/lines,
two-dimensional (2D) systems can possess stable nodal structures only when
proper crystalline symmetry exists. Here we show that 2D spin-polarized band
structures of perovskite oxides generally support symmetry-protected nodal
lines and points that govern both the sign and the magnitude of the AHE. To
demonstrate this, we performed angle-resolved photoemission studies of
ultrathin films of SrRuO$_3$, a representative metallic ferromagnet with SOC.
We show that the sign-changing AHE upon variation in the film thickness,
magnetization, and chemical potential can be well explained by theoretical
models. Our study is the first to directly characterize the topological band
structure of 2D spin-polarized bands and the corresponding AHE, which could
facilitate new switchable devices based on ferromagnetic ultrathin films.",1912.04757v2
2021-10-05,Slow oxidation of magnetite nanoparticles elucidates the limits of the Verwey transition,"Magnetite (Fe3O4) is of fundamental importance as the original magnetic
material and also for the Verwey transition near T_V = 125 K, below which a
complex lattice distortion and electron orders occur. The Verwey transition is
suppressed by strain or chemical doping effects giving rise to well-documented
first and second-order regimes, but the origin of the order change is unclear.
Here, we show that slow oxidation of monodisperse Fe3O4 nanoparticles leads to
an intriguing variation of the Verwey transition that elucidates the doping
effects. Exposure to various fixed oxygen pressures at ambient temperature
leads to an initial drop to TV minima as low as 70 K after 45-75 days, followed
by recovery to a constant value of 95 K after 160 days that persists in all
experiments for aging times up to 1070 days. A physical model based on both
doping and doping-gradient effects accounts quantitatively for this evolution
and demonstrates that the persistent 95 K value corresponds to the lower limit
for homogenously doped magnetite and hence for the first order regime. In
comparison, further suppression down to 70 K results from inhomogeneous strains
that characterize the second-order region. This work demonstrates that slow
reactions of nanoparticles can give exquisite control and separation of
homogenous and inhomogeneous doping or strain effects on an nm scale and offers
opportunities for similar insights into complex electronic and magnetic phase
transitions in other materials.",2110.01817v1
2021-12-15,Magnetic field robust high quality factor NbTiN superconducting microwave resonators,"We systematically study the performance of compact lumped element planar
microwave $\mathrm{Nb_{70}Ti_{30}N}$ (NbTiN) resonators operating at 5 GHz in
external in-plane magnetic fields up to 440 mT, a broad temperature regime from
2.2 K up to 13 K, as well as mK temperatures. For comparison, the resonators
have been fabricated on thermally oxidized and pristine, (001) oriented silicon
substrates. When operating the resonators in the multi-photon regime at $T=2.2$
K, we find internal quality factors $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ for
NbTiN resonators grown on pristine Si substrates, while resonators grown on
thermally oxidized substrates show a reduced value of $Q_{\mathrm{int}}\simeq$
$1\cdot10^4$, providing evidence for additional loss channels for the latter
substrate. In addition, we investigate the $Q$-factors of the resonators on
pristine Si substrates at millikelvin temperatures to asses their applicability
for quantum applications. We find $Q_{\mathrm{int}}\simeq$ $2\cdot10^5$ in the
single photon regime and $Q_{\mathrm{int}}\simeq$ $5\cdot10^5$ in the high
power regime at $T=7$ mK.",2112.08296v1
2022-01-17,Tailoring Mie Resonances in Cupric Oxide Particles for Use as Nanoantennas,"The field of nano-optics has grown with plasmonic metals. Metals such as
silver, gold, and copper nanoparticles, can concentrate electromagnetic (EM)
fields at the nanoscale, due to the special property called localized surface
plasmon resonance (LSPR). This laid the foundation for a wide range of
applications, including nanoscale optics, solar energy harvesting,
photocatalysis, and biosensing. However, there are inherent problems associated
with plasmonic metals, such as high heating losses, and their inability to be
scaled-up like semiconductor fabrication processes. In addition, the field
enhancement is restricted only to electric fields. All together these inhibit
the broader use of PMNs in practical applications. In this work, we report
submicron cupric oxide (CuO) particles with a medium refractive index that can
exhibit strong electric and magnetic Mie resonances with strong
extinction/scattering cross-sections comparable to or slightly exceeding those
of their plasmonic counterparts. Through the development of particle synthesis
techniques with strong shape and size control, optical spectroscopy, and
finite-difference-time-domain simulations we show that the Mie resonance peak
wavelengths are size- and shape-dependent. This gives tunability in the visible
to near-infrared regions for harvesting a wider fraction of the solar spectrum.
Therefore, submicron CuO particles exhibit strong potential in emerging as
high-performance alternatives to PMNs. The strong electric and magnetic
Mie-resonance-mediated nanoantenna effect attribute that CuO particles can be
potentially used in a plethora of applications, including surface-enhance Raman
spectroscopy, metamaterials, photocatalysis, and photovoltaics.",2201.06608v1
2024-01-16,Controlled synthesis and characterization of porous silicon nanoparticles for dynamic nuclear polarization,"Si nanoparticles (NPs) have been actively developed as a hyperpolarized
magnetic resonance imaging (MRI) agent with an imaging window of more than one
hour. However, the progress in the development of NPs has been hampered by the
incomplete understanding of their structural properties that correspond to
efficient hyperpolarization build up and long polarization decays. In this work
we study dynamic nuclear polarization (DNP) of single crystal porous Si (PSi)
NPs with defined doping densities ranging from nominally undoped to highly
doped with boron or phosphorus. To develop such PSi NPs we perform low-load
metal-assisted catalytic etching for electronic grade Si powder followed by
thermal oxidation to form the dangling bonds in the $\text{Si/SiO}_2$
interface, the $P_b$ centers, which are the endogenous source of the unpaired
electron spins necessary for DNP. The controlled fabrication and oxidation
procedures allow us to thoroughly investigate the impact of the magnetic field,
temperature and doping on the DNP process, as well as to identify the rate
limiting step for the polarization buildup and decay. We argue that the buildup
and decay rate constants are limited by the polarization transfer across the
nuclear spin diffusion barrier determined by the large hyperfine shift of the
central \textsuperscript{29}Si nuclei of the $P_b$ centers. Finally, we find
the room temperature relaxation of low boron doped PSi NPs reaching $75 \pm 3$
minutes and nuclear polarization levels exceeding $\sim 6$ % when polarized at
6.7 T and 1.4 K. Our study thus establishes solid grounds for further
development of Si NPs.",2401.08320v1
2006-04-11,Superconductor made by electrolyzed and oxidized water,"By deintercalation of Na+ followed by inserting bilayers of water molecules
into the host lattice, the layered cobalt oxide of gamma-Na0.7CoO2 undergoes a
topotactic transformation to a layered cobalt oxyhydrate of
Na0.35(H2O)1.3CoO2-delta with the c-axis expanded from c = 10.9 anstrom to c =
19.6 anstrom. In this paper, we demonstrate that the superconducting phase of c
= 19.6 anstrom can be directly obtained by simply immersing gamma-Na0.7CoO2
powders in electrolyzed/oxidized (EO) water, which is readily available from a
commercial electrolyzed water generator. We found that high oxidation-reduction
potential of EO water drives the oxidation of the cobalt ions accompanying by
the formation of the superconductive c = 19.6 anstrom phase. Our results
demonstrate how EO water can be used to oxidize the cobalt ions and hence form
superconducting cobalt oxyhydrates in a clean and simple way and may provide an
economic and environment-friendly route to oxidize the transition metal of
complex metal oxides",0604264v1
2007-01-31,CO oxidation at Pd(100): A first-principles constrained thermodynamics study,"The possible formation of oxides or thin oxide films (surface oxides) on late
transition metal surfaces is recently being recognized as an essential
ingredient when aiming to understand catalytic oxidation reactions under
technologically relevant gas phase conditions. Using the CO oxidation at
Pd(100) as example, we investigate the composition and structure of this model
catalyst surface over a wide range of (T,p)-conditions within a multiscale
modeling approach where density-functional theory is linked to thermodynamics.
The results show that under the catalytically most relevant gas phase
conditions a thin surface oxide is the most stable ""phase"" and that the system
is actually very close to a transition between this oxidic state and a reduced
state in form of a CO covered Pd(100) surface.",0701777v1
2007-11-30,Comparative study of the growth of sputtered aluminum oxide films on organic and inorganic substrates,"We present a comparative study of the growth of the technologically highly
relevant gate dielectric and encapsulation material aluminum oxide in inorganic
and also organic heterostructures. Atomic force microscopy studies indicate
strong similarities in the surface morphology of aluminum oxide films grown on
these chemically different substrates. In addition, from X-ray reflectivity
measurements we extract the roughness exponent \beta of aluminum oxide growth
on both substrates. By renormalising the aluminum oxide roughness by the
roughness of the underlying organic film we find good agreement with \beta as
obtained from the aluminum oxide on silicon oxide (\beta = 0.38 \pm 0.02),
suggesting a remarkable similarity of the aluminum oxide growth on the two
substrates under the conditions employed.",0711.5019v1
2008-05-30,A brief comment on the chemical formulae of the rare earth iron arsenide oxide superconductors,"Just a brief comment on the chemical formulae of the rare earth iron arsenide
oxide superconductors",0805.4668v1
2010-02-18,Nanocrystal Growth on Graphene with Various Degrees of Oxidation,"We show a general two-step method to grow hydroxide and oxide nanocrystals of
the iron family elements (Ni, Co, Fe) on graphene with two degrees of
oxidation. Drastically different nanocrystal growth behaviors were observed on
low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in
hydrothermal reactions. Small particles pre-coated on GS with few
oxygen-containing surface groups diffused and recrystallized into
single-crystalline nickel hydroxide Ni(OH)2 hexagonal nanoplates or iron oxide
Fe2O3 nanorods with well defined morphologies. In contrast, particles
pre-coated on GO were pinned by the high-concentration oxygen groups and
defects on GO without recrystallization into well-defined shapes. Adjusting
reaction temperature can be combined to further control materials grown on
graphene. For materials with weak interactions with graphene, increasing the
reaction temperature can lead to diffusion and recrystallization of surface
species into larger crystals even on highly oxidized and defective GO. Our
results suggest an interesting new approach to controlling the morphology of
nanomaterials grown on graphene by tuning the surface chemistry of graphene as
substrates for crystal nucleation and growth.",1002.3435v1
2011-04-06,Crucible aperture: an effective way to reduce source oxidation in oxide molecular beam epitaxy process,"Growing multi-elemental complex-oxide structures using an MBE (Molecular Beam
Epitaxy) technique requires precise control of each source flux. However, when
the component elements have significantly different oxygen affinities,
maintaining stable fluxes for easily oxidizing elements is challenging because
of a source oxidation problem. Here, using Sr as a test source, we show that a
crucible aperture insert scheme significantly reduces the source oxidation in
an oxide-MBE environment. The crucible aperture insert was shaped like a disk
with a hole at the center and was mounted inside the crucible; it blocks most
of the oxygen species coming to the source, thus reducing the source oxidation.
However, the depth of the aperture disk was critical for its performance; an
ill-positioned aperture could make the flux stability even worse. With an
optimally positioned aperture insert, the crucible exhibited more than four
times improvement in Sr flux stability, compared to a conventional,
non-apertured crucible.",1104.1120v1
2016-02-22,Iron Oxide Surfaces,"The surface science of iron oxides is comprehensively reviewed. For the full
abstract please see pdf.",1602.06774v1
2016-10-26,"Atomic bonding and electrical potential at metal/oxide interfaces, a first principle study","A number of electronic devices involve metal/oxide interfaces in their
structure where the oxide layer plays the role of electrical insulator. As the
downscaling of devices continues, the oxide thickness can spread over only a
few atomic layers, making the role of interfaces prominent on its insulating
properties. The prototypical Al/SiO2 metal/oxide interface is investigated
using first principle calculations, and the effect of the interfacial atomic
bonding is evidenced. It is shown that the interface bonding configuration
critically dictates the mechanical and electronic properties of the interface.
Oxygen atoms are found to better delimit the oxide boundaries than cations.
Interfacial cation-metal bonds allow the metal potential to leak inside the
oxide layer, without atomic diffusion, leading to a virtual oxide thinning.",1610.08371v1
2018-02-21,Precursors of gate oxide degradation in SiC power MOSFETs,"Gate oxide degradation is more critical in Silicon-Carbide (SiC) MOSFETs than
in Silicon (Si) MOSFETs. This is because of the smaller gate oxide thickness
and the higher electric field that develops across the gate oxide in SiC
MOSFETs. While multiple precursors have been identified for monitoring the gate
oxide degradation in Si MOSFETs, very few precursors have been identified for
SiC MOSFETs. The purpose of this paper is to demonstrate that gate oxide
degradation precursors used in Si MOSFETs: a) threshold voltage, b) gate
plateau voltage and c) gate plateau time, can also be used as precursors for
SiC MOSFETS. Moreover, all three precursors are found to exhibit a simultaneous
increasing trend (during the stress time) leading to an increase in on-state
loss, switching loss and switching time of the SiC MOSFET. The existing studies
of gate oxide degradation mechanisms in SiC MOSFETs, and their effects on
threshold voltage and mobility were extended to correlate a variation of all
three precursors using analytical expressions. The increasing trends of
precursors were experimentally confirmed by inducing gate oxide degradation in
commercial SiC MOSFET samples.",1802.08085v1
2014-03-05,Strong Oxidation Resistance of Atomically Thin Boron Nitride Nanosheets,"Investigation on oxidation resistance of two-dimensional (2D) materials is
critical for many of their applications, because 2D materials could have higher
oxidation kinetics than their bulk counterparts due to predominant surface
atoms and structural distortions. In this study, the oxidation behavior of
high-quality boron nitride (BN) nanosheets of 1-4 layer thick has been examined
by heating in air. Atomic force microscopy and Raman spectroscopy analyses
reveal that monolayer BN nanosheets can sustain up to 850 {\deg}C and the
starting temperature of oxygen doping/oxidation of BN nanosheets only slightly
increases with the increase of nanosheet layer and depends on heating
conditions. Elongated etch lines are found on the oxidized monolayer BN
nanosheets, suggesting that the BN nanosheets are first cut along the
chemisorbed oxygen chains and then the oxidative etching grows perpendicularly
to these cut lines. The stronger oxidation resistance of BN nanosheets suggests
that they are more preferable for high-temperature applications than graphene.",1403.1002v1
2008-07-22,Modelling the onset of oxide formation on metal surfaces from first principles,"The formation of ultrathin oxide layers on metal surfaces is a
non-thermally-activated process which takes place spontaneously at very low
temperatures within nanoseconds. This paper reports mechanistic details of the
initial oxidation of bare metal surfaces, in particular Al(111) and TiN(001),
as obtained by means of first-principles molecular dynamics modelling within
the Density-Functional Theory. It is shown that the reactions of bare metal
surfaces with O2 molecules take place according to a 'hot-atom' dissociative
mechanism which is triggered by the filling of the sigma-star antibonding
molecular orbital and is characterised by a sudden release of a large amount of
kinetic energy. This released energy provides a driving force for metal/oxygen
place-exchange processes which are responsible for the onset of oxide formation
at virtually 0 K and at oxygen coverages well below 1 monolayer (ML). Further
simulations of the oxidation reactions reveal that a disordered ultrathin oxide
forms on Al(111), whereas a rather ordered structure develops on TiN(001)
following a selective oxidation process which leaves clusters of Ti vacancies
in the TiN lattice underneath the oxide layer.",0807.3430v1
2013-09-22,Fine tuning of micropillar cavity modes through repetitive oxidations,"Repetitive wet thermal oxidations of a tapered oxide aperture in a
micropillar structure are demonstrated. After each oxidation step the confined
optical modes are analyzed at room temperature. Three regimes are identified.
First, the optical confinement increases when the aperture oxidizes towards the
center. Then, the cavity modes shift by more than 30 nm, when the taper starts
to oxidize through the center, leading to a decrease in the optical path
length. Finally, the resonance frequency levels o?f, when the aperture is
oxidized all the way through the micropillar, but confined optical modes with a
high quality factor remain. This repetitive oxidation technique therefore
enables precise control of the optical cavity volume or wavelength.",1309.5943v1
2015-12-11,Chromatic annuli formation and sample oxidation on copper thin films by femtosecond laser,"We report an experimental investigation on the irradiation of copper thin
films with high repetition rate femtosecond laser pulses (1040 nm, 50 MHz), in
ambient air and liquid water. We observe a novel, striking phenomenon of
chromatic copper oxides (cupric oxide and cuprous oxide) annuli generation. The
characteristic features of the chromatic copper oxide annuli are studied by
exploiting micro-Raman Spectroscopy, Optical and Scanning Electron
Microscopies. In the case of irradiation in water, the seldom investigated
effects of the immersion time, after irradiation with a fixed number of pulses,
is analyzed, and an intriguing dependence of the color of the chromatic annuli
on the immersion time is observed. This remarkable behavior is explained by
proposing an interpretation scenario addressing the various processes involved
in the process. Our experimental findings show that cuprous oxide nanoparticles
(size of ~20 nm) and cuprous oxide nanocubes (nanocube edges of ~30, ~60 nm)
with extremely fine sizes can be effectively generated by exploiting high
repetition rate laser-assisted oxidation.",1512.03546v1
2017-10-08,Chemical Bonding Analysis on Amphoteric Hydrogen - Alkaline Earth Ammine Borohydrides,"Usually the ions in solid are in the positive oxidation states or in the
negative oxidation state depending upon the chemical environment. It is highly
unusual for an ion having both positive as well as negative oxidation state in
a particular compound. Structural analysis suggest that the alkaline earth
ammine borohydrides (AABH) with the chemical formula M (BH4)2(NH3)2 (M = Mg,
Ca, or Sr) where hydrogen is present in +1 and -1 oxidation states. In order to
understand the oxidation states of hydrogen and also the character of chemical
bond present in AABH we have made charge density, electron localization
function, Born effective charge, Bader effective charge, and density of states
analyses using result from the density functional calculations. Our detailed
analyses show that hydrogen is in amphoteric behavior with hydrogen closer to
boron is in negative oxidation state and that closer to nitrogen is in the
positive oxidation state. Due to the presence of finite covalent bonding
between the consitutents in AABH the oxidation state of hydrogen is
non-interger value. The confirmation of the presence of amphtoric behavior of
hydrogen in AABH has implication in hydrogen storage applications.",1710.04272v1
2019-07-10,Symmetry-Protected Degeneracies in the Electronic Band Structure of Oxidized Black Phosphorous,"We explore the oxidation of a single layer of black phosphorous using ab
initio density functional theory calculation. We search for the equilibrium
structures of phosphorene oxides, PO$_x$ with various oxygen concentrations $x$
($0{\le}x{\le}1$). By evaluating the formation energies with diverse
configurations and their vibrational properties for each of various $x$ values,
we identify a series of stable oxidized structures with $x$ and confirm that
the oxidation occurs naturally. We also find that oxidation makes some modes
from the P-O bonds P-P bonds IR-active implying that the infrared spectra can
be used to determine the degree of oxidation of phosphorene. Our electronic
structure calculation reveals that the fully oxidized phosphorene (PO) has a
direct band gap of 0.83 eV similar to the pristine phosphorene. Intriguingly,
the PO possesses two nonsymmorphic symmetries with the inversion symmetry
broken, guaranteeing a symmetry-protected band structures including the band
degeneracy and four-fold degenerate Dirac points. Our results may provide a
significant insight into the intriguing relations between symmetry of lattice
and band topology of electrons.",1907.04550v1
2017-05-19,Charge transfer driven emergent phenomena in oxide heterostructures,"Complex oxides exhibit many intriguing phenomena, including metal-insulator
transition, ferroelectricity/multiferroicity, colossal magnetoresistance and
high transition temperature superconductivity. Advances in epitaxial thin film
growth techniques enable us to combine different complex oxides with atomic
precision and form an oxide heterostructure. Recent theoretical and
experimental work has shown that charge transfer across oxide interfaces
generally occurs and leads to a great diversity of emergent interfacial
properties which are not exhibited by bulk constituents. In this report, we
review mechanisms and physical consequence of charge transfer across interfaces
in oxide heterostructures. Both theoretical proposals and experimental
measurements of various oxide heterostructures are discussed and compared. We
also review the theoretical methods that are used to calculate charge transfer
across oxide interfaces and discuss the success and challenges in theory.
Finally, we present a summary and perspectives for future research.",1705.06962v1
2021-02-26,Data Analytics Approach to Predict High-Temperature Cyclic Oxidation Kinetics of NiCr-based Alloys,"Although of practical importance, there is no established modeling framework
to accurately predict high-temperature cyclic oxidation kinetics of
multi-component alloys due to the inherent complexity. We present a data
analytics approach to predict the oxidation rate constant of NiCr-based alloys
as a function of composition and temperature with a highly consistent and
well-curated experimental dataset. Two characteristic oxidation models, i.e., a
simple parabolic law and a statistical cyclic-oxidation model, have been chosen
to numerically represent the high-temperature oxidation kinetics of commercial
and model NiCr-based alloys. We have successfully trained machine learning (ML)
models using highly ranked key input features identified by correlation
analysis to accurately predict experimental parabolic rate constants (kp). This
study demonstrates the potential of ML approaches to predict oxidation kinetics
of alloys over a wide composition and temperature ranges. This approach can
also serve as a basis for introducing more physically meaningful ML input
features to predict the comprehensive cyclic oxidation behavior of
multi-component high-temperature alloys with proper constraints based on the
known underlying mechanisms.",2102.13261v1
2021-06-09,High diffusivity pathways govern massively enhanced oxidation during tribological sliding,"The lifetime of moving metallic components is often limited by accelerated
oxidation. Yet, the mechanisms and pathways for oxidation during tribological
loading are not well understood. Using copper as a model system,
tribologically-induced oxidation is systematically investigated by varying the
sliding speed and test duration under mild tribological loading. We demonstrate
that tribo-oxidation is controlled by test duration rather than the number of
cycles or the sliding speed. Plastic deformation from tribological loading
creates dislocations, grain and phase boundaries that act as high diffusivity
pathways. A combination of electron microscopy and atom probe tomography
revealed significantly enhanced atomic concentration of the diffusing species
around dislocations. Oxygen diffusion into the bulk as well as of copper
towards the free surface along these defects control the oxide formation
kinetics. Our work paves the way for formulating a physics-based understanding
for tribo-oxidation, which is crucial to develop strategies to prevent
oxidation and to strategically tailor surfaces to increase the lifetime of
engineering systems.",2106.04849v2
2022-02-27,Molecular rectifiers with very high rectification ratio enabled by oxidative damage in double-stranded DNA,"In this work, we report a novel strategy to construct molecular diodes with a
record tunable rectification ratio of as high as 10^6 using oxidatively damaged
DNA molecules. Being exposed to several endogenous and exogenous events, DNA
suffers constant oxidative damages leading to oxidation of guanine to
8-Oxoguanine (8oxoG). Here, we study the charge migration properties of native
and oxidatively damaged DNA using a multiscale multiconfigurational methodology
comprising of molecular dynamics, density functional theory and kinetic Monte
Carlo simulations. We perform a comprehensive study to understand the effect of
different concentrations and locations of 8oxoG in a dsDNA sequence on its CT
properties and find tunable rectifier properties having potential applications
in molecular electronics such as molecular switches and molecular rectifiers.
We also discover the negative differential resistance properties of fully
oxidized Drew-Dickerson sequence. The presence of 8oxoG guanine leads to the
trapping of charge, thus operates as a charge sink, which reveals how oxidized
guanine saves the rest of the genome from further oxidative damage.",2202.13443v1
2022-09-01,Why Ultrafast Photo-induced CO Desorption Dominates over Oxidation on Ru(0001),"CO oxidation on Ru(0001) is a long-standing example of a reaction that, being
thermally forbidden in ultra-high vacuum, can be activated by femtosecond laser
pulses. In spite of its relevance, the precise dynamics of the photo-induced
oxidation process as well as the reasons behind the dominant role of the
competing CO photo-desorption remain unclear. Here we use ab initio molecular
dynamics with electronic friction that account for the highly excited and
non-equilibrated system created by the laser to investigate both reactions. Our
simulations successfully reproduce the main experimental findings: the
existence of photo-induced oxidation and desorption, the large desorption to
oxidation branching ratio, and the changes in the O K-edge X-ray absorption
spectra attributed to the initial stage of the oxidation process. Now, we are
able to monitor in detail the ultrafast CO desorption and CO oxidation
occurring in the highly-excited system and to disentangle what causes the
unexpected inertness to the otherwise energetically favored oxidation.",2209.00518v1
2022-11-29,Composition based oxidation state prediction of materials using deep learning,"Oxidation states are the charges of atoms after their ionic approximation of
their bonds, which have been widely used in charge-neutrality verification,
crystal structure determination, and reaction estimation. Currently only
heuristic rules exist for guessing the oxidation states of a given compound
with many exceptions. Recent work has developed machine learning models based
on heuristic structural features for predicting the oxidation states of metal
ions. However, composition based oxidation state prediction still remains
elusive so far, which is more important in new material discovery for which the
structures are not even available. This work proposes a novel deep learning
based BERT transformer language model BERTOS for predicting the oxidation
states of all elements of inorganic compounds given only their chemical
composition. Our model achieves 96.82\% accuracy for all-element oxidation
states prediction benchmarked on the cleaned ICSD dataset and achieves 97.61\%
accuracy for oxide materials. We also demonstrate how it can be used to conduct
large-scale screening of hypothetical material compositions for materials
discovery.",2211.15895v1
2023-05-19,A stable and low loss oxide for superconducting qubits,"The dielectric loss of amorphous oxide layers is a major limiting factor for
the coherent time of superconducting qubits. Usually, the surface oxides of
superconductor film are lossy and unstable in air. To increase the coherence
time, it is essential for qubits to have stable and low dielectric loss oxides,
either as barrier or passivation layers. Here, we demonstrate that a kind of
amorphous tantalum oxide on Ta film is robust and stable by means of chemical
and structural analysis. Such kind of oxide layer forms in a self-limiting
process on the surface of {\alpha}-Ta (110) film in piranha solution, yielding
stable thickness and steady chemical composition. Quarter-wavelength coplanar
waveguide resonators are made to study the loss of this oxide. An internal
quality factor of above three million is measured at single photon level for
fresh device, and it is still over two million even after exposed to air for
months. Furthermore, we propose a method to fabricate all-tantalum
superconducting qubits using this kind of oxide as the dielectric and
passivation layers.",2305.11395v1
2023-12-11,Features of nanocontact formed using point electrical breakdown of a niobium oxide nanolayer,"The electrical characteristics of a point section of niobium oxide between a
massive cathode made of a superconducting indium-tin alloy and a niobium film
before the oxide breakdown and the nanocontact that appears after the breakdown
of the oxide at room temperature have been studied. The dependences of the
point breakdown voltage of the oxide and the resistance of nanocontacts on the
method of breakdown and the thickness of the oxide in the range of 15-60 nm
have been established. In particular, a minimum value of the breakdown current
has been established (about 1 {\mu}A), below which breakdown does not occur.
The voltage-current characteristic (VCC) of the oxide has a semiconductor
character and indicates the dependence of the breakdown voltage of the oxide on
its polarity. The VCC of the nanocontact is nonlinear, which is associated with
phase transitions in the nanocontact material caused by its heating by the
transport current.",2312.06816v1
2024-01-30,Electrical characterization of gadolinium oxide deposited by high pressure sputtering with in situ plasma oxidation,"In this work, we characterized gadolinium oxide films deposited on silicon by
high pressure sputtering with a two-step process: first, we sputtered metallic
gadolinium in an argon atmosphere and then, we performed an in-situ plasma
oxidation of the metallic layer previously deposited. By means of high
resolution transmission electron microscopy, we can detect the oxidation degree
of the metallic film. Under optimized deposition conditions, fully oxidized
Gd2O3 films are obtained. In addition, the capacitance and conductance as a
function of gate voltage of Pt gated metal-insulator-semiconductor capacitors
confirm stable dielectric behavior of the fully oxidized films. The devices
show low gate leakage currents (1e5 A/cm2 at 1 V for 2.2 nm of equivalent oxide
thickness), low interface trap density and an almost negligible hysteresis and
frequency dispersion.",2402.00889v1
2024-02-29,Three-dimensional atomic interface between metal and oxide in Zr-ZrO2 nanoparticles,"Metal-oxide interfaces with poor coherency have unique properties comparing
to the bulk materials and offer broad applications in the fields of
heterogeneous catalysis, battery, and electronics. However, current
understanding of the three-dimensional (3D) atomic metal-oxide interfaces
remains limited because of their inherent structural complexity and limitations
of conventional two-dimensional imaging techniques. Here, we determine the 3D
atomic structure of metal-oxide interfaces in zirconium-zirconia nanoparticles
using atomic-resolution electron tomography. We quantitatively analyze the
atomic concentration and the degree of oxidation, and find the coherency and
translational symmetry of the interfaces are broken. Moreover, we observe
porous structures such as Zr vacancies and nano-pores and investigate their
distribution. Our findings provide a clear 3D atomic picture of metal-oxide
interface with direct experimental evidence. We anticipate this work could
encourage future studies on fundamental problems of oxides such as interfacial
structures in semiconductor and atomic motion during oxidation process.",2402.18943v1
2004-09-27,On the Magnetic Excitation Spectra of High Tc Cu Oxides up to the Energies far above the Resonance Energy,"Magnetic excitation spectra c""(q,w) of YBa2Cu3Oy and La214 systems have been
studied. For La1.88Sr0.12CuO4, c""(q,w) have been measured up to ~30 meV and
existing data have been analyzed up to the energy w~150 meV by using the
phenomenological expression of the generalized magnetic susceptibility
c(q,w)=c0(q,w)/{1+J(q)c0(q,w)}, where c0(q,w) is the susceptibility of the
electrons without the exchange coupling J(q) among them. In the relatively low
energy region up to slightly above the resonance energy Er, it has been
reported by the authors' group that the expression can explain characteristics
of the q- and w-dependence of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here,
it is also pointed out that the expression can reproduce the rotation of four
incommensurate peaks of c""(q,w) within the a*-b* plane about (p/a, p/a) {or
so-called (p, p)} point by 45 degree, which occurs as w goes to the energy
region far above Er from E below Er. For La2-xSrxCuO4 and La2-xBaxCuO4,
agreements between the observed results and the calculations are less
satisfactory than for YBCO, indicating that we have to take account of the
existence of the ""stripes"" to consistently explain the observed c""(q,w) of
La214 system especially near x=1/8.",0409675v1
2005-12-20,Magnetoresistance Effects in SrFeO(3-x): Dependence on Phase Composition and Relation to Magnetic and Charge Order,"Single crystals of iron(IV) rich oxides SrFeO(3-x) with controlled oxygen
content have been studied by Moessbauer spectroscopy, magnetometry,
magnetotransport measurements, Raman spectroscopy, and infrared ellipsometry in
order to relate the large magnetoresistance (MR) effects in this system to
phase composition, magnetic and charge order. It is shown that three different
types of MR effects occur. In cubic SrFeO3 (x = 0) a large negative MR of 25%
at 9 T is associated with a hitherto unknown 60 K magnetic transition and a
subsequent drop in resistivity. The 60 K transition appears in addition to the
onset of helical ordering at ~130 K. In crystals with vacancy-ordered
tetragonal SrFeO(3-x) as majority phase (x ~0.15) a coincident
charge/antiferromagnetic ordering transition near 70 K gives rise to a negative
giant MR effect of 90% at 9 T. A positive MR effect is observed in tetragonal
and orthorhombic materials with increased oxygen deficiency (x = 0.19, 0.23)
which are insulating at low temperatures. Phase mixtures can result in a
complex superposition of these different MR phenomena. The MR effects in
SrFeO(3-x) differ from those in manganites as no ferromagnetic states are
involved.",0512510v1
2006-02-14,Magnetic properties of superconducting cobalt oxides NaxCoO2.yH2O,"Studies of the NMR Knight shift K of Na0.3CoO2.yH2O have been carried out in
detail. The suppression of K by the occurrence of the superconductivity
reported previously by the present authors in both magnetic field directions
perpendicular and parallel to the c axis has been confirmed, indicating that
the Cooper pairs are in the singlet state. The anisotropy of the suppression
amplitudes is consistent with the anisotropy of the hyperfine coupling constant
Aspin estimated by the K-kai plot. It has also been found that even samples,
which do not exhibit a significant amount of the Curie-Weiss-like increase of
the uniform magnetic susceptibility kai with decreasing temperature T, exhibit
the superconducting transition, which indicates that the superconducting
Na0.3CoO2.1.3H2O is not necessarily be in the proximity region of the
ferromagnetic phase. It has also been confirmed that the superconducting
transition temperature Tc of the samples prepared by mixing Na0.7CoO2, H2O (or
D2O) and bromine for 4 h, and separating the resultant powder from the solution
by filtration, depends on the elapsed time t after filtration. For these
samples, the Curie constant of kai estimated at low temperatures increases with
t, supporting the idea that the number of the lattice imperfection possibly due
to the oxygen-vacancy-formation increases with t. Even for such samples, the
superconductivity appears, which seems to exclude the possibility of the
anisotropic superconducting order parameter. These results are favorable for
the full-gapped superconductivity.",0602323v1
2006-12-06,Epitaxial Bi2FeCrO6 Multiferroic Thin Films,"We present here experimental results obtained on Bi2FeCrO6 (BFCO) epitaxial
films deposited by laser ablation directly on SrTiO3 substrates. It has been
theoretically predicted, by Baettig and Spaldin, using first-principles density
functional theory that BFCO is ferrimagnetic (with a magnetic moment of 2 Bohr
magneton per formula unit) and ferroelectric (with a polarization of ~80
microC/cm2 at 0K). The crystal structure has been investigated using X-ray
diffraction which shows that the films are epitaxial with a high crystallinity
and have a degree of orientation depending of the deposition conditions and
that is determined by the substrate crystal structure. Chemical analysis
carried out by X-ray Microanalysis and X-ray Photoelectron Spectroscopy (XPS)
indicates the correct cationic stoichiometry in the BFCO layer, namely
(Bi:Fe:Cr = 2:1:1). XPS depth profiling revealed that the oxidation state of Fe
and Cr ions in the film remains 3+ throughout the film thickness and that both
Fe and Cr ions are homogeneously distributed throughout the depth.
Cross-section high-resolution transmission electron microscopy images together
with selected area electron diffraction confirm the crystalline quality of the
epitaxial BFCO films with no identifiable foreign phase or inclusion. The
multiferroic character of BFCO is proven by ferroelectric and magnetic
measurements showing that the films exhibit ferroelectric and magnetic
hysteresis at room temperature. In addition, local piezoelectric measurements
carried out using piezoresponse force microscopy (PFM) show the presence of
ferroelectric domains and their switching at the sub-micron scale.",0612168v1
2009-07-17,A First-Principles Study of Zinc Oxide Honeycomb Structures,"We present a first-principles study of the atomic, electronic, and magnetic
properties of two-dimensional (2D), single and bilayer ZnO in honeycomb
structure and its armchair and zigzag nanoribbons. In order to reveal the
dimensionality effects, our study includes also bulk ZnO in wurtzite,
zincblende, and hexagonal structures. The stability of 2D ZnO, its nanoribbons
and flakes are analyzed by phonon frequency, as well as by finite temperature
ab initio molecular-dynamics calculations. 2D ZnO in honeycomb structure and
its armchair nanoribbons are nonmagnetic semiconductors but acquire net
magnetic moment upon the creation of zinc-vacancy defect. Zigzag ZnO
nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms
at the edges and have high spin polarization at the Fermi level. However, they
change to nonmagnetic metal upon termination of their edges with hydrogen
atoms. From the phonon calculations, the fourth acoustical mode specified as
twisting mode is also revealed for armchair nanoribbon. Under tensile stress
the nanoribbons are deformed elastically maintaining honeycomblike structure
but yield at high strains. Beyond yielding point honeycomblike structure
undergo a structural change and deform plastically by forming large polygons.
The variation in the electronic and magnetic properties of these nanoribbons
have been examined under strain. It appears that plastically deformed
nanoribbons may offer a new class of materials with diverse properties.",0907.3070v2
2010-04-02,Flux pinning on nano-sized defects and critical current in HTc superconductors,"New results of the investigations critical current problems in the high
temperature oxide superconductors are presented, basing on an analysis of the
flux pinning on nano-sized centers. New model of the interaction pancake
vortices with the nano-sized centers is proposed, while comparison of obtained
results with others pinning forces approaches presented. The energy balance
approach is applied, which leads to the appearance of the potential barrier
determining the pancake vortices movement in the flux creep process. Various
initial positions of the captured vortex have been analyzed, while variation of
the screening currents for such configuration has been considered and initial
calculations of the influence this effect on the current-voltage
characteristics performed. The dependence of the critical current on the
pinning centers parameters has been obtained while comparison with experimental
data is given. Pinning force has been calculated and its temperature
dependence, which is in qualitative agreement with an experiment. Critical
current determines the magnetic induction profiles and therefore flux trapping,
very important parameter from the point of view of an application HTc
superconductors as permanent magnets. The influence of the critical current on
the flux trapping in ceramic granular superconductors is calculated as well as
influence of various other material parameters - grain radius, surface barrier,
fulfillment of the ceramic with superconducting grains. Influence of the
critical current on a.c. losses in second generation HTc tapes with magnetic
substrate is discussed briefly too.",1004.0316v1
2010-06-10,NMR study on the stability of the magnetic ground state in MnCr${}_2$O${}_4$,"The canting angles and fluctuation of the magnetic ion spins of spinel oxide
MnCr${}_2$O${}_4$ were studied by nuclear magnetic resonance (NMR) at low
temperatures, which has a collinear ferrimagnetic order below $T_C$ and a
ferrimagnetic spiral order below $T_s < T_C$. Contrary to previous reports,
only one spin canting angle of Cr ions was observed. The spin canting angles of
Mn and Cr ions in the ferrimagnetic spiral obtained at a liquid-He temperature
were $43\,^{\circ}$ and $110\,^{\circ}$, respectively. The nuclear spin-spin
relaxation was determined by the Suhl-Nakamura interaction at low temperatures
but the relaxation rate $T_2^{-1}$ increases rapidly as the temperature
approaches $T_s$. This indicates that the fluctuation of the spiral component
becomes faster as the temperature increases but not fast enough to leave an
averaged hyperfine field to nuclei in the time scale of nuclear spin precession
in the ferrimagnetic phase, which is on the order of $10^{-8}$ s. The spiral
volume fraction measured for various temperatures reveals that the collinear
and the spiral ferrimagnetic phases are mixed below the transition temperature
of the spiral order. The temperature hysteresis in the volume fraction implies
that this transition has first-order characteristics.",1006.1983v1
2010-09-28,Absence of Ferromagnetism in Mn-doped Tetragonal Zirconia,"In a recent letter, it has been predicted within first principle studies that
Mn-doped ZrO2 compounds could be good candidate for spintronics application
because expected to exhibit ferromagnetism far beyond room temperature. Our
purpose is to address this issue experimentally for Mn-doped tetragonal
zirconia. We have prepared polycrystalline samples of Y0.15(Zr0.85-yMny)O2
(y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at
equilibrium. The obtained samples were carefully characterized by using x-ray
diffraction, scanning electron microscopy, elemental color mapping, X-ray
photoemission spectroscopy and magnetization measurements. From the detailed
structural analyses, we have observed that the 5% Mn doped compound
crystallized into two symmetries (dominating tetragonal & monoclinic), whereas
higher Mn doped compounds are found to be in the tetragonal symmetry only. The
spectral splitting of the Mn 3s core-level x-ray photoelectron spectra confirms
that Mn ions are in the Mn3+ oxidation state and indicate a local magnetic
moment of about 4.5 {\mu}B/Mn. Magnetic measurements showed that compounds up
to 10% of Mn doping are paramagnetic with antiferromagnetic interactions.
However, higher Mn doped compound exhibits local ferrimagnetic ordering. Thus,
no ferromagnetism has been observed for all Mn-doped tetragonal ZrO2 samples.",1009.5583v2
2011-08-10,"Interactions between Magnetic Nanowires and Living Cells : Uptake, Toxicity and Degradation","We report on the uptake, toxicity and degradation of magnetic nanowires by
NIH/3T3 mouse fibroblasts. Magnetic nanowires of diameters 200 nm and lengths
comprised between 1 {\mu}m and 40 {\mu}m are fabricated by controlled assembly
of iron oxide ({\gamma}-Fe2O3) nanoparticles. Using optical and electron
microscopy, we show that after 24 h incubation the wires are internalized by
the cells and located either in membrane-bound compartments or dispersed in the
cytosol. Using fluorescence microscopy, the membrane-bound compartments were
identified as late endosomal/lysosomal endosomes labeled with lysosomal
associated membrane protein (Lamp1). Toxicity assays evaluating the
mitochondrial activity, cell proliferation and production of reactive oxygen
species show that the wires do not display acute short-term (< 100 h) toxicity
towards the cells. Interestingly, the cells are able to degrade the wires and
to transform them into smaller aggregates, even in short time periods (days).
This degradation is likely to occur as a consequence of the internal structure
of the wires, which is that of a non-covalently bound aggregate. We anticipate
that this degradation should prevent long-term asbestos-like toxicity effects
related to high aspect ratio morphologies and that these wires represent a
promising class of nanomaterials for cell manipulation and microrheology.",1108.2081v1
2011-08-29,"Magnetization Dynamics, Throughput and Energy Dissipation in a Universal Multiferroic Nanomagnetic Logic Gate with Fan-in and Fan-out","The switching dynamics of a multiferroic nanomagnetic NAND gate with
fan-in/fan-out is simulated by solving the Landau-Lifshitz-Gilbert (LLG)
equation while neglecting thermal fluctuation effects. The gate and logic wires
are implemented with dipole-coupled 2-phase (magnetostrictive/piezoelectric)
multiferroic elements that are clocked with electrostatic potentials of ~50 mV
applied to the piezoelectric layer generating 10 MPa stress in the
magnetostrictive layers for switching. We show that a pipeline bit throughput
rate of ~ 0.5 GHz is achievable with proper magnet layout and sinusoidal
four-phase clocking. The gate operation is completed in 2 ns with a latency of
4 ns. The total (internal + external) energy dissipated for a single gate
operation at this throughput rate is found to be only ~ 1000 kT in the gate and
~3000 kT in the 12-magnet array comprising two input and two output wires for
fan-in and fan-out. This makes it respectively 3 and 5 orders of magnitude more
energy-efficient than complementary-metal-oxide-semiconductor-transistor (CMOS)
based and spin-transfer-torque-driven nanomagnet based NAND gates. Finally, we
show that the dissipation in the external clocking circuit can always be
reduced asymptotically to zero using increasingly slow adiabatic clocking, such
as by designing the RC time constant to be 3 orders of magnitude smaller than
the clocking period. However, the internal dissipation in the device must
remain and cannot be eliminated if we want to perform fault-tolerant classical
computing.
  Keywords: Nanomagnetic logic, multiferroics, straintronics and spintronics,
Landau-Lifshitz-Gilbert equation.",1108.5758v1
2011-12-12,"Crystal Growth and Physical Properties of SrCu2As2, SrCu2Sb2 and BaCu2Sb2","We report the growth of single crystals of SrCu2As2, SrCu2Sb2,
SrCu2(As{0.84}Sb{0.16})2 and BaCu2Sb2 using the self-flux technique and their
structural, magnetic, thermal and transport properties that were investigated
by powder x-ray diffraction (XRD), magnetic susceptibility chi, specific heat
Cp and electrical resistivity rho measurements versus temperature T from 1.8 to
350 K. Rietveld refinements of XRD patterns for crushed crystals confirm that
SrCu2As2 crystallizes in the ThCr2Si2-type structure and SrCu2Sb2 crystallizes
in the CaBe2Ge2-type structure. However, BaCu2Sb2 is found to have a large unit
cell consisting of three blocks. Here a ThCr2Si2-type block is sandwiched
between two CaBe2Ge2-type blocks along the c-axis, as reported, but likely with
a monoclinic distortion. The chi data of all these compounds are diamagnetic
and reveal nearly T-independent anisotropic behavior. The finite values of the
Sommerfeld linear specific heat coefficients gamma and the T dependences of rho
reveal metallic character of all four compounds. The electronic and magnetic
properties indicate that these compounds are sp metals with Cu in the 3d^{10}
electronic configuration corresponding to the oxidation state Cu^{+1}, as
previously predicted theoretically for (Sr,Ba)Cu2As2 by D. J. Singh. We find
that SrCu2As2 has a collapsed-tetragonal structure. The electronic character of
the Cu and the strength of the As-As interlayer bonding are both expected to
drastically change between weakly Cu-substituted BaFe2As and pure BaCu2As2.",1112.2722v2
2012-09-23,Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components,"Heterostructured material systems devoid of ferroic components are presumed
not to display ordering associated with ferroelectricity. In heterostructures
composed of transition metal oxides, however, the disruption introduced by an
interface can affect the balance of the competing interactions among electronic
spins, charges and orbitals. This has led to the emergence of properties absent
in the original building blocks of a heterostructure, including metallicity,
magnetism and superconductivity. Here we report the discovery of
ferroelectricity in artificial tri-layer superlattices consisting solely of
non-ferroelectric NdMnO3/SrMnO3/LaMnO3 layers. Ferroelectricity was observed
below 40 K exhibiting strong tunability by superlattice periodicity.
Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of
the polarization. Density functional calculations indicate that broken space
inversion symmetry and mixed valency, because of cationic asymmetry and
interfacial polar discontinuity, respectively, give rise to the observed
behavior. Our results demonstrate the engineering of asymmetric layered
structures with emergent ferroelectric and magnetic field tunable functions
distinct from that of normal devices, for which the components are typically
ferroelectrics.",1209.5070v1
2012-09-28,"Quantum dynamics of a single, mobile spin impurity","Quantum magnetism describes the properties of many materials such as
transition metal oxides and cuprate superconductors. One of its elementary
processes is the propagation of spin excitations. Here we study the quantum
dynamics of a deterministically created spin-impurity atom, as it propagates in
a one-dimensional lattice system. We probe the full spatial probability
distribution of the impurity at different times using single-site-resolved
imaging of bosonic atoms in an optical lattice. In the Mott-insulating regime,
a post-selection of the data allows to reduce the effect of temperature, giving
access to a space- and time-resolved measurement of the quantum-coherent
propagation of a magnetic excitation in the Heisenberg model. Extending the
study to the bath's superfluid regime, we determine quantitatively how the bath
strongly affects the motion of the impurity. The experimental data shows a
remarkable agreement with theoretical predictions allowing us to determine the
effect of temperature on the coherence and velocity of impurity motion. Our
results pave the way for a new approach to study quantum magnetism, mobile
impurities in quantum fluids, and polarons in lattice systems.",1209.6468v1
2013-02-06,Magnetic irreversibility in ultrafine ZnFe2O4 partices,"Pure ultrafine ZnFe2O4 particles have been obtained from mechanosynthesis of
the ZnO and Fe2O3 oxides. The average grain diameter was estimated from x-ray
diffraction to be <d> = 36(6) nm. Refinement of neutron diffraction (ND) data
showed that the resulting cubic spinel structure is oxygen-deficient, with ~7%
of Fe3+ ions occupying the tetrahedral A sites. Magnetization curves taken at
4.2 K showed absence of saturation up to fields H = 9 Tesla, associated to a
spin-canted produced by the milling process. Field-cooled (FC) and
zero-field-cooled (ZFC) curves showed irreversible behavior extending well
above room temperature, which is associated to spin disorder. Annealing samples
at 300 {\deg}C yields an average grain size <d> = 50(6) nm, and ~16% of Fe3+
ions at A sites. Partial oxygen recovery is also deduced from neutron data
refinement in annealed samples. Concurrently, decrease of magnetic
irreversibility is noticed, assigned to partial recovery of the collinear spin
structure. Complex M\""ossbauer spectra were observed at room temperature and 80
K, with broad hyperfine field distributions spanning from ~10 T to ~40 T. At T
= 4.2 K, hyperfine field distributions indicate high disorder in Fe local
environments. The above data suggest the existence of Fe-rich clusters,
yielding strong superexchange interactions between Fe ions at A and B sites of
the spinel structure.",1302.1276v1
2013-02-20,Spin-Triplet Superconductivity Induced by Longitudinal Ferromagnetic Fluctuations in UCoGe: Theoretical Aspect,"Identification of pairing mechanisms leading to the unconventional
superconductivity realized in copper-oxide, heavy-fermions, and organic
compounds is one of the most challenging issues in condensed-matter physics.
Clear evidence for an electron-phonon mechanism in conventional superconductors
is seen by the isotope effect on the superconducting transition temperatures
$T_{\rm SC}$, since isotopic substitution varies the phonon frequency without
affecting the electronic states. In unconventional superconductors, magnetic
fluctuations have been proposed to mediate superconductivity, and considerable
efforts have been made to unravel relationships between normal-state magnetic
fluctuations and superconductivity. Here, we show that characteristic
experimental results on the ferromagnetic (FM) superconductor UCoGe ($T_{\rm
Curie} \sim 2.5 $ K and $T_{\rm SC} \sim 0.6$ K) can be understood consistently
within a scenario of the spin-triplet superconductivity induced by FM spin
fluctuations. Temperature and angle dependencies of the upper critical magnetic
field of the superconductivity ($H_{c2}$) are calculated on the basis of the
above scenario by solving the Eliashberg equation. Calculated $H_{c2}$ well
agrees with the characteristic experimental results observed in UCoGe. This is
a first example that FM fluctuations are shown to be a pairing glue of
superconductivity.",1302.4827v1
2015-04-29,"Study of grain boundary transparency in (Yb1-xCax)Ba2Cu3O bi-crystal thin films over a wide temperature, field and field orientation range","The residual low angle grain boundary (GB) network is still the most
important current-limiting mechanism operating in bi-axially textured rare
earth barium copper oxide (REBCO) coated conductors. While Ca-doping is well
established to improve super-current flow across low angle GBs in weak fields
at high temperatures, Ca-doping also depresses Tc, making it so far impractical
for high temperature applications of REBCO coated conductors. On the other
hand, high field magnet applications of REBCO require low temperatures. Here we
systematically evaluate the effectiveness of Ca-doping in improving the GB
transparency, r$^{GB}$= Jc$^{GB}$/Jc$^{grain}$ , of low angle Yb1-xCaxBaCuO
[001] tilt bi-crystal films down to 10K and with magnetic fields perpendicular
and parallel to the film surfaces, while varying the Ca and oxygen doping
level. Using Low Temperature Scanning Laser Microscopy (LTSLM) and
Magneto-Optical Imaging (MOI), we found rGB to strongly depend on the angle
between magnetic field and the GB plane and clearly identified regimes in which
Jc$^{GB}$ can exceed Jc$^{grain}$ (r$^{GB}$>1) where the GB pinning is
optimized by the field being parallel to the GB dislocations. However, even in
this favorable situation, we found that r$^{GB}$ became much smaller at lower
temperatures. Calculations of the GB Ca segregation profile predict that the
high Jc channels between the GB dislocation cores are almost Ca-free. It may be
therefore that the positive effects of Ca doping seen by many authors near Tc
are partly a consequence of the higher Tc of these Ca-free channels.",1504.07861v1
2015-07-21,First principles study of the adsorption of MgO molecules on a clean Fe(001) surface,"The adsorption of MgO molecules on a Fe(001) surface was studied using
density functional theory (DFT) and projector augmented wave methods. The
energetically most favored configurations for different adsorption sites
considered were identified. The most preferable adsorption geometry is when the
MgO molecules are parallel to the surface, with Mg in the interstitial site and
O in on-top of the Fe atom. During the adsorption of subsequent MgO molecules
in this geometry, a sharp, non-oxidized interface is formed between the MgO
adlayer and Fe(001) surface. The adsorption of MgO perpendicular to the
surface, with oxygen incorporated in the topmost Fe layer is less probable, but
may lead to the formation of the FeO layer when stabilized with an excess of
oxygen atoms. Structural, electronic and magnetic properties of both interface
types were examined for the MgO coverage from 1/9 to 1 monolayer (ML).
Electronic and magnetic properties are sensitive to the MgO coverage. For lower
coverage of MgO, clear hybridization between the Fe 3d and O 2p states is
shown. The average magnetic moment of the surface Fe atoms is reduced with
coverage, achieving 2.78 $\mu_{\rm B}$ for 1 ML of MgO.",1507.05803v2
2015-10-29,Magnetic mechanisms of pairing in strongly correlated electron system of copper oxides,"The multielectron LDA+GTB approach has been developed to calculate electronic
structure of strongly correlated cuprates. At low energies the effective
Hamiltonian of the $t - t' - t"" - {t_ \bot } - {J^ * } - {J_ \bot }$-model has
been derived with parameters coming from the ab initio calculation for LSCO.
The electronic structure of LSCO has been calculated self-consistently with the
short-range antiferromagnetic order for various doping level. Two Lifshitz-type
quantum phase transitions with Fermi surface topology changes have been found
at dopings $x_{c1}=0.15$ and $x_{c2}=0.24$. Its effect on normal and
superconducting properties has been calculated. The interatomic exchange
parameter and its pressure dependence has been calculated within LDA+GTB
scheme. The magnetic mechanisms of d-wave pairing induced by static and
dynamical spin correlations are discussed. Simultaneous treatment of magnetic
and phonon pairing results in the conclusion that both contributions are of the
same order. For two layer cuprates like YBCO the interlayer hopping and
exchange effects on the electronic structure and doping dependence of $T_c$ is
discussed as well as the Coulomb interaction induced mechanism of pairing.",1510.08640v2
2016-02-02,Rydberg systems in parallel electric and magnetic fields: an improved method for finding exceptional points,"Exceptional points are special parameter points in spectra of open quantum
systems, at which resonance energies degenerate and the associated eigenvectors
coalesce. Typical examples are Rydberg systems in parallel electric and
magnetic fields, for which we solve the Schr\""odinger equation in a complete
basis to calculate the resonances and eigenvectors. Starting from an avoided
crossing within the parameter-dependent spectra and using a two-dimensional
matrix model, we develop an iterative algorithm to calculate the field
strengths and resonance energies of exceptional points and to verify their
basic properties. Additionally, we are able to visualise the wave functions of
the degenerate states. We report the existence of various exceptional points.
For the hydrogen atom these points are in an experimentally inaccessible regime
of field strengths. However, excitons in cuprous oxide in parallel electric and
magnetic fields, i. e., the corresponding hydrogen analogue in a solid state
body, provide a suitable system, where the high-field regime can be reached at
much smaller external fields and for which we propose an experiment to detect
exceptional points.",1602.00909v3
2016-06-07,Intra pseudogap- and superconductivity-pair spin and charge fluctuations and underdome metal-insulator (fermion-boson)-crossover phenomena as keystones of cuprate physics,"The most intriguing observation of cuprate experiments is most likely the
metal-insulator-crossover (MIC), seen in the underdome region of the
temperature-doping phase diagram of copper-oxides under a strong magnetic
field, when the superconductivity is suppressed. This MIC, which results in
such phenomena as heat conductivity downturn, anomalous Lorentz ratio,
nonlinear entropy, insulating ground state, nematicity- and stripe-phases and
Fermi pockets, reveals the nonconventional dielectric property of the
pseudogap-normal phase. Since conventional superconductivity appears from a
conducting normal phase, the understanding of how superconductivity arises from
an insulating state becomes a fundamental problem and thus the keystone for all
of cuprate physics. Recently, in interpreting the physics of visualization in
scanning tunneling microscopy (STM) real space nanoregions (NRs), which exhibit
an energy gap, we have succeeded in understanding that the minimum size for
these NRs provides pseudogap and superconductivity pairs, which are single
bosons. In this work, we discuss the intra-particle magnetic spin and charge
fluctuations of these bosons, observed recently in hidden magnetic order and
STM experiments. We find that all the mentioned MIC phenomena can be obtained
in the Coulomb single boson and single fermion two liquid model, which we
recently developed, and the MIC is a crossover of sample percolating NRs of
single fermions into those of single bosons.",1606.02065v1
2016-10-13,Monte Carlo Simulations of Spin Transport in a Strained Nanoscale InGaAs Field Effect Transistor,"Spin-based logic devices could operate at very high speed with very low
energy consumption and hold significant promise for quantum information
processing and metrology. Here, an in-house developed, experimentally verified,
ensemble self-consistent Monte Carlo device simulator with a Bloch equation
model using a spin-orbit interaction Hamiltonian accounting for Dresselhaus and
Rashba couplings is developed and applied to a spin field effect transistor
(spinFET) operating under externally applied voltages on a gate and a drain. In
particular, we simulate electron spin transport in a \SI{25}{nm} gate length
\chem{In_{0.7}Ga_{0.3}As} metal-oxide-semiconductor field-effect transistor
(MOSFET) with a CMOS compatible architecture. We observe non-uniform decay of
the net magnetization between the source and gate and a magnetization recovery
effect due to spin refocusing induced by a high electric field between the gate
and drain. We demonstrate coherent control of the polarization vector of the
drain current via the source-drain and gate voltages, and show that the
magnetization of the drain current is strain-sensitive and can be increased
twofold by strain induced into the channel.",1610.04114v3
2017-08-04,Interaction effects in assembly of magnetic nanoparticles,"A specific absorption rate of a dilute assembly of various random clusters of
iron oxide nanoparticles in alternating magnetic field has been calculated
using Landau- Lifshitz stochastic equation. This approach simultaneously takes
into account both the presence of thermal fluctuations of the nanoparticle
magnetic moments, and magneto-dipole interaction between the nanoparticles of
the clusters. It is shown that for usual 3D clusters the intensity of magneto-
dipole interaction is determined mainly by the cluster packing density eta =
Np*V/Vcl, where Np is the average number of the particles in the cluster, V is
the nanoparticle volume, and Vcl is the cluster volume. The area of the low
frequency hysteresis loop and the assembly specific absorption rate have been
found to be considerably reduced when the packing density of the clusters
increases in the range of 0.005 < eta < 0.4. The dependence of the specific
absorption rate on the mean nanoparticle diameter is retained with increase of
eta, but becomes less pronounced. For fractal clusters of nanoparticles, which
arise in biological media, in addition to considerable reduction of the
absorption rate, the absorption maximum is shifted to smaller particle
diameters. It is found also that the specific absorption rate of fractal
clusters increases appreciably with increase of the thickness of nonmagnetic
shells at the nanoparticle surfaces.",1708.01474v1
2018-02-26,Capacitively Driven Global Interconnect with Magnetoelectric Switching Based Receiver for Higher Energy Efficiency,"We propose capacitively driven low-swing global interconnect circuit using a
receiver that utilizes magnetoelectric (ME) effect induced magnetization
switching to reduce the energy consumption. Capacitively driven wire has
recently been shown to be effective in improving the performance of global
interconnects. Such techniques can reduce the signal swing in the interconnect
by using a capacitive divider network and does not require an additional
voltage supply. However, the large reduction in signal swing makes it necessary
to use differential signaling and amplification for successful regeneration at
the receiver, which add area and static power. ME effect induced magnetization
reversal has recently been proposed which shows the possibility of using a low
voltage to switch a nanomagnet adjacent to a multi-ferroic oxide. Here, we
propose an ME effect based receiver that uses the low voltage at the receiving
end of the global wire to switch a nanomagnet. The nanomagnet is also used as
the free layer of a magnetic tunnel junction (MTJ), the resistance of which is
tuned through the ME effect. This change in MTJ resistance is converted to full
swing binary signals by using simple digital components. This process allows
capacitive low swing interconnection without differential signaling or
amplification, which leads to significant energy efficiency. Our simulation
results indicate that for 5-10 mm long global wires in IBM 45 nm technology,
capacitive ME design consumes 3x lower energy compared to full-swing CMOS
design and 2x lower energy compared to differential amplifier based low-swing
capacitive CMOS design.",1802.10431v1
2018-04-01,Structural color tuning in 1D photonic crystals with electric field and magnetic field,"A tuning of the light transmission properties of 1D photonic structures
employing an external stimulus is very attracting and opens the way to the
fabrication of optical switches for colour manipulation in sensing, lighting,
and display technology. We present the electric field-induced tuning of the
light transmission in a photonic crystal device, made by alternating layers of
silver nanoparticles and titanium dioxide nanoparticles. We show a shift of
around 10 nm for an applied voltage of 10 V. We ascribe the shift to an
accumulation of charges at the silver/TiO2 interface due to electric field,
resulting in an increase of the number of charges contributing to the plasma
frequency in silver, giving rise to a blue shift of the silver plasmon band,
with concomitant blue shift of the photonic band gap. The employment of a
relatively low applied voltage gives the possibility to build a compact and
low-cost device. We also propose the fabrication of 1D photonic crystal and
microcavities employing a magneto-optical material as TGG (Tb3Ga5O12). With
these structures we can observe a shift of 22 nm with a magnetic field of 5 T,
at low temperature (8 K). The option to tune the colour of a photonic crystal
with magnetic field is interesting because of the possibility to realize
contactless optical switches. We also discuss the possibility to achieve the
tuning of the photonic band gap with UV light in photonic crystals made with
indium tin oxide (ITO).",1804.04491v1
2018-04-17,Enhanced magnetic and thermoelectric properties in epitaxial polycrystalline SrRuO3 thin film,"Transition metal oxide thin films show versatile electrical, magnetic, and
thermal properties which can be tailored by deliberately introducing
macroscopic grain boundaries via polycrystalline solids. In this study, we
focus on the modification of the magnetic and thermal transport properties by
fabricating single- and polycrystalline epitaxial SrRuO3 thin films using
pulsed laser epitaxy. Using epitaxial stabilization technique with atomically
flat polycrystalline SrTiO3 substrate, epitaxial polycrystalline SrRuO3 thin
film with crystalline quality of each grain comparable to that of
single-crystalline counterpart is realized. In particular, alleviated
compressive strain near the grain boundaries due to coalescence is evidenced
structurally, which induced enhancement of ferromagnetic ordering of the
polycrystalline epitaxial thin film. The structural variations associated with
the grain boundaries further reduce the thermal conductivity without
deteriorating the electronic transport, and lead to enhanced thermoelectric
efficiency in the epitaxial polycrystalline thin films, compared with their
single-crystalline counterpart.",1804.06077v1
2020-07-09,Large magnetoresistance and non-zero Berry phase in the nodal-line semimetal MoO2,"We performed calculations of the electronic band structure and the Fermi
surface as well as measured the longitudinal resistivity rhoxx(T,H), Hall
resistivity rhoxy(T,H) and quantum oscillations of the magnetization as a
function of temperature at various magnetic fields for MoO2 with monoclinic
crystal structure. The band structure calculations show that MoO2 is a
nodal-line semimetal when spin-orbit coupling is ignored. It was found that a
large magnetoresistance reaching 5.03x10^4% at 2 K and 9 T, its nearly
quadratic field dependence and a field-induced up-turn behavior of rhoxx(T),
the characteristics common for many topologically non-trivial as well as
trivial semimetals, emerge also in MoO2. The observed properties are attributed
to a perfect charge-carrier compensation, evidenced by both calculations
relying on the Fermi surface topology and the Hall resistivity measurements.
Both the observation of negative magnetoresistance for magnetic field along the
current direction and the non-zero Berry phase in de Haas-van Alphen
measurements indicate that pairs of Weyl points appear in MoO2, which may be
due to the crystal symmetry breaking. These results highlight MoO2 as a new
platform materials for studying the topological properties of oxides.",2007.04814v1
2013-08-12,Diamond Magnetometry of Superconducting Thin Films,"In recent years diamond magnetometers based on the nitrogen-vacancy (NV)
center have been of considerable interest for magnetometry applications at the
nanoscale. An interesting application which is well suited for NV centers is
the study of nanoscale magnetic phenomena in superconducting materials. We
employ the magnetic sensitivity of NV centers in diamond to interrogate the
magnetic properties of a thin-layer yttrium barium copper oxide (YBCO)
superconductor. Using fluorescence-microscopy methods and samples integrated
with an NV sensor on a microchip, we measure the temperature of phase
transition in the layer to be 70.0(2) K, and the penetration field of vortices
to be 46(4) G. We observe the pinning of the vortices in the layer at 65 K, and
estimate their density after cooling the sample in a ~ 10 G field to be 0.45(1)
\mu m^{-2}. These measurements are done with a 10 nm thick NV layer, so that
high spatial resolution may be enabled in the future. Based on these results,
we anticipate that this magnetometer could be useful for imaging the structure
and dynamics of vortices. As an outlook, we present a fabrication method for a
superconductor chip designed for this purpose.",1308.2689v3
2013-08-21,Asymmetry of collective excitations in electron and hole doped cuprate superconductors,"High-temperature superconductivity (HTSC) mysteriously emerges upon doping
holes or electrons into insulating copper oxides with antiferromagnetic (AFM)
order. It has been thought that the large energy scale of magnetic excitations,
compared to phonon energies for example, lies at the heart of an
electronically-driven superconducting phase at high temperatures. However,
despite extensive studies, little information is available for comparison of
high-energy magnetic excitations of hole- and electron-doped superconductors to
assess a possible correlation with the respective superconducting transition
temperatures. Here, we use resonant inelastic x-ray scattering (RIXS) at the Cu
L3-edge to reveal high-energy collective excitations in the archetype
electron-doped cuprate Nd2-xCexCuO4 (NCCO). Surprisingly, despite the fact that
the spin stiffness is zero and the AFM correlations are short-ranged, magnetic
excitations harden significantly across the AFM-HTSC phase boundary, in stark
contrast with the hole-doped cuprates. Furthermore, we find an unexpected and
highly dispersive mode in superconducting NCCO that is undetected in the
hole-doped compounds, which emanates from the zone center with a characteristic
energy comparable to the pseudogap, and may signal a quantum phase distinct
from superconductivity. The uncovered asymmetry in the high-energy collective
excitations with respect to hole and electron doping provides additional
constraints for modeling the HTSC cuprates.",1308.4740v2
2018-05-24,Vortex excitations in the Insulating State of an Oxide Interface,"In two-dimensional (2D) superconductors an insulating state can be induced
either by applying a magnetic field, $H$, or by increasing disorder. Many
scenarios have been put forth to explain the superconductor to insulator
transition (SIT): dominating fermionic physics after the breaking of Cooper
pairs, loss of phase coherence between superconducting islands embedded in a
metallic or insulating matrix and localization of Cooper pairs with concomitant
condensation of vortex-type excitations. The difficulty in characterizing the
insulating state and its origin stems from the lack of a continuous mapping of
the superconducting to insulating phase diagram in a single sample. Here we use
the two-dimensional (2D) electron liquid formed at the interface between the
two insulators (111) SrTiO$_3$ and LaAlO$_3$ to study the superconductor to
insulator transition. This crystalline interface surprisingly exhibits very
strong features previously observed only in amorphous systems. By use of
electrostatic gating and magnetic fields, the sample is tuned from the metallic
region, where supeconductivity is fully manifested, deep into the insulating
state. Through examination of the field dependence of the sheet resistance and
comparison of the response to fields in different orientations we identify a
new magnetic field scale, H$_{pairing}$, where superconducting fluctuations are
muted. Our findings show that vortex fluctuations excitations and Cooper pair
localization are responsible for the observed SIT and that these excitations
surprisingly persist deep into the insulating state.",1805.09574v1
2011-11-17,Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6,"Resonant magnetic excitations are widely recognized as hallmarks of
unconventional superconductivity in copper oxides, iron pnictides, and
heavy-fermion compounds. Numerous model calculations have related these modes
to the microscopic properties of the pair wave function, but the mechanisms
underlying their formation are still debated. Here we report the discovery of a
similar resonant mode in the non-superconducting, antiferromagnetically ordered
heavy-fermion metal CeB6. Unlike conventional magnons, the mode is
non-dispersive, and its intensity is sharply concentrated around a wave vector
separate from those characterizing the antiferromagnetic order. The magnetic
intensity distribution rather suggests that the mode is associated with a
coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6,
which has long remained ""hidden"" to the neutron-scattering probes. The mode
energy increases continuously below the onset temperature for
antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap
throughout the Brillouin zone. These attributes bear strong similarity to those
of the resonant modes observed in unconventional superconductors below their
critical temperatures. This unexpected commonality between the two disparate
ground states indicates the dominance of itinerant spin dynamics in the ordered
low-temperature phases of CeB6 and throws new light on the interplay between
antiferromagnetism, superconductivity, and ""hidden"" order parameters in
correlated-electron materials.",1111.4151v1
2014-06-10,Role of MgO impurity on the superconducting properties of MgB2,"We address the effect of MgO impurity on the superconducting properties of
MgB2. The synthesis of MgB2 is very crucial because of sensitivity of Mg to
oxidation which may lead to MgO as a secondary phase. Rietveld refinement was
performed to determine the quantitative volume fraction of MgO in the samples
synthesized by two different techniques. Both the samples were subjected to
magnetization measurements under dc and ac applied magnetic fields and the
observed results were compared as a function of temperature. Paramagnetic
Meissner effect has been observed in a sample of MgB2 having more amount of MgO
(with Tc = 37.1K) whereas the pure sample MgB2 having minor quantity of MgO
shows diamagnetic Meissner effect with Tc = 38.8K. M-H measurements at 10K
reveal a slight difference in irreversibility field which is due to MgO
impurity along with wide transition observed from ac magnetic susceptibility
measurements. The magnetotransport measurements R(T)H using RN = 90%, 50% and
10% criterion on pure sample of MgB2 has been used to determine the upper
critical field whereas the sample having large quantity of MgO does not allow
these measurements due to its high resistance.",1406.2414v2
2014-06-20,Spin-orbit density wave: A new phase of matter applicable to the hidden order state of URu2Si2,"We provide a brief review and detailed analysis of the spin-orbit density
wave (SODW), proposed as a possible explanation to the `hidden order' phase of
URu2Si2. Due to the interplay between inter-orbital Coulomb interaction and
spin-orbit coupling (SOC) in this compound, the SODW is shown to arise from
Fermi surface nesting instability between two spin-orbit split bands. An
effective low-energy Hamiltonian including single-particle SOC and two-particle
SODW is derived, while numerical results are calculated by using
density-functional theory (DFT) based band structure input. Computed gapped
quasiparticle spectrum, entropy loss and spin-excitation spectrum are in
detailed agreement with experiments. Interestingly, despite the fact that SODW
governs dynamical spin-excitations, the static magnetic moment is calculated to
be zero, owing to the time-reversal invariance imposed by SOC. As a
consequence, SODW can be destroyed by finite magnetic field even at zero
temperature. Our estimation of the location of the quantum critical point is
close to the experimental value of Bc ~ 35 T. Finally, we extend the idea of
SODW to other SOC systems including iridium oxides (iridates) and
two-dimensional electronic systems such as BiAg2 surface and LaAlO3/SrTiO3
interface. We show hints of quasiparticle gapping, reduction of preexisting
magnetic moment, large magneto-resistance etc. in these systems which can be
explained consistently within the SODW theory.",1406.5271v2
2016-05-02,Interfilament Resistance at 77 K in Striated HTS Coated Conductors,"Striating HTS coated conductor (CC) tapes into narrow filaments offers the
possibility of reducing the tapes' magnetization losses without unreasonably
decreasing their current-carrying capability. However, realizing well-separated
striations presents technological challenges, especially if the number of
filaments is large and/or if a thick layer of metallic stabilizer is present.
In these situations, the filaments can be easily coupled and their
effectiveness to reduce magnetization losses is strongly diminished or
eliminated. While the onset of coupling is well visible from magnetization loss
measurements, the actual path of the coupling current is unknown. In this
contribution we present a systematic study of the transverse resistance in HTS
CC samples in order to get a deeper understanding of those paths. The measured
samples differ in terms of manufacturer (SuperPower and SuperOx), and presence
and thickness of stabilizer material. In addition, oxidation is used as a means
to increase the resistance between the filaments in non-stabilized samples. The
results are interpreted with a chain network model. This work provides useful
insights on the factors determining the transverse resistance in striated HTS
CCs, thus indicating ways to improve the effectiveness of the striation process
for AC loss reduction.",1605.00401v2
2016-08-17,Electronic tunability of the frustrated triangular-lattice cluster magnet LiZn$_{2-x}$Mo$_3$O$_8$,"LiZn$_2$Mo$_3$O$_8$ is an electrically insulating geometrically frustrated
antiferromagnet in which inorganic Mo$_3$O$_{13}$ clusters each behaves as a
single $S = 1/2$ unit, with the clusters arranged on a two-dimensional
triangular lattice. Prior results have shown that LiZn$_2$Mo$_3$O$_8$ does not
exhibit static magnetic order down to at least $T = 0.05\,K$, and instead
possesses a valence bond ground state. Here, we show that LiZn$_2$Mo$_3$O$_8$
can be hole doped by oxidation with $\mathrm{I}_2$ and subsequent removal of
$\mathrm{Zn}^{2+}$ cations to access the entire range of electron count, from
one to zero unpaired electrons per site on the triangular lattice. Contrary to
expectations, no metallic state is induced; instead, the primary effect is to
suppress the number of sites contributing to the condensed valence-bond state.
Further, diffraction and pair-distribution function analysis show no evidence
for local Jahn-Teller distortions or other deviations from the parent trigonal
symmetry as a function of doping or temperature. Taken together, the data and
density functional theory calculations indicate that removal of electrons from
the magnetic layers favors Anderson localization of the resulting hole and an
increase in the electrical band-gap over the formation of a metallic and
superconducting state. These results put strong constraints on the chemical
conditions necessary to realize metallic states from parent insulating
geometrically frustrated antiferromagnets.",1608.05022v1
2017-07-07,Exciton-phonon interaction breaking all antiunitary symmetries in external magnetic fields,"Recent experimental investigations by M. A{\ss}mann et al. [Nature Mater. 15,
741 (2016)] on the spectrum of magnetoexcitons in cuprous oxide revealed the
statistics of a Gaussian unitary ensemble (GUE). The model of F. Schweiner et
al. [Phys. Rev. Lett. 118, 046401 (2017)], which includes the complete cubic
valence band structure of the solid, can explain the appearance of GUE
statistics if the magnetic field is not oriented in one of the symmetry planes
of the cubic lattice. However, it cannot explain the experimental observation
of GUE statistics for all orientations of the field. In this paper we
investigate the effect of quasi-particle interactions or especially the
exciton-phonon interaction on the level statistics of magnetoexcitons and show
that the motional Stark field induced by the exciton-phonon interaction leads
to the occurrence of GUE statistics for arbitrary orientations of the magnetic
field in agreement with experimental observations. Importantly, the breaking of
all antiunitary symmetries can be explained only by considering both the
exciton-phonon interaction and the cubic crystal lattice.",1707.02869v1
2017-12-10,"Tuning the Interfacial Charge, Orbital and Spin Polarization Properties in La0.67Sr0.33MnO3/ La1-xSrxMnO3 Bilayers","The possibility of controlling the interfacial properties of artificial oxide
heterostructures is still attracting researchers in the field of materials
engineering. Here, we used surface sensitive techniques and high-resolution
transmission electron microscopy to investigate the evolution of the surface
spin-polarization and lattice strains across the interfaces between
La0.66Sr0.33MnO3 thin films and low-doped manganites as capping layers. We have
been able to finely tune the interfacial spin-polarization by changing the
capping layer thickness and composition. The spin-polarization was found to be
highest at a critical capping thickness that depends on the Sr doping. We
explain the non-trivial magnetic profile by the combined effect of two
mechanisms. On one hand, the extra carriers supplied by the low-doped
manganites that tend to compensate the overdoped interface, favouring locally a
ferromagnetic double-exchange coupling. On the other hand, the evolution from a
tensile-strained structure of the inner layers to a compressed structure at the
surface that changes gradually the orbital occupation and hybridization of the
3d-Mn orbitals, being detrimental for the spin polarization. The finding of an
intrinsic spin-polarization at the A-site cation observed in XMCD measurements
reveals also the existence of a complex magnetic configuration at the
interface, different from the magnetic phases observed at the inner layers.",1712.03611v1
2018-09-24,Probing spin correlations using angle resolved photoemission in a coupled metallic/Mott insulator system,"A nearly free electron metal and a Mott insulating state can be thought of as
opposite ends of possibilities for the motion of electrons in a solid. In the
magnetic oxide metal PdCrO$_{2}$, these two coexist as alternating layers.
Using angle resolved photoemission, we surprisingly find sharp band-like
features in the one-electron removal spectral function of the correlated
subsystem. We show that these arise because a hole created in the Mott layer
moves to and propagates in the metallic layer while retaining memory of the
Mott layer's magnetism. This picture is quantitatively supported by a strong
coupling analysis capturing the physics of PdCrO$_{2}$ in terms of a Kondo
lattice Hamiltonian. Our findings open new routes to use the non-magnetic probe
of photoemission to gain insights into the spin-susceptibility of correlated
electron systems.",1809.08972v2
2018-10-24,Magnetostriction studies up to megagauss fields using fiber Bragg grating technique,"We here report magnetostriction measurements under pulsed megagauss fields
using a high-speed 100 MHz strain monitoring system devised using fiber Bragg
grating (FBG) technique with optical filter method. The optical filter method
is a detection scheme of the strain of FBG, where the changing Bragg wavelength
of the FBG reflection is converted to the intensity of reflected light to
enable the 100 MHz measurement. In order to show the usefulness and reliability
of the method, we report the measurements for solid oxygen, spin-controlled
crystal, and volborthite, a deformed Kagom\'{e} quantum spin lattice, using
static magnetic fields up to 7 T and non-destructive millisecond pulse magnets
up to 50 T. Then, we show the application of the method for the
magnetostriction measurements of CaV$_{4}$O$_{9}$, a two-dimensional
antiferromagnet with spin-halves, and LaCoO$_{3}$, an anomalous spin-crossover
oxide, in the megagauss fields.",1810.10472v2
2019-07-30,Antiferromagnetic Topological Insulator MnBi2Te4: Synthesis and Magnetic properties,"Recently, MnBi2Te4 has been discovered as the first intrinsic
antiferromagnetic topological insulator (AFM TI), and will become a promising
material to discover exotic topological quantum phenomena. In this work, we
have realized the successful synthesis of high-quality MnBi2Te4 single crystals
by solid-state reactions. The as-grown MnBi2Te4 single crystal exhibits a van
der Waals layered structure, which is composed of septuple Te-Bi-Te-Mn-Te-Bi-Te
sequences as determined by powder X-ray diffraction (PXRD) and high-resolution
high-angle annular dark field scanning transmission electron microscopy
(HAADF-STEM). The magnetic order below 25 K as a consequence of A-type
antiferromagnetic interaction between Mn layers in the MnBi2Te4 crystal
suggests the unique interplay between antiferromagnetism and topological
quantum states. The transport measurements of MnBi2Te4 single crystals further
confirm its magnetic transition. Moreover, the unstable surface of MnBi2Te4,
which is found to be easily oxidized in air, deserves attention for onging
research on few-layer samples. This study on the first AFM TI of MnBi2Te4 will
guide the future research on other potential candidates in the MBixTey family
(M = Ni, V, Ti, etc.).",1907.13018v1
2019-09-11,Magnetic anisotropy in single crystal high entropy perovskite oxide La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films,"Local configurational disorder can have a dominating role in the formation of
macroscopic functional responses in strongly correlated materials. Here, we use
entropy-stabilization synthesis to create single crystal epitaxial ABO3
perovskite thin films with equal atomic concentration of 3d transition metal
cations on the B-site sublattice. X-ray diffraction, atomic force microscopy,
and scanning transmission electron microscopy of
La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 (L5BO) films demonstrate excellent
crystallinity, smooth film surfaces, and uniform mixing of the 3d transition
metal cations throughout the B-site sublattice. The magnetic properties are
strongly dependent on substrate-induced lattice anisotropy and suggest the
presence of long-range magnetic order in these exceptionally disordered
materials. The ability to populate multiple elements onto a single sublattice
in complex crystal structures opens new possibilities to design functionality
in correlated systems and enable novel fundamental studies seeking to
understand how diverse local bonding environments can work to generate
macroscopic responses, such as those driven by electron-phonon channels and
complex exchange interaction pathways.",1909.05019v1
2019-09-20,Giant topological Hall effect in correlated oxide thin films,"Strong electronic correlations can produce remarkable phenomena such as
metal-insulator transitions and greatly enhance superconductivity,
thermoelectricity, or optical non-linearity. In correlated systems, spatially
varying charge textures also amplify magnetoelectric effects or
electroresistance in mesostructures. However, how spatially varying spin
textures may influence electron transport in the presence of correlations
remains unclear. Here we demonstrate a very large topological Hall effect (THE)
in thin films of a lightly electron-doped charge-transfer insulator, (Ca,
Ce)MnO3. Magnetic force microscopy reveals the presence of magnetic bubbles,
whose density vs. magnetic field peaks near the THE maximum, as is expected to
occur in skyrmion systems. The THE critically depends on carrier concentration
and diverges at low doping, near the metal-insulator transition. We discuss the
strong amplification of the THE by correlation effects and give perspectives
for its non-volatile control by electric fields.",1909.09305v1
2019-10-03,Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe$_2$O$_3$ under ultra-high pressures,"The archetypal $3d$ Mott insulator hematite, Fe$_2$O$_3$, is one of the basic
oxide components playing an important role in mineralogy of Earth's lower
mantle. Its high pressure-temperature behavior, such as the electronic
properties, equation of state, and phase stability is of fundamental importance
for understanding the properties and evolution of the Earth's interior. Here,
we study the electronic structure, magnetic state, and lattice stability of
Fe$_2$O$_3$ at ultra-high pressures using the density functional plus dynamical
mean-field theory (DFT+DMFT) approach. In the vicinity of a Mott transition,
Fe$_2$O$_3$ is found to exhibit a series of complex electronic, magnetic, and
structural transformations. In particular, it makes a phase transition to a
metal with a post-perovskite crystal structure and site-selective local moments
upon compression above 75 GPa. We show that the site-selective phase transition
is accompanied by a charge disproportionation of Fe ions, with Fe$^{3\pm
\delta}$ and $\delta \sim 0.05$-$0.09$, implying a complex interplay between
electronic correlations and the lattice. Our results suggest that
site-selective local moments in Fe$_2$O$_3$ persist up to ultra-high pressures
of $\sim$200-250 GPa, i.e., sufficiently above the core-mantle boundary. The
latter can have important consequences for understanding of the velocity and
density anomalies in the Earth's lower mantle.",1910.01702v1
2019-10-21,Satellite orbital drag during magnetic storms,"We investigate satellite orbital drag effects at low-Earth orbit (LEO)
associated with thermosphere heating during magnetic storms caused by coronal
mass ejections. CHAllenge Mini-satellite Payload (CHAMP) and Gravity Recovery
And Climate Experiment (GRACE) neutral density data are used to compute orbital
drag. Storm-to-quiet density comparisons are performed with background
densities obtained by the Jacchia-Bowman 2008 (JB2008) empirical model. Our
storms are grouped in different categories regarding their intensities as
indicated by minimum values of the SYM-H index. We then perform superposed
epoch analyses with storm main phase onset as zero epoch time. In general, we
find that orbital drag effects are larger for CHAMP (lower altitudes) in
comparison to GRACE (higher altitudes). Results show that storm-time drag
effects manifest first at high latitudes, but for extreme storms particularly
observed by GRACE stronger orbital drag effects occur during early main phase
at low/equatorial latitudes, probably due to heating propagation from high
latitudes. We find that storm-time orbital decay along the satellites' path
generally increases with storm intensity, being stronger and faster for the
most extreme events. For these events, orbital drag effects decrease faster
probably due to elevated cooling effects caused by nitric oxide, which
introduce modeled density uncertainties during storm recovery phase. Errors
associated with total orbit decay introduced by JB2008 are generally the
largest for the strongest storms, and increase during storm times, particular
during recovery phases. We discuss the implication of these uncertainties for
the prediction of collision between space objects at LEO during magnetic
storms.",1910.09622v1
2020-01-16,L1 data fitting for robust reconstruction in magnetic particle imaging: quantitative evaluation on Open MPI dataset,"Magnetic particle imaging is an emerging quantitative imaging modality,
exploiting the unique nonlinear magnetization phenomenon of superparamagnetic
iron oxide nanoparticles for recovering the concentration. Traditionally the
reconstruction is formulated into a penalized least-squares problem with
nonnegativity constraint, and then solved using a variant of Kaczmarz method
which is often stopped early after a small number of iterations. Besides the
phantom signal, measurements additionally include a background signal and a
noise signal. In order to obtain good reconstructions, a preprocessing step of
frequency selection to remove the deleterious influences of the noise is often
adopted. In this work, we propose a complementary pure variational approach to
noise treatment, by viewing highly noisy measurements as outliers, and
employing the l1 data fitting, one popular approach from robust statistics.
When compared with the standard approach, it is easy to implement with a
comparable computational complexity. Experiments with a public domain dataset,
i.e., Open MPI dataset, show that it can give accurate reconstructions, and is
less prone to noisy measurements, which is illustrated by quantitative (PSNR /
SSIM) and qualitative comparisons with the Kaczmarz method. We also investigate
the performance of the Kaczmarz method for small iteration numbers
quantitatively.",2001.06083v2
2021-01-19,Room-temperature colossal magnetoresistance in terraced single-layer graphene,"Disorder-induced magnetoresistance (MR) effect is quadratic at low
perpendicular magnetic fields and linear at high fields. This effect is
technologically appealing, especially in the two-dimensional (2D) materials
such as graphene, since it offers potential applications in magnetic sensors
with nanoscale spatial resolution. However, it is a great challenge to realize
a graphene magnetic sensor based on this effect because of the difficulty in
controlling the spatial distribution of disorder and enhancing the MR
sensitivity in the single-layer regime. Here, we report a room-temperature
colossal MR of up to 5,000% at 9 T in terraced single-layer graphene. By
laminating single-layer graphene on a terraced substrate, such as TiO2
terminated SrTiO3, we demonstrate a universal one order of magnitude
enhancement in the MR compared to conventional single-layer graphene devices.
Strikingly, a colossal MR of >1,000% was also achieved in the terraced graphene
even at a high carrier density of ~1012 cm-2. Systematic studies of the MR of
single-layer graphene on various oxide- and non-oxide-based terraced surfaces
demonstrate that the terraced structure is the dominant factor driving the MR
enhancement. Our results open a new route for tailoring the physical property
of 2D materials by engineering the strain through a terraced substrate.",2101.07595v1
2017-04-29,Competing spin liquids and hidden nematic order in spin ice with frustrated transverse exchange,"Frustration in magnetic interactions can give rise to disordered ground
states with subtle and beautiful properties. The spin ices Ho2Ti2O7 and
Dy2Ti2O7 exemplify this phenomenon, displaying a classical spin liquid state,
with fractionalized magnetic--monopole excitations. Recently there has been
great interest in closely-related ""quantum spin ice"" materials, following the
realization that anisotropic exchange interactions could convert spin ice into
a massively-entangled, quantum, spin liquid, where magnetic monopoles become
the charges of an emergent quantum electrodynamics. Here we show that even the
simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice,
can realise a still-richer scenario. Using a combination of classical Monte
Carlo simulation, semi--classical molecular--dynamics simulation, and analytic
field theory, we explore the properties of this model for frustrated transverse
exchange. We find not one, but three, competing forms of spin liquid, as well
as a phase with hidden, spin-nematic, order. We explore the experimental
signatures of each of these different states, making explicit predictions for
inelastic neutron scattering. These results show an intriguing similarity to
experiments on a range of pyrochlore oxides.",1705.00148v2
2017-11-21,Spontaneous Hall effect induced by strain in Pr$_2$Ir$_2$O$_7$ epitaxial thin films,"Strongly correlated iridate pyrochlores with geometrically frustrated spins
have been recognized as a potentially interesting group of oxide materials
where novel topological phases may appear. A particularly attractive system is
the metallic Pr$_2$Ir$_2$O$_7$, as it is known as a Fermi node semimetal
characterized by quadratic band touching at the Brillouin zone center,
suggesting that the topology of its electronic states can be tuned by moderate
lattice strain. In this work we report the growth of epitaxial
Pr$_2$Ir$_2$O$_7$ thin films grown by solid-state epitaxy. We show that the
strained parts of the films give rise to a spontaneous Hall effect that
persists up to 50 K without having spontaneous magnetization within our
experimental accuracy. This indicates that a macroscopic time reversal symmetry
(TRS) breaking appears at a temperature scale that is too high for the
magnetism to be due to Pr 4$f$ moments, and must thus be related to magnetic
order of the iridium 5$d$ electrons. The magnetotransport and Hall analysis
results are consistent with the formation of a Weyl semimetal state that is
induced by a combination of TRS breaking and cubic symmetry breaking due to
lattice strain.",1711.07813v1
2018-03-05,Widefield imaging of superconductor vortices with electron spins in diamond,"Understanding the mechanisms behind high-$T_{c}$ Type-II superconductors (SC)
is still an open task in condensed matter physics. One way to gain further
insight into the microscopic mechanisms leading to superconductivity is to
study the magnetic properties of the SC in detail, for example by studying the
properties of vortices and their dynamics. In this work we describe a new
method of wide-field imaging magnetometry using nitrogen-vacancy (NV) centers
in diamond to image vortices in an yttrium barium copper oxide (YBCO) thin
film. We demonstrate quantitative determination of the magnetic field strength
of the vortex stray field, the observation of vortex patterns for different
cooling fields and direct observation of vortex pinning in our disordered YBCO
film. This method opens prospects for imaging of the magnetic-stray fields of
vortices at frequencies from DC to several megahertz within a wide range of
temperatures which allows for the study of both high-$T_{C}$ and low-$T_{C}$
SCs. The wide temperature range allowed by NV center magnetometry also makes
our approach applicable for the study of phenomena like island
superconductivity at elevated temperatures (e.g. in metal nano-clusters).",1803.01957v1
2018-03-28,Perpendicular magnetic anisotropy at the Fe/MgAl$_2$O$_4$ interface: Comparative first-principles study with Fe/MgO,"We present a theoretical study on interfacial magnetocrystalline anisotropy
for Fe/MgAl$_2$O$_4$. This system has a very small lattice mismatch at the
interface and therefore is suitable for realizing a fully coherent
ferromagnet/oxide interface for magnetic tunnel junctions. On the basis of
density functional theory, we calculate the interfacial anisotropy constant
$K_{\rm i}$ and show that this system has interfacial perpendicular magnetic
anisotropy (PMA) with $K_{\rm i} \approx 1.2\,{\rm mJ/m^2}$, which is a little
bit smaller than that of Fe/MgO ($K_{\rm i} \approx$ 1.5--1.7$\,{\rm mJ/m^2}$).
Second-order perturbation analysis with respect to the spin-orbit interaction
clarifies that the difference in $K_{\rm i}$ between Fe/MgAl$_2$O$_4$ and
Fe/MgO originates from the difference in contributions from spin-flip
scattering terms at the interface. We propose that the insertion of tungsten
layers into the interface of Fe/MgAl$_2$O$_4$ is a promising way to obtain huge
interfacial PMA with $K_{\rm i} \gtrsim 3\,{\rm mJ/m^2}$.",1803.10428v5
2018-06-07,High Performance Metallic Amorphous Magnetic Flake-based Magnetodielectric Inductors,"Flake-shaped FeSi-based metallic amorphous alloy particles, having an aspect
ratio as high as 175 to 1, were prepared by ball milling gas atomized amorphous
powders of an effective diameter of 20 micrometers. The starting powder had a
saturation magnetic flux density, Bs, of 1.5 T and a coercivity, Hc, of 94 A/m.
The aspect ratio of the flakes, as well as their magnetic properties, were
controlled by milling process parameters, such as duration, speed, and the
type, mass and diameter of the milling balls. To minimize the oxidation of the
charge, the powders were handled in an argon gas-purged glove box, milled in
toluene, and subsequently dried in vacuo. Subsequently, soft magnetodielectric
composites were prepared by suspending and aligning the FeSi-based powders in
paraffin wax or epoxy resin. The composites were then pressed into toroids for
measurements of their high frequency complex permeability by a vector network
analyzer. The influence of the flake aspect ratio and volume loading fraction
on the permeability of the composites were investigated. Results indicate that
the composite permeability increases with the flake aspect ratio. For example,
for a given loading factor of 30 vol.%, the composite permeability at 0.1 GHz
nearly tripled and approached the value of 10 by increasing the aspect ratio of
the FeSi-based inclusions from 1 (spheres) to greater than 175 to 1 (flakes).",1806.02486v2
2018-08-16,Stabilization of three-dimensional charge order in YBa$_2$Cu$_3$O$_{6+x}$ via epitaxial growth,"Incommensurate charge order (CO) has been identified as the leading
competitor of high-temperature superconductivity in all major families of
layered copper oxides, but the perplexing variety of CO states in different
cuprates has confounded investigations of its impact on the transport and
thermodynamic properties. The three-dimensional (3D) CO observed in
YBa$_2$Cu$_3$O$_{6+x}$ in high magnetic fields is of particular interest,
because quantum transport measurements have revealed detailed information about
the corresponding Fermi surface. Here we use resonant X-ray scattering to
demonstrate 3D-CO in underdoped YBa$_2$Cu$_3$O$_{6+x}$ films grown epitaxially
on SrTiO$_3$ in the absence of magnetic fields. The resonance profiles indicate
that Cu sites in the charge-reservoir layers participate in the CO state, and
thus efficiently transmit CO correlations between adjacent CuO$_2$ bilayer
units. The results offer fresh perspectives for experiments elucidating the
influence of 3D-CO on the electronic properties of cuprates without the need to
apply high magnetic fields.",1808.05411v1
2019-02-01,Nanoscale ferroelastic twins formed in strained LaCoO3 films,"The coexistence and coupling of ferroelasticity and magnetic ordering in a
single material offers a great opportunity to realize novel devices with
multiple tuning knobs. Complex oxides are a particularly promising class of
materials to find multiferroic interactions as they often possess rich phase
diagrams and the interactions are very sensitive to external perturbations.
Still, there are very few examples of these systems. Here we report the
observation of twinning domains in ferroelastic LaCoO3 epitaxial thin films and
their geometric control of structural symmetry that are intimately linked to
the material electronic and magnetic states. A unidirectional structural
modulation is achieved by selective choice of substrates possessing two-fold
rotational symmetry. This modulation perturbs the crystal field splitting
energy, leading to unexpected in plane anisotropy of orbital configuration and
magnetization. These findings demonstrate the utilization of structural
modulation to control multiferroic interactions and may enable a great
potential for stimulation of exotic phenomena through artificial domain
engineering.",1902.00162v1
2019-03-21,Quantum Spin Ice Dynamics in the Dipole-Octupole Pyrochlore Magnet Ce$_2$Zr$_2$O$_7$,"Neutron scattering measurements on the pyrochlore magnet Ce$_2$Zr$_2$O$_7$
reveal an unusual crystal field splitting of its lowest $J$=5/2 multiplet, such
that its ground state doublet is composed of m$_J$=$\pm$3/2, giving these
doublets a dipole - octupole (DO) character with local Ising anisotropy. Its
magnetic susceptibility shows weak antiferromagnetic correlations with
$\theta_{CW}$=-0.4(2)K, leading to a naive expectation of an All-In, All-Out
ordered state at low temperatures. Instead our low energy inelastic neutron
scattering measurements show a dynamic quantum spin ice state, with suppressed
scattering near |$\textbf{Q}$|=0, and no long range order at low temperatures.
This is consistent with recent theory predicting symmetry enriched U(1) quantum
spin liquids for such DO doublets decorating the pyrochlore lattice. Finally,
we show that disorder, especially oxidation of powder samples, is important in
Ce$_2$Zr$_2$O$_7$ and could play an important role in the low temperature
behaviour of this material.",1903.09207v1
2019-04-04,Impact of single and double oxygen vacancies on electronic transport in Fe/MgO/Fe magnetic tunnel junctions,"To study the impact of oxygen vacancies on spin-polarized transport, we have
computed the electronic and transport properties of single (F centers) and
paired (M centers) oxygen vacancies using density functional theory. These
point defects can generate barrier heights as low as 0.4V for FeCo electrodes
irrespective of the defect's spatial position within the barrier, and of the
orientation of the M center. These defects promote a strong decrease in the
conductance of the spin up channel in the magnetic tunnel junctions (MTJ)'s
parallel (P) magnetic state that mainly accounts for an order-of-magnitude drop
in TMR, from about 10000$\%$ in the ideal case toward values more in line with
experiment. When placed in the middle layer of the MgO barrier, the F center
introduces additional P $\uparrow$ transmission away from the $\Gamma$ point.
This scattering lowers TMR to 145$\%$. In contrast, the M center merely
broadens this transmission around $\Gamma$, thereby boosting TMR to 315$\%$.
Rotating a M center so as to partly point along the transmission direction
sharpens transmission around $\Gamma$, further increasing TMR to 1423$\%$. When
these defects are placed at the MTJ interface, the transmission and ensuing
TMR, which reaches $\approx$ 4000$\%$, suggest that such junctions behave as
would an ideal MTJ, only with a much lower barrier height. Our results thus
theoretically reconcile the concurrent observations of high TMR and low barrier
heights, such as post-deposition oxidation of metallic Mg, which can generate
oxygen vacancies at the lower MTJ interface, and annealing which can promote M
centers over F centers.",1904.02554v1
2019-04-04,Resonant inelastic x-ray scattering study of bond order and spin excitations in nickelate thin-film structures,"We used high-resolution resonant inelastic x-ray scattering (RIXS) at the Ni
$L_3$ edge to simultaneously investigate high-energy interband transitions
characteristic of Ni-O bond ordering and low-energy collective excitations of
the Ni spins in the rare-earth nickelates $R$NiO$_3$ ($R$ = Nd, Pr, La) with
pseudocubic perovskite structure. With the support of calculations based on a
double-cluster model we quantify bond order (BO) amplitudes for different thin
films and heterostructures and discriminate short-range BO fluctuations from
long-range static order. Moreover we investigate magnetic order and exchange
interactions in spatially confined $R$NiO$_3$ slabs by probing dispersive
magnon excitations. While our study of superlattices (SLs) grown in the (001)
direction of the perovskite structure reveals a robust non-collinear spin
spiral magnetic order with dispersive magnon excitations that are essentially
unperturbed by BO modulations and spatial confinement, we find magnons with
flat dispersions and strongly reduced energies in SLs grown in the
$(111)_{\text{pc}}$ direction that exhibit collinear magnetic order. These
results give insight into the interplay of different collective ordering
phenomena in a prototypical 3$d$ transition metal oxide and establish RIXS as a
powerful tool to quantitatively study several order parameters and the
corresponding collective excitations within one experiment.",1904.02782v2
2019-04-28,Non-van der Waals honeycomb antiferromagnet SrRu$_2$O$_6$ down to a few layers,"The current family of experimentally realized two-dimensional magnetic
materials consist of 3$d$ transition metals with very weak spin-orbit coupling.
In contrast, we report a new platform in a chemically bonded and layered 4$d$
oxide, with strong electron correlations and competing spin-orbit coupling. We
synthesize ultra-thin sheets of SrRu$_2$O$_6$ using scalable liquid
exfoliation. These exfoliated sheets are characterized by complementary
experimental and theoretical techniques. The thickness of the nano-sheets
varies between three to five monolayers, and within the first-principles
calculations, we show that antiferromagnetism survives in these ultra-thin
layers. Experimental data suggest that exfoliation occurs from the planes
perpendicular to the $c$-axis as the intervening hexagonal Sr-lattice separates
the two-dimensional magnetic honeycomb Ru-layers. The high-resolution
transmission electron microscope images indicate that the average inter-atomic
spacing between the Ru-layers is slightly reduced, which agrees with the
present calculations. The signatures of rotational stacking of the nanosheets
are also observed. Such new two-dimensional platform offers enormous
possibilities to explore emergent properties that appear due to the interplay
between magnetism, strong correlations and spin-orbit coupling. Moreover, these
effects can be further tuned as a function of layer thickness.",1904.12326v2
2019-11-18,Atomic-scale fragmentation and collapse of antiferromagnetic order in a doped Mott insulator,"Disentangling the relationship between the insulating state with a charge gap
and the magnetic order in an antiferromagnetic (AF) Mott insulator remains
difficult due to inherent phase separation as the Mott state is perturbed.
Measuring magnetic and electronic properties at the atomic length scales would
provide crucial insight, but this is yet to be experimentally achieved. Here we
use spectroscopic-imaging spin-polarized scanning tunneling microscopy (SP-STM)
to visualize periodic spin-resolved modulations originating from the AF order
in a relativistic Mott insulator Sr2IrO4, and study these as a function of
doping. We find that near insulator-to-metal transition (IMT), the long-range
AF order melts into a fragmented state with short-range AF correlations.
Crucially, we discover that the short-range AF order is locally uncorrelated
with the observed spectral gap magnitude. This strongly suggests that short
range AF correlations are unlikely to be the culprit behind inhomogeneous gap
closing and the emergence of pseudogap regions near IMT. Our work establishes
SP-STM as a powerful tool for revealing atomic-scale magnetic information in
complex oxides.",1911.07801v1
2019-12-10,Partial FOV Center Imaging (PCI): A Robust X-Space Image Reconstruction for Magnetic Particle Imaging,"Magnetic Particle Imaging (MPI) is an emerging medical imaging modality that
images the spatial distribution of superparamagnetic iron oxide (SPIO)
nanoparticles using their nonlinear response to applied magnetic fields. In
standard x-space approach to MPI, the image is reconstructed by gridding the
speed-compensated nanoparticle signal to the instantaneous position of the
field free point (FFP). However, due to safety limits on the drive field, the
field-of-view (FOV) needs to be covered by multiple relatively small partial
field-of-views (pFOVs). The image of the entire FOV is then pieced together
from individually processed pFOVs. These processing steps can be sensitive to
non-ideal signal conditions such as harmonic interference, noise, and
relaxation effects. In this work, we propose a robust x-space reconstruction
technique, Partial FOV Center Imaging (PCI), with substantially simplified pFOV
processing. PCI first forms a raw image of the entire FOV by mapping MPI signal
directly to pFOV center locations. The corresponding MPI image is then obtained
by deconvolving this raw image by a fully known, compact kernel, which solely
depends on the pFOV size. We analyze the performance of the proposed
reconstruction via extensive simulations, as well as imaging experiments on our
in-house FFP MPI scanner. The results show that PCI offers a trade-off between
noise robustness and interference robustness, outperforming standard x-space
reconstruction in terms of both robustness against non-ideal signal conditions
and image quality.",1912.04851v1
2020-03-06,Assembly and disorder dissipation in superparamagnetic nanoparticle chains in a rotating magnetic field,"We investigate the formation of chains of superparamagnetic iron oxide
nanoparticles (SPIONs) in a rotating magnetic field, combining two
well-explored chain-forming systems: larger micron-scale beads in a rotating
magnetic field, and SPIONs in a static field. This simple combination is
interesting because it features self-assembly that occurs both far from
equilibrium and at a finite temperature, with the better-explored systems
constituting respectively its zero temperature and near-equilibrium limits.
Theories applicable to either of the two limits qualitatively predict the chain
length distributions, except that chains in our experiments are shorter, which
we attribute to the simultaneous presence of thermal fluctuations and fluid
shear forces that work in concert to break chains apart. Our most striking
result is that the disorder in the SPION chains gradually dissipates over a
timescale of tens of minutes, about two orders of magnitude slower than the
characteristic chain assembly time. The disorder dissipation can be sped up by
increasing particle concentration and solution ionic strength, both of which
increase the speed of chain assembly. This strongly suggests that the
improvement in chain order with time is not due to thermal fluctuations but
rather to energy imparted by the self-assembly process, which continually
causes chains to grow and break apart, even when a steady state distribution
has obtained. More generally, our results indicate that self-assembly away from
equilibrium may sometimes lead to better ordered assemblies than under
near-equilibrium conditions.",2003.03008v2
2020-03-29,Robust ferromagnetism in highly strained SrCoO3 thin films,"Epitaxial strain provides important pathways to control the magnetic and
electronic states in transition metal oxides. However, the large strain is
usually accompanied by a strong reduction of the oxygen vacancy formation
energy, which hinders the direct manipulation of their intrinsic properties.
Here using a post-deposition ozone annealing method, we obtained a series of
oxygen stoichiometric SrCoO3 thin films with the tensile strain up to 3.0%. We
observed a robust ferromagnetic ground state in all strained thin films, while
interestingly the tensile strain triggers a distinct metal to insulator
transition along with the increase of the tensile strain. The persistent
ferromagnetic state across the electrical transition therefore suggests that
the magnetic state is directly correlated with the localized electrons, rather
than the itinerant ones, which then calls for further investigation of the
intrinsic mechanism of this magnetic compound beyond the double-exchange
mechanism.",2003.12982v2
2020-09-09,Accretion disk's magnetic field controlled the composition of the terrestrial planets,"Chondrites, the building blocks of the terrestrial planets, have mass and
atomic proportions of oxygen, iron, magnesium, and silicon totaling $\geq$90\%
and variable Mg/Si ($\sim$25\%), Fe/Si (factor of $\geq$2), and Fe/O (factor of
$\geq$3). The Earth and terrestrial planets (Mercury, Venus, and Mars) are
differentiated into three layers: a metallic core, a silicate shell (mantle and
crust), and a volatile envelope of gases, ices, and, for the Earth, liquid
water. Each layer has different dominant elements (e.g., increasing Fe content
with depth and increasing oxygen content to the surface). What remains an
unknown is to what degree did physical processes during nebular disk accretion
versus those during post-nebular disk accretion (e.g., impact erosion)
influence these final bulk compositions. Here we predict terrestrial planet
compositions and show that their core mass fractions and uncompressed densities
correlate with their heliocentric distance, and follow a simple model of the
magnetic field strength in the protoplanetary disk. Our model assesses the
distribution of iron in terms of increasing oxidation state, aerodynamics, and
a decreasing magnetic field strength outward from the Sun, leading to
decreasing core size of the terrestrial planets with radial distance. This
distribution would enhance habitability in our solar system, and would be
equally applicable to exo-planetary systems.",2009.04311v1
2020-09-15,Spin-orbital polarization of Majorana edge states in oxides nanowires,"We investigate a paradigmatic case of topological superconductivity in a
one-dimensional nanowire with $d-$orbitals and a strong interplay of
spin-orbital degrees of freedom due to the competition of orbital Rashba
interaction, atomic spin-orbit coupling, and structural distortions. We
demonstrate that the resulting electronic structure exhibits an orbital
dependent magnetic anisotropy which affects the topological phase diagram and
the character of the Majorana bound states (MBSs). The inspection of the
electronic component of the MBSs reveals that the spin-orbital polarization
generally occurs along the direction of the applied Zeeeman magnetic field, and
transverse to the magnetic and orbital Rashba fields. The competition of
symmetric and antisymmetric spin-orbit coupling remarkably leads to a
misalignment of the spin and orbital moments transverse to the orbital Rashba
fields, whose manifestation is essentially orbital dependent. The behavior of
the spin-orbital polarization along the applied Zeeman field reflects the
presence of multiple Fermi points with inequivalent orbital character in the
normal state. Additionally, the response to variation of the electronic
parameters related with the degree of spin-orbital entanglement leads to
distinctive evolution of the spin-orbital polarization of the MBSs. These
findings unveil novel paths to single-out hallmarks relevant for the
experimental detection of MBSs.",2009.06956v1
2020-10-17,Multiscale modelling of magnetostatic effects on magnetic nanoparticles with application to hyperthermia,"We extend a renormalization group-based course-graining method for
micromagnetic simulations to include properly scaled magnetostatic
interactions. We apply the method in simulations of dynamic hysteresis loops at
clinically relevant sweep rates and at 310 K of iron oxide nanoparticles (NPs)
of the kind that have been used in preclinical studies of magnetic
hyperthermia. The coarse-graining method, along with a time scaling involving
sweep rate and Gilbert damping parameter, allow us to span length scales from
the unit cell to NPs approximately 50 nm in diameter with reasonable simulation
times. For both NPs and the nanorods composing them, we report effective
uniaxial anisotropy strengths and saturation magnetizations, which differ from
those of the bulk materials magnetite and maghemite of which they are made, on
account of the combined non-trivial effects of temperature, inter-rod exchange,
magnetostatic interactions and the degree of orientational order within the
nanorod composites. The effective parameters allow treating the NPs as single
macrospins, and we find for the test case of calculating loops for two aligned
NPs that using the dipole approximation is sufficient for distances beyond 1.5
times the NP diameter. We also present a study on relating integration time
step to micromagnetic cell size, finding that the optimal time step size scales
approximately linearly with cell volume.",2010.08848v1
2021-01-30,Colossal Magnetoresistance without Mixed Valence in a Layered Phosphide Crystal,"Materials with strong magnetoresistive responses are the backbone of
spintronic technology, magnetic sensors, and hard drives. Among them, manganese
oxides with a mixed valence and a cubic perovskite structure stand out due to
their colossal magnetoresistance (CMR). A double exchange interaction underlies
the CMR in manganates, whereby charge transport is enhanced when the spins on
neighboring Mn3+ and Mn4+ ions are parallel. Prior efforts to find different
materials or mechanisms for CMR resulted in a much smaller effect. Here we show
an enormous CMR at low temperatures in EuCd2P2 without manganese, oxygen, mixed
valence, or cubic perovskite structure. EuCd2P2 has a layered trigonal lattice
and exhibits antiferromagnetic ordering at 11 K. The magnitude of CMR (104
percent) in as-grown crystals of EuCd2P2 rivals the magnitude in optimized thin
films of manganates. Our magnetization, transport, and synchrotron X-ray data
suggest that strong magnetic fluctuations are responsible for this phenomenon.
The realization of CMR at low temperatures without heterovalency leads to a new
regime for materials and technologies related to antiferromagnetic spintronics.",2102.00204v1
2021-05-26,Imaging antiferromagnetic domain fluctuations and the effect of atomic-scale disorder in a doped spin-orbit Mott insulator,"Correlated oxides can exhibit complex magnetic patterns, characterized by
domains with vastly different size, shape and magnetic moment spanning the
material. Understanding how magnetic domains form in the presence of chemical
disorder and their robustness to temperature variations has been of particular
interest, but atomic-scale insight into this problem has been limited. We use
spin-polarized scanning tunneling microscopy to image the evolution of
spin-resolved modulations originating from antiferromagnetic (AF) ordering in a
spin-orbit Mott insulator Sr3Ir2O7 as a function of chemical composition and
temperature. We find that replacing only several percent of La for Sr leaves
behind nanometer-scale AF puddles clustering away from La substitutions
preferentially located in the middle SrO layer within the unit cell. Thermal
erasure and re-entry into the low-temperature ground state leads to a spatial
reorganization of the AF modulations, indicating multiple stable AF
configurations at low temperature. Interestingly, regardless of this
rearrangement, the AF puddles maintain scale-invariant fractal geometry in each
configuration. Our experiments reveal spatial fluctuations of the AF order in
electron doped Sr3Ir2O7, and shed light on its sensitivity to different types
of atomic-scale disorder.",2105.12648v1
2021-08-21,Transport Spin Polarization of Noncollinear Antiferromagnetic Antiperovskites,"Spin-polarized currents play a key role in spintronics. Recently, it has been
found that antiferromagnets with a non-spin-degenerate band structure can
efficiently spin-polarize electric currents, even though their net
magnetization is zero. Among the antiferromagnetic metals with magnetic space
group symmetry supporting this functionality, the noncollinear
antiferromagnetic antiperovskites ANMn$_3$ (A = Ga, Ni, Sn, and Pt) are
especially promising. This is due to their high N\'eel temperatures and a good
lattice match to perovskite oxide substrates, offering possibilities of high
structural quality heterostructures based on these materials. Here, we
investigate the spin polarization of antiferromagnetic ANMn$_3$ metals using
first-principles density functional theory calculations. We find that the spin
polarization of the longitudinal currents in these materials is comparable to
that in widely used ferromagnetic metals, and thus can be exploited in magnetic
tunnel junctions and spin transfer torque devices. Moreover, for certain film
growth directions, the out-of-plane transverse spin currents with a giant
charge-to-spin conversion efficiency can be achieved, implying that the
ANMn$_3$ antiperovskites can be used as efficient spin sources. These
properties make ANMn$_3$ compounds promising for application in spintronics.",2108.09540v2
2021-08-27,An overview of the structural correlation of magnetic and electrical properties of Pr2NiMnO6 Double perovskite,"Double perovskites R2NiMnO6 (R= Rare earth element) (RNMO) are a significant
class of materials owing to their varied tunability of the magnetic and
electrical properties with the structural modifications. Pr2NiMnO6 (PNMO) is
one of the least explored members of this series, which shows spin-phonon
coupling, magnetocaloric effect, and electrochemical performance for various
applications such as spintronics, magnetocaloric refrigerant, and solid oxide
fuel cells. Most of the studies in PNMO are limited to the application domain
and focus on the comparative study with different rare earth elements. Detailed
structural studies like neutron diffraction are sparse in PNMO samples which
will give a perception to the ordering in the compound that strongly depends on
the physical and chemical properties. This review article goes through the
various aspects of PNMO materials that have been reported till now and showcase
the octahedral distortions and corresponding structural changes and the
exchange interactions, which in turn correlates with the magnetic and
electrical properties. The comparison study of PNMO with other members of the
RNMO family and the relevance of PNMO over other members is also tried to
showcase through this article. Hope this article provides an insight into the
scope of studies in PNMO material for exploring unexposed properties of the
materials in the double perovskite family.",2108.12498v1
2021-09-20,Towards Non-Volatile Spin Orbit Devices: Deposition of Ferroelectric Hafnia on Monolayer Graphene/Co/HM Stacks,"Although technologically challenging, the integration of ferroelectric thin
films with graphene spintronics potentially allows the realization of highly
efficient, electrically tuneable, non-volatile memories. Here, the atomic layer
deposition (ALD) of ferroelectric Hf$_{0.5}$Zr$_{0.5}$O$_2$ (HZO) directly on
graphene (Gr)/Co/heavy metal (HM) epitaxial stacks is investigated via the
implementation of several nucleation methods. With an in-situ method employing
an Al$_2$O$_3$ layer, the HZO demonstrates a remanent polarization (2Pr) of
19.2 $\mu C/cm^2$. An ex-situ, naturally oxidized sputtered Ta layer for
nucleation produces a film with 2Pr of 10.81 $\mu C/cm^2$, but a lower coercive
field over the stack and switching enduring over subsequent cycles. Magnetic
hysteresis measurements taken before and after ALD deposition show strong
perpendicular magnetic anisotropy (PMA), with only slight deviations in the
magnetic coercive fields due to the HZO deposition process, thus pointing to a
good preservation of the single-layer Gr. X-ray diffraction measurements
further confirm that the high-quality interfaces demonstrated in the stack
remain unperturbed by the ferroelectric deposition and anneal.",2109.09543v3
2021-12-20,Spin current transport in hybrid Pt / multifunctional magnetoelectric Ga0.6Fe1.4O3 bilayers,"The low power manipulation of magnetization is currently a highly
sought-after objective in spintronics. Non ferromagnetic large spin-orbit
coupling heavy metal (NM) / ferromagnet (FM) heterostructures offer interesting
elements of response to this issue, by granting the manipulation of the FM
magnetization by the NM spin Hall effect (SHE) generated spin current.
Additional functionalities, such as the electric field control of the spin
current generation, can be offered using multifunctional ferromagnets. We have
studied the spin current transfer processes between Pt and the multifunctional
magnetoelectric Ga0.6Fe1.4O3 (GFO). In particular, via angular dependent
magnetotransport measurements, we were able to differentiate between magnetic
proximity effect (MPE)-induced anisotropic magnetoresistance (AMR) and spin
Hall magnetoresistance (SMR). Our analysis shows that SMR is the dominant
phenomenon at all temperatures and is the only one to be considered near room
temperature, with a magnitude comparable to those observed in Pd/YIG or Pt/YIG
heterostructures. These results indicate that magnetoelectric GFO thin films
show promises for achieving an electric-field control of the spin current
generation in NM/FM oxide-based heterostructures.",2112.10406v1
2022-02-03,Thickness and temperature dependence of the atomic-scale structure of SrRuO$_3$ thin films,"Due to the strong lattice-property relationships which exist in complex oxide
epitaxial layers, their electronic and magnetic properties can be modulated by
structural distortions induced at the atomic scale. The modification and
control can be affected at coherent heterointerfaces by epitaxial strain
imposed by the substrate or by structural modifications to accommodate the
film-substrate symmetry mismatch. Often these act in conjunction with a strong
dependence on the layer thickness, especially for ultrathin layers. Moreover,
as a result of these effects, the temperature dependence of the structure may
deviate largely from that of the bulk. The temperature-dependent structure of 3
to 44 unit cell thick ferromagnetic SrRuO$_3$ films grown on Nb-doped SrTiO$_3$
substrates are investigated using a combination of high-resolution synchrotron
X-ray diffraction and high-resolution electron microscopy. This aims to shed
light on the intriguing magnetic and magnetotransport properties of epitaxial
SRO layers, subjected to extensive investigations lately. The oxygen octahedral
tilts and rotations are found to be strongly dependent on the temperature, the
film thickness, and the distance away from the film-substrate interface. As a
striking manifestation of the coupling between magnetic order and lattice
structure, the Invar effect is observed below the ferromagnetic transition
temperature in epitaxial layers as thin as 8 unit cells, similar to bulk
ferromagnetic SrRuO$_3$.",2202.01652v1
2022-03-23,Highly sensitive and high throughput magnetic resonance thermometry using superparamagnetic nanoparticles,"Magnetic resonance imaging (MRI) enables non-invasive 3D thermometry during
thermal ablation of cancerous tumors. While T1 or T2 contrast MRI are
relatively insensitive to temperature, techniques with greater temperature
sensitivity such as chemical shift or diffusion imaging suffer from motional
artifacts and long scan times. We describe an approach for highly sensitive and
high throughput MR thermometry that is not susceptible to motional artifacts.
We use superparamagnetic iron oxide nanoparticles (SPIONs) to spoil T2 of water
protons. Motional narrowing results in proportionality between T2 and the
diffusion constant, dependent only on the temperature in a specific
environment. Our results show, for pure water, the nuclear magnetic resonance
(NMR) linewidth and T2 follow the same temperature dependence as the
self-diffusion constant of water. Thus, T2 mapping is a diffusion mapping in
the presence of SPIONs, and T2 is a thermometer. For pure water, a T2 mapping
of a 64 x 64 image (voxel size = 0.5 mm x 0.5 mm x 3 mm) in a 9.4 T MRI scanner
resulted in a temperature resolution of 0.5 K for a scan time of 2 minutes.
This indicates a highly sensitive and high throughput MR thermometry technique
potentially useful for monitoring of biological tissues during thermal
therapies or for diagnosis.",2203.12544v4
2022-03-25,Reconciling monolayer and bilayer $J_{\rm eff} = 1/2$ square lattices in hybrid oxide superlattice,"The number of atomic layers confined in a two-dimensional structure is
crucial for the electronic and magnetic properties. Single-layer and bilayer
$J_{\rm eff} = 1/2$ square lattices are well-known examples where the presence
of the extra layer turns the XY-anisotropy to the $c$-axis anisotropy. We
report on experimental realization of a hybrid SrIrO$_3$/SrTiO$_3$ superlattice
that integrates monolayer and bilayer square lattices in one layered structure.
By synchrotron x-ray diffraction, resonant x-ray magnetic scattering,
magnetization, and resistivity measurements, we found that the hybrid
superlattice exhibits properties that are distinct from both the single-layer
and bilayer systems and cannot be explained by a simple addition of them. In
particular, the entire hybrid superlattice orders simultaneously through a
single antiferromagnetic transition at temperatures similar to the bilayer
system but with all the $J_{\rm eff} = 1/2$ moments mainly pointing in the
$ab$-plane similar to the single-layer system. The results show that bringing
monolayer and bilayer with orthogonal properties in proximity to each other in
a hybrid superlattice structure is a powerful way to stabilize a unique state
not obtainable in a uniform structure.",2203.13426v1
2022-11-18,Synthesis of infinite-layer nickelates and influence of the capping-layer on magnetotransport,"The recent discovery of a zero-resistance state in nickel-based compounds has
generated a re-excitement about the long-standing problem in condensed matter
of high-critical-temperature superconductivity, in light of the analogies
between infinite-layer nickelates and cuprates. However, despite some formal
valence and crystal symmetry analogies, the electronic properties of
infinite-layer nickelates are remarkably original accounting, among other
properties, of a unique Nd5d-Ni3d hybridization. This designates infinite-layer
nickelates as a new class of oxide superconductors which should be considered
on their own. Here we report about Nd1-xSrxNiO2 (x = 0, 0.05 and 0.2) thin
films synthesized with and without a SrTiO3 capping-layer, showing very smooth
and step-terraced surface morphologies. Angle-dependent anisotropic
magnetoresistance measurements performed with a magnetic field rotating
in-plane or out-of-plane with respect to the sample surface, rendered important
information about the magnetic properties of undoped SrTiO3-capped and uncapped
samples. The results point at a key role of the capping-layer in controlling
the magnitude and the anisotropy of the anisotropic magnetoresistance
properties. We discuss this control in terms of a combined effect between the
Nd-Ni hybridization and an intra-atomic exchange coupling between the Nd-4f and
Nd-5d states, the latter essentially contributing to the (magneto)transport.
Further studies foresee the influence of the capping layer on infinite-layer
nickelates with no magnetic rare-earth.",2211.10251v1
2022-12-23,Hybridization driving distortions and multiferroicity in rare-earth nickelates,"For decades transition-metal oxides have generated a huge interest due to the
multitude of physical phenomena they exhibit. In this class of materials, the
rare-earth nickelates, $R$NiO$_3$, stand out for their rich phase diagram
stemming from complex couplings between the lattice, electronic and magnetic
degrees of freedom. Here, we present a first-principles study of the
low-temperature phase for two members of the $R$NiO$_3$ series, with $R=$ Pr,
Y. We employ density-functional theory with Hubbard corrections accounting not
only for the on-site localizing interactions among the Ni--$3d$ electrons
($U$), but also the inter-site hybridization effects between the
transition-metals and the ligands ($V$). All the \textit{U} and \textit{V}
parameters are calculated from first-principles using density-functional
perturbation theory, resulting in a fully \emph{ab initio} methodology. Our
simulations show that the inclusion of the inter-site interaction parameters
$V$ is necessary to simultaneously capture the features well-established by
experimental characterizations of the low-temperature state: insulating
character, antiferromagnetism and bond disproportionation. On the contrary, for
some magnetic orderings the inclusion of on-site interaction parameters $U$
alone completely suppresses the breathing distortion occurring in the
low-temperature phase and produces an erroneous electronic state with a
vanishing band gap. In addition -- only when both the \textit{U} and \textit{V}
are considered -- we predict a polar phase with a magnetization-dependent
electric polarization, supporting very recent experimental observations that
suggest a possible occurrence of type-II multiferroicity for these materials.",2212.12529v1
2023-01-04,Preparation and Characterization of NixMn0.25-xMg0.75Fe2O4 Nano-ferrite as NO2 Gas Sensing Material,"NixMn0.25-xMg0.75Fe2O4 nano-ferrites (where x = 0.00, 0.05, 0.10, 0.15 and
0.20) were produced via sol-gel auto-combustion technique. Investigations were
done into how the incorporation of Ni ions affects the Mn0.25Mg0.75Fe2O4
ferrite's structure, morphological, magnetic, and NO2 gas sensing features. All
the samples are single-phase, based on the structural study utilizing the X-ray
diffraction (XRD) pattern. In terms of the structure of the cubic spinel,
according to the XRD study, the crystallite sizes range from 24.30 to 28.32 nm,
indicating nano-crystallinity. The synthesis of spherical nanoparticles with a
small modification in particle size distribution was verified via FE-SEM
images. The study found that the size of particles is tiny enough to act
superparamagnetically. The area of hysteresis loop is almost non-existing, thus
reflecting typical soft magnetic materials according to magnetic measurements
by VSM carried out at room temperature. Furthermore, the conductance responses
of the NixMn0.25-xMg0.75Fe2O4 nano-ferrite were measured by exposing the
ferrite to oxidizing (NO2) gas at different operating temperatures. The results
show that the sensor boasts shorter response and recovery times, as well as a
higher sensitivity 707.22% of the sample (x=0.20) for nano-ferrite.",2301.01728v1
2023-09-24,Novel one-pot sol-gel synthesis route of Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon matrix,"Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon
matrix are synthesized by a novel two-step surfactant sol-gel strategy, where
the processes of hydrolysis, polycondensation and drying take place in a
one-pot. The present approach is based on the combined action of oleic acid and
oleylamine, which act sterically on the precursor micelles when a densification
temperature is performed in a reducing atmosphere. The structural and magnetic
evolution of the formed compounds is investigated, ranging from iron oxides
such as Fe3O4 and FeO, to the formation of pure Fe3C/C samples from 700 {\deg}C
onwards. Interestingly, Fe3C nanoparticles with a size of ~20 nm crystallize
immersed in the carbon matrix and the surrounding environment forms an oriented
encapsulation built by few-layered graphene. The nanostructures show a
saturation magnetization of ~43 emu/g and a moderate coercivity of ~500 Oe.
Thereby, an innovative chemical route to produce single phase Fe3C
nanoparticles is described, and an effective method of few-layered graphene
passivation is proposed, yielding a product with a high magnetic response and
high chemical stability against environmental corrosion.",2309.15858v1
2023-11-15,Growth and Characterization of $β$-Mn Structured CoZn Thin Films,"Thin films of polycrystalline $\beta$-Mn structure CoZn have been grown on
thermally oxidized Si substrates by co-sputtering from elemental targets
followed by annealing. A range of films grown with variable Co deposition power
and fixed Zn deposition power were produced, so as to vary the proportions of
the two elements reaching the substrate, which were annealed post-growth.
Whilst all films exhibited a (211) $\beta$-Mn structure CoZn texture in X-ray
diffraction, transmission electron microscopy showed that the composition with
the highest integrated intensity for that Bragg peak contained large vacancies
and was covered by a thick ZnO cap owing to being Co-deficient overall. CoZn
films deposited at ratios tuned to give the optimal volume fraction of
$\beta$-Mn were continuous, with crystallites up to 200~nm in size, with a much
thinner ZnO cap layer. Magnetic measurements show that such optimal CoZn films
have a Curie temperature $T_\mathrm{C} \sim 420$~K and saturation magnetization
of 120~emu/cm$^3$, properties close to those reported for bulk crystals. The
$\beta$-Mn structure is chiral (P4$_{1}$32/P4$_{3}$32 space group) and is known
to give rise to a Dzyaloshinkii-Moriya interaction (DMI) that stabilizes
room-temperature skyrmions in the bulk. Our thin films are thus a potential
materials platform, compatible with planar processing technology, for magnetic
skyrmions arising from a bulk DMI.",2311.08824v2
2018-10-11,Effect of thermal treatments in high purity Ar on the oxidation behavior of arc-PVD c-Al0.66Ti0.33N coatings,"The effect of temperature in high purity Ar (low oxygen partial pressure) on
the oxidation and crystal phase evolution of c-Al0.66Ti0.33N arc-PVD coatings
was investigated. High temperature tribology in Ar jet and adhesion behavior of
the oxidized coating were addressed. The use of Ar protects the coating from
the oxidation reactions and allowed to shed light into the details and paths of
the nitride oxidation process. The c-Al0.66Ti0.33N nitrides were slightly
oxidized in Ar even at high temperature. The surface chemistry evaluation shows
very thin Al- and Ti-based oxide layers formation after 700C in Ar. However,
the onset formation of the rutile TiO2 oxide was detected only after 900C and
was clearly found by low-angle XRD diffraction after 1000C. XPS analysis of the
oxidized samples at 800C indicated the formation of extremely thin layers
mainly composed of mixed oxides a-Al2O3 g-Al2O3 and r-TiO2. Gradual changes in
the chemical composition of the oxidized coatings observed at 900C clearly
demonstrate the formation of gradient boundaries between Al-rich and Ti-rich
oxy-nitride layers. After 1000C at least four oxides and oxi-nitrides layers
and interlayers were found. Additionally, it is suspected that the transition
oxide phases such as c-TiO, c-Al0.54Ti2.46O0.28N4.58, alpha-Al2TiO5 and TiOxNy
might be precursors leading to the formation of thermodynamically stable rutile
and alumina phases. Surface inspection after high temperature tribology in Ar
jet showed formation of tensile cracks in the wear tracks and wear processes
due to high size particle adhesion-abrasion and low size particle
micro-ploughing of hard nitrides, oxi-nitrides and brittle oxide particles.
Adhesion tests performed after high temperature tribology in Ar showed critical
load decrease related to cohesive and adhesive damages at the contact point of
the scratch track.",1810.05029v2
2018-06-18,Degradation of Methylene Blue using Graphene Oxide-Tin Oxide Nanocomposite as Photocatalyst,"Environmental contamination and human exposure to dyes have dramatically
increased over the past decades because of their increasing use in such
industries as textiles, paper, plastics, tannery and paints. These dyes can
cause deterioration in water quality by imparting color to the water and
inducing the photosynthetic activity of aquatic organisms by hindering light
penetration. Moreover, some of the dyes are considered carcinogenic and
mutagenic for human health. Therefore, efficient treatment and removal of dyes
from wastewater have attracted considerable attention in recent years.
Photocatalysis, due to its mild reaction condition, high degradation, broad
applied area and facile manipulation, is a promising method of solving
environmental pollution problems. In this paper, we report the synthesis of
graphene oxide-tin oxide (GO-SnO2) nanocomposite and the effectiveness of this
composite in decolorizing Methylene Blue. Tin oxide was prepared by liquid
phase co-precipitation method and graphene oxide-tin oxide (GOSnO2)
nanocomposite were prepared by solution mixing method. Tin oxide (SnO2)
nanoparticles have been ardently investigated as photocatalyst for water
purification and environment decontamination but the photon generated electron
and hole pair (EHP) recombination is one of the limiting factors. Graphene
oxide-tin oxide (GO-SnO2) nanocomposite is very propitious to overcome this
limitation for photocatalytic application. The as-synthesized graphene oxide
(GO) and GO-SnO2 nanocomposite were characterized by X-ray Diffraction (XRD),
Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX).
The GO-SnO2 nanocomposite showed better photocatalytic degradation efficiency
for Methylene Blue compared to SnO2 and Graphene oxide.
  Keywords: Graphene Oxide(GO),Methylene Blue, Nanocomposite, Photocatalyst,
Photodegradation, Tin Oxide(SnO2).",1806.06481v1
2005-01-28,Transport and magnetic properties of GdBaCo_{2}O_{5+x} single crystals: A cobalt oxide with square-lattice CoO_2 planes over a wide range of electron and hole doping,"Single crystals of the layered perovskite GdBaCo_{2}O_{5+x} (GBCO) have been
grown by the floating-zone method, and their transport, magnetic, and
structural properties have been studied in detail over a wide range of oxygen
contents. The obtained data are used to establish a rich phase diagram centered
at the ""parent'' compound GdBaCo_{2}O_{5.5} -- an insulator with Co ions in the
3+ state. An attractive feature of GBCO is that it allows a precise and
continuous doping of CoO_{2} planes with either electrons or holes, spanning a
wide range from the charge-ordered insulator at 50% electron doping (x=0) to
the undoped band insulator (x=0.5), and further towards the heavily hole-doped
metallic state. This continuous doping is clearly manifested in the behavior of
thermoelectric power which exhibits a spectacular divergence with approaching
x=0.5, where it reaches large absolute values and abruptly changes its sign. At
low temperatures, the homogeneous distribution of doped carriers in GBCO
becomes unstable, and both the magnetic and transport properties point to an
intriguing nanoscopic phase separation. We also find that throughout the
composition range the magnetic behavior in GBCO is governed by a delicate
balance between ferromagnetic (FM) and antiferromagnetic (AF) interactions,
which can be easily affected by temperature, doping, or magnetic field,
bringing about FM-AF transitions and a giant magnetoresistance (MR) phenomenon.
An exceptionally strong uniaxial anisotropy of the Co spins, which dramatically
simplifies the possible spin arrangements, together with the possibility of
continuous ambipolar doping turn GBCO into a model system for studying the
competing magnetic interactions, nanoscopic phase separation and accompanying
magnetoresistance phenomena.",0501706v1
2012-07-13,Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films,"We report room-temperature ferromagnetism in highly conducting transparent
anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on
LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray
diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption
spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry
(TOF-SIMS) indicated negligible magnetic contaminants in the films. The
presence of ferromagnetism with concomitant large carrier densities was
determined by a combination of superconducting quantum interference device
(SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic
circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD)
and was supported by first-principle calculations. SXMCD and XAS measurements
revealed a 90% contribution to ferromagnetism from the Ti ions and a 10%
contribution from the O ions. RBS/channelling measurements show complete Ta
substitution in the Ti sites though carrier activation was only 50% at 5% Ta
concentration implying compensation by cationic defects. The role of Ti vacancy
and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS)
respectively. It was found that in films with strong ferromagnetism, the Ti
vacancy signal was strong while Ti3+ signal was absent. We propose (in the
absence of any obvious exchange mechanisms) that the localised magnetic
moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers.
Cationic-defect-induced magnetism is an alternative route to ferromagnetism in
wide-band-gap semiconducting oxides without any magnetic elements.",1207.3156v1
2012-12-17,Magnetic field strength influence on the reactive magnetron sputter deposition of Ta2O5,"Reactive magnetron sputtering enables the deposition of various thin films to
be used for protective as well as optical and electronic applications. However,
progressing target erosion during sputtering results in increased magnetic
field strengths at the target surface. Consequently, the glow discharge, the
target poisoning, and hence the morphology, crystal structure and stoichiometry
of the prepared thin films are influenced. Therefore, these effects were
investigated by varying the cathode current Im between 0.50 and 1.00 A, the
magnetic field strength B between 45 and 90 mT, and the O2/(Ar+O2) flow rate
ratio between 0 and 100%. With increasing oxygen flow ratio a
sub-stoichiometric TaOx oxide forms at the metallic Ta target surface which
further transfers to a non-conductive tantalum pentoxide Ta2O5, impeding a
stable DC glow discharge. These two transition zones (from Ta to TaOx and from
TaOx to Ta2O5) shift to higher oxygen flow rates for increasing target
currents. Contrary, increasing the magnetic field strength (e.g., due to
sputter erosion) mainly shifts the TaOx to Ta2O5 transition to lower oxygen
flow rates while marginally influencing the Ta to TaOx transition. To allow for
a stable DC glow discharge (and to suppress the formation of non-conductive
Ta2O5 at the target) even at a flow rate ratio of 100% either a high target
current (Im >= 1 A) or a low magnetic field strength (B <= 60 mT) is necessary.
These conditions are required to prepare stoichiometric and fully crystalline
Ta2O5 films. Our investigations clearly demonstrate the importance of the
magnetic field strength, which changes during sputter erosion, on the target
poisoning and the resulting film quality.",1212.4089v2
2014-08-30,"Magnetic, electrical and structural properties of the new Re-doped ruthenocuprate Ru1-xRexSr2GdCu2Oy","Despite the discovery of new superconductors classes, high-Tc oxides continue
to be a current topic, because of their complex phase diagrams and
doping-dependant effects (allowing one to investigate the interaction between
orbitals), as well as structural properties such as lattice distortion and
charge ordering, among many others. Ruthenocuprates are magnetic
superconductors in which the magnetic transition temperature is much higher
than the critical superconducting temperature, making them unique compounds.
With the aim of investigating the dilution of the magnetic Ru sub-lattice, we
proposed the synthesis of the new Ru1-xRexSr2GdCu2Oy ruthenocupratetype family,
adapting the known two-step process (double perovskite + CuO)by directly doping
the double perovskite, thus obtaining the new perovskite compound
Sr2GdRu1-xRexOy, which represents a new synthesis process to the best of our
knowledge. Our samples were structurally characterised through X-ray
diffraction, and the patterns were analysed via Rietveld refinement. A complete
magnetic characterisation as a function of temperature and applied field, as
well as transport measurements were carried out. We discuss our results in the
light of the two-lattice model for ruthenocuprates, and a relation between RuO2
(magnetic) and CuO2 (superconductor) sublattices can clearly be observed.",1409.0152v1
2016-02-18,Electronic and magnetic structure of epitaxial NiO/Fe$_3$O$_4$(001) heterostructures grown on MgO(001) and Nb-doped SrTiO$_3$(001),"We study the underlying chemical, electronic and magnetic properties of a
number of magnetite based thin films. The main focus is placed onto
NiO/Fe$_3$O$_4$(001) bilayers grown on MgO(001) and Nb-SrTiO$_3$(001)
substrates. We compare the results with those obtained on pure Fe$_3$O$_4$(001)
thin films. It is found that the magnetite layers are oxidized and Fe$^{3+}$
dominates at the surfaces due to maghemite ($\gamma$-Fe$_2$O$_3$) formation,
which decreases with increasing magnetite layer thickness. From a layer
thickness of around 20 nm on the cationic distribution is close to that of
stoichiometric Fe$_3$O$_4$. At the interface between NiO and Fe$_3$O$_4$ we
find the Ni to be in a divalent valence state, with unambiguous spectral
features in the Ni 2p core level x-ray photoelectron spectra typical for NiO.
The formation of a significant NiFe$_2$O$_4$ interlayer can be excluded by
means of XMCD. Magneto optical Kerr effect measurements reveal significant
higher coercive fields compared to magnetite thin films grown on MgO(001), and
a 45$^{\circ}$ rotated magnetic easy axis. We discuss the spin magnetic moments
of the magnetite layers and find that the moment increases with increasing thin
film thickness. At low thickness the NiO/Fe$_3$O$_4$ films grown on
Nb-SrTiO$_3$ exhibits a significantly decreased spin magnetic moments. A
thickness of 20 nm or above leads to spin magnetic moments close to that of
bulk magnetite.",1602.05804v1
2019-07-02,Néel-type skyrmions and their current-induced motion in van der Waals ferromagnet-based heterostructures,"Since the discovery of ferromagnetic two-dimensional (2D) van der Waals (vdW)
crystals, significant interest on such 2D magnets has emerged, inspired by
their appealing properties and integration with other 2D family for unique
heterostructures. In known 2D magnets, spin-orbit coupling (SOC) stabilizes
perpendicular magnetic anisotropy (PMA). Such a strong SOC could also lift the
chiral degeneracy, leading to the formation of topological magnetic textures
such as skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here, we
report the experimental observation of N\'eel-type chiral magnetic skyrmions
and their lattice (SkX) formation in a vdW ferromagnet Fe3GeTe2 (FGT). We
demonstrate the ability to drive individual skyrmion by short current pulses
along a vdW heterostructure, FGT/h-BN, as highly required for any
skyrmion-based spintronic device. Using first principle calculations supported
by experiments, we unveil the origin of DMI being the interfaces with oxides,
which then allows us to engineer vdW heterostructures for desired chiral
states. Our finding opens the door to topological spin textures in the 2D vdW
magnet and their potential device application.",1907.01425v4
2019-07-18,Tuning spinterface properties in Iron/Fullerene thin films,"In ferromagnetic (FM) metal/organic semiconductor (OSC) heterostructures
charge transfer can occur which leads to induction of magnetism in the
non-magnetic OSC. This phenomenon has been described by the change in the
density of states in the OSC which leads to a finite magnetic moment at the OSC
interface and it is called the ""spinterface"". One of the main motivation in
this field of organic spintronics is how to control the magnetic moment in the
spinterface. In this regard, there are several open questions such as (i) which
combination of FM and OSC can lead to more moment at the spinterface? (ii) Is
the thickness of OSC also important? (iii) How does the spinterface moment vary
with the FM thickness? (iv) Does the crystalline quality of the FM matters? (v)
What is the effect of spinterface on magnetization reversal, domain structure
and anisotropy? In this context, we have tried to answer the last three issues
in this paper by studying Fe/C$_{60}$ bilayers of variable Fe thickness
deposited on Si substrates. We find that both the induced moment and thickness
of the spinterface vary proportionally with the Fe thickness. Such behavior is
explained in terms of the growth quality of the Fe layer on the native oxide of
the Si (100) substrate. The magnetization reversal, domain structure and
anisotropy of these bilayer samples were studied and compared with their
respective reference samples without having the C$_{60}$ layer. It is observed
that the formation of spinterface leads to reduction in uniaxial anisotropy in
Fe/C$_{60}$ on Si (100) in comparison to their reference samples.",1907.08248v1
2019-09-30,Simultaneous individual and dipolar collective properties in binary assemblies of magnetic nanoparticles,"Applications based on aggregates of magnetic nanoparticles are becoming
increasingly widespread, ranging from hyperthermia to magnetic recording.
However, although some uses require a collective behavior, other need a more
individual-like response, the conditions leading to either of these behaviors
are still poorly understood. Here we use nanoscale-uniform binary random dense
mixtures with different proportions of oxide magnetic nanoparticles with
low$/$high anisotropy as a valuable tool to explore the crossover from
individual to collective behavior. Two different anisotropy scenarios have been
studied in two series of binary compacts: M1, comprising maghemite
($\gamma$-Fe$_2$O$_3$) nanoparticles of different sizes (9.0 nm $/$ 11.5 nm)
with barely a factor of 2 between their anisotropy energies and M2, mixing
equally-sized pure maghemite (low-anisotropy) and Co-doped maghemite
(high-anisotropy) nanoparticles with a large difference in anisotropy energy
(ratio $>$ 8). Interestingly, while the M1 series exhibits collective behavior
typical of strongly-coupled dipolar systems, the M2 series presents a more
complex scenario where different magnetic properties resemble either
""individual-like"" or ""collective"", crucially emphasizing that the collective
character must be ascribed to specific properties and not to the system as a
whole. The strong differences between the two series, offer new insight
(systematically ratified by simulations) into the subtle interplay between
dipolar interactions, local anisotropy and sample heterogeneity, to determine
the behavior of dense assemblies of magnetic nanoparticles.",1909.13500v1
2020-02-05,Magnetic Induction in Convecting Galilean Oceans,"To date, analyses of magnetic induction in putative oceans in Jupiter's large
icy moons have assumed uniform conductivity in the modeled oceans. However, the
phase and amplitude response of the induced fields will be influenced by the
increasing electrical conductivity along oceans' convective adiabatic
temperature profiles. Here, we examine the amplitudes and phase lags for
magnetic diffusion in modeled oceans of Europa, Ganymede, and Callisto. We
restrict our analysis to spherically symmetric configurations, treating
interior structures based on self-consistent thermodynamics, which account for
variations in electrical conductivity with depth in convective oceans (Vance et
al., 2018). The numerical approach considers tens of radial layers. The
induction response of the adiabatic conductivity profile differs from oceans
with uniform conductivity based on the ice-ocean interface or the mean value of
the adiabatic profile by more than 10% in many cases. In addition, we consider
the generation of induced magnetic fields by oceanic fluid motions that might
be used to probe the ocean flows directly (e.g., Chave, 1983; Tyler, 2011;
Minami, 2017). Assuming turbulent convection (Soderlund et al., 2014), we find
that these signals can dominate induction signal at low latitudes, which
underscores the need for spatial coverage in magnetic induction investigations.
Based on end-member ocean compositions (Zolotov, 2008; Zolotov & Kargel, 2009),
we quantify the residual magnetic induction signals that might be used to infer
the oxidation state of Europa's ocean and to investigate stable liquids within
and under high-pressure ices in Ganymede and Callisto. Fully exploring this
parameter space for the sake of planned missions requires electrical
conductivity measurements in fluids at low temperature and to high salinity and
pressure.",2002.01636v3
2020-02-26,Magneto-Stark and Zeeman effect as origin of second harmonic generation of excitons in Cu$_2$O,"We report on the experimental and theoretical investigation of
magnetic-field-induced second harmonic generation (SHG) and two-photon
absorption (TPA) of excited exciton states ($n \geq 3$) of the yellow series in
Cu$_2$O. In this centrosymmetric material, SHG can occur due to constructive
interplay of electric dipole and electric quadrupole/magnetic dipole
transitions for light propagating along the low-symmetry directions [111] or
[112]. By application of a magnetic field in Voigt configuration, SHG gets also
allowed for excitation along the [110]-axis and even the high-symmetry cubic
direction [001]. Combining a symmetry analysis and a microscopic theory, we
uncover the two key contributions to the magnetic-field-induced SHG: the Zeeman
effect and the magneto-Stark effect. We demonstrate systematic dependencies of
the SHG intensity on the linear polarization angles of the ingoing fundamental
laser and the outgoing SHG beam. In general, the resulting contour plots in
combination with a symmetry analysis allow one to determine uniquely the
character of involved transitions. Moreover, we can separate in magnetic field
the Zeeman and the magneto-Stark effect through appropriate choice of the
experimental geometry and polarization configuration. We present a microscopic
theory of the second harmonic generation of excitons in a centrosymmetric cubic
semiconductor taking into account the symmetry and the band structure of
cuprous oxide. Based on the developed microscopic theory we identify the main
contributions to the second-order nonlinear susceptibility of $S$-, $P$- and
$D$-excitons. We analyze the redistribution of SHG intensities between the
excitonic states both in the absence and presence of the magnetic field and
show good agreement with the experimental data. With increasing exciton
principal quantum number the magneto-Stark effect overpowers the influence of
the Zeeman effect.",2002.11560v1
2019-04-18,"Probing the Griffiths like phase, unconventional dual glassy states, giant exchange bias effects and its correlation with its electronic structure in Pr2-xSrxCoMnO6","Electronic structure, electrical transport, dc and ac magnetization
properties of the hole substituted (Sr2+) partially B-site disordered double
perovskite Pr2-xSrxCoMnO6 system have been investigated. Electronic structure
was probed by employing X-ray photoemission spectroscopy (XPS) measurements.
The study suggested the presence of mixed valence states of the B-site ions
(Co2+/Co3+ and Mn3+/Mn4+) with significant enhancement of the average oxidation
states due to hole doping. The mere absence of electronic states near the Fermi
level in the valence band (VB) spectra for both of the pure (x=0.0) and Sr
doped (x=0.5) systems indicated the insulating nature of the samples. Sr
substitution is observed to increase the spectral weight near the Fermi level
suggesting for an enhanced conductivity of the hole doped system. The
temperature variation of electrical resistivity measurements revealed the
insulating nature for both the systems, thus supporting the VB spectra results.
The dc magnetization data divulged a Griffiths like phase above the long range
ordering temperature. A typical re-entrant spin glass like phase driven by the
inherent anti-site disorder (ASD) has been maidenly recognized by ac
susceptibility study for both the pure and doped systems. Most interestingly,
the emergence of a new cluster glass like phase (immediately below the magnetic
ordering temperature and above the spin-glass transition temperature) solely
driven by the Sr substitution has been unravelled by ac magnetization dynamics
study. The isothermal magnetization measurements further probed the exhibition
of the giant exchange bias effect emanated from the existence of multiple
magnetic phases.",1904.08817v2
2019-08-16,"Evolution of electronic and magnetic properties in a series of iridate double perovskites Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1.0)","Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic
properties of 5$d$ iridates. In this paper we have experimentally investigated
the structural and physical properties of a series of Ir-based double
perovskite compounds Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1; hereafter
abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have
recently been proposed to undergo a transition from the spin-orbit-coupled Mott
insulating phase at $x$ = 0 to the elusive half-metallic antiferromagnetic
(HMAFM) state with Sr doping at $x$ = 1. However, our detailed magnetic and
electrical measurements refute any kind of HMAFM possibility in either of the
doped samples. In addition, we establish that within these
Pr$_{2-x}$Sr$_x$MgIrO$_6$ double perovskites, changes in Ir-oxidation states
(4+ for PMIO to 5+ for PSMIO via mixed 4+/5+ for PSMIO1505) lead to markedly
different magnetic behaviors. While SOC on Ir is at the root of the observed
insulating behaviors for all three samples, the correlated magnetic properties
of these three compounds develop entirely due to the contribution from local Ir
moments. Additionally, the magnetic Pr$^{3+}$ (4$f^2$) ions, instead of showing
any kind of ordering, only contribute to the total paramagnetic moment. It is
seen that the PrSrMgIrO$_6$ sample does not order down to 2 K despite
antiferromagnetic interactions. But, the $d^5$ iridate Pr$_2$MgIrO$_6$ shows a
sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed
valent Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ sample the AFM transition is shifted to a
much lower temperature ($\sim$ 6 K) due to weakening of the AFM exchange.",1908.05973v1
2020-05-19,The benefits of a Bayesian analysis for the characterization of magnetic nanoparticles,"Magnetic nanoparticles offer a unique potential for various biomedical
applications, but prior to commercial usage a standardized characterization of
their structural and magnetic properties is required. For a thorough
characterization, the combination of conventional magnetometry and advanced
scattering techniques has shown great potential. In the present work, we
characterize a powder sample of high-quality iron oxide nanoparticles that are
surrounded with a homogeneous thick silica shell by DC magnetometry and
magnetic small-angle neutron scattering (SANS). To retrieve the particle
parameters such as their size distribution and saturation magnetization from
the data, we apply standard model fits of individual data sets as well as
global fits of multiple curves, including a combination of the magnetometry and
SANS measurements. We show that by combining a standard least-squares fit with
a subsequent Bayesian approach for the data refinement, the probability
distributions of the model parameters and their cross correlations can be
readily extracted, which enables a direct visual feedback regarding the quality
of the fit. This prevents an overfitting of data in case of highly correlated
parameters and renders the Bayesian method as an ideal component for a
standardized data analysis of magnetic nanoparticle samples.",2005.09325v3
2021-03-09,Tuning the tilting of the spiral plane by Mn doping in YBaCuFeO5 multiferroic,"The layered perovskite YBaCuFeO5 (YBCFO) is considered one of the best
candidates to high-temperature chiral multiferroics with strong magnetoelectric
coupling. In RBaCuFeO5 perovskites (R: rare-earth or Y) A-site cations are
fully ordered whereas their magnetic properties strongly depend on the
preparation process. They exhibit partial cationic disorder at the B-site that
generates a magnetic spiral stabilized through directionally assisted long
range coupling between canted locally frustrated spins. Moreover the
orientation of its magnetic spiral can be critical for the magnetoelectric
response of this chiral magnetic oxide. We have synthesized and studied
YBaCuFe1-xMnxO5 samples doped with Mn, with the aim of increasing spin-orbit
coupling effects, and found that the overall Fe/Cu cation disorder at the
B-sites can be increased by doping without changing the sample preparation
process. In YBaCuFe1-xMnxO5 samples prepared under the same conditions, the T-x
magnetic phase diagram have been constructed in the range 10K-500K combining
magnetometry, X-ray and neutron powder diffraction measurements. The tilting
angles of the spins in the collinear, {\theta}col , and spiral phases,
{\theta}spiral, barely vary with temperature. In the collinear phase
{\theta}col is also independent of the Mn content. In contrast, the presence of
Mn produces a progressive reorientation of the plane of the magnetic helix in
the incommensurate phase, capable to transform the helicoidal spin ordering
into a cycloidal one, which may critically determine the ferroelectric and
magnetoelectric behavior in these compounds. Some of the observations are of
interest for engineering and developing this family of potential
high-temperature multiferroics.",2103.05540v1
2023-03-14,The rise and fall of Mott insulating gaps in YNiO$_3$ paramagnets as a reflection of symmetry breaking and remaking,"The YNiO$_3$ nickelate is a paradigm d-electron oxide that manifests the
intriguing temperature-mediated sequence of three phases transitions from (i)
magnetically ordered insulator to (ii) paramagnetic (PM) insulator and then to
(iii) PM metal. Such phenomena raised the question of the nature of the
association of magnetism and structural symmetry breaking with the appearance
in (i) and (ii) and disappearance in (iii) of insulating band gaps. It is
demonstrated here that first-principles mean-field-like density functional
theory (DFT), driven by molecular dynamics temperature evolution, can describe
not only the origin of the magnetically long-range ordered insulating phase
(i), but also the creation of an insulating paramagnet (ii) that lacks
spin-long-range order, and of a metallic paramagnet (iii) as temperature rises.
This approach provides the patterns of structural and magnetic symmetry
breaking at different temperatures, in parallel with band gaps obtained when
the evolving geometries are used as input to DFT electronic band structure
calculations. This disentangles the complex interplay among spin, charge and
orbital degrees of freedom. Analysis shows that the success in describing the
rise and fall of the insulating band gaps along the phase transition sequence
is enabled by allowing sufficient flexibility in describing diverse local
structural and magnetic motifs as input to DFT. This entails using sufficiently
large supercells that allow expressing structural disproportionation of
octahedra, as well as a description of PM phases as a distribution of local
magnetic moments. It appears that the historic dismissal of mean-field-like DFT
as being unable to describe such Mott-like transitions was premature, as it was
based on consideration of averaged crystallographic unit cells, a description
that washes out local symmetry-breaking motifs.",2303.08199v1
2009-12-31,Novel Structural Motifs in Oxidized Graphene,"The structural and electronic properties of oxidized graphene are
investigated on the basis of the genetic algorithm and density functional
theory calculations. We find two new low energy semiconducting phases of the
fully oxidized graphene (C1O). In one phase, there is parallel epoxy pair
chains running along the zigzag direction. In contrast, the ground state phase
with a slightly lower energy and a much larger band gap contains epoxy groups
in three different ways: normal epoxy, unzipped epoxy, and epoxy pair. For
partially oxidized graphene, a phase separation between bare graphene and fully
oxidized graphene is predicted.",1001.0171v1
2012-07-31,Ge condensation under SiGe oxidization: from Molecular Dynamics simulation to one-dimensional analytic modeling,"Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol
based on molecular dynamics simulation and rules for the oxygen insertions.
These rules, deduced from ab-initio calculations, favor the formation of SiO_2
against GeO_2 oxide which leads to segregation of Ge atoms into the alloy
during the oxidization front advance. Ge condensation is then observed close to
the SiO_2/Ge interface due to the strain induced by oxydization in this region.
From the analysis of the simulation process, we propose a one-dimensional
description of Ge condensation wich perfectly reproduces the evolution of the
Ge concentration during oxidization of the SiGe alloy.",1207.7238v1
2015-11-24,Structural Properties and Thermodynamics of Hafnium sub-oxides in RRAM,"We study the structural and electronic properties of various hafnium
sub-oxides HfzO from z = 9 to z = 0.5, by ab initio simulation using Density
Functional Theory. The stability of these sub-oxides is studied against
monoclinic HfO2. The progressive oxidation of a given HfzO is also envisaged
toward stoichiometric HfO2. The analogy with a conductive region of electrons
inside a HfO2 matrix is discussed within the context of Oxide-based Resistive
Random Access Memories (OxRRAM) devices which employ hafnium dioxide as an
insulator.",1511.07665v1
2016-02-26,Epitaxially Stabilized Oxide Composed of Twisted Triangular-Lattice Layers,"Layered oxides have been intensively studied due to their high designability
for various electronic functions. Here we synthesize a new oxide as epitaxial
thin film form by pulsed laser deposition. Film characterizations including
cross-section and plan-view transmission electron microscopy confirm that the
film is composed of twisted stack of triangular-lattice Rh and Bi layers. We
foresee that the concept of twisted oxide layers will open up a new route to
design further functional layered oxides.",1602.08192v1
2016-10-31,Buffer Layer Engineering on Graphene via Various Oxidation Methods for Atomic Layer Deposition,"The integration of high-k oxide on graphene using atomic layer deposition
requires an electrically reliable buffer layer. In this study, Y was selected
as the buffer layer due to the highest oxidation ability in rare earth elements
and various oxidation methods (atmospheric, high-pressure O2 and ozone) were
applied to the Y metal buffer layer. By optimizing oxidation conditions of the
top gate insulator, we successfully improve the capacitance of top gate Y2O3
insulator and demonstrate a large Ion/Ioff ratio for bilayer graphene under an
external electric field.",1610.09857v1
2020-01-08,Electrical and optical properties of hydrated amorphous vanadium oxide,"Electrical and optical properties of amorphous vanadium oxide thin films
obtained by electrochemical anodic oxidation are studied. It is shown that
under cathodic polarization the hydrogen insertion into vanadium oxide from an
electrolyte occurs. Metal-insulator transition in amorphous HxVO2 is found to
be preserved up to high concentration (x ~ 1.5) of hydrogen. Memory switching
with the N-type negative differential resistance, associated with the H+ ionic
transfer, is observed in ""V/hydrated amorphous vanadium oxide/Au"" sandwich
structures.",2001.02418v1
2020-09-25,Current progress in vanadium oxide nanostructures and its composites as supercapacitor electrodes,"In recent years, vanadium oxides have gained immense attention in the field
of energy storage devices due to their low-cost, layered structure and
multi-valency despite their limited electrical conductivity and lower
structural stability. In this brief review, we have tried to focus on
electrochemical properties of the stoichiometric vanadium oxides along with
VO_x composites. The morphology engineering, doping with heteroatom and
formation of composites with carbon-based materials and/or conducting polymers
in enhancing the supercapacitive performances of the vanadium oxides are
discussed in details. Finally, the potentiality and challenges of vanadium
oxides nanocomposites for supercapacitor applications are discussed.",2009.12034v1
2021-02-23,Structure and hardness of in situ synthesized nano-oxide strengthened CoCrFeNi high entropy alloy thin films,"In this study, we report on face-centered cubic structured CoCrFeNi
high-entropy alloy thin films with finely dispersed nano-oxide particles which
are formed by internal oxidation. Analytical scanning transmission electron
microscopy imaging found that the particles are Cr2O3. The oxide particles
contribute to the hardening of the film increasing its hardness by 14% compared
to that of the film without precipitates, through the Orowan-type strengthening
mechanism. Our novel approach paves the way to design medium- and high-entropy
alloys with high strength by making use of oxide phases.",2102.11950v1
2011-09-02,A first-principles study of helium storage in oxides and at oxide--iron interfaces,"Density-functional theory calculations based on conventional as well as
hybrid exchange-correlation functionals have been carried out to study the
properties of helium in various oxides (Al2O3, TiO2, Y2O3, YAP, YAG, YAM, MgO,
CaO, BaO, SrO) as well as at oxide-iron interfaces. Helium interstitials in
bulk oxides are shown to be energetically more favorable than substitutional
helium, yet helium binds to existing vacancies. The solubility of He in oxides
is systematically higher than in iron and scales with the free volume at the
interstitial site nearly independently of the chemical composition of the
oxide. In most oxides He migration is significantly slower and He--He binding
is much weaker than in iron. To quantify the solubility of helium at oxide-iron
interfaces two prototypical systems are considered (Fe|MgO, Fe|FeO|MgO). In
both cases the He solubility is markedly enhanced in the interface compared to
either of the bulk phases. The results of the calculations allow to construct a
schematic energy landscape for He interstitials in iron. The implications of
these results are discussed in the context of helium sequestration in oxide
dispersion strengthened steels, including the effects of interfaces and lattice
strain.",1109.0433v2
2015-06-26,Influence of van der Waals interactions on morphology and dynamics in ultrathin liquid films at silicon oxide interfaces,"Single molecule tracer diffusion studies of evaporating (thinning) ultrathin
tetrakis-2-ethyl-hexoxysilane (TEHOS) films on silicon with 100 nm thermal
oxide reveal a considerable slowdown of the molecular mobility within less than
4 nm above the substrate (corresponding to a few molecular TEHOS layers). This
is related to restricted mobility and structure formation of the liquid in this
region, in agreement with information obtained from a long-time ellipsometric
study of thinning TEHOS films on silicon substrates with 100 nm thermal or 2 nm
native oxide. Both show evidence for the formation of up to four layers.
Additionally, on thermal oxide, a lateral flow of the liquid is observed, while
the film on the native oxide forms an almost flat surface and shows negligible
flow. Thus, on the 2 nm native oxide the liquid mobility is even more
restricted in close vicinity to the substrate as compared to the 100 nm thermal
oxide. In addition, we found a significantly smaller initial film thickness in
case of the native oxide under similar dipcoating conditions. We ascribe these
differences to van der Waals interactions with the underlying silicon in case
of the native oxide, whereas the thermal oxide suffices to shield those
interactions.",1506.08144v1
2016-04-21,Superconductivity in the antiperovskite Dirac-metal oxide Sr$_3$SnO,"Oxides with perovskite-based structures have been known as essential
materials for fascinating phenomena such as high-temperature and unconventional
superconductivity. Discoveries of these oxide superconductors have driven the
science community to vastly extend the concepts of strongly correlated electron
systems. The base of these materials, the cubic perovskite oxides, $AB$O$_3$,
also exhibit superconductivity with $T_{\mathrm{c}}$ of up to 30 K, as reported
for Ba$_{0.6}$K$_{0.4}$BiO$_3$. Perovskite oxides have their counterparts,
antiperovskite oxides $A_3B$O (or ""$B$O$A_3$""), in which the position of metal
and oxygen ions are reversed and therefore metallic $B$ ions take unusual
negative valence states. However, no superconductivity has been reported among
antiperovskite oxides. Here, we report the discovery of the first
superconducting antiperovskite oxide Sr$_3$SnO with $T_{\mathrm{c}}$ of around
5 K. Sr$_3$SnO possesses Dirac points in its electronic structure, originating
from the inversion of bands with different parities. Based on theoretical
analysis, we propose possibility of topological odd-parity superconductivity
analogous to the superfluid $^3$He-B, in moderately hole-doped Sr$_3$SnO,
originating from unusual orbital texture on the Fermi surface. We envision that
this discovery of a new class of oxide superconductor with the inverted valence
configuration will stimulate the exploration of topological materials science
based on a variety of antiperovskite oxides.",1604.06238v2
2014-03-10,Ethylene oxide and Acetaldehyde in hot cores,"[Abridged] Ethylene oxide and its isomer acetaldehyde are important complex
organic molecules because of their potential role in the formation of amino
acids. Despite the fact that acetaldehyde is ubiquitous in the interstellar
medium, ethylene oxide has not yet been detected in cold sources. We aim to
understand the chemistry of the formation and loss of ethylene oxide in hot and
cold interstellar objects (i) by including in a revised gas-grain network some
recent experimental results on grain surfaces and (ii) by comparison with the
chemical behaviour of its isomer, acetaldehyde. We test the code for the case
of a hot core. The model allows us to predict the gaseous and solid ethylene
oxide abundances during a cooling-down phase prior to star formation and during
the subsequent warm-up phase. We can therefore predict at what temperatures
ethylene oxide forms on grain surfaces and at what temperature it starts to
desorb into the gas phase. The model reproduces the observed gaseous abundances
of ethylene oxide and acetaldehyde towards high-mass star-forming regions. In
addition, our results show that ethylene oxide may be present in outer and
cooler regions of hot cores where its isomer has already been detected. Despite
their different chemical structures, the chemistry of ethylene oxide is coupled
to that of acetaldehyde, suggesting that acetaldehyde may be used as a tracer
for ethylene oxide towards cold cores.",1403.2355v1
2018-09-25,Evaluating transition-metal oxides within DFT-SCAN and SCAN+U frameworks for solar thermochemical applications,"Using the strongly constrained and appropriately normed (SCAN) and SCAN+U
approximations for describing electron exchange-correlation (XC) within density
functional theory, we investigate the oxidation energetics, lattice constants,
and electronic structure of binary Ce-, Mn-, and Fe-oxides, which are crucial
ingredients for generating renewable fuels using two-step, oxide-based, solar
thermochemical reactors. Unlike other common XC functionals, we find that SCAN
does not over-bind the O2 molecule, based on direct calculations of its bond
energy and robust agreement between calculated formation enthalpies of main
group oxides versus experiments. However, in the case of transition-metal
oxides (TMOs), SCAN systematically overestimates (i.e., yields too negative)
oxidation enthalpies due to remaining self-interaction errors in the
description of their ground-state electronic structure. Adding a Hubbard U term
to the transition-metal centers, where the magnitude of U is determined from
experimental oxidation enthalpies, significantly improves the qualitative
agreement and marginally improves the quantitative agreement of
SCAN+U-calculated electronic structure and lattice parameters, respectively,
with experiments. Importantly, SCAN predicts the wrong ground-state structure
for a few oxides, namely, Ce2O3, Mn2O3, and Fe3O4, while SCAN+U predicts the
right polymorph for all systems considered in this work. Hence, the SCAN+U
framework, with an appropriately determined U, will be required to accurately
describe ground-state properties and yield qualitatively consistent electronic
properties for most transition- metal and rare earth oxides.",1809.09713v1
2018-10-11,Factors controlling oxygen interstitial diffusion in the Ruddlesden-Popper oxide La2-xSrxNiO4+delta,"The development of Ruddlesden-Popper (RP) oxides as oxygen exchange and
transport materials will benefit from mechanistic understanding of how oxygen
transports through these materials. Using Density Functional Theory, we found
there are two distinct oxygen interstitial diffusion mechanisms involving two
different oxygen interstitial species that can be active in La2-xSrxNiO4+delta,
and, we believe, in hyperstoichiometric RP oxides in general. The first
mechanism is the previously proposed interstitialcy-mediated mechanism, which
consists of diffusing oxide interstitials. The second mechanism is newly
discovered in this work, and consists of both oxide and peroxide interstitial
species. This mechanism exhibits a similar or possibly lower migration barrier
than the interstitialcy mechanism for high oxidation states. Which mechanism
contributes to the oxygen interstitial diffusion is the result of the change in
relative stability between the oxide interstitial and peroxide interstitial.
The stability of the oxide and peroxide, and the competition between the two
oxygen diffusion mechanisms, is sensitive to the overall oxidation state of the
system. Therefore, the oxygen diffusion mechanism is a function of the material
composition, oxygen off-stoichiometry, operating temperature and oxygen partial
pressure. We also examined the effect of epitaxial strain on both oxygen
diffusion mechanisms, and found that tensile and compressive epitaxial strain
of up to 2% had less than 100 meV/(% strain) effects on oxygen interstitial
formation, migration, and activation energies, and that total achievable
activation energy reductions are likely less than 100 meV for -2% to +2%
epitaxial strain. The presented understanding of factors governing interstitial
oxygen diffusion has significant implications for the engineering of RP oxides
in numerous alternative energy technologies.",1810.05209v1
2018-12-31,Diffusion- Migration-Reaction-Limited Aggregation of Point Defects: A Model for the Stability of Oxide-layers on Metals and Its Breakdown,"A thin oxide layer protects metals from electrochemical corrosion and hence
the stability of this oxide layer is crucial for corrosion resistance of
metals. The dynamics of cationic and anionic point defects which are injected
into this oxide layer at the metal-oxide-layer interface and the
oxide-layer-environment interface during electrochemical processes determine
the stability of this oxide-layer.
  The point defect model originally advanced by Digby Macdonald and perfected
into a correct and complete theory by Bosco Emmanuel provides a concrete basis
for investigating this stability question. We have formulated a system of 3
coupled differential equations (2 PDEs and one ODE) with appropriate initial
and boundary conditions that include the defect injection reactions. This
system of equations recognize the diffusion, migration and clustering of the
point defects in the oxide-layer. The defect clustering is modelled using the
Avrami Theorem and the area-volume laws for random agglomerates.
  This research is expected to provide insights into the criticality associated
with the oxide-layer breakdown and the periodic, aperiodic and chaotic
oscillations in the electrical current / potential which signal the breakdown
of the passive oxide-layer. A large body of experimental data is waiting to be
understood within a frame-work such as the present. Some initial results from
the model are also reported.",1812.11807v1
2021-02-18,Crystal orientation-dependent oxidation of epitaxial TiN films with tunable plasmonics,"Titanium nitride (TiN) is a paradigm of refractory transition metal nitrides
with great potential in vast applications. Generally, the plasmonic performance
of TiN can be tuned by oxidation, which was thought to be only temperature-,
oxygen partial pressure-, and time-dependent. Regarding the role of
crystallographic orientation in the oxidation and resultant optical properties
of TiN films, little is known thus far. Here we reveal that both the oxidation
resistance behavior and the plasmonic performance of epitaxial TiN films follow
the order of (001) < (110) < (111). The effects of crystallographic orientation
on the lattice constants, optical properties, and oxidation levels of epitaxial
TiN films have been systematically studied by combined high-resolution X-ray
diffraction, spectroscopic ellipsometry, X-ray absorption spectroscopy, and
X-ray photoemission spectroscopy. To further understand the role of
crystallographic orientation in the initial oxidation process of TiN films,
density-functional-theory calculations are carried out, indicating the energy
cost of oxidation is (001) < (110) < (111), consistent with the experiments.
The superior endurance of the (111) orientation against mild oxidation can
largely alleviate the previously stringent technical requirements for the
growth of TiN films with high plasmonic performance. The crystallographic
orientation can also offer an effective controlling parameter to design
TiN-based plasmonic devices with desired peculiarity, e.g., superior chemical
stability against mild oxidation or large optical tunability upon oxidation.",2102.09126v1
2023-07-02,Optoelectronic properties of silver doped copper oxide thin films,"Thin films have found a wide variety of applications because of the
substantial improvement in their properties as compared to bulk metals. Metal
oxide thin films are increasingly being used in various fields and are
especially important in functional applications. They can be either p- or
n-type in nature depending on the materials, dopants, and preparation route.
Copper oxide is an example of a p-type metal oxide, which finds application in
solar cells, photo-electrochemical cells, gas sensors, supercapacitors, and
thermoelectric touch detectors. Both copper (I) and copper (II) oxides can be
grown with the lower valence state oxide stable at low temperature and the
higher valence state obtained by annealing at higher temperatures. In this
work, we modify the optical and electrical properties of copper oxide thin
films, by doping of silver through a thermal evaporation process route. Copper
is thermally evaporated onto the substrate and silver is co-evaporated during
this process. The films are then annealed in ambient under various conditions
to obtain copper oxide. Structural and functional comparison is made between
undoped and silver doped copper oxide thin films, prepared under the same
conditions. Thermal evaporation is a simple route for obtaining doped metal
oxides and the process can be extended to a variety of other systems as well.",2307.13649v1
1993-11-05,Correlated Electrons in High Temperature Superconductors,"Theoretical ideas and experimental results concerning high temperature
superconductors are reviewed. Special emphasis is given to calculations carried
out with the help of computers applied to models of strongly correlated
electrons proposed to describe the two dimensional ${\rm Cu O_2}$ planes. The
review also includes results using several analytical techniques. The one and
three band Hubbard models, and the ${\rm t-J}$ model are discussed, and their
behavior compared against experiments when available. Among the conclusions of
the review, we found that some experimentally observed unusual properties of
the cuprates have a natural explanation through Hubbard-like models. In
particular abnormal features like the mid-infrared band of the optical
conductivity $\sigma(\omega)$, the new states observed in the gap in
photoemission experiments, the behavior of the spin correlations with doping,
and the presence of phase separation in the copper oxide superconductors may be
explained, at least in part, by these models. Finally, the existence of
superconductivity in Hubbard-like models is analyzed. Some aspects of the
recently proposed ideas to describe the cuprates as having a $\dx2y2$
superconducting condensate at low temperatures are discussed. Numerical results
favor this scenario over others....(continues).",9311013v1
1995-01-06,Non-magnetic impurities in two dimensional superconductors,"A numerical approach to disordered 2D superconductors described by BCS mean
field theory is outlined. The energy gap and the superfluid density at zero
temperature and the quasiparticle density of states are studied. The method
involves approximate self-consistent solutions of the Bogolubov-de$\,$Gennes
equations on finite square lattices. Where comparison is possible, the results
of standard analytic approaches to this problem are reproduced. Detailed
modeling of impurity effects is practical using this approach. The {\it range}
of the impurity potential is shown to be of {\it quantitative importance} in
the case of strong potential scatterers. We discuss the implications for
experiments, such as the rapid suppression of superconductivity by Zn doping in
Copper-Oxide superconductors.",9501016v1
1996-06-09,NiO Exchange Bias Layers Grown by Direct Ion Beam Sputtering of a Nickel Oxide Target,"A new process for fabricating NiO exchange bias layers has been developed.
The process involves the direct ion beam sputtering (IBS) of a NiO target. The
process is simpler than other deposition techniques for producing NiO buffer
layers, and facilitates the deposition of an entire spin-valve layered
structure using IBS without breaking vacuum. The layer thickness and
temperature dependence of the exchange field for NiO/NiFe films produced using
IBS are presented and are similar to those reported for similar films deposited
using reactive magnetron sputtering. The magnetic properties of highly textured
exchange couples deposited on single crystal substrates are compared to those
of simultaneously deposited polycrystalline films, and both show comparable
exchange fields. These results are compared to current theories describing the
exchange coupling at the NiO/NiFe interface.",9606052v1
1996-12-10,A scenario for the electronic state in the manganase perovskites: the orbital correlated metal,"We argue that, at low temperatures and well into the ferromagnetic phase, the
physics of the manganase perovskites may be characterized by a correlated
metallic state near a metal insulator transition where the orbital degrees of
freedom play a main role. This follows from the observation that a two-band
degenerate Hubbard model under a strong magnetic field can be mapped onto a
para-orbital single band model. We solve the model numerically using the
quantum Monte Carlo technique within a dynamical mean field theory which is
exact in the limit of large lattice connectivity. We argue that the proposed
scenario may allow for the qualitative interpretation of a variety of
experiments which were also observed in other (early) transition metal oxides.",9612089v2
1997-05-01,Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T,"We have found weak long range antiferromagnetic order in the
quasi-two-dimensional insulating oxide $ KCr_3(OD)_6(SO_4)_2$ which contains
Cr$^{3+}$ S=3/2 ions on a kagom\'{e} lattice. In a sample with $\approx$ 76%
occupancy of the chromium sites the ordered moment is 1.1(3)$\mu_B$ per
chromium ion which is only one third of the N\'{e}el value $g\mu_BS=3\mu_B$.
The magnetic unit cell equals the chemical unit cell, a situation which is
favored by inter-plane interactions. Gapless quantum spin-fluctuations
($\Delta/k_B <0.25$K) with a bandwidth of 60K >> $T_N$ = 1.6K are the dominant
contribution to the spin correlation function, $S(Q,\omega)$ in the ordered
phase.",9705014v1
1997-09-08,Spin Density Functional Based Search for Half-Metallic Antiferromagnets,"We present results based on local spin density calculations of a
computational search for half-metallic (HM) antiferromagnetic (AFM) materials
within the class of double perovskite structure oxides LaM'M''O3 that
incorporate open shell 3d (or 4d) transition metal ions M', M''. The pairs
M'M'' = MnCo, CrFe, CrRu, CrNi, MnV, and VCu are studied. La2VMnO6 is the most
promising candidate, with the HM AFM phase more stable by 0.17 eV/cell than the
ferromagnetic phase. La2VCuO6 is another promising possibility, but due to
S=1/2 ions quantum fluctuations my play an important role in determining the
ground state magnetic and electronic structure. This study indicates that HM
AFM materials should not be prohibitively difficult to find.",9709100v1
1998-05-10,Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides,"Different mechanisms of spin-dependent tunneling are analyzed with respect to
their role in tunnel magnetoresistance (TMR). Microscopic calculation within a
realistic model shows that direct tunneling in iron group systems leads to
about a 30% change in resistance, which is close but lower than experimentally
observed values. The larger observed values of the tunnel magnetoresistance
(TMR) might be a result of tunneling involving surface polarized states. It is
found that tunneling via resonant defect states in the barrier radically
decreases the TMR by order of magnitude. One-magnon emission is shown to reduce
the TMR, whereas phonons increase the effect. The inclusion of both magnons and
phonons reasonably explains an unusual bias dependence of the TMR. The model
presented here is applied qualitatively to half-metallics with 100% spin
polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO2/TiO2 and CrO2/RuO2.",9805114v1
1998-07-16,On the Theory of Metal-Insulator Transitions in Gated Semiconductors,"It is shown that recent experiments indicating a metal-insulator transition
in 2D electron systems can be interpreted in terms of a simple model, in which
the resistivity is controlled by scattering at charged hole traps located in
the oxide layer. The gate voltage changes the number of charged traps which
results in a sharp change in the resistivity. The observed exponential
temperature dependence of the resistivity in the metallic phase of the
transition follows from the temperature dependence of the trap occupation
number. The model naturally describes the experimentally observed scaling
properties of the transition and effects of magnetic and electric fields.",9807245v1
1999-03-15,Metal-insulator transition in CMR materials,"We report on resistivity measurements in La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ and
Nd$_{0.7}$Sr$_{0.3}$MnO$_{3}$ thin films in order to elucidate the underlying
mechanism for the CMR behavior. The experimental results are analyzed in terms
of quantum phase transition ideas to study the nature of the metal-insulator
transition in manganese oxides. Resistivity curves as functions of
magnetization for various temperatures show the absence of scaling behavior
expected in a continuous quantum phase transition, which leads us to conclude
that the observed metal-insulator transition is most likely a finite
temperature crossover phenomenon.",9903238v2
1999-08-12,The Essential Interactions in Oxides and Spectral Weight Transfer in Doped Manganites,"We calculate the value of the Fr\""ohlich electron-phonon interaction in
manganites, cuprates, and some other charge-transfer insulators and show that
this interaction is much stronger than any relevant magnetic interaction. A
polaron shift due to the Fr\""ohlich interaction, which is about 1 eV, suggests
that carriers in those systems are small (bi)polarons at all temperatures and
doping levels, in agreement with the oxygen isotope effect and other data. An
opposite conclusion, recently suggested in the literature, is shown to be
incorrect. The frequency and temperature dependence of the optical conductivity
of ferromagnetic manganites is explained within the framework of the bipolaron
theory.",9908183v3
1999-10-16,Charge and orbital order in half-doped manganites,"An explanation is given for the charge order, orbital order and insulating
state observed in half-doped manganese oxides, such as
Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$. The competition between the kinetic energy of
the electrons and the magnetic exchange energy drives the formation of
effectively one-dimensional ferromagnetic zig-zag chains. Due to a topological
phase factor in the hopping, the chains are intrinsically insulating and
orbital-ordered. Most surprisingly, the strong Coulomb interaction between
electrons on the same Mn-ion leads to the experimentally observed charge
ordering. For doping less than 1/2 the system is unstable towards phase
separation into a ferromagnetic metallic and charge-ordered insulating phase.",9910253v1
2000-03-14,"Magnetoresistance in ordered and disordered double perovskite oxide, Sr$_2$FeMoO$_6$","We have prepared crystallographically ordered and disorder specimens of the
double perovskite, Sr$_2$FeMoO$_6$ and investigated their magnetoresistance
behaviour. The extent of ordering between the Fe and Mo sites in the two
samples is determined by Rietveld analysis of powder x-ray diffraction patterns
and reconfirmed by M\""{o}ssbauer studies. While the ordered sample exhibits the
sharp low-field response, followed by moderate changes in the magnetoresistance
at higher fields, the disordered sample is characterised by the absence of the
spectacular low-field response. We argue that the low field response depends
crucially on the half-metallic ferromagnetism, while the high-field response
follows from the overall magnetic nature of the sample, even in absence of the
half-metallic state.",0003237v1
2001-03-02,Sharp resonant multiplet in femto-second optical pair-breaking spectroscopy of YBa2Cu3O7-delta,"Femto-second optical pair breaking spectroscopy is performed on optimally
doped YBa2Cu3O7-delta near 1.5eV. Dramatic photon energy dependence with a
sharp triplet fine structure is seen for the first time. The peak separations
are attributable to the reported phonon and magnetic excitations in the system.
The power dependence is non-linear with differing exponents for the three
contributions. These results imply the presence of insulating antiferromagnetic
domains in the superconducting state of YBCO over sub-picosecond time scale,
and thereby favor an electronic phase separation picture.",0103046v1
2001-06-21,207Pb and 17O NMR Study of the Electron Density Distribution in Metal Phase of BaPb_{1-x}Bi_xO_3,"The 17O and 207Pb NMR spectra were measured in ceramic samples in the
metallic phase of BaPb_{1-x}Bi_{x}O_3 oxides (0<x< 0.33). The inhomogeneous
magnetic broadening which appears due to a distribution of the Knight shifts
was analyzed in detail. It is shown that Bi atoms, which are randomly
incorporated in BaPbO_3 parent compound give rise to an increased conduction
electron spin density within an area which is delimited by its two first cation
shells. According to NMR data the percolative overlap of these areas occurs in
superconducting compositions and it is accompanied by a sharp growth of the
average Knight shift <Ks>. The decrease of <17Ks> with temperature revealed for
x=0.33 evidences for an opening of the energy gap near E_F near the
metal-semiconductor transition (x=0.35).",0106431v1
2002-01-22,Anisotropic Exchange in LiCuVO$_4$ probed by ESR,"We investigated the paramagnetic resonance in single crystals of LiCuVO$_4$
with special attention to the angular variation of the absorption spectrum. To
explain the large resonance linewidth of the order of 1 kOe, we analyzed the
anisotropic exchange interaction in the chains of edge-sharing CuO$_6$
octahedra, taking into account the ring-exchange geometry of the
nearest-neighbor coupling via two symmetric rectangular Cu-O bonds. The
exchange parameters, which can be estimated from theoretical considerations,
nicely agree with the parameters obtained from the angular dependence of the
linewidth. The anisotropy of this magnetic ring exchange is found to be much
larger than it is usually expected from conventional estimations which neglect
the bonding geometry. Hence, the data yield the evidence that in copper oxides
with edge-sharing structures the role of the orbital degrees of freedom is
strongly enhanced. These findings establish LiCuVO$_4$ as one-dimensional
compound at high temperatures.
  PACS: 76.30.-v, 76.30.Fc, 75.30.Et",0201403v1
2002-04-24,Superconducting Transition and Vortex Pinning in Nb Films Patterned with Nano-scale Hole-arrays,"Nb films containing extended arrays of holes with 45-nm diameter and 100-nm
spacing have been fabricated using anodized aluminum oxide (AAO) as substrate.
Pronounced matching effects in the magnetization and Little-Parks oscillations
of the superconducting critical temperature have been observed in fields up to
9 kOe. Flux pinning in the patterned samples is enhanced by two orders of
magnitude as compared to unpatterned reference samples in applied fields
exceeding 5 kOe. Matching effects are a dominant contribution to vortex pinning
at temperatures as low as 4.2 K due to the extremely small spacing of the
holes.",0204535v1
2002-07-05,On the two-dimensional metallic state in silicon-on-insulator structures,"It is shown that the electronic conduction in silicon-on-insulator (SOI)
layers exhibits a metallic regime which is very similar to that in
high-mobility Si-metal oxide semiconductor structures (MOS). The peak in the
electron mobility versus density, the strong drop in resistivity and the
critical concentration for the metal-insulator transition are all consistent.
On the basis of our SOI data for the temperature and in-plane magnetic field
dependence of the resistivity, we discuss several models for the metallic state
in two dimensions. We find that the observed behavior can be well described by
the theory on the interaction corrections in the ballistic regime. For the
investigated regime, the temperature dependent screening of scattering
potentials gives also a good description of the data.",0207170v1
2002-07-31,Transport anisotropy in biaxially strained La(2/3)Ca(1/3)MnO(3) thin films,"Due to the complex interplay of magnetic, structural, electronic, and orbital
degrees of freedom, biaxial strain is known to play an essential role in the
doped manganites. For coherently strained La(2/3)Ca(1/3)MnO(3) thin films grown
on SrTiO(3) substrates, we measured the magnetotransport properties both
parallel and perpendicular to the substrate and found an anomaly of the
electrical transport properties. Whereas metallic behavior is found within the
plane of biaxial strain, for transport perpendicular to this plane an
insulating behavior and non-linear current-voltage characteristics (IVCs) are
observed. The most natural explanation of this anisotropy is a strain induced
transition from an orbitally disordered ferromagnetic state to an orbitally
ordered state associated with antiferromagnetic stacking of ferromagnetic
manganese oxide planes.",0207730v1
2002-08-06,Ground state of the three-band Hubbard model,"The ground state of the two-dimensional three-band Hubbard model in oxide
superconductors is investigated by using the variational Monte Carlo method.
The Gutzwiller-projected BCS and spin- density wave (SDW) functions are
employed in the search for a possible ground state with respect to dependences
on electron density. Antiferromagnetic correlations are considerably enhanced
near half-filling. It is shown that the d-wave state may exist away from
half-filling for both the hole and electron doping cases. The overall structure
of the phase diagram obtained by the calculations qualitatively agrees with
experimental indications. The superconducting condensation energy is in
reasonable agreement with the experimental value obtained from specific heat
and critical magnetic field measurements for optimally doped samples. The
inhomogeneous SDW state is also examined near 1/8-hole doping.",0208105v1
2002-09-05,Ground state properties of ferromagnetic metal/conjugated polymer interfaces,"We theoretically investigate the ground state properties of ferromagnetic
metal/conjugated polymer interfaces. The work is partially motivated by recent
experiments in which injection of spin polarized electrons from ferromagnetic
contacts into thin films of conjugated polymers was reported. We use a
one-dimensional nondegenerate Su-Schrieffer-Heeger (SSH) Hamiltonian to
describe the conjugated polymer and one-dimensional tight-binding models to
describe the ferromagnetic metal. We consider both a model for a conventional
ferromagnetic metal, in which there are no explicit structural degrees of
freedom, and a model for a half-metallic ferromagnetic colossal
magnetoresistance (CMR) oxide which has explicit structural degrees of freedom.
The Fermi energy of the magnetic metallic contact is adjusted to control the
degree of electron transfer into the polymer. We investigate electron charge
and spin transfer from the ferromagnetic metal to the organic polymer, and
structural relaxation near the interface. Bipolarons are the lowest energy
charge state in the bulk polymer for the nondegenerate SSH model Hamiltonian.
As a result electrons (or holes) transferred into the bulk of the polymer form
spinless bipolarons. However, there can be spin density in the polymer
localized near the interface.",0209145v1
2002-11-04,Unveiling New Magnetic Phases of Undoped and Doped Manganites,"Novel ground-state spin structures in undoped and lightly-doped manganites
are here investigated based on the orbital-degenerate double-exchange model, by
using mean-field and numerical techniques. In undoped manganites, a new
antiferromagnetic (AFM) state, called the E-type phase, is found adjacent in
parameter space to the A-type AFM phase. Its structure is in agreement with
recent experimental results. This insulating E-AFM state is also competing with
a ferromagnetic metallic phase as well, suggesting that large magneto-resistant
effects could exist even in undoped Mn oxides. For doped layered manganites,
the phase diagram includes another new AFM phase of the ${\rm C_x
E_{1-x}}$-type. Experimental signatures of the new phases are discussed.",0211049v2
2002-11-11,V-V Bond-Length Fluctuations in Vox,"We report a significantly stronger suppression of the phonon contribution to
the thermal conductivity in VOx than can be accounted for by disorder of the 16
% atomic vacancies present in VO. Since the transition from localized to
itinerant electronic behavior is first-order and has been shown to be
characterized by bond-length fluctuations in several transition-metal oxides
with the perovskite structure, we propose that cooperative V-V bond-length
fluctuations play a role in VO similar to the M-O bond-length fluctuations in
the perovskites. This model is able to account for the strong suppression of
the thermal conductivity, the existence of a pseudogap confirmed by
thermoelectric power, an anomalously large Debye-Waller factor, the temperature
dependence of the magnetic susceptibility, and the inability to order atomic
vacancies in VO.",0211208v1
2002-12-02,Anisotropic Optic Conductivities due to Spin and Orbital Orderings in LaVO3 and YVO3: First-Principles Studies,"The anisotropy of low energy (0$\sim$5eV) optical excitations in strongly
correlated transition-metal oxides is closely related to the spin and orbital
orderings. The recent successes of LDA+$U$ method in describing the magnetic
and electronic structures enable us to calculate the optical conductivity from
first-principles. The LaVO$_3$ and YVO$_3$, both of which have $3d^2$
configuration and have various spin and orbital ordered phases at low
temperature, show distinct anisotropy in the optical spectra. The effects of
spin and orbital ordering on the anisotropy are studied in detail based on our
first-principles calculations. The experimental spectra of both compounds at
low temperature phases can be qualitatively explained with our calculations,
while the studies for the intermediate temperature phase of YVO$_3$ suggest the
substantial persistence of the low temperature phase at elevated temperature.",0212024v1
2003-05-28,59Co-NQR study on superconducting NaxCoO2.yH2O,"Layered Co oxide NaxCoO2.yH2O with a superconducting transition temperature
Tc =4.5 K has been studied by 59Co NQR. The nuclear spin relaxation rate 1/59T1
is nearly proportional to temperature T in the normal state. In the
superconducting state, it exhibits the coherence peak and decreases with
decreasing T below ~0.8Tc. Detailed comparison of the 1/T1T values and the
magnetic susceptibilities between NaxCoO2.yH2O and NaxCoO2 implies that the
metallic state of the former system is closer to a ferromagnetic phase than
that of the latter. These experimental results impose a restriction on the
mechanism of the superconductivity.",0305649v2
2003-06-11,59Co-NMR Knight Shift of the Superconducting NaxCoO2.yH2O,"Layered Co oxide NaxCoO2.yH2O with the superconducting transition temperature
Tc =4.5 K has been studied by 59Co-NMR. The Knight shift K estimated from the
observed spectra for powder sample exhibits almost temperature(T)-independent
behavior above Tc and decreases with decreasing T below Tc. This result and the
existence of the coherence peak in the spin-lattice-relaxation-rate versus T
curve reported by the present authors indicate, naively speaking, that the
singlet order parameter with s-wave symmetry is realized in NaxCoO2.yH2O.
Differences of the observed behaviors between the spectra of the non-aligned
sample and the one aligned in epoxy adhesive by applying the external magnetic
field are discussed.",0306264v2
2003-06-25,Superlight bipolarons and a checkerboard d-wave condensate in cuprates,"The seminal work by Bardeen, Cooper and Schrieffer taken further by
Eliashberg to the intermediate coupling solved the problem of conventional
superconductors about half a century ago. The Froehlich and Jahn-Teller
electron-phonon interactions were identified as an essential piece of physics
in all novel superconductors. The BCS theory provides a qualitatively correct
description of some of them like magnesium diborade and doped fullerenes (if
the polaron formation is taken into account). However, cuprates remain a
problem. Here I show that the bipolaron extension of the BCS theory to the
strong-coupling regime could be a solution. Low-energy physics in this regime
is that of small 'superlight' bipolarons, which are real-space mobile bosonic
pairs dressed by phonons. The symmetry and space modulations of the order
parameter are explained in the framework of the bipolaron theory. A d-wave
Bose-Einstein condensate of bipolarons reveals itself as a checkerboard
modulation of the hole density and of the gap below Tc.",0306649v2
2003-07-09,Frequency Dependence of Magnetoelectric Interactions in Layered Structures of Ferromagnetic Alloys and Piezoelectric Oxides,"Magnetoelectric (ME) interactions in layered structures of magnetostrictive
and piezoelectric phases are mediated by mechanical deformation. Here we
discuss the frequency dependence of ME coupling in bilayers and trilayers of
Permendur, a ferromagnetic alloy, and lead zirconate titanate. Data on ME
voltage coefficient versus frequency profiles reveal a giant ME coupling at
electromechanical resonance. The maximum voltage coefficient of 90 V/cm Oe is
three orders of magnitude higher than low-frequency values. The ME interactions
for transverse fields is an order of magnitude stronger than for longitudinal
fields. These results are in agreement with theory. The resonance ME effect,
therefore, is a novel tool for enhancing the magnetic-to-electric field
conversion efficiency in the composites.",0307208v1
2003-07-25,Superconductivity-Related Insulating Behavior,"We present the results of an experimental study of superconducting,
disordered, thin-films of amorphous Indium Oxide. These films can be driven
from the superconducting phase to a reentrant insulating state by the
application of a perpendicular magnetic field ($B$). We find that the high-$B$
insulator exhibits activated transport with a characteristic temperature,
$T_I$. $T_I$ has a maximum value ($T_{I}^p$) that is close to the
superconducting transition temperature ($T_c$) at $B$ = 0, suggesting a
possible relation between the conduction mechanisms in the superconducting and
insulating phases. $T_{I}^p$ and $T_c$ display opposite dependences on the
disorder strength.",0307648v2
2003-10-10,The Silicon Inversion Layer With A Ferromagnetic Gate: A Novel Spin Source,"Novel spin transport behavior is theoretically shown to result from replacing
the usual metal (or poly-silicon) gate in a silicon field-effect transistor
with a ferromagnet, separated from the semiconductor by an ultra-thin oxide.
The spin-dependent interplay between the drift current (due to a source-drain
bias) and the diffusion current (due to carrier leakage into the ferromagnetic
gate) results in a rich variety of spin dependence in the current that flows
through such a device. We examine two cases of particular interest: (1)
creating a 100% spin-polarized electrical current and (2) creating a pure spin
current without a net electrical current. A spin-valve consisting of two
sequential ferromagnetic gates is shown to exhibit magnetoresistance dependent
upon the relative orientations of the magnetization of the two ferromagnets.
The magnetoresistance ratio grows to arbitrarily large values in the regime of
low source-drain bias, and is limited only by the spin-flip time in the
channel.",0310259v1
2003-10-15,Continuous Charge Modulated Diagonal Phase in Manganites,"We present a novel ground state that explain the continuous modulated charge
diagonal order recently observed in manganese oxides, at hole densities $x$
larger than one half. In this diagonal phase the charge is modulated with a
predominant Fourier component inversely proportional to $1-x$. Magnetically
this state consist of antiferromagnetic coupled zig-zag chains. For a wide
range of relevant physical parameters as electron-phonon coupling,
antiferromagnetic interaction between Mn ions and on-site Coulomb repulsion,
the diagonal phase is the ground state of the system. The diagonal phase is
favored by the modulation of the hopping amplitude along the zig-zag chains,
and it is stabilized with respect to the one dimensional straight chain by the
electron phonon coupling. For realistic estimation of the physical parameters,
the diagonal modulation of the electron density is only a small fraction of the
average charge, a modulation much smaller than the obtained by distributing
Mn$^{+3}$ and Mn$^{+4}$ ions. We discuss also the spin and orbital structure
properties of this new diagonal phase.",0310333v1
2003-11-23,"A brief review of recent advances on the Mott transition: unconventional transport, spectral weight transfers, and critical behaviour","Strongly correlated metals close to the Mott transition display unusual
transport regimes, together with large spectral weight transfers in optics and
photoemission. We briefly review the theoretical understanding of these
effects, based on the dynamical mean-field theory, and emphasize the key role
played by the two energy scales associated with quasiparticle coherence scale
and with the Mott gap. Recent experimental results on two-dimensional organic
compounds and transition metal oxides are considered in this perspective. The
liquid-gas critical behaviour at the Mott critical endpoint is also discussed.
Transport calculations using the numerical renormalization group are presented.",0311520v2
2004-01-14,Substrate surface engineering for tailoring properties of functional ceramic thin films,"Using oxide substrates for functional ceramic thin film deposition beyond
their usual application as chemical inert, lattice-matched support for the
films represents a novel concept in ceramic thin film research. The substrates
are applied as a functional element in order to controllably modify the atom
arrangement and the growth mode of ceramic prototype materials such as cuprate
superconductors and colossal magnetoresistance manganites. One example is the
use of epitaxial strain to adjust the relative positions of cations and anions
in the film and thus modify their physical properties. The other makes use of
vicinal cut SrTiO3 which enables the fabrication of regular nanoscale step and
terrace structures. In YBa2Cu3O7-x thin films grown on vicinal cut SrTiO3
single crystals a regular array of antiphase boundaries is generated causing an
anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin
films grown on vicinal cut substrates it could be demonstrated that magnetic
in-plane anisotropy is achieved.",0401233v1
2004-02-09,"Oxygen and Cation Ordered Perovskite, Ba2Y2Mn4O11","A three-step route has been developed for the synthesis of a new
oxygen-ordered double perovskite, BaYMn2O5.5 or Ba2Y2Mn4O11. (i) The A-site
cation ordered perovskite, BaYMn2O5+d, is first synthesized at d ~ 0 by an
oxygen-getter-controlled low-O2-pressure encapsulation technique utilizing FeO
as the getter for excess oxygen. (ii) The as-synthesized, oxygen-deficient
BaYMn2O5.0 phase is then readily oxygenated to the d ~ 1 level by means of
1-atm-O2 annealing at low temperatures. (iii) By annealing this
fully-oxygenated BaYMn2O6.0 in flowing N2 gas at moderate temperatures the new
intermediate-oxygen-content oxide, BaYMn2O5.5 or Ba2Y2Mn4O11, is finally
obtained. From thermogravimetric observation it is seen that the final oxygen
depletion from d ~ 1.0 to 0.5 occurs in a single sharp step about 600 C,
implying that the oxygen stoichiometry of BaYMn2O5+d is not continuously
tunable within 0.5 < d < 1.0. For BaYMn2O5.5 synchrotron x-ray diffraction
analysis reveals an orthorhombic crystal lattice and a long-range ordering of
the excess oxygen atoms in the YO0.5 layer. The magnetic behavior of BaYMn2O5.5
(with a ferromagnetic transition at ~ 133 K) is found different from those
previously reported for the known phases, BaYMn2O5.0 and BaYMn2O6.0.",0402230v1
2004-03-18,Experimental evidence for a collective insulating state in two-dimensional superconductors,"We present the results of an experimental study of the current-voltage
characteristics in strong magnetic field ($B$) of disordered, superconducting,
thin-films of amorphous Indium-Oxide. As the $B$ strength is increased
superconductivity degrades, until a critical field ($B_c$) where the system is
forced into an insulating state. We show that the differential conductance
measured in the insulating phase vanishes abruptly below a well-defined
temperature, resulting in a clear threshold for conduction. Our results
indicate that a new collective state emerges in two-dimensional superconductors
at high $B$.",0403480v2
2004-03-30,Persistence of an Energy Scale in Over-Doped High-Tc Superconductors,"Citing the disappearance of a sharp peak in the electron self-energy,
extracted from optics and angle-resolved photoemission spectroscopy (ARPES)
experiments in deeply over-doped copper-oxide superconductors with Tc of
55-60K, Hwang, Timusk et al. argue that sharp modes, be they phononic or
magnetic in origin, are not important for superconductivity in the cuprates. If
true, this would have been an important progress. We show, however, their
conclusions are unfounded because of the insensitivity of the optics experiment
in studying strongly anisotropic material like the cuprates, and a
misrepresentation of existing ARPES data. In an added note, we refute the claim
by Valla, Timusk et. al. that the doping level of the data presented in the
first part of this comment is lower than reported.",0403743v2
2004-04-10,A novel heavy-fermion state in CaCu_3Ru_4O12,"We have measured susceptibility, specific heat, resistivity, and thermopower
of CaCu$_3$Ti$_{4-x}$Ru$_x$O$_{12}$ and CaCu$_{3-y}$Mn$_y$Ru$_4$O$_{12}$, and
have found that CaCu$_3$Ru$_4$O$_{12}$ can be regarded as a heavy-fermion oxide
in d-electron systems. The Kondo temperature is near 200 K, and the
susceptibility (1.4$\times10^{-3}$ emu/Cu mol) and the electron specific heat
coefficient (28 mJ/Cu molK$^2$) are moderately enhanced. The resistivity is
proportional to $T^2$ at low temperatures, and satisfies the Kadowaki-Woods
relation. The heavy-fermion state comes from the interaction between the
localized moment of Cu 3d and the conduction electron of Ru 4d. An
insulator-metal transition occurs between $x=1.5$ and 4 in
CaCu$_3$Ti$_{4-x}$Ru$_x$O$_{12}$, which can be regarded as a transition from
magnetic insulator to heavy-fermion metal.",0404247v1
2004-04-23,Percolation and Colossal Magnetoresistance in Eu-based Hexaborides,"Upon substituting Ca for Eu in the local-moment ferromagnet EuB$_6$, the
Curie temperature $T_C$ decreases substantially with increasing dilution of the
magnetic sublattice and is completely suppressed for $x$ $\leq$ 0.3. The Ca
substitution leads to significant changes of the electronic properties across
the Eu$_x$Ca$_{1-x}$B$_6$ series. Electron microscopy data for $x$ $\approx$
0.27 indicate a phase separation into Eu- and Ca-rich clusters of 5 to 10 nm
diameter, leading to percolation-type phenomena in the electrical transport
properties. The related critical concentration $x_p$ is approximately 0.3. For
$x$ $\approx$ 0.27, we observe colossal negative magnetoresistance effects at
low temperatures, similar in magnitude as those reported for manganese oxides.",0404570v1
2004-06-09,Exchange coupling in Eu monochalcogenides from first principles,"Using a density functional method with explicit account for strong Coulomb
repulsion within the 4f shell, we calculate effective exchange parameters and
the corresponding ordering temperatures of the (ferro)magnetic insulating Eu
monochalcogenides (EuX; X=O,S,Se,Te) at ambient and elevated pressure
conditions. Our results provide quantitative account of the many-fold increase
of the Curie temperatures with applied pressure and reproduce well the
enhancement of the tendency toward ferromagnetic ordering across the series
from telluride to oxide, including the crossover from antiferromagnetic to
ferromagnetic ordering under pressure in EuTe and EuSe. The first and second
neighbor effective exchange are shown to follow different functional
dependencies. Finally, model calculations indicate a significant contribution
of virtual processes involving the unoccupied f states to the effective
exchange.",0406229v1
2004-06-17,Re-entrant Behavior and Gigantic Response in Disordered Spin-Peierls System,"Effects of disorder and external field on the competing spin-Peierls and
antiferromagnetic states are studied theoretically in terms of the numerical
transfer matrix method applied to a quasi one-dimensional spin 1/2 Heisenberg
model coupled to the lattice degree of freedom. We show that, at temperatures
above the impurity-induced antiferromagnetic phase, inhomogeneous spin-Peierls
lattice distortions remain to exist showing a re-entrant behavior. This feature
can be drastically altered by very weak perturbations, e.g., the staggered
magnetic field or the change in interchain exchange coupling $J_\perp$, leading
to a huge response, which is analogous to the colossal magnetoresistance
phenomenon in perovskite manganese oxides.",0406386v1
2004-06-21,An Origin of CMR: Competing Phases and Disorder-Induced Insulator-to-Metal Transition in Manganites,"We theoretically explore the mechanism of the colossal magnetoresistance in
manganese oxides by explicitly taking into account the phase competition
between the double-exchange ferromagnetism and the charge-ordered insulator. We
find that quenched disorder causes a drastic change of the multicritical phase
diagram by destroying the charge-ordered state selectively. As a result, there
appears a nontrivial phenomenon of the disorder-induced insulator-to-metal
transition in the multicritical regime. On the contrary, the disorder induces a
highly-insulating state above the transition temperature where charge-ordering
fluctuations are much enhanced. The contrasting effects provide an
understanding of the mechanism of the colossal magnetoresistance. The obtained
scenario is discussed in comparison with other theoretical proposals such as
the polaron theory, the Anderson localization, the multicritical-fluctuation
scenario, and the percolation scenario.",0406463v1
2004-06-22,Stability and electronic structure of the complex K$_2$PtCl$_6$ structure-type hydrides,"The stability and bonding of the ternary complex K$_2$PtCl$_6$ structure
hydrides is discussed using first principles density functional calculations.
The cohesion is dominated by ionic contributions, but ligand field effects are
important, and are responsible for the 18-electron rule. Similarities to oxides
are discussed in terms of the electronic structure. However, phonon
calculations for Sr$_2$RuH$_6$ also show differences, particularly in the
polarizability of the RuH$_6$ octahedra. Nevertheless, the yet to be made
compounds Pb$_2$RuH$_6$ and Be$_2$FeH$_6$ are possible ferroelectrics. The
electronic structure and magnetic properties of the decomposition product,
FeBe$_2$ are reported. Implications of the results for H storage are discussed.",0406506v1
2004-07-22,Strongly correlated crystal-field approach to Mott insulator LaCoO3,"Our success in description of recent electron-spin-resonance results on Mott
insulator LaCoO3, Phys. Rev. B 67 (2003) 172401, lies in taking into account
strong electron correlations among d electrons and the relativistic spin-orbit
coupling. In the developed by us Quantum Atomistic Solid State Theory (QUASST)
we assume that the atomic-like integrity of the 3d^6 system is preserved in the
Co^3+ ion in LaCoO3 and that intra-atomic correlations are much stronger than
crystal field interactions. We conclude that in LaCoO3 there is no intermediate
spin state as came out from band-structure calculations. The excited states
originate from the high-spin 5T2g term, being 12 meV above the ground 1A1
state. We are convinced that many-electron CEF approach with strong
correlations and the atomic-scale orbital magnetism is physically adequate
approach to 3d oxides.
  Keywords: Mott insulator, crystal field, spin-orbit coupling, LaCoO3",0407580v2
2004-09-08,Non-linear Temperature Dependence of Resistivity in Single Crystalline Ag$_5$Pb$_2$O$_6$,"We measured electrical resistivity, specific heat and magnetic susceptibility
of single crystals of highly conductive oxide Ag_5Pb_2O_6, which has a layered
structure containing a Kagome lattice. Both the out-of-plane and in-plane
resistivity show T^2 dependence in an unusually wide range of temperatures up
to room temperature. This behavior cannot be accounted for either by electron
correlation or by electron-phonon scattering with high frequency optic phonons.
In addition, a phase transition with a large diamagnetic signal was found in
the ac susceptibility, which strongly suggests the existence of a
superconducting phase below 48 mK.",0409184v2
2004-09-21,Spin Frustration and Orbital Order in Vanadium Spinels,"We present the results of our theoretical study on the effects of geometrical
frustration and the interplay between spin and orbital degrees of freedom in
vanadium spinel oxides $A$V$_2$O$_4$ ($A$ = Zn, Mg or Cd). Introducing an
effective spin-orbital-lattice coupled model in the strong correlation limit
and performing Monte Carlo simulation for the model, we propose a reduced spin
Hamiltonian in the orbital ordered phase to capture the stabilization mechanism
of the antiferromagnetic order. Orbital order drastically reduces spin
frustration by introducing spatial anisotropy in the spin exchange
interactions, and the reduced spin model can be regarded as weakly-coupled
one-dimensional antiferromagnetic chains. The critical exponent estimated by
finite-size scaling analysis shows that the magnetic transition belongs to the
three-dimensional Heisenberg universality class. Frustration remaining in the
mean-field level is reduced by thermal fluctuations to stabilize a collinear
ordering.",0409526v1
2004-10-20,Variation of Specific Heat with x and y in NaxCoO2-yH2O/D2O,"We report specific heat measurements down to 0.4 K on the layered oxide
Na$_x$CoO$_2\cdot\it{y}$H$_2$O/D$_2$O with 0 $\le$ $\it{x}$ $\le$ 0.74 and
$\it{y}$ = 0 and 1.4. For the nonhydrated system ($\it{y}$ = 0), the electronic
specific heat coefficient $\gamma_N$ and the Debye temperature $\Theta_D$ vary
nonmonotonically with $\it{x}$, both displaying minima when $\it{x}$ is close
to 0.5. This indicates a systematic change of the electronic and vibrational
structures with Na content. For both hydrated and deuterated systems ($\it{x}$
= 0.35 and $\it{y}$ = 1.4), the specific heat reveals a sharp peak with
$\Delta$C$_p \sim$ 45.5 mJ/mol-K at T$_c^{mid} \sim$ 4.7 K and an anomaly at
T$_x \sim$ 0.8 K. While the origin of the later is unknown, the former
corresponds to the superconducting transition. Interestingly, the electronic
specific heat, after subtracting lattice and Schottky contributions, exhibits
roughly T$^2$ behavior between 0.2T$_c$ and T$_c$. This can be explained by
assuming an unconventional superconducting symmetry with line nodes. The
results obtained under applied magnetic field further support this scenario.",0410517v1
2005-01-31,Colossal magnetoresistance and quenched disorder in manganese oxides,"We give an overview on several recent topics of colossal magnetoresistive
manganites in both experiments and theories, focusing on the effect of quenched
disorder. The disorder is intrinsically involved since the compounds are solid
solutions, and its importance has been pointed out in several experiments of
transport and magnetic properties. Recent progress in the experimental control
of the strength of disorder is also reviewed. Theoretically, the effect of the
disorder has been explored within the framework of the double-exchange
mechanism. Several efforts to understand the phase diagram and the electronic
properties are reviewed. We also briefly discuss a recent topic on the effect
of disorder on competing phases and the origin of colossal magnetoresistance.",0501738v1
2005-02-04,Critical point and the nature of the pseudogap of single-layered copper-oxide Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+δ}$ superconductors,"We apply strong magnetic fields of H=28.5 \sim 43 T to suppress
superconductivity (SC) in the cuprates Bi_{2}Sr_{2-x}La_xCuO_{6+\delta}
(x=0.65, 0.40, 0.25, 0.15 and 0), and investigate the low temperature (T)
normal state by ^{63}Cu nuclear spin-lattice relaxation rate (1/T_1)
measurements. We find that the pseudogap (PG) phase persists deep inside the
overdoped region but terminates at x \sim 0.05 that corresponds to the hole
doping concentration of approximately 0.21. Beyond this critical point, the
normal state is a Fermi liquid characterized by the T_1T=const relation. A
comparison of the superconducting state with the H-induced normal state in the
x=0.40 (T_c = 32 K) sample indicates that there remains substantial part of the
Fermi surface even in the fully-developed PG state, which suggests that the PG
and SC are coexisting matters.",0502117v1
2005-03-10,Ferromagnetic and triplet-pairing instabilities controlled by the trigonal distortion of the CoO_6 octahedra in Na_xCoO_2*yH_2O,"In the recently discovered Co-oxide superconductor Na_xCoO_2*yH_2O, the
edge-shared CoO6 octahedra are trigonally contracted along the c-axis in the
CoO2-plane. We study how this CoO6 distortion affects the magnetic properties
and superconductivity in this compound by analyzing the multiorbital Hubbard
model using the fluctuation-exchange approximation. It is shown that through
generating the trigonal crystal field, the distortion pushes the Co e'g bands
up and consequently gives rise to the hole-pocket Fermi surfaces, which have
been predicted in the band calculations. As the distortion increases, the hole
pockets are enlarged and the ferromagnetic fluctuation as well as the pairing
instability increases, which is in good agreement with recent NQR results.",0503233v2
2005-05-10,Novel organic-inorganic layered oxide with spin ladder structure,"Structural analysis of a layered manganese tungstate diaminoalkane hybrid
series suggests that this compound forms a spin-5/2 spin-ladder structure. We
use X-ray diffraction, electron microscopy and x-ray absorption spectroscopy
results to infer the structure. DC magnetization of the manganese compound and
a possible copper analogue appear to show that the manganese system behaves
like 1-dimensional antiferromagnetic Heisenberg chains (i.e. $J_{\parallel} \gg
J_{\perp})$ while the copper system is fitted well by a $S = {1/2}$ spin ladder
model, giving the parameters $g = 1.920 \pm 0.008$, $J_{\parallel}/k_B = -0.3
\pm 1.4$K; $J_{\perp}/k_B = 213.6 \pm 1.1$K. The ability to tune adjacent
inorganic layers of the hybrid materials by altering the length of the organic
`spacer' molecules gives enormous promise for the use of these materials,
especially when doped, to provide a greater understanding of spin ladder
systems.",0505224v1
2005-05-19,"Fish-tail Effect and Irreversibility Field of (Cu,C)Ba$_{2}$Ca$_{3}$Cu$_{4}$O$_{x}$-(LiF)$_{y}$ superconductor","Addition of (LiF)$_{y<0.15}$, and of proper amount of (AgO)$_{z=0.45-0.8}$ as
oxidizing agent, to (Cu,C)Ba$_{2}$Ca$_{3}$Cu$_{4}$O$_{10+d}$ superconductor is
useful to control and shift the doping characteristics (hole density and
distribution, and level of disorder) into the region where the irreversible
properties, i.e. fish-tail effect (FTE) and irreversibility field H$_{irr}$,
are improved. Among notable effects are the development of the second
magnetization peak with a higher amplitude J$_{c}$, max and the enhancement of
H$_{irr}$ at high temperatures, above a certain value T* which depends on both
y$_{LiF}$ and z$_{AgO}$. The best results are obtained for the sample with
y$_{LiF}$=0.1 and z$_{AgO}$=0.73. This sample preserves its single phase
Cu,C-1234 composition. The influence on the FTE and H$_{irr}$ of the interplay
between doping characteristics, controlled by LiF and AgO content, is
discussed.",0505494v1
2005-06-05,On the unusual behavior of nitride compounds,"This report presents consistent insight into the mechanism behind the unusual
behavior of nitride compounds from the perspective of tetrahedron bond
formation and its consequence on valence density of states. An extension of the
recent bond-band-barrier (BBB) correlation mechanism for oxidation [Sun CQ,
Prog Mater Sci 2003;48:521-685] to the electronic process of nitridation has
led to the essentiality of sp-orbital hybridization for a nitrogen atom upon
interacting with atoms in solid phase of arbitrary less-electronegative
element. In the process of nitridation, a nitrogen atom forms a
quasi-tetrahedron with surrounding host atoms through bonding and nonbonding
interaction associated with production of electronic holes and antibonding
dipoles, which add corresponding density of states to the valence band of the
host. It is suggested that the valance alteration of the system takes the
responsibility for the blue shift in photoluminescence, lowered work function
for cold cathode field emission, corrosion and wear resistant, high elasticity,
and magnetic modulation as well.",0506109v1
2005-07-15,2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4,"muSR experiments on the geometrically frustrated spinel oxide, Li2Mn2O4, show
the development of spin correlations over a range of length scales with
decreasing temperature. Increased relaxation below 150 K is consistent with the
onset of spin correlations. Below 50 K, spin order on a length scale, which is
long range for the muSR probe, appears abruptly in temperature, consistent with
prior neutron diffraction results. The oscillations in the zero field asymmetry
are analyzed using a three frequency model. By locating the muon site this is
shown to be consistent with the unexpected 2D q = root 3 x root 3 structure on
the Kagome planes proposed originally from neutron data. Longitudinal field
data demonstrate that some spin dynamics persist even at 2 K. Thus, a very
complex magnetic ground state, featuring the co-existence of long length scale
2D ordering and significant spin dynamics, is proposed. This is unusual
considering the 3D topology of the Mn3+ spins in this material.",0507355v1
2005-07-15,Metamagnetic quantum criticality in Sr3Ru2O7 studied by thermal expansion,"We report low-temperature thermal expansion measurements on the bilayer
ruthenate Sr$_3$Ru$_2$O$_7$ as a function of magnetic field applied
perpendicular to the Ruthenium-oxide planes. The field-dependence of the c-axis
expansion coefficient indicates the accumulation of entropy close to 8 Tesla,
related to an underlying quantum critical point. The latter is masked by two
first-order metamagnetic transitions which bound a regime of enhanced entropy.
Outside this region the singular thermal expansion behavior is compatible with
the predictions of the itinerant theory for a two-dimensional metamagnetic
quantum critical end point.",0507359v3
2005-07-30,Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7,"We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7
as a function of magnetic field and temperature using 17O-NMR. This system sits
close to a metamagnetic quantum critical point (MMQCP) for the field
perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior
at low temperatures except for a narrow field region close to the MMQCP. The
nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced
on approaching the metamagnetic critical field of 7.9 T and at the critical
field 1/T1T continues to increase and does not show Fermi- liquid behavior down
to 0.3 K. The temperature dependence of T1T in this region suggests the
critical temperature Theta to be 0 K, which is a strong evidence that the spin
dynamics possesses a quantum critical character. Comparison between uniform
susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of
two-dimensional ferromagnetic fluctuations dominate the spin fluctuation
spectrum at the critical field, which is unexpected for itinerant
metamagnetism.",0508012v1
2005-08-08,Novel phase diagram of superconductor NaxCoO2-yH2O in a 75 % relative humidity,"We succeeded in synthesizing the powder samples of bilayer-hydrate sodium
cobalt oxide superconductors NaxCoO2-yH2O with Tc = 0 ~ 4.6 K by systematically
changing the keeping duration in a 75 % relative humidity atmosphere after
intercalation of water molecules. From the magnetic measurements, we found that
the one-day duration sample does not show any superconductivity down to 1.8 K,
and that the samples kept for 2 ~ 7 days show superconductivity, in which Tc
increases up to 4.6 K with increasing the duration. Tc and the superconducting
volume fraction are almost invariant between 7 days and 1month duration. The
59Co NQR spectra indicate a systematic change in the local charge distribution
on the CoO2 plane with change in duration.",0508196v1
2005-09-21,Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy,"We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer
system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer.
The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room
temperature which increases to 14.7% at 4.2K. The layers show clear separate
switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in
the NiMnSb layer leads to different switching characteristics depending on the
direction in which the magnetic field is applied, an effect which can be used
for sensor applications.",0509538v1
2005-10-03,Buffer-Enhanced Electrical-Pulse-Induced-Resistive Memory Effect in Thin Film Perovskites,"A multilayer perovskite thin film resistive memory device has been developed
comprised of: a Pr0.7Ca0.3MnO3 (PCMO) perovskite oxide epitaxial layer on a
YBCO bottom thin film electrode; a thin yttria stabilized zirconia (YSZ) buffer
layer grown on the PCMO layer, and a gold thin film top electrode. The
multi-layer thin film lattice structure has been characterized by XRD and TEM
analyses showing a high quality heterostructure. I-AFM analysis indicated nano
granular conductivity distributed uniformly throughout the PCMO film surface.
With the addition of the YSZ buffer layer, the pulse voltage needed to switch
the device is significantly reduced and the resistance-switching ratio is
increased compared to a non-buffered resistance memory device, which is very
important for the device fabrication. The magnetic field effect on the
multilayer structure resistance at various temperatures shows CMR behavior for
both high and low resistance states implying a bulk material component to the
switch behavior.",0510060v1
2005-10-15,Quasiparticle Self-Consistent GW Theory,"In past decades the scientific community has been looking for a reliable
first-principles method to predict the electronic structure of solids with high
accuracy. Here we present an approach which we call the quasiparticle
self-consistent GW approximation (QpscGW). It is based on a kind of
self-consistent perturbation theory, where the self-consistency is constructed
to minimize the perturbation. We apply it to selections from different classes
of materials, including alkali metals, semiconductors, wide band gap
insulators, transition metals, transition metal oxides, magnetic insulators,
and rare earth compounds. Apart some mild exceptions, the properties are very
well described, particularly in weakly correlated cases. Self-consistency
dramatically improves agreement with experiment, and is sometimes essential.
Discrepancies with experiment are systematic, and can be explained in terms of
approximations made.",0510408v2
2005-10-19,Oxygen Isotope Effect on the Spin State Transition in (Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$,"Oxygen isotope substitution is performed in the perovskite cobalt oxide
(Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$ which shows a sharp spin
state transition from the intermediate spin (IS) state to the low spin (LS)
state at a certain temperature. The transition temperature of the spin state
up-shifts with the substitution of $^{16}O$ by $^{18}$O from the resistivity
and magnetic susceptibility measurements. The up-shift value is 6.8 K and an
oxygen isotope exponent ($\alpha_S$) is about -0.8. The large oxygen isotope
effect indicates strong electron-phonon coupling in this material. The
substitution of $^{16}$O by $^{18}$O leads to a decrease in the frequency of
phonon and an increase in the effective mass of electron ($m$$^\ast$), so that
the bandwidth W is decreased and the energy difference between the different
spin states is increased. This is the reason why the $T_s$ is shifted to high
temperature with oxygen isotopic exchange.",0510499v1
2005-10-31,Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars,"We report time-resolved measurements of current-induced reversal of a free
magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to
160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations
of the free layer switching yields numerical values for the spin torque and the
Gilbert damping parameters as functions of T. The damping is strongly
T-dependent, which we attribute to the antiferromagnetic pinning behavior of a
thin permalloy oxide layer around the perimeter of the free layer. This
adventitious antiferromagnetic pinning layer can have a major impact on spin
torque phenomena.",0510798v2
2006-02-16,Manifestation of the Exchange Enhancement of the Valley Splitting in the Quantum Hall Effect Regime,"We report a new ""dip"" effect in the Hall resistance, R_{xy}, of a Si
metal-oxide-semiconductor field-effect transistor in the quantum Hall effect
regime. With increasing magnetic field, the Hall resistance moves from the
plateau at Landau filling factor \nu=6 directly to the plateau at \nu=4,
skipping the plateau at \nu=5. However, when the filling factor approaches
\nu=5, the Hall resistance sharply ""dives"" to the value 1/5(h/e^2)
characteristic of the \nu=5 plateau, and then returns to 1/4(h/e^2). This is
interpreted as a manifestation of the oscillating exchange enhancement of the
valley splitting when the Fermi level is in the middle between two adjacent
valley-split Landau bands with the asymmetric position of the extended states.",0602376v1
2006-03-31,Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals,"We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.",0603850v1
2006-05-19,23Na NMR study of non-superconducting double-layer hydrate NaxCoO2.yH2O,"We report 23Na NMR studies of the polycrystalline samples of double-layer
hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the
superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated
NaxCoO2 (x ~ 0.35). The hyperfine field and the electric field gradient at the
Na sites in the non-hydrated Na0.7CoO2 and the dehydrated Na0.35CoO2 are found
to be significantly reduced by the hydration, which indicates a strong
shielding effect of the intercalated water molecules on the Na sites. The
temperature dependence of 23 Na nuclear spin-lattice relaxation rate 1/23T1 of
the non-superconducting double-layer hydrate NaxCoO2.yH2O is found to be
similar to that of the non-hydrated Na0.7CoO2, whose spin dynamics is
understood by A-type (intra-layer ferromagnetic and inter-layer
antiferromagnetic) spin fluctuations. The superconducting phase is located
close to the quantum critical point with the A-type magnetic instability.",0605487v2
2006-06-02,Effects of spin-phonon interaction on the properties of in high-T$_C$ superconductors,"The mechanism of spin-phonon coupling in high-T$_C$ copper oxides is explored
from band calculations on La$_{(2-x)}$Sr$_x$CuO$_4$ and HgBa$_2$CuO$_4$
systems. The LMTO band calculations, based on the local density approximation,
are made for cells containing frozen phonon displacements and/or spin waves
within the CuO plane. The virtual crystal approximation is used for studies of
hole doped systems. The main result is that phonons are favorable for spin
waves and vice-versa, and that pseudogaps appear naturally in the band
structures of striped materials with strong SPC. The qualitative results are
compatible with many observations showing that the properties of high-T$_C$
superconductors depend both on lattice interactions and magnetic fluctuations.
The band results are used to model various properties, mainly of the normal
state, such as isotope effects, pseudogaps, Fermi surface broadening,
T-dependence of the pseudogap, phonon softening and some aspects of
superconductivity. The possibility of perpendicular SPC is investigated, partly
by the use of a nearly free electron model.",0606066v1
2006-07-06,Strongly correlated electrons,"We review theoretical concepts and models for materials with strongly
correlated d- or f electrons. We discuss low-energy effective models and the
renormalized band method for Ce-based Kondo lattice systems. They are applied
to the analysis of associated magnetic and superconducting instabilities. In
addititon quantum phase transitions are investigated. Special emphasis is given
to the partial localisation of 5f electrons in U compounds and its consequences
for unconventional superconductivity. Wigner crystallisation in the homogeneous
electron gas and its generalisation to 4f pnictide and 3d oxide materials is
covered extensively. We analyse simultaneous charge order and lattice
instabilities in geometrically frustrated V-oxide spinels. Using a spinless
fermion model we also discuss the emergence of fractional charges in the
frustrated pyrochlore or checkerboard lattice. Finally we focus on the
signature of strong electronic correlations in high-energy excitations.",0607165v1
2006-07-31,Optical study of MgTi$_2$O$_4$: Evidence for an orbital-Peierls state,"Dimension reduction due to the orbital ordering has recently been proposed to
explain the exotic charge, magnetic and structural transitions in some
three-dimensional (3D) transitional metal oxides. We present optical
measurement on a spinel compound MgTi$_2$O$_4$ which undergoes a sharp
metal-insulator transition at 240 K, and show that the spectral change across
the transition can be well understood from the proposed picture of 1D Peierls
transition driven by the ordering of $d_{yz}$ and $d_{zx}$ orbitals. We further
elaborate that the orbital-driven instability picture applies also very well to
the optical data of another spinel CuIr$_2$S$_4$ reported earlier.",0607813v2
2006-10-05,Anomalous Superconducting Proximity Effect in Hybrid Oxide Heterostructures with Antiferromagnetic Layer,"We report an investigation of current transport in Nb/Au/CaSrCuO/YBaCuO
heterostructures including an antiferromagnetic interlayer (CaSrCuO). Epitaxial
thin films of YBaCuO and CaSrCuO were grown by laser ablation on NdGaO
substrates; the thicknesses of CaSrCuO films were 20 and 50 nm, and x=0.15 or
0.5. Our experimental results show that the superconducting current transport
is increased in the Nb/Au/CaSrCuO/YBaCuO heterostructures in comparison with
the ones observed in previously studied Nb/Au/YBaCuO heterostructures. It was
found that the critical current of the structure is very sensitive to the
absolute value and direction of the external magnetic field.",0610140v1
2006-10-27,NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6,"We report nuclear magnetic resonance studies on the beta-pyrochlore oxide
superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused
by fluctuations of electric field gradient, which we ascribe to highly
anharmonic low frequency oscillation (rattling) of K ions. A phenomenological
analysis shows a crossover from overdamped to underdamped behavior of the
rattling phonons with decreasing temperature and its sudden sharpening below
the superconducting transition temperature Tc. Absence of the Hebel-Slichter
peak in the relaxation rate at the O sites below Tc also indicates strong
electron-phonon coupling.",0610760v2
2006-11-25,Long-range ferromagnetic correlations between Anderson impurities in a semiconductor host,"We study the two-impurity Anderson model for a semiconductor host using the
quantum Monte Carlo technique. We find that the impurity spins exhibit
ferromagnetic correlations with a range which can be much more enhanced than in
a half-filled metallic band. In particular, the range is longest when the Fermi
level is located above the top of the valence band and decreases as the
impurity bound state becomes occupied. Comparisons with the photoemission and
optical absorption experiments suggest that this model captures the basic
electronic structure of Ga_{1-x}Mn_xAs, the prototypical dilute magnetic
semiconductor (DMS). These numerical results might also be useful for
synthesizing DMS or dilute-oxide ferromagnets with higher Curie temperatures.",0611641v1
2006-12-29,Intrinsic Nanoscale Inhomogeneities in Transition Metal Oxides,"Neutron elastic, inelastic and high energy x-ray scattering techniques are
used to explore the nature of the polaron order and dynamics in La0.7Ca0.3MnO3.
Static polaron correlations develop within a narrow temperature regime as the
Curie temperature is approached from low temperatures, with a nanoscale
correlation length that is only weakly temperature dependent. The static nature
of these short-range polaron correlations indicates the presence of a
glass-like state, similar to the observations for the bilayer manganite in the
metallic-ferromagnetic doping region. In addition to this elastic component,
inelastic scattering measurements reveal dynamic correlations with a comparable
correlation length, and with an energy distribution that is quasielastic. The
elastic component disappears at a higher temperature T*, above which the
correlations are purely dynamic. The overall behavior bears a remarkable
resemblance to the magnetic fluctuation spectrum recently observed in
underdoped cuprates.",0701001v1
2007-01-19,"Reversible Ferromagnetic Switching in Zno:(Co,Mn) Powders","We report here on the magnetic properties of ZnO:Mn and ZnO:Co doped
nanoparticles. We have found that the ferromagnetism of ZnO:Mn can be switched
on and off by consecutive low-temperature annealings in O2 and N2 respectively,
while the opposite phenomenology was observed for ZnO:Co. These results suggest
that different defects (presumably n-type for ZnO:Co and p-type for ZnO:Mn) are
required to induce a ferromagnetic coupling in each case. We will argue that
ferromagnetism is likely to be restricted to a very thin, nanometric layer, at
the grain surface. These findings reveal and give insight into the dramatic
relevance of surface effects for the occurrence of ferromagnetism in ZnO doped
oxides.",0701473v1
2007-02-12,Wannier functions and exchange integrals: The example of LiCu$_{2}$O$_{2}$,"Starting from a single band Hubbard model in the Wannier function basis, we
revisit the problem of the ligand contribution to exchange and derive explicit
formulae for the exchange integrals in metal oxide compounds in terms of atomic
parameters that can be calculated with constrained LDA and LDA+U. The analysis
is applied to the investigation of the isotropic exchange interactions of
LiCu$_{2}$O$_{2}$, a compound where the Cu-O-Cu angle of the dominant exchange
path is close to 90$^{\circ}$. Our results show that the magnetic moments are
localized in Wannier orbitals which have strong contribution from oxygen atomic
orbitals, leading to exchange integrals that considerably differ from the
estimates based on kinetic exchange only. Using LSDA+U approach, we also
perform a direct {\it ab-initio} determination of the exchange integrals
LiCu$_{2}$O$_{2}$. The results agree well with those obtained from the Wannier
function approach, a clear indication that this modelization captures the
essential physics of exchange. A comparison with experimental results is also
included, with the conclusion that a very precise determination of the Wannier
function is crucial to reach quantitative estimates.",0702276v1
2007-03-21,DFT investigation of 3d transition metal NMR shielding tensors in diamagnetic systems using the gauge-including projector augmented-wave method,"We present a density functional theory based method for calculating NMR
shielding tensors for 3d transition metal nuclei using periodic boundary
conditions. Calculations employ the gauge-including projector augmented-wave
pseudopotentials method. The effects of ultrasoft pseudopotential and induced
approximations on the second-order magnetic response are intensively examined.
The reliability and the strength of the approach for 49Ti and 51V nuclei is
shown by comparison with traditional quantum chemical methods, using benchmarks
of finite organometallic systems. Application to infinite systems is validated
through comparison to experimental data for the 51V nucleus in various vanadium
oxide based compounds. The successful agreement obtained for isotropic chemical
shifts contrasts with full estimation of the shielding tensor eigenvalues,
revealing the limitation of pure exchange-correlation functionals compared to
their exact-exchange corrected analogues.",0703553v2
2000-10-03,Modeling of an Inductive Adder Kicker Pulser for Darht-II,"An all solid-state kicker pulser for a high current induction accelerator
(the Dual-Axis Radiographic Hydrodynamic Test facility DARHT-2) has been
designed and fabricated. This kicker pulser uses multiple solid state
modulators stacked in an inductive-adder configuration. Each modulator is
comprised of multiple metal-oxide-semiconductor field-effect transistors
(MOSFETs) which quickly switch the energy storage capacitors across a magnetic
induction core. Metglas is used as the core material to minimize loss. Voltage
from each modulator is inductively added by a voltage summing stalk and
delivered to a 50 ohm output cable. A lumped element circuit model of the
inductive adder has been developed to optimize the performance of the pulser.
Results for several stalk geometries will be compared with experimental data.",0010007v2
2005-03-21,Photonic band structure of ZnO photonic crystal slab laser,"We recently reported on the first realization of ultraviolet photonic crystal
laser based on zinc oxide [Appl. Phys. Lett. {\bf 85}, 3657 (2004)]. Here we
present the details of structural design and its optimization. We develop a
computational super-cell technique, that allows a straightforward calculation
of the photonic band structure of ZnO photonic crystal slab on sapphire
substrate. We find that despite of small index contrast between the substrate
and the photonic layer, the low order eigenmodes have predominantly
transverse-electric (TE) or transverse-magnetic (TM) polarization. Because
emission from ZnO thin film shows strong TE preference, we are able to limit
our consideration to TE bands, spectrum of which can possess a complete
photonic band gap with an appropriate choice of structure parameters. We
demonstrate that the geometry of the system may be optimized so that a sizable
band gap is achieved.",0503170v1
2007-06-30,Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8,"We report the observation of quantum oscillations in the underdoped cuprate
superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed
magnetic fields up to 85T. There is a clear signal, periodic in inverse field,
with frequency 660+/-15T and possible evidence for the presence of two
components of slightly different frequency. The quasiparticle mass is
m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for
YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a
general feature of underdoped copper oxide planes and provide information about
the doping dependence of the Fermi surface.",0707.0057v2
2007-08-29,Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films,"Electronic properties of transition metal oxides at interfaces are influenced
by strain, electric polarization and oxygen diffusion. Linear dichroism (LD)
x-ray absorption, diffraction, transport and magnetization on thin
La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface
effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at
the interface, suppressing the double exchange mechanism. This surface orbital
reconstruction is opposite of that favored by residual strain and independent
of dipolar fields, chemical nature of the substrate and capping.",0708.3973v2
2007-09-04,Spin-Filtering Multiferroic-Semiconductor Heterojunctions,"We report on the structural and electronic properties of the interface
between the multiferoic oxide YMnO$_3$ and wide band-gap semiconductor GaN
studied with the Hubbard-corrected local spin density approximation (LSDA+U) to
density-functional theory (DFT). We find that the band offsets at the interface
between antiferromagnetically ordered YMnO$_3$ and GaN are different for
spin-up and spin-down states. This behavior is due to the spin splitting of the
valence band induced by the interface. The energy barrier depends on the
relative orientation of the electric polarization with respect to the
polarization direction of the GaN substrate suggesting an opportunity to create
magnetic tunnel junctions in this materials system.",0709.0318v1
2007-10-03,Scaling analysis of normal state properties of high-temperature superconductors,"We propose a model-independent scaling method to study the physical
properties of high-temperature superconductors in the normal state. We have
analyze the experimental data of the c-axis resistivity, the in-plane
resistivity, the Hall coefficient, the magnetic susceptibility, the
spin-lattice relaxation rate, and the thermoelectric power using this method.
It is shown that all these physical quantities exhibit good scaling behaviors,
controlled purely by the pseudogap energy scale in the normal state. The doping
dependence of the pseudogap obtained from this scaling analysis agrees with the
experimental results of angle-resolved photoemission and other measurements. It
sheds light on the understanding of the basic electronic structure of high-Tc
oxides.",0710.0693v3
2007-10-11,Exploiting B Site Disorder for Phase Control in the Manganites,"Disorder on the active d element site is usually very disruptive for
conduction and long range order in perovskite transition metal oxides. However,
in the background of phase competition such `B site' dopants also act to
promote one ordered phase at the expense of another. This occurs either through
valence change of the transition metal or via creation of `defects' in the
parent magnetic state. We provide a framework for understanding the complex
variety of phenomena observed in B site doped manganites and identify the key
parameters that control the physics. Using a spatially resolved analysis of B
ions in various manganite phases we explain the existing data and predict new
situations where highly polarisable phase separated states can be created.",0710.2278v3
2007-10-17,Superfluid density of superconductor-ferromagnet bilayers,"We report the first measurements of the effective superfluid density n_S(T)
\propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where
\lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers
were sputtered in ultrahigh vacuum in quick succession onto oxidized Si
substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses
vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as
Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at
d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several
times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni
thickness long after T_C has stopped changing. We argue that this indicates a
substantial superfluid density inside the ferromagnetic Ni films.",0710.3376v1
2007-11-01,Relationship between ferroelectricity and Dzyaloshinskii-Moriya interaction in multiferroics and the effect of bond-bending,"We studied the microscopic mechanism of multiferroics, in particular with the
""spin current"" model (Hosho Katsura, Naoto Nagaosa and Aleander V. Balatsky,
Phys. Rev. Lett. 95, 057205 (2005)). Starting from a system with helical spin
configuration, we solved for the forms of the electron wave functions and
analyzed their characteristics. The relation between ferroelectricity and
Dzyaloshinskii-Moriya interaction (I. Dzyaloshinskii, J. Phys. Chem. Solids 4,
241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)) is clearly established.
There is also a simple relation between the electric polarization and the wave
vector of magnetic orders. Finally, we show that the bond-bending exists in
transition metal oxides can enhance ferroelectricity.",0711.0100v2
2007-11-29,Systematic changes of the electronic structure of the diluted ferromagnetic oxide Li-doped Ni$_{1-x}$Fe$_x$O with hole doping,"The electronic structure of Li-doped Ni$_{1-x}$Fe$_x$O has been investigated
using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS).
The Ni $2p$ core-level PES and XAS spectra were not changed by Li doping. In
contrast, the Fe$^{3+}$ intensity increased with Li doping relative to the
Fe$^{2+}$ intensity. However, the increase of Fe$^{3+}$ is only $\sim 5%$ of
the doped Li content, suggesting that most of the doped holes enter the O $2p$
and/or the charge-transferred configuration Ni $3d^8\underline{L}$. The Fe 3d
partial density of states and the host valence-band emission near valence-band
maximum increased with Li content, consistent with the increase of electrical
conductivity. Based on these findings, percolation of bound magnetic polarons
is proposed as an origin of the ferromagnetic behavior.",0711.4658v1
2007-12-04,Pressure dependence of the superconducting transition and electron correlations in Na_xCoO_2 \cdot 1.3H_2O,"We report T_c and ^{59}Co nuclear quadrupole resonance (NQR) measurements on
the cobalt oxide superconductor Na_{x}CoO_{2}\cdot 1.3H_{2}O (T_c=4.8 K) under
hydrostatic pressure (P) up to 2.36 GPa. T_c decreases with increasing pressure
at an average rate of -0.49\pm0.09 K/GPa. At low pressures P\leq0.49 GPa, the
decrease of T_c is accompanied by a weakening of the spin correlations at a
finite wave vector and a reduction of the density of states (DOS) at the Fermi
level. At high pressures above 1.93 GPa, however, the decrease of T_c is mainly
due to a reduction of the DOS. These results indicate that the
electronic/magnetic state of Co is primarily responsible for the
superconductivity. The spin-lattice relaxation rate 1/T_1 at P=0.49 GPa shows a
T^3 variation below T_c down to T\sim 0.12T_c, which provides compelling
evidence for the presence of line nodes in the superconducting gap function.",0712.0419v1
2008-01-28,Hybridization between the conduction band and 3d orbitals in the oxide-based diluted magnetic semiconductor In$_{2-x}$V$_x$O$_3$,"The electronic structure of In$_{2-x}$V$_x$O$_3$ ($x=0.08$) has been
investigated using photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). The V $2p$ core-level PES and XAS spectra revealed
trivalent electronic state of the V ion, consistent with the substitution of
the V ion for the In site. The V 3d partial density of states obtained by the
resonant PES technique showed a sharp peak above the O $2p$ band. While the O
$1s$ XAS spectrum of In$_{2-x}$V$_x$O$_3$ was similar to that of In$_2$O$_3$,
there were differences in the In $3p$ and 3d XAS spectra between V-doped and
pure In$_2$O$_3$. The observations give clear evidence for hybridization
between the In conduction band and the V 3d orbitals in In$_{2-x}$V$_x$O$_3$.",0801.4244v1
2008-02-08,"Superconducting Transition in the $β$-Pyrochlore AOs$_2$O$_6$ (A=Cs, Rb, K) under Pressure","Pressure dependence of superconducting transition temperature $T_{\rm c}$ has
been determined through the DC magnetic measurements under pressure up to
$P$=10 GPa for $\beta$-pyrochlore oxides AOs$_2$O$_6$ with A=Cs ($T_{\rm
c}$=3.3 K), Rb (6.3 K) and K (9.6 K). Both for A=Rb and Cs, $T_{\rm c}$
increases with increasing $P$ and shows a saturation at $T_{\rm cm}$$\sim$8.8
K, which is considered as the upper limit of $T_{\rm c}$ inherent in
AOs$_2$O$_6$. In contrast, the $T_{\rm c}-P$ curve for KOs$_2$O$_6$ shows a
sharp maximum of $\sim$10 K at $P$$\sim$0.5 GPa, and $T_{\rm c}$ is higher than
$T_{\rm cm}$ for 0$\leq$$P$$\leq$1.5GPa, suggesting the enhanced
superconductivity due to the rattling of K ions.",0802.1179v1
2008-03-04,Magneto-Dielectric phenomena in charge and spin frustrated system of layered iron oxide,"Dielectric and magnetic phenomena in spin and charge frustrated system RFe2O4
(R is a rare-earth metal ion) are studied. An electronic model for charge, spin
and orbital degrees in a pair of triangular-lattice planes is derived. We
analyze this model by utilizing the mean-field approximation and the
Monte-Carlo simulation in a finite size cluster. A three fold-type charge
ordered structure with charge imbalance between the planes is stabilized in
finite temperatures. This polar charge order is reinforced by spin ordering of
Fe ions. This novel magneto-dielectric phenomenon is caused by spin frustration
and charge-spin coupling in the exchange interaction. We show cross-correlation
effect in magnetic- and electric-field responses. Oxygen deficiency effect as
an impurity effect in a frustrated charge-spin coupled system is also examined.",0803.0394v1
2008-03-06,Tight-Binding Theory of Manganese and Iron Oxides,"The electronic structure is found to be understandable in terms of free-atom
term values and universal interorbital coupling parameters, since
self-consistent tight-binding calculations indicate that Coulomb shifts of the
d-state energies are small. Special-point averages over the bands are seen to
be equivalent to treatment of local octahedral clusters. The cohesive energy
per manganese for MnO, Mn2O3, and MnO2, in which manganese exists in valence
states Mn2+, Mn3+, and Mn4+, is very nearly the same and dominated by the
transfer of manganese s electrons to oxygen p states. There are small
corrections, one eV per Mn in all cases, from couplings of minority-spin
states. Transferring one majority-spin electron from an upper cluster state to
a nonbonding oxygen state adds 1.67 eV to the cohesion for Mn2O3, and two
transfers adds twice that for MnO2 . The electronic and magnetic properties are
consistent with this description and appear to be understandable in terms of
the same parameters.",0803.0994v1
2008-03-20,Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4,"We investigated electronic structure of 5d transition-metal oxide Sr2IrO4
using angle-resolved photoemission, optical conductivity, and x-ray absorption
measurements and first-principles band calculations. The system was found to be
well described by novel effective total angular momentum Jeff states, in which
relativistic spin-orbit (SO) coupling is fully taken into account under a large
crystal field. Despite of delocalized Ir 5d states, the Jeff-states form so
narrow bands that even a small correlation energy leads to the Jeff = 1/2 Mott
ground state with unique electronic and magnetic behaviors, suggesting a new
class of the Jeff quantum spin driven correlated-electron phenomena.",0803.2927v1
2008-03-27,Hydroxyl vacancies in single-walled aluminosilicate and aluminogermanate nanotubes,"We report the first theoretical study of hydroxyl vacancies in
aluminosilicate and aluminogermanate single-walled metal-oxide nanotubes. The
defects are modeled on both sides of the tube walls and lead to occupied and
empty states in the band gap which are highly localized both in energy and in
real space. We find different magnetization states depending on both the
chemical composition and the specific side with respect to the tube cavity. The
defect-induced perturbations to the pristine electronic structure are related
to the electrostatic polarization across the tube walls and the ensuing change
in Br{\o}nsted acid-base reactivity. Finally, the capacity to counterbalance
local charge accumulations, a characteristic feature of these systems, is
discussed in view of their potential application as insulating coatings for
one-dimensional conducting nanodevices.",0803.3915v1
2008-08-15,Magneto-Optical Trap for Polar Molecules,"We propose a method for laser cooling and trapping a substantial class of
polar molecules, and in particular titanium (II) oxide (TiO). This method uses
pulsed electric fields to nonadiabatically remix the ground-state magnetic
sublevels of the molecule, allowing us to build a magneto-optical trap (MOT)
based on a quasi-cycling $J'=J""-1$ transition. Monte-Carlo simulations of this
electrostatically remixed MOT (ER-MOT) demonstrate the feasibility of cooling
TiO to a temperature of 10 $\mathrm{\mu}K$ and trapping it with a
radiation-pumping-limited lifetime on the order of 80 ms.",0808.2171v2
2008-09-16,Interaction Effects in Conductivity of a Two-Valley Electron System in High-Mobility Si Inversion Layers,"We have measured the conductivity of high-mobility (001) Si
metal-oxide-semiconductor field effect transistors (MOSFETs) over wide ranges
of electron densities n=(1.8-15)x10^11cm^2, temperatures T=30mK-4.2K, and
in-plane magnetic fields B=0-5T. The experimental data have been analyzed using
the theory of interaction effects in the conductivity of disordered 2D systems.
The parameters essential for comparison with the theory, such as the
intervalley scattering time and valley splitting, have been measured or
evaluated in independent experiments. The observed behavior of the
conductivity, including its quasi-linear increase with decreasing T down to
~0.4K and its downturn at lower temperatures, is in agreement with the theory.
The values of the Fermi- liquid parameter obtained from the comparison agree
with the corresponding values extracted from the analysis of Shubnikov-de Haas
oscillations based on the theory of magnetooscillations in interacting 2D
systems.",0809.2750v1
2008-10-29,Tetragonal CuO: A new end member of the 3d transition metal monoxides,"Monoclinic CuO is anomalous both structurally as well as electronically in
the 3$d$ transition metal oxide series. All the others have the cubic rock salt
structure. Here we report the synthesis and electronic property determination
of a tetragonal (elongated rock salt) form of CuO created using an epitaxial
thin film deposition approach. In situ photoelectron spectroscopy suggests an
enhanced charge transfer gap $\Delta$ with the overall bonding more ionic. As
an end member of the 3d transition monoxides, its magnetic properties should be
that of a high $T_N$ antiferromagnet.",0810.5231v1
2008-11-12,Slow Dynamics in Hard Condensed Matter: A Case Study of the Phase Separating System NdNiO$_3$,"We report the time dependent response of electrical resistivity in the
non-magnetic perovskite oxide NdNiO$_3$ in its phase separated state and
provide a physical explanation of the observations. We also model the system
and do an accurate Monte Carlo simulation of the observed behavior. While
cooling a phase separation takes place in this system below its metal-insulator
transition temperature and in this state the material exhibits various
dynamical phenomena such as relaxation of resistivity, dependence of
resistivity on cooling rate and rejuvenation of the material after ageing.
These phenomena signal that the phase separated state of NdNiO$_3$ is not in
thermodynamic equilibrium and we conjecture that it consists of supercooled
paramagnetic metallic and antiferromagnetic insulating phases. The supercooled
phases are metastable and they switch over to the insulating equilibrium state
stochastically and this can account for the slow dynamics observed in our
system. We also verify the predictive power of our model by simulating the
result of a new experiment and confirming it by actual measurements.",0811.1836v1
2008-11-26,"Does Mesophase Ag4+xPb2O6-z (0 <= x <= 1, 0,5 <= z <= 0,75) Appeal for a Point Contact ATc Superconductivity?","Weakly compacted fine particles of Ag4+xPb2O6-z which is iso-structural with
Bystroem-Evers oxide Ag5Pb2O6 exhibit a novel class of physical properties,
which includes an appearance of diamagnetism at t < 78 degrees Celsius, with
corresponding absence of electric resistance, both events sounding for possible
superconductivity. Weak compaction was performed by controlled pressing of
introductory components Ag2O and PbO2. Pellets were heated from room
temperature in an evacuated chamber, and solid state reaction proceeded at
340-350 degrees Celsius in an oxygen atmosphere released by reaction itself (60
< p < 100 mbar). Electric and magnetic properties appealing for an ambient
temperature superconductivity may be attributed to scattering processes
indicated by tunnelling of Ag-Ag clusters between states localized on the point
contacts formed between adjacent particles. As compared to the work on the
subject during past two decades, reproducibility of output data is
satisfactory, and their correlations to the input preparation conditions appear
as to be conclusive.",0811.4352v1
2008-12-08,Orbital reconstruction and two-dimensional electron gas at the LaAlO3/SrTiO3 interface,"Conventional two-dimensional electron gases are realized by engineering the
interfaces between semiconducting compounds. In 2004, Ohtomo and Hwang
discovered that an electron gas can be also realized at the interface between
large gap insulators made of transition metal oxides [1]. This finding has
generated considerable efforts to clarify the underlying microscopic mechanism.
Of particular interest is the LaAlO3/SrTiO3 system, because it features
especially striking properties. High carrier mobility [1], electric field
tuneable superconductivity [2] and magnetic effects [3], have been found. Here
we show that an orbital reconstruction is underlying the generation of the
electron gas at the LaAlO3/SrTiO3 n-type interface. Our results are based on
extensive investigations of the electronic properties and of the orbital
structure of the interface using X-ray Absorption Spectroscopy. In particular
we find that the degeneracy of the Ti 3d states is fully removed, and that the
Ti 3dxy levels become the first available states for conducting electrons.",0812.1444v1
2008-12-31,Structural distortion and frustrated magnetic interactions in the layered copper oxychloride [CuCl]LaNb(2)O(7),"We present a computational study of the layered copper oxychloride
[CuCl]LaNb(2)O(7) that has been recently proposed as a spin-1/2 frustrated
square lattice compound. Our results evidence an orbitally degenerate ground
state for the reported tetragonal crystal structure and reveal a
Jahn-Teller-type structural distortion. This distortion heavily changes the
local environment of copper -- CuO(2)Cl(2) plaquettes are formed instead of
CuO(2)Cl(4) octahedra -- and restores the single-orbital scenario typical for
copper oxides and oxyhalides. The calculated distortion is consistent with the
available diffraction data and the experimental results on the electric field
gradients for the Cu and Cl sites. The band structure suggests a complex
three-dimensional spin model with the interactions up to the fourth neighbors.
Despite the layered structure of (CuCl)LaNb(2)O(7), the spin system has
pronounced one-dimensional features. Yet, sizable interchain interactions lead
to the strong frustration and likely cause the spin-gap behavior. Computational
estimates of individual exchange couplings are in qualitative agreement with
the experimental data.",0901.0154v2
2009-02-09,Unconventional metamagnetic electron states in orbital band systems,"We extend the study of the Fermi surface instability of the Pomeranchuk type
into systems with orbital band structures, which are common features in
transition metal oxides. Band hybridization significantly shifts the spectra
weight of the Landau interactions from the conventional s-wave channel to
unconventional non-s-wave channels, which results in anisotropic (nematic)
Fermi surface distortions even with ordinary interactions in solids. The
Ginzburg-Landau free energy is constructed by coupling the charge-nematic,
spin-nematic and ferromagnetic order parameters together, which shows that
nematic electron states can be induced by metamagnetism. The connection between
this mechanism to the anisotropic metamagnetc states observed in
Sr$_3$Ru$_2$O$_7$ at high magnetic fields is studied in a multi-band Hubbard
model with the hybridized quasi-one dimensional $d_{xz}$ and $d_{yz}$-bands.",0902.1337v3
2009-02-09,Superexchange Interaction and Magnetic Moment in Antiferromagnetic High-T_c Copper-oxide Superconductors,"Extensive Cu-NMR studies on multilayered high-Tc cuprates have deduced the
following results;(1) Antiferromagnetic (AFM) moment M_{AFM} is decreased with
doping, regardless of the number of CuO_2 layers n, and collapses around a
carrier density N_h = 0.17. (2) The AFM ordering temperature is enhanced as the
out-of-plane coupling J_{out} increases with increasing n. (3) The in-plane
superexchange J_{in} is invariant with doping, but is even increased. (4) The
dome shape of T_c from the underdoped to the overdoped regime with a maximum
T_c at N_h = 0.22 does not depend on n, but its maximum value of T_c seems to
depend on n moderately. The present results strongly suggest that the AFM
interaction plays the vital role as the glue for the Cooper pairs, which will
lead us to a genuine understanding of why the T_c of cuprate superconductors is
so high.",0902.1381v1
2009-02-10,Application of Secondary Neutral Mass Spectrometry in the investigation of doped perovskites,"Electromagnetic properties of doped perovskites depend sensitively on the
doping level. Both the superconducting transition temperature of
Bi2Sr2Ca(Pr)Cu2O8+d compounds and the magnetic and electronic transport
properties of La(Sr)Co(Fe)O3 perovskites change dramatically with the doping
level. Apart from doping, oxygen deficiency is influenced by the details of
preparation processes such as calcination and sintering. Simultaneous
determination of constituents is of crucial importance from sample
characterization point of view. Quantitative analysis of perovskite oxides can
be performed by Secondary Neutral Mass Spectrometry (SNMS) which is a suitable
technique to measure the chemical composition of almost any sample because the
flux of atoms sputtered from the sample is representative of the stoichiometry
of the top-most layers. The composition and oxygen content of
Bi2Sr2Ca0.86Pr0.14Cu2O8.4 and La1-xSrxCo0.975Fe0.025O3-d, where 0<x<0.5, were
determined by SNMS. The results show that the method is equally applicable for
insulating and conducting compounds. The observed electromagnetic properties
reflect well the compositions obtained experimentally.",0902.1649v1
2009-02-18,The energy scale behind the metallic behaviors in low-density Si-MOSFETs,"We show that the unexpected metallic behavior (the so-called two-dimensional
metal-insulator transition) observed in low-density Silicon
metal-oxide-semiconductor field-effect transistors (Si-MOSFETs) is controlled
by a unique characteristic energy scale, the polarization energy. On one hand,
we perform Quantum Monte Carlo calculations of the energy needed to polarize
the two dimensional electron gas at zero temperature, taking into account
Coulomb interactions, valley degeneracy and electronic mobility (disorder). On
the other hand, we identify the characteristic energy scale controlling the
physics in eight different sets of experiments. We find that our {\it
ab-initio} polarization energies (obtained without any adjustable parameters)
are in perfect agreement with the observed characteristic energies for all
available data, both for the magnetic field and temperature dependence of the
resistivities. Our results put strong constraints on possible mechanisms
responsible for the metallic behavior. In particular, there are strong
indications that the system would eventually become insulating at low enough
temperature.",0902.3171v3
2009-03-14,Electron coherent and incoherent pairing instabilities in inhomogeneous bipartite and nonbipartite nanoclusters,"Exact calculations of collective excitations and charge/spin (pseudo)gaps in
an ensemble of bipartite and nonbipartite clusters yield level crossing
degeneracies, spin-charge separation, condensation and recombination of
electron charge and spin, driven by interaction strength, inter-site couplings
and temperature. Near crossing degeneracies, the electron configurations of the
lowest energies control the physics of electronic pairing, phase separation and
magnetic transitions. Rigorous conditions are found for the smooth and dramatic
phase transitions with competing stable and unstable inhomogeneities.
Condensation of electron charge and spin degrees at various temperatures offers
a new mechanism of pairing and a possible route to superconductivity in
inhomogeneous systems, different from the BCS scenario. Small bipartite and
frustrated clusters exhibit charge and spin inhomogeneities in many respects
typical for nano and heterostructured materials. The calculated phase diagrams
in various geometries may be linked to atomic scale experiments in high T$_c$
cuprates, manganites and other concentrated transition metal oxides.",0903.2586v1
2009-03-16,Superconductivity and quantum oscillations in crystalline Bi nanowires,"While bulk bismuth (Bi) is a semimetal, we have found clear evidence of
superconductivity in a crystalline 72 nm diameter Bi nanowire below 1.3 K. In a
parallel magnetic field (H), the residual resistance of the nanowire below Tc
displays periodic oscillations with H, and the period corresponds to the
superconducting flux quantum. This result provides evidence that the
superconductivity comes from the interface shell between Bi and the surface
oxide. In a perpendicular H, the resistance in the superconducting state shows
Shubnikov-de Haas (SdH) oscillations, a signature of a normal metal. These
results indicate a novel coexistence of Bosonic and Fermionic states in the
surface shell of nanowires.",0903.2855v1
2009-03-23,Spin-like susceptibility of metallic and insulating thin films at low temperature,"Susceptibility measurements of patterned thin films at sub-K temperatures
were carried out using a scanning SQUID microscope that can resolve signals
corresponding to a few hundred Bohr magnetons. Several metallic and insulating
thin films, even oxide-free Au films, show a paramagnetic response with a
temperature dependence that indicates unpaired spins as the origin. The
observed response exhibits a measurable out-of-phase component, which implies
that these spins will create 1/f-like magnetic noise. The measured spin density
is consistent with recent explanations of low frequency flux noise in SQUIDs
and superconducting qubits in terms of spin fluctuations, and suggests that
such unexpected spins may be even more ubiquitous than already indicated by
earlier measurements. Our measurements set several constraints on the nature of
these spins.",0903.3748v2
2009-03-30,Room-temperature ferromagnetism in the mixtures of the TiO2 and Co3O4 powders,"We report here the observation of ferromagnetism (FM) at 300 K in mixtures of
TiO2 and Co3O4 powders despite the antiferromagnetic and diamagnetic character
of both oxides respectively. The ferromagnetic behavior is found in the early
stages of reaction and only for TiO2 in anatase structure; no FM is found for
identical samples prepared with rutile-TiO2. Optical spectroscopy and X-ray
absorption spectra confirm a surface reduction of octahedral Co+3->Co+2 in the
mixtures which is in the origin of the observed magnetism",0903.5214v1
2009-04-08,Spin--orbital physics in transition metal oxides,"We present the main features of the spin-orbital superexchange which
describes the magnetic and optical properties of Mott insulators with orbital
degrees of freedom. In contrast to the SU(2) symmetry of spin superexchange,
the orbital part of the superexchange obeys the lower cubic symmetry of the
lattice and is intrinsically frustrated. This intrinsic frustration and
spin-orbital entanglement induce enhanced quantum fluctuations, and we point
out a few situations where this leads to disordered states. Strong coupling
between the spin and orbital degrees of freedom is discussed on the example of
the $R$VO$_3$ perovskites, with $R$ standing for rare-earth ion, La,...,Lu. We
explain the observed evolution of the orbital $T_{\rm OO}$ and N\'eel $T_{N1}$
transition temperature in the $R$VO$_3$ series with decreasing ionic radius
$r_R$. A few open problems and the current directions of research in the field
of spin-orbital physics are pointed out.",0904.1297v1
2009-05-01,Directional field-induced metallization of quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$,"We report a detailed magnetotransport study of the highly anisotropic
quasi-one-dimensional oxide Li$_{0.9}$Mo$_6$O$_{17}$ whose in-chain electrical
resistivity diverges below a temperature $T_{\rm min} \sim$ 25 K. For $T <
T_{\rm min}$, a magnetic field applied parallel to the conducting chain induces
a large negative magnetoresistance and ultimately, the recovery of a metallic
state. We show evidence that this insulator/metal crossover is a consequence of
field-induced suppression of a density-wave gap in a highly one-dimensional
conductor. At the highest fields studied, there is evidence for the possible
emergence of a novel superconducting state with an onset temperature $T_c >$ 10
K.",0905.0098v1
2009-08-02,Spin-dependent transport in nanocomposite C:Co films,"The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co)
thin films are investigated. The films were grown by ion beam co-sputtering on
thermally oxidized silicon substrates in the temperature range from 200 to 500
degC. Two major effects are reported: (i) a large anomalous Hall effect
amounting to 2 \mu ohm cm, and (ii) a negative magnetoresistance. Both the
field-dependent resistivity and Hall resistivity curves coincide with the
rescaled magnetization curves, a finding that is consistent with spin-dependent
transport. These findings suggest that C:Co nanocomposites are promising
candidates for carbon-based Hall sensors and spintronic devices.",0908.0127v1
2009-08-24,Half-Skyrmion theory for high-temperature superconductivity,"We review the half-Skyrmion theory for copper-oxide high-temperature
superconductivity. In the theory, doped holes create a half-Skyrmion spin
texture which is characterized by a topological charge. The formation of the
half-Skyrmion is described in the single hole doped system, and then the
half-Skyrmion excitation spectrum is compared with the angle-resolved
photoemission spectroscopy results in the undoped system. Multi-half-Skyrmion
configurations are studied by numerical simulations. We show that
half-Skyrmions carry non-vanishing topological charge density below a critical
hole doping concentration \sim 30% even in the absence of antiferromagnetic
long-range order. The magnetic structure factor exhibits incommensurate peaks
in stripe ordered configurations of half-Skyrmions and anti-half-Skyrmions. The
interaction mediated by half-Skyrmions leads to d_{x^2-y^2}-wave
superconductivity. We also describe pseudogap behavior arising from the
excitation spectrum of a composite particle of a half-Skyrmion and doped hole.",0908.3385v1
2009-09-15,Anisotropy of the low-temperature magnetostriction of Sr3Ru2O7,"We use high-resolution capacitive dilatometry to study the low-temperature
linear magnetostriction of the bilayer ruthenate Sr$_3$Ru$_2$O$_7$ as a
function of magnetic field applied perpendicular to the ruthenium-oxide planes
($B\parallel c$). The relative length change $\Delta L(B)/L$ is detected either
parallel or perpendicular to the c-axis close to the metamagnetic region near
B=8 T. In both cases, clear peaks in the coefficient $\lambda(B)=d(\Delta
L/L)/dB$ at three subsequent metamagnetic transitions are observed. For $\Delta
L\perp c$, the third transition at 8.1 T bifurcates at temperatures below 0.5
K. This is ascribed to the effect of an in-plane uniaxial pressure of about 15
bar, unavoidable in the dilatometer, which breaks the original fourfold
in-plane symmetry.",0909.2731v1
2009-09-28,Exciton doublet in the Mott-Hubbard LiCuVO$_4$ insulator identified by spectral ellipsometry,"Spectroscopic ellipsometry was used to study the dielectric function of
LiCuVO$_{4}$, a compound comprised of chains of edge-sharing CuO$_4$
plaquettes, in the spectral range (0.75 - 6.5) eV at temperatures (7-300) K.
For photon polarization along the chains, the data reveal a weak but
well-resolved two-peak structure centered at 2.15 and 2.95 eV whose spectral
weight is strongly enhanced upon cooling near the magnetic ordering
temperature. We identify these features as an exciton doublet in the
Mott-Hubbard gap that emerges as a consequence of the Coulomb interaction
between electrons on nearest and next-nearest neighbor sites along the chains.
Our results and methodology can be used to address the role of the long-range
Coulomb repulsion for compounds with doped copper-oxide chains and planes.",0909.5157v1
2010-02-04,Origin of half-semimetallicity induced at interfaces of C-BN heterostructures,"First-principles density functional calculations are performed in C-BN
heterojunctions. It is shown that the magnetism of the edge states in zigzag
shaped graphene strips and polarity effects in BN strips team up to give a spin
asymmetric screening that induces half-semimetallicity at the interface, with a
gap of at least a few tenths of eV for one spin orientation and a tiny gap of
hundredths of eV for the other. The dependence with ribbon widths is discussed,
showing that a range of ribbon widths is required to obtain
half-semimetallicity. These results open new routes for tuning electronic
properties at nanointerfaces and exploring new physical effects similar to
those observed at oxide interfaces, in lower dimensions.",1002.1018v1
2010-02-24,Magnetic Structure of CaBaCo4O7: Lifting of Geometrical Frustration towards Ferrimagnetism,"CaBaCo4O7 represents a new class of ferrimagnets whose structure is built up
of CoO4 tetrahedra only, similarly to other members LnBaCo4O7 of the 114
series, forming an alternate stacking of kagome and triangular layers. Neutron
powder diffraction reveals, that this compound exhibits the largest distortion
within the 114 series, characterized by a strong buckling of the kagome layers.
Differently from all other members it shows charge ordering, with Co2+ sitting
on two sites (Co2, Co3) and mixed valent cobalt Co3+/Co2+L sitting on two other
sites (Co1, Co4). The unique ferrimagnetic structure of this cobaltite at 4 K
can be described as the assemblage of ferrimagnetic triple chains (Co1 Co2 Co3)
running perpendicular to the kagome layers, ferromagnetically coupled within
the layers, and antiferromagnetically coupled with a fourth cobalt species Co4.
The lifting of the geometrical frustration towards ferrimagnetism, which
appears in spite of the triangular topology of the cobalt lattice, is explained
by the very large structural distortion, charge ordering phenomena and large
cobalt valence compared to other LnBaCo4O7 oxides.",1002.4544v1
2010-03-08,Origin of the magnetoelectric coupling effect in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures,"The electronic valence state of Mn in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3
multiferroic heterostructures is probed by near edge x-ray absorption
spectroscopy as a function of the ferroelectric polarization. We observe a
temperature independent shift in the absorption edge of Mn associated with a
change in valency induced by charge carrier modulation in the La0.8Sr0.2MnO3,
demonstrating the electronic origin of the magnetoelectric effect.
Spectroscopic, magnetic, and electric characterization shows that the large
magnetoelectric response originates from a modified interfacial spin
configuration, opening a new pathway to the electronic control of spin in
complex oxide materials.",1003.1752v1
2010-06-07,A Robust Approach for the Growth of Epitaxial Spinel Ferrite Films,"Heteroepitaxial spinel ferrites NiFe2O4 and CoFe2O4 films have been prepared
by pulsed laser deposition (PLD) at various temperatures (175 - 690 {\deg}C)
under ozone/oxygen pressure of 10 mTorr. Due to enhanced kinetic energy of
ablated species at low pressure and enhanced oxidation power of ozone, epitaxy
has been achieved at significantly lower temperatures than previously reported.
Films grown at temperature below 550 {\deg}C show a novel growth mode, which we
term ""vertical step-flow"" growth mode. Epitaxial spinel ferrite films with
atomically flat surface over large areas and enhanced magnetic moment can be
routinely obtained. Interestingly, the growth mode is independent of the nature
of substrates (spinel MgAl2O4, perovskite SrTiO3, and rock salt MgO) and film
thicknesses. The underlying growth mechanism is discussed.",1006.1161v1
2010-08-18,Field-dependent low-field enhancement in effective paramagnetic moment with nano-scaled Co3O4,"Paramagnetic (PM) properties of columnar cobaltosic oxide (Co3O4)
nanoparticles, about 75 nm in diameter, have been investigated by magnetization
measurements at T > TN = 39 K. In zero or low applied field, the effective PM
moment per formula unit (FU), Mu_eff, enhances significantly from the bulk
value of 4.14 Mu_B/FU. It decreases asymptotically from 5.96 Mu_B/FU at Happ =
50 Oe down to 4.21 Mu_B/FU as the applied field increases to Happ = 10 kOe. The
field dependent PM properties are explained by a structural inversion, from the
normal spinel (spin-only moment ~ 3.9 Mu_B/FU) to the inverse spinel structure
(spin-only moment ~ 8.8 Mu_B/FU). The structural inversion is reversible with
the variation of the applied field. The lattice structure becomes almost 100%
normal spinel in the high field exceeding 10 kOe, as revealed by the magnitude
of the effective PM moment. The reversible, field dependent structure inversion
is an important property with promising application potential. It is
interesting for the future investigations.",1008.3156v1
2010-09-24,Control of Correlations in Sr4V2O6Fe2As2 by Chemical Stoichiometry,"We show using a combination of powder X-ray and neutron diffraction, first
principles calculations, temperature- and field-dependent magnetization, heat
capacity and resistivity data that the superconducting behavior of
`Sr$_4$V$_2$O$_6$Fe$_2$As$_2$' is dependent on synthesis conditions,
particularly, heating profiles result in unintentional chemical doping. This
compound can be tuned from a state in which the vanadium electrons are
itinerant with a high electronic density of states, to a state where the
vanadium-oxide layers are insulating and presumably antiferromagnetic.",1009.4911v1
2010-12-17,Observation of Andreev bound states at spin-active interfaces,"We report on high-resolution differential conductance experiments on
nanoscale superconductor/ferromagnet tunnel junctions with ultra-thin oxide
tunnel barriers. We observe subgap conductance features which are symmetric
with respect to bias, and shift according to the Zeeman energy with an applied
magnetic field. These features can be explained by resonant transport via
Andreev bound states induced by spin-active scattering at the interface. From
the energy and the Zeeman shift of the bound states, both the magnitude and
sign of the spin-dependent interfacial phase shifts between spin-up and
spin-down electrons can be determined. These results contribute to the
microscopic insight into the triplet proximity effect at spin-active
interfaces.",1012.3867v2
2010-12-31,Orbital reflectometry,"The occupation of d-orbitals controls the magnitude and anisotropy of the
inter-atomic electron transfer in transition metal oxides and hence exerts a
key influence on their chemical bonding and physical properties. Atomic-scale
modulations of the orbital occupation at surfaces and interfaces are believed
to be responsible for massive variations of the magnetic and transport
properties, but could thus far not be probed in a quantitative manner. Here we
show that it is possible to derive quantitative, spatially resolved orbital
polarization profiles from soft x-ray reflectivity data, without resorting to
model calculations. We demonstrate that the method is sensitive enough to
resolve differences of 3 % in the occupation of Ni e_g orbitals in adjacent
atomic layers of a LaNiO3-LaAlO3 superlattice, in good agreement with ab-initio
electronic-structure calculations. The possibility to quantitatively correlate
theory and experiment on the atomic scale opens up many new perspectives for
orbital physics in d-electron materials.",1101.0238v1
2011-01-27,Magnetic excitations in one-dimensional spin-orbital models,"We study the dynamics and thermodynamics of one-dimensional spin-orbital
models relevant for transition metal oxides. We show that collective spin,
orbital, and combined spin-orbital excitations with infinite lifetime can
exist, if the ground state of both sectors is ferromagnetic. Our main focus is
the case of effectively ferromagnetic (antiferromagnetic) exchange for the spin
(orbital) sector, respectively, and we investigate the renormalization of spin
excitations via spin-orbital fluctuations using a boson-fermion representation.
We contrast a mean-field decoupling approach with results obtained by treating
the spin-orbital coupling perturbatively. Within the latter self-consistent
approach we find a significant increase of the linewidth and additional
structures in the dynamical spin structure factor as well as Kohn anomalies in
the spin-wave dispersion caused by the scattering of spin excitations from
orbital fluctuations. Finally, we analyze the specific heat c(T) by comparing a
numerical solution of the model obtained by the density-matrix renormalization
group with perturbative results. At low temperatures T we find numerically c(T)
T pointing to a low-energy effective theory with dynamical critical exponent
z=1.",1101.5301v1
2011-01-30,Controlling electrostatic co-assembly using ion-containing copolymers : from surfactants to nanoparticles,"In this review, we address the issue of the electrostatic complexation
between charged-neutral diblock copolymers and oppositely charged nanocolloids.
We show that nanocolloids such as surfactant micelles and iron oxide magnetic
nanoparticles share similar properties when mixed with charged-neutral
diblocks. Above a critical charge ratio, core-shell hierarchical structures
form spontaneously under direct mixing conditions. The core-shell structures
are identified by a combination of small-angle scattering techniques and
transmission electron microscopy. The formation of multi-level objects is
driven by the electrostatic attraction between opposite charges and by the
release of the condensed counterions. Alternative mixing processes inspired
from molecular biology are also described. The protocols applied here consist
in screening the electrostatic interactions of the mixed dispersions, and then
removing the salt progressively as example by dialysis. With these techniques,
the oppositely charged species are intimately mixed before they can interact,
and their association is monitored by the desalting kinetics. As a result,
sphere- and rod-like aggregates with remarkable superparamagnetic and stability
properties are obtained. These findings are discussed in the light of a new
paradigm which deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of supracolloidal assemblies
with enhanced functionalities.",1101.5821v1
2011-03-15,Spin filling of valley-orbit states in a silicon quantum dot,"We report the demonstration of a low-disorder silicon
metal-oxide-semiconductor (Si MOS) quantum dot containing a tunable number of
electrons from zero to N=27. The observed evolution of addition energies with
parallel magnetic field reveals the spin filling of electrons into valley-orbit
states. We find a splitting of 0.10 meV between the ground and first excited
states, consistent with theory and placing a lower bound on the valley
splitting. Our results provide optimism for the realization in the near future
of spin qubits based on silicon quantum dots.",1103.2895v2
2011-03-15,Oxygen hyperstoichiometric hexagonal ferrite CaBaFe4O7+δ(δ \approx 0.14) : coexistence of ferrimagnetism and spin glass behavior,"An oxygen hyperstoichiometric ferrite CaBaFe4O7+\delta (\delta \approx 0.14)
has been synthesized using ""soft"" reduction of CaBaFe4O8. Like the oxygen
stoichiometric ferrimagnet CaBaFe4O7, this oxide also keeps the hexagonal
symmetry (space group: P63mc), and exhibits the same high Curie temperature of
270 K. However, the introduction of extra oxygen into the system weakens the
ferrimagnetic interaction significantly at the cost of increased magnetic
frustration at low temperature. Moreover, this canonical spin glass (Tg ~ 166
K) exhibits an intriguing cross-over from de Almeida-Thouless type to
Gabay-Toulouse type critical line in the field temperature plane above a
certain field strength, which can be identified as the anisotropy field. Domain
wall pinning is also observed below 110 K. These results are interpreted on the
basis of cationic disordering on the iron sites.",1103.2939v1
2011-03-17,Magneto-Transport Properties of Exfoliated Graphene on GaAs,"We studied the magneto-transport properties of graphene prepared by
exfoliation on a III V semiconductor substrate. Tuneability of the carrier
density of graphene was achieved by using a doped GaAs substrate as a
back-gate. A GaAs/AlAs multilayer, designed to render the exfoliated graphene
flakes visible, also provides the required back-gate insulation. Good
tuneability of the graphene carrier density is obtained, and the typical Dirac
resistance characteristic is observed despite the limited height of the
multilayer barrier compared to the usual SiO2 oxide barrier on doped silicon.
In a magnetic field weak localization effects as well as the quantum Hall
effect of a graphene monolayer are studied.",1103.3367v4
2011-05-31,Octahedral rotation-induced ferroelectricity in cation ordered perovskites,"Increasing demands for electric field-tunable electric, magnetic, and orbital
(EMO) materials has renewed interests in ferroelectricity and its coupling to
EMO properties in complex perovskite oxides. The historic design strategy to
achieve a spontaneous polarization involves the incorporation of second-order
Jahn-Teller (SOJT) active cations. The challenge, however, is that this
mechanism is limited to specific chemistries and the polar distortions that
arise are largely decoupled from EMO properties, limiting their use as
field-tunable multifunctional technology materials. Here we report the
crystal-chemistry criteria which circumvents those restrictions and enables the
rational design of new materials displaying octahedral rotation-induced
ferroelectricity - an innovative route to realize electric polarization without
the need for SOJT cations - from non-polar building blocks. The strategy
exploits the centric octahedral rotation patterns, which strongly couple to EMO
properties, and cation ordering commonly observed in non-polar $AB$O$_3$
perovskites. By uniting switchable electric polarizations to the connectivity
of the transition-metal oxygen octahedra, electric-field control over materials
properties is possible.",1106.0049v3
2011-06-02,Microscopic Study of Electronic and Magnetic Properties for Ir Oxide,"The exact diagonalization and the variational cluster approximation (VCA) are
used to study the nature of a novel Mott insulator induced by a strong
spin-orbit coupling for a two-dimensional three-band Hubbard model consisting
of the $t_{2g}$ manifold of $5d$ orbitals. To characterize the ground state, we
introduce a local Kramer's doublet which can represent a state with effective
angular momentum $J_{\rm eff}=|{\bm S}-{\bm L}|=1/2$ as well as spin $S=1/2$.
Our systematic study of the pseudo-spin structure factor defined by the
Kramer's doublet shows that the $J_{\rm eff}=1/2$ Mott insulator is smoothly
connected to the $S=1/2$ Mott insulator. Using the Kramer's doublet as a
variational state for the VCA, we examine the one-particle excitations for the
Mott insulating phase. These results are compared with recent experiments on
Sr$_2$IrO$_4$.",1106.0413v1
2011-06-12,Electrodynamics of Correlated Electron Materials,"We review studies of the electromagnetic response of various classes of
correlated electron materials including transition metal oxides, organic and
molecular conductors, intermetallic compounds with $d$- and $f$-electrons as
well as magnetic semiconductors. Optical inquiry into correlations in all these
diverse systems is enabled by experimental access to the fundamental
characteristics of an ensemble of electrons including their self-energy and
kinetic energy. Steady-state spectroscopy carried out over a broad range of
frequencies from microwaves to UV light and fast optics time-resolved
techniques provide complimentary prospectives on correlations. Because the
theoretical understanding of strong correlations is still evolving, the review
is focused on the analysis of the universal trends that are emerging out of a
large body of experimental data augmented where possible with insights from
numerical studies.",1106.2309v1
2011-06-13,Iron-chalcogenide FeSe$_{0.5}$Te$_{0.5}$ coated superconducting tapes for high field applications,"The high upper critical field characteristic of the recently discovered
iron-based superconducting chalcogenides opens the possibility of developing a
new type of non-oxide high-field superconducting wires. In this work, we
utilize a buffered metal template on which we grow a textured
FeSe$_{0.5}$Te$_{0.5}$ layer, an approach developed originally for high
temperature superconducting coated conductors. These tapes carry high critical
current densities (>1$\times10^{4}$A/cm$^{2}$) at about 4.2K under magnetic
field as high as 25 T, which are nearly isotropic to the field direction. This
demonstrates a very promising future for iron chalcogenides for high field
applications at liquid helium temperatures. Flux pinning force analysis
indicates a point defect pinning mechanism, creating prospects for a
straightforward approach to conductor optimization.",1106.2466v1
2011-08-15,Polar octahedral rotations: a path to new multifunctional materials,"Perovskite ABO$_3$ oxides display an amazing variety of phenomena that can be
altered by subtle changes in the chemistry and internal structure, making them
a favorite class of materials to explore the rational design of novel
properties. Here we highlight a recent advance in which rotations of the BO$_6$
octahedra give rise to a novel form of ferroelectricity -- hybrid improper
ferroelectricity. Octahedral rotations also strongly influence other
structural, magnetic, orbital, and electronic degrees of freedom in perovskites
and related materials. Octahedral rotation-driven ferroelectricity consequently
has the potential to robustly control emergent phenomena with an applied
electric field. The concept of `functional' octahedral rotations is introduced
and the challenges for materials chemistry and the possibilities for new
rotation-driven phenomena in multifunctional materials are explored.",1108.2915v2
2011-09-07,Possible interaction driven topological phases in (111) bilayers of LaNiO3,"We use the variational mean-field approach to systematically study the phase
diagram of a bilayer heterostructure of the correlated transition metal oxide
LaNiO3, grown along the (111) direction. The Ni 3+ ions with d7 (or eg1)
configuration form a buckled honeycomb lattice. We show that as a function of
the strength of the on-site interactions, various topological phases emerge. In
the presence of a reasonable size of the Hund's coupling, as the correlation is
tuned from intermediate to strong, the following sequence of phases is found:
(1) a Dirac half-semimetal phase, (2) a quantum anomalous hall insulator (QAHI)
phase with Chern number one, and (3) a ferromagnetic nematic phase breaking the
lattice point group symmetry. The spin-orbit couplings and magnetism are both
dynamically generated in the QAHI phase.",1109.1551v2
2011-09-09,Conditions determining the morphology and nanoscale magnetism of Co nanoparticles: Experimental and numerical studies,"Co-based nanostructures ranging from core-shell to hollow nanoparticles were
produced by varying the reaction time and the chemical environment during the
thermal decomposition of Co2(CO)8. Both structural characterization and kinetic
model simulation illustrate that the diffusivities of Co and oxygen determine
the growth ratio and the final morphology of the nanoparticles. Exchange
coupling between Co and Co-oxide in core/shell nanoparticles induced a shift of
field-cooled hysteresis loops that is proportional to the shell thickness, as
verified by numerical studies. The increased nanocomplexity when going from
core/shell to hollow particles, also leads to the appearance of hysteresis
above 300 K due to an enhancement of the surface anisotropy resulting from the
additional spin-disordered surfaces.",1109.2024v1
2011-10-07,Overlapping-gate architecture for silicon Hall bar MOSFET devices in the low electron density and high magnetic field regime,"A common issue in low temperature measurements of enhancement-mode
metal-oxide-semiconductor (MOS) field-effect transistors (FETs) in the low
electron density regime is the high contact resistance dominating the device
impedance. In that case a voltage bias applied across the source and drain
contact of a Hall bar MOSFET will mostly fall across the contacts (and not
across the channel) and therefore magneto-transport measurements become
challenging. However, from a physical point of view, the study of MOSFET
nanostructures in the low electron density regime is very interesting (impurity
limited mobility [1], carrier interactions [2,3] and spin-dependent transport
[4]) and it is therefore important to come up with solutions [5,6] that work
around the problem of a high contact resistance in such devices (c.f. Fig. 1
(a)).",1110.1418v1
2012-02-20,Correlation effects on 3D topological phases: from bulk to boundary,"Topological phases of quantum matter defy characterization by conventional
order parameters but can exhibit quantized electro-magnetic response and/or
protected surface states. We examine such phenomena in a model for
three-dimensional correlated complex oxides, the pyrochlore iridates. The model
realizes interacting topological insulators with and without time-reversal
symmetry, and topological Weyl semimetals. We use cellular dynamical mean field
theory, a method that incorporates quantum-many-body effects and allows us to
evaluate the magneto-electric topological response coefficient in correlated
systems. This invariant is used to unravel the presence of an interacting axion
insulator absent within a simple mean field study. We corroborate our bulk
results by studying the evolution of the topological boundary states in the
presence of interactions. Consequences for experiments and for the search for
correlated materials with symmetry-protected topological order are given.",1202.4460v2
2012-02-23,Quantum-fluctuation effects in transport properties of superconductors above the paramagnetic limit,"We study the transport in ultrathin disordered film near the quantum critical
point induced by the Zeeman field. We calculate corrections to the normal state
conductivity due to quantum pairing fluctuations. The fluctuation-induced
transport is mediated by virtual rather than real quasi-particles. We find that
at zero temperature, where the corrections come from purely quantum
fluctuations, the Aslamazov-Larkin paraconductivity term, the Maki-Thompson
interference contribution and the density of states effects are all of the same
order. The total correction leads to the negative magnetoresistance. This
result is in qualitative agreement with the recent transport observations in
the parallel magnetic field of the homogeneously disordered amorphous films and
superconducting two-dimensional electron gas realized at the oxide interfaces.",1202.5082v1
2012-03-08,Covalent functionalization of strained graphene,"Enhancement of the chemical activity of graphene is evidenced by
first-principles modelling of chemisorption of the hydrogen, fluorine, oxygen
and hydroxyl groups on strained graphene. For the case of negative strain or
compression, chemisorption of the single hydrogen, fluorine or hydroxyl group
is energetically more favourable than those of their pairs on different
sublattices. This behaviour stabilizes the magnetism caused by the
chemisorption being against its destruction by the pair formations. Initially
flat, compressed graphene is shown to buckle spontaneously right after
chemisorption of single adatoms. Unlike hydrogenation or fluorination, the
oxidation process turns from the endothermic to exothermic for all types of the
strain and depends on the direction of applied strains. Such properties will be
useful in designing graphene devices utilizing functionalization as well as
mechanical strains.",1203.1710v1
2012-03-12,Disentangling a quantum antiferromagnet with resonant inelastic X-ray scattering,"Low-dimensional copper oxide lattices naturally manifest electronic states
with strong short range quantum entanglement, which are known to lead to
remarkable emergent material properties. However the nanometer scale many-body
wavefunction is challenging to measure or manipulate in a simple way. In this
study, X-ray induced $dd$ electronic transitions are used to suppress spin
entanglement across a single lattice site in the spin-1/2 antiferromagnetic
chain compound SrCuO$_2$, revealing a class of cuprate magnetic excitations
that result from breaking the spin chain. These measurements are the first to
employ two closely spaced X-ray resonances of copper (M$_2$ and M$_3$) as a
form of natural 2-slit interferometer to distinguish between different types of
electronic transition and resolve how they influence the dynamics of nearby
spin-entangled electrons.",1203.2397v1
2012-03-15,Temperature dependent magnetotransport around $ν$= 1/2 in ZnO heterostructures,"The sequence of prominent fractional quantum Hall states up to $\nu$=5/11
around $\nu$=1/2 in a high mobility two-dimensional electron system confined at
oxide heterointerface (ZnO) is analyzed in terms of the composite fermion
model. The temperature dependence of $\Rxx$ oscillations around $\nu$=1/2
yields an estimation of the composite fermion effective mass, which increases
linearly with the magnetic field. This mass is of similar value to an enhanced
electron effective mass, which in itself arises from strong electron
interaction. The energy gaps of fractional states and the temperature
dependence of $\Rxx$ at $\nu$=1/2 point to large residual interactions between
composite fermions.",1203.3349v1
2012-03-28,"Nut-charged black holes in matter-coupled N=2, D=4 gauged supergravity","Using the results of arXiv:0804.0009, where all timelike supersymmetric
backgrounds of N=2, D=4 matter-coupled supergravity with Fayet-Iliopoulos
gauging were classified, we construct genuine nut-charged BPS black holes in
AdS_4 with nonconstant moduli. The calculations are exemplified for the
SU(1,1)/U(1) model with prepotential F=-iX^0X^1. The resulting supersymmetric
black holes have a hyperbolic horizon and carry two electric, two magnetic and
one nut charge, which are however not all independent, but are given in terms
of three free parameters. We find that turning on a nut charge lifts the flat
directions in the effective black hole potential, such that the horizon values
of the scalars are completely fixed by the charges. We also oxidize the
solutions to eleven dimensions, and find that they generalize the geometry
found in hep-th/0105250 corresponding to membranes wrapping holomorphic curves
in a Calabi-Yau five-fold. Finally, a class of nut-charged Nernst branes is
constructed as well, but these have curvature singularities at the horizon.",1203.6179v1
2012-06-14,TiO2 as an electrostatic template for epitaxial growth of EuO on MgO(001) by reactive molecular beam epitaxy,"We investigate the initial growth modes and the role of interfacial
electrostatic interactions of EuO epitaxy on MgO(001) by reactive molecular
beam epitaxy. A TiO2 interfacial layer is employed to produce high quality
epitaxial growth of EuO on MgO(001) with a 45{\deg} in plane rotation. For
comparison, direct deposition of EuO on MgO, without the TiO2 layer shows a
much slower time evolution in producing a single crystal film. Conceptual
arguments of electrostatic repulsion of like-ions are introduced to explain the
increased EuO quality at the interface with the TiO2 layer. It is shown that
ultrathin EuO films in the monolayer regime can be produced on the TiO2 surface
by substrate-supplied oxidation and that such films have bulk-like magnetic
properties.",1206.2981v1
2012-06-29,Double exchange model on triangular lattice: non-coplanar spin configuration and phase transition near quarter filling,"Unconventional anomalous Hall effect in frustrated pyrochlore oxides is
originated from spin chirality of non-coplanar localized spins, which can also
be induced by the competition between ferromagnetic (FM) double exchange
interaction $J_{H}$ and antiferromagnetic superexchange interaction $J_{AF}$.
Here truncated polynomial expansion method and Monte Carlo simulation are
adopted to investigate the above model on two-dimensional triangular lattice.
We discuss the influence of the range of FM-type spin-spin correlation and
strong electron-spin correlation on the truncation error of spin-spin
correlation near quarter filling. Two peaks of the probability distribution of
spin-spin correlation in non-coplanar spin configuration clearly show that
non-coplanar spin configuration is an intermediate phase between FM and
120-degree spin phase. Near quarter filling, there is a phase transition from
FM into non-coplanar and further into 120-degree spin phase when $J_{AF}$
continually increases. Finally the effect of temperature on magnetic structure
is discussed.",1206.6944v2
2012-07-04,Kondo-like behavior near the metal-to-insulator transition of nano-scale granular aluminum,"We show that the normal state transport properties of nano-scale granular
Aluminum films, near the metal to insulator transition, present striking
similarities with those of Kondo systems. Those include a negative
magneto-resistance, a minimum of resistance R at a temperature Tm in metallic
films, a logarithmic rise at low temperatures and a negative curvature of R(T)
at high temperatures. These normal state properties are interpreted in terms of
spin-flip scattering of conduction electrons by local magnetic moments,
possibly located at the metal/oxide interfaces. Their co-existence with the
enhanced superconductivity seen in these films is discussed.",1207.0970v3
2012-08-15,Two-dimensional electron-gas-like charge transport at magnetic Heusler alloy-SrTiO$_3$ interface,"We report remarkably low residual resistivity, giant residual resistivity
ratio, free-electron-like Hall resistivity and high mobility ($\approx$ 10$^4$
cm$^2$V$^{-1}$s$^{-1}$) charge transport in epitaxial films of Co$_2$MnSi and
Co$_2$FeSi grown on (001) SrTiO$_3$. This unusual behavior is not observed in
films deposited on other cubic oxide substrates of comparable lattice
parameters. The scaling of the resistivity with thickness of the films allow
extraction of interface conductance, which can be attributed to a layer of
oxygen vacancies confined within 1.9 nm of the interface as revealed by
atomically resolved electron microscopy and spectroscopy. The high mobility
transport observed here at the interface of a fully spin polarized metal is
potentially important for spintronics applications.",1208.3099v2
2012-08-29,Floating Zone Growth of Large Single Crystals of SrFeO_3-x,"The Fe^{4+}-containing cubic perovskite phase SrFeO_3-x is of interest both
for its high-temperature, oxygen-conducting properties as a solid oxide fuel
cell component, and at low temperatures, where it exhibits a plethora of
helical magnetic phases and a candidate Skyrmion lattice. However, a sequence
of structural phase transitions encountered on cooling to room temperature has
limited the size of single crystals. We report the floating-zone growth and
oxygen-annealing of multiple-cubic-centimetre-sized single crystals of
SrFeO_3-x, suitable for inelastic neutron scattering and other measurement
techniques requiring large sample volumes.",1208.6030v1
2012-09-18,Magneto-optical trapping of diatomic molecules,"The development of the magneto-optical trap revolutionized the fields of
atomic and quantum physics by providing a simple method for the rapid
production of ultracold, trapped atoms. A similar technique for producing a
diverse set of dense, ultracold diatomic molecular species will likewise
transform the study of strongly interacting quantum systems, precision
measurement, and physical chemistry. We demonstrate one- and two-dimensional
transverse laser cooling and magneto-optical trapping of the polar molecule
yttrium (II) oxide (YO). Using a quasicycling optical transition we observe
transverse Doppler cooling of a YO molecular beam to a temperature of 5 mK,
limited by interaction time. With the addition of an oscillating magnetic
quadrupole field we demonstrate a transverse magneto-optical trap and achieve
temperatures of 2 mK.",1209.4069v1
2012-10-12,"Layered pnictide-oxide Na$_2$Ti$_2$Pn$_2$O (Pn=As, Sb): a paradigm for spin density waves","From the first-principles calculations, we have studied the electronic and
magnetic structures of compound Na$_2$Ti$_2$Pn$_2$O (Pn = As or Sb). We find
that in the ground state Na$_2$Ti$_2$As$_2$O is a blocked checkerboard
antiferromagnetic semiconductor with a small band gap of about 0.15 eV, in
contrast, Na$_2$Ti$_2$Sb$_2$O is a bi-collinear antiferromagnetic semimetal,
both with a small moment of about 0.5$\mu_B$ around each Ti atom. We show that
there is a strong Fermi surface nesting in Na$_2$Ti$_2$Pn$_2$O. And we verify
that the blocked checkerboard and bi-collinear antiferromagnetic states both
are the spin density waves induced by the Fermi surface nesting. A tetramer
structural distortion is found in company with the formation of a blocked
checkerboard antiferromagnetic order, in good agreement with the experimentally
observed commensurate structural distortion but with space group symmetry
retained after the anomaly happening. Further analysis and discussion in
connection with experimental observations are given as well.",1210.3481v1
2012-12-02,Lateral spin injection and detection through electrodeposited Fe/GaAs contacts,"Efforts to achieve efficient injection of spin-polarized electrons into a
semiconductor, a key prerequisite for developing electronics that exploit the
electron's spin degree of freedom, have so far met with limited success. Here
we report experimental studies of lateral spin injection and detection through
electrodeposited Fe/GaAs tunnel contacts. We demonstrate spin injection
efficiencies two orders of magnitude higher than for state-of-the-art contacts
fabricated via ultra-high-vacuum methods, including those with MgO or Al2O3
tunnel barriers. To account for this enhancement, we propose that an iron oxide
layer that forms at the Fe/GaAs interface during electrodeposition, being
magnetic, acts as a tunnel barrier with a spin-dependent height, presenting
quantum spin transport calculations for such systems. This serendipitous
discovery of greatly enhanced efficiency of spin injection into GaAs via
electrodeposited contacts introduces a promising new direction for the
development of practical semiconductor spintronic devices.",1212.0258v1
2012-12-06,Quantum transport modeling of Fe/MgO/Fe magnetic tunnel junction with FeO$_{0.5}$ buffer layer: the effects of correlations,"We report \textit{ab initio} simulations of quantum transport properties of
Fe/MgO/Fe trilayer structures with FeO$_{0.5}$ buffer iron oxide layer, where
on-site Coulomb interaction is explicitly taken into account by local density
approximation + Hubbard \textit{U} approach. We show that on-site Coulomb
repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel
magnetoresistance of the system. We present an understanding of microscopic
details of this phenomenon, connecting it to localization of the Fermi
electrons of particular symmetry, which takes place in the buffer Fe-O layer,
when on-site Coulomb repulsion is introduced. We further study the possible
influence of the symmetry reduction in the buffer Fe-O layer on the transport
properties of the Fe/MgO/Fe interface.",1212.1374v1
2012-12-24,Competing Antiferromagnetic and Spin-Glass Phases in a Hollandite Structure,"We introduce a simple lattice model with Ising spins to explain recent
experimental results on spin freezing in a hollandite-type structure. We argue
that geometrical frustration of the lattice in combination with
nearest-neighbour antiferromagnetic (AFM) interactions is responsible for the
appearance of a spin-glass phase in presence of disorder. We investigate this
system numerically using parallel tempering. The model reproduces the magnetic
behaviour of oxides with hollandite structure, such as $\alpha-\text{MnO}_2$
and presents a rich phenomenology: in absence of disorder three types of ground
states are possible, depending on the relative strength of the interactions,
namely AFM ordered and two different disordered, macroscopically degenerate
families of ground states. Remarkably, for sets of AFM couplings having an AFM
ground state in the clean system, there exists a critical value of the disorder
for which the ground state is replaced by a spin-glass phase while maintaining
all couplings AFM. To the best of our knowledge this is the only existing model
that presents this kind of transition with short-range AFM interactions. We
argue that this model could be useful to understand the relation between AFM
coupling, disorder and the appearance of a spin-glass phase.",1212.5954v1
2013-01-21,The origin of the dead-layer at the La0.67Sr0.33MnO3/SrTiO3 interface and dead-layer reduction via interfacial engineering,"Transition metal oxide hetero-structure has great potential for
multifunctional devices. However, the degraded physical properties at
interface, known as dead-layer behavior, present a main obstacle for device
applications. Here we present the systematic study of the dead-layer behavior
in La0.67Sr0.33MnO3 thin film grown on SrTiO3 substrate with ozone assisted
molecular beam epitaxy. We found that the evolution of electric and magnetic
properties as a function of thickness shows a remarkable resemblance to the
phase diagram as a function of doping for bulk materials, providing compelling
evidences of the hole depletion in near interface layers that causes
dead-layer. Detailed electronic and surface structure studies indicate that the
hole depletion is due to the intrinsic oxygen vacancy formation. Furthermore,
we show that oxygen vacancies are partly caused by interfacial electric dipolar
field, and thus by doping-engineering at the single-atomic-layer level, we
demonstrate the dead-layer reduction in films with higher interfacial hole
concentration.",1301.4822v1
2013-01-24,"Superconductivity, Antiferromagnetism, and Neutron Scattering","High-temperature superconductivity in both the copper-oxide and the
iron-pnictide/chalcogenide systems occurs in close proximity to
antiferromagnetically ordered states. Neutron scattering has been an essential
technique for characterizing the spin correlations in the antiferromagnetic
phases and for demonstrating how the spin fluctuations persist in the
superconductors. While the nature of the spin correlations in the
superconductors remains controversial, the neutron scattering measurements of
magnetic excitations over broad ranges of energy and momentum transfer provide
important constraints on the theoretical options. We present an overview of the
neutron scattering work on high-temperature superconductors and discuss some of
the outstanding issues.",1301.5888v1
2013-02-05,Spin-valley lifetimes in a silicon quantum dot with tunable valley splitting,"Although silicon is a promising material for quantum computation, the
degeneracy of the conduction band minima (valleys) must be lifted with a
splitting sufficient to ensure formation of well-defined and long-lived spin
qubits. Here we demonstrate that valley separation can be accurately tuned via
electrostatic gate control in a metal-oxide-semiconductor quantum dot,
providing splittings spanning 0.3 - 0.8 meV. The splitting varies linearly with
applied electric field, with a ratio in agreement with atomistic tight-binding
predictions. We demonstrate single-shot spin readout and measure the spin
relaxation for different valley configurations and dot occupancies, finding
one-electron lifetimes exceeding 2 seconds. Spin relaxation occurs via phonon
emission due to spin-orbit coupling between the valley states, a process not
previously anticipated for silicon quantum dots. An analytical theory describes
the magnetic field dependence of the relaxation rate, including the presence of
a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings
coincide.",1302.0983v2
2013-02-10,Single Dirac-Cone State and Quantum Hall Effects in Honeycomb Structure,"A honeycomb lattice system has four types of Dirac electrons corresponding to
the spin and valley degrees of freedom. We consider a state that contains only
one type of massless electrons and three types of massive ones, which we call
the single Dirac-cone state. We analyze quantum Hall (QH) effects in this
state. We make a detailed investigation of the Chern and spin-Chern numbers. We
make clear the origin of unconventional QH effects discovered in graphene. We
also show that the single Dirac-cone state may have arbitrary large spin-Chern
numbers in magnetic field. Such a state will be generated in antiferromagnetic
transition-metal oxides under electric field or silicene with antiferromagnetic
order under electric field.",1302.2284v2
2013-04-02,Ab initio study of the TiO$_2$ Rutile(110)/Fe interface,"Adsorption of Fe on the rutile (110)-surface is investigated by means of {\it
ab initio} density functional theory calculations. We discuss the deposition of
single Fe atoms, an increasing Fe coverage, as well as the adsorption of small
Fe clusters. It is shown that the different interface structures found in
experiment can be understood in terms of the adsorption of the Fe atoms landing
first on the rutile surface. On the one hand, strong interface bonds form if
single Fe atoms are deposited. On the other hand, the Fe-Fe bonds in deposited
Fe clusters lead to a three-dimensional growth mode. Mainly ionic Fe-oxide
bonds are formed in both cases and the electronic band gap of the surface is
reduced due to interface states. Besides the structural and electronic
properties, we discuss the influence of the interface on the magnetic
properties finding stable Fe moments and induced moments within the interface
which leads to a large spin polarization of the Fe atoms at the rutile (110)/Fe
interface.",1304.0570v1
2013-04-24,Spin Resolution and Evidence for Superexchange on NiO(001) observed by Force Microscopy,"The spin order of the nickel oxide (001) surface is resolved, employing
non-contact atomic force microscopy at 4.4 K using bulk Fe- and SmCo-tips
mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The
spin-dependent signal is hardly detectable with Fe-tips. In contrast, SmCo-tips
yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips
even show a small height contrast on the O atoms of 0.5 pm within the 2x1 spin
unit cell, pointing to the observation of superexchange. We attribute this to
the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes
the magnetic moment at the apex. Atomic force spectroscopy on the Ni up, Ni
down and O lattice site reveals a magnitude of the exchange energy of merely 1
meV at the closest accessible distance with an exponential decay length of
\lambda_exc = 18 pm.",1304.6515v3
2013-04-29,Engineering Correlation Effects via Artificially Designed Oxide Superlattices,"Ab initio calculations are used to predict that a superlattice composed of
layers of LaTiO3 and LaNiO3 alternating along the [001] direction is a S=1 Mott
insulator with large magnetic moments on the Ni sites, negligible moments on
the Ti sites and a charge transfer gap set by the energy difference between Ni
d and Ti d states, distinct from conventional Mott insulators. Correlation
effects are enhanced on the Ni sites via filling the oxygen p states and
reducing the Ni-O-Ni bond angle. Small hole (electron) doping of the
superlattice leads to a two-dimensional single-band situation with holes
(electrons) residing on Ni dx2-y2 (Ti dxy) orbital and coupled to
antiferromagnetically correlated spins in the NiO2 layer.",1304.7815v1
2013-05-29,Thermal drag in spin ladders coupled to phonons,"We study the spin-phonon drag effect in the magnetothermal transport of
spin-1/2 two-leg ladders coupled to lattice degrees of freedom. Using a bond
operator description for the triplon excitations of the spin ladder and
magnetoelastic coupling to acoustic phonons, we employ the time convolutionless
projection operator method to derive expressions for the diagonal and
off-diagonal thermal conductivities of the coupled two-component triplon-phonon
system. We find that for magnetoelastic coupling strengths and diagonal
scattering rates relevant to copper-oxide spin-ladders the drag heat
conductivity can be of similar magnitude as the diagonal triplon heat
conductivity. Moreover, we show that the drag and diagonal conductivities
display very similar overall temperature dependences. Finally, the drag
conductivity is shown to be rather susceptible to external magnetic fields.",1305.6911v1
2013-06-09,Quantum nucleation of effective Minkowski spacetime in hyperbolic metamaterials based on high Tc superconductors,"We demonstrate that high Tc superconductors exhibit hyperbolic metamaterial
behavior in the far infrared and THz frequency ranges. In the THz range the
hyperbolic behavior occurs only in the normal state, while no propagating modes
exist in the superconducting state. Wave equation, which describes propagation
of extraordinary light inside a hyperbolic metamaterial exhibits 2+1
dimensional Lorentz symmetry. The role of time in the corresponding effective
3D Minkowski spacetime is played by the spatial coordinate aligned
perpendicular to the copper oxide layers. Such superconductor-based hyperbolic
metamaterials exhibit a quantum phase transition at T=0, in which the effective
Minkowski spacetime arise in the mixed state of the superconductor at some
critical value of external magnetic field. Nucleation of Minkowski spacetime
occurs via formation of quantized Abrikosov vortices, so that these vortices
play the role of effective Minkowski spacetime quanta.",1306.1975v2
2013-07-02,Non-volatile ferroelastic switching of the Verwey transition and resistivity of epitaxial Fe3O4/PMN-PT (011),"A central goal of electronics based on correlated materials or 'Mottronics'
is the ability to switch between distinct collective states with a control
voltage. Small changes in structure and charge density near a transition can
tip the balance between competing phases, leading to dramatic changes in
electronic and magnetic properties. In this work, we demonstrate that an
electric field induced two-step ferroelastic switching pathway in (011)
oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates can be used to
tune the Verwey metal-insulator transition in epitaxial Fe3O4 films in a stable
and reversible manner. We also observe robust non-volatile resistance switching
in Fe3O4 up to room temperature, driven by ferroelastic strain. These results
provides a framework for realizing non-volatile and reversible tuning of order
parameters coupled to lattice-strain in epitaxial oxide heterostructures over a
broad range of temperatures, with potential device applications.",1307.0838v1
2013-07-17,Growth modes of nanoparticle superlattice thin films,"We report about the fabrication and characterization of iron oxide
nanoparticle thin film superlattices. The formation into different film
morphologies is controlled by tuning the particle plus solvent-to-substrate
interaction. It turns out that the wetting vs. dewetting properties of the
solvent before the self-assembly process during solvent evaporation plays a
major role to determine the resulting film morphology. In addition to layerwise
growth also three-dimensional mesocrystalline growth is evidenced. The
understanding of the mechanisms ruling nanoparticle self-assembly represents an
important step toward the fabrication of novel materials with tailored optical,
magnetic or electrical transport properties.",1307.4693v4
2013-11-05,Mixed valency and site-preference chemistry for Cerium and its compounds: A predictive DFT study,"Cerium and its technologically relevant compounds are examples of anomalous
mixed valency, originating from two competing oxidation states -- itinerant
Ce$^{3+}$ and localized Ce$^{4+}$. Under applied stress, anomalous transitions
are observed but not well understood. Here we treat mixed valency as an ""alloy""
involving two valences with competing and numerous site-occupancy
configurations, and we use density functional theory with Hubbard U ($i.e.$,
DFT+U) to evaluate the effective valence and predict properties, including
controlling valence by pseudo-ternary alloying. For Ce and its compounds, such
as (Ce-La)$_2$(Fe-Co)$_{14}$B permanent magnets, we find a stable mixed-valent
$\alpha$-state near the spectroscopic value of $\nu_s=3.53$. Ce valency in
compounds depends on its steric volume and local chemistry; for La doping,
Ce-valency shifts towards $\gamma$-like Ce$^{3+}$, as expected from steric
volume; for Co doping, valency depends on local Ce-site chemistry and steric
volume. Our approach captures the key origins of anomalous valency and
site-preference chemistry in complex compounds.",1311.0962v1
2013-11-07,Imaging the Nanoscale Band Structure of Topological Sb,"Many promising building blocks of future electronic technology - including
non-stoichiometric compounds, strongly correlated oxides, and strained or
patterned films - are inhomogeneous on the nanometer length scale. Exploiting
the inhomogeneity of such materials to design next-generation nanodevices
requires a band structure probe with nanoscale spatial resolution. To address
this demand, we report the first simultaneous observation and quantitative
reconciliation of two candidate probes - Landau level spectroscopy and
quasiparticle interference imaging - which we employ here to reconstruct the
multi-component surface state band structure of the topological semimetal
antimony(Sb). We thus establish the technique of band structure tunneling
microscopy (BSTM), whose unique advantages include nanoscale access to
non-rigid band structure deformation, empty state dispersion, and magnetic
field dependent states. We use BSTM to elucidate the relationship between bulk
conductivity and surface state robustness in topological materials, and to
quantify essential metrics for spintronics applications.",1311.1758v1
2013-11-13,A new route to spin-orbit torque engineering via oxygen manipulation,"Spin transfer torques allow for electrical manipulation of magnetization at
room temperature, which is utilized to build future electronic devices such as
spin transfer torque memories. Recent experiments have discovered that the
combination of the spin transfer torque with the spin Hall effect enables more
efficient manipulation. A versatile control mechanism of such spin-orbit
torques is beneficial to envision device applications with competitive
advantages over the existing schemes. Here we report that the oxidation
manipulation of spin-orbit torque devices triggers a new mechanism, and the
resulting torques are estimated to be about two times stronger than that of the
spin Hall effect. Our result introduces an entirely new way to engineer the
spin-orbit torques for device operation via oxygen manipulation. Combined with
electrical gating for the control of the oxygen content, our finding may also
pave the way for towards reconfigurable logic devices.",1311.3032v1
2013-11-20,Electron Correlation in Oxygen Vacancy in SrTiO$_3$,"Oxygen vacancies are an important type of defect in transition metal oxides.
In SrTiO$_3$ they are believed to be the main donors in an otherwise intrinsic
crystal. At the same time, a relatively deep gap state associated with the
vacancy is widely reported. To explain this inconsistency we investigate the
effect of electron correlation in an oxygen vacancy (OV) in SrTiO$_3$. When
taking correlation into account, we find that the OV-induced localized level
can at most trap one electron, while the second electron occupies the
conduction band. Our results offer a natural explanation of how the OV in
SrTiO$_3$ can produce a deep in-gap level (about 1 eV below the conduction band
bottom) in photoemission, and at the same time be an electron donor. Our
analysis implies an OV in SrTiO$_3$ should be fundamentally regarded as a
magnetic impurity, whose deep level is always partially occupied due to the
strong Coulomb repulsion. An OV-based Anderson impurity model is derived, and
its implications are discussed.",1311.5160v1
2013-11-23,Thirty Femtograms Detection of Iron in Mammalian Cells,"Inorganic nanomaterials and particles with enhanced optical, mechanical or
magnetic attributes are currently being developed for a wide range of
applications. Safety issues have been formulated however concerning their
potential cyto- and genotoxicity. For in vivo and in vitro experimentations,
recent developments have heightened the need of simple and facile methods to
measure the amount of nanoparticles taken up by cells or tissues. In this work,
we present a rapid and highly sensitive method for quantifying the uptake of
iron oxide nanoparticles in mammalian cells. Our approach exploits the
digestion of incubated cells with concentrated hydrochloric acid reactant and a
colorimetric based UV-Visible absorption technique. The technique allows the
detection of iron in cells over 4 decades in masses, from 0.03 to 300 picograms
per cell. Applied on particles of different surface chemistry and sizes, the
protocol demonstrates that the coating is the key parameter in the
nanoparticle/cell interactions. The data are corroborated by scanning and
transmission electron microscopy and stress the importance of resiliently
adsorbed nanoparticles at the plasma membrane.",1311.6019v1
2013-12-05,p-Type Zinc Oxide Spinels: Application to Transparent Conductors and Spintronics,"We report on the electronic and optical properties of two theoretically
predicted stable spinel compounds of the form ZnB2O4, where B = Ni or Cu;
neither compound has been previously synthesized, so we compare them to the
previously studied p-type ZnCo2O4 spinel. These new materials exhibit spin
polarization that is ideal for spintronics applications, and broad conductivity
maxima near the valence band edge that facilitate p-type dopability. We show
that 3d electrons on the octahedrally coordinated Zn atom fall deep within the
valence band and do not contribute significantly to the electronic structure of
the material, while the O 2p and tetrahedrally coordinated B 3d electrons
hybridize broadly in the shallow valence states, resulting in increasing
curvature (i.e., decreased electron effective mass) of valence bands near the
band edge. In particular, ZnCu2O4 exhibits high electrical conductivities near
the valence band edge that, at sigma = 2 x 10^4 S/cm, are twice the maximum
found for ZnCo2O4, a previously synthesized compound in this class of
materials. This material also exhibits ferromagnetism in all of its most stable
structures, which makes it a good candidate for further study as a dilute
magnetic semiconductor.",1312.1728v1
2014-02-05,First-Principles Study of the Honeycomb-Lattice Iridates Na2IrO3 in the Presence of Strong Spin-Orbit Interaction and Electron Correlations,"An effective low-energy Hamiltonian of itinerant electrons for iridium oxide
Na2IrO3 is derived by an ab initio downfolding scheme. The model is then
reduced to an effective spin model on a honeycomb lattice by the strong
coupling expansion. Here we show that the ab initio model contains spin-spin
anisotropic exchange terms in addition to the extensively studied Kitaev and
Heisenberg exchange interactions, and allows to describe the experimentally
observed zigzag magnetic order, interpreted as the state stabilized by the
antiferromagnetic coupling of the ferromagnetic chains. We clarify possible
routes to realize quantum spin liquids from existing Na2IrO3.",1402.1030v2
2014-02-12,Refinement of Nb3Sn grain size by the generation of ZrO2 precipitates in Nb3Sn wires,"In this letter we demonstrate that if oxygen can be properly supplied to
(Nb-Zr)-Sn wires, ZrO2 precipitates will form during the heat treatment,
refining the Nb3Sn grain size markedly. Here, a Nb3Sn subelement was fabricated
in which Nb-1Zr alloy was used, and oxygen was supplied via SnO2 powder. The
results showed that such a design could supply sufficient oxygen to internally
oxidize the Zr in the Nb-1Zr alloy, and that the sample reacted at 650 {\deg}C
had grain sizes of ~45 nm, less than half the size of the grains in present
Nb3Sn conductors. Magnetic measurements showed that the peak of the pinning
force vs. field (Fp-B) curve was shifted to ~0.3Birr (the irreversibility
field).",1402.3001v2
2014-04-07,Structural insight into $Co_{3-x}Mn_xTeO_6$; ($0 \lt x \le 2$) solid solutions using Synchrotron X-ray diffraction and XANES,"Structural investigation on $Co_{3-x}Mn_xTeO_6$; ($0 \lt x \le 2$) solid
solutions as a function of Mn concentration using Synchrotron X-ray diffraction
(SXRD) and XANES measurements are presented. Phase diagram obtained from
Rietveld Refinement on SXRD data as a function of Mn concentration indicates
doping disproportionate mixing of both monoclinic (C2/c) and rhombohedral (R-3)
structure (for $x \lt 0.5$) while only R-3 symmetry for $x \ge 0.5$.
Furthermore, Rietveld analysis on SXRD data shows increase in lattice
parameters and average transition metal oxygen (Co/Mn-O) bond lengths for $x
\ge 0.5$. Co and Mn K-edge XANES spectra reveal that both Co and Mn are in
mixed oxidation state of $Co^{2+}/Mn^{2+}$ and $Co^{3+}/Mn^{3+}$. Relative
ratio of $Co^{3+}/Co^{2+}$ and $Mn^{3+}/Mn^{2+}$ using Linear combination fit
(LCF) decrease with increasing $x$ for $x \ge 0.5$. These structural and
spectroscopic evidences are used to provide possible interpretation of the
reported observations of maximum Neel Temperature (TN) at $x ~\sim 0.5$ and
enhancements of antiferro/ferro-magnetic interactions in $Co_{3-x}Mn_xTeO_6$
solid solutions.",1404.1666v1
2014-06-12,Tube filling technique influence on superconductivity in MgB2-based conductors prepared using laboratory made boron,"Here we report a systematic study of superconductive properties of
mono-filamentary MgB2-based wires, manufactured with different filling
technique. A detailed comparison of the influence of filling technique and
final heat treatment on superconducting properties has been given. Boron used
was synthesized in laboratory following magnesiothermic reduction of boron
oxide, purified thanks to several acid leaching and heat treated at high
temperature, to enhance crystalline degree. Critical current density and
critical temperature have been investigated at different synthesis/sintering
temperature in order to evaluate their dependence to applied final heat
treatment. Critical current density has been evaluated on short wire pieces by
magnetic measurement in a MPMS 5.5T Quantum Design SQUID, while critical
temperature has been measured with a four probe system, by the drop of
resistivity during the cooling of the sample in a liquid helium dewar.",1407.2111v1
2014-07-24,Extraordinary Tunability of the Superexchange Interactions in Nanoparticles of the Multiferroic 0.50BiFeO3-0.50PbTiO3,"The coexistence and coupling of magnetic and ferroelectric orderings in
single phase multiferroics has evinced enormous scientific interest as it
involves breaking of time reversal and space inversion symmetries in the same
material. The mutual controllability of the two diverse orderings in
multiferroics has potential for developing new generation multifunctional
sensor, actuator and data storage devices. We present here evidence for a new
exotic facet of multiferroicity, whereby one can raise the strength of
antiferromagnetic (AFM) superexchange interaction and hence tune the N\'eel
temperature (TN) from ~120K in bulk to ~350K in 18nm size particles by tuning
the ferroelectric distortion in the tetragonal phase of multiferroic
(1-x)BiFeO3 -xPbTiO3 solid solutions . This observation is unique to
multiferroics only as the TN in non-multiferroic AFM oxides decreases with
particle size. Our results provide a scientific basis for designing room
temperature single phase multiferroics, useful for making multifunctional
device operating at room temperature.",1407.6485v1
2014-09-30,"Coupling and Electrical Control of Structural, Orbital and Magnetic Orders in Perovskites","Perovskite oxides are already widely used in industry and have huge potential
for novel device applications thanks to the rich physical behaviour displayed
in these materials. The key to the functional electronic properties exhibited
by perovskites is often the so-called Jahn-Teller distortion. For applications,
an electrical control of the Jahn-Teller distortions, which is so far out of
reach, would therefore be highly desirable. Based on universal symmetry
arguments, we determine new lattice mode couplings that can provide exactly
this paradigm, and exemplify the effect from first-principles calculations. The
proposed mechanism is completely general, however for illustrative purposes, we
demonstrate the concept on vanadium based perovskites where we reveal an
unprecedented orbital ordering and Jahn-Teller induced ferroelectricity. Thanks
to the intimate coupling between Jahn-Teller distortions and electronic degrees
of freedom, the electric field control of Jahn-Teller distortions is of general
relevance and may find broad interest in various functional devices.",1409.8422v1
2014-10-07,Decoding Spatial Complexity in Strongly Correlated Electronic Systems,"Inside the metals, semiconductors, and magnets of our everyday experience,
electrons are uniformly distributed throughout the material. By contrast,
electrons often form clumpy patterns inside of strongly correlated electronic
systems (SCES) such as colossal magnetoresistance materials and high
temperature superconductors. In copper-oxide based high temperature
superconductors, scanning tunneling microscopy (STM) has detected an electron
nematic on the surface of the material, in which the electrons form nanoscale
structures which break the rotational symmetry of the host crystal. These
structures may hold the key to unlocking the mystery of high temperature
superconductivity in these materials, but only if the nematic also exists
throughout the entire bulk of the material. Using newly developed methods for
decoding these surface structures, we find that the nematic indeed persists
throughout the bulk of the material. We furthermore find that the intricate
pattern formation is set by a delicate balance among disorder, interactions,
and material anisotropy, leading to a fractal nature of the cluster pattern.
The methods we have developed can be extended to many other surface probes and
materials, enabling surface probes to determine whether surface structures are
confined only to the surface, or whether they extend throughout the material.",1410.1787v1
2014-11-06,Facetted growth of Fe3Si shells around GaAs nanowires on Si(111),"GaAs nanowires and GaAs/Fe3Si core/shell nanowire structures were grown by
molecular-beam epitaxy on oxidized Si(111) substrates and characterized by
transmission electron microscopy. The surfaces of the original GaAs NWs are
completely covered by magnetic Fe3Si exhibiting nanofacets and an enhanced
surface roughness compared to the bare GaAs NWs. Shell growth at a substrate
temperature of T{S} = 200 {\deg}C leads to regular nanofacetted Fe3Si shells.
These facets, which lead to thickness inhomogeneities of the shells, consist
mainly of well pronounced Fe3Si(111) planes. The crystallographic orientation
of core and shell coincide, i.e. they are pseudomorphic. The nanofacetted Fe3Si
shells found in the present work are probably the result of the Vollmer-Weber
island growth mode of Fe3Si on the {110} side facets of the GaAs NWs.",1411.1556v2
2014-11-07,Numerical evidence of quantum melting of spin ice: quantum-classical crossover,"Unbiased quantum Monte-Carlo simulations are performed on the
nearest-neighbor spin-$\frac{1}{2}$ pyrochlore XXZ model with an
antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange
couplings, $J$ and $J_\perp$. The specific heat exhibits a broad peak at
$T_{\mathrm{CSI}}\sim0.2J$ associated with a crossover to a classical Coulomb
liquid regime showing a suppressed spin-ice monopole density, a broadened
pinch-point singularity, and the Pauling entropy for $|J_\perp|\ll J$, as in
classical spin ice. On further cooling, the entropy restarts decaying for
$J_\perp>J_{\perp c}\sim-0.104J$, producing another broad specific heat peak
for a crossover to a bosonic quantum Coulomb liquid, where the spin correlation
contains both photon and quantum spin-ice monopole contributions. With
negatively increasing $J_\perp$ across $J_{\perp c}$, a first-order thermal
phase transition occurs from the quantum Coulomb liquid to an XY ferromagnet.
Relevance to magnetic rare-earth pyrochlore oxides is discussed.",1411.1918v3
2015-01-21,Large exchange bias in polycrystalline MnN/CoFe bilayers at room temperature,"We report on the new polycrystalline exchange bias system MnN/CoFe, which
shows exchange bias of up to 1800Oe at room temperature with a coercive field
around 600Oe. The room temperature values of the interfacial exchange energy
and the effective uniaxial anisotropy are estimated to be $J_\mathrm{eff} =
0.41\,\mathrm{mJ}/\mathrm{m}^2$ and $K_\mathrm{eff} =
37\,\mathrm{kJ}\,/\,\mathrm{m}^3$. The thermal stability was found to be
tunable by controlling the nitrogen content of the MnN. The maximum blocking
temperature exceeds $325^\circ$C, however the median blocking temperature in
the limit of thick MnN is $160^\circ$C. Good oxidation stability through
self-passivation was observed, enabling the use of MnN in lithographically
defined microstructures. As a proof-of-principle we demonstrate a simple GMR
stack exchange biased with MnN, which shows clear separation between parallel
and antiparallel magnetic states. These properties come along with a
surprisingly simple manufacturing process for the MnN films.",1501.05162v2
2015-02-24,"Electro-mechanical properties of REBCO coated conductors from various industrial manufacturers at 77 K, self-field and 4.2 K, 19 T","Rare-earth-barium-copper-oxide (REBCO) tapes are now available from several
industrial manufacturers and are very promising conductors in high field
applications. Due to diverging materials and deposition processes, these
manufacturers' tapes can be expected to differ in their electro-mechanical and
mechanical properties. For magnets designers, these are together with the
conductors' in-field critical current performance of the highest importance in
choosing a suitable conductor. In this work, the strain and stress dependence
of the current carrying capabilities as well as the stress and strain
correlation are investigated for commercial coated conductors from Bruker HTS,
Fujikura, SuNAM, SuperOx and SuperPower at 77 K, self-field and 4.2 K, 19 T.",1502.06713v1
2015-02-24,High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent Annealing,"We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG)
by annealing in oxygen atmosphere. Our findings show that well below the
melting temperature the material transforms into a fully epitaxial layer with
exceptional quality, both structural and magnetic.\\ In ferromagnetic resonance
(FMR) ultra low damping and extremely narrow linewidth can be observed. For a
56 nm thick layer a damping constant of
$\alpha$=(6.63$\pm$1.50)$\cdot$10$^{-5}$ is found and the linewidth at 9.6 GHz
is as small as 1.30$\pm$0.05 Oe which are the lowest values for PLD grown thin
films reported so far. Even for a 20 nm thick layer a damping constant of
$\alpha$=(7.51$\pm$1.40)$\cdot$10$^{-5}$ is found which is the lowest value for
ultrathin films published so far. The FMR linewidth in this case is
3.49$\pm$0.10 Oe at 9.6 GHz. Our results not only present a method of
depositing thin film YIG of unprecedented quality but also open up new options
for the fabrication of thin film complex oxides or even other crystalline
materials.",1502.06724v2
2015-02-26,Inhomogeneous multi-carrier superconductivity at LaXO3/SrTiO3 (X=Al or Ti) oxide interfaces,"Several experiments reveal the inhomogeneous character of the superconducting
state that occurs when the carrier density of the two-dimensional electron gas
formed at the LaXO3/SrTiO3 (X=Al or Ti) interface is tuned above a threshold
value by means of gating. Re-analyzing previous measurements, that highlight
the presence of two kinds of carriers, with low and high mobility, we shall
provide a description of multi-carrier magneto-transport in an inhomogeneous
two-dimensional electron gas, gaining insight into the properties of the
physics of the systems under investigation. We shall then show that the
measured resistance, superfluid density, and tunneling spectra result from the
percolative connection of superconducting ""puddles"" with randomly distributed
critical temperatures, embedded in a weakly localizing metallic matrix. We
shall also show that this scenario is consistent with the characteristics of
the superconductor-to-metal transition driven by a magnetic field. A
multi-carrier description of the superconducting state, within a weak-coupling
BCS-like model, will be finally discussed.",1502.07572v1
2015-04-06,Probing the electron-phonon interaction in correlated systems with coherent lattice fluctuation spectroscopy,"Tailoring the properties of correlated oxides is accomplished by chemical
doping, pressure, temperature or magnetic field. Photoexcitation is a valid
alternative to reach out-of-equilibrium states otherwise inaccessible. Here, we
quantitatively estimate the coupling between a lattice distortion and the
charge-transfer excitation in (La$_2$CuO$_{4+\delta}$). We photoinduce a
coherent La ion vibration and monitor the response of the optical constants in
a broad energy range, providing quantitative information on the electron-phonon
matrix element that can be compared to theoretical models. We propose the same
methodology to probe electron-electron interactions in other materials.",1504.02760v1
2015-07-06,Quantum Oscillations in Hole-Doped Cuprates,"One of the leading challenges of condensed matter physics in the past few
decades in an understanding of the high-temperature copper-oxide
superconductors. While the d-wave character of the superconducting state is
well understood, the normal state in the underdoped regime has eluded
understanding. Here we review the past few years of quantum oscillation
measurements performed in the underdoped cuprates that have culminated in an
understanding of the normal ground state of these materials. A nodal electron
pocket created by charge order is found to characterise the normal ground state
in YBa2Cu3O6+x and is likely universal to a majority of the cuprate
superconductors. An open question remains regarding the origin of the
suppression of the antinodal density of states at the Fermi energy in the
underdoped normal state, either from mainly charge correlations, or more
likely, from mainly pairing and / or magnetic correlations that precede charge
order.",1507.01315v1
2015-07-07,Chemical modification of silicene,"Silicene is a two-dimensional material, which is composed of a single layer
of silicon atoms with sp2-sp3 mixed hybridization. The sp2-sp3 mixed
hybridization renders silicene excellent reactive ability, facilitating the
chemical modification of silicene. It has been demonstrated that chemical
modification effectively enables the tuning of the properties of silicene. We
now review all kind of chemical modification methods for silicene including
hydrogenation, halogenation, organic surface modification, oxidation, doping
and alloying. The effects of these chemical modification methods on the
geometrical, electronic, optical and magnetic properties of silicene are
discussed. The potential applications of chemically modified silicene in a
variety of fields such as electronics, optoelectronics and magnetoelectronics
are introduced. We finally envision future work on the chemical modification of
silicene for the sake of further advancing the development of silicene.",1507.01658v1
2015-07-09,Casimir and van der Waals forces: Advances and problems,"We review modern achievements and problems in physics of the van der Waals
and Casimir forces which arise due to zero-point and thermal fluctuations of
the electromagnetic field between closely spaced material surfaces. This
subject attracted great experimental and theoretical attention during the last
few years because the fluctuation-induced forces find a lot of applications in
both fundamental physics and nanotechnology. After a short introduction to the
subject, we describe main experimental and theoretical results obtained in the
field during the last fifteen years. In the following presentation, we discuss
some of the recent results by the authors and their collaborators which are of
high promise for future developments. Specifically, we consider new features of
the Casimir force acting between a gold sphere and an indium tin oxide plate,
present the experimental and theoretical results on measuring the Casimir
interaction between two gold surfaces by means of dynamic atomic force
microscope, and outline first measurements of the Casimir interaction between
magnetic surfaces and related theory. Special attention is devoted to the
Casimir effect for graphene, which is the prospective material for
microelectromechanical devices of next generations.",1507.02393v1
2015-08-01,Exchange-driven spin relaxation in ferromagnet/oxide/semiconductor heterostructures,"We investigate electron spin relaxation in GaAs in the proximity of a Fe/MgO
layer using spin-resolved optical pump-probe spectroscopy, revealing a strong
dependence of the spin relaxation time on the strength of an exchange-driven
hyperfine field. The temperature dependence of this effect reveals a strong
correlation with carrier freeze out, implying that at low temperatures the free
carrier spin lifetime is dominated by inhomogeneity in the local hyperfine
field due to carrier localization. This result resolves a long-standing and
contentious question of the origin of the spin relaxation in GaAs at low
temperature when a magnetic field is present. Further, this improved
fundamental understanding paves the way for future experiments exploring the
time-dependent exchange interaction at the ferromagnet/semiconductor interface
and its impact on spin dissipation and transport in the regime of
dynamically-driven spin pumping.",1508.00164v1
2015-08-03,Theory of Valence Transition in BiNiO$_3$,"Motivated by the colossal negative thermal expansion recently found in
BiNiO$_3$, the valence transition accompanied by the charge transfer between
the Bi and Ni sites is theoretically studied. We introduce an effective model
for Bi-$6s$ and Ni-$3d$ orbitals with taking into account the valence skipping
of Bi cations, and investigate the ground-state and finite-temperature phase
diagrams within the mean-field approximation. We find that the valence
transition is caused by commensurate locking of the electron filling in each
orbital associated with charge and magnetic orderings, and the critical
temperature and the nature of the transitions are strongly affected by the
relative energy between the Bi and Ni levels and the effective
electron-electron interaction in the Bi sites. The obtained phase diagram well
explains the temperature- and pressure-driven valence transitions in BiNiO$_3$
and the systematic variation of valence states for a series of Bi and Pb
perovskite oxides.",1508.00296v1
2015-10-09,Better Band Gaps with Asymptotically Corrected Local Exchange Potentials,"We formulate a spin-polarized van Leeuwen and Baerends (vLB) correction to
the local density approximation (LDA) exchange potential [Phys. Rev. A 49, 2421
(1994)] that enforces the ionization potential (IP) theorem following Stein et
al. [Phys. Rev. Lett. 105, 266802 (2010)]. For electronic-structure problems,
the vLB-correction replicates the behavior of exact-exchange potentials, with
improved scaling and well-behaved asymptotics, but with the computational cost
of semi-local functionals. The vLB+IP corrections produces large improvement in
the eigenvalues over that from LDA due to correct asympotic behavior and atomic
shell structures, as shown on rare-gas, alkaline-earth, zinc-based oxides,
alkali-halides, sulphides, and nitrides. In half-Heusler alloys, this
asymptotically-corrected LDA reproduces the spin-polarized properties
correctly, including magnetism and half-metallicity. We also considered
finite-sized systems [e.g., ringed boron-nitirde (B$_{12}$N$_{12}$) and
graphene (C$_{24}$)] to emphasize the wide applicability of the method.",1510.02688v3
2015-10-26,Spin-dependent transport properties of a GaMnAs-based vertical spin metal-oxide- semiconductor field-effect transistor structure,"We fabricate a vertical spin metal-oxide-semiconductor field-effect
transistor (spin-MOSFET) structure, which is composed of an epitaxial
single-crystal heterostructure with a ferromagnetic-semiconductor GaMnAs
source/drain, and investigate its spin-dependent transport properties. We
modulate the drain-source current IDS by ~+ or -0.5 % with a gate-source
voltage of + or -10.8 V and also modulate IDS by up to 60 % with changing the
magnetization configuration of the GaMnAs source/drain at 3.5 K. The
magnetoresistance ratio is more than two orders of magnitude higher than that
obtained in the previous studies on spin MOSFETs. Our result shows that a
vertical structure is one of the hopeful candidates for spin MOSFET when the
device size is reduced to a sub-micron or nanometer scale.",1510.07497v1
2015-10-31,Controlled formation of high-mobility shallow electron gases in SrTiO3 single crystal,"We report controlled formation of sub-100 nm-thin electron channels in
SrTiO$_3$ by doping with oxygen vacancies induced by Ar$^+$-ion irradiation.
The conducting channels exhibit a consistent high electron mobility (~15,000
cm$^2$V$^{-1}$s$^{-1}$), which enables clear observation of magnetic quantum
oscillations, and gate-tunable linear magnetoresistance. Near the onset of
electrical conduction, the metal-insulator transition is induced by the
mobility suppression. With the high electron mobility and the ease of
controlled channel formation, this ion-irradiation doping method may provide an
excellent basis for developing oxide electronics.",1511.00093v1
2015-11-22,Passively Q-switched EDFL using Fe3O4-nanoparticle saturable absorber,"We experimentally demonstrate a passively Q-switched erbium-doped fiber laser
(EDFL) operation by using a saturable absorber based on Fe3O4 nanoparticles
(FONP) in magnetic fluid (MF). As a kind of transition metal oxide, the FONP
has a large nonlinear optical response with a fast response time for saturable
absorber. By depositing MF at the end of optical fiber ferrule, we fabricated a
FONP-based saturable absorber, which enables a strong light-matter interaction
owing to the confined transmitted optical field within the single mode fiber.
Because of large third-order optical nonlinearities of FONP-based saturable
absorber, large modulation depth of 8.2% and non saturable absorption of 56.6%
are demonstrated. As a result, stable passively Q-switched EDFL pulses with
maximum output pulse energy of 23.76 nJ, repetition rate of 33.3 kHz, and pulse
width of 3.2 {\mu}s are achieved when the input pump power is 110 mW at the
wavelength of 980 nm. The laser features a low threshold pump power of ~15 mW.",1511.07016v1
2015-11-23,Direct probing of the Mott crossover in the SU($N$) Fermi-Hubbard model,"The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter
theory. Developed for interacting electrons in solids, which typically exhibit
SU($2$) symmetry, it describes a wide range of phenomena, such as metal to
insulator transitions and magnetic order. Its generalized SU($N$)-symmetric
form, originally applied to multi-orbital materials such as transition-metal
oxides, has recently attracted much interest owing to the availability of
ultracold SU($N$)-symmetric atomic gases. Here we report on a detailed
experimental investigation of the SU($N$)-symmetric FHM using local probing of
an atomic gas of ytterbium in an optical lattice to determine the equation of
state through different interaction regimes. We prepare a low-temperature
SU($N$)-symmetric Mott insulator and characterize the Mott crossover,
representing important steps towards probing predicted novel SU($N$)-magnetic
phases.",1511.07287v1
2016-03-03,Unconventional electron states in $δ$-doped SmTiO$_3$,"The Mott-insulating distorted perovskite SmTiO$_3$, doped with a single SrO
layer in a quantum-well architecture is studied by the combination of density
functional theory with dynamical mean-field theory. A rich correlated
electronic structure in line with recent experimental investigations is
revealed by the given realistic many-body approach to a large-unit-cell oxide
heterostructure. Coexistence of conducting and Mott-insulating TiO$_2$ layers
prone to magnetic order gives rise to multi-orbital electronic transport beyond
standard Fermi-liquid theory. First hints towards a pseudogap opening due to
electron-electron scattering within a background of ferromagnetic and
antiferromagnetic fluctuations are detected.",1603.01031v4
2016-03-10,Engineering charge ordering into multiferroicity,"Multiferroic materials have attracted great interests but are rare in nature.
In many transitional metal oxides, charge ordering and magnetic ordering
coexist, so that a method of engineering charge-ordered materials into
ferroelectric materials would lead to a large class of multiferroic materials.
We propose a strategy for designing new ferroelectric or even multiferroic
materials by inserting a spacing layer into each two layers of charge-ordered
materials and artificially making a superlattice. One example of the model
demonstrated here is the perovskite (LaFeO$_3$)$_2$/LaTiO$_3$ (111)
superlattice, in which the LaTiO$_3$ layer acts as the donor and the spacing
layer, and the LaFeO$_3$ layer is half doped and performs charge ordering. The
collaboration of the charge ordering and the spacing layer breaks the space
inversion symmetry, resulting in a large ferroelectric polarization. As the
charge ordering also leads to a ferrimagnetic structure, the
(LaFeO$_3$)$_2$/LaTiO$_3$ is multiferroic. It is expected that this work can
encourage the designing and experimentally implementation of a large class of
multiferroic structures with novel properties.",1603.03253v1
2016-03-30,Quantum Monte Carlo analysis of a charge ordered insulating antiferromagnet: the Ti$_4$O$_7$ Magnéli phase,"The Magn\'eli phase Ti$_4$O$_7$ is an important transition metal oxide with a
wide range of applications because of its interplay between charge, spin, and
lattice degrees of freedom. At low temperatures, it has non-trivial magnetic
states very close in energy, driven by electronic exchange and correlation
interactions. We have examined three low-lying states, one ferromagnetic and
two antiferromagnetic, and calculated their energies as well as Ti spin moment
distributions using highly accurate Quantum Monte Carlo methods. We compare our
results to those obtained from density functional theory-based methods that
include approximate corrections for exchange and correlation. Our results
confirm the nature of the states and their ordering in energy, as compared with
density-functional theory methods. However, the energy differences and spin
distributions differ. A detailed analysis suggests that non-local
exchange-correlation functionals, in addition to other approximations such as
LDA+U to account for correlations, are needed to simultaneously obtain better
estimates for spin moments, distributions, energy differences and energy gaps.",1603.09367v2
2016-04-25,Quantitative determination of bond order and lattice distortions in nickel oxide heterostructures by resonant x-ray scattering,"We present a combined study of Ni $K$-edge resonant x-ray scattering and
density functional calculations to probe and distinguish electronically driven
ordering and lattice distortions in nickelate heterostructures. We demonstrate
that due to the low crystal symmetry, contributions from structural distortions
can contribute significantly to the energy-dependent Bragg peak intensities of
a bond-ordered NdNiO$_3$ reference film. For a LaNiO$_3$-LaAlO$_3$ superlattice
that exhibits magnetic order, we establish a rigorous upper bound on the
bond-order parameter. We thus conclusively confirm predictions of a dominant
spin density wave order parameter in metallic nickelates with a
quasi-two-dimensional electronic structure.",1604.07317v1
2016-06-06,New perspectives in the ultrafast spectroscopy of many-body excitations in correlated materials,"Ultrafast spectroscopies constitute a fundamental tool to investigate the
dynamics of non-equilibrium many-body states in correlated materials.
Two-pulses (pump-probe) experiments have shed new light on the interplay
between high-energy electronic excitations and the emerging low-energy
properties, such as superconductivity and charge-order, in many interesting
materials. Here we will review some recent results on copper oxides and we will
propose the use of high-resolution multi-dimensional techniques to investigate
the decoherence processes of optical excitations in these systems. This novel
piece of information is expected to open a new route toward the understanding
of the fundamental interactions that lead to the exotic electronic and magnetic
properties of correlated materials.",1606.01702v1
2016-06-21,Instability of insulators near quantum phase transitions,"Thin films of Amorphous indium oxide undergo a magnetic field driven
superconducting to insulator quantum phase transition. In the insulating phase,
the current-voltage characteristics show large current discontinuities due to
overheating of electrons. We show that the onset voltage for the
discontinuities vanishes as we approach the quantum critical point.
  As a result the insulating phase becomes unstable with respect to any applied
voltage making it, at least experimentally, immeasurable.
  We emphasize that unlike previous reports of the absence of linear response
near quantum phase transitions, in our system, the departure from equilibrium
is discontinuous. Because the conditions for these discontinuities are
satisfied in most insulators at low temperatures, and due to the decay of all
characteristic energy scales near quantum phase transitions, we believe that
this instability is general and should occur in various systems while
approaching their quantum critical point. Accounting for this instability is
crucial for determining the critical behavior of systems near the transition.",1606.06606v2
2016-06-24,Spin glass state and enhanced spiral phase in doped delafossite oxide CuCrO2,"In this work, we study the doping effects on the magnetic states of CuCrO2
based on the classical frustrated spin model [Lin et al., Phys. Rev. B 89,
220405(R) (2014)]. Several experimental observations can be well reproduced by
the Monte Carlo simulations of the modified spin models. Our work suggests that
the disorder induced by V/Al doping cooperated with the frustration in the
system may contribute to the emergence of the spin glass state. Furthermore,
the hole-doping by Mg2+ substituting Cr3+ enhances the quantum fluctuations and
bond disorder which modulate the biquadratic exchanges, and in turn results in
the promotion of the spiral phase, consistent with the experimental report.",1606.07854v1
2016-06-29,Physics of ultrathin films and heterostructures of rare earth nickelates,"The electronic structure of transition metal oxides featuring correlated
electrons can be rationalized within the Zaanen-Sawatzky-Allen framework.
Following a brief description of the present paradigms of electronic behavior,
we focus on the physics of rare earth nickelates as an archetype of complexity
emerging within the charge transfer regime. The intriguing prospect of
realizing the physics of high $T_c$ cuprates through heterostructuring resulted
in a massive endeavor to epitaxially stabilize these materials in ultra-thin
form. A plethora of new phenomena unfolded in such artificial structures due to
the effect of epitaxial strain, quantum confinement, and interfacial charge
transfer. Here we review the present status of artificial rare-earth nickelates
in an effort to uncover the interconnection between the electronic and magnetic
behavior and the underlying crystal structure. We conclude by discussing future
directions to disentangle the puzzle regarding the origin of the
metal-insulator transition, the role of oxygen holes, and the true nature of
the antiferromagnetic spin configuration in the ultra-thin limit.",1606.09291v1
2016-07-05,Effects of intense optical phonon pumping on the structure and electronic properties of yttrium barium copper oxide,"We investigate the structural modulations induced by optical excitation of a
polar phonon mode in YBa$_2$Cu$_3$O$_7$, using first-principles calculations
based on density functional theory. We focus on the intense-excitation regime
in which we expect that fourth-order phonon-phonon coupling terms dominate, and
model the structural modulations induced by pulses of such intensity. Our
calculations of the phonon-phonon anharmonicities confirm that the cubic
coupling between modes, shown in earlier work to cause a quasi-static change in
the apical O - Cu distance and a buckling of the CuO$_2$ planes, is the leading
contribution at moderate pump strengths. At higher pump strengths ($\sim$10
MV/cm) the previously neglected quartic couplings become relevant and produce
an additional shearing of the CuO$_2$ planes. Finally, we analyze the changes
in the electronic and magnetic properties associated with the induced
structural changes.",1607.01180v2
2016-09-21,Universal self-field critical current for thin-film superconductors,"For any practical superconductor the magnitude of the critical current
density, $J_\textrm{c}$, is crucially important. It sets the upper limit for
current in the conductor. Usually $J_\textrm{c}$ falls rapidly with increasing
external magnetic field but even in zero external field the current flowing in
the conductor generates a self-field which limits $J_\textrm{c}$. Here we show
for thin films of thickness less than the London penetration depth, $\lambda$,
this limiting $J_\textrm{c}$ adopts a universal value for all superconductors -
metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type
I superconductors, it is $H_{\textrm{c}}/\lambda$ where $H_\textrm{c}$ is the
thermodynamic critical field. But surprisingly for type II superconductors we
find the self-field $J_\textrm{c}$ is $H_{\textrm{c}1}/\lambda$ where
$H_{\textrm{c}1}$ is the lower critical field. $J_\textrm{c}$ is thus
fundamentally determined and this provides a simple means to extract absolute
values of $\lambda(T)$ and, from its temperature dependence, the symmetry and
magnitude of the superconducting gap.",1609.06397v1
2016-09-22,Quantum-Many-Body Intermetallics: Phase Stability of Fe$_3$Al and Small-Gap Formation in Fe$_2$VAl,"Various intermetallic compounds harbor subtle electronic correlation effects.
To elucidate this fact for the Fe-Al system, we perform a realistic many-body
investigation based on the combination of density functional theory with
dynamical mean-field theory in a charge self-consistent manner. A better
characterization and understanding of the phase stability of bcc-based
D0$_3$-Fe$_3$Al through an improved description of the correlated charge
density and the magnetic-energy is achevied. Upon replacement of one Fe
sublattice by V, the Heusler compound Fe$_2$VAl is realized, known to display
bad-metal behavior and increased specific heat. We here document a charge-gap
opening at low temperatures in line with previous experimental work. The gap
structure does not match conventional band theory and is reminiscent of
(pseudo)gap charateristics in correlated oxides.",1609.06928v2
2016-10-17,Observation of semi-localized dispersive states in the strongly correlated electron-doped ferromagnet Eu$_{1-x}$Gd$_{x}$O,"Chemical substitution plays a key role in controlling the electronic and
magnetic properties of complex materials. For instance, in EuO, carrier doping
can induce a spin-polarized metallic state, colossal magnetoresistance, and
significantly enhance the Curie temperature. Here, we employ a combination of
molecular-beam epitaxy, angle-resolved photoemission spectroscopy, and an
effective model calculation to investigate and understand how semi-localized
states evolve in lightly electron doped Eu$_{1-x}$Gd$_{x}$O above the
ferromagnetic Curie temperature. Our studies reveal a characteristic length
scale for the spatial extent of the donor wavefunctions which remains constant
as a function of doping, consistent with recent tunneling studies of doped EuO.
Our work sheds light on the nature of the semiconductor-to-metal transition in
Eu$_{1-x}$Gd$_{x}$O and should be generally applicable for doped complex
oxides.",1610.05337v1
2016-10-19,Applications and non-idealities of submicron Al-AlOx-Nb tunnel junctions,"We have developed a technique to fabricate sub-micron, 0.6 um x 0.6 um
Al-AlOx-Nb tunnel junctions using a standard e-beam resist, angle evaporation
and double oxidation of the tunneling barrier, resulting in high quality
niobium, as determined by the the high measured values of the critical
temperature TC 7.5 K and the gap 1.3 meV. The devices show great promise for
local nanoscale thermometry in the temperature range 1 - 7.5 K. Electrical
characterization of the junctions was performed at sub-Kelvin temperatures both
with and without an external magnetic field, which was used to suppress
superconductivity in Al and thus bring the junction into a
normal-metal-insulator-superconductor (NIS) configuration. We observed excess
sub-gap current, which could not be explained by the standard tunneling theory.
Evidence points towards materials science issues of the barrier or Nb/AlOx
interface as the culprit.",1610.05903v1
2017-02-09,Spin Transfer Torque Driven Coupled Oscillators for Self-Oscillating RF Mixers,"Spin transfer torque oscillators (STOs) based on magnetic tunnel junction
(MTJ) devices are emerging as a possible replacement for complementary
metal-oxide semiconductors for radio-frequency (RF) signal generation.
Advantages include low power consumption, small device area, and large
frequency tunability. But such a single device cannot achieve the necessary
noise performance for RF applications. It has been reported lately that a
network of globally coupled STOs achieves significant improvement in phase
noise. The study here is to propose use of such coupled STOs as
self-oscillating RF mixers. Critical mixer performance parameters, including
conversion gain, output power, and linearity, are discussed.",1702.02746v5
2017-02-14,Inelastic Light Scattering Spectroscopy of Magnons and Phonons in Nickel Oxide: Effects of Temperature,"We report results of an investigation of the temperature dependence of the
magnon and phonon frequencies in NiO. A combination of Brillouin - Mandelstam
and Raman spectroscopies allowed us to elucidate the evolution of the phonon
and magnon spectral signatures from the Brillouin zone center (GHz range) to
the second-order peaks from the zone boundary (THz range). The
temperature-dependent behavior of the magnon and phonon bands in the NiO
spectrum indicates the presence of antiferromagnetic (AF) order fluctuation or
a persistent AF state at temperatures above the Neel temperature (T=523 K).
Tuning the intensity of the excitation laser provides a method for
disentangling the features of magnons from acoustic phonons without the
application of a magnetic field. Our results are useful for interpretation of
the inelastic-light scattering spectrum of NiO, and add to the knowledge of its
magnon properties important for THz spintronic devices.",1702.04366v1
2017-02-22,Prediction of High Temperature Quantum Anomalous Hall Effect in Two Dimensional Transition-Metal Oxides,"Quantum anomalous Hall (QAH) insulator is a topological phase which exhibits
chiral edge states in the absence of magnetic field. The celebrated Haldane
model is the first example of QAH effect, but difficult to realize. Here, we
predict the two-dimensional single-atomic-layer V2O3 with a honeycomb-Kagome
structure is a QAH insulator with a large band gap (large than 0.1 eV) and a
high ferromagnetic Curie temperature (about 900 K). Combining the
first-principle calculations with the effective Hamiltonian analysis, we find
that the spin-majority dxy and dyz orbitals of V atoms on the honeycomb lattice
form a massless Dirac cone near the Fermi level which becomes massive when the
on-site spin-orbit coupling is included. Interestingly, we find that the large
band gap is caused by a cooperative effect of electron correlation and
spin-orbit coupling. Both first-principle calculations and the effective
Hamiltonian analysis confirm that 2D V2O3 has a non-zero Chern number (i.e.,
one). Our work paves a new direction towards realizing the QAH effect at room
temperature.",1702.07022v1
2017-03-14,Thermal-error regime in high-accuracy gigahertz single-electron pumping,"Single-electron pumps based on semiconductor quantum dots are promising
candidates for the emerging quantum standard of electrical current. They can
transfer discrete charges with part-per-million (ppm) precision in nanosecond
time scales. Here, we employ a metal-oxide-semiconductor silicon quantum dot to
experimentally demonstrate high-accuracy gigahertz single-electron pumping in
the regime where the number of electrons trapped in the dot is determined by
the thermal distribution in the reservoir leads. In a measurement with
traceability to primary voltage and resistance standards, the averaged pump
current over the quantized plateau, driven by a \mbox{$1$-GHz} sinusoidal wave
in the absence of magnetic field, is equal to the ideal value of $ef$ within a
measurement uncertainty as low as $0.27$~ppm.",1703.04795v2
2018-02-21,Design of Chern Insulating Phases in Honeycomb Lattices,"The search for robust examples of the magnetic version of topological
insulators, referred to as quantum anomalous Hall insulators or simply Chern
insulators, so far lacks success. Our groups have explored two distinct
possibilities based on multiorbital 3d oxide honeycomb lattices. Each has a
Chern insulating phase near the ground state, but materials parameters were not
appropriate to produce a viable Chern insulator. Further exploration of one of
these classes, by substituting open shell 3d with 4d and 5d counterparts, has
led to realistic prediction of Chern insulating ground states. Here we recount
the design process, discussing the many energy scales that are active in
participating (or resisting) the desired Chern insulator phase.",1802.07411v1
2018-04-06,Spatially modulated susceptibility in thin film La$_{2-x}$Ba$_x$CuO$_4$,"The high critical temperature superconductor Lanthanum Barium Copper Oxide
(La2-xBaxCuO4 or LBCO) exhibits a strong anomaly in critical temperature at
1/8th doping, nematicity, and other interesting properties. We report here
Scanning Superconducting Quantum Interference Device (SQUID) imaging of the
magnetic fields and susceptibility in a number of thin film LBCO samples with
doping in the vicinity of the 1/8th anomaly. Spatially resolved measurements of
the critical temperatures of these samples do not show a pronounced depression
at 1/8th doping. They do, however, exhibit strong, nearly linear modulations of
the susceptibility (""straie"") of multiple samples with surprisingly long
periods of 1-4 microns. Counterintuitively, vortices trap in positions of
largest diamagnetic susceptibility in these striae. Given the rich interplay of
different orders in this material system and its known sensitivity to epitaxial
strain, we propose phase separation as a possible origin of these features and
discuss scenarios in which that might arise.",1804.02483v1
2018-04-12,Stabilizing Single Ni adatoms on a Two-dimensional Porous Titania Overlayer at the SrTiO$_3$(110) Surface,"Nickel vapor-deposited on the SrTiO$_3$(110) surface was studied using
scanning tunneling microscopy, photoemission spectroscopy (PES), and density
functional theory calculations. This surface forms a (4 $\times$ 1)
reconstruction, composed of a 2-D titania structure with periodic six- and
ten-membered nanopores. Anchored at these nanopores, Ni single adatoms are
stabilized at room temperature. PES measurements show that the Ni adatoms
create an in-gap state located at 1.9 eV below the conduction band minimum and
induce an upward band bending. Both experimental and theoretical results
suggest that Ni adatoms are positively charged. Our study produces
well-dispersed single-adatom arrays on a well-characterized oxide support,
providing a model system to investigate single-adatom catalytic and magnetic
properties.",1804.04461v1
2018-04-17,"Synthesis and physical properties of Na$_x$TO$_2$ (T=Mn, Co) nanostructures for cathode materials in Na--ion batteries","We prepared Na$_x$TO$_2$ (T = Mn, Co) nanostructures to use as cathode
material in Na-ion batteries. The Rietveld refinement of x-ray diffraction data
confirms the hexagonal symmetry. Scanning and transmission electron microscopy
measurements show hexagonal and rod-shape morphology for T = Co and Mn,
respectively. The magnetic measurements indicate the presence of variable
oxidation states of Mn/Co ions, but no long range ordering till 5~K. We find
that the Na$_{0.6}$MnO$_2$ is highly insulating whereas Na$_{0.7}$CoO$_2$ is
semiconducting in nature. The conduction in Na$_{0.7}$CoO$_2$ takes place
through both variable range hopping (VRH) as well as activation mechanisms in
different temperature ranges. However, for Na$_{0.6}$MnO$_2$ the VRH prevails
at elevated temperatures. Furthermore, the coin cells have been fabricated and
tested the electrochemical behavior using cyclic voltammetry, which confirms
the reversibility of Na--ions during intercalation/de-intercalation.",1804.06157v1
2019-05-07,Structure-mining: screening structure models by automated fitting to the atomic pair distribution function over large numbers of models,"A new approach is presented to obtain candidate structures from atomic pair
distribution function (PDF) data in a highly automated way. It fetches, from
web-based structural databases, all the structures meeting the experimenter's
search criteria and performs structure refinements on them without human
intervention. It supports both x-ray and neutron PDFs. Tests on various
material systems show the effectiveness and robustness of the algorithm in
finding the correct atomic crystal structure. It works on crystalline and
nanocrystalline materials including complex oxide nanoparticles and nanowires,
low-symmetry and locally distorted structures, and complicated doped and
magnetic materials. This approach could greatly reduce the traditional
structure searching work and enable the possibility of high-throughput
real-time auto analysis PDF experiments in the future.",1905.02677v2
2019-05-14,Fermi-Bose mixtures and BCS-BEC crossover in high-Tc superconductors,"In this review article we consider theoretically and give experimental
support to the models of the Fermi-Bose mixtures and the BCS-BEC crossover
compared with the strong-coupling approach, which can serve as the cornerstones
on the way from high-temperature to room-temperature superconductivity in
pressurized metallic hydrides. We discuss some key theoretical ideas and
mechanisms proposed for unconventional superconductors (cuprates, pnictides,
chalcogenides, bismuthates, diborides, heavy-fermions, organics, bilayer
graphene, twisted graphene, oxide hetero-structures), superfluids and balanced
or imbalanced ultracold Fermi gases in magnetic traps. We build a bridge
between unconventional superconductors and recently discovered pressurized
hydrides superconductors H3S and LaH10 with the critical temperature close to
room temperature. We discuss systems with line of nodal Dirac points close to
the Fermi surface, superconducting shape resonances and hyperbolic
superconducting networks which are very important for the development of novel
topological superconductors, for the energetics, for the applications in
nano-electronics and quantum computations.",1905.05419v4
2020-07-02,Terahertz spectroscopy evidence of possible 40 K superconductivity in rhenium-doped strontium ruthenates,"Strontium ruthenates have many similarities with copper oxide superconductors
and are of particular interest for the investigation of the mechanisms and
conditions which lead to high-temperature superconductivity. We report here on
multiple experimental indications of superconductivity with onset at 40 K in
strontium ruthenate doped by rhenium and selenium with chlorine used as the
flux. The main experimental evidence arises from terahertz spectroscopy of this
material followed by AC and DC magnetization, as well as measurements of its
heat capacity and magnetoresistance. Structural and morphological studies
revealed the heterophase nature of this polycrystalline material as well as the
changes of lattice parameters relative to the original phases. Experimental
data show a higher critical temperature on the surface compared to that of the
bulk of the sample.",2007.06509v1
2020-07-14,"Recent advances, perspectives and challenges in ferroelectric synapses","The multiple ferroelectric polarization tuned by external electric field
could be used to simulate the biological synaptic weight. Ferroelectric
synaptic devices have two advantages compared with other reported ones: One is
the intrinsic switching of ferroelectric domains without invoking of defect
migration as in resistive oxides contributes reliable performance in these
ferroelectric synapses. Another tremendous advantage is the extremely low
energy consumption because the ferroelectric polarization is manipulated by
electric field which eliminate the Joule heating by current as in magnetic and
phase change memory. Ferroelectric synapses are potential for the construction
of low-energy and effective brain-like intelligent networks. Here we summarize
recent pioneering work of ferroelectric synapses involving the structure of
ferroelectric tunnel junctions (FTJs), ferroelectric diodes (FDs) and
ferroelectric field effect transistors (FeFETs), respectively, and shed light
on future work needed to accelerate their application for efficient neural
network.",2007.06914v1
2020-07-20,Anisotropic vortices on superconducting Nb(110),"We investigate the electronic properties of type-II superconducting Nb(110)
in an external magnetic field. Scanning tunneling spectroscopy reveals a
complex vortex shape which develops from circular via coffee bean-shaped to
elliptical when decreasing the energy from the edge of the superconducting gap
to the Fermi level. This anisotropy is traced back to the local density of
states of Caroli-de-Gennes-Matricon states which exhibits a direction-dependent
splitting. Oxidizing the Nb(110) surface triggers the transition from the clean
to the dirty limit, quenches the vortex bound states, and leads to an isotropic
appearance of the vortices. Density functional theory shows that the Nb(110)
Fermi surface is stadium-shaped near the \Gamma point. Calculations within the
Bogoliubov-de-Gennes theory using these Fermi contours consistently reproduce
the experimental results.",2007.09924v1
2013-08-08,"Effects of Edge Oxidation on the Structural, Electronic, and Magnetic Properties of Zigzag Boron Nitride Nanoribbons","The effects of edge chemistry on the relative stability and electronic
properties of zigzag boron nitride nanoribbons (ZBNNRs) are investigated. Among
all functional groups considered, fully hydroxylated ZBNNRs are found to be the
most energetically stable. When an in-plane external electric field is applied
perpendicular to the axis of both hydrogenated and hydroxylated ZBNNRs, a
spin-polarized half-metallic state is induced, whose character is different
than that predicted for ZGNRs. The onset field for achieving the half-metallic
state is found to mainly depend on the width of the ribbon. Our results
indicate that edge functionalization of ZBNNRs may open the way for the design
of new nano-electronic and nano-spintronic devices.",1308.1894v1
2013-08-13,Coulomb interaction and valley-orbit coupling in Si quantum dots,"The valley-orbit coupling in a few-electron Si quantum dot is expected to be
a function of its occupation number N. We study the spectrum of multivalley Si
quantum dots for 2 <= N <= 4, showing that, counterintuitively,
electron-electron interaction effects on the valley-orbit coupling are
negligible. For N=2 they are suppressed by valley interference, for N=3 they
vanish due to spinor overlaps, and for N = 4 they cancel between different
pairs of electrons. To corroborate our theoretical findings, we examine the
experimental energy spectrum of a few-electron metal-oxide-semiconductor
quantum dot. The measured spin-valley state filling sequence in a magnetic
field reveals that the valley-orbit coupling is definitively unaffected by the
occupation number.",1308.2728v1
2014-03-11,Spin correlated electronic state on the surface of a spin-orbit Mott system (Layered Iridates),"Novel phases of two dimensional electron systems resulting from new surface
or interface modified electronic structures have generated significant interest
in material science. We utilize photoemission spectroscopy to show that the
near-surface electronic structure of a bulk insulating iridate
Sr$_3$Ir$_2$O$_7$ lying near metal-Mott insulator transition exhibit weak
metallicity signified by finite electronic spectral weight at the Fermi level.
The surface electrons exhibit a unique spin structure resulting from an
interplay of spin-orbit, Coulomb interaction and surface quantum magnetism,
distinct from a topological insulator state. Our results suggest the
experimental realization of a novel quasi two dimensional interacting electron
surface ground state, opening the door for exotic quantum entanglement and
transport phenomena in iridate-based oxide devices.",1403.2704v1
2014-03-14,Investigation on Mn$_{3-δ}$Ga/MgO interface for magnetic tunneling junctions,"The Mn$_3$Ga Heusler compound and related alloys are the most promising
materials for the realization of spin-transfer-torque switching in magneto
tunneling junctions. Improved performance can be achieved by high quality
interfaces in these multilayered structured devices. In this context, the
interface between Mn$_{1.63}$Ga and MgO is of particular interest because of
its spin polarization properties in tunneling junctions. We performed a
chemical characterization of the MgO/Mn$_{1.63}$Ga junction by hard x-ray
photoelectron spectroscopy (HAXPES). The experiment indicated the formation of
Ga-O bonds at the interface and evidenced changes in the local environment of
Mn atoms in the proximity of the MgO film. In addition, we show that the
insertion of a metallic Mg-layer interfacing the MgO and Mn--Ga film strongly
suppresses the oxidation of gallium.",1403.3556v4
2014-03-20,A New Type of Quantum Criticality in the Pyrochlore Iridates,"Magnetic fluctuations and electrons couple in intriguing ways in the vicinity
of zero temperature phase transitions - quantum critical points - in conducting
materials. Quantum criticality is implicated in non-Fermi liquid behavior of
diverse materials, and in the formation of unconventional superconductors. Here
we uncover an entirely new type of quantum critical point describing the onset
of antiferromagnetism in a nodal semimetal engendered by the combination of
strong spin-orbit coupling and electron correlations, and which is predicted to
occur in the iridium oxide pyrochlores. We formulate and solve a field theory
for this quantum critical point by renormalization group techniques, show that
electrons and antiferromagnetic fluctuations are strongly coupled, and that
both these excitations are modified in an essential way. This quantum critical
point has many novel features, including strong emergent spatial anisotropy, a
vital role for Coulomb interactions, and highly unconventional critical
exponents. Our theory motivates and informs experiments on pyrochlore iridates,
and constitutes a singular realistic example of a non-trivial quantum critical
point with gapless fermions in three dimensions.",1403.5255v1
2016-11-09,Nanosize effect: Enhanced compensation temperature and existence of magneto-dielectric coupling in SmFeO3,"In transition metal oxides, quantum confinement arising from a large surface
to volume ratio often gives rise to novel physico-chemical properties at
nanoscale. Their size dependent properties have potential applications in
diverse areas, including therapeutics, imaging, electronic devices,
communication systems, sensors, and catalysis. We have analyzed structural,
magnetic, dielectric, and thermal properties of weakly ferromagnetic SmFeO3
nanoparticles of sizes about 55 nm and 500 nm. The nano-size particles exhibit
several distinct features that are neither observed in their larger-size
variants nor reported previously for the single crystals. In particular, for
the 55 nm particle, we observe six-fold enhancement of compensation
temperature, an unusual rise in susceptibility in the temperature range 550 to
630 K due to spin pinning, and coupled antiferromagnetic-ferroelectric
transition, directly observed in the dielectric constant.",1611.02850v2
2016-11-22,The interface between Sr$_2$RuO$_4$ and Ru-metal inclusion--Implications for its superconductivity,"Under various conditions of the growth process, when the presumably
unconventional superconductor Sr$_2$RuO$_4$ (SRO) contains micro-inclusions of
Ru metal, the superconducting critical temperature increases significantly. An
STEM study shows a sharp interface geometry which allows crystals of SRO and of
Ru-metal to grow side by side by forming a commensurate superlattice structure
at the interface. In an attempt to shed light as to why this happens, we
investigated the atomic structure and electronic properties of the interface
between the oxide and the metal micro-inclusions using density functional
theory (DFT) calculations. Our results support the observed structure
indicating that it is energetically favored over other types of Ru-metal/SRO
interfaces. We find that a $t_{2g}$-$e_g$ orbital mixing occurs at the
interface with significantly enhanced magnetic moments. Based on our findings,
we argue that an inclusion mediated interlayer coupling reduces phase
fluctuations of the superconducting order parameter which could explain the
observed enhancement of the superconducting critical temperature in SRO samples
containing micro-inclusions.",1611.07130v1
2017-01-05,Relationship between electronic and crystal structure in Nd1+xBa2-xCu3O6+d,"In accordance with a relation between the lattice parameter c and the
concentration of holes p, which has been found earlier for the YBa2Cu3O6+d
compound, we obtain the p parameter in the same manner for the solid solution
Nd1.2Ba1.8Cu3O6+d with substitution of Nd3+ for Ba2+ in barium sites. For this,
structural and superconducting properties of the Nd1.2Ba1.8Cu3O6+d samples
stored for specified times t after quenching from annealing temperatures have
been studied. The investigation shows that Nd1.2Ba1.8Cu3O6+d stored for a long
time has quite a low critical temperature Tc extending only to Tconset = 55 K
for the most oxidized sample with d = 0.953. We find that the d-dependence of
the lattice parameter c significantly changes with time t. When using the
relation between c and p, the existence of electron doping of 0.045 per Cu in
Nd1.2Ba1.8Cu3O6+d can be inferred. This doping explains well reduced Tc in
Nd1.2Ba1.8Cu3O6+d. In addition, we observe a local drop of Tc by up to 20 K for
the samples with p ~ 0.095 (d ~ 0.8) similar to decreasing Tc known as ""anomaly
1/8"".",1701.01397v2
2017-01-16,A Deep Mixing Solution to the Aluminum and Oxygen Isotope Puzzles in Presolar Grains,"We present here the application of a model for a mass circulation mechanism
in between the H-burning shell and the base of the convective envelope of low
mass AGB stars, aimed at studying the isotopic composition of those presolar
grains showing the most extreme levels of 18O depletion and high concentration
of 26Mg from the decay of 26Al. The mixing scheme we present is based on a
previously suggested magnetic-buoyancy process, already shown to account
adequately for the formation of the main neutron source for slow neutron
captures in AGB stars. We find that this scenario is also capable of
reproducing for the first time the extreme values of the 17O/16O, the 18O/16O,
and the 26Al/27Al isotopic ratios found in the mentioned oxide grains,
including the highest amounts of 26Al there measured.",1701.04445v1
2017-01-25,Excitonic giant-dipole potentials in cuprous oxide,"In this work we predict the existence of a novel species of Wannier excitons
when exposed to crossed electric and magnetic fields. In particular, we present
a theory of giant-dipole excitons in $\textrm{Cu}_2\rm O$ in crossed fields.
Within our theoretical approach we perform a pseudoseparation of the
center-of-mass motion for the field-dressed excitonic species, thereby
obtaining an effective single-particle Hamiltonian for the relative motion. For
arbitrary gauge fields we exactly separate the gauge-dependent kinetic energy
terms from the effective single-particle interaction potential. Depending on
the applied field strengths and the specific field orientation, the potential
for the relative motion of electron and hole exhibits an outer well at spatial
separations up to several micrometers and depths up to $380\, \mu \rm eV$,
leading to possible permanent excitonic electric dipole moments of around three
million Debye.",1701.08847v2
2017-04-11,Tuning Interfacial Ferromagnetism in LaNiO$_3$/CaMnO$_3$ Superlattices by Stabilizing Non-Equilibrium Crystal Symmetry,"Perovskite oxide heterostructures offer an important path forward for
stabilizing and controlling low-dimensional magnetism. One of the guiding
design principles for these materials systems is octahedral connectivity. In
superlattices composed of perovskites with different crystal symmetries,
variation of the relative ratio of the constituent layers as well as the
individual layer thicknesses gives rise to non-equilibrium crystal symmetries
that, in turn, lead to unprecedented control of interfacial ferromagnetism. We
have found that in superlattices of CaMnO$_3$ (CMO) and LaNiO$_3$ (LNO),
interfacial ferromagnetism can be modulated by a factor of three depending on
LNO and CMO layer thicknesses as well as their relative ratio. Such an effect
is only possible due to the non-equilibrium crystal symmetries at the
interfaces and can be understood in terms of the anisotropy of the exchange
interactions and modifications in the interfacial Ni-O-Mn and Mn-O-Mn bond
angles and lengths with increasing LNO layer thickness. These results
demonstrate the potential of engineering non-equilibrium crystal symmetries in
designing ferromagnetism.",1704.03154v2
2017-04-25,Strain-controlled Insulator-Metal Transition in YTiO3/SrTiO3 Superlattices: A First-Principles Study,"The structural, magnetic, and electronic properties of (STO)$_4$/(YTO)$_2$
superlattice consisting of Mott insulator YTiO$_3$ (YTO) and band insulator
SrTiO$_3$ (STO) under strain are investigated by the density-functional-theory
plus \emph{U} method. It is found that an insulator-metal transition occurs
when a compressive strain of 0.2\% is applied. The structural analyses reveal
that the presence of metallic state in such superlattices accompanies
structural phase transition with restoring of inversion symmetry. Further study
shows that this strain-induced structural transition makes the $d$ energy level
of the interfacial Ti atoms of the YTO layer move upward due to the decreasing
of the TiO$_{6}$ octahedral volume and induces the electron reconstruction in
the whole superlattice systems. In addition, when the on-site interaction $U$
is changed from 5 to 4 eV, a similar insulator-metal transition also occurs in
such superlattices due to the weakened electron correlation. These findings can
improve our understanding of the insulator-metal transitions in such oxide
superlattices.",1704.07687v1
2018-05-09,Hund nodal line semimetals: The case of twisted magnetic phase in the double-exchange model,"We propose a class of topological metals, which we dub \emph{Hund nodal line
semimetals}, arising from the strong Coulomb interaction encoded in the Hund's
coupling between itinerant electrons and localized spins. We here consider a
particular twisted spin configuration, which is realized in the double exchange
model which describes the manganite oxides. The resulting effective tetragonal
lattice of electrons with hoppings tied to the local spin features an
antiunitary \emph{non-symmorphic} symmetry that in turn, together with another
non-symmorphic but unitary, glide mirror symmetry, protects crossings of a
double pair of bands along a high-symmetry line on the Brillouin zone boundary.
We also discuss symmetry breaking arising from various perturbations of the
twisted phase. Our results may motivate further studies of other realizations
of this state of matter, for instance in different spin backgrounds, properties
of its drumhead surface states, as well as its stability to disorder and
interactions among the itinerant electrons.",1805.03640v2
2018-05-30,The role of interstitial hydrogen in SrCoO$_{2.5}$ antiferromagnetic insulator,"Hydrogen exhibits qualitatively different charge states depending on the host
material, as nicely explained by the state-of-the-art impurity-state
calculation. Motivated by a recent experiment [Nature 546, 124 (2017)], we show
that the complex oxide SrCoO$_{2.5}$ represents an interesting example, in
which the interstitial H appears as a deep-level center according to the
commonly-used transition level calculation, but no bound electron can be found
around the impurity. Via a combination of charge difference analysis, density
of states projection and constraint magnetization calculation, it turns out
that the H-doped electron is spontaneously trapped by a nonunique Co ion and is
fully spin-polarized by the onsite Hund's rule coupling. Consequently, the
doped system remains insulating, whereas the antiferromagnetic exchange is
slightly perturbed locally.",1805.11766v2
2008-07-11,Electronic liquid crystal state in the high-temperature superconductor YBCO(6.45),"Electronic phases with symmetry properties matching those of conventional
liquid crystals have recently been discovered in transport experiments on
semiconductor heterostructures and metal oxides at milli-Kelvin temperatures.
We report the spontaneous onset of a onedimensional, incommensurate modulation
of the spin system in the high-temperature superconductor YBa2Cu3O6.45 upon
cooling below ~150 K, while static magnetic order is absent above 2 K. The
evolution of this modulation with temperature and doping parallels that of the
in-plane anisotropy of the resistivity, indicating an electronic nematic phase
that is stable over a wide temperature range. The results suggest that soft
spin fluctuations are a microscopic route towards electronic liquid crystals,
and nematic order can coexist with high-temperature superconductivity in
underdoped cuprates.",0807.1861v1
2009-12-05,"Structural, electrical and magnetic properties of Mo1-xFexO2 (x=0-0.05) thin films grown by pulsed laser ablation","We report the growth of undoped and Fe (2 and 5 at. percentage) doped
molybdenum oxide thin films on c-plane of sapphire substrate using pulsed laser
ablation. X-ray diffraction results show that the films are oriented in (100)
direction and have monoclinic structure based on MoO2 phase as also supported
by Raman spectroscopy. The x-ray photoelectron spectroscopy reveals chemical
state of Fe is +2, which favors the substitutional occupancy of Fe ion in the
MoO2 matrix. The room temperature resistivity of all the films are very low
(approx.100 microohm-cm). The Fe doped samples show ferromagnetic behavior at
room temperature.",0912.0978v1
2009-12-06,Spectrum of extended systems from Reduced Density Matrix Functional Theory,"We present a method for calculating the spectrum of extended solids within
reduced density matrix functional theory. An application of this method to the
strongly correlated transition metal oxide series demonstrates that (i) an
insulating state is found in the absence of magnetic order and, in addition,
(ii) the interplay between the change transfer and Mott-Hubbard correlation is
correctly described. In this respect we find that while NiO has a strong charge
transfer character to the electronic gap, with substantial hybridization
between $t_{2g}$ and oxygen-$p$ states in the lower Hubbard band, for MnO this
is almost entirely absent. As a validation of our method we also calculate the
spectra for a variety of weakly correlated materials, finding good agreement
with experiment and other techniques.",0912.1118v2
2009-12-17,"Multiferroic double perovskites: Opportunities, Issues and Challenges","Despite the great technological and scientific importance, a well-controlled
coupled behavior in magnetoelectric multiferroic materials at room temperature
remains challenging. We demonstrate that the self-ordered A2BBO6 (e.g., A = La,
B = Mn, and B = Ni) double perovskites provide a unique alternative opportunity
to control and/or to induce such behavior in oxides. In this paper, we outline
and discuss the various challenges and bottleneck issues related to this class
of materials using La2NiMnO6 as a prototype. Details of the synthesis
strategies, using pulsed laser deposition as a central tool, to obtain a
meticulous control over cation ordering is illustrated. The possible impact of
Ni/Mn cation ordering on the magnetic ground states, ferromagnetic transition
temperature, phonon behavior, and spin-phonon coupling are presented. Our
results are also compared with the current literature on related compounds.",0912.3292v1
2009-12-21,Electronic Ferroelectricity and Frustration,"Beyond a conventional classification of ferroelectricity, there is a class of
materials where electronic degrees of freedom and electronic interactions are
directly responsible for electric polarization and ferroelectric transition.
This is termed electronic ferroelectricity. In this article, we review
electronic ferroelectricity from a view point of frustration. Experimental and
theoretical examinations in spin driven ferroelectric materials, recently
termed multiferroics, are introduced. Spin frustration caused by competing
magnetic interactions is of prime importance for this type of ferroelectricity.
Charge driven ferroelectricity where electronic charge order induces electric
polarization is reviewed. In particular, exotic dielectric and
magneto-dielectric properties in layered iron oxides are focused on. Through a
number of recent experimental and theoretical researches, charge fluctuation
due to frustrated geometry plays essential roles on electronic ferroelectricity
in this compound.",0912.4083v1
2011-11-14,Layer-by-layer epitaxial growth of polar FeO(111) thin films on MgO(111),"We report on the structural properties of epitaxial FeO layers grown by
molecular beam epitaxy on MgO(111). The successful stabilization of polar FeO
films as thick as 16 monolayers (ML), obtained by deposition and subsequent
oxidation of single Fe layers, is presented. FeO/MgO(111) thin films were
chemically and structurally characterized using low-energy electron
diffraction, Auger electron spectroscopy and conversion electron Mossbauer
spectroscopy (CEMS). Detailed in situ CEMS measurements as a function of the
film thickness demonstrated a size-effect-induced evolution of the hyperfine
parameters, with the thickest film exhibiting the bulk-wustite hyperfine
pattern. Ex situ CEMS investigation confirmed the magnetic ordering of the
wustite thin film phase at liquid nitrogen temperature.",1111.3161v1
2011-11-21,Ab initio Derivation of Correlated Superatom Model for Potassium Loaded Zeolite A,"We derive an effective low-energy Hamiltonian for potassium loaded zeolite A,
a unique ferromagnet from non-magnetic elements. We perform ab initio density
functional calculations and construct maximally localized Wannier functions for
low-energy states made from potassium s electrons. The resulting Wannier
orbitals, spreading widely in the alminosilicate cage, are found to be the
superatomic s and p orbitals in the confining potential formed by the host
cage. We then make a tight-binding model for these superatomic orbitals and
introduce interaction parameters such as the Hubbard U. After mean-field
calculations for the effective model, we find that ab initio spin density
functional results are well reproduced by choosing appropriate sets of the
interaction parameters. The interaction parameters turn out to be as large as
the band width, $\sim$ 0.5 eV, indicating the importance of electron
correlation, and that the present system is an interesting analog of correlated
multi-orbital transition metal oxides.",1111.4815v2
2011-11-25,Exact diagonalization results for resonant inelastic x-ray scattering spectra of one-dimensional Mott insulators,"We examine the momentum-dependent excitation spectra of indirect as well as
direct resonant inelastic x-ray scattering (RIXS) processes in half-filled
(extended) Hubbard rings. We determine the fundamental features of the
groundstate RIXS response and discuss the experimental conditions that can
allow for the low-energy part of these features to be distinguished in
one-dimensional copper-oxide materials, focusing particularly on the different
magnetic excitations occurring in indirect and direct RIXS processes. We study
the dependence of spin and charge excitations on the choice of and detuning
from resonance. Moreover, final state excitation weights are calculated as a
function of the core-hole potential strength and lifetime. We show that these
results can be used to determine material characteristics, such as the
core-hole properties, from RIXS measurements.",1111.6028v2
2012-01-04,Non-Kondo mechanism for resistivity minimum in spin ice conduction systems,"We present a mechanism of resistivity minimum in conduction electron systems
coupled with localized moments, which is distinguished from the Kondo effect.
Instead of the spin-flip process in the Kondo effect, electrons are elastically
scattered by local spin correlations which evolve in a particular way under
geometrical frustration as decreasing temperature. This is demonstrated by the
cellular dynamical mean-field theory for a spin-ice type Kondo lattice model on
a pyrochlore lattice. Peculiar temperature dependences of the resistivity,
specific heat, and magnetic susceptibility in the non-Kondo mechanism are
compared with the experimental data in metallic Ir pyrochlore oxides.",1201.0929v2
2012-04-15,A Structural Phase Transition in Ca3Co4O9 Associated with Enhanced High Temperature Thermoelectric Properties,"Temperature dependent electrical resistivity, crystal structure and heat
capacity measurements reveal a resistivity drop and metal to semiconductor
transition corresponding to first order structural phase transition near 400 K
in Ca3Co4O9. The lattice parameter c varies smoothly with increasing
temperature, while anomalies in the a, b1 and b2 lattice parameters occur at ~
400 K. Both Ca2CoO3 and CoO2 layers become distorted above ~ 400 K associated
with the metal to semiconductor transport behavior change. Resistivity and heat
capacity measurements as a function of temperature under magnetic field
indicates low spin contribution to this transition. Reduced resistivity
associated with this first order phase transition from metallic to
semiconducting behavior enhances the thermoelectric properties at high
temperatures and points to the metal to semiconductor transition as a mechanism
for improved ZT in high temperature thermoelectric oxides.",1204.3231v1
2013-09-20,Jeff=1/2 Mott spin-orbit insulating state close to the cubic limit in Ca4IrO6,"The Jeff=1/2 state is manifested in systems with large cubic crystal field
splitting and spin-orbit coupling that are comparable to the on-site Coulomb
interaction, U. 5d transition metal oxides host parameters in this regime and
strong evidence for this state in Sr2IrO4, and additional iridates, has been
presented. All the candidates, however, deviate from the cubic crystal field
required to provide an unmixed canonical Jeff=1/2 state, impacting the
development of a robust model of this novel insulating and magnetic state. We
present results that not only show Ca4IrO6 hosts the state, but furthermore
uniquely resides close to the ideal case required for an unmixed Jeff=1/2
state.",1309.5411v1
2014-06-29,Evidence for a Finite Temperature Insulator,"In superconductors the zero-resistance current-flow is protected from
dissipation at finite temperatures (T) by virtue of the short-circuit condition
maintained by the electrons that remain in the condensed state. The recently
suggested finite-T insulator and the ""superinsulating"" phase are different
because any residual mechanism of conduction will eventually become dominant as
the finite-T insulator sets-in. If the residual conduction is small it may be
possible to observe the transition to these intriguing states. We show that the
conductivity of the high magnetic-field insulator terminating superconductivity
in amorphous indium-oxide exhibits an abrupt drop, and seem to approach a zero
conductance at T<0.04 K. We discuss our results in the light of theories that
lead to a finite-T insulator.",1406.7510v4
2015-12-18,Substrate-tuning of correlated spin-orbit oxides,"We have systematically investigated substrate-strain effects on the
electronic structures of two representative Sr-iridates, a correlated-insulator
Sr$_2$IrO$_4$ and a metal SrIrO$_3$. Optical conductivities obtained by the
\emph{ab initio} electronic structure calculations reveal that the tensile
strain shifts the optical peak positions to higher energy side with altered
intensities, suggesting the enhancement of the electronic correlation and
spin-orbit coupling (SOC) strength in Sr-iridates. The response of the
electronic structure upon tensile strain is found to be highly correlated with
the direction of magnetic moment, the octahedral connectivity, and the SOC
strength, which cooperatively determine the robustness of $J_{eff}$=1/2 ground
states. Optical responses are analyzed also with microscopic model calculation
and compared with corresponding experiments. In the case of SrIrO$_3$, the
evolution of the electronic structure near the Fermi level shows high
tunability of hole bands, as suggested by previous experiments.",1512.05932v1
2015-12-30,Topological insulator associated with quantum anomalous Hall phase in ferromagnetic perovskite superlattices,"We do a search for topological insulators which are associated with
ferromagnetic ordering and show anomalous quantum Hall effect, among transition
metal oxide superlattices taking the parent compounds as LaAlO3 and SrTiO3.
Among the various superlattices which are studied here, (LaAlO3)10/(LaOsO3)2
exhibits a ferromagnetic ground state with a topologically non-trivial energy
gap when a spin-orbit interaction is turned on. The study of transverse
conductivity shows that the system has quantized Hall conductivity inside the
topological energy gap without applying any external magnetic field. The
ferromagnetic order parameters and the ordering temperature (Tc) have been
estimated by taking a simple Heisenberg model of ferromagnetism.",1512.08843v1
2016-05-13,Controlling Kondo-like Scattering at the SrTiO3-based Interfaces,"The observation of magnetic interaction at the interface between nonmagnetic
oxides has attracted much attention in recent years. In this report, we show
that the Kondo-like scattering at the SrTiO3-based conducting interface is
enhanced by increasing the lattice mismatch and growth oxygen pressure PO2. For
the 26-unit-cell LaAlO3/SrTiO3 (LAO/STO) interface with lattice mismatch being
3.0%, the Kondo-like scattering is observed when PO2 is beyond 1 mTorr. By
contrast, when the lattice mismatch is reduced to 1.0% at the
(La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 (LSAT/STO) interface, the metallic state is
always preserved up to PO2 of 100 mTorr. The data from Hall measurement and
X-ray absorption near edge structure (XANES) spectroscopy reveal that the
larger amount of localized Ti3+ ions are formed at the LAO/STO interface
compared to LSAT/STO. Those localized Ti3+ ions with unpaired electrons can be
spin-polarized to scatter mobile electrons, responsible for the Kondo-like
scattering observed at the LAO/STO interface.",1605.04038v1
2016-05-23,Soft X-ray Absorption Spectroscopy Study of Multiferroic Bi-substituted Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3),"The electronic structures of multiferroic oxides of
Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) (0 < x < 0.12) have been investigated by
employing photoemission spectroscopy and soft x-ray absorption spectroscopy
(XAS). The measured Fe and Ti 2p XAS spectra show that Ti ions are in the Ti4+
states for all x and that Fe ions are Fe2+-Fe3+ mixed-valent for x > 0. The
valence states of Fe ions are found to be nearly trivalent for x=0, and
decreases with increasing x from being nearly trivalent (v(Fe)~ 3) for x=0 to
v(Fe)~ 2.6 for x=0.12. The valence states of both Ti and Ba ions do not change
for all x < 0.12. Based on the obtained valence states of Fe ions, the
electronic and magnetic properties of Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) are
explored.",1605.06869v1
2016-12-14,Bulk superconductivity at 84 K in the strongly overdoped regime of cuprates,"By means of magnetization, specific heat and muon-spin relaxation
measurements, we investigate high-pressure oxidized \mohpo, in which overdoping
is achieved up to $p \sim 0.45$ hole/Cu, well beyond the $T_c - p$
superconducting dome of cuprates, where Fermi liquid behavior is expected.
Surprisingly, we find bulk superconductivity with $T_c$=84 K and superfluid
density similar to those of optimally doped Y123. On the other hand, specific
heat data display a large electronic contribution at low temperature,
comparable to that of nonsuperconducting overdoped La214. These results point
at an unusual high-$T_c$ phase with a large fraction of unpaired holes. Further
experiments may assess the Fermi liquid properties of the present phase, which
would put into question the paradigm that the high $T_c$ of cuprates originates
from a non-Fermi liquid ground state.",1612.04707v1
2016-12-15,Correlation-Induced Band Competition in SrTiO3/LaAlO3,"The oxide interface SrTiO3/LaAlO3 supports a 2D electron liquid displaying
superconductivity and magnetism, while allowing for a continuous control of the
electron density using a gate. Our recent measurements have shown a similar
surprising nonmonotonic behavior as function of the gate voltage (carrier
density) of three quantities: the superconducting critical temperature and
field, the inverse Hall coefficient, and the frequency of quantum oscillations.
While the total density has to be monotonic as function of gate, the last
result indicates that one of the involved bands has a nonmontonic occupancy as
function of the chemical potential. We show how electronic interactions can
lead to such an effect, by creating a competition between the involved bands
and making their structure non-rigid, and thus account for all these effects.
Adding Fock terms to our previous Hartree treatment makes this scenario even
more generic.",1612.05094v4
2016-12-20,Enhanced Superconductivity in TiO Epitaxial Thin Films,"Titanium oxides have many fascinating optical and electrical properties, such
as the superconductivity at 2.0 K in cubic titanium monoxide TiO
polycrystalline bulk. However, the lack of TiO single crystals or epitaxial
films has prevented systematic investigations on its superconductivity. Here,
we report the basic superconductivity characterizations of cubic TiO films
epitaxially grown on (0001)-oriented Al2O3 substrates. The magnetic and
electronic transport measurements confirmed that TiO is a type-II
superconductor and the record high Tc is about 7.4 K. The lower critical field
(Hc1) at 1.9 K, the extrapolated upper critical field Hc2(0) and coherence
length are about 18 Oe, 13.7 T and 4.9 nm, respectively. With increasing
pressure, the value of Tc shifts to lower temperature while the normal state
resistivity increases. Our results on the superconducting TiO films confirm the
strategy to achieve higher Tc in epitaxial films, which may be helpful for
finding more superconducting materials in various related systems.",1612.06506v1
2016-12-30,Itinerant Antiferromagnetism in RuO$_{2}$,"Bulk rutile RuO$_2$ has long been considered a Pauli paramagnet. Here we
report that RuO$_2$ exhibits a hitherto undetected lattice distortion below
approximately 900 K. The distortion is accompanied by antiferromagnetic order
up to at least 300 K with a small room temperature magnetic moment of
approximately 0.05 $\mu_B$ as evidenced by polarized neutron diffraction.
Density functional theory plus $U$ (DFT+$U$) calculations indicate that
antiferromagnetism is favored even for small values of the Hubbard $U$ of the
order of 1 eV. The antiferromagnetism may be traced to a Fermi surface
instability, lifting the band degeneracy imposed by the rutile crystal field.
The combination of high N\'eel temperature and small itinerant moments make
RuO$_2$ unique among ruthenate compounds and among oxide materials in general.",1612.09589v1
2017-06-06,Time-spliced X-ray Diffraction Imaging,"Diffraction imaging of non-equilibrium dynamics at atomic resolution is
becoming possible with X-ray free-electron lasers. However, there are
unresolved problems with applying this method to objects that are confined in
only one dimension. Here I show that one-dimensional coherent diffraction
imaging is possible by splicing together images recovered from different delays
in a time-resolved experiment. This is used to image the time and space
evolution of antiferromagnetic order in a complex oxide heterostructure from
measurements of a resonant soft X-ray diffraction peak. Mid-infrared excitation
of the substrate is shown to lead to a magnetic front that propagates at a
velocity exceeding the speed of sound, a critical observation for the
understanding of driven phase transitions in complex condensed matter.",1706.01718v3
2017-06-20,High-pressure synthesis of an unusual antiferromagnetic metal CaCoO$_{3}$ with GdFeO$_{3}$-type perovskite structure,"The GdFeO$_{3}$-type perovskite CaCoO$_{3}$ has been successfully synthesized
by high-pressure oxygen annealing for the oxygen deficient perovskite. A
detailed structural analysis based on synchrotron X-ray diffraction data and a
thermogravimetric analysis show that the valence of Co is +4 and the sample is
free from oxygen deficiency. This compound shows an antiferromagnetic ordering
at 95 K, which has presumably helical spin arrangement, with keeping the
incoherent metallic state down to the lowest temperature. This work
demonstrates that the Co$^{4+}$-perovskite oxides exhibit a variety of magnetic
phases by the band-width control through the lattice distortion.",1706.06373v2
2017-06-16,An argon ion beam milling process for native $\text{AlO}_\text{x}$ layers enabling coherent superconducting contacts,"We present an argon ion beam milling process to remove the native oxide layer
forming on aluminum thin films due to their exposure to atmosphere in between
lithographic steps. Our cleaning process is readily integrable with
conventional fabrication of Josephson junction quantum circuits. From
measurements of the internal quality factors of superconducting microwave
resonators with and without contacts, we place an upper bound on the residual
resistance of an ion beam milled contact of 50$\,\mathrm{m}\Omega \cdot \mu
\mathrm{m}^2$ at a frequency of 4.5 GHz. Resonators for which only $6\%$ of the
total foot-print was exposed to the ion beam milling, in areas of low electric
and high magnetic field, showed quality factors above $10^6$ in the single
photon regime, and no degradation compared to single layer samples. We believe
these results will enable the development of increasingly complex
superconducting circuits for quantum information processing.",1706.06424v1
2017-10-30,Strain induced Jahn-Teller distortions in BaFeO3 : A first-principles study,"The effect of epitaxial strain on structural, magnetic and electronic
properties of BaFeO 3 per- ovskite oxide are investigated from first principles
calculations, using the Density Functional The- ory (DFT) plus the Hubbard
approach (DFT+U) within the Generalized Gradient Approximation (GGA). Hybrid
functional calculations, based on mixed exact Hartree-Fock (HF) and DFT
exchange energy functionals, are also performed. For the ground state
calculations,the DFT+U is found more suitable to describe the half metallic and
ferromagnetic state of cubic BaFeO 3 . The possible oc- curence of oxygen
octahedra rotations, Jahn-Teller distortions and charge orderings through
biaxial strain are explored. The obtained results reveal that the Jahn-teller
distortion is induced under tensile biaxial strain while the oxygen octahedra
rotations and breathing are unusualy not observed. Then, the strained BaFeO 3
is considered as a particular Jahn-Teller distorted perovskite with excep-
tional properties when compared to CaFeO 3 and SrFeO 3 . These findings lead to
a strain engineering of the JT distortions in BaFeO 3 , and thus for high
fundamental and technological interests.",1710.10997v1
2017-11-30,Nonlinear Pauli Susceptibilities in Sr$_3$Ru$_2$O$_7$ and Universal Features of Itinerant Metamagnetism,"We report, for the first time, measurements of the third order, $\chi_3$ and
fifth order, $\chi_5$, susceptibilities in an itinerant oxide metamagnet,
Sr$_3$Ru$_2$O$_7$ for magnetic fields both parallel and perpendicular to the
c-axis. These susceptibilities exhibit maxima in their temperature dependence
such that $T_1 \approx 2T_3 \approx 4T_5$ where the $T_i$ are the position in
temperature where a peak in the $i$-th order susceptibility occurs. These
features taken together with the scaling of the critical field with the
temperature $T_1$ observed in a diverse variety of itinerant metamagnets find a
natural explanation in a single band model with one Van Hove singularity (VHS)
and onsite repulsion $U$. The separation of the VHS from the Fermi energy
$\Delta$, sets a single energy scale, which is the primary driver for the
observed features of itinerant metamagnetism at low temperatures.",1712.00113v1
2017-12-04,Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films,"Electrons confined to two dimensions display an unexpected diversity of
behaviors as they are cooled to absolute zero. Noninteracting electrons are
predicted to eventually ""localize"" into an insulating ground state, and it has
long been supposed that electron correlations stabilize only one other phase:
superconductivity. However, many two-dimensional (2D) superconducting materials
have shown surprising evidence for metallic behavior, where the electrical
resistivity saturates in the zero-temperature limit, the nature of this
unexpected metallic state remains under intense scrutiny. We report electrical
transport properties for two disordered 2D superconductors, indium oxide and
tantalum nitride, and observe a magnetic field-tuned transition from a true
superconductor to a metallic phase with saturated resistivity. This metallic
phase is characterized by a vanishing Hall resistivity, suggesting that it
retains particle-hole symmetry from the disrupted superconducting state.",1712.00947v1
2017-12-14,Muon spin relaxation and inelastic neutron scattering investigations of all-in/all-out antiferromagnet Nd2Hf2O7,"Nd2Hf2O7, belonging to the family of geometrically frustrated cubic rare
earth pyrochlore oxides, was recently identified to order antiferromagnetically
below T_N = 0.55 K with an all-in/all-out arrangement of Nd3+ moments, however
with a much reduced ordered state moment. Herein we investigate the spin
dynamics and crystal field states of Nd2Hf2O7 using muon spin relaxation (muSR)
and inelastic neutron scattering (INS) measurements. Our muSR study confirms
the long range magnetic ordering and shows evidence for coexisting persistent
dynamic spin fluctuations deep inside the ordered state down to 42 mK. The INS
data show the crytal electric field (CEF) excitations due to the transitions
both within the ground state multiplet and to the first excited state
multiplet. The INS data are analyzed by a model based on CEF and crystal field
states are determined. Strong Ising-type anisotropy is inferred from the ground
state wavefunction. The CEF parameters indicate the CEF-split Kramers doublet
ground state of Nd3+ to be consistent with the dipolar-octupolar character.",1712.05201v1
2017-12-26,Nanoscale electrical conductivity imaging using a nitrogen-vacancy center in diamond,"The electrical conductivity of a material can feature subtle, nontrivial, and
spatially-varying signatures with critical insight into the material's
underlying physics. Here we demonstrate a conductivity imaging technique based
on the atom-sized nitrogen-vacancy (NV) defect in diamond that offers local,
quantitative, and noninvasive conductivity imaging with nanoscale spatial
resolution. We monitor the spin relaxation rate of a single NV center in a
scanning probe geometry to quantitatively image the magnetic fluctuations
produced by thermal electron motion in nanopatterned metallic conductors. We
achieve 40-nm scale spatial resolution of the conductivity and realize a
25-fold increase in imaging speed by implementing spin-to-charge conversion
readout of a shallow NV center. NV-based conductivity imaging can probe
condensed-matter systems in a new regime, and as a model example, we project
readily achievable imaging of nanoscale phase separation in complex oxides.",1712.09209v1
2018-09-13,In situ soft x-ray absorption spectroscopic study of Fe/MgO interfaces,"Interfacial reaction between iron and MgO has been studied in situ during
deposition of iron on MgO surface, using soft x-ray absorption spectroscopy.
High sensitivity of the technique which is capable of detecting even a sub
monolayer of a given phase, combined with in situ measurements as a function of
iron layer thickness, allowed one to make a quantitative estimate of
interfacial phases. Two different substrates namely, MgO (001) single crystal,
and a polycrystalline MgO film on Si substrate have been used in order to
elucidate the role of the state of MgO surface in controlling the interface
structure. It is found that at the interface of iron and MgO film, about two
monolayers of Fe3O4 is formed. Fe3O4 being the oxide of iron with the highest
heat of formation, the reaction appears to be controlled thermodynamically. On
the other hand, on the interface with MgO (001) surface, FeO is formed,
suggesting that the reaction is limited by the availability of oxygen atoms.
Magnetic behaviour of the FeO layer gets modified significantly due to
proximity effect of the bulk ferromagnetic iron layer.",1809.04782v2
2018-10-15,Possible High TC Layered Ferromagnetic Insulator Sr2NiRuO4: An ab initio Study,"Magnetic insulators are often antiferromagnetic (AFM) and layered AFM
compounds usually show low ordering temperature. On the other hand, layered
ferromagnetic (FM) insulators with high-TC are very rare although they could be
quite useful for spintronic applications. Here, using crystal field level
analysis in combination with density functional theory calculations as well as
Monte Carlo simulations, we predict that the layered insulator Sr2NiRuO4 would
have a strong FM coupling with TC as high as 240 K. The tetragonal crystal
field in the Ni-O-Ru square plane stabilizes the S=1/2 Ni+ and S=3/2 Ru3+
states. The unique level ordering and occupation optimize the FM Ni-Ru
superexchange interactions in the checkerboard arrangement, thus suggesting
Sr2NiRuO4 as an unusual high-TC layered FM insulator. This work highlights the
potential of charge-spin-orbital degrees of freedom for stabilizing strong FM
coupling in layered oxides.",1810.06142v1
2018-10-18,R1 dispersion contrast at high field with fast field-cycling MRI,"Contrast agents with a strong $R_1$ dispersion have been shown to be
effective in generating target-specific contrast in MRI. The utilization of
this $R_1$ field dependence requires the adaptation of a MRI scanner for fast
field-cycling (FFC). Here, we present the first implementation and validation
of FFC-MRI at a clinical field strength of 3 T. A field-cycling range of
$\pm$100 mT around the nominal $B_0$ field was realized by inserting an
additional insert coil into an otherwise conventional MRI system. System
validation was successfully performed with selected iron oxide magnetic
nanoparticles and comparison to FFC-NMR relaxometry measurements. Furthermore,
we show proof-of-principle $R_1$ dispersion imaging and demonstrate the
capability of generating R1 dispersion contrast at high field with suppressed
background signal. With the presented ready-to-use hardware setup it is
possible to investigate MRI contrast agents with a strong R1 dispersion at a
field strength of 3 T.",1810.07930v1
2018-10-02,"Design and development of a low temperature, inductance based high frequency ac susceptometer","We report on the development of an induction based low temperature high
frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz
and at temperatures between 2 K and 300 K. Careful balancing of the detection
coils and calibration have allowed a sample magnetic moment resolution of
$5\times10^{-10} Am^2$ at 1 MHz. We will discuss the design and
characterization of the susceptometer, and explain the calibration process. We
also include some example measurements on the spin ice material CdEr$_2$S$_4$
and iron oxide based nanoparticles to illustrate functionality.",1810.09559v1
2019-06-28,High pO2 Floating Zone Crystal Growth of the Perovskite Nickelate PrNiO3,"Single crystals of PrNiO3 were grown under an oxygen pressure of 295 bar
using a unique high-pressure optical-image floating zone furnace. The crystals,
with volume in excess of 1 mm3, were characterized structurally using single
crystal and powder X-ray diffraction. Resistivity, specific heat, and magnetic
susceptibility were measured, all of which evidenced an abrupt, first order
metal-insulator transition (MIT) at ~130 K, in agreement with previous
literature reports on polycrystalline specimens. Temperature-dependent single
crystal diffraction was performed to investigate changes through the MIT. Our
study demonstrates the opportunity space for high fugacity, reactive
environments for single crystal growth specifically of perovskite nickelates
but more generally to correlated electron oxides.",1907.00078v1
2019-09-01,Observation of a charge-neutral muon-polaron complex in antiferromagnetic Cr$_2$O$_3$,"We report a comprehensive muon spin rotation ($\mu$SR) study of the
prototypical magnetoelectric antiferromagnet Cr$_2$O$_3$. We find the
positively charged muon ($\mu^+$) occupies several distinct interstitial sites,
and displays a rich dynamic behavior involving local hopping, thermally
activated site transitions and the formation of a charge-neutral complex
composed of a muon and an electron polaron. The discovery of such a complex has
implications for the interpretation of $\mu$SR spectra in a wide range of
magnetic oxides, and opens a route to study the dopant characteristics of
interstitial hydrogen impurities in such materials. We address implications
arising from implanting a $\mu^+$ into a linear magnetoelectric, and discuss
the challenges of observing a local magnetoelectric effect generated by the
charge of the muon.",1909.00416v1
2020-01-20,First-principles studies of electronic properties in Lithium metasilicate (Li2SiO3),"Lithium metasilicate (Li2SiO3) has attracted considerable interest as a
promising electrolyte material for potential use in lithium batteries. However,
its electronic properties are still not thoroughly understood. In this work,
density functional theory calculations were adopted, our calculations find out
that Li2SiO3 exhibits unique lattice symmetry (orthorhombic crystal), valence
and conduction bands, charge density distribution, and van Hove singularities.
Delicate analyses, the critical multi-orbital hybridizations in Li-O and Si-O
bonds 2s- (2s, 2px, 2py, 2pz) and (3s, 3px, 3py, 3pz)- (2s, 2px, 2py, 2pz),
respectively was identified. In particular, this system shows a huge
indirect-gap of 5.077 eV. Therefore, there exist many strong covalent bonds,
with obvious anisotropy and non-uniformity. On the other hand, the
spin-dependent magnetic configurations are thoroughly absent. The theoretical
framework could be generalized to explore the essential properties of cathode
and anode materials of oxide compounds.",2001.07128v1
2020-01-21,Field-Driven Gapless Spin Liquid in the Spin-1 Kitaev Honeycomb Model,"Recent proposals for spin-1 Kitaev materials, such as honeycomb Ni oxides
with heavy elements of Bi and Sb, have shown that these compounds naturally
give rise to antiferromagnetic (AFM) Kitaev couplings. Conceptual interest in
such AFM Kitaev systems has been sparked by the observation of a transition to
a gapless $U(1)$ spin liquid at intermediate field strengths in the AFM
spin-1/2 Kitaev model. However, all hitherto known spin-1/2 Kitaev materials
exhibit ferromagnetic bond-directional exchanges. Here we discuss the physics
of the spin-1 Kitaev model in a magnetic field and show, by extensive numerical
analysis, that for AFM couplings it exhibits an extended gapless quantum spin
liquid at intermediate field strengths. The close analogy to its spin-1/2
counterpart suggests that this gapless spin liquid is a $U(1)$ spin liquid with
a neutral Fermi surface, that gives rise to enhanced thermal transport
signatures.",2001.07699v1
2020-02-16,"First-principles Study on Piezoelectricity and Spontaneous Polarization in Bi(Fe,Co)O3","Solid solution BiFe1-xCoxO3 shows anti-ferromagnetic order and pyroelectric
order, simultaneously. It has been known that BiFe1-xCoxO3 exhibits a
structural phase transition between monoclinic and tetragonal phases as x
increases. This kinds of transition is often called morphotoropic phase
boundary, which is well known to take place in a representative piezoelectric
oxide, PbZr1-xTixO3. In order to theoretically understand the piezoelectric
property in BiFe1-xCoxO3, we performed ab-initio electronic-structure
calculations and studied the structural stability, the magnetic property, and
the electronic polarization by means of super-cell approach. It turns out that
the large electric polarization and the particular pyramidal coordination
suppress the response of the electric polarization under strain. A way to
enhance the piezoelectric effect in BiFe1-xCoxO3 is proposed.",2002.06510v1
2020-02-23,Local polarization in oxygen-deficient LaMnO$_3$ induced by charge localization in the Jahn-Teller distorted structure,"The functional properties of transition metal perovskite oxides are known to
result from a complex interplay of magnetism, polarization, strain, and
stoichiometry. Here, we show that for materials with a cooperative Jahn-Teller
distortion, such as LaMnO$_3$ (LMO), the orbital order can also couple to the
defect chemistry and induce novel material properties. At low temperatures, LMO
exhibits a strong Jahn-Teller distortion that splits the $e_g$ orbitals of the
high-spin Mn$^{3+}$ ions and leads to alternating long, short, and intermediate
Mn--O bonds. Our DFT+$U$ calculations show that, as a result of this orbital
order, the charge localization in LMO upon oxygen vacancy formation differs
from other manganites, like SrMnO$_3$, where the two extra electrons reduce the
two Mn sites adjacent to the vacancy. In LMO, relaxations around the defect
depend on which type of Mn--O bond is broken, affecting the $d$-orbital
energies and leading to asymmetric and hence polar excess-electron localization
with respect to the vacancy. Moreover, we show that the Mn--O bond lengths,
orbital order and consequently the charge localization and polarity are tunable
via strain.",2002.09921v1
2020-04-03,Plasma-enhanced atomic layer deposition of nickel nanotubes with low resistivity and coherent magnetization dynamics for 3D spintronics,"We report plasma-enhanced atomic layer deposition (ALD) to prepare conformal
nickel thin films and nanotubes by using nickelocene as a precursor, water as
the oxidant agent and an in-cycle plasma enhanced reduction step with hydrogen.
The optimized ALD pulse sequence, combined with a post-processing annealing
treatment, allowed us to prepare 30 nm thick metallic Ni layers with a
resistivity of 8 $\mu\Omega$cm at room temperature and good conformality both
on the planar substrates and nanotemplates. Thereby we fabricated several
micrometer-long nickel nanotubes with diameters ranging from 120 to 330 nm. We
report on the correlation between ALD growth and functional properties of
individual Ni nanotubes characterized in terms of magneto-transport and the
confinement of spin wave modes. The findings offer novel perspectives for
Ni-based spintronics and magnonic devices operated in the GHz frequency regime
with a 3D device architecture.",2004.01592v2
2020-12-07,Van der Waals Multiferroic Tunnel Junctions,"Multiferroic tunnel junctions (MFTJs) have aroused significant interest due
to their functional properties useful for non-volatile memory devices. So far,
however, all the existing MFTJs have been based on perovskite-oxide
heterostructures limited by a relatively high resistance-area (RA) product
unfavorable for practical applications. Here, using first-principles
calculations, we explore spin-dependent transport properties of van der Waals
(vdW) MFTJs which consist of two-dimensional (2D) ferromagnetic FenGeTe2 (n =
3, 4, 5) electrodes and 2D ferroelectric In2Se3 barrier layers. We demonstrate
that such FemGeTe2/In2Se3/FenGeTe2 (m, n = 3, 4, 5) MFTJs exhibit multiple
non-volatile resistance states associated with different polarization
orientation of the ferroelectric In2Se3 layer and magnetization alignment of
the two ferromagnetic FenGeTe2 layers. We find a remarkably low RA product
which makes the proposed vdW MFTJs superior to the conventional MFTJs in terms
of their promise for non-volatile memory applications.",2012.03546v1
2020-12-22,Crystalline symmetry-dependent magnon formation in itinerant ferromagnet SrRuO3,"SrRuO3 (SRO) is an itinerant ferromagnet with strong coupling between the
charge, spin, and lattice degrees of freedom. This strong coupling suggests
that the electronic and magnetic behaviors of SRO are highly susceptible to
changes in the lattice distortion. Here we show how the spin interaction and
resultant magnon formation change with the modification in the crystallographic
orientation. We fabricated SRO epitaxial thin films with (100), (110), and
(111) surface orientations, to systematically modulate the spin interaction and
spin dimensionality. The reduced spin dimensionality and enhanced exchange
interaction in the (111)-oriented SRO thin film significantly suppresses magnon
formation. Our study comprehensively demonstrates the facile tunability of
magnon formation and spin interaction in correlated oxide thin films.",2012.11865v1
2021-01-19,Robust ferromagnetism in insulating La$_2$NiMnO$_6$ thin films,"The field of oxide spintronics can strongly benefit from the establishment of
robust ferromagnetic insulators with near room-temperature Curie temperature.
Here we investigate the structural, electronic, and magnetic properties of
atomically-precise epitaxially-strained thin films of the double perovskite
La$_2$NiMnO$_6$ (LNMO) grown by off-axis radio-frequency magnetron sputtering.
We find that the films retain both a strong insulating behavior and a bulk-like
Curie temperature in the order of 280 K, nearly independently from epitaxial
strain conditions. These results suggest a prospective implementation of LNMO
films in multi-layer device architectures where a high-temperature
ferromagnetic insulating state is a prerequisite.",2101.07530v2
2012-05-18,Measurements of the gate tuned superfluid density in superconducting LaAlO3/SrTiO3,"The interface between the insulating oxides LaAlO3 and SrTiO3 exhibits a
superconducting two-dimensional electron system that can be modulated by a gate
voltage. While gating of the conductivity has been probed extensively and
gating of the superconducting critical temperature has been demonstrated, the
question whether, and if so how, the gate tunes the superfluid density and
superconducting order parameter is unanswered. We present local magnetic
susceptibility, related to the superfluid density, as a function of
temperature, gate voltage and location. We show that the temperature dependence
of the superfluid density at different gate voltages collapse to a single curve
characteristic of a full superconducting gap. Further, we show that the dipole
moments observed in this system are not modulated by the gate voltage.",1205.4064v1
2012-05-20,Dimensionality Driven Spin-Flop Transition in Layered Iridates,"Using resonant x-ray diffraction, we observe an easy c-axis collinear
antiferromagnetic structure for the bilayer Sr$_3$Ir$_2$O$_7$, a significant
contrast to the single layer Sr$_2$IrO$_4$ with in-plane canted moments. Based
on a microscopic model Hamiltonian, we show that the observed spin-flop
transition as a function of number of IrO$_2$ layers is due to strong
competition among intra- and inter-layer bond-directional pseudo-dipolar
interactions of the spin-orbit entangled $J_{eff}$=1/2 moments. With this we
unravel the origin of anisotropic exchange interactions in a Mott insulator in
the strong spin-orbit coupling regime, which holds the key to the various types
of unconventional magnetism proposed in 5$d$ transition metal oxides.",1205.4381v1
2017-05-01,High pressure floating-zone growth of perovskite nickelate LaNiO3 single crystals,"We report the first single crystal growth of the correlated metal LaNiO3
using a high-pressure optical-image floating zone furnace. The crystals were
studied using single crystal/powder x-ray diffraction, resistivity, specific
heat, and magnetic susceptibility. The availability of bulk LaNiO3 crystals
will (i) promote deep understanding in this correlated material, including the
mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich
opportunities as a substrate for thin film growth such as important
ferroelectric and/or multiferroic materials. This study demonstrates the power
of high pO2 single crystal growth of nickelate perovskites and correlated
electron oxides more generally.",1705.00570v1
2017-05-06,Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3,"We theoretically study the dynamic time evolution following laser pulse
pumping in an antiferromagnetic insulator Cr$_{2}$O$_{3}$. From the
photoexcited high-spin quartet states to the long-lived low-spin doublet
states, the ultrafast demagnetization processes are investigated by solving the
dissipative Schr\""odinger equation. We find that the demagnetization times are
of the order of hundreds of femtosecond, in good agreement with recent
experiments. The switching times could be strongly reduced by properly tuning
the energy gaps between the multiplet energy levels of Cr$^{3+}$. Furthermore,
the relaxation times also depend on the hybridization of atomic orbitals in the
first photoexcited state. Our results suggest that the selective manipulation
of electronic structure by engineering stress-strain or chemical substitution
allows effective control of the magnetic state switching in photoexcited
insulating transition-metal oxides.",1705.02439v2
2017-08-22,ZnO/LSMO Nanocomposites for Energy Harvesting,"The composites of strontium-doped lanthanum manganite (LSMO) with zinc oxide
(ZnO) are candidate materials for energy harvesting by virtue of their magnetic
and piezoelectric characteristics. They could be used to harvest energy from
stray sources, such as the vibrations and electromagnetic noise from
transformers and compressors within electrical grid power stations to power
small diagnostic sensors, among other applications. The LSMO/ZnO nanocomposites
were made by: (i) milling the two bulk powders and, (ii) a wet chemical process
which resulted in core-shell structures. The electrical, piezoelectric, and
magnetoelectric properties showed strong dependence on the fabrication method.
Growth of ZnO nanopillars on the particulate core of LSMO surface appears to
have improved the piezoelectric properties. Moreover, the chemical bath
deposition process can be easily modified to incorporate dopants to augment
these properties further.",1709.01797v1
2017-09-26,Possibility to realize spin-orbit-induced correlated physics in iridium fluorides,"Recent theoretical predictions of ""unprecedented proximity"" of the electronic
ground state of iridium fluorides to the SU(2) symmetric $j_{\mathrm{eff}}=1/2$
limit, relevant for superconductivity in iridates, motivated us to investigate
their crystal and electronic structure. To this aim, we performed
high-resolution x-ray powder diffraction, Ir L$_3$-edge resonant inelastic
x-ray scattering, and quantum chemical calculations on Rb$_2$[IrF$_6$] and
other iridium fluorides. Our results are consistent with the Mott insulating
scenario predicted by Birol and Haule [Phys. Rev. Lett. 114, 096403 (2015)],
but we observe a sizable deviation of the $j_{\mathrm{eff}}=1/2$ state from the
SU(2) symmetric limit. Interactions beyond the first coordination shell of
iridium are negligible, hence the iridium fluorides do not show any magnetic
ordering down to at least 20 K. A larger spin-orbit coupling in iridium
fluorides compared to oxides is ascribed to a reduction of the degree of
covalency, with consequences on the possibility to realize spin-orbit-induced
strongly correlated physics in iridium fluorides.",1709.09027v1
2017-11-27,Control of surface plasmon-polaritons in magnetoelectric heterostructures,"The work is devoted to the investigation of the surface plasmon polaritons in
the metal - dielectric heterostructures containing materials with
magnetoelectric properties. The analysis of various possible configurations
shows that the magnetoelectric effect influences the plasmonic surface wave
polarization, localization and dispersion. The essential case of chromium (III)
oxide as a magnetoelectric dielectric is described in detail, revealing the
switching between different regimes of magnetoelectric impact on
plasmon-polaritons. Plasmonic heterostructures with magnetoelectric
constituents can be used as a polarization- and dispersion-sensitive instrument
to reveal the magnetoelectric coupling and besides might act as an optical tool
for control of the surface plasmon-polariton dispersion and dynamics via
external electric and magnetic fields. Apart from that, the described effects
can be applied to the manipulation of the far-field optical response of
plasmonic structures. Composite magnetoelectric materials like
$\mathrm{BaTiO_3/BiFeO_3}$ that exhibit giant magnetoelectric effect are very
promising for these purposes.",1711.09606v1
2018-03-04,Ultrafast optically induced ferromagnetic/anti-ferromagnetic phase transition in GdTiO$_3$ from first principles,"Epitaxial strain and chemical substitution have been the workhorses of
functional materials design. These static techniques have shown immense success
in controlling properties in complex oxides through the tuning of subtle
structural distortions. Recently, an approach based on the excitation of an
infrared active phonon with intense mid-infrared light has created an
opportunity for dynamical control of structure through special nonlinear
coupling to Raman phonons. We use first-principles techniques to show that this
approach can dynamically induce a magnetic phase transition from the
ferromagnetic ground state to a hidden antiferromagnetic phase in the rare
earth titanate GdTiO$_3$ for realistic experimental parameters. We show that a
combination of a Jahn-Teller distortion, Gd displacement, and infrared phonon
motion dominate this phase transition with little effect from the octahedral
rotations, contrary to conventional wisdom.",1803.01323v1
2018-03-28,Split Fermi Surfaces of the Spin-Orbit-Coupled Metal Cd2Re2O7 Probed by de Haas-van Alphen Effect,"The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition
with inversion symmetry breaking (ISB) at Ts1 = 200 K. A recent theory [L. Fu,
Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic
instability that leads to a multipolar order in the spin-orbit-coupled metal.
To observe the Fermi surface of the low-temperature phase of Cd2Re2O7, we
perform de Haas-van Alphen effect measurements by means of magnetic torque. In
reference to a calculated band structure, the spin-split Fermi surfaces with
large cyclotron masses of 5-9m0 are revealed. The splitting is suggested to be
due to an antisymmetric spin-orbit coupling induced by ISB, the strength of
which is estimated to be approximately 67 K, which is rather smaller than those
of typical non-centrosymmetric metals.",1803.10472v1
2018-06-05,Observation of out-of-plane spin texture in a SrTiO3 (111) two-dimensional electron gas,"We explore the second order bilinear magnetoelectric resistance (BMER) effect
in the d-electron-based two-dimensional electron gas (2DEG) at the SrTiO3 (111)
surface. We find an evidence of a spin-split band structure with the archetypal
spin-momentum locking of the Rashba effect for the in-plane component. Under an
out-of-plane magnetic field, we find a BMER signal that breaks the six-fold
symmetry of the electronic dispersion, which is a fingerprint for the presence
of a momentum dependent out-of-plane spin component. Relativistic electronic
structure calculations reproduce this spin-texture and indicate that the
out-of-plane component is a ubiquitous property of oxide 2DEGs arising from
strong crystal field effects. We further show that the BMER response of the
SrTiO3 (111) 2DEG is tunable and unexpectedly large.",1806.01533v1
2018-06-06,Emergent topological spin structures in a centrosymmetric cubic perovskite,"The skyrmion crystal (SkX) characterized by a multiple-q helical spin
modulation has been reported as a unique topological state that competes with
the single-q helimagnetic order in non-centrosymmetric materials. Here we
report the discovery of a rich variety of multiple-q helimagnetic spin
structures in the centrosymmetric cubic perovskite SrFeO3. On the basis of
neutron diffraction measurements, we have identified two types of robust
multiple-q topological spin structures that appear in the absence of external
magnetic fields: an anisotropic double-q spin spiral and an isotropic
quadruple-q spiral hosting a three-dimensional lattice of hedgehog
singularities. The present system not only diversifies the family of SkX host
materials, but furthermore provides an experimental missing link between
centrosymmetric lattices and topological helimagnetic order. It also offers
perspectives for integration of SkXs into oxide electronic devices.",1806.02309v1
2018-06-08,A superconducting absolute spin valve,"A superconductor with a spin-split excitation spectrum behaves as an ideal
ferromagnetic spin-injector in a tunneling junction. It was theoretical
predicted that the combination of two such spin-split superconductors with
independently tunable magnetizations, may be used as an ideal $absolute$
spin-valve. Here we report on the first switchable superconducting spin-valve
based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier.
The spin-valve shows a relative resistance change between the parallel and
antiparallel configuration of the EuS layers up to 900% that demonstrates a
highly spin-polarized currents through the junction. Our device may be pivotal
for realization of thermoelectric radiation detectors, logical element for a
memory cell in cryogenics superconductor-based computers and superconducting
spintronics in general.",1806.03151v1
2018-07-13,"Defect-induced modulation of magnetic, electronic and optical properties of double perovskite oxide La$_2$CoMnO$_6$","Electron- and hole-doped La$_2$CoMnO$_6$(LCMO) are investigated using first
principles DFT calculations. Hole and electron doping are achieved respectively
by introducing Sr$^{2+}$ at La$^{3+}$ sites and by inducing O-site vacancies in
LCMO. Electronic structure calculations suggest that hole doping alters the
charge and valence state of Co ions, whereas electron doping influences the Mn
ions. Introduction of defects is found to enhance antisite disorder(ASD) at
Co/Mn site, which is expected to influence the magnetodielectric properties of
the system. Our calculations suggest that while ASD and/or hole doping induces
half-metallicity in LCMO, electron doping restores its insulating state.
Mean-field calculations performed using exchange constants obtained by mapping
DFT total energies of different collinear spin configurations onto the Ising
Hamiltonian find that defects tend to reduce the Curie temperature ($T_C$).
Interestingly, the calculated linear optical properties of the system suggest
that the material becomes optically active with high values of birefringence in
the presence of defects, a property that is highly sought-after in the optical
communications and laser industry.",1807.05019v2
2018-07-13,Layered palladates and their relation to nickelates and cuprates,"We explore the layered palladium oxides La$_2$PdO$_4$, LaPdO$_2$ and
La$_4$Pd$_3$O$_8$ via ab initio calculations. La$_2$PdO$_4$, being low spin
$d^8$, is quite different from its high spin nickel analog. Hypothetical
LaPdO$_2$, despite its $d^9$ configuration, has a paramagnetic electronic
structure very different from cuprates. On the other hand, the hypothetical
trilayer compound La$_4$Pd$_3$O$_8$ ($d^{8.67}$) is more promising in that its
paramagnetic electronic structure is very similar to that of overdoped
cuprates. But even in the $d^9$ limit (achieved by partial substitution of La
with a 4+ ion), we find that an antiferromagnetic insulating state cannot be
stabilized due to the less correlated nature of Pd ions. Therefore, this
material, if it could be synthesized, would provide an ideal platform for
testing the validity of magnetic theories for high-temperature
superconductivity.",1807.05046v1
2018-07-18,"The pyrochlore Ho2Ti2O7: Synthesis, crystal growth and stoichiometry","We have investigated the effect of synthesis and growth conditions on the
magnetic, structural, and compositional properties of pyrochlore oxide holmium
titanate and demonstrate a method for growing high quality stoichiometric
single crystals. A series of polycrystalline samples with various contents of
Ti (-0.08 \leqslant x \leqslant 0.08, and nominal compositions of Ho2Ti2+xO7)
were synthesized at different temperatures, and characterized using powder
X-ray diffraction. The results show that synthesizing powders at a higher
temperature of 1500 {\deg}C yield single phase compounds. Ti deficient powders
showed an increase of lattice constant due to stuffing (Ho into Ti positions),
while Ti rich powders showed a decrease in lattice constant due to
anti-stuffing (Ti into Ho positions). A post annealing in O2 was found to be
necessary to accomplish the anti-stuffing process. Use of the conventional
floating zone (FZ) technique introduced Ti deficiency, stuffing, and oxygen
vacancies in the grown crystal. Growth of high structural quality and
stoichiometric single crystals of Ho2Ti2O7 by the traveling solvent floating
zone (TSFZ) is reported. AC susceptibility measurements revealed that the
stoichiometric crystal shows a higher ice freezing temperature, indicating that
crystal quality and stoichiometry play a key role on low temperature spin ice
properties of this compound.",1807.06788v1
2018-07-19,Three-Dimensional Quantum Anomalous Hall Effect in Ferromagnetic Insulators,"The quantum anomalous Hall effect (QAHE) hosts the dissipationless chiral
edge states associated with the nonzero Chern number, providing potentially
significant applications in future spintronics. The QAHE usually occurs in a
two-dimensional (2D) system with time-reversal symmetry breaking. In this work,
we propose that the QAHE can exist in three-dimensional (3D) ferromagnetic
insulators. By imposing inversion symmetry, we develop the topological
constraints dictating the appearance of 3D QAHE based on the parity analysis at
the time-reversal invariant points in reciprocal space. Moreover, using
first-principles calculations, we identify that 3D QAHE can be realized in a
family of intrinsic ferromagnetic insulating oxides, including layered and
non-layered compounds that share a centrosymmetric structure with space group
$R\bar{3}m$ (No. 166). The Hall conductivity is quantized to be
$-\frac{3e^2}{hc}$ with the lattice constant $c$ along $c$-axis. The chiral
surface sheet states are clearly visible and uniquely distributed on the
surfaces that are parallel to the magnetic moment. Our findings open a
promising pathway to realize the QAHE in 3D ferromagnetic insulators.",1807.07262v1
2018-12-20,Magnon-polarons in cubic collinear Antiferromagnets,"We present a theoretical study of excitations formed by hybridization between
magnons and phonons - magnon-polarons - in antiferromagnets. We first outline a
general approach to determining which magnon and phonon modes can and cannot
hybridize in a system thereby addressing the qualitative questions concerning
magnon-polaron formation. As a specific and experimentally relevant case, we
study Nickel Oxide quantitatively and find perfect agreement with the
qualitative analysis, thereby highlighting the strength of the former. We find
that there are two distinct features of antiferromagnetic magnon-polarons which
differ from the ferromagnetic ones. First, hybridization between magnons and
the longitudinal phonon modes is expected in many cubic antiferromagnetic
structures. Second, we find that the very existence of certain hybridizations
can be controlled via an external magnetic field, an effect which comes in
addition to the ability to move the magnon modes relative to the phonons modes.",1812.09239v1
2019-02-27,High-performance dendritic metamaterial absorber for broadband and near-meter wave radar,"Absorbing materials in ultra-high frequency (UHF) band has constantly been a
major challenge. The size of the absorber in UHF band is large, whereas the
resonant frequency band is narrow. According to Rozanov's theory, two kinds of
composite metamaterial absorbers are designed to realize the requirements of
low-frequency broadband metamaterial microwave absorber: the
magnetic-metamaterial composite absorber1 (MA1) and the dielectric-metamaterial
composite absorber 2 (MA2). In the range of approximately 300-1000MHz, both
absorbers achieve absorption of over 90% and feature good adaptability to the
incident angle of the incident wave. The absorbers also present good absorption
rate of over 80% in the range of 0-45 degree. Processing samples of indium tin
oxide (ITO) resistance film and polymethacrylimide (PMI) foam board feature
simple preparation and low cost, and the most important thing is to consider
the weight problem, which features certain advantages in terms of use.",1902.10398v1
2019-02-27,Coulomb gap induced by electronic correlation and enlarged superconducting gap in laterally confined Pb islands grown on SrTiO3,"We report high-resolution scanning tunneling microscopy (STM) study of
nano-sized Pb islands grown on SrTiO3, where three distinct types of gaps with
different energy scales are revealed. At low temperature, an enlarged
superconducting gap ({\Delta}s) emerges while there is no enhancement in
superconducting transition temperature (Tc), giving rise to a larger BCS ratio
2{\Delta}s/kBTc ~ 6.22. The strong coupling here may originate from the
electron-phonon coupling on the metal-oxide interface. As the superconducting
gap is suppressed under applied magnetic field or at elevated temperature,
Coulomb gap and pseudogap appear, respectively. The Coulomb gap is sensitive to
the lateral size of Pb islands, indicating that quantum size effect is able to
influence electronic correlation, which is usually ignored in low-dimensional
superconductivity. Our experimental results shall shed important light on the
interplay between quantum size effect and correlations in nano-sized
superconductors.",1902.10539v1
2019-03-26,Dynamical Bonding Driving Mixed Valency in a Metal Boride,"Samarium hexaboride is an anomaly, having many exotic and seemingly mutually
incompatible properties. It was proposed to be a mixed-valent semiconductor,
and later - a topological Kondo insulator, and yet has a Fermi surface despite
being an insulator. We propose a new and unified understanding of SmB$_6$
centered on the hitherto unrecognized dynamical bonding effect: the coexistence
of two Sm-B bonding modes within SmB$_6$, corresponding to different oxidation
states of the Sm. The mixed valency arises in SmB$_6$ from thermal population
of these distinct minima enabled by motion of B. Our model simultaneously
explains the thermal valence fluctuations, appearance of magnetic Fermi
surface, excess entropy at low temperatures, pressure-induced phase
transitions, and related features in Raman spectra and their unexpected
dependence on temperature and boron isotope.",1903.10650v2
2019-04-26,Terahertz spin dynamics driven by a field-derivative torque,"Efficient manipulation of magnetization at ultrashort time scales is of
particular interest for future technology. Here, we numerically investigate the
influence of the so-called field-derivative torque, which was derived earlier
based on relativistic Dirac theory [Mondal et al., Phys. Rev. B 94, 144419
(2016)], on the spin dynamics triggered by ultrashort laser pulses. We find
that only considering the THz Zeeman field can underestimate the spin
excitation in antiferromagnetic oxide systems as, e.g., NiO and CoO. However,
accounting for both, the THz Zeeman torque and the field-derivative torque, the
amplitude of the spin excitation increases significantly. Studying the damping
dependence of field-derivative torque we observe larger effects for materials
having larger damping constants.",1904.11768v2
2019-04-29,First Observed Metal-like to Insulator Transition in the vacant 3d orbital Quantum Spin Liquid Tb$_2$Ti$_2$O$_7$,"We report the observation of metal-like to insulator transition (MTI) in the
3dpyrochlore oxide Tb2Ti2O7 at 603 K due to the interaction of empty 3d
orbitals of Ti4+ with O2- ions, evidenced by the transition in resistivity.
Magnetisation, specific heat capacity and differential scanning calorimetry
support the MTI, and the transition is of second order. An appreciable change
in magnetisation with temperature, without any magnetic phase transition, is a
behaviour typical in this family of compounds which is seldom observed in empty
d orbital pyrochlores. The possible mechanism that supports the MTI in Tb2Ti2O7
is discussed. Subsequently, a broad change in magnetisation from 696 K is also
seen. Thermogravimetric analysis confirms the observed MTI (603 K) and the
broad change in magnetisation (696 K)are not due to oxygen vacancy",1904.12478v6
2019-08-02,Machine-learning-assisted thin-film growth: Bayesian optimization in molecular beam epitaxy of SrRuO3 thin films,"Materials informatics exploiting machine learning techniques, e.g., Bayesian
optimization (BO), has the potential to offer high-throughput optimization of
thin-film growth conditions through incremental updates of machine learning
models in accordance with newly measured data. Here, we demonstrated BO-based
molecular beam epitaxy (MBE) of SrRuO3, one of the most-intensively studied
materials in the research field of oxide electronics, mainly owing to its
unique nature as a ferromagnetic metal. To simplify the intricate search space
of entangled growth conditions, we ran the BO for a single condition while
keeping the other conditions fixed. As a result, high-crystalline-quality
SrRuO3 film exhibiting a high residual resistivity ratio (RRR) of over 50 as
well as strong perpendicular magnetic anisotropy was developed in only 24 MBE
growth runs in which the Ru flux rate, growth temperature, and
O3-nozzle-to-substrate distance were optimized. Our BO-based search method
provides an efficient experimental design that is not as dependent on the
experience and skills of individual researchers, and it reduces experimental
time and cost, which will accelerate materials research.",1908.00739v1
2019-08-07,Compressive-strain induced enhancement of exchange interactions and short-range magnetic order in Sr$_2$IrO$_4$ investigated by Raman spectroscopy,"We have carried out Raman spectroscopy experiments to investigate two-magnon
excitations in epitaxial thin films of the quasi-two-dimensional
antiferromagnetic Mott insulator Sr$_2$IrO$_4$ under in-plane misfit strain.
With in-plane biaxial compression, the energy of the two-magnon peak increases,
and the peak remains observable over a wider temperature range above the N\'eel
temperature, indicating strain-induced enhancement of the superexchange
interactions between $\it{J}_{eff}$ = 1/2 pseudospins. From density functional
theory calculations, we have found an increase of the nearest-neighbor hopping
parameter and exchange interaction with increasing biaxial compressive strain,
in agreement with the experimental observations. Our experimental and
theoretical results provide perspectives for systematic, theory-guided strain
control of the primary exchange interactions in 5$\it{d}$ transition metal
oxides.",1908.02716v1
2019-08-18,Influence of chemical stability on the fabrication of MnGa-based devices,"Ferromagnetic films of L10-ordered MnGa have shown promise not only in the
applications in ultrahigh-density magnetic recording and spintronic memories,
oscillators, and sensors, but also in controllable studies of novel electrical
transport phenomena. However, the stability of MnGa in chemicals and oxygen
plasma that are commonly used in the standard micro-/nano-fabrication process
has unsettled. In this work, we report a systematic study on the chemical
stability of the MnGa films in acids, acetone, ethanol, deionized water,
tetramethylammonium hydroxide (TMAOH) and oxygen plasma. We find that MnGa is
very stable in acetone and ethanol, while can be attacked substantially if
soaked in TMAOH solution for sufficiently long time. Deionized water and acids
(e.g., HCl, H3PO4 and H2SO4 solutions) attack MnGa violently and should be
avoided whenever possible. In addition, oxygen plasma can passivate the MnGa
surface by oxidizing the surface. These results provide important information
for the fabrication and the integration of MnGa based spintronic devices.",1908.06536v1
2019-08-19,Planar Hall Effect and Anisotropic Magnetoresistance in a polar-polar interface of LaVO$_3$-KTaO$_3$ with strong spin-orbit coupling,"Among the perovskite oxide family, KTaO$_3$ (KTO) has recently attracted
considerable interest as a possible system for the realization of the Rashba
effect. In this work, we improvise a novel conducting interface by juxtaposing
KTO with another insulator, namely LaVO$_3$ (LVO) and report planar Hall effect
(PHE) and anisotropic magnetoresistance (AMR) measurements. This interface
exhibits a signature of strong spin-orbit coupling. Our experimental
observation of two fold AMR at low magnetic fields can be intuitively
understood using a phenomenological theory for a Rashba spin-split system. At
high fields ($\sim$8 T), we see a two fold to four fold transition in the AMR
that could not be explained using only Rashba spin-split energy spectra. We
speculate that it might be generated through an intricate process arising from
the interplay between strong spin-orbit coupling, broken inversion symmetery,
relativistic conduction electron and possible uncompensated localized vanadium
spins.",1908.06636v1
2019-08-25,The Critical Current of Disordered Superconductors near T=0,"An increasing current through a superconductor can result in a discontinuous
increase in the differential resistance at the critical current. This critical
current is typically associated either with breaking of Cooper-pairs
(de-pairing) or with a collective motion of vortices (de-pinning). In this work
we measure superconducting amorphous indium oxide films at low temperatures and
high magnetic fields. Using heat-balance considerations we demonstrate that the
current-voltage characteristics are well explained by electron overheating that
occurs due to the thermal decoupling of the electrons from the host phonons. As
a result the electrons overheat to a significantly higher temperature than that
of the lattice. By solving the heat-balance equation we are able to accurately
predict the critical currents in a variety of experimental conditions. The
heat-balance approach stems directly from energy conservation. As such it is
universal and applies to diverse situations from critical currents in
superconductors to climate bi-stabilities that can initiate another ice-age.
One disadvantage of the universal nature of this approach is that it is
insensitive to the microscopic details of the system, which limits our ability
to draw conclusions regarding the initial departure from equilibrium.",1908.09303v1
2019-12-01,Designing Disorder into Crystalline Materials,"Crystals are a state of matter characterised by periodic order. Yet
crystalline materials can harbour disorder in many guises, such as
non-repeating variations in composition, atom displacements, bonding
arrangements, molecular orientations, conformations, charge states, orbital
occupancies, or magnetic structure. Disorder can sometimes be random, but more
usually it is correlated. Frontier research into disordered crystals now seeks
to control and exploit the unusual patterns that persist within these
correlated disordered states in order to access functional responses
inaccessible to conventional crystals. In this review we survey the core design
principles at the disposal of materials chemists that allow targeted control
over correlated disorder. We show how these principles---often informed by
long-studied statistical mechanical models---can be applied across an
unexpectedly broad range of materials, including organics, supramolecular
assemblies, oxide ceramics, and metal--organic frameworks. We conclude with a
forward-looking discussion of the exciting link to function in responsive
media, thermoelectrics, topological phases, and information storage.",1912.00366v1
2019-12-16,Micromagnetic modelling and imaging of vortex|merons structures in an oxide|metal heterostructure,"Using micromagnetic simulations, we have modelled the formation of imprinted
merons and anti-merons in cobalt overlayers of different thickness (1-8 nm),
stabilised by interfacial exchange with antiferromagnetic vortices in
$\alpha$-Fe2O3. Structures similar to those observed experimentally could be
obtained with reasonable exchange parameters, also in the presence of surface
roughness. We produce simulated meron|antimeron images by magnetic force
microscopy (MFM) and nitrogen-vacancy (N-V) centre microscopy, and established
signatures of these topological structures in different experimental
configurations.",1912.07511v4
2019-11-27,The Itinerancy and Interactions of the Linear Strings of Holes in Copper Oxide Superconductors,"Here I present a new model for the itinerancy of the strings of holes in the
Cuprates HTSC. The model assumes various scenarios with respect to the order of
the holes hopping and evaluates the weighting parameters for the different
scenarios. The new model still results in the aggregation of holes into
strings, but yields a spectral distribution for the itinerancy rates of the
strings. From this distribution I infer a spectral distribution for the
magnetic interaction between the strings, which suggests also a spectral
distribution for the pseudogap parameter, and some relevant experimental
functions. Apart from these distributions, the basic assumptions of former
relevant theories remain intact. Such assumptions are the existence of the
anti-ferromagnetic phases A and B, the basic structure of the pseudogap ground
state, the excitation operators, and the field. The ground state and the field
are basically divided into two bands, the gapless low energy band, and the high
energy band. Due to the wide distributions, the bands may be partially
overlapped.",1912.11080v1
2020-03-20,Theoretical investigation of superconductivity in trilayer square-planar nickelates,"The discovery of superconductivity in Sr-doped NdNiO$_{2}$ is a crucial
breakthrough in the long pursuit for nickel oxide materials with electronic and
magnetic properties similar to those of the cuprates. NdNiO$_2$ is the
infinite-layer member of a family of square-planar nickelates with general
chemical formula R$_{n+1}$Ni$_n$O$_{2n+2}$ (R = La, Pr, Nd, $n= 2, 3, ...
\infty$). In this letter, we investigate superconductivity in the trilayer
member of this series (R$_4$Ni$_3$O$_8$) using a combination of
first-principles and $t-J$ model calculations. R$_4$Ni$_3$O$_8$ compounds
resemble cuprates more than RNiO$_2$ materials in that only
Ni-$d_{x^{2}-y^{2}}$ bands cross the Fermi level, they exhibit a largely
reduced charge transfer energy, and as a consequence superexchange interactions
are significantly enhanced. We find that the superconducting instability in
doped R$_4$Ni$_3$O$_8$ compounds is considerably stronger with a maximum gap
about four times larger than that in Sr$_{0.2}$Nd$_{0.8}$NiO$_2$.",2003.09132v1
2020-05-09,Quest for New Quantum States via Field-Editing Technology,"We report new quantum states in spin-orbit-coupled single crystals that are
synthesized using a game-changing technology that ""field-edits"" crystal
structures (borrowing from the phrase ""genome editing"") via application of
magnetic field during crystal growth. This study is intended to fundamentally
address a major challenge facing the research community today: A great deal of
theoretical work predicting exotic states for strongly spin-orbit-coupled,
correlated materials has thus far met very limited experimental confirmation.
These conspicuous discrepancies are due chiefly to the extreme sensitivity of
these materials to structural distortions. The results presented here
demonstrate that the ""field-edited"" materials not only are much less distorted
but also exhibit novel phenomena absent in their ""non-edited"" counterparts. The
field-edited materials include an array of 4d and 5d transition metal oxides,
and three representative materials presented here are Ba4Ir3O10, Ca2RuO4, and
Sr2IrO4. This study provides an entirely new paradigm for discovery of new
quantum states and materials otherwise unavailable.",2005.04327v3
2020-05-17,Spin-orbital liquid in Ba$_3$CuSb$_2$O$_9$ stabilized by oxygen holes,"Both the Jahn-Teller distortion of Cu$^{2+}$O$_6$ octahedra and magnetic
ordering are absent in hexagonal Ba$_3$CuSb$_2$O$_9$ suggesting a Cu 3$d$
spin-orbital liquid state. Here, by means of resonant x-ray scattering and
absorption experiment, we show that oxygen 2$p$ holes play crucial role in
stabilizing this spin-orbital liquid state. These oxygen holes appear due to
the ""reaction"" Sb$^{5+}$$\rightarrow$Sb$^{3+}$ $+$ two oxygen holes, with these
holes being able to attach to Cu ions. The hexagonal phase with oxygen 2$p$
holes exhibits also a novel charge-orbital dynamics which is absent in the
orthorhombic phase of Ba$_3$CuSb$_2$O$_9$ with Jahn-Teller distortion and Cu
3$d$ orbital order. The present work opens up a new avenue towards
spin-charge-orbital entangled liquid state in transition-metal oxides with
small or negative charge transfer energy.",2005.08200v1
2020-06-01,Magnetocaloric effect and spin-phonon correlations in RFe0.5Cr0.5O3 (R = Er and Yb) compounds,"We report the results of our investigation of the physical properties of
mixed metal oxides RFe0.5Cr0.5O3 (R = Er and Yb). ErFe0.5Cr0.5O3 undergoes an
antiferromagnetic ordering around 270 K followed by spin reorientation (SR)
transitions around 150 and 8 K respectively. In contrast, in YbFe0.5Cr0.5O3 a
single SR transition is noted at 36 K, below the AFM ordering temperature of
280 K. In ErFe0.5Cr0.5O3, a significant value of magnetic entropy change
({\Delta}SM) ~ -12.4 J/kg-K is noted near the 2nd SR transition, however, this
value is suppressed in YbFe0.5Cr0.5O3. Temperature dependent dielectric
permittivity of ErFe0.5Cr0.5O3 and YbFe0.5Cr0.5O3 at different frequencies,
reveal the presence of Debye-like relaxation behaviour in both compounds, which
can be due to the effect of charge carrier hopping between localized states of
Fe and Cr ions. Temperature dependent Raman scattering studies divulge that
spin-phonon coupling plays a crucial role in defining the physical properties
of these compounds.",2006.00736v1
2020-06-24,Microwave response of interacting oxide two-dimensional electron systems,"We present an experimental study on microwave illuminated high mobility
MgZnO/ZnO based two-dimensional electron systems with different electron
densities and, hence, varying Coulomb interaction strength. The photoresponse
of the low-temperature dc resistance in perpendicular magnetic field is
examined in low and high density samples over a broad range of illumination
frequencies. In low density samples a response due to cyclotron resonance (CR)
absorption dominates, while high density samples exhibit pronounced
microwave-induced resistance oscillations (MIRO). Microwave transmission
experiments serve as a complementary means of detecting the CR over the entire
range of electron densities and as a reference for the band mass unrenormalized
by interactions. Both CR and MIRO-associated features in the resistance permit
extraction of the effective mass of electrons but yield two distinct values.
The conventional cyclotron mass representing center-of-mass dynamics exhibits
no change with density and coincides with the band electron mass of bulk ZnO,
while MIRO mass reveals a systematic increase with lowering electron density
consistent with renormalization expected in interacting Fermi liquids.",2006.13627v1
2020-08-02,Design and analysis of guided modes in photonic waveguides using optical neural network,"We present a deep learning approach using an optical neural network to
predict the fundamental modal indices $n_{\rm{eff}}$ in a silicon (Si) channel
waveguide. We use three inputs, e.g., two geometric parameters and one material
property, and predict the $n_{\rm{eff}}$ for the transverse electric and
transverse magnetic polarizations. With the least number (i.e., $3^3$ or $4^3$)
of exact mode solutions from Maxwell's equations, we can uncover the solutions
which correspond to $10^3$ numerical simulations. Note that this consumes the
lowest amount of computational resources. The mean squared errors of the exact
and the predicted results are $<10^{-5}$. Moreover, our parameters' ranges are
compatible with current photolithography and complementary
metal-oxide-semiconductor (CMOS) fabrication technology. We also show the
impacts of different transfer functions and neural network layouts on the
model's performance. Our approach presents a unique advantage to uncover the
guided modes in any photonic waveguides within the least possible numerical
simulations.",2008.00398v1
2020-09-04,Geometric and Electronic Properties of Li$_2$GeO$_3$,"The 3D ternary Li$_2$GeO$_3$ compound, which could serve as the electrolyte
material in Li+-based batteries, exhibits an unusual lattice symmetry
(orthorhombic crystal), band structure, charge density distribution and density
of states. The essential properties are fully explored through the
first-principles method. In the delicate calculations and analyses, the main
features of atom-dominated electronic energy spectrum, space-charge
distribution, and atom-/orbital-projected density of states are suffi$cient to
identify the critical multi-orbital hybridizations of the chemical bonds:
2s-(2p$_x, 2p$_y$, 2p$_z$) and (4s, 4p$_x$, 4p$_y$, 4p$_z$)-(2s, 2p$_x$,
2p$_y$, 2p$_z$), respectively, for Li-O and Ge-O. This system possesses a large
indirect gap of Eg = 3.77 eV. There exist a lot of significant covalent bonds,
with an obvious non-uniformity and anisotropy. In addition, spin-dependent
magnetic configurations are completely absent. The theoretical framework could
be developed to investigate the important features of anode and cathode
materials related to lithium oxide compounds.",2009.02154v1
2020-09-13,Electric field control of disorder-tunable superconductivity and the emergence of quantum metal at an oxide interface,"We report on an extraordinary field effect of the superconducting
LaAlO3/KTaO3(111) interface with Tc ~2 K. By applying a gate voltage (VG)
across KTaO3, the interface can be continuously tuned from superconducting into
insulating states, yielding a dome-shaped Tc-VG dependence. The electric gating
has only a minor effect on carrier density as evidenced in the Hall-effect
measurement, while it changes spatial profile of the carriers in the interface,
hence the carrier's disorder level significantly. As temperature is decreased,
the resistance saturates at lowest temperature in both superconducting and
insulating sides, despite an initial dramatic dropping or increasing, which
suggests an emergence of quantum metallic state associated with failed
superconductor and/or fragile insulator. A VG-modulation of the
magnetic-field-driven superconductor to insulator quantum phase transition
reveals a non-universal criticality.",2009.05896v1
2020-09-19,Enhanced Ferromagnetism of CrI3 Bilayer by Self-Intercalation,"Two-dimensional (2D) ferromagnets with high Curie temperature have long been
the pursuit for electronic and spintronic applications. CrI3 is a rising star
of intrinsic 2D ferromagnets, however, it suffers from weak exchange coupling.
Here we propose a general strategy of self-intercalation to achieve enhanced
ferromagnetism in bilayer CrI3. We showed that filling either Cr or I atoms
into the van der Waals gap of stacked and twisted CrI3 bilayers can induce the
double exchange effect and significantly strengthen the interlayer
ferromagnetic coupling. According to our first-principles calculations, the
intercalated native atoms act as covalent bridge between two CrI3 layers and
lead to discrepant oxidation states for the Cr atoms. These theoretical results
offer a facile route to achieve high-Curie-temperature 2D magnets for device
implementation.",2009.09212v1
2021-02-02,"Coupled spin-orbital fluctuations in a three orbital model for $4d$ and $5d$ oxides with electron fillings $n=3,4,5$ -- Application to $\rm NaOsO_3$, $\rm Ca_2RuO_4$, and $\rm Sr_2IrO_4$","A unified approach is presented for investigating coupled spin-orbital
fluctuations within a realistic three-orbital model for strongly spin-orbit
coupled systems with electron fillings $n=3,4,5$ in the $t_{2g}$ sector of
$d_{yz},d_{xz},d_{xy}$ orbitals. A generalized fluctuation propagator is
constructed which is consistent with the generalized self-consistent
Hartree-Fock approximation where all Coulomb interaction contributions
involving orbital diagonal and off-diagonal spin and charge condensates are
included. Besides the low-energy magnon, intermediate-energy orbiton and
spin-orbiton, and high-energy spin-orbit exciton modes, the generalized
spectral function also shows other high-energy excitations such as the Hund's
coupling induced gapped magnon modes. We relate the characteristic features of
the coupled spin-orbital excitations to the complex magnetic behavior resulting
from the interplay between electronic bands, spin-orbit coupling, Coulomb
interactions, and structural distortion effects, as realized in the compounds
$\rm NaOsO_3$, $\rm Ca_2RuO_4$, and $\rm Sr_2IrO_4$.",2102.01400v2
2021-02-04,Spin-orbit-entangled electronic phases in 4$d$ and 5$d$ transition-metal compounds,"Complex oxides with $4d$ and $5d$ transition-metal ions recently emerged as a
new paradigm in correlated electron physics, due to the interplay between
spin-orbit coupling and electron interactions. For $4d$ and $5d$ ions, the
spin-orbit coupling, $\zeta$, can be as large as 0.2-0.4 eV, which is
comparable with and often exceeds other relevant parameters such as Hund's
coupling $J_{\rm H}$, noncubic crystal field splitting $\Delta$, and the
electron hopping amplitude $t$. This gives rise to a variety of
spin-orbit-entangled degrees of freedom and, crucially, non-trivial
interactions between them that depend on the $d$-electron configuration, the
chemical bonding, and the lattice geometry. Exotic electronic phases often
emerge, including spin-orbit assisted Mott insulators, quantum spin liquids,
excitonic magnetism, multipolar orderings and correlated topological
semimetals. This paper provides a selective overview of some of the most
interesting spin-orbit-entangled phases that arise in $4d$ and $5d$
transition-metal compounds.",2102.02740v1
2021-02-12,Probing the evolution of electronic phase-coexistence in complex systems by terahertz radiation,"In complex oxides, the electrons under the influence of competing energetics
are the cornerstone of coexistence (or phase-separation) of two or more
electronic/magnetic phases in same structural configuration. Probing of growth
and evolution of such phase-coexistence state is crucial to determine the
correct mechanism of related phase-transition. Here, we demonstrate the
combination of terahertz (THz) time-domain spectroscopy and DC transport as a
novel strategy to probe the electronic phase-coexistence. This is demonstrated
in disorder controlled phase-separated rare-earth nickelate thin films which
exhibit metal-insulator transition in dc conductivity at around 180 K but lack
this transition in terahertz (THz) dynamics conductivity down to low
temperature. Such pronounced disparity exploits two extreme attributes: i)
enormous sensitivity of THz radiation to a spatial range of its
wavelength-compatible electronic inhomogeneities and ii) insensitivity to a
range beyond the size of its wavelength. This feature is generic in nature
(sans a photo-induced effect), depends solely on the size of
insulating/metallic clusters and formulates a methodology with unique
sensitivity to investigate electronic phase-coexistence and phase transition of
any material system.",2102.06353v1
2021-02-12,Topological surface currents accessed through reversible hydrogenation of the three-dimensional bulk,"Hydrogen, the smallest and most abundant element in nature, can be
efficiently incorporated within a solid and drastically modify its electronic
state - it has been known to induce novel magnetoelectric effects in complex
perovskites and modulate insulator-to-metal transition in a correlated Mott
oxide. Here we demonstrate that hydrogenation resolves an outstanding challenge
in chalcogenide classes of three-dimensional (3D) topological insulators and
magnets - the control of intrinsic bulk conduction that denies access to
quantum surface transport. With electrons donated by a reversible binding of H+
ions to Te(Se) chalcogens, carrier densities are easily changed by over 10^20
cm^-3, allowing tuning the Fermi level into the bulk bandgap to enter
surface/edge current channels. The hydrogen-tuned topological materials are
stable at room temperature and tunable disregarding bulk size, opening a
breadth of platforms for harnessing emergent topological states.",2102.06639v1
2021-03-08,The fate of compound with AgF$_2$ plus AgO stoichiometry. A theoretical study,"Metal oxyfluorides constitute a broad group of chemical compounds with rich
spectrum of crystal structures and properties. Here we predict, based on
evolutionary algorithm approach, the crystal structure and selected properties
of Ag$_2$OF$_2$. This system may be considered as the 1 to 1 adduct of AgF$_2$
(i.e. an antiferromagnetic charge transfer positive U insulator) and AgO (i.e.
a disproportionated negative U insulator). We analyze oxidation states of
silver in each structure, possible magnetic interactions, as well as energetic
stability. Prospect is outlined for synthesis of polytypes of interest using
diverse synthetic approaches.",2103.04733v1
2021-03-16,Hard x-ray photoemission study on strain effect in LaNiO$_3$ thin films,"The strain effect from a substrate is an important experimental route to
control electronic and magnetic properties in transition-metal oxide (TMO) thin
films. Using hard x-ray photoemission spectroscopy, we investigate the strain
dependence of the valence states in LaNiO$_{3}$ thin films, strongly correlated
perovskite TMO, grown on four substrates: LaAlO$_{3}$,
(LaAlO$_{3}$)$_{0.3}$(SrAl$_{0.5}$Ta$_{0.5}$O$_{3}$)$_{0.7}$, SrTiO$_{3}$, and
DyScO$_{3}$. A Madelung potential analysis of core-level spectra suggests that
the point-charge description is valid for the La ions while it breaks down for
Ni and O ions due to a strong covalent bonding between the two. A clear x-ray
photon-energy dependence of the valence spectra is analyzed by the density
functional theory, which points to a presence of the La 5$p$ state near the
Fermi level.",2103.09208v1
2021-03-19,Entangled radicals may explain lithium effects on hyperactivity,"It is known that bipolar disorder and its lithium treatment involve the
modulation of oxidative stress. Moreover, it has been observed that lithium's
effects are isotope-dependent. Based on these findings, here we propose that
lithium exerts its effects by influencing the recombination dynamics of a
naturally occurring radical pair involving oxygen. We develop a simple model
inspired by the radical-pair mechanism in cryptochrome in the context of avian
magnetoreception and xenon-induced anesthesia. Our model reproduces the
observed isotopic dependence in the lithium treatment of hyperactivity in rats.
It predicts a magnetic-field dependence of the effectiveness of lithium, which
provides one potential experimental test of our hypothesis. Our findings show
that Nature might harness quantum entanglement for the brain's cognitive
processes.",2103.11057v1
2021-05-24,A non-perturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition,"Solid systems with strong correlations and interactions under light
illumination have the potential for exhibiting interesting bulk photovoltaic
behavior in the non-perturbative regime, which has remained largely unexplored
in the past theoretical studies. We investigate the bulk photovoltaic response
of a perovskite manganite with strongly coupled electron-spin-lattice dynamics,
using real-time simulations performed with a tight-binding model. The transient
changes in the band structure and the photoinduced phase transitions, emerging
from spin and phonon dynamics, result in a nonlinear current versus intensity
behavior beyond the perturbative limit. The current rises sharply across a
photoinduced magnetic phase transition, which later saturates at higher light
intensities due to excited phonon and spin modes. The predicted peak
photoresponsivity is orders of magnitude higher than other known ferroelectric
oxides such as BiFeO$_3$. We disentangle phonon-and spin-assisted components to
the ballistic photocurrent, showing that they are comparable in magnitude. Our
results illustrate a promising alternative way for controlling and optimizing
the bulk photovoltaic response through the photoinduced phase transitions in
strongly-correlated systems.",2105.11310v1
2021-06-25,Charged Defects and Phonon Hall Effects in Ionic Crystals,"It has been known for decades that a magnetic field can deflect phonons as
they flow in response to a thermal gradient, producing a thermal Hall effect.
Several recent experiments have revealed ratios of the phonon Hall conductivity
to the phonon longitudinal conductivity in oxide dielectrics that are larger
than $10^{-3}$ when phonon mean-free-paths exceed phonon wavelengths. At the
same time $\kappa_{H}/\kappa_{L}$ is not strongly temperature dependent. We
argue that these two properties together imply a mechanism related to phonon
scattering from defects that break time-reversal symmetry, and we show that
Lorentz forces acting on charged defects produce substantial skew-scattering
amplitudes, and related thermal Hall effects that are consistent with recent
observations.",2106.13889v3
2021-07-16,First principles studies of the electronic and structural properties of the rutile VO$_{2}$(110) surface and its oxygen-rich terminations,"We present a Density Functional Theory (DFT) study of the structural and
electronic properties of bare rutile VO$_{2}$(110) surfaces and its oxygen-rich
terminations. We discuss the performance of various DFT functionals, including
PBE, PBE+U (U = 2 eV), SCAN and SCAN+rVV functionals with non-magnetic and
ferromagnetic spin ordering. We predict the presence of a ring-like termination
that is electronically and structurally related to a V$_{2}$O$_{5}$(001)
monolayer and shows a higher stability than pure oxygen adsorption phases.
Despite the fact that the calculated phase stabilities depend on the chosen
functional, our results show that employing the spin-polarized SCAN functional
offers a good compromise yielding both a reasonable description of the
structural and electronic properties of the rutile VO$_{2}$ bulk phase and the
enthalpy of formation for different stages of vanadium oxidation.",2107.07899v1
2021-07-22,Variability of electron and hole spin qubits due to interface roughness and charge traps,"Semiconductor spin qubits may show significant device-to-device variability
in the presence of spin-orbit coupling mechanisms. Interface roughness, charge
traps, layout or process inhomogeneities indeed shape the real space wave
functions, hence the spin properties. It is, therefore, important to understand
how reproducible the qubits can be, in order to assess strategies to cope with
variability, and to set constraints on the quality of materials and
fabrication. Here we model the variability of single qubit properties (Larmor
and Rabi frequencies) due to disorder at the Si/SiO$_2$ interface (roughness,
charge traps) in metal-oxide-semiconductor devices. We consider both electron
qubits (with synthetic spin-orbit coupling fields created by micro-magnets) and
hole qubits (with intrinsic spin-orbit coupling). We show that charge traps are
much more limiting than interface roughness, and can scatter Rabi frequencies
over one order of magnitude. We discuss the implications for the design of spin
qubits and for the choice of materials.",2107.10902v2
2021-09-01,On the resistance minimum in LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ heterostructures,"In this paper we study LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ structures
with nominally x = 0, 0.1 and different thicknesses of the
Eu$_{1-x}$La$_x$TiO$_3$ layer. We observe that both systems have many
properties similar to previously studied LaAlO$_3$/EuTiO$_3$/SrTiO$_3$ and
other oxide interfaces, such as the formation of a 2D electron liquid for 1 or
2 unit cells of Eu$_{1-x}$La$_x$TiO$_3$; a metal-insulator transition driven by
the thickness increase of Eu$_{1-x}$La$_x$TiO$_3$ layer; the presence of an
Anomalous Hall effect (AHE) when driving the systems above the Lifshitz point
with a backgate voltage; and a minimum in the temperature dependence of the
sheet resistance below the Lifshitz point in the one-band regime, which becomes
more pronounced with increasing gate voltage. However, and notwithstanding the
likely presence of magnetism in the system, we do not attribute that minimum to
the Kondo effect, but rather to the properties of SrTiO$_3$ crystal and the
inevitable effects of charge trapping when using back gates.",2109.00620v1
2021-10-04,Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-($\sqrt{3}\times \sqrt{3}$)-R30$^\textrm{o}$,"Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a
combinatorial molecular beam epitaxy system integrated with cryogenic scanning
tunneling microscopy, we investigate the electronic structure of a
modulation-doped Mott insulator Sn/Si(111)-($\sqrt{3}\times
\sqrt{3}$)-R30$^\textrm{o}$. In underdoped regions, we observe a universal
pseudogap opening around the Fermi level, which changes little with the applied
magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared
out at elevated temperatures and alters in size with the spatial confinement of
the Mott insulating phase. Our findings, along with the previously observed
superconductivity at a higher doping level, are highly reminiscent of the
electronic phase diagram in the doped copper oxide compounds.",2110.01136v1
2021-10-19,Effect of the electronic charge gap on LO bond-stretching phonons in undoped La$_2$CuO$_4$ calculated using LDA+U,"Typical density-functional theory calculations that wrongly predict undoped
cuprates to be metallic also predict Cu-O half- and full-breathing phonon
energies that are significantly softer than observed, presumably because of
weak on-site Coulomb repulsion on the Cu 3d orbitals. We used DFT+U
calculations with antiferromagnetic supercells of La$_2$CuO$_4$ to establish
correlation between the on-site repulsion strength, tuned via adjusting the
value of U, and phonon dispersions. We find that breathing and half-breathing
phonons reach experimental values when U is tuned to obtain the correct optical
gap and magnetic moments. We demonstrate that using distorted supercells within
DFT+U is a promising framework to model phonons in undoped cuprates and other
perovskite oxides with complex, interrelated structural and electronic degrees
of freedom.",2110.10274v2
2022-01-04,Energy dissipation in composites with hybrid nacre-like helicoidal microstructures,"Natural ceramic composites present complex microstructures that lead to
tortuous crack paths and confer them high toughness. Current microreinforced
composites do not yet reach the same level of complexity in their
microstructures, resulting in poorer properties. To achieve complex
microstructuration, magnetically-assisted slip casting (MASC) was conducted
using a setup with 4 degrees of freedom. Among all possible microstructures, a
hybrid design between nacre-like and helicoidal arrangements was selected due
to its ability to tilt and twist the crack path. The hybrid microstructured
specimen fabricated, consisting of aluminum oxide micro platelets in a silicone
matrix, were tested under compression and their mechanical performance
compared. Although nacre-like composites exhibited the highest strength and
toughness, helicoidal hybrids could show some ductility and higher stiffness.
The fabrication strategy proposed here could thus be a simple route to study
more complex microstructures in view of increasing the toughness of
microplatelet reinforced composites.",2201.04955v1
2022-01-26,High precision scalable power converter for accelerator magnets,"The lower conduction power losses and the positive temperature coefficient
that favours parallel connections, make Silicon Carbide (SiC) metal oxide
semiconductor field-effect transistors (MOSFETs) to be an excellent replacement
of existing Silicon insulated gate bipolar transistors (IGBTs) technology.
These characteristics combined with high switching frequency operation, enables
the design of high-accuracy DC-DC converters with minimised filtering
requirements. This paper investigates the design for a converter with
high-accuracy current (0.9ppm) supplying a 0.05H electromagnetic load, aiming
to achieve the accuracy without the use of active filters, by using SiC MOSFETs
and a scalable module-based converter design.",2201.10824v2
2022-02-09,Gate tunable anomalous Hall effect at (111) LaAlO$_3$/SrTiO$_3$ interface,"We present the theoretical prediction of a gate tunable anomalous Hall effect
(AHE) in an oxide interface as a hallmark of spin-orbit coupling. The observed
AHE at low-temperatures in the presence of an external magnetic field emerges
from a complex structure of the Berry curvature of the electrons on the Fermi
surface and strongly depends on the orbital character of the occupied bands. A
detailed picture of the results comes from a multiband low-energy model with a
generalized Rashba interaction that supports characteristic out-of-plane spin
and orbital textures. We discuss strategies for optimizing the intrinsic AHE in
(111) SrTiO$_3$ heterostructure interfaces.",2202.04664v1
2022-04-07,Where to find lossless metals?,"Hypothetical metals having optical absorption losses as low as those of the
transparent insulators, if found, could revolutionize optoelectronics. We
perform the first high-throughput search for lossless metals among all known
inorganic materials in the databases of over 100,000 entries. The 381
candidates are identified -- having well-isolated partially-filled bands -- and
are analyzed by defining the figures of merit and classifying their real-space
conductive connectivity. The existing experimental evidence of most candidates
being insulating, instead of conducting, is due to the limitation of current
density functional theory in predicting narrow-band metals that are unstable
against magnetism, structural distortion, or electron-electron interactions. We
propose future research directions including conductive oxides, intercalating
layered materials, and compressing these false-metal candidates under high
pressures into eventual lossless metals.",2204.03222v2
2022-04-12,First-principles electronic structure investigation of HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+x}$ with the SCAN density functional,"We perform first-principles calculation to study the electronic structure of
HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+x}$ copper oxides up to $n = 6$ for the
undoped parent compound $(x = 0)$ and up to $n = 3$ for the doped compound $(x
> 0)$ by means of the SCAN meta-GGA density functional. Our calculations
predict an antiferromagnetic insulator ground state for the parent compounds
with an energy gap that decreases with the number of CuO$_{2}$ planes. We
report structural, electronic and magnetic order evolution with $x$ which agree
with experiments. We find an enhanced density of states at Fermi level at $x
\approx 0.25$ for the single-layered compound manifesting in a peak of the
Sommerfeld parameter, which recently has been discussed as a possible signature
of quantum criticality generic to all cuprates.",2204.05719v3
2022-05-09,Coupling Spin Defects in Hexagonal Boron Nitride to Titanium Oxide Ring Resonators,"Spin-dependent optical transitions are attractive for a plethora of
applications in quantum technologies. Here we report on utilization of high
quality ring resonators fabricated from TiO2 to enhance the emission from
negatively charged boron vacancies in hexagonal Boron Nitride. We show that the
emission from these defects can efficiently couple into the whispering gallery
modes of the ring resonators. Optically coupled boron vacancy showed
photoluminescence contrast in optically detected magnetic resonance signals
from the hybrid coupled devices. Our results demonstrate a practical method for
integration of spin defects in 2D materials with dielectric resonators which is
a promising platform for quantum technologies.",2205.04031v1
2022-06-30,Current Mapping of Amorphous LaAlO3/SrTiO3 near the Metal-Insulator Transition,"The two-dimensional electron system found between LaAlO3 and SrTiO3 hosts a
variety of physical phenomena that can be tuned through external stimuli. This
allows for electronic devices controlling magnetism, spin-orbit coupling, and
superconductivity. Controlling the electron density by varying donor
concentrations and using electrostatic gating are convenient handles to modify
the electronic properties, but the impact on the microscopic scale,
particularly of the former, remains underexplored. Here, we image the current
distribution at 4.2 K in amorphous-LaAlO3/SrTiO3 using scanning
superconducting-quantum-interference-device microscopy while changing the
carrier density in situ using electrostatic gating and oxygen annealing. We
show how potential disorder affects the current and how homogeneous 2D flow
evolves into several parallel conducting channels when approaching the
metal-to-insulator transition. We link this to ferroelastic domains and oxygen
vacancies. This has important consequences for micro- and nanoscale devices
with low carrier density and fundamental studies on quantum effects in oxides.",2206.15458v1
2022-07-07,Asymmetric Ground States in La$_{0.67}$Sr$_{0.33}$MnO$_3$/BaTiO$_3$ heterostructures Induced by Flexoelectric Bending,"Misfit strain delivered from single-crystal substrates typically modifies the
ground states of transition metal oxides, generating increasing interests in
designing modern transducers and sensors. Here, we demonstrate that
magnetotransport properties of La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) films were
continuously tuned by uniaxial strain produced by a home-designed bending jig.
The electrical conductivity and Curie temperature of LSMO films are enhanced by
bending stresses. The resistivity of a u-shape bended LSMO decays three times
faster than that of a n-shape bended LSMO as a response to the same magnitude
of strain. The asymmetric magnetic states in uniaxially strained LSMO are
attributed to the dual actions of Jahn-Teller distortion and strain gradient
mediated flexoelectric fields in an adjacent ferroelectric layer. These
findings of multi-field regulation in a single material provide a feasible
means for developing flexible electronic and spintronic devices.",2207.03297v1
2022-07-13,Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in Cr1-xPtx,"We report on a spin-orbit torque study of the spin current generation in
Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current
detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co
bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer,
with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find
that the spin current generation in the Cr1-xPtx alloy can be fully understood
by the characteristic trade-off between the intrinsic spin Hall conductivity of
Pt and the carrier lifetime in the dirty limit. We find no evidence for the
spin current generation by other mechanisms in this material, revealing that
the role of Cr is found to be simply the same as other metals and oxides in
previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as
an energy-efficient spin-orbit torque provider for magnetic memory and
computing technologies.",2207.05992v2
2022-07-21,New CuSO4-related high-temperature polymorph of AgIISO4,"Silver(II) compounds exhibit powerful oxidizing properties and strong
magnetic superexchange. AgSO4 is a rare fluorine-free salt of Ag(II) which
found some application in organic chemistry. Here, we report a discovery of a
new AgSO4 polymorph (\b{eta}). The distinct nature of the two polytypes of
AgSO4 is established using powder x-ray diffraction, vibrational spectroscopy
and theoretical calculations. The \b{eta} polymorph crystallizes in the
monoclinic system (P21/n) and shows structural similarities with CuSO4. DFT
calculations indicate very small differences in the energy of the two
polymorphs AgSO4, but the relative stability of the \b{eta} polymorph should
increase with temperature. The monoclinic distortion of the orthorhombic CuSO4
prototype originates from an unprecedented strong antiferromagnetic interaction
between Ag sites along the unit cell diagonal.",2207.10393v1
2022-07-23,Coexistence of Weyl semimetal and Weyl nodal loop semimetal phases in a collinear antiferromagnet,"Antiferromagnets (AFMs) with anomalous quantum responses have lead to new
progress for the understanding of their magnetic and electronic structures from
symmetry and topology points of view. Two typical topological states are the
collinear antiferromagnetic Weyl semimetal (WSM) and Weyl nodal loop semimetal
(WNLSM). In comparison with the counterparts in ferromagnets and non-collinear
AFMs, the WSMs and WNLSMs in collinear AFMs are still waiting for experimental
verification. In this work, we theoretically predicted the coexistence of Weyl
points (WPs) and Weyl nodal loops (WNLs) in transition metal oxide RuO2. Owing
to the small magnetocrystalline anisotropy energy, the WPs and WNLs can
transform to each other via tuning the Neel vector. Moreover, since the WPs are
very close to Fermi level and the WNLs are even crossing Fermi level, the
topological states in RuO2 can be easily probed by photoemission and STM
methods. Our result provides a promising material platform for the study of WSM
and WNLSM states in collinear AFMs.",2207.11472v1
2022-07-29,Structural investigation of Ayurveda Lauha (Iron) Bhasma,"In Ayurveda, Lauha (Iron) bhasma is primarily used to cure diseases related
with iron deficiency in humans. It is produced from purified raw metallic iron
using a combination of multi-step traditional preparation processes described
in the Ayurveda literature. Here, we present results of structural
investigation performed on the medicinal grade Lauha bhasma using various X-ray
based techniques. Our results indicate that after several rounds of heating and
cooling in specific conditions following the Ayurvedic preparation procedure,
metallic iron eventually converts to a natural iron-oxide mineral belonging to
the Magnetite group. Scanning electron microscopy (SEM) and X-ray standing wave
assisted fluorescence measurements carried out on powdered bhasma specimen
reveal that the Magnetite micro-particles in the bhasma specimen are usually
present in the form of agglomerates of nano-particles. We anticipate that the
Ayurvedic Lauha Bhasma has great potential for noninvasive localized target
killing of cancer cells, particularly in sensitive parts of the human body such
as brain, spinal cord, and lungs, via necrosis by application of an alternating
external magnetic field or photo electron generation through X-rays.",2207.14615v3
2022-08-09,Effect of annealing in the formation of well crystallized and textured SrFe$_{12}$O$_{19}$ films grown by RF magnetron sputtering,"We have studied the influence of annealing treatment on the crystalline
growth of SrFe_12_O_19 previously deposited on Si (100) substrates using radio
frequency (RF) magnetron sputtering. For this goal, two grown films, with and
without \textit{ex-situ} heating step, have been analysed and compared to
determine the differences in their structural, compositional and magnetic
properties. The results obtained by the different analysis techniques, in
particular M\""ossbauer spectroscopy together with EXAFS and XANES data, suggest
that the as-grown film is composed of nanocrystalline maghemite nanoparticles
and amorphous strontium oxide. A strontium hexaferrite canonical structure with
c-axis orientation in the sample plane was found for the annealed film.",2208.04658v1
2022-09-06,Preserving Metamagnetism in Self-Assembled FeRh Nanomagnets,"We present self-assembly routes of metamagnetic FeRh nanoisland arrays using
sputter deposition processing. Controlling the growth parameters and epitaxy
allows tuning the size and shape of the FeRh nanoislands. While the phase
transition between antiferromagnetic and ferromagnetic order is largely
suppressed in nanoislands formed on oxide substrates via thermodynamic
nucleation, we find that metamagnetism is largely preserved in nanomagnet
arrays formed through solid-state dewetting. This behavior is strongly
dependent on the resulting crystal faceting of the nanoislands, which is
characteristic of each assembly route. Comparing the calculated surface
energies for each magnetic phase of the nanoislands reveals that metamagnetism
can be suppressed or allowed by specific geometrical configurations of the
facets. Furthermore, we find that the spatial confinement leads to very
pronounced supercooling and the absence of phase separation in the nanoislands.
Finally, the supported nanomagnets are chemically etched away from the
substrates to inspect the phase transition properties of self-standing
nanoparticles. We demonstrate that solid-state dewetting is a feasible and
scalable way to obtain supported and free-standing FeRh nanomagnets with
preserved metamagnetism.",2209.02469v1
2022-10-19,Near-Field Optical MIMO Communication with Polarization-dependent Metasurfaces,"The ability to control waves at the nanoscale has attracted considerable
attention to ultrathin metasurface lenses (metalenses) in optical imaging and
encryption systems. We propose an approach to active tuning metasurfaces by
integrating an ultrathin layer of indium-tin-oxide (ITO) into a unit cell as an
electro-optically tunable material. A proposed design features two orthogonal
wings that can independently manipulate waves with corresponding orthogonal
polarizations. The charge carrier concentration in the ITO accumulation layer
is altered by modulating the applied bias voltage. This bias voltage generates
phase variations at terahertz frequencies for the reflected transverse electric
and transverse magnetic polarized waves. It is possible to move both focal
points of a metalens without any physical movement by varying the bias voltage.
In addition, this paper explores the application of virtually moving metalens
for a novel multiple-input and multiple-output (MIMO) communication
architecture. We demonstrate a communication system based on single-point
binary data communication and hexadecimal orbital angular momentum (OAM) data
communication. Then, orthogonal channels can be used for MIMO communication
with high capacity. The proposed design paves the way for high-speed
communications as well as polarization-controlled molecular imaging systems.",2210.10237v1
2022-12-05,Room temperature multiferroicity in a transition metal dichalcogenide,"The coexistence of multiple ferroic orders, i.e. multiferroicity, is a scarce
property to be found in materials. Historically, this state has been found
mainly in 3-dimensional complex oxides, but so far this state has still been
elusive for the most widely studied and characterized family of 2-dimensional
compounds, the transition metal dichalcogenides. In this study we report the
experimental realization of multiferroic states in this family of materials, at
room temperature, in bulk single crystals of Te-doped WSe2. We observe the
coexistence of ferromagnetism and ferroelectricity, evidenced in the presence
of magnetization and piezoresponse force microscopy hysteresis loops. These
findings open the possibility of widening the use and study of van der
Waals-based multifunctional devices for new nanoelectronics and spintronics
applications.",2212.02490v2
2022-12-22,Tunneling anisotropic spin galvanic effect,"We show that pure spin injection from a magnetic electrode into an inversion
symmetry-broken system composed of a tunnel barrier and a metallic region
generates a transverse charge current. Such a tunnelling spin galvanic
conversion is robust to disorder and non-local, i.e. injection and detection
contacts do not coincide, and is strongly anisotropic whenever the internal
spin-orbit field has a non-trivial angular dependence. The anisotropy shows up
in linear response, contrary to what happens in bulk conversion setups lacking
tunnelling elements. This is particularly relevant for spin-charge conversion
at oxide interfaces, where both the tunnel barrier and the receiving
low-dimensional metallic system host effective spin-orbit fields with complex
angular symmetries.",2212.11698v2
2023-01-21,Replica theory for disorder-free spin-lattice glass transition on a tree-like simplex network,"A class of pyrochlore oxides, $A_2$Mo$_2$O$_7$ ($A =$ Ho, Y, Dy, Tb) with
magnetic ions on corner-sharing tetrahedra is known to exhibit spin-glass
transitions without appreciable amount of quenched disorder. Recently a
disorder-free theoretical model for such a system has been proposed which takes
into account not only spins but also lattice distortions as dynamical variables
[K. Mitsumoto, C. Hotta and H. Yoshino, Phys. Rev. Lett. 124, 087201 (2020)].
In the present paper we develop and analyze an exactly solvable disorder-free
mean-field model which is a higher-dimensional counterpart of the model. We
find the system exhibit complex free-energy landscape accompanying replica
symmetry breaking through the spin-lattice coupling.",2301.08884v1
2023-01-26,Unraveling the effects of inter-site Hubbard interactions in spinel Li-ion cathode materials,"Accurate first-principles predictions of the structural, electronic,
magnetic, and electrochemical properties of cathode materials can be key in the
design of novel efficient Li-ion batteries. Spinel-type cathode materials
Li$_x$Mn$_2$O$_4$ and Li$_x$Mn$_{1.5}$Ni$_{0.5}$O$_4$ are promising candidates
for Li-ion battery technologies, but they present serious challenges when it
comes to their first-principles modeling. Here, we use density-functional
theory with extended Hubbard functionals - DFT+$U$+$V$ with on-site $U$ and
inter-site $V$ Hubbard interactions - to study the properties of these
transition-metal oxides. The Hubbard parameters are computed from
first-principles using density-functional perturbation theory. We show that
while $U$ is crucial to obtain the right trends in properties of these
materials, $V$ is essential for a quantitative description of the structural
and electronic properties, as well as the Li-intercalation voltages. This work
paves the way for reliable first-principles studies of other families of
cathode materials without relying on empirical fitting or calibration
procedures.",2301.11143v2
2023-02-03,Ligand hole driven metal-insulator transition in a prototypical transition metal double perovskite oxide Ca$_2$FeMnO$_6$,"Ca$_2$FeMnO$_6$ (CFMO) double perovskite was studied using first principles
density functional theory and tight-binding (TB) Hamiltonian modeling using
extended Hubbard model. We have shown by electronic structure analysis that
charge- and magnetic-ordering are driven by charge disproportionation at low
temperature caused by partial localization of O-$2p$ ligand holes at alternate
Fe sites that creates Jahn-Teller distortion, which leads to metal to insulator
transition (MIT) in CFMO. Our results suggests MIT was triggered by negative
charge-transfer energy of self-hole doping, responsible for symmetry lowering
transitions. Notably, the band-gap was found to fundamentally controlled by the
strength of the charge-transfer energy, and not by the Mott-Hubbard
interactions, which can be modeled by composition, pressure or stoichiometry
modulations. The fundamental insights presented in this work will help
understand similar physics and mechanisms in other class of perovskites and
correlated metals.",2302.01545v2
2023-02-13,Thickness and temperature dependent damping in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ epitaxial films,"The damping of La0.67Sr0.33MnO3 (LSMO) epitaxial films as a function of
thickness at different temperatures was studied. The competition between two
scattering types (\r{ho}-like and {\sigma}-like) with entirely distinct
thickness and temperature dependencies resulted in complicated damping
behavior. The behavior of {\sigma}-like damping in LSMO films is consistent
with the behavior in magnetic metal films. However, because \r{ho}-like damping
is sensitive to the fine electron structure near the Fermi surface, the
distortion of the oxygen octahedra controlled by the film thickness is an
important factor in controlling the damping. Our study demonstrates that the
complexity of damping in LSMO epitaxial films is a consequence of
strong-correlation effects, which are characteristic of complex
transition-metal oxides.",2302.06099v3
2023-03-05,Real-Space Observation of Ligand Hole State in Cubic Perovskite SrFeO$_3$,"An anomalously high valence state sometimes shows up in transition-metal
oxide compounds. In such systems, holes tend to occupy mainly the ligand $p$
orbitals, giving rise to interesting physical properties such as
superconductivity in cuprates and rich magnetic phases in ferrates. However, no
one has ever observed the distribution of ligand holes in real space. Here, we
report a successful observation of the spatial distribution of valence
electrons in cubic perovskite SrFeO$_3$ by high-energy X-ray diffraction
experiments and precise electron density analysis using a core differential
Fourier synthesis method. A real-space picture of ligand holes formed by the
orbital hybridization of Fe 3$d$ and O 2$p$ is revealed. The anomalous valence
state in Fe is attributed to the considerable contribution of the ligand hole,
which is related to the metallic nature and the absence of Jahn-Teller
distortions in this system.",2303.02571v2
2023-03-20,Thermal decomposition of the Kitaev material $α$-RuCl$_3$ and its influence on low-temperature behavior,"We explore the effect of heat treatment in argon atmosphere under various
temperatures up to $500^\circ$C on single crystals of $\alpha$-RuCl$_3$ by
study of the mass loss, microprobe energy dispersive x-ray spectroscopy, powder
x-ray diffraction, electrical resistance as well as low-temperature magnetic
susceptibility and specific heat. Clear signatures of dechlorination and
oxidation of Ru appear for annealing temperatures beyond $300^\circ$C. Analysis
of the specific heat below 2~K reveals a RuO$_2$ mass fraction of order $1\%$
for pristine $\alpha$-RuCl$_3$ which increases up to $20\%$ after thermal
annealing, fully consistent with mass-loss analysis. The small RuO$_2$
inclusions drastically reduce the global electrical resistance and may thus
significantly affect low-temperature thermal transport and Hall effect.",2303.11308v1
2023-03-24,Simulation of 1/f charge noise affecting a quantum dot in a Si/SiGe structure,"Due to presence of magnetic field gradient needed for coherent spin control,
dephasing of single-electron spin qubits in silicon quantum dots is often
dominated by $1/f$ charge noise. We investigate theoretically fluctuations of
ground state energy of an electron in gated quantum dot in realistic Si/SiGe
structure. We assume that the charge noise is caused by motion of charges
trapped at the semiconductor-oxide interface. We consider a realistic range of
trapped charge densities, $\rho \! \sim \! 10^{10}$ cm$^{-2}$, and typical
lenghtscales of isotropically distributed displacements of these charges,
$\delta r \! \leq \! 1$ nm, and identify pairs $(\rho,\delta r)$ for which the
amplitude and shape of the noise spectrum is in good agreement with spectra
reconstructed in recent experiments on similar structures.",2303.13968v1
2023-04-20,Noncollinear DFT+$U$ and Hubbard parameters with fully-relativistic ultrasoft pseudopotentials,"The magnetic, noncollinear parametrization of Dudarev's DFT+$U$ method is
generalized to fully-relativistic ultrasoft pseudopotentials. We present the
definition of the DFT+$U$ total energy functional, and the calculation of
forces and stresses in the case of orthogonalized atomic orbitals defining the
localised Hubbard manifold, where additional contributions arising from the
derivative of the inverse square root of the overlap matrix appear. We further
extend the perturbative calculation of the Hubbard $U$ parameters within
density-functional perturbation theory to the noncollinear relativistic case,
by exploiting an existing and recently developed theoretical approach that
takes advantage of the time-reversal operator to solve a second Sternheimer
equation. We validate and apply the new scheme by studying the electronic
structure and the thermodynamics of the binary compounds EuX (where X = O, S,
Se, Te is a chalcogen atom), as representative simple crystals, and of the
pyrochlore Cd$_2$Os$_2$O$_7$, representative of a more structurally complex
oxide.",2304.10178v1
2023-04-29,Natural orbitals and two-particle correlators as tools for analysis of effective exchange couplings in solids,"Using generalizations of natural orbitals, spin-averaged natural orbitals,
and two-particle charge correlators for solids, we investigate electronic
structure of antiferromagnetic transition-metal oxides with a fully
self-consistent, finite-temperature GW method. Our findings disagree with
Goodenough-Kanamori (GK) rules, commonly used for qualitative interpretation of
such solids. First, we found a strong dependence of natural orbital occupancies
on momenta contradicting GK assumptions. Second, along the momentum path, the
character of natural orbitals changes. In particular, contributions of oxygen
2s orbitals are important, which has not been considered in the GK rules. To
analyze the influence of electronic correlation on the values of effective
exchange coupling constants, we use both natural orbitals and two-particle
correlators and show that electronic screening modulates the degree of
superexchange by stabilizing the charge-transfer contributions, greatly
affecting these coupling constants. Finally, we give a set of predictions and
recommendations regarding the use of density functional, Green's function, and
wave-function methods for evaluating effective magnetic couplings in molecules
and solids.",2305.00325v1
2023-05-04,Two-particle bound states on a lattice,"Two-particle lattice states are important for physics of magnetism,
superconducting oxides, and cold quantum gases. The quantum-mechanical lattice
problem is exactly solvable for finite-range interaction potentials. A two-body
Schroedinder equation can be reduced to a system of linear equations whose
numbers scale with the number of interacting sites. For the simplest cases such
as on-site or nearest-neighbor attractions, many pair properties can be derived
analytically, although final expressions can be quite complicated. In this
work, we systematically investigate bound pairs in one-, two-, and
three-dimensional lattices. We derive pairing conditions, plot phase diagrams,
and compute effective masses, radii, and energies. Along the way, we analyze
nontrivial physical effects such as light pairs and the dependence of binding
thresholds on pair momenta. At the end, we discuss the preformed-pair mechanism
of superconductivity and stability of many-pair systems against phase
separation. The paper is a combination of original work and pedagogical
tutorial.",2305.02548v2
2023-05-10,Correlations of spin splitting and orbital fluctuations due to 1/f charge noise in the Si/SiGe Quantum Dot,"Fluctuations of electric fields can change the position of a gate-defined
quantum dot in a semiconductor heterostructure. In the presence of magnetic
field gradient, these stochastic shifts of electron's wavefunction lead to
fluctuations of electron's spin splitting. The resulting spin dephasing due to
charge noise limits the coherence times of spin qubits in isotopically purified
Si/SiGe quantum dots. We investigate the spin splitting noise caused by such
process caused by microscopic motion of charges at the semiconductor-oxide
interface. We compare effects of isotropic and planar displacement of the
charges, and estimate their densities and typical displacement magnitudes that
can reproduce experimentally observed spin splitting noise spectra. We predict
that for defect density of $10^{10}$ cm$^{-2}$, visible correlations between
noises in spin splitting and in energy of electron's ground state in the
quantum dot, are expected.",2305.06011v1
2023-05-25,Optimizing Experimental Parameters for Orbital Mapping,"A new material characterization technique is emerging for the transmission
electron microscope (TEM). Using electron energy-loss spectroscopy, real space
mappings of the underlying electronic transitions in the sample, so called
orbital maps, can be produced. Thus, unprecedented insight into the electronic
orbitals responsible for most of the electrical, magnetic and optical
properties of bulk materials can be gained. However, the incredibly demanding
requirements on spatial as well as spectral resolution paired with the low
signal-to-noise ratio severely limits the day-to-day use of this new technique.
With the use of simulations, we strive to alleviate these challenges as much as
possible by identifying optimal experimental parameters. In this manner, we
investigate representative examples of a transition metal oxide, a material
consisting entirely of light elements, and an interface between two different
materials to find and compare acceptable ranges for sample thickness,
acceleration voltage and electron dose for a scanning probe as well as for
parallel illumination.",2305.16039v1
2023-05-25,A tunable and versatile 28nm FD-SOI crossbar output circuit for low power analog SNN inference with eNVM synapses,"In this work we report a study and a co-design methodology of an analog SNN
crossbar output circuit designed in a 28nm FD-SOI technology node that
comprises a tunable current attenuator and a leak-integrate and fire neurons
that would enable the integration of emerging non-volatile memories (eNVMs) for
synaptic arrays based on various technologies including phase change (PCRAM),
oxide-based (OxRAM), spin transfer and spin orbit torque magnetic memories
(STT, SOT-MRAM). Circuit SPICE simulation results and eNVM experimental data
are used to showcase and estimate the neurons fan-in for each type of eNVM
considering the technology constraints and design trade-offs that set its
limits such as membrane capacitance and supply voltage, etc.",2305.16187v1
2023-05-29,Essential L-Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation,"The colloidal 2D materials based on graphene and its modifications are of
great interest when it comes to forming LC phases. These LC phases allow
controlling the orientational order of colloidal particles, paving the way for
the efficient processing of modified graphene with anisotropic properties.
Here, we present the peculiarities of AA functionalization of GO, along with
the formation of its LC phase and orientational behavior in an external
magnetic field. We discuss the influence of pH on the GOLC, ultimately showing
its pH-dependent behavior for GO-AA complexes. In addition, we observe
different GO morphology changes due to the presence of AA functional groups,
namely L-cysteine dimerization on the GO platform. The pH dependency of
AA-functionalized LC phase of GO is examined for the first time. We believe
that our studies will open new possibilities for applications in
bionanotechnologies due to self-assembling properties of LCs and magnificent
properties of GO.",2305.17919v1
2023-06-08,Hidden Hydroxides in KOH-Grown BaNiO3 Crystals: A Potential Link to Their Catalytic Behavior,"The hexagonal perovskite BaNiO3, prepared via non-ceramic approaches, is
known to act as a good catalyst for the oxygen-evolution reaction (OER) in
alkaline media. Here we report our observation that BaNiO3 synthesized via KOH
flux growth and high O2 pressure ceramic synthesis have different magnetic
properties. We show that this is because the KOH flux-grown crystals made in
open-air are actually a hydroxide-containing form of BaNiO3 that can be dried
upon annealing in O2 flow. This work not only unveils a previously unknown
aspect of the BaNiO3 OER catalyst and offers some insights into the underlying
mechanism, but also suggests that hydroxide ions may be present in other
hexagonal perovskite oxides prepared in wet conditions.",2306.05488v2
2023-07-03,"Strain, Young's modulus, and structural transition of EuTiO3 thin films probed by micro-mechanical methods","EuTiO3 (ETO) is a well-known complex oxide mainly investigated for its
magnetic properties and its incipient ferro-electricity. In this work, we
demonstrate the realization of suspended micro-mechanical structures, such as
cantilevers and micro-bridges, from 100 nm-thick single-crystal epitaxial ETO
films deposited on top of SrTiO3(100) substrates. By combining profile analysis
and resonance frequency measurements of these devices, we obtain the Young's
modulus, strain, and strain gradients of the ETO thin films. Moreover, we
investigate the ETO anti-ferro-distorsive transition by temperature-dependent
characterizations, which show a non-monotonic and hysteretic mechanical
response. Comparison between experimental and literature data allows us to
weight the contribution from thermal expansion and softening to the tuning
slope, while a full understanding of the origin of such a wide hysteresis is
still missing. We also discuss the influence of oxygen vacancies on the
reported mechanical properties by comparing stoichiometric and oxygen-deficient
samples.",2307.01022v2
2023-09-24,Tuning the Néel temperature in an antiferromagnet: the case of NixCo1-xO microstructures,"We show that it is possible to tune the N\'eel temperature of
nickel(II)-cobalt(II) oxide films by changing the Ni to Co ratio. We grow
single crystalline micrometric triangular islands with tens of nanometers
thickness on a Ru(0001) substrate using high temperature oxygen-assisted
molecular beam epitaxy. Composition is controlled by adjusting the deposition
rates of Co and Ni. The morphology, shape, crystal structure and composition
are determined by low-energy electron microscopy and diffraction, and
synchrotron-based x-ray absorption spectromicroscopy. The antiferromagnetic
order is observed by x-ray magnetic linear dichroism. Antiferromagnetic domains
up to micrometer width are observed.",2309.13721v1
2023-09-28,Full Breit Hamiltonian in the Multiwavelets Framework,"New techniques in core-electron spectroscopy are necessary to resolve the
structures of oxides of $f$-elements and other strongly correlated materials
that are present only as powders and not as single crystals. Thus, accurate
quantum chemical methods need to be developed to calculate core spectroscopic
properties in such materials. In this contribution, we present an important
development in this direction, extending our fully adaptive real-space
multiwavelet basis framework to tackle the 4-component Dirac-Coulomb-Breit
Hamiltonian. We show that Multiwavelets are able to reproduce one-dimensional
grid-based approaches. They are however a fully three-dimensional approach
which can later on be extended to molecules and materials. Our Multiwavelet
implementation attained precise results irrespective of the chosen nuclear
model, provided that the error threshold is tight enough and the chosen
polynomial basis is sufficiently large. Furthermore, our results confirmed that
in two-electron species, the magnetic and Gauge contributions from $s$-orbitals
are identical in magnitude and can account for the experimental evidence from
$K$ and $L$ edges.",2309.16183v2
2023-10-09,Isolation of Single Donors in ZnO,"The shallow donor in zinc oxide (ZnO) is a promising semiconductor spin qubit
with optical access. Single indium donors are isolated in a commercial ZnO
substrate using plasma focused ion beam (PFIB) milling. Quantum emitters are
identified optically by spatial and frequency filtering. The indium donor
assignment is based on the optical bound exciton transition energy and magnetic
dependence. The single donor emission is intensity and frequency stable with a
transition linewidth less than twice the lifetime limit. The isolation of
optically stable single donors post-FIB fabrication is promising for optical
device integration required for scalable quantum technologies based on single
donors in direct band gap semiconductors.",2310.05806v3
2023-10-16,First-Principle Investigation Of Near-Field Energy Transfer Between Localized Quantum Emitters in Solids,"We present a predictive and general approach to investigate near-field energy
transfer processes between localized defects in semiconductors, which couples
first principle electronic structure calculations and a nonrelativistic quantum
electrodynamics description of photons in the weak-coupling regime. We apply
our approach to investigate an exemplar point defect in an oxide, the F center
in MgO, and we show that the energy transfer from a magnetic source, e.g., a
rare earth impurity, to the vacancy can lead to spin non conserving long-lived
excitation that are dominant processes in the near field, at distances relevant
to the design of photonic devices and ultra-high dense memories. We also define
a descriptor for coherent energy transfer to predict geometrical configurations
of emitters to enable long-lived excitations, that are useful to design optical
memories in semiconductor and insulators.",2310.10028v1
2023-10-27,Nanostructured Superconductors,"The relevant length scales for superconductivity are of the order of
nanometers. By confining the superconducting condensate to such dimensions,
many physical properties change substantially, and novel phenomena emerge,
which are absent in the pristine material. We discuss various methods of
creating artificial nanostructures by top-down approaches in metallic and
copper-oxide superconductors and their applications. Such nanostructures can be
used to control magnetic flux quanta in superconductors, anchoring them to
engineered defects to avoid dissipation, guiding their motion, or building
artificial flux-quanta arrangements. Nanopatterned superconductors are
essential for creating model systems for basic research and enable building
almost dissipationless and ultrafast electronic devices and highly sensitive
sensors.",2310.18232v1
2023-11-01,A complementary experimental study of epitaxial La0.67Sr0.33MnO3 to identify morphological and chemical disorder,"Gaining insight into the characteristics of epitaxial complex oxide films is
essential to control the behavior of devices and catalytic processes. It is
known that substrate induced strain, doping, and layer growth can affect the
electronic and magnetic properties of the film's bulk. In this study, we
demonstrate a clear distinction between the bulk and surface of thin films of
La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and
surface morphology. We employed a combined experimental approach of X-ray based
characterization methods and scanning probe microscopy. X-ray diffraction and
resonant X-ray reflectivity revealed surface non-stochiometry in the strontium
and lanthanum, as well as an accumulation of oxygen vacancies. Scanning
tunneling microscopy showed a staggered growth surface morphology accompanied
by an electronic phase separation (EPS) related to this non-stochiometry. The
EPS is likely responsible for the temperature-dependent resistivity transition
and is a cause of a proposed mixed-phase ferromagnetic and paramagnetic state
near room temperature in these thin films.",2311.00504v1
2023-11-08,Mie-scattering controlled all-dielectric resonator-antenna for bright and directional point dipole emission,"Designing a deterministic, bright, robust, room temperature stable, on-demand
solid-state single photon source has been a major demand in the field of
quantum-photonics. For this, various single-photon resonator and antenna
schemes are being actively explored. Here, using the Cartesian multi-polar
decomposition of the excited Mie-scattering moments, we present the design of a
all-dielectric coupled-dipolar antenna comprising of two dielectric (Tin-oxide,
TiO$_2$) cylinders sandwiching a nanodiamond based nitrogen-vacancy (NV$^-$)
center trapped in a poly-vinyl alcohol (PVA) matrix. The Mie-scattering
resonant cavity formed in the middle PVA layer provides more than an order of
magnitude decay rate or Purcell enhancement. The balancing of the electric and
magnetic dipolar moments (a phenomenon commonly known as the Kerker condition)
of the coupled TiO$_2$ cylinders under NV$^-$ dipole excitation, provides
significant directionality to the radiation pattern. Using a collection lens
with a numerical aperture (NA) of 0.9 the vertical collection efficiency (VCE)
was observed to be around 80\% at the NV$^-$ center's zero-phonon line
wavelength.",2311.04500v2
2023-11-12,Quantum Griffiths singularity in three-dimensional superconductor to Anderson critical insulator transition,"Disorder is ubiquitous in real materials and can have dramatic effects on
quantum phase transitions. Originating from the disorder enhanced quantum
fluctuation, quantum Griffiths singularity (QGS) has been revealed as a
universal phenomenon in quantum criticality of low-dimensional superconductors.
However, due to the weak fluctuation effect, QGS is very challenging to detect
experimentally in three-dimensional (3D) superconducting systems. Here we
report the discovery of QGS associated with the quantum phase transition from
3D superconductor to Anderson critical insulator in a spinel oxide MgTi2O4
(MTO). Under both perpendicular and parallel magnetic field, the dynamical
critical exponent diverges when approaching the quantum critical point,
demonstrating the existence of 3D QGS. Among 3D superconductors, MTO shows
relatively strong fluctuation effect featured as a wide superconducting
transition region. The enhanced fluctuation, which may arise from the mobility
edge of Anderson localization, finally leads to the occurrence of 3D quantum
phase transition and QGS. Our findings offer a new perspective to understand
quantum phase transitions in strongly disordered 3D systems.",2311.06710v1
2023-12-06,Surface termination effect of SrTiO3 substrate on ultrathin SrRuO3,"A uniform one-unit-cell-high step on the SrTiO3 substrate is a prerequisite
for growing high-quality epitaxial oxide heterostructures. However, it is
inevitable that defects induced by mixed substrate surface termination exist at
the interface, significantly impacting the properties of ultrathin films. In
this study, we microscopically identify the origin for the lateral
inhomogeneity in the growth of ultrathin SrRuO3 films due to the step effects
of SrTiO3(001). By using atomic-resolved scanning transmission electron
microscopy, we observe two distinct types of step propagation along the [011]
and [0-11]crystallographic direction in SrTiO3-SrRuO3 heterostructures,
respectively. In particular, the type-II [0-11] step results in lateral
discontinuity of monolayer SrRuO3 and originates from the SrO-terminated
regions along the TiO2-terminated step edge. Such an induced lateral
discontinuity should be responsible for the distinct electronic and magnetic
properties of monolayer SrRuO3. Our findings underscore the critical importance
of using single termination STO substrate to achieve high-quality termination
selective films and to unveil the intrinsic properties of epitaxial films in
the atomic limit.",2312.14944v1
2024-01-04,Emergent transverse-field Ising model in $\boldsymbol{d}^\mathbf{4}$ spin-orbit Mott insulators,"Mott-insulating transition metal oxides containing $t_{2g}^4$ ions with
strong spin-orbit coupling were recently demonstrated to display unusual
magnetism due to a dynamical mixing of the low-energy multiplet states via
exchange processes. Here we derive exchange interactions in the situation where
a tetragonal or trigonal crystal field selects a single relevant excited state
on top of the singlet ionic ground state, producing an effective
spin-$\frac12$. We show that these moments universally obey antiferromagnetic
transverse-field Ising model (TFIM) with an intrinsic transverse field
generated by the splitting of the two ionic singlets. Using Ru$^{4+}$ as a
example ion, we provide quantitative estimates of the exchange and illustrate
the emergent TFIM physics based on phase diagrams and excitation spectra
obtained for several 2D lattices - square, honeycomb, as well as for the
frustrated triangular lattice.",2401.02532v1
2024-02-03,Reducing disorder in PbTe nanowires for Majorana research,"Material challenges are the key issue in Majorana nanowires where surface
disorder constrains device performance. Here, we tackle this challenge by
embedding PbTe nanowires within a latticematched crystal, an oxide-free
environment. The wire edges are shaped by self-organized growth instead of
lithography, resulting in nearly-atomic-flat facets along both cross-sectional
and longitudinal directions. Quantized conductance plateaus are observed at
zero magnetic field with channel lengths reaching 1.54 $\mu$m, significantly
surpassing the state-of-the-art of III-V nanowires (nearly an
order-of-magnitude improvement compared to InSb). Coupling PbTe to a Pb film
unveils a flat interface spanning microns and a large superconducting gap of 1
meV. Our results meet the stringent low-disorder requirement for the definitive
observation of Majoranas.",2402.02132v1
2024-03-07,Pressure tuning of hydrogen bond ordering in the metal-organic framework [(CH3)2NH2]Mn(HCOO)3,"The influence of pressure on the hydrogen bond ordering in the perovskite
metal-organic framework [(CH3)2NH2]Mn(HCOO)3 has been investigated by
dielectric, pyroelectric adn magnetic measurements in a piston-cylinder cell.
Under ambient pressure the ordering of hydrogen bonds takes place at TC = 188 K
and induces a first-order ferroelectric phase transition. With increasing
pressure to p = 3.92 kbar, the order-disorder transition shifts to a lower
temperature and retains the first-order ferroelectric nature. However, under
higher pressures, the ordering process of hydrogen bonds is split into two
transitions: a broad antiferroelectric transition at high temperature and a
first-order ferroelectric transition at low temperature. With increasing
pressure, the antiferroelectric phase is enhanced whereas the ferroelectric
phase is greatly suppressed, which implies that compression of the perovskite
framework favors antiparallel arrangement of the hydrogen bonds. The canted
anti-ferromagnetic transition was almost unchanged when pressure up to 10.85
kbar. Our study demonstrated that the perovskite metal-organic frameworks are
more sensitive to external pressure than conventional perovskite oxides so that
their electric properties can be easily tuned by pressure.",2403.04241v1
2024-04-08,Vortex matching at 6 T in YBa$_2$Cu$_3$O$_{7-δ}$ thin films by imprinting a 20 nm-periodic pinning array with a focused helium ion beam,"Controlled engineering of vortex pinning sites in copper-oxide
superconductors is a critical issue in manufacturing devices based on magnetic
flux quanta. To address this, we employed a focused He-ion beam (He-FIB) to
irradiate thin YBa$_2$Cu$_3$O$_{7-\delta}$ films and create ultradense
hexagonal arrays of defects with lattice spacings as small as 20 nm. Critical
current and magnetoresistance measurements demonstrate efficient pinning by an
unprecedentedly high matching field of 6 T visible in a huge temperature range
from the critical temperature $T_c$ down to 2 K. These results show that He-FIB
irradiation provides excellent opportunities for the development and
application of superconducting fluxonic devices based on Abrikosov vortices. In
particular, our findings suggest that such devices can operate at temperatures
far below $T_c$, where superconductivity is robust.",2404.05382v1
1999-06-03,Transition to Long Range Magnetic Order in the Highly Frustrated Insulating Pyrochlore Antiferromagnet Gd_2Ti_2O_7,"Experimental evidence from measurements of the a.c. and d.c. susceptibility,
and heat capacity data show that the pyrochlore structure oxide, Gd_2Ti_2O_7,
exhibits short range order that starts developing at 30K, as well as long range
magnetic order at $T\sim 1$K. The Curie-Weiss temperature, $\theta_{CW}$ =
-9.6K, is largely due to exchange interactions. Deviations from the Curie-Weiss
law occur below $\sim$10K while magnetic heat capacity contributions are found
at temperatures above 20K. A sharp maximum in the heat capacity at $T_c=0.97$K
signals a transition to a long range ordered state, with the magnetic specific
accounting for only $\sim$ 50% of the magnetic entropy. The heat capacity above
the phase transition can be modeled by assuming that a distribution of random
fields acts on the $^8S_{7/2}$ ground state for Gd$^{3+}$. There is no
frequency dependence to the a.c. susceptibility in either the short range or
long range ordered regimes, hence suggesting the absence of any spin-glassy
behavior. Mean field theoretical calculations show that no long range ordered
ground state exists for the conditions of nearest-neighbor antiferromagnetic
exchange and long range dipolar couplings. At the mean-field level, long range
order at various commensurate or incommensurate wave vectors is found only upon
inclusion of exchange interactions beyond nearest-neighbor exchange and dipolar
coupling. The properties of Gd$_2Ti_2O_7 are compared with other geometrically
frustrated antiferromagnets such as the Gd_3Ga_5O_{12} gadolinium gallium
garnet, RE_2Ti_2O_7 pyrochlores where RE = Tb, Ho and Tm, and Heisenberg-type
pyrochlore such as Y_2Mo_2O_7, Tb_2Mo_2O_7, and spinels such as ZnFe_2O_4",9906043v1
2004-05-18,Structural and magnetic properties of the single-layer manganese oxide La{1-x}Sr{1+x}MnO4,"Using x-ray and neutron scattering, we have studied the structural and
magnetic properties of the single-layer manganite La{1-x}Sr{1+x}MnO4 (0 < x <
0.7). Single crystals were grown by the traveling-solvent floating-zone method
at 18 La/Sr concentrations. The low-temperature phase diagram can be understood
by considering the strong coupling of the magnetic and orbital degrees of
freedom, and it can be divided into three distinct regions: low (x < 0.12),
intermediate (0.12< x < 0.45), and high (x > 0.45) doping. LaSrMnO_4 (x=0) is
an antiferromagnetic Mott insulator,and its spin-wave spectrum is
well-described by linear spin-wave theory for the spin-2 square-lattice
Heisenberg Hamiltonian with Ising anisotropy. Upon doping, as the e_g electron
concentration (1-x) decreases, both the two-dimensional antiferromagnetic spin
correlations in the paramagnetic phase and the low-temperature ordered moment
decrease due to an increase of frustrating interactions, and Neel order
disappears above xc = 0.115(10). In the intermediate region, there exists
neither long-range magnetic nor superstructural order. Short-range-correlated
structural ""nanopatches"" begin to form above x ~ 0.25. At high doping (x >
0.45), the ground state of La{1-x}Sr{1+x}MnO4 exhibits long-range
superstructural order and a complex (CE-type) antiferromagnetic order which
differs from that at low doping. The superstructural order is thought to arise
from charge and orbital ordering on the Mn sites. For x > 0.50, the
superstructural order becomes incommensurate with the lattice, with a
modulation wavevector that depends linearly on the e_g electron concentration.
On the other hand, the magnetic order remains commensurate, but loses its
long-range coherence upon doping beyond x = 0.50.",0405424v1
2008-08-27,Epitaxial Zn(x)Fe(3-x)O(4) Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties,"The ferrimagnetic spinel oxide Zn(x)Fe(3-x)O(4) combines high Curie
temperature and spin polarization with tunable electrical and magnetic
properties, making it a promising functional material for spintronic devices.
We have grown epitaxial thin films with 0<=x<=0.9 on MgO(001) substrates with
excellent structural properties both in pure Ar atmosphere and an Ar/O2 mixture
by laser molecular beam epitaxy. We find that the electrical conductivity and
the saturation magnetization can be tuned over a wide range during growth. Our
extensive characterization of the films provides a clear picture of the
underlying physics of this spinel ferrimagnet with antiparallel Fe moments on
the A and B sublattice: (i) Zn substitution removes both Fe3+ moments from the
A sublattice and itinerant charge carriers from the B sublattice, (ii) growth
in finite oxygen partial pressure generates Fe vacancies on the B sublattice
also removing itinerant charge carriers, and (iii) application of both Zn
substitution and excess oxygen results in a compensation effect as Zn
substitution partially removes the Fe vacancies. A decrease (increase) of
charge carrier density results in a weakening (strengthening) of double
exchange and thereby a decrease (increase) of conductivity and the saturation
magnetization. This scenario is confirmed by the observation that the
saturation magnetization scales with the longitudinal conductivity. The
combination of tailored films with semiconductor materials such as ZnO in
multi-functional heterostructures seems to be particularly appealing.",0808.3642v3
2010-09-05,Cell death induced by the application of alternating magnetic fields to nanoparticle-loaded dendritic cells,"In this work, the capability of primary, monocyte-derived dendritic cells
(DCs) to uptake iron oxide magnetic nanoparticles (MNPs) is assessed and a
strategy to induce selective cell death in these MNP-loaded DCs using external
alternating magnetic fields (AMFs) is reported. No significant decrease in the
cell viability of MNP-loaded DCs, compared to the control samples, was observed
after five days of culture. The amount of MNPs incorporated into the cytoplasm
was measured by magnetometry, which confirmed that 1 to 5 pg of the particles
were uploaded per cell. The intracellular distribution of these MNPs, assessed
by transmission electron microscopy, was found to be primarily inside the
endosomic structures. These cells were then subjected to an AMF for 30 min, and
the viability of the blank DCs (i.e., without MNPs), which were used as control
samples, remained essentially unaffected. However, a remarkable decrease of
viability from approximately 90% to 2-5% of DCs previously loaded with MNPs was
observed after the same 30 min exposure to an AMF. The same results were
obtained using MNPs having either positive (NH2+) or negative (COOH-) surface
functional groups. In spite of the massive cell death induced by application of
AMF to MNP-loaded DCs, the amount of incorporated magnetic particles did not
raise the temperature of the cell culture. Clear morphological changes at the
cell structure after magnetic field application were observed using scanning
electron microscopy. Therefore, local damage produced by the MNPs could be the
main mechanism for the selective cell death of MNP-loaded DCs under an AMF.
Based on the ability of these cells to evade the reticuloendothelial system,
these complexes combined with an AMF should be considered as a potentially
powerful tool for tumour therapy.",1009.0907v2
2013-12-04,Structure and Properties of α-NaFeO2-type Ternary Sodium Iridates,"The synthesis, structure, and elementary magnetic and electronic properties
are reported for layered compounds of the type Na3-xMIr2O6 and Na3-xM2IrO6,
where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn).
The rhombohedral structures, in space group R-3m, were determined by refinement
of neutron and synchrotron powder diffraction data. No clear evidence for long
range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder
diffraction patterns except in the case of M = Zn, thus in general the
compounds are best designated as sodium deficient {\alpha}-NaFeO2-type phases
with formulas Na1-xM1/3Ir2/3O2 or Na1-xM2/3Ir1/3O2. Synchrotron powder
diffraction patterns indicate that several of the compounds likely have
honeycomb in-plane metal-iridium ordering with disordered stacking of the
layers. All the compounds are sodium deficient under our synthetic conditions
and are black and insulating. Weiss constants derived from magnetic
susceptibility measurements indicate that Na0.62Mn0.61Ir0.39O2,
Na0.80Fe2/3Ir1/3O2, Na0.92Ni1/3Ir2/3O2, Na0.86Cu1/3Ir2/3O2, and
Na0.89Zn1/3Ir2/3O2 display dominant antiferromagnetic interactions. For
Na0.90Co1/3Ir2/3O2 the dominant magnetic interactions at low temperature are
ferromagnetic while at high temperatures they are antiferromagnetic; there is
also a change in the effective moment. Low temperature specific heat
measurements (to 2 K) on Na0.92Ni1/3Ir2/3O2 indicate the presence of a broad
magnetic ordering transition. X-ray absorption spectroscopy shows that iridium
is at or close to the 4+ oxidation state in all compounds. 23Na nuclear
magnetic resonance measurements comparing Na2IrO3 to Na0.92Ni1/3Ir2/3O2 and
Na0.89Zn1/3Ir2/3O2 provide strong indications that the electron spins are
short-range ordered in the latter two materials. All of the compounds are spin
glasses.",1312.0995v1
2018-02-12,"Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr2VFeAsO3-delta, a superconductor","We elucidate the magnetic phases and superconducting transition temperatures
(Tc) in Sr2VFeAsO3-delta (21113V), an iron-based superconductor with a
thick-blocking layer fabricated from a perovskite-related transition metal
oxide. At low temperatures (T < 37.1 K), 21113V exhibited a superconducting
phase in the range 0.031 =< delta =< 0.145 and an antiferromagnetic (AFM) iron
sublattice in the range 0.267 =< delta =< 0.664. Mixed-valent vanadium
exhibited a dominant AFM phase in 0.031 =< delta =< 0.088, and a partial
ferrimagnetic (Ferri.) phase in the range 0.124 =< delta =< 0.664. The Ferri.
phase was the most dominant at a delta value of 0.267, showing an AFM phase of
Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the
magnetic shielding volume fraction due to the superconducting phase. This
result was attributed to the magnetic phase of vanadium, which dominates the
superconductivity of Fe in 21113V. The Tc-delta curve showed two maxima. The
smaller and larger of Tc maxima occurred at delta = 0.073 and delta = 0.145,
respectively; the latter resides on the phase boundary between AFM and the
partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new
mechanisms of Tc enhancement in iron-based superconductors.",1802.03907v2
2016-08-28,Magnetic order and spin-orbit coupled Mott state in double perovskite (La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$,"Double-perovskite oxides that contain both 3d and 5d transition metal
elements have attracted growing interest as they provide a model system to
study the interplay of strong electron interaction and large spin-orbit
coupling (SOC). Here, we report on experimental and theoretical studies of the
magnetic and electronic properties of double-perovskites
(La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$ ($x$ = 0.0, 0.1, 0.2, and 0.3). The undoped
La$_2$CuIrO$_6$ undergoes a magnetic phase transition from paramagnetism to
antiferromagnetism at T$_N$ $\sim$ 74 K and exhibits a weak ferromagnetic
behavior below $T_C$ $\sim$ 52 K. Two-dimensional magnetism that was observed
in many other Cu-based double-perovskites is absent in our samples, which may
be due to the existence of weak Cu-Ir exchange interaction. First-principle
density-functional theory (DFT) calculations show canted antiferromagnetic
(AFM) order in both Cu$^{2+}$ and Ir$^{4+}$ sublattices, which gives rise to
weak ferromagnetism. Electronic structure calculations suggest that
La$_2$CuIrO$_6$ is an SOC-driven Mott insulator with an energy gap of $\sim$
0.3 eV. Sr-doping decreases the magnetic ordering temperatures ($T_N$ and
$T_C$) and suppresses the electrical resistivity. The high temperatures
resistivity can be fitted using a variable-range-hopping model, consistent with
the existence of disorders in these double-pervoskite compounds.",1608.07763v2
2019-06-04,Influence of interface and microstructure on magnetization of epitaxial Fe4N thin film,"Epitaxial Fe4N thin films grown on lattice-matched LaAlO3 (LAO) substrate
using sputtering and molecular beam epitaxy techniques have been studied in
this work. Within the sputtering process, films were grown with conventional
direct current magnetron sputtering (dcMS) and for the first time, using a high
power impulse magnetron sputtering (HiPIMS) process. Surface morphology and
depth profile reveal that HiPIMS deposited film has the lowest roughness, the
highest packing density and the sharpest interface. La from the LAO substrate
and Fe from the film interdiffuse and forms an undesired interface spreading to
an extent of about 10-20 nm. In the HiPIMS process, layer by layer type growth
leads to a globular microstructure which restricts the extent of the
interdiffused interface. Such substrate-film interactions and microstructure
play a vital role in affecting the electronic hybridization and magnetic
properties of Fe4N films. The magnetic moment (Ms) was compared using bulk,
element-specific and magnetic depth profiling techniques. We found that Ms was
the highest when the thickness of the interdiffused layer was lowest and only
be achieved in the HiPIMS grown samples. Presence of small moment at the N site
was also evidenced by element-specific x-ray circular dichroism measurement in
HiPIMS grown sample. A large variation in the Ms values of Fe4N found in the
experimental works carried out so far could be due to such interdiffused layer
which is generally not expected to form in otherwise stable oxide substrate. In
addition, a consequence of substrate-film interdiffusion and microstructure
results in different kinds of different kind of magnetic anisotropies in films
grown using different techniques.",1906.01238v1
2019-10-01,"Oxygen deficiency and migration mediated electric polarization in Fe,Co-substituted SrTiO$_{3-δ}$","We use density functional theory (DFT) calculations to show that oxygen
vacancies ($v_\mathrm{O}$) and mobility induce noncentrosymmetric polar
structures in SrTi$_{1-x-y}$Fe$_{x}$Co$_{y}$O$_{3-\delta}$ ($x=y=0.125$) with
$\delta = \{0.125, 0.25\}$, enhance the saturation magnetization and give rise
to large changes in the electric polarization $\vert\Delta P\vert$. We present
an intuitive set of rules for SrTiFeCoO$_{3-\delta}$ (STFC), which are based on
the interplay between (Co/Fe)-$v_\mathrm{O}$ defects, magnetic cations
coordination and topological vacancy disorder. STFC structures convey layered
crystals with sheets of linear organized O$_{4,5,6}$-coordinated Fe-Co pairs,
sandwiched with layers of O$_{5}$-coordinated Ti. Co,Fe-$v_\mathrm{O}$ defects
are the source of the crystal distortions, cations off-centering and bending of
the oxygen octahedra, which added to the charge redistribution mediated by
$v_\mathrm{O}$, the cations electronegativity and valence states trigger an
effective electric polarization. Oxygen migrations for $\delta=0.125$ provides
us with $\vert\Delta \mathbf{P}\vert$ $>\sim10 \mu$C/cm$^2$ due to a
quantum-of-polarization differences between $\delta=0.125$ structures.
Increasing the deficiency to $\delta=0.25$ yields $\vert\Delta \mathbf{P}\vert$
whose O-migration resolved polarization for $\delta=0.25$ is $>\sim3
\mu$C/cm$^2$ in the worst case scenario. Magnetism is dominated by the Fe,Co
spin states for $\delta=0.125$ while there is a raid of Ti magnetic moments
($\sim1\mu_{B}$) for $\delta=0.25$. Magnetic and electric order parameters
change for variations of $\delta$ or oxygen migrations for a given deficiency.
Our results capture characteristics observed in the end-members of the series
SrTi(Co,Fe)O$_{3}$, and suggest the existence of a broader set of rules for
oxygen deficient multiferroic oxides.",1910.00176v2
2020-04-23,Effective point-charge analysis of crystal electric fields -- application to rare-earth pyrochlores and tripod kagome magnets R3Mg2Sb3O14,"An indispensable step to understand collective magnetic phenomena in
rare-earth compounds is the determination of spatially-anisotropic single-ion
properties resulting from spin-orbit coupling and crystal field (CF). The CF
Hamiltonian has a discrete energy spectrum -- accessible to spectroscopic
probes such as neutron scattering -- controlled by a number of independent
parameters reflecting the point-symmetry of the magnetic sites. Determining
these parameters in low-symmetry systems is often challenging. Here, we
describe a general method to analyze CF excitation spectra using adjustable
effective point-charges. We benchmark our method to existing neutron-scattering
measurements on pyrochlore rare-earth oxides and obtain a universal
point-charge model that describes a large family of related materials. We adapt
this model to the newly discovered tripod Kagome magnets
($R_{3}$Mg$_2$Sb$_{3}$O$_{14}$, $R$ = Tb, Ho, Er, Yb) for which we report
broadband inelastic neutron-scattering spectra. Analysis of these data using
adjustable point-charges yields the CF wave-functions for each compound. From
this, we calculate thermomagnetic properties that accurately reflect our
measurements on powder samples, and predict the effective gyromagnetic tensor
for pseudo-spin degrees of freedom -- a crucial step to understand the exotic
collective properties of these kagome magnets at low temperature. We present
further applications of our method to other tripod kagome materials and
triangular rare-earth compounds $R$MgGaO$_4$ ($R$ =Yb, Tm). Overall, this study
establishes a widely applicable methodology to predict CF and single-ion
properties of rare-earth compounds based on interpretable and adjustable models
of effective point-charges.",2004.10957v3
2017-11-15,A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K,"Polarized light microscopy, as a contrast-enhancing technique for optically
anisotropic materials, is a method well suited for the investigation of a wide
variety of effects in solid-state physics, as for example birefringence in
crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy
setup that combines a widefield microscope and a confocal scanning laser
microscope with polarization-sensitive detectors. By using a high numerical
aperture objective, a spatial resolution of about 240 nm at a wavelength of 405
nm is achieved. The sample is mounted on a $^4$He continuous flow cryostat
providing a temperature range between 4 K and 300 K, and electromagnets are
used to apply magnetic fields of up to 800 mT with variable in-plane
orientation and 20 mT with out-of-plane orientation. Typical applications of
the polarizing microscope are the imaging of the in-plane and out-of-plane
magnetization via the longitudinal and polar MOKE, imaging of magnetic flux
structures in superconductors covered with a magneto-optical indicator film via
Faraday effect or imaging of structural features, such as twin-walls in
tetragonal SrTiO$_3$. The scanning laser microscope furthermore offers the
possibility to gain local information on electric transport properties of a
sample by detecting the beam-induced voltage change across a current-biased
sample. This combination of magnetic, structural and electric imaging
capabilities makes the microscope a viable tool for research in the fields of
oxide electronics, spintronics, magnetism and superconductivity.",1711.06204v1
2021-03-08,Magnetic and electronic ordering phenomena in the [Ru$_2$O$_6$] honeycomb lattice compound AgRuO$_3$,"The silver ruthenium oxide AgRuO$_3$ consists of honeycomb
[Ru$_2^{5+}$O$_6^{2-}$] layers, and can be considered an analogue of
SrRu$_2$O$_6$ with a different intercalation stage. We present measurements of
magnetic susceptibility and specific heat on AgRuO$_3$ single crystals which
reveal a sharp antiferromagnetic transition at 342(3)K. The electrical
transport in single crystals of AgRuO$_3$ is determined by a combination of
activated conduction over an intrinsic semiconducting gap of $\approx$ 100 meV
and carriers trapped and thermally released from defects. From powder neutron
diffraction data a N\'eel-type antiferromagnetic structure with the Ru moments
along the $c$ axis is derived. Raman and muon spin rotation spectroscopy
measurements on AgRuO$_3$ powder samples indicate a further weak phase
transition or a crossover in the temperature range 125-200 K. The transition
does not show up in magnetic susceptibility and its origin is argued to be
related to defects but cannot be fully clarified. The experimental findings are
complemented by DFT-based electronic structure calculations. It is found that
the magnetism in AgRuO$_3$ is similar to that of SrRu$_2$O$_6$, however with
stronger intralayer and weaker interlayer magnetic exchange interactions.",2103.04815v1
2021-03-09,Ferromagnetic metallic Sr-rich Ln$_{1/2}$A$_{1/2}$CoO$_3$ cobaltites with spontaneous spin rotation,"The Pr$_{0.50}$Sr$_{0.5}$0CoO$_3$ perovskite exhibits unique
magnetostructural properties among the rest of ferromagnetic/metallic
Ln$_{0.50}$Sr$_{0.50}$CoO$_3$ compounds. The sudden orthorhombic-tetragonal
(Imma $\to$ I4/mcm) structural transition produces an unusual magnetic behavior
versus temperature and external magnetic fields. In particular, the symmetry
change is responsible for a spontaneous spin rotation in this metallic oxide.
We have studied half-doped Ln$_{0.50}$(Sr$_{1-x}$A$_x$)$_{0.50}$CoO$_3$
cobaltites varying the ionic radius rA of A-site cations (divalent cations and
lanthanides) in order to complete the T-rA phase diagram. The influence of the
structural distortion and the A-cations size for the occurrence of a
spontaneous spin reorientation in the metallic state has been investigated. As
the reorientation of the magnetization is driven by the temperature induced
collapse of the orthorhombic distortion, a careful investigation of the
structural symmetry is presented varying the structural distortion of the
Sr-rich half-doped cobaltites by means of both compositional and temperature
changes. The region in the phase diagram of these perovskites where the phase
of magnetic symmetry Fm'm'm replaces that of Im'm'a symmetry was determined in
this family of ferromagnetic/metallic cobaltites. In that region the
magnetization direction has rotated 45 degrees within the a-b plane with
respect to the second.",2103.05410v1
2021-07-09,Failure to achieve the $J_{eff}$~=~0 state even in nearly isolated Ir$^{5+}$ in Sr$_3$NaIrO$_6$: are iridates enough for realizing true $j$-$j$ coupling?,"Spin-orbit coupling (SOC) often gives rise to interesting electronic and
magnetic phases in an otherwise ordinary pool of paramagnetic heavy metal
oxides. In presence of strong SOC, assumed to be working in $j$-$j$ coupling
regime, 5$d^4$ iridates are generally speculated to possess a nonmagnetic
$J_{eff}$~=~0 singlet ground state, which invariably gets masked due to
different solid-state effects (e.g. hopping). Here, we try to probe the
trueness of the atomic SOC-based proposal in an apparently 1-dimensional
system, Sr$_3$NaIrO$_6$, possessing a 2$H$ hexagonal structure with well
separated Ir$^{5+}$ (5$d^4$) ions. But all the detailed experimental as well as
theoretical characterizations reveal that the ground state of Sr$_3$NaIrO$_6$
is not nonmagnetic, rather accommodating a significantly high effective
magnetic moment on Ir$^{5+}$ ion. However our combined dc susceptibility
($\chi$), ${}^{23}$Na nuclear magnetic resonance (NMR),
muon-spin-relaxation/rotation ($\mu$SR) and heat capacity ($C_p$) measurements
clearly refute any sign of spin-freezing or ordered magnetism among the
Ir$^{5+}$ moments due to geometrical exchange frustration, while in-depth
zero-field (ZF) and longitudinal field (LF) $\mu$SR investigations strongly
point towards inhomogeneous quantum spin-orbital liquid (QSOL)-like ground
state. In addition, the linear temperature dependence of both the NMR
spin-lattice relaxation rate and the magnetic heat capacity at low temperatures
suggest low-lying gapless spin excitations in the QSOL phase of this material.
Finally, we conclude that the effective SOC realised in $d^4$ iridates are
unlikely to offer a ground state which will be consistent with a purely atomic
$j$-$j$ coupling description.",2107.04431v1
2022-02-16,Enhanced magnetism and suppressed magnetoelastic coupling induced by electron doping in Ca$_{1-x}$Y$_{x}$MnReO$_6$,"The Ca$_2$MnReO$_6$ double perovskite is a spin-orbit-assisted Mott insulator
with exotic magnetic properties, including a largely non-collinear Mn$^{2+}$
spin arrangement and nearly orthogonal coupling between such spins and the much
smaller Re $5d$ magnetic moments. Here, the electron-doped compound
Ca$_{1.7}$Y$_{0.3}$MnReO$_6$ is investigated. Neutron and X-ray powder
diffraction confirm that nearly full chemical order is maintained at the Mn and
Re sites under the Y substitution at the Ca site. X-ray absorption measurements
and an analysis of the Mn-O/Re-O bond distances show that the Mn oxidation
state remains stable at +2 whereas Re is reduced upon doping. The electron
doping increases the magnetic ordering temperature from $T_c = 121$ to $150$ K
and also enhances significantly the ferromagnetic component of the Mn spins at
the expense of the antiferromagnetic component at the base temperature ($T=3$
K). The lattice parameter anomalies at $T_c$ observed in the parent compound
are suppressed by the electron doping. The possible reasons for the enhanced
magnetism and the suppressed magnetoelastic coupling in
Ca$_{1.7}$Y$_{0.3}$MnReO$_6$ are discussed.",2202.08220v1
2022-04-26,"Electronic and structural properties of RbCeX$_2$ (X$_2$: O$_2$, S$_2$, SeS, Se$_2$, TeSe, Te$_2$)","Triangular lattice delafossite compounds built from magnetic lanthanide ions
are a topic of recent interest due to their frustrated magnetism and
realization of quantum disordered magnetic ground states. Here we report the
evolution of the structure and electronic ground states of RbCe$X_2$ compounds,
built from a triangular lattice of Ce$^{3+}$ ions, upon varying their anion
character ($X_2$= O$_2$, S$_2$, SeS, Se$_2$, TeSe, Te$_2$). This includes the
discovery of a new member of this series, RbCeO$_2$, that potentially realizes
a quantum disordered ground state analogous to NaYbO$_2$. Magnetization and
susceptibility measurements reveal that all compounds manifest mean-field
antiferromagnetic interactions and, with the exception of the oxide, possess
signatures of magnetic correlations onset below 1 K. The crystalline electric
field level scheme is explored via neutron scattering and \textit{ab initio}
calculations in order to model the intramultiplet splitting of the $J=5/2$
multiplet. In addition to the two excited doublets expected within the $J=5/2$
manifold, we observe one extra, local mode present across the sample series.
This added mode shifts downward in energy with increasing anion mass and
decreasing crystal field strength, suggesting a long-lived anomalous mode
endemic to anion motion about the Ce$^{3+}$ sites.",2204.12086v2
2022-11-12,Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic $\rm Pr_2Ti_2O_7$,"Little is so far known about the magnetism of the $\rm A_2B_2O_7$ monoclinic
layered perovskites that replace the spin-ice supporting pyrochlore structure
for $r_A/r_B>1.78$. We show that high quality monoclinic Pr$_2$Ti$_2$O$_7$
single crystals with a three-dimensional network of non-Kramers Pr$^{3+}$ ions
that interact through edge-sharing super-exchange interactions, form a singlet
ground state quantum paramagnet that does not undergo any magnetic phase
transitions down to at least 1.8 K. The chemical phase stability, structure,
and magnetic properties of the layered perovskite Pr$_2$Ti$_2$O$_7$ were
investigated using x-ray diffraction, transmission electron microscopy, and
magnetization measurements. Synthesis of polycrystalline samples with the
nominal compositions of Pr$_2$Ti$_{2+x}$O$_7$ ($-0.16 \leq x \leq 0.16$) showed
that deviations from the Pr$_2$Ti$_2$O$_7$ stoichiometry lead to secondary
phases of related, structures including the perovskite phase Pr$_{2/3}$TiO$_3$
and the orthorhombic phases Pr$_4$Ti$_9$O$_{24}$ and Pr$_2$TiO$_5$. No
indications of site disordering (stuffing and anti-stuffing) or vacancy defects
were observed in the Pr$_2$Ti$_2$O$_7$ majority phase. A procedure for growth
of high-structural-quality, stoichiometric single crystals of Pr$_2$Ti$_2$O$_7$
by the traveling solvent floating zone (TSFZ) method is reported.
Thermo-magnetic measurements of single-crystalline Pr$_2$Ti$_2$O$_7$ reveal an
isolated singlet ground state that we associate with the low symmetry crystal
electric field environments that split the $2J+1=9$-fold degenerate
spin-orbital multiplets of the four differently coordinated Pr$^{3+}$ ions into
36 isolated singlets resulting in an anisotropic temperature independent
van-Vleck susceptibility at low $T$. A small isotropic Curie term is associated
with 0.96(2)\% non-interacting Pr$^{4+}$ impurities.",2211.06758v2
2022-11-28,"Insulating band gaps both below and above the Néel temperature in d-electron LaTiO3, LaVO3, SrMnO3, and LaMnO3 perovskites as a symmetry-breaking event","Compounds having an odd number of electrons with the same orbital character
in occupied and unoccupied band edge states would be expected to have band
degeneracy at the Fermi energy, making such reference system metals. Yet, many
ABO3 oxide perovskites with a magnetic 3d B-atom are, in fact, insulators both
below and above the Neel temperature. These inconsistencies between
experimental observation and expectation have been traditionally resolved by
invoking degeneracy-breaking physics based largely on high-order electron
effects, such as strong interelectronic correlation (the Mott mechanism). Such
explanations generally utilize the highest symmetry structure, considering
microscopic degrees of freedom (m-DOF) as largely passive spectators. Yet, it
has long been known that ABO3 perovskites can manifest an arrangement of m-DOFs
in the form of octahedral tilting, bond dimerization, Jahn-Teller distortions,
and ordering of local magnetic moments as part of the stabilizing intrinsic
symmetry. Such m-DOFs are seen both by local experimental probes and
theoretically in total energy minimization of its Born-Oppenheimer state. While
such local structural and magnetic symmetry breaking motifs were often
considered to be the reason for gapping of the reference system below the
transition into Para phases, it was also often thought that above the
transition those local motifs might vanish, requiring a different mechanism for
gapping - such as strong correlation. Here we examine if such intrinsic
structural and magnetic symmetry breaking might systematically explain the
formation of insulating band gaps both below and above the magnetic transition
and account at the same time for specific and non-accidental exceptions of the
absence of gaping in some compounds, such as SrVO3.",2211.15563v2
2023-10-06,"Correlations between laboratory line lists for FeH, CrH, and NiH and M-star spectra collected with ESPaDOnS and SPIRou","Molecular bands of metal oxides and hydrides dominate the optical and
near-infrared spectra of M dwarfs. High-resolution spectra of these bands have
immense potential for determining many properties of these stars, such as
effective temperature, surface gravity, elemental abundances, radial velocity,
or surface magnetic fields. Techniques are being developed to do this but
remain limited by the current availability and accuracy of molecular data and
spectral line lists. This paper reports metal monohydride line lists selected
from near-infrared and visible laboratory data to show that specific bands in
several electronic transitions can be used to identify CrH, NiH, and FeH in M
stars and to determine radial velocities from Doppler shifts. The possibility
of measuring magnetic fields is also investigated for FeH and CrH. We used
systematic cross-correlation analysis between unpolarised spectra from a
selection of M stars and state-specific laboratory line lists. These lists were
generated from a combination of existing data and new laboratory
laser-excitation spectra recorded at Doppler-limited resolution, in zero-field
conditions or in magnetic fields up to 0.6 tesla. Results. We show that
transitions at visible wavelengths in FeH and NiH, usually neglected in the
analysis of the spectra of M-type stars, do in fact contribute to the spectra,
and we demonstrate the influence of magnetic sensitivity on selected
transitions in CrH and FeH. Although the new line lists focus on transitions
recorded at temperatures significantly lower than those of stellar objects,
they remain pertinent because they cover some band-head regions of high
spectral density. FeH bands can provide a useful supplement to atomic lines for
the analysis of high-resolution optical and near-infrared spectra of M dwarfs.
We demonstrate the influence of a magnetic field on CrH signatures around 862
nm.",2310.04497v1
2024-02-28,Unveiling unconventional magnetism at the surface of Sr$_2$RuO$_4$,"Materials with strongly correlated electrons exhibit physical properties that
are often difficult to predict as they result from the interactions of large
numbers of electrons combined with several quantum degrees of freedom. The
layered oxide perovskite Sr$_2$RuO$_4$ is a strongly correlated electron
material that has been intensively investigated since its discovery due to its
unusual physical properties. Whilst recent experiments have reopened the debate
on the exact symmetry of the superconducting state in Sr$_2$RuO$_4$, a deeper
understanding of the Sr$_2$RuO$_4$ normal state appears crucial as this is the
background in which electron pairing occurs. Here, by using low-energy muon
spin spectroscopy we discover the existence of magnetism at the surface of
Sr$_2$RuO$_4$ in its normal state. We detect static weak dipolar fields yet
manifesting below a relatively high onset temperature larger than 50 K, which
reveals the unconventional nature of the observed magnetism. We relate the
origin of this phase breaking time reversal symmetry to electronic ordering in
the form of orbital loop currents that originate at the reconstructed
Sr$_2$RuO$_4$ surface. Our observations set a reference for the discovery of
the same magnetic phase in other materials and unveil an electronic ordering
mechanism that can influence unconventional electron pairing with broken time
reversal symmetry in those materials where the observed magnetic phase coexists
with superconductivity.",2402.18359v1
2024-03-01,Emergence of interfacial magnetism in strongly-correlated nickelate-titanate superlattices,"Strongly-correlated transition-metal oxides are widely known for their
various exotic phenomena. This is exemplified by rare-earth nickelates such as
LaNiO$_{3}$, which possess intimate interconnections between their electronic,
spin, and lattice degrees of freedom. Their properties can be further enhanced
by pairing them in hybrid heterostructures, which can lead to hidden phases and
emergent phenomena. An important example is the LaNiO$_{3}$/LaTiO$_{3}$
superlattice, where an interlayer electron transfer has been observed from
LaTiO$_{3}$ into LaNiO$_{3}$ and is predicted to result in a high-spin state.
However, macroscopic emergence of magnetic order has so far not been observed.
Here, by using muon spin rotation, x-ray absorption, and resonant inelastic
x-ray scattering, we present direct evidence of an emergent antiferromagnetic
order with high magnon energy and exchange interactions at the
LaNiO$_{3}$/LaTiO$_{3}$ interface. As the magnetism is purely interfacial, a
single LaNiO$_{3}$/LaTiO$_{3}$ interface can essentially behave as an
atomically thin quasi-two-dimensional antiferromagnet, potentially allowing its
technological utilisation in advanced spintronic devices. Furthermore, its
strong quasi-two-dimensional magnetic correlations and orbitally-polarized
planar ligand holes make its electronic and magnetic configurations resemble
the precursor states of superconducting cuprates and nickelates, but with an S
$\rightarrow$ 1 spin state instead.",2403.00728v1
2009-01-24,"Uniform mixing of antiferromagnetism and high-T_c superconductivity in multilayered copper oxides Ba_2Ca_{n-1}Cu_nO_{2n}F_2 with apical fluorines (n=2,3,4): Cu-NMR/NQR and F-NMR","We report Cu-NMR/NQR and F-NMR studies on the multilayered high-T_c copper
oxides Ba_2Ca_{n-1}Cu_nO_{2n}F_2 with n=2,3,4, where n is the number of CuO_2
planes. It is revealed that bi-layered Ba_2CaCu_2O_4F_2 is an underdoped
superconductor with hole carriers, which are introduced into CuO_2 planes by an
unexpected deviation from the nominal content of apical fluorines. In a
previous paper, we proposed a self-doping mechanism as the origin of carrier
doping in n=3 and n=4; in the mechanism, electrons are transferred from the
inner CuO_2 plane (IP) to the outer one (OP). However, since it has been found
that the bi-layered compound is hole doped, we have reexamined the
superconducting and magnetic properties in n=3 and n=4 by Cu-NMR/NQR and F-NMR.
The extensive NMR studies have confirmed that the apical-fluorine compounds are
not self-doped but hole-doped, and that antiferromagnetism (AFM) and
superconductivity (SC) coexist in a single CuO_2 plane. In n=4, the AFM
ordering occurs at T_N = 80 K, well above T_c=55 K, where the respective AFM
moments are M_AFM=0.11 mu_B and 0.18 mu_B at the OP and the IP. In n=3, on the
other hand, the underdoped single IP exhibits a spontaneous moment M_AFM=0.12
mu_B at low temperatures and a peak in the nuclear-spin-lattice relaxation rate
1/T_1 of F at T_N=23 K, much lower than T_c = 76 K. We note that the increase
in the number of IPs from one to two leads to an increase in T_N due to
strengthening the interlayer coupling, although the doping levels for both
compounds are almost comparable. The present results strongly suggest that the
uniform mixing of AFM and SC is a general property inherent to a single CuO_2
plane in the underdoped regime for hole-doping.",0901.3811v1
2010-11-17,Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain,"Recently a metallic state was discovered at the interface between insulating
oxides, most notably LaAlO3 and SrTiO3. Properties of this two-dimensional
electron gas (2DEG) have attracted significant interest due to its potential
applications in nanoelectronics. Control over this carrier density and mobility
of the 2DEG is essential for applications of these novel systems, and may be
achieved by epitaxial strain. However, despite the rich nature of strain
effects on oxide materials properties, such as ferroelectricity, magnetism, and
superconductivity, the relationship between the strain and electrical
properties of the 2DEG at the LaAlO3/SrTiO3 heterointerface remains largely
unexplored. Here, we use different lattice constant single crystal substrates
to produce LaAlO3/SrTiO3 interfaces with controlled levels of biaxial epitaxial
strain. We have found that tensile strained SrTiO3 destroys the conducting
2DEG, while compressively strained SrTiO3 retains the 2DEG, but with a carrier
concentration reduced in comparison to the unstrained LaAlO3/SrTiO3 interface.
We have also found that the critical LaAlO3 overlayer thickness for 2DEG
formation increases with SrTiO3 compressive strain. Our first-principles
calculations suggest that a strain-induced electric polarization in the SrTiO3
layer is responsible for this behavior. It is directed away from the interface
and hence creates a negative polarization charge opposing that of the polar
LaAlO3 layer. This both increases the critical thickness of the LaAlO3 layer,
and reduces carrier concentration above the critical thickness, in agreement
with our experimental results. Our findings suggest that epitaxial strain can
be used to tailor 2DEGs properties of the LaAlO3/SrTiO3 heterointerface.",1011.4082v1
2012-06-19,K-edge X-ray absorption spectra in transition metal oxides beyond the single particle approximation: shake-up many body effects,"The near edge structure (XANES) in K-edge X-ray absorption spectroscopy (XAS)
is a widely used tool for studying electronic and local structure in materials.
The precise interpretation of these spectra with the help of calculations is
hence of prime importance, especially for the study of correlated materials
which have a complicated electronic structure per se. The single particle
approach, for example, has generally limited itself to the dominant dipolar
cross-section. It has long been known however that effects beyond this approach
should be taken into account, both due to the inadequacy of such calculations
when compared to experiment and the presence of shake-up many-body satellites
in core-level photoemission spectra of correlated materials. This effect should
manifest itself in XANES spectra and the question is firstly how to account for
it theoretically and secondly how to verify it experimentally. By using
state-of-the-art first principles electronic structure calculations and 1s
photoemission measurements we demonstrate that shake-up many-body effects are
present in K-edge XAS dipolar spectra of NiO, CoO and CuO at all energy scales.
We show that shake-up effects can be included in K-edge XAS spectra in a simple
way by convoluting the single-particle first-principles calculations including
core-hole effects with the 1s photoemission spectra. We thus describe all
features appearing in the XAS dipolar cross-section of NiO and CoO and obtain a
dramatic improvement with respect to the single-particle calculation in CuO.
These materials being prototype correlated magnetic oxides, our work points to
the presence of shake-up effects in K-edge XANES of most correlated transition
metal compounds and shows how to account for them, paving the way to a precise
understanding of their electronic structure.",1206.4235v1
2012-12-12,Impurity-induced frustration: low-energy model of diluted oxides,"We provide a detailed derivation of the low-energy model for Zn-diluted
La2CuO4 in the limit of low doping together with a study of the ground-state
properties of that model. We consider Zn-doped La2CuO4 within a framework of
the three-band Hubbard model, which closely describes high-Tc cuprates on the
energy scale of the most relevant atomic orbitals. Qualitatively, we find that
the hybridization of zinc and oxygen orbitals can result in an impurity state
with the energy \varepsilon, which is lower than the effective Hubbard gap U.
The low-energy, spin-only Hamiltonian includes terms of the order t^2/U and
t^4/\varepsilon^3. That is, besides the usual nearest-neighbor superexchange
J-terms of order t^2/U, the low-energy model contains impurity-mediated,
further-neighbor frustrating interactions among the Cu spins surrounding
Zn-sites in an otherwise unfrustrated antiferromagnetic background. These terms
can be substantial when \varepsilon ~ U/2, the latter value corresponding to
the realistic CuO2 parameters. In order to verify this spin-only model, we
subsequently apply the T-matrix approach to study the effect of impurities on
the antiferromagnetic order parameter. Previous theoretical studies, which
include only the dilution effect of impurities, show a large discrepancy with
experimental data in the doping dependence of the staggered magnetization at
low doping. We demonstrate that this discrepancy is eliminated by including
impurity-induced frustrations into the effective spin model with realistic CuO2
parameters. Recent experimental study shows a significantly stronger
suppression of spin stiffness in the case of Zn-doped La2CuO4 compared to the
Mg-doped case and thus gives a strong support to our theory. We argue that the
proposed impurity-induced frustrations should be important in other strongly
correlated oxides and charge-transfer insulators.",1212.2976v2
2013-07-15,Topotactic phase transformation of the brownmillerite SrCoO2.5 to the perovskite SrCoO3-δ,"Oxygen stoichiometry is one of the most important elements in determining the
physical properties of transition metal oxides (TMOs). A small fractional
change in the oxygen content, resulting in the variation of valence state of
the transition metal, can drastically modify the materials functionalities. In
particular, TMOs with mixed valences have attracted attention for many energy
applications. Previous studies also showed that the ability to control the
number of d-band electron populations and detailed spin configurations is
critical for improved catalytic performance of TMOs. In this context,
SrCoO$_{x}$ (2.5 < x < 3.0) is an ideal class of materials due to the existence
of two structurally distinct topotatic phases, i.e. the brownmillerite
SrCoO$_{2.5}$(BM-SCO) and the perovskite SrCoO$_{3}$. Especially, BM-SCO has
atomically-ordered one-dimensional vacancy channels, which can accommodate
additional oxygen. Moreover, SrCoO$_{x}$ exhibits a wide spectrum of physical
properties depending on the oxygen stoichiometry. Since SrCoOx has only a
single knob to control the Co valence state without cation doping, it is an
attractive material for studying the valence state dependent physical
properties. However, so far, the growth of high quality single crystalline
materials has not been much studied due to difficulty in controlling the right
oxidation state. In this work, we report on the epitaxial growth of BM-SCO
single crystalline films on SrTiO3 by pulsed laser epitaxy. In order to examine
the topotactic phase transformation to the perovskite SrCoO$_{3-\delta}$, some
of samples were subsequently in-situ annealed at various oxygen pressure
P(O$_{2}$). We found that post-annealing in high P(O$_{2}$) (> several hundreds
of Torr) could fill some of oxygen vacancies accompanying systematic evolution
in electronic, magnetic, and thermoelectric properties.",1307.3932v1
2014-01-07,Superparamagnetic iron oxide polyacrylic acid coated γ-Fe2O3 nanoparticles does not affect kidney function but causes acute effect on the cardiovascular function in healthy mice,"This study describes the distribution of intravenously injected polyacrylic
acid (PAA) coated {\gamma}-Fe2O3 NPs (10 mg kg-1) at the organ, cellular and
subcellular levels in healthy BALB/cJ mice and in parallel addresses the
effects of NP injection on kidney function, blood pressure and vascular
contractility. Magnetic resonance imaging (MRI) and transmission electron
microscopy (TEM) showed accumulation of NPs in the liver within 1h after
intravenous infusion, accommodated by intracellular uptake in endothelial and
Kupffer cells with subsequent intracellular uptake in renal cells, particularly
the cytoplasm of the proximal tubule, in podocytes and mesangial cells. The
renofunctional effects of NPs were evaluated by arterial acid-base status and
measurements of glomerular filtration rate (GFR) after instrumentation with
chronically indwelling catheters. Arterial pH was 7.46 and 7.41 in mice 0.5 h
after injections of saline or NP, and did not change over the next 12h. In
addition, the injections of NP did not affect arterial PCO2 or [HCO3-] either.
Twenty-four and 96h after NP injections, the GFR averaged 11.0 and 13.0 ml
min-1 g-1, respectively, values which were statistically comparable with
controls (14.0 and 14.0 ml min-1 g-1). Mean arterial blood pressure (MAP)
decreased 12-24h after NP injections (111 vs 123 min-1) associated with a
decreased contractility of small mesenteric arteries revealed by myography to
characterise endothelial function. In conclusion, our study demonstrates that
accumulation of superparamagnetic iron oxide nanoparticles does not affect
kidney function in healthy mice but temporarily decreases blood pressure.",1401.1847v1
2015-01-20,Anomalous High-Energy Waterfall-Like Electronic Structure in 5d Transition Metal Oxide Sr2IrO4 with a Strong Spin-Orbit Coupling,"The layered 5d transition metal oxides like Sr2IrO4 have attracted
significant interest recently due to a number of exotic and new phenomena
induced by the interplay between the spin-orbit coupling, bandwidth W and
on-site Coulomb correlation U. In contrast to a metallic behavior expected from
the Mott-Hubbard model due to more spatially extended 5d orbitals and moderate
U, an insulating ground state has been observed in Sr2IrO4. Such an insulating
behavior can be understood by an effective J_eff=1/2 Mott insulator model by
incorporating both electron correlation and strong spin-orbital coupling,
although its validity remains under debate at present. In particular, Sr2IrO4
exhibits a number of similarities to the high temperature cuprate
superconductors in the crystal structure, electronic structure, magnetic
structure, and even possible high temperature superconductivity. Here we report
a new observation of the anomalous high energy electronic structure in Sr2IrO4.
By taking high-resolution angle-resolved photoemission measurements on Sr2IrO4
over a wide energy range, we have revealed that the high energy electronic
structures show unusual nearly-vertical bands that extend over a large energy
range. Such anomalous high energy behaviors resemble the high energy waterfall
features observed in the cuprate superconductors, adding one more important
similarity between these two systems. While strong electron correlation plays
an important role in producing high energy waterfall features in the cuprate
superconductors, the revelation of the high energy anomalies in Sr2IrO4 points
to a novel route in generating exotic electronic excitations from the strong
spin-orbit coupling and a moderate electron correlation.",1501.04687v1
2016-01-19,Strong evidence for d-electron spin transport at room temperature at a LaAlO3/SrTiO3 interface,"A d-orbital electron has an anisotropic electron orbital and is a source of
magnetism. The realization of a 2-dimensional electron gas (2DEG) embedded at a
LaAlO3/SrTiO3 interface surprised researchers in materials and physical
sciences because the 2DEG consists of 3d-electrons of Ti with extraordinarily
large carrier mobility, even in the insulating oxide heterostructure. To date,
a wide variety of physical phenomena, such as ferromagnetism and the quantum
Hall effect, have been discovered in this 2DEG systems, demonstrating the
ability of the d-electron 2DEG systems to provide a material platform for the
study of interesting physics. However, because of both ferromagnetism and the
Rashba field, long-range spin transport and the exploitation of spintronics
functions have been believed difficult to implement in the d-electron 2DEG
systems. Here, we report the experimental demonstration of room-temperature
spin transport in the d-electron-based 2DEG at a LaAlO3/SrTiO3 interface, where
the spin relaxation length is ca. exceeding 200 nm. Our finding, which counters
the conventional understandings to d-electron 2DEGs, opens a new field of
d-electron spintronics. Furthermore, this work highlights a novel spin function
in the conductive oxide system.",1601.07568v2
2018-11-21,Beneficial influence of Hf and Zr additions to Nb4at.%Ta on the vortex pinning of Nb$_{3}$Sn with and without an O source,"Here we show that addition of Hf to Nb4Ta can significantly improve the high
field performance of Nb$_{3}$Sn, making it suitable for dipole magnets for
Future Circular Collider (FCC). A big challenge for the FCC is that a realistic
production target for FCC Nb3Sn requires ~30% improvement over current
conductor performance. Recent success with internal oxidation(IO) of Nb-Zr
precursor has shown significant improvement in the layer J$_{c}$ of Nb$_{3}$Sn
wires, albeit the complication of providing an internal O$_{2}$ diffusion path
and avoiding degradation of irreversibility field($_{irr}$). We compare Zr and
Hf additions to the standard Nb4Ta alloy of maximum H$_{c2}$ and H$_{irr}$.
Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without
SnO$_{2}$ and their properties measured over the entire superconducting range
up to 31 T. We found that group IV alloying of Nb4Ta raises H$_{irr}$, though
adding O$_{2}$ still degrades this slightly. As noted in Nb1Zr studies, the
pinning force density F$_{p}$ is strongly enhanced and its peak value shifted
to higher field by IO. A surprising result of this work is that we found better
properties in Nb4Ta1Hf without SnO$_{2}$, F$_{pmax}$ achieving 2.35 times that
of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54
times that of the Nb4Ta alloy. The highest layer J$_{c}$ (16 T, 4.2 K) of 3700
A/mm$^{2}$ was found in the SnO$_{2}$-free wire made with Nb4Ta1Hf alloy. Using
a standard A15 cross-section fraction of 60% for modern PIT and RRP wires, we
estimated that a non-Cu J$_{c}$ of 2200 A/mm$^{2}$ is obtainable in modern
conductors, well above the 1500A/mm$^{2}$ FCC specification. Moreover, the best
properties were obtained without SnO$_{2}$, the Nb4Ta1Hf alloy appears to open
a straightforward route to enhanced properties in Nb$_{3}$Sn wires.",1811.08867v1
2018-05-16,Insight into bulk niobium superconducting RF cavities performances by tunneling spectroscopy,"Point contact tunneling (PCT) spectroscopy measurements are reported over
wide areas of cm-sized cut outs from niobium superconducting RF cavities. A
comparison is made between a high-quality, conventionally processed (CP) cavity
with a high field Q drop for acceleration field E $>$ 20 MV/m and a nitrogen
doped (N-doped) cavity that exhibits an increasing Q up to fields approaching
15 MV/m. The CP cavity displays hot spot regions at high RF fields where Q-drop
occurs as well as unaffected regions (cold spots). PCT data on cold spots
reveals a near ideal BCS density of states (DOS) with gap parameters, $\Delta$
as high as 1.62 meV, that are among the highest values ever reported for Nb.
Hot spot regions exhibit a wide distribution of gap values down to $\Delta
\sim$ 1.0 meV and DOS broadening characterized by a relatively large value of
pair-breaking rate, $\Gamma$, indicating surface regions of significantly
reduced superconductivity. In addition, hot spots commonly exhibit Kondo
tunneling peaks indicative of surface magnetic moments attributed to a
defective oxide. N-doped cavities reveal a more homoegeneous gap distribution
centered at $\Delta \sim$ 1.5 meV and relatively small values of
$\Gamma/\Delta$. The absence of regions of significantly reduced
superconductivity indicates that the N interstitials are playing an important
role in preventing the formation of hydride phases and other macroscopic
defects which might otherwise severely affect the local, surface
superconductivity that lead to hot spot formation. The N-doped cavities also
display a significantly improved surface oxide, i.e., increased thickness and
tunnel barrier height, compared to CP cavities. These results help explain the
improved performance of N-doped cavities and give insights into the origin of
the initial increasing Q with RF amplitude.",1805.06359v1
2018-01-24,$Ab-initio$ investigation of the thermodynamics of cation distribution and the electronic and magnetic structures in the LiMn$_2$O$_4$ spinel,"The spinel-structured lithium manganese oxide (LiMn$_2$O$_4$) is a material
currently used as cathode for secondary lithium-ion batteries, but whose
properties are not yet fully understood. Here, we report a computational
investigation of the inversion thermodynamics and electronic behaviour of
LiMn$_2$O$_4$ derived from spin-polarised density functional theory
calculations with a Hubbard Hamiltonian and long-range dispersion corrections
(DFT+$U-$D3). Based on the analysis of the configurational free energy, we have
elucidated a partially inverse equilibrium cation distribution for the
LiMn$_2$O$_4$ spinel. This equilibrium degree of inversion is rationalised in
terms of the crystal field stabilisation effects and the difference between the
size of the cations. We compare the atomic charges with the oxidation numbers
for each degree of inversion. We found segregation of the Mn charge once these
ions occupy the tetrahedral and octahedral sites of the spinel. We have
obtained the atomic projections of the electronic band structure and density of
states, showing that the normal LiMn$_2$O$_4$ has half-metallic properties,
while the fully inverse spinel is an insulator. This material is in the
ferrimagnetic state for the inverse and partially inverse cation arrangement.
The optimised lattice and oxygen parameters, as well as the equilibrium degree
of inversion, are in agreement with the available experimental data. The
partially inverse equilibrium degree of inversion is important in the
interpretation of the lithium ion migration and surface properties of the
LiMn$_2$O$_4$ spinel.",1801.08013v1
2020-04-28,Charge transfer induced interfacial ferromagnetism in La$_{0.7}$Sr$_{0.3}$MnO$_3$/NdNiO$_3$,"Charge transfer induced interfacial ferromagnetism and its impact on the
exchange bias effect in La$_{0.7}$Sr$_{0.3}$MnO$_3$/NdNiO$_3$ correlated oxide
heterostructures were investigated by soft x-ray absorption and x-ray magnetic
circular dichroism spectra in a temperature range from 10 to 300 K. Besides the
antiferromagnetic Ni$_3^+$ cations which are naturally part of the NdNiO$_3$
layer, Ni$_2^+$ ions are formed at the interface due to a charge transfer
mechanism involving the Mn element of the adjacent layer. They exhibit a
ferromagnetic behavior due to the exchange coupling to the Mn$_4^+$ ions in the
La$_{0.7}$Sr$_{0.3}$MnO$_3$ layer. This can be seen as detrimental to the
strength of the unidirectional anisotropy since a significant part of the
interface does not contribute to the pinning of the ferromagnetic layer. By
analyzing the line shape changes of the x-ray absorption at the Ni L$_{2,3}$
edges, the metal-insulator transition of the NdNiO$_3$ layer is resolved in an
element specific manner. This phase transition is initiated at about 120 K, way
above the paramagnetic to antiferromagnetic transition of NdNiO$_3$ layer which
measured to be 50 K. Exchange bias and enhanced coercive fields were observed
after field cooling the sample through the Neel temperature of the NdNiO$_3$
layer. Different from La$_{0.7}$Sr$_{0.3}$MnO$_3$/LaNiO$_3$, the exchange bias
observed in La$_{0.7}$Sr$_{0.3}$MnO$_3$/NdNiO$_3$ is due to the
antiferromagnetism of NdNiO$_3$ and the frustration at the interface. These
results suggest that reducing the interfacial orbital hybridization may be used
as a tunable parameter for the strength of the exchange bias effect in
all-oxide heterostructures which exhibit a charge transfer mechanism.",2004.13593v1
2018-12-18,Two-dimensional Ca-Cl crystals under ambient conditions observed directly by cryo-electron microscopy,"Recently, we report the direct observation, under ambient conditions, of
Na2Cl and Na3Cl as two-dimensional (2D) Na-Cl crystals, together with regular
NaCl, on reduced graphene oxide membranes and on the surfaces of natural
graphite powders from salt solutions far below the saturated concentration.
However, what are these abnormal stoichiometries for high valence ions, such as
calcium ions and copper ions still remain unknown. Here, using cryo-electron
microscopy, we report the direct observation of two-dimensional (2D) Ca-Cl
crystals on reduced graphene oxide (rGO) membranes, in which the calcium ions
are only monovalent (i.e. +1). Remarkably, metallic properties rather than
insulating are displayed by those CaCl crystals. We note that such CaCl
crystals are obtained by simply incubating rGO membranes in salt solutions
below the saturated concentration, under ambient conditions. Theoretical
studies show that the formation of those abnormal crystals is attributed to the
strong cation-pi interactions of the Ca2+ ions with the aromatic rings in the
graphitic surfaces. Since strong cation-pi interactions also exist between
other metal ions (such as Mg2+, Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+) and
graphitic surfaces, similar 2D crystals with abnormal valence state of the
metal cations and corresponding abnormal properties are highly expected. The 2D
crystals with monovalent calcium ions show unusual electronic properties, and
can be applicated in catalyzer, hydrogen storage, high-performance conducting
electrodes and sensors. These findings also produce functionalized graphene
including compact ""graphene-metallic CaCl-insulating CaCl2"" junction that can
serve as transistors down to the atomic scale, and other devices for magnetic,
optical and mechanical applications.",1812.07195v1
2019-03-01,Anisotropic Magnetoresistance in Multiband Systems: 2DEGs and Polar Metals at Oxide Interfaces,"Low density two-dimensional electron gases (2DEGs) with spin-orbit coupling
are highly sensitive to an in-plane magnetic field, which impacts their Fermi
surfaces and transport properties. Such 2DEGs, formed at transition metal oxide
surfaces or interfaces, can also undergo surface phase transitions leading to
polar metals which exhibit electronic nematicity. Motivated by experiments on
such systems, we theoretically study magnetotransport in $t_{2g}$ orbital
systems, using Hamiltonians which include atomic spin-orbit coupling (SOC) and
broken inversion symmetry, for both square symmetry (001) and hexagonal
symmetry (111) 2DEGs. Using a numerical solution to the full multiband
matrix-Boltzmann equation, together with insights gleaned from the impurity
scattering overlap matrix, we explore the anisotropic magnetoresistance (AMR)
in the presence of impurities which favor small momentum scattering. We find
that transport in the (001) 2DEG is dominated by a single pair of bands, weakly
coupled by impurity scattering, one of which has a larger Fermi velocity while
the other provides an efficient current-relaxation mechanism. This leads to
strong angle-dependent current damping and a large AMR with many angular
harmonics. In contrast, AMR in the (111) 2DEG typically features a single
$\cos(2\vartheta)$ harmonic, with the angle-averaged magnetoresistance being
highly tunable by a symmetry-allowed trigonal distortion. We also explore how
the (111) 2DEG Fermi sufaces are impacted by electronic nematicity via a
surface phase transition into a 2D polar metal for which we discuss a Landau
theory, and show that this leads to distinct symmetry components and higher
angular harmonics in the AMR. Our results are in qualitative agreement with
experiments from various groups for 2DEGs at the SrTiO$_3$ surface or the
LaAlO$_3$-SrTiO$_3$ interface.",1903.00476v2
2021-04-29,Observation of perfect diamagnetism and interfacial effect on the electronic structures in Nd0.8Sr0.2NiO2 superconducting infinite layers,"Nickel-based complex oxides have served as a playground for decades in the
quest for a copper-oxide analog of the high-temperature superconductivity. They
may provide clues towards understanding the mechanism and an alternative route
for high-temperature superconductors. The recent discovery of superconductivity
in the infinite-layer nickelate thin films has fulfilled this pursuit. However,
material synthesis remains challenging, direct demonstration of perfect
diamagnetism is still missing, and understanding of the role of the interface
and bulk to the superconducting properties is still lacking. Here, we show
high-quality Nd0.8Sr0.2NiO2 thin films with different thicknesses and
demonstrate the interface and strain effects on the electrical, magnetic and
optical properties. Perfect diamagnetism is achieved, confirming the occurrence
of superconductivity in the films. Unlike the thick films in which the
normal-state Hall-coefficient changes signs as the temperature decreases, the
Hall-coefficient of films thinner than 5.5 nm remains negative, suggesting a
thickness-driven band structure modification. Moreover, X-ray absorption
spectroscopy reveals the Ni-O hybridization nature in doped infinite-layer
nickelates, and the hybridization is enhanced as the thickness decreases.
Consistent with band structure calculations on the nickelate/SrTiO3
heterostructure, the interface and strain effect induce a dominating
electron-like band in the ultrathin film, thus causing the sign-change of the
Hall-coefficient.",2104.14195v2
2022-06-23,Suppressing initial capacity fade in Li-rich Li$_5$FeO$_4$ with anionic redox by partial Co substitution,"The increasing relevance of energy storage technologies demands high-capacity
cathode materials for Li-ion batteries. Recently, Li-rich defect anti-fluorite
Li$_5$FeO$_4$ has emerged as a high-capacity cathode material exhibiting
simultaneous anionic and cationic redox without significant oxygen release. But
suffers from irreversible structural change and capacity fade during cycling.
Herein we investigate the suppressed capacity fade reported in Co substituted
Li$_5$FeO$_4$ and establish the optimal performance through tuning the
concentration and oxidation state of Co. We have substituted Co at the Fe site
and carried out a detailed analysis of structural, magnetic, electronic, and
electrochemical properties using first-principles density functional theory
calculations. The extended stability and suppressed capacity fading are found
only in specific compositions depending on the Co/Li concentration and the
oxidation state of Co. The reasons behind suppressed capacity fading in Co
substituted systems have been unveiled on the basis of bonding analyses and
proposed as a strategy to suppress the voltage fading reported in Li-rich
materials due to transition metal migration. From the evaluation of
thermodynamic stability and electronic structure,
Li$_{5.5}$Fe$_{0.5}$Co$_{0.5}$O$_4$, Li$_5$Fe$_{0.25}$Co$_{0.75}$O$_4$, and
Li$_{4.5}$Fe$_{0.5}$Co$_{0.5}$O$_4$ are found to exhibit better electrical
conductivity than Li$_5$FeO$_4$. All these systems have voltage in the range of
3 to 5 V and exhibit three dimensional Li diffusion pathway with a diffusion
barrier height of around 0.3 eV. From Li$_5$Fe$_{0.25}$Co$_{0.75}$O$_4$, one
can delithiate three Li-ions without structural change and oxygen release,
therefore expected to acquire a reversible capacity of around 513 mAh/g.
Moreover, as in pristine Li$_5$FeO$_4$, the selected Co substituted systems
also exhibit simultaneous anionic and cationic redox without significant O2
release.",2206.11496v1
2022-06-29,Ultra-High Carrier Mobilities in Ferroelectric Domain Wall Corbino Cones at Room Temperature,"Recently, electrically conducting heterointerfaces between dissimilar
band-insulators (such as lanthanum aluminate and strontium titanate) have
attracted considerable research interest. Charge transport has been thoroughly
explored and fundamental aspects of conduction firmly established. Perhaps
surprisingly, similar insights into conceptually much simpler conducting
homointerfaces, such as the domain walls that separate regions of different
orientations of electrical polarisation within the same ferroelectric
band-insulator, are not nearly so well-developed. Addressing this disparity, we
herein report magnetoresistance in approximately conical 180o charged domain
walls, which occur in partially switched ferroelectric thin film single crystal
lithium niobate. This system is ideal for such measurements: firstly, the
conductivity difference between domains and domain walls is extremely and
unusually large (a factor of at least 1013) and hence currents driven through
the thin film, between planar top and bottom electrodes, are overwhelmingly
channelled along the walls; secondly, when electrical contact is made to the
top and bottom of the domain walls and a magnetic field is applied along their
cone axes (perpendicular to the thin film surface), then the test geometry
mirrors that of a Corbino disc, which is a textbook arrangement for geometric
magnetoresistance measurement. Our data imply carriers at the domain walls with
extremely high room temperature Hall mobilities of up to ~ 3,700cm2V-1s-1. This
is an unparalleled value for oxide interfaces (and for bulk oxides too) and is
most comparable to mobilities in other systems typically seen at cryogenic,
rather than at room, temperature.",2206.14585v1
2022-08-30,Distinct electridelike nature of infinite-layer nickelates and the resulting theoretical challenges to calculate their electronic structure,"We demonstrate in this paper that the recently discovered infinite-layer (IL)
nickelates have much in common with a class of materials known as electrides.
Oxide based electrides are compounds in which topotactic removal of loosely
bound oxygens leaves behind voids with a landscape of attractive potentials for
electrons. We show that this is also what happens in the IL nickelates, where
one of the two electrons (per formula unit) freed during the topotactic
synthesis is to a large degree located in the oxygen vacancy position,
occupying partially a local $s$-symmetry interstitial orbital, rather than
taking part alongside the other electon in converting Ni from 3+ to a full 1+
oxidation state. We demonstrate that the interstitial orbital in question,
referred to by us as the zeronium $s$ or Z $s$ orbital, forms strong covalent
bonds with neighboring Ni $3d_{3z^2-r^2}$ orbitals, which in turn facilitates
the one-dimensional-like dispersion of the Ni $3d_{3z^2-r^2}$ band along the
$c$-axis direction, leading also to a possible large out-of-plane coupling
between Ni magnetic moments. This finding, reinforced by our electron
localization function analysis, points to a fundamental distinction between the
nickelates and the structurally analogous cuprates, may explain the absence of
superconductivity in hydrogen-poor samples, and is certainly in agreement with
the observed large $z$-polarized component in the Ni $L_3$-edge x-ray
absorption spectra. In addition, by using DFT+U calculations as an
illustration, we show that the electride-like nature of the IL nickelates is
one of the main reasons for the theoretical difficulty in determining the much
debated elusive Fermi surface of these novel superconductors and aslo in
exploring the possibility of them becoming excitonic insulators at low
temperatures.",2208.14556v2
2019-04-10,Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction,"The Fe/MgO magnetic tunnel junction is a classic spintronic system, with
current importance technologically, and interest for future innovation. The key
magnetic properties are linked directly to the structure of hard-to-access
buried interfaces, and the Fe and MgO components near the surface are unstable
when exposed to air, making a deeper probing, non-destructive, in-situ
measurement ideal for this system. We have thus applied hard x-ray
photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few keV
energy range to probe the structure of an epitaxially-grown MgO/Fe
superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by
magnetron sputtering on an MgO (001) substrate, with a protective Al2O3 capping
layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and
ordered, with a period of 33 $\pm$ 4 angstrom, with minor presence of FeO at
the interfaces and a significantly distorted top bilayer with ca. 3 times the
oxidation of the lower layers at the top MgO/Fe interface. There is evidence of
asymmetrical oxidation on the top and bottom of the Fe layers. We find
agreement with dark-field scanning transmission electron microscope (STEM) and
x-ray reflectivity measurements. Through the STEM measurements we confirm an
overall epitaxial stack with dislocations and warping at the interfaces of ca.
5 angstrom. We also note a distinct difference in the top bilayer, especially
MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used
to probe deep buried interfaces of novel magnetic devices with few angstrom
precision.",1904.04999v2
2008-08-08,Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors,"Layered d-metal pnictide oxides are a unique class of compounds which
consists of characteristic d-metal pnictide layers and metal oxide layers. More
than 100 of these layered compounds, including the recently discovered Fe-based
superconducting pnictide oxides, can be classified into 9 structure types.
These structure types and the chemical and physical properties of the
characteristic d-metal pnictide layers and metal oxide layers of the layered
d-metal pnictide oxides are reviewed and discussed. Furthermore, possible
approaches to design new superconductors based on these layered d-metal
pnictide oxides are proposed.",0808.1158v6
2009-08-12,Electronic structure and ionicity of actinide oxides from first principles calculations,"The ground state electronic structures of the actinide oxides AO, A2O3 and
AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles
calculations, using the self-interaction corrected local spin-density (SIC-LSD)
approximation. Emphasis is put on the degree of f-electron localization, which
for AO2 and A2O3 is found to follow the stoichiometry, namely corresponding to
A(4+) ions in the dioxide and A(3+) ions in the sesquioxides. In contrast, the
A(2+) ionic configuration is not favorable in the monoxides, which therefore
become metallic. The energetics of the oxidation and reduction of the actinide
dioxides is discussed, and it is found that the dioxide is the most stable
oxide for the actinides from Np onwards. Our study reveals a strong link
between preferred oxidation number and degree of localization which is
confirmed by comparing to the ground state configurations of the corresponding
lanthanide oxides. The ionic nature of the actinide oxides emerges from the
fact that only those compounds will form where the calculated ground state
valency agrees with the nominal valency expected from a simple charge counting.",0908.1806v1
2010-04-29,Internal Interface Strains Effects on UO2/U3O7 Oxidation Behaviour,"The growth of a U3O7 oxide layer during the anionic oxidation of UO2 pellets
induced very important mechanical stresses due to the crystallographic lattice
parameters differences between UO2 and its oxide. These stresses, combined with
the chemical processes of oxidation, can lead to the cracking of the system,
called chemical fragmentation. We study the crystallographic orientation of the
oxide lattice growing at the surface of UO2, pointing the fact that epitaxy
relations at interface govern the coexistence of UO2 and U3O7. In this work,
several results are given: - Determination of the epitaxy relations between the
substrate and its oxide thanks to the Bollmann's method; epitaxy strains are
deduced. - Study of the coexistence of different domains in the U3O7
(crystallographic compatibility conditions at the interface between two phases:
Hadamard conditions). - FEM simulations of a multi-domain U3O7 connected to a
UO2 substrate explain the existence of a critical thickness of U3O7 layer.",1004.5295v1
2011-06-16,Silicon dry oxidation kinetics at low temperature in the nanometric range: Modeling and experiment,"Kinetics of silicon dry oxidation are investigated theoretically and
experimentally at low temperature in the nanometer range where the limits of
the Deal and Grove model becomes critical. Based on a fine control of the
oxidation process conditions, experiments allow the investigation of the growth
kinetics of nanometric oxide layer. The theoretical model is formulated using a
reaction rate approach. In this framework, the oxide thickness is estimated
with the evolution of the various species during the reaction. Standard
oxidation models and the reaction rate approach are confronted with these
experiments. The interest of the reaction rate approach to improve silicon
oxidation modeling in the nanometer range is clearly demonstrated.",1106.3160v2
2012-03-09,Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution,"We introduce an approach to calculate the thermodynamic oxidation and
reduction potentials of semiconductors in aqueous solution. By combining a
newly-developed ab initio calculation for compound formation energy and band
alignment with electrochemistry experimental data, this approach can be used to
predict the stability of almost any compound semiconductor in aqueous solution.
30 photocatalytic semiconductors have been studied, and a graph (a simplified
Pourbaix diagram) showing their valence/conduction band levels and
oxidation/reduction potentials is produced. Based on this graph, we have
studied the stabilities and trends against the oxidative and reductive
photocorrosion for compound semiconductors. We found that, only metal oxides
can be thermodynamically stable when used as the n-type photoanodes. All the
non-oxides are unstable due to easy oxidation by the photogenerated holes, but
they can be resistant to the reduction by electrons, thus stable as the p-type
photocathodes.",1203.1970v1
2012-12-27,Molecular theory of graphene oxide,"Applying to graphene oxides, molecular theory of graphene is based on the
oxide molecular origin when it is considered as a final product in the
succession of a graphene molecule polyderivatives related to a particular
oxidation reaction. The graphene oxide structure is created in due course of
calculations following the algorithms that take into account the graphene
molecules natural radicalization, correlation of odd electrons, an extremely
strong influence of structure on properties, a sharp response of the molecule
behavior on small action of external factors. Taking together, the theory
facilities has allowed for getting a clear, transparent and understandable
explanation of hot points of the graphene oxide chemistry and suggesting
reliable models of both chemically produced and chemically reduced graphene
oxides.",1212.6413v1
2013-04-30,Carbon mono and dioxide hydrogenation over pure and metal oxide decorated graphene oxide substrates: insight from DFT,"Based on first principles density functional theory calculations we explore
the energetics of the conversion of carbon mono and dioxide to methane over
graphene oxide surfaces. Similar to the recently discovered hydration of
various organic species over this catalyst, the transfer of hydrogen atoms from
hydroxyl groups of graphene oxide provide a step by step transformation
hydrogenation of carbon oxides. Estimated yields of modeled reactions at room
temperature are about 0.01% for the carbon mono and dioxide. For the modeling
of graphene oxide/metal oxide composites, calculations in the presence of MO_2
(where M = V, Cr, Mn, Fe) have been performed. Results of these calculations
demonstrate significant decreases of the energy costs and increases of reaction
yields to 0.07%, which is comparable to the efficiency of these reactions over
platinum and ruthenium-based photocatalysts. Increasing the temperature to the
value 100C should provide the total conversion of carbon mono and dioxides.",1304.7929v1
2013-07-23,Untangling the role of oxide in Ga-assisted growth of GaAs nanowires on Si substrates,"The influence of the oxide in Ga-assisted growth of GaAs nanowires on Si
substrates is investigated. Three different types of oxides with different
structure and chemistry are considered. We observe that the critical oxide
thicknesses needed for achieving nanowire growth depends on the nature of oxide
and how it is processed. Additionally, we find that different growth conditions
such as temperature and Ga rate are needed for successful nanowire growth on
different oxides. We generalize the results in terms of the characteristics of
the oxides such as surface roughness, stoichiometry and thickness. These
results constitute a step further towards the integration of GaAs technology on
the Si platform.",1307.6113v1
2014-07-31,Compact chromium oxide thin film resistors for use in nanoscale quantum circuits,"We report on the electrical characterisation of a series of thin chromium
oxide films, grown by dc sputtering, to evaluate their suitability for use as
on-chip resistors in nanoelectronics. By increasing the level of oxygen doping,
the room-temperature sheet resistance of the chromium oxide films was varied
from 28$\Omega / \square$ to 32.6k$\Omega / \square$. The variation in
resistance with cooling to 4.2K in liquid helium was investigated; the sheet
resistance at 4.2K varied with composition from 65$\Omega / \square$ to above
20G$\Omega / \square$. All of the films measured displayed ohmic behaviour at
all measured temperatures. For on-chip devices for quantum phase-slip
measurements using niobium-silicon nanowires, interfaces between
niobium-silicon and chromium oxide are required. By characterising the
interface contact resistance, we found that a gold intermediate layer is
favourable: the specfic contact resistivity of chromium-oxide-to-gold
interfaces was 0.15 m$\Omega$cm$^2$, much lower than the value for direct
chromium-oxide to niobium-silicon interfaces, 65m$\Omega$cm$^2$. We conclude
that these chromium oxide films are suitable for use in nanoscale circuits as
high-value resistors, with resistivity tunable by oxygen content.",1407.8467v1
2015-05-18,High-Q Tantalum Oxide Nanomechanical Resonators by Laser-Oxidation of TaSe2,"Controlling the strain in two-dimensional materials is an interesting avenue
to tailor the mechanical properties of nanoelectromechanical systems. Here we
demonstrate a technique to fabricate ultrathin tantalum oxide nanomechanical
resonators with large stress by laser-oxidation of nano-drumhead resonators
made out of tantalum diselenide (TaSe2), a layered 2D material belonging to the
metal dichalcogenides. Prior to the study of their mechanical properties with a
laser interferometer, we checked the oxidation and crystallinity of the
freely-suspended tantalum oxide in a high-resolution electron microscope. We
show that the stress of tantalum oxide resonators increase by 140 MPa (with
respect to pristine TaSe2 resonators) which causes an enhancement of quality
factor (14 times larger) and resonance frequency (9 times larger) of these
resonators.",1505.04727v2
2016-04-21,Effects of Oxygen Contamination on Monolayer GeSe: A computational study,"Natural oxidation is a common degradation mechanism of both mechanical and
electronic properties for most of the new two-dimensional materials. From
another perspective, controlled oxidation is an option to tune material
properties, expanding possibilities for real-world applications. Understanding
the electronic structure modifications induced by oxidation is highly desirable
for new materials like monolayer GeSe, which is a new candidate for
near-infrared photodetectors. By means of first-principles calculations, we
study the influence of oxygen defects on the structure and electronic
properties of the single layer GeSe. Our calculations show that the oxidation
is an exothermic process, and it is nucleated in the germanium sites. The
oxidation can cause severe local deformations on the monolayer GeSe structure
and introduces a deep state in the bandgap or a shallow state near the
conduction band edge. Furthermore, the oxidation increases the bandgap by up to
23 %, and may induce direct to indirect bandgap transitions. These results
suggest that the natural or intentionally induced monolayer GeSe oxidation can
be a source of new optoelectronic properties, adding another important building
block to the two-dimensional layered materials.",1604.06322v1
2016-06-09,"Oxygen Point Defect Chemistry in Ruddlesden-Popper Oxides (La$_{1-x}$Sr$_{x}$)$_{2}$MO$_{4{\pm}δ}$ (M = Co, Ni, Cu)","Stability of oxygen point defects in Ruddlesden-Popper oxides
(La$_{1-x}$Sr$_{x}$)$_{2}$MO$_{4{\pm}{\delta}}$ (M = Co, Ni, Cu) is studied
with density functional theory calculations to determine their stable sites,
charge states, and energetics as functions of Sr content ($x$), transition
metal (M) and defect concentration ({\delta}). We demonstrate that the dominant
O point defects can change between oxide interstitials, peroxide interstitials,
and vacancies. Generally, increasing $x$ and atomic number of M stabilizes
peroxide over oxide interstitials, as well as vacancies over both peroxide and
oxide interstitials; increasing {\delta} destabilizes both oxide interstitials
and vacancies, but affects little peroxide interstitials. We also demonstrate
that the O 2$p$-band center is a powerful descriptor for these materials and
correlates linearly with the formation energy of all the defects. The trends of
formation energy versus $x$, M and {\delta} and the correlation with O
2$p$-band center are explained in terms of oxidation chemistry and electronic
structure.",1606.02963v1
2017-08-10,Numerical simulation of oxidation processes in a cross-flow around tube bundles,"An oxidation process is simulated for a bundle of metal tubes in a
cross-flow. A fluid flow is governed by the incompressible Navier-Stokes
equations. To describe the transport of oxygen, the corresponding
convection-diffusion equation is applied. The key point of the model is related
to the description of oxidation processes taking into account the growth of a
thin oxide film in the quasi-stationary approximation. Mathematical modeling of
oxidant transport in a tube bundle is carried out in the 2D approximation. The
numerical algorithm employed in the work is based on the finite-element
discretization in space and the fully implicit discretization in time. The tube
rows of a bundle can be either in-line or staggered in the direction of the
fluid flow velocity. The growth of the oxide film on tube walls is predicted
for various bundle structures using the developed oxidation model.",1708.04138v1
2018-02-21,Non-equilibrium Solute Capture in Passivating Oxide Films,"If all humans vanished tomorrow, almost every metal structure would collapse
within a century or less, the metal converting to an oxide. In applications
ranging from the mature technology of nuts and bolts to high technology
batteries, nuclear fuels and turbine engines, protective oxide films are
critical to limiting oxidation. To date models of these oxide films have
assumed that they form thermodynamic equilibrium stable or metastable phases
doped within thermodynamic solubility limits. Here we demonstrate
experimentally and theoretically the formation of unusual non-equilibrium oxide
phases, that can be predicted using a scientific framework for solute capture
at a moving oxide/substrate interface. The theory shows that solute capture is
likely a generic process for many electrochemical processes, and suggests that
similar phenomena yielding non-equilibrium phases can occur and be predicted
for a wide range of other processes involving solid-fluid and solid-solid
chemical reactions.",1802.07685v1
2014-03-19,Graphene Oxide flakes: methods and techniques for properties at interfaces,"Graphene Oxide and reduced Graphene Oxide are intriguing materials for
photonics and electronic devices both for intrinsic characteristics and as
precursors for the synthesis of graphene. Whatever the application and the
engineering purpose, a fine control of the chemical and physical properties is
required since the performances of graphene based systems depend on the
reduction state of Graphene Oxide and can be strongly affected by interfaces
interactions and neighboring effects. Then, a method for a local control of
electric, electronic and chemical properties is required. The synergic
application of Near Edge X ray Absorption Fine Structure Spectroscopy and
Conductive Atomic Force Microscopy is a powerful way for such purpose allowing
a full characterization of simple and composite samples, including specimens
with dielectric discontinuities. Graphene Oxide/Gold (GO/Au) and Graphene
Oxide/Silicon Oxide (GO/SiO2) have been selected as proof by example. The
results show that the approach allow to relate chemical, electronic and
physical properties to morphological features and local conductance behavior.",1403.4738v1
2018-09-01,Controlled Layer-by-Layer Oxidation of MoTe2 via O3 Exposure,"Growing uniform oxides with various thickness on TMDs is one of the biggest
challenges to integrate TMDs into complementary metal oxide semiconductor
(CMOS) logic circuits. Here, we report a layer-by-layer oxidation of atomically
thin MoTe2 flakes via ozone (O3) exposure. The thickness of MoOx oxide film
could be tuning with atomic-level accuracy simply by varying O3 exposure time.
Additionally, MoOx-covered MoTe2 shows a hole-dominated transport behavior. Our
findings point to a simple and effective strategy for growing homogenous
surface oxide film on MoTe2, which is promising for several purposes in
metal-oxide-semiconductor transistor, ranging from surface passivation to
dielectric layers.",1809.00119v1
2019-10-25,Macroscopic visualization of fast electrochemical reaction of SrCoOx oxygen sponge,"Strontium cobaltite (SrCoOx) is known as a material showing fast topotactic
electrochemical Redox reaction so-called oxygen sponge. Although atomic scale
phenomenon of the oxidation of SrCoO2.5 into SrCoO3 is known, the macroscopic
phenomenon has not been clarified yet thus far. Here, we visualize the
electrochemical oxidation of SrCoOx macroscopically. SrCoOx epitaxial films
with various oxidation states were prepared by the electrochemical oxidation of
SrCoO2.5 film into SrCoO3-d film. Steep decrease of both resistivity and the
absolute value of thermopower of electrochemically oxidized SrCoOx epitaxial
films indicated the columnar oxidation firstly occurred along with the surface
normal and then spread in the perpendicular to the normal. Further, we directly
visualized the phenomena using the conductive AFM. This macroscopic image of
the electrochemical oxidation would be useful to develop a functional device
utilizing the electrochemical redox reaction of SrCoOx.",1910.11465v1
2020-12-08,Scaled Atomic-Layer-Deposited Indium Oxide Nanometer Transistors with Maximum Drain Current Exceeding 2 A/mm at Drain Voltage of 0.7 V,"In this work, we demonstrate scaled back-end-of-line (BEOL) compatible indium
oxide (In2O3) transistors by atomic layer deposition (ALD) with channel
thickness (Tch) of 1.0-1.5 nm, channel length (Lch) down to 40 nm, and
equivalent oxide thickness (EOT) of 2.1 nm, with record high drain current of
2.0 A/mm at VDS of 0.7 V among all oxide semiconductors. Enhancement-mode In2O3
transistors with ID over 1.0 A/mm at VDS of 1 V are also achieved by
controlling the channel thickness down to 1.0 nm at atomic layer scale. Such
high current density in a relatively low mobility amorphous oxide semiconductor
is understood by the formation of high density 2D channel beyond 4E13 /cm2 at
HfO2/In2O3 oxide/oxide interface.",2012.04789v1
2017-04-30,Band offsets at amorphous-crystalline $Al_2O_3-SrTiO_3$ oxide interfaces,"2D electron gases (2DEGs) formed at oxide interfaces provide a rich testbed
for fundamental physics and device applications. While the discussion of the
physical origins of this phenomenon continues, the recent discovery of oxide
2DEGs at non-epitaxial interfaces between amorphous and crystalline oxides
provides useful insight onto this debate. Furthermore, using amorphous oxides
offers a low-cost route towards realizing 2DEGs for device applications. In
this work, the band offsets of a simple model system of amorphous-crystalline
oxide interface are investigated. The model system consists of amorphous
$Al_2O_3$ grown on single-crystalline (001) $SrTiO_3$. X-ray photoelectron
spectroscopy is employed to study the chemical states, band gap and band
offsets at the interface. The density of ionic defects near the interface is
found to be below the detection limit, and the interface is found to be
insulating. Analysis of the relative band structure yields significant
interfacial barriers, exceeding 1.05 eV for holes and 2.0 eV for electrons. The
barrier for holes is considerably larger than what is known for related
materials systems, outlining the promise of using amorphous $Al_2O_3$ as an
effective and simple insulator, an important building block for oxide-based
field effect devices.",1705.00315v2
2018-06-21,Anomalous dielectric response at intermixed oxide heterointerfaces,"Two-dimensional charge carrier accumulation at oxide heterointerfaces
presents a paradigm shift for oxide electronics. Like a capacitor, interfacial
charge buildup couples to an electric field across the dielectric medium. To
prevent the so-called polar catastrophe, several charge screening mechanisms
emerge, including polar distortions and interfacial intermixing which reduce
the sharpness of the interface. Here, we examine how atomic intermixing at
oxide interfaces affect the balance between polar distortions and electric
potential across the dielectric medium. We find that intermixing moves the peak
charge distribution away from the oxide/oxide interface; thereby changing the
direction of polar distortions away from this boundary with minimal effect on
the electric field. This opposing electric field and polar distortions is
equivalent to the transient phase transition tipping point observed in double
well ferroelectrics; resulting in an anomalous dielectric response -- a
possible signature of local negative differential capacitance, with
implications for designing dissipationless oxide electronics.",1806.08382v1
2018-08-07,Thresholds and bistability in HIV infection models with oxidative stress,"Oxidative stress, a reaction caused by the imbalance between the reactive
oxygen species of human organism and its ability to detoxify reactive
intermediates and to repair the resulting damage plays an important role in
HIV-infections. On one hand, HIV infection is responsible for the chronic
oxidative stress of the patients. On the other hand, the oxidative stress
contributions to the HIV disease pathogenesis. In this paper, we integrate
oxidative stress into an HIV infection model to investigate its effects on the
virus dynamics. Through mathematical analysis, we obtain the basic reproduction
number R0 of the model which describes the persistence of viruses. In
particular, we show that for R0 > 1, the model has a bistable interval with
virus rebound threshold and elite control threshold. Numerical simulations and
bifurcation analysis are presented to illustrate the viral dynamics under
oxidative stress. Our investigation reveals the interplay between viruses and
the reaction of human organism including immune response and oxidative stress,
and their effects on the health of human being.",1808.02276v1
2018-12-05,Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam,"FeCrAl alloys are proposed and being intensively investigated as alternative
accident tolerant fuel (ATF) cladding for nuclear fission application. Herein,
the influence of major alloy elements (Cr and Al), reactive element effect and
heating schedules on the oxidation behavior of FeCrAl alloys in steam up to
1500{\deg}C was examined. In case of transient ramp tests, catastrophic
oxidation, i.e. rapid and complete consumption of the alloy, occurred during
temperature ramp up to above 1200{\deg}C for specific alloys. The maximum
compatible temperature of FeCrAl alloys in steam increases with raising Cr and
Al content, decreasing heating rates during ramp period and doping of yttrium.
Isothermal oxidation resulted in catastrophic oxidation at 1400{\deg}C for all
examined alloys. However, formation of a protective alumina scale at
1500{\deg}C was ascertained despite partial melting. The occurrence of
catastrophic oxidation seems to be controlled by dynamic competitive mechanisms
between mass transfer of Al from the substrate and transport of oxidizing gas
through the scale both toward the metal/oxide scale interface.",1812.01850v1
2019-02-12,Electro-Oxidation of p-Silicon in Fluoride-Containing Electrolyte: A Physical Model for the Regime of Negative Differential Resistance,"When Si is anodically oxidized in a fluoride containing electrolyte, an oxide
layer is grown. Simultaneously, the layer is etched by the fluoride containing
electrolyte. The resulting stationary state exhibits a negative slope of the
current-voltage characteristics in a certain range of applied voltage. We
propose a physical model that reproduces this negative slope. In particular,
our model assumes that the oxide layer consists of both partially and fully
oxidized Si and that the etch rate depends on the effective degree of
oxidation. Finally, we show that our simulations are in good agreement with
measurements of the current-voltage characteristics, the oxide layer thickness,
the dissolution valence, and the impedance spectra of the electrochemical
system.",1902.04328v1
2019-02-15,Record-high photocatalytic rate at single atomic metal oxide,"Metal oxides have been extensively investigated and applied in environmental
remediation and protection, energy conversion and storage. Most of these
diverse applications are results of a large diversity of the electronic states
of metal oxides. Noticeably, however, numerous metal oxides have obstacles for
applications in catalysis because of low density of active sites in these
materials. Size reduction of oxide catalyst is a strategy to improve the active
site density. Here, we demonstrate the fabrication of single atomic metal oxide
in which the oxide size reaches its minimum. However, the catalytic mechanism
in this SATO is determined by a quasi atom physics which is fundamentally
distinct from the traditional size effect, and also is in contrast to the
standard condensed matter physics. SATO results in a record high and stable
sunlight photocatalytic degradation rate of 0.24, which exceeds those of
available photocatalysis by approximately two orders of magnitude. The
photocatalytic process is enabled by a quasi atom physical mechanism, in which,
an electron in the spin up channel is excited from HOMO to LUMO+1 state, which
can only occur in SATO with W5+.",1902.05697v1
2019-02-18,Asymmetric Oxidation of Giant Vesicles triggers Curvature-associated Shape Transition and Permeabilization. Running title: Oxidation of Vesicles produces Curvature,"(200 words) Oxidation of unsaturated lipids is a fundamental process involved
in cell bioenergetics as well as in cell death. Using giant unilamellar
vesicles and a chlorin photosensitizer, we asymmetrically oxidized the outer or
inner monolayers of lipid membranes. We observed different shape transitions
such as oblate to prolate and budding, which are typical of membrane curvature
modifications. The asymmetry of the shape transitions is in accordance with a
lowered effective spontaneous curvature of the leaflet being targeted. We
interpret this effect as a decrease in the preferred area of the targeted
leaflet compared to the other, due to the secondary products of oxidation
(cleaved-lipids). Permeabilization of giant vesicles by light-induced oxidation
is observed after a lag and is characterized in relation with the
photosensitizer concentration. We interpret permeabilization as the opening of
a pore above a critical membrane tension, resulting from the budding of
vesicles. The evolution of photosensitized giant vesicle lysis tension was
measured and yields an estimation of the effective spontaneous curvature at
lysis. Additionally photo-oxidation was shown to be fusogenic.",1902.06638v1
2019-11-20,Two-dimensional modeling of the self-limiting oxidation in silicon and tungsten nanowires,"Self-limiting oxidation of nanowires has been previously described as a
reaction- or diffusion-controlled process. In this letter, the concept of
finite reactive region is introduced into a diffusion-controlled model, based
upon which a two-dimensional cylindrical kinetics model is developed for the
oxidation of silicon nanowires and is extended for tungsten. In the model,
diffusivity is affected by the expansive oxidation reaction induced stress. The
dependency of the oxidation upon curvature and temperature is modeled. Good
agreement between the model predictions and available experimental data is
obtained. The developed model serves to quantify the oxidation in
two-dimensional nanostructures and is expected to facilitate their fabrication
via thermal oxidation techniques. https://doi.org/10.1016/j.taml.2016.08.002",1911.08908v1
2020-04-14,Amorphous Mo-Ta oxide nanotubes for long-term stable Mo oxide based supercapacitors,"With a large-scale usage of portable electric appliances, a high demand for
increasingly high density energy storage devices has emerged. MoO3 has, in
principle, a large potential as negative electrode material in supercapacitive
devices, due to high charge densities that can be obtained from its reversible
redox reactions. Nevertheless, the extremely poor electrochemical stability of
MoO3 in aqueous electrolytes prevents a practical use in high capacitance
devices. In this work, we describe how to overcome this severe stability issue
by forming amorphous molybdenum oxide/tantalum oxide nanotubes by anodic
oxidation of a Mo-Ta alloy. The presence of a critical amount of Ta-oxide (> 20
at-%) prevents the electrochemical decay of the MoO3 phase and thus yields an
extremely high stability. Due to the protection provided by tantalum oxide, no
capacitance losses are measureable after 10000 charg-ing/discharging cycles.",2005.00532v1
2020-06-10,Investigation of energetics of 1:1 stoichiometric Al/PVP-fuel and nc-CeO2-oxidizer nanocomposite material,"The investigations of the nanostructured-Al (nano-Al) based thermo-oxidative
reaction attributes are detailed in this chapter-5. Two products are selected
for the thermo-oxidative reaction studies. They are (1) Nano-Al embedded in the
PVP matrix (will be termed as fuel) and (2) its physically mixed 1:1
stoichiometric nanocomposite processed with the ultrafine nc-ceria oxidizer
(also will be termed as nanoenergetic material (NEM)), respectively. The
graphical abstract presented below illustrates an overview of the
thermo-oxidative reaction of fuel tracked employing thermogravimetric analysis
(TGA) investigation. Similar TGA experimentation of the designed NEMs is
carried out to gather scientific information validating, whether or not a
desired enhanced attribute is achieved. Also, in coincidence with the TGA
oxidation event, a synchronous exothermic energy release event in differential
scanning calorimetry (DSC) trace is observed. The above mentioned two products
and their thermo-oxidative reaction behavior employing TGA/DTA and TGA/DSC
thermal traces are compared and interpreted based on the data available in the
literature.",2006.05972v1
2020-11-17,Effect of surface mechanical treatment on the oxidation behavior of FeAl-model alloy,"Fe based alloys are commonly used in almost every sector of human life. For
different reasons, the surfaces of the real parts are prepared using different
methods, e.g., mirror-like polishing, grit-blasting, etc. The purpose of the
present work is to answer the question how the surface preparation influences
the oxidation behavior of Fe-based alloys. To answer this question, a high
purity model alloy, Fe 5 wt Al, was isothermally oxidized in a
thermogravimetrical furnace. The post-exposure analysis included SEM/EDS (WDS)
and XRD. The surface roughness was determined by a contact and laser
profilometer. The obtained results demonstrate that the mechanical surface
preparation influences oxidation kinetics as well as the microstructure of the
oxide scale formed on the alloy at both studied temperatures. Namely, polishing
and grinding caused local formation of Fe-rich nodules and sub-layer of
protective Al2O3. In contrast, gritblasting leads to the formation of a thick
outer Fe-oxide and internal aluminum nitridation. A significant increase in the
oxidation rate of the material after gritblasting was attributed to grain
refinement in the near-surface region, resulting in an increase in easy
diffusion paths, namely grain boundaries.",2011.08913v1
2021-02-01,Thermal Conductivity Mapping of Oxidized SiC SiC Composites by Time Domain Thermoreflectance with Heterodyne Detection,"Silicon carbide silicon carbide (SiC SiC) composites are often used in
oxidizing environments at high temperatures. Measurements of the thermal
conductance of the oxide layer provide a way to better understand the oxidation
process with high spatial resolution. We use time domain thermoreflectance
(TDTR) to map the thermal conductance of the oxide layer and the thermal
conductivity of the SiC SiC composite with a spatial resolution of 3 {\mu}m.
Heterodyne detection using a 50 kHz modulated probe beam and a 10 MHz modulated
pump suppresses the coherent pick-up and enables faster data acquisition than
what has previously been possible using sequential demodulation. By analyzing
the noise of the measured signals, we find that in the limit of small
integration time constants or low laser powers, the dominant source of noise is
the input noise of the preamplifier. The thermal conductance of the oxide that
forms on the fiber region is lower than the oxide on the matrix due to small
differences in thickness and thermal conductivity.",2102.01233v1
2021-10-22,The interaction between phosphorene oxide and the villin headpiece,"Phosphorene, a novel member of the two-dimensional nanomaterial family, has
been demonstrated a great potential in biomedical applications, such as
photothermal therapy, drug delivery and antibacterial. However, phosphorene is
unstable and easily oxidized in an aerobic environment. In this paper, using
the larger-scale molecular dynamics simulations, we investigated the disruption
of phosphorene oxide (PO) to the structure of a model protein, villin headpiece
subdomain (HP35). It shows that the disruption of PO nanosheets to protein
structure enhances with the increase of the oxidation concentration of PO, but
the oxidation mode has almost no effect on the PO-HP35 interaction. At low
oxidation concentration, PO is good biocompatibility to HP35. Oxygen atoms
filled into the groove region in puckered surface of phosphorene enhances the
dispersion interaction between phosphorene and HP35. Thus, oxidation enhances
the destructive effect of phosphorene on the structure of HP35. These findings
might shed light on understanding the biological toxicity of PO nanosheets and
would be helpful for the future potential biomedical applications of PO
nanosheets, such as nanodrugs and antibacterial agents.",2110.11880v1
2023-02-04,Distinct melting behaviour of partially oxidized Cu nanoparticles and nanowires,"While most of the experimental studies are dealing with partially oxidized
metallic nanosolids, their behaviour is not well understood theoretically. To
this end we utilized molecular dynamics simulation and charge-optimized
many-body potential to probe melting of Cu nanoparticles and nanowires with and
without a monolayer of Cu$_2$O as a shell. It is shown that partially oxidized
nanosolids present a different melting behaviour than the widely accepted
picture of melting, and especially different than surface melting. (i) For both
types of nanosolids we observed inward diffusion of $\sim$40\% of atomic oxygen
into the metallic core at room temperature. (ii) For the nanowire with oxide
shell we observed a solid state phase transition in the Cu core that is not
present for the case without the oxide. (iii) Prior to melting, the oxide shell
shrinks, and this process continues after melting, to form a particulate oxide,
for both types of nanosolids.",2302.02219v1
2023-04-23,Third Harmonic Generation And Photoluminescence Measurements in Zinc Oxide And Aluminum doped Zinc Oxide Thin Films Grown by Atomic Layer Deposition,"Zinc Oxide is a thoroughly studied wide-bandgap semiconductor possessing
excellent optical and electronic properties at room temperature. The renewed
interest in this material has been generated by doping with various impurities
in order to further enhance versatile optoelectronic responses for practical
applications. Specifically, Aluminum-doped Zinc Oxide is an emerging
transparent conducting oxide for photovoltaic applications. Here I propose to
conduct a series of experimental studies on broadband optical nonlinearity as
well as photoluminescence from Aluminum doped Zinc Oxide as a function of
Aluminum doping. The results of this study include studies including 1) Bandgap
measurements 2) wavelength-dependent third harmonic generation and 3)
one-photon-induced Photoluminescence. The most notable result is a multifold
enhanced third-order nonlinear optical response from weakly doped Aluminum
doped Zinc Oxide (up to 4%) in comparison with the undoped counterpart. The
observed nonlinear optical trend as a function of Aluminum doping is correlated
to the modification of the corresponding band structure. The Aluminum doping
effect is extensively investigated in the context of absorption and
Photoluminescence.",2304.11724v1
2023-06-30,Substrate suppression of oxidation process in pnictogen monolayers,"2D materials present an interesting platform for device designs. However,
oxidation can drastically change the system's properties, which need to be
accounted for. Through {\it ab initio} calculations, we investigated
freestanding and SiC-supported As, Sb, and Bi mono-elemental layers. The
oxidation process occurs through an O$_2$ spin-state transition, accounted for
within the Landau-Zener transition. Additionally, we have investigated the
oxidation barriers and the role of spin-orbit coupling. Our calculations
pointed out that the presence of SiC substrate reduces the oxidation time scale
compared to a freestanding monolayer. We have extracted the energy barrier
transition, compatible with our spin-transition analysis. Besides, spin-orbit
coupling is relevant to the oxidation mechanisms and alters time scales. The
energy barriers decrease as the pnictogen changes from As to Sb to Bi for the
freestanding systems, while for SiC-supported, they increase across the
pnictogen family. Our computed energy barriers confirm the enhanced robustness
against oxidation for the SiC-supported systems.",2307.00138v1
2011-04-18,Self-limited oxide formation in Ni(111) oxidation,"The oxidation of the Ni(111) surface is studied experimentally with low
energy electron microscopy and theoretically by calculating the electron
reflectivity for realistic models of the NiO/Ni(111) surface with an ab-initio
scattering theory. Oxygen exposure at 300 K under ultrahigh-vacuum conditions
leads to the formation of a continuous NiO(111)-like film consisting of
nanosized domains. At 750 K, we observe the formation of a nano-heterogeneous
film composed primarily of NiO(111)-like surface oxide nuclei, which exhibit
virtually the same energy-dependent reflectivity as in the case of 300 K and
which are separated by oxygen-free Ni(111) terraces. The scattering theory
explains the observed normal incidence reflectivity R(E) of both the clean and
the oxidized Ni(111) surface. At low energies R(E) of the oxidized surface is
determined by a forbidden gap in the k_parallel=0 projected energy spectrum of
the bulk NiO crystal. However, for both low and high temperature oxidation a
rapid decrease of the reflectivity in approaching zero kinetic energy is
experimentally observed. This feature is shown to characterize the thickness of
the oxide layer, suggesting an average oxide thickness of two NiO layers.",1104.3481v2
2018-04-12,Pt$_3$Zr(0001): A substrate for growing well-ordered ultrathin zirconia films by oxidation,"We have studied the surface of pure and oxidized Pt$_3$Zr(0001) by scanning
tunneling microscopy (STM), Auger electron microscopy, and density functional
theory (DFT). The well-annealed alloy surface shows perfect long-range chemical
order. Occasional domain boundaries are probably caused by nonstoichiometry.
Pt$_3$Zr exhibits ABAC stacking along [0001]; only the A-terminated surfaces
are seen by STM, in agreement with DFT results showing a lower surface energy
for the A termination. DFT further predicts a stronger inward relaxation of the
surface Zr than for Pt, in spite of the larger atomic size of Zr. A closed
ZrO$_2$ film is obtained by oxidation in $10^{-7}$ mbar O$_2$ at 400 $^\circ$C
and post-annealing at $\approx 800 ^\circ$C. The oxide consists of an O-Zr-O
trilayer, equivalent to a (111) trilayer of the fluorite structure of cubic
ZrO$_2$, but contracted laterally. The oxide forms a $(\sqrt{19} \times
\sqrt{19})$R23$^\circ$ superstructure. The first monolayer of the substrate
consists of Pt and contracts, similar to the metastable reconstruction of pure
Pt(111). DFT calculations show that the oxide trilayer binds rather weakly to
the substrate. In spite of the O-terminated oxide, bonding to the substrate
mainly occurs via the Zr atoms in the oxide, which strongly buckle down towards
the Pt substrate atoms, if near a Pt position. According to DFT, the oxide has
a bandgap; STM indicates that the conduction band minimum lies $\approx 2.3$ eV
above $E_\mathrm{F}$.",1804.04405v1
2018-04-24,Elucidation of the atomic-scale mechanism of the anisotropic oxidation rate of 4H-SiC between the ($0001$) Si-face and ($000\overline{1}$) C-face by using a new Si-O-C interatomic potential,"Silicon carbide (SiC) is an attractive semiconductor material for
applications in power electronic devices. However, fabrication of a
high-quality SiC/SiO${}_2$ interface has been a challenge. It is well-known
that there is a great difference in oxidation rate between the Si-face and
C-face, and that the quality of oxide on the Si-face is greater than that on
the C-face. However, the atomistic mechanism of the thermal oxidation of SiC
remains to be solved. In this paper, a new Si-C-O interatomic potential was
developed to reproduce the kinetics of the thermal oxidation of SiC. Using this
newly developed potential, large-scale SiC oxidation simulations at various
temperature were performed. The results showed that the activation energy of
the Si-face is much larger than that of the C-face. In the case of the Si-face,
a flat and aligned interface structure including Si${}^{1+}$ was created. Based
on the estimated activation energies of the intermediate oxide states, it is
proposed that the stability of the flat interface structure is the origin of
the high activation energy of the oxidation of the Si-face. In contrast, in the
case of the C-face, it is found that the Si atom at the interface are easily
pulled up by the O atoms. This process generates the disordered interface and
decreases the activation energy of the oxidation. It is also proposed that many
excess C atoms are created in the case of the C-face.",1804.08860v1
2013-09-09,High-Mobility Two-Dimensional Electron Gases at Oxide Interfaces: Origins and Opportunities,"The discovery of two-dimensional electron gas (2DEG) at well-defined
interfaces between insulating complex oxides provides the opportunity for a new
generation of all-oxide electronics. Particularly, the 2DEG at the interface
between two perovskite insulators represented by the formula of ABO3, such as
LaAlO3 and SrTiO3, has attracted significant attention. In recent years,
progresses have been made to decipher the puzzle of the origin of interface
conduction, to design new types of oxide interfaces, and to improve the
interfacial carrier mobility significantly. These achievements open the door to
explore fundamental as well as applied physics of complex oxides. Here, we
review our recent experimental work on metallic and insulating interfaces
controlled by interfacial redox reactions in SrTiO3-based heterostructures. Due
to the presence of oxygen-vacancies at the SrTiO3 surface, metallic conduction
can be created at room temperature in perovskite-type interfaces when the
overlayer oxide ABO3 involves Al, Ti, Zr, or Hf elements at the B-sites.
Furthermore, relying on interface-stabilized oxygen vacancies, we have created
a new type of 2DEG at the heterointerface between SrTiO3 and a spinel
{\gamma}-Al2O3 epitaxial film with compatible oxygen ions sublattices. The
spinel/perovskite oxide 2DEG exhibits an electron mobility exceeding 100,000
cm2V-1s-1, more than one order of magnitude higher than those of hitherto
investigated perovskite-type interfaces. Our findings pave the way for design
of high-mobility all-oxide electronic devices and open a route towards studies
of mesoscopic physics with complex oxides.",1309.2124v1
2019-08-07,Part I: Theoretical Predictions of Preferential Oxidation in Refractory High Entropy Materials,"High entropy materials, which include high entropy alloys, carbides, and
borides, are a topic of substantial research interest due to the possibility of
a large number of new material compositions that could fill gaps in application
needs. There is a current need for materials exhibiting high temperature
stability, particularly oxidation resistance. A systematic understanding of the
oxidation behavior in high entropy materials is therefore required. Prior work
notes large differences in the thermodynamic favorability between oxides formed
upon oxidation of high entropy materials. This work uses both analytical and
computational thermodynamic approaches to investigate and quantify the effects
of this large variation and the resulting potential for preferential component
oxidation in refractory high entropy materials including group IV-, V- and
VI-element based alloys and ceramics. Thermodynamic calculations show that a
large tendency towards preferential oxidation is expected in these materials,
even for elements whose oxides exhibit a small difference in thermodynamic
favorability. The effect is reduced in carbides, compared to their alloy
counterparts. Further, preferential oxidation in high entropy refractory
materials could result in possible destabilization of the solid solution or
formation of other, competing phases, with corresponding changes in bulk
material properties.",1908.02654v2
2022-02-08,Kinetic Monte Carlo Modelling of Nano-oxide Precipitation and its Associated Stability under Neutron Irradiation for the Fe-Ti-Y-O system,"While developing nuclear materials, predicting their behavior under long-term
irradiation regimes spanning decades poses a significant challenge. We
developed a novel Kinetic Monte Carlo (KMC) model to explore the precipitation
behavior of Y-Ti-O oxides along grain boundaries within nanostructured ferritic
alloys (NFA). This model also assessed the response of the oxides to neutron
irradiation, even up simulated radiation damage levels in the desired long dpa
range for reactor components. Our simulations investigated how temperature and
grain boundary sinks influenced the oxide characteristics of a 12YWT-like alloy
during heat treatments at 1023 K, 1123 K, and 1223 K. The oxide characteristics
observed in our simulations were in good agreement with existing literature.
Furthermore, the impact of grain boundaries on precipitation was found to be
minimal. The resulting oxide configurations and positions were used in
subsequent simulations that exposed them to simulated neutron irradiation to a
total accumulated dose of 8 dpa at three temperatures: 673 K, 773 K, and 873 K,
and at dose rates of 10^(-3), 10^(-4), and 10^(-5) dpa/s. This demonstrated the
expected inverse relationship between oxide size and dose rate. In a long-term
irradiation simulation at 873 K and 10^(-3) dpa/s was taken out to 66 dpa and
found the oxides in the vicinity of the grain boundary were more susceptible to
dissolution. Additionally, we conducted irradiation simulations of a 14YWT-like
alloy to reproduce findings from neutron irradiation experiments. The larger
oxides in the 14YWT-like alloy did not dissolve and displayed stability similar
to the experimental results.",2202.03641v3
2023-10-09,Detecting Iron Oxidation States in Liquids with the VOXES Bragg Spectrometer,"Determining the oxidation states of metals assumes great importance in
various applications because a variation in the oxidation number can
drastically influence the material properties. As an example, this becomes
evident in edible liquids like wine and oil, where a change in the oxidation
states of the contained metals can significantly modify both the overall
quality and taste. To this end, here we present the MITIQO project, which aims
to identify oxidation states of metals in edible liquids utilizing X-ray
emission with Bragg spectroscopy. This is achieved using the VOXES crystal
spectrometer, developed at INFN National Laboratories of Frascati (LNF),
employing mosaic crystal (HAPG) in the Von Hamos configuration. This
combination allow us to work with effective source sizes of up to a few
millimeters and improves the typical low efficiency of Bragg spectroscopy, a
crucial aspect when studying liquids with low metal concentration. Here we
showcase the concept behind MITIQO, for a liquid solution containing oxidized
iron. We performed several high-resolution emission spectra measurements, for
the liquid and for different powdered samples containing oxidized and pure
iron. By looking at the spectral features of the iron's K$\beta$ emission
lineshape, we were able to obtain, for a liquid, a result consistent with the
oxidized iron powders and successfully quantifying the effect of oxidation.",2310.06062v1
1997-07-11,Intermediate Valence Model for the Colossal Magnetoresistance in Tl_{2}Mn_{2}O_{7},"The colossal magnetoresistance exhibited by Tl_{2}Mn_{2}O_{7} is an
interesting phenomenon, as it is very similar to that found in perovskite
manganese oxides although the compound differs both in its crystalline
structure and electronic properties from the manganites. At the same time,
other pyrochlore compounds, though sharing the same structure with
Tl_{2}Mn_{2}O_{7}, do not exhibit the strong coupling between magnetism and
transport properties found in this material. Mostly due to the absence of
evidence for significant doping into the Mn-O sublattice, and the tendency of
Tl to form conduction bands, the traditional double exchange mechanism
mentioned in connection with manganites does not seem suitable to explain the
experimental results in this case. We propose a model for Tl_{2}Mn_{2}O_{7}
consisting of a lattice of intermediate valence ions fluctuating between two
magnetic configurations, representing Mn-3d orbitals, hybridized with a
conduction band, which we associate with Tl. This model had been proposed
originally for the analysis of intermediate valence Tm compounds. With a
simplified treatment of the model we obtain the electronic structure and
transport properties of Tl_{2}Mn_{2}O_{7}, with good qualitative agreement to
experiments. The presence of a hybridization gap in the density of states seems
important to understand the reported Hall data.",9707130v2
1999-02-17,Quantum Monte Carlo Study of Weakly Coupled Spin Ladders,"We report a quantum Monte Carlo study of the thermodynamic properties of
arrays of spin ladders with various widths ($n$), coupled via a weak
inter-ladder exchange coupling $\alpha J$, where $J$ is the intra-ladder
coupling both along and between the chains. This coupled ladder system serves
as a simplified model for the magnetism of presumed ordered spin and charge
stripes in the two-dimensional CuO$_2$ planes of hole-doped copper oxides. Our
results for $n=3$ with weak inter-ladder coupling $\alpha=0.05$, estimated from
the $t-t'-t''-J$ model, show good agreement with the ordering temperature of
the recently observed spin density wave condensation in La$_2$CuO$_{4+y}$. We
show that there exists a quantum critical point at $\alpha_c \simeq 0.07$ for
$n=4$, and determine the phase diagram. Our data at this quantum critical point
agree quantitatively with the universal scaling predicted by the quantum
nonlinear $\sigma$ model. We also report results on random mixtures of $n=2$
and $n=3$ ladders, which correspond to the doping region near but above 1/8.
Our study on the magnetic static structure factor reveals a saturation of the
incommensurability of the spin correlations around 1/8, while the
incommensurability of the charge stripes grows linearly with hole
concentration. The implications of this result for the interpretation of
neutron scattering experiments on the dynamic spin fluctuations in
La$_{2-x}$Sr$_x$CuO$_4$ are discussed.",9902248v1
2000-11-28,Tunneling conductance of SIN junctions with different gap symmetries and non-magnetic impurities by direct solution of real-axis Eliashberg equations,"We theoretically investigate the effect of various symmetries of the
superconducting order parameter Delta(omega) on the normalized tunneling
conductance of SIN junctions by directly solving the real-axis Eliashberg
equations (EEs) for a half-filled infinite band, with the simplifying
assumption mu*=0. We analyze six different symmetries of the order parameter:
s, d, s+id, s+d, extended s and anisotropic s, by assuming that the spectral
function alpha^{2}F(Omega) contains an isotropic part alpha^{2}F(Omega)_{is}
and an anisotropic one, alpha^{2}F(Omega)_{an}, such that
alpha^{2}F(Omega)_{an} = g alpha^{2}F(Omega)_{is}, where g is a constant.
  We compare the resulting conductance curves at T=2 K to those obtained by
analytical continuation of the imaginary-axis solution of the EEs, and we show
that the agreement is not equally good for all symmetries. Then, we discuss the
effect of non-magnetic impurities on the theoretical tunneling conductance
curves at T=4 K for all the symmetries considered.
  Finally, as an example, we apply our calculations to the case of
optimally-doped high-T_{c} superconductors (HTSC). Surprisingly, although the
possibility of explaining the very complex phenomenology of HTSC is probably
beyond the limits of the Eliashberg theory, the comparison of the theoretical
curves calculated at T=4 K with the experimental ones obtained in various
optimally-doped copper-oxides gives fairly good results.",0011472v3
2000-12-01,Magnetic and orbital ordering in cuprates and manganites,"The mechanisms of magnetic and orbital interactions due to double exchange
(DE) and superexchange (SE) in transition metal oxides with degenerate e_g
orbitals are presented. Specifically, we study the effective spin-orbital
models derived for the d^9 ions as in KCuF_3, and for the d^4 ions as in
LaMnO_3, for spins S=1/2 and S=2, respectively. Such models are characterized
by three types of elementary excitations: spin waves, orbital waves, and
spin-and-orbital waves. The SE interactions between Cu^{2+} (d^9) ions are
inherently frustrated, which leads to a new mechanism of spin liquid which
operates in three dimensions. The SE between Mn^{3+} (d^4) ions explains the
A-type antiferromagnetic order in LaMnO_3 which coexists with the orbital
order. In contrast, the ferromagnetic metallic phase and isotropic spin waves
observed in doped manganites are explained by DE for degenerate e_g orbitals.
It is shown that although a hole does not couple to spin excitations in
ferromagnetic planes of LaMnO_3, the orbital excitations change the energy
scale for the coherent hole propagation and cause a large redistribution of
spectral weight. Finally, we point out some open problems in the present
understanding of doped manganites.",0012013v1
2001-04-09,Enhancement of the high-field critical current density of superconducting MgB2 by proton irradiation,"A relatively high critical temperature, Tc, approaching 40 K, places the
recently-discovered superconductor magnesium diboride (MgB2) intermediate
between the families of low- and copper-oxide-based high-temperature
superconductors (HTS). Supercurrent flow in MgB2 is unhindered by grain
boundaries, unlike the HTS materials. Thus, long polycrystalline MgB2
conductors may be easier to fabricate, and so could fill a potentially
important niche of applications in the 20 to 30 K temperature range. However,
one disadvantage of MgB2 is that in bulk material the critical current density,
Jc, appears to drop more rapidly with increasing magnetic field than it does in
the HTS phases. The magnitude and field dependence of Jc are related to the
presence of structural defects that can ""pin"" the quantised magnetic vortices
that permeate the material, and prevent them from moving under the action of
the Lorentz force. Vortex studies suggest that it is the paucity of suitable
defects in MgB2 that causes the rapid decay of Jc with field. Here we show that
modest levels of atomic disorder, induced by proton irradiation, enhance the
pinning, and so increase Jc significantly at high fields. We anticipate that
chemical doping or mechanical processing should be capable of generating
similar levels of disorder, and so achieve technologically-attractive
performance in MgB2 by economically-viable routes.",0104156v2
2002-09-14,"Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of $La_{0.6}Y_{0.1}Ca_{0.3}MnO_3$ in Zero Magnetic Field, and the Effect of $Mn-O-Mn$ Bond Environment","$La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}$, an $ABO_{3}$ perovskite manganite oxide,
exhibits a non trivial behavior in the vicinity of the sharp peak found in the
resistivity $\rho$ as a function of temperature $T$ in zero magnetic field. The
various features seen on $d\rho/dT$ are discussed in terms of competing phase
transitions. They are related to the $Mn-O-Mn$ bond environment depending on
the content of the $A$ crystallographic site. A Ginzburg-Landau type theory is
presented for incorporating concurrent phase transitions. The specific heat $C$
of such a compound is also examined from 50 till 200 K. A log-log analysis
indicates different regimes. In the low temperature conducting ferromagnetic
phase, a collective magnon signature ($C \simeq T^{3/2}$) is found as for what
are called magnon-polaron excitations. A $C \simeq T^{2/3}$ law is found at
high temperature and discussed in terms of the fractal dimension of the
conducting network of the weakly conducting (so-called insulating) phase and
Orbach estimate of the excitation spectral behaviors. The need of considering
both independent spin scattering and collective spin scattering is thus
emphasized. The report indicates a remarkable agreement for the Fisher-Langer
formula, i.e. $C$ $\sim$ $d\rho/dT$ at second order phase transitions. Within
the Attfield model, we find an inverse square root relationship between the
critical temperature(s) and the total local $Mn-O-Mn$ strain.",0209340v1
2004-05-26,Microwave Magnetoelectric Effects in Single Crystal Bilayers of Yttrium Iron Garnet and Lead Magnesium Niobate-Lead Titanate,"The first observation of microwave magnetoelectric (ME) interactions through
ferromagnetic resonance (FMR) in bilayers of single crystal
ferromagnetic-piezoelectric oxides and a theoretical model for the effect are
presented. An electric field E produces a mechanical deformation in the
piezoelectric phase, resulting in a shift dHE in the resonance field for the
ferromagnet. The strength of ME coupling is obtained from data on dHE vs E.
Studies were performed at 9.3 GHz on bilayers of (111) yttrium iron garnet
(YIG) films and (001) lead magnesium niobate-lead titanate (PMN-PT). The
samples were positioned outside a TE102-reflection type cavity. Resonance
profiles were obtained for E = 0-8 kV/cm for both in-plane and out-of-plane
magnetic fields H. Important results are as follows. (i) The ME coupling in the
bilayers is an order of magnitude stronger than in polycrystalline composites
and is in the range 1-5.4 Oe cm/kOe, depending on the YIG film thickness. (ii)
The coupling strength is dependent on the magnetic field orientation and is
higher for out-of-plane H than for in-plane H. (iii) Estimated ME constant and
its dependence on volume ratio for the two phases are in good agreement with
the data.",0405622v1
2005-03-31,Synthesis and characterization of Na03RhO206H2O - a semiconductor with a weak ferromagnetic component,"We have prepared the oxyhydrate Na03RhO206H2O by extracting Na+ cations from
NaRhO2 and intercalating water molecules using an aqueous solution of Na2S2O8.
Synchrotron X-ray powder diffraction, thermogravimetric analysis (TGA), and
energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric
Na03(H2O)06 network separates layers of edge-sharing RhO6 octahedra containing
Rh3+(4d6, S=0) and Rh4+ (4d5, S=1/2). The resistivities of NaRhO2 and
Na03RhO206H2O (T < 300) reveal insulating and semi-conducting behavior with
activation gaps of 134 meV and 7.8 meV, respectively. Both Na03RhO206H2O and
NaRhO2 show paramagnetism at room temperature, however, the sodium-deficient
sample exhibits simultaneously a weak but experimentally reproducible
ferromagnetic component. Both samples exhibit a temperature-independent Pauli
paramagnetism, for NaRhO2 at T > 50 K and for Na03RhO206H2O at T > 25 K. The
relative magnitudes of the temperature-independent magnetic susceptibilities,
that of the oxide sample being half that of the oxyhydrate, is consistent with
a higher density of thermally accessible electron states at the Fermi level in
the hydrated sample. At low temperatures the magnetic moments rise sharply,
providing evidence of localized and weakl -ordered electronic spins.",0504007v1
2005-05-04,From Finite-Size and Surface Effects to Glassy Behaviour in Ferrimagnetic Nanoparticles,"This chapter is aimed at studying the anomalous magnetic properties (glassy
behaviour) observed at low temperatures in nanoparticles of ferrimagnetic
oxides. This topic is discussed both from numerical results and experimental
data. Ferrimagnetic fine particles show most of the features of glassy systems
due to the random distribution of anisotropy axis, interparticle interactions
and surface effects. Experiments have shown that the hysteresis loops display
high closure fields with high values of the differential susceptibility. Low
magnetisation as compared to bulk, shifted loops after field-cooling, highfield
irreversibilities between zero-field and field cooling processes and ageing
phenomena in the time-dependence of the magnetisation, are also observed. This
phenomenology indicates the existence of some kind of freezing phenomenon
arising from a complex hierarchy of the energy levels, whose origin is
currently under discussion. Two models have been proposed to account for it: i)
the existence of a spin-glass state at the surface of the particle which is
coupled to the particle core through an exchange field; and ii) the collective
behaviour induced by interparticle interactions. In real systems, both
contributions simultaneously occur, being difficult to distinguish their
effects. In contrast, numerical simulations allow us to build a model just
containing the essential ingredients to study solely one of two phenomena.",0505112v1
2005-07-05,Valence instability of cerium under pressure in the Kondo-like perovskite La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$,"Effect of hydrostatic pressure and magnetic field on electrical resistance of
the Kondo-like perovskite manganese oxide,
La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$ with a ferrimagnetic ground state, have
been investigated up to 2.1 GPa and 9 T. In this compound, the Mn-moments
undergo double exchange mediated ferromagnetic ordering at $T_{\rm C}$ $\sim$
280 K and there is a resistance maximum, $T_{\rm max}$ at about 130 K which is
correlated with an antiferromagnetic ordering of {\it cerium} with respect to
the Mn-sublattice moments. Under pressure, the $T_{\rm max}$ shifts to lower
temperature at a rate of d$T_{max}$/d$P$ = -162 K/GPa and disappears at a
critical pressure $P_{\rm c}$ $\sim$ 0.9 GPa. Further, the coefficient, $m$ of
$-logT$ term due to Kondo scattering decreases linearly with increase of
pressure showing an inflection point in the vicinity of $P_{\rm c}$. These
results suggest that {\it cerium} undergoes a transition from Ce$^{3+}$ state
to Ce$^{4+}$/Ce$^{3+}$ mixed valence state under pressure. In contrast to
pressure effect, the applied magnetic field shifts $T_{\rm max}$ to higher
temperature presumably due to enhanced ferromagnetic Mn moments.",0507094v1
2007-01-17,Heisenberg exchange in magnetic monoxides,"The superexchange intertacion in transition-metal oxides, proposed initially
by Anderson in 1950, is treated using contemporary tight-binding theory and
existing parameters. We find also a direct exchange for nearest-neighbor metal
ions, larger by a factor of order five than the superexchange. This direct
exchange arises from Vddm coupling, rather than overlap of atomic charge
densities, a small overlap exchange contribution which we also estimate. For
FeO and CoO there is also an important negative contribution, related to Stoner
ferromagnetism, from the partially filled minority-spin band which broadens
when ionic spins are aligned. The corresponding J1 and J2 parameters are
calculated for MnO, FeO, CoO, and NiO. They give good accounts of the Neel and
the Curie-Weiss temperatures, show appropriate trends, and give a reasonable
account of their volume dependences. For MnO the predicted value for the
magnetic susceptibility at the Neel temperature and the crystal distortion
arising from the antiferromagnetic transition were reasonably well given.
Application to CuO2 planes in the cuprates gives J=1220oK, compared to an
experimental 1500oK, and for LiCrO2 gives J1=4 50oK compared to an experimental
230oK.",0701423v3
2007-08-17,Quantum spin correlations through the superconducting-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-d,"The quantum spin fluctuations of the S = 1/2 Cu ions are important in
determining the physical properties of the high-transition temperature
(high-Tc) copper oxide superconductors, but their possible role in the electron
pairing for superconductivity remains an open question. The principal feature
of the spin fluctuations in optimally doped high-Tc superconductors is a well
defined magnetic resonance whose energy (Er) tracks Tc (as the composition is
varied) and whose intensity develops like an order parameter in the
superconducting state. We show that the suppression of superconductivity and
its associated condensation energy by a magnetic field in the electron-doped
high-Tc superconductor, Pr0.88LaCe0.12CuO4-d (Tc = 24 K), is accompanied by the
complete suppression of the resonance and the concomitant emergence of static
antiferromagnetic (AF) order. Our results demonstrate that the resonance is
intimately related to the superconducting condensation energy, and thus suggest
that it plays a role in the electron pairing and superconductivity.",0708.2326v1
2008-03-25,"Structural and Magnetic Properties of Pyrochlore Solid Solutions (Y,Lu)2Ti2-x(Nb,Ta)xO7+/-y","The synthesis and characterization of the pyrochlore solid solutions,
Y2Ti2-xNbxO7-y, Lu2Ti2-xNbxO7-y, Y2Ti2-xTaxO7-y and Lu2TiTaO7-y (-0.4<y<0.5),
is described. Synthesis at 1600 C, and 10-5 Torr yields oxygen deficiency in
all systems. All compounds are found to be paramagnetic and semiconducting,
with the size of the local moments being less, in some cases substantially
less, than the expected value for the number of nominally unpaired electrons
present. Thermogravimetric analysis (TGA) shows that all compounds can be fully
oxidized while retaining the pyrochlore structure, yielding oxygen rich
pyrochlores as white powders. Powder neutron diffraction of Y2TiNbO7-based
samples was done. Refinement of the data for oxygen deficient Y2TiNbO6.76
indicates the presence of a distribution of oxygen over the 8b and 48f sites.
Refinement of the data for oxygen rich Y2TiNbO7.5 shows these sites to be
completely filled, with an additional half filling of the 8a site. The magnetic
and TGA data strongly suggest a preference for a Ti3+/(Nb,Ta)5+ combination, as
opposed to Ti4+/(Nb,Ta)4+, in this pyrochlore family. In addition, the evidence
clearly points to Ti3+ as the source of the localized moments, with no evidence
for localized Nb4+ moments.",0803.3568v1
2008-06-17,Superconductivity in Silicon Nanostructures,"We present the findings of the superconductivity in the silicon
nanostructures prepared by short time diffusion of boron after preliminary
oxidation of the n-type Si (100) surface. These Si-based nanostructures
represent the p-type high mobility silicon quantum well (Si-QW) confined by the
delta - barriers heavily doped with boron. The ESR studies show that the delta
- barriers appear to consist of the trigonal dipole centers, B(+)-B(-), which
are caused by the negative-U reconstruction of the shallow boron acceptors,
2B(0)=>B(+)-B(-). The temperature and magnetic field dependencies of the
resistance, thermo-emf, specific heat and magnetic susceptibility demonstrate
that the high temperature superconductivity observed seems to result from the
transfer of the small hole bipolarons through these negative-U dipole centers
of boron at the Si-QW - delta - barrier interfaces. The value of the
superconductor energy gap obtained is in a good agreement with the data derived
from the oscillations of the conductance in normal state and of the
zero-resistance supercurrent in superconductor state as a function of the bias
voltage. These oscillations appear to be correlated by on- and off-resonance
tuning the two-dimensional subbands of holes with the Fermi energy in the
superconductor delta - barriers. Finally, the proximity effect in the S- Si-QW
-S structure is revealed by the findings of the multiple Andreev reflection
(MAR) processes and the quantization of the supercurrent.",0806.2800v1
2010-04-04,"Adsorption of molecular oxygen on doped graphene: atomic, electronic and magnetic properties","Adsorption of molecular oxygen on B-, N-, Al-, Si-, P-, Cr- and Mn-doped
graphene is theoretically studied using density functional theory in order to
clarify if O2 can change the possibility of using doped graphene for gas
sensors, electronic and spintronic devices. O2 is physisorbed on B-, and Ndoped
graphene with small adsorption energy and long distance from the graphene
plane, indicating the oxidation will not happen; chemisorption is observed on
Al-, Si-, P-, Cr- and Mn-doped graphene. The local curvature caused by the
large bond length of X-C (X represents the dopants) relative to CC bond plays a
very important role in this chemisorption. The chemisorption of O2 induces
dramatic changes of electronic structures and localized spin polarization of
doped graphene, and in particular, chemisorption of O2 on Cr-doped graphene is
antiferromagnetic. The analysis of electronic density of states shows the
contribution of the hybridization between O and dopants is mainly from the p or
d orbitals. Furthermore, spin density shows that the magnetization locates
mainly around the doped atoms, which may be responsible for the Kondo effect.
These special properties supply a good choice to control the electronic
properties and spin polarization in the field of graphene engineering.",1004.0518v2
2010-07-01,Electric-Field-control of spin rotation in bilayer graphene,"The manipulation of the electron spin degree of freedom is at the core of the
spintronics paradigm, which offers the perspective of reduced power
consumption, enabled by the decoupling of information processing from net
charge transfer. Spintronics also offers the possibility of devising hybrid
devices able to perform logic, communication, and storage operations. Graphene,
with its potentially long spin-coherence length, is a promising material for
spin-encoded information transport. However, the small spin-orbit interaction
is also a limitation for the design of conventional devices based on the
canonical Datta-Das spin-FET. An alternative solution can be found in magnetic
doping of graphene, or, as discussed in the present work, in exploiting the
proximity effect between graphene and Ferromagnetic Oxides (FOs). Graphene in
proximity to FO experiences an exchange proximity interaction (EPI), that acts
as an effective Zeeman field for electrons in graphene, inducing a spin
precession around the magnetization axis of the FO. Here we show that in an
appropriately designed double-gate field-effect transistor, with a bilayer
graphene channel and FO used as a gate dielectric, spin-precession of carriers
can be turned ON and OFF with the application of a differential voltage to the
gates. This feature is directly probed in the spin-resolved conductance of the
bilayer.",1007.0091v1
2010-10-14,Growth mechanism of nanostructured superparamagnetic rods obtained by electrostatic co-assembly,"We report on the growth of nanostructured rods fabricated by electrostatic
co-assembly between iron oxide nanoparticles and polymers. The nanoparticles
put under scrutiny, {\gamma}-Fe2O3 or maghemite, have diameter of 6.7 nm and
8.3 nm and narrow polydispersity. The co-assembly is driven by i) the
electrostatic interactions between the polymers and the particles, and by ii)
the presence of an externally applied magnetic field. The rods are
characterized by large anisotropy factors, with diameter 200 nm and length
comprised between 1 and 100 {\mu}m. In the present work, we provide for the
first time the morphology diagram for the rods as a function of ionic strength
and concentration. We show the existence of a critical nanoparticle
concentration and of a critical ionic strength beyond which the rods do not
form. In the intermediate regimes, only tortuous and branched aggregates are
detected. At higher concentrations and lower ionic strengths, linear and stiff
rods with superparamagnetic properties are produced. Based on these data, a
mechanism for the rod formation is proposed. The mechanism proceeds in two
steps : the formation and growth of spherical clusters of particles, and the
alignment of the clusters induced by the magnetic dipolar interactions. As far
as the kinetics of these processes is concerned, the clusters growth and their
alignment occur concomitantly, leading to a continuous accretion of particles
or small clusters, and a welding of the rodlike structure.",1010.2852v1
2011-01-06,Quantum phase transitions in a strongly entangled spin-orbital chain: A field-theoretical approach,"Motivated by recent experiments on quasi-1D vanadium oxides, we study quantum
phase transitions in a one-dimensional spin-orbital model describing a Haldane
chain and a classical Ising chain locally coupled by the relativistic
spin-orbit interaction. By employing a field-theoretical approach, we analyze
the topology of the ground-state phase diagram and identify the nature of the
phase transitions. In the strong coupling limit, a long-range N\'eel order of
entangled spin and orbital angular momentum appears in the ground state. We
find that, depending on the relative scales of the spin and orbital gaps, the
linear chain follows two distinct routes to reach the N\'eel state. First, when
the orbital exchange is the dominating energy scale, a two-stage ordering takes
place in which the magnetic transition is followed by melting of the orbital
Ising order; both transitions belong to the two-dimensional Ising universality
class. In the opposite limit, the low-energy orbital modes undergo a continuous
reordering transition which represents a line of Gaussian critical points. On
this line the orbital degrees of freedom form a Tomonaga-Luttinger liquid. We
argue that the emergence of the Gaussian criticality results from merging of
the two Ising transitions in the strong hybridization region where the
characteristic spin and orbital energy scales become comparable. Finally, we
show that, due to the spin-orbit coupling, an external magnetic field acting on
the spins can induce an orbital Ising transition.",1101.1268v3
2011-09-20,"Hybrid functional electronic structure of PbPdO$_2$, a small-gap semiconductor","PbPdO$_2$, a ternary compound containing the lone-pair active ion Pb$^{2+}$
and the square-planar d$^8$ Pd$^{2+}$ ion, has attracted recent interest
because of the suggestion that its electronic structure, calculated within
density functional theory using either the local density or the generalized
gradient approximations, displays zero-gap behavior. In light of the potential
ease of doping magnetic ions in this structure, it has been suggested that the
introduction of spin, in conjunction with zero band gap, can result in unusual
magnetic ground states and unusual magnetotransport. It is known that most
electronic structure calculations do not properly obtain a band gap even for
the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor.
Here we present density functional calculations employing a screened hybrid
functional (HSE) which correctly obtain a band gap for the electronic structure
of PdO. When employed to calculate the electronic ground state of PbPdO$_2$, a
band gap is again obtained, which is consistent both with the experimental data
on this compound, as well as a consideration of valence states and of
metal-oxygen connectivity in the crystal structure. We also present comparisons
of the absolute positions (relative to the vacuum level) of the conduction band
minima and the valence band maxima in {\alpha}-PbO, PdO and PbPdO$_2$, which
suggest ease of $p$-type doping in PbPdO$_2$ that has been observed even in
nominally pure materials.",1109.4446v2
2011-12-19,Quantum-Hall plateau-plateau transition in top-gated epitaxial graphene grown on SiC (0001),"We investigate the low-temperature magneto-transport properties of monolayer
epitaxial graphene films formed on the Si-face of semi-insulating 4H-SiC
substrates by a high temperature sublimation process. A high-k top-gate on the
epitaxial graphene is realized by inserting a fully oxidized nanometer thin
aluminum film as a seeding layer, followed by an atomic layer deposition
process. At low temperatures, the devices demonstrate a strong field effect by
the top gate with an on/off ratio of ~7 and an electron mobility up to ~3250
cm^2/Vs. After the observation of the half-integer quantum Hall effect for
monolayer epitaxial graphene films, detailed magneto-transport measurements
have been carried out including varying densities, temperatures, magnetic
fields and currents. We study the width of the distinguishable quantum-Hall
plateau to plateau transition (Landau level index n=0 to n=1) as temperature
(T) and current are varied. For both gate voltage and magnetic field sweeps and
T>10 K the transition width goes as T^{-\kappa} with exponent \kappa ~0.42.
This universal scaling exponent agrees well with those found in III-V
heterojunctions with short range alloy disorders and in exfoliated graphene.",1112.4345v2
2012-06-20,Ga$^{3+}$-substitution effects in the weak ferromagnetic oxide LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$,"Magnetization and x-ray diffraction have been measured on polycrystalline
samples of LaCo$_{0.8-y}$Rh$_{0.2}$Ga$_{y}$O$_{3}$ for $0 \leq y \leq 0.15$ in
order to understand the spin state of Co$^{3+}$ through the Ga$^{3+}$
substitution effect. The ferromagnetic order in LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$
below 15 K is dramatically suppressed by the Ga$^{3+}$ substitution, where the
ferromagnetic volume fraction is linearly decreased. The normal state
susceptibility also systematically decreases with the Ga content, from which we
find that one Ga$^{3+}$ ion reduces 4.6 $\mu_{\rm B}$ per formula unit. We have
evaluated how the concentration of the high-spin state Co$^{3+}$ changes with
temperature by using an extended Curie-Weiss law, and have found that the
substituted Rh$^{3+}$ ion stabilizes the high-spin state Co$^{3+}$ ion down to
low temperatures. We find that Ga$^{3+}$ preferentially replaces the high-spin
state Co$^{3+}$, which makes a remarkable contrast to our previous finding that
Rh$^{3+}$ preferentially replaces the low-spin state Co$^{3+}$. These results
strongly suggest that the magnetically excited state of LaCoO$_{3}$ at room
temperature is a mixed state of high-spin state Co$^{3+}$ and low-spin state
Co$^{3+}$.",1206.4472v1
2013-02-15,Road to room-temperature superconductivity: A universal model,"In a semiclassical view superconductivity is attributed exclusively to the
advance of atoms' outer s electrons through the nuclei of neighbor atoms in a
solid. The necessary progression of holes in the opposite direction has the
electric and magnetic effect as if two electrons were advancing instead of each
actual one. Superconductivity ceases when the associated lateral oscillation of
the outer s electrons extends between neighbor atoms. If such overswing occurs
already at T = 0, then the material is a normal conductor. Otherwise, lateral
overswing can be caused by lattice vibrations at a critical temperature Tc or
by a critical magnetic field Bc. Lateral electron oscillations are reduced -
and Tc is increased - when the atoms of the outer s electrons are squeezed, be
it in the bulk crystal, in a thin film, or under external pressure on the
sample. The model is applied to alkali metals and alkali-doped fullerenes.
Aluminum serves as an example of a simple metal with superconductivity.
Application of the model to transition metals, intertransitional alloys and
compounds of transition metals with other elements sheds light on the pattern
of their critical temperature. More examples of the squeeze effect are provided
by the superconductivity of PdH, MgB2, borocarbides, ferropnictides, and
organic charge-transfer salts. The model also provides the superconduction
mechanism in the oxide superconductors, exemplified by YBa2Cu3O7. Finally the
model suggests which steps to take in order to reach superconductivity at room
temperature and above.",1302.5043v2
2013-02-26,Colloidal Anisotropic ZnO-Fe@FexOy Nanoarchitectures with Interface-Mediated Exchange-Bias and Band-Edge Ultraviolet Fluorescence,"Hybrid nanocrystals (HNCs), based on ZnO nanorods (NRs) decorated with
magnetic Fe-based domains, were synthesized via a colloidal seeded-growth
method. The approach involved heterogeneous nucleation of Fe nanocrystals on
size-tailored ZnO nanorod seeds in a noncoordinating solvent, followed by
partial surface oxidation of the former to the corresponding Fe@FexOy
core@shell domains. HNCs with variable population and size of the Fe-based
nanodomains could be synthesized depending on the surface reactivity of the ZnO
seeds. The structure-property relationships in these HNCs were carefully
studied. In HNCs characterized by a large number of small Fe@FexOy core@shell
nanodomains on the ZnO seed surface, the interfacial communication across the
Fe-core and FexOy-shell generated a sizeable exchange-bias effect mediated by
frozen interfacial spins. On the other hand, in HNCs carrying a lower density
of comparatively larger Fe@FexOy domains, partial removal of the Fe core
created an inner void in-between that led to suppressed exchange coupling
anisotropy. As a further proof of functionality, the HNCs exhibited pronounced
band-edge ultraviolet fluorescence. The latter was blue-shifted compared to the
parent ZnO NRs, inferring coupling of the semiconductor and magnet sections.",1302.6347v1
2013-03-05,Anomalous Transport in Sketched Nanostructures at the LaAlO3/SrTiO3 Interface,"The oxide heterostructure LaAlO3/SrTiO3 supports a two-dimensional electron
liquid with a variety of competing phases including magnetism,
superconductivity and weak antilocalization due to Rashba spin-orbit coupling.
Further confinement of this 2D electron liquid to the quasi-one-dimensional
regime can provide insight into the underlying physics of this system and
reveal new behavior. Here we describe magnetotransport experiments on narrow
LaAlO3/SrTiO3 structures created by a conductive atomic force microscope
lithography technique. Four-terminal local transport measurements on
~10-nm-wide Hall bar structures yield longitudinal resistances that are
comparable to the resistance quantum h/e2 and independent of the channel
length. Large nonlocal resistances (as large as 10^4 ohms) are observed in some
but not all structures with separations between current and voltage that are
large compared to the 2D mean-free path. The nonlocal transport is strongly
suppressed by the onset of superconductivity below ~200 mK. The origin of these
anomalous transport signatures is not understood, but may arise from coherent
transport defined by strong spin-orbit coupling and/or magnetic interactions.",1303.1079v1
2013-03-12,Démixtion et ségrégation superficielle dans les alliages fer-chrome,"Ferritic steels possibly strengthened by oxide dispersion are candidates as
structural materials for generation IV and fusion nuclear reactors. Their use
is limited by incomplete knowledge of the iron-chromium phase diagram at low
temperatures and of the phenomena inducing preferential segregation of one
element at grain boundaries or at surfaces. In this context, this work
contributes to the multi-scale study of the model iron-chromium alloy and their
free surfaces by numerical simulations. This study begins with ab initio
calculations of properties related to the mixture of atoms of iron and
chromium. We highlight complex dependency of the magnetic moments of the
chromium atoms on their local chemical environment. Surface properties are also
proving sensitive to magnetism. This is the case of impurity segregation of
chromium in iron and of their interactions near the surface. In a second step,
we construct a simple energy model for high numerical efficiency. It is based
on pair interactions on a rigid lattice to which are given local chemical
environment and temperature dependencies. With this model, we reproduce the ab
initio results at zero temperature and experimental results at high
temperature. We also deduce the solubility limits at all intermediate
temperatures with mean field approximations that we compare to Monte Carlo
simulations. The last step of our work is to introduce free surfaces in our
model. We then study the effect of ab initio calculated bulk and surface
properties on surface segregation. Finally, we calculate segregation isotherms.
We therefore propose an evolution model of surface composition of iron-chromium
alloys as a function of bulk composition.",1303.2938v1
2013-11-03,Thickness-dependent ferromagnetic metal to paramagnetic insulator transition in La$_{0.6}$Sr$_{0.4}$MnO$_3$ thin films studied by x-ray magnetic circular dichroism,"Metallic transition-metal oxides undergo a metal-to-insulator transition
(MIT) as the film thickness decreases across a ritical thickness of several
monolayers (MLs), but its driving mechanism remains controversial. We have
studied the thickness-dependent MIT of the ferromagnetic metal
La$_{0.6}$Sr$_{0.4}$MnO$_3$ by x-ray absorption spectroscopy and x-ray magnetic
circular dichroism. As the film thickness was decreased across the critical
thickness of the MIT (6-8 ML), a gradual decrease of the ferromagnetic signals
and a concomitant increase of paramagnetic signals were observed, while the Mn
valence abruptly decreased towards Mn$^{3+}$. These observations suggest that
the ferromagnetic phase gradually and most likely inhomogeneously turns into
the paramagnetic phase and both phases abruptly become insulating at the
critical thickness.",1311.0520v4
2014-07-21,Direct epitaxial integration of the ferromagnetic semiconductor EuO with silicon for spintronic applications,"Materials in which charge and spin degrees of freedom interact strongly offer
applications known as spintronics. Following a remarkable success of metallic
spintronics based on the giant-magnetoresistive effect, tremendous efforts have
been invested into the less developed semiconductor spintronics, in particular,
with the aim to produce three-terminal spintronic devices, e.g. spin
transistors. One of the most important prerequisites for such a technology is
an effective injection of spin-polarized carriers from a ferromagnetic
semiconductor into a nonmagnetic semiconductor, preferably one of those
currently used for industrial applications such as Si - a workhorse of modern
electronics. Ferromagnetic semiconductor EuO is long believed to be the best
candidate for integration of magnetic semiconductor with Si. Although EuO
proved to offer optimal conditions for effective spin injection into silicon
and in spite of considerable efforts, the direct epitaxial stabilization of
stoichiometric EuO thin films on Si without any buffer layer has not been
demonstrated to date. Here we report a new technique for control of EuO/Si
interface on submonolayer level which may have general implications for the
growth of functional oxides on Si. Using this technique we solve a
long-standing problem of direct epitaxial growth on silicon of thin EuO films
which exhibit structural and magnetic properties of EuO bulk material. This
result opens up new possibilities in developing all-semiconductor spintronic
devices.",1407.5431v1
2014-08-18,Unquenched $e_g^1$ orbital moment in the Mott insulating antiferromagnet KOsO4,"Applying the correlated electronic structure method based on density
functional theory plus the Hubbard $U$ interaction, we have investigated the
tetragonal scheelite structure Mott insulator KOsO$_4$, whose $e_g^1$
configuration should be affected only slightly by spin-orbit couping (SOC). The
method reproduces the observed antiferromagnetic Mott insulating state,
populating the Os $d_{z^2}$ majority orbital. The quarter-filled $e_g$ manifold
is characterized by a symmetry breaking due to the tetragonal structure, and
the Os ion shows a crystal field splitting $\Delta_{cf}$ = 1.7 eV from the
$t_{2g}$ complex, which is relatively small considering the high formal
oxidation state Os$^{7+}$. The small magnetocrystalline anisotropy before
including correlation (i.e., in the metallic state) is increased by more than
an order of magnitude in the Mott-insulating state, a result of a strong
interplay between large SOC and a strong correlation. In contrast to
conventional wisdom that the $e_g$ complex will not support orbital magnetism,
we find that for the easy axis [100] direction the substantial Os orbital
moment $M_L\approx-0.2 \mu_B$ compensates half of the Os spin moment $M_S$ =
0.4$\mu_B$. The origin of the orbital moment is analyzed and understood in
terms of additional spin-orbital lowering of symmetry, and beyond that due to
structural distortion, for magnetization along [100]. Further interpretation is
assisted by analysis of the spin density and the Wannier function with SOC
included.",1408.4078v2
2015-06-12,Mechanisms and origins of half-metallic ferromagnetism in CrO2,"Chromium dioxide (CrO2) offers a rare example of metallic ferromagnetism
among stoichiometric transition-metal oxides. What makes it even more
remarkable is the half-metallic electronic structure. Today, CrO2 is widely
used in magnetorecording and regarded as a promising spintronic material.
Nevertheless, the key question ""Why is it ferromagnetic?"" remains largely
unanswered, despite general interest to the problem and practical importance of
CrO2. In the present work we challenge this question by combining
first-principles electronic structure calculations with the model Hamiltonian
approach and modern many-body methods for treating electron correlations. Our
analysis demonstrates that the problem is indeed highly nontrivial: at the
first glance, the ferromagnetism in CrO2 can be easily explained by Hund's rule
related exchange processes in the narrow t2g band. However, the electron
correlations, rigorously treated in the frameworks of dynamical mean-field
theory, tend to destabilize this state. The ferromagnetism reemerges if,
besides conventional kinetic energy changes in the t2g band, to consider other
mechanism, involving direct exchange and magnetic polarization of the oxygen
band. We show how all these contributions can be evaluated using
first-principles electronic structure calculations. Our results explain the
overall stability of the ferromagnetic state and provide the firm microscopic
basis for understanding the magnetism of CrO2.",1506.03886v1
2015-07-17,Phonons in ultrathin oxide films - 2D to 3D transition in FeO on Pt(111),"The structural and magnetic properties of ultrathin FeO(111) films on Pt(111)
with thicknesses from 1 to 16 monolayers (ML) were studied using the nuclear
inelastic scattering (NIS) of synchrotron radiation. Distinct evolution of
vibrational characteristics with thickness that is revealed in the phonon
density of states (PDOS) witnesses a textbook transition from 2D to 3D lattice
dynamics. For the thinnest films of 1 and 2 ML, the low energy part of the PDOS
followed a linear dependence in energy that is characteristic for 2-dimensional
systems. This dependence gradually transforms with thickness to the bulk
~E-square relation. Density functional theory phonon calculations perfectly
reproduced the measured 1 ML PDOS within a simple model of a pseudomorphic
FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due
to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of
the vibrational properties with an increasing thickness is closely related to a
transient long range magnetic order and stabilization of an unusual structural
phase.",1507.04874v6
2015-08-29,First-principles studies of multiferroic and magnetoelectric materials,"Multiferroics are materials where two or more ferroic orders coexist owing to
the interplay between spin, charge, lattice and orbital degrees of freedom. The
explosive expansion of multiferroics literature in recent years demon-strates
the fast growing interest in this field. In these studies, the first-principles
calculation has played a pioneer role in the experiment explanation, mechanism
discovery and prediction of novel multiferroics or magnetoelectric materials.
In this review, we discuss, by no means comprehensively, the extensive
applications and successful achievements of first-principles approach in the
study of multiferroicity, magnetoelectric effect and tunnel junc-tions. In
particular, we introduce some our recently developed methods, e.g., the orbital
selective external potential (OSEP) method, which prove to be powerful tools in
the finding of mechanisms responsible for the intriguing phe-nomena occurred in
multiferroics or magnetoelectric materials. We also summarize first-principles
studies on three types of electric control of magnetism, which is the common
goal of both spintronics and multiferroics. Our review offers in depth
understanding on the origin of ferroelectricity in transition metal oxides, and
the coexistence of fer-roelectricity and ordered magnetism, and might be
helpful to explore novel multiferroic or magnetoelectric materi-als in the
future.",1508.07414v1
2015-11-10,Topological magnetic phase in LaMnO$_3$ (111) bilayer,"Candidates for correlated topological insulators, originated from the
spin-orbit coupling as well as Hubbard type correlation, are expected in the
($111$) bilayer of perovskite-structural transition-metal oxides. Based on the
first-principles calculation and tight-binding model, the electronic structure
of a LaMnO$_3$ ($111$) bilayer sandwiched in LaScO$_3$ barriers has been
investigated. For the ideal undistorted perovskite structure, the Fermi energy
of LaMnO$_3$ ($111$) bilayer just stays at the Dirac point, rendering a
semi-metal (graphene-like) which is also a half-metal (different from graphene
nor previous studied LaNiO$_3$ ($111$) bilayer). The Dirac cone can be opened
by the spin-orbit coupling, giving rise to nontrivial topological bands
corresponding to the (quantized) anomalous Hall effect. For the realistic
orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard
repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens,
establishing a phase boundary between the Mott insulator and topological
magnetic insulator. Our calculation finds that the gap opened by spin-orbit
coupling is much smaller in the orthorhombic distorted lattice ($\sim$$1.7$
meV) than the undistorted one ($\sim$$11$ meV). Therefore, to suppress the
lattice distortion can be helpful to enhance the robustness of topological
phase in perovskite ($111$) bilayers.",1511.02968v1
2016-01-20,Orbital Order and Spin Nematicity in the Tetragonal Phase of Electron-doped Iron-Pnictides NaFe$_{1-x}$Co$_{x}$As,"In copper-oxide and iron-based high temperature (high-$T_{\rm c}$)
superconductors, many physical properties exhibit in-plane anisotropy, which is
believed to be caused by a rotational symmetry-breaking nematic order, whose
origin and its relationship to superconductivity remain elusive. In many
iron-pnictides, a tetragonal-to-orthorhombic structural transition temperature
$T_{\rm s}$ coincides with the magnetic transition temperature $T_{\rm N}$,
making the orbital and spin degrees of freedom highly entangled. NaFeAs is a
system where $T_{\rm s}$ = 54 K is well separated from $T_{\rm N}$ = 42 K,
which helps simplify the experimental situation. Here we report nuclear
magnetic resonance (NMR) measurements on NaFe$_{1-x}$Co$_x$As (0 $\leq x \leq$
0.042) that revealed orbital and spin nematicity occurring at a temperature
$T^{\rm *}$ far above $T_{\rm s}$ in the tetragonal phase. We show that the NMR
spectra splitting and its evolution can be explained by an incommensurate
orbital order that sets in below $T^{\rm *}$ and becomes commensurate below
$T_{\rm s}$, which brings about the observed spin nematicity.",1601.05293v1
2016-02-10,Oxygen vacancy induced room temperature metal-insulator transition in nickelates films and its potential application in photovoltaics,"Oxygen vacancy is intrinsically coupled with magnetic, electronic and
transport properties of transition-metal oxide materials and directly
determines their multifunctionality. Here, we demonstrate reversible control of
oxygen content by post-annealing at temperature lower than 300 degree
centigrade and realize the reversible metal-insulator transition in epitaxial
NdNiO3 films. Importantly, over six orders of magnitude in the resistance
modulation and a large change in optical band gap are demonstrated at room
temperature without destroying the parent framework and changing the p-type
conductive mechanism. Further study revealed that oxygen vacancies stabilized
the insulating phase at room temperature is universal for perovskite nickelates
films. Acting as electron donors, oxygen vacancies not only stabilize the
insulating phase at room temperature, but also induce a large magnetization of
~50 emu/cm3 due to the formation of strongly correlated Ni2+ t2g6eg2 states.
The band gap opening is an order of magnitude larger than that of the thermally
driven metal-insulator transition and continuously tunable. Potential
application of the newly found insulating phase in photovoltaics has been
demonstrated in the nickelates-based heterojunctions. Our discovery opens up
new possibilities for strongly correlated perovskite nickelates.",1602.03310v1
2016-07-05,Probing the core and shell contributions to exchange bias in Co/Co$_3$O$_4$ nanoparticles of controlled size,"Coupling at the interface of core/shell magnetic nanoparticles is known to be
responsible for the exchange bias (EB) and the relative sizes of core and shell
components are supposed to influence the associated phenomenology. In this
work, we have prepared core/shell structured nanoparticles with the total
averaged diameter around $\sim$ 27 nm and a wide range of shell thicknesses
through the controlled oxidation of Co nanoparticles well dispersed in an
amorphous silica host. Structural characterizations give compelling evidence of
the formation of Co$_3$O$_4$ crystallite phase at the shells surrounding the Co
core. Field cooled hysteresis loops display nonmonotonous dependence of the
exchange bias $H_E$ and coercive $H_C$ fields, that become maximum for a sample
with an intermediate shell thickness, at which lattice strain is also maximum
for both the phases. Results of our atomistic Monte Carlo simulations of the
particles with the same size and compositions as in experiments are in
agreement with the experimental observations and have allowed us to identify a
change in the contribution of the interfacial surface spins to the
magnetization reversal giving rise to the maximum in $H_E$ and $H_C$.",1607.01336v1
2016-09-22,Quantum meets classical phase transition: Low-temperature anomaly in disordered superconductors near $B_{c2}$,"Strongly disordered superconductors in a magnetic field display many
characteristic properties of type-II superconductivity--- except at low
temperatures where an anomalous linear $T$-dependence of the resistive critical
field $B_{c2}$ is routinely observed. This behavior violates the conventional
theory of superconductivity, and its origin remains a long-standing puzzle.
Here we report on systematic measurements of the critical magnetic field and
current on amorphous indium oxide films of various levels of disorder.
Surprisingly, our measurements show that the $B_{c2}$ anomaly near
zero-temperature is accompanied by a clear mean-field like scaling behavior of
the critical current. We demonstrate theoretically that these are consequences
of the vortex-glass ground state and its thermal fluctuations. This theory
further predicts the linear-$T$ anomaly to occur in films as well as bulk
superconductors with a slope that depends on the normal-state sheet
resistance---in agreement with experimental data. Thus, our combined
experimental and theoretical study reveals universal low-temperature behavior
of $B_{c2}$ in a large class of disordered superconductors.",1609.07105v4
2017-03-08,Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu2Si2,"In exotic superconductors including high-$T_c$ copper-oxides, the
interactions mediating electron Cooper-pairing are widely considered to have a
magnetic rather than the conventional electron-phonon origin. Interest in such
exotic pairing was initiated by the 1979 discovery of heavy-fermion
superconductivity in CeCu$_2$Si$_2$, which exhibits strong antiferromagnetic
fluctuations. A hallmark of unconventional pairing by anisotropic repulsive
interactions is that the superconducting energy gap changes sign as a function
of the electron momentum, often leading to nodes where the gap goes to zero.
Here, we report low-temperature specific heat, thermal conductivity and
magnetic penetration depth measurements in CeCu$_2$Si$_2$, demonstrating the
absence of gap nodes at any point on the Fermi surface. Moreover,
electron-irradiation experiments reveal that the superconductivity survives
even when the electron mean free path becomes substantially shorter than the
superconducting coherence length. This indicates that superconductivity is
robust against impurities, implying that there is no sign change in the gap
function. These results show that, contrary to long-standing belief, heavy
electrons with extremely strong Coulomb repulsions can condense into a
fully-gapped s-wave superconducting state, which has an on-site attractive
pairing interaction.",1703.02800v1
2017-03-22,Hard superconducting gap and vortex-state spectroscopy in NbSe$_2$ van der Waals tunnel junctions,"Device-based tunnel spectroscopy of superconductors was first performed by
Giaever, whose seminal work provided clear evidence for the spectral gap in the
density of states (DOS) predicted by the Bardeen-Cooper-Schrieffer (BCS)
theory. Since then, tunnel-barrier-based heterostructure devices have revealed
myriad physical phenomena and found a range of applications. Most of these
devices rely on a limited number of oxides, which form high-quality insulating,
non-magnetic barriers. These barriers, however, do not grow well on all
surfaces. Promising alternatives are van der Waals (vdW) materials, ultrathin
layers of which can be precisely positioned on many surfaces; they have been
shown to form tunnel barriers when engaged with graphene. Here we demonstrate
that vdW semiconductors MoS$_2$ and WSe$_2$ deposited on the superconductor
NbSe$_2$ form high quality tunnel barriers, with transparencies in the
$10^{-8}$ range. Our measurements of the NbSe$_2$ DOS at 70mK show a hard
superconducting gap, and a quasiparticle peak structure with clear evidence of
contributions from two bands, with intrinsic superconductivity in both bands.
In both perpendicular and parallel magnetic fields, we observe a sub-gap DOS
associated with vortex bound states. The linear dependence of the zero-bias
signal on perpendicular field allows us to confirm the s-wave nature of
superconductivity in NbSe$_2$. As vdW tunnel barriers can be deployed on many
solid surfaces, they extend the range of superconducting and other materials
addressable not only by high resolution tunneling spectroscopy but also
non-equilibrium and/or non-local transport.",1703.07677v1
2017-08-28,Manipulating Multiple Order Parameters via Oxygen Vacancies: The case of Eu0.5Ba0.5TiO3-δ,"Controlling functionalities, such as magnetism or ferroelectricity, by means
of oxygen vacancies (VO) is a key issue for the future development of
transition metal oxides. Progress in this field is currently addressed through
VO variations and their impact on mainly one order parameter. Here we reveal a
new mechanism for tuning both magnetism and ferroelectricity simultaneously by
using VO. Combined experimental and density-functional theory studies of
Eu0.5Ba0.5TiO3-{\delta}, we demonstrate that oxygen vacancies create Ti3+ 3d1
defect states, mediating the ferromagnetic coupling between the localized Eu
4f7 spins, and increase an off-center displacement of Ti ions, enhancing the
ferroelectric Curie temperature. The dual function of Ti sites also promises a
magnetoelectric coupling in the Eu0.5Ba0.5TiO3-{\delta}.",1708.08235v1
2010-05-24,Magnetic and Electronic Properties of Li$_x$CoO$_2$ Single Crystals,"Measurements of electrical resistivity ($\rho$), DC magnetization ($M$) and
specific heat ($C$) have been performed on layered oxide Li$_x$CoO$_2$
(0.25$\leq$$x$$\leq$0.99) using single crystal specimens. The $\rho$ versus
temperature ($T$) curve for $x$=0.90 and 0.99 is found to be insulating but a
metallic behavior is observed for 0.25$\leq$$x$$\leq$0.71. At $T_{\rm
S}$$\sim$155 K, a sharp anomaly is observed in the $\rho$$-$$T$, $M$$-$$T$ and
$C$$/$$T$$-$$T$ curves for $x$=0.66 with thermal hysteresis, indicating the
first-order charactor of the transition. The transition at $T_{\rm S}$$\sim$155
K is observed for the wide range of $x$=0.46$-$0.71. It is found that the
$M$$-$$T$ curve measured after rapid cool becomes different from that after
slow cool below $T_{\rm F}$, which is $\sim$130 K for $x$=0.46$-$0.71. $T_{\rm
F}$ is found to agree with the temperature at which the motional narrowing in
the $^7$Li NMR line width is observed, indicating that the Li ions stop
diffusing and order at the regular site below $T_{\rm F}$. The ordering of Li
ions below $T_{\rm F}$$\sim$130 K is likely to be triggered and stabilized by
the charge ordering in CoO$_2$ layers below $T_{\rm S}$.",1005.4253v3
2014-03-26,Unconventional pairing and electronic dimerization instabilities in the doped Kitaev-Heisenberg model,"We study the quantum many-body instabilities of the $t -J_{\mathrm{K}} -
J_{\mathrm{H}}$ Kitaev-Heisenberg Hamiltonian on the honeycomb lattice as a
minimal model for a doped spin-orbit Mott insulator. This spin-$1/2$ model is
believed to describe the magnetic properties of the layered transition-metal
oxide Na$_2$IrO$_3$. We determine the ground-state of the system with finite
charge-carrier density from the functional renormalization group (fRG) for
correlated fermionic systems. To this end, we derive fRG flow-equations adapted
to the lack of full spin-rotational invariance in the fermionic interactions,
here represented by the highly frustrated and anisotropic Kitaev exchange term.
Additionally employing a set of Ward identities for the Kitaev-Heisenberg
model, the numerical solution of the flow equations suggests a rich phase
diagram emerging upon doping charge carriers into the ground-state manifold
($\mathbb{Z}_2$ quantum spin liquids and magnetically ordered phases). We
corroborate superconducting triplet $p$-wave instabilities driven by
ferromagnetic exchange and various singlet pairing phases. For filling $\delta
> 1/4$, the $p$-wave pairing gives rise to a topological state with protected
Majorana edge-modes. For antiferromagnetic Kitaev and ferromagnetic Heisenberg
exchange we obtain bond-order instabilities at van Hove filling supported by
nesting and density-of-states enhancement, yielding dimerization patterns of
the electronic degrees of freedom on the honeycomb lattice. Further, our flow
equations are applicable to a wider class of model Hamiltonians.",1403.6762v2
2017-04-20,Orbital and spin ordering physics of the Mn$_3$O$_4$ spinel,"Motivated by recent experiments, we present a comprehensive theoretical study
of the geometrically frustrated strongly correlated magnetic insulator
Mn$_3$O$_4$ spinel oxide based on a microscopic Hamiltonian involving lattice,
spin and orbital degrees of freedom. Possessing the physics of degenerate e$_g$
orbitals, this system shows a strong Jahn-Teller effect at high temperatures.
Further, careful attention is paid to the special nature of the superexchange
physics arising from the 90$^o$ Mn-O-Mn bonding angle. The Jahn-Teller and
superexchange-based orbital-spin Hamiltonians are then analysed in order to
track the dynamics of orbital and spin ordering. We find that a
high-temperature structural transition results in orbital ordering whose nature
is mixed with respect to the two originally degenerate $e_{g}$ orbitals. This
ordering of orbitals is shown to relieve the intrinsic geometric frustration of
the spins on the spinel lattice, leading to ferrimagnetic Yafet-Kittel ordering
at low-temperatures. Finally, we develop a model for a magnetoelastic coupling
in Mn$_3$O$_4$, enabling a systematic understanding of the experimentally
observed complexity in the low-temperature structural and magnetic
phenomenology of this spinel. Our analysis predicts that a quantum
fluctuation-driven orbital-spin liquid phase may be stabilised at low
temperatures upon the application of pressure.",1704.06026v1
2018-05-18,Strain-Engineering Mott-Insulating La$_2$CuO$_4$,"The transition temperature $T_\textrm{c}$ of unconventional superconductivity
is often tunable. For a monolayer of FeSe, for example, the sweet spot is
uniquely bound to titanium-oxide substrates. By contrast for
La$_{2-\mathrm{x}}$Sr$_\mathrm{x}$CuO$_4$ thin films, such substrates are
sub-optimal and the highest $T_\textrm{c}$ is instead obtained using
LaSrAlO$_4$. An outstanding challenge is thus to understand the optimal
conditions for superconductivity in thin films: which microscopic parameters
drive the change in $T_\mathrm{c}$ and how can we tune them? Here we
demonstrate, by a combination of x-ray absorption and resonant inelastic x-ray
scattering spectroscopy, how the Coulomb and magnetic-exchange interaction of
La$_2$CuO$_4$ thin films can be enhanced by compressive strain. Our experiments
and theoretical calculations establish that the substrate producing the largest
$T_\textrm{c}$ under doping also generates the largest nearest neighbour
hopping integral, Coulomb and magnetic-exchange interaction. We hence suggest
optimising the parent Mott state as a strategy for enhancing the
superconducting transition temperature in cuprates.",1805.07173v3
2018-04-18,Heteroatomic jet fuel components: Lichen substances as fuel component and potential additives,"This article presents chemical analysis of jet fuel (Jet A-1) heteroatomic
fuel components with identification of an antioxidant lichen substance in
methanol extracted fuel samples. Thermal stressing of jet fuel produces soluble
macromolecular oxidatively reactive species (SMORS) and heteroatomic deposits.
SMORS are deposit precursors and elementary heteroatomic units containing
unsaturated and aromatic hydrocarbons. Fuel additives such as antioxidants can
inhibit SMORS and deposit formation within limited heating residence time and
temperature range. Jet A-1 was thermally stressed in the autoxidation regime
(150 to 300 0C) followed by spectroscopic analysis. Thermally stressed jet fuel
static tests electrospray ionization mass spectra (ESI-MS) show higher
molecular weight compounds in the mass range 300-1000 Da compared with
unstressed fuel samples supporting deposition. Jet A-1 samples were analyzed by
electrospray ion source mass spectrometry (ESI-MS), Fourier transform infrared
(FTIR) and 13C nuclear magnetic resonance (NMR) spectroscopy. FTIR bands for
oxygen containing species reveal the presence of alcohol, phenol and ether
groups. 13C nuclear magnetic resonance (NMR) standard and distorsionless
enhancement polarization transfer (DEPT 135) spectra recorded heteroatomic
alkoxy species in both unstressed and thermally stressed fuel samples. Natural
products polyphenols and lichen derived oxygenated compounds are excellent
antioxidants. A new perspective of using lichen substances as fuel additives
emerged in this study. Exploring further, natural products extraction methods
optimization remains a key challenge and advantages of polyphenolic lichen
acids as potential fuel and chemical additives are discussed.",1805.11675v1
2008-07-03,Electric Field Control of the LaAlO$_{3}$/SrTiO$_{3}$ Interface Ground State,"Interfaces between complex oxides are emerging as one of the most interesting
playgrounds in condensed matter physics. In this special setting, in which
translational symmetry is artificially broken, a variety of novel electronic
phases can be promoted. Theoretical studies predict complex phase diagrams and
suggest the key role of the carrier density in determining the systems ground
states. A particularly fascinating system is the interface between the
insulators LaAlO$_{3}$ and SrTiO$_{3}$, which displays conductivity with high
mobility. Recently two possible ground states have been experimentally
identified: a magnetic state and a two dimensional (2D) superconducting
condensate. In this Letter we use the electric field effect to explore the
phase diagram of the system. The electrostatic tuning of the carrier density
allows an on/off switching of superconductivity and drives a quantum phase
transition (QPT) between a 2D superconducting state and an insulating state
(2D-QSI). Analyses of the magnetotransport properties in the insulating state
are consistent with weak localisation and do not provide evidence for
magnetism. The electric field control of superconductivity demonstrated here
opens the way to the development of novel mesoscopic superconducting circuits",0807.0585v1
2008-07-08,Dispersing bimagnons and doping induced bimagnon-charge modes in superconducting cuprates,"In the early days of high temperature superconductivity it was already
recognized that magnetic properties of these materials are intimately related
to the superconducting ones . When doped, the long-range ordered
antiferromagnetic background of pristine copper-oxide insulators melts away and
makes room for a spin liquid and superconductivity. By resonant inelastic x-ray
scattering (RIXS) in the soft regime we probe the hitherto inaccessible
dynamical multiple-spin correlations of the magnetic background in a series of
parent compounds and in high Tc materials [NCCO (Nd2-xCexCuO4) and LSCO
(La2-xSrxCuO4)]. High resolution measurements allows the clear observation of
dispersing bimagnon excitations. In the undoped compounds the theory, fits the
data on these coherent spin excitations without free parameters. In nearly
optimally doped LSCO we observe the appearance of a new collective excitation
at an energy of 250 +/- 60 meV having the signature of a coupled
bimagnon-charge mode. It has a strongly reduced dispersion and lies in a so far
unexplored region of momentum and energy space in the mid-infrared.",0807.1140v1
2013-09-23,Zinc Oxide - From Dilute Magnetic Doping to Spin Transport,"During the past years there has been renewed interest in the wide-bandgap
II-VI semiconductor ZnO, triggered by promising prospects for spintronic
applications. First, ferromagnetism was predicted for dilute magnetic doping.
In comprehensive investigation of ZnO:Co thin films based on the combined
measurement of macroscopic and microscopic properties, we find no evidence for
carrier-mediated itinerant ferromagnetism. Phase-pure, crystallographically
excellent ZnO:Co is uniformly paramagnetic. Superparamagnetism arises when
phase separation or defect formation occurs, due to nanometer-sized metallic
precipitates. Other compounds like ZnO:(Li,Ni) and ZnO:Cu do not exhibit
indication of ferromagnetism.
  Second, its small spin-orbit coupling and correspondingly large spin
coherence length makes ZnO suitable for transporting or manipulating spins in
spintronic devices. From optical pump/optical probe experiments, we find a spin
dephasing time of the order of 15 ns at low temperatures which we attribute to
electrons bound to Al donors. In all-electrical magnetotransport measurements,
we successfully create and detect a spin-polarized ensemble of electrons and
transport this spin information across several nanometers. We derive a spin
lifetime of 2.6 ns for these itinerant spins at low temperatures, corresponding
well to results from an electrical pump/optical probe experiment.",1309.5857v1
2014-05-16,Mixed configuration ground state in Iron(II) Phthalocyanine,"We calculate the angular dependence of the x-ray linear and circular
dichroism at the $L_{2,3}$ edges of $\alpha$-Fe(II) Phthalocyanine (FePc) thin
films using a ligand field model with full configuration interaction. We find
the best agreement with the experimental spectra for a mixed ground state of
$^3E_{g}(a_{1g}^2e_g^3b_{2g}^1)$ and $^3B_{2g}(a_{1g}^1e_g^4b_{2g}^1)$ with the
two configurations coupled by the spin-orbit interaction. The $^3E_{g}(b)$ and
$^3B_{2g}$ states have an easy axis and plane anisotropies, respectively. Our
model accounts for an easy-plane magnetic anisotropy and the measured
magnitudes of the in-plane orbital and spin moments. The proximity in energy of
the two configurations allows a switching of the magnetic anisotropy from easy
plane to easy axis with a small change in the crystal field, as recently
observed for FePc adsorbed on an oxidized Cu surface. We also discuss the
possibility of a quintet ground state ($^5A_{1g}$ is 250~meV above the ground
state) with planar anisotropy by manipulation of the Fe-C bond length by
depositing the complex on a substrate that is subjected to a mechanical strain.",1405.4313v4
2016-12-15,The properties of ultrapure delafossite metals,"Although they were first synthesized in chemistry laboratories nearly fifty
years ago, the physical properties of the metals PdCoO2, PtCoO2 and PdCrO2 have
only more recently been studied in detail. The delafossite structure contains
triangular co-ordinated atomic layers, and electrical transport in the
delafossite metals is strongly two-dimensional. Their most notable feature is
their in-plane conductivity, which is amazingly high for oxide metals. At room
temperature, the conductivity of non-magnetic PdCoO2 and PtCoO2 is higher per
carrier than those of any alkali metal and even the most conductive elements,
copper and silver. At low temperatures the best crystals have resistivities of
a few n{\Omega}cm, corresponding to mean free paths of tens of microns. PdCrO2
is a frustrated antiferromagnetic metal, with magnetic scattering contributing
to the resistivity at high temperatures and small gaps opening in the Fermi
surface below the N\'eel temperature. There is good evidence that electronic
correlations are weak in the Pd/Pt layers but strong in the Co/Cr layers;
indeed the Cr layer in PdCrO2 is thought to be a Mott insulator. The
delafossite metals therefore act like natural heterostructures between strongly
correlated and nearly free electron sub-systems. Combined with the extremely
high conductivity, they provide many opportunities to study electrical
transport and other physical properties in new regimes. The purpose of this
review is to describe current knowledge of these fascinating materials and set
the scene for what is likely to be a considerable amount of future research.",1612.04948v1
2017-06-30,A review and prospects for Nb3Sn superconductor development,"Nb3Sn superconductors have significant applications in constructing
high-field (> 10 T) magnets. This article briefly reviews development of Nb3Sn
superconductor and proposes prospects for further improvement. It is shown that
significant improvement of critical current density (Jc) is needed for future
accelerator magnets. After a brief review of the development of Nb3Sn
superconductors, the factors controlling Jc are summarized and correlated with
their microstructure and chemistry. The non-matrix Jc of Nb3Sn conductors is
mainly determined by three factors: the fraction of current-carrying Nb3Sn
phase in the non-matrix area, the upper critical field Bc2, and the flux-line
pinning capacity. Then prospects to improve the three factors are discussed
respectively. An analytic model was developed to show how the ratios of
precursors determine the phase fractions after heat treatment, based on which
it is predicted that the limit of current-carrying Nb3Sn fraction in
subelements is ~65%. Then, since Bc2 is largely determined by the Nb3Sn
stoichiometry, a thermodynamic/kinetic theory was presented to show what
essentially determines the Sn content of Nb3Sn conductors. This theory explains
the influences of Sn sources and Ti addition on stoichiometry and growth rate
of Nb3Sn layers. Next, to improve flux pinning, previous efforts in this
community to introduce additional pinning centers (APC) to Nb3Sn wires are
reviewed, and an internal oxidation technique is described. Finally, prospects
for further improvement of non-matrix Jc of Nb3Sn conductors are discussed, and
it is seen that the only opportunity for further significantly improving Jc
lies in improving the flux pinning.",1706.10253v1
2017-12-12,Engineering the eigenstates of coupled spin-1/2 atoms on a surface,"Quantum spin networks having engineered geometries and interactions are
eagerly pursued for quantum simulation and access to emergent quantum phenomena
such as spin liquids. Spin-1/2 centers are particularly desirable because they
readily manifest coherent quantum fluctuations. Here we introduce a
controllable spin-1/2 architecture consisting of titanium atoms on a magnesium
oxide surface. We tailor the spin interactions by atomic-precision positioning
using a scanning tunneling microscope (STM), and subsequently perform electron
spin resonance (ESR) on individual atoms to drive transitions into and out of
quantum eigenstates of the coupled-spin system. Interactions between the atoms
are mapped over a range of distances extending from highly anisotropic dipole
coupling, to strong exchange coupling. The local magnetic field of the magnetic
STM tip serves to precisely tune the superposition states of a pair of spins.
The precise control of the spin-spin interactions and ability to probe the
states of the coupled-spin network by addressing individual spins will enable
exploration of quantum many-body systems based on networks of spin-1/2 atoms on
surfaces.",1712.04082v1
2018-01-16,Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers,"We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in
ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched
between Pt and MgO layers. We find that the FM layer in contact with the Pt
layers dominantly determines that spin Hall angle, which is consistent with the
spin-transparency model. By contrast, the FMR linewidths are considerably
influenced not only by the spin-pumping effect across the Pt|FM in terface but
also by the spin relaxation such as two-magnon scattering at the FMMgO
interface.The CoMgO interface leads to notably increased FMR linewidths, while
the Py|MgO interface has less effect. This different contribution of each
interface to the spin Hall angel and dissipation parameter suggests that the
stack configuration of Pt|Co|Py|MgO requires less writing energy than
Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach
offers a promising method to optimize material parameters by engineering either
interfaces in contact with the heavy-metal or the oxide layer.",1801.05131v2
2018-09-05,Tuning interactions in the spin-ice materials Dy$_2$Ge$_{2-x}$Si$_x$O$_7$ by silicon substitution,"We report that the lattice constant of Dy$_2$Ge$_{2-x}$Si$_x$O$_7$ ($x=0,
0.02, 0.08, 0.125$) can be systematically reduced by substituting the
non-magnetic germanium ion in the cubic pyrochlore oxide with silicon. A
multi-anvil high-pressure synthesis was performed up to 16 GPa and 1100
$^\circ$C to obtain polycrystalline samples in a solid-state reaction.
Measurements of magnetization, ac susceptibility, and heat capacity reveal the
typical signatures of a spin-ice phase. From the temperature shift of the
peaks, observed in the temperature-dependent heat capacity, we deduce an
increase of the strength of the exchange interaction. In conclusion, the
reduced lattice constant leads to a changed ratio of the competing exchange and
dipolar interaction. This puts the new spin-ice compounds closer towards the
phase boundary of short-range spin-ice arrangement and antiferromagnetic
long-range order consistent with an observed reduction of the monopole energy
scale.",1809.01480v2
2019-06-06,Novel Mechanocaloric Materials for Solid-State Cooling Applications,"Solid-state cooling is an environmentally friendly and highly scalable
technology that may solve most of the problems associated with current
refrigerant methods. Solid-state cooling consists of applying external fields
on caloric materials, which react thermally as a result of induced phase
transformations. From an energy efficiency point of view, mechanocaloric
compounds, in which the phase transitions of interest are driven by mechanical
stresses, probably represent the most encouraging type of caloric materials.
Conventional mechanocaloric materials like shape-memory alloys already display
good cooling performances however in most cases they also present critical
mechanical fatigue and hysteresis problems that limit their applicability.
Finding new mechanocaloric materials and mechanisms able to overcome those
problems while simultaneously rendering large temperature shifts, is necessary
to further advance the field of solid-state cooling. In this article, we review
novel families of mechanocaloric materials that in recent years have been shown
to be specially promising in the aspects that conventional mechanocaloric
materials are not, and which exhibit unconventional but significant caloric
effects. We put an emphasis on elastocaloric materials, in which the targeted
cooling spans are obtained through uniaxial stresses, since from an applied
perspective these appear to be the most accomplished. Two different types of
mechanocaloric materials emerge as particularly hopeful from our analysis,
compounds that exhibit field-induced order disorder phase transitions involving
either ions or molecules (fast-ion conductors and plastic crystals), and
multiferroics in which the structural parameters are strongly coupled with
polar and/or magnetic degrees of freedom (magnetic alloys and oxide
perovskites).",1906.02363v1
2019-06-10,Néel and stripe ordering from spin-orbital entanglement in $α$-Sr$_2$CrO$_4$,"The rich phenomenology engendered by the coupling between the spin and
orbital degrees of freedom has become appreciated as a key feature of many
strongly-correlated electron systems. The resulting emergent physics is
particularly prominent in a number of materials, from Fe-based unconventional
superconductors to transition metal oxides, including manganites and vanadates.
Here, we investigate the electronic ground states of $\alpha$-Sr$_2$CrO$_4$, a
compound that is a rare embodiment of the spin-1 Kugel-Khomskii model on the
square lattice -- a paradigmatic platform to capture the physics of coupled
magnetic and orbital electronic orders. We have used resonant X-ray diffraction
at the Cr-$K$ edge to reveal N\'{e}el magnetic order at the in-plane wavevector
$\mathbf{Q}_N = (1/2, 1/2)$ below $T_N = 112$ K, as well as an additional
electronic order at the 'stripe' wavevector $\mathbf{Q}_s = (1/2, 0)$ below
T$_s$ $ \sim 50$ K. These findings are examined within the framework of the
Kugel-Khomskii model by a combination of mean-field and Monte-Carlo approaches,
which supports the stability of the spin N\'{e}el phase with subsequent
lower-temperature stripe orbital ordering, revealing a candidate mechanism for
the experimentally observed peak at $\mathbf{Q}_s$. On the basis of these
findings, we propose that $\alpha$-Sr$_2$CrO$_4$ serves as a new platform in
which to investigate multi-orbital physics and its role in the low-temperature
phases of Mott insulators.",1906.04194v2
2020-04-15,Interfacial-hybridization-modified Ir Ferromagnetism and Electronic Structure in LaMnO$_3$/SrIrO$_3$ Superlattices,"Artificially fabricated 3$d$/5$d$ superlattices (SLs) involve both strong
electron correlation and spin-orbit coupling in one material by means of
interfacial 3$d$-5$d$ coupling, whose mechanism remains mostly unexplored. In
this work we investigated the mechanism of interfacial coupling in
LaMnO$_3$/SrIrO$_3$ SLs by several spectroscopic approaches. Hard x-ray
absorption, magnetic circular dichroism and photoemission spectra evidence the
systematic change of the Ir ferromagnetism and the electronic structure with
the change of the SL repetition period. First-principles calculations further
reveal the mechanism of the SL-period dependence of the interfacial electronic
structure and the local properties of the Ir moments, confirming that the
formation of Ir-Mn molecular orbital is responsible for the interfacial
coupling effects. The SL-period dependence of the ratio between spin and
orbital components of the Ir magnetic moments can be attributed to the
realignment of electron spin during the formation of the interfacial molecular
orbital. Our results clarify the nature of interfacial coupling in this
prototypical 3$d$/5$d$ SL system and the conclusion will shed light on the
study of other strongly correlated and spin-orbit coupled oxide
hetero-interfaces.",2004.06864v1
2020-12-25,Superconductivity to 262 kelvin via catalyzed hydrogenation of yttrium at high pressures,"Room temperature superconductivity has been achieved under high pressure in
an organically derived carbonaceous sulfur hydride with a critical
superconducting transition temperature (Tc) of 288 kelvin. This development is
part of a new class of dense, hydrogen rich materials with remarkably high
critical temperatures. Metal superhydrides are a subclass of these materials
that provide a different and potentially more promising route to very high Tc
superconductivity. The most promising binary metal superhydrides contain
alkaline or rare earth elements, and recent experimental observations of LaH10
have shown them capable of Tc s up to 250 to 260 kelvin. Predictions have shown
yttrium superhydrides to be the most promising with an estimated Tc in excess
of 300 kelvin for YH10. Here we report the synthesis of an yttrium superhydride
that exhibits superconductivity at a critical temperature of 262 kelvin at 182
gigapascal. A palladium thin film assists the synthesis by protecting the
sputtered yttrium from oxidation and promoting subsequent hydrogenation. Phonon
mediated superconductivity is established by the observation of zero
resistance, an isotope effect and the reduction of Tc under an external
magnetic field. The upper critical magnetic field is 103 tesla at zero
temperature. We suggest YH9 is the synthesized product based on comparison of
the measured Raman spectra and Tc to calculated Raman results.",2012.13627v1
2021-01-06,Experimental System for Molecular Communication in Pipe Flow With Magnetic Nanoparticles,"In the emerging field of molecular communication (MC), testbeds are needed to
validate theoretical concepts, motivate applications, and guide further
modeling efforts. To this end, this paper presents a flexible and extendable
in-vessel testbed for flow-based macroscopic MC, abstractly modeling, e.g., a
part of a chemical reactor or a blood vessel. Signaling is based on injecting
non-reactive superparamagnetic iron oxide nanoparticles (SPIONs) dispersed in
an aqueous suspension into a tube with background flow. A commercial magnetic
susceptometer is used for non-intrusive downstream signal reception. To shed
light on the operation of the testbed, we identify the physical mechanisms
governing the transmission, propagation, and reception of the
information-carrying SPIONs. Moreover, to facilitate system design, we propose
a closed-form parametric expression for the end-to-end channel impulse response
(CIR). The proposed CIR model is shown to consistently capture the
experimentally observed distance-dependent impulse response peak heights and
peak decays for transmission distances from 5cm to 40cm. Moreover, to validate
our testbed, reliable communication is demonstrated based on experimental data
for model-agnostic and model-based detection methods.",2101.02201v2
2021-01-19,"Quantitative analysis of iron sand mineral content from the south coast of Cidaun, West Java using rietveld refinement method","Iron sand is one of the abundant natural resources in Indonesia, especially
on the south coast of Cidaun; West Java which is the basic material for
building and metal industry. Iron mineral content is generally metal oxide such
as magnetite, hematite and silica/quartz. Sand with iron content used in this
study is derived from beach sand Desa Kertajadi, Kecamatan Cidaun, Kabupaten
Cianjur, Jawa Barat. Then mass of 2 kg sand was separated using a magnetic
separator in order to obtain magnetic and nonmagnetic mineral content. After
nine rounds of separation takes two different types of samples that are no
separation sand (TS) sample and concentrate in the third separation (S3)
sample. The sample is then examined by X-Ray Diffraction (XRD) measurement and
analyzed quantitatively using MAUD software to determine the content of Fe3O4
(magnetite) by using the Rietveld refinement method from XRD data. As the
analysis result, the magnetite content contained in iron sand is counted
quantitatively for each different sample. For iron sand samples (TS) yielding a
24.27 percent of magnetite and a third concentrate separation sample (S3)
yields 61.98 percent.",2101.10442v1
2017-05-05,Nanostructured complex oxides as a route towards thermal behavior in artificial spin ice systems,"We have used soft x-ray photoemission electron microscopy to image the
magnetization of single domain La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ nano-islands
arranged in geometrically frustrated configurations such as square ice and
kagome ice geometries. Upon thermal randomization, ensembles of nano-islands
with strong inter-island magnetic coupling relax towards low-energy
configurations. Statistical analysis shows that the likelihood of ensembles
falling into low-energy configurations depends strongly on the annealing
temperature. Annealing to just below the Curie temperature of the ferromagnetic
film (T$_{C}$ = 338 K) allows for a much greater probability of achieving low
energy configurations as compared to annealing above the Curie temperature. At
this thermally active temperature of 325 K, the ensemble of ferromagnetic
nano-islands explore their energy landscape over time and eventually transition
to lower energy states as compared to the frozen-in configurations obtained
upon cooling from above the Curie temperature. Thus, this materials system
allows for a facile method to systematically study thermal evolution of
artificial spin ice arrays of nano-islands at temperatures modestly above room
temperature.",1705.02309v1
2017-11-08,Surface impedance and optimum surface resistance of a superconductor with imperfect surface,"We calculate a low-frequency surface impedance of a dirty, s-wave
superconductor with an imperfect surface incorporating either a thin layer with
a reduced pairing constant or a thin, proximity-coupled normal layer. Such
structures model realistic surfaces of superconducting materials which can
contain oxide layers, absorbed impurities or nonstoichiometric composition. We
solved the Usadel equations self-consistently and obtained spatial
distributions of the order parameter and the quasiparticle density of states
which then were used to calculate a low-frequency surface resistance $R_s(T)$
and the magnetic penetration depth $\lambda(T)$ as functions of temperature in
the limit of local London electrodynamics. It is shown that the imperfect
surface in a single-band s-wave superconductor results in a non-exponential
temperature dependence of $Z(T)$ at $T\ll T_c$ which can mimic the behavior of
multiband or d-wave superconductors. The imperfect surface and the broadening
of the gap peaks in the quasiparticle density of states $N(\epsilon)$ in the
bulk give rise to a weakly temperature-dependent residual surface resistance.
We show that the surface resistance can be optimized and even reduced below its
value for an ideal surface by engineering $N(\epsilon)$ at the surface using
pairbreaking mechanisms, particularly, by incorporating a small density of
magnetic impurities or by tuning the thickness and conductivity of the normal
layer and its contact resistance. The results of this work address the limit of
$R_s$ in superconductors at $T\ll T_c$, and the ways of engineering the optimal
density of states by surface nano-structuring and impurities to reduce losses
in superconducting micro-resonators, thin film strip lines, and radio frequency
cavities for particle accelerators.",1711.03077v1
2017-11-27,Spectroscopy of bulk and few-layer superconducting NbSe$_2$ with van der Waals tunnel junctions,"Tunnel junctions, a well-established platform for high-resolution
spectroscopy of superconductors, require defect-free insulating barriers with
clean engagement to metals on both sides. Extending the range of materials
accessible to tunnel junction fabrication, beyond the limited selection which
allows high-quality oxide formation, requires the development of alternative
fabrication techniques. Here we show that van-der-Waals (vdW) tunnel barriers,
fabricated by stacking layered semiconductors on top of the transition metal
dichalcogenide (TMD) superconductor NbSe$_2$, sustain a stable, low noise
tunneling current, and exhibit strong suppression of sub-gap tunneling. We
utilize the technique to measure the spectra of bulk (20 nm) and ultrathin (3-
and 4-layer) devices at 70 mK. The spectra exhibit two distinct energy gaps,
the larger of which decreases monotonously with thickness and $T_C$, in
agreement with BCS theory. The spectra are analyzed using a two-band model
modified to account for depairing. We show that in the bulk, the smaller gap
exhibits strong depairing in an in-plane magnetic field, consistent with a high
Fermi velocity. In the few-layer devices, depairing of the large gap is
negligible, consistent with out-of-plane spin-locking due to Ising spin-orbit
coupling. Our results demonstrate the utility of vdW tunnel junctions in
mapping the intricate spectral evolution of TMD superconductors over a range of
magnetic fields.",1711.09615v2
2018-12-07,"Ab-initio approach to the stability and the structural, electronic and magnetic properties of the (001) Znfe2O4 surface terminations","We present a Density Functional Theory (DFT) based study of the structural
and magnetic properties of the (001) surface of the semiconducting oxide
ZnFe2O4 (spinel structure). The calculations were performed using the DFT based
ab initio plane wave and pseudopotential method as implemented in the Quantum
Espresso code. The all electron Full-potential linearized-augmented-plane-wave
method (FP-LAPW) was also employed to check the accuracy of plane wave method.
In both calculations the DFT+U methodology was employed and different (001)
surface terminations of ZnFe2O4 were studied: We find that the surface
terminated in Zn is the stable one. For all the (001) surface terminations our
calculations predict that the Zn-Fe cationic inversion (antisites), which are
defects in bulk ZnFe2O4, becomes stable and an integral part of the surface.
Also, a ferrimagnetic behavior is predicted for the case of antisites in the
superficial layer. Our results for different properties of the surface of
ZnFe2O4 are compared with those obtained in bulk samples and those reported in
the literature.",1812.03129v2
2019-04-29,Metal to Orthogonal Metal Transition,"Orthogonal metal is a new quantum metallic state that conducts electricity
but acquires no Fermi surface (FS) or quasiparticles, and hence orthogonal to
the established paradigm of Landau's Fermi-liquid (FL). Such a state may hold
the key of understanding the perplexing experimental observations of quantum
metals that are beyond FL, i.e., dubbed non-Fermi-liquid (nFL), ranging from
the Cu- and Fe-based oxides, heavy fermion compounds to the recently discovered
twisted graphene heterostructures. However, to fully understand such an exotic
state of matter, at least theoretically, one would like to construct a lattice
model and to solve it with unbiased quantum many-body machinery. Here we
achieve this goal by designing a 2D lattice model comprised of fermionic and
bosonic matter fields coupled with dynamic $\mathbb Z_2$ gauge fields, and
obtain its exact properties with sign-free quantum Monte Carlo simulations. We
find that as the bosonic matter fields become disordered, with the help of
deconfinement of the $\mathbb Z_2$ gauge fields, the system reacts with
changing its nature from the conventional normal metal with an FS to an
orthogonal metal of nFL without FS and quasiparticles and yet still responds to
magnetic probe like an FL. Such a quantum phase transition from a normal metal
to an orthogonal metal, with its electronic and magnetic spectral properties
revealed, is calling for the establishment of new paradigm of quantum metals
and their transition with conventional ones.",1904.12872v2
2019-11-07,Metal-Insulator and Magnetic Phase Diagram of Ca$_2$RuO$_4$ from Auxiliary Field Quantum Monte Carlo and Dynamical Mean Field Theory,"Layered perovskite ruthenium oxides exhibit a striking series of
metal-insulator and magnetic-nonmagnetic phase transitions easily tuned by
temperature, pressure, epitaxy, and nonlinear drive. In this work, we combine
results from two complementary state of the art many-body methods, Auxiliary
Field Quantum Monte Carlo and Dynamical Mean Field Theory, to determine the
low-temperature phase diagram of Ca$_2$RuO$_4$. Both methods predict a low
temperature, pressure-driven metal-insulator transition accompanied by a
ferromagnetic-antiferromagnetic transition. The properties of the ferromagnetic
state vary non-monotonically with pressure and are dominated by the ruthenium
$d_{xy}$ orbital, while the properties of the antiferromagnetic state are
dominated by the $d_{xz}$ and $d_{yz}$ orbitals. Differences of detail in the
predictions of the two methods are analyzed. This work is theoretically
important as it presents the first application of the Auxiliary Field Quantum
Monte Carlo method to an orbitally-degenerate system with both Mott and Hunds
physics, and provides an important comparison of the Dynamical Mean Field and
Auxiliary Field Quantum Monte Carlo methods.",1911.02702v1
2019-11-25,Phase Instability amid Dimensional Crossover in Artificial Oxide Crystal,"Artificial crystals synthesized by atomic-scale epitaxy provides the ability
to control the dimensions of the quantum phases and associated phase
transitions via precise thickness modulation. In particular, reduction in
dimensionality via quantized control of atomic layers is a powerful approach to
revealing hidden electronic and magnetic phases. Here, we demonstrate a
dimensionality-controlled and induced metal-insulator transition (MIT) in
atomically designed superlattices by synthesizing a genuine two dimensional
(2D) SrRuO3 crystal with highly suppressed charge transfer. The tendency to
ferromagnetically align the spins in SrRuO3 layer diminishes in 2D as the
interlayer exchange interaction vanishes, accompanying the 2D localization of
electrons. Furthermore, electronic and magnetic instabilities in the two SrRuO3
unit cell layers induce a thermally-driven MIT along with a metamagnetic
transition.",1911.10665v1
2020-03-03,Parabolic diamond scanning probes for single spin magnetic field imaging,"Enhancing the measurement signal from solid state quantum sensors such as the
nitrogen-vacancy (NV) center in diamond is an important problem for sensing and
imaging of condensed matter systems. Here we engineer diamond scanning probes
with a truncated parabolic profile that optimizes the photonic signal from
single embedded NV centers, forming a high-sensitivity probe for nanoscale
magnetic field imaging. We develop a scalable fabrication procedure based on
dry etching with a flowable oxide mask to reliably produce a controlled tip
curvature. The resulting parabolic tip shape yields a median saturation count
rate of 2.1 $\pm$ 0.2 MHz, the highest reported for single NVs in scanning
probes to date. Furthermore, the structures operate across the full NV
photoluminescence spectrum, emitting into a numerical aperture of 0.46 and the
end-facet of the truncated tip, located near the focus of the parabola, allows
for small NV-sample spacings and nanoscale imaging. We demonstrate the
excellent properties of these diamond scanning probes by imaging ferromagnetic
stripes with a spatial resolution better than 50 nm. Our results mark a 5-fold
improvement in measurement signal over the state-of-the art in scanning-probe
based NV sensors.",2003.01733v1
2020-03-06,Mössbauer parameters of $^{57}$Fe substituents in the topological insulator $Bi_2Se_3$,"$^{57}$Fe M\""ossbauer spectroscopy can probe several \emph{local} structural,
electronic and magnetic properties of Fe-containing systems. However, to
establish a direct relationship between these properties and a system's
geometric structure, the experimental M\""ossbauer parameters need to be
analyzed \emph{via} electronic structure calculations. Herein, structural,
electronic and magnetic effects of iron substituents in the topological
insulator $Bi_2Se_3$, as uniquely probed by $^{57}$Fe M\""ossbauer spectroscopy,
have been determined \emph{via} spin-polarized electronic structure
calculations. The iron ion substituents, of \emph{nominal} Fe$^{3+}(S = 5/2)$
oxidation and spin state, are unequivocally shown to substitute Bi$^{3+}$ sites
in epitaxial $Bi_2Se_3$ thin-films used for M\""ossbauer measurements.
Concomitant with iron substitution, \emph{localized} structural rearrangements
take place whereby the longer Bi-Se bonds of the native system are replaced by
significantly shorter Fe-Se counterparts in the Fe-containing system. The
resulting distorted-octahedral environment about substituent iron ions gives
rise to characteristic M\""ossbauer parameters ($\delta_{Fe} \approx$ 0.51 mm/s,
$\Delta E_{Q} \approx$ 0.20 mm/s) which have been calculated in excellent
agreement with measured values for Fe-doped $Bi_2Se_3$ thin films. Consistent
with a substituent Fe$^{3+}$ ion's \emph{nominal} high-spin electronic
configuration ($t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$),
an Fe-centered spin density has been established which, nevertheless, extends
towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant
Fe(d)-Se(p) hybridization.",2003.03458v1
2020-03-16,Spin orbit field in a physically defined p type MOS silicon double quantum dot,"We experimentally and theoretically investigate the spin orbit (SO) field in
a physically defined, p type metal oxide semiconductor double quantum dot in
silicon. We measure the magnetic field dependence of the leakage current
through the double dot in the Pauli spin blockade. A finite magnetic field
lifts the blockade, with the lifting least effective when the external and SO
fields are parallel. In this way, we find that the spin flip of a tunneling
hole is due to a SO field pointing perpendicular to the double dot axis and
almost fully out of the quantum well plane. We augment the measurements by a
derivation of SO terms using group symmetric representations theory. It
predicts that without in plane electric fields (a quantum well case), the SO
field would be mostly within the plane, dominated by a sum of a Rashba and a
Dresselhaus like term. We, therefore, interpret the observed SO field as
originated in the electric fields with substantial in plane components.",2003.07079v2
2020-05-16,Vacancy-driven non-cubic local structure and magnetic anisotropy tailoring in Fe$_x$O-Fe$_{3-δ}$O$_4$ nanocrystals,"In contrast to bulk materials, nanoscale crystal growth is critically
influenced by size- and shape-dependent properties. However, it is challenging
to decipher how stoichiometry, in the realm of mixed-valence elements, can act
to control physical properties, especially when complex bonding is implicated
by short and long-range ordering of structural defects. Here, solution-grown
iron-oxide nanocrystals (NCs) of the pilot wustite system are found to convert
into iron-deficient rock-salt and ferro-spinel sub-domains, but attain a
surprising tetragonally distorted local structure. Cationic vacancies within
chemically uniform NCs are portrayed as the parameter to tweak the underlying
properties. These lattice imperfections are shown to produce local
exchange-anisotropy fields that reinforce the nanoparticles magnetization and
overcome the influence of finite-size effects. The concept of atomic-scale
defect control in subcritical size NCs, aspires to become a pathway to
tailor-made properties with improved performance for hyperthermia heating over
defect-free NCs.",2005.07947v1
2020-06-30,Magnetic exchange coupling in cuprate-analog $d^9$ nickelates,"Motivated by the recent discovery of superconductivity in doped NdNiO$_2$, we
study the magnetic exchange interaction $J$ in layered $d^9$ nickelates from
first principles. The mother compounds of the high-$T_{\rm c}$ cuprates belong
to the charge-transfer regime in the Zaanen-Sawatzky-Allen diagram and have $J$
larger than 100 meV. While this feature makes the cuprates very different from
other transition metal oxides, it is of great interest whether layered $d^9$
nickelates can also have such a large $J$. However, one complexity is that
NdNiO$_2$ is not a Mott insulator due to carrier doping from the block layer.
To compare the cuprates and $d^9$ nickelates on an equal basis, we study
RbCa$_2$NiO$_3$ and $A_{2}$NiO$_{2}$Br$_2$ ($A$: a cation with the valence of
$2.5+$), which were recently designed theoretically by block-layer engineering.
These nickelates are free from the self-doping effect and belong to the
Mott-Hubbard regime. We show that these nickelates share a common thread with
the high-$T_{\rm c}$ cuprates in that they also have a significant exchange
interaction $J$ as large as about 100 meV.",2006.16943v3
2021-03-29,Surface NMR using quantum sensors in diamond,"Characterization of the molecular properties of surfaces under ambient or
chemically reactive conditions is a fundamental scientific challenge. Moreover,
many traditional analytical techniques used for probing surfaces often lack
dynamic or molecular selectivity, which limits their applicability for
mechanistic and kinetic studies under realistic chemical conditions. Nuclear
magnetic resonance spectroscopy (NMR) is a widely used technique and would be
ideal for probing interfaces due to the molecular information it provides
noninvasively. However, it lacks the sensitivity to probe the small number of
spins at surfaces. Here, we use nitrogen vacancy (NV) centers in diamond as
quantum sensors to optically detect nuclear magnetic resonance signals from
chemically modified aluminum oxide surfaces, prepared with atomic layer
deposition (ALD). With the surface NV-NMR technique, we are able to monitor in
real-time the formation kinetics of a self assembled monolayer (SAM) based on
phosphonate anchoring chemistry to the surface. This demonstrates the
capability of quantum sensors as a new surface-sensitive tool with
sub-monolayer sensitivity for in-situ NMR analysis with the additional
advantage of a strongly reduced technical complexity.",2103.15955v1
2021-03-30,Competing correlated states around the zero field Wigner crystallization transition of electrons in two-dimensions,"The competition between kinetic energy and Coulomb interactions in electronic
systems can lead to complex many-body ground states with competing
superconducting, charge density wave, and magnetic orders. Here we study the
low temperature phases of a strongly interacting zinc-oxide-based high mobility
two dimensional electron system that displays a tunable metal-insulator
transition. Through a comprehensive analysis of the dependence of electronic
transport on temperature, carrier density, in-plane and perpendicular magnetic
fields, and voltage bias, we provide evidence for the existence of competing
correlated metallic and insulating states with varying degrees of spin
polarization. Our system features an unprecedented level of agreement with the
state-of-the-art Quantum Monte Carlo phase diagram of the ideal jellium model,
including a Wigner crystallization transition at a value of the interaction
parameter $r_s\sim 30$ and the absence of a pure Stoner transition. In-plane
field dependence of transport reveals a new low temperature state with partial
spin polarization separating the spin unpolarized metal and the Wigner crystal,
which we examine against possible theoretical scenarios such as an
anti-ferromagnetic crystal, Coulomb induced micro-emulsions, and disorder
driven puddle formation.",2103.16586v1
2021-05-06,Growth and Characterisation Studies of Eu$_3$O$_4$ Thin Films Grown on Si/SiO$_2$ and Graphene,"We report the growth, structural and magnetic properties of the less studied
Eu-oxide phase, Eu$_3$O$_4$, thin films grown on a Si/SiO$_2$ substrate and
Si/SiO$_2$/graphene using molecular beam epitaxy. The X-ray diffraction scans
show that highly-textured crystalline Eu$_3$O$_4$(001) films are grown on both
substrates, whereas the film deposited on graphene has a better crystallinity
than that grown on the Si/SiO$_2$ substrate. The SQUID measurements show that
both films have a Curie temperature of about 5.5 K, with a magnetic moment of
0.0032 emu/g at 2 K. The mixed-valency of the Eu cations has been confirmed by
the qualitative analysis of the depth-profile X-ray photoelectron spectroscopy
measurements with the Eu$^{2+}$ : Eu$^{3+}$ ratio of 28 : 72. However,
surprisingly, our films show no metamagnetic behaviour as reported for the bulk
and powder form. Furthermore, the Raman spectroscopy scans show that the growth
of the Eu$_3$O$_4$ thin films has no damaging effect on the underlayer graphene
sheet. Therefore, the graphene layer is expected to retain its properties.",2105.02705v1
2021-05-10,Observation of the Orbital Rashba-Edelstein Magnetoresistance,"We report the observation of magnetoresistance (MR) originating from the
orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu
(Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The
angular dependence of the MR depends on the relative angle between the induced
OAM and the magnetization in a similar fashion as the spin Hall
magnetoresistance (SMR). Despite the absence of elements with large spin-orbit
coupling, we find a sizable MR ratio, which is in contrast to the conventional
SMR which requires heavy elements. By varying the thickness of the Cu* layer,
we confirm that the interface is responsible for the MR, suggesting that the
orbital Rashba-Edelstein effect is responsible for the generation of the OAM.
Through Py thickness-dependence studies, we find that the effective values for
the spin diffusion and spin dephasing lengths of Py are significantly larger
than the values measured in Py / Pt bilayers, approximately by the factor of 2
and 4, respectively. This implies that another mechanism beyond the
conventional spin-based scenario is responsible for the MR observed in Py / Cu*
structures originated in a sizeable transport of OAM. Our findings not only
unambiguously demonstrate the current-induced torque without using any heavy
element via the OAM channel but also provide an important clue towards the
microscopic understanding of the role that OAM transport can play for
magnetization dynamics.",2105.04495v2
2021-06-03,Oxygen out-diffusion in REBCO coated conductor due to heating,"Rare earth barium copper oxide (REBCO) coated conductor has emerged as one of
the high Tc superconductors suitable for future ultrahigh field superconducting
magnet applications. In the design and fabrication of such ultrahigh field
REBCO magnets, it is essential to understand the behavior of REBCO coated
conductor. The effect of heating on the properties of commercial REBCO coated
conductors is very important for many practical reasons. Nevertheless, a
comprehensive study on this effect have not yet been presented in the published
literature. This work studies a commercial REBCO coated conductor heat-treated
at temperatures between 175 {\deg}C and 300 {\deg}C for various durations.
Critical current and lap joint resistivity were measured at 77 K and 4.2 K for
the heat-treated samples. We found that critical current degrades with heat
treatment time and temperature. This degradation can be described by a
one-dimensional oxygen out-diffusion model with a diffusion coefficient of D =
2.5 x 10-6 exp (-1.17 eV/kT) m2/s. The heat treatment also causes appreciable
increase in joint resistivity. Comprehensive structural and chemical analyses
were performed on Cu/Ag/RECBO interfaces by transmission electron microscopy
(TEM). Our electron energy loss spectroscopy (EELS) study provided direct
evidence of oxygen deficiency in the heat treated REBCO samples. In addition,
it is found that the oxygen diffused out of the REBCO layer forms mostly Cu2O
at both Ag/REBCO and Cu/Ag interfaces. Cu2O is also observed at grain
boundaries of the Ag layer. The oxygen out-diffusion model proposed in this
work is used to predict REBCO thermal degradation in several engineering
scenarios.",2106.01905v1
2021-06-08,"Superconducting microresonators for electron spin resonance, the good, the bad, and the future","The field of electron spin resonance is in constant need to improve its
capabilities. Among other things, this means having better resonators which
would provide improved spin sensitivity, as well as enable larger microwave
magnetic field power conversion factors. Surface micro resonators, made of
small metallic patches on a dielectric substrate, provide very good absolute
spin sensitivity and high conversion factors due to their very small mode
volume. However, such resonators suffer from having a relatively low quality
factor, which offsets some of their significant potential advantages. The use
of superconducting patches to replace the metallic layer seems like a
reasonable and straightforward solution to the quality factor issue, at least
for measurements carried out at cryogenic temperatures. Nevertheless,
superconducting materials are not easily incorporated into setups requiring
high magnetic fields, due to electric current vortices generated in the
latter's surface. This makes the transition from normal conducing materials to
superconductors highly nontrivial. Here we present the design, fabrication, and
testing results of surface micro resonators made of yttrium barium copper oxide
(YBCO) superconducting material. We show that with a unique experimental setup,
these resonators can be made to operate well even at high fields of about 1.2
T. Furthermore, we analyze the effect of current vortices on the ESR signal and
the spins' coherence times. Finally, we provide a head to head comparison of
YBCO vs copper resonators of the same dimensions, which clearly shows their
pros and cons and directs us to future potential developments and improvements
in this field.",2106.04163v2
2021-06-18,"Growth and characterization of large (Y,La)TiO$_3$ and (Y,Ca)TiO$_3$ single crystals","The Mott-insulating rare-earth titanates (RTiO$_3$, R being a rare-earth ion)
are an important class of materials that encompasses interesting spin-orbital
phases as well as ferromagnet-antiferromagnet and insulator-metal transitions.
The growth of these materials has been plagued by difficulties related to
overoxidation, which arises from a strong tendency of Ti$^{3+}$ to oxidize to
Ti$^{4+}$. We describe our efforts to grow sizable single crystals of YTiO$_3$
and its La-substituted and Ca-doped variants with the optical
travelling-solvent floating-zone technique. We present sample characterization
$via$ chemical composition analysis, magnetometry, charge transport, neutron
scattering, x-ray absorption spectroscopy and x-ray magnetic circular dichroism
to understand macroscopic physical property variations associated with
overoxidation. Furthermore, we demonstrate a good signal-to-noise ratio in
inelastic magnetic neutron scattering measurements of spin-wave excitations. A
superconducting impurity phase, found to appear in Ca-doped samples at high
doping levels, is identified as TiO.",2106.10253v1
2021-07-06,Structural modulation in potassium birnessite single crystals,"We report on the growth of single-crystal potassium birnessite
(K0.31MnO2*0.41H2O) and present both the average and local structural
characterization of this frustrated magnetic system. Single crystals were
obtained employing a flux growth method with a KNO3/B2O3 flux at 700 {\deg}C.
Single-crystal X-ray diffraction revealed an average orthorhombic symmetry,
with space group Cmcm. A combination of high angle annular dark field scanning
transmission electron microscopy (HAADF-STEM) with atomic resolution energy
dispersive X-ray spectroscopy (EDS) demonstrated the layered structure of
potassium birnessite with manganese-containing planes well separated by layers
of potassium atoms. MnO6 octahedra and the K/H2O planes were clearly imaged via
integrated differential phase contrast (iDPC) STEM. Furthermore, iDPC-STEM also
revealed the existence of local domains with alternating contrast of the
manganese oxide planes, most likely originating from charge ordering of Mn3+
and Mn4+ along the c-axis. These charge-ordered domains are clearly correlated
with a reduction in the c-lattice parameter compared to the rest of the matrix.
The insight gained from this work allows for a better understanding of the
correlation between structure and magnetic properties.",2107.02880v1
2021-09-26,Electronic phase separation: recent progress in the old problem,"We consider the nanoscale electronic phase separation in a wide class of
different materials, mostly in strongly correlated electron systems. The phase
separation turns out to be quite ubiquitous manifesting itself in different
situations, where the itineracy of charge carriers competes with their tendency
toward localization. The latter is often related to some specific type of
magnetic ordering, e.g. antiferromagnetic in manganites and low-spin states in
cobaltites. The interplay between the localization-induced lowering of
potential energy and metallicity (which provides the gain in the kinetic
energy) favors an inhomogeneous ground state such as nanoscale ferromagnetic
droplets in an antiferromagnetic insulating background. The present review
article deals with the advances in the subject of electronic phase separation
and formation of different types of nanoscale ferromagnetic (FM) metallic
droplets (FM polarons or ferrons) in antiferromagnetically ordered (AFM),
charge-ordered (CO), or orbitally-ordered (OO) insulating matrices, as well as
the colossal magnetoresistance (CMR) effect and tunneling electron transport in
the nonmetallic phase-separated state of complex magnetic oxides. It also
touches upon the compounds with spin-state transitions, inhomogeneous
phase-separated state in strongly correlated multiband systems, and electron
polaron effect. A special, attention is paid to the systems with the imperfect
Fermi surface nesting such as chromium alloys, iron-based pnictides, and AA
stacked graphene bilayers.",2109.12684v2
2021-11-11,Current-induced superconducting anisotropy of Sr$\mathsf{_2}$RuO$\mathsf{_4}$,"In the unconventional superconductor Sr$\mathsf{_2}$RuO$\mathsf{_4}$, unusual
first-order superconducting transition has been observed in the low-temperature
and high-field region, accompanied by a four-fold anisotropy of the in-plane
upper critical magnetic field $H_{c2}$. The origin of such unusual $H_{c2}$
behavior should be closely linked to the debated superconducting symmetry of
this oxide. Here, toward clarification of the unusual $H_{c2}$ behavior, we
performed the resistivity measurements capable of switching in-plane current
directions as well as precisely controlling the field directions. Our results
reveal that resistive $H_{c2}$ under the in-plane current exhibits an
additional two-fold anisotropy. By systematically analyzing $H_{c2}$ data taken
under various current directions, we succeeded in separating the two-fold
$H_{c2}$ component into the one originating from applied current and the other
originating from certain imperfection in the sample. The former component,
attributable to vortex flow effect, is weakened at low temperatures where
$H_{c2}$ is substantially suppressed. The latter component is enhanced in the
first order transition region, possibly reflecting a change in the nature of
the superconducting state under high magnetic field.",2111.06097v1
2021-11-23,Li-ion diffusion in single crystal LiFePO$_4$ measured by muon spin spectroscopy,"Muon spin spectroscopy ($\mu^+$SR) is now an established method to measure
atomic scale diffusion coefficients of ions in oxides. This is achieved via the
ion hopping rate, which causes periodic change in the local magnetic field at
the muon site(s). We present here the first systematic study on a single
crystalline sample. The highly anisotropic diffusion of Li-ions in the battery
cathode material LiFePO$_4$, combined with the extensive investigation of this
material with $\mu^+$SR and other techniques make it a perfect model compound
for this study. With this experiment we can confirm that Li diffusion in the
bulk LiFePO$_4$ is measurable with $\mu^+$SR. Hence, surface/interface effects,
which might play a crucial role in case of powders/nano crystals, are less
significant for macroscopic single crystals where bulk diffusion is in fact
present. We observe that the internal magnetic field fluctuations caused by the
diffusing Li-ions are different depending on the crystal orientation. This is
not obviously expected based on theoretical considerations. Such fluctuation
rates were used to estimate the diffusion coefficient, which agrees well with
values estimated by first principle calculations considering anisotropic
diffusion.",2111.11941v1
2022-01-16,Physical realization of topological Roman surface by spin-induced ferroelectric polarization in cubic lattice,"Topology, a mathematical concept in geometry, has become an ideal theoretical
tool for describing topological states and phase transitions. Many topological
concepts have found their physical entities in real or reciprocal spaces
identified by topological/geometrical invariants, which are usually defined on
orientable surfaces such as torus and sphere. It is natural to quest whether it
is possible to find the physical realization of more intriguing non-orientable
surfaces. Herein, we show that the set of spin-induced ferroelectric
polarizations in cubic perovskite oxides AMn3Cr4O12 (A = La and Tb) resides on
the topological Roman surface, a non-orientable two-dimensional manifold formed
by sewing a Mobius strip edge to that of a disc. The induced polarization may
travel in a loop along the non-orientable Mobius strip or orientable disc
depending on how the spin evolves as controlled by external magnetic field.
Experimentally, the periodicity of polarization can be the same or the twice of
the rotating magnetic field, being well consistent with the orientability of
disc and Mobius strip, respectively. This path dependent topological
magnetoelectric effect presents a way to detect the global geometry of the
surface and deepens our understanding of topology in both mathematics and
physics",2201.06018v1
2022-04-08,Quantum Dots / Spin Qubits,"Spin qubits in semiconductor quantum dots represent a prominent family of
solid-state qubits in the effort to build a quantum computer. They are formed
when electrons or holes are confined in a static potential well in a
semiconductor, giving them a quantized energy spectrum. The simplest spin qubit
is a single electron spin located in a quantum dot, but many additional
varieties have been developed, some containing multiple spins in multiple
quantum dots, each of which has different benefits and drawbacks. While these
spins act as simple quantum systems in many ways, they also experience complex
effects due to their semiconductor environment. They can be controlled by both
magnetic and electric fields depending on their configuration and are therefore
dephased by magnetic and electric field noise, with different types of spin
qubits having different control mechanisms and noise susceptibilities. While
initial experiments were primarily performed in gallium arsenide (GaAs) based
materials, silicon qubits have developed substantially and research on qubits
in metal-oxide-semiconductor (Si-MOS), silicon/silicon germanium (Si/SiGe)
heterostructures, and donors in silicon is also being pursued. An increasing
number of spin qubit varieties have attained error rates that are low enough to
be compatible with quantum error correction for single-qubit gates and
two-qubit gates have been performed in several with success rates, or
fidelities, of 90-95%.",2204.04261v1
2022-05-06,Magnetic frustration in the cubic double perovskite Ba2NiIrO6,"Hybrid transition metal oxides continue to attract attention due to their
multiple degrees of freedom ($e.g.$, lattice, charge, spin, and orbital) and
versatile properties. Here we investigate the magnetic and electronic
properties of the newly synthesized double perovskite Ba$_2$NiIrO$_6$, using
crystal field theory, superexchange model analysis, density functional
calculations, and parallel tempering Monte Carlo (PTMC) simulations. Our
results indicate that Ba$_2$NiIrO$_6$ has the Ni$^{2+}$
($t_{2g}^{6}e_{g}^{2}$)-Ir$^{6+}$ ($t_{2g}^{3}$) charge states. The first
nearest-neighboring (1NN) Ni$^{2+}$-Ir$^{6+}$ ions prefer a ferromagnetic (FM)
coupling as expected from the Goodenough-Kanamori-Anderson rules, which
contradicts the experimental antiferromagnetic (AF) order in Ba$_2$NiIrO$_6$.
We find that the strong 2NN AF couplings are frustrated in the fcc sublattices,
and they play a major role in determining the observed AF ground state. We also
prove that the $J_{\rm eff}$ = 3/2 and $J_{\rm eff}$ = 1/2 states induced by
spin-orbit coupling, which would be manifested in low-dimensional (e.g.,
layered) iridates, are however not the case for cubic Ba$_2$NiIrO$_6$. Our PTMC
simulations show that when the long-range (2NN and 3NN) AF interactions are
included, an AF transition with $T_{\rm N}$ = 66 K would be obtained and it is
well comparable with the experimental 51 K. Meanwhile, we propose a possible
2$\times$2$\times$2 noncollinear AF structure for Ba$_2$NiIrO$_6$.",2205.03049v1
2022-05-14,Anomalous metallic oxygen band in the potential superconductor KCa$_2$Fe$_4$As$_4$O$_2$,"The electronic structure, magnetism and Fermi surface of a hole self-doped
potential iron-based superconductor KCa$_2$Fe$_4$As$_4$O$_2$ (12442) were
studied by a first-principes DFT/GGA approach. The projection onto Wannier
functions basis is proposed to calculate directly the self-doping value. In
particular for KCa$_2$Fe$_4$As$_4$O$_2$ it is 0.75 hole on Fe-3d states.
Surprisingly, for the KCa$_2$Fe$_4$As$_4$O$_2$ it was found that except the
Fe-3d bands the O-2p bands also cross the Fermi level, which is quite anomalous
behavior for O-2p states. In general, the O-2p states are usually fully
occupied in transition metal oxides. Here it is not the case due to the fact
that CaO layer gives some of the electrons to the FeAs layer, thus leaving O-2p
states partially occupied. The O-2p states form additional Fermi surface sheet
with propeller-like shape around $\Gamma$-point and modify the Fe-3d Fermi
surface sheets due to the hybridization. To prove the presence of anomalous
metallic O-2p band in KCa$_2$Fe$_4$As$_4$O$_2$ the comparative study with the
same family systems KCa$_2$Fe$_4$As$_4$F$_2$ and RbGd$_2$Fe$_4$As$_4$O$_2$
(where it is not the case) was performed. The magnetic ground state is found to
be antiferromagnetic with checkerboard ordering. Therefore, we expect that the
KCa$_2$Fe$_4$As$_4$O$_2$ might be a potential superconductor with unusual
properties.",2205.07007v1
2022-08-23,Topotactic-hydrogen forms chains in $AB$O$_2$ nickelate superconductors,"Despite enormous experimental and theoretical efforts, obtaining generally
accepted conclusions regarding the intrinsic magnetic and electronic properties
of superconducting nickelates remains exceptionally challenging. Experiments
show a significant degree of uncertainty, indicating hidden factors in the
synthesized films, which call for further investigations. One of those ""hidden
factors"" is the possibility of intercalating hydrogen during the chemical
reduction process from Nd(La)NiO$_3$ to Nd(La)NiO$_2$ using CaH$_2$. While
hydrogen has been detected in experimental samples, not much is known about its
distribution through the crystal and its influence on the electronic
environment. Here, we show the tendency toward the formation of one-dimensional
hydrogen chains in infinite-layers LaNiO$_2$ superconductors using
density-functional theory (DFT) supplemented by dynamical mean-field theory
(DMFT). The formation of such hydrogen chains induces a coexistence of
different oxidation states of Ni and competing magnetic phases, and possibly
explains the recently observed charge order states in nickelate
superconductors. Furthermore, it contributes to the difficulty of synthesizing
homogeneous nickelates and determining their ground states. The smoking gun to
detect excess hydrogen in nickelates are flat phonon modes, which are infrared
active and quite insensitive to the exact arrangement of the H atoms.",2208.11085v2
2022-11-30,A proposal for leaky integrate-and-fire neurons by domain walls in antiferromagnetic insulators,"Brain-inspired neuromorphic computing is a promising path towards next
generation analogue computers that are fundamentally different compared to the
conventional von Neumann architecture. One model for neuromorphic computing
that can mimic the human brain behavior are spiking neural networks (SNNs), of
which one of the most successful is the leaky integrate-and-fire (LIF) model.
Since conventional complementary metal-oxide-semiconductor (CMOS) devices are
not meant for modelling neural networks and are energy inefficient in network
applications, recently the focus shifted towards spintronic-based neural
networks. In this work, using the advantage of antiferromagnetic insulators, we
propose a non-volatile magnonic neuron that could be the building block of a
LIF spiking neuronal network. In our proposal, an antiferromagnetic domain wall
in the presence of a magnetic anisotropy gradient mimics a biological neuron
with leaky, integrating, and firing properties. This single neuron is
controlled by polarized antiferromagnetic magnons, activated by either a
magnetic field pulse or a spin transfer torque mechanism, and has properties
similar to biological neurons, namely latency, refraction, bursting and
inhibition. We argue that this proposed single neuron, based on
antiferromagnetic domain walls, is faster and has more functionalities compared
to previously proposed neurons based on ferromagnetic systems.",2211.16845v2
2022-12-27,"Interrelations among critical current density, irreversibility field and pseudogap in hole doped high-Tc cuprates","The effects of hole content (p) and oxygen deficiency (delta) on the
zero-field critical current density, Jc0, were investigated for high-quality
c-axis oriented Y1-xCaxBa2Cu3O7-delta (x = 0, 0.05, 0.10, and 0.20) thin films.
Low temperature critical current density of these films above the optimum
doping were found to be high and were primarily determined by the hole
concentration, reaching a maximum at p ~ 0.185 +/- 0.005, irrespective of the
level of oxygen deficiency. This implies that oxygen disorder plays only a
secondary role and the intrinsic Jc0 is primarily governed by the carrier
concentration in the copper oxide planes. Further support in favor of this was
found from the analysis of the in-plane resistive transitions of c-axis
oriented crystalline thin films of YBa2Cu3O7-delta (YBCO) under magnetic fields
(H) applied along the c-direction, over a wide range of doped holes. The
characteristic magnetic field (H0), linked to the vortex activation energy and
the irreversibility field, exhibits similar p-dependence as shown by Jc0(p). We
have explained these observations in terms of the doping dependent pseudogap
(PG) in the low-energy electronic energy density of states. Both the intrinsic
critical current density and the irreversibility field depend directly on the
superconducting condensation energy, which in turn is largely controlled by the
magnitude of the hole concentration dependent PG in the quasiparticle spectral
density.",2212.13339v1
2023-02-01,From a superconductor NdNiO$_2$ to a Mott multiferroic BiNiO$_2$,"Motivated by the recently discovered superconductivity in Sr-doped nickelate
oxides NdNiO$_2$, we predict a material BiNiO$_2$ that provides an opportunity
to study the intertwined ferroelectricity, metallicity, and magnetism in a
crystal with very simple atomic structures. There is a ferroelectric structural
transition from the nonpolar phase with the P4/mmm space group to the polar
phase with the P4mm space group, which is driven by the lone pair on Bi.
Calculations based on the Heyd-Scuseria-Ernzerhof hybrid density functional
reveal that both the nonmagnetic and ferromagnetic states are metallic for
nonpolar and polar phases, while the lowest energy ground-state for polar
BiNiO$_2$ is a Hubbard Mott insulator with the G-type antiferromagnetic spin
configurations. As a ferroelectric material with an electric polarization of
0.49 C/m2, it may be possible to control the magnetic order in BiNiO$_2$ by an
applied electric field. The replacement of Nd by Bi serves as a connecting link
between a high-temperature superconductor and a Mott multiferroic. Our work
supports a route towards strongly correlated ferroelectrics.",2302.00172v1
2023-02-19,Hysteresis and training effect in the electric control of spin current in Pt/Y3Fe5O12 heterostructures,"We have reported on the hysteresis and training effect of spin current in
Pt/Y3Fe5O12 heterostructures during subsequent cycles of ionic liquid gate
voltage Vg. The inverse spin Hall effect voltage in spin pumping and spin Hall
magnetoresistance exhibit diode-like behaviors in the first half cycle of Vg
andalsoshowhysteresisinthe first cycle of Vg. Both the diode-like behavior and
the hysteresis become weak and even vanish in the second cycle of Vg due to the
training effect. The above experimental results can be well explained by the
screening charge doping model, in which the charge and the local magnetic
moment are asymmetrically distributed in the Pt layer. The applicability of
this model is further confirmed by measurements of anisotropic
magnetoresistance and ferromagnetic resonance. The diode-like behavior is
attributed to interplay between the asymmetrically distributed local magnetic
moment and the spin current relaxation in the Pt layer. The hysteresis and the
training effect arise from the incompletely reversible process between
oxidation and reduction of Pt atoms and the evolution of the surface morphology
at the ionic liquid/Pt interface under electric gating. This work provides new
insights to improve the functional performance of electrically controlled spin
current devices.",2302.09505v1
2023-04-03,Nonrelativistic and nonmagnetic control of terahertz charge currents via electrical anisotropy in RuO2 and IrO2,"Precise and ultrafast control over photo-induced charge currents across
nanoscale interfaces could lead to important applications in energy harvesting,
ultrafast electronics, and coherent terahertz sources. Recent studies have
shown that several relativistic mechanisms, including inverse spin-Hall effect,
inverse Rashba-Edelstein effect and inverse spin-orbit-torque effect, can
convert longitudinally injected spin-polarized currents from magnetic materials
to transverse charge currents, thereby harnessing these currents for terahertz
generation. However, these mechanisms typically require external magnetic
fields and suffer from low spin-polarization rates and low efficiencies of
relativistic spin-to-charge conversion. In this work, we present a novel
nonrelativistic and nonmagnetic mechanism that directly utilizes the
photo-excited high-density charge currents across the interface. We demonstrate
that the electrical anisotropy of conductive oxides RuO2 and IrO2 can
effectively deflect injected charge currents to the transverse direction,
resulting in efficient and broadband terahertz radiation. Importantly, this new
mechanism has the potential to offer much higher conversion efficiency compared
to previous methods, as conductive materials with large electrical anisotropy
are readily available, whereas further increasing the spin-Hall angle of
heavy-metal materials would be challenging. Our new findings offer exciting
possibilities for directly utilizing these photo-excited high-density currents
across metallic interfaces for ultrafast electronics and terahertz
spectroscopy.",2304.00692v1
2023-04-13,Direct experimental evidence of tunable charge transfer at the $LaNiO_{3}/CaMnO_{3}$ ferromagnetic interface,"Interfacial charge transfer in oxide heterostructures gives rise to a rich
variety of electronic and magnetic phenomena. Designing heterostructures where
one of the thin-film components exhibits a metal-insulator transition opens a
promising avenue for controlling such phenomena both statically and
dynamically. In this letter, we utilize a combination of depth-resolved soft
X-ray standing-wave and hard X-ray photoelectron spectroscopies in conjunction
with polarization-dependent X-ray absorption spectroscopy to investigate the
effects of the metal-insulator transition in $LaNiO_{3}$ on the electronic and
magnetic states at the $LaNiO_{3}/CaMnO_{3}$ interface. We report on a direct
observation of the reduced effective valence state of the interfacial Mn
cations in the metallic superlattice with an above-critical $LaNiO_{3}$
thickness (6 u.c.) due to the leakage of itinerant Ni 3d $e_{g}$ electrons into
the interfacial $CaMnO_{3}$ layer. Conversely, in an insulating superlattice
with a below-critical $LaNiO_{3}$ thickness of 2 u.c., a homogeneous effective
valence state of Mn is observed throughout the $CaMnO_{3}$ layers due to the
blockage of charge transfer across the interface. The ability to switch and
tune interfacial charge transfer enables precise control of the emergent
ferromagnetic state at the $LaNiO_{3}/CaMnO_{3}$ interface and, thus, has
far-reaching consequences on the future strategies for the design of
next-generation spintronic devices.",2304.06688v1
2023-04-14,Recent advances in La2NiMnO6 Double Perovskites for various applications; Challenges and opportunities,"Double perovskites R2NiMnO6 (R= Rare earth element) (RNMO) are a significant
class of materials owing to their Multifunctional properties with structural
modifications. In particular, multifunctional double perovskite oxides
La2NiMnO6 (LNMO) which possess both electric and magnetic orderings, chemical
flexibility, versatility, and indispensable properties like high ferromagnetic
curie temperature, high absorption rates, dielectrics, etc. have drawn a lot of
attention due their rich physics and diverse applications in various
technology. This justifies the intense research in this class of materials, and
the keen interest they are subject to both the fundamental and practical side.
In view of the demands of this material in lead-free perovskite solar cells,
photocatalytic degradation of organic dyes, clean hydrogen production, electric
tuneable devices, Fuel cells, gas sensing, and Biomedical applications, there
is a need for an overview of all the literature so far, the ongoing research
and the future prospective. This review summarised all the Physical and
Structural Properties of LNMO such as electric, magnetic, catalytic, and
dielectric properties with their underlying mechanisms. This review article
provides insight into the scope of studies in LNMO material for exploring
unexposed properties in new material research and to identify areas of future
investigation of the materials in the double perovskite family.",2304.06951v1
2023-06-16,Magneto-ionic modulation of the interlayer exchange interaction in synthetic antiferromagnets,"The electric-field control of magnetism is a highly promising and potentially
effective approach for achieving energy-efficient applications. In recent
times, there has been significant interest in the magneto-ionic effect in
synthetic antiferromagnets, primarily due to its strong potential in the
realization of high-density storage devices with ultra-low power consumption.
However, the underlying mechanism responsible for the magneto-ionic effect on
the interlayer exchange coupling (IEC) remains elusive. In this study, we have
successfully identified that the magneto-ionic control of the properties of the
top ferromagnetic layer of the synthetic antiferromagnet (SyAFM), which is in
contact with the high ion mobility oxide, plays a pivotal role in driving the
observed gate-induced changes to the IEC. Our findings provide crucial insights
into the intricate interplay between stack structure and magnetoionic-field
effect on magnetic properties in synthetic antiferromagnetic thin film systems.",2306.09888v1
2023-08-18,Magnetoresistance anomaly during the electrical triggering of a metal-insulator transition,"Phase separation naturally occurs in a variety of magnetic materials and it
often has a major impact on both electric and magnetotransport properties. In
resistive switching systems, phase separation can be created on demand by
inducing local switching, which provides an opportunity to tune the electronic
and magnetic state of the device by applying voltage. Here we explore the
magnetotransport properties in the ferromagnetic oxide (La,Sr)MnO3 (LSMO)
during the electrical triggering of an intrinsic metal-insulator transition
(MIT) that produces volatile resistive switching. This switching occurs in a
characteristic spatial pattern, i.e., the formation of an insulating barrier
perpendicular to the current flow, enabling an electrically actuated
ferromagnetic-paramagnetic-ferromagnetic phase separation. At the threshold
voltage of the MIT triggering, both anisotropic and colossal magnetoresistances
exhibit anomalies including a large increase in magnitude and a sign flip.
Computational analysis revealed that these anomalies originate from the
coupling between the switching-induced phase separation state and the intrinsic
magnetoresistance of LSMO. This work demonstrates that driving the MIT material
into an out-of-equilibrium resistive switching state provides the means to
electrically control of the magnetotransport phenomena.",2308.09260v2
2023-10-23,First Chromospheric Activity and Doppler Imaging Study of PW And Using a New Doppler Imaging Code: SpotDIPy,"Measuring coverage of dark spots on cool stars is important in understanding
how stellar magnetic activity scales with the rotation rate and convection zone
depth. In this respect, it is crucial to infer surface magnetic patterns on G
and K stars, to reveal solar-like stellar dynamos in action. Molecular bands
serve as invaluable indicators of cool spots on the surfaces of stars, as they
play a crucial role in enabling accurate assessments of the extent of spot
coverage across the stellar surface. Therefore, more reliable surface images
can be obtained considering the inversion of atomic lines with molecular bands.
In this context, we simultaneously carry out Doppler imaging (DI) using atomic
lines as well as Titanium Oxide (TiO) band profiles of PW And (K2 V) and also
investigate chromospheric activity indicators for the first time in the
literature, using the high-resolution spectra. The surface spot distribution
obtained from the inversion process represents both atomic line and TiO-band
profiles quite accurately. The chromospheric emission is also correlated with
photospheric spot coverage, except during a possible flare event during the
observations. We detect frequent flare activity, using TESS photometry. We also
introduce a new open-source, Python-based DI code SpotDIPy that allows
performing surface reconstructions of single stars using the maximum entropy
method. We test the code by comparing surface reconstruction simulations with
the extensively used DoTS code. We show that the surface brightness
distribution maps reconstructed via both codes using the same simulated data
are consistent with each other.",2310.14865v1
2024-01-24,Mesoscale self-organization of polydisperse magnetic nanoparticles at the water surface,"In this study, we investigated the self-ordering process in Langmuir films of
polydisperse iron oxide nanoparticles on a water surface, employing in-situ
X-ray scattering, surface pressure-area isotherm analysis, and Brewster angle
microscopy. X-ray reflectometry confirmed the formation of a monolayer, while
grazing incidence small-angle X-ray scattering revealed short-range lateral
correlations with a characteristic length equal to the mean particle size.
Remarkably, our findings indicated that at zero surface pressure, the particles
organized into submicrometer clusters, merging upon compression to form a
homogeneous layer. These layers were subsequently transferred to a solid
substrate using the Langmuir-Schaefer technique and further characterized via
scanning electron microscopy and polarized neutron reflectometry. Notably, our
measurements unveiled a second characteristic length in the lateral
correlations, orders of magnitude longer than the mean particle diameter, with
polydisperse particles forming circular clusters densely packed in a hexagonal
lattice. Furthermore, our evidence suggested that the lattice constant of this
mesocrystal depended on the characteristics of the particle size distribution,
specifically the mean particle size and the width of the size distribution.
Additionally, we observed internal size separation within these clusters, where
larger particles were positioned closer to the center of the cluster. Finally,
polarized neutron reflectometry measurements provided valuable insights into
the magnetization profile across the layer.",2401.13768v1
2024-01-26,Engineering strong magnetoelectricity using a hexagonal 2D material on electron-doped hexagonal LuFeO$_3$,"Cubic perovskite-structure ABO$_3$ and A$_{1-x}$A$^{\prime}$$_x$BO$_3$-type
oxides have been investigated extensively while their hexagonal-structure
versions have received minimal attention, even though they are multiferroic and
can form heterostructures with the manifold hexagonal two-dimensional
materials. Hexagonal ferrites of the form RFeO$_3$, where R is yttrium or a
rare-earth element such as Lu, Yb, etc., feature coupled ferroelectricity (FE)
and weak-ferromagnetism (wFM), exhibiting linear magnetoelectricity. Their only
drawback is weak ferromagnetism. In this paper, we employ
density-functional-theory (DFT) calculations on hexagonal LuFeO$_3$ ($h$-LFO),
targeting its magnetic ordering by electron doping,anticipating
spin-disproportionation of the Fe sublattices. Indeed, we show that
spin-disproportionation in heavily-electron-doped versions
Lu$_{1-x}$Hf$_x$FeO$_3$ ($h$-LHFO), especially for x=1/3 and 1/2, leads to
robust out-of-plane collinear ferrimagnetism that is stable at room
temperature. Furthermore, the robust ferroelectricity of $h$-LFO persists via a
Jahn-Teller metal-to-insulator transition. Finally, we construct a
$h$-LHFO/$h$-2D heterostructure, where $h$-2D stands for the FE/FM monolayer
MnSTe, and demonstrate strong magnetoelectric coupling, namely manipulation of
magnetic skyrmions in MnSTe by an external electric field through the $h$-LHFO
polarization, opening up a new realm for magnetoelectric applications.",2401.15053v1
2004-04-09,New beta-Pyrochlore Oxide Superconductor CsOs2O6,"The discovery of a new beta-pyrochlore oxide superconductor CsOs2O6 with Tc =
3.3 K is reported. It is the third superconductor in the family of
beta-pyrochlore oxides, following KOs2O6 with Tc = 9.6 K and RbOs2O6 with Tc =
6.3 K. The Tc of this series decreases with increasing the ionic radius of
alkaline metal ions, imposing negative chemical pressure upon the Os pyrochlore
lattice.",0404220v1
2006-05-11,First-Principles Modeling of Ferroelectric Oxide Nanostructures,"The aim of this Chapter is to provide an account of recent advances in the
first-principles modeling of ferroelectric oxide nanostructures. Starting from
a microscopic description of ferroelectricity in bulk materials and considering
then, successively, different kinds of nanostructures (films, multilayers,
wires, and particles), we try to identify the main trends and to provide a
coherent picture of the role of finite size effects in ferroelectric oxides.",0605299v1
2008-12-16,Electrical properties of vanadium oxide subject to hydrogen plasma treatment,"The effect of doping with hydrogen on the electrical properties of vanadium
oxide is studied. For vanadium oxide films, subject to cold hydrogen plasma
treatment, the temperature dependence of resistance with a maximum at T ~ 100 K
is observed. Also, the dependence of the a.c. resistance on frequency is
studied. A strategy for fabrication new superconducting materials is discussed.",0812.2973v1
2009-10-07,An oxide thermal rectifier,"We have experimentally demonstrated thermal rectification as bulk effect.
According to a theoretical design of a thermal rectifier, we have prepared an
oxide thermal rectifier made of two cobalt oxides with different thermal
conductivities, and have made an experimental system to detect the thermal
rectification. The rectifying coefficient of the device is found to be 1.43,
which is in good agreement with the numerical calculation.",0910.1153v1
2011-02-18,Formation and Rupture of the Nanosized Metal Filament inside Oxide Matrix,"The paper presents a model of the electrically actuated formation and rupture
of the nanosized metal filament inside oxide matrix. NiO oxide is used as an
example for this model of ReRAM operation.",1102.3840v1
2011-05-29,General considerations of the electrostatic boundary conditions in oxide heterostructures,"This is a book chapter that covers general considerations of the
electrostatic stability of oxide surfaces and interfaces.",1105.5779v1
2013-10-15,The chemical state of complex uranium oxides,"We report here the first direct observation of U(V) in uranium binary oxides
and analyze the gradual conversion of the U oxidation state in the mixed
uranium systems. Our finding clarifies previous contradicting results and
provides important input for the geological disposal of spent fuel, recycling
applications and chemistry of uranium species.",1310.4003v1
2012-06-07,Resistive and magnetoresistive properties of CrO2 pressed powders with different types of inter-granular dielectric layers,"Resistive, magnetoresistive and magnetic properties of four kinds of pressed
CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been
investigated. The particles in powders constituted of rounded particles
(diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm
and average length of 302 nm. All of the particles had a surface dielectric
shell of varying thickness and different types (such as oxyhydroxide -CrOOH or
chromium oxide Cr2O3). For all the samples at low temperatures we found
non-metallic temperature dependence of resistivity and giant negative
magnetoresistance (MR). The maximum value of MR at low temperatures (T \approx
5 K) is \approx 37% in relatively small fields (0.5 T). At higher temperatures
there was a rapid decrease of MR (up to \approx 1% / T at T \approx 200 K). The
main objective of this work was studying the influence of properties and
thickness of the intergranular dielectric layers, as well as CrO2 particle
shape, on the magnitude of the tunneling resistance and MR of the pressed
powder. The new results obtained in this study include: (1) detection at low
temperatures in powders with needle-like particles a new type of MR hysteresis,
and nonmonotonic MR behaviour with increasing magnetic field (absolute value of
the MR at first grows rather rapidly with the field, and then begins
diminishing markedly, forming a maximum), and (2) detection of non-monotonic
temperature dependence, where - a field in which the resistance in a magnetic
field has a maximum, as well as finding discrepancies in values of and
coercivity fields, (3) detection of the anisotropy of MR, depending on the
relative orientation of the transport current and the magnetic field, (4) a new
method of synthesis, to regulate the thickness of dielectric coating.",1206.1533v1
2014-02-13,A new spin-anisotropic harmonic honeycomb iridate,"The physics of Mott insulators underlies diverse phenomena ranging from high
temperature superconductivity to exotic magnetism. Although both the electron
spin and the structure of the local orbitals play a key role in this physics,
in most systems these are connected only indirectly --- via the Pauli exclusion
principle and the Coulomb interaction. Iridium-based oxides (iridates) open a
further dimension to this problem by introducing strong spin-orbit
interactions, such that the Mott physics has a strong orbital character. In the
layered honeycomb iridates this is thought to generate highly spin-anisotropic
interactions, coupling the spin orientation to a given spatial direction of
exchange and leading to strongly frustrated magnetism. The potential for new
physics emerging from such interactions has driven much scientific excitement,
most recently in the search for a new quantum spin liquid, first discussed by
Kitaev \cite{kitaev_anyons_2006}. Here we report a new iridate structure that
has the same local connectivity as the layered honeycomb, but in a
three-dimensional framework. The temperature dependence of the magnetic
susceptibility exhibits a striking reordering of the magnetic anisotropy,
giving evidence for highly spin-anisotropic exchange interactions. Furthermore,
the basic structural units of this material suggest the possibility of a new
family of structures, the `harmonic honeycomb' iridates. This compound thus
provides a unique and exciting glimpse into the physics of a new class of
strongly spin-orbit coupled Mott insulators.",1402.3254v2
2014-04-08,What constitutes a nanoswitch? A Perspective,"Progress in the last two decades has effectively integrated spintronics and
nanomagnetics into a single field, creating a new class of spin-based devices
that are now being used both to Read (R) information from magnets and to Write
(W) information onto magnets. Many other new phenomena are being investigated
for nano-electronic memory as described in Part II of this book. It seems
natural to ask whether these advances in memory devices could also translate
into a new class of logic devices.
  What makes logic devices different from memory is the need for one device to
drive another and this calls for gain, directionality and input-output
isolation as exemplified by the transistor. With this in mind we will try to
present our perspective on how W and R devices in general, spintronic or
otherwise, could be integrated into transistor-like switches that can be
interconnected to build complex circuits without external amplifiers or clocks.
We will argue that the most common switch used to implement digital logic based
on complementary metal oxide semiconductor (CMOS) transistors can be viewed as
an integrated W-R unit having an input-output asymmetry that give it gain and
directionality. Such a viewpoint is not intended to provide any insight into
the operation of CMOS switches, but rather as an aid to understanding how W and
R units based on spins and magnets can be combined to build transistor-like
switches. Next we will discuss the standard W and R units used for magnetic
memory devices and present one way to integrate them into a single unit with
the input electrically isolated from the output. But we argue that this
integrated W-R unit would not provide the key property of gain. We will then
show that the recently discovered giant spin Hall effect could be used to
construct a W-R unit with gain and suggest other possibilities for spin
switches with gain.",1404.2254v1
2014-09-29,Magnetotransport Measurements of the Surface States of Samarium Hexaboride using Corbino Structures,"The recent conjecture of a topologically-protected surface state in SmB$_6$
and the verification of robust surface conduction below 4 K have prompted a
large effort to understand the surface states. Conventional Hall transport
measurements allow current to flow on all surfaces of a topological insulator,
so such measurements are influenced by contributions from multiple surfaces of
varying transport character. Instead, we study magnetotransport of SmB$_6$
using a Corbino geometry, which can directly measure the conductivity of a
single, independent surface. Both (011) and (001) crystal surfaces show a
strong negative magnetoresistance at all magnetic field angles measured. The
(011) surface has a carrier mobility of $122\text{
cm}^2/\text{V}\cdot\text{sec}$ with a carrier density of $2.5\times10^{13}
\text{ cm}^{-2}$, which are significantly smaller than indicated by Hall
transport studies. This mobility value can explain a failure so far to observe
Shubnikov-de Haas oscillations. Analysis of the angle-dependence of
conductivity on the (011) surface suggests a combination of a field-dependent
enhancement of the carrier density and a suppression of Kondo scattering from
native oxide layer magnetic moments as the likely origin of the negative
magnetoresistance. Our results also reveal a hysteretic behavior whose
magnitude depends on the magnetic field sweep rate and temperature. Although
this feature becomes smaller when the field sweep is slower, does not disappear
or saturate during our slowest sweep-rate measurements, which is much slower
than a typical magnetotransport trace. These observations cannot be explained
by quantum interference corrections such as weak anti-localization, but are
more likely due to an extrinsic magnetic effect such as the magnetocaloric
effect or glassy ordering.",1409.8199v2
2016-09-02,Semiclassical theory of anisotropic transport at LaAlO3/SrTiO3 interfaces under in-plane magnetic field,"The unconventional magnetotransport at the interface between transition-metal
oxides $LaAlO_3$ (LAO) and $SrTiO_3$ (STO) is frequently related to mobile
electrons interacting with localized magnetic moments. However nature and
properties of magnetism at this interface are not well understood so far. In
this paper, we focus on transport effects driven by spin-orbit coupling and
intentionally neglect possible strong correlations. The electrical resistivity
tensor is calculated as a function of the magnitude and orientation of an
external magnetic field parallel to the interface. The semiclassical Boltzmann
equation is solved numerically for the two-dimensional system of spin-orbit
coupled electrons accelerated by an electric field and scattered by
spatially-correlated impurities. At temperatures of a few Kelvin and densities
such that the chemical potential crosses the second pair of spin-orbit split
bands, we find a strongly anisotropic modulation of the (negative)
magnetoresistance above 10 T, characterized by multiple maxima and minima away
from the crystalline axes. Along with the drop of the magnetoresistance, an
abrupt enhancement of the transverse resistivity occurs. The angular modulation
of the latter considerably deviates from a (low-field) sinusoidal dependence to
a (high-field) step-like behaviour. These peculiar features are the
consequences of the anisotropy of both (intra-band and inter-band )
scattering-amplitudes in the Brillouin zone when the relevant energy scales in
the system - chemical potential, spin-orbit interaction and Zeeman energy - are
all comparable to each other. The theory provides good qualitative agreement
with experimental data in the literature.",1609.00663v3
2018-11-01,Ordered magnetism in the intrinsically decorated $j\rm{_{eff}}$ = $\frac{1}{2}$ $α$-CoV$_{3}$O$_{8}$,"The antiferromagnetic mixed valence ternary oxide $\alpha$-CoV$_{3}$O$_{8}$
displays disorder on the Co$^{2+}$ site that is inherent to the $Ibam$ space
group. The zero field structural and dynamic properties of
$\alpha$-CoV$_{3}$O$_{8}$~have been investigated using a combination of neutron
and x-ray diffraction, DC susceptibility, and neutron spectroscopy. The low
temperature magnetic and structural properties are consistent with a random
macroscopic distribution of Co$^{2+}$ over the 16$k$ metal sites. However, by
applying the sum rules of neutron scattering we observe the collective magnetic
excitations are parameterized with an ordered Co$^{2+}$ arrangement and
critical scattering consistent with a three dimensional Ising universality
class. The low energy spectrum is well-described by Co$^{2+}$ cations coupled
$via$ a three dimensional network composed of competing ferromagnetic and
stronger antiferromagnetic superexchange within the $ab$ plane and along $c$,
respectively. While the extrapolated Weiss temperature is near zero, the 3D
dimensionality results in long range antiferromagnetic order at
$T\rm{_{N}}\sim$ 19 K. A crystal field analysis finds two bands of excitations
separated in energy at $\hbar \omega$ $\sim$ 5 meV and 25 meV, consistent with
a $j\rm{_{eff}}=\frac{1}{2}$ ground state with little mixing between spin-orbit
split Kramers doublets. A comparison of our results to the random 3D Ising
magnets and other compounds where spin-orbit coupling is present indicate that
the presence of an orbital degree of freedom, in combination with strong
crystal field effects and well-separated $j\rm{_{eff}}$ manifolds may play a
key role in making the dynamics largely insensitive to disorder.",1811.00395v2
2014-03-11,Emergent quantum phases in a frustrated J1-J2 Heisenberg model on hyperhoneycomb lattice,"We investigate possible quantum ground states as well as the classical limit
of a frustrated J1-J2 Heisenberg model on the three-dimensional (3D)
hyperhoneycomb lattice. Our study is inspired by the recent discovery of
beta-Li2IrO3, where Ir^{4+} ions form a 3D network with each lattice site being
connected to three nearest neighbors. We focus on the influence of magnetic
frustration caused by the second-nearest neighbor spin interactions. Such
interactions are likely to be significant due to large extent of 5d orbitals in
iridates or other 5d transition metal oxides. In the classical limit, the
ground state manifold is given by line degeneracies of the spiral
magnetic-order wavevectors when J2/J1\gtrsim 0.17 while the collinear stripy
order is included in the degenerate manifold when J2/J1 = 0.5. Quantum
order-by-disorder effects are studied using both the semi-classical $1/S$
expansion in the spin wave theory and Schwinger boson approach. In general,
certain coplanar spiral orders are chosen from the classical degenerate
manifold for a large fraction of the phase diagram. Nonetheless quantum
fluctuations favor the collinear stripy order over the spiral orders in an
extended parameter region around J2/J1 = 0.5, despite the spin-rotation
invariance of the underlying Hamiltonian. This is in contrast to the emergence
of stripy order in the Heisenberg-Kitaev model studied earlier on the same
lattice, where the Kitaev-type Ising interactions are important for stabilizing
the stripy order. As quantum fluctuations become stronger, U(1) and Z2 quantum
spin liquid phases are shown to arise via quantum disordering of the Neel,
stripy and spiral magnetically-ordered phases. The effects of magnetic
anisotropy and their relevance to future experiments are also discussed.",1403.2724v1
2016-11-14,Impact of strain and morphology on magnetic properties of Fe$_3$O$_4$/NiO bilayers grown on Nb:SrTiO$_3$(001) and MgO(001),"We present a comparative study on the morphology and structural as well as
magnetic properties of crystalline Fe$_3$O$_4$/NiO bilayers grown on both
MgO(001) and SrTiO$_3$(001) substrates by reactive molecular beam epitaxy.
These structures are investigated by means of x-ray photoelectron spectroscopy,
low energy electron diffraction, x-ray reflectivity and diffraction as well as
vibrating sample magnetometry. While the lattice mismatch of NiO grown on
MgO(001) is only 0.8%, it is exposed to a lateral lattice mismatch of -6.9% if
grown on SrTiO$_3$. In the case of Fe$_3$O$_4$, the misfit strain on MgO(001)
and SrTiO$_3$(001) amounts to 0.3% and -7.5%, respectively. To clarify the
relaxation process of the bilayer system, the film thicknesses of the magnetite
and nickel oxide films have been varied between 5 and 20nm. While NiO films are
well ordered on both substrates, Fe$_3$O$_4$ films grown on NiO/SrTiO$_3$
exhibit a higher surface roughness as well as lower structural ordering
compared to films grown on NiO/MgO. Further, NiO films grow pseudomorphic in
the investigated thickness range on MgO substrates without any indication of
relaxation, whereas on SrTiO$_3$ the NiO films show strong strain relaxation.
Fe$_3$O$_4$ films exhibit also strong relaxation even for films of 5nm
thickness on both NiO/MgO as well as on NiO/SrTiO$_3$. The magnetite layers on
both substrates show a fourfold magnetic in-plane anisotropy with magnetic easy
axes pointing in $\left\langle100\right\rangle$ directions. The coercive field
is strongly enhanced for magnetite grown on NiO/SrTiO$_3$ due to higher density
of structural defects, compared to magnetite grown on NiO/MgO.",1611.04402v2
2008-07-09,Effects of Strain on Orbital Ordering and Magnetism at the Perovskite Oxide Interfaces: LaMnO$_3$/SrMnO$_3$,"We study how strain affects orbital ordering and magnetism at the interface
between SrMnO$_3$ and LaMnO$_3$ from density-functional calculations and
interpret the basic results in terms of a three-site Mn-O-Mn model. Magnetic
interaction between the Mn atoms is governed by a competition between the
antiferromagnetic superexchange of the Mn t$_{2g}$ core spins and the
ferromagnetic double exchange of the itinerant e$_g$ electrons. While the core
electrons are relatively unaffected by the strain, the orbital character of the
itinerant electron is strongly affected, which in turn causes a large change in
the strength of the ferromagnetic double exchange. The epitaxial strain
produces the tetragonal distortion of the MnO$_6$ octahedron, splitting the
Mn-e$_g$ states into x$^2$-y$^2$ and 3z$^2$-1 states, with the former being
lower in energy, if the strain is tensile in the plane, and opposite if the
strain is compressive. For the case of the tensile strain, the resulting higher
occupancy of the x$^2$-y$^2$ orbital enhances the in-plane ferromagnetic double
exchange owing to the larger electron hopping in the plane, causing at the same
time a reduction of the out-of-plane double exchange. This reduction is large
enough to be overcome by antiferromagnetic superexchange, which wins to produce
a net antiferromagnetic interaction between the out-of-plane Mn atoms. For the
case of the in-plane compressive strain, the reverse happens, viz., that the
higher occupancy of the 3z$^2$-1 orbital results in the out-of-plane
ferromagnetic interaction, while the in-plane magnetic interaction remains
antiferromagnetic. Concrete density-functional results are presented for the
(LaMnO$_3$)$_1$/(SrMnO$_3$)$_1$ and (LaMnO$_3$)$_1$/(SrMnO$_3$)$_3$
superlattices for various strain conditions.",0807.1479v1
2017-06-19,A Large-Diameter Hollow-Shaft Cryogenic Motor Based on a Superconducting Magnetic Bearing for Millimeter-Wave Polarimetry,"In this paper we present the design and measured performance of a novel
cryogenic motor based on a superconducting magnetic bearing (SMB). The motor is
tailored for use in millimeter-wave half-wave plate (HWP) polarimeters, where a
HWP is rapidly rotated in front of a polarization analyzer or
polarization-sensitive detector. This polarimetry technique is commonly used in
cosmic microwave background (CMB) polarization studies. The SMB we use is
composed of fourteen yttrium barium copper oxide (YBCO) disks and a contiguous
neodymium iron boron (NdFeB) ring magnet. The motor is a hollow-shaft motor
because the HWP is ultimately installed in the rotor. The motor presented here
has a 100 mm diameter rotor aperture. However, the design can be scaled up to
rotor aperture diameters of approximately 500 mm. Our motor system is composed
of four primary subsystems: (i) the rotor assembly, which includes the NdFeB
ring magnet, (ii) the stator assembly, which includes the YBCO disks, (iii) an
incremental encoder, and (iv) the drive electronics. While the YBCO is cooling
through its superconducting transition, the rotor is held above the stator by a
novel hold and release mechanism (HRM). The encoder subsystem consists of a
custom-built encoder disk read out by two fiber optic readout sensors. For the
demonstration described in this paper, we ran the motor at 50 K and tested
rotation frequencies up to approximately 10 Hz. The feedback system was able to
stabilize the the rotation speed to approximately 0.4%, and the measured rotor
orientation angle uncertainty is less than 0.15 deg. Lower temperature
operation will require additional development activities, which we will
discuss.",1706.05963v3
2020-12-08,Large magneto-optical effect and magnetic anisotropy energy in two-dimensional metallic ferromagnet Fe$_3$GeTe$_2$,"Few layers Fe$_3$GeTe$_2$ is currently the only atomically thin ferromagnetic
metal, and thus has drawn huge attention in the field of two-dimensional (2D)
magnetism. In this paper, we perform a systematic first principle study on the
electronic structure, magnetic anisotropy energy (MAE), and magneto-optical
(MO) effects in monolayer (ML), bilayer (BL) and trilayer (TL) as well as bulk
Fe$_3$GeTe$_2$. All the considered structures of Fe$_3$GeTe$_2$ are predicted
to have large MAE of order $\sim$3.0 meV/f.u., being larger than reported 2D
ferromagnetic semiconductors Cr$_2$Ge$_2$Te$_6$ and CrI$_3$ and also being
comparable to that of FePt which has the largest MAE among the transition metal
alloys. This large MAE thus stabilizes the long range ferromagnetic order down
to atomically thin layers and also suggests promising applications of 2D
Fe$_3$GeTe$_2$ in high density data storage. Furthermore, the calculated
magneto-optical spectra show large magnetic circular dichroism, thus resulting
in large MO Kerr rotation and Faraday rotation angles. In visible frequency
range, Kerr rotation angles up to $\sim$1.0$^\circ$ for TL Fe$_3$GeTe$_2$ are
found. Such values are larger than famous MO transition metal alloy MnBi. Also,
large Faraday rotation angles are predicted for all considered Fe$_3$GeTe$_2$
structures. In particular, ML Fe$_3$GeTe$_2$ has a Faraday rotation angle of
-156$^\circ$/$\mu m$, which is three times larger than famous MO oxide
Bi$_3$Fe$_5$O$_{12}$. These important findings are analysed in terms of the
calculated orbital-decomposed density of states and dipole selection rule
derived from the group theory. Our findings thus suggest that few layers and
bulk Fe$_3$GeTe$_2$ are promising MO materials and could be widely applied to
nano MO devices in the future.",2012.04285v2
2018-12-20,Single-spin qubits in isotopically enriched silicon at low magnetic field,"Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or
above to enable quantum state readout via spin-dependent-tunnelling. This
requires demanding microwave engineering for coherent spin resonance control
and significant on-chip real estate for electron reservoirs, both of which
limit the prospects for large scale multi-qubit systems. Alternatively,
singlet-triplet (ST) readout enables high-fidelity spin-state measurements in
much lower magnetic fields, without the need for reservoirs. Here, we
demonstrate low-field operation of metal-oxide-silicon (MOS) quantum dot qubits
by combining coherent single-spin control with high-fidelity, single-shot,
Pauli-spin-blockade-based ST readout. We discover that the qubits decohere
faster at low magnetic fields with $T_{2}^{Rabi}=18.6$~$\mu$s and
$T_2^*=1.4$~$\mu$s at 150~mT. Their coherence is limited by spin flips of
residual $^{29}$Si nuclei in the isotopically enriched $^{28}$Si host material,
which occur more frequently at lower fields. Our finding indicates that new
trade-offs will be required to ensure the frequency stabilization of spin
qubits and highlights the importance of isotopic enrichment of device
substrates for the realization of a scalable silicon-based quantum processor.",1812.08347v5
2020-06-23,Electron doping of the layered nickelate La$_4$Ni$_3$O$_{10}$ by aluminum substitution: A combined experimental and DFT study,"The physical properties of La$_4$Ni$_3$O$_{10}$ with a 2D-like
Ruddlesden-Popper-type crystal structure are extraordinarily dependent on
temperature and chemical substitution. By introducing Al$^{3+}$ atoms ($x$)
randomly at the Ni-sites, the average oxidation state for the two
non-equivalent Ni-cations is tuned and adopt values below the average of +2.67
in La$_4$Ni$_3$O$_{10}$. La$_4$Ni$_{3-x}$Al$_x$O$_{10}$ is a solid solution for
$x=0.00$ to 1.00, and are prepared by the citric acid method. The samples adopt
a slightly distorted monoclinic structure (P21/a), evidenced by peak broadening
of the (117) reflection. We report on a remarkable effect on the electronic
properties induced by tiny amounts of homogeneously distributed Al-cations,
with clear correspondence between resistivity, magnetization, diffraction, and
DFT data. DFT shows that electronically there is no significant difference
between the non-equivalent Ni atoms and no tendency towards any
Ni$^{3+}$/Ni$^{2+}$ charge ordering. The electron doping via Al-substitution
has a profound effect on electric and magnetic properties. The resistivity
changes from metallic to semiconducting with increasing band-gap at higher
Al-levels, consistent with results from DFT. The metal-to-metal transition
reported for La$_4$Ni$_3$O$_{10}$, which is often interpreted as a charge
density wave, is maintained until $x = 0.15$ Al-level. However, the temperature
characteristics of the resistivity change already at very low Al-levels (below
0.03). A coupling of the metal-to-metal transition to the lattice is evidenced
by an anomaly in the unit cell dimensions. No long-range magnetic order is
detected by powder neutron diffraction. The introduction of the non-magnetic
Al$^{3+}$ changes the Ni$^{3+}$/Ni$^{2+}$ ratio and is likely to block
double-exchange pathways by means of -Ni-O-Al-O-Ni- fragments into the network
of corner shared octahedra with the emergence of possible short-range order in
ferromagnetic like islands.",2006.12854v1
2021-04-23,Roadmap of spin-orbit torques,"Spin-orbit torque (SOT) is an emerging technology that enables the efficient
manipulation of spintronic devices. The initial processes of interest in SOTs
involved electric fields, spin-orbit coupling, conduction electron spins and
magnetization. More recently interest has grown to include a variety of other
processes that include phonons, magnons, or heat. Over the past decade, many
materials have been explored to achieve a larger SOT efficiency. Recently,
holistic design to maximize the performance of SOT devices has extended
material research from a nonmagnetic layer to a magnetic layer. The rapid
development of SOT has spurred a variety of SOT-based applications. In this
Roadmap paper, we first review the theories of SOTs by introducing the various
mechanisms thought to generate or control SOTs, such as the spin Hall effect,
the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients,
magnons, and strain effects. Then, we discuss the materials that enable these
effects, including metals, metallic alloys, topological insulators,
two-dimensional materials, and complex oxides. We also discuss the important
roles in SOT devices of different types of magnetic layers. Afterward, we
discuss device applications utilizing SOTs. We discuss and compare
three-terminal and two-terminal SOT-magnetoresistive random-access memories
(MRAMs); we mention various schemes to eliminate the need for an external
field. We provide technological application considerations for SOT-MRAM and
give perspectives on SOT-based neuromorphic devices and circuits. In addition
to SOT-MRAM, we present SOT-based spintronic terahertz generators,
nano-oscillators, and domain wall and skyrmion racetrack memories. This paper
aims to achieve a comprehensive review of SOT theory, materials, and
applications, guiding future SOT development in both the academic and
industrial sectors.",2104.11459v2
2023-03-03,Comparative study of magnetocaloric properties for Gd$^{3+}$ compounds with different frustrated lattice geometries,"As materials with suppressed ordering temperatures and enhanced ground state
entropies, frustrated magnetic oxides are ideal candidates for cryogenic
magnetocaloric refrigeration. While previous materials design has focused on
tuning the magnetic moments, their interactions, and density of moments on the
lattice, there has been relatively little attention to frustrated lattices.
Prior theoretical work has shown that the magnetocaloric cooling rate at the
saturation field is proportional to a macroscopic number of soft mode
excitations that arise due to the classical ground state degeneracy. The number
of these modes is directly determined by the geometry of the frustrating
lattice. For corner-sharing geometries, the pyrochlore has 50\% more modes than
the garnet and kagome lattices, whereas the edge-sharing \emph{fcc} has only a
subextensive number of soft modes. Here, we study the role of soft modes in the
magnetocaloric effect of four large-spin Gd$^{3+}$ ($L=0$, $J=S=7/2$)
Heisenberg antiferromagnets on a kagome, garnet, pyrochlore, and \emph{fcc}
lattice. By comparing measurements of the magnetic entropy change $\Delta S_m$
of these materials at fields up to $9$~T with predictions using mean-field
theory and Monte Carlo simulations, we are able to understand the relative
importance of spin correlations and quantization effects. We observe that
tuning the value of the nearest neighbor coupling has a more dominant
contribution to the magnetocaloric entropy change in the liquid-He cooling
regime ($2$-$20$~K), rather than tuning the number of soft mode excitations.
Our results inform future materials design in terms of dimensionality, degree
of magnetic frustration, and lattice geometry.",2303.01773v1
2023-08-22,"Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: a comprehensive stoichiometric determination","Iron manganese trioxide (Fe0.25Mn0.75)2O3 nanocrystals were synthesized by
the sol-gel method. The 80 K Mossbauer spectrum was well-fitted using two
doublets representing the 8b and 24d crystallographic sites of the
(FexMn1-x)2O3 phase and two weak extra sextets which were attributed to
crystalline and amorphous hematite. Our findings showed formation of a bixbyite
primary phase. The Raman spectrum exhibits six Raman active modes, typical of
(Fe,Mn)2O3, and two extra Raman modes associated with the secondary hematite
phase. X-ray photoelectron spectroscopy analysis confirmed the presence of
oxygen vacancy onto the (FexMn1-x)2O3 particle surface, with varying oxidation
states. X-band magnetic resonance data revealed a single broad resonance line
in the whole temperature range (3.8 K - 300 K). The temperature dependence of
both resonance field and resonance linewidth shows a remarkable change in the
range of 40 - 50 K, herein credited to surface spin glass behavior. The model
picture used assumes (FexMn1-x)2O3 nanoparticles with a core-shell structure.
Results indicate that below about 50 K the spin system of shell reveals a
paramagnetic to spin glass-like transition upon cooling, with a critical
temperature estimated at 43 K. In the higher temperature range, the
superparamagnetic hematite (secondary) phase contributes remarkably to the
temperature dependence of the resonance linewidth. Zero-field-cooled (ZFC) and
fieldcooled (FC) data show strong irreversibility and a peak in the ZFC curve
at 33 K, attributed to a paramagnetic-ferrimagnetic transition of the main
phase. Hysteresis curve at 5 K shows a low coercive field of 4 kOe, with the
magnetization not reaching saturation at 70 kOe, suggesting the occurrence of a
ferrimagnetic core with a magnetic disorder at surface, characteristic of
core-shell spin-glass-like behavior.",2308.11128v2
2002-08-07,First-principles theoretical evaluation of crystalline zirconia and hafnia as gate oxides for Si microelectronics,"Parameters determining the performance of the crystalline oxides zirconia
(ZrO_2) and hafnia (HfO_2) as gate insulators in nanometric Si electronics are
estimated via ab initio calculations of the energetics, dielectric properties,
and band alignment of bulk and thin-film oxides on Si (001). With their large
dielectric constants, stable and low-formation-energy interfaces, large valence
offsets, and reasonable (though not optimal) conduction offsets (electron
injection barriers), zirconia and hafnia appear to have a considerable
potential as gate oxides for Si electronics.",0208149v1
2003-01-07,Transient-Enhanced Surface Diffusion on Native-Oxide-Covered Si(001) Nano-Structures during Vacuum Annealing,"We report on the transient-enhanced shape transformation of nano-structured
Si(001) surfaces upon in vacuo annealing at relatively low temperatures of
1175K - 1225K for a few minutes. We find dramatic surface mass transport
concomitant with the development of low-energy facets on surfaces that are
covered by native oxide. The enhanced surface mass transport ceases after the
oxide is completely desorbed, and it is also not observed on surfaces where the
native oxide had been removed by HF before annealing.",0301074v1
2005-04-11,Ab-initio simulations on growth and interface properties of epitaxial oxides on silicon,"The replacement of SiO2 by so-called high-k oxides is one of the major
challenges for the semiconductor industry to date. Based on electronic
structure calculations and ab-initio molecular dynamics simulations, we are
able to provide a consistent picture of the growth process of a class of
epitaxial oxides around SrO and SrTiO3. The detailed understanding of the
interfacial binding principles has also allowed us to propose a way to engineer
the band-offsets between the oxide and the silicon substrate.",0504256v1
2008-04-04,Modeling of graphite oxide,"Based on density functional calculations, optimized structures of graphite
oxide are found for various coverage by oxygen and hydroxyl groups, as well as
their ratio corresponding to the minimum of total energy. The model proposed
describes well known experimental results. In particular, it explains why it is
so difficult to reduce the graphite oxide up to pure graphene. Evolution of the
electronic structure of graphite oxide with the coverage change is
investigated.",0804.0784v2
2010-09-06,Graphene produced by radiation-induced reduction of graphene oxide,"Effect of irradiation on graphene oxide by sunlight, UV light and KrF excimer
laser has been investigated in detail. Both sunlight and ultraviolet light
reduce graphene oxide well after prolonged irradiation, but laser irradiation
produces graphene with negligible oxygen functionalities within a short time.
Laser irradiation is also useful for one-step synthesis of metal particle
decorated graphene. Laser irradiation of graphene oxide appears to be an
efficient procedure for large-scale synthesis of graphene.",1009.1028v2
2011-07-13,High-temperature oxide thermoelectrics,"We have evaluated the power factor of transition metal oxides at high
temperatures using the Heikes formula and the Ioffe-Regel conductivity. The
evaluated power factor is found to be nearly independent of carrier
concentration in a wide range of doping, and well explains the experimental
data for cobalt oxides. This suggests that the same power factor can be
obtained with a thermopower larger than $2k_B/e$, and also suggests a
reasonably high value of the dimensionless figure of merit $ZT$. We propose an
oxide thermoelectric power generator by using materials having a thermopower
larger than 300 $\mu$V/K.",1107.2530v1
2012-12-03,Formation enthalpy of BaCe0.7Nd0.2In0.1O2.85,"In this paper for the first time we synthesized the compound
BaCe0.7Nd0.2In0.1O2.85 by solid-state reaction. The phase has orthorhombic
structure (space group Pmcn). We also measured the standard formation
enthalpies of BaCe0.7Nd0.2In0.1O2.85 by solution calorimetry in 1 M HCl with
0.1 M KI. We determined the stability of Nd(In)-doped barium cerate with
respect to mixtures of binary oxides. On the basis of these data we established
that above-mentioned mixed oxide is thermodynamically stable with respect to
their decomposition into binary oxides at room temperatures. We also
established that BaCe0.7Nd0.2In0.1O2.85 oxide is thermodynamically favoured
than BaCe0.8Nd0.2O2.9.",1212.0344v1
2013-01-15,Massive production of graphene oxide from expanded graphite,"In a deviation from the conventional Hummers method, a spontaneous expansion
approach was introduced with expanded graphite as the precursors. The
intercalating agent (H2SO4) was able to penetrate into the expanded graphite;
this had further expanded the graphite and as a result, a foam-like
intermediate was produced. The foam-like graphite was more easily oxidized in
reaction with the oxidant (KMnO4) to form graphene oxide (GO). Fully exfoliated
GO was obtained with expanded graphite having the median diameter ~ 15 {\mu}m
as the precursors. This procedure was much safer and productive in scalable
applications than the conventional Hummers methods.",1301.3253v1
2013-03-18,Exploring Morphology-Activity Relationships: Ab Initio Wulff Construction for RuO2 Nanoparticles under Oxidizing Conditions,"We present a density-functional theory based Wulff construction of the
equilibrium shape of RuO2 particles in an oxygen environment. The obtained
intricate variations of the crystal habit with the oxygen chemical potential
allow for a detailed discussion of the dependence on the oxidizing pretreatment
observed in recent powder catalyst studies. The analysis specifically indicates
an incomplete particle shape equilibration in previously employed low
temperature calcination. Equilibrated particles could be active CO oxidation
catalysts with long-term stability in oxidizing feed and then represent an
interesting alternative to the previously suggested core-shell concept.",1303.4203v1
2013-05-24,Interatomic potential for the calculation of barrier distributions in amorphous oxides,"Amorphous oxides are important for implants, optics, and gate insulators.
Understanding the effects of oxide doping is crucial to optimize performance.
Here we report energy barrier distributions for amorphous tantala and doped
oxides using a new set of computationally efficient, two-body potentials that
reproduce the structural properties of the samples. The distributions can be
directly compared to experiment and used to calculate physical quantities such
as internal friction.",1305.5821v1
2013-07-30,Synthesis of Self-assembled Iron Silicon Oxide Nanowires onto Single-crystalline Si(100),"Iron silicon oxide nanowire has been synthesized by putting single
crystalline Si(100) wafer into ammonium iron sulfate, hydrogen peroxide, and
triethylamine solution heated to from 70 to 100 degree in the air. The prepared
iron silicon oxide nanowires with diameters of about 10nm (onto non etched
Si(100) wafer) and about 75nm(onto etched Si(100) wafer) and their self
assembles were characterized. The possible mechanism that accounted for the
formation of iron silicon oxide nanowire is suggested based on experimental
evidence.",1307.7783v1
2015-02-11,Excited States at Interfaces of a Metal-Supported Ultrathin Oxide Film,"We report layer-resolved measurements of the \textit{unoccupied} electronic
structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states
at the metal/oxide interface, the oxide band gap as well as a surface core
exciton involving an image-potential state of the vacuum are revealed through
resonant Auger spectroscopy of the Mg $KL_{23}L_{23}$ Auger transition. Our
results demonstrate how to obtain new insights on \textit{empty} states at
interfaces of metal-supported ultrathin oxide films.",1502.03227v3
2016-03-07,Flexible Metal Oxide/Graphene Oxide Hybrid Neuromorphic Devices on Flexible Conducting Graphene Substrates,"Flexible metal oxide/graphene oxide hybrid multi-gate neuron transistors were
fabricated on flexible graphene substrates. Dendritic integrations in both
spatial and temporal modes were successfully emulated, and spatiotemporal
correlated logics were obtained. A proof-of-principle visual system model for
emulating lobula giant motion detector neuron was investigated. Our results are
of great interest for flexible neuromorphic cognitive systems.",1609.00032v1
2016-10-30,On Static Dielectric Response of Microcomposites of the Type Ferrolastics-Dielectrics For Application in Solid Oxide Fuel Cells (SOFC),"We describe the static dielectric response of ferroelastic-dielectric
microcomposites. Dependence on temperature, pressure and concentration is
considered for temperatures in the paraelastic transition. In recent years
there has been considerable interest in perovskite oxides for application in
solid oxide fuel cells (SOFC), exhaust gas sensors in automobiles, membranes
for separation processes and as catalysts, which are of the ferroeleastic
nature, f.e. of the ($ LaSrCoO_{3}$) type. Ferroelastic-dielectric
microcomposites and measurement of their properties may improve properties of
perovskite oxides for these applications.",1610.09617v1
2020-07-29,Order-Disorder Behavior at Thin Film Oxide Interfaces,"Order-disorder processes fundamentally determine the structure and properties
of many important oxide systems for energy and computing applications. While
these processes have been intensively studied in bulk materials, they are less
investigated and understood for nanostructured oxides in highly non-equilibrium
conditions. These systems can now be realized through a range of deposition
techniques and probed at exceptional spatial and chemical resolution, leading
to a greater focus on interface dynamics. Here we survey a selection of recent
studies of order-disorder behavior at thin film oxide interfaces, with a
particular emphasis on the emergence of order during synthesis and disorder in
extreme irradiation environments. We summarize key trends and identify
directions for future study in this growing research area.",2007.15136v1
2010-05-26,Substrate coherency-driven octahedral rotations in perovskite oxide films,"We perform first-principles density functional calculations to explore the
role of substrate proximity effects on the octahedral rotation patterns in
perovskite oxide superlattices. With cubic perovskite SrFeO$_3$ as our model
film and tetragonal SrTiO$_3$ as the substrate, we show that in most cases the
substrate octahedral rotation patterns propagate into the film across the
heterointerface. We also identify elastic boundary conditions for which the
enforced structural coherence induces atomic displacement patterns that are not
found in the bulk phase diagram of either individual constituent. We suggest
that such substrate coherency-induced octahedral texturing of thin film oxides
is a promising approach for tuning the electronic structure of functional oxide
thin films.",1005.4835v1
2016-11-08,Reduced Graphene Oxide and Its Natural Counterpart Shungite Carbon,"Large variety of structure and chemical-composition of reduced graphene oxide
(RGO) is explained from a quantum-chemical standpoint. The related molecular
theory of graphene oxide, supported by large experience gained by the modern
graphene science, has led the foundation of the concept of a multi-stage
graphene oxide reduction. This microscopic approach has found a definite
confirmation when analyzing the available empirical data concerning both
synthetic and natural RGO products, the latter in view of shungite carbon,
suggesting the atomic-microscopic model for its structure.",1611.02696v1
2016-08-31,Spontaneous dehydrogenation of methanol over defect-free MgO(100) thin film deposited on molybdenum,"The dehydrogenation reaction of methanol on metal supported MgO(100) films
has been studied by employing periodic density functional calculations. As far
as we know, the dehydrogenation of single methanol molecule over inert oxide
insulators such as MgO has never been realized before without the introduction
of defects and low coordinated atoms. By depositing the very thin oxide films
on Mo substrate we have successfully obtained the dissociative state of
methanol. The dehydrogenation reaction is energetically exothermic and nearly
barrierless. The metal supported thin oxide films studied here provide a
versatile approach to enhance the activity and properties of oxides.",1608.08827v1
2017-06-19,An efficient and reliable growth method for epitaxial complex oxide films by molecular beam epitaxy,"Transition metal oxide heterostructures and interfaces host a variety of
exciting quantum phases and can be grown with atomic-scale precision by
utilising the intensity oscillations of $in$ $situ$ reflection high-energy
electron diffraction (RHEED). However, establishing a stable oscillation
pattern in the growth calibration of complex oxides films is very challenging
and time consuming. Here, we develop a substantially more efficient and
reliable growth calibration method for complex oxide films using molecular beam
epitaxy.",1706.05797v1
2017-10-25,Ordered C vacancies in titanium carbides: a correlation between crystal structure and the effects on oxidation behavior at elevated temperature,"It has been widely accepted that the introduction of titanium carbides into
titanium-based alloys can significantly enhance the oxidation resistance due to
their superior physicochemical stability at elevated temperatures. The present
study reported for the first time that the ordered C vacancies within titanium
carbides could lead to an uncommon phenomenon particularly at the very initial
stage of oxidation. The intrinsic micro-to-macro oxidation mechanisms were
systematically clarified with the aids of transmission electron microscope and
ab-initio molecular dynamics simulation.",1710.09311v1
2018-10-24,On the effect of Ti on Oxidation Behaviour of a Polycrystalline Nickel-based Superalloy,"Titanium is commonly added to nickel superalloys but has a well-documented
detrimental effect on oxidation resistance. The present work constitutes the
first atomistic-scale quantitative measurements of grain boundary and bulk
compositions in the oxide scale of a current generation polycrystalline nickel
superalloy performed through atom probe tomography. Titanium was found to be
particularly detrimental to oxide scale growth through grain boundary
diffusion.",1810.10444v1
2021-01-19,High temperature oxidation behavior of disordered (Ti0.5Zr0.5)2AlC MAX phase via a Machine Learning-Augmented DFT Approach,"The Zr-based MAX phases have attracted considerable attention for their
outstanding irradiation behavior and high neutron transparency relevant to
nuclear power generation technologies. In spite of increased understanding of
physical behavior crystalline MAX phases, the high-temperature oxidation
behavior and reaction mechanism of disordered MAX phases both from theory and
experiments are not well understood due to increased system complexity. Here,
we present a detailed comparative assessment of high-temperature
thermodynamic-stability and oxidation behavior (reaction-products and chemical
activity) of ordered Ti2AlC and disordered (Ti0.5Zr0.5)2AlC. We believe that
the new insights will enhance our understanding of oxidation process in
disordered MAX phases.",2101.07460v1
2019-01-27,A simple INDIUM TIN OXIDE/glass DRA,"A novel Dielectric Resonator Antenna, simply made of INDIUM TIN OXIDE coated
glass slides placed on a microstrip transmission line, for communication
applications is presented. Changes in the bandwidth and gain of the antenna are
observed by modifying the dimensions of the INDIUM TIN OXIDE coated glass
slides. Changes in gain, directivity and reflection coefficient are observed. A
parametric study is conducted on the size of the DRA to understand the effect
on bandwidth, reflection coefficient and gain.",1901.09340v1
2021-12-23,Metal Oxide Nanoparticles and Their Applications: A Report,"Herein, we report a brief introduction of metal oxide nanoparticles and their
diverse applications in different scientific and medical fields. This report
will be updated frequently to give a complete review in similar fields of
nanotechnology. In the present version of the report, an introduction to
nanotechnology and nanomaterials with some synthesis routes (such as
Hydrothermal synthesis and Sol-Gel synthesis etc.) to prepare the metal oxide
nanoparticles is given. In this version we have primarily included the basic
introduction of application of metal oxide nanoparticles in the fields of
biomedical, resistive switching and photovoltaic etc.",2201.04938v1
2023-04-13,Probing magnetic ordering in air stable iron-rich van der Waals minerals,"In the rapidly expanding field of two-dimensional materials, magnetic
monolayers show great promise for the future applications in nanoelectronics,
data storage, and sensing. The research in intrinsically magnetic
two-dimensional materials mainly focuses on synthetic iodide and telluride
based compounds, which inherently suffer from the lack of ambient stability. So
far, naturally occurring layered magnetic materials have been vastly
overlooked. These minerals offer a unique opportunity to explore air-stable
complex layered systems with high concentration of local moment bearing ions.
We demonstrate magnetic ordering in iron-rich two-dimensional phyllosilicates,
focusing on mineral species of minnesotaite, annite, and biotite. These are
naturally occurring van der Waals magnetic materials which integrate local
moment baring ions of iron via magnesium/aluminium substitution in their
octahedral sites. Due to self-inherent capping by silicate/aluminate
tetrahedral groups, ultra-thin layers are air-stable. Chemical
characterization, quantitative elemental analysis, and iron oxidation states
were determined via Raman spectroscopy, wavelength disperse X-ray spectroscopy,
X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy.
Superconducting quantum interference device magnetometry measurements were
performed to examine the magnetic ordering. These layered materials exhibit
paramagnetic or superparamagnetic characteristics at room temperature. At low
temperature ferrimagnetic or antiferromagnetic ordering occurs, with the
critical ordering temperature of 38.7 K for minnesotaite, 36.1 K for annite,
and 4.9 K for biotite. In-field magnetic force microscopy on iron bearing
phyllosilicates confirmed the paramagnetic response at room temperature,
present down to monolayers.",2304.06533v1
2021-04-28,Graphene oxide doped ethanol droplet combustion: Ignition delay and contribution of atomization to burning rate,"Effects of graphene oxide nanomaterials addition and oxidation level on
ignition delay and burning rate of ethanol droplets are experimentally
investigated. Three graphene oxide samples are synthesized and characterized.
Separate high-speed OH* chemiluminescence and high-speed shadowgraphy images
are collected. The results suggest that increasing the loading concentration
from 0 to 0.1% generally increases the ignition delay, except for ethanol doped
with the highly oxidized graphene. The probability density function of the
atomized baby droplet diameter, initial projected velocity, and length of the
projected trajectory are similar for all tested conditions and independent of
the oxidation level and loading concentration of the additives. The joint
probability density function calculated for the atomization-related parameters
against one another suggests that the majority of the baby droplets feature a
relatively short lifetime, indicating they may potentially burn inside the
flame envelope. Using droplet surface regression curves versus time, the
burning rate for periods in which the atomization does not occur, and for the
periods that the atomization is present are estimated. The former burning rate
is shown to enhance by increasing the loading concentration and reducing the
oxidation level of graphene. However, it is found that a maximum increase in
the latter burning rate for both loading concentrations occurs for ethanol
doped with the graphene oxide that features maximum amount of infrared
radiation absorption. It is shown that relatively intense atomization
suppresses the mass loss. Doping ethanol with graphene oxide and increasing the
loading concentration from 0.01 to 0.1% enhances the overall burning rate, with
a maximum enhancement of 8.4% pertaining to addition of reduced oxidized
graphene oxide and for the loading concentration of 0.1%.",2104.13544v1
2022-04-29,Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach,"Silicon together with its native oxide SiO$_2$ was recognized as an
outstanding material system for the semiconductor industry in the 1950s. In
state-of-the-art device technology, SiO$_2$ is widely used as an insulator in
combination with high-$k$ dielectrics such as HfO$_2$, demanding fabrication of
ultra-thin interfacial layers. The classical standard model derived by Deal and
Grove accurately describes the oxidation of Si in a progressed stage, however,
strongly underestimates growth rates for thin oxide layers. Recent studies
report a variety of oxidation mechanisms during the growth of oxide films in
the range of \SI{10}{\angstrom} with various details still under debate. This
paper presents a first-principles based approach to theoretically assess the
thermal oxidation process of the technologically relevant Si(100) surfaceduring
this initial stage. Our investigations range from the chemisorption of single
O$_2$ molecules onto the $p(2\times2)$ reconstructed Si surface to oxidized Si
surface layers with a thickness of up to \SI{20}{\angstrom}. The initially
observed enhanced growth rate is assigned to barrierless O$_2$ chemisorption
events upon which the oxygen molecule dissociate. We present strong evidence
for an immediate amorphization of the oxide layer from the onset of oxidation.
Surface reactions dominate until the surface is saturated with oxygen and
separated from the Si substrate by a \SI{5}{\angstrom} transition region. The
saturated surface becomes inert to dissociative reactions and enables the
diffusion of molecular oxygen to the \interface interface as assumed within the
Deal-Grove model. Further oxidation of the Si substrate is then provided by
O$_2$ dissociations at the interface due to the same charge transfer process
responsible for the chemisorption at the surface.",2204.13954v2
2023-02-13,The ignition of fine iron particles in the Knudsen transition regime,"A theoretical model is considered to predict the minimum ambient gas
temperature at which fine iron particles can undergo thermal runaway--the
ignition temperature. The model accounts for Knudsen transition transport
effects, which become significant when the particle size is comparable to, or
smaller than, the molecular mean free path of the surrounding gas. Two kinetic
models for the high-temperature solid-phase oxidation of iron are analyzed. The
first model (parabolic kinetics) considers the inhibiting effect of the iron
oxide layers at the particle surface on the rate of oxidation, and a kinetic
rate independent of the gaseous oxidizer concentration. The ignition
temperature is solved as a function of particle size and initial oxide layer
thickness with an unsteady analysis considering the growth of the oxide layers.
In the small-particle limit, the thermal insulating effect of transition heat
transport can lead to a decrease of ignition temperature with decreasing
particle size. However, the presence of the oxide layer slows the reaction
kinetics and its increasing proportion in the small-particle limit can lead to
an increase of ignition temperature with decreasing particle size. This effect
is observed for sufficiently large initial oxide layer thicknesses. The
continuum transport model is shown to predict the ignition temperature of iron
particles exceeding an initial diameter of 30 $\mu$m to a difference of 3% (30
K) or less when compared to the transition transport model. The second kinetic
model (first-order kinetics) considers a porous, non-hindering oxide layer, and
a linear dependence of the kinetic rate of oxidation on the gaseous oxidizer
concentration. The ignition temperature is resolved as a function of particle
size with the transition and continuum transport models, and the differences
between the ignition characteristics predicted by the two models are discussed.",2302.06704v1
2013-04-01,A high-mobility two-dimensional electron gas at the heteroepitaxial spinel/perovskite complex oxide interface of γ-Al2O3/SrTiO3,"The discovery of two-dimensional electron gases (2DEGs) at the
heterointerface between two insulating perovskite-type oxides, such as LaAlO3
and SrTiO3, provides opportunities for a new generation of all-oxide electronic
and photonic devices. However, significant improvement of the interfacial
electron mobility beyond the current value of approximately 1,000 cm2V-1s-1 (at
low temperatures), remains a key challenge for fundamental as well as applied
research of complex oxides. Here, we present a new type of 2DEG created at the
heterointerface between SrTiO3 and a spinel {\gamma}-Al2O3 epitaxial film with
excellent quality and compatible oxygen ions sublattices. This
spinel/perovskite oxide heterointerface exhibits electron mobilities more than
one order of magnitude higher than those of perovskite/perovskite oxide
interfaces, and demonstrates unambiguous two-dimensional conduction character
as revealed by the observation of quantum magnetoresistance oscillations.
Furthermore, we find that the spinel/perovskite 2DEG results from
interface-stabilized oxygen vacancies and is confined within a layer of 0.9 nm
in proximity to the heterointerface. Our findings pave the way for studies of
mesoscopic physics with complex oxides and design of high-mobility all-oxide
electronic devices.",1304.0336v1
2014-04-16,Origin of High Temperature Oxidation Resistance of Ti-Al-Ta-N Coatings,"Alloying Ti-Al-N coatings with Ta has proven to enhance their hardness,
thermal stability, and oxidation resistance. However, especially for
arc-evaporated Ti-Al-Ta-N coatings only limited information on the detailed
influence of the elements on various properties is available. Therefore, we
have developed arc-evaporated Ti1-x-yAlxTayN coatings with various Al (x = 0.50
- 0.65) and Ta (y = 0.00 - 0.15) contents. While the thermal stability of our
coatings during annealing in inert He atmosphere increases with increasing Ta
content, best results are obtained for specific Ta-Al ratios during oxidation.
Single phase cubic Ti0.32Al0.60Ta0.08N yields a mass-gain of only ~5 % after 5
h at 950 {\deg}C in synthetic air, whereas Ti0.35Al0.65N is completely oxidized
after 15 min. This is in part based on the suppressed anatase and direct rutile
TiO2 formation at a defined Ta-Al content. Consequently, the anatase-to-rutile
transformation, generally observed for Ti1-xAlxN, is absent. This reduces the
generation of pores and cracks within the oxide scale and especially at the
nitride-oxide interface, leading to the formation of a protective rutile and
corundum based oxide scale. This is also reflected in the pronounced decrease
in activation energy for the protective scale formation from 232 kJ/mol for
Ti0.35Al0.65N down to 14.5 kJ/mol for Ti0.32Al0.60Ta0.08N. Based on our results
we can conclude that especially phase transformations within the oxide scale
need to be suppressed, as the connected volume changes lead to the formation of
cracks and pores.",1404.4345v1
2015-02-02,Efficient Electro-Optical Modulation Based on Indium Tin Oxide,"We experimentally demonstrate several electro-optical modulators based on
transparent conducting oxides. Our previous work demonstrated the modulator
structure on glass substrate with broadband bias polarity-dependent modulation.
Further exploration shows similar modulation effect of the modulator on quartz
and silicon substrate.",1502.00651v1
2015-02-22,Optimum High-k Oxide for the Best Performance of Ultra-scaled Double-Gate MOSFETs,"A widely used technique to mitigate the gate leakage in the ultra-scaled
metal oxide semiconductor field effect transistors (MOSFETs) is the use of
high-k dielectrics, which provide the same equivalent oxide thickness (EOT) as
$\rm SiO_2$, but thicker physical layers. However, using a thicker physical
dielectric for the same EOT has a negative effect on the device performance due
to the degradation of 2D electrostatics. In this letter, the effects of high-k
oxides on double-gate (DG) MOSFET with the gate length under 20 nm are studied.
We find that there is an optimum physical oxide thickness ($\rm T_{OX}$) for
each gate stack, including $\rm SiO_2$ interface layer and one high-k material.
For the same EOT, $\rm Al_2O_3$ (k=9) over 3 $\rm\AA$ $\rm SiO_2$ provides the
best performance, while for $\rm HfO_2$ (k=20) and $\rm La_2O_3$ (k=30), $\rm
SiO_2$ thicknesses should be 5 $\rm\AA$ and 7 $\rm\AA$, respectively. The
effects of using high-k oxides and gate stacks on the performance of
ultra-scaled MOSFETs are analyzed. While thin oxide thickness increases the
gate leakage, the thick oxide layer reduces the gate control on the channel.
Therefore, the physical thicknesses of gate stack should be optimized to
achieve the best performance.",1502.06178v1
2016-05-26,Design of ternary alkaline-earth metal Sn(II) oxides with potential good p-type conductivity,"Oxides with good p-type conductivity have been long sought after to achieve
high performance all-oxide optoelectronic devices. Divalent Sn(II) based oxides
are promising candidates because of their rather dispersive upper valence bands
caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known
Sn(II) oxides being p-type conductive suitable for device applications. Here,
we present via first-principles global optimization structure searches a
material design study for a hitherto unexplored Sn(II)-based system, ternary
alkaline-earth metal Sn(II) oxides in the stoichiometry of MSn2O3 (M = Mg, Ca,
Sr, Ba). We identify two stable compounds of SrSn2O3 and BaSn2O3, which can be
stabilized by Sn-rich conditions in phase stability diagrams. Their structures
follow the Zintl behaviour and consist of basic structural motifs of SnO3
tetrahedra. Unexpectedly they show distinct electronic properties with band
gaps ranging from 1.90 (BaSn2O3) to 3.15 (SrSn2O3) eV, and hole effective
masses ranging from 0.87 (BaSn2O3) to above 6.0 (SrSn2O3) m0. Further
exploration of metastable phases indicates a wide tunability of electronic
properties controlled by the details of the bonding between the basic
structural motifs. This suggests further exploration of alkaline-earth metal
Sn(II) oxides for potential applications requiring good p-type conductivity
such as transparent conductors and photovoltaic absorbers.",1605.08252v1
2017-06-30,Graphene-Complex-oxide Nanoscale Device Concepts,"The integration of graphene with complex-oxide heterostructures such as
LaAlO$_3$/SrTiO$_3$ offers the opportunity to combine the multifunctional
properties of an oxide interface with the electronic properties of graphene.
The ability to control interface conduction through graphene and understanding
how it affects the intrinsic properties of an oxide interface are critical to
the technological development of novel multifunctional devices. Here we
demonstrate several device archetypes in which electron transport at an oxide
interface is modulated using a patterned graphene top gate. Nanoscale devices
are fabricated at the oxide interface by conductive atomic force microscope
(c-AFM) lithography, and transport measurements are performed as a function of
the graphene gate voltage. Experiments are performed with devices written
adjacent to or directly underneath the graphene gate. Unique capabilities of
this approach include the ability to create highly flexible device
configurations, the ability to modulate carrier density at the oxide interface,
and the ability to control electron transport up to the
single-electron-tunneling regime, while maintaining intrinsic transport
properties of the oxide interface. Our results facilitate the design of a
variety of nanoscale devices that combine unique transport properties of these
two intimately coupled two-dimensional electron systems.",1706.10254v2
2017-09-06,Silicon-Oxide Interfaces: Structure and Electronic Properties,"The paper reviews methods used to study the electronic and structural
properties of silicon/insulator interfaces. Methodological approaches to study
the interface states and charge trapping in the oxide are considered. An
overview of archetypical structural defects of the Si/SiO2 interface is given.",1709.01917v1
2019-03-21,Doped-MoSe2 nanoflakes/3d metal oxide-hydr(oxy)oxides hybrid catalysts for pH-universal electrochemical hydrogen evolution reaction,"Clean hydrogen production through efficient and cost-effective
electrochemical water splitting is highly promising to meeting future global
energy demands. The design of Earth-abundant materials with both high activity
for hydrogen evolution reaction (HER) and electrochemical stability in both
acidic and alkaline environments summarize the outcomes needed for practical
applications. Here, we report a non-noble 3d metal Cl-chemical doping of liquid
phase exfoliated single/few-layer flakes of MoSe2 for creating MoSe2
nanoflakes/3d metal oxide-hydr(oxy)oxide hybrid HER-catalysts. We propose that
the electron-transfer from MoSe2 nanoflakes to metal cations and the chlorine
complexation-induced both neutralization, as well as the in situ formation of
metal oxide-hydr(oxy)oxides on MoSe2 nanoflake's surface, tailor the proton
affinity of the derived catalysts, increasing the number and HER-kinetic of
their active sites in both acidic and alkaline electrolytes. The
electrochemical coupling between the doped-MoSe2 nanoflakes/metal
oxide-hydr(oxy)oxide hybrids and single-walled carbon nanotubes
heterostructures further accelerates the HER process. Lastly, monolithic
stacking of multiple heterostructures is reported as a facile electrode
assembly strategy to achieve overpotential for a cathodic current density of
10mAcm-2 of 0.081V and 0.064V in 0.5M H2SO4 and 1M KOH, respectively. This
opens up new opportunities to address the current density vs. overpotential
requirements targeted in pH-universal H2 production.",1903.08947v1
2020-08-24,Bond Synergy Model for Bond Energies in Alloy Oxides,"In this work we introduce a metal-oxide bond-energy model for alloy oxides
based on pure-phase bond energies and bond synergy factors that describe the
effect of alloying on the bond energy between cations and oxygen, an important
quantity to understand formation and stability of passive films. This model is
parameterized for binary cation-alloy oxides using density-functional theory
energies and is shown to be directly transferable to multi-component alloy
oxides. We parameterized the model for alloy oxide energies with metal cations
that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo,
Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of
pure-phase bond energies in oxides and that the calculated bond energy values
give sensible results compared to common experience, including the role of Cr
as the passive-layer former in Fe-Ni-Cr alloys for corrosion applications.
Additionally, the bond synergy factors give insights into the mutual
strengthening and weakening effects of alloying on cation-oxygen bonds and can
be related to enthalpy of mixing and charge neutrality constraints. We
demonstrate how charge neutrality can be identified and achieved by the
oxidation states that the different cations assume depending on alloy
composition and the presence of defects.",2008.10172v1
2021-08-04,Comprehensive study of amorphous metal oxide and Ta$_2$O$_5$-based mixed oxide coatings for gravitational-wave detectors,"High finesse optical cavities of current interferometric gravitational-wave
detectors are significantly limited in sensitivity by laser quantum noise and
coating thermal noise. The thermal noise is associated with internal energy
dissipation in the materials that compose the test masses of the
interferometer. Our understanding of how the internal friction is linked to the
amorphous material structure is limited due to the complexity of the problem
and the lack of studies that span over a large range of materials. We present a
systematic investigation of amorphous metal oxide and Ta$_2$O$_5$-based mixed
oxide coatings to evaluate their suitability for low Brownian noise
experiments. It is shown that the mechanical loss of metal oxides is correlated
to their amorphous morphology, with continuous random network materials such as
SiO$_2$ and GeO$_2$ featuring the lowest loss angles. We evaluated different
Ta$_2$O$_5$-based mixed oxide thin films and studied the influence of the
dopant in the optical and elastic properties of the coating. We estimated the
thermal noise associated with high-reflectance multilayer stacks that employ
each of the mixed oxides as the high index material. We concluded that the
current high index material of TiO$_2$-doped Ta$_2$O$_5$ is the optimal choice
for reduced thermal noise among Ta$_2$O$_5$-based mixed oxide coatings with low
dopant concentrations.",2108.02127v1
2021-10-22,Design and realization of Ohmic and Schottky interfaces for oxide electronics,"Understanding band alignment and charge transfer at complex oxide interfaces
is critical to tailoring and utilizing their diverse functionality. Towards
this goal, we design and experimentally validate both Ohmic- and Schottky-like
charge transfers at oxide/oxide semiconductor/metal interfaces. We utilize a
method for predicting band alignment and charge transfer in ABO3 perovskites,
where previously established rules for simple semiconductors fail. The
prototypical systems chosen are the rare class of oxide metals, SrBO3 with
B=V-Ta, when interfaced with the multifaceted semiconducting oxide, SrTiO3. For
B=Nb and Ta, we confirm that a large accumulation of charge occurs in SrTiO3
due to higher energy Nb and Ta d-states relative to Ti; this gives rise to a
high mobility metallic interface, which is an ideal epitaxial oxide/oxide Ohmic
contact. On the other hand, for B=V, there is no charge transfer into the
SrTiO3 interface, which serves as a highly conductive epitaxial gate metal.
Going beyond these specific cases, this work opens the door to integrating the
vast phenomena of ABO3 perovskites into a wide range of practical devices.",2110.12032v1
2021-10-28,A Quantitative Analysis of the Ignition Characteristics of Fine Iron Particles,"Ignition of iron particles in an oxidizing environment marks the onset of a
self-sustained combustion. The objective of the current study is to
quantitatively examine the ignition characteristics of fine iron particles
governed by the kinetics of solid-phase iron oxidation. The oxidation rates are
inversely proportional to the thickness of the oxide layer and calibrated using
the experimentally measured growth of iron-oxide layers over time. Steady-state
and unsteady analysis have been performed to probe the dependence of the
critical gas temperature required to trigger a thermal runaway (namely, the
ignition temperature $T_\mathrm{ign}$) on particle size, initial thickness of
oxide layer, inert gas species, radiative heat loss, and the collective heating
effect in a suspension of particles. Both analyses indicate that
$T_\mathrm{ign}$ depends on $\delta_0$, i.e., the ratio between the initial
oxide layer thickness and particle size, regardless of the absolute size of the
particle. The unsteady analysis predicts that, for $\delta_0 \lesssim 0.003$,
$T_\mathrm{ign}$ becomes independent of $\delta_0$. Under standard conditions
in air, $T_\mathrm{ign}$ is approximately 1080 K for any particle size greater
than 5 microns. Radiative heat loss has a minor effect on $T_\mathrm{ign}$. The
collective effect of a suspension of iron particles in reducing
$T_\mathrm{ign}$ is demonstrated. The transition behavior between
kinetic-controlled and external-diffusion-controlled combustion regimes of an
ignited iron particle is systematically examined. The influences of initial
oxide-layer thickness and particle temperature on the ignition delay time,
$\tau_\mathrm{ign}$, of iron particles are parametrically probed. A $d^2$-law
scaling between $\tau_\mathrm{ign}$ and particle size is identified.",2110.15461v2
2022-01-31,Ti Passivation from a Dissipative Structure of the Oxide Layer,"For the long-standing riddle of metallic passivation, the second law of
thermodynamics helps little. But this study shows that Ti passivation layer
coming from room-temperature spontaneous oxidation possesses a dissipative
structure which naturally extends from the lattice structure of Ti matrix.
Macroscopically, its oxidation degree, oxygen content and amorphous structures
exhibit a gradient decline from its surface to its bottom. Beneath a stable
chemisorbed oxygen-metal atom monolayer, residue Ti lattice structures resemble
stones and amorphous structures composed of TiO2, Ti2O3 and TiO resemble
mortar, together they forming a heterogeneous stone-wall like structure. The
rapid formation of the stable chemisorbed monolayer passivates the outmost Ti
atoms to start Ti passivation, and subsequently a dissipative mechanism of
oxidation cracks the Ti lattice structures and thus the oxide layer is formed
and effect passivation. The solid phase formed by the open, stable,
macroscopically-ordered, non-equilibrium oxide film, which can be aptly called
""the dissipative oxidation phase"", theoretically does not end in complete
oxidation of thermodynamic stability. This study derails both the adsorption
theory of passivation and the theory of passivity film, and thus sheds new
light on the metallic passivation.",2201.12964v1
2022-12-13,On the evolution of oxidative etching of few layer graphene (FLG) in FLG /TiO$_2$ nanocomposites. Interfacial dipole signature and chemical shift in C1s X-ray photoemission spectra,"We present the effect of oxidative etching in FLG/TiO$_2$ hybrids on FLG
edges chemistry/morphology addressing also the catalytic activity of TiO$_2$
NPs. According to the XPS and TGA analysis the oxidation degree strongly
depends on TiO$_2$:FLG ratio. The preparation of two series of FLG/TiO$_2$
hybrids via sol-gel method and in-situ oxidation permitted to correctly
describe and distinguish the chemical composition, core shift and charge
distribution in C1s XPS with Tip peak as reference. Such analysis is
challenging in carbon materials due the overlapping of C1s peaks from the
sample and adventitious carbon reference. We claim the formation of interfacial
dipole as possible direct signature of charge transfer from TiO$_2$ to FLG. A
downward shift of C1s (sp$^2$C) up to 1.4 eV is measured and contributions of
non sp$^2$C are determined in the composites. The modifications related to the
oxidation are supported by TEM/SEM observations, and referred to non-catalytic
oxidation and oxidation in mechanically mixed components.
  KEYWORDS: oxidative etching, graphene edges, TiO$_2$ catalyst, interfacial
dipole, XPS, charge transfer",2212.06697v1
2023-01-25,"Bioabsorbable WE43 Mg alloy wires modified by continuous plasma-electrolytic oxidation for implant applications. Part I: processing, microstructure and mechanical properties","In our work, a novel processing strategy for the continuous fabrication and
surface modification of wires from Magnesium alloy WE43 by means of
plasma-electrolytic oxidation (PEO) is presented. In the first step, wires with
a strong basal texture and small grain size ($\approx$ 1 $\mu$m) were
manufactured by combined cold drawing and in-line stress-relief heat treatment
steps that optimized the mechanical properties (in terms of strength and
ductility) by means of annealing. In a second step, and to the best of our
knowledge for the first time ever, the wires were continuously surface-modified
with a novel plasma electrolytic oxidation process, which was able to create a
homogeneous porous oxide layer made of MgO and Mg$_3$(PO4)$_2$ on the wire
surface. While the oxide layer slightly diminished the tensile properties, the
strength of the surface-modified wires could be maintained close to 300 MPa
with a strain-to-failure $\approx$ 8\%. Furthermore, the thickness of the oxide
layer could be controlled by immersion time within the electrolytic bath and
was adjusted to realize a thicknesses of $\approx$ 8 $\mu$m, which could be
obtained in $<$ 20 s. Our experiments showed that the chemical composition,
morphology and porosity of the oxide layer could be tailored by changing
electrical parameters. The combined cold drawing and heat treatment process
with additional continuous plasma electrolytic oxidation processing can be
upscaled to produce a novel generation of bioabsorbable Mg wires with optimized
mechanical, degradation and biological performance for use in biomedical
applications.",2301.10479v1
2023-07-27,Super-tetragonal Sr4Al2O7: a versatile sacrificial layer for high-integrity freestanding oxide membranes,"Releasing the epitaxial oxide heterostructures from substrate constraints
leads to the emergence of various correlated electronic phases and paves the
way for integrations with advanced semiconductor technologies. Identifying a
suitable water-soluble sacrificial layer, compatible with the high-quality
epitaxial growth of oxide heterostructures, is currently the key to the
development of large-scale freestanding oxide membranes. In this study, we
unveil the super-tetragonal Sr4Al2O7 (SAOT) as a promising water-soluble
sacrificial layer. The distinct low-symmetric crystal structure of SAOT enables
a superior capability to sustain epitaxial strain, thus allowing for broad
tunability in lattice constants. The resultant structural coherency and
defect-free interface in perovskite ABO3/SAOT heterostructures effectively
restrain crack formations during the water-assisted release of freestanding
oxide membranes. For a variety of non-ferroelectric oxide membranes, the
crack-free areas can span up to a few millimeters in length scale. These
compelling features, combined with the inherent high-water solubility, make
SAOT a versatile and feasible sacrificial layer for producing high-quality
freestanding oxide membranes, thereby boosting their potential for innovative
oxide electronics and flexible device designs.",2307.14966v2
2003-04-08,Oxide formation at the surface of late 4d transition metals: Insights from first-principles atomistic thermodynamics,"Using density-functional theory we assess the stability of bulk and surface
oxides of the late 4d transition metals in a ``constrained equilibrium'' with a
gas phase formed of O2 and CO. While the stability range of the most stable
bulk oxide extends for ruthenium well into gas phase conditions representative
of technological CO oxidation catalysis, this is progressively less so for the
4d metals to its right in the periodic system. Surface oxides could
nevertheless still be stable under such conditions. These thermodynamic
considerations are discussed in the light of recent experiments, emphasizing
the role of (surface) oxides as the active phase of model catalysts formed from
these metals.",0304184v1
2003-11-24,Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures,"The oxidation of the Pd(100) surface at oxygen pressures in the 10^-6 to 10^3
mbar range and temperatures up to 1000 K has been studied in-situ by surface
x-ray diffraction (SXRD). The results provide direct structural information on
the phases present in the surface region and on the kinetics of the oxide
formation. Depending on the (T,p) environmental conditions we either observe a
thin sqrt(5) x sqrt(5) R27 surface oxide or the growth of a rough, poorly
ordered bulk oxide film of PdO predominantly with (001) orientation. By either
comparison to the surface phase diagram from first-principles atomistic
thermodynamics or by explicit time-resolved measurements we identify a strong
kinetic hindrance to the bulk oxide formation even at temperatures as high as
675 K.",0311541v1
2004-06-23,White Lines and 3d-Occupancy for the 3d Transition-Metal Oxides,"Electron energy-loss spectrometry was employed to measure the white lines at
the L23 absorption edges of the 3d transition-metal oxides and lithium
transition-metal oxides. The white-line ratio (L3/L2) was found to increase
between d^0 and d^5 and decrease between d^5 and d^10, consistent with previous
results for the transition metals and their oxides. The intensities of the
white lines, normalized to the post-edge background, are linear for the 3d
transition-metal oxides and lithium transition-metal oxides. An empirical
correlation between normalized white-line intensity and 3d occupancy is
established. It provides a method for measuring changes in the 3d-state
occupancy. As an example, this empirical relationship is used to measure
changes in the transition-metal valences of Li_{1-x}Ni_{0.8}Co_{0.2}O_2 in the
range of 0 < x < 0.64. In these experiments the 3d occupancy of the nickel ion
decreased upon lithium deintercalation, while the cobalt valence remained
constant.",0406561v1
2005-03-18,"Oxide nanotemplates for self-assembling ""solid"" building blocks","It is widely accepted that self-assembling building blocks is one of the
promising ways for engineering new materials. Recent years reveal substantial
progress in fabricating colloidal particles, polymer blocks and supramolecular
aggregates of organic molecules. Despite of substantial progress in molecular
self-assembly there is still a lack of simple blocks made of ""solid matter""
(e.g. metals, oxides etc.) with well-defined crystal structure and spatial
order. Here we demonstrate that ordered arrays of metal nanoclusters can be
fabricated by self-assembly on a wide range of oxide templates. These
nano-templates are produced either by depositing an alien oxide film or by
oxidizing a metal/metal oxide substrate.",0503484v2
2005-07-11,Precipitation-Redispersion of Cerium Oxide Nanoparticles with Poly(Acrylic Acid) : Towards Stable Dispersions,"We exploit a precipitation-redispersion mechanism for complexation of short
chain polyelectrolytes with cerium oxide nanoparticles to extend their
stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of
monodisperse cationic nanocrystalline particles having a hydrodynamic diameter
of 10 nm and a molecular weight 400000 gmol-1. We show that short chain
uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads
to macroscopic precipitation. As the pH is increased, the solution
spontaneously redisperses into a clear solution of single particles with an
anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide
nanosols and their hybrid polymer-inorganic complexes in solution are
investigated by static and dynamic light scattering, X-ray scattering, and by
chemical analysis. Quantitative analysis of the redispersed sol gives rise to
an estimate of 40 - 50 polymer chains per particle for stable suspension. This
amount represents 20 % of the mass of the polymer-nanoparticle complexes. This
complexation adds utility to the otherwise unstable cerium oxide dispersions by
extending the range of stability of the sols in terms of pH, ionic strength and
concentration.",0507238v2
2006-01-31,Local oxidation of Ga[Al]As heterostructures with modulated tip-sample voltages,"Nanolithography based on local oxidation with a scanning force microscope has
been performed on an undoped GaAs wafer and a Ga[Al]As heterostructure with an
undoped GaAs cap layer and a shallow two-dimensional electron gas. The oxide
growth and the resulting electronic properties of the patterned structures are
compared for constant and modulated voltage applied to the conductive tip of
the scanning force microscope. All the lithography has been performed in
non-contact mode. Modulating the applied voltage enhances the aspect ratio of
the oxide lines, which significantly strengthens the insulating properties of
the lines on GaAs. In addition, the oxidation process is found to be more
reliable and reproducible. Using this technique, a quantum point contact and a
quantum wire have been defined and the electronic stability, the confinement
potential and the electrical tunability are demonstrated to be similar to the
oxidation with constant voltage.",0601704v1
2008-11-27,Two-dimensional manganese oxide nanolayers on Pd(100): Surface phase diagram,"Two-dimensional manganese oxide layers have been grown on Pd(100) and have
been characterized by scanning tunnelling microscopy (STM), low-energy electron
diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The complex
surface phase diagram of MnOx on Pd(100) is reported, where nine different
novel Mn oxide phases have been detected as a function of the chemical
potential of oxygen mO. Three regions of the chemical potential of oxygen can
be identified, in which structurally related oxide phases are formed, often in
coexistence at the surface. The different regions of mO are reflected in the
oxidation states of the respective Mn oxide nanolayers as revealed by the Mn 2p
and O 1s XPS binding energies. The MnOx nanolayers form two-dimensional wetting
layers and it is speculated that they mediate the epitaxial growth of MnO on
Pd(100) by providing structurally graded interfaces.",0811.4555v1
2009-03-23,Modeling of autoignition and NO sensitization for the oxidation of IC engine surrogate fuels,"This paper presents an approch for modeling with one single kinetic mechanism
the chemistry of the autoignition and combustion processes inside an internal
combustion engine, as well as the chemical kinetics governing the
post-oxidation of unburned hydrocarbons in engine exhaust gases. Therefore a
new kinetic model was developed, valid over a wide range of temperatures
including the negative temperature coefficient regime. The model simulates the
autoignition and the oxidation of engine surrogate fuels composed of n-heptane,
iso-octane and toluene, which are sensitized by the presence of nitric oxides.
The new model was obtained from previously published mechanisms for the
oxidation of alkanes and toluene where the coupling reactions describing
interactions between hydrocarbons and NOx were added. The mechanism was
validated against a wide range of experimental data obtained in jet-stirred
reactors, rapid compression machines, shock tubes and homogenous charge
compression ignition engines. Flow rate and sensitivity analysis were performed
in order to explain the low temperature chemical kinetics, especially the
impact of NOx on hydrocarbon oxidation.",0903.3809v1
2009-10-14,Experimental study of the interfacial cobalt oxide in Co3O4/a-Al2O3(0001) epitaxial films,"A detailed spectroscopic and structural characterization of ultrathin cobalt
oxide films grown by O-assisted molecular beam epitaxy on a-Al2O3(0001) single
crystals is reported. The experimental results show that the cobalt oxide films
become progressively more disordered with increasing thickness, starting from
the early stages of deposition. Low energy electron diffraction patterns
suggest that the unit cell remains similar to that of a-Al2O3(0001) up to a
thickness of 17 A, while at larger thicknesses a pattern identified with that
of Co3O4(111) becomes visible. X-ray photoelectron spectroscopy reveals sudden
changes in the shape of the Co 2p lines from 3.4 to 17 A cobalt oxide
thickness, indicating the transition from an interfacial cobalt oxide layer
towards [111]-oriented Co3O4. In particular, the absence of characteristic
satellite peaks in the Co 2p lines indicates the formation of a trivalent,
octahedrally coordinated, interfacial cobalt oxide layer during the early
stages of growth, identified as the Co2O3 corundum phase.",0910.2647v1
2010-02-04,Activated O2 dissociation and formation of oxide islands on the Be(0001) surface: Another atomistic model for metal oxidation,"By simulating the dissociation of O2 molecules on the Be(0001) surface using
the first-principles molecular dynamics approach, we propose a new atomistic
model for the surface oxidation of sp metals. In our model, only the
dissociation of the first oxygen molecule needs to overcome an energy barrier,
while the subsequent oxygen molecules dissociate barrierlessly around the
adsorption area. Consequently, oxide islands form on the metal surface, and
grow up in a lateral way. We also discover that the firstly dissociated oxygen
atoms are not so mobile on the Be(0001) surface, as on the Al(111) surface. Our
atomistic model enlarges the knowledge on metal surface oxidations by perfectly
explaining the initial stage during the surface oxidation of Be, and might be
applicable to some other sp metal surfaces.",1002.0967v2
2010-11-19,Bond-specific reaction kinetics during the oxidation of (111) Si: Effect of n-type doping,"It is known that a higher concentration of free carriers leads to a higher
oxide growth rate in the thermal oxidation of silicon. However, the role of
electrons and holes in oxidation chemistry is not clear. Here, we report
real-time second-harmonic-generation data on the oxidation of H-terminated
(111)Si that reveal that high concentrations of electrons increase the chemical
reactivity of the outer-layer Si-Si back bonds relative to the Si-H up bonds.
However, the thicknesses of the natural oxides of all samples stabilize near 1
nm at room temperature, regardless of the chemical kinetics of the different
bonds.",1011.4386v1
2011-02-01,Universality of transport properties of ultra-thin oxide films,"We report low-temperature measurements of current-voltage characteristics for
highly conductive Nb/Al-AlOx-Nb junctions with thicknesses of the Al interlayer
ranging from 40 to 150 nm and ultra-thin barriers formed by diffusive oxidation
of the Al surface. In the superconducting state these devices have revealed a
strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents
across the devices, we conclude that the strong suppression of the subgap
resistance comparing with conventional tunnel junctions originates from a
universal bimodal distribution of transparencies across the Al-oxide barrier
proposed earlier by Schep and Bauer. We suggest a simple physical explanation
of its source in the nanometer-thick oxide films relating it to strong local
barrier-height fluctuations which are generated by oxygen vacancies in thin
aluminum oxide tunnel barriers formed by thermal oxidation.",1102.0139v2
2012-11-20,Full field chemical imaging of buried native sub-oxide layers on doped silicon patterns,"Fully energy-filtered X-ray photoelectron emission microscopy is used to
analyze the spatial distribution of the silicon sub-oxide structure at the
SiO2/Si interface as a function of underlying doping pattern. Using a
spectroscopic pixel-by-pixel curve fitting analysis, we obtain the sub-oxide
binding energy and intensity distributions over the full field of view. Binding
energy maps for each oxidation state are obtained with a spatial resolution of
120 nm. Within the framework of a five-layer model, the experimental data are
used to obtain quantitative maps of the sub-oxide layer thickness and also
their spatial distribution over the p-n junctions. Variations in the sub-oxide
thicknesses are found to be linked to the level and type of doping. The
procedure, which takes into account instrumental artefacts, enables the
quantitative analysis of the full 3D dataset.",1211.4724v1
2013-01-15,Oxidation of In2S3 films to synthetize In2S3(1-x)O3x thin films as a buffer layer in solar cells,"In2S3(1-x)O3x is known from preceding studies to have a bandgap varying
continuously as a function of x, the reason why this solid solution is
potentially interesting in the field of photovoltaics. In this work, we present
results on oxidation of In2S3 by heating in air atmosphere to obtain the
desired material. The oxidation is accompanied by a mass loss due to the
substitution of S by O atoms that is studied by means of thermogravimetric
analysis. It appears that the temperature region in which the oxidation occurs
is strongly dependent on the texture of deposited films. As-grown films
deposited by chemical bath deposition are subjected to nano-oxidation occurring
at lower temperature than oxidation of materials that are characterized by a
better crystallinity and larger crystallite size. X ray diffraction and
scanning electron microscopy (including EDX) were used to get information on
the compounds and the texture of films. The main conclusion of the paper opens
the perspective of practical applications for producing layers for solar cells.",1301.3467v2
2013-03-29,Adsorbate-Mediated Growth of Rare-Earth Oxides on Silicon,"Ultrathin cerium oxide films have been deposited on chlorine, gallium, and
silver passivated Si(111) by reactive molecular beam epitaxy in a comparative
study. The crystallinity of these films has been characterized by x-ray
standing waves while the oxidation state of the rare-earth oxide (REOx) films
and the chemical interface composition have been revealed by hard x-ray
photoelectron spectroscopy. The use of Cl as passivating agent results in the
epitaxial growth of highly crystalline REOx films with the RE metal in the 3+
oxidation state while effectively suppressing silicate and silicon oxide
formation at the interface. In contrast, Ga and Ag preadsorption yield films of
inferior quality, in the case of Ag of even lower crystallinity than without
passivation. Further investigations show that Cl-passivation also results in
ultrathin lanthana films of superior quality, which facilitate the growth of
well-ordered ceria on lanthana REOx multilayers.",1303.7414v1
2013-12-27,Characterization of low-temperature microwave loss of thin aluminum oxide formed by plasma oxidation,"We report on the characterization of microwave loss of thin aluminum oxide
films at low temperatures using superconducting lumped resonators. The oxide
films are fabricated using plasma oxidation of aluminum and have a thickness of
5 nm. We measure the dielectric loss versus microwave power for resonators with
frequencies in the GHz range at temperatures from 54 to 303 mK. The power and
temperature dependence of the loss is consistent with the tunneling two-level
system theory. These results are relevant to understanding decoherence in
superconducting quantum devices. The obtained oxide films are thin and robust,
making them suitable for capacitors in compact microwave resonators.",1312.7362v1
2014-09-03,Dynamics of stress p53: Nitric oxide induced transition of states and synchronization,"We study the temporal and the synchronous behaviours in p53-Mdm2 regulatory
network due to the interaction of its complex network components with the
nitric oxide molecule. In single cell process, increase in nitric oxide
concentration gives rise the transition to various p53 temporal behaviours,
namely fixed point oscillation, damped oscillation and sustain oscillation
indicating stability, weakly activated and strongly activated states. The noise
in stochastic system is found to help to reach these states much faster as
compared to deterministic case which is evident from permutation entropy
dynamics. In coupled system with nitric oxide as diffusively coupling molecule,
we found nitric oxide as strong coupling molecule within a certain range of
coupling strength \epsilon beyond which it become weak synchronizing agent. We
study these effects by using correlation like synchronization indicator \gamma
obtained from permutation entropies of the coupled system, and found five
important regimes in (\epsilon-\gamma) phase diagram, indicating
desynchronized, transition, strongly synchronized, moderately synchronized and
weakly synchronized regimes respectively. We claim that there is the
competition between the toxicity and the synchronizing role of nitric oxide
that lead the cell in different stressed conditions.",1409.1944v1
2014-09-25,Characterization of Interface Traps in SiO$_2$/SiC Structures Close to the Conduction Band by Deep-Level Transient Spectroscopy,"The effects of the oxidation atmosphere and crystal faces on the
interface-trap density was examined by using constant-capacitance deep-level
transient spectroscopy to clarify the origin of them. By comparing the DLTS
spectra of the low-mobility interfaces oxidized in a N$_2$O atmosphere with
those of the high-mobility interfaces on C-face oxidized in a wet atmosphere,
it was found that a high density of traps are commonly observed around the
energy of 0.16 eV from the edge of the conduction band ($C1$ traps) in
low-mobility interfaces irrespective of crystal faces. It was also found that
the generation and elimination of traps specific to crystal faces: (1) the $C1$
traps can be eliminated by wet oxidation only on the C-face, and (2) the $O2$
traps (0.37 eV) can be observed in the SiC/SiO$_2$ interface only on the
Si-face. The generation of $O2$ traps on the Si-face and the elimination of
$C1$ traps on the C-face by wet oxidation may be caused by the oxidation
reaction specific to the crystal faces.",1409.7170v1
2015-02-25,Porous nanostructured metal oxides synthesized through atomic layer deposition on a carbonaceous template followed by calcination,"Porous metal oxides with nano-sized features attracted intensive interest in
recent decades due to their high surface area which is essential for many
applications, e.g. Li ion batteries, photocatalysts, fuel cells and
dye-sensitized solar cells. Various approaches were so far investigated to
synthesize porous nanostructured metal oxides, including self-assembly and
template-assisted synthesis. For the latter approach, forests of carbon
nanotubes are considered as particularly promising templates, with respect to
their one dimensional nature and the resulting high surface area. In this work,
we systematically investigate the formation of porous metal oxides (Al2O3,
TiO2, V2O5 and ZnO) with different morphologies using atomic layer deposition
on multi-walled carbon nanotubes followed by post deposition calcination. X-ray
diffraction, scanning electron microscopy accompanied with X-ray energy
dispersive spectroscopy and transmission electron microscopy were used for the
investigation of morphological and structural transitions at the micro- and
nano-scale during the calcination process. The crystallization temperature and
the surface coverage of the metal oxides and the oxidation temperature of the
carbon nanotubes were found to produce significant influence on the final
morphology.",1502.07233v1
2015-02-26,"Chemical interaction, space-charge layer and molecule charging energy for metal oxide / organic interfaces","Three driving forces control the energy level alignment between
transition-metal oxides and organic materials: the chemical interaction between
the two materials, the organic electronegativity and the possible space charge
layer formed in the oxide. This is illustrated in this letter by analyzing
experimentally and theoretically a paradigmatic case, the TiO2(110) / TCNQ
interface: due to the chemical interaction between the two materials, the
organic electron affinity level is located below the Fermi energy of the
n-doped TiO2. Then, one electron is transferred from the oxide to this level
and a space charge layer is developed in the oxide inducing an important
increase in the interface dipole and in the oxide work function.",1502.07554v1
2015-04-23,Interfacial Effects on the Optical Properties of CdTe/CdS Quantum Dots,"Using a combination of continuous wave and time-resolved spectroscopy, we
study the effects of interfacial conditions on the radiative lifetimes and
photoluminescence intensities of colloidal CdTe/CdS quantum dots (QDs) embedded
in a three-dimensional nanostructured silicon (NSi) matrix. The NSi matrix was
thermally oxidized under different conditions to change the interfacial oxide
thickness. QDs embedded in a NSi matrix with ~0.5 nm of interfacial oxide
exhibited reduced photoluminescence intensity and nearly five times shorter
radiative lifetimes (~16 ns) compared to QDs immobilized within completely
oxidized, nanostructured silica (NSiO2) frameworks (~78 ns). Optical absorption
by the sub-nm oxidized NSi matrix partially lowers QD emission intensities
while non-radiative carrier recombination and phonon assisted transitions
influenced by defect sites within the oxide and NSi are believed to be the
primary factors limiting the QD exciton lifetimes in the heterostructures.",1504.06269v1
2015-08-14,In-situ Raman study of laser-induced graphene oxidation,"We present in-situ Raman measurements of laser-induced oxidation in
exfoliated single-layer graphene. By using high-power laser irradiation, we can
selectively and in a controlled way initiate the oxidation process and
investigate its evolution over time. Our results show that the laser-induced
oxidation process is divided into two separate stages, namely tensile strain
due to heating and subsequent $p$-type doping due to oxygen binding. We discuss
the temporal evolution of the $D/G$-mode ratio during oxidation and explain the
unexpected steady decrease of the defect-induced $D$ mode at long irradiation
times. Our results provide a deeper understanding of the oxidation process in
single-layer graphene and demonstrate the possibility of sub-$\mu$m patterning
of graphene by an optical method.",1508.03457v1
2015-08-19,Combinatorial approach for development of new metal oxides materials for all oxide photovoltaics,"The combinatorial approach to all oxide material and device research is based
on the synthesis of hundreds of related materials in a single experiment. This
approach requires the development of new tools to rapidly characterize these
materials libraries and new techniques to analyze the resulting data. The
research presented here is intended to make a contribution towards meeting this
demand, and thereby advance the pace of materials research. In many cases
photovoltaic determinations are well-suited for high throughput methodologies,
enabling direct quantitative analysis of properties whose implementation I
demonstrate my thesis. This thesis focuses on the development and utilization
of high throughput and combinatorial methods that have incorporated, or are
associated with, the all-oxide photovoltaic field. The development of new
absorbers often requires novel buffer layers, contact materials, and interface
engineering. The importance and contribution of the combinatorial material
science approach for the development and rapid characterization of new and
known metal oxide thin films for all oxide photovoltaics have been shown and
discussed in my thesis.",1508.04626v1
2015-09-24,Selective electrochemical generation of hydrogen peroxide from water oxidation,"Water is a life-giving source, fundamental to human existence, yet, over a
billion people lack access to clean drinking water. Present techniques for
water treatment such as piped, treated water rely on time and resource
intensive centralized solutions. In this work, we propose a decentralized
device concept that can utilize sunlight to split water into hydrogen and
hydrogen peroxide. The hydrogen peroxide can oxidize organics while the
hydrogen bubbles out. In enabling this device, we require an electrocatalyst
that can oxidize water while suppressing the thermodynamically favored oxygen
evolution and form hydrogen peroxide. Using density functional theory
calculations, we show that the free energy of adsorbed OH$^*$ can be used as a
descriptor to screen for selectivity trends between the 2e$^-$ water oxidation
to H$_2$O$_2$ and the 4e$^-$ oxidation to O$_2$. We show that materials that
bind oxygen intermediates sufficiently weakly, such as SnO$_2$, can activate
hydrogen peroxide evolution. We present a rational design principle for the
selectivity in electrochemical water oxidation and identify new material
candidates that could perform H$_2$O$_2$ evolution selectively.",1509.07444v1
2016-01-21,Patterning of high mobility electron gases at complex oxide interfaces,"Oxide interfaces provide an opportunity for electronics. However, patterning
of electron gases at complex oxide interfaces is challenging. In particular,
patterning of complex oxides while preserving a high electron mobility remains
underexplored and inhibits the study of quantum mechanical effects where
extended electron mean free paths are paramount. This letter presents an
effective patterning strategy of both the amorphous-LaAlO$_3$/SrTiO$_3$
(a-LAO/STO) and modulation-doped amorphous-
LaAlO$_3$/La$_{7/8}$Sr$_{1/8}$MnO$_3$/SrTiO$_3$ (a-LAO/LSM/STO) oxide
interfaces. Our patterning is based on selective wet etching of amorphous-LSM
(a-LSM) thin films which acts as a hard mask during subsequent depositions.
Strikingly, the patterned modulation-doped interface shows electron mobilities
up to ~8,700 cm$^2$/Vs at 2 K, which is among the highest reported values for
patterned conducting complex oxide interfaces that usually are ~1,000 cm$^2$/Vs
at 2 K.",1601.05571v1
2016-06-17,Ultra-high oxidation potential of Ti/Cu-SnO2 anodes fabricated by spray pyrolysis for wastewater treatment,"High oxidation potential indicates anodes have high oxidation power and high
current efficiency for organics oxidation. In this paper, we prepared
Ti/Cu-SnO2 anodes using spray pyrolysis method. The Ti/Cu-SnO2 anodes have an
ultra-high oxidation potential of about 2.7 V vs NHE, suitable for use in
wastewater treatment. The Ti/Cu-SnO2 anodes exhibit the preferred orientation
along (110) plane at high Cu doped concentration. First-principles calculations
suggest that work function of Cu-SnO2 increases with the Cu doping
concentration. It is obtained that the preferred (110) plane and the high work
function are responsible for the enhanced oxidation potential of Ti/Cu-SnO2
anodes.",1606.06332v1
2016-09-21,Hollow carbon sphere/metal oxide nanocomposite anodes for lithium-ion batteries,"Hollow carbon spheres (HCS) covered with metal oxide nanoparticles (SnO2 and
MnO2, respectively) were successfully synthesized and investigated regarding
their potential as anode materials for lithium-ion batteries. Raman
spectroscopy shows a high degree of graphitization for the HCS host structure.
The mesoporous nature of the nanocomposites is confirmed by
Brunauer-Emmett-Teller analysis. For both metal oxides under study, the metal
oxide functionalization of HCS yields a significant increase of electrochemical
performance. The charge capacity of HCS/SnO2 is 370 mAh/g after 45 cycles (266
mAh/g in HCS/MnO2) which clearly exceeds the value of 188 mAh/g in pristine
HCS. Remarkably, the data imply excellent long term cycling stability after 100
cycles in both cases. The results hence show that mesoporous HCS/metal oxide
nanocomposites enable exploiting the potential of metal oxide anode materials
in Lithium-ion batteries by providing a HCS host structure which is both
conductive and stable enough to accommodate big volume change effects.",1609.06523v1
2019-05-29,The effect of atomic structure on the electrical response of aluminium oxide tunnel junctions,"Many nanoelectronic devices rely on thin dielectric barriers through which
electrons tunnel. For instance, aluminium oxide barriers are used as Josephson
junctions in superconducting electronics. The reproducibility and drift of
circuit parameters in these junctions are affected by the uniformity,
morphology, and composition of the oxide barriers. To improve these circuits
the effect of the atomic structure on the electrical response of aluminium
oxide barriers must be understood. We create three-dimensional atomistic models
of aluminium oxide tunnel junctions and simulate their electronic transport
properties with the non-equilibrium Green's function formalism. Increasing the
oxide density is found to produce an exponential increase in the junction
resistance. In highly oxygen-deficient junctions we observe metallic channels
which decrease the resistance significantly. Computing the charge and current
density within the junction shows how variation in the local potential
landscape can create channels which dominate conduction. An atomistic approach
provides a better understanding of these transport processes and guides the
design of junctions for nanoelectronics applications.",1905.12214v1
2020-07-20,Expanding materials selection via transfer learning for high-temperature oxide selection,"Materials with higher operating temperatures than today's state of the art
can improve system performance in several applications and enable new
technologies. Under most scenarios, a protective oxide scale with high melting
temperatures and thermodynamic stability as well as low ionic diffusivity is
required. Thus, the design of high-temperature systems would benefit from
knowledge of these properties and related ones for all known oxides. While some
properties of interest are known for many oxides (e.g. elastic constants exist
for over 1,000 oxides), melting temperature is known for a relatively small
subset. The determination of melting temperatures is time consuming and costly,
both experimentally and computationally, thus we use data science tools to
develop predictive models from the existing data. The relatively small number
of available melting temperature values precludes the use of standard tools;
therefore, we use a multi-step approach based on sequential learning where
surrogate data from first-principles calculations is leveraged to develop
models using small datasets. We use these models to predict the desired
properties for nearly 11,000 oxides and quantify uncertainties in the space.",2007.12262v1
2017-04-23,Band alignment of metal/amorphous-oxide interface using atomic orbitals projection of plane-wave: a first principle study at the Al/a-SiO2 interface,"Amorphous insulating oxides play a significant role in the contemporary
electronic industry. Understanding the band alignment of heterogeneous
interfaces containing amorphous structures helps to better control the carrier
transport property at the interface. Classical band offset methods developed
previously line-up eigenlevels with respect to an ideal bulk reference or
vacuum level. However, the local disorder of amorphous structures makes the
bulk reference ambiguous. Therefore, classical methods cannot be applied. In
this study, we introduce a new approach based on the Linear Combination of
Atomic Orbital (LCAO) projection of wave-function to line-up bands at
metal/oxide interfaces. The LCAO projection of wave-function accounts for all
metal/oxide interface effects, such as build-in voltage, interface dipole,
virtual oxide thinning, barrier deformation, etc. Therefore, it provides
accurate band alignments. Calculations performed at an Al/amorphous-SiO2
exhibit a good agreement between existing experiments and simulation data. We
Also observed a space charge region at the interface resulting in non-linear
band bending in the oxide, which virtually decreases its thickness, hence
lowering the dielectric strength.",1704.06978v2
2018-05-15,Measurement of the Oxidation state of Fe in the ISM using X-ray Absorption Spectroscopy,"The oxidation state of iron in the interstellar medium (ISM) can provide
constraints on the processes that operated on material in the protosolar disk.
We used synchrotron-based X-ray absorption spectra of several mineral standards
and two kinds of primitive extraterrestrial materials to constrain the
oxidation state and mineralogy of the host-phase of ISM Fe as measured by X-ray
observations of Fe-L ISM absorption from the {\em Chandra X-ray Observatory}.
Given the initial oxidation state of the building blocks of the Solar System,
we explore nebular and parent-body processes that eventually led to the
remarkable diversity of oxidation states of primitive Solar System materials.
Oxidation of cometary material appears to have taken place in the nebula,
before incorporation into cometary nuclei, although the mechanism is unknown.",1805.05921v1
2008-07-22,Stress Development and Impurity Segregation during Oxidation of the Si(100) Surface,"We have studied the segregation of P and B impurities during oxidation of the
Si(100) surface by means of combined static and dynamical first-principles
simulations based on density functional theory. In the bare surface, dopants
segregate to chemically stable surface sites or to locally compressed
subsurface sites. Surface oxidation is accompanied by development of tensile
surface stress up to 2.9 N/m at a coverage of 1.5 monolayers of oxygen and by
formation of oxidised Si species with charges increasing approximately linearly
with the number of neighbouring oxygen atoms. Substitutional P and B defects
are energetically unstable within the native oxide layer, and are
preferentially located at or beneath the Si/SiOx interface. Consistently,
first-principles molecular dynamics simulations of native oxide formation on
doped surfaces reveal that dopants avoid the formation of P-O and B-O bonds,
suggesting a surface oxidation mechanism whereby impurities remain trapped at
the Si/SiOx interface. This seems to preclude a direct influence of impurities
on the surface electrostatics and, hence, on the interactions with an external
environment.",0807.3426v1
2009-12-08,The Deposition of High-Quality HfO2 on Graphene and the Effect of Remote Oxide Phonon Scattering,"We demonstrate the atomic layer deposition of high-quality HfO2 film on
graphene and report the magnitude of remote oxide phonon (ROP) scattering in
dual-oxide graphene transistors. Top gates with 30 nm HfO2 oxide layer exhibit
excellent doping capacity of greater than 1.5x10^(13)/cm^(2). The carrier
mobility in HfO2-covered graphene reaches 20,000 cm^(2)/Vs at low temperature,
which is the highest among oxide-covered graphene and compares to that of
pristine samples. The temperature-dependent resistivity exhibits the effect of
ROP scattering from both the SiO2 substrate and the HfO2 over-layer. At room
temperature, surface phonon modes of the HfO2 film centered at 54 meV dominate
and limit the carrier mobility to ~20,000 cm^(2)/Vs. Our results highlight the
important choice of oxide in graphene devices.",0912.1378v2
2012-01-04,Zinc in a +III oxidation state,"The possibility of Group 12 elements, such as Zn, Cd, and Hg existing in an
oxidation state of +III or higher and hence transforming them into transition
metals has fascinated chemists for decades. It took nearly 20 years before
experiment could confirm the theoretical prediction that Hg indeed can exist in
an oxidation state of +IV. While this unusual property of Hg is attributed to
the relativistic effects, Zn being much lighter than Hg has not been expected
to have an oxidation state higher than +II. Using density functional theory we
show that an oxidation state of +III for Zn can be realized by choosing
specific ligands with large electron affinities. We demonstrate this by a
systematic study of the interaction of Zn with F, BO2, and AuF6 ligands whose
electron affinities are progressively higher, namely, 3.4 eV, 4.5 eV, and 8.6
eV, respectively. Discovery of higher oxidation states of elements can help in
the formulation of new reactions and hence in the development of new chemistry.",1201.1014v1
2012-01-23,Effect of oxidation on the Mechanical Properties of Liquid Gallium and Eutectic Gallium-Indium,"Liquid metals exhibit remarkable mechanical properties, in particular large
surface tension and low viscosity. However, these properties are greatly
affected by oxidation when exposed to air. We measure the viscosity, surface
tension, and contact angle of gallium (Ga) and a eutectic gallium-indium alloy
(eGaIn) while controlling such oxidation by surrounding the metal with an acid
bath of variable concentration. Rheometry measurements reveal a yield stress
directly attributable to an oxide skin that obscures the intrinsic behavior of
the liquid metals. We demonstrate how the intrinsic viscosity can be obtained
with precision through a scaling technique that collapses low- and
high-Reynolds number data. Measuring surface tension with a pendant drop
method, we show that the oxide skin generates a surface stress that mimics
surface tension and develop a simple model to relate this to the yield stress
obtained from rheometry. We find that yield stress, surface tension, and
contact angle all transition from solid-like to liquid behavior at the same
critical acid concentration, thereby quantitatively confirming that the
wettability of these liquid metals is due to the oxide skin.",1201.4828v1
2015-12-06,"Anisotropy, band-to-band transitions, phonon modes, and oxidation properties of cobalt-oxide core-shell slanted columnar thin films","Highly-ordered and spatially-coherent cobalt slanted columnar thin films were
deposited by glancing angle deposition onto silicon substrates, and
subsequently oxidized by annealing at 475 $^{\circ}$C. Scanning electron
microscopy, Raman scattering, generalized ellipsometry, and density functional
theory investigations reveal shape-invariant transformation of the slanted
nanocolumns from metallic to transparent metal-oxide core-shell structures with
properties characteristic of spinel cobalt oxide. We find passivation of
Co-SCTFs yielding CoAl$_2$O$_3$ core-shell structures produced by conformal
deposition of a few nanometers of alumina using atomic layer deposition fully
prevents cobalt oxidation in ambient and from annealing up to 475 $^{\circ}$C.",1512.01860v1
2016-12-12,Revisiting Graphene Oxide Chemistry via Spatially-Resolved Electron Energy Loss Spectroscopy,"The type and distribution of oxygen functional groups in graphene oxide (GO)
and reduced graphene oxide (RGO) remain still a subject of great debate. Local
analytic techniques are required to access the chemistry of these materials at
a nanometric scale. Electron energy loss spectroscopy in a scanning
transmission electron microscope can provide the suitable resolution, but GO
and RGO are extremely sensitive to electron irradiation. In this work we employ
a dedicated experimental setup to reduce electron illumination below damage
limit. GO oxygen maps obtained at a few nanometers scale show separated domains
with different oxidation levels. The C/O ratio varies from about 4:1 to 1:1,
the latter corresponding to a complete functionalization of the graphene
flakes. In RGO the residual oxygen concentrates mostly in regions few tens
nanometers wide. Specific energy-loss near-edge structures are observed for
different oxidation levels. By combining these findings with first-principles
simulations we propose a model for the highly oxidized domains where graphene
is fully functionalized by hydroxyl groups forming a 2D-sp$^3$ carbon network
analogous to that of graphane.",1612.03594v1
2016-12-19,Three-dimensional patterning of solid microstructures through laser reduction of colloidal graphene oxide in liquid-crystalline dispersions,"Graphene materials and structures have become an essential part of modern
electronics and photovoltaics. However, despite many production methods,
applications of graphene-based structures are hindered by high costs, lack of
scalability and limitations in spatial patterning. Here we fabricate
three-dimensional functional solid microstructures of reduced graphene oxide in
a lyotropic nematic liquid crystal of graphene oxide flakes using a pulsed
near-infrared laser. This reliable, scalable approach is mask-free, does not
require special chemical reduction agents, and can be implemented at ambient
conditions starting from aqueous graphene oxide flakes. Orientational ordering
of graphene oxide flakes in self-assembled liquid-crystalline phases enables
laser patterning of complex, three-dimensional reduced graphene oxide
structures and colloidal particles, such as trefoil knots, with ""frozen""
orientational order of flakes. These structures and particles are mechanically
rigid and range from hundreds of nanometres to millimetres in size, as needed
for applications in colloids, electronics, photonics and display technology.",1612.06030v1
2019-06-05,Inverted Perovskite Photovoltaics using Flame Spray Pyrolysis Solution based CuAlO2/Cu-O Hole Selective Contact,"We present the functionalization process of a conductive and transparent
copper aluminum oxide, copper oxide alloy. The copper aluminum oxide, copper
oxide powders were developed by flame spray pyrolysis and their stabilized
dispersions were treated by sonication and centrifugation methods. We show that
when the supernatant part of the treated copper aluminum oxide, copper oxide
dispersions is used for the development of hole transporting layers the
corresponding inverted perovskite solar cells show improved functionality and
power conversion efficiency with negligible hysteresis effect.",1906.01989v1
2019-07-25,Stainless Steel Surface Structure and Initial Oxidation at Nanometric and Atomic Scales,"The durability of passivable metals and alloys is often limited by the
stability of the surface oxide film, the passive film, providing
self-protection against corrosion in aggressive environments. Improving this
stability requires to develop a deeper understanding of the surface structure
and initial surface reactivity at the nanometric or atomic scale. In this work
we applied scanning tunneling microscopy to unravel the surface structure of a
model stainless steel surface in the metallic state and its local modifications
induced by initial reaction in dioxygen gas. The results show a rich and
complex structure of the oxide-free surface with reconstructed atomic lattice
and self-organized lines of surface vacancies at equilibrium. New insight is
brought into the mechanisms of initial oxidation at steps and vacancy injection
on terraces leading to Cr-rich oxide nuclei and locally Cr-depleted terraces,
impacting the subsequent mechanism of chromium enrichment essential to the
stability of the surface oxide.",1907.10911v1
2019-10-19,Wafer-size VO2 film prepared by water-vapor oxidant,"The growth of wafer-scale and uniform monoclinic VO2 film was a challenge if
considering the multivalent vanadium atom and the various phase structures of
VO2 compound. Directly oxidizing metallic vanadium film in oxygen gas seemed to
be an easy way, while the oxidation parameters were extremely sensitive due to
the critical preparation window. Here we proposed a facile thermal oxidation by
water-vapor to produce wafer-scale VO2 films with high quality. Results
indicated that by using the water-vapor oxidant, the temperature window for VO2
growth was greatly broadened. In addition, the obtained wafer-size VO2 film
showed very uniform surface and sharp resistance change. The chemical reaction
routes with water-vapor were calculated, which favored the VO2 film growth. Our
results not only demonstrated that the water-vapor could be used as a modest
oxidizing agent, but also showed the unique advantage for large size VO2 film
preparation.",1910.08776v3
2020-01-05,Two-section reactor model for autothermal reforming of methane to synthesis gas,"A one-dimensional and stationary reactor model is presented to describe the
catalytic conversion of a gaseous hydrocarbon fuel with air and steam to
synthesis gas by autothermal reforming (ATR) and catalytic partial oxidation
(CPO). The model defines two subsequent sections in the reactor, namely an
upstream oxidation section, and a downstream reforming section. In the
oxidation section all of the oxygen is converted, with partial conversion of
the fuel. An empirical fuel utilization ratio is used to quantify which part of
the fuel is converted in the oxidation section as function of the relative
flows of air and steam. In the oxidation section, the gas temperature rapidly
increases toward the toptemperature at the intersection with the reforming
section. In this section the temperature decreases while the fuel is further
converted with water and CO2 as oxidant. For methane as fuel, simulation
results are presented and compared with experiments. For multicomponent fuels
such as natural gas and naphtha, it is described how the two-section model can
be applied.",2001.01282v1
2020-01-08,Novel hypostasis of old materials in oxide electronics: metal oxides for resistive random access memory applications,"Transition-metal oxide films, demonstrating the effects of both threshold and
nonvolatile memory resistive switching, have been recently proposed as
candidate materials for storage-class memory. In this work we describe some
experimental results on threshold switching in a number of various transition
metal (V, Ti, Fe, Nb, Mo, W, Hf, Zr, Mn, Y, and Ta) oxide films obtained by
anodic oxidation. Then, the results concerning the effects of bistable
resistive switching in MOM and MOS structures on the basis of such oxides as
V2O5, Nb2O5, and NiO are presented. It is shown that sandwich structures on the
basis of the Au/V2O5/SiO2/Si, Nb/Nb2O5/Au, and Pt/NiO/Pt can be used as memory
elements for ReRAM applications. Finally, model approximations are developed in
order to describe theoretically the effect of nonvolatile unipolar switching in
Pt NiO-Pt structures.",2001.03026v1
2020-12-12,Single-Phase Duodenary High-Entropy Fluorite/Pyrochlore Oxides with an Order-Disorder Transition,"Improved thermomechanical properties have been reported for various
high-entropy oxides containing typically five metal cations. This study further
investigates a series of duodenary (11 metals + oxygen) high-entropy oxides by
mixing different fractions of a five-cation fluorite-structured niobate and a
seven-cation pyrochlore (both containing Yb) with matching lattice constants.
Nine compositions of duodenary high-entropy oxides have been examined. All of
them exhibit single high-entropy phases of either disordered fluorite or
ordered pyrochlore structure. An order-disorder transition (ODT) is evident
with changing composition, accompanied by a reduction in thermal conductivity
(k). In comparison with the ODT criteria developed from ternary oxides, these
duodenary oxides are more prone to disorder, but the ODT is still controlled by
similar factors (but at different thresholds). Interestingly, there are abrupt
increases in Young's modulus (E) at low mixing concentrations near both
endmembers. The E/k ratios are increased, in comparison with both endmembers.
This study suggests a new route to tailor high-entropy ceramics via controlling
cation ordering vs. disordering.",2012.12866v1
2017-11-20,Atomic and electronic structures of stable linear carbon chains on Ag-nanoparticles,"In this work, we report X-ray photoelectron (XPS) and valence band (VB)
spectroscopy measurements of surfactant-free silver nanoparticles and
silver/linear carbon chains (Ag@LCC) structures prepared by pulse laser
ablation (PLA) in water. Our measurements demonstrate significant oxidation
only on the surfaces of the silver nanoparticles with many covalent
carbon-silver bonds but only negligible traces of carbon-oxygen bonds.
Theoretical modeling also provides evidence of the formation of robust
carbon-silver bonds between linear carbon chains and pure and partially
oxidized silver surfaces. A comparison of theoretical and experimental
electronic structures also provides evidence of the presence of non-oxidized
linear carbon chains on silver surfaces. To evaluate the chemical stability, we
investigated the energetics of the physical adsorption of oxidative species
(water and oxygen) and found that this adsorption is much preferrable on
oxidized or pristine silver surfaces than the adsorption of linear carbon
chains, which makes the initial step in the oxidation of LCC energetically
unfavorable.",1711.07119v1
2019-04-08,Probing the correlation between phase evolution and growth kinetics in the oxide layers of tungsten using Raman spectroscopy and EBSD,"Tungsten, a plasma-facing material for future fusion reactors, may be exposed
to air during abnormal operation or accidents. Only limited information is
available on the evolution of related oxide phases. This work addresses the
effect of substrate orientation on structural variations of tungsten oxides.
Annealing experiments in an argon-oxygen atmosphere have been conducted at T =
400 {\deg}C under varying oxygen partial pressure and oxidation time. A
combination of EBSD, Raman spectroscopy and confocal microscopy shows
preferential oxidation initially on {111} base material planes. The oxide scale
changes its phase composition dynamically, influencing the kinetics of its
growth.",1904.04392v2
2020-08-10,Interface-Confined Doubly Anisotropic Oxidation of Two-Dimensional MoS2,"Despite their importance, chemical reactions confined in a low dimensional
space are elusive and experimentally intractable. In this work, we report
doubly anisotropic, in-plane and out-of-plane, oxidation reactions of
two-dimensional crystals, by resolving interface-confined thermal oxidation of
a single and multilayer MoS2 supported on silica substrates from their
conventional surface reaction. Using optical second-harmonic generation
spectroscopy of artificially stacked multilayers, we directly proved that
crystallographically oriented triangular oxides (TOs) were formed in the
bottommost layer while triangular etch pits (TEs) were generated in the topmost
layer and that both structures were terminated with zigzag edges. The formation
of the Mo oxide layer at the interface demonstrates that O2 diffuses
efficiently through the van der Waals (vdW) gap but not MoO3, which would
otherwise sublime. The fact that TOs are several times larger than TEs
indicates that oxidation is greatly enhanced when MoS2 is in direct contact
with silica substrates, which suggests a catalytic effect. This study indicates
that the vdW-bonded interfaces are essentially open to mass transport and can
serve as a model system for investigating chemistry in low dimensional spaces.",2008.03933v1
2020-10-14,Trends of epitaxial perovskite oxide films catalyzing the oxygen evolution reaction in alkaline media,"The oxygen evolution reaction (OER) is considered a key reaction for
electrochemical energy conversion but slow kinetics hamper application in
electrolyzers, metal-air batteries and other applications that rely on
sustainable protons from water oxidation. In this review, the prospect of
epitaxial perovskite oxides for the OER at room temperature in alkaline media
is reviewed with respect to fundamental insight into systematic trends of the
activity. First, we thoroughly define the perovskite structure and its
parameter space. Then, the synthesis methods used to make electrocatalytic
epitaxial perovskite oxide are surveyed, and we classify the different kinds of
electrodes that can be assembled for electrocatalytic investigations. We
discuss the semiconductor physics of epitaxial perovskite electrodes and their
consequences for the interpretation of catalytic results. Prototypical
mechanisms of the OER are introduced and comparatively discussed. OER
investigations on epitaxial perovskite oxides are comprehensively surveyed and
selected trends are graphically highlighted. The review concludes with a short
perspective on opportunities for future electrocatalytic research on epitaxial
perovskite oxide systems.",2010.06860v1
2020-11-17,Synthetically Encapsulated \& Self-Organized Transition Metal Oxide Nano Structures inside Carbon Nanotubes as Robust Li-ion Battery Anode Materials,"We report a comprehensive study on the electrochemical performance of four
different Transition Metal Oxides encapsulated inside carbon nanotubes (CNT).
Irrespective of the type of oxide-encapsulate, all these samples exhibit
superior cyclic stability as compared to the bare-oxide. Innovative use of
camphor during sample synthesis enables precise control over the morphology of
these self-organized carbon nanotube structures, which in turn appears to play
a crucial role in the magnitude of the specific capacity. A comparative
evaluation of the electrochemical data on different samples bring forward
interesting inferences pertaining to the morphology, filling fraction of the
oxide-encapsulate, and the presence of oxide nano-particles adhering outside
the filled CNT. Our results provides useful pointers towards the optimization
of critical parameters, thus paving the way for using these synthetically
encapsulated and self-organized carbon nanotube structures as anode materials
for Li-ion batteries, and possibly other electrochemical applications.",2011.08619v1
2020-11-17,Effect of Surface Roughness on Early Stage Oxidation Behavior of Ni-Base Superalloy IN 625,"In the present work the effect of surface roughness on oxidation behavior
during the early stages of high temperature exposure of Ni-base superalloy IN
625 is described. The surface roughness was described using standard contact
profilometer as well as novel method, fractal analysis. It was found that the
different surface preparation resulted in a difference in roughness with a
parameter increase of at least one order of magnitude for the ground sample as
compared with the polished sample. The oxidation test was performed in a
horizontal tube furnace. Post exposure analyses including glow discharge
optical emission spectrometry (GD OES) and scanning electron microscopy (SEM),
which revealed that grinding lowers the oxidation kinetics of IN 625. It was
found that surface preparation influences the oxide scale composition and
morphology. The hypothesis explaining the mechanism responsible for the changes
in oxidation behavior is proposed as well.",2011.08931v1
2020-11-21,Fabrication of zinc oxide/graphene-carbon nanotubes nanocomposite with enhanced dye degradation ability,"A comparative study between zinc oxide graphene-carbon nanotubes
nanocomposite and ZnO nanoparticles was carried out to investigate their
abilities in the degradation of Rhodamine B dye. We utilized the Modified
Hummer method to prepare the graphene oxide nanosheet. Moreover,
graphene-carbon nanotubes had been synthesized from GO and multi-walled carbon
nanotubes with a hydroxyl group. The hydrothermal method was employed to
fabricate the zinc oxide graphene-carbon nanotubes nanocomposite from ZnO
nanoparticles and graphene-carbon nanotubes. During the characterization by
X-ray Diffraction (XRD), all the significant peaks of ZnO and zinc oxide
graphene-carbon nanotubes nanocomposite were found in the same phase angle. In
addition, the final nanocomposite was also characterized by Field Emission
Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray Spectroscopy
(EDS). Finally, from the dye degradation test, it was apparent that zinc oxide
graphene-carbon nanotubes nanocomposite showed superior dye removal ability
compared to the ZnO nanoparticles.",2011.10841v2
2021-05-12,Iron-silica interaction during reduction of precipitated silica-promoted iron oxides using in situ XRD and TEM,"The effect of silica-promotion on the reduction of iron oxides in hydrogen
was investigated using in situ X-ray diffraction and aberration-corrected
transmission electron microscopy to understand the mechanism of reduction and
the identity of the iron(II) silicate phase that has historically been
designated as the cause of the iron-silica interaction in such materials. In
the absence of a silica promoter the reduction of hematite to {\alpha}-Fe
proceeds via magnetite. Silica promoted amorphous iron oxide is reduced to
{\alpha}-Fe via stable magnetite and w\""ustite phases. During reduction of
silica-promoted iron oxide, Fe0 diffuses out of the amorphous silica-promoted
iron oxide matrix upon reduction from Fe2+ and coexists with an amorphous
Fe-O-Si matrix. Certain portions of w\""ustite remain difficult to reduce to
{\alpha}-Fe owing to the formation of a protective silica-containing layer
covering the remaining iron oxide regions. Given sufficient energy, this
amorphous Fe-O-Si material forms ordered, crystalline fayalite.",2105.05620v1
2021-12-11,Elucidating the Influence of Native Defects on Electrical and Optical Properties in Semiconducting Oxides: An Experimental and Theoretical Investigation,"Defect engineering using self-doping or creating vacancies in polycrystalline
oxide based materials has profound influence on optical absorption, UV photo
detection, and electrical switching. However, defects induced semiconducting
oxide devices show enhancement in photo detection and photosensitivity, and
hence still remain interesting in the field of optoelectronics. In this study,
defect engineering in semiconducting oxide materials is discussed along with
their roles in optoelectronic device-based applications. Theoretical
investigations have been done for identifying defect states by performing
first-principles electronic structure calculations, employing the
density-functional theory. Particularly, in this work, we have focused on
probing the defect-induced changes in optical and electrical processes by means
of experimental as well as computational investigations. Hence, systematic
experimental measurements of optical absorption, electrical switching, charge
density, and photocurrent in defect-rich semiconducting oxide samples have been
performed. Our results suggest that defects can lead to enhancement of
optoelectronic properties such as photocurrent, switching speed, optical
absorption, etc. for semiconducting oxide based devices.",2112.05926v1
2022-04-11,On the fluctuation-dissipation of the oxide trapped charge in a MOSFET operated down to deep cryogenic temperatures,"An analysis of the oxide trapped charge noise in a MOSFET operated down to
deep cryogenic temperatures is proposed. To this end, a revisited derivation of
the interface trap conductance Gp and oxide trapped charge noise SQt at the
SiO2/Si MOS interface is conducted under very low temperature condition, where
Fermi-Dirac statistics applies. A new relation between the oxide trapped charge
noise SQt and the interface trap conductance Gp is established, showing the
inadequacy of the Nyquist relation at very low temperature. Finally, a new
formula for the oxide trapped charge 1/f noise, going beyond the classical
Boltzmann expression, is developed in terms of oxide trap density and effective
temperature accounting for degenerate statistics.",2204.04958v2
2023-03-20,Oxide spinels with superior Mg conductivity,"Mg batteries with oxide cathodes have the potential to significantly surpass
existing Li-ion technologies in terms of sustainability, abundance, and energy
density. However, Mg intercalation at the cathode is often severely hampered by
the sluggish kinetics of Mg$^{2+}$ migration within oxides. Here we report a
combined theoretical and experimental study addressing routes to identify
cathode materials with an improved Mg-ion mobility. Using periodic density
functional theory calculations, Mg$^{2+}$ migration in oxide spinels has been
studied, revealing key features that influence the activation energy for
Mg$^{2+}$ migration. Furthermore, the electronic and geometrical properties of
the oxide spinels as well as their stability have been analyzed for a series of
different transition metals in the spinels. We find that electronegative
transition metals enable a high Mg-ion mobility in the oxide spinel frameworks
and thus a favorable cathode functionality. Based on the theoretical findings,
some promising candidates have been identified, prepared and structurally
characterized. Our combined theoretical and experimental findings open up an
avenue toward the utilization of functional cathode materials with improved
Mg$^{2+}$ transport properties for Mg-metal batteries.",2303.11122v1
2023-04-26,Elucidating the active phases of CoOx films on Au(111) in the CO Oxidation Reaction,"Using CoOx thin films supported on Au(111) single crystal surfaces as model
catalysts for the CO oxidation reaction we show that three reaction regimes
exist in response to chemical and topographic restructuring of the CoOx
catalyst as a function of reactant gas phase CO/O2 stoichiometry a finding that
highlights the versatility of catalysts and their evolution in response to
reaction conditions. Under oxygen-lean conditions and moderate temperatures
(below 150C degrees) partially oxidized films containing CoO were found to be
efficient catalysts. In contrast, stoichiometric CoO films containing only Co2+
form carbonates in the presence of CO that poison the reaction below 300 C
degrees. Under oxygen-rich conditions a more oxidized catalyst phase forms
containing Co3+ species that is effective in a wide temperature range. Resonant
photoemission spectroscopy (ResPES) revealed the unique role of Co3+ sites in
catalyzing the CO oxidation. DFT calculations provided deeper insights into the
pathway and free energy barriers for the reactions on these oxide phases.",2304.13859v1
2023-05-02,"Data-Driven, Physics-Informed Descriptors of Cation Ordering in Multicomponent Oxides","The structural tunability and compositional diversity of multicomponent
perovskite oxides have enabled their various applications, including catalysis
and electronics. The cation ordering in these oxides, ranging from disordered
(i.e., high-entropy) to ordered (e.g., rocksalt), profoundly influences their
properties. While computational design tools can typically predict properties
associated with a particular ordering, inferring which ordering -- if any --
will be observed in synthesized oxides remains challenging. Here, we leveraged
first-principles simulations and machine learning to develop data-driven,
physics-informed descriptors of experimental ordering in multicomponent
perovskites and compared them with traditional physicochemical descriptors,
e.g., ionic radii and oxidation states. The fitted low-dimensional
classification models correctly rank up to 93% of compositions in an
experimental dataset of 190 perovskites between cation-ordered and disordered,
offering a rigorous benchmark between theory and experiments. Furthermore,
these descriptors accelerate high-throughput virtual screening of
multicomponent oxides by predicting their dominant ordering to avoid costly,
exhaustive simulations of cation arrangements.",2305.01806v1
2023-05-11,Interfacial two-dimensional oxide enhances photocatalytic activity of graphene/titania via electronic structure modification,"A two-dimensional layer of oxide reveals itself as a essential element to
drive the photocatalytic activity in a nanostructured hybrid material, which
combines high-quality epitaxial graphene and titanium dioxide nanoparticles. In
particular, it has been revealed that the addition of a 2D Ti oxide layer
sandwiched between graphene and metal induces a p-doping of graphene and a
consistent shift in the Ti d states. These modifications induced by the
interfacial oxide layer induce a reduction of the probability of charge carrier
recombination and enhance the photocatalytic activity of the heterostructure.
This is indicative of a capital role played by thin oxide films in fine-tuning
the properties of heterostructures based on graphene and pave the way to new
combinations of graphene/oxides for photocatalysis-oriented applications.",2305.06708v1
2023-07-19,Oxide layer dependent orbital torque efficiency in ferromagnet/Cu/Oxide heterostructures,"The utilization of orbital transport provides a versatile and efficient spin
manipulation mechanism. As interest in orbital-mediated spin manipulation
grows, we face a new issue to identify the underlying physics that determines
the efficiency of orbital torque (OT). In this study, we systematically
investigate the variation of OT governed by orbital Rashba-Edelstein effect at
the Cu/Oxide interface, as we change the Oxide material. We find that OT varies
by a factor of ~2, depending on the Oxide. Our results suggest that the active
electronic interatomic interaction (hopping) between Cu and oxygen atom is
critical in determining OT. This also gives us an idea of what type of material
factors is critical in forming a chiral orbital Rashba texture at the Cu/Oxide
interface.",2307.09824v1
2023-08-07,Modeling of electrochemical oxide film growth -- impact of band-to-band tunneling,"The Point Defect Model (PDM) describes the corrosion resistance properties of
oxide films based on interfacial reactions and defect transport, which are
affected by the electric field inside the oxide film. The PDM assumes a
constant electric field strength due to band-to-band tunneling (BTBT) of
electrons and the separation of electrons and holes by high electric fields. In
this manuscript we present a more complex expansion of the common models to
simulate steady state oxide films to test this assumption. The R-PDM was
extended by including the transport of electrons and holes and BTBT. It could
be shown that BTBT only occurs in very rare cases of narrow band gaps and high
electric fields and the impact of electrons and holes does indeed lead to a
buffering effect on the electric field, but does not lead to a constant
electric field strength. Modeling the transport of electrons and holes on the
oxide film allows to specifically estimate their potential impact on the film
growth. Especially during modeling of oxide films with narrow band gap and/or
electrochemical reactions at the film/solution interface the electrons and
holes needs to be included to the model.",2308.05113v1
2023-08-24,Modeling for heterogeneous oxidative aging of polymers using coarse-grained molecular dynamics,"This study presents a coarse-grained molecular dynamics simulation model to
investigate the process of oxidative aging in polymers. The chemical aging
effect is attributed to the auto-oxidation mechanism, which is initiated by
radicals, leading to the chain scission and crosslinking of polymer chains. In
this study, we integrate a thermal oxidation kinetic model in the oxygen excess
regime into the Kremer-Grest model, thereby enabling a reactive coarse-grained
molecular dynamics simulation to capture the process of oxidative degradation.
Our simulation reveals that when the timescale of the characteristic reaction
step of oxidative degradation is shorter than the longest relaxation time of
polymer chains, the scission sites exhibit spatial heterogeneity. This
innovative simulation model possesses the potential to enhance our
comprehension of polymer aging phenomena, thus making noteworthy contributions
to the realm of polymer science and degradation chemistry.",2308.12620v1
2023-11-22,Mechanistic Insights into the Hydrazine-induced Chemical Reduction Pathway of Graphene Oxide,"Hydrazine stands out as the most generally used chemical-reducing agent for
reducing graphene oxide. Despite numerous experimental and theoretical
investigations into the reduction reaction, the reduction mechanism remains
unclear. In this study, we propose that, in aqueous hydrazine solutions, both
hydrazine and hydroxide ions could initiate the reduction of graphene oxide. We
introduce a chemical reaction pathway involving C-H cleavage and a
dehydroxylation process for the reduction of graphene oxide. By utilizing
density functional theory calculations, the reduction reactions mediated by
hydrazine and hydroxide ions are separately investigated. The reaction routes
on the basal plane and edge regions of graphene oxide are discussed
independently. The density functional theory calculations demonstrate that the
proposed mechanism is both thermodynamically and dynamically feasible. This
work might contribute to an atomic-level comprehension of a longstanding
challenge in the field of graphene oxide.",2311.13086v1
2024-02-06,High-temperature oxidation and nitridation of substoichiometric zirconium carbide in isothermal air,"The influence of nitrogen on the oxidation behavior of hot-pressed zirconium
carbide was investigated using a flow-tube furnace at temperatures ranging from
1000 to 1600 {\deg}C. Mass gain, oxide formation characteristics, and oxide
transitions were evaluated at various experimental conditions. Differences in
oxidation behavior across the range of temperatures investigated show both
kinetic and microstructural dependence with implications pointing to this
materials efficacy in ultra-high temperature applications. Results suggest that
at temperatures above 1400 {\deg}C, although oxidation mechanisms remain
dominant, nitridation and reduction mechanisms may be appreciable enough to
require consideration. Supporting discussions regarding polymorphism and
microstructural influences are outlined.",2402.04337v1
1998-12-14,Estimation of the charge carrier localization length from Gaussian fluctuations in the magneto-thermopower of La_{0.6}Y_{0.1}Ca_{0.3}MnO_3,"The magneto-thermoelectric power (TEP) $\Delta S(T,H)$ of perovskite type
manganise oxide $La_{0.6}Y_{0.1}Ca_{0.3}MnO_3$ is found to exhibit a sharp peak
at some temperature $T^{*}=170K$. By approximating the true shape of the
measured magneto-TEP in the vicinity of $T^{*}$ by a linear triangle of the
form $\Delta S(T,H)\simeq S_p(H)\pm B^{\pm}(H)(T^{*}-T)$, we observe that $B
^{-}(H)\simeq 2B ^{+}(H)$. We adopt the electron localization scenario and
introduce a Ginzburg-Landau (GL) type theory which incorporates the two
concurrent phase transitions, viz., the paramagnetic-ferromagnetic transition
at the Curie point $T_C$ and the ""metal-insulator"" (M-I) transition at
$T_{MI}$. The latter is characterized by the divergence of the field-dependent
charge carrier localization length $\xi (T,H)$ at some characteristic field
$H_0$. Calculating the average and fluctuation contributions to the total
magnetization and the transport entropy related magneto-TEP $\Delta S(T,H)$
within the GL theory, we obtain a simple relationship between $T^{*}$ and the
above two critical temperatures ($T_{C}$ and $T_{MI}$). The observed slope
ratio $B ^{-}(H)/B ^{+}(H)$ is found to be governed by the competition between
the electron-spin exchange $JS$ and the induced magnetic energy $M_sH_0$. The
comparison of our data with the model predictions produce $T_{C}=195K$,
$JS=40meV$, $M_0=0.4M_s$, $\xi_0=10\AA$, and $n_e/n_i=2/3$ for the estimates of
the Curie temperature, the exchange coupling constant, the critical
magnetization, the localization length, and the free-to-localized carrier
number density ratio, respectively.",9812219v1
2013-07-28,Novel multiferroics with ferromagnetic phase induced in paraelectric antiferromagnets by electric field application,"The phase diagram of a quantum paraelectric antiferromagnet EuTiO3 under an
external electric field was calculated using Landau-Ginzburg-Devonshire theory.
It was shown that the application of an external electric field E leads to the
appearance of a ferromagnetic phase due to the magnetoelectric coupling. In
particular, electric field application decreases the transition temperature
TAFM to antiferromagnetic (AFM) phase and induces ferromagnetic (FM) phase, so
that at some E field larger than the critical field (Ecr), TFM becomes higher
than TAFM and the FM phase appears. Note that Ecr increases and magnetization
decreases as the temperature increases. The value of the critical field Ecr =
0.40*10^6 V/cm we calculated appeared close to the value Ecr = 0.5*10^6 V/cm
obtained recently by Ryan et al. with the help of density functional theory for
EuTiO3 film under a compressive strain produced by substrate. At the fields E
>0.83*10^6 V/cm, AFM disappears for all considered temperatures and so FM
becomes the only stable magnetic phase. We find that ferromagnetic phase can be
induced by an E-field in other paraelectric antiferromagnet oxides with a
positive AFM-type magnetoelectric (ME) coupling coefficient and negative
FM-type ME coupling coefficient. In particular, the critical E-field was
estimated for another paraelectric antiferromagnet Sr0.7Ba0.3MnO3 as
0.2x10^5V/cm at 0 K. Analysis of the dependence of magnetization and
antimagnetization on the external electric field and the polarization induced
by the field, which yields the magnetoelectric coupling, is reported. The
results show the possibility to control multiferroicity, including the FM and
AFM phases, with help of an electric field application.",1307.7402v1
2015-10-08,Phonons and Stability of Infinite-Layer Iron Oxides SrFeO2 and CaFeO2,"We present detailed ab-initio lattice dynamical analysis of the Fe-O
infinite-layer compounds CaFeO2 and SrFeO2 in various magnetic configurations.
These indicate strong spin-phonon coupling in SrFeO2 in contrast to that in
case of CaFeO2. Powder neutron inelastic scattering experiments on SrFeO2 have
also been performed at temperatures from 5 K to 353 K in the antiferromagnetic
phase and analyzed using the ab-initio calculations. These suggest distortion
of the ideal infinite planer structure above 300 K. From our ab-initio
calculations in SrFeO2 as a function of volume, we suggest that the distortion
in SrFeO2 above 300 K is similar to that known in CaFeO2 at ambient conditions.
The distortion of the planer structure of CaFeO2 involves doubling of the
planer unit cell that may be usually expected to be due to a soft phonon mode
at the M-point (1/2 1/2 0). However, our ab-initio calculations show quite
unusually that all the M-point (1/2 1/2 0) phonons are stable, but two stable
M3+ and M2-modes anharmonically couple with an unstable Bu mode at the zone
centre and lead to the cell doubling and the distorted structure. Magnetic
exchange interactions in both the compounds have been computed on the basis of
the ideal planar structure (P4/mmm space group) and with increasing amplitude
of the Bu phonon mode. These reveal that the magnetic exchange interactions
reduce significantly with increasing distortion. We have extended the ab-initio
phonon calculation to high pressures, which reveal that, above 20 GPa of
pressure, the undistorted planer CaFeO2 becomes dynamically stable. We also
report computed phonon spectra in SrFeO3 that has a cubic structure, which is
useful to understand the role of the difference in geometry of oxygen atoms
around the Fe atom with respect to planer SrFeO2.",1510.02294v1
2016-06-14,Nickel-cobalt-titanate thin films - new sustainable magnetic oxides,"Single phase nickel-cobalt-titanate thin films with a formula A1+2xTi1-xO3,
where A is Ni2+,Co2+ and -0.25<x<1, were grown by pulsed laser deposition on
sapphire substrates. There is a large window in which both Ni/Co ratio and x
can be chosen independently. In the prototype ilmenite and corundum structures
one third of the octahedra are vacant. The reported structure is obtained by
filling vacant (x>0) or emptying filled (x<0) octahedra. When x = 1 all
octahedra are filled. Two factors controlling the magnetism and crystal
distortion are identified. First is a direct overlap between the adjacent
cation d-orbitals resulting in a bond formation and magnetic interactions
between the cations. This is most clearly revealed as a crystal distortion in
the x approximately 0 compositions with approximately equal amounts of Ni and
Co: the distortion of the x approximately 0 compound is a function of Ni/Co
ratio. The second factor is x, which controls the cation shift towards a vacant
octahedron. The displacement decreases and the symmetry increases with
decreasing Ti content as was revealed by x-ray diffraction and Raman
spectroscopy. When all octahedra are filled the cations prefer octahedron
center positions. Also the number density of cations has increased by a factor
of 50 percent when compared to the ilmenite structure. The number density
ratios of Ni/Co cations between x=1 and x=0 compounds is 3. The Raman and x-ray
diffraction data collected on samples with x = 1 or close to 1 are interpreted
in terms of P63/mmc space group.",1606.04256v3
2020-07-17,"Crystalline and magnetic structures, magnetization, heat capacity and anisotropic magnetostriction effect in a yttrium-chromium oxide","We have studied a nearly stoichiometric insulating
Y$_{0.97(2)}$Cr$_{0.98(2)}$O$_{3.00(2)}$ single crystal by performing
measurements of magnetization, heat capacity, and neutron diffraction. Albeit
that the YCrO$_3$ compound behaviors like a soft ferromagnet with a coersive
force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions
between Cr$^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss
temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and
antiferromagnetism may indicate a canted AFM structure. The AFM phase
transition occurs at $T_\textrm{N} =$ 141.5(1) K, which increases to
$T_\textrm{N}$(5T) = 144.5(1) K at 5 T. Within the accuracy of the present
neuron-diffraction studies, we determine a G-type AFM structure with a
propagation vector \textbf{k} = (1 1 0) and Cr$^{3+}$ spin directions along the
crystallographic \emph{c} axis of the orthorhombic structure with space group
\emph{Pnma} below $T_\textrm{N}$. At 12 K, the refined moment size is 2.45(6)
$\mu_\textrm{B}$, $\sim$ 82\% of the theoretical saturation value 3
$\mu_\textrm{B}$. The Cr$^{3+}$ spin interactions are probably two-dimensional
Ising like within the reciprocal (1 1 0) scattering plane. Below
$T_\textrm{N}$, the lattice configuration (\emph{a}, \emph{b}, \emph{c}, and
\emph{V}) deviates largely downward from the Gr$\ddot{\textrm{u}}$neisen law,
displaying an anisotropic magnetostriction effect and a magnetoelastic effect.
Especially, the sample contraction upon cooling is enhanced below the AFM
transition temperature. There is evidence to suggest that the actual
crystalline symmetry of YCrO$_3$ compound is probably lower than the currently
assumed one. Additionally, we compared the $t_{2\textrm{g}}$ YCrO$_3$ and the
$e_\textrm{g}$ La$_{7/8}$Sr$_{1/8}$MnO$_3$ single crystals for a further
understanding of the reason for the possible symmetry lowering.",2007.08985v2
2016-11-16,Quantized Ballistic Transport of Electrons and Electron Pairs in LaAlO$_3$/SrTiO$_3$ Nanowires,"SrTiO$_3$-based heterointerfaces support quasi-two-dimensional (2D) electron
systems that are analogous to III-V semiconductor heterostructures, but also
possess superconducting, magnetic, spintronic, ferroelectric, and ferroelastic
degrees of freedom. Despite these rich properties, the relatively low
mobilities of 2D complex-oxide interfaces appear to preclude ballistic
transport in 1D. Here we show that the 2D LaAlO$_3$/SrTiO$_3$ interface can
support quantized ballistic transport of electrons and (non-superconducting)
electron pairs within quasi-1D structures that are created using a
well-established conductive atomic-force microscope (c-AFM) lithography
technique. The nature of transport ranges from truly single-mode (1D) to
three-dimensional (3D), depending on the applied magnetic field and gate
voltage. Quantization of the lowest $e^2/h$ plateau indicate a ballistic
mean-free path $l_{MF}\sim$ 20 $\mu$m, more than two orders of magnitude larger
than for 2D LaAlO$_3$/SrTiO$_3$ heterostructures. Non-superconducting electron
pairs are found to be stable in magnetic fields as high as $B=11$ T, and
propagate ballistically with conductance quantized at 2$e^2/h$. Theories of
one-dimensional (1D) transport of interacting electron systems depend crucially
on the sign of the electron-electron interaction, which may help explain the
highly ballistic transport behavior. The 1D geometry yields new insights into
the electronic structure of the LaAlO$_3$/SrTiO$_3$ system and offers a new
platform for the study of strongly interacting 1D electronic systems.",1611.05127v4
2016-05-26,Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff,"Zircon crystals offer a unique combination of suitability for high-precision
radiometric dating and high resistance to alteration. Paleomagnetic experiments
on ancient zircons may potentially constrain the earliest geodynamo, which
holds broad implications for the early Earth interior and atmosphere. However,
the ability of zircons to record accurately the geomagnetic field has not been
fully demonstrated. Here we conduct thermal and room temperature alternating
field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons
from the Bishop Tuff, California. The rapid emplacement of these zircons in a
well-characterized magnetic field provides a high-fidelity test of the zircons
intrinsic paleomagnetic recording accuracy. Successful dual heating experiments
on nine zircons measured using a superconducting quantum interference device
(SQUID) microscope yield a mean paleointensity of 46.2 +/- 18.8 microtesla
(1sigma), which agrees closely with high-precision results from Bishop Tuff
whole rock (43.0 +/- 3.2 microtesla). High-resolution quantum diamond magnetic
mapping, electron microscopy, and X-ray tomography indicate that the bulk of
the remanent magnetization in Bishop Tuff zircons is carried by Fe oxides
associated with apatite inclusions, which would be susceptible to destruction
via metamorphism and aqueous alteration in older zircons. As such, while
zircons can reliably record the geomagnetic field, robust zircon-derived
paleomagnetic results require careful characterization of the ferromagnetic
carrier and demonstration of their occurrence in primary inclusions. We further
conclude that a combination of quantum diamond magnetometry and high-resolution
imaging can provide detailed, direct characterization of the ferromagnetic
mineralogy of geological samples.",1605.08479v1
2018-07-27,Controlling spin-orbit interactions in silicon quantum dots using magnetic field direction,"Silicon quantum dots are considered an excellent platform for spin qubits,
partly due to their weak spin-orbit interaction. However, the sharp interfaces
in the heterostructures induce a small but significant spin-orbit interaction
which degrade the performance of the qubits or, when understood and controlled,
could be used as a powerful resource. To understand how to control this
interaction we build a detailed profile of the spin-orbit interaction of a
silicon metal-oxide-semiconductor double quantum dot system. We probe the
derivative of the Stark shift, $g$-factor and $g$-factor difference for two
single-electron quantum dot qubits as a function of external magnetic field and
find that they are dominated by spin-orbit interactions originating from the
vector potential, consistent with recent theoretical predictions. Conversely,
by populating the double dot with two electrons we probe the mixing of singlet
and spin-polarized triplet states during electron tunneling, which we conclude
is dominated by momentum-term spin-orbit interactions that varies from 1.85 MHz
up to 27.5 MHz depending on the magnetic field orientation. Finally, we exploit
the tunability of the derivative of the Stark shift of one of the dots to
reduce its sensitivity to electric noise and observe an 80 % increase in
$T_2^*$. We conclude that the tuning of the spin-orbit interaction will be
crucial for scalable quantum computing in silicon and that the optimal setting
will depend on the exact mode of qubit operations used.",1807.10415v4
2021-02-12,"Oxygen magnetic polarization, nodes in spin density, and zigzag spin order in oxides","Recent DFT calculations for Ba2CoO4 (BCO) and neutron scattering experiments
for SrRuO3 (SRO) have shown that oxygen develops a magnetic polarization.
Moreover, DFT calculations for these compounds also unveiled unexpected nodes
in the spin density, both along Co-O and Ru-O. For BCO, the overall
antiferromagnetic state in its triangular lattice contains unusual zigzag spin
patterns. Here, using simple model calculations supplemented by DFT we explain
and extend these results. We predict that ligands that in principle should be
spinless, such as O$^{2-}$, will develop a net polarization when they act as
electronic bridges between transition metal (TM) spins ferromagnetically
ordered, regardless of the number of intermediate ligand atoms. The reason is
the hybridization between atoms and mobility of the electrons with spins
opposite to those of the closest TM atoms. Moreover, for bonds with TMs
antiferromagnetically ordered, counterintuitively our calculations show that
oxygens should also have a net magnetization for the super-super-exchange cases
TM-O-O-TM while for only one oxygen, as in Cu-O-Cu, the O-polarization should
cancel. Our simple model also allows us to explain the presence of nodes based
on the antibonding character of the dominant singly occupied molecular orbitals
along the TM-O bonds. Finally, the zigzag pattern order becomes the ground
state mainly due to the influence of the Hubbard $U$, that creates the moments,
in combination with a robust easy-axis anisotropy that suppresses the competing
120$^{\circ}$ degree antiferromagnetic order of a triangular lattice. Our
predictions are generic and should be applicable to any other compound with
characteristics similar to those of BCO and SRO.",2102.06669v2
2023-06-21,Sayonara BCS: Realization of Room Temperature Superconductivity as a result of a First Order Phase Transition,"By making periodic thru-holes in a suspended film, the phonon system can be
modified. Motivated by the BCS theory, the technique -- so-called phonon
engineering -- was applied to a metallic niobium sheet. It was found that its
electrical resistance dropped to zero at 175 K, and the zero-resistance state
persisted up to 290 K in the subsequent warming process. Despite the initial
motivation, neither these high transition temperatures nor the phase transition
with thermal hysteresis can be accounted for by the BCS theory. Therefore, we
abandon the BCS theory. Instead, it turns out that the metallic holey sheet is
partly oxidized to form a niobium-oxygen square lattice, which has points of
resemblance to a copper-oxygen plane, the fundamental component of cuprate
high-$T_{c}$ superconductors. Therefore, the pairing mechanism underlying this
study should be related to that of cuprate high-$T_{c}$ superconductors, which
we may not yet understand. In addition to the electrical results of zero
resistance, the holey sheet exhibited a decrease in magnetization upon cooling,
i.e., the Meissner effect. Moreover, the remnant magnetization was clearly
detected at 300 K, which can only be attributed to persistent currents flowing
in a superconducting sample. Thus, this study meets the established criteria
for a conclusive demonstration of true superconductivity. Finally, the
superconducting transition with the unambiguous thermal hysteresis is
discussed. According to Halperin, Lubensky, and Ma, or HLM for short, any
superconducting transition must always be first order with thermal hysteresis
because of the intrinsic fluctuating magnetic field. The HLM theory is very
compatible with the highly oriented system harboring two-dimensional
superconductivity.",2306.13172v3
2024-01-15,Room-temperature intrinsic ferromagnetism of two-dimensional Na2Cl crystals originated by s- and p-orbitals,"Ferromagnetism, as one of the most valuable properties of materials, has
attracted sustained and widespread interest in basic and applied research from
ancient compasses to modern electronic devices. Traditionally, intrinsic
ferromagnetism has been attributed to the permanent magnetic moment induced by
partially filled d- or f-orbitals. However, the development of ferromagnetic
materials has been limited by this electronic structure convention. Thus, the
identification of additional materials that are not constrained by this
conventional rule but also exhibit intrinsic ferromagnetism is highly expected
and may impact all the fields based on ferromagnetism. Here, we report the
direct observation of room-temperature intrinsic ferromagnetism in
two-dimensional (2D) Na2Cl crystals, in which there are only partially filled
s- and p-orbitals rather than d- or f-orbitals, using the superconducting
quantum interference device (SQUID) and magnetic force microscope (MFM). These
Na2Cl crystals formed in reduced graphene oxide (rGO) membranes have an
unconventional stoichiometric structure leading to unique electron and spin
distributions. And the structure of these 2D Na2Cl crystals, including the Na
and Cl sites, is characterized in situ for the first time and directly observed
by cryo-electron microscopy (cryo-EM) based on the observed difference in
contrast between Na stacked with Cl and single Na. These findings break the
conventional rule of intrinsic ferromagnetism and provide new insights into the
design of novel magnetic and electronic devices and transistors with a size
down to the atomic scale.",2401.07524v1
2011-08-02,Analysis of Sulfur Poisoning on a PEM Fuel Cell Electrode,"The extent of irreversible deactivation of Pt towards hydrogen oxidation
reaction (HOR) due to sulfur adsorption and subsequent electrochemical
oxidation is quantified in a functional PEM fuel cell. At 70 {\deg}C,
sequential hydrogen sulfide (H2S) exposure and electrochemical oxidation
experiments indicate that as much as 6% of total Pt sites are deactivated per
monolayer sulfur adsorption at open circuit potential of a PEM fuel cell
followed by its removal. The extent of such deactivation is much higher when
the electrode is exposed to H2S when the fuel cell is operating at a finite
load, and is dependent on the local overpotential and the duration of exposure.
Regardless of this deactivation, the H2/O2 polarization curves obtained on
post-recovery electrodes do not show performance losses suggesting that such
performance curves alone cannot be used to assess the extent of recovery due to
sulfur poisoning. A concise mechanism for the adsorption and electro-oxidation
of H2S on Pt anode is presented. H2S dissociatively adsorbs onto Pt as two
different sulfur species and at intermediate oxidation potentials, undergoes
electro-oxidation to sulfur and then to sulfur dioxide (SO2). This mechanism is
validated by charge balances between hydrogen desorption and sulfur
electro-oxidation on Pt. The ignition potential for sulfur oxidation decreases
with increase in temperature, which coupled with faster electro-oxidation
kinetics result in the easier removal of adsorbed sulfur at higher
temperatures. Furthermore, the adsorption potential is found to influence
sulfur coverage of an electrode exposed to H2S. As an implication, the local
potential of a PEM fuel cell anode exposed to H2S contaminated fuel should be
kept below the equilibrium potential for sulfur oxidation to prevent
irreversible loss of Pt sites.",1108.0609v1
2016-11-10,Evolutionary optimization of a charge transfer ionic potential model for Ta/Ta-oxide hetero-interfaces,"Tantalum, tantalum oxide and their hetero-interfaces are of tremendous
technological interest in several applications spanning electronics, thermal
management, catalysis and biochemistry. For example, local oxygen stoichiometry
variation in TaOx memristors comprising of metallic (Ta) and insulating oxide
(Ta2O5) have been shown to result in fast switching on the sub-nanosecond
timescale over a billion cycles, relevant to neuromorphic computation. Despite
its broad importance, an atomistic scale understanding of oxygen stoichiometry
variation across Ta/TaOx hetero-interfaces, such as during early stages of
oxidation and oxide growth, is not well understood. This is mainly due to the
lack of a variable charge interatomic potential model for tantalum oxides that
can accurately describe the ionic interactions in the metallic (Ta) and oxide
(TaOx) environment as well as at their interfaces. To address this challenge,
we introduce a charge transfer ionic potential (CTIP) model for Ta/Ta-oxide
system by training against lattice parameters, cohesive energies, equations of
state, and elastic properties of various experimentally observed Ta2O5
polymorphs. The best set of CTIP parameters are determined by employing a
single-objective global optimization scheme driven by genetic algorithms
followed by local Simplex optimization. Our newly developed CTIP potential
accurately predicts structure, thermodynamics, energetic ordering of
polymorphs, as well as elastic and surface properties of both Ta and Ta2O5, in
excellent agreement with DFT calculations and experiments. We employ our newly
parameterized CTIP potential to investigate the early stages of oxidation of Ta
at different temperatures and atomic/molecular nature of the oxidizing species.",1611.03519v2
2017-10-25,High-temperature cyclic oxidation kinetics and microstructural transition mechanisms of Ti-6Al-4V composites reinforced with hybrid (TiC+TiB) networks,"The microstructural features and high-temperature oxidation resistance of
hybrid (TiC+TiB) networks reinforced Ti-6Al-4V composites were investigated
after fabricated with reaction hot pressing technique. The inhomogeneous
distribution of hybrid reinforcers resulted in a sort of stress-induced grain
refinement for {\alpha}-Ti matrix phase, which was further facilitated by
heterogeneous nucleation upon additive interfaces. HRTEM analyses revealed the
crystallographic orientation relation between TiB and alpha-Ti phases as
(201)TiB//(-1100)alpha-Ti plus [11-2]//[0001] alpha-Ti, while TiC and
{\alpha}-Ti phases maintained the interrelation of (-200)TiC//(-2110)
{\alpha}-Ti and [001]TiC//[01-10] alpha-Ti. The hybridly reinforced
Ti-6Al-4V/(TiC+TiB) composites displayed superior oxidation resistance to both
the sintered matrix alloy and the two composites reinforced solely with TiC or
TiB addition during the cyclic oxidation at 873, 973 and 1073 K respectively
for 100 h. The hybrid reinforcers volume fraction was a more influential factor
to improve oxidation resistance than the matrix alloy powder size. As
temperature rose from 873 to 1073 K, the oxidation kinetics transferred from
the nearly parabolic type through qusilinear tendency into the finally linear
mode. This corresponded to the morphological transition of oxide scales from a
continuous protective film to a partially damaged layer and ended up with the
complete spallation of alternating alumina and rutile multilayers. A
phenomenological model was proposed to elucidate the growth process of oxides
scales. The release of thermal stress, the suppression of oxygen diffusion and
the fastening of oxide adherence were found as the three major mechanisms to
enhance the oxidation resistance of hybrid reinforced composites.",1710.09315v1
2019-10-24,Hybrid Organic-Metal Oxide Multilayer Channel Transistors with Record Operational Stability,"Metal oxide thin-film transistors are fast becoming a ubiquitous technology
for application in driving backplanes of organic light-emitting diode displays.
Currently all commercial products rely on metal oxides processed via physical
vapor deposition methods. Transition to simpler, higher throughput
manufacturing methods such as solution-based processes, are currently been
explored as cost-effective alternatives. However, developing printable oxide
transistors with high carrier mobility and bias-stable operation has proved
challenging. Here we show that hybrid multilayer channels composed of
alternating ultra-thin layers ($\leq$4 nm) of indium oxide, zinc oxide
nanoparticles, ozone-treated polystyrene and a compact zinc oxide layer, all
solution-processed in ambient atmosphere, can be used to create TFTs with
remarkably high electron mobility (50 cm$^{2}$/Vs) and record operational
stability. Insertion of the ozone-treated polystyrene interlayer is shown to
reduce the concentration of electron traps at the metal oxide surfaces and
heterointerfaces. The resulting transistors exhibit dramatically enhanced bias
stability over 24 h continuous operation and while subjected to large electric
field flux density (2.1$\times$10$^{-6}$ C/cm$^{2}$) with no adverse effects on
the electron mobility. Density functional theory calculations identify the
origin of this enhanced stability as the passivation of the oxygen
vacancy-related gap states due to interaction between ozonolyzed styrene
moieties and the oxides. Our results sets new design guidelines for bias-stress
resilient metal oxide transistors.",1910.11013v1
2018-06-04,Water Oxidation Chemistry of Oxynitrides and Oxides: Comparing NaTaO$_3$ and SrTaO$_2$N,"The oxygen evolution reaction (OER) plays an important role in evaluating a
photocatalyst and to understand its surface chemistry. In this work we present
a comparative study of the OER on the oxide NaTaO$_3$ (113) surface and the
oxynitride SrTaO$_2$N (001) surface. Oxynitrides are highly promising
photocatalysts due to their smaller band gap and resulting better visible light
absorption compared to oxides but our knowledge about their surface structure
and chemistry is still very limited. With the goal to compare the surface
chemistry of oxides and oxynitrides, we perform density functional theory
calculations to obtain the free energy changes associated with the OER reaction
steps. For the OER at the Ta site of the clean surfaces, our results predict
the rate-limiting step for both materials to be the formation of the *OOH
intermediate, with a larger overpotential for the oxide than the oxynitride
(1.30 V vs 1.01 V). The Na site is found to be more active than the Ta site on
the oxide surface with an OER overpotential of 0.88 V, whereas the OER at the
Sr site on the oxynitride has an overpotential of 1.14 V. For the A sites,
contrary to the Ta site, the deprotonation of *OH was found to be the
rate-limiting step. Computed Pourbaix diagrams show that at relevant
(photo)electrochemical conditions all surfaces are covered with oxygen
adsorbates. Oxygen adsorbates at A (Na, Sr) sites are however found to couple
and desorb as O$_2$, leaving these sites empty under typical operating
conditions. Following this desorption, we find the OER to proceed by the
conventional *OOH mechanism on the SrO termination of the oxynitride but by a
direct coupling of neighbouring *O at Na sites on the oxide surface. This
coupling mechanism on the oxide has the smallest overpotential of 0.79 V
compared to 0.88 V for the oxynitride, implying that the oxide is a better OER
catalyst.",1806.01252v1
1996-07-15,Non Fermi-Liquid States and Pairing of a general Model of Copper-Oxide Metals,"A model of copper-oxygen bonding and anti-bonding bands with the most general
two-body interactions allowable by symmetry is considered. The model has a
continuous transition as a function of hole-density x and temperature T to a
phase in which a current circulates in each unit cell. This phase preserves the
translational symmetry of the lattice while breaking time-reversal invariance
and the four-fold rotational symmetry. The product of time-reversal and
four-fold rotation is preserved. The circulating current phase terminates at a
critical point at $x=x_c, T=0$. In the quantum-critical region about this point
the logarithm of the frequency of the current fluctuations scales with their
momentum. The microscopic basis for the marginal Fermi-liquid phenemenology and
the observed long wavelength transport anomalies near $x=x_c$ are derived from
such fluctuations. The symmetry of the current fluctuations is such that the
associated magnetic field fluctuations are absent at oxygen sites and have the
correct form to explain the anomalous copper nuclear relaxation rate.
Cross-overs to the Fermi-liquid phase on either side of $x_c$ and the role of
disorder are briefly considered. The current fluctuations promote
superconductive instability with a propensity towards ``D-wave"" symmetry or
``extended S-wave""symmetry depending on details of the band-structure.",9607105v2
1999-06-30,Spin gap and magnetic coherence in a clean high-T_c superconductor,"A notable aspect of high-temperature superconductivity in the copper oxides
is the unconventional nature of the underlying paired-electron state. A direct
manifestation of the unconventional state is a pairing energy - that is, the
energy required to remove one electron from the superconductor - that varies
(between zero and a maximum value) as a function of momentum or wavevector: the
pairing energy for conventional superconductors is wavevector-independent. The
wavefunction describing the superconducting state will include not only the
pairing of charges, but also of the spins of the paired charges. Each pair is
usually in the form of a spin singlet, so there will also be a pairing energy
associated with transforming the spin singlet into the higher energy spin
triplet form without necessarily unbinding the charges. Here we use inelastic
neutron scattering to determine the wavevector-dependence of spin pairing in
La_{2-x}Sr_xCuO_4, the simplest high-temperature superconductor. We find that
the spin pairing energy (or 'spin gap') is wavevector independent, even though
superconductivity significantly alters the wavevector dependence of the spin
fluctuations at higher energies.",9906456v1
2002-03-22,Roles of Electron Correlations in the Spin-Triplet Superconductivity of Sr2RuO4,"We discuss a microscopic mechanism of the spin-tiplet superconductivity in
the quasi-two-dimensional ruthenium oxide Sr2RuO4 on the basis of
two-dimensional three-band Hubbard model. We solve the linearized Eliashberg
equation by taking into account the full momentum-frequency dependence of the
order parameter for the spin-triplet and the spin-singlet states, and estimate
the transition temperature as a function of the Coulomb integrals. The
effective pairing interaction is expanded perturbatively with respect to the
Coulomb interaction at the Ru sites up to the third order. As a result, we show
that the spin-triplet p-wave state is more stable than the spin-singlet d-wave
state for moderately strong Coulomb interaction. Our results suggest that one
of the three bands, $\gamma$, plays a dominant role in the superconducting
transition, and the pairing on the other two bands($\alpha$ and $\beta$) is
induced passively through the inter-orbit couplings. The most significant
momentum dependence for the p-wave pairing originates from the vertex
correction terms, while the incommensurate antiferromagnetic spin fluctuations,
which are observed in inelastic neutron scattering experiments, are expected to
disturb the p-wave pairing by enhancing the d-wave pairing. Therefore we can
regard the spin-triplet superconductivity in Sr2RuO4 as one of the natural
results of the electron correlations, and cannot consider as a result of some
strong magnetic fluctuations. We will also mention the normal Fermi liquid
properties of Sr2RuO4.",0203453v2
2002-08-27,Angle-resolved photoemission spectroscopy of the cuprate superconductors,"This paper reviews the most recent ARPES results on the cuprate
superconductors and their insulating parent and sister compounds, with the
purpose of providing an updated summary of the extensive literature in this
field. The low energy excitations are discussed with emphasis on some of the
most relevant issues, such as the Fermi surface and remnant Fermi surface, the
superconducting gap, the pseudogap and d-wave-like dispersion, evidence of
electronic inhomogeneity and nano-scale phase separation, the emergence of
coherent quasiparticles through the superconducting transition, and many-body
effects in the one-particle spectral function due to the interaction of the
charge with magnetic and/or lattice degrees of freedom. The first part of the
paper introduces photoemission spectroscopy in the context of strongly
interacting systems, along with an update on the state-of-the-art
instrumentation. The second part provides a brief overview of the scientific
issues relevant to the investigation of the low energy electronic structure by
ARPES. The rest of the paper is devoted to the review of experimental results
from the cuprates and the discussion is organized along conceptual lines:
normal-state electronic structure, interlayer interaction, superconducting gap,
coherent superconducting peak, pseudogap, electron self energy and collective
modes. Within each topic, ARPES data from the various copper oxides are
presented.",0208504v1
2003-05-19,Superconductivity Phase Diagram of Na(x)CoO(2).1.3H(2)O,"Although the microscopic origin of the superconductivity in high Tc copper
oxides remains the subject of active inquiry, several of their electronic
characteristics are well established as universal to all the known materials,
forming the experimental foundation that all theories must address. The most
fundamental of those characteristics is the dependence of the superconducting
transition temperature on the degree of electronic band filling. Since the
discovery of cuprate superconductivity in 1986 (1), the search for other
families of superconductors that might help shed light on the superconducting
mechanism of the cuprates has been of great interest. The recent report of
superconductivity near 4K in the triangular lattice, layered sodium cobalt
oxyhydrate, Na0.35CoO2.1.3H2O, is the best indication that superconductors
related to the cuprates may be found (2). Here we show that the superconducting
transition temperature of this compound displays the same kind of band-filling
behavior that is observed in the cuprates. Specifically, that the optimal
superconducting Tc occurs in a narrow range of band filling, and decreases for
both underdoped and overdoped materials, in dramatic analogy to the phase
diagram of the cuprate superconductors. Our results suggest that
characterization of the detailed electronic and magnetic behavior of these new
materials may help establish which of the many special characteristics of the
cuprates is fundamental to their high Tc superconductivity.",0305450v2
2004-03-13,Interplay of structural and electronic phase separation in single crystalline La(2)CuO(4.05) studied by neutron and Raman scattering,"We report a neutron and Raman scattering study of a single-crystal of
La(2)CuO(4.05) prepared by high temperature electrochemical oxidation. Elastic
neutron scattering measurements show the presence of two phases, corresponding
to the two edges of the first miscibility gap, all the way up to 300 K. An
additional oxygen redistribution, driven by electronic energies, is identified
at 250 K in Raman scattering (RS) experiments by the simultaneous onset of
two-phonon and two-magnon scattering, which are fingerprints of the insulating
phase. Elastic neutron scattering measurements show directly an
antiferromagnetic ordering below a N\'eel temperature of T_N =210K. The opening
of the superconducting gap manifests itself as a redistribution of electronic
Raman scattering below the superconducting transition temperature, T_c = 24K. A
pronounced temperature-dependent suppression of the intensity of the (100)
magnetic Bragg peak has been detected below T_c. We ascribe this phenomenon to
a change of relative volume fraction of superconducting and antiferromagnetic
phases with decreasing temperature caused by a form of a superconducting
proximity effect.",0403340v1
2004-04-02,Stability of $π$ junction configurations in ferromagnet-superconductor heterostructures,"We investigate the stability of possible order parameter configurations in
clean layered heterostructures of the $SFS...FS$ type, where $S$ is a
superconductor and $F$ a ferromagnet. We find that for most reasonable values
of the geometric parameters (layer thicknesses and number) and of the material
parameters (such as magnetic polarization, wavevector mismatch, and oxide
barrier strength) several solutions of the {\it self consistent} microscopic
equations can coexist, which differ in the arrangement of the sequence of ``0''
and ``$\pi$'' junction types (that is, with either same or opposite sign of the
pair potential in adjacent $S$ layers). The number of such coexisting self
consistent solutions increases with the number of layers. Studying the relative
stability of these configurations requires an accurate computation of the small
difference in the condensation free energies of these inhomogeneous systems. We
perform these calculations, starting with numerical self consistent solutions
of the Bogoliubov-de Gennes equations. We present extensive results for the
condensation free energies of the different possible configurations, obtained
by using efficient and accurate numerical methods, and discuss their relative
stabilities. Results for the experimentally measurable density of states are
also given for different configurations and clear differences in the spectra
are revealed. Comprehensive and systematic results as a function of the
relevant parameters for systems consisting of three and seven layers (one or
three junctions) are given, and the generalization to larger number of layers
is discussed.",0404058v1
2004-06-05,Dependence of the superconducting critical temperature on the number of layers in homologous series of high-Tc cuprates,"We study a model of $n$-layer high-temperature cuprates of homologous series
like HgBa_2Ca_(n-1)Cu_nO_(2+2n+\delta) to explain the dependence of the
critical temperature Tc(n) on the number $n$ of Cu-O planes in the elementary
cell. Focusing on the description of the high-temperature superconducting
system in terms of the collective phase variables, we have considered a
semi-microscopic anisotropic three-dimensional vector XY model of stacked
copper-oxide layers with adjustable parameters representing microscopic
in-plane and out-of-plane phase stiffnesses. The model captures the layered
composition along c-axis of homologous series and goes beyond the
phenomenological Lawrence-Doniach model for layered superconductors.
Implementing the spherical closure relation for vector variables we have solved
the phase XY model exactly with the help of transfer matrix method and
calculated Tc(n) for arbitrary block size $n$, elucidating the role of the
c-axis anisotropy and its influence on the critical temperature. Furthermore,
we accommodate inhomogeneous charge distribution among planes characterized by
the charge imbalance coefficient $R$ being the function of number of layers
$n$. By making a physically justified assumption regarding the doping
dependence of the microscopic phase stiffnesses, we have calculated the values
of parameter $R$ as a function of block size $n$ in good agreement with the
nuclear magnetic resonance data of carrier distribution in multilayered high-Tc
cuprates.",0406142v1
2004-07-20,Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films,"We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots
and the preparation of room-temperature ferromagnetic nanocrystalline thin
films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation
reaction in DMSO under atmospheric conditions. Synthesis was monitored by
electronic absorption and electron paramagnetic resonance (EPR) spectroscopies.
Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the
synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from
the surfaces of as-prepared nanocrystals using dodecylamine to yield
high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and
uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and
Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic
susceptibilities, confirmed that the manganese is substitutionally incorporated
into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing
from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was
observed in spin-coated thin films of the nanocrystals, with 300 K saturation
moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct
ferromagnetic resonance signal was observed in the EPR spectra of the
ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its
dependence on synthetic variables are discussed in the context of these and
previous theoretical and experimental results.",0407500v1
2004-10-29,Quantum Mott Transition and Multi-Furcating Criticality,"Phenomenological theory of the Mott transition is presented. When the
critical temperature of the Mott transition is much higher than the quantum
degeneracy temperature, the transition is essentially described by the Ising
universality class. Below the critical temperature, phase separation or
first-order transition occurs. However, if the critical point is involved in
the Fermi degeneracy region, a marginal quantum critical point appears at zero
temperature. The originally single Mott critical point generates subsequent
many unstable fixed points through various Fermi surface instabilities induced
by the Mott criticality characterized by the diverging charge susceptibility or
doublon susceptibility. This occurs in marginal quantum-critical region.
Charge, magnetic and superconducting instabilitites compete severely under
these critical charge fluctuations. The quantum Mott transition triggers
multi-furcating criticality, which goes beyond the conventional concept of
multicriticality in quantum phase transitions. Near the quantum Mott
transition, the criticality generically drives growth of inhomogeneous
structure in the momentum space with singular points of flat dispersion on the
Fermi surface. The singular points determine the quantum dynamics of the Mott
transition by the dynamical exponent $z=4$. We argue that many of
filling-control Mott transitions are classified to this category. Recent
numerical results as well as experimental results on strongly correlated
systems including transition metal oxides, organic materials and $^3$He layer
adsorbed on a substrate are consistently analyzed especially in two-dimensional
systems.",0410753v1
2004-11-04,W=0 pairing in Hubbard and related models of low-dimensional superconductors,"Lattice Hamiltonians with on-site interaction $W$ have W=0 solutions, that
is, many-body {\em singlet} eigenstates without double occupation. In
particular, W=0 pairs give a clue to understand the pairing force in repulsive
Hubbard models. These eigenstates are found in systems with high enough
symmetry, like the square, hexagonal or triangular lattices. By a general
theorem, we propose a systematic way to construct all the W=0 pairs of a given
Hamiltonian. We also introduce a canonical transformation to calculate the
effective interaction between the particles of such pairs. In geometries
appropriate for the CuO$_{2}$ planes of cuprate superconductors, armchair
Carbon nanotubes or Cobalt Oxides planes, the dressed pair becomes a bound
state in a physically relevant range of parameters. We also show that W=0 pairs
quantize the magnetic flux like superconducting pairs do. The pairing mechanism
breaks down in the presence of strong distortions. The W=0 pairs are also the
building blocks for the antiferromagnetic ground state of the half-filled
Hubbard model at weak coupling. Our analytical results for the $4\times 4$
Hubbard square lattice, compared to available numerical data, demonstrate that
the method, besides providing intuitive grasp on pairing, also has quantitative
predictive power. We also consider including phonon effects in this scenario.
Preliminary calculations with small clusters indicate that vector phonons
hinder pairing while half-breathing modes are synergic with the W=0 pairing
mechanism both at weak coupling and in the polaronic regime.",0411101v1
2005-01-05,Hole crystallization in the spin ladder of Sr14Cu24O41,"One of the deepest questions in condensed matter physics concerns what other
phases compete with superconductivity in high-transition-temperature (high-Tc)
superconductors. One candidate is the ""stripe"" phase, in which the carriers
(holes) condense into rivers of charge separating regions of
antiferromagnetism. A related but lesser known system is the ""spin ladder"",
which consists of two coupled chains of magnetic ions forming an array of
rungs. A doped ladder can be thought of as a high-Tc material with lower
dimensionality, and has been predicted to exhibit both superconductivity and an
insulating ""hole crystal"" phase in which the carriers are localised through
many-body interactions. The competition between the two resembles that between
static stripes and superconductivity in high-Tc materials. Here we report
evidence, from resonant x-ray scattering, for the existence of a hole crystal
in the doped spin ladder of Sr14Cu24O41. This phase exists without a detectable
distortion in the structural lattice, indicating it arises from many-body
effects. Our measurements confirm theoretical predictions and support the
picture that proximity to charge ordered states is a general property of
superconductivity in copper-oxides.",0501087v1
2005-09-21,Effect of iron-doping on spin-state transition and ferromagnetism in Pr$_{0.5}$Ca$_{0.5}$CoO$_{3-δ}$ cobalt oxides,"Resistivity and dc magnetization measurements were performed for the
polycrystalline Pr$_{0.5}$Ca$_{0.5}$Co$_{1-x}$Fe$_{x}$O$_{3-\delta}$ ($x$ = 0,
0.05, 0.10 and 0.15) samples. The as-fabricated samples exhibit ferromagnetic
(FM) transition and the transition temperature increases with increasing the
iron doping level. Annealing under high oxygen pressure induces a spin-state
transition of Co ions in the \emph{iron-free} sample and such transition is
reinforced with increasing the annealing oxygen pressure, while the annealing
under high oxygen pressure suppresses the ferromagnetic ordering. Contrary to
the case of the \emph{iron-free} sample, no spin-state transition is induced by
the annealing under high oxygen pressure for the \emph{iron-doped} samples, and
the ferromagnetic transition temperature is nearly independent of the annealing
procedures. The enhancement of the spin-state transition in the
\emph{iron-free} sample after annealing under high oxygen pressure should be
attributed to the reduction of the cell volume. The suppression of the
spin-state transition by the Fe doping is related to the enlargement of the
cell volume and the stronger Fe-O bonds than Co-O bonds. The enhancement of the
ferromagnetism by the iron-doping might arise from the ferromagnetic exchange
interaction between Fe$^{3+}$ and Co$^{4+}$ through oxygen
(Fe$^{3+}$-O-Co$^{4+}$).",0509533v1
2005-11-01,"Spatially modulated ""Mottness"" in La2-xBaxCuO4","Stripe phases were predicted to arise in doped antiferromagnets through
competition between magnetism and the kinetic energy of mobile carriers
(typically holes). In copper-oxides the main experimental evidence for stripes
is neutron scattering from La1.48Nd0.4Sr0.12CuO4 (LNSCO) and La1.875Ba0.125CuO4
(LBCO) which reveals coexisting static spin and charge order whose wavelengths
differ by a factor of two, reminiscent of charged rivers separating regions of
oppositely-phased antiferromagnetism. A neutron is an electrically neutral
object, however, so does not detect charge but rather its associated lattice
distortion ; it is not known if the ""stripe"" phase in LNSCO and LBCO actually
involves ordering of the doped holes. Here we present a study of the charge
order in LBCO with resonant soft x-ray scattering (RSXS). We observe giant
resonances at both the mobile carrier and upper-Hubbard band features in the OK
edge. These demonstrate a substantial modulation in the doped hole density as
well as the amount of spectral weight near the correlated gap, i.e. the degree
of ""Mottness"". The peak-to-trough amplitude of the valence modulation is
estimated to be 0.063 holes, which if interpreted with a model of the stripe
form factor suggests an integrated area of 0.59 holes under a single stripe.
While only an estimate, this number agrees with what is expected for
half-filled stripes.",0511019v1
2005-12-03,Electron-phonon coupling reflecting dynamic charge inhomogeneity in copper-oxide superconductors,"The attempt to understand cuprate superconductors is complicated by the
presence of multiple strong interactions. While many believe that
antiferromagnetism is important for the superconductivity, there has been
revived interest in the role of electron-lattice coupling. The recently studied
conventional superconductor MgB2 has a very strong electron-lattice coupling,
involving a particular vibrational mode (phonon), that was predicted by
standard theory and confirmed quantitatively by experiment. Here we present
inelastic scattering measurements that show a similarly strong anomaly in the
Cu-O bond-stretching phonon in the cuprate superconductors La2-xSrxCuO4 (with
x=0.07, 0.15). This is in contrast to conventional theory, which does not
predict such behavior. The anomaly is strongest in La1.875Ba0.125CuO4 and
La1.48Nd0.4Sr0.12CuO4, compounds that exhibit spatially modulated charge and
magnetic order, often called stripe order. It occurs at a wave vector
corresponding to the charge order. These results suggest that this giant
electron-phonon anomaly, which is absent in undoped and over-doped
non-superconductors, is associated with charge inhomogeneity. It follows that
electron-phonon coupling may be important to our understanding of
superconductivity, although its contribution to the mechanism is likely to be
indirect.",0512063v2
2006-03-01,Theoretical Aspects of Charge Ordering in Molecular Conductors,"Theoretical studies on charge ordering phenomena in quarter-filled molecular
(organic) conductors are reviewed. Extended Hubbard models including not only
the on-site but also the inter-site Coulomb repulsion are constructed in a
straightforward way from the crystal structures, which serve for individual
study on each material as well as for their systematic understandings. In
general the inter-site Coulomb interaction stabilizes Wigner crystal-type
charge ordered states, where the charge localizes in an arranged manner
avoiding each other, and can drive the system insulating. The variety in the
lattice structures, represented by anisotropic networks in not only the
electron hopping but also in the inter-site Coulomb repulsion, brings about
diverse problems in low-dimensional strongly correlated systems. Competitions
and/or co-existences between the charge ordered state and other states are
discussed, such as metal, superconductor, and the dimer-type Mott insulating
state which is another typical insulating state in molecular conductors.
Interplay with magnetism, e.g., antiferromagnetic state and spin gapped state
for example due to the spin-Peierls transition, is considered as well. Distinct
situations are pointed out: influences of the coupling to the lattice degree of
freedom and effects of geometrical frustration which exists in many molecular
crystals. Some related topics, such as charge order in transition metal oxides
and its role in new molecular conductors, are briefly remarked.",0603008v2
2007-08-29,X-ray Anomalous Scattering of Diluted Magnetic Oxide Semiconductors: Possible Evidence of Lattice Deformation for High Temperature Ferromagnetism,"We have examined whether the Co ions crystallographically substitute on the
Ti sites in rutile and anatase Ti_{1-x}$Co$_{x}$O$_{2-delta}$ thin films that
exhibit room-temperature ferromagnetism. Intensities of the x-ray Bragg
reflection from the films were measured around the $K$-absorption-edge of Co.
If the Co ions randomly substitute on the Ti sites, the intensity should
exhibit an anomaly due to the anomalous dispersion of the atomic scattering
factor of Co. However, none of the anatase and rutile samples did exhibit an
anomaly, unambiguously showing that the Co ions in
Ti$_{1-x}$Co$_{x}$O$_{2-delta}$ are not exactly located at the Ti sites of
TiO$_2$. The absence of the anomaly is probably caused by a significant
deformation of the local structure around Co due to the oxygen vacancy. We have
applied the same method to paramagnetic Zn$_{1-x}$Co$_{x}$O thin films and
obtained direct evidence that the Co ions are indeed substituted on the Zn
sites.",0708.3876v1
2007-09-14,An inhomogeneous Josephson phase in thin-film and High-Tc superconductors,"In many cases inhomogeneities are known to exist near the metal (or
superconductor)-insulator transition, as follows from well-known domain-wall
arguments. If the conducting regions are large enough (i.e. when the T=0
superconducting gap is much larger than the single-electron level spacing), and
if they have superconducting correlations, it becomes energetically favorable
for the system to go into a Josephson-coupled zero-resistance state before
(i.e. at higher resistance than) becoming a ""real"" metal. We show that this is
plausible by a simple comparison of the relevant coupling constants. For small
grains in the above sense, the electronic grain structure is washed out by
delocalization and thus becomes irrelevant. When the proposed ""Josephson state""
is quenched by a magnetic field, an insulating, rather then a metallic, state
should appear. This has been shown to be consistent with the existing data on
oxide materials as well as ultra-thin films. We discuss the Uemura correlations
versus the Homes law, and derive the former for the large-grain Josephson array
(inhomogenous superconductor) model. The small-grain case behaves like a dirty
homogenous metal. It should obey the Homes law provided that the system is in
the dirty supeconductivity limit. A speculation why that is typically the case
for d-wave superconductors is presented.",0709.2321v1
2007-12-10,"Long Range Antiferromagnetic Ordering in the S = 1/2 Ordered Rock Salt Oxide, Li5OsO6: Comparison with the Isoelectronicand Isostructural Spin Glass, Li4MgReO6","Li5OsO6 and Li5ReO6 polycrystalline samples were synthesized by conventional
solid state methods. Employing powder neutron diffraction data, the crystal
structure of Li5OsO6 was re-investigated. Li5OsO6 crystallizes in C2/m space
group in an ordered NaCl structure type where a = 5.0472(1) A, b = 8.7827(2) A,
c = 5.0079(1) A, Beta = 109.777(2) degree and V = 208.90(1).A^3 Magnetic
susceptibility and heat capacity data indicate an AFM long range order below
40K although there is evidence for low dimensional short range order above 80K.
As well, the frustration index, f = |theta|/TN ~1, in contrast to the
isostructural and isoelectronic compound, Li4MgReO6, which is a spin glass
below 12K and has f ~ 14. An attempt was made to rationalize these differences
using spin dimer analysis. The key results are that the spin exchange
interactions in the Re-based compound are stronger and are consistent with a
frustrated triangular lattice model while a low dimensional short range order
model is better for Li5OsO6. The main reason for this is a strong Jahn-Teller
distortion in the OsO6 octahedron material which constrains the unpaired
electron to occupy the dxy orbital.",0712.1580v1
2008-02-20,Intersite 4p-3d hybridization in cobalt oxides: a resonant x-ray emission spectroscopy study,"We report on strong dipole transitions to 3d orbitals of neighboring Co atoms
in the Co 1s x-ray absorption pre-edge. They are revealed by applying
high-resolution resonant x-ray emission spectroscopy (RXES) to compounds
containing CoO6 clusters. When contrasted to quadrupole local 1s3d excitations,
these non-local 1s3d transitions are identified by their energy dispersion and
angular dependence, their sensitivity to second-shell effects (i.e. the
connection mode of the CoO6 octahedra and the bond lengths), and an upwards
energy shift of 2.5 eV due to the poorer screening of the core hole. The
experiment reveals that the intensity of the non-local transitions gauges the
oxygen-mediated 4p-O-3d intersite hybridization. We propose a revised
interpretation of the pre-edges of transition metal compounds. Detailed
analysis of these new features in the pre-edge offers a unique insight in the
oxygen mediated metal-metal interactions in transition metal-based systems,
which is a crucial aspect in orbital ordering and related electronic and
magnetic properties. In addition, the exceptional resolving power of the
present 1s2p RXES experiment allows us to demonstrate the coherent second-order
nature of the underlying scattering process.",0802.2744v1
2008-05-08,Anomalous Hall Effect in Magnetite: Universal Scaling Relation Between Hall and Longitudinal Conductivity in Low-Conductivity Ferromagnets,"The anomalous Hall effect (AHE) has been studied systematically in the
low-conductivity ferromagnetic oxide Fe$_{3-x}$Zn$_x$O$_4$ with $x = 0$, 0.1,
and 0.5. We used (001), (110), and (111) oriented epitaxial
Fe$_{3-x}$Zn$_x$O$_4$ films grown on MgO and sapphire substrates in different
oxygen partial pressure to analyze the dependence of the AHE on
crystallographic orientation, Zn content, strain state, and oxygen deficiency.
Despite substantial differences in the magnetic properties and magnitudes of
the anomalous Hall conductivity $\sigma_{xy}^{\rm AHE}$ and the longitudinal
conductivity $\sigma_{xx}$ over several orders of magnitude, a universal
scaling relation $\sigma_{xy}^{\rm AHE} \propto \sigma_{xx}^{\alpha}$ with
$\alpha = 1.69 \pm 0.08$ was found for all investigated samples. Our results
are in agreement with recent theoretical and experimental findings for
ferromagnetic metals in the dirty limit, where transport is by metallic
conduction. We find the same scaling relation for magnetite, where hopping
transport prevails. The fact that this relation is independent of
crystallographic orientation, Zn content, strain state, and oxygen deficiency
suggests that it is universal and particularly does not depend on the nature of
the transport mechanism.",0805.1120v1
2008-05-15,Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors,"In high transition temperature (T_c) superconductivity, charge doping is a
natural tuning parameter that takes copper oxides from the antiferromagnet to
the superconducting region. In the metallic state above T_c the standard
Landau's Fermi-liquid theory of metals as typified by the temperature squared
(T^2) dependence of resistivity appears to break down. Whether the origin of
the non-Fermi-liquid behavior is related to physics specific to the cuprates is
a fundamental question still under debate. We uncover a new transformation from
the non-Fermi- to a standard Fermi-liquid state driven not by doping but by
magnetic field in the overdoped high-T_c superconductor Tl_2Ba_2CuO_{6+x}. From
the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid
features appear above a sufficiently high field which decreases linearly with
temperature and lands at a quantum critical point near the superconductivity's
upper critical field -- with the Fermi-liquid coefficient of the T^2 dependence
showing a power-law diverging behavior on the approach to the critical point.
This field-induced quantum criticality bears a striking resemblance to that in
quasi-two dimensional heavy-Fermion superconductors, suggesting a common
underlying spin-related physics in these superconductors with strong electron
correlations.",0805.2215v1
2008-06-05,"Antiferromagnetic, Charge and Orbital Ordered States of Na0.5CoO2 Based on the Two-Dimensional Triangular Lattice d-p Model","We investigate the electronic state of a CoO_2 plane in the layered cobalt
oxides Na_xCoO_2 using the 11 band d-p model on a two-dimensional triangular
lattice, where the tight-binding parameters are determined so as to fit the LDA
band structure. Effects of the Coulomb interaction at a Co site: the intra- and
inter-orbital direct terms U and U', the exchange coupling J and the
pair-transfer J', are treated within the Hartree-Fock approximation. We also
consider the effect of the Na order at x=0.5, where Na ions form
one-dimensional chains, by taking into account of an effective one-dimensional
potential Delta epsilon_{d}. It is found that the one-dimensional Na order
enhances the Fermi surface nesting and antiferromagnetism is caused which is
suppressed due to the frustration effect in the case without the Na order. %It
is found that the Na order enhances the Fermi surface nesting resulting in a
metallic antiferromagnetism which is suppressed due to the frustration effect
in the case without the Na order. Furthermore, we consider the effect of the
Coulomb interaction between the nearest-neighbor Co sites V and find that a
coexistence of the magnetic, charge and orbital ordered state takes place for
V>V_c where the system becomes insulator.",0806.0911v1
2008-06-10,Unusual electron correlations in NaxCoO2 due to the spin-state quasidegeneracy of cobalt ions,"Recent studies exposed many remarkable properties of layered cobaltates
NaxCoO2. Surprisingly, many-body effects have been found to increase at
sodium-rich compositions of NaxCoO2 where one expects a simple, nearly free
motion of the dilute S=1/2 holes doped into a band insulator NaCoO2. Here we
discuss the origin of enigmatic correlations that turn a doped NaCoO2 into a
strongly correlated electronic system. A minimal model including orbital
degeneracy is proposed and its predictions are discussed. The model is based on
a key property of cobalt oxides - the spin-state quasidegeneracy of CoO6
octahedral complex - which has been known, e.g., in the context of an unusual
physics of LaCoO3 compound. Another important ingredient of the model is the
90-degree Co-O-Co bonding in NaxCoO2 which allows nearest-neighbor $t_{2g}-e_g$
hopping. This hopping introduces a dynamical mixture of electronic
configurations $t_{2g}^6, S=0$ and $t_{2g}^5e_g^1, S=1$ of neighboring cobalt
ions. We show that scattering of charge carriers on spin-state fluctuations
suppresses their coherent motion and leads to the spin-polaron physics at
$x\sim 1$. At larger doping when coherent fermionic bands are formed, the model
predicts singlet superconductivity of extended s-wave symmetry. The presence of
low-lying spin states of Co$^{3+}$ is essential for the pairing mechanism.
Implications of the model for magnetic orderings are also discussed.",0806.1682v1
2008-06-25,Spin dynamics in the pseudogap state of a high-temperature superconductor,"The pseudogap is one of the most pervasive phenomena of high temperature
superconductors. It is attributed either to incoherent Cooper pairing setting
in above the superconducting transition temperature Tc, or to a hidden order
parameter competing with superconductivity. Here we use inelastic neutron
scattering from underdoped YBa(2)Cu(3)O(6.6) to show that the dispersion
relations of spin excitations in the superconducting and pseudogap states are
qualitatively different. Specifically, the extensively studied ""hour glass""
shape of the magnetic dispersions in the superconducting state is no longer
discernible in the pseudogap state and we observe an unusual ""vertical""
dispersion with pronounced in-plane anisotropy. The differences between
superconducting and pseudogap states are thus more profound than generally
believed, suggesting a competition between these two states. Whereas the
high-energy excitations are common to both states and obey the symmetry of the
copper oxide square lattice, the low-energy excitations in the pseudogap state
may be indicative of collective fluctuations towards a state with broken
orientational symmetry predicted in theoretical work.",0806.4134v1
2008-06-27,Electron pockets in the Fermi surface of hole-doped high-Tc superconductors,"High-temperature superconductivity occurs as copper oxides are chemically
tuned to have a carrier concentration intermediate between their metallic state
at high doping and their insulating state at zero doping. The underlying
evolution of the electron system in the absence of superconductivity is still
unclear and a question of central importance is whether it involves any
intermediate phase with broken symmetry. The Fermi surface of underdoped
YBa2Cu3Oy and YBa2Cu4O8 was recently shown to include small pockets in contrast
with the large cylinder characteristic of the overdoped regime1, pointing to a
topological change in the Fermi surface. Here we report the observation of a
negative Hall resistance in the magnetic field-induced normal state of
YBa2Cu3Oy and YBa2Cu4O8, which reveals that these pockets are electron-like. We
propose that electron pockets arise most likely from a reconstruction of the
Fermi surface caused by the onset of a density-wave phase, as is thought to
occur in the electron-doped materials near the onset of antiferromagnetic order
Comparison with materials of the La2CuO4 family that exhibit spin/charge
density-wave order suggests that a Fermi surface reconstruction also occurs in
those materials, pointing to a generic property of high-Tc superconductors.",0806.4621v1
2009-02-12,"Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in LnBaMn1.96Fe0.04O5, LnBaMn1.96Fe0.04O6 and LnBaMn1.96Fe0.04O5.5 (Ln=Y, Gd, Sm, Nd, Pr, La)","The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La)
have been synthesized for y=5, 5.5 and 6. In the oxygen-saturated state (y=6)
they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd,
Sm, but unordered eg-electronic system for Ln=La,Pr,Nd. Fourfold increase of
quadrupole splitting was observed owing to the charge and orbital ordering.
This is in agreement with the jumplike increase in distortion of the reduced
perovskite-like cell for the charge and orbitally ordered manganites compared
to the unordered ones. Substitution of 2 percents of Mn by Fe suppresses the
temperatures of structural and magnetic transitions by 20 to 50 K. Parameters
of the crystal lattices and the room-temperature M\""{o}ssbauer spectra were
studied on forty samples whose structures were refined within five symmetry
groups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fe
species are undifferentiated in the M\""{o}ssbauer spectra for most of the
samples. Such the single-component spectra in the two-site structures are
explained by the preference of Fe towards the site of Mn(III) and by the
segmentation of the charge and orbitally ordered domains.",0902.2027v2
2009-04-26,Anomalous Hall effect,"We present a review of experimental and theoretical studies of the anomalous
Hall effect (AHE), focusing on recent developments that have provided a more
complete framework for understanding this subtle phenomenon and have, in many
instances, replaced controversy by clarity. Synergy between experimental and
theoretical work, both playing a crucial role, has been at the heart of these
advances. On the theoretical front, the adoption of Berry-phase concepts has
established a link between the AHE and the topological nature of the Hall
currents which originate from spin-orbit coupling. On the experimental front,
new experimental studies of the AHE in transition metals, transition-metal
oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors, have
more clearly established systematic trends. These two developments in concert
with first-principles electronic structure calculations, strongly favor the
dominance of an intrinsic Berry-phase-related AHE mechanism in metallic
ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in
terms of Berry-phase curvatures and it is therefore an intrinsic quantum
mechanical property of a perfect cyrstal. An extrinsic mechanism, skew
scattering from disorder, tends to dominate the AHE in highly conductive
ferromagnets. We review the full modern semiclassical treatment of the AHE
together with the more rigorous quantum-mechanical treatments based on the Kubo
and Keldysh formalisms, taking into account multiband effects, and demonstrate
the equivalence of all three linear response theories in the metallic regime.
Finally we discuss outstanding issues and avenues for future investigation.",0904.4154v1
2009-05-18,Two-orbital SU(N) magnetism with ultracold alkaline-earth atoms,"Fermionic alkaline-earth atoms have unique properties that make them
attractive candidates for the realization of novel atomic clocks and degenerate
quantum gases. At the same time, they are attracting considerable theoretical
attention in the context of quantum information processing. Here we demonstrate
that when such atoms are loaded in optical lattices, they can be used as
quantum simulators of unique many-body phenomena. In particular, we show that
the decoupling of the nuclear spin from the electronic angular momentum can be
used to implement many-body systems with an unprecedented degree of symmetry,
characterized by the SU(N) group with N as large as 10. Moreover, the interplay
of the nuclear spin with the electronic degree of freedom provided by a stable
optically excited state allows for the study of spin-orbital physics. Such
systems may provide valuable insights into strongly correlated physics of
transition metal oxides, heavy fermion materials, and spin liquid phases.",0905.2610v2
2009-10-23,139La NMR evidence for phase solitons in the ground state of overdoped manganites,"Hole doped transition metal oxides are famous due to their extraordinary
charge transport properties, such as high temperature superconductivity
(cuprates) and colossal magnetoresistance (manganites). Astonishing, the mother
system of these compounds is a Mott insulator, whereas important role in the
establishment of the metallic or superconducting state is played by the way
that holes are self-organized with doping. Experiments have shown that by
adding holes the insulating phase breaks into antiferromagnetic (AFM) regions,
which are separated by hole rich clumps (stripes) with a rapid change of the
phase of the background spins and orbitals. However, recent experiments in
overdoped manganites of the La(1-x)Ca(x)MnO(3) (LCMO) family have shown that
instead of charge stripes, charge in these systems is organized in a uniform
charge density wave (CDW). Besides, recent theoretical works predicted that the
ground state is inhomogeneously modulated by orbital and charge solitons, i.e.
narrow regions carrying charge (+/-)e/2, where the orbital arrangement varies
very rapidly. So far, this has been only a theoretical prediction. Here, by
using 139La Nuclear Magnetic Resonance (NMR) we provide direct evidence that
the ground state of overdoped LCMO is indeed solitonic. By lowering temperature
the narrow NMR spectra observed in the AFM phase are shown to wipe out, while
for T<30K a very broad spectrum reappears, characteristic of an incommensurate
(IC) charge and spin modulation. Remarkably, by further decreasing temperature,
a relatively narrow feature emerges from the broad IC NMR signal, manifesting
the formation of a solitonic modulation as T->0.",0910.4494v1
2010-02-22,Quasiparticle Interference in the Unconventional Metamagnetic Compound Sr$_3$Ru$_2$O$_7$,"Quasiparticle interference (QPI) in spectroscopic imaging scanning tunneling
microscopy provides a powerful method to detect orbital band structures and
orbital ordering patterns in transition metal oxides. We use the $T$-matrix
formalism to calculate the QPI spectra for the unconventional metamagnetic
system of Sr$_3$Ru$_2$O$_7$ with a $t_{2g}$-orbital band structure. A detailed
tight-binding model is constructed accounting for features such as spin-orbit
coupling, bilayer splitting, and the staggered rotation of the RuO octahedra.
The band parameters are chosen by fitting the calculated Fermi surfaces with
those measured in the angular-resolved photo-emission spectroscopy experiment.
The calculated quasiparticle interference at zero magnetic field exhibits a
hollow square-like feature arising from the nesting of the quasi-1d $d_{xz}$
and $d_{yz}$ orbital bands, in agreement with recent measurements by J. Lee
{\it et al.} (Nature Physics {\bf 5}, 800 (2009)). Rotational symmetry breaking
in the nematic metamagnetic state also manifests in the quasi-particle
interference spectra.",1002.4079v5
2010-06-02,"Electric and magnetic polarizabilities of hexagonal Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb)","We investigated the rare-earth transition metal oxide series, Ln2CuTiO6
(Ln=Y, Dy, Ho, Er and Yb), crystallizing in the hexagonal structure with
non-centrosymmetric P63cm space group for possible occurrences of multiferroic
properties. Our results show that while these compounds, except Ln=Y, exhibit a
low temperature antiferromagnetic transition due to the ordering of the
rare-earth moments, the expected ferroelectric transition is frustrated by the
large size difference between Cu and Ti at the B-site. Interestingly, this
leads these compounds to attain a rare and unique combination of desirable
paraelectric properties with high dielectric constants, low losses and weak
temperature and frequency dependencies. First-principles calculations establish
these exceptional properties result from a combination of two effects. A
significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti
suppress the expected co-operative tilt pattern of these polyhedra, required
for the ferroelectric transition, leading to relatively large values of the
dielectric constant for every compound investigated in this series.
Additionally, it is shown that the majority contribution to the dielectric
constant arises from intermediate-frequency polar vibrational modes, making it
relatively stable against any temperature variation. Changes in the temperature
stability of the dielectric constant amongst different members of this series
are shown to arise from changes in relative contributions from soft polar
modes.",1006.0417v2
2010-07-14,Combining DFT and Many-Body Methods to Understand Correlated Materials,"The electronic and magnetic properties of many strongly-correlated systems
are controlled by a limited number of states, located near the Fermi level and
well isolated from the rest of the spectrum. This opens a formal way for
combining the methods of first-principles electronic structure calculations,
based on the density-functional theory (DFT), with many-body models, formulated
in the restricted Hilbert space of states close to the Fermi level. The core of
this project is the so-called ""realistic modeling"" or the construction of the
model many-body Hamiltonians entirely from the first principles. Such a
construction should be able to go beyond the conventional local-density
approximation (LDA), which typically supplements the density-functional theory,
and incorporate the physics of Coulomb correlations. It should also provide a
transparent physical picture for the low-energy properties of strongly
correlated materials. In this review article, we will outline the basic ideas
of such a realistic modeling. The entire procedure will be illustrated on the
series of examples, including the distorted transition-metal perovskite oxides,
the compounds with the inversion symmetry breaking caused by the defects, and
the alkali hyperoxide KO2, which can be regarded as an analog of
strongly-correlated systems where the localized electrons reside on the
molecular orbitals of the O2- dimer. In order to illustrate abilities of the
realistic modeling, we will also consider solutions of the obtained low-energy
models for a number of systems, and argue that it can be used as a powerful
tool for the exploration and understanding of properties of strongly correlated
materials.",1007.2271v1
2010-07-19,Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states,"In the high-transition-temperature (high-Tc) superconductors the pseudogap
phase becomes predominant when the density of doped holes is reduced1. Within
this phase it has been unclear which electronic symmetries (if any) are broken,
what the identity of any associated order parameter might be, and which
microscopic electronic degrees of freedom are active. Here we report the
determination of a quantitative order parameter representing intra-unit-cell
nematicity: the breaking of rotational symmetry by the electronic structure
within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling
microscope images of the intra-unit-cell states in underdoped
Bi2Sr2CaCu2O8+{\delta} and, using two independent evaluation techniques, find
evidence for electronic nematicity of the states close to the pseudogap energy.
Moreover, we demonstrate directly that these phenomena arise from electronic
differences at the two oxygen sites within each unit cell. If the
characteristics of the pseudogap seen here and by other techniques all have the
same microscopic origin, this phase involves weak magnetic states at the O
sites that break 90o -rotational symmetry within every CuO2 unit cell.",1007.3216v1
2010-12-07,Pauli Spin Blockade in a Highly Tunable Silicon Double Quantum Dot,"Double quantum dots are convenient solid-state platforms to encode quantum
information. Two-electron spin states can be conveniently detected and
manipulated using strong quantum selection rules based on the Pauli exclusion
principle, leading to the well-know Pauli spin blockade of electron transport
for triplet states. Coherent spin states would be optimally preserved in an
environment free of nuclear spins, which is achievable in silicon by isotopic
purification. Here we report on a deliberately engineered, gate-defined silicon
metal-oxide-semiconductor double quantum dot system. The electron occupancy of
each dot and the inter-dot tunnel coupling are independently tunable by
electrostatic gates. At weak inter-dot coupling we clearly observe Pauli spin
blockade and measure a large intra-dot singlet-triplet splitting $>$ 1 meV. The
leakage current in spin blockade has a peculiar magnetic field dependence,
unrelated to electron-nuclear effects and consistent with the effect of
spin-flip cotunneling processes. The results obtained here provide excellent
prospects for realizing singlet-triplet qubits in silicon.",1012.1410v2
2010-12-10,Pairing mechanism of high-temperature superconductivity: Experimental constraints,"Developing a theory of high-temperature superconductivity in copper oxides is
one of the outstanding problems in physics. It is a challenge that has defeated
theoretical physicists for more than twenty years. Attempts to understand this
problem are hindered by the subtle interplay among a few mechanisms and the
presence of several nearly degenerate and competing phases in these systems.
Here we present some crucial experiments that place essential constraints on
the pairing mechanism of high-temperature superconductivity. The observed
unconventional oxygenisotope effects in cuprates have clearly shown strong
electron-phonon interactions and the existence of polarons and/or bipolarons.
Angle-resolved photoemission and tunneling spectra have provided direct
evidence for strong coupling to multiple-phonon modes. In contrast, these
spectra do not show strong coupling features expected for magnetic resonance
modes. Angle-resolved photoemission spectra and the oxygen-isotope effect on
the antiferromagnetic exchange energy J in undoped parent compounds
consistently show that the polaron binding energy is about 2 eV, which is over
one order of magnitude larger than J = 0.14 eV. The normal-state
spin-susceptibility data of holedoped cuprates indicate that intersite
bipolarons are the dominant charge carriers in the underdoped region while the
component of Fermi-liquid-like polarons is dominant in the overdoped region.
All the experiments to test the gap or order-parameter symmetry consistently
demonstrate that the intrinsic gap (pairing) symmetry for the Fermi-liquid-like
component is anisotropic s-wave and the order-parameter symmetry of the
Bose-Einstein condensation of bipolarons is d-wave.",1012.2368v2
2011-06-30,Hole spectral functions in lightly doped quantum antiferromagnets,"We study the hole and magnon spectral functions as a function of hole doping
in the two-dimensional (2D) t-J and t-t'-t""-J models working within the limits
of the spin-wave theory, by linearizing the hole-spin-deviation interaction and
by adapting the non-crossing approximation (NCA). We find that the staggered
magnetization decreases rather rapidly with doping and it goes to zero at a few
percent of hole concentration in both t-J and the t-t'-t""-J model. We find that
with doping, the residue of the quasiparticle peak at G=(pi/2,pi/2) decreases
rapidly with doping and the spectral function is in agreement with high
resolution angle-resolved photo-emission spectroscopy (ARPES) studies of the
copper-oxide superconductors. The observed large shift of the chemical
potential inside the Mott gap is found to be a result of broadening of the
quasiparticle peak. We find pockets centered at G, similar to those observed by
quantum oscillation measurements, (i) with an elliptical shape with large
eccentricity along the anti-nodal direction in the case of the t-J model, and
(ii) with an almost circular shape in the case of the t-t'-t""-J model. We also
find that the spectral intensity distribution in the doped antiferromagnet has
a waterfall-like patten along the nodal direction of the Brillouin zone, a
feature that is also seen in ARPES measurements.",1106.6332v1
2011-09-27,Boron Nitride Nanotubes as Templates for Half-Metal Nanowires,"We investigate by means of DFT/GGA+U calculations the electronic and
structural properties of magnetic nanotubes composed of an iron oxide monolayer
and (n,0) Boron Nitride (BN) nanotubes, with n ranging from 6 up to 14. The
formation energy per FeO molecule of FeO covered tubes is smaller than the
formation energy of small FeO nanoparticles which suggest that the FeO
molecules may cover the BN nanotubes rather than to aggregate to form the FeO
bulk. We propose a continuous model for the FeO covered BN nanotubes formation
energy which predicts that BN tubes with diameter of roughly 13 \AA are the
most stable. Unlike carbon nanotubes, the band structure of FeO covered BN
nanotubes can not be obtained by slicing the band structure of a FeO layer, the
curvature and the interaction with the BN tube is determinant for the
electronic behavior of FeO covered tubes. As a result the tubes are
semiconductors, intrinsic half-metals or semi-half-metals that can become
half-metals charged with either electrons and holes. Such a result may be
important in the spintronics context.",1109.5936v1
2011-10-27,Effect of spin relaxation rate on the interfacial spin depolarization in ferromagnet/oxide/semiconductor contacts,"Combined measurements of normal and inverted Hanle effects in
CoFe/MgO/semiconductor (SC) contacts reveal the effect of spin relaxation rate
on the interfacial spin depolarization (ISD) from local magnetic fields.
Despite the similar ferromagnetic electrode and interfacial roughness in both
CoFe/MgO/Si and CoFe/MgO/Ge contacts, we have observed clearly different
features of the ISD depending on the host SC. The precession and relaxation of
spins in different SCs exposed to the local fields from more or less the same
ferromagnets give rise to a notably different ratio of the inverted Hanle
signal to the normal one. At room temperature, a large ISD is observed in the
CoFe/MgO/Si contact, but a small ISD in the CoFe/MgO/Ge contact. The ISD of the
CoFe/MgO/Ge contact has been substantially increased at low temperature. These
results can be ascribed to the difference of spin relaxation in host SCs. A
model calculation of the ISD, considering the spin precession due to the local
field and the spin relaxation in the host SC, explains the temperature and bias
dependence of the ISD consistently.",1110.5978v2
2011-11-30,Semimetal and Topological Insulator in Perovskite Iridates,"The two-dimensional layered perovskite Sr2IrO4 was proposed to be a
spin-orbit Mott insulator, where the effect of Hubbard interaction is amplified
on a narrow J_{eff} = 1/2 band due to strong spin-orbit coupling. On the other
hand, the three-dimensional orthorhombic perovskite (Pbnm) SrIrO3 remains
metallic. To understand the physical origin of the metallic state and possible
transitions to insulating phases, we construct a tight-binding model for
SrIrO3. The band structure possesses a line node made of J_{eff} = 1/2 bands
below the Fermi level. As a consequence, instability towards magnetic ordering
is suppressed and the system remains metallic. This line node, originating from
the underlying crystal structure, turns into a pair of three-dimensional nodal
points on the introduction of a staggered potential or spin-orbit coupling
strength between alternating layers. Increasing this potential beyond a
critical strength induces a transition to a strong topological insulator,
followed by another transition to a normal band insulator. We propose that
materials constructed with alternating Ir- and Rh-oxide layers along the (001)
direction, such as Sr2IrRhO6, are candidates for a strong topological
insulator.",1112.0015v2
2011-12-21,"Resonant soft x-ray scattering, stripe order, and the electron spectral function in cuprates","We review the current state of efforts to use resonant soft x-ray scattering
(RSXS), which is an elastic, momentum-resolved, valence band probe of strongly
correlated electron systems, to study stripe-like phenomena in copper-oxide
superconductors and related materials. We review the historical progress
including RSXS studies of Wigner crystallization in spin ladder materials,
stripe order in 214-phase nickelates, 214-phase cuprates, and other systems.
  One of the major outstanding issues in RSXS concerns its relationship to more
established valence band probes, namely angle-resolved photoemission (ARPES)
and scanning tunneling microscopy (STM). These techniques are widely understood
as measuring a one-electron spectral function, yet a relationship between RSXS
and a spectral function has so far been unclear. Using physical arguments that
apply at the oxygen $K$ edge, we show that RSXS measures the square modulus of
an advanced version of the Green's function measured with STM. This indicates
that, despite being a momentum space probe, RSXS is more closely related to STM
than to ARPES techniques.
  Finally, we close with some discussion of the most promising future
directions for RSXS. We will argue that the most promising area lies in high
magnetic field studies, particularly of edge states in strongly correlated
heterostructures, and the vortex state in superconducting cuprates, where RSXS
may clarify the anomalous periodicities observed in recent quantum oscillation
experiments.",1112.5112v2
2012-09-20,Virtual Synthesis of Nanoscale Systems with Pre-Designed Properties: Fundamentals and Applications. Chapter 7. Nickel Oxide Quantum Dots and Polymer Nanowires,"The virtual (i.e., fundamental many body quantum theory-based, computational)
synthesis method is used to establish electronic templates of about 30
non-stoichiometric nanosystems composed of nickel and oxygen atoms and ranging
from about 6 {\AA} to 6 nm in linear dimensions. Flexible and stretchable Ni-O
bond in such structures accommodates various ratios of Ni to O atoms, and both
antiferromagnetic and ferromagnetic spin alignments. Depending on synthesis
conditions, smaller Ni-O quantum dots (QDs) composed of up to 14 atoms or so
may have both types of spin alignments, while quantum-confined, quasi one
dimensional Ni-O nanowires (QWs) appear to be nanopolymers with
antiferromagnetic spin alignment. Ni-O bond flexibility and related ease of
spin re-arrangement may facilitate physical mechanisms leading to the
development or loss of exchange bias when such Ni-O quantum dots and wires
(QDWs) interact with surfaces or each other at some thermochemical conditions.
These structural and compositional flexibility is reflected by QDWs' molecular
electrostatic potential (MEP) and electronic level structure (ELS). In
particular, the direct optical transition energy (OTE) of the studied Ni-O
systems may vary within an order of magnitude, and their electronic and
magnetic properties can be finely tuned to match applications requirements by
manipulations with synthesis conditions, the structure and composition of
quantum confinement. The developed electronic templates are available upon
request.",1209.4666v1
2012-10-25,Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity,"Large-grain Nb has become a viable alternative to fine-grain Nb for the
fabrication of superconducting radio-frequency cavities. In this contribution
we report the results from a heat treatment study of a large-grain 1.5 GHz
single-cell cavity made of ""medium purity"" Nb. The baseline surface preparation
prior to heat treatment consisted of standard buffered chemical polishing. The
heat treatment in the range 800 - 1400 C was done in a newly designed vacuum
induction furnace. Q0 values of the order of 2x1010 at 2.0 K and peak surface
magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0-value of
(5+-1)1010 at 2.0 K and Bp = 90 mT was obtained after heat treatment at 1400 C.
This is the highest value ever reported at this temperature, frequency and
field. Samples heat treated with the cavity at 1400 C were analyzed by
secondary ion mass spectrometry, secondary electron microscopy, energy
dispersive X-ray, point contact tunneling and X-ray diffraction and revealed a
complex surface composition which includes titanium oxide, increased carbon and
nitrogen content but reduced hydrogen concentration compared to a non
heat-treated sample.",1210.6875v4
2012-11-14,Synthesis of Homogeneous Manganese-Doped Titanium Oxide Nanotubes from Titanate Precursors,"We report a novel synthesis route of homogeneously manganese-doped titanium
dioxide nanotubes in a broad concentration range. The scroll-type trititanate
(H(2)Ti(3)O(7)) nanotubes prepared by hydrothermal synthesis were used as
precursors. Mn2+ ions were introduced by an ion exchange method resulting
Mn(x)H(2-x)Ti(3)O(7). In a subsequent heat-treatment they were transformed into
Mn(y)Ti(1-y)O(2) where y=x/(3+x). The state and the local environment of the
Mn2+ ions in the precursor and final products were studied by Electron Spin
Resonance (ESR) technique. It was found that the Mn2+ ions occupy two
positions: the first having an almost perfect cubic symmetry while the other is
in a strongly distorted octahedral site. The ratio of the two Mn2+ sites is
independent of the doping level and amounts to 15:85 in Mn(x)H(2-x)Ti(3)O(7)
and to 5:95 in Mn(y)Ti(1-y)O(2). SQUID magnetometry does not show long-range
magnetic order in the homogeneously Mn2+-doped nanotubes.",1211.3459v2
2013-03-20,Performance of Titanium-Oxide/Polymer Insulation in Bi-2212/Ag-alloy Round Wire Wound Superconducting Coils,"Conductor insulation is one of the key components needed to make Ag-alloy
clad Bi2Sr2CaCu2O8+x (Bi-2212/Ag) superconducting round wire (RW) successful
for high field magnet applications as dielectric standoff and high winding
current densities (Jw) directly depend on it. In this study, a TiO2/polymer
insulation coating developed by nGimat LLC was applied to test samples and a
high field test coil. The insulation was investigated by differential thermal
analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy
(SEM), dielectric properties measurement, and transport critical current (Ic)
properties measurement. About 29% of the insulation by weight is polymer. When
the Bi-2212/Ag wire is full heat treated, this decomposes with slow heating to
400{\deg}C in pure O2. After the full reaction, we found that the TiO2 did not
degrade the critical current properties, adhered well to the conductor, and
provided a breakdown voltage of >100 V, which allowed the test coil to survive
quenching in 31.2 T background field, while providing a 2.6 T field increment.
For Bi-2212/Ag RW with a typical diameter of 1.0-1.5 mm, this ~15 um thick
insulation allows a very high coil packing factor of ~0.74, whereas earlier
alumino-silicate braid insulation only allows packing factors of 0.38-0.48.",1303.4810v1
2013-03-28,Microscopic and Spectroscopic Evidence for a Slater Metal-Insulator Transition in Sr2IrO4,"Layered 5d transition metal oxides (TMOs) have attracted significant interest
in recent years because of the rich physical properties induced by the
interplay between spin-orbit coupling, bandwidth and on-site Coulomb repulsion.
In Sr2IrO4, this interplay opens a gap near the Fermi energy and stabilizes a
Jeff=1/2 spin-orbital entangled insulating state at low temperatures. Whether
this metal-insulating transition (MIT) is Mott-type (electronic-correlation
driven) or Slater-type (magnetic-order driven) has been under intense debate.
We address this issue via spatially resolved imaging and spectroscopic studies
of the Sr2IrO4 surface using scanning tunneling microscopy/spectroscopy
(STM/S). The STS results clearly illustrate the opening of the (~150-250 meV)
insulating gap at low temperatures, in qualitative agreement with our
density-functional theory (DFT) calculations. More importantly, the measured
temperature dependence of the gap width coupled with our DFT+dynamical mean
field theory (DMFT) results strongly support the Slater-type MIT scenario in
Sr2IrO4. The STS data further reveal a pseudogap structure above the Neel
temperature, presumably related to the presence of antiferromagnetic
fluctuations.",1303.7265v2
2013-05-17,Onsager's Wien Effect on a Lattice,"The Second Wien Effect describes the non-linear, non-equilibrium response of
a weak electrolyte in moderate to high electric fields. Onsager's 1934
electrodiffusion theory along with various extensions has been invoked for
systems and phenomena as diverse as solar cells, surfactant solutions, water
splitting reactions, dielectric liquids, electrohydrodynamic flow, water and
ice physics, electrical double layers, non-Ohmic conduction in semiconductors
and oxide glasses, biochemical nerve response and magnetic monopoles in spin
ice. In view of this technological importance and the experimental ubiquity of
such phenomena, it is surprising that Onsager's Wien effect has never been
studied by numerical simulation. Here we present simulations of a lattice
Coulomb gas, treating the widely applicable case of a double equilibrium for
free charge generation. We obtain detailed characterisation of the Wien effect
and confirm the accuracy of the analytical theories as regards the field
evolution of the free charge density and correlations. We also demonstrate that
simulations can uncover further corrections, such as how the field-dependent
conductivity may be influenced by details of microscopic dynamics. We conclude
that lattice simulation offers a powerful means by which to investigate
system-specific corrections to the Onsager theory, and thus constitutes a
valuable tool for detailed theoretical studies of the numerous practical
applications of the Second Wien Effect.",1305.4072v2
2013-05-17,"Spins, Stripes, and Superconductivity in Hole-Doped Cuprates","One of the major themes in correlated electron physics over the last quarter
century has been the problem of high-temperature superconductivity in
hole-doped copper-oxide compounds. Fundamental to this problem is the
competition between antiferromagnetic spin correlations, a symptom of strong
Coulomb interactions, and the kinetic energy of the doped carriers, which
favors delocalization. After discussing some of the early challenges in the
field, I describe the experimental picture provided by a variety of
spectroscopic and transport techniques. Then I turn to the technique of neutron
scattering, and discuss how it is used to determine spin correlations,
especially in model systems of quantum magnetism. Neutron scattering and
complementary techniques have determined the extent to which antiferromagnetic
spin correlations survive in the cuprate superconductors. One experimental case
involves the ordering of spin and charge stripes. I first consider related
measurements on model compounds, such as La(2-x)Sr(x)NiO(4+d), and then discuss
the case of La(2-x)Ba(x)CuO(4). In the latter system, recent transport studies
have demonstrated that quasi-two-dimensional superconductivity coexists with
the stripe order, but with frustrated phase order between the layers. This has
led to new concepts for the coexistence of spin order and superconductivity.
While the relevance of stripe correlations to high-temperature
superconductivity remains a subject of controversy, there is no question that
stripes are an intriguing example of electron matter that results from strong
correlations.",1305.4118v1
2013-10-17,Insights into the Phase Diagram of Bismuth Ferrite from Quasi-Harmonic Free Energy Calculations,"We have used first-principles methods to investigate the phase diagram of
multiferroic bismuth ferrite (BiFeO3 or BFO), revealing the energetic and
vibrational features that control the occurrence of various relevant
structures. More precisely, we have studied the relative stability of four
low-energy BFO polymorphs by computing their free energies within the
quasi-harmonic approximation, introducing a practical scheme that allows us to
account for the main effects of spin disorder. As expected, we find that the
ferroelectric ground state of the material (with R3c space group) transforms
into an orthorhombic paraelectric phase (Pnma) upon heating. We show that this
transition is not significantly affected by magnetic disorder, and that the
occurrence of the Pnma structure relies on its being vibrationally (although
not elastically) softer than the R3c phase. We also investigate a
representative member of the family of nano-twinned polymorphs recently
predicted for BFO [Prosandeev et al., Adv. Funct. Mater. 23, 234 (2013)] and
discuss their possible stabilization at the boundaries separating the R3c and
Pnma regions in the corresponding pressure-temperature phase diagram. Finally,
we elucidate the intriguing case of the so-called super-tetragonal phases of
BFO: Our results explain why such structures have never been observed in the
bulk material, despite their being stable polymorphs of very low energy.
Quantitative comparison with experiment is provided whenever possible, and the
relative importance of various physical effects (zero-point motion, spin
fluctuations, thermal expansion) and technical features (employed
exchange-correlation energy density functional) is discussed. Our work attests
the validity and usefulness of the quasi-harmonic scheme to investigate the
phase diagram of this complex oxide, and prospective applications are
discussed.",1310.4703v1
2013-11-25,Theory of nodal s+- wave pairing symmetry in the Pu-based 115 superconductor family,"The spin-fluctuation mechanism of superconductivity usually results in the
presence of gapless or nodal quasiparticle states in the excitation spectrum.
Nodal quasiparticle states are well established in copper-oxide, and
heavy-fermion superconductors, but not in iron-based superconductors. Here, we
study the pairing symmetry and mechanism of a new class of plutonium-based
high-Tc superconductors and predict the presence of a nodal $s^{+-}$ wave
pairing symmetry in this family. Starting from a density-functional theory
(DFT) based electronic structure calculation we predict several
three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We
identify the dominant Fermi surface ``hot-spots' in the inter-band scattering
channel, which are aligned along the wavevector ${\bf Q}\sim(\pi,\pi,\pi)$,
where degeneracy could induce sign-reversal of the pairing symmetry. Our
calculation demonstrates that the $s^{+-}$ wave pairing strength is stronger
than the previously thought $d$-wave pairing; and more importantly, this
pairing state allows for the existence of nodal quasiparticles. Finally, we
predict the shape of the momentum- and energy-dependent magnetic resonance
spectrum for the identification of this pairing symmetry.",1311.6410v2
2013-11-26,Local Reconstructions of Silicene Induced by Adatoms,"The interaction of silicene with Si, C, H, O, Ti atoms along with H$_2$,
H$_2$O and O$_2$ molecules are investigated and the induced functionalities
thereof are analyzed using first principles density functional theory. Si
adatom initially adsorbed at the top site of silicene pushes down the Si atom
underneath to form a dumbbell like structure with 3+1 coordination. This
prediction is important for silicene research and reveal new physical phenomena
related with the formation of multilayer Si, which is apparently the precursor
state for missing layered structure of silicon. We found that dumbbell
structure attributes coverage dependent electronic and magnetic properties to
nonmagnetic bare silicene. Even more interesting is that silicene with
dumbbells is energetically more favorable than the pristine silicene: The more
dense the dumbbell coverage, the stronger is the cohesion. Incidentally, these
structures appear to be intermediate between between silicene and silicon.
Carbon adatom, which is initially adsorbed to the bridge position, substitutes
one Si atom, if it overcomes a small energy barrier. Oxygen molecule can
dissociate on silicene surface, whereby constituent oxygen atoms oxidize
silicene by forming strong bonds. By varying the concentration and decoration
of carbon, hydrogen and oxygen atoms one can tune the band gap of silicene.
Through the adsorption of hydrogen or titanium adatom, silicene acquires spin
polarized state. A half metallic ferromagnetic behavior is attained at specific
uniform coverage of Ti adatom, which may function as a spin valve.",1311.6657v1
2014-04-24,Competition between heavy-fermion and Kondo interaction in isoelectronic A-site ordered perovskites,"With current research efforts shifting towards the 4$d$ and 5$d$ transition
metal oxides, understanding the evolution of the electronic and magnetic
structure as one moves away from 3$d$ materials is of critical importance. Here
we perform X-ray spectroscopy and electronic structure calculations on $A$-site
ordered perovskites with Cu in the $A$-site and the $B$-sites descending along
the 9th group of the periodic table to elucidate the emerging properties as
$d$-orbitals change from partially filled 3$d$, 4$d$, to 5$d$. The results show
that when descending from Co to Ir the charge transfers from the cuprate like
Zhang-Rice state on Cu to the t$_{2g}$ orbital of the B site. As the Cu
$d$-orbital occupation approaches the Cu$^{2+}$ limit, a mixed-valence state in
CaCu$_3$Rh$_4$O$_{12}$ and heavy fermion state in CaCu$_3$Ir$_4$O$_{12}$ are
obtained. The investigated d-electron compounds are mapped onto the Doniach
phase diagram of the competing RKKY and Kondo interactions developed for
f-electron systems.",1404.6137v4
2014-08-14,Iron based superconductors: A brief overview,"Fe-based superconductors were discovered in 2008. This discovery with T$_c$
values up to 56 K, generated a new belief in the field of superconductivity.
Till its discovery, high temperature superconductivity in cuprates, created a
prejudice that Cu-oxides are essential building blocks for a high temperature
superconducting material. These Fe based superconductors do not contain Cu-O
planes (some of the materials are even O free). It will be argued in this
review, that these iron pnictide and chalcogenide (FePn/Ch) superconductors
have Fe electrons at the Fermi surface together with an unusual Fermiology that
can change rapidly with doping. This may lead to very different normal and
superconducting state properties compared to those in standard electron-phonon
coupled {\it conventional} superconductors. There are a large number of
evidences showing that superconductivity, magnetism, orbital fluctuations are
intimately related and coexist in these materials although the mechanism of
superconductivity in these compounds is still unknown. The electronic specific
heat, $\frac{2\Delta}{k_B T_c}$ ratio, phase diagrams, isotope effect, crystal
structures and there correlation to T$_c$ from various available experimental
data are main inputs of this review to show the above.",1408.3244v1
2014-10-12,"Spin-orbit coupling, strong correlation, and insulator-metal transitions: the J$_{\rm eff}$ =3\2 ferromagnetic Mott insulator Ba$_{2}$NaOsO$_{6}$","The double perovskite Ba$_{2}$NaOsO$_{6}$ (BNOO), an exotic example of a very
high oxidation state (heptavalent) osmium $d^1$ compound and also uncommon by
being a ferromagnetic Mott insulator without Jahn-Teller (JT) distortion, is
modeled using the density functional theory (DFT) hybrid functional based exact
exchange for correlated electrons (oeeHyb) method and including spin-orbit
coupling (SOC). The experimentally observed narrow gap ferromagnetic insulating
ground state is obtained, with easy axis along [110] in accord with experiment,
providing support that this approach provides a realistic method for studying
this system. The predicted spin density for [110] spin orientation is nearly
cubic (unlike for other directions), providing an explanation for the absence
of JT distortion. An orbital moment of -0.4$\mu_B$ strongly compensates the
+0.5$\mu_B$ spin moment on Os, leaving a strongly compensated moment more in
line with experiment. Remarkably, the net moment lies primarily on the oxygen
ions. An insulator-metal transition by rotating the magnetization direction
with an external field under moderate pressure is predicted as one consequence
of strong SOC, and metallization under moderate pressure is predicted.
Comparison is made with the isostructural, isovalent insulator Ba$_2$LiOsO$_6$
which however orders antiferromagnetically.",1410.3167v1
2014-10-20,Al/AlO$_{\rm {x}}$/Al-Josephson-junction-based microwave generators for weak-signal applications below 100 mK,"An application-specific Josephson generator is being developed as an on-chip
calibration source for single-microwave-photon detectors operating below $T
\sim $100 mK in the frequency range from 110 to 170 GHz. The targeted
calibration power corresponds to the photon detection rate of 0.01 to 10 counts
per second. We analyze the Josephson oscillations within the framework of the
tunnel junction microscopic (TJM) model and find the corrections to be made to
a standard RSJ model of the junction, operating as a quasi-monochromatic source
of microwaves. Experimentally, we implemented a number of aluminium-based
two-junction interferometers connected to the leads via microstripline
resistors made of partly oxidized titanium films. The $I$-$V$ curves exhibit a
behaviour ensuring generation of the microwave signal in the frequency range
required. By setting the biasing point $\bar{V}$ and applying the magnetic
field, one can tune the generator's frequency and power, respectively. A small
oscillation linewidth, down to a few GHz, and a low level of black-body
radiation emitted by hot parts of the circuit are predicted, using the
experimental parameters.",1410.5314v1
2014-10-27,Scaling behavior of the thermopower of the archetypical heavy-fermion metal $\rm{YbRh_2Si_2}$,"We reveal and explain a scaling behavior of the thermopower $S/T$ exhibiting
by the archetypical heavy-fermion (HF) metal $\rm{YbRh_2Si_2}$ under the
application of magnetic field $B$ at temperatures $T$. We show that the same
scaling is demonstrated by such different HF compounds as $\beta$-${\rm
YbAlB_4}$ and the strongly correlated layered cobalt oxide $\rm
[BiBa_{0.66}K_{0.36}O_{2}]CoO_{2}$. Using $\rm{YbRh_2Si_2}$ as an example, we
demonstrate that the scaling behavior of $S/T$ is violated at the
antiferromagnetic phase transition, while both the residual resistivity
$\rho_0$ and the density of states $N$ experience jumps at the phase
transition, making the thermopower experience two jumps and change its sign.
Our elucidation is based on flattening of the single-particle spectrum that
profoundly affects $\rho_0$ and $N$. To depict the main features of the $S/T$
behavior, we construct the $T-B$ schematic phase diagram of $\rm{YbRh_2Si_2}$.
Our calculated $S/T$ for the HF compounds are in good agreement with
experimental facts and support our observations.",1410.7299v4
2014-12-02,Exploring intertwined orders in cuprate superconductors,"The concept of intertwined orders has been introduced to describe the
cooperative relationship between antiferromagnetic spin correlations and
electron (or hole) pair correlations that develop in copper-oxide
superconductors. This contrasts with systems in which, for example,
charge-density-wave (CDW) order competes for Fermi surface area with
superconductivity. La$_{2-x}$Ba$_x$CuO$_4$ with $x=0.125$ provides an example
in which the ordering of spin stripes coincides with the onset of
two-dimensional superconducting correlations. The apparent frustration of the
interlayer Josephson coupling has motivated the concept of the
pair-density-wave superconductor, a state that theoretical calculations show to
be energetically competitive with the uniform $d$-wave superconductor. Even at
$x=0.095$, where there is robust superconductivity below 32~K in zero field,
the coexistence of strong, low-energy, incommensurate spin excitations implies
a spatially modulated and intertwined pair wave function. Recent observations
of CDW order in YBa$_2$Cu$_3$O$_{6+x}$ and other cuprate families have raised
interesting questions regarding the general role of charge modulations and the
relation to superconductivity. While there are differences in the doping
dependence of the modulation wave vectors in YBa$_2$Cu$_3$O$_{6+x}$ and
La$_{2-x}$Ba$_x$CuO$_4$, the maximum ordering strength is peaked at the hole
concentration of 1/8 in both cases. There are also possible connections with
the quantum oscillations that have been detected about the same hole
concentration but at high magnetic fields. Resolving these relationships
remains a research challenge.",1412.1011v1
2015-01-29,Interface observation of heat-treated Co/Mo2C multilayers,"We study the interface evolution of a series of periodic Co/Mo2C multilayers
as a function of the annealing temperature up to 600{\textdegree}C. Different
complementary techniques are implemented to get information on the phenomenon
taking place at the interfaces of the stack. The periodical structure of
Co/Mo2C multilayer is proven by Time-of-flight secondary ion mass spectrometry
(ToF-SIMS) depth profiles which demonstrate the formation of an oxide layer at
both air/stack and stack/substrate interfaces. From Nuclear magnetic resonance
(NMR) spectra, we observed the intermixing phenomenon of Co and C atoms for the
as-deposited sample, and then at annealing temperature above 300{\textdegree}C
Co and C atoms separate from their mixed regions. Comparison of NMR results
between Co/Mo 2 C and Co/C references confirms this phenomenon. This is in
agreement with x-ray emission spectroscopy (XES) measurements. Furthermore the
calculation of the Co-C, Co-Mo and Mo-C mixing enthalpy using Miedema's model
gives a proof of the demixing of Co and C atoms present within the stacks above
300{\textdegree}C. From the transmission electron microscopy (TEM) analysis, we
found the presence of some crystallites within the as-deposited sample as well
as the mainly amorphous nature of all layers. This is confirmed using x-ray
diffraction (XRD) patterns which also demonstrate the growth of crystallites
induced upon annealing.",1501.07360v1
2015-03-12,High On/Off Ratio Memristive Switching of Manganite-Cuprate Bilayer by Interfacial Magnetoelectricity,"Memristive switching serves as the basis for a new generation of electronic
devices. Memristors are two-terminal devices in which the current is turned on
and off by redistributing point defects, e.g., vacancies, which is difficult to
control. Memristors based on alternative mechanisms have been explored, but
achieving both the high On/Off ratio and the low switching energy desirable for
use in electronics remains a challenge. Here we report memristive switching in
a La0.7Ca0.3MnO3/PrBa2Cu3O7 bilayer with an On/Off ratio greater than 10^3 and
demonstrate that the phenomenon originates from a new type of interfacial
magnetoelectricity. Using results from first-principles calculations, we show
that an external electric-field induces subtle displacements of the interfacial
Mn ions, which switches on/off an interfacial magnetic ""dead"" layer, resulting
in memristive behavior for spin-polarized electron transport across the
bilayer. The interfacial nature of the switching entails low energy cost about
of a tenth of atto Joule for write/erase a ""bit"". Our results indicate new
opportunities for manganite/cuprate systems and other transition-metal-oxide
junctions in memristive applications.",1503.03601v1
2015-06-03,Development of hard x-ray photoelectron SPLEED-based spectrometer applicable for probing of buried magnetic layer valence states,"A novel design of high-voltage compatible polarimeter for spin-resolved hard
x-ray photoelectron spectroscopy (Spin-HAXPES) went into operation at beamline
BL09XU of SPring-8 in Hyogo, Japan. The detector is based on the
well-established principle of electron diffraction from a W(001) single-crystal
at a scattering energy of 103.5 eV. Its special feature is that it can be
operated at a high negative bias potential up to 10 kV, necessary to access the
HAXPES range. The polarimeter is operated behind a large hemispherical analyzer
(Scienta R-4000). It was optimized for high transmission of the transfer
optics. The exit plane of the analyzer contains a delay-line detector (20 mm
dia.) for conventional multichannel intensity spectroscopy simultaneously with
single-channel spin analysis. The performance of the combined setup is
demonstrated by the first spin-resolved data for the valence-region of a FeCo
functional layer of a tunneling device, buried beneath 3 nm of oxidic material.
The well-structured spin polarization spectrum validates Spin-HAXPES in the
valence energy range as powerful method for bulk electronic structure analysis.
The spin polarization spectrum exhibits a rich structure, originating from
clearly discernible transitions in the majority and minority partial spin
spectra.",1506.01356v1
2015-06-29,Strain Doping: Reversible Single-Axis Control of a Complex Oxide Lattice via Helium Implantation,"We report on the use of helium ion implantation to independently control the
out-of-plane lattice constant in epitaxial La0.7Sr0.3MnO3 thin films without
changing the in-plane lattice constants. The process is reversible by a vacuum
anneal. Resistance and magnetization measurements show that even a small
increase in the out-of-plane lattice constant of less than 1% can shift the
metal-insulator transition and Curie temperatures by more than 100 {\deg}C.
Unlike conventional epitaxy-based strain tuning methods which are constrained
not only by the Poisson effect but by the limited set of available substrates,
the present study shows that strain can be independently and continuously
controlled along a single axis. This permits novel control over orbital
populations through Jahn-Teller effects, as shown by Monte Carlo simulations on
a double-exchange model. The ability to reversibly control a single lattice
parameter substantially broadens the phase space for experimental exploration
of predictive models and leads to new possibilities for control over materials'
functional properties.",1506.08659v1
2015-09-10,Metal insulator transition and magnetotransport anomalies in perovskite SrIr0.5Ru0.5O3 thin films,"We investigated the nature of transport and magnetic properties in
SrIr0.5Ru0.5O3, (SIRO) which has characteristics intermediate between a
correlated non-Fermi liquid state and an itinerant Fermi liquid state, by
growing perovskite thin films on various substrates (SrTiO3 (001),
(LaAlO3)0.3(Sr2TaAlO6)0.7 (001) and LaAlO3 (001)). We observed systematic
variation of underlying substrate dependent metal-to-insulator transition
temperatures at 80 K on SrTiO3, 90 K on (LaAlO3)0.3(Sr2TaAlO6)0.7 and 100 K on
LaAlO3) in resistivity. Resistivity in the metallic region follows a T3/2 power
law; whereas insulating nature at low T is due to the localization effect.
Magnetoresistance (MR) measurement of SIRO on SrTiO3 (001) shows negative MR
upto 25 K and positive MR above 25 K, with negative MR proportional to B1/2 and
positive MR proportional to B2; consistent with the localized-to-normal
transport crossover dynamics. Furthermore, observed spin glass like behavior of
SIRO on SrTiO3 (001) in the localized regime, validates the hypothesis that
(Anderson) localization favors glassy ordering. These remarkable features
provide a promising approach for future applications and of fundamental
interest in oxide thin films.",1509.02990v1
2015-11-22,Review of Spin Orbit Coupled Semimetal SrIrO3 in thin film form,"Spin orbit coupling provides a mechanism to lock the momentum of electron to
its spin degree, recent years was revealed to be essential in arousing many
novel physical behaviors. SrIrO3 is a typical metallic member of the strong
spin orbit coupling iridate family. Its orthorhombic phase was confirmed as a
particular spin orbit coupling assistant electron correlated semimetal with
small electron and hole pockets, and was supposed to host versatile topological
phases, with prospect of opening a new topological matter field based on
oxides. The existing experiments have demonstrated that orthorhombic SrIrO3 can
be easily synthesized at two dimensional scale films under the substrate
lattice constraint, and the films display Fermi-liquid behavior in high
temperature and generally two dimensional weak localization resulted metal
insulator transition. The properties of orthorhombic SrIrO3 film are sensitive
to the rotation and tilting angle, as well as the interlayer coupling of the
IrO6 octahedras, consequently can be tuned through substrate strain engineering
and size scale. For example, the film was approached a state similar to Sr2IrO4
at the ultrathin limit to several unit cell, becoming a canted
antiferromagnetic semiconductor/insulator. The existing knowledges suggest
urgent demands of researches on the superlattices constructed with orthorhombic
SrIrO3, for further understanding the evolution mechanism of the electron
structure, and so the relevant magnetic state and topological phases in the
orthorhombic SrIrO3 and its family.",1511.06979v2
2016-01-20,"Mechanism, time-reversal symmetry and topology of superconductivity in noncentrosymmetric systems","We analyze the possible interaction-induced superconducting instabilities in
noncentrosymmetric systems based on symmetries of the normal state. It is
proven that pure electron-phonon coupling will always lead to a fully gapped
superconductor that does not break time-reversal symmetry and is topologically
trivial. We show that topologically nontrivial behavior can be induced by
magnetic doping without gapping out the resulting Kramers pair of Majorana edge
modes. In case of superconductivity arising from the particle-hole fluctuations
associated with a competing instability, the properties of the condensate
crucially depend on the time-reversal behavior of the order parameter of the
competing instability. When the order parameter preserves time-reversal
symmetry, we obtain exactly the same properties as in case of phonons. If it is
odd under time-reversal, the Cooper channel of the interaction will be fully
repulsive leading to sign changes of the gap and making spontaneous
time-reversal symmetry breaking possible. To discuss topological properties, we
focus on fully gapped time-reversal symmetric superconductors and derive
constraints on possible pairing states that yield necessary conditions for the
emergence of topologically nontrivial superconductivity. These conditions might
serve as a tool in the search for topological superconductors. We also discuss
implications for oxides heterostructures and single-layer FeSe.",1601.05459v1
2016-02-10,Superconductor Digital Electronics: Scalability and Energy Efficiency Issues,"Superconductor digital electronics using Josephson junctions as ultrafast
switches and magnetic-flux encoding of information was proposed over 30 years
ago as a sub-terahertz clock frequency alternative to semiconductor electronics
based on complementary metal-oxide-semiconductor (CMOS) transistors. Recently,
interest in developing superconductor electronics has been renewed due to a
search for energy saving solutions in applications related to high-performance
computing. The current state of superconductor electronics and fabrication
processes are reviewed in order to evaluate whether this electronics is
scalable to a very large scale integration (VLSI) required to achieve
computation complexities comparable to CMOS processors. A fully planarized
process at MIT Lincoln Laboratory, perhaps the most advanced process developed
so far for superconductor electronics, is used as an example. The process has
nine superconducting layers: eight Nb wiring layers with the minimum feature
size of 350 nm, and a thin superconducting layer for making compact
high-kinetic-inductance bias inductors. All circuit layers are fully planarized
using chemical mechanical planarization (CMP) of SiO2 interlayer dielectric.
The physical limitations imposed on the circuit density by Josephson junctions,
circuit inductors, shunt and bias resistors, etc., are discussed. Energy
dissipation in superconducting circuits is also reviewed in order to estimate
whether this technology, which requires cryogenic refrigeration, can be energy
efficient. Fabrication process development required for increasing the density
of superconductor digital circuits by a factor of ten and achieving densities
above 10^7 Josephson junctions per cm^2 is described.",1602.03546v2
2016-02-25,Phase diagram and collective excitation in excitonic insulator: from the orbital physics viewpoint,"Excitonic insulating system is studied from the viewpoints of the orbital
physics in strongly correlated electron systems. An effective model Hamiltonian
for low-energy electronic states is derived from the two-orbital Hubbard model
with a finite energy difference corresponding to the crystalline field
splitting. The effective model is represented by the spin operators and the
pseudo-spin operators for the spin-state degrees of freedom. The ground state
phase diagram is analyzed by the mean-field approximation. In addition to the
low-spin state and high-spin state phases, two kinds of the excitonic
insulating phases emerge as a consequence of the competition between the
crystalline field effect and the Hund coupling. The excitonic transition is
classified to be an Ising-like transition reflecting a spontaneous breaking of
the $Z_2$ symmetry. Magnetic structures in the two excitonic insulating phases
are different from each other; an antiferromagnetic order and a spin nematic
order. Collective excitations in each phase are examined by using the
generalized spin-wave method. The Goldstone modes in the excitonic insulating
phases appear in the dynamical correlation functions for the spins and
pseudo-spin operators. Both the transverse and longitudinal spin excitation
modes are active in the two excitonic insulating phases in contrast to the
low-spin state and high-spin state phases. Connections of the present results
to the perovskite cobalt oxides are discussed.",1602.07831v2
2016-06-13,Observation of Spatial Charge and Spin Correlations in the 2D Fermi-Hubbard Model,"Strong electron correlations lie at the origin of transformative phenomena
such as colossal magneto-resistance and high-temperature superconductivity.
Already near room temperature, doped copper oxide materials display remarkable
features such as a pseudo-gap and a ""strange metal"" phase with unusual
transport properties. The essence of this physics is believed to be captured by
the Fermi-Hubbard model of repulsively interacting, itinerant fermions on a
lattice. Here we report on the site-resolved observation of charge and spin
correlations in the two-dimensional (2D) Fermi-Hubbard model realized with
ultracold atoms. Antiferromagnetic spin correlations are maximal at
half-filling and weaken monotonically upon doping. Correlations between singly
charged sites are negative at large doping, revealing the Pauli and correlation
hole\textemdash a suppressed probability of finding two fermions near each
other. However, as the doping is reduced below a critical value, correlations
between such local magnetic moments become positive, signaling strong bunching
of doublons and holes. Excellent agreement with numerical linked-cluster
expansion (NLCE) and determinantal quantum Monte Carlo (DQMC) calculations is
found. Positive non-local moment correlations directly imply potential energy
fluctuations due to doublon-hole pairs, which should play an important role for
transport in the Fermi-Hubbard model.",1606.04089v1
2016-06-24,Spintronic nano-devices for bio-inspired computing,"Bio-inspired hardware holds the promise of low-energy, intelligent and highly
adaptable computing systems. Applications span from automatic classification
for big data management, through unmanned vehicle control, to control for
bio-medical prosthesis. However, one of the major challenges of fabricating
bio-inspired hardware is building ultra-high density networks out of complex
processing units interlinked by tunable connections. Nanometer-scale devices
exploiting spin electronics (or spintronics) can be a key technology in this
context. In particular, magnetic tunnel junctions are well suited for this
purpose because of their multiple tunable functionalities. One such
functionality, non-volatile memory, can provide massive embedded memory in
unconventional circuits, thus escaping the von-Neumann bottleneck arising when
memory and processors are located separately. Other features of spintronic
devices that could be beneficial for bio-inspired computing include tunable
fast non-linear dynamics, controlled stochasticity, and the ability of single
devices to change functions in different operating conditions. Large networks
of interacting spintronic nano-devices can have their interactions tuned to
induce complex dynamics such as synchronization, chaos, soliton diffusion,
phase transitions, criticality, and convergence to multiple metastable states.
A number of groups have recently proposed bio-inspired architectures that
include one or several types of spintronic nanodevices. In this article we show
how spintronics can be used for bio-inspired computing. We review the different
approaches that have been proposed, the recent advances in this direction, and
the challenges towards fully integrated spintronics-CMOS (Complementary metal -
oxide - semiconductor) bio-inspired hardware.",1606.07700v2
2016-07-18,Robust Upward Dispersion of the Neutron Spin Resonance in the Heavy Fermion Superconductor Ce$_{1-x}$Yb$_{x}$CoIn$_5$,"The neutron spin resonance is a collective magnetic excitation that appears
in copper oxide, iron pnictide, and heavy fermion unconventional
superconductors. Although the resonance is commonly associated with a
spin-exciton due to the $d$($s^{\pm}$)-wave symmetry of the superconducting
order parameter, it has also been proposed to be a magnon-like excitation
appearing in the superconducting state. Here we use inelastic neutron
scattering to demonstrate that the resonance in the heavy fermion
superconductor Ce$_{1-x}$Yb$_{x}$CoIn$_5$ with $x=0,0.05,0.3$ has a ring-like
upward dispersion that is robust against Yb-doping. By comparing our
experimental data with random phase approximation calculation using the
electronic structure and the momentum dependence of the $d_{x^2-y^2}$-wave
superconducting gap determined from scanning tunneling microscopy for
CeCoIn$_5$, we conclude the robust upward dispersing resonance mode in
Ce$_{1-x}$Yb$_{x}$CoIn$_5$ is inconsistent with the downward dispersion
predicted within the spin-exciton scenario.",1607.05326v1
2016-07-20,Epitaxial growth of complex oxides on silicon by enhanced surface diffusion in large area pulsed laser deposition,"Homogeneous highly epitaxial LaSrMnO3 (LSMO) thin films have been grown on
Yttria-stabilized-Zirconia (YsZ) / CeO2 buffer layers on technological relevant
4"" silicon wafers using a Twente Solid State Technology B.V. (TSST) developed
large area Pulsed Laser Deposition (PLD) setup. We study and show the results
of the effect of an additional SrRuO3 buffer layer on the growth temperature
dependent structural and magnetic properties of LSMO films. With the
introduction of a thin SrRuO3 layer on top of the buffer stack, LSMO films show
ferromagnetic behaviour for growth temperatures as low as 250C. We suggest that
occurrence of epitaxial crystal growth of LSMO at these low growth temperatures
can be understood by an improved surface diffusion, which ensures sufficient
intermixing of surface species for formation of the correct phase. This
intermixing is necessary because the full plume is collected on the 4"" wafer
resulting in a compositional varying flux of species on the wafer, in contrast
to small scale experiments.",1607.05955v1
2016-09-05,Field-induced Conductance Switching by Charge-state Alternation in Organometallic Single-Molecule Junctions,"Charge transport through single molecules can be influenced by the charge and
spin states of redox-active metal centres placed in the transport pathway.
These molecular intrinsic properties are usually addressed by varying the
molecules electrochemical and magnetic environment, a procedure that requires
complex setups with multiple terminals. Here we show that oxidation and
reduction of organometallic compounds containing either Fe, Ru or Mo centres
can solely be triggered by the electric field applied to a two-terminal
molecular junction. Whereas all compounds exhibit bias-dependent hysteresis,
the Mo-containing compound additionally shows an abrupt voltage-induced
conductance switching, yielding high to low current ratios exceeding 1000 at
voltage stimuli of less than 1.0 V. DFT calculations identify a localized,
redox active molecular orbital that is weakly coupled to the electrodes and
closely aligned with the Fermi energy of the leads because of the
spin-polarised ground state unique to the Mo centre. This situation opens an
additional slow and incoherent hopping channel for transport, triggering a
transient charging effect of the entire molecule and a strong hysteresis with
unprecedented high low-to-high current ratios.",1609.01200v1
2017-03-21,Anisotropic electrical resistance in mesoscopic LaAlO$_3$/SrTiO$_3$ devices with individual domain walls,"The crystal structure of bulk SrTiO$_3$(STO) transitions from cubic to
tetragonal at around 105K. Recent local scanning probe measurements of
LaAlO$_3$/SrTiO$_3$ (LAO/STO) interfaces indicated the existence of spatially
inhomogeneous electrical current paths and electrostatic potential associated
with the structural domain formation in the tetragonal phase of STO. However,
how these effects impact the electron conduction in LAO/STO devices has not
been fully studied. Here we report a study of temperature dependent electronic
transport in combination with the polarized light microscopy of structural
domains in mesoscopic scale LAO/STO devices. By reducing the spatial size of
the conductive interface to be comparable to the size of a single tetragonal
domain of STO, the anisotropy of interfacial electron conduction in
relationship to the domain wall and its direction was characterized in the
temperature range $T$=10-300K. It was found that the four-point resistance
measured with current parallel to the domain wall in device is larger than the
resistance measured perpendicular to the domain wall. This observation is
qualitatively consistent with the current diverting effect from a more
conductive domain wall within the sample. Among all the samples studied, the
maximum resistance ratio found is at least 10 and could be as large as 10$^5$
at $T$=10K. This electronic anisotropy may have implications on other oxide
hetero-interfaces and the further understanding of electronic/magnetic
phenomena found in LAO/STO.",1703.07229v1
2017-03-25,Structure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O,"The structure and physical properties of superconducting compounds
Y(La)-Ba(Sr)-Cu-O are studied, the compounds being prepared by the method of
cryogenic dispersion of a charge consisting of premix oxides and carbonates.
Electrical conductivity and critical current density of the superconductors are
measured over a wide temperature range of 10~$mK$ to 300~$K$. Degradation of
the superconductor critical parameters in time and structural characteristics,
magnetic susceptibility, heat capacity and acoustic properties are studied, and
current-voltage characteristics are determined.",1703.08707v1
2018-02-06,Via Method for Lithography Free Contact and Preservation of 2D Materials,"Atomically thin 2D materials span the common components of electronic
circuits as metals, semi-conductors, and insulators, and can manifest
correlated phases such as superconductivity, charge density waves, and
magnetism. An ongoing challenge in the field is to incorporate these 2D
materials into multi-layer hetero-structures with robust electrical contacts
while preventing disorder and degradation. In particular, preserving and
studying air-sensitive 2D materials has presented a significant challenge since
they readily oxidize under atmospheric conditions. We report a new technique
for contacting 2D materials, in which metal via contacts are integrated into
flakes of insulating hexagonal boron nitride, and then placed onto the desired
conducting 2D layer, avoiding direct lithographic patterning onto the 2D
conductor. The metal contacts are planar with the bottom surface of the boron
nitride and form robust contacts to multiple 2D materials. These structures
protect air-sensitive 2D materials for months with no degradation in
performance. This via contact technique will provide the capability to produce
atomic printed circuit boards that can form the basis of more complex
multi-layer heterostructures.",1802.02197v1
2018-02-09,Superconducting properties of under- and over-doped Ba$_{x}$K$_{1-x}$BiO$_{3}$ perovskite oxide,"In the present study, we investigate the thermodynamic properties of the
Ba$_{x}$K$_{1-x}$BiO$_{3}$ (BKBO) superconductor in the under- ($x=0.5$) and
over-doped ($x=0.7$) regime, within the framework of the Migdal-Eliashberg
formalism. The analysis is conducted to verify that the electron-phonon pairing
mechanism is responsible for the induction of the superconducting phase in the
mentioned compound. In particular, we show that BKBO is characterized by the
relatively high critical value of the Coulomb pseudopotential, which changes
with doping level and does not follow the Morel-Anderson model. In what
follows, the corresponding superconducting band gap size and related
dimensionless ratio are estimated to increase with the doping, in agreement
with the experimental predictions. Moreover the effective mass of electrons is
found to take on high values in the entire doping and temperature region.
Finally, the characteristic dimensionless ratios for the superconducting band
gap, the critical magnetic field and the specific heat for the superconducting
state are predicted to exceed the limits set within the
Bardeen-Cooper-Schrieffer theory, suggesting pivotal role of the
strong-coupling and retardation effects in the analyzed compound. Presented
results supplement our previous investigations and account for the
strong-coupling phonon-mediated character of the superconducting phase in BKBO
at any doping level.",1802.03434v3
2018-04-09,Boiling crisis dynamics: low gravity experiments at high pressure,"To understand the boiling crisis mechanism, one can take advantage of the
slowing down of boiling at high pressures, in the close vicinity of the
liquid-vapor critical point of the given fluid. To preserve conventional bubble
geometry, such experiments need to be carried out in low gravity. We report
here two kinds of saturated boiling experiments. First we discuss the spatial
experiments with SF$_6$ at 46$^\circ$ C. Next we address two ground-based
experiments under magnetic gravity compensation with H$_2$ at 33 K. We compare
both kinds of experiments and show their complementarity. The dry spots under
vapor bubbles are visualized by using transparent heaters made with metal oxide
films. We evidence two regimes of the dry spots growth: the regime of circular
dry spots and the regime of chain coalescence of dry spots that immediately
precedes the heater dryout. A recent H$_2$ experiment is shown to bridge the
gap between the near-critical and low pressure boiling experiments.",1804.03050v1
2018-04-09,Charged black strings and black branes in Lovelock theories,"It is well known that the Reissner-Norstrom solution of Einstein-Maxwell
theory cannot be cylindrically extended to higher dimension, as with the black
hole solutions in vacuum. In this paper we show that this result is
circumvented in Lovelock gravity. We prove that the theory containing only the
quadratic Lovelock term, the Gauss-Bonnet term, minimally coupled to a $U(1)$
field, admits homogeneous black string and black brane solutions characterized
by the mass, charge and volume of the flat directions. We also show that
theories containing a single Lovelock term of order $n$ in the Lagrangian
coupled to a $(p-1)$-form field admit simple oxidations only when $n$ equals
$p$, giving rise to new, exact, charged black branes in higher curvature
gravity. For General Relativity this stands for a Lagrangian containing the
Einstein-Hilbert term coupled to a massless scalar field, and no-hair theorems
in this case forbid the existence of black branes. In all these cases the field
equations acquire an invariance under a global scaling scale transformation of
the metric. As explicit examples we construct new magnetically charged black
branes for cubic Lovelock theory coupled to a Kalb-Ramond field in dimensions
$(3m+2)+q$, with $m$ and $q$ integers, and the latter denoting the number of
extended flat directions. We also construct dyonic solutions in quartic
Lovelock theory in dimension $(4m+2)+q$.",1804.03130v2
2018-04-27,Interacting topological insulators: a review,"The discovery of the quantum spin Hall effect and topological insulators more
than a decade ago has revolutionized modern condensed matter physics. Today,
the field of topological states of matter is one of the most active and
fruitful research areas for both experimentalists and theorists. The physics of
topological insulators is typically well described by band theory and systems
of non-interacting fermions. In contrast, several of the most fascinating
effects in condensed matter physics merely exist due to electron-electron
interactions, examples include unconventional superconductivity, the Kondo
effect, and the Mott-Hubbard transition. The aim of this review article is to
give an overview of the manifold directions which emerge when topological
bandstructures and correlation physics interfere and compete. These include the
study of the stability of topological bandstructures and correlated topological
insulators. Interaction-induced topological phases such as the topological
Kondo insulator provide another exciting topic. More exotic states of matter
such as topological Mott insulator and fractional Chern insulators only exist
due to the interplay of topology and strong interactions and do not have any
bandstructure analogue. Eventually the relation between topological
bandstructures and frustrated quantum magnetism in certain transition metal
oxides is emphasized.",1804.10656v3
2018-11-28,Computational Design of Flexible Electrides with Non-trivial Band Topology,"Electrides, with their excess electrons distributed in crystal cavities
playing the role of anions, exhibit a variety of unique electronic and magnetic
properties. In this work, we employ the first-principles crystal structure
prediction to identify a new prototype of A$_3$B electride in which both
interlayer spacings and intralayer vacancies provide channels to accommodate
the excess electrons in the crystal. This A$_3$B type of structure is
calculated to be thermodynamically stable for two alkaline metals oxides
(Rb$_3$O and K$_3$O). Remarkably, the unique feature of multiple types of
cavities makes the spatial arrangement of anionic electrons highly flexible via
elastic strain engineering and chemical substitution, in contrast to the
previously reported electrides characterized by a single topology of
interstitial electrons. More importantly, our first-principles calculations
reveal that Rb$_3$O is a topological Dirac nodal line semimetal, which is
induced by the Rb-$s$ $\rightarrow$ O-$p$ band inversion at the general
electronic k momentums in the Brillouin zone associated with the intersitial
electric charges. The discovery of flexible electride in combining with
topological electronic properties opens an avenue for electride design and
shows great promises in electronic device applications.",1811.11334v2
2019-05-08,Room Temperature Ferroelectric Ferromagnet in 1D Tetrahedral Chain Network,"Ferroelectricity occurs in crystals with broken spatial inversion symmetry.
In conventional perovskite oxides, concerted ionic displacements within a
three-dimensional network of transition metal-oxygen polyhedra (MOx) manifest
spontaneous polarization. Meanwhile, some two-dimensional networks of MOx can
foster geometric ferroelectricity with magnetism, owing to the distortion of
the polyhedra. Because of the fundamentally different mechanism of
ferroelectricity in a two-dimensional network, one can further challenge an
uncharted mechanism of ferroelectricity in a one-dimensional channel of MOx and
estimate its feasibility. This communication presents ferroelectricity and
coupled ferromagnetism in a one-dimensional FeO4 tetrahedral chain network of a
brownmillerite SrFeO2.5 epitaxial thin film. The result provides a new paradigm
for designing low-dimensional MOx networks, which is expected to benefit the
realization of macroscopic ferro-ordering materials including ferroelectric
ferromagnets.",1905.02931v1
2020-07-11,Magnon-bipolar carrier drag thermopower in antiferromagnetic/ferromagnetic semiconductors: theoretical formulation and experimental evidence,"Quantized spin-wave known as magnon, a bosonic quasiparticle, can drag
electrons or holes via sd exchange interaction and boost the thermopower over
the conventional diffusive thermopower. P-type magnon-drag thermopower has been
observed in both ferromagnetic and antiferromagnetic metallic and degenerate
semiconductors. However, it has been less reported for intrinsic or n-type
magnetic semiconductors; therefore, the impact of magnon-bipolar carrier drag
on thermopower has remained unexplored. Here, a theoretical model for
magnon-bipolar carrier drag thermopower is derived based on the magnon-carrier
interaction lifetimes. The model predicts that the bipolar carrier drag
thermopower becomes independent of both the carrier and magnon relaxation
times. A proof of concept experiment is presented that confirms this
prediction. We also report the observation of magnon-carrier drag thermopower
in n-type and intrinsic ferromagnetic semiconductors experimentally. The p-type
antiferromagnetic MnTe is doped with different amounts of Cr to produce
non-degenerate and n-type semiconductors of various carrier concentrations. Cr
dopants have a donor nature and create ferromagnetic-antiferromagnetic clusters
due to the Cr3+ oxidation state. Heat capacity measurements confirm the
presence of magnons in Cr-doped MnTe. It is shown that the magnon-drag
thermopower is significantly reduced for 3%-5% Cr-doped samples due to bipolar
drag effects and becomes negative for 14% and 20% Cr-doped MnTe due to dominant
magnon-electron drag thermopower.",2007.05682v1
2020-07-13,Molecule Oxygen Induced Ferromagnetism and Half-metallicity in α-BaNaO4: A First Principles Study,"Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin
ordering and electron strong correlated behaviors in compounds. The
ferromagnetic spin ordering and half-metallicity, however, are quite elusive
and have not been well acknowl-edged. In this article, we address this issue to
study how spins will interact each other if the oxygen dimers are arranged in a
dif-ferent way from that in the known super- and per-oxides by first principles
calculations. Based on the results of structure search, thermodynamic study and
lattice dynamics, we show that tetragonal {\alpha}-BaNaO4 is a stable
half-metal with a Curie temperature at 120 K, a first example in this class of
compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment
0.5 {\mu}B due to the unpaired electrons in its {\pi}* orbitals. This compound
can be regarded as forming from the O2 dimer layers stacking in a head to head
way. Different from that in AO2 (A=K, Rb, Cs), the spins are both
ferromagnetically coupled within and between the layers. Spin polarization
occurs in {\pi}* orbitals with spin-up electrons fully occupying the valence
band and spin-down electrons partially the conduction band, forming the
semiconducting and metallic channels, respectively. Our results highlight the
im-portance of geometric arrangement of O2 dimers in inducing ferromagnetism
and other novel properties in O2 dimer containing compounds.",2007.06433v1
2020-07-15,Effects of paramagnetic fluctuations on the thermochemistry of MnO (100) surfaces in the oxygen evolution reaction,"We investigated the effects of paramagnetic (PM) fluctuations on the
thermochemistry of the MnO(100) surface in the oxygen evolution reaction (OER)
using the ""noncollinear magnetic sampling method \textit{plus} $U$""
(NCMSM$+U$). Various physical properties, such as the electronic structure,
free energy, and charge occupation, of the MnO (100) surface in the PM state
with several OER intermediates, were reckoned and compared to those in the
antiferromagnetic (AFM) state. We found that PM fluctuation enhances charge
transfer from a surface Mn ion to each of the intermediates and strengthens the
chemical bond between them, while not altering the overall features, such as
the rate determining step and resting state, in reaction pathways. The enhanced
charge transfer can be attributed to the delocalized nature of valence bands
observed in the PM surface. In addition, it was observed that chemical-bond
enhancement depends on the intermediates, resulting in significant deviations
in reaction energy barriers. Our study suggests that PM fluctuations play a
significant role in the thermochemistry of chemical reactions occurring on
correlated oxide surfaces.",2007.07790v2
2020-07-20,Revealing the site selective local electronic structure of Co$_{3}$O$_{4}$ using $2p3d$ resonant inelastic X-ray scattering,"We investigate mixed-valence oxide Co$_3$O$_4$ using Co $2p3d$ resonant
inelastic X-ray scattering (RIXS). By setting resonant edges at Co$^{2+}$ and
Co$^{3+}$ ions, the $dd$ excitations on the two Co sites are probed
selectively, providing detailed information on the local electronic structure
of Co$_3$O$_4$. The $2p3d$ RIXS result reveals the $^4$T$_{2}$ excited state of
tetrahedral Co$^{2+}$ site at 0.5 eV beyond the discriminative power of optical
absorption spectroscopies. Additionally, the $^3$T$_{2g}$ excited stated at 1.3
eV is uniquely identified for the octahedral Co$^{3+}$ site. Guided by cluster
multiplet simulations, the ground-state character of the Co$^{2+}$ and
Co$^{3+}$ site is determined to be high-spin $^4$A$_{2}$(T$_d$) and low-spin
$^1$A$_{1g}$(O$_h$), respectively. This indicates that only the Co$^{2+}$ site
is magnetically active site at low-temperatures in Co$_3$O$_4$. The
ligand-to-metal charge transfer analysis suggests a formation of a strong
covalent bonding between Co and O ions at the Co$^{3+}$ site, while Co$^{2+}$
is rather ionic.",2007.10280v1
2010-05-14,"Electron Confinement, Orbital Ordering, and Orbital Moments in $d^0$-$d^1$ Oxide Heterostructures","The (SrTiO$_3$)$_m$/(SrVO$_3$)$_n$ $d^0-d^1$ multilayer system is studied
with first principles methods through the observed insulator-to-metal
transition with increasing thickness of the SrVO$_3$ layer. When correlation
effects with reasonable magnitude are included, crystal field splittings from
the structural relaxations together with spin-orbit coupling (SOC) determines
the behavior of the electronic and magnetic structures. These confined slabs of
SrVO$_3$ prefer $Q_{orb}$=($\pi,\pi$) orbital ordering of $\ell_z = 0$ and
$\ell_z = -1$ ($j_z=-1/2$) orbitals within the plane, accompanied by
$Q_{spin}$=(0,0) spin order (ferromagnetic alignment). The result is a
SOC-driven ferromagnetic Mott insulator. The orbital moment of 0.75 $\mu_B$
strongly compensates the spin moment on the $\ell_z = -1$ sublattice. The
insulator-metal transition for $n = 1 \to 5$ (occurring between $n$=4 and
$n$=5) is reproduced. Unlike in the isoelectronic $d^0-d^1$ TiO$_2$/VO$_2$
(rutile structure) system and in spite of some similarities in orbital
ordering, no semi-Dirac point [{\it Phys. Rev. Lett.} {\bf 102}, 166803 (2009)]
is encountered, but the insulator-to-metal transition occurs through a
different type of unusual phase. For n=5 this system is very near (or at) a
unique semimetallic state in which the Fermi energy is topologically determined
and the Fermi surface consists of identical electron and hole Fermi circles
centered at $k$=0. The dispersion consists of what can be regarded as a
continuum of radially-directed Dirac points, forming a ""Dirac circle"".",1005.2484v1
2013-08-01,Electronic superlattice revealed by resonant scattering from random impurities in Sr3Ru2O7,"Resonant elastic x-ray scattering (REXS) is an exquisite element-sensitive
tool for the study of subtle charge, orbital, and spin superlattice orders
driven by the valence electrons, which therefore escape detection in
conventional x-ray diffraction (XRD). Although the power of REXS has been
demonstrated by numerous studies of complex oxides performed in the soft x-ray
regime, the cross section and photon wavelength of the material-specific
elemental absorption edges ultimately set the limit to the smallest
superlattice amplitude and periodicity one can probe. Here we show -- with
simulations and REXS on Mn-substituted Sr$_3$Ru$_2$O$_7$ -- that these
limitations can be overcome by performing resonant scattering experiments at
the absorption edge of a suitably-chosen, dilute impurity. This establishes
that -- in analogy with impurity-based methods used in electron-spin-resonance,
nuclear-magnetic resonance, and M\""ossbauer spectroscopy -- randomly
distributed impurities can serve as a non-invasive, but now momentum-dependent
probe, greatly extending the applicability of resonant x-ray scattering
techniques.",1308.0185v1
2013-08-01,Topological Flat Band Models and Fractional Chern Insulators,"Topological insulators and their intriguing edge states can be understood in
a single-particle picture and can as such be exhaustively classified.
Interactions significantly complicate this picture and can lead to entirely new
insulating phases, with an altogether much richer and less explored
phenomenology. Most saliently, lattice generalizations of fractional quantum
Hall states, dubbed fractional Chern insulators, have recently been predicted
to be stabilized by interactions within nearly dispersionless bands with
non-zero Chern number, $C$. Contrary to their continuum analogues, these states
do not require an external magnetic field and may potentially persist even at
room temperature, which make these systems very attractive for possible
applications such as topological quantum computation. This review recapitulates
the basics of tight-binding models hosting nearly flat bands with non-trivial
topology, $C\neq 0$, and summarizes the present understanding of interactions
and strongly correlated phases within these bands. Emphasis is made on
microscopic models, highlighting the analogy with continuum Landau level
physics, as well as qualitatively new, lattice specific, aspects including
Berry curvature fluctuations, competing instabilities as well as novel
collective states of matter emerging in bands with $|C|>1$. Possible
experimental realizations, including oxide interfaces and cold atom
implementations as well as generalizations to flat bands characterized by other
topological invariants are also discussed.",1308.0343v2
2014-03-06,Spin-orbital Entangled Molecular $j_{\rm eff}$ States in Lacunar Spinel Compounds,"The entanglement of the spin and orbital degrees of freedom through the
spin-orbit coupling has been actively studied in condensed matter physics. In
several iridium-oxide systems, the spin-orbital entangled state, identified by
the effective angular momentum $j_{\rm eff}$, can host novel quantum phases
with the help of electron correlations. Here, we show that a series of lacunar
spinel compounds, Ga$M_4X_8$ ($M$ = Nb, Mo, Ta, and W and $X$ = S, Se, and Te),
gives rise to a $\textit{molecular}$ $j_{\rm eff}$ state as a new spin-orbital
composite on which the low energy effective Hamiltonian is based. A wide range
of electron correlations is accessible by tuning the bandwidth under external
and/or chemical pressure, enabling us to investigate the interesting
cooperation between spin-orbit coupling and electron correlations. As
illustrative examples, a two-dimensional topological insulating phase and an
anisotropic spin Hamiltonian are investigated in the weak and strong coupling
regimes, respectively. Our finding can provide an ideal platform for exploring
$j_{\rm eff}$ physics and the resulting emergent phenomena.",1403.1358v2
2014-03-06,Channelling study of La$_{1-x}$Sr$_x$CoO$_3$ films on different substrates,"The cobalt oxide system LaCoO$_3$ and its Sr-doped child compounds have been
intensively studied for decades due to their intriguing magnetic and electronic
properties. Preparing thin La$_{1-x}$Sr$_x$CoO$_3$ (LSCO) films on different
substrates allows for studies with a new type of perturbation, as the films are
subject to substrate-dependent epitaxial strain. By choosing a proper substrate
for a thin film grow, not only compressing but also tensile strain can be
applied. The consequences for the fundamental physical properties are dramatic:
while compressed films are metallic, as the bulk material, films under tensile
strain become insulating. The goal of this work is to determine the strain
tensor in LSCO films prepared on LaAlO$_3$ and SrTiO$_3$ substrates by pulsed
laser deposition using RBS/channelling methods. Apart from the composition and
defect structure of the samples, the depth dependence of the strain tensor, the
cell parameters, and the volume of the unit cell are also determined.
Asymmetric behaviour of the strained cell parameters is found on both
substrates. This asymmetry is rather weak in the case of LSCO film grown on
LaAlO$_3$, while stronger on SrTiO$_3$ substrate. The strain is more effective
at the interface, some relaxation can be observed near to the surface.",1403.1439v1
2016-11-08,Experimental simulation of next-nearest-neighbor Heisenberg chain with photonic crystal waveguide array,"Next-nearest-neighbor Heisenberg chain plays important roles in solid state
physics, such as predicting exotic electric properties of two-dimensional
materials or magnetic properties of organic compounds. Direct experimental
studies of the many-body electron systems or spin systems associating to these
materials are challenging tasks, while optical simulation provides an effective
and economical way for immediate observation. Comparing with bulk optics,
integrated optics are more of fascinating for steady, large scale and long-time
evolution simulations. Photonic crystal is an artificial microstructure
material with multiple methods to tune the propagation properties, which are
essential for various simulation tasks. Here we report for the first time an
experimental simulation of next-nearest-neighbor Heisenberg chain with an
integrated optical chip of photonic crystal waveguide array. The use of
photonic crystal enhances evanescent field thus allows coupling between
next-nearest-neighbor waveguides in such a planar waveguide array, without
breaking the weak coupling condition of the coupled mode equation.
Particularly, similarities between the model and coherent light propagation
could reach 0.99 in numerical simulations and 0.89 in experiment. Localization
effect induced by second-order coupling and coupling strengthening with
increasing wavelengths were also revealed in both numerical simulations and
experiments. The platform proposed here is compatible with mature complementary
metal oxide semiconductor technology thus possesses the potential for
larger-scale problems and photonic crystals further allows simulations of
specific target Hamiltonians.",1611.02520v1
2017-01-09,Cooperative elastic fluctuations provide tuning of the metal-insulator transition,"Metal to insulator transitions (MITs) driven by strong electronic
correlations are common in condensed matter systems, and are associated with
some of the most remarkable collective phenomena in solids, including
superconductivity and magnetism. Tuning and control of the transition holds the
promise of novel, low power, ultrafast electronics, but the relative roles of
doping, chemistry, elastic strain and other applied fields has made systematic
understanding difficult to obtain. Here we point out that existing data on
tuning of the MIT in perovskite transition metal oxides through ionic size
effects provides evidence of systematic and large effects on the phase
transition due to dynamical fluctuations of the elastic strain, which have been
usually neglected. This is illustrated by a simple yet quantitative statistical
mechanical calculation in a model that incorporates cooperative lattice
distortions coupled to the electronic degrees of freedom. We reproduce the
observed dependence of the transition temperature on cation radius in the
well-studied manganite and nickelate materials. Since the elastic couplings are
generically quite strong, these conclusions will broadly generalize to all MITs
that couple to a change in lattice symmetry.",1701.02318v3
2017-04-11,Competition between electron pairing and phase coherence in superconducting interfaces,"The large diversity of exotic electronic phases displayed by two-dimensional
superconductors confronts physicists with new challenges. These include the
recently discovered quantum Griffith singularity in atomic Ga films,
topological phases in proximized topological insulators and unconventional
Ising pairing in transition metal dichalcogenide layers. In LaAlO3/SrTiO3
heterostructures, a gate tunable superconducting electron gas is confined in a
quantum well at the interface between two insulating oxides. Remarkably, the
gas coexists with both magnetism and strong Rashba spin-orbit coupling and is a
candidate system for the creation of Majorana fermions. However, both the
origin of superconductivity and the nature of the transition to the normal
state over the whole doping range remain elusive. Missing such crucial
information impedes harnessing this outstanding system for future
superconducting electronics and topological quantum computing. Here we show
that the superconducting phase diagram of LaAlO3/SrTiO3 is controlled by the
competition between electron pairing and phase coherence. Through resonant
microwave experiments, we measure the superfluid stiffness and infer the gap
energy as a function of carrier density. Whereas a good agreement with the
Bardeen-Cooper-Schrieffer (BCS) theory is observed at high carrier doping, we
find that the suppression of Tc at low doping is controlled by the loss of
macroscopic phase coherence instead of electron pairing as in standard BCS
theory. We find that only a very small fraction of the electrons condenses into
the superconducting state and propose that this corresponds to the weak filling
of a high-energy dxz/yz band, more apt to host superconductivity",1704.03365v1
2017-04-19,Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO$_{3}$/SrTiO$_{3}$/SmTiO$_{3}$ Quantum Well Structures,"Heterointerfaces of SrTiO$_{3}$ with other transition metal oxides make up an
intriguing family of systems with a bounty of coexisting and competing physical
orders. Some examples, such as LaAlO$_{3}$/SrTiO$_{3}$, support a high carrier
density electron gas at the interface whose electronic properties are
determined by a combination of lattice distortions, spin-orbit coupling,
defects, and various regimes of magnetic and charge ordering. Here, we study
electronic transport in mesoscale devices made with heterostructures of
SrTiO$_{3}$ sandwiched between layers of SmTiO$_{3}$, in which the transport
properties can be tuned from a regime of Fermi-liquid like resistivity ($\rho
\sim T^{2}$) to a non-Fermi liquid ($\rho \sim T^{5/3}$) by controlling the
SrTiO$_{3}$ thickness. In mesoscale devices at low temperatures, we find
unexpected voltage fluctuations that grow in magnitude as $T$ is decreased
below 20 K, are suppressed with increasing contact electrode size, and are
independent of the drive current and contact spacing distance.
Magnetoresistance fluctuations are also observed, which are reminiscent of
universal conductance fluctuations but not entirely consistent with their
conventional properties. Candidate explanations are considered, and a mechanism
is suggested based on mesoscopic temporal fluctuations of the Seebeck
coefficient. An improved understanding of charge transport in these model
systems, especially their quantum coherent properties, may lead to insights
into the nature of transport in strongly correlated materials that deviate from
Fermi liquid theory.",1704.05744v1
2018-05-24,"Evolution of electronic and crystal structure during room-temperature annealing of quenched REBa2Cu3O6+d, RE=Y, Nd","The crystal structure parameters and the low-temperature magnetic moment of
the HTSC cuprates YBa2Cu3O6+d, Y1-xCaxBa2Cu3O6+d, and Nd1+xBa2-xCu3O6+d, x =
0.2 are recorded after quenching them from the temperature of oxidative
annealing. The subject of the present study is the aging effect, which results
in an increase in the critical temperature Tc and a decrease in the c parameter
of the crystal lattice for a while after the quenching. On the example of
YBa2Cu3O6+d, it is shown that the oxygen content dependence of c undergoes the
following changes with time: (1) there is an increase in the dependence slope
with respect to the (6+d)-axis; (2) there is an increase in the dependence
nonlinearity. The first type of changes is explained by an increase in the
valence of copper ions in the CuOd planes that is accompanied by a decrease in
their radius. The second type is explained by the electrostatic interaction of
the CuO2 structural planes due to the accumulation on them electron holes.
Calculation of the parameter c changes shows good quantitative agreement with
the experimental data. The data obtained for the compounds Y1-xCaxBa2Cu3O6+d,
and Nd1+xBa2-xCu3O6+d (the cases of the hole and electron doping of
CuO2-planes) are discussed on the basis of the model representation developed
by us for YBa2Cu3O6+d.",1805.09788v1
2008-07-13,Electronic structure of the iron-based superconductor LaOFeP,"The recent discovery of superconductivity in the so-called iron-oxypnictide
family of compounds has generated intense interest. The layered crystal
structure with transition metal ions in planar square lattice form and the
discovery of spin-density-wave order near 130 K seem to hint at a strong
similarity with the copper oxide superconductors. A burning current issue is
the nature of the ground state of the parent compounds. Two distinct classes of
theories have been put forward depending on the underlying band structures:
local moment antiferromagnetic ground state for strong coupling approach and
itinerant ground state for weak coupling approach. The local moment magnetism
approach stresses on-site correlations and proximity to a Mott insulating state
and thus the resemblance to cuprates; while the latter approach emphasizes the
itinerant electron physics and the interplay between the competing
ferromagnetic and antiferromagnetic fluctuations. Such a controversy is partly
due to the lack of conclusive experimental information on the electronic
structures. Here we report the first angle-resolved photoemission spectroscopy
(ARPES) investigation of LaOFeP (Tc = 5.9 K), the first reported iron-based
superconductor. Our results favor the itinerant ground state, albeit with band
renormalization. In addition, our data reveal important differences between
these and copper based superconductors.",0807.2009v1
2011-11-11,Surface-enhanced charge-density-wave instability in underdoped Bi2201,"Neutron and x-ray scattering experiments have provided mounting evidence for
spin and charge ordering phenomena in underdoped cuprates. These range from
early work on stripe correlations in Nd-LSCO to the latest discovery of
charge-density-waves in YBCO. Both phenomena are characterized by a pronounced
dependence on doping, temperature, and an externally applied magnetic field.
Here we show that these electron-lattice instabilities exhibit also a
previously unrecognized bulk-surface dichotomy. Surface-sensitive electronic
and structural probes uncover a temperature-dependent evolution of the CuO2
plane band dispersion and apparent Fermi pockets in underdoped Bi2201, which is
directly associated with an hitherto-undetected strong temperature dependence
of the incommensurate superstructure periodicity below 130K. In stark contrast,
the structural modulation revealed by bulk-sensitive probes is temperature
independent. These findings point to a surface-enhanced incipient
charge-density-wave instability, driven by Fermi surface nesting. This
discovery is of critical importance in the interpretation of single-particle
spectroscopy data and establishes the surface of cuprates and other complex
oxides as a rich playground for the study of electronically soft phases.",1111.2673v3
2012-01-27,Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3,"Searching for superconducting materials with high transition temperature (TC)
is one of the most exciting and challenging fields in physics and materials
science. Although superconductivity has been discovered for more than 100
years, the copper oxides are so far the only materials with TC above 77 K, the
liquid nitrogen boiling point. Here we report an interface engineering method
for dramatically raising the TC of superconducting films. We find that one
unit-cell (UC) thick films of FeSe grown on SrTiO3 (STO) substrates by
molecular beam epitaxy (MBE) show signatures of superconducting transition
above 50 K by transport measurement. A superconducting gap as large as 20 meV
of the 1 UC films observed by scanning tunneling microcopy (STM) suggests that
the superconductivity could occur above 77 K. The occurrence of
superconductivity is further supported by the presence of superconducting
vortices under magnetic field. Our work not only demonstrates a powerful way
for finding new superconductors and for raising TC, but also provides a
well-defined platform for systematic study of the mechanism of unconventional
superconductivity by using different superconducting materials and substrates.",1201.5694v1
2014-05-07,"Density, porosity, mineralogy, and internal structure of cosmic dust and alteration of its properties during high velocity atmospheric entry","X-ray microtomography (XMT), X-ray diffraction (XRD) and magnetic hysteresis
measurements were used to determine micrometeorite internal structure,
mineralogy, crystallography, and physical properties at ~{\mu}m resolution. The
study samples include unmelted, partially melted (scoriaceous) and completely
melted (cosmic spherules) micrometeorites. This variety not only allows
comparison of the mineralogy and porosity of these three micrometeorite types,
but also reveals changes in meteoroid properties during atmospheric entry at
various velocities. At low entry velocities, meteoroids do not melt, and their
physical properties do not change. The porosity of unmelted micrometeorites
varies considerably (0-12%) with one friable example having porosity around
50%. At higher velocities, the range of meteoroid porosity narrows, but average
porosity increases (to 16-27%) due to volatile evaporation and partial melting
(scoriaceous phase). Metal distribution seems to be mostly unaffected at this
stage. At even higher entry velocities, complete melting follows the
scoriaceous phase. Complete melting is accompanied by metal oxidation and
redistribution, loss of porosity (1 $\pm$ 1%), and narrowing of the bulk (3.2
$\pm$ 0.5 g/cm$^{3}$) and grain (3.3 $\pm$ 0.5 g/cm$^{3}$) density range.
Melted cosmic spherules with a barred olivine structure show an oriented
crystallographic structure, whereas other subtypes do not.",1405.1596v2
2015-12-05,Coherent coupling between a quantum dot and a donor in silicon,"Individual donors in silicon chips are used as quantum bits with extremely
low error rates. However, physical realizations have been limited to one donor
because their atomic size causes fabrication challenges. Quantum dot qubits, in
contrast, are highly adjustable using electrical gate voltages. This
adjustability could be leveraged to deterministically couple donors to quantum
dots in arrays of qubits. In this work, we demonstrate the coherent interaction
of a $^{31}$P donor electron with the electron of a metal-oxide-semiconductor
quantum dot. We form a logical qubit encoded in the spin singlet and triplet
states of the two-electron system. We show that the donor nuclear spin drives
coherent rotations between the electronic qubit states through the contact
hyperfine interaction. This provides every key element for compact two-electron
spin qubits requiring only a single dot and no additional magnetic field
gradients, as well as a means to interact with the nuclear spin qubit.",1512.01606v3
2015-12-07,Computational and experimental investigation of unreported transition metal selenides and sulphides,"Expanding the library of known inorganic materials with functional electronic
or magnetic behavior is a longstanding goal in condensed matter physics and
materials science. Recently, the transition metal chalchogenides including
selenium and sulfur have been of interest because of their correlated-electron
properties, as seen in the iron based superconductors and the transition metal
dichalcogenides. However, the chalcogenide chemical space is less explored than
that of oxides, and there is an open question of whether there may be new
materials heretofore undiscovered. We perform a systematic combined theoretical
and experimental search over ternary phase diagrams that are empty in the
Inorganic Crystal Structure Database containing cations, transition metals, and
one of selenium or sulfur. In these 27 ternary systems, we use a probabilistic
model to reduce the likelihood of false negative predictions, which results in
a list of 24 candidate materials. We then conduct a variety of synthesis
experiments to check the candidate materials for stability. While the
prediction method did obtain previously unknown compositions that are predicted
stable within density functional theory, none of the candidate materials formed
in our experiments. We come to the conclusion that these phase diagrams are
""empty"" in the case of bulk synthesis, but it remains a possibility that
alternate synthesis routes may produce some of these phases.",1512.02214v3
2015-12-27,Two types of superconducting domes in unconventional superconductors,"Uncovering the origin of unconventional superconductivity is often plagued by
the overwhelming material diversity with varying normal and superconducting
(SC) properties. In this article, we deliver a comprehensive study of the SC
properties and phase diagrams using multiple tunings (such as disorder,
pressure or magnetic field in addition to doping and vice versa) across several
families of unconventional superconductors, including the copper-oxides,
heavy-fermions, organics and the recently discovered iron-pnictides,
iron-chalcogenides, and oxybismuthides. We discover that all these families
often possess two types of SC domes, with lower and higher superconducting
transition temperatures Tc, both unconventional but with distinct SC and normal
states properties. The lower Tc dome arises with or without a quantum critical
point (QCP), and not always associated with a non-Fermi liquid (NFL)
background. On the contrary, the higher-Tc dome clearly stems from a NFL or
strange metal phase, without an apparent intervening phase transition or a QCP.
The two domes appear either fully separated in the phase diagram, or merged
into one, or arise independently owing to their respective normal state
characteristics. Our findings suggest that a QCP-related mechanism is an
unlikely scenario for the NFL phase in these materials, and thereby narrows the
possibility towards short-range fluctuations of various degrees of freedom in
the momentum and frequency space. We also find that NFL physics may be a
generic route to higher-Tc superconductivity.",1512.08186v2
2016-05-03,On the Structural Origin of the Single-ion Magnetic Anisotropy in LuFeO3,"Electronic structures for the conduction bands of both hexagonal and
orthorhombic LuFeO3 thin films have been measured using x-ray absorption
spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectra
shape and the linear dichroism are observed. These differences in the spectra
can be explained using the differences in crystal field splitting of the metal
(Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d
hybridizations. While the oxidation states has not changed, the spectra are
sensitive to the changes in the local environments of the Fe3+ and Lu3+ sites
in the hexagonal and orthorhombic structures. Using the crystal-field splitting
and the hybridizations that are extracted from the measured electronic
structures and the structural distortion information, we derived the
occupancies of the spin minority states in Fe3+, which are non-zero and uneven.
The single ion anisotropy on Fe3+ sites is found to originate from these uneven
occupancies of the spin minority states via spin-orbit coupling in LuFeO3.",1605.01111v1
2016-05-23,Electron doping evolution of the neutron spin resonance in NaFe$_{1-x}$Co$_{x}$As,"Neutron spin resonance, a collective magnetic excitation coupled to
superconductivity, is one of the most prominent features shared by a broad
family of unconventional superconductors including copper oxides, iron
pnictides, and heavy fermions. In this work, we study the doping evolution of
the resonances in NaFe$_{1-x}$Co$_x$As covering the entire superconducting
dome. For the underdoped compositions, two resonance modes coexist. As doping
increases, the low-energy resonance gradually loses its spectral weight to the
high-energy one but remains at the same energy. By contrast, in the overdoped
regime we only find one single resonance, which acquires a broader width in
both energy and momentum, but retains approximately the same peak position even
when $T_c$ drops by nearly a half compared to optimal doping. These results
suggest that the energy of the resonance in electron overdoped
NaFe$_{1-x}$Co$_x$As is neither simply proportional to $T_c$ nor the
superconducting gap, but is controlled by the multi-orbital character of the
system and doped impurity scattering effect.",1605.06890v1
2017-06-01,Leakage-free electrolytes with different conductivity for non-volatile memory device utilizing insulator/metal ferromagnet transition of SrCoOx,"The electrochemical switching of SrCoOx-based non-volatile memory with
thin-film-transistor structure was examined by using liquid-leakage-free
electrolytes with different conductivity (s) as the gate insulator. We first
examined leakage-free water, which is incorporated in the amorphous (a-) 12CaO
7Al2O3 film with nanoporous structure (CAN), but the electrochemical
oxidation/reduction of SrCoOx layer required the application of high gate
voltage (Vg) up to 20 V for a very long retention-time (t) 40 minutes,
primarily due to the low s (2.0 x 10-8 S cm-1 at RT) of leakage-free water.We
then controlled the s of leakage-free electrolyte, infiltrated in the a-NaxTaO3
film with nanopillar array structure, from 8.0 x 10-8 S cm-1 to 2.5 x 10-6 S
cm-1 at RT by changing the x = 0.01-1.0. As the result, the t, required for the
metallization of SrCoOx layer under small Vg = -3 V, becomes two orders of
magnitude shorter with increase of the s of the a-NaxTaO3 leakage-free
electrolyte. These results indicate that the ion migration in the leakage-free
electrolyte is the rate-determining step for the electrochemical switching,
compared to the other electrochemical process, and the high s of the
leakage-free electrolyte is the key factor for the development of the
non-volatile SrCoOx-based electro-magnetic phase switching device.",1706.00132v1
2017-10-18,Using MRI Cell Tracking to Monitor Immune Cell Recruitment in Response to a Peptide-Based Cancer Vaccine,"Purpose: MRI cell tracking can be used to monitor immune cells involved in
the immunotherapy response, providing insight into the mechanism of action,
temporal progression of tumour growth and individual potency of therapies. To
evaluate whether MRI could be used to track immune cell populations in response
to immunotherapy, CD8+ cytotoxic T cells (CTLs), CD4+CD25+FoxP3+ regulatory T
cells (Tregs) and myeloid derived suppressor cells (MDSCs) were labelled with
superparamagnetic iron oxide (SPIO) particles.
  Methods: SPIO-labelled cells were injected into mice (one cell type/mouse)
implanted with an HPV-based cervical cancer model. Half of these mice were also
vaccinated with DepoVaxTM, a lipid-based vaccine platform that was developed to
enhance the potency of peptide-based vaccines.
  Results: MRI visualization of CTLs, Tregs and MDSCs was apparent 24 hours
post-injection, with hypointensities due to iron labelled cells clearing
approximately 72 hours post-injection. Vaccination resulted in increased
recruitment of CTLs and decreased recruitment of MDSCs and Tregs to the tumour.
We also found that MDSC and Treg recruitment was positively correlated with
final tumour volume.
  Conclusion: This type of analysis can be used to non-invasively study changes
in immune cell recruitment in individual mice over time, potentially allowing
improved application and combination of immunotherapies.",1710.06817v1
2018-01-14,Spin filling and orbital structure of the first six holes in a silicon metal-oxide-semiconductor quantum dot,"The spin states of electrons confined in semiconductor quantum dots form a
promising platform for quantum computation. Recent studies of silicon CMOS
qubits have shown coherent manipulation of electron spin states with extremely
high fidelity. However, manipulation of single electron spins requires large
oscillatory magnetic fields to be generated on-chip, making it difficult to
address individual qubits when scaling up to multi-qubit devices. The
spin-orbit interaction allows spin states to be controlled with electric
fields, which act locally and are easier to generate. While the spin-orbit
interaction is weak for electrons in silicon, valence band holes have an
inherently strong spin-orbit interaction. However, creating silicon quantum
dots in which a single hole can be localised, in an architecture that is
suitable for scale-up to a large number of qubits, is a challenge. Here we
report a silicon quantum dot, with an integrated charge sensor, that can be
operated down to the last hole. We map the spin states and orbital structure of
the first six holes, and show they follow the Fock-Darwin spectrum. We also
find that hole-hole interactions are extremely strong, reducing the two-hole
singlet-triplet splitting by 90% compared to the single particle level spacing
of 3.5 meV. These results provide a route to single hole spin quantum bits in a
planar silicon CMOS architecture.",1801.04494v1
2018-01-15,The cellular uptake mechanism of SPIONs: an in-vitro study,"The Superparamagnetic Iron Oxide Nanoparticles (SPIONs) of sizes ranging from
10-50 nm are being used in a large number of biological studies because of
their peculiar characteristics of inducing local hyperthermia, MR imaging,
specific targeting and drug delivery. An in-vitro study of the cytotoxicity and
an understanding of the specific pathway of cellular uptake will enable
manipulation of conditions for optimal cellular uptake of SPIONs for targeted
therapy. The objective of the present study was to identify the endocytotic
pathway through which the SPIONs are taken up by C6 glioma cells. The cells
were pre-incubated with different concentrations of pharmacological inhibitors
and then exposed to SPIONs for a few hours. The endocytosed particles were
localized and quantitatively estimated using Perl's or Prussian Blue reaction.
There was significant reduction in the uptake of SPIONs when incubated with the
inhibitor indicating the uptake of nanoparticles is being inhibited. This
reduction in SPION uptake was found to be dependent on the concentration of the
inhibitors and also the nature of the inhibitors. By a systematic study of
choosing various inhibitors, the data can be narrowed down to the final pathway
that may be involved in the SPION uptake. The present preliminary investigation
is expected to provide insight of testing the possible mechanisms with
complementary techniques.",1801.04825v1
2018-09-21,Electronic Spin transition in FeO$_{2}$: evidence for Fe(II) with peroxide O$_{2}^{2-}$,"The discovery of FeO$_{2}$ containing more oxygen than hematite
(Fe$_{2}$O$_{3}$) that was previously believed to be the most oxygen rich iron
compounds, has important implications on the study of the deep lower mantle
compositions. Compared to other iron compounds, there are limited reports on
FeO$_{2}$ making studies of its physical properties of great interest in
fundamental condensed matter physics and geoscience. Even the oxidation state
of Fe in FeO$_{2}$ is the subject of debate in theoretical works and there have
not been reports from experimental electronic and magnetic properties
measurements. Here, we report the pressure-induced spin state transition from
synchrotron experiments and our computational results explain the underlying
mechanism. Using density functional theory and dynamical mean field theory, we
calculated spin states of Fe with volume and Hubbard interaction $U$ change,
which clearly demonstrate that Fe in FeO$_{2}$ consists of Fe(II) and peroxide
O$_{2}^{2-}$. Our study suggests that localized nature of both Fe 3$d$ orbitals
and O$_{2}$ molecular orbitals should be correctly treated for unveiling the
structural and electronic properties of FeO$_{2}$.",1809.07969v1
2018-10-18,Andreev reflection at the interface with an oxide in the quantum Hall regime,"Quantum Hall/superconductor junctions have been an attractive topic as the
two macroscopically quantum states join at the interface. Despite longstanding
efforts, however, experimental understanding of this system has not been
settled yet. One of the reasons is that most semiconductors hosting
high-mobility two-dimensional electron systems (2DES) usually form Schottky
barriers at the metal contacts, preventing efficient proximity between the
quantum Hall edge states and Cooper pairs. Only recently have relatively
transparent 2DES/superconductor junctions been investigated in graphene. In
this study, we propose another material system for investigating
2DES/superconductor junctions, that is ZnO-based heterostrcuture. Due to the
ionic nature of ZnO, a Schottky barrier is not effectively formed at the
contact with a superconductor MoGe, as evidenced by the appearance of Andreev
reflection at low temperatures. With applying magnetic field, while clear
quantum Hall effect is observed for ZnO 2DES, conductance across the junction
oscillates with the filling factor of the quantum Hall states. We find that
Andreev reflection is suppressed in the well developed quantum Hall regimes,
which we interpret as a result of equal probabilities of normal and Andreev
reflections as a result of multiple Andreev reflection at the
2DES/superconductor interface.",1810.08198v1
2019-06-15,Symmetry-Breaking Polymorphous Descriptions for Complex Materials without Interelectronic U,"Correlated materials with open-shell d- and f-ions having degenerate band
edge states show a rich variety of interesting properties ranging from
metal-insulator transition to unconventional superconductivity. The textbook
view for the electronic structure of these materials is that mean-field
approaches are inappropriate, as the interelectronic interaction U is required
to open a band gap between the occupied and unoccupied degenerate states while
retaining symmetry. We show that the latter scenario often defining what Mott
insulators are, is in fact not needed for the 3d binary oxides MnO, FeO, CoO,
and NiO. The mean-field band theory can indeed lift such degeneracies in the
binaries when nontrivial unit cell representations (polymorphous networks) are
allowed to break symmetries, in conjunction with a recently developed
non-empirical exchange and correlation density-functional without an on-site
interelectronic interaction U. We explain how density-functional theory (DFT)
in the polymorphous representation achieves band gap opening in correlated
materials through a separate mechanism to the Mott-Hubbard approach. We show
the method predicts magnetic moments and gaps for the four binary monoxides in
both the antiferromagnetic and paramagnetic phases, offering an effective
alternative to symmetry-conserving approaches for studying a range of
functionalities in open d- and f-shell complex materials.",1906.06467v3
2019-06-17,Imaging Antiferromagnetic Domains in Nickel-oxide Thin Films by Magneto-optical Voigt Effect,"Recent demonstrations of electrical detection and manipulation of
antiferromagnets (AFMs) have opened new opportunities towards robust and
ultrafast spintronics devices. However, it is difficult to establish the
connection between the spin-transport behavior and the microscopic AFM domain
states due to the lack of the real-time AFM domain imaging technique under the
electric field. Here we report a significant Voigt rotation up to 60 mdeg in
thin NiO(001) films at room temperature. Such large Voigt rotation allows us to
directly observe AFM domains in thin-film NiO by utilizing a wide-field optical
microscope. Further complementary XMLD-PEEM measurement confirms that the Voigt
contrast originates from the NiO AFM order. We examine the domain pattern
evolution at a wide range of temperature and with the application of external
magnetic field. Comparing to large-scale-facility techniques such as the X-ray
photoemission electron microscopy, the use with a wide-field, tabletop optical
imaging method enables straightforward access to domain configurations of
single-layer AFMs.",1906.06844v2
2019-07-28,Field-dependent nonlinear surface resistance and its optimization by surface nano-structuring in superconductors,"We propose a theory of nonlinear surface resistance of a dirty superconductor
in a strong radio-frequency (RF) field, taking into account magnetic and
nonmagnetic impurities, finite quasiparticle lifetimes, and a thin
proximity-coupled normal layer characteristic of the oxide surface of many
materials. The Usadel equations were solved to obtain the quasiparticle density
of states (DOS) and the low-frequency surface resistance $R_s$ as functions of
the RF field amplitude $H_0$. It is shown that the interplay of the broadening
of the DOS peaks and a decrease of a quasiparticle gap caused by the RF
currents produces a minimum in $R_s(H_0)$ and an extended rise of the quality
factor $Q(H_0)$ with the RF field. Paramagnetic impurities shift the minimum in
$R_s(H_0)$ to lower fields and can reduce $R_s(H_0)$ in a wide range of $H_0$.
Subgap states in the DOS can give rise to a residual surface resistance while
reducing $R_s$ at higher temperatures. A proximity-coupled normal layer at the
surface can shift the minimum in $R_s(H_0)$ to either low and high fields and
can reduce $R_s$ below that of an ideal surface. The theory shows that the
behavior of $R_s(H_0)$ changes as the temperature and the RF frequency are
increased, and the field dependence of $Q(H_0)$ can be very sensitive to the
materials processing. Our results suggest that the nonlinear RF losses can be
minimized by tuning pairbreaking effects at the surface using impurity
management or surface nanostructuring.",1907.12040v1
2019-09-02,Electronic structure of interstitial hydrogen in In-Ga-Zn-O semiconductor simulated by muon,"We report on the local electronic structure of interstitial muon (Mu) as
pseudo-hydrogen in In-Ga-Zn oxide (IGZO) semiconductor studied by muon spin
rotation/relaxation ($\mu$SR) experiment. In polycrystalline (c-) IGZO, it is
inferred that Mu is in a diamagnetic state, where the $\mu$SR time spectra
under zero external field is perfectly described by the Gaussian Kubo-Toyabe
relaxation function with the linewidth $\Delta$ serving as a sensitive measure
for the random local fields from In/Ga nuclear magnetic moments. The magnitude
of $\Delta$ combined with the density functional theory calculations for H (to
mimic Mu) suggests that Mu occupies Zn-O bond-center site (Mu$_{\rm BC}$)
similar to the case in crystalline ZnO. This implies that the diamagnetic state
in c-IGZO corresponds to Mu$_{\rm BC}^+$, thus serving as an electron donor. In
amorphous (a-) IGZO, the local Mu structure in as-deposited films is nearly
identical with that in c-IGZO, suggesting Mu$_{\rm BC}^+$ for the electronic
state. In contrast, the diamagnetic signal in heavily hydrogenated a-IGZO films
exhibits the Lorentzian Kubo-Toyabe relaxation, implying that Mu accompanies
more inhomogeneous distribution of the neighboring nuclear spins that may
involve Mu$^-$H$^-$-complex state in an oxygen vacancy.",1909.00503v1
2019-09-11,Full control of Co valence in isopolar LaCoO3 / LaTiO3 perovskite heterostructures via interfacial engineering,"We report charge-transfer up to a single electron per interfacial unit cell
across non-polar heterointerfaces from the Mott insulator LaTiO3 to the charge
transfer insulator LaCoO3. In high-quality bi- and tri-layer systems grown
using pulsed laser deposition, soft X-ray absorption, dichroism and STEM-EELS
are used to probe the cobalt 3d-electron count and provide an element-specific
investigation of the magnetic properties. The experiments prove a
deterministically-tunable charge transfer process acting in the LaCoO3 within
three unit cells of the heterointerface, able to generate full conversion to
3d7 divalent Co, which displays a paramagnetic ground state. The number of
LaTiO3 / LaCoO3 interfaces, the thickness of an additional ""break"" layer
between the LaTiO3 and LaCoO3, and the LaCoO3 film thickness itself in
tri-layers provide a trio of sensitive control knobs for the charge transfer
process, illustrating the efficacy of O2p-band alignment as a guiding principle
for property design in complex oxide heterointerfaces.",1909.05247v1
2019-09-13,Gate-tunable spin exclusive or operation in a silicon-based spin device at room temperature,"Room temperature operation of a spin exclusive or (XOR) gate was demonstrated
in lateral spin valve devices with nondegenerate silicon (Si) channels. The
spin XOR gate is a fundamental part of the magnetic logic gate (MLG) that
enables reconfigurable and nonvolatile NAND or OR operation in one device. The
device for the spin XOR gate consists of three iron (Fe)/cobalt (Co)/magnesium
oxide (MgO) electrodes, i.e., two input and one output electrodes. Spins are
injected into the Si channel from the input electrodes whose spin angular
momentum corresponds to the binary input 1 or 0. The spin drift effect is
controlled by a lateral electric field in the Si channel to adjust the spin
accumulation voltages under two different parallel configurations,
corresponding to (1, 1) and (0, 0), so that they exhibit the same value. As a
result, the spin accumulation voltage detected by the output electrode exhibits
three different voltages, represented by an XOR gate. The one-dimensional spin
drift-diffusion model clearly explains the obtained XOR behavior. Charge
current detection of the spin XOR gate is also demonstrated. The detected
charge current has a maximum of 0.94 nA, the highest value in spin XOR gates
reported thus far. Furthermore, gate voltage modulation of the spin XOR gate is
also demonstrated, which enables operation of multiple MLG devices.",1909.06080v1
2019-10-04,Large Magnetoelectric Response in Sr2IrO4/SrTiO3 superlattices with non-equivalent interfaces,"Large magnetoelectric response in thin films is highly desired for
high-throughput and high-density microelectronic applications. However, the d0
rule in single-phase compounds usually results in a weak interaction between
ferroelectric and magnetic orders; the magnetoelectric coupling via elastic
resonance in composites restricts their thin-film integration in broadband.
Here, we effectuate a concurrence of ferroelectric-like and antiferromagnetic
phase transitions in Sr2IrO4/SrTiO3 superlattices by artificial design
periodically non-equivalent interfaces, where a maximum magnetoelectric
coefficient of ~980 mV cm-1 Oe-1 can be measured. Evidenced by synchrotron
X-ray absorption and electron energy loss spectroscopies, a lopsided electron
occupation occurs at the interfacial Ti ions. From perturbative calculations
and numerical results, a strong coupling of antiferromagnetism and asymmetric
electron occupation mediated by spin-orbit interaction leads to a large bulk
magnetoelectric response. This atomic tailoring of the quantum order parameters
in 3d and 5d oxides provides an alternative pathway towards strong
magnetoelectric effects with thin-film integrations.",1910.01787v1
2020-01-26,Electronically driven spin-reorientation transition of the correlated polar metal Ca$_3$Ru$_2$O$_7$,"Polar distortions in solids give rise to the well-known functionality of
switchable macroscopic polarisation in ferroelectrics and, when combined with
strong spin-orbit coupling, can mediate giant spin splittings of electronic
states. While typically found in insulators, ferroelectric-like distortions can
remain robust against increasing itineracy, giving rise to so-called ""polar
metals"". Here, we investigate the temperature-dependent electronic structure of
Ca$_3$Ru$_2$O$_7$, a correlated oxide metal in which octahedral tilts and
rotations combine to mediate pronounced polar distortions. Our angle-resolved
photoemission measurements reveal the destruction of a large hole-like Fermi
surface upon cooling through a coupled structural and spin-reorientation
transition at 48 K, accompanied by a sudden onset of quasiparticle coherence.
We demonstrate how these result from band hybridisation mediated by a hidden
Rashba-type spin-orbit coupling. This is enabled by the bulk structural
distortions and unlocked when the spin reorients perpendicular to the local
symmetry-breaking potential at the Ru sites. We argue that the electronic
energy gain associated with the band hybridisation is actually the key driver
for the phase transition, reflecting a delicate interplay between spin-orbit
coupling and strong electronic correlations, and revealing a new route to
control magnetic ordering in solids.",2001.09499v1
2020-04-11,Understanding the mechanism of oxygen evolution reaction (OER) with the consideration of spin,"Oxygen evolution reaction (OER) with intractable high overpotential is the
rate-limiting step for rechargeable metal-air battery, water electrolysis
systems, and solar fuels devices. There exists a spin state transition from
spin singlet OH-/H2O reactant to spin triplet O2 product, which has not
received enough attention yet. In this perspective, we attempt to retrospect
electron behaviours during the whole OER process, with the consideration of
spin attribute. Regardless of the adopted mechanisms by different
electrocatalysts, for example, adsorbate evolution mechanism (AEM) or lattice
oxygen mechanism (LOM), the underlying rationale is that active sites have to
extract three in four electrons with the same spin direction before the
formation of O=O. This spin-sensitive nature of OER superimposes additional
high requirements on the electrocatalysts, especially on the spin structure, to
compliment the fast electron transfer in the interface with spin selection and
smoothly delivery afterwards. When optimizing the geometric and electronic
structures catering for the spin-sensitive OER, awareness of the couplings
between spin, charge, orbital and lattice is necessary. Some spin-correlated
physical properties, such as (1) crystal field, (2) coordination, (3)
oxidation, (4) bonding, (5) eg electron number, (6) conductivity and (7)
magnetism, are also discussed briefly. It is hoped that our perspective could
shed lights on the underlying physics of the slow kinetics of OER, providing a
rational guidance for more effective energy conversion electrocatalysts
designs.",2004.05326v1
2020-12-11,Isotropic Pauli-Limited Superconductivity in the Infinite Layer Nickelate Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$,"The recent observation of superconductivity in thin film infinite-layer
nickelates$^{1-3}$ offers a different angle to investigate superconductivity in
layered oxides$^{4}$. A wide range of candidate models have been
proposed$^{5-10}$, emphasizing single- or multi-orbital electronic structure,
Kondo or Hund's coupling, and analogies to cuprates. Clearly, further
experimental characterization of the superconducting state is needed to develop
a full understanding of the nickelates. Here we use magnetotransport
measurements to probe the superconducting anisotropy in
Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$. We find that the upper critical field is
surprisingly isotropic at low temperatures despite the layered crystal
structure. In a magnetic field the superconductivity is strongly Pauli-limited,
such that the paramagnetic effect dominates over orbital de-pairing. Underlying
this isotropic response is a substantial anisotropy in the superconducting
coherence length, which is at least four times longer in-plane than
out-of-plane. A prominent low-temperature upturn in the upper critical field
indicates the presence of an unconventional ground state.",2012.06560v1
2020-12-18,Methodology for In-flight Flat-field Calibration of the Lyman-alpha Solar Telescope (LST),"Flat-field reflects the non-uniformity of the photometric response at the
focal plane of an instrument, which uses digital image sensors, such as Charge
Coupled Device (CCD) and Complementary Metal-Oxide-Semiconductor (CMOS). This
non-uniformity must corrected before being used for scientific research. In
this paper, we assess various candidate methods via simulation using available
data so as to figure the in-flight flat-field calibration methodology for the
Lyman-alpha Solar Telescope (LST). LST is one of the payloads for the Advanced
Space-based Solar Observatory (ASO-S) mission and consists of three
instruments: a White-light Solar Telescope (WST), a Solar Disk Imager (SDI) and
a dual-waveband Solar Corona Imager (SCI). In our simulations, data from the
Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA)
onboard the Solar Dynamics Observatory (SDO) mission are used. Our results show
that the normal KLL method is appropriate for in-flight flat-field calibration
of WST and implementing a transmissive diffuser is applicable for SCI. For the
in-flight flat-field calibration of SDI, we recommend the KLL method with
off-pointing images with defocused resolution of around 18"", and use the local
correlation tracking (LCT) algorithm instead of limb-fitting to determine the
relative dis-placements between different images.",2012.10110v1
2021-01-12,Non-volatile reconfigurable spin logic device: parallel operations,"A new proposal is given for designing a non-volatile, completely spin logic
device, that can be reprogrammed for different functional classical logical
operations. We use the concept of bias driven spin dependent circular current
and current induced magnetic field in a quantum ring under asymmetric
ring-to-electrode interface configuration to implement all the Boolean
operations. We extend our idea to build two kinds of parallel computing
architectures for getting parallelized operations, all at a particular time.
For one case, different kinds of parallel operations are performed in a single
device, whereas in the other type all the possible inputs of a logic gate are
processed in parallel and all the outputs are read simultaneously. The
performance and reliability are investigated in terms of power, delay and
power-delay-product and finally the system temperature. We find that both the
individual and simultaneous logic operations studied here are much superior
compared to the operations performed in different conventional logic families
like complementary metal oxide semiconductor logic, transistor-transistor
logic, etc. The key advantage is that we can perform several logic operations,
as many as we wish, repeating the same or different logic gates using a single
setup, which indeed reduces wiring in the circuits and hence consumes much less
power. Our analysis can be utilized to design optimized logic circuits at
nano-scale level.",2101.04311v1
2012-05-25,Anisotropic ferromagnetism in carbon doped zinc oxide from first-principles studies,"A density functional theory study of substitutional carbon impurities in ZnO
has been performed, using both the generalized gradient approximation (GGA) and
a hybrid functional (HSE06) as exchange-correlation functional. It is found
that the non-spinpolarized C$_\mathrm{Zn}$ impurity is under almost all
conditions thermodynamically more stable than the C$_\mathrm{O}$ impurity which
has a magnetic moment of $2\mu_{\mathrm{B}}$, with the exception of very O-poor
and C-rich conditions. This explains the experimental difficulties in sample
preparation in order to realize $d^{0}$-ferromagnetism in C-doped ZnO. From GGA
calculations with large 96-atom supercells, we conclude that two
C$_\mathrm{O}$-C$_\mathrm{O}$ impurities in ZnO interact ferromagnetically, but
the interaction is found to be short-ranged and anisotropic, much stronger
within the hexagonal $ab$-plane of wurtzite ZnO than along the c-axis. This
layered ferromagnetism is attributed to the anisotropy of the dispersion of
carbon impurity bands near the Fermi level for C$_{\mathrm{O}}$ impurities in
ZnO. From the calculated results, we derive that a C$_{\mathrm{O}}$
concentration between 2% and 6% should be optimal to achieve
$d^{0}$-ferromagnetism in C-doped ZnO.",1205.5830v1
2017-09-20,Optical time reversal from time-dependent Epsilon-Near-Zero media,"Materials with a spatially uniform but temporally varying optical response
have applications ranging from magnetic field-free optical isolators to
fundamental studies of quantum field theories. However, these effects typically
become relevant only for time-variations oscillating at optical frequencies,
thus presenting a significant hurdle that severely limits the realisation of
such conditions. Here we present a thin-film material with a permittivity that
pulsates (uniformly in space) at optical frequencies and realises a
time-reversing medium of the form originally proposed by Pendry [Science 322,
71 (2008)]. We use an optically pumped, 500 nm thick film of epsilon-near-zero
(ENZ) material based on Al-doped zinc oxide (AZO). An incident probe beam is
both negatively refracted and time-reversed through a reflected
phase-conjugated beam. As a result of the high nonlinearity and the refractive
index that is close to zero, the ENZ film leads to time reversed beams
(simultaneous negative refraction and phase conjugation) with near-unit
efficiency and greater-than-unit internal conversion efficiency. The ENZ
platform therefore presents the time-reversal features required e.g. for
efficient subwavelength imaging, all-optical isolators and fundamental quantum
field theory studies.",1709.06972v1
2017-09-27,Pressure induced spin crossover in disordered α-LiFeO2,"Structural, magnetic and electrical-transport properties of {\alpha}-LiFeO2,
crystallizing in the rock salt structure with random distribution of Li and Fe
ions, have been studied by synchrotron X-ray diffraction, 57Fe M\""ossbauer
spectroscopy and electrical resistance measurements at pressures up to 100 GPa
using diamond anvil cells. It was found that the crystal structure is stable at
least to 82 GPa, though a significant change in compressibility has been
observed above 50 GPa. The changes in the structural properties are found to be
on a par with a sluggish Fe3+ high- to low-spin (HS-LS) transition (S=5/2 to
S=1/2) starting at 50 GPa and not completed even at ~100 GPa. The HS-LS
transition is accompanied by an appreciable resistance decrease remaining a
semiconductor up to 115 GPa and is not expected to be metallic even at about
200 GPa. The observed feature of the pressure-induced HS-LS transition is not
an ordinary behavior of ferric oxides at high pressures. The effect of Fe3+
nearest and next nearest neighbors on the features of the spin crossover is
discussed.",1709.09680v1
2017-10-31,Spin susceptibility of charge ordered YBa2Cu3Oy across the upper critical field,"The value of the upper critical field Hc2, a fundamental characteristic of
the superconducting state, has been subject to strong controversy in high-Tc
copper-oxides. Since the issue has been tackled almost exclusively by
macroscopic techniques so far, there is a clear need for local-probe
measurements. Here, we use 17O NMR to measure the spin susceptibility
$\chi_{spin}$ of the CuO2 planes at low temperature in charge ordered
YBa2Cu3Oy. We find that $\chi_{spin}$ increases (most likely linearly) with
magnetic field H and saturates above field values ranging from 20 to 40 T. This
result is consistent with Hc2 values claimed by G. Grissonnanche et al. [Nat.
Commun. 5, 3280 (2014)] and with the interpretation that the
charge-density-wave (CDW) reduces Hc2 in underdoped YBa2Cu3Oy. Furthermore, the
absence of marked deviation in $\chi_{spin}(H)$ at the onset of long-range CDW
order indicates that this Hc2 reduction and the Fermi-surface reconstruction
are primarily rooted in the short-range CDW order already present in zero
field, not in the field-induced long-range CDWorder. Above Hc2, the relatively
low values of $\chi_{spin}$ at T=2 K show that the pseudogap is a ground-state
property, independent of the superconducting gap.",1711.00109v1
2017-11-21,Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas,"The coherent tunnelling of Cooper pairs across Josephson junctions (JJs)
generates a nonlinear inductance that is used extensively in quantum
information processors based on superconducting circuits, from setting qubit
transition frequencies and interqubit coupling strengths, to the gain of
parametric amplifiers for quantum-limited readout. The inductance is either set
by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by
parallelizing multiple JJs in superconducting quantum interference devices
(SQUIDs) with local current-biased flux lines. JJs based on
superconductor-semiconductor hybrids represent a tantalizing all-electric
alternative. The gatemon is a recently developed transmon variant which employs
locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control.
Here, we go beyond proof-of-concept and demonstrate that semiconducting
channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a
suitable platform for building a scalable gatemon-based quantum computer. We
show 2DEG gatemons meet the requirements by performing voltage-controlled
single qubit rotations and two-qubit swap operations. We measure qubit
coherence times up to ~2 us, limited by dielectric loss in the 2DEG host
substrate.",1711.07665v3
2018-06-11,Towards understanding the special stability of ${\text{SrCo}\text{O}_{2.5}}$ and ${\text{HSrCo}\text{O}_{2.5}}$,"Reversible hydrogen incorporation was recently attested [N. Lu, $\textit{et
al.}$, Nature $\textbf{546}$, 124 (2017)] in ${\text{SrCo}\text{O}_{2.5}}$, the
brownmillerite phase (BM) of strontium cobalt oxide (SCO), opening new avenues
in catalysis and energy applications. However, existing theoretical studies of
BM-SCO are insufficient, and that of ${\text{HSrCo}\text{O}_{2.5}}$, the
newly-reported hydrogenated SCO (H-SCO), is especially scarce. In this work, we
demonstrate how the electron-counting model (ECM) can be used in understanding
the phases, particularly in explaining the stability of the oxygen-vacancy
channels (OVCs), and in examining the Co valance problem. Using
density-functional theoretical (DFT) methods, we analyze the crystalline,
electronic, and magnetic structures of BM- and H-SCO. Based on our structure
search, we discovered stable phases with large bandgaps (> 1 eV) for both
BM-SCO and H-SCO, agreeing better with experiments on the electronic
structures. Our calculations also indicate limited charge transfer from H to O
that may explain the special stability of the H-SCO phase and the reversibility
of H incorporation observed in experiments. In contrary to the initial study,
our calculation also suggests intrinsic antiferromagnetism (AFM) of H-SCO,
showing how the measured ferromagnetism (FM) has possible roots in hole doping.",1806.03917v2
2018-06-25,A materials informatics approach to the identification of one-band correlated materials analogous to the cuprates,"One important yet exceedingly rare property of the cuprate high-temperature
superconductors is the presence of a single correlated $d$ band in the
low-energy spectrum, leading to the one-band Hubbard model as the minimal
description. In order to search for materials with interesting strong
correlation physics as well as possible benchmark systems for the one-band
Hubbard model, here we present a new approach to find one-band correlated
materials analogous to the cuprates by leveraging the emerging area of
materials informatics. Using the composition, structure, and formation energy
of more than half a million real and hypothetical inorganic crystalline
materials in the Open Quantum Materials Database, we search for synthesizable
materials whose nominal transition metal $d$ electron count and crystal field
are compatible with achieving an isolated half-filled $d$ band. Five Cu
compounds, including bromide, oxide, selenate, and pyrophosphate chemistries,
are shown to successfully achieve the one-band electronic structure based on
density functional theory band structure calculations. Further calculations
including magnetism and explicit on-site Coulomb interaction reveal significant
evidence for strong correlation physics in the five candidates, including Mott
insulating behavior and antiferromagnetism. The success of our data-driven
approach to discovering new correlated materials opens up new avenues to design
and discover materials with rare electronic properties.",1806.09662v1
2018-07-09,High tunability of the transport properties in macroscopically in-plane modulated two-dimensional system,"Gate-controllable two dimensional systems with in-plane modulation of
properties could serve as highly tunable effective media. Intuitively, such
systems may bring novel functionality provided that the period of the lateral
modulation is much less than the relevant scattering lengths (mean free path,
coherence length etc.). Our work experimentally demonstrates the opposite,
disordered limit of such system, defined in the macroscopically modulated
metal-oxide-semiconductor structure. The system consists of parent
two-dimensional gas with periodic array of islands (dots/antidots), filled with
two-dimensional gas of different density, and surrounded by depletion regions
(shells). Carrier densities of both parent gas and islands are controlled by
two independent gate electrodes, allowing us to explore a rich phase diagram of
low-temperature transport properties of this modulated two-dimensional system,
resembling various transport regimes: insulating, shell-dominated,
gas-dominated, island-dominated. These regimes can be identified by various
Hall resistance and its magnetic field dependence, temperature dependencies of
the resistivity, and Shubnikov-de Haas patterns. We also suggest the
theoretical approach for description of such inhomogeneous but periodical
systems. Theory based on the classical mean field approach qualitatively
describes our system as theoretical dependencies reproduce the main features of
the experimental behavior of the effective Hall concentration from gate
voltage. Thus, our work demonstrates feasibility of the macroscopically
inhomogeneous two-dimensional system as a tunable platform for novel physics
and proposes the approach for the theoretical description of such systems.",1807.03421v2
2018-07-13,Disentangling orbital and spin exchange interactions for Co$^{2+}$ on a rocksalt lattice,"Neutron spectroscopy was applied to study the magnetic interactions of
orbitally degenerate Co$^{2+}$ on a host MgO rocksalt lattice where no long
range spin or orbital order exists. The paramagnetic nature of the substituted
monoxide Co$_{0.03}$Mg$_{0.97}$O allows for the disentanglement of
spin-exchange and spin-orbit interactions. By considering the prevalent
excitations from Co$^{2+}$ spin pairs, we extract 7 exchange constants out to
the fourth coordination shell. An antiferromagnetic next nearest neighbor
180$^{\circ}$ exchange interaction is dominant, however dual ferromagnetic and
antiferromagnetic interactions are observed for pairings with other pathways.
These interactions can be understood in terms of a combination of orbital
degeneracy in the $t_{2g}$ channel and the Goodenough-Kanamori-Anderson (GKA)
rules. Our work suggests that such a hierarchy of exchange interactions exists
in transition metal-based oxides with a $t_{2g}$ orbital degeneracy.",1807.05012v2
2018-08-11,Novel Superconducting SrSnP with Strong Sn-P Antibonding Interaction: Is the Sn Atom Single or Mixed Valent?,"The large single crystals of SrSnP were prepared using Sn self-flux method.
The superconductivity in the tetragonal SrSnP is observed with the critical
temperature of ~2.3 K. The results of a crystallographic analysis,
superconducting characterization, and theoretical assessment of tetragonal
SrSnP are presented. The SrSnP crystallizes in the CaGaN structure type with
space group P4/nmm (S.G.129, Pearson symbol tP6) according to the single
crystal X-ray diffraction characterization. A combination of magnetic
susceptibility, resistivity, and heat capacity measurements confirms the bulk
superconductivity with Tc = 2.3(1) K in SrSnP. According to the X-ray
photoelectron spectroscopy (XPS) measurement, the assignments of Sr2+ and P3-
are consistent with the chemical valence electron balance principles. Moreover,
it is highly likely that Sn atom has only one unusual oxidation state.
First-principles calculations indicate the bands around Fermi level are
hybridized among Sr-d, Sn-p, and P-p orbitals. The strong Sn-P and Sr-P
interactions pose as keys to stabilize the crystallographic structure and
induce the superconductivity, respectively. The physics-based electronic and
phononic calculations are consistent with the molecular viewpoint. After
including the spin-orbit coupling (SOC) into the calculation, the band
degeneracies at gamma-point in the first Brillouin zone (BZ) split into two
bands, which yield to the van Hove singularities around Fermi level.",1808.03828v1
2018-08-15,Chirality and intrinsic dissipation of spin modes in two-dimensional electron liquids,"We review recent theoretical and experimental developments concerning
collective spin excitations in two-dimensional electron liquid (2DEL) systems,
with particular emphasis on the interplay between many-body and spin-orbit
effects, as well as the intrinsic dissipation due to the spin-Coulomb drag.
Historically, the experimental realization of 2DELs in silicon inversion layers
in the 60s and 70s created unprecedented opportunities to probe subtle quantum
effects, culminating in the discovery of the quantum Hall effect. In the
following years, high quality 2DELs were obtained in doped quantum wells made
in typical semiconductors like GaAs or CdTe. These systems became important
test beds for quantum many-body effects due to Coulomb interaction, spin
dynamics, spin-orbit coupling, effects of applied magnetic fields, as well as
dissipation mechanisms. Here we focus on the recent results involving chiral
effects and intrinsic dissipation of collective spin modes: these are not only
of fundamental interest but also important towards demonstrating new concepts
in spintronics. Moreover, new realizations of 2DELs are emerging beyond
traditional semiconductors, for instance in multilayer graphene, oxide
interfaces, dichalcogenide monolayers, and many more. The concepts discussed in
this review will be relevant also for these emerging systems.",1808.05266v2
2018-08-17,Yang-Mills Structure for Electron-Phonon Interactions,"This work presents a method of grouping the electron spinors and the acoustic
phonon modes of polar crystals such as metal oxides into an SU(2) gauge theory.
The gauge charge is the electron spin, which is assumed to couple to the
transverse acoustic phonons on the basis of spin ordering phenomena in crystals
such as V$_{2}$O$_{3}$ and VO$_{2}$, while the longitudinal mode is neutral. A
generalization the Peierls mechanism is presented based on the discrete gauge
invariance of crystals and the corresponding Ward-Takahashi identity. The
introduction of a band index violates the Ward-Takahashi identity for interband
transitions resulting in a longitudinal component appearing in the upper phonon
band. Thus both the spinors and the vector bosons acquire mass and a crystal
with an electronic band gap and optical phonon modes results. In the limit that
the coupling of bosons charged under the SU(2) gauge group goes to zero,
breaking the electron U(1) symmetry recovers the BCS mechanism. In the limit
that the neutral boson decouples, a Cooper instability mediated by spin-wave
exchange results from symmetry breaking, i.e. unconventional superconductivity
mediated by magnetic interactions.",1808.05769v2
2018-12-15,Anomalous behavior of the quasi-one-dimensional quantum material Na$_{2}$OsO$_{4}$ at high pressure,"Na$_{2}$OsO$_{4}$ is an unusual quantum material that, in contrast to the
common 5${d}^{2}$ oxides with spins = 1, owns a magnetically silent ground
state with spin = 0 and a band gap at Fermi level attributed to a distortion in
the OsO$_{6}$ octahedral sites. In this semiconductor, our low-temperature
electrical transport measurements indicate an anomaly at 6.3 K with a power-law
behavior inclining through the semiconductor-to-metal transition observed at 23
GPa. Even more peculiarly, we discover that before this transition, the
material becomes more insulating instead of merely turning into a metal
according to the conventional wisdom. To investigate the underlying mechanisms,
we applied experimental and theoretical methods to examine the electronic and
crystal structures comprehensively, and conclude that the enhanced insulating
state at high pressure originates from the enlarged distortion of the
OsO$_{6}$. It is such a distortion that widens the band gap and decreases the
electron occupancy in Os's ${t}_{2g}$ orbital through an interplay of the
lattice, charge, and orbital in the material, which is responsible for the
changes observed in our experiments.",1812.06256v3
2018-12-15,Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics,"A single-sample synthesis concept based on multi-element ceramic samples can
produce a variety of local products. When applied to cuprate superconductors
(SC), statistical modelling predicts the occurrence of possible compounds in a
concentration range of about 50 ppm. In samples with such low concentrations,
determining which compositions are superconducting is a challenging task and
requires local probes or separation techniques. Here, we report results from
samples with seven components: BaO2, CaCO3, SrCO3, La2O3, PbCO3, ZrO2 and CuO
oxides and carbonates, starting from different grain sizes. The reacted
ceramics show different phases, particular grain growth, as well as variations
in homogeneity and superconducting properties. High-Tc superconductivity up to
118 K was found. Powder x-ray diffraction (XRD) in combination with
energy-dispersive spectroscopy (EDS), scanning transmission electron microscopy
(STEM) can assign Pb1223 and (Sr,Ca,Ba)0.7-1.0CuO2 phases in inhomogeneous
samples milled with 10 mm ball sizes. Rather uniform samples featuring strong
grain growth were obtained with 3 mm ball sizes, resulting in Tc =70 K
superconductivity of the La(Ba,Ca)2Cu3Ox based phase. Scanning SQUID microscopy
(SSM) establishes locally formed superconducting areas at a level of a few
microns in inhomogeneous superconducting particles captured by a magnetic
separation technique. The present results demonstrate a new synthetic approach
for attaining high-Tc superconductivity in compounds without Bi, Tl, Hg, or the
need for high-pressure synthesis.",1812.06273v1
2019-01-19,Resolving the nature of electronic excitations in resonant inelastic x-ray scattering,"The study of elementary bosonic excitations is essential toward a complete
description of quantum electronic solids. In this context, resonant inelastic
X-ray scattering (RIXS) has recently risen to becoming a versatile probe of
electronic excitations in strongly correlated electron systems. The nature of
the radiation-matter interaction endows RIXS with the ability to resolve the
charge, spin and orbital nature of individual excitations. However, this
capability has been only marginally explored to date. Here, we demonstrate a
systematic method for the extraction of the character of excitations as
imprinted in the azimuthal dependence of the RIXS signal. Using this novel
approach, we resolve the charge, spin, and orbital nature of elastic
scattering, (para-)magnon/bimagnon modes, and higher energy dd excitations in
magnetically-ordered and superconducting copper-oxide perovskites (Nd2CuO4 and
YBa2Cu3O6.75). Our method derives from a direct application of scattering
theory, enabling us to deconstruct the complex scattering tensor as a function
of energy loss. In particular, we use the characteristic tensorial nature of
each excitation to precisely and reliably disentangle the charge and spin
contributions to the low energy RIXS spectrum. This procedure enables to
separately track the evolution of spin and charge spectral distributions in
cuprates with doping. Our results demonstrate a new capability that can be
integrated into the RIXS toolset, and that promises to be widely applicable to
materials with intertwined spin, orbital, and charge excitations.",1901.06583v1
2019-02-04,Auxiliary Field Quantum Monte Carlo for Multiband Hubbard Models: Controlling the Sign and Phase Problems to Capture Hund's Physics,"In the study of strongly-correlated, many-electron systems, the Hubbard
Kanamori (HK) model has emerged as one of the prototypes for transition metal
oxide physics. The model is multi-band in nature and contains Hund's coupling
terms, which have pronounced effects on metal-insulator transitions,
high-temperature superconductivity, and other physical properties. In the
following, we present a complete theoretical framework for treating the HK
model using the ground state Auxiliary Field Quantum Monte Carlo (AFQMC) method
and analyze its performance on few-band models whose parameters approximate
those observed in ruthenate, rhodates, and other materials exhibiting Hund's
physics. Unlike previous studies, the constrained path and phaseless
approximations are used to respectively control the sign and phase problems,
which enables high accuracy modeling of the HK model's ground state properties
within parameter regimes of experimental interest. We demonstrate that, after
careful consideration of the Hubbard-Stratonovich transformations and trial
wave functions employed, relative errors in the energy of less than 1% can
routinely be achieved for moderate to large values of the Hund's coupling
constant. Crucially, our methodology also accurately predicts magnetic ordering
and phase transitions. The results presented open the door to more predictive
modeling of Hund's physics within a wide range of strongly-correlated materials
using AFQMC.",1902.01463v1
2019-04-03,Spin waves and spin-state transitions in a ruthenate high-temperature antiferromagnet,"Ruthenium compounds play prominent roles in materials research ranging from
oxide electronics to catalysis, and serve as a platform for fundamental
concepts such as spin-triplet superconductivity, Kitaev spin-liquids, and
solid-state analogues of the Higgs mode in particle physics. However, basic
questions about the electronic structure of ruthenates remain unanswered,
because several key parameters (including the Hund's-rule, spin-orbit, and
exchange interactions) are comparable in magnitude, and their interplay is
poorly understood - partly due to difficulties in synthesizing sizable single
crystals for spectroscopic experiments. Here we introduce a resonant inelastic
x-ray scattering (RIXS) technique capable of probing collective modes in
microcrystals of $4d$-electron materials. We present a comprehensive set of
data on spin waves and spin-state transitions in the honeycomb antiferromagnet
SrRu$_{2}$O$_{6}$, which possesses an unusually high N\'eel temperature. The
new RIXS method provides fresh insight into the unconventional magnetism of
SrRu$_{2}$O$_{6}$, and enables momentum-resolved spectroscopy of a large class
of $4d$ transition-metal compounds.",1904.01930v2
2019-08-07,Chern and $Z_{2}$ topological insulating phases in perovskite-derived $4d$ and $5d$ oxide buckled honeycomb lattices,"Based on density functional theory calculations including a Coulomb repulsion
parameter $U$, we explore the topological properties of
(La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$(111) with $X=$ $4d$ and $5d$ cations. The
metastable ferromagnetic phases of LaTcO$_3$ and LaPtO$_3$ preserve P321
symmetry and emerge as Chern insulators (CI) with $C$=2 and 1 and band gaps of
41 and 38 meV at the lateral lattice constant of LaAlO$_3$, respectively. Berry
curvatures, spin textures as well as edge states provide additional insight
into the nature of the CI states. While for $X$=Tc the CI phase is further
stabilized under tensile strain, for $X$=Pd and Pt a site disproportionation
takes place when increasing the lateral lattice constant from $a_{\rm LAO}$ to
$a_{\rm LNO}$. The CI phase of $X$=Pt shows a strong dependence on the Hubbard
$U$ parameter with sign reversal for higher values associated with the change
of band gap opening mechanism. Parallels to the previously studied
($X_2$O$_3$)$_1$/(Al$_2$O$_3$)$_5$(0001) honeycomb corundum layers are
discussed. Additionally, non-magnetic systems with $X$=Mo and W are identified
as potential candidates for $Z_2$ topological insulators at $a_{\rm LAO}$ with
band gaps of 26 and 60 meV, respectively. The computed edge states and $Z_{2}$
invariants underpin the non-trivial topological properties.",1908.02835v1
2019-08-17,Electronic phase separation at LaAlO3/SrTiO3 interfaces tunable by oxygen deficiency,"Electronic phase separation is crucial for the fascinating macroscopic
properties of the LaAlO3/SrTiO3 (LAO/STO) paradigm oxide interface, including
the coexistence of superconductivity and ferromagnetism. We investigate this
phenomenon using angle-resolved photoelectron spectroscopy (ARPES) in the
soft-X-ray energy range, where the enhanced probing depth combined with
resonant photoexcitation allow access to fundamental electronic structure
characteristics (momentum-resolved spectral function, dispersions and ordering
of energy bands, Fermi surface) of buried interfaces. Our experiment uses X-ray
irradiation of the LAO/STO interface to tune its oxygen deficiency, building up
a dichotomic system where mobile weakly correlated Ti t2g-electrons co-exist
with localized strongly correlated Ti eg-ones. The ARPES spectra dynamics under
X-ray irradiation shows a gradual intensity increase under constant Luttinger
count of the Fermi surface. This fact identifies electronic phase separation
(EPS) where the mobile electrons accumulate in conducting puddles with fixed
electronic structure embedded in an insulating host phase, and allows us to
estimate the lateral fraction of these puddles. We discuss the physics of EPS
invoking a theoretical picture of oxygen-vacancy clustering, promoted by the
magnetism of the localized Ti eg-electrons, and repelling of the mobile
t2g-electrons from these clusters. Our results on the irradiation-tuned EPS
elucidate the intrinsic one taking place at the stoichiometric LAO/STO
interfaces.",1908.06321v1
2019-11-13,Estimation of Cooper pair density and its relation to the critical current density in hole doped high-Tc cuprate superconductors,"Hole concentration in the CuO2 plane largely controls all the properties in
the normal and superconducting states of high-Tc cuprates. The critical current
density, Jc, is no exception. Previous hole content dependent studies have
demonstrated that the role of intrinsic depairing current density in
determining the observed critical current density in copper oxide
superconductors. It is also widely agreed upon that the temperature and
magnetic field dependent vortex pinning energy plays a major role the Jc of a
system.This pinning energy depends directly on the superconducting condensation
energy. Superconducting condensation energy, on the other hand, is proportional
to the Cooper pair density (superpair density), which is found to be highly
dependent on the hole concentration, p, within the CuO2 plane. We have
calculated the Cooper pair density, rho_s, of YBCO (Y123), a typical hole doped
cuprate, as a function of p, in this study. A triangular pseudogap (PG), pinned
at the Fermi level, in the quasiparticle spectral density has been considered.
The low-temperature critical current density of a number of Y(Ca)BCO
superconductors over wide range of compositions and hole concentrations have
been explored. The normalized values of the superpair density and the critical
current density exhibit a clear correspondence as the in-plane hole content is
varied. This systematic behavior provides us with strong evidence that the
critical current density of hole doped cuprates is primarily dependent on the
superpair density, which in turn depends on the magnitude of the PG energy.The
agreement between the estimated p-dependent superpair density and the
previously experimentally determined superfluid density of Y(Ca)BCO is quite
remarkable.",1911.05237v1
2019-11-13,"Anomalous thickness-dependent electrical conductivity in van der Waals layered transition metal halide, Nb_3Cl_8","Understanding the electronic transport properties of layered, van der Waals
transition metal halides (TMHs) and chalcogenides is a highly active research
topic today. Of particular interest is the evolution of those properties with
changing thickness as the 2D limit is approached. Here, we present the
electrical conductivity of exfoliated single crystals of the TMH, cluster
magnet, Nb3Cl8, over a wide range of thicknesses both with and without
hexagonal boron nitride (hBN) encapsulation. The conductivity is found to
increase by more than three orders of magnitude when the thickness is decreased
from 280 {\mu}m to 5 nm, at 300 K. At low temperatures and below ~50 nm, the
conductance becomes thickness independent, implying surface conduction is
dominating. Temperature dependent conductivity measurements indicate Nb3Cl8 is
an insulator, however the effective activation energy decreases from a bulk
value of 310 meV to 140 meV by 5nm. X-ray photoelectron spectroscopy (XPS)
shows mild surface oxidation in devices without hBN capping, however, no
significant difference in transport is observed when compared to the capped
devices, implying the thickness dependent transport behavior is intrinsic to
the material. A conduction mechanism comprised of a higher conductivity surface
channel in parallel with a lower conductivity interlayer channel is discussed.",1911.05379v1
2019-11-18,Thermally Activated Processes for Ferromagnet Intercalation in Graphene-Heavy Metal Interfaces,"The development of graphene (Gr) spintronics requires the ability to engineer
epitaxial Gr heterostructures with interfaces of high quality, in which the
intrinsic properties of Gr are modified through proximity with a ferromagnet to
allow for efficient room temperature spin manipulation or the stabilization of
new magnetic textures. These heterostructures can be prepared in a controlled
way by intercalation through graphene of different metals. Using photoelectron
spectroscopy (XPS) and Scanning Tunneling Microscopy (STM), we achieve a
nanoscale control of thermal activated intercalation of homogeneous
ferromagnetic (FM) layer underneath epitaxial Gr grown onto (111)-oriented
heavy metal (HM) buffers deposited in turn onto insulating oxide surfaces. XPS
and STM demonstrate that Co atoms evaporated on top of Gr arrange in 3D
clusters, and, upon thermal annealing, penetrate through and diffuse below Gr
in a 2D fashion. The complete intercalation of the metal occurs at specific
temperatures depending on the type of metallic buffer. The activation energy
and the optimum temperature for the intercalation processes are determined. We
describe a reliable method to fabricate and characterize in-situ high quality
Gr-FM/HM heterostructures enabling the realization of novel spin-orbitronic
devices that exploits the extraordinary properties of Gr.",1911.07549v2
2019-11-28,Hund-Heisenberg model in superconducting infinite-layer nickelates,"We theoretically investigate the unconventional superconductivity in the
newly discovered infinite-layer nickelates Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ based on
a two-band model. By analyzing the transport experiments, we propose that the
doped holes dominantly enter the Ni $d_{xy}$ or/and $d_{3z^{2}-r^{2}}$ orbitals
as charged carriers, and form a conducting band. Via the onsite Hund coupling,
the doped holes are coupled to the Ni localized holes in the $d_{x^{2}-y^{2}}$
orbital band. We demonstrate that this two-band model could be further reduced
to a Hund-Heisenberg model. Using the reduced model, we show the non-Fermi
liquid state above the critical $T_{c}$ could stem from the carriers coupled to
the spin fluctuations of the localized holes. In the superconducting phase, the
short-range spin fluctuations mediate the carriers into Cooper pairs and
establish $d_{x^{2}-y^{2}}$-wave superconductivity. We further predict that the
doped holes ferromagnetically coupled with the local magnetic moments remain
itinerant even at very low temperature, and thus the pseudogap hardly emerges
in nickelates. Our work provides a new superconductivity mechanism for strongly
correlated multi-orbital systems and paves a distinct way to exploring new
superconductors in transition or rare-earth metal oxides.",1911.12731v3
2019-11-28,Magnon damping in the zigzag phase of the Kitaev-Heisenberg-$Γ$ model on a honeycomb lattice,"We calculate magnon dispersions and damping in the Kitaev-Heisenberg model
with an off-diagonal exchange $\Gamma$ and isotropic third-nearest-neighbor
interaction $J_3$ on a honeycomb lattice. This model is relevant to a
description of the magnetic properties of iridium oxides $\alpha$-Li$_2$IrO$_3$
and Na$_2$IrO$_3$, and Ru-based materials such as $\alpha$-RuCl$_3$. We use an
unconventional parametrization of the spin-wave expansion, in which each
Holstein-Primakoff boson is represented by two conjugate hermitian operators.
This approach gives us an advantage over the conventional one in identifying
parameter regimes where calculations can be performed analytically. Focusing on
the parameter regime with the zigzag spin pattern in the ground state that is
consistent with experiments, we demonstrate that one such region is $\Gamma =
K>0$, where $K$ is the Kitaev coupling. Within our approach we are able to
obtain explicit analytical expressions for magnon energies and eigenstates and
go beyond the standard linear spin-wave theory approximation by calculating
magnon damping and demonstrating its role in the dynamical structure factor. We
show that the magnon damping effects in both Born and self-consistent
approximations are very significant, underscoring the importance of non-linear
magnon coupling in interpreting broad features in the neutron-scattering
spectra.",1911.12829v2
2019-12-19,Unravelling competing microscopic interactions at a phase boundary: a single crystal study of the metastable antiferromagnetic pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$,"We report inelastic neutron scattering measurements from our newly
synthesized single crystals of the structurally metastable antiferromagnetic
pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$. We determine the four symmetry-allowed
nearest-neighbor anisotropic exchange parameters via fits to linear spin wave
theory supplemented by fits of the high-temperature specific heat. The exchange
parameters so-determined are strongly correlated to the values determined for
the $g$-tensor components, as previously observed for the related Yb pyrochlore
Yb$_{2}$Ti$_{2}$O$_{7}$. To address this issue, we directly determined the
$g$-tensor from electron paramagnetic resonance of 1% Yb-doped
Lu$_{2}$Ge$_{2}$O$_{7}$, thus enabling an unambiguous determination of the
exchange parameters. Our results show that Yb$_{2}$Ge$_{2}$O$_{7}$ resides
extremely close to the classical phase boundary between an antiferromagnetic
$\Gamma_5$ phase and a splayed ferromagnet phase. By juxtaposing our results
with recent ones on Yb$_{2}$Ti$_{2}$O$_{7}$, our work illustrates that the Yb
pyrochlore oxides represent ideal systems for studying quantum magnets in close
proximity to classical phase boundaries.",1912.09448v2
2019-12-30,The Fermi surface of PtCoO2 from quantum oscillations and electronic structure calculations,"The delafossite series of layered oxides include some of the highest
conductivity metals ever discovered. Of these, PtCoO2, with a room temperature
resistivity of 1.8 microOhmcm for in-plane transport, is the most conducting of
all. The high conduction takes place in triangular lattice Pt layers, separated
by layers of Co-O octahedra, and the electronic structure is determined by the
interplay of the two types of layer. We present a detailed study of quantum
oscillations in PtCoO2, at temperatures down to 35 mK and magnetic fields up to
30 T. As for PdCoO2 and PdRhO2, the Fermi surface consists of a single cylinder
with mainly Pt character, and an effective mass close to the free electron
value. Due to Fermi-surface warping, two close-lying high frequencies are
observed. Additionally, a pronounced difference frequency appears. By analysing
the detailed angular dependence of the quantum-oscillation frequencies, we
establish the warping parameters of the Fermi surface. We compare these results
to the predictions of first-principles electronic structure calculations
including spin-orbit coupling on Pt and Co and on-site correlation U on Co, and
hence demonstrate that electronic correlations in the Co-O layers play an
important role in determining characteristic features of the electronic
structure of PtCoO2.",1912.13071v1
2020-03-03,Ab Initio Full Cell GW+DMFT for Correlated Materials,"Quantitative prediction of electronic properties in correlated materials
requires simulations without empirical truncations and parameters. We present a
method to achieve this goal through a new ab initio formulation of dynamical
mean-field theory (DMFT). Instead of using small impurities defined in a
low-energy subspace, which require complicated downfolded interactions which
are often approximated, we describe a full cell $GW$+DMFT approach, where the
impurities comprise all atoms in a unit cell or supercell of the crystal. Our
formulation results in large impurity problems, which we treat here with
efficient quantum chemistry impurity solvers that work on the real-frequency
axis, combined with a one-shot $G_0W_0$ treatment of long-range interactions.
We apply our full cell approach to bulk Si, two antiferromagnetic correlated
insulators NiO and $\alpha$-Fe$_2$O$_3$, and the paramagnetic correlated metal
SrMoO$_3$, with impurities containing up to 10 atoms and 124 orbitals. We find
that spectral properties, magnetic moments, and two-particle spin correlation
functions are obtained in good agreement with experiments. In addition, in the
metal oxide insulators, the balanced treatment of correlations involving all
orbitals in the cell leads to new insights into the orbital character around
the insulating gap.",2003.01349v2
2020-03-26,Buried Moire supercells through SrTiO$_3$ nanolayer relaxation,"The interface of complex oxide heterostructures sets the stage for various
electronic and magnetic phenomena. Many of these collective effects originate
from the precise structural arrangement at the interface that in turn governs
local spin- and charge interactions. Currently, interfacial straining, so the
naturally evolving compressive or tensile strain by mismatch of the neighboring
lattices, is the most common route towards engineering collective material
properties -- yet, significant progress might require exploration of entirely
new approaches towards interface correlations. In this work, we turn the page
by looking at the interface of a perfectly relaxed, unstrained heterostructure,
where we identify a highly ordered Moire lattice at an inherently disordered
SrTiO$_3$ (STO) - LSAT interface. Using high-resolution reciprocal space
mapping via synchrotron based X-Ray diffraction, we find long-ranged ordered
supercells of 106/107 unit cells of STO/LSAT, caused by lattice relaxation
through high-temperature annealing. Model calculations confirm the
experimentally observed scattering phenomena, showing that cross-interfacial
bonding is locally different at the Moire-overlap points. Notably, the presence
of such super-ordered structures in the family of 2D electron gas systems sets
the ideal conditions for Moire-motif tuned plasmonic responses and
ferroelectric super-crystallinity and opens up the possibility to novel
interface functionalities in these simple perovskites.",2003.11762v3
2020-06-14,Ferroelastic-switching-driven colossal shear strain and piezoelectricity in a hybrid ferroelectric,"Materials that can produce large controllable strains are widely used in
shape memory devices, actuators and sensors. Great efforts have been made to
improve the strain outputs of various material systems. Among them,
ferroelastic transitions underpin giant reversible strains in
electrically-driven ferro/piezoelectrics and thermally- or magneticallydriven
shape memory alloys. However, large-strain ferroelastic switching in
conventional ferroelectrics is very challenging while magnetic and thermal
controls are not desirable for applications. Here, we demonstrate an
unprecedentedly large shear strain up to 21.5 % in a hybrid ferroelectric,
C6H5N(CH3)3CdCl3. The strain response is about two orders of magnitude higher
than those of top-performing conventional ferroelectric polymers and oxides. It
is achieved via inorganic bond switching and facilitated by the structural
confinement of the large organic moieties, which prevents the undesired
180-degree polarization switching. Furthermore, Br substitution can effectively
soften the bonds and result in giant shear piezoelectric coefficient (d35 ~
4800 pm/V) in Br-rich end of the solid solution, C6H5N(CH3)3CdBr3xCl3(1-x). The
superior electromechanical properties of the compounds promise their potential
in lightweight and high energy density devices, and the strategy described here
should inspire the development of next-generation piezoelectrics and
electroactive materials based on hybrid ferroelectrics.",2006.07883v1
2020-06-15,Room-temperature quantum spin Hall phase in laser-patterned few-layer 1T'- MoS2,"The quantum-spin-Hall (QSH) phase of 2D topological insulators has attracted
increased attention since the onset of 2D materials research. While large bulk
gaps with vanishing edge gaps in atomically thin layers have been reported,
verifications of the QSH phase by resistance measurements are comparatively
few. This is partly due to the poor uniformity of the bulk gap induced by the
substrate over a large sample area and/or defects induced by oxidation. Here,
we report the observation of the QSH phase at room-temperature in the 1T'-phase
of few-layer MoS2 patterned onto the 2H semiconducting phase using low-power
and short-time laser beam irradiation. Two different resistance measurements
reveal hallmark transport conductance values, ~e2/2h and e2/4h, as predicted by
the theory. Magnetic-field dependence, scanning tunneling spectra, and
calculations support the emergence of the room-temperature QSH phase. Although
further experimental verification is still desirable, our results provide
feasible application to room-temperature topological devices.",2006.08125v2
2020-06-23,Antiferromagnetic Half-skyrmions and Bimerons at room temperature,"In the quest for post-CMOS technologies, ferromagnetic skyrmions and their
anti-particles have shown great promise as topologically protected solitonic
information carriers in memory-in-logic or neuromorphic devices. However, the
presence of dipolar fields in ferromagnets, restricting the formation of
ultra-small topological textures, and the deleterious skyrmion Hall effect when
driven by spin torques have thus far inhibited their practical implementations.
Antiferromagnetic analogues, which are predicted to demonstrate relativistic
dynamics, fast deflection-free motion and size scaling have recently come into
intense focus, but their experimental realizations in natural antiferromagnetic
systems are yet to emerge. Here, we demonstrate a family of topological
antiferromagnetic spin-textures in $\alpha$-Fe$_2$O$_3$ - an earth-abundant
oxide insulator - capped with a Pt over-layer. By exploiting a first-order
analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons
(half-skyrmions), and bimerons, which can be erased by magnetic fields and
re-generated by temperature cycling. These structures have characteristic sizes
of the order ~100 nm that can be chemically controlled via precise tuning of
the exchange and anisotropy, with pathways to further scaling. Driven by
current-based spin torques from the heavy-metal over-layer, some of these AFM
textures could emerge as prime candidates for low-energy antiferromagnetic
spintronics at room temperature.",2006.12699v2
2020-08-05,From Mott Insulators to Quantum Metals,"High critical temperature cuprate superconducting materials are composed of
copper oxide layers and interlayer charge reservoirs. When not doped, these
cuprates are antiferromagnetic insulators. We propose to design new materials
by combining alternating layers of parents of hole-doped and electron-doped of
these cuprates and modifications thereof. Our goal is to find undoped cuprates
that can be either an antiferromagnetic insulator or a quantum metal. The term
quantum metal means a metal characterized by long range antiferromagnetic order
or only strong antiferromagnetic correlations, i.e., it is thus a stable ground
state against any other perturbations. The new metallic states sought here
could be precursors to new superconducting states in the absence or presence of
doping. Using the density functional theory, we report on two compounds
{La}{Pr}CuO4 and {La}{V}CuO4 that illustrate the different physics described
above. The curly brackets mean that the preparation of these compounds shall be
done by depositing a layer containing Pr, then one CuO2 layer, then finally the
La layer in {La}{Pr}CuO4 for example. The configuration formed by the positions
of the charge reservoir atoms with respect to the CuO2 layer is an important
factor in the new procedure we propose here. This paper reports on the X-ray
diffraction, electronic, optical, and magnetic properties of these hypothetical
materials. We found that {La}{Pr}CuO4 is a Mott insulator, but {La}{V}CuO4 is
an undoped correlated quantum metal with long-range order. Our calculations
were performed using the linearized plane wave method (FP-LAPW) implemented
within the Wien2k software.",2008.02360v1
2020-08-27,Odd-frequency pair density wave correlations in underdoped cuprates,"Pair density waves, identified by Cooper pairs with finite center-of-mass
momentum, have recently been observed in copper oxide based high T$_\textrm{c}$
superconductors (cuprates). A charge density modulation or wave is also
ubiquitously found in underdoped cuprates. Within a general mean-field one-band
model we show that the coexistence of charge density waves and uniform
superconductivity in $d$-wave superconductors like cuprates, generates an
odd-frequency spin-singlet pair density wave, in addition to the even-frequency
counterparts. The strength of the induced odd-frequency pair density wave
depends on the modulation wave vector of the charge density wave, with the
odd-frequency pair density waves even becoming comparable to the even-frequency
ones in parts of the Brillouin zone. We show that a change in the modulation
wave vector of the charge density wave from bi-axial to uni-axial, can enhance
the odd-frequency component of the pair density waves. Such a coexistence of
superconductivity and uni-axial charge density wave has already been
experimentally verified at high magnetic fields in underdoped cuprates. We
further discuss the possibility of an odd-frequency spin-triplet pair density
wave generated in the coexistence regime of superconductivity and spin density
waves, applicable to the iron-based superconductors. Our work thus presents a
route to bulk odd-frequency superconductivity in high T$_c$ superconductors.",2008.12021v2
2020-09-28,A hybrid optoelectronic Mott insulator,"The coupling of electronic degrees of freedom in materials to create
hybridized functionalities is a holy grail of modern condensed matter physics
that may produce novel mechanisms of control. Correlated electron systems often
exhibit coupled degrees of freedom with a high degree of tunability which
sometimes lead to hybridized functionalities based on external stimuli.
However, the mechanisms of tunability and the sensitivity to external stimuli
are determined by intrinsic material properties which are not always
controllable. A Mott metal-insulator transition, which is technologically
attractive due to the large changes in resistance, can be tuned by doping,
strain, electric fields, and orbital occupancy but cannot be, in and of itself,
controlled externally with light. Here we present a new approach to produce
hybridized functionalities using a properly engineered
photoconductor/strongly-correlated hybrid heterostructure, showing control of
the Metal-to-Insulator transition (MIT) using optical means. This approach
combines a photoconductor, which does not exhibit an MIT, with a strongly
correlated oxide, which is not photoconducting. Due to the close proximity
between the two materials, the heterostructure exhibits large volatile and
nonvolatile, photoinduced resistivity changes and substantial photoinduced
shifts in the MIT transition temperatures. This approach can potentially be
extended to other judiciously chosen combinations of strongly correlated
materials with systems which exhibit optically, electrically or magnetically
controllable behavior.",2009.13606v1
2020-10-13,"High-pressure synthesis of Ba$_2$RhO$_4$, a rhodate analogue of the layered perovskite Sr-ruthenate","A new layered perovskite-type oxide Ba$_2$RhO$_4$ was synthesized by a
high-pressure technique with the support of convex-hull calculations. The
crystal and electronic structure were studied by both experimental and
computational tools. Structural refinements for powder x-ray diffraction data
showed that Ba$_2$RhO$_4$ crystallizes in a K$_2$NiF$_4$-type structure,
isostructural to Sr$_2$RuO$_4$ and Ba$_2$IrO$_4$. Magnetic, resistivity, and
specific heat measurements for polycrystalline samples of Ba$_2$RhO$_4$
indicate that the system can be characterized as a correlated metal. Despite
the close similarity to its Sr$_2$RuO$_4$ counterpart in the electronic
specific heat coefficient and the Wilson ratio, Ba$_2$RhO$_4$ shows no
signature of superconductivity down to 0.16 K. Whereas the Fermi surface
topology has reminiscent pieces of Sr$_2$RuO$_4$, an electron-like
e$_g$-($d_{x^2-y^2}$) band descends below the Fermi level, making of this
compound unique also as a metallic counterpart of the spin-orbit-coupled Mott
insulator Ba$_2$IrO$_4$.",2010.06556v1
2020-10-23,Superconductor-metal quantum transition at the EuO-KTaO3 interface,"Superconductivity has been one of the most fascinating quantum states of
matter for over several decades. Among the superconducting materials,
LaAlO3/SrTiO3 interface is of particularly interest since superconductivity
exists between two insulating materials, which provides it with various unique
applications compared with bulk superconductors and makes it a suitable
platform to study the quantum Hall effect, charge density wave,
superconductivity and magnetism in one device. Therefore, a lot of efforts have
been made to search new superconducting oxide interface states with higher
superconducting critical temperature (TC). Recently, a superconducting state
with TC ~ 2 K has been found at the interface between a ferromagnetic insulator
EuO and a band insulator (111)-KTaO3. Here, we report the experimental
investigation of the superconductor-metal quantum phase transition of the
EuO/KTaO3 interface. Around the transition, a divergence of the dynamical
critical exponent is observed, which supports the quantum Griffiths singularity
in the EuO/KTaO3 interface. The quantum Griffiths singularity could be
attributed to large rare superconducting regions and quenched disorders at the
interface. Our results could pave the way for studying the exotic
superconducting properties at the EuO/KTaO3 interface.",2010.12204v2
2020-11-11,Domain Wall Leaky Integrate-and-Fire Neurons with Shape-Based Configurable Activation Functions,"Complementary metal oxide semiconductor (CMOS) devices display volatile
characteristics, and are not well suited for analog applications such as
neuromorphic computing. Spintronic devices, on the other hand, exhibit both
non-volatile and analog features, which are well-suited to neuromorphic
computing. Consequently, these novel devices are at the forefront of
beyond-CMOS artificial intelligence applications. However, a large quantity of
these artificial neuromorphic devices still require the use of CMOS, which
decreases the efficiency of the system. To resolve this, we have previously
proposed a number of artificial neurons and synapses that do not require CMOS
for operation. Although these devices are a significant improvement over
previous renditions, their ability to enable neural network learning and
recognition is limited by their intrinsic activation functions. This work
proposes modifications to these spintronic neurons that enable configuration of
the activation functions through control of the shape of a magnetic domain wall
track. Linear and sigmoidal activation functions are demonstrated in this work,
which can be extended through a similar approach to enable a wide variety of
activation functions.",2011.06075v1
2021-02-19,Surface and interface effects in oxygen deficient SrMnO$_3$ thin films grown on SrTiO$_3$,"Complex oxide functionality, such as ferroelectricity, magnetism or
superconductivity is often achieved in epitaxial thin-film geometries. Oxygen
vacancies tend to be the dominant type of defect in these materials but a
fundamental understanding of their stability and electronic structure has so
far mostly been established in the bulk or strained bulk, neglecting interfaces
and surfaces present in a thin-film geometry. We investigate here, via density
functional theory calculations, oxygen vacancies in the model system of a
SrMnO$_3$ (SMO) thin film grown on a SrTiO$_3$ (STO) (001) substrate.
Structural and electronic differences compared to bulk SMO result mainly from
undercoordination at the film surface. The changed crystal field leads to a
depletion of subsurface valence-band states and transfer of this charge to
surface Mn atoms, both of which strongly affect the defect chemistry in the
film. The result is a strong preference of oxygen vacancies in the surface
region compared to deeper layers. Finally, for metastable oxygen vacancies in
the substrate, we predict a spatial separation of the defect from its excess
charge, the latter being accommodated in the film but close to the substrate
boundary. These results show that surface and interface effects lead to
significant differences in stability and electronic structure of oxygen
vacancies in thin-film geometries compared to the (strained) bulk.",2102.10141v1
2021-03-30,Positive magnetoresistance and chiral anomaly in exfoliated type-II Weyl semimetal $T_\mathrm{d}$-WTe$_{2}$,"Layered van der Waals semimetallic $T_\mathrm{d}$-WTe$_{2}$, exhibiting
intriguing properties which include non-saturating extreme positive
magnetoresistance (MR) and tunable chiral anomaly, has emerged as model
topological type-II Weyl semimetal system. Here, $\sim$45 nm thick mechanically
exfoliated flakes of $T_\mathrm{d}$-WTe$_{2}$ are studied $via$ atomic force
microscopy, Raman spectroscopy, low-$T$/high-$\mu_{0}H$ magnetotransport
measurements and optical reflectivity. The contribution of anisotropy of the
Fermi liquid state to the origin of the large positive transverse
$\mathrm{MR}_\perp$ and the signature of chiral anomaly of the type-II Weyl
fermions are reported. The samples are found to be stable in air and no
oxidation or degradation of the electronic properties are observed. A
transverse $\mathrm{MR}_\perp$ $\sim$1200\,\% and an average carrier mobility
of $5000$\, cm$^{2}$V$^{-1}$s$^{-1}$ at $T=5\,\mathrm{K}$ for an applied
perpendicular field $\mu_{0}H_{\perp} = 7\,\mathrm{T}$ are established. The
system follows a Fermi liquid model for $T\leq50\,\mathrm{K}$ and the
anisotropy of the Fermi surface is concluded to be at the origin of the
observed positive MR. The anisotropy of the electronic behaviour is also
confirmed by optical reflectivity measurements. The relative orientation of the
crystal axes and of the applied electric and magnetic fields is proven to give
rise to the observed chiral anomaly in the in-plane magnetotransport.",2103.16326v1
2021-04-01,Absence of moment fragmentation in the mixed $B$-site pyrochlore Nd$_{2}$GaSbO$_{7}$,"Nd-based pyrochlore oxides of the form Nd$_{2}B_{2}$O$_{7}$ have garnered a
significant amount of interest owing to the moment fragmentation physics
observed in Nd$_{2}$Zr$_{2}$O$_{7}$ and speculated in Nd$_{2}$Hf$_{2}$O$_{7}$.
Notably this phenomenon is not ubiquitous in this family, as it is absent in
Nd$_{2}$Sn$_{2}$O$_{7}$, which features a smaller ionic radius on the $B$-site.
Here, we explore the necessary conditions for moment fragmentation in the Nd
pyrochlore family through a detailed study of the mixed $B$-site pyrochlore
Nd$_{2}$GaSbO$_{7}$. The $B$-site of this system is characterized by
significant disorder and an extremely small average ionic radius. Similarly to
Nd$_{2}$Sn$_{2}$O$_{7}$, we find no evidence for moment fragmentation through
our bulk characterization and neutron scattering experiments, indicating that
chemical pressure (and not necessarily the $B$-site disorder) plays a key role
in the presence or absence of this phenomenon in this material family.
Surprisingly, the presence of significant $B$-site disorder in
Nd$_{2}$GaSbO$_{7}$ does not generate a spin glass ground state and instead the
same all-in-all-out magnetic order identified in other Nd pyrochlores is found
here.",2104.00791v1
2021-04-26,Manipulation of polar vortex chirality in oxide superlattices,"Topological polar vortices that are the electric analogues of magnetic
objects, present great potential in applications of future nanoelectronics due
to their nanometer size, anomalous dielectric response, and chirality. To
enable the functionalities, it is prerequisite to manipulate the polar states
and chirality by using external stimuli. Here, we probe the evolutions of polar
state and chirality of polar vortices in PbTiO3/SrTiO3 superlattices under
electric field by using atomically resolved in situ scanning transmission
electron microscopy and phase-field simulations. We find that the adjacent
clockwise and counterclockwise vortex usually have opposite chirality. The
phase-field simulations suggest that the rotation reversal or axial
polarization switching can lead to the chirality change. Guided by which, we
experimentally validate that the vortex rotation direction can be changed by
applying and subsequently removing of electric fields, offering a potential
strategy to manipulate the vortex chirality. The revealed details of dynamic
behavior for individual polar vortices at atomic scale and the proposed
strategy for chirality manipulation provide fundamentals for future device
applications.",2104.12310v1
2021-05-05,Ni$_{80}$Fe$_{20}$ Nanotubes with Optimized Spintronic Functionalities Prepared by Atomic Layer Deposition,"Permalloy Ni$_{80}$Fe$_{20}$ is one of the key magnetic materials in the
field of magnonics. Its potential would be further unveiled if it could be
deposited in three dimensional (3D) architectures of sizes down to the
nanometer. Atomic Layer Deposition, ALD, is the technique of choice for
covering arbitrary shapes with homogeneous thin films. Early successes with
ferromagnetic materials include nickel and cobalt. Still, challenges in
depositing ferromagnetic alloys reside in the synthesis via decomposing the
consituent elements at the same temperature and homogeneously. We report
plasma-enhanced ALD to prepare permalloy Ni$_{80}$Fe$_{20}$ thin films and
nanotubes using nickelocene and iron(III) tert-butoxide as metal precursors,
water as the oxidant agent and an in-cycle plasma enhanced reduction step with
hydrogen. We have optimized the ALD cycle in terms of Ni:Fe atomic ratio and
functional properties. We obtained a Gilbert damping of 0.013, a resistivity of
28 $\mu\Omega$cm and an anisotropic magnetoresistance effect of 5.6 $\%$ in the
planar thin film geometry. We demonstrate that the process also works for
covering GaAs nanowires, resulting in permalloy nanotubes with high aspect
ratios and diameters of about 150 nm. Individual nanotubes were investigated in
terms of crystal phase, composition and spin-dynamic response by microfocused
Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and
magnonic devices in curved and complex topology operated in the GHz frequency
regime.",2105.01969v1
2021-05-08,Evidence for strong electron correlations in a non-symmorphic Dirac semimetal,"Metallic iridium oxides (iridates) provide a fertile playground to explore
new phenomena resulting from the interplay between topological protection,
spin-orbit and electron-electron interactions. To date, however, few studies of
the low energy electronic excitations exist due to the difficulty in
synthesising crystals with sufficiently large carrier mean-free-paths. Here, we
report the observation of Shubnikov-de Haas quantum oscillations in
high-quality single crystals of monoclinic SrIrO$_3$ in magnetic fields up to
35~T. Analysis of the oscillations reveals a Fermi surface comprising multiple
small pockets with effective masses up to 4.5 times larger than the calculated
band mass. \textit{Ab-initio} calculations reveal robust linear band-crossings
at the Brillouin zone boundary, due to its non-symmorphic symmetry, and overall
we find good agreement between the angular dependence of the oscillations and
the theoretical expectations. Further evidence of strong electron correlations
is realized through the observation of signatures of non-Fermi liquid transport
as well as a large Kadowaki-Woods ratio. These collective findings, coupled
with knowledge of the evolution of the electronic state across the
Ruddlesden-Popper iridate series, establishes monoclinic SrIrO$_3$ as a
topological semimetal on the boundary of the Mott metal-insulator transition.",2105.03740v2
2021-05-19,"Polyrotaxane: New Generation of Sustainable, Ultra-flexible, Form-stable and Smart Phase Change Materials","The development of thermal energy storage materials is the most attractive
strategy to harvest the solar energy and increase the energy utilization
efficiency. Phase change materials (PCMs) have received much attention in this
research field for several decades. Herein, we reported a new kind of PCM micro
topological structure, design direction, and the ultra-flexible, form-stable
and smart PCMs, polyrotaxane. The structure of polyrotaxane was fully confirmed
by 1H nuclear magnetic resonance,attenuated total reflection-fourier transform
infrared and X-ray diffraction. Then the tensile properties,thermal stability
in the air, phase change energy storage and shape memory properties of the
films were systematically analyzed. The results showed that all the mechanical
performance, thermal stability in air and shape memory properties of
polyrotaxanes were enhanced significantly compared to those of polyethylene
oxide (PEO). The form stability at temperatures above the melting point of PEO
significantly increased with the {\alpha}-CD addition. Further with the high
phase transition enthalpy and excellent cycle performance, the polyrotaxane
films are therefore promising sustainable and advanced form-stable phase change
materials for thermal energy storage. Notably, its ultra-high flexibility,
remolding ability and excellent shape memory properties provide a convenient
way for the intelligent heat treatment packaging of complex and flexible
electronic devices. In addition, this is a totally novel insight for
polyrotaxane application and new design method for form-stable PCMs.",2105.09074v1
2021-05-27,"Nickelate superconductivity without rare-earth magnetism: (La,Sr)NiO$_{2}$","The observation of superconductivity in infinite layer nickelate
(Nd,Sr)NiO$_{2}$ thin films has led to rapid theoretical and experimental
investigations of these copper-oxide-analogue systems [1-15]. Superconductivity
has also been found in (Pr,Sr)NiO$_{2}$ [16,17], but not previously in
(La,Sr)NiO$_{2}$ [2], raising a fundamental question whether superconductivity
is associated with the presence of rare-earth moments [18,19]. Here we show
that with significant materials optimization, substantial portions of the
La$_{1-x}$Sr$_{x}$NiO$_{2}$ phase diagram can enter the regime of coherent
low-temperature transport ($x$ = 0.14 - 0.20), with subsequent superconducting
transitions and a maximum onset of ~ 9 K at $x$ = 0.20. Additionally, we
observe the unexpected indication of a superconducting ground state in undoped
LaNiO$_{2}$, which likely reflects the self-doped nature of the electronic
structure. Combining the results of (La/Pr/Nd)$_{1-x}$Sr$_{x}$NiO$_{2}$ reveals
a generalized superconducting dome, characterized by systematic shifts in the
unit cell volume and in the relative electron-hole populations across the
lanthanides.",2105.13494v1
2021-06-07,The ground state in a proximity to a possible Kitaev spin liquid: An undistorted honeycomb iridate NaxIrO3 (0.60 < x < 0.80),"We report results of our study of a newly synthesized honeycomb iridate
NaxIrO3 (0.60 < x < 0.80). Single-crystal NaxIrO3 adopts a honeycomb lattice
noticeably without distortions and stacking disorder inherently existent in its
sister compound Na2IrO3. The oxidation state of the Ir ion is a mixed valence
state resulting from a majority Ir5+(5d4) ion and a minority Ir6+(5d3) ion.
NaxIrO3 is a Mott insulator likely with a predominant pseudospin = 1 state. It
exhibits an effective moment of 1.1 Bohr Magneton/Ir and a Curie-Weiss
temperature of -19 K but with no discernable long-range order above 1 K. The
physical behavior below 1 K features two prominent anomalies at Th = 0.9 K and
Tl = 0.12 K in both the heat capacity and AC magnetic susceptibility.
Intermediate between Th and Tl lies a pronounced temperature linearity of the
heat capacity with a large slope of 77 mJ/mole K2, a feature expected for
highly correlated metals but not at all for insulators. These results along
with comparison drawn with the honeycomb lattices Na2IrO3 and (Na0.2Li0.8)2IrO3
point to an exotic ground state in a proximity to a possible Kitaev spin
liquid.",2106.04012v1
2021-07-15,Epitaxial stabilization of metastable 3C BaRuO3 thin film with ferromagnetic non-Fermi liquid phase,"Thin films of perovskite Ruthenates of the general formula ARuO3 (A = Ca and
Sr) are versatile electrical conductors for viable oxide electronics. They are
also scientifically intriguing, as they exhibit non-trivial electromagnetic
ground states depending on the A-site element. Among them, realization of the
cubic perovskite (3C) BaRuO3 thin film has been a challenge so far, because the
3C phase is metastable with the largest formation energy among the various
polymorph phases of BaRuO3. In this study, we successfully prepared 3C BaRuO3
thin films employing epitaxial stabilization. The 3C BaRuO3 thin films show
itinerant ferromagnetism with a transition temperature of ~48 K and a non-Fermi
liquid phase. The epitaxial stabilization of the 3C BaRuO3 further enabled us
to make a standard comparison of perovskite Ruthenates thin films, thereby
establishing the importance of the Ru-O orbital hybridization in understanding
the itinerant magnetic system.",2107.07181v1
2021-07-16,Long-Range Superconducting Proximity Effect in Nickel Nanowires,"When a ferromagnet is placed in contact with a superconductor, owing to
incompatible spin order, the Cooper pairs from the superconductor cannot
survive more than one or two nanometers inside the ferromagnet. This is
confirmed in the measurements of ferromagnetic nickel (Ni) nanowires contacted
by superconducting niobium (Nb) leads. However, when a 3 nm thick copper oxide
(CuO) buffer layer made by exposing an evaporated or a sputtered 3 nm Cu film
to air, is inserted between the Nb electrodes and the Ni wire, the spatial
extent of the superconducting proximity range is dramatically increased from 2
to a few tens of nanometers. Scanning transmission electron microscope study
confirms the formation of a 3 nm thick CuO layer when an evaporated Cu film is
exposed to air. Magnetization measurements of such a 3 nm CuO film on a SiO2/Si
substrate and on Nb/SiO2/Si show clear evidence of ferromagnetism. One way to
understand the long-range proximity effect in the Ni nanowire is that the CuO
buffer layer with ferromagnetism facilitates the conversion of singlet
superconductivity in Nb into triplet supercurrent along the Ni nanowires.",2107.08018v3
2021-07-26,Electrically Enhanced Exchange Bias via Solid State Magneto-Ionics,"Electrically induced ionic motion offers a new way to realize
voltage-controlled magnetism, opening the door to a new generation of logic,
sensor, and data storage technologies. Here, we demonstrate an effective
approach to magneto-ionically and electrically tune exchange bias in
Gd/Ni$_{1-x}$Co$_{x}$O thin films (x=0.50, 0.67), where neither of the layers
alone is ferromagnetic at room temperature. The Gd capping layer deposited onto
antiferromagnetic Ni$_{1-x}$Co$_{x}$O initiates a solid-state redox reaction
that reduces an interfacial region of the oxide to ferromagnetic NiCo. Exchange
bias is established after field cooling, which can be enhanced by up to 35%
after a voltage conditioning and subsequently reset with a second field
cooling. These effects are caused by the presence of an interfacial
ferromagnetic NiCo layer, which further alloys with the Gd layer upon field
cooling and voltage application, as confirmed by electron microscopy and
polarized neutron reflectometry studies. These results highlight the viability
of the solid-state magneto-ionic approach to achieve electric control of
exchange bias, with potentials for energy-efficient magneto-ionic devices.",2107.12503v2
2021-07-28,Dynamics of Polar Skyrmion Bubbles under Electric Fields,"Room-temperature polar skyrmion bubbles that are recently found in oxide
superlattice, have received enormous interests for their potential applications
in nanoelectronics due to the nanometer size, emergent chirality, and negative
capacitance. For practical applications, the ability to controllably manipulate
them by using external stimuli is prerequisite. Here, we study the dynamics of
individual polar skyrmion bubbles at the nanoscale by using in situ biasing in
a scanning transmission electron microscope. The reversible electric
field-driven phase transition between topological and trivial polar states are
demonstrated. We create, erase and monitor the shrinkage and expansion of
individual polar skyrmions. We find that their transition behaviors are
substantially different from that of magnetic analogue. The underlying
mechanism is discussed by combing with the phase-field simulations. The
controllable manipulation of nanoscale polar skyrmions allows us to tune the
dielectric permittivity at atomic scale and detailed knowledge of their phase
transition behaviors provides fundamentals for their applications in
nanoelectronics.",2107.13390v1
2021-08-08,On the Electron Pairing Mechanism of Copper-Oxide High Temperature Superconductivity,"The elementary CuO2 plane sustaining cuprate high-temperature
superconductivity occurs typically at the base of a periodic array of
edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent
planar Cu and O atoms, occurring at a rate $t/{\hbar}$ and across the
charge-transfer energy gap E, generate 'superexchange' spin-spin interactions
of energy $J\approx4t^4/E^3$ in an antiferromagnetic correlated-insulator
state. However, Hole doping the CuO2 plane converts this into a very high
temperature superconducting state whose electron-pairing is exceptional. A
leading proposal for the mechanism of this intense electron-pairing is that,
while hole doping destroys magnetic order it preserves pair-forming
superexchange interactions governed by the charge-transfer energy scale E. To
explore this hypothesis directly at atomic-scale, we combine single-electron
and electron-pair (Josephson) scanning tunneling microscopy to visualize the
interplay of E and the electron-pair density nP in ${Bi_2Sr_2CaCu_2O_{8+x}}$.
The responses of both E and nP to alterations in the distance {\delta} between
planar Cu and apical O atoms are then determined. These data reveal the
empirical crux of strongly correlated superconductivity in CuO2, the response
of the electron-pair condensate to varying the charge transfer energy.
Concurrence of predictions from strong-correlation theory for hole-doped
charge-transfer insulators with these observations, indicates that
charge-transfer superexchange is the electron-pairing mechanism of
superconductive ${Bi_2Sr_2CaCu_2O_{8+x}}$.",2108.03655v3
2021-09-05,Isostructural Metal-Insulator Transition Driven by Dimensional-Crossover in SrIrO3 Heterostructures,"Dimensionality reduction induced metal-insulator transitions in oxide
heterostructures are usually coupled with structural and magnetic phase
transitions, which complicate the interpretation of the underlying physics.
Therefore, achieving isostructural MIT is of great importance for fundamental
physics and even more for applications. Here, we report an isostructural
metal-insulator transition driven by dimensional-crossover in spin-orbital
coupled SrIrO3 films. By using in-situ pulsed laser deposition and
angle-resolved photoemission spectroscopy, we synthesized and investigated the
electronic structure of SrIrO3 ultrathin films with atomic-layer precision.
Through inserting orthorhombic CaTiO3 buffer layers, we demonstrate that the
crystal structure of SrIrO3 films remains bulk-like with similar oxygen
octahedra rotation and tilting when approaching the ultrathin limit. We observe
that a dimensional-crossover metal-insulator transition occurs in isostructural
SrIrO3 films. Intriguingly, we find the bandwidth of Jeff=3/2 states reduces
with lowering the dimensionality and drives the metal-insulator transition. Our
results establish a bandwidth controlled metal-insulator transition in the
isostructural SrIrO3 thin films.",2109.02056v1
2021-09-27,Ultrafast renormalization of the onsite Coulomb repulsion in a cuprate superconductor,"Ultrafast lasers are an increasingly important tool to control and stabilize
emergent phases in quantum materials. Among a variety of possible excitation
protocols, a particularly intriguing route is the direct light-engineering of
microscopic electronic parameters, such as the electron hopping and the local
Coulomb repulsion (Hubbard $U$). In this work, we use time-resolved x-ray
absorption spectroscopy to demonstrate the light-induced renormalization of the
Hubbard $U$ in a cuprate superconductor, La$_{1.905}$Ba$_{0.095}$CuO$_4$. We
show that intense femtosecond laser pulses induce a substantial redshift of the
upper Hubbard band, while leaving the Zhang-Rice singlet energy unaffected. By
comparing the experimental data to time-dependent spectra of single- and
three-band Hubbard models, we assign this effect to a $\sim140$ meV reduction
of the onsite Coulomb repulsion on the copper sites. Our demonstration of a
dynamical Hubbard $U$ renormalization in a copper oxide paves the way to a
novel strategy for the manipulation of superconductivity, magnetism, as well as
to the realization of other long-range-ordered phases in light-driven quantum
materials.",2109.13229v1
2021-10-12,Bridging the Band Gap: What Device Physicists Need to Know About Machine Learning,"This article surveys the landscape of semiconductor materials and devices
research for the acceleration of machine learning (ML) algorithms. We observe a
disconnect between the semiconductor and device physics and engineering
communities, and the digital logic and computer hardware architecture
communities. The article first provides an overview of the principles of
computational complexity and fundamental physical limits to computing and their
relation to physical systems. The article then provides an introduction to ML
by presenting three key components of ML systems: representation, evaluation,
and optimisation. The article then discusses and provides examples of the
application of emerging technologies from the demiconductor and device physics
domains as solutions to computational problems, alongside a brief overview of
emerging devices for computing applications. The article then reviews the
landscape of ML accelerators, comparing fixed-function and reprogrammable
digital logic with novel devices such as memristors, resistive memories,
magnetic memories, and probabilistic bits. We observe broadly lower performance
of ML accelerators based on novel devices and materials when compared to those
based on digital complimentary metal-oxide semiconductor (CMOS) technology,
particularly in the MNIST optical character recognition task, a common ML
benchmark, and also highlight the lack of a trend of progress in approaches
based on novel materials and devices. Lastly, the article proposes figures of
merit for meaningful evaluation and comparison of different ML implementations
in the hope of fostering a dialogue between the materials science, device
physics, digital logic, and computer architecture communities by providing a
common frame of reference for their work.",2110.05910v2
2021-11-25,NV microscopy of thermally controlled stresses caused by Cr$_2$O$_3$ thin films,"Many modern applications, including quantum computing and quantum sensing,
use substrate-film interfaces. Particularly, thin films of chromium or titanium
and their oxides are commonly used to bind various structures, such as
resonators, masks, or microwave antennas, to a diamond surface. Due to
different thermal expansions of involved materials, such films and structures
could produce significant stresses, which need to be measured or predicted. In
this paper, we demonstrate imaging of stresses in the top layer of diamond with
deposited structures of Cr$_2$O$_3$ at temperatures 19$^{\circ}$C and
37$^{\circ}$C by using stress-sensitive optically detected magnetic resonances
(ODMR) in NV centers. We also calculated stresses in the diamond-film interface
by using finite-element analysis and correlated them to measured ODMR frequency
shifts. As predicted by the simulation, the measured high-contrast
frequency-shift patterns are only due to thermal stresses, whose spin-stress
coupling constant along the NV axis is 21$\pm$1 MHz/GPa, that is in agreement
with constants previously obtained from single NV centers in diamond
cantilever. We demonstrate that NV microscopy is a convenient platform for
optically detecting and quantifying spatial distributions of stresses in
diamond-based photonic devices with micrometer precision and propose thin films
as a means for local application of temperature-controlled stresses. Our
results also show that thin film structures produce significant stresses in
diamond substrates, which should be accounted for in NV-based applications.",2111.12979v2
2021-12-06,Interior Structure Models Of Venus,"Venus' mass and radius are similar to those of Earth. However,
dissimilarities in atmospheric properties, geophysical activity and magnetic
field generation could hint towards significant differences in the chemical
composition and interior evolution of the two planets. Although various
explanations for the differences between Venus and Earth have been proposed,
the currently available data are insufficient to discriminate among the
different solutions. Here we investigate the possible range of Venus structure
models. We assume that core segregation happened as a single-stage event. The
mantle composition is inferred from the core composition using a prescription
for metal-silicate partitioning. We consider three different cases for the
composition of Venus defined via the bulk Si and Mg content, and the core's S
content. Permissible ranges for the core size, mantle and core composition as
well as the normalized moment of inertia (MoI) are presented for these
compositions. A solid inner core could exist for all compositions. We estimate
that Venus' MoI is 0.317-0.351 and its core size 2930-4350 km for all assumed
compositions. Higher MoI values correspond to more oxidizing conditions during
core segregation. A determination of the abundance of FeO in Venus' mantle by
future missions could further constrain its composition and internal structure.
This can reveal important information on Venus' formation and evolution, and
possibly, the reasons for the differences between Venus and our home planet.",2112.03225v2
2021-12-31,Ferromagnetic Enhancement in LaMnO3 Films with Release and Flexure,"A variety of novel phenomena and functionalities emerge from lowering the
dimensionality of materials and enriching the degrees of freedom in modulation.
In this work, it is found that the saturation magnetization of LaMnO3 (LMO)
films is largely enhanced by 56% after releasing from a brand-new phase of
tetragonal strontium aluminate buffer layer, and is significantly increased by
92% with bending films to a curvature of 1 mm-1 using a water-assisted
direct-transferring method. Meanwhile, the Curie temperature of LMO films has
been improved by 13 K. High-resolution spherical aberration-corrected scanning
transmission electron microscopy and first-principles calculations
unambiguously demonstrate that the enhanced ferromagnetism is attributed to the
strengthened Mn-O-Mn super-exchange interactions from the augmented
characteristics of the unconventional P21/n structure caused by the
out-of-plane lattice shrinking after strain releasing and increased flexure
degree of freestanding LMO films. This work paves a way to achieve large-scale
and crack-and-wrinkle-free freestanding films of oxides with largely improved
functionalities.",2112.15307v1
2022-01-21,A single hole spin with enhanced coherence in natural silicon,"Semiconductor spin qubits based on spin-orbit states are responsive to
electric field excitation allowing for practical, fast and potentially scalable
qubit control. Spin-electric susceptibility, however, renders these qubits
generally vulnerable to electrical noise, which limits their coherence time.
Here we report on a spin-orbit qubit consisting of a single hole
electrostatically confined in a natural silicon metal-oxide-semiconductor
device. By varying the magnetic field orientation, we reveal the existence of
operation sweet spots where the impact of charge noise is minimized while
preserving an efficient electric-dipole spin control. We correspondingly
observe an extension of the Hahn-echo coherence time up to 88 $\mu$s, exceeding
by an order of magnitude the best reported values for hole-spin qubits, and
approaching the state-of-the-art for electron spin qubits with synthetic
spin-orbit coupling in isotopically-purified silicon. This finding largely
enhances the prospects of silicon-based hole spin qubits for scalable quantum
information processing.",2201.08637v2
2022-02-01,Proximity-Induced Superconductivity in Atomically Precise Nanographene,"Obtaining a robust superconducting state in atomically precise nanographene
(NG) structures by proximity to a superconductor could foster the discovery of
topological superconductivity in graphene. On-surface synthesis of such NGs has
been achieved on noble metals or metal oxides, however, it is still absent on
superconductors. Here, we present a synthetic method to induce
superconductivity to polymeric chains and NGs adsorbed on the superconducting
Nb(110) substrate covered by thin Ag films. Using atomic force microscopy at
low-temperature, we characterize the chemical structure of each sub-product
formed on the superconducting Ag layer. Scanning tunneling spectroscopy further
allows us to elucidate electronic properties of these nanostructures, which
consistently show a superconducting gap. We foresee our approach to become a
promising platform for exploring the interplay between carbon magnetism and
superconductivity at the fundamental level.",2202.00460v1
2022-02-09,An electrically-driven single-atom `flip-flop' qubit,"The spins of atoms and atom-like systems are among the most coherent objects
in which to store quantum information. However, the need to address them using
oscillating magnetic fields hinders their integration with quantum electronic
devices. Here we circumvent this hurdle by operating a single-atom `flip-flop'
qubit in silicon, where quantum information is encoded in the electron-nuclear
states of a phosphorus donor. The qubit is controlled using local electric
fields at microwave frequencies, produced within a metal-oxide-semiconductor
device. The electrical drive is mediated by the modulation of the
electron-nuclear hyperfine coupling, a method that can be extended to many
other atomic and molecular systems. These results pave the way to the
construction of solid-state quantum processors where dense arrays of atoms can
be controlled using only local electric fields.",2202.04438v3
2022-03-15,Formation of CuO$_2$ sublattices by suppression of interlattice correlations in tetragonal CuO,"We investigate the tetragonal phase of the binary transition metal oxide CuO
(t-CuO) within the context of cellular dynamical mean-field theory. Due to its
strong antiferromagnetic correlations and simple structure, analysing the
physics of t-CuO is of high interest as it may pave the way towards a more
complete understanding of high temperature superconductivity in hole-doped
antiferromagnets. In this work we give a formal justification for the weak
coupling assumption that has previously been made for the interconnected
sublattices within a single layer of t-CuO by studying the non-local
self-energies of the system. We compute momentum-resolved spectral functions
using a Matrix Product State (MPS)-based impurity solver directly on the real
axis, which does not require any numerically ill-conditioned analytic
continuation. The agreement with photoemission spectroscopy indicates that a
single band Hubbard model is sufficient to capture the material's low energy
physics. We perform calculations on a range of different temperatures, finding
two magnetic regimes, for which we identify the driving mechanism behind their
respective insulating state. Finally, we show that in the hole-doped regime the
sublattice structure of t-CuO has interesting consequences on the symmetry of
the superconducting state.",2203.07880v2
2022-03-29,Accurate electronic properties and intercalation voltages of olivine-type Li-ion cathode materials from extended Hubbard functionals,"The design of novel cathode materials for Li-ion batteries would greatly
benefit from accurate first-principles predictions of structural, electronic,
and magnetic properties as well as intercalation voltages in compounds
containing transition-metal elements. For such systems, density-functional
theory (DFT) with standard (semi-)local exchange-correlation functionals is of
limited use as it often fails due to strong self-interaction errors that are
especially relevant in the partially filled $d$ shells. Here, we perform a
detailed comparative study of the phospho-olivine cathode materials
Li$_x$MnPO$_4$, Li$_x$FePO$_4$, and the mixed transition metal
Li$_x$Mn$_{1/2}$Fe$_{1/2}$PO$_4$ ($x=0, 1/4, 1/2, 3/4, 1$) using four
electronic-structure methods: DFT, DFT+$U$, DFT+$U$+$V$, and HSE06. We show
that DFT+$U$+$V$, with onsite $U$ and intersite $V$ Hubbard parameters
determined from first principles and self-consistently with respect to the
structural parameters by means of density-functional perturbation theory
(linear response), provides the most accurate description of the electronic
structure of these challenging compounds. In particular, we demonstrate that
DFT+$U$+$V$ displays very clearly ""digital"" changes in oxidation states of the
transition-metal ions in all compounds, including the mixed-valence phases
occurring at intermediate Li concentrations, leading to voltages in remarkable
agreement with experiments. We show that the inclusion of intersite Hubbard
interactions is essential for the accurate prediction of thermodynamic
quantities, balancing the drive for localization induced by the onsite $U$ with
intersite $V$ orbital hybridizations.",2203.15732v2
2022-04-29,Anomalous Josephson Coupling and High-Harmonics in Non-Centrosymmetric Superconductors with $S$-wave Spin-Triplet Pairing,"We study the Josephson effects arising in junctions made of
non-centrosymmetric superconductors with spin-triplet pairing having $s$-wave
orbital-singlet symmetry. We demonstrate that the orbital dependent character
of the spin-triplet order parameter determines its non-trivial texture in the
momentum space due to the inversion symmetry breaking and spin-orbit
interactions. The emergence of this pattern is responsible for the occurrence
of an anomalous Josephson coupling and a dominance of high-harmonics in the
current phase relation. Remarkably, due to the spin-orbital couplings,
variations in the electronic structure across the heterostructure can generally
turn the ground state of the junction from 0- to a generic value of the
Josephson phase, thus realizing the so-called $\varphi$-junction. Hallmarks of
the resulting Josephson behavior, apart from non-standard current-phase
relation, are provided by an unconventional temperature and magnetic field
dependence of the critical current. These findings indicate the path for the
design of superconducting orbitronics devices and account for several observed
anomalies of the supercurrent in oxide interface superconductors.",2204.14083v2
2022-05-06,Anisotropic carrier dynamics in a laser-excited Fe$_{1}$/(MgO)$_{3}$(001) heterostructure from real-time time-dependent DFT,"The interaction of a femtosecond optical pulse with a
Fe$_{1}$/(MgO)$_{3}$(001) metal/oxide heterostructure is investigated using
time-dependent density functional theory (TDDFT) calculations in the real-time
domain. We systematically study electronic excitations as a function of laser
frequency, peak power density and polarization direction. While spin-orbit
coupling is found to result in only a small time-dependent reduction of
magnetization (less than 10%), we find a marked anisotropy in the response to
in-plane and out-of-plane polarized light, which changes its character
qualitatively depending on the excitation energy: the Fe-layer is efficiently
addressed at low frequencies by in-plane polarized light, whereas for
frequencies higher than the MgO band gap, we find a particularly strong
response of the central MgO-layer for cross-plane polarized light. For laser
excitations between the charge transfer gap and the MgO band gap, the interface
plays the most important role, as it mediates concerted transitions from the
valence band of MgO into the $3d$ states of Fe closely above the Fermi level
and from the Fe-states below the Fermi level into the conduction band of MgO.
As these transitions can occur simultaneously altering charge balance of the
layers, they could potentially lead to an efficient transfer of excited
carriers into the MgO bulk, where the corresponding electron and hole states
can be separated by an energy which is significantly larger than the photon
energy.",2205.03178v1
2022-08-14,Chern insulators and high Curie temperature Dirac half-metal in two-dimensional metal-organic frameworks,"Two-dimensional (2D) magnetic materials with nontrivial topological states
have drawn considerable attention recently. Among them, 2D metal-organic
frameworks (MOFs) are standing out due to their advantages, such as the easy
synthesis in practice and less sensitivity to oxidation that are distinctly
different from inorganic materials. By means of density-functional theory
calculations, we systematically investigate the electronic and topological
properties of a class of 2D MOFs X(C21H15N3) (X = transition metal element from
3d to 5d). Excitingly, we find that X(C21H15N3) (X = Ti, Zr, Ag, Au) are Chern
insulators with sizable band gaps (~7.1 meV). By studying a four-band effective
model, it is revealed that the Chern insulator phase in X(C21H15N3) (X = Ti,
Zr, Ag, Au) is caused cooperatively by the band inversion of the p orbitals of
the C21H15N3 molecule and the intrinsic ferromagnetism of X(C21H15N3).
Additionally, Mn(C21H15N3) is a Dirac half-metal ferromagnet with a high Curie
temperature up to 156 K. Our work demonstrates that 2D MOFs X(C21H15N3) are
good platforms for realizing Quantum anomalous Hall effect and designing novel
spintronic devices based on half-metals with high-speed and long-distance spin
transport.",2208.06891v2
2022-09-01,Reflective Dielectric Cavity Enhanced Emission from Hexagonal Boron Nitride Spin Defect Arrays,"Among the various kinds of spin defects in hBN, the negatively charged boron
vacancy ($\rm V_B^-$) spin defect that can be deterministically generated is
undoubtedly a potential candidate for quantum sensing, but its low quantum
efficiency restricts its %use in practical applications. Here, we demonstrate a
robust enhancement structure with advantages including easy on-chip
integration, convenient processing, low cost and suitable broad-spectrum
enhancement for $\rm V_B^-$ defects. %Improved photoluminescence (PL) intensity
and optically detected magnetic resonance (ODMR) contrast of $\rm V_B^-$ defect
arrays. In the experiment, we used a metal reflective layer under the hBN
flakes, filled with a transition dielectric layer in the middle, and adjusted
the thickness of the dielectric layer to achieve the best coupling between the
reflective dielectric cavity and the hBN spin defect. Using a reflective
dielectric cavity, we achieved a PL enhancement of approximately 7-fold, and
the corresponding ODMR contrast achieved 18\%. Additionally, the oxide layer of
the reflective dielectric cavity can be used as an integrated material for
micro-nano photonic devices for secondary processing, which means that it can
be combined with other enhancement structures to achieve stronger enhancement.
This work has guiding significance for realizing the on-chip integration of
spin defects in two-dimensional materials.",2209.00256v1
2022-09-07,Ab initio Quantum Simulation of Strongly Correlated Materials with Quantum Embedding,"Quantum computing has shown great potential in various quantum chemical
applications such as drug discovery, material design, and catalyst
optimization. Although significant progress has been made in quantum simulation
of simple molecules, ab initio simulation of solid-state materials on quantum
computers is still in its early stage, mostly owing to the fact that the system
size quickly becomes prohibitively large when approaching the thermodynamic
limit. In this work, we introduce an orbital-based multi-fragment approach on
top of the periodic density matrix embedding theory, resulting in a
significantly smaller problem size for the current near-term quantum computer.
We demonstrate the accuracy and efficiency of our method compared with the
conventional methodologies and experiments on solid-state systems with complex
electronic structures. These include spin polarized states of a hydrogen chain
(1D-H), the equation of states of a boron nitride layer (h-BN) as well as the
magnetic ordering in nickel oxide (NiO), a prototypical strongly correlated
solid. Our results suggest that quantum embedding combined with a chemically
intuitive fragmentation can greatly advance quantum simulation of realistic
materials, thereby paving the way for solving important yet classically hard
industrial problems on near-term quantum devices.",2209.03202v2
2023-01-11,Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3,"NiPSe3 is regarded as a bandwidth-controlled Mott insulator, distinct from
the widely studied Mott insulating magnetic graphene MPSe3 (M = Mn and Fe)
family. By employing high-pressure synchrotron X-ray diffraction, we observe
two structural transitions as a function of pressure. With the help of
first-principles calculations, we discover the antiferromagnetic (AFM) moment
directions of NiPSe3 switch from out-of-plane to in-plane and the honeycomb
layers slide relative to each other at the first structural transition. The
in-plane AFM order persists until the second structural transition, whereupon
the two-dimensional (2D) structure assumes a more three-dimensional (3D)
character. A bandwidth-controlled Mott insulator-metal transition (IMT) occurs
between the two structural transitions at 8.0 GPa, concomitant with the
emergence of superconductivity with 4.8 K. The superconductivity in NiPSe3
emerging in the 2D monoclinic phase coexists with the in-plane AFM order and
continues into the 3D trigonal phase. Our electronic structure calculations
reveal that the Mott IMT and superconductivity in NiPSe3 are both closely
related to the enhanced Se2- 4p and Ni2+ 3d electronic hybridizations under
pressure. From these results, we construct the temperature-pressure electronic
phase diagram of NiPSe3, revealing rich physics and many similarities with
copper oxide and iron-based superconductors.",2301.04329v1
2023-01-12,The Role of Electrolytes in the Relaxation of Near-Surface Spin Defects in Diamond,"Quantum sensing with spin defects in diamond, such as the nitrogen-vacancy
(NV) center, enables the detection of various chemical species on the
nanoscale. Molecules or ions with unpaired electronic spins are typically
probed by their influence on the NV center's spin relaxation. Whereas it is
well-known that paramagnetic ions reduce the NV center's relaxation time
($T_1$), here we report on the opposite effect for diamagnetic ions. We
demonstrate that millimolar concentrations of aqueous diamagnetic electrolyte
solutions increase the $T_1$ time of near-surface NV center ensembles compared
to pure water. To elucidate the underlying mechanism of this surprising effect,
single and double quantum NV experiments are performed, which indicate a
reduction of magnetic and electric noise in the presence of diamagnetic
electrolytes. In combination with ab initio simulations, we propose that a
change in the interfacial band bending due to the formation of an electric
double layer leads to a stabilization of fluctuating charges at the interface
of an oxidized diamond. This work not only helps to understand noise sources in
quantum systems but could also broaden the application space of quantum sensors
towards electrolyte sensing in cell biology, neuroscience and electrochemistry.",2301.04952v2
2023-02-28,Quantum criticality of bandwidth-controlled Mott transition,"Metallic states near the Mott insulator show a variety of quantum phases
including various magnetic, charge ordered states and high-temperature
superconductivity in various transition metal oxides and organic solids. The
emergence of a variety of phases and their competitions are likely intimately
associated with quantum transitions between the electron-correlation driven
Mott insulator and metals characterized by its criticality, and is related to
many central questions of condensed matter. The quantum criticality is,
however, not well understood when the transition is controlled by the bandwidth
through physical parameters such as pressure. Here, we quantitatively estimate
the universality class of the transition characterized by a comprehensive set
of critical exponents by using a variational Monte Carlo method implemented as
an open-source innovated quantum many-body solver, with the help of established
scaling laws at a typical bandwidth-controlled Mott transition. The criticality
indicates a weaker charge and density instability in contrast to the
filling-controlled transition realized by carrier doping, implying a weaker
instability to superconductivity as well. The present comprehensive
clarification opens up a number of routes for quantitative experimental studies
for complete understanding of elusive quantum Mott transition and nearby
strange metal that cultivate future design of functionality.",2302.14605v2
2023-03-01,Influence of Structural Defects on Charge Density Waves in 1T-TaS2,"The influence of intrinsic defects of 1T-TaS2 on charge density waves (CDW)
is studied using scanning tunneling microscopy and spectroscopy (STM, STS),
angle-resolved photoelectron spectroscopy (ARPES), and density functional
theory (DFT). We identify several types of structural defects and find that
most have a local character limited to the single CDW site, with single
exception which effectively behaves as a dopant, leading to band bending and
affecting multiple neighboring sites. While only one type of defect can be
observed by STM topographic imaging, all defects are easily resolved by local
density of states (LDOS) mapping with STS. We correlate atomically-resolved STM
periodicity of defect-free 1T-TaS2 to top sulfur atoms and introduce tiling of
the surface using equiangular hexagon. DFT calculations (with included Coulomb
interactions) are used to investigate the electronic structure by introducing
sulfur vacancy or substituting sulfur with oxygen. The sulfur vacancy is
characterized by metallic properties and is identified as an origin of one of
observed experimentally defects. Whereas in the case of the latter, the
oxidation of 1T-TaS2 is found to result in the loss of magnetic properties
expected in defect-free material.",2303.00256v1
2023-04-05,Observation of charge-to-spin conversion with giant efficiency at Ni$_{0.8}$Fe$_{0.2}$/Bi$_{2}$WO$_{6}$ interface,"Magnetization switching using spin-orbit torque offers a promising route to
developing non-volatile memory technologies. The prerequisite, however, is the
charge-to-spin current conversion, which has been achieved traditionally by
harnessing the spin-orbit interaction in heavy metals, topological insulators,
and heterointerfaces hosting a high-mobility two-dimensional electron gas.
Here, we report the observation of charge-to-spin current conversion at the
interface between ferromagnetic Ni$_{0.8}$Fe$_{0.2}$ and ferroelectric
Bi$_{2}$WO$_{6}$ thin films. The resulting spin-orbit torque consists of
damping-like and field-like components, and the estimated efficiency amounts to
about 0.48 $\pm$ 0.02, which translates to 0.96 $\pm$ 0.04 nm$^{-1}$ in terms
of interfacial efficiency. These numbers are comparable to contemporary
spintronic materials exhibiting giant spin-orbit torque efficiency. We suggest
that the Rashba Edelstein effect underpins the charge-to-spin current
conversion on the interface side of Ni$_{0.8}$Fe$_{0.2}$. Further, we provide
an intuitive explanation for the giant efficiency in terms of the spin-orbit
proximity effect, which is enabled by orbital hybridization between W and Ni
(Fe) atoms across the interface. Our work highlights that Aurivillius compounds
are a potential addition to the emerging transition metal oxide-based
spin-orbit materials.",2304.02751v1
2023-04-12,CMOS + stochastic nanomagnets: heterogeneous computers for probabilistic inference and learning,"Extending Moore's law by augmenting complementary-metal-oxide semiconductor
(CMOS) transistors with emerging nanotechnologies (X) has become increasingly
important. One important class of problems involve sampling-based Monte Carlo
algorithms used in probabilistic machine learning, optimization, and quantum
simulation. Here, we combine stochastic magnetic tunnel junction (sMTJ)-based
probabilistic bits (p-bits) with Field Programmable Gate Arrays (FPGA) to
create an energy-efficient CMOS + X (X = sMTJ) prototype. This setup shows how
asynchronously driven CMOS circuits controlled by sMTJs can perform
probabilistic inference and learning by leveraging the algorithmic
update-order-invariance of Gibbs sampling. We show how the stochasticity of
sMTJs can augment low-quality random number generators (RNG). Detailed
transistor-level comparisons reveal that sMTJ-based p-bits can replace up to
10,000 CMOS transistors while dissipating two orders of magnitude less energy.
Integrated versions of our approach can advance probabilistic computing
involving deep Boltzmann machines and other energy-based learning algorithms
with extremely high throughput and energy efficiency.",2304.05949v3
2023-05-07,Evaluation of P3-type layered oxides as K-ion battery cathodes,"Given increasing energy storage demands and limited natural resources of Li,
K-ion batteries (KIBs) could be promising next-generation systems having
natural abundance, similar chemistry and energy density. Here, we have
investigated the P3-type K$_{0.5}$TMO$_2$ (where TM = Ti, V, Cr, Mn, Co, or Ni)
systems using density functional theory calculations, as potential positive
intercalation electrodes (or cathodes) for KIBs. Specifically, we have
identified the ground state configurations, and calculated the average
topotactic voltages, electronic structures, on-site magnetic moments, and
thermodynamic stabilities of all P3-K$_{0.5}$TMO$_2$ compositions and their
corresponding depotassiated P3-TMO$_2$ frameworks. We find that K adopts the
honeycomb or zig-zag configuration within each K-layer of all P3 structures
considered, irrespective of the TM. In terms of voltages, we find the Co- and
Ti-based compositions to exhibit the highest (4.59 V vs. K) and lowest (2.24 V)
voltages, respectively, with the TM contributing to the redox behavior upon K
(de-)intercalation. We observe all P3-K$_{0.5}$TMO$_2$ to be (meta)stable, and
hence experimentally synthesizeable according to our 0 K convex hull
calculations, while all depotassiated P3-TMO$_2$ configurations are unstable
and may appear during electrochemical cycling. Also, we verified the stability
of the prismatic coordination environment of K compared to octahedral
coordination at the K$_{0.5}$TMO$_2$ compositions using Rouxel and cationic
potential models. Finally, combining our voltage and stability calculations, we
find P3-K$_x$CoO$_2$ to be the most promising cathode composition, while
P3-K$_x$NiO$_2$ is worth exploring. Our work should contribute to the
exploration of strategies and materials required to make practical KIBs.",2305.04299v1
2023-05-12,Microscopic Examination of SRF-quality Nb Films through Local Nonlinear Microwave Response,"The performance of superconducting radio-frequency (SRF) cavities is
sometimes limited by local defects. To investigate the RF properties of these
local defects, a near-field magnetic microwave microscope is employed. Local
third harmonic response (P3f) and its temperature-dependence and RF
power-dependence are measured for one Nb/Cu film grown by Direct Current
Magnetron Sputtering (DCMS) and six Nb/Cu films grown by High Power Impulse
Magnetron Sputtering (HiPIMS) with systematic variation of deposition
conditions. Five out of the six HiPIMS Nb/Cu films show a strong third harmonic
response that is likely coming from a low-Tc surface defect with a transition
temperature between 6.3 K and 6.8 K, suggesting that this defect is a generic
feature of air-exposed HiPIMS Nb/Cu films. One possible origin of such a defect
is grain boundaries hosting a low-Tc impurity such as oxidized Nb.
Time-Dependent Ginzburg-Landau (TDGL) simulations are performed to better
understand the measured third harmonic response. The simulation results show
that the third harmonic response of RF vortex nucleation caused by surface
defects can qualitatively explain the experimental data. Moreover, the density
of surface defects that nucleate RF vortices, and how deep an RF vortex travels
through these surface defects, can be extracted qualitatively from third
harmonic response measurements. From the point of view of these two properties,
the best Nb/Cu film for SRF applications can be identified.",2305.07746v1
2023-05-19,Measurements of the amplitude-dependent microwave surface resistance of an Au/Nb bilayer,"Surface properties are critical to the capabilities of superconducting
microwave devices. The native oxide of niobium-based devices is thought to
consist of a thin normal conducting layer. To improve understanding on the
importance of this layer, an attempt was made to replace it with a more easily
controlled gold film. A niobium sample host microwave cavity was used to
measure the surface resistance in continuous wave operation at 4.0 GHz and 5.2
GHz. Sample conditions studied include temperatures ranging from 1.6 K to 4.2 K
with RF magnetic fields on the sample surface ranging from 1 mT to the maximum
field before the superconducting properties were lost (quench field). The
nominal film thickness of the gold layer was increased from 0.1 nm to 2.0 nm in
five steps to study the impact of the normal layer thickness on surface
resistance on a single niobium substrate. The 0.1 nm film was found to reduce
the surface resistance of the sample and to enhance the quench field. With the
exception of the final step from a 1.5 nm gold film to 2.0 nm, the magnitude of
the surface resistance increased substantially with gold film thickness. The
nature of the surface resistance field-dependence appeared to be roughly
independent from the gold layer thickness. This initial study provides new
perspectives and suggests avenues for optimizing and designing surfaces for
resonant cavities in particle accelerators and quantum information
applications.",2305.12035v2
2023-06-19,Formation of spin-orbital entangled 2D electron gas in layer delta-doped bilayer iridate La$_δ$Sr$_3$Ir$_2$O$_7$,"5$d$ transition metal oxides host a variety of exotic phases due to the
comparable strength of Coulomb repulsion and spin-orbit coupling. Herein, by
pursuing density-functional studies on a delta-doped quasi-two-dimensional
iridate Sr$_3$Ir$_2$O$_7$, where a single SrO layer is replaced by LaO layer,
we predict the formation of a spin-orbital entangled two-dimensional electron
gas (2DEG) which is sharply confined on two IrO$_2$ layers close to the LaO
layer. In this bilayer crystal structure, an existing potential well is further
augmented with the inclusion of positively charged LaO layer which results in
confining the extra valence electron made available by the La$^{3+}$ ion. The
confined electron is bound along crystal $a$ direction and is highly mobile in
the $bc$ plane. From the band structure point of view, now the existing
half-filled $J_{eff}$ = 1/2 states are further electron doped to destroy the
antiferromagnetic Mott insulating state of IrO$_2$ layers near to the
delta-doped layer. This leads to partially occupied Ir upper-Hubbard subbands
which host the spin-orbital entangled 2DEG. The IrO$_2$ layers far away from
the interface remain insulating and preserve the collinear G-type magnetic
ordering of pristine Sr$_3$Ir$_2$O$_7$. The conductivity tensors calculated
using semi-classical Boltzmann theory at room temperature reveal that the 2DEG
exhibits large electrical conductivity of the order of 10$^{19}$.",2306.10978v2
2023-06-20,Optimizing the Ullmann coupling reaction efficiency on an oxide surface by metal atom addition,"The bottom-up synthesis of carbon based nanomaterials directly on
semiconductor surfaces allows to decouple their electronic and magnetic
properties from the substrates. However, the lack of reactivity on these
non-metallic surfaces hinders or reduces significantly the yield of these
reactions. Such hurdles practically precludes transferring bottom-up synthesis
strategies onto semiconducting and insulating surfaces. Here, we achieve a high
polymerization yield of terphenyl molecules on the semiconductor TiO$_2$(110)
surface by incorporating cobalt atoms as catalysts in the Ullmann coupling
reaction. Cobalt atoms trigger the debromination of 4,4-dibromo-p-terphenyl
(DBTP) molecules on TiO$_2$(110) and the formation of an intermediate
organometallic phase already at room-temperature (RT). As the debromination
temperature is drastically reduced, the homo-coupling temperature is also
significantly lowered, preventing the desorption of DBTP molecules from the
TiO$_2$(110) surface and leading to a radical improvement on the
poly-para-phenylene (PPP) polymerization yield. The universality of this
mechanism is demonstrated with an iodinated terphenyl derivative (DITP), which
shows analogous dehalogenation and polymerization temperatures with a very
similar reaction yield. Consequently, we propose to use minute amounts of metal
catalyst to drive forward generic bottom-up synthesis strategies on
non-metallic surfaces.",2306.11388v1
2023-06-27,Spin-orbital Jahn-Teller bipolarons,"Polarons and spin-orbit (SO) coupling are distinct quantum effects that play
a critical role in charge transport and spin-orbitronics. Polarons originate
from strong electron-phonon interaction and are ubiquitous in polarizable
materials featuring electron localization, in particular $\mathrm{3d}$
transition metal oxides (TMOs). On the other hand, the relativistic coupling
between the spin and orbital angular momentum is notable in lattices with heavy
atoms and develops in $\mathrm{5d}$ TMOs, where electrons are spatially
delocalized. Here we combine ab initio calculations and magnetic measurements
to show that these two seemingly mutually exclusive interactions are entangled
in the electron-doped SO-coupled Mott insulator
$\mathrm{Ba_2Na_{1-x}Ca_xOsO_6}$ ($0< x < 1$), unveiling the formation of
spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller
lattice activity, converts the Os $\mathrm{5d^1}$ spin-orbital
$\mathrm{J_{eff}=3/2}$ levels, characteristic of the parent compound
$\mathrm{Ba_2NaOsO_6}$ (BNOO), into a bipolaron $\mathrm{5d^2}$
$\mathrm{J_{eff}=2}$ manifold, leading to the coexistence of different
J-effective states in a single-phase material. The gradual increase of
bipolarons with increasing doping creates robust in-gap states that prevents
the transition to a metal phase even at ultrahigh doping, thus preserving the
Mott gap across the entire doping range from $\mathrm{d^1}$ BNOO to
$\mathrm{d^2}$ $\mathrm{Ba_2CaOsO_6}$ (BCOO).",2306.15757v1
2023-09-27,Interfacial and thickness effects in La$_{2/3}$Sr$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7}$ superlattices,"Superlattices of correlated oxides have been used to explore interfacial
effects and to achieve additional control over the physical properties of
individual constituents. In this work, we present a first-principles
perspective of the strain and thickness effects in
La$_{2/3}$Sr$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7}$ (LSMO/YBCO) superlattices. Our
findings indicate that the presence of epitaxial strain and LSMO leads to a
reduction of buckling parameters of the interfacial CuO$_2$ planes, as well as
the transfer of electrons from LSMO to YBCO. In addition, the change in Cu-3$d$
valence is slightly dependent on the LSMO layer thickness. More interestingly,
the in-plane ferromagnetic ground state within the CuO$_2$ planes near the
interface is induced due to the local moments centered at the copper atoms.
These local moments are decoupled from the charge transfer and, according to
our calculations, appear mainly due to the Mn $3d$-O $2p$-Cu $3d$ hybridization
being restricted to the interfacial region. The induced net magnetic ordering
in interfacial copper atoms may have implications in the control of the
superconducting state in the LSMO/YBCO superlattices.",2309.16013v2
2024-01-16,"Mass inversion at the Lifshitz transition in monolayer graphene by diffusive, high-density, on-chip, doping","Experimental setups for charge transport measurements are typically not
compatible with the ultra-high vacuum conditions for chemical doping, limiting
the charge carrier density that can be investigated by transport methods.
Field-effect methods, including dielectric gating and ionic liquid gating,
achieve too low a carrier density to induce electronic phase transitions. To
bridge this gap, we developed an integrated flip-chip method to dope graphene
by alkali vapour in the diffusive regime, suitable for charge transport
measurements at ultra-high charge carrier density. We introduce a cesium
droplet into a sealed cavity filled with inert gas to dope a monolayer graphene
sample by the process of cesium atom diffusion, adsorption and ionization at
the graphene surface, with doping beyond an electron density of
$4.7\times10^{14}~\mathrm{cm}^{-2}$ monitored by operando Hall measurement. The
sealed assembly is stable against oxidation, enabling measurement of charge
transport versus temperature and magnetic field. Cyclotron mass inversion is
observed via the Hall effect, indicative of the change of Fermi surface
geometry associated with the Liftshitz transition at the hyperbolic $M$ point
of monolayer graphene. The transparent quartz substrate also functions as an
optical window, enabling non-resonant Raman scattering. Our findings show that
chemical doping, hitherto restricted to ultra-high vacuum, can be applied in a
diffusive regime at ambient pressure in an inert gas environment and thus
enable charge transport studies in standard cryogenic environments",2401.08051v1
2024-02-07,Gaussian-process-regression-based method for the localization of exceptional points in complex resonance spectra,"Resonances in open quantum systems depending on at least two controllable
parameters can show the phenomenon of exceptional points (EPs), where not only
the eigenvalues but also the eigenvectors of two or more resonances coalesce.
Their exact localization in the parameter space is challenging, in particular
in systems, where the computation of the quantum spectra and resonances is
numerically very expensive. We introduce an efficient machine learning
algorithm to find exceptional points based on Gaussian process regression
(GPR). The GPR-model is trained with an initial set of eigenvalue pairs
belonging to an EP and used for a first estimation of the EP position via a
numerically cheap root search. The estimate is then improved iteratively by
adding selected exact eigenvalue pairs as training points to the GPR-model. The
GPR-based method is developed and tested on a simple low-dimensional matrix
model and then applied to a challenging real physical system, viz., the
localization of EPs in the resonance spectra of excitons in cuprous oxide in
external electric and magnetic fields. The precise computation of EPs, by
taking into account the complete valence band structure and central-cell
corrections of the crystal, can be the basis for the experimental observation
of EPs in this system.",2402.05972v1
2024-02-20,Antiferromagnetic Chern insulator with large charge gap in heavy transition-metal compounds,"Despite the discovery of multiple intrinsic magnetic topological insulators
in recent years the observation of Chern insulators is still restricted to very
low temperatures due to the negligible charge gaps. Here, we uncover the
potential of heavy transition-metal compounds for realizing a collinear
antiferromagnetic Chern insulator (AFCI) with a charge gap as large as 300 meV.
Our analysis relies on the Kane-Mele-Kondo model with a ferromagnetic Hund
coupling $J_{\rm H}$ between the spins of itinerant electrons and the localized
spins of size $S$. We show that a spin-orbit coupling $\lambda_{\rm SO} \gtrsim
0.03t$, where $t$ is the nearest-neighbor hopping element, is already large
enough to stabilize an AFCI provided the alternating sublattice potential
$\delta$ is in the range $\delta \approx SJ_{\rm H}$. We establish a remarkable
increase in the charge gap upon increasing $\lambda_{\rm SO}$ in the AFCI
phase. Using our results we explain the collinear AFCI recently found in
monolayers of CrO and MoO with charge gaps of 1 and $50$ meV, respectively. In
addition, we propose bilayers of heavy transition-metal oxides of perovskite
structure as candidates to realize a room-temperature AFCI if grown along the
$[111]$ direction and subjected to a perpendicular electric field.",2402.12918v1
2024-02-28,Embracing Disorder in Quantum Materials Design,"Many of the most exciting materials discoveries in fundamental condensed
matter physics are made in systems hosting some degree of intrinsic disorder.
While disorder has historically been regarded as something to be avoided in
materials design, it is often of central importance to correlated and quantum
materials. This is largely driven by the conceptual and theoretical ease to
handle, predict, and understand highly uniform systems that exhibit complex
interactions, symmetries and band structures. In this perspective, we highlight
how flipping this paradigm has enabled exciting possibilities in the emerging
field of high entropy oxide (HEO) quantum materials. These materials host high
levels of cation or anion compositional disorder while maintaining unexpectedly
uniform single crystal lattices. The diversity of atomic scale interactions of
spin, charge, orbital, and lattice degrees of freedom are found to emerge into
coherent properties on much larger length scales. Thus, altering the variance
and magnitudes of the atomic scale properties through elemental selection can
open new routes to tune global correlated phases such as magnetism,
metal-insulator transitions, ferroelectricity, and even emergent topological
responses. The strategy of embracing disorder in this way provides a much
broader pallet from which functional states can be designed for next-generation
microelectronic and quantum information systems.",2402.18379v1
2024-03-05,Microelectronic readout of a diamond quantum sensor,"Quantum sensors based on the nitrogen-vacancy (NV) centre in diamond are
rapidly advancing from scientific exploration towards the first generation of
commercial applications. While significant progress has been made in developing
suitable methods for the manipulation of the NV centre spin state, the
detection of the defect luminescence has so far limited the performance of
miniaturized sensor architectures. The recent development of photoelectric
detection of the NV centre's spin state offers a path to circumvent these
limitations, but has to-date required research-grade low current amplifiers to
detect the picoampere-scale currents obtained from these systems. Here we
report on the photoelectric detection of magnetic resonance (PDMR) with NV
ensembles using a complementary metal-oxide semiconductor (CMOS) device. The
integrated circuit delivers a digitized output of the diamond sensor with low
noise and 50 femtoampere resolution. This integration provides the last missing
component on the path to a compact, diamond-based quantum sensor. The device is
suited for continuous wave (CW) as well as pulsed operation. We demonstrate its
functionality with DC and AC magnetometry up to several megahertz, coherent
spin rotation and multi-axial decoupling sequences for quantum sensing.",2403.03090v2
2003-05-14,"Insights into the function of silver as an oxidation catalyst by ab initio, atomistic thermodynamics","To help understand the high activity of silver as an oxidation catalyst,
e.g., for the oxidation of ethylene to epoxide and the dehydrogenation of
methanol to formaldehyde, the interaction and stability of oxygen species at
the Ag(111) surface has been studied for a wide range of coverages. Through
calculation of the free energy, as obtained from density-functional theory and
taking into account the temperature and pressure via the oxygen chemical
potential, we obtain the phase diagram of O/Ag(111). Our results reveal that a
thin surface-oxide structure is most stable for the temperature and pressure
range of ethylene epoxidation and we propose it (and possibly other similar
structures) contains the species actuating the catalysis. For higher
temperatures, low coverages of chemisorbed oxygen are most stable, which could
also play a role in oxidation reactions. For temperatures greater than about
775 K there are no stable oxygen species, except for the possibility of O atoms
adsorbed at under-coordinated surface sites Our calculations rule out thicker
oxide-like structures, as well as bulk dissolved oxygen and molecular
ozone-like species, as playing a role in the oxidation reactions.",0305312v1
2004-02-05,The interface between silicon and a high-k oxide,"The ability to follow Moore's Law has been the basis of the tremendous
success of the semiconductor industry in the past decades. To date, the
greatest challenge for device scaling is the required replacement of silicon
dioxide-based gate oxides by high-k oxides in transistors. Around 2010 high-k
oxides are required to have an atomically defined interface with silicon
without any interfacial SiO2 layer. The first clean interface between silicon
and a high-K oxide has been demonstrated by McKee et al. Nevertheless, the
interfacial structure is still under debate. Here we report on first-principles
calculations of the formation of the interface between silicon and SrTiO3 and
its atomic structure. Based on insights into how the chemical environment
affects the interface, a way to engineer seemingly intangible electrical
properties to meet technological requirements is outlined. The interface
structure and its chemistry provide guidance for the selection process of other
high-k gate oxides and for controlling their growth. Our study also shows that
atomic control of the interfacial structure can dramatically improve the
electronic properties of the interface. The interface presented here serves as
a model for a variety of other interfaces between high-k oxides and silicon.",0402173v1
2010-03-24,Renormalized ionic polarizability functional applied to evaluate the molecule-oxide interactions for gas-sensing applications,"Metal-oxide sensors are widely used due to their sensitivities to different
types of gaseous, and these sensors are suitable for long-term applications,
even in the presence of corrosive environments. However, the microscopic
mechanisms with quantum effects, which are required to understand the gas-oxide
interactions are not well developed despite the oxide sensors potential
applications in numerous fields, namely, medicine (breath-sensors), engineering
(gas-sensors) and food processing (odor-sensors). Here, we develop a rigorous
theoretical strategy based on the ionization energy theory (IET) to
unambiguously explain why and how a certain gas molecule intrinsically prefers
a particular oxide surface. We make use of the renormalized ionic displacement
polarizability functional derived from the IET to show that the gas/surface
interaction strength (sensing sensitivity) between an oxide surface and an
isolated gas molecule can be predicted from the polarizability of these two
systems. Such predictions are extremely important for the development of health
monitoring bio-sensors, as well as to select the most suitable oxide to detect
a particular gas with optimum sensitivity.",1003.4625v4
2010-06-22,Three-terminal field effect devices utilizing thin film vanadium oxide as the channel layer,"Electrostatic control of the metal-insulator transition (MIT) in an oxide
semiconductor could potentially impact the emerging field of oxide electronics.
Vanadium dioxide is of particular interest due to the fact that the MIT happens
in the vicinity of room temperature and it is considered to exhibit the Mott
transition. We present a detailed account of our experimental investigation
into three-terminal field effect transistor-like devices using thin film VO2 as
the channel layer. The gate is separated from the channel through an insulating
gate oxide layer, enabling true probing of the field effect with minimal or no
interference from large leakage currents flowing directly from the electrode.
The influence of the fabrication of multiple components of the device,
including the gate oxide deposition, on the VO2 film characteristics is
discussed. Further, we discuss the effect of the gate voltage on the device
response, point out some of the unusual characteristics including temporal
dependence. A reversible unipolar modulation of the channel resistance upon the
gate voltage is demonstrated for the first time in optimally engineered
devices. The results presented in this work are of relevance towards
interpreting gate voltage response in such oxides as well as addressing
challenges in advancing gate stack processing for oxide semiconductors.",1006.4373v1
2010-09-14,Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7x7) surfaces: Influence of short range order on the substrate,"Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been
investigated by reflection high energy electron diffraction (RHEED) and
scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images
show the presence of short range (7x7) order on the air-oxidized surface.
Comparison with FTs of STM images from a clean Si(111)-(7x7) surface shows that
only the 1/7th order spots are present on the air-oxidized surface. The oxide
layer is ~ 2-3 nm thick, as revealed by cross-sectional transmission electron
microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(111)-(7x7)
surfaces has been investigated by in-situ RHEED and STM and ex-situ XTEM and
scanning electron microscopy. Ag deposition at room temperature leads to the
growth of randomly oriented Ag islands while preferred orientation evolves when
Ag is deposited at higher substrate temperatures. For deposition at 550{\deg}C
face centered cubic Ag nanoislands grow with a predominant epitaxial
orientation [1 -1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si along with its twin
[-1 1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si, as observed for epitaxial growth
of Ag on Si(111) surfaces. The twins are thus rotated by a 180{\deg} rotation
of the Ag unit cell about the Si [111] axis. It is intriguing that Ag
nanoislands follow an epitaxial relationship with the Si(111) substrate in
spite of the presence of a 2-3 nm thick oxide layer between Ag and Si.
Apparently the short range order on the oxide surface influences the
crystallographic orientation of the Ag nanoislands.",1009.2633v1
2013-02-05,Impact Dynamics of Oxidized Liquid Metal Drops,"With exposure to air, many liquid metals spontaneously generate an oxide
layer on their surface. In oscillatory rheological tests, this skin is found to
introduce a yield stress that typically dominates the elastic response but can
be tuned by exposing the metal to hydrochloric acid solutions of different
concentration. We systematically studied the normal impact of eutectic
gallium-indium (eGaIn) drops under different oxidation conditions and show how
this leads to two different dynamical regimes. At low impact velocity (or low
Weber number), eGaIn droplets display strong recoil and rebound from the
impacted surface when the oxide layer is removed. In addition, the degree of
drop deformation or spreading during the impact is controlled by the oxide
skin. We show that the scaling law known from ordinary liquids for the maximum
spreading radius as a function of impact velocity can still be applied to the
case of oxidized eGaIn if an effective Weber number $We^{\star}$ is employed
that uses an effective surface tension factoring in the yield stress. In
contrast, no influence on spreading from different oxidations conditions is
observed for high impact velocity. This suggests that the initial kinetic
energy is mostly damped by bulk viscous dissipation. Results from both regimes
can be collapsed in an impact phase diagram controlled by two variables, the
maximum spreading factor $P_m = R_0/R_m$, given by the ratio of initial to
maximum drop radius, and the impact number $K = We^{\star}/Re^{4/5}$, which
scales with the effective Weber number $We^{\star}$ as well as the Reynolds
number $Re$. The data exhibit a transition from capillary to viscous behavior
at a critical impact number $K_c \sim 0.1$.",1302.0921v1
2013-04-11,Resistance switching in oxides with inhomogeneous conductivity,"Electric-field-induced resistance switching (RS) phenomena have been studied
for over 60 years in metal/dielectrics/metal structures. In these experiments a
wide range of dielectrics have been studied including binary transition metal
oxides, perovskite oxides, chalcogenides, carbon- and silicon-based materials,
as well as organic materials. RS phenomena can be used to store information and
offer an attractive performance, which encompasses fast switching speeds, high
scalability, and the desirable compatibility with Si-based
complementary-metal-oxide-semiconductor fabrication. This is promising for
nonvolatile memory technology, i.e. resistance random access memory (RRAM).
However, a comprehensive understanding of the underlying mechanism is still
lacking. This impedes a faster product development as well as an accurate
assessment of the device performance potential. Generally speaking, RS occurs
not in the entire dielectric but only a small, confined region, which results
from the local variation of conductivity in dielectrics. In this review, we
focus on the RS in oxides with such an inhomogeneous conductivity. According to
the origin of the conductivity inhomogeneity, the RS phenomena and their
working mechanism are reviewed by dividing them into two aspects: interface RS,
based on the change of contact resistance at metal/oxide interface due to the
change of Schottky barrier and interface chemical layer, and bulk RS, realized
by the formation, connection, and disconnection of conductive channels in the
oxides. Finally the current challenges of RS investigation and the potential
improvement of the RS performance for the nonvolatile memories are discussed.",1304.3290v1
2014-02-22,An Acetate Bound Cobalt Oxide Catalyst for Water Oxidation: Role of Monovalent Anions and Cations In Lowering Overpotential,"Co(II) dissolved in acetate buffer at pH 7 is found to be a good water
oxidation catalyst (WOC) showing electrocatalytic water oxidation current
significantly greater than Co(II) in phosphate buffer under the same conditions
owing to the higher solubility of the former. When electrodeposited on ITO/FTO
electrodes it forms acetate bound cobalt(II)oxide based material (Co-Ac-WOC)
showing catalytic water oxidation current density of 0.1 mA/cm$^{2}$ at 830 mV
and 1 mA/cm$^{2}$ at 1 V in a pH 7 buffer solution. The morphology of Co-Ac-OEC
is investigated with AFM, HR-TEM and SEM (at different times and
electrodeposition potentials). The chemical composition of Co-Ac-OEC is
investigated using XPS, EDX, combustion analysis and ATR-FTIR which indicates
that this material has a CoO core with chloride and acetate anions bound to the
Co center. Sodium is found to be integrated in the Co-Ac-WOC. The presence of
the sodium ions and the chloride ions lowers the onset potential for oxygen
evolution reaction (OER) by 240 mV relative to the classic Co-Pi at pH 7. The
lower onset potential and higher OER current lowers the exchange current
density to 10$^{-6.7}$ in Co-Ac-WOC relative to 10$^{-8}$-10$^{-10}$ in Co-Pi
and its derivatives.",1402.5491v1
2015-09-29,Molecular mechanism of water permeation in helium impermeable graphene and graphene oxide membrane,"The layers of graphene oxide (GO) are found to be good for permeation of
water but not for helium (Science 2012 335 (6067): 442-444) suggesting that the
GO layers are dynamic in the formation of permeation route depending on the
environment they are in (i.e, water or helium). To probe the microscopic origin
of this observation we calculate the potential of mean force (PMF) of GO sheets
(oxidized and reduced parts), with inter-planar distance as reaction coordinate
in helium and water. Our PMF calculation shows that equilibrium interlayer
distance between oxidized part of GO sheets in helium is at 4.8 {\AA} leaving
no space for helium permeation. In contrast PMF of oxidized part of GO in water
shows two minima one at 4.8 {\AA} and another at 6.8 {\AA} corresponding to no
water and water filled region and thus giving rise to permeation path. The
increased electrostatic interaction between water with the oxidized part of the
sheet helps the sheet opening up and pushing water inside. Based on the entropy
calculations for water trapped between graphene sheets and oxidized graphene
sheets at different inter-sheet spacing we also show the thermodynamics of
filling.",1509.08683v1
2016-01-15,Surface Oxidation of the Topological Insulator Bi2Se3,"A comprehensive picture of the aging and oxidation of the (0001) surface of
Bi2Se3 is critical to understanding the physical origin of changes in its
topologically protected surface states. We find that surface aging in ambient
conditions occurs in two major steps. Within two hours of exfoliation, a series
of ~ 3.6 A high islands are observed by atomic force microscopy over
approximate 10% of the surface. Subsequently, patch growth stops, and oxidation
begins after the two hours and continues until one quintuple layer has been
oxidized. X-ray photoelectron spectroscopy shows no sign of oxidation before ~
120 minutes of exposure to air, and the oxygen 1s peak is clearly present after
~ 190 minutes of ambient exposure. Variable angle spectroscopic ellipsometry
also indicates that the oxidation of a full quintuple layer occurs on the time
scale of days. These results are in good agreement with the time dependent
changes previously observed in the surface crystal structure by second harmonic
generation. In addition to providing the ability to non-destructively measure
oxide on the surface of Bi2Se3 crystals, ellipsometry can be used to identify
the thickness of Bi2Se3 flakes. These results are consistent with non-linear
optical methods including rotational anisotropy second harmonic generation,
which follow the time dependence of the changes to the top quintuple layer.",1601.04057v1
2016-09-22,Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers,"The paper presents a new approach, based on controlled oxidation of nanoscale
metallic multilayers, to produce strong and hard oxide/metal nanocomposite
coatings with high strength and good thermal stability. The approach is
demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale
metallic multilayers and investigating the evolution of their microstructure
and mechanical properties by combining analytical transmission electron
microscopy, nano-mechanical tests and finite element models. As-deposited
multilayers were annealed at 350 C in air for times ranging between 1 - 336
hours. The elastic modulus increased by approx. 20% and the hardness by approx.
42% after 15 hours of annealing. Longer annealing times did not lead to changes
in hardness, although the elastic modulus increased up to 35% after 336 hrs.
The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first
15 hours), while the Nb layers were progressively oxidised, from top surface
down towards the substrate, to form an amorphous oxide phase at a much lower
rate. The sequential oxidation of Zr and Nb layers was key for the oxidation to
take place without rupture of the multi-layered structure and without coating
spallation, as the plastic deformation of the metallic Nb layers allowed for
the partial relieve of the residual stresses developed as a result of the
volumetric expansion of the Zr layers upon oxidation. Moreover, the development
of residual stresses induced further changes in mechanical properties in
relation to the annealing time, as revealed by finite element simulations.",1609.06882v1
2017-08-14,Structure of Native Two-dimensional Oxides on III--Nitride Surfaces,"When pristine material surfaces are exposed to air, highly reactive broken
bonds can promote the formation of surface oxides with structures and
properties differing greatly from bulk. Determination of the oxide structure,
however, is often elusive through the use of indirect diffraction methods or
techniques that probe only the outer most layer. As a result, surface oxides
forming on widely used materials, such as group III-nitrides, have not been
unambiguously resolved, even though critical properties can depend sensitively
on their presence. In this work, aberration corrected scanning transmission
electron microscopy reveals directly, and with depth dependence, the structure
of native two--dimensional oxides that form on AlN and GaN surfaces. Through
atomic resolution imaging and spectroscopy, we show that the oxide layers are
comprised of tetrahedra--octahedra cation--oxygen units, similar to bulk
$\theta$--Al$_2$O$_3$ and $\beta$--Ga$_2$O$_3$. By applying density functional
theory, we show that the observed structures are more stable than previously
proposed surface oxide models. We place the impact of these observations in the
context of key III-nitride growth, device issues, and the recent discovery of
two-dimnesional nitrides.",1708.03997v1
2018-05-10,Evaluation of Reduced-Graphene-Oxide Aligned with WO3-Nanorods as Support for Pt Nanoparticles during Oxygen Electroreduction in Acid Medium,"Hybrid supports composed of chemically-reduced graphene-oxide-aligned with
tungsten oxide nanowires are considered here as active carriers for dispersed
platinum with an ultimate goal of producing improved catalysts for
electroreduction of oxygen in acid medium. Here WO3 nanostructures are expected
to be attached mainly to the edges of graphene thus making the hybrid structure
not only highly porous but also capable of preventing graphene stacking and
creating numerous sites for the deposition of Pt nanoparticles. Comparison has
been made to the analogous systems utilizing neither reduced graphene oxide nor
tungsten oxide component. By over-coating the reduced-graphene-oxide support
with WO3 nanorods, the electrocatalytic activity of the system toward the
reduction of oxygen in acid medium has been enhanced even at the low Pt loading
of 30 microg cm-2. The RRDE data are consistent with decreased formation of
hydrogen peroxide in the presence of WO3. Among important issues are such
features of the oxide as porosity, large population of hydroxyl groups, high
Broensted acidity, as well as fast electron transfers coupled to unimpeded
proton displacements. The conclusions are supported with mechanistic and
kinetic studies involving double-potential-step chronocoulometry as an
alternative diagnostic tool to rotating ring-disk voltammetry.",1805.12594v1
2012-01-25,Covalent Hybrid of Spinel Manganese-Cobalt Oxide and Gra-phene as Advanced Oxygen Reduction Electrocatalysts,"Through direct nanoparticle nucleation and growth on nitrogen doped, reduced
graphene oxide sheets and cation substitution of spinel Co3O4 nanoparticles, a
manganese-cobalt spinel MnCo2O4/graphene hybrid was developed as a highly
efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline
conditions. Electrochemical and X-ray near edge structure (XANES)
investigations revealed that the nucleation and growth method for forming
inorganic-nanocarbon hybrid results in covalent coupling between spinel oxide
nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge
and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the
N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between
N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge
XANES suggested substitu-tion of Co3+ sites by Mn3+, which increased the
activity of the catalytic sites in the hybrid materials, further boosting the
ORR activity compared to the pure cobalt oxide hybrid. The covalently bonded
hybrid afforded much greater activity and durability than the physi-cal mixture
of nanoparticles and carbon materials including N-rmGO. At the same mass
loading, the MnCo2O4/N-graphene hybrid can outperform Pt/C in ORR current
density at medium overpotentials with superior stability to Pt/C in alkaline
solutions.",1201.5193v1
2017-06-09,Nucleation of dislocations and their dynamics in layered oxides cathode materials during battery charging,"Defects and their interactions in crystalline solids often underpin material
properties and functionality as they are decisive for stability, result in
enhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-rich
layered oxides have emerged among the leading candidates for the
next-generation energy storage cathode material, delivering 50 % excess
capacity over commercially used compounds. Oxygen-redox reactions are believed
to be responsible for the excess capacity, however, voltage fading has
prevented commercialization of these new materials. Despite extensive research
the understanding of the mechanisms underpinning oxygen-redox reactions and
voltage fade remain incomplete. Here, using operando three-dimensional Bragg
coherent diffractive imaging, we directly observe nucleation of a mobile
dislocation network in nanoparticles of lithium-rich layered oxide material.
Surprisingly, we find that dislocations form more readily in the lithium-rich
layered oxide material as compared with a conventional layered oxide material,
suggesting a link between the defects and the anomalously high capacity in
lithium-rich layered oxides. The formation of a network of partial dislocations
dramatically alters the local lithium environment and contributes to the
voltage fade. Based on our findings we design and demonstrate a method to
recover the original high voltage functionality. Our findings reveal that the
voltage fade in lithium-rich layered oxides is reversible and call for new
paradigms for improved design of oxygen-redox active materials.",1706.03031v1
2020-12-23,Site-Selective Oxygen Vacancy Formation Derived from the Characteristic Crystal Structures of in Sn-Nb complex Oxides,"Divalent tin oxides have attracted considerable attention as novel p-type
oxide semiconductors, which are essential for realizing future oxide electronic
devices. Recently, p-type Sn2Nb2O7 and SnNb2O6 were developed; however,
enhanced hole mobility by reducing defect concentrations is required for
practical use. In this work, we investigate the correlation between the
formation of oxygen vacancy which may reduce the hole-generation efficiency and
hole mobility, and the crystal structure in Sn-Nb complex oxides. Extended
X-ray absorption fine structure spectroscopy and Rietveld analysis of x-ray
diffraction revealed the preferential formation of oxygen vacancy at the O site
bonded to the Sn ions in both the tin niobates. Moreover, a large amount of
oxygen vacancy around the Sn ions were found in the p-type Sn2Nb2O7, thereby
indicating the effect of oxygen vacancy to the low hole-generation efficiency.
The dependence of the formation of oxygen vacancy on the crystal structure can
be elucidated from the Sn-O bond strength that is evaluated based on the bond
valence sum and Debye temperature. The differences in the bond strengths of the
two Sn-Nb complex oxides are correlated through the steric hindrance of Sn2+
with asymmetric electron density distribution. This suggests the importance of
the material design with a focus on the local structure around the Sn ions to
prevent the formation of oxygen vacancy in p-type Sn2+ oxides.",2012.12921v1
2018-03-03,Sulfate Radical Oxidation of Aromatic Contaminants: A Detailed Assessment of Density Functional Theory and High-Level Quantum Chemical Methods,"Advanced oxidation processes that utilize highly oxidative radicals are
widely used in water reuse treatment. In recent years, the application of
sulfate radical (SO$_4\cdot^-$) as a promising oxidant for water treatment has
gained increasing attention. To understand the efficiency of SO$_4\cdot^-$ in
the degradation of organic contaminants in wastewater effluent, it is important
to be able to predict the reaction kinetics of various SO$_4\cdot^-$-driven
oxidation reactions. In this study, we utilize density functional theory (DFT)
and high-level wavefunction-based methods (including computationally-intensive
coupled cluster methods), to explore the activation energies and kinetic rates
of SO$_4\cdot^-$-driven oxidation reactions on a series of benzene-derived
contaminants. These high-level calculations encompassed a wide set of reactions
including 110 forward/reverse reactions and 5 different computational methods
in total. Based on the high-level coupled-cluster quantum calculations, we find
that the popular M06-2X DFT functional is significantly more accurate for
HO-additions than for SO$_4\cdot^-$ reactions. Most importantly, we highlight
some of the limitations and deficiencies of other computational methods, and we
recommend the use of high-level quantum calculations to spot-check
environmental chemistry reactions that may lie outside the training set of the
M06-2X functional, particularly for water oxidation reactions that involve
SO$_4\cdot^-$ and other inorganic species.",1803.01227v1
2018-08-30,Modeling Selective Intergranular Oxidation of Binary Alloys,"Intergranular attack of alloys under hydrothermal conditions is a complex
problem that depends on metal and oxygen transport kinetics via solid-state and
channel-like pathways to an advancing oxidation front. Experiments reveal very
different rates of intergranular attack and minor element depletion distances
ahead of the oxidation front for nickel-based binary alloys depending on the
minor element. For example, a significant Cr depletion up to 9 microns ahead of
grain boundary crack tips were documented for Ni-5Cr binary alloy, in contrast
to relatively moderate Al depletion for Ni-5Al (~100s of nm). We present a
mathematical kinetics model that adapts Wagner's model for thick film growth to
intergranular attack of binary alloys. The transport coefficients of elements
O, Ni, Cr, and Al in bulk alloys and along grain boundaries were estimated from
the literature. For planar surface oxidation, a critical concentration of the
minor element can be determined from the model where the oxide of minor element
becomes dominant over the major element. This generic model for simple grain
boundary oxidation can predict oxidation penetration velocities and minor
element depletion distances ahead of the advancing front that are comparable to
experimental data. The significant distance of depletion of Cr in Ni-5Cr in
contrast to the localized Al depletion in Ni-5Al can be explained by the model
due to the combination of the relatively faster diffusion of Cr along the grain
boundary and slower diffusion in bulk grains, relative to Al.",1808.10397v1
2020-03-06,Anodic Decomposition of Surface Films on High Voltage Spinel Surfaces -- Density Function Theory and Experimental Study,"Oxidative decomposition of organic-solvent-based liquid electrolytes at
cathode material interfaces has been identified as a main reason for rapid
capacity fade in high-voltage lithium ion batteries. The evolution of ""cathode
electrolyte interphase: (CEI) films, partly or completely consisting of
electrolyte decomposition products, has also recently been demonstrated to be
correlated with battery cycling behavior at high potentials. Using Density
Functional Theory (DFT) calculations, the hybrid PBE0 functional, and the (001)
surfaces of spinel oxides as models, we examine these two interrelated
processes. Consistent with previous calculations, ethylene carbonate (EC)
solvent molecules are predicted to be readily oxidized on the Li(x)Mn(2)O(4)
(001) surface at modest operational voltages, forming adsorbed organic
fragments. Further oxidative decompostion of such CEI fragments to release CO2
gas is however predicted to require higher voltages consistent with
Li(x)Ni(0.5)Mn(1.5)O(4) (LNMO) at smaller x values. We argue that multi-step
reactions, involving first formation of CEI films and then further oxidization
of CEI at higher potentials, are most relevant to capacity fade. Mechanisms
associated with dissolution or oxidation of native Li2CO3 films, which is
removed before the electrolyte is in contact with oxide surfaces, are also
explored.",2003.03443v1
2020-08-12,O2-Oxidation of Individual Graphite and Graphene Nanoparticles in the 1200 to 2200 K Range: Particle-to-Particle Variations and the Evolution of the Reaction Rates and Optical Properties,"The kinetics for O2 oxidation of individual graphite and graphene platelet
nanoparticles (NPs) were studied as a function of temperature (1200 to 2200 K)
at varying oxygen partial pressures, using a single nanoparticle mass
spectrometry method. NP temperature (TNP) was measured by measuring the NP
thermal emission spectra during the kinetics studies. The initial oxidation
efficiency is found to peak in the 1200 to 1500 K range, dropping by an order
of magnitude as TNP was increased above 2000 K. There were large NP-to-NP
variations in the oxidation rates, attributed to variations in the NP surface
structure. In addition, the oxidation efficiencies decreased,
non-monotonically, as the NPs reacted, by factors of between 10 and 300. This
evolution of reactivity is attributed to changes in the NP surface structure
due to the combination of oxidation and annealing. The optical properties,
including wavelength dependence of the emissivity, and the absorption cross
section for the 532 nm heating laser, also tend to evolve as the NPs oxidize,
but differently for each individual NP, presumably reflecting differences in
the initial structures, and how they evolve under different reaction
conditions.",2008.05078v1
2020-10-25,Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox,"Stabilizing high-valent redox couples and exotic electronic states
necessitate an understanding of the stabilization mechanism. In oxides, whether
they are being considered for energy storage or computing, highly oxidized
oxide-anion species rehybridize to form short covalent bonds and are related to
significant local structural distortions. In intercalation oxide electrodes for
batteries, while such reorganization partially stabilizes oxygen redox, it also
gives rise to substantial hysteresis. In this work, we investigate oxygen redox
in layered Na2-XMn3O7, a positive electrode material with ordered Mn vacancies.
We show that coulombic interactions between oxidized oxide-anions and the
interlayer Na vacancies can disfavor rehybridization and stabilize hole
polarons on oxygen at 4.2 V vs. Na/Na+. These coulombic interactions provide
thermodynamic energy saving as large as O-O covalent bonding and enable ~ 40 mV
voltage hysteresis over multiple electrochemical cycles with negligible voltage
fade. Our results establish a complete picture of redox energetics by
highlighting the role of coulombic interactions across several atomic distances
and suggest avenues to stabilize highly oxidized oxygen for applications in
energy storage and beyond.",2010.13107v1
2021-05-11,Combinatorial screening of crystal structure in Ba-Sr-Mn-Ce perovskite oxides with ABO3 stoichiometry,"ABO3 oxides with the perovskite-related structures are attracting significant
interest due to their promising physical and chemical properties for many
applications requiring tunable chemistry, including fuel cells, catalysis, and
electrochemical water splitting. Here we report on the crystal structure of the
entire family of perovskite oxides with ABO3 stoichiometry, where A and B are
Ba, Sr, Mn, Ce. Given the vast size of this chemically complex material system,
exploration for stable perovskite-related structures with respect to its
constituent elements and annealing temperature is performed by combinatorial
pulsed laser deposition and spatially-resolved characterization of composition
and structure. As a result of this high-throughput experimental study, we
identify hexagonal perovskite-related polytypic transformation as a function of
composition in the Ba1-xSrxMnO3 oxides after annealing at different
temperatures. Furthermore, a hexagonal perovskite-related polytype is observed
in a narrow composition-temperature range of the BaCexMn1-xO3 oxides. In
contrast, a tetragonally-distorted perovskite is observed across a wider range
of compositions and annealing temperatures in the Sr1-xCexMnO3 oxides. This
structure stability is further enhanced along the BaCexMn1-xO3 - Sr1-xCexMnO3
pseudo-binary tie-line at x=0.25 by increasing Ba-incorporation and annealing
temperature. These results indicate that the BaCexMn1-xO3 - Sr1-xCexMnO3
pseudo-binary oxide alloys (solid solutions) with tetragonal perovskite
structure and broad composition-temperature range of stability are promising
candidates for thermochemical water splitting applications.",2105.05206v2
2021-05-21,"Cerium (III) and (IV) containing mesoporous glasses/alginate beads for bone regeneration: bioactivity, biocompatibility and reactive oxygen species activity","A very small number of biomaterials investigated for bone regeneration was
reported as able to prevent the oxidative stress. In this study beads based on
alginate hydrogel and mesoporous glasses (MG) containing different amounts of
cerium oxides (Ce3+/Ce4+) exhibiting antioxidant properties were investigated
as a good approach to mimic the action of antioxidant enzymes in our organism.
The effect of cerium contents on the bioactivity and biocompatibility of beads
were investigated. Moreover, the potential capability of Ce-containing MG to
prevent the oxidative stress caused by the activity of reactive oxygen species
(ROS) was here investigated for the first time. The increment of cerium oxide
from 1.2, to 3.6 and 5.3 mol-% decreases the surface area and porosity of MG
and increases the catalase mimetic activity after 168 h. Swelling tests in
different cell culture media (D- and {\alpha}-MEM) demonstrated the rehydration
capability of beads. The presence of beads with the highest Ce-contents (3.6
and 5.3 %) improved the proliferation of pre-osteoblastic cells MC3T3-C1 cells.
However, the cell differentiation decreased when increased the cerium content.
Lactate dehydrogenase assays showed beads are cytocompatible materials.
Moreover, oxidative stress tests with H2O2 showed a better response related to
cell viability and the elimination of oxidant species when increased cerium
content. Beads of glasses with 1.2 and 3.6 % of CeO2 are excellent candidates
as bioactive scaffolds for bone regeneration capable of counteract the
oxidative stress.",2105.10231v1
2021-10-24,Investigation of the Imperfect Interface at the Si/GaAs Heterojunction Formed by Ultra-Thin Oxide Interfacial Layer,"The structure property of non-ideal Si/GaAs heterostructures that were
integrated with the ultra-thin oxide (UO) tunneling interfacial layer has been
systematically investigated. Si nanomembranes (NMs) were oxidized in different
time periods prior to the hetero-integration process to create the non-ideal
single-side passivated Si/GaAs heterostructure. The atomic level oxygen
distribution and the degree of oxygen content in Si NM and GaAs were carefully
investigated using the atom probe tomography (APT) and X-ray photoelectron
spectroscopy (XPS) to trace the changes in chemical composition and reactional
mechanism across the UO interface when the surface of Si NM was exposed to air
for different period of time. The negatively induced charges at the UO layer
caused the oxygen diffusion to GaAs layer and formed the unwanted GaAs oxide
layer. This native oxide stack noticeably degraded the thermal properties of
the Si/GaAs heterostructure as Si NMs were more oxidized. This study revealed
that the poor surface passivation on the one side of the heterointerface leads
to a both-side oxidation, thus severely deteriorating the transport properties
across the heterojunction that is formed with the UO layer.",2110.12496v1
2022-07-29,Theory of layered-oxide cathode degradation in Li-ion batteries by oxidation-induced cation disorder,"Disorder-driven degradation phenomena, such as structural phase
transformations and surface reconstructions, can significantly reduce the
lifetime of Li-ion batteries, especially those with nickel-rich layered-oxide
cathodes. We develop a general free energy model for layered-oxide
ion-intercalation materials as a function of the degree of disorder, which
represents the density of defects in the host crystal. The model accounts for
defect core energies, long-range dipolar electrostatic forces, and
configurational entropy of the solid solution. In the case of nickel-rich
oxides, we hypothesize that nickel with a high concentration of defects is
driven into the bulk by electrostatic forces as oxidation reactions at the
solid-electrolyte interface reduce nickel and either evolve oxygen gas or
oxidize the organic electrolyte at high potentials (>4.4V vs. Li/Li+). The
model is used in battery cycling simulations to describe the extent of cathode
degradation when using different voltage cutoffs, in agreement with
experimental observations that lower-voltage cycling can substantially reduce
cathode degradation. The theory provides a framework to guide the development
of cathode compositions, coatings and electrolytes to enhance rate capability
and enhance battery lifetime. The general theory of cation-disorder formation
may also find applications in electrochemical water treatment and ion
separations, such as lithium extraction from brines, based on competitive ion
intercalation in battery materials.",2207.14699v3
2023-02-13,Growth of Zr/ZrO2 core-shell structures by Fast Thermal Oxidation,"This research has been conducted to characterize and validate the resistive
heating as a synthesis method for zirconium oxides (ZrO$_2$). A wire of Zr has
been oxidized to form a core shell structure, in which the core is the metal
wire, and the shell is an oxide layer around 10${\mu}$m thick. The
characterization This research has been conducted to characterize and validate
the resistive heating as a synthesis method for zirconium oxides (ZrO$_2$). A
wire of Zr has been oxidized to form a core shell structure, in which the core
is the metal wire, and the shell is an oxide layer around 10${\mu}$m thick. The
characterization of the samples has been performed by means of Scanning
Electron Microscopy (SEM). The chemical composition was analysed by X-ray
spectroscopy (EDX). X-ray diffraction (XRD) and Raman spectroscopy have been
used to assess crystallinity and crystal structure. Photoluminescence (PL) and
cathodoluminescence (CL) measurements have allowed us to study the distribution
of defects along the shell, and to confirm the degree of uniformity. The oxygen
vacancies, either as isolated defects or forming complexes with impurities,
play a determinant role in the luminescent processes. Colour centres, mainly
electron centres as F, F$_A$ and F$_{AA}$, give rise to several visible
emissions extending from blue to green, with main components around 2eV,
2.4-2.5eV and 2.7eV. The differences between PL and CL are also discussed.",2302.06296v1
2023-04-21,Constraining the Origin of Mars via Simulations of Multi-Stage Core Formation,"It remains an elusive goal to simultaneously model the astrophysics of Solar
System accretion while reproducing the mantle chemistry of more than one inner
terrestrial planet. Here, we used a multistage core-mantle differentiation
model based on Rubie et al. (2011,2015) to track the formation and composition
of Earth and Mars in various Grand Tack formation simulations. Prior studies
showed that in order to recreate Earth's mantle composition, it must grow first
from reduced (Fe-metal rich and O-poor) building blocks and then from
increasingly oxidized (FeO rich) material. This accretion chemistry occurs when
an oxidation gradient exists across the disk so that the innermost solids are
reduced and increasingly oxidized material is found at greater heliocentric
distances. For a suite of Grand Tack simulations, we investigated whether Earth
and Mars can be simultaneously produced by the same oxidation gradient. Our
model did not find an oxidation gradient that simultaneously reproduces the
mantle composition of Earth and Mars. Due to its small mass and rapid
formation, the formation history of Mars-like planets is very stochastic which
decreases the likelihood of compatibility with an Earth-producing oxidation
gradient in any given realization. To reconcile the accretion history and ideal
chemistry of the Mars-like planet with the oxidation gradient of an
Earth-producing disk, we determined where in the Earth-producing disk Mars must
have formed. We find that the FeO-rich composition of the Martian mantle
requires that Mars' building blocks must originate exterior to 1.0 astronomical
units (AU).",2304.11236v1
2023-05-05,Shock induced atomisation of a liquid metal droplet,"The present study uses Galinstan as a test fluid to investigate the
shock-induced aerobreakup of a liquid metal droplet in a high Weber number
regime (We ~ 400 - 8000). Atomization dynamics is examined for three test
environments: oxidizing (Galinstan-air), inert (Galinstan-nitrogen), and
conventional fluids (DI water-air). Due to the readily oxidizing nature of
liquid metals, their atomization in an industrial scale system is generally
carried in inert atmosphere conditions. However, no previous study has
considered gas-induced secondary atomization of liquid metals in inert
conditions. Due to experimental challenges associated with molten metals,
laboratory scale models are generally tested for conventional fluids like DI
water, liquid fuels, etc. The translation of results obtained from conventional
fluid to liquid metal atomization is rarely explored. Here a direct multi-scale
spatial and temporal comparison is provided between the atomization dynamics of
conventional fluid and liquid metals under oxidizing and inert conditions. The
liquid metal droplet undergoes breakup through Shear-Induced Entrainment (SIE)
mode for the studied range of Weber number values. The prevailing mechanism is
explained based on the relative dominance of droplet deformation and KH wave
formation. The study provides quantitative and qualitative similarities for the
three test cases and explains the differences in morphology of fragmenting
secondary droplets in the oxidizing test case (Galinstan-air) due to rapid
oxidation of the fragmenting ligaments. A phenomenological framework is
postulated for predicting the morphology of secondary droplets. The formation
of flake-like secondary droplets in the Galinstan air test case is based on the
oxidation rate of liquid metals and the properties of the oxide layer formed on
the atomizing ligament surface.",2305.03525v1
2023-05-23,Modeling of Surface Damage at the Si/SiO$_2$-interface of Irradiated MOS-capacitors,"Surface damage caused by ionizing radiation in SiO$_2$ passivated silicon
particle detectors consists mainly of the accumulation of a positively charged
layer along with trapped-oxide-charge and interface traps inside the oxide and
close to the Si/SiO$_2$-interface. High density positive interface net charge
can be detrimental to the operation of a multi-channel $n$-on-$p$ sensor since
the inversion layer generated under the Si/SiO$_2$-interface can cause loss of
position resolution by creating a conduction channel between the electrodes. In
the investigation of the radiation-induced accumulation of oxide charge and
interface traps, a capacitance-voltage characterization study of n/$\gamma$-
and $\gamma$-irradiated Metal-Oxide-Semiconductor (MOS) capacitors showed that
close agreement between measurement and simulation were possible when oxide
charge density was complemented by both acceptor- and donor-type deep interface
traps with densities comparable to the oxide charges. Corresponding inter-strip
resistance simulations of a $n$-on-$p$ sensor with the tuned oxide charge
density and interface traps show close agreement with experimental results. The
beneficial impact of radiation-induced accumulation of deep interface traps on
inter-electrode isolation may be considered in the optimization of the
processing parameters of isolation implants on $n$-on-$p$ sensors for the
extreme radiation environments.",2305.14316v3
2023-07-12,Multimodal Operando X-ray Mechanistic Studies of a Bimetallic Oxide Electrocatalyst in Alkaline Media,"Furthering the understanding of the catalytic mechanisms in the oxygen
reduction reaction (ORR) is critical to advancing and enabling fuel cell
technology. In this work, we use multimodal operando synchrotron X-ray
diffraction (XRD) and resonant elastic X-ray scattering (REXS) to investigate
the interplay between the structure and oxidation state of a Co-Mn spinel oxide
electrocatalyst, which has previously shown ORR activity that rivals Pt in
alkaline fuel cells. During cyclic voltammetry, the electrocatalyst exhibited a
reversible and rapid increase in tensile strain at low potentials, suggesting
robust structural reversibility and stability of Co-Mn oxide electrocatalysts
during normal fuel cell operating conditions. At low potential holds, exploring
the limit of structural stability, an irreversible tetragonal-to-cubic phase
transition was observed, which may be correlated to reduction in both Co and Mn
valence states. Meanwhile, joint density-functional theory (JDFT) calculations
provide insight into how reactive adsorbates induce strain in spinel oxide
nanoparticles. Through this work, strain and oxidation state changes that are
possible sources of degradation during the ORR in Co-Mn oxide electrocatalysts
are uncovered, and the unique capabilities of combining structural and chemical
characterization of electrocatalysts in multimodal operando X-ray studies are
demonstrated.",2307.05912v1
2023-09-07,Enhanced strength-ductility combination by introducing bimodal grains structures in high-density oxide dispersion strengthened FeCrAl alloys fabricated by spark plasma sintering technology,"Oxide dispersion strengthened FeCrAl alloys dispersed high-density
nano-oxides in the matrix show outstanding corrosion resistance and mechanical
properties. However, ODS FeCrAl alloys achieve the high strength generally at
the expense of ductility in some way. Here, a method by introducing a bimodal
grain structure was designed to overcome the strength-ductility tradeoff. In
this work, ODS FeCrAl alloys were successfully fabricated through various
mechanical alloying time, combined with spark plasma sintering under the vacuum
of less than 4Pa. Microstructural characterization showed that the average
grains size and nano-oxides size decrease gradually, and the density of
nano-oxides increases, as the milling time increases. Mechanical properties
revealed that both the strength and ductility were significantly synergistic
enhanced with increasing milling time. The bimodal grain distribution
characterized by electron backscatter diffraction (EBSD) (vacuum degree was
less than 5E-5pa) was beneficial for the activation of the back stress
strengthening and the annihilation of these microcracks, thus achieving the
excellent ductility (27.65%). In addition, transmission electron microscope
(TEM) characterization under the vacuum degree of less than 10-6pa illustrated
that ultra-high-density nano-oxides (9.61E22/m3) was crucial for enhancing the
strength of ODS FeCrAl alloys (993MPa). The strengthening mechanism
superposition, based on the model of nano-oxides interrelated with the
dislocation, illustrated an excellent agreement with experimental results from
yield strength strengthening mechanisms. To our best knowledge, H40 (milled for
40h, and sintered at 1100C) alloy presents the outstanding strength with the
exceptional ductility among all studied ODS FeCrAl alloys, which makes it the
promising cladding materials for the accident tolerant fuel cladding.",2309.03703v1
2024-01-26,E-Beam Induced Micropattern Generation and Amorphization of L-Cysteine-Functionalized Graphene Oxide Nano-composites,"The evolution of dynamic processes in graphene-family materials are of great
interest for both scientific purposes and technical applications. Scanning
electron microscopy and transmission electron microscopy outstand among the
techniques that allow both observing and controlling such dynamic processes in
real time. On the other hand, functionalized graphene oxide emerges as a
favorable candidate from graphene-family materials for such an investigation
due to its distinctive properties, that encompass a large surface area, robust
thermal stability, and noteworthy electrical and mechanical properties after
its reduction. Here, we report on studies of surface structure and adsorption
dynamics of L-Cysteine on electrochemically exfoliated graphene oxides basal
plane. We show that electron beam irradiation prompts an amorphization of
functionalized graphene oxide along with the formation of micropatterns of
controlled geometry composed of L-Cysteine-Graphene oxide nanostructures. The
controlled growth and predetermined arrangement of micropatterns as well as
controlled structure disorder induced by e beam amorphization, in its turn
potentially offering tailored properties and functionalities paving the way for
potential applications in nanotechnology, sensor development, and surface
engineering. Our findings demonstrate that graphene oxide can cover L-Cysteine
in such a way to provide a control on the positioning of emerging
microstructures about 10-20 um in diameter. Besides, Raman and SAED measurement
analyses yield above 50% amorphization in a material. The results of our
studies demonstrate that such a technique enables the direct creation of
micropatterns of L-Cysteine-Graphene oxide eliminating the need for complicated
mask patterning procedures.",2401.14783v1
2019-06-02,Oxidation of Monolayer WS$_{2}$ in Ambient is a Photoinduced Process,"We have studied the ambient air oxidation of chemical vapor deposition (CVD)
grown monolayers of the semiconducting transition metal dichalcogenide (S-TMD)
WS$_{2}$ using optical microscopy, laser scanning confocal microscopy (LSCM),
photoluminescence (PL) spectroscopy, and atomic force microscopy (AFM).
Monolayer WS$_{2}$ exposed to ambient conditions in the presence of light
(typical laboratory ambient light for weeks, or typical PL spectroscopy map),
exhibits damage due to oxidation which can be detected with the LSCM and AFM;
though may not be evident in conventional optical microscopy due to poorer
contrast and resolution. Additionally, this oxidation was not random, and
correlated with 'high-symmetry' and red-shifted areas in the PL spectroscopy
map - areas thought to contain a higher concentration of sulfur vacancies. In
contrast, samples kept in ambient and darkness showed no signs of oxidation for
up to 10 months. Low-irradiance/fluence experiments showed that samples
subjected to excitation energies at or above the trion excitation energy (532
nm/2.33 eV and 660 nm/1.88 eV) oxidized in as little as 7 days, even for
irradiances and fluences eight and four orders of magnitude lower
(respectively) than previously reported. No significant oxidation was observed
for 760 nm/1.63 eV light exposure, which lies below the trion excitation energy
in WS$_{2}$. The strong wavelength dependence and apparent lack of irradiance
dependence suggests that ambient oxidation of WS$_{2}$ is initiated by
photon-mediated electronic band transitions, that is, photo-oxidation. These
findings have important implications for prior, present and future studies
concerning S-TMDs measured, stored or manipulated in ambient conditions.",1906.00375v2
2018-06-18,Significantly enhanced photocatalytic degradation of Methylene Blue using rGO-SnO2 nanocomposite under natural sunlight and UV light irradiation,"In this paper, we report the synthesis of reduced Graphene Oxide-Tin Oxide
nanocomposite and the effectiveness of this composite in decolorizing and
degrading Methylene Blue (MB). Tin Oxide was prepared by liquid phase
co-precipitation method and reduced Graphene Oxide-Tin Oxide (rGO-SnO2)
nanocomposite was prepared by solution mixing method. Tin Oxide nanoparticles
(NPs) have been ardently investigated as photocatalyst for water purification
and environment decontamination but the photon generated electron and hole pair
(EHP) recombination is one of the limiting factors. Reduced Graphene Oxide-Tin
Oxide (rGO-SnO2) nanocomposite is very efficient to overcome this limitation
for photocatalytic application. The as-synthesized GO, SnO2, GO-SnO2, rGO and
rGO-SnO2 nanocomposite were characterized by X-ray Diffraction, Scanning
Electron Microscopy, Energy Dispersive X-ray spectroscopy and Fourier Transform
Infrared spectroscopy. The XRD data confirms the sharp peak at 2Theta=10.44
degree corresponding to (002) reflection of GO with interlayer d spacing of
8.46 Angstrom indication of successful preparation of GO by oxidation of
graphite. Moreover, the diffraction peak shifts from 2Theta=10.44 degree to
2Theta=23.31 degree confirm successful synthesis of rGO as well. SEM image
shows the morphology of all the photocatalysts. EDX studies are carried out to
investigate the elemental composition and purity of the sample by giving all
the elements present in the nanomaterials. The presence of functional groups
was identified by FTIR. The rGO-SnO2 (1:10) nanocomposite shows an efficient
photodegradation efficiency of ~94% and ~95% under natural sunlight and UV
light irradiation respectively for Methylene Blue (MB) within 15 minutes.
Furthermore, the degradation kinetics of MB is also studied in this paper as
well.",1808.02107v1
2024-02-02,"Size, nanostructure, and composition dependence of bimetallic Au-Pd supported on ceria-zirconia mixed oxide catalysts for selective oxidation of benzyl alcohol","A bimetallic Au-Pd catalyst supported on ceriazirconia with Au:Pd molar ratio
0.8 has been synthesized using a simultaneous deposition-precipitation method
and oxidized at 250, 450, and 700 $^\circ$C in order to modify its particle
size, nanostructure, and composition. Combined Xray energy dispersive
spectroscopy and Xray photoelectron spectroscopy analysis clearly evidence that
the bimetallic Au-Pd catalyst oxidized at 250 $^\circ$C is made up of a mixture
of monometallic Au and Pd and bimetallic Au-Pd nanoparticles with Au:Pd ratios
varying over a wide range. Increasing oxidation temperature leads to a stronger
interaction between Au and Pd. Meanwhile, a slight increase of particle size
and a narrowing of the Au:Pd ratio in the bimetallic nanoparticles take place.
Compared with titania and activated carbon supports, the resistance against
sintering at high temperatures of Au-Pd metal particles supported on
ceriazirconia is proven to be higher. A synergistic effect has been observed
for selective oxidation of benzyl alcohol on these catalysts. The catalytic
activity decreases only slightly after oxidation at 450 $^\circ$C. However,
oxidation at 700 $^\circ$C results in much lower catalytic activity. Migration
of Pd onto Au particles during oxidation of benzyl alcohol enhances the
catalytic activity of a physical mixture of monometallic Au and Pd supported on
ceriazirconia catalysts. This fact, jointly with an analysis of the intrinsic
activity, reveals the influence of the actual nature of Au-Pd interactions in
the bimetallic particles, which points to higher activity of Au@Pd or Au@Pd@Pd
nanostructures on ceria-zirconia support.",2403.03958v1
2005-12-21,"Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide","Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO),
is the first member of a new class of organometallic hybrids which adopts the
structural pattern and physical properties of classical perovskites in two
dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be
tailored by intercalation of organic donor molecules, such as
tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF),
and by the inorganic acceptor SbF$_3$. Integration of donor molecules leads to
a more insulating behavior of poly-MTO, whereas SbF$_3$ insertion does not
cause any significant change in the resistivity. The resistivity data of pure
poly-MTO is remarkably well described by a two-dimensional electron system.
Below 38 K an unusual resistivity behavior, similar to that found in doped
cuprates, is observed: The resistivity initially increases approximately as
$\rho \sim$ ln$(1/T$) before it changes into a $\sqrt{T}$ dependence below 2 K.
As an explanation we suggest a crossover from purely two-dimensional
charge-carrier diffusion within the \{ReO$_2$\}$_{\infty}$ planes at high
temperatures to three-dimensional diffusion at low temperatures in a
disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov
correction). Furthermore, a linear positive magnetoresistance was found in the
insulating regime, which is caused by spatial localization of itinerant
electrons at some of the Re atoms, which formally adopt a $5d^1$ electronic
configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent
magnetization and specific heat measurements in various magnetic fields suggest
that the electronic structure of poly-MTO can safely be approximated by a
purely 2D conductor.",0512544v1
2007-02-05,Quantum phase transitions in magnetism and superconductivity: emergent spin topology seen with neutrons,"Magnetic spins and charges interact strongly in high-temperature
superconductors. New physics emerges as layers of copper oxide are tuned
towards the boundary of the superconducting phase. As the pseudogap increases
the characteristic spin excitation energy decreases. We show that our
well-annealed YBa2Cu3O6+x (YBCO6+x) single crystals are orthorhombic and
superconducting but not antiferromagnetically ordered. Near the critical
concentration for superconductivity for x = 0.35 the spins fluctuate on two
energy scales, one a relaxational spin response at ~2 meV and the other a slow
central mode that is resolution-limited in energy (<0.08 meV) but broad in
momentum. The gradual formation on cooling of a central mode over a range of
momenta suggests that the spin ground state from which coherent superconducting
pairing emerges may be quantum disordered. We show that YBCO6.35 adopts a
homogeneous state that consists of highly-organized frozen sub-critical
three-dimensional spin correlations. The continuous spin evolution indicates
that a single quantum state occurs in contrast to claims from site-based probes
that lightly doped YBCO undergoes a transition to antiferromagnetic Bragg order
followed by a sharp transition to a cluster glass phase. For x = 0.35, where Tc
= 18 K is reduced to 1/5 of Tcmax, the spin ground state is reached without a
sharp transition and consists of short correlations extending over only 8
Angstrom between cells and 42 Angstrom within the planes. Polarized neutrons
show the angular spin distribution to be isotropic unlike the AF insulator.
Since moment is conserved we interpret this as evidence for hole-induced spin
rotations rather than decay.",0702062v2
2007-03-12,"Metal-insulator (fermion-boson)-crossover origin of pseudogap phase of cuprates I: anomalous heat conductivity, insulator resistivity boundary, nonlinear entropy","Among all experimental observations of cuprate physics, the
metal-insulator-crossover (MIC), seen in the pseudogap (PG) region of the
temperature-doping phase diagram of copper-oxides under a strong magnetic
field, when the superconductivity is suppressed, is most likely the most
intriguing one. Since it was expected that the PG-normal state for these
materials, as for conventional superconductors, is conducting. This MIC,
revealed in such phenomena as heat conductivity downturn, anomalous Lorentz
ratio, insulator resistivity boundary, nonlinear entropy, resistivity
temperature upturn, insulating ground state, nematicity- and stripe-phases and
Fermi pockets, unambiguously indicates on the insulating normal state, from
which the high-temperature superconductivity (HTS) appears. In the present work
(article I), we discuss the MIC phenomena mentioned in the title of article.
The second work (article II) will be devoted to discussion of other listed
above MIC phenomena and also to interpretation of the recent observations in
the hidden magnetic order and scanning tunneling microscopy (STM) experiments
spin and charge fluctuations as the intra PG and HTS pair ones. We find that
all these MIC (called in the literature as non-Fermi liquid) phenomena can be
obtained within the Coulomb single boson and single fermion two liquid model,
which we recently developed, and the MIC is a crossover of single fermions into
those of single bosons. We show that this MIC originates from bosons of Coulomb
two liquid model and fermions, whose origin is these bosons. At an increase of
doping up to critical value or temperature up to PG boundary temperature, the
boson system undegoes bosonic insulator - bosonic metal - fermionic metal
transitions.",0703290v3
2007-10-03,Gapped itinerant spin excitations account for missing entropy in the hidden order state of URu$_2$Si$_2$,"One of the primary goals of modern condensed matter physics is to elucidate
the nature of the ground state in various electronic systems. Many correlated
electron materials, such as high temperature superconductors, geometrically
frustrated oxides, and low-dimensional magnets are still the objects of
fruitful study because of the unique properties which arise due to poorly
understood many-body effects. Heavy fermion metals - materials which have high
effective electron masses due to these effects - represent a class of materials
with exotic properties, such as unusual magnetism, unconventional
superconductivity, and ""hidden order"" parameters. The heavy fermion
superconductor URu2Si2 has held the attention of physicists for the last two
decades due to the presence of a ""hidden order"" phase below 17.5 K. Neutron
scattering measurements indicate that the ordered moment is 0.03 $\mu_{B}$,
much too small to account for the large heat capacity anomaly at 17.5 K. We
present recent neutron scattering experiments which unveil a new piece of this
puzzle - the spin excitation spectrum above 17.5 K exhibits well-correlated,
itinerant-like spin excitations up to at least 10 meV emanating from
incommensurate wavevectors. The gapping of these excitations corresponds to a
large entropy release and explains the reduction in the electronic specific
heat through the transition.",0710.0896v2
2008-08-25,Low energy theory of the t-t'-t''-U Hubbard Model at half-filling: interaction strengths in cuprate superconductors and an effective spin-only description of La_2CuO_4,"Spin-only descriptions of the half-filled one-band Hubbard model are relevant
for a wide range of Mott insulators. In addition to the usual Heisenberg
exchange, many new types of interactions, including ring exchange, appear in
the effective Hamiltonian in the intermediate coupling regime. In order to
improve on the quantitative description of magnetic excitations in the
insulating antiferromagnetic phase of copper-oxide (cuprate) materials, and to
be consistent with band structure calculations and photoemission experiments on
these systems, we include second and third neighbor hopping parameters, t' and
t'', into the Hubbard Hamiltonian. A unitary transformation method is used to
find systematically the effective Hamiltonian and any operator in the spin-only
representation. The results include all closed, four hop electronic pathways in
the canonical transformation. The method generates many ring exchange terms
that play an important role in the comparison with experiments on La2CuO4.
Performing a spin wave analysis, we calculate the magnon dispersion as a
function of U,t,t' and t''. The four parameters are estimated by fitting the
magnon dispersion to the experimental results of Coldea et al. [Phys. Rev.
Lett. 86, 5377, {2001}] for La2CuO4. The ring exchange terms are found
essential, in particular to determine the relative sign of t' and t'', with the
values found in good agreement with independent theoretical and experimental
estimates for other members of the cuprate family. The zero temperature
sublattice magnetization is calculated using these parameters and also found to
be in good agreement with the experimental value estimated by Lee et al. [Phys.
Rev. B 60, 3643 (1999)]. We find a value of the interaction strength U~8t
consistent with Mott insulating behavior.",0808.3167v1
2010-05-31,The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf,"Main sequence M stars pose an interesting problem for astrobiology: their
abundance in our galaxy makes them likely targets in the hunt for habitable
planets, but their strong chromospheric activity produces high energy radiation
and charged particles that may be detrimental to life. We studied the impact of
the 1985 April 12 flare from the M dwarf, AD Leonis (AD Leo), simulating the
effects from both UV radiation and protons on the atmospheric chemistry of a
hypothetical, Earth-like planet located within its habitable zone. Based on
observations of solar proton events and the Neupert effect we estimated a
proton flux associated with the flare of $5.9\times 10^{8}$ protons cm$^{-2}$
sr$^{-1}$ s$^{-1}$ for particles with energies >10 MeV. Then we calculated the
abundance of nitrogen oxides produced by the flare by scaling the production of
these compounds during a large solar proton event called the ""Carrington
event"". The simulations were performed using a 1-D photochemical model coupled
to a 1-D radiative/convective model. Our results indicate that the ultraviolet
radiation emitted during the flare does not produce a significant change in the
ozone column depth of the planet. When the action of protons is included, the
ozone depletion reached a maximum of 94% two years after the flare for a planet
with no magnetic field. At the peak of the flare, the calculated UV fluxes that
reach the surface, in the wavelength ranges that are damaging for life, exceed
those received on Earth during less than 100 s. Flares may therefore not
present a direct hazard for life on the surface of an orbiting habitable
planet. Given that AD Leo is one of the most magnetically-active M dwarfs
known, this conclusion should apply to planets around other M dwarfs with lower
levels of chromospheric activity.",1006.0022v1
2013-10-11,Neutron spectroscopic study of crystal field excitations in Tb2Ti2O7 and Tb2Sn2O7,"We present time-of-flight inelastic neutron scattering measurements at low
temperature on powder samples of the magnetic pyrochlore oxides Tb2Ti2O7 and
Tb2Sn2O7. These two materials possess related, but different ground states,
with Tb2Sn2O7 displaying ""soft"" spin ice order below Tn~0.87 K, while Tb2Ti2O7
enters a hybrid, glassy spin ice state below Tg~0.2 K. Our neutron
measurements, performed at T=1.5 K and 30 K, probe the crystal field states
associated with the J=6 states of Tb3+ within the appropriate Fd\bar{3}m
pyrochlore environment. These crystal field states determine the size and
anisotropy of the Tb3+ magnetic moment in each material's ground state,
information that is an essential starting point for any description of the
low-temperature phase behavior and spin dynamics in Tb2Ti2O7 and Tb2Sn2O7.
While these two materials have much in common, the cubic stanate lattice is
expanded compared to the cubic titanate lattice. As our measurements show, this
translates into a factor of ~2 increase in the crystal field bandwidth of the
2J+1=13 states in Tb2Ti2O7 compared with Tb2Sn2O7. Our results are consistent
with previous measurements on crystal field states in Tb2Sn2O7, wherein the
ground state doublet corresponds primarily to m_J=|\pm 5> and the first excited
state doublet to mJ=|\pm 4>. In contrast, our results on Tb2Ti2O7 differ
markedly from earlier studies, showing that the ground state doublet
corresponds to a significant mixture of mJ=|\pm 5>, |\mp 4>, and |\pm 2>, while
the first excited state doublet corresponds to a mixture of mJ=|\pm 4>, |\mp
5>, and |\pm 1>. We discuss these results in the context of proposed mechanisms
for the failure of Tb2Ti2O7 to develop conventional long-range order down to 50
mK.",1310.3264v2
2013-10-23,Functional Renormalization Group for multi-orbital Fermi Surface Instabilities,"Technological progress in material synthesis, as well as artificial
realization of condensed matter scenarios via ultra-cold atomic gases in
optical lattices or epitaxial growth of thin films, is opening the gate to
investigate a plethora of unprecedented strongly correlated electron systems.
In a large subclass thereof, a metallic state of layered electrons undergoes an
ordering transition below some temperature into unconventional states of matter
driven by electronic correlations, such as magnetism, superconductivity, or
other Fermi surface instabilities. While this type of phenomena has been a
well-established direction of research in condensed matter for decades, the
variety of today's accessible scenarios pose fundamental new challenges to
describe them. A core complication is the multi-orbital nature of the
low-energy electronic structure of these systems, such as the multi-d orbital
nature of electrons in iron pnictides and transition-metal oxides in general,
but also electronic states of matter on lattices with multiple sites per unit
cell such as the honeycomb or kagome lattice. In this review, we propagate the
functional renormalization group (FRG) as a suited approach to investigate
multi-orbital Fermi surface instabilities. The primary goal of the review is to
describe the FRG in explicit detail and render it accessible to everyone both
at a technical and intuitive level. Summarizing recent progress in the field of
multi-orbital Fermi surface instabilities, we illustrate how the unbiased
fashion by which the FRG treats all kinds of ordering tendencies guarantees an
adequate description of electronic phase diagrams and often allows to obtain
parameter trends of sufficient accuracy to make qualitative predictions for
experiments. This review includes detailed and illustrative illustrations of
magnetism and, in particular, superconductivity for the iron pnictides from the
viewpoint of FRG. Furthermore, it discusses candidate scenarios for topological
bulk singlet superconductivity and exotic particle-hole condensates on
hexagonal lattices such as sodium-doped cobaltates, graphene doped to van Hove
Filling, and the kagome Hubbard model. In total, the FRG promises to be one of
the most versatile and revealing numerical approaches to address unconventional
Fermi surface instabilities in future fields of condensed matter research.",1310.6191v1
2014-09-10,"ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets","The affordable, robust, compact (ARC) reactor conceptual design study aims to
reduce the size, cost, and complexity of a combined fusion nuclear science
facility (FNSF) and demonstration fusion Pilot power plant. ARC is a 200-250
MWe tokamak reactor with a major radius of 3.3 m, a minor radius of 1.1 m, and
an on-axis magnetic field of 9.2 T. ARC has rare earth barium copper oxide
(REBCO) superconducting toroidal field coils, which have joints to enable
disassembly. This allows the vacuum vessel to be replaced quickly, mitigating
first wall survivability concerns, and permits a single device to test many
vacuum vessel designs and divertor materials. The design point has a plasma
fusion gain of Q_p~13.6, yet is fully non-inductive, with a modest bootstrap
fraction of only ~63%. Thus ARC offers a high power gain with relatively large
external control of the current profile. This highly attractive combination is
enabled by the ~23 T peak field on coil with newly available REBCO
superconductor technology. External current drive is provided by two innovative
inboard RF launchers using 25 MW of lower hybrid and 13.6 MW of ion cyclotron
fast wave power. The resulting efficient current drive provides a robust,
steady state core plasma far from disruptive limits. ARC uses an all-liquid
blanket, consisting of low pressure, slowly flowing fluorine lithium beryllium
(FLiBe) molten salt. The liquid blanket is low-risk technology and provides
effective neutron moderation and shielding, excellent heat removal, and a
tritium breeding ratio >= 1.1. The large temperature range over which FLiBe is
liquid permits blanket operation at 900 K with single phase fluid cooling and a
high-efficiency Brayton cycle, allowing for net electricity generation when
operating ARC as a Pilot power plant.",1409.3540v2
2016-01-20,The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors,"The condensation of an electron superfluid from a conventional metallic state
at a critical temperature $T_c$ is described well by the BCS theory. In the
underdoped copper-oxides, high-temperature superconductivity condenses instead
from a nonconventional metallic ""pseudogap"" phase that exhibits a variety of
non-Fermi liquid properties. Recently, it has become clear that a charge
density wave (CDW) phase exists within the pseudogap regime, appearing at a
temperature $T_{CDW}$ just above $T_c$. The near coincidence of $T_c$ and
$T_{CDW}$, as well the coexistence and competition of CDW and superconducting
order below $T_c$, suggests that they are intimately related. Here we show that
the condensation of the superfluid from this unconventional precursor is
reflected in deviations from the predictions of BSC theory regarding the
recombination rate of quasiparticles. We report a detailed investigation of the
quasiparticle (QP) recombination lifetime, $\tau_{qp}$, as a function of
temperature and magnetic field in underdoped HgBa$_{2}$CuO$_{4+\delta}$
(Hg-1201) and YBa$_{2}$Cu$_{3}$O$_{6+x}$ (YBCO) single crystals by ultrafast
time-resolved reflectivity. We find that $\tau_{qp}(T)$ exhibits a local
maximum in a small temperature window near $T_c$ that is prominent in
underdoped samples with coexisting charge order and vanishes with application
of a small magnetic field. We explain this unusual, non-BCS behavior by
positing that $T_c$ marks a transition from phase-fluctuating SC/CDW composite
order above to a SC/CDW condensate below. Our results suggest that the
superfluid in underdoped cuprates is a condensate of coherently-mixed
particle-particle and particle-hole pairs.",1601.05224v1
2016-03-01,"Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses","The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of
the oxides Sr3NiIrO6, Sr2IrO4 and Na2IrO3 exhibit preferred orientations with
respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of
these S = 1/2 ions on the basis of DFT calculations including spin-orbit
coupling (SOC), and probed their origin by performing perturbation theory
analyses with SOC as perturbation within the LS coupling scheme. The observed
spin orientations of Sr3NiIrO6 and Sr2IrO4 are correctly predicted by DFT
calculations, and are accounted for by the perturbation theory analysis. As for
the spin orientation of Na2IrO3, both experimental studies and DFT calculations
have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation
of Na2IrO3 should have nonzero components along the c- and a-axes directions.
The spin orientations determined by DFT calculations are sensitive to the
accuracy of the crystal structures employed, which is explained by perturbation
theory analyses when interactions between adjacent Ir4+ ions are taken into
consideration. There are indications implying that the 5d electrons of Na2IrO3
are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4. This
implication was confirmed by showing that the Madelung potentials of the Ir4+
ions are less negative in Na2IrO3 than in Sr3NiIrO6, Sr2IrO4. Most
transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC
induces interactions among their crystal-field split d-states, and the
associated mixing of the states modifies only the orbital parts of the states.
This finding cannot be mimicked by a spin Hamiltonian because this model
Hamiltonian lacks the orbital degree of freedom, thereby leading to the
spin-half syndrome. The spin-orbital entanglement for the 5d spin-half ions
Ir4+ is not as strong as has been assumed lately.",1603.00523v2
2016-04-28,"Highly-anisotropic exchange interactions of $j_{\rm eff}=1/2$ iridium moments on the fcc lattice in La$_2B$IrO$_6$ ($B$ $=$ Mg, Zn)","We have performed inelastic neutron scattering (INS) experiments to
investigate the magnetic excitations in the weakly distorted
face-centered-cubic (fcc) iridate double perovskites La$_2$ZnIrO$_6$ and
La$_2$MgIrO$_6$, which are characterized by A-type antiferromagnetic ground
states. The powder inelastic neutron scattering data on these geometrically
frustrated $j_{\rm eff}=1/2$ Mott insulators provide clear evidence for gapped
spin wave excitations with very weak dispersion. The INS results and
thermodynamic data on these materials can be reproduced by conventional
Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable
second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange
interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only
arise from the weak crystal distortions away from the ideal fcc limit. This may
suggest that even weak distortions in $j_{\rm eff}=1/2$ Mott insulators might
lead to strong exchange anisotropies. More tantalizingly, however, we find an
alternative viable explanation of the INS results in terms of spin models with
a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the
highly-directional Kitaev interaction is a type of exchange anisotropy which is
symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon
gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev
couplings generated by the symmetry-lowering due to lattice distortions, can
pin the order and enhance the magnon gap. Our findings highlight how even
conventional magnetic orders in heavy transition metal oxides may be driven by
highly-directional exchange interactions rooted in strong spin-orbit coupling.",1604.08431v1
2011-11-24,Modern trends in Superconductivity and Superfluidity. Selected Chapters,"In Chapter 1 we start with general Landau scheme of the conservation laws for
the hydrodynamics of classical liquids and superfluids. On the basis of Landau
scheme we consider hydrodynamics of rotating superfluids with large number of
vortices. We study different regimes of slow and fast rotations. In Chapter 4
we consider complicated and yet unresolved problem of chiral anomaly in
superfluid 3He-A and present two competing approaches. The first one is based
on supersymmetric hydrodynamics, another one on the formal analogy with Dirac
equation in QED. In Chapters 6 and 7 we study composed fermions and bosons
which correspond to the different bound states consisting of two fermions, two
bosons and fermion and boson in ultracold quantum gasses and mixtures. We also
elucidate the exact solutions of the Skorniakov-Ter-Martirosian integral
equations. We present the basic ideas of Nozieres-Schmitt Rink and Legget
theory on BCS-BEC crossover in quantum gasses and construct the phase diagrams
for the s-wave and p-wave pairings. In Chapters 9 and 10 we discuss non-phonon
mechanisms of superconductivity of the Kohn-Luttinger type for different models
in 3D and 2D electron systems at low densities including Fermi-gas, Hubbard and
Shubin-Vonsovsky models. We complete the superconductive phase-diagrams of
p-wave and d-wave pairing and discuss the possibility to increase Tc already at
low density. In Chapters 15 and 16 the mechanisms of electron nanoscale
phase-separation in manganite-type oxide materials are analyzed. The
instability of magnetic (or charge) homogeneous ordering towards the formation
of droplet structures (magnetic polarons) is predicted for a wide parameter
range on the phase-diagram. The transport properties of these materials in the
phase-separated state are also discussed.",1111.5711v5
2015-12-07,Recent progress on correlated electron systems with strong spin-orbit coupling,"Emergence of novel quantum ground states in correlated electron systems with
strong spin-orbit coupling has been a recent subject of intensive studies.
While it has been realized that spin-orbit coupling can provide non-trivial
band topology in weakly interacting electron systems, as in topological
insulators and semi-metals, the role of electron-electron interaction in
strongly spin-orbit coupled systems has not been fully understood. The
availability of new materials with significant electron correlation and strong
spin-orbit coupling now makes such investigations possible. Many of these
materials contain 5d or 4d transition metal elements; the prominent examples
are iridium oxides or iridates. In this review, we succinctly discuss recent
theoretical and experimental progress on this subject. After providing a brief
overview, we focus on pyrochlore iridates and three-dimensional honeycomb
iridates. In pyrochlore iridates, we discuss the quantum criticality of the
bulk and surface states, and the relevance of the surface/boundary states in a
number of topological and magnetic ground states, both in the bulk and thin
film configurations. Experimental signatures of these boundary and bulk states
are discussed. Domain wall formation and strongly-direction-dependent
magneto-transport are also discussed. Regarding the three-dimensional honeycomb
iridates, we consider possible quantum spin liquid phases and unusual magnetic
orders in theoretical models with strongly bond-dependent interactions. These
theoretical ideas and results are discussed in light of recent resonant X-ray
scattering experiments on three-dimensional honeycomb iridates. We also
contrast these results with the situation in two-dimensional honeycomb
iridates. We conclude with the outlook on other related systems.",1512.02224v1
2016-12-16,Experimental verification of orbital engineering at the atomic scale: charge transfer and symmetry breaking in nickelate heterostructures,"Epitaxial strain, layer confinement and inversion symmetry breaking have
emerged as powerful new approaches to control the electronic and atomic-scale
structural properties in complex metal oxides. Nickelate heterostructures,
based on RENiO$_3$, where RE is a trivalent rare-earth cation, have been shown
to be relevant model systems since the orbital occupancy, degeneracy, and,
consequently, the electronic/magnetic properties can be altered as a function
of epitaxial strain, layer thickness and superlattice structure. One such
recent example is the tri-component LaTiO$_3$-LaNiO$_3$-LaAlO$_3$ superlattice,
which exhibits charge transfer and orbital polarization as the result of its
interfacial dipole electric field. A crucial step towards control of these
parameters for future electronic and magnetic device applications is to develop
an understanding of both the magnitude and range of the octahedral network's
response towards interfacial strain and electric fields. An approach that
provides atomic-scale resolution and sensitivity towards the local octahedral
distortions and orbital occupancy is therefore required. Here, we employ
atomic-resolution imaging coupled with electron spectroscopies and first
principles theory to examine the role of interfacial charge transfer and
symmetry breaking in a tricomponent nickelate superlattice system. We find that
nearly complete charge transfer occurs between the LaTiO$_3$ and LaNiO$_3$
layers, resulting in a Ni$^{2+}$ valence state. We further demonstrate that
this charge transfer is highly localized with a range of about 1 unit cell,
within the LaNiO$_3$ layers. The results presented here provide important
feedback to synthesis efforts aimed at stabilizing new electronic phases that
are not accessible by conventional bulk or epitaxial film approaches.",1612.05610v1
2017-07-13,Probing low noise at the MOS interface with a spin-orbit qubit,"The silicon metal-oxide-semiconductor (MOS) material system is
technologically important for the implementation of electron spin-based quantum
information technologies. Researchers predict the need for an integrated
platform in order to implement useful computation, and decades of advancements
in silicon microelectronics fabrication lends itself to this challenge.
However, fundamental concerns have been raised about the MOS interface (e.g.
trap noise, variations in electron g-factor and practical implementation of
multi-QDs). Furthermore, two-axis control of silicon qubits has, to date,
required the integration of non-ideal components (e.g. microwave strip-lines,
micro-magnets, triple quantum dots, or introduction of donor atoms). In this
paper, we introduce a spin-orbit (SO) driven singlet-triplet (ST) qubit in
silicon, demonstrating all-electrical two-axis control that requires no
additional integrated elements and exhibits charge noise properties equivalent
to other more model, but less commercially mature, semiconductor systems. We
demonstrate the ability to tune an intrinsic spin-orbit interface effect, which
is consistent with Rashba and Dresselhaus contributions that are remarkably
strong for a low spin-orbit material such as silicon. The qubit maintains the
advantages of using isotopically enriched silicon for producing a quiet
magnetic environment, measuring spin dephasing times of 1.6 $\mu$s using 99.95%
$^{28}$Si epitaxy for the qubit, comparable to results from other isotopically
enhanced silicon ST qubit systems. This work, therefore, demonstrates that the
interface inherently provides properties for two-axis control, and the
technologically important MOS interface does not add additional detrimental
qubit noise.",1707.04357v1
2020-01-22,Superconductivity by Hidden Spin Fluctuations in Electron-Doped Iron Selenide,"Berg, Metlitski and Sachdev, Science 338, 1606 (2012), have shown that the
exchange of hidden spin fluctuations by conduction electrons with two orbitals
can result in high-temperature superconductivity in copper-oxide materials. We
introduce a similar model for high-temperature iron-selenide superconductors
that are electron doped. Conduction electrons carry the minimal 3d xz and 3d yz
iron-atom orbitals. Low-energy hidden spin fluctuations at the checkerboard
wavevector Q_AF result from nested Fermi surfaces at the center and at the
corner of the unfolded (one-iron) Brillouin zone. Magnetic frustration from
super-exchange interactions via the selenium atoms stabilize hidden spin
fluctuations at Q_AF versus true spin fluctuations. At half filling, Eliashberg
theory based purely on the exchange of hidden spin fluctuations reveals a
Lifshitz transition to electron/hole Fermi surface pockets at the corner of the
folded (two-iron) Brillouin zone, but with vanishing spectral weights. The
underlying hidden spin-density wave groundstate is therefore a Mott insulator.
Upon electron doping, Eliashberg theory finds that the spectral weights of the
hole Fermi surface pockets remain vanishingly small, while the spectral weights
of the larger electron Fermi surface pockets become appreciable. This
prediction is therefore consistent with the observation of electron Fermi
surface pockets alone in electron-doped iron selenide by angle-resolved
photoemission spectroscopy (ARPES). Eliashberg theory also finds an instability
to S+- superconductivity at electron doping, with isotropic Cooper pairs that
alternate in sign between the visible electron Fermi surface pockets and the
faint hole Fermi surface pockets. Comparison with the isotropic energy gaps
observed in electron-doped iron selenide by ARPES and by scanning tunneling
microscopy (STM) is consistent with short-range hidden magnetic order.",2001.07908v3
2020-12-28,"Structural, optical and magnetic properties of nanostructured Cr-substituted Ni-Zn spinel ferrites synthesized by a microwave combustion method","Nanoparticles of Cr3+-substituted Ni-Zn ferrites with a general formula
Ni0.4Zn0.6-xCrxFe2O4 (x = 0.0 - 0.6) have been synthesized via a facile
microwave combustion route. The crystalline phase has been characterized by
XRD, TEM, FT-I and XPS revealing the spinel ferrite structure without extra
phases. Crystallite sizes of 23 - 32 nm as estimated by XRD analyses, after
corrections for crystal stains by Williamson-Hall method, are comparable to the
average particle sizes observed by TEM which indicates successfully synthesized
nanocrystals. Rietveld refinement analyses of the XRD patterns have inferred a
monotonic decrease behavior of the lattice parameter with Cr doping in
agreement with Vegard's law of solid solution series. Furthermore, cations
distribution with an increased inversion factor indicate the B-site preference
of Cr3+ ions. The oxidation states and cations distribution indicated by XPS
results imply the Cr3+ doping on the account of Zn2+ ions and a partial
reduction of Fe3+ to Fe2+ to keep the charge balance in a composition series of
(Ni2+)0.4(Zn2+, Cr3+)0.6(Fe2+, Fe3+)2(O2-)4. The optical properties were
explored by optical UV-Vis spectroscopy indicating allowed direct transitions
with band gap energy that decreases from 3.9 eV to 3.7 eV with Cr doping.
Furthermore, the photocatalytic activity for the degradation of methyl orange
(MO) dye was investigated showing largely enhanced photodecomposition up to 30%
of MO dye over Ni0.4Cr0.6Fe2O4 for 6 hours. A vibrating sample magnetometry
(VSM) measurements at room temperature show further enhancement in the
saturation magnetization of Ni0.4Zn0.6Fe2O4 , the highest in Ni-Zn ferrites,
from about 60 to 70 emu/g with the increase of Cr concentration up to x = 0.1,
while the coercivity shows a general increase in the whole range of Cr doping.",2012.14232v1
2019-01-15,Ferromagnetic Epitaxial μ-Fe$_{2}$O$_{3}$ on β-Ga$_{2}$O$_{3}$: A New Monoclinic form of Fe$_{2}$O$_{3}$,"Here we demonstrate a new monoclinic iron oxide phase
({\mu}-Fe$_{2}$O$_{3}$), epitaxially stabilized by growth on (010)
{\beta}-Ga$_{2}$O$_{3}$. Density functional theory (DFT) calculations find that
the lattice parameters of freestanding {\mu}-Fe$_{2}$O$_{3}$ are within ~1% of
those of {\beta}-Ga$_{2}$O$_{3}$ and that its energy of formation is comparable
to that of naturally abundant Fe$_{2}$O$_{3}$ polytypes. A superlattice of
{\mu}-Fe$_{2}$O$_{3}$/{\beta}-Ga$_{2}$O$_{3}$ is grown by plasma assisted
molecular beam epitaxy, with resulting high-resolution x-ray diffraction (XRD)
measurements indicating that the {\mu}-Fe$_{2}$O$_{3}$ layers are
lattice-matched to the substrate. The measured out-of-plane (b) lattice
parameter of 3.12 $\pm$ 0.4 {\AA} is in agreement with the predicted lattice
constants and atomic-resolution scanning transmission electron microscopy
(STEM) images confirm complete registry of the {\mu}-Fe$_{2}$O$_{3}$ layers
with {\beta}-Ga$_{2}$O$_{3}$. Finally, DFT modeling predicts that bulk
{\mu}-Fe$_{2}$O$_{3}$ is antiferromagnetic, while the interface region between
{\mu}-Fe$_{2}$O$_{3}$ and {\beta}-Ga$_{2}$O$_{3}$ leads to ferromagnetic
coupling between interface Fe$^{3+}$ cations selectively occupying tetrahedral
positions. Magnetic hysteresis persisting to room temperature is observed via
SQUID measurements, consistent with the computationally predicted interface
magnetism.",1901.04844v2
2020-09-25,Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4,"In the high spin-orbit coupled Sr2IrO4, the high sensitivity of the ground
state to the details of the local lattice structure shows a large potential for
the manipulation of the functional properties by inducing local lattice
distortions. We use epitaxial strain to modify the Ir-O bond geometry in
Sr2IrO4 and perform momentum-dependent Resonant Inelastic X-ray Scattering
(RIXS) at the metal and at the ligand sites to unveil the response of the low
energy elementary excitations. We observe that the pseudospin-wave dispersion
for tensile-strained Sr2IrO4 films displays large softening along the [h,0]
direction, while along the [h,h] direction it shows hardening. This evolution
reveals a renormalization of the magnetic interactions caused by a
strain-driven crossover from anisotropic to isotropic interactions between the
magnetic moments. Moreover, we detect dispersive electron-hole pair excitations
which shift to lower (higher) energies upon compressive (tensile) strain,
manifesting a reduction (increase) in the size of the charge gap. This behavior
shows an intimate coupling between charge excitations and lattice distortions
in Sr2IrO4, originating from the modified hopping elements between the t2g
orbitals. Our work highlights the central role played by the lattice degrees of
freedom in determining both the pseudospin and charge excitations of Sr2IrO4
and provides valuable information towards the control of the ground state of
complex oxides in the presence of high spin-orbit coupling.",2009.12262v1
2020-10-22,"Synthesis and physical properties of perovskite Sm$_{1-x}$Sr$_x$NiO$_3$ (x = 0, 0.2) and infinite-layer Sm$_{0.8}$Sr$_{0.2}$NiO$_2$ nickelates","Recently, superconductivity at about 9-15K was discovered in
Nd$_{1-x}$Sr$_x$NiO$_2$ infinite-layer thin films, which has stimulated
enormous interests in related rare-earth nickelates. Usually, the first step to
synthesize this 112 phase is to fabricate the RNiO$_3$ phase, however, it was
reported that the 113 phase is very difficult to be synthesized successfully
due to the formation of unusual Ni$^{3+}$ oxidation state. And the difficulty
of preparation is enhanced as the ionic radius of rare-earth element decreases.
In this work, we report the synthesis and investigation on multiple physical
properties of polycrystalline perovskites Sm$_{1-x}$Sr$_x$NiO$_3$ (x = 0, 0.2)
in which the ionic radius of Sm$^{3+}$ is smaller than that of Pr$^{3+}$ and
Nd$^{3+}$ in related superconducting thin films. The structural and
compositional analyses conducted by X-ray diffraction and energy dispersive
X-ray spectrum reveal that the samples mainly contain the perovskite phase of
Sm$_{1-x}$Sr$_x$NiO$_3$ with small amount of NiO impurities. Magnetization and
resistivity measurements indicate that the parent phase SmNiO$_3$ undergoes a
paramagnetic-antiferromagnetic transition at about 224K on a global insulating
background. In contrast, the Sr-doped sample Sm$_{0.8}$Sr$_{0.2}$NiO$_3$ shows
a metallic behavior from 300K down to about 12K, while below 12K the
resistivity exhibits a slight logarithmic increase. Meanwhile, from the
magnetization curves, we can see that a possible spin-glass state occurs below
12K in Sm$_{0.8}$Sr$_{0.2}$NiO$_3$. Using a soft chemical reduction method, we
also obtain the infinite-layer phase Sm$_{0.8}$Sr$_{0.2}$NiO$_2$ with square
NiO$_2$ planes. The compound shows an insulating behavior which can be
described by the three-dimensional variable-range-hopping model. And
superconductivity is still absent in the polycrystalline
Sm$_{0.8}$Sr$_{0.2}$NiO$_2$.",2010.11777v2
2022-02-16,Giant oscillatory tunnel magnetoresistance in CoFe/MgO/CoFe(001) junctions,"The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel
junctions (MTJs) is commonly used in many spintronic applications because the
effect can easily convert from local magnetic states to electric signals in a
wide range of device resistances. In this study, we demonstrated TMR ratios of
up to 631% at room temperature (RT), which is two or more times larger than
those used currently for magnetoresistive random access memory (MRAM) devices,
using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at
10 K, which corresponds to an effective tunneling spin polarization of 0.923.
The observed large TMR ratios resulted from the fine-tuning of atomic-scale
structures of the MTJs, such as crystallographic orientations and MgO interface
oxidation, in which the well-known Delta1 coherent tunneling mechanism for the
giant TMR effect is expected to be pronounced. However, behavior that is not
covered by the standard coherent tunneling theory was unexpectedly manifested;
i.e., (i) TMR saturation at a thick MgO barrier region and (ii) enhanced TMR
oscillation with a 0.32 nm period in MgO thickness. Particularly, the TMR
oscillatory behavior dominates the transport in a wide range of MgO
thicknesses; the peak-to-valley difference of the TMR oscillation exceeded 140%
at RT, attributable to the appearance of large oscillatory components in
resistance area product (RA). Further, we found that the oscillatory behaviors
of the TMR ratio and RA survive, even under a +-1 V bias voltage application,
indicating the robustness of the oscillation. Our demonstration of the giant
RT-TMR ratio will be an essential step for establishing spintronic
architectures, such as large-capacity MRAMs and spintronic artificial neural
networks. More essentially, the present observations can trigger us to revisit
the true TMR mechanism in crystalline MTJs.",2202.07847v1
2022-04-06,First principles investigation of anionic redox in bisulfate lithium battery cathodes,"The search for an alternative high-voltage polyanionic cathode material for
Li-ion batteries is vital to improve the energy densities beyond the
state-of-the-art, where sulfate frameworks form an important class of
high-voltage cathode materials due to the strong inductive effect of the
S$^{6+}$ ion. Here, we have investigated the mechanism of cationic and/or
anionic redox in Li$_x$M(SO$_4$)$_2$ frameworks (M = Mn, Fe, Co, and Ni and 0
$\leq$ x $\leq$ 2) using density functional calculations. Specifically, we have
used a combination of Hubbard $U$ corrected strongly constrained and
appropriately normed (SCAN+$U$) and generalized gradient approximation
(GGA+$U$) functionals to explore the thermodynamic (polymorph stability),
electrochemical (intercalation voltage), geometric (bond lengths), and
electronic (band gaps, magnetic moments, charge populations, etc.) properties
of the bisulfate frameworks considered. Importantly, we find that the anionic
(cationic) redox process is dominant throughout delithiation in the Ni (Mn)
bisulfate, as verified using our calculated projected density of states, bond
lengths, and on-site magnetic moments. On the other hand, in Fe and Co
bisulfates, cationic redox dominates the initial delithiation (1 $\leq$ x
$\leq$ 2), while anionic redox dominates subsequent delithiation (0 $\leq$ x
$\leq$ 2). In addition, evaluation of the crystal overlap Hamilton population
reveals insignificant bonding between oxidizing O atoms throughout the
delithiation process in the Ni bisulfate, indicating robust battery performance
that is resistant to irreversible oxygen evolution. Finally, we observe both
GGA+$U$ and SCAN+$U$ predictions are in qualitative agreement for the various
properties predicted. Our work should open new avenues for exploring lattice
oxygen redox in novel high voltage polyanionic cathodes, especially using the
SCAN+$U$ functional.",2204.02673v1
2022-06-22,Oxygen vacancy formation and electronic reconstruction in strained LaNiO$_3$ and LaNiO$_3$/LaAlO$_3$ superlattices,"By using DFT+U, we explore the formation of oxygen vacancies and their impact
on the electronic and magnetic structure in strained bulk LaNiO3 and
(LaNiO3)$_1$/(LaAlO3)$_1$(001) superlattices. For bulk LaNiO3, we find that
epitaxial strain induces a substantial anisotropy in the oxygen vacancy
formation energy. In particular, tensile strain promotes the selective
reduction of apical oxygen, which may explain why the recently observed
superconductivity of infinite-layer nickelates is limited to strained films.
For (LaNiO3)$_1$/(LaAlO3)$_1$(001) superlattices, the simulations reveal that
the NiO2 layer is most prone to vacancy formation, whereas the AlO2 layer
exhibits generally the highest formation energies. The reduction is
consistently endothermic, and a largely repulsive vacancy-vacancy interaction
is identified as a function of the vacancy concentration. The released
electrons are accommodated exclusively in the NiO2 layer, reducing the vacancy
formation energy in the AlO2 layer by 70% with respect to bulk LaAlO3. By
varying the vacancy concentration from 0% to 8.3% in the NiO2 layer at tensile
strain, we observe an unexpected transition from a localized
site-disproportionated (0.5%) to a delocalized (2.1%) charge accommodation, a
re-entrant site disproportionation leading to a metal-to-insulator transition
despite a half-filled majority-spin Ni $e_g$ manifold (4.2%), and finally a
magnetic phase transition (8.3%). While a band gap of up to 0.5 eV opens at
4.2% for compressive strain, it is smaller for tensile strain or the system is
metallic, which is in sharp contrast to the defect-free superlattice. The
strong interplay of electronic reconstructions and structural modifications
induced by oxygen vacancies in this system highlights the key role of an
explicit supercell treatment and exemplifies the complex response to defects in
artificial transition metal oxides.",2206.11028v1
2023-06-29,Optimization strategies developed on NiO for Heisenberg exchange coupling calculations using projector augmented wave based first-principles DFT+U+J,"High-performance batteries, heterogeneous catalysts and next-generation
photovoltaics often centrally involve transition metal oxides (TMOs) that
undergo charge or spin-state changes. Demand for accurate DFT modeling of TMOs
has increased in recent years, driving improved quantification and correction
schemes for approximate DFT's characteristic errors, notably those pertaining
to self-interaction and static correlation. Of considerable interest,
meanwhile, is the use of DFT-accessible quantities to compute parameters of
coarse-grained models such as for magnetism. To understand the interference of
error corrections and model mappings, we probe the prototypical Mott-Hubbard
insulator NiO, calculating its electronic structure in its antiferromagnetic
I/II and ferromagnetic states. We examine the pronounced sensitivity of the
first principles calculated Hubbard U and Hund's J parameters to choices
concerning Projector Augmented Wave (PAW) based population analysis, we
reevaluate spin quantification conventions for the Heisenberg model, and we
seek to develop best practices for calculating Hubbard parameters specific to
energetically meta-stable magnetic orderings of TMOs. Within this framework, we
assess several corrective functionals using in situ calculated U and J
parameters, e.g., DFT+U and DFT+U+J. We find that while using a straightforward
workflow with minimal empiricism, the NiO Heisenberg parameter RMS error with
respect to experiment was reduced to 13%, an advance upon the state-of-the-art.
Methodologically, we used a linear-response implementation for calculating the
Hubbard U available in the open-source plane-wave DFT code Abinit. We have
extended its utility to calculate the Hund's exchange coupling J, however our
findings are anticipated to be applicable to any DFT+U implementation.",2306.17148v2
2024-03-24,The nontrivial effects of annealing on superconducting properties of Nb single crystals,"The effect of annealing on the superconducting properties of niobium single
crystals cut from the same master boule was studied by local and global
magnetic measurements, as well as scanning tunneling microscopy (STM). The
formation of large hydride precipitates was observed in unannealed samples. The
variation in structural and magnetic properties was studied after annealing
under high vacuum at 800 C, 1400 C, and near the melting point of niobium (2477
C) for a few seconds. The initial samples had a high hydrogen content.
Polarized optics and magneto-optical studies show that the formation of large
niobium hydride precipitates is suppressed already by 800 C annealing. However,
the overall superconducting properties in the annealed samples did not improve
after annealing, and in fact, worsened. The superconducting transition
temperature decreased, the upper critical field increased, and the pinning
strength increased. Parallel studies were conducted using STM, where the sample
was annealed initially at 400 C, measured, annealed again at 1700 C, and
measured again. These studies revealed a ``dirty'' superconducting gap with a
significant spatial variation of tunneling conductance after annealing at 400
C. The clean gap was recovered after annealing at 1700 C. It is likely that
these results are due to oxygen redistribution near the surface, which is
always covered by oxide layers in as-grown crystals. Overall, the results
indicate that vacuum annealing at least up to 1400 C, while expected to remove
a large amount of hydrogen, introduces additional nanosized defects, perhaps
hydride precipitates, that act as efficient pair-breaking and pinning centers.",2403.16279v1
1995-11-08,On the Stereochemistry of the Cations in the Doping Block of Superconducting Copper-Oxides,"Metal-oxygen complexes containing Cu,- Tl-, Hg-, Bi- and Pb-cations are
electronically active in superconducting copper-oxides by stabilizing single
phases with enhanced $T_c$, whereas other metal-oxygen complexes deteriorate
copper-oxide superconductivity. Cu, Tl, Hg, Bi, Pb in their actual oxidation
states are closed shell $d^{10}$ or inert $s^2$ pair ions. Their electronic
configurations have a strong tendency to polarize the oxygen environment. The
closed shell $d$ ions with low lying $nd^{10}\leftrightarrow nd^9(n+1)s$
excitations form linear complexes through $d_{z^2}-s$ hybridization polarizing
the apical oxygens. Comparatively low $nd^9(n+1)s$ excitation energies
distinguish $\rm Cu^{1+,3+}, Tl^{3+}, Hg^{2+}$ from other closed shell $d^{10}$
ions deteriorating copper-oxide superconductivity, {\it e.g.} $\rm Zn^{2+}$.",9511041v2
1999-01-28,Diffusion-reaction in thermal growth of silicon oxide films on Si,"The thermal growth of silicon oxide films on Si in dry O2 is modelled as a
dynamical system, assuming that it is basically a diffusion-reaction
phenomenon. Relevant findings of the last decade are incorporated, as structure
and composition of the oxide/Si interface and O2 transport and reaction at
initial stages of growth. The present model departs from the well established
Deal and Grove framework (Deal, B.E. and Grove, A. S. General Relationship for
the Thermal Oxidation of Silicon, J. Appl. Phys. 36, 3770-3778 (1965))
indicating that its basic assumptions, steady-state regime and reaction between
O2 and Si at a sharp oxide/Si interface are only attained asymptotically.
Experimental growth kinetics by various authors, obtained for a wide range of
growth parameters are shown to collapse into one single curve when the scaling
properties of this model equations are explored.",9901335v1
2005-07-01,Silver-assisted growth of NdBa2Cu3O7-d thin films: A novel approach for the growth of superior quality ceramic oxide films,"We have grown NdBa2Cu3O7-d films under silver atomic flux by molecular beam
epitaxy, which show a drastic improvement in microstructure and also
crystallinity leading to 30 % enhancement in critical current density. The most
remarkable point is that the final film is free from silver. The key to our
process in achieving a silver-free film was the use of RF-activated oxygen that
oxidizes silver, nonvolatile, to silver oxide, volatile at the deposition
temperature. This process enables one to utilize the beneficial effects of
silver in the growth of oxide films and at the same time ensures that the final
film be free from silver, which is important for high-frequency applications.
This method can be made use in the growth of thin films of other complex oxide
materials.",0507006v1
2005-08-16,Low frequency noise statistics for the breakdown characterization of ultra-thin gate oxides,"We have investigated the statistics of low frequency noise in the tunneling
current of ultrathin oxides (2.5nm-4nm) in metal oxide semiconductor capacitors
as a function of the applied voltage stress. The statistical analysis includes
(i) non-Gaussianity (nG), which is a measure of the degree of temporal
correlation in the noise, and (ii) ratio of integrated noise power to the DC
leakage current (R). The occurrence of high peaks in nG indicates the
appearance of new percolation paths, and the subsequent conduction through
these paths is indicated by R. Our results show that the nG and R
characteristics are generic for the oxides of different thickness and growth
quality and have the potential, in conjunction with leakage itself, of being
used as a prognosticator of oxide reliability.",0508370v1
2006-09-05,First-principles statistical mechanics study of the stability of a sub-nanometer thin surface oxide in reactive environments: CO oxidation at Pd(100),"We employ a multiscale modeling approach to study the surface structure and
composition of a Pd(100) model catalyst in reactive environments. Under gas
phase conditions representative of technological CO oxidation (~1 atm, 300-600
K) we find the system on the verge of either stabilizing sub-nanometer thin
oxide structures or CO adlayers at the surface. Under steady-state operation
this suggests the presence or continuous formation and reduction of oxidic
patches at the surface, which could be key to understand the observable
catalytic function.",0609083v1
2006-12-04,Superconductivity and Disorder in High-Tc Materials: Crystalline Copper Oxides and Liquid Metallic Hydrogen,"Our goals are to assist a non-practitioner understand likely resolution of
the controversy about the boson that couples Cooper pairs in Cu oxides and to
consider if high temperature superconductivity (HTS) in solid oxides might be
related to predicted HTS in liquid metallic hydrogen (LMH) near 0 K. High
temperatures (T~Tc~!D~100 K, where Tc is superconducting critical temperature
and !D is the Debye temperature) induce phonon-phonon scattering in ordered
materials, which is sensitive to impurities and disorder. Experimental results
suggest the boson that couples Cooper pairs in Bi2SrCa2Cu2O8 is incoherent ion
vibration caused by disorder, which is observed from ~100 K down to 4 K.
Phonons are not well-defined in BSSCO and its coherence length is comparable to
the dimension of its unit cell (~1 nm), as for other oxides. Sr2CuO3+d (Tc=95
K) has a crystal structure that enables experimental demonstration that
disorder of apical oxygen atoms has a strong affect on Tc. Disorder in sold
oxides on an atomic scale and the temperature dependence of phonons at high
temperatures (T~!D) probably must be taken into account to understand HTS.
There are several reasons to believe that LMH will be a high temperature
superconductor and no known reason why LMH cannot be one.",0612069v1
2002-12-03,The group theory of oxidation II: Cosets of non-split groups,"The oxidation program of hep-th/0210178 is extended to cover oxidation of 3-d
sigma model theories on a coset G/H, with G non-compact (but not necessarily
split), and H the maximal compact subgroup. We recover the matter content, the
equations of motion and Bianchi identities from group lattice and Cartan
involution. Satake diagrams provide an elegant tool for the computations, the
maximal oxidation dimension, and group disintegration chains can be directly
read off. We give a complete list of theories that can be recovered from
oxidation of a 3 dimensional coset sigma model on G/H, where G is a simple
non-compact group.",0212024v2
2007-07-13,Ultrathin oxides: bulk-oxide-like model surfaces or unique films?,"To better understand the electronic and chemical properties of wide-gap oxide
surfaces at the atomic scale, experimental work has focused on epitaxial films
on metal substrates. Recent findings show that these films are considerably
thinner than previously thought. This raises doubts about the transferability
of the results to surface properties of thicker films and bulk crystals. By
means of density-functional theory and approximate GW corrections for the
electronic spectra we demonstrate for three characteristic wide-gap oxides
(silica, alumina, and hafnia) the influence of the substrate and highlight
critical differences between the ultrathin films and surfaces of bulk
materials. Our results imply that monolayer-thin oxide films have rather unique
properties.",0707.2031v1
2007-10-03,The effect of ozone oxidation on single-walled carbon nanotubes,"Exposing single-walled carbon nanotubes to room temperature UV-generated
ozone leads to an irreversible increase in their electrical resistance. We
demonstrate that the increased resistance is due to ozone oxidation on the
sidewalls of the nanotubes rather than at the end caps. Raman and x-ray
photoelectron spectroscopy show an increase in the defect density due to the
oxidation of the nanotubes. Using ultraviolet photoelectron spectroscopy we
show that these defects represent the removal of pi-conjugated electron states
near the Fermi level, leading to the observed increase in electrical
resistance. Oxidation of carbon nanotubes is an important first step in many
chemical functionalization processes. Since the oxidation rate is controllable
with short exposures, UV-generated ozone offers the potential for use as a
low-thermal budget processing tool.",0710.0803v1
2007-12-05,"The epitaxial-graphene/graphene-oxide junction, an essential step towards epitaxial graphene electronics","Graphene oxide (GO) flakes have been deposited to bridge the gap between two
epitaxial graphene electrodes to produce all-graphene devices. Electrical
measurements indicate the presence of Schottky barriers (SB) at the
graphene/graphene oxide junctions, as a consequence of the band-gap in GO. The
barrier height is found to be about 0.7 eV, and is reduced after annealing at
180 $^\circ$C, implying that the gap can be tuned by changing the degree of
oxidation. A lower limit of the GO mobility was found to be 850 cm$^2$/Vs,
rivaling silicon. {\it In situ} local oxidation of patterned epitaxial graphene
has been achieved.",0712.0820v2
2008-11-12,Synthesis of infinite-layer LaNiO2 films by metal-organic deposition,"We report the synthesis of infinite-layer LaNiO2 thin films by metal organic
decomposition. Our work is aimed to synthesize perovskite-like oxides with 3d9
electronic configuration, which is common to high-Tc copper oxides. The 3d9
configuration is very rare in oxides other than cuprates. Ni1+ oxides, even
though Ni1+ is an unusual oxidation state, may be one of very few candidates.
One example of the Ni1+ phases is infinite-layer LaNiO2. The bulk synthesis of
LaNiO2 is difficult, but we demonstrate in this article that the thin-film
synthesis of LaNiO2 by metal organic decomposition is rather easy. This is due
to the advantage of thin films with a large-surface-to-volume ratio, which
makes oxygen diffusion prompt. Resistivity measurements indicate that LaNiO2 is
essentially a metal but unfortunately with no trace of superconductivity yet.",0811.1858v1
2009-03-06,Ab initio structure modeling of complex thin-film oxides: thermodynamical stability of TiC/thin-film alumina,"We present an efficient and general method to identify promising candidate
configurations for thin-film oxides and to determine structural characteristics
of (metastable) thin-film structures using ab initio calculations. At the heart
of this method is the complexity of the oxide bulk structure, from which a
large number of thin films with structural building blocks, that is motifs,
from metastable bulk oxide systems can be extracted. These span a coarse but
well-defined network of initial configurations for which density functional
theory (DFT) calculations predict and implement dramatic atomic relaxations in
the corresponding, resulting thin-film candidates. The network of thin-film
candidates (for various film thicknesses and stoichiometries) can be ordered
according to their variation in ab initio total energy or in ab initio
equilibrium Gibbs free energy. Analysis of the relaxed atomic structures for
the most favored structures gives insight into the nature of stable and
metastable thin-film oxides. We investigate ultrathin alumina nucleated on TiC
as a model system to illustrate this method.",0903.1252v1
2009-03-25,"Adsorption of benzene, phenol, propane and carbonic acid molecules on oxidized Al(111) and alpha-Al2O3(0001) surfaces: A first-principles study","We present the results of ab initio calculations describing the adsorption of
certain small organic molecules on clean and oxidized Al(111) surfaces as well
as on the alpha-Al2O3(0001) surface. Our results show that adsorption of
benzene on the clean and oxidized Al(111) surfaces is generally weak, the
adsorption energy being at most around -0.5 eV per benzene molecule, and the
molecule adsorbed at a considerable distance from the surfaces. The adsorption
energy varies weakly at the different adsorption sites and as a function of the
oxygen coverage. For the alumina surface, we find no benzene adsorption at all.
We have also calculated a phenol molecule on the aluminium and alumina
surfaces, since it is similar to the benzene molecule. The results show a weak
adsorption for phenol on the alumina surface and no adsorption on the aluminium
or oxidized aluminium surfaces at all. For the propane molecule there is no
adsorption on either the oxidized aluminium or the alumina surface, whereas the
carbonic acid molecule binds strongly to the alumina but not to the aluminium
surface.",0903.4306v1
2009-04-14,Density functional theory study of Fe(II) adsorption and oxidation on goethite surfaces,"We study the interactions between Fe(II) aqua complexes and surfaces of
goethite (alpha-FeOOH) by means of density functional theory calculations
including the so-called Hubbard U correction to the exchange-correlation
functional. Using a thermodynamic approach, we find that (110) and (021)
surfaces in contact with aqueous solutions are almost equally stable, despite
the evident needlelike shape of goethite crystals indicating substantially
different reactivity of the two faces. We thus suggest that crystal anisotropy
may result from different growth rates due to virtually barrierless adsorption
of hydrated ions on the (021) but not on the (110) surface. No clear evidence
is found for spontaneous electron transfer from an adsorbed Fe(II) hex-aqua
complex to a defect-free goethite substrate. Crystal defects are thus inferred
to play an important role in assisting such electron transfer processes
observed in a recent experimental study. Finally, goethite surfaces are
observed to enhance the partial oxidation of adsorbed aqueous Fe(II) upon
reaction with molecular oxygen. We propose that this catalytic oxidation effect
arises from donation of electronic charge from the bulk oxide to the oxidizing
agent through shared hydroxyl ligands anchoring the Fe(II) complexes on the
surface.",0904.2111v1
2009-04-23,Microscopic origin of bipolar resistive switching of nanoscale titanium oxide thin films,"We report a direct observation of the microscopic origin of the bipolar
resistive switching behavior in nanoscale titanium oxide films. Through a
high-resolution transmission electron microscopy, an analytical TEM technique
using energy-filtering transmission electron microscopy and an in situ x-ray
photoelectron spectroscopy, we demonstrated that the oxygen ions piled up at
top interface by an oxidation-reduction reaction between the titanium oxide
layer and the top Al metal electrode. We also found that the drift of oxygen
ions during the on/off switching induced the bipolar resistive switching in the
titanium oxide thin films.",0904.3628v2
2011-01-29,Multi-component Transparent Conducting Oxides: Progress in Materials Modelling,"Transparent conducting oxides (TCOs) play an essential role in modern
optoelectronic devices through their combination of electrical conductivity and
optical transparency. We review recent progress in our understanding of
multi-component TCOs formed from solid-solutions of ZnO, In2O3, Ga2O3 and
Al2O3, with a particular emphasis on the contributions of materials modelling,
primarily based on Density Functional Theory. In particular, we highlight three
major results from our work: (i) the fundamental principles governing the
crystal structures of multi-component oxide structures including (In2O3)(ZnO)n,
named IZO, and (In2O3)m(Ga2O3)l(ZnO)n, named IGZO; (ii) the relationship
between elemental composition and optical and electrical behaviour, including
valence band alignments; (iii) the high-performance of amorphous oxide
semiconductors. From these advances, the challenge of the rational design of
novel electroceramic materials is discussed.",1101.5720v1
2012-03-12,Graphene coatings: An efficient protection from oxidation,"We demonstrate that graphene coating can provide an efficient protection from
oxidation by posing a high energy barrier to the path of oxygen atom, which
could have penetrated from the top of graphene to the reactive surface
underneath. Graphene bilayer, which blocks the diffusion of oxygen with a
relatively higher energy barrier provides even better protection from
oxidation. While an oxygen molecule is weakly bound to bare graphene surface
and hence becomes rather inactive, it can easily dissociates into two oxygen
atoms adsorbed to low coordinated carbon atoms at the edges of a vacancy. For
these oxygen atoms the oxidation barrier is reduced and hence the protection
from oxidation provided by graphene coatings is weakened. Our predictions
obtained from the state of the art first-principles calculations of electronic
structure, phonon density of states and reaction path will unravel how a
graphene can be used as a corrosion resistant coating and guide further studies
aiming at developing more efficient nanocoatings.",1203.2580v1
2012-06-25,Local Conduction at the BiFeO3-CoFe2O4 Tubular Oxide Interface,"In strongly correlated oxides, heterointerfaces, manipulating the
interaction, frustration, and discontinuity of lattice, charge, orbital, and
spin degrees of freedom, generate new possibilities for next generation
devices. In this study, we went back to examine the existing oxide
heterostructures and found the local conduction at the BiFeO3-CoFe2O4 vertical
interface. In such hetero-nanostructure, the tubular interface, surrounding
BiFeO3-CoFe2O4 vertical interface, can not only be the medium to the coupling
between phases, but also be a new state of the matter. Our study demonstrates a
novel concept on oxide interface design and opens a pathway alternative for the
explorations of diverse functionalities in complex oxide interfaces.",1206.5599v2
2012-09-28,Oxidation effects on graded porous silicon anti-reflection coatings,"Efficient anti-reflection coatings (ARC) improve the light collection and
thereby increase the current output of solar cells. By simple electrochemical
etching of the Si wafer, porous silicon (PS) layers with excellent broadband
anti-reflection properties can be fabricated. In this work, ageing of graded PS
has been studied using Spectroscopic Ellipsometry, Transmission Electron
Microscopy and X-ray Photoelectron Spectroscopy. During oxidation of PS
elements such as pure Si (Si$^0$), Si$_2$O (Si$^+$), SiO (Si$^{2+}$),
Si$_2$O$_3$ (Si$^{3+}$), and SiO$_2$ (Si$^{4+}$) are present. In addition both
hydrogen and carbon is introduced to the PS in the form of Si$_3$SiH and CO.
The oxide grows almost linearly with time when exposed to oxygen, from an
average thickness of 0 - 3.8 nm for the surface PS. The oxidation is then
correlated to the optical stability of multi-layered PS ARCs. It is found that
even after extensive oxidation, the changes in the optical properties of the PS
structures are small.",1210.0038v1
2012-11-28,Stability of xenon oxides at high pressures,"Xenon, which is quite inert under ambient conditions, may become reactive
under pressure. The possibility of formation of stable xenon oxides and
silicates in the interior of the Earth could explain the atmospheric missing
xenon paradox. Using the ab initio evolutionary algorithm, we predict the
thermodynamical stabilization of Xe-O compounds at high pressures (XeO, XeO2
and XeO3 at pressures above 83, 102 and 114 GPa, respectively). Our
calculations indicate large charge transfer in these oxides, suggesting that
large electronegativity difference and pressure are the key factors favoring
the formation of xenon compounds. Xenon compounds in the Earth's mantle,
however, cannot directly explain the missing xenon paradox: xenon oxides are
unstable in equilibrium with metallic iron in the Earth's lower mantle, while
xenon silicates are predicted to spontaneously decompose at all mantle
pressures (<136 GPa). This does not preclude Xe atoms from being retained in
defects of mantle silicates and oxides.",1211.6520v2
2013-01-15,CO oxidation on Pd(100) vs. PdO(sqrt5xsqrt5)R27^o: First-Principles Kinetic Phase Diagrams and Bistability Conditions,"We present first-principles kinetic Monte Carlo (1p-kMC) simulations
addressing the CO oxidation reaction at Pd(100) for gas-phase conditions
ranging from ultra-high vacuum (UHV) to ambient pressures and elevated
temperatures. For the latter technologically relevant regime there is a
long-standing debate regarding the nature of the active surface. The pristine
metallic surface, an ultra-thin (sqrt5xsqrt5)R27^o PdO(101) surface oxide, and
thicker oxide layers have each been suggested as the active state. We
investigate these hypotheses with 1p-kMC simulations focusing on either the
Pd(100) surface or the PdO(101) surface oxide and intriguingly obtain a range
of (T, p)-conditions where both terminations appear metastable. The predicted
bistability regime nicely ties in with oscillatory behavior reported
experimentally by Hendriksen and coworkers [Catal. Today 105, 234 (2005)].
Within this regime we find that both surface terminations exhibit very similar
intrinsic reactivity, which puts doubts on attempts to assign the catalytic
function to just one active state.",1301.3285v1
2013-01-26,Monitoring the formation of oxide apertures in micropillar cavities,"An imaging technique is presented that enables monitoring of the wet thermal
oxidation of a thin AlAs layer embedded between two distributed Bragg reflector
(DBR) mirrors in a micropillar. After oxidation we confirm by white light
reflection spectroscopy that high quality optical modes confined to a small
volume have been formed. The combination of these two optical techniques
provides a reliable and efficient way of producing oxide apertured micropillar
cavities for which the wet thermal oxidation is a critical fabrication step.",1301.6248v2
2013-03-16,The influence of residual oxidizing impurities on the synthesis of graphene by atmospheric pressure chemical vapor deposition,"The growth of graphene on copper by atmospheric pressure chemical vapor
deposition in a system free of pumping equipment is investigated. The emphasis
is put on the necessity of hydrogen presence during graphene synthesis and
cooling. In the absence of hydrogen during the growth step or cooling at slow
rate, weak carbon coverage, consisting mostly of oxidized and amorphous carbon,
is obtained on the copper catalyst. The oxidation originates from the
inevitable occurrence of residual oxidizing impurities in the reactor's
atmosphere. Graphene with appreciable coverage can be grown within the
vacuum-free furnace only upon admitting hydrogen during the growth step. After
formation, it is preserved from the destructive effect of residual oxidizing
contaminants once exposure at high temperature is minimized by fast cooling or
hydrogen flow. Under these conditions, micrometer-sized hexagon-shaped graphene
domains of high structural quality are achieved.",1303.3951v2
2013-06-11,A Preliminary Study of Oxidation of Lignin from Rubber Wood to Vanillin in Ionic Liquid Medium,"In this study, lignin was oxidised to vanillin by means of oxygen in ionic
liquid (1,3-dimethylimidazolium methylsulphate) medium. The parameters of the
oxidation reaction that have been investigated were the following:
concentration of oxygen (5, 10, 15 and 20 ft3 h-1), reaction time (2, 4, 6, 8
and 10 h) and reaction temperature (25, 40, 60, 80 and 100{\deg}C). The Fourier
transform infrared spectroscopy, high performance liquid chromatography and
ultraviolet-visible analyses were used to characterise the product. The results
revealed vanillin as the product obtained via the oxidation reaction. The
optimum parameters of vanillin production were 20 ft3 h-1 of oxygen for 10 h at
100{\deg}C. In conclusion, 1,3-dimethylimidazolium methylsulphate could be used
as an oxidation reaction medium for the production of vanillin from rubber wood
lignin.",1306.2442v1
2013-07-24,Origin of Anomalous Water Permeation through Graphene Oxide Membrane,"Water inside the low dimensional carbon structures has been considered
seriously owing to fundamental interest in its flow and structures as well as
its practical impact. Recently, the anomalous perfect penetration of water
through graphene oxide membrane was demonstrated although the membrane was
impenetrable for other liquids and even gases. The unusual auxetic behavior of
graphene oxide in the presence of water was also reported. Here, based on
first-principles calculations, we establish atomistic models for hybrid systems
composed of water and graphene oxides revealing the anomalous water behavior
inside the stacked graphene oxides. We show that formation of hexagonal ice
bilayer in between the flakes as well as melting transition of ice at the edges
of flakes are crucial to realize the perfect water permeation across the whole
stacked structures. The distance between adjacent layers that can be controlled
either by oxygen reduction process or pressure is shown to determine the water
flow thus highlighting a unique water dynamics in randomly connected
two-dimensional spaces.",1307.6312v1
2014-08-03,Thermopower enhancement by fractional layer control in 2D oxide superlattices,"We have investigated two-dimensional thermoelectric properties in transition
metal oxide heterostructures. In particular, we adopted an unprecedented
approach to direct tuning of the 2D carrier density using fractionally
{\delta}-doped oxide superlattices. By artificially controlling the carrier
density in the 2D electron gas that emerges at a LaxSr1-xTiO3 {\delta}-doped
layer, we demonstrate that a thermopower as large as 408 {\mu}V K-1 can be
reached. This approach also yielded a power factor of the 2D carriers 117
{\mu}Wcm-1K-2, which is one of the largest reported values from transition
metal oxide based materials. The promising result can be attributed to the
anisotropic band structure in the 2D system, indicating that {\delta}-doped
oxide superlattices can be a good candidate for advanced thermoelectrics.",1408.0449v1
2014-10-27,Band-gap engineering at a semiconductor - crystalline oxide interface,"The epitaxial growth of crystalline oxides on semiconductors provides a
pathway to introduce new functionalities to semiconductor devices. Key to
electrically coupling crystalline oxides with semiconductors to realize
functional behavior is controlling the manner in which their bands align at
interfaces. Here we apply principles of band gap engineering traditionally used
at heterojunctions between conventional semiconductors to control the band
offset between a single crystalline oxide and a semiconductor. Reactive
molecular beam epitaxy is used to realize atomically abrupt and structurally
coherent interfaces between SrZr$_{x}$Ti$_{1-x}$O$_3$ and Ge, in which the
band-gap of the former is enhanced with Zr content $x$. We present structural
and electrical characterization of SrZr$_{x}$Ti$_{1-x}$O$_3$-Ge heterojunctions
for $x$ = 0.2 to 0.75 and demonstrate the band offset can be tuned from type-II
to type-I, with the latter being verified using photoemission measurements. The
type-I band offset provides a platform to integrate the dielectric,
ferroelectric and ferromagnetic functionalities of oxides with semiconducting
devices.",1410.7327v1
2015-06-19,Inverse spin Hall effect in a complex ferromagnetic oxide heterostructure,"Complex oxide heterostructures are hot candidates for post CMOS
multi-functional devices. Especially in spintronics applications ferromagnetic
oxides may play a key role because they can exhibit extraordinary high spin
polarization. Indeed, there are already plenty of examples in spintronics,
notably in the area of spin pumping and inverse spin Hall effect (ISHE)
\cite{Azevedo2011, Czeschka2011, Hahn2013, Obstbaum2014}. Although complex
oxides have been used in these experiments as a source of spin currents, they
have never been demonstrated to act as a spin sink that exhibits ISHE. Here we
show that in a heterostructure consisting of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$
(LSMO) and SrRuO$_{3}$ (SRO) the low temperature ferromagnet SRO can act as a
spin sink and exhibit a sizeable ISHE which persists even below its Curie
temperature. This result opens up new possibilities for application of all
oxide heterostructures in spintronics and may significantly extend the research
on spin Hall effect and related phenomena.",1506.05921v1
2015-06-24,Resonant tunneling in a quantum oxide superlattice,"Resonant tunnelling is a quantum mechanical process that has long been
attracting both scientific and technological attention owing to its intriguing
underlying physics and unique applications for high-speed electronics. The
materials system exhibiting resonant tunnelling, however, has been largely
limited to the conventional semiconductors, partially due to their excellent
crystalline quality. Here we show that a deliberately designed transition metal
oxide superlattice exhibits a resonant tunnelling behaviour with a clear
negative differential resistance. The tunnelling occurred through an atomically
thin, lanthanum {\delta}-doped SrTiO3 layer, and the negative differential
resistance was realized on top of the bipolar resistance switching typically
observed for perovskite oxide junctions. This combined process resulted in an
extremely large resistance ratio (~10^5) between the high and low-resistance
states. The unprecedentedly large control found in atomically thin
{\delta}-doped oxide superlattices can open a door to novel oxide-based
high-frequency logic devices.",1506.07583v1
2015-09-28,Solid-state chemistry of glassy antimony oxides,"The amorphous phases of antimony oxide at three different oxidation levels
have been investigated by {\it ab initio} molecular-dynamics calculations using
a simulated `melt-quench' approach. The atomic and electronic structure of the
amorphous phases are analyzed and compared to their crystalline counterparts.
The amorphous structure of the trioxide ({\it a\,}--Sb$_2$O$_3$) resembles the
$\beta$-phase of the crystalline form (valentinite), in agreement with previous
observations. In the relaxed athermal structure, however, more
senarmontite-like structural features are apparent. The phase diagram of the
amorphous phases with respect to oxygen chemical potential has been calculated
within the framework of {\it ab initio} thermodynamics. At elevated oxidation
levels, the resulting tetraoxide and pentoxide materials show distinct
variation in electronic structure compared to the trioxide, with the electronic
density of states indicating a narrowing of the electronic gap with increasing
oxidation level.",1509.08192v1
2015-10-29,Degenerate epitaxy-driven defects in monolayer silicon oxide onto ruthenium,"The structure of the ultimately-thin crystalline allotrope of silicon oxide,
prepared onto a ruthenium surface, is unveiled down to atomic scale with
chemical sensitivity, thanks to high resolution scanning tunneling microscopy
and first principle calculations. An ordered oxygen lattice is imaged which
coexists with the two-dimensional monolayer oxide. This coexistence signals a
displacive transformation from an oxygen reconstructed-Ru(0001) to silicon
oxide, along which latterally-shifted domains form, each with equivalent and
degenerate epitaxial relationships with the substrate. The unavoidable
character of defects at boundaries between these domains appeals for the
development of alternative methods capable of producing single-crystalline
two-dimensional oxides.",1510.08607v1
2015-11-21,Single Crystal Functional Oxides on Silicon,"Single crystalline thin films of complex oxides show a rich variety of
functional properties such as ferroelectricity, piezoelectricity, ferro and
antiferromagnetism etc. that have the potential for completely new electronic
applications (1-2). Direct synthesis of such oxides on Si remains challenging
due to the fundamental crystal chemistry and mechanical incompatibility of
dissimilar interfaces (3-16). Here we report integration of thin (down to 1
unit cell) single crystalline, complex oxide films onto Si substrates, by
epitaxial transfer at room temperature. In a field effect transistor using a
transferred Pb0.2Zr0.8TiO3 (PZT) layer as the gate insulator, we demonstrate
direct reversible control of the semiconductor channel charge with polarization
state. These results represent the realization of long pursued but yet to be
demonstrated single crystal functional oxides on-demand on silicon.",1511.06832v1
2016-01-27,Graphene oxide and adsorption of chloroform: a density functional study,"Chlorinated hydrocarbon compounds are of environmental concerns, since they
are toxic to humans and other mammals, are widespread, and exposure is hard to
avoid. Understanding and improving methods to reduce the amount of the
substances is important. We present an atomic-scale calculational study of the
adsorption of chlorine-based substance chloroform (CHCl3) on graphene oxide, as
a step in estimating the capacity of graphene oxide for filtering out such
substances, e.g., from drinking water. The calculations are based on density
functional theory (DFT), and the recently developed consistent-exchange
functional for the van der Waals density-functional method (vdW-DF-cx) is
employed. We obtain values of the chloroform adsorption energy varying from
roughly 0.2 to 0.4 eV per molecule. This is comparable to previously found
results for chloroform adsorbed directly on clean graphene, using similar
calculations. In a wet environment, like filters for drinking water, the
graphene will not stay clean and will likely oxidize, and thus adsorption onto
graphene oxide, rather than clean graphene, is a more relevant process to
study.",1601.07329v1
2016-02-22,Laser-assisted Oxidation of Multi-layer Tungsten Diselenide Nanosheets,"We report the structural and electrical characterization of tungsten oxides
formed by illuminating multi-layer tungsten diselenide (WSe2) nanosheets with
an intense laser beam in the ambient environment. A noninvasive microwave
impedance microscope (MIM) was used to perform electrical imaging of the
samples. The local conductivity ~100 S/m of the oxidized product, measured by
the MIM and conventional transport experiments, is much higher than that of the
pristine WSe2, suggesting the formation of sub-stoichiometric WO3-x
polycrystals with n-type carriers. With further efforts to improve the
conductivity of the oxides, the laser-assisted oxidation process may be useful
for patterning conductive features on WSe2 or forming electrical contacts to
various transition metal dichalcogenides.",1602.06639v1
2016-07-08,High Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides,"At interfaces between complex oxides it is possible to generate electronic
systems with unusual electronic properties, which are not present in the
isolated oxides. One important example is the appearance of superconductivity
at the interface between insulating oxides, although, until now, with very low
Tc. We report the occurrence of high Tc superconductivity in the bilayer
CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to
obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized
between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case
extra oxygen ions can be incorporated in the interface Ca plane, acting as
apical oxygen for Cu and providing holes to the CuO2 planes. A detailed hole
doping spatial profile has been obtained by STEM/EELS at the O K-edge, clearly
showing that the (super)conductivity is confined to about 1-2 CaCuO2 unit cells
close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3
interface can be extended to multilayered high Tc cuprates, contributing to
explain the dependence of Tc on the number of CuO2 planes in these systems.",1607.02449v1
2016-10-27,Hybrid electrochromic device with Tungsten oxide (WO3-x) and nafion membrane: performance with varying tungsten oxide thickness,"Electrochromic devices, which dynamically change color under the applied
potential, are widely studied because of its wide range of applications such as
energy-efficient smart windows, rear view mirrors and display devices etc. In
this study we are reporting four layer electrochromic device based on tungsten
oxide as a electrochromic layer and nafion membrane as a ionic conducting
layer. Nafion membranes are generally used in fuel cell applications because of
its high ionic conductivity and high optical transparency which is suitable for
electrochromic device to attain higher efficiencies. We have prepared an
electrochromic device by sandwiching ITO coated glass and WO3 coated ITO thin
film between nafion membrane. The overall structure of the device is
Glass/ITO/WO3/Nafion/ITO/Glass. We deposited tungsten oxide thin films with
different thickness on ITO coated glass substrate at room temperature by using
reactive DC Magnetron sputtering and we studied the performance of the
electrochromic device with the function of thickness. We have observed that
electrochromic efficiency is increasing with increase in the tungsten oxide
layer thickness. The efficiency of the device increased from 24.8 cm2/C to
184.3 cm2/C.",1610.08807v1
2017-08-05,Copper-oxide Nanowires based Humidity Sensor,"This paper presents investigated results of copper-oxide nanowires used as a
humidity sensor. Copper-oxide nanowires films were grown over cross-comb type
gold electrodes on a SiO2 substrate using thermal annealing technique, and its
humidity sensitive characteristics were investigated through resistance across
the gold electrodes. These copper-oxide nanowires films revealed high
sensitivity and long-term stability with fast response time. It was found that
resistance across gold electrodes of the fabricated sensor decreases with
increase in humidity almost linearly on a logarithmic scale. It appears that
copper-oxide nanowires can be used as low-cost humidity sensor with high output
reliability and reproduction rate. The observations were carried out at room
temperature (RT) and relative humidity (RH) in the range of 6% to 97%.",1708.01720v1
2018-02-07,"Stability of boron-doped graphene/copper interface: DFT, XPS and OSEE studies","Two different types of boron-doped graphene/copper interfaces synthesized
using two different flow rates of Ar through the bubbler containing the boron
source were studied. X-ray photoelectron spectra (XPS) and optically stimulated
electron emission (OSEE) measurements have demonstrated that boron-doped
graphene coating provides a high corrosion resistivity of Cu-substrate with the
light traces of the oxidation of carbon cover. The density functional theory
calculations suggest that for the case of substitutional (graphitic)
boron-defect only the oxidation near boron impurity is energetically favorable
and creation of the vacancies that can induce the oxidation of copper substrate
is energetically unfavorable. In the case of non-graphitic boron defects
oxidation of the area, a nearby impurity is metastable that not only prevent
oxidation but makes boron-doped graphene. Modeling of oxygen reduction reaction
demonstrates high catalytic performance of these materials.",1802.02345v1
2018-04-13,Subsurface Cation Vacancy Stabilization of the Magnetite (001) Surface,"Iron oxides play an increasingly prominent role in heterogeneous catalysis,
hydrogen production, spintronics and drug delivery. The surface or material
interface can be performance limiting in these applications, so it is vital to
determine accurate atomic-scale structures for iron oxides and understand why
they form. Using a combination of quantitative low-energy electron diffraction,
scanning tunneling microscopy, and density functional theory calculations, we
show that an ordered array of subsurface iron vacancies and interstitials
underlies the well-known (rt2xrt2)R45{\deg} reconstruction of Fe3O4(001). This
hitherto unobserved stabilization mechanism occurs because the iron oxides
prefer to redistribute cations in the lattice in response to oxidizing or
reducing environments. Many other metal oxides also achieve stoichiometric
variation in this way, so such surface structures are likely commonplace.",1804.04836v1
2018-11-06,"Effect of pre-oxidation treatments on the structural, microstructural, and chemical properties of (Ni,Pt)Al systems","The effect of isothermal pre-oxidation treatments on the \b{eta}-(Ni,Pt)Al +
Ren\'e N5 system degradation is here reported. The oxidation treatments were
carried out from 900 (mostly {\theta}-Al2O3 growing conditions) to 1200{\deg}C
(mainly {\alpha}-Al2O3 growing conditions) for 5 h, under a purified Ar-stream
with a fixed pO2= 1 x 10-5 atm. Results are discussed based on the correlation
between the structural, microstructural and chemical properties of the
\b{eta}-(Ni,Pt)Al BC showing that pre-oxidation parameters have an important
effect on the multi-elemental counter diffusion phenomena along BC. For
instance, a significant BC+IDZ thickness increase of 55% at 1200 {\deg}C was
observed with respect to as-received sample just after 5 h of oxidation
resulting in a severe BC degradation.",1811.02176v1
2019-05-07,Mechanism of CO-oxidation on Pd/CeO2(100): The unique surface-structure of CeO2(100) and the role of peroxide,"Understanding the atomic mechanism of low-temperature CO oxidation on a
heterogeneous catalyst is challenging. We performed density functional theory
(DFT) calculations to identify the surface structure and reaction mechanism
responsible for low-temperature CO oxidation on Pd/CeO2 (100) surfaces. DFT
calculations reveal the formation of a unique zigzag chain structure by the
oxygen and Ce atoms of the topmost surface of CeO2(100) with Pd atoms located
between the zigzag chains. O2 adsorbed on such Pd atoms is stable in the
presence of CO but plays a very important role in lowering the activation
barrier for low-temperature CO oxidation by forming a square-planar PdO4
structure and facilitating further O2 adsorption. In-situ Raman spectroscopy
studies confirm the adsorbed oxygen species to be peroxides. The calculated
activation barrier for CO oxidation, based on the mechanism suggested by these
unique structures and peroxides, is 31.2 kJ/mol, in excellent agreement with
our experimental results.",1905.02398v1
2013-08-20,Quantifying Oxidation Rates of Carbon Monoxide on a Pt/C Electrode,"The electrochemical oxidation of carbon monoxide adsorbed (COad) on
platinum-on-carbon electrodes was studied via a methodology in which
pre-adsorbed CO was partially oxidized by applying potentiostatic pulses for
certain durations. The residual COad was analyzed using stripping voltammetry
that involved the deconvolution of COad oxidation peaks of voltammograms to
quantify the weakly and strongly bound species of COad. The data obtained for
various potentials and temperatures were fit to a model based on a nucleation
and growth mechanism. The resulting fit produced potential- and
temperature-dependent rate parameters that provided insight into the oxidation
mechanism of the two COad species. Irrespective of the applied potential or
temperature, the concentration of weakly bound COad species decreased
exponentially with time. In contrast, the strongly bound COad species showed a
gradual transition of mechanisms, from progressive nucleation at relatively low
potentials to exponential decay at high potentials.",1308.4317v1
2018-05-02,Local anodic oxidation on hydrogen-intercalated graphene layers: oxide composition analysis and role of the silicon carbide substrate,"We investigate nanoscale local anodic oxidation (LAO) on
hydrogen-intercalated graphene grown by controlled sublimation of silicon
carbide (SiC). Scanning probe microscopy (SPM) was used as a lithographic and
characterization tool in order to investigate the local properties of the
nanofabricated structures. The anomalous thickness observed after the graphene
oxidation process is linked to the impact of LAO on the substrate. Micro-Raman
spectroscopy was employed to demonstrate the presence of two oxidation regimes
depending on the applied bias. We show that partial and total etching of
monolayer graphene can be achieved by tuning the bias voltage during LAO.
Finally, a complete compositional characterization was achieved by scanning
electron microscopy and energy dispersive spectroscopy (EDS).",1805.00673v1
2018-05-07,Chemistry with Graphene and Graphene Oxide - Challenges for Synthetic Chemists,"The chemical production of graphene as well as its controlled wet- chemical
modification is a challenge for synthetic chemists and the characterization of
reaction products requires sophisticated analytic methods. In this review we
first describe the structure of graphene and graphene oxide. We then outline
the most important synthetic methods which are used for the production of these
carbon based nanomaterials. We summarize the state-of-the-art for their
chemical functionalization by non-covalent and covalent approaches. We put
special emphasis on the differentiation of the terms graphite, graphene,
graphite oxide and graphene oxide. An improved fundamental knowledge about the
structure and the chemical properties of graphene and graphene oxide is an
important prerequisite for the development of practical applications.",1805.03088v1
2018-05-08,Reduced-Graphene-Oxide with Traces of Iridium or Gold as Active Support for Pt Catalyst at Low Loading during Oxygen Electroreduction,"Chemically-reduced graphene-oxide-supported gold or iridium nanoparticles are
considered here as active carriers for dispersed platinum with an ultimate goal
of producing improved catalysts for electroreduction of oxygen in acid medium.
Comparison is made to the analogous systems not utilizing reduced graphene
oxide. High electrocatalytic activity of platinum (loading up to 30 {\mu}g
cm-2) dispersed over the reduced-graphene oxide-supported Au (up to 30 {\mu}g
cm-2) or Ir (up to 1.5 {\mu}g cm-2) nanoparticles toward reduction of oxygen
has been demonstrated using cyclic and rotating ring-disk electrode (RRDE)
voltammetric experiments. Among important issues are possible activating
interactions between gold and the support, as well as presence of structural
defects existing on poorly organized graphitic structure of reduced graphene
oxide. The RRDE data are consistent with decreased formation of hydrogen
peroxide.",1805.03147v1
2009-12-01,Oxidation States of Graphene: Insights from Computational Spectroscopy,"When it is oxidized, graphite can be easily exfoliated forming graphene oxide
(GO). GO is a critical intermediate for massive production of graphene, and it
is also an important material with various application potentials. With many
different oxidation species randomly distributed on the basal plane, GO has a
complicated nonstoichiometric atomic structure that is still not well
understood in spite of of intensive studies involving many experimental
techniques. Controversies often exist in experimental data interpretation. We
report here a first principles study on binding energy of carbon 1s orbital in
GO. The calculated results can be well used to interpret experimental X-ray
photoelectron spectroscopy (XPS) data and provide a unified spectral
assignment. Based on the first principles understanding of XPS, a GO structure
model containing new oxidation species epoxy pair and epoxy-hydroxy pair is
proposed. Our results demonstrate that first principles computational
spectroscopy provides a powerful means to investigate GO structure.",0912.0085v1
2012-04-25,A Computational Investigation of the Catalytic Properties of Graphene Oxide: Exploring Mechanisms Using DFT Methods,"Here we describe a computational study undertaken in an effort to elucidate
the reaction mechanisms behind the experimentally observed oxidations and
hydrations catalyzed by graphene oxide (GO). Using the oxidation of benzyl
alcohol to benzaldehyde as a model reaction, density functional theory (DFT)
calculations revealed that this reactivity stemmed from the transfer of
hydrogen atoms from the organic molecule to the GO surface. In particular,
neighbouring epoxide groups decorating GO's basal plane were ring-opened,
resulting in the formation of diols, followed by dehydration. Consistent with
the experimentally-observed dependence of this chemistry on molecular oxygen,
our calculations revealed that the partially reduced catalyst was able to be
recharged by molecular oxygen, allowing for catalyst turnover. Functional
group-free carbon materials, such as graphite, were calculated to have
substantially higher reaction barriers, indicating that the high chemical
potential and rich functionality of GO are necessary for the observed
reactivity.",1204.5557v1
2012-04-28,Low Frequency Dielectric Loss of Metal/Insulator/Organic Semiconductor Junctions in Ambient Conditions,"The complex admittance of metal/oxide/pentacene thin film junctions is
investigated under ambient conditions. At low frequencies, a contribution
attributed to proton diffusion through the oxide is seen. This diffusion is
shown to be anomalous and is believed to be also at the origin of the bias
stress effect observed in organic field effect transistors. At higher
frequencies, two dipolar contributions are evidenced, attributed to defects
located one at the organic/oxide interface or within the organic, and the other
in the bulk of the oxide. These two dipolar responses show different dynamic
properties that manifest themselves in the admittance in the form of a Debye
contribution for the defects located in the oxide, and of a Cole-Cole
contribution for the defects related to the organic.",1204.6406v1
2016-08-22,Cohesive energy and structural parameters of binary oxides of groups IIA and IIIB from diffusion quantum Monte Carlo,"We have applied the diffusion quantum Monte Carlo (DMC) method to calculate
the cohesive energy and the structural parameters of the binary oxides CaO,
SrO, BaO, Sc2O3, Y2O3 and La2O3. The aim of our calculations is to
systematically quantify the accuracy of the DMC method to study this type of
metal oxides. The DMC results were compared with local, semi-local and hybrid
Density Functional Theory (DFT) approximations as well as with experimental
measurements. The DMC method yields cohesive energies for these oxides with a
mean absolute deviation from experimental measurements of 0.18(2) eV, while
with local, semi-local and hybrid DFT approximations the deviation is 3.06,
0.94 and 1.23 eV, respectively. For lattice constants, the mean absolute
deviation in DMC, local, semi-local and hybrid DFT approximations, are
0.017(1), 0.07, 0.05 and 0.04 {\AA}, respectively. DMC is highly accurate
method, outperforming the DFT approximations in describing the cohesive
energies and structural parameters of these binary oxides.",1608.06321v1
2018-01-22,Transfer of Graphene with Protective Oxide Layers,"Transfer of graphene, grown by Chemical Vapor Deposition (CVD), to a
substrate of choice, typically involves deposition of a polymeric layer
(typically, poly(methyl methacrylate, PMMA or polydimethylsiloxane, PDMS).
These polymers are quite hard to remove without leaving some residues behind.
Here we study a transfer of graphene with a protective thin oxide layer. The
thin oxide layer is grown by Atomic Deposition Layer (ALD) on the graphene
right after the growth stage on Cu foils. One can further aid the
oxide-graphene transfer by depositing a very thin polymer layer on top of the
composite (much thinner than the usual thickness) following by a more
aggressive polymeric removal methods, thus leaving the graphene intact. We
report on the nucleation growth process of alumina and hafnia films on the
graphene, their resulting strain and on their optical transmission. We suggest
that hafnia is a better oxide to coat the graphene than alumina in terms of
uniformity and defects.",1801.07338v2
2018-09-13,Dendritic Oxide Growth in Zero-Valent Iron Nanofilms Revealed by Atom Probe Tomography,"Atom probe tomography (APT) analysis of chemically pure nanofilms of
zero-valent iron (Fe(0), or ZVI) and their thermal oxide nano-overlayers
reveals the presence of dendritic iron oxide features that extend from the
oxide nano-overlayer surface into the ZVI bulk. The dendrites are observed by
APT to be in the 5 nm x 10 nm size range and form quickly under natural
atmospheric conditions. Their growth into the ZVI lalyer is, within the limit
of our three-month long study, self-limiting (i.e. their initial growth appears
to quickly discontinue). The atomistic views presented here shed first light on
the atmospheric corrosion process of Fe(0)-bearing engineered nanostructures
and their surfaces in the limit of low bulk impurities. Possible roles of the
newly identified oxidized iron dendrites are also discussed in the context of
passivation processes limiting technological applications of Fe(0).",1809.04909v2
2018-10-24,Calculation of the equilibrium composition of metallic and oxide melts during their interaction,"Thermodynamic equilibrium can be sometimes reached at the interaction between
metal and oxide melts in high temperature welding and metallurgical processes.
Calculation of equilibrium phase composition is also one of the stages (along
with kinetics analysis) of building an end-to-end physical and chemical model
of real processes. Developing a thermodynamic model of high temperature
processes is described in many scientific sources (1-18). Thermodynamic
patterns of oxidation-reduction reactions on the metal-slag melt interface are
also taken into account when building phenomenological models of real welding,
facing, and metallurgical processes (19-30). This paper deals with calculating
an equilibrium phase composition for a specific reaction. A method proposed
herein also takes into account an interaction among any number of chemical
reactions in the metal-oxide melt interface that form an equilibrium phase
composition",1810.10163v1
2018-10-24,Simulation of metal-oxide melt interaction in view of kinetics of chemical reactions in the interphase boundary,"Thermodynamics analysis of oxidation-reduction reactions between metal melt
and slag (1) provides answers to certain practical issues such as the path of
specific chemical reactions, final (equilibrium) phase composition, and the
elements that are reduced and oxidized at given physical parameters. Although
considerable, this is obviously not enough to analyze real technological
systems, because the required equilibrium cannot be normally achieved despite
high temperatures of welding and metallurgical processes. Hence, a dynamic
problem has to be resolved here, which is calculating phase composition as a
function of time. This cannot be achieved without knowing the rates of element
concentration changes in each and every phase, and also technological
parameters of the process. Relevant studies are detailed in(2-19). This paper
analyzes special kinetic features of physical and chemical processes in the
metal and oxide melt interface.",1810.10166v1
2019-06-19,Correlation between the Dzyaloshinskii-Moriya interaction and the orbital angular momentum at an oxide / ferromagnet interface,"We report on the Dzyaloshinskii-Moriya (DMI) interaction at the interface
between a ferromagnet and an oxide. We demonstrate experimentally that oxides
can give rise to DMI. By comparison of systems comprised of Pt/Co90Fe10/Oxide
and Cu/Co90Fe10/Oxide, we also show how oxidation of one interface can enhance
and add to the total DMI of that generated by the Pt interface. This is due to
the fact that the DMI on both interfaces promotes left-handed chirality.
Finally, by use of ferromagnetic resonance spectroscopy, we show that the DMI
and the spectroscopic splitting factor, which is a measure of the orbital
momentum, are correlated. This indicates the importance of hybridization and
charge transfer at the oxide interface for the DMI.",1906.08395v1
2019-10-27,Mechanoradicals in tensed tendon collagen as a new source of oxidative stress,"As established nearly a century ago, mechanoradicals originate from homolytic
bond scission in polymers. The existence, nature and biological relevance of
mechanoradicals in proteins, instead, are unknown. We here show that mechanical
stress on collagen produces radicals and subsequently reactive oxygen species,
essential biological signaling molecules. Electron-paramagnetic resonance (EPR)
spectroscopy of stretched rat tail tendon, atomistic Molecular Dynamics
simulations and quantum calculations show that the radicals form by bond
scission in the direct vicinity of crosslinks in collagen. Radicals migrate to
adjacent clusters of aromatic residues and stabilize on oxidized tyrosyl
radicals, giving rise to a distinct EPR spectrum consistent with a stable
dihydroxyphenylalanine (DOPA) radical. The protein mechanoradicals, as a yet
undiscovered source of oxidative stress, finally convert into hydrogen
peroxide. Our study suggests collagen I to have evolved as a radical sponge
against mechano-oxidative damage and proposes a new mechanism for
exercise-induced oxidative stress and redox-mediated pathophysiological
processes.",1910.12190v1
2012-02-13,Effect of nanostructured zinc oxide additives on the humidity and temperature sensing properties of cuprous oxide,"Present paper reports the effect of ZnO additives on humidity and temperature
sensing properties of cuprous oxide. The cuprous oxide powder was mixed with
10% and 25% ZnO by weight and these samples were pelletized by using hydraulic
pressing machine. The sensing materials were also investigated by Scanning
Electron Microscope (SEM) and X-ray Diffraction (XRD). SEM images show
morphology and porosity of material. The average particles size of cuprous
oxide was found to be 1.2 micron. The sheet like structures of ZnO is evident
in micrographs. From XRD all peaks are well identified and crystallite size for
defferent peaks has also been calculated. The pellets of sensing materials were
subjected to annealing at temperatures 200, 400 and 600 degrees C respectively
and were exposed to humidity and temperature variations. Electrical resistances
of pellets were found to vary with humidity and temperature and were recorded.
The sensitivity of sensors at various temperature and humidity levels was
calculated.",1205.2707v1
2012-05-29,Influence of polarizability on metal oxide properties studied by molecular dynamics simulations,"We have studied the dependence of metal oxide properties in molecular
dynamics (MD) simulations on the polarizability of oxygen ions. We present
studies of both liquid and crystalline structures of silica (SiO2), magnesia
(MgO) and alumina (Al2O3). For each of the three oxides, two separately
optimized sets of force fields were used: (i) Long-range Coulomb interactions
between oxide and metal ions combined with a short-range pair potential. (ii)
Extension of force field (i) by adding polarizability to the oxygen ions. We
show that while an effective potential of type (i) without polarizable oxygen
ions can describe radial distributions and lattice constants reasonably well,
potentials of type (ii) are required to obtain correct values for bond angles
and the equation of state. The importance of polarizability for metal oxide
properties decreases with increasing temperature.",1205.6296v4
2017-05-09,Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultra-low thermal conductivity,"A detailed understanding of the relation between microscopic structure and
phonon propagation at the nan oscale is essential to design materials with
desired phononic and thermal properties.Here we uncover a new mechanism of
phonon interaction in surface oxidized membranes, i.e., native oxide layers
interact with phonons in ultra-thin silicon membranes through local resonances.
The local resonances reduce the low frequency phonon group velocities and
shorten their mean free path. This effect opens up a new strategy for ultralow
thermal conductivity design as it complements the scattering mechanism which
scatters higher frequency modes effectively. The combination of native oxide
layer and alloying with germanium in concentration as small as 5% reduces the
thermal conductivity of silicon membranes to 100 time lower than the bulk. In
addition, the resonance mechanism produced by native oxide surface layers is
particularly effective for thermal condutivity reduction even at very low
temperatures, at which only low frequency modes are populated.",1705.03143v1
2017-09-11,Signature of growth-deposition technique on the properties of PECVD and thermal SiO2,"In this article, we report the process induced variation in the
characteristics of PECVD deposited and thermally grown silicon dioxide (SiO2)
thin film. We find key differences in the porosity, arrangement of the
nano-pores, surface roughness, refractive index and electrical resistivity of
the SiO2 thin films obtained by the two methods. While the occurrence of the
nanoporous structure is an inherent property of the material and independent of
the process of film growth or deposition, the arrangements of these nano-pores
in the oxide film is process dependent. The distinct arrangements of the
nano-pores are signatures of the deposition/growth processes. Morphological
analysis has been carried out to demonstrate the difference between oxides
either grown by thermal oxidation or through PECVD deposition. The tunable
conductive behavior of the metal filled nano-porous oxides is also
demonstrated, which has potential to be used as conductive oxides in various
applications.",1709.03257v1
2017-09-20,Thermodynamic investigations on the growth of CuAlO$_2$ delafossite crystals,"Simultaneous differential thermal analysis (DTA) and thermogravimetric (TG)
measurements with copper oxide/aluminum oxide mixtures were performed in
atmospheres with varying oxygen partial pressures and with crucibles made of
different materials. Only sapphire and platinum crucibles proved to be stable
under conditions that are useful for the growth of CuAlO$_2$ delafossite single
crystals. Then the ternary phase diagram Al$_2$O$_3$-CuO-Cu and its isopleth
section Cu$_2$O-Al$_2$O$_3$ were redetermined. Millimeter sized crystals could
be obtained from copper oxide melts with 1-2 mol % addition of aluminum oxide
that are stable in platinum crucibles held in oxidizing atmosphere containing
15-21 % oxygen.",1709.06776v1
2017-11-09,Graphene oxide dielectric permittivity at GHz and its applications for wireless humidity sensing,"Graphene oxide relative dielectric permittivity, both its real and imaginary
parts, have been measured under various humidity conditions at GHz. It is
demonstrated that the relative dielectric permittivity increases with
increasing humidity due to water uptake. This electrical property of graphene
oxide was used to create a battery-free wireless radio-frequency identification
(RFID) humidity sensor by coating printed graphene antenna with the graphene
oxide layer. The resonance frequency as well as the backscattering phase of
such graphene oxide/graphene antenna become sensitive to the surrounding
humidity and can be detected by the RFID reader. This enables batteryless
wireless monitoring of the local humidity with digital identification attached
to any location or item and paves the way for low-cost efficient sensors for
Internet of Things applications.",1711.03435v1
2017-11-15,NC-AFM and XPS Investigation of Single-crystal Surfaces Supporting Cobalt (III) Oxide Nanostructures Grown by a Photochemical Method,"The work of this thesis comprises extensive Noncontact Atomic Force
Microscopy (NC-AFM) characterization of clean metal-oxide (YSZ(100)/(111) and
MgO(100)) and graphitic (HOPG) supports as templates for the novel,
photochemically induced nucleation of cobalt oxide nanostructures, particularly
Cobalt (III) Oxide. The nanostructure-support surfaces were also studied by
X-ray Photoelectron Spectroscopy (XPS) to verify the nature of the supported
cobalt oxide and to corroborate the surface topographic and phase NC-AFM data.
Heteroepitaxial growth of Co2O3 nanostructures proves to exhibit a variety of
different growth modes based on the structure of the support surface. On this
basis, single-crystal support surfaces ranging from nonpolar to polar and
atomically flat to highly defective and reactive were chosen, again, yielding
numerous substrate-nanostructure interactions that could be probed by
high-performance surface science techniques.",1711.09971v1
2018-06-07,Idiosyncratic Approach to Visualize Degradation of Black Phosphorus,"Black Phosphorus (BP) is an excellent material for post graphene era due to
its layer dependent band gap, high mobility and high Ion/Ioff. However, its
poor stability in ambient poses a great challenge in its practical and
long-term usage. Optical visualization of oxidized BP is the key and foremost
step for its successful passivation from the ambience. Here, we have done a
systematic study of the oxidation of BP and developed a technique to optically
identify the oxidation of BP using Liquid Crystal (LC). Interestingly we found
that rapid oxidation of thin layers of BP makes them disappear and can be
envisaged by using the alignment of LC. The molecular dynamics simulations also
proved the preferential alignment of LC on oxidized BP. We believe that this
simple technique will be effective in passivation efforts of BP and will enable
it for exploitation of its properties in the field of electronics.",1806.02872v1
2018-06-30,Nanoscale compositional evolution in complex oxide based resistive memories,"Functional oxides based resistive memories are recognized as potential
candidate for the next-generation high density data storage and neuromorphic
applications. Fundamental understanding of the compositional changes in the
functional oxides is required to tune the resistive switching characteristics
for enhanced memory performance. Herein, we present the micro/nano-structural
and compositional changes induced in a resistive oxide memory during resistive
switching. Oxygen deficient amorphous chromium doped strontium titanate
(Cr:$a$-SrTiO$_{3-x}$) based resistance change memories are fabricated in a
Ti/Cr:$a$-SrTiO$_{3-x}$ heterostructure and subjected to different biasing
conditions to set memory states. Transmission electron microscope based
cross-sectional analyses of the memory devices in different memory states shows
that the micro/nano-structural changes in amorphous complex oxide and
associated redox processes define the resistive switching behavior. These
experimental results provide insights and supporting material for Ref. [1].",1807.00185v1
2018-07-07,Oxygen Potential Transition in Mixed Conducting Oxide Electrolyte,"It is generally assumed that oxygen potential in a thin oxide electrolyte
follows a linear distribution between electrodes. Jacobsen and Mogensen have
shown, however, that this is not the case for thin zirconia membranes in solid
oxide electrochemical cells. Here we demonstrate that there is a ubiquitous
oxygen potential transition rooted in the p-type/n-type transition of
electronic conductivity inside mixed conducting oxides, and that the transition
is extremely sensitive to electrode potential and current density. It is also
remarkably sensitive to the conductivity ratio of electrons and holes, as well
as their association with lattice oxygens and vacancies, which tends to
increase the oxygen flow. Direct evidence of a sharp oxygen potential
transition has been found in an equally sharp grain size transition in
electrically loaded zirconia. More broadly speaking, the oxygen potential
transition is akin to a first-order phase transition. Therefore, it will suffer
interface instability, especially in high-current-density devices. These
findings provide new opportunities to understand several disparate observations
in the literature, from microstructural degradation and stress distribution in
solid oxide fuel/electrolyzer cells, to field-assisted sintering, to conducting
filaments in resistance memory, to dendrite formation in electrochemical cells.",1807.02704v1
2018-08-23,Oxide Heterostructures from a Realistic Many-Body Perspective,"Oxide heterostructures are a new class of materials by design, that open the
possibility for engineering challenging electronic properties, in particular
correlation effects beyond an effective single-particle description. This short
review tries to highlight some of the demanding aspects and questions,
motivated by the goal to describe the encountered physics from first
principles. The state-of-the-art methodology to approach realistic many-body
effects in strongly correlated oxides, the combination of density functional
theory with dynamical mean-field theory, will be briefly introduced. Discussed
examples deal with prominent Mott-band- and band-band-insulating type of oxide
heterostructures, where different electronic characteristics may be stabilized
within a single architectured oxide material.",1808.07672v1
2019-02-12,Deal-Grove Oxidation and Nanoparticle Adhesion - an AFM Study,"We study the formation of nanometer thick oxide layers around nanoparticles
(plateaus) in a wet nitrogen environment over 32 days. We determine both the
plateau height and the lateral force needed to remove the particles with an
atomic force microscope (AFM). The height is well described by the Deal-Grove
model for a thermally activated diffusion limited oxidation process.
Furthermore, we observe that height and force appear to be correlated
suggesting that the rise in adhesion forces is mainly governed by an oxidation
process. Since the plateaus are the result of a change in the chemical
structure, the surface remains permanently altered even after the removal of
the nanoparticles. This observation is of great importance for many
applications requiring smooth silicon surfaces, such as photolithography, where
small contamination can cause the observed oxidation process and significantly
increase the surface roughness.",1902.04494v1
2019-02-14,Coherent optical modulation of partially mode-locked fiber laser based on coherent population oscillation in reduced oxide graphene,"Optical control of graphene-based photonic devices and systems has been under
extensive explorations, nevertheless, the requirement of high power pump laser
due to incoherent modulation makes those schemes low efficient. Here, we
demonstrate coherent manipulation of the operating states of partially
mode-locked fiber laser based on coherent population oscillation in reduced
graphene oxide for the first time. We couple a much weaker continuous wave
laser into the resonator operating with parametric instability state, and
observe significant depression/enhancement of the sidebands when the coherent
population oscillation conditions are satisfied. Besides, significant
depression of partially mode-locked fiber laser is achieved. The experimental
results reveal that the coherent population oscillation in reduced graphene
oxide is highly effective in manipulating mode-locked fiber laser system, and
the induced phase variation is highly asymmetrical. The discovery of coherent
population oscillation in reduced graphene oxide facilitates coherent optical
modulation of reduced graphene oxide-based photonic devices and systems with a
much weaker controlling laser.",1902.05901v1
2019-03-13,Nanoscale Oxygen Defect Gradients in the Actinide Oxides,"Oxygen defects govern the behavior of a range of materials spanning
catalysis, quantum computing, and nuclear energy. Understanding and controlling
these defects is particularly important for the safe use, storage, and disposal
of actinide oxides in the nuclear fuel cycle, since their oxidation state
influences fuel lifetimes, stability, and the contamination of groundwater.
However, poorly understood nanoscale fluctuations in these systems can lead to
significant deviations from bulk oxidation behavior. Here we describe the first
use of aberration-corrected scanning transmission electron microscopy and
electron energy loss spectroscopy to resolve changes in the local oxygen defect
environment in UO$_2$ surfaces. We observe large image contrast and spectral
changes that reflect the presence of sizable gradients in interstitial oxygen
content at the nanoscale, which we quantify through first principles
calculations and image simulations. These findings reveal an unprecedented
level of excess oxygen incorporated in a complex near-surface spatial
distribution, offering new insight into defect formation pathways and kinetics
during UO$_2$ oxidation.",1903.05741v1
2019-03-14,Nano-engineering of electron correlation in oxide superlattices,"Oxide heterostructures and superlattices have attracted a great deal of
attention in recent years owing to the rich exotic properties encountered at
their interfaces. We focus on the potential of tunable correlated oxides by
investigating the spectral function of the prototypical correlated metal SrVO3,
using soft x-ray absorption spectroscopy (XAS) and resonant inelastic soft
x-ray scattering (RIXS) to access both unoccupied and occupied electronic
states, respectively. We demonstrate a remarkable level of tunability in the
spectral function of SrVO3 by varying its thickness within the SrVO3/SrTiO3
superlattice, showing that the effects of electron correlation can be tuned
from dominating the energy spectrum in a strongly correlated Mott-Hubbard
insulator, towards a correlated metal. We show that the effects of
dimensionality on the correlated properties of SrVO3 are augmented by
interlayer coupling, yielding a highly flexible correlated oxide that may be
readily married with other oxide systems.",1903.05911v1
2020-03-31,Conductive Domain Walls in Non-Oxide Ferroelectrics Sn2P2S6,"The conductive domain wall (CDW) is extensively investigated in
ferroelectrics, which can be considered as a quasi-two-dimensional
reconfigurable conducting channel embedded into an insulating material.
Therefore, it is highly important for the application of ferroelectric
nanoelectronics. Hitherto, most CDW investigations are restricted in oxides,
and limited work has been reported in non-oxides to the contrary. Here, by
successfully synthesizing the non-oxide ferroelectric Sn2P2S6 single crystal,
we observed and confirmed the domain wall conductivity by using different
scanning probe techniques which origins from the nature of inclined domain
walls. Moreover, the domains separated by CDW also exhibit distinguishable
electrical conductivity due to the interfacial polarization charge with
opposite signs. The result provides a novel platform for understanding
electrical conductivity behavior of the domains and domain walls in non-oxide
ferroelectrics.",2003.13927v1
2020-08-13,Where are the Extrasolar Mercuries?,"We utilize observations of 16 white dwarf stars to calculate and analyze the
oxidation states of the parent bodies accreting onto the stars. Oxygen
fugacity, a measure of overall oxidation state for rocks, is as important as
pressure and temperature in determining the structure of a planet. We find that
most of the extrasolar rocky bodies formed under oxidizing conditions, but
approximately 1/4 of the polluted white dwarfs have compositions consistent
with more reduced parent bodies. The difficulty in constraining the oxidation
states of relatively reduced bodies is discussed and a model for the
time-dependent evolution of the apparent oxygen fugacity for a hypothetical
reduced body engulfed by a WD is investigated. Differences in diffusive fluxes
of various elements through the WD envelope yield spurious inferred bulk
elemental compositions and oxidation states of the accreting parent bodies
under certain conditions. The worst case for biasing against detection of
reduced bodies occurs for high effective temperatures. For moderate and low
effective temperatures, evidence for relatively reduced parent bodies is
preserved under most circumstances for at least several characteristic
lifetimes of the debris disk.",2008.05992v1
2020-11-17,Orbital Rashba effect in surface oxidized Cu film,"Recent experimental observation of unexpectedly large current-induced
spin-orbit torque in surface oxidized Cu on top of a ferromagnet suggested a
possible role of the orbital Rashba effect (ORE). With this motivation, we
investigate the ORE from first principles by considering an oxygen monolayer on
top of a Cu(111) film. We show that surface oxidization of Cu film leads to
gigantic enhancement of the ORE for states near the Fermi surface. The
resulting chiral orbital texture in the momentum space is exceptionally strong,
reaching $\sim 0.5\hbar$ in magnitude. We find that resonant hybridization
between O $p$-states and Cu $d$-states is responsible for the emergence of the
ORE. We demonstrate that application of an external electric field generates
huge orbital Hall current, which is an order of magnitude larger than the spin
Hall current found in heavy metals. This implies that ""orbital torque""
mechanism may be significant in surface oxidized Cu/ferromagnet structures. It
also encourages experimental verification of the orbital texture in surface
oxidized Cu through optical measurements such as angle-resolved photoemission
spectroscopy.",2011.08601v1
2021-05-22,Scaling Theory of Two-Dimensional Field Effect Transistors,"We present a scaling theory of two-dimensional (2D) field effect transistors
(FETs). For devices with channel thickness less than 4 nm, the device
electrostatics is dominated by the physical gate oxide thickness and not the
effective oxide thickness. Specifically, for symmetric double gate (DG) FETs
the scale length ({\Lambda}) varies linearly with the gate oxide
thickness(t_{ox}) as {\Lambda} ~ 3/4t_{ox}. The gate oxide dielectric
permittivity and the semiconductor channel thickness do not affect the device
electrostatics for such device geometries. For an asymmetric device such as
single gate (SG) FETs, the fringing fields have a second order effect on the
scale length. However, like symmetric DG FETs, the scale length in asymmetric
FETs is also ultimately limited by the physical gate oxide thickness. We
compare our theoretical predictions for scaled monolayer MoS2 DG FETs.",2105.10791v1
2021-10-09,Deciphering the role of Al$_2$O$_3$ formed during isothermal oxidation in a dual-phase AlCoCrFeNi$_{2.1}$ Eutectic High-Entropy Alloy,"In recent times,there has been a significant volume of work on Eutectic High
Entropy Alloys (EHEAs) owing to their remarkable castability combined with
excellent mechanical properties,which aids in clearing obstacles for their
technological applications. One of the most common EHEAs,which has been of
enormous interest at present, primarily owing to its solidification and tensile
behavior, is AlCoCrFeNi$_{2.1}$. However,to aim for high-temperature
applications,oxidation behaviour of material is one of the major aspects that
needs to be extensively investigated.To this end,the present work aims to study
the phases evolved during oxidation at elevated temperatures as high as 950 and
1000$^\circ$C in AlCoCrFeNi$_{2.1}$ using XRD and also to determine the rate
law followed for isothermal oxidation of this alloy at 950 and 1000$^\circ$C,in
order to understand the role of Al$_2$O$_3$ phase formed during isothermal
oxidation at 950 and 1000$^\circ$C.",2110.09222v1
2021-11-01,Noble-Metal-Assisted Fast Interfacial Oxygen Migration with Topotactic Phase Transition in Perovskite Oxides,"Transition-metal perovskite oxides constitute a series of functional material
systems for electronics, catalysis and energy-conversion processes, in which
oxygen migration and evolution play a key role. However, the stable
metal-oxygen (M-O) bond forms large energy barrier inhibiting ion diffusion.
Therefore, seeking efficient and facile approaches to accelerate oxygen
kinetics has become a significant issue. Here, the interaction (interfacial
charge transfer and cooperative bonding) between noble metal (Pt, Ag) and
perovskites oxide (SrCoO3-delta) is employed to weaken (M-O) bond and decrease
the energy barrier of oxygen migration. Noble metal layers serving as oxygen
pumps can continuously extract oxygen from oxide films to atmosphere. The
temperature of topotactic phase transition from perovskite (SrCoO3) to
brownmillerite (SrCoO2.5) is remarkably lowered from 200 K to room temperature.
Furthermore, this approach can also be applied to SrFeO3 for similar topotactic
phase reduction by moderate thermal activation. Our finding paves a promising
and general pathway to achieve fast oxygen migration in perovskite oxides, with
important application prospect in low-temperature electrodes and high-activity
catalysis interface.",2111.00663v1
2021-11-23,Eliminating Delocalization Error to Improve Heterogeneous Catalysis Predictions with Molecular DFT+U,"Approximate semi-local density functional theory (DFT) is known to
underestimate surface formation energies yet paradoxically overbind adsorbates
on catalytic transition-metal oxide surfaces due to delocalization error. The
low-cost DFT+U approach only improves surface formation energies for early
transition-metal oxides or adsorption energies for late transition-metal
oxides. In this work, we demonstrate that this inefficacy arises due to the
conventional usage of metal-centered atomic orbitals as projectors within
DFT+U. We analyze electron density rearrangement during surface formation and O
atom adsorption on rutile transition-metal oxides to highlight that a standard
DFT+U correction fails to tune properties when the corresponding density
rearrangement is highly delocalized across both metal and oxygen sites. To
improve both surface properties simultaneously while retaining the simplicity
of a single-site DFT+U correction, we systematically construct
multi-atom-centered molecular-orbital-like projectors for DFT+U. We demonstrate
this molecular DFT+U approach for tuning adsorption energies and surface
formation energies of minimal two-dimensional models of representative early
(i.e., TiO2) and late (i.e., PtO2) transition-metal oxides. Molecular DFT+U
simultaneously corrects adsorption energies and surface formation energies of
multi-layer models of rutile TiO2(110) and PtO2(110) to resolve the paradoxical
description of surface stability and surface reactivity of semi-local DFT.",2111.11614v1
2022-02-03,Tuning carrier density and phase transitions in oxide semiconductors using focused ion beams,"We demonstrate spatial modification of the optical properties of thin-film
metal oxides, zinc oxide and vanadium dioxide as representatives, using a
commercial focused ion beam (FIB) system. Using a Ga+ FIB and thermal
annealing, we demonstrated variable doping of a band semiconductor, zinc oxide
(ZnO), achieving carrier concentrations from 10^18 cm-3 to 10^20 cm-3. Using
the same FIB without subsequent thermal annealing, we defect-engineered a
correlated semiconductor, vanadium dioxide (VO2), locally modifying its
insulator-to-metal transition (IMT) temperature by range of ~25 degrees C. Such
area-selective modification of metal oxides by direct writing using a FIB
provides a simple, mask-less route to the fabrication of optical structures,
especially when multiple or continuous levels of doping or defect density are
required.",2202.01777v3
2022-02-22,Stabilization of Co oxide during oxygen evolution in alkaline media by the introduction of Mn oxide,"Improving the stability of electrocatalysts for the oxygen evolution reaction
(OER) through materials design has received less attention than improving their
catalytic activity. We explored the effect of Mn addition to a cobalt oxide for
stabilizing the catalyst by comparing Na-containing CoOx and (Co0.7Mn0.3)Ox
films electrodeposited in alkaline solution. The obtained disordered films were
classified as layered oxides using X-ray absorption spectroscopy (XAS). The
CoOx films showed a constant decrease in the catalytic activity during cycling,
confirmed by oxygen detection, while that of (Co0.7Mn0.3)Ox slightly increased
as measured by electrochemical metrics. These trends were rationalized based on
XAS analysis of the metal oxidation states, which were Co2.8+ and Mn3.7+ near
the surface after cycling. Thus, adding Mn to CoOx successfully stabilized the
catalyst material and its activity during OER cycling. The development of
stabilization approaches is essential to extend the durability of OER
catalysts.",2202.10836v1
2022-03-13,Mixed excitonic nature in water-oxidized BiVO$_4$ surfaces with defects,"BiVO$_4$ is a promising photocatalyst for efficient water oxidation, with
surface reactivity determined by the structure of active catalytic sites.
Surface oxidation in the presence of oxygen vacancies induces electron
localization, suggesting an atomistic route to improve the charge transfer
efficiency within the catalytic cycle. In this work, we study the effect of
oxygen vacancies on the electronic and optical properties at BiVO$_4$ surfaces
upon water oxidation. We use density functional theory and many-body
perturbation theory to explore the change in the electronic and quasiparticle
energy levels and to evaluate the electron-hole coupling as a function of the
underlying structure. We show that while the presence of defects alters the
atomic structure and largely modifies the wavefunction nature, leading to
defect-localized states at the quasipatricle gap region, the optical
excitations remain largely unchanged due to substantial hybridization of defect
and non-defect electron-hole transitions. Our findings suggest that
defect-induced surface oxidation supports improved electron transport, both
through bound and tunable electronic states and via a mixed nature of the
optical transitions, expected to reduce electron-hole defect trapping.",2203.06636v1
2022-03-21,Thermodynamic descriptors to predict oxide formation in aqueous solutions,"We formulate the maximum driving force (MDF) parameter as a descriptor to
capture the thermodynamic stability of aqueous surface scale creation over a
range of environmental conditions. We use formation free energies, $\Delta_f
G$s, sourced from high-throughput density functional theory (DFT) calculations
and experimental databases to compute the maximum driving force for a wide
variety of materials, including simple oxides, intermetallics, and alloys of
varying compositions. We show how to use the MDF to describe trends in aqueous
corrosion of nickel thin films determined from experimental
linear-sweep-voltometry data. We also show how to account for subsurface
oxidation behavior using depth-dependent effective chemical potentials. We
anticipate this approach will increase overall understanding of oxide formation
on chemically complex multielement alloys, where competing oxide phases can
form during transient aqueous corrosion.",2203.11013v1
2022-08-26,What is in a Name: Defining -High Entropy- Oxides,"High entropy oxides are emerging as an exciting new avenue to design highly
tailored functional behaviors that have no traditional counterparts. Study and
application of these materials are bringing together scientists and engineers
from physics, chemistry, and materials science. The diversity of each of these
disciplines comes with perspectives and jargon that may be confusing to those
outside of the individual fields, which can result in miscommunication of
important aspects of research. In this perspective, we provide examples of
research and characterization taken from these different fields to provide a
framework for classifying the differences between compositionally complex
oxides, high entropy oxides, and entropy stabilized oxides, which is intended
to bring a common language to this emerging area. We highlight the critical
importance of understanding a materials crystallinity, composition, and mixing
length scales in determining its true definition.",2208.12709v2
2022-09-12,Origin of superconductivity in hole doped SrBiO3 bismuth oxide perovskite from parameter-free first-principles simulations,"The recent discovery nickel oxides superconductors have highlighted the
importance of first-principles simulations for understanding the formation of
the bound electrons at the core of superconductivity. Nevertheless,
superconductivity in oxides is often ascribed to strong electronic correlation
effects that Density Functional Theory (DFT) cannot properly take into account,
thereby disqualifying this technique. Being isostructural to nickel oxides,
Sr1-xKxBiO3 superconductors form an ideal testbed for unveiling (i) the lowest
theory level needed to model complex superconductors and (ii) the underlying
pairing mechanism yielding superconductivity. Here I show that parameter-free
DFT simulations capture all the experimental features and related quantities of
Sr1-xKxBiO3 superconductors, encompassing the prediction of an insulating to
metal phase transition upon increasing the K doping content and of an
electron-phonon coupling constant of 1.22 in sharp agreement with the
experimental value of 1.3 +/- 0.2. Proximity of a disproportionated phase is
further demonstrated to be a prerequisite for superconductivity in bismuthates.
This work highlights that appropriately executed DFT is a sufficient platform
for studying superconductivity in complex oxides.",2209.05198v1
2022-09-16,Epitaxy of hexagonal ABO$_3$ quantum materials,"Hexagonal $AB$O$_3$ oxides ($A$, $B$ = cation) are a rich materials class for
realizing novel quantum phenomena. Their hexagonal symmetry, oxygen trigonal
bipyramid coordination and quasi-two dimensional layering give rise to
properties distinct from those of the cubic $AB$O$_3$ perovskites. As bulk
materials, most of the focus in this materials class has been on the rare earth
manganites, $R$MnO$_3$ ($R$ = rare earth); these materials display coupled
ferroelectricity and antiferromagnetic order. In this review, we focus on the
thin film manifestations of the hexagonal $AB$O$_3$ oxides. We cover the
stability of the hexagonal oxides and substrates which can be used to template
the hexagonal structure. We show how the thin film geometry not only allows for
further tuning of the bulk-stable manganites but also the realization of
metastable hexagonal oxides such as the $R$FeO$_3$ that combine
ferroelectricity with weak ferromagnetic order. The thin film geometry is a
promising platform to stabilize additional metastable hexagonal oxides to
search for predicted high-temperature superconductivity and topological phases
in this materials class.",2209.08006v1
2023-01-07,Visible-light photocatalytic oxygen production on a high-entropy oxide by multiple-heterojunction introduction,"High-entropy oxides (HEOs), as multi-component ceramics with high
configurational entropy, have been of recent interest due to their attractive
properties including photocatalytic activity for H2 production and CO2
conversion. However, the photocatalytic activity of HEOs is still limited to
ultraviolet light. In this study, to achieve visible-light-driven
photocatalysis, 10 different heterojunctions were simultaneously introduced in
the Ti-Zr-Nb-Ta-W-O system. The oxide, which was synthesized by a high-pressure
torsion method and oxidation, successfully produced oxygen from water under
visible light without co-catalyst addition. The photocatalytic performance was
attributed to high visible-light absorption, narrow bandgap, appropriate band
structure, presence of multiple heterojunctions and accordingly easy
electron-hole separation and slow recombination. These results not only show
the potential of high-entropy oxides as new visible-light-active
photocatalysts, but also introduce the multiple-heterojunction introduction as
a strategy to achieve photocatalysis under visible light.",2301.05016v1
2023-04-27,Wavelength Dependent Nonlinear Spectroscopic Study of Third Harmonic Generation Probed by Rotational Maker Fringes Method,"Efficient third-order nonlinearities of the Zinc Oxide and Al-doped Zinc
Oxide were studied by Third Harmonic Generation (Third Harmonic Generation)
Maker fringes to establish the effect Aluminum of Aluminum doping(Al-doping) on
the cubic nonlinearities. The addition of the Al-dopant to the Zinc Oxide
crystal structure results in changes that affected the optical and nonlinear
characteristics. Presented results indicate that magnitude of the third-order
nonlinear susceptibility tensor was enhanced at single experimental
wavelengths, however, across the broadband experimental spectrum the effect of
Al-doping remained relatively constant. The observed enhancement of third-order
nonlinearity was purely from the bound electronic response and the observation
is attributed to increased charge carriers and spontaneous polarization in the
Zinc Oxide and Al-doped Zinc Oxide crystal structure.",2304.14523v1
2023-04-29,The Combination of Metal Oxides as Oxide Layers for RRAM and Artificial Intelligence,"Resistive random-access memory (RRAM) is a promising candidate for
next-generation memory devices due to its high speed, low power consumption,
and excellent scalability. Metal oxides are commonly used as the oxide layer in
RRAM devices due to their high dielectric constant and stability. However, to
further improve the performance of RRAM devices, recent research has focused on
integrating artificial intelligence (AI). AI can be used to optimize the
performance of RRAM devices, while RRAM can also power AI as a hardware
accelerator and in neuromorphic computing. This review paper provides an
overview of the combination of metal oxides-based RRAM and AI, highlighting
recent advances in these two directions. We discuss the use of AI to improve
the performance of RRAM devices and the use of RRAM to power AI. Additionally,
we address key challenges in the field and provide insights into future
research directions",2305.00166v1
2023-06-08,Iron Oxide Nanoparticles as a Contrast Agent for Synchrotron Imaging of Sperm,"Fast phase-contrast imaging offered by modern synchrotron facilities opens
the possibility of imaging dynamic processes of biological material such as
cells. Cells are mainly composed of carbon and hydrogen, which have low X-ray
attenuation, making cell studies with X-ray tomography challenging. At specific
low energies, cells provide contrast, but cryo-conditions are required to
protect the sample from radiation damage. Thus, non-toxic labelling methods are
needed to prepare living cells for X-ray tomography at higher energies. We
propose using iron oxide nanoparticles due to their proven compatibility in
other biomedical applications. We show how to synthesize and attach iron oxide
nanoparticles and demonstrate that cell-penetrating peptides facilitate iron
oxide nanoparticle uptake into sperm cells. We show results from the TOMCAT
Nanoscope (Swiss Light Source), showing that iron oxide nanoparticles allow the
heads and midpiece of fixed sperm samples to be reconstructed from X-ray
projections taken at 10 keV.",2309.03908v1
2023-10-12,Localization of vibrational modes in high-entropy oxides,"The recently-discovered high-entropy oxides offer a paradoxical combination
of crystalline arrangement and high disorder. They differ qualitatively from
established paradigms for disordered solids such as glasses and alloys. In
these latter systems, it is well known that disorder induces localized
vibrational excitations. In this article, we explore the possibility of
disorder-induced localization in (MgCoCuNiZn)O, the prototypical high-entropy
oxide with rock-salt structure. To describe phononic excitations, we model the
interatomic potentials for the cation-oxygen interactions by fitting to the
physical properties of the parent binary oxides. We validate our model against
the experimentally determined crystal structure, bond lengths, and optical
conductivity. The resulting phonon spectrum shows wave-like propagating modes
at low energies and localized modes at high energies. Localization is reflected
in signatures such as participation ratio and correlation amplitude. Finally,
we explore the possibility of increased mass disorder in the oxygen sublattice.
Admixing sulphur or tellurium atoms with oxygen enhances localization. It even
leads to localized modes in the middle of the spectrum. Our results suggest
that high-entropy oxides are a promising platform to study Anderson
localization of phonons.",2310.08668v1
2023-10-21,Advances in Complex Oxide Quantum Materials Through New Approaches to Molecular Beam Epitaxy,"Molecular beam epitaxy (MBE), a workhorse of the semiconductor industry, has
progressed rapidly in the last few decades in the development of novel
materials. Recent developments in condensed matter and materials physics have
seen the rise of many novel quantum materials that require ultra-clean and
high-quality samples for fundamental studies and applications. Novel
oxide-based quantum materials synthesized using MBE have advanced the
development of the field and materials. In this review, we discuss the recent
progress in new MBE techniques that have enabled synthesis of complex oxides
that exhibit ""quantum"" phenomena, including superconductivity and topological
electronic states. We show how these techniques have produced breakthroughs in
the synthesis of 4d and 5d oxide films and heterostructures that are of
particular interest as quantum materials. These new techniques in MBE offer a
bright future for the synthesis of ultra-high quality oxide quantum materials.",2310.13902v1
2024-03-02,"A peridynamic investigation of particle oxidation, size and material during cold-spray","Cold spray technology, distinguished by its unique ability to deposit
particles in a solid state, offers unparalleled potential for applications such
as coating, repair, and additive manufacturing. In this research, we employed a
peridynamic modeling approach to systematically analyze the effects of key
powder features on deposit properties. Notably, our model incorporates the
explicit modeling of nanometer-sized oxide layers, providing a more accurate
representation of real-world conditions. We assessed the influence of
parameters such as particle size, oxidation conditions, and material type on
crucial deposition indicators like critical velocity and compression ratio. Our
results demonstrated excellent agreement with reported experimental data,
affirming the effectiveness of the proposed numerical framework. Specifically,
our findings highlighted that, for a given impact velocity, smaller particles,
thicker oxide layers, and harder materials contribute to limited oxide removal
and a decreased likelihood of successful adhesion. Additionally, we present a
predictive framework that establishes a correlation between particle size and
critical velocity, providing valuable insights for optimizing cold spray
deposition parameters. This innovative approach not only enhances our
understanding of the intricate interplay between powder features and deposit
properties but also paves the way for a more efficient and cost-effective
optimization process in cold spray applications.",2403.01311v1
2024-03-18,Theoretical Study on Optoelectronic properties of Layered In2O3 and Ga2O3,"Composite oxides have been indeed proved to be valuable materials in
optoelectronic applications. The combination of indium oxide and gallium oxide
and other materials can lead to enhanced optical and electronic properties,
making them suitable for a variety of optoelectronic devices. Meticulous
analysis of the various optical properties helped to draw conclusions about the
heterostructure of Indium and Gallium oxide and its use as a suitable
semiconducting material in the medium bandgap range. The density of states and
the band structure have been obtained from the density functional theory
calculations. Real frequency phonon density of states supports dynamical
stability of the crystal structure. A favorable energy band gap is achieved in
the visible region of the spectrum, indicating that this mixed oxide is well
suited for optoelectronic devices such as LEDs and solar cells.",2403.11619v1
2004-05-15,Ordinary Chondrite Formation from two Components: Implied Connection to Planet Mercury,"Major element fractionation among chondrites has been discussed for decades
as ratios relative to Si or Mg. Expressing ratios relative to Fe leads to a new
relationship admitting the possibility that ordinary chondrite meteorites are
derived from two components: one is a relatively undifferentiated, primitive
component, oxidized like the CI or C1 chondrites; the other is a somewhat
differentiated, planetary component, with oxidation state like the reduced
enstatite chondrites. Such a picture would seem to explain for the ordinary
chondrites, their major element compositions, their intermediate states of
oxidation, and their ubiquitous deficiencies of refractory siderophile
elements. I suggest that the planetary component of ordinary chondrite
formation consists of planet Mercury's missing complement of elements.",0405298v1
1996-08-01,Collective rotations in oxides,"Based on bond arguments, a Hamiltonian is introduced to describe the
fundamental physics of the collective rotations of oxygen atoms in oxides.
Values for the relevant material parameters are estimated for silica and Cu
oxides. Zero-temperature phase diagrams are presented; the different phases and
associated transitions are characterized. Phases with non-phononic excitations
are found.",9608002v1
1997-05-30,Polar Jahn-Teller Centers and Isotope Effect in Copper Oxide high-T_c-Superconductors,"The $CuO_4$-cluster based copper oxides are considered as generalized quantum
lattice bose-gas or a system of the local singlet bosons moving in a lattice of
the hole Jahn-Teller centers $[CuO_{4}^{5-}]_{JT}$. The model is illustrated by
the qualitative and quantitative description of the various peculiarities of an
isotope shift (IS-) effect in a series of 123-like oxides.",9705306v1
1999-03-10,Large Thermopower in a Layered Oxide NaCo_2O_4,"A transition-metal oxide NaCo_2O_4 is a layered oxide in which CoO_2 and Na
alternately stack along the c axis. Recently we have found that this compound
shows unusually large thermopower with low resistivity, which is comparable to
those of Bi_2Te_3. The negative transverse magnetoresistance and the strongly
temperature-dependent Hall coefficient suggest that electron correlation
dominates the conduction mechanism in NaCo_2O_4.",9903162v1
2002-02-19,Production of a hafnium silicate dielectric layer for use as a gate oxide by solid-state reaction,"The formation of hafnium silicate films (HfSixOy) for use as gate oxides with
large dielectric constant by solid state reaction of Hf metal and SiO2 was
investigated. Thin, fully reacted silicate films could be formed, and were
thermally stable in vacuum to temperatures in excess of 800 C. The interface
between a hafnium silicate layer and the silicon substrate was shown to be
stable against SiO2 formation. The results suggest a new processing route for
production of a gate insulator having low equivalent oxide thickness.",0202328v1
2002-06-28,"Electron localization : band-by-band decomposition, and application to oxides","Using a plane wave pseudopotential approach to density functional theory we
investigate the electron localization length in various oxides. For this
purpose, we first set up a theory of the band-by-band decomposition of this
quantity, more complex than the decomposition of the spontaneous polarization
(a related concept), because of the interband coupling. We show its
interpretation in terms of Wannier functions and clarify the effect of the
pseudopotential approximation. We treat the case of different oxides: BaO,
$\alpha$-PbO, BaTiO$_3$ and PbTiO$_3$. We also investigate the variation of the
localization tensor during the ferroelectric phase transitions of BaTiO$_3$ as
well as its relationship with the Born effective charges.",0206580v1
2004-05-31,Electron-phonon interaction enhanced by antiferromagnetic and superconducting fluctuations in cuprate oxide superconductors,"An electron-phonon interaction arising from the modulation of the
superexchange interaction by phonons is studied within the theoretical
framework of Kondo lattices. It is relevant in strongly correlated electron
liquids in cuprate oxide superconductors, which lie in the vicinity of the
Mott-Hubbard metal-insulator transition. It is enhanced by antiferromagnetic
and superconducting fluctuations, which are developed mainly because of the
superexchange interaction. When the enhancement of the electron-phonon
interaction is large enough, it can explain the softening of phonons and kinks
in the quasiparticle dispersion in cuprate oxide superconductors. However, the
superexchange interaction itself must be mainly responsible for the formation
of Cooper pairs.",0405703v1
2006-01-25,The energetics of water on oxide surfaces by quantum Monte Carlo,"Density functional theory (DFT) is widely used in surface science, but gives
poor accuracy for oxide surface processes, while high-level quantum chemistry
methods are hard to apply without losing basis-set quality. We argue that
quantum Monte Carlo techniques allow these difficulties to be overcome, and we
present diffusion Monte Carlo results for the formation energy of the MgO(001)
surface and the adsorption energy of H$_2$O on this surface, using periodic
slab geometry. The results agree well with experiment. We note other oxide
surface problems where these techniques could yield immediate progress.",0601572v2
2006-03-28,Tungsten oxide nanowire growth by chemically-induced strain,"We have investigated the formation of tungsten oxide nanowires under
different CVD conditions. We find that exposure of oxidized tungsten films to
hydrogen and methane at 900C leads to the formation of a dense array of
typically 10 nm diameter nanowires. Structural and chemical analysis shows that
the wires are crystalline WO3. We propose a chemically-driven whisker growth
mechanism in which interfacial strain associated with the formation of tungsten
carbide stimulates nanowire growth. This might be a general concept, applicable
also in other nanowire systems.",0603746v1
2006-04-09,MgB2 tunnel junctions with native or thermal oxide barriers,"MgB2 tunnel junctions (MgB2/barrier/MgB2) were fabricated using a native
oxide grown on the bottom MgB2 film as the tunnel barrier. Such barriers
therefore survive the deposition of the second electrode at 300oC, even over
junction areas of ~1 mm2. Studies of such junctions, and those of the type
MgB2/native or thermal oxide/metal (Pb, Au, or Ag) show that tunnel barriers
grown on MgB2 exhibit a wide range of barrier heights and widths.",0604229v1
2007-02-09,X-ray photoemission study of CoFeB/MgO thin film bi-layers,"We present results from an X-ray photoemission spectroscopy (XPS) study of
CoFeB/MgO bi-layers where we observe process-dependent formation of B, Fe, and
Co oxides at the CoFeB/MgO interface due to oxidation of CoFeB during MgO
deposition. Vacuum annealing reduces the Co and Fe oxides but further
incorporates B into the MgO forming a composite MgBxOy layer. Inserting an Mg
layer between CoFeB and MgO introduces an oxygen sink, providing increased
control over B content in the barrier.",0702232v1
2003-12-22,Cosmological billiards and oxidation,"We show how the properties of the cosmological billiards provide useful
information (spacetime dimension and $p$-form spectrum) on the oxidation
endpoint of the oxidation sequence of gravitational theories. We compare this
approach to the other available methods: $GL(n,R)$ subgroups and the
superalgebras of dualities.",0312251v2
2007-04-29,Pinned Low Energy Electronic Excitation in Metal Exchanged Vanadium Oxide Nanoscrolls,"We measured the optical properties of mixed valent vanadium oxide nanoscrolls
and their metal exchanged derivatives in order to investigate the charge
dynamics in these compounds. In contrast to the prediction of a metallic state
for the metal exchanged derivatives within a rigid band model, we find that the
injected charges in Mn$^{2+}$ exchanged vanadium oxide nanoscrolls are pinned.
A low-energy electronic excitation associated with the pinned carriers appears
in the far infrared and persists at low temperature, suggesting that the
nanoscrolls are weak metals in their bulk form, dominated by inhomogeneous
charge disproportionation and Madelung energy effects.",0704.3861v1
2007-07-23,Chemical nanomachining of silicon by gold-catalyzed oxidation,"A chemical nanomachining process for the rapid, scalable production of
nanostructure assemblies from silicon-on-insulator is demonstrated. The process
is based on the spontaneous, local oxidation of Si induced by Au, which is
selectively evaporated onto the Si surface. The Au-catalyzed oxide forms a
pattern that serves as a robust mask for the underlying Si, enabling the use of
simple wet chemistry to sculpt arrays of nanostructures of diverse shapes
including rings, pillars, wires, and nanopores. The remarkable simplicity of
this chemical nanomachining process makes it widely accessible as an enabling
technique for applications from photonics to biotechnology.",0707.3307v1
2007-08-31,Phase stability of hafnium oxide and zirconium oxide on silicon substrate,"Phase stabilities of Hf-Si-O and Zr-Si-O have been studied with
first-principles and thermodynamic modeling. From the obtained thermodynamic
descriptions, phase diagrams pertinent to thin film processing were calculated.
We found that the relative stability of the metal silicates with respect to
their binary oxides plays a critical role in silicide formation. It was
observed that both the HfO$_2$/Si and ZrO$_2$/Si interfaces are stable in a
wide temperature range and silicide may form at low temperatures, partially at
the HfO$_2$/Si interface.",0708.4356v1
2008-04-30,Crystal chemical simulation of superconductors on the basis of oxide and intermetallic layers,"Simulation of 'hybrid' superconductors of 3d-, 4d- and 5d-transition elements
consisting of two different superconducting fragments located between
positively charged ions planes - B'O2 oxide planes and B2C2 intermetallic
layers - has been performed on the basis of the structure of Sr2Mn3As2O2
(A2(B2C2)(B'O2)). The oxide planes are similar to those of CuO2 in
high-temperature superconducting cuprates while the intermetallic layers - to
those of Ni2B2 in low-temperature superconducting borocarbides RNi2B2C and
Fe2As2 layers in high-temperature superconducting oxypnictides RFeAsO1-xFx.",0804.4763v2
2008-08-13,Coreless Terrestrial Exoplanets,"Differentiation in terrestrial planets is expected to include the formation
of a metallic iron core. We predict the existence of terrestrial planets that
have differentiated but have no metallic core--planets that are effectively a
giant silicate mantle. We discuss two paths to forming a coreless terrestrial
planet, whereby the oxidation state during planetary accretion and
solidification will determine the size or existence of any metallic core. Under
this hypothesis, any metallic iron in the bulk accreting material is oxidized
by water, binding the iron in the form of iron oxide into the silicate minerals
of the planetary mantle. The existence of such silicate planets has
consequences for interpreting the compositions and interior density structures
of exoplanets based on their mass and radius measurements.",0808.1908v1
2008-11-21,Si3N4 single-crystal nanowires grown from silicon micro and nanoparticles near the threshold of passive oxidation,"A simple and most promising oxide-assisted catalyst-free method is used to
prepare silicon nitride nanowires that give rise to high yield in a short time.
After a brief analysis of the state of the art, we reveal the crucial role
played by the oxygen partial pressure: when oxygen partial pressure is slightly
below the threshold of passive oxidation, a high yield inhibiting the formation
of any silica layer covering the nanowires occurs and thanks to the synthesis
temperature one can control nanowire dimensions.",0811.3575v1
2009-01-25,Sketching the Theory of Copper Oxide High Temperature Superconductivity,"The role of the anti-bonding state in the electron correlations in Copper
Oxide HTSC is analyzed. Then the t-J Hamiltonian is used to establish the
formation of the charge stripes in underdoped oxides. It is proposed that these
stripes make up the boundaries between the two degenerate anti-ferromagnetic
(AFM) states, and that they are a key factor in switching between these states.
We also provide a theoretical expression for the charge driven AFM magnons that
have been observed by Neutron scattering experiments. Finally, the double
correlation theory is applied to the stripe phase of holes to result in the
superconductive gap and in the ""pseudogap"".",0901.3896v2
2009-02-10,Exchange bias in laterally oxidized Au/Co/Au nanopillars,"Au/Co/Au nanopillars fabricated by colloidal lithography of continuous
trilayers exhibit and enhanced coercive field and the appearance of an exchange
bias field with respect to the continuous layers. This is attributed to the
lateral oxidation of the Co interlayer that appears upon disc fabrication. The
dependence of the exchange bias field on the Co nanodots size and on the
oxidation degree is analyzed and its microscopic origin clarified by means of
Monte Carlo simulations based on a model of a cylindrical dot with lateral
core/shell structure.",0902.1687v1
2009-08-21,Structural and Electronic Properties of Oxidized Graphene,"We have systematically investigated the effect of oxidation on the structural
and electronic properties of graphene based on first-principles calculations.
Energetically favorable atomic configurations and building blocks are
identified, which contain epoxide and hydroxyl groups in close proximity with
each other. Different arrangements of these units yield an LDA band gap over a
range of a few eV. These results suggest the possibility of creating and tuning
the band gap in graphene by varying the oxidation level and the relative amount
of epoxide and hydroxyl functional groups on the surface.",0908.3172v1
2009-10-12,Chemical-etch-assisted growth of epitaxial zinc oxide,"We use real-time spectroscopic polarimetric observations of growth and a
chemical model derived therefrom, to develop a method of growing dense,
two-dimensional zinc oxide epitaxially on sapphire by metalorganic chemical
vapor deposition. Particulate zinc oxide formed in the gas phase is used to
advantage as the deposition source. Our real-time data provide unequivocal
evidence that: a seed layer is required; unwanted fractions of ZnO are
deposited; but these fractions can be removed by cycling between brief periods
of net deposition and etching. The transition between deposition and etching
occurs with zinc precursor concentrations that only differ by 13%. These
processes are understood by considering the chemistry involved.",0910.2199v1
2010-02-25,"Trends in Metal Oxide Stability for Nanorods, Nanotubes, and Surfaces","The formation energies of nanostructures play an important role in
determining their properties, including the catalytic activity. For the case of
15 different rutile and 8 different perovskite metal oxides, we find that the
density functional theory (DFT) calculated formation energies of (2,2)
nanorods, (3,3) nanotubes, and the (110) and (100) surfaces may be described
semi-quantitatively by the fraction of metal--oxygen bonds broken and the
bonding band centers in the bulk metal oxide.",1002.4834v1
2010-06-11,"First Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5] with Extremely Thick Blocking Layers","We have discovered first homologous series of iron pnictide oxide
superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5]. These compounds have
extremely thick blocking layers up to quintuple perovskite oxide layers
sandwiched by the Fe2As2 layers. These samples exhibited bulk superconductivity
with relatively high Tc up to 42 K. The relationship between Tc and the
iron-plane interlayer distance suggested that superconductivity due to the mono
Fe2As2 layer is substantially 40 K-class.",1006.2355v2
2010-07-02,$sp^{2}$/$sp^{3}$ carbon ratio in graphite oxide with different preparation times,"Graphite oxide is an amorphous insulator. Although several models have been
suggested, its structure remains controversial. To elucidate this issue, 5
samples were prepared by the Brodie process and the Staudenmaier process. The
electronic structure of graphite oxide was examined with x-ray absorption near
edge structure and the ratio of $sp^{2}$ to $sp^{3}$ bonded carbon atoms was
investigated with x-ray photoemission spectroscopy as a function of sample
preparation times. It was found that this ratio approaches 0.3 exponentially
with a characteristic time of 1.5 weeks. We believe this long characteristic
time is the reason the structure has remained unclear.",1007.0287v2
2010-10-01,Thermally induced 0-pi phase transition in Josephson junctions through a ferromagnetic oxide film,"We investigate the Josephson transport through a ferromagnetic oxide film,
e.g., La$_2$BaCuO$_5$, theoretically. Using the recursive Green's function
technique, we found the formation of a pi-junction in such systems. Moreover
the 0-pi phase transition is induced by increasing the temperature. Such
ferromagnetic-oxide based Josephson junctions may become an element in the
architecture of future quantum computers.",1010.0042v1
2010-10-26,Transparent and conductive graphene oxide-polyethylenglycol diacrylate coatings obtained by photopolymerization,"Water dispersed graphene oxide sheets were used to prepare
graphene-polyethylenglycol diacrylate resin composites by photopolymerization.
It was found that graphene sheets undergo excellent morphological distribution
within the resin system, giving rise to transparent composites with unaltered
thermal properties with respect to the neat resin, that are electrically
conductive at loading ratios as low as 0.02 %wt of graphene oxide . The
proposed strategy based on photopolymerization provides an easy, energy-saving
and environmental friendly technique that can find a wide application in
coating technology, mainly for electromagnetic shielding and antistatic
coatings.",1010.5409v1
2010-11-16,Field-induced water electrolysis switches an oxide semiconductor from an insulator to a metal,"Here we demonstrate that water-infiltrated nanoporous glass electrically
switches an oxide semiconductor from an insulator to metal. We fabricated the
field effect transistor structure on an oxide semiconductor, SrTiO3, using
100%-water-infiltrated nanoporous glass - amorphous 12CaO*7Al2O3 - as the gate
insulator. For positive gate voltage, electron accumulation, water electrolysis
and electrochemical reduction occur successively on the SrTiO3 surface at room
temperature, leading to the formation of a thin (~3 nm) metal layer with an
extremely high electron concentration of 10^15-10^16 cm^-2, which exhibits
exotic thermoelectric behaviour.",1011.3681v1
2010-12-22,Thermoelectric effect of multiferroic oxide interfaces,"We investigate the thermoelectric properties of electrons at the interface of
oxide heterostructure and in the presence of a multiferroic oxide with spiral
spin order. We find there is no (spin) Hall current generated by the
temperature gradient. A Seebeck effect is however present. Due to the
magnetoelectric coupling, the charge and thermal conductivities are
electrically controllable via the spin spiral helicity. Moreover, the
thermopower exhibits a sign change when tuning electro-statically the carrier
density.",1012.4865v1
2011-08-24,"Wettability and ""petal effect"" of GaAs native oxides","We discuss unreported transitions of oxidized GaAs surfaces between
(super)hydrophilic and hydrophobic states when stored in ambient conditions.
Contact angles higher than 90deg and high adhesive force were observed for
several air-aged epitaxial samples grown under different conditions as well as
on epi-ready wafers. Regardless of the morphologies of the surface,
superhydrophilicity of oxygen-plasma treated samples was observed, an effect
disappearing with storage time. Reproducible hydrophobicity was likewise
observed, as expected, after standard HCl surface etching. The relation between
surface oxides and hydrophobic/hydrophilic behavior is discussed.",1108.4789v1
2012-07-03,Doping of Si nanoparticles: the effect of oxidation,"The preferred location of boron and phosphorus in oxidized free-standing Si
nanoparticles was investigated using a first-principles density functional
approach. The calculated formation energies indicate that P should segregate to
the silicon core, whereas B is equally stable in the Si and SiO_2 regions. Our
models thus suggest that, in contrast with nanocrystals with H-terminated
surfaces, the efficiency of phosphorus incorporation in oxidized Si
nanoparticles can be improved by thermal annealing.",1207.0770v2
2012-11-21,Atomic scale characterization of the nucleation and growth of SnO2 particles in oxidized CuSn alloys,"The internal oxidation of Sn was investigated to understand the oxidation
kinetics of monophase CuSn alloys. SnO2 particles were characterized by
analytical transmission electron microscopy. The orientation relationship
between SnO2 and Cu was determined with a special emphasis on the atomic scale
structure of Cu/SnO2 interfaces (misfit dislocations and chemical structure).
Habit planes with a pure oxygen plane terminating the SnO2 phase are greatly
favored and large misfits promote the growth of plate shaped precipitates.",1211.5038v1
2012-11-22,Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO$_{2\pm x}$,"We have conducted a detailed thin film growth structure of oxygen engineered
monoclinic HfO$_{2\pm x}$ grown by reactive molecular beam epitaxy (MBE). The
oxidation conditions induce a switching between ($\bar{1}11$) and (002) texture
of hafnium oxide. The band gap of oxygen deficient hafnia decreases with
increasing amount of oxygen vacancies by more than 1 eV. For high oxygen
vacancy concentrations, defect bands form inside the band gap that induce
optical transitions and $p$-type conductivity. The resistivity changes by
several orders of magnitude as a function of oxidation conditions. Oxygen
vacancies do not give rise to ferromagnetic behavior.",1211.5215v1
2013-02-13,Theory of ferromagnetism in vanadium-oxide based perovskites,"The conditions under which ferromagnetism may occur in transition metal
oxides with partially filled $t_{2g}$ shells such as vanadium-based perovskites
are studied using a combination of density functional and single-site dynamical
mean field methods. For reasonable values of the correlation strength,
rotations of the VO$_6$ octahedra play an important role in enabling
ferromagnetism, with ferromagnetism typically occurring for rotations larger
than a nonzero critical value. Ferromagnetism is suppressed near the Mott
insulating phase but the phase boundary is otherwise only weakly dependent on
carrier concentration. Design rules are suggested for new oxide systems
exhibiting ferromagnetism.",1302.3062v2
2013-12-14,Formation and anisotropic magnetoresistance of Co/Pt nano-contacts through aluminum oxide barrier,"We report on the observation of anisotropic magnetoresistance (AMR) in
vertical asymmetric nano-contacts (NCs) made through AlO$_x$ nano-oxide layer
(NOL) formed by ion-assisted oxidation method in the film stack of
Co/AlO$_x$-NOL/Pt. Analysis of NC formation was based on \emph{in situ}
conductive atomic force microscopy and transmission electron microscopy.
Depending on the purity of NCs from Al contamination, we observed up to 29% AMR
ratio at room temperature.",1312.4061v1
2014-01-29,Thermodynamic properties of yttrium cuprate,"The standard formation enthalpy and enthalpy from binary oxide of yttrium
cuprate have been determined by solution calorimetry combining the solution
enthalpies of Y2Cu2O5 and Y2O3 + 2CuO mixture in 6 M HCl at 323.15 K and
literature data. The heat capacity of Y2Cu2O5 has been measured by adiabatic
calorimetry from 8 up to 303 K. Smoothed values of heat capacities, entropies
and enthalpies were calculated on the basis of experimental data. The
thermodynamic functions (heat capacity, entropy and enthalpy) at 298.15 K have
been calculated. On the basis of obtained data it has been obtained that
above-mentioned complex oxide is thermodynamically unstable with respect to
their decomposition into binary oxides at room temperatures.",1401.7422v1
2014-11-23,Structural and electrochemical properties of MnO2-Carbon based supercapacitor electrodes,"We present results of an approach to incorporate redox-active manganese oxide
into the 3-dimensional porous structure of carbon xerogels under self-limiting
electroless conditions. By varying the structure of the carbon backbone, we
found that deposition of manganese oxide preferably takes place on the external
surface area of the carbon xerogels. From our detailed analysis we conclude
that 3-dimensional carbon xerogels with particle and pore sizes ranging from 10
to 20 nm and low manganese oxide precursor concentration combined with long
deposition times are beneficial for fast operating pseudocapacitance electrodes
with high capacitance and effective use of the redox active component.",1411.6278v1
2015-06-04,In situ TEM observation of oxygen evolution reaction in GDC-Pt half cell at elevated temperatures,"Gadolinium-doped ceria was studied in a half SOFCs at elevated temperatures.
In situ electron holography could reveal ionic activity in a single GDC-Pt
interface at the elevated temperatures that result in further oxidation of the
GDC. In situ EELS measurements confirmed holography results and showed the
existence of the gadolinium in a new oxidation state. Also, it was found that
the doped cations are the active ions in the oxygen evolution reaction from the
solid oxide electrolyte.",1506.02067v1
2015-10-01,Krypton oxides under pressure,"Under high pressure, krypton, one of the most inert elements is predicted to
become sufficiently reactive to form a new class of krypton compounds; krypton
oxides. Using modern ab-initio evolutionary algorithms in combination with
Density Functional Theory, we predict the existence of several
thermodynamically stable Kr/O species at elevated pressures. In particular, our
calculations indicate that at approx. 300 GPa the monoxide, KrO, should form
spontaneously and remain thermo- and dynamically stable with respect to
constituent elements and higher oxides. The monoxide is predicted to form
non-molecular crystals with short Kr-O contacts, typical for genuine chemical
bonds.",1510.00255v1
2016-03-15,Infrared dielectric properties of low-stress silicon oxide,"Silicon oxide thin films play an important role in the realization of optical
coatings and high-performance electrical circuits. Estimates of the dielectric
function in the far- and mid-infrared regime are derived from the observed
transmittance spectrum for a commonly employed low-stress silicon oxide
formulation. The experimental, modeling, and numerical methods used to extract
the dielectric function are presented.",1603.04815v1
2017-02-06,On the oxidation state of titanium in titanium dioxide,"The oxidation state of titanium in titanium dioxide is commonly assumed to be
+4. This assumption is used ubiquitously to rationalize phenomena observed with
TiO2. We present a comprehensive electronic structure investigation of Ti ions,
TiO2 molecules and TiO2 bulk crystals, using different density functional
theory and wave function-based approaches, which suggests a lower oxidation
state (+3). Specifically, there is evidence of a significant remaining
contribution from valence s and d electrons of Ti, including the presence of a
nuclear cusp around the Ti core. The charge corresponding to valence s and d
states of Ti amounts to 1 e. The commonly assumed picture may therefore have to
be revised.",1702.01555v1
2017-02-18,Delta-doped Beta- Gallium Oxide Field Effect Transistor,"We report silicon delta doping in Gallium Oxide (\b{eta}-Ga2O3) grown by
plasma assisted molecular beam epitaxy using a shutter pulsing technique. We
describe growth procedures that can be used to realize high Si incorporation in
an oxidizing oxygen plasma environment. Delta doping was used to realize thin
(12 nm) low-resistance layers with sheet resistance of 320 Ohm/square (mobility
of 83 cm^2/Vs, integrated sheet charge of 2.4x10^14 cm^-2). A single
delta-doped sheet of carriers was employed as a channel to realize a field
effect transistor with current ID,MAX =292 mA/mm and transconductance gM = 27
mS/mm.",1702.06584v1
2017-03-01,Infrared properties of micromachined vanadium oxide thin films,"This paper discusses questions of synthesizing and pressing vanadium oxides
to create film-forming materials that can be used in producing optical
coatings. Based on the film-forming materials thus created, technological
processes have been developed for fabricating coatings from vanadium dioxide by
two methods of producing thin films: vacuum evaporation and magnetron
sputtering. Questions of using films made from vanadium oxide in optical
instrumentation are considered.",1703.00127v1
2018-02-23,Independence of surface morphology and reconstruction during the thermal preparation of perovskite oxide surfaces,"Using a CO$_2$ laser to directly heat the crystals from the back side,
SrTiO$_3$ substrates may be thermally prepared in situ for epitaxy without the
need for ex-situ etching and annealing. We find that the formation of large
terraces with straight steps at 900-1100 {\deg}C is independent from the
formation of the ideal surface reconstruction for epitaxy, which requires
temperatures in excess of 1200 {\deg}C to complete. The process may be
universal, at least for perovskite oxide surfaces, as it also works, at
different temperatures, for LaAlO$_3$ and NdGaO$_3$, two other widely used
oxide substrate materials.",1802.08423v1
2018-03-30,Nanostructured Ceramic Oxides with a Slow Crack Growth Resistance Close to Covalent Materials,"Oxide ceramics are sensitive to slow crack growth because adsorption of water
can take place at the crack tip, leading to a strong decrease of the surface
energy in humid (or air) conditions. This is a major drawback concerning
demanding, long-term applications such as orthopaedic implants. Here we show
that a specific nanostructuration of ceramic oxides can lead to a crack
resistance never reached before, similar to that of covalent ceramics.",1804.01393v1
2020-07-04,Data-Mining Element Charges in Inorganic Materials,"Oxidation states are well-established in chemical science teaching and
research. We data-mine more than 168,000 crystallographic reports to find an
optimal allocation of oxidation states to each element. In doing so we uncover
discrepancies between text-book chemistry and reported charge states observed
in materials. We go on to show how the oxidation states we recommend can
significantly facilitate materials discovery and heuristic design of novel
inorganic compounds.",2007.02085v1
2016-11-28,Dynamical mean field theory for oxide heterostructures,"Transition metal oxide heterostructures often, but by far not always, exhibit
strong electronic correlations. State-of-the-art calculations account for these
by dynamical mean field theory (DMFT). We discuss the physical situations in
which DMFT is needed, not needed, and where it is actually not sufficient. By
means of an example, SrVO$_3$/SrTiO$_3$, we discuss step-by-step and
figure-by-figure a density functional theory(DFT)+DMFT calculation. The second
part reviews DFT+DMFT calculations for oxide heterostructure focusing on
titanates, nickelates, vanadates, and ruthenates.",1611.09044v1
2017-04-04,Continuum model for hydrogen pickup in Zirconium alloys of LWR fuel cladding,"A continuum model for calculating the time-dependent hydrogen pickup
fractions in various Zirconium alloys under steam and pressured water oxidation
has been developed in this study. Using only one fitting parameter, the
effective hydrogen gas partial pressure at the oxide surface, a qualitative
agreement is obtained between the predicted and previously measured hydrogen
pickup fractions. The calculation results therefore demonstrate that H
diffusion through the dense oxide layer plays an important role in the hydrogen
pickup process. The limitations and possible improvement of the model are also
discussed.",1704.01201v1
2017-04-04,Multibit memory operation of metal-oxide bi-layer memristors,"In this work, we evaluate a multitude of metal-oxide bi-layers and
demonstrate the benefits from increased memory stability via multibit memory
operation. We introduce a programming methodology that allows for operating
metal-oxide memristive devices as multibit memory elements with highly packed
yet clearly discernible memory states. We finally demonstrate a 5.5-bit memory
cell (47 resistive states) with excellent retention and power consumption
performance. This paves the way for neuromorphic and non-volatile memory
applications.",1704.03313v1
2008-07-18,AFM local oxidation nanolithography of graphene,"We demonstrate the local oxidation nanopatterning of graphene films by an
atomic force microscope. The technique provides a method to form insulating
trenches in graphene flakes and to fabricate nanodevices with sub-nm precision.
We demonstrate fabrication of a 25-nm-wide nanoribbon and sub-micron size
nanoring from a graphene flake. We also found that we can write either trenches
or bumps on the graphene surface depending on the lithography conditions. We
attribute the bumps to partial oxidation of the surface and incorporation of
oxygen into the graphene lattice.",0807.2886v2
2009-12-01,How Graphene Is Cut upon Oxidation?,"Our first principles calculations reveal that oxidative cut of graphene is
realized by forming epoxy and then carbonyl pairs. Direct forming carbonyl pair
to tear graphene up from an edge position is not favorable in energy. This
atomic picture is valuable for developing effective graphene manipulation
means. The proposed epoxy pairs may be related to some long puzzling
experimental observations on graphene oxide.",0912.0083v1
2009-12-04,Nanophotonic devices on thin buried oxide Silicon-On-Insulator substrates,"We demonstrate a silicon photonic platform using thin buried oxide
silicon-on-insulator (SOI) substrates using localized substrate removal. We
show high confinement silicon strip waveguides, micro-ring resonators and
nanotapers using this technology. Propagation losses for the waveguides using
the cutback method are 3.88 dB/cm for the quasi-TE mode and 5.06 dB/cm for the
quasi-TM mode. Ring resonators with a loaded quality factor (Q) of 46,500 for
the quasi-TM mode and intrinsic Q of 148,000 for the quasi-TE mode have been
obtained. This process will enable the integration of photonic structures with
thin buried oxide SOI based electronics.",0912.0775v1
2011-11-08,Unusual ferromagnetism in nanoparticles of doped oxides and manganites,"The observation of unusually large ferromagnetism in the nanoparticles of
doped oxides and enhanced ferromagnetic tendencies in manganite nanoparticles
have been in focus recently. For the transition metal-doped oxide nanoparticles
a phenomenological `charge transfer ferromagnetism' model is recently proposed
by Coey et al. From a microscopic calculation with charge transfer between the
defect band and mixed valent dopants, acting as reservoir, we show how the
unusually high ferromagnetic response develops. The puzzle of nanosize-induced
ferromagnetic tendencies in manganites is also addressed within the same
framework where lattice imperfections and uncompensated charges at the surface
of the nanoparticle are shown to reorganize the surface electronic structures
with enhanced double exchange.",1111.1778v1
2012-01-26,Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces,"In order to determine the key parameters that control the resistive switching
mechanism in metal-complex oxides interfaces, we have studied the electrical
properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different
oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the
surface of a YBCO ceramic sample. By analyzing the IV characteristics of the
contact interfaces and the temperature dependence of their resistance, we
inferred that ion migration may generate or cancel conducting filaments, which
modify the resistance near the interface, in accordance with the predictions of
a recent model.",1201.5670v1
2012-04-10,Analytical and numerical study of particles with binary adsorption,"Electro-oxidation of ethanol represents a key process in fuel-cells
technology. We introduce a generalization of the random sequential adsorption
model to study the long timescale and large length scale properties of the
electro-oxidation process. We provide an analytical solution for one dimension
and Monte Carlo results in two dimensions. We characterize the coverage and
percolation properties of the jammed state and unveil the influence of quenched
impurities in the selectivity of oxidation products.",1204.2093v1
2012-04-25,Intrinsic Origin of Negative Fixed Charge in Wet Oxidation for Silicon Carbide,"We demonstrate on the basis of first-principles calculations that the
formation of carbonate-like moiety in SiO$_2$ could be the intrinsic origin of
negative fixed charge in SiC thermal oxidation. We find that two possible
origins for the negative fixed charges are O-lone-pair state and a negatively
charged CO$_3$ ion in SiO$_2$. Such CO$_3$ ion is able to be formed as a result
of the existence of residual C atoms in SiO$_2$, which are expected to be
emitted from the interface between SiC and SiO$_2$, and the incorporation of H
atoms during wet oxidation.",1204.5556v1
2015-12-08,Analysis of high quality superconducting resonators: consequences for TLS properties in amorphous oxides,"$1/f$ noise caused by microscopic Two-Level Systems (TLS) is known to be very
detrimental to the performance of superconducting quantum devices but the
nature of these TLS is still poorly understood. Recent experiments with
superconducting resonators indicates that interaction between TLS in the oxide
at the film-substrate interface is not negligible. Here we present data on the
loss and $1/f$ frequency noise from two different Nb resonators with and
without Pt capping and discuss what conclusions can be drawn regarding the
properties of TLS in amorphous oxides. We also estimate the concentration and
dipole moment of the TLS.",1512.02553v1
2016-08-18,Geometrical lattice engineering of complex oxide heterostructures: a designer approach to emergent quantum states,"Epitaxial heterostructures composed of complex oxides have fascinated
researchers for over a decade as they offer multiple degrees of freedom to
unveil emergent many-body phenomena often unattainable in bulk. Recently, apart
from stabilizing such artificial structures along the conventional
[001]-direction, tuning the growth direction along unconventional
crystallographic axes has been highlighted as a promising route to realize
novel quantum many-body phases. Here we illustrate this rapidly developing
field of geometrical lattice engineering with the emphasis on a few
prototypical examples of the recent experimental efforts to design complex
oxide heterostructures along the (111) orientation for quantum phase discovery
and potential applications.",1608.05283v1
2017-06-08,Ab initio studies of carbon dioxide affinity to carbon compounds and minerals,"We have performed quantum chemical computational studies to determine carbon
dioxide affinity to carbon compounds and minerals, which could be present in
shales. These studies shed light on the microscopic mechanisms of the possible
carbon oxide sequestration processes. Our studies reveal that the carbon oxide
can be adsorbed to various forms of carbon structures and also minerals such as
periclase or illite. We find out that the strongest affinity of carbon oxide
towards carbon structures occurs when the carbon structures exhibit $sp^3$
bonds.",1706.02572v1
2017-10-10,Growth of Antiperovskite Oxide Ca3SnO Films by Pulsed Laser Deposition,"We report the epitaxial growth of Ca3SnO antiperovskite oxide films on
(001)-oriented cubic yttria-stabilized zirconia (YSZ) substrates by using a
conventional pulsed laser deposition (PLD) technique. In this work, a sintered
Ca3SnO pellet is used as the ablation target. X-ray diffraction measurements
demonstrate the (001) growth of Ca3SnO films with the antiperovskite structure
and a cube-on-cube orientation relationship to the YSZ substrate. The
successful synthesis of the antiperovskite phase is further confirmed by x-ray
photoemission spectroscopy. These results strongly suggest that
antiperovskite-oxide films can be directly grown on substrates from the target
material using a PLD technique.",1710.03406v1
2020-04-28,High mobility conducting channel at semi-insulating GaAs -- metal oxide interfaces,"Absence of an efficient technology of GaAs passivation limits the use of
III-V semiconductors in modern electronics. The effect reported here can
possibly lead to a solution of this long standing problem. We found that an
electrically conducting interfacial channel is formed when insulating metal
oxide dielectrics are deposited on untreated semi-insulating GaAs wafers by
reactive RF sputtering in argon/oxygen plasma. The conducting channel is n-type
with the surface charge density of 10^7 to 10^10 cm^-2 and Hall mobility as
high as 6000 cm^2/Vsec, depending on the RF plasma excitation power and oxygen
content during the deposition. The conducting channel is formed by depositing
any of the tested metal oxide dielectrics: MgO, SiO2, Al2O3 and HfO2.",2004.13543v1
2012-05-02,Nanoscale Plasmonic and Optical Modulators Based on Transparent Conducting Oxides,"Recent experiments showed that unity-order index change in a transparent
conducting oxide (TCO) can be achieved in a metal-oxide-semiconductor (MOS)
structure by accumulation charge. However, the ultrathin (~5nm) accumulation
layer and inherent absorption of TCOs impede the practical applications of this
effect. Herein, we propose and explore a novel waveguide, namely ""TCO-slot
waveguide"", which combines both the tunable property of a TCO and field
enhancement of a slot waveguide. In particular, light absorption can be sharply
enhanced when the slot dielectric constant is tuned close to zero. Based on
TCO-slot waveguides, efficient electro-absorption modulation can be achieved
within 200 nm with small insertion loss.",1205.0502v1
2017-05-02,Carbon Ejection from a SiO2/SiC(0001) Interface by Annealing in High-Purity Ar,"We found that carbon-associated byproducts formed at the dry-oxidized
SiO2/SiC(0001) interface could be decomposed and be taken out to the SiO2 side
by high-purity Ar annealing. We evaluated the concentration of the ejected
carbon atoms in the SiO2 by secondary ion mass spectrometry, and discovered
that it clearly depends on the condition of oxide formation (dry-oxidation,
nitridation treatment, and phosphorus treatment). This work provides an
indirect but unambiguous evidence for the carbon-byproducts existing at the
SiO2/SiC interfaces, and also indicates that the phosphorus treatment removes
the carbon-byproducts, leading to significant reduction of interface defects.",1705.00814v1
2017-11-20,"Structural, Optical and Electronic properties of Magnetron Sputtered Si and Ge thin films","We report the results of GIXRR, UV-VIS NIR and XPS measurements on Si and Ge
thin films of various thicknesses. While GIXRR measurements show no presence of
oxide on the top of these films, XPS measurements show small amount of oxides.
Also, a sharp increase in surface roughness is seen with thickness in agreement
with the columnar growth of films. In contrast, in case of Si films, oxide is
present even inside the layers but in a very small amount and is not detected
in GIXRR/absorption measurements.",1711.07174v1
2019-01-08,Structure and Synthesis of graphene oxide,"Graphene oxide (GO) is regarded as one typical two-dimension structured
oxygenated planar molecular material. Researchers across multiple disciplines
have paid enormous attention to it due to unique physiochemical properties.
However, models used to describe the structure of GO are still in argument and
ongoing to update. Currently, synthesis methods for massive production are
seemingly abundant but in fact, dominated by few thought systems. We herein aim
to give a mini but critical review over the synthesis of graphene oxide as well
as its structure, involving relative peer work.",1901.02274v2
2019-08-06,Surface terraces in pure tungsten formed by high-temperature oxidation,"We observe large-scale surface terraces in tungsten oxidised at high
temperature and in high vacuum. Their formation is highly dependent on crystal
orientation, with only {111} grains showing prominent terraces. Terrace facets
are aligned with {100} crystallographic planes, leading to an increase in total
surface energy, making a diffusion-driven formation mechanism unlikely. Instead
we hypothesize that preferential oxidation of {100} crystal planes controls
terrace formation. Grain height profiles after oxidation and the morphology of
samples heat treated with limited oxygen supply are consistent with this
hypothesis. Our observations have important implications for the use of
tungsten in extreme environments.",1908.02036v1
2021-03-20,Influence of nonlinear- and saturable-absorption on laser lift-off threshold of oxide/metal structure,"In this work, a new model of effective lift-off threshold of oxide/metal
target is presented. The influence of nonlinear processes in the oxide layer on
its removal from the metallic samples using picosecond laser was investigated.
Nonlinear and saturable absorption in the layer was incorporated into modeling
for prediction of effective laser lift-off threshold fluence change with
varying peak intensities in z-scan type experiment for the first time. The new
model coincides well with the experimental results.",2103.11140v2
2022-07-25,Experimental evaluation of a silicone oil as an oxidation inhibitor for magnesium alloy under contact sliding at elevated temperatures,"This paper experimentally investigated the effects of silicone oil on the
tribological behaviour of AZ31B/86CrMoV7 contact pair under a pin-on-disk
configuration. A commercial silicone oil was used as an oxidation inhibiter for
the AZ31B at elevated temperatures to 300 oC. The wear mechanism of the contact
pair was explored by SEM morphologies of worn surfaces. The analysis revealed
that silicone oil can effectively minimize surface oxidation. Compared with dry
sliding, silicone oil can considerably lower down the friction coefficient and
specific wear rate. Under lubrication, the abrasive wear at a lower temperature
can transit to the combined wear of abrasion, fatigue and adhesion when the
temperature rises.",2207.11908v1
2022-12-21,Impact of different metal electrodes on the ferroelectric properties of hafnium-zirconium oxide in M1/FE/M2 structures during the electric field cycling,"The interest in the ferroelectric non-volatile memory as a candidate for low
power consumption electronic memories was raised after the discovery of
ferroelectricity in hafnium oxide. Doping by different elements of hafnia films
allows improving their ferroelectric properties. In this work, the transport
experiments are combined with the simulations to study the evolution of
ferroelectric properties and the mean distance between oxygen vacancies during
the endurance of hafnium-zirconium oxide in metal-ferroelectric-metal
structures to study the impact of different metal electrodes.",2212.10858v1
2023-03-23,Antiferromagnetic insulatronics: spintronics in insulating 3d metal oxides with antiferromagnetic coupling,"Antiferromagnetic transition metal oxides are an established and widely
studied materials system in the context of spin-based electronics, commonly
used as passive elements in exchange bias-based memory devices. Currently,
major interest has resurged due to the recent observation of long-distance spin
transport, current-induced switching, and THz emission. As a result, insulating
transition metal oxides are now considered to be attractive candidates for
active elements in novel spintronic devices. Here, we discuss some of the most
promising materials systems and highlight recent advances in reading and
writing antiferromagnetic ordering. This article aims to provide an overview of
the current research and potential future directions in the field of
antiferromagnetic insulatronics.",2303.13369v1
2003-02-06,Sub-surface Oxygen and Surface Oxide Formation at Ag(111): A Density-functional Theory Investigation,"To help provide insight into the remarkable catalytic behavior of the
oxygen/silver system for heterogeneous oxidation reactions, purely sub-surface
oxygen, and structures involving both on-surface and sub-surface oxygen, as
well as oxide-like structures at the Ag(111) surface have been studied for a
wide range of coverages and adsorption sites using density-functional theory.
Adsorption on the surface in fcc sites is energetically favorable for low
coverages, while for higher coverage a thin surface-oxide structure is
energetically favorable. This structure has been proposed to correspond to the
experimentally observed (4x4) phase. With increasing O concentrations, thicker
oxide-like structures resembling compressed Ag2O(111) surfaces are
energetically favored. Due to the relatively low thermal stability of these
structures, and the very low sticking probability of O2 at Ag(111), their
formation and observation may require the use of atomic oxygen (or ozone, O3)
and low temperatures. We also investigate diffusion of O into the sub-surface
region at low coverage (0.11 ML), and the effect of surface Ag vacancies in the
adsorption of atomic oxygen and ozone-like species. The present studies,
together with our earlier investigations of on-surface and
surface-substitutional adsorption, provide a comprehensive picture of the
behavior and chemical nature of the interaction of oxygen and Ag(111), as well
as of the initial stages of oxide formation.",0302122v1
2007-02-15,Tip artifact in atomic force microscopy observations of InAs quantum dots grown in Stranski-Krastanow mode,"The tip artifact in atomic force microscopy (AFM) observations of InAs
islands was evaluated quantitatively. The islands were grown in the
Stranski-Krastanow mode of molecular beam epitaxy. The width and height of the
islands were determined using transmission electron microscopy (TEM) and AFM.
The average $[\bar{1}10]$ in-plane width and height determined using TEM
excluding native oxide were 22 and 7 nm, respectively; those determined using
AFM including the oxide were 35 and 8 nm, respectively. The difference in width
was due to the oxide and the tip artifact. The sizes including the oxide were
deduced from TEM observations to be a width of 27 nm and a height of 6 nm with
correction for the thickness of the oxide. The residual difference of 8 nm
between the width determined using AFM and that determined using TEM including
the oxide was ascribed to the tip artifact. The results enable us to determine
the actual size of the islands from their AFM images.",0702354v1
2007-08-03,Time course of oxidative damage in different brain regions following transient cerebral ischemia in gerbils,"The time course of oxidative damage in different brain regions was
investigated in the gerbil model of transient cerebral ischemia. Animals were
subjected to both common carotid arteries occlusion for 5 min. After the end of
ischemia and at different reperfusion times (2, 6, 12, 24, 48, 72, 96 h and 7
days), markers of lipid peroxidation, reduced and oxidized glutathione levels,
glutathione peroxidase, glutathione reductase, manganese-dependent superoxide
dismutase (MnSOD) and copper/zinc containing SOD (Cu/ZnSOD) activities were
measured in hippocampus, cortex and striatum. Oxidative damage in hippocampus
was maximal at late stages after ischemia (48-96 h) coincident with a
significant impairment in glutathione homeostasis. MnSOD increased in
hippocampus at 24, 48 and 72 h after ischemia, coincident with the marked
reduction in the activity of glutathione-related enzymes. The late disturbance
in oxidant-antioxidant balance corresponds with the time course of delayed
neuronal loss in the hippocampal CA1 sector. Cerebral cortex showed early
changes in oxidative damage with no significant impairment in antioxidant
capacity. Striatal lipid peroxidation significantly increased as early as 2 h
after ischemia and persisted until 48 h with respect to the sham-operated
group. These results contribute significant information on the timing and
factors that influence free radical formation following ischemic brain injury,
an essential step in determining effective antioxidant intervention.",0708.0572v1
2009-01-23,The DNA Single-Strand Break Repair Machinery Facilitates CAF-1-Mediated Histone Deposition at Oxidative DNA Strand Breaks,"Oxidative DNA single strand breaks arise continuously in cells and defects in
their repair have been implicated in neurological disease. While much progress
has been made in understanding how chromosomal single strand breaks are
repaired little is known about the changes chromatin structure that accompany
this process. Here, we show that nascent recombinant histone H3.1 protein
accumulates and is deposited into chromatin at sites of DNA strand breakage in
quiescent human cells following oxidative stress, and that core components of
the single-strand break repair machinery are required for this process. We show
that the SSBR sensor and scaffold proteins poly (ADP-ribose) polymerase and
XRCC1 facilitate accumulation of chromatin assembly factor-1 (CAF-1) at sites
of oxidative DNA strand breakage, which in turn mediates the deposition of
Histone H3.1. We also demonstrate that depletion of CAF-1 slows global rates of
DNA strand break repair in quiescent cells following oxidative stress,
demonstrating that single-strand break repair and histone deposition are
tightly coordinated processes. These data describe a novel role for the DNA
singlestrand break repair machinery and implicate histone turnover as a core
component of the cellular response of quiescent cells to oxidative damage.",0901.3719v4
2010-01-25,Novel Multifunctional Materials Based on Oxide Thin Films and Artificial Heteroepitaxial Multilayers,"Transition metal oxides show fascinating physical properties such as high
temperature superconductivity, ferro- and antiferromagnetism, ferroelectricity
or even multiferroicity. The enormous progress in oxide thin film technology
allows us to integrate these materials with semiconducting, normal conducting,
dielectric or non-linear optical oxides in complex oxide heterostructures,
providing the basis for novel multi-functional materials and various device
applications. Here, we report on the combination of ferromagnetic,
semiconducting, metallic, and dielectric materials properties in thin films and
artificial heterostructures using laser molecular beam epitaxy. We discuss the
fabrication and characterization of oxide-based ferromagnetic tunnel junctions,
transition metal-doped semiconductors, intrinsic multiferroics, and artificial
ferroelectric/ferromagetic heterostructures - the latter allow for the detailed
study of strain effects, forming the basis of spin-mechanics. For
characterization we use X-ray diffraction, SQUID magnetometry, magnetotransport
measurements, and advanced methods of transmission electron microscopy with the
goal to correlate macroscopic physical properties with the microstructure of
the thin films and heterostructures.",1001.4447v2
2012-02-03,Temperature-dependent electron microscopy study of Au thin films on Si (100) with and without native oxide layer as barrier at the interface,"Real time electron microscopy observation on morphological changes in gold
nano structures deposited on Si (100) surfaces as a function of annealing
temperatures has been reported. Two types of interfaces with the substrate
silicon were used prior to gold thin film deposition: (i) without native oxide
and on ultra-clean reconstructed Si surfaces and (ii) with native oxide covered
Si surfaces. For a \approx 2.0 nm thick Au films deposited on reconstructed
Si(100) surfaces using molecular beam epitaxy method under ultra high vacuum
conditions, aligned four-fold symmetric nanogold silicide structures formed at
relatively lower temperatures (compared with the one with native oxide at the
interface). For this system, 82% of the nanostructures were found to be nano
rectangles like structures with an average length \approx 27 nm and aspect
ratio of 1.13 at \approx 700{\deg}C. For \approx 5.0 nm thick Au films
deposited on Si (100) surface with native oxide at the interface, formation of
rectangular structures were observed at higher temperatures (\approx 850{\deg}
C). At these high temperatures, desorption of the gold silicide followed the
symmetry of the substrate. Native oxide at the interface was found to act like
a barrier for the inter-diffusion phenomena. Structural characterization was
carried out using advanced electron microscopy methods.",1202.0647v1
2012-09-29,Passivity of Metals in the Point Defect Model: Effect of Chloride [Part-III],"In this paper we study the effect of addition of chloride on the stability of
the compact oxide layer pre-existing on a metal surface at a given impressed
potential and . The variant of the point defect model (PDM)advanced by us
recently is used to construct a theory for the chloride-induced build-up of
metal vacancies at the metal-film interface and the chloride-induced
dissolution of the compact oxide layer. Under the quasi-steady-state
approximation the relevant moving boundary value problem is solved exactly and
analytical expressions are found for the incubation time, oxide dissolution
time, and critical pitting potential, the time evolution of the passive current
density and the metal vacancy concentration and the dependence of these
quantities on the chloride ion concentration. Some diagnostics are also
provided. The replacement of a reaction of the original PDM by another reaction
in the variant is shown to have important consequences for the chloride-ion
effect. While the original PDM invoked the Schottky-pair reaction to couple the
chloride ion to the cation flux and to the metal vacancy generation, the
present model couples the chloride ion directly to the metal vacancy
annihilation without invoking the Schottky-pair reaction. The anion
flux-pinning by chloride is shown to be sufficient to destabilize the oxide
layer. An interesting conclusion of the present work is that thicker oxide
layers are in general more susceptible to pitting due to the chloride ion and
thinner oxide layers destabilize by simple dissolution in the presence of
chloride.",1210.0099v1
2013-11-04,Molecular responses of mouse macrophages to copper and copper oxide nanoparticles inferred from proteomic analyses,"The molecular responses of macrophages to copper-based nanoparticles have
been investigated via a combination of proteomic and biochemical approaches,
using the RAW264.7 cell line as a model. Both metallic copper and copper oxide
nanoparticles have been tested, with copper ion and zirconium oxide
nanoparticles used as controls. Proteomic analysis highlighted changes in
proteins implicated in oxidative stress responses (superoxide dismutases and
peroxiredoxins), glutathione biosynthesis, the actomyosin cytoskeleton, and
mitochondrial proteins (especially oxidative phosphorylation complex subunits).
Validation studies employing functional analyses showed that the increases in
glutathione biosynthesis and in mitochondrial complexes observed in the
proteomic screen were critical to cell survival upon stress with copper-based
nanoparticles; pharmacological inhibition of these two pathways enhanced cell
vulnerability to copper-based nanoparticles, but not to copper ions.
Furthermore, functional analyses using primary macrophages derived from bone
marrow showed a decrease in reduced glutathione levels, a decrease in the
mitochondrial transmembrane potential, and inhibition of phagocytosis and of
lipopolysaccharide-induced nitric oxide production. However, only a fraction of
these effects could be obtained with copper ions. In conclusion, this study
showed that macrophage functions are significantly altered by copper-based
nanoparticles. Also highlighted are the cellular pathways modulated by cells
for survival and the exemplified cross-toxicities that can occur between
copper-based nanoparticles and pharmacological agents.",1311.0802v1
2014-11-02,Re-visiting the O/Cu(111) system -- When metastable surface oxides could become an issue!,"Surface oxidation processes are crucial for the functionality of Cu-based
catalytic systems used for methanol synthesis, partial oxidation of methanol or
the water-gas shift reaction. We assess the stability and population of the
""8""-structure, a $|\begin{smallmatrix} 3&2\\ -1&2 \end{smallmatrix}|$ oxide
phase, on the Cu(111) surface. This structure has been observed in x-ray
photoelectron spectroscopy and low-energy electron diffraction experiments as a
Cu(111) surface reconstruction that can be induced by a hyperthermal oxygen
molecular beam. Using density-functional theory calculations in combination
with \textit{ab initio} atomistic thermodynamics and Boltzmann statistical
mechanics, we find that the proposed oxide superstructure is indeed metastable
and that the population of the ""8""-structure is competitive with the known ""29""
and ""44"" oxide film structures on Cu(111). We show that the configuration of O
and Cu atoms in the first and second layers of the ""8""-structure closely
resembles the arrangement of atoms in the first two layers of Cu$_2$O(110),
where the atoms in the ""8""-structure are more constricted. Cu$_2$O(110) has
been suggested in the literature as the most active low index facet for
reactions such as water splitting under light illumination. If the
""8""-structure were to form during a catalytic process, it is therefore likely
to be one of the reactive phases.",1411.0276v1
2014-12-15,High-Mobility Bismuth-based Transparent P-Type Oxide from High-throughput Material Screening,"Transparent oxides are essential building blocks to many technologies,
ranging from components in transparent electronics, transparent conductors, to
absorbers and protection layers in photovoltaics and photoelectrochemical
devices. However, thus far, it has been difficult to develop p-type oxides with
wide band gap and high hole mobility; current state-of-art transparent p-type
oxides have hole mobility in the range of < 10 cm$^2$/Vs, much lower than their
n-type counterparts. Using high-throughput computational screening to guide the
discovery of novel oxides with wide band gap and high hole mobility, we report
the computational identification and the experimental verification of a
bismuth-based double-perovskite oxide that meets these requirements. Our
identified candidate, Ba$_2$BiTaO$_6$, has an optical band gap larger than 4 eV
and a Hall hole mobility above 30 cm$^2$/Vs. We rationalize this finding with
molecular orbital intuitions; Bi$^{3+}$ with filled s-orbitals strongly overlap
with the oxygen p, increasing the extent of the metal-oxygen covalency and
effectively reducing the valence effective mass, while Ta$^{5+}$ forms a
conduction band with low electronegativity, leading to a high band gap beyond
the visible range. Our concerted theory-experiment effort points to the growing
utility of a data-driven materials discovery and the combination of both
informatics and chemical intuitions as a way to discover future technological
materials.",1412.4429v1
2014-12-20,Surface Energetics of Alkaline-Earth Metal Oxides: Trends in Stability and Adsorption of Small Molecules,"We present a systematic theoretical investigation of the surface properties,
stability and reactivity, of rock-salt type alkaline-earth metal oxides
including MgO, CaO, SrO, and BaO. The accuracy of commonly used
exchange-correlation density functionals (LDA, PBE, RPBE, PBEsol, BEEF-vdW and
hybrid HSE) and random-phase approximation (RPA) is evaluated and compared to
existing experimental values. Calculated surface energies of the four most
stable surface facets under vacuum conditions: the (100) surface, the metal and
oxygen terminated octopolar (111), and the (110) surfaces exhibit a monotonic
increase in stability from MgO to BaO. On the MgO(100) surface, adsorption of
CO, NO, CH4 is characterized by physisorption while H2O chemisorbs, which is in
agreement with experimental findings. We further use the on-top metal
adsorption of CO and NO molecules to map out the surface energetics of each
alkaline-earth metal oxide surface. The considered functionals all
qualitatively predict similar adsorption energy trends. The ordering between
the adsorption energies on different surface facets can be attributed to
differences in the local geometrical surface structure and the electronic
structure of the metal constituent of the alkaline-earth metal oxide. The
striking observation that CO adsorption strength is weaker than NO adsorption
on the (100) terraces as the period of the alkaline-earth metal in the oxide
increases, is analyzed in detail in terms of charge redistribution within the
{\sigma} and {\pi} channels of adsorbates. Finally, we also present oxygen
adsorption and oxygen vacancy formation energies in these oxide systems.",1412.6585v2
2015-07-14,Thermal Oxidation of WSe2 Nano-sheets Adhered on SiO2/Si Substrates,"Due to the drastically different intralayer versus interlayer bonding
strengths, the mechanical, thermal, and electrical properties of
two-dimensional (2D) materials are highly anisotropic between the in-plane and
out-of-plane directions. The structural anisotropy may also play a role in
chemical reactions, such as oxidation, reduction, and etching. Here, the
composition, structure, and electrical properties of mechanically exfoliated
WSe2 nano- sheets on SiO2/Si substrates were studied as a function of the
extent of thermal oxidation. A major component of the oxidation, as indicated
from optical and Raman data, starts from the nano-sheet edges and propagates
laterally towards the center. Partial oxidation also occurs in certain areas at
the surface of the flakes, which are shown to be highly conductive by microwave
impedance microscopy. Using secondary ion mass spectroscopy, we also observed
extensive oxidation at the WSe2/SiO2 interface. The combination of multiple
microcopy methods can thus provide vital information on the spatial evolution
of chemical reactions on 2D materials and the nanoscale electrical properties
of the reaction products.",1507.04048v1
2015-10-08,Nearly-free electrons in a 5d delafossite oxide metal,"Understanding the role of electron correlations in strong spin-orbit
transition-metal oxides is key to the realisation of numerous exotic phases
including spin-orbit assisted Mott insulators, correlated topological solids,
and prospective new high-temperature superconductors. To date, most attention
has been focussed on the $5d$ iridium-based oxides. Here, we instead consider
the Pt-based delafossite oxide PtCoO$_2$. Our transport measurements, performed
on single-crystal samples etched to well-defined geometries using focussed
ion-beam techniques, yield a room-temperature resistivity of only
2.1~$\mu\Omega$cm, establishing PtCoO$_2$ as the most conductive oxide known.
From angle-resolved photoemission and density-functional theory, we show that
the underlying Fermi surface is a single cylinder of nearly hexagonal
cross-section, with very weak dispersion along k$_z$. Despite being
predominantly composed of $d$-orbital character, the conduction band is
remarkably steep, with an average effective mass of only 1.14$m_e$. Moreover,
the sharp spectral features observed in photoemission remain well-defined with
little additional broadening for over 500~meV below E$_F$, pointing to
suppressed electron-electron scattering. Together, our findings establish
PtCoO$_2$ as a model nearly-free electron system in a $5d$ delafossite
transition-metal oxide.",1510.02439v1
2016-03-09,Quantization of Hall Resistance at the Metallic Interface between an Oxide Insulator and SrTiO$_{3}$,"The two-dimensional metal forming at the interface between an oxide insulator
and SrTiO3 provides new opportunities for oxide electronics. However, the
quantum Hall effect, one of the most fascinating effects of electrons confined
in two dimensions, remains underexplored at these complex oxide
heterointerfaces. Here, we report the experimental observation of quantized
Hall resistance in a SrTiO3 heterointerface based on the modulation-doped
amorphous-LaAlO$_{3}$/SrTiO$_{3}$ heterostructure, which exhibits both high
electron mobility exceeding 10000 cm$^{2}$/Vs and low carrier density on the
order of ~10$^{12}$ cm$^{-2}$. Along with unambiguous Shubnikov-de Haas
oscillations, the spacing of the quantized Hall resistance suggests that the
interface is comprised of a single quantum well with ten parallel conducting
two-dimensional subbands. This provides new insight into the electronic
structure of conducting oxide interfaces and represents an important step
towards designing and understanding advanced oxide devices.",1603.02850v2
2016-07-28,Two-Dimensional Boron Oxides with Dirac Loop and Strongly anisotropic Carrier Mobility,"Recently, two-dimensional boron sheets have attracted a lot of attentions
owing to their structural polymorphs and outstanding properties. And, due to
chemical complexity and electron deficiency of B atoms, the 2D boron sheets are
easy affected by the environment. So, exploring novel 2D boron oxides gets
highly needed. In this study, we theoretically explored 2D boron oxides
structures and their basic properties. We found 2D boron oxides are metals or
semimetals, when oxygen concentration is low. More interesting, the B6O1
exhibits Dirac Loop near the Fermi level and the maximum Fermi velocity is
estimated as high as 0.61*10E6 m/s, which much close to that in graphene. In
addition, when the oxygen concentration is one forth, the most stable B4O1 get
a semiconductor with a direct band gap of 1.24 eV and a strong anisotropic
carrier mobility. Such huge differences of carrier mobility between two
directions have not been reported in other 2D materials. Besides, when oxygen
concentra-tion is higher than one forth, the 2D boron sheets will get unstable
based our results. We also proposed a method how to synthesize these systems.
Our work provide a basic knowledge of 2D boron oxides and may lead to novel 2D
boron oxides discovered. The unique electronic properties of the B6O1 and B4O1
render them promising 2D materials for applications in high-performance
nanodevices.",1607.08290v1
2017-03-08,Oxidation-Mediated Fingering in Liquid Metals,"We identify and characterize a new class of fingering instabilities in liquid
metals; these instabilities are unexpected due to the large interfacial tension
of metals. Electrochemical oxidation lowers the effective interfacial tension
of a gallium-based liquid metal alloy to values approaching zero, thereby
inducing drastic shape changes, including the formation of fractals. The
measured fractal dimension ($D = 1.3 \pm 0.05$) places the instability in a
different universality class than other fingering instabilities. By
characterizing changes in morphology and dynamics as a function of droplet
volume and applied electric potential, we identify the three main forces
involved in this process: interfacial tension, gravity, and oxidative stress.
Importantly, we find that electrochemical oxidation can generate compressive
interfacial forces that oppose the tensile forces at a liquid interface. Thus,
the surface oxide layer not only induces instabilities, but ultimately provides
a physical barrier that halts the instabilities at larger positive potentials.
Controlling the competition between surface tension and oxidative (compressive)
stresses at the interface is important for the development of reconfigurable
electronic, electromagnetic, and optical devices that take advantage of the
metallic properties of liquid metals.",1703.03011v1
2017-08-15,Effects of ultrasound waves intensity on the removal of Congo red color from the textile industry wastewater by Fe3O4@TiO2 core-shell nanospheres,"Environmental pollutants, such as colors from the textile industry, affect
water quality indicators like color, smell, and taste. These substances in the
water cause the obstruction of filters and membranes and thereby reduce the
efficiency of advanced water treatment processes. In addition, they are harmful
to human health because of reaction with disinfectants and production of
by-products. Iron oxide nanoparticles are considered effective absorbents for
the removal of pollutants from aqueous environments. In order to increase the
stability and dispersion, nanospheres with iron oxide core and titanium dioxide
coating were used in this research and their ability to absorb Congo red color
was evaluated. Iron oxide-titanium oxide nanospheres were prepared based on the
coprecipitation method and then their physical properties were determined using
a tunneling electron microscope (TEM) and an X-ray diffraction device.
Morphological investigation of the absorbent surface showed that iron
oxide-titanium oxide nanospheres sized about 5 to 10 nm. X-ray dispersion
survey also suggested the high purity of the sample. In addition, the
absorption rate was measured in the presence of ultrasound waves and the
results indicated that the capacity of the synthesized sample to absorb Congo
red is greatly dependent on the intensity power of ultrasound waves, as the
absorption rate reaches 100% at powers above 30 watts.",1708.04683v2
2018-11-06,Effect of surface oxidation on electron spin coherence of single nitrogen-vacancy centers in nanodiamonds,"Fluorescent nanodiamonds (NDs) are crystal defect-based light-emitting
nanoparticles that can be applied to quantum information science and quantum
sensing. Of particular interest are nitrogen vacancy (NV) centers that allow
optical access to their coherently controllable electron spin systems, leading
to spin-photon quantum devices and nanoscale sensing of various physical
parameters. However, the NV spin coherence time (T2) in NDs has been limited to
one or two orders of magnitude shorter than those in bulk diamonds owing to the
complicated surface effect that decoheres the NV spin systems. Here, we study
the relation between the surface properties and T2 of single NV centers in NDs
by systematically analyzing the effect of surface oxidation. We apply aerobic
and acidic oxidation methods with various heating temperatures and processing
times and find that aerobic oxidation most effectively oxidizes the surface and
extends T2 by a factor of 1.6 to the original NDs. The ND-size dependence of T2
clearly shows that the surface oxidation removes a constant decoherence
contribution irrespective of the ND size and that a new surface derived
decoherence source emerges when the ND size reduces below 50 nm. The present
results provide quantitative information on the decoherence sources of NV spin
systems of NDs and will enable a strategic surface modification for better spin
manipulations of NV centers in the context of quantum information science and
nanoscale quantum sensing.",1811.02235v2
2018-11-12,Laser writable high-K dielectric for van der Waals nano-electronics,"Like silicon-based semiconductor devices, van der Waals heterostructures will
require integration with high-K oxides. This is needed to achieve suitable
voltage scaling, improved performance as well as allowing for added
functionalities. Unfortunately, commonly used high-k oxide deposition methods
are not directly compatible with 2D materials. Here we demonstrate a method to
embed a multi-functional few nm thick high-k oxide within van der Waals devices
without degrading the properties of the neighbouring 2D materials. This is
achieved by in-situ laser oxidation of embedded few layer HfS2 crystals. The
resultant oxide is found to be in the amorphous phase with a dielectric
constant of k~15 and break-down electric fields in the range of 0.5-0.6 V/nm.
This transformation allows for the creation of a variety of fundamental
nano-electronic and opto-electronic devices including, flexible Schottky
barrier field effect transistors, dual gated graphene transistors as well as
vertical light emitting and detecting tunnelling transistors. Furthermore, upon
dielectric break-down, electrically conductive filaments are formed. This
filamentation process can be used to electrically contact encapsulated
conductive materials. Careful control of the filamentation process also allows
for reversible switching between two resistance states. This allows for the
creation of resistive switching random access memories (ReRAMs). We believe
that this method of embedding a high-k oxide within complex van der Waals
heterostructures could play an important role in future flexible
multi-functional van der Waals devices.",1811.04829v1
2020-06-30,Growth kinetics and atomistic mechanisms of native oxidation of ZrS$_x$Se$_{2-x}$ and MoS$_2$ crystals,"A thorough understanding of native oxides is essential for designing
semiconductor devices. Here we report a study of the rate and mechanisms of
spontaneous oxidation of bulk single crystals of ZrS$_x$Se$_{2-x}$ alloys and
MoS$_2$. ZrS$_x$Se$_{2-x}$ alloys oxidize rapidly, and the oxidation rate
increases with Se content. Oxidation of basal surfaces is initiated by
favorable O$_2$ adsorption and proceeds by a mechanism of Zr-O bond switching,
that collapses the van der Waals gaps, and is facilitated by progressive redox
transitions of the chalcogen. The rate-limiting process is the formation and
out-diffusion of SO$_2$. In contrast, MoS$_2$ basal surfaces are stable due to
unfavorable oxygen adsorption. Our results provide insight and quantitative
guidance for designing and processing semiconductor devices based on
ZrS$_x$Se$_{2-x}$ and MoS$_2$, and identify the atomistic-scale mechanisms of
bonding and phase transformations in layered materials with competing anions.",2007.00117v3
2018-05-09,Development of nanostructured-graphene-supported silver nanoparticles as catalysts for electroreduction of oxygen in alkaline electrolyte,"Here we develop a class off face centred cubic structure of metallic silver
nanocrystals, to enable high ORR activity process. Silver nanoparticles
deposited within different carbon supports: carboxylated-graphene, SiO2-doted
reduced- graphene-oxide (Gr/SiO2) and reduced-graphene-oxide (Gr) were
prepared. The reduction of silver ions and the formation of silver
nanoparticles deposited within graphene-type supports have been assessed by
UV-Vis spectroscopy and was confirmed by XRD studies. The major advantage of
the proposed chemical synthetic method is the integration of the superb
properties of both silver nanoparticles and graphene supports in a single-step
synthesis with a 100% usage of the silver precursor (AgNO3). The choice of the
carbon support strongly affected catalytic activity of the resulting Ag
nanoparticles towards oxygen electroreduction in alkaline medium. We show that
SiO2-doted reduced- graphene-oxide supported silver nanoparticles display
significantly enhanced catalytic activity towards the oxygen reduction reaction
(ORR) in alkaline solutions compared to the silver nanoparticles immobilized
within carboxylated-graphene support and chemically reduced graphene oxide
(Gr). Moreover under RRDE conditions the hybrid material based on SiO2-doted
reduced- graphene-oxide supported silver nanoparticles displays the most
impressive electrocatalytic performance toward ORR and shows the highest number
of exchanged electrons (n) ranging from 3.96 to 3.998 when compared to the
silver nanoparticles immobilized within carboxylated-graphene support
(3.90-3.994) and reduced-graphene-oxide (Gr) supported silver nanoparticles
(3.88-3.991).",1805.03389v1
2012-04-23,Integrating Functional Oxides with Graphene,"Graphene-oxide hybrid structures offer the opportunity to combine the
versatile functionalities of oxides with the excellent electronic transport in
graphene. Understanding and controlling how the dielectric environment affects
the intrinsic properties of graphene is also critical to fundamental studies
and technological development of graphene. Here we review our recent effort on
understanding the transport properties of graphene interfaced with
ferroelectric Pb(Zr,Ti)O_3 (PZT) and high-k HfO_2. Graphene field effect
devices prepared on high-quality single crystal PZT substrates exhibit up to
tenfold increases in mobility compared to SiO_2-gated devices. An unusual and
robust resistance hysteresis is observed in these samples, which is attributed
to the complex surface chemistry of the ferroelectric. Surface polar optical
phonons of oxides in graphene transistors play an important role in the device
performance. We review their effects on mobility and the high source-drain bias
saturation current of graphene, which are crucial for developing graphene-based
room temperature high-speed amplifiers. Oxides also introduce scattering
sources that limit the low temperature electron mobility in graphene. We
present a comprehensive study of the transport and quantum scattering times to
differentiate various scattering scenarios and quantitatively evaluate the
density and distribution of charged impurities and the effect of dielectric
screening. Our results can facilitate the design of multifunctional
nano-devices utilizing graphene-oxide hybrid structures.",1204.5161v1
2017-06-05,"Ultra-small (r<2 nm), stable (>1 year), mixed valence copper oxide quantum dots with anomalous band gap","Ultra-small (r<2 nm) semiconductor quantum dots (QDs) have attracted
attention for applications ranging from dye sensitized solar cells to sensing
due to its tunable electronic structure and band gap, and large specific
surface area. However obtaining monodisperse QDs and stabilization in this size
regime remains a challenge. A recent report on digestive ripening of an oxide
system showed substantial promise in addressing these requirements of QDs. In
this work, we report a green solution, soft chemical (chimie douce) approach
for synthesis of quasi-spherical, ultra-small, stable, and monodispersed copper
oxide QDs (r<2 nm) based on digestive ripening (DR). It may be noted this is
only the second transition metal oxide system in which DR is reported so far.
DR involves the refluxing of polydispersed colloidal nanoparticles in the
presence of surface active agents (e.g. triethanolamine (TEA)) that leads to
fairly monodispersed nanoparticles. It has been noticed that capping with TEA
results in reduction in the average particle diameter from 6 +/- 4 nm to 2.4
+/- 0.5 nm and an increase of zeta potential ({\xi}) from +12 +/- 2 mV to +31
+/- 2 mV. These copper oxide QDs are monodispersed (size ~ 2.4 +/- 0.5 nm), and
stable (>1 year). In addition, these quantum dots show an anomalous increase in
band gap (5.3 eV), inexplicable using Brus' equation. XPS indicates that Cu
exists in mixed valence state in this material. Based on our observations, we
suggest that off-stoichiometry in copper oxide, which is seemingly substantial
at these length scales, is responsible for the observed anomaly in band gap.",1706.01261v1
2017-12-11,Homolytic Cleavage of Water on Magnesia Film Promoted by Interfacial Oxide-Metal Nanocomposite,"The atomic scale insights into the interaction of water with oxide surface
are essential for elucidating the mechanism of physiochemical processes in
various scientific and practical fields, since the water is ubiquitous and
coats multifarious material surface under ambient conditions. By utilizing
periodic density functional theory calculations with van der Waals corrections,
herein we report for the first time the energetically and thermodynamically
favorable homolytic dissociative adsorption behavior of water over magnesia
(001) films deposited on metal substrate. The water adsorption on pristine
magnesia (001) is quite weak and the heterolytic dissociation is the only
fragmentation pathway, which is highly endothermic with large activation
barrier of 1.167 eV. The binding strength for the molecular and dissociative
adsorption configurations of water on hybrid MgO(001) films are significantly
larger than corresponding configurations on bare magnesia (001). The homolytic
dissociative adsorption energy of water on monolayer oxide is calculated to be
-1.192 eV, which is even larger than all the heterolytic dissociative
adsorption states. With the increase of the oxide thickness, the homolytic
dissociative adsorption energy decreases promptly, indicating the nanoscale of
oxide film play a crucial role in homolytic splitting of water. The homolytic
dissociative adsorption structure could be obtained by transformation reaction
from heterolytic dissociative adsorption structure, presenting activation
barriers 0.733, 1.103, 1.306, 1.571, and 1.849 eV for reactions on 1 ML to 5 ML
films. It is anticipated that the results here could provide inspiring clue and
versatile strategy for enhancing chemical reactivity and properties of
insulating oxide toward homolytic water splitting processes involved in novel
and unprecedented applications.",1712.03762v1
2017-12-20,Interaction between U/UO2 bilayers and hydrogen studied by in-situ X-ray diffraction,"This paper reports experiments investigating the reaction of H$_{2}$ with
uranium metal-oxide bilayers. The bilayers consist of $\leq$ 100 nm of
epitaxial $\alpha$-U (grown on a Nb buffer deposited on sapphire) with a
UO$_{2}$ overlayer of thicknesses of between 20 and 80 nm. The oxides were made
either by depositing via reactive magnetron sputtering, or allowing the uranium
metal to oxidise in air at room temperature. The bilayers were exposed to
hydrogen, with sample temperatures between 80 and 200 C, and monitored via
in-situ x-ray diffraction and complimentary experiments conducted using
Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy
(STEM-EELS). Small partial pressures of H$_{2}$ caused rapid consumption of the
U metal and lead to changes in the intensity and position of the diffraction
peaks from both the UO$_{2}$ overlayers and the U metal. There is an
orientational dependence in the rate of U consumption. From changes in the
lattice parameter we deduce that hydrogen enters both the oxide and metal
layers, contracting the oxide and expanding the metal. The air-grown oxide
overlayers appear to hinder the H$_{2}$-reaction up to a threshold dose, but
then on heating from 80 to 140 C the consumption is more rapid than for the
as-deposited overlayers. STEM-EELS establishes that the U-hydride layer lies at
the oxide-metal interface, and that the initial formation is at defects or
grain boundaries, and involves the formation of amorphous and/or
nanocrystalline UH$_{3}$. This explains why no diffraction peaks from UH$_{3}$
are observed. {\textcopyright British Crown Owned Copyright 2017/AWE}",1712.07387v1
2019-10-09,Surface-charge-mediated Formation of H-TiO2@Ni(OH)2 Heterostructures for High-Performance Supercapcitors,"Supercapacitors or ultracapacitors are promising for efficient energy storage
applications, owing to their high power density, high charge-discharge rates,
and long cycle life performance. To achieve this goal, a large specific surface
area, an high electronic conductivity and a fast cation intercalation
de-intercalation process are generally required in the design and preparation
of materials for high-performance supercapacitors. Recently, core-shell
heterostructures with multifunctionalities are regarded as one of promising
materials for supercapacitors or ultracapacitors applications. In particular,
one-dimensional (1D) core-shell heterostructures have sparked great scientific
and technological interests due to their high versatility and applicability as
the essential components in nanoscale electronics, catalysis, chemical sensing,
and energy conversion storage devices. Various metal metal oxide, metal metal,
metal oxide metal oxide and metal oxide conductive polymers so far have been
investigated. Transition metal hydroxide oxide Co3O4, Co(OH)2, MnO2, Mn(OH)2,
NiO, Ni(OH)2 and their compounds storing energy by surface faradaic (redox)
reactions were generally integrated with conducting scaffold to build
core-shell structure. Intensive studies show that an enlarged active surface
area of transition metal hydroxide oxide enables a promoted surface redox
reaction and enhanced electrochemical performance. Therefore, controllable
synthesis of a hierarchically porous construction with high surface areas is
critically important for energy storage.",1910.03813v1
2019-10-29,Nickel oxide-based heterostructures with large band offsets,"We present research results on the electronic transport in heterostructures
based on p-type nickel oxide (NiO) with the n-type oxide semiconductors zinc
oxide (ZnO) and cadmium oxide (CdO). NiO is a desirable candidate for
application in (opto-)electronic devices. However, because of its small
electron affinity, heterojunctions with most n-type oxide semiconductors
exhibit conduction and valence band offsets at the heterointerface in excess of
1 eV. ZnO/NiO junctions exhibit a so called type-II band alignment, making
electron-hole recombination the only process by which a current can vertically
flow through the structure. These heterojunctions are nevertheless shown to be
of practical use in efficient optoelectronic devices, as exemplified here by
our UV-converting transparent solar cells. These devices, although exhibiting
high conversion efficiencies, suffer from two light-activated recombination
channels connected to the type-II interface, one of which we identify and
analyse in more detail here. Furthermore, CdO/NiO contacts were studied - a
heterostructure with even larger band offsets such that a type-III band
alignment is achieved. This situation theoretically enables the development of
a 2-dimensional electronic system consisting of topologically protected states.
We present experiments demonstrating that the CdO/NiO heterostructure indeed
hosts a conductive layer absent in both materials when studied separately.",1910.13169v1
2020-12-19,H$_2$O$_2$-induced Greenhouse Warming on Oxidized Early Mars,"The existence of liquid water within an oxidized environment on early Mars
has been inferred by the Mn-rich rocks found during recent explorations on
Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be
comprised of CO$_2$ and H$_2$O without any reduced greenhouse gases such as
H$_2$ and CH$_4$. So far, however, it has been thought that early Mars could
not have been warm enough to sustain water in liquid form without the presence
of reduced greenhouse gases. Here, we propose that H$_2$O$_2$ could have been
the gas responsible for warming the surface of the oxidized early Mars. Our
one-dimensional atmospheric model shows that only 1 ppm of H$_2$O$_2$ is enough
to warm the planetary surface because of its strong absorption at far-infrared
wavelengths, in which the surface temperature could have reached over 273~K for
a CO$_2$ atmosphere with a pressure of 3~bar. A wet and oxidized atmosphere is
expected to maintain sufficient quantities of H$_2$O$_2$ gas in its upper
atmosphere due to its rapid photochemical production in slow condensation
conditions. Our results demonstrate that a warm and wet environment could have
been maintained on an oxidized early Mars, thereby suggesting that there may be
connections between its ancient atmospheric redox state and possible aqueous
environment.",2012.10616v2
2018-08-05,Apparatus for Operando X-ray Diffraction of Fuel Electrodes in High Temperature Solid State Electrochemical Cells,"Characterizing electrochemical energy conversion devices during operation is
an important strategy for correlating device performance with the properties of
cell materials under real operating conditions. While operando characterization
has been used extensively for low temperature electrochemical cells, these
techniques remain challenging for solid oxide electrochemical cells due to the
high temperatures and reactive gas atmospheres these cells require. Operando
X-ray diffraction measurements of solid oxide electrochemical cells could
detect changes in the crystal structure of the cell materials, which can be
useful for understanding degradation process that limit device lifetimes, but
the experimental capability to perform operando X-ray diffraction on the fuel
electrodes of these cells has not been demonstrated. Here we present the first
experimental apparatus capable of performing X-ray diffraction measurements on
the fuel electrodes of high temperature solid oxide electrochemical cells
during operation under reducing gas atmospheres. We present data from an
example experiment with a model solid oxide cell to demonstrate that this
apparatus can collect X-ray diffraction spectra during electrochemical cell
operation at high temperatures in humidified H2 gas. Measurements performed
using this apparatus can reveal new insights about solid oxide fuel cell and
solid oxide electrolyzer cell degradation mechanisms to enable the design of
durable, high performance devices.",1808.01551v1
2020-08-19,Polymer coated cerium oxide nanoparticles as oxidoreductase-like catalysts,"Cerium oxide nanoparticles have been shown to mimic oxidoreductase enzymes by
catalyzing the decomposition of organic substrates and reactive oxygen species.
This mimicry can be found in superoxide radicals and hydrogen peroxides,
harmful molecules produced in oxidative stress asso-ciated diseases. Despite
the fact that nanoparticle functionalization is mandatory in the context of
nanomedicine, the influence of polymer coatings on their enzyme-like catalytic
activity is poorly understood. In this work, six polymer coated cerium oxide
nanoparticles are prepared by associa-tion of 7.8 nm cerium oxide cores with
two poly(sodium acrylate) and four poly(ethylene glycol) (PEG) grafted
copolymers with different terminal or anchoring end groups, such as phosphonic
acids. The superoxide dismutase-, catalase-, peroxidase- and oxidase-like
catalytic activities of the coated nanoparticles were systematically studied.
It is shown that the polymer coatings do not af-fect the superoxide
dismutase-like, impair the catalase-like and oxidase-like and surprisingly
im-proves peroxidase-like catalytic activities of cerium oxide nanoparticles.
It is also demonstrated that the particles coated with the PEG-grafted
copolymers perform better than the poly(acrylic acid) coated ones as
oxidoreductase-like enzymes, a result that confirms the benefit of having
phosphon-ic acids as anchoring groups at the particle surface.",2008.08492v1
2020-08-28,Precursor Selection in Hybrid Molecular Beam Epitaxy of Alkaline-Earth Stannates,"One of the challenges of oxide molecular beam epitaxy (MBE) is the synthesis
of oxides containing metals with high electronegativity (metals that are hard
to oxidize). The use of reactive organometallic precursors can potentially
address this issue. To investigate the formation of radicals in MBE, we
explored three carefully chosen metal-organic precursors of tin for SnO2 and
BaSnO3 growth: tetramethyltin (TMT), tetraethyltin (TET), and hexamethylditin
(HMDT). All three precursors produced single-crystalline, atomically smooth,
and epitaxial SnO2 (101) films on r-Al2O3 in the presence of an oxygen plasma.
The study of growth kinetics revealed reaction-limited and flux-limited regimes
except for TET, which also exhibited a decrease in deposition rate with
increasing temperature above 800 C. Contrary to these similarities, the
performance of these precursors was dramatically different for BaSnO3 growth.
TMT and TET were ineffective in supplying adequate tin whereas HMDT yielded
phase-pure, stoichiometric BaSnO3 films. Significantly, HMDT resulted in
phase-pure and stoichiometric BaSnO3 films even without the use of an oxygen
plasma (i.e., with molecular oxygen alone). These results are discussed using
the ability of HMDT to form tin radicals and therefore, assisting with Sn to
Sn4+ oxidation reaction. Structural and electronic transport properties of
films grown using HMDT with and without oxygen plasma are compared. This study
provides guideline for the choice of precursors that will enable synthesis of
metal oxides containing hard-to-oxidize metals using reactive radicals in MBE.",2008.12762v1
2021-03-17,Advanced Raman spectroscopy detection of oxidative damage in nucleic acid bases: probing chemical changes and intermolecular interactions in guanosine at ultralow concentration,"DNA/RNA synthesis precursors are especially vulnerable to damage induced by
reactive oxygen species occurring following oxidative stress. Guanosine
triphosphates are the prevalent oxidized nucleosites, which can be
misincorporated during replication, leading to mutations and cell death. Here,
we present a novel method based on micro-Raman spectroscopy, combined with ab
initio calculations, for the identification, detection, and quantification of
low concentrations of oxidized nucleotides. We also show that the Raman
signature in the terahertz spectral range (< 100 cm$^{-1}$) contains
information on the intermolecular assembly of guanine in tetrads, which allows
to further boost the oxidative damage detection limit. Eventually, we provide
evidence that similar analyses can be carried out on samples in very small
volumes at very low concentrations by exploiting the high sensitivity of
Surface Enhanced Raman Scattering combined with properly designed
superhydrophobic substrates. These results pave the way for employing such
advanced spectroscopic methods for quantitatively sensing the oxidative damage
of nucleotides in the cell.",2103.09524v1
2021-04-02,Fluxional Behavior at the Atomic Level and its Impact on Activity: CO Oxidation over CeO$_{2}$-supported Pt Catalysts,"Reducible oxides are widely used catalyst supports that can increase
oxidation reaction rates by transferring their lattice oxygen at the
metal-support interface. The interfacial oxidation process is typically
described in terms of a Mars-van Krevelen mechanism. However, many outstanding
questions remain unanswered regarding the atomic-scale structure and dynamic
meta-stability (i.e., fluxional behavior) of the interface $\textit{during
catalysis}$. Here, we employ aberration-corrected $\textit{operando}$ electron
microscopy to visualize the structural dynamics occurring at and near
Pt/CeO$_{2}$ interfaces during CO oxidation. Finite element simulations are
performed to develop a reaction rate analysis wherein the atomic-level
structural observations are directly correlated with the catalyst's turnover
frequency for CO oxidation. We show that the increasing frequency of catalytic
turnover correlates with dynamic fluxional behavior that (a) destablizes the
supported Pt particle, (b) marks an enhanced rate of oxygen vacancy creation
and annihilation, and (c) leads to increased strain and reduction in the
surface of the CeO$_{2}$ support. Overall, the results implicate the
interfacial Pt-O-Ce bonds anchoring the Pt to the support as being involved
also in the catalytically-driven oxygen transfer process, and they suggest that
oxygen reduction takes place on the highly reduced nearby CeO2 surface before
migrating to the interfacial perimeter for reaction with CO. The
$\textit{operando}$ electron microscopy approach described here should be
applicable to a large number of nanoparticle catalysts. This technique will
enable the identification of catalytically functional surface structures and
strengthen our ability to establish (dynamic) structure-activity relationships.",2104.00821v1
2021-06-08,Insights into the Coadsorption and Reactivity of O and CO on Ru(0001) and Their Coverage Dependence,"Using density functional theory and an exchange-correlationfunctional that
includes the van der Waals interaction, we study the coadsorption of CO on
Ru(0001) saturated with 0.5 ML of oxygen. Different coexisting CO coverages are
considered that are experimentally motivated, the room temperaturecoverage
consisting of 0.5 ML-O + 0.25 ML-CO (low coverage), the saturation coverage
achieved at low temperatures (0.5 ML-O + 0.375 ML-CO, intermediate coverage),
and the equally mixed monolayer that is stable according to our calculations
but not experimentally observed yet (0.5 ML-O + 0.5 ML-CO, high coverage). For
each coverage, we study the competition between the desorption and oxidation of
CO on the corresponding optimized structure by analyzing their reaction
energies and minimum energy reaction paths. The desorption process is
endothermic at all coverages, although the desorption energy decreases as the
CO coverage increases. The process itself (and also the reverted adsorption)
becomes more involved at the intermediate and high coverages because of the
appearance of a physisorption well and concomitant energy barrier separating it
from the chemisorbed state. Remarkably, the oxidation of CO, which is
endothermic at low coverages, turns exothermic at the intermediate and high
coverages. In all cases, the minimum reaction path for oxidation, which
involves the chemisorbed and physisorbed CO2, is ruled by one of the large
energy barriers that protect these molecular states. Altogether, the larger
activation energies for oxidation as compared to those for desorption and the
extreme complexity of the oxidation against the desorption paths explain that
CO desorption dominates over the oxidation in experiments.",2106.04234v1
2021-10-22,Thermal conductivity of oxide scale and its components in the range from 0 C to 1300 C: Generalized estimates with account for movability of phase transitions,"The data of different authors on the thermal conductivity of wustite Fe1-xO,
magnetite F3O4, hematite Fe2O3 and pure iron are systematized. The generalized
values are described by piecewise smooth functions containing as varying
parameters the temperatures of magnetiv and polymorphic (for iron)
transformations as well as the thermodynamic stability boundary (for wustite).
At polymorphic transformation a finite break of the thermal conductivity
function is envisaged, at othet critical points only a break of its temperature
derivative is acceptable. The proposed formulas are presented in two forms: the
general form that allow varying the values of critical temperatures and the
particular form corresponding to their basic values: the boundary of
thermodynamic stability of wustite - 570 C, the Curie points of magnetite - 575
C, hematite - 677 C, iron - 770 C and polymorphic transformation temperature of
iron - 912 C. To calculate the thermal conductivity of oxide scale as a whole,
it is proposed to take into account separately metallic iron and composite
matrix of iron oxides. Model computations using the proposed formulas shows
that the true thermal conductivity of oxide scale (without pores), depending on
the temperature may be from 3 to 6 W / (m K) in the absence of metallic iron
and up to 15 W / (m K) if free iron is released in the eutectoid decay of
wustite. The effective thermal conductivity of oxide scale, taking into account
its real porosity, may be lower by 15-35%. The obtained dependencies are
recommended for use in mathematical simulation of production and processing of
steel products in the presence of oxide scale on their surface.",2110.11632v1
2021-11-02,Structure and motifs of iron oxides from 1 to 3 TPa,"Iron oxides are fundamental components of planet-forming materials.
Understanding the Fe-O system's behavior and properties under high pressure can
help us identify many new phases and states possible in exoplanetary interiors,
especially terrestrial ones. Using the adaptive genetic algorithm (AGA), we
investigate the structure of iron oxides for a wide range of stoichiometries
($0.25\leq x_O \leq 0.8$) at 1, 2, and 3 TPa. Five unreported ground-state
structures with Fe$_2$O, FeO, Fe$_3$O$_5$, FeO$_2$, and FeO$_4$ compositions
are identified. The calculated density of states (DOS) suggests that, except
for FeO$_4$, all phases are metallic, but their carrier densities decrease with
increasing pressure and oxygen content. The cluster alignment analysis of
stable and metastable phases shows that several motifs may co-exist in a
structure of iron oxides with low O content. In contrast, most iron oxides with
high O content adopt a simple BCC motif at TPa pressures. Our results provide a
crystal structure database of iron oxides for modeling and understanding the
interiors of exoplanets.",2111.01305v2
2021-11-29,Modeling of nucleobase/oligonucleotide interaction with graphene and graphene oxide: the role of charging and/or oxidizing the graphene surface,"We analyze the influence of the charge and the degree of oxidation of the
surface of graphene (Gr) on its interaction with cytosine and oligonucleotide
r(C)10. This is a computational study involving DFT calculations and molecular
dynamics simulations. It is shown that cytosine interacts stronger with
graphene oxide (GO) than with Gr, while the energy of the interaction of
cytosine with GO only weakly depends on the degree of the Gr oxidation. A
correlation between the shifts of vibrational frequencies of cytosine due to
complexation with GO and the degree of the Gr oxidation is found. The
adsorption of anionic oligonucleotide r(C)10 onto neutral and positively
charged surfaces has a certain conformational similarity to conformations
formed with similar van der Waals interactions. Also, for charged surfaces, the
Coulombic attraction gives a noticeable contribution to the total interaction
energy. For a negatively charged graphene surface the electrostatic repulsion
between Gr surface and negatively charged phosphate backbone of oligonucleotide
weakens the total binding energy. Competition between the Coulombic repulsion
and the van der Waals attraction results in formation of a unique
oligonucleotide conformation where all 10 cytosines are stacked onto Gr.",2111.14435v1
2022-01-06,Chemically edge-carboxylated graphene enhances thermal conductivity of polyetherimide-graphene nanocomposites,"In this work, we demonstrate that edge-oxidation of graphene can enable
larger enhancement in thermal conductivity (k) of graphene-nanoplatelet
(GnP)/polyetherimide (PEI) composites relative to oxidation of the basal plane
of graphene. Edge oxidation (EGO) offers the advantage of leaving the basal
plane of graphene intact, preserving its high in-plane thermal conductivity
(kin > 2000 Wm-1K-1), while, simultaneously, the oxygen groups introduced on
graphene edge enhance interfacial thermal conductance through hydrogen bonding
with oxygen groups of polyetherimide (PEI), enhancing overall polymer composite
thermal conductivity. Edge oxidation is achieved in this work, by oxidizing
graphene in presence of sodium chlorate and hydrogen peroxide, introducing
carboxyl groups on the edge of graphene. Basal-plane oxidation of graphene
(BGO), on the other hand, achieved through Hummers method, distorts sp2
carbon-carbon network of graphene, dramatically lowering its intrinsic thermal
conductivity, causing the BGO/PEI composite k to be even lower than pristine
GnP/PEI composite k value. The resulting thermal conductivity of EGO/PEI
composite is found to be enhanced by 18%, whereas that of BGO/PEI composite is
diminished by 57%, with respect to pristine GnP/PEI composite for 10 weight%
GnP content. 2-dimensional Raman mapping of graphene nanoplatelets is used to
confirm and distinguish the location of oxygen functional groups on graphene.
The superior effect of edge bonding presented in this work can lead to
fundamentally novel pathways for achieving high thermal conductivity polymer
composites.",2201.03395v2
2022-01-19,Simulations of the Electrochemical Oxidation of Pt Nanoparticles of Various Shapes,"The activity and stability of a platinum nanoparticle (NP) is not only
affected by its size but additionally depends on its shape. To this end,
simulations can identify structure-property relationships to make a priori
decisions on the most promising structures. While activity is routinely probed
by electronic structure calculations on simplified surface models, modeling the
stability of NP model systems in electrochemical reactions is challenging due
to the long timescale of relevant processes such as oxidation beyond the point
of reversibility. In this work, a routine for simulating electrocatalyst
stability is presented. The procedure is referred to as GREG after its main
ingredients - a grand-canonical simulation approach using reactive force fields
to model electrochemical reactions as a function of the galvanic cell
potential. The GREG routine is applied to study the oxidation of 3 nm
octahedral, cubic, dodecahedral, cuboctahedral, spherical, and tetrahexahedral
platinum NPs. The oxidation process is analyzed using adsorption isobars as
well as interaction energy heat maps that provide the basis for constructing
electrochemical phase diagrams. Onset potentials for surface oxidation increase
in the sequence cube ~= dodecahedron <= octahedron <= tetrahexahdron < sphere <
cuboctahedron, establishing a relationship between oxidation behavior and
surface facet structure. The electrochemical results are rationalized using
structural and electronic analysis.",2201.07605v2
2022-01-27,Hubbard-corrected oxide formation enthalpies without adjustable parameters,"A density functional theory (DFT) approach to computing transition metal
oxide heat of formation without adjustable parameters is presented. Different
degrees of $d$-electron localization in oxides are treated within the DFT+$U$
approach with site-dependent, first-principles Hubbard $U$-parameters obtained
from linear response theory, and delocalized states in the metallic phases are
treated without Hubbard corrections. Comparison of relative stabilities of
these differently treated phases is enabled by a local $d$-electron density
matrix-dependent model, which was found by genetic programming against
experimental reference formation enthalpies. This mathematically simple model
does not explicitly depend on the Hubbard-corrected ionic species and is shown
to reproduce the heats of formation of the Mott insulators Ca$_2$RuO$_4$ and
Y$_2$Ru$_2$O$_7$ within $\sim$3% of experimental results, where the
experimental training data did not contain Ru oxides. This newly developed
method thus absolves from the need for element-specific corrections fitted to
experiments in existing Hubbard-corrected approaches to the prediction of
reaction energies of transition metal oxides and metals. The absence of fitting
parameters opens up here the possibility to predict relative thermodynamic
stabilities and reaction energies involving $d$-states of varying degree of
localization at transition metal oxide interfaces and defects, where
site-dependent $U$-parameters will be particularly important and devising a
fitting scheme against experimental data with predictive power would be
exceedingly difficult.",2201.11644v2
2022-08-29,Multi Spectral Switchable Infra-Red Reflectance Resonances in Highly Subwavelength Partially Oxidized Vanadium Thin Films,"Phase transition materials are promising for realization of switchable
optics. In this work, we show reflectance resonances in the near-infrared and
long-wave infrared wavelengths in highly subwavelength partially oxidized
Vanadium thin films. These partially oxidized films consist of a multilayer of
Vanadium dioxide and Vanadium as shown using Raman spectroscopy and four-probe
measurements. As Vanadium dioxide is a phase transition material that shows
insulator to metal phase transition at 68 C, the observed infra-red resonances
can be switched with temperature into a high-reflectance state. The wavelength
of these resonances are passively tunable as a function of the oxidation
duration. The obtained reflectance resonance at near-infrared wavelength red
shifts from 1.78 um to 2.68 um with increasing oxidation duration while the
long-wavelength infrared resonance blue shifts from 12.68 um to 9.96 um. To
find the origin of the reflectance resonances, we model the reflectance spectra
as a function of the oxidation duration using the transfer matrix method. The
presented model captures the dual reflectance resonances reasonably well. These
passive wavelength-tunable and switchable resonances with easy to fabricate
lithography-free multilayer structure will be useful for multispectral
applications such as camouflage, spectral selective microbolometer, and thermal
management.",2208.13458v1
2022-09-22,Tuning SMSI Kinetics on Pt-loaded TiO$_2$(110) by Choosing the Pressure: A Combined UHV / Near-Ambient Pressure XPS Study,"Pt catalyst particles on reducible oxide supports often change their activity
significantly at elevated temperatures due to the strong metal-support
interaction (SMSI), which induces the formation of an encapsulation layer
around the noble metal particles. However, the impact of oxidizing and reducing
treatments at elevated pressures on this encapsulation layer remains
controversial, partly due to the 'pressure gap' between surface science studies
and applied catalysis. In the present work, we employ synchrotron-based
near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the
effect of O$_2$ and H$_2$ on the SMSI-state of well-defined Pt/TiO$_2$(110)
catalysts at pressures of up to 0.1 Torr. By tuning the O$_2$ pressure, we can
either selectively oxidize the TiO$_2$ support or both the support and the Pt
particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows
rapidly in 1x10$^{-5}$ Torr O$_2$, but orders of magnitudes less effective at
higher O$_2$ pressures, where Pt is in an oxidic state. While the
oxidation/reduction of Pt particles is reversible, they remain embedded in the
support once encapsulation has occurred.",2209.10971v1
2023-01-11,Defect engineering over anisotropic brookite towards substrate-specific photo-oxidation of alcohols,"Generally adopted design strategies for enhancing the photocatalytic activity
are aimed at tuning properties such as the visible light response, the exposed
crystal facets, and the nanocrystal shape. Here, we present a different
approach for designing efficient photocatalysts displaying a substrate-specific
reactivity upon defect engineering. The defective anisotropic brookite TiO2
photocatalyst functionalized with Pt nanocrystals are tested for alcohol
photoreforming showing up to an 11-fold increase in methanol oxidation rate,
compared to the unreduced one, whilst presenting much lower ethanol or
isopropanol specific oxidation rates. We demonstrate that the alcohol oxidation
and hydrogen evolution reactions are tightly related, and when the
substrate-specific alcohol oxidation ability is increased, the hydrogen
evolution is significantly boosted. The reduced anisotropic brookite shows up
to twenty-six-fold higher specific photoactivity with respect to anatase and
brookite with isotropic nanocrystals, reflecting the different type of
defective catalytic sites formed depending on the TiO2 polymorph and its
crystal shape. Advanced in-situ characterizations and theoretical
investigations reveal that controlled engineering over oxygen vacancies and
lattice strain produces large electron polarons hosting the substrate-specific
active sites for alcohol photo-oxidation.",2301.04375v1
2023-01-27,Machine-guided Design of Oxidation Resistant Superconductors for Quantum Information Applications,"Decoherence in superconducting qubits has long been attributed to two level
systems arising from the surfaces and interfaces present in real devices. A
recent significant step in reducing decoherence was the replacement of
superconducting niobium by superconducting tantalum, resulting in a tripling of
transmon qubit lifetimes (T1). One of these surface variables, the identity,
thickness, and quality of the native surface oxide, is thought to play a major
role as tantalum only has one oxide whereas niobium has several. Here we report
the development of a thermodynamic metric to rank materials based on their
potential to form a well-defined, thin, surface oxide. We first compute this
metric for known binary and ternary metal alloys using data available from
Materials Project, and experimentally validate the strengths and limits of this
metric through preparation and controlled oxidation of 8 known metal alloys.
Then we train a convolutional neural network to predict the value of this
metric from atomic composition and atomic properties. This allows us to compute
the metric for materials that are not present in materials project, including a
large selection of known superconductors, and, when combined with Tc, allow us
to identify new candidate superconductors for quantum information science
(QISE) applications. We test the oxidation resistance of a pair of these
predictions experimentally. Our results are expected to lay the foundation for
tailored and rapid selection of improved superconductors for QISE.",2301.11543v1
2023-02-13,A computational model for the design of a nitrous oxide--paraffin wax hybrid rocket engine,"A computational model is developed to assist the design of the first hybrid
rocket engine of the McGill Rocket Team, using liquid nitrous oxide as an
oxidizer and solid paraffin wax as a fuel. The model is developed in three
phases: In the first phase, a steady-state model which neglects transient
performance decrease of the hybrid engine is considered. The steady-state model
considers: a constant oxidizer mass flow rate; a combustion chamber in chemical
equilibrium; a one-dimensional isentropic nozzle; and a one-dimensional
constant-thrust rocket ascent. The steady-state model is used to conduct
parametric studies on engine performance as a function of design parameters
such as: oxidizer mass flow rate, fuel grain dimensions, and nozzle dimensions.
The engine design point is selected to optimize specific impulse, given
physical and structural constraints of the system. In the second phase, an
unsteady model incorporating transient performance decrease of the hybrid
engine is considered. The transient model considers: a self-pressurizing
oxidizer tank in quasi-steady liquid-vapor equilibrium; a combustion chamber in
quasi-steady chemical equilibrium; a one-dimensional non-isentropic nozzle; and
a one-dimensional rocket ascent model. The transient performance profile of the
engine is established, and the unsteady model is used to predict propellant
requirements for the launch vehicle, given a target apogee of 3048 m (10,000
ft). In the third stage, the unsteady model is compared to hot fire testing
data of the McGill Rocket Team. Semi-empirical parameters used in the
formulation are calibrated against testing data, and the validity of the model
is assessed.",2302.06725v1
2023-03-14,Chemical and structural characterization of the native oxide scale on a Mg-based alloy,"In this study, the structure and composition of the native oxide forming on
the basal plane (0001) of Mg-2Al-0.1Ca is investigated by a correlative
approach, combining scanning transmission electron microscopy (STEM) and atom
probe tomography (APT). Atom probe specimens were prepared conventionally in a
Ga focused ion beam (FIB) as well as a Xe plasma FIB in a cryogenic setup and
subsequently cleaned in the atom probe to remove surface contamination before
oxidation. While thermal energy input from the laser and longer atmospheric
exposure time increased the measured hydrogen content in the specimen's apex
region, cryo preparation revealed, that the hydrogen uptake in magnesium is
independent of the employment of conventional or cryogenic FIB preparation. TEM
measurements demonstrated the growth of a (111) MgO oxide layer with 3-4 nm
thickness on the basal (0001) plane of the Mg atom probe specimen. APT data
further revealed the formation of an aluminum-rich region between bulk Mg and
the native oxide. The aluminum enrichment of up to ~20 at.% at the interface is
consistent with an inward growth of the oxide scale.",2303.07763v3
2023-04-05,Effects of molecular contamination and sp$^2$ carbon on oxidation of (100) single-crystal diamond surfaces,"The efficacy of oxygen (O) surface terminations of specific moieties and
densities on diamond depends on factors such as crystallinity, roughness, and
crystal orientation. Given the wide breadth of diamond-like materials and
O-termination techniques, it can be difficult to discern which method would
yield the highest and most consistent O coverage on a particular subset of
diamond. We first review the relevant physical parameters for O-terminating
single-crystalline diamond (SCD) surfaces and summarize prior oxidation work on
(100) SCD. We then report on our experimental study on X-ray Photoelectron
Spectroscopy (XPS) characterization of (100) diamond surfaces treated with
oxidation methods that include wet chemical oxidation, photochemical oxidation
with UV illumination, and steam oxidation using atomic layer deposition. We
describe a rigorous XPS peak-fitting procedure for measuring the
functionalization of O-terminated samples and recommend that the reporting of
peak energy positions, line shapes, and full-width-half-maximum values of the
individual components, along with the residuals, are important for evaluating
the quality of the peak fit. Two chemical parameters on the surface, sp$^2$ C
and molecular contaminants, are also crucial towards interpreting the O
coverage on the diamond surface and may account for the inconsistency in prior
reported values in literature.",2304.02217v1
2023-05-04,"Surface oxides, carbides, and impurities on RF superconducting Nb and Nb3Sn: A comprehensive analysis","Surface structures on radio-frequency (RF) superconductors are crucially
important in determining their interaction with the RF field. Here we
investigate the surface compositions, structural profiles, and valence
distributions of oxides, carbides, and impurities on niobium (Nb) and
niobium-tin (Nb3Sn) in situ under different processing conditions. We establish
the underlying mechanisms of vacuum baking and nitrogen processing in Nb and
demonstrate that carbide formation induced during high-temperature baking,
regardless of gas environment, determines subsequent oxide formation upon air
exposure or low-temperature baking, leading to modifications of the electron
population profile. Our findings support the combined contribution of surface
oxides and second-phase formation to the outcome of ultra-high vacuum baking
(oxygen processing) and nitrogen processing. Also, we observe that
vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically
synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental
mechanisms of baking and processing Nb and Nb3Sn surface structures for
high-performance superconducting RF and quantum applications",2305.02467v2
2023-05-17,Synthesis of stable cerium oxide nanoparticles coated with phosphonic acid-based functional polymers,"Functional polymers, such as poly(ethylene glycol) (PEG) terminated with a
single phosphonic acid, hereafter PEGik-Ph are often applied to coat metal
oxide surfaces during post synthesis steps, but are not sufficient to stabilize
sub-10 nm particles in protein-rich biofluids. The instability is attributed to
the weak binding affinity of post-grafted phosphonic acid groups, resulting in
a gradual detachment of the polymers the surface. Here, we assess these
polymers as coating agents using an alternative route, namely the one-step
wet-chemical synthesis, where PEGik-Ph is introduced with cerium precursors
during the synthesis. Characterization of the coated cerium oxide nanoparticles
indicates a core-shell structure, where the cores are 3 nm cerium oxide and the
shell consists of functionalized PEG polymers in a brush configuration. Results
show that cerium oxide nanoparticles coated with PEG1k-Ph and PEG2k-Ph are of
potential interest for applications as nanomedicine due to their high Ce(III)
content and increased colloidal stability in cell culture media. We further
demonstrate that the cerium oxide nanoparticles in the presence of hydrogen
peroxide show an additional absorbance band in the UV-vis spectrum, which is
attributed to Ce-O22- peroxo-complexes and could be used in the evaluation of
their catalytic activity for scavenging reactive oxygen species.",2305.10179v1
2023-12-15,Tunable 2D Electron- and 2D Hole States Observed at Fe/SrTiO$_3$ Interfaces,"Oxide electronics provide the key concepts and materials for enhancing
silicon-based semiconductor technologies with novel functionalities. However, a
basic but key property of semiconductor devices still needs to be unveiled in
its oxidic counterparts: the ability to set or even switch between two types of
carriers - either negatively (n) charged electrons or positively (p) charged
holes. Here, we provide direct evidence for individually emerging n- or p-type
2D band dispersions in STO-based heterostructures using resonant photoelectron
spectroscopy. The key to tuning the carrier character is the oxidation state of
an adjacent Fe-based interface layer: For Fe and FeO, hole bands emerge in the
empty band gap region of STO due to hybridization of Ti and Fe-derived states
across the interface, while for Fe$_3$O$_4$ overlayers, an 2D electron system
is formed. Unexpected oxygen vacancy characteristics arise for the hole-type
interfaces, which as of yet had been exclusively assigned to the emergence of
2DESs. In general, this finding opens up the possibility to straightforwardly
switch the type of conductivity at STO interfaces by the oxidation state of a
redox overlayer. This will extend the spectrum of phenomena in oxide
electronics, including the realization of combined n/p-type all-oxide
transistors or logic gates.",2312.09798v1
2024-03-25,Facile synthesis of CoSi alloy with rich vacancy for base- and solvent-free aerobic oxidation of aromatic alcohols,"Rational design and green synthesis of low-cost and robust catalysts
efficient for the selective oxidation of various alcohols are full of
challenges. Herein, we report a fast and solvent-free arc-melting (AM) method
to controllably synthesize semimetal CoSi alloy (abbreviated as AM-CoSi) that
is efficient for the base- and solvent-free oxidation of six types of aromatic
alcohols. X-ray absorption fine structure (XAFS), electron paramagnetic
resonance (EPR), and aberration corrected high angle annular dark field
scanning transmission electron microscope (AC HAADF-STEM) confirmed the
successful synthesis of AM-CoSi with rich Si vacancy (Siv). The as-prepared
CoSi alloy catalysts exhibit an order of magnitude activity enhancement in the
oxidation of model reactant benzyl alcohol (BAL) to benzyl benzoate (BBE)
compared with its mono counterparts, whereas 70 % yield of BBE which is the
highest yield to date. Experimental results and DFT calculations well verify
that the CoSi alloy structure improves the BAL conversion and Si vacancy mainly
contributes to the generation of BBE. After that, CoSi alloy maintains high
stability and a potential pathway is rationally proposed. Besides, CoSi alloy
also efficiently works for the selective oxidation of various alcohols with
different groups. This work demonstrates for the first time that semimetal CoSi
alloy is robust for the green oxidation of various alcohols and provides a vast
opportunity for reasonable design and application of other semimetal alloy
catalysts.",2403.16708v1
2024-04-04,Modeling of Zircaloy Oxidation Through Dynamic Mesh Deformation,"Zircaloy cladding corrosion in Light Water Reactors (LWRs) results in the
formation of an outer oxide layer and in the thinning of the metallic portion
of the cladding. At the \'Ecole Polytechnique F\'ed\'erale de Lausanne (EPFL),
we aim to investigate the impact of asymmetric oxide or crud layers and their
feedback on thermal-hydraulics. To achieve this, we are implementing
mechanistic capabilities for the treatment of corrosion within the open-source
multi-dimensional code OFFBEAT. In this work, we outline our approach based on
the combination of traditional laws for predicting the growth of the oxide
layer with methods to dynamically modify the mesh points and topology.
Specifically, our methodology employs routines available in the OpenFOAM
library to add or remove layers of cells according to the growth of the oxide
layer, along with a mesh motion solver to maintain mesh quality. We verify the
methodologys against an analytical test case and then we demonstrate its
potential for the study of non-uniform oxide distributions by modeling a
simplified cladding ring with asymmetric temperature profile, mimicking the
conditions of azimuthal power peaking in a Boiling Water Reactor (BWR).",2404.03454v1
1997-08-22,Theory of Photoemission from the Copper Oxide Material,"A mean-field theory which satisfying the electron on-site local constraint in
the relevant regime of density for the high temperature superconductors is
developed. Within this approach, the electron spectral function, the electron
dispersion, and the electron density of states of copper oxide materials are
discussed, and the results are qualitative consistent with the numerical
simulations.",9708177v1
1998-07-19,Optical Conductivity in the Copper Oxide Materials,"The frequency- and temperature-dependent optical conductivity of the copper
oxide materials in the underdoped and optimal doped regimes are studied within
the t-J model. The conductivity spectrum shows the unusual behavior at low
energies and anomalous midinfrared peak in the low temperatures. However, this
midinfrared peak is severely depressed with increasing temperatures, and
vanishes at higher temperatures.",9807267v1
1998-12-29,Phase Analysis of Thin Film Oxide Systems by AES and EELS,"Auger electron spectroscopy (AES) and electron energy loss spectroscopy
(EELS) in a reflection mode are compared as the methods for phase composition
investigation of thin film oxide systems by ion profiling. As an example, the
Al/Al2O3/Si and YBa2Cu3O7/CeO2/Al2O3 systems are considered. The adaptation of
applied statistics methods for AES and EELS data treatment is discussed.",9812411v1
2002-02-10,Filling Control of the Pyrochlore Oxide Y2Ir2O7,"We report the filling control of the pyrochlore oxide Y2Ir2O7. Metallic
ground state appears with increasing substitution content x (x >= 0.3). We have
revealed that the density of states at the Fermi level rapidly changes with x
by this filling control of Y2Ir2O7.",0202169v2
2003-02-21,Evidence for Unconventional Superconductivity in the Non-Oxide Perovskite $\mathrm{MgCNi_3}$ from Penetration Depth Measurements,"The London penetration depth, $\lambda(T)$, was measured in polycrystalline
powders of the non-oxide perovskite superconductor $\mathrm{MgCNi_3}$ by using
a sensitive tunnel-diode resonator technique. The penetration depth exhibits
distinctly non s-wave BCS low-temperature behavior, instead showing quadratic
temperature dependence, suggestive of a nodal order parameter.",0302431v1
2004-08-09,Temperature dependence of exciton Auger decay process in Cuprous Oxide,"We report theoretical and experimental study on Auger decay of excitons in
Cuprous Oxide in a wide range of temperatures, from 2 Kelvin to 325 Kelvin, in
single-photon surface excitation. We find that the Auger constant linearly
increases with temperature above 100 Kelvin. This constant is important for
experiments on Bose condensation of excitons.",0408184v2
2004-11-25,On the Bistable Behavior of a Low-Frequency Raman-Active Phonon Line in Superconducting Oxide Ba1-xKxBiO3,"The two-loop temperature hysteresis of integrated intensity of Raman
scattering of light is explained theoretically for a line of frequency 50 cm-1
in a superconducting oxide Ba1-xKxBiO3 single crystal.",0411639v1
2005-01-17,Dependence of Zinc Oxide Thin Films Properties on Filtered Vacuum Arc Deposition Parameters,"The micro-properties (structure and composition), and macro-properties
(electrical and optical properties) of zinc oxide (ZnO) thin films deposited on
glass substrates using a filtere vacuum arc deposition (FVAD) system were
investigated as a function of oxygen pressure (0.37 - 0.5 Pa) and arc current
(100 - 300 A). Correlations between the various properties were investigated.",0501374v1
2008-04-11,"Structural and 121Sb Mössbauer Spectroscopic Investigations of the Antimonide Oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) and REZnSbO (RE = La, Ce, Pr)","The quaternary antimonide oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb)
and REZnSbO (RE = La, Ce, Pr) were synthesized from the RESb monoantimonides
and MnO, respectively ZnO. We report on single crystal X-ray data and a
detailed 121Sb M\""ossbauer spectroscopic investigation.",0804.1855v1
2009-10-22,Microscopic mechanisms of spin-dependent electric polarization in 3d oxides,"We present a short critical overview of different microscopic models for
nonrelativistic and relativistic magnetoelectric coupling including the
so-called ""spin current scenario"", ab-initio calculations, and several recent
microscopic approaches to a spin-dependent electric polarization in 3d oxides.",0910.4254v1
2010-03-05,A coupled map lattice model for spontaneous pore formation in anodic oxidation,"We construct a coupled map lattice model for the spontaneous pore formation
in anodic oxidation in two dimensions and perform numerical simulations, after
we explain steady flat solutions, their linear stability and a single pore
solution for a model of Parkhutik and Shershulsky.",1003.1213v1
2010-04-25,Electron-Hole Liquids in Transition Metal Oxide Heterostructures,"Appropriately designed transition metal oxide heterostructures involving
small band gap Mott insulators are argued to support spatially separated
electron and hole gasses at equilibrium. Spatial separations and carrier
densities favoring the formation of excitonic states are achievable. The
excitonic states may exhibit potentially novel properties. Energetic estimates
are given, candidate material systems are discussed, and the possibility of
large photvoltaic effects is mentioned",1004.4354v1
2010-09-02,Sensitivity of Biomarkers to Changes in Chemical Emissions in the Earth's Proterozoic Atmosphere,"The search for life beyond the Solar System is a major activity in exoplanet
science. However, even if an Earth-like planet were to be found, it is unlikely
to be at a similar stage of evolution as the modern Earth. It is therefore of
interest to investigate the sensitivity of biomarker signals for life as we
know it for an Earth-like planet but at earlier stages of evolution. Here, we
assess biomarkers i.e. species almost exclusively associated with life, in
present-day and in 10% present atmospheric level oxygen atmospheres
corresponding to the Earth's Proterozoic period. We investigate the impact of
proposed enhanced microbial emissions of the biomarker nitrous oxide, which
photolyses to form nitrogen oxides which can destroy the biomarker ozone. A
major result of our work is regardless of the microbial activity producing
nitrous oxide in the early anoxic ocean, a certain minimum ozone column can be
expected to persist in Proterozoic-type atmospheres due to a stabilising
feedback loop between ozone, nitrous oxide and the ultraviolet radiation field.
Atmospheric nitrous oxide columns were enhanced by a factor of 51 for the
Proterozoic ""Canfield ocean"" scenario with 100 times increased nitrous oxide
surface emissions. In such a scenario nitrous oxide displays prominent spectral
features, so may be more important as a biomarker than previously considered in
such cases. The run with ""Canfield ocean"" nitrous oxide emissions enhanced by a
factor of 100 also featured additional surface warming of 3.5K. Our results
suggest that the Proterozoic ozone layer mostly survives the changes in
composition which implies that it is indeed a good atmospheric biomarker.",1009.0439v1
2011-09-07,The effect of p-type doping on the oxidation of H-Si(111) studied by second-harmonic generation,"Atomic force microscopy and second-harmonic generation data show that boron
doping enhances the rate of oxidation of H-terminated silicon. Holes cause a
greater increase in the reactivity of the Si-H up bonds than that of the Si-Si
back bonds.",1109.1486v1
2011-09-19,Atomic layer deposition of high-k oxides on graphene,Atomic layer deposition of high-k oxides on graphene.,1109.4026v1
2013-10-09,"Electrical, Optical and Structural Properties of Improved Transparent Conductive Oxide TCO Films","High Frequency (GW) Post Processing of Transparent Conductive Oxide, ITO,
leads to a significant improvement of Optical Transmission and Electrical
Conduction. This is also true in case of ITO films in multilayered structures.
The improvements happen without any affecting the lower layers (other layers of
the multilayered Device). This Method is extremely selective and can process
only the targeted film (layer).",1310.2826v1
2015-03-02,Andreev Reflection Spectroscopy in Transition Metal Oxides,"Here we review the literature concerning measurement of the Andreev
reflection between a superconductor (S) and ferromagnet (F), with particular
attention to the case where the ferromagnet is a transition metal oxide. We
discuss the practicality of utilisation of the current models for determination
of the transport current spin polarisation and examine the evidence for Andreev
bound states.",1503.00533v1
2015-11-23,Endurance Write Speed Tradeoffs in Nonvolatile Memories,"We derive phenomenological model for endurance-write time switching tradeoff
for nonvolatile memories with thermally activated switching mechanisms. The
model predicts linear to cubic dependence of endurance on write time for metal
oxide memristors and flash memories, which is partially supported by
experimental data for the breakdown of metal-oxide thin films.",1511.07109v1
2009-12-13,Systematic Control of Carrier Doping without Disorder at Interface of Oxide Heterostructures,"We propose a method to systematically control carrier densities at the
interface of transition-metal oxide heterostructures without introducing
disorders. By inserting non-polar layers sandwiched by polar layers, continuous
carrier doping into the interface can be realized. This method enables us to
control the total carrier densities per unit cell systematically up to high
values of the order unity.",0912.2484v1
2012-05-24,Principles of crystal growth of intermetallic and oxide compounds from molten solutions,"We present a tutorial on the principles of crystal growth of intermetallic
and oxide compounds from molten solutions, with an emphasis on the fundamental
principles governing the underlying phase equilibria and phase diagrams of
multicomponent systems.",1205.5592v1
2019-11-15,Energy conversion processes with perovskite-type materials,"Mixed oxides derived from the perovskite structure by combination of A- and
B-site elements and by partial substitution of oxygen provide an immense
playground of physico-chemical properties. Here, we account for own research
conducted at the Paul Scherrer Institute on perovskite-type oxides and
oxynitrides used in electrochemical, photo(electro)chemical and catalytic
processes aiming at facing energy relevant issues.",1911.06658v1
2020-03-07,A Study of Selectively Digital Etching Silicon-Germanium with Nitric and Hydrofluoric Acids,"A digital etching method was proposed to achieve excellent control of etching
depth. The digital etching characteristics of p+ Si and Si0.7Ge0.3 using the
combinations of HNO3 oxidation and BOE oxide removal processes were studied.
Experiments showed that oxidation saturates with time due to low activation
energy. A physical model was presented to describe the wet oxidation process
with nitric acid. The model was calibrated with experimental data and the
oxidation saturation time, final oxide thickness, and selectivity between
Si0.7Ge0.3 and p+ Si were obtained. The digital etch of laminated Si0.7Ge0.3/p+
Si was also investigated. The depth of the tunnels formed by etching SiGe
layers between two Si layers was found in proportion to digital etching cycles.
And oxidation would also saturate and the saturated relative etched amount per
cycle (REPC) was 0.5 nm (4 monolayers). A corrected selectivity calculation
formula was presented. The oxidation model was also calibrated with
Si0.7Ge0.3/p+ Si stacks, and selectivity from model was the same with the
corrected formula. The model can also be used to analyze process variations and
repeatability. And it could act as a guidance for experiment design.
Selectivity and repeatability should make a trade-off.",2003.03529v1
2021-03-23,"Ultrathin 2D-oxides: a perspective on fabrication, structure, defect, transport, electron and phonon properties","In the field of atomically thin 2D materials, oxides are relatively
unexplored in spite of the large number of layered oxide structures amenable to
exfoliation. There is an increasing interest in ultra-thin film oxide
nanostructures from applied points of view. In this perspective paper, recent
progress in understanding the fundamental properties of 2D oxides is discussed.
Two families of 2D oxides are considered: (1) van der Waals bonded layered
materials in which the transition metal is in its highest valence state
(represented by V$_2$O$_5$ and MoO$_3$) and (2) layered materials with ionic
bonding between positive alkali cation layers and negatively charged transition
metal oxide layers (LiCoO$_2$). The chemical exfoliation process and its
combinaton with mechanical exfoliation are presented for the latter. Structural
phase stability of the resulting nanoflakes, the role of cation size and the
importance of defects in oxides are discussed. Effects of two-dimensionality on
phonons, electronic band structures and electronic screening are placed in the
context of what is known on other 2D materials, such as transition metal
dichalcogenides. Electronic structure is discussed at the level of
many-body-perturbation theory using the quasiparticle self-consistent $GW$
method, the accuracy of which is critically evaluated including effects of
electron-hole interactions on screening and electron-phonon coupling. The
predicted occurence of a two-dimensional electron gas on Li covered surfaces of
LiCoO$_2$ and its relation to topological aspects of the band structure and
bonding is presented as an example of the essential role of the surface in
ultrathin materials. Finally, some case studies of the electronic transport and
the use of these oxides in nanoscale field effect transistors are presented.",2103.12530v1
2021-04-15,Quantum many-body effects on Rydberg excitons in cuprous oxide,"We investigate quantum many-body effects on Rydberg excitons in cuprous oxide
induced by the surrounding electron-hole plasma. Line shifts and widths are
calculated by full diagonalisation of the plasma Hamiltonian and compared to
results in first order perturbation theory, and the oscillator strength of the
exciton lines is analysed.",2104.07344v1
2021-04-19,The effects of intrinsic local distortions vs. dynamic thermal motions on the stability and band gaps of cubic oxide and halide perovskites,"Corner-shared ABX$_3$ perovskites have long featured prominently in
solid-state chemistry and condensed matter physics. Still, the joint
understanding of their two main subgroups-halides and oxides-has not been fully
developed. Indeed, unlike the case that compounds having a single repeated
motif (""monomorphous""), certain cubic perovskites can manifest a non-thermal
distribution of local motifs (""polymorphous networks""). Such intrinsic
deformations can include positional degrees of freedom. Unlike thermal motion,
such intrinsic distortions do not time-average to zero. The present study
compares electronic structure features of oxide and halide perovskites starting
from the intrinsic polymorphous network described by DFT minimization of the
internal energy, continuing to finite temperature thermal disorder using AIMD.
We find that (i) different oxide vs. halide ABX$_3$ compounds adopt different
energy-lowering distortion modes. The DFT calculated pair distribution function
(PDF) of SrTiO$_3$ agrees with the recently measured PDF. (ii) In both oxides
and halides, such intrinsic distortions lead to bandgap blueshifts with respect
to monomorphous structure. (iii) For oxide perovskites, high-temperature AIMD
simulations initiated from the polymorphous structures reveal that the
thermally-induced distortions can lead to a bandgap redshift. (iv) In contrast,
for cubic CsPbI$_3$, both the intrinsic distortions and the thermal distortions
contribute in tandem to bandgap blueshift, the former, intrinsic effect being
dominant. (v) In the oxide SrTiO$_3$ and CaTiO$_3$ (but not in halide),
octahedral tilting leads to the emergence of a distinct $\Gamma$-$\Gamma$
direct bandgap component as a secondary valley minimum to the well-known
indirect R-$\Gamma$ gap. Understanding such intrinsic vs. thermal effects on
oxide vs. halide perovskites holds the potential for designing target
electronic properties.",2104.09361v2
2021-06-16,Oxidation of 2D electrenes: structural transition and the formation of half-metallic channels protected by oxide layers,"Based on first-principles calculations we performed a systematic study of the
energetic stability, structural characterization, and electronic properties of
the fully oxidized $A_{2}B$, electrenes, with the following combinations, (i)
$A$=Ca, Sr, and Ba for $B$=N; (ii) $A$=Sr and Ba for $B$=P; and Y$_{2}$C, and
Ba$_{2}$As. We have considered one side oxidation of single layer electrenes
$(O/A_{2}B)$, and two side oxidation of bilayer electrenes
$(O/(A_{2}B)_{2}/O)$. We show that the hexagonal lattice of the pristine host
is no longer the ground state structure in the oxidized systems. Our total
energy results reveal an exothermic structural transition from hexagonal to
tetragonal (h$\rightarrow$t) geometry, resulting in layered tetragonal
structures [$(AOAB)^{t}$, and $(AO(AB)_{2}AO)^{t}$]. Phonon spectra
calculations and molecular dynamic simulations show that the $O/A_{2}B$, and
$O/(A_{2}B)_{2}/O$ systems, with $A$=Ba, Ca, Sr, and $B$=N, become dynamically
and structurally stable upon such a h$\rightarrow$t transition. Further
structural characterizations were performed based on simulations of the near
edge X-ray absorption spectroscopy at the nitrogen K-edge. Finally, the
electronic structure calculations and transport calculations reveal the
formation of half-metallic bands spreading out through the $A$N layers, which
are shielded by oxide $A$O sheets. These findings indicate that $(AOAB)^{t}$,
and $(AO(AB)_{2}AO)^{t}$, (with $B$=N) are quite interesting platforms for
application in spintronics; since the half-metallic channels along the $A$N or
$(A\text{N})_2$ layers (core) are protected against the environment conditions
by the oxidized $A\text{O}$ sheets (cover shells).",2106.09102v5
2022-02-11,Towards controllable Si-doping in oxide molecular beam epitaxy using a solid SiO source: Application to $β$-Ga2O3,"The oxidation-related issues in controlling Si doping from the Si source
material in oxide molecular beam epitaxy (MBE) is addressed by using solid SiO
as an alternative source material in a conventional effusion cell.
Line-of-sight quadrupole mass spectrometry of the direct SiO-flux
($\Phi_{SiO}$) from the source at different temperatures ($T_{SiO}$) confirmed
SiO molecules to sublime with an activation energy of 3.3eV. The
$T_{SiO}$-dependent $\Phi_{SiO}$ was measured in vacuum before and after
subjecting the source material to an O$_{2}$-background of $10^{-5}$ mbar
(typical oxide MBE regime). The absence of a significant $\Phi_{SiO}$
difference indicates negligible source oxidation in molecular O$_{2}$. Mounted
in an oxygen plasma-assisted MBE, Si-doped $\beta$-Ga2O3 layers were grown
using this source. The $\Phi_{SiO}$ at the substrate was evaluated [from
2.9x10$^{9}$ cm$^{-2}$s$^{-1}$ ($T_{SiO}$=700{\deg}C) to 5.5x10$^{13}$
cm$^{-2}$s$^{-1}$ (T$_{SiO}$=1000{\deg}C)] and Si-concentration in the
$\beta$-Ga2O3 layers measured by secondary ion mass spectrometry highlighting
unprecedented control of continuous Si-doping for oxide MBE, i.e., $N_{Si}$
from 4x10$^{17}$ cm$^{-3}$ ($T_{SiO}$=700{\deg}C) up to 1.7x10$^{20}$ cm$^{-3}$
($T_{SiO}$=900{\deg}C). For a homoepitaxial $\beta$-Ga2O3 layer an Hall charge
carrier concentration of 3x10$^{19}$ cm$^{-3}$ in line with the provided
$\Phi_{SiO}$ ($T_{SiO}$=800{\deg}C) is demonstrated. No SiO-incorporation
difference was found between $\beta$-Ga2O3(010) layers homoepitaxially grown at
750{\deg}C and $\beta$-Ga2O3(-201) layers heteroepitaxially grown at
550{\deg}C. The presence of activated oxygen (plasma) resulted in partial
source oxidation and related decrease of doping concentration (particularly at
$T_{SiO}$<800{\deg}C) which has been tentatively explained with a simple model.
Degassing the source at 1100{\deg}C reverted the oxidation.",2202.05762v1
2023-10-23,"Mass uptake during oxidation of metallic alloys: literature data collection, analysis, and FAIR sharing","The area-normalized change of mass ($\Delta$m/A) with time during the
oxidation of metallic alloys is commonly used to assess oxidation resistance.
Analyses of such data can also aid in evaluating underlying oxidation
mechanisms. We performed an exhaustive literature search and digitized
normalized mass change vs. time data for 407 alloys. To maximize the impact of
these and future mass uptake data, we developed and published an open, online,
computational workflow that fits the data to various models of oxidation
kinetics, uses Bayesian statistics for model selection, and makes the raw data
and model parameters available via a queryable database. The tool, Refractory
Oxidation Database (https://nanohub.org/tools/refoxdb/), uses nanoHUB's Sim2Ls
to make the workflow and data (including metadata) findable, accessible,
interoperable, and reusable (FAIR). We find that the models selected by the
original authors do not match the most likely one according to the Bayesian
information criterion (BIC) in 71% of the cases. Further, in 56% of the cases,
the published model was not even in the top 3 models according to the BIC.
These numbers were obtained assuming an experimental noise of 2.5% of the mass
gain range, a smaller noise leads to more discrepancies. The RefOxDB tool is
open access and researchers can add their own raw data (those to be included in
future publications, as well as negative results) for analysis and to share
their work with the community. Such consistent and systematic analysis of open,
community generated data can significantly accelerate the development of
machine-learning models for oxidation behavior and assist in the understanding
and improvement of oxidation resistance.",2310.15083v1
2024-03-12,Lattice dynamics of altermagnetic ruthenium oxide RuO$_{2}$,"Altermagnetic ruthenium oxide RuO$_{2}$ crystallizes with P4$_{2}$/mnm
symmetry. Here we discuss the lattice dynamics of this structure. We show and
discuss the phonon dispersion and density of states. The phonon dispersion
curves contain several Dirac nodal lines and highly degenerate Dirac points. We
present the characteristic frequencies and their irreducible representations at
the $\Gamma$ point. Theoretically obtained frequencies of the Raman active
modes nicely reproduce the ones reported experimentally.",2403.07609v1
2004-10-25,Room-temperature electric field effect and carrier-type inversion in graphene films,"The ability to control electronic properties of a material by externally
applied voltage is at the heart of modern electronics. In many cases, it is the
so-called electric field effect that allows one to vary the carrier
concentration in a semiconductor device and, consequently, change an electric
current through it. As the semiconductor industry is nearing the limits of
performance improvements for the current technologies dominated by silicon,
there is a constant search for new, non-traditional materials whose properties
can be controlled by electric field. Most notable examples of such materials
developed recently are organic conductors [1], oxides near a superconducting or
magnetic phase transition [2] and carbon nanotubes [3-5]. Here, we describe
another system of this kind - thin monocrystalline films of graphite - which
exhibits a pronounced electric field effect, such that carriers in the
conductive channel can be turned into either electrons or holes. The films
remain metallic, continuous and of high quality down to a few atomic layers in
thickness. The demonstrated ease of preparing such films of nearly macroscopic
sizes and of their processing by standard microfabrication techniques, combined
with submicron-scale ballistic transport even at room temperature, offer a new
two-dimensional system controllable by electric-field doping and provide a
realistic promise of device applications.",0410631v1
2007-06-13,Electronic spin transport and spin precession in single graphene layers at room temperature,"The specific band structure of graphene, with its unique valley structure and
Dirac neutrality point separating hole states from electron states has led to
the observation of new electronic transport phenomena such as anomalously
quantized Hall effects, absence of weak localization and the existence of a
minimum conductivity. In addition to dissipative transport also supercurrent
transport has already been observed. It has also been suggested that graphene
might be a promising material for spintronics and related applications, such as
the realization of spin qubits, due to the low intrinsic spin orbit
interaction, as well as the low hyperfine interaction of the electron spins
with the carbon nuclei. As a first step in the direction of graphene
spintronics and spin qubits we report the observation of spin transport, as
well as Larmor spin precession over micrometer long distances using single
graphene layer based field effect transistors. The non-local spin valve
geometry was used, employing four terminal contact geometries with
ferromagnetic cobalt electrodes, which make contact to the graphene sheet
through a thin oxide layer. We observe clear bipolar (changing from positive to
negative sign) spin signals which reflect the magnetization direction of all 4
electrodes, indicating that spin coherence extends underneath all 4 contacts.
No significant changes in the spin signals occur between 4.2K, 77K and room
temperature. From Hanle type spin precession measurements we extract a spin
relaxation length between 1.5 and 2 micron at room temperature, only weakly
dependent on charge density, which is varied from n~0 at the Dirac neutrality
point to n = 3.6 10^16/m^2. The spin polarization of the ferromagnetic contacts
is calculated from the measurements to be around 10%.",0706.1948v1
2007-11-13,Cyclooxygenase Inhibition Limits Blood-Brain Barrier Disruption following Intracerebral Injection of Tumor Necrosis Factor-alpha in the Rat,"Increased permeability of the blood-brain barrier (BBB) is important in
neurological disorders. Neuroinflammation is associated with increased BBB
breakdown and brain injury. Tumor necrosis factor-a (TNF-a) is involved in BBB
injury and edema formation through a mechanism involving matrix
metalloproteinase (MMP) upregulation. There is emerging evidence indicating
that cyclooxygenase (COX) inhibition limits BBB disruption following ischemic
stroke and bacterial meningitis, but the mechanisms involved are not known. We
used intracerebral injection of TNF-a to study the effect of COX inhibition on
TNF-a-induced BBB breakdown, MMP expression/activity and oxidative stress. BBB
disruption was evaluated by the uptake of 14C-sucrose into the brain and by
magnetic resonance imaging (MRI) utilizing Gd-DTPA as a paramagnetic contrast
agent. Using selective inhibitors of each COX isoform, we found that COX-1
activity is more important than COX-2 in BBB opening. TNF-a induced a
significant upregulation of gelatinase B (MMP-9), stromelysin-1 (MMP-3) and
COX-2. In addition, TNF-a significantly depleted glutathione as compared to
saline. Indomethacin (10 mg/kg; i.p.), an inhibitor of COX-1 and COX-2, reduced
BBB damage at 24 h. Indomethacin significantly attenuated MMP-9 and MMP-3
expression and activation, and prevented the loss of endogenous radical
scavenging capacity following intracerebral injection of TNF-a. Our results
show for the first time that BBB disruption during neuroinflammation can be
significantly reduced by administration of COX inhibitors. Modulation of COX in
brain injury by COX inhibitors or agents modulating prostaglandin E2
formation/signaling may be useful in clinical settings associated with BBB
disruption.",0711.2096v1
2007-12-31,Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ},"A complete knowledge of its excitation spectrum could greatly benefit efforts
to understand the unusual form of superconductivity occurring in the lightly
hole-doped copper-oxides. Here we use tunnelling spectroscopy to measure the
T\to 0 spectrum of electronic excitations N(E) over a wide range of
hole-density p in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta}. We
introduce a parameterization for N(E) based upon an anisotropic energy-gap
/Delta (\vec k)=/Delta_{1}(Cos(k_{x})-Cos(k_{y}))/2 plus an effective
scattering rate which varies linearly with energy /Gamma_{2}(E) . We
demonstrate that this form of N(E) allows successful fitting of differential
tunnelling conductance spectra throughout much of the
Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta} phase diagram. The resulting average
/Delta_{1} values rise with falling p along the familiar trajectory of
excitations to the 'pseudogap' energy, while the key scattering rate
/Gamma_{2}^{*}=/Gamma_{2}(E=/Delta_{1}) increases from below ~1meV to a value
approaching 25meV as the system is underdoped from p~16% to p<10%. Thus, a
single, particle-hole symmetric, anisotropic energy-gap, in combination with a
strongly energy and doping dependent effective scattering rate, can describe
the spectra without recourse to another ordered state. Nevertheless we also
observe two distinct and diverging energy scales in the system: the energy-gap
maximum /Delta_{1} and a lower energy scale /Delta_{0} separating the spatially
homogeneous and heterogeneous electronic structures.",0801.0087v1
2008-08-04,Local structures of polar wurtzites Zn_{1-x}Mg_{x}O studied by Raman and {67}Zn/{25}Mg NMR spectroscopies and by total neutron scattering,"Local compositions and structures of Zn_{1-x}Mg_{x}O alloys have been
investigated by Raman and solid-state {67}Zn/{25}Mg nuclear magnetic resonance
(NMR) spectroscopies, and by neutron pair-distribution-function (PDF) analyses.
The E2(low) and E2(high) Raman modes of Zn_{1-x}Mg_{x}O display Gaussian- and
Lorentzian-type profiles, respectively. At higher Mg substitutions, both modes
become broader, while their peak positions shift in opposite directions. The
evolution of Raman spectra from Zn_{1-x}Mg_{x}O solid solutions are discussed
in terms of lattice deformation associated with the distinct coordination
preferences of Zn and Mg. Solid-state magic-angle-spinning (MAS) NMR studies
suggest that the local electronic environments of {67}Zn in ZnO are only weakly
modified by the 15% substitution of Mg for Zn. {25}Mg MAS spectra of
Zn_{0.85}Mg_{0.15}O show an unusual upfield shift, demonstrating the prominent
shielding ability of Zn in the nearby oxidic coordination sphere. Neutron PDF
analyses of Zn_{0.875}Mg_{0.125}O using a 2x2x1 supercell corresponding to
Zn_{7}MgO_{8} suggest that the mean local geometry of MgO_{4} fragments concurs
with previous density functional theory (DFT)-based structural relaxations of
hexagonal wurtzite MgO. MgO_{4} tetrahedra are markedly compressed along their
c-axes and are smaller in volume than ZnO_{4} units by ~6%. Mg atoms in
Zn_{1-x}Mg_{x}O have a shorter bond to the $c$-axial oxygen atom than to the
three lateral oxygen atoms, which is distinct from the coordination of Zn. The
precise structure, both local and average, of Zn_{0.875}Mg_{0.125}O obtained
from time-of-flight total neutron scattering supports the view that
Mg-substitution in ZnO results in increased total spontaneous polarization.",0808.0492v1
2009-01-07,Synthesis and characterization of single phase Mn doped ZnO,"Different samples of Zn1-xMnxO series have been prepared by conventional
solid state sintering method. It has been identified, up to what extent of
doping enable us to synthesize single-phase polycrystalline Mn doped ZnO
samples which is one of the prerequisite for dilute magnetic semiconductor and
we have analyzed its certain other physical aspects. In synthesizing the
samples proportion of Mn varies from 1 at% to 5 at%. However the milling times
have been varied (6, 12, 24, 48 & 96 hours) for only 2 at% Mn doped samples
while for other samples (1, 3, 4 & 5 at% Mn doped) the milling time has been
kept fixed at 96 hours. Room temperature X-Ray diffraction (XRD) data reveal
that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type
structure, no segregation of Mn and/or its oxides has been found. The 4 at% Mn
doped samples show a weak peak of ZnMn2O4 apart from usual other peaks of ZnO
and the intensity of this impurity peak has been further increased for 5 at% of
Mn doping. So beyond 3 at% doping single-phase behavior is destroyed. Band gap
for all the 2 at% Mn doped samples have been estimated as between 3.21 to 3.19
eV and reason for this low band gap values has been explained through the grain
boundary trapping model. The room temperature resistivity measurement shows
increase of resistivity up to 48 hours of milling and with further milling it
saturates. The defect state of these samples has been investigated by using
positron annihilation lifetime (PAL) spectroscopy technique. Here all the
relevant lifetime parameters of positron i.e. free annihilation (tau 1), at
defect site (tau 2) and average (tau av) increases with milling time.",0901.0807v1
2009-01-28,Extension of the spin-1/2 frustrated square lattice model: the case of layered vanadium phosphates,"We study the influence of the spin lattice distortion on the properties of
frustrated magnetic systems and consider the applicability of the spin-1/2
frustrated square lattice model to materials lacking tetragonal symmetry. We
focus on the case of layered vanadium phosphates AA'VO(PO4)2 (AA' = Pb2, SrZn,
BaZn, and BaCd). To provide a proper microscopic description of these
compounds, we use extensive band structure calculations for real materials and
model structures and supplement this analysis with simulations of thermodynamic
properties, thus facilitating a direct comparison with the experimental data.
Due to the reduced symmetry, the realistic spin model of layered vanadium
phosphates AA'VO(PO4)2 includes four inequivalent exchange couplings: J1 and
J1' between nearest-neighbors and J2 and J2' between next-nearest-neighbors.
The estimates of individual exchange couplings suggest different regimes, from
J1'/J1 and J2'/J2 close to 1 in BaCdVO(PO4)2, a nearly regular frustrated
square lattice, to J1'/J1 ~ 0.7 and J2'/J2 ~ 0.4 in SrZnVO(PO4)2, a frustrated
square lattice with sizable distortion. The underlying structural differences
are analyzed, and the key factors causing the distortion of the spin lattice in
layered vanadium compounds are discussed. We propose possible routes for
finding new frustrated square lattice materials among complex vanadium oxides.
Full diagonalization simulations of thermodynamic properties indicate the
similarity of the extended model to the regular one with averaged couplings. In
case of moderate frustration and moderate distortion, valid for all the
AA'VO(PO4)2 compounds reported so far, the distorted spin lattice can be
considered as a regular square lattice with the couplings (J1+J1')/2 between
nearest-neighbors and (J2+J2')/2 between next-nearest-neighbors.",0901.4498v2
2009-09-28,Single ion implantation for single donor devices using Geiger mode detectors,"Electronic devices that are designed to use the properties of single atoms
such as donors or defects have become a reality with recent demonstrations of
donor spectroscopy, single photon emission sources, and magnetic imaging using
defect centers in diamond. Improving single ion detector sensitivity is linked
to improving control over the straggle of the ion as well as providing more
flexibility in lay-out integration with the active region of the single donor
device construction zone by allowing ion sensing at potentially greater
distances. Using a remotely located passively gated single ion Geiger mode
avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency
at a distance of >75 um from the center of the collecting junction. This
detection efficiency is achieved with sensitivity to ~600 or fewer
electron-hole pairs produced by the implanted ion. Ion detectors with this
sensitivity and integrated with a thin dielectric, for example 5 nm gate oxide,
using low energy Sb implantation would have an end of range straggle of <2.5
nm. Significant reduction in false count probability is achieved by modifying
the ion beam set-up to allow for cryogenic operation of the SIGMA detector.
Using a detection window of 230 ns at 1 Hz, the probability of a false count
was measured as 1E-1 and 1E-4 for operation temperatures of 300K and 77K,
respectively. Low temperature operation and reduced false, dark, counts are
critical to achieving high confidence in single ion arrival. For the device
performance in this work, the confidence is calculated as a probability of >98%
for counting one and only one ion for a false count probability of 1E-4 at an
average ion number per gated window of 0.015.",0909.5189v1
2010-03-13,Single-shot readout of an electron spin in silicon,"The size of silicon transistors used in microelectronic devices is shrinking
to the level where quantum effects become important. While this presents a
significant challenge for the further scaling of microprocessors, it provides
the potential for radical innovations in the form of spin-based quantum
computers and spintronic devices. An electron spin in Si can represent a
well-isolated quantum bit with long coherence times because of the weak
spin-orbit coupling and the possibility to eliminate nuclear spins from the
bulk crystal. However, the control of single electrons in Si has proved
challenging, and has so far hindered the observation and manipulation of a
single spin. Here we report the first demonstration of single-shot,
time-resolved readout of an electron spin in Si. This has been performed in a
device consisting of implanted phosphorus donors coupled to a
metal-oxide-semiconductor single-electron transistor - compatible with current
microelectronic technology. We observed a spin lifetime approaching 1 second at
magnetic fields below 2 T, and achieved spin readout fidelity better than 90%.
High-fidelity single-shot spin readout in Si opens the path to the development
of a new generation of quantum computing and spintronic devices, built using
the most important material in the semiconductor industry.",1003.2679v3
2010-10-21,Metal-insulator transition in Nd1-xEuxNiO3 probed by specific heat and anelastic measurements,"Oxides RNiO3 (R = rare-earth, R # La) exhibit a metal-insulator (MI)
transition at a temperature TMI and an antiferromagnetic (AF) transition at TN.
Specific heat (CP) and anelastic spectroscopy measurements were performed in
samples of Nd1-xEuxNiO3, 0 <= x <= 0.35. For x = 0, a peak in CP is observed
upon cooling and warming at essentially the same temperature TMI = TN ~ 195 K,
although the cooling peak is much smaller. For x >= 0.25, differences between
cooling and warming curves are negligible, and two well defined peaks are
clearly observed: one at lower temperatures, that define TN, and the other one
at TMI. An external magnetic field of 9 T had no significant effect on these
results. The elastic compliance (s) and the reciprocal of the mechanical
quality factor (Q^-1) of NdNiO3, measured upon warming, showed a very sharp
peak at essentially the same temperature obtained from CP, and no peak is
observed upon cooling. The elastic modulus hardens below TMI much more sharply
upon warming, while the cooling and warming curves are reproducible above TMI.
On the other hand, for the sample with x = 0.35, s and Q^-1 curves are very
similar upon warming and cooling. The results presented here give credence to
the proposition that the MI phase transition changes from first to second order
with increasing Eu doping.",1010.4414v1
2010-11-17,Deep Mixing in Evolved Stars: I. The Effect of Reaction Rate Revisions from C to Al,"We present computations of nucleosynthesis in low-mass red-giant-branch and
asymptotic-giant-branch stars of Population I experiencing extended mixing. We
adopt the updated version of the FRANEC evolutionary model, a new post-process
code for non-convective mixing and the most recent revisions for solar
abundances. In this framework, we discuss the effects of recent improvements in
relevant reaction rates for proton captures on intermediate-mass nuclei (from
carbon to aluminum). For each nucleus we briefly discuss the new choices and
their motivations. The calculations are then performed on the basis of a
parameterized circulation, where the effects of the new nuclear inputs are best
compared to previous works. We find that the new rates (and notably the one for
the 14N(p,g)15O reaction) imply considerable modifications in the composition
of post-main sequence stars. In particular, the slight temperature changes due
to the reduced efficiency of proton captures on 14N induce abundance variations
at the first dredge up (especially for 17O, whose equilibrium ratio to 16O is
very sensitive to the temperature). In this new scenario presolar oxide grains
of AGB origin turn out to be produced almost exclusively by very-low mass stars
(M<=1.5-1.7Msun), never becoming C-rich. The whole population of grains with
18O/16O below 0.0015 (the limit permitted by first dredge up) is now explained.
Also, there is now no forbidden area for very low values of 17O/16O (below
0.0005), contrary to previous findings. A rather shallow type of transport
seems to be sufficient for the CNO changes in RGB stages. Both thermohaline
diffusion and magnetic-buoyancy-induced mixing might provide a suitable
physical mechanism for this. Thermohaline mixing is in any case certainly
inadequate to account for the production of 26Al on the AGB. Other transport
mechanisms must therefore be at play.",1011.3948v3
2013-05-27,Euclidian crystals in many-body systems: breakdown of Goldstone's theorem,"In accord with Nambu-Goldstone theorem spontaneous breaking of a global
continuous symmetry of the system by a mean-field order parameter causes
appearance of massless Goldstone bosons, called also gapless Goldstone modes.
It is demonstrated below that the theorem can be violated, i.e. the Goldstone
modes possess finite gap, in the case of a novel ""Euclidian crystal"" (quantum
ordered) state of interacting fermions, that was proposed recently {mukhin
2011}. This result may lead to the important consequences when considered in
combination with another peculiar properties of the quantum order parameter
(QOP) that where recently found: QOP's Green's function is finite and periodic
along the Matsubara's axis, but Wick-rotated to the axis of real frequencies,
possesses infinite periodic ""chain"" of \it{second order poles} along this axis
{mukhin 2011}. This property of QOP leads to a remarkable physical consequence:
\it{QOP does not scatter anything in Minkowski world} ! Hence, the present
theory, we believe, may naturally indicate that two effects: ""hidden order""
revealed in ARPES spectra of fermi-excitations and ""neutron resonance"" feature
at finite frequency in the magnetic (bosonic) excitations spectrum in lightly
hole-doped copper oxides, could be emerging fingerprints of the Euclidian
crystal state. A peculiar manifestation of the QOP self-consistent solution in
the form of non-classical phonon states is described for an ""electromagnetic
Euclidian crystal"" predicted recently {mukhin,fistul 2013} in the array of
Josephson junctions coupled via electromagnetic field in the superconducting
resonator. It is demonstrated that it may constitute a stable state of the
system, that, for a particular quantum disordering model, exists inside the
stability domain of the classical photonic condensate delimited by the critical
value of the quantum disordering strength.",1305.6125v2
2014-07-22,Observation of antiferromagnetic correlations in the Hubbard model with ultracold atoms,"Ultracold atoms in optical lattices have great potential to contribute to a
better understanding of some of the most important issues in many-body physics,
such as high-$T_c$ superconductivity. The Hubbard model describes many of the
features shared by the copper oxides, including an interaction-driven Mott
insulating state and an antiferromagnetic (AFM) state. Optical lattices filled
with a two-spin-component Fermi gas of ultracold atoms can faithfully realise
the Hubbard model with readily tunable parameters, and thus provide a platform
for the systematic exploration of its phase diagram. Realisation of strongly
correlated phases, however, has been hindered by the need to cool the atoms to
temperatures as low as the magnetic exchange energy, and also by the lack of
reliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of
light to measure AFM spin correlations in a realisation of the 3D Hubbard model
at temperatures down to 1.4 times that of the AFM phase transition. This
temperature regime is beyond the range of validity of a simple high-temperature
series expansion, which brings our experiment close to the limit of the
capabilities of current numerical techniques. We reach these low temperatures
using a unique compensated optical lattice technique, in which the confinement
of each lattice beam is compensated by a blue-detuned laser beam. The
temperature of the atoms in the lattice is deduced by comparing the light
scattering to determinantal quantum Monte Carlo and numerical linked-cluster
expansion calculations. Further refinement of the compensated lattice may
produce even lower temperatures which, along with light scattering thermometry,
would open avenues for achieving and characterising other novel quantum states
of matter, such as the pseudogap regime of the 2D Hubbard model.",1407.5932v2
2016-01-26,Ultrafast optical spectroscopy of strongly correlated materials and high-temperature superconductors: a non-equilibrium approach,"In the last two decades, non-equilibrium spectroscopies have evolved from
avant-garde studies to crucial tools for expanding our understanding of the
physics of strongly correlated materials. The possibility of obtaining
simultaneously spectroscopic and temporal information has led to insights that
are complementary to (and in several cases beyond) those attainable by studying
the matter at equilibrium. Multiple phase transitions and new orders arising
from competing interactions are benchmark examples where the interplay among
electrons, lattice, and spin dynamics can be disentangled because of the
different timescales that characterize the recovery of the initial ground
state. The nature of the broken-symmetry phases and of the bosonic excitations
that mediate the electronic interactions, eventually leading to
superconductivity or other exotic states, can be revealed by observing the
sub-picosecond dynamics of impulsively excited states. Recent experimental
developments have made possible to monitor the time-evolution of both the
single-particle and collective excitations under extreme conditions, such as
those arising from strong and selective photo-stimulation.
  Here, we review the most recent achievements in the experimental and
theoretical studies of the non-equilibrium electronic, optical, structural and
magnetic properties of correlated materials. The focus will be mainly on the
prototypical case of correlated oxides that exhibit unconventional
superconductivity or other exotic phases, even though the discussion will
extend also to other topical systems. The necessity of extending the actual
experimental capabilities and the numerical and analytic tools to
microscopically treat the non-equilibrium phenomena beyond the simple
phenomenological approaches represents one of the most challenging new frontier
in physics.",1601.07204v2
2016-09-26,Electron and phonon transport in shandite-structured Ni$_3$Sn$_2$S$_2$,"The shandite family of solids, with hexagonal structure and composition
A3M2X2 (A = Ni,Co,Rh,Pd; M = Pb,In,Sn,Tl; X = S,Se), has attracted recent
research attention due to promising applications as thermoelectric materials.
Herein we discuss the electron and phonon transport properties of
shandite-structured Ni3Sn2S2, based on a combination of density functional
theory (DFT), Boltzmann transport theory, and experimental measurements.
Ni3Sn2S2 exhibits a metallic and non-magnetic groundstate with Ni$^0$ oxidation
state and very low charge on Sn and S atoms. Seebeck coefficients obtained from
theoretical calculations are in excellent agreement with those measured
experimentally between 100 and 600 K. From the calculation of the ratio
$\sigma$/$\tau$ between the electronic conductivity and relaxation time, and
the experimental determination of electron conductivity, we extract the
variation of the scattering rate (1/$\tau$) with temperature between 300 and
600 K, which turns out to be almost linear, thus implying that the dominant
electron scattering mechanism in this temperature range is via phonons. The
electronic thermal conductivity, which deviates only slightly from the
Wiedemann-Franz law, provides the main contribution to thermal transport. The
small lattice contribution to the thermal conductivity is calculated from the
phonon structure and third-order force constants, and is only ~2
Wm$^{-1}$K$^{-1}$ at 300 K (less than 10% of the total thermal conductivity),
which is confirmed by experimental measurements. Overall, Ni$_3$Sn$_2$S$_2$ is
a poor thermoelectric material (ZT~0.01 at 300 K), principally due to the low
absolute value of the Seebeck coefficient. However, the understanding of its
transport properties will be useful for the rationalization of the
thermoelectric behavior of other, more promising members of the shandite
family.",1609.08085v1
2016-10-14,Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates,"In this study, we systematically investigate 3D momentum($\hbar k$)-resolved
electronic structures of Ruddlesden-Popper-type iridium oxides
Sr$_{n+1}$Ir$_n$O$_{3n+1}$ using soft-x-ray (SX) angle-resolved photoemission
spectroscopy (ARPES). Our results provide direct evidence of an
insulator-to-metal transition that occurs upon increasing the dimensionality of
the IrO$_2$-plane structure. This transition occurs when the spin-orbit-coupled
$j_{\rm eff}$=1/2 band changes its behavior in the dispersion relation and
moves across the Fermi energy. In addition, an emerging band along the
$\Gamma$(0,0,0)-R($\pi$,$\pi$,$\pi$) direction is found to play a crucial role
in the metallic characteristics of SrIrO$_3$. By scanning the photon energy
over 350 eV, we reveal the 3D Fermi surface in SrIrO$_3$ and $k_z$-dependent
oscillations of photoelectron intensity in Sr$_3$Ir$_2$O$_7$. In contrast to
previously reported results obtained using low-energy photons, folded bands
derived from lattice distortions and/or magnetic ordering make significantly
weak (but finite) contributions to the $k$-resolved photoemission spectrum. At
the first glance, this leads to the ambiguous result that the observed
$k$-space topology is consistent with the unfolded Brillouin zone (BZ) picture
derived from a non-realistic simple square or cubic Ir lattice. Through careful
analysis, we determine that a superposition of the folded and unfolded band
structures has been observed in the ARPES spectra obtained using photons in
both ultraviolet and SX regions. To corroborate the physics deduced using
low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful
complementary technique, as this method surveys more than one whole BZ and
provides a panoramic view of electronic structures.",1610.04361v1
2018-02-25,The role of spin in the calculation of Hubbard $U$ and Hund's $J$ parameters from first principles,"The density functional theory (DFT)+$U$ method is a pragmatic and effective
approach for calculating the ground-state properties of strongly-correlated
systems, and linear response calculations are widely used to determine the
requisite Hubbard parameters from first principles. We provide a detailed
treatment of spin within this linear response approach, demonstrating that the
conventional Hubbard $U$ formula, unlike the conventional DFT+$U$ corrective
functional, incorporates interactions that are off-diagonal in the spin indices
and places greater weight on one spin channel over the other. We construct
alternative definitions for Hubbard and Hund's parameters that are consistent
with the contemporary DFT+$U$ functional, expanding upon the minimum-tracking
linear response method. This approach allows Hund's $J$ and spin-dependent $U$
parameters to be calculated with the same ease as for the standard Hubbard $U$.
Our methods accurately reproduce the experimental band gap, local magnetic
moments, and the valence band edge character of manganese oxide, a canonical
strongly-correlated system. We also apply our approach to a complete series of
transition-metal complexes [M(H$_2$O)$_6$]$^{n+}$ (for M = Ti to Zn), showing
that Hubbard corrections on oxygen atoms are necessary for preserving bond
lengths, and demonstrating that our methods are numerically well-behaved even
for near-filled subspaces such as in zinc. However, spectroscopic properties
appear beyond the reach of the standard DFT+$U$ approach. Collectively, these
results shed new light on the role of spin in the calculation of the corrective
parameters $U$ and $J$, and point the way towards avenues for further
development of DFT+$U$-type methods.",1802.09048v2
2019-05-09,"Novel two-dimensional Ca-Cl crystals with metallicity, piezoelectric effect and room-temperature ferromagnetism","Recently we have reported the direct observation of two-dimensional (2D)
Ca-Cl crystals on reduced graphene oxide (rGO) membranes, in which the calcium
ions are only about monovalent (i.e. ~+1) and metallic rather than insulating
properties are displayed by those CaCl crystals. Here, we report the
experimental observation and demonstration of the formation of graphene-Ca-Cl
heterojunction owing to the metallicity of 2D Ca-Cl crystals, unexpected
piezoelectric effect, room-temperature ferromagnetism, as well as the distinct
hydrogen storage and release capability of the Ca-Cl crystals in rGO membranes.
Theoretical studies show that the formation of those abnormal crystals is
attributed to the strong cation-pi interactions of the Ca2+ with the aromatic
rings in the graphitic surfaces. Since strong cation-pi interactions also exist
between other metal ions (such as Mg2+, Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+)
and graphitic surfaces, similar 2D crystals with abnormal valence state of the
metal cations and corresponding abnormal properties as well as novel
applications are highly expected. Those findings further show the realistically
potential applications of such abnormal CaCl material with unusual electronic
properties in designing novel transistors and magnetic devices, hydrogen
storage, catalyzer, high-performance conducting electrodes and sensors, with a
size down to atomic scale.",1905.04135v1
2020-07-18,Resistive AC-Coupled Silicon Detectors: principles of operation and first results from a combined analysis of beam test and laser data,"This paper presents the principles of operation of Resistive AC-Coupled
Silicon Detectors (RSDs) and measurements of the temporal and spatial
resolutions using a combined analysis of laser and beam test data. RSDs are a
new type of n-in-p silicon sensor based on the Low-Gain Avalanche Diode (LGAD)
technology, where the $n^+$ implant has been designed to be resistive, and the
read-out is obtained via AC-coupling. The truly innovative feature of RSD is
that the signal generated by an impinging particle is shared isotropically
among multiple read-out pads without the need for floating electrodes or an
external magnetic field. Careful tuning of the coupling oxide thickness and the
$n^+$ doping profile is at the basis of the successful functioning of this
device. Several RSD matrices with different pad width-pitch geometries have
been extensively tested with a laser setup in the Laboratory for Innovative
Silicon Sensors in Torino, while a smaller set of devices have been tested at
the Fermilab Test Beam Facility with a 120 GeV/c proton beam. The measured
spatial resolution ranges between $2.5\; \mu m$ for 70-100 pad-pitch geometry
and $17\; \mu m$ with 200-500 matrices, a factor of 10 better than what is
achievable in binary read-out ($bin\; size/ \sqrt{12}$). Beam test data show a
temporal resolution of $\sim 40\; ps$ for 200-$\mu m$ pitch devices, in line
with the best performances of LGAD sensors at the same gain.",2007.09528v4
2016-11-16,Tunneling anomalous Hall effect in the nanogranular CoFe-B-Al-O films near the metal-insulator transition,"We present results of experimental studies of structural, magneto-transport
and magnetic properties of CoFe-B-Al-O films deposited onto a glass ceramic
substrate by the ion-beam sputtering of the target composed of Co40Fe40B20 and
Al2O3 plates. The system consists on the strained crystalline CoFe metallic
nanogranules with the size 2-5 nm which are embedded into the B-Al-O oxide
insulating matrix. Our investigations are focused on the anomalous Hall effect
(AHE) resistivity Rh and longitudinal resistivity R at T=5-200 K on the
metallic side of metal-insulator transition in samples with the metal content
x=49-56 at.%, that nominally corresponds to (Co40Fe40B20)x(Al2O3)100-x in the
formula approximation. The conductivity at T > 15 K follows the lnT behavior
that matches a strong tunnel coupling between nanogranules. It is shown that
the scaling power-laws between AHE resistivity and longitudinal resistivity
strongly differ, if temperature T or metal content x are variable parameters:
Rh(T)~R(T)^0.4-0.5 obtained from the temperature variation of R and Rh at fixed
x, while Rh(x)/x~R(x)^0.24, obtained from measurements at the fixed low
temperature region (10-40 K) for samples with different x. We qualitatively
describe our experimental data in the frame of phenomenological model of two
sources of AHE e.m.f. arising from metallic nanogranules and insulating
tunneling regions, respectively, at that the tunneling AHE (TAHE) source is
strongly shunted due to generation of local circular Hall currents. We consider
our experimental results as the first experimental proof of the TAHE
manifestation.",1611.05195v1
2008-07-14,Tight-binding theory of lanthanum strontium manganate,"An earlier analysis of manganese oxides in various charge states indicated
that free-atom term values and universal coupling gave a reasonable account of
the cohesion. This approach is here extended to LaxSr(1-x)MnO3 in a perovskite
structure, and a wide range of properties, with comparable success, including
the cohesion, as a function of x. Magnetic and electronic properties are
treated in terms of the same parameters and the cluster orbitals used for
cohesion. This includes an estimate of the Neel and Curie-Weiss temperatures
for SrMnO3, an antiferromagnetic insulator, and the magnitude of a Jahn-Teller
distortion in LaMnO3 which makes it also insulating with (100) ferromagnetic
planes (due to a novel double-exchange for the distorted state),
antiferromagnetically stacked, as observed. We estimate the Neel temperature
and its volume dependence, and the ferromagnetic Curie-Weiss temperature which
applies between the Neel and Jahn-Teller temperatures. We expect hopping
conductivity when there is doping (0<x<1) and estimate it in the context of
small-polaron theory. It is in accord with experiment between the Neel and
Jahn-Teller temperatures, but below the Neel temperature the conduction appears
to be band-like, for which we estimate a hole mass as enhanced in large-polaron
theory. We see that above the Jahn-Teller temperature LaMnO3 should be metallic
as observed, and paramagnetic with a ferromagnetic Curie-Weiss constant which
we estimate. Many of these predictions are not so accurate, but are
sufficiently close to provide a clear understanding of all of these properties
in terms of a simple theory and parameters known at the outset. We provide also
these parameters for Fe, Co, and Ca so that formulae for the properties can
readily be evaluated for similar systems.",0807.2248v2
2017-10-09,Pressure-induced spin pairing transition of Fe$^{3+}$ in oxygen octahedra,"High pressure can provoke spin transitions in transition metal-bearing
compounds. These transitions are of high interest not only for fundamental
physics and chemistry, but also may have important implications for
geochemistry and geophysics of the Earth and planetary interiors. Here we have
carried out a comparative study of the pressure-induced spin transition in
compounds with trivalent iron, octahedrally coordinated by oxygen.
High-pressure single-crystal M\""{o}ssbauer spectroscopy data for FeBO$_3$,
Fe$_2$O$_3$ and Fe$_3$(Fe$_{1.766(2)}$Si$_{0.234(2)}$)(SiO$_4$)$_3$ are
presented together with detailed analysis of hyperfine parameter behavior. We
argue that $\zeta$-Fe$_2$O$_3$ is an intermediate phase in the reconstructive
phase transition between $\iota$-Fe$_2$O$_3$ and $\theta$-Fe$_2$O$_3$ and
question the proposed perovskite-type structure for $\zeta$-Fe$_2$O$_3$.The
structural data show that the spin transition is closely related to the volume
of the iron octahedron. The transition starts when volumes reach 8.9-9.3
\AA$^3$, which corresponds to pressures of 45-60 GPa, depending on the
compound. Based on phenomenological arguments we conclude that the spin
transition can proceed only as a first-order phase transition in
magnetically-ordered compounds. An empirical rule for prediction of cooperative
behavior at the spin transition is proposed. The instability of iron octahedra,
together with strong interactions between them in the vicinity of the critical
volume, may trigger a phase transition in the metastable phase. We find that
the isomer shift of high spin iron ions depends linearly on the octahedron
volume with approximately the same coefficient, independent of the particular
compounds and/or oxidation state. For eight-fold coordinated Fe$^{2+}$ we
observe a significantly weaker nonlinear volume dependence.",1710.03192v1
2017-10-14,Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy,"We explore the effects of disordered charged defects on the electronic
excitations observed in the photoemission spectra of doped transition metal
oxides in the Mott insulating regime by the example of the
$R_{1-x}$Ca$_x$VO$_3$ perovskites, where $R=$La,$\dots$,Lu. A fundamental
characteristic of these vanadium $d^2$ compounds with partly filled $t_{2g}$
valence orbitals is the persistence of spin and orbital order up to high
doping, in contrast to the loss of magnetic order in high-$T_c$ cuprates at low
defect concentration. We demonstrate that the disordered electronic structure
of doped Mott-Hubbard insulators can be obtained with high precision within the
unrestricted Hartree-Fock approximation. In particular: (i) the atomic
multiplet excitations in the inverse photoemission spectra and the various
defect-related states and satellites are well reproduced, (ii) a robust Mott
gap survives up to large doping, and (iii) we show that the defect states
inside the Mott gap develop a soft gap at the Fermi energy. The soft defect
states gap can be characterized by a shape and a scale parameter extracted from
a Weibull statistical sampling of the density of states near the chemical
potential. We demonstrate that charge defects trigger small spin-orbital
polarons, with their internal kinetic energy responsible for the opening of the
soft defect states gap. The small size of spin-orbital polarons is inferred by
an analysis of the inverse participation ratio which explains the origin of the
robustness of spin and orbital order. Using realistic parameters for
La$_{1-x}$Ca$_x$VO$_3$, we show that its soft gap is well reproduced as well as
the marginal doping dependence of the position of the chemical potential
relative to the center of the lower Hubbard band.",1710.05171v1
2020-12-14,Hard x-ray standing-wave photoemission study of the interfaces in a BiFeO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ superlattice,"Hybrid multiferroics such as BiFeO$_3$ (BFO) and La$_{0.7}$Sr$_{0.3}$MnO$_3$
(LSMO) heterostructures are highly interesting functional systems due to their
complex electronic and magnetic properties. One of the key parameters
influencing the emergent properties is the quality of interfaces, where varying
interdiffusion lengths can give rise to different chemistry and distinctive
electronic states. Here we report high-resolution depth resolved chemical and
electronic investigation of BFO/LSMO superlattice using standing-wave hard
X-ray photoemission spectroscopy in the first-order Bragg as well as
near-total-reflection geometry. Our results show that the interfaces of BFO on
top of LSMO are atomically abrupt, while the LSMO on top of BFO interfaces show
an interdiffusion length of around 1.2 unit cells. The two interfaces also
exhibit different chemical gradients, with the BFO/LSMO interface being
Sr-terminated by a spectroscopically distinctive high binding energy component
in Sr 2p core-level spectra, which is spatially contained within 1 unit cell
from the interface. From the electronic point of view, unique valence band
features were observed for bulk-BFO, bulk-LSMO and their interfaces. Our X-ray
optical analysis revealed a unique electronic signature at the BFO/LSMO
interface, which we attribute to the coupling between those respective layers.
Valence band decomposition based on the Bragg-reflection standing-wave
measurement also revealed the band alignment between BFO and LSMO layers. Our
work demonstrates that standing-wave hard x-ray photoemission is a reliable
non-destructive technique for probing depth-resolved electronic structure of
buried layers and interfaces with sub-unit-cell resolution. Equivalent
investigations can be successfully applied to a broad class of material such as
perovskite complex oxides with emergent interfacial phenomena.",2012.07993v1
2020-12-31,Room-temperature superconductivity in an artificial 2D Mott-insulating square lattice and its advanced condensed phase that generates a low-loss current in the atmosphere: A possible perpetual motion machine,"A 2D metallic phononic crystal (PnC), which is fabricated by drilling
periodic holes in a suspended niobium (Nb) film, is repeatedly cooled and
warmed in the temperature range of 2--300 K. During the first five temperature
cycles, the resistance of the metallic PnC gradually increases in accordance
with the Friedel sum rule, indicating that narrow Nb bridges between adjacent
thru-holes are converted into $d$-orbital-filled Mott insulators. The
consequent 2D Mott-insulating square lattice is a crystallographic analog of a
copper oxide layer in high-temperature superconductors such as YBCO and BSCCO.
Subsequent temperature cycles of the thus produced ideal Hubbard crystal
realize zero resistance at 60 K, and the zero-resistance state remains up to
300 K, being retained in the atmosphere (i.e., at room temperature, in a
terrestrial magnetic field, and under atmospheric pressure). The necessity of
the latter temperature cycles remains unclear in this study; however, a
possible transition mechanism involving the combined Josephson and charging
effects is discussed. The critical current and critical field of the
room-temperature superconductor (RTSC) are $I_{C}$ = 18.8 mA and
$\mu_{0}H_{\perp}$ = 12 T, respectively. Once a large current exceeding $I_{C}$
is applied to the RTSC, some of the $d$ electrons are forced out, and a special
interface consisting of the p-type semiconducting and superconducting states is
formed. Carriers diffuse because of the nonequilibrium charge concentration,
but they are Andreev-reflected back. In the reversible, thermally isolated
system, the entropy never increases, and a simple experiment confirms a
low-loss current generated from the interface spontaneously. That is, this
study challenges the forbidden perpetual motion machine which can be a solution
to the World energy crisis.",2012.15858v1
2018-07-09,Evidence for Primal sp2 Defects at the Diamond Surface: Candidates for Electron Trapping and Noise Sources,"Diamond materials are central to an increasing range of advanced
technological demonstrations, from high power electronics, to nano-scale
quantum bio-imaging with unprecedented sensitivity. However, the full
exploitation of diamond for these applications is often limited by the
uncontrolled nature of the diamond material surface, which suffers from
Fermi-level pinning and hosts a significant density of electro-magnetic noise
sources. These issues occur despite the oxide-free and air-stable nature of the
diamond crystal surface, which should be an ideal candidate for
functionalization and chemical-engineering. In this work we reveal a family of
previously unidentified and near-ubiquitous primal surface defects which we
assign to differently reconstructed surface vacancies. The density of these
defects is quantified with X-ray absorption spectroscopy, their energy
structures are elucidated by ab initio calculations, and their effect on
near-surface quantum probes is measured directly. Subsequent ab-initio
calculation of band-bending from these defects suggest they are the source of
Fermi-level pinning at most diamond surfaces. Finally, an investigation is
conducted on a broad range of post-growth surface treatments and concludes that
none of them can reproducibly reduce this defect density below the
Fermi-pinning threshold, making this defect a prime candidate as the source for
decoherence-limiting noise in near-surface quantum probes.",1807.02946v1
2018-08-24,Novel electronic states realized by the interplay between Li diffusion and Co$^{\rm 3+}$$/$Co$^{\rm 4+}$ charge ordering in Li$_{\rm x}$CoO$_2$,"Measurements of dc magnetization ($M$) and electrical resistivity ($\rho$)
have been carried out as a function of temperature ($T$) for layered oxide
Li$_{\rm x}$CoO$_2$ (0.51$\leq$$x$$\leq$1.0) using single crystal specimens.
After slow cool of the specimens down to 10 K, both of the $M$($T$) and
$\rho$($T$) curves are found to exhibit a clear anomaly due to the occurrence
of Co$^{\rm 3+}$$/$Co$^{\rm 4+}$ charge ordering (CO) at $T_{\rm S}$$\sim$155 K
for 0.6$\leq$$x$$\leq$0.98 (at $T_{\rm S}$$\sim$180$-$190 K for
0.5$\leq$$x$$\leq$0.55). After rapid cool of the specimens, additional
anomalies are observed related to the onset of Li diffusion at $T_{\rm
F1}$$\sim$370 K and$/$or $T_{\rm F2}$=120$-$130 K. Due to phase mixing with
compositions of nearly LiCoO$_2$ and Li$_{\rm 2/3}$CoO$_2$, the specimens with
0.7$\lesssim$$x$$\lesssim$0.9 show anomlies both at $T_{\rm F1}$ and $T_{\rm
F2}$. For 0.6$\lesssim$$x$$\lesssim$0.9, the resistivity measured after rapid
cool is found to be fairly larger than that measured after slow cool below
$T_{\rm S}$. The enhanced resistivity can be explained by the scenario that
disordered Co$^{\rm 3+}$$/$Co$^{\rm 4+}$ arrangements, which have been observed
and revealed to have an insulating electronic structure contrasting to the
regular CO state in the previous scanning tunneling microscopy measurements
[Phys. Rev. Lett. {\bf 111}, 126104 (2013)], are realized due to the formation
of an amorphous-like structure of Li ions after rapid cool via the interlayer
Coulomb coupling. An electronic phase diagram for 0.5$\leq$$x$$\leq$1.0 is
proposed.",1808.08010v2
2020-06-17,Mass enhancement in 3d and s-p perovskites from symmetry breaking,"In some d-electron oxides the measured effective mass m(exptl) has long been
known to be significantly larger than the model effective mass m(model) deduced
from mean-field band theory, i.e., m(exptl) = beta * m(model), where beta > 1
is the ""mass enhancement"", or ""mass renormalization"" factor. Previous
applications of density functional theory (DFT), based on the smallest number
of possible magnetic, orbital, and structural degrees of freedom, missed such
mass enhancement, a fact that was taken as evidence of strong electronic
correlation being the exclusive enabling physics. The current paper reports
that known modalities of energy-lowering symmetry-broken spin and structural
effects included in mean-field DFT show mass enhancement for both electrons and
holes in a range of d-electron perovskites SrVO3, SrTiO3, BaTiO3, and LaMnO3 as
well as p-electron perovskites CsPbI3 and SrBiO3, including metals (SrVO3) and
insulators (the rest). This is revealed only when enlarged unit cells of the
same parent global symmetry, which are large enough to allow for symmetry
breaking distortions and concomitant variations in spin order, are explored for
their ability to lower the total energy. The paper analyzes the contributions
of different symmetry-broken modalities to mass enhancement, finds common
effects in the range of d- as well as p-electron perovskites. Thus, symmetry
breaking in mean-field theory could describe effects that were previously
attributed exclusively to complex correlated treatments. Indeed, broken
symmetries are often experimentally observed, e.g., octahedral tilting,
Jahn-Teller distortions, or bond disproportionation, and often provide
intuitive explanations in terms of degeneracy removal due to lowering of
structural symmetry, or as shifting of band energies in explainable directions.",2006.10099v3
2020-10-21,Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds,"Biocompatible nanoscale probes for sensitive detection of paramagnetic
species and molecules associated with their (bio)chemical transformations would
provide a desirable tool for a better understanding of cellular redox
processes. Here, we describe an analytical tool based on quantum sensing
techniques. We magnetically coupled negatively charged nitrogen-vacancy (NV)
centers in nanodiamonds (NDs) with nitroxide radicals present in a bioinert
polymer coating of the NDs. We demonstrated that the T1 spin relaxation time of
NV centers is very sensitive to the number of nitroxide radicals, with a
resolution down to ~10 spins per ND (detection of approximately $ 10^-23 $ mol
in a localized volume). The detection is based on T1 shortening upon the
radical attachment and we propose a theoretical model describing this
phenomenon. We further show this colloidally stable, water-soluble system can
be used dynamically for spatiotemporal readout of a redox chemical process
(oxidation of ascorbic acid) occurring near the ND surface in an aqueous
environment under ambient conditions.",2010.11257v1
2021-04-15,Two-band Conduction and Nesting Instabilities in Superconducting Ba$_2$CuO$_{3+δ}$: a First Principles Study,"First principles investigations of the high temperature superconducting
system Ba$_2$CuO$_{3+\delta}$, recently discovered at $\delta\approx0.2$ at
$T_c=70$ K, are applied to demonstrate the effects of oxygen ordering on the
electronic and magnetic properties. The observed `highly over-doped'
superconducting phase displays stretched Cu-planar oxygen O$_{\rm P}$ distances
and anomalously shortened Cu-apical O$_{\rm A}$ separations compared with other
cuprates. The stoichiometric system $\delta=0$, with its strongly
one-dimensional (1D) Cu-O$_{\rm P}$ chain structure, when nonmagnetic shows 1D
Fermi surfaces that lead, within density functional theory, to
antiferromagnetic Cu-O$_{\rm P}$ chains (a spin-Peierls instability).
Accounting for 1D fluctuations and small interchain coupling according to the
theory of Schulz indicates this system, like Sr$_2$CuO$_3$, is near the 1D
Luttinger-liquid quantum critical phase. The unusual Cu-O bond lengths per se
have limited effects on other properties for $\delta$=0. We find that a
`doubled bilayer' structure of alternating Cu-O$_{\rm P}$ chains and wide rung
Cu$_3$O$_4$ ladders is the energetically preferred one of three possibilities
where the additional oxygen ions bridge Cu-O$_{\rm P}$ chains in the
superconducting phase $\delta=1/4$. Nominal formal valences of the three Cu
sites are discussed. The six-fold (octahedral) site is the most highly
oxidized, accepting somewhat more holes in the $d_{z^2}$ orbital than in the
$d_{x^2-y^2}$ orbital. The implication is that two-band physics is involved in
the pairing mechanism and the superconducting carriers. The Fermi surfaces of
this metallic bilayer structure show both 1D and 2D strong (incipient) nesting
instabilities, possibly accounting for the lack of clean single-phase samples
based on this structure and suggesting importance for the pairing mechanism.",2104.07258v3
2021-04-21,Electronic Structure of Mononuclear Cu-based Molecule from Density-Functional Theory with Self-Interaction Correction,"We investigate the electronic structure of a planar mononuclear Cu-based
molecule [Cu(C$_6$H$_4$S$_2$)$_2$]$^z$ in two oxidation states ($z$$=$$-2$,
$-$1) using density-functional theory (DFT) with Fermi-L\""owdin orbital (FLO)
self-interaction correction (SIC). The dianionic Cu-based molecule was proposed
to be a promising qubit candidate. Self-interaction error within approximate
DFT functionals renders severe delocalization of electron and spin densities
arising from 3$d$ orbitals. The FLO-SIC method relies on optimization of
Fermi-L\""owdin orbital descriptors (FODs) with which localized occupied
orbitals are constructed to create the SIC potentials. Starting with many
initial sets of FODs, we employ a frozen-density loop algorithm within the
FLO-SIC method to study the Cu-based molecule. We find that the electronic
structure of the molecule remains unchanged despite somewhat different final
FOD configurations. In the dianionic state (spin $S=1/2$), FLO-SIC spin density
originates from the Cu $d$ and S $p$ orbitals with an approximate ratio of 2:1,
in quantitative agreement with multireference calculations, while in the case
of SIC-free DFT, the orbital ratio is reversed. Overall, FLO-SIC lowers the
energies of the occupied orbitals and in particular the 3$d$ orbitals
unhybridized with the ligands significantly, which substantially increases the
energy gap between the highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) compared to SIC-free DFT results. The
FLO-SIC HOMO-LUMO gap of the dianionic state is larger than that of the
monoionic state, which is consistent with experiment. Our results suggest a
positive outlook of the FLO-SIC method in the description of magnetic exchange
coupling within 3$d$-element based systems.",2104.10327v1
2022-03-02,Stacking Faults Assist Lithium-Ion Conduction in a Halide-Based Superionic Conductor,"In the pursuit of urgently-needed, energy dense solid-state batteries for
electric vehicle and portable electronics applications, halide solid
electrolytes offer a promising path forward with exceptional compatibility
against high-voltage oxide electrodes, tunable ionic conductivities, and facile
processing. For this family of compounds, synthesis protocols strongly affect
cation site disorder and modulate Li+ mobility. In this work, we reveal the
presence of a high concentration of stacking faults in the superionic conductor
Li3YCl6 and demonstrate a method of controlling its Li+ conductivity by tuning
the defect concentration with synthesis and heat treatments at select
temperatures. Leveraging complementary insights from variable temperature
synchrotron X-ray diffraction, neutron diffraction, cryogenic transmission
electron microscopy, solid-state nuclear magnetic resonance, density functional
theory, and electrochemical impedance spectroscopy, we identify the nature of
planar defects and the role of nonstoichiometry in lowering Li+ migration
barriers and increasing Li site connectivity in mechanochemically-synthesized
Li3YCl6. We harness paramagnetic relaxation enhancement to enable 89Y
solid-state NMR, and directly contrast the Y cation site disorder resulting
from different preparation methods, demonstrating a potent tool for other
researchers studying Y-containing compositions. With heat treatments at
temperatures as low as 333 K (60{\deg}C), we decrease the concentration of
planar defects, demonstrating a simple method for tuning the Li+ conductivity.
Findings from this work are expected to be generalizable to other halide solid
electrolyte candidates and provide an improved understanding of defect-enabled
Li+ conduction in this class of Li-ion conductors.",2203.00814v1
2022-03-13,Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide,"Electronic anisotropy (or `nematicity') has been detected in all main
families of cuprate superconductors by a range of experimental techniques --
electronic Raman scattering, THz dichroism, thermal conductivity, torque
magnetometry, second-harmonic generation -- and was directly visualized by
scanning tunneling microscope (STM) spectroscopy. Using angle-resolved
transverse resistance (ARTR) measurements, a very sensitive and background-free
technique that can detect 0.5$\%$ anisotropy in transport, we have observed it
also in La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) for $0.02 \leq x \leq 0.25$.
Arguably the key enigma in LSCO is the rotation of the nematic director with
temperature; this has not been seen before in any material. Here, we address
this puzzle by measuring the angle-resolved transverse magnetoresistance
(ARTMR) in LSCO. We report a discovery of colossal transverse magnetoresistance
(CTMR) -- an order-of-magnitude drop in the transverse resistivity in the
magnetic field of $6\,$T, while none is seen in the longitudinal resistivity.
We show that the apparent rotation of the nematic director is caused by
superconducting phase fluctuations, which are much more anisotropic than the
normal-electron fluid, and their respective directors are not parallel. This
qualitative conclusion is robust and follows straight from the raw experimental
data. We quantify this by modelling the measured (magneto-)conductivity by a
sum of two conducting channels that correspond to distinct anisotropic Drude
and Cooper-pair effective mass tensors. Strikingly, the anisotropy of
Cooper-pair stiffness is significantly larger than that of the normal
electrons, and it grows dramatically on the underdoped side, where the
fluctuations become effectively quasi-one dimensional.",2203.06769v1
2022-03-16,Discovery of an electronic crystal in a cuprate Mott insulator,"Copper oxide high temperature superconductors universally exhibit multiple
forms of electronically ordered phases that break the native translational
symmetry of the CuO2 planes. The interplay between these orders and the
superconducting ground state, as well as how they arise through doping a Mott
insulator, is essential to decode the mechanisms of high-temperature
superconductivity. Over the years, various forms of electronic liquid crystal
phases including charge/spin stripes and incommensurate charge-density-waves
(CDWs) were found to emerge out of a correlated metallic ground state in
underdoped cuprates. Early theoretical studies also predicted the emergence of
a Coulomb-frustrated 'charge crystal' phase in the very lightly-doped,
insulating limit of the CuO2 planes. Here, we use resonant X-ray scattering,
electron transport, and muon spin rotation measurements to fully resolve the
electronic and magnetic ground state and search for signatures of charge order
in very lightly hole-doped cuprates from the RBa2Cu3O7-d family (RBCO; R: Y or
rare earth). X-ray scattering data from RBCO films reveal a breaking of
translational symmetry more pervasive than was previously known, extending down
to the Mott limit. The ordering vector of this charge crystal state is linearly
connected to the charge-density-waves of underdoped RBCO, suggesting that the
former phase is a precursor to the latter as hole doping is increased. Most
importantly, the coexistence of charge and spin order in RBCO suggests that
this electronic symmetry-breaking state is common to the CuO2 planes in the
very lightly-doped regime. These findings bridge the gap between the Mott
insulating state and the underdoped metallic state and underscore the prominent
role of Coulomb-frustrated electronic phase separation among all cuprates.",2203.08872v1
2022-08-10,Exoplanet weather and climate regimes with clouds and thermal ionospheres: A model grid study in support of large-scale observational campaigns,"With observational efforts moving from the discovery into the
characterisation mode, systematic campaigns that cover large ranges of global
stellar and planetary parameters will be needed. We aim to uncover cloud
formation trends and globally changing chemical regimes due to the host star's
effect on the thermodynamic structure of their atmospheres. We aim to provide
input for exoplanet missions like JWST, PLATO, and Ariel, as well as potential
UV missions ARAGO, PolStar or POLLUX. Pre-calculated 3D GCMs for M, K, G, F
host stars are the input for our kinetic cloud model. Gaseous exoplanets fall
broadly into three classes: i) cool planets with homogeneous cloud coverage,
ii) intermediate temperature planets with asymmetric dayside cloud coverage,
and iii) ultra-hot planets without clouds on the dayside. In class ii),} the
dayside cloud patterns are shaped by the wind flow and irradiation. Surface
gravity and planetary rotation have little effect. Extended atmosphere profiles
suggest the formation of mineral haze in form of metal-oxide clusters (e.g.
(TiO2)_N). The dayside cloud coverage is the tell-tale sign for the different
planetary regimes and their resulting weather and climate appearance. Class (i)
is representative of planets with a very homogeneous cloud particle size and
material compositions across the globe (e.g., HATS-6b, NGTS-1b), classes (ii,
e.g., WASP-43b, HD\,209458b) and (iii, e.g., WASP-121b, WP0137b) have a large
day/night divergence of the cloud properties. The C/O ratio is, hence,
homogeneously affected in class (i), but asymmetrically in class (ii) and
(iii). The atmospheres of class (i) and (ii) planets are little affected by
thermal ionisation, but class (iii) planets exhibit a deep ionosphere on the
dayside. Magnetic coupling will therefore affect different planets differently
and will be more efficient on the more extended, cloud-free dayside.",2208.05562v1
2022-11-14,Antiferromagnetic metal phase in an electron-doped rare-earth nickelate,"Long viewed as passive elements, antiferromagnetic materials have emerged as
promising candidates for spintronic devices due to their insensitivity to
external fields and potential for high-speed switching. Recent work exploiting
spin and orbital effects has identified ways to electrically control and probe
the spins in metallic antiferromagnets, especially in noncollinear or
noncentrosymmetric spin structures. The rare earth nickelate NdNiO3 is known to
be a noncollinear antiferromagnet where the onset of antiferromagnetic ordering
is concomitant with a transition to an insulating state. Here, we find that for
low electron doping, the magnetic order on the nickel site is preserved while
electronically a new metallic phase is induced. We show that this metallic
phase has a Fermi surface that is mostly gapped by an electronic reconstruction
driven by the bond disproportionation. Furthermore, we demonstrate the ability
to write to and read from the spin structure via a large zero-field planar Hall
effect. Our results expand the already rich phase diagram of the rare-earth
nickelates and may enable spintronics applications in this family of correlated
oxides.",2211.07525v1
2023-01-25,Investigation of Planckian behavior in a high-conductivity oxide: PdCrO$_2$,"The layered delafossite metal PdCrO$_2$ is a natural heterostructure of
highly conductive Pd layers Kondo coupled to localized spins in the adjacent
Mott insulating CrO$_2$ layers. At high temperatures $T$ it has a $T$-linear
resistivity which is not seen in the isostructural but non-magnetic PdCoO$_2$.
The strength of the Kondo coupling is known, as-grown crystals are extremely
high purity and the Fermi surface is both very simple and experimentally known.
It is therefore an ideal material platform in which to investigate 'Planckian
metal' physics. We do this by means of controlled introduction of point
disorder, measurement of the thermal conductivity and Lorenz ratio and studying
the sources of its high temperature entropy. The $T$-linear resistivity is seen
to be due mainly to elastic scattering and to arise from a sum of several
scattering mechanisms. Remarkably, this sum leads to a scattering rate within
10$\%$ of the Planckian value of $k_BT/$$\hbar$.",2301.10631v1
2023-04-28,Structural and Optoelectronic Properties of Thin Film LaWN$_3$,"Nitride perovskites are an emerging class of materials that have been
predicted to display a range of interesting physics and functional properties,
but they are under-explored due to the difficulty of synthesizing oxygen-free
nitrides. LaWN3, recently reported as the first oxygen-free nitride perovskite,
exhibited polar symmetry and a large piezoelectric coefficient. However, the
predicted ferroelectric switching was hindered by large leakage current, which
motivates better understanding of its electronic structure and optical
properties. Here, we study the structure and optoelectronic properties of thin
film LaWN3 in greater detail, employing combinatorial techniques to correlate
these properties with cation stoichiometry. We report a two-step synthesis that
utilizes a more common RF substrate bias instead of a nitrogen plasma source,
yielding nanocrystalline films that are crystallized by ex-situ annealing. We
investigate the structure and composition of these films, finding
polycrystalline La-rich and highly textured W-rich films. The optical
absorption onset and temperature- and magnetic field-dependent resistivity are
consistent with semiconducting behavior and are highly sensitive to cation
stoichiometry, which may be related to amorphous impurities: metallic W or WNx
in W-rich samples and insulating La2O3 in La-rich samples. The fractional
magnetoresistance is linear and small, consistent with defect scattering, and a
W-rich sample has n-type carriers with high densities and low mobilities. We
demonstrate a photoresponse in LaWN3: the resistivity of a La-rich sample is
enhanced by 28% at low temperature, likely due to a defect trapping mechanism.
The physical properties of LaWN3 are highly sensitive to cation stoichiometry,
like many oxide perovskites, which therefore calls for precise composition
control to utilize the interesting properties observed in this nitride
perovskite.",2305.00098v1
2023-06-13,Oxygen isotope effect on the superfluid density within the $d-$wave and $s-$wave pairing channels of YBa$_2$Cu$_4$O$_8$,"We report on measurements of the oxygen isotope ($^{16}$O/$^{18}$O) effect
(OIE) on the transition temperature $T_{\rm c}$ and the zero-temperature
in-plane magnetic penetration depth $\lambda_{\rm ab}(0)$ in the stoichiometric
cuprate superconductor YBa$_2$Cu$_4$O$_8$ by means of muon-spin
rotation/relaxation. An analysis of the temperature evolution of
$\lambda^{-2}_{\rm ab}$ in terms of coexisting $s+d-$wave order parameters
reveals that the OIE on the superfluid density $\rho_{\rm
s}(0)\propto\lambda^{-2}_{\rm ab}(0)$ stems predominantly from the $d-$wave
component while the contribution of the $s-$wave one is almost zero. The OIE on
the transition temperature $T_{\rm c}$ is found to be rather small: $\delta
T_{\rm c}/T_{\rm c}= -0.32(7)$%, compared to the total OIE on the superfluid
density $\rho_{\rm s}(0)$: $\delta \rho_{\rm s}(0)/\rho_{\rm s}(0)=
-2.8(1.0)$%. The partial OIE's on the corresponding $d-$wave and $s-$wave
components of $\rho_{\rm s}(0)$ are $\delta \rho_{\rm s,d}(0)/\rho_{\rm s}(0)=
-3.0(1.2)$%, and $\delta \rho_{\rm s,s}(0)/\rho_{\rm s}(0)= 0.2(1.2)$%,
respectively. Our results demonstrate that polaron formation in the CuO$_2$
planes is the origin of the observed OIE in the $d-$wave channel. In the much
weaker $s-$wave channel, fermionic quasiparticles are present, which do not
contribute to the OIE on $\rho_{\rm s}(0)$. Our results support the original
idea of K. Alex M\""{u}ller on the polaronic nature of the supercarries in
high-temperature cuprate superconductors.",2306.08112v1
2023-06-27,Formation of droplets of the order parameter and superconductivity in inhomogeneous Fermi-Bose mixtures (Brief review),"The studies of a number of systems treated in terms of an inhomogeneous
(spatially separated) Fermi-Bose mixture with superconducting clusters or
droplets of the order parameter in a host medium with unpaired normal states
are reviewed. A spatially separated Fermi-Bose mixture is relevant to
superconducting BaKBiO3 bismuth oxides. Droplets of the order parameter can
occur in thin films of a dirty metal, described in the framework of the
strongly attractive two-dimensional Hubbard model at a low electron density
with a clearly pronounced diagonal disorder. The Bose-Einstein condensate
droplets are formed in mixtures and dipole gases with an imbalance in the
densities of the Fermi and Bose components. The Bose-Einstein condensate
clusters also arise at the center or at the periphery of a magnetic trap
involving spin-polarized Fermi gases. Exciton and plasmon collapsing droplets
can emerge in the presence of the exciton-exciton or plasmon-plasmon
interaction. The plasmon contribution to the charge screening in MgB2 leads to
the formation of spatially modulated inhomogeneous structures. In metallic
hydrogen and metal hydrides, droplets can be formed in shock-wave experiments
at the boundary of the first-order phase transition between the metallic and
molecular phases. In a spatially separated Fermi-Bose mixture arising in an
Aharonov-Bohm interference ring with a superconducting bridge in a
topologically nontrivial state, additional Fano resonances may appear and
collapse due to the presence of edge Majorana modes in the system.",2306.15770v1
2023-09-09,High pressure-temperature proton migration in P-3 brucite [Mg(OH)2]: Implication for electrical conductivity in deep mantle,"Hydrous minerals contribute largely to the transport and distribution of
water into the mantle of earth to regulate the process of deep-water cycle.
Brucite is one of the simplest layered dense hydrous mineral belonging to
MgO-SiO2-H2O ternary system, which contains significant amount of water in the
form of OH- groups, spanning a wide range of pressure stability.
Simultaneously, the pressure (p) and temperature (T) induced mobility of
protons within the layered structure of brucite is crucial for consequences on
electrical conductivity of the mantle. Using ab initio molecular dynamics
(AIMD) simulations, we investigate the diffusion of H in high-pressure trigonal
P-3 polymorph of brucite in a combined p-T range of 10-85 GPa and 1250-2000K,
relevant to the mantle of earth. The AIMD simulations reveal an unusual
pressure-dependence of the proton migration in brucite characterized by maximum
H-diffusion in the pressure range of 72-76 GPa along different isotherms. We
predict that in the P-3 brucite the H mobility is onset only when a critical
hydrostatic pressure is attained. The onset pressure is observed to drop with
increasing temperature. The H-diffusion in brucite phase at elevated p-T takes
place in such a manner that the process results in the amorphization of the
H-sublattice, without disturbing the Mg- and O-sublattices. This selective
amorphization yields a pool of highly mobile protons causing a subsequent
increment in the electrical conductivity in P-3 brucite. Our calculated values
of conductivity are compared with ex-situ geophysical magnetic satellite data
indicating that brucite can be present in larger quantities in the lower mantle
than previously observed. This hydroxide phase can occur as segregated patches
between the dominant constituents e.g., silicates and oxides of the lower
mantle and thus can explain the origin of high electrical conductivity therein.",2309.04759v1
2023-12-11,Experimental demonstration of a robust training method for strongly defective neuromorphic hardware,"The increasing scale of neural networks needed to support more complex
applications has led to an increasing requirement for area- and
energy-efficient hardware. One route to meeting the budget for these
applications is to circumvent the von Neumann bottleneck by performing
computation in or near memory. An inevitability of transferring neural networks
onto hardware is that non-idealities such as device-to-device variations or
poor device yield impact performance. Methods such as hardware-aware training,
where substrate non-idealities are incorporated during network training, are
one way to recover performance at the cost of solution generality. In this
work, we demonstrate inference on hardware neural networks consisting of 20,000
magnetic tunnel junction arrays integrated on a complementary
metal-oxide-semiconductor chips that closely resembles market-ready spin
transfer-torque magnetoresistive random access memory technology. Using 36
dies, each containing a crossbar array with its own non-idealities, we show
that even a small number of defects in physically mapped networks significantly
degrades the performance of networks trained without defects and show that, at
the cost of generality, hardware-aware training accounting for specific defects
on each die can recover to comparable performance with ideal networks. We then
demonstrate a robust training method that extends hardware-aware training to
statistics-aware training, producing network weights that perform well on most
defective dies regardless of their specific defect locations. When evaluated on
the 36 physical dies, statistics-aware trained solutions can achieve a mean
misclassification error on the MNIST dataset that differs from the
software-baseline by only 2 %. This statistics-aware training method could be
generalized to networks with many layers that are mapped to hardware suited for
industry-ready applications.",2312.06446v1
1998-09-02,Nonlocal electrical conductivity coefficient sigma sub-k,"A nonlocal functional is used to calculate superconducting properties of
barium yttrium copper oxide.",9809047v1
1999-05-07,"Pseudo-Gap Phase, the Quantum-Critical Point and superconductivity in Copper-Oxide Metals","A systematic solution of a general model for Copper-Oxides reveals a line of
transitions $T = T_p (x)$ for $x$, the doping away from half-filling less than
a critical value, to a phase with broken time reversal and rotational symmetry
but with translational symmetry preserved. The single-particle spectrum in this
phase is calculated to have a gap of $d_{x^2 - y^2}$ symmetry. The properties
in this phase are compared to the properties of the so called ''pseudo-gap
phase'' in the Copper-Oxides. The fluctuations towards this phase promote
superconductivity which is either of the $d_{x^2-y^2}$ or the generalised
s-symmetry depending on whether the projected density of states at the chemical
potential is larger in the $d_{x^2-y^2}$ channel, as in the hole-doped
copper-oxides, or in the s-wave channel.",9905100v1
2000-01-19,Pseudogap effects on the c-axis charge dynamics in copper oxide materials,"The c-axis charge dynamics of copper oxide materials in the underdoped and
optimally doped regimes has been studied by considering the incoherent
interlayer hopping. It is shown that the c-axis charge dynamics for the chain
copper oxide materials is mainly governed by the scattering from the in-plane
fluctuation, and the c-axis charge dynamics for the no-chain copper oxide
materials is dominated by the scattering from the in-plane fluctuation
incorporating with the interlayer disorder, which would be suppressed when the
holon pseudogap opens at low temperatures and lower doping levels, leading to
the crossovers to the semiconducting-like range in the c-axis resistivity and
the temperature linear to the nonlinear range in the in-plane resistivity.",0001260v1
2001-03-14,Superconductivity in the non-oxide Perovskite MgCNi3,"The oxide perovskites are a large family of materials with many important
physical properties. Of particular interest has been the fact that this
structure type provides an excellent structural framework for the existence of
superconductivity. The high Tc copper oxides are the most famous examples of
superconducting perovskites, but there are many others [1]. Intermetallic
compounds have been the source of many superconducting materials in the past,
but they have been eclipsed in recent years by the perovskite oxides. The
recent discovery of superconductivity in MgB2 [2] suggests that intermetallic
compounds with simple structure types are worth serious reconsideration as
sources of new superconducting materials. Here we report the observation of
superconductivity at 8 K in the perovskite structure intermetallic compound
MgCNi3, linking what appear at first sight to be mutually exclusive classes of
superconducting materials. The observation of superconductivity in MgCNi3
indicates that MgB2 will not be the only one of its kind within the chemical
paradigm that it suggests for new superconducting materials.",0103296v1
2001-05-29,Atomic-Scale Dynamics of the Formation and Dissolution of Carbon Clusters in SiO2,"Oxidation of SiC produces SiO2 while CO is released. A `reoxidation' step at
lower temperatures is, however, necessary to produce high-quality SiO2. This
step is believed to cleanse the oxide of residual C without further oxidation
of the SiC substrate. We report first-principles calculations that describe the
nucleation and growth of O-deficient C clusters in SiO2 under oxidation
conditions, fed by the production of CO at the advancing interface, and their
gradual dissolution by the supply of O under reoxidation conditions. We predict
that both CO and CO2 are released during both steps.",0105572v1
2001-06-13,RHEED Studies of Epitaxial Oxide Seed-Layer Growth on RABiTS Ni(001): The Role of Surface Structure and Chemistry,"The epitaxial deposition of the first oxide buffer layer (seed layer) on
biaxially textured Ni tape for coated conductors is a critical step that is
dependent on the atomistic surface condition of the metal. We present a study
of the {100}<100> biaxially textured Ni (001) surface and seed-layer growth
using in situ reflection high-energy electron diffraction (RHEED) and Auger
electron spectroscopy (AES). Our observations are consistent with formation of
a c(2 x 2) 2-D superstructure due to surface segregation of sulfur contained in
the metal. We show that this superstructure can have a dramatic effect on the
heteroepitaxial growth of oxide seed layers. In particular, the surface
superstructure promotes the (200) epitaxial oxide growth of Y2O3-stabilized
ZrO2 (YSZ), which is necessary for the development of high-Jc superconducting
films for coated conductors.",0106254v1
2001-09-26,Metastable precursors during the oxidation of the Ru(0001) surface,"Using density-functional theory, we predict that the oxidation of the
Ru(0001) surface proceeds via the accumulation of sub-surface oxygen in
two-dimensional islands between the first and second substrate layer. This
leads locally to a decoupling of an O-Ru-O trilayer from the underlying metal.
Continued oxidation results in the formation and stacking of more of these
trilayers, which unfold into the RuO_2(110) rutile structure once a critical
film thickness is exceeded. Along this oxidation pathway, we identify various
metastable configurations. These are found to be rather close in energy,
indicating a likely lively dynamics between them at elevated temperatures,
which will affect the surface chemical and mechanical properties of the
material.",0109491v1
2002-04-05,Atomic-scale images of charge ordering in a mixed-valence manganite,"Transition-metal perovskite oxides exhibit a wide range of extraordinary but
imperfectly understood phenomena. Charge, spin, orbital, and lattice degrees of
freedom all undergo order-disorder transitions in regimes not far from where
the best-known of these phenomena, namely high-temperature superconductivity of
the copper oxides, and the 'colossal' magnetoresistance of the manganese
oxides, occur. Mostly diffraction techniques, sensitive either to the spin or
the ionic core, have been used to measure the order. Unfortunately, because
they are only weakly sensitive to valence electrons and yield superposition of
signals from distinct mesoscopic phases, they cannot directly image mesoscopic
phase coexistence and charge ordering, two key features of the manganites. Here
we describe the first experiment to image charge ordering and phase separation
in real space with atomic-scale resolution in a transition metal oxide. Our
scanning tunneling microscopy (STM) data show that charge order is correlated
with structural order, as well as with whether the material is locally metallic
or insulating, thus giving an atomic-scale basis for descriptions of the
manganites as mixtures of electronically and structurally distinct phases.",0204146v1
2002-06-30,"Systematic trends in the electronic structure parameters of 4d transition metal oxides SrMO_{3} (M = Zr, Mo, Ru, and Rh)","We investigated the electronic structures of the perovskite-type 4$d$
transition metal oxides Sr$M$O$_3$ ($M$ = Zr, Mo, Ru, and Rh) using their
optical conductivity spectra $\sigma (\omega)$. The interband transitions in
$\sigma (\omega)$ are assigned, and some important physical parameters, such as
on-site Coulomb repulsion energy $U$, charge transfer energy $\Delta_{pd}$, and
crystal field splitting $10Dq$, are estimated. It is observed that $\Delta
_{pd}$ and 10$Dq$ decrease systematically with the increase in the atomic
number of the 4$d$ transition metal. Compared to the case of 3$d$ transition
metal oxides, the magnitudes of $\Delta_{pd}$ and 10$Dq$ are larger, but those
of $U$ are smaller. These behaviors can be explained by the more extended
nature of the orbitals in the 4$d$ transition metal oxides.",0207012v1
2002-08-26,"Sub-unit cell layer-by-layer growth of Fe3O4, MgO, and Sr2RuO4 thin films","The use of oxide materials in oxide electronics requires their controlled
epitaxial growth. Recently, it was shown that Reflection High Energy Electron
Diffraction (RHEED) allows to monitor the growth of oxide thin films even at
high oxygen pressure. Here, we report the sub-unit cell molecular or block
layer growth of the oxide materials Sr2RuO4, MgO, and magnetite using Pulsed
Laser Deposition (PLD) from stoichiometric targets. Whereas for perovskites
such as SrTiO3 or doped LaMnO3 a single RHEED intensity oscillation is found to
correspond to the growth of a single unit cell, in materials where the unit
cell is composed of several molecular layers or blocks with identical
stoichiometry, a sub-unit cell molecular or block layer growth is established
resulting in several RHEED intensity oscillations during the growth of a single
unit-cell.",0208495v1
2002-10-03,Block-Layer Concept for the Layered Co Oxide: A Design for Thermoelectric Oxides,"High-Tc Cu oxides consist of the alternating stack of the superconductive
CuO2 layer and the block layer, such as Bi2Sr2O4 or La2-xSrxO2. By changing the
block layer, we can change their physical properties, such as transition
temperature Tc. The thermoelectric Co oxides have a similar layered structure
composed of the conductive CoO2 layer and the blocking layer. Thus, we propose
that their thremoelectric properties can be finely tuned by modifying the block
layer.",0210071v1
2003-01-04,Photocarrier Injection to Transition Metal Oxides,"This paper has been withdrawn by the author(s), due a crucial error in the
data.",0301033v2
2003-01-23,Epitaxy of Fe3O4 on Si(001) by pulsed laser deposition using a TiN/MgO buffer layer,"Epitaxy of oxide materials on silicon (Si) substrates is of great interest
for future functional devices using the large variety of physical properties of
the oxides as ferroelectricity, ferromagnetism, or superconductivity. Recently,
materials with high spin polarization of the charge carriers have become
interesting for semiconductor-oxide hybrid devices in spin electronics. Here,
we report on pulsed laser deposition of magnetite (Fe3O4) on Si(001) substrates
cleaned by an in situ laser beam high temperature treatment. After depositing a
double buffer layer of titanium nitride (TiN) and magnesium oxide (MgO), a high
quality epitaxial magnetite layer can be grown as verified by RHEED intensity
oscillations and high resolution x-ray diffraction.",0301443v4
2003-12-18,Dispersive charge transport along the surface of an insulating layer observed by Electrostatic Force Microscopy,"We report the observation in the direct space of the transport of a few
thousand charges submitted to a tunable electric field along the surface of a
silicon oxide layer. Charges are both deposited and observed using the same
Electrostatic Force Microscope. During the time range accessible to our
measurements (i.e. $t=1\sim1000\un{s}$), the transport of electrons is mediated
by traps in the oxide. We measure the mobility of electrons in the ""surface""
states of the silicon oxide layer and show the dispersive nature of their
motion. It is also demonstrated that the saturation of deep oxide traps
strongly enhance the transport of electrons under lateral electric field.",0312471v1
2004-05-12,Layered tungsten oxide-based organic/inorganic hybrid materials I: Infrared and Raman study,"Tungsten oxide-organic layered hybrid materials have been studied by infrared
and Raman spectroscopy, and demonstrate a difference in bonding nature as the
length of the interlayer organic `spacer' molecule is increased.
Ethylenediamine-tungsten oxide clearly displays a lack of terminal -NH3+
ammonium groups which appear in hybrids with longer alkane molecules, thus
indicating that the longer chains are bound by electrostatic interactions as
well as or in place of the hydrogen bonding that must be present in the shorter
chain ethylenediamine hybrids. The presence of organic molecules between the
tungsten oxide layers, compared with the layered tungstic acid H2WO4, shows a
decrease in the apical W=O bond strength, as might be expected from the
aforementioned electrostatic interaction.",0405241v2
2004-08-02,Ab initio study of reflectance anisotropy spectra of a sub-monolayer oxidized Si(100) surface,"The effects of oxygen adsorption on the reflectance anisotropy spectrum (RAS)
of reconstructed Si(100):O surfaces at sub-monolayer coverage (first stages of
oxidation) have been studied by an ab initio DFT-LDA scheme within a
plane-wave, norm-conserving pseudopotential approach. Dangling bonds and the
main features of the characteristic RAS of the clean Si(100) surface are mostly
preserved after oxidation of 50% of the surface dimers, with some visible
changes: a small red shift of the first peak, and the appearance of a distinct
spectral structure at about 1.5 eV. The electronic transitions involved in the
latter have been analyzed through state-by-state and layer-by-layer
decompositions of the RAS. We suggest that new interplay between present
theoretical results and reflectance anisotropy spectroscopy experiments could
lead to further clarification of structural and kinetic details of the Si(100)
oxidation process in the sub-monolayer range.",0408028v2
2004-11-05,Multiple layer local oxidation for fabricating semiconductor nanostructures,"Coupled semiconductor nanostructures with a high degree of tunability are
fabricated using local oxidation with a scanning force microscope. Direct
oxidation of the GaAs surface of a Ga[Al]As heterostructure containing a
shallow two-dimensional electron gas is combined with the local oxidation of a
thin titanium film evaporated on top. A four-terminal quantum dot and a double
quantum dot system with integrated charge readout are realized. The structures
are tunable via in-plane gates formed by isolated regions in the electron gas
and by mutually isolated regions of the Ti film acting as top gates. Coulomb
blockade experiments demonstrate the high quality of this fabrication process.",0411129v1
2005-01-14,Oxygen stoichiometry and instability in aluminium oxide tunnel barrier layers,"We present X-ray photoelectron spectroscopy data which show that the
chemisorbed oxygen previously observed to be on the surface of thin AlOx layers
formed by room temperature thermal oxidation is bound by oxygen vacancies in
the oxide. Increasing the electric field across the oxide, either by
over-coating with a metallic electrode, or by electron bombardment, drives this
surface chemisorbed oxygen into the vacancy sites. Due to the low bonding
energies of these oxygen sites, subsequent oxygen exposures draw these ions
back to the surface, reforming chemisorbed O$_2^-$. Al/AlOx/Al tunnel junctions
incorporating electron bombarded AlOx barriers show a significant reduction in
the low frequency junction resistance noise level at 4.2 K.",0501354v2
2005-01-17,Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies,"We have investigated the electronic structure of nano-sized iron oxide by
scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by
photoelectron spectroscopy. Nano particles were produced by thermal treatment
of Ferritin molecules containing a self-assembled core of iron oxide. Depending
on the thermal treatment we were able to prepare different phases of iron oxide
nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently
contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure
of these materials were studied under reducing conditions. We show that the
surface band gap of the electronic excitation spectrum can differ from that of
bulk material and is dominated by surface effects.",0501377v1
2005-07-06,"Oxidation Resistant Germanium Nanowires: Bulk Synthesis, Long Chain Alkanethiol Functionalization and Langmuir-Blodgett Assembly","A simple method is developed to synthesize gram quantities of uniform Ge
nanowires (GeNWs) by chemical vapor deposition on preformed, monodispersed
seed-particles loaded onto high surface area silica support. Various chemical
functionalization schemes are investigated to passivate the GeNW surfaces using
alkanethiols and alkyl Grignard reactions. The stability of functionalization
against oxidation of germanium for various alkyl chain lengths is elucidated by
X-ray photoelectron spectroscopy. Among all schemes tested, long chain
alkanethiols (>=C12) are found to impart the most stable GeNW passivation
against oxidation upon extended exposure to ambient air. Further, the
chemically functionalized oxidation-resistant nanowires are soluble in organic
solvents and can be readily assembled into close-packed Langmuir-Blodgett films
potentially useful for future high performance electronic devices.",0507145v2
2005-12-08,Disorder and electron interaction control in low-doped silicon metal-oxide-semiconductor field effect transistors,"We fabricated silicon metal-oxide-semiconductor field effect transistors
where an additional sodium-doped layer was incorporated into the oxide to
create potential fluctuations at the Si-SiO2 interface. The amplitude of these
fluctuations is controlled by both the density of ions in the oxide and their
position relative to the Si-SiO2 interface. Owing to the high mobility of the
ions at room temperature, it is possible to move them with the application of a
suitable electric field. We show that, in this configuration, such a device can
be used to control both the disorder and the electron-electron interaction
strength at the Si-SiO2 interface.",0512172v3
2005-12-28,Crystal structure of the pyrochlore oxide superconductor KOs$_2$O$_6$,"We report the single-crystal X-ray analysis of the structure of the
pyrochlore oxide superconductor KOs$_2$O$_6$. The structure was identified as
the $\beta$-pyrochlore structure with space group $Fd\bar{3}m$ and lattice
constant $a$ = 10.089(2)~\AA at 300 K: the K atom is located at the 8$b$ site,
not at the 16$d$ site as in conventional pyrochlore oxides. We found an
anomalously large atomic displacement parameter $U_\mathrm{iso}$ =
0.0735(8)~\AA$^2$ at 300 K for the K cation, which suggests that the K cation
weakly bound to an oversized Os$_{12}$O$_{18}$ cage exhibits intensive
rattling, as recently observed for clathrate compounds. The rattling of A
cations is a common feature in the series of $\beta$-pyrochlore oxide
superconductors AOs$_2$O$_6$ (A = Cs, Rb and K), and is greatest for the
smallest K cation.",0512683v1
2006-02-22,An Improved Description of the Dielectric Breakdown in Oxides Based on a Generalized Weibull distribution,"In this work, we address modal parameter fluctuations in statistical
distributions describing charge-to-breakdown $(Q_{BD})$ and/or
time-to-breakdown $(t_{BD})$ during the dielectric breakdown regime of
ultra-thin oxides, which are of high interest for the advancement of electronic
technology. We reobtain a generalized Weibull distribution ($q$-Weibull), which
properly describes $(t_{BD})$ data when oxide thickness fluctuations are
present, in order to improve reliability assessment of ultra-thin oxides by
time-to-breakdown $(t_{BD})$ extrapolation and area scaling. The incorporation
of fluctuations allows a physical interpretation of the $q$-Weibull
distribution in connection with the Tsallis statistics. In support to our
results, we analyze $t_{BD}$ data of SiO$_2$-based MOS devices obtained
experimentally and theoretically through a percolation model, demonstrating an
advantageous description of the dielectric breakdown by the $q$-Weibull
distribution.",0602515v1
2006-04-03,Electrical conduction of silicon oxide containing silicon quantum dots,"Current-voltage measurements have been made at room temperature on a Si-rich
silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced
Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$ ^\circ$C. The
thickness of oxide between Si quantum dots embedded in the film increases with
the increase of annealing temperature. This leads to the decrease of current
density as the annealing temperature is increased. Assuming the Fowler-Nordheim
tunneling mechanism in large electric fields, we obtain an effective barrier
height $\phi_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling
through an oxide layer between Si quantum dots. The Frenkel-Poole effect can
also be used to adequately explain the electrical conduction of the film under
the influence of large electric fields. We suggest that at room temperature Si
quantum dots can be regarded as traps that capture and emit electrons by means
of tunneling.",0604028v1
2007-05-05,Theory of enhanced dynamical photo-thermal bi-stability effects in cuprous oxide/organic hybrid heterostructure,"We theoretically demonstrate the formation of multiple bi-stability regions
in the temperature pattern on the interface between a cuprous oxide quantum
well and DCM2:CA:PS organic compound. The Frenkel molecular exciton of the DCM2
is brought into resonance with the $1S$ quadrupole Wannier-Mott exciton in the
cuprous oxide by ""solvatochromism"" with CA. The resulting hybrid is thermalized
with surrounding helium bath. This leads to strongly non-linear temperature
dependence of the laser field detuning from the quadrupole exciton energy band
which is associated with the temperature induced red shift of the Wannier
exciton energy. Numerical up and down-scan for the detuning reveals
hysteresis-like temperature distribution. The obtained \emph{multiple}
bi-stability regions are at least three orders of magnitude bigger ($meV$) than
the experimentally observed bi-stability in bulk cuprous oxide ($\mu eV$). The
effective absorption curve exhibits highly asymmetrical behavior for the
Frenkel-like (above the $1S$ energy) and Wannier-like (below the $1S$ energy)
branches of the hybrid.",0705.0731v1
2007-08-14,"Theory of oxidation/reduction-induced chromium ion valence transformations in Cr,Ca:YAG crystals","In their paper [Opt. Mater. 24, 333, 2003], Feldman et al conducted an
experimental study of the dynamics of chromium ion valence transformations in
Cr,Ca:YAG crystals among the trivalent Cr3+ state, and two tetravalent Cr4+
ones, of octahedral and tetrahedral coordination. The temperatures used ranged
between ~800 and 1,000 C. The basic effects are the transition of Cr3+ into
Cr4+ under high-temperature annealing in an oxidizing atmosphere, and the
reverse transition under a reducing atmosphere, or in vacuum. In the present
theory, we interpret the processes by oxygen-vacancy diffusion in the bulk of
the YAG. The quasi-chemical reaction VO2- + Cr4+ = Cr3+/VO- between the
chromium ions and the vacancies VO2- is responsible for the valence
transformations. Dynamical analysis provides profiles of the Cr3+ and Cr4+
concentrations in the crystal during oxidation and during reduction. Reaction
rate profiles are also calculated, establishing the reaction front position and
width. A comparison with existing experimental results on the integrated Cr4+
concentration as a function of time during oxidation [Opt. Mater. 24, 333,
2003] shows reasonable agreement.",0708.1798v2
2007-10-02,Microscopic mechanisms of spin-dependent electric polarization in 3d oxides,"We address a systematic microscopic theory of spin-dependent electric
polarization in 3d oxides starting with a generic three-site two-hole cluster.
A perturbation scheme realistic for 3d oxides is applied which implies the
quenching of orbital moments by low-symmetry crystal field, strong intra-atomic
correlations, the dp-transfer effects, and rather small spin-orbital coupling.
An effective spin operator of the electric dipole moment is deduced
incorporating both nonrelativistic and relativistic terms. The nonrelativistic
electronic polarization mechanism related with the effects of the
redistribution of the local on-site charge density due to $pd$ covalency and
exchange coupling is believed to govern the multiferroic behaviour in 3d
oxides. The relativistic exchange-dipole moment is mainly stems from the
nonrelativistic one due to the perturbation effect of Dzyaloshinsky-Moriya
coupling and is estimated to be a weak contributor to the electric polarization
observed in the most of 3d multiferroics.",0710.0496v1
2007-10-05,Self-consistent simulation of quantum wires defined by local oxidation of Ga[Al]As heterostructures,"We calculate the electronic width of quantum wires as a function of their
lithographic width in analogy to experiments performed on nanostructures
defined by local oxidation of Ga[Al]As heterostructures. Two--dimensional
simulations of two parallel oxide lines on top of a Ga[Al]As heterostructure
defining a quantum wire are carried out in the framework of Density Functional
Theory in the Local Density Approximation and are found to be in agreement with
measurements. Quantitative assessment of the influence of various experimental
uncertainties is given. The most influential parameter turns out to be the
oxide line depth, followed by its exact shape and the effect of background
doping (in decreasing order).",0710.1160v2
2007-10-30,"Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion","Performing molecular dynamics simulations for all-atom models, we
characterize the conformational and structural relaxations of poly(ethylene
oxide) and poly(propylene oxide) melts. The temperature dependence of these
relaxation processes deviates from an Arrhenius law for both polymers. We
demonstrate that mode-coupling theory captures some aspects of the glassy
slowdown, but it does not enable a complete explanation of the dynamical
behavior. When the temperature is decreased, spatially heterogeneous and
cooperative translational dynamics are found to become more important for the
structural relaxation. Moreover, the transitions between the conformational
states cease to obey Poisson statistics. In particular, we show that, at
sufficiently low temperatures, correlated forward-backward motion is an
important aspect of the conformational relaxation, leading to strongly
nonexponential distributions for the waiting times of the dihedrals in the
various conformational states",0710.5598v1
2008-04-23,The role of metallic impurities in oxide semiconductors: first-principles calculations and PAC experiments,"We report an ab-initio comparative study of the electric-field-gradient
tensor (EFG) and structural relaxations introduced by acceptor (Cd) and donor
(Ta) impurities when they replace cations in a series of binary oxides: TiO2,
SnO2, and In2O3. Calculations were performed with the Full-Potential
Linearized-Augmented Plane Waves method that allows us to treat the electronic
structure and the atomic relaxations in a fully self-consistent way. We
considered different charge states for each impurity and studied the dependence
on these charge states of the electronic properties and the structural
relaxations. Our results are compared with available data coming from PAC
experiments and previous calculations, allowing us to obtain a new insight on
the role that metal impurities play in oxide semiconductors. It is clear from
our results that simple models can not describe the measured EFGs at impurities
in oxides even approximately.",0804.3644v1
2008-06-08,Novel electronic structure induced by a highly strained oxide interface with incommensurate crystal fields,"The misfit oxide, Bi$_{2}$Ba$_{1.3}$K$_{0.6}$Co$_{2.1}$O$_{y}$, made of
alternating rocksalt-structured [BiO/BaO] layers and hexagonal CoO$_{2}$
layers, was studied by angle-resolved photoemission spectroscopy. Detailed
electronic structure of such a highly strained oxide interfaces is revealed for
the first time. We found that under the two incommensurate crystal fields,
electrons are confined within individual sides of the interface, and scattered
by umklapp scattering of the crystal field from the other side. In addition,
the high strain on the rocksalt layer raises its chemical potential and induces
large charge transfer to the CoO$_{2}$ layer. Furthermore, a novel interface
effects, the interfacial enhancement of electron-phonon interactions, is
discovered. Our findings of these electronic properties lay a foundation for
designing future functional oxide interfaces.",0806.1338v1
2008-09-16,Microscopic Bardeen-Cooper-Schrieffer formulation of the critical temperature of multilayer copper-oxide superconductors,"We study superconductivity in multilayer copper oxides, in the frame of a
realistic microscopic formulation. Solving the full temperature dependent BCS
gap equations, we obtain a maximum in the transition temperature Tc for M=3 or
4 CuO2 layers in the unit cell for appropriate values of the interlayer
tunneling (negative pair tunneling), and via the consideration of the doping
imbalance between the inner and outer layers. This is the ubiquitous
experimental result for Ca intercalated copper oxides, as opposed to other
intercalating elements. Further, using a restricted set of parameters, we
obtain an exact fit of Tc(M=1-4) for five different Ca intercalated homologuous
copper oxide families.",0809.2656v5
2008-09-29,Charge state of the O$_{2}$ molecule during silicon oxidation through hybrid functional calculations,"We study the charge state of the diffusing O$_2$ molecule during silicon
oxidation through hybrid functional calculations. We calculate charge
transition levels of O$_2$ in bulk SiO$_2$ and use theoretical band offsets to
align these levels with respect to the Si band edges. To overcome the band-gap
problem of semilocal density fuctionals, we employ hybrid functionals with both
predefined and empirically adjusted mixing coefficients. We find that the
charge transition level $\epsilon^{0/-}$ in bulk SiO$_2$ occurs at $\sim$1.1 eV
above the silicon conduction band edge, implying that the O$_2$ molecule
diffuses through the oxide in the neutral charge state. While interfacial
effects concur to lower the charge transition level, our estimates suggest that
the neutral charge state persists until silicon oxidation.",0809.4905v1
2008-11-28,Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method,"We have applied the bond valence method to cerium oxides to determine the
oxidation states of the Ce ion at the various site symmetries of the crystals.
The crystals studied include cerium dioxide and the two sesquioxides along with
some selected intermediate phases which are crystallographically well
characterized. Our results indicate that cerium dioxide has a mixed-valence
ground state with an f-electron population on the Ce site of 0.27 while both
the A- and C-sesquioxides have a nearly pure f^1 configuration. The Ce sites in
most of the intermediate oxides have non-integral valences. Furthermore, many
of these valences are different from the values predicted from a naive
consideration of the stoichiometric valence of the compound.",0811.4634v1
2009-03-16,Polarization properties of real aluminum mirrors; I. Influence of the aluminum oxide layer,"In polarimetry it is important to characterize the polarization properties of
the instrument itself to disentangle real astrophysical signals from
instrumental effects. This article deals with the accurate measurement and
modeling of the polarization properties of real aluminum mirrors, as used in
astronomical telescopes. Main goals are the characterization of the aluminum
oxide layer thickness at different times after evaporation and its influence on
the polarization properties of the mirror. The full polarization properties of
an aluminum mirror are measured with Mueller matrix ellipsometry at different
incidence angles and wavelengths. The best fit of theoretical Mueller matrices
to all measurements simultaneously is obtained by taking into account a model
of bulk aluminum with a thin aluminum oxide film on top of it. Full Mueller
matrix measurements of a mirror are obtained with an absolute accuracy of ~1%
after calibration. The determined layer thicknesses indicate logarithmic growth
in the first few hours after evaporation, but it remains stable at a value of
4.12+/-0.08 nm on the long term. Although the aluminum oxide layer is
established to be thin, it is necessary to consider it to accurately describe
the mirror's polarization properties.",0903.2740v1
2009-03-22,Influence of EGR compounds on the oxidation of an HCCI-diesel surrogate,"This paper presents an experimental and numerical study of the impact of
various additives on the oxidation of a typical automotive surrogate fuel
blend, i.e. n-heptane and toluene. It examines the impact of engine re-cycled
exhaust has compounds on the control of an Homogeneous Charge
Compression-Ignition (HCCI) engine. Series of experiments were performed in a
hihly diluted Jet-Stirred Reactor (JDR) at pressures of 1 and 10 atm (1 atm =
101,325 Pa). The chosen thermo-chemical conditions were close to those
characteristices of the pre-ignition period in an HCCI engine. The influence of
various additives, namely nitric oxide (NO), ethylene (C2H4) and methanol
(CH3OH), on the oxidation of a n-heptane/toluene blend was studied over a wide
range of temperatures (550-1100 K), including the zone of the Negative
Temperature Coefficient (NTC).",0903.3707v1
2009-04-23,Characterization of a novel angular dioxygenase from fluorene-degrading Sphingomonas sp. strain LB126,"In this study, the genes involved in the initial attack on fluorene by
Sphingomonas sp. LB126 were investigated. The ? and ? subunits of a dioxygenase
complex (FlnA1A2), showing 63% and 51% sequence identity respectively, with the
subunits of an angular dioxygenase from Gram-positive Terrabacter sp. DBF63,
were identified. When overexpressed in E. coli, FlnA1A2 was responsible for the
angular oxidation of fluorene, fluorenol, fluorenone, dibenzofuran and
dibenzo-p-dioxin. Moreover, FlnA1A2 was able to oxidize polycyclic aromatic
hydrocarbons and heteroaromatics, some of which were not oxidized by the
dioxygenase from Terrabacter sp. DBF63. Quantification of resulting oxidation
products showed that fluorene and phenanthrene were preferred substrates.",0904.3654v1
2009-05-27,Coulomb explosion sputtering of selectively oxidized Si,"We have studied multiply charged Arq+ ion induced potential sputtering of a
unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such
surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where
ripple structures are formed and one side of each ripple gets more oxidized. It
is observed that higher the potential energy of Arq+ ion, higher the sputtering
yield of the non conducting (oxide) side of the ripple as compared to the
semiconducting side. The results are explained in terms of Coulomb explosion
model where potential sputtering depends on the conductivity of the ion impact
sites.",0905.4343v2
2009-09-14,A thermodynamic approach of the mechano-chemical coupling during the oxidation of uranium dioxide,"The aim of the present work is to introduce a thermodynamic model to describe
the growth of an oxide layer on a metallic substrate. More precisely, this
paper offers a study of oxygen dissolution into a solid, and its consequences
on the apparition of mechanical stresses. They strongly influence the oxidation
processes and may be, in some materials, responsible for cracking. To realize
this study, mechanical considerations are introduced into the classical
diffusion laws. Simulations were made for the particular case of uranium
dioxide, which undergoes the chemical fragmentation. According to our
simulations, the hypothesis of a compression stress field into the oxidised UO2
compound near the internal interface is consistent with the interpretation of
the mechanisms of oxidation observed experimentally.",0909.2605v1
2009-09-16,"Theoretical Study of Coupling Mechanisms between Oxygen Diffusion, Chemical Reaction, Mechanical Stresses in a Solid-Gas Reactive System","This paper offers a study of oxygen dissolution into a solid, and its
consequences on the mechanical behaviour of the material. In fact, mechanical
strains strongly influence the oxidation processes and may be, in some
materials, responsible for cracking. To realize this study, mechanical
considerations are introduced into the classical diffusion laws. Simulations
were made for the particular case of uranium dioxide, which undergoes the
chemical fragmentation. According to our simulations, the hypothesis of a
compression stress field into the oxidised UO2 compound near the internal
interface is consistent with some oxidation mechanisms of oxidation
experimentally observed. More generally, this work will be extended to the
simulation to an oxide layer growth on a metallic substrate.",0909.2950v1
2010-02-05,Quantifying octahedral rotations in strained perovskite oxide films,"Epitaxial strain is a proven route to enhancing the properties of complex
oxides, however, the details of how the atomic structure accommodates strain
are poorly understood due to the difficulty of measuring the oxygen positions
in thin films. We present a general methodology for determining the atomic
structure of strained oxide films via x-ray diffraction, which we demonstrate
using LaNiO3 films. The oxygen octahedral rotations and distortions have been
quantified by comparing the intensities of half-order Bragg peaks, arising from
the two unit cell periodicity of the octahedral rotations, with the calculated
structure factor. Combining ab initio density functional calculations with
these experimental results, we determine systematically how strain modifies the
atomic structure of this functional oxide.",1002.1317v1
2010-02-12,Experimental Study of Resistive Bistability in Metal Oxide Junctions,"We have studied resistive bistability (memory) effects in junctions based on
metal oxides, with a focus on sample-to-sample reproducibility which is
necessary for the use of such junctions as crosspoint devices of hybrid
CMOS/nanoelectronic circuits. Few-nm-thick layers of NbOx, CuOx and TiOx have
been formed by thermal and plasma oxidation, at various deposition and
oxidation conditions, both with or without rapid thermal post-annealing (RTA).
The resistive bistability effect has been observed for all these materials,
with particularly high endurance (over 1000 switching cycles) obtained for
single-layer TiO2 junctions, and the best reproducibility reached for
multi-layer junctions of the same material. Fabrication optimization has
allowed us to improve the OFF/ON resistance ratio to about 1000, but the
sample-to-sample reproducibility is so far lower than that required for large
scale integration.",1002.2650v1
2010-02-26,Measuring individual overpotentials in an operating solid-oxide electrochemical cell,"We use photo-electrons as a non-contact probe to measure local electrical
potentials in a solid-oxide electrochemical cell. We characterize the cell in
operando at near-ambient pressure using spatially-resolved X-ray photoemission
spectroscopy. The overpotentials at the interfaces between the Ni and Pt
electrodes and the yttria-stabilized zirconia (YSZ) electrolyte are directly
measured. The method is validated using electrochemical impedance spectroscopy.
Using the overpotentials, which characterize the cell's inefficiencies, we
compare without ambiguity the electro-catalytic efficiencies of Ni and Pt,
finding that on Ni H_2O splitting proceeds more rapidly than H2 oxidation,
while on Pt, H2 oxidation proceeds more rapidly than H2O splitting.",1003.0035v2
2010-04-23,Synthesis of novel Mesoporous Fullerene and its application to electro-oxidation of methanol,"One pot synthetic technique was used to synthesize mesoporous fullerene using
highly ordered mesoporous template such as KIT6-150 and SBA-15-150. Highly
ordered porous fullerene with cross linkage between the fullerene molecules was
obtained at high temperature 900 0C. This type of highly ordered and high
surface area mesoporous fullerence was used as catalyst to study anodic
performance in sulphuric acid medium. Finally, it was used to test its
catalytic activity for electrochemical methanol oxidation. For anodic
performance and methanol oxidation experiment, mesofullerene was impregnated
with pt-nano particles. Mesoporous Fullerene-Pt nano-composite showed quite an
unusual electrochemical property for electro oxidation of methanol and good
anodic performance in acidic electrolyte. The anodic performance was much
better than the commercially available carbon black. This short communiation is
a report mentioning the synthetic strategy to prepare mesofullerene and
electrode preparation to study its electrochemical performance. This
mesofullerene is potential catalyst for fuel cell application.",1004.4046v4
2010-04-26,"Chemical control of orbital polarization in artificially structured transition-metal oxides: La2NiXO6 (X=B, Al, Ga, In) from first principles","The application of modern layer-by-layer growth techniques to
transition-metal oxide materials raises the possibility of creating new classes
of materials with rationally designed correlated electron properties. An
important step toward this goal is the demonstration that electronic structure
can be controlled by atomic composition. In compounds with partially occupied
transition-metal d shells, one important aspect of the electronic structure is
the relative occupancy of different d orbitals. Previous work has established
that strain and quantum confinement can be used to influence orbital occupancy.
In this paper we demonstrate a different modality for orbital control in
transition-metal oxide heterostructures, using density-functional band
calculations supplemented by a tight-binding analysis to show that the choice
of nontransition-metal counterion X in transition-metal oxide heterostructures
composed of alternating LaNiO3 and LaXO3 units strongly affects orbital
occupancy, changing the magnitude and in some cases the sign of the orbital
polarization.",1004.4678v2
2010-06-07,Evidence Of Protein Collective Motions On The Picosecond Time Scale,"We investigate the presence of structural collective motions on a picosecond
time scale for the heme protein, cytochrome c, as a function of oxidation and
hydration, using terahertz (THz) time-domain spectroscopy and molecular
dynamics simulations. The THz response dramatically increases with oxidation,
with the largest increase for lowest hydrations and highest frequencies. For
both oxidation states the THz response rapidly increases with hydration
saturating above ~25% (g H2O/g protein). Quasi-harmonic vibrational modes and
dipole-dipole correlation functions are calculated from molecular dynamics
trajectories. The collective mode density of states alone reproduces the
measured hydration dependence providing strong evidence of the existence of
these motions. The large oxidation dependence is reproduced only by the
dipole-dipole correlation function, indicating the contrast arises from
diffusive motions consistent with structural changes occurring in the vicinity
of a buried internal water molecule.",1006.1314v1
2010-06-15,Quantum Dielectric Fluctuation in an Electronic Ferroelectricity studied by Variational Monte-Carlo Method,"Electronic structure and dielectric property in an electronic
ferroelectricty, where electric polarization is driven by an electronic charge
order without inversion symmetry, are studied. Motivated from layered iron
oxides, roles of quantum fluctuation on ferroelectricity in a paired-triangular
lattice are focused on. Three types of the extended V-t model are examined by
the variational Monte-Carlo method with the Gutzwiller-type correlation factor.
It is shown that electron transfer between the triangular layers corresponding
to the inter-layer polarization fluctuation promotes the three-fold charge
order associated with an electric polarization. This result is in highly
contrast to the usual manner of quantum fluctuation in the hydrogen-bond type
ferroelectricities and the quantum paraelectric oxides. Spin degree of freedom
of electron and a realistic crystal structure for the layered iron oxides
further stabilize the polar charge ordered state. Implications of the numerical
results for layered iron oxides are discussed.",1006.2889v1
2010-08-18,A Stepped Oxide Hetero-Material Gate Trench Power MOSFET for Improved Performance,"In this work, we propose a new Stepped Oxide Hetero-Material Trench (SOHMT)
power MOSFET with three sections in the trench gate (an N+ poly gate sandwiched
between two P+ poly gates) and having different gate oxide thicknesses
(increasing from source side to drain side). The different gate oxide thickness
serves the purpose of simultaneously achieving (i) a good gate control on the
channel charge and (ii) a lesser gate to drain capacitance. As a result, we
obtain higher transconductance as well as reduced switching delays, making the
proposed device suitable for both RF amplification and high speed switching
applications. In addition, the sandwiched gate with different work function
gate materials modifies the electric field profile in the channel resulting in
an improved breakdown voltage. Using two-dimensional simulations, we have shown
that the proposed device structure exhibits about 32% enhancement in breakdown
voltage, 25% reduction in switching delays, 20% enhancement in peak
transconductance and 10% reduction in figure of merit (product of ON-resistance
and gate charge) as compared to the conventional trench gate MOSFET.",1008.3022v1
2010-11-29,"Contact effects on transport in magnetite, an archetypal correlated transition metal oxide","Multiterminal measurements have typically been employed to examine electronic
properties of strongly correlated electronic materials such as transition metal
oxides without the influence of contact effects. In contrast, in this work we
investigate the interface properties of Fe$_3$O$_4$ with different metals, with
the contact effects providing a window on the physics at work in the correlated
oxide. Contact resistances are determined by means of four-terminal electrical
measurements as a function of source voltage and temperature. Contact
resistances vary systematically with the work function of the electrode metal,
$\phi(M)$, $M=$Cu, Au and Pt, with higher work function yielding lower contact
resistance. This trend and the observation that contact resistances are
directly proportional to the Fe$_3$O$_4$ resistivity are consistent with
modeling the oxide as an effective $p$-type semiconductor with hopping
transport. The jumps in contact resistance values at the bias-driven
insulator-metal transition have a similar trend with $\phi$($M$), consistent
with the transition mechanism of charge gap closure by electric field.",1011.6407v1
2011-02-22,High-Tc BaTiO3 ferroelectric films with frozen negative pressure states,"We report that an energetic plasma process is extremely effective in
enlarging the unit cell volume and ferroelectric distortion of the
ferroelectric oxides, resulting in a significant increase in its Tc. We
demonstrate experimentally that c-axis oriented BaTiO3 films can be deposited
directly on quartz glass and Si substrates using such a process and that the
material shows an approximately 5% expansion of its unit cell volume and
approximately 4 times the ferroelectric tetragonal distortion of the bulk
crystals. Such a frozen negative pressure results in a Tc value that is
approximately 580 K higher than that of bulk single crystals, providing a wide
range of operating temperatures for the devices. The present results suggest an
approach to producing ferroelectric oxides with unique properties that might be
extended to ferromagnetic or superconductor oxides and demonstrate a route to a
lead-free ferroelectric oxide for capacitive, ferroelectric memory, and
electro-optical devices.",1102.4473v1
2011-04-27,Size-reduction of nanodiamonds via air oxidation,"Here we report the size reduction and effects on nitrogen-vacancy centres in
nanodiamonds by air oxidation using a combined atomic force and confocal
microscope. The average height reduction of individual crystals as measured by
atomic force microscopy was 10.6 nm/h at 600 {\deg}C air oxidation at
atmospheric pressure. The oxidation process modified the surface including
removal of non-diamond carbon and organic material which also led to a decrease
in background fluorescence. During the course of the nanodiamond size
reduction, we observed the annihilation of nitrogen-vacancy centres which
provided important insight into the formation of colour centres in small
crystals. In these unirradiated samples, the smallest nanodiamond still hosting
a stable nitrogen-vacancy centre observed was 8 nm.",1104.5075v1
2011-07-21,Density functional calculation of the heats of formation of rare-earth orthophosphates,"Electronic structure calculations are carried out to estimate the heats of
formation of rare-earth orthophosphates from their oxides. The calculated heats
of formation are systematically about 40 kJ/mol less exothermic than the
measured values. Based on estimated corrections for zero-point energies and
H(298.15)-H(0), the discrepancy is almost entirely electronic in origin. The
decreasingly exothermic {\Delta}Hfox with decreasing ionic radius (i.e. LaPO4
more exothermic than ScPO4) results from the higher charge localization on the
oxide anion (O2-) relative to the phosphate anion (PO43-). The lattice energy,
of course, becomes more negative with decreasing ionic radius for both oxide
and phosphate phases, but does so more rapidly for the oxide, making the
reaction less exothermic as ionic radius becomes smaller. This effect should
carry over to {\Delta}Hfox other oxyacids, such as silicates and sulfates.",1107.4261v1
2011-07-27,Properties and characterization of ALD grown dielectric oxides for MIS structures,"We report on an extensive structural and electrical characterization of
under-gate dielectric oxide insulators Al2O3 and HfO2 grown by Atomic Layer
Deposition (ALD). We elaborate the ALD growth window for these oxides, finding
that the 40-100 nm thick layers of both oxides exhibit fine surface flatness
and required amorphous structure. These layers constitute a base for further
metallic gate evaporation to complete the Metal-Insulator-Semiconductor
structure. Our best devices survive energizing up to ~3 MV/cm at 77 K with the
leakage current staying below the state-of-the-art level of 1 nA. At these
conditions the displaced charge corresponds to a change of the sheet carrier
density of 3 \times 1013 cm-2, what promises an effective modulation of the
micromagnetic properties in diluted ferromagnetic semiconductors.",1107.5401v1
2011-08-10,Microscopic Property of Amorphous Semiconductor Metal Oxide InGaZnO$_{4}$ and Role of O-deficiency,"We investigated the microscopic and electronic structures amorphous oxide
semiconductors InGaZnO$_{4}$ (a-IGZO) and the role of O-deficiency through the
first-principle calculations. The structure of the amorphous oxide is
complicated by the admixture of many different kinds of substructures, however
it is surprisingly found that the band tail states, which are well-known to be
present in the amorphous semiconductors, are few generated for the conduction
band minimum (CBM). The electronic structure around CBM is little affected by
the disorder and also by the O-deficiency. Free electron carriers can be
generated without a creation of donor-level in the O-deficient amorphous oxide.",1108.2086v2
2011-08-30,Probing the Thermal Deoxygenation of Graphene Oxide using High Resolution In Situ X-Ray based Spectroscopies,"Despite the recent developments in Graphene Oxide due to its importance as a
host precursor of Graphene, the detailed electronic structure and its evolution
during the thermal reduction remain largely unknown, hindering its potential
applications. We show that a combination of high resolution in situ X-ray
photoemission and X-ray absorption spectroscopies offer a powerful approach to
monitor the deoxygenation process and comprehensively evaluate the electronic
structure of Graphene Oxide thin films at different stages of the thermal
reduction process. It is established that the edge plane carboxyl groups are
highly unstable, whereas carbonyl groups are more difficult to remove. The
results consistently support the formation of phenol groups through reaction of
basal plane epoxide groups with adjacent hydroxyl groups at moderate degrees of
thermal activation (~400 {\deg}C). The phenol groups are predominant over
carbonyl groups and survive even at a temperature of 1000 {\deg}C. For the
first time a drastic increase in the density of states (DOS) near the Fermi
level at 600 {\deg}C is observed, suggesting a progressive restoration of
aromatic structure in the thermally reduced graphene oxide",1108.5911v1
2011-10-17,In Situ Imaging of the Conducting Filament in a Silicon Oxide Resistive Switch,"The nature of the conducting filaments in many resistive switching systems
has been elusive. Through in situ transmission electron microscopy, we image
the real-time formation and evolution of the filament in a silicon oxide
resistive switch. The electroforming process is revealed to involve the local
enrichment of silicon from the silicon oxide matrix. Semi-metallic silicon
nanocrystals with structural variations from the conventional diamond cubic
form of silicon are observed, which likely accounts for the conduction in the
filament. The growth and shrinkage of the silicon nanocrystals in response to
different electrical stimuli show energetically viable transition processes in
the silicon forms, offering evidence to the switching mechanism. The study here
also provides insights into the electrical breakdown process in silicon oxide
layers, which are ubiquitous in a host of electronic devices.",1110.3755v1
2011-10-25,Intrinsic Defects and Electronic Conductivity of TaON: First-Principles Insights,"As a compound in between the tantalum oxide and nitride, the tantalum
oxynitride TaON is expected to combine their advantages and act as an efficient
visible-light-driven photocatalyst. In this letter, using hybrid functional
calculations we show that TaON has different defect properties from the binary
tantalum oxide and nitride: (i) instead of O or N vacancies or Ta
interstitials, the $O_N$ antisite is the dominant defect, which determines its
intrinsic n-type conductivity and the p-type doping difficulty; (ii) the $O_N$
antisite has a shallower donor level than O or N vacancies, with a delocalized
distribution composed mainly of the Ta $5d$ orbitals, which gives rise to
better electronic conductivity in the oxynitride than in the oxide and nitride.
The phase stability analysis reveals that the easy oxidation of TaON is
inevitable under O rich conditions, and a relatively O poor condition is
required to synthesize stoichiometric TaON samples.",1110.5603v1
2011-12-16,Low-temperature photoluminescence of oxide-covered single-layer MoS2,"We present a photoluminescence study of single-layer MoS2 flakes on SiO2
surfaces. We demonstrate that the luminescence peak position of flakes prepared
from natural MoS2, which varies by up to 25 meV between individual as-prepared
flakes, can be homogenized by annealing in vacuum, which removes adsorbates
from the surface. We use HfO2 and Al2O3 layers prepared by atomic layer
deposition to cover some of our flakes. We clearly observe a suppression of the
low-energy luminescence peak observed for as-prepared flakes at low
temperatures, indicating that this peak originates from excitons bound to
surface adsorbates. We also observe different temperature-induced shifts of the
luminescence peaks for the oxide-covered flakes. This effect stems from the
different thermal expansion coefficients of the oxide layers and the MoS2
flakes. It indicates that the single-layer MoS2 flakes strongly adhere to the
oxide layers and are therefore strained.",1112.3747v3
2012-02-21,Wide band gap tunability in complex transition metal oxides by site-specific substitution,"Fabricating complex transition metal oxides with a tuneable band gap without
compromising their intriguing physical properties is a longstanding challenge.
Here we examine the layered ferroelectric bismuth titanate and demonstrate
that, by site-specific substitution with the Mott insulator lanthanum
cobaltite, its band gap can be narrowed as much as one electron volt, while
remaining strongly ferroelectric. We find that when a specific site in the host
material is preferentially substituted, a split-off state responsible for the
band gap reduction is created just below the conduction band of bismuth
titanate. This provides a route for controlling the band gap in complex oxides
for use in emerging oxide opto-electronic and energy applications.",1202.4785v1
2012-06-20,Ultrathin Oxide Films by Atomic Layer Deposition on Graphene,"In this paper, a method is presented to create and characterize mechanically
robust, free standing, ultrathin, oxide films with controlled, nanometer-scale
thickness using Atomic Layer Deposition (ALD) on graphene. Aluminum oxide films
were deposited onto suspended graphene membranes using ALD. Subsequent etching
of the graphene left pure aluminum oxide films only a few atoms in thickness. A
pressurized blister test was used to determine that these ultrathin films have
a Young's modulus of 154 \pm 13 GPa. This Young's modulus is comparable to much
thicker alumina ALD films. This behavior indicates that these ultrathin
two-dimensional films have excellent mechanical integrity. The films are also
impermeable to standard gases suggesting they are pinhole-free. These
continuous ultrathin films are expected to enable new applications in fields
such as thin film coatings, membranes and flexible electronics.",1206.4587v1
2012-07-16,CVD Synthesis of Small-Diameter Single Walled Carbon Nanotubes on Silicon,"A simple process for chemical vapor deposition of ultra SD single wall carbon
nanotubes has been developed. In this process, an iron nitrate nonahydrate
solution in isopropyl alcohol with a concentration of 400 ug/mlit was used to
catalyze nanoparticles formation on an oxidized silicon wafer. The oxide on the
substrate was made of a thick layer of wet oxide sandwiched between tow thin
layers of dry oxide. The process results in semiconducting single-walled carbon
nanotubes (SWNTs) with diameter of less than 0.7nm and more than 1ev band gap
energy, which are amongst the smallest diameters of SWNTs ever reported.",1207.3555v1
2012-10-04,Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser,"In this work we demonstrate comprehensive studies on graphene oxide (GO) and
reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of
Er-doped fiber lasers. The paper describes the fabrication process of both
saturable absorbers and detailed comparison of their parameters. Our results
show, that there is no significant difference in the laser performance between
the investigated SA. Both provided stable, mode-locked operation with sub-400
fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center
wavelength. It has been shown that GO might be successfully used as an
efficient SA without the need of its reduction to rGO. Taking into account
simpler manufacturing technology and the possibility of mass production, GO
seems to be a good candidate as a cost-effective material for saturable
absorbers for Er-doped fiber lasers.",1210.1469v1
2012-12-17,Reactive self-heating model of aluminum spherical nanoparticles,"Aluminum-oxygen reaction is important in many highly energetic, high pressure
generating systems. Recent experiments with nanostructured thermites suggest
that oxidation of aluminum nanoparticles occurs in a few microseconds. Such
rapid reaction cannot be explained by a conventional diffusion-based mechanism.
We present a rapid oxidation model of a spherical aluminum nanoparticle, using
Cabrera-Mott moving boundary mechanism, and taking self-heating into account.
In our model, electric potential solves the nonlinear Poisson equation. In
contrast with the Coulomb potential, a ""double-layer"" type solution for the
potential and self-heating leads to enhanced oxidation rates. At maximal
reaction temperature of 2000 C, our model predicts overall oxidation time scale
in microseconds range, in agreement with experimental evidence.",1212.4113v1
2013-02-19,"Structure and Dielectric Properties of Amorphous High-kappa Oxides: HfO2, ZrO2 and their alloys","High-$\kappa$ metal oxides are a class of materials playing an increasingly
important role in modern device physics and technology. Here we report
theoretical investigations of the properties of structural and lattice
dielectric constants of bulk amorphous metal oxides by a combined approach of
classical molecular dynamics (MD) - for structure evolution, and quantum
mechanical first principles density function theory (DFT) - for electronic
structure analysis. Using classical MD based on the Born-Mayer-Buckingham
potential function within a melt and quench scheme, amorphous structures of
high-$\kappa$ metal oxides Hf$_{1-x}$Zr$_x$O$_2$ with different values of the
concentration $x$, are generated. The coordination numbers and the radial
distribution functions of the structures are in good agreement with the
corresponding experimental data. We then calculate the lattice dielectric
constants of the materials from quantum mechanical first principles, and the
values averaged over an ensemble of samples agree well with the available
experimental data, and are very close to the dielectric constants of their
cubic form.",1302.4534v1
2013-02-20,Search for correlations between morphological characteristics and the crystallite sizes in thin zinc oxide films,"Size-property relations in plasma-modified ZnO thin films have been
investigated as a function of plasma treatment duration. The correlations
between crystallite sizes and the morphological characteristics of films have
been extracted on the basis of the frontier computational analysis of the
scanning probe microscope (SPM) data matrices. The nanocluster structure of
oxide films have been studied in detail with high accuracy. The strong
plasma-induced changes in crystallite sizes have been interpreted as a
size-structure phase transition. Direct measurements of X-ray diffraction and
optical transmittance spectra have confirmed the results obtained with
computational approaches. The discovery size-morphology correlations in thin
oxide films might open new avenues ultimately leading towards deeper insight
into unsolved problems of evaluation of optimal technological conditions for
thin oxide film designing.",1302.4821v1
2013-04-22,Low Hole Effective Mass p-type Transparent Conducting Oxides: Identification and Design Principles,"The development of high performance transparent conducting oxides (TCOs) is
critical to many technologies from transparent electronics to solar cells.
While n-type TCOs are present in many devices, current p-type TCOs are not
largely commercialized as they exhibit much lower carrier mobilities, due to
the large hole effective masses of most oxides. Here, we conduct a
high-throughput computational search on thousands of binary and ternary oxides
and identify several highly promising compounds displaying exceptionally low
hole effective masses (up to an order of magnitude lower than state of the art
p-type TCOs) as well as wide band gaps. In addition to the discovery of
specific compounds, the chemical rationalization of our findings opens new
directions, beyond current Cu-based chemistries, for the design and development
of future p-type TCOs.",1304.6054v1
2013-06-03,Physical properties of Co/n-Ge Schottky contacts,"To investigate the role of the interface state on the physical properties of
Schottky contacts, Co/n-Ge Schottky diodes that have undergone various cleaning
methods (HF etching and in-situ thermal cleaning) were studied by Transmission
Electron Microscopy (TEM), Deep-level Transient Spectroscopy (DLTS) and by a
detailed analysis of the temperature dependence of the diodes characteristics.
It is shown that Schottky barrier height characteristics are sensitive to the
nature of the interface. The strongest Fermi level pinning and the highest
spatial inhomogeneities are observed for intimate metal/semiconductor contacts.
The presence of a thin oxide interlayer, even of Ge native oxide, allows the
Fermi level to be released towards the conduction band and leads to more
homogeneous contacts. Finally our results suggest that a pure GeO2 oxide
interlayer should present a better depinning efficiency than the native Ge
oxide.",1306.0459v1
2013-11-27,Multi-wavelength Raman scattering of nanostructured Al-doped zinc oxide,"In this work we present a detailed Raman scattering investigation of zinc
oxide and aluminum-doped zinc oxide (AZO) films characterized by a variety of
nanoscale structure and morphology and synthesized by pulsed laser deposition
(PLD) under different oxygen pressure conditions. The comparison of Raman data
for pure ZnO and AZO films with similar morphology at the nano/mesoscale allows
to investigate the relation between Raman features (peak or band positions,
width, relative intensity) and material properties such as local structural
order, stoichiometry and doping. Moreover Raman measurements with three
different excitation lines (532, 457 and 325 nm) point out a strong correlation
between vibrational and electronic properties. This observation confirms the
relevance of a multi-wavelength Raman investigation to obtain a complete
structural characterization of advanced doped oxide materials.",1311.7028v1
2014-04-17,Polarization degenerate micropillars fabricated by designing elliptical oxide apertures,"A method for fabrication of polarization degenerate oxide apertured
micropillar cavities is demon- strated. Micropillars are etched such that the
size and shape of the oxide front is controlled. The polarization splitting in
the circular micropillar cavities due to the native and strain induced bire-
fringence can be compensated by elongating the oxide front in the [110]
direction, thereby reducing stress in this direction. By using this technique
we fabricate a polarization degenerate cavity with a quality factor of
1.7*?10^4 and a mode volume of 2.7 u?m3, enabling a calculated maximum Purcell
factor of 11.",1404.4597v1
2014-07-19,Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate,"The interaction of the dye molecule N3
(cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarboxylato)-ruthenium(II))
with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied
using synchrotron radiation based photoelectron spectroscopy, resonant
photoemission spectroscopy (RPES) and near edge X-ray absorption fine structure
spectroscopy (NEXAFS). Calibrated X-ray absorption and valence band spectra of
the monolayer and multilayer coverages reveal that charge transfer is possible
from the molecule to the AlNi(110) substrate via tunnelling through the
ultra-thin oxide layer and into the conduction band edge of the substrate. This
charge transfer mechanism is possible from the LUMO+2&3 in the excited state
but not from the LUMO, therefore enabling core-hole clock analysis, which gives
an upper limit of $6.0\pm$2.5fs for the transfer time. This indicates that
ultra-thin oxide layers are a viable material for use in dye-sensitized solar
cells (DSSC), which may lead to reduced recombination effects and improved
efficiencies of future devices.",1407.5186v1
2014-09-03,Manganese oxide nanosheets and a 2D hybrid of graphene-manganese oxide nanosheets synthesized by liquid-phase exfoliation,"Manganese oxide nanosheets were synthesized using liquid phase exfoliation
that achieved suspensions in isopropanol with concentrations of up to 0.45
mg/ml. A study of solubility parameters showed that the exfoliation was optimum
in DMF followed by isopropanol and diethylene glycol. Isopropanol was the
solvent of choice due to its environmentally friendly nature and ease of use
for further processing. The 2D hybrid was synthesized in isopropanol
suspensions with concentrations of up to 0.5 mg/ml and demonstrated stability
against reaggregation for up to six months. The coexfoliation was found to be
an energetically favorable process in which both solutes, graphene and
manganese oxide nanosheets, exfoliate with an improved yield as compared to the
single solute exfoliation procedure. This work demonstrates the remarkable
versatility of liquid phase exfoliation with respect to the synthesis of
hybrids with tailored properties, and it provides proof of concept ground work
for further future investigation and exploitation of hybrids made of two or
more 2D nanomaterials that have key complementary properties for various
technological applications.",1409.1087v1
2014-10-16,Large spin accumulation voltages in epitaxial Mn5Ge3 contacts on Ge without oxide tunnel barrier,"Spin injection in high-quality epitaxial Mn5Ge3 Schottky contacts on n-type
Ge has been investigated using a three-terminal Hanle effect measurement. Clear
Hanle and inverted Hanle signals with features characteristic of spin
accumulation and spin precession are observed up to 200 K. Strikingly, the
observed spin voltage is several orders of magnitude larger than predicted by
the theory of spin injection and diffusive spin transport. Since the devices
have no oxide tunnel barrier, the discrepancy between theory and experiments
cannot be explained by the often-invoked spin accumulation in localized states
associated with the oxide or oxide/semiconductor interface. The observed spin
voltages therefore must originate from the Ge itself, either from spins in the
Ge bulk bands or its depletion region.",1410.4277v1
2015-01-14,Yeast caspase 1 suppresses the burst of reactive oxygen species and maintains mitochondrial stability in Saccharomyces cerevisiae,"Caspases are a family of cysteine proteases that play essential roles during
apoptosis, and we presume some of them may also protect the cell from oxidative
stress. We found that the absence of yeast caspase 1(Yca1)in Saccharomyces
cerevisiae leads to a more intense burst of mitochondrial reactive oxygen
species (ROS) In addition, compared to wild type yeast cells, the ability of
yca1 mutant cells to maintain mitochondrial activity is significantly reduced
after either oxidative stress treatment or aging. During mitochondrial ROS
burst, deletion of the yca1 gene delayed structural damage of a green
fluorescent protein (GFP) reporter bound in the inner mitochondrial membrane.
This work implies that yeast caspase 1 is closely connected to the oxidative
stress response. We speculate that Yca1 can discriminate proteins damaged by
oxidation and accelerate their hydrolysis to attenuate the ROS burst.",1501.03258v1
2015-02-04,The reversible lithiation of SnO: a three-phase process,"A high reversible capacity is a key feature for any rechargeable battery. In
the lithium-ion battery technology, tin-oxide anodes do fulfill this
requirement, but a fast loss of capacity hinders a full commercialization.
Using first-principles calculations, we propose a microscopic model that sheds
light on the reversible lithiation/delithiation of SnO and reveals that a
sintering of Sn causes a strong degradation of SnO-based anodes. When the
initial irreversible transformation ends, active anode grains consist of
Li-oxide layers separated by Sn bilayers. During the following reversible
lithiation, the Li-oxide undergoes two phase transformations that give rise to
a Li-enrichment of the oxide and the formation of a layered SnLi composite. We
find that the model-predicted anode volume expansion and voltage profile agree
well with experiment, and a layered anode grain is highly-conductive and has a
theoretical reversible capacity of 4.5 Li atoms per a SnO host unit. The model
suggests that the grain structure has to remain layered to sustain its
reversible capacity and a thin-film design of battery anodes could be a remedy
for the capacity loss.",1502.01110v2
2015-02-05,Influence of oxygen on thermal stability of nanocrystalline aluminum studied by positron annihilation spectroscopy,"The thermal stability of nanocrystalline (nc) Al has been studied by means of
positron lifetime spectroscopy and X-ray diffraction (XRD), prepared by
compacting nanoparticles under high pressures. Those nanoparticles were
produced by the flow-levitation (FL) method [1] and the arc-discharge (DC)
method. Effect of oxide at nanoparticle surface on structure stability was
investigated especially in this experiment. The positron lifetime results
reveal that vacancy clusters in grain boundaries are dominant positron traps
according to the high relative intensity of the positron lifetime {\tau}2 in
both samples. The mean grain size of the sample consisting of nanoparticles
with partially oxidized surfaces is almost unchanged after aging at 150 for 84
h, with that of the sample consisting of pure nc Al increasing. The partially
oxidized surfaces of nanoparticles hinder the growth of grain when aging at
150, vacancy clusters related to Al2O3 need longer aging time to decompose,
which implies that the oxide stabilizes the microstructure of the
nanomaterials. The effect is beneficial for nc materials to keep excellent
properties.",1502.01511v1
2015-03-06,Constructing ab initio models of ultra-thin Al-AlOx-Al barriers,"The microscopic structure of ultra-thin oxide barriers often plays a major
role in modern nano-electronic devices. In the case of superconducting
electronic circuits, their operation depends on the electrical non-linearity
provided by one or more such oxide layers in the form of ultra-thin tunnel
barriers (also known as Josephson junctions). Currently available fabrication
techniques manufacture an amorphous oxide barrier, which is attributed as a
major noise source within the device. The nature of this noise is currently an
open question and requires both experimental and theoretical investigation.
Here, we present a methodology for constructing atomic scale computational
models of Josephson junctions using a combination of molecular mechanics,
empirical and ab initio methods. These junctions consist of ultra-thin
amorphous aluminium-oxide layers sandwiched between crystalline aluminium. The
stability and structure of these barriers as a function of density and
stoichiometry are investigated, which we compare to experimentally observed
parameters",1503.01859v2
2015-04-05,Pathway to oxide photovoltaics via band-structure engineering of SnO,"The prospects of scaling current photovoltaic technologies to terawatt levels
remain uncertain. All-oxide photovoltaics could open rapidly scalable
manufacturing routes, if only oxide materials with suitable electronic and
optical properties were developed. A potential candidate material is tin
monoxide (SnO), which has exceptional doping and transport properties among
oxides, but suffers from a low adsorption coefficient due to its strongly
indirect band gap. Here, we address this shortcoming of SnO by band-structure
engineering through isovalent but heterostructural alloying with divalent
cations (Mg, Ca, Sr, Zn). Using first-principles calculations, we show that
suitable band gaps and optical properties close to that of direct-gap
semiconductors are achievable in such SnO based alloys. Due to the defect
tolerant electronic structure of SnO, the dispersive band-structure features
and comparatively small effective masses are preserved in the alloys. Initial
Sn1-xZnxO thin films deposited by sputtering exhibit crystal structure and
optical properties in accord with the theoretical predictions, which confirms
the feasibility of the alloying approach. Thus, the implications of this work
are important not only for terawatt scale photovoltaics, but also for other
large-scale energy technologies where defect-tolerant semiconductors with high
quality electronic properties are required.",1504.01168v2
2015-04-29,Graphene Oxide as an Optimal Candidate Material for Methane Storage,"Methane, the primary constituent of natural gas, binds too weakly to
nanostructured carbons to meet the targets set for on-board vehicular storage
to be viable. We show, using density functional theory calculations, that
replacing graphene by graphene oxide increases the adsorption energy of methane
by 50%. This enhancement is sufficient to achieve the optimal binding strength.
In order to gain insight into the sources of this increased binding, that could
also be used to formulate design principles for novel storage materials, we
consider a sequence of model systems, that progressively take us from graphene
to graphene oxide. A careful analysis of the various contributions to the weak
binding between the methane molecule and the graphene oxide shows that the
enhancement has important contributions from London dispersion interactions as
well as Debye interactions and higher-order electrostatic interactions, aided
by geometric curvature induced primarily by the presence of epoxy groups.",1504.07994v1
2015-06-09,"Comment on ""Selective Interface Control of Order Parameters in Complex Oxides"" (arXiv:1505.07451)","We show that the experimental evidence presented in this paper is
insufficient to support its conclusions.",1506.02787v1
2015-07-10,Compensation of radiation damages for SOI pixel detector via tunneling,"We are developing monolithic pixel detectors based on SOI technology for high
energy physics, X-ray applications and so on.To employ SOI pixel detector on
such radiation environments, we have to solve effects of total ionizing dose
(TID) for transistors which are enclosed in oxide layer.The holes which are
generated and trapped in the oxide layers after irradiation affect
characteristics of near-by transistors due to its positive electric
field.Annealing and radiation of ultraviolet are not realistic to remove
trapped holes for a fabricated detector due to thermal resistance of components
and difficulty of handling. We studied compensation of TID effects by tunneling
using a high-voltage. For decrease of trapped holes, applied high-voltage to
buried p-well which is under oxide layer to inject the electrons into the oxide
layer.In this report, recent progress of this study is shown.",1507.02797v2
2015-07-24,Spin relaxation characteristics in Ag nanowire covered with various oxides,"We have studied spin relaxation characteristics in a Ag nanowire covered with
various oxide layers of Bi2O3, Al2O3, HfO2, MgO or AgOx by using non-local spin
valve structures. The spin-flip probability, a ratio of momentum relaxation
time to spin relaxation time at 10 K, exhibits a gradual increase with an
atomic number of the oxide constituent elements, Mg, Al, Ag and Hf.
Surprisingly the Bi2O3 capping was found to increase the probability by an
order of magnitude compared with other oxide layers. This finding suggests the
presence of an additional spin relaxation mechanism such as Rashba effect at
the Ag/Bi2O3 interface, which cannot be explained by the simple Elliott-Yafet
mechanism via phonon, impurity and surface scatterings. The Ag/Bi2O3 interface
may provide functionality as a spin to charge interconversion layer.",1507.06813v2
2015-07-27,Local environment and oxidation state of Mn impurity in SrTiO3 determined from XAFS data,"The local environment and oxidation state of Mn impurity in strontium
titanate doped with 3% Mn were studied by X-ray absorption fine structure
spectroscopy. The influence of the preparation conditions on the incorporation
of the impurity into the $A$ and $B$ sites was studied. It was established that
Mn ions substituting for Ti are in the Mn$^{4+}$ oxidation state and on-center.
Mn ions substituting for Sr are in the Mn$^{2+}$ oxidation state, are
off-center and displaced from the lattice sites by $\sim$0.32 {\AA}. It was
demonstrated that studies of the X-ray absorption near-edge structure can be
used to determine the concentration ratio of Mn atoms located at the $A$ and
$B$ sites.",1507.07342v1
2015-07-31,"Intrinsic defects, fluctuations of the local shape, and the photo-oxidation of black phosphorus","Black phosphorus is a monoatomic semiconducting layered material that
degrades exothermically in the presence of light and ambient contaminants. Its
degradation dynamics remain largely unknown. Even before degradation,
local-probe studies indicate non-negligible local curvature --through a
non-constant height distribution-- due to the unavoidable presence of intrinsic
defects. We establish that these intrinsic defects are photo-oxidation sites
because they lower the chemisorption barrier of ideal black phosphorus (> 10 eV
and out of visible-range light excitations) right into the visible and
ultra-violet range (1.6 to 6.8 eV), thus enabling photo-induced oxidation and
dissociation of oxygen dimers. A full characterization of the material's shape
and of its electronic properties at the early stages of the oxidation process
is presented as well. This study thus provides fundamental insights into the
degradation dynamics of this novel layered material.",1507.08994v1
2015-08-15,Structure Sensitivity in Oxide Catalysis: First-Principles Kinetic Monte Carlo Simulations for CO Oxidation at RuO$_2$(111),"We present a density-functional theory based kinetic Monte Carlo study of CO
oxidation at the (111) facet of RuO$_2$. We compare the detailed insight into
elementary processes, steady-state surface coverages and catalytic activity to
equivalent published simulation data for the frequently studied RuO$_2$(110)
facet. Qualitative differences are identified in virtually every aspect ranging
from binding energetics over lateral interactions to the interplay of
elementary processes at the different active sites. Nevertheless, particularly
at technologically relevant elevated temperatures, near-ambient pressures and
near-stoichiometric feeds both facets exhibit almost identical catalytic
activity. These findings challenge the traditional definition of structure
sensitivity based on macroscopically observable turnover frequencies and allow
to scrutinize the applicability of structure sensitivity classifications
developed for metals to oxide catalysis.",1508.03697v1
2016-01-07,"First principles search for $n$-type oxide, nitride, and sulfide thermoelectrics","Oxides have many potentially desirable characteristics for thermoelectric
applications, including low cost and stability at high temperatures, but thus
far there are few known high $zT$ $n$-type oxide thermoelectrics. In this work,
we use high-throughput first principles calculations to screen transition metal
oxides, nitrides, and sulfides for candidate materials with high power factors
and low thermal conductivity. We find a variety of promising materials, and we
investigate these materials in detail in order to understand the mechanisms
that cause them to have high power factors. These materials all combine a high
density of states near the Fermi level with dispersive bands, reducing the
trade-off between the Seebeck coefficient and the electrical conductivity, but
they do so for several different reasons. In addition, our calculations
indicate that many of our candidate materials have low thermal conductivity.",1601.01622v2
2016-01-25,Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation,"The thermal gradient along indium-arsenide nanowires was engineered by a
combination of fabricated micro- trenches in the supporting substrate and
focused laser irradiation. This allowed local control of thermally activated
oxidation reactions of the nanowire on the scale of the diffraction limit. The
locality of the oxidation was detected by micro-Raman mapping, and the results
were found consistent with numerical simulations of the temperature profile.
Applying the technique to nanowires in electrical devices the locally oxidized
nanowires remained conducting with a lower conductance as expected for an
effectively thinner conducting core.",1601.06583v1
2016-02-13,Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films,"The ability to manipulate oxygen anion defects rather than metal cations in
complex oxides can facilitate creating new functionalities critical for
emerging energy and device technologies. However, the difficulty in activating
oxygen at reduced temperatures hinders the deliberate control of important
defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to
demonstrate that epitaxial strain is a powerful tool for manipulating the
oxygen vacancy concentration even under highly oxidizing environments and at
annealing temperatures as low as 300 C. By applying a small biaxial tensile
strain (2%), the oxygen activation energy barrier decreases by ~30%, resulting
in a tunable oxygen deficient steady-state under conditions that would normally
fully oxidize unstrained cobaltite. These strain-induced changes in oxygen
stoichiometry drive the cobaltite from a ferromagnetic metal towards an
antiferromagnetic insulator. The ability to decouple the oxygen vacancy
concentration from its typical dependence on the operational environment is
useful for effectively designing oxides materials with a specific oxygen
stoichiometry.",1602.04280v1
2016-06-27,Structural and electrical properties of Sn substituted double sintering derived Ni-Zn ferrite,"The Sn substituted Ni-Zn ferrites were synthesized by the standard double
sintering technique using nano powders of nickel oxide (NiO), zinc oxide (ZnO),
iron oxide (Fe2O3) and tin oxide (SnO2). The structural and electrical
properties have been investigated by the X-ray diffraction, scanning electron
microscopy, DC resistivity and dielectric measurements. Extra intermediate
phase has been detected along with the inverse cubic spinel phase of Ni-Zn
ferrite. Enhancement of grain size is observed in Sn substituted Ni-Zn
ferrites. DC resistivity as a function of temperature has been investigated by
two probe method. The DC resistivity was found to decrease whereas the
dielectric constants increase with increasing Sn content in Ni-Zn ferrites. The
dielectric constant of the as prepared samples is high enough to use these
materials in miniaturized memory devices based capacitive components or energy
storage principles.",1606.08118v1
2016-06-27,Hafnium carbide formation in oxygen deficient hafnium oxide thin films,"On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO$_{2-x}$)
contaminated with adsorbates of carbon oxides, the formation of hafnium carbide
(HfC$_x$) at the surface during vacuum annealing at temperatures as low as 600
{\deg}C is reported. Using X-ray photoelectron spectroscopy the evolution of
the HfC$_x$ surface layer related to a transformation from insulating into
metallic state is monitored in situ. In contrast, for fully stoichiometric
HfO$_2$ thin films prepared and measured under identical conditions, the
formation of HfC$_x$ was not detectable suggesting that the enhanced adsorption
of carbon oxides on oxygen deficient films provides a carbon source for the
carbide formation. This shows that a high concentration of oxygen vacancies in
carbon contaminated hafnia lowers considerably the formation energy of hafnium
carbide. Thus, the presence of a sufficient amount of residual carbon in
resistive random access memory devices might lead to a similar carbide
formation within the conducting filaments due to Joule heating.",1606.08227v1
2016-09-09,Oxidation-assisted graphene heteroepitaxy on copper foil,"We propose an innovative, easy-to-implement approach to synthesize large-area
singlecrystalline graphene sheets by chemical vapor deposition on copper foil.
This method doubly takes advantage of residual oxygen present in the gas phase.
First, by slightly oxidizing the copper surface, we induce grain boundary
pinning in copper and, in consequence, the freezing of the thermal
recrystallization process. Subsequent reduction of copper under hydrogen
suddenly unlocks the delayed reconstruction, favoring the growth of
centimeter-sized copper (111) grains through the mechanism of abnormal grain
growth. Second, the oxidation of the copper surface also drastically reduces
the nucleation density of graphene. This oxidation/reduction sequence leads to
the synthesis of aligned millimeter-sized monolayer graphene domains in
epitaxial registry with copper (111). The as-grown graphene flakes are
demonstrated to be both single-crystalline and of high quality.",1609.02761v1
2016-09-29,Electrical domain writing and nanoscale potential modulation on LaVO$_3$/SrTiO$_3$,"The high-mobility 2DEGs formed at the interfaces between certain insulating
perovskite oxides have been known to be a novel playground of exotic physical
orders like, superconductivity and ferromagnetism and their inter-coupling.
There have been efforts to accomplish even more exotic properties at such
interfaces of oxide heterostructures through nano-structuring of the surface.
In this paper we report writing and erasing charge domains on such an oxide
heterostructure LaVO$_3$/SrTiO$_3$ using a conductive AFM cantilever. We have
patterned these domains in a periodic fashion in order to create artificial
lattices on the surface. Through kelvin probe microscopy, electrostatic force
microscopy and conductivity mapping of such artificial lattices we found that
the domains not only trap charge carriers but also develop a controllable
potential landscape on the surface which coincides with a modulation of local
electrical conductivity. The ability to pattern such nanostructures reversibly
offers unprecedented opportunities of realizing ultra-high storage density
devices in high mobility oxide heterostructures.",1609.09271v1
2016-10-06,Improved Performance and Reliability of p-i-n Perovskite Solar Cells via Doped Metal Oxides,"Perovskite photovoltaics (PVs) have attracted attention because of their
excellent power conversion efficiency (PCE). Critical issues related to large
area PV performance, reliability and lifetime need to be addressed. Here, we
show that doped metal oxides can provide ideal electron selectivity, improved
reliability and stability for perovskite PVs. We report p-i-n perovskite PVs
with device areas ranging from 0.09cm2 to 0.5cm2 incorporating a thick aluminum
doped zinc oxide (AZO) electron selective contact with hysteresis-free PCE of
over 13% and high fill factor values in the range of 80%. AZO provides suitable
energy levels for carrier selectivity, neutralizes the presence of pinholes and
provides intimate interfaces. Devices using AZO exhibit an average PCE increase
of over 20% compared with the devices without AZO and maintain the high PCE for
the larger area devices reported. Furthermore, the device stability of p-i-n
perovskite solar cells under the ISOS-D-1 is enhanced when AZO is used, and
maintains 100% of the initial PCE for over 1000 hours of exposure when AZO/Au
is used as the top electrode. Our results indicate the importance of doped
metal oxides as carrier selective contacts to achieve reliable and high
performance long lived large area perovskite solar cells.",1610.01776v1
2016-10-17,Molten o-H3PO4 - A New Electrolyte for the Anodic Synthesis of Self-Organized Oxide Structures: WO3 Nanochannel Layers and Others,"We introduce the use of pure molten ortho-phosphoric acid (o-H3PO4) as an
electrolyte for selforganizing electrochemistry. This electrolyte allows for
the formation of self-organized oxide architectures (one-dimensional nanotubes,
nanochannels, nanopores) on metals such as tungsten that up to now were
regarded as very difficult to grow self-ordered anodic oxide structures. In
this work, we show particularly the fabrication of thick, vertically aligned
tungsten oxide nanochannel layers, with pore diameter of ca. 10 nm, and
illustrate their potential use in some typical applications.",1610.05079v1
2016-10-26,First principles study of band line up at defective metal-oxide interface: oxygen point defects at Al/SiO_2 interface,"The dielectric breakdown at metal-oxide interfaces is a critical electronic
device failure mechanism. Electronic tunneling through dielectric layers is a
well-accepted explanation for this phenomenon. Theoretical band alignment
studies, providing information about tunneling, have already been conducted in
the literature for metal-oxide interfaces. However, most of the time materials
were assumed defect free. Oxygen vacancies being very common in oxides, their
effect on band lineup is of prime importance in understanding electron
tunneling in realistic materials and devices. This work explores the effect of
oxygen vacancy and oxygen di-vacancy at the Al/SiO2 interface on the band line
up within Density Functional Theory using PBE0 hybrid exchange and correlation
functional. It is found that the presence of defects at the interface, and
their charge state, strongly alters the band line up.",1610.08550v1
2017-02-13,An Atomic-Scale View of CO and H2 Oxidation on a Pt-Fe3O4 Model Catalyst,"Metal-support interactions are frequently invoked to explain the enhanced
catalytic activity of metal nanoparticles dispersed over reducible metal-oxide
supports, yet the atomic scale mechanisms are rarely known. Here, we use
scanning tunneling microscopy to study a Pt1-6/Fe3O4 model catalyst exposed to
CO, H2, O2, and mixtures thereof, at 550 K. CO extracts lattice oxygen at the
cluster perimeter to form CO2, creating large holes in the metal-oxide surface.
H2 and O2 dissociate on the metal clusters and spill over onto the support. The
former creates create surface hydroxyl groups, which react with the support to
desorb water, while atomic oxygen reacts with Fe from the bulk to create new
Fe3O4(001) islands. The presence of the Pt is crucial because it catalyses
reactions that already occur on the bare iron-oxide surface, but at higher
temperatures.",1702.03998v1
2017-03-01,Ferroelectric metal-oxide-semiconductor capacitors using ultrathin single crystalline SrZrxTi1-xO3,"The epitaxial growth of multifunctional oxides on semiconductors has opened a
pathway to introduce new functionalities to semiconductor device technologies.
In particular, ferroelectric materials integrated on semiconductors could lead
to low-power field-effect devices that can be used for logic and memory.
Essential to realizing such field-effect devices is the development of
ferroelectric metal-oxide-semiconductor (MOS) capacitors, in which the
polarization of a ferroelectric gate is coupled to the surface potential of a
semiconducting channel. Here we demonstrate that ferroelectric MOS capacitors
can be realized using single crystalline SrZrxTi1-xO3 (x = 0.7) that has been
epitaxially grown on Ge. We find that the ferroelectric properties of
SrZrxTi1-xO3 are exceptionally robust, as gate layers as thin as 5 nm
corresponding to an equivalent-oxide-thickness of just 1.0 nm exhibit a ~ 2 V
hysteretic window in the capacitance-voltage characteristics. The development
of ferroelectric MOS capacitors with nanoscale gate thicknesses opens new
vistas for nanoelectronic devices.",1703.00126v1
2017-03-23,Microscopic Mechanism of Carbon Annihilation upon SiC Oxidation due to Phosphorous Treatment: Density-Functional Calculations Combined with Ion Mass Spectrometry,"We report first-principles static and dynamic calculations that clarify the
microscopic mechanism of carbon annihilation due to phosphorous treatment upon
oxidation of silicon carbide (SiC). We identify the most stable form of the
phosphorus (P) in the oxide as the four-fold coordinated with the dangling PO
unit and find that the unit attracts carbon ejected from the interface, thus
operating as a carbon absorber. This finding provides a microscopic reasoning
for the first time for the promotion of the oxidation reaction on one hand and
the annihilation of the C-related defects at the interface on the other.
Secondary ion mass spectrometry measurements are also performed and the
obtained carbon profile corroborates the theoretical finding above.",1703.08063v1
2018-04-26,Role of substrate on interaction of water molecules with graphene oxide and reduced graphene oxide,"We study local electronic properties of graphene oxide (GO) and reduced
graphene oxide (RGO) on metallic (Pt) and insulating (Si3N4) substrates in
controlled humidity environment. We demonstrate that the supporting substrate
plays a crucial role in interaction of these materials with water, with Pt
making both GO and RGO insensitive to humidity variations and change in
environment. On the other hand, in the case of Si3N4 substrate a significant
difference between GO and RGO with respect to humidity variations is
demonstrated, indicating complete water coverage at ~60% R.H for RGO and ~30%
R.H. for GO. Irrespective of the substrate, both GO and RGO demonstrate
relative independence of their electronic properties on the material thickness,
with similar trends observed for 1, 2 and 3 layers when subject to humidity
variations. This indicates a relatively minor role of material thickness in
GO-based humidity sensors.",1804.09984v1
2018-11-10,Atomic process of oxidative etching in monolayer molybdenum disulfide,"The microscopic process of oxidative etching of two-dimensional molybdenum
disulfide (2D MoS2) at an atomic scale is investigated using a correlative
TEM-etching study. MoS2 flakes on graphene TEM grids are precisely tracked and
characterized by TEM before and after the oxidative etching. This allows us to
determine the structural change with an atomic resolution on the edges of the
domains, of well-oriented triangular pits and along the grain boundaries. We
observe that the etching mostly starts from the open edges, grain boundaries
and pre-existing atomic defects. A zigzag Mo edge is assigned as the dominant
termination of the triangular pits, and profound terraces and grooves are
observed on the etched edges. Based on the statistical TEM analysis, we reveal
possible routes for the kinetics of the oxidative etching in 2D MoS2, which
should also be applicable for other 2D transition metal dichalcogenide
materials like MoSe2 and WS2.",1811.04242v1
2018-11-04,"Characterization of Phosphorite Bearing Uraniferous Anomalies of Bijawar region, Madhya Pradesh, India","The uranium containing phosphatic shale sub surface samples collected from
Bijawar region Madhya Pradesh (M.P.), India as a part of the uranium
exploration programme of the Atomic Minerals Directorate for Exploration and
Research (AMD), Department of Atomic Energy (DAE) were characterized by a
variety of molecular spectroscopic techniques such as photoluminiscence (PL),
time resolved photoluminiscence spectroscopy (TRPL), X-ray absorption near edge
spectroscopy (XANES), Raman spectroscopy and structural techniques such as
X-ray diffraction (XRD) to identify the oxidation state, physical and chemical
form of uranium in this region. Oxidation state analysis by fluorescence
spectroscopy revealed majority of the samples in U(VI) oxidation state. The
most abundant form of uranium was identified as uranate (UO66-) ion, as a
substituent of Ca++ in Ca5(PO4)3F, Flourapatite (FAP). Two uranium species in
U(VI) and U(IV) state; (UO2)2+ adsorbed on silica and uranium oxide species
(UO2) were also identified. The study provided baseline information on the
speciation of uranium in Bijawar region.",1811.05541v1
2018-11-25,Identification of two-dimensional $FeO_2$ termination of hematite $α-Fe_2O_3(0001)$ surface,"Iron oxides are among the most abundant compounds on Earth and have
consequently been studied and used extensively in industrial processes. Despite
these efforts, concrete understanding of some of their surface phase structures
has remained elusive, in particular the oxidized ${\alpha}-Fe_2O_3(0001)$
hematite surface. We detail an optimized recipe to produce this phase over the
entire hematite surface and study the geometrical parameters and composition of
its complex structure by means of atomically resolved microscopy, electron
diffraction and surface-sensitive spectroscopies. We conclude that the oxidized
${\alpha}-Fe_2O_3(0001)$ surface is terminated by a two-dimensional iron oxide
with structure, lattice parameters, and orientation different from the bulk
substrate. Using total-energy density functional theory for simulation of a
large-scale atomic model, we identify the structure of the surface layer as
antiferromagnetic, conductive $1T-FeO_2$ attached on half-metal terminated
bulk. The model succeeds in reproducing the characteristic modulations observed
in the atomically resolved images and electron diffraction patterns.",1811.09996v1
2018-11-26,Synthesis of Oxidation-Resistant Electrochemical-Active Copper Nanowires Using Phenylenediamine Isomers,"Phenylenediamine (PDA) was chosen as a coordinating, reducing, and capping
agent to effectively direct growth and protect against oxidation of Cu
nanowires (Cu NWs) in an aqueous solution. PDA was found to reduce Cu (II) to
Cu (I) at room temperature, and stabilize the resulting Cu (I) by forming a
coordination complex. The presence of a stable Cu (I) complex is the key step
in the synthesis of Cu NWs under mild conditions. Different PDA isomers lead to
different growth paths of forming Cu NWs. Both pPDA and mPDA-synthesized Cu NWs
were covered with a thin layer of polyphenylenediamine and show excellent
anti-oxidation properties, even in the presence of water. The usefulness of the
present and electrochemical active Cu NWs for a variety of nanotechnology
applications is discussed.",1811.10510v1
2018-11-27,Highly enhanced field emission current density of copper oxide coated vertically aligned carbon nanotubes: Role of interface and electronic structure,"We report the field emission (FE) properties of Cu coated vertically aligned
carbon nanotubes (VACNTs) before and after oxidation. The current density was
found to be the maximum (20 mA/cm$^2$) for 3 nm thick Cu coated VACNTs after
oxidation. The variation in conventionally monitored parameters like work
function and field enhancement factor does not explain the experimentally
determined FE current density. A critical analysis of the electronic structure
reveals the importance of presence of Cu$_2$O at the interface of CuO and
VACNTs, which in turn controls the current density of these films. The highly
enhanced FE current density of 3 nm Cu coated VACNTs after oxidation suggests
its potential as a next generation electron source in vacuum microelectronic
devices.",1811.10951v1
2019-05-20,Improved Description of Perovskite Oxide Crystal Structure and Electronic Properties using Self-Consistent Hubbard $U$ Corrections from ACBN0,"The wide variety of complex physical behavior exhibited in transition metal
oxides, particularly the perovskites A$B$O$_3$, makes them a material family of
interest in many research areas, but the drastically different electronic
structures possible in these oxides raises challenges in describing them
accurately within density functional theory (DFT) and related methods. Here we
evaluate the ability of the ACBN0, a recently developed first-principles
approach to computing the Hubbard $U$ correction self-consistently, to describe
the structural and electronic properties of the first-row transition metal
perovskites with $\left(B=\textrm{V}-\textrm{Ni} \right)$. ACBN0 performs
competitively with hybrid functional approaches such as the
Heyd-Scuseria-Ernzerhof (HSE) functional even when they are optimized
empirically, at a fraction of the computational cost. ACBN0 also describes both
the structure and band gap of the oxides more accurately than a conventional
Hubbard $U$ correction performed by using $U$ values taken from the literature.",1905.08328v3
2020-07-01,Colossal Seebeck coefficient in Aurivillius Phase-Perovskite Oxide Composite,"We propose an inexpensive scalable approach for achieving extremely high
values of Seebeck coefficient ($\alpha$) by exploiting the natural superlattice
structure in Aurivillius phase oxides. In particular, we report an $\alpha
\approx $ 319\,mV/K at 300\,K in a composite of Aurivillius phase compound
SrBi$_4$Ti$_4$O$_{15}$ (as a matrix) and a perovskite phase material (e.g.,
La$_{0.7}$Sr$_{0.3}$MnO$_3$ or, La$_{0.7}$Sr$_{0.3}$CoO$_3$ as filler). Such a
colossal value of $\alpha$ can be attributed to contributions from the enhanced
density of states due to the effective low dimensional character of Bi$_2$O$_2$
layer. The corresponding thermal conductivity ($\kappa$) and the electrical
conductivity ($\sigma$) lies in the range 0.7 - 1.25 W/m-K and 10 - 100
$\mu$S/m, respectively at 300\,K. Attributed to the high $\alpha$ values, such
oxide composites can be used as thermopile sensors and highly sensitive
bolometric applications. We anticipate that the demonstration of colossal
$\alpha$ in oxide composites using a simple synthesis strategy also sets the
stage for future material innovations for high temperature thermoelectric
applications.",2007.00632v2
2020-07-28,A Novel Compact Si-B-N Barrier on Mg-Li Alloys via Plasma Treatment,"Mg-Li alloys have attracted much attention due to their superior properties.
However, it is a great challenge to improve their inferior oxidation and
corrosion resistance. We report a novel Si-B-N ceramic film deposited on the
Mg-9.6Li alloy surface as an effective barrier against oxidation and corrosion.
The films were deposited by using plasma enhanced chemical vapor deposition
from a N2-B2H6-SiH4 gas mixtures, showing compact structure and adhesive
attachment to the alloy surface. The barrier revealed excellent protection
against oxidation in humid air for 500 days, and no observable changes were
found in immersion test of the 3.5 wt.% NaCl solution for 10 min. The superior
oxidation and corrosion resistance are attributed to the excellent material
property of Si-B-N coatings with compact structure via plasma treatment.
Moreover, it is found that moderate proportion of B_2 H_6 in the source gas
mixture is beneficial to the protection of alloys, where the hydrogen release
reaction nearly disappeared and no bubbles were generated on the surface in the
immersion test.",2007.14170v1
2013-08-10,A large energy-gap oxide topological insulator based on the superconductor BaBiO3,"Mixed-valent perovskite oxides based on BaBiO3 (BBO) are, like cuperates,
well-known high-Tc superconductors. Recent ab inito calculations have assigned
the high-Tc superconductivity to a correlation-enhanced electron--phonon
coupling mechanism, stimulating the prediction and synthesis of new
superconductor candidates among mixed-valent thallium perovskites. Existing
superconductivity has meant that research has mainly focused on hole-doped
compounds, leaving electron-doped compounds relatively unexplored. Here we
demonstrate through ab inito calculations that BBO emerges as a topological
insulator (TI) in the electron-doped region, where the spin-orbit coupling
(SOC) effect is significant. BBO exhibits the largest topological energy gap of
0.7 eV among currently known TI materials, inside which Dirac-type topological
surface states (TSSs) exit. As the first oxide TI, BBO is naturally stable
against surface oxidization and degrading, different from chalcoginide TIs. An
extra advantage of BBO lies in its ability to serve an interface between the
TSSs and the superconductor for the realization of Majorana Fermions.",1308.2303v1
2013-08-24,Gold and Methane: A Noble Combination for Delicate Oxidation,"The ability to partially oxidize methane at low temperatures and pressures
would have important environmental and economic applications. Although methane
oxidation on gold nanoparticles has been observed experimentally, our density
functional theory (DFT) calculations indicate neither CH4, CH3, nor H adsorb on
a neutral gold nanoparticle. However, by positively charging gold
nanoparticles, e.g. through charge transfer to the TiO2 substrate, CH4 binding
increases while O2 binding remains relatively unchanged. We demonstrate that
CH4 adsorption is via bonding with the metal s levels. This holds from small
gold clusters (Au2) to large gold nanoparticles (Au201), and for all fcc
transition metal dimers. These results provide the chemical understanding
necessary to tune the catalytic activity of metal nanoparticles for the partial
oxidation of methane under delicate conditions.",1308.5266v1
2014-03-03,Methane Oxidation to Methanol without CO2 Emission: Catalysis by Atomic Negative Ions,"The catalytic activities of the atomic Y-, Ru-, At-, In-, Pd-, Ag-, Pt-, and
Os- ions have been investigated theoretically using the atomic Au- ion as the
benchmark for the selective partial oxidation of methane to methanol without
CO2 emission. Dispersion-corrected density-functional theory has been used for
the investigation. From the energy barrier calculations and the thermodynamics
of the reactions, we conclude that the catalytic effect of the atomic Ag-, At-,
Ru-, and Os- ions is higher than that of the atomic Au- ion catalysis of CH4
conversion to methanol. By controlling the temperature around 290K (Os-), 300K
(Ag-), 310K (At-), 320K (Ru-) and 325K (Au-) methane can be completely oxidized
to methanol without the emission of CO2. We conclude by recommending the
investigation of the catalytic activities of combinations of the above negative
ions for significant enhancement of the selective partial oxidation of methane
to methanol.",1403.0597v1
2016-11-30,The Effects of Vacancy and Oxidation on Black Phosphorus Nanoresonators,"Black phosphorene is not stable at ambient conditions, so atomic defects and
oxidation effects are unavoidable in black phosphorus samples in the
experiment. The effects of these defects on the performance of the black
phosphorus nanoresonators are still unclear. Here, we perform classical
molecular dynamics to investigate the effects of the vacancy and oxidation on
single-layer black phosphorus nanoresonators at different temperatures. We find
that the vacancy causes strong reduction in the quality factor of the
nanoresonators, while the oxidation has weaker effect on the nanoresonators.
More specifically, a 2% concentration of randomly distributed single vacancies
is able to reduce the quality factor by about 80% and 40% at 4.2K and 50K,
respectively. We also find that the quality factor of the nanoresonator is not
sensitive to the distribution pattern of the vacancy defects.",1611.10048v1
2017-01-20,Oxygen reduction mechanisms in nanostructured La0.8Sr0.2MnO3 cathodes for Solid Oxide Fuel Cells,"In this work we outline the mechanisms contributing to the oxygen reduction
reaction in nanostructured cathodes of La0.8Sr0.2MnO3 (LSM) for Solid Oxide
Fuel Cells (SOFC). These cathodes, developed from LSM nanostructured tubes, can
be used at lower temperatures compared to microstructured ones, and this is a
crucial fact to avoid the degradation of the fuel cell components. This
reduction of the operating temperatures stems mainly from two factors: i) the
appearance of significant oxide ion diffusion through the cathode material in
which the nanostructure plays a key role and ii) an optimized gas phase
diffusion of oxygen through the porous structure of the cathode, which becomes
negligible. A detailed analysis of our Electrochemical Impedance Spectroscopy
supported by first principles calculations point towards an improved overall
cathodic performance driven by a fast transport of oxide ions through the
cathode surface.",1701.05928v1
2017-01-23,In situ X-ray diffraction studies of graphite oxidation reaction indicating different exfoliation mechanism than ex site studies,"We offer a brief overview of the solvent-based graphene production and
summarize the current knowledge on the formation mechanism of graphite oxide
that proceeds via graphite intercalation compounds. In addition, the results of
our in situ X-ray diffraction investigation into this process are presented,
discussed and contrasted to the findings by other authors, who employed the
same oxidation protocol but examined the samples by ex situ X-ray diffraction.
Our results suggest that, contrary to the numerous reports by other authors, no
strong crystalline order, unique to graphite intercalation compounds as well as
graphite oxide, develops if they remain in concentrated acid. Furthermore, it
also appears that, depending on the concentration, sulfuric acid molecules
significantly weaken graphene-graphene interactions in graphite. Consequently,
concentrated sulfuric acid may be a good solvent for graphene dispersions, if
only there is sufficient energy input to separate the layers of graphene.",1701.06493v1
2018-05-13,In-situ angle-resolved photoemission spectroscopy of copper-oxide thin films synthesized by molecular beam epitaxy,"Angle-resolved photoemission spectroscopy (ARPES) is the key
momentum-resolved technique for direct probing of the electronic structure of a
material. However, since it is very surface-sensitive, it has been applied to a
relatively small set of complex oxides that can be easily cleaved in ultra-high
vacuum. Here we describe a new multi-module system at Brookhaven National
Laboratory (BNL) in which an oxide molecular beam epitaxy (OMBE) is
interconnected with an ARPES and a spectroscopic-imaging scanning tunneling
microscopy (SI-STM) module. This new capability largely expands the range of
complex-oxide materials and artificial heterostructures accessible to these two
most powerful and complementary techniques for studies of electronic structure
of materials. We also present the first experimental results obtained using
this system - the ARPES studies of electronic band structure of a
La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) thin film grown by OMBE.",1805.04811v1
2018-05-23,High-throughput study of the static dielectric constant at high temperatures in oxide and fluoride cubic perovskites,"Using finite-temperature phonon calculations and the Lyddane-Sachs-Teller
relations, we calculate ab initio the static dielectric constants of 78
semiconducting oxides and fluorides with cubic perovskite structures at 1000 K.
We first compare our method with experimental measurements, and we find that it
succeeds in describing the temperature dependence and the relative ordering of
the static dielectric constant $\epsilon_{DC}$ in the series of oxides
BaTiO$_{3}$, SrTiO$_{3}$, KTaO$_{3}$. We show that the effects of anharmonicity
on the ion-clamped dielectric constant, on Born charges, and on phonon
lifetimes, can be neglected in the framework of our high-throughput study.
Based on the high-temperature phonon spectra, we find that the dispersion of
$\epsilon_{DC}$ is one order of magnitude larger amongst oxides than fluorides
at 1000 K. We display the correlograms of the dielectric constants with simple
structural descriptors, and we point out that $\epsilon_{DC}$ is actually well
correlated with the infinite-frequency dielectric constant $\epsilon_{\infty}$,
even in those materials with phase transitions in which $\epsilon_{DC}$ is
strongly temperature-dependent.",1805.09199v2
2018-05-25,Evidence for Incipient Ferroelectricity in YCrO3,"Cubic structure is one of the most commonly found structures for oxides at
high temperature. As the temperature is lowered only a handful of these oxides
exhibit ferroelectricity which is rather surprising. In this paper, we use the
example of YCrO3 (YCO), an incipient ferroelectric material to show that in
most oxides there are two competing phenomenon -onset of ferroelectricity due
to rotation of CrO6 octahedra and displacement of Y atom leading to suppression
of ferroelectricity. This competition reveals that while the octahedral
rotations favor a lower symmetry state, the Y atom displacement opposes it
leaving YCO to exhibit only an incipient ferroelectric state. These results
while being in agreement with the earlier theoretical predictions can also help
suggest a pathway to a more stable ferroelectric state in these oxides by using
a larger cationic substitution at the Y site.",1805.10077v1
2008-07-16,Cleaving-temperature dependence of layered-oxide surfaces,"The surfaces generated by cleaving non-polar, two-dimensional oxides are
often considered to be perfect or ideal. However, single particle
spectroscopies on Sr2RuO4, an archetypal non-polar two dimensional oxide, show
significant cleavage temperature dependence. We demonstrate that this is not a
consequence of the intrinsic characteristics of the surface: lattice parameters
and symmetries, step heights, atom positions, or density of states. Instead, we
find a marked increase in the density of defects at the mesoscopic scale with
increased cleave temperature. The potential generality of these defects to
oxide surfaces may have broad consequences to interfacial control and the
interpretation of surface sensitive measurements.",0807.2672v1
2011-11-22,Multilayer Edge Molecular Devices Based on Plasma Oxidation of Photolithographically Defined Bottom Metal Electrode,"A multilayer edge molecular electronics device (MEMED), which utilize the two
metal electrodes of a metal-insulator-metal tunnel junction as the two
electrical leads to molecular channels, can overcome the long standing
fabrication challenges for developing futuristic molecular devices. However,
producing ultrathin insulator is the most challenging step in MEMED
fabrication. A simplified molecular device approach was developed by avoiding
the need of depositing a new materiel on the bottom electrode for growing
ultrathin insulator. This paper discuss the approach for MEMED's insulator
growth by one-step oxidation of a tantalum (Ta) bottom electrode, in the
pholithographically defined region; i.e. ultrathin tantalum oxide (TaOx)
insulator was grown by oxidizing bottom metal electrode itself. Organometallic
molecular clusters (OMCs) were bridged across 1-3 nm TaOx along the perimeter
of a tunnel junction to establish the highly efficient molecular conduction
channels. OMC transformed the asymmetric transport profile of TaOx based tunnel
junction into symmetric one. A TaOx based tunnel junction with top
ferromagnetic (NiFe) electrode exhibited the transient current suppression by
several orders. Further studies will be needed to strengthen the current
suppression phenomenon, and to realize the full potential of TaOx based
multilayer edge molecular spintronics devices.",1111.5087v1
2012-01-09,Resonant charge transfer at dielectric surfaces,"We report on the theoretical description of secondary electron emission due
to resonant charge transfer occurring during the collision of metastable
nitrogen molecules with dielectric surfaces. The emission is described as a two
step process consisting of electron capture to form an intermediate shape
resonance and subsequent electron emission by decay of this ion, either due to
its natural life time or its interaction with the surface. The electron capture
is modeled using the Keldysh Green's function technique and the negative ion
decay is described by a combination of the Keldysh technique and a rate
equation approach. We find the resonant capture of electrons to be very
efficient and the natural decay to be clearly dominating over the
surface-induced decay. Secondary electron emission coefficients are calculated
for aluminum oxide, magnesium oxide, silicon oxide, and diamond at several
kinetic energies of the projectile. With the exception of magnesium oxide the
coefficients turn out to be of the order of 0.1 over the whole range of kinetic
energies. This rather large value is a direct consequence of the shape
resonance acting as a relay state for electron emission.",1201.1724v1
2012-04-20,Dynamic and Static Transmission Electron Microscopy Studies on Structural Evaluation of Au nano islands on Si (100) Surface,"Transmission electron microscopy (TEM) study on morphological changes in gold
nanostructures deposited on Si (100) upon annealing under different vacuum
conditions has been reported. Au thin films of thickness ~2.0 nm were deposited
under high vacuum condition (with the native oxide at the interface of Au and
Si) using thermal evaporation. In-situ, high temperature (from room temperature
(RT) to 850\degreeC) real time TEM measurements showed the evaluation of gold
nanoparticles into rectangular/square shaped gold silicide structures. This has
been attributed to selective thermal decomposition of native oxide layer.
Ex-situ annealing in low vacuum (10-2 mbar) at 850\degreeC showed no growth of
nano-gold silicide structures. Under low vacuum annealing conditions, the
creation of oxide could be dominating compared to the decomposition of oxide
layers resulting in the formation of barrier layer between Au and Si.",1204.4618v1
2013-09-24,Oxidation of GaN: An ab initio thermodynamic approach,"GaN is a wide-bandgap semiconductor used in high-efficiency LEDs and solar
cells. The solid is produced industrially at high chemical purities by
deposition from a vapour phase, and oxygen may be included at this stage.
Oxidation represents a potential path for tuning its properties without
introducing more exotic elements or extreme processing conditions. In this
work, ab initio computational methods are used to examine the energy potentials
and electronic properties of different extents of oxidation in GaN. Solid-state
vibrational properties of Ga, GaN, Ga2O3 and a single substitutional oxygen
defect have been studied using the harmonic approximation with supercells. A
thermodynamic model is outlined which combines the results of ab initio
calculations with data from experimental literature. This model allows free
energies to be predicted for arbitrary reaction conditions within a wide
process envelope. It is shown that complete oxidation is favourable for all
industrially-relevant conditions, while the formation of defects can be opposed
by the use of high temperatures and a high N2:O2 ratio.",1309.6232v1
2015-12-25,Transformation of germanium to fluogermanates,"The surface of a single crystal Germanium wafer was transformed to crystals
of germanium fluorides and oxides upon exposure to a vapor of HF and HNO3
chemical mixture. Structure analysis indicate that the transformation results
in a germanate polycrystalline layer consisting of germanium oxide and ammonium
fluogermanate with a preferential crystal growth orientation in <101>
direction. Local vibrational mode analysis confirms the presence of N-H and
Ge-F vibrational modes in addition to Ge-O stretching modes. Energy dispersive
studies reveal the presence of hexagonal {\alpha}-phase GeO2 crystal clusters
and ammonium fluogermanates around these clusters in addition to a surface
oxide layer. Electronic band structure as probed by ellipsometry has been
associated with the germanium oxide crystals and disorder induced band tailing
effects at the interface of the germanate layer and the bulk Ge wafer. The acid
vapor exposure causes Ge surface to emit a yellow photoluminescence at room
temperature.",1512.08001v1
2015-12-30,Thermal radiative near field transport between vanadium dioxide and silicon oxide across the metal insulator transition,"The thermal radiative near field transport between vanadium dioxide and
silicon oxide at submicron distances is expected to exhibit a strong dependence
on the state of vanadium dioxide which undergoes a metal-insulator transition
near room temperature. We report the measurement of near field thermal
transport between a heated silicon oxide micro-sphere and a vanadium dioxide
thin film on a titanium oxide (rutile) substrate. The temperatures of the 15 nm
vanadium dioxide thin film varied to be below and above the
metal-insulator-transition, the sphere temperatures were varied in a range
between 100 and 200 Celsius. The measurements were performed using a
vacuum-based scanning thermal microscope with a cantilevered resistive thermal
sensor. We observe a thermal conductivity per unit area between the sphere and
the film with a distance dependence following a power law trend and a
conductance contrast larger than 2 for the two different phase states of the
film.",1512.09050v2
2016-05-24,First-principles Modelling of SrTiO3 based Oxides for Thermoelectric Applications,"Using first-principles electronic structure calculations, we studied the
electronic and thermoelectric properties of SrTiO3 based oxide materials and
their nanostructures identifying those nanostructures which possess highly
anisotropic electronic bands. We showed recently that highly anisotropic
flat-and-dispersive bands can maximize the thermoelectric power factor, and at
the same time they can produce low dimensional electronic transport in bulk
semiconductors. Although most of the considered nanostructures show such highly
anisotropic bands, their predicted thermoelectric performance is not improved
over that of SrTiO3. Besides highly anisotropic character, we emphasize the
importance of the large weights of electronic states participating in transport
and the small effective mass of charge carriers along the transport direction.
These requirements may be better achieved in binary transition metal oxides
than in ABO3 perovskite oxide materials.",1605.07387v1
2016-05-27,Hydrostatic pressure response of an oxide two-dimensional electron system,"Two-dimensional electron systems with fascinating properties exist in
multilayers of standard semiconductors, on helium surfaces, and in oxides.
Compared to the two-dimensional (2D) electron gases of semiconductors, the 2D
electron systems in oxides are typically more strongly correlated and more
sensitive to the microscopic structure of the hosting lattice. This sensitivity
suggests that the oxide 2D systems are highly tunable by hydrostatic pressure.
Here we explore the effects of hydrostatic pressure on the well-characterized
2D electron system formed at LaAlO$_{3}$ -SrTiO$_{3}$ interfaces[1] and measure
a pronounced, unexpected response. Pressure of $\sim$2 GPa reversibly doubles
the 2D carrier density $n_{s}$ at 4 K. Along with the increase of $n_{s}$, the
conductivity and mobility are reduced under pressure. First-principles pressure
simulations reveal the same behavior of the carrier density and suggest a
possible mechanism of the mobility reduction, based on the dielectric
properties of both materials and their variation under external pressure.",1605.08528v1
2016-12-08,Superconductivity in higher titanium oxides,"Recent renewal of the highest transition temperature in a conventional
superconductor of the sulfer hydride attracts much attention to exploring
simple compounds with the lighter elements, situated in unconventional
conditions. We report the discovery of superconductivity in simple oxides of
Ti4O7 and g-Ti3O5 in a thin-film form having deliberately tuned epitaxial
structures and off-stoichiometry. These higher titanium oxides join in a class
of simple-oxide superconductors, and g-Ti3O5 now holds the highest
superconducting transition temperature of 7.1 kelvin among them. The mechanism
behind the superconductivity is discussed on the basis of electrical
measurements and theoretical predictions. We conclude that superconductivity
arises from unstabilized bipolaronic insulating states.",1612.02502v1
2016-12-12,ARPES Studies of Two-Dimensional Electron Gases at Transition Metal Oxide Surfaces,"High mobility two-dimensional electron gases (2DEGs) underpin today's silicon
based devices and are of fundamental importance for the emerging field of oxide
electronics. Such 2DEGs are usually created by engineering band offsets and
charge transfer at heterointerfaces. However, in 2011 it was shown that highly
itinerant 2DEGs can also be induced at bare surfaces of different transition
metal oxides where they are far more accessible to high resolution angle
resolved photoemission (ARPES) experiments. Here we review work from this
nascent field which has led to a systematic understanding of the subband
structure arising from quantum confinement of highly anisotropic transition
metal d-states along different crystallographic directions. We further discuss
the role of different surface preparations and the origin of surface 2DEGs, the
understanding of which has permitted control over 2DEG carrier densities.
Finally, we discuss signatures of strong many-body interactions and how
spectroscopic data from surface 2DEGs may be related to the transport
properties of interface 2DEGs in the same host materials.",1612.03571v1
2016-12-20,Oxidation dynamics of ultrathin GaSe probed through Raman spectroscopy,"Gallium selenide (GaSe) is a 2D material with a thickness-dependent gap,
strong non-linear optical coefficients and uncommon interband optical selection
rules, making it interesting for optoelectronic and spintronic applications. In
this work, we monitor the oxidation dynamics of GaSe with thicknesses ranging
from 10 to 200 nm using Raman spectroscopy. In ambient temperature and humidity
conditions, the intensity of all Raman modes and the luminescence decrease
rapidly with moderate exposure to above-gap illumination. Concurrently, several
oxidation products appear in the Raman spectra: Ga$_2$Se$_3$, Ga$_2$O$_3$ and
amorphous and crystalline selenium. We find that no safe measurement power
exists for optical measurements on ultrathin GaSe in ambient conditions. We
demonstrate that the simultaneous presence of oxygen, humidity, and above-gap
illumination is required to activate this photo-oxidation process, which is
attributed to the transfer of photo-generated charge carriers towards aqueous
oxygen at the sample surface, generating highly reactive superoxide anions that
rapidly degrade the sample and quench the optical response of the material.",1612.06907v3
2016-12-21,Pure spin current transport in gallium doped zinc oxide,"We study the flow of a pure spin current through zinc oxide by measuring the
spin Hall magnetoresistance (SMR) in thin film trilayer samples consisting of
bismuth-substituted yttrium iron garnet (Bi:YIG), gallium-doped zinc oxide
(Ga:ZnO), and platinum. We investigate the dependence of the SMR magnitude on
the thickness of the Ga:ZnO interlayer and compare to a Bi:YIG/Pt bilayer. We
find that the SMR magnitude is reduced by almost one order of magnitude upon
inserting a Ga:ZnO interlayer, and continuously decreases with increasing
interlayer thickness. Nevertheless, the SMR stays finite even for a
$12\;\mathrm{nm}$ thick Ga:ZnO interlayer. These results show that a pure spin
current indeed can propagate through a several nm-thick degenerately doped zinc
oxide layer. We also observe differences in both the temperature and the field
dependence of the SMR when comparing tri- and bilayers. Finally, we compare our
data to predictions of a model based on spin diffusion. This shows that
interface resistances play a crucial role for the SMR magnitude in these
trilayer structures.",1612.07239v1
2017-06-09,Effect of oxygen plasma on nanomechanical silicon nitride resonators,"Precise control of tensile stress and intrinsic damping is crucial for the
optimal design of nanomechanical systems for sensor applications and quantum
optomechanics in particular. In this letter we study the in uence of oxygen
plasma on the tensile stress and intrinsic damping of nanomechanical silicon
nitride resonators. Oxygen plasma treatments are common steps in micro and
nanofabrication. We show that oxygen plasma of only a few minutes oxidizes the
silicon nitride surface, creating several nanometer thick silicon dioxide
layers with a compressive stress of 1.30(16)GPa. Such oxide layers can cause a
reduction of the e ective tensile stress of a 50 nm thick stoichiometric
silicon nitride membrane by almost 50%. Additionally, intrinsic damping
linearly increases with the silicon dioxide lm thickness. An oxide layer of
1.5nm grown in just 10s in a 50W oxygen plasma almost doubled the intrinsic
damping. The oxide surface layer can be e ciently removed in bu ered HF.",1706.02957v1
2017-07-01,Hydration Peculiarities of Graphene Oxides with Multiple Oxidation Degrees,"Hydration properties of graphene oxide (GO) are essential for most of its
potential applications. In this work, we employ atomistic molecular dynamics
simulations to investigate seven GO compositions with different levels of
oxygenation. Two atomic charge models for GO are compared: (1) sp2 carbons are
purely Lennard-Jones sites; (2) sp2 carbon charges are consistent with the
CHELPG scheme. Structural properties were found to depend insignificantly on
the charge model, whereas thermodynamics appeared very sensitive. In
particular, the simplified model provides systematically stronger GO/water
coupling, as compared to the more accurate model. For all GO compositions,
hydration free energies are in the range -5 to -45 kJ mol-1 indicating that
hydration is thermodynamically favorable even for modest oxidation degrees,
thus differing drastically from the case of pristine graphene and graphite. The
results and discussion presented hereby provide a physical background for
modern applications of GO, e.g. in electrodes of supercapacitors and inhibitors
in processes involving biological molecules.",1707.00126v2
2017-07-21,The Efficacy of Fiction or More on the Charge State of Ti in TiO2 and Formal Oxidation States,We argue that Ti4+ is not a realistic description of Ti in TiO2.,1707.06851v1
2017-10-23,Tuning the two-dimensional electron liquid at oxide interfaces by buffer-layer-engineered redox reactions,"Polar discontinuities and redox reactions provide alternative paths to create
two-dimensional electron liquids (2DELs) at oxide interfaces. Herein, we report
high mobility 2DELs at interfaces involving SrTiO3 (STO) achieved using polar
La7/8Sr1/8MnO3 (LSMO) buffer layers to manipulate both polarities and redox
reactions from disordered overlayers grown at room temperature. Using resonant
x-ray reflectometry experiments, we quantify redox reactions from oxide
overlayers on STO as well as polarity induced electronic reconstruction at
epitaxial LSMO/STO interfaces. The analysis reveals how these effects can be
combined in a STO/LSMO/disordered film trilayer system to yield high mobility
modulation doped 2DELs, where the buffer layer undergoes a partial
transformation from perovskite to brownmillerite structure. This uncovered
interplay between polar discontinuities and redox reactions via buffer layers
provides a new approach for the design of functional oxide interfaces.",1710.08121v1
2017-10-26,Super nucleation and orientation of poly (butylene terephthalate) crystals in nanocomposites containing highly reduced graphene oxide,"The ring opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO)
is an effective method for the preparation of polymer nanocomposites. The
inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT,
shifting crystallization peak temperature to higher temperatures and, overall,
increasing the crystallization rate. This was due to a super nucleating effect
caused by RGO, which is maximized by highly reduced graphene oxide.
Furthermore, combined analyses by differential scanning calorimetry (DSC)
experiments and wide angle X-ray diffraction (WAXS) showed the formation of a
thick {\alpha}-crystalline form pCBT lamellae with a melting point of ~250
{\deg}C, close to the equilibrium melting temperature of pCBT. WAXS also
demonstrated the pair orientation of pCBT crystals with RGO nanoflakes,
indicating a strong interfacial interaction between the aromatic rings of pCBT
and RGO planes, especially with highly reduced graphene oxide. Such surface
self-organization of the polymer onto the RGO nanoflakes may be exploited for
the enhancement of interfacial properties in their polymer nanocomposites.",1710.09658v1
2017-12-08,Imaging Pulsed Laser Deposition oxide growth by in-situ Atomic Force Microscopy,"To visualize the topography of thin oxide films during growth, thereby
enabling to study its growth behavior quasi real-time, we have designed and
integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD)
vacuum setup. The AFM scanner and PLD target are integrated in a single support
frame, combined with a fast sample transfer method, such that in-situ
microscopy can be utilized after subsequent deposition pulses. The in-situ
microscope can be operated from room temperature (RT) up to 700$^\circ$C and at
(process) pressures ranging from the vacuum base pressure of 10$^{-6}$ mbar up
to 1 mbar, typical PLD conditions for the growth of oxide films. The
performance of this instrument is demonstrated by resolving unit cell height
surface steps and surface topography under typical oxide PLD growth conditions.",1712.02988v1
2017-12-13,Atomic-scale mechanisms of defect- and light-induced oxidation and degradation of InSe,"Layered indium selenide (InSe), a new two-dimensional (2D) material with a
hexagonal structure and semiconducting characteristic, is gaining increasing
attention owing to its intriguing electronic properties. Here, by using
first-principles calculations, we reveal that perfect InSe possesses a high
chemical stability against oxidation, superior to MoS2. However, the presence
of intrinsic Se vacancy (VSe) and light illumination can markedly affect the
surface activity. In particular, the excess electrons associated with the
exposed In atoms at the VSe site under illumination are able to remarkably
reduce the dissociation barrier of O2 to ~0.2 eV. Moreover, at ambient
conditions, the splitting of O2 enables the formation of substitutional
(apical) oxygen atomic species, which further cause the trapping and subsequent
rapid splitting of H2O molecules and ultimately the formation of hydroxyl
groups. Our findings uncover the causes and underlying mechanisms of InSe
surface degradation via the defect-photo promoted oxidations. Such results will
be beneficial in developing strategies for the storage of InSe material and its
applications for surface passivation with boron nitride, graphene or In-based
oxide layers.",1712.04662v1
2018-09-28,Strong phonon anharmonicity and low thermal conductivity of monolayer tin oxides driven by lone-pair electrons,"Motivated by the excellent electronic and optoelectronic properties of
two-dimensional (2D) tin oxides, we systematically investigated the thermal
conductivity of monolayer SnO and SnO2by the first-principles calculations. The
room-temperature thermal conductivity of monolayer SnO and SnO2reaches 9.6
W/(mK) and 98.8 W/(mK), respectively. The size effect is much weaker for
monolayer SnO than for monolayer SnO2, due to the coexistence of size dependent
and independent component in the thermal conductivity of monolayer SnO. The
large difference between the thermal conductivity of 2D tin oxides can be
attributed to the small phonon group velocity and strong anharmonicity strength
of monolayer SnO. Further electronic structure analysis reveals that the
existence of lone-pair Sn-5s electrons is the key factor for the small \k{appa}
of monolayer SnO. These results provide a guide for the manipulation of thermal
transport in the electronic or thermoelectric devices based on 2D tin oxides.",1809.11124v2
2018-10-18,Coating of Aluminum Alloys by Micro Arc Oxidation in Nitrate Salt,"Plasma electrolytic oxidation (PEO) is a process for obtaining oxide coatings
on valve metals. Mostly PEO is done in an aqueous solution electrolyte which
limits the size of treated parts due to the system heating up. In presented
work an alternative method of PEO processing applied in aluminum 1050 alloy in
nitrate molten salt was investigated. The morphology, phase and chemical
compositions, micro-hardness, and corrosion resistance were examined using. The
obtained results showed that formed coating contains from two sub-layers, outer
soft layer with the thickness of 4 micrometer and inner, denser layer with the
thickness of 5 micrometer. The formed coating consists of corundum, {\gamma} -
Al2O3, {\theta} - Al2O3 and is free of any contaminants originated from the
electrolyte.",1810.08018v1
2018-10-31,A polaron cloud of correlated electron states in ceria,"The electronic structure of cerium oxide is investigated here using a
combination of ab initio one-electron theory and many-body physics, with
emphasis on the nature of the 4f electron shell of cerium ions. We propose to
use the hybridization function as a convenient measure for the degree of
localization of the 4f shell of this material, and observe that changing the
oxidation state is related to distinct changes in the hybridization between the
4f shell and ligand states. The theory reveals that CeO$_2$ has essentially
itinerant 4f states, and that in the least oxidized form of ceria, Ce$_2$O$_3$,
the 4f states are almost (but not fully) localized. Most importantly, our model
points to that diffusion of oxygen vacancies in cerium oxide may be seen as
polaron hopping, involving a correlated 4f electron cloud, which is located
primarily on Ce ions of atomic shells surrounding the vacancy.",1810.13211v1
2019-06-15,Oxide layer thickness effects on the resistance switching characteristics of Ti/TiO2-NT/Au structure,"Self-ordered nanotubular titania TiO2-NT with outer tube diameter of 45 nm
are synthesized using the anodic oxidation of titanium foil. Four sets of
memristors with 100 ${\mu}m$ diameter based on Ti/TiO2-NT/Au sandwich
structures with an oxide layer thickness of 80, 120, 160 and 200 nm are
fabricated. Current-voltage (CV) characteristics for the obtained samples in
the static and dynamic operation modes are studied. Resistance in high and low
resistance states is estimated. Basing on the analysis of the CV
characteristics in dynamic mode (> 14 000 switchings) a prospective of use for
synthesized Ti/TiO2-NT/Au micromemristors with oxide layer thickness of 160 nm
in non-volatile memory is shown.
  Keywords: anodic titania, titanium dioxide nanotubes, nanotubular structure,
memristor, resistive switching",1906.06555v1
2019-07-16,In situ Auger electron spectroscopy of complex oxide surfaces grown by pulsed laser deposition,"The authors report in situ Auger electron spectroscopy (AES) of the surfaces
of complex oxides thin films grown by pulsed laser deposition (PLD). The
authors demonstrate the utility of the technique in studying chemical
composition by collecting characteristic Auger spectra of elements from samples
such as complex oxide thin films and single crystals as well as metal foils. In
the case of thin films, AES studies can be performed with single unit cell
precision by monitoring thickness during deposition with reflection high energy
electron diffraction (RHEED). The authors address some of the challenges in
achieving in situ and real time AES studies on complex oxide thin films grown
by PLD. Sustained layer-by-layer PLD growth of a CaTiO3/LaMnO3 superlattice
allows depth-resolved chemical composition analysis during the growth process.
The evolution of the Auger spectra of the elements from individual layers were
used to perform chemical analysis with monolayer-depth resolution.",1907.07272v1
2020-02-05,Gate-controlled photo-oxidation of graphene for electronic structure modification,"Graphene is an ultrathin material, which allows us to control surface
phenomena by means of field-effect gating. Among various surface phenomena,
photo-oxidation is known to be a facile method to largely control the
electronic structure of graphene. In this study, gate controllability of
photo-oxidation of graphene is thoroughly examined using a
field-effect-transistor configuration. The presence of water molecules enhances
gate controllability, which can be explained using water-oxygen co-adsorption
picture. In addition, the photo-oxidation reaction evolves from the edge and
proceeds towards the center of the graphene channel, which can be understood by
the fringing field effect. Semiconducting characteristics are successfully
obtained by narrowing of the graphene channel, suggesting possible formation of
a graphene nanoribbon under mild conditions, i.e., in air at room temperature.",2002.01694v1
2020-04-14,Structural dynamics in thermal-treatment of amorphous indium-oxide films,"Thermally-treating amorphous indium-oxide films is used in various basic
studies as a means of tuning the system disorder. In this process the
resistance of a given sample decreases while its amorphous structure and
chemical composition is preserved. The main effect of the process is an
increase in the system density which in turn leads to improved interatomic
overlap which is easily detected as improved conductivity. A similar effect has
been observed in studies of other amorphous systems that were subjected to
pressure. In the current work we show that the Raman spectra of amorphous
indium-oxide change in response to thermal-treatment in a similar way as in
pressure experiments performed on other disordered and amorphous systems. We
present a study of how thermal-treatment changes the system dynamics by
monitoring the resistance versus time of indium-oxide films following various
stages of thermal-treatment. The time dependence of the sample resistance fits
the stretched exponential law with parameters that change systematically with
further annealing. Implication of these results to slow dynamics phenomena that
are governed by the Kohlrausch's law are discussed.",2004.06322v1
2020-04-14,Temperature overshoot as the cause of physical changes in resistive switching devices during electro-formation,"Resistive switching devices based on transition metal oxides require
formation of a conductive filament in order for the device to be able to
switch. Such filaments have been proposed to form by the reduction of the oxide
due to application of the electric field, but this report seeks to rebut that
interpretation. Frequently reported physical changes during electro-formation
include delamination of electrodes, crystallization of functional oxide,
intermixing of electrode and oxide materials, and extensive loss of oxygen
presumably to the ambient. Here we show that most of these effects are not
inherent to the formation and switching processes and instead are due to an
experimental artifact: the discharge of parasitic capacitances in the forming
circuit. Discharge of typical BNC cables can raise the temperature of the
filament to between 2,000 and 5,000 K resulting in extensive physical changes.
Discharge and associated effects mentioned above can be eliminated using an
on-chip load element without affecting the ability to switch.",2004.06571v1
2020-12-21,Frequency Response of Metal-Oxide Memristors,"Memristors have been at the forefront of nanoelectronics research for the
last decade, offering a valuable component to reconfigurable computing. Their
attributes have been studied extensively along with applications that leverage
their state-dependent programmability in a static fashion. However, practical
applications of memristor-based AC circuits have been rather sparse, with only
a few examples found in the literature where their use is emulated at higher
frequencies. In this work, we study the behavior of metal-oxide memristors
under an AC perturbation in a range of frequencies, from 10^3 to 10^7 Hz.
Metal-oxide memristors are found to behave as RC low-pass filters and they
present a variable cut-off frequency when their state is switched, thus
providing a window of reconfigurability when used as filters. We further study
this behaviour across distinct material systems and we show that the usable
reconfigurability window of the devices can be tailored to encompass specific
frequency ranges by amending the devices' capacitance. This study extends
current knowledge on metal-oxide memristors by characterising their frequency
dependent characteristics, providing useful insights for their use in
reconfigurable AC circuits.",2012.11519v1
2021-01-18,Manipulating the anisotropic phase separation in strained VO2 epitaxial films by nanoscale ion-implantation,"Manipulating the strain induced poly-domains and phase transition in
correlated oxide material are important for high performance devices
fabrication. Though the electronic transport in the strained oxide film at
macroscopic scales can be directly measured, the anisotropic electronic state
and the controllable phase separation cross the insulator-to-metal transition
within nanoscale size are still elusive. Here, we selected VO2 crystal film as
a prototypical oxide and achieved the manipulation of anisotropy electronic
phase separation via injecting He+ nanobeam into VO2 film at room temperature.
In addition, this nanoscale phase separation was directly visualized by
infrared near-field imaging measurements, showing the pronounced and unique
cR-axis dependent anisotropy on VO2 surface. Our results offered new insights
towards understanding the anisotropic nanoscale phase separation in strained
metal oxide films.",2101.07093v2
2012-05-15,Probing individual layers in functional oxide multilayers by wavelength-dependent Raman scattering,"Integration of functional oxides on silicon requires the use of complex
heterostructures involving oxides of which the structure and properties
strongly depend on the strain state and strain-mediated interface coupling. The
experimental observation of strain-related effects of the individual components
remains challenging. Here we report a Raman scattering investigation of complex
multilayer BaTiO3/LaNiO3/CeO2/YSZ thin film structures on silicon. It is shown
that the Raman signature of the multilayers differs significantly for three
different laser wavelengths (633, 442 and 325 nm). Our results demonstrate that
Raman scattering at various wavelengths allows both the identification of the
individual layers of a functional oxide multilayers and monitoring their strain
state. It is shown that all layers of the investigated multilayer are strained
with respect to the bulk reference samples, and that strain induces a new
crystal structure in the embedded LaNiO3. Based on this, we demonstrate that
Raman scattering at various wavelengths offers a well-adapted, non-destructive
probe for the investigation of strain and structure changes, even in complex
thin film heterostructures.",1205.3334v2
2012-05-18,Surface oxide on thin films of yttrium hydride studied by neutron reflectometry,"The applicability of standard methods for compositional analysis is limited
for H-containing films. Neutron reflectometry is a powerful, non-destructive
method that is especially suitable for these systems due to the large negative
scattering length of H. In this work we demonstrate how neutron reflectometry
can be used to investigate thin films of yttrium hydride. Neutron reflectometry
gives a strong contrast between the film and the surface oxide layer, enabling
us to estimate the oxide thickness and oxygen penetration depths. A surface
oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride
films.",1205.4132v1
2017-04-25,Graphene oxide adsorptive power from better to more via an enhanced route in perspective,"Adsorption is one important way applied to water decontamination, where
carbon is commonly used as highly effective absorbent. Carbon of different
morphologies and structures normally demonstrate distinct capabilities to
adsorption-typed decontaminations. Graphene oxide is regarded as the oxidative
derivative of graphene, maintaining its 2D morphology-featuring structure while
location-dependently immobilized with a large amount of various
oxygen-involving functional moieties on both sides. Free-standing graphene
oxide tends to fully unfold in water and behave in macromolecular-like Brownian
motion. Therefore, high-performance adsorption occurs during the process of
interacting with large amount of sorbates, during which an unevenness of
effective adsorptive site distribution turns out for targeted matter due to
functional group-to-sorbate interaction mechanism differentiation as well as
groups'inherent location specifications. Thus, oriented manipulation of
surficial functional moieties and their site distribution is potentially a way
to further enhance the adsorptive performances, and this could go even better
if considering combining adsorption and an in-situ manipulation at the same
time.",1705.00523v1
2017-05-07,Two-Dimensional Arsenene Oxide: A Realistic Large-gap Quantum Spin Hall Insulator,"Searching for two-dimensional (2D) realistic materials able to realize
room-temperature quantum spin Hall (QSH) effects is currently a growing field.
Here, we through ab initio calculations to identify arsenene oxide, AsO, as an
excellent candidate, which demonstrates high stability, flexibility, and
tunable spin-orbit coupling (SOC) gaps. In contrast to known pristine or
functionalized arsenene, the maximum nontrivial band gap of AsO reaches 89 meV,
and can be further enhanced to 130 meV under biaxial strain. By sandwiching 2D
AsO between BN sheets, we propose a quantum well in which the band topology of
AsO is preserved with a sizeable band gap. Considering that AsO having fully
oxidized surfaces are naturally stable against surface oxidization and
degradation, this functionality provides a viable strategy for designing
topological quantum devices operating at room temperature.",1705.02538v1
2017-11-26,Manganese oxide nano flakes onto simultaneously activated defective CNTs for the creation of CNTs-graphene supported oxygen reduction composite catalysts applied in air fuel cell,"Rational combination holds the key for non-precious metal oxides and economic
carbon materials to the creation of high performance air electrode materials.
Carbon nanotubes (CNTs)-supported manganese oxides composite catalysts (CMnCs)
were obtained by reacting commercial CNTs with MnO$_4^-$ in diluted H$_2$SO$_4$
with cancelling conventional hydrothermal processing or adding surfantant
templates. CMnCs were then assembled into commercial air cathodes equipped in
metal air fuel cells. CNTs demonstrated structurally much defective. Outer CNT
walls were cracked into graphene nano pieces yet remaining partially attached
to inner carbon tubes during synthesis. This exposure of graphene planes
exhibited additional oxygen reduction reactivity. Manganese oxide flakes
identified as {\gamma}-MnOOH were homogeneously grown on surfaces of CNTs at
nano sizes. Its deposition density was closely related to the additive amount
of KMnO$_4$ with regard to CNTs. The ORR activities of sole CMnCs exceeded both
raw CNTs and competent market catalysts under identical conditions, and with
current production technics the CMnCs-ingrediented air fuel cells were capable
of outputting ~15% more power at 100 mA/cm$^2$.",1711.09403v1
2018-06-11,Study of the oxidation process of crystalline powder of In 2 S 3 and thin films obtained by Dr Blade method,"Good quality In2S3 films were grown by Dr Blade method from a powder
synthesized in a chemical bath, and oxidized to obtain In2O3 films and films of
intermediate composition. The oxidation process and kinetics are studied by
means of thermogravimetric analysis, which shows complex phenomena. The study
is completed by scanning electron microscopy and EDX measurements. X-ray
diffraction and UV-visible spectroscopy results are also shown. The oxidation
process begins significantly above 420 C, and it appears that at least one
intermediate crystal phase takes place in the solid solution, suggesting that
the replacement of sulfur by oxygen atoms occurs at different temperatures in
the different crystallographic sites. The obtained samples show a band gap
varying continuously between 1.94 eV and 3.72 eV.",1806.03946v1
2018-08-24,Thermally Oxidized Two-dimensional TaS2 as a High-\k{appa} Gate Dielectric for MoS2 Field-Effect Transistors,"We report a new approach to integrating high-\k{appa} dielectrics in both
bottom- and top-gated MoS2 field-effect transistors (FETs) through thermal
oxidation and mechanical assembly of layered twodimensional (2D) TaS2. Combined
X-ray photoelectron spectroscopy (XPS), optical microscopy, atomic force
microscopy (AFM), and capacitance-voltage (C-V) measurements confirm that
multilayer TaS2 flakes can be uniformly transformed to Ta2O5 with a high
dielectric constant of ~ 15.5 via thermal oxidation, while preserving the
geometry and ultra-smooth surfaces of 2D TMDs. Top-gated MoS2 FETs fabricated
using the thermally oxidized Ta2O5 as gate dielectric demonstrate a high
current on/off ratio approaching 106, a subthreshold swing (SS) down to 61
mV/dec, and a field-effect mobility exceeding 60 cm2V-1 s-1 at room
temperature, indicating high dielectric quality and low interface trap density.",1808.08303v1
2018-08-27,A Micro-mechanical Approach to Model Thermo-Oxidative Aging in Elastomers,"This paper presents a micro-mechanical approach to describe the effects of
thermo-oxidation on the constitutive behavior of aged elastomers at the
long-range timescales. In particular, this model focuses on the effects of
thermo-oxidative aging on the quasi-static mechanical response of elastomer and
their inelastic responses such as Mullins effect and permanent set over time.
The model is validated with respect to a comprehensive set of experimental data
designed by Johlitz et al. to capture thermo-oxidative effect on constitutive
behavior of elastomers. Besides accuracy, the model is relatively simple and
easy to fit. It requires ten material parameters, all with clear physical
meaning, which can be derived from only one set of experiment.",1808.08934v2
2018-08-28,Metal Oxidation Kinetics and the Transition from Thin to Thick Films,"We report an investigation of growth kinetics and transition from thin to
thick films during metal oxidation. In the thin film limit (< 20 nm), Cabrera
and Mott's theory is usually adopted by explicitly considering ionic drift
through the oxide in response to electric fields, where the growth kinetics
follow an inverse logarithmic law. It is generally accepted that Wagner's
theory, involving self-diffusion, is valid only in the limit of thick film
regime and leads to parabolic growth kinetics. Theory presented here unifies
the two models and provides a complete description of oxidation including the
transition from thin to thick film. The range of validity of Cabrera and Mott's
theory and Wagner's theory can be well defined in terms of the Debye-Huckel
screening length. The transition from drift-dominated ionic transport for thin
film to diffusion-dominated transport for thick film is found to strictly
follow the direct logarithmic law that is frequently observed in many
experiments.",1808.09570v1
2019-02-25,Molybdenum oxide hole selective transport layer by hot wire oxidation-sublimation deposition for silicon heterojunction solar cells,"In this article, a novel hot wire oxidation-sublimation deposition (HWOSD)
technique was developed to prepare molybdenum oxide (MoOx) thin films with high
quality. Silicon heterojunction (SHJ) solar cells with the HWOSD MoOx as a hole
selective transport layer (HSL) were fabricated. Thickness of the MoOx layer
and annealing process of the solar cells were studied and optimized. A power
conversion efficiency up to 21.10% was achieved on a SHJ solar cell using a
14nm MoOx layer as the HSL. Dark current density-voltage-temperature (J-V-T)
characteristics of the SHJ solar cell were measured at the temperatures from
200K to 380K. Transport processes including thermionic emission of electrons
over the potential barrier and quantum assisted tunneling of holes through the
gap states in the MoOx layer were proposed for the MoOx/n c-Si heterojunction.
The investigation of the transport mechanisms provides us a better
understanding of the characteristics of the novel SHJ solar cells and it is
helpful for us to fully demonstrate the potential of such kind of solar cells
in the future.",1902.09127v1
2019-03-28,Quantized conductance in a one-dimensional ballistic oxide nanodevice,"Electric-field effect control of two-dimensional electron gases (2-DEG) has
enabled the exploration of nanoscale electron quantum transport in
semiconductors. Beyond these classical materials, transition metal-oxide-based
structures have d-electronic states favoring the emergence of novel quantum
orders absent in conventional semiconductors. In this context, the
LaAlO3/SrTiO3 interface that combines gate-tunable superconductivity and
sizeable spin-orbit coupling is emerging as a promising platform to realize
topological superconductivity. However, the fabrication of nanodevices in which
the electronic properties of this oxide interface can be controlled at the
nanoscale by field-effect remains a scientific and technological challenge.
Here, we demonstrate the quantization of conductance in a ballistic quantum
point contact (QPC), formed by electrostatic confinement of the LaAlO3/SrTiO3
2-DEG with a split-gate. Through finite source-drain voltage, we perform a
comprehensive spectroscopic investigation of the 3d energy levels inside the
QPC, which can be regarded as a spectrometer able to probe Majorana states in
an oxide 2-DEG.",1903.12134v1
2019-04-11,Asymmetric Lattice Disorder Induced at Oxide Interfaces,"Control of order-disorder phase transitions is a fundamental materials
science challenge, underpinning the development of energy storage technologies
such as solid oxide fuel cells and batteries, ultra-high temperature ceramics,
and durable nuclear waste forms. At present, the development of promising
complex oxides for these applications is hindered by a poor understanding of
how interfaces affect lattice disordering processes and defect transport. Here
we explore the evolution of local disorder in ion-irradiated La$_2$Ti$_2$O$_7$
/ SrTiO$_3$ thin film heterostructures using a combination of high-resolution
scanning transmission electron microscopy (STEM), position-averaged convergent
beam electron diffraction (PACBED), electron energy loss spectroscopy
(STEM-EELS), and \textit{ab initio} theory calculations. We observe highly
non-uniform lattice disordering driven by asymmetric oxygen vacancy formation
across the interface. Our calculations indicate that this asymmetry results
from differences in the polyhedral connectivity and vacancy formation energies
of the two interface components, suggesting ways to manipulate lattice disorder
in functional oxide heterostructures.",1904.05932v2
2019-04-18,Anomalous conduction band fluctuation in silicon carbide metal-oxide-semiconductor structures revealed by electrical characterization of field effect transistors combined with self-consistent numerical calculations,"We determined the interface state density ($D_{\rm it}$) distributions in the
vicinity of the conduction band edge in silicon carbide (SiC)
metal-oxide-semiconductor (MOS) structures by reproducing the experimental
current-voltage characteristics of MOS field effect transistors (MOSFETs) with
numerical calculations. In the calculation, potential distributions and energy
sub-bands in the inversion layer were calculated by solving Poisson and
Schr\""{o}dinger equations, respectively. We demonstrate that gate
characteristics of the MOSFETs are well described by considering that the
interface states are caused by fluctuation of free-electron density of states
in a two-dimensional system. The $D_{\rm it}$ distributions are almost uniquely
determined by the oxide formation process (as oxidation or interface
nitridation) and independent of the acceptor concentration
($3\times10^{15}-1\times10^{18}\ {\rm cm^{-3}}$).",1904.08574v1
2019-04-21,Oxidized silicon sulfide: stability and electronic properties of a novel two-dimensional material,"Isolated oxygen impurities and fully oxidized structures of four stable
two-dimensional (2D) SiS structures are investigated by {\em ab initio} density
functional calculations. Binding energies of oxygen impurities for all the four
2D SiS structures are found larger than those for phosphorene, due to the lower
electronegativity of Si atoms. The most stable configurations of isolated
oxygen impurities for different 2D SiS structures are decided and the
corresponding 2D structures with saturated oxidation (SiSO) are predicted.
Among all the four fully oxidized structures, $\alpha$-SiSO is demonstrated to
be stable by phonon spectra calculations and molecular dynamics (MD)
simulations. Electronic structure calculations indicate that $\alpha$-SiSO
monolayer is semiconducting with a direct band gap of ${\approx}2.28$~eV, which
can be effectively tuned by in-layer strain. The value of band gap and
thermodynamic stability are found depending sensitively on the saturation level
of oxygen.",1904.09614v1
2019-08-19,Symbolic Regression Discovery of New Perovskite Catalysts with High Oxygen Evolution Reaction Activity,"Symbolic regression (SR) is an emerging method for building analytical
formulas to find models that best fit data sets. Here, SR was used to guide the
design of new oxide perovskite catalysts with improved oxygen evolution
reaction (OER) activities. An unprecedentedly simple descriptor, {\mu}/t, where
{\mu} and t are the octahedral and tolerance factors, respectively, was
identified, which accelerated the discovery of a series of new oxide perovskite
catalysts with improved OER activity. We successfully synthesized five new
oxide perovskites and characterized their OER activities. Remarkably, four of
them, Cs0.4La0.6Mn0.25Co0.75O3, Cs0.3La0.7NiO3, SrNi0.75Co0.25O3, and
Sr0.25Ba0.75NiO3, outperform the current state-of-the-art oxide perovskite
catalyst, Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF). Our results demonstrate the potential
of SR for accelerating data-driven design and discovery of new materials with
improved properties.",1908.06778v1
2019-11-12,Structure and Chemistry of Graphene Oxide in Liquid Water from First Principles,"Graphene oxide is a rising star among 2D materials, yet its interaction with
liquid water remains a fundamentally open question: experimental
characterization at the atomic scale is difficult, and modelling by classical
approaches cannot properly describe chemical reactivity. Here, we bridge the
gap between simple computational models and complex experimental systems, by
realistic first-principles molecular simulations of graphene oxide (GO) in
liquid water. We construct chemically accurate GO models and study their
behavior in water, showing that oxygen-bearing functional groups (hydroxyl and
epoxides) are preferentially clustered on the graphene oxide layer. We
demonstrated the specific properties of GO in water, an unusual combination of
both hydrophilicity and fast water dynamics. Finally, we evidence that GO is
chemically active in water, acquiring an average negative charge of the order
of 10~mC m$^{-2}$. The ab initio modelling highlights the uniqueness of GO
structures for applications as innovative membranes for desalination and water
purification.",1911.04987v2
2019-11-14,Bandgap Measurement of Reduced Graphene Oxide Monolayers through Scanning Tunnelling Spectroscopy,"Most popular atomically thin carbon material, called graphene, has got no
band gap and this particular property of graphene makes it less useful from the
aspect of nanoscale transistor devices. The band gap can be introduced in the
graphene if it is synthesized through chemical route. First, Graphene Oxide
(GO) is made which further go under reduction and turns into Reduced Graphene
Oxide (RGO). Band structure investigation of monolayer sheets of reduced
graphene oxide (RGO) by Scanning Tunneling Spectroscopy (STS) has been
investigated here. The GO sheets are 1-1.2 nm thick and become more thinner
after reduction. The band gap of GO was found in the range of 0.8 eV. The RGO
showed up a variety of band structure. RGO opens a new field of study of
atomically thin layers of carbon because it has got non zero band gap which is
not the case for graphene.",1911.06230v1
2019-11-15,Yttrium Tantalum Oxynitride Multiphases as Photoanodes for Water Oxidation,"Perovskite yttrium tantalum oxynitride is theoretically proposed as a
promising semiconductor for solar water splitting because of the predicted
bandgap and energy positions of band edges. In experiment, however, we show
here that depending on processing parameters, yttrium tantalum oxynitrides
exist in multiphases, including the desired perovskite YTaON2, defect fluorite
YTa(O,N,o)4, and N-doped YTaO4. These multiphases have bandgaps ranging between
2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4,
perovskite main phase, and fluorite main phase derived from crystalline
fergusonite oxide precursors exhibit interesting photoelectrochemical
performances for water oxidation, while the defect fluorite derived from low
crystallized scheelite-type oxide precursors show negligible activity.
Preliminarily measurements show that loading IrOx cocatalyst on N-doped YTaO4
significantly improves its photoelectrochemical performance encouraging further
studies to optimize this new material for solar fuel production.",1911.06550v1
2019-11-27,"Controlled Preparation, Characterization, and Bandgap Modulation of RF Sputtered Antimony Vanadium Oxide (SbVO4) Thin Films","In this paper, RF sputtered antimony vanadium oxide (SbVO4) thin films and
its characterization are reported. High purity sputtering targets were
fabricated by sintering a mixture of Sb2O3 and V2O5 powders. Thin films were
deposited by reactive sputtering at various temperature and argon/oxygen
partial pressures. Several growth parameters and surface chemistry were studied
by applying numerous optical and electrochemical characterization technique. It
is found that SbVO4 exhibits an indirect band gap in the range of 1.89 eV to
2.36 eV and has desirable valence band position to drive water oxidation
reaction under illumination. The bandgap depends heavily on stoichiometry of
the film and can be modulated by incorporating controlled amount of oxygen gas
in plasma environment. Optimized SbVO4 photoanodes was designed and tested for
photoelectrochemical water oxidation catalysis. Preliminary studies show that
these electrodes possess n-type catalytic behavior in alkaline media. The
prepared SbVO4 thin films, with typical film thickness was around 400 nm,
contain nanoparticles having the sizes of 10-15 nm.",1911.12171v1
2020-03-06,Emerging classes of antioxidant to cancer therapy: a review of clinical and experimental studies,"This review mainly focuses on the relation between antioxidants with cancer
therapy. Antioxidants have been reported to play an essential role to reduce
free radical species. Free radicals commonly cause oxidative damage which is a
common factor in the aging process, and also the vital factor of formation, and
development of major disease specially cancer. Although, since last many
decades several antioxidants belong to natural and synthetic origin have been
tested in clinical trials against oxidative stress, however these clinical
trials end up with undesirable effects. This review also complied with the most
recent findings of oxidative stress, highlighting of free racial production,
and its related oxidative damage at cellular and molecular level, with the new
and existing natural and synthetic classes of free radical scavenger and their
related clinical trials.",2003.04538v1
2020-03-25,Birefringent Graphene Oxide Liquid Crystals in Micro-channels for Optical Switch,"We propose a mechanical-hydrodynamical experimental setup in which the
microfluidic motion manipulates the optical birefringence of levitated graphene
oxide liquid crystal. The birefringence of the sample is changed by flowing
graphene oxide liquid crystal in the micro-channel. By measuring the ordinary
and extraordinary refractive indices at five flow rates, one can determine the
value of the birefringence of the samples, precisely. Our results demonstrate
that, by adjusting the concentration and flow rate of dispersion of the
graphene oxide nano flakes, the induced birefringence can be controlled. It is
also shown that this approach can be used as an optical switch.",2003.11600v1
2020-05-07,"Combining density functional theories to correctly describe the energy, lattice structure and electronic density of functional oxide perovskites","Functional oxide perovskites are the pillar of cutting-edge technological
applications. Density functional theory (DFT) simulations are the theoretical
methods of choice to understand and design perovskite materials. However, tests
on the reliability of DFT to describe fundamental properties of oxide
perovskites are scarce and mostly ill-defined due to a lack of rigorous
theoretical benchmarks for solids. Here, we present a quantum Monte Carlo
benchmark study of DFT on the archetypal perovskite BaTiO$_{3}$ (BTO). It shows
that no DFT approximation can simultaneously reproduce the energy, structure,
and electronic density of BTO. Traditional protocols to select DFT
approximations are empirical and fail to detect this shortcoming. An approach
combining two different non-empirical DFT schemes, ""SCAN"" and ""HSE06"", is able
to holistically describe BTO with accuracy. Combined DFT approaches should thus
be considered as a promising alternative to standard methods for simulating
oxide perovskites.",2005.03792v1
2020-05-15,Optimization of allotropic and hardness of aluminum oxide coating by PEO,"One of the most important methods of producing materials and oxide coating is
plasma electrolytic oxidation (PEO). Coatings made on aluminum in PEO method
have two allotropes of $\alpha$-Al$_2$O$_3$ and $\gamma$-Al$_2$O$_3$. Coatings
containing $\alpha$-Al$_2$O$_3$ have more hardness and wear resistance;
therefore, the main goal of the present study is to optimize aluminum oxide
allotrope for increasing the ratio of $\alpha$-Al$_2$O$_3$ in coating made with
PEO method. Results of the present study shows that the optimum electrolyte
compound for making highest phase of $\alpha$-Al$_2$O$_3$ has 2.9 g/lit of KOH,
1.15 g/lit of Na4P2O7, and 0.34 g/lit of NaAlO2 and ratio of highest allotropic
pick of $\alpha$-Al$_2$O$_3$ to highest allotropic pick of $\gamma$-Al$_2$O$_3$
(in XRD test) in the optimum condition is 0.622 and hardness is 1648 Vickers.",2005.07471v1
2020-06-19,Predicting the phase stability of multi-component high entropy compounds,"A generic method to estimate the relative feasibility of formation of high
entropy compounds in a single phase, directly from first principles, is
developed. As a first step, the relative formation abilities of 56
multi-component, AO, oxides were evaluated. These were constructed from 5
cation combinations chosen from A={Ca, Co, Cu, Fe, Mg, Mn, Ni, Zn}. Candidates
for multi-component oxides are predicted from descriptors related to the
enthalpy and configurational entropy obtained from the mixing enthalpies of two
component oxides. The utility of this approach is evaluated by comparing the
predicted combinations with the experimentally realized entropy stabilized
oxide, (MgCoCuNiZn)O. In the second step, Monte Carlo simulations are utilized
to investigate the phase composition and local ionic segregation as a function
of temperature. This approach allows for the evaluation of potential secondary
phases, thereby making realistic predictions of novel multi-component compounds
that can be synthesized.",2006.11231v2
2020-06-24,Tip-induced oxidation of silicene nano-ribbons,"We report on the oxidation of self-assembled silicene nanoribbons grown on
the Ag(110) surface using Scanning Tunneling Microscopy and High-Resolution
Photoemission Spectroscopy. The results show that silicene nanoribbons present
a strong resistance towards oxidation using molecular oxygen. This can be
overcome by increasing the electric field in the STM tunnel junction above a
threshold of +2.6 V to induce oxygen dissociation and reaction. The higher
reactivity of the silicene nanoribbons towards atomic oxygen is observed as
expected. The HR-PES confirm these observations: Even at high exposures of
molecular oxygen, the Si 2p core-level peaks corresponding to pristine silicene
remain dominant, reflecting a very low reactivity to molecular oxygen. Complete
oxidation is obtained following exposure to high doses of atomic oxygen; the Si
2p core level peak corresponding to pristine silicene disappears.",2006.13780v1
2020-08-06,Electrochemical oxidation of CO on Cu single crystals under alkaline conditions,"We perform a joint experimental-theoretical study of the electrochemical
oxidation of CO on copper (Cu) under alkaline conditions. Using cyclic
voltammetry on Cu single crystal surfaces, we demonstrate that both Cu terraces
and steps show CO oxidation activity at potentials just slightly positive
(0.03-0.14 V) of the thermodynamic equilibrium potential. The overpotentials
are 0.23-0.12 V lower than that of gold (approx. 0.26 V), which up until now
has been considered to be the most active catalyst for this process. Our
theoretical calculations suggest that Cu's activity arises from the
advantageous combination of simultaneous *OH adsorption under CO oxidation
potentials and surmountable *CO-*OH coupling barriers. Experimentally observed
onset potentials are in agreement with the computed onsets of *OH adsorption.
We furthermore show that the onsets of *OH adsorption on steps are more
affected by *CO-*OH interactions than on terraces due to a stronger competitive
adsorption. Overall, Cu(100) shows the lowest overpotential (0.03 V) of the
facets considered.",2008.02675v2
2020-08-25,Cathode Materials for Lithium Ion Batteries (LIBs): A Review on Materials related aspects towards High Energy Density LIBs,"This article reviews the development of cathode materials for secondary
lithium ion batteries since its inception with the introduction of lithium
cobalt oxide in early 1980s. The time has passed and numerous cathode materials
are designed and developed to realize not only the enhanced capacity but also
the power density simultaneously. However, there are numerous challenges such
as the cyclic stability of cathode materials, their structural and thermal
stability, higher operating voltage together with high ionic and electronic
conductivity for efficient ion and charge transport during charging and
discharging. This article will cover the development of materials in
chronological order classifying as the lithium ion cathode materials in
different generations. The ternary oxides such as LiTMOx (TM=Transition Metal)
are considered as the first generation materials, whereas modified ternary and
quaternary oxide systems are considered as the second generation materials. The
current i.e. third generation includes complex oxide systems with higher
lithium content such as Li2TMSiO4 aiming for higher energy density. Further,
developments are heading towards lithium metal based batteries with a
possibility for very high energy densities.",2008.10896v2
2020-09-10,Effect of oxygen adsorption and oxidation on the strain state of Pd nanocrystals,"X-ray powder diffraction using a synchrotron light source reveals significant
modifications to both morphology and strain state in Palladium nanocubes after
oxidation. Short-range strain measured by the static component of the
Debye-Waller coefficient is observed to be higher in the oxidized
nanoparticles; while long-range strain related to the line broadening of the
diffraction peaks is seen to decrease. Using multiscale modelling with
classical molecular dynamics and density functional theory, we connect the
decrease in long-range strain to the increased truncation of the oxidized
nanocubes, while the higher short-range strain is shown to be due to surface
softening from oxygen adsorption. Different surface disorder on different
crystallographic facets lead to opposing trends for oxygen activation on the
different exposed surfaces of the truncated nanoparticles.",2009.04736v1
2020-10-20,Signatures of technetium oxidation states: a new approach,"A general strategy for the determination of Tc oxidation state by new
approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L3
edge is shown. A comprehensive series of 99Tc compounds, ranging from oxidation
states I to VII, was measured and subsequently simulated within the framework
of crystal-field multiplet theory. The observable trends in the absorption edge
energy shift in combination with the spectral shape allow for a deeper
understanding of complicated Tc coordination chemistry. This approach can be
extended to numerous studies of Tc systems as this method is one of the most
sensitive methods for accurate Tc oxidation state and ligand characterization.",2010.10164v2
2020-11-12,Topological phonons in oxide perovskites controlled by light,"Perovskite oxides exhibit a rich variety of structural phases hosting
different physical phenomena that generate multiple technological applications.
We find that topological phonons, i.e., nodal rings, nodal lines, and Weyl
points, are ubiquitous in oxide perovskites in terms of structures (tetragonal,
orthorhombic, and rhombohedral), compounds (BaTiO3, PbTiO3, and SrTiO3), and
external conditions (photoexcitation, strain, and temperature). In particular,
in the tetragonal phase of these compounds, all types of topological phonons
can simultaneously emerge when stabilized by photoexcitation, whereas the
tetragonal phase stabilized by thermal fluctuations only hosts a more limited
set of topological phonon states. Additionally, we find that the photoexcited
carrier concentration can be used to tune the topological phonon states and
induce topological transitions even without associated structural phase
changes. Overall, we propose oxide perovskites as a versatile platform in which
to study topological phonons and their manipulation with light.",2011.06269v1
2020-11-16,Artificial oxide heterostructures with non-trivial topology,"In the quest for topological insulators with large band gaps,
heterostructures with Rashba spin-orbit interactions come into play. Transition
metal oxides with heavy ions are especially interesting in this respect. We
discuss the design principles for stacking oxide Rashba layers. Assuming a
single layer with a two-dimensional electron gas (2DEG) on both interfaces as a
building block, a two-dimensional topological insulating phase is present when
negative coupling between the 2DEGs exists. When stacking multiple building
blocks, a two-dimensional or three-dimensional topological insulator is
artificially created, depending on the intra- and interlayer coupling strengths
and the number of building blocks. We show that the three-dimensional
topological insulator is protected by reflection symmetry, and can therefore be
classified as a topological crystalline insulator. In order to isolate the
topological states from bulk states, the intralayer coupling term needs to be
quadratic in momentum. It is described how such a quadratic coupling could
potentially be realized by taking buckling within the layers into account. The
buckling, thereby, brings the idea of stacked Rashba system very close to the
alternative approach of realizing the buckled honeycomb lattice in
[111]-oriented perovskite oxides.",2011.07988v1
2020-11-17,Effect of Substrate Roughness on Oxidation Resistance of an Aluminized Ni-Base Superalloy,"In the present work, it is shown that the surface preparation method used on
two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD)
is one of the most important factors determining the oxidation resistance of
aluminized Ni-based superalloys. It was found that grit blasting the substrate
surface negatively affects the oxidation resistance of the aluminized coatings.
For grit blasted and aluminized IN 625, a thicker outer NiAl coating was formed
compared to that of IN 738. In contrast, no effect on NiAl coating thickness
was found for grit blasted and aluminized IN 738. However, a thicker
interdiffusion zone (IDZ) was observed. It was shown that the systems with
grit-blasted surfaces reveal worse oxidation resistance during thermal shock
tests, namely, a higher mass loss was observed for both grit blasted and
aluminized alloys, as compared to ground and aluminized alloys. A possible
reason for this effect of remaining alumina particles originating from surface
grit blasting on the diffusion processes and stress distribution at the
coating/substrate is proposed.",2011.08921v1
2021-02-15,Universal Fabrication of Two-Dimensional Electron Systems in Functional Oxides,"Two-dimensional electron systems (2DESs) in functional oxides are promising
for applications, but their fabrication and use, essentially limited to
SrTiO$_3$-based heterostructures, are hampered by the need of growing complex
oxide over-layers thicker than 2~nm using evolved techniques. This work shows
that thermal deposition of a monolayer of an elementary reducing agent suffices
to create 2DESs in numerous oxides.",2102.07748v1
2021-02-23,Combined Iodine- and Sulfur-based Treatments for an Effective Passivation of GeSn Surface,"GeSn alloys are metastable semiconductors that have been proposed as building
blocks for silicon-integrated short-wave and mid-wave infrared photonic and
sensing platforms. Exploiting these semiconductors requires, however, the
control of their epitaxy and their surface chemistry to reduce non-radiative
recombination that hinders the efficiency of optoelectronic devices. Herein, we
demonstrate that a combined sulfur- and iodine-based treatments yields
effective passivation of Ge and Ge0.9Sn0.1 surfaces. X-ray photoemission
spectroscopy and in situ spectroscopic ellipsometry measurements were used to
investigate the dynamics of surface stability and track the reoxidation
mechanisms. Our analysis shows that the largest reduction in oxide after HI
treatment, while HF+(NH4)2S results in a lower re-oxidation rate. A combined
HI+(NH4)2S treatment preserves the lowest oxide ratio <10 % up to 1 hour of air
exposure, while less than half of the initial oxide coverage is reached after 4
hours. These results highlight the potential of S- and I-based treatments in
stabilizing the GeSn surface chemistry thus enabling a passivation method that
is compatible with materials and device processing.",2102.11908v1
2021-03-30,Oxide spin-orbitronics: spin-charge interconversion and topological spin textures,"Quantum oxide materials possess a vast range of properties stemming from the
interplay between the lattice, charge, spin and orbital degrees of freedom, in
which electron correlations often play an important role. Historically, the
spin-orbit coupling was rarely a dominant energy scale in oxides. It however
recently came to the forefront, unleashing various exotic phenomena connected
with real and reciprocal-space topology that may be harnessed in spintronics.
In this article, we review the recent advances in the new field of oxide
spin-orbitronics with a special focus on spin-charge interconversion from the
direct and inverse spin Hall and Edelstein effects, and on the generation and
observation of topological spin textures such as skyrmions. We highlight the
control of spin-orbit-driven effects by ferroelectricity and give perspectives
for the field.",2103.16271v1
2021-03-30,Cluster Catalysis with Lattice Oxygen: Tracing Oxygen Transport from a Magnetite(001) Support onto Small Pt Clusters,"Oxidation catalysis on reducible oxide-supported small metal clusters often
involves lattice oxygen. In the present work, we trace the path of lattice
oxygen from Fe3O4(001) onto small Pt clusters during the CO oxidation, aiming
at differentiating whether the reaction takes place at the cluster/support
interface or on the cluster. While oxygen vacancies form on many other
supports, magnetite maintains its surface stoichiometry upon reduction thanks
to a high cation mobility. In order to investigate whether size-dependent
oxygen affinities play a role, we study two specific cluster sizes, Pt5 and
Pt19. By separating different reaction steps in our experiment, lattice oxygen
can be accumulated on the clusters. Temperature programmed desorption (TPD) and
sophisticated pulsed valve experiments indicate that the CO oxidation takes
place on the Pt clusters rather than at the interface. Scanning tunneling
microscopy (STM) shows a decrease in apparent height of the clusters, which
density functional theory (DFT) explains as a restructuring following lattice
oxygen reverse spillover.",2103.16413v2
2021-04-04,Characterization of Nb22O54 microrods grown from niobium oxide powders recovered from mine tailings,"In this work, the possibility of using niobium oxide recovered from tailings
from the Penouta Sn-Nb-Ta deposit (located at the North of Spain) as starting
material for growing microstructures is demonstrated. The properties of the
starting material have been studied to understand its crystal structure,
quality and purity. Recovered niobium oxide powders are mainly of TT-Nb2O5.
These powders have been used to grow Nb22O54 microrods by an evaporation method
in an argon atmosphere. Different characterization techniques (X-Ray
diffraction, scanning electron microscopy, micro-Raman spectroscopy,
luminescence) have been used to determine the properties of Nb22O54 microrods,
mainly focusing on the crystal quality and refractive index. The present study
opens the way to the transformation of waste (mine tailings) into a material of
high technological value as niobium oxide, and its reintroduction into the
value chain for a wide range of applications, from coatings to batteries and
supercapacitors.",2104.01640v1
2021-04-28,"A Quantum Chemical Approach for the Characterization of the Interaction Potential of Propylene Oxide with Rare-Gas Atoms (He, Ne, Ar)","Propylene oxide is one of the simplest organic chiral molecules and has
attracted considerable interest from the scientific community a few years ago,
when it was discovered in the interstellar medium. Here, we report a
preliminary study on the interaction between propylene oxide and rare-gas
atoms, specifically He, Ne, and Ar. The interaction potentials as a function of
the distance between the center-of-mass of propylene oxide and the
rare-gas-atom are calculated for fourteen leading configurations at
CCSD(T)/aug-cc-pVDZ level of theory. Symmetry Adapted Perturbation Theory has
been employed for the analysis of the intermolecular potential, revealing that
most of the contribution is given by dispersion and exchange forces.",2104.13670v1
2021-05-31,Stable High Power deep-UV Enhancement Cavity in Ultra High Vacuum with Fluoride Coatings,"We demonstrate the superior performance of fluoride coated versus oxide
coated mirrors in long term vacuum operation of a high power deep-ultraviolet
enhancement cavity. In high vacuum ($10^{-8}$ mbar), the fluoride optics can
maintain up to a record-high 10 w of stable intracavity power on one hour time
scales, whereas for the oxide optics, we observe rapid degradation at lower
intracavity powers with a rate that increases with power. After observing
degradation in high vacuum, we can recover the fluoride and oxide optics with
oxygen; however, this recovery process becomes ineffective after several
applications. For fluoride coatings, we see that initial UV conditioning in an
oxygen environment helps to improve the performances of the optics. In
oxygen-rich environments from $\sim 10^{-4}$ mbar to 1 mbar, the fluoride
optics can stably maintain up to 20 W of intracavity power on several-hour time
scales whereas for the oxide optics there is immediate degradation with a rate
that increases with decreasing oxygen pressure.",2105.14977v1
2021-06-04,A statistical analysis of pores and micro-cracks in nuclear graphite,"Microstructure characterization is of great value to understanding nuclear
graphite's properties and irradiation behavior. However, graphite is soft and
could be easily damaged during sample preparation. A three-step polishing
method involving mechanical polishing, ion milling and rapid oxidation is
proposed for graphite. Ion milling is adopted to remove the broken graphite
pieces produced by mechanical polishing. Rapid oxidation is then adopted to
remove irradiation-induced damage layer during ion milling. The Raman spectra
show very low G peak width and ID/IG ratio after rapid oxidation, indicating a
surface completely free from artificial defects. The micro-cracks which were
conventionally observed via a transmission electron microscope can be observed
on rapid-oxidized surface in a scanning electron microscope. By digital image
processing, the micro-cracks along with the gas-escape pores in nuclear
graphite IG-110 are statistically analyzed. Porosity's distributions on crack
(pore) size (spanning from 10 nm to 100 um) are given, which could help to
understand and simulate graphite's performances in reactors.",2106.02321v1
2021-07-02,Machine learning of microscopic ingredients for graphene oxide/cellulose interaction,"Understanding the role of microscopic attributes in nanocomposites allows for
a controlled and, therefore, acceleration in experimental system designs. In
this work, we extracted the relevant parameters controlling the graphene oxide
binding strength to cellulose by combining first-principles calculations and
machine learning algorithms. We were able to classify the systems among two
classes with higher and lower binding energies, which are well defined based on
the isolated graphene oxide features. By a theoretical X-ray photoelectron
spectroscopy analysis, we show the extraction of these relevant features.
Additionally, we demonstrate the possibilities of a refined control within a
machine learning regression between the binding energy values and the system's
characteristics. Our work presents a guiding map to the control graphene
oxide/cellulose interaction.",2107.01040v1
2021-07-05,"First Principles, Explicit Interface Studies of Oxygen Vacancy and Chloride in Alumina Films for Corrosion Applications","Pitting corrosion is a much-studied and technologically relevant subject.
However, the fundamental mechanisms responsible for the breakdown of the
passivating oxide layer are still subjects of debate. Chloride anions are known
to accelerate corrosion; relevant hypotheses include Cl insertion into
positively charged oxygen vacancies in the oxide film, and Cl adsorption on
passivating oxide surfaces, substituting for surface hydroxyl groups. In this
work, we conduct large-scale first principles modeling of explicit
metal/Al(2)O(3) interfaces to investigate the energetics and electronic
structures associated with these hypotheses. The explicit interface models
allow electron transfer that mimics electrochemical events, and the
establishment of the relation between atomic structures at different interfaces
and the electronic band alignment. For multiple model interfaces, we find that
doubly charged oxygen vacancies, which are key ingredients of the point defect
model (PDM) often used to analyze corrosion data, can only occur in the
presence of a potential gradient that raises the voltage. Cl-insertion into
oxide films can be energetically favorable in some oxygen vacancy sites,
depending on the voltage. We also discuss the challenges associated with
explicit DFT modeling of these complex interfaces.",2107.02251v1
2021-09-30,Alkaline CO electro-oxidation: Mechanistic Differences between Copper and Gold Single Crystals and Peculiarities of various Copper Facets,"Understanding CO electro-oxidation is crucial towards designing catalysts for
electrochemically oxidizing complex organic molecules. Earth-abundant Copper
(Cu) has recently been demonstrated to exhibit high alkaline CO
electro-oxidation activity, rivaling the previously acclaimed Gold (Au).
Herein, we combine single crystal rotating disc electrode (RDE) experiments and
ab initio microkinetic modeling to understand the underlying reaction
mechanisms on Cu and Au surfaces. Cu exhibits a facet-dependent activity with
Cu(111) having a 0.27 V lower overpotential than Au(111) and a comparable CO
oxidation current density. Using Koutecky-Levich analysis and DFT based
microkinetic modeling, we identify the rate-limiting pathway to be
Langmuir-Hinshelwood on Cu whereas Eley-Rideal on Au. We additionally present
strikingly variant RDE responses on four Cu facets (111, 100, 110 and 211) and
long-term stability analysis on Cu(111) and Au(111). We find a combined
reset-reaction profile helps Cu retain its high activity and pose a strong
competition to the expensive Au catalysts.",2109.15269v2
2021-10-14,Unveiling Structural Disorders in Honeycomb Layered Oxide: $\rm Na_2Ni_2TeO_6$,"Honeycomb layered oxides have garnered tremendous research interest in a wide
swath of disciplines owing not only to the myriad physicochemical properties
they exhibit, but also their rich crystal structural versatility. Herein, a
comprehensive crystallographic study of a sodium-based $\rm Na_2Ni_2TeO_6$
honeycomb layered oxide has been performed using atomic-resolution transmission
electron microscopy, elucidating a plethora of atomic arrangement (stacking)
disorders in the pristine material. Stacking disorders in the arrangement of
honeycomb metal slab layers (stacking faults) occur predominantly perpendicular
to the slabs with long-range coherence length and enlisting edge dislocations
in some domains. Moreover, the periodic arrangement of the distribution of
alkali atoms is altered by the occurrence of stacking faults. The multitude of
disorders innate in $\rm Na_2Ni_2TeO_6$ envisage broad implications in the
functionalities of related honeycomb layered oxide materials and hold promise
in bolstering renewed interest in their material science.",2110.09287v1
2021-10-27,Synthesis and Characterisation of Iron Oxide Nanoparticles with Tunable Sizes by Hydrothermal Method,"The present study investigates the effect of different reaction times on the
crystallinity, surface morphology and size of iron oxide nanoparticles. In this
synthetic system, aqueous iron (III) nitrate (Fe(NO$_3$)$_3\cdot9$H$_2$O)
nonahydrate, provided the iron source and triethylamine was the precipitant and
alkaline agent. The as-synthesised iron oxide nanoparticles were characterised
by X-ray diffraction (XRD), Rietveld analysis, Scanning Electron Microscopy
(SEM) and Fourier transform infrared spectroscopy (FTIR). Prolonged reaction
times indicated the change on nanoparticle shape from elongated nanorods to
finally distorted nanocubes. Analysis on the crystallinity of the iron oxide
nanoparticles suggest that the samples mainly consist of two phases, which are
Goethite ($\alpha$-FeOOH) and Hematite $(\alpha$-Fe$_2$O$_3$), respectively.",2110.14774v1
2021-11-15,Probing the polar-nonpolar oxide interfaces using resonant x-ray standing wave techniques,"Transition metal (TM) oxide heterostructure superlattices have attracted
great attention in research communities because of their emergent interfacial
phenomena that do not exist in the bulk form. In order to understand the
mechanisms that cause these phenomena, it is important to use depth-resolved
spectroscopies to study the electronic structure across the buried oxide
interfaces. In this review, we focus on the recent applications of standing
wave (SW) photoemission (SW-XPS) and resonant inelastic x-ray scattering
(SW-RIXS) spectroscopy to study the depth profiles of electronic structure or
carriers around the polar-nonpolar oxide interfaces. Using the incident photon
energies near the TM x-ray absorption resonance, the created SW excitation can
enhance the spectral response and certain electronic transitions, providing
important insight into the interfacial electronic structure in the energy and
real space regimes. Following the background introductions, we describe two SW
experiments and demonstrate that the combination of SW-XPS and SW-RIXS has the
potential to obtain the depth distribution of electronic/orbital states around
the buried interfaces with Angstrom precision.",2111.07539v1
2021-11-15,Covalent Functionalization of HiPco Single-Walled Carbon Nanotubes: Differences in the Oxidizing Action of H2SO4 and HNO3 during a Soft Oxidation Process,"The results of a study on the evolution of HiPco single-walled carbon
nanotubes during the oxidizing action of H2SO4 and HNO3 are presented. The
process conditions used have been chosen so as to avoid any significant damage
to the nanotube structure. The type and level of functionalization, the
location of the grafted functions on the surface of the nanotube and the
changes in morphological characteristics of the samples were examined by using
a wide and complementary range of analytical techniques. We propose an
explanation for the differences in the oxidizing action of sulfuric and nitric
acids. The combined results allow us to suggest possible reaction mechanisms
that occur on the surface of the nanotube.",2111.07623v1
2022-01-08,Electronic Defects in Metal Oxide Photocatalysts,"A deep understanding of defects is essential for the optimisation of
materials for solar energy conversion. This is particularly true for metal
oxide photo(electro)catalysts, which typically feature high concentrations of
charged point defects that are electronically active. In photovoltaic
materials, except for selected dopants, defects are considered detrimental and
should be eliminated to minimise charge recombination. However, photocatalysis
is a more complex process where defects can play an active role, for example,
by stabilising charge separation and mediating rate-limiting catalytic steps.
Here, we review the behaviour of electronic defects in metal oxides, paying
special attention to the principles underpinning the formation and function of
trapped charges in the form of polarons. We focus on how defects alter the
electronic structure, statically or transiently upon illumination, and discuss
the implications of such changes in light-driven catalytic reactions. Finally,
we consider the applicability of lessons learned from oxide defect chemistry to
new photocatalysts based on carbon nitrides, polymers and metal halide
perovskites.",2201.02808v1
2022-01-31,Photocatalytic water oxidation on SrTiO$_3$ [001] surfaces,"SrTiO$_3$ is a highly efficient photocatalyst for the overall water splitting
reaction under UV irradiation. However, an atomic-level understanding of the
active surface sites responsible for the oxidation and reduction reactions is
still lacking. Here we present a unified experimental and computational account
of the photocatalytic activity at the SrO- and TiO$_2$- terminations of
aqueous-solvated [001] SrTiO$_3$. Our experimental findings show that the
overall water-splitting reaction proceeds on the SrTiO$_3$ surface only when
the two terminations are simultaneously exposed to water. Our simulations
explain this, showing that the photogenerated hole-driven oxidation primarily
occurs at SrO surfaces in a sequence of four single hole transfer reactions,
while the TiO$_2$ termination effects the crucial band alignment of the
photocatalyst relative to the water oxidation potential. The present work
elucidates the interdependence of the two chemical terminations of SrTiO$_3$
surfaces, and has consequent implications for maximizing sustainable
solar-driven water splitting.",2201.13443v1
2022-02-03,Atomistic Engineering of Phonons in Functional Oxide Heterostructures,"Engineering of phonons, i.e., collective lattice vibrations in crystals, is
essential for manipulating physical properties of materials such as thermal
transport, electron-phonon interaction, confinement of lattice vibration, and
optical polarization. Most approaches to phonon-engineering have been largely
limited to the high-quality heterostructures of typical semiconductors. Yet,
artificial engineering of phonons in a variety of materials with functional
properties, such as complex oxides, will yield unprecedented applications of
coherent tunable phonons in future quantum acoustic devices. In this study, we
demonstrate artificial engineering of phonons in the atomic-scale SrRuO3/SrTiO3
superlattices, wherein tunable phonon modes were observed via confocal Raman
spectroscopy. In particular, the coherent superlattices led to the backfolding
of acoustic phonon dispersion, resulting in zone-folded acoustic phonons in the
THz frequency domain. We could further fine-tune the frequencies from 1 to 2
THz via atomic-scale precision thickness control. In addition, we observed a
polar optical phonon originating from the local inversion symmetry breaking in
the artificial oxide superlattices, exhibiting emergent functionality. Our
approach of atomic-scale heterostructuring of complex oxides will vastly expand
material systems for quantum acoustic devices, especially with the viability of
functionality integration.",2202.01450v1
2022-02-12,Theoretical investigation of vacancy related defects at 4H-SiC(000$\bar{1}$)/SiO$_2$ interface after wet oxidation,"The stability and formation mechanism of the defects relevant to silicon and
carbon vacancies at the 4H-SiC(000$\bar{1}$)/SiO$_2$ interface after wet
oxidation are investigated by first-principles calculation based on the density
functional theory. The difference in the total energy of the defects agrees
with the experimental results concerning the dencity of defects. We found that
the characteristic behaviors of the generation of defects are explained by the
positions of vacancies and antisites in the SiC(000$\bar{1}$) substrate and
that the formation of silicon and carbon vacancies is relevant to the
generation mechanism of defects. The generation of silicon and carbon vacancies
is attributed to the termination of dangling bonds by H atoms introduced by wet
oxidation, resulting in generation of carbon-antisite--carbon-vacancy and
divacancies defects in wet oxidation.",2202.06067v1
2022-02-13,Kinetic Monte Carlo modelling of Helium Bubble Nucleation onto Oxides in the Fe-Ti-Y-O System,"A Kinetic Monte Carlo (KMC) model was created to simulate the insertion of
transmutation He atoms into nanostructured ferritic alloys (NFAs) under neutron
irradiation. Interstitial He atoms migrate through the NFA until becoming
trapped in bubbles of other He atoms and vacancies created from irradiation.
The Y-Ti-O nano-oxides in the NFAs were found to be effective in capturing
these He atoms and preventing bubbles from forming at the grain boundary and
appear to replicate the characteristics (size and number density) observed in
other experiments. The bubbles were found to prefer the <111> oxide interface
as a nucleation site and the stable bubbles have a He/Vac ratio between 1.3 and
1.8 He/Vac. The influence of He bubbles on the segregation of solutes to the
grain boundaries or on the stability of the nano-oxides were negligible.",2202.06189v1
2022-03-10,Electric Double Layer at the Metal-Oxide/Electrolyte Interface,"Metal-oxide surfaces act as both Br{\o}nsted acids and bases, which allows
the exchange of protons with the electrolyte solution and generates either
positive or negative proton charges depending on the environmental pH. These
interfacial proton charges are then compensated by counter-ions from the
electrolyte solution, which leads to the formation of the electric double layer
(EDL). Because the EDL plays a crucial role in electrochemistry, geochemistry
and colloid science, understanding the structure-property relationship of the
EDL in metal-oxide systems from both experimental and theoretical approaches is
necessary. This chapter focuses on the physical chemistry of the protonic
double layer at the metal-oxide/electrolyte interface. In particular,
determinations of the EDL capacitance and the double-layer potential from
potentiometric titration experiments, electrochemical methods,
surface-sensitive vibrational spectroscopy and X-ray photoelectron spectroscopy
are summarized. This is followed by discussions from the atomistic modelling
aspect of the EDL, with an emphasis on the density-functional theory-based
molecular dynamics simulations. A conclusion and outlook for future works on
this topic are also given.",2203.05486v1
2022-05-05,Light absorption and emission by defects in doped nickel oxide,"Nickel oxide is a versatile p-type semiconducting oxide with many
applications in opto-electronic devices, but high doping concentrations are
often required to achieve necessary electrical conductivity. In contrast to
many other transparent oxide semiconductors, even moderate levels of doping of
NiO can lead to significant optical absorption in the visible spectral range,
limiting the application range of the material. This correlation has been
reported extensively in literature, but its origin has been unknown until now.
This work combines experimental data on optical properties from a variety of
NiO samples with results from hybrid density functional theory calculations. It
shows that strong electron-phonon interaction leads to a significant blue shift
(0.6-1 eV) of electronic transitions from the valence band maximum to defect
states by light absorption with respect to the thermodynamic charge transition
levels. This essentially renders NiO a narrow-gap semiconductor by defect band
formation already at moderate doping levels, with strong light absorption for
photon energies of approximately 1 eV. The calculations are also shown to be
fully consistent with experimental data on defect-related light emission in
NiO.",2205.02606v1
2022-05-06,Lattice dynamical properties of antiferromagnetic oxides calculated using self-consistent extended Hubbard functional method,"We study the lattice dynamics of antiferromagnetic transition-metal oxides by
using self-consistent Hubbard functionals. We calculate the ground states of
the oxides with the on-site and intersite Hubbard interactions determined
self-consistently within the framework of density functional theory. The
on-site and intersite Hubbard terms fix the errors associated with the electron
self-interaction in the local and semilocal functionals. Inclusion of the
intersite Hubbard terms in addition to the on-site Hubbard terms produces
accurate phonon dispersion of the transition-metal oxides. Calculated Born
effective charges and high-frequency dielectric constants are in good agreement
with experiment. Our study provides a computationally inexpensive and accurate
set of first-principles calculations for strongly-correlated materials and
related phenomena.",2205.02972v1
2022-07-09,Near-Infrared plasmon induced hot electron extraction evidence in an indium tin oxide nanoparticle / monolayer molybdenum disulphide heterostructure,"In this work, we observe plasmon induced hot electron extraction in a
heterojunction between indium tin oxide nanocrystals and monolayer molybdenum
disulphide. We study the sample with ultrafast differential transmission
exciting the sample at 1750 nm where the intense localized plasmon surface
resonance of the indium tin oxide nanocrystals is and where the monolayer
molybdenum disulphide does not absorb light. With the excitation at 1750 nm we
observe the excitonic features of molybdenum disulphide in the visible range,
close to the exciton of molybdenum disulphide. Such phenomenon can be ascribed
to a charge transfer between indium tin oxide nanocrystals and monolayer
molybdenum disulphide upon plasmon excitation. These results are a first step
towards the implementation of near infrared plasmonic materials for
photoconversion.",2207.04195v2
2022-07-26,$Ab$ $initio$ material design of Ag-based oxides for high-$T_c$ superconductor,"We propose silver-based oxides with layered perovskite structure as
candidates of exhibiting intriguing feature of strongly correlated electrons.
The compounds show unique covalence between Ag d and O p orbitals with the
strong electron correlation of their antibonding orbital similar to the copper
oxide high-temperature superconductors, but stronger covalency and slightly
smaller correlation strength. We examine $A_2$AgO$_2X_2$ with $A$ =Sr and Ba
and $X$ =F, I and Cl in detail. Among them, Sr$_2$AgO$_2$F$_2$ has the largest
effective onsite Coulomb repulsion and shows an antiferromagnetic insulating
ground state, which competes with correlated metals. It offers features both
similar and distinct from the copper oxides, and paves a new route. The
possibility of superconductivity in doped systems is discussed.",2207.12595v1
2022-09-10,Visible Light-Driven C-C Coupling Reaction of Terminal Alkynes at Atmospheric Temperature and Pressure Reaction Conditions using Hybrid Cu2O-Pd Nanostructures,"Carbon-carbon (C-C) coupling reactions are widely used reactions in the
production of fine chemicals, agrochemicals, and pharmaceuticals. In our recent
contribution (Green Chemistry, 2019, 21, 5284-5290), cuprous oxide (Cu2O)
nanospheres are shown to be efficient catalysts for C-C coupling reactions of
terminal alkynes such as phenylacetylene. Specifically, Cu2O nanospheres are
shown to successfully catalyze oxidative C-C homocoupling reaction of
phenylacetylene to form a coupling product, diphenyl diacetylene (DPDA).
However, these Cu2O nanocatalyst requires a relatively high temperature of ~110
0C. Herein, we report that photocatalysts built on hybrid palladium
nanoclusters decorated on Cu2O (i.e., Cu2O-Pd) can utilize visible light as
energy input and successfully catalyze oxidative homocoupling of
phenylacetylene at atmospheric temperature and pressure reaction condition.
This was displayed by the comparison of oxidative homocoupling reactions both
in the presence and without the presence of visible light. Our findings
indicate that photocatalysts through Cu2O-Pd nanospheres present to be a
logical substitute, moving toward more efficient and sustainable industrial
processes.",2209.04568v1
2022-09-20,Stabilizing polar phases in binary metal oxides by hole doping,"The recent observation of ferroelectricity in the metastable phases of binary
metal oxides, such as HfO2, ZrO2, Hf0.5Zr0.5O2, and Ga2O3, has garnered a lot
of attention. These metastable ferroelectric phases are typically stabilized
through epitaxial growth, alloying, or defect engineering. Here, we propose
hole doping plays a key role in stabilizing the polar phases in binary metal
oxides. Using first-principles density-functional-theory calculations, we show
that holes in these oxides mainly occupy one of the two oxygen sublattices.
This hole localization, which is more pronounced in the polar phase than in the
nonpolar phase, lowers the electrostatic energy of the system, and makes the
polar phase more stable at sufficiently large concentrations. We demonstrate
that this electrostatic mechanism is responsible for stabilization of the
ferroelectric phase of HfO2 aliovalently doped with elements that introduce
holes to the system, such as La and N. Finally, we show that the spontaneous
polarization in HfO2 is robust to hole doping, and a large polarization
persists even under a high concentration of holes.",2209.09436v3
2022-09-29,Emergent topological states via digital (001) oxide superlattices,"Oxide heterostructures exhibit many intriguing properties. Here we provide
design principles for inducing multiple topological states in (001)
($AM$O$_3$)$_1$/($AM'$O$_3$)$_1$ oxide superlattices. Aided by first-principles
calculations and model analysis, we show that a (Sr$M$O3)$_1$/(Sr$M'$O$_3$)$_1$
superlattice ($M$ = Nb, Ta and $M'$ = Rh, Ir) is a strong topological insulator
with $Z_2$ index (1;001). More remarkably, a (SrMoO3)$_1$/(SrIrO3)$_1$
superlattice exhibits multiple coexisting topological insulator (TI) and
topological Dirac semi-metal (TDS) states. The TDS state has a pair of type-II
Dirac points near the Fermi level and symmetry-protected Dirac node lines. The
surface TDS Dirac cone is sandwiched by two surface TI Dirac cones in the
energy-momentum space. The non-trivial topological properties arise from the
band inversion between $d$ orbitals of two dissimilar transition metal atoms
and a particular parity property of (001) superlattice geometry. Our work
demonstrates how to induce nontrivial topological states in (001) perovskite
oxide heterostructures by rational design.",2209.14674v1
2022-10-27,Characterization of AlW oxide coatings on aluminum formed by pulsed direct current plasma electrolytic oxidation at ultralow duty cycles,"The growth of thin oxide coatings on the aluminum substrate in water-based
sodium tungstate electrolyte by plasma electrolytic oxidation (PEO) is
discussed and experimentally illustrated. The growth is carried out using a
distinctive ultra-low duty cycle pulsed direct current (DC) power supply.
During the PEO processing elements present in micro-discharges are identified
using standard optical emission spectroscopy (OES) technique. The spectral line
shape analysis of the first two hydrogen Balmer lines shows the presence of two
types of micro-discharges. Obtained coatings are also characterized with
respect to their morphology and chemical and phase composition. It is shown
that coatings are composed of Al, O, and W, featuring low roughness and
porosity. Partial crystallization of the coatings resulted in identification of
WO3, W3O8, and gamma-Al2O3 crystalline phases.",2210.15719v1
2022-12-20,Engineering superconducting properties of multiferroic copper oxide heterostructures,"Oxide heterostructures have repeatedly been shown to display apical
properties at the interfaces, some of which favorable to the formation of
two-dimensional electron systems, as well as high transition temperature
superconductivity. In this study, we propose a novel heterostructure to
potentially achieve near room-temperature superconductivity, via the carrier
injection in cuprate interfaces with ferro-electrics. Using a digital design
approach guided by density-functional theory, the systems of XTiO3/XCuO3/XTiO3
are thoroughly examined, confirming the formation of a two-dimensional electron
gas at the cuprous oxide interface. Via the manipulation of lattice parameters,
the key ingredients for two-dimensional electron gas formation is explored. We
apply cluster dynamical mean-field theory on the cuprous oxide plane and probe
the superconducting properties of the system XTiO3/XCuO3/XTiO3 . As a result,
we see a marked increase of superconducting ordering parameter near the fully
occupied regime, a known marker for the superconducting transition temperature.",2212.10109v1
2023-01-16,The fate of water in hydrogen-based iron oxide reduction,"Gas-solid reactions are cornerstones of many catalytic and redox processes
that will underpin the energy and sustainability transition. The specific case
of hydrogen-based iron oxide reduction is the foundation to render the global
steel industry fossil-free, an essential target as iron production is the
largest single industrial emitter of carbon dioxide. Our perception of
gas-solid reactions has not only been limited by the availability of
state-of-the-art techniques which can delve into the reacted solids in great
structural and chemical detail, but we continue to miss an important reaction
partner that defines the thermodynamics and kinetics of gas phase reactions:
the gas molecules. In this investigation, we use the latest development in
cryogenic atom probe tomography to study the quasi in-situ evolution of gas
phase heavy water at iron-iron oxide interfaces resulting from the direct
reduction of iron oxide by deuterium gas at 700{\deg}C. The findings provide
new insights into the formation kinetics and location of water formed during
hydrogen-based reduction of FeO, an its interaction with the ongoing redox
reaction.",2301.06391v1
2023-03-15,Artificial ageing of thin films of the indium-free transparent conducting oxide SrVO3,"SrVO3 (SVO) is a prospective candidate to replace the conventional
indium-tin-oxide (ITO) among the new transparent conducting oxide (TCO)
generation. In this study, the structural, electrical, and optical properties
of SVO thin films, both epitaxial and polycrystalline, are determined during
and after heat treatments in the 150-250 {\deg}C range and under ambient
environment in order to explore the chemical stability of this material. The
use of these relatively low temperatures speeds up the natural ageing of the
films, and allows to follow the evolution of their related properties. The
combination of techniques rather sensitive to the film surface and of
techniques sampling the film volume will emphasize the presence of a surface
oxidation evolving in time at low annealing temperatures, whereas the
perovskite phase is destroyed throughout the film for treatments above 200
{\deg}C. The present study is designed to understand the thermal degradation
and long-term stability issues of vanadate-based TCOs, and to identify
technologically viable solutions for the application of this group as new TCOs.",2303.08449v1
2023-04-27,Comparison of Raman imaging assessment methods in phase determination and stress analysis of zirconium oxide layer,"This work describes Raman imaging and its data evaluation methods by using
the softwares original features: built-in fitting function and K-means cluster
analysis KMC followed by fitting in an external environment. For the first
time, these methods were compared in terms of their principles, limitations,
versatility, and process duration. The performed analysis showed the
indispensability of Raman imaging in terms of phase distribution, phase content
calculation, and stress determination. Zirconium oxide formed on different
zirconium alloys under various oxidation conditions was selected as an
exemplary material for this analysis. The reason for the material choice is
that it is an excellent example of the application of this type of Raman
analysis since both phase distribution and stress analysis in zirconium oxide
are of crucial importance for the development of zirconium alloys, especially
for nuclear applications. The juxtaposition of the results showed advantages
and limitations of both procedures allowing a definition of the criteria for
selecting the evaluation method for different applications.",2304.13982v1
2023-07-04,"Disentangling the Role of Electrons and Phonons in the Photoinduced CO Desorption and CO Oxidation on (O,CO)-Ru(0001)","The role played by electronic and phononic excitations in the femtosecond
laser induced desorption and oxidation of CO coadsorbed with O on Ru(0001) is
investigated using ab initio molecular dynamics with electronic friction. To
this aim, simulations that account for both kind of excitations and that only
consider electronic excitations are performed. Results for three different
surface coverages are obtained. We unequivocally demonstrate that CO desorption
is governed by phononic excitations. In the case of oxidation the low
statistics does not allow to give a categorical answer. However, the analysis
of the adsorbates kinetic energy gain and displacements strongly suggest that
phononic excitations and surface distortion also play an important role in the
oxidation process.",2307.01553v1
2023-07-06,Boron-doped graphene -- DFT study of the role of dopant concentration and oxidation on sodium and aluminium storage applications,"Graphene is thought to be a promising materials for many applications.
However, pristine graphene is not suitable for most electrochemical devices,
where defect engineering is crucial for its performance. We demonstrate how
boron doping of graphene can alter its reactivity, electrical conductivity and
potential application for sodium and aluminium storage, with the emphasis on
novel metal-ion batteries. Using DFT calculations, we investigate both the
influence of boron concentration and the oxidation of the material, on the
mentioned properties. It is demonstrated that the presence of boron in graphene
increases its reactivity towards atomic hydrogen and oxygen-containing species,
in other words, it makes B-doped graphene more prone to oxidation.
Additionally, the presence of these surface functional groups significantly
alters the type and strength of the interaction of Na and Al with the given
materials. Boron-doping and oxidation of graphene is found to increase Na
storage capacity of graphene by the factor of up to 4.",2307.02885v1
2023-07-11,Stabilization of Ferroelectric Hf0.5Zr0.5O2 Epitaxial Films via Monolayer Reconstruction Driven by Interfacial Redox Reaction,"The binary fluorite oxide Hf0.5Zr0.5O2 tends to grab a significant amount of
notice due to the distinct and superior ferroelectricity found in its
metastable phase. Stabilizing the metastable ferroelectric phase and
delineating the underlying growth mechanism, however, are still challenging.
Recent discoveries of metastable ferroelectric Hf0.5Zr0.5O2 epitaxially grown
on structurally dissimilar perovskite oxides have triggered intensive
investigations on the ferroelectricity in materials that are nonpolar in bulk
form. Nonetheless, the growth mechanism for the unique fluorite/perovskite
heterostructures has yet to be fully explored. Here we show that the metastable
ferroelectric Hf0.5Zr0.5O2 films can be stabilized even on a
one-unit-cell-thick perovskite La0.67Sr0.33MnO3 buffer layer. In collaboration
with scanning transmittance electron microscopy (STEM) based characterizations,
we show that monolayer reconstruction driven by interfacial redox reactions
plays a vital role in the formation of a unique heterointerface between the two
structurally dissimilar oxides, providing the template monolayer that
facilitates the epitaxial growth of the metastable HZO films. Our findings
offer significant insights into the stabilization mechanism of the
ferroelectric Hf0.5Zr0.5O2, and this mechanism could be extended for exploring
functional metastable phases of various metal oxides.",2307.05346v1
2023-08-27,Reconstruction changes drive surface diffusion and determine the flatness of oxide surfaces,"Surface diffusion on metal oxides is key in many areas of materials
technology, yet it has been scarcely explored at the atomic scale. This work
provides phenomenological insights from scanning tunneling microscopy on the
link between surface diffusion, surface atomic structure, and oxygen chemical
potential based on three model oxide surfaces: Fe$_2$O$_3(1\overline{1}02)$,
La$_{1-x}$Sr$_x$MnO$_3$(110), and In$_2$O$_3$(111). In all instances, changing
the oxygen chemical potential used for annealing stabilizes reconstructions of
different compositions while promoting the flattening of the surface morphology
-- a sign of enhanced surface diffusion. It is argued that thermodynamics,
rather than kinetics, rules surface diffusion under these conditions: The
composition change of the surface reconstructions formed at differently
oxidizing conditions drives mass transport across the surface.",2308.14043v1
2023-09-08,Prediction of the Cu Oxidation State from EELS and XAS Spectra Using Supervised Machine Learning,"Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy
(XAS) provide detailed information about bonding, distributions and locations
of atoms, and their coordination numbers and oxidation states. However,
analysis of XAS/EELS data often relies on matching an unknown experimental
sample to a series of simulated or experimental standard samples. This limits
analysis throughput and the ability to extract quantitative information from a
sample. In this work, we have trained a random forest model capable of
predicting the oxidation state of copper based on its L-edge spectrum. Our
model attains an $R^2$ score of 0.89 and a root mean square valence error of
0.21 on simulated data. It has also successfully predicted experimental L-edge
EELS spectra taken in this work and XAS spectra extracted from the literature.
We further demonstrate the utility of this model by predicting simulated and
experimental spectra of mixed valence samples generated by this work. This
model can be integrated into a real time EELS/XAS analysis pipeline on mixtures
of copper containing materials of unknown composition and oxidation state. By
expanding the training data, this methodology can be extended to data-driven
spectral analysis of a broad range of materials.",2309.04067v1
2023-09-18,Disassembling one-dimensional chains in molybdenum oxides,"The dimensionality of quantum materials strongly affects their physical
properties. Although many emergent phenomena, such as charge-density wave and
Luttinger liquid behavior, are well understood in one-dimensional (1D) systems,
the generalization to explore them in higher dimensional systems is still a
challenging task. In this study, we aim to bridge this gap by systematically
investigating the crystal and electronic structures of molybdenum-oxide family
compounds, where the contexture of 1D chains facilitates rich emergent
properties. While the quasi-1D chains in these materials share general
similarities, such as the motifs made up of MoO6 octahedrons, they exhibit vast
complexity and remarkable tunability. We disassemble the 1D chains in
molybdenum oxides with different dimensions and construct effective models to
excellently fit their low-energy electronic structures obtained by ab initio
calculations. Furthermore, we discuss the implications of such chains on other
physical properties of the materials and the practical significance of the
effective models. Our work establishes the molybdenum oxides as simple and
tunable model systems for studying and manipulating the dimensionality in
quantum systems.",2309.09729v1
2023-09-19,Electronic Properties and Interlayer Interactions in Antimony Oxide Homo- and Heterobilayers,"Antimony shows promise as a two-dimensional (2D) mono-elemental crystal,
referred to as antimonene. When exposed to ambient conditions, antimonene
layers react with oxygen, forming new crystal structures, leading significant
changes in electronic properties. These changes are influenced by the degree of
oxidation. Utilizing Density Functional Theory (DFT) calculations, stable
configurations of bilayer antimony oxide and their corresponding electronic
properties are studied. Additionally, different stacking arrangements and their
effects on the physical properties of the materials are investigated.
Furthermore, the analysis encompasses strain-free hetero-bilayers containing
both pristine and oxidized antimonene layers, aiming to understand the
interplay between these materials and their collective impact on the bilayer
properties. Our results provide insight into how the properties of
antimony-based bilayer structures can be modified by adjusting stoichiometry
and stacking configurations.",2309.10653v2
2024-01-29,Anomalous thermal oxidation of gadolinium thin films deposited on silicon by high pressure sputtering,"Thin gadolinium metallic layers were deposited by high-pressure sputtering in
pure Ar atmosphere. Subsequently, in situ thermal oxidation was performed at
temperatures ranging from 150 to 750 $^\circ$C. At an oxidation temperature of
500 $^\circ$C the films show a transition from monoclinic structure to a
mixture of monoclinic and cubic. Regrowth of interfacial SiO$_x$ is observed as
temperature is increased, up to 1.6 nm for 750 $^\circ$C. This temperature
yields the lowest interface trap density, 4e10 eV$^{-1}$ cm$^{-2}$, but the
effective permittivity of the resulting dielectric is only 7.4. The reason of
this low value is found on the oxidation mechanism, which yields a surface with
located bumps. These bumps increase the average thickness, thus reducing the
capacitance and therefore the calculated permittivity.",2402.10925v1
2024-02-16,Standardization of chemically selective atomic force microscopy for metal-oxide surfaces,"The complex atomic structures and defects of metal-oxide surfaces are vital
for a variety of applications in material science and chemistry. While scanning
probe microscopy allows accessing atomic-scale structures in real space,
elemental discrimination and defect characterization usually rely on indirect
assumptions and extensive theoretical modelling. By investigating a variety of
different sample systems with increasing structural complexity and inherent
defects, we demonstrate that noncontact atomic force microscopy with an
O-terminated copper tip allows imaging metal-oxide surfaces with a clear
elemental contrast. This universal approach provides not only immediate access
to the metal- and oxygen sub-lattices, but also to the chemical and structural
configuration of atomic-scale defect structures. The observed contrast can be
explained by purely electrostatic interactions between the negatively charged
tip apex and the strongly varying electrostatic potential between metal- and
oxygen surface sites. These results offer a standardized methodology for the
direct structural characterization of even most-complex metal-oxide surfaces,
which is highly relevant for a fundamental understanding of atomic-scale
processes on these material systems.",2402.11045v1
2024-03-19,Micro-Raman spectroscopy of graphene defects and tracing the oxidation process caused by UV exposure,"Raman spectroscopy is one of the widely used methods in the analysis of
various samples including carbon-based materials. This study aimed to identify
the number of layers and defects in graphene using micro-Raman spectroscopy.
More specifically, the study examined tracing the oxidation process of graphene
under UV exposure. Investigation of the effect of the power density of the
Raman excitation laser reveals a linear dependence between the ratio of I2D/IG
and the power density of the excitation laser. Also, the absence of peak D due
to the increase in power density provides evidence for the non-destructive
nature of micro-Raman spectroscopy. Given the value of I2D/IG, one of the
parameters for determining the number of layers in graphene which has reached
1.39 at the edge, the findings indicate the possibility of an edge fold of
single-layer graphene. During the oxidation process, the intensity and position
of the D peak increase as a function of exposure time. Alterations in the
graphene Raman spectrum, comprising the disappearance of the 2D peak and the
appearance of the D peak, trace and confirm the oxidation process of the
sample.",2403.13191v1
2005-06-22,Superconductivity and Cobalt Oxidation State in Metastable Na(x)CoO(2-delta)*yH2O (x ~ 1/3; y ~ 4x),"We report the synthesis and superconducting properties of a metastable form
of the known superconductor NaxCoO2*yH2O (x ~ 1/3, y ~ 4x). Instead of using
the conventional bromine-acetonitrile mixture for sodium deintercalation, we
use an aqueous bromine solution. Using this method, we oxidize the sample to a
point that the sodium cobaltate becomes unstable, leading to formation of other
products if not controlled. This compound has the same structure as the
reported superconductor, yet it exhibits a systematic variation of the
superconducting transition temperature (Tc) as a function of time. Immediately
after synthesis, this compound is not a superconductor, even though it contains
appropriate amounts of sodium and water. The samples become superconducting
with low Tc values after ~ 90 h. Tc continually increases until it reaches a
maximum value (4.5 K) after about 260 h. Then Tc drops drastically, becoming
non-superconducting approximately 100 h later. Corresponding time-dependent
neutron powder diffraction data shows that the changes in superconductivity
exhibited by the metastable cobaltate correspond to slow formation of oxygen
vacancies in the CoO2 layers. In effect, the formation of these defects
continually reduces the cobalt oxidation state causing the sample to evolve
through its superconducting life cycle. Thus, the dome-shaped superconducting
phase diagram is mapped as a function of cobalt oxidation state using a single
sample. The width of this dome based on the formal oxidation state of cobalt is
very narrow - approximately 0.1 valence units wide. Interestingly, the maximum
Tc in NaxCoO2*yH2O occurs when the cobalt oxidation state is near 3.5. Thus, we
speculate that the maximum Tc occurs near the charge ordered insulating state
that correlates with the average cobalt oxidation state of 3.5.",0506549v1
2010-10-04,Doping Dependence of Thermal Oxidation on n-type 4H-SiC,"The doping dependence of dry thermal oxidation rates in n-type 4H-SiC was
investigated. The oxidation was performed in the temperature range 1000C to
1200C for samples with nitrogen doping in the range of 6.5e15/cm3 to
9.3e18/cm3, showing a clear doping dependence. Samples with higher doping
concentrations displayed higher oxidation rates. The results were interpreted
using a modified Deal-Grove model. Linear and parabolic rate constants and
activation energies were extracted. Increasing nitrogen led to an increase in
linear rate constant pre-exponential factor from 10-6m/s to 10-2m/s and the
parabolic rate constant pre-exponential factor from 10e9m2/s to 10e6m2/s. The
increase in linear rate constant was attributed to defects from doping-induced
lattice mismatch, which tend to be more reactive than bulk crystal regions. The
increase in the diffusion-limited parabolic rate constant was attributed to
degradation in oxide quality originating from the doping-induced lattice
mismatch. This degradation was confirmed by the observation of a decrease in
optical density of the grown oxide films from 1.4 to 1.24. The linear
activation energy varied from 1.6eV to 2.8eV, while the parabolic activation
energy varied from 2.7eV to 3.3eV, increasing with doping concentration. These
increased activation energies were attributed to higher nitrogen content,
leading to an increase in effective bond energy stemming from the difference in
C-Si (2.82eV) and Si-N (4.26eV) binding energies. This work provides crucial
information in the engineering of SiO2 dielectrics for SiC MOS structures,
which typically involve regions of very different doping concentrations, and
suggests that thermal oxidation at high doping concentrations in SiC may be
defect mediated.",1010.0473v1
2015-04-22,Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces via charge transfer induced modulation doping,"The discovery of two-dimensional electron gases (2DEGs) at the interface
between two insulating complex oxides, such as LaAlO3 (LAO) or gamma-Al2O3
(GAO) epitaxially grown on SrTiO3 (STO) 1,2, provides an opportunity for
developing all-oxide electronic devices3,4. These 2DEGs at complex oxide
interfaces involve many-body interactions and give rise to a rich set of
phenomena5, for example, superconductivity6, magnetism7,8, tunable
metal-insulator transitions9, and phase separation10. However, large
enhancement of the interfacial electron mobility remains a major and
long-standing challenge for fundamental as well as applied research of complex
oxides11-15. Here, we inserted a single unit cell insulating layer of polar
La1-xSrxMnO3 (x=0, 1/8, and 1/3) at the interface between disordered LaAlO3 and
crystalline SrTiO3 created at room temperature. We find that the electron
mobility of the interfacial 2DEG is enhanced by more than two orders of
magnitude. Our in-situ and resonant x-ray spectroscopic in addition to
transmission electron microscopy results indicate that the manganite layer
undergoes unambiguous electronic reconstruction and leads to modulation doping
of such atomically engineered complex oxide heterointerfaces. At low
temperatures, the modulation-doped 2DEG exhibits clear Shubnikov-de Haas
oscillations and the initial manifestation of the quantum Hall effect,
demonstrating an unprecedented high-mobility and low electron density oxide
2DEG system. These findings open new avenues for oxide electronics.",1504.05986v1
2015-07-31,Calibrating transition metal energy levels and oxygen bands in first principles calculations: accurate prediction of redox potentials and charge transfer in lithium transition metal oxides,"Transition metal (TM) oxides play an increasingly important role in
technology today including applications such as catalysis, solar energy
harvesting, and energy storage. In many of these applications, the details of
their electronic structure near the Fermi level are critically important for
their properties. We propose a first-principles based computational methodology
for the accurate prediction of oxygen charge transfer in TM oxides and lithium
TM (Li-TM) oxides. To obtain accurate electronic structures, the
Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional is adopted and the amount of
exact Hartree-Fock exchange (mixing parameter) is adjusted to reproduce
reference band gaps. We show that the HSE06 functional with optimal mixing
parameter yields not only improved electronic densities of states but also
better energetics (Li-intercalation voltages) for LiCoO2 and LiNiO2 as compared
to GGA, GGA+U and standard HSE06. We find that the optimal mixing parameters
for TM oxides are system-specific and correlate with the covalency (ionicity)
of the TM species. Strong covalent (ionic) nature of TM-O bonding leads to
lower (higher) optimal mixing parameters. We find that optimized HSE06
functionals predict stronger hybridization of the Co 3d and O 2p orbitals than
GGA, resulting in a greater contribution from oxygen states to charge
compensation upon delithiation in LiCoO2. We also find that the band gaps of
Li-TM oxides increase linearly with the mixing parameter, enabling the
straightforward determination of optimal mixing parameters based on GGA
({\alpha} = 0.0) and HSE06 ({\alpha} = 0.25) calculations. Our results also
show that G0W0@GGA+U band gaps of TM oxides (MO, M = Mn, Co, Ni) and LiCoO2
agree well with experimental references, suggesting that G0W0 calculations can
be used as a reference for the calibration of the mixing parameter in case no
experimental band gap has been reported.",1507.08768v1
2019-09-02,Resolving the Nucleation Stage in Atomic Layer Deposition of Hafnium Oxide on Graphene,"The integration of two-dimensional (2D) materials with functional non-2D
materials such as metal oxides is of key importance for many applications, but
underlying mechanisms for such non-2D/2D interfacing remain largely elusive at
the atomic scale. To address this, we here investigate the nucleation stage in
atomic layer deposition (ALD) of the important metal oxide HfO2 on chemical
vapor deposited graphene using atomically resolved and element specific
scanning transmission electron microscopy (STEM). To avoid any deleterious
influence of polymer residues from pre-ALD graphene transfers we employ a
substrate-assisted ALD process directly on the as grown graphene still
remaining on its Cu growth catalyst support. Thereby we resolve at the atomic
scale key factors governing the integration of non-2D metal oxides with 2D
materials by ALD: Particular to our substrate-assisted ALD process we find a
graphene-layer-dependent catalytic participation of the supporting Cu catalyst
in the ALD process. We further confirm at high resolution the role of surface
irregularities such as steps between graphene layers on oxide nucleation.
Employing the energy transfer from the scanning electron beam to in situ
crystallize the initially amorphous ALD HfO2 on graphene, we observe HfO2
crystallization to non-equilibrium HfO2 polymorphs (cubic/tetragonal). Finally
our data indicates a critical role of the graphene's atmospheric adventitious
carbon contamination on the ALD process whereby this contamination acts as an
unintentional seeding layer for metal oxide ALD nucleation on graphene under
our conditions. As atmospheric adventitious carbon contamination is hard to
avoid in any scalable 2D materials processing, this is a critical factor in ALD
recipe development for 2D materials coating. Combined our work highlights
several key mechanisms underlying scalable ALD oxide growth on 2D materials.",1909.00712v1
2021-03-11,"A coupled model of episodic warming, oxidation and geochemical transitions on early Mars","Reconciling the geology of Mars with models of atmospheric evolution remains
a major challenge. Martian geology is characterized by past evidence for
episodic surface liquid water, and geochemistry indicating a slow and
intermittent transition from wetter to drier and more oxidizing surface
conditions. Here we present a new model incorporating randomized injection of
reducing greenhouse gases and oxidation due to hydrogen escape, to investigate
the conditions responsible for these diverse observations. We find that Mars
could have transitioned repeatedly from reducing (H2-rich) to oxidizing
(O2-rich) atmospheric conditions in its early history. Our model predicts a
generally cold early Mars, with mean annual temperatures below 240 K. If peak
reducing gas release rates and background CO2 levels are high enough, it
nonetheless exhibits episodic warm intervals sufficient to degrade crater
walls, form valley networks and create other fluvial/lacustrine features. Our
model also predicts transient buildup of atmospheric O2, which can help explain
the occurrence of oxidized mineral species such as manganese oxides at Gale
Crater. We suggest that the apparent Noachian--Hesperian transition from
phyllosilicate deposition to sulfate deposition around 3.5 billion years ago
can be explained as a combined outcome of increasing planetary oxidation,
decreasing groundwater availability and a waning bolide impactor flux, which
dramatically slowed the remobilization and thermochemical destruction of
surface sulfates. Ultimately, rapid and repeated variations in Mars' early
climate and surface chemistry would have presented both challenges and
opportunities for any emergent microbial life.",2103.06736v1
2022-12-13,On the surface chemisorption of oxidizing fine iron particles: insights gained from molecular dynamics simulations,"Molecular dynamics (MD) simulations are performed to investigate the thermal
and mass accommodation coefficients (TAC and MAC, respectively) for the
combination of iron(-oxide) and air. The obtained values of TAC and MAC are
then used in a point-particle Knudsen model to investigate the effect of
chemisorption and the Knudsen transition regime on the combustion behavior of
(fine) iron particles. The thermal accommodation for the interactions of
$\mathrm{Fe}$ with $\mathrm{N_2}$ and $\mathrm{Fe_xO_y}$ with $\mathrm{O_2}$ is
investigated for different surface temperatures, while the mass accommodation
coefficient for iron(-oxide) with oxygen is investigated for different initial
oxidation stages $Z_\mathrm{O}$, which represents the molar ratio of
$\mathrm{O}/\left(\mathrm{O} + \mathrm{Fe}\right)$, and different surface
temperatures. The MAC decreases fast from unity to 0.03 as $Z_\mathrm{O}$
increases from 0 to 0.5 and then diminishes as $Z_\mathrm{O}$ further increases
to 0.57. By incorporating the MD-informed accommodation coefficients into the
single iron particle combustion model,a new temperature evolution for single
iron particles is observed compared to results obtained with previously
developed continuum models. Specifically, results of the present simulations
show that the oxidation process continues after the particle reaching the peak
temperature, while previous models predicting that the maximum temperature was
attained when the particle is oxidized to $Z_\mathrm{O} = 0.5$. Since the rate
of oxidation slows down as the MAC decreases with an increasing oxidation
stage, the rate of heat loss exceeds the rate of heat release upon reaching the
maximum temperature, while the particle is not yet oxidized to $Z_\mathrm{O} =
0.5$. Finally, the effect of transition-regime heat and mass transfer on the
combustion behavior of fine iron particles is investigated and discussed.",2212.06432v2
2023-03-06,Ternary oxides of $\textit{s}$- and $\textit{p}$-block metals for photocatalytic solar-to-hydrogen conversion,"Oxides containing metals or metalloids from the {\it p}-block of the periodic
table ({\it e.g.}, In, Sn, Sb, Pb, Bi) are of technological interest as
transparent conductors and light absorbers for solar energy conversion due to
the tunability of their electronic conductivity and optical absorption.
Comparatively, these oxides have found limited applications in hydrogen
photoelectrolysis primarily due to their high electronegativity, which impedes
electron transfer for reducing protons into hydrogen. We have shown recently
that inserting {\it s}-block cations into {\it p}-block metal oxides is
effective at lowering electronegativities while affording further control of
band gaps. Here, we explain the origins of this dual tunability by
demonstrating the mediator role of {\it s}-block cations in modulating orbital
hybridization while not contributing to frontier electronic states. From this
result, we carry out a comprehensive computational study of 109 ternary oxides
of {\it s}- and {\it p}-block metal elements as candidate photocatalysts for
solar hydrogen generation. We downselect the most desirable materials using
band gaps and band edges obtained from Hubbard-corrected density-functional
theory with Hubbard parameters computed entirely from first principles,
evaluate the stability of these oxides in aqueous conditions, and characterize
experimentally four of the remaining materials, synthesized with high phase
uniformity, to validate and further develop the computational models. We thus
propose nine oxide semiconductors, including CsIn$_3$O$_5$, Sr$_2$In$_2$O$_5$,
and KSbO$_2$ which, to the extent of our literature review, have not been
previously considered as water-splitting photocatalysts.",2303.03332v2
2023-04-12,Selective thermal evolution of native oxide layer in Nb and Nb3Sn-coated SRF grade Nb: An in-situ angular XPS study,"This contribution discusses the results of an in-situ angular XPS study on
the thermal evolution of the native oxide layer on Nb3Sn and pure Nb. XPS data
were recorded with conventional spectrometers using an AlK(alpha) X-ray source
for spectra collected up to 600 C, and an MgK(Alpha) X-rays source for
temperatures above 600 C. The effect of the thickness, composition, and thermal
stability of that oxide layer is relevant to understanding the functional
properties of superconducting radiofrequency (SRF) cavities used in particle
accelerators. There is a consensus that oxide plays a role in surface
resistance (Rs). The focus of this study is Nb3Sn, which is a promising
material that is used in the manufacturing of superconducting radiofrequency
(SRF) cavities as well as in quantum sensing, and pure Nb, which was included
in the study for comparison. The thermal evolution of the oxide layer in these
two materials is found to be quite different, which is ascribed to the
influence of the Sn atom on the reactivity of the Nb atom in Nb3Sn films. Nb
and Sn atoms in this intermetallic solid have different electronegativity, and
the Sn atom can reduce electron density around neighbouring Nb atoms in the
solid, thus reducing their reactivity for oxygen. This is shown in the
thickness, composition, and thermal stability of the oxide layer formed on
Nb3Sn. The XPS spectra were complemented by grazing incident XRD patterns
collected using the ESRF synchrotron radiation facility. The results discussed
herein shed light on oxide evolution in the Nb3Sn compound and guide its
processing for potential applications of the Nb3Sn-based SRF cavities in
accelerators and other superconducting devices.",2304.06112v1
2023-12-10,Understanding muon diffusion in perovskite oxides below room temperature based on harmonic transition state theory,"In positive muon spin rotation and relaxation ($\mu^+$SR) spectroscopy,
positive muons ($\mu^+$) implanted into solid oxides are conventionally treated
as immobile spin-probes at interstitial sites below room temperature. This is
because each $\mu^+$ is thought to be tightly bound to an oxygen atom in the
host lattice to form a muonic analogue of the hydroxy group. On the basis of
this concept, anomalies in $\mu^+$SR spectra observed in oxides have been
attributed in most cases to the intrinsic properties of host materials. On the
other hand, global $\mu^+$ diffusion with an activation energy of $\sim$0.1~eV
has been reported in some chemically-substituted perovskite oxides at cryogenic
temperatures, although the reason for the small activation energy despite the
formation of the strong O$\mu$ bond has not yet been quantitatively understood.
In this study, we investigated interstitial $\mu^+$ diffusion in the perovskite
oxide lattice using KTaO$_3$ cubic perovskite as a model system. We used the
$\mu^+$SR method and density functional theory calculations along with the
harmonic transition state theory to study this phenomenon both experimentally
and theoretically. Experimental activation energies for global $\mu^+$
diffusion obtained below room temperature were less than a quarter of the
calculated classical potential barrier height for a bottleneck $\mu^+$ transfer
path. The reduction in the effective barrier height could be explained by the
harmonic transition state theory with a zero-point energy correction; a
significant difference in zero-point energies for $\mu^+$ at the positions in
the O$\mu$ bonding equilibrium state and a bond-breaking transition state was
the primary cause of the reduction. This suggests that the assumption of
immobile $\mu^+$ in solid oxides is not always satisfied since such a
significant decrease in diffusion barrier height can also occur in other
oxides.",2312.05755v1
2004-02-03,Aluminum Oxide Layers as Possible Components for Layered Tunnel Barriers,"We have studied transport properties of Nb/Al/AlOx/Nb tunnel junctions with
ultrathin aluminum oxide layers formed by (i) thermal oxidation and (ii) plasma
oxidation, before and after rapid thermal post-annealing of the completed
structures at temperatures up to 550 deg C. Post-annealing at temperatures
above 300 deg C results in a significant decrease of the tunneling conductance
of thermally-grown barriers, while plasma-grown barriers start to change only
at annealing temperatures above 450 deg C. Fitting the experimental I-V curves
of the junctions using the results of the microscopic theory of direct
tunneling shows that the annealing of thermally-grown oxides at temperatures
above 300 deg C results in a substantial increase of their average tunnel
barriers height, from ~1.8 eV to ~2.45 eV, versus the practically unchanged
height of ~2.0 eV for plasma-grown layers. This difference, together with high
endurance of annealed barriers under electric stress (breakdown field above 10
MV/cm) may enable all-AlOx and SiO2/AlOx layered ""crested"" barriers for
advanced floating-gate memory applications.",0402092v1
2005-01-03,Density-functional theory study of the initial oxygen incorporation in Pd(111),"Pd(111) has recently been shown to exhibit a propensity to form a
sub-nanometer thin surface oxide film already well before a full monolayer
coverage of adsorbed O atoms is reached on the surface. Aiming at an
atomic-scale understanding of this finding, we study the initial oxygen
incorporation into the Pd(111) surface using density-functional theory. We find
that oxygen incorporation into the sub-surface region starts at essentially the
same coverage as formation of the surface oxide. This implies that the role of
sub-surface oxygen should be considered as that of a metastable precursor in
the oxidation process of the surface. The mechanisms found to play a role
towards the ensuing stabilization of an ordered oxidic structure with a mixed
on-surface/sub-surface site occupation follow a clear trend over the late 4d
transition metal series, as seen by comparing our data to previously published
studies concerned with oxide formation at the basal surface of Ru, Rh and Ag.
The formation of a linearly aligned O-TM-O trilayered structure (TM = Ru, Rh,
Pd, Ag), together with an efficient coupling to the underlying substrate seem
to be key ingredients in this respect.",0501018v1
2006-05-24,KrF pulsed laser deposition of chromium oxide thin films from Cr8O21 targets,"Chromium oxides, CrxOy, are of great interest due to the wide variety of
their technological applications. Among them, CrO2 has been extensively
investigated in recent years because it is an attractive compound to be used in
spintronic heterostructures. However, its synthesis at low temperatures has
been a difficult task due to the metastable nature of this oxide. This is
indeed essential to ensure interface quality and the ability to coat
thermal-sensitive materials such as those envisaged in spintronic devices.
Pulsed Laser Deposition (PLD) is a technique that has the potential to meet the
requirements stated above. In this work, we describe our efforts to grow
chromium oxide thin films by PLD from Cr8O21 targets, using a KrF excimer
laser. The as-deposited films were investigated by X-ray diffraction and
Rutherford backscattering spectrometry. Structural and chemical composition
studies showed that the films consist of a mixture of amorphous chromium oxides
exhibiting different stoichiometries depending on the processing parameters,
where nanocrystals of mainly Cr2O3 are dispersed. The analyses do not exclude
the possibility of co-deposition of Cr2O3 and a low fraction of CrO2.
  PACS: 81.15.Fg, 75.50.Dd",0605594v1
2006-10-06,"Theoretical study of the insulating oxides and nitrides: SiO2, GeO2, Al2O3, Si3N4, and Ge3N4","An extensive theoretical study is performed for wide bandgap crystalline
oxides and nitrides, namely, SiO_{2}, GeO_{2}, Al_{2}O_{3}, Si_{3}N_{4}, and
Ge_{3}N_{4}. Their important polymorphs are considered which are for SiO_{2}:
$\alpha$-quartz, $\alpha$- and $\beta$-cristobalite and stishovite, for
GeO_{2}: $\alpha$-quartz, and rutile, for Al_{2}O_{3}: $\alpha$-phase, for
Si_{3}N_{4} and Ge_{3}N_{4}: $\alpha$- and $\beta$-phases. This work
constitutes a comprehensive account of both electronic structure and the
elastic properties of these important insulating oxides and nitrides obtained
with high accuracy based on density functional theory within the local density
approximation. Two different norm-conserving \textit{ab initio}
pseudopotentials have been tested which agree in all respects with the only
exception arising for the elastic properties of rutile GeO_{2}. The agreement
with experimental values, when available, are seen to be highly satisfactory.
The uniformity and the well convergence of this approach enables an unbiased
assessment of important physical parameters within each material and among
different insulating oxide and nitrides. The computed static electric
susceptibilities are observed to display a strong correlation with their mass
densities. There is a marked discrepancy between the considered oxides and
nitrides with the latter having sudden increase of density of states away from
the respective band edges. This is expected to give rise to excessive carrier
scattering which can practically preclude bulk impact ionization process in
Si_{3}N_{4} and Ge_{3}N_{4}.",0610176v2
2007-09-04,A first--order irreversible thermodynamic approach to a simple energy converter,"Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.",0709.0321v1
2010-02-25,"Tuning the properties of complex transparent conducting oxides: role of crystal symmetry, chemical composition and carrier generation","The electronic properties of single- and multi-cation transparent conducting
oxides (TCOs) are investigated using first-principles density functional
approach. A detailed comparison of the electronic band structure of
stoichiometric and oxygen deficient In$_2$O$_3$, $\alpha$- and
$\beta$-Ga$_2$O$_3$, rock salt and wurtzite ZnO, and layered InGaZnO$_4$
reveals the role of the following factors which govern the transport and
optical properties of these TCO materials: (i) the crystal symmetry of the
oxides, including both the oxygen coordination and the long-range structural
anisotropy; (ii) the electronic configuration of the cation(s), specifically,
the type of orbital(s) -- $s$, $p$ or $d$ -- which form the conduction band;
and (iii) the strength of the hybridization between the cation's states and the
p-states of the neighboring oxygen atoms. The results not only explain the
experimentally observed trends in the electrical conductivity in the
single-cation TCO, but also demonstrate that multicomponent oxides may offer a
way to overcome the electron localization bottleneck which limits the charge
transport in wide-bandgap main-group metal oxides. Further, the advantages of
aliovalent substitutional doping -- an alternative route to generate carriers
in a TCO host -- are outlined based on the electronic band structure
calculations of Sn, Ga, Ti and Zr-doped InGaZnO$_4$. We show that the
transition metal dopants offer a possibility to improve conductivity without
compromising the optical transmittance.",1002.4827v1
2010-06-18,Consistent Asymptotic Expansion of Mott's Solution for Oxide Growth,"Many relatively thick metal oxide films grow according to what is called the
parabolic law L = 2At + . . . . Mott explained this for monovalent carriers by
assuming that monovalent ions and electrons are the bulk charge carriers, and
that their number fluxes vary as t^{-1/2} at sufficiently long t. In this
theory no charge is present in the bulk, and surface charges were not
discussed. However, it can be analyzed in terms of a discharging capacitor,
with the oxide surfaces as the plates. The theory is inconsistent because the
field decreases, corresponding to discharge, but there is no net current to
cause discharge. The present work, which also includes non-monovalent carriers,
systematically extends the theory and obtains the discharge current. Because
the Planck-Nernst equations are nonlinear (although Gauss's Law and the
continuity equations are linear) this leads to a systematic order-by-order
expansion in powers of t^{-1/2} for the number currents, concentrations, and
electric field during oxide growth. At higher order the bulk develops a
non-zero charge density, with a corresponding non-uniform net current, and
there are corrections to the electric field and the ion currents. The second
order correction to ion current implies a logarithmic term in the thickness of
the oxide layer: L = (2At)^{1/2} + B ln t + . . . . It would be of interest to
verify this result with high-precision measurements.",1006.3819v1
2010-06-25,Effect of doping of zinc oxide on the hole mobility of poly(3-hexylthiophene) in hybrid transistors,"Hybrid field effect transistors based on the organic polymer
poly(3-hexylthiophene) (P3HT) and inorganic zinc oxide were investigated. In
this report we present one of the first studies on hybrid transistors employing
one polymeric transport layer. The sol-gel processed ZnO was modified via Al
doping between 0.8 and 10 at.%, which allows a systematic variation of the zinc
oxide properties, i.e. electron mobility and morphology. With increasing doping
level we observe on the one hand a decrease of the electron mobilities by two
orders of magnitude,on the other hand doping enforces a morphological change of
the zinc oxide layer which enables the infiltration of P3HT into the inorganic
matrix. X-ray reflectivity (XRR) measurements confirm this significant change
in the interface morphology for the various doping levels. We demonstrate that
doping of ZnO is a tool to adjust the charge transport in ZnO/P3HT hybrids,
using one single injecting metal (Au bottom contact) on a SiO2 dielectric. We
observe an influence of the zinc oxide layer on the hole mobility in P3HT which
we can modify via Al doping of ZnO. Hence, maximum hole mobility of 5e-4
cm^2/Vs in the hybrid system with 2 at.% Al doping. 5 at.% Al doping leads to a
balanced mobility in the organic/inorganic hybrid system but also to a small
on/off ratio due to high off-currents.",1006.4971v1
2010-08-01,How and why electrostatic charge of combustible nanoparticles can radically change the mechanism and rate of their oxidation in humid atmosphere,"Electrostatically charged aerosol nanoparticles strongly attract surrounding
polar gas molecules due to a charge-dipole interaction. In humid air, the
substantial electrostatic attraction and acceleration of surrounding water
vapour molecules towards charged combustible nanoparticles cause intense
electrostatic hydration and preferential oxidation of these nanoparticles by
accelerated water vapor molecules rather than non-polar oxygen molecules. In
particular, electrostatic acceleration, acquired by surrounding water vapour
molecules at a distance of their mean free path from the minimally charged iron
metal nanoparticle can increase an oxidative activity of these polar molecules
with respect to the nanoparticle by a factor of one million. Intense
electrostatic hydration of charged metal nanoparticles converts the
nanoparticle's oxide based shells into the hydroxide based electrolyte shells,
transforming these nanoparticles into metal/air core-shell nanobatteries,
periodically short-circuited by intra-particle field and thermionic electron
emission. Partially synchronized breakdowns within trillions of
nanoparticles-nanobatteries turn a cloud of charged nanoparticles-nanobatteries
- ball lightning - into a powerful radio-frequency aerosol generator.
Electrostatic hydration and charge-catalyzed oxidation of charged combustible
nanoparticles also contribute to a self-oscillating thermocycling process of
evolution and periodic auto-ignition of inflammable gases near to the
nanoparticle's surface. The described effects might be of interest for the
improvement of certain nanotechnological processes and to better understand
ball lightning phenomenon.",1008.0162v1
2011-02-13,Density functional theory based study of graphene and dielectric oxide interfaces,"We study the effects of insulating oxides in their crystalline forms on the
energy band structure of monolayer and bilayer graphene using a \textit{first
principles} density functional theory based electronic structure method and a
local density approximation. We consider the dielectric oxides, SiO$_{2}$
($\alpha$-quartz) and Al$_{2}$O$_{3}$ (alumina or $\alpha$-sapphire) each with
two surface terminations. Our study suggests that atomic relaxations and
resulting equilibrium separations play a critical role in perturbing the linear
band structure of graphene in contrast to the less critical role played by
dangling bonds that result from cleaving the crystal in a particular direction.
We also see that with the addition of a second graphene layer, the Dirac cone
is restored for the quartz surface terminations. Alumina needs more than two
graphene layers to preserve the Dirac cone. Our results are at best
semi-quantitative for the common amorphous forms of the oxides considered.
However, crystalline oxides for which our results are quantitative provide an
interesting option for graphene based electronics, particularly in light of
recent experiments on graphene with crystalline dielectrics (hexagonal BN) that
find considerable improvements in transport properties as compared to the those
with amorphous dielectrics.",1102.2557v1
2011-06-06,Evolution of an oxygen NEXAFS transition in the upper Hubbard band in α-Fe2O3 upon electrochemical oxidation,"Electrochemical oxidation of hematite ({\alpha}-Fe2O3) nano-particulate films
at 600 mV vs. Ag+/AgCl reference in KOH electrolyte forms a species at the
hematite surface which causes a new transition in the upper Hubbard band
between the Fe(3d)-O(2p) state region and the Fe(4sp)-O(2p) region, as
evidenced by oxygen near edge x-ray absorption fine structure (NEXAFS) spectra.
The electrochemical origin of this transition suggests that it is related with
a surface state. This transition, not known for pristine {\alpha}-Fe2O3 is at
about the same x-ray energy, where pristine 1% Si doped Si:Fe2O3 has such
transition. Occurrence of this state coincides with the onset of an oxidative
dark current wave at around 535 mV - a potential range, where the tunneling
exchange current has been previously reported to increase by three orders of
magnitude with the valence band and the transfer coefficient by a factor of 10.
Oxidation to only 200 mV does not form such extra NEXAFS feature, supporting
that a critical electrochemical potential between 200 and 600 mV is necessary
to change the electronic structure of the iron oxide at the surface. Decrease
of the surface roughness, as suggested by visual inspection, profilometry and
x-ray reflectivity, points to faceting as potential structural origin of the
surface state.",1106.1089v1
2013-01-08,Simulation of Metal/Oxide Interface Mobility: Effects of Mechanical Stresses on Geometrical Singularities,"During the last decade, an increasing importance has been given to the
feedback of mechanical stresses on the chemical diffusion and, further, on
corrosion. Many works point the active role of stresses on the material ageing
especially on their negative consequences leading to the damaging of
structures. Based on a theoretical study and using numerical tools and
experimental results our previous works [1, on stress/diffusion coupling,
highlight the strong influence of stress field on the diffusion process. The
aim of the present paper is to describe the influence of some particular
morphologies of the metal/oxide interface on both diffusion and oxidation
process. The oxidation is assumed to be driven by a mass conservation law
(Stefan's law) while the diffusion coefficient of oxygen in metal is locally
influenced by the stress field. The stability of a waved-shape interface is
studied in both cases: simple diffusion and coupled stress/diffusion process.
In this purpose we have developed an original numerical model using a virtual
metal/oxide interface of a mono-material with oxygen concentration-dependent
parameters, which allows to operate easily with any shape of interface and to
use simple finite element meshes. Furthermore, in order to underline in a more
obvious way the consequences of mechanical stress on the diffusion process, a
particular geometry is studied.",1301.1620v2
2013-04-15,Salmonella chemoreceptors McpB and McpC mediate a repellent response to L-cystine: a potential mechanism to avoid oxidative conditions,"Chemoreceptors McpB and McpC in Salmonella enterica have been reported to
promote chemotaxis in LB motility-plate assays. Of the chemicals tested as
potential effectors of these receptors, the only response was towards
L-cysteine and its oxidized form, L-cystine. Although enhanced radial migration
in plates suggested positive chemotaxis to both amino acids, capillary assays
failed to show an attractant response to either, in cells expressing only these
two chemoreceptors. In vivo fluorescence resonance energy transfer (FRET)
measurements of kinase activity revealed that in wild-type bacteria, cysteine
and cystine are chemoeffectors of opposing sign, the reduced form being a
chemoattractant and the oxidized form a repellent. The attractant response to
cysteine was mediated primarily by Tsr, as reported earlier for E. coli. The
repellent response to cystine was mediated by McpB / C. Adaptive recovery upon
cystine exposure required the methyl-transferase/-esterase pair, CheR / CheB,
but restoration of kinase activity was never complete (i.e. imperfect
adaptation). We provide a plausible explanation for the attractant-like
responses to both cystine and cysteine motility plates, and speculate that the
opposing signs of response to this redox pair might afford Salmonella a
mechanism to gauge and avoid oxidative environments.",1304.4006v1
2014-11-07,An embryo of protocell membrane: The capsule of graphene oxide,"Many signs indicate that the graphene could widely occur on the early Earth.
Here, we report a new theory that graphene might be an embryo of protocell
membrane, and found several evidences. Firstly, the graphene oxide and
phospholipid-graphene oxide composite would curl into capsules in strongly
acidic saturated solution of Pb(NO3)2 at low temperature, providing a
protective space for biochemical reactions. Secondly, L-animi acids exhibit
higher reactivity than D-animi acids for graphene oxides in favor of the
formation of left-handed proteins. Thirdly, monolayer graphene with nanopores
prepared by unfocused 84Kr25+ has high selectivity for permeation of the
monovalent metal ions (Rb+ > K+ > Cs+ > Na+ > Li+), but does not allow Cl-
through, which could be attributed to the ion exchange of oxygen-containing
groups on the rim of nanopores. It is similar to K+ channels, which would cause
efflux of some ions from capsule of graphene oxides with the decrease of pH in
the primitive ocean, creating a suitable inner condition for the origin of
life. Consequently, the strongly acidic, high salinity and strong radiation as
well as temperature changes in the early Earth, regarded as negative factors,
would be indispensable for the origin of protocell. In short, graphene bred
life, but digested gradually by the evolution.",1411.1903v2
2014-12-25,Theoretical and experimental investigation of vacancy-based doping of monolayer MoS$_2$ on oxide,"Monolayer transition metal dichalcogenides are novel, gapped two-dimensional
materials. Toward device applications, we consider MoS$_2$ layers on
dielectrics, in particular in this work, the effect of vacancies on the
electronic structure. In density-functional based simulations, we consider the
effects of near-interface O vacancies in the oxide slab, and Mo or S vacancies
in the MoS$_2$ layer. Band structures and atom-projected densities of states
for each system and with differing oxide terminations were calculated, as well
as those for the defect-free MoS$_2$-dielectrics system and for isolated
dielectric layers for reference. Among our results, we find that with O
vacancies, both the Hf-terminated HfO$_2$-MoS$_2$ system, and the O-terminated
and H-passivated Al$_2$O$_3$-MoS$_2$ systems appear metallic due to doping of
the oxide slab followed by electron transfer into the MoS$_2$, in manner
analogous to modulation doping. The n-type doping of monolayer MoS$_2$ by
high-k oxides with oxygen vacancies then is experimentally demonstrated by
electrically and spectroscopically characterizing back-gated monolayer MoS$_2$
field effect transistors encapsulated by oxygen deficient alumina and hafnia.",1412.7852v3
2015-03-23,Implications of the band gap problem on oxidation and hydration in acceptor-doped barium zirconate,"Charge carrier concentrations in acceptor-doped proton-conducting perovskites
are to a large extent determined by the hydration and oxidation of oxygen
vacancies, which introduce protons and holes, respectively. First-principles
modeling of these reactions involves calculation of formation energies of
charged defects, which requires an accurate description of the band gap and the
position of the band edges. Since density-functional theory (DFT) with local
and semi-local exchange-correlation functionals (LDA and GGA) systematically
fails to predict these quantities this can have serious implications on the
modeling of defect reactions. In this study we investigate how the description
of band gap and band edge positions affects the hydration and oxidation in
acceptor-doped BaZrO$_3$. First-principles calculations are performed in
combination with thermodynamic modeling in order to obtain equilibrium charge
carrier concentrations at different temperatures and partial pressures. Three
different methods have been considered: DFT with both semi-local (PBE) and
hybrid (PBE0) exchange-correlation functionals, and many-body perturbation
theory within the $G_0W_0$-approximation. All three methods yield similar
results for the hydration reaction, which are consistent with experimental
findings. For the oxidation reaction, on the other hand, there is a qualitative
difference. PBE predicts the reaction to be exothermic while the two others
predict an endothermic behavior. Results from thermodynamic modeling are
compared with available experimental data, such as enthalpies, concentrations
and conductivities, and only the results obtained with PBE0 and $G_0W_0$, with
an endothermic oxidation behavior, give a satisfactory agreement with
experiments.",1503.06612v1
2015-07-06,Final-state effect on x-ray photoelectron spectrum of nominally $d^1$ and $n$-doped $d^0$ transition metal oxides,"We investigate the x-ray photoelectron spectroscopy (XPS) of nominally $d^1$
and $n$-doped $d^0$ transition metal oxides including NbO$_2$, SrVO$_3$, and
LaTiO$_3$ (nominally $d^1$), as well as $n$-doped SrTiO$_3$ (nominally $d^0$).
In the case of single phase $d^1$ oxides, we find that the XPS spectra
(specifically photoelectrons from Nb $3d$, V $2p$, Ti $2p$ core levels) all
display at least two, and sometimes three distinct components, which can be
consistently identified as $d^0$, $d^1$, and $d^2$ oxidation states (with
decreasing order in binding energy). Electron doping increases the $d^2$
component but decreases the $d^0$ component, whereas hole doping reverses this
trend; a single $d^1$ peak is never observed, and the $d^0$ peak is always
present even in phase-pure samples. In the case of $n$-doped SrTiO$_3$, the
$d^1$ component appears as a weak shoulder with respect to the main $d^0$ peak.
We argue that these multiple peaks should be understood as being due to the
final-state effect and are intrinsic to the materials. Their presence does not
necessarily imply the existence of spatially localized ions of different
oxidation states nor of separate phases. A simple model is provided to
illustrate this interpretation, and several experiments are discussed
accordingly. The key parameter to determine the relative importance between the
initial-state and final-state effects is also pointed out.",1507.01507v1
2015-09-05,Two-Dimensional Oxide Topological Insulator With Iron-Pnictide Superconductor LiFeAs Structure,"By using first-principles calculations, we propose that ZrSiO can be looked
as a three-dimensional (3D) oxide weak topological insulator (TI) and its
single layer is a long-sought-after 2D oxide TI with a band gap up to 30 meV.
Calculated phonon spectrum of the single layer ZrSiO indicates it is
dynamically stable and the experimental achievements in growing oxides with
atomic precision ensure that it can be readily synthesized. This will lead to
novel devices based on TIs, the so called ""topotronic"" devices, operating under
room-temperature and stable when exposed in the air. Thus, a new field of
""topotronics"" will arise. Another intriguing thing is this oxide 2D TI has the
similar crystal structure as the well-known iron-pnictide superconductor
LiFeAs. This brings great promise in realizing the combination of
superconductor and TI, paving the way to various extraordinary quantum
phenomena, such as topological superconductor and Majorana modes. We further
find that there are many other isostructural compounds hosting the similar
electronic structure and forming a $WHM$-family with $W$ being Zr, Hf or La,
$H$ being group IV or group V element, and $M$ being group VI one.",1509.01686v2
2015-11-08,Stress Evolution in Lithium-ion Composite Electrodes during Electrochemical Cycling and Resulting Internal Pressures on the Cell Casing,"Composite cathode coatings made of a high energy density layered oxide
(Li1.2Ni0.15Mn0.55Co0.1O2, theoretical capacity ~377 mAh/g), polyvinylidene
fluoride (PVdF) binder, and electron-conduction additives, were bonded to an
elastic substrate. An electrochemical cell, built by pairing the cathode with a
capacity-matched graphite anode, was electrochemically cycled and the real-time
average stress evolution in the cathode coating was measured using a
substrate-curvature technique. Features in the stress evolution profile showed
correlations with phase changes in the oxide, thus yielding data complementary
to in situ XRD studies on this material. The stress evolution showed a complex
variation with lithium concentration suggesting that the volume changes
associated with phase transformations in the oxide are not monotonically
varying functions of lithium concentration. The peak tensile stress in the
cathode during oxide delithiation was approximately 1.5 MPa and the peak
compressive stress during oxide lithiation was about 6 MPa. Stress evolution in
the anode coating was also measured separately using the same technique. The
measured stresses are used to estimate the internal pressures that develop in a
cylindrical lithium-ion cell with jelly-roll electrodes.",1511.02445v1
2016-04-26,Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers,"A promising route to tailoring the electronic properties of quantum materials
and devices rests on the idea of orbital engineering in multilayered oxide
heterostructures. Here we show that the interplay of interlayer charge
imbalance and ligand distortions provides a knob for tuning the sequence of
electronic levels even in intrinsically stacked oxides. We resolve in this
regard the $d$-level structure of layered Sr$_2$IrO$_4$ by electron spin
resonance. While canonical ligand-field theory predicts $g_{\parallel}$-factors
$\!<\!2$ for positive tetragonal distortions as present in Sr$_2$IrO$_4$, the
experiment indicates $g_{\parallel}\!>\!2$. This implies that the iridium $d$
levels are inverted with respect to their normal ordering. State-of-the-art
electronic-structure calculations confirm the level switching in Sr$_2$IrO$_4$,
whereas we find them in Ba$_2$IrO$_4$ to be instead normally ordered. Given the
nonpolar character of the metal-oxygen layers, our findings highlight the
tetravalent transition-metal 214 oxides as ideal platforms to explore
$d$-orbital reconstruction in the context of oxide electronics.",1604.07780v1
2016-10-11,2D surprises at the surface of 3D materials: confined electron systems in transition metal oxides,"The scope of this article is to review the state-of-the-art in the field of
confined electron systems generated at the bare surfaces of transition metal
oxides (TMOs). This scientific field is a prime example of a domain where
two-dimensional physics and photoemission-based spectroscopic techniques have
together set up the development of the story. The discovery of a high-mobility
two-dimensional electron system (2DES) at interfaces of transition metal oxides
has attracted an immense scientific interest due to new opportunities opened in
the emerging field of oxide electronics. The subsequent paradigm shift from
interfaces to the bare surfaces of TMOs made the confined electron system
accessible to surface-sensitive spectroscopic techniques and this new era is
the focus of the present article. We describe how results by means of
Angle-Resolved Photoemission Spectroscopy (ARPES) establish the presence of
confined electron carriers at the bare surface of SrTiO$_{3}$(100), which
exhibit complex physics phenomena such as orbital ordering, electron-phonon
interactions and spin splitting. The key element behind the 2DES generation is
oxygen vacancies. Moreover, we review the experimental evidence on the
generation of 2DESs on surfaces with different orientation, as well as on
different TMO substrates. The electronic structure of the confined electron
system responds to such changes, thereby providing external means for
engineering its properties. Finally, we identify new directions for future
research by introducing a device-friendly fabrication protocol for the
generation of 2DESs on TMO surfaces.",1610.03221v1
2017-02-01,Water Permeation through Layered Graphene-based Membranes: A Fully Atomistic Molecular Dynamics Investigation,"Graphene-based membranes have been investigated as promising candidates for
water filtration and gas separation applications. Experimental evidences have
shown that graphene oxide can be impermeable to liquids, vapors and gases,
while allowing a fast permeation of water molecules. This phenomenon has been
attributed to the formation of a network of nano capillaries that allow nearly
frictionless water flow while blocking other molecules by steric hindrance
effects. It is supposed that water molecules are transported through the
percolated two-dimensional channels formed between graphene-based sheets.
Although these channels allow fast water permeation in such materials, the flow
rates are strongly dependent on how the membranes are fabricated. Also, some
fundamental issues regarding the nanoscale mechanisms of water permeation are
still not fully understood and their interpretation remains controversial. In
this work, we have investigated the dynamics of water permeation through
pristine graphene and graphene oxide model membranes. We have carried out fully
atomistic classical molecular dynamics simulations of systems composed of
multiple layered graphene-based sheets into contact with a water reservoir
under controlled thermodynamics conditions (e. g., by varying temperature and
pressure values). We have systematically analyzed how the transport dynamics of
the confined nanofluids depend on the interlayer distances and the role of the
oxide functional groups. Our results show the water flux is much more effective
for graphene than for graphene oxide membranes. These results are attributed to
the H-bonds formation between oxide functional groups and water, which traps
the water molecules and precludes ultrafast water transport through the
nanochannels.",1702.00250v1
2017-03-16,Enhanced atomic layer etching of native aluminum oxide for ultraviolet optical applications,"We report on the development and application of an atomic layer etching (ALE)
procedure based on alternating exposures of trimethylaluminum and anhydrous
hydrogen fluoride (HF) implemented to controllably etch aluminum oxide. Our ALE
process utilizes the same chemistry previously demonstrated in the atomic layer
deposition of aluminum fluoride thin films, and can therefore be exploited to
remove the surface oxide from metallic aluminum and replace it with thin
fluoride layers in order to improve the performance of ultraviolet aluminum
mirrors. This ALE process is modified relative to existing methods through the
use of a chamber conditioning film of lithium fluoride, which is shown to
enhance the loss of fluorine surface species and results in conformal
layer-by-layer etching of aluminum oxide films. Etch properties were explored
over a temperature range of 225 to 300 {\deg}C with the Al2O3 etch rate
increasing from 0.8 to 1.2 {\AA} per ALE cycle at a fixed HF exposure of 60 ms
per cycle. The effective etch rate has a dependence on the total HF exposure,
but the process is shown to be scalable to large area substrates with a
post-etch uniformity of better than 2% demonstrated on 125 mm diameter wafers.
The efficacy of the ALE process in reducing interfacial native aluminum oxide
on evaporated aluminum mirrors is demonstrated with characterization by x-ray
photoelectron spectroscopy and measurements of ultraviolet reflectance at
wavelengths down to 120 nm.",1703.05469v1
2018-04-28,Ambient condition production of high quality reduced graphene oxide,"Reduced graphene oxide becomes one of the most popular materials for
applications in various optical, electronic and sensor devices. Even though
many methods have been already reported for reduced graphene oxide synthesis,
they usually rise issues related to their efficiency, quality and environmental
impact. This work demonstrates a simple, environmentally friendly and effective
method for reducing graphene oxide under ambient conditions using nanosecond
infrared laser irradiation. As a result, a Raman band intensity ratio of
I(G)/I(D) of 4.59 was achieved with an average crystallite size of ~90 nm. This
graphene is of higher quality than what can be achieved with most of the
existing methods. Additionally, the demonstrated reduction technique allows the
selective reduction of graphene oxide and control the amount of functional
groups on the surface of the material. Gas sensors fabricated according to the
proposed technique efficiently detect NO$_2$, NH$_3$, and H$_2$S with the
sensitivity down to 10 ppm.",1804.10836v2
2018-10-31,Modelling N2O dynamics of activated sludge biomass under nitrifying and denitrifying conditions: pathway contributions and uncertainty analysis,"Nitrous oxide (N2O) is a potent greenhouse gas emitted during biological
wastewater treatment. A pseudo-mechanistic model describing three biological
pathways for nitric oxide (NO) and N2O production was calibrated for mixed
culture biomass from an activated sludge process using laboratory-scale
experiments. The model (NDHA) comprehensively describes N2O producing pathways
by both autotrophic ammonium oxidizing bacteria and heterotrophic bacteria.
Extant respirometric assays and anaerobic batch experiments were designed to
calibrate endogenous and exogenous processes (heterotrophic denitrification and
autotrophic ammonium/nitrite oxidation) together with the associated net N2O
production. Ten parameters describing heterotrophic processes and seven for
autotrophic processes were accurately estimated (variance/mean < 25%). The
model predicted NO and N2O dynamics at varying dissolved oxygen, ammonium and
nitrite levels and was validated against an independent set of experiments with
the same biomass. Aerobic ammonium oxidation experiments at two oxygen levels
used for model evaluation (2 and 0.5 mg/L) indicated that both the nitrifier
denitrification (42, 64%) and heterotrophic denitrification (7, 17%) pathways
increased and dominated N2O production at high nitrite and low oxygen
concentrations; while the nitrifier nitrification pathway showed the largest
contribution at high dissolved oxygen levels (51, 19%). The uncertainty of the
biological parameter estimates was propagated to N2O model outputs via Monte
Carlo simulations as 95% confidence intervals. The accuracy of the estimated
parameters resulted in a low uncertainty of the N2O emission factors (4.6 +-
0.6% and 1.2 +- 0.1%).",1811.00004v1
2019-05-20,Effect of UV radiation on the structure of graphene oxide in water and its impact on cytotoxicity and As(III) adsorption,"Graphene oxide (GO) is widely used in different applications, however once
release into the environment it can change its structure and affect the
transport of important contaminants such as arsenic. In this work we show that
UV radiation, even in the range of 28-74 uW/cm2 of irradiance up to 120 h of
exposure, can induce important changes in the structure of graphene oxide, by
eliminating -OH and C=O functional groups. This reduction affected the
stability of graphene oxide in water by decreasing its zeta potential from 41
to 37 mV with the increase of the exposure time. Our results showed that after
24 h of UV exposure, As(III) adsorption capacity decreased from 5 mg/g to 4.7
mg/g, however after 48 h of irradiation the adsorption increased with time,
reaching 5.1 mg/g at 120 h under 74 uW/cm2 of irradiation. Computer modelling
showed that even a degraded GO structure can have an interaction energy of 53
kcal/mol with H3AsO3. Furthermore, we observed that despite clear changes in
surface composition and particle size, the reduction of graphene oxide
maintained a high degree of cytotoxicity since cell viability decreased to 60%
with a 50 ug/ml dose; except for the sample irradiated at 74 uW/cm2 for five
days, which showed 20% with the same concentration.",1905.12167v1
2010-05-20,Comparison of the Oxidation State of Fe in Comet 81P/Wild 2 and Chondritic-Porous Interplanetary Dust Particles,"The fragile structure of chondritic-porous interplanetary dust particles (CP-
IDPs) and their minimal parent-body alteration have led researchers to believe
these particles originate in comets rather than asteroids where aqueous and
thermal alteration have occurred. The solar elemental abundances and
atmospheric entry speed of CP-IDPs also suggest a cometary origin. With the
return of the Stardust samples from Jupiter-family comet 81P/Wild 2, this
hypothesis can be tested. We have measured the Fe oxidation state of 15 CP-IDPs
and 194 Stardust fragments using a synchrotron-based x-ray microprobe. We
analyzed ~300 nanograms of Wild 2 material - three orders of magnitude more
material than other analyses comparing Wild 2 and CP-IDPs. The Fe oxidation
state of these two samples of material are >2{\sigma} different: the CP-IDPs
are more oxidized than the Wild 2 grains. We conclude that comet Wild 2
contains material that formed at a lower oxygen fugacity than the parent body,
or parent bodies, of CP-IDPs. If all Jupiter-family comets are similar, they do
not appear to be consistent with the origin of CP-IDPs. However, comets that
formed from a different mix of nebular material and are more oxidized than Wild
2 could be the source of CP-IDPs.",1005.3858v1
2016-11-21,The enabling electronic motif for topological insulation in ABO3 perovskites and its structural stability,"Stable oxide topological insulators (TIs) that could bring together the
traditional oxide functionalities with the dissipationless surface states of
TIs have been sought for years but none was found. Yet, heavier chalcogenides
(selenides, tellurides) were readily found to be TIs. We clarify here the basic
contradiction between TI-ness and stability which is maximal for oxides, and
trace the basic design principles necessary to identify the window of
opportunity of stable TIs. We first identify the electronic motif that can
achieve topological band inversion (""topological gene"") in ABO3 as being a
lone-pair electron-rich B atom (e.g. Te, I, Bi) at the octahedral site. We then
illustrate that poorly screened oxide systems with large inversion energies can
undergo energy-lowering atomic distortions that remove the band inversion. We
identify the coexistence windows of TI functionality and structure stability
for different pressures and find that the common cubic ABO3 structures have
inversion energies lying outside this coexistence window at zero pressure but
could be moved into the coexistence window at moderate pressures. Our study
demonstrates the interplay between topological band inversion and structural
stability and traces the basic principles needed to design stable oxide
topological insulators at ambient pressures.",1611.06839v3
2018-05-04,Silicon Oxide Electron-Emitting Nanodiodes,"Electrically driven on-chip electron sources that do not need to be heated
have been long pursued because the current thermionic electron sources show the
problems of high power consumption, slow temporal response, bulky size, etc.,
but their realization remains challenging. Here we show that a nanogap formed
by two electrodes on a silicon oxide substrate functions as an
electron-emitting nanodiode after the silicon oxide in the nanogap is
electrically switched to a high-resistance conducting state. A nanodiode based
on graphene electrodes can be turned on by a voltage of ~7 V in ~100 ns and
show an emission current of up to several microamperes, corresponding to an
emission density of ~10^6 A cm^-2 and emission efficiency as high as 16.6%. We
attribute the electron emission to be generated from a metal-insulator-metal
tunneling diode on the substrate surface formed by the rupture of conducting
filaments in silicon oxide. An array of 100 nanodiodes exhibits a global
emission density of 5 A cm^-2 and stable emission with negligible current
degradation over tens of hours under modest vacuum. The combined advantages of
a low operating voltage, fast temporal response, high emission density and
efficiency, convenient fabrication and integration, and stable emission in
modest vacuum make silicon oxide electron-emitting nanodiodes a promising
on-chip alternative to thermionic emission sources.",1805.01602v1
2018-05-08,Evaluation of reduced-graphene-oxide-supported gold nanoparticles as catalytic system for electroreduction of oxygen in alkaline electrolyte,"Chemically-reduced graphene-oxide-supported gold nanoparticles are considered
here as catalytic materials for the reduction of oxygen in alkaline medium.
Gold nanoparticles are prepared by the chemical reduction method, in which the
NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the
reducing agent for the precursor (HAuCl4). Polyoxmetallate (PMo12O403-) capping
ligands stabilize gold nanoparticle deposits, facilitate their dispersion and
attachment to carbon supports. Indeed, it is apparent from the independent
diagnostic voltammetric experiments (in 0.5 mol dm-3 H2SO4) that
heteropolymolybdates form readily stable adsorbates on nanostructures of both
gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect
that the polyoxometallate-assisted nucleation of gold has occurred in the
proximity of oxygenated defects existing on carbon substrates. Under conditions
of electrochemical diagnostic experiments (performed in 0.1 mol dm-3 KOH): (i)
the phosphomolybdate adsorbates are removed from the interface as they undergo
dissolution in alkaline medium; and (ii) the Au nanoparticles (Au loading, 30
{\mu}g cm-2) remain well-dispersed on the carbon as evident from transmission
electron microscopy. High electrocatalytic activity of the reduced-graphene
oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium
is demonstrated using cyclic and rotating ring-disk voltammetric experiments.
Among important issues are possible activating interactions between gold and
the support, as well as presence of structural defects existing on poorly
organized graphitic structure of reduced graphene oxide (as evident from Raman
spectroscopy).",1805.03156v1
2011-11-29,Electronic properties of layered multicomponent wide-bandgap oxides: a combinatorial approach,"The structural, electronic, and optical properties of twelve multicomponent
oxides with layered structure, RAMO$_4$, where R$^{3+}$=In or Sc; A$^{3+}$=Al
or Ga; and M$^{2+}$=Ca, Cd, Mg, or Zn, are investigated using first-principles
density functional approach. The compositional complexity of RAMO$_4$ leads to
a wide range of band gap values varying from 2.45 eV for InGaCdO$_4$ to 6.29 eV
for ScAlMgO$_4$. Strikingly, despite the different band gaps in the oxide
constituents, namely, 2-4 eV in CdO, In$_2$O$_3$, or ZnO; 5-6 for Ga$_2$O$_3$
or Sc$_2$O$_3$; and 7-9 eV in CaO, MgO, or Al$_2$O$_3$, the bottom of the
conduction band in the multicomponent oxides is formed from the s-states of all
cations and their neighboring oxygen p-states. We show that the hybrid nature
of the conduction band in multicomponent oxides originates from the unusual
five-fold atomic coordination of A$^{3+}$ and M$^{2+}$ cations which enables
the interaction between the spatially-spread s-orbitals of adjacent cations via
shared oxygen atoms. The effect of the local atomic coordination on the band
gap, the electron effective mass, the orbital composition of the conduction
band, and the expected (an)isotropic character of the electron transport in
layered RAMO$_4$ is thoroughly discussed.",1111.6864v1
2014-06-02,Superconductivity in titanium-based pnictide oxide compounds,"Superconductivity in a novel class of layered materials, Ti-based pnictide
oxides, was recently discovered. These compounds have attracted interest since
they combine features of copper oxide and iron pnictide superconductors. Here
the transition metal (titanium) forms two-dimensional Ti$_2$O layers (anti
structure to the CuO$_2$ planes), capped by pnictogen ions (similar to
Fe$_2$As$_2$ layers). The pnictide oxide compounds show a spin or charge
density wave phase which coexists with superconductivity in some members of the
family. Unlike the cuprates, but similar to iron pnictides, the parent
compounds of pnictide oxides are metals with specific nesting properties of the
Fermi surface which leads to the density wave instability. The nature of the
superconductivity, coexisting with the density wave order, and the possible
competition or mutual interaction between both states is one of the central
questions of recent studies. This short review summarizes the current knowledge
from an experimental as well as theoretical point of view and discusses some of
the open questions and possible future developments.",1406.0442v1
2016-05-10,Two Dimensional Phosphorus Oxides as Energy and Information Materials,"Two-dimensional (2D) black phosphorus (i.e., phosphorene) has become a rising
star in electronics. Recently, 2D phosphorus oxides with higher stability have
been synthesized. In this work, we systematically explore the structures and
properties of 2D phosphorus oxides on the basis of global optimization approach
and first-principles calculations. We find that the structural features of 2D
phosphorus oxides PxOy vary with the oxygen concentration. When the oxygen
content is poor, the most stable 2D PxOy can be obtained by adsorbing O atoms
on phosphorene. However, when the oxygen concentration becomes rich, stable
structures are no longer based on phosphorene and will contain P-O-P motifs.
For the 2D P4O4, we find that it has a direct band gap (about 2.24 eV), good
optical absorption, and high stability in water, suggesting that it may be good
candidate for photochemical water splitting application. Interestingly, 2D P2O3
adopt two possible stable ferroelectric structures (P2O3-I and P2O3-II) as the
lowest energy configurations within a given layer thickness. The electric
polarizations of P2O3-I and P2O3-II are perpendicular and parallel to the
lateral plane, respectively. We propose that 2D P2O3 could be used in a novel
nanoscale multiple-state memory device. Our work suggests that 2D phosphorus
oxides may be excellent functional materials.",1605.02830v1
2017-10-24,Strong localization of oxidized Co3+ state in cobalt-hexacyanoferrate,"Secondary batteries are important energy storage devices for a mobile
equipment, an electric car, and a large-scale energy storage. Nevertheless,
variation of the local electronic state of the battery materials in the charge
(or oxidization) process are still unclear. Here, we investigated the local
electronic state of cobalt-hexacyanoferrate (Na$_x$Co[Fe(CN)$_6$]$_{0.9}$), by
means of resonant inelastic X-ray scattering (RIXS) with high energy resolution
(~100 meV). The L-edge RIXS is one of the most powerful spectroscopic technique
with element- and valence-selectivity. We found that the local electronic state
around Co$^{2+}$ in the partially-charged
Na$_{1.1}$Co$^{2+}$$_{0.5}$Co$^{3+}$$_{0.5}$[Fe$^{2+}$(CN)$_6$]$_{0.9}$ film (x
= 1.1) is the same as that of the discharged
Na$_{1.6}$Co$^{2+}$[Fe$^{2+}$(CN)$_6$]$_{0.9}$ film (x = 1.6) within the energy
resolution, indicating that the local electronic state around Co$^{2+}$ is
invariant against the partial oxidization. In addition, the local electronic
state around the oxidized Co$^{3+}$ is essentially the same as that of the
fully-charged film
Co$^{3+}$[Fe$^{2+}$(CN)$_6$]$_{0.3}$[Fe$^{3+}$(CN)$_6$]$_{0.6}$ (x = 0.0) film.
Such a strong localization of the oxidized Co$^{3+}$ state is advantageous for
the reversibility of the redox process, since the localization reduces extra
reaction within the materials and resultant deterioration.",1710.08657v1
2017-10-26,Microwave Irradiation Assisted Deposition of Ga2O3 on III-nitrides for deep-UV opto-electronics,"We report on the deposition of gallium oxide using microwave irradiation
technique on III nitride epi layers. We also report on the first demonstration
of a gallium oxide device, a visible blind deep UV detector, with GaN based
heterostructure as the substrate. The film deposited in the solution medium, at
less than 200 C, using a metalorganic precursor, was nanocrystalline. XRD
confirms that as deposited film when annealed at high temperature turns
polycrystalline beta gallium oxide. SEM shows the as deposited film to be
uniform, with a surface roughness of 4 to 5 nm, as revealed by AFM.
Interdigitated metal semiconductor metal MSM devices with Ni,Au contact
exhibited peak spectral response at 230 nm and a good visible rejection ratio.
This first demonstration of a deep-UV detector on beta-gallium oxide on III
nitride stack is expected to open up new possibilities of functional and
physical integration of beta gallium oxide and GaN material families towards
enabling next generation high performance devices by exciting band and
heterostructure engineering.",1710.09615v3
2017-12-22,The Role of Oxygen in Ionic Liquid Gating on 2D Cr2Ge2Te6: a Non-Oxide Material,"Ionic liquid gating can markedly modulate the materials' carrier density so
as to induce metallization, superconductivity, and quantum phase transitions.
One of the main issues is whether the mechanism of ionic liquid gating is an
electrostatic field effect or an electrochemical effect, especially for oxide
materials. Recent observation of the suppression of the ionic liquid
gate-induced metallization in the presence of oxygen for oxide materials
suggests the electrochemical effect. However, in more general scenarios, the
role of oxygen in ionic liquid gating effect is still unclear. Here, we perform
the ionic liquid gating experiments on a non-oxide material: two-dimensional
ferromagnetic Cr2Ge2Te6. Our results demonstrate that despite the large
increase of the gate leakage current in the presence of oxygen, the oxygen does
not affect the ionic liquid gating effect (< 5 % difference), which suggests
the electrostatic field effect as the mechanism on non-oxide materials.
Moreover, our results show that the ionic liquid gating is more effective on
the modulation of the channel resistances compared to the back gating across
the 300 nm thick SiO2.",1712.08281v1
2018-09-03,Atomic and electronic structure of graphene oxide/Cu interface,"The results of X-ray photoemission (XPS) and valence bands spectroscopy,
optically stimulated electron emission (OSEE) measurements and density
functional theory based modeling of graphene oxide (GO) placed on Cu via an
electrophoretic deposition (EPD) are reported. The comparison of XPS spectra of
EPD prepared GO/Cu composites with those of as prepared GO, strongly reduced
GO, pure and oxidized copper demonstrate the partial (until C/O ratio about
two) removal of oxygen-containing functional groups from GO simultaneously with
the formation of copper oxide-like layers over the metallic substrate. OSEE
measurements evidence the presence of copper oxide phase in the systems
simultaneously with the absence of contributions from GO with corresponding
energy gap. All measurements demonstrate the similarity of the results for
different thickness of GO cover of the copper surface. Theoretical modeling
demonstrates favorability of migration of oxygen-containing functional groups
from GO to the copper substrate only for the case of C/O ratio below two and
formation of Cu-O-C bonds between substrate and GO simultaneously with the
vanishing of the energy gap in GO layer. Basing on results of experimental
measurements and theoretical calculations we suggest the model of atomic
structure for Cu/GO interface as Cu/CuO/GO with C/O ratio in gapless GO about
two.",1809.00450v1
2019-07-30,Energy Conversion via Metal Nanolayers,"Current approaches for electric power generation from nanoscale conducting or
semi-conducting layers in contact with moving aqueous droplets are promising as
they show efficiencies of around 30 percent, yet, even the most successful ones
pose challenges regarding fabrication and scaling. Here, we report stable,
all-inorganic single-element structures synthesized in a single step that
generate electrical current when alternating salinity gradients flow along its
surface in a liquid flow cell. 10 nm to 30 nm thin nanolayers of iron,
vanadium, or nickel produce several tens of mV and several microA cm^-2 at
aqueous flow velocities of just a few cm s^-1. The principle of operation is
strongly sensitive to charge-carrier motion in the thermal oxide nano-overlayer
that forms spontaneously in air and then self terminates. Indeed, experiments
suggest a role for intra-oxide electron transfer for Fe, V, and Ni nanolayers,
as their thermal oxides contain several metal oxidation states, whereas
controls using Al or Cr nanolayers, which self-terminate with oxides that are
redox inactive under the experimental conditions, exhibit dramatically
diminished performance. The nanolayers are shown to generate electrical current
in various modes of application with moving liquids, including sliding liquid
droplets, salinity gradients in a flowing liquid, and in the oscillatory motion
of a liquid without a salinity gradient.",1907.13170v1
2020-04-21,Role of interfacial oxidation in generation of spin-orbit torques,"We report that current-induced spin-orbit torques (SOTs) in
heavy-metal/ferromagnetic-metal bilayers are strongly altered by the oxidation
of the ferromagnetic layer near the interface. We measured damping-like (DL)
and field-like (FL) SOTs for Pt/Co and Pt/Ni$_{81}$Fe$_{19}$ (Pt/Py) films
using spin-torque ferromagnetic resonance. In the Pt/Co film, we found that the
oxidation of the Co layer near the interface enhances both DL and FL SOTs in
spite of the insulating nature of the CoO$_x$ layer. The enhancement of the
SOTs disappears by inserting a thin Ti layer at the Pt/CoO$_x$ interface,
indicating that the dominant source of the SOTs in the Pt/CoO$_x$/Co film is
the spin-orbit coupling at the Pt/CoO$_x$ interface. In contrast to the
Pt/CoO$_x$/Co film, the SOTs in the Pt/PyO$_x$/Py film are dominated by the
bulk spin-orbit coupling. Our result shows that the interfacial oxidation of
the Pt/Py film suppresses the DL-SOT and reverses the sign of the FL-SOT. The
change of the SOTs can be attributed to the change of the real and imaginary
parts of the spin mixing conductance induced by the insertion of the insulating
PyO$_x$ layer. These results show that the interfacial oxidation provides an
effective way to manipulate the strength and sign of the SOTs.",2004.09837v1
2020-12-05,Origin of ferroelectricity and multiferroicity in binary oxide thin films,"The observation of ferroelectric, ferromagnetic and ferroelastic phases in
thin films of binary oxides attract the broad interest of scientists and
engineers. However, the theoretical consideration of observed behaviour
physical nature was performed mainly for HfO2 thin films from the first
principles, and in the framework of Landau-Ginzburg-Devonshire (LGD)
phenomenological approach with a special attention to the role of oxygen
vacancies in both cases. Allowing for generality of the LGD theory we applied
it to the group of binary oxides in this work. The calculations have been
performed in the assumption that oxygen vacancies, as elastic dipoles, can be
partially transformed into electric dipoles due to the defect site-induced
and/or surface-induced inversion symmetry breaking (via e.g. piezoelectric
effect), and can ""migrate"" entire the depth of an ultra-thin film. We
calculated the dependence of the film polarization on the applied voltage for
room temperature and different film thickness. Since the many films of binary
oxide are ferroelectric and ferromagnetic due to the same oxygen vacancies,
they can be multiferroics. Performed calculations have shown that thin films of
binary oxides can be considered as a new wide class of multiferroics with broad
spectra of physical properties useful for application in nanoelectronics and
nanotechnology. The properties can be controlled by the choice of oxygen
vacancies concentration, film thickness and special technological treatment,
such as annealing.",2012.03136v1
2017-05-13,Effects of layer thickness on the mechanical behavior of oxidation-strengthened Zr/Nb nanoscale multilayers,"The mechanical behaviour and deformation mechanisms of magnetron-sputtered
Zr/Nb nanoscale multilayers were analysed as a function of the periodicity (L =
10 and 75 nm) and annealing time at 350C (2-336 hrs). The strength of the
as-deposited multilayers was independent of the layer thickness and it was
controlled by the co-deformation of the Zr and Nb layers. Annealing led to
transformation of the Zr layers into ZrO2 after a few hours, while the Nb
layers oxidised at a much slower rate. The volumetric expansion associated with
the oxidation led to the formation of cracks at the interfaces and within the
ZrO2 layers for the multilayers with L = 75 nm but not in the case of L = 10
nm. The nanoindentation hardness increased significantly after annealing due to
the contribution of the residual stresses associated with the volume increase
due to oxidation and to the higher strength of the oxides. The strength
increase after annealing, as measured by micropillar compression tests, was
smaller than that measured by nanoindentation, as it did not include the
contribution of the residual stresses, which were relieved during micropillar
fabrication. The nanolaminate with L = 10 nm presented the highest strength and
toughness as damage during oxidation was suppressed, and a deformation
mechanism controlled by the formation of shear bands.",1705.04805v2
2017-11-13,Electronic Reconstruction Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films,"Quantum mechanical tunneling of electrons across ultrathin insulating oxide
barriers has been studied extensively for decades due to its great potential in
electronic device applications. In the few-nanometer-thick epitaxial oxide
films, atomic-scale structural imperfections, such as the ubiquitously existed
one-unit-cell-high terrace edges, can dramatically affect the tunneling
probability and device performance. However, the underlying physics has not
been investigated adequately. Here, taking ultrathin BaTiO3 films as a model
system, we report an intrinsic tunneling conductance enhancement near the
terrace edges. Scanning probe microscopy results demonstrate the existence of
highly-conductive regions (tens of nanometers-wide) near the terrace edges.
First-principles calculations suggest that the terrace edge geometry can
trigger an electronic reconstruction, which reduces the effective tunneling
barrier width locally. Furthermore, such tunneling conductance enhancement can
be discovered in other transition-metal-oxides and controlled by surface
termination engineering. The controllable electronic reconstruction could
facilitate the implementation of oxide electronic devices and discovery of
exotic low-dimensional quantum phases.",1711.04622v1
2018-06-06,Epitaxial Strain-Dependence of Band Gaps in Oxynitrides compared to Oxides,"Perovskite oxynitrides are a promising class of material for photocatalytic
water-splitting due to their small band gaps and suitably aligned band edges.
Recently, epitaxially strained oxynitrides started to attract interest due to
the possibility to engineer the anion order and ferroelectric distortions.
However, contrary to oxides there have been no studies on the band-gap
evolution in oxynitrides with epitaxial strain. Here, we investigate, using
density functional theory calculations, the influence of epitaxial strain on
the band gap of two different oxynitrides and compare our results with oxides.
As opposed to cubic oxides, where both compressive and tensile strain narrow
the band-gap, we find that the anion order leads to non-degenerate N
\textit{2p} bands already at zero strain, which leads to opposite and anion
order-dependent evolutions of the band gap under compressive and tensile
strain. Further, we find that in oxynitrides polar distortions increase the
band gap by up to 1 eV for 4% strain whereas for oxides the increase is only
about 0.1 eV for the same amount of strain. The reason for this difference is
the larger ionic radius of nitrogen leading to larger ferroelectric distortions
and a stronger dependence of the band gap on the distortions amplitude. These
results imply that ferroelectric distortions are strongly detrimental to light
absorption and that their suppression, for example above a critical
temperature, should result in a marked decrease in band gap and enhanced
absorption of visible light.",1806.02050v1
2019-02-18,Giant Conductivity Modulation of Aluminum Oxide using Focused Ion Beam,"Precise control of the conductivity of semiconductors through doping has
enabled the creation of advanced electronic devices, similarly, the ability to
control the conductivity in oxides can enable novel advanced electronic and
optoelectronic functionalities. While this was successfully shown for
moderately insulating oxides, such as In2O3, a reliable method for increasing
the conductivity of highly insulating, wide bandgap dielectrics, such as
aluminum oxide (Al2O3), has not been reported yet. Al2O3 is a material of
significant technological interest, permeating diverse fields of application,
thanks to its exceptional mechanical strength and dielectric properties. Here
we present a versatile method for precisely changing the conductivity of Al2O3
. Our approach greatly exceeds the magnitude of the best previously reported
change of conductivity in an oxide. Our method uses focused ion beam to produce
conductive zones with nanoscale resolution within the insulating Al2O3 matrix.
We investigated the source of conductivity modulation and identified
trap-assisted conduction in the ion damage-induced defects as the main charge
transport mechanism. Temperature-dependency of the conductivity and optical
characterization of the patterned areas offer further insight into the nature
of the conduction mechanism. We also show that the process is extremely
reproducible and robust against moderate annealing temperatures and chemical
environment. The record conductivity modulation, combined with the nanoscale
patterning precision allows the creation of conductive zones within a highly
insulating, mechanically hard, chemically inert, and bio-compatible matrix,
which could find broad applications in electronics, optoelectronics, and
medical implants",1902.06821v1
2019-03-05,Selecting between two transition states by which water oxidation intermediates on an oxide surface decay,"While catalytic mechanisms on electrode surfaces have been proposed for
decades, the pathways by which the product's chemical bonds evolve from the
initial charge-trapping intermediates have not been resolved in time. Here, we
discover a reactive population of charge-trapping intermediates with states in
the middle of a semiconductor's band-gap to reveal the dynamics of two parallel
transition state pathways for their decay. Upon photo-triggering the water
oxidation reaction from the n-SrTiO3 surface with band-gap, pulsed excitation,
the intermediates' microsecond decay reflects transition state theory (TST)
through: (1) two distinct and reaction dependent (pH, T, Ionic Strength, and
H/D exchange) time constants, (2) a primary kinetic salt effect on each
activation barrier and an H/D kinetic isotope effect on one, and (3) realistic
activation barrier heights (0.4 - 0.5 eV) and TST pre-factors (10^11 - 10^12
Hz). A photoluminescence from midgap states in n-SrTiO3 reveals the reaction
dependent decay; the same spectrum was previously assigned by us to
hole-trapping at parallel Ti-O(dot)-Ti (bridge) and perpendicular Ti-O(dot)
(oxyl) O-sites using in situ ultrafast vibrational and optical spectroscopy.
Therefore, the two transition states are naturally associated with the decay of
these respective intermediates. Furthermore, we show that reaction conditions
select between the two pathways, one of which reflects a labile intermediate
facing the electrolyte (the oxyl) and the other a lattice oxygen (the bridge).
Altogether, we experimentally isolate an important activation barrier for water
oxidation, which is necessary for designing water oxidation catalysts with high
O2 turn over. Moreover, in isolating it, we identify competing mechanisms for
O2 evolution at surfaces and show how to use reaction conditions to select
between them.",1903.01675v1
2019-03-07,Low-loss waveguides on Y-cut thin film lithium niobate: towards acousto-optic applications,"We investigate the dependence of photonic waveguide propagation loss on the
thickness of the buried oxide layer in Y-cut lithium niobate on insulator
substrate to identify trade-offs between optical losses and electromechanical
coupling of surface acoustic wave (SAW) devices for acousto-optic applications.
Simulations show that a thicker oxide layer reduces the waveguide loss but
lowers the electromechanical coupling coefficient of the SAW device. Optical
racetrack resonators with different lengths were fabricated by argon plasma
etching to experimentally extract waveguide losses. By increasing the thickness
of the oxide layer from 1 {\mu}m to 2 {\mu}m, propagation loss of 2 {\mu}m (1
{\mu}m) wide waveguide was reduced from 1.85 dB/cm (3 dB/cm) to as low as 0.37
dB/cm (0.77 dB/cm), and, resonators with quality factor greater than 1 million
were demonstrated. An oxide thickness of approximately 1.5 {\mu}m is sufficient
to significantly reduce propagation loss due to leakage into the substrate and
simultaneously attain good electromechanical coupling in acoustic devices. This
work not only provides insights on the design and realization of low-loss
photonic waveguides in lithium niobate, but most importantly offers
experimental evidence on how the oxide thickness directly impacts losses and
guides its selection for the synthesis of high-performance acousto-optic
devices in Y-cut lithium niobate on insulator.",1903.07567v1
2019-03-27,Ferroelectric ZrO$_{2}$ monolayers as buffer layers between SrTiO$_{3}$ and Si,"A monolayer of ZrO$_{2}$ has recently been grown on the Si(001) surface and
shown to have ferroelectric properties, which signifies the realization of the
lowest possible thickness in ferroelectric oxides [M. Dogan et al., Nano Lett.,
18 (1) (2018)]. In our previous computational study, we reported on the
multiple (meta)stable configurations of ZrO$_{2}$ monolayers on Si, and how
switching between a pair of differently polarized configurations may explain
the observed ferroelectric behavior of these films [M. Dogan and S.
Ismail-Beigi, arXiv:1902.01022 (2019)]. In the current study, we conduct a
DFT-based investigation of (i) the effect of oxygen content on the ionic
polarization of the oxide, and (ii) the role of zirconia monolayers as buffer
layers between silicon and a thicker oxide film that is normally paraelectric
on silicon, e.g. SrTiO$_{3}$. We find that (i) total energy-vs-polarization
behavior of the monolayers, as well as interface chemistry, is highly dependent
on the oxygen content; and (ii) SrTiO$_{3}$/ZrO$_{2}$/Si stacks exhibit
multiple (meta)stable configurations and polarization profiles, i.e. zirconia
monolayers can induce ferroelectricity in oxides such as SrTiO$_{3}$ when used
as a buffer layer. This may enable a robust non-volatile device architecture
where the thickness of the gate oxide (here strontium titanate) can be chosen
according to the desired properties.",1903.11716v1
2019-11-11,Strain-driven superplasticity and modulation of electronic properties of ultrathin tin (II) oxide: A first-principles study,"2D-layered tin (II) oxide (SnO) has recently emerged as a promising bipolar
channel material for thin-film transistors and complementary
metal-oxide-semiconductor devices. In this work, we present a first-principles
investigation of the mechanical properties of ultrathin SnO, as well as the
electronic implications of tensile strain ($\epsilon$) under both uniaxial and
biaxial conditions. Bulk-to-monolayer transition is found to significantly
lower the Young's and shear moduli of SnO, highlighting the importance of
interlayer Sn-Sn bonds in preserving structural integrity. Unprecedentedly,
few-layer SnO exhibits superplasticity under uniaxial deformation conditions,
with a critical strain to failure of up to 74% in the monolayer. Such
superplastic behavior is ascribed to the formation of a tri-coordinated
intermediate (referred to here as h-SnO) beyond $\epsilon$ = 14%, which
resembles a partially-recovered orthorhombic phase with relatively large work
function and wide indirect band gap. The broad structural range of tin (II)
oxide under strongly anisotropic mechanical loading suggests intriguing
possibilities for realizing novel hybrid nanostructures of SnO through strain
engineering. The findings reported in this study reveal fundamental insights
into the mechanical behavior and strain-driven electronic properties of tin
(II) oxide, opening up exciting avenues for the development of SnO-based
nanoelectronic devices with new, non-conventional functionalities.",1911.04039v1
2019-10-21,Experimental Investigation of the Settling Characteristics of Carbon and Metal Oxide Nanofuels,"Fuels dispersed with engineered nanoparticle additives, or nanofuels, are
desirable for the vastly different combustion properties such as combustion
rate and ignition delay they exhibit compared to base fuels. The stability of
such nanofuels over time and under different particle loadings is a very
important parameter to consider before they can be put into practical use. Many
techniques exist today to analyze suspension stability, which have been
developed to analyze water-based nanofluids. Sometimes these techniques can be
expensive, and/or require specialized equipment, and/or require a method that
is invasive and disturbs the suspension. Present research uses a non-contact,
non-invasive, low-cost experimental setup to analyze suspension stability over
long periods of time. Nanofuels made from carbon-based nanomaterials (acetylene
black, multiwalled carbon nanotubes) and metal oxide nanomaterials (copper
oxide, aluminum oxide) with hydrocarbon fuels (canola biodiesel, petrodiesel)
have been prepared and their settling rates have been analyzed over the period
of three days. It is found that metal oxides go through several metastable
states as they settle. The effect of initial concentration and liquid column
height is shown. It is hoped that present research showcases the positive
traits of the presented technique and will spark further interest in nanofuel
stability.",1911.12238v1
2020-08-22,High-Performance Thermoelectric Oxides Based on Spinel Structure,"High-performance thermoelectric oxides could offer a great energy solution
for integrated and embedded applications in sensing and electronics industries.
Oxides, however, often suffer from low Seebeck coefficient when compared with
other classes of thermoelectric materials. In search of high-performance
thermoelectric oxides, we present a comprehensive density functional
investigation, based on GGA$+U$ formalism, surveying the 3d and 4d
transition-metal-containing ferrites of the spinel structure. Consequently, we
predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm
600$ $\mu$V K$^{-1}$ at near room temperature, achieved by light hole and
electron doping. Furthermore, CrFe$_2$O$_4$ and MoFe$_2$O$_4$ have even higher
ambient Seebeck coefficients at $\sim \pm 700$ $\mu$V K$^{-1}$. In the latter
compounds, the Seebeck coefficient is approximately a flat function of
temperature up to $\sim 700$ K, offering a tremendous operational convenience.
Additionally, MoFe$_2$O$_4$ doped with $10^{19}$ holes/cm$^3$ has a calculated
thermoelectric power factor of $689.81$ $\mu$W K$^{-2}$ m$^{-1}$ at $300$ K,
and $455.67$ $\mu$W K$^{-2}$ m$^{-1}$ at $600$ K. The thermoelectric properties
predicted here can bring these thermoelectric oxides to applications at lower
temperatures traditionally fulfilled by more toxic and otherwise burdensome
materials.",2008.09759v1
2020-10-29,Disassembling of TEMPO-oxidized cellulose fibers: intersheet and interchain interactions in the isolation of nanofibers and unitary chains,"Cellulose disassembly is an important issue in designing nanostructures using
cellulose-based materials. In this work, we present a joint of experimental and
theoretical study addressing the disassembly of cellulose nanofibrils. Through
2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidation processes,
combined with atomic force microscopy results, we find the formation of
nanofibers with diameters corresponding to a single cellulose polymer chain.
The formation of these polymer chains is ruled by repulsive electrostatic
interactions between the oxidized chains. Further first-principles calculations
have been done in order to provide an atomistic understanding the cellulose
disassembling processes, focusing on the balance of the interchain and
intersheet interactions upon oxidation. Firstly we analyse these interaction in
pristine systems, where we found the intersheet interaction stronger than the
interchain one. In the oxidized systems, we have considered the formation of
(charged) carboxylate groups along the inner sites of elementary fibrils. We
show a net charge concentration on the carboxylate groups, supporting the
emergence of repulsive electrostatic interactions between the cellulose
nanofibers. Indeed, our total energy results show that the weakening of the
binding strength between the fibrils is proportional to the concentration and
the net charge density of the carboxylate group. Moreover, by comparing
interchain and intersheet binding energies, we found that most of the
disassembly processes should take place by breaking the interchain
O--H$\cdots$O hydrogen bond interactions, and thus supporting the experimental
observation of single and double cellulose polymeric chains.",2010.15686v2
2020-11-17,Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides,"Immobilization of polyoxometalates (POMs) onto oxides is relevant to many
applications in the fields of catalysis, energy conversion/storage or molecular
electronics. Optimization and understanding the molecule/oxide interface is
crucial to rationally improve the performance of the final molecular materials.
We herein describe the synthesis and covalent grafting of POM hybrids with
remote carboxylic acid functions onto flat Si/SiO2 substrates. Special
attention has been paid to the characterization of the molecular layer and to
the description of the POM anchoring mode at the oxide interface through the
use of various characterization techniques, including ellipsometry, AFM, XPS
and FTIR. Finally, electron transport properties were probed in a vertical
junction configuration and energy level diagrams have been drawn and discussed
in relation with the POM molecular electronic features inferred from
cyclic-voltammetry, UV-visible absorption spectra and theoretical calculations.
The electronic properties of these POM-based molecular junctions are driven by
the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring
group.",2011.08953v1
2021-04-07,Antioxidant activity and toxicity study of cerium oxide nanoparticles stabilized with innovative functional copolymers,"Oxidative stress, which is one of the main harmful mechanisms of pathologies
including is-chemic stroke, contributes to both neurons and endothelial cell
damages, leading to vascular lesions. Although many antioxidants have been
tested in preclinical studies, no treatment is currently available for stroke
patients. Since cerium oxide nanoparticles (CNPs) exhibit remarkable
antioxidant capacities, our objective is to develop an innovative coating to
enhance CNPs biocompatibility without disrupting their antioxidant capacities
or enhance their toxicity. This study reports the synthesis and
characterization of functional polymers and their impact on the enzyme-like
catalytic activity of CNPs. To study the toxicity and the antioxidant
properties of CNPs for stroke and particularly endothelial damages, in vitro
studies are conducted on a cerebral endothelial cell line (bEnd.3). Despite
their internalization in bEnd.3 cells, coated CNPs are devoid of cytotoxicity.
Microscopy studies report an intracellular localization of CNPs, more precisely
in endosomes. All CNPs reduces glutamate-induced intracellular production of
ROS in endothelial cells but one CNP significantly reduces both the production
of mitochondrial super-oxide anion and DNA oxidation. In vivo studies report a
lack of toxicity in mice. This study there-fore describes and identifies
biocompatible CNPs with interesting antioxidant properties for ischemic stroke
and related pathologies.",2104.03005v1
2021-05-21,Deciphering the Rotational Spectrum of the First Excited Torsional State of Propylene Oxide,"The first excited torsional state of the chiral molecule propylene oxide,
$\mathrm{CH_{3}C_{2}H_{3}O}$, is investigated from millimeter up to
sub-millimeter wavelengths (75-950 GHz). The first excited vibrational mode of
propylene oxide, $\upsilon_{24}$, is analysed using the programs ERHAM and
XIAM. Rotational constants and tunneling parameters are provided, and a
description of the A-E splittings due to internal rotation is given.
Furthermore, the potential barrier height to internal rotation $V_{3}$ is
determined to be $V_{3} = 894.5079(259) \mathrm{cm^{-1}}$ . Our results are
compared with quantum chemical calculations and literature values. We present a
line list of the dense spectrum of the first excited torsional state of
propylene oxide in the (sub-)millimeter range. Our results will be useful for
further studies of chiral molecules in vibrationally excited states, and will
enable astronomers to search for rotational transitions originating from
$\upsilon_{24}$ of propylene oxide in interstellar space.",2105.10248v1
2021-07-01,Solid Source Metal-Organic Molecular Beam Epitaxy of Epitaxial RuO2,"A seemingly simple oxide with a rutile structure, RuO2 has been shown to
possess several intriguing properties ranging from strain-stabilized
superconductivity to a strong catalytic activity. Much interest has arisen
surrounding the controlled synthesis of RuO2 films but, unfortunately,
utilizing atomically-controlled deposition techniques like molecular beam
epitaxy (MBE) has been difficult due to the ultra-low vapor pressure and low
oxidation potential of Ru. Here, we demonstrate the growth of epitaxial,
single-crystalline RuO2 films on different substrate orientations using the
novel solid-source metal-organic (MO) MBE. This approach circumvents these
issues by supplying Ru using a pre-oxidized solid metal-organic precursor
containing Ru. High-quality epitaxial RuO2 films with bulk-like
room-temperature resistivity of 55 micro-ohm-cm were obtained at a substrate
temperature as low as 300 C. By combining X-ray diffraction, transmission
electron microscopy, and electrical measurements, we discuss the effect of
substrate temperature, orientation, film thickness, and strain on the structure
and electrical properties of these films. Our results illustrating the use of
novel solid-source MOMBE approach paves the way to the atomic-layer controlled
synthesis of complex oxides of stubborn metals, which are not only difficult to
evaporate but also hard to oxidize.",2107.00193v1
2021-07-06,Reactivity of Ru oxides with air radiolysis products investigated by theoretical calculations,"Quantitative predictions of the release of volatile radiocontaminants of
ruthenium (Ru) in the environment from either nuclear power plants (NPP) or
fuel recycling accidents present significant uncertainties while estimated by
severe accidents nuclear analysis codes. Observations of Ru from either
experimental or modeling works suggest that the main limitations relate to the
poor evaluation of the kinetics of gaseous Ru in the form of RuO$_3$ and
RuO$_4$. This work presents relativistic correlated quantum chemical
calculations performed to determine the possible reactions pathways leading to
the formation of gaseous Ru oxides under NPP severe accident conditions, as a
result of reactions of RuO$_2$ gaseous with air radiolysis products, namely
nitrous and nitrogen oxides. The geometries of the relevant species were
optimized with the TPSSh-5%HF functional of the density, while the total
electronic energies were computed at the CCSD(T) level with extrapolations to
the complete basis set CBS limit. The reaction pathways were fully
characterized by localizing the transition states and all intermediate
structures using the internal coordinate reaction algorithm (IRC). The rate
constants were determined over the temperature range 250-2500 K. It is revealed
that the less kinetically limiting pathway to form Ru gaseous fraction is the
oxidation of Ru by nitrogen oxide, corroborating experimental observations.",2107.02631v2
2021-08-04,Quasi-HfO$_x$/ AlO$_y$ and AlO$_y$/ HfO$_x$ Based Memristor Devices: Role of Bi-layered Oxides in Digital Set and Analog Reset Switching,"Understanding the resistive switching behavior, or the resistance change, of
oxide-based memristor devices, is critical to predicting their responses with
known electrical inputs. Also, with the known electrical response of a
memristor, one can confirm its usefulness in non-volatile memory and/or in
artificial neural networks. Although bi- or multi-layered oxides have been
reported to improve the switching performance, compared to the single oxide
layer, the detailed explanation about why the switching can easily be improved
for some oxides combinations is still missing. Herein, we fabricated two types
of bi-layered heterostructure devices, quasi-HfO$_x$/AlO$_y$ and
AlO$_y$/HfO$_x$ sandwiched between Au electrodes, and their electrical
responses are investigated. For a deeper understanding of the switching
mechanism, the performance of a HfOx only device is also considered, which
serves as a control device. The role of bi-layered heterostructures is
investigated using both the experimental and simulated results. Our results
suggest that synergistic switching performance can be achieved with a proper
combination of these materials and/or devices. These results open the avenue
for designing more efficient double- or multi-layers memristor devices for an
analog response.",2108.02247v2
2021-08-16,Physics-based Constitutive Modeling of Photo-oxidative Aging in Semi-Crystalline Polymers based on Chemical Characterization Techniques,"This paper proposes a physio-chemically-based constitutive framework to
simulate and predict the response of semi-crystalline low-density polyethylene
(LDPE) to severe photo-oxidation. Photo-oxidation induced by exposure to
Ultra-Violet (UV) light and oxygen is the dominant degradation mechanism
affecting the lifespan of LDPE. In this work, we propose evolution functions
for the material properties in the constitutive equations of
\cite{boyce2000constitutive} to incorporate the effects of photo-oxidation on
the mechanical response of LDPE. The evolution functions are based on
chemically verified processes that are responsible for material degradation,
namely the change in crystallinity and mass loss relative to the initial
pristine films over exposure time. Changes in crystallinity and mass loss are
characterized by Differential Scanning Calorimetry (DSC) and Quartz Crystal
Microbalance with Dissipation Monitoring (QCM-D) experiments, respectively.
Connecting the physio-chemical processes affecting polymer network evolution to
the mechanical response of LDPE bypasses the need for defining fitting
parameters that carry no physical meaning. The developed constitutive framework
is validated with respect to a series of in-house uniaxial tensile tests
performed on LDPE aged for different UV exposure times. Comparison of the
constitutive framework versus experimental mechanical tests also confirms the
accuracy of DSC and QCM-D as rigorous techniques to monitor and characterize
degradation in LDPE films. The outcome shed light on the evolution of the
macromolecular network in LDPE under extreme photo-oxidation and the evolution
of the associated mechanical material properties.",2108.07143v1
2021-10-12,Topological Defects and Unique Stacking Disorders in Honeycomb Layered Oxide $\rm K_2Ni_2TeO_6$ Nanomaterials: Implications for Rechargeable Batteries,"Endowed with a multitude of exquisite properties such as rich
electrochemistry, superb topology and eccentric electromagnetic phenomena,
honeycomb layered oxides have risen to the top echelons of science with
applications in diverse fields ranging from condensed matter physics,
solid-state chemistry, materials science, solid-state ionics to
electrochemistry. However, these oxides are vastly underutilised as their
underlying atomistic mechanisms remain unexplored. Therefore, in this study,
atomic-resolution imaging on pristine $\rm K_2Ni_2TeO_6$ along multiple zone
axes was conducted using spherical aberration-corrected scanning transmission
electron microscopy (Cs-corrected STEM) to reveal hitherto unreported nanoscale
topological defects and curvature which can be associated with various phase
transitions. Furthermore, we discover the coexistence of a stacking variant
with P3-type sequence alongside the well-reported P2-type stacking sequence in
such honeycomb layered oxides. Our findings have the potential to inspire
further experimental and theoretical studies into the role of stacking and
topology in the functionality of honeycomb layered oxides, for instance, as
high-performance electrode materials for rechargeable batteries.",2110.09233v1
2021-12-16,Collisional excitation and non-LTE modelling of interstellar chiral propylene oxide,"The first set of theoretical cross sections for propylene oxide (CH3CHCH2O)
colliding with cold He atoms has been obtained at the full quantum level using
a high-accuracy potential energy surface. By scaling the collision reduced
mass, rotational rate coefficients for collisions with para-H2 are deduced in
the temperature range 5-30 K. These collisional coefficients are combined with
radiative data in a non-LTE radiative transfer model in order to reproduce
observations of propylene oxide made towards the Sagittarius B2(N) molecular
cloud with the Green Bank and Parkes radio telescopes. The three detected
absorption lines are found to probe the cold (~ 10 K) and translucent (nH ~
2000 cm-3) gas in the outer edges of the extended Sgr B2(N) envelope. The
derived column density for propylene oxide is Ntot ~ 3e12 cm-2, corresponding
to a fractional abundance relative to total hydrogen of ~ 2.5e-11. The present
results are expected to help our understanding of the chemistry of propylene
oxide, including a potential enantiomeric excess, in the cold interstellar
medium.",2112.08924v2
2022-01-31,Performance Analysis of Novel Propellant Oxidizers using Molecular Modelling and Nozzle Flow Simulations,"The primary target of this paper is to present novel compounds in view of
their possible use as oxidizers in propulsion applications using molecular
modeling calculations and supersonic flow simulations. Carbon-based
heterocyclic compounds tend to have strained molecular structures leading to
high heats of formation and energetic behavior. In the present work, molecular
modeling calculations for molecules of 37 such potential propellant oxidizers
are presented. Density functional theory (B3LYP) was employed for the geometry
optimization of the proposed molecular structures using the 6-311++G(d,p) basis
set. Heats of formation of the compounds were calculated using the molecular
modeling results. Appropriate propellant compositions were considered with the
proposed compounds as oxidizer components and Ideal specific impulse
(Ivac,ideal*) was calculated for each composition assuming isentropic flow,
computed using the NASA CEA software package. To predict the actual delivered
specific impulse (Ivac,act*), supersonic nozzle flow simulations of equilibrium
product gases of each propellant composition have been carried out using
OpenFOAM. The standard k-epsilon turbulence model for compressible flows
including rapid distortion theory (RDT) based compression term, has been
employed. As the problem is inherently transient in nature, local time stepping
(LTS) methodology has been further implemented to reach a steady-state
solution. These simulations accounted for divergence losses, turbulence losses
and boundary layer losses and gave a more realistic estimation of the specific
impulse. It was observed that the Ivac,act* for all propellant compositions lie
between 88% to 91% of the corresponding ideal value. The newly proposed
oxidizers showed considerable improvement in propulsion performance as compared
to ammonium perchlorate.",2202.00107v2
2022-02-09,Scalable $\rm Al_2O_3-TiO_2$ Conductive Oxide Interfaces as Defect Reservoirs for Resistive Switching Devices,"Resistive switching devices herald a transformative technology for memory and
computation, offering considerable advantages in performance and energy
efficiency. Here we employ a simple and scalable material system of conductive
oxide interfaces and leverage their unique properties for a new type of
resistive switching device. For the first time, we demonstrate an $\rm
Al_2O_3-TiO_2$ based valence-change resistive switching device, where the
conductive oxide interface serves both as the back electrode and as a reservoir
of defects for switching. The amorphous-polycrystalline $\rm Al_2O_3-TiO_2$
conductive interface is obtained following the technological path of
simplifying the fabrication of the two-dimensional electron gases (2DEGs),
making them more scalable for practical mass integration. We combine physical
analysis of the device chemistry and microstructure with comprehensive
electrical analysis of its switching behavior and performance. We pinpoint the
origin of the resistive switching to the conductive oxide interface, which
serves as the bottom electrode and as a reservoir of oxygen vacancies. The
latter plays a key role in valence-change resistive switching devices. The new
device, based on scalable and complementary metal-oxide-semiconductor (CMOS)
technology-compatible fabrication processes, opens new design spaces towards
increased tunability and simplification of the device selection challenge.",2202.04477v2
2022-06-18,Free-Standing Epitaxial SrTiO$_3$ Nanomembranes via Remote Epitaxy using Hybrid Molecular Beam Epitaxy,"The epitaxial growth of functional materials using a substrate with a
graphene layer is a highly desirable method for improving structural quality
and obtaining free-standing epitaxial nano-membranes for scientific study,
applications, and economical reuse of substrates. However, the aggressive
oxidizing conditions typically employed to grow epitaxial perovskite oxides can
damage graphene. Here, we demonstrate a technique based on hybrid molecular
beam epitaxy that does not require an independent oxygen source to achieve
epitaxial growth of complex oxides without damaging the underlying graphene.
The technique produces films with self-regulating cation stoichiometry control
and epitaxial orientation to the oxide substrate. Furthermore, the films can be
exfoliated and transferred to foreign substrates while leaving the graphene on
the original substrate. These results open the door to future studies of
previously unattainable free-standing nano-membranes grown in an
adsorption-controlled manner by hybrid molecular beam epitaxy, and has
potentially important implications for the commercial application of perovskite
oxides in flexible electronics.",2206.09094v1
2022-08-02,Highly Efficient and Selective Extraction of Gold by Reduced Graphene Oxide,"Materials that are capable of extracting gold from complex sources,
especially electronic waste (e-waste) with high efficiency are needed for gold
resource sustainability and effective e-waste recycling. However, it remains
challenging to achieve high extraction capacity to trace amount of gold, and
precise selectivity to gold over a wide range of complex co-existing elements.
Here we report a reduced graphene oxide (rGO) material that has an ultrahigh
extraction capacity for trace amounts of gold (1,850 mg/g and 1,180 mg/g to 10
ppm and 1 ppm gold). The excellent gold extraction behavior is accounted to the
graphene areas and oxidized regions of rGO. The graphene areas spontaneously
reduce gold ions to metallic gold, and the oxidized regions provide a good
dispersibility so that efficient adsorption and reduction of gold ions by the
graphene area can be realized. The rGO is also highly selective to gold ions.
By controlling the protonation process of the functional groups on the oxidized
regions of rGO, it shows an exclusive gold extraction without adsorption of 14
co-existing elements seen in e-waste. These discoveries are further exploited
in highly efficient, continuous gold recycling from e-waste with good
scalability and economic viability, as exemplified by extracting gold from
e-waste using a rGO membrane based flow-through process.",2208.01435v1
2022-08-03,"Reactive Laser Synthesis of Ultra-high-temperature Ceramics HfC, ZrC, TiC, HfN, ZrN, and TiN for Additive Manufacturing","Ultra-high-temperature ceramics (UHTCs) are optimal structural materials for
applications that require extreme temperature resilience, resistance to
chemically aggressive environments, wear, and mechanical stress. Processing
UHTCs with laser-based additive manufacturing (AM) has not been fully realized
due to a variety of obstacles. In this work, selective laser reaction sintering
(SLRS) techniques were investigated for the production of near net-shape UHTC
ceramics such as HfC, ZrC, TiC, HfN, ZrN, and TiN. Group IV transition metal
and metal oxide precursor materials were chemically converted and
reaction-bonded into layers of UHTCs using single-step selective laser
processing in CH4 or NH3 gas that might be compatible with prevailing powder
bed fusion techniques. Conversion of either metals (Hf, Zr and Ti) or metal
oxides (HfO2, ZrO2, and TiO2) particles was first investigated to examine
reaction mechanisms and volume changes associated with SLRS of single-component
precursor systems. SLRS processing of metal or metal oxide alone produced near
stoichiometric UHTC phases with yields up to 100 wt% total for carbides and
nitrides. However, for single component precursors, gas-solid reactivity
induced volumetric changes resulted in residual stresses and cracking in the
product layer. To mitigate conversion-induced stresses, composite metal/metal
oxide precursors were employed to compensate for the volume changes of either
the metal (which expands during conversion) or the metal oxide precursor (which
contracts).",2208.02041v2
2022-09-02,Oxygen dissociation on the C3N monolayer: A first-principles study,"The oxygen dissociation and the oxidized structure on the pristine C3N
monolayer in exposure to air are the inevitably critical issues for the C3N
engineering and surface functionalization yet have not been revealed in detail.
Using the first-principles calculations, we have systematically investigated
the possible O2 adsorption sites, various O2 dissociation pathways and the
oxidized structures. It is demonstrated that the pristine C3N monolayer shows
more O2 physisorption sites and exhibits stronger O2 adsorption than the
pristine graphene. Among various dissociation pathways, the most preferable one
is a two-step process involving an intermediate state with the chemisorbed O2
and the barrier is lower than that on the pristine graphene, indicating that
the pristine C3N monolayer is more susceptible to oxidation than the pristine
graphene. Furthermore, we found that the most stable oxidized structure is not
produced by the most preferable dissociation pathway but generated from a
direct dissociation process. These results can be generalized into a wide range
of temperatures and pressures using ab initio atomistic thermodynamics. Our
findings deepen the understanding of the chemical stability of 2D crystalline
carbon nitrides under ambient conditions, and could provide insights into the
tailoring of the surface chemical structures via doping and oxidation.",2209.01193v4
2022-11-08,Gallium-doped Zinc Oxide: Nonlinear Reflection and Transmission Measurements and Modeling in the ENZ Region,"Strong nonlinear materials have been sought after for decades for
applications in telecommunications, sensing, and quantum optics. Gallium-doped
zinc oxide is a II-VI transparent conducting oxide that shows promising
nonlinearities similar to indium tin oxide and aluminum-doped zinc oxide for
the telecommunications band. Here we explore its nonlinearities in the epsilon
near zero (ENZ) region and show n2,eff values on the order of 4.5x10-3 cm2GW-1
for IR pumping on 200-300 nm thin films. Measuring nonlinear changes in
transmission and reflection with a white light source probe in the near-IR
while exciting in the near-IR provides data in both time and wavelength. Three
films varying in thickness, optical loss, and ENZ crossover wavelength are
numerically modeled and compared to experimental data showing agreement for
both dispersion and temporal relaxation. In addition, we discuss optimal
excitation and probing wavelengths occur around ENZ for thick films but are
red-shifted for thin films where our model provides an additional degree of
freedom to explore. Obtaining accurate nonlinear measurements is a difficult
and time-consuming task where our method in this paper provides experimental
and modeled data to the community for an ENZ material of interest.",2211.04306v2
2023-03-22,Open-tunneled oxides as intercalation host for multivalent ion (Ca and Al) batteries: A DFT study,"Lithium-ion batteries (LIBs) are ubiquitous in everyday applications.
However, Lithium (Li) is a limited resource on the planet and is therefore not
sustainable. As an alternative to lithium, earth-abundant and cheaper
multivalent metals such as aluminum (Al) and calcium (Ca) have been actively
researched in battery systems. However, finding suitable intercalation hosts
for multivalent-ion batteries is urgently needed. Open-tunneled oxides are a
particular category of microparticles distinguished by the presence of
integrated one-dimensional channels or nanopores. This work focuses on two
promising open-tunnel oxides, viz: Niobium Tungsten Oxide (NTO) and Molybdenum
Vanadium Oxide (MoVO). We find that the MoVO structure can adsorb greater
numbers of multivalent ions than NTO due to its larger surface area and
different shapes. The MoVO structure can adsorb Ca, Li, and Al ions with
adsorption potential at around 4 to 5 eV. However, the adsorption potential for
hexagonal channels of Al ion drops to 1.73 eV because of less channel area. NTO
structure has an insertion/adsorption potential of 4.4 eV, 3.4 eV, and 0.9 eV
for one Li, Ca, and Al, respectively. In general, Ca ion is more adsorbable
than Al ion in both MoVO and NTO structures. Bader charge analysis and charge
density plot reveals the role of charge transfer and ion size on the insertion
of multivalent ions such as Ca and Al into MoVO and NTO systems. Our results
provide general guidelines to explore other multivalent ions for battery
applications.",2303.12301v1
2023-03-27,Understanding the chemical coupling between ground-level ozone and oxides of nitrogen in ambient air at industrial and commercial sites in central India,"This study investigates the hourly concentrations of Ground-level Ozone (O3),
Nitric Oxide (NO), Nitrogen Dioxide (NO2), and Oxides of Nitrogen (NOx) in
ambient air, along with the various meteorological parameters viz., ambient
temperature, relative humidity, wind speed, and solar radiation over one year,
from August 2020 to July 2021 for an industrial and commercial site in Madhya
Pradesh, a central state in India. We also analyze the chemical coupling
between the O3 and ambient NO, NO2, and NOx at both sites during the daytime.
We focus on understanding how the concentration of the oxidant OX (a
combination of ozone and nitrogen dioxide) changes in relation to levels of NOx
(a combination of nitrogen oxides) to determine whether the atmospheric sources
of OX are dependent on the NOx-independent or regional contributions and
NOx-dependent or local contributions. We also observe a significant positive
correlation of O3 with ambient temperature and solar radiation but a strong
negative correlation with relative humidity for the considered period. We found
the monthly variations of the pollutants' concentrations show a strong
seasonality dependence. O3 concentration becomes highest/lowest during
summer/monsoon for both sites. In contrast, NOx exhibits the maximum and
minimum concentration during monsoon and summer for both sites. The daily
variation shows the opposite trend for O3 and NOx. O3 reaches a peak at mid-day
around 14: 00 Hrs when ambient temperature also goes to maximum and has the
minimum value at night time due to lack of sunlight.",2303.15238v1
2023-04-21,Conversion of La$_2$Ti$_2$O$_7$ to LaTiO$_2$N via Ammonolysis: An ab-initio Investigation,"Perovskite oxynitrides are, due to their reduced band gap compared to oxides,
promising materials for photocatalytic applications. They are most commonly
synthesized from {110} layered Carpy-Galy (A$_2$B$_2$O$_7$}) perovskites via
thermal ammonolysis, i.e. the exposure to a flow of ammonia at elevated
temperature. The conversion of the layered oxide to the non-layered oxynitride
must involve a complex combination of nitrogen incorporation, oxygen removal
and ultimately structural transition by elimination of the interlayer shear
plane. Despite the process being commonly used, little is known about the
microscopic mechanisms and hence factors that could ease the conversion. Here
we aim to derive such insights via density functional theory calculations of
the defect chemistry of the oxide and the oxynitride as well as the oxide's
surface chemistry. Our results point to the crucial role of surface oxygen
vacancies in forming clusters of NH$_3$ decomposition products and in
incorporating N, most favorably substitutionally at the anion site. N then
spontaneously diffuses away from the surface, more easily parallel to the
surface and in interlayer regions, while diffusion perpendicular to the
interlayer plane is somewhat slower. Once incorporation and diffusion lead to a
local N concentration of about 70% of the stoichiometric oxynitride
composition, the nitridated oxide spontaneously transforms to a
nitrogen-deficient oxynitride.",2304.10999v2
2023-05-07,Photocatalytic oxidation in few-layer Tellurene for loss-invariant integrated photonic resonance trimming,"Two-dimensional materials with unique physicochemical properties promote
photocatalytic activities. As the 2D material composites research studies the
statistical average of complex catalytic behaviors, an integrated photonic
platform allows clean and single flake level photo-catalytic investigations
with precisely quantified photocatalytic activities. In this paper, we track
fluence-dependent photo-oxidation in two-dimensional Tellurene (2D Te) by the
evanescently coupled micro-resonator. Nearly 32 perent of oxidation is achieved
in 10 nm 2D Te flake, compared to only 4.5% oxidation in 30 nm sample, probed
by the resonance shift in silicon microring resonators (MRRs) substrate. The
wider bandgap in the few layers of 2D Te allows faster charge transfer to
adsorbed oxygen for a more efficient photocatalytic redox reaction. The
photo-oxidation in hybrid 2D Te results in an invariant lineshapes of optical
transmission resonance for wavelength trimming (more than 3 times resonance
bandwidth). The low threshold power, near-infrared, and in-waveguide resonance
trimming scheme is compatible with most integrated photonic setups for easy
fixing the nanofabrication-induced random resonance deviation for integrated
photonic circuit applications in wavelength-division-multiplexing systems and
spin qubits quantum computing.",2305.04342v1
2023-05-12,Two-dimensional layered materials meet perovskite oxides: A combination for high-performance electronic devices,"As the Si-based transistors scale down to atomic dimensions, the basic
principle of current electronics, which heavily relies on the tunable charge
degree of freedom, faces increasing challenges to meet the future requirements
of speed, switching energy, heat dissipation, packing density as well as
functionalities. Heterogeneous integration, where dissimilar layers of
materials and functionalities are unrestrictedly stacked at an atomic scale, is
appealing to next-generation electronics, such as multi-functional,
neuromorphic, spintronic and ultra-low power devices, because it unlocks
technologically useful interfaces of distinct functionalities. Recently, the
combination of functional perovskite oxides and the two-dimensional layered
materials (2DLMs) led to unexpected functionalities and enhanced device
performance. In this review, we review the recent progress of the heterogeneous
integration of perovskite oxides and 2DLMs from the perspectives of fabrication
and interfacial properties, electronic applications, challenges as well as
outlooks. In particular, we focus on three types of attractive applications,
namely field-effect transistors, memory, and neuromorphic electronics. The van
der Waals integration approach is extendible to other oxides and 2DLMs, leading
to almost unlimited combinations of oxides and 2DLMs and contributing to future
high-performance electronic and spintronic devices.",2305.15418v1
2023-05-26,Topotactic Transition: A Promising Opportunity for Creating New Oxides,"Topotactic transition is a structural phase change in a matrix crystal
lattice mediated by the ordered loss/gain and rearrangement of atoms, leading
to unusual coordination environments and metal atoms with rare valent states.
As early as in 1990s, low temperature hydride reduction was utilized to realize
the topotactic transition. Since then, topological transformations have been
developed via multiple approaches. Especially, the recent discovery of the
Ni-based superconductivity in infinite-layer nickelates has greatly boosted the
topotactic transition mean to synthesizing new oxides for exploring exotic
functional properties. In this review, we have provided a detailed and
generalized introduction to oxygen-related topotactic transition. The main body
of our review include four parts: the structure-facilitated effects, the
mechanism of the topotactic transition, some examples of topotactic transition
methods adopted in different metal oxides (V, Mn, Fe, Co, Ni) and the related
applications. This work is to provide timely and thorough strategies to
successfully realize topotactic transitions for researchers who are eager to
create new oxide phases or new oxide materials with desired functions.",2305.16605v1
2023-11-19,Fast and Facile Synthesis Route to Epitaxial Oxide Membrane Using a Sacrificial Layer,"The advancement in thin-film exfoliation for synthesizing oxide membranes has
opened up new possibilities for creating artificially-assembled
heterostructures with structurally and chemically incompatible materials. The
sacrificial layer method is a promising approach to exfoliate as-grown films
from a compatible material system, allowing their integration with dissimilar
materials. Nonetheless, the conventional sacrificial layers often possess
intricate stoichiometry, thereby constraining their practicality and
adaptability, particularly when considering techniques like Molecular Beam
Epitaxy (MBE). This is where easy-to-grow binary alkaline earth metal oxides
with a rock salt crystal structure are useful. These oxides, which include (Mg,
Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range
of lattice parameters compared to conventional sacrificial layers and are
easily dissolvable in deionized water. In this study, we show the epitaxial
growth of single-crystalline perovskite SrTiO3 (STO) on sacrificial layers
consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE
method. Our results highlight the rapid (< 5 minutes) dissolution of the
sacrificial layer when immersed in deionized water, facilitating the
fabrication of millimeter-sized STO membranes. Using high-resolution x-ray
diffraction, atomic-force microscopy, scanning transmission electron
microscopy, impedance spectroscopy, and scattering-type near-field optical
microscopy (SNOM), we demonstrate epitaxial STO membranes with bulk-like
intrinsic dielectric properties. The employment of alkaline earth metal oxides
as sacrificial layers is likely to simplify membrane synthesis, particularly
with MBE, thus expanding research possibilities.",2311.11448v1
2010-11-11,Nonlinear Insulator in Complex Oxides,"The insulating state is one of the most basic electronic phases in condensed
matter. This state is characterised by an energy gap for electronic excitations
that makes an insulator electrically inert at low energy. However, for complex
oxides, the very concept of an insulator must be re-examined. Complex oxides
behave differently from conventional insulators such as SiO2, on which the
entire semiconductor industry is based, because of the presence of multiple
defect levels within their band gap. As the semiconductor industry is moving to
such oxides for high-dielectric (high-k) materials, we need to truly understand
the insulating properties of these oxides under various electric field
excitations. Here we report a new class of material called nonlinear insulators
that exhibits a reversible electric-field-induced metal-insulator transition.
We demonstrate this behaviour for an insulating LaAlO3 thin film in a
metal/LaAlO3/Nb-SrTiO3 heterostructure. Reproducible transitions were observed
between a low-resistance metallic state and a high-resistance non-metallic
state when applying suitable voltages. Our experimental results exclude the
possibility that diffusion of the metal electrodes or oxygen vacancies into the
LaAlO3 layer is occurring. Instead, the phenomenon is attributed to the
formation of a quasi-conduction band (QCB) in the defect states of LaAlO3 that
forms a continuum state with the conduction band of the Nb-SrTiO3. Once this
continuum (metallic) state is formed, the state remains stable even when the
voltage bias is turned off. An opposing voltage is required to deplete the
charges from the defect states. Our ability to manipulate and control these
defect states and, thus, the nonlinear insulating properties of complex oxides
will open up a new path to develop novel devices.",1011.2629v1
2020-07-27,"Plasma-assisted molecular beam epitaxy of SnO(001) films: Metastability, hole transport properties, Seebeck coefficient, and effective hole mass","Transparent conducting or semiconducting oxides are important materials for
(transparent) optoelectronics and power electronics applications. While most of
these oxides can be doped n-type only with room-temperature electron mobilities
on the order of 100cm^2/Vs p-type oxides are needed for the realization of
pn-junction devices but typically suffer from exessively low (<<1cm^2/Vs) hole
mobilities. Tin monoxide (SnO) is one of the few p-type oxides with a higher
hole mobility, lacking a well-established understanding of its hole transport
properties. Moreover, growth of SnO is complicated by its metastability with
respect to SnO2 and Sn, requiring epitaxy for the realization of single
crystalline material typically required for high-end applications. Here, we
give a comprehensive account on the epitaxial growth of SnO, its
(meta)stability, and its thermoelectric transport properties in the context of
the present literature. Textured and single-crystalline, unintentionally-doped
p-type SnO(001) films are grown by plasma-assisted molecular beam epitaxy. The
metastability of this semiconducting oxide is addressed theoretically through
an equilibrium phase diagram. Experimentally, the related SnO growth window is
rapidly determined by an in-situ growth kinetics study as function of
Sn-to-O-plasma flux ratio and growth temperature. The presence of secondary Sn
and SnOx (1 < x <= 2) phases is comprehensively studied by different methods,
indicating the presence of Sn3O4 or Sn as major secondary phases, as well as a
fully oxidized SnO2 film surface. The hole transport properties, Seebeck
coefficient, and density-of-states effective mass are determined and critically
discussed in the context of the present literature on SnO, considering its
anisotropic hole-effective mass.",2007.13448v2
2011-11-19,First-principles study on oxidation effects in uranium oxides and high-pressure high-temperature behavior of point defects in uranium dioxide,"Formation Gibbs free energy of point defects and oxygen clusters in uranium
dioxide at high-pressure high-temperature conditions are calculated from first
principles, using the LSDA+U approach for the electronic structure and the
Debye model for the lattice vibrations. The phonon contribution on Frenkel
pairs is found to be notable, whereas it is negligible for the Schottky defect.
Hydrostatic compression changes the formation energies drastically, making
defect concentrations depend more sensitively on pressure. Calculations show
that, if no oxygen clusters are considered, uranium vacancy becomes predominant
in overstoichiometric UO2 with the aid of the contribution from lattice
vibrations, while compression favors oxygen defects and suppresses uranium
vacancy greatly. At ambient pressure, however, the experimental observation of
predominant oxygen defects in this regime can be reproduced only in a form of
cuboctahedral clusters, underlining the importance of defect clustering in
UO2+x. Making use of the point defect model, an equation of state for
non-stoichiometric oxides is established, which is then applied to describe the
shock Hugoniot of UO2+x. Furthermore, the oxidization and compression behavior
of uranium monoxide, triuranium octoxide, uranium trioxide, and a series of
defective UO2 at zero Kelvin are investigated. The evolution of mechanical
properties and electronic structures with an increase of the oxidation degree
are analyzed, revealing the transition of the groundstate of uranium oxides
from metallic to Mott insulator and then to charge-transfer insulator due to
the interplay of strongly correlated effects of 5f orbitals and the shift of
electrons from uranium to oxygen atoms.",1111.4548v1
2020-12-15,Oxidation Processes Diversify the Metabolic Menu on Enceladus,"The Cassini mission to the Saturn system discovered a plume of ice grains and
water vapor erupting from cracks on the icy surface of the satellite Enceladus.
This moon has a global ocean in contact with a rocky core beneath its icy
exterior, making it a promising location to search for evidence of
extraterrestrial life in the solar system. The previous detection of H$_2$ in
the plume indicates that there is free energy available for methanogenesis, the
metabolic reaction of H$_2$ with CO$_2$ to form methane and water. Additional
metabolic pathways could provide sources of energy in Enceladus' ocean, but
require the use of other oxidants that have not been detected in the plume.
Here, we perform chemical modeling to determine how the production of
radiolytic O$_2$ and H$_2$O$_2$, and abiotic redox chemistry in the ocean and
rocky core, contribute to chemical disequilibria that could support metabolic
processes in Enceladus' ocean. We consider three possible cases for ocean redox
chemistry: Case I in which reductants are not present in appreciable amounts
and oxidants accumulate over time, and Cases II and III in which aqueous
reductants or seafloor minerals, respectively, convert O$_2$ and H$_2$O$_2$ to
SO$_4^{2-}$ and ferric oxyhydroxides. We calculate the upper limits on the
concentrations of oxidants and chemical energy available for metabolic
reactions in all three cases, neglecting additional abiotic reactions. For all
three cases, we find that many aerobic and anaerobic metabolic reactions used
by microbes on Earth could meet the minimum free energy threshold required for
terrestrial life to convert ADP to ATP, as well as sustain positive cell
density values within the Enceladus seafloor and/or ocean. These findings
indicate that oxidant production and oxidation chemistry could contribute to
supporting possible life and a metabolically diverse microbial community on
Enceladus.",2012.08582v1
2017-05-09,Atomically flat single terminated oxide substrate surfaces,"To achieve high quality epitaxial thin films and heterostructures of
transition metal oxides with atomically controlled interfaces, one critical
requirement is the use of atomically flat single terminated oxide substrates
since the atomic arrangements and the reaction chemistry of the topmost surface
layer of substrates determine the growth and consequent properties of the
overlying films. Achieving the atomically flat and chemically single terminated
surface state of commercially available substrates, however, requires judicious
efforts because the surface of as-received substrates is of chemically mixed
nature and also often polar. In this review, we summarize the surface treatment
procedures to accomplish atomically flat surfaces with single terminating layer
for various metal oxide substrates. We particularly focus on the substrates
with lattice constant ranging from 4.00 to 3.70 angstrom, as the lattice
constant of most perovskite materials falls into this range. For materials
outside the range, one can utilize the substrates to induce compressive or
tensile strain on the films and explore new states not available in bulk. The
substrates covered in this review, which have been chosen with commercial
availability and, most importantly, experimental practicality as a criterion,
are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3,
La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), NdGaO3, LaAlO3, SrLaAlO4, and YAlO3.
Analyzing all the established procedures, we conclude that atomically flat
surfaces with selective A- or B-site single termination would be obtained for
most commercially available oxide substrates. We further note that this topmost
surface layer selectivity would provide an additional degree of freedom in
searching for unforeseen emergent phenomena and functional applications in
epitaxial oxide thin films and heterostructures with atomically controlled
interfaces.",1705.03436v2
2017-05-10,Effect of Dynamic Surface Polarization on the Oxidative Stability of Solvents in Nonaqueous Li-O$_2$ Batteries,"Polarization-induced renormalization of the frontier energy levels of
interacting molecules and surfaces can cause significant shifts in the
excitation and transport behavior of electrons. This phenomenon is crucial in
determining the oxidative stability of nonaqeous electrolytes in high energy
density electrochemical systems such as the Li-O$_2$ battery. On the basis of
partially self-consistent first-principles ScGW0 calculations, we
systematically study how the electronic energy levels of four commonly used
solvent molecules, namely dimethylsulfoxide (DMSO), dimethoxyethane (DME),
tetrahydrofuran (THF) and acetonitrile (ACN), renormalize when physisorbed on
the different stable surfaces of Li$_2$O$_2$, the main discharge product. Using
band level alignment arguments, we propose that the difference between the
solvent's highest occupied molecular orbital (HOMO) level and the surface's
valence band maximum (VBM) is a refined metric of oxidative stability. This
metric and a previously used descriptor, solvent's gas phase HOMO level, agree
quite well for physisorbed cases on pristine surfaces where ACN is oxidatively
most stable followed by DME, THF and DMSO. However, this effect is
intrinsically linked to the surface chemistry of solvent's interaction with the
surfaces states and defects, and depends strongly on their nature. We
conclusively show that the propensity of solvent molecules to oxidize will be
significantly higher on Li$_2$O$_2$ surfaces with defects as compared to
pristine surfaces. This suggests that the oxidatively stability of solvent is
dynamic and is a strong function of surface electronic properties. Thus, while
gas phase HOMO levels could be used for preliminary solvent candidate
screening, a more refined picture of solvent stability requires mapping out the
solvent stability as a function of the state of the surface under the operating
conditions.",1705.03862v1
2019-08-27,A combinatorial guide to phase formation and surface passivation of tungsten titanium oxide prepared by thermal oxidation,"TiO$_2$ and WO$_3$ are two of the most important earth-abundant electronic
materials with applications in countless industries. Recently alloys of WO$_3$
and TiO$_2$ have been investigated leading to improvements of key performance
indicators for a variety of applications ranging from photo-electrochemical
water splitting to electrochromic smart windows. These positive reports and the
complexity of the ternary W-Ti-O phase diagram motivate a comprehensive
experimental screening of this phase space. Using combinatorial thermal
oxidation of solid solution W$_{1-x}$Ti$_{x}$ precursors combined with bulk and
surface analysis mapping we investigate the oxide phase formation and surface
passivation of tungsten titanium oxide in the entire compositional range from
pure WO$_3$ to TiO$_2$. The system shows a remarkable structural transition
from monoclinic over cubic to tetragonal symmetry with increasing Ti
concentration. In addition, a strong Ti surface enrichment is observed for
precursor Ti-concentrations in excess of 55 at.%, resulting in the formation of
a protective rutile-structured TiO$_2$ surface layer. Despite the structural
transitions, the optical properties of the oxide alloys remain largely
unaltered demonstrating an independent control of multiple functional
properties in W$_{1-x}$Ti$_{x}$O$_{n}$. The results from this study provide
valuable guidelines for future development of W$_{1-x}$Ti$_{x}$O$_{n}$ for
electronic and energy applications, but also novel engineering approaches for
surface functionalization and additive manufacturing of Ti-based alloys.",1908.10067v1
2020-05-19,"Post-mortem analysis of tungsten plasma facing components in tokamaks: Raman microscopy measurements on compact, porous oxide and nitride films and nanoparticles","Raman microscopy is one of the methods that could be used for future
post-mortem analyses of samples extracted from ITER plasma facing. This study
shows that this technique is useful for studying tungsten-based materials
containing impurities including oxides and nitrides. Here, we apply pulsed
laser deposition and DC argon glow discharges to produce tungsten-containing
synthetic films (compact, porous) and nanoparticles and investigate the
influence of their morphology on the measured Raman spectra. The amounts of
oxygen and/or nitrogen in the films are also investigated. Comparative data are
obtained by X-ray Photoelectrons Spectroscopy, Atomic Force Microscopy,
Electron Microscopies (Scanning and Transmission), Energy Dispersive X-ray
spectroscopy, Time-of-Flight Elastic Recoil Detection Analysis. The power
density of the laser beam used to perform Raman microscopy is varied by up to 4
orders of magnitude (0.01-20 mW/$\mu$m 2) to investigate thermal stability of
films and nanoparticles. As a first result, we give evidence that Raman
microscopy is sensitive enough to detect surface native oxides. Secondly, more
tungsten oxides are detected in porous materials and nanoparticles than in
compact films, and the intensities of the Raman band correlate to their oxygen
content. Thirdly, thermal stability of these films (i.e. structural and
chemical modification under laser heating) is poor when compact films contain a
sufficiently large amount of nitrogen. This finding suggests that nitrogen can
be substituted by oxygen during Raman laser induced heating occurring in
ambient air. Finally, our methodology can be used to rapidly characterize
morphology and chemistry of the samples analyzed, and also to create oxides at
the micrometer scale. keywords: PLD, Raman spectroscopy, tungsten oxide,
tungsten nitride, plasma wall interaction, laser heating, post-mortem analysis
2",2005.09295v1
2020-06-30,High-Voltage Honeycomb Layered Oxide Positive Electrodes for Rechargeable Sodium Batteries,"Natural abundance, impressive chemical characteristics and economic
feasibility have rekindled the appeal for rechargeable sodium (Na) batteries as
a practical solution for the growing energy demand, environmental
sustainability and energy independence. However, the scarcity of viable
positive electrode materials remains a huge impediment to the actualization of
this technology. In this paper, we explore honeycomb layered oxides adopting
the composition Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ ($x = 0, 0.25$ and $0.50$) as
feasible positive electrode (cathode) materials for rechargeable sodium
batteries at both room- and elevated temperatures using ionic liquids. Through
standard galvanostatic assessments and analyses we demonstrate that
substitution of nickel with cobalt in Na$_2$Ni$_2$TeO$_6$ leads to an increase
in the discharge voltage to nearly $4$ V (versus Na$^+$ / Na) for the
Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ family of honeycomb layered oxide materials,
which surpasses the attained average voltages for most layered oxide positive
electrode materials that facilitate Na-ion desertion. We also verify the
increased kinetics within the Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ honeycomb layered
oxides during operations at elevated temperatures which lead to an increase in
reversible capacity of the rechargeable Na battery. This study underpins the
doping of congener transition metal atoms to the honeycomb structure of
Na$_2$Ni$_2$TeO$_6$ in addition to elevated-temperature operation as a
judicious route to enhance the electrochemical performance of analogous layered
oxides.",2006.16656v1
2021-02-19,Thermal and Oxidation Stability of Ti$_x$W$_{1-x}$ Diffusion Barriers Investigated by Soft and Hard X-ray Photoelectron Spectroscopy,"The binary alloy of titanium-tungsten (TiW) is an established diffusion
barrier in high-power semiconductor devices, owing to its ability to suppress
the diffusion of copper from the metallisation scheme into the surrounding
silicon substructure. However, little is known about the response of TiW to
high temperature events or its behaviour when exposed to air. Here, a combined
soft and hard X-ray photoelectron spectroscopy (XPS) characterisation approach
is used to study the influence of post-deposition annealing and titanium
concentration on the oxidation behaviour of a 300~nm-thick TiW film. The
combination of both XPS techniques allows for the assessment of the chemical
state and elemental composition across the surface and bulk of the TiW layer.
The findings show that in response to high-temperature annealing, titanium
segregates out of the mixed metal system and upwardly migrates, accumulating at
the TiW/air interface. Titanium shows remarkably rapid diffusion under
relatively short annealing timescales and the extent of titanium surface
enrichment is increased through longer annealing periods or by increasing the
precursor titanium concentration. Surface titanium enrichment enhances the
extent of oxidation both at the surface and in the bulk of the alloy due to the
strong gettering ability of titanium. Quantification of the soft X-ray
photoelectron spectra highlights the formation of three tungsten oxidation
environments, attributed to WO$_2$, WO$_3$ and a WO$_3$ oxide coordinated with
a titanium environment. This combinatorial characterisation approach provides
valuable insights into the thermal and oxidation stability of TiW alloys from
two depth perspectives, aiding the development of future device technologies.",2102.09845v1
2021-10-29,Spatially-Modulated Silicon Interface Energetics via Hydrogen Plasma-Assisted Atomic Layer Deposition of Ultrathin Alumina,"Atomic layer deposition (ALD) is a key technique for the continued scaling of
semiconductor devices, which increasingly relies on reproducible and scalable
processes for interface manipulation of 3D structured surfaces on the atomic
scale. While ALD allows the synthesis of conformal films at low temperature
with utmost control over the thickness, atomically-defined closed coatings and
surface modifications are still extremely difficult to achieve because of
three-dimensional growth during nucleation. Here, we present a route towards
sub-nanometer thin and continuous aluminum oxide (AlOx) coatings on silicon
(Si) substrates for the spatial control of the surface charge density and
interface energetics. We use trimethylaluminum (TMA) in combination with remote
hydrogen plasma instead of a gas-phase oxidant for the transformation of
silicon oxide into alumina (AlOx). During the initial ALD cycles, TMA reacts
with the surface oxide (SiO2) on silicon until there is a saturation of
bindings sites, after which the oxygen from the underlying surface oxide is
consumed, thereby transforming the silicon oxide into Si capped with AlOx.
Depending on the number of ALD cycles, the SiO2 can be partially or fully
transformed, which we exploit to create sub-nanometer thin and continuous AlOx
layers deposited in selected regions defined by lithographic patterning. The
resulting patterned surfaces are characterized by lateral AlOx/SiO2 interfaces
possessing step heights as small as 0.3 nm and surface potential steps in
excess of 0.4 V. In addition, the introduction of fixed negative charges of $9
\times 10^{12}$ cm$^{-2}$ enables modulation of the surface band bending, which
is relevant to the field-effect passivation of Si and low-impedance charge
transfer across contact interfaces.",2111.00054v2
2023-02-27,Engineering of Niobium Surfaces Through Accelerated Neutral Atom Beam Technology For Quantum Applications,"A major roadblock to scalable quantum computing is phase decoherence and
energy relaxation caused by qubits interacting with defect-related two-level
systems (TLS). Native oxides present on the surfaces of superconducting metals
used in quantum devices are acknowledged to be a source of TLS that decrease
qubit coherence times. Reducing microwave loss by surface engineering (i.e.,
replacing uncontrolled native oxide of superconducting metals with a thin,
stable surface with predictable characteristics) can be a key enabler for
pushing performance forward with devices of higher quality factor. In this
work, we present a novel approach to replace the native oxide of niobium
(typically formed in an uncontrolled fashion when its pristine surface is
exposed to air) with an engineered oxide, using a room-temperature process that
leverages Accelerated Neutral Atom Beam (ANAB) technology at 300 mm wafer
scale. This ANAB beam is composed of a mixture of argon and oxygen, with
tunable energy per atom, which is rastered across the wafer surface. The
ANAB-engineered Nb-oxide thickness was found to vary from 2 nm to 6 nm
depending on ANAB process parameters. Modeling of variable-energy XPS data
confirm thickness and compositional control of the Nb surface oxide by the ANAB
process. These results correlate well with those from transmission electron
microscopy and X-ray reflectometry. Since ANAB is broadly applicable to
material surfaces, the present study indicates its promise for modification of
the surfaces of superconducting quantum circuits to achieve longer coherence
times.",2302.14113v1
2023-03-20,Machine learning assisted phase and size-controlled synthesis of iron oxides,"The controllable synthesis of iron oxides particles is a critical issue for
materials science, energy storage, biomedical applications, environmental
science, and earth science. However, synthesis of iron oxides with desired
phase and size are still a time-consuming and trial-and-error process. This
study presents solutions for two fundamental challenges in materials synthesis:
predicting the outcome of a synthesis from specified reaction parameters and
correlating sets of parameters to obtain products with desired outcomes. Four
machine learning algorithms, including random forest, logistic regression,
support vector machine, and k-nearest neighbor, were trained to predict the
phase and particle size of iron oxide based on experimental conditions. Among
the models, random forest exhibited the best performance, achieving 96% and 81%
accuracy when predicting the phase and size of iron oxides in the test dataset.
Premutation feature importance analysis shows that most models (except logistic
regression) rely on known features such as precursor concentration, pH, and
temperature to predict the phases from synthesis conditions. The robustness of
the random forest models was further verified by comparing prediction and
experimental results based on 24 randomly generated methods in additive and
non-additive systems not included in the datasets. The predictions of product
phase and particle size from the models are in good agreement with the
experimental results. Additionally, a searching and ranking algorithm was
developed to recommend potential synthesis parameters for obtaining iron oxide
products with desired phase and particle size from previous studies in the
dataset.",2303.11244v1
2023-10-31,"Electronic structure study of YNbTiO$_6$ vs. CaNb$_2$O$_6$ with U, Pu and minor actinide substitutions using compound-tunable embedding potential method","The compound-tunable embedding potential (CTEP) method is applied to study
actinide substitutions in the niobate crystals YNbTiO$_6$ and CaNb$_2$O$_6$.
Two one-center clusters centered on Ca and Y are built and 20 substitutions of
Ca and Y with U, Np, Pu, Am, and Cm in four different oxidation states were
made for each cluster. Geometry relaxation is performed for each resulting
structure, and electronic properties are analyzed by evaluating the spin
density distribution and X-ray emission spectra chemical shifts. Though the
studied embedded clusters with actinides having the same oxidation state are
found in general to yield similar local structure distortions, for Am and Cm in
high ""starting"" oxidation states the electron transfer from the environment was
found, resulting in decrease of their oxidation states, while for ""starting""
U$^{\rm III}$ state the electron transfer goes in the opposite direction,
resulting in increase of its oxidation state to U$^{\rm IV}$.
  The U substitutions are additionally studied with the use of multi-center
models, which can provide both more structural and electronic relaxation and
also include charge-compensating vacancies. For ""starting"" U$^{\rm VI}$ case,
the decrease in oxidation state similar to that of Am$^{\rm VI}$ and Cm$^{\rm
VI}$ in one-center clusters is observed in our calculations but in a different
way.
  Since the really synthesized YNbTiO$_6$ structures can not be considered as
perfect (periodic) crystals because the Nb and Ti atoms are statistically
distributed within them occupying the same Wyckoff positions, different Ti
$\leftrightarrow$ Nb substitutions are studied and corresponding structural
changes are estimated.",2310.20595v1
2023-12-18,Computational insights into phase equilibria between wide-gap semiconductors and contact materials,"Novel wide-band-gap semiconductors are needed for next-generation power
electronic but there is a gap between a promising material and a functional
device. Finding stable contacts is one of the major challenges, which is
currently dealt with mainly via trial and error. Herein, we computationally
investigate the thermochemistry and phase co-existence at the junction between
three wide gap semiconductors, $\beta$-Ga$_{2}$O$_{3}$, GeO$_2$, and GaN, and
possible contact materials. The pool of possible contacts includes 47 elemental
metals and 4 common $n$-type transparent conducting oxides (ZnO, TiO$_2$,
SnO$_2$, and In$_2$O$_3$). We use first-principles thermodynamics to model the
Gibbs free energies of chemical reactions as a function of the gas pressure
(p$_{\mathrm{O}_2}$/p$_{\mathrm{N}_2}$) and equilibrium temperature. We deduce
whether a semiconductor/contact interface will be stable at relevant
conditions, possibly influencing the long-term reliability and performance of
devices. We generally find that most elemental metals tend to oxidize or
nitridize and form various interface oxide/nitride layers. Exceptions include
select late- and post-transition metals, and in case of GaN also the alkali
metals, which are predicted to exhibit stable coexistence, although in many
cases at relatively low gas partial pressures. Similar is true for the
transparent conducting oxides, for which in most cases we predict a preference
toward forming ternary oxides when in contact with $\beta$-Ga$_{2}$O$_{3}$ and
GeO$_{2}$. The only exception is SnO$_2$, which can form stable contacts with
both oxides. Finally, we show how the same approach can be used to predict gas
partial pressure vs. temperature phase diagrams to help direct synthesis of
ternary compounds. We believe these results provide a valuable guidance in
selecting contact materials to wide-gap semiconductors and suitable growth
conditions.",2312.11749v1
2024-02-01,Exploring inverse orbital Hall and orbital Rashba effects: unveiling the oxidation states of the Cu surface,"In this work, employing spin-pumping techniques driven by both ferromagnetic
resonance (SP-FMR) and longitudinal spin Seebeck effect (LSSE) to manipulate
and direct observe orbital currents, we investigated the volume conversion of
spin-orbital currents into charge-current in YIG(100nm)/Pt(2nm)/NM2 structures,
where NM2 represents Ti or Ru. While the YIG/Ti bilayer displayed a negligible
SP-FMR signal, the YIG/Pt/Ti structure exhibited a significantly stronger
signal attributed to the orbital Hall effect of Ti. Substituting the Ti layer
with Ru revealed a similar phenomenon, wherein the effect is ascribed to the
combined action of both spin and orbital Hall effects. Furthermore, we measured
the SP-FMR signal in the YIG/Pt(2)/Ru(6)/Ti(6) and YIG/Pt(2)/Ti(6)/Ru(6)
heterostructures by just altering the stack order of Ti and Ru layers, where
the peak value of the spin pumping signal is larger for the first sample. To
verify the influence on the oxidation of Ti and Ru films, we studied a series
of thin films subjected to controlled and natural oxidation. As Cu and CuOx is
a system that is already known to be highly influenced by oxidation, this metal
was chosen to carry out this study. We investigated these samples using SP-FMR
in YIG/Pt(2)/CuOx(tCu) and X-ray absorption spectroscopy and concluded that
samples with natural oxidation of Cu exhibit more significant results than
those when the CuOx is obtained by reactive sputtering. In particular, samples
where the Cu layer is naturally oxidized exhibit a Cu2O-rich phase. Our
findings help to elucidate the mechanisms underlying the inverse orbital Hall
and inverse orbital Rashba-Edelstein-like effects. These insights indeed
contribute to the advancement of devices that rely on orbital-charge
conversion.",2402.00297v1
1998-07-15,Driven Morse Oscillator: Model for Multi-photon Dissociation of Nitrogen Oxide,"Within a one-dimensional semi-classical model with a Morse potential the
possibility of infrared multi-photon dissociation of vibrationally excited
nitrogen oxide was studied. The dissociation thresholds of typical driving
forces and couplings were found to be similar, which indicates that the results
were robust to variations of the potential and of the definition of
dissociation rate.
  PACS: 42.50.Hz, 33.80.Wz",9807020v1
1995-01-05,Two-Color Coherent Photodissociation of Nitrogen Oxide in Intense Laser Fields,"A simple one-dimensional semi-classical model with a Morse potential is used
to investigate the possibility of two-color infrared multi-photon dissociation
of vibrationally excited nitrogen oxide. The amplitude ratio effects and
adiabatic effects are investigated. Some initial states are found to have
thresholds smaller than expected from single-mode considerations and multiple
thresholds exist for initial states up to 32.
  PACS: 42.50.Hz",9501001v2
1994-01-02,Driven Morse Oscillator: Model for Multi-photon Dissociation of Nitrogen Oxide,"Within a one-dimensional semi-classical model with a Morse potential the
possibility of microwave multi-photon dissociation of vibrationally excited
nitrogen oxide was studied. The dissociation thresholds of typical driving
forces and couplings were found to be similar, which indicates that the results
were robust to variations of the potential and the definition of dissociation
rate.",9312098v1
1994-03-16,Asymptotically exact solution of a local copper-oxide model,"We present an asymptotically exact solution of a local copper-oxide model
abstracted from the multi-band models. The phase diagram is obtained through
the renormalization-group analysis of the partition function. In the strong
coupling regime, we find an exactly solved line, which crosses the quantum
critical point of the mixed valence regime separating two different
Fermi-liquid (FL) phases. At this critical point, a many-particle resonance is
formed near the chemical potential, and a marginal-FL spectrum can be derived
for the spin and charge susceptibilities.",9403059v1
1994-07-13,Large Phase Separation and Superconductivity in the Copper Oxide Chain,"The phase diagram of the copper-oxide chain as a function of density and the
nearest-neighbour Coulomb interaction, V, is determined. Phase separation takes
place above a critical value of $V$ when the Cu2+ to Cu+ valence fluctuations
dominate. In the proximity of the phase separation boundary the superconducting
correlations are the most divergent. We identify the parameter regions where
the Luttinger Liquid theory applies and calculate the contours of the
charge-charge correlation exponent K_{\rho}. We show that anomalous flux
quantization occurs as K_{\rho} diverges. At n = 1, for V > t, a gap opens in
the spectrum and the ground state is a charge-density wave.",9407064v1
1994-07-13,Phase Separation and Superconductivity in the Copper Oxide Chain,"The phase diagram of the copper-oxide chain as a function of density and the
nearest-neighbour Coulomb interaction, V, is determined. Phase separation takes
place above a critical value of $V$ when the Cu2+ to Cu+ valence fluctuations
dominate. In the proximity of the phase separation boundary the superconducting
correlations are the most divergent. We identify the parameter regions where
the Luttinger Liquid theory applies and calculate the contours of the
charge-charge correlation exponent K_{\rho}. We show that anomalous flux
quantization occurs as$K_{\rho} diverges. At n = 1, for V > t, a gap opens in
the spectrum and the ground state is a charge-density wave.",9407067v1
1996-05-31,c axis superfluid response of Copper-Oxide superconductors,"A novel interplay between d-wave superconducting order parameter symmetry and
the underlying Cu 3d orbital based electronic structure of Copper-Oxides leads
to a striking anisotropy in the superfluid response of these systems. In clean
tetragonal materials the c-axis penetration depth increases as T^5 at low
temperature T, in contrast to linear T behavior in the ab-plane. Disorder is a
relevant perturbation which causes all components of the superfluid response to
depend quadratically on temperature at low temperature. However, the cross-over
temperature scale from the intrinsic d-wave behavior to the disorder dominated
behavior for the in-plane response may be different from that for the out-plane
response.",9605196v1
1996-08-06,Evolution of photoemission spectral functions in doped transition metal oxides,"We discuss the experimental photoemission and inverse photoemission of early
transition metal oxides, in the light of the dynamical mean field theory of
correlated electrons which becomes exact in the limit of infinite dimensions.
We argue that a comprehensive description of the experimental data requires
spatial inhomogeneities and present a calculation of the evolution of the
spectral function in an inhomogenous system with various degrees of
inhomogeneity. We also point out that comparaison of experimental results and
large d calculations require that the degree of correlation and disorder is
larger in the surface than in the bulk.",9608021v1
1997-02-04,Anomalous Behavior of Ru for Catalytic Oxidation: A Theoretical Study of the Catalytic Reaction CO + 1/2 O_2 --> CO_2,"Recent experiments revealed an anomalous dependence of carbon monoxide
oxidation at Ru(0001) on oxygen pressure and a particularly high reaction rate.
Below we report density functional theory calculations of the energetics and
reaction pathways of the speculated mechanism. We will show that the
exceptionally high rate is actuated by a weakly but nevertheless well bound
(1x1) oxygen adsorbate layer. Furthermore it is found that reactions via
scattering of gas-phase CO at the oxygen covered surface may play an important
role. Our analysis reveals, however, that reactions via adsorbed CO molecules
(the so-called Langmuir-Hinshelwood mechanism) dominate.",9702040v1
1997-02-10,Non-Nominal Value of the Dynamical Effective Charge in Alkaline-Earth Oxides,"We calculate ab-initio the electronic states and the Born dynamical charge Z*
of the alkaline-earth oxides in the local-density approximation. We investigate
the trend of increasing Z* values through the series, using band-by-band
decompositions and computational experiments performed on fake materials with
artificially-modified covalence. The deviations of Z* from the nominal value 2
are due to the increasing interaction between O 2p orbitals and unoccupied
cation d states. We also explain the variations, along the series, of the
individual contributions to Z* arising from the occupied band manifolds.",9702086v1
1997-02-26,Formation of localized hole states in complex oxides,"Defect electrons (holes) play an important role in most technologically
important complex oxides; many of which possess perovskite-related structures.
In this contribution we present the first detailed characterization of
localized hole states in such materials. Our investigations employ advanced
embedded-cluster calculations which consistently include electron correlations
and defect-induced lattice relaxations. This is necessary in order to account
for the variety of possible hole-state manifestations.",9702223v1
1997-08-21,Charge Dynamics from Copper Oxide Materials,"The charge dynamics of the copper oxide materials in the underdoped and
optimal doped regimes is studied within the framework of the fermion-spin
theory. The conductivity spectrum shows the non-Drude behavior at low energies
and unusual midinfrared peak, and the resistivity exhibits a linear behavior in
the temperature, which are consistent with experiments and numerical
simulations.",9708165v2
1998-03-20,Universal Spin Response in Copper Oxide Materials,"The spin response in the copper oxide materials at finite temperatures in the
underdoped and optimal doped regimes is studied within the framework of the
fermion-spin theory. The integrated dynamical spin structure factor is almost
temperature independent, the integrated susceptibility shows the particularly
universal behavior as $I(\omega, T) \propto arctan [ a_{1}\omega/T +
a_{3}(\omega/T)^{3}]$, and the spin-lattice relaxation time is weakly
temperature dependent, which are consistent with experiments and numerical
simulations.",9803246v2
1998-11-28,Low energy excitations in crystalline perovskite oxides: Evidence from noise experiments,"In this paper we report measurements of 1/f noise in a crystalline metallic
oxide with perovskite structure down to 4.2K. The results show existence of
localized excitations with average activation energy $\approx$ 70-80 meV which
produce peak in the noise at T $\approx$ 35-40K. In addition, it shows clear
evidence of tunnelling type two-level-systems (as in glasses) which show up in
noise measurements below 30K.",9811398v1
1998-12-08,On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous oxide,"We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1})
and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the
cuprous oxide. A detailed analysis based on a comparison of the temperature
dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active
fundamental vibrations results in assignment of the former to a biphonon.",9812122v3
1998-12-22,Modified Double Exchange Model with Novel Spin and Orbital Coupling: Phase Diagram of The Manganites,"From a general model of the Mn oxides R_{1-x}A_{x}MnO_3, we derive an
effective Hamiltonian in the low-energy subspace using the projection operator
method, in which a novel coupling between the spin and orbital degrees of
freedom is included. A phase diagram for temperature T versus doping
concentration x is computed by means of Monte Carlo simulation. Our result is
consistent with experimental observations in the Mn oxides with relatively wide
conduction band, such as Pr_{1-x}Sr_{x} MnO_{3} and La_{1-x}Sr_{x}MnO_{3}.
According to the obtained orbital ordering, we also predict that the motion of
charge carriers transforms from three-dimensional to two-dimensional as x is
increased beyond a critical value.",9812374v1
1999-02-16,Forward Electron-Phonon Scattering and HTS,"Tunneling and point contact spectroscopy show clear phonon features and
together with optic measurements give strong support that the electron-phonon
interaction (EPI) is large in HTS oxides. Strong correlations in HTS oxides
renormalize the EPI (and interaction with impurities) so that the forward
scattering peak (FSP) develops for small hole doping \delta<<1. The FSP
mechanism explains important properties of the normal and superconducting
state.",9902232v1
1999-03-20,Comparison of superconductivity in Sr_2RuO_4 and copper oxides,"To compare the superconductivity in strongly correlated electron systems with
the antiferromagnetic fluctuations in the copper oxides and with the
ferromagnetic fluctuations in Sr_2RuO_4 a t-J-I model is proposed. The
antiferromagnetic coupling J results in the superconducting state of
d_{x^2-y^2} symmetry and the ferromagnetic coupling constant I results in the
spin-triplet p-type state. The difference in the gap anisotropies provides the
large difference in T_c values, for the typical values of the coupling
constants: T_c of order of 1K for the ruthenate and T_c of order of 100K for
the cuprates.",9903314v1
1999-05-28,Energetics of the oxidation and opening of a carbon nanotube,"We apply first principles calculations to study the opening of single-wall
carbon nanotubes (SWNT's) by oxidation. We show that an oxygen rim can
stabilize the edge of the open tube. The sublimation of CO$_2$ molecules from
the rim with the subsequent closing of the tube changes from endothermic to
exothermic as the tube radius increases, within the range of experimental
feasible radii. We also obtain the energies for opening the tube at the cap and
at the wall, the latter being significantly less favorable.",9905419v1
2000-04-13,Oscillatory Exchange Coupling and Positive Magnetoresistance in Epitaxial Oxide Heterostructures,"Oscillations in the exchange coupling between ferromagnetic
$La_{2/3}Ba_{1/3}MnO_3$ layers with paramagnetic $LaNiO_3$ spacer layer
thickness has been observed in epitaxial heterostructures of the two oxides.
This behavior is explained within the RKKY model employing an {\it ab initio}
calculated band structure of $LaNiO_3$, taking into account strong electron
scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a
positive current-in-plane magnetoresistance.",0004230v1
2000-04-18,"Momentum and doping dependence of the electron spectrum and ($π$,0) feature in copper oxide materials","The momentum and doping dependence of the electron spectrum of copper oxide
materials in the underdoped regime is studied within the t-J model. It is shown
that the pseudogap opens near ($\pi$,0) point in the Brillouin zone, and the
electron dispersion exhibits the flat band around ($\pi$,0), which are
consistent with the experiments.",0004299v1
2000-11-14,Nature of traps responsible for failure of MOS devices,"A failure of chips in a huge amount of modern electronic devices is connected
as a rule with the undesirable capturing of charge (electrons and holes) by
traps in a thin insulating film of silicon oxide in transistors. It leads to a
breakdown of transistors or to a destructive change of their characteristics.
It is suggested that silicon oxide will be replaced in the next generation of
nanoscale devices by silicon oxynitride. Therefore, it is very important to
understand the nature of traps in this material. We discuss this nature using
the quantum-chemical simulation.",0011241v1
2001-05-23,CO oxidation on a single Pd atom supported on magnesia,"The oxidation of CO on single Pd atoms anchored to MgO(100) surface oxygen
vacancies is studied with temperature-programmed-reaction mass-spectrometry and
infrared spectroscopy. In one-heating-cycle experiments CO$_2$, formed from
O$_2$ and CO preadsorbed at 90 K, is detected at 260 K and 500 K. Ab-initio
simulations suggest two reaction routes, with Pd(CO)$_2$O$_2$ and Pd(CO$_3$)CO
found as precursors for the low and high temperature channels, respectively.
Both reactions result in annealing of the vacancy and induce migration and
coalescence of the remaining Pd-CO to form larger clusters.",0105460v1
2001-07-10,Titanium single electron transistor fabricated by electron-beam lithography,"A new method to fabricate non-superconducting mesoscopic tunnel junctions by
oxidation of Ti is presented. The fabrication process uses conventional
electron beam lithography and shadow deposition through an organic resist mask.
Superconductivity in Ti is suppressed by performing the deposition under a
suitable background pressure. We demonstrate the method by making a single
electron transistor which operated at $T < 0.4$ K and had a moderate charge
noise of $2.5 \times 10^{-3}$ e/$\sqrt{\mathrm{Hz}}$ at 10 Hz. Based on
nonlinearities in the current-voltage characteristics at higher voltages, we
deduce the oxide barrier height of approximately 110 mV.",0107199v1
2001-08-02,Theory of Raman Scattering from Orbital Excitations in Manganese Oxides,"We present a theory of the Raman scattering from the orbital wave excitations
in manganese oxides. Two excitation processes of the Raman scattering are
proposed. The Raman scattering cross section is formulated by using the
pseudospin operator for orbital degree of freedom in a Mn ion. The Raman
spectra from the orbital wave excitations are calculated and their implications
in the recent experimental results reported in LaMnO$_3$ are discussed.",0108032v2
2001-08-21,Thermal conductivity of the A_xBO_2 type layered oxides Na_0.77MnO_2 and LiCoO_2,"We prepared polycrystalline samples of the A_xBO_2 type layered oxides
Na_0.77MnO_2 and LiCoO_2, and measured thermal conductivity from 15 to 280 K.
Na0.77MnO_2 shows a low thermal conductivity of 15 mW/cmK, while LiCoO_2 shows
a much higher value of 40 mW/cmK at 280 K. By comparing them with the data of
NaCo_2O_4, we have found that the low thermal conductivity of A_xBO_2 comes
essentially from the A-ion deficiency, not from the layered structure itself.",0108327v1
2002-01-08,Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands,"The electronic structure of nanoscopic oxide-coated aluminum islands is
investigated using a tight-binding model that incorporates the geometry,
chemistry and disorder of the particle. The oxide coat is found to
significantly increase the volume accessible to electrons at the Fermi level.
The level statistics agree with random matrix theory predictions. States near
the Fermi level show pronounced clustering regardless of disorder. It is
suggested that the observed clusters of tunneling resonances may have a more
complex origin than if they were solely due to many-body non-equilibrium
effects.",0201086v1
2002-03-08,The second phase transition in the pyrochlore oxide Cd2Re2O7,"Evidence for another phase transition at 120 K in the metallic pyrochlore
oxide Cd2Re2O7, following the structural transition at 200 K and followed by
the superconducting transition at 1.0 K, is given through resistivity,
magnetoresistance, specific heat, and X-ray diffraction measurements. The
results indicate unique successive structural and electronic transitions
occurring in the pyrochlore compound, revealing an interesting interplay
between the crystal and electronic structures on the itinerant electron system
in the pyrochlore lattice.",0203178v1
2002-04-27,A Percolative Model of Soft Breakdown in Ultrathin Oxides,"The degradation of ultrathin oxide layers in the presence of a stress voltage
is modeled in terms of two antagonist percolation processes taking place in a
random resistor network. The resistance and leakage current fluctuations are
studied by MonteCarlo simulations for voltages below the breakdown threshold.
An increase of excess noise together with a noticeable non-Gaussian behavior is
found in the pre-breakdown regime in agreement with experimental results.",0204586v1
2002-05-13,Pseudogap effects on the charge dynamics in the underdoped copper oxide materials,"Within the t-J model, the charge dynamics of copper oxide materials in the
underdoped regime is studied based on the fermion-spin theory. It is shown that
both in-plane charge dynamics and c-axis charge dynamics are mainly governed by
the scattering from the in-plane fluctuation, which would be suppressed when
the holon pseudogap opens at low temperatures, leading to the temperature
linear to the nonlinear range in the in-plane resistivity and crossovers to the
semiconducting-like range in the c-axis resistivity.",0205248v1
2002-07-12,Transport properties and electronic states of the thermoelectric oxide NaCo_2O_4,"Physical properties of the thermoelectric oxide NaCo_2O_4 are briefly
reviewed. The high thermoelectric properties of this material are attributed to
the substantially enhanced effective mass, which comes from the large entropy
of Co$^{4+}$ in the low spin state. The large entropy confined in the CoO_2
block causes a spin-density-wave transition at 22 K upon Cu substitution for
Co, which can be regarded as ``order from disorder''.",0207315v1
2002-07-20,Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7,"We report the X-ray study for the pyrochlore oxide Cd2Re2O7. Two
symmetry-lowering structural transitions were observed at Ts1=200K and
Ts2=120K. The former is of the second order from the ideal cubic pyrochlore
structure with space group Fd-3m to a tetragonally distorted structure with
I-4m2, while the latter is of the first order likely to another tetragonal
space group I4122. We discuss the feature of the lattice deformation.",0207497v2
2002-10-02,Anomalous Pd substitution effects in the thermoelectric oxide NaCo_{2-x}Pd_xO_4,"We prepared a set of polycrystalline samples of the thermoelectric oxide
NaCo_{2-x}Pd_xO_4 (x= 0, 0.05, 0.1 and 0.2), and investigated the Pd
substitution effects on transport phenomena. The effects are so drastic that
only 5-10% Pd ions reduce the resistivity and the Seebeck coefficient to
one-third of the values for x=0, and increase the magnitude of the Hall
coefficient by three times. A semi-quantitative analysis has revealed that the
x=0.2 sample has much smaller effective mass and carrier concentration than the
x=0.05 sample. This is difficult to explain within a rigid-band picture, and is
qualitatively consistent with a strong-correlation picture applied to the
Ce-based heavy fermion systems.",0210043v1
2002-10-31,A new synchronization mechanism via Turing-like microscopic structures for CO oxidation on Pt(110),"We discuss an alternative to the traditional gas-phase coupling approach in
order to explain synchronized global oscillations in CO oxidation on Pt(110).
We use a minimalist microscopic model which includes structural Pt surface
reconstruction via front propagation, and large diffusion rates for CO. The
synchronization mechanism is associated with the formation of a Turing-like
structure of the substrate. By using large parallel microscopic simulations we
derive a scaling laws which allow us to extrapolate to realistic diffusion
rates, pattern size, and oscillation periods.",0210699v1
2002-11-22,Correlations and Semimetallic Behaviors in Pyrochlore Oxide Cd2Re2O7,"Electronic properties of the metallic pyrochlore oxide Cd2Re2O7 are studied
by means of electrical resistivity and Hall measurements. Semimetallic band
structures are revealed as expected from band structure calculations. It is
found that large changes in carrier density and mass occur at the structural
phase transition at Ts1 = 200 K. A large mass enhancement is observed,
particularly for the high-temperature phase with the ideal pyrochlore
structure, suggesting that an anomalous correlation has an important effect on
the itinerant electrons in the pyrochlore lattice.",0211517v1
2002-12-22,Changes in the surface electronic structure upon martensitic transformation in TiNi and TiPd,"The electronic structure of some low index surfaces for martensitic B19'-TiNi
and B19-TiPd were investigated using the full-potential linearized augmented
plane wave method. The alteration of the electronic structure upon martensitic
transformation on the surface were analyzed. According to the surface
calculations only insignificant changes in the electronic structure near the
Fermi level were found as for bulk ground state. The formation of oxides top
layers is also discussed. It is shown that the influence of TiNi substrate is
insignificant when three oxides layers are formed.",0212553v1
2003-01-21,Charge ordering in oxides : a conundrum solved by resonant diffraction,"We show that in mixed-valence 3d transition metal oxides undergoing a
structural transition, the low temperature phase results from an effective
ordering of the charge. This arrangement and the quantitative evaluation of the
atomic charges are determined by using resonant x-ray scattering experiments
further analyzed with the help of ab initio calculations of the corresponding
scattering factors. We have found that this reorganization concerns only a
small fraction of electron and is necessary to reconcile all the experimental
data.",0301377v1
2003-03-02,AFM local oxidation nanopatterning of a high mobility shallow 2D hole gas,"Recently developed AFM local anodic oxidation (LAO) technique offers a
convenient way of patterning nanodevices, but imposes even more stringent
requirements on the underlying quantum well structure. We developed a new very
shallow quantum well design which allows the depth and density of the 2D gas to
be independently controlled during the growth. A high mobility (0.5 10^6
cm^2/Vs at 4.2 K) 2D hole gas just 350A below the surface is demonstrated. A
quantum point contact, fabricated by AFM LAO nanopatterning from this wafer,
shows 9 quantum steps at 50 mK.",0303011v1
2003-06-06,Structural evidence against current-induced destruction of charge-ordering in manganese oxides,"High-resolution x-ray scattering, in the presence of an applied current, has
been used for studying the stability of the charge ordered phase of manganese
oxides upon current biasing. We find that the charge ordered structure is
unchanged when a current is flowing in the sample. Such a result indicates that
the non-linear conduction observed in charge ordered manganites can not be
ascribed to a current-induced destabilisation of charge ordering.",0306160v1
2003-09-18,Order-Disorder Transitions and Melting in a Helical Polymer Crystal: Molecular Dynamics Calculations of Poly(Ethylene Oxide),"Structural transitions and the melting behavior of crystalline poly(ethylene
oxide),(CH2-CH2-O)n, (PEO) has been investigated using fully atomistic,
constant pressure-constant temperature (NPT) molecular dynamics (MD)
simulations. Melting of PEO proceeds in two stages; Order parameters reveal the
loss of interchain orientational correlations and of chain helicity in the
first and second stages of melting respectively. Sliding diffusion and
anisotropic reorientational dynamics of the polymer backbone are observed in
the solid state, in agreement with 1H NMR experiments.",0309431v1
2003-12-09,The oxygen isotope effect on critical temperature in superconducting copper oxides,"The isotope effect provided a crucial key to the development of the BCS
(Bardeen-Cooper-Schrieffer) microscopic theory of superconductivity for
conventional superconductors. In superconducting cooper oxides (cuprates)
showing an unconventional type of superconductivity, the oxygen isotope effect
is very peculiar: the exponential coefficient strongly depends on doping level.
No consensus has been reached so far on the origin of the isotope effect in the
cuprates. Here we show that the oxygen isotope effect in cuprates is in
agreement with the bisoliton theory of superconductivity.",0312229v2
2003-12-23,Electron localization in pure and defective ceria by a unified LDA+U approach,"The electronic and structural properties of pure and defective cerium oxide
are investigated using a unified LDA+U approach which allows to treat the
different valence states of Ce occurring for different stoichiometries on a
same ground, without any {\it a priori} assumptions on the defect chemistry.
The method correctly predicts the atomistic and electronic structures of the
\4ce and \3ce bulk phases, as well as the subtle defect chemistry in reduced
materials \xce, which controls the oxygen storage functionality of cerium-based
oxides. The analysis of the energetics highlights the limits of the LDA+U
method and possible extensions are proposed.",0312601v1
2003-12-29,La0.95Sr0.05CoO3: An efficient room-temperature thermoelectric oxide,"We present measurements of electrical resistivity, thermal conductivity and
thermopower of polycrystalline Sr-doped LaCoO3 with composition
La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very
respectable room temperature thermoelectric figure of merit value of 0.18. Our
results not only show that oxides are promising candidates for thermoelectric
cooling applications, but also point towards the need for careful theoretical
calculations that will serve as a guide in producing the next generation of
thermoelectric materials.",0312670v1
2004-02-02,Universal charge transport of the Mn oxides in the high temperature limit,"We have found that various Mn oxides have the universal resistivity and
thermopower in the high temperature limit. The resistivities and thermopowers
of all the samples go toward constant values of 7$\pm$1 m$\Omega$cm and
$-79\pm$3 $\mu$V/K, which are independent of carrier density and crystal
structures. We propose that the electric conduction occurs in a highly
localized way in the high temperature limit, where the exchange of entropy and
charge occurs in the neighboring Mn$^{3+}$ and Mn$^{4+}$ ions.",0402032v1
2004-02-09,Electronic structure and light-induced conductivity in a transparent refractory oxide,"Combined first-principles and experimental investigations reveal the
underlying mechanism responsible for a drastic change of the conductivity (by
10 orders of magnitude) following hydrogen annealing and UV-irradiation in a
transparent oxide, 12CaO.7Al2O3, found by Hayashi et al. The charge transport
associated with photo-excitation of an electron from H, occurs by electron
hopping. We identify the atoms participating in the hops, determine the exact
paths for the carrier migration, estimate the temperature behavior of the
hopping transport and predict a way to enhance the conductivity by specific
doping.",0402218v1
2004-04-10,Thermal conductivity of the thermoelectric layered cobalt oxides measured by the Harman method,"In-plane thermal conductivity of the thermoelectric layered cobalt oxides has
been measured using the Harman method, in which thermal conductivity is
obtained from temperature gradient induced by applied current. We have found
that the charge reservoir block (the block other than the CoO$_2$ block)
dominates the thermal conduction, where a nano-block integration concept is
effective for material design. We have further found that the thermal
conductivity shows a small but finite in-plane anisotropy between $a$ and $b$
axes, which can be ascribed to the misfit structure.",0404248v1
2004-06-10,Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation,"We present experimental results on the photoluminescence (PL) of
gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO
targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL
spectra in the UV spectral region correspond to the exciton recombination in
the nanoclusters which are crystallized and cooled down to the temperature of
the ambient gas in the ablation chamber. The time evolution of the spectra as
well as their dependence on the ambient gas pressure are discussed.",0406251v1
2004-09-10,Non-generality of the Kadowaki-Woods ratio in correlated oxides,"An explicit expression for the Kadowaki-Woods ratio in correlated metals is
derived by invoking saturation of the (high-frequency) Fermi-liquid scattering
rate at the Mott-Ioffe-Regel limit. Significant deviations observed in a number
of oxides are quantitatively explained due to variations in carrier density,
dimensionality, unit cell volume and the number of individual sheets in the
Brillouin zone. A generic re-scaling of the original Kadowaki-Woods plot is
also presented.",0409252v1
2004-09-30,"Comment on Phys. Stat. Sol. (b) 236 (2003) 281 paper by A. M. Oles ""Orbital ordering and orbital fluctuations in transition metal oxides""","We argue that the 3A2 state considered by Oles in Phys. Stat. Sol. (b) 236
(2003) 281 for the d2 system occurring in the V3+ ion in V2O3 and LaVO3 as well
as in Ti2+ ion in TiO and in many other oxides is wrong. The proper ground
state is 3T1g - its 9-fold degeneracy is further split in a crystal by
intra-atomic spin-orbit interactions and lattice distortions.",0409777v1
2004-11-10,Quantum Monte Carlo study of MnO solid,"Electronic structure of the manganese oxide solid is studied by the quantum
Monte Carlo (QMC) methods. The trial wavefunctions are built using orbitals
from unrestricted Hartree-Fock and Density Functional Theory, and the
electron-electron correlation is recovered by the fixed-node QMC. The
correlation effects are significant and QMC estimations of the gap and cohesion
show a very good agreement with experiment. Comparison with hybrid functional
results points out the importance of the exact exchange for improvement of the
Density Functional description of transition metal oxide systems.",0411247v2
2005-01-07,Achieving fast oxygen diffusion in perovskites by cation ordering,"The oxygen-exchange behavior has been studied in half-doped manganese and
cobalt perovskite oxides. We have found that the oxygen diffusivity in
Gd_{0.5}Ba_{0.5}MnO_{3-\delta} can be enhanced by orders of magnitude by
inducing crystallographic ordering among lanthanide and alkali-earth ions in
the A-site sublattice. Transformation of a simple cubic perovskite, with
randomly occupied A-sites, into a layered crystal GdBaMn_2O_{5+x} (or
isostructural GdBaCo_2O_{5+x} for cobalt oxide) with alternating lanthanide and
alkali-earth planes reduces the oxygen bonding strength and provides
disorder-free channels for ion motion, pointing to an efficient way to design
new ionic conductors.",0501127v1
2005-02-10,Electronic Structure of Sodium Cobalt Oxide: Comparing Mono- and Bilayer-hydrate,"To shed new light on the mechanism of superconductivity in sodium cobalt
oxide bilayer-hydrate (BLH), we perform a density functional calculation with
full structure optimization for BLH and its related nonsuperconducting phase,
monolayer hydrate (MLH). We find that these hydrates have similar band
structures, but a notable difference can be seen in the $a_{1g}$ band around
the Fermi level. While its dispersion in the $z$ direction is negligibly small
for BLH, it is of the order of 0.1 eV for MLH. This result implies that the
three dimensional feature of the $a_{1g}$ band may be the origin for the
absence of superconductivity in MLH.",0502256v1
2005-03-19,Tunneling spectroscopy studies of aluminum oxide tunnel barrier layers,"We report scanning tunneling microscopy and ballistic electron emission
microscopy studies of the electronic states of the uncovered and
chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states
change when chemisorbed oxygen ions are moved into the oxide by either flood
gun electron bombardment or by thermal annealing. The former, if sufficiently
energetic, results in locally well defined conduction band onsets at ~1 V,
while the latter results in a progressively higher local conduction band onset,
exceeding 2.3 V for 500 and 600 C thermal anneals.",0503495v1
2005-04-08,Production of Indium Doped Zinc Oxide Thin Films by Pulsed Laser Ablation,"An original modification of the standard Pulse Laser Deposition (PLD) method
for preparing both undoped and indium doped zinc oxide (ZnO:In) thin films at
low substrate temperature is proposed. This preparation method does not demand
any further post-deposition annealing treatment of the grown films. The
developed method allows to grow thin films at low substrate temperature that
prevents them from the considerable loss of their intrinsic electrical and
optical properties. The influence of deposition parameters on the electrical
and optical parameters of the undoped and the indium doped ZnO thin films is
also analysed.",0504200v1
2005-04-14,High Throughput Oxide Lattice Engineering by Parallel Laser Molecular Beam Epitaxy and Concurrent X-ray Diffraction,"A novel laser molecular beam epitaxy (LMBE) system for the fabrication of
atomically controlled oxides superlattices and an x-ray diffractometer that
measures spatially-resolved x-ray diffraction spectra have been developed based
on the concept of combinatorial methodology. The LMBE chamber has two moving
masks, an automated target stage, a substrate heating laser, and an in-situ
scanning reflection high-energy electron diffraction system. The x-ray
diffractometer with a curved monochromator and two-dimensional detector is used
for rapid concurrent x-ray diffraction intensity mapping with the two axes of
the detector corresponding to the diffraction angle and a position in the
sample.",0504352v1
2005-04-19,"Evidence against strong correlation in 4d transition metal oxides, CaRuO3 and SrRuO3","We investigate the electronic structure of 4d transition metal oxides, CaRuO3
and SrRuO3. The analysis of the photoemission spectra reveals significantly
weak electron correlation strength (U/W ~ 0.2) as expected in 4d systems and
resolves the long standing issue that arose due to the prediction of large U/W
similar to 3d-systems. It is shown that the bulk spectra, thermodynamic
parameters and optical properties in these systems can consistently be
described using first principle approaches. The observation of different
surface and bulk electronic structures in these weakly correlated 4d systems is
unusual.",0504466v1
2005-05-03,Ferroelectricity in ultra-thin perovskite films,"We report studies of ferroelectricity in ultra-thin perovskite films with
realistic electrodes. The results reveal stable ferroelectric states in thin
films less than 10 \AA thick with polarization normal to the surface. Under
short-circuit boundary conditions, the screening effect of realistic electrodes
and the influence of real metal/oxide interfaces on thin film polarization are
investigated. Our studies indicate that metallic screening from the electrodes
is affected by the difference in work functions at oxide surfaces. We
demonstrate this effect in ferroelectric PbTiO$_3$ and BaTiO$_3$ films.",0505051v1
2005-05-08,Orbital Disordering and metal-insulator transition with hole-doping in perovskite-type vanadium oxides,"Filling-control metal-insulator transitions (MITs) and related electronic
phase diagrams have been investigated for hole-doped vanadium oxides,
Pr_{1-x}Ca_xVO_3, Nd_{1-x}Sr_xVO_3 and Y_{1-x}Ca_xVO_3, with perovskite
structure. The increase of the doping level x causes the melting of the G-type
(and C-type) orbital order, prior to or concomitantly with the MIT, due partly
to the doped-hole motion and partly to the ramdom potential arising from the
quenched disorder. In particular, the G-type spin- and C-type orbital-ordered
phase present in Y_{1-x}Ca_xVO_3 disappears immediately upon hole doping,
around x=0.02. On the other hand, the critical doping level x for MIT is
governed by the electron-correlation strength of the undoped parent compound.",0505190v1
2005-05-13,Quantitative Analysis of Photo-Thermal Stability of CdSe/CdS Core-Shell Nanocrystals,"We report here investigations on the instability in luminescence of bare
(TOPO-stabilized) and CdS- capped CdSe particles under infrared radiation.
During photo-thermal annealing the formation of oxide layers on the surfaces of
the particles create defect states. Consequently there is a reduction in
particle size. These two effects control the light output from the samples. We
make a quantitative comparison of the stability of bare CdSe and core-shell
type CdSe-CdS particles under photo-annealing. Using diffusion theory, we show
that the volume of the oxide layer, adhered to the crystallites, play a
dominant role in controlling the luminosity of the particles.",0505342v1
2005-06-29,First-principles study of epitaxial strain in perovskites,"Using an extension of a first-principles method developed by King-Smith and
Vanderbilt [Phys. Rev. B {\bf 49}, 5828 (1994)], we investigate the effects of
in-plane epitaxial strain on the ground-state structure and polarization of
eight perovskite oxides: BaTiO$_3$, SrTiO$_3$, CaTiO$_3$, KNbO$_3$, NaNbO$_3$,
PbTiO$_3$, PbZrO$_3$, and BaZrO$_3$. In addition, we investigate the effects of
a nonzero normal stress. The results are shown to be useful in predicting the
structure and polarization of perovskite oxide thin films and superlattices.",0506777v1
2005-08-29,Spin-Phonon Coupling in High-T_c Copper Oxides,"Band calculations on HgBa$_2$CuO$_4$ and La$_{(2-x)}$Sr$_x$CuO$_4$ with
phonon and spin-waves within the CuO planes show that partial gaps are created
at various energies depending on wavelengths. Spin and phonon gaps appear at
different energies when the modulations are along [1,1,0], while they are at
the same energy for modulations along [1,0,0].
  It is shown that the ability to form gaps and antiferromagnetic waves is
correlated with the strength of the interaction parameter $\lambda_{sf}$ for
spin fluctuations. Many unusual properties of the high-T$_C$ oxides can be
understood from spin-phonon coupling.",0508672v1
2005-09-21,Nearly free electrons in the layered oxide superconductor Ag5Pb2O6,"We present first measurements of quantum oscillations in the layered oxide
superconductor
  Ag5Pb2O6. From a detailed angular and temperature dependent study of the dHvA
effect we determine the electronic structure and demonstrate that the electron
masses are very light, m^* is approximately equalt to 1.2 m_e. The Fermi
surface we observe is essentially that expected of nearly-free electrons -
establishing
  Ag5Pb2O6 as the first known example of a monovalent, nearly-free electron
superconductor at ambient pressure.",0509547v1
2006-01-24,Electric-field-dependent spectroscopy of charge motion using a single-electron transistor,"We present observations of background charge fluctuators near an Al-AlO_x-Al
single-electron transistor on an oxidized Si substrate. The transistor design
incorporates a heavily doped substrate and top gate, which allow for
independent control of the substrate and transistor island potentials. Through
controlled charging of the Si/SiO_2 interface we show that the fluctuators
cannot reside in the Si layer or in the tunnel barriers. Combined with the
large measured signal amplitude, this implies that the defects must be located
very near the oxide surface.",0601553v2
2006-03-19,Electronic properties of silica nanowires,"Thin nanowires of silicon oxide were studied by pseudopotential density
functional electronic structure calculations using the generalized gradient
approximation. Infinite linear and zigzag Si-O chains were investigated. A wire
composed of three-dimensional periodically repeated Si4O8 units was also
optimized, but this structure was found to be of limited stability. The
geometry, electronic structure, and Hirshfeld charges of these silicon oxide
nanowires were computed. The results show that the Si-O chain is metallic,
whereas the zigzag chain and the Si4O8 nanowire are insulators.",0603485v1
2006-03-23,Interface controlled electronic charge inhomogeneities in correlated heterostructures,"For heterostructures of ultrathin, strongly correlated copper-oxide films and
dielectric perovskite layers, we predict inhomogeneous electronic interface
states. Our study is based on an extended Hubbard model for the cuprate film.
The interface is implemented by a coupling to the electron and phonon degrees
of freedom of the dielectric oxide layer. We find that electronic ordering in
the film is associated with a strongly inhomogeneous polaron effect. We propose
to consider the interfacial tuning as a powerful mechanism to control the
charge ordering in correlated electronic systems.",0603629v2
2006-06-01,Cluster assimilation and collisional filtering on metal-oxide surfaces,"We present the first ab initio molecular dynamics study of collisions between
metal-oxide clusters and surfaces. The resulting trajectories reveal that the
internal degrees of freedom of the cluster play a defining role in collision
outcome. The phase space of incoming internal temperature and translational
energy exhibits regions where the collision process itself ensures that each
cluster which does not rebound from the surface assimilates seamlessly onto it
upon impact. This filtering may explain recent observations of a ""fast
smoothing mechanism"" during pulsed laser deposition.",0606014v2
2006-07-24,The interface between a polar perovskite oxide and silicon from monoatomic lines,"We report a study on the interface between polar high-k materials and the
Si(001)-(2X1) reconstructed surface with LaAlO3 taken as a prototype material.
The construction of the interface is based on the prior growth of metal lines
followed by oxidation, whose stability against oxygen coverage is studied.
Electronic structure calculations within the Density Functional Theory
framework help in building the interface and understanding its bonding
structure. Moreover, we computed a conduction band offset of 1.9 eV, in
agreement with electronic applications requirement. The results may provide a
guidance for interface processing.",0607609v2
2006-08-28,Photoluminescence of nanocrystals embedded in oxide matrices,"We used the theory of finite periodic systems to explain the
photoluminescence spectra dependence on the average diameter of nanocrystals
embedded in oxide matrices. Because of the broad matrix band gap, the
photoluminescence response is basically determined by isolated nanocrystals and
sequences of a few of them. With this model we were able to reproduce the shape
and displacement of the experimentally observed photoluminescence spectra.",0608605v3
2006-09-14,Strain induced pressure effect in pulsed laser deposited thin films of the strongly correlated oxide V2O3,"V2O3 thin films about 10 nm thick were grown on Al2O3 (0001) by pulsed laser
deposition. The XRD analysis is in agreement with R-3c space group. Some of
them exhibit the metal / insulator transition characteristic of V2O3 bulk
material and others samples exhibit a metallic behavior. For the latter, the
XPS analysis indicates an oxidation state of +III for vanadium. There is no
metal / insulator transition around 150 K in this sample and a strongly
correlated Fermi liquid rho = AT2 behavior of the resistivity at low
temperature is observed, with a value of A of 1.2 10-4 ohm cm, 3 times larger
than the bulk value at 25 kbar.",0609342v1
2006-12-06,Configurational electronic entropy and the phase diagram of mixed-valence oxides: the case of Li$_x$FePO$_4$,"We demonstrate that configurational electronic entropy, previously neglected,
in {\it ab initio} thermodynamics of materials can qualitatively modify the
finite-temperature phase stability of mixed-valence oxides. While
transformations from low-T ordered or immiscible states are almost always
driven by configurational disorder (i.e. random occupation of lattice sites by
multiple species), in FePO$_4$--LiFePO$_4$ the formation of a solid solution is
almost entirely driven by electronic, rather than ionic configurational
entropy. We argue that such an electronic entropic mechanism may be relevant to
most other mixed-valence systems.",0612163v1
2006-12-29,Chemical trends of superconducting properties in pyrochlore oxides,"Chemical trends of fundamental superconducting parameters and normal-state
properties are described for a family of pyrochlore oxide superconductors.
Particularly, the change of Tc from 1.0 K for alpha-pyrochlore Cd2Re2O7 to 3.3
K (A = Cs), 6.3 K (Rb), and 9.6 K (K) for beta-pyrochlore AOs2O6 is discussed
on the basis of the conventional BCS scheme. Enhanced Tc and anomalous features
observed for KOs2O6 are ascribed to low-energy phonons probably coming from the
rattling of the K cations.",0612682v1
2007-01-19,Chemical Liquid Phase Deposition of Thin Aluminum Oxide Films,"Thin aluminum oxide films were deposited by a new and simple physicochemical
method called chemical liquid phase deposition (CLD) on semiconductor
materials. Aluminum sulfate with crystallized water and sodium bicarbonate were
used as precursors for film growth, and the control of the system pH value
played an important role in this experiment. The growth rate is 12 nm/h at room
temperature. Post-growth annealing not only densifies and purifies the films,
but results in film crystallization as well. Excellent quality of Al2O3 films
in this work is supported by electron dispersion spectroscopy, Fourier
transform infrared spectrum, X-ray diffraction spectrum and scanning electron
microscopy photograph.",0701488v1
2000-01-27,Spiral Turbulence: From the Oxidation of CO on Pt(110) to Ventricular Fibrillation,"We give a brief overview of systems that show spiral patterns and
spatiotemporally chaotic states. We concentrate on two physical systems: (1)
the oxidation of CO on Pt(110) and (2) ventricular fibrillation in hearts. The
equations that have been suggested as simple models for these two different
systems are closely related for they are both {\it excitable media}. We present
these equations and give a short summary of the phenomena they yield.}",0001063v1
2001-11-12,Pattern Formation on the Edge of Chaos: CO Oxidation on Pt(110) under Global Delayed Feedback,"Experiments with catalytic CO oxidation on Pt(110) show that chemical
turbulence in this system can be suppressed by application of appropriate
global delayed feedbacks. Different spatiotemporal patterns, seen near a
transition from turbulence to uniform oscillations, are investigated. Using a
method based on the Hilbert transform, spatial distributions of local phase and
amplitude in such patterns are reconstructed from the experimental data. The
observed phenomena are reproduced in simulations using a theoretical model of
the reaction.",0111026v1
2003-10-23,Photoluminescence properties of forsterite (Mg2SiO4) nanobelts synthesized from Mg and SiO2 powders,"Ternary oxide forsterite Mg2SiO4 single-crystalline nanobelts have been
synthesized at high yields via SiO2 assistant-oxide through a VS process. The
PL properties of the forsterite Mg2SiO4 nanobelts were observed. The emission
peak at 625 nm is attributed to the 4T1 - 6A1 transition of the trace Mn2+
ions. The other emission peak at 400nm may be due to the defects.",0310114v1
2006-12-06,Electrically addressing a single self-assembled quantum dot,"We report on the use of an aperture in an aluminum oxide layer to restrict
current injection into a single self-assembled InAs quantum dot, from an
ensemble of such dots within a large mesa. The insulating aperture is formed
through the wet-oxidation of a layer of AlAs. Under photoluminescence we
observe that only one quantum dot in the ensemble exhibits a Stark shift, and
that the same single dot is visible under electroluminescence. Autocorrelation
measurements performed on the electroluminescence confirm that we are observing
emission from a single quantum dot.",0612046v1
2007-05-05,Evanescent quadrupole polariton,"In the work we demonstrate the formation of new type of polariton on the
interface between a cuprous oxide slab and a polystyrene micro-sphere placed on
the slab. The evanescent field of the resonant whispering gallery mode (WGM)
has a substantial gradient, and therefore effectively couples with the
quadrupole $1S$ excitons in cuprous oxide. This evanescent polariton has a long
life-time ($1.7 ns$), which is determined only by its excitonic component. The
polariton lower branch has a well pronounced minimum. This suggests that this
excitation can be utilized for BEC. The spatial coherence of the polariton can
be improved by assembling the micro-spheres in a linear chain.",0705.0749v1
2007-05-23,XANES determination of chromium oxidation states in glasses: comparison with optical absorption spectroscopy,"The oxidation state of chromium in glasses melted in an air atmosphere with
and without refining agents was investigated by Cr K-edge X-ray Absorption
Near-Edge Structure (XANES) and optical absorption spectroscopy. A good
agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between
both methods. We show that the chemical dependence of the absorption
coefficient of Cr(III) is less important in XANES than in optical absorption
spectroscopy. The comparison of glasses melted under different conditions
provides an indirect assessment of the molar extinction coefficient of Cr(VI)
in glasses.",0705.3355v1
2007-06-12,High-quality all-oxide Schottky junctions fabricated on heavily Nb-doped SrTiO3 substrates,"We present a detailed investigation of the electrical properties of epitaxial
La0.7Sr0.3MnO3/SrTi0.98Nb0.02O3 Schottky junctions. A fabrication process that
allows reduction of the junction dimensions to current electronic device size
has been employed. A heavily doped semiconductor has been used as a substrate
in order to suppress its series resistance. We show that, unlike standard
semiconductors, high-quality oxide-based Schottky junctions maintain a highly
rectifying behavior for doping concentration of the semiconductor larger than
10^20 cm^(-3). Moreover, the junctions show hysteretic current-voltage
characteristics.",0706.1620v2
2007-06-20,Conformal oxide coating of Carbon Nanotubes,"The International Roadmap for Ferroelectric Memories requires
three-dimensional integration of high-dielectric materials onto metal
interconnects or bottom electrodes by 2010. We report the first integration of
high-dielectric oxide films onto carbon nanotube electrodes with an aim of
ultra-high integration density of FeRAMs (Tb/in2).",0706.2998v1
2007-06-21,Self-interaction correction with Wannier functions,"We describe the behavior of the Perdew-Zunger self-interaction-corrected
local density approximation (SIC-LDA) functional when implemented in a
plane-wave pseudopotential formalism with Wannier functions. Prototypical
semiconductors and wide-bandgap oxides show a large overcorrection of the LDA
bandgap. Application to transition-metal oxides and elements with d electrons
is hindered by a serious breaking of the spherical symmetry, which appears even
in a closed shell free atom. Our results indicate that, when all spherical
approximations are lifted, the general applicability of orbital-dependent
potentials is very limited and should be reconsidered in favor of rotationally
invariant functionals.",0706.3210v1
2007-07-12,Properties of high-T$_C$ copper oxides from the nearly-free electron model,"The generic band structure of high-T$_C$ copper oxides is simulated by the
nearly free-electron model (NFE) in two dimensions (2-D) with parameters from
band calculations. Interaction between phonons and spin waves will cause
potential modulations and pseudogaps, and the strength of the modulations, the
wave lengths and the doping, are all related. A Fermi-surface ""arc"" is found
for dynamic spin/phonon waves. The confinement of superconductivity between two
limiting dopings can be a result of competition with the pseudogap at low
doping and weak coupling at high doping.",0707.1804v1
2007-07-20,A mechanism for unipolar resistance switching in oxide non-volatile memory devices,"Building on a recently introduced model for non-volatile resistive switching,
we propose a mechanism for unipolar resistance switching in
metal-insulator-metal sandwich structures. The commutation from the high to low
resistance state and back can be achieved with successive voltage sweeps of the
same polarity. Electronic correlation effects at the metal-insulator interface
are found to play a key role to produce a resistive commutation effect in
qualitative agreement with recent experimental reports on binary transition
metal oxide based sandwich structures.",0707.3077v1
2007-08-02,Reduction of the Casimir force using aerogels,"By using silicon oxide based aerogels we show numerically that the Casimir
force can be reduced several orders of magnitude, making its effect negligible
in nanodevices. This decrease in the Casimir force is also present even when
the aerogels are deposited on metallic substrates. To calculate the Casimir
force we model the dielectric function of silicon oxide aerogels using an
effective medium dielectric function such as the Clausius-Mossotti
approximation. The results show that both the porosity of the aerogel and its
thickness can be use as control parameters to reduce the magnitude of the
Casimir force.",0708.0434v1
2007-08-14,Nimesulide limits kainate-induced oxidative damage in the rat hippocampus,"Kainate induces a marked expression of cyclooxygenase-2 after its systemic
administration. Because cyclooxygenase-2 activity is associated to the
production of reactive oxygen species, we investigated the effects of
nimesulide, a selective cyclooxygenase-2 inhibitor, on kainate-induced in vivo
oxidative damage in the rat hippocampus. A clinically relevant dose of
nimesulide (6 mg/kg, i.p.) was administered three times following kainate
application (9 mg/kg, i.p.). After 24 h of kainate administration, the drastic
decrease in hippocampal glutathione content and the significant increase in
lipid peroxidation were attenuated in nimesulide-treated rats, suggesting that
the induction of cyclooxygenase-2 is involved in kainate-mediated free radicals
formation.",0708.1971v1
2007-09-13,Oxide-apertured microcavity single-photon emitting diode,"We have developed a microcavity single-photon source based on a single
quantum dot within a planar cavity in which wet-oxidation of a high-aluminium
content layer provides lateral confinement of both the photonic mode and the
injection current. Lateral confinement of the optical mode in optically pumped
structures produces a strong enhancement of the radiative decay rate. Using
microcavity structures with doped contact layers, we demonstrate a
single-photon emitting diode where current may be injected into a single dot.",0709.2105v1
2007-10-03,Calculated Momentum Dependence of Zhang-Rice States in Transition Metal Oxides,"Using a combination of local density functional theory and cluster exact
diagonalization based dynamical mean field theory, we calculate many body
electronic structures of several Mott insulating oxides including undoped high
T_{c} materials. The dispersions of the lowest occupied electronic states are
associated with the Zhang-Rice singlets in cuprates and with doublets,
triplets, quadruplets and quintets in more general cases. Our results agree
with angle resolved photoemission experiments including the decrease of the
spectral weight of the Zhang--Rice band as it approaches k=0.",0710.0678v4
2007-10-11,Enhancement of surface activity in CO oxidation on Pt(110) through spatiotemporal laser actuation,"We explore the effect of spatiotemporally varying substrate temperature
profiles on the dynamics and resulting reaction rate enhancement for the
catalytic oxidation of CO on Pt(110). The catalytic surface is ""addressed"" by a
focused laser beam whose motion is computer-controlled. The averaged reaction
rate is observed to undergo a characteristic maximum as a function of the speed
of this moving laser spot. Experiments as well as modelling are used to explore
and rationalize the existence of such an optimal laser speed.",0710.2161v1
2007-11-06,Surface Effects on Oxide Heterostructures,"We report on surface effects on the electronic properties of interfaces in
epitaxial LaAlO$_3$/SrTiO$_3$ heterostructures. Our results are based on
first-principles electronic structure calculations for well-relaxed multilayer
configurations, terminated by an ultrathin LaAlO$_3$ surface layer. On varying
the thickness of this layer, we find that the interface conduction states are
subject to almost rigid band shifts due to a modified Fermi energy. Confirming
experimental data, the electronic properties of heterointerfaces therefore can
be tuned systematically by alterating the surface-interface distance. We expect
that this mechanism is very general and applies to most oxide heterostructures.",0711.0813v1
2007-11-15,Effect of surface nanostructure on temperature programmed reaction spectroscopy: First-principles kinetic Monte Carlo simulations of CO oxidation at RuO2(110),"Using the catalytic CO oxidation at RuO2(110) as a showcase, we employ
first-principles kinetic Monte Carlo simulations to illustrate the intricate
effects on temperature programmed reaction spectroscopy data brought about by
the mere correlations between the locations of the active sites at a
nanostructured surface. Even in the absence of lateral interactions, this
nanostructure alone can cause inhomogeneities that cannot be grasped by
prevalent mean-field data analysis procedures, which thus lead to wrong
conclusions on the reactivity of the different surface species.",0711.2493v1
2007-11-27,First-principles study of ferroelectric oxide epitaxial thin films and superlattices: role of the mechanical and electrical boundary conditions,"In this review, we propose a summary of the most recent advances in the
first-principles study of ferroelectric oxide epitaxial thin films and
multilayers. We discuss in detail the key roles of mechanical and electrical
boundary conditions, providing to the reader the basic background for a simple
and intuitive understanding of the evolution of the ferroelectric properties in
many nanostructures. Going further we also highlight promising new avenues and
future challenges within this exciting field or researches.",0711.4201v1
2007-12-11,Thermoelectric properties of LaRh$_{1-x}$Ni$_x$O$_3$,"We report measurements and analyses of resistivity, thermopower, and thermal
conductivity of polycrystalline samples of perovskite LaRh$_{1-x}$Ni$_x$O$_3$.
The thermopower is found to be large at 800 K (185 $\mu$V/K for $x=$0.3), which
is ascribed to the high-temperature stability of the low-spin state of
Rh$^{3+}$/Rh$^{4+}$ ions. This clearly contrasts with the thermopower of the
isostructural oxide LaCoO$_3$, which rapidly decreases above 500 K owing to the
spin-state transition. The spin state of the transition-metal ions is one of
the most important parameters in oxide thermoelectrics.",0712.1626v2
2008-02-15,Quantitative analysis of electronic transport through weakly-coupled metal/organic interfaces,"Using single-crystal transistors, we have performed a systematic experimental
study of electronic transport through oxidized copper/rubrene interfaces as a
function of temperature and bias. We find that the measurements can be
reproduced quantitatively in terms of the thermionic emission theory for
Schottky diodes, if the effect of the bias-induced barrier lowering is
included. Our analysis emphasizes the role of the coupling between metal and
molecules, which in our devices is weak due to the presence of an oxide layer
at the surface of the copper electrodes.",0802.2153v1
2008-03-04,Conservation of dielectric constant upon amorphization in perovskite oxides,"We report calculations indicating that amorphous RAO$_3$ oxides, with R and A
trivalent cations, have approximately the same static dielectric constant as
their perovskite crystal phase. The effect is due to the disorder-activated
polar response of non-polar crystal modes at low frequency, which compensates a
moderate but appreciable reduction of the ionic dynamical charges. The
dielectric response was studied via density-functional perturbation theory.
Amorphous samples were generated by molecular dynamics melt-and-quench
simulations.",0803.0478v1
2008-05-15,Growth of Oxide Compounds under Dynamic Atmosphere Composition,"Commercially available gases contain residual impurities leading to a
background oxygen partial pressure of typically several 10^{-6} bar,
independent of temperature. This oxygen partial pressure is inappropriate for
the growth of some single crystals where the desired oxidation state possesses
a narrow stability field. Equilibrium thermodynamic calculations allow the
determination of dynamic atmosphere compositions yielding such self adjusting
and temperature dependent oxygen partial pressures, that crystals like ZnO,
Ga2O3, or Fe{1-x}O can be grown from the melt.",0805.2217v1
2008-05-23,Atomic Layer Deposition of Metal Oxides on Pristine and Functionalized Graphene,"We investigate Atomic Layer Deposition (ALD) of metal oxide on pristine and
functionalized graphene. On pristine graphene, ALD coating can only actively
grow on edges and defect sites, where dangling bonds or surface groups react
with ALD precursors. This affords a simple method to decorate and probe single
defect sites in graphene planes. We used perylene tetracarboxylic acid (PTCA)
to functionalize graphene surface and selectively introduced densely packed
surface groups on graphene. Uniform ultrathin ALD coating on PTCA graphene was
achieved over large area. The functionalization method could be used to
integrate ultrathin high-k dielectrics in future graphene electronics.",0805.3712v1
2008-08-08,New Insight into the Properties of Proton Conducting Oxides from Neutron Total Scattering,"In this paper we investigated the most important family of proton conducting
oxides, i.e. cerates, by means of pair distribution function analysis (PDF)
obtained from total neutron scattering data. The results clearly demonstrates
that the local structure plays a fundamental role in the protonation process.
Oxygen vacancy creation by acceptor doping reduces the local structure symmetry
which is then restored upon water uptake. This mechanism mainly involves the
Ba-O shell which flexibility seems to be at the basis of the proton conduction
mechanism, thus providing a direct insight on the design of optimal proton
conducting materials.",0808.1162v1
2008-09-08,Quantum spin Hall effect in a transition metal oxide Na2IrO3,"We study theoretically the electronic states in a $5d$ transition metal oxide
Na$_2$IrO$_3$, in which both the spin-orbit interaction and the electron
correlation play crucial roles. Tight-binding model analysis together with the
fisrt-principles band structure calculation predicts that this material is a
layered quantum spin Hall system. Due to the electron correlation, an
antiferromagnetic order first develops at the edge, and later inside the bulk
at low temperatures.",0809.1317v2
2008-09-18,Band Offsets at Semiconductor-Oxide Interfaces from Hybrid Density Functional Calculations,"Band offsets at semiconductor-oxide interfaces are determined through a
scheme based on hybrid density functionals, which incorporate a fraction
$\alpha$ of Hartree-Fock exchange. For each bulk component, the fraction
$\alpha$ is tuned to reproduce the experimental band gap, and the conduction
and valence band edges are then located with respect to a reference level. The
lineup of the bulk reference levels is determined through an interface
calculation, and shown to be almost independent of the fraction $\alpha$.
Application of this scheme to the Si-SiO$_2$, SiC-SiO$_2$, and Si-HfO$_2$
interfaces yields excellent agreement with experiment.",0809.3119v1
2008-12-04,Impurity-induced frustration in correlated oxides,"Using the example of Zn-doped La2CuO4, we demonstrate that a spinless
impurity doped into a non-frustrated antiferromagnet can induce substantial
frustrating interactions among the spins surrounding it. This counterintuitive
result is the key to resolving discrepancies between experimental data and
earlier theories. Analytic and quantum Monte Carlo studies of the
impurity-induced frustration are in a close accord with each other and
experiments. The mechanism proposed here should be common to other correlated
oxides as well.",0812.1023v3
2008-12-26,Germanium Segregation in CVD Grown Sige Layers for Flash Memory Application,"A 2D layer of spherical, crystalline Ge nanodots embedded in SiO2 was formed
by low pressure chemical vapour deposition combined with furnace oxidation and
rapid thermal annealing. The samples were characterized structurally by using
transmission electron microscopy and rutherford back scattering spectrometry,
as well as electrically by measuring CV and IV characteristics. It was found
that formation of a high density Ge dots took place due to oxidation induced Ge
segregation. The dots are situated in the SiO2 on the average distance 5 nm
from the substrate. Strong evidence of charge storage effect in the crystalline
Ge nanodot layer is demonstrated by the hysteresis behavior of the high
frequency CV curves.",0812.4680v1
2009-01-28,Mechanism of orbital reconstruction at the interfaces of transition metal oxides,"Orbital reconstruction at interfaces between YBa2Cu3O6 and SrO-terminated
SrTiO3 is studied using local spin density approximation (LSDA) with
intra-atomic Coulomb repulsion (LSDA+U). The change of population of
interfacial Cu 3d orbitals results in stabilization of a new oxidation state
$3d^8$ which involves an additional modification of orbital occupancies in the
nearest SrO and TiO2 layers. We find that an increase of electron charge in Cu
3d_{x^2-y^2} states counterbalances a depopulation of 3d_{3z^2-r^2} orbitals
which induces, on account of the onsite Coulomb repulsion U, a splitting of
3d_{3z^2-r^2} states at CuO2-SrO interfaces.",0901.4406v2
2009-01-29,Self-Doping Induced Orbital-Selective Mott Transition in Hg2Ru2O7,"Pyrochlore oxides are fascinating systems where strong, multi-orbital
correlations in concert with geometrical frustration give rise to unanticipated
physical properties. The detailed mechanism of the insulator-metal transitions
(IMT) underpinning these phenomena is, however, ill-understood in general.
Motivated thereby, we study the IMT in the pyrochlore ${\rm Hg_{2}Ru_{2}O_{7}}$
using LDA+DMFT. In contrast to the well-known examples of Mott transitions in
TMO, we show that, in the negative charge-transfer situation characteristic of
\hg, self-doping plays a crucial role in the emergence of an orbital-selective
IMT. We argue that this mechanism has broader relevance to other correlated
pyrochlore oxides.",0901.4658v1
2009-02-03,Current-perpendicular-to-plane magnetoresistance of a domain wall confined in a nano-oxide-layer,"We theoretically study the current-perpendicular-to-plane magnetoresistance
of a domain wall confined in a current-confined-path (CCP) structure made of a
nano-oxide-layer (NOL). In order to calculate the MR ratio of the system, the
continuity equations for charge and spin currents are numerically solved with
the three-dimensional CCP geometry by use of finite element method. It is
confirmed that the MR ratio is enhanced by the CCP structure, which is
consistent with the experimental results.",0902.0644v1
2009-02-16,Sensor/ROIC Integration using Oxide Bonding,"We explore the Ziptronix Direct Bond Interconnect technology for the
integration of sensors and readout integrated circuits (ROICs) for high energy
physics. The technology utilizes an oxide bond to form a robust mechanical
connection between layers which serves to assist with the formation of metallic
interlayer connections. We report on testing results of sample sensors bonded
to ROICs and thinned to 100 microns.",0902.2801v1
2009-02-18,Effects of external global noise on the catalytic CO oxidation on Pt(110),"Oxidation reaction of CO on a single platinum crystal is a reaction-diffusion
system that may exhibit bistable, excitable, and oscillatory behavior. We
studied the effect of a stochastic signal artificially introduced into the
system through the partial pressure of CO. First, the external signal is
employed as a turbulence suppression tool, and second, it modifies the
boundaries in the bistable transition between the CO and oxygen covered phases.
Experiments using photoemission electron microscopy (PEEM) together with
numerical simulations performed with the Krischer-Eiswirth-Ertl (KEE) model are
presented.",0902.3162v1
2009-02-20,Properties of high-$T_c$ copper oxides from band models of spin-phonon coupling,"The mechanism of spin-phonon coupling (SPC) and possible consequencies for
the properties of high-$T_C$ copper oxides are presented. The results are based
on ab-initio LMTO band calculations and a nearly free-electron (NFE) model of
the band near $E_F$. Many observed properties are compatible with SPC, as for
the relation between doping and $\vec{q}$ for spin excitations and their energy
dependence. The main pseudogap is caused by SPC and waves along [1,0,0], but it
is suggested that secondary waves, generated along [1,1,0], contribute to a
'waterfall' structure. Conditions for optimal $T_C$, and the possiblities for
spin enhancement at the surface are discussed.",0902.3580v1
2009-04-07,Réduction de la nuisance olfactive par oxydation photocatalytique,"Heterogeneous photocatalysis is an interesting alternative for the
purification, decontamination and smell abatment of air. In the present work,
the photocatalytic oxidation of 2-butanone (MEK : methyl ethyle ketone) is
investigated, this low molecular mass product being the source of serious smell
pollution. The influence of light and of the pollutant concentration were
investigated in an annular photoreactor. As most VOC's, the degradation rate of
MEK follows a Langmuir-Hinshelwood type law. Intermediate products were
analysed by GC-MD ; acetaldehyde is the dominant byproduct of the
photocatalytic oxidation.",0904.1196v1
2009-04-14,Stress-driven oxidation chemistry of wet silicon surfaces,"The formation of a hydroxylated native oxide layer on Si(001) under wet
conditions is studied by means of first principles molecular dynamics
simulations. Water molecules are found to adsorb and dissociate on the oxidised
surface leading to rupture of Si-O bonds and producing reactive sites for
attack by dissolved dioxygen or hydrogen peroxide molecules. Tensile strain is
found to enhance the driving force for the dissociative adsorption of water,
suggesting that similar reactions could be responsible for
environmentally-driven sub-critical crack propagation in silicon.",0904.2091v1
2009-05-18,Insulator to semi-metal transition in graphene oxide,"Transport properties of progressively reduced graphene oxide (GO) are
described. Evolution of the electronic properties reveals that as-synthesized
GO undergoes insulator-semiconductor-semi-metal transitions with reduction. The
apparent transport gap ranges from 10 ~ 50 meV and approaches zero with
extensive reduction. Measurements at varying degrees of reduction reveal that
transport in reduced GO occurs via variable-range hopping and further reduction
leads to increased number of available hopping sites.",0905.2799v1
2009-06-05,Evaluation of the optical axis tilt of Zinc oxide films via noncollinear second harmonic generation,"We investigated noncollinear second harmonic generation form Zinc oxide
films, grown on glass substrates by dual ion beam sputtering technique. At a
fixed incidence angle, the generated signal is investigated by scanning the
polarization state of both fundamental beams. We show that the map of the
generated signal as a function of polarization states of both pump beams,
together with the analytical curves, allows to retrieve the orientation of the
optical axis and, eventually, its angular tilt, with respect to the surface
normal",0906.1156v1
2009-07-31,New Correlated Model of Colossal Magnetoresistive Manganese Oxides,"A new minimal model is constructed for the doped manganese oxides which
exhibit colossal magnetoresistance (CMR), involving broad spin-majority
conduction band as well as nearly localised spin-minority electron states. A
simple mean field analysis yields a temperature-dependent hybridised band
structure with suppressed carrier weight at the Fermi level. Spin stiffness is
complex, indicating unusually strong spin wave damping. Experimental and
theoretical investigations are needed to further verify the relevance of the
proposed model.",0907.5512v3
2009-08-11,Electronic structure of alkaline earth and post-transition metal oxides,"The electronic structure in alkaline earth AeO (Ae = Be, Mg, Ca, Sr, Ba) and
post-transition metal oxides MeO (Me = Zn, Cd, Hg) is probed with oxygen K-edge
X-ray absorption and emission spectroscopy. The experimental data is compared
with density functional theory electronic structure calculations. We use our
experimental spectra of the oxygen K-edge to estimate the bandgaps of these
materials, and compare our results to the range of values available in the
literature.",0908.1581v2
2009-09-08,Berry-phase theory of polar discontinuities at oxide-oxide interfaces,"In the framework of the modern theory of polarization, we rigorously
establish the microscopic nature of the electric displacement field D. In
particular, we show that the longitudinal component of D is preserved at a
coherent and insulating interface. To motivate and elucidate our derivation, we
use the example of LAO/STO interfaces and superlattices, where the validity of
the above conservation law is not immediately obvious. Our results generalize
the ""locality principle"" of constrained-D density functional theory to the
first-principles modeling of charge-mismatched systems.",0909.1500v1
2009-11-11,Transport properties of the layered Rh oxide K_0.49RhO_2,"We report measurements and analyses of resistivity, thermopower and Hall
coefficient of single-crystalline samples of the layered Rh oxide K_0.49RhO_2.
The resistivity is proportional to the square of temperature up to 300 K, and
the thermopower is proportional to temperature up to 140 K. The Hall
coefficient increases linearly with temperature above 100 K, which is ascribed
to the triangular network of Rh in this compound. The different transport
properties between Na_xCoO_2 and K_0.49RhO_2 are discussed on the basis of the
different band width between Co and Rh evaluated from the magnetotransport.",0911.2156v1
2009-11-12,Melt Grown ZnO Bulk Crystals,"Bulk crystals of zinc oxide can be grown from the melt by a Bridgman
technique under pressure. This new technology using an iridium crucible shows
the potential to yield large single crystals of good crystalline perfection.
Crystals with diameters up to 33 mm and a length of up to 50 mm have been
demonstrated. The impurity content can be strongly reduced by using the
crucibles repeatedly.",0911.2318v1
2010-01-05,Mechanism for bipolar resistive switching in transition metal oxides,"We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model.",1001.0703v1
2010-01-26,Theory of oxygen K-edge x-ray absorption spectra of cuprates,"The dynamical mean-field theory of the three-band model of copper-oxide
superconductors is used to calculate the doping dependence of the intensity of
the oxygen K-edge x-ray absorption spectra of high-$T_c$ copper oxide
superconductors. The model is found not to reproduce the results of a recent
experiment, suggesting that at sufficiently high doping the physics beyond the
conventional three-band model becomes important.",1001.4791v2
2010-01-30,High yield fabrication of chemically reduced graphene oxide field effect transistors by dielectrophoresis,"We demonstrate high yield fabrication of field effect transistors (FET) using
chemically reduced graphene oxide (RGO) sheets suspended in water assembled via
dielectrophoresis. The two terminal resistances of the devices were improved by
an order of magnitude upon mild annealing at 200 0C in Ar/H2 environment for 1
hour. With the application of a backgate voltage, all of the devices showed FET
behavior with maximum hole and electron mobilities of 4.0 and 1.5 cm2/Vs
respectively. This study shows promise for scaled up fabrication of graphene
based nanoelectronic devices.",1002.0086v2
2010-02-02,Effective-mass model of surface scattering in locally oxidized Si nanowires,"We present a simple model to describe the lowest-subbands surface scattering
in locally oxidized silicon nanowires grown in the [110] direction. To this
end, we employ an atomistically scaled effective mass model projected from a
three-dimensional effective mass equation and apply a quantum transport
formalism to calculate the conductance for typical potential profiles.
Comparison of our results with hole-transport calculations using atomistic
models in conjunction with density functional theory (DFT) points to an
intra-subband scattering mechanism from a potential well.",1002.0435v1
2010-02-05,A survey of fractured SrTiO$_3$ surfaces: from the micro-meter to nano-meter scale,"Cross-sectional scanning tunneling microscopy was utilized to study fractured
perovskie oxide surfaces. It was found for the non-cleavable perovskite oxide,
SrTiO$_{3}$, that atomically flat terraces could be routinely created with a
controlled fracturing procedure. Optical and scanning electron microscopy as
well as a profilometer were used to obtain the information from sub-millimeter
to sub-micrometer scales of the fractured surface topography.",1002.1158v1
2010-02-17,Position dependent photodetector from large area reduced graphene oxide thin films,"We fabricated large area infrared photodetector devices from thin film of
chemically reduced graphene oxide (RGO) sheets and studied their photoresponse
as a function of laser position. We found that the photocurrent either
increases, decreases or remain almost zero depending upon the position of the
laser spot with respect to the electrodes. The position sensitive photoresponse
is explained by Schottky barrier modulation at the RGO film-electrode
interface. The time response of the photocurrent is dramatically slower than
single sheet of graphene possibly due to disorder from the chemically synthesis
and interconnecting sheets.",1002.3191v1
2010-03-30,Decoupling Graphene from SiC(0001) via Oxidation,"When epitaxial graphene layers are formed on SiC(0001), the first carbon
layer (known as the ""buffer layer""), while relatively easy to synthesize, does
not have the desirable electrical properties of graphene. The conductivity is
poor due to a disruption of the graphene pi-bands by covalent bonding to the
SiC substrate. Here we show that it is possible to restore the graphene
pi-bands by inserting a thin oxide layer between the buffer layer and SiC
substrate using a low temperature, CMOS-compatible process that does not damage
the graphene layer.",1003.5702v1
2010-04-01,Interaction of Gold Nanoparticles in Barium Titanate Thin Films,"A novel approach to control the grain size of oxide thin film materials has
been investigated. Perovskite BaTiO3 shows interesting grain structures when
deposited on gold predeposited, (111)-oriented, singlecrystal SrTiO3
substrates. Solid oxide films grow epitaxially on patterned seed layers and
show variations in grain size relative to the films deposited on SrTiO3
directly.",1004.0225v1
2010-04-22,Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond,"We report on sub-bandgap optoelectronic phenomena of hydrogen-terminated
diamond patterned with a submicron oxidized line. The line acts as an energy
barrier for the two-dimensional hole gas located below the hydrogenated diamond
surface. A photoconductive gain of the hole conductivity across the barrier is
measured for sub-bandgap illumination. The findings are consistent with
photogenerated electrons being trapped in defect levels within the barrier. We
discuss the spatial and energetic characteristics of the optoelectronic
phenomena, as well as possible photocurrent effects.",1004.3900v1
2010-06-11,Structural Features of Layered Iron Pnictide Oxides (Fe2As2)(Sr4M2O6),"Structural features of newly found perovskite-based iron pnictide oxide
system have been systematically studied. Compared to REFePnO system,
perovskite-based system tend to have lower Pn-Fe-Pn angle and higher pnictogen
height owing to low electronegativity of alkaline earth metal and small
repulsive force between pnictogen and oxygen atoms. As-Fe-As angles of
(Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to
ideal tetrahedron and those pnictogen heights of about 1.40 A are close to
NdFeAsO with optimized carrier concentration. These structural features of this
system may leads to realization of high Tc superconductivity.",1006.2351v1
2010-06-23,Space charge limited conduction with exponential trap distribution in reduced graphene oxide sheets,"We elucidate on the low mobility and charge traps of the chemically reduced
graphene oxide (RGO) sheets by measuring and analyzing temperature dependent
current-voltage characteristics. The RGO sheets were assembled between source
and drain electrodes via dielectrophoresis. At low bias voltage the conduction
is Ohmic while at high bias voltage and low temperatures the conduction becomes
space charge limited with an exponential distribution of traps. We estimate an
average trap density of 1.75x10^16 cm^-3. Quantitative information about charge
traps will help develop optimization strategies of passivating defects in order
to fabricate high quality solution processed graphene devices.",1006.4430v1
2010-08-16,Electronic phase separation in the pyrochlore double-exchange model,"Electronic phase separation and related inhomogeneity is ubiquitously seen in
strongly-correlated systems. A typical example is found between ferromagnetic
metal and antiferromagnetic insulator in CMR manganese oxides. Here we
demonstrate that the geometrical frustration brings distinctive aspects into
the phase separation phenomena. From Monte Carlo simulation and a simple energy
comparison for the pyrochlore double-exchange model, we show that such phase
separation takes place between ferromagnetic and paramagnetic metals. We
discuss the relevance of our results to a spin-glassy metallic phase found in
Mo pyrochlore oxides under external pressure.",1008.2786v1
2010-09-26,Superconductivity above 10 K in Non-Cuprate Oxides,"Beginning in 1973, several non-cuprate transition metal and non-transition
metal oxides were discovered with superconducting transition temperatures
between 10 and 30 K. Retrospectives about these discoveries in spinel structure
LiTi2O4 and perovskite structure (Ba,K)(Bi,Pb)O3 are given.",1009.5134v2
2010-09-28,Electric field modulation of thermopower for transparent amorphous oxide thin film transistors,"To clarify the electronic density of states (DOS) around the conduction band
bottom for state of the art transparent amorphous oxide semiconductors (TAOSs),
InGaZnO4 and In2MgO4, we fabricated TAOS-based transparent thin film
transistors (TTFTs) and measured their gate voltage dependence of thermopower
(S). TAOS-based TTFTs exhibit an unusual S behavior. The |S|-value abruptly
increases, but then gradually decreases as Vg increases, clearly suggesting the
anti-parabolic shaped DOS is hybridized with the original parabolic shaped DOS
around the conduction band bottom.",1009.5548v1
2010-10-20,Templated self-assembly of iron oxide nanoparticles,"We report on self-assembled iron oxide nanoparticle films on silicon
substrates. In addition to homogeneously assembled layers, we fabricated
patterned trenches of 40-1000 nm width using electron beam lithography for the
investigation of assisted self-assembly. The nanoparticles with a diameter of
20 nm +/- 7% were synthesized by thermal decomposition of iron oleate complexes
in trioctylamine in presence of oleic acid. Samples with different track widths
and nanoparticle concentration were characterized by scanning electron
microscopy and by superconducting quantum interference device magnetometry.",1010.4166v1
2010-10-20,Phase separation of multicomponent excitonic Bose-Einstein condensates,"For the observation of Bose-Einstein condensation, excitons in cuprous oxide
are regarded as promising candidates due to their large binding energy and long
lifetime. High particle densities may be achieved by entrapment in a stress
induced potential. We consider a multi-component gas of interacting para- and
orthoexcitons in cuprous oxide confined in a three-dimensional potential trap.
Based on the Hartree-Fock-Bogoliubov theory, we calculate density profiles as
well as decay luminescence spectra which exhibit signatures of the separation
of the Bose-condensed phases.",1010.4171v1
2011-01-08,Synthesis and Thermal Stability of Cubic ZnO in the Salt Nanocomposites,"Cubic zinc oxide (rs-ZnO), metastable under normal conditions, was
synthesized from the wurtzite modification (w-ZnO) at 7.7 GPa and ~800 K in the
form of nanoparticles isolated in the NaCl matrix. The phase transition rs-ZnO
\rightarrow w-ZnO in nanocrystalline zinc oxide under ambient pressure was
experimentally studied for the first time by differential scanning calorimetry
and high-temperature X-ray diffraction. It was shown that the transition occurs
in the 370-430 K temperature range and its enthalpy at 400 K is -10.2 \pm 0.5
kJ mol-1.",1101.1588v1
2011-01-17,Imprinting nanoporous alumina patterns into the magneto-transport of oxide superconductors,"We used oxygen ion irradiation to transfer the nanoscale pattern of a porous
alumina mask into high- superconducting thin films. This causes a nanoscale
spatial modulation of superconductivity and strongly affects the
magneto-transport below, which shows a series of periodic oscillations
reminiscent of the Little-Parks effect in superconducting wire networks. This
irradiation technique could be extended to other oxide materials in order to
induce ordered nanoscale phase segregation.",1101.3172v1
2011-01-18,Metal-insulator transition and electrically-driven memristive characteristics of SmNiO3 thin films,"The correlated oxide SmNiO3 (SNO) exhibits an insulator to metal transition
(MIT) at 130 {\deg}C in bulk form. We report on synthesis and electron
transport in SNO films deposited on LaAlO3 (LAO) and Si single crystals. X-ray
diffraction studies show that compressively strained single-phase SNO grows
epitaxially on LAO while on Si, mixed oxide phases are observed. MIT is
observed in resistance-temperature measurements in films grown on both
substrates, with charge transport in-plane for LAO/SNO films and out-of-plane
for Si/SNO films. Electrically-driven memristive behavior is realized in
LAO/SNO films, suggesting that SNO may be relevant for neuromorphic devices.",1101.3538v1
2011-02-04,Initial oxidation of Fe-Al and Fe-Cr-Al alloys: Cr as an alumina booster,"The boosting effect of Cr on the growth of the protective alumina scale on
Fe-Al alloys is investigated by x-ray photoelectron spectroscopy. Using low
oxygen pressure the surface chemistry of the alloys is monitored starting from
the first moments of oxidation. Chromium effect on the Fe-Al surface-bulk
exchange is clearly detected by analyzing the measured surface concentrations
within the atomic concentration models. Previous ab initio calculations agree
well with the present experiments.",1102.0912v1
2011-03-09,Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution,"A self-consistent, mean-field model of charge-carrier injection and unipolar
transport in an organic semiconductor diode is developed utilizing the
effective transport energy concept and taking into account a realistic
density-of-states distribution as well as the presence of trap states in an
organic material. The consequences resulting from the model are discussed
exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic
conductor structure. A comparison of the theory to experimental data of a
unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.",1103.1752v1
2011-05-21,LaCrO3 heteroepitaxy on SrTiO3(001) by molecular beam epitaxy,"Stoichiometric, epitaxial LaCrO3 films have been grown on TiO2-terminated
SrTiO3(001) substrates by molecular beam epitaxy using O2 as the oxidant. Film
growth occurred in a layer-by-layer fashion, giving rise to structurally
excellent films and surfaces which preserve the step-terrace structure of the
substrate. The critical thickness is in excess of 500 {\AA}. Near-surface
Cr(III) is highly susceptible to further oxidation to Cr(V), leading to the
formation of a disordered phase upon exposure to atomic oxygen. Recovery of the
original epitaxial LaCrO3 phase is readily achieved by vacuum annealing.",1105.4290v1
2011-06-14,Rigorous definition of oxidation states of ions in solids,"We present justification and rigorous procedure for electron partitioning
among atoms in extended systems. The method is based on wavefunction topology
and the modern theory of polarization, rather than charge density partitioning
or wavefunction projection, and, as such, re-formulates the concept of
oxidation state without assuming real-space charge transfer between atoms. This
formulation provides rigorous electrostatics of finite extent solids, including
films and nanowires.",1106.2836v2
2011-08-03,Reduction of the Casimir force from indium tin oxide film by UV treatment,"A significant decrease in the magnitude of the Casimir force (from 21% to
35%) was observed after an indium tin oxide (ITO) sample interacting with an Au
sphere was subjected to the UV treatment. Measurements were performed by using
an atomic force microscope (AFM) in high vacuum. The experimental results are
compared with theory, and a hypothetical explanation for the observed
phenomenon is proposed.",1108.0923v1
2011-08-16,Re-determination of the Pseudobinary System Li2O-MoO3,"The quasi-binary phase diagram lithium oxide - molybdenum(VI) oxide was
investigated by differential scanning calorimetry and X-ray diffraction. The
four intermediate phases Li4MoO5, Li2MoO4, Li4Mo5O17, and Li2Mo4O13 show
incongruent melting. The system has one eutectic point at 50.5 mol% MoO3 and
49.5 mol% LiO0.5 with a eutectic temperature of 524.6 deg C. At this point the
melt is in equilibrium with Li2MoO4 and Li4Mo5O17.",1108.3248v1
2011-08-30,Ferroelectricity in Silver Perovskite Oxides,"There are two silver perovskite oxides: AgNbO3 and AgTaO3. AgNbO3 has a
noncentrosymmetric group of Pmc21 at room temperature with a ferri-electric
ordering of polarization. Such a ferri-electric state with small polarization
can be changed into a ferroelectric state with very large polarization by a
high electric field or by a chemical modification. The induced ferroelectric
phase shows promising electromechanical response for applications in
piezoelectric devices. In contrast, AgTaO3 is a quantum paraelectric, but
ferroelectricity also can be induced through chemical substitution. The
findings of good ferroelectric and piezoelectric performance in the silver
perovskites are hoped to trigger further theoretical and experimental
investigations on these systems.",1108.5819v1
2011-09-14,Electric field induced reversible control of visible photoluminescence from ZnO nanoparticles,"Reversible control of the photoluminescence of ZnO occurring in the visible
range, has been achieved by application of a few volts (< 5V) to a device
consisting of nanostructured ZnO film sandwiched between Indium Tin Oxide
electrode and polyethylene oxide-lithium perchlorate, a solid polymer
electrolyte. The photoluminescence intensity shows nearly 100% modulation with
a response time less than 30 seconds, when the bias is applied at the
electrolyte-electrode. A model is proposed for the observed effect that is
based on defect states of ZnO and the band bending at the ZnO-electrolyte
interface that can be changed by the applied bias.",1109.2968v1
2011-10-27,Intrinsic Cut-off Frequency in Scaled Graphene Transistors,"Using 2-D self-consistent ballistic quantum transport simulations, we
investigate the short-channel behavior of graphene field-effect transistors and
its impact on the device transconductance and subsequently the intrinsic
cut-off frequency (fT). Although with thin oxides, fT expectedly scales
inversely with the gate length, significant band-to-band tunneling at OFF state
leads to a departure from this trend in case of thick oxides. We also examine
the effect of achieving better electrostatics at the cost of increased gate
capacitance and illustrate that this can indeed degrade the fT. These
considerations should be implicit in the optimization of graphene transistors
for high-frequency applications.",1110.6211v1
2012-03-06,Reduction of Copper Oxide by Formic Acid an ab-initio study,"Four cluster models for a copper(I)oxide (111) surface have been designed, of
which three were studied with respect to their applicability in density
functional calculations in the general gradient approximation. Formic acid
adsorption on these systems was modelled and yielded four different adsorption
structures, of which two were found to have a high adsorption energy. The
energetically most favourable adsorption structure was further investigated
with respect to its decomposition and a few reactions with adsorbed H and OH
species using synchronous transit methods to estimate reaction barriers and
single point energy calculations for the reaction energy.",1203.1163v1
2012-08-27,STM-induced surface aggregates on metals and oxidized silicon,"We have observed an aggregation of carbon or carbon derivatives on platinum
and natively oxidized silicon surfaces during STM measurements in ultra-high
vacuum on solvent-cleaned samples previously structured by e-beam lithography.
We have imaged the aggregated layer with scanning tunneling microscopy (STM) as
well as scanning electron microscopy (SEM). The amount of the aggregated
material increases with the number of STM scans and with the tunneling voltage.
Film thicknesses of up to 10 nm with five successive STM measurements have been
obtained.",1208.5336v1
2012-10-07,Types of single particle symmetry breaking in transition metal oxides due to electron correlation,"Very accurate wave functions are calculated for small transition metal oxide
molecules. These wave functions are decomposed using reduced density matrices
to study the underlying correlation of electrons. The correlation is primarily
of left-right type between the transition metals and the oxygen atoms, which is
mediated by excitations from the nominal single Slater ground state into
antibonding and d-type orbitals. In a localized representation, this
correlation manifests itself in a 2-electron hopping term that is off-diagonal.
This term is of similar magnitude to the commonly considered Hubbard-type
on-site interaction.",1210.2115v2
2012-11-22,Observation of Phonon-Assisted Magnon Absorption in Spin-Orbit Coupling Induced Mott Insulator Sr$_{2}$IrO$_{4}$,"The infrared transmission measurement was performed for a two-dimensional
spin-orbit coupling induced Mott insulator Sr$_{2}$IrO$_{4}$ with a
layered-perovskite structure. A phonon-assisted magnon mode was observed at
around 1870 cm$^{-1}$ in the absorption spectrum below 180 K. The
nearest-neighbor superexchange interaction $J$ was estimated to be 57 meV,
which is about a half of the $J$ value of a copper oxide La$_{2}$CuO$_{4}$. Our
results indicate the possibility that nontrivial properties such as
superconductivity are realized at rather high temperature in iridium oxides.",1211.5241v2
2012-12-02,"Linearly polarized, Q-switched Er-doped fiber laser based on reduced graphene oxide saturable absorber","We demonstrate generation of linearly polarized pulses from a passively
Q-switched Erbium-doped fiber laser. The cavity was designed using only
polarization maintaining (PM) fibers and components, resulting in linearly
polarized output beam with degree of polarization (DOP) at the level of 97.6%.
Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched
operation. The laser was capable of delivering 1.85us pulses with 125nJ pulse
energy at 115kHz repetition rate.",1212.0201v1
2012-12-04,Anion-radical oxygen centers in small (AgO)n clusters: density functional theory predictions,"Anion-radical form of the oxygen centers O(-) is predicted at the DFT level
for small silver oxide particles having the AgO stoichiometry. Model clusters
(AgO)n appear to be ferromagnetic with appreciable spin density at the oxygen
centers. In contrast to these clusters, the Ag2O model cluster have no unpaired
electrons in the ground state. The increased O/Ag ratio in the oxide particles
is proved to be responsible for the spin density at oxygen centers.",1212.0712v1
2013-03-16,Designing ferromagnetism in vanadium-oxide based superlattices,"Motivated by recent reports (Phys. Rev. B\textbf{80}, 241102) of
room-temperature ferromagnetism in vanadium-oxide based superlattices, a
single-site dynamical mean field study of the dependence of the
paramagnetic-ferromagnetic phase boundary on superlattice geometry was
performed. An examination of variants of the experimentally determined crystal
structure indicate that ferromagnetism is found only in a small and probably
inaccessible region of the phase diagram. Design criteria for increasing the
range over which ferromagnetism might exist are proposed.",1303.4016v2
2013-04-10,Single Hole Transport in a Silicon Metal-Oxide-Semiconductor Quantum Dot,"We describe a planar silicon metal-oxide-semiconductor (MOS) based single
hole transistor, which is compatible with conventional Si CMOS fabrication. A
multi-layer gate design gives independent control of the carrier density in the
dot and reservoirs. Clear Coulomb blockade oscillations are observed, and
source-drain biasing measurements show that it is possible to deplete the dot
down to the few hole regime, with excited states clearly visible. The
architecture is sufficiently versatile that a second hole dot could be induced
adjacent to the first one.",1304.2871v2
2013-06-30,Effect of encapsulated graphene oxide on alginate-based bead adsorption to remove acridine orange from aqueous solutions,"Environmentally-benign high-performance graphene oxide (GO)/alginate-based
absorbents were prepared to eliminate acridine orange selected as a typical
dye. Characterizations demonstrated GO well encapsulated and its promotion of
pore formation on structure. Kinetic studies exhibited that the addition of GO
shortened the adsorption equilibrium time, raised the initial rate and the
adsorption capacity. Isotherm studies indicated the adsorptive behavior
followed Langmuir type, and higher maximum capacity was obtained in the
presence of GO. The adsorption positively responded to pH increased from acidic
to weakly alkaline. At low pH, GO would contribute dominantly to the
adsorption, whereas alginate component was inhibited.",1307.0223v1
2013-07-03,Simple approach for detection and estimation of photoactivity of silver particles on graphene oxide in aqueous-organic dispersion,"In the aqueous-organic (containing dimethylformamide) dispersion of graphene
oxide flakes with deposited thereon Ag-particles, under the action of light in
visible range, apparently for the first time, the effect of sediment flotation
was observed with subsequent stabilization of the dispersion, which does not
occur in the absence of Ag-particles. The main reason for such a laser light
induced movement of sediment GO flakes may be explained with the appearance of
small bubbles. The further development of this approach seem to be able to
estimate photo activity of graphene flakes with different activation particles.",1307.0926v1
2013-10-17,Improved Interfacial and Electrical Properties of GaSb Metal Oxide Semiconductor Devices Passivated with Acidic (NH4)2S Solution,"Surface passivation with acidic (NH4)2S solution is shown to be effective in
improving the interfacial and electrical properties of HfO2/GaSb metal oxide
semiconductor devices. Compared with control samples, those treated with acidic
(NH4)2S solution showed great improvements in frequency dispersion, gate
leakage current and interface trap density. These improvements were attributed
to the acidic (NH4)2S solution enhancing passivation of the substrates, which
was analyzed from the perspective of chemical mechanism and confirmed by X-ray
photoelectron spectroscopy and high-resolution cross-sectional transmission
electron microscopy.",1310.4591v1
2013-11-14,Photo-oxidation of Graphene in the Presence of Water,"Oxygen molecules are found to exhibit non-negligible reactivity with graphene
under strong light irradiation in the presence of water. The reaction is
triggered by the laser Raman spectroscopy measurement itself, and the D band
(ca. 1340 cm-1) becomes larger as the laser irradiation is prolonged. The
electronic transport properties of the graphene derivative are also
investigated and both the electron and hole mobility are found to be reduced.
These results are attributed to oxidation of graphene. This primitive
modification method can be exploited to manipulate the structural and
electronic properties of graphene.",1311.3447v1
2013-12-13,Room temperature formation of high-mobility two-dimensional electron gases at crystalline complex oxide interfaces,"Well-controlled sub-unit-cell layer-by-layer epitaxial growth of spinel
alumina is achieved at room temperature on the TiO2-terminated SrTiO3 single
crystalline substrate. By tailoring the interface redox reaction,
two-dimensional electron gases with mobilities exceeding 3000 cm2V-1s-1 are
achieved at this novel oxide interface.",1312.3719v1
2013-12-27,Third Harmonic Generation in Cuprous Oxide: Efficiency Determination,"The efficiency of third harmonic generation in cuprous oxide was measured.
Intensities followed a non-cubic power law which indicates nonperturbative
behavior. Polarization anisotropy of the harmonic generation was demonstrated
and related to the third order susceptibility. The results will influence the
understanding of harmonic generation in centrosymmetric materials and are
potentially relevant to device design and the interpretation of exciton
behavior.",1312.7371v1
2013-12-27,Unexpectedly Slow Two Particle Decay of Ultra-Dense Excitons in Cuprous Oxide,"For an ultra-dense exciton gas in cuprous oxide (Cu$_2$O), exciton-exciton
interactions are the dominant cause of exciton decay. This study demonstrates
that the accepted Auger recombination model overestimates the exciton decay
rate following intense two photon excitation. Two exciton decay is relevant to
the search for collective quantum behavior of excitons in bulk systems. These
results suggest the existence of a new high density regime of exciton behavior.",1312.7372v1
2014-01-06,Band offsets in heterojunctions between cubic perovskite oxides,"The band offsets for nine heterojunctions between titanates, zirconates, and
niobates with the cubic perovskite structure were calculated from first
principles. The effect of strain in contacting oxides on their energy
structure, many-body corrections to the position of the band edges (calculated
in the GW approximation), and the splitting of the conduction band resulting
from spin-orbit interaction were consistently taken into account. It was shown
that the neglect of the many-body effects can lead to errors in determination
of the band offsets up to 0.36 eV. The failure of the transitivity rule, which
is often used to determine the band offsets in heterojunctions, was
demonstrated and its cause was explained.",1401.1157v1
2014-01-09,Functionalization of Amorphous Chalcogenide and Titanium Oxide Layers by Gold Nanoparticles,"The technology problems of fabricating different, nanometers sized gold
particles in the layered composites like light-sensitive chalcogenide
glass/gold nanoparticles/transparent substrate or titanium/titanium oxide/gold
nanoparticles were investigated in our work. Combination of ion implantation,
plasma deposition with annealing processes results physical routes for creation
of gold nanoparticles in the mentioned structures, which possess plasmon
effects. These functionalized structures are planned to use for investigations
of optical recording processes, biocompatibility of titanium implants.",1401.1963v1
2014-01-09,Microwave Assisted Synthesis and Characterization of Perovskite Oxides,"The use of microwave irradiation is a promising alternative heat source for
the synthesis of inorganic materials such as perovskite oxides. The method
offers massive energy and time savings as compared to the traditional ceramic
method. In this work we review the basic principles of the microwave heating
mechanism based on interactions between dipoles in the material and the
electromagnetic microwave. Furthermore, we comment on and classify all
different sub-types of microwave synthesis such as solid-state microwave and
microwave assisted hydrothermal synthesis. In the experimental part of this
work we present a large range of materials that were synthesized in our
laboratories by one of the microwave techniques, where such materials include
superconducting, ferromagnetic, ferroelectric, dielectric and multiferroic
perovskite systems.",1401.1965v1
2014-01-15,X-ray absorption spectroscopy characterization of iron-oxide nanoparticles synthesized by high temperature plasma processing,"Iron-oxide nanoparticles have been synthesized by high temperature arc plasma
route with different plasma currents and characterized for their structure,
morphology and local atomic order. Fe K-edge x-ray absorption spectra reveal
distinct local structure of the samples grown with different plasma currents.
We have shown that the local disorder is higher for the higher plasma current
grown samples that also have a larger average particle-size. The results
provide useful information to control structural and morphological properties
of nanoparticles grown by high temperature plasma synthesis process.",1401.3655v1
2014-01-17,Solution-Processable Graphene Oxide as an Efficient Hole Injection Layer for High Luminance Organic Light-Emitting Diodes,"The application of solution-processable graphene oxide (GO) as hole injection
layer in organic light-emitting diodes (OLEDs) is demonstrated. High luminance
of over 53,000 cd m-2 is obtained at only 10 V. The results will unlock a route
of applying GO in flexible OLEDs and other electrode applications.",1401.4427v1
2014-02-11,Scaling properties in the adsorption of ionic polymeric surfactants on generic nanoparticles of metallic oxides by mesoscopic simulation,"We study the scaling of adsorption isotherms of polyacrylic dispersants on
generic surfaces of metallic oxides $XnOm$ as a function of the number of
monomeric units, using Electrostatic Dissipative Particle Dynamics simulations.
The simulations show how the scaling properties in these systems emerge and how
the isotherms rescale to a universal curve, reproducing reported experimental
results. The critical exponent for these systems is also obtained, in perfect
agreement with the scaling theory of deGennes. Some important applications are
mentioned.",1402.2661v1
2014-09-29,Cross-phase modulation instability in mode-locked laser based on reduced graphene oxide,"Cross-phase modulation instability (XPMI) is experimentally observed in a
fiber ring cavity with net normal dispersion and mode-locked by long fiber
taper. The taper is deposited with reduced graphene oxide, which can decrease
the threshold of XPMI due to the enhanced nonlinearity realized by 8 mm
evanescent field interaction length and strong mode confinement. Experimental
results indicate that the phase matching conditions in two polarization
directions are different, and sidebands with different intensities are
generated. This phase matching condition can be satisfied even the polarization
state of the laser varies greatly under different pump strengths.",1409.8210v1
2014-11-09,Application of gold in the field of heterogeneous catalysis,"Gold has been long thought as an inert metal which finds most of its use in
jewelry and monetary exchange. However, catalysis by gold has rapidly become a
hot topic in chemistry ever since Haruta and Hutchings found gold to be an
extraordinary good heterogeneous catalyst in certain reactions. Here in this
paper, several model reactions which made gold historically famous as a
catalyst and a currently hot topic will be demonstrated, such as oxidation of
CO, selective oxidation, and hydrodechlorination. Conclusions on the chemical
nature of gold will be made as well as future perspectives of designing gold as
a better catalyst.",1411.2583v1
2014-12-15,Pinball liquid phase from Hund's coupling in frustrated transition metal oxides,"The interplay of non-local Coulomb repulsion and Hund's coupling in the
d-orbital manifold in frustrated triangular lattices is analyzed by a mutliband
extended Hubbard model. We find a rich phase diagram with several competing
phases, including a robust pinball liquid phase, which is an unconventional
metal characterized by threefold charge order, bad metallic behavior and the
emergence of high spin local moments. Our results naturally explain the
anomalous charge-ordered metallic state observed in the triangular layered
compound AgNiO2. The potential relevance to other triangular transition metal
oxides is discussed.",1412.4696v2
2014-12-23,Effects of Manganese Addition on the Electronic Structure of BaTiO$_3$,"Mn is used as a dopant to improve the electromechanical properties of
perovskite oxides. We elucidate the role of Mn defects and associated vacancies
on the electronic, atomic and ferroelectric properties of BaTiO$_3$. Using
density functional theory (DFT) and DFT+U we investigate the equilibrium
geometry and electronic properties of Mn ion on A or B sites and with
compensating oxygen vacancies. We study the change in the oxidation state of Mn
in response to local environment changes, such as the presence of oxygen
vacancies.",1412.7458v1
2015-01-09,Enhancing triplet superconductivity by the proximity to a singlet superconductor in oxide heterostructures,"We show how in principle a coherent coupling between two superconductors of
opposite parity can be realized in a three-layer oxide heterostructure. Due to
strong intraionic spin-orbit coupling in the middle layer, singlet Cooper pairs
are converted into triplet ones and vice versa. This results in a large
enhancement of the triplet superconductivity, persisting well above the native
triplet critical temperature.",1501.02077v2
2015-02-10,Strength of the dominant scatterer in graphene on silicon oxide,"A large variability of carrier mobility of graphene-based field effect
transistors hampers graphene science and technology. We determine the
scattering strength of the dominant scatterer responsible for the variability
of graphene-based transistors on silicon oxide. The strength of the scatterer
is found to be more consistent with charged impurities than with resonant
impurities.",1502.03043v2
2015-03-20,Proposed cavity Josephson plasmonics with complex-oxide heterostructures,"We discuss how complex-oxide heterostructures that include high-Tc
superconducting cuprates can be used to realize an array of sub-millimeter
cavities that support Josephson plasmon polaritons. These cavities have several
attractive features for new types of light matter interaction studies and we
show that they promote ""ultrastrong"" coupling between THz frequency radiation
and Josephson plasmons. Cavity electrodynamics of Josephson plasmons allows to
manipulate the superconducting order-parameter phase coherence. As an example,
we discuss how it could be used to cool superconducting phase fluctuations with
light.",1503.06117v2
2015-04-03,Plane Wave Density Functional Theory Studies of the Structural and the Electronic Properties of Amino Acids Attached to Graphene Oxide via Peptide Bonding,"We studied the electronic and the structural properties of amino acids
(alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide
bonding, via plane wave pseudopotential total-energy calculations within the
local spin density approximation (LSDA). The HOMO-LUMO gap, the Hirshfeld
charges, and the equilibrium geometrical structures exhibit keen variations
depending on the species of the attached amino acid. The GO-amino acid system
appears to be a good candidate as a biosensor.",1504.00741v1
2015-06-26,Characterizing the Structure of Topological Insulator Thin Films,"We describe the characterization of structural defects that occur during
molecular beam epitaxy of topological insulator thin films on commonly used
substrates. Twinned domains are ubiquitous but can be reduced by growth on
smooth InP (111)A substrates, depending on details of the oxide desorption.
Even with a low density of twins, the lattice mismatch between (Bi,Sb)2Te3 and
InP can cause tilts in the film with respect to the substrate. We also briefly
discuss transport in simultaneously top and back electrically gated devices
using SrTiO3 and the use of capping layers to protect topological insulator
films from oxidation and exposure.",1506.08175v1
2015-09-23,Optical Properties of ITO/ZnO Schottky Diode with Enhanced UV Photoresponse,"Photoluminescence (PL) spectra of zinc oxide (ZnO) samples with different
hydrogen peroxide (H2O2) treatment durations were measured to examine several
point defects on the surface of the films. These results suggest successful
oxidation through the reaction between oxygen radicals dissociated from H2O2
and the ZnO surface. To further confirm the defect induced gain mechanism, we
fabricate highly transparent Schottky diodes, and measure the key diode
characteristics. Photocurrents are measured under different wavelengths, and
possible explanations of the high optical gain within the ultraviolet (UV)
region are provided.",1509.06871v1
2015-10-18,Quasiparticle Mass Enhancement and Fermi Surface Shape Modification in Oxide Two-Dimensional Electron Gases,"We propose a model intended to qualitatively capture the electron-electron
interaction physics of two-dimensional electron gases formed near
transition-metal oxide heterojunctions containing $t_{2g}$ electrons with a
density much smaller than one electron per metal atom. Two-dimensional electron
systems of this type can be described perturbatively using a $GW$ approximation
which predicts that Coulomb interactions enhance quasiparticle effective masses
more strongly than in simple two-dimensional electron gases, and that they
reshape the Fermi surface, reducing its anisotropy.",1510.05299v1
2016-01-23,"Vanadium Dioxide: Metal-Insulator Transition, Electrical Switching and Oscillations. A Review of State of the Art and Recent Progress","Vanadium dioxide is currently considered as one of the most promising
metarials for oxide elcteronics. Both planar and sandwich thin-film MOM devices
based on VO2 exhibit electrical switching with an S-shaped I-V characteristic,
and this switching effect is associated with the metal-insulator transition
(MIT). In an electrical circuit containing such a switching device, relaxation
oscillations are observed if the load line intersects the I-V curve at a unique
point in NDR region. All these effects are potentially prospective for
designing various devices of oxide electronics, particularly, elements of
dynamical neural networks based on coupled oscillators.",1601.06246v1
2016-02-16,N-Type Oxide Thermoelectrics Via Visual Search Strategies,"We discuss and present search strategies for finding new thermoelectric
compositions based on first principles electronic structure and transport
calculations. We illustrate them by application to a search for potential
n-type oxide thermoelectric materials. This includes a screen based on
visualization of electronic energy isosurfaces. We report compounds that show
potential as thermoelectric materials along with detailed properties, including
SrTiO3, which is a known thermoelectric, and appropriately doped KNbO3 and
rutile TiO2.",1602.05054v1
2016-04-15,The growth mechanism of CuO nanowires synthesized by the thermal oxidation method,"Large-scale CuO nanowires are commonly synthesized by the thermal oxidation
method. However, the growth mechanism remains controversial between diffusion
growth mechanism and vapor-solid (VS) growth mechanism. In this study, we
investigated the morphology and atomic structure of the CuO nanowires by
electron microscopes to clarify the growth mechanism. We found that they were
grown with the annealing ambient during the cooling process and there were
screw dislocations in the nanowires. These features indicate that the VS growth
mechanism is applicable to explain the growth of the CuO nanowires. In
addition, the kinetic consideration also supports the VS growth mechanism.",1604.04411v2
2016-04-29,Monolithic AlGaAs second-harmonic nanoantennas,"We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical
anoantennas. Using a selective oxidation technique, we fabricate such epitaxial
semiconductor nanoparticles on an aluminum oxide substrate. Second harmonic
generation from an AlGaAs nanocylinder of height h=400 nm and varying radius
pumped with femtosecond pulses delivered at 1554-nm wavelength has been
measured, revealing a peak conversion efficiency exceeding 10-5 for
nanocylinders with an otpimized geometry.",1604.08881v1
2016-06-08,"Can we prevent the ""dead layer"" formation at manganite interfaces?","The present work theoretically studies the possibility to hinder the
formation of a ""dead"" layer at the interfaces in manganite superlattices. We
showed that this goal can be reached by using alkaline-earth simple oxides as
alternating layers in very thin superlattices. Indeed, such alternating layer
promotes the contraction of manganite layers at the interfaces and
$d_{x^2-y^2}$ preferred $e_g$ orbital occupancy, while Boltzman's transport
calculations show an increase in conductivity. This result hold for different
manganites, different alkaline-earth simple oxides as well as different
thicknesses of the two layers.",1606.02764v1
2016-10-06,Temperature dependence of long coherence times of oxide charge qubits,"The ability to maintain coherence and control in a qubit is a major
requirement for quantum computation. We show theoretically that long coherence
times can be achieved above boiling point of liquid helium in charge qubits of
oxide double quantum dots. Detuning the dots to a fraction of the optical
phonon energy, increasing the electron-phonon coupling, reducing the
adiabaticity, or decreasing the temperature enhances the coherence time. We
consider a system that is initially decoupled from the phonon bath in the
polaronic frame of reference and solve the non-Markovian quantum master
equation; we find that the system decoheres after a long time, despite the fact
that no energy is exchanged with the bath.",1610.01866v1
2016-10-12,Anodic TiO2 nanotube layers: why does self-organized growth occur - A mini review,"The present review gives an overview of the highlights of more than 10 years
of research on synthesis and applications of ordered oxide structures (nanotube
layers, hexagonal pore arrangements) that are formed by self-organizing
anodization of metals. In particular we address the questions after the
critical factors that lead to the spectacular self-ordering during the growth
of anodic oxides that finally yield morphologies such as highly ordered TiO2
nanotube arrays and similar structures. Why are tubes and pores formed - what
are the key parameters controlling these processes?",1610.03643v1
2016-10-13,Ar+-ion Bombardment of TiO2 Nanotubes Creates Co-catalytic Effect for Photocatalytic Open Circuit Hydrogen Evolution,"In the present work, extended Argon ion bombardment was used to modify
anatase TiO2 nanotube (NTs) layers. In situ X-ray photoelectron spectroscopy
revealed a high content of sub-oxide formed (Ti3+, Ti2+ states) in the nanotube
layers. These samples were tested for their ability to show open-circuit
photocatalytic hydrogen evolution. We found for UV (cw laser 325nm)
illumination as well as for AM1.5 conditions, a strongly enhanced H2 evolution
activity in absence of the usual noble metal-nanoparticle decoration. We
conclude therefore that these sub-oxide states can play an important role in
the activation of TiO2 nanotubes - namely as a H2 evolution co-catalyst.",1610.04136v1
2017-02-11,Oxides in an oxygen potential gradient: coupled morphological stability of the multiple phase boundaries,"In materials that are exposed to thermodynamic potential gradients, i.e.,
gradients of chemical potentials, electrical potential, temperature, or
pressure, transport processes of the mobile components occur. These transport
processes and the coupling between different processes are not only of
fundamental interest, but are also the origin of several degradation processes,
such as kinetic unmixing and decomposition. In addition, changes in the
morphology of the material surfaces and interfaces may appear. In this paper, a
comprehensive formal treatment of the coupled morphological stability of
multiple phase boundaries will be given for oxides that are exposed to an
oxygen potential gradient.",1702.04238v1
2017-02-21,Flexible Transparent Field-Effect Diodes Fabricated at Low-Temperature with All Oxide Materials,"Flexible fully transparent diodes with high rectification ratio of 5 e 8 are
fabricated with all oxide materials at low temperature. The devices are
optically transparent in visible spectra range and electrically robust while
mechanically bending. Distinguished from other diodes, these diodes utilize
diode-connected thin-film transistor architecture and follow field-effect
principles.",1702.06351v1
2018-02-16,The mechanisms of hot salt stress corrosion cracking in titanium alloy Ti-6Al-2Sn-4Zr-6Mo,"Hot salt stress corrosion cracking in Ti 6246 alloy has been investigated to
elucidate the chemical mechanisms that occur. Cracking was found to initiate
beneath salt particles in the presence of oxidation. The observed transgranular
fracture was suspected to be due to hydrogen charging; XRD and high-resolution
transmission electron microscopy detected the presence of hydrides that were
precipitated on cooling. SEM-EDS showed oxygen enrichment near salt particles,
alongside chlorine and sodium. Aluminium and zirconium were also involved in
the oxidation reactions. The role of intermediate corrosion products such as
Na2TiO3, Al2O3, ZrO2, TiCl2 and TiH are discussed.",1802.06045v1
2018-04-20,Redox reaction enhanced Schottky contact at a \LNO{}(001)/Al interface,"Emergent phenomena at interfaces between oxides and metals can appear due to
charge transfer and mass transport that modify the bulk properties. By coating
the metallic oxide LaNiO$_3$ by aluminium, we fabricated a junction exhibiting
a diode-like behaviour. At the equilibrium, the interface is insulating. The
metallic behaviour can be recovered by applying a voltage drop across the
junction in one polarity only. The electrical properties in direct and reverse
bias are investigated. The observed electro-resistive effect rises up to $10^5$
\% and can be interpreted in terms of (i) a spontaneous redox reaction
occurring at the interface and (ii) its reversal induced by charge injection in
direct bias.",1804.07574v1
2018-10-08,Carbon Monoxide Adsorption and Carbon Monoxide Oxidation Studies on Thiolate Supported Gold Nanoclusters Dispensed on Metallic Oxides,"Thiolate-protected gold nanoclusters represent atomically well-defined active
centers for catalysis with resolved crystal structures, enabling the creation
of a homogeneous and defined surface. The correlation of characterization via
FT-IR spectroscopy with kinetics studies gives insight into the gold clusters
activity and tests their utilization to bridge the gap between organometallic
complex-based homogenous catalysis and nanoparticle based heterogeneous
catalysis as well as the gap between the bulk crystal structure model catalysis
and real-world catalysis.",1811.01999v1
2018-11-17,Fluorescence coherence with anodic aluminum oxide hybrid photonic-plasmonic structure,"A class of hybrid photonic-plasmonic structures (HPPS) with vertical
cylindrical cavities is proposed and its performance in providing a coherent
light from spontaneous emission is investigated. It is shown that the proposed
easy-to-fabricate and robust anodic aluminum oxide structure dramatically
enhances the temporal and spatial coherence compared to the previously examined
HPPS. The physical mechanism of achieving the temporal and spatial coherence is
explained based on the special optical properties of the proposed HPPS and it
is discussed how this structure enables one adjusting hybrid photonic-plasmonic
optical modes to obtain coherence for emitters of different frequencies.",1811.10465v3
2019-05-07,Band gap evolution in Ruddlesden-Popper phases,"We investigate the variation of the band gap across the Ruddlesden-Popper
(RP) series (An+1BnX3n+1) in model chalcogenide, oxide, and halide materials to
understand the factors influencing band gap evolution. In contrast to the
oxides and halides, we find the band gap of the chalcogenides evolve
differently with the thickness of the perovskite blocks in these natural
superlattices. We show that octahedral rotations (i.e. deviation of the B-X-B
bond angles from 180) and quantum confinement effects compete to decide the
band gap evolution of RP phases. The insights gained here will allow us to
rationally design layered perovskite phases for electronics and
optoelectronics.",1905.02598v1
2020-07-15,Roughness and scaling properties of oxide glass surfaces at the nanoscale,"Using atomistic computer simulations we determine the roughness and
topographical features of melt-formed (MS) and fracture surfaces (FS) of oxide
glasses. We find that the topography of the MS is described well by the frozen
capillary wave theory. The FS are significant rougher than the MS and depend
strongly on glass composition. The height-height correlation function for the
FS shows an unexpected logarithmic dependence on distance, in contrast to the
power-law found in experiments. We thus conclude that on length scales less
than 10 nm FS are not self-affine fractals.",2007.07474v1
2010-05-31,Transparent and flexible polymerized graphite oxide thin film with frequency-dependent dielectric constant,"Here we report on the preparation of transparent and flexible polymerized
graphite oxide, which is composed of carbons with sp3-hybridized orbitals and a
non-planar ring structure, and which demonstrates dispersion in its dielectric
constant at room temperature. This frequency dependence renders the material
suitable for creating miniaturized, flexible, and transparent variable
capacitors, allowing for smaller and simpler integrated electronic devices. We
discuss this polarizability in terms of space charge effects.",1005.5576v1
2013-08-02,Electronic structure modification of Si-nanocrystals with F4 -TCNQ,"We use first-principles models to demonstrate how an organic oxidizing agent,
F4 -TCNQ (7,7,8,8- tetracyano-2,3,5,6-tetrafluoroquinodimethane), modifies the
electronic structure of silicon nanocrys- tals, suggesting it may enhance
p-type carrier density and mobility. The proximity of the lowest unoccupied
level of F4 -TCNQ to the highest occupied level of the Si-nanocrystals promotes
the formation of an empty hybrid state overlapping both nanocrystal and
molecule, reducing the exci- tation energy to about 0.8-1 eV in vacuum. Hence,
it is suggested that F4 -TCNQ can serve both as a surface oxidant and a
mediator for hole hopping between adjacent nanocrystals.",1308.0444v1
2013-08-05,Optical conductivity of the $t_{2g}$ two-dimensional electron gas,"Motivated by recent interest in perovskite surfaces and heterostructures, we
present an analysis of the Kubo conductivity of a two-dimensional electron gas
(2DEG) formed in the $t_{2g}$ bands of an oxide with perovskite structure. We
find that when the electric field is polarized in the plane of the 2DEG, the
optical conductivity is dominated by nearly independent Drude contributions
from two-dimensional subband Fermi surfaces, whereas for perpendicular-to-plane
polarization it has strong intersubband features. Our analysis suggests that
perpendicular-to-plane optical conductivity studies may help advance
understanding of the interplay between lattice distortions and
electron-electron interactions in complex oxide 2DEG quantum confinement
physics.",1308.1000v1
2013-08-25,Breakdown of Fast Water Transport in Graphene Oxides,"Fast slip flow was reported for water inside the interlayer gallery between
graphene layers or carbon nanotubes. We report here that this flow rate
enhancement (over two orders) breaks down with the presence of chemical
functionalization and relaxation of the nanoconfinement in graphene oxides.
Molecular dynamics simulation results show that hydrodynamics applies in this
circumstance, even at length scales down to nanometers. However, corrections on
the slip boundary condition and viscosity of nanoconfined flow must be included
to make quantitative predictions. These results were discussed with structural
characteristics of the liquid water and hydrogen bond networks.",1308.5367v1
2016-11-03,Structural and electrical properties of electrodeposited single junction of cuprous (I) oxide copper,"Cuprous (I) oxide (Cu_{2}O) based solar cells were fabricated with the use of
the electrodeposition technique at nanometre scale, and the structural,
morphological and electrical properties were investigated. The Cu_{2}O layers
were electrodeposited on crystalline and polycrystalline copper substrates. To
complete the Cu_{2}O/Cu(100) and Cu_{2}O/Cu interfaces as the solar cells the
top electrodes of silver paste were painted on the rear of Cu_{2}O. The
theoretical analysis of the current voltage curve was provided to determine the
values of electrical parameters of the most efficient solar cell of
Ag/Cu_{2}O/Cu(100) and clearly indicate presence of two Schottky barriers at
interfaces.",1611.00969v1
2017-04-17,"Electron counting in solids: oxidation states, partial charges and ionicity","In this short viewpoint, we discuss the assignment of ionic charges in
solids. We argue that formal oxidation states serve a useful function, and that
absolute values of partial charges should be interpreted and applied with
caution; the charge assigned can never be definitive and depends on the type of
property studied and the type of analysis performed. Careful analysis can be
used to avoid unphysical conclusions such as a recent report on the Ti(III)
nature of Ti in stoichiometric TiO$_2$.",1704.05140v1
2008-07-04,Lattice dynamical calculations of infinite layer iron oxides SrFeO2 and CaFeO2,"We report extensive lattice dynamical calculations of the newly discovered
infinite-layer iron oxides SrFeO2 and CaFeO2. For SrFeO2, the parameters of the
interatomic potential have been determined to reproduce the zone-centre phonon
frequencies reported using ab-initio calculations. Further we have extended the
potential model for calculations of CaFeO2. The potential parameters are found
to be transferable between the two compounds, and are used to calculate the
phonon spectra in the whole Brillouin zone and several thermodynamic properties
for these compounds. The calculations show fair agreement with the available
experimental data of structure, thermal expansion, and mean-squared amplitudes
of the atoms.",0807.0716v1
2012-01-18,Enhanced two dimensional electron gas charge densities at III-III/I-V oxide heterostructure interfaces,"In this paper, density functional theory calculations are used to explore the
electronic and atomic reconstruction at interfaces between III-III/I-V oxides.
In particular, at these interfaces, two dimensional electron gases (2DEGs) with
twice the interfacial charge densities of the prototypical LaTiO3/SrTiO3
heterostructure are observed. Furthermore, a significant decrease in the band
effective masses of the conduction electrons is shown, suggesting that possible
enhancements in electron mobilities may be achievable. These findings represent
a framework for chemically modulating 2DEGs, thereby providing a platform
through which the underlying physics of electron confinement can be explored
with implications for modern microelectronic devices.",1201.3871v1
2012-01-31,"Magnetoresistance, noise properties and the Koshino-Taylor effect in the quasi-1D oxide KRu_4O_8","The low temperature electronic and galvanomagnetic transport properties of
the low dimensional oxide KRu_4O_8 are experimentally considered. A quadratic
temperature variation of the resistivity is observed to be proportional to the
residual resistivity. It shows the role of inelastic electron scattering
against impurities, i.e. a large Koshino-Taylor effect, rather than a
consequence of strong electronic correlations. In the same temperature range,
the Kohler rule is not fulfilled. The resistance noise increases also sharply,
possibly due to a strong coupling of carriers with lattice fluctuations in this
low dimensional compound.",1201.6474v1
2012-04-04,Chemical Synthesis of Nano-Sized particles of Lead Oxide and their Characterization Studies,"The quantum dots of semiconductor display novel and interesting phenomena
that have not been in the bulk material. The color tunability is one of the
most attractive characteristics in II-VI semiconductor nanoparticles such as
CdS, ZnS, CdSe, ZnSe and PbO. In this work, the semiconductor lead oxide
nanoparticles are prepared by chemical method. The average particle size,
specific surface area, crystallinity index are estimated from XRD analysis. The
structural, functional groups and optical characters are analyzed with using of
SEM, FTIR and UV- Visible techniques. The optical band gap value has also been
determined.",1204.0896v1
2012-04-30,Graphene Battery made of Low Cost Reduced Graphene Oxide,"Graphene can collect energy from the ambient heat and convert it to
electricity, which makes it an ideal candidate for the fabrication of
self-powered devices. However, this technology is suffering the high cost,
which limits the practical use of it. In this work, we demonstrated that the
cost can be reduced by using low cost reduced graphene oxide (RGO), graphite
electrodes and low cost glass substrates. The results showed that this
technology can be of practical value for the ""battery"" industry.",1204.6688v1
2014-05-06,Dispersion engineering of high-Q silicon microresonators via thermal oxidation,"We propose and demonstrate a convenient and sensitive technique for precise
engineering of group-velocity dispersion in high-Q silicon microresonators. By
accurately controlling the surface-oxidation thickness of silicon microdisk
resonators, we are able to precisely manage the zero-dispersion wavelength
while simultaneously further improving the high optical quality of our devices,
with the optical Q close to a million. The demonstrated dispersion management
allows us to achieve parametric generation with precisely engineerable emission
wavelengths, which shows great potential for application in integrated silicon
nonlinear and quantum photonics.",1405.1224v1
2016-05-22,"Many body quantum physics in XANES of highly correlated materials, mixed valence oxides and high temperature superconductors","The x-ray absorption near edge structure (XANES), developed in these last 40
years using synchrotron radiation, is a unique tool probing electronic
correlations in complex systems via quantum many body final state effects.
Multi electron excitations have been observed first in the sixties in x-ray
absorption spectra of atoms and later in molecules and solids. The applications
of XANES many body final states to probe unique features of electronic
correlation in heavy fermions, mixed valence systems, mixed valence oxides and
high temperature superconductors are discussed.",1605.06850v2
2016-08-25,Two-dimensional Superconductors with Atomic-scale Thicknesses,"Recent progress in two-dimensional superconductors with atomic-scale
thicknesses is reviewed mainly from the experimental point of view. The
superconducting systems treated here involve a variety of materials and forms:
elemental-metal ultrathin films and atomic layers on semiconductor surfaces;
interfaces and superlattices of heterostructures made of cuprates, perovskite
oxides, and rare-earth metal heavy-fermion compounds; interfaces of
electric-double-layer transistors; graphene and atomic sheets of
transition-metal dichalcogenide; iron selenide and organic conductors on oxide
and metal surfaces, respectively. Unique phenomena arising from the ultimate
two-dimensionality of the system and the physics behind them are discussed.",1608.06997v1
2016-08-28,Unusual Fe-H bonding associated with oxygen vacancies at the (001) surface of Fe3O4,"An unusual Fe-H bonding rather than conventional OH bonding is identified at
Fe3O4 (001) surface. This abnormal behavior is associated with the oxygen
vacancies which exist on the surface region but also penetrate deep into the
bulk Fe3O4. In contrast, OH bonding becomes preferential as generally expected
on an ozone processed surface, which has appreciably less oxygen vacancies.
Such bonding site selective behavior, depending on oxygen vacancy
concentrations, is further confirmed with DFT calculations. The results
demonstrate an opportunity for tuning the chemical properties of oxide surfaces
or oxide clusters.",1608.07773v1
2016-12-05,Determining the energetics of vicinal perovskite oxide surfaces,"The energetics of vicinal SrTiO$_3$(001) and DyScO$_3$(110), prototypical
perovskite vicinal surfaces, has been studied using topographic atomic force
microscopy imaging. The kink formation and strain relaxation energies are
extracted from a statistical analysis of the step meandering. Both perovskite
surfaces have very similar kink formation energies and exhibit a similar
triangular step undulation. Our experiments suggest that the energetics of
perovskite oxide surfaces is mainly governed by the local oxygen coordination.",1612.01381v1
2017-06-11,On the thermodynamic aspect of zinc oxide polymorphism. Calorimetric study of metastable rock salt ZnO,"The enthalpies of dissolution of metastable rock salt and thermodynamically
stable wurtzite polymorphs of zinc oxide in aqueous H2SO4 have been measured in
direct calorimetric experiments at 303 K and 0.1 MPa and the obtained results
enabled determination of the standard enthalpy of the rock salt-to-wurtzite
phase transition in ZnO, {\Delta}trH = -11.7+/-0.3 kJ/mol.",1706.03368v1
2017-06-18,Neuron-inspired flexible memristive device on silicon (100),"Comprehensive understanding of the world's most energy efficient powerful
computer, the human brain, is an elusive scientific issue. Still, already
gained knowledge indicates memristors can be used as a building block to model
the brain. At the same time, brain cortex is folded allowing trillions of
neurons to be integrated in a compact volume. Therefore, we report flexible
aluminium oxide based memristive devices fabricated and then derived from
widely used bulk mono-crystalline silicon (100). We use complementary metal
oxide semiconductor based processes to layout the foundation for ultra large
scale integration (ULSI) of such memory devices to advance the task of
comprehending a physical model of human brain.",1706.05645v1
2017-06-18,Theoretical evidence for unexpected O-rich phases at corners of MgO surfaces,"Realistic oxide materials are often semiconductors, in particular at elevated
temperatures, and their surfaces contain undercoordiated atoms at structural
defects such as steps and corners. Using hybrid density-functional theory and
ab initio atomistic thermodynamics, we investigate the interplay of
bond-making, bond-breaking, and charge-carrier trapping at the corner defects
at the (100) surface of a p-doped MgO in thermodynamic equilibrium with an O2
atmosphere. We show that by manipulating the coordination of surface atoms one
can drastically change and even reverse the order of stability of reduced
versus oxidized surface sites.",1706.05695v1
2017-06-20,Scaling of the Hall effects beyond the quantum resistance threshold in oxidized CoFeB,"The ordinary and the extraordinary Hall effects were studied in gradually
oxidized amorphous CoFeB ferromagnets over six orders of resistivity from the
metallic to the strongly insulating regime. Polarity of the extraordinary Hall
effect reverses, and the amplitude of both the ordinary and the extraordinary
Hall effects increases quadratically with resistivity when resistance exceeds
the quantum resistance threshold. The absolute value of the extraordinary Hall
effect scales linearly with the ordinary one in the entire range over eight
orders of magnitude between the metallic and the insulating states. The
behavior differs qualitatively and quantitatively from theoretically predicted
and experimentally known in other materials.",1706.06392v1
2017-06-23,Scanning Microwave Microscopy of Aluminum CMOS Interconnect Lines Buried in Oxide and Water,"Using a scanning microwave microscope, we imaged in water aluminum
interconnect lines buried in aluminum and silicon oxides fabricated through a
state-of-the-art 0.13 um SiGe BiCMOS process. The results were compared with
that obtained by using atomic force microscopy both in air and water. It was
found the images in water was degraded by only approximately 60% from that in
air.",1706.07538v1
2017-10-13,The electronic-structure origin of cation disorder in transition-metal oxides,"Cation disorder is an important design criterion for technologically relevant
transition-metal (TM) oxides, such as radiation-tolerant ceramics and Li-ion
battery electrodes. In this letter, we use a combination of first-principles
calculations, normal mode analysis, and band-structure arguments to pinpoint a
specific electronic-structure effect that influences the stability of
disordered phases. We find that the electronic configuration of a TM ion
determines to which extent the structural energy is affected by site
distortions. This mechanism explains the stability of disordered phases with
large ionic radius differences and provides a concrete guideline for the
discovery of novel disordered compositions.",1710.05097v1
2019-06-25,Influence of electron-hole plasma on Rydberg excitons in cuprous oxide,"We develop a many-body approach to the behavior of exciton bound states and
the conduction electron band edge in a surrounding electron-hole plasma with a
focus on the absorption spectrum of Rydberg excitons in cuprous oxide. The
interplay of band edge and exciton levels is analyzed numerically, whereby the
self-consistent solution is compared to the semiclassical Debye approximation.
Our results provide criteria which allow to verify or rule out the different
band edge models against future experimental data.",1906.10384v2
2019-07-11,Percolation description of charge transport in amorphous oxide semiconductors,"The charge transport mechanism in amorphous oxide semiconductors (AOS) is a
matter of controversial debates. Most theoretical studies so far neglected the
percolation nature of the phenomenon. In this article, a recipe for theoretical
description of charge transport in AOSs is formulated using the percolation
arguments. Comparison with the previous theoretical studies shows a superiority
of the percolation approach. The results of the percolation theory are compared
to experimental data obtained in various InGaZnO materials revealing parameters
of the disorder potential in such AOS.",1907.05107v1
2019-07-11,Percolation description of charge transport in the random barrier model applied to amorphous oxide semiconductors,"Charge transport in amorphous oxide semiconductors is often described as the
band transport affected by disorder in the form of random potential barriers
(RB). Theoretical studies in the framework of this approach neglected so far
the percolation nature of the phenomenon. In this article, a recipe for
theoretical description of charge transport in the RB model is formulated using
percolation arguments. Comparison with the results published so far evidences
the superiority of the percolation approach.",1907.05113v2
2019-10-16,Boron doping in gallium oxide from first principles,"We study the feasibility of boron doping in gallium oxide
($\text{Ga}_2\text{O}_3$) for neutron detection. $\text{Ga}_2\text{O}_3$ is a
wide band-gap, radiation hard material which has potential for neutron
detection if it can be doped with a neutron active element. We investigate the
boron-10 isotope as a possible neutron active dopant. Intrinsic and boron
induced defects in $\text{Ga}_2\text{O}_3$ are studied with semi-local and
hybrid density-functional-theory calculations. We find that in growth
conditions favourable for boron, boron substitutional defects are likely to
form making boron doping of $\text{Ga}_2\text{O}_3$ feasible.",1910.07371v2
2020-04-02,Synthesis and $\textit{in-situ}$ characterization of photochromic yttrium oxyhydride grown by reactive $e^-$-beam evaporation,"We report on controlled growth of photochromic yttrium oxyhydride thin films
monitored by $\textit{in-situ}$ composition depth profiling. Films were grown
by reactive $e^-$-beam evaporation and subsequently oxidized, while
simultaneously tracking the oxygen and hydrogen concentrations. Sample
composition and photochromic response were characterized $\textit{in-situ}$
using non destructive ion beam analysis and image analysis, respectively - as
well as complementary $\textit{ex-situ}$ ion beam methods, X-ray diffraction
and optical spectrophotometry. We show that photochromic yttrium oxyhydride can
be grown as yttrium dihydride, which is then oxidized to O/H ratios triggering
the photochromic response.",2004.01093v2
2020-12-30,Carbon Nanomaterials to Combat Virus: A perspective in view of COVID-19,"The rapid outbreaks of lethal viruses necessitate the development of novel
antiviral substance. Besides the conventional antiviral substances,
biocompatible nanomaterials also have significant potential in combating the
virus at various stages of infection. Carbon nanomaterials have an impressive
record against viruses and can deal with many crucial healthcare issues. In
accordance with the published literature, biocompatible carbon nanomaterials
have a promising prospect as an antiviral substance. Subsequently, the
antiviral properties of different carbon nanomaterials namely fullerene, carbon
nanotube, carbon dot and graphene oxide have been reviewed.",2012.15101v1
2021-01-12,From high-$T_c$ to low-$T_c$: Multi-orbital effects in transition metal oxides,"Despite the structural resemblance of certain cuprate and nickelate parent
compounds there is a striking spread of $T_c$ among such transition metal oxide
superconductors. We adopt a minimal two-orbital $e_g$ model which covers
cuprates and nickelate heterostructures in different parametric limits, and
analyse its superconducting instabilities. The joint consideration of
interactions, doping, Fermiology, and in particular the $e_g$ orbital splitting
allows us to explain the strongly differing pairing propensities in cuprate and
nickelate superconductors.",2101.04689v1
2021-01-28,Phonon Self-Energy Effects in Migdal-Eliashberg Theory,"Recent work on an electron-phonon model in two-dimensions is reviewed and
some new results are presented. We utilize both Quantum Monte Carlo simulations
and Migdal-Eliashberg theory. The type of electron-ion coupling considered is
on-site. Competing instabilities are charge density wave (CDW) and singlet
superconductivity. When the electron band is half-filled, the charge density
wave dominates. Away from half-filling CDW correlations actually suppress
superconductivity.",2101.12084v1
2000-06-06,Normal-state pseudogap and electron flat dispersion in copper oxide materials,"The anomalous momentum and doping dependence of the electron spectral
function and electron dispersion for copper oxide materials in the underdoped
regime are studied within the t-J model. It is shown that the electron spectrum
is changed with dopings, and the electron dispersion exhibits a flat band
around ($\pi$,0) point in the Brillouin zone, which leads to the normal-state
pseudogap formation. The theoretical results are consistent with the
experiments and numerical simulations.",0006084v1
2012-05-07,Junctionless dual-gate electrostatic modulation of self-aligned oxide channels by chitosan-based proton conductors,"Dual-gate electrostatic modulation gives an attractive approach for
transistors performance improvement, threshold voltage (Vth) and operation mode
modulation, which is favorable for chemical sensor and logic applications.
Here, a self-aligned junctionless semiconducting oxide channels are dual-gate
electrostatic modulated by solution-processed chitosan-based proton conductors
on paper substrates. The low-voltage junctionless paper transistors can be
effectively tuned from depletion mode to enhancement mode by the second
in-plane gate. OR logic gate was experimentally demonstrated on such
dual-in-plane gate junctionless transistors. Such dual-gate organic/inorganic
hybrid paper transistors are promising for portable paper electronics.",1205.1309v1
2012-05-24,The polarizability model for ferroelectricity in perovskite oxides,"This article reviews the polarizability model and its applications to
ferroelectric perovskite oxides. The motivation for the introduction of the
model is discussed and nonlinear oxygen ion polarizability effects and their
lattice dynamical implementation outlined. While a large part of this work is
dedicated to results obtained within the self-consistent-phonon approximation
(SPA), also nonlinear solutions of the model are handled which are of interest
to the physics of relaxor ferroelectrics, domain wall motions, incommensurate
phase transitions. The main emphasis is to compare the results of the model
with experimental data and to predict novel phenomena.",1205.5377v1
2017-05-16,Defects and oxidation resilience in $InSe$,"We use density functional theory to study intrinsic defects and oxygen
related defects in indium selenide. We find that ${InSe}$ is prone to
oxidation, but however not reacting with oxygen as strongly as phosphorene. The
dominant intrinsic defects in ${In}$-rich material are the ${In}$ interstitial,
a shallow donor, and the ${Se}$ vacancy, which introduces deep traps. The
latter can be passivated by oxygen, which is isoelectronic with ${Se}$. The
dominant intrinsic defects in ${Se}$-rich material have comparatively higher
formation energies.",1705.05519v2
2017-11-27,On femtosecond laser shock peening of stainless steel AISI 316,"In this paper we report on the competition in metal surface hardening between
the femtosecond shock peening on the one hand, and formation of laser-induced
periodic surface structures (LIPSS) and surface oxidation on the other hand.
Peening of the stainless steel AISI 316 due to shock loading induced by
femtosecond laser ablation was successfully demonstrated. However, for some
range of processing parameters, surface erosion due to LIPSS and oxidation seem
to dominate over the peening effect. Strategies to increase the peening
efficiency are discussed.",1711.09868v1
2018-05-31,Auxiliary-field quantum Monte Carlo calculations of the structural properties of nickel oxide,"Auxiliary-field quantum Monte Carlo (AFQMC) has repeatedly demonstrated
itself as one of the most accurate quantum many-body methods, capable of
simulating both real and model systems. In this article we investigate the
application of AFQMC to realistic strongly correlated materials in periodic
Gaussian basis sets. Using nickel oxide (NiO) as an example, we investigate the
importance of finite size effects and basis set errors on the structural
properties of the correlated solid. We provide benchmark calculations for NiO
and compare our results to both experiment measurements and existing
theoretical methods. (LLNL-JRNL-752156)",1806.00122v1
2018-08-15,Femtosecond laser crystallization of amorphous titanium oxide thin films,"In this paper we demonstrate experimentally that crystalline phases appear in
amorphous titanium oxide upon processing with ultrafast laser pulses. Amorphous
titanium thin films were produced by plasma-enhanced chemical vapor deposition
(PECVD) and exposed to femtosecond laser pulses. Formation of rutile phase was
confirmed by X-ray diffraction, Raman measurements and electron backscattering
diffraction. A rang of processing parameters for the crystallization is
reported and possible background mechanisms are discussed.",1808.05061v1
2019-02-13,Static and Dynamic Oxide-Trapped-Charge-Induced Variability in Nanoscale CMOS Circuits,"The inter-device mismatch and intra-device temporal instability in the
nanoscale CMOS circuits is examined from a unified point of view as a static
and dynamic parts of the variability con-cerned with stochastic oxide charge
trapping and de-trapping. This approach has been benchmarked on the recent
evidence of the radiation-induced increase of inter-transistor mismatch in 60
nm ICs. A possible reliability limitation in ultrascale circuits concerned with
the single or a few charged defect instability is pointed out and estimated.",1902.04974v2
2019-02-25,Environmental Remediation Applications of Carbon Nanotube and Graphene Oxide: Adsorption and Catalysis,"Environmental issues such as the wastewater have influenced each aspect of
our lives. Coupling the existing remediation solutions with exploring new
functional carbon nanomaterials (e.g. carbon nanotube, graphene oxide,
graphene) by various perspectives shall open up a new venue to understand the
environmental issues, phenomenon and find out the ways to get along with the
nature. This review makes an attempt to provide an overview of potential
environmental remediation solutions to the diverse challenges happening by
using low-dimensional carbon nanomaterials and their composites as adsorbents,
catalysts or catalysts support towards for the social sustainability.",1903.00468v1
2019-03-20,Molecular beam epitaxy growth of superconducting Sr2RuO4 films,"We report growth of superconducting Sr2RuO4 films by oxide molecular beam
epitaxy (MBE). Careful tuning of the Ru flux with an electron beam evaporator
enables us to optimize growth conditions including the Ru/Sr flux ratio and
also to investigate stoichiometry effects on the structural and transport
properties. The highest onset transition temperature of about 1.1 K is observed
for films grown in a slightly Ru-rich flux condition in order to suppress Ru
deficiency. The realization of superconducting Sr2RuO4 films via oxide MBE
opens up a new route to study the unconventional superconductivity of this
material.",1903.08629v1
2019-04-26,Anti-Localization in Oxides: Effective Spin-3/2 Model,"Weak anti-localization offers an experimental tool to address spin--orbit
coupling of two-dimensional oxide surfaces and interfaces via
magneto-transport. To overcome the shortcomings of the formulation for
single-band spin-1/2 electrons, we consider an effective three-band model that
allows a decomposition into a pseudo-spin representation 1/2+3/2. Whereas the
well-established spin-1/2 transport signature results from the singlet and
triplet sectors in the Cooperon equation, a new structure originates from the
quintet and septet sectors generated by the spin 3/2x3/2 representation.",1904.11770v1
2019-11-16,Multilayer plasmonic photonic structures embedding photochromic molecules or optical gain molecules,"We design photonic structures embedding different functional molecular
systems of photochromic switching and lasing. We study the light absorption of
two photochromic molecules and of 4,4'-bis[(N-carbazole)styryl]biphenyl
(BSB-Cz) with density functional theory. For the photochromic diarylethene we
derivate the refractive index with Kramers-Kronig relations and we design
multilayer photonic structures alternating diarylethene with either poly vinyl
carbazole or fluorine indium co-doped cadmium oxide (FICO) nanoparticlebased
layers. For BSB-Cz we design a one-dimensional photonic crystal alternating
BSB-Cz layers with $SiO_{2}$ layers and a microcavity embedding BSB-Cz between
indium tin oxide (ITO) / FICO nanoparticle-based multilayers.",1911.07070v1
2019-11-22,Nonlinear optical conductance from photon-assisted tunneling in a nanoantenna-coupled tunnel diode,"Ultrafast photon-assisted tunneling is shown to lead to large nonlinear
dynamic currents that can be used to generate dc rectified current as well as
higher order harmonic response from a metasurface-coupled tunnel diode. This
artificial nonlinear media can have tailored resonances in the infrared around
the longitudinal optical phonon modes of various compatible restrahlen oxides
leading to enhanced electric field confinement in a metal-oxide-semiconductor
tunnel diode. This provides a new avenue for the examination and design of
nonlinear phenomena extending the concept of nonlinear susceptibility to
nonlinear conductance and the dynamic current in these devices.",1911.10080v1
2020-03-18,Interaction of charged impurities and Rydberg excitons in cuprous oxide,"We investigate the influence of a static, uncorrelated distribution of
charged impurities on the spectrum of bound excitons in the copper oxide
Cu$_{\text{2}}$O. We show that the statistical distribution of Stark shifts and
ionisation rates leads to the vanishing of Rydberg resonances into an apparent
continuum. The appearance of additional absorption lines due to the broken
rotational symmetry, together with spatially inhomogeneous Stark shifts, leads
to a modification of the observed line shapes that agree qualitatively with the
changes observed in the experiment.",2003.08115v2
2020-06-16,Enhanced Electromechanical Response in Defective Sm and Nd Co-doped Ceria,"Highly oxygen defective cerium oxide, e.g. Gd-doped ceria is a sustainable
non-classical electrostrictor with electromechanical properties that are
superior to lead-based piezoelectric metal oxides. Here, we report
electrostriction in co-doped ceria (Sm, Nd) with a nominally low short-range
vacancy-dopant association energy. Such a strategy results in a higher
electrostrictive strain coefficient at lower-frequencies, and unexpected
electromechanical strain saturation and relaxation effects. These outcomes
support the hypothesis that electrostriction is strongly influenced by the
local environment of oxygen vacancy and by the ionic migration blocking factors
built-in the microstructure.",2006.09032v1
2020-08-11,"On the stability and existence of nitro-graphene, nitro-graphane, and nitro-graphene oxide","Here, the possibility of the existence of nitro-graphene derivatives with
undisturbed graphene backbone is considered. Based on the first-principles
calculation, it is shown that while NO$_2$ is unable to form a covalent bond
with bare graphene, it becomes possible in some structures of graphane,
fluorographene, and graphene oxide. This paper presents, among others, an
analysis of the surrounding influence on the C-NO$_2$ bond strength. The author
believes, that potential prospects of these materials and discussion about
possible synthesizing routes may help further research on graphene-based
materials.",2008.04749v1
2020-09-26,Improved Buildup Model for Radiation-Induced Defects in MOSFET Isolation Oxides,"Ionizing radiation induces defects in STI oxides in current MOSFETs. These
defects may degrade the performance of the MOS circuit. Analytical models for
the buildup of these defects during the radiation exposure are available in
literature. In this paper, we show that the classical model used to estimate
the buildup of TID-induced traps in MOSTs predicts inaccurate results at high
radiation levels. We, further, introduce an improved model to estimate the
buildup of defects that is valid for both low and high radiation doses. Our
improved model is compared to published data showing its validity.",2009.12652v1
2020-10-05,Resolving fast gas transients with Metal-Oxide sensors,"Electronic olfaction can help detect and localise harmful gases and
pollutants, but the turbulence of natural environment presents a particular
challenge: odor encounters are intermittent, and an effective electronic nose
must therefore be able to resolve short odor pulses. The slow responses of the
widely-used Metal-Oxide (MOX) gas sensors complicate the task. Here we combine
high-resolution data acquisition with a processing method based on Kalman
filtering and absolute-deadband sampling to extract fast transients. We find
that our system can resolve the precise time of odor onset events, allowing
direction estimation with a pair of MOX sensors in stereo-osmic configuration.",2010.01903v2
2020-10-16,Trends in the valence band electronic structures of mixed uranium oxides,"Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7,
U3O8, UO3) has been studied by the resonant inelastic X-ray scattering (RIXS)
technique at the U M5 edge and by computational methods. We show here that the
RIXS technique and recorded U 5f-O 2p charge transfer excitations can be used
to proof the validity of theoretical approximations",2010.08301v1
2021-05-27,Experimental validation of density functional theory calculations on the Zr/Al oxide nanocluster formation in bcc Fe,"Ab initio simulations carried out in different atomic cluster configurations
in bcc Fe matrix containing Zr and Al suggest energetic favorability of Y-Zr-O
phase nucleation, preferably with trigonal Y4Zr3O12 structure. Subsequently,
the HRTEM investigation of the as-prepared Fe - 14 Cr-0.3 Y2O3 - 0.6 Zr - 4Al
oxide dispersion strengthened (ODS) alloy shows 78% of precipitates with
Y4Zr3O12 structure, thereby confirming the predictive power of ab initio
simulations on the secondary formation in multi-component alloys.",2105.12963v2
2021-06-30,Femtosecond LIPSS on indium-tin-oxide thin films at IR wavelengths,"We investigated laser-induced periodic surface structures (LIPSS) generated
on indium-tin-oxide (ITO) thin films with femtosecond laser pulses in the
infrared region. Using pulses between 1.6 and 2.4 ${\mu}$m central wavelength,
we observed robust LIPSS morphologies with a periodicity close to
${\lambda}$/10. Supporting finite-difference time-domain calculations suggest
that the surface forms are rooted in the field localization in the surface pits
leading to a periodically increased absorption of the laser pulse energy that
creates the observed periodic structures.",2106.15999v4
2021-08-23,Interseries dipole transitions from yellow to green excitons in cuprous oxide,"We study dipole interseries transitions between the yellow and green exciton
series in cuprous oxide including the complex valence band structure. To this
end, we extend previous studies of the spectrum of complex green exciton
resonances [Phys. Rev. B 101, 075208 (2020)] to optical transitions between
different exciton states in addition to transitions from the crystal ground
state. This allows us to augment the calculations on interseries transitions
using a hydrogen-like model [Phys. Rev. B 100, 085201 (2019)] by a more
comprehensive treatment of the valence band structure.",2108.10441v1
2021-09-19,Superionic states formation in group III oxides irradiated with ultrafast lasers,"A number of group III-metal oxides are studied via density functional theory
in order to establish a possibility of nonthermal transition of these materials
into a superionic state. Atomic and electronic properties of the materials are
analyzed during the transitions to acquire insights into physical mechanisms
guiding such transformations. This knowledge is then used to suggest a
criterion allowing to predict the possibility of such transitions without
employing computationally heavy methods.",2109.09084v1
2022-06-30,"Doppler-free high resolution continuous wave optical UV-spectroscopy on the $\mathrm{A}\,^2Σ^+ \leftarrow \mathrm{X}\,^2Π_{3/2}$ transition in nitric oxide","We report on Doppler-free continuous-wave optical UV-spectroscopy resolving
the hyperfine structure of the $\mathrm{A}\,^2\Sigma^+ \leftarrow
\mathrm{X}\,^2\Pi_{3/2}$ transition in nitric oxide for total angular momenta
$J_X=1.5-19.5$ on the $\mathrm{oP_{12ee}}$ branch. The resulting line
splittings are compared to calculated splittings and fitted determining new
values for the molecular constants $b, c, eQq_0$ and $b_F$ for the
$\mathrm{A}\,^2\Sigma^+$ state. The constants are in good agreement with values
previously determined by quantum beat spectroscopy.",2206.15243v1
2022-08-17,The computational simulation of the reflection spectra of copper red glaze,"Owing to the limitation of traditional analytical methods, the coloration
mechanism of copper red glaze has been disputed in the academic field for a
long time, which mainly focuses on whether the color agent is metallic copper
nanoparticles or cuprous oxide (Cu2O) nanoparticles. Based on Mie scattering
theory, this work calculated the reflection spectra of nanoparticles uniformly
dispersed in transparent glaze with different types, diameters and volume
fractions, then discussed the differences between the reflection spectra of
metallic copper and cuprous oxide as scatters, calculated the corresponding
L*a*b* values, and compared them with the experimental results. This work
provides a feasible and convenient method to distinguish these two coloration
mechanisms.",2208.08043v1
2022-09-20,Large Rashba parameter for 4d strongly correlated perovskite oxide SrNbO3 ultrathin films,"To elucidate the spin relaxation mechanism of SrNbO3 (SNO) ultrathin films,
the transport properties of a series of SNO films with various thicknesses were
measured on both sides of the metal insulator transition. The spin orbit
scattering time was deduced from the analysis of the magnetoresistance with
weak antilocalization theory, and it was found that the spin orbit scattering
time was inversely proportional to the momentum scattering time. This result
was explained in terms of the D`Yakonov Perel` mechanism, indicative of the
dominant Rashba effect. The values of the Rashba parameter were largest in the
values reported for other ultrathin films of metallic oxides.",2209.09730v1
2022-10-19,Superlens with copper and copper oxide,"We investigate the imaging properties of copper-based superlens surrounded by
copper oxide (Cu$_2$O). A subwavelength image resolution of the order
$\lambda/9$ is demonstrated theoretically and verified in numerical
simulations. It is shown that the existence of excitons in Cu$_2$O influence
the static and dynamical optical properties of the lens. In particular, an
improvement of image quality caused by absorption in the spectral region of
excitonic resonances is investigated. The plasmon-exciton interaction in the
system may pave the way to a tunable, highly nonlinear superlens designs.",2210.10376v1
2022-11-08,Role of the annealing parameters on the resistance of indium tin oxide nanocrystalline films,"The optical and electrical properties of films made of nanoparticles of
indium tin oxide (ITO) are widely studied because of the significance of this
material for transparent electrodes, smart windows, and nonlinear optics
components. In this work, a systematic study of the resistance in ITO
nanocrystalline films, as a function of post-fabrication parameters, such as
the temperature and time of annealing, has been performed. A tunability of the
resistance with the annealing parameters, in a range of three orders of
magnitude, has been demonstrated.",2211.04144v2
2022-11-17,Nanoarchitectonics in fully printed perovskite solar cells with carbon-based electrodes,"A sacrificial film of polystyrene nanoparticles was utilized to introduce
nano-cavities in mesoporous metal oxide layers. This enabled the growth of
larger perovskite crystals inside the oxide scaffold with significantly
suppressed non-radiative recombination and improving device performance. This
work exemplifies potential applications of such nanoarchitectonic approaches in
perovskite opto-electronic devices.",2211.09424v1
2022-11-18,Acidity of graphene oxide aqueous solutions: the role of hydroxyls unveiled,"Nonempirical modeling of hydrated single-layer graphene oxide (GO) fragments
revealed that at least one, but substantial origin of the acidity of aqueous GO
solutions is the dissociation in closely grouped and favorably H-bonded
hydroxyls. The process can further be promoted by the adjacent $\pi$-conjugated
carbon segments at the edges of GO flakes or their inner defects. The apparent
$pK_a$ values of the groups fall in a range of ca. 2.0 to 5.3. Under certain
conditions the ionization may become spontaneous.",2211.10208v2
2023-04-03,Synthesis parameter effect detection using quantitative representations and high dimensional distribution distances,"Detection of effects of the parameters of the synthetic process on the
microstructure of materials is an important, yet elusive goal of materials
science. We develop a method for detecting effects based on copula theory, high
dimensional distribution distances, and permutational statistics to analyze a
designed experiment synthesizing plutonium oxide from Pu(III) Oxalate. We
detect effects of strike order and oxalic acid feed on the microstructure of
the resulting plutonium oxide, which match the literature well. We also detect
excess bivariate effects between the pairs of acid concentration, strike order
and precipitation temperature.",2304.01120v1
2023-04-26,Quantifying microstructure features for high performance solid oxide cells,"Focused ion beam (FIB)-scanning electron microscopy (SEM) allowed the
characterization of the microstructure of two solid oxide fuel cells prepared
at different sintering temperatures. 3D volume reconstruction showed that a
relatively low sintering temperature significantly and positively affected
distribution, volume and particle size of yttria-stabilized zirconia, nickel,
and pore phases inside the anode, as well as the extent of the important
triple-phase boundary interface.",2304.13572v1
2023-04-26,K. Alex Müller and his important role in ferroelectricity,"In this review we concentrate on the work of K. Alex M\""uller in connection
with his activities on oxide perovskites and ferroelectrics which were central
to his research career long before he successfully discovered the first high
temperature superconductor (HTSC) together with J. G. Bednorz in 1986. Not
accidentally, but taking his long experience in perovskite ferroelectrics into
account, the first HTSC was an oxide perovskite which had never been considered
before to be superconducting.",2304.13642v1
2023-04-16,Second-Order Non Linear Optical Properties of Zinc Oxide and Aluminum doped Zinc Oxide Thin Films grown by Atomic Layer deposition,"In this paper, Second-order NLO properties of ZnO and AZO thin films from
experimental results are discussed. Measurements were a single wavelength of
1.064 micrometers using the standard rotational Maker fringes technique in a
transmission scheme. Further broadband dispersion of $\chi^{(2)}$ as
characterized by harmonic generation over a broadband wavelength of 1.2-2.1
micrometers are discussed. Experimental results for the p-and s-polarization of
the fundamental beam are presented. In the analysis alpha-Quartz was used as
the standard reference material. All the experiments were conducted at room
temperature.",2304.14234v1
2023-05-25,Excess noise in the anomalous metallic phase in amorphous indium oxide,"More than 25 years ago, unexpected metallic behavior was discovered on the
superconducting side of the superconductor-to-insulator transition. To this
day, the origin of this behavior is unclear. In this work, we present
resistance and broadband voltage noise measurements in the kilohertz regime in
amorphous indium oxide. We find that the metallic behavior gives rise to excess
noise much larger than what is expected from thermal noise with an unexpected
frequency and temperature dependence whose origin remains elusive.",2305.15931v1
2023-07-05,Visible-Light Assisted Covalent Surface Functionalization of Reduced Graphene Oxide Nanosheets with Arylazo Sulfones,"We present an environmentally benign methodology for the covalent
functionalization (arylation) of reduced graphene oxide (rGO) nanosheets with
arylazo sulfones. A variety of tagged aryl units were conveniently accommodated
at the rGO surface via visible light irradiation of suspensions of carbon
nanostructured materials in aqueous media. Mild reaction conditions, absence of
photosensitizers, functional group tolerance and high atomic fractions (XPS
analysis) represent some of the salient features characterizing the present
methodology. Control experiments for the mechanistic elucidation (Raman
analysis) and chemical nanomanipulation of the tagged rGO surfaces are also
reported.",2307.02353v1
2023-07-31,Proximitized insulators from disordered superconductors,"We present an experimental study of bilayers of a disordered Ag metal layer
close to the metal-insulator transition and an Indium Oxide film which is on
the insulating side of the superconductor-insulator-transition. Our results
show that superconducting fluctuations within the indium-oxide film, that
proximitize the underlying metal layer, induce insulating rather than
superconducting behavior. This is ascribed to suppression of density of states
(due to the superconducting energy gap) for quasiparticles in the proximitized
regions. Our results present a novel manifestation of the proximity effect
phenomenon and provide important insight into the nature of the insulating
phase of the disorder driven superconductor-insulator-transition.",2307.16602v1
2023-07-31,Transparent conductive oxides and low loss nitride-rich silicon waveguides as building blocks for neuromorphic photonics,"Fully CMOS-compatible photonic memory holding devices hold a potential in a
development of ultrafast artificial neural networks. Leveraging the benefits of
photonics such as high-bandwidth, low latencies, low-energy interconnect and
high speed they can overcome the existing limits of the electronic processing.
To satisfy all these requirements a new photonic platform is proposed that
combines low-loss nitride-rich silicon as a guide and low-loss transparent
conductive oxides as an active material that can provide high nonlinearity and
bistability under both electrical and optical signals.",2308.00178v1
2023-08-11,Statistical Material Law Support for Room Temperature Superconductivity in the Lead Apatite System,"Quantum mechanics calculations of an electronic orbital coupling distribution
of the new possible Room Temperature (RT) system of lead apatite Pb10(PO4)6O
system show that the complex orbital coupling characteristics of the new system
are similar to those of copper oxide and with multiple orbital interactions.
The overall bandwidth is significantly larger than the current largest copper
oxide system, which can also be compared to near RT high-pressure hydride
systems. By applying a material dependence law relating overall bandwidth to
superconducting critical temperature across various typical superconducting
systems, we predict that the electronic structure of the new material can
support achieving RT superconductivity in the condition of a flatter band.",2308.06349v1
2023-09-11,Valley splitting by extended zone effective mass approximation incorporating strain in silicon,"Silicon metal-oxide-semiconductor field effect transistors (MOSFETs)
fabricated on a SIMOX (001) substrate, which is a kind of silicon on insulator
(SOI) substrate, that is annealed at high temperature for a long time are known
to exhibit large valley splitting, but the origin of this splitting has long
been unknown. Extended zone effective-mass approximation (EMA) predicts that
strain significantly affects valley splitting. In this study, we analyzed
valley splitting based on this theory and found that the shear strain along
<110> of approximately 5% near the buried oxide (BOX) interface is a promising
source for large valley splitting.",2309.05219v1
2023-10-13,Pushing the limits of ab-initio-NEGF transport using efficient dissipative Mode-Space algorithms for realistic simulations of low-dimensional semiconductors including their oxide interfaces,"We investigate the trade-offs between accuracy and efficiency for several
flavors of the dissipative mode-space NEGF algorithm with the self-consistent
Born approximation for DFT Hamiltonians. Using these models, we then
demonstrate the dissipative self-consistent DFT-NEGF simulations of realistic
2D-material devices including their oxide interfaces with large slab dimensions
(up to 1000 atoms) and up to several 100,000 atoms in the full device, pushing
the limit of ab-initio transport.",2310.09029v1
2024-01-04,Three-wave mixing experiments in indium-tin-oxide thin-films with no phase matching,"One challenge of using nonlinear optical phenomena for practical applications
is the need to perform phase-matching. Recently, epsilon-near-zero materials
have been shown to demonstrate strong optical nonlinearities, in addition to
their other unique properties. As suggested by their name, the permittivity of
the material is close to zero for a certain wavelength range. We demonstrate
that this small permittivity allows for efficient three-wave mixing
interactions to take place in indium-tin-oxide thin films without the need for
phase matching the pump and signal beams. The efficiency of the second-order
nonlinear interactions is characterized, and cascaded three-wave mixing is
demonstrated.",2401.02492v1
2024-01-29,Optimization of gadolinium oxide growth deposited on Si by high pressure sputtering,"High k gadolinium oxide thin layers were deposited on silicon by
high-pressure sputtering (HPS). In order to optimize the properties for
microelectronic applications, different deposition conditions were used. Ti
(scavenger) and Pt (nonreactive) were e-beam evaporated to fabricate
metal-insulator-semiconductor (MIS) devices. According to x-ray diffraction,
x-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy,
policrystaline stoichiometric Gd2O3 films were obtained by HPS. MIS with the
dielctric deposited at higher pressures also present lower flatband voltage
shifts in the C-V hysteris curves.",2401.16499v1
1996-02-29,Hole photoproduction in insulating copper oxide,"Basing on t-J model we calculate the k-dependence of a single hole
photoproduction probability for CuO2 plane at zero doping. We also discuss the
radiation of spin-waves which can substantially deform the shape of
photoemission spectra.",9602160v1
1997-10-21,Momentum density of high Tc Copper Oxydes,"We discuss the work aimed at studying the momentum density of high Tc
superconducting oxides using Compton profile and positron annihilation
spectroscopies.",9710216v1
1999-05-24,Density-functional theory study of the catalytic oxidation of CO over transition metal surfaces,"In recent years due to improvements in calculation methods and increased
computer power, it has become possible to perform first-principles
investigations for ``simple'' chemical reactions at surfaces. We have carried
out such studies for the catalytic oxidation of CO at transition metal
surfaces, in particular, at the ruthenium surface for which unusual behavior
compared to other transition metal catalysts has been reported. High gas
pressure catalytic reactor experiments have revealed that the reaction rate
over Ru for oxidizing conditions is the highest of the transition metals
considered -- in contrast, under ultra high vacuum conditions, the rate is by
far the lowest. We find that important for understanding the pressure
dependence of the reaction is the fact that Ru(0001) can support high
concentrations of oxygen at the surface. Under these conditions, the O-metal
bond is atypically weak compared to that at lower coverages. We have
investigated a number of possible reaction pathways for CO oxidation for the
conditions of high oxygen coverages, including scattering reactions of
gas-phase CO at the oxygen covered surface (Eley-Rideal mechanism) as well as
the Langmuir-Hinshelwood mechanism involving reaction between adsorbed CO
molecules and O atoms.",9905341v1
2000-04-17,In search for the vortex charge and the Cooper pair mass,"A novel experiment for determination of the charge related to vortices in
thin superconducting film is proposed and a number of related experimental
set-ups are also theoretically considered. The methods are based on the
Torricelli-Bernoulli effect in superconductors and the phenomenology of the
effect is briefly discussed. The vortex charge is expressed via the effective
mass of the Cooper pairs, thus both parameters, inaccessible by now, could be
simultaneously determined. The experiment would require layered
metal-insulator-superconductor structures and standard electronics employed in
kinetic measurements. The quality of the insulator-superconductor interface
should be high enough as to allow for observation of electric field effects
similar to those investigated in superconducting field-effect transistors. The
development of layer-by-layer growth technology of oxide superconductors
provides unique possibility for investigation of new fundamental effects in
these materials. In particular, the structures necessary for determination of
the vortex charge could be used to study the superconducting surface Hall
effect, Bernoulli effect, the superfluid density, etc.. In conclusion, the
systematic investigation of new effects in oxide superconductors is envisaged
as an important part of the material science underlying the oxide electronics.",0004286v2
2002-01-28,p-Type semiconducting properties in lithium-doped MgO single crystals,"The phenomenally large enhancement in conductivity observed when Li-doped MgO
crystals are oxidized at elevated temperatures was investigated by dc and ac
electrical measurements in the temperature interval 250-673 K. The
concentration of ([Li]^{0}) centers (Li^{+} ions each with a trapped hole)
resulting from oxidation was monitored by optical absorption measurements.
  Both dc and ac experiments provide consistent values for the bulk resistance.
The electricalconductivity of oxidized MgO:Li crystals increases linearly with
the concentration of ([Li]^{0}) centers. The conductivity is thermally
activated with an activation energy of (0.70 +/- 0.01) eV, which is independent
of the ([Li]^{0}) content. The \textit{standard semiconducting} mechanism
satisfactorily explains these results. Free holes are the main contribution to
band conduction as they are trapped at or released from the ([Li]^{0})-acceptor
centers.
  In as-grown MgO:Li crystals, electrical current increases dramatically with
time due to the formation of ([Li]^{0}) centers. The activation energy values
between 1.3 and 0.7 eV are likely a combination of the activation energy for
the creation of ([Li]^{0}) centers and the activation energy of ionization of
these centers. Destruction of ([Li]^{0}) centers can be induced in oxidized
crystals by application of an electric field due to Joule heating up to
temperatures at which ([Li]^{0}) centers are not stable.",0201502v1
2005-10-17,Syntheses of a heterogeneous catalysts using vapor phase self-assembly,"The first vapor phase self-assembled heterocatalytic structure on surface is
build from cobalt 5,10,15,20 tetrakis (4-aminophenyl)-21H, 23H-porphine through
imide bonds. This heterogeneous catalyst possesses essential thermal and
temporal stability along with catalytic activity in oxidation processes of
organic substrates.",0510453v1
2006-03-03,Chain-driven superconductivity of copper oxide identified by nuclear resonance,This paper has been withdrawn by the author due to time-consuming revision.,0603067v2
2006-07-14,"High-dielectric constant and wide band gap inverse silver oxide phases of the ordered ternary alloys of SiO$_{2}$, GeO$_{2}$ and SnO$_{2}$","High-dielectric constant and wide band gap oxides have important
technological applications. The crystalline oxide polymorphs having lattice
constant compatibility to silicon are particularly desirable. One recently
reported candidate is the inverse silver oxide phase of SiO$_2$.
First-principles study of this system together with its isovalent equivalents
GeO$_{2}$, SnO$_{2}$ as well as their ternary alloys are performed. Within the
framework of density functional theory both generalized gradient approximation
and local density approximation (LDA) are employed to obtain their structural
properties, elastic constants and the electronic band structures. To check the
stability of these materials, phonon dispersion curves are computed which
indicate that GeO$_{2}$ and SnO$_{2}$ have negative phonon branches whereas
their ternary alloys Si$_{0.5}$Ge$_{0.5}$O$_{2}$, Si$_{0.5}$Sn$_{0.5}$O$_{2}$,
and Ge$_{0.5}$Sn$_{0.5}$O$_{2}$ are all stable within LDA possessing dielectric
constants ranging between 10 to 20. Furthermore, the lattice constant of
Si$_{0.5}$Ge$_{0.5}$O$_{2}$ is virtually identical to the Si(100) surface. The
$GW$ band gaps of the stable materials are computed which restore the wide band
gap values in addition to their high dielectric constants.",0607353v2
2003-09-25,Cosmological backgrounds of superstring theory and Solvable Algebras: Oxidation and Branes,"We develop a systematic algorithm to construct, classify and study exact
solutions of type II A/B supergravity which are time--dependent and homogeneous
and hence represent candidate cosmological backgrounds. Using the formalism of
solvable Lie algebras to represent the geometry of non--compact coset manifolds
U/H we are able to reduce the supergravity field equations to the geodesic
equations in U/H and rephrase these latter in a completely algebraic setup by
means of the so called Nomizu operator representation of covariant derivatives
in solvable group manifolds. In this way a systematic method of integration of
supergravity equations is provided. We show how the possible D=3 solutions are
classified by non--compact subalgebras G of E8(8) and their ten--dimensional
physical interpretation (oxidation) depends on the classification of the
different embeddings of G inside E8(8). We give some preliminary examples of
explicit solutions based on the simplest choice G=A2. We also show how, upon
oxidation, these solutions provide a smooth and exact realization of the
bouncing phenomenon on Weyl chamber walls envisaged by the cosmological
billiards of Damour et al. We also show how this physical phenomenon is
triggered by the presence of euclidean $D$--branes possibly interpretable at
the microscopic level as S--branes. We outline how our analysis could be
extended to a wider setup where, by further reducing to $D=2,1$, more general
backgrounds could be constructed applying our method to the infinite algebras
E9 and E10.",0309237v2
2000-04-19,Structures and Stabilities of CaO and MgO Clusters and Cluster Ions: An alternative interpretation of the experimental mass spectra,"The structures and relative stabilities of doubly-charged nonstoichiometric
(CaO)$_n$Ca$^{2+}$ (n=1--29) cluster ions and of neutral stoichiometric
(MgO)$_n$ and (CaO)$_n$ (n=3,6,9,12,15,18) clusters are studied through {\em ab
initio} Perturbed Ion plus polarization calculations. The large
coordination-dependent polarizabilities of oxide anions favor the formation of
surface sites, making the critical cluster size where anions with bulk
coordination first appear larger than that found in the related case of alkali
halides. Thus, we show that there are substantial structural differences
between alkali halide and alkaline-earth oxide cluster ions, contrary to what
is suggested by the similarities in the experimental mass spectra. An
alternative interpretation of the magic numbers for the case of oxides is
proposed, which involves an explicit consideration of isomer structures
different from the ground states. A comparison with the previously studied
(MgO)$_n$Mg$^{2+}$ cluster ions shows that the emergence of bulklike structural
properties with size is slower for calcium oxide. Nevertheless, the structures
of the doubly charged clusters are rather similar for the two materials. On the
contrary, the study of the neutrals reveals interesting structural differences
between MgO and CaO, similar to those found in the case of alkali halides.",0004041v4
2007-06-14,The autoignition of cyclopentane and cyclohexane in a shock tube,"Ignition delay times of cyclohexane-oxygen-argon and
cyclopentane-oxygen-argon mixtures have been measured in a shock tube, the
onset of ignition being detected by OH radical emission. Mixtures contained 0.5
or 1 % of hydrocarbon for equivalence ratios ranging from 0.5 to 2. Reflected
shock waves allowed temperatures from 1230 to 1800 K and pressures from 7.3 to
9.5 atm to be obtained. These measurements have shown that cyclopentane is much
less reactive than cyclohexane, as for a given temperature the observed
autoignition delay times were about ten times higher for the C5 compound
compared to the C6. Detailed mechanisms for the combustion of cyclohexane and
cyclopentane have been proposed to reproduce these results. The elementary
steps included in the kinetic models of the oxidation of cyclanes are close to
those proposed to describe the oxidation of acyclic alkanes and alkenes.
Consequently, it has been possible to obtain these models by using an improved
version of software EXGAS, a computer package developed to perform the
automatic generation of detailed kinetic models for the gas-phase oxidation and
combustion of linear and branched alkanes and alkenes. Nevertheless, the
modelling of the oxidation of cyclanes requires to consider new types of
generic reactions, and especially to define new correlations for the estimation
of the rate constants. Ab initio calculations have been used to better know
some of the rate constants used in the case of cyclopentane. The main reaction
pathways have been derived from flow rate and sensitivity analyses.",0706.2060v1
2007-08-03,Delayed treatment with nimesulide reduces measures of oxidative stress following global ischemic brain injury in gerbils,"Metabolism of arachidonic acid by cyclooxygenase is one of the primary
sources of reactive oxygen species in the ischemic brain. Neuronal
overexpression of cyclooxygenase-2 has recently been shown to contribute to
neurodegeneration following ischemic injury. In the present study, we examined
the possibility that the neuroprotective effects of the cyclooxygenase-2
inhibitor nimesulide would depend upon reduction of oxidative stress following
cerebral ischemia. Gerbils were subjected to 5 min of transient global cerebral
ischemia followed by 48 h of reperfusion and markers of oxidative stress were
measured in hippocampus of gerbils receiving vehicle or nimesulide treatment at
three different clinically relevant doses (3, 6 or 12 mg/kg). Compared with
vehicle, nimesulide significantly (P<0.05) reduced hippocampal glutathione
depletion and lipid peroxidation, as assessed by the levels of malondialdehyde
(MDA), 4-hydroxy-alkenals (4-HDA) and lipid hydroperoxides levels, even when
the treatment was delayed until 6 h after ischemia. Biochemical evidences of
nimesulide neuroprotection were supported by histofluorescence findings using
the novel marker of neuronal degeneration Fluoro-Jade B. Few Fluoro-Jade B
positive cells were seen in CA1 region of hippocampus in ischemic animals
treated with nimesulide compared with vehicle. These results suggest that
nimesulide may protect neurons by attenuating oxidative stress and reperfusion
injury following the ischemic insult with a wide therapeutic window of
protection.",0708.0559v1
2007-08-15,Selective vulnerability to kainate-induced oxidative damage in different rat brain regions,"Some markers of oxidative injury were measured in different rat brain areas
(hippocampus, cerebral cortex, striatum, hypothalamus, amygdala/piriform cortex
and cerebellum) after the systemic administration of an excitotoxic dose of
kainic acid (KA, 9 mg kg(-1) i.p.) at two different sampling times (24 and 48
h). Kainic acid was able to lower markedly (P < 0.05) the glutathione (GSH)
levels in hippocampus, cerebellum and amygdala/piriform cortex (maximal
reduction at 24 h). In a similar way, lipid peroxidation, as assessed by
malonaldehyde and 4-hydroxyalkenal levels, significantly increased (P < 0.05)
in hippocampus, cerebellum and amygdala/piriform cortex mainly at 24 h after
KA. In addition, hippocampal superoxide dismutase (SOD) activity decreased
significantly (P < 0.05) with respect to basal levels by 24 h after KA
application. On the other hand, brain areas such as hypothalamus, striatum and
cerebral cortex seem to be less susceptible to KA excitotoxicity. According to
these findings, the pattern of oxidative injury induced by systemically
administered KA seems to be highly region-specific. Further, our results have
shown that a lower antioxidant status (GSH and SOD) seems not to play an
important role in the selective vulnerability of certain brain regions because
it correlates poorly with increases in markers of oxidative damage.",0708.2061v1
2007-10-09,Critical Oxide Thickness for Efficient Single-walled Carbon Nanotube Growth on Silicon Using Thin SiO2 Diffusion Barriers,"The ability to integrate carbon nanotubes, especially single-walled carbon
nanotubes, seamlessly onto silicon would expand the range of applications
considerably. Though direct integration using chemical vapor deposition is the
simplest method, the growth of single-walled carbon nanotubes on bare silicon
and on ultra-thin oxides is greatly inhibited due to the formation of a
non-catalytic silicide. Using x-ray photoelectron spectroscopy, we show that
silicide formation occurs on ultra-thin oxides due to thermally activated metal
diffusion through the oxide. Silicides affect the growth of single-walled
nanotubes more than multi-walled nanotubes due to the increased kinetics at the
higher single-walled nanotube growth temperature. We demonstrate that nickel
and iron catalysts, when deposited on clean silicon or ultra-thin silicon
dioxide layers, begin to form silicides at relatively low temperatures, and
that by 900C, all of the catalyst has been incorporated into the silicide,
rendering it inactive for subsequent single-walled nanotube growth. We further
show that a 4 nm silicon dioxide layer is the minimum diffusion barrier
thickness which allows for efficient single-walled nanotube growth.",0710.1769v1
2008-04-21,Redispersible Hybrid Nanopowders: Cerium Oxide Nanoparticle Complexes with Phosphonated-PEG Oligomers,"Rare earth cerium oxide (ceria) nanoparticles are stabilized using
end-functional phosphonated-PEG oligomers. The complexation process and
structure of the resulting hybrid core-shell singlet nanocolloids are
described, characterized and modeled using light and neutron scattering data.
The adsorption mechanism is non-stoichiometric, yielding the number of adsorbed
chains per particle Nads = 270 at saturation. Adsorption isotherms show a high
affinity of the phosphonate head for the ceria surface (adsorption energy ~ -16
kT) suggesting an electrostatic driving force for the complexation. The ease,
efficiency and integrity of the complexation is highlighted by the formation of
nanometric sized cerium oxide particles covered with a well anchored PEG layer,
maintaining the characteristics of the original sol. This solvating brush-like
layer is sufficient to solubilize the particles and greatly expand the
stability range of the original sol up to pH = 9. We underscore two key
attributes of the tailored sol: i) strong UV absorption capability after
functionalization and ii) ability to re-disperse after freeze-drying as powder
in aqueous or organic solvents in varying concentrations as singlet
nanocolloids. This robust platform enables translation of intrinsic properties
of mineral oxide nanoparticles to critical end use.",0804.3410v1
2008-06-11,Detection of C3O in the low-mass protostar Elias 18,"We have performed new laboratory experiments which gave us the possibility to
obtain an estimate of the amount of carbon chain oxides (namely C3O2, C2O, and
C3O) formed after irradiation (with 200 keV protons) of pure CO ice, at 16 K.
The analysis of laboratory data indicates that in dense molecular clouds, when
high CO depletion occurs, an amount of carbon chain oxides as high as 2-3x10^-3
with respect to gas phase carbon monoxide can be formed after ion irradiation
of icy grain mantles. Then we have searched for gas phase C2O and C3O towards
ten low-mass young stellar objects. Among these we have detected the C3O line
at 38486.891 MHz towards the low-mass protostar Elias 18. On the basis of the
laboratory results we suggest that in dense molecular clouds gas phase carbon
chain oxides are formed in the solid phase after cosmic ion irradiation of
CO-rich icy mantles and released to the gas phase after desorption of icy
mantles. We expect that the Atacama Large Millimeter Array (ALMA), thanks to
its high sensitivity and resolution, will increase the number of carbon chain
oxides detected in dense molecular clouds.",0806.1830v1
2008-12-10,An experimental and kinetic modelling study of the oxidation of the four isomers of butanol,"Butanol, an alcohol which can be produced from biomass sources, has received
recent interest as an alternative to gasoline for use in spark ignition engines
and as a possible blending compound with fossil diesel or biodiesel. Therefore,
the autoignition of the four isomers of butanol (1-butanol, 2-butanol,
iso-butanol, and tert-butanol) has been experimentally studied at high
temperatures in a shock tube and a kinetic mechanism for description of their
high-temperature oxidation has been developed. Ignition delay times for
butanol/oxygen/argon mixtures have been measured behind reflected shock waves
at temperatures and pressures ranging from approximately 1200 to 1800 K and 1
to 4 bar. Electronically excited OH emission and pressure measurements were
used to determine ignition delay times. A detailed kinetic mechanism has been
developed to describe the oxidation of the butanol isomers and validated by
comparison to the shock tube measurements. Reaction flux and sensitivity
analysis indicate that the consumption of 1 butanol and iso-butanol, the most
reactive isomers, takes place primarily by H-atom abstraction resulting in the
formation of radicals, the decomposition of which yields highly reactive
branching agents, H-atoms and OH radicals. Conversely, the consumption of tert
butanol and 2-butanol, the least reactive isomers, takes place primarily via
dehydration, resulting in the formation of alkenes, which lead to resonance
stabilized radicals with very low reactivity. To our knowledge, the ignition
delay measurements and oxidation mechanism presented here for 2-butanol,
iso-butanol, and tert butanol are the first of their kind..",0812.1874v1
2009-04-23,Purification and Characterization of an Arene cis-Dihydrodiol Dehydrogenase Endowed with Broad Substrate Specificity toward Polycyclic Aromatic Hydrocarbon Dihydrodiols,"Initial reactions involved in the bacterial degradation of polycyclic
aromatic hydrocarbons (PAHs) include a ring-dihydroxylation catalyzed by a
dioxygenase and a subsequent oxidation of the dihydrodiol products by a
dehydrogenase. In this study, the dihydrodiol dehydrogenase from the
PAH-degrading Sphingomonas strain CHY-1 has been characterized. The bphB gene
encoding PAH dihydrodiol dehydrogenase (PDDH) was cloned and overexpressed as a
His-tagged protein. The recombinant protein was purified as a homotetramer with
an apparent Mr of 110,000. PDDH oxidized the cis-dihydrodiols derived from
biphenyl and eight polycyclic hydrocarbons, including chrysene,
benz[a]anthracene, and benzo[a]pyene, to corresponding catechols. Remarkably,
the enzyme oxidized pyrene 4,5-dihydrodiol, whereas pyrene is not metabolized
by strain CHY-1. The PAH catechols produced by PDDH rapidly auto-oxidized in
air but were regenerated upon reaction of the o-quinones formed with NADH.
Kinetic analyses performed under anoxic conditions revealed that the enzyme
efficiently utilized two- to four-ring dihydrodiols, with Km values in the
range of 1.4 to 7.1 $\mu$M, and exhibited a much higher Michaelis constant for
NAD+ (Km of 160 $\mu$M). At pH 7.0, the specificity constant ranged from (1.3
$\pm$ 0.1) x 106 M?1 s?1 with benz[a]anthracene 1,2-dihydrodiol to (20.0 $\pm$
0.8) x 106 M?1 s?1 with naphthalene 1,2-dihydrodiol. The catalytic activity of
the enzyme was 13-fold higher at pH 9.5. PDDH was subjected to inhibition by
NADH and by 3,4-dihydroxyphenanthrene, and the inhibition patterns suggested
that the mechanism of the reaction was ordered Bi Bi. The regulation of PDDH
activity appears as a means to prevent the accumulation of PAH catechols in
bacterial cells.",0904.3616v1
2009-06-18,Oxide tunnel junctions supporting a two-dimensional electron gas,"The discovery of a two-dimensional electron gas (2DEG) at the interface
between insulating oxides has led to a well-deserved level of excitement due to
possible applications as ""in-plane"" all-oxide nanoelectronics. Here we expand
the range of possibilities to the realm of ""out-of-plane"" nanoelectronics by
examining such all-oxide heterostructures as barriers in tunnel junctions. As
an example system we perform first-principles electronic structure and
transport calculations of a tunnel junction with a [SrTiO3]4/[LaO]1/[SrTiO3]4
heterostructure tunneling barrier embedded between SrRuO3 electrodes. The
presence of the LaO atomic layer induces the formation of a 2DEG within the
tunneling barrier which acts as an extended defect perpendicular to the
transport direction, providing a route for resonant tunneling. Our calculations
demonstrate that the tunneling conductance in this system can be strongly
enhanced compared to a pure SrTiO3 barrier due to resonant tunneling, but that
lattice polarization effects play a significant role in determining this
behavior. In addition we find that this resonant tunneling is highly selective
of the orbital symmetry of the tunneling states due to the ""orbital
polarization"" of the 2DEG. We also discuss how the properties of the 2DEG are
affected by the presence of metal electrodes.",0906.3543v1
2009-09-30,Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study,"Stable oxygen sites on a PdO film over a Pd(100) thin structures with a
(sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the
first-principles electronic structure calculations with the generalized
gradient approximation. The adsorbed monatomic oxygen goes to a site bridging
two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd
atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO
oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by
oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom
between the two stable sites is evaluated using the nudged elastic band method,
where an energy barrier for a translational motion of the adsorbed oxygen may
become sim 0.45 eV, which is low enough to allow fluxionality of the surface
oxygen at high temperatures. The oxygen fluxionality is allowed by existence of
2-fold-coordinated Pd atoms on the PdO film, whose local structure has
similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling.
Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by
the PdO film, we conclude that there may happen continual redox reactions
mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the
influx of NO_x and CO continues, and when the reaction cycle is kept on a
well-designed oxygen surface.",0909.5477v1
2010-02-11,Real-time observation of bond-by-bond interface formation during the oxidation of (111) Si,"Atomic-level structure of solids is typically determined by techniques such
as X-ray and electron diffraction,1, 2, 3, 4 which are sensitive to atomic
positions. It is hardly necessary to mention the impact that these techniques
have had on almost every field of science. However, the bonds between atoms are
critical for determining the overall structure. The dynamics of these bonds
have been difficult to quantify. Here, we combine second-harmonic generation
and the bond-charge model of nonlinear optics5, 6 to probe, in real time, the
dynamics of bond-by-bond chemical changes during the oxidation of H-terminated
(111)Si, a surface that has been well characterized by static methods. We thus
demonstrate that our approach provides new information about this exhaustively
studied system. For example, oxidation is activated by a surprisingly small
applied macroscopic strain, and exhibits anisotropic kinetics with one of the
three equivalent back-bonds of on-axis samples reacting differently from the
other two. Anisotropic oxidation kinetics also leads to observed transient
changes in bond directions. By comparing results for surfaces strained in
different directions, we find that in-plane control of surface chemistry is
possible. The use of nonlinear optics as a bond-specific characterization tool
is readily adaptable for studying structural and chemical dynamics in many
other condensed-matter systems.",1002.2263v2
2010-06-18,"Polarons, free charge localisation and effective dielectric permittivity in oxides","This review will deal with several types of free charge localisation in
oxides and their consequences on the effective dielectric spectra of such
materials. The first one is the polaronic localisation at the unit cell scale
on residual impurities in ferroelectric networks. The second one is the
collective localisation of free charge at macroscopic interfaces like surfaces,
electrodes and grain boundaries in ceramics. Polarons have been observed in
many oxide perovskites mostly when cations having several stable electronic
configurations are present. In manganites, the density of such polarons is so
high as to drive a net lattice of interacting polarons. On the other hand, in
ferroelectric materials like BaTiO3 and LiNbO3, the density of polarons is
usually very small but they can influence strongly the macroscopic
conductivity. The contribution of such polarons to the dielectric spectra of
ferroelectric materials is described. Even residual impurities as for example
Iron can induce well defined anomalies at very low temperatures. This is mostly
resulting from the interaction between localised polarons and the highly
polarisable ferroelectric network in which they are embedded. The case of such
residual polarons in SrTiO3 will be described in more details, emphasizing the
quantum polaron state at liquid helium temperatures. Recently, several
non-ferroelectric oxides have been shown to display giant effective dielectric
permittivity. It is first shown that the frequency/temperature behaviour of
such parameters is very similar in very different compounds (donor doped
BaTiO3, CaCu3Ti4O12, LuFe2O4,Li doped NiO,...). This similarity calls for a
common origin of the giant dielectric permittivity in these compounds. A space
charge localisation at macroscopic interfaces can be the key for such extremely
high dielectric permittivity.",1006.3719v1
2010-08-11,Defect engineering in oxide heterostructures by enhanced oxygen surface exchange,"The synthesis of materials with well-controlled composition and structure
improves our understanding of their intrinsic electrical transport properties.
Recent developments in atomically controlled growth have been shown to be
crucial in enabling the study of new physical phenomena in epitaxial oxide
heterostructures. Nevertheless, these phenomena can be influenced by the
presence of defects that act as extrinsic sources of both doping and impurity
scattering. Control over the nature and density of such defects is therefore
necessary, are we to fully understand the intrinsic materials properties and
exploit them in future device technologies. Here, we show that incorporation of
a strontium copper oxide nano-layer strongly reduces the impurity scattering at
conducting interfaces in oxide LaAlO3-SrTiO3(001) heterostructures, opening the
door to high carrier mobility materials. We propose that this remote cuprate
layer facilitates enhanced suppression of oxygen defects by reducing the
kinetic barrier for oxygen exchange in the hetero-interfacial film system. This
design concept of controlled defect engineering can be of significant
importance in applications in which enhanced oxygen surface exchange plays a
crucial role.",1008.1896v2
2010-08-27,Large magnetoelectric effect in the Al1-xGaxFeO3 family of multiferroic Oxides,"AlFeO3, GaFeO3 and Al0.5Ga0.5FeO3, all crystallizing in a non-centrosymmetric
space group, are multiferroic and also exhibit magnetoelectric properties, with
Al0.5Ga0.5FeO3 showing unusually large magnetocapacitance at 300 K.",1008.4672v1
2010-10-07,The route to high temperature superconductivity in transition metal oxides,"The discovery of high temperature superconductivity in cuprates was possible
only through an intimate knowledge of perovskite oxides which have been
synthesized and characterized for decades at the IBM in the Z\""urich
laboratoty. Especially SrTiO3 and LaAlO3 have been in the focus at IBM as was
presented in Volume 1 of a series [1]. Probably for the first time detailed
microscopic investigations of the local properties of these compounds have been
obtained by studying by means of EPR the surroundings of transition metal
impurities in these materials. These experiments enabled the identification of
the order parameter of the structural instability observed in these oxides.
However, the idea to search for superconductivity came later motivated by
theoretical considerations that metallic hydrogen could become superconducting
at high temperatures. Since SrTiO3 is an insulator it was thought that the
implantation of hydrogen would render it metallic and eventually also
superconducting. This approach failed since the carrier density remained always
too small. In sequence it was then tried to achieve a metallic state in oxide
perovskites by varying their composition which was in so far promising as
reduced SrTiO3 exhibits superconductivity at 0.3K [2]. Furthermore it was
subsequently shown [3] that Tc can be enhanced to 1.2K by doping SrTiO3 with
Nb. In spite of the fact that Tc was far below values achieved in A15
compounds, a remarkable observation was connected with the Nb doped perovskite,
namely for the first time long before predicted two-gap superconductivity was
realized here.",1010.1377v1
2011-06-19,Oxidation mechanism in metal nanoclusters: Zn nanoclusters to ZnO hollow nanoclusters,"Zn nanoclusters (NCs) are deposited by Low-energy cluster beam deposition
technique. The mechanism of oxidation is studied by analysing their
compositional and morphological evolution over a long span of time (three
years) due to exposure to ambient atmosphere. It is concluded that the
mechanism proceeds in two steps. In the first step, the shell of ZnO forms over
Zn NCs rapidly up to certain limiting thickness: with in few days -- depending
upon the size -- Zn NCs are converted to Zn-ZnO (core-shell), Zn-void-ZnO, or
hollow ZnO type NCs. Bigger than ~15 nm become Zn-ZnO (core-shell) type: among
them, NCs above ~25 nm could able to retain their initial geometrical shapes
(namely triangular, hexagonal, rectangular and rhombohedral), but ~25 to 15 nm
size NCs become irregular or distorted geometrical shapes. NCs between ~15 to 5
nm become Zn-void-ZnO type, and smaller than ~5 nm become ZnO hollow sphere
type i.e. ZnO hollow NCs. In the second step, all Zn-void-ZnO and Zn-ZnO
(core-shell) structures are converted to hollow ZnO NCs in a slow and gradual
process, and the mechanism of conversion proceeds through expansion in size by
incorporating ZnO monomers inside the shell. The observed oxidation behaviour
of NCs is compared with theory of Cabrera - Mott on low-temperature oxidation
of metal.",1106.3752v2
2011-07-08,Anchoring ceria nanoparticles on reduced graphene oxide and their electronic transport properties,This paper has been withdrawn.,1107.1745v2
2011-08-23,Does H2O improve the catalytic activity of Au1-4/MgO towards CO oxidation?,"The present density functional theory study addresses the question whether
the presence of H2O influences the catalytic activity of small gold clusters,
Au1-4/MgO(100), towards the oxidation of carbon monoxide. To this end, we
studied the (co-)adsorption of H2O and CO/O2 on these gold clusters. The ground
state structures in the presence of all three molecular species, that we found,
are Au1O2/MgO and Au2-4CO/MgO with H2O adsorbed on the surface in the proximity
of the clusters-molecule complex. In this configuration the catalytic activity
of Au1-4/MgO is indifferent to the presence of H2O. We also found that a
stable, highly activated hydroperoxyl-hydroxyl complex, O2H\dot\dot OH, can be
formed on Au1,3/MgO. For the catalytic active system Au8/MgO, it has been
predicted that this complex opens an alternative catalytic reaction pathway
towards CO oxidation. Our results suggest that this water mediated catalytic
cycle is unlikely to occur on Au1,3/MgO. In the case of Au1/MgO the cycle is
interrupted by the dissociation of the remaining (OH)2 complex after forming
the first CO2 molecule. On Au3 /MgO the O2 H\dot\dot OH complex is likely to
decompose upon the impact of a CO molecule, since three of its bond
dissociation energies are comparable to the reaction barrier of the CO to CO2
oxidation.",1108.4669v1
2011-08-24,The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles,"Engineered inorganic nanoparticles are essential components in the
development of nanotechnologies. For applications in nanomedicine, particles
need to be functionalized to ensure a good dispersibility in biological fluids.
In many cases however, functionalization is not sufficient : the particles
become either coated by a corona of serum proteins or precipitate out of the
solvent. In the present paper, we show that by changing the coating of iron
oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small
carboxylated polymers (poly(acrylic acid)), the colloidal stability of the
dispersion is improved and the adsorption/internalization of iron towards
living mammalian cells is profoundly affected. Citrate-coated particles are
shown to destabilize in all fetal-calf-serum based physiological conditions
tested, whereas the polymer coated particles exhibit an outstanding
dispersibility as well as a structure devoid of protein corona. The
interactions between nanoparticles and human lymphoblastoid cells are
investigated by transmission electron microscopy and flow cytometry. Two types
of nanoparticle/cell interactions are underlined. Iron oxides are found either
adsorbed on the cellular membranes, or internalized into membrane-bound
endocytosis compartments. For the precipitating citrate-coated particles, the
kinetics of interactions reveal a massive and rapid adsorption of iron oxide on
the cell surfaces. The quantification of the partition between adsorbed and
internalized iron was performed from the cytometry data. The results highlight
the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.",1108.4779v1
2011-08-30,Decomposition of formic acid,"Formic acid is known to act as a reduction agent for copper oxide. Its
thermal uni-molecular decomposition was studied by means of DFT with special
attention to reaction paths and kinetics.",1108.5891v1
2012-02-02,Observation of reduction in Casimir force without change of dielectric permittivity,"Additional information is provided on the effect of the significant (up to
35%) reduction in the magnitude of the Casimir force between an Au-coated
sphere and an indium tin oxide film which was observed after UV treatment of
the latter. A striking feature of this effect is that the reduction is not
accompanied with a corresponding variation of the dielectric permittivity, as
confirmed by direct ellipsometry measurements. The measurement data are
compared with computations using the Lifshitz theory. It is shown that the data
for the untreated sample are in a very good agreement with theory taking into
account the free charge carriers in the indium tin oxide. The data for the
UV-treated sample exclude the theoretical results obtained with account of free
charge carriers. These data are found to be in a very good agreement with
theory disregarding the free charge carriers in an indium tin oxide film. A
possible theoretical explanation of our observations as a result of phase
transition of indium tin oxide from metallic to dielectric state is discussed
in comparison with other related experiments.",1202.0478v1
2012-08-18,"Structural/microstructural, optical and electrical investigations of Sb-SnO2 thin films deposited by spray pyrolysis","The structural, optical and electrical properties of spray deposited antimony
(Sb) doped tin oxide (SnO2) thin films, prepared from SnCl4 precursor, have
been studied as a function of antimony doping concentration. The doping
concentration was varied from 0 to 1.5 wt.% of Sb. The analysis of x-ray
diffraction patterns revealed that the as deposited doped and undoped tin oxide
thin films are pure crystalline tetragonal rutile phase of tin oxide which
belongs to the space group P42/mnm (number 136). The surface morphological
examination with field emission scanning electron microscopy (FESEM) revealed
the fact that the grains are closely packed and pores/voids between the grains
are very few. The transmittance spectra for as-deposited films were recorded in
the wavelength range of 200 to 1000 nm. The transmittance of the films was
observed to increase from 57% to 68% (at 800 nm) on initial addition of Sb (up
to [Sb]/[Sn] = 0.5 wt.%) and then it is decreased for higher level of antimony
doping ([Sb]/[Sn] > 0.5 wt.%). The sheet resistance of tin oxide films was
found to decrease from 48 \Omega/sq for undoped films to 8 \Omega/sq for
antimony doped films.",1208.4094v1
2012-09-12,Modelling of c-C2H4O formation on grain surfaces,"Despite its potential reactivity due to ring strain, ethylene oxide (c-C2H4O)
is a complex molecule that seems to be stable under the physical conditions of
an interstellar dense core; indeed it has been detected towards several
high-mass star forming regions with a column density of the order of 10e13cm-2
(Ikeda et al. 2001). To date, its observational abundances cannot be reproduced
by chemical models and this may be due to the significant contribution played
by its chemistry on grain surfaces. Recently, Ward and Price (2011) have
performed experiments in order to investigate the surface formation of ethylene
oxide starting with oxygen atoms and ethylene ice as reactants. We present a
chemical model which includes the most recent experimental results from Ward
and Price (2011) on the formation of c-C2H4O. We study the influence of the
physical parameters of dense cores on the abundances of c-C2H4O. We verify that
ethylene oxide can indeed be formed during the cold phase (when the ISM dense
cores are formed), via addition of an oxygen atom across the C=C double bond of
the ethylene molecule, and released by thermal desorption during the hot core
phase. A qualitative comparison between our theoretical results and those from
the observations shows that we are able to reproduce the abundances of ethylene
oxide towards high-mass star-forming regions.",1209.2540v1
2012-10-06,Atomic layer engineering of perovskite oxides for chemically sharp heterointerfaces,"Advances in synthesis techniques and materials understanding have given rise
to oxide heterostructures with intriguing physical phenomena that cannot be
found in their constituents. In these structures, precise control of interface
quality, including oxygen stoichiometry, is critical for unambiguous tailoring
of the interfacial properties, with deposition of the first monolayer being the
most important step in shaping a well-defined functional interface. Here, we
studied interface formation and strain evolution during the initial growth of
LaAlO3 on SrTiO3 by pulsed laser deposition, in search of a means for
controlling the atomic-sharpness of the interfaces. Our experimental results
show that growth of LaAlO3 at a high oxygen pressure dramatically enhances
interface abruptness. As a consequence, the critical thickness for strain
relaxation was increased, facilitating coherent epitaxy of perovskite oxides.
This provides a clear understanding of the role of oxygen pressure during the
interface formation, and enables the synthesis of oxide heterostructures with
chemically-sharper interfaces.",1210.2007v1
2012-10-25,Photochemistry in Terrestrial Exoplanet Atmospheres I: Photochemistry Model and Benchmark Cases,"We present a comprehensive photochemistry model for exploration of the
chemical composition of terrestrial exoplanet atmospheres. The photochemistry
model is designed from the ground up to have the capacity to treat all types of
terrestrial planet atmospheres, ranging from oxidizing through reducing, which
makes the code suitable for applications for the wide range of anticipated
terrestrial exoplanet compositions. The one-dimensional chemical transport
model treats up to 800 chemical reactions, photochemical processes, dry and wet
deposition, surface emission and thermal escape of O, H, C, N and S bearing
species, as well as formation and deposition of elemental sulfur and sulfuric
acid aerosols. We validate the model by computing the atmospheric composition
of current Earth and Mars and find agreement with observations of major trace
gases in Earth's and Mars' atmospheres. We simulate several plausible
atmospheric scenarios of terrestrial exoplanets, and choose three benchmark
cases for atmospheres from reducing to oxidizing. The most interesting finding
is that atomic hydrogen is always a more abundant reactive radical than the
hydroxyl radical in anoxic atmospheres. Whether atomic hydrogen is the most
important removal path for a molecule of interest also depends on the relevant
reaction rates. We also find that volcanic carbon compounds (i.e., CH4 and CO2)
are chemically long-lived and tend to be well mixed in both reducing and
oxidizing atmospheres, and their dry deposition velocities to the surface
control the atmospheric oxidation states. Furthermore, we revisit whether
photochemically produced oxygen can cause false positives for detecting
oxygenic photosynthesis, and find that in 1-bar CO2-rich atmospheres oxygen and
ozone may build up to levels that have been previously considered unique
signatures of life, if there is no surface emission of reducing gases...",1210.6885v1
2013-03-15,Chromium-doped silica optical fibres : influence of the core composition on the Cr oxidation states and crystal field,"We have made chromium-doped, silica-based preforms and optical fibres by
Modified Chemical Vapour Deposition and have studied the influence of the
chemical composition of the doped region on the Cr-oxidation states and the
spectroscopic properties of the samples. Chromium, introduced initially as
Cr3+, is partially or totally oxidized during the fabrication process, and is
stabilized in the core of the preforms and fibres as Cr3+ in octahedral
coordination, and/or as Cr4+ in distorded tetrahedral coordination (Cs). Small
concentrations (~1-2 mol%) of codopants in silica, such as germanium or
aluminium, suffice to promote a particular oxidation state. Particularly, 1 mol
% of aluminium stabilizes all present chromium into Cr4+. The ligand field
parameters, Dq, B and Dq/B, for Cr3+ and Cr4+ are derived. It is shown that the
chromium ions in our samples are in low to intermediate ligand field and that
Dq and Dq/B decrease when the aluminium content increases. The absorption cross
sections of Cr3+ are similar to that reported in glasses and crystals, whereas
Cr4+ has lower values than reference laser materials.",1303.3835v1
2013-04-05,Optical constants of refractory oxides at high temperatures,"Many cosmic dust species, among them refractory oxides, form at temperatures
higher than 300 K. Nevertheless, most astrophysical studies are based on the
room-temperature optical constants of solids, such as corundum and spinel. A
more realistic approach is needed for these materials, especially in the
context of modeling late-type stars. We aimed at deriving sets of optical
constants of selected, astrophysically relevant oxide dust species with high
melting points. A high-temperature-high-pressure-cell and a Fourier-transform
spectrometer were used to measure reflectance spectra of polished samples. For
corundum (alpha-Al$_2$O$_3$), spinel (MgAl$_2$O$_4$), and alpha-quartz
(SiO$_2$), temperature-dependent optical constants were measured from 300 K up
to more than 900 K. Small particle spectra were also calculated from these
data. All three examined oxides show a significant temperature dependence of
their mid-IR bands. For the case of corundum, we find that the 13$\mu$m
emission feature - seen in the IR spectra of many AGB stars - can very well be
assigned to this mineral species. The best fit of the feature is achieved with
oblate corundum grains at mean temperatures around 550 K. Spinel remains a
viable carrier of the 13$\mu$m feature as well, but only for T < 300 K and
nearly spherical grain shapes. Under such circumstances, spinel grains may also
account for the 31.8$\mu$m band that is frequently seen in sources of the
13$\mu$m feature and which has not yet been identified with certainty.",1304.1717v1
2013-06-21,Multi-orbital Cluster Perturbation Theory for transition metal oxides,"We present an extension of Cluster Perturbation Theory to include many body
correlations associated to local e-e repulsion in real materials. We show that
this approach can describe the physics of complex correlated materials where
different atomic species and different orbitals coexist. The prototypical case
of MnO is considered.",1306.5231v1
2013-11-12,Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks,"Context. The observation of carbon-rich disks have motivated several studies
questioning the influence of the C/O ratio on their gas phase composition in
order to establish the connection between the metallicity of hot-Jupiters and
that of their parent stars.
  Aims. We to propose a method that allows the characterization of the adopted
C/O ratio in protoplanetary disks independently from the determination of the
host star composition. Titanium and vanadium chemistries are investigated
because they are strong optical absorbers and also because their oxides are
known to be sensitive to the C/O ratio in some exoplanet atmospheres.
  Methods. We use a commercial package based on the Gibbs energy minimization
technique to compute the titanium and vanadium equilibrium chemistries in
protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations
are performed for pressures ranging from 1e-6 to 1e-2 bar, and for temperatures
ranging from 50 to 2000 K.
  Results. We find that the vanadium nitride/vanadium oxide and titanium
hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the
hot parts of disks (T > 1000 K). Our calculations suggest that, in these
regions, these ratios can be used as tracers of the C/O value in protoplanetary
disks.",1311.2916v1
2014-01-28,"Persistent metal-insulator transition at the surface of an oxygen-deficient, epitaxial manganite film","The oxygen stoichiometry has a large influence on the physical and chemical
properties of complex oxides. Most of the functionality in e.g. catalysis and
electrochemistry depends in particular on control of the oxygen stoichiometry.
In order to understand the fundamental properties of intrinsic surfaces of
oxygen-deficient complex oxides, we report on in situ temperature dependent
scanning tunnelling spectroscopy experiments on pristine oxygen deficient,
epitaxial manganite films. Although these films are insulating in subsequent ex
situ in-plane electronic transport experiments at all temperatures, in situ
scanning tunnelling spectroscopic data reveal that the surface of these films
exhibits a metal-insulator transition (MIT) at 120 K, coincident with the onset
of ferromagnetic ordering of small clusters in the bulk of the oxygen-deficient
film. The surprising proximity of the surface MIT transition temperature of
nonstoichiometric films with that of the fully oxygenated bulk suggests that
the electronic properties in the surface region are not significantly affected
by oxygen deficiency in the bulk. This carries important implications for the
understanding and functional design of complex oxides and their interfaces with
specific electronic properties for catalysis, oxide electronics and
electrochemistry.",1401.7201v1
2014-04-09,Melanin Made by Dopamine Oxidation: Thin Films and Interactions with Polyelectrolyte Multilayers,"The spontaneous oxidation of dopamine in slightly alkaline solutions was
investigated on the basis of the work of Lee and others [Science, 318:426-430,
2007], and the reaction product was identified as dopamine-melanin. The ability
of melanin to covalently bind amine functional groups was confirmed by
quantification of the corresponding binding sites on dopamine-melanin
aggregates. Furthermore it is possible to redissolve dopamine-melanin
aggregates in strongly alkaline solutions. The obtained small melanin grains
were used to build layer-by-layer deposits with poly(diallyldimethylammonium).
  Different methods of dopamine oxidation to grow melanin films at
solid--liquid interfaces were developed. All examined methods lead to
continuous dopamine-melanin films with very similar surface morphologies. The
dopamine-melanin films become impermeable to electrochemical probes at a
thickness in the 10 nm range. In this context a higher permeability for
positively charged and neutral probes than for negatively charged ones was
confirmed for one preparation method.
  The adsorption of proteins on dopamine-melanin coatings was explained as
combination of electrostatic and strong, most probably covalent, interactions.
To obtain this explanation, the zeta-potential of dopamine-melanin deposits has
been measured as a function of pH.
  The formation of melanin by dopamine oxidation in layer-by-layer films of
poly(L-lysine) (PLL) and hyaluronate (HA) was studied: Melanin is able to
homogeneously fill $(\text{PLL-HA})_n$ films and the obtained
polyelectrolyte-melanin composites can be detached from their substrate as
free-standing membranes prepared by a biomimetic method in mild conditions.",1404.2408v1
2014-07-10,Analysis of cellular responses of macrophages to zinc ions and zinc oxide nanoparticles: a combined targeted and proteomic approach,"Two different zinc oxide nanoparticles, as well as zinc ions, are used to
study the cellular responses of the RAW 264 macrophage cell line. A proteomic
screen is used to provide a wide view of the molecular effects of zinc, and the
most prominent results are cross-validated by targeted studies. Furthermore,
the alteration of important macrophage functions (e.g. phagocytosis) by zinc is
also investigated. The intracellular dissolution/uptake of zinc is also studied
to further characterize zinc toxicity. Zinc oxide nanoparticles dissolve
readily in the cells, leading to high intracellular zinc concentrations, mostly
as protein-bound zinc. The proteomic screen reveals a rather weak response in
the oxidative stress response pathway, but a strong response both in the
central metabolism and in the proteasomal protein degradation pathway. Targeted
experiments confirm that carbohydrate catabolism and proteasome are critical
determinants of sensitivity to zinc, which also induces DNA damage. Conversely,
glutathione levels and phagocytosis appear unaffected at moderately toxic zinc
concentrations.",1407.2732v1
2014-07-28,Effect of Dielectric Properties of Ceramic-Solvent Interface on the Binding of Protein to Oxide Ceramics: a Non Local Electrostatic Approach,"The contribution of electrostatic interactions to the free energy of binding
between model protein and a ceramic implant surface in the aqueous solvent,
considered in the framework of the non-local electrostatic model, is calculated
as a function of the implant low-frequency dielectric constant. We show that
the existence of a dynamically ordered (low-dielectric) interfacial solvent
layer at the protein-solvent and ceramic-solvent interface markedly increases
charging energy of the protein and ceramic implant, and consequently makes the
electrostatic contribution to the protein-ceramic binding energy more favorable
(attractive). Our analysis shows that the corresponding electrostatic energy
between protein and oxide ceramics depends non-monotonically on the dielectric
constant of ceramic. Obtained results indicate that protein can attract
electrostatically to the surface if ceramic material has a moderate dielectric
constant below or about 35 (in particularly ZrO2 or Ta2O5). This is in contrast
to classical (local) consideration of the solvent, which demonstrates an
unfavorable electrostatic interaction of protein with typical metal oxide
ceramic materials (dielectric constant>10). Thus, a solid implant coated by
combining oxide ceramic with a reduced dielectric constant can be beneficial to
strengthen the electrostatic binding of the protein-implant complex.",1407.7482v1
2014-10-03,Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors,"Recent theoretical studies employing density-functional theory have predicted
BaBiO$_{3}$ (when doped with electrons) and YBiO$_{3}$ to become a topological
insulator (TI) with a large topological gap (~ 0.7 eV). This, together with the
natural stability against surface oxidation, makes the Bismuth-Oxide family of
special interest for possible applications in quantum information and
spintronics. The central question, we study here, is whether the hole-doped
Bismuth Oxides, i.e. Ba$_{1-x}$K$_{x}$BiO$_{3}$ and
BaPb$_{1-x}$Bi$_{x}$O$_{3}$, which are ""high-Tc"" bulk superconducting near 30
K, additionally display in the further vicinity of their Fermi energy $E_{F}$ a
topological gap with a Dirac-type of topological surface state. Our electronic
structure calculations predict the K-doped family to emerge as a TI, with a
topological gap above $E_{F}$. Thus, these compounds can become superconductors
with hole-doping and potential TIs with additional electron doping.
Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac
cone below $E_{F}$ for further hole doping, which manifests these systems to be
candidates for both electron- and hole-doped topological insulators.",1410.0821v2
2015-01-07,A two-component flavin-dependent monooxygenase involved in actinorhodin biosynthesis in Streptomyces coelicolor,"The two-component flavin-dependent monooxygenases belong to an emerging class
of enzymes involved in oxidation reactions in a number of metabolic and
biosynthetic pathways in microorganisms. One component is a NAD(P)H:flavin
oxidoreductase, which provides a reduced flavin to the second component, the
proper monooxygenase. There, the reduced flavin activates molecular oxygen for
substrate oxidation. Here, we study the flavin reductase ActVB and ActVA-ORF5
gene product, both reported to be involved in the last step of biosynthesis of
the natural antibiotic actinorhodin in Streptomyces coelicolor. For the first
time we show that ActVA-ORF5 is a FMN-dependent monooxygenase that together
with the help of the flavin reductase ActVB catalyzes the oxidation reaction.
The mechanism of the transfer of reduced FMN between ActVB and ActVA-ORF5 has
been investigated. Dissociation constant values for oxidized and reduced flavin
(FMNox and FMNred) with regard to ActVB and ActVA-ORF5 have been determined.
The data clearly demonstrate a thermodynamic transfer of FMNred from ActVB to
ActVA-ORF5 without involving a particular interaction between the two protein
components. In full agreement with these data, we propose a reaction mechanism
in which FMNox binds to ActVB, where it is reduced, and the resulting FMNred
moves to ActVA-ORF5, where it reacts with O2 to generate a flavinperoxide
intermediate. A direct spectroscopic evidence for the formation of such species
within ActVA-ORF5 is reported.",1501.01469v1
2015-03-04,Boron Nitride Nanosheets for Metal Protection,"Although the high impermeability of graphene makes it an excellent barrier to
inhibit metal oxidation and corrosion, graphene can form a galvanic cell with
the underlying metal that promotes corrosion of the metal in the long term.
Boron nitride (BN) nanosheets which have a similar impermeability could be a
better choice as protective barrier, because they are more thermally and
chemically stable than graphene and, more importantly, do not cause galvanic
corrosion due to their electrical insulation. In this study, the performance of
commercially available BN nanosheets grown by chemical vapor deposition as a
protective coating on metal has been investigated. The heating of the copper
foil covered with the BN nanosheet at 250 {\deg}C in air over 100 h results in
dramatically less oxidation than the bare copper foil heated for 2 h under the
same conditions. The electrochemical analyses reveal that the BN nanosheet
coating can increase open circuit potential and possibly reduce oxidation of
the underlying copper foil in sodium chloride solution. These results indicate
that BN nanosheets are a good candidate for oxidation and corrosion protection,
although conductive atomic force microscopy analyses show that the
effectiveness of the protection relies on the quality of BN nanosheets.",1503.01295v1
2015-03-04,Ligand-Hole in SnI6 Unit and Origin of Band Gap in Photovoltaic Perovskite Variant Cs2SnI6,"This paper has been published in Bulletin of the Chemical Society of Japan,
which can be viewed at the following URL: http://doi.org/10.1246/bcsj.20150110
  Cs2SnI6, a variant of perovskite CsSnI3, is expected for a photovoltaic
material. Based on a simple ionic model, it is expected that Cs2SnI6 is
composed of Cs+, I-, and Sn4+ ions and that the band gap is primarily made of
occupied I- 5p6 valence band maximum (VBM) and unoccupied Sn4+ 5s conduction
band minimum (CBM) similar to SnO2. In this work, we performed density
functional theory (DFT) calculations and revealed that the real oxidation state
of the Sn ion in Cs2SnI6 is +2 similar to CsSnI3. The +2 oxidation state of Sn
originates from 2 ligand holes in the [SnI6]2- octahedron unit, where the
ligand [I6] cluster has the apparent [I66-L+2]4- oxidation state, because the
band gap is formed mainly by occupied I 5p VBM and unoccupied I 5p CBM. The +2
oxidation state of Sn and the band gap are originated from the intracluster
hybridization and stabilized by the strong covalent interaction between Sn and
I.",1503.01458v3
2015-04-20,Interface Engineering to Create a Strong Spin Filter Contact to Silicon,"Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on
silicon is a perfect route to enrich silicon nanotechnology with spin filter
functionality.
  To date, the inherent chemical reactivity between EuO and Si has prevented a
heteroepitaxial integration without significant contaminations of the interface
with Eu silicides and Si oxides.
  We present a solution to this long-standing problem by applying two
complementary passivation techniques for the reactive EuO/Si interface:
  ($i$) an $in\:situ$ hydrogen-Si $(001)$ passivation and ($ii$) the
application of oxygen-protective Eu monolayers --- without using any additional
buffer layers.
  By careful chemical depth profiling of the oxide-semiconductor interface via
hard x-ray photoemission spectroscopy, we show how to systematically minimize
both Eu silicide and Si oxide formation to the sub-monolayer regime --- and how
to ultimately interface-engineer chemically clean, heteroepitaxial and
ferromagnetic EuO/Si $(001)$ in order to create a strong spin filter contact to
silicon.",1504.05108v4
2015-06-24,"Mn$_3$O$_4$(001) film growth on Ag(001) - a systematic study using NEXAFS, STM, and LEED","The film growth of Mn$_3$O$_4$(001) films on Ag(001) up to film thicknesses
of almost seven unit cells of Mn$_3$O$_4$ has been monitored using a
complementary combination of near-edge X-ray absorption fine structure
spectroscopy (NEXAFS), scanning tunneling microscopy (STM), and low-energy
electron diffraction (LEED). The oxide films have been prepared by molecular
beam epitaxy. Using NEXAFS, the identity of the Mn oxide has clearly been
determined as Mn$_3$O$_4$. For the initial stages of growth, oxide islands with
p(2$\times$1) and p(2$\times$2) structures are formed, which are embedded into
the substrate. For Mn$_3$O$_4$ coverages up to 1.5 unit cells a p(2$\times$1)
structure of the films is visible in STM and LEED. Further increase of the
thickness leads to a phase transition of the oxide films resulting in an
additional c(2$\times$2) structure with a 45$^\circ$ rotated atomic pattern.
The emerging film structures are discussed on the basis of a sublayer model of
the Mn$_3$O$_4$ spinel unit cell. While the polarity of the island edges
determines the structure of initial islands, the surface energy of thicker
layers is remarkably reduced by a film restructuring.",1506.07294v1
2015-06-26,Fluorescence correlation spectroscopy in thin films at reflecting substrates as a means to study nanoscale structure and dynamics at soft-matter interfaces,"Structure and dynamics at soft-matter interfaces play an important role in
nature and technical applications. Optical single-molecule investigations are
non-invasive and capable to reveal heterogeneities at the nanoscale. In this
work we develop an autocorrelation function (ACF) approach to retrieve tracer
diffusion parameters obtained from fluorescence correlation spectroscopy (FCS)
experiments in thin liquid films at reflecting substrates. This approach then
is used to investigate structure and dynamics in 100 nm thick 8CB liquid
crystal films on silicon wafers with five different oxide thicknesses. We find
a different extension of the structural reorientation of 8CB at the
solid-liquid interface for thin and for thick oxide. For the thin oxides, the
perylenediimide tracer diffusion dynamics in general agrees with the
hydrodynamic modeling using no-slip boundary conditions with only a small
deviation close to the substrate, while a considerably stronger decrease of the
interfacial tracer diffusion is found for the thick oxides.",1506.08129v4
2015-08-27,Selective control of oxygen sublattice stability by epitaxial strain in Ruddlesden-Popper films,"Oxygen-defect control has long been considered an influential tuning knob for
producing various property responses in complex oxide films. In addition to
physical property changes, modification to the lattice structure, specifically
lattice expansion, with increasing oxygen vacancy concentrations has been
reported often and has become the convention for oxide materials. However, the
current understanding of the lattice behavior in oxygen-deficient films becomes
disputable when considering compounds containing different bonding environments
or atomic layering. Moreover, tensile strain has recently been discovered to
stabilize oxygen vacancies in epitaxial films, which further complicates the
interpretation of lattice behavior resulting from their appearance. Here, we
report on the selective strain control of oxygen vacancy formation and
resulting lattice responses in the layered, Ruddlesden-Popper phases,
La1.85Sr0.15CuO4. We found that a drastically reduced Gibbs free energy for
oxygen vacancy formation near the typical growth temperature for
tensile-strained epitaxial LSCO accounts for the large oxygen
non-stoichiometry. Additionally, oxygen vacancies form preferentially in the
equatorial position of the CuO2 plane, leading to a lattice contraction, rather
than the expected expansion, observed with apical oxygen vacancies. Since
oxygen stoichiometry plays a key role in determining the physical properties of
many complex oxides, the strong strain coupling of oxygen nonstoichiometry and
the unusual structural response reported here can provide new perspectives and
understanding to the structure and property relationships of many other
functional oxide materials.",1508.06971v1
2016-02-17,Heart and diamond Fermi arcs in Pd and Pt oxide topological Dirac semimetals,"Topological Dirac semimetals (DSMs) exhibit nodal points through which energy
bands disperse linearly in three-dimensional (3D) momentum space, a 3D analogue
of graphene. The first experimentally confirmed DSMs with a pair of Dirac
points (DPs), Na$_{3}$Bi and Cd$_{3}$As$_{2}$, show topological surface Fermi
arc states and exotic magneto-transport properties, boosting the interest in
the search for stable and nontoxic DSM materials. Here, based on the {\it
ab-initio} band structure calculations we predict a family of palladium and
platinum oxides as robust 3D DSMs. The novel topological properties of these
compounds are distinct from all other previously reported DSMs, they are
rendered by the multiple number of DPs in the compounds. We show that along
three unit axes of the cubic lattice there exist three pairs of DPs, which are
linked by Fermi arcs on the surface. The Fermi arcs display a Lifshitz
transition from a heart- to a diamond-shape upon varying the chemical
potential. Corresponding oxides are already available as high-quality single
crystals, which is an excellent precondition for the verification of our
prediction by photoemission and magneto-transport experiments. Our findings not
only predict a number of much robust 3D DSM candidates but also extend DSMs to
transition metal oxides, a versatile family of materials, which opens the door
to investigate the interplay between DSMs and electronic correlations that is
not possible in the previously discovered DSM materials.",1602.05533v1
2016-03-13,"Influence of the ""second gap"" on the transparency-conductivity compromise in transparent conducting oxides: an ab initio study","Transparent conducting oxides (TCOs) are essential to many technologies.
These materials are doped (\emph{n}- or \emph{p}-type) oxides with a large
enough band gap (ideally $>$3~eV) to ensure transparency. However, the high
carrier concentration present in TCOs lead additionally to the possibility for
optical transitions from the occupied conduction bands to higher states for
\emph{n}-type materials and from lower states to the unoccupied valence bands
for \emph{p}-type TCOs. The ""second gap"" formed by these transitions might
limit transparency and a large second gap has been sometimes proposed as a
design criteria for high performance TCOs. Here, we study the influence of this
second gap on optical absorption using \emph{ab initio} computations for
several well-known \emph{n}- and \emph{p}-type TCOs. Our work demonstrates that
most known \emph{n}-type TCOs do not suffer from second gap absorption in the
visible even at very high carrier concentrations. On the contrary,
\emph{p}-type oxides show lowering of their optical transmission for high
carrier concentrations due to second gap effects. We link this dissimilarity to
the different chemistries involved in \emph{n}- versus typical \emph{p}-type
TCOs. Quantitatively, we show that second gap effects lead to only moderate
loss of transmission (even in p-type TCOs) and suggest that a wide second gap,
while beneficial, should not be considered as a needed criteria for a working
TCO.",1603.04038v1
2016-03-22,Polaronic contributions to oxidation and hole conductivity in acceptor-doped BaZrO$_3$,"Acceptor-doped perovskite oxides like BaZrO$_3$ are showing great potential
as materials for renewable energy technologies where hydrogen acts an energy
carrier, such as solid oxide fuel cells and hydrogen separation membranes.
While ionic transport in these materials has been investigated intensively, the
electronic counterpart has received much less attention and further exploration
in this field is required. Here, we use density functional theory (DFT) to
study hole polarons and their impact on hole conductivity in Y-doped BaZrO$_3$.
Three different approaches have been used to remedy the self-interaction error
of local and semi-local exchange-correlation functionals: DFT$+U$, pSIC-DFT and
hybrid functionals. Self-trapped holes are found to be energetically favorable
by about $-$0.1 eV and the presence of yttrium results in further
stabilization. Polaron migration is predicted to occur through intraoctahedral
transfer and polaron rotational processes, which are associated with adiabatic
barriers of about 0.1 eV. However, the rather small energies associated with
polaron formation and migration suggest that the hole becomes delocalized and
band-like at elevated temperatures. These results together with an endothermic
oxidation reaction [A. Lindman et al., Phys. Rev. B 91, 245114 (2015)] yield a
picture that is consistent with experimental data for the hole conductivity.
The results we present here provide new insight into hole transport in
acceptor-doped BaZrO$_3$ and similar materials, which will be of value in the
future development of sustainable technologies.",1603.06728v2
2016-04-08,Detection of H2O and evidence for TiO/VO in an ultra hot exoplanet atmosphere,"We present a primary transit observation for the ultra hot (Teq~2400K) gas
giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field
Camera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range.
The 1.4 micron water absorption band is detected at high confidence (5.4 sigma)
in the planetary atmosphere. We also reanalyze ground-based photometric
lightcurves taken in the B, r', and z' filters. Significantly deeper transits
are measured in these optical bandpasses relative to the near-infrared
wavelengths. We conclude that scattering by high-altitude haze alone is
unlikely to account for this difference, and instead interpret it as evidence
for titanium oxide and vanadium oxide absorption. Enhanced opacity is also
inferred across the 1.12-1.3 micron wavelength range, possibly due to iron
hydride absorption. If confirmed, WASP-121b will be the first exoplanet with
titanium oxide, vanadium oxide, and iron hydride detected in transmission. The
latter are important species in M/L dwarfs, and their presence is likely to
have a significant effect on the overall physics and chemistry of the
atmosphere, including the production of a strong thermal inversion.",1604.02310v1
2016-06-18,Suppression of magnetoresistance in thin $WTe_2$ flakes by surface oxidation,"Recent renewed interest in layered transition metal dichalcogenides stems
from the exotic electronic phases predicted and observed in the single- and
few-layer limit. Realizing these electronic phases requires preserving the
desired transport properties down to a monolayer, which is challenging. Here,
using semimetallic $WTe_2$ that exhibits large magnetoresistance, we show that
surface oxidation and Fermi level pinning degrade the transport properties of
thin $WTe_2$ flakes significantly. With decreasing $WTe_2$ flake thickness, we
observe a dramatic suppression of the large magnetoresistance. This is
explained by fitting a two-band model to the transport data, which shows that
mobility of the electron and hole carriers decreases significantly for thin
flakes. The microscopic origin of this mobility decrease is attributed to a ~ 2
nm-thick amorphous surface oxide layer that introduces disorder. The oxide
layer also shifts the Fermi level by ~ 300 meV at the $WTe_2$ surface. However,
band bending due to this Fermi level shift is not the dominant cause for the
suppression of magnetoresistance as the electron and hole carrier densities are
balanced down to ~ 13 nm based on the two-band model. Our study highlights the
critical need to investigate often unanticipated and sometimes unavoidable
extrinsic surface effects on the transport properties of layered
dichalcogenides and other 2D materials.",1606.05756v1
2016-09-02,"High pressure structural, elastic and vibrational properties of green energetic oxidizer ammonium dinitramide","Ammonium DiNitramide (ADN) is one of the most promising green energetic
oxidizers for future rocket propellant formulations. In the present work, we
report a detailed theoretical study on structural, elastic, and vibrational
properties of the emerging oxidizer under hydrostatic compression using various
dispersion correction methods to capture weak intermolecular (van der Waals and
hydrogen bonding) interactions. The calculated ground state lattice parameters,
axial compressibilities, and equation of state are in good accord with the
available experimental results. Strength of intermolecular interactions has
been correlated using the calculated compressibility curves and elastic moduli.
Apart from this, we also observe discontinuities in the structural parameters
and elastic constants as a function of pressure. Pictorial representation and
quantification of intermolecular interactions are described by the 3D Hirshfeld
surfaces and 2D finger print maps. In addition, the computed infra-red (IR)
spectra at ambient pressure reveal that ADN is found to have more hygroscopic
nature over Ammonium Perchlorate (AP) due to the presence of strong hydrogen
bonding. Pressure dependent IR spectra show blue- and red-shift of bending and
stretching frequencies which leads to weakening and strengthening of the
hydrogen bonding below and above 5 GPa, respectively. The abrupt changes in the
calculated structural, mechanical, and IR spectra suggest that ADN might
undergo a first order structural transformation to a high pressure phase around
5-6 GPa. From the predicted detonation properties, ADN is found to have high
and low performance characteristics when compared with ammonium based energetic
oxidizers and well-known secondary explosives, respectively.",1609.00472v1
2017-03-20,In depth nano spectroscopic analysis on homogeneously switching double barrier memristive devices,"Memristors based on a double barrier design have been analysed by various
nano spectroscopic methods to unveil details about its microstructure and
conduction mechanism. The device consists of an AlOx tunnel barrier and a
NbOy/Au Schottky barrier sandwiched between Nb bottom electrode and Au top
electrode. As it was anticipated that the local chemical composition of the
tunnel barrier, i.e. oxidation state of the metals as well as concentration and
distribution of oxygen ions, have a major influence on electronic conduction,
these factors were carefully analysed. A combined approach was chosen in order
to reliably investigate electronic states of Nb and O by electron energy-loss
spectroscopy as well as map elements whose transition edges exhibit a different
energy range by energy-dispersive X-ray spectroscopy like Au and Al. The
results conclusively demonstrate significant oxidation of the bottom electrode
as well as a small oxygen vacancy concentration in the Al oxide tunnel barrier.
Possible scenarios to explain this unexpected additional oxide layer are
discussed and kinetic Monte Carlo simulations were applied in order to identify
its influence on conduction mechanisms in the device. In light of the strong
deviations between observed and originally sought layout, this study highlights
the robustness in terms of structural deviations of the double barrier
memristor device.",1703.06741v1
2018-02-15,Achieving Direct Electrochemical Oxidation of Carbon below 600oC through a Novel Direct Carbon Fuel Cell,"Direct carbon fuel cells (DCFCs) are highly efficient power generators fueled
by abundant and cheap solid carbons. However, the limited formation of triple
phase boundaries (TPBs) within fuel electrodes inhibits their performance even
at high temperatures due to the limitation of mass transfer. It also results in
low direct-utilization of the fuel. To address the challenges of low carbon
oxidation activity and low carbon utilization simultaneously, a highly
efficient, 3-D solid-state architected anode has been developed to enhance the
performance of DCFCs below 600C. The cells with the 3-D textile anode,
Gd:CeO2-Li/Na2CO3 composite electrolyte, and Sm0.5Sr0.5CoO3 (SSC) cathode have
demonstrated excellent performance with maximum power densities of 143, 196,
and 325 mW cm-2 at 500, 550, and 600C, respectively. At 500C, the cells could
be operated steadily with a rated power density of ~0.13 W cm-2 at a constant
current density of 0.15 A cm-2 with a carbon utilization over 86%. The
significant improvement of the cell performance at such temperatures attributes
to the high synergistic conduction of the composite electrolyte and the
superior 3-D anode structure which offers more paths for carbon catalytic
oxidation. Our results indicate the feasibility of direct electrochemical
oxidation of solid carbon at 500-600C with a high carbon utilization,
representing a promising strategy to develop 3-D architected electrodes for
fuel cells and other electrochemical devices.",1802.05789v1
2018-02-26,III-V Tri-Gate Quantum Well MOSFET: Quantum Ballistic Simulation Study for 10nm Technology and Beyond,"In this work, quantum ballistic simulation study of a III-V tri-gate MOSFET
has been presented. At the same time, effects of device parameter variation on
ballistic, subthrshold and short channel performance is observed and presented.
The ballistic simulation result has also been used to observe the electrostatic
performance and Capacitance-Voltage characteristics of the device. With
constant urge to keep in pace with Moore's law as well as aggressive scaling
and device operation reaching near ballistic limit, a full quantum transport
study at 10nm gate length is necessary. Our simulation reveals an increase in
device drain current with increasing channel cross-section. However short
channel performance and subthreshold performance get degraded with channel
cross-section increment. Increasing device cross-section lowers threshold
voltage of the device. The effect of gate oxide thickness on ballistic device
performance is also observed. Increase in top gate oxide thickness affects
device performance only upto a certain value. The thickness of the top gate
oxide however shows no apparent effect on device threshold voltage. The
ballistic simulation study has been further used to extract ballistic injection
velocity of the carrier and ballistic carrier mobility in the channel. The
effect of device dimension and gate oxide thickness on ballistic velocity and
effective carrier mobility is also presented.",1802.09136v1
2018-11-13,"Computationally-driven, high throughput identification of CaTe and Li$_\textrm{3}$Sb as promising candidates for high mobility $p$-type transparent conducting materials","High-performance $p$-type transparent conducting materials (TCMs) must
exhibit a rare combination of properties including high mobility, transparency
and $p$-type dopability. The development of high-mobility/conductivity $p$-type
TCMs is necessary for many applications such as solar cells, or transparent
electronic devices. Oxides have been traditionally considered as the most
promising chemical space to dig out novel $p$-type TCMs. However, non-oxides
might perform better than traditional $p$-type TCMs (oxides) in terms of
mobility. We report on a high-throughput (HT) computational search for
non-oxide $p$-type TCMs from a large dataset of more than 30,000 compounds
which identified CaTe and Li$_\textrm{3}$Sb as very good candidates for
high-mobility $p$-type TCMs. From our calculations, both compounds are expected
to be $p$-type dopable: intrinsically for Li$_\textrm{3}$Sb while CaTe would
require extrinsic doping. Using electron-phonon computations, we estimate hole
mobilities at room-temperature to be about 20 and 70 cm$^2$/Vs for CaTe and
Li$_\textrm{3}$Sb, respectively. The computed hole mobility for
Li$_\textrm{3}$Sb is quite exceptional and comparable with the electron
mobility in the best $n$-type TCMs.",1811.05390v1
2018-11-27,A protonated brownmillerite electrolyte for superior low-temperature proton conductivity,"Design novel solid oxide electrolyte with enhanced ionic conductivity forms
one of the Holy Grails in the field of materials science due to its great
potential for wide range of energy applications. Conventional solid oxide
electrolyte typically requires elevated temperature to activate the ionic
transportation, while it has been increasing research interests to reduce the
operating temperature due to the associated scientific and technological
importance. Here, we report a conceptually new solid oxide electrolyte,
HSrCoO2.5, which shows an exceptional enhanced proton conductivity at low
temperature region (from room temperature to 140 oC). Combining both the
experimental results and corresponding first-principles calculations, we
attribute these intriguing properties to the extremely-high proton
concentration as well as the well-ordered oxygen vacancy channels inherited
from the novel crystalline structure of HSrCoO2.5. This result provides a new
strategy to design novel solid oxide electrolyte with excellent proton
conductivity for wide ranges of energy-related applications.",1811.10802v1
2018-11-29,Detection and spatial mapping of conductive filaments in metal/oxide/metal cross-point devices,"A simple means of detecting and spatially mapping volatile and nonvolatile
conductive filaments in metal/oxide/metal cross-point devices is introduced and
its application demonstrated. The technique is based on thermal discolouration
of a thin photoresist layer deposited on the top electrode of the cross-point
device and relies on the increase in temperature produced by local Joule
heating of an underlying conductive filament. Finite element modelling of the
temperature distribution and its dependencies shows that the maximum
temperature at the top-electrode/photoresist interface is particularly
sensitive to the top-electrode thickness. The technique is demonstrated on NbOx
based metal-oxide-metal cross-point devices with a 25 nm thick top (Pt)
electrode, where it is used to undertake a statistical analysis of the filament
location as a function of device area. This shows that filament formation is
heterogeneous. The majority of filaments form preferentially along the
top-electrode edge and the fraction of these increases with decreasing device
area. Transmission electron microscopy of the top and bottom electrode edges is
used to explain this observation and suggests that it is due to a reduction in
the effective oxide thickness in this region.",1811.11889v1
2019-05-03,Strain engineering of epitaxial oxide heterostructures beyond substrate limitations,"The limitation of commercially available single-crystal substrates and the
lack of continuous strain tunability preclude the ability to take full
advantage of strain engineering for further exploring novel properties and
exhaustively studying fundamental physics in complex oxides. Here we report an
approach for imposing continuously tunable, large epitaxial strain in oxide
heterostructures beyond substrate limitations by inserting an interface layer
through tailoring its gradual strain relaxation. Taking BiFeO3 as a model
system, we demonstrate that the introduction of an ultrathin interface layer
allows the creation of a desired strain that can induce phase transition and
stabilize a new metastable super-tetragonal phase as well as morphotropic phase
boundaries overcoming substrate limitations. Furthermore, continuously tunable
strain from tension to compression can be generated by precisely adjusting the
thickness of the interface layer, leading to the first achievement of
continuous O-R-T phase transition in BiFeO3 on a single substrate. This
proposed route could be extended to other oxide heterostructures, providing a
platform for creating exotic phases and emergent phenomena.",1905.01070v2
2019-05-29,Growth of metallic delafossite PdCoO2 by molecular beam epitaxy,"The Pd, and Pt based ABO2 delafossites are a unique class of layered,
triangular oxides with 2D electronic structure and a large conductivity that
rivals the noble metals. Here, we report successful growth of the metallic
delafossite PdCoO2 by molecular beam epitaxy (MBE). The key challenge is
controlling the oxidation of Pd in the MBE environment where phase-segregation
is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium.
This is overcome by combining low temperature (300 {\deg}C) atomic
layer-by-layer MBE growth in the presence of reactive atomic oxygen with a
post-growth high-temperature anneal. Thickness dependence (5-265 nm) reveals
that in the thin regime (<75 nm), the resistivity scales inversely with
thickness, likely dominated by surface scattering; for thicker films the
resistivity approaches the values reported for the best bulk-crystals at room
temperature, but the low temperature resistivity is limited by structural
twins. This work shows that the combination of MBE growth and a post-growth
anneal provides a route to creating high quality films in this interesting
family of layered, triangular oxides.",1905.12549v2
2020-07-01,Closing the gap between theory and experiment for lithium manganese oxide spinels using a high-dimensional neural network potential,"Many positive electrode materials in lithium ion batteries include transition
metals which are difficult to describe by electronic structure methods like
density functional theory (DFT) due to the presence of multiple oxidation
states. A prominent example is the lithium manganese oxide spinel
Li$_x$Mn$_2$O$_4$ with $0\leq x\leq2$. While DFT, employing the local hybrid
functional PBE0r, provides a reliable description, the need for extended
computer simulations of large structural models remains a significant
challenge. Here, we close this gap by constructing a DFT-based high-dimensional
neural network potential (HDNNP) providing accurate energies and forces at a
fraction of the computational costs. As different oxidation states and the
resulting Jahn-Teller distortions represent a new level of complexity for
HDNNPs, the potential is carefully validated by performing X-ray diffraction
experiments. We demonstrate that the HDNNP provides atomic level details and is
able to predict a series of properties like the lattice parameters and
expansion with increasing Li content or temperature, the orthorhombic to cubic
transition, the lithium diffusion barrier, and the phonon frequencies. We show
that for understanding these properties access to large time and length scales
as enabled by the HDNNP is essential to close the gap between theory and
experiment.",2007.00327v2
2020-07-07,Crystal Engineering and Ferroelectricity at the Nanoscale in Epitaxial 1D Manganese Oxide on Silicon,"Ferroelectric oxides have attracted much attention due to their wide range of
applications, especially in electronic devices such as nonvolatile memories and
tunnel junctions. As a result, the monolithic integration of these materials
into silicon technology and its nanostructuration to develop alternative
cost-effective processes are among the central points in current technology. In
this work, we used a chemical route to obtain nanowire thin films of a novel
Sr1+{\delta}Mn8O16 (SMO) hollandite-type manganese oxide on silicon. Scanning
transmission electron microscopy combined with crystallographic computing
reveals a crystal structure comprising hollandite and pyrolusite units sharing
the edges of their MnO6 octahedra, resulting in three types of tunnels arranged
along the c axis, where ordering of the Sr atoms produces a natural symmetry
breaking. The novel structure gives rise to a ferroelectricity and
piezoelectricity, as revealed by local Direct Piezoelectric Force Microscopy
measurements, which confirmed the ferroelectric nature of SMO nanowire thin
films at room temperature and showed a piezoelectric coefficient d33 value of
22,6 pC/N. Moreover, we proved that flexible vertical SMO nanowires can be
harvested and converted into electric output energy through the piezoelectric
effect, showing an excellent deformability and high interface recombination.
This work indicates the possibility of engineering the integration of 1D
manganese oxides on silicon, a step which precedes the production of
microelectronic devices.",2007.03452v2
2020-07-27,Primordial black holes in a dimensionally oxidizing Universe,"The spontaneous creation of primordial black holes in a violently expanding
Universe is a well studied phenomenon. Based on quantum gravity arguments, it
has been conjectured that the early Universe might have undergone a lower
dimensional phase before relaxing to the current $(3 + 1)$ dimensional state.
In this article we combine the above phenomena: we calculate the pair creation
rates of black holes nucleated in an expanding Universe, by assuming a
dimensional evolution, we term ``oxidation'', from $(1 + 1)$ to $(2 + 1)$ and
finally to $(3 + 1)$ dimensions. Our investigation is based on the no boundary
proposal that allows for the construction of the required gravitational
instantons. If, on the one hand, the existence of a dilaton non-minimally
coupled to the metric is necessary for black holes to exist in the $(1 + 1)$
phase, it becomes, on the other hand, trivial in $(2 + 1)$ dimensions.
Nevertheless, the dilaton might survive the oxidation and be incorporated in a
modified theory of gravity in $(3 + 1)$ dimensions: by assuming that our
Universe, in its current state, originates from a lower-dimensional oxidation,
one might be led to consider the pair creation rate in a sub-class of the
Horndeski action. Our findings for this case show that, for specific values of
the Galileon coupling to the metric, the rate can be unsuppressed. This would
imply the possibility of compelling parameter bounds for non-Einstein theories
of gravity by using the spontaneous black hole creation.",2007.13653v2
2020-07-29,Ligand Dependent Oxidation Dictates the Performance Evolution of High Efficiency PbS Quantum Dot Solar Cells,"Lead sulfide (PbS) quantum dot (QD) photovoltaics have reached impressive
efficiencies of 12%, making them particularly promising for future
applications. Like many other types of emerging photovoltaic devices, their
environmental instability remains the Achilles heel of this technology. In this
work, we demonstrate that the degradation processes in PbS QDs which are
exposed to oxygenated environments are tightly related to the choice of
ligands, rather than their intrinsic properties. In particular, we demonstrate
that while 1,2-ethanedithiol (EDT) ligands result in significant oxidation of
PbS, lead iodide/lead bromide (PbX2) coated PbS QDs show no signs of oxidation
or degradation. Consequently, since the former is ubiquitously used as a hole
extraction layer in QD solar cells, it is predominantly responsible for the
device performance evolution. The oxidation of EDT-PbS QDs results in a
significantly reduced effective QD size, which triggers two competing
processes: improved energetic alignment that enhances electron blocking, but
reduced charge transport through the layer. At early times, the former process
dominates, resulting in the commonly reported, but so far not fully explained
initial increase in performance, while the latter governs the onset of
degradation and deterioration of the photovoltaic performance. Our work
highlights that the stability of PbS quantum dot solar cells can be
significantly enhanced by an appropriate choice of ligands for all device
components.",2007.14678v1
2020-07-30,Thermal Stability of Hafnium Zirconium Oxide on Transition Metal Dichalcogenides,"Ferroelectric oxides interfaced with transition metal dichalcogenides (TMDCs)
offer a promising route toward ferroelectric-based devices due to lack of
dangling bonds on the TMDC surface leading to a high-quality and abrupt
ferroelectric/TMDC interface. In this work, the thermal stability of this
interface is explored by first depositing hafnium zirconium oxide (HZO)
directly on geological MoS2 and as-grown WSe2, followed by sequential annealing
in ultra-high vacuum (UHV) over a range of temperatures (400-800 {\deg}C), and
examining the interface through X-ray photoelectron spectroscopy (XPS). We show
that the nucleation and stability of HZO grown through atomic layer deposition
(ALD) varied depending on functionalization of the TMDC, and the deposition
conditions can cause tungsten oxidation in WSe2. It was observed that HZO
deposited on non-functionalized MoS2 was unstable and volatile upon annealing,
while HZO on functionalized MoS2 was stable in the 400-800 {\deg}C range. The
HZO/WSe2 interface was stable until 700 {\deg}C, after which Se began to evolve
from the WSe2. In addition, there is evidence of oxygen vacancies in the HZO
film being passivated at high temperatures. Lastly, X-ray diffraction (XRD) was
used to confirm crystallization of the HZO within the temperature range
studied.",2007.15685v1
2010-05-05,Ni(OH)2 Nanoplates Grown on Graphene as Advanced Electrochemical Pseudocapacitor Materials,"Ni(OH)2 nanocrystals grown on graphene sheets with various degrees of
oxidation are investigated as electrochemical pseudocapacitor materials for
potential energy storage applications. Single-crystalline Ni(OH)2 hexagonal
nanoplates directly grown on lightly-oxidized, electrically-conducting graphene
sheets (GS) exhibit a high specific capacitance of ~1335F/g at a charge and
discharge current density of 2.8A/g and ~953F/g at 45.7A/g with excellent
cycling ability. The high specific capacitance and remarkable rate capability
are promising for applications in supercapacitors with both high energy and
power densities. Simple physical mixture of pre-synthesized Ni(OH)2 nanoplates
and graphene sheets show lower specific capacitance, highlighting the
importance of direct growth of nanomaterials on graphene to impart intimate
interactions and efficient charge transport between the active nanomaterials
and the conducting graphene network. Single-crystalline Ni(OH)2 nanoplates
directly grown on graphene sheets also significantly outperform small Ni(OH)2
nanoparticles grown on heavily-oxidized, electrically-insulating graphite oxide
(GO), suggesting that the electrochemical performance of these composites are
dependent on the quality of graphene substrates and the morphology and
crystallinity of the nanomaterials grown on top. These results suggest the
importance of rational design and synthesis of graphene-based nanocomposite
materials for high-performance energy applications.",1005.0853v1
2010-05-20,Oxidation of CO on surface hematite in high CO2 atmospheres,"We propose a mechanism for the oxidation of gaseous CO into CO2 occurring on
the surface mineral hematite (Fe2O3(s)) in hot, CO2-rich planetary atmospheres,
such as Venus. This mechanism is likely to constitute an important source of
tropospheric CO2 on Venus and could at least partly address the CO2 stability
problem in Venus' stratosphere, since our results suggest that atmospheric CO2
is produced from CO oxidation via surface hematite at a rate of 0.4 Petagrammes
(Pg) CO2 per (Earth) year on Venus which is about 45% of the mass loss of CO2
via photolysis in the Venusian stratosphere. We also investigated CO oxidation
via the hematite mechanism for a range of planetary scenarios and found that
modern Earth and Mars are probably too cold for the mechanism to be important
because the rate-limiting step, involving CO(g) reacting onto the hematite
surface, proceeds much slower at lower temperatures. The mechanism may feature
on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can
maintain solid surface hematite which e.g. starts to melt above about 1200K.
The mechanism may also be important for hot Hadean-type environments and for
the emerging class of hot Super-Earths with planetary surface temperatures
between about 600-900K.",1005.3588v1
2014-03-12,First Principles Study of Photo-oxidation Degradation Mechanisms in P3HT for Organic Solar Cells,"We present a theoretical study of degradation mechanisms for photoinduced
oxidation in organic polymers in the condensed phase, using
poly(3-hexylthiophene)(P3HT) as an example. Applying density functional theory
with a hybrid density functional and periodic boundary conditions that account
for steric effects and permit the modeling of interchain chemical reactions, we
investigate reaction pathways that may lead to the oxidation of thiophene
backbone as a critical step toward disrupting the polymer conjugation. We
calculate energy barriers for reactions of the P3HT backbone with oxidizing
agents including hydroxyl radical (OH$\cdot$), hydroperoxide (ROOH), and
peroxyl radical (ROO$\cdot$), following a UV-driven radical reaction starting
at the $\alpha$-carbon of the alkyl side chain as suggested by infrared (IR)
and X-ray photoemission (XPS) spectrosocopy studies. The results strongly
suggest that an attack of OH$\cdot$ on sulfur in P3HT is unlikely to be
thermodynamically favored. On the other hand, an attack of a peroxyl radical on
the side chain on the P3HT backbone may provide low barrier reaction pathways
to photodegradation of P3HT and other polymers with side chains. The condensed
phase setting is found to qualitatively affect predictions of degradation
processes.",1403.3102v2
2016-11-07,Unique catalytic decomposition and reduction of hydrogen peroxide and organic peroxides on magnesia (001) promoted by oxide-metal hybrid nanostructure,"The detection, removal and reduction of hydrogen peroxide is of significant
importance for its increasing application in the areas of environment, food,
electrochemistry and clinical laboratory. Herein the dissociative adsorption
behavior of hydrogen peroxide on ultrathin magnesia (001) films deposited on
transition metal is uncovered for the first time by employing periodic
density-functional theory calculations with van der Waals corrections. The
hydrogen peroxide is dissociated smoothly and reduced to surface hydroxyls on
MgO(001)/TM, and the dissociative adsorption energies of all the considered
fragmentation configurations are substantially negative, demonstrating
dissociation and reduction of hydrogen peroxide on MgO(001)/TM is
thermodynamically favorable. The dissociative adsorption energy decreases
monotonously with increasing film thickness, demonstrating the lower reactivity
of thick oxide films. Moreover, we examined the suitability of several
transition metal slabs (molybdenum, silver, vanadium, tungsten and gold)
combined with magnesia for splitting hydrogen peroxide. The dissociative
adsorption energies enhance when the lattice constants of substrate slabs
increase, indicating the chemisorption strength can be tuned by category of
metal slabs as well as thickness of oxide film. The mechanism of reactivity
enhancement for energetically and dynamically favorable decomposition of
hydrogen peroxide on supported magnesia is elucidated by characterizing the
geometric structures and electronic properties. The fragmentation and reduction
of diethyl peroxide and peroxyacetone are also studied to reveal the catalytic
activity of ultrathin magnesia toward splitting organic peroxides. The results
are wished to provide useful clue for detecting and reducing hydrogen peroxide
and organic peroxides by employing oxide-metal hybrid nanostructure.",1611.01897v2
2016-11-16,First-principles calculations that clarify energetics and reactions of oxygen adsorption and carbon desorption on 4H-SiC ($11\bar20$) surface,"We report static and dynamic first-principles calculations that provide
atomistic pictures of the initial stage of the oxidation processes occurring at
the ($11\bar20$) surface of 4H-SiC. Our results unveil reaction pathways and
their associated free-energy barriers for the adsorption of oxygen and the
desorption of carbon atoms. We find that oxygen adsorption shows structural
multi-stability and that the surface-bridge sites are the most stable and
crucial sites for subsequent oxidation. We find that an approaching O$_2$
molecule is adsorbed, then dissociated and finally migrates toward these
surface-bridge sites with a free-energy barrier of 0.7 eV at the ($11\bar20$)
surface. We also find that a CO molecule is desorbed from the metastable
oxidized structure upon the overcoming of a free-energy barrier of 2.4$\sim$2.6
eV, thus constituting one of the annihilation process of C during the
oxidation. The results of the CO molecule desorption on the ($11\bar20$)
surface are compared with the ($000\bar1$) surface. A catalytic effect of
dangling bonds at the surface, causing a drastic reduction of the CO desorption
energy, is found on the ($000\bar1$) surface and the microscopic picture of the
effect is ascribed to an electron transfer from the Si to C dangling bonds. The
intrinsic ($11\bar20$) surface does not show this catalytic effect, and this is
because the surface consists of an equal amount of Si and C dangling bonds and
the electron transfer occurs before the desorption.",1611.05189v1
2015-12-25,Controlled thinning and surface smoothening of silicon nanopillars,"A convenient method has been developed to thin electron beam fabricated
Silicon nanopillars under controlled surface manipulation by transforming the
surface of the pillars to an oxide shell layer followed by the growth of
sacrificial ammonium silicon fluoride coating. The results show the formation
of an oxide shell and a Silicon core without significantly changing the
original length and shape of the pillars. The oxide shell layer thickness can
be controlled from few nanometers up to few hundred nanometers. While down
sizing in diameter, smooth Si pillar surfaces of less than 10 nm roughness
within 2 {\mu}m were produced after exposure to vapors of HF and HNO3 mixture
as evidenced by transmission electron microscopy (TEM) analysis. The attempt to
expose for long durations leads to the growth of a thick oxide whose strain
effect on pillars can be assessed by coupled LO-TO vibrational modes of Si-O
bonds. Photoluminescence (PL) on the pillar structures which have been down
sized exhibit visible and infrared emissions, which are attributable to
microscopic pillars and to the confinement of excited carriers in Si core,
respectively. The formation of a smooth core-shell structures while reducing
the diameter of the Si pillars has a potential in fabricating nanoscale
electronic devices and functional components.",1512.07996v1
2015-12-30,Modelling the Role of Nitric Oxide in Cerebral Autoregulation,"Malfunction of the system which regulates the bloodflow in the brain is a
major cause of stroke and dementia, costing many lives and many billions of
pounds each year in the UK alone. This regulatory system, known as cerebral
autoregulation, has been the subject of much experimental and mathematical
investigation yet our understanding of it is still quite limited. One area in
which our understanding is particularly lacking is that of the role of nitric
oxide, understood to be a potent vasodilator. The interactions of nitric oxide
with the better understood myogenic response remain un-modelled and poorly
understood. In this thesis we present a novel model of the arteriolar control
mechanism, comprising a mixture of well-established and new models of
individual processes, brought together for the first time. We show that this
model is capable of reproducing experimentally observed behaviour very closely
and go on to investigate its stability in the context of the vasculature of the
whole brain. In conclusion we find that nitric oxide, although it plays a
central role in determining equilibrium vessel radius, is unimportant to the
dynamics of the system and its responses to variation in arterial blood
pressure. We also find that the stability of the system is very sensitive to
the dynamics of Ca$^{2+}$ within the muscle cell, and that self-sustaining
Ca$^{2+}$ waves are not necessary to cause whole-vessel radius oscillations
consistent with vasomotion.",1512.09160v1
2016-12-01,Mechanisms of initial oxidation of 4H-SiC (0001) and (000$\bar{1}$) surfaces unraveled by first-principles calculations,"We have performed electronic state calculations to clarify the initial stage
of the oxidation of the Si- and C-faces in 4H-SiC based on the
density-functional theory. We investigate how each Si and C atomic site is
oxidized on C- and Si-face, and explore most probable reaction pathways,
corresponding energy barriers, and possible defects generated during the
oxidation. We have found that carbon annihilation process is different between
on Si- and on C-face, and this difference causes different defects in
interface; In C-face case, (1), carbon atoms are dissociated directly from the
substrate as CO molecules. (2), after CO dissociation, 3-fold coordinated
oxygen atoms (called Y-lid) are observed at the interface. (3), high density of
C-dangling bonds can remain at the interface. In Si-face case, (1), C atoms
inevitably form carbon nano clusters (composed of a few atoms) in interface to
reduce the number of dangling bonds there. Moreover, we have found that the
carbon nano clusters are composed of not only single but also double chemical
bonds. (2), We have observed that CO molecules are dissociated from the carbon
nano clusters in MD simulations. Furthermore, we have investigated whether
H$_2$ and NO molecules react with the defects found in this study.",1612.00189v1
2017-07-10,Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO$_2$(110),"Photocatalytic nitrogen fixation provides a promising route to produce
reactive nitrogen compounds at benign conditions. Titania has been reported as
an active photocatalyst for reduction of dinitrogen to ammonia; however there
is little fundamental understanding of how this process occurs. In this work
the rutile (110) model surface is hypothesized to be the active site, and a
computational model based on the Bayesian error estimation functional
(BEEF-vdW) and computational hydrogen electrode is applied in order to analyze
the expected dinitrogen coverage at the surface as well as the overpotentials
for electrochemical reduction and oxidation. This is the first application of
computational techniques to photocatalytic nitrogen fixation, and the results
indicate that the thermodynamic limiting potential for nitrogen reduction on
rutile (110) is considerably higher than the conduction band edge of rutile
TiO$_2$, even at oxygen vacancies and iron substitutions. This work provides
strong evidence against the most commonly reported experimental hypotheses, and
indicates that rutile (110) is unlikely to be the relevant surface for nitrogen
reduction. However, the limiting potential for nitrogen oxidation on rutile
(110) is significantly lower, indicating that oxidative pathways may be
relevant on rutile (110). These findings suggest that photocatalytic dinitrogen
fixation may occur via a complex balance of oxidative and reductive processes.",1707.03031v3
2018-01-08,The effect of heavy tars (toluene and naphthalene) on the electrochemical performance of an anode-supported SOFC running on bio-syngas,"The effect of heavy tar compounds on the performance of a Ni-YSZ anode
supported solid oxide fuel cell was investigated. Both toluene and naphthalene
were chosen as model compounds and tested separately with a simulated
bio-syngas. Notably, the effect of naphthalene is almost negligible with pure
H2 feed to the SOFC, whereas a severe degradation is observed when using a
bio-syngas with an H2:CO = 1. The tar compound showed to have a remarkable
effect on the inhibition of the WGS shift-reaction, possibly also on the CO
direct electro-oxidation at the three-phase-boundary. An interaction through
adsorption of naphthalene on nickel catalytic and electrocatalytic active sites
is a plausible explanation for observed degradation and strong performance
loss. Different sites seem to be involved for H2 and CO electro-oxidation and
also with regard to catalytic water gas shift reaction. Finally, heavy tars
(C>=10) must be regarded as a poison more than a fuel for SOFC applications,
contrarily to lighter compounds such benzene or toluene that can directly
reformed within the anode electrode. The presence of naphthalene strongly
increases the risk of anode re-oxidation in a syngas stream as CO conversion to
H2 is inhibited and also CH4 conversion is blocked.",1801.02557v1
2018-09-21,Spectroscopic Signature of Oxidized Oxygen States in Peroxides,"Recent debates on the oxygen redox behaviors in battery electrodes have
triggered a pressing demand for the reliable detection and understanding of
non-divalent oxygen states beyond conventional absorption spectroscopy. Here,
enabled by high-efficiency mapping of resonant inelastic X-ray scattering
(mRIXS) coupled with first-principles calculations, we report distinct mRIXS
features of the oxygen states in Li2O, Li2CO3, and especially, Li2O2, which are
successfully reproduced and interpreted theoretically. mRIXS signals are
dominated by valence-band decays in Li2O and Li2CO3. However, the oxidized
oxygen in Li2O2 leads to partially unoccupied O-2p states that yield a specific
intra-band excitonic feature in mRIXS. Such a feature displays a specific
emission energy in mRIXS, which disentangles the oxidized oxygen states from
the dominating transition-metal/oxygen hybridization features in absorption
spectroscopy, thus providing critical hints for both detecting and
understanding the oxygen redox reactions in transition-metal oxide based
battery materials.",1809.08292v2
2018-10-02,Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings,"In this work, we investigate the correlation between morphology, composition,
and the mechanical properties of metallic amorphous tungsten-oxygen and
amorphous tungsten-oxide films deposited by Pulsed Laser Deposition. This
correlation is investigated by the combined use of Brillouin Spectroscopy and
the substrate curvature method. The stiffness of the films is strongly affected
by both the oxygen content and the mass density. The elastic moduli show a
decreasing trend as the mass density decreases and the oxygen-tungsten ratio
increases. A plateaux region is detected in correspondence of the transition
between metallic and oxide films. The compressive residual stresses, moderate
stiffness and high local ductility that characterize compact amorphous
tungsten-oxide films make them promising for applications involving thermal or
mechanical loads. The coefficient of thermal expansion is quite high (i.e. 8.9
$\cdot$ 10$^{-6}$ K$^{-1}$), being strictly correlated to the amorphous
structure and stoichiometry of the films. Under thermal treatments they show a
quite low relaxation temperature (i.e. 450 K). They crystallize into the
$\gamma$ monoclinic phase of WO$_3$ starting from 670 K, inducing an increase
by about 70\% of material stiffness.",1810.01201v2
2019-06-13,Passivation-induced physicochemical alterations of the native surface oxide film on 316L austenitic stainless steel,"Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron
Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis
were combined to characterize the physicochemical alterations induced by
electrochemical passivation of the surface oxide film providing corrosion
resistance to 316L stainless steel. The as-prepared surface is covered by a ~2
nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner
layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is
concentrated, mostly as Mo(VI), in the outer layer. Nickel is only present at
trace level. These inner and outer layers have band gap values of 3.0 and
2.6-2.7 eV, respectively, and the oxide film would behave as an insulator.
Electrochemical passivation in sulfuric acid solution causes the preferential
dissolution of Fe(III) resulting in the thickness decrease of the outer layer
and its increased enrichment in Cr(III) and Mo(IV-VI). The further Cr(III)
enrichment of the inner layer causes loss of photoactivity and improved
corrosion protection with the anodic shift of the corrosion potential and the
increase of the polarization resistance by a factor of ~4. Aging in the passive
state promotes the Cr enrichment in the inner barrier layer of the passive
film.",1906.05544v1
2019-06-25,Titanium Contacts to MoS2 with Interfacial Oxide: Interface Chemistry and Thermal Transport,"The deposition of a thin oxide layer at metal/semiconductor interfaces has
been previously reported as a means of reducing contact resistance in 2D
electronics. Using X-ray photoelectron spectroscopy with in-situ Ti deposition,
we fabricate Au/Ti/TiOx/MoS2 samples as well as Au/Ti/MoS2 and Au/TiOx/MoS2 for
comparison. Elemental titanium reacts strongly with MoS2 whereas no interface
reactions are observed in the two types of samples containing TiOx/MoS2
interfaces. Using time domain thermoreflectance for the measurement of thermal
boundary conductance, we find that samples contacted with Ti and a thin TiOx
layer at the interface (less than or equal to 1.5 nm) exhibit the same behavior
as samples contacted solely with pure Ti. The Au/TiOx/MoS2 samples exhibit
approximately 20% lower thermal boundary conductance, despite having the same
MoS2 interface chemistry as the samples with thin oxide at the Ti/MoS2
interface. We identify the mechanism for this phenomenon, attributing it to the
different interfaces with the top Au contact. Our work demonstrates that the
use of thin interfacial oxide layers to reduce electrical contact resistance
does not compromise heat flow in 2D electronic devices. We note that the
thicknesses of the Ti and TiOx layers must be considered for optimal thermal
transport.",1906.10727v1
2019-06-26,Near 100% CO Selectivity in Nanoscaled Iron-Based Oxygen Carriers for Chemical Looping Methane Partial Oxidation,"Chemical looping methane partial oxidation provides an energy and cost
effective route for methane utilization. However, there is considerable CO2
co-production in state-of-the-art chemical looping systems, rendering a
decreased productivity in value-added fuels or chemicals. In this work, we show
that the co-production of CO2 can be dramatically suppressed in methane partial
oxidation reactions using iron oxide nanoparticles, with a size of 2~8 nm, as
the oxygen carrier. To stabilize these nanoparticles at high temperatures, they
are embedded in an ordered, gas-permeable mesoporous silica matrix. We
experimentally obtained near 100% CO selectivity in a cyclic redox system at
750{\deg}C to 935{\deg}C, which is a significantly lower temperature range than
in conventional oxygen carrier systems. Density functional theory calculations
elucidate the origins for such selectivity and reveal that CH4 adsorption
energies decrease with increasing nanoparticle size. These calculations also
show that low-coordinated lattice oxygen atoms on the surface of nanoparticles
significantly promote Fe-O bond cleavage and CO formation. We envision that
embedded nanostructured oxygen carriers have the potential to serve as a
general materials platform for achieving 100% selectivity in redox reactions at
high temperatures.",1906.11160v1
2019-07-28,Effect of Functional Group on Electrical Switching Behaviour of an Imidazole Derivative in Langmuir-Blodgett Film,"Here we report the design and synthesis of an imidazole derivative namely
1-benzyl-2,4,5-triaryl imidazole and its switching behaviour assembled onto
Langmuir-Blodgett films. Monolayer characteristic of imidazole at the air-water
interface has been studied by surface pressure vs area per molecule isotherm,
hysteresis analysis and insitu Brewster Angle Microscopy . These studies
indicated the formation of stable floating Langmuir film at the water subphase.
Atomic Force Microscopy investigation confirmed the successful deposition of
the Langmuir film onto solid substrate. Device consisted of 60 layers LB films
of imidazole showed resistive bipolar switching behaviour irrespective of the
first applied bias voltage polarity. Observed bipolar switching has been
explained in terms of reduction oxidation process. Due to the presence of
strong reducible group C double bond N in the imidazole core, reduction
oxidation process takes place easily during bias. Presence of sharp reduction
and oxidation peaks in the Cyclic Voltammetry measurement of 2 also supported
this hypothesis. Presence of benzyl group with the imidazole core played the
crucial rule in the reduction oxidation process and hence the switching
behaviour. When benzyl group was replaced by a H then bipolar switching was not
observed. In that case oxidizable group NH opposed the reduction process during
bias. This type of bipolar switching is very promising for future technological
applications in organic electronics.",1907.12004v1
2019-09-26,Pd/Pt embedded CN monolayer as efficient catalysts for CO oxidation,"Single atom catalysts (SACs) based on 2D materials are identified to be
efficient in many catalytic reaction. In this work, the catalytic performance
of Pd/Pt embedded planar carbon nitride (CN) for CO oxidation, has been
investigated via spin$-$polarized density functional theory calculations. We
find that Pd/Pt can be firmly anchored in the porous CN monolayer due to the
strong hybridization between Pd/Pt-d orbitals and adjacent N-2p orbitals. The
resulting high adsorption energy and large diffusion barrier of Pd/Pt, ensuring
the remarkable stability of the catalyst Pd/Pt@CN during CO oxidation reaction.
The three distinct CO reaction mechanisms, namely, Eley-Rideal (ER),
Langmuir-Hinshelwood (LH), and Tri-molecular Eley-Rideal (TER), are taken into
consideration comparatively. Intriguingly, the oxidation reaction on Pd@CN
prefers to proceed through the less common TER mechanism, where two CO
molecules and one O2 molecule need to cross a small reaction barrier of 0.48
eV, and finally dissociate into two CO2 molecules. However, the LH mechanism is
the most relevant one on Pt@CN with a rate-limiting reaction barrier of 0.68
eV. Moreover, the origin of SAC's reactivity enhancement is the electronic
""acceptance$-$donation"" interaction caused by orbital hybridization between
Pd/Pt and preadsorbed O2/CO. Our findings are expected to widen the catalytic
application of carbon based 2D materials.",1909.11922v1
2019-10-11,Low work function thin film growth for high efficiency thermionic energy converter: Coupled Kelvin probe and photoemission study of potassium oxide,"Recent researches in thermal energy harvesting have revealed the remarkable
efficiency of thermionic energy converters comprising very low work function
electrodes. From room temperature and above, this kind of converter could
supply low power devices such as autonomous sensor networks. In this type of
thermoelectric converters, current injection is mainly governed by a mechanism
of thermionic emission at the hot electrode which explains the interest for low
work function coating materials. In particular, alkali metal oxides have been
identified as excellent candidates for coating converter electrodes. This paper
is devoted to the synthesis and characterization of potassium peroxide K2O2
onto silicon surfaces. To determine optimal synthesis conditions of K2O2, we
present diagrams showing the different oxides as a function of temperature and
oxygen pressure from which phase stability characteristics can be determined.
From the experimental standpoint, we present results on the synthesis of
potassium oxide under ultra high vacuum and controlled temperature. The
resulting surface is characterized in situ by means of photoemission
spectroscopy (PES) and contact potential difference (CPD) measurements. A work
function of 1.35 eV is measured which and the expected efficiency of the
corresponding converter is discussed. It is generally assumed that the decrease
of the work function in the alkali/oxygen/ silicon system, is attributed to the
creation of a surface dipole resulting from a charge transfer between the
alkali metal and oxygen.",1910.05166v1
2019-10-28,Tailored Graphenic Structures Directly Grown on Titanium Oxide Boost the Interfacial Charge Transfer,"The successful application of titanium oxide-graphene hybrids in the fields
of photocatalysis, photovoltaics and photodetection strongly depends on the
interfacial contact between both materials. The need to provide a good coupling
between the enabling conductor and the photoactive phase prompted us to
directly grow conducting graphenic structures on TiO2 crystals. We here report
on the direct synthesis of tailored graphenic structures by using Plasma
Assisted Chemical Vapour Deposition that present a clean junction with the
prototypical titanium oxide (110) surface. Chemical analysis of the interface
indicates chemical bonding between both materials. Photocurrent measurements
under UV light illumination manifest that the charge transfer across the
interface is efficient. Moreover, the influence of the synthesis atmosphere,
gas precursor (C2H2) and diluents (Ar, O2), on the interface and on the
structure of the as-grown graphenic material is assessed. The inclusion of O2
promotes vertical growth of partially oxidized carbon nanodots/rods with
controllable height and density. The deposition with Ar results in continuous
graphenic films with low resistivity (6.8x10-6 ohm x m). The synthesis
protocols developed here are suitable to produce tailored carbon-semiconductor
structures on a variety of practical substrates as thin films, pillars or
nanoparticles.",1910.12667v1
2019-12-24,First-principles study on luminescence properties of Eu-doped defect pyrochlore oxide KNbWO$_6\cdot$H$_2$O:Eu$^{3+}$,"Defect pyrochlore oxides have attracted a great interest as promising
luminescent materials due to their flexible composition and high electron/hole
mobility. In this work, we investigate the structural and electronic properties
of lanthanide-doped (Ln) defect pyrochlore oxides \ce{KNbWO6}:0.125Ln$^{3+}$ by
using first-principles calculations. We perform structural optimizations of
various defect pyrochlore models and calculate their electronic structures,
revealing that hydration has a significant influence on both local symmetry
around Eu$^{3+}$ ion and band structures with an alteration of their
luminescent behaviour. In the hydrated compounds, the electric-dipole
$^5$D$_0-^7$F$_2$ transition is found to be partially suppressed by the raised
local symmetry, and the water molecules in the compounds can mediate the
non-radiative energy transfer between the activator Eu$^{3+}$ ions and the
host, resulting in the quenching effect. It turns out that the oxygen vacancies
are detrimental to luminescence as they reduce the Eu$^{3+}$ ion in its
vicinity to Eu$^{2+}$ ion and also serve as traps for conduction electrons
excited by incident light. Our calculations for \ce{KNbWO6}:0.125Ln$^{3+}$ (Ln
= Ce, Pr, Nd, Pm, Sm) support that defect pyrochlore oxide \ce{KNbWO6} can also
be used as luminescence host for Ln$^{3+}$ ion doping, giving a valuable
insight into a variation trend in luminescent properties of these materials at
atomic level.",2001.02059v1
2019-12-29,Bio-inspired Band Gap Engineering of Zinc Oxide by Intracrystalline Incorporation of Amino Acids,"During a bioInspired crystallization process, incorporation of amino acids
into the crystal structure of ZnO induces lattice strain that leads to linear
bandgap shifts.",2001.02064v1
2020-01-14,"Interplay among Work Function, electronic structure and stoichiometry in nanostructured vanadium oxides films","The work function is the parameter of greatest interest in many technological
applications involving charge exchange mechanisms at the interface. The
possibility to produce samples with a controlled work function is then
particularly interesting, albeit challenging. We synthetized nanostructured
vanadium oxides films by a room temperature Supersonic Cluster Beam Deposition
method, obtaining samples with tunable stoichiometry and work function (3.7-7
eV). We present an investigation of the electronic structure of several
vanadium oxides films as a function of the oxygen content via in-situ Auger,
valence-band photoemission spectroscopy and work function measurements. The
experiments probed the partial 3d density of states, highlighting the presence
of strong V3d-O2p and V3d-V4s hybridization which influence 3d occupation. We
show how controlling the stoichiometry of the sample implies a control over
work function, and that the access to nanoscale quantum confinement can be
exploited to increase the work function of the sample relative to the bulk
analogue. In general, the knowledge of the interplay among work function,
electronic structure, and stoichiometry is strategic to match nanostructured
oxides to their target applications.",2001.04695v1
2020-12-19,Investigation of microwave loss induced by oxide regrowth in high-Q Nb resonators,"The coherence of state-of-the-art superconducting qubit devices is
predominantly limited by two-level-system defects, found primarily at amorphous
interface layers. Reducing microwave loss from these interfaces by proper
surface treatments is key to push the device performance forward. Here, we
study niobium resonators after removing the native oxides with a hydrofluoric
acid etch. We investigate the reappearance of microwave losses introduced by
surface oxides that grow after exposure to the ambient environment. We find
that losses in quantum devices are reduced by an order of magnitude, with
internal Q-factors reaching up to 7 $\cdot$ 10$^6$ in the single photon regime,
when devices are exposed to ambient conditions for 16 min. Furthermore, we
observe that Nb2O5 is the only surface oxide that grows significantly within
the first 200 hours, following the extended Cabrera-Mott growth model. In this
time, microwave losses scale linearly with the Nb$_2$O$_5$ thickness, with an
extracted loss tangent tan$\delta$ = 9.9 $\cdot$ 10$^{-3}$. Our findings are of
particular interest for devices spanning from superconducting qubits,
quantum-limited amplifiers, microwave kinetic inductance detectors to single
photon detectors.",2012.10761v2
2021-01-26,Deterministic influence of substrate-induced oxygen vacancy diffusion on $Bi_{2}WO_{6}$ thin film growth,"In oxide epitaxy, the growth temperature and background oxygen partial
pressure are considered as the most critical factors that control the phase
stability of an oxide thin film. Here, we report an unusual case wherein
diffusion of oxygen vacancies from the substrate overpowers the growth
temperature and oxygen partial pressure to deterministically influence the
phase stability of $Bi_{2}WO_{6}$ thin film grown by the pulsed laser
deposition technique. We show that when grown on an oxygen-deficient
$SrTiO_{3}$ substrate, the $Bi_{2}WO_{6}$ film exhibits a mixture of (001) and
(100)/(010)-oriented domains alongside (001)-oriented impurity $WO_{3}$ phases.
The (100)/(010)-oriented $Bi_{2}WO_{6}$ phases form a self-organized 3D
nanopillar-structure, yielding a very rough film surface morphology. Oxygen
annealing of the substrate or using a few monolayer-thick $SrRuO_{3}$ as the
blocking layer for oxygen vacancy diffusion enables growing high-quality
single-crystalline $Bi_{2}WO_{6}$ (001) thin film exhibiting an atomically
smooth film surface with step-terrace structure. We propose that the large
oxide-ion conductivity of $Bi_{2}WO_{6}$ facilitates diffusion of oxygen
vacancies from the substrate during the film growth, accelerating the
evaporation of volatile Bismuth (Bi), which hinders the epitaxial growth. Our
work provides a general guideline for high-quality thin film growth of
Aurivillius compounds and other oxide-ion conductors containing volatile
elements.",2101.10559v1
2012-05-07,Uniform wafer-scale synthesis of graphene on evaporated Cu (111) film with quality comparable to exfoliated monolayer,"Monolayer graphene has been grown on crystallized Cu (111) films on standard
oxidized Si 100 mm wafers. The monolayer graphene demonstrates high uniformity
(>97% coverage), with immeasurable defects (>95% defect-negligible) across the
entire wafer. Key to these results is the phase transition of evaporated copper
films from amorphous to crystalline at the growth temperature as corroborated
by X-ray diffraction and electron backscatter diffraction. Noticeably, phase
transition of copper film is observed on technologically ubiquitous oxidized Si
wafer where the oxide is a standard amorphous thermal oxide. Ion mass
spectroscopy indicates that the copper films can be purposely hydrogen-enriched
during a hydrogen anneal which subsequently affords graphene growth with a sole
carbonaceous precursor for low defect densities. Owing to the strong hexagonal
lattice match, the graphene domains align to the Cu (111) domains, suggesting a
pathway for increasing the graphene grains by maximizing the copper grain
sizes. Fabricated graphene transistors on a flexible polyimide film yield a
peak carrier mobility ~4,930 cm2/Vs.",1205.1546v1
2017-05-17,Calibration of the NDHA model to describe N2O dynamics from respirometric assays,"The NDHA model comprehensively describes nitrous oxide (N2O) producing
pathways by both autotrophic ammonium oxidizing and heterotrophic bacteria. The
model was calibrated via a set of targeted extant respirometric assays using
enriched nitrifying biomass from a lab-scale reactor. Biomass response to
ammonium, hydroxylamine, nitrite and N2O additions under aerobic and anaerobic
conditions were tracked with continuous measurement of dissolved oxygen (DO)
and N2O. The sequential addition of substrate pulses allowed the isolation of
oxygen-consuming processes. The parameters to be estimated were determined by
the information content of the datasets using identifiability analysis. Dynamic
DO profiles were used to calibrate five parameters corresponding to endogenous,
nitrite oxidation and ammonium oxidation processes. The subsequent N2O
calibration was not significantly affected by the uncertainty propagated from
the DO calibration because of the high accuracy of the estimates. Five
parameters describing the individual contribution of three biological N2O
pathways were estimated accurately (variance/mean < 10% for all estimated
parameters). The NDHA model response was evaluated with statistical metrics
(F-test, autocorrelation function). The 95% confidence intervals of DO and N2O
predictions based on the uncertainty obtained during calibration are studied
for the first time. The measured data fall within the 95% confidence interval
of the predictions, indicating a good model description. Overall, accurate
parameter estimation and identifiability analysis of ammonium removal
significantly decreases the uncertainty propagated to N2O production, which is
expected to benefit N2O model discrimination studies and reliable full scale
applications.",1705.05962v1
2017-11-02,Non-equilibrium character of resistive switching and negative differential resistance in Ga-doped Cr2O3 system,"We have synthesized Ga-doped Cr2O3 system with compositions Cr1.45Ga0.55O3
and Cr1.17Ga0.83O3 by chemical co-precipitation route and post annealing at
800^C. The samples have been stabilized in rhombohedral crystal structure with
space group R3C. The present work focuses on the study of non-linear
current-voltage (I-V) characteristics of the samples, which exhibited many
interesting electronic properties, e.g., I-V loop, resistive switching,
bi-stable electronic states, and negative differential resistance. The
non-equilibrium character of the I-V characteristics has been studied by
measurement of bias voltage cycling up to 20 times and current relaxation with
time at set bias voltage. The charge conduction process in the samples has been
understood by analysing I-V curves using different phenomenological models
based on electrode-limited and bulk-limited charge conduction mechanisms
proposed for metal electrode-metal oxide-metal electrode (M-MO-M) junctions. It
is understood that competitions between injection of charge carriers from metal
electrode to metal oxide, charge flow through the material
(trapping/de-trapping and recombination of charge carriers at the defect
sites), space charge formation at the junctions of electrodes and metal oxides,
and ejection of electrons from metal oxide to metal electrode control the
non-equilibrium I-V characteristics in the present samples.",1711.00687v1
2018-03-29,Designing hybrid graphene oxide- gold nanoparticles for nonlinear optical response: Experiment and theory,"Nonlinear optical absorption of light by materials are weak due to its
perturbative nature, although a strong nonlinear response is of crucial
importance to applications in optical limiting and switching. Here we
demonstrate experimentally and theoretically an extremely efficient scheme of
excited state absorption by charge transfer between donor and acceptor
materials as the new method to enhance the nonlinear absorption by orders of
magnitude. With this idea, we have demonstrated strong excited state absorption
(ESA) in reduced graphene oxide that otherwise shows increased transparency at
high fluence and enhancement of ESA by one orders of magnitude in graphene
oxide by attaching gold nanoparticles (AuNP) in the tandem configuration that
acts as an efficient charge transfer pair when excited at the plasmonic
wavelength. To explain the unprecedented enhancement, we have developed a
five-level rate equation model based on the charge transfer between the two
materials and numerically simulated the results. To understand the correlation
of interfacial charge-transfer with the concentration and type of the
functional ligands attached to the graphene oxide sheet, we have investigated
the AuNP-graphene oxide interface with various possible ligand configurations
from first-principles calculations. By using the strong ESA of our hybrid
materials, we have fabricated liquid cell-based high-performance optical
limiters with important device parameters better than that of the benchmark
optical limiters.",1803.10919v1
2018-08-30,Facile synthesis of 2D graphene oxide sheet enveloping ultrafine 1D LiMn2O4 as interconnected framework to enhance cathodic property for Li-ion battery,"Cubic spinel lithium manganese oxide (LiMn2O4) has been able to attract a
great deal of attention over the years as a promising cathode material for
large scale lithium ion batteries. Here a facile hydrothermal route followed by
solid state reaction is developed using as grown ultrafine alpha-MnO2 nanorods
to prepare one dimensional LiMn2O4 with 10-50nm diameters. To enhance the
cathodic property of these nanorods, a unique synthesis technique of heat
treatment is developed to grow 2D graphene oxide sheet enveloping 1D LiMn2O4 as
interconnected framework. This nanocomposite 3D porous cathode exhibits a high
specific charge capacity of 130mAh/g at 0.05C rate and Coulombic efficiency of
about 98% after 100 cycles in the potential window of 3.5 to 4.3V versus Li/Li+
with promising initial charge capacity retention of about 87%, and outstanding
structural stability even after 100 cycles. Enhancement in the lithiation and
delithiation processes leading to improved performance is likely to have its
origin in the 2D conducting graphene oxide sheets. It allows for decreasing the
Mn dissolution, improve the electron conductivity and reduce the Li-ion path
diffusion inside the favourable morphology and crystallinity of the ultrafine
1D LiMn2O4 nanorods, giving rise to a promising cathode nanocomposite.",1808.10150v1
2019-01-30,Modelling functional properties of ferroelectric oxide thin films with a three-domain structure,"The properties of a ferroelectric, (001)-oriented, thin film clamped to a
substrate are investigated analytically and numerically. The emphasis is on the
tetragonal, polydomain, ferroelectric phase, using a three domain structure, as
is observed experimentally. The previously used, very restrictive set of
boundary conditions, arising from the domain walls, is relaxed, creating more
modes for energy relaxation. It is argued that this approach gives a more
realistic description of the clamped ferroelectric film.
  It is shown that for the ferroelectric oxides PbZr_(1-x)Ti_xO_3} the
tetragonal, polydomain phase is present over a wide range of substrate induced
strains for x_Ti>0.5, corresponding to the tetragonal side of the bulk phase
diagram. A polydomain, rhombohedral phase is present for x_Ti<0.5, at the bulk
rhombohedral side. Phase-temperature diagrams, and ferroelectric, dielectric
and piezoelectric properties, as well as lattice parameters, are calculated as
function of substrate induced strain and applied field. The analytical
formulation allows the decomposition of these properties into three different
causes: domain wall motion, field induced elastic effects and piezoelectric
effects. It is found that domain wall motion and polarization rotation of the
in-plane oriented domains under an applied field contribute most to the
properties, while the out-of-plane oriented domains hardly contribute.",1901.10883v2
2019-02-11,Determination of conduction and valence band electronic structure of LaTiOxNy thin film,"The nitrogen substitution into the oxygen sites of several oxide materials
leads to a reduction of the band gap to the visible light energy range, which
makes these oxynitride semiconductors potential photocatalysts for efficient
solar water splitting. Oxynitrides typically show a different crystal structure
compare to the pristine oxide material. Since the band gap is correlated to
both the chemical composition and the crystal structure, it is not trivial to
distinguish what modifications of the electronic structure induced by the
nitrogen substitution are related to compositional and/or structural effects.
Here, X-ray emission and absorption spectroscopy is used to investigate the
electronic structures of orthorhombic perovskite LaTiOxNy thin films in
comparison with films of the pristine oxide LaTiOx with similar orthorhombic
structure and cationic oxidation state. Experiment and theory show the expected
upward shift in energy of the valence band maximum that reduces the band gap as
a consequence of the nitrogen incorporation. But this study also shows that the
conduction band minimum, typically considered almost unaffected by the nitrogen
substitution, undergoes a significant downward shift in energy. For a rational
design of oxynitride photocatalysts the observed changes of both the unoccupied
and occupied electronic states have to be taken into account to justify the
total band gap narrowing induced by the nitrogen incorporation.",1902.03845v1
2019-02-12,Electronic band structure of ultimately thin silicon oxide on Ru(0001),"Silicon oxide can be formed in a crystalline form, when prepared on a
metallic substrate. It is a candidate support catalyst and possibly the
ultimately-thin version of a dielectric host material for two-dimensional
materials (2D) and heterostructures. We determine the atomic structure and
chemical bonding of the ultimately thin version of the oxide, epitaxially grown
on Ru(0001). In particular, we establish the existence of two sub-lattices
defined by metal-oxygen-silicon bridges involving inequivalent substrate sites.
We further discover four electronic bands below Fermi level, at high binding
energies, two of them forming a Dirac cone at K point, and two others forming
semi-flat bands. While the latter two correspond to hybridized states between
the oxide and the metal, the former relate to the topmost silicon-oxygen plane,
which is not directly coupled to the substrate. Our analysis is based on high
resolution X-ray photoelectron spectroscopy, angle-resolved photoemission
spectroscopy, scanning tunneling microscopy, and density functional theory
calculations.",1902.04514v1
2019-02-13,Strain Controlling Catalytic Efficiency of Water Oxidation for Ni1-xFexOOH alloy,"A catalyst surface may be exposed to strain due to application of load or
interfacing with a substrate with large lattice mismatch. In order to test the
effect of strain on catalytic efficiency, we use Density Functional Theory +U
(DFT+U) to model water oxidation on expanded and contracted surfaces of the
Ni1-xFexOOH alloy, one of the best known catalysts for water splitting. We find
that a low amount of iron content has a similar effect as of applying
compressive strain. Due to high oxidation state of Fe4+ at the active site, the
Fe-O bond is shorter than in pure FeOOH, which is beneficial for extracting
electrons from states delocalized on Fe and Ni atoms. At 33% of Fe content the
efficiency is even better since Fe3+ is at the active site and can easily
change oxidation state during the reaction. However, the efficiency drops at
higher iron percentages since the surface is unstable and may form FeOOH
aggregates. We find that the best performance is obtained at 33% iron content
and 5% expansion. Therefore, in addition to changing iron content, strain can
also be used as a control handle for improving water splitting catalysis.",1902.04788v1
2019-02-26,Bonding and oxidation protection of Ti${_2}$AlC and Cr${_2}$AlC for a Ni-based Superalloy,"Alumina forming, oxidation and thermal shock resistant MAX phases are of a
high interest for high temperature applications. Herein we report, on bonding
and resulting interactions between a Ni-based superalloy, NSA, and two alumina
forming MAX phases. The diffusion couples Cr${_2}$AlC/Inconel-718/Ti${_2}$AlC
were assembled and heated to 1000 or 1100{\deg}C in a vacuum hot press under
loads corresponding to stresses of either 2 MPa or 20 MPa. The resulting
interfaces were examined using X-ray diffraction, scanning electron microscopy
and energy-dispersive X-ray spectroscopy. Good bonding between Cr${_2}$AlC and
NSA was achieved after hot pressing at 1000{\deg}C and a contact pressure of
only 2 MPa; in the case of Ti${_2}$AlC a higher temperature (1100{\deg}C) and
pressure (20 MPa) were needed. In both cases, a diffusion bond was realized
with no evidence of interfacial damage or cracking after cooling to room
temperature. Twenty thermal cycles from room temperature to 1000{\deg}C showed
that Ti${_2}$AlC is a poor oxidation barrier for Inconel-718. However, in the
case of Cr${_2}$AlC no cracks, delamination nor surface degradation were
observed, suggesting that this material could be used to protect Inconel-718
from oxidation.",1902.10001v2
2019-04-03,Reproducible Performance Improvements to Monolayer MoS2 Transistors through Exposed Material Forming Gas Annealing,"Metal-mediated exfoliation has been demonstrated as a promising approach for
obtaining large-area flakes of 2D materials to fabricate prototypical
nanoelectronics. However, several processing challenges related to organic
contamination at the interfaces of the 2D material and the gate oxide must be
overcome to realize robust devices with high yield. Here, we demonstrate an
optimized process to realize high-performance field-effect transistor (FET)
arrays from large-area (~5000 um2) monolayer MoS2 with a yield of 85 %. A
central element of this process is an exposed material forming gas anneal
(EM-FGA) that results in uniform FET performance metrics (i.e., field-effect
mobilities, threshold voltages, and contact performance). Complementary
analytical measurements show that the EM-FGA process reduces deleterious
channel doping effects by decreasing organic contamination, while also reducing
the prevalence of insulating molybdenum oxide, effectively improving the
MoS2-gate oxide interface. The uniform FET performance metrics and high device
yield achieved by applying the EM-FGA technique on large-area 2D material
flakes will help advance the fabrication of complex 2D nanoelectronics devices
and demonstrates the need for improved engineering of the 2D material-gate
oxide interface.",1904.02189v1
2019-08-05,Antioxidant capacity is repeatable across years but does not consistently correlate with a marker of peroxidation in a free-living passerine bird,"Oxidative stress occurs when reactive oxygen species (ROS) exceed antioxidant
defences, which can have deleterious effects on cell function, health and
survival. Therefore, organisms are expected to finely regulate pro-oxidant and
antioxidant processes. ROS are mainly produced through aerobic metabolism and
vary in response to changes in energetic requirements, whereas antioxidants may
be enhanced, depleted or show no changes in response to changes in ROS levels.
We investigated the repeatability, within-individual variation and correlation
across different conditions of two plasmatic markers of the oxidative balance
in 1108 samples from 635 free-living adult collared flycatchers (Ficedula
albicollis). We sought to manipulate energy constraints by increasing wing load
in 2012 and 2013 and by providing additional food in 2014. We then tested the
relative importance of within- and between-individual variation on reactive
oxygen metabolites (ROMs), a marker of lipid and protein peroxidation, and on
non-enzymatic antioxidant defences (OXY test). We also investigated whether the
experimental treatments modified the correlation between markers. Antioxidant
defences were repeatable (range of repeatability estimates = 0.128--0.581),
whereas ROMs were not (0--0.061). Antioxidants varied neither between
incubation and nestling feeding nor between sexes. ROMs increased from
incubation to nestling feeding in females and were higher in females than
males. Antioxidant defences and ROM concentration were globally positively
correlated, but the correlation varied between experimental conditions and
between years. Hence, the management of oxidative balance in wild animals
appears flexible under variable environmental conditions, an observation which
should be confirmed over a wider range of markers.",1908.01488v1
2019-11-29,Negative ionic states of tin in the oxide superconductor Sr$_{3-x}$SnO revealed by Mössbauer spectroscopy,"We report the temperature variation of the $^{119}$Sn-M\""{o}ssbauer spectra
of the antiperovskite (inverse perovskite) oxide superconductor Sr$_{3-x}$SnO.
Both superconductive (Sr-deficient) and non-superconductive (nearly
stoichiometric) samples exhibit major $\gamma$-ray absorption with isomer shift
similar to that of Mg$_2$Sn. This fact shows that Sr$_{3-x}$SnO contains the
metallic anion Sn$^{4-}$, which is rare especially among oxides. In both
samples, we observed another $\gamma$-ray absorption with a larger isomer
shift, indicating that there is another ionic state of Sn with a higher
oxidation number. The temperature dependence of the absorption intensities
reveals that the Sn ions exhibiting larger isomer shifts have a lower energy of
the local vibration. The larger isomer shift and lower vibration energy are
consistent with the values estimated from the first-principles calculations for
hypothetical structures with various Sr-deficiency arrangements. Therefore, we
conclude that the additional $\gamma$-ray absorptions originate from the Sn
atoms neighboring the Sr deficiency.",1911.12934v1
2020-03-18,Pickling Behaviour of 2205 Duplex Stainless Steel Hot-rolled Strips in Sulfuric Acid Electrolytes,"Pickling behaviour of the oxide layer on hot-rolled 2205 duplex stainless
steel (DSS) was studied in H2SO4 solutions with electrolytic workstation.",2003.08174v1
2020-05-18,Strain-Induced Room-Temperature Ferroelectricity in SrTiO$_3$ Membranes,"Advances in complex oxide heteroepitaxy have highlighted the enormous
potential of utilizing strain engineering via lattice mismatch to control
ferroelectricity in thin-film heterostructures. This approach, however, lacks
the ability to produce large and continuously variable strain states, thus
limiting the potential for designing and tuning the desired properties of
ferroelectric films. Here, we observe and explore dynamic strain-induced
ferroelectricity in SrTiO$_3$ by laminating freestanding oxide films onto a
stretchable polymer substrate. Using a combination of scanning probe
microscopy, optical second harmonic generation measurements, and atomistic
modeling, we demonstrate robust room-temperature ferroelectricity in SrTiO$_3$
with 2.0% uniaxial tensile strain, corroborated by the notable features of
180{\deg} ferroelectric domains and an extrapolated transition temperature of
400 K. Our work reveals the enormous potential of employing oxide membranes to
create and enhance ferroelectricity in environmentally benign lead-free oxides,
which hold great promise for applications ranging from non-volatile memories
and microwave electronics.",2005.09101v1
2020-06-12,Probing Emergent Surface and Interfacial Properties in Complex Oxides via in situ X-ray Photoelectron Spectroscopy,"Emergent behavior at complex oxide interfaces has driven much of the research
in the oxide thin film community for the past twenty years. Interfaces have
been engineered for potential applications in spintronics, topological quantum
computing, and high-speed electronics in cases where the bulk materials would
not exhibit the desired properties. Advances in thin film growth have made the
synthesis of these interfaces possible, while surface characterization tools
such as X-ray photoelectron spectroscopy have been critical to understanding
surface and interfacial phenomena in these materials. In this review we discuss
the leading research in the oxide field over the past 5-10 years with a focus
on connecting the key results to the X-ray photoelectron spectroscopy studies
that enabled them. We describe how in situ integration of synthesis and
spectroscopy can be used to improve the film growth process and to perform
immediate experiments on specifically tailored interfacial heterostructures.
These studies can include determination of interfacial intermixing, valence
band alignment, and interfacial charge transfer. We also show how advances in
synchrotron-based spectroscopy techniques have answered questions that cannot
be addressed in a lab-based system. By further tying together synthesis and
spectroscopy through in situ techniques, we conclude by discussing future
opportunities in the field through the careful design of thin film
heterostructures that are optimized for X-ray studies.",2006.07492v1
2020-06-27,"Computational investigation of the plasmonic properties of TiN, ZrN, and HfN nanoparticles: The role of particle size, medium, and surface oxidation","Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong
plasmonic responses in the visible and near-infrared regimes, exhibit high
melting points and significant chemical stability and thus are potential
earth-abundant alternatives to Au and Ag based plasmonic applications. However,
a detailed understanding of the relationship between TMN NP properties and
plasmonic response is required to maximize their utility. In this study, the
localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction
of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN)
NPs were examined as a function of the particle size, surface oxidation, and
refractive index of the surrounding medium using finite element method (FEM). A
linear redshift in the LSPR frequency and a linear increase in the associated
full-width at half maximum (FWHM) was observed with increasing the particle
size, oxidation layer thickness, and medium refractive index. We show that the
effect of surface oxidation on plasmonic properties of TMN NPs is strongly
size-dependent with a significant LSPR redshift, intensity reduction, and
broadening in small NPs compared to larger NPs. Furthermore, the performance
and efficiency of HfN, ZrN, TiN as well as Au NPs for a narrowband application
- photothermal therapy (PTT), and a broadband application - solar energy
conversion, was investigated in detail. The results indicate that narrowband
and broadband photothermal performance of NPs strongly depend on the particle
size, surface properties and in case of narrowband absorption, excitation
wavelength.",2006.15246v1
2020-08-10,Extraordinarily Large Permittivity Modulation in Zinc Oxide for Dynamic Nanophotonics,"The dielectric permittivity of a material encapsulates the essential physics
of light-matter interaction into the material's local response to optical
excitation. Dynamic, photo-induced modulation of the permittivity can enable an
unprecedented level of control over the phase, amplitude, and polarization of
light. Therefore, the detailed dynamic characterization of technology-relevant
materials with substantially tunable optical properties and fast response times
is a crucial step in the realization of tunable optical devices. This work
reports on the extraordinarily large permittivity changes in zinc oxide thin
films (up to -3.6 relative change in the real part of the dielectric
permittivity at 1600 nm wavelength) induced by optically generated free
carriers. We demonstrate broadband reflectance modulation up to 70 percent in
metal-backed oxide mirrors at the telecommunication wavelengths, with
picosecond-scale relaxation times. The epsilon near zero points of the films
can be dynamically shifted from 8.5 microns to 1.6 microns by controlling the
pump fluence. Finally, we show that the modulation can be selectively enhanced
at specific wavelengths employing metal-backed ZnO disks while maintaining
picosecond-scale switching times. This work provides insights into the
free-carrier assisted permittivity modulation in zinc oxide and could enable
the realization of novel dynamic devices for beam-steering, polarizers, and
spatial light modulators.",2008.03896v1
2020-08-10,On-Stack Two-Dimensional Conversion of MoS2 into MoO3,"Chemical transformation of existing two-dimensional (2D) materials can be
crucial in further expanding the 2D crystal palette required to realize various
functional heterostructures. In this work, we demonstrate a 2D 'on-stack'
chemical conversion of single-layer crystalline MoS2 into MoO3 with a precise
layer control that enables truly 2D MoO3 and MoO3/MoS2 heterostructures. To
minimize perturbation of the 2D morphology, a nonthermal oxidation using O2
plasma was employed. The early stage of the reaction was characterized by a
defect-induced Raman peak, drastic quenching of photoluminescence (PL) signals
and sub-nm protrusions in atomic force microscopy images. As the reaction
proceeded from the uppermost layer to the buried layers, PL and optical second
harmonic generation signals showed characteristic modulations revealing a
layer-by-layer conversion. The plasma-generated 2D oxides, confirmed as MoO3 by
x-ray photoelectron spectroscopy, were found to be amorphous but extremely flat
with a surface roughness of 0.18 nm, comparable to that of 1L MoS2. The rate of
oxidation quantified by Raman spectroscopy decreased very rapidly for buried
sulfide layers due to protection by the surface 2D oxides, exhibiting a
pseudo-self-limiting behavior. As exemplified in this work, various on-stack
chemical transformations can be applied to other 2D materials in forming
otherwise unobtainable materials and complex heterostructures, thus expanding
the palette of 2D material building blocks.",2008.03926v1
2020-09-10,Solid-state Li-ion batteries operating at room temperature using new borohydride argyrodite electrolytes,"Using a new class of (BH4)- substituted argyrodite Li6PS5Z0.83(BH4)0.17, (Z =
Cl, I) solid electrolyte, Li-metal solid-state batteries operating at room
temperature have been developed. The cells were made by combining the modified
argyrodite with an In-Li anode and two types of cathode: an oxide, LixMO2 (M =
1/3Ni, 1/3Mn, 1/3Co; so called NMC) and a titanium disulfide, TiS2. The
performance of the cells was evaluated through galvanostatic cycling and
Alternating Current AC electrochemical impedance measurements. Reversible
capacities were observed for both cathodes for at least tens of cycles.
However, the high-voltage oxide cathode cell shows lower reversible capacity
and larger fading upon cycling than the sulfide one. The AC impedance
measurements revealed an increasing interfacial resistance at the cathode side
for the oxide cathode inducing the capacity fading. This resistance was
attributed to the intrinsic poor conductivity of NMC and interfacial reactions
between the oxide material and the argyrodite electrolyte. On the contrary, the
low interfacial resistance of the TiS2 cell during cycling evidences a better
chemical compatibility between this active material and substituted
argyrodites, allowing full cycling of the cathode material, 240 mAhg-1, for at
least 35 cycles with a coulombic efficiency above 97%.",2009.04779v1
2020-09-25,External control of GaN band bending using phosphonate self-assembled monolayers,"We report on the optoelectronic properties of GaN$(0001)$ and $(1\bar{1}00)$
surfaces after their functionalization with phosphonic acid derivatives. To
analyze the possible correlation between the acid's electronegativity and the
GaN surface band bending, two types of phosphonic acids, n-octylphosphonic acid
(OPA) and 1H,1H,2H,2H-perfluorooctanephosphonic acid (PFOPA), are grafted on
oxidized GaN$(0001)$ and GaN$(1\bar{1}00)$ layers as well as on GaN nanowires.
The resulting hybrid inorganic/organic heterostructures are investigated by
X-ray photoemission and photoluminescence spectroscopy. The GaN work function
is changed significantly by the grafting of phosphonic acids, evidencing the
formation of dense self-assembled monolayers. Regardless of the GaN surface
orientation, both types of phosphonic acids significantly impact the GaN
surface band bending. A dependence on the acids' electronegativity is, however,
only observed for the oxidized GaN$(1\bar{1}00)$ surface, indicating a
relatively low density of surface states and a favorable band alignment between
the surface oxide and acids' electronic states. Regarding the optical
properties, the covalent bonding of PFOPA and OPA on oxidized GaN layers and
nanowires significantly affect their external quantum efficiency, especially in
the nanowire case due to the large surface-to-volume ratio. The variation in
the external quantum efficiency is related to the modication of both the
internal electric fields and surface states. These results demonstrate the
potential of phosphonate chemistry for the surface functionalization of GaN,
which could be exploited for selective sensing applications.",2009.12089v1
2020-10-08,"Microstructure, mechanical properties, corrosion resistance and cytocompatibility of WE43 Mg alloy scaffolds fabricated by laser powder bed fusion for biomedical applications","Open-porous scaffolds of WE43 Mg alloy with a body-center cubic cell pattern
were manufactured by laser powder bed fusion with different strut diameters.
The geometry of the unit cells was adequately reproduced during additive
manufacturing and the porosity within the struts was minimized. The
microstructure of the scaffolds was modified by means of thermal solution and
ageing heat treatments and was analysed in detail by means of X-ray
microtomography, optical, scanning and transmission electron microscopy.
Moreover, the corrosion rates and the mechanical properties of the scaffolds
were measured as a function of the strut diameter and metallurgical condition.
The microstructure of the as-printed scaffolds contained a mixture of Y-rich
oxide particles and Rare Earth-rich intermetallic precipitates. The latter
could be modified by heat treatments. The lowest corrosion rates of 2-3 mm/year
were found in the as-printed and solution treated scaffolds and they could be
reduced to ~0.1 mm/year by surface treatments using plasma electrolytic
oxidation. The mechanical properties of the scaffolds improved with the strut
diameter: the yield strength increased from 8 to 40 MPa and the elastic modulus
improved from 0.2 to 0.8 GPa when the strut diameter increased from 275 \mu m
to 800 \mu m. Nevertheless, the strength of the scaffolds without plasma
electrolytic oxidation treatment decreased rapidly when immersed in simulated
body fluid. In vitro biocompatibility tests showed surface treatments by plasma
electrolytic oxidation were necessary to ensure cell proliferation in scaffolds
with high surface-to-volume ratio.",2010.03812v1
2020-10-12,Laser Assisted Solution Synthesis of High Performance Graphene Supported Electrocatalysts,"Simple, yet versatile, methods to functionalize graphene flakes with metal
(oxide) nanoparticles are in demand, particularly for the development of
advanced catalysts. Herein, based on light-induced electrochemistry, a
laser-assisted, continuous, solution route for the simultaneous reduction and
modification of graphene oxide with catalytic nanoparticles is reported.
Electrochemical graphene oxide (EGO) is used as starting material and
electron-hole pair source due to its low degree of oxidation, which imparts
structural integrity and an ability to withstand photodegradation. Simply
illuminating a solution stream containing EGO and metal salt (e.g., H2PtCl6 or
RuCl3) with a 248 nm wavelength laser produces reduced EGO (rEGO, oxygen
content 4.0 at%) flakes, decorated with Pt (~2.0 nm) or RuO2 (~2.8 nm)
nanoparticles. The RuO2-rEGO flakes exhibit superior catalytic activity for the
oxygen evolution reaction, requiring a small overpotential of 225 mV to reach a
current density of 10 mA cm-2. The Pt-rEGO flakes (10.2 wt% of Pt) show
enhanced mass activity for the hydrogen evolution reaction, and similar
performance for oxygen reduction reaction compared to a commercial 20 wt% Pt/C
catalyst. This simple production method is also used to deposit PtPd alloy and
MnOx nanoparticles on rEGO, demonstrating its versatility in synthesizing
functional nanoparticle-modified graphene materials.",2010.05556v1
2020-10-16,Towards the surface hydroxyl species in CeO$_2$ nanoparticles,"Understanding the complex chemistry of functional nanomaterials is of
fundamental importance. Controlled synthesis and characterization at the atomic
level is essential to gain deeper insight into the unique chemical reactivity
exhibited by many nanomaterials. Cerium oxide nanoparticles have many
industrial and commercial applications,resulting from very strong catalytic,
pro-and anti-oxidant activity. However, the identity of the active species and
the chemical mechanisms imparted by nanoceria remain elusive, impeding the
further development of new applications. Here, we explore the behavior of
cerium oxide nanoparticles of different sizes at different temperatures and
trace the electronic structure changes by state-of-the-art soft and hard X-ray
experiments combined with computational methods. We confirm the absence of the
Ce(III) oxidation state at the surface of CeO2nanoparticles, even for particles
as small as 2 nm. Synchrotron X-ray absorption experiments at Ce L3and M5edges,
combined with X-ray diffraction (XRD), high-resolution transmission electron
microscopy (HRTEM) and small angle X-ray scattering (SAXS) and theoretical
calculations demonstrate that in addition to the nanoceria charge stability,
the formation of hydroxyl groups at the surface profoundly affects the chemical
performance of these nanomaterials",2010.08206v1
2020-11-02,Boron Nitride and Oxide Supported on Dendritic Fibrous Nanosilica for Catalytic Oxidative Dehydrogenation of Propane,"In this work, we were able to significantly increase the activity of boron
nitride catalysts used for the oxidative dehydrogenation (ODH) of propane by
designing and synthesising boron nitride (BN) supported on dendritic fibrous
nanosilica (DFNS). DFNS/BN showed a markedly increased catalytic efficiency,
accompanied by exceptional stability and selectivity. Textural characterisation
together with solid-state NMR and X-ray photoelectron spectroscopic analyses
indicate the presence of a combination of unique fibrous morphology of DFNS and
various boron sites connected to silica to be the reason for this increase in
the catalytic performance. Notably, DFNS/B${}_2$O${}_3$ also showed catalytic
activity, although with more moderate selectivity compared to that of DFNS/BN.
Solid-state NMR spectra indicates that the higher selectivity of DFNS/BN might
stem from a larger amount of hydrogen-bonded hydroxyl groups attached to B
atoms. This study indicates that both boron nitride and oxide are active
catalysts and by using high surface area support (DFNS), conversion from
propane to propene as well as productivity of olefins was significantly
increased.",2011.00831v1
2020-11-13,A physical method for investigating defect chemistry in solid metal oxides,"The investigation of the defect chemistry of solid oxides is of central
importance for the understanding of redox processes. This can be performed by
measuring conductivity as a function of the oxygen partial pressure, which is
conventionally established by using buffer gas mixtures or oxygen pumps based
on zirconia. However, this approach has some limitations, such as difficulty
regulating oxygen partial pressure in some intermediate-pressure regions or the
possibility of influencing the redox process by gases that can also be
incorporated into the oxide or react with the surface via heterogeneous
catalysis. Herein, we present an alternative physical method in which the
oxygen partial pressure is controlled by dosing pure oxygen inside an
ultra-high vacuum chamber. To monitor the conductivity of the oxide under
investigation, we employ a dedicated four-probe measurement system that relies
on the application of a very small AC voltage, in combination with lock-in data
acquisition using highly sensitive electrometers, minimizing the
electrochemical polarization or electro-reduction and degradation effects. By
analyzing the model material SrTiO3, we demonstrate that its characteristic
redox behavior can be reproduced in good agreement with the theory when
performing simultaneous electrical conductivity relaxation (ECR) and
high-temperature equilibrium conductivity (HTEC) measurements. We show that the
use of pure oxygen allows for a direct analysis of the characteristic oxygen
dose, which opens up various perspectives for a detailed analysis of the
surface chemistry of redox processes.",2011.06877v1
2020-11-26,A two-dimensional electron gas based on a 5s oxide with high room-temperature mobility and strain sensitivity,"The coupling of optical and electronic degrees of freedom together with
quantum confinement in low-dimensional electron systems is particularly
interesting for achieving exotic functionalities in strongly correlated oxide
electronics. Recently, high room-temperature mobility has been achieved for a
large bandgap transparent oxide - BaSnO$_3$ upon extrinsic La or Sb doping,
which has excited significant research attention. In this work, we report the
observation of room-temperature ferromagnetism in BaSnO$_3$ thin films and the
realization of a two-dimensional electron gas (2DEG) on the surface of
transparent BaSnO$_3$ via oxygen vacancy creation, which exhibits a high
carrier density of $\sim 7.72*10^{14} /{\rm cm}^2$ and a high room-temperature
mobility of ~18 cm$^2$/V/s. Such a 2DEG is rather sensitive to strain and a
less than 0.1% in-plane biaxial compressive strain leads to a giant resistance
enhancement of 350% (more than 540 kOhm/Square) at room temperature. Thus, this
work creates a new path to exploring the physics of low-dimensional oxide
electronics and devices applicable at room temperature.",2011.13106v2
2020-11-25,Contrary Effect of B and N Doping into Graphene and Graphene Oxide Heterostructures with MoS$_2$ on Interface Function and Hydrogen Evolution,"Molybdenum disulfide (MoS$_2$) attracts attention as a high efficient and low
cost photocatalyst for hydrogen production, but suffers from low conductance
and high recombination rate of photo-generated charge carriers. In this work,
we investigate the MoS$_2$ heterostructures with graphene variants (GVs),
including graphene, graphene oxide, and their boron- and nitrogen-doped
variants, by using first-principles calculations. Systematic comparison between
graphene and graphene oxide composites is performed, and contrary effect of B
and N doping on interface function and hydrogen evolution is clarified. We find
that upon the formation of the interfaces some amount of electronic charge
transfers from the GV side to the MoS$_2$ layer, inducing the creation of
interface dipole and the reduction of work function, which is more pronounced
in the graphene oxide composites. Moreover, our results reveal that N doping
enhances the interface functions by forming donor-type interface states,
whereas B doping reduces those functions by forming acceptor-type interface
states. However, the B-doped systems exhibit lower Gibbs free energy difference
for hydrogen adsorption on GV side than the N-doped systems, which deserves
much consideration in the design of new functional photocatalysts.",2011.14000v1
2021-02-12,Atomic scale mechanisms controlling the oxidation of polyethylene: a first principles study,"Understanding the degradation mechanisms of aliphatic polymers by thermal
oxidation and radio-oxidation is very important in order to assess their
lifetime in a variety of industrial applications. We focus here on polyethylene
as a prototypical aliphatic polymer. Kinetic models describing the time
evolution of the concentration of chain defects and radicals species in the
material identify a relevant step in the formation and subsequent decomposition
of transient hydroperoxides species, finally leading to carbonyl defects, in
particular ketones. In this paper we first summarize the most relevant
mechanistic paths proposed in the literature for hydroperoxide formation and
decomposition and, second, revisit them using first principles calculations
based on Density Functional Theory (DFT). We investigate the reaction paths for
several chemical reactions, for both isolated alkane molecules and a
crystalline model of polyethylene, and confirm, in some cases, the accepted
activation energies; in some other cases, we challenge the accepted view
finding alternative, more favourable, reaction paths for which we estimate the
activation energy. We highlight the infuence of the environment -- crystalline
or not -- on the outcome of some of the studied chemical reactions. A
remarkable results of our calculations is that hydroxyl radicals play an
important role in the decomposition of hydroperoxides. Based on our findings,
it should be possible to improve the set of equations and parameters used in
current kinetic simulations of polyethylene radio-oxidation.",2102.06397v2
2021-02-16,Mesospheric nitric oxide model from SCIAMACHY data,"We present an empirical model for nitric oxide NO in the mesosphere
($\approx$60--90 km) derived from SCIAMACHY (SCanning Imaging Absorption
spectroMeter for Atmospheric CHartoghraphY) limb scan data. This work
complements and extends the NOEM (Nitric Oxide Empirical Model; Marsh et al.,
2004) and SANOMA (SMR Acquired Nitric Oxide Model Atmosphere; Kiviranta et al.,
2018) empirical models in the lower thermosphere. The regression ansatz builds
on the heritage of studies by Hendrickx et al. (2017) and the superposed epoch
analysis by Sinnhuber et al. (2016) which estimate NO production from particle
precipitation.
  Our model relates the daily (longitudinally) averaged NO number densities
from SCIAMACHY (Bender et al., 2017a, b) as a function of geomagnetic latitude
to the solar Lyman-alpha and the geomagnetic AE (auroral electrojet) indices.
We use a non-linear regression model, incorporating a finite and seasonally
varying lifetime for the geomagnetically induced NO. We estimate the parameters
by finding the maximum posterior probability and calculate the parameter
uncertainties using Markov chain Monte Carlo sampling. In addition to providing
an estimate of the NO content in the mesosphere, the regression coefficients
indicate regions where certain processes dominate.",2102.08455v1
2021-02-27,Ion-Beam Modification of Metastable Gallium Oxide Polymorphs,"Gallium oxide with a corundum structure ({\alpha}-Ga2O3) has recently
attracted great attention in view of electronic and photonic applications due
to its unique properties including a wide band gap exceeding that of the most
stable beta phase (\b{eta}-Ga2O3). However, the lower thermal stability of the
{\alpha}-phase at ambient conditions in comparison with the \b{eta}-phase
requires careful investigation of its resistance to other external influences
such as ion irradiation, ion doping, etc. In this work, the structural changes
under the action of Al+ ion irradiation have been investigated for a
polymorphic gallium oxide layers grown by hydride vapor phase epitaxy on
c-plane sapphire and consisting predominantly of {\alpha}-phase with inclusions
of {\alpha}(\k{appa})-phase. It is established by the X-ray diffraction
technique that inclusions of {\alpha}(\k{appa})-phase in the irradiated layer
undergo the expansion along the normal to the substrate surface, while there is
no a noticeable deformation for the {\alpha}-phase. This speaks in favor of the
different radiation tolerance of various Ga2O3 polymorphs, especially the
higher radiation tolerance of the {\alpha}-phase. This fact should be taken
into account when utilizing ion implantation to modify gallium oxide properties
in terms of development of efficient doping strategies.",2103.00317v1
2021-04-19,Bipolar conduction and giant positive magnetoresistance in doped metallic titanium oxide heterostructures,"Empowering conventional materials with unexpected magnetoelectric properties
is appealing to the multi-functionalization of existing devices and the
exploration of future electronics. Recently, owing to its unique effect in
modulating a matter's properties, ultra-small dopants, e.g. H, D, and Li,
attract enormous attention in creating emergent functionalities, such as
superconductivity, and metal-insulator transition. Here, we report an
observation of bipolar conduction accompanied by a giant positive
magnetoresistance in D-doped metallic Ti oxide (TiOxDy) films. To overcome the
challenges in intercalating the D into a crystalline oxide, a series of TiOxDy
were formed by sequentially doping Ti with D and surface/interface oxidation.
Intriguingly, while the electron mobility of the TiOxDy increases by an order
of magnitude larger after doping, the emergent holes also exhibit high
mobility. Moreover, the bipolar conduction induces a giant magnetoresistance up
to 900% at 6 T, which is ~6 times higher than its conventional phase. Our study
paves a way to empower conventional materials in existing electronics and
induce novel electronic phases.",2104.09322v1
2021-07-14,Electrical and Thermal Property of Si/GaAs Heterojunction Formed by Ultra-Thin Oxide Interfacial Layer,"We have successfully demonstrated Si/GaAs p-n heterostructures using Al2O3
ultra-thin oxide interfacial layers. The band diagram and band offsets were
investigated using X-ray photoelectron spectroscopy and confirm a small
discontinuity in the conduction band (0.03 eV) at the interface. The interface
defect density (Dit) values of the heterointerface with different ultra-thin
oxide (UO) thicknesses ranged from 0.35 nm to 3.5 nm and were also
characterized based on a metal-oxide-semiconductor capacitor (MOSCAP) structure
using a capacitance-voltage measurement. The results revealed that a thin UO
interfacial layer (around 1 nm) maximizes carrier transport property due to
better surface passivation and efficient tunneling properties. Thermal property
investigation also shows that the Al2O3 UO interfacial layer offers a good
tunneling layer but also facilitates phonon transport across the interface.
Finally, the electrical characterization of Si/GaAs heterojunction p-n diodes
confirms reliable rectifying behavior with an extremely low ideality factor;
thus, heterogeneous integration using the UO approach offers a robust way to
create more types of heterojunctions between dissimilar semiconductors.",2107.06983v2
2021-07-20,"The role of etching anisotropy in the fabrication of freestanding oxide microstructures on SrTiO3(100), SrTiO3(110), and SrTiO3(111) substrates","The release process for the fabrication of freestanding oxide microstructures
relies on appropriate, controllable and repeatable wet etching procedures.
SrTiO3 is among the most employed substrates for oxide thin films growth and
can be decomposed in HF:water solution. Such process is strongly anisotropic
and is affected by local defects and substrate cut-plane. We analyze the
etching behavior of SrTiO3 substrates having (100), (110), and (111) cut-planes
during immersion in a 5% HF:water solution. The etching process over the three
substrates is compared in terms of pitting, anisotropy, macroscopic etch rate
and underetching effects around HF-resistant (La,Sr)MnO3 thin film
micropatterns. The release of targeted structures, such as the reported
(La,Sr)MnO3 freestanding microbridges, depends on the substrate
crystallographic symmetry and on the in-plane orientation of the structures
themselves along the planar directions. By comparing the etching evolution at
two different length scales, we distinguish two regimes for the propagation of
the etching front: an intrinsic one, owning to a specific lattice direction,
and a macroscopic one, resulting from the mixing of different etching fronts.
We report the morphologies of the etched SrTiO3 surfaces and the geometries of
the underetched regions as well as of the microbridge clamping zones. The
reported analysis will enable the design of complex MEMS devices by allowing to
model the evolution of the etching process required for the release of
arbitrary structures made of oxide thin films deposited on top of STO.",2107.09441v1
2021-09-23,Observation of metallic electronic structure in a single-atomic-layer oxide,"Correlated electrons in transition metal oxides (TMOs) exhibit a variety of
emergent phases. When TMOs are confined to a single-atomic-layer thickness,
experiments so far have shown that they usually lose diverse properties and
become insulators. In an attempt to extend the range of electronic phases of
the single-atomic-layer oxide, we search for a metallic phase in a
monolayer-thick epitaxial SrRuO$_3$ film. Combining atomic-scale epitaxy and
angle-resolved photoemission measurements, we show that the monolayer SrRuO$_3$
is a strongly correlated metal. Systematic investigation reveals that the
interplay between dimensionality and electronic correlation makes the monolayer
SrRuO$_3$ an incoherent metal with orbital-selective correlation. Furthermore,
the unique electronic phase of the monolayer SrRuO$_3$ is found to be highly
tunable, as charge modulation demonstrates an incoherent-to-coherent crossover
of the two-dimensional metal. Our work emphasizes the potentially rich phases
of single-atomic-layer oxides and provides a guide to the manipulation of their
two-dimensional correlated electron systems.",2109.11090v1
2021-09-29,An Idealised Approach of Geometry and Topology to the Diffusion of Cations in Honeycomb Layered Oxide Frameworks,"Honeycomb layered oxides are a novel class of nanostructured materials
comprising alkali or alkaline earth metals intercalated into transition metal
slabs. The intricate honeycomb architecture and layered framework endows this
family of oxides with a tessellation of features such as exquisite
electrochemistry, unique topology and fascinating electromagnetic phenomena.
Despite having innumerable functionalities, these materials remain highly
underutilized as their underlying atomistic mechanisms are vastly unexplored.
Therefore, in a bid to provide a more in-depth perspective, we propose an
idealised diffusion model of the charged alkali cations (such as lithium,
sodium or potassium) in the two-dimensional (2D) honeycomb layers within the
three-dimensional (3D) crystal of honeycomb layered oxide frameworks. This
model not only explains the correlation between the excitation of cationic
vacancies (by applied electromagnetic fields) and the Gaussian curvature
deformation of the 2D surface, but also takes into consideration, the quantum
properties of the cations and their inter-layer mixing through quantum
tunnelling. Through this work, we offer a novel theoretical framework for the
study of 3D layered materials with 2D cationic diffusion currents, as well as
providing pedagogical insights into the role of topological phase transitions
in these materials in relation to Brownian motion and quantum geometry.",2109.14679v1
2021-10-19,Generalized estimates for the density of oxide scale in the range from 0 C to 1300 C,"Oxide scale formed on the surface of steel products during high-teperature
processes is studied as a composite material, the main solid components of
which, in general, are wustite, magnetite, hematite and metallic iron. To
estimate the density of each of these components in the temperature range from
0 C to 1300 C, formulas are proposed that are consistent with the empirical
functions of the coefficient of linear thermal expansion, which the authors
obtained earlier by generaizing data from open sources. The Curie and
polymorphic transformation temperatures are included in these generalized
formulas as variable parameters, which allows one to take into account the
movability of phase transitions due to impurities, crystal lattice defects,
particle sizes, cooling rate, and other factors. When specifying the particular
values of critical temperatures, the other parameters of the formulas are
recalculated automatically. In a particular form, the proposed formulas
correspond to the basic values of critical temperatures. According to the
calculation examples given, the true (not including pores) density of oxide
scale can be about 5200 to 5600 kg/m3, depending on the temperature and
percentage of components, whereby a local density minimum may be observed in
the region of 570 C due to eutectoid decomposition of wustite into magnetite
and iron. The proposed methods are recommended for use in mathematical
simulation of processing of steel products in the presence of oxide scale on
its surface.",2110.09791v1
2021-12-01,Oxygen and Aluminum-Magnesium Isotopic Systematics of Presolar Nanospinel Grains from CI Chondrite Orgueil,"Presolar oxide grains have been previously divided into several groups (Group
1 to 4) based on their isotopic compositions, which can be tied to several
stellar sources. Much of available data was acquired on large grains, which may
not be fully representative of the presolar grain population present in
meteorites. We present here new O isotopic data for 74 small presolar oxide
grains (~200 nm in diameter on average) from Orgueil and Al-Mg isotopic
systematics for 25 of the grains. Based on data-model comparisons, we show that
(i) Group 1 and Group 2 grains more likely originated in low-mass first-ascent
(red giant branch; RGB) and/or second-ascent (asymptotic giant branch; AGB) red
giant stars and (ii) Group 1 grains with (26Al/27Al)0 >= 5x10^-3 and Group 2
grains with (26Al/27Al)0 <= 1x10^-2 all likely experienced extra circulation
processes in their parent low-mass stars but under different conditions,
resulting in proton-capture reactions occurring at enhanced temperatures. We do
not find any large 25Mg excess in Group 1 oxide grains with large 17O
enrichments, which provides evidence that 25Mg is not abundantly produced in
low-mass stars. We also find that our samples contain a larger proportion of
Group 4 grains than so far suggested in the literature for larger presolar
oxide grains (~400 nm). We also discuss our observations in the light of
stellar dust production mechanisms.",2112.00512v1
2021-12-09,Comparative studies of hydrogen dissolution and release behavior in zirconate oxides by TDS and TMAP4 analysis,"Proton-conducting oxides are potential materials for electrochemical devices
such as fuel cells, hydrogen pumps, hydrogen sensors, and the tritium
purification and recovery system in nuclear fusion reactors. The hydrogen
concentration in oxide materials is important, but its precise measurement is
difficult. In this study, thermal desorption spectroscopy (TDS) was used to
investigate hydrogen dissolution and release behavior in proton-conducting
oxides, yttrium (Y), and cobalt (Co) doped barium-zirconates in the temperature
range of 673-1273 K using deuterium (D2) and heavy water (D2O). Specimens were
prepared with conventional powder metallurgy: the powder of three zirconates,
BaZr0.9Y0.1O3-a (BZY), BaZr0.955Y0.03Co0.015O3-a (BZYC), and CaZr0.9In0.1O2.95
(CZI) was pressed into discs and fired in the air at 1873 K for 20 h. The
densities of the sintered BZY, BZYC, and CZI specimens were 98 percent, 99.7
percent, and 99.5 percent of the theoretical densities respectively. XRD, SEM,
and EDX were performed for the structural and morphological analysis of the
sintered samples. From TDS measurement, a similar trend of
temperature-dependent hydrogen solubility was obtained for all samples compared
to the tritium imaging plate (TIP) methods literature data of HT- and
DTO-exposed samples. To compare the experimental results of the deuterium
desorption profile derived by TDS analysis, the simulation code of the tritium
migration analysis program, version 4 (TMAP4) was employed.",2112.04649v1
2021-12-18,Nitrogen incorporated Zinc oxide thin film for efficient ethanol detection,"Zinc oxide which is a n-type semiconducting metal oxide (SMO) has been a
promising material for detecting ethanol vapor. However, pure ZnO based ethanol
sensors often suffer from high working temperature, cross sensitivity towards
methanol and poor stability against humidity. Doping ZnO with various metal
ions has been widely explored as a proficient approach to improve its ethanol
sensing properties, while anionic dopants have been rarely considered. Here in
we demonstrate the effect of nitrogen doping on the ethanol sensing
characteristics of ZnO thin films. Nitrogen doped ZnO (N-ZnO) thin films have
been synthesized following sol-gel technique with urea as nitrogen precursor.
Ethanol sensing characteristics of the N-ZnO thin film has been com-pared with
pure ZnO sensor over a wide range of temperature and relative humidity
conditions. The N-ZnO sensor exhibits significantly large ethanol sensing
response at a lower operating temperature (~99 % at 225 {\deg}C vs ~81 % at 250
{\deg}C for ZnO), faster response time (12 s vs 33 s for ZnO), long term
stability, improved resilience against humidity and selectivity towards ethanol
over methanol and acetone. The experimental observations have been supplemented
by estimating the adsorption energies of ethanol on ZnO and N-ZnO surface using
density functional theory (DFT) calculations. We discuss that the microscopic
origin of improved ethanol sensing of N-ZnO is related to the facile adsorption
of ethanol molecules on the oxide surface which is promoted by modification of
electronic properties of ZnO by the nitrogen dopant atoms.",2112.09889v1
2022-02-22,Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films,"We report the measurement of efficient charge-to-spin conversion at room
temperature in Weyl semimetal/ferromagnet heterostructures with both oxidized
and pristine interfaces. Polycrystalline films of the Weyl semimetal, TaAs, are
grown by molecular beam epitaxy on (001) GaAs and interfaced with a metallic
ferromagnet (Ni$_{0.8}$Fe$_{0.2}$). Spin torque ferromagnetic resonance
(ST-FMR) measurements in samples with an oxidized interface yield a spin torque
efficiency as large as $\xi_{\mathrm{FMR}}=0.45\pm 0.25$ for a 8 nm
Ni$_{0.8}$Fe$_{0.2}$ layer thickness. By studying ST-FMR in these samples with
varying Ni$_{0.8}$Fe$_{0.2}$ layer thickness, we extract a damping-like torque
efficiency as high as $\xi_{\mathrm{DL}}=1.36\pm 0.66$. In samples with a
pristine (unoxidized) interface, the spin torque efficiency has opposite sign
to that observed in oxidized samples ($\xi_{\mathrm{FMR}}=-0.27\pm 0.14$ for a
5 nm Ni$_{0.8}$Fe$_{0.2}$ layer thickness). We also find a lower bound on the
spin Hall conductivity ($424 \pm 110 \frac{\hbar}{e}$ S/cm) which is
surprisingly consistent with theoretical predictions for the single crystal
Weyl semimetal state of TaAs.",2202.10656v1
2022-02-22,Toward Functionalized Ultrathin Oxide Films: the Impact of Surface Apical Oxygen,"Thin films of transition metal oxides open up a gateway to nanoscale
electronic devices beyond silicon characterized by novel electronic
functionalities. While such films are commonly prepared in an oxygen
atmosphere, they are typically considered to be ideally terminated with the
stoichiometric composition. Using the prototypical correlated metal SrVO$_3$ as
an example, it is demonstrated that this idealized description overlooks an
essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen
adatoms, which persist even in an ultrahigh vacuum environment, are shown to
severely affect the intrinsic electronic structure of a transition metal oxide
film. Their presence leads to the formation of an electronically dead surface
layer but also alters the band filling and the electron correlations in the
thin films. These findings highlight that it is important to take into account
surface apical oxygen or -- mutatis mutandis -- the specific oxygen
configuration imposed by a capping layer to predict the behavior of ultrathin
films of transition metal oxides near the single unit-cell limit.",2202.10778v1
2022-03-14,Emergent dynamics in an astrocyte-neuronal network coupled via nitric oxide,"In the brain, both neurons and glial cells work in conjunction with each
other during information processing. Stimulation of neurons can cause calcium
oscillations in astrocytes which in turn can affect neuronal calcium dynamics.
The ""glissandi"" effect is one such phenomenon, associated with a decrease in
infraslow fluctuations, in which synchronized calcium oscillations propagate as
a wave in hundreds of astrocytes. Nitric oxide molecules released from the
astrocytes contribute to synaptic functions on the basis of the underlying
astrocyte-neuron interaction network. In this study, by defining an
astrocyte-neuronal (A-N) unit as an integrated circuit of one neuron and one
astrocyte, we developed a minimal model of neuronal stimulus-dependent and
nitric oxide-mediated emergence of calcium waves in astrocytes. Incorporating
inter-unit communication via nitric oxide molecules, a coupled network of 1,000
such A-N units is developed in which multiple stable regimes were found to
emerge in astrocytes. We examined the ranges of neuronal stimulus strength and
the coupling strength between A-N units that give rise to such dynamical
behaviors. We also report that there exists a range of coupling strength,
wherein units not receiving stimulus also start showing oscillations and become
synchronized. Our results support the hypothesis that glissandi-like phenomena
exhibiting synchronized calcium oscillations in astrocytes help in efficient
synaptic transmission by reducing the energy demand of the process.",2203.07193v1
2022-03-26,Tailoring the Thickness-Dependent Optical Properties of Conducting Nitrides and Oxides for Epsilon-Near-Zero-Enhanced Photonic Applications,"The unique properties of the emerging photonic materials - conducting
nitrides and oxides - especially their tailorability, large damage thresholds,
and the so-called epsilon-near-zero (ENZ) behavior, have enabled novel photonic
phenomena spanning optical circuitry, tunable metasurfaces, and nonlinear
optical devices. This work explores direct control of the optical properties of
polycrystalline titanium nitride (TiN) and aluminum-doped zinc oxide (AZO) by
tailoring the film thickness, and their potential for ENZ-enhanced photonic
applications. We demonstrate that TiN-AZO bilayers act as Ferrell-Berreman
metasurfaces with thickness-tailorable epsilon-near-zero resonances in the AZO
films operating in the telecom wavelengths spanning from 1470 to 1750 nm. The
bilayer stacks also act as strong light absorbers in the ultraviolet regime
employing the radiative ENZ modes and the Fabry-Perot modes in the constituent
TiN films. The studied Berreman metasurfaces exhibit optically-induced
reflectance modulation of 15% with picosecond response-time. Together with the
optical response tailorability of conducting oxides and nitrides, utilizing the
field-enhancement near the tunable ENZ regime could enable a wide range of
nonlinear optical phenomena, including all-optical switching, time refraction,
and high-harmonic generation.",2203.14170v1
2022-04-07,Graphene oxide 2D films integrated with nanowires and ring resonators for enhanced nonlinear optics,"We report enhanced nonlinear optics in nanowires, waveguides, and ring
resonators by introducing layered two-dimensional (2D) graphene oxide (GO)
films through experimental demonstration. The GO films are integrated on
silicon-on-insulator nanowires (SOI), high index doped silica glass, and
silicon nitride (SiN) waveguides and microring resonators (MRRs), to
demonstrate an improved optical nonlinearity including Kerr nonlinearity and
four-wave mixing (FWM). By using a large-area, transfer-free, layer-by-layer GO
coating method with photolithography and lift-off processes, we integrate GO
films on these complementary metal-oxide-semiconductor (CMOS)-compatible
devices. For SOI nanowires, significant spectral broadening of optical pulses
in GO-coated SOI nanowires induced by self-phase modulation (SPM) is observed,
achieving a high spectral broadening factor of 4.34 for a device with a
patterned film including 10 layers of GO. A significant enhancement in the
nonlinear figure of merit (FOM) for silicon nanowires by a factor of 20 is also
achieved, resulting in a FOM > 5. For Hydex and SiN waveguides, enhanced FWM in
the GO-coated waveguides is achieved, where conversion efficiency (CE)
enhancements of up to 6.9 dB and 9.1 dB relative to the uncoated waveguides.
For MRRs, an increase of up to ~10.3 dB in the FWM CE is achieved due to the
resonant enhancement effect. These results reveal the strong potential of GO
films to improve the nonlinear optics of nanowires, waveguides, and ring
resonators.",2204.03184v1
2022-04-14,Non-equilibrium Phonon Thermal Resistance at MoS2/Oxide and Graphene/Oxide Interfaces,"Accurate measurements and physical understanding of thermal boundary
resistance (R) of two-dimensional (2D) materials are imperative for effective
thermal management of 2D electronics and photonics. In previous studies, heat
dissipation from 2D material devices was presumed to be dominated by phonon
transport across the interfaces. In this study, we find that in addition to
phonon transport, thermal resistance between non-equilibrium phonons in the 2D
materials could play a critical role too when the 2D material devices are
internally self-heated, either optically or electrically. We accurately measure
R of oxide/MoS2/oxide and oxide/graphene/oxide interfaces for three oxides
(SiO2, HfO2, Al2O3) by differential time-domain thermoreflectance (TDTR). Our
measurements of R across these interfaces with external heating are 2-to-4
times lower than previously reported R of the similar interfaces measured by
Raman thermometry with internal self-heating. Using a simple model, we show
that the observed discrepancy can be explained by an additional internal
thermal resistance (Rint) between non-equilibrium phonons present during Raman
measurements. We subsequently estimate that for MoS2 and graphene, Rint is
about 31 and 22 m2 K/GW, respectively. The values are comparable to the thermal
resistance due to finite phonon transmission across interfaces of 2D materials
and thus cannot be ignored in the design of 2D material devices. Moreover, the
non-equilibrium phonons also lead to a different temperature dependence than
that by phonon transport. As such, our work provides important insights into
physical understanding of heat dissipation in 2D material devices.",2204.06975v1
2022-04-22,Versatile coating platform for metal oxide nanoparticles: applications to materials and biological science,"In this feature article, we provide an overview of our research on
statistical copolymers as a coating material for metal oxide nanoparticles and
surfaces. These copolymers contain functional groups enabling non-covalent
binding to oxide surfaces and poly(ethylene glycol) (PEG) polymers for
colloidal stability and stealthiness. The functional groups are organic
derivatives of phosphorous acid compounds R-H$_2$PO$_3$, also known as
phosphonic acids that have been screened for their strong affinity to metals
and their ability to build multidentate binding. Herein we develop a
polymer-based coating platform that shares features with the techniques of
self-assembled monolayers (SAM) and Layer-by-Layer (L-b-L) deposition. The
milestones of this endeavor are the synthesis of PEG-based copolymers
containing multiple phosphonic acid groups, the implementation of simple
protocols combining versatility with high particle production yields and the
experimental demonstration of the colloidal stability of the coated particles.
As a demonstration, coating studies are conducted on cerium (CeO$_2$), iron
($\gamma$-Fe$_2$O$_3$), aluminum (Al$_2$O$_3$) and titanium (TiO$_2$) oxides of
different sizes and morphologies. We finally discuss applications in the domain
of nanomaterials and nanomedicine. We evaluate the beneficial effects of
coating on redispersible nanopowders, contrast agents for In Vitro/Vivo assays
and stimuli-responsive particles.",2204.10547v2
2022-04-30,A Nanometer-Thick Oxide Semiconductor Transistor with Ultra-High Drain Current,"High drive current is a critical performance parameter in semiconductor
devices for high-speed, low-power logic applications or high-efficiency,
high-power, high-speed radio frequency (RF) analog applications. In this work,
we demonstrate an In2O3 transistor grown by atomic layer deposition (ALD) at
back-end-of-line (BEOL) compatible temperatures with a record high drain
current exceeding 10 A/mm, the performance of which is 2-3 times better than
all known transistors with semiconductor channels. A record high
transconductance of 4 S/mm is also achieved among all transistors with a planar
structure. It is found that a high carrier density and high electron velocity
both contribute to this remarkably high on-state performance in ALD In2O3
transistors, which is made possible by the high-quality oxide/oxide interface,
the metal-like charge-neutrality-level (CNL) alignment, and the high band
velocities induced by the low density-of-state (DOS). Experimental Hall, I-V
and split C-V measurements at room temperature confirm a high carrier density
up to 6-7*10^13 /cm2 and a high velocity of about 10^7 cm/s. Ultra-thin oxide
semiconductors, with a CNL located deep inside the conduction band, represent a
promising new direction for the search of alternative channel materials for
high-performance semiconductor devices.",2205.00357v1
2022-07-04,Electrically switchable Casimir forces using transparent conductive oxides,"Casimir forces between charge-neutral bodies originate from quantum vacuum
fluctuations of electromagnetic fields, which exhibit a critical dependence on
material's electromagnetic properties. Over the years, in-situ modulation of
material's optical properties has been enabled through various means and has
been widely exploited in a plethora of applications such as electro-optical
modulation, transient color generation, bio- or chemical sensing, etc. Yet
Casimir force modulation has been hindered by difficulty in achieving high
modulation signals due to the broadband nature of the Casimir interaction. Here
we propose and investigate two configurations that allow for in-situ modulation
of Casimir forces through electrical gating of a metal-insulator-semiconductor
(MIS) junction comprised of transparent conductive oxide (TCO) materials. By
switching the gate voltage on and off, a force modulation of > 400 pN is
predicted due to substantive charge carrier accumulation in the TCO layer,
which can be easily measured using state-of-the-art force measurement
techniques in an atomic force microscope (AFM). We further examine the
influence of the oxide layer thickness on the force modulation, suggesting the
importance of the fine control of the oxide layer deposition. Our work provides
a promising pathway for modulating the Casimir effect in-situ with
experimentally measurable force contrast.",2207.02305v1
2022-07-08,High-speed laser writing of structural colors for full-color inkless printing,"It is a formidable challenge to simultaneously achieve wide gamut, high
resolution, high-speed while low-cost manufacturability, long-term stability,
and viewing-angle independence in structural colors for practical applications.
The conventional nanofabrication techniques fail to match the requirement in
low-cost, large-scale and flexible manufacturing. Processing by ultrashort
lasers can achieve extremely high throughput while suffering from a narrow
gamut of 15% sRGB or angle-dependent colors. Here, we demonstrate an all-in-one
solution for ultrafast laser-produced structural colors on ultrathin hybrid
films that comprise an absorbent TiAlN layer coating on a metallic TiN layer.
Under pulsed laser irradiation, the absorption behaviors of the TiAlN-TiN
hybrid films are tailored by photothermal-induced oxidation on the topmost
TiAlN. The oxidized films exhibit double-resonance absorption, which is
attributed to the non-trivial phase shifts both at the oxide-TiAlN interface,
and at the TiAlN-TiN interface. By varying the accumulated laser fluence to
modulate the oxidation depth, an unprecedented large gamut of 90% sRGB is
obtained. Our highly reproducible printing technique manifests
angle-insensitive colors the variation of Hue is <0.14pi when viewing angles
changing from 6 to 60. The full-color printing speed reaches to 1.4 cm2/s and
the highest printing resolution exceeds 25000 dpi. The durability of the
laser-printed colors is confirmed by fastness examination, including salt fog,
double-85, light bleaching, and adhesion tests. These features render our
technique to be competitive for high-throughput industrial applications.",2207.03649v1
2022-07-14,Magnetron Sputtered Non-Toxic and Precious Element-Free Ti-Zr-Ge Metallic Glass Nanofilms with Enhanced Biocorrosion Resistance,"The chemical composition and structural state of advanced alloys are the
decisive factors in optimum biomedical performance. This contribution presents
unique Ti-Zr-Ge metallic glass thin-film compositions fabricated by magnetron
sputter deposition targeted for nanocoatings for biofouling prevention. The
amorphous nanofilms with nanoscale roughness exhibit a large relaxation and
supercooled liquid regions as revealed by flash differential scanning
calorimetry. Ti\textsubscript{68}Zr\textsubscript{8}Ge\textsubscript{24} shows
the lowest corrosion (0.17 \textmu A cm\textsuperscript{\textminus2}) and
passivation (1.22 \textmu A cm\textsuperscript{\textminus2}) current densities,
with the lowest corrosion potential of \textminus0.648 V and long-range
stability against pitting, corroborating its excellent performance in phosphate
buffer solution at 37 {\textdegree}C. The oxide layer is comprised of
TiO\textsubscript{2}, TiO\textsubscript{\emph{x}} and
ZrO\textsubscript{\emph{x}}, as determined using X-ray photoelectron
spectroscopy by short-term ion-etching of the surface layer. The two orders of
magnitude increase in the oxide and interface resistance (from 14 to 1257
{\textOmega} cm\textsuperscript{2}) along with an order of magnitude decrease
in the capacitance parameter of the oxide interface (from 1.402 x
10\textsuperscript{\textminus5} to 1.677 x 10\textsuperscript{\textminus6} S
s\textsuperscript{n} cm\textsuperscript{\textminus2}) of the same composition
is linked to the formation of carbonyl groups and reduction of the native oxide
layer during linear sweep voltammetry.",2207.07000v2
2022-07-28,Resolving oxidation states and Sn-halide interactions of perovskites through Auger parameter analysis in XPS,"Reliable chemical state analysis of Sn semiconductors by XPS is hindered by
the marginal observed shift in the Sn 3d region. For hybrid Sn-based
perovskites especially, errors associated with charge referencing can easily
exceed chemistry-related shifts. Studies based on the modified Auger parameter
${\alpha}'$ provide a suitable alternative and have been used previously to
resolve different chemical states in Sn alloys and oxides. However, the
meaningful interpretation of Auger parameter variations on Sn-based perovskite
semiconductors requires fundamental studies. In this work, we perform a
comprehensive Auger parameter study through systematic compositional variations
of Sn halide perovskites. We find that in addition to the oxidation state,
${\alpha}'$ is highly sensitivity to the composition of the halide-site,
inducing shifts of up to ${\Delta}{\alpha}' = 2 eV$ between ASnI$_3$ and
ASnBr$_3$ type perovskites. The reported dependencies of ${\alpha}'$ on the Sn
oxidation state, coordination and local chemistry provide a framework that
enables reliable tracking of degradation as well as X-site interaction for
Sn-based perovskites and related compounds. The higher robustness and
sensitivity of such studies not only enables more in-depth surface analysis of
Sn-based perovskites than previously performed, but also increases
reproducibility across laboratories.",2207.14123v1
2022-07-29,"Selective Laser Reaction Synthesis of SiC, Si$_3$N$_4$ and HfC/SiC Composites for Additive Manufacturing","Selective laser reaction sintering techniques (SLRS) techniques were
investigated for the production of near net-shape non-oxide ceramics including
SiC, Si$_3$N$_4$, and HfC/SiC composites that might be compatible with
prevailing powder bed fusion additive manufacturing processes. Reaction bonded
layers of covalent ceramics were produced using in-situ reactions that occur
during selective laser processing and layer formation. During SLRS, precursor
materials composed of metal and/or metal oxide powders were fashioned into
powder beds for conversion to non-oxide ceramic layers. Laser-processing was
used to initiate simultaneous chemical conversion and local interparticle
bonding of precursor particles in CH4 or NH3 gases. Several factors related to
the reaction synthesis process (precursor chemistry, gas-solid and gas-liquid
synthesis mechanisms, precursor vapor pressures) were investigated in relation
to resulting microstructures and non-oxide yields. Results indicated that the
volumetric changes which occurred during in-situ conversion of single component
precursors negatively impacted the surface layer microstructure. To circumvent
the internal stresses and cracking that accompanied the conversion of Si or Hf
(that expands upon conversion) or SiO$_x$ (that contracts during conversion),
optimized ratios of the precursor constituents were used to produce near
isovolumetric conversion to the product phase. The results demonstrate that
under appropriate processing conditions and precursor selection, the formation
of near net-shape SiC and SiC composites might be achieved through single-step
AM-compatible techniques.",2208.00054v1
2022-08-12,The effect of ambient air pollution on birth outcomes in Norway,"Ambient air pollution is harmful to the fetus even in countries with
relatively low levels of pollution. In this paper, I examine the effects of
ambient air pollution on birth outcomes in Norway. I find that prenatal
exposure to ambient nitric oxide in the last trimester causes significant birth
weight and birth length loss under the same sub-postcode fixed effects and
calendar month fixed effects, whereas other ambient air pollutants such as
nitrogen dioxide and sulfur dioxide appear to be at safe levels for the fetus
in Norway. In addition, the marginal adverse effect of ambient nitric oxide is
larger for newborns with disadvantaged parents. Both average concentrations of
nitric oxide and occasional high concentration events can adversely affect
birth outcomes. The contributions of my work include: first, my finding that
prenatal exposure to environmental nitric oxide has an adverse effect on birth
outcomes fills a long-standing knowledge gap. Second, with the large sample
size and geographic division of sub-postal codes in Norway, I can control for a
rich set of spatio-temporal fixed effects to overcome most of the endogeneity
problems caused by the choice of residential area and date of delivery. In
addition, I study ambient air pollution in a low-pollution setting, which
provides new evidence on the health effects of low ambient air pollution.",2208.06271v6
2022-09-19,Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures,"Perovskite structured transition metal oxides are important technological
materials for catalysis and solid oxide fuel cell applications. Their
functionality often depends on oxygen diffusivity and mobility through complex
oxide heterostructures, which can be significantly impacted by structural and
chemical modifications, such as doping. Further, when utilized within
electrochemical cells, interfacial reactions with other components (e.g. Ni-
and Cr-based alloy electrodes and interconnects) can influence the perovskite's
reactivity and ion transport, leading to complex dependencies that are
difficult to control in real-world environments. Here we use isotopic tracers
and atom probe tomography to directly visualize oxygen diffusion and transport
pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr
coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in
elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO
while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways.
Complementary density functional theory (DFT) calculations at experimental
conditions provide rationale for OE reaction mechanisms and reveal a complex
interplay of different thermodynamic and kinetic drivers. Our results shed
light on the fundamental coupling of defects and oxygen transport in an
important class of catalytic materials.",2209.09302v1
2022-09-26,Molecular filtration by reduced graphene oxide sandwiched between wood sheets,"This study investigates the prospect of using reduced graphene oxide
encapsulated between thin wood membranes as a composite filter for water
filtration. Graphene oxide (GO) with a volume range of 0.2 to 0.5 mL was
deposited on a 95 mm2 area of thin sheets of Balsa wood with a thickness range
of 2.20 - 3.50 mm. The dried GO deposits were laser treated in reduced oxygen
environment to prepare a reduced graphene oxide-wood composite (rGO-wood). The
rGO substrate of the composite was sandwiched between 2 wood sheets which were
glued using polydimethylsiloxane (PDMS) to give a stable membrane. Fabricated
membranes improved the Allura red rejection from 8.29 $\pm$ 0.69% in the
controls (sandwiched wood sheets without rGO) to 93.14 $\pm$ 1.31% in the 1 mL
total rGO composites. The ratio of percentage permeance drop of the treatments
over the controls ranged from 62.8 $\pm$ 4.3 to 85.4 $\pm$ 5.2% from the 0.4 to
1 mL rGO composites respectively. The correlation coefficient (r) between the
GO volume and rejection was 0.94 suggesting that the GO treatments provided
some control over the transport of molecules through the membrane. The
correlation coefficient between wood thickness, and Allura red rejection shows
that the wood sheets did not influence the rejection. The permeance was weakly
affected by the membrane thickness (r = -0.46). An 93% improvement in rejection
performance of the composite membranes over the controls was observed. The
overall data suggests that the wood-rGO composite has potential for water
filtration applications.",2209.12983v1
2022-10-11,First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications,"The surfaces of most metals immersed in aqueous electrolytes have a
several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the
existence of both metal|oxide and oxide|liquid electrotlyte interfaces, and
makes it challenging to correlate atomic length-scale structures with
electrochemical properties such the potential-of-zero-charge (PZC). The PZC
value has been shown to be correlated the pitting onset potential for
corrosion. In this work, we conduct large-scale Density Functional Theory and
ab initio molecular dynamics to calculate the PZC of a
Al(111)|gamma-Al(2)O(3)(110)|water double-interface model within the context of
aluminum corrosion. By partitioning the multiple interfaces involved into
binary components with additive contributions to the overall work function and
voltage, we predict the PZC to be -1.53 V vs. SHE for this model. We also
calculate the orbital energy levels of defects like oxygen vacancies in the
oxide, which are critical parameters in theories associated with pitting
corrosion. We predict that the Fermi level at the PZC lies above the impurity
defect levels of the oxygen vacancies, which are therefore uncharged at the
PZC. From the PZC estimate, we predict the voltage needed to create oxygen
vacancies with net positive charges within a flat-band approximation.",2210.05830v1
2022-10-26,Liquid Metal Printed Ultrathin Oxides for Monolayer WS2 Top-Gate Transistors,"Two-dimensional (2D) semiconductors are promising channel materials for
continued downscaling of complementary metal-oxide-semiconductor (CMOS) logic
circuits. However, their full potential continues to be limited by a lack of
scalable high-k dielectrics that can achieve atomically smooth interfaces,
small equivalent oxide thicknesses (EOT), excellent gate control, and low
leakage currents. Here, we report liquid metal printed ultrathin and scalable
Ga2O3 dielectric for 2D electronics and electro-optical devices. We directly
visualize the atomically smooth Ga2O3/WS2 interfaces enabled by the conformal
nature of liquid metal printing. We demonstrate atomic layer deposition
compatibility with high-k Ga2O3/HfO2 top-gate dielectric stacks on chemical
vapour deposition grown monolayer WS2, achieving EOTs of ~1 nm and subthreshold
swings down to 84.9 mV/dec. Gate leakage currents are well within requirements
for ultra-scaled low-power logic circuits. Our results show that liquid metal
printed oxides can bridge a crucial gap in scalable dielectric integration of
2D materials for next-generation nano-electronics.",2210.14426v1
2022-11-12,Evaluation of the hydrogen solubility and diffusivity in proton-conducting oxides by converting the PSL values of a tritium imaging plate,"Proton-conducting oxides have potential applications in hydrogen sensors,
hydrogen pumps, and other electrochemical devices including the tritium
purification and recovery systems of nuclear fusion reactors. Although the
distribution of hydrogen (H) in such oxide materials is an important aspect,
its precise measurement is difficult. In the present study, the hydrogen
solubility and diffusivity behavior of BaZr0.9Y0.1O2.95 (BZY),
BaZr0.955Y0.03Co0.015O2.97 (BZYC), and CaZr0.9In0.1O2.95 (CZI) were studied
using tritiated heavy water vapor i.e., DTO (~2 kPa, tritium (T) = 0.1%) by
converting the photostimulated luminescence (PSL) values of the imaging plate
(IP). The samples were exposed to DTO vapor at 673 K for 2 h or at 873 K for 1
h. The disc-shaped oxide specimens (diameter ~7.5 mm; thickness ~2.3 mm;
theoretical density (TD) > 98 %) were prepared by conventional powder
metallurgy. The IP images of the specimen surfaces of all the three materials
T-exposed revealed that BZY showed the most uniform T distribution with the
highest tritium activity. The cross-sectional T concentration profiles of the
cut specimens showed that T diffused deeper into BZY and BZYC than into CZI.
The hydrogen solubility and diffusivity in the CZI specimen were lower than
that in the BZY and BZYC specimens. This suggested that barium zirconates were
more favorable proton conductors than calcium zirconates.",2211.11531v1
2023-02-15,Discovery of Atomic Clock-Like Spin Defects in Simple Oxides from First Principles,"Virtually noiseless due to the scarcity of spinful nuclei in the lattice,
simple oxides hold promise as hosts of solid-state spin qubits. However, no
suitable spin defect has yet been found in these systems. Using high-throughput
first-principles calculations, we predict spin defects in calcium oxide with
electronic properties remarkably similar to those of the NV center in diamond.
These defects are charged complexes where a dopant atom -- Sb, Bi, or I --
occupies the volume vacated by adjacent cation and anion vacancies. The
predicted zero phonon line shows that the Bi complex emits in the
telecommunication range, and the computed many-body energy levels suggest a
viable optical cycle required for qubit initialization. Notably, the high-spin
nucleus of each dopant strongly couples to the electron spin, leading to many
controllable quantum levels and the emergence of atomic clock-like transitions
that are well protected from environmental noise. Specifically, the Hanh-echo
coherence time increases beyond seconds at the clock-like transition in the
defect with \ch{^{209}Bi}. Our results pave the way to designing quantum states
with long coherence times in simple oxides, making them attractive platforms
for quantum technologies.",2302.07523v3
2023-02-28,Correlating Chemical Reaction and Mass Transport in Hydrogen-based Direct Reduction of Iron Oxide,"Steelmaking contributes 8% to the total CO2 emissions globally, primarily due
to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable
performance because the dominant gas-solid reduction mechanism is set by the
defects and pores inside the mm-nm sized oxide particles that change
significantly as the reaction progresses. While these governing dynamics are
essential to establish continuous flow of iron and its ores through reactors,
the direct link between agglomeration and chemistry is still contested due to
missing measurements. In this work, we directly measure the connection between
chemistry and agglomeration in the smallest iron oxides relevant to magnetite
ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we
resolve the formation and consumption of w\""ustite (FeO) - the step most
commonly attributed to agglomeration. Using X-ray scattering and microscopy, we
resolve crystallographic anisotropy in the rate of the initial reaction, which
becomes isotropic as the material sinters. Complementing with imaging, we
demonstrate how the particles self-assemble, subsequently react and sinter into
~100x oblong grains. Our insights into how morphologically uniform iron oxide
particles react and agglomerate H2 reduction enable future size-dependent
models to effectively describe the multiscale iron ore reduction.",2302.14215v2
2023-03-09,Mechanisms of SiO oxidation: Implications for dust formation,"Reactions of SiO molecules have been postulated to initiate efficient
formation of silicate dust particles in outflows around dying (AGB) stars. Both
OH radicals and H$_2$O molecules can be present in these environments and their
reactions with SiO and the smallest SiO cluster, Si$_2$O$_2$, affect the
efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation
and clustering reactions of SiO, Si$_2$O$_2$ and Si$_2$O$_3$ have been
calculated using master equation calculations based on density functional
theory calculations. The calculations show that the reactions involving OH are
fast. Reactions involving H$_2$O are not efficient routes to oxidation but may
under the right conditions lead to hydroxylated species. The reaction of
Si$_2$O$_2$ with H$_2$O, which has been suggested as efficient producing
Si$_2$O$_3$, is therefore not as efficient as previously thought. If H$_2$O
molecules dissociate to form OH radicals, oxidation of SiO and dust formation
could be accelerated. Kinetics simulations of oxygen-rich circumstellar
environments using our proposed reaction scheme suggest that under typical
conditions only small amounts of SiO$_2$ and Si$_2$O$_2$ are formed and that
most of the silicon remains as molecular SiO.",2303.05184v1
2023-03-10,Hematite $α-Fe_{2}O_{3}(0001)$ in top and side view: resolving long-standing controversies about its surface structure,"Hematite ${\alpha}-Fe_{2}O_{3}(0001)$ is the most-investigated iron oxide
model system in photo and electrocatalytic research. The rich chemistry of Fe
and O allows for many bulk and surface transformations, but their control is
challenging. This has led to controversies regarding the structure of the
topmost layers. This comprehensive study combines surface methods (nc-AFM, STM,
LEED, and XPS) complemented by structural and chemical analysis of the
near-surface bulk (HRTEM and EELS). The results show that a compact 2D layer
constitutes the topmost surface of ${\alpha}-Fe_{2}O_{3}(0001)$; it is locally
corrugated due to the mismatch with the bulk. Assessing the influence of
naturally-occurring impurities shows that these can force the formation of
surface phases that are not stable on pure samples. Impurities can also cause
the formation of ill-defined inclusions in the subsurface and modify the
oxidation phase diagram of hematite. The results provide a significant step
forward in determining the hematite surface structure that is crucial for
accurately modeling catalytic reactions. Combining surface and cross-sectional
imaging provided the full view that is essential for understanding the
evolution of the near-surface region of oxide surfaces under oxidative
conditions.",2303.06023v1
2023-03-28,Optimizing compositional and atomic-level information of oxides in atom probe tomography,"Atom probe tomography (APT) is a 3D analysis technique that offers unique
chemical accuracy and sensitivity with sub-nanometer spatial resolution.
Recently, there is an increasing interest in the application of APT to complex
oxides materials, giving new insight into the relation between local variations
in chemical composition and emergent physical properties. However, in contrast
to the field of metallurgy, where APT is routinely applied to study materials
at the atomic level, complex oxides and their specific field evaporation
mechanisms are much less explored. Here, we perform APT measurements on the
hexagonal manganite ErMnO3 and systematically study the effect of different
experimental parameters on the measured composition and atomic structure. We
demonstrate that both the mass resolving power (MRP) and compositional accuracy
can be improved by increasing the charge-state ratio (CSR) working at low laser
energy (< 5 pJ). Furthermore, we observe a substantial preferential retention
of Er atoms, which is suppressed at higher CSRs. We explain our findings based
on fundamental field evaporation concepts, expanding the knowledge about the
impact of key experimental parameters and the field evaporation process in
complex oxides in general.",2303.16233v1
2023-04-17,Mechanical behavior of ion-irradiated ODS RAF steels strengthened with different types of refractory oxides,"In the present work, authors focused on verifying structural and mechanical
properties of Oxide Dispersed Strengthening (ODS) steels strengthened by three
different types of refractory oxides submitted to ion-irradiation. Three
materials strengthened with Y2O3 or Al2O3 or ZrO2 were produced by mechanical
alloying and Spark Plasma Sintering technique. Specimens have been submitted to
high energy Ar-ion irradiation at room temperature with three fluences. This
procedure allowed to generate strongly damaged zone with a thickness of 230nm.
SEM/EBSD and TEM observations, GIXRD analysis, and nanoindentation tests have
been included in examination of modified layers. Investigation revealed
alteration of structural and mechanical features as a result of Ar-irradiation.
Obtained results showed a strong correlation between the strengthening oxide
and materials' behavior under radiation damage. It has been proved that below
1x1015ions/cm2 mechanical properties in the modified layer of all materials are
very similar. Reported behavior may be related to the efficient annealing of
the radiation defect process. Above this limit, significant differences between
the materials are visible. It is believed that described phenomenon is directly
related to the presence of the structural features and their capacity to act as
defect sinks. Consequently, type of dominant mechanisms occurring in modified
layer is proposed.",2304.08266v1
2023-04-30,Factors determining surface oxygen vacancy formation energy in ternary spinel structure oxides with zinc,"Spinel oxides are an important class of materials for heterogeneous catalysis
including photocatalysis and electrocatalysis. The surface O vacancy formation
energy (EOvac) is a critical quantity on catalyst performance because the
surface of metal oxide catalysts often acts as reaction sites, for example, in
the Mars-van Krevelen mechanism. However, experimental evaluation of EOvac is
very challenging. We obtained the EOvac for (100), (110), and (111) surfaces of
normal zinc-based spinel oxides ZnAl2O4, ZnGa2O4, ZnIn2O4, ZnV2O4, ZnCr2O4,
ZnMn2O4, ZnFe2O4, and ZnCo2O4. The most stable surface is (100) for all
compounds. The smallest EOvac for a surface is the largest in the (100) surface
except for ZnCo2O4. For (100) and (110) surfaces, there is a good correlation,
over all spinels, between the smallest EOvac for the surface and bulk formation
energy, while the ionization potential correlates well in (111) surfaces.
Machine learning over EOvac of all surface sites in all orientations and all
compounds to find the important factors, or descriptors, that decide the EOvac
revealed that bulk and surface-dependent descriptors are the most important,
namely the bulk formation energy, a Boolean descriptor on whether the surface
is (111), and the ionization potential, followed by geometrical descriptors
that are different in each O site.",2305.00395v1
2023-05-11,Reactive pulsed direct current magnetron sputtering deposition of semiconducting yttrium oxide thin film in ultralow oxygen atmosphere: A spectroscopic and structural investigation of growth dynamics,"An experimental investigation was conducted to explore spectroscopic and
structural characterization of semiconducting yttrium oxide thin film deposited
at 623 K (+/- 5K) utilizing reactive pulsed direct current magnetron
sputtering. Based on the results obtained from both x-ray diffraction and
transmission electron microscope measurements, yttrium monoxide is very likely
formed in the transition region between {\beta}-Y2O3 and {\alpha}-Y2O3, and
accompanied by the crystalline Y2O3. Resulting from either the low energy
separation between 4d and 5s orbitals and/or different spin states of the
corresponding orbitals' sublevels, the stability of monoxide is most presumably
self-limited by the size of the crystal in thermodynamic terms. This behavior
develops a distortion in the structure of the crystal compared to the metal
oxide cubic structure and it also effectuates the arrangement in
nanocrystalline/amorphous phase. In addition to this, spectroscopic
ellipsometry denotes that the semiconducting yttrium oxide has the dominant,
mostly amorphous, formation character over crystalline Y2O3. Our purpose, by
means of the current findings, is to advance the understanding of formation
kinetics/conditions of yttrium with an unusual valency (2+).",2305.06757v1
2023-05-15,Superconducting-insulating quantum phase transition associated with valence change in compressed perovskite bismuth-oxides,"Searching for a universal trend by the same tuning method in different
high-temperature superconductors with a similar crystal structure is a common
strategy to find clues for a better understanding of the superconducting
mechanism in a unified way. It is known that the hole-doped bismuth-oxide
Ba1-xKxBiO3 possesses a similar perovskite structure to that of the hole-doped
copper-oxide (cuprate) superconductors but also holds a comparatively high
superconducting transition temperature. In this study, we report the first
observation of the pressure-induced quantum phase transition (QPT) from
superconducting to insulating states in a series of Ba1-xKxBiO3 single-crystal
samples. A similar QPT has also been observed recently in the compressed
cuprate superconductors1. Significantly, we found that the QPT observed in
Ba1-xKxBiO3 is intriguingly associated with the valence change of the Bi ions
in the material. These results lead us to propose that the pressure-induced
valence change from Bi3+ to Bi5+ destroys the hole-doping effect on stabilizing
the conductivity and corresponding superconductivity. By comparing the
high-pressure behaviors observed in these two kinds of oxides, we identified
another prominent feature shared by them - the more the hole-doping
concentration, the higher the critical pressure required for driving the QPT.",2305.08406v1
2023-07-07,Robust atmospherically stable hybrid SrVO3/Graphene//SrTiO3 template for fast and facile large-area transfer of complex oxides onto Si,"Heterogenous integration of complex epitaxial oxides onto Si and other target
substrates is recently gaining traction. One of the popular methods involves
growing a water-soluble and highly reactive sacrificial buffer layer, such as
Sr3Al2O6 (SAO) at the interface, and a functional oxide on top of this. To
improve the versatility of layer transfer techniques, it is desired to utilize
stable (less reactive) sacrificial layers, without compromising on the transfer
rates. In this study, we utilized a combination of chemical vapor deposited
(CVD) graphene as a 2D material at the interface and pulsed laser deposited
(PLD) water-soluble SrVO3 (SVO) as a sacrificial buffer layer. We show that the
graphene layer enhances the dissolution rate of SVO over ten times without
compromising its atmospheric stability. We demonstrate the versatility of our
hybrid template by growing ferroelectric BaTiO3 (BTO) via PLD and Pb(Zr, Ti)O3
(PZT) via Chemical Solution Deposition (CSD) technique and transferring them
onto the target substrates and establishing their ferroelectric properties. Our
hybrid templates allow for the realization of the potential of complex oxides
in a plethora of device applications for MEMS, electro-optics, and flexible
electronics.",2307.03342v1
2023-07-27,$ \mathrm{Sr}_{4}\mathrm{Al}_{2}\mathrm{O}_{7}$: A New Sacrificial Layer with High Water Dissolution Rate for the Synthesis of Freestanding Oxide Membranes,"Freestanding perovskite oxide membranes have drawn great attention recently
since they offer exceptional structural tunability and stacking ability,
providing new opportunities in fundamental research and potential device
applications in silicon-based semiconductor technology. Among different types
of sacrificial layers, the $ \mathrm{(Ca, Sr,
Ba)}_{3}\mathrm{Al}_{2}\mathrm{O}_{6}$ compounds are most widely used since
they can be dissolved in water and prepare high-quality perovskite oxide
membranes with clean and sharp surfaces and interfaces. However, the typical
transfer process takes a long time (up to hours) in obtaining millimeter-size
freestanding membranes, let alone realize wafer-scale samples with high yield.
Here, we introduce a new member of the $
\mathrm{SrO-}\mathrm{Al}_{2}\mathrm{O}_{3}$ family,$
\mathrm{Sr}_{4}\mathrm{Al}_{2}\mathrm{O}_{7},$, and demonstrate its high
dissolution rate, about 10 times higher than that of $
\mathrm{Sr}_{3}\mathrm{Al}_{2}\mathrm{O}_{6}$. The high-dissolution-rate of $
\mathrm{Sr}_{4}\mathrm{Al}_{2}\mathrm{O}_{7}$ is most likely related to the
more discrete Al-O networks and higher concentration of water-soluble Sr-O
species in this compound. Our work significantly facilitates the preparation of
freestanding membranes and sheds light on the integration of multifunctional
perovskite oxides in practical electronic devices.",2307.14584v1
2023-08-01,Autonomous data extraction from peer reviewed literature for training machine learning models of oxidation potentials,"We present an automated data-collection pipeline involving a convolutional
neural network and a large language model to extract user-specified tabular
data from peer-reviewed literature. The pipeline is applied to 74 reports
published between 1957 and 2014 with experimentally-measured oxidation
potentials for 592 organic molecules (-0.75 to 3.58 V). After data curation
(solvents, reference electrodes, and missed data points), we trained multiple
supervised machine learning models reaching prediction errors similar to
experimental uncertainty ($\sim$0.2 V). For experimental measurements of
identical molecules reported in multiple studies, we identified the most likely
value based on out-of-sample machine learning predictions. Using the trained
machine learning models, we then estimated oxidation potentials of $\sim$132k
small organic molecules from the QM9 data set, with predicted values spanning
0.21 to 3.46 V. Analysis of the QM9 predictions in terms of plausible
descriptor-property trends suggests that aliphaticity increases the oxidation
potential of an organic molecule on average from $\sim$1.5 V to $\sim$2 V,
while an increase in number of heavy atoms lowers it systematically. The
pipeline introduced offers significant reductions in human labor otherwise
required for conventional manual data collection of experimental results, and
exemplifies how to accelerate scientific research through automation.",2308.00389v1
2023-08-06,Mechanically exfoliated low-layered [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]: A single-crystalline p-type transparent conducting oxide,"Transparent conducting oxides (TCOs) are essential components of
optoelectronic devices and various materials have been explored for highly
efficient TCOs having a combination of high transmittance and low sheet
resistance. Here, we focus on a misfit thermoelectric oxide
[Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] and fabricate the transparent low-layered
crystals by a mechanical tape-peeling method using the single-crystalline
samples. From the transmittance measurement, we find that the thickness of
low-layered samples is several orders of hundred nanometers, which is
comparable with the estimation from the scanning electron microscopy images.
Compared to the previous results on the polycrystalline and $c$-axis oriented
transparent films, the electrical resistivity is reduced owing to the
single-crystalline nature. The figure of merit for the transparent conducting
materials in the present low-layered samples is then evaluated to be higher
than the values in the previous reports. The present results on the low-layered
single-crystalline [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] may offer a unique class
of multi-functional transparent thermoelectric oxides.",2308.03221v1
2023-08-23,Atomic scale understanding of initial Cu-Ni oxidation from machine-learning accelerated first-principles simulations and in situ TEM experiments,"The development of accurate methods for determining how alloy surfaces
spontaneously restructure under reactive and corrosive environments is a key,
long-standing, grand challenge in materials science. Current oxidation models,
such as Cabrera-Mott, are based on macroscopic empirical knowledge that lacks
fundamental insight at the atomic level. Using machine learning-accelerated
density functional theory with in situ environmental transmission electron
microscopy (ETEM), we examine the interplay between surface reconstructions and
preferential segregation tendencies of CuNi(100) surfaces under oxidation
conditions. Our modeling approach based on molecular dynamics and grand
canonical Monte Carlo simulations shows that oxygen-induced Ni segregation in
CuNi alloy favors Cu(100)-O c(2x2) reconstruction and destabilizes the
Cu(100)-O missing row reconstruction. The underpinnings of these stabilization
tendencies are rationalized based on the similar atomic coordination and bond
lengths in NiO rock salt and Cu(100)-O c(2x2) structures. In situ ETEM
experiments show Ni segregation followed by NiO nucleation and growth in
regions without MRR, with secondary nucleation and growth of Cu2O in MRR
regions. This further corroborates the simulated surface oxidation and
segregation modelling outcomes. Our findings are general and are expected to
extend to other alloy systems.",2308.11867v1
2023-09-21,Shedding Light on the Ageing of Extra Virgin Olive Oil: Probing the Impact of Temperature with Fluorescence Spectroscopy and Machine Learning Techniques,"This work systematically investigates the oxidation of extra virgin olive oil
(EVOO) under accelerated storage conditions with UV absorption and total
fluorescence spectroscopy. With the large amount of data collected, it proposes
a method to monitor the oil's quality based on machine learning applied to
highly-aggregated data. EVOO is a high-quality vegetable oil that has earned
worldwide reputation for its numerous health benefits and excellent taste.
Despite its outstanding quality, EVOO degrades over time owing to oxidation,
which can affect both its health qualities and flavour. Therefore, it is highly
relevant to quantify the effects of oxidation on EVOO and develop methods to
assess it that can be easily implemented under field conditions, rather than in
specialized laboratories. The following study demonstrates that fluorescence
spectroscopy has the capability to monitor the effect of oxidation and assess
the quality of EVOO, even when the data are highly aggregated. It shows that
complex laboratory equipment is not necessary to exploit fluorescence
spectroscopy using the proposed method and that cost-effective solutions, which
can be used in-field by non-scientists, could provide an easily-accessible
assessment of the quality of EVOO.",2309.12377v1
2023-09-27,Optical tuning of the diamond Fermi level measured by correlated scanning probe microscopy and quantum defect spectroscopy,"Quantum technologies based on quantum point defects in crystals require
control over the defect charge state. Here we tune the charge state of shallow
nitrogen-vacancy and silicon-vacancy centers by locally oxidizing a
hydrogenated surface with moderate optical excitation and simultaneous spectral
monitoring. The loss of conductivity and change in work function due to
oxidation are measured in atmosphere using conductive atomic force microscopy
(C-AFM) and Kelvin probe force microscopy (KPFM). We correlate these scanning
probe measurements with optical spectroscopy of the nitrogen-vacancy and
silicon-vacancy centers created via implantation and annealing 15-25 nm beneath
the diamond surface. The observed charge state of the defects as a function of
optical exposure demonstrates that laser oxidation provides a way to precisely
tune the Fermi level over a range of at least 2.00 eV. We also observe a
significantly larger oxidation rate for implanted surfaces compared to
unimplanted surfaces under ambient conditions. Combined with knowledge of the
electron affinity of a surface, these results suggest KPFM is a powerful,
high-spatial resolution technique to advance surface Fermi level engineering
for charge stabilization of quantum defects.",2309.15969v1
2023-10-11,Thickness-dependent Characteristics and Oxidation of Cadmium,"In this study, the structural, electronic and vibrational properties of
thinnest possible Cadmium crystal are investigated by performing
first-principle calculations. Total energy optimization and dynamic stability
calculations reveal that the thinnest possible crystal structure is a
double-layered structure consisting of alternating layers formed by trigonal
arrangements of Cd atoms. Excessive softening of optical phonons occurs as a
result of structural relaxation when going from a bulk to a single layer (SL)
structure. It is also shown that thinnest structure obtained from bulk Cd
crystals maintains its metallic feature despite the dimensional crossover. In
addition, it is predicted through calculations that the SL Cd crystal strongly
interacts with oxygen and that the oxidized regions even undergo chemical
transformation to form the CdO crystal. In the double-layer CdO crystal
resulting from the oxidation of individual Cd layers, the layers are connected
to each other with strong covalent bonds, and this structure is a semiconductor
with a band gap of 2.10 eV. While the robust metallic structure of the thinnest
possible Cd crystal provides flexibility in terms of its use in nanoscale
applications, on the other hand, the fact that its electronic properties can be
changed by oxidation is important for optoelectronic device applications.",2310.07909v2
2023-11-08,Direct electrochemical reduction of graphene oxide thin film for aptamer-based selective and highly sensitive detection of Matrix metalloproteinase 2,"Simple and low-cost biosensing solutions are suitable for point-of-care
applications aiming to overcome the gap between scientific concepts and
technological production. To compete with sensitivity and selectivity of golden
standards, such as liquid chromatography, the functionalization of biosensors
is continuously optimized to enhance the signal and improve their performance,
often leading to complex chemical assay development. In this research, the
efforts are made on optimizing the methodology for electrochemical reduction of
graphene oxide to produce thin film-modified gold electrodes. Under the
employed specific conditions, 20 cycles of cyclic voltammetry (CV) are shown to
be optimal for superior electrical activation of graphene oxide into
electrochemically reduced graphene oxide (ERGO). This platform is further used
to develop a matrix metalloproteinase 2 (MMP-2) biosensor, where specific
anti-MMP2 aptamers are utilized as a biorecognition element. MMP-2 is a protein
which is typically overexpressed in tumor tissues, with important roles in
tumor invasion, metastasis as well as in tumor angiogenesis. Based on
impedimetric measurements, we were able to detect as low as 3.32 pg/mL of MMP-2
in PBS with a dynamic range of 10 pg/mL - 10 ng/mL. Besides high specificity,
ERGO-based aptasensor showed a potential of reuse due to demonstrated
successful signal restoration after experimental detection of MMP-2.",2311.04674v2
2023-11-27,Tailoring the Opto-Electronic Properties of Oxide-Metal-Oxide Transparent Electrode Using Cu Seed Layer,"The oxide-metal-oxide architecture is a promising approach for the
development of the high-performance indium-free transparent electrode (TE),
which is a key component of various optoelectronic applications such as solar
cells, organic LEDs, and touchscreen panels. Here in this work, we have shown
high-performance TE consisting of TiO2/Ag/TiO2 (TAT), with the incorporation of
a copper seed layer. The seed layer increases the wettability and improves the
adhesion of deposited Ag film on the bottom TiO2 layer. Before the experimental
realization, optical modeling is performed by using MATLAB code based on the
transfer matrix method. The optimum thickness obtained from the simulation is
30 nm for both undercoat and overcoat TiO2 with the average transmittance in
the visible region >85% with the Ag thickness of 9nm. With inputs from the
optical modeling, TEs were experimentally realized with and without the Cu seed
layer. It has been found that the TE with an additional sputtered Cu (1 nm)
seed layer is essential for the smooth growth of silver film and shows better
electro-optical performance (sheet resistance < 10 and average transmittance in
the visible spectral range > 80%) than TAT-TE without any seed layer. The
electro-optical and morphological properties of the TiO2/Cu/Ag/TiO2 structure
make it suitable for optoelectronic applications.",2311.15535v2
2023-11-28,Metal-to-insulator transition in oxide semimetals by anion doping,"Oxide semimetals exhibiting both nontrivial topological characteristics stand
as exemplary parent compounds and multiple degrees of freedom, offering great
promise for the realization of novel electronic states. In this study, we
present compelling evidence of profound structural and transport phase shifts
in a recently uncovered oxide semimetal, SrNbO3, achieved through effective
in-situ anion doping. Notably, a remarkable increase in resistivity of more
than three orders of magnitude at room temperature is observed upon
nitrogen-doping. The extent of electronic modulation in SrNbO3 is strongly
correlated with the misfit strain, underscoring its phase instability to both
chemical doping and crystallographic symmetry variations. Using
first-principles calculations, we discern that elevating the level of nitrogen
doping induces an upward shift in the conductive bands of SrNbO3-dNd.
Consequently, a transition from a metallic state to an insulating state becomes
apparent as the nitrogen concentration reaches a threshold of 1/3. This
investigation sheds light on the potential of anion engineering in oxide
semimetals, offering pathways for manipulating their physical properties. These
insights hold promise for future applications that harness these materials for
tailored functionalities.",2311.16405v1
2023-12-11,Investigating intrinsic silicon oxide and a lightly doped p-type layer for evolution of tail states and estimating its impact as a passivation layer in a HIT type device,"Hydrogenated amorphous silicon is well known for its various alloys and wide
ranging opto-electronic properties. Hydrogenated silicon sub-oxide (aSiO:H) is
one of them. The effect of boron doping on optoelectronic properties of the
aSiO:H have been investigated with intrinsic and delta-doped materials. The
Urbach energy of the tail and midgap defect states of the intrinsic and lightly
doped(0.01% gas phase doping) materials were found to be 103, 151 meV and
8.19x1016 , 5.47x1017 cm-3 respectively. As a result of the 0.01% doping a
reduction in optical gap was observed from 1.99 to 1.967 eV along with a shift
in Fermi level by 0.258eV, indicating an efficient boron doping of the
intrinsic silicon oxide material. The lightly doped p-type layer was used to
simulate device characteristics in amorphous silicon (aSi:H) and HIT-type solar
cell. In the aSi:H device the power conversion efficiency (PCE) was moderate
while in a HIT-type device the PCE was 26.4%. It indicated that a good quality
silicon oxide layer can be an attractive passivation layer for a HIT type
device. It further indicated that defect density of the passivation layer can
have a significant impact on performance of a HIT type device. The primary
difference of the two passivation layers (intrinsic and delta-doped) are the
difference in mid-gap and tail states. Passivation layer with a higher mid-gap
state leads to poorer device performance. Therefore, it highlights the
importance of using a less defective passivation layer to improve device
performance.",2312.06111v1
2024-01-07,Dynamic Multi Color Switching using Ultrathin Vanadium Oxide on Aluminium based Asymmetric Fabry-Perot Resonant Structure,"Vanadium dioxide ($VO_{2}$) exhibits strong infrared optical switching due to
its insulator-metal phase-transition property. However, in the visible
wavelengths, it's intrinsic optical switching is quite low. Current research
explores solutions like multilayering, intricate structural patterning, high
thermal budget processes and costly metals for improved color switching.
Nonetheless, the color gamut coverage with these methodologies remains notably
limited. This work overcomes these limitations and demonstrates dynamic
multi-colour switching covering a large color gamut using a simple,
unpatterned, ultrathin ($\sim$ $\frac{\lambda}{14}$, where wavelength $\lambda$
is taken as 575 nm at the center of visible spectrum) asymmetric
Fabry-P\'{e}rot structure of $VO_{2}$ on Aluminium (Al). We use the transfer
matrix method to design the $VO_{2}/Aluminium\,(Al)/Sapphire$ structure for
maximum visible reflectance switching. $VO_{2}$ films are synthesized using a
simple, low thermal budget atmospheric oxidation of Vanadium (V). With varying
oxidation durations, different colors of the oxidized samples are observed.
Consistent and reversible color-switching is observed visibly and in
reflectance measurements with the change in temperature from low (RT $\sim$
30$^{\circ}$C) to high (HT $\sim$ 100$^{\circ}$C) or vice versa due to the
phase transition property of the $VO_{2}$ layer in the structure. Compared to
the existing studies, this work shows a significant change in chromaticities
and covers a large color gamut when plotted on the CIE chromaticity diagram.
This work has potential applications in the fields of display, thermochromic
structures, and visible camouflage.",2401.03543v1
2024-01-14,Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile suboxide: The examples of Ga and Ge,"The delivery of an elemental cation flux to the substrate surface in the
oxide molecular beam epitaxy (MBE) chamber has been utilized not only for the
epitaxial growth of oxide thin films in the presence of oxygen but also in the
absence of oxygen for the growth temperature calibration (by determining the
adsorption temperature of the elements) and in-situ etching of oxide layers (e.
g., Ga2O3 etched by Ga). These elemental fluxes may, however, leave unwanted
cation adsorbates or droplets on the surface, which traditionally require
removal by in-situ superheating or ex-situ wet-chemical etching with
potentially surface-degrading effects. This study demonstrates a universal
in-situ approach to remove the residual cation elements from the surface via
conversion into a volatile suboxide by a molecular O2-flux in an MBE system
followed by suboxide evaporation at temperatures significantly below the
elemental evaporation temperature. We experimentally investigate the in-situ
etching of Ga and Ge cation layers and their etching efficiency using in-situ
line-of-sight quadrupole mass spectrometry (QMS) and reflection high-energy
electron diffraction (RHEED). The application of this process is demonstrated
by the in-situ removal of residual Ga droplets from a SiO2 mask after
structuring a Ga2O3 layer by in-situ Ga-etching. This approach can be generally
applied in MBE and MOCVD to remove residual elements with vapor pressure lower
than that of their suboxides, such as B, In, La, Si, Sn, Sb, Mo, Nb, Ru, Ta, V,
and W.",2401.07374v1
2024-01-15,Alternating Bias Assisted Annealing of Amorphous Oxide Tunnel Junctions,"We demonstrate a transformational technique for controllably tuning the
electrical properties of fabricated thermally oxidized amorphous aluminum-oxide
tunnel junctions. Using conventional test equipment to apply an alternating
bias to a heated tunnel barrier, giant increases in the room temperature
resistance, greater than 70%, can be achieved. The rate of resistance change is
shown to be strongly temperature-dependent, and is independent of junction size
in the sub-micron regime. In order to measure their tunneling properties at mK
temperatures, we characterized transmon qubit junctions treated with this
alternating-bias assisted annealing (ABAA) technique. The measured frequencies
follow the Ambegaokar-Baratoff relation between the shifted resistance and
critical current. Further, these studies show a reduction of
junction-contributed loss on the order of $\approx 2 \times10^{-6}$, along with
a significant reduction in resonant- and off-resonant-two level system defects
when compared to untreated samples. Imaging with high-resolution TEM shows that
the barrier is still predominantly amorphous with a more uniform distribution
of aluminum coordination across the barrier relative to untreated junctions.
This new approach is expected to be widely applicable to a broad range of
devices that rely on amorphous aluminum oxide, as well as the many other
metal-insulator-metal structures used in modern electronics.",2401.07415v2
2024-01-22,Two New Members of the Covalent Organic Frameworks Family: Crystalline 2D-Oxocarbon and 3D-Borocarbon Structures,"While graphene oxide (GO) is representative of a disordered phase of
oxocarbons with lackluster electronic properties, the coexistence of ordered,
stoichiometric solid-state carbon oxides with graphene brings renewed momentum
to the exploration of two-dimensional crystalline oxocarbons. This enduring
subject, spanning decades, has recently witnessed significant advancements. In
this context, our study delves into a novel material class, COF-66, notable for
its meticulously ordered two-dimensional crystalline structure and intrinsic
porosity. Employing a global optimization algorithm alongside
density-functional calculations, our investigation highlights a standout member
within the COF-66 family exceptional quasi-flat oxocarbon (C6O6)exhibiting an
unconventional oxygen-decorated pore configuration. This pioneering study
introduces C6O6 as an innovative entrant into the crystalline carbon oxide
arena, augmenting the established understanding alongside the well-recognized
graphene oxide and two graphene monoxide, i.e. {\alpha}-GMO and \b{eta}-GMO.
Expanding the exploration, the COF-66 series encompasses 2D-porous carbon
nitride (C6N6) and the recently synthesized 2D-porous boroxine (B6O6), adhering
to a generalized stoichiometry of X6Y6, where X = B, C, and Y = B, N, O, with X
6= Y. Remarkably, the entire COF-66 ensemble adopts a 2D-crystalline framework,
with the exception of C6B6, which assumes a distinct 3D-crystalline
arrangement. Employing the PBE (HSE06) level of theory, our electronic
structure calculations yield band gap values of 0.01 (0.05) eV, 3.68 (5.29) eV,
0.00 (0.23) eV, and 1.53 (3.09) eV for B6N6, B6O6, C6B6, and C6N6,
respectively, reinforcing and aligning with prior investigations.",2401.11843v1
2024-03-05,Highly Reproducible and CMOS-compatible VO2-based Oscillators for Brain-inspired Computing,"With remarkable electrical and optical switching properties induced at low
power and near room temperature (68C), vanadium dioxide (VO2) has sparked
rising interest in unconventional computing among the phase-change materials
research community. The scalability and the potential to compute beyond the von
Neumann model make VO2 especially appealing for implementation in oscillating
neural networks for artificial intelligence (AI) applications, to solve
constraint satisfaction problems, and for pattern recognition. Its integration
into large networks of oscillators on a Silicon platform still poses challenges
associated with the stabilization in the correct oxidation state and the
ability to fabricate a structure with predictable electrical behavior showing
very low variability. In this work, the role played by the different annealing
parameters applied by three methods (slow thermal annealing, flash annealing,
and rapid thermal annealing), following the vanadium oxide atomic layer
deposition (ALD), on the formation of VO2 grains is studied and an optimal
substrate stack configuration that minimizes variability between devices is
proposed. Material and electrical characterizations are performed on the
different films and a step-by-step recipe to build reproducible VO2-based
oscillators is presented, which is argued to be made possible thanks to the
introduction of a hafnium oxide (HfO2) layer between the silicon substrate and
the vanadium oxide layer. Up to seven nearly identical VO2-based devices are
contacted simultaneously to create a network of oscillators, paving the way for
large-scale implementation of VO2 oscillating neural networks.",2403.02822v1
2024-03-14,Multi-droplet combustion in the presence of homogeneous and heterogeneous atomizations,"The effects of heterogeneous and homogeneous atomizations on combustion
dynamics and flame spread rates of multi-droplets are experimentally
investigated. The utilized fuel is biodiesel, which is doped with graphene
oxide and blended with ethanol. Stable fuel suspensions are prepared. Either
one droplet is positioned at the intersection of two thin fibers or an array of
three droplets are positioned along a horizontal line and at the intersections
of fibers. Simultaneous and time-resolved flame chemiluminescence and
shadowgraphy techniques are utilized for imaging the flame and droplets,
respectively. It is observed that, for a single droplet combustion of
biodiesel, relatively low frequency (about 10 Hz) dynamics appear in the second
half of the droplet life-time, which is due to heterogeneous atomizations.
Blending with ethanol leads to homogeneous atomizations with dynamics featuring
frequencies smaller than 50 Hz and at the beginning of the droplet lifetime. It
is reported that the homogeneous atomizations lead to at least three times
larger root-mean-square oscillations of the flame chemiluminescence compared to
that for heterogeneous atomizations. For all tested multi-droplet
configurations, independent of the graphene oxide doping concentration and
blending with ethanol, the most dominant frequency of flame chemiluminescence
oscillations is about 10-15 Hz. It is observed that the heterogeneous
atomizations lead to a flame spread rate of about 6-8 mm2/s, with largest
values reported for doping with moderate concentration of graphene oxide.
Compared to that for heterogeneous atomizations, the flame spread rate for
homogeneous atomizations are significantly larger 10-40 mm2/s, are not
sensitive to graphene oxide doping concentration, and feature a positive
relation with the root-mean-square of the flame chemiluminescence oscillations.",2403.09823v1
2024-03-25,Direct activation of PMS by highly dispersed amorphous CoOx clusters in anatase TiO2 nanosheets for efficient oxidation of biomass-derived alcohols,"Developing a green and cost-effective catalytic system for the selective
oxidation of biomass-derived alcohols is vital for the sustainable synthesis of
fine chemicals. Herein, highly dispersed subnanometric amorphous CoOx clusters
in anatase TiO2 nanosheets (Co-TiO2) fabricated by green solvent CO2 assisted
approach could directly activate peroxymonosulfate (PMS) for the highly
selective oxidation of various biomass-derived alcohols. Advanced
characterizations (e.g., EXAFS, EPR, AC HAADF-STEM) reveal that a strong
interaction of CoOx clusters and the anatase TiO2 support exist in Co-TiO2 and
Co atom in Co-TiO2 is mainly consisted of Co2+ and Co3+. The Co-TiO2 catalyst
offers superior catalytic performance in the conversion of six types of
alcohols (e.g., benzyl alcohol (BAL), 5-hydroxymethylfurfural (HMF)) with high
selectivity to produce corresponding aldehydes. Highly dispersed CoOx clusters
and the interaction between CoOx clusters and TiO2 support contribute to the
superior performance. Mechanism studies show that SO4 radicals play the
dominant role in the selective oxidation of model reactant BAL and 1O2
participates in the non-radical pathway. DFT calculations are well matched with
experiment and decipher that the strong interaction between CoOx clusters and
TiO2 support promotes the formation of SO4 and SO5.",2403.16733v1
2006-12-04,Discovery of Fundamental Mass Ratio Relationships of Whole-Rock Chondritic Major Elements: Implications on Ordinary Chondrite Formation and on Planet Mercury's Composition,"The high occurrence on Earth of ordinary chondrite meteorites and the making
of models based upon arbitrary assumptions has led to some confusion about the
origin of ordinary chondrites. Major element fractionation among chondrites has
been discussed for decades as ratios relative to Si or Mg. Expressing ratios
relative to Fe leads to a new relationship admitting the possibility that
ordinary chondrite meteorites are derived from two components: one is a
relatively undifferentiated, primitive component, oxidized like the CI or C1
chondrites; the other is a somewhat differentiated, planetary component, with
oxidation state like the reduced enstatite chondrites. Such a picture would
seem to explain for the ordinary chondrites, their major element compositions,
their intermediate states of oxidation, and their ubiquitous defiencies of
refractory siderophile elements. I suggest that the planetary component of
ordinary chondrite formation consists of planet Mercury's missing complement of
elements, presumably separated from protoplanetary Mercury during its
formation.",0612062v1
1996-05-07,Electronic Hamiltonian for Transition Metal Oxide Compounds,"An effective electronic Hamiltonian for transition metal oxide compounds is
presented. For Mn-oxides, the Hamiltonian contains spin-2 ``spins'' and
spin-3/2 ``holes'' as degrees of freedom. The model is constructed from the
Kondo-lattice Hamiltonian for mobile $e_g$ electrons and localized $t_{2g}$
spins, in the limit of a large Hund's coupling. The effective electron bond
hopping amplitude fluctuates in sign as the total spin of the bond changes. In
the large spin limit, the hopping amplitude for electrons aligned with the core
ions is complex and a Berry phase is accumulated when these electrons move in
loops. The new model is compared with the standard double exchange Hamiltonian.
Both have ferromagnetic ground states at finite hole density and low
temperatures, but their critical temperatures could be substantially different
due to the frustration effects induced by the Berry phase.",9605041v1
1996-09-12,Ferromagnetism in Electronic Models for Manganites,"Ground state properties of the Kondo model for manganese oxides in one
dimension are studied using numerical techniques. The large Hund coupling
($J_{H}$) limit is specially analyzed. A robust region of fully saturated
ferromagnetism (FM) is identified at all densities. For open boundary
conditions it is shown exactly that the ground state is FM at $J_{H} = \infty$.
Hole-spin phase separation competing with FM was also observed when a large
exchange $J$ between the $Mn^{3+}$ ions is used. As the spin of the transition
metal ion grows, the hole mobility decreases providing a tentative explanation
for the differences between Cu-oxides and Mn-oxides.",9609111v2
1997-09-30,Electron Correlation and Jahn-Teller Interaction in Manganese Oxides,"The interplay between the electron repulsion $U$ and the Jahn-Teller
electron-phonon interation $E_{LR}$ is studied with a large $d$ model for the
ferromagnetic state of the manganese oxides. These two interactions collaborate
to induce the local isospin (orbital) moments and reduce the bandwidth $B$.
Especially the retardation effect of the Jahn-Teller phonon with the frequency
$\Omega$ is effective to reduce $B$, but the strong $\Omega$-dependence occurs
even when the Coulombic interaction is dominating ($ U >> E_{LR}$) as long as
$E_{LR} > \Omega$. The phonon spectrum consists of two components, i.e., the
temperature independent sharp peak at $\omega = {\tilde \Omega} = \Omega [(U +4
E_{LR})/U]^{1/2}$ and that corresponding to the Kondo peak. These results
compared with the experiments suggest that $\Omega <E_{LR} <U$ in the metallic
manganese oxides.",9709335v1
1998-05-27,Nanolithography by non-contact AFM induced local oxidation : Fabrication of tunneling barriers suitable for single electron devices,"We study local oxidation induced by dynamic atomic force microscopy (AFM),
commonly called TappingMode AFM. This minimizes the field induced forces, which
cause the tip to blunt, and enables us to use very fine tips. We are able to
fabricate Ti/TiOx line grids with 18 nm period and well defined isolating
barriers as small as 15 nm. These junctions show a non-linear current-voltage
characteristic and an exponential dependence of the conductance on the oxide
width, indicating tunneling as the dominant conduction mechanism. From the
conductance - barrier width dependence we derive a barrier height of 178 meV.
Numerical calculations of the lateral field distribution for different tip
geometries allow to design the optimum tip for the most localised electric
field. The electron-beam-deposition (EBD) technique makes it possible to
actually produce tips of the desired geometry.",9805350v1
1998-11-06,Structure and oxidation kinetics of the Si(100)-SiO2 interface,"We present first-principles calculations of the structural and electronic
properties of Si(001)-SiO2 interfaces. We first arrive at reasonable structures
for the c-Si/a-SiO2 interface via a Monte-Carlo simulated annealing applied to
an empirical interatomic potential, and then relax these structures using
first-principles calculations within the framework of density-functional
theory. We find a transition region at the interface, having a thickness on the
order of 20\AA, in which there is some oxygen deficiency and a corresponding
presence of sub-oxide Si species (mostly Si^+2 and Si^+3). Distributions of
bond lengths and bond angles, and the nature of the electronic states at the
interface, are investigated and discussed. The behavior of atomic oxygen in
a-SiO2 is also investigated. The peroxyl linkage configuration is found to be
lower in energy than interstitial or threefold configurations. Based on these
results, we suggest a possible mechanism for oxygen diffusion in a-SiO2 that
may be relevant to the oxidation process.",9811098v1
1999-03-23,X-ray photoelectron 3s spectra of transition metal oxides,"We present metal 3s x-ray photoelectron spectra of different transition metal
oxides. The values of the 3s exchange splitting for the 3d metal oxides are
given as a function of the 3d electron number in the ground state. The spectra
were analysed using the simple two-configuration model of the interatomic
configuration mixing. The change of the 3s spectra is ascribed to the change of
the charge-transfer energy.",9903354v1
1999-11-12,Temperature-Dependent Pseudogaps in Colossal Magnetoresistive Oxides,"Direct electronic structure measurements of a variety of the colossal
magnetoresistive oxides show the presence of a pseudogap at the Fermi energy
E_F which drastically suppresses the electron spectral function at E_F. The
pseudogap is a strong function of the layer number of the samples (sample
dimensionality) and is strongly temperature dependent, with the changes
beginning at the ferromagnetic transition temperature T_c. These trends are
consistent with the major transport trends of the CMR oxides, implying a direct
relationship between the pseudogap and transport, including the ""colossal""
conductivity changes which occur across T_c. The k-dependence of the
temperature-dependent effects indicate that the pseudogap observed in these
compounds is not due to the extrinsic effects proposed by Joynt.",9911189v1
2000-03-16,"Structural properties and quasiparticule energies of cubic SrO, MgO and SrTiO3","The structural properties and the band structures of the charge-transfer
insulating oxides SrO, MgO and SrTiO3 are computed both within density
functional theory in the local density approximation (LDA) and in the Hedin's
GW scheme for self-energy corrections, by using a model dielectric function,
which approximately includes local field and dynamical effects. The deep
valence states are shifted by the GW method to higher binding energies, in very
good agreement with photoemission spectra. Since in all of these oxides the
direct gaps at high-symmetry points of the Brillouin zone may be very sensitive
to the actual value of the lattice parameter a, already at the LDA level,
self-energy corrections are computed both at the theoretical and the
experimental a. For MgO and SrO, the values of the transition energies between
the valence and the conduction bands are improved by GW corrections, while for
SrTiO3 they are overestimated. The results are discussed in relation to the
importance of local field effects and to the nature of the electronic states in
these insulating oxides.",0003275v1
2001-05-26,Discrete saturation thickness and anomalous potential height of native ultrathin aluminum oxide tunnel barriers,"We have investigated planar metal - insulator - metal tunnel junctions with
aluminum oxide as dielectricum. These oxide barriers were grown on an aluminum
electrode in pure oxygen at room temperature till saturation. We observed
discrete barrier widths separated by \Delta s \approx 0.38 nm, corresponding to
the addition of one layer of oxygen atoms. The minimum thickness of s_0 \approx
0.54 nm is due to a double layer of oxygen. We found a strong and systematic
dependence of the barrier height \Phi_0 on the thickness s like \Phi_0 \approx
2.5 eV / s^2(nm), which nearly coincides with the kinetic electron energy E =
h^2/2ms^2 for which the deBroglie wavelength matches the width of the barrier.",0105511v1
2002-02-06,Thermoelectric properties of the brownmillerite oxide Ca_{2-y}La_yCo_{2-x}Al_xO_5,"We prepared the brownmillerite oxide Ca_{2-y}La_yCo_{2-x}Al_xO_5, and found
that it was an n-type conductor. The thermopower and the resistivity of the
single crystal are -90 microV/K and 68 mOhm cm along the ab direction at 440 K,
which suggest relatively good thermoelectrical properties, compared with other
transition-metal oxides. Their temperature dependences are of activation type,
and the activation energies are 0.2 eV for the resistivity and 0.04 eV for the
thermopower. These energies differ by one order in magnitude, which implies
that a polaron dominates the charge transport. A sign of the thermopower of the
polycrystals changes from negative to positive at 500 K, indicating that holes
are excited thermally to decrease the magnitude of thermopower.",0202087v1
2002-02-07,Statistical properties of charged interfaces,"We consider the equilibrium statistical properties of interfaces submitted to
competing interactions; a long-range repulsive Coulomb interaction inherent to
the charged interface and a short-range, anisotropic, attractive one due to
either elasticity or confinement. We focus on one-dimensional interfaces such
as strings. Model systems considered for applications are mainly aggregates of
solitons in polyacetylene and other charge density wave systems, domain lines
in uniaxial ferroelectrics and the stripe phase of oxides. At zero temperature,
we find a shape instability which lead, via phase transitions, to tilted
phases. Depending on the regime, elastic or confinement, the order of the
zero-temperature transition changes. Thermal fluctuations lead to a pure
Coulomb roughening of the string, in addition to the usual one, and to the
presence of angular kinks. We suggest that such instabilities might explain the
tilting of stripes in cuprate oxides. The 3D problem of the charged wall is
also analyzed. The latter experiences instabilities towards various tilted
phases separated by a tricritical point in the elastic regime. In the
confinement regime, the increase of dimensionality favors either the melting of
the wall into a Wigner crystal of its constituent charges or a strongly
inclined wall which might have been observed in nickelate oxides.",0202122v2
2002-07-06,Charge transfer in molecular conductors -- oxidation or reduction?,"We discuss the nature of charge transfer in molecular conductors upon
connecting to two metallic contacts and imposing a voltage bias across them.
The sign of the charge transfer (oxidation vs. reduction) depends on the
position of the metal Fermi energy with respect to the molecular levels. In
addition, the charge transfer depends on the strength of the coupling
(chemisorption vs. physisorption) with the contacts. A convenient way to
establish the nature and onset of the charge transfer and the corresponding
features in the I-V is to draw an energy level diagram for each spin species.
Starting from such a level diagram, we argue that transport in the Tour-Reed
switching molecules, which consist of a central phenyl ring with a nitroamine
redox center, involves the oxidation of a highest occupied molecular orbital
(HOMO)-based level.",0207174v1
2002-09-25,Nanoscale Electric Phenomena at Oxide Surfaces and Interfaces by Scanning Probe Microscopy,"Scanning Probe Microscopy is used to study and quantify the nanoscale
electric phenomena in the two classes of oxide systems, namely transport at
electroactive grain boundaries and surface behavior of ferroelectric materials.
Scanning Impedance Microscopy is developed to study the capacitance and local
C-V characteristic of the interfaces combining the spatial resolution of
traditional SPMs with the precision of conventional electrical measurements.
SPM of SrTiO3 grain boundaries in conjunction with variable temperature
impedance spectroscopy and I-V measurements allowed to find and theoretically
justify the effect of field suppression of dielectric constant in the vicinity
of the electroactive interfaces in strontium titanate. Similar approaches were
used to study ferroelectric properties and ac and dc transport behavior in a
number of polycrystalline oxides.
  In the second part, the effects of local charge density on the chemistry and
physics of ferroelectric surfaces are studied. The kinetics and thermodynamics
parameters of adsorption are assessed by variable temperature SPM.
Piezoresponse force microscopy is used to engineer domain patterns on
ferroelectric surfaces. Localized photochemical activity of ferroelectric
surfaces is explored as a new tool for metallic nanostructures fabrication.",0209599v1
2002-09-30,Nanoscale Phase Separation in Colossal Magnetoresistance Materials: A Lesson for the Cuprates?,"A recent vast experimental and theoretical effort in manganites has shown
that the colossal magnetoresistance effect can be understood based on the
competition of charge-ordered and ferromagnetic phases. The general aspects of
the theoretical description appear to be valid for any compound with intrinsic
phase competition. In high temperature superconductors, recent experiments have
shown the existence of intrinsic inhomogeneities in many materials, revealing a
phenomenology quite similar to that of manganese oxides. Here, the results for
manganites are briefly reviewed with emphasis on the general aspects. In
addition, theoretical speculations are formulated in the context of Cu-oxides
by mere analogy with manganites. This includes a tentative explanation of the
spin-glass regime as a mixture of antiferromagnetic and superconducting
islands, the rationalization of the pseudogap temperature T* as a Griffiths
temperature where clusters start forming upon cooling, the prediction of
""colossal"" effects in cuprates, and the observation that quenched disorder may
be far more relevant in Cu-oxides than previously anticipated.",0209689v2
2002-11-23,Two-dimensional charge order in layered 2-1-4 perovskite oxides,"Monte Carlo simulations are performed on the three-dimensional (3D) Ising
model with the 2-1-4 layered perovskite structure as a minimal model for
checkerboard charge ordering phenomena in layered perovskite oxides. Due to the
interlayer frustration, only 2D long-range order emerges with a finite
correlation length along the c axis. Critical exponents of the transition
change continuously as a function of the interlayer coupling constant. The
interlayer long-range Coulomb interaction decays exponentially and is
negligible even between the second-neighbor layers. Instead, monoclinic
distortion of a tetragonal unit cell lifts the macroscopic degeneracy to induce
a 3D charge ordering. The dimensionality of the charge order in
La$_{0.5}$Sr$_{1.5}$MnO$_4$ is discussed from this viewpoint.",0211520v2
2003-03-06,Vibrational dynamics of solid poly(ethylene oxide),"Molecular dynamics (MD) simulations of crystalline poly(ethylene oxide) (PEO)
have been carried out in order to study its vibrational properties. The
vibrational density of states has been calculated using a normal mode analysis
(NMA) and also through the velocity autocorrelation function of the atoms.
Results agree well with experimental spectroscopic data. System size effects in
the crystalline state, studied through a comparison between results for 16 unit
cells and that for one unit cell has shown important differences in the
features below 100 cm^-1. Effects of interchain interactions are examined by a
comparison of the spectra in the condensed state to that obtained for an
isolated oligomer of ethylene oxide. Calculations of the local character of the
modes indicate the presence of collective excitations for frequencies lower
than 100 cm^-1, in which around 8 to 12 successive atoms of the polymer
backbone participate. The backbone twisting of helical chains about their long
axes is dominant in these low frequency modes.",0303102v2
2003-05-13,Why is a noble metal catalytically active? The role of the O-Ag interaction in the function of silver as an oxidation catalyst,"Extensive density-functional theory calculations, and taking into account
temperature and pressure, affords a comprehensive picture of the behavior and
interaction of oxygen and Ag(111), and provides valuable insight into the
function of silver as an oxidation catalyst. The obtained phase-diagram reveals
the most stable species present in a given environment and thus identifies (and
excludes) possibly active oxygen species. In particular, for the conditions of
ethylene epoxidation, a thin oxide-like structure is most stable, suggesting
that such atomic O species are actuating the catalysis, in contrast to hitherto
proposed molecular-like species.",0305297v1
2003-05-24,Studies on La2-xPrxCayBa2Cu4+yOz (0.1 < x < 0.5) type mixed oxide superconductors,"The La2-xPrxCayBa2Cu4+yOz (LaPrCaBCO) mixed oxides have been studied for
their structural and superconducting properties using X-ray diffraction (XRD),
d. c. resistivity, d. c. susceptibility and iodometric double titration. All
the LaPrCaBCO samples for x = 0.1 - 0.5, exhibit tetragonal crystalline
structure with P 4/mmm space group as determined by Rietveld analysis of the
X-ray diffraction data. With increasing x, enhancement in Tc is observed, which
is quite interesting for Pr substituted high Tc oxides. Maximum Tc ~ 58 K has
been observed for x = 0.5(La-2125 stoichiometry). The results of structural
studies and superconducting property measurements are presented in light of
increase in Tc in LaPrCaBCO system with increasing Pr concentration.",0305579v1
2003-05-30,A Low-Temperature Atomic Layer Deposition Liftoff Method for Microelectronic and Nanoelectronic Applications,"We report a novel method for depositing patterned dielectric layers with
sub-micron features using atomic layer deposition (ALD). The patterned films
are superior to sputtered or evaporated films in continuity, smoothness,
conformality, and minimum feature size. Films were deposited at 100-150C using
several different precursors and patterned using either PMMA or photoresist.
The low deposition temperature permits uniform film growth without significant
outgassing or hardbaking of resist layers. A liftoff technique presented here
gives sharp step edges with edge roughness as low as ~10 nm. We also measure
dielectric constants (k) and breakdown fields for the high-k materials aluminum
oxide (k ~ 8-9), hafnium oxide (k ~ 16-19) and zirconium oxide (k ~ 20-29),
grown under similar low temperature conditions.",0305711v2
2003-07-02,O adsorption and incipient oxidation of the Mg(0001) surface,"First principles density functional calculations are used to study the early
oxidation stages of the Mg(0001) surface for oxygen coverages 1/16 <= Theta <=
3 monolayers. It is found that at very low coverages O is incorporated below
the topmost Mg layer in tetrahedral sites. At higher oxygen-load the binding in
on-surface sites is increased but at one monolayer coverage the on-surface
binding is still about 60 meV weaker than for subsurface sites. The subsurface
octahedral sites are found to be unfavorable compared to subsurface tetrahedral
sites and to on-surface sites. At higher coverages oxygen adsorbs both under
the surface and up. Our calculations predict island formation and clustering of
incorporated and adsorbed oxygen in agreement with previous calculations. The
calculated configurations are compared with the angle-scanned x-ray
photoelectron diffraction experiment to determine the geometrical structure of
the oxidized Mg(0001) surface.",0307038v1
2003-08-14,Effect of interface bonding on spin-dependent tunneling from the oxidized Co surface,"We demonstrate that the factorization of the tunneling transmission into the
product of two surface transmission functions and a vacuum decay factor allows
one to generalize Julliere's formula and explain the meaning of the ``tunneling
density of states'' in some limiting cases. Using this factorization we
calculate spin-dependent tunneling from clean and oxidized fcc Co surfaces
through vacuum into Al using the principal-layer Green's function approach. We
demonstrate that a monolayer of oxygen on the Co (111) surface creates a
spin-filter effect due to the Co-O bonding which produces an additional
tunneling barrier in the minority-spin channel. This changes the minority-spin
dominated conductance for the clean Co surface into a majority spin dominated
conductance for the oxidized Co surface.",0308268v2
2003-08-25,Polarons in Complex Oxides and Molecular Nanowires,"There is a growing understanding that transport properties of complex oxides
and individual molecules are dominated by polaron physics. In superconducting
oxides the long-range Froehlich and short-range Jahn-Teller electron-phonon
interactions bind carriers into real space pairs - small bipolarons with
surprisingly low mass but sufficient binding energy, while the long-range
Coulomb repulsion keeps bipolarons apart preventing their clustering. The
bipolaron theory numerically explains high Tc values without any fitting
parameters and describes other key features of the cuprates. The same approach
provides a new insite into the theory of transport through molecular nanowires
and quantum dots (MQD). Attractive polaron-polaron correlations lead to a
""switching"" phenomenon in the current-voltage characteristics of MQD. The
degenerate MQD with strong electron-vibron coupling has two stable current
states (a volatile memory), which might be useful in molecular electronics.",0308489v1
2004-02-18,Oxidation State of Cobalt in the NaxCoO2-d yH2O Superconductor,"Here we present results of accurate wet-chemical redox analyses, revealing
that the oxidation number of cobalt in the newly discovered CoO2-layer
superconductor, NaxCoO2 yH2O (x ~ 0.36, y ~ 1.3) is ~ 3.46. This value is
significantly lower than the one (~ 3.64) expected on the basis of the value
determined for the Na to Co stoichiometry ratio, x. The ""lower-than-expected""
value for the Co oxidation state may be alternatively explained by presence of
oxygen vacancies or excess protons. Moreover, the result implies that rather
than an electron-doped Co(IV) lattice the phase should be considered as a
hole-doped Co(III) lattice.",0402484v1
2004-02-27,Field-Induced Resistive Switching in Metal-Oxide Interfaces,"We investigate the polarity-dependent field-induced resistive switching
phenomenon driven by electric pulses in perovskite oxides. Our data show that
the switching is a common occurrence restricted to an interfacial layer between
a deposited metal electrode and the oxide. We determine through impedance
spectroscopy that the interfacial layer is no thicker than 10 nm and that the
switch is accompanied by a small capacitance increase associated with charge
accumulation. Based on interfacial I-V characterization and measurement of the
temperature dependence of the resistance, we propose that a field-created
crystalline defect mechanism, which is controllable for devices, drives the
switch.",0402687v1
2004-04-07,Hopping versus bulk conductivity in transparent oxides: 12CaO.7Al2O3,"First-principles calculations of the mayenite-based oxide,
[Ca12Al14O32]{2+}(2e-), reveal the mechanism responsible for its high
conductivity. A detailed comparison of the electronic and optical properties of
this material with those of the recently discovered novel transparent
conducting oxide, H-doped UV-activated Ca12Al14O33, allowed us to conclude that
the enhanced conductivity in [Ca12Al14O32]{2+}(2e-) is achieved by elimination
of the Coulomb blocade of the charge carriers. This results in a transition
from variable range hopping behavior with a Coulomb gap in H-doped
UV-irradiated Ca12Al14O33 to bulk conductivity in [Ca12Al14O32]{2+}(2e-).
Further, the high degree of the delocalization of the conduction electrons
obtained in [Ca12Al14O32]{2+}(2e-) indicate that it cannot be classified as an
electride, originally suggested.",0404187v1
2004-05-12,A novel route to phase formation of cobalt oxyhydrates using KMnO4 as an oxidizing agent,"We have first succeefully synthesized the sodium cobalt oxyhydrate
superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a
novel route to form the superconductive phase of NaxCoO2.yH2O without resorting
to the commonly used Br2/CH3CN solution. The role of the KMnO4 is to
de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co
ion as a result. The higher molar ratio of KMnO4 relative to the sodium content
tends to remove more Na+ from the parent compound and results in a slight
expansion of the c-axis in the unit cell. The superconducting transition
temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with
the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and
2.29.",0405244v1
2004-07-08,Surface Chemistry and Electrical Properties of Germanium Nanowires,"Germanium nanowires with p- and n-dopants were synthesized by chemical vapor
deposition and used to construct complementary field effect transistors .
Electrical transport and x-ray photoelectron spectroscopy data are correlated
to glean the effects of Ge surface chemistry to the electrical characteristics
of GeNWs. Large hysteresis due to water molecules strongly bound to GeO2 on
GeNWs is revealed. Different oxidation behavior and hysteresis characteristics
and opposite band bending due to Fermi level pinning by interface states
between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum
annealing above 400C is used to remove surface oxides and eliminate hysteresis
in GeNW FETs. High-k dielectric HfO2 films grown on clean GeNW surfaces by
atomic layer deposition (ALD) using an alkylamide precursor is effective
serving as the first layer of surface passivation. Lastly, the depletion length
along the radial direction of nanowires is evaluated. The result suggests that
surface effects could be dominant over the bulk properties of small diameter
wires.",0407186v1
2004-07-22,Strongly Enhanced Thermal Stability of Crystalline Organic Thin Films Induced by Aluminum Oxide Capping Layers,"We show that the thermal stability of thin films of the organic semiconductor
diindenoperylene (DIP) can be strongly enhanced by aluminum oxide capping
layers. By thermal desorption spectroscopy and in-situ X-ray diffraction we
demonstrate that organic films do not only stay on the substrate, but even
remain crystalline up to 460C, i.e. 270 deg. above their desorption point for
uncapped films (190C). We argue that this strong enhancement of the thermal
stability compared to uncapped and also metal-capped organic layers is related
to the very weak diffusion of aluminum oxide and the structurally well-defined
as-grown interfaces. We discuss possible mechanisms for the eventual breakdown
at high temperatures.",0407588v1
2004-07-29,Structural Distortion and Disappearance of Layer Ordering in LixCoO2x2H2O,"The structure of a new member of the AxCoO2 x nH2O family (A=Li,Na,K) was
determined by high-resolution synchrotron X-ray powder diffraction. Layered
lithium cobalt oxide hydrate LixCoO2 x 2H2O crystallizes in a disordered
monoclinic structure (space group C2/m) with lattice parameters a = 4.8915(2)
A, b = 2.8239(1) A, c = 10.7033(9) A, beta = 112.386(4)deg. Unlike the
superconducting sodium cobalt oxide hydrate, this material possesses a
structure with lithium-water layers intercalated between disordered octahedral
sheets of cobalt oxide. The interlayer spacing is slightly larger (~0.9%) due
to the higher water content, and one of the two lithium sites extends into the
water layer. This material shows no superconducting transition above 2K.",0407778v1
2005-01-28,High-Performance Carbon Nanotube Field-Effect Transistor with Tunable Polarities,"State-of-the-art carbon nanotube field-effect transistors (CNFETs) behave as
Schottky barrier (SB)-modulated transistors. It is known that vertical scaling
of the gate oxide significantly improves the performance of these devices.
However, decreasing the oxide thickness also results in pronounced ambipolar
transistor characteristics and increased drain leakage currents. Using a novel
device concept, we have fabricated high-performance, enhancement-mode CNFETs
exhibiting n or p-type unipolar behavior, tunable by electrostatic and/or
chemical doping, with excellent OFF-state performance and a steep subthreshold
swing (S =63 mV/dec). The device design allows for aggressive oxide thickness
and gate length scaling while maintaining the desired device characteristics.",0501690v1
2005-03-22,Improvement of current-control induced by oxide crenel in very short field-effect-transistor,"A 2D quantum ballistic transport model based on the non-equilibrium Green's
function formalism has been used to theoretically investigate the effects
induced by an oxide crenel in a very short (7 nm) thin-film
metal-oxide-semiconductor-field-effect-transistor. Our investigation shows that
a well adjusted crenel permits an improvement of on-off current ratio Ion/Ioff
of about 244% with no detrimental change in the drive current Ion. This
remarkable result is explained by a nontrivial influence of crenel on
conduction band-structure in thin-film. Therefore a well optimized crenel seems
to be a good solution to have a much better control of short channel effects in
transistor where the transport has a strong quantum behavior.",0503556v1
2005-04-12,"First-principles study of cubic perovskites SrMO_3 (M = Ti, V, Zr and Nb)","Using the full-potential linearized-augmented-plane-wave (FLAPW) method, we
have analyzed systematically the trends in the structural and electronic
properties of the 3d and 4d transition-metal oxides SrMO_3 (M = Ti, V, Zr and
Nb). The optimized lattice parameters, bulk modules, densities of states, band
structures and charge density distributions are obtained and compared with the
available theoretical and experimental data. The energy gap between O2p - Md
bands increases as the covalency of the system decreases going from 3d to 4d
based perovskites. The electron configurations of Sr(Ti,Zr)O_3 and Sr(V,Nb)O_3
usually referred to as d^0 and d^1 oxides, respectively, differ considerably
from these idealized ""ionic"" configurations, and the deviations increase with
increasing of the d-p covalent overlap in the oxides.",0504286v1
2005-05-06,Oxygen diffusion in nanostructured perovskites,"Nonstoichiometric perovskite-related oxides (such as ferrites and cobaltites,
etc.) are characterized by fast oxygen transport at ambient temperatures, which
relates to the microstructural texturing of these materials, consisting wholly
of nanoscale microdomains.
  We have developed an inhomogeneous diffusion model to describe the kinetics
of oxygen incorporation into nanostructured oxides. Nanodomain boundaries are
assumed to be the high diffusivity paths for oxygen transport whereas diffusion
into the domains proceeds much slower. Using Laplace transform methods, an
exact solution is found for a ramped stepwise potential, allowing fitting of
the experimental data to theoretical curves (in Laplace transforms).
  A further model generalization is considered by introducing additional
parameters for the size distribution of domains and particles.
  The model has been applied for qualitative evaluation of oxygen diffusion
parameters from the data on wet electrochemical oxidation of nano-structured
perovskite SrCo_0.5Fe_0.2Ta_0.3O_{3-y} samples.",0505149v2
2005-06-01,Selective epitaxial growth of sub-micron complex oxide structures by amorphous SrTiO3,"A chemical-free technique for fabricating submicron complex oxide structures
has been developed based on selective epitaxial growth. The crystallinity and
hence the conductivity of the complex oxide is inhibited by amorphous SrTiO3
(STO). Using a combination of pulsed laser deposition and electron-beam
lithography, amorphous STO barriers are first deposited on a single crystal
substrate. A thin film is then deposited on the patterned substrate with the
amorphous STO barriers acting to electrically and physically isolate different
regions of the film. Since no chemical or physical etchants come in contact
with the deposited film, its integrity and stability are preserved. This
technique has successfully produced sub-micron YBCO and LCMO structures.",0506001v1
2005-09-08,Real-time observation of non-equilibrium liquid condensate confined at tensile crack tips in oxide glasses,"Since crack propagation in oxide materials at low crack velocities is partly
determined by chemical corrosion, proper knowledge of the crack tip chemistry
is crucial for understanding fracture in these materials. Such knowledge can be
obtained only from in situ studies because the processes that occur in the
highly confined environment of the crack tip are very different from those that
take place at free surfaces, or that can be traced post mortem. We report the
occurrence of hydrous liquid condensate between the two fracture surfaces in
the vicinity of the tip of tensile cracks in silica. Observations are performed
in real-time by means of atomic force microscopy (AFM) at continuously
controlled crack velocities in the regime of stress corrosion. Condensate
formation and changes in extent and shape are demonstrated for a wide range of
macroscopic humidity at different crack speeds. Its liquid character is
confirmed by the study of AFM phase-contrast data. It is believed that this
evidence of a nanoscale liquid hydrous phase at the crack tip will enable novel
insights in the chemistry of failure of oxide materials.",0509209v1
2007-01-15,Microscopic annealing process and its impact on superconductivity in T'-structure electron-doped copper oxides,"High-transition-temperature superconductivity arises in copper oxides when
holes or electrons are doped into the CuO2 planes of their insulating parent
compounds. While hole-doping quickly induces metallic behavior and
superconductivity in many cuprates, electron-doping alone is insufficient in
materials such as R2CuO4 (R is Nd, Pr, La, Ce, etc.), where it is necessary to
anneal an as-grown sample in a low-oxygen environment to remove a tiny amount
of oxygen in order to induce superconductivity. Here we show that the
microscopic process of oxygen reduction repairs Cu deficiencies in the as-grown
materials and creates oxygen vacancies in the stoichiometric CuO2 planes,
effectively reducing disorder and providing itinerant carriers for
superconductivity. The resolution of this long-standing materials issue
suggests that the fundamental mechanism for superconductivity is the same for
electron- and hole-doped copper oxides.",0701345v1
2007-02-26,Nonpolar resistance switching of metal/binary-transition-metal oxides/metal sandwiches: homogeneous/inhomogeneous transition of current distribution,"Exotic features of a metal/oxide/metal (MOM) sandwich, which will be the
basis for a drastically innovative nonvolatile memory device, is brought to
light from a physical point of view. Here the insulator is one of the
ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe2O3,
NiO, and CoO. The sandwich exhibits a resistance that reversibly switches
between two states: one is a highly resistive off-state and the other is a
conductive on-state. Several distinct features were universally observed in
these binary TMO sandwiches: namely, nonpolar switching, non-volatile threshold
switching, and current--voltage duality. From the systematic sample-size
dependence of the resistance in on- and off-states, we conclude that the
resistance switching is due to the homogeneous/inhomogeneous transition of the
current distribution at the interface.",0702564v1
2007-03-28,Electronic parameters for the hole transfer in DNA duplex oligomers,"We report on our calculations of the inner-sphere reorganization energy and
the interaction of the pi orbitals within DNA oligomers. The exponential
decrease of the electronic coupling between the highest and second highest
occupied base orbitals of the intrastrand nucleobases in the (A-T)n and (G-C)n
oligomers have been found with an increase of the sequence number n in the DNA
structure. We conclude that for realistic estimation of the electronic coupling
values between the nucleobases within the DNA molecule, a DNA chain containing
at least four base pairs is required. We estimate the geometry relaxation of
the base pairs within the (A-T)n and (G-C)n oligomers (n=1-6) due to their
oxidation. The decrease of the inner-sphere reorganization energy with
elongation of the oligomer structure participating in the oxidation process
have been observed. The maximum degree of geometry relaxation of the nucleobase
structures and correspondingly the higher charge density in the oxidized state
are found to be located close to the oligomer center.",0703764v1
2002-12-04,Oxidation = group theory,"Dimensional reduction of theories involving (super-)gravity gives rise to
sigma models on coset spaces of the form G/H, with G a non-compact group, and H
its maximal compact subgroup. The reverse process, called oxidation, is the
reconstruction of the possible higher dimensional theories, given the lower
dimensional theory. In 3 dimensions, all degrees of freedom can be dualized to
scalars. Given the group G for a 3 dimensional sigma model on the coset G/H, we
demonstrate an efficient method for recovering the higher dimensional theories,
essentially by decomposition into subgroups. The equations of motion, Bianchi
identities, Kaluza-Klein modifications and Chern-Simons terms are easily
extracted from the root lattice of the group G. We briefly discuss some aspects
of oxidation from the E_{8(8)}/SO(16) coset, and demonstrate that our formalism
reproduces the Chern-Simons term of 11-d supergravity, knows about the
T-duality of IIA and IIB theory, and easily deals with self-dual tensors, like
the 5-tensor of IIB supergravity.",0212050v1
2004-12-09,Zirconium oxidation under high energy heavy ion irradiation,"This paper concerns the study of zirconium oxidation under irradiation with
high energetic Xe ions. The irradiations were performed on the IRRSUD beam line
at GANIL (Caen). The oxygen partial pressure was fixed at 10$^{-3}$ Pa and two
temperature conditions were used, either 480$\circ$C reached by Joule effect
heating or 280$\circ$C due to Xe energy deposition. Zirconia was fully
characterized by Rutherford Backscattering Spectrometry, Transmission Electron
Microscopy and Grazing Angle X-ray Diffraction. Apparent diffusion coefficients
of oxygen in ZrO2 were determined from these experiments by using a model which
takes into account a surface exchange between oxygen gas and the ZrO2 surface.
These results are compared with thermal oxidation data.",0412056v1
2002-08-31,Oxide-Semiconductor Materials for Quantum Computation,"Scalable fault-tolerant quantum computer architectures require quantum gates
that operate within a small fraction of the qubit decoherence time and with
high accuracy over a bandwidth set by the decoherence rate. Electron spin
quantum bits in Si are promising because of long decoherence times (~0.5 ms),
but electrical gating schemes still seem problematic. Oxide-semiconductor
heterostructures have the potential for precise electrical control of gate
operations in the semiconductor, using optical rectification in the
ferroelectric oxide. Accurate (~80 dB), local (~10 nm), dynamic (>THz) and
programmable optical control over electric polarization in the ferroelectric
can be achieved using existing technology. Optical techniques may also be
useful in rapid initialization of the quantum computer, and for providing a
source of initialized qubits to use for quantum error correction. Advantages of
optical methods will be discussed within a framework proposed for a quantum
information processor using ferroelectrically coupled electron spins and Ge
quantum dots in Si.",0209008v1
2007-04-06,Millimeter-Thick Single-Walled Carbon Nanotube Forests: Hidden Role of Catalyst Support,"A parametric study of so-called ""super growth"" of single-walled carbon
nanotubes(SWNTs) was done by using combinatorial libraries of iron/aluminum
oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and
those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs.
Although nanotube forests grew under a wide range of reaction conditions such
as gas composition and temperature, the window for SWNT was narrow. Fe
catalysts rapidly grew nanotubes only when supported on aluminum oxide.
Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays
an essential role in enhancing the nanotube growth rates.",0704.0915v1
2007-04-11,Unconventional approaches to combine optical transparency with electrical conductivity,"Combination of electrical conductivity and optical transparency in the same
material -- known to be a prerogative of only a few oxides of post-transition
metals, such as In, Sn, Zn and Cd -- manifests itself in a distinctive band
structure of the transparent conductor host. While the oxides of other elements
with $s^2$ electronic configuration, for example, Mg, Ca, Sc and Al, also
exhibit the desired optical and electronic features, they have not been
considered as candidates for achieving good electrical conductivity because of
the challenges of efficient carrier generation in these wide-bandgap materials.
Here we demonstrate that alternative approaches to the problem not only allow
attaining the transport and optical properties which compete with those in
currently utilized transparent conducting oxides (TCO), but also significantly
broaden the range of materials with a potential of being developed into novel
functional transparent conductors.",0704.1494v1
2007-04-11,Averaging of the electron effective mass in multicomponent transparent conducting oxides,"We find that layered materials composed of various oxides of cations with
$s^2$ electronic configuration, $XY_2$O$_4$, $X$=In or Sc, $Y$=Ga, Zn, Al, Cd
and/or Mg, exhibit isotropic electron effective mass which can be obtained via
averaging over those of the corresponding single-cation oxide constituents.
This effect is due to a hybrid nature of the conduction band formed from the
s-states of {\it all} cations and the oxygen p-states. Moreover, the observed
insensitivity of the electron effective mass to the oxygen coordination and to
the distortions in the cation-oxygen chains suggests that similar behavior can
be expected in technologically important amorphous state. These findings
significantly broaden the range of materials as efficient transparent conductor
hosts.",0704.1499v2
2007-04-15,Ab initio wavefunction based methods for excited states in solids: correlation corrections to the band structure of ionic oxides,"Ab initio wavefunction based methods are applied to the study of electron
correlation effects on the band structure of oxide systems. We choose MgO as a
prototype closed-shell ionic oxide. Our analysis is based on a local
Hamiltonian approach and performed on finite fragments cut from the infinite
solid. Localized Wannier functions and embedding potentials are obtained from
prior periodic Hartree-Fock (HF) calculations. We investigate the role of
various electron correlation effects in reducing the HF band gap and modifying
the band widths. On-site and nearest-neighbor charge relaxation as well as
long-range polarization effects are calculated. Whereas correlation effects are
essential for computing accurate band gaps, we found that they produce smaller
changes on the HF band widths, at least for this material. Surprisingly, a
broadening effect is obtained for the O 2p valence bands. The ab initio data
are in good agreement with the energy gap and band width derived from
thermoreflectance and x-ray photoemission experiments. The results show that
the wavefunction based approach applied here allows for well controlled
approximations and a transparent identification of the microscopic processes
which determine the electronic band structure.",0704.1906v1
2007-04-15,Theory of enhanced second-harmonic generation by the quadrupole-dipole hybrid exciton,"We report calculated substantial enhancement of the second harmonic
generation (SHG) in cuprous oxide crystals resonantly hybridized with an
appropriate organic material (DCM2:CA:PS 'solid-state solvent'). The quadrupole
origin of the inorganic part of the quadrupole-dipole hybrid provides inversion
symmetry breaking and the organic part contributes to the oscillator strength
of the hybrid. We show that the enhancement of the SHG, compared to bulk
cuprous oxide crystal, is proportional to the ratio of the DCM2 dipole moment
and the effective dipole moment of the quadrupole transitions in the cuprous
oxide. It is also inversely proportional to the line-width of the hybrid and
bulk excitons. The enhancement may be regulated by adjusting the organic blend
(mutual concentration of the DCM2 and CA part of the solvent) and pumping
conditions(varying the angle of incidence in case of optical pumping or
populating the minimum of the lower branch of the hybrid in case of electrical
pumping).",0704.1923v3
2007-05-07,Vibrational Infrared Lifetime of the Anesthetic nitrous oxide gas in solution,"The lifetime of the asymmetric fundamental stretching 2218 cm$^{-1}$
vibration of the anesthetic gas nitrous oxide (N$_2$O) dissolved in octanol and
olive oil is reported. These solvents are model systems commonly used to assess
anesthetic potency. Picosecond time-scale molecular dynamics simulations have
suggested that protein dynamics or membrane dynamics play a role in the
molecular mechanism of anesthetic action. Ultrafast infrared spectroscopy with
100 fs time resolution is an ideal tool to probe dynamics of anesthetic
molecules on such timescales. Pump-probe studies at the peak of the vibrational
band yield a lifetime of $55 \pm 1$ ps in olive oil and $52 \pm 1 ps$ in
octanol. The similarity of lifetimes suggests that energy relaxation of the
anesthetic is determined primarily by the hydrophobic nature of the
environment, consistent with models of anesthetic action. The results show that
nitrous oxide is a good model system for probing anesthetic-solvent
interactions using nonlinear infrared spectroscopy.",0705.0835v1
2007-08-03,Hubbard-Thomas-Fermi Theory of Transition Metal Oxide Heterostructures,"We demonstrate that the charge distributions in Hubbard-model representations
of transition metal oxide heterojucntions can be described by a Thomas-Fermi
theory in which the energy is approximated as the sum of the electrostatic
energy and the uniform three-dimensional Hubbard model energy per site at the
local density equals to a constant. When charged atomic layers in the oxides
are approximated as two-dimensional sheets with uniform charge density, the
electrostatic energy is simply evaluated. We find that this Thomas-Fermi theory
can reproduce results obtained from full Hartree-Fock theory for various
different heterostructures. We also show explicitly how Thomas-Fermi theory can
be used to estimate some key properties qualitatively.",0708.0554v1
2007-08-23,Elliptical hole pockets in the Fermi surfaces of unhydrated and hydrated sodium cobalt oxides,"The surprise discovery of superconductivity below 5K in sodium cobalt oxides
when hydrated with water has caught the attention of experimentalists and
theorists alike. Most explanations for its occurence have focused heavily on
the properties of some small elliptically shaped pockets predicted to be the
electronically dominant Fermi surface sheet, but direct attempts to look for
them have instead cast serious doubts over their existence. Here we present
evidence that these pockets do indeed exist, based on bulk measurements of the
electron momentum distribution in unhydrated and hydrated sodium cobalt oxides
using the technique of x-ray Compton scattering.",0708.3133v1
2007-10-04,Testing the Hydrogen Peroxide-Water Hypothesis for Life on Mars with the TEGA instrument on the Phoenix Lander,"Since Viking has conducted its life detection experiments on Mars, many
missions have enhanced our knowledge about the environmental conditions on the
Red Planet. However, the Martian surface chemistry and the Viking lander
results remain puzzling. Non-biological explanations that favor a strong
inorganic oxidant are currently favored (e.g., Mancinelli, 1989; Quinn and
Zent, 1999; Klein, 1999, Yen et al., 2000), but problems remain regarding the
life time, source, and abundance of that oxidant to account for the Viking
observations (Zent and McKay, 1994). Alternatively, a hypothesis favoring the
biological origin of a strong oxidizer has recently been advanced (Houtkooper
and Schulze-Makuch, 2007). Here, we report about laboratory experiments that
simulate the experiments to be conducted by the Thermal and Evolved Gas
Analyzer (TEGA) instrument of the Phoenix lander, which is to descend on Mars
in May 2008. Our experiments provide a baseline for an unbiased test for
chemical versus biological responses, which can be applied at the time the
Phoenix Lander transmits its first results from the Martian surface.",0710.1036v1
2007-11-12,Electrochemical lithium intercalation in nanosized manganese oxides,"X-ray amorphous manganese oxides were prepared by reduction of sodium
permanganate by lithium iodide in aqueous medium (MnOx-I) and by decomposition
of manganese carbonate at moderate temperature (MnOx-C). TEM showed that these
materials are not amorphous, but nanostructured, with a prominent spinel
substructure in MnOx-C. These materials intercalate lithium with capacities up
to 200 mAh/g at first cycle (potential window 1.8-4.3 V) and 175 mAh/g at 100th
cycle. Best performances for MnOx-C are obtained with cobalt doping. Potential
electrochemical spectroscopy shows that the initial discharge induces a 2-phase
transformation in MnOx-C phases, but not in MnOx-I ones. EXAFS and XANES
confirm the participation of manganese in the redox process, with variations in
local structure much smaller than in known long-range crystallized manganese
oxides. X-ray absorption spectroscopy also shows that cobalt in MnOx-C is
divalent and does not participate in the electrochemical reaction.",0711.1785v1
2007-12-21,First-principles investigation of Ag-Cu alloy surfaces in an oxidizing environment,"In this paper we investigate by means of first-principles density functional
theory calculations the (111) surface of the Ag-Cu alloy under varying
conditions of pressure of the surrounding oxygen atmosphere and temperature.
This alloy has been recently proposed as a catalyst with improved selectivity
for ethylene epoxidation with respect to pure silver, the catalyst commonly
used in industrial applications. Here we show that the presence of oxygen leads
to copper segregation to the surface. Considering the surface free energy as a
function of the surface composition, we construct the convex hull to
investigate the stability of various surface structures. By including the
dependence of the free surface energy on the oxygen chemical potential, we are
able compute the phase diagram of the alloy as a function of temperature,
pressure and surface composition. We find that, at temperature and pressure
typically used in ethylene epoxidation, a number of structures can be present
on the surface of the alloy, including clean Ag(111), thin layers of copper
oxide and thick oxide-like structures. These results are consistent with, and
help explain, recent experimental results.",0712.3652v1
2008-01-07,DC transferred arc thermal plasma assisted growth of nanoparticles with different crystalline phases,"The control of the crystalline phases of the nanoparticles grown in a
direct-current transferred-arc plasma-assisted reactor is reported. The
crystalline phases of the as synthesized nanoparticles are shown to critically
depend on the operating gas pressure. The paper reports about the change in the
crystalline phases of three distinct compounds namely aluminium oxide (Al2O3),
aluminium nitride (AlN) and iron oxide (FexOy). The major outcome of the
present work is that the phases having higher defect densities are more
probable to form at the sub-atmospheric operating pressure. The variations in
the crystalline structures are discussed on the basis of the equilibrium defect
density formed during the homogeneous nucleation. The as synthesized
nanoparticles were examined by X-ray diffraction analysis and transmission
electron microscopy. In addition, the confirmatory analysis for the crystalline
phases of the as synthesized iron oxides was carried out with the help of
Mossbauer spectroscopy.",0801.0945v1
2008-01-14,Charge transfer in heterostructures of strongly correlated materials,"In this manuscript, recent theoretical investigations by the authors in the
area of oxide multilayers are briefly reviewed. The calculations were carried
out using model Hamiltonians and a variety of non-perturbative techniques.
Moreover, new results are also included here. They correspond to the generation
of a metallic state by mixing insulators in a multilayer geometry, using the
Hubbard and Double Exchange models. For the latter, the resulting metallic
state is also ferromagnetic. This illustrates how electron or hole doping via
transfer of charge in multilayers can lead to the study of phase diagrams of
transition metal oxides in the clean limit. Currently, these phase diagrams are
much affected by the disordering standard chemical doping procedure, which
introduces quenched disorder in the material.",0801.2174v2
2008-04-15,Pathways of bond topology transitions at the interface of silicon nanocrystals and amorphous silica matrix,"The interface chemistry of silicon nanocrystals (NCs) embedded in amorphous
oxide matrix is studied through molecular dynamics simulations with the
chemical environment described by the reactive force field model. Our results
indicate that the Si NC-oxide interface is more involved than the previously
proposed schemes which were based on solely simple bridge or double bonds. We
identify different types of three-coordinated oxygen complexes, previously not
noted. The abundance and the charge distribution of each oxygen complex is
determined as a function of the NC size as well as the transitions among them.
The oxidation at the surface of NC induces tensile strain to Si-Si bonds which
become significant only around the interface, while the inner core remains
unstrained. Unlike many earlier reports on the interface structure, we do not
observe any double bonds. Furthermore, our simulations and analysis reveal that
the interface bond topology evolves among different oxygen bridges through
these three-coordinated oxygen complexes.",0804.2322v1
2008-05-20,Unification of bulk and interface electroresistive switching in oxide systems,"We demonstrate that the physical mechanism behind electroresistive switching
in oxide Schottky systems is electroformation, as in insulating oxides.
Negative resistance shown by the hysteretic current-voltage curves proves that
impact ionization is at the origin of the switching. Analyses of the
capacitance-voltage and conductance-voltage curves through a simple model show
that an atomic rearrangement is involved in the process. Switching in these
systems is a bulk effect, not strictly confined at the interface but at the
charge space region.",0805.3159v3
2008-06-13,Remote hole-doping of Mott insulators on the nanometer scale,"At interfaces between polar and nonpolar perovskite oxides, an unusual
electron-doping has been previously observed, due to electronic
reconstructions. We report on remote hole-doping at an interface composed of
only polar layers, revealed by high-resolution hard x-ray core-level
photoemission spectroscopy. In LaAlO3/LaVO3/LaAlO3 trilayers, the vanadium
valence systematically evolves from the bulk value of V3+ to higher oxidation
states with decreasing LaAlO3 cap layer thickness. These results provide a
synthetic approach to hole-doping transition metal oxide heterointerfaces
without invoking a polar discontinuity.",0806.2191v1
2008-08-25,Nano-Graphene Oxide for Cellular Imaging and Drug Delivery,"Two-dimensional graphene offers interesting electronic, thermal and
mechanical properties that are currently explored for advanced electronics,
membranes and composites. Here we synthesize and explore the biological
application of nano-graphene oxide NGO, single-layer graphene oxide sheets down
to a few nanometers in lateral width. We develop functionalization chemistry to
impart solubility and compatibility of NGO in biological environments. We
obtain size separated pegylated NGO sheets that are soluble in buffers and
serum without agglomeration. The NGO sheets are found to be photoluminescent in
the visible and infrared regions. The intrinsic photoluminescence of NGO is
used for live cell imaging in the near-infrared with little background. We
found that simple physisorption via pi-stacking can be used for loading
doxorubicin, a widely used cancer drug onto NGO functionalized with antibody
for selective cancer cell killing in vitro. Owing to the small size, intrinsic
optical properties, large specific surface area,low cost, and useful
non-covalent interactions with aromatic drug molecules, NGO is a promising new
material for biological and medical applications.",0808.3396v1
2008-09-11,Modeling of the evolution of dielectric loss with processing temperature in ferroelectric and dielectric thin oxide films,"It was experimentally found that the evolution of dielectric loss with
processing temperature displays a common trend in ferroelectric and dielectric
thin oxide films: firstly an increase and then a decrease in dielectric loss
when the processing temperature is gradually raised. Such a dielectric response
of ferroelectric/dielectric thin films has been theoretically addressed in this
work. We propose that at the initial stage of the crystallization process in
thin films, the transformation from amorphous to crystalline phase should
increase substantially the dielectric loss; then, with further increase in the
processing temperature, the coalescent growth of small crystalline grains into
big ones could be helpful in reducing the dielectric loss by lowering grain
boundary densities. The obtained experimental data for (Ba,Sr)TiO3 thin films
with 500 nm in thickness were analyzed in terms of the model developed and
shown to be in a reasonable agreement with the theoretical results.",0809.2008v1
2008-09-26,Understanding the nature of electronic effective mass in double-doped SrTiO$_{3}$,"We present an approach to tune the effective mass in an oxide semiconductor
by a double doping mechanism. We demonstrate this in a model oxide system
Sr$_{1-x}$La$_x$TiO$_{3-\delta}$, where we can tune the effective mass ranging
from 6--20$\mathrm{m_e}$ as a function of filling or carrier concentration and
the scattering mechanism, which are dependent on the chosen lanthanum and
oxygen vacancy concentrations. The effective mass values were calculated from
the Boltzmann transport equation using the measured transport properties of
thin films of Sr$_{1-x}$La$_x$TiO$_{3-\delta}$. Our method, which shows that
the effective mass decreases with carrier concentration, provides a means for
understanding the nature of transport processes in oxides, which typically have
large effective mass and low electron mobility, contrary to the tradional high
mobility semiconductors.",0809.4706v2
2008-11-18,Kinetics of the thermal degradation of Erica arborea by DSC: Hybrid kinetic method,"The scope of this work was the determination of kinetic parameters of the
thermal oxidative degradation of a Mediterranean scrub using a hybrid method
developed at the laboratory. DSC and TGA were used in this study under air
sweeping to record oxidative reactions. Two dominating and overlapped
exothermic peaks were recorded in DSC and individualized using an experimental
and numerical separation. This first stage allowed obtaining the enthalpy
variation of each exothermic phenomenon. In a second time, a model free method
was applied on each isolated curve to determine the apparent activation
energies. A reactional kinetic scheme was proposed for the global exotherm
composed of two independent and consecutive reactions. In fine mean values of
enthalpy variation and apparent activation energy previously determined were
injected in a model fitting method to obtain the reaction order and the
preexponential factor of each oxidative reaction. We plan to use these data in
a sub-model to be integrated in a wildland fire spread model.",0811.2985v1
2008-11-21,Kinetic study of the oxide-assisted catalyst-free synthesis of silicon nitride nanowires,"The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles
with N2 in the 1200-1440 C temperature range is reported. The nitridation
conditions are such that the reaction with nitrogen is favoured by the presence
of silicon oxide in the particles and by the active oxidation of silicon
without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on
the amount of silicon particles used in the experiments and that, in general,
the reaction slows down for greater amounts. This trend is explained by
particle stacking, which restricts the exchange of gases between the furnace
atmosphere and the atmosphere around the inner particles. In a first stage,
local oxygen partial pressure increases around the inner particles and inhibits
nitridation locally. If the amount of reactant Si nanoparticles is small
enough, this extrinsic effect is avoided and the intrinsic nitridation kinetics
can be measured. Experiments show that intrinsic kinetics does not depend on
temperature.",0811.3525v1
2008-11-29,Fabrication of graphene nanoribbon by local anodic oxidation lithography using atomic force microscope,"We conducted local anodic oxidation (LAO) lithography in single-layer,
bilayer, and multilayer graphene using tapping-mode atomic force microscope.
The width of insulating oxidized area depends systematically on the number of
graphene layers. An 800-nm-wide bar-shaped device fabricated in single-layer
graphene exhibits the half-integer quantum Hall effect. We also fabricated a
55-nm-wide graphene nanoribbon (GNR). The conductance of the GNR at the charge
neutrality point was suppressed at low temperature, which suggests the opening
of an energy gap due to lateral confinement of charge carriers. These results
show that LAO lithography is an effective technique for the fabrication of
graphene nanodevices.",0812.0048v1
2008-12-11,Difference of Oxide Hetero-Structure Junctions with Semiconductor Electronic Devices,"Charge carrier injection performed in Pr0.7Ca0.3MnO3 (PCMO) hetero-structure
junctions exhibits stable without electric fields and dramatic changes in both
resistances and interface barriers, which are entirely different from behaviors
of semiconductor devices. Disappearance and reversion of interface barriers
suggest that the adjustable resistance switching of such hetero-structure oxide
devices should associate with motion of charge carriers across interfaces. The
results suggested that injected carriers should be still staying in devices and
resulted in changes in properties, which guided to a carrier self-trapping and
releasing picture in strongly correlated electronic framework. Observations in
PCMO and oxygen deficient CeO2 devices show that oxides as functional materials
could be used in microelectronics with some novel properties, in which
interface is very important.",0812.2071v1
2009-01-23,Halving the Casimir force with conductive oxides,"The possibility to modify the strength of the Casimir effect by tailoring the
dielectric functions of the interacting surfaces is regarded as a unique
opportunity in the development of Micro- and NanoElectroMechanical Systems. In
air, however, one expects that, unless noble metals are used, the electrostatic
force arising from trapped charges overcomes the Casimir attraction, leaving no
room for exploitation of Casimir force engineering at ambient conditions. Here
we show that, in the presence of a conductive oxide, the Casimir force can be
the dominant interaction even in air, and that the use of conductive oxides
allows one to reduce the Casimir force up to a factor of 2 when compared to
noble metals.",0901.3720v2
2009-01-29,The melting behavior of lutetium aluminum perovskite LuAlO3,"DTA measurements with mixtures of aluminum oxide and lutetium oxide around
the 1:1 perovskite composition were performed up to 1970 deg. C. A peak with
onset 1901 deg C was due to the melting of the eutectic Lu4Al2O9 (monoclinic
phase) and LuAlO3 (perovskite). Neither peritectic melting of the perovskite
nor its decomposition in the solid phase could be resolved experimentally. The
maximum of the eutectic peak size is near x=0.44, on the Lu-rich side of the
perovskite, which is consistent with the conclusion that LuAlO3 melts
peritectically at ca. 1907 deg. C as proposed by Wu, Pelton, J. Alloys Compd.
179 (1992) 259. Thermodynamic equilibrium calculations reveal, that under
strongly reducing conditions (oxygen partial pressure <10^{-13} bar)
aluminum(III) oxide can be reduced to suboxides or even Al metal. It is shown
that under such conditions a new phase field with liquid Al can appear.",0901.4654v3
2009-04-22,Modeling Study of the Low-Temperature Oxidation of Large Methyl Esters,"This study focuses on the automatic generation by the software EXGAS of
kinetic models for the oxidation of large methyl esters using a single set of
kinetic parameters. The obtained models allow to well reproduce the oxidation
of n-decane / methyl palmitate mixture in a jet-stirred reactor. This paper
also presents the construction and a comparison of models for methyl esters
from C7 up to C17 in terms f conversion in a jet-stirred reactor and of
ignition delay time in a shock tube. This comparison study showed that methyl
esters larger than methyl octanoate behave similarly and have very close
reactivities.",0904.3536v1
2009-04-30,Polaronic hole localization and multiple hole binding of acceptors in oxide wide-gap semiconductors,"Acceptor-bound holes in oxides often localize asymmetrically at one out of
several equivalent oxygen ligands. Whereas Hartree-Fock (HF) theory overly
favors such symmetry-broken polaronic hole-localization in oxides, standard
local density (LD) calculations suffer from spurious delocalization among
several oxygen sites. These opposite biases originate from the opposite
curvatures of the energy as a function of the fractional occupation number n,
i.e., d2E/dn2 < 0 in HF and d2E/dn2 > 0 in LD. We recover the correct linear
behavior, d2E/dn2 = 0, that removes the (de)localization bias by formulating a
generalized Koopmans condition. The correct description of oxygen
hole-localization reveals that the cation-site nominal single-acceptors in ZnO,
In2O3, and SnO2 can bind multiple holes.",0905.0018v1
2009-06-17,Resonant structures based on amorphous silicon sub-oxide doped with Er3+ with silicon nanoclusters for an efficient emission at 1550 nm,"We present a resonant approach to enhance 1550nm emission efficiency of
amorphous silicon sub-oxide doped with Er3+ (a-SiOx<Er>) layers with silicon
nanoclusters (Si-NC). Two distinct techniques were combined to provide a
structure that allowed increasing approximately 12x the 1550nm emission. First,
layers of SiO2 were obtained by conventional wet oxidation and a-SiOx<Er>
matrix was deposited by reactive RF co-sputtering. Secondly, an extra pump
channel (4I15/2 to 4I9/2) of Er3+ was created due to Si-NC formation on the
same a-SiOx<Er> matrix via a hard annealing at 1150 C. The SiO2 and the
a-SiOx<Er> thicknesses were designed to support resonances near the pumping
wavelength (~500nm), near the Si-NC emission (~800nm) and near the a-SiOx<Er>
emission (~1550nm) enhancing the optical pumping process.",0906.3274v1
2009-07-02,"Spin, Orbital, and Spin-Orbital Polarons in Transition Metal Oxides","I give a brief overview of a polaron formation in three distinct transition
metal oxides: (i) spin polaron when a hole is added to the antiferromagnetic
(AF) ordered plane in La$_2$CuO$_4$, (ii) orbital polaron when a hole is added
to the alternating orbital (AO) ordered plane in LaMnO$_3$, and (iii)
spin-orbital polaron when a hole is added to the AF and AO ordered plane in
LaVO$_3$. Comparison of the distinct features of the above polarons can shed
some light on the basic differences between the experimental phase diagrams of
the lightly doped transition metal oxides La$_{2-x}$Sr$_x$CuO$_4$,
La$_{1-x}$Sr$_x$MnO$_3$, and La$_{1-x}$Sr$_{x}$VO$_3$.",0907.0420v1
2009-07-06,Electrosteric enhanced stability of functional sub-10 nm cerium and iron oxide particles in cell culture medium,"Applications of nanoparticles in biology require that the nanoparticles
remain stable in solutions containing high concentrations of proteins and
salts, as well as in cell culture media. In this work, we developed simple
protocols for the coating of sub-10 nm nanoparticles and evaluated the
colloidal stability of dispersions in various environments. Ligands (citric
acid), oligomers (phosphonate-terminated poly(ethylene oxide)) and polymers
(poly(acrylic acid)) were used as nanometer-thick adlayers for cerium (CeO2)
and iron (gamma-Fe2O3) oxide nanoparticles. The organic functionalities were
adsorbed on the particle surfaces via physical (electrostatic) forces.
Stability assays at high ionic strength and in cell culture media were
performed by static and dynamic light scattering. Among the three coating
examined, we found that only poly(acrylic acid) fully preserved the dispersion
stability on the long term (> weeks). The improved stability was explained by
the multi-point attachments of the chains onto the particle surface, and by the
adlayer-mediated electrosteric interactions. These results suggest that
anionically charged polymers represent an effective alternative to conventional
coating agents.",0907.1008v1
2009-07-30,Solvothermal Reduction of Chemically Exfoliated Graphene Sheets,"Graphene has attracted much attention due to its interesting properties and
potential applications. Chemical exfoliation methods have been developed to
make graphene recently, aimed at large-scale assembly and applications such as
composites and Li ion batteries. Although efficient, the chemical exfoliation
methods involve oxidation of graphene and introduce defects in the as-made
sheets. Hydrazine reduction at 100 has shown to partially restore the structure
and conductance of graphite oxide. However, the reduced GO still shows strong
defect peaks in Raman spectra with higher resistivity than pristine graphene by
2 to 3 orders of magnitude. It is important to produce much less defective
graphene sheets than GO, and develop more effective graphene reduction.
Recently, we reported a mild exfoliation-reintercalation-expansion method to
form high-quality GS with higher conductivity and lower oxidation degree than
GO.5 Here, we present a 180 solvothermal reduction method for our GS and GO.
The solvothermal reduction is more effective than the earlier reduction methods
in lowering the oxygen and defect levels in GS, increasing the graphene
domains, and bringing the conductivity of GS close to pristine graphene. The
reduced GS possess the highest degree of pristinity among chemically derived
graphene.",0907.5417v1
2009-08-14,Electrostatically induced phase transitions in superconducting complex oxides,"We describe quantum phase transitions in superconducting complex oxides which
could be tuned by electrostatic charge transfer. Using a simple model for the
superconductivity of a thin film or surface of a bulk copper oxide, we show
that tuning the carrier density may allow the visitation of several
superconducting phases with different pairing symmetries such as extended $s$-
$(se)$, $d$- and $(se \pm id)$-wave. We construct a universal phase diagram for
single-band superconductors with $se$- and d-wave components of the order
parameter based on symmetry considerations alone. For a specific model with
nearest neighbor attraction, we obtain the phase diagram in the interaction
versus filling factor space showing the boundaries of the possible phases.
Finally, we calculate the superfluid density and penetration depth as
characteristic properties of each phase.",0908.2011v1
2009-10-13,Appearance of ferroelectricity in BaO nanowires,"We predict that ferroelectric phase can be induced by the strong intrinsic
surface stress inevitably present under the curved surface in the high aspect
ratio cylindrical nanoparticles of nonferroelectric binary oxides (BaO, EuO,
MgO, etc). We calculated the sizes and temperature range of the ferroelectric
phase in BaO nanowires. The analytical calculations were performed within
Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted
from the first principle calculations [E. Bousquet et al, Strain-induced
ferroelectricity in simple rocksalt binary oxides. arXiv:0906.4235v1] and
tabulated experimental data. In accordance with our calculations BaO nanowires
of radius ~(1-10) nm can be ferroelectric at room temperature (with spontaneous
polarization values up to 0.5 C/m2) for the typical surface stress coefficients
~ (10-50) N/m. We hope that our prediction can stimulate both experimental
studies of rocksalt binary oxides nanoparticles polar properties as well as the
first principle calculations of their spontaneous dipole moment induced by the
intrinsic stress under the curved surface.",0910.2421v1
2010-02-02,Ballistic Conductance in Oxidized Si Nanowires,"The influence of local oxidation in silicon nanowires on hole transport, and
hence the effect of varying the oxidation state of silicon atoms at the wire
surface, is studied using density functional theory in conjunction with a
Green's function scattering method. For silicon nanowires with growth direction
along [110] and diameters of a few nanometers, it is found that the
introduction of oxygen bridging and back bonds does not significantly degrade
hole transport for voltages up to several hundred millivolts relative to the
valence band edge. As a result, the mean free paths are comparable to or longer
than the wire lengths envisioned for transistor and other nanoelectronics
applications. Transport along [100]-oriented nanowires is less favorable, thus
providing an advantage in terms of hole mobilities for [110] nanowire
orientations, as preferentially produced in some growth methods.",1002.0430v1
2010-02-16,Suppression of Octahedral Tilts and Associated Changes of Electronic Properties at Epitaxial Oxide Heterostructure Interfaces,"Epitaxial oxide interfaces with broken translational symmetry have emerged as
a central paradigm behind the novel behaviors of oxide superlattices. Here, we
use scanning transmission electron microscopy to demonstrate a direct,
quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen
octahedral rotations across the BiFeO3-La0.7Sr0.3MnO3 interface to elucidate
how the change of crystal symmetry is accommodated. Combined with low-loss
electron energy loss spectroscopy imaging, we demonstrate a mesoscopic
antiferrodistortive phase transition and elucidate associated changes in
electronic properties in a thin layer directly adjacent to the interface.",1002.2989v1
2010-03-09,Femtosecond Pump-Probe Studies of Reduced Graphene Oxide Thin Films,"The dynamics of photocarriers in reduced graphene oxide thin films is studied
by using ultrafast pump-probe spectroscopy. Time dependent differential
transmissions are measured with sample temperatures ranging from 9 to 300 K. At
each sample temperature and probe delay, the sign of differential transmission
remains positive. A fast energy relaxation of hot carriers is observed, and is
found to be independent of sample temperature. Our experiments show that the
carrier dynamics in reduced graphene oxide is similar to other types of
graphene, and that the differential transmission is caused by phase-state
filling of carriers.",1003.1972v2
2010-03-22,Colossal dielectric constants in transition-metal oxides,"Many transition-metal oxides show very large (""colossal"") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.",1003.4272v1
2010-06-11,"New Iron Arsenide Oxides (Fe2As2)(Sr4(Sc,Ti)3O8), (Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5)","We synthesized new layered iron arsenide oxides
(Fe2As2)(Sr4(Sc,Ti)3O8),(Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5). The
crystal structures of these compounds are tetragonal with a space group of
I4/mmm. The structure of (Fe2As2)(Sr4(Sc,Ti)3O8) and (Fe2As2)(Ba4Sc3O7.5)
consists of the alternate stacking of antifluorite Fe2As2 layers and triple
perovskite-type oxide layers. The interlayer distance between the Fe planes of
(Fe2As2)(Ba4Sc3O7.5) is ~18.7 A. Moreover, the a-axis of (Fe2As2)(Ba3Sc2O5) is
the longest among the layered iron pnictides, indicating the structural
flexibility of the layered iron pnictide containing perovskite-type layers. The
bulk sample of (Fe2As2)(Sr4(Sc0.6Ti0.4)3O8) exhibited diamagnetism up to 28 K
in susceptibility measurements.",1006.2353v1
2010-07-22,Oxygen-Induced Surface Reconstruction of SrRuO3 and Its Effect on the BaTiO3 Interface,"Atomically engineered oxide multilayers and superlattices display unique
properties responsive to the electronic and atomic structures of the
interfaces. We have followed the growth of ferroelectric BaTiO3 on SrRuO3
electrode with in situ atomic scale analysis of the surface structure at each
stage. An oxygen-induced surface reconstruction of SrRuO3 leads to formation of
SrO rows spaced at twice the bulk periodicity. This reconstruction modifies the
structure of the first BaTiO3 layers grown subsequently, including intermixing
observed with cross-section spectroscopy. These observations reveal that this
common oxide interface is much more interesting than previously reported, and
provide a paradigm for oxygen engineering of oxide structure at an interface.",1007.4006v1
2010-09-09,First-principles computational study of defect clustering in solid solutions of ThO$_{2}$ with trivalent oxides,"The energetics of mixing and defect ordering in solid solutions of
fluorite-structured ThO$_{2}$ with oxides of trivalent cations (Sc, In, Y, Nd,
La) are investigated by electronic density-functional-theory (DFT). Through DFT
calculations of structures enumerated by lattice-algebra techniques, we
identify the lowest-energy patterns for defect clustering for four separate
dopant concentrations. The most stable structures are characterized by a
repulsive interaction between nearest-neighbor vacancies on the oxygen
sublattice. The enthalpies of formation with respect to constituent oxides are
positive for all dopants considered, and show a tendency to decrease in
magnitude as the size and electronegativity of the trivalent dopant decrease.
Due to the small positive formation enthalpies and low oxygen-vacancy binding
energy with La dopants, La$_{2}$O$_{3}$-ThO$_{2}$ solid solutions are predicted
to have relatively high ionic conductivities relative to those for the other
aliovalent dopants considered. Our results are compared with those for the more
widely studied ZrO$_{2}$ and CeO$_{2}$ fluorite-structured solid solutions with
trivalent cations.",1009.1850v1
2010-10-19,Reflexion Mössbauer analysis of the in situ oxidation products hydroxycarbonate green rust,"The purpose of this study is to determine the nature of the oxidation
products of FeII-III hydroxycarbonate FeII4FeIII2(OH)12CO3~3H2O (green rust
GR(CO32-)) by using the miniaturised M\""ossbauer spectrometer MIMOS II. Two
M\""ossbauer measurements methods are used: method (i) with green rust pastes
coated with glycerol and spread into Plexiglas sample holders, and method (ii)
with green rust pastes in the same sample holders but introduced into a
gas-tight cell with a beryllium window under a continuous nitrogen flow. Method
(ii) allows us to follow the continuous deprotonation of GR(CO32-) into the
fully ferric deprotonated form FeIII6O4(OH)8CO3~3H2O by adding the correct
amount of H2O2, without any further oxidation or degradation of the samples.",1010.3852v1
2010-11-17,Oxidation resistance of graphene-coated Cu and Cu/Ni alloy,"The ability to protect refined metals from reactive environments is vital to
many industrial and academic applications. Current solutions, however,
typically introduce several negative effects, including increased thickness and
changes in the metal physical properties. In this paper, we demonstrate for the
first time the ability of graphene films grown by chemical vapor deposition to
protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy
from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the
metal surface is well protected from oxidation even after heating at 200
\degree C in air for up to 4 hours. Our work further shows that graphene
provides effective resistance against hydrogen peroxide. This protection method
offers significant advantages and can be used on any metal that catalyzes
graphene growth.",1011.3875v1
2010-12-24,Correlation between structural defects and optical properties of Cu2O nanowires grown by thermal oxidation,"Cuprous oxide (Cu2O) nanowires were grown by a simple, catalyst-free thermal
oxidation method starting from a copper foil substrate. Wire growth was
performed at different conditions by varying oxygen partial pressure and
heating temperature, and produced structural defects such as stacking faults
and twin structures of grown nanowires were characterized by transmission
electron microscopy. A moderate oxygen partial pressure ~5% with a relatively
high temperature at 500 oC is found to be an optimal condition for growing
high-quality Cu2O nanowires, while either lowering temperature or enhancing O2
partial pressure can yield higher density of planar defects. In order to
further investigate optical properties of grown nanowires, photoluminescence
measurements were also performed and correlated with structural
characterization results, indicating that increase of structural defects such
as stacking faults and twins tended to enhance broad defect-related emissions
and suppress the exciton emissions near Cu2O band-edge.",1012.5338v2
2011-02-18,Rapid Surface Oxidation as a Source of Surface Degradation Factor for Bi2Se3,"Bi2Se3 is a topological insulator with metallic surface states residing in a
large bulk bandgap. It is believed that Bi2Se3 gets additional n-type doping
after exposure to atmosphere, thereby reducing the relative contribution of
surface states in total conductivity. In this letter, transport measurements on
Bi2Se3 nanoribbons provide additional evidence of such environmental doping
process. Systematic surface composition analyses by X-ray photoelectron
spectroscopy reveal fast formation and continuous growth of native oxide on
Bi2Se3 under ambient conditions. In addition to n-type doping at the surface,
such surface oxidation is likely the material origin of the degradation of
topological surface states. Appropriate surface passivation or encapsulation
may be required to probe topological surface states of Bi2Se3 by transport
measurements.",1102.3935v1
2011-02-21,Uranium oxides investigated by X-ray absorption and emission spectroscopies,"X-ray absorption and resonant X-ray emission measurements at the O 1s edge of
the uranium oxides UO2, U3O8 and UO3 are presented. The spectral shapes of the
O K{\alpha} X-ray emission spectra of UO3 exhibit significant excitation energy
dependence, from an asymmetric to a symmetric form, which differs from those of
UO2 and U3O8. This energy dependence is attributed to a significant difference
in the oxygen-uranium hybridization between two different sites in the crystal
structure of UO3. The spectral shapes of UO2 and U3O8 are also found to be
different but without significant energy dependence. The experimental spectra
of the valence and conduction bands of the uranium oxides are compared to the
results of electronic structure calculations available in the literature.",1102.4242v2
2011-03-22,Structure and properties of functional oxide thin films: Insights from electronic-structure calculations,"The confluence of state-of-the-art electronic-structure computations and
modern synthetic materials growth techniques is proving indispensable in the
search for and discovery of new functionalities in oxide thin films and
heterostructures. Here, we review the recent contributions of
electronic-structure calculations to predicting, understanding, and discovering
new materials physics in thin-film perovskite oxides. We show that such
calculations can accurately predict both structure and properties in advance of
film synthesis, thereby guiding the search for materials combinations with
specific targeted functionalities. In addition, because they can isolate and
decouple the effects of various parameters which unavoidably occur
simultaneously in an experiment -- such as epitaxial strain, interfacial
chemistry and defect profiles -- they are able to provide new fundamental
knowledge about the underlying physics. We conclude by outlining the
limitations of current computational techniques, as well as some important open
questions that we hope will motivate further methodological developments in the
field.",1103.4418v1
2011-06-03,Selective tuning of high-Q silicon photonic crystal nanocavities via laser-assisted local oxidation,"We examine the cavity resonance tuning of high-Q silicon photonic crystal
heterostructures by localized laser-assisted thermal oxidation using a 532 nm
continuous wave laser focused to a 2.5 mm radius spot-size. The total shift is
consistent with the parabolic rate law. A tuning range of up to 8.7 nm is
achieved with ~ 30 mW laser powers. Over this tuning range, the cavity Q
decreases from 3.2\times10^5 to 1.2\times10^5. Numerical simulations model the
temperature distributions in the silicon photonic crystal membrane and the
cavity resonance shift from oxidation.",1106.0705v1
2011-06-24,Observation of drift and diffusion processes in Ti/TiOx/Ti memristive devices prepared by local anodic oxidation,"We demonstrate that memristive devices can be fabricated by tip-induced
oxidation of thin metallic films using atomic force microscope. Electrical
measurements of such prepared Ti/TiOx/Ti test structures confirmed their
memristive behavior and inferred diffusion of oxygen vacancies in the TiOx
barrier. Consequent Kelvin probe force microscopy studies provided evidence for
the diffusion, as well as for expected oxygen vacancy drift. Time evolution of
the space distribution of the vacancies due to the diffusion process revealed
minute-scale (at least) retention times of the devices. The work presents
technology alternative for fabrication of memristive nanodevices in geometry
favouring advantageous scanning probe microscopy studies of their in-barrier
processes, as well as widely utilizable approach to search for novel oxide
materials for perspective memristive applications.",1106.5006v3
2011-07-12,High Tc superconductivity in superlattices of insulating oxides,"We report the occurrence of superconductivity, with maximum Tc = 40 K, in
superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3.
In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block,
which is an antiferromagnetic insulator. Superconductivity, confined within few
unit cells at the CaCuO2/SrTiO3 interface, shows up only when the SLs are grown
in a highly oxidizing atmosphere, because of extra oxygen ions entering at the
interfaces. Evidence is reported that the hole doping of the CuO2 planes is
obtained by charge transfer from the interface layers, which act as charge
reservoir.",1107.2239v3
2011-08-04,Oxides and nitrides as alternative plasmonic materials in the optical range,"As alternatives to conventional metals, new plasmonic materials offer many
advantages in the rapidly growing fields of plasmonics and metamaterials. These
advantages include low intrinsic loss, semiconductor-based design,
compatibility with standard nanofabrication processes, tunability, and others.
Transparent conducting oxides such as Al:ZnO, Ga:ZnO and indium-tin-oxide (ITO)
enable many high-performance metamaterial devices operating in the near-IR.
Transition-metal nitrides such as TiN or ZrN can be substitutes for
conventional metals in the visible frequencies. In this paper we provide the
details of fabrication and characterization of these new materials and discuss
their suitability for a number of metamaterial and plasmonic applications.",1108.0993v1
2011-08-07,A comparative study of semiconductor-based plasmonic metamaterials,"Recent metamaterial (MM) research faces several problems when using
metal-based plasmonic components as building blocks for MMs. The use of
conventional metals for MMs is limited by several factors: metals such as gold
and silver have high losses in the visible and near-infrared (NIR) ranges and
very large negative real permittivity values, and in addition, their optical
properties cannot be tuned. These issues that put severe constraints on the
device applications of MMs could be overcome if semiconductors are used as
plasmonic materials instead of metals. Heavily doped, wide bandgap oxide
semiconductors could exhibit both a small negative real permittivity and
relatively small losses in the NIR. Heavily doped oxides of zinc and indium
were already reported to be good, low loss alternatives to metals in the NIR
range. Here, we consider these transparent conducting oxides (TCOs) as
alternative plasmonic materials for many specific applications ranging from
surface-plasmon-polariton waveguides to MMs with hyperbolic dispersion and
epsilon-near-zero (ENZ) materials. We show that TCOs outperform conventional
metals for ENZ and other MM-applications in the NIR.",1108.1531v1
2011-12-19,Transfer-free fabrication of graphene transistors,"We invented a method to fabricate graphene transistors on oxidized silicon
wafers without the need to transfer graphene layers. To stimulate the growth of
graphene layers on oxidized silicon a catalyst system of nanometer thin
aluminum/nickel double layer is used. This catalyst system is structured via
liftoff before the wafer enters the catalytic chemical vapor deposition (CCVD)
chamber. In the subsequent methane based growth process monolayer graphene
field-effect transistors (MoLGFETs) and bilayer graphene transistors (BiLGFETs)
are realized directly on oxidized silicon substrate, whereby the number of
stacked graphene layers is determined by the selected CCVD process parameters,
e.g. temperature and gas mixture. Subsequently, Raman spectroscopy is performed
within the channel region in between the catalytic areas and the Raman spectra
of fivelayer, bilayer and monolayer graphene confirm the existence of graphene
grown by this silicon-compatible, transfer-free and in-situ fabrication
approach. These graphene FETs will allow a simple and low-cost integration of
graphene devices for nanoelectronic applications in a hybrid silicon CMOS
environment.",1112.4320v1
2011-12-21,Instability of Amorphous Oxide Semiconductors via Carrier-Mediated Structural Transition between Disorder and Peroxide State,"The excited holes occupying the valence band tail states in amorphous oxide
semiconductors are found to induce formation of meta-stable O$_2^{2-}$ peroxide
defects. The valence band tail states are at least partly characterized by the
O-O pp{\sigma}* molecular orbital, and the localized-hole-mediated lattice
instability results in the formation of the peroxide defects. Along with the
O-O bond formation, the pp{\sigma}* state is heightened up into the conduction
bands, and two electrons are accordingly doped in the electronic ground state.
The energy barrier from the O$_2^{2-}$ peroxide state to the normal disorder
state is found to be 0.97 eV in hybrid density functional theory. The
hole-mediated formation of the meta-stable peroxide defects and their
meta-stability is suggested as an origin of the negative bias and/or
illumination stress instability in amorphous oxide semiconductors.",1112.4914v1
2012-03-05,Growth of Oriented Au Nanostructures: Role of Oxide at the Interface,"We report on the formation of oriented gold nano structures on Si(100)
substrate by annealing procedures in low vacuum (\approx10-2 mbar) and at high
temperature (\approx 975^{\circ} C). Various thicknesses of gold films have
been deposited with SiOx (using high vacuum thermal evaporation) and without
SiOx (using molecular beam epitaxy) at the interface on Si(100). Electron
microscopy measurements were performed to determine the morphology, orientation
of the structures and the nature of oxide layer. Interfacial oxide layer, low
vacuum and high temperature annealing conditions are found to be necessary to
grow oriented gold structures. These gold structures can be transferred by
simple scratching method.",1203.0819v1
2012-06-08,Gate Stack Dielectric Degradation of Rare-Earth Oxides Grown on High Mobility Ge Substrates,"We report on the dielectric degradation of Rare-Earth Oxides (REOs), when
used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2)
on high mobility Ge substrates. Metal-Oxide-Semiconductor (MOS) devices with
these stacks,show dissimilar charge trapping phenomena under varying levels of
Constant- Voltage-Stress (CVS) conditions, which also influences the measured
densities of the interface (Nit) and border (NBT) traps. In the present study
we also report on C-Vg hysteresis curves related to Nit and NBT. We also
propose a new model based on Maxwell-Wagner instabilities mechanism that
explains the dielectric degradations (current decay transient behavior) of the
gate stack devices grown on high mobility substrates under CVS bias from low to
higher fields, and which is unlike to those used for other MOS devices.
Finally, the time dependent degradation of the corresponding devices revealed
an initial current decay due to relaxation, followed by charge trapping and
generation of stress-induced leakage which eventually lead to hard breakdown
after long CVS stressing.",1206.1887v2
2012-06-12,Effect of Oxygen Adsorption on the Local Properties of Epitaxial Graphene on SiC (0001),"The effect of oxygen adsorption on the local structure and electronic
properties of monolayer graphene grown on SiC(0001) has been studied by means
of Low Energy Electron Microscopy (LEEM), microprobe Low Energy Electron
Diffraction (\muLEED) and microprobe Angle Resolved Photoemission (\muARPES).
We show that the buffer layer of epitaxial graphene on SiC(0001) is partially
decoupled after oxidation. The monitoring of the oxidation process demonstrates
that the oxygen saturates the Si dangling bonds, breaks some Si-C bonds at the
interface and intercalates the graphene layer. Accurate control over the
oxidation parameters enables us to tune the charge density modulation in the
layer.",1206.2474v1
2012-07-04,Solvent effect on the Thermodynamics of the Oxidation of Potential Antioxidant Garlic Compounds,"Antioxidant capacity of garlic has been attributed to organic sulfur
compounds such us allyl methyl disulfide. Using quantum chemical calculations
at B3LYP/6-31+G (d) and G3MP2B3/6-31+G (d) levels of theory, we study three
possible oxidation reactions of this compound against hydrogen peroxide, a
reactive oxygen species, from a thermodynamic point of view. Because these
reactions are supposed to occur in biological media, solvent effect was taken
into consideration. Oxidation over the double bond that leads to the formation
of an epoxide is more thermodynamically feasible, limiting the antioxidant
capacity of this compound.",1207.1092v2
2012-07-16,Ultrafast carrier phonon dynamics in NaOH-reacted graphite oxide film,"NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in
graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast
carrier dynamics of the sample were studied by time-resolved transient
differential reflection (\DeltaR/R). The data show two exponential relaxation
processes. The slow relaxation process (\sim2ps) is ascribed to low energy
acoustic phonon mediated scattering. The electron-phonon coupling and
first-principles calculation results demonstrate that - OH and -ONa groups in
the sample are strongly coupled. Thus, we attribute the fast relaxation process
(\sim0.17ps) to the coupling of hydroxyl and -ONa groups in the sample.",1207.3643v1
2012-08-28,Modulation doping to control the high-density electron gas at a polar/non-polar oxide interface,"A modulation-doping approach to control the carrier density of the
high-density electron gas at a prototype polar/non-polar oxide interface is
presented. It is shown that the carrier density of the electron gas at a
GdTiO3/SrTiO3 interface can be reduced by up to 20% from its maximum value (~
3x10^14 cm^-2) by alloying the GdTiO3 layer with Sr. The Seebeck coefficient of
the two-dimensional electron gas increases concurrently with the decrease in
its carrier density. The experimental results provide insight into the origin
of charge carriers at oxide interfaces exhibiting a polar discontinuity.",1208.5711v1
2012-08-30,Spectroscopic fingerprints of valence and spin states in manganese oxides and fluorides,"We performed a systematic study of soft X-ray absorption spectroscopy in
various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F)
K-edges are presented and compared with each other. Despite the distinct
crystal structure and covalent/ionic nature in different systems, the Mn-L
spectra fingerprint the Mn valence and spin states through spectral lineshape
and energy position consistently and evidently. The clear O- and F- K pre-edge
features in our high resolution spectra enable a quantitative definition of the
molecular orbital diagram with different Mn valence. In addition, while the
binding energy difference of the O-1s core electrons leads to a small shift of
the O-K leading edges between trivalent and quadrivalent manganese oxides, a
significant edge shift, with an order of magnitude larger in energy, was found
between divalent and trivalent compounds, which is attributed to the spin
exchange stabilization of half- filled 3d system. This shift is much enhanced
in the ionic fluoride system. This work provides the spectroscopic foundation
for further studies of complicated Mn compounds.",1208.6319v2
2012-09-04,Fractionally delta-doped oxide superlattices for higher carrier mobilities,"A 2D electron gas system in an oxide heterostructure serves as an important
playground for novel phenomena. Here, we show that, by using fractional
delta-doping to control the interface's composition in LaxSr1-xTiO3/SrTiO3
artificial oxide superlattices, the filling-controlled 2D insulator-metal
transition can be realized. The atomic-scale control of d-electron band
filling, which in turn contributes to the tuning of effective mass and density
of the charge carriers, is found to be a fascinating route to substantially
enhanced carrier mobilities.",1209.0721v1
2012-09-15,First Principles Modeling of the Initial Stages of Organic Solvent Decomposition on Li(x)Mn(2)O(4) (100) Surfaces,"Density functional theory and ab initio molecular dynamics simulations are
applied to investigate the initial steps of ethylene carbonate (EC)
decomposition on spinel Li(0.6)Mn(2)O(4) (100) surfaces. EC is a key component
of the electrolyte used in lithium ion batteries. We predict an slightly
exothermic EC bond breaking event on this oxide facet, which facilitates
subsequent EC oxidation and proton transfer to the oxide surface. Both the
proton and the partially decomposed EC fragment weaken the Mn-O ionic bonding
network. Implications for interfacial film made of decomposed electrolyte on
cathode surfaces, and Li(x)Mn(2)O(4) dissolution during power cycling, are
discussed.",1209.3428v1
2012-09-19,Thulium and ytterbium-doped titanium oxide thin films deposited by ultrasonic spray pyrolysis,"Thin films of thulium and ytterbium-doped titanium oxide were grown by
metal-organic spray pyrolysis deposition from titanium(IV)oxide
bis(acetylacetonate), thulium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate)
and ytterbium(III) tris(acetylacetonate). Deposition temperatures have been
investigated from 300{\deg}C to 600{\deg}C. Films have been studied regarding
their crystallity and doping quality. Structural and composition
characterisations of TiO2:Tm,Yb were performed by electron microprobe, X-ray
diffraction and Fourier transform infrared spectroscopy. The deposition rate
can reach 0.8 \mum/h. The anatase phase of TiO2 was obtained after synthesis at
400{\deg}C or higher. Organic contamination at low deposition temperature is
eliminated by annealing treatments.",1209.4226v1
2012-09-20,Nucleating Acicular Ferrite with Galaxite (Al2O3MnO) and Manganese Oxide (MnO2) in FeMnAlC steels,"Effectiveness of galaxite (Al2O3MnO) and manganese oxide (MnO2) in nucleating
acicular ferrite was demonstrated in a steel with composition of
Fe-13.92Mn-4.53Al-1.28Si-0.11C. The hot rolled and quenched steel had a duplex
microstructure of delta-ferrite and partially transformed austenite. Thermal
treatments were used to manipulate the concentration and type of oxides and the
ferrite plate density was found to correlate with inclusions of low misfit.
Both bainitic and acicular ferrite were observed and the prior austenite had a
grain diameter of 16.5 micrometers. Upon tensile testing the retained austenite
transformed to alpha-martensite. Ultimate tensile strength and elongation were
970 MPa and 40 percent. The yield strength was found to be dependent on the
ferrite plate size, which varied linearly with the strength of the austenite.
Ductility decreased as the strength disparity between delta-ferrite and
deformation-induced alpha-martensite increased.",1209.4546v1
2012-09-28,The formation of Er-oxide nanoclusters in SiO$_2$ thin films with excess Si,"The nucleation, distribution and composition of erbium embedded in a
SiO$_2$-Si layer were studied with High Resolution Transmission Electron
Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), Energy Filtered
TEM (EFTEM), Scanning Transmission Electron Microscopy (STEM) and X-ray
Photoelectron Spectroscopy (XPS). When the SiO$_2$ layer contains small amounts
of Si and Er, nanoclusters of Er-oxide are formed throughout the whole layer.
Exposure of the oxide to an electron beam with 1.56*10$^6$
electrons/nm$^2$/sec. causes nanocluster growth. Initially this growth matches
the Ostwald ripening model, but eventually it stagnates at a constant
nanocluster radius of 2.39 nm.",1210.0016v1
2012-10-20,One-way Tamm plasmon-polaritons on the interface of magnetophotonic crystals and conducting metal oxides,"We demonstrate theoretically the existence of one-way Tamm plasmon-polaritons
on the interface between magnetophotonic crystals and conducting metal oxides.
In contrast to conventional surface plasmon-polaritons (SPPs), Tamm
plasmon-polariton (TPPs) occur at frequencies above the bulk plasma frequency
of the conducting materials, provided that the dispersion curves of such
surface modes lie outside the light cone for the conducting oxides and
simultaneously fall into the photonic band gap of the magnetophotonic crystal.
The nonreciprocal properties of TPPs are caused by violation of the periodicity
and time reversal symmetry in the structure. Calculations on the field
distribution and transmission spectra through the structure are employed to
confirm the theoretical results, which could potentially impact on a broad
range of SPP-related phenomena in applications.",1210.5668v1
2012-11-27,Two Dimensional Polymerization of Graphene Oxide: Bottom-up Approach,"We demonstrate a bottom-up synthesis of structures similar to graphene oxide
via a two dimensional polymerization. Experimental evidence and discussion are
conveyed as well as a general framework for this two dimensional
polymerization. The proposed morphologies and lattice structures of these
graphene oxides are derived from aldol condensation of alternating three
nucleophilic and three electrophilic centers of benzenetriol.",1211.6259v2
2012-12-17,Topological Crystalline Insulators in Transition Metal Oxides,"Topological crystalline insulators (TCI) possess electronic states protected
by crystal symmetries, rather than time-reversal symmetry. We show that the
transition metal oxides with heavy transition metals are able to support
nontrivial band topology resulting from mirror symmetry of the lattice. As an
example, we consider pyrochlore oxides of the form A$_2$M$_2$O$_7$. As a
function of spin-orbit coupling strength, we find two $Z_2$ topological
insulator phases can be distinguished from each other by their mirror Chern
numbers, each of which indicates a different TCI. We also derive an effective
$\bf{k\cdot p}$ Hamiltonian, similar to the model introduced for
$\mathrm{Pb_{1-x}Sn_{x}Te}$, and discuss the effect of an on-site Hubbard
interaction on the topological crystalline insulator phase using slave-rotor
mean-field theory, which predicts new classes of topological quantum spin
liquids.",1212.4162v2
2012-12-19,Chemical Capping Synthesis of Nickel Oxide Nanoparticles and their Characterizations Studies,"This work reports aspect related to chemical capping synthesis of nano-sized
particles of nickel oxide. It is a simple, novel and cost effective method. The
average particle size, specific surface area, crystallinity index are estimated
from XRD analysis. The structural, functional groups and optical characters are
analyzed with using of SEM, FTIR and UV- visible techniques. XRD studies
confirm the presence of high degree of crystallinity nature of nickel oxide
nanoparticles. Their particle size is found to be 12 nm and specific surface
area (SSA) is 74m2 g-1. The optical band gap energy value 3.83ev has also been
determined from UV-vis spectrum.",1212.4595v1
2013-01-03,Oxide Heterostructures for Efficient Solar Cells,"We propose an unexplored class of absorbing materials for high-efficiency
solar cells: heterostructures of transition-metal oxides. In particular, LaVO_3
grown on SrTiO_3 has a direct band gap ~1.1 eV in the optimal range as well as
an internal potential gradient, which can greatly help to separate the
photo-generated electron-hole pairs. Furthermore, oxide heterostructures afford
the flexibility to combine LaVO_3 with other materials such as LaFeO_3 in order
to achieve even higher efficiencies with band-gap graded solar cells. We use
density-functional theory to demonstrate these features.",1301.1314v3
2013-01-08,Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids,"Our recent modelling works and corresponding numerical simulations realized
to describe the UO2 oxidation processes confirm the theory showing that an
applied mechanical strain can strongly affect the local oxygen diffusion in a
stressed solid. This result allows us to assume that stress field, previously
applied at the surface of a metallic sample on several microns, will delay the
degradation during its oxidation. Considering this hypothesis, we implemented a
FEM simulation code developed in our laboratory to numerically investigate some
different stress fields applied on a sample sub-surface, that might
significantly modify the volume diffusion of oxygen during the oxidation
process. The results of our simulations are presented and discussed from the
perspective to study the consequences of a surface mechanical treatment on the
durability of a metallic material.",1301.1619v2
2013-01-10,Influence of the U3O7 domain structure on cracking during the oxidation of UO2,"Cracking is observed when a UO_{2} single crystal is oxidised in air.
Previous studies led to the hypothesis that cracking occurs once a critical
depth of U_{3}O_{7} oxidised layer is reached. We present some \mu-Laue X-ray
diffraction results, which evidence that the U_{3}O_{7} layer, grown by
topotaxy on UO_{2}, is made of domains with different crystalline orientations.
This observation was used to perform a modelling of oxidation coupling chemical
and mechanical parameters, which showed that the domain patterning induces
stress localisation. This result is discussed in comparison with stress
localisation observed in thin layer deposited on a substrate and used to
propose an interpretation of UO_{2} oxidation and cracking.",1301.2072v1
2013-01-13,Direct k-space mapping of the electronic structure in an oxide-oxide interface,"The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron
system of itinerant carriers, although both oxides are band insulators.
Interface ferromagnetism coexisting with superconductivity has been found and
attributed to local moments. Experimentally, it has been established that Ti 3d
electrons are confined to the interface. Using soft x-ray angle-resolved
resonant photoelectron spectroscopy we have directly mapped the interface
states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction
contributes to Fermi surface sheets, whereas a localized portion at higher
binding energies is tentatively attributed to electrons trapped by O-vacancies
in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be
excluded, the apparent absence of surface-related Fermi surface sheets could
also be fully reconciled in a recently proposed electronic reconstruction
picture where the built-in potential in the LaAlO3 is compensated by surface
O-vacancies serving also as charge reservoir.",1301.2824v2
2013-01-21,Variable resistor made by repeated steps of epitaxial deposition and lithographic structuring of oxide layers by using wet chemical etchants,"Variable resistors were constructed from epitaxial SrRuO3 (SRO),
La0.67Sr0.33MnO3 (LSMO) and SrTiO3 layers with perovskite crystal structure.
Each layer was patterned separately by lithographic methods. Optimized wet
chemical etchants and several polishing steps in organic solvents allowed good
epitaxy of subsequent layers, comparable to epitaxy on pristine substrates.
Periodate as the oxidizing agent for SRO and iodide with ascorbic acid as the
reducing agents for LSMO were used to attack these chemically resistant oxides.
The final devices changed their conductance in a similar manner to previously
described variable resistors that were defined with shadow masks.",1301.4828v1
2013-02-04,Efficient Estimation of Band Gaps in Transition-Metal Oxides and Chalcogenides using Density Functional Theory,"The performance of two modern density-functionals, HSE06 and TB-mBJ, on
predicting electronic structures of metal oxides, chalcogenides and nitrides,
is studied in terms of band gaps, band structure and projected
density-of-states. Contrary to GGA, hybrid functionals and GGA+U, both new
functionals are able to predict band gaps with an appreciable accuracy of 25%
and thus allow the screening of various classes of (mixed) metal oxides at
modest computational cost. The calculated electronic structures are largely
unaffected by the choice of basis functions and software implementation.",1302.0733v3
2013-02-18,Hot electron transport in a strongly correlated transition metal oxide,"Oxide heterointerfaces are ideal for investigating strong correlation effects
to electron transport, relevant for oxide-electronics. Using hot-electrons, we
probe electron transport perpendicular to the La$_{0.7}$Sr$_{0.3}$MnO$_{3}$
(LSMO)- Nb-doped SrTiO$_3$ (Nb:STO) interface and find the characteristic
hot-electron attenuation length in LSMO to be 1.48 $\pm$ 0.10 unit cells (u.c.)
at -1.9 V, increasing to 2.02 $\pm$ 0.16 u.c. at -1.3 V at room temperature.
Theoretical analysis of this energy dispersion reveals the dominance of
electron-electron and polaron scattering. Direct visualization of the local
electron transport shows different transmission at the terraces and at the
step-edges.",1302.4177v1
2013-02-18,Effect of Ambient Gas Pressure on the Thermal Exfoliation of Graphite Oxide: Tuning the Number of Graphene Sheets,"We have investigated the effect of ambient gas pressure (Argon) used during
thermal exfoliation of graphite oxide on the number of graphene sheets in the
resulting graphene. The ambience gas Ar pressures used are 80, 25, 1 atmosphere
and 10-3 as well as 10-5 torr. We have found curious result that the number of
graphene sheets in exfoliated graphene stack is dependent on the applied
pressure for exfoliation of graphite oxide (GO). By lowering the exfoliation
pressure, the numbers of sheets get reduced. The numbers of sheets in
exfoliated graphene stack have been determined by Lorentzian fit of their
respective 002 peak of XRD profile. The numbers of sheets have also been
confirmed with high resolution transmission electron microscopy (HRTEM). The
numbers of sheets in exfoliated graphene stack samples have been found to be
28, 12, 8, 5 and 3 at 80 atm, 25 atm, 1 atm, 10-3 torr and 10-5 torr pressures
respectively. The results of present investigation suggest a simple but
effective method for synthesizing graphene with a specific number of sheets.",1302.4220v1
2013-02-21,Probing hot electron transport across an epitaxial Schottky interface of SrRuO3/Nb:SrTiO3,"SrRuO3 (SRO), a conducting transition metal oxide, is commonly used for
engineering domains in BiFeO3. New oxide devices can be envisioned by
integrating SRO with an oxide semiconductor as Nb doped SrTiO3 (Nb:STO). Using
a three-terminal device configuration, we study vertical transport in a
SRO/Nb:STO device at the nanoscale and find local differences in transport,
that originate due to the high selectivity of SRO growth on the underlying
surface terminations in Nb:STO. This causes a change in the interface energy
band characteristics and is explained by the differences in the spatial
distribution of the interface-dipoles at the local Schottky interface.",1302.5360v1
2013-03-13,A Ni-Fe Layered Double Hydroxide-Carbon Nanotube Complex for Water Oxidation,"Highly active, durable and cost-effective electrocatalysts for water
oxidation to evolve oxygen gas hold a key to a range of renewable energy
solutions including water splitting and rechargeable metal-air batteries. Here,
we report the synthesis of ultrathin nickel iron layered double hydroxide
nanoplates on mildly oxidized multi-walled carbon nanotubes. Incorporation of
Fe into the nickel hydroxide induced the formation of NiFe-layered double
hydroxide. The nanoplates were covalently attached to a network of nanotubes,
affording excellent electrical wiring to the nanoplates. The ultra-thin Ni-Fe
layered double hydroxide nanoplates/carbon nanotube complex was found to
exhibit unusually high electro-catalytic activity and stability for oxygen
evolution and outperformed commercial precious metal Ir catalysts.",1303.3308v2
2013-05-22,Concentration of Vacancies at Metal Oxide Surfaces: Case Study of MgO (100),"We investigate effects of doping on formation energy and concentration of
oxygen vacancies at a metal oxide surface, using MgO (100) as an example. Our
approach employs density-functional theory, where the performance of the
exchange-correlation functional is carefully analyzed, and the functional is
chosen according to a fundamental condition on DFT ionization energies. The
approach is further validated by CCSD(T) calculations for embedded clusters. We
demonstrate that the concentration of oxygen vacancies at a doped oxide surface
is largely determined by formation of a macroscopically extended space charge
region.",1305.5157v2
2013-07-03,Enhanced Hot-Carrier Luminescence in Multilayer Reduced Graphene Oxide Nanospheres,"We report a method to promote photoluminescence emission in graphene
materials by enhancing carrier scattering instead of directly modifying band
structure in multilayer reduced graphene oxide (rGO) nanospheres. We
intentionally curl graphene layers to form nanospheres by reducing graphene
oxide with spherical polymer templates to manipulate the carrier scattering.
These nanospheres produce hot-carrier luminescence with more than ten-fold
improvement of emission efficiency as compared to planar nanosheets. With
increasing excitation power, hot-carrier luminescence from nanospheres exhibits
abnormal spectral redshift with dynamic feature associated to the strengthened
electron-phonon coupling. These experimental results can be well understood by
considering the screened Coulomb interactions. With increasing carrier density,
the reduced screening effect promotes carrier scattering which enhances
hot-carrier emission from such multilayer rGO nanospheres. This
carrier-scattering scenario is further confirmed by pump-probe measurements.",1307.0940v1
2013-07-23,Solution calorimetry investigations of new phase BaCe0.6Y0.3In0.1O2.8,"The preparation of BaCeO3 doped by yttrium and indium oxides
(BaCe0.6Y0.3In0.1O2.8) has been performed by solid-state reaction from BaCO3,
CeO2, Y2O3, In2O3. The compound BaCe0.6Y0.3In0.1O2.8 has been synthesized for
the first time. The X-ray measurements have showed that BaCe0.6Y0.3In0.1O2.8
has an orthorhombic structure (space group Pmcn). The standard formation
enthalpies of BaCe0.6Y0.3In0.1O2.8 have been determined by solution calorimetry
combining the solution enthalpies of BaCe0.6Y0.3In0.1O2.8 and BaCl2 + 0.6CeCl3
+ 0.3YCl3 + 0.1InCl3 mixtures in 1 M HCl with 0.1 M KI at 298.15 K and
literature data. It has been obtained that above-mentioned mixed oxide is
thermodynamically stable with respect to their decomposition into binary oxides
at room temperatures. It has been also shown that BaCe0.6Y0.3In0.1O2.8 has been
more thermodynamically favored than BaCe0.9In0.1O2.95.",1307.5940v1
2013-10-03,Orienting oxygen vacancies for fast catalytic reaction,"Catalysis is indispensable to chemical processes and relevant to many aspects
of modern life. Owing to the intriguing electronic structures and good ionic
properties, multivalent transition metal oxides have attracted attention as key
catalysts for various energy and environmental applications. Here, we
demonstrate that brownmillerite strontium cobaltite (SrCoO2.5) can be a good
cathode material for sold oxide fuel cells and rechargeable batteries due to
the open oxygen frameworks. When the orientation of oxygen vacancy channels
(OVCs) is properly controlled, one can drastically increase the surface oxygen
exchange rate approximately up to two orders of magnitude. The improved oxygen
reduction kinetics is attributed to a substantial decrease in the thermal
activation energy. Importantly, the strong enhancement of crystallographic
orientation-dependent oxygen reduction reaction required the creation of
neither structural disorders nor chemical doping. Thus, our epitaxial approach
can pave a novel pathway to providing precise interpretation of oxygen
reduction reactions and to developing oxide-based energy materials.",1310.0984v1
2013-10-08,Mechanism for Radiation Damage Resistance in Yttrium Oxide Dispersion Strengthened Steels,"ODS steels based on yttrium oxide have been suggested as potential fusion
reactor wall materials due to their observed radiation resistance properties.
Presumably this radiation resistance can be related to the interaction of the
particle with vacancies,self-interstitial atoms (SIAs) and other radiation
damage debris. Density functional theory has been used to investigate this at
the atomic scale. Four distinct interfaces, some based on HRTEM observations,
between iron and yttrium oxide were investigated. It is been shown that the
Y$_2$O$_3$-Fe interface acts as a strong trap with long-range attraction for
both interstitial and vacancy defects, allowing recombination without altering
the interface structure. The catalytic elimination of defects without change to
the microstructure explains the improved behaviour of ODS steels with respect
to radiation creep and swelling.",1310.2061v1
2013-11-10,Geometric Ferroelectricity in Fluoro-Perovskites,"We used first-principles calculations to investigate the existence and origin
of the ferroelectric in- stability in the ABF3 fluoro-perovskites. We find that
many fluoro-perovskites have a ferroelectric instability in their high symmetry
cubic structure, which is of similar amplitude to that commonly found in oxide
perovskites. In contrast to the oxides, however, the fluorides have nominal
Born effective charges, indicating a different mechanism for the instability.
We show that the instability originates from ionic size effects, and is
therefore in most cases largely insensitive to pressure and strain, again in
contrast to the oxide perovskites. An exception is NaMnF3, where coherent
epitaxial strain matching to a substrate with equal in-plane lattice constants
destabilizes the bulk Pnma structure leading to a ferroelectric, and indeed
multiferroic, ground state with an unusual polarization/strain response.",1311.2244v1
2013-12-23,Shape Resonances in superconducting gaps in a 2DEG at oxide-oxide interface,"In multiband superconductivity, the case where the single electron hopping
between different Fermi surface spots of different symmetry is forbidden by
selection rules is recently attracting a large interest. The focus is addressed
to superconductivity made of multiple condensates with different symmetry where
the chemical potential crosses a 2.5 Lifshitz transition. This can now be
investigated experimentally by fine-tuning of the chemical potential in the
range of tens meV around a band edge using gate voltage control. We discuss
here the case of the two-dimensional electron gas (2DEG), at the interface
between two insulating oxides confined within a slab of 5 nanometers thickness,
where the electronic structure is made of subbands generated by quantum size
effects. We focus on the case of the BCS-BEC transition in the upper subband
for different pairing strength in the shallow Fermi surface.",1312.6669v2
2014-01-07,"Wavelength Spacing Tunable, Multiwavelength Q-Switched Mode-Locked Laser Based on Graphene-Oxide-Deposited Tapered Fiber","A wavelength spacing tunable, multiwavelength Q-switched mode-locked (QML)
fiber laser in an erbium-doped fiber cavity based on graphene oxide deposited
on tapered fiber is proposed by choosing the diameter and length of the taper,
graphene oxide thickness and cavity dispersion, in which the wavelength spacing
could be tuned by pump power. The evolutions of temporal and spectral with
different pump strengths are investigated. Results show that the tunability of
the multiwavelength laser can be interpreted by the bound states of QML laser
resulting from a mutual interaction of dispersion, nonlinear effect, insertion
loss, and pump power. To the best of our knowledge, it is the first
experimental observation of bound states of QML, which provides a new mechanism
to fabricate tunable multiwavelength laser.",1401.1299v1
2014-01-16,Separating electric field and thermal effects across the metal-insulator transition in vanadium oxide nanobeams,"We present results from an experimental study of the equilibrium and
non-equilibrium transport properties of vanadium oxide nanobeams near the
metal-insulator transition (MIT). Application of a large electric field in the
insulating phase across the nanobeams produces an abrupt MIT and the individual
roles of thermal and non-thermal effects in driving the transition are studied.
Transport measurements at temperatures ($T$) far below the critical temperature
($T_c$) of MIT, in several nanoscale vanadium oxide devices, show that both $T$
and electric field play distinctly separate, but critical roles in inducing the
MIT. Specifically, at $T << T_c$ electric field dominates the MIT through an
avalanche-type process, whereas thermal effects become progressively critical
as $T$ approaches $T_c$.",1401.4129v1
2014-01-17,A Carbon Corrosion Model to Evaluate the Effect of Steady State and Transient Operation of a Polymer Electrolyte Membrane Fuel Cell,"A carbon corrosion model is developed based on the formation of surface
oxides on carbon and platinum of the polymer electrolyte membrane fuel cell
electrode. The model predicts the rate of carbon corrosion under potential hold
and potential cycling conditions. The model includes the interaction of carbon
surface oxides with transient species like OH radicals to explain observed
carbon corrosion trends under normal PEM fuel cell operating conditions. The
model prediction agrees qualitatively with the experimental data supporting the
hypothesis that the interplay of surface oxide formation on carbon and platinum
is the primary driver of carbon corrosion.",1401.4285v1
2014-01-18,Formation of a Buffer Layer for Graphene on C-face SiC{0001},"Graphene films prepared by heating the SiC(000-1) surface (the C-face of the
{0001} surfaces) in a Si-rich environment are studied using low-energy electron
diffraction (LEED) and low-energy electron microscopy (LEEM). Upon
graphitization, an interface with rt(43) x rt(43)-R7.6 degree symmetry is
observed by in situ LEED. After oxidation, the interface displays rt(3) x
rt(3)-R30 degree symmetry. Electron reflectivity measurements indicate that
these interface structures arise from a graphene-like ""buffer layer"" that forms
between the graphene and the SiC, similar to that observed on Si-face SiC. From
a dynamical LEED structure calculation for the oxidized C-face surface, it is
found to consist of a graphene layer sitting on top of a silicate (Si2O3)
layer, with the silicate layer having the well-known structure as previously
studied on bare SiC(000-1) surfaces. Based on this result, the structure of the
interface prior to oxidation is discussed.",1401.4552v1
2014-01-24,Photo-oxidative tuning of individual and coupled GaAs photonic crystal cavities,"We demonstrate a new photo-induced oxidation technique for tuning GaAs
photonic crystal cavities using a $390~\mathrm{nm}$ pulsed laser with an
average power of $10~\mathrm{\mu W}$. The laser oxidizes a small $\left(\sim
500~\mathrm{nm}\right)$ diameter spot, reducing the local index of refraction
and blueshifting the cavity. The tuning progress can be actively monitored in
real time. We also demonstrate tuning an individual cavity within a pair of
proximity-coupled cavities, showing that this method can be used to correct
undesired frequency shifts caused by fabrication imperfections in cavity
arrays.",1401.6241v3
2014-01-31,Alleviating polarity-conflict at the heterointerfaces of KTaO$_3$/GdScO$_3$ polar complex-oxides,"We have synthesized and investigated the heterointerfaces of KTaO$_3$ (KTO)
and GdScO$_3$ (GSO), which are both polar complex-oxides along the pseudo-cubic
[001] direction. Since their layers have the same, conflicting net charges at
interfaces, i.e. KO(-1)/ScO$_2$(-1) or TaO$_2$(+1)/GdO(+1), forming the
heterointerface of KTO/GSO should be forbidden due to strong Coulomb repulsion,
the so-called $\textit{polarity conflict}$. However, we have discovered that
atomic reconstruction occurs at the heterointerfaces between KTO thin-films and
GSO substrates, which effectively alleviates the polarity conflict without
destroying the hetero-epitaxy. Our result demonstrates one of the important
ways to create artificial heterostructures from polar complex-oxides.",1401.8225v2
2014-02-05,Understanding water permeation in graphene oxide membranes,"Water transport through graphene-derived membranes has gained much interest
recently due to its promising potential in filtration and separation
applications. In this work, we explore water permeation in graphene oxide
membranes using atomistic simulations, by considering flow through interlayer
gallery, expanded pores such as wrinkles of interedge spaces, and pores within
the sheet. We find that although flow enhancement can be established by
nanoconfinement, fast water transport through pristine graphene channels is
prohibited by a prominent side-pinning effect from capillaries formed between
oxidized regions. We then discuss flow enhancement in situations according to
several recent experiments. These understandings are finally integrated into a
complete picture to understand water permeation through the layer-by-layer and
porous microstructure and could guide rational design of functional membranes
for energy and environmental applications.",1402.1014v1
2014-02-13,New insights on the thermal decomposition of lanthanide(III) and actinide(III) oxalates: from neodymium and cerium to plutonium,"Lanthanides are often used as surrogates to study the properties of actinide
compounds. Their behaviour is considered to be quite similar as they both
possess f valence electrons and are close in size and chemical properties. This
study examines the potential of using two lanthanides (neodymium and cerium) as
surrogates for plutonium during the thermal decomposition of isomorphic oxalate
compounds, in the trivalent oxidation state, into oxides. Thus, the thermal
decomposition of neodymium, cerium and plutonium (III) oxalates are
investigated by several coupled thermal analyses (TG-DTA/DSC-MS/FT-IR) and
complementary characterisation techniques (XRD, UV-vis, FT-IR, SEM, carbon
analyser) under both oxidizing and inert atmosphere. The thermal decomposition
mechanisms determined in this study confirmed some previous results reported in
the literature, among diverging propositions, while also elucidating some
original mechanisms not previously considered. Calculated thermodynamic and
kinetic parameters for the studied systems under both atmospheres are reported
and compared with available literature data. Similarities and differences
between the thermal behaviour of plutonium(III) and lanthanide(III) oxalates
are outlined.",1402.3046v1
2014-04-18,Systematic control of carrier concentration and resisitivity in RF sputtered Zinc oxide thin films,"RF sputtered ZnO and Al:ZnO films are attractive transparent conductive
oxides for fabrication of opto-electronic devices. In this paper we present
efforts to control carrier concentration and mobility of ZnO/Al:ZnO thin films
by controlling deposition parameters (RF power, pressure and substrate
temperature. Al:ZnO thin film with resistivity as low as $\rho$ = $3.8\times
10^{-4}$ $\Omega$.cm at deposition temperature of 250{\deg}C has been achieved.
Zinc oxide thin film with low resistivity of $\rho$ = $3.7\times 10^{-2}$
$\Omega$.cm and high electron mobility of $30$ $\mathrm{cm^{-2}V^{-1}s^{-1}}$
at deposition temperature of 250{\deg}C with acceptable electronic parameters
stability has been obtained.Light transmission of Al:ZnO and ZnO samples
deposited on glass at different substrate temperature has been studied.
Investigation were made to assess the effect of deposition temperature on the
photoluminescence spectra (PL) of ZnO/Al:ZnO sputtered on silicon and glass
substrate. The evolution of near band edge (NBE) and deep level emission (DLE)
photoluminescence peaks with deposition temperature in ZnO/Al:ZnO sputtered on
Silicon and glass substrate have been studied.",1404.4902v1
2014-08-05,Patterning and tuning of electrical and optical properties of graphene by laser induced two-photon oxidation,"Graphene, being an ultrathin, durable, flexible, transparent material with
superior conductivity and unusual optical properties, promises many novel
applications in electronics, photonics and optoelectronics. For applications in
electronics, patterning and modification of electrical properties is very
desirable since pristine graphene has no band gap. Here we demonstrate a simple
all-optical patterning method for graphene, based on laser induced two-photon
oxidation. By tuning the intensity of irradiation and the number of pulses the
level of oxidation can be controlled to high precision and, therefore, a band
gap can be introduced and electrical and optical properties can be continuously
tuned. Arbitrary complex patterning can be performed for air-suspended
monolayer graphene or for graphene on substrates. The method works at room
temperature in ambient air and no additional processing step is needed. The
presented concept allows development of all-graphene electronic and
optoelectronic devices and complex circuits with an all-optical method.",1408.0905v1
2014-08-27,Tunable Band gap of Iron-Doped Lanthanum-Modified Bismuth Titanate Synthesized by the Thermal Decomposition of a Secondary Phase,"The photoelectric properties of complex oxides have prompted interest in
materials with a tunable band gap, because the absorption The substitution of
iron atoms in La-modified bismuth titanate (BLT) can lead to dramatic
improvements in the band gap, however, the substitution of iron atoms in BLT
without forming a BiFeO3 secondary phase is quite challenging. Therefore, a
series of Fe-doped BLT (Fe-BLT) samples were characterized using a solid
reaction at various calcination temperatures (300~900{\deg}C) to remove the
secondary phase. The structural and optical properties were analyzed by X-ray
diffraction and ultraviolet-visible absorption spectroscopy. This paper reports
a new route to synthesize a pure Fe-BLT phase with a reduced optical band gap
by high temperature calcination due to the thermal decomposition of BiFeO3
during high temperature calcination. This simple route to reduce the second
phase can be adapted to other complex oxides for use in emerging oxide
optoelectronic devices.",1408.6294v1
2014-09-08,Prediction of pressure-induced stabilization of noble-gas-atom compounds with alkali oxides and alkali sulfides,"The cubic antifluorite structure comprises a face-centered cubic sublattice
of anions with cations on the tetrahedral sites. The voids in the antifluorite
structure that are crucial for superionicity in Li2O might also act as atomic
traps. Trapping of guest atoms and small molecules within voids of a host
structure leads to the formation of what are known as clathrate compounds. Here
we investigate the possibility of trapping helium or larger neon guest atoms
under pressure within alkali metal oxide and sulfide structures. We find stable
helium and neon-bearing compounds at very low pressures. These structures are
stabilized by a reduction in volume from incorporation of helium or neon atoms
within the antifluorite structure. We predict that NeCs2S could be stable at
ambient pressure. Our study suggests a novel class of alkali oxide and sulfide
materials incorporating noble gas atoms that might potentially be useful for
gas storage.",1409.2227v2
2014-09-10,Electronic reconstruction at the interface between band insulating oxides: the LaAlO3/SrTiO3 system,"The conducting quasi-two dimensional electron system (q2DES) formed at the
interface between LaAlO3 and SrTiO3 band insulators is confronting the
condensed matter physics community with new paradigms. While the mechanism for
the formation of the q2DES is debated, new conducting interfaces have been
discovered paving the way to possible applications in electronics, spintronics
and optoelectronics. This chapter is an overview of the research on the LAO/STO
sys-tem, presenting some of the most important results obtained in the last
decade to clarify the mechanism of formation of the q2DES at the oxide
interfaces and its peculiar electronic properties as compared to semiconducting
2D-electron gas.",1409.3098v1
2014-09-15,Direct observation of charge mediated lattice distortions in complex oxide solid solutions,"Material properties depend sensitively on picometer scale atomic
displacements introduced by local chemical fluctuations. Direct real-space,
high spatial-resolution measurements of this compositional variation and
corresponding distortion can provide new insights into materials behavior at
the atomic scale. Using aberration corrected scanning transmission electron
microscopy combined with advanced imaging methods, we observed atom column
specific, picometer-scale displacements induced by local chemistry in a complex
oxide solid solution. Displacements predicted from density functional theory
were found to correlate with the observed experimental trends. Further analysis
of bonding and charge distribution were used to clarify the mechanisms
responsible for the detected structural behavior. By extending the experimental
electron microscopy measurements to previously inaccessible length scales, we
identified correlated atomic displacements linked to bond differences within
the complex oxide structure.",1409.4432v1
2014-09-23,Fabrication of Flexible Super Capacitor Using Laser Lightscribe Technique,"Super capacitors are promising energy storage devices due to their capability
of delivering high peak current and storing high amount of energy in a short
time with very low internal power loss. We fabricated the graphene or graphite
oxide super-capacitor using laser Lightscribe technique. We prepared graphite
oxide by modified hummers method and used PET film as a flexible substrate on
which graphite oxide (GO) was coated. Using Lightscribe drive and software, the
super-capacitor configuration was patterned on the GO coated PET film. During
the writing process, the laser converts GO into graphene. We characterized the
fabricated flexible super-capacitor which exhibits high resistance of 20KOhm
with applied voltage of 10V and further increase of voltage (20V) decreases the
resistance to 8KOhm. We also analyzed the frequency response of the capacitor
using impedance measurement which shows high frequency response and estimated
capacitance is 120nF. We optimized the patterns by running the Lightscribe
repeatedly on the GO coated PET substrate.",1409.6396v1
2014-10-01,Varistor characteristics of a nano-device containing graphene and oxidized graphene: Verification by DFT + NEGF,"Electron transport and quantum conductance through an armchair graphene and
its oxidized graphene- containing form were investigated by the density
functional theory (DFT) method and the implementation of the non-equilibrium
Green function (NEGF) approach. The computed $I-V_b$(current as a function of
bias voltage) characteristic of the studied systems showed the tunneling
phenomenon in bias and gate voltages considered. Along with the transport
properties, electronic properties including density of states (DOS) were
calculated in the studied systems. A close examination of the results showed
that the $I-V_b$ curve for graphene behaved $I\propto V_be^{\lambda V_b}$ like
at some bias voltages, while for the oxidized graphene-containing form, its
trend was the same as that of a Voltage Dependent Resistor (VDR-VARiable
resISTOR), $I\propto V_b^\beta$, at the whole range of the applied bias.",1410.0285v4
2014-11-13,Graphene-Passivated Nickel as an Oxidation-Resistant Electrode for Spintronics,"We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin
devices. GPFE are shown to act as spin-polarized oxidation-resistant
electrodes. The direct coating of nickel with few layer graphene through a
readily scalable chemical vapour deposition (CVD) process allows the
preservation of an unoxidized nickel surface upon air exposure. Fabrication and
measurement of complete reference tunneling spin valve structures demonstrates
that the GPFE is maintained as a spin polarizer and also that the presence of
the graphene coating leads to a specific sign reversal of the
magneto-resistance. Hence, this work highlights a novel oxidation-resistant
spin source which further unlocks low cost wet chemistry processes for
spintronics devices.",1411.3476v1
2014-11-13,The characterization of Co-nanoparticles supported on graphene,"The results of density functional theory (DFT) calculations and measurements
of X-ray photoelectron (XPS) and X-ray emission (XES) spectra of
Co-nanoparticles dispersed on graphene/Cu composites are presented. It is found
that for 0.02nm and 0.06nm Co coverage the Co atoms form islands which are
strongly oxidized under exposure at the air. For Co (2nm) coverage the upper
Co-layers is oxidized whereas the lower layers contacting with graphene is in
metallic state. Therefore Co (2 nm) coverage induces the formation of
protective oxide layer providing the ferromagnetic properties of Co
nanoparticles which can be used as spin filters in spintronics devices.",1411.3611v3
2014-12-05,Tuning the Band Gap in Silicene by Oxidation,"Silicene monolayers grown on Ag(111) surfaces demonstrate a band gap that is
tunable by oxygen adatoms from semimetallic to semiconducting type. By using
low-temperature scanning tunneling microscopy, it is found that the adsorption
configurations and amounts of oxygen adatoms on the silicene surface are
critical for band-gap engineering, which is dominated by different buckled
structures in R13xR13, 4x4, and 2R3x2R3 silicene layers. The Si-O-Si bonds are
the most energy-favored species formed on R13xR13, 4x4, and 2R3x2R3 structures
under oxidation, which is verified by in-situ Raman spectroscopy as well as
first-principles calculations. The silicene monolayers retain their structures
when fully covered by oxygen adatoms. Our work demonstrates the feasibility of
tuning the band gap of silicene with oxygen adatoms, which, in turn, expands
the base of available two-dimensional electronic materials for devices with
properties that is hardly achieved with graphene oxide.",1412.1886v1
2014-12-05,"Oxidation of copper during physical sputtering deposition: mechanism, avoidance and utilization","In this paper, oxidation of Cu during physical sputtering deposition in a
high purity and low pressure Ar atmosphere without introducing O2 gas flow was
studied systemically. It was found that various flexible Cu-based films could
be obtained by simply adjusting deposition parameters. Electrical and optical
testing results showed that the achieved pure Cu films and Cu+Cu2O composite
films both presented an intriguing combination of metal and semiconductor
characteristics. It is expected that such Cu-based films with a superior
conductivity and a solar-window bandgap may have fascinating potential
applications such as in high electron mobility transistors, electrodes and
solar cells. Further, the oxidation mechanisms of Cu under different deposition
parameters and the main O2 source during physical sputtering deposition were
also explored.",1412.2031v1
2014-12-08,Evaluation of defects in cuprous oxide through exciton luminescence imaging,"The various decay mechanisms of excitons in cuprous oxide (Cu2O) are highly
sensitive to defects which can relax selection rules. Here we report cryogenic
hyperspectral imaging of exciton luminescence from cuprous oxide crystals grown
via the floating zone method showing the samples have few defects. Some
locations, however, show strain splitting of the 1s orthoexciton triplet
polariton luminescence. Strain is reduced by annealing. In addition, annealing
causes annihilation of oxygen and copper vacancies, which leads to a negative
correlation between luminescence of unlike vacancies.",1412.2707v1
2014-12-12,A Monolithic active pixel sensor for ionizing radiation using a 180nm HV-SOI process,"An improved SOI-MAPS (Silicon On Insulator Monolithic Active Pixel Sensor)
for ionizing radiation based on thick-film High Voltage SOI technology (HV-SOI)
has been developed. Similar to existing Fully Depleted SOI-based (FD-SOI) MAPS,
a buried silicon oxide inter-dielectric (BOX) layer is used to separate the
CMOS electronics from the handle wafer which is used as a depleted charge
collection layer. FD-SOI MAPS suffer from radiation damage such as transistor
threshold voltage shifts due to charge traps in the oxide layers and charge
states created at the silicon oxide boundaries (back gate effect). The X-FAB
180-nm HV-SOI technology offers an additional isolation by deep non-depleted
implant between the BOX layer and the active circuitry witch mitigates this
problem. Therefore we see in this technology a high potential to implement
radiation-tolerant MAPS with fast charge collection property. The design and
measurement results from a first prototype are presented including charge
collection in neutron irradiated samples.",1412.3973v2
2014-12-15,Percolation conductivity in hafnium sub-oxides,"In this study, we demonstrated experimentally that formation of chains and
islands of oxygen vacancies in hafnium sub-oxides (HfO$_x$, $x<2$) leads to
percolation charge transport in such dielectrics. Basing on the model of
\'{E}fros-Shklovskii percolation theory good quantitative agreement between the
experimental and theoretical data of current-voltage characteristics were
achieved. Based on the percolation theory suggested model shows that hafnium
sub-oxides consist of mixtures of metallic Hf nanoscale clusters of 1-2 nm
distributed onto non-stoichiometric HfO$_x$. It was shown that reported
approach might describe low resistance state current-voltage characteristics of
resistive memory elements based on HfO$_x$.",1412.4478v1
2015-01-08,Multi-Lattice Kinetic Monte Carlo Simulations from First-Principles: Reduction of the Pd(100) Surface Oxide by CO,"We present a multi-lattice kinetic Monte Carlo (kMC) approach that
efficiently describes the atomistic dynamics of morphological transitions
between commensurate structures at crystal surfaces. As an example we study the
reduction of a $(\sqrt{5}\times \sqrt{5})R27^{\circ}$ PdO(101) overlayer on
Pd(100) in a CO atmosphere. Extensive density-functional theory calculations
are used to establish an atomistic pathway for the oxide reduction process.
First-principles multi-lattice kMC simulations on the basis of this pathway
fully reproduce the experimental temperature dependence of the reduction rate
[Fernandes et al., Surf. Sci. 2014, 621, 31-39] and highlight the crucial role
of elementary processes special to the boundary between oxide and metal
domains.",1501.01710v1
2015-01-28,Dimensional oxidation and modular completion of non-geometric type IIB action,"Utilizing a setup of type IIB superstring theory compactified on an
orientifold of T^6/(Z2xZ2), we propose a modular invariant dimensional
oxidation of the four-dimensional scalar potential. In the oxidized
ten-dimensional supergravity action, the standard NS-NS and RR three form
fluxes (H-, F-) as well as the non-geometric fluxes (Q-, P-) are found to
nicely rearrange themselves to form generalized flux-combinations. As an
application towards moduli stabilization, using the same S-duality invariant
scalar potential, we examine the recently proposed No-Go theorem (in
arXiv:1409.7075) about creating a mass-hierarchy between universal-axion and
the dilaton relevant for axionic-inflation. Considering a two-field dynamics of
universal axion and dilaton while assuming the other moduli/axions being
stabilized, we find a part of the No-Go arguments to be quite robust even with
the inclusion of non-geometric (Q-, P-) fluxes.",1501.07248v4
2015-03-12,The influence of electron beam irradiation on the chemical and structural properties of medical grade Polyurethane,"Thermo plastic polyurethane (TPU) provides excellent bio-compatibility,
flexibility and good irradiation resistance; however, extremely high
irradiation doses can alter the structure and function of macromolecules,
resulting in oxidation, chain scission and cross-linking. In this study, the
effects of e-beam irradiation on the medical grade thermo plastic polyurethane
were studied. The changes in the chain length and their distribution as well as
the changes in molecular structure were studied. The GPC (Gel Permeation
Chromatography) results show that the oxidative decomposition is followed by a
decrease in molecular mass together with an increase in polydispersity. This
indicates a very inhomogeneous degradation, which is a consequence of the
specific course and of the intensity of oxidative degradation. This was
confirmed by means of mechanical property measurements. Overall, this study
demonstrated that the medical grade TPU was affected by radiation exposure,
particularly at high irradiation doses.",1503.03590v1
2015-03-16,Lithiation of Tin Oxide: A Computational Study,"We suggest that the lithiation of pristine SnO forms a layered Li$_\text{X}$O
structure while the expelled tin atoms agglomerate into 'surface' planes
separating the Li$_\text{X}$O layers. The proposed lithiation model widely
differs from the common assumption that tin segregates into nano-clusters
embedded in the lithia matrix. With this model we are able to account for the
various tin bonds that are seen experimentally and explain the three volume
expansion phases that occur when SnO undergoes lithiation: (i) at low
concentrations Li behaves as an intercalated species inducing small volume
increases; (ii) for intermediate concentrations SnO transforms into lithia
causing a large expansion; (iii) finally, as the Li concentration further
increases a saturation of the lithia takes place until a layered Li$_2$O is
formed. A moderate volume expansion results from this last process. We also
report a 'zipper' nucleation mechanism that could provide the seed for the
transformation from tin oxide to lithium oxide.",1503.04647v1
2015-03-25,"Identification of novel Cu, Ag, and Au ternary oxides from global structural prediction","We use ab initio global structural prediction, and specifically the minima
hopping method, to explore the periodic table in search of novel oxide phases.
In total, we study 183 different compositions of the form MXO2, where M=(Cu,
Ag, Au) and X is an element of the periodic table. This set includes the
well-known Cu delafossite compounds that are, up to now, the best p-type
transparent conductive oxides known to mankind. Our calculations discover 81
stable compositions, out of which only 36 are included in available databases.
Some of these new phases are potentially good candidates for transparent
electrodes. These results demonstrate, on one hand, how incomplete is still our
knowledge of the phase-space of stable ternary materials. On the other hand, we
show that structural prediction combined with high-throughput approaches is a
powerful tool to extend that knowledge, paving the way for the experimental
discovery of new materials on a large scale.",1503.07327v1
2015-04-09,Spin responses and effective Hamiltonian for the two dimensional electron gas at oxide interface {LaAlO}$_3$/{SrTiO}$_3$,"Strong Rashba spin-orbit coupling (SOC) of the two-dimensional electron gas
(2DEG) at the oxide interface $\mathrm{LaAlO_{3}/SrTiO_{3}}$ underlies a
variety of exotic physics, but its nature is still under debate. We derive an
effective Hamiltonian for the 2DEG at the oxide interface
$\mathrm{LaAlO_{3}/SrTiO_{3}}$ and find a different anisotropic Rashba SOC for
the $d_{xz}$ and $d_{yz}$ orbitals. This anisotropic Rashba SOC leads to
anisotropic static spin susceptibilities and also distinctive behavior of the
spin Hall conductivity. These unique spin responses may be used to determine
the nature of the Rashba SOC experimentally and shed light on the orbital
origin of the 2DEG.",1504.02177v3
2015-04-13,Scaling Theory of Electrically Doped 2D Transistors,"In this letter, it is shown that the existing scaling theories for chemically
doped transistors cannot be applied to the novel class of electrically doped 2D
transistors and the concept of equivalent oxide thickness (EOT) is not
applicable anymore. Hence, a novel scaling theory is developed based on
analytic solutions of the 2D Poisson equation. Full band atomistic quantum
transport simulations verify the theory and show that the critical design
parameters are the physical oxide thickness and distance between the gates.
Accordingly, the most optimized electrically doped devices are those with the
smallest spacing between the gates and the thinnest oxide, and not the smallest
EOT.",1504.03387v3
2015-05-11,Oxide 2D electron gases as a route for high carrier densities on (001) Si,"Two dimensional electron gases (2DEGs) formed at the interfaces of oxide
heterostructures draw considerable interest owing to their unique physics and
potential applications. Growing such heterostructures on conventional
semiconductors has the potential to integrate their functionality with
semiconductor device technology. We demonstrate 2DEGs on a conventional
semiconductor by growing $GdTiO_3-SrTiO_3$ on silicon. Structural analysis
confirms the epitaxial growth of heterostructures with abrupt interfaces and a
high degree of crystallinity. Transport measurements show the conduction to be
an interface effect, with $\sim 9\times 10^{13} \; cm^{-2}$ electrons per
interface. Good agreement is demonstrated between the electronic behavior of
structures grown on Si and on an oxide substrate, validating the robustness of
this approach to bridge between lab-scale samples to a scalable,
technologically relevant materials system.",1505.02738v1
2015-05-20,"III-V/Si Wafer Bonding Using Transparent, Conductive Oxide Interlayers","We present a method for low temperature plasma-activated direct wafer bonding
of III-V materials to Si using a transparent, conductive indium zinc oxide
interlayer. The transparent, conductive oxide (TCO) layer provides excellent
optical transmission as well as electrical conduction, suggesting suitability
for Si/III-V hybrid devices including Si-based tandem solar cells. For bonding
temperatures ranging from 100$^{\circ}$C to 350$^{\circ}$C, Ohmic behavior is
observed in the sample stacks, with specific contact resistivity below 1
$\Omega$cm$^2$ for samples bonded at 200$^{\circ}$C. Optical absorption
measurements show minimal parasitic light absorption, which is limited by the
III-V interlayers necessary for Ohmic contact formation to TCOs. These results
are promising for Ga$_{0.5}$In$_{0.5}$P/Si tandem solar cells operating at one
sun or low concentration conditions.",1505.05453v2
2015-05-29,Enhanced Li capacity in functionalized graphene: A first principle study with van der Waals correction,"We have investigated the adsorption of Li on graphene oxide using density
functional theory. We show a novel and simple approach to achieve a positive
lithiation potential on epoxy and hydroxyl functionalized graphene, compared to
the negative lithiation potential that has been found on prestine graphene. We
included the van der Waals correction into the calculation so as to get better
picture of weak interactions. A positive lithiation potential suggests a
favorable adsorption of Li on graphene oxide sheets that can lead to an
increase in the specific capacity, which in turn can be used as an anode
material in Li-batteries. We find a high specific capacity of ~860 mAh/g by
functionalizing the graphene sheet. This capacity is higher than the previously
reported capacities that were achieved on graphene with high concentration of
Stone-Wales (75%) and divacancy (16%) defects. Creating such high density of
defects can make the entire system energetically unstable, whereas graphene
oxide is a naturally occurring substance.",1505.07918v1
2015-06-18,Evidence for the Active Phase of Heterogeneous Catalysts through In Situ Reaction Product Imaging and Multiscale Modeling,"We use multi-scale modeling to analyze laser-induced fluorescence (LIF)
measurements of the CO oxidation reaction over Pd(100) at near-ambient reaction
conditions. Integrating density-functional theory based kinetic Monte Carlo
simulations of the active catalyst into fluid-dynamical simulations of the mass
transport inside the reactor chamber we calculate the reaction product
concentration directly above the catalyst surface. Comparing corresponding data
calculated for different surface models against the measured LIF signals we can
discriminate the one that predominantly actuates the experimentally measured
catalytic activity. For the probed CO oxidation reaction conditions the
experimental activity is due to pristine Pd(100), possibly coexisting with
other (oxidic) domains on the surface.",1506.05542v1
2015-07-02,Low Operation Voltage Ferroelectric Field-Effect Transistor Based on Polarization Rotation Effect,"The effect of polarization rotation on the performance of metal oxide
semiconductor field-effect transistors was investigated with a
Landau-Ginzburg-Devonshire theory based model. In this analytical model,
depolarization field, polarization rotations and the electrostatic properties
of the doped silicon substrate are considered to illustrate the size effect of
ferroelectric oxides and the stability of polarization in each direction. Based
on this model, we demonstrate that MOSFET operation could be achieved by
polarization reorientation with a low operating voltage, if the thickness of
ferroelectric oxide is properly selected. Polarization reorientation can boost
the surface potential of the silicon substrate, leading to a subthreshold swing
S lower than 60 mV/decade. We believe that this model could provide guidance in
designing electronic logic devices with low operating voltages and low active
energy consumption.",1507.00764v1
2015-07-07,The Effect of Polar Fluctuation and Lattice Mismatch on Carrier Mobility at Oxide Interfaces,"Since the discovery of two-dimensional electron gas (2DEG) at the oxide
interface of LaAlO3/SrTiO3, improving carrier mobility has become an important
issue for device applications. In this paper, by using an alternate polar
perovskite insulator (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) for reducing lattice
mismatch from 3.0% to 1.0%, the low-temperature carrier mobility has been
increased 30 fold to 35,000 cm2V-1s-1. Moreover, two critical thicknesses for
the LSAT/SrTiO3 (001) interface are found: one at 5 unit cell for appearance of
the 2DEG, the other at 12 unit cell for a peak in the carrier mobility. By
contrast, the conducting (110) and (111) LSAT/STO interfaces only show a single
critical thickness of 8 unit cells. This can be explained in terms of polar
fluctuation arising from LSAT chemical composition. In addition to lattice
mismatch and crystal symmetry at the interface, polar fluctuation arising from
composition has been identified as an important variable to be tailored at the
oxide interfaces to optimise the 2DEG transport.",1507.01675v1
2015-07-11,Structure and Energetics of Graphene Oxide Isomers: Ab Initio Thermodynamic Analysis,"Graphene oxide (GO) holds significant promise for electronic devices and
nanocomposite materials. A number of models were proposed for GO structure,
combining carboxyl, hydroxyl, carbonyl and epoxide groups at different
locations. The complexity and variety of GO isomers, whose thermodynamic
stability and formation kinetics depend on applied conditions, make
determination of GO structure with atomistic precision challenging. We report
high level theoretical investigation of multiple molecular configurations,
which are anticipated in GO. We conclude that all oxygen containing groups at
the GO surface are thermodynamically permitted, whereas the edge positions are
systematically more favorable than the center and side positions. We discuss a
potentially novel type of chemical bond or bonding reinforcement in GO, which
consists of a covalent bond and a strong electrostatic contribution from a
polarized graphene plane. We observe and analyze significant modifications of
graphene geometry and electronic structure upon oxidation. The reported
thermodynamic data guide experiments aimed at deciphering GO chemical
composition and structure, and form the basis for predicting GO properties
required for nano-technological applications.",1507.03138v1
2015-07-31,Surface Passivation in Empirical Tight Binding,"Empirical Tight Binding (TB) methods are widely used in atomistic device
simulations. Existing TB methods to passivate dangling bonds fall into two
categories: 1) Method that explicitly includes passivation atoms is limited to
passivation with atoms and small molecules only. 2) Method that implicitly
incorporates passivation does not distinguish passivation atom types. This work
introduces an implicit passivation method that is applicable to any passivation
scenario with appropriate parameters. This method is applied to a Si quantum
well and a Si ultra-thin body transistor oxidized with SiO2 in several
oxidation configurations. Comparison with ab-initio results and experiments
verifies the presented method. Oxidation configurations that severely hamper
the transistor performance are identified. It is also shown that the commonly
used implicit H atom passivation overestimates the transistor performance.",1507.08712v1
2015-08-10,"Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked against $GW$ band structure calculations and experiments","We investigate band gaps, equilibrium structures, and phase stabilities of
several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO2,ZrO2, and
WO3. We are particularly concerned with assessing the performance of hybrid
functionals built with the fraction of Hartree-Fock exact exchange obtained
from the computed electronic dielectric constant of the material. We provide
comparison with more standard density-functional theory and GW methods. We
finally analyze the chemical reduction of TiO2 into Ti2O3, involving a change
in oxide stoichiometry. We show that the dielectric-dependent hybrid functional
is generally good at reproducing both ground-state (lattice constants, phase
stability sequences, and reaction energies) and excited-state (photoemission
gaps) properties within a single, fully ab initio framework.",1508.02174v2
2015-09-13,Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: the case of oxygen vacancies in metal oxides,"We investigate the behavior of oxygen vacancies in three different
metal-oxide semiconductors (rutile and anatase TiO2, monoclinic WO3, and
tetragonal ZrO2) using a recently proposed hybrid density-functional method in
which the fraction of exact exchange is material-dependent but obtained ab
initio in a self-consistent scheme. In particular, we calculate
charge-transition levels relative to the oxygen-vacancy defect and compare
computed optical and thermal excitation/emission energies with the available
experimental results, shedding light on the underlying excitation mechanisms
and related materials properties. We find that this novel approach is able to
reproduce not only ground-state properties and band structures of perfect bulk
oxide materials, but also provides results consistent with the optical and
electrical behavior observed in the corresponding substoichiometric defective
systems.",1509.03889v1
2015-09-22,Antisite defects at oxide interfaces,"We use \textit{ab initio} calculations to estimate formation energies of
cation (transition metal) antisite defects at oxide interfaces and to
understand the basic physical effects that drive or suppress the formation of
these defects. Antisite defects are found to be favored in systems with
substantial charge transfer across the interface, while Jahn-Teller distortions
and itinerant ferromagnetism can prevent antisite defects and help stabilize
atomically sharp interfaces. Our results enable identification of classes of
systems that may be more and less susceptible to the formation of antisite
defects and motivate experimental studies and further theoretical calculations
to elucidate the local structure and stability of oxide interface systems.",1509.06643v2
2015-09-28,Phase Stability and Properties of Manganese Oxide Polymorphs: Assessment and Insights from Diffusion Monte Carlo,"We present an analysis of the polymorphic energy ordering and properties of
the rock salt and zincblende structures of manganese oxide using fixed node
diffusion Monte Carlo (DMC). Manganese oxide is a correlated, antiferromagnetic
material that has proven to be challenging to model from first principles
across a variety of approaches. Unlike conventional density functional theory
and some hybrid functionals, fixed node diffusion Monte Carlo finds the rock
salt structure to be more stable than the zincblende structure, and thus
recovers the correct energy ordering. Analysis of the site-resolved charge
fluctuations of the wave functions according to DMC and other electronic
structure descriptions give insights into elements that are missing in other
theories. While the calculated band gaps within DMC are in agreement with
predictions that the zincblende polymorph has a lower band gap, the gaps
themselves overestimate reported experimental values.",1509.08321v2
2015-09-28,Conducting interfaces between amorphous oxide layers and SrTiO3(110) and SrTiO3(111),"Interfaces between (110) and (111)SrTiO3 (STO) single crystalline substrates
and amorphous oxide layers, LaAlO3 (a-LAO), Y:ZrO2 (a-YSZ), and SrTiO3 (a-STO)
become conducting above a critical thickness tc. Here we show that tc for a-LAO
is not depending on the substrate orientation, i.e. tc (a-LAO/(110)STO) ~
tc(a-LAO/(111)STO) interfaces, whereas it strongly depends on the composition
of the amorphous oxide: tc(a-LAO/(110)STO) < tc(a-YSZ/(110)STO) <
tc(a-STO/(110)STO). It is concluded that the formation of oxygen vacancies in
amorphous-type interfaces is mainly determined by the oxygen affinity of the
deposited metal ions, rather than orientational-dependent enthalpy vacancy
formation and diffusion. Scanning transmission microscopy characterization of
amorphous and crystalline LAO/STO(110) interfaces shows much higher amount of
oxygen vacancies in the former, providing experimental evidence of the distinct
mechanism of conduction in these interfaces.",1509.08385v1
2015-09-30,Unusual dissociative adsorption of H2 over stoichiometric MgO thin film supported on molybdenum,"The dissociation of a hydrogen molecule on MgO(001) films deposited on
Mo(001) surface is investigated systematically using periodic
density-functional theory method. The unusual adsorption behavior of
heterolytic dissociative hydrogen molecule at neighboring surface oxygen and
surface magnesium, is clarified here. To my knowledge, this heterolytic
dissociative state has never been found before on bulk MgO(001) or metal
supported MgO(001) surfaces. The results confirm that, in all cases, the
heterolytic dissociation is much more favorable that homolytic dissociation
both energetically and kinetically. The energy difference between two
dissociative states are very large, in the range of 1.1 eV ~ 1.5 eV for Mo
supported 1 ML ~ 3 ML oxide films, which inhibits, to a great extent, the
homolytic dissociation in the respect of reaction thermodynamics. The energy
barrier of heterolytic dissociation are about 0.5 eV, much lower that the
barrier of homolytic dissociation. The transformation reaction on thick films
will be more endothermic. Passing through heterolytic dissociation state have
significantly lowered the reaction heat and the energy barrier for obtaining
homolytic dissociative structure, which make the homolytic splitting of H2
easier on 2 ML oxide films. The results provides a useful strategy for
enhancing the reactivity of the nonreducible metal oxide.",1509.09244v1
2015-10-21,Proton Conducting Graphene Oxide Coupled Neuron Transistors for Brain-Inspired Cognitive Systems,"Neuron is the most important building block in our brain, and information
processing in individual neuron involves the transformation of input synaptic
spike trains into an appropriate output spike train. Hardware implementation of
neuron by individual ionic/electronic hybrid device is of great significance
for enhancing our understanding of the brain and solving sensory processing and
complex recognition tasks. Here, we provide a proof-of-principle artificial
neuron based on a proton conducting graphene oxide (GO) coupled oxide-based
electric-double-layer (EDL) transistor with multiple driving inputs and one
modulatory input terminal. Paired-pulse facilitation, dendritic integration and
orientation tuning were successfully emulated. Additionally, neuronal gain
control (arithmetic) in the scheme of rate coding is also experimentally
demonstrated. Our results provide a new-concept approach for building
brain-inspired cognitive systems.",1510.06115v1
2015-11-20,Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides,"We report the successful growth of high-quality SrO films on highly-ordered
pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy.
The SrO layers have (001) orientation as confirmed by x-ray diffraction (XRD)
while atomic force microscopy measurements show continuous pinhole-free films
having rms surface roughness of <1.5 {\AA}. Transport measurements of
exfoliated graphene after SrO deposition show a strong dependence between the
Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer
layer for more complex oxide integration via the demonstration of (001)
oriented SrTiO3 grown atop a SrO/HOPG stack.",1511.06496v1
2016-01-08,On the nature of change in Ni oxidation state in BaTiO3-SrTiO3 system,"XAFS studies of Ni-doped Ba$_{1-x}$Sr$_x$TiO$_3$ solid solution reveal that
the Ni oxidation state changes from 4 in SrTiO$_3$ to 2.5 in BaTiO$_3$ when
varying $x$. This change is accompanied by a noticeable change in the
interatomic Ni-O distances in the first shell. The first-principles
calculations show that nickel creates an impurity band in the forbidden band
gap of BaTiO$_3$ and SrTiO$_3$, which explains the appearance of intense
absorption of Ni-doped samples in the visible region. The analysis of the
electronic structure of doped crystals and calculations of the oxygen vacancy
formation energy in them show that different oxidation states of Ni in
SrTiO$_3$ and BaTiO$_3$ can be explained by different formation energies of the
oxygen vacancies in these compounds.",1601.01961v2
2016-02-17,Atomically flat reconstructed rutile TiO2(001) surfaces for oxide film growth,"The availability of low-index rutile TiO2 single crystal substrates with
atomically flat surfaces is essential for enabling epitaxial growth of rutile
transition metal oxide films. The high surface energy of the rutile (001)
surface often leads to surface faceting, which precludes the sputter and
annealing treatment commonly used for the preparation of clean and atomically
flat TiO2(110) substrate surfaces. In this work, we reveal that stable and
atomically flat rutile TiO2(001) surfaces can be prepared with an atomically
ordered reconstructed surface already during a furnace annealing treatment in
air. We tentatively ascribe this result to the decrease in surface energy
associated with the surface reconstruction, which removes the driving force for
faceting. Despite the narrow temperature window where this morphology can
initially be formed, we demonstrate that it persists in homoepitaxial growth of
TiO2(001) thin films. The stabilization of surface reconstructions that prevent
faceting of high-surface-energy crystal faces may offer a promising avenue
towards the realization of a wider range of high quality epitaxial transition
metal oxide heterostructures.",1602.05518v1
2016-04-19,Tuning the work function in transition metal oxides and their heterostructures,"The development of novel functional materials in experimental labs combined
with computer-based compound simulation brings the vision of materials design
on a microscopic scale continuously closer to reality. For many applications
interface and surface phenomena rather than bulk properties are key. One of the
most fundamental qualities of a material-vacuum interface is the energy
required to transfer an electron across this boundary, i.e. the work function.
It is a crucial parameter for numerous applications, including organic
electronics, field electron emitters, and thermionic energy converters. Being
generally very resistant to degradation at high temperatures, transition metal
oxides present a promising materials class for such devices. We have performed
a systematic study for perovskite oxides that provides reference values and,
equally important, reports on materials trends and the tunability of work
functions. Our results identify and classify dependencies of the work function
on several parameters including specific surface termination, surface
reconstructions, oxygen vacancies, and heterostructuring.",1604.05615v1
2016-06-07,Enhancing Perovskite Electrocatalysis through Strain Tuning of the Oxygen Deficiency,"Oxygen vacancies in transition metal oxides facilitate catalysis critical for
energy storage and generation. However, it has proven elusive to promote
vacancies at the lower temperatures required for operation in devices such as
metal-air batteries and portable fuel cells. Here, we use thin films of the
perovskite-based strontium cobaltite (SrCoOx) to show that epitaxial strain is
a powerful tool towards manipulating the oxygen content under conditions
consistent with the oxygen evolution reaction, yielding increasingly oxygen
deficient states in an environment where the cobaltite would normally be fully
oxidized. The additional oxygen vacancies created through tensile strain
enhance the cobaltite catalytic activity towards this important reaction by
over an order of magnitude, equaling that of precious metal catalysts,
including IrO2. Our findings demonstrate that strain in these oxides can
dictate oxygen stoichiometry independent of ambient conditions, allowing
unprecedented control over oxygen vacancies essential in catalysis near room
temperature.",1606.02256v1
2016-06-10,High throughput thermal conductivity of high temperature solid phases: The case of oxide and fluoride perovskites,"Using finite-temperature phonon calculations and machine-learning methods, we
calculate the mechanical stability of about 400 semiconducting oxides and
fluorides with cubic perovskite structures at 0 K, 300 K and 1000 K. We find 92
mechanically stable compounds at high temperatures -- including 36 not
mentioned in the literature so far -- for which we calculate the thermal
conductivity. We demonstrate that the thermal conductivity is generally smaller
in fluorides than in oxides, largely due to a lower ionic charge, and describe
simple structural descriptors that are correlated with its magnitude.
Furthermore, we show that the thermal conductivities of most cubic perovskites
decrease more slowly than the usual $T^{-1}$ behavior. Within this set, we also
screen for materials exhibiting negative thermal expansion. Finally, we
describe a strategy to accelerate the discovery of mechanically stable
compounds at high temperatures.",1606.03279v1
2016-06-19,Controlling hybrid nonlinearities in transparent conducting oxides via two-colour excitation,"Nanophotonics and metamaterials have revolutionised the way we think about
optical space (epsilon, mu), enabling us to engineer the refractive index
almost at will, to confine light to the smallest of the volumes, and to
manipulate optical signals with extremely small footprints and energy
requirements. Significant efforts are now devoted to finding suitable materials
and strategies for the dynamic control of the optical properties. Transparent
conductive oxides exhibit large ultrafast nonlinearities under both interband
and intraband excitations. Here, we show that combining these two effects in
aluminium-doped zinc oxide via a two colour laser field discloses new material
functionalities. Owing to the independence of the two nonlinearities the
ultrafast temporal dynamics of the material permittivity can be designed by
acting on the amplitude and delay of the two fields. We demonstrate the
potential applications of this novel degree of freedom by dynamically
addressing the modulation bandwidth and optical spectral tuning of a probe
optical pulse.",1606.05824v3
2016-06-23,Discovery of the Interstellar Chiral Molecule Propylene Oxide (CH$_3$CHCH$_2$O),"Life on Earth relies on chiral molecules, that is, species not superimposable
on their mirror images. This manifests itself in the selection of a single
molecular handedness, or homochirality, across the biosphere. We present the
astronomical detection of a chiral molecule, propylene oxide (CH$_3$CHCH$_2$O),
in absorption toward the Galactic Center. Propylene oxide is detected in the
gas phase in a cold, extended molecular shell around the embedded, massive
protostellar clusters in the Sagittarius B2 star-forming region. This material
is representative of the earliest stage of solar system evolution in which a
chiral molecule has been found.",1606.07483v1
2016-07-19,Graphene and MoS2 interacting with water: a comparison by ab initio calculations,"Although very similar in many technological applications, graphene and MoS2
bear significant differences if exposed to humid environments. As an example,
lubrication properties of graphene are reported to improve while those of MoS2
to deteriorate: it is unclear whether this is due to oxidation from disulfide
to oxide or to water adsorption on the sliding surface. By means of ab initio
calculations we show here that these two layered materials have similar
adsorption energies for water on the basal planes. They both tend to avoid
water intercalation between their layers and to display only mild reactivity of
defects located on the basal plane. It is along the edges where marked
differences arise: graphene edges are more reactive at the point that they
immediately prompt water splitting. MoS2 edges are more stable and consequently
water adsorption is much less favoured than in graphene. We also show that
water-driven oxidation of MoS2 layers is unfavoured with respect to adsorption.",1607.05607v1
2016-09-02,Controlling effective dimensionality and competition between spin liquid and chiral orders by new multiorbital effects in $S=\frac{1}{2}$ pyrochlore oxides,"In frustrated systems, some or many states are competed due to frustration of
exchange interactions, and this competition often results in exotic states,
such as spin liquid and chiral orders. We consider a pyrochlore oxide, a
three-dimensional frustrated system, and study its $S=\frac{1}{2}$ effective
model, consisting of the Heisenberg-type and Dzyaloshinsky-Moriya-type
superexchange interactions between the nearest-neighbor transition-metal ions.
We show that by using new multiorbital effects of the $t_{2g}$ orbitals on
coefficients of those interactions, we can change the effective dimensionality
from three-dimensional to two-dimensional, and control the competition between
chiral orders and spin liquid. We also show that the new multiorbital effects
are vital to stabilize three-in-one-out chiral order, distorted
four-in-four-out chiral order, and distorted three-in-one-out chiral order, and
can be used to hold macroscopic degeneracy, resulting in the spin liquid, even
with the finite Dzyaloshinsky-Moriya interactions. Those results open up new
multiorbital physics in spin systems, and make the essential step for the
realistic mechanism for the spin liquid in pyrochlore oxides.",1609.00445v2
2016-09-15,Accurate X-Ray Absorption Predictions for Transition Metal Oxides: An Advanced Self-Consistent-Field Approach Inspired by Many-Body Perturbation Theory,"Constrained-occupancy self-consistent-field ($\Delta$SCF) methods and
many-body perturbation theories (MBPT) are two strategies for obtaining
electronic excitations from first-principles. Using the two distinct
approaches, we study the O $1s$ core excitations that have become increasingly
important for characterizing transition metal oxides and developing theory of
strong correlations. Interestingly, we find that the $\Delta$SCF approach, in
its current single-particle form, systematically underestimates the pre-edge
intensity for chosen oxides, despite its success in weakly correlated systems.
By contrast, the Bethe-Salpeter equation within MBPT predicts much better
lineshapes. This inspires us to reexamine the many-electron dynamics of X-ray
excitations. We find that the single-particle $\Delta$SCF approach can be
rectified by explicitly calculating many-body transition amplitudes, producing
X-ray spectra in excellent agreement with experiments. Our study paves the way
to accurately predict X-ray near-edge spectral fingerprints for physics and
materials science beyond the Bethe-Salpether equation.",1609.04872v2
2016-09-26,Effects of processing on the stability of molybdenum oxide ultra-thin films,"The effects of wet chemical processing conventionally employed in device
fabrication standards are systematically studied on molybdenum oxide (MoOx)
ultra-thin films. We have combined x-ray photoelectron spectroscopy (XPS),
angle resolved XPS and x-ray reflectivity techniques to provide deep insights
into the changes in composition, structure and electronic states upon treatment
of films with different initial stoichiometry prepared by reactive sputtering.
Our results show significant reduction effects associated with the development
of gap states in MoOx, as well as changes in the composition, density and
structure of the films, systematically correlated with the initial oxidation
state of Mo.",1609.07993v1
2016-10-17,Polydopamine-Coated TiO2 Nanotubes for Selective Photocatalytic Oxidation of Benzyl Alcohol to Benzaldehyde under Visible Light,"TiO2 nanotube arrays grown by anodization were coated with thin layers of
polydopamine as visible light sensitizer. The PDA-coated TiO2 scaffolds were
used as photocatalyst for selective oxidation of benzyl alcohol under
monochromatic irradiation at 473 nm. Benzaldehyde was selectively formed and no
by-products could be detected. A maximized reaction yield was obtained in
O2-saturated acetonitrile. A mechanism is proposed that implies firstly the
charge carrier generation in polydopamine as a consequence of visible light
absorption. Secondly, photo-promoted electrons are injected in TiO2 conduction
band, and subsequently transferred to dissolved O2 to form oxygen radical
anions. These radicals react with benzyl alcohol and lead to its selective
dehydrogenation oxidation towards benzaldehyde.",1610.05154v1
2016-10-20,Stable Co-Catalyst-Free Photocatalytic H2 Evolution From Oxidized Titanium Nitride Nanopowders,"In the present work, a simple strategy is used to thermally oxidize TiN
nanopowder (ca. 20 nm) to an anatase phase of a TiO2:Ti3+:N compound. In
contrast to the rutile phase of such a compound this photocatalyst provides
photocatalytic activity for hydrogen evolution under AM1.5 conditions - this
without the use of any noble metal co-catalyst. Moreover the photocatalyst is
active and stable over extended periods of time (tested for 4 months).
Importantly, to achieve successful conversion to the active anatase polymorph,
sufficiently small starting particles of TiN are needed. The key factor for
catalysis is the stabilization of the co-catalytically active Ti3+ species
against oxidation by nitrogen present in the starting material.",1610.06335v1
2016-10-20,Self-ordered Mo-oxide Nanotube Arrays as Precursor for Aligned MoOx/MoS2 Core-Shell Nanotubular Structures with a High Density of Reactive Sites,"In the present work we demonstrate the self-organized formation of anodic
Mo-oxide nanotube arrays grown on a Mo sheet under suitable electrochemical
conditions in glycerol/NH4F electrolytes. The resulting amorphous tubes can be
crystallized by annealing to MoO2 or MoO3. The tube walls then can be further
sulfurized fully or partially to Mo-sulfide to form well-ordered arrays of
vertically aligned MoOx/MoS2 nanotubes. Under optimized conditions, defined
MoS2 sheets form on the oxide walls in a layer by layer low angle zig-zag
arrangement that provide a high density of reactive stacking faults. These
core-shell nanotube arrays, consisting of tubes with a conductive suboxide core
and a functional high defect density MoS2 coating, are highly promising for
applications such as electrocatalysis (hydrogen evolution) or ion insertion
devices.",1610.06350v1
2016-10-21,Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy,"Advancements in nanoscale engineering of oxide interfaces and
heterostructures have led to discoveries of emergent phenomena and new
artificial materials. Combining the strengths of reactive molecular-beam
epitaxy and pulsed-laser deposition, we show here, with examples of
Sr1+xTi1-xO3+delta, Ruddlesden-Popper phase Lan+1NinO3n+1 (n = 4), and
LaAl1+yO3(1+0.5y)/SrTiO3 interfaces, that atomic layer-by-layer laser
molecular-beam epitaxy (ALL-Laser MBE) significantly advances the state of the
art in constructing oxide materials with atomic layer precision and control
over stoichiometry. With ALL-Laser MBE we have produced conducting
LaAlO3/SrTiO3 interfaces at high oxygen pressures that show no evidence of
oxygen vacancies, a capability not accessible by existing techniques. The
carrier density of the interfacial two-dimensional electron gas thus obtained
agrees quantitatively with the electronic reconstruction mechanism.",1610.06885v1
2016-10-26,Hydrogen release at metal-oxide interfaces: A first principle study of hydrogenated Al/SiO$_2$ interfaces,"The Anode Hydrogen Release (AHR) mechanism at interfaces is responsible for
the generation of defects, that traps charge carriers and can induce dielectric
breakdown in Metal-Oxide-Semiconductor Field Effect Transistors. The AHR has
been extensively studied at Si/SiO$_2$ interfaces but its characteristics at
metal-silica interfaces remain unclear. In this study, we performed Density
Functional Theory (DFT) calculations to study the hydrogen release mechanism at
the typical Al/SiO$_2$ metal-oxide interface. We found that interstitial
hydrogen atoms can break interfacial Al-Si bonds, passivating a Si $sp^3$
orbital. Interstitial hydrogen atoms can also break interfacial Al-O bonds, or
be adsorbed at the interface on aluminum, forming stable Al-H-Al bridges. We
showed that hydrogenated O-H, Si-H and Al-H bonds at the Al/SiO$_2$ interfaces
are polarized. The resulting bond dipole weakens the O-H and Si-H bonds, but
strengthens the Al-H bond under the application of a positive bias at the metal
gate. Our calculations indicate that Al-H bonds and O-H bonds are more
important than Si-H bonds for the hydrogen release process.",1610.08365v1
2016-10-28,Hard X-rays as pump and probe of atomic motion in oxide glasses,"Nowadays powerful X-ray sources like synchrotrons and free-electron lasers
are considered as ultimate tools for probing microscopic properties in
materials. However, the correct interpretation of such experiments requires a
good understanding on how the beam affects the properties of the sample,
knowledge that is currently lacking for intense X-rays. Here we use X-ray
photon correlation spectroscopy to probe static and dynamic properties of oxide
and metallic glasses. We find that although the structure does not depend on
the flux, strong fluxes do induce a non-trivial microscopic motion in oxide
glasses, whereas no such dependence is found for metallic glasses. These
results show that high fluxes can alter dynamical properties in hard materials,
an effect that needs to be considered in the analysis of X-ray data but which
also gives novel possibilities to study materials properties since the beam can
not only be used to probe the dynamics but also to pump it.",1610.09236v1
2017-03-16,"Mitochondrial oxidative phosphorylation: Debunking the concepts of electron transport chain, proton pumps, chemiosmosis and rotary ATP synthesis","Herein (the first part of my work), I debunk the long-standing hypotheses
that explain mitochondrial oxidative phosphorylation. Simple calculations point
out that mitochondria are highly proton-deficient microcosms and therefore,
elaborate proton pump machinery are not tenable. Further, other elements like
the elaborate electron transport chain, chemiosmosis, rotary ATP synthesis,
etc. are also critically evaluated to point out that such complicated systems
are non-viable. The communication necessitates a new explanatory paradigm for
cellular respiration. In the second part of my work, I have put forward a
viable alternative explanatory paradigm for mitochondrial oxidative
phosphorylation.",1703.05826v1
2017-08-18,First principles study of oxidation of Si segregated α-Ti(0001) surfaces,"The oxidation of {\alpha}-Ti(0001) surface was studied using density
functional theory. In order to enhance the oxidation resistance, we substituted
Ti atoms with Si atoms in Ti(0001) surface. We observe that Si prefers to
segregate at the surface layer of Ti(0001) compared to other sub-surface
layers. The Si solubility on the Ti(0001) surface was estimated to be around 75
at.%. While Si segregation was found to reduce the binding between the oxygen
atom and the Ti(0001) surface, the barrier for oxygen to diffuse into the slab
increases. The dissociation of the oxygen molecule on the clean and Si
segregated surfaces of Ti was found to be barrier-less. Overall, the Si
segregation on the Ti(0001) surface was found to hinder the dissolution of
oxygen in Ti.",1708.05481v1
2018-04-10,Phosphorus oxide gate dielectric for black phosphorus field effect transistors,"The environmental stability of the layered semiconductor black phosphorus
(bP) remains a challenge. Passivation of the bP surface with phosphorus oxide,
POx, grown by a reactive ion etch with oxygen plasma is known to improve
photoluminescence efficiency of exfoliated bP flakes. We apply phosphorus oxide
passivation in the fabrication of bP field effect transistors using a gate
stack consisting of a POx layer grown by reactive ion etching followed by
atomic layer deposition of Al2O3. We observe room temperature top-gate
mobilities of 115 cm2/Vs in ambient conditions, which we attribute to the low
defect density of the bP/POx interface.",1804.03639v1
2018-04-13,Reaction of O2 with Subsurface Oxygen Vacancies on TiO2 Anatase (101),"Oxygen (O2) adsorbed on metal oxides is important in catalytic oxidation
reactions, chemical sensing, and photocatalysis. Strong adsorption requires
transfer of negative charge from oxygen vacancies (VOs) or dopants, for
example. With scanning tunneling microscopy, we observed, transformed, and, in
conjunction with theory, identified the nature of O2 molecules on the (101)
surface of anatase (titanium oxide, TiO2) doped with niobium. VOs reside
exclusively in the bulk, but we pull them to the surface with a strongly
negatively charged scanning tunneling microscope tip. O2 adsorbed as superoxo
(O2)- at fivefold-coordinated Ti sites was transformed to peroxo (O2)2- and,
via reaction with a VO, placed into an anion surface lattice site as an (O2)O
species. This so-called bridging dimer also formed when O2 directly reacted
with VOs at or below the surface.",1804.04926v1
2018-04-16,Adsorption of water at the SrO surface of ruthenates,"Although perovskite oxides hold promise in applications ranging from solid
oxide fuel cells to catalysts, their surface chemistry is poorly understood at
the molecular level. Here we follow the formation of the first monolayer of
water at the (001) surfaces of Sr$_{n+1}$Ru$_n$O$_{3n+1}$ ($n$ = 1, 2) using
low-temperature scanning tunnelling microscopy, X-ray photoelectron
spectroscopy, and density functional theory. These layered perovskites cleave
between neighbouring SrO planes, yielding almost ideal, rocksalt-like surfaces.
An adsorbed monomer dissociates and forms a pair of hydroxide ions. The OH
stemming from the original molecule stays trapped at Sr-Sr bridge positions,
circling the surface OH with a measured activation energy of 187 $\pm$ 10 meV.
At higher coverage, dimers of dissociated water assemble into one-dimensional
chains and form a percolating network where water adsorbs molecularly in the
gaps. Our work shows the limitations of applying surface chemistry concepts
derived for binary rocksalt oxides to perovskites.",1804.05612v1
2018-10-31,Probing itinerant antiferromagnetism with $d$-wave Andreev reflection spectroscopy,"To study how Andreev reflection (AR) is affected by itinerant
antiferromagnetism, we perform $d$-wave AR spectroscopy with superconducting
YBa$_2$Cu$_3$O$_{7-\delta}$ on TiAu and on variously-oxidized Nb (NbO$_x$)
samples. X-ray photoelectron spectroscopy is also used on the latter to measure
their surface oxide composition. Below the N\'eel temperatures ($T_N$) of both
TiAu and NbO$_x$, the conductance spectra show a dip-like structure instead of
a zero-bias peak within the superconducting energy gap; for NbO$_x$,
higher-oxidized samples show a stronger spectral dip at zero bias. These
observations indicate that itinerant antiferromagnetic order suppresses the AR
process. Interestingly, the spectral dip persists above $T_N$ for both TiAu and
NbO$_x$, implying that spin fluctuations can also suppress AR. Our results
suggest that $d$-wave AR spectroscopy may be used to probe the degree of spin
ordering in itinerant antiferromagnets.",1811.00160v1
2018-11-07,Inverted orbital polarization in strained correlated oxide films,"Manipulating the orbital occupation of valence electrons via epitaxial strain
in an effort to induce new functional properties requires considerations of how
changes in the local bonding environment affect the band structure at the Fermi
level. Using synchrotron radiation to measure the x-ray linear dichroism of
epitaxially strained films of the correlated oxide CaFeO3, we demonstrate that
the orbital polarization of the Fe valence electrons is opposite from
conventional understanding. Although the energetic ordering of the Fe 3d
orbitals is confirmed by multiplet ligand field theory analysis to be
consistent with previously reported strain-induced behavior, we find that the
nominally higher energy orbital is more populated than the lower. We ascribe
this inverted orbital polarization to an anisotropic bandwidth response to
strain in a compound with nearly filled bands. These findings provide an
important counterexample to the traditional understanding of strain-induced
orbital polarization and reveal a new method to engineer otherwise unachievable
orbital occupations in correlated oxides.",1811.03075v1
2018-11-14,Direct observation of state-filling at hybrid tin oxide/organic interfaces,"Electroluminescence (EL) spectra from hybrid charge transfer excitons at
metal oxide/organic type-II heterojunctions exhibit pronounced bias-induced
spectral shifts. The reasons for this phenomenon have been discussed
controversially and arguments for both electric field-induced effects as well
as filling of trap states at the oxide surface have been put forward. Here, we
combine the results from EL and photovoltaic measurements to eliminate the
disguising effects of the series resistance. For SnOx combined with the
conjugated polymer MeLPPP, we find a one-to-one correspondence between the
blueshift of the EL peak and the increase of the quasi-Fermi level splitting at
the hybrid heterojunction, which we unambiguously assign to state filling. Our
data is resembled best by a model considering the combination an exponential
density of states with a doped semiconductor.",1811.05880v2
2018-11-30,Nanonionics and interfaces for energy and information technologies,"There is a growing interest in the development of functional metal oxides
with mixed ionic electronic conduction for their application in different
strategic fields. In particular, ionic transport-related phenomena are of
primary importance in energy transformation and storage devices, such as solid
oxides fuel cells (SOFC) or batteries. Traditionally, the main issue that
hindered a wide spread of solid state electrochemical devices is the slow ionic
conduction and the reduced number of families of materials with pure ionic
conductivity able to play the role of the electrolyte. This is due to the low
mobility of the ionic charge carriers and their mechanical and coulombic
interactions with their host crystal structures. For relatively big and charged
ions, e.g. O2- or Na+, the low ionic conductivity imposes operating at high
temperatures, which is incompatible with some applications such as portable
electronics.",1811.12744v1
2019-04-30,Ultrathin complex oxide nanomechanical resonators,"Complex oxide thin films and heterostructures exhibit a profusion of exotic
phenomena, often resulting from the intricate interplay between film and
substrate. Recently it has become possible to isolate epitaxially grown
single-crystalline layers of these materials, enabling the study of their
properties in the absence of interface effects. In this work, we create
ultrathin membranes of strongly correlated materials and demonstrate top-down
fabrication of nanomechanical resonators made out of \ce{SrTiO3} and
\ce{SrRuO3}. Using laser interferometry, we successfully actuate and measure
the motion of the nanodrum resonators. By measuring their temperature-dependent
mechanical response, we observe signatures of structural phase transitions in
\ce{SrTiO3}, which affect the strain and mechanical dissipation in the
resonators. This approach can be extended to investigate phase transitions in a
wide range of materials. Our study demonstrates the feasibility of integrating
ultrathin complex oxide membranes for realizing nanoelectromechanical systems
on arbitrary substrates.",1905.00056v1
2019-05-02,The pH Dependence of Ultrafast Charge Dynamics in Graphene Oxide Dispersions,"The pH dependence of emission from graphene oxide is believed to be due to
the protonation of surface functional groups. In this study we use transient
absorption spectroscopy to study the sub-picosecond charge dynamics in graphene
oxide over a range of pH values, observing dynamics consistent with an excited
state protonation step for pH < 9.3. The timescale of this process is ~ 1.5 ps,
and a corresponding change in recombination dynamics follows. A broad
photo-induced absorption peak centred at 530 nm associated with excited state
protonation is also observed.",1905.00859v1
2019-05-08,Synergetic Behavior in 2D Layered Material/Complex Oxide Heterostructures,"The marriage between a two-dimensional layered material (2DLM) and a complex
transition metal oxide (TMO) results in a variety of physical and chemical
phenomena that would not have been achieved in either material alone.
Interesting recent discoveries in systems such as graphene/SrTiO3,
graphene/LaAlO3/SrTiO3, graphene/ferroelectric oxide, MoS2/SrTiO3, and
FeSe/SrTiO3 heterostructures include voltage scaling in field-effect
transistors, charge state coupling across an interface, quantum conductance
probing of the electrochemical activity, novel memory functions based on charge
traps, and greatly enhanced superconductivity. In this progress report, we
review various properties and functionalities appearing in numerous different
2DLM/TMO heterostructure systems. The results imply that the multidimensional
heterostructure approach based on the disparate material systems leads to an
entirely new platform for the study of condensed matter physics and materials
science. The heterostructures are also highly relevant technologically, as each
constituent material is a promising candidate for next-generation
opto-electronic devices.",1905.02930v1
2020-07-02,Effects of Alloying Elements on Surface Oxides of Hot-Dip Galvanized Press Hardened Steel,"Effects of steel alloying elements on the formation of the surface oxide
layer of hot-dip galvanized press hardened steel after austenitization
annealing were examined with various advanced microscopy and spectroscopy
techniques. The main oxides on top of the original thin Al2O3 layer,
originating from the primary galvanizing process, are identified as ZnO and
(Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, a non-uniform,
several nanometer thick Cr enriched, additional film was found at the Al2O3
layer. At a sufficiently high concentration, Cr can act as a substitute for Al
during annealing, strengthening and regenerating the original Al2O3 layer with
Cr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable
distinction between ZnO and Zn(OH)2.",2007.01050v1
2020-07-15,Atomic origin for hydrogenation promoted bulk oxygen vacancies removal in vanadium dioxide,"Oxygen vacancies (VO), a common type of point defects in metal oxides
materials, play important roles on the physical and chemical properties. To
obtain stoichiometric oxide crystal, the pre-existing VO is always removed via
careful post-annealing treatment at high temperature in air or oxygen
atmosphere. However, the annealing conditions is difficult to control and the
removal of VO in bulk phase is restrained due to high energy barrier of VO
migration. Here, we selected VO2 crystal film as the model system and developed
an alternative annealing treatment aided by controllable hydrogen doping, which
can realizes effective removal of VO defects in VO2-{\delta} crystal at lower
temperature. This finding is attributed to the hydrogenation accelerated oxygen
vacancies recovery in VO2-{\delta} crystal. Theoretical calculations revealed
that the H-doping induced electrons are prone to accumulate around the oxygen
defects in VO2-{\delta} film, which facilitates the diffusion of VO and thus
makes it easier to be removed. The methodology is expected to be applied to
other metal oxides for oxygen-related point defects control.",2007.07505v1
2020-07-27,The effect of manganese and silicon additions on the corrosion resistance of a polycrystalline nickel-based superalloy,"The service lives of nickel superalloys are often limited by environmental
degradation. The present study compares oxidation, sulfidation and hot
corrosion at 750C of three variants of a polycrystalline superalloy: a baseline
alloy, a variant containing 1wt% Mn and one containing 0.5wt% Si. Mn reduced
the oxidation rate without changing the scale morphology. The MnCr2O4 scale
formed proved more protective against sulfidation and hot corrosion, but
internal sulfides extended the damage depth. Si modified the oxide morphology
to a continuous Cr2O3-Al2O3 dual layer. This provided improved protection,
reducing the sulfidation depth by 2/3 and the hot corrosion depth by 1/2.",2007.13416v1
2010-05-04,Sub-monolayer nucleation and growth of complex oxide heterostructures at high supersaturation and rapid flux modulation,"We report on the non-trivial nanoscale kinetics of the deposition of novel
complex oxide heterostructures composed of a unit-cell thick correlated metal
LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good
crystallinity and surface morphology maintained over the large number of
layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To
elucidate the physics behind the growth, the temperature of the substrate and
the deposition rate were varied over a wide range and the results were treated
in the framework of a two-layer model. These results are of fundamental
importance for synthesis of new phases of complex oxide heterostructures.",1005.0570v1
2010-05-08,Femtosecond Photoexcited Carrier Dynamics in Reduced Graphene Oxide Suspensions and Films,"We report ultrafast response of femtosecond photoexcited carriers in single
layer reduced graphene oxide flakes suspended in water as well as few layer
thick film deposited on indium tin oxide coated glass plate using pump-probe
differential transmission spectroscopy at 790 nm. The carrier relaxation
dynamics has three components: ~200 fs, 1 to 2 ps, and ~25 ps, all of them
independent of pump fluence. It is seen that the second component (1 to 2 ps)
assigned to the lifetime of hot optical phonons is larger for graphene in
suspensions whereas other two time constants are the same for both the
suspension and the film. The value of third order nonlinear susceptibility
estimated from the pump-probe experiments is compared with that obtained from
the open aperture Z-scan results for the suspension.",1005.1322v2
2013-08-04,Shungite as loosely packed fractal nets of graphene-based quantum dots,"The current paper presents the first attempt to recreate the origin of
shungite carbon at microscopic level basing on knowledge accumulated by
graphene science. The main idea of our approach is that different efficacy of
chemical transformation of primarily generated graphene flakes (aromatic
lamellae in geological literature), subjected to oxidation/reduction reactions
in aqueous environment, lays the foundation of the difference in graphite and
shungite derivation under natural conditions. Low-efficient reactions in the
case of graphite do not prevent from the formation of large graphite layers
while high-efficient oxidation/reduction transforms the initial graphene flakes
into those of reduced graphene oxide of ~1nm in size. Multistage aggregation of
these basic structural units, attributed to graphene quantum dots of shungite,
leads to the fractal structure of shungite carbon thus exhibiting it as a new
allotrope of natural carbon. The suggested microscopic view has finds a
reliable confirmation when analyzing the available empirical data.",1308.0794v1
2013-08-22,Symmetry-Tunable Environment in Functional Ferroic Heterostructures,"We demonstrate a concept for post-growth symmetry control in oxide
heterostructures. A functional oxide is sandwiched between two ferroelectric
layers and inversion symmetry at the position of the oxide constituent is
reversibly switched on or off by layer-selective electric-field poling. The
functionality of this process is monitored by optical second harmonic
generation. The generalization of our approach to other materials and
symmetries is considered. We thus establish ferroic trilayer structures as
device components in which symmetry-driven charge-, spin-, and strain-related
functionalities can be activated and deactivated at will.",1308.4796v1
2013-08-29,Niobium-based sputtered thin films for Corrosion Protection of proton-irradiated liquid water targets for [18F] production,"Chemically inert Coatings on Havar entrance foils of the targets for [18F]
production via proton irradiation of enriched water at pressurized conditions
are needed to decrease the amount of ionic contaminants released from Havar. In
order to find the most effective protective coatings, the Nb-based coating
microstructure and barrier properties have been correlated with deposition
parameters as: substrate temperature, applied bias, deposition rate and
sputtering gas pressure. Aluminated quartz used as a substrate allowed us to
verify the protection efficiency of the desirable coatings as diffusion
barriers. Two modeling corrosion tests based on the extreme susceptibility of
aluminum to liquid gallium and acid corrosion were applied. Pure Niobium
coatings have been found less effective barriers than Niobium-titanium
coatings. But Niobium oxide films, according to the corrosion tests performed,
showed superior barrier properties. Therefore Multi-layered Niobium-Niobium
oxide films have been suggested, since they combine the high thermal
conductivity of Niobium with the good barrier properties of Niobium oxide.",1308.6605v1
2014-03-14,Holographic patterning of graphene-oxide films by light-driven reduction,"We report on the patterning and reduction of graphene-oxide films by
holographic lithography. Light reduction can be used to engineer low-cost
graphene-based devices by performing a local conversion of insulating oxide
into the conductive graphene. In this work, computer generated holograms have
been exploited to realize complex graphene patterns in a single shot,
differently from serial laser writing or mask-based photolithographic
processes. The technique has been further improved by achieving speckle noise
reduction: submicron and diffraction-limited features have been obtained. In
addition we have also demonstrated that the gray-scale lithography capability
can be used to obtain different reduction levels in a single exposure.",1403.3504v1
2016-11-09,Interfacial interaction in monolayer transition metal dichalcogenides (MX2)/metal oxide heterostructures and its effects on electronic and optical properties: The case of MX2/CeO2,"Two-dimensional transition metal dichalcogenides (MX2)/metal oxide
heterostructures have shown unique physical properties, making them promising
materials for various applications ranging from photocatalysis to solar energy
conversion. Understanding the interfacial interactions is highly desirable for
designing these heterostructures having excellent performance. Here we
systematically study the interfacial interaction in monolayer MX2 (M=Mo, W;
X=S, Se)/CeO2 heterostructures and its effects on electronic and optical
properties by density functional theory. It is found that the interfacial
interaction in the MX2/CeO2 depends predominantly on the chalcogen (X) element.
Particularly, the band gap variation and important electronic states at
conduction band minimum or valence band maximum of the heterostructures are
determined by the strength of interfacial interaction. The MX2/CeO2
heterostructures with the same chalcogen (X) element have similar absorption
spectra from ultraviolet to near-infrared regions. These results suggest that
the chalcogen (X) element is a key factor in tuning the properties of MX2/metal
oxide heterostructures.",1611.02799v1
2016-11-10,First principle thermodynamic study of oxygen vacancy at metal/oxide interface,"The oxygen vacancy is a crucial intrinsic defect in metal-ultrathin oxide
semiconductor heterostructures, and its formation at an interface is of great
importance in determining the device performance and degradation. This paper
presents an ab initio thermodynamic study of oxygen vacancies at metal/oxide
interfaces. Electronic energies and entropies are calculated for defective
interface systems, as a function of interface-vacancy distance. The study
indicates that oxygen vacancies near the interface modify its bonding
structure, and significantly change the thermodynamic properties of the system
(i.e., electronic energy and entropy) compared to bulk-like oxygen vacancies.
We illustrate that different factors, including the vacancy location dependence
on the energy and entropy, the temperature dependence on the entropy, and the
temperature and partial pressure dependence on the oxygen chemical potential,
are all important in determining the Gibbs free energy of formation of oxygen
vacancy.",1611.03411v1
2016-11-24,In-situ Atom Probe Deintercalation of Lithium-Manganese-Oxide,"Atom probe tomography is routinely used for the characterisation of materials
microstructures usually assuming that the microstructure is unaltered by the
analysis. When analysing ionic conductors, however, gradients in the chemical
potential and the electric field penetrating dielectric atom probe specimens
can cause significant ionic mobility. While ionic mobility is undesired when
aiming for materials characterisation it offers a strategy to manipulate
materials directly in-situ in the atom probe. Here, we present experimental
results on the analysis of the ionic conductor Lithium-Manganese-Oxide with
different atom probe techniques. We demonstrate that at a temperature of 30K
characterisation of the materials microstructure is possible without measurable
Li mobility. Contrary, we show that at 298K the material can be deintercalated
in-situ in the atom probe without changing the Manganese-Oxide host structure.
Combining in-situ atom probe deintercalation and subsequent conventional
characterisation we demonstrate a new methodological approach to study ionic
conductors even in early stages of deintercalation.",1611.08114v1
2016-11-27,Vacancy Relaxation in Cuprous Oxide (Cu$_{2-x}$O$_{1-y}$),"Phonons are produced when an excited vacancy in cuprous oxide (Cu$_2$O)
relaxes. Time resolved luminescence was used to find the excited copper vacancy
(acceptor) and oxygen vacancy (donor) trap levels and lifetimes. It was also
used to determine the typical energy and number of phonons in the phonon pulses
emitted by vacancies. The vacancy properties of cuprous oxide are controlled by
several synthesis parameters and by the temperature. We directly demonstrate
the absorption of light by oxygen vacancies with transient absorption. Copper
and oxygen vacancies behave differently, in part because the two kinds of traps
capture carriers from different states. For example, the copper vacancy
luminescence lifetime is around 25 times greater at low temperature. However,
both kinds of vacancy luminescence are consistent with a Poissonian multiple
phonon emission model.",1611.08793v2
2016-11-30,Band bending at the interface in Polyethylene-MgO nanocomposite dielectric,"Polymer nanocomposite dielectrics are promising materials for electrical
insulation in high voltage applications. However, the physics behind their
performance is not yet fully understood. We use density functional theory to
investigate electronic properties of the interfacial area in magnesium
oxide-polyethylene nanocomposite. Our results demonstrate polyethylene
conduction band matching with conduction bands of different surfaces of
magnesium oxide. Such band bending results in long range potential wells of up
to 2.6 eV deep. Furthermore, the fundamental influence of silicon treatment on
magnesium oxide surface properties is assessed. We report a reduction of the
surface-induced states at the silicon-treated interface. The simulations
provide information used to propose a new model for charge trapping in
nanocomposite dielectrics.",1611.10251v1
2017-01-03,Rapid laser-induced photochemical conversion of sol-gel precursors to In2O3 layers and their application in thin-film transistors,"We report the development of indium oxide (In2O3) transistors via a single
step laser-induced photochemical conversion process of a sol-gel metal oxide
precursor. Through careful optimization of the laser annealing conditions we
demonstrated successful conversion of the precursor to In2O3 and its subsequent
implementation in n-channel transistors with electron mobility up to 13 cm2/Vs.
Importantly, the process does not require thermal annealing making it
compatible with temperature sensitive materials such as plastic. On the other
hand, the spatial conversion/densification of the sol-gel layer eliminates
additional process steps associated with semiconductor patterning and hence
significantly reduces fabrication complexity and cost. Our work demonstrates
unambiguously that laser-induced photochemical conversion of sol-gel metal
oxide precursors can be rapid and compatible with large-area electronics
manufacturing.",1701.00859v1
2017-01-07,"Spatially uniform resistance switching of low current, high endurance titanium-niobium-oxide memristors","We analyzed micrometer-scale titanium-niobium-oxide prototype memristors,
which exhibited low write-power (<3 {\mu}W) and energy (<200 fJ/bit/{\mu}m2),
low read-power (~nW), and high endurance (>millions of cycles). To understand
their physico-chemical operating mechanisms, we performed in-operando
synchrotron x-ray transmission nanoscale spectromicroscopy using an
ultra-sensitive time-multiplexed technique. We observed only spatially uniform
material changes during cell operation, in sharp contrast to the frequently
detected formation of a localized conduction channel in transition-metal-oxide
memristors. We also associated the response of assigned spectral features
distinctly to non-volatile storage (resistance change) and writing of
information (application of voltage and Joule heating). These results provide
critical insights into high-performance memristors that will aid in device
design, scaling and predictive circuit-modeling, all of which are essential for
the widespread deployment of successful memristor applications.",1701.01784v1
2017-01-19,Comparative study of LaNiO$_3$/LaAlO$_3$ heterostructures grown by pulsed laser deposition and oxide molecular beam epitaxy,"Variations in growth conditions associated with different deposition
techniques can greatly affect the phase stability and defect structure of
complex oxide heterostructures. We synthesized superlattices of the
paramagnetic metal LaNiO3 and the large band gap insulator LaAlO3 by atomic
layer-by-layer molecular beam epitaxy (MBE) and pulsed laser deposition (PLD)
and compared their crystallinity, microstructure as revealed by high-resolution
transmission electron microscopy images and resistivity. The MBE samples show a
higher density of stacking faults, but smoother interfaces and generally higher
electrical conductivity. Our study identifies the opportunities and challenges
of MBE and PLD growth and serves as a general guide for the choice of
deposition technique for perovskite oxides.",1701.05366v1
2017-04-12,"Thermopower modulation clarification of the intrinsic effective mass in a transparent oxide semiconductor, BaSnO3","Although there are so many reports on the carrier effective mass (m*) of a
transparent oxide semiconductor BaSnO3, it is almost impossible to know the
intrinsic m* value because the reported m* values are scattered from 0.06 to
3.7 m0. Here we successfully clarified the intrinsic m* of BaSnO3, m*=0.40 0.01
m0, by the thermopower modulation clarification method. We also found the
threshold of degenerate/non-degenerate semiconductor of BaSnO3; At the
threshold, the thermopower value of both La-doped BaSnO3 and BaSnO3 TFT
structure was 240 microvolt k-1, bulk carrier concentration was 1.4E19 cm-3,
and two-dimensional sheet carrier concentration was 1.8E12 cm-2. When the EF
locates above the parabolic shaped conduction band bottom, rather high mobility
was observed. On the contrary, very low carrier mobility was observed when the
EF lays below the threshold, most likely due to that the tail states suppress
the carrier mobility. The present results are useful for further development of
BaSnO3 based oxide electronics.",1704.03653v1
2018-05-11,Statistical-Raman-Microscopy and Atomic-Force-Microscopy on Heterogeneous Graphene Obtained after Reduction of Graphene Oxide,"Graphene oxide can be used as a precursor to graphene but the quality of
graphene flakes is highly heterogeneous. Scanning-Raman-Microscopy (SRM) is
used to characterize films of graphene derived from flakes of graphene oxide
with an almost intact carbon framework (ai-GO). The defect density of these
flakes is visualized in detail by analyzing the intensity and full-width at
half-maximum of the most pronounced Raman peaks. In addition, we superimpose
the SRM results with AFM images and correlate the spectroscopic results with
the morphology. Furthermore, we use SRM technique to display the amount of
defects in a film of graphene. Thus, an area of 250 x 250 {\my}m2 of graphene
is probed with a step-size increment of 1 {\mu}m. We are able to visualize the
position of graphene flakes, edges and the substrate. Finally, we alter
parameters of measurement to analyze the quality of graphene fast and reliable.
The described method can be used to probe and visualize the quality of graphene
films.",1805.04248v1
2009-12-20,The Effected Oxide Capacitor in CMOS Structure of Integrated Circuit Level 5 Micrometer Technology,"This article is present the effected oxide capacitor in CMOS structure of
integrated circuit level 5 micrometer technology. It has designed and basic
structure of MOS diode. It establish with aluminum metallization layer by
sputtering method, oxide insulator layer mode from silicon dioxide, n+ and p+
semiconductor layer, it has high capacitance concentrate. From the MOS diode
structure silicon dioxide thickness 0.5 micrometer, it will get capacitance
between aluminum metal layer and p+ semiconductor at 28.62 pF, the capacitance
between aluminum metal layer and n+ semiconductor at 29.55 pF. In this article
establish second metal layer for measurement density values of first aluminum
metal layer with second aluminum metal layer, it has density values at 16 pF.",0912.3971v1
2011-11-18,"Structural and electronic properties of ScnOm (n=1~3, m=1~2n) clusters: Theoretical study using screened hybrid density functional theory","The structural and electronic properties of small scandium oxide clusters
ScnOm (n = 1 - 3, m = 1 - 2n) are systematically studied within the screened
hybrid density functional theory. It is found that the ground states of these
scandium oxide clusters can be obtained by the sequential oxidation of small
""core"" scandium clusters. The fragmentation analysis demonstrates that the ScO,
Sc2O2, Sc2O3, Sc3O3, and Sc3O4 clusters are especially stable. Strong
hybridizations between O-2p and Sc-3d orbitals are found to be the most
significant character around the Fermi level. In comparison with standard
density functional theory calculations, we find that the screened hybrid
density functional theory can correct the wrong symmetries and yield more
precise description for the localized 3d electronic states of scandium.",1111.4294v1
2012-01-16,The role of non-local exchange in the electronic structure of correlated oxides,"We present a systematic study of the electronic structure of several
prototypical correlated transition-metal oxides: VO2, V2O3, Ti2O3, LaTiO3, and
YTiO3. In all these materials, in the low-temperature insulating phases the
local and semilocal density approximations (LDA and GGA) of density-functional
theory yield a metallic Kohn-Sham band structure. Here we show that, without
invoking strong-correlation effects, the role of non-local exchange is
essential to cure the LDA/GGA delocalization error and provide a band-structure
description of the electronic properties in qualitative agreement with the
experimental photoemission results. To this end, we make use of hybrid
functionals that mix a portion of non-local Fock exchange with the local LDA
exchange-correlation potential. Finally, we discuss the advantages and the
shortcomings of using hybrid functionals for correlated transition-metal
oxides.",1201.3308v1
2012-04-01,Gated Conductance of Thin Indium Tin Oxide - The Simplest Transistor,"Transistors are the fundamental building block of modern electronic devices.
So far, all transistors are based on various types of semiconductor junctions.
The most common bipolar-junction transistors and metal-oxide-semiconductor
field-effect transistors contain p-n junctions to control the current,
depending on applied biases across the junctions. Thin-film transistors need
metal-semiconductor junctions for injecting and extracting electrons from their
channels. Here, by coating a heavily-doped thin indium-tin-oxide (ITO) film
through a shadow mask onto a biopolymer chitosan/ITO/glass substrate, we can
have a high-performance junctionless transparent organic-inorganic hybrid thin
film transistor. This could be the simplest transistor in the world, to our
knowledge, not only in its structure, but also its fabrication process. In
addition, the device performance is found to be greatly enhanced using a
reinforced chitosan/SiO2 hybrid bilayer dielectric stack. Our results clearly
show that this architecture can lead to a new class of low-cost transistors.",1204.0169v1
2012-04-09,Reduced graphene oxide as ultra fast temperature sensor,"We demonstrate the excellent temperature sensing property of a chemically
synthesized reduced graphene oxide (rGO). It is found that with increase in
temperature from 80 to 375K, the resistivity of reduced graphene oxide
monotonically decreases. The ultra-fast temperature sensing property is
demonstrated by keeping and removing a block of ice under the rGO sensor, which
shows the resistance of rGO increases by 15% in 592 miliseconds and recovers in
8.92 seconds. The temperature sensing of rGO is compared with a standard
platinum thermo sensor (Pt 111) and found the sensitivity is much better in
rGO.",1204.1928v2
2012-04-16,Complementary Resistive Switching in Tantalum Oxide-Based Resistive Memory Devices,"Complementary resistive switches (CRS) are considered as a potential solution
for the sneak path problem in large-scale integration of passive crossbar
resistive memory arrays. A typical CRS is composed of two bipolar memory cells
that are connected anti-serially. Here we report a tantalum-oxide based
resistive memory that achieves the complementary switching functionality within
a single memory cell. The complementary switching effect is accompanied by
switching polarity reversal in different voltage bias regimes. These effects
were explained by the redistribution of oxygen vacancies inside the
tantalum-oxide layers. The effects of symmetry breaking on bipolar switching
and complementary switching were also discussed.",1204.3515v2
2013-09-19,High-throughput synthesis of thermoelectric Ca$_3$Co$_4$O$_9$ films,"Properties of complex oxide thin films can be tuned over a range of values as
a function of mismatch, composition, orientation, and structure. Here, we
report a strategy for growing structured epitaxial thermoelectric thin films
leading to improved Seebeck coefficient. Instead of using single-crystal
sapphire substrates to support epitaxial growth, Ca$_3$Co$_4$O$_9$ films are
deposited, using the Pulsed Laser Deposition technique, onto Al$_2$O$_3$
polycrystalline substrates textured by Spark Plasma Sintering. The structural
quality of the 2000 \AA thin film was investigated by Transmission Electron
Microscopy, while the crystallographic orientation of the grains and the
epitaxial relationships were determined by Electron Back Scatter Diffraction.
The use of a polycrystalline ceramic template leads to structured films that
are in good local epitaxial registry. The Seebeck coefficient is about 170
$\mu$V/K at 300 K, a typical value of misfit material with low carrier density.
This high-throughput process, called combinatorial substrate epitaxy, appears
to facilitate the rational tuning of functional oxide films, opening a route to
the epitaxial synthesis of high quality complex oxides.",1309.4885v1
2013-09-20,Effects of dopants in InOx-based amorphous oxide semiconductors for thin-film transistor applications,"Amorphous metal oxide thin-film transistors (TFT) are fabricated using
InOx-based semiconductors doped with TiO2, WO3 or SiO2. Although density of
dopant is low in the film, change in the electrical properties showed strong
dependence on the dopant species. We found that the dependence could be
reasonably explained by the bond-dissociation energy. By incorporating the
dopant with higher bond-dissociation energy, the film becomes less sensitive to
oxygen partial pressure used during sputtering deposition and remains
electrically stable to thermal annealing treatment. The concept of
bond-dissociation energy can contribute to the realization of more stable metal
oxide TFTs for flat panel displays.",1309.5183v1
2014-05-02,Unusual synchronization phenomena during electrodissolution of silicon: the role of nonlinear global coupling,"The photoelectrodissolution of n-type silicon constitutes a convenient model
system to study the nonlinear dynamics of oscillatory media. On the silicon
surface, a silicon oxide layer forms. In the lateral direction, the thickness
of this layer is not uniform. Rather, several spatio-temporal patterns in the
oxide layer emerge spontaneously, ranging from cluster patterns and turbulence
to quite peculiar dynamics like chimera states. Introducing a nonlinear global
coupling in the complex Ginzburg-Landau equation allows us to identify this
nonlinear coupling as the essential ingredient to describe the patterns found
in the experiments. The nonlinear global coupling is designed in such a way, as
to capture an important, experimentally observed feature: the spatially
averaged oxide-layer thickness shows nearly harmonic oscillations. Simulations
of the modified complex Ginzburg-Landau equation capture the experimental
dynamics very well.",1405.0414v1
2016-07-30,Environmental Instability and Degradation of Single- and Few-Layer WTe2 Nanosheets in Ambient Conditions,"Since the discovery of large, non-saturating magnetoresistance in bulk WTe2
which allows microexfoliation, single- and few-layer WTe2 crystals have
attracted increasing interests. However, as it mentioned in existing studies,
WTe2 flakes appear to degrade in ambient conditions. Here we report
experimental observations of saturating degradation in few-layer WTe2 through
Raman spectroscopy characterization and careful monitoring of the degradation
of single-, bi- and tri-layer (1L, 2L & 3L) WTe2 over long time. Raman peak
intensity decreases during WTe2 degradation and 1L flakes degrade faster than
2L and 3L flakes. The relatively faster degradation in 1L WTe2 could be
attributed to low energy barrier of oxygen reaction with WTe2. We further
investigate the degradation mechanisms of WTe2 using XPS and AES and find that
oxidation of Te and W atoms is the main reason of WTe2 degradation. In
addition, we observe oxidation occurs only in the depth of 0.5nm near the
surface, and the oxidized WTe2 surface could help prevent inner layers from
further degradation.",1608.00097v2
2016-08-01,Growth and engineering of perovskite SrIrO3 thin films,"5d transition-metal-based oxides display emergent phenomena due to the
competition between the relevant energy scales of the correlation, bandwidth,
and most importantly, the strong spin-orbit coupling (SOC). Starting from the
prediction of novel oxide topological insulators in bilayer ABO3 (B = 5d
elements) thin-film grown along the (111) direction, 5d-based perovskites (Pv)
form a new paradigm in the thin-film community. Here, we reviewed the
scientific accomplishments in Pv-SrIrO3 thin films, a popular candidate for
observing non-trivial topological phenomena. Although the predicted topological
phenomena are unknown, the Pv-SrIrO3 thin film shows many emergent properties
due to the delicate interplay between its various degrees of freedom. These
observations provide new physical insight and encourage further research on the
design of new 5d-based heterostructures or superlattices for the observation of
the hidden topological quantum phenomena in strong spin-orbit coupled oxides.",1608.00482v2
2016-08-08,Observation of field emission from GeSn nanoparticles epitaxially grown on silicon nanopillar arrays,"We apply molecular beam epitaxy to grow GeSn-nanoparticles on top of
Si-nanopillars patterned onto p-type Si wafers. We use X-ray photoelectron
spectroscopy to confirm a metallic behavior of the nanoparticle surface due to
partial Sn segregation as well as the presence of a superficial Ge oxide. We
report the observation of stable field emission current from the
GeSn-nanoparticles. We prove that field emission can be enhanced by preventing
GeSn nanoparticles oxidation or by breaking the oxide layer through electrical
stress. Finally, we show that GeSn/p-Si junctions have a rectifying behavior.",1608.02511v1
2016-08-16,On the origin of field-like spin-orbit torques in heavy metal-ferromagnet-oxide thin film heterostructures,"We report measurements of the thickness and temperature (T) dependencies of
current-induced spin-orbit torques, especially the field-like (FL) component,
in various heavy metal (HM)/normal metal (NM) spacer/ferromagnet (FM)/Oxide
(MgO and HfOx/MgO) heterostructures. The FL torque in these samples originates
from spin current generated by the spin Hall effect (SHE) in the HM. For a FM
layer sufficiently thin that a substantial portion of this spin current can
reach the FM/Oxide interface, T-dependent spin scattering there can yield a
strong FL torque that is, in some cases, opposite in sign to that exerted at
the NM/FM interface.",1608.04443v1
2016-12-01,Dimethylsilanone generation from pyrolysis of polysiloxanes filled with nanosized silica and ceria/silica,"Polydimethylsiloxane (PDMS) is a widely used organosilicon polymer often
employed in formulations with fine oxide particles for various high temperature
applications. Although PDMS is considered to be thermally stable and chemically
inert, it is not always clear how the oxide filler influences its
thermoresistance, decomposition chemistry and what reactive products are formed
in the underlying thermal reactions. In this work we use temperature programmed
desorption mass spectrometry (TPD MS) to study the pyrolysis of PDMS and its
composites with nanosized silica and ceria/silica. Our results suggest that the
elusive organosilicon compound - dimethylsilanone is generated from PDMS over a
broad temperature range (in some cases starting at 70${\deg}$C). The presence
of nano-oxides catalyzed this process. Ions characteristic of the fragmentation
of dimethylsilanone under electron ionization were assigned with the aid of DFT
structure calculations. Possible reaction mechanisms for generating
dimethylsilanone were discussed in the context of the calculated kinetic
parameters. Observed accompanying products of PDMS pyrolysis, such as
tetramethylcyclodisiloxane and hexamethylcyclotrisiloxane, indicate that
multiple channels are involved in the dimethylsilanone release.",1612.00223v1
2016-12-26,Semi-Dirac Semimetal in Silicene Oxide,"Semi-Dirac semimetal is a material exhibiting linear band dispersion in one
direction and quadratic band dispersion in the orthogonal direction and,
therefore, hosts massless and massive fermions at the same point in the
momentum space. While a number of interesting physical properties have been
predicted in semi-Dirac semimetals, it has been rare to realize such materials
in condensed matters. Based on the fact that some honeycomb materials are
easily oxidized or chemically absorb other atoms, here, we theoretically
propose an approach of modifying their band structures by covalent addition of
group-VI elements and strain engineering. We predict a silicene oxide with
chemical formula of Si2O to be a candidate of semi-Dirac semimetal. Our
approach is backed by the analysis and understanding of the effect of p-orbital
frustration on the band structure of the graphene-like materials.",1612.08458v1
2017-06-16,Heterogeneous nucleation of pits via step pinning during Si(100) homoepitaxy,"Using scanning tunneling microscopy (STM), we investigate oxide-induced
growth pits in Si thin films deposited by molecular beam epitaxy. In the
transition temperature range from 2D adatom islanding to step-flow growth,
systematic controlled air leaks into the growth chamber induce pits in the
growth surface. We show that pits are also correlated with oxygen-contaminated
flux from Si sublimation sources. From a thermodynamic standpoint, multilayer
growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation
is a known cause for step pinning, roughening, and faceting on elemental
surfaces, both with and without growth flux. Not surprisingly, pits are
thermodynamically metastable and heal by annealing to recover a smooth periodic
step arrangement. STM reveals new details about the pits' atomistic origins and
growth dynamics. We give a model for heterogeneous nucleation of pits by
preferential adsorption of {\AA}-sized oxide nuclei at intrinsic growth
antiphase boundaries, and subsequent step pinning and bunching around the
nuclei.",1706.05127v1
2017-06-22,Theory of the spin galvanic effect at oxide interfaces,"The spin galvanic effect (SGE) describes the conversion of a non-equilibrium
spin polarization into a transverse charge current. Recent experiments have
demonstrated a large conversion efficiency for the two-dimensional electron gas
formed at the interface between two insulating oxides, LaAlO$_3$ and SrTiO$_3$.
Here we analyze the SGE for oxide interfaces within a three-band model for the
Ti t$_{2g}$ orbitals which displays an interesting variety of effective
spin-orbit couplings in the individual bands that contribute differently to the
spin-charge conversion. Our analytical approach is supplemented by a numerical
treatment where we also investigate the influence of disorder and temperature,
which turns out to be crucial to provide an appropriate description of the
experimental data.",1706.07243v1
2017-07-31,Transparent perovskite barium stannate with high electron mobility and thermal stability,"Transparent conducting oxides (TCOs) and transparent oxide semiconductors
(TOSs) have become necessary materials for a variety of applications in the
information and energy technologies, ranging from transparent electrodes to
active electronics components. Perovskite barium stannate (BaSnO3), a new TCO
or TOS system, is a potential platform for realizing optoelectronic devices and
observing novel electronic quantum states due to its high electron mobility,
excellent thermal stability, high transparency, structural versatility, and
flexible doping controllability at room temperature. This article reviews
recent progress in the doped BaSnO3 system, discussing the wide physical
properties, electron-scattering mechanism, and demonstration of key
semiconducting devices such as pn diodes and field-effect transistors.
Moreover, we discuss the pathways to achieving two-dimensional electron gases
at the interface between BaSnO3 and other perovskite oxides and describe
remaining challenges for observing novel quantum phenomena at the
heterointerface.",1707.09778v1
2017-10-11,Solution Monolayer Epitaxy for Tunable Atomically Sharp Oxide Interfaces,"Epitaxial growth of atomically-sharp interfaces serves as one of the main
building blocks of nanofabrication. Such interfaces are crucial for the
operation of various devices including transistors, photo-voltaic cells, and
memory components. In order to avoid charge traps that may hamper the operation
of such devices, it is critical for the layers to be atomically-sharp.
Fabrication of atomically sharp interfaces normally requires ultra-high vacuum
techniques and high substrate temperatures. We present here a new self-limiting
wet chemical process for deposition of epitaxial layers from alkoxide
precursors. This method is fast, cheap, and yields perfect interfaces as we
validate by various analysis techniques. It allows the design of
heterostructures with half-unit cell resolution. We demonstrate our method by
designing hole-type oxide interfaces SrTiO3/BaO/LaAlO3. We show that transport
through this interface exhibits properties of mixed electron-hole contributions
with hole mobility exceeding that of electrons. Our method and results are an
important step forward towards a controllable design of a p-type oxide
interface.",1710.04216v1
2017-10-17,Unified mechanism of the surface Fermi level pinning in III-As nanowires,"Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs,
InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe
microscopy, we show that the Fermi level at oxidized cleavage surfaces of
ternary Al$_{x}$Ga$_{1-x}$As (0$\le$x$\le$0.45) and Ga$_{x}$In$_{1-x}$As
(0$\le$x$\le$1) alloys is pinned at the same position of 4.8$\pm$0.1 eV with
regard to the vacuum level. The finding implies a unified mechanism of the
Fermi level pinning for such surfaces. Further investigation, performed by
Raman scattering and photoluminescence spectroscopy, shows that photooxidation
of the Al$_{x}$Ga$_{1-x}$As and Ga$_{x}$In$_{1-x}$As nanowires leads to the
accumulation of an excess arsenic on their crystal surfaces which is
accompanied by a strong decrease of the band-edge photoluminescence intensity.
We conclude that the surface excess arsenic in crystalline or amorphous forms
is responsible for the Fermi level pinning at oxidized (110) surfaces of III-As
nanowires.",1710.06227v2
2017-10-23,Scavenging of oxygen vacancies at modulation-doped oxide interfaces: Evidence from oxygen isotope tracing,"The introduction of manganite buffer layers, La7/8Sr1/8MnO3 (LSMO) in
particular, at the metallic interface between SrTiO3 (STO) and another band
insulator suppresses the carrier density of the interfacial two-dimensional
electron gas (2DEG) and improves significantly the electron mobility. However,
the mechanisms underlying the extreme mobility enhancement remain elusive.
Herein, we used 18O isotope exchanged SrTi18O3 as substrates to create 2DEG at
room temperature with and without the LSMO buffer layer. By mapping the oxygen
profile across the interface between STO18 and disordered LaAlO3 or
yttria-stabilized zirconia (YSZ), we provide unambiguous evidence that redox
reactions occur at oxide interfaces even grown at room temperature. Moreover,
the manganite buffer layer not only suppresses the carrier density but also
strongly suppresses the oxygen exchange dynamics of the STO substrate, which
likely prevents the reduction of STO during the formation of the 2DEG. The
underlying mechanism on the enhanced electron mobility at buffered oxide
interfaces is also discussed.",1710.08118v1
2017-10-25,Theoretical Investigation of Li and Na Oxides Adsorption on TiC(111) Surface for Metal-Air Rechargeable Batteries,"We analyze, with Density Functional Theory (DFT) calculations, the adsorption
energies of Li$_2$O$_2$, Na$_2$O$_2$ and NaO$_2$ on clean and oxygen passivated
TiC (111) surfaces. We show, that after deposition of two molecular layers of
alkali metal oxides, the initial state of the TiC surface becomes unimportant
for the adsorption energy and that all adsorption energies approach their
native crystal values. The structure of the adsorbed molecular layers is
analyzed and compared to their native oxide crystal structure. Finally, we
discuss the possible implications for electrode optimization for Li-air and
Na-air batteries.",1710.09463v1
2017-10-26,Thermally and Electrically Conductive Nanopapers from Reduced Graphene Oxide: effect of nanoflakes thermal annealing on the film structure and properties,"In this study, we report a different strategy to prepare graphene nanopapers
from direct vacuum filtration. Instead of the conventional method, i.e. thermal
annealing nanopapers at extremely high temperatures prepared from graphene
oxide (GO) or partially reduced GO, we fabricate our graphene nanopapers
directly from suspensions of fully reduced graphene oxide (RGO), obtained after
RGO and thermally annealing at 1700 {\deg}C in vacuum. By using this approach,
we studied the effect of thermal annealing on the physical properties of the
macroscopic graphene-based papers. Indeed, we demonstrated that the enhancement
of the thermal and electrical properties of graphene nanopapers prepared from
annealed RGO is strongly influenced by the absence of oxygen functionalities
and the morphology of the nanoflakes. Hence, our methodology can be considered
as a valid alternative to the classical approach.",1710.09665v1
2017-10-29,Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films,"It is known that solid-state reaction in high-pressure oxygen can stabilize
high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend
this superoxygenation concept of synthesis to thin films which, due to their
large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial
thin films of $\rm{YBa_2Cu_3O_{7-\delta}}$ grown by pulsed laser deposition are
annealed at up to 700 atm O$_2$ and 900$^\circ$C, in conjunction with Cu
enrichment by solid-state diffusion. The films show clear formation of
$\rm{Y_2Ba_4Cu_7O_{15-\delta}}$ and $\rm{Y_2Ba_4Cu_8O_{16}}$ as well as regions
of $\rm{YBa_2Cu_5O_{9-\delta}}$ and YBa$_2$Cu$_6$O$_{10-\delta}$ phases,
according to scanning transmission electron microscopy, x-ray diffraction and
x-ray absorption spectroscopy. Similarly annealed $\rm{YBa_2Cu_3O_{7-\delta}}$
powders show no phase conversion. Our results demonstrate a novel route of
synthesis towards discovering more complex phases of cuprates and other
superconducting oxides.",1710.10672v2
2017-12-11,Pyrochlore Oxide Superconductor Cd2Re2O7 Revisited,"The superconducting pyrochlore oxide Cd2Re2O7 is revisited with a particular
emphasis on the sample-quality issue. The compound has drawn attention as the
only superconductor (Tc = 1.0 K) that has been found in the family of
{\alpha}-pyrochlore oxides since its discovery in 2001. Moreover, it exhibits
two characteristic structural transitions from the cubic pyrochlore structure,
with the inversion symmetry broken at the first one at 200 K. Recently, it has
attracted increasing attention as a candidate spin-orbit coupled metal (SOCM),
in which specific Fermi liquid instability is expected to lead to an odd-parity
order with spontaneous inversion-symmetry breaking [L. Fu, Phys. Rev. Lett.
115, 026401 (2015)] and parity-mixing superconductivity [V. Kozii and L. Fu:
Phys. Rev. Lett. 115 (2015) 207002; Y. Wang et al., Phys. Rev. B 93 (2016)
134512]. We review our previous experimental results in comparison with those
of other groups in the light of the theoretical prediction of the SOCM, which
we consider meaningful and helpful for future progress in understanding this
unique compound.",1712.03617v1
2017-11-21,Three-dimensional printed Yttria-stabilized Zirconia self-supported electrolytes for Solid Oxide Fuel Cell applications,"Additive manufacturing represents a revolution due to its unique capabilities
for freeform fabrication of near net shapes with strong reduction of waste
material and capital cost. These unfair advantages are especially relevant for
expensive and energy-demanding manufacturing processes of advanced ceramics
such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid
Oxide Fuel Cell applications. In this study, self-supported electrolytes of
yttria-stabilized zirconia have been printed by using a stereolithography
three-dimensional printer. Printed electrolytes and complete cells fabricated
with cathode and anode layers of lanthanum strontium manganite- and nickel
oxide-yttria-stabilized zirconia composites, respectively, were electrochemical
characterized showing full functionality. In addition, more complex
configurations of the electrolyte have been printed yielding an increase of the
performance entirely based on geometrical aspects. Complementary, a numerical
model has been developed and validated as predictive tool for designing more
advanced configurations that will enable highly performing and fully customized
devices in the next future",1712.04036v1
2018-01-16,Recent progress on the fabrication of silver nanowire-based transparent electrodes,"Transparent electrodes (TEs) made of metallic nanowires, such as Ag, Au, Cu,
and Ni, have attracted rising attention for several reasons: 1) they can act as
a substitute for tin oxide-based TEs such as indium-tin oxide (ITO) and
fluorine-doped tin oxide (FTO); 2) various methods exist for fabricating such
TEs such as filtration, spraying and meyer bar coating; 3) greater
compatibility with different substrates can be achieved due to the variety of
fabrication methods; and 4) extra functions in addition to serving as
electrodes, such as catalytic abilities, can be obtained due to the metals that
compose the TEs. There are a large number of applications for TEs, ranging from
electronics and sensors to biomedical devices. This short review is a summary
of recent progress, mainly during the past five years, on silver nanowire-based
TEs. The focus of the review will be on theory development, mechanical,
chemical and thermal stability and optical properties. The many applications of
TEs are outside the scope of this review.",1801.05238v1
2018-09-20,Effect of TCNQ layer cover on oxidation dynamics of black phosphorus,"The puckered surface of black phosphorus represents an ideal substrate for an
unconventional arrangement of physisorbed species and the resulting specific
two-dimensional chemistry of this system. This opens the way to investigate the
chemical and physical properties of locally confined areas of black phosphorus
without the necessity for further physical downscaling of the material. We have
evaporated TCNQ on top of black phosphorus under over-saturation
non-equilibrium conditions in vacuum. The evolution of linear density and
height of droplets formed through oxidation during exposure to air was studied
time-dependently by scanning-force microscopy. Our study suggests that the TCNQ
molecules spontaneously arrange in a thin layer of the order of a few nm
height, which, however, is fragmented with a periodicity of about 100 nm. It is
shown that within the confined space separating the layer fragments the
chemical dynamics of the oxidation process is remarkably different than on a
bare black phosphorus surface.",1809.08915v1
2018-09-30,Ultra-low Power Microwave Oscillators based on Phase Change Oxides as Solid-State Neurons,"Neuro-inspired computing architectures are one of the leading candidates to
solve complex, large-scale associative learning problems. The two key building
blocks for neuromorphic computing are the synapse and the neuron, which form
the distributed computing and memory units. Solid state implementations of
these units remain an active area of research. Specifically, voltage or current
controlled oscillators are considered a minimal representation of neurons for
hardware implementations. Such oscillators should demonstrate synchronization
and coupling dynamics for demonstrating collective learning behavior, besides
the desirable individual characteristics such as scaling, power, and
performance. To this end, we propose the use of nanoscale, epitaxial
heterostructures of phase change oxides and oxides with metallic conductivity
as a fundamental unit of an ultralow power, tunable electrical oscillator
capable of operating in the microwave regime. Our simulations show that
optimized heterostructure design with low thermal boundary resistance can
result in operation frequency of up to 3 GHz and power consumption as low as 15
fJ/cycle with rich coupling dynamics between the oscillators.",1810.00454v1
2018-10-01,"Quantified Degeneracy, Entropy and Metal-Insulator Transition in Complex Transition-Metal Oxides","Understanding complex correlated oxides and their phase transitions has long
been a challenge. The difficulty largely arises from the intriguing interplay
between multiple degrees of freedoms. While degeneracy can play an important
role in determining material characteristics, there is no well-defined way to
quantify and to unveil its role in real materials having complicated band
structures. Here we suggest a way to quantify the `effective degeneracy'
relevant to metal-insulator transition by introducing entropy-like terms. This
new quantity well describes the electronic behaviors of transition-metal oxides
as a function of external and internal parameters. With $3d$ titanates, $4d$
ruthenates, and $5d$ iridates as our examples, we show that this new effective
quantity provides useful insights to understand these systems and their phase
transitions. For LaTiO$_3$/LaAlO$_3$ superlattice, we suggest a novel
`degeneracy control' metal-insulator transition.",1810.00502v1
2018-10-01,Synchrotron radiation based photoemission studies of indium oxide passivation of ZnO(0001) surface at high temperature,"Passivation of surface reactive ZnO(0001)-Zn terminated surface is carried
out by in-situ deposition of indium metal and post deposition annealing at high
temperature (600 C - 1000 C). After the every cycle of indium deposition and
annealing the ZnO(0001) surface is characterised by synchrotron radiation based
photoemission. The photoemission studies confirmed the formation of deposited
indium turned into indium oxide (In2O3 and In2Ox) as surface passivation layer.
The core level spectra for Zn, C, O, were acquired at different photon energy
for high surface sensitivity. Overall core level peaks (Zn 3p, In 4d, O 1s)
having average binding shift ranging from 0.5 eV to 0.8 eV. The valance band
spectra shows fermi level shift of 0.9 eV after passivation at 1000 C and work
function raises form 4.06 eV to 4.77 eV. Downward band bending of ZnO(0001)
surface is turned into upward bending of 0.98 eV by indium oxide passivation at
high temperature, which is suitable for making ZnO schotty contact and devices.",1810.00899v1
2018-10-04,Electronic structure and properties of lithium-rich complex oxides,"Lithium-rich complex transition-metal oxides Li$_2$MoO$_3$, Li$_2$RuO$_3$,
Li$_3$RuO$_4$, Li$_3$NbO$_4$, Li$_5$FeO$_4$, Li$_5$MnO$_4$ and their
derivatives are of interest for high-capacity battery electrodes. Here, we
report a first-principles density-functional theory study of the atomic and
electronic structure of these materials using the Heyd-Scuseria-Ernzerhof (HSE)
screened hybrid functional which treats all orbitals in the materials on equal
footing. Dimerization of the transition-metal ions is found to occur in layered
Li$_2$MoO$_3$, in both fully lithiated and partially delithiated compounds. The
Ru--Ru dimerization does not occur in fully lithiated Li$_2$RuO$_3$, in
contrast to what is commonly believed; Ru--Ru dimers are, however, found to
occur in the presence of lithium vacancies caused by lithium loss during
synthesis and/or lithium removal during use. We also analyze the electronic
structure of the complex oxides and discuss the delithiation mechanism in these
battery electrode materials.",1810.02039v1
2018-10-08,Creation of oxide coating on Al 1050 alloy,"Plasma electrolytic oxidation (PEO) is a surface processing for oxide
coatings formation with advanced properties. Mostly, PEO is performed in an
aqueous solution electrolyte which limits the dimension of treated parts due to
the system heating up. Therefore, treatment of large surfaces cannot be applied
in aqueous electrolyte. In current work an alternative approach of PEO
treatment applied in aluminum 1050 alloy in nitrate molten salt was
investigated. The structure, phase and chemical compositions, and
micro-hardness were examined using XRD, SEM, EDS and micro-hardness tests. The
obtained results showed that formed coating contains from two phases of
{\alpha}- Al2O3 and {\gamma}- Al2O3. It was found that formed coating is free
of any contaminants originated from the electrolyte and has no damages, which
are usually present in coatings formed in PEO treatment in aqueous solution
electrolyte.",1810.03300v1
2018-10-22,Strain-induced heteronuclear charge disproportionation in EuMnO$_3$,"Charge disproportionation transitions in complex oxides most commonly link
high-temperature phases containing identical cations with the same oxidation
state and crystallographic site, to low-temperature phases in which charge
transfer between these ions results in unequal oxidation states. Here we
propose, based on density functional calculations, a related concept that we
term \textit{heteronuclear} charge disproportionation, in which charge transfer
occurs between different elements on different crystallographic sites. We show
for the case of EuMnO$_3$ that such a transition from the experimentally
observed Eu$^{3+}$Mn$^{3+}$O$_3$ phase to the so far unknown
Eu$^{2+}$Mn$^{4+}$O$_3$ phase can be triggered by pressure and epitaxial
strain. We then identify measurable signatures to aid in an experimental
exploration of the complex pressure- and biaxial strain-dependent phase
stability of EuMnO$_3$ that we hope to motivate with our predictions. We
suggest other candidate crystal chemistries for heteronuclear charge
disproportionation, in which novel physics could emerge from the coexistence of
instabilities.",1810.09204v1
2018-10-22,First-principles studies of spin-orbital physics in pyrochlore oxides,"The pyrochlore oxides $A_2B_2$O$_7$ exhibit a complex interplay between
geometrical frustration, electronic correlations, and spin-orbit coupling, due
to the lattice structure and active charge, spin, and orbital degrees of
freedom. Understanding the properties of these materials is a theoretical
chalenge, because their intricate nature depends on material-specific details
and quantum many-body effects. Here we review our recent studies based on
first-principles calculations and quantum many-body theories for 4$d$ and 5$d$
pyrochlore oxides with $B$=Mo, Os, and Ir. In these studies, the spin-orbit
coupling and local electron correlations are treated within the LDA+$U$ and
LDA+dynamical mean-field theory formalisms. We also discuss the technical
aspects of these calculations.",1810.09596v2
2018-10-24,Gold Nanoparticle Superlattice in Porous Silica and Low Temperature Catalytic CO Oxidation,"The practical use of nanoparticle superlattices (NPSLs) which are of great
interest as materials with designed functionalities is often limited by their
lack of structural stability under various utilization conditions. Here, we
report a new method for directly synthesizing NPSL fully embedded in
hierarchically porous silica which provides exceptional stability and efficient
pathways for reactant molecules, making the NPSL highly efficient catalyst. The
superlattices made of 12 nm gold nanoparticles exhibit exceptionally high
catalytic activity for CO oxidation at low temperature, showing higher activity
than that of small gold nanoparticles (ca. 3 nm) supported on metal oxides. The
gold NPSL also shows unprecedented stability, maintaining its structural
stability and catalytic activity without any signature of degradation over a
month of continuous catalytic reaction, which present one significant step
forward to realizing the great potentials of gold catalysts in automotive
emission control and green chemistry industry.",1810.10228v2
2019-06-29,Ultra-Low Surface Resistance via Vacuum Heat Treatment of Superconducting Radiofrequency Cavities,"We report on an effort to improve the performance of superconducting
radiofrequency cavities by the use of heat treatment in a temperature range
sufficient to dissociate the natural surface oxide. We find that the residual
resistance is significantly decreased, and we find an unexpected reduction in
the BCS resistance. Together these result in extremely high quality factor
values at relatively large accelerating fields Eacc ~20 MV/m: Q0 of 3-4x10^11
at <1.5 K and Q0 ~5x10^10 at 2.0 K. In one cavity, measurements of surface
resistance versus temperature showed an extremely small residual resistance of
just 0.63+/-0.06 nOhms at 16 MV/m. SIMS measurements confirm that the oxide was
significantly dissociated, but they also show the presence of nitrogen after
heat treatment. We also present studies of surface oxidation via exposure to
air and to water, as well as the effects of very light surface removal via HF
rinse. The possibilities for applications and the planned future development
are discussed.",1907.00147v1
2019-07-01,Stable structures and electronic properties of perovskite oxide monolayers,"It is highly desirable to search for promising two-dimensional (2D) monolayer
materials for deep insight of 2D materials and applications. We use
first-principles method to investigate tetragonal perovskite oxide monolayers
as 2D materials. We find four stable 2D monolayer materials from SrTiO$_3$,
LaAlO$_3$, KTaO$_3$, and BaFeO$_3$, denoting them as STO-ML, LAO-ML, KTO-ML,
and BFO-ML. Our further study shows that through overcoming dangling bonds the
first three monolayers are 2D wide-gap semiconducotors, and BFO-ML is a 2D
isotropic Heisenberg ferromagnetic metal. There is a large electrostatic
potential energy difference between the two sides, reflecting a large
out-of-plane dipole, in each of the monolayers. These make a series of 2D
monolayer materials, and should be useful in novel electronic devices
considering emerging phenomena in perovskite oxide heterostructures.",1907.00898v2
2019-07-19,Tunable coupling and isolation of single electrons in silicon metal-oxide-semiconductor quantum dots,"Extremely long coherence times, excellent single-qubit gate fidelities and
two-qubit logic have been demonstrated with silicon metal-oxide-semiconductor
spin qubits, making it one of the leading platforms for quantum information
processing. Despite this, a long-standing challenge in this system has been the
demonstration of tunable tunnel coupling between single electrons. Here we
overcome this hurdle with gate-defined quantum dots and show couplings that can
be tuned on and off for quantum operations. We use charge sensing to
discriminate between the (2,0) and (1,1) charge states of a double quantum dot
and show excellent charge sensitivity. We demonstrate tunable coupling up to 13
GHz, obtained by fitting charge polarization lines, and tunable tunnel rates
down to below 1 Hz, deduced from the random telegraph signal. The demonstration
of tunable coupling between single electrons in a silicon
metal-oxide-semiconductor device provides significant scope for high-fidelity
two-qubit logic toward quantum information processing with standard
manufacturing.",1907.08523v2
2019-07-23,"Strain Tuning of Plasma Frequency in Vanadate, Niobate, and Molybdate Perovskite Oxides","A novel approach for finding new transparent conductors involves taking
advantage of electronic correlations in metallic transition metal oxides, such
as SrVO$_3$, to enhance the electronic effective mass and suppress the plasma
frequency ($\omega_P$) to infrared. Success of this approach relies on finding
a compound with the right electron effective mass and quasiparticle weight $Z$.
Biaxial strain can in principle be a fruitful way to manipulate the electronic
properties of materials to tune both of these quantities. In this study, we
elucidate the behavior of the electronic properties of early transition metal
oxides SrVO$_3$, SrNbO$_3$, and SrMoO$_3$ under strain, using first principles
density functional theory and dynamical mean field theory. We show that strain
is not an effective way to manipulate the plasma frequency, but dimensionality
of the crystal structure and origin of electronic correlations strongly affect
the trends in both $\omega_P$ and $Z$.",1907.09860v1
2019-07-25,High Performance Fin-FET electrochemical sensor with high-k dielectric materials,"In this work we combine a Fin Field Effect Transistor (Fin-FET) characterised
by a high height to width aspect ratio with high-k dielectric materials to
study the optimized design for chemical-FETs to provide higher transconductance
(and thus a better signal to noise ratio), increased dynamic range and chemical
stability. We used pH sensing to verify the design. We explored the sensitivity
and response linearity of silicon dioxide, alumina and hafnium oxide as
dielectric materials sensing pH, and compared their chemical stability in
different acids. The high aspect ratio fin geometry of the sensor provides high
currents, as well as a planar conduction channel more reliable than traditional
silicon nanowires. The hafnium oxide Fin-FET configuration performed the best
delivering the most linear response both for the output and transfer
characteristics providing a wider dynamic range. Hafnium oxide also showed the
best chemical stability. Thus, we believe that the developed high aspect ratio
Fin-FETs/high-k dielectric system can offer the best compromise of performance
of FET-based sensors.",1907.11022v1
2019-07-27,Microwave derived monoclinic Ba1-xSnxNb2O6 materials as an alternative of ITO,"Microwave synthesis was optimized for preparing novel monoclinic Tin-doped
Barium Niobate ceramics (Ba1-xSnxNb2O6; x= 0.0, 0.01, 0.05, 0.1, 0.2, 0.3) BSN.
The intensity of monoclinic phase formation was observed to decrease on
increasing tin as dopant indicating decreased crystallinity. Strained
crystalline phase was observed in undoped sample that became severe on doping
tin. Monoclinic metal alloy Sn2O3 formation was confirmed on increasing tin
doping beyond 5%. Electronic configuration of tin (II) oxide supports the local
site-wise monoclinic disorder in crystal structure due to sterically active
lone pair. Such a disorder arranges increased number of degenerate energy
states and reduce effective energy gap between conduction band minimum and
valence band maximum. All BSN compositions were investigated for monoclinic
phase stabilization, ultra-violet absorption, dielectric response, raman modes
and type of carrier concentration along with hall resistivity. All measurements
possessed inflexion corresponding to 5 atomic % tin doping indicating
successful site substitution and estimated Sn2O3 metal formation beyond this.
The values of reducing optical energy band gap, transparency to visible
spectrum and hall resistivity indicated utility of these materials as a
substitute transparent conducting oxide (TCO) for well-known indium tin oxide
(ITO).",1907.11946v1
2019-07-29,Mechanical Characterisation of the Protective Al$_2$O$_3$ Scale in Cr$_2$AlC MAX phases,"MAX phases have great potential under demands of both high-temperature and
high-stress performance, with their mixed atomic bonding producing the
temperature and oxidation resistance of ceramics with the mechanical resilience
of metals. Here, we measure the mechanical properties up to 980C by
nanoindentation on highly dense and pure Cr$_2$AlC, as well as after oxidation
with a burner rig at 1200C for more than 29 hours. Only modest reductions in
both hardness and modulus up to 980C were observed, implying no change in
deformation mechanism. Furthermore, micro-cantilever fracture tests were
carried out at the Cr$_2$AlC/Cr$_7$C$_3$ and Cr$_7$C$_3$/Al$_2$O$_3$ interfaces
after the oxidation of the Cr$_2$AlC substrates with said burner rig. The
values are typical of ceramic-ceramic interfaces, below 4 MPa/m, leading to the
hypothesis that the excellent macroscopic behaviour is due to a combination of
low internal strain due to the match in thermal expansion coefficient as well
as the convoluted interface.",1907.12341v1
2019-09-03,Two-Dimensional Antimony Oxide,"Two-dimensional (2D) antimony, so-called antimonene, can form antimonene
oxide when exposed to air. We present different types of single- and few-layer
antimony oxide structures, based on density functional theory (DFT)
calculations. Depending on stoichiometry and bonding type, these novel 2D
layers have different structural stability and electronic properties, ranging
from topological insulators to semiconductors with direct and indirect band
gaps between 2.0 and 4.9 eV. We discuss their vibrational properties and Raman
spectra for experimental identification of the predicted structures.",1909.01204v4
2019-09-04,Structural and electronic phenomena at oxyfluoride KTaO$_3$/K$M$F$_3$ ($M$ = Zn and Ni) superlattices: Rashba splitting and 2DEG,"Here, we present the theoretical analysis of the structural and electronic
degrees of freedom of two different oxide/fluoride perovskite superlattices,
KTaO$_3$/KZnF$_3$ and KTaO$_3$/KNiF$_3$. Using first-principles calculations,
we found the appearance of a two-dimensional electron, 2DEG, and hole, 2DHG,
gases as a function of the number of layers of the different pristine
materials. We demonstrate that the phonon-dynamics at the KTO/K$M$F
superlattices play a crucial role in the appearance of these effects.
Additionally, our results reveal a rather sizeable Rashba-type spin-splitting
at these interfaces in comparison to another oxide/oxide counterparts.",1909.01921v1
2019-09-09,High Dielectric Ternary Oxides from Crystal Structure Prediction and High-throughput Screening,"The development of new high dielectric materials is essential for advancement
in modern electronics. Oxides are generally regarded as the most promising
class of high dielectric materials for industrial applications as they possess
both high dielectric constants and large band gaps. Most previous researches on
high dielectrics were limited to already known materials. In this study, we
conducted an extensive search for high dielectrics over a set of ternary oxides
by combining crystal structure prediction and density functional perturbation
theory calculations. From this search, we adopted multiple stage screening to
identify 440 new low-energy high dielectric materials. Among these materials,
33 were identified as potential high dielectrics favorable for modern device
applications. Our research has opened an avenue to explore novel high
dielectric materials by combining crystal structure prediction and high
throughput screening.",1909.04195v1
2019-09-17,Rational design principles for giant spin Hall effect in 5d-transition metal oxides,"Spin Hall effect (SHE), a mechanism by which materials convert a
\textit{charge} current into a \textit{spin} current, invokes interesting
physics and promises to empower transformative, energy-efficient memory
technology. However, fundamental questions remain about the essential factors
that determine SHE. Here we solve this open problem, presenting a comprehensive
theory of five \textit{foundational factors} that control the value of
intrinsic SHE in transition metal oxides. Arising from our key insight
regarding the inherently geometric nature of SHE, we demonstrate that two of
these factors are crystal field strength and structural distortions. Moreover,
we discover that a new class of materials (anti-perovskites) promises to
demonstrate \textit{giant} SHE, that is an order of magnitude larger than that
reported for any oxide. We derive three other factors that control SHE and
demonstrate the nuanced role of electron correlations. Our findings bring
deeper insight into the physics driving SHE, and could help enhance, as well
as, externally control SHE values.",1909.07544v2
2019-09-18,Investigating the high-temperature thermoelectric properties of n-type rutile TiO$_2$,"Transition metal oxides are considered promising thermoelectric materials for
harvesting high-temperature waste heat due to their stability, abundance and
low toxicity. Despite their typically strong ionic character, they can exhibit
surprisingly high power factors $\sigma S^2$, as in n-type SrTiO$_3$ for
instance. Thus, it is worth examining other transition metal oxides that might
surpass the performances of SrTiO$_3$. This theoretical paper investigates the
thermoelectric properties of n-type rutile TiO$_2$, which is the most stable
phase of titanium oxide up to 2000 K. The electronic structure is obtained
through ab initio calculations, while the prominent features of strong
electron-phonon interaction and defects states are modelled using a small
number of parameters. The theoretical results are compared with a wealth of
experimental data from the literature, yielding very good agreements over a
wide range of carrier concentrations. This validates the hypothesis of band
conduction in rutile TiO$_2$ and allows the prediction of the high-temperature
thermoelectric properties.",1909.08554v2
2019-10-08,Molecular Beam Epitaxy of lithium niobium oxide multifunctional materials,"The role of stoichiometry and growth temperature in the preferential
nucleation of material phases in the Li-Nb-O family are explored yielding an
empirical growth phase diagram. It is shown that while single parameter
variation often produces multi-phase films, combining substrate temperature
control with the previously published lithium flux limited growth allows the
repeatable growth of high quality single crystalline films of many different
oxide phases. Higher temperatures (800-1050 {\deg}C) than normally used in MBE
were necessary to achieve high quality materials. At these temperatures the
desorption of surface species is shown to play an important role in film
composition. Using this method single phase films of NbO, NbO$_{2}$,
LiNbO$_{2}$, Li$_{3}$NbO$_{4}$, LiNbO$_{3}$, and LiNb$_{3}$O$_{8}$ have been
achieved in the same growth system, all on c-plane sapphire. Finally, the
future of these films in functional oxide heterostructures is briefly
discussed.",1910.03703v1
2019-10-11,Fabrication of condense and thin YSZ electrolyte layer using novel thermal-assisted slurry spin coating method for IT-SOFC,"A simple spin coating approach is introduced to fabricate Yttria-Stabilized
Zirconia (YSZ) electrolyte layer on NiO-YSZ anode substrate for solid oxide
fuel cell applications. Heating the substrate during the slurry spin coating
process enhances the affected area through the layer and leads to optimize the
compacting amount of coated electrolyte particles before sintering procedure.
On top of this bilayer substrate, LCFN is deposited as an intermediate
temperature solid oxide fuel cell cathode, in order to have suitable output
performances at intermediate temperature ranges. Applying humidified hydrogen
as fuel and ambient air as the oxidant, cell performance characterizations
exhibit higher power outputs for prepared sample. Electrochemical Impedance
Spectroscopy measurements on single cells also demonstrate that both
interfacial and Ohmic resistances are reduced. These results along with
Scanning Electron Microscope micrographs reveal that the density of the YSZ
layer which is coated by the suggested approach is better than the usual slurry
spin coating method.",1910.05373v2
2019-10-17,Substoichiometric ultrathin zirconia films cause strong metal-support interaction,"The strong metal-support interaction (SMSI) leads to substantial changes of
the properties of an oxide-supported catalyst after annealing under reducing
conditions. The common explanation is the formation of heavily reduced,
ultrathin oxide films covering metal particles. This is typically encountered
for reducible oxides such as TiO2 or Fe3O4. Zirconia (ZrO2), a typical catalyst
support, is difficult to reduce and therefore no obvious candidate for the SMSI
effect. In this work, we use inverse model systems with Rh(111), Pt(111), and
Ru(0001) as supports. Contrary to expectations, we show that SMSI is
encountered for zirconia. Upon annealing in ultra-high vacuum, oxygen-deficient
ultrathin zirconia films ($\approx$ZrO$_{1.5}$) form on all three substrates.
However, Zr remains in its preferred charge state of 4+, as electrons are
transferred to the underlying metal. At high temperatures, the stability of the
ultrathin zirconia films depends on whether alloying of Zr and the substrate
metal occurs. The SMSI effect is reversible; the ultrathin suboxide films can
be removed by annealing in oxygen.",1910.07798v1
2019-10-28,Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets,"Oxygen fugacity is a measure of rock oxidation that influences planetary
structure and evolution. Most rocky bodies in the Solar System formed at oxygen
fugacities approximately five orders of magnitude higher than a hydrogen-rich
gas of solar composition. It is unclear whether this oxidation of rocks in the
Solar System is typical among other planetary systems. We exploit the elemental
abundances observed in six white dwarfs polluted by the accretion of rocky
bodies to determine the fraction of oxidized iron in those extrasolar rocky
bodies and therefore their oxygen fugacities. The results are consistent with
the oxygen fugacities of Earth, Mars, and typical asteroids in the Solar
System, suggesting that at least some rocky exoplanets are geophysically and
geochemically similar to Earth.",1910.12989v1
2020-01-04,Which glass stability parameters can assess the glass-forming ability of oxide systems?,"Glass forming ability (GFA) is a property of utmost importance in glass
science and technology. In this paper, we used a statistical
methodology---involving bootstrap sampling and the Wilcoxon test---to find out
which glass stability parameters can better predict the glass forming ability.
We collected or measured the necessary data for twelve stoichiometric oxide
glasses that underwent predominant heterogeneous nucleation (the most common
case). We found that some GS parameters could predict the GFA of these oxide
glasses quite well, whereas others perform poorly. Parameter $K_w$ was the top
ranked, closely followed by the $K_H$, $\gamma$, $H^{'}$, $\Delta T_{rg}$, and
$K_{cr}$. Our results corroborate previous reports carried out using a smaller
number of glasses, much less GS parameters, and less rigorous statistics. We
also found that using $T_c$ instead of $T_x$ improved the predictive power of
these parameters. Finally, the Jezica, the only parameter considered here that
predicts the GFA without requiring the production of a glass piece (i.e.,
without relying on any crystallization information), ranked reasonably well in
our analysis.",2001.01113v1
2020-01-08,Electronic model of a volcano-shaped size dependence in CO oxidation by gold nanoparticles,"The theoretical model of a volcano-type size dependence of extraordinary
catalytic activity of gold nanoparticles in CO oxidation is proposed based on
the electronic theory of catalysis, the jellium model of metal clusters and the
d-band model of formation bonds in transition metals. The kinetics of the
general mechanism of CO oxidation reaction catalyzed by gold nanoparticles
through dissociative adsorption of oxygen molecules and interaction with CO
molecules from the gas-phase is considered by introducing electronic steps into
3-step mechanism of the reaction, corresponding to transitions between weak and
strong chemisorbed states of intermediates. By introducing the exponential
dependences of the fractions of weak and strong chemisorbed intermediates (O,
CO2) on the size dependent Fermi level of the metal cluster with respect to
antibonding energy levels of the intermediates, a volcano-type dependence of
reaction rate on the size of gold nanoparticles is obtained. The dependence of
the reaction rate upon the supports is taken into account by introducing the
additional energy term into the Fermi level of the metal catalyst.",2001.02647v1
2020-01-08,Vanadium oxide thin films and fibers obtained by acetylacetonate sol-gel method,"Vanadium oxide films and fibers have been fabricated by the acetylacetonate
sol-gel method followed by annealing in wet nitrogen. The samples are
characterized by X-ray diffraction and electrical conductivity measurements.
The effects of a sol aging, the precursor decomposition and the gas atmosphere
composition on the annealing process, structure and properties of the films are
discussed. The two-stage temperature regime of annealing of amorphous films in
wet nitrogen for formation of the well crystallized VO2 phase is chosen: 1)
25-550 C and 2) 550-600 C. The obtained films demonstrate the metal-insulator
transition and electrical switching. Also, the effect of the
polyvinylpyrrolidone additive concentration and electrospinning parameters on
qualitative (absence of defects and gel drops) and quantitative (length and
diameter) characteristics of vanadium oxide fibers is studied.",2001.11329v1
2020-02-24,Coupling lattice instabilities across the interface in ultrathin oxide heterostructures,"Oxide heterointerfaces constitute a rich platform for realizing novel
functionalities in condensed matter. A key aspect is the strong link between
structural and electronic properties, which can be modified by interfacing
materials with distinct lattice symmetries. Here we determine the effect of the
cubic-tetragonal distortion of $\text{SrTiO}_3$ on the electronic properties of
thin films of $\text{SrIrO}_3$, a topological crystalline metal hosting a
delicate interplay between spin-orbit coupling and electronic correlations. We
demonstrate that below the transition temperature at 105 K, $\text{SrIrO}_3$
orthorhombic domains couple directly to tetragonal domains in $\text{SrTiO}_3$.
This forces the in-phase rotational axis to lie in-plane and creates a binary
domain structure in the $\text{SrIrO}_3$ film. The close proximity to the
metal-insulator transition in ultrathin $\text{SrIrO}_3$ causes the individual
domains to have strongly anisotropic transport properties, driven by a
reduction of bandwidth along the in-phase axis. The strong structure-property
relationships in perovskites make these compounds particularly suitable for
static and dynamic coupling at interfaces, providing a promising route towards
realizing novel functionalities in oxide heterostructures.",2002.10555v1
2020-03-03,High-Speed Femto-Joule per Bit Silicon-Conductive Oxide Nanocavity Modulator,"By combining the large Purcell effect of photonic crystal nanocavity and the
strong plasma dispersion effect of the transparent conductive oxides,
ultra-compact silicon modulators with heterogeneously integrated
indium-tin-oxide (ITO) can potentially achieve unprecedented energy efficiency
to atto-joule per bit. In this article, we report the first high-speed silicon
nanocavity modulator driven by an ITO gate, achieving 2.2 GHz bandwidth.
On-off-key modulation is measured up to 5 Gb/s with only 2 V voltage swing and
18.3 fJ/bit energy efficiency. In addition, we perform in-depth analysis of the
energy efficiency and high frequency simulation of the nanocavity modulator,
revealing the critical role played by the semiconductor conduction path and the
overlapping factor between the accumulated free carriers and the cavity
resonant mode. Based on our analysis, we propose a strategy to further improve
the modulation bandwidth to 23.5 GHz by node-matched doping and reduce the
energy consumption to the range of hundreds of atto-joule per bit.",2004.00983v1
2020-04-02,In-situ Synthesis of Bismuth/Reduced Graphene Oxide Nanocomposites as High Capacity Anode Materials for Mg-ion Battery,"Herein, in-situ reduction of bismuth and graphene oxide was performed by a
solvothermal method under a nitrogen atmosphere, and the resulting Bi on RGO
nanocomposites were used as an anode material for Mg-ion batteries. The
nanocomposite of 60% Bi:40% RGO is a beneficial anode material, delivering a
discharge capacity as high as 413 and 372 mAh per g at the specific current of
39 mA per g in the 1st and 50th cycles, respectively. In addition, it shows
high-rate capability with the discharge capacities of 381, 372, 354, 295, and
238 mAh per g at the specific currents of 53, 100, 200, 500, and 700 mA per g,
respectively. The better electrochemical performance of the nanocomposite is
due to improvement in the electronic conductivity and significant reduction of
volume changes during electrochemical cycling. This study demonstrates the
bismuth (Bi) on reduced graphene oxide (RGO) nanocomposite as a promising
high-capacity anode for magnesium-ion batteries with longer life cycle and
high-rate performance.",2004.06485v1
2020-04-29,"Raman spectroscopy of ion irradiated SiC: chemical defects, strain, annealing, and oxidation","Raman spectroscopy has been used to identify defective bonding in neon and
silicon ion irradiated single crystals of 6H-SiC. Observable differences exist
in the C-C bonding region corresponding to different defect structures for neon
and silicon ion implantations. Raman spectra of ion irradiated SiC show less
tensile strain than neutron irradiations, explained by a residual compressive
stress caused by the swelling constrained by the undamaged substrate. Evidence
of oxidation during high temperature ion implantation is observed as C-O and
Si-O Raman signals. Annealing irradiated SiC while acquiring Raman spectra
shows rapid recovery of Si-C bonding, but not a complete recovery of the
unirradiated structure. Annealing irradiated SiC causes surface oxidation where
unirradiated SiC does not oxidise. Comparisons are made to the apparent
radiation resistance of diamond and silicon which have similar crystal
structures, but are monatomic, leading to the suggestion that chemical defects
are responsible for increased radiation damage in SiC.",2004.14335v3
2020-12-02,Bio-Based Polyether from Limonene Oxide Catalytic ROP as Green Polymeric Plasticizer for PLA,"In this work, the polymerization of Limonene Oxide (LO) has been achieved
using an Earth abundant metal-based catalyst developed in our group, that is
very active in ring opening polymerization (ROP) processes. The bio-based
polylimonene ether (PLO) obtained had low molecular weight and good thermal
properties, thus being a potential green polymeric additive for other bio-based
polymers such as PLA. Hence, we have explored its ability to influence PLA
properties. The addition of only 10 wt %, led to the modification and
improvement of PLA properties in terms of flexibility, thermal stability, and
hydrophobicity. The results obtained are promising and open up the potential
industrial application of polylimonene oxide (PLO) for the melt-processing of
blends based on PLA/PLO. These new materials are totally based on renewable
sources and may be interesting for many applications where biodegradability and
reduced water adsorption is required, such as food packaging or agricultural
mulch films.",2012.01297v1
2020-12-25,Graphene oxide based synaptic memristor device for neuromorphic computing,"Brain-inspired neuromorphic computing which consist neurons and synapses,
with an ability to perform complex information processing has unfolded a new
paradigm of computing to overcome the von Neumann bottleneck. Electronic
synaptic memristor devices which can compete with the biological synapses are
indeed significant for neuromorphic computing. In this work, we demonstrate our
efforts to develop and realize the graphene oxide (GO) based memristor device
as a synaptic device, which mimic as a biological synapse. Indeed, this device
exhibits the essential synaptic learning behavior including analog memory
characteristics, potentiation and depression. Furthermore,
spike-timing-dependent-plasticity learning rule is mimicked by engineering the
pre- and post-synaptic spikes. In addition, non-volatile properties such as
endurance, retentivity, multilevel switching of the device are explored. These
results suggest that Ag/GO/FTO memristor device would indeed be a potential
candidate for future neuromorphic computing applications.
  Keywords: RRAM, Graphene oxide, neuromorphic computing, synaptic device,
potentiation, depression",2012.13556v1
2021-01-29,"Comment on ""A compilation and bioenergetic evaluation of syntrophic microbial growth yields in anaerobic digestion"" by Patón, M. and Rodríguez, J. [Water Research 162 (2019), 516-517]","Recent efforts have focused on providing a systematic analysis of syntrophic
microbial growth yields. These biokinetic parameters are key to developing an
accurate mathematical description of the anaerobic digestion process. The
agreement between experimentally determined growth yields and those obtained
from bioenergetic estimations is therefore of great interest. Considering five
important syntrophic groups, including acetoclastic and hydrogenotrophic
methanogens, as well as propionate, butyrate and lactate oxidizers, previous
findings suggest that measured and estimated growth yields were consistent only
for acetoclastic methanogens. A re-analysis revealed that data are also
consistent for lactate oxidizers and hydrogenotrophic methanogens, whereas the
limited data available for propionate and butyrate oxidizers are unsupportive
of firm conclusions. These results highlight pertinent challenges in the
analysis of microbial syntrophy and encourage more accurate measurements of
syntrophic microbial growth yields in the future.",2101.12342v1
2012-05-17,Microscopic understanding of the orbital splitting and its tuning at oxide interfaces,"By means of a Wannier projection within the framework of density functional
theory, we are able to identify the modified c-axis hopping and the energy
mismatch between the cation bands as the main source of the $t_{2g}$ splitting
around the $\Gamma$ point for oxide heterostructures, excluding previously
proposed mechanisms such as Jahn-Teller distortions or electric field
asymmetries. Interfacing LaAlO$_3$, LaVO$_3$, SrVO$_3$ and SrNbO$_3$ with
SrTiO$_3$ we show how to tune this orbital splitting, designing
heterostructures with more $d_{xy}$ electrons at the interface. Such an
""orbital engineering"" is the key for controlling the physical properties at the
interface of oxide heterostructures.",1205.4001v1
2017-05-12,Highly oriented SrTiO3 thin film on graphene substrate,"Growth of perovskite oxide thin films on Si in crystalline form has long been
a critical obstacle for the integration of multifunctional oxides into Si-based
technologies. In this study, we propose pulsed laser deposition of a
crystalline SrTiO3 thin film on a Si using graphene substrate. The SrTiO3 thin
film on graphene has a highly (00l)-oriented crystalline structure which
results from the partial epitaxy. Moreover, graphene promotes a sharp interface
by highly suppressing the chemical intermixing. The important role of graphene
as a 2D substrate and diffusion barrier allows expansion of device applications
based on functional complex oxides.",1705.04412v1
2017-05-16,The Structural Fate of Individual Multicomponent Metal-Oxide Nanoparticles in Polymer Nanoreactors,"Multicomponent nanoparticles can be synthesized with either homogeneous or
phase-segregated architectures depending on the synthesis conditions and
elements incorporated. To understand the parameters that determine their
structural fate, multicomponent metal-oxide nanoparticles consisting of
combinations of Co, Ni, and Cu were synthesized via scanning probe block
copolymer lithography and characterized using correlated electron microscopy.
These studies revealed that the miscibility, ratio of the metallic components,
and the synthesis temperature determine the crystal structure and architecture
of the nanoparticles. A Co-Ni-O system forms a rock salt structure largely due
to the miscibility of CoO and NiO, while Cu-Ni-O, which has large miscibility
gaps, forms either homogeneous oxides, heterojunctions, or alloys depending on
the annealing temperature and composition. Moreover, a higher ordered
structure, Co-Ni-Cu-O, was found to follow the behavior of lower ordered
systems.",1705.05760v2
2017-05-06,Three-fold Constructive Perturbation for Significant Enhancement in Field Emission from Nickel Oxide Nano-Thorn,"A power efficient and stable field emission (FE) has been reported here from
Nickel Oxide nanostructures. Modification in device geometry and surface micro-
(nano-) structure has been found helpful in addressing the bottlenecks in
achieving an efficient FE . In terms of threshold and turn on fields, three
orders of magnitude better electron FE has been observed in the nickel oxide
nanopetals (NiO-NPs) fabricated using simple hydrothermal technique. Uniform
and vertically aligned NiO-NPs structures, grown on very flat conducting
surface (FTO coated glass), show sharp needles like structures on the top edges
of the flakes. These ultrafine structures play the main role in field emission
to start at such a low turn on fields. The FE data (J-E plot) has been fitted
with Fowler-Nordheim (FN) equation to estimate threshold field value and field
enhancement factor which are found to be 3 V/mm and $\sim$ 5 $\times$ 10$^6$
respectively.",1705.07715v1
2017-09-07,Synthesis of mixed hypermetallic oxide BaOCa$^+$ from laser-cooled reagents in an atom-ion hybrid trap,"Hypermetallic alkaline earth (M) oxides of formula MOM have been studied
under plasma conditions that preclude insight into their formation mechanism.
We present here the application of emerging techniques in ultracold physics to
the synthesis of a mixed hypermetallic oxide, BaOCa$^+$. These methods,
augmented by high-level electronic structure calculations, permit detailed
investigation of the bonding and structure, as well as the mechanism of its
formation via the barrierless reaction of Ca $(^3P_J)$ with BaOCH$_{3}^+$.
Further investigations of the reaction kinetics as a function of collision
energy over the range 0.005 K to 30 K and of individual Ca fine-structure
levels compare favorably with calculations based on long-range capture theory.",1709.02399v1
2017-09-22,Palladium gates for reproducible quantum dots in silicon,"We replace the established aluminium gates for the formation of quantum dots
in silicon with gates made from palladium. We study the morphology of both
aluminium and palladium gates with transmission electron microscopy. The native
aluminium oxide is found to be formed all around the aluminium gates, which
could lead to the formation of unintentional dots. Therefore, we report on a
novel fabrication route that replaces aluminium and its native oxide by
palladium with atomic-layer-deposition-grown aluminium oxide. Using this
approach, we show the formation of low-disorder gate-defined quantum dots,
which are reproducibly fabricated. Furthermore, palladium enables us to further
shrink the gate design, allowing us to perform electron transport measurements
in the few-electron regime in devices comprising only two gate layers, a major
technological advancement. It remains to be seen, whether the introduction of
palladium gates can improve the excellent results on electron and nuclear spin
qubits defined with an aluminium gate stack.",1709.07699v2
2018-03-12,Simultaneous nanopatterning and reduction of graphene oxide by femtosecond laser pulses,"This paper presents a novel one-step method for the periodical nanopatterning
and reduction of graphene oxide (GO). Self-organized periodic structures of
reduced graphene oxide (rGO) appear on GO surfaces upon processing with a
femtosecond laser at fluences slightly higher than the fluence needed for
reduction of the GO. This indicates that the periodic pattern is formed either
simultaneously with or due to the reduction of the GO. The laser-induced
reduction of GO was identified by sheet resistance measurements, Raman and
X-ray photoelectron spectroscopy. This fast and simple method to both reduce
and periodically structure GO offers a variety of possible applications in
printed and flexible electronics.",1803.04350v1
2018-03-14,Bond-Derived Orbitalwise Coordination Number as an Accurate Reactivity Descriptor for Oxygen Electrochemistry in Transition-Metal Oxides,"Unraveling a descriptor that is correlated with catalytic reactivity is
essential for fast screening for the optimal catalysts for a given catalytic
reaction. Herein, we propose bond-derived orbitalwise coordination number
($\overline{CN}^\alpha$, $\alpha$= $s$ or $d$) as a simple and accurate
descriptor used for transition metal (TM) oxides that takes into account both
geometrical and electronic structures around active sites, and avoids excessive
computation burden. This descriptor has a strong scaling relation with the
activity in oxygen electrochemistry, enabling us to readily screen for the
optimal catalyst for $\beta$-MnO$_2$. $\beta$-MnO$_2$ with
$\overline{CN}^\alpha$=5.6 by creating an oxygen vacancy on (110) surface
exhibits the best oxygen electrochemical activity, which is well consistent
with experimetal result. This descriptor can be universally applied to other TM
oxides, e.g. RuO$_2$, opening up a new route as a guideline to design novel
catalysts in catalytic reactions.",1803.05146v2
2018-03-20,Facile synthetic route to transition metal oxyfluorides via reactions between metal oxides and PTFE,"Inorganic oxyfluorides have significant importance in the development of new
functionalities for energy production and storage, photonics, catalysis, etc.
In order to explore a simple preparation route that avoids the use of toxic HF
or F2 gas as a reaction reagent, we have employed polytetrafluoroethylene
(PTFE). Five oxyfluorides including Nb5O12F, Nb3O7F, Ta3O7F, TaO2F, and
Mo4O11.2F0.8 were synthesized by reactions between PTFE and transition metal
oxides in sealed quartz ampules. The reaction mechanism was studied by means of
gas analysis, which detected SiF4 as a main product gas during the reaction. A
possible reaction mechanism between the PTFE and transition metal oxides is
discussed.",1803.07229v1
2018-03-21,Formation of periodical metal oxide multilayer structures for the X-ray standing wave applications,"Periodical multilayer (ML) structures can be used as generators of X-ray
standing waves (XSW) for investigation of objects and processes on solid/liquid
and solid/gas interfaces. In this paper, we investigate the specific
requirements to the structural properties of the multilayer structures for XSW
application. We consider the effect of typical defects in the ML structure on
the X-ray standing wave formation and show that the X-ray standing wave is very
robust against the random imperfection in the multilayer structure. In
contrast, the roughness of the topmost layer will have a strong influence on
the XSW experimental results, as the ML serves as a support for the
investigated objects, so that the surface geometry gets directly translated
into the objects. In the experimental part of this work, we have used the
ion-beam deposition to grow Ni/Al metal- and metal oxide-based multilayers and
investigate with AFM their surface quality. The presented results demonstrate
that metal oxides can be successfully used as basic material for X-ray
multilayer standing wave generators.",1803.07971v1
2018-06-09,Origin of interfacial conductivity at complex oxide heterointerfaces: possibility of electron transfer from water chemistry at surface oxygen vacancies,"Variety of conducting heterointerfaces have been made between SrTiO3
substrates and thin capping layers of distinctly different oxide materials that
can be classified into polar band insulators (e.g. LaAlO3), polar Mott
insulators (e.g. LaTiO3), apparently non-polar band insulators (e.g.
{\gamma}-Al2O3), and amorphous oxides (e.g. amorphous SrTiO3). A fundamental
question to ask is if there is a common mechanism that governs interfacial
conductivity in all these heterointerfaces. Here, we examined the conductivity
of different kinds of heterointerfaces by annealing in oxygen and surface
treatment with water. It was found that the conductivity of all the
heterointerfaces show a strong dependence on annealing, and can be universally
tuned by surface treatment whose effect is determined by the annealing
condition. These observations, together with ambient-pressure X-ray
photoelectron spectroscopy measurements, suggest that water chemistry at
surface oxygen vacancies is a common mechanism that supplies electrons to the
interface.",1806.03407v1
2018-06-14,Strain-induced tuning of the electronic Coulomb interaction in 3d transition metal oxide perovskites,"Epitaxial strain offers an effective route to tune the physical parameters in
transition metal oxides. So far, most studies have focused on the effects of
strain on the bandwidths and crystal field splitting, but recent experimental
and theoretical works have shown that also the effective Coulomb interaction
changes upon structural modifications. This effect is expected to be of
paramount importance in current material engineering studies based on
epitaxy-based material synthesization. Here, we perform constrained random
phase approximation calculations for prototypical oxides with a different
occupation of the d shell, LaTiO3 (d1), LaVO3 (d2), and LaCrO3 (d3), and
systematically study the evolution of the effective Coulomb interactions
(Hubbard U and Hund's J) when applying epitaxial strain. Surprisingly, we find
that the response upon strain is strongly dependent on the material. For
LaTiO3, the interaction parameters are determined by the degree of localization
of the orbitals, and grow with increasing tensile strain. In contrast, LaCrO3
shows the opposite trends: the interactions parameters shrink upon tensile
strain. This is caused by the enhanced screening due to the larger electron
filling. LaVO3 shows an intermediate behavior.",1806.05503v1
2018-06-26,Spatiotemporal pattern formation in a three-variable CO oxidation reaction model,"The spatiotemporal pattern formation is studied in the catalytic carbon
monoxide oxidation reaction that takes into account the diffusion processes
over the Pt(110) surface, which may contain structurally different areas. These
areas are formed during CO-induced transition from a reconstructed phase with
$1\times2$ geometry of the overlayer to a bulk-like ($1\times1$) phase with
square atomic arrangement. Despite the CO oxidation reaction being
non-autocatalytic, we have shown that the analytic conditions of the existence
of the Turing and the Hopf bifurcations can be satisfied in such systems. Thus,
the system may lose its stability in two ways --- either through the Hopf
bifurcation leading to the formation of temporal patterns in the system or
through the Turing bifurcation leading to the formation of regular spatial
patterns. At a simultaneous implementation of both scenarios, spatiotemporal
patterns for CO and oxygen coverages are obtained in the system.",1806.09960v1
2018-07-27,Current developments of nanoscale insight into corrosion protection by passive oxide films,"Oxide passive films are a key for the durability of metals and alloys
components as well as a central issue in corrosion science and engineering.
Herein, we discuss current developments of the nanometer and sub-nanometer
scale knowledge of the barrier properties and adsorption properties of passive
oxide films brought by recent model experimental and theoretical
investigations. The discussed aspects include (i) the chromium enrichment and
its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys
such as stainless steel, (ii) the corrosion properties of grain boundaries in
early intergranular corrosion before penetration and propagation in the grain
boundary network, and (iii) the interaction of organic inhibitor molecules with
incompletely passivated metallic surfaces. In all three cases, key issues are
highlighted and future developments that we consider as most relevant are
identified.",1807.10689v2
2018-08-04,Implementation and Analysis of Stable PUFs Using Gate Oxide Breakdown,"We implement and analyze highly stable PUFs using two random gate oxide
breakdown mechanisms: plasma induced breakdown and voltage stressed breakdown.
These gate oxide breakdown PUFs can be easily implemented in commercial silicon
processes, and they are highly stable. We fabricated bit generation units for
the stable PUFs on 99 testchips with 65nm CMOS bulk technology. Measurement
results show that the plasma induced breakdown can generate complete stable
responses. For the voltage stressed breakdown, the responses are with 0.12\%
error probability at a worst case corner, which can be effectively accommodated
by taking the majority vote from multiple measurements. Both PUFs show
significant area reduction compared to SRAM PUF. We compare methods for
evaluating the security level of PUFs such as min-entropy, mutual information
and guesswork as well as inter- and intra-FHD, and the popular NIST test suite.
We show that guesswork can be viewed as a generalization of min-entropy and
mutual information. In addition, we analyze our testchip data and show through
various statistical distance measures that the bits are independent. Finally,
we propose guesswork as a new statistical measure for the level of statistical
independence that also has an operational meaning in terms of security.",1808.01516v1
2018-06-18,Energy and exergy analysis of solar stills with micro/nano particles: A comprehensive study,"In this paper, a comparative study between modified solar stills (with
graphite or copper oxide micro/nano particles) and classical solar still is
carried out, based on the productivity and the thermal performance. Exergy
destructions in various components of the solar stills have been calculated,
analyzed and discussed. Evaporation is faster and the exergy of evaporation is
higher at the modified solar stills than that of the classical one.
Furthermore, the energy and exergy efficiencies of the modified stills are
enhanced compared with the classical one. A brief discussion regarding the
effect of different parameters on solar stills efficiency is also presented.
The daytime energy efficiency of graphite/water and copper oxide/water mixtures
are 41.18% and 38.61%, respectively, but for the classical still is only
29.17%. Moreover, the daytime exergy efficiencies of graphite, copper oxide
nanofluid based stills and classical still are 4.32%, 3.78% and 2.63%,
respectively.",1808.01875v1
2018-08-09,Amphoteric behavior of Hydrogen in Bimetallic Molecular like Hydrides,"Generally hydrogen will adopt the +1, 0 or -1 oxidation state in solids
depending upon the chemical environment it occupy. Typically, there are some
exceptional cases in which hydrogen exhibits both anionic and cationic behavior
in the same structural frame works. In this study we briefly explore an
amphoteric behavior of hydrogen present in ammine bimetallic borohydrides with
the chemical formula M1M2 (BH4)3 (NH3)2 (M1= Na; M2 = Zn, Mg) using the
state-of-the-art density functional calculations. In order to establish the
amphoteric behavior of hydrogen in M1M2 (BH4)3 (NH3)2, we have made detailed
chemical bonding analyses using partial density of states, charge density,
electron localization function, and Born effective charge. From these analyses
we found that the hydrogen closer to boron is in negative oxidation state
whereas the hydrogen closer to nitrogen is in positive oxidation state. The
establishment of the present of hydrogen with amphoteric behavior in solids has
large implication on hydrogen storage application.",1808.03020v1
2018-08-09,Switchable and tunable Rashba-type spin splitting in covalent perovskite oxides,"In transition metal perovskites (ABO3) most physical properties are tunable
by structural parameters such as the rotation of the BO6 octahedra. Examples
include the N\'eel temperature of orthoferrites, the conductivity of
mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides
often host large internal electric dipoles and can accommodate heavy elements,
they also emerge as prime candidates to display Rashba spin-orbit coupling,
through which charge and spin currents may be efficiently interconverted.
However, despite a few experimental reports in SrTiO3-based interface systems,
the Rashba interaction has been little studied in these materials, and its
interplay with structural distortions remain unknown. In this Letter, we
identify a bismuth-based perovskite with a giant, electrically-switchable
Rashba interaction whose amplitude can be controlled by both the ferroelectric
polarization and the breathing mode of oxygen octahedra. This particular
structural parameter arises from the strongly covalent nature of the Bi-O
bonds, reminiscent of the situation in perovskite nickelates. Our results not
only provide novel strategies to craft agile spin-charge converters but also
highlight the relevance of covalence as a powerful handle to design emerging
properties in complex oxides.",1808.03123v1
2018-08-13,Reduced graphene oxide for control of octahedral distortion in orthorhombic Pbnm perovskite,"Perovskites and related structures are renowned for technologically useful
applications. The structural variations in perovskite crystals result in novel
properties which can be regulated by external forces. The study attempts to
regulate distortion of a perovskite compound LaFeO3 driven solely by reduced
graphene oxide (RGO) and to demonstrate the effect using a critical parameter -
electrochemical conductivity. A series of graphene concentration varied
nanocomposites were synthesized via hydrothermal method. The crystal distortion
is investigated using X-ray diffraction and Rietveld refinement. By analysis of
the oxygen and Fe ion peaks of X-ray photoelectron spectroscopy, along with
Raman spectra, a clear understanding of the distortion process is developed.
The remarkable effect of distortion on dispersed phases generated by graphene
matrix is coined with a new phrase Graphenostortion. The study revealed that
the environment for the graphenostrotion originated from the interaction of
oxygen functional groups of RGO with LaFeO3. The variation in bond covalency
influenced by the percentage concentration of non-lattice oxygen, distorted the
Pbnm geometry of the graphene nanocomposite. The developed mechanism for
distortion is in good agreement with electrochemical activity studies. RGO as a
tool to control distortion in metal oxide could facilitate new facets in
technological applications of graphene nanocomposites.",1808.04105v1
2018-08-16,Investigating Unipolar Switching in Niobium Oxide Resistive Switches: Correlating Quantized Conductance and Mechanism,"Memory devices based on resistive switching (RS) have not been fully realised
due to lack of understanding of the underlying switching mechanisms. Nature of
ion transport responsible for switching and growth of conducting filament in
transition metal oxide based RS devices is still in debate. Here, we
investigated the mechanism in Niobium oxide based RS devices, which shows
unipolar switching with high ON/OFF ratio, good endurance cycles and high
retention times. We controlled the boundary conditions between low-conductance
insulating and a high-conductance metallic state where conducting filament (CF)
can form atomic point contact and exhibit quantized conductance behaviour.
Based on the statistics generated from quantized steps data, we demonstrated
that the CF is growing atom by atom with the applied voltage sweeps. We also
observed stable quantized states, which can be utilized in multistate
switching.",1808.05600v1
2018-12-07,Gate-tunable near-field heat transfer,"Active control over the flow of heat in the near-field holds promise for
nanoscale thermal management, with applications in refrigeration,
thermophotovoltaics, and thermal circuitry. Analogously to its electronic
counterpart, the metal-oxide-semiconductor (MOS) capacitor, we propose a
thermal switching mechanism based on accumulation and depletion of charge
carriers in an ultra-thin plasmonic film, via application of external bias. In
our proposed configuration, the plasmonic film is placed on top of a
polaritonic dielectric material that provides a surface phonon polariton (SPhP)
thermal channel, while also ensuring electrical insulation for application of
large electric fields. The variation of carrier density in the plasmonic film
enables the control of the surface plasmon polariton (SPP) thermal channel. We
show that the interaction of the SPP with the SPhP significantly enhances the
net heat transfer. We study SiC as the oxide and explore three classes of
gate-tunable plasmonic materials: transparent conductive oxides, doped
semiconductors, and graphene, and theoretically predict contrast ratios as high
as 225%.",1812.02882v1
2018-09-30,Main-chain poly(ionic liquid)-derived nitrogen-doped micro/mesoporous carbons for CO2 capture and selective aerobic oxidation of alcohols,"Sustainable development and the recent fast growing global demands for energy
and functional chemicals urgently call for effective methods for CO2
remediation and efficient metal-free catalysts for selective oxidation of
aromatic alcohol. Herein, a unique main-chain poly(ionic liquid) (PIL) is
employed as the precursor to prepare nitrogen doped micro and mesoporous
carbons via simultaneous carbonization and activation, which bear high yield,
large specific surface area above 1700 m2 per g and rich nitrogen dopant. The
porous carbon products deliver a high CO2 adsorption capacity up to 6.2 mmol
per g at 273 K and 1 bar with outstanding reversibility and satisfactory
selectivity. Besides, they work excellently as metal free carbocatalysts for
the selective aerobic oxidation of benzyl alcohol to benzaldehyde with high
selectivity. It is believed that this work not only provides a facile approach
to prepare nitrogen-doped porous carbon, but also advances the related research
in the fields of environment and catalysis.",1812.11014v1
2018-12-29,Understanding the origin of bandgap problem in transition and post-transition metal oxides,"Improving electronic structure calculations for practical and
technologically-important materials has been a never-ending pursue. This is
especially true for transition and post-transition metal oxides for which the
current first-principles approaches still suffer various drawbacks. Here we
present a hierarchical-hybrid functional approach built on the use of
pseudopotentials. The key is to introduce a discontinuity in the exchange
functional between core and valence electrons. It allows for treating the
localization errors of sp and d electrons differently, which have been known to
be an important source of error for the band gap. Using ZnO as a prototype, we
show the approach is successful in simultaneously reproducing the band gap and
d-band position. Remarkably, the same approach, without having to change the
hybrid mixing parameters from those of Zn, works reasonably well for other
binary 3d transition and post-transition metal oxides across board. Our
findings point to a new direction of systematically improving the exchange
functional in first-principles calculations.",1812.11288v2
2019-01-09,Exploitation of Transparent Conductive Oxides in the Implementation of a Window-Integrated Wireless Sensor Node,"Exploitation of transparent conductive oxides (TCO) to implement an
energy-autonomous sensor node for a wireless sensor network (WSN) is studied
and a practical solution presented. In the practical implementations, flexible
and rigid substrates that is polyimide and glass, are coated with TCO, namely
aluminum doped zinc oxide (AZO). AZO-coated flexible substrates are used to
form thermoelectric generators (TEG) that produce electricity for the sensor
electronics of the node from thermal gradients on a window. As the second
solution to utilize AZO, its conductive properties are exploited to implement
transparent antennas for the sensor node. Antennas for a UHF RFID transponder
and the Bluetooth radio of the node are implemented. A prototype of a flexible
transparent TEG, with the area of 67 cm2 when folded, was measured to produce
power of 1.6 uW with a temperature difference of 43 K. A radiation efficiency
of -9.1 dB was measured for the transparent RFID antenna prototype with the
center frequency of 900 MHz. Radiation efficiencies between -3.8 dB and -0.4
dB, depending on the substrate, were obtained for the 2.45 GHz Bluetooth
antenna.",1901.02699v1
2019-01-17,Reduction of interface state density in SiC (0001) MOS structures by low-oxygen-partial-pressure annealing,"We report that annealing in low-oxygen-partial-pressure (low-p$_{\rm O2}$)
ambient is effective in reducing the interface state density (D$_{\rm IT}$) at
a SiC (0001)/SiO$_{\rm 2}$ interface near the conduction band edge (E$_{\rm
C}$) of SiC. The D$_{\rm IT}$ value at E$_{\rm C}$$-$0.2 eV estimated by a high
(1 MHz)-low method is 6.2$\times$10$^{12}$ eV$^{-1}$cm$^{-2}$ in as-oxidized
sample, which is reduced to 2.4${\times}$10$^{12}$ eV$^{-1}$cm$^{-2}$ by
subsequent annealing in O$_{\rm 2}$ (0.001%) at 1500${}^\circ$C, without
interface nitridation. Although annealing in pure Ar induces leakage current in
the oxide, low-p$_{\rm O2}$ annealing (p$_{\rm O2}$ = 0.001 - 0.1 %) does not
degrade the oxide dielectric property (breakdown field ~ 10.4 MVcm$^{-1}$).",1901.05681v1
2019-01-17,Surface coating with oxide layers to enhance the spin properties of shallow NV centers in diamond,"We present an enhancement of spin properties of the shallow (<5nm) NV centers
by using ALD to deposit titanium oxide layer on the diamond surface. With the
oxide layer of an appropriate thickness, increases about 2 up to 3.5 times of
both relaxation time and evolution time were achieved and the shallow NV center
charge states stabilized as well. Moreover, the coherence time kept almost
unchanged. This surface coating technique could produce a protective coating
layer of controllable thickness without any damages to the solid quantum system
surface, making it possible to prolong T1 time and T2* time, which would be a
possible approach to the further packaging technique for the applicating solid
quantum devices.",1901.05728v4
2019-01-23,Hydrogen sensing characteristics of perovskite based calcium doped BiFeO3 thin films,"Perovskite oxide based thin film gas sensors have long been considered as
potential alternatives to commonly investigated binary metal oxides based
sensors. BiFeO3, which is a prototype of p-type perovskite based semiconducting
oxides, has recently drawn significant attention for its promising gas sensing
characteristics. In the present work, the hydrogen sensing characteristics of
calcium doped BiFeO3 has been reported by varying the film thickness, doping
concentration, operating temperature, and test gas concentration. The films
were deposited on glass substrates by sol-gel route using spin coating. X-ray
diffraction analyses confirmed formation of phase pure films and scanning
electron microscopy confirmed their uniform and dense microstructure. The
Ca-doped BiFeO3 sensors exhibit higher sensitivity compared to pure BiFeO3
sensors. It is reported that the film thickness and Ca doping concentration
play major role to control hydrogen sensing characteristics of the deposited
films. The sensor based on 15% Ca-doped BiFeO3 sensor exhibited very high
sensitivity (~212 % at 500 ppm H2), and excellent selectivity towards hydrogen
at a moderate operating temperature (~250 {\deg}C).The enhanced gas sensing
response of the doped BiFeO3 films has been attributed to the higher oxygen
vacancy concentration induced by incorporation of aliovalent Ca2+.",1901.07745v1
2019-02-09,"Comparative first-principles study of antiperovskite oxides and nitrides as thermoelectric material: multiple Dirac cones, low-dimensional band dispersion, and high valley degeneracy","We perform a comparative study on thermoelectric performance of
antiperovskite oxides $Ae_3Tt$O and nitrides $Ae_3Pn$N ($Ae=$ Ca, Sr, Ba; $Tt=$
Ge, Sn, Pb; $Pn=$ As, Sb, Bi) by means of first-principles calculation. As for
the oxides with the cubic structure, Ca$_3$GeO with a sizable band gap exhibits
high thermoelectric performance at high temperatures, while Ba$_3$PbO with
Dirac cones without the gap is favorable at low temperatures. The latter high
performance owes to high valley degeneracy including the multiple Dirac cones
and the valleys near the $\Gamma$ and R points. For the nitrides with the cubic
structure, insulator with strong quasi-one-dimensionality exhibits high
thermoelectric performance. We also find that the orthorhombic structural
distortion sometimes sizably enhances thermoelectric performance, especially
for Ba$_3$GeO and Sr$_3$AsN where the high valley degeneracy is realized in the
$Pnma$ phase. Our calculation reveals that antioerpvskites offer a fertile
playground of various kinds of characteristic electronic structure, which
enhance the thermoelectric performance, and provides promising candidates of
high-performance thermoelectric materials.",1902.03424v2
2019-02-19,"Mono- versus multi-phosphonic acid based PEGylated polymers for functionalization and stabilization of metal (Ce, Fe, Ti, Al)oxide nanoparticles in biological media","For applications in nanomedicine, particles need to be functionalized to
prevent protein corona formation and or aggregation. Most advanced strategies
take advantage of functional polymers and assembly techniques. Nowadays there
is an urgent need for coatings that are tailored according to a broad range of
surfaces and that can be produced on a large scale. Herein, we synthesize mono-
and multi-phosphonic acid based poly(ethylene glycol) (PEG) polymers with the
objective of producing efficient coats for metal oxide nanoparticles. Cerium,
iron, titanium and aluminum oxide nanoparticles of different morphologies
(spheres, platelets, nanoclusters) and sizes ranging from 7 to 40 nm are
studied in physiological and in protein rich cell culture media. It is found
that the particles coated with mono-functionalized polymers exhibit a mitigated
stability over time, whereas the multi-functionalized copolymers provide
resilient coatings and long-term stability (months). With the latter, PEG
densities in the range 0.2 - 0.5 nm-2 and layer thickness about 10 nm provide
excellent performances. The study suggests that the proposed coating allows
controlling nanomaterial interfacial properties in biological environments.",1902.07172v1
2019-03-07,Electrochemical performance of decorated reduced graphene oxide by MoO3 nanoparticles as a counter electrode,"We present an efficient electrocatalytic material based on anchored MoO3
nanoparticles on reduced graphene oxide (RGO) nanosheets. After preparation of
graphene oxide (GO), the MoO3 nanoparticles anchored on GO nanosheet by using
the arc-discharge method. X-ray diffraction patterns show that the MoO3
nanoparticles are well crystallized on RGO in the orthorhombic crystalline
phase with a crystallite size of 83 nm. In addition, FT-IR and Raman
spectroscopy results show that during the arc-discharge process, the GO
nanosheets have been reduced and RGO nanosheets are decorated with MoO3
nanoparticles which form a porous structure. The surface energy of the prepared
electrode was measured as 44.56 mJ/m2, which shows the desirable spreading
ability of the electrolyte on the electrode. Finally, electrochemical
performance was measured in the symmetrical dummy cell by impedance
spectroscopy and cyclic voltammogram, and the photochemical test was measured
in the dye-sensitized solar cell by current density measurement. Our results
show that the electrochemical performance of the RGM electrode is better than
the RGO electrode and is comparable with the Platinum electrode and also the
efficiency of RGM electrode used in a dye-sensitized solar cell as a counter
electrode is 5.55% near to Platinum electrode performance.",1903.02914v2
2019-03-08,Quantised conductance of one-dimensional strongly-correlated electrons in an oxide heterostructure,"Oxide heterostructures are versatile platforms with which to research and
create novel functional nanostructures. We successfully develop one-dimensional
(1D) quantum-wire devices using quantum point contacts on MgZnO/ZnO
heterostructures and observe ballistic electron transport with conductance
quantised in units of 2e^{2}/h. Using DC-bias and in-plane field measurements,
we find that the g-factor is enhanced to around 6.8, more than three times the
value in bulk ZnO. We show that the effective mass m^{*} increases as the
electron density decreases, resulting from the strong electron-electron
interactions. In this strongly interacting 1D system we study features matching
the 0.7 conductance anomalies up to the fifth subband. This paper demonstrates
that high-mobility oxide heterostructures such as this can provide good
alternatives to conventional III-V semiconductors in spintronics and quantum
computing as they do not have their unavoidable dephasing from nuclear spins.
This paves a way for the development of qubits benefiting from the low defects
of an undoped heterostructure together with the long spin lifetimes achievable
in silicon.",1903.03476v1
2019-03-10,Monolayer black phosphorus by sequential wet-chemical surface oxidation,"We report a straightforward chemical methodology for controlling the
thickness of black phosphorus flakes down to the monolayer limit by
layer-by-layer oxidation and thinning, using water as solubilizing agent.
Moreover, the oxidation process can be stopped at will by two different
passivation procedures, namely the non-covalent functionalization with perylene
diimide chromophores, which prevents the photooxidation, or by using a
protective ionic liquid layer. The obtained flakes preserve their electronic
properties as demonstrated by fabricating a BP field-effect transistor (FET).
This work paves the way for the preparation of BP devices with controlled
thickness",1903.03972v1
2019-03-12,Plasmon Standing Waves by Oxidation of Si(553)-Au,"Self-assembled Au atomic wires on stepped Si surfaces are metallic, as
evidenced by a one-dimensionally dispersing plasmonic excitation. Here we
investigate the effects of oxidization on metallicity along such Au atomic
wires on a regularly stepped Si(553) surface, by employing infrared absorption
and high resolution electron energy loss spectroscopies. Our results indicate
that only the Si environment undergoes oxidation, which has a remarkably small
effect on the plasmon dispersion. Only close to $k_{\parallel}\rightarrow 0$
the plasmon dispersion ends at increasingly higher energies as a function of
oxygen exposure, which is attributed to standing wave formation on small
sections of Au wires generated by the introduction of O atoms as scattering
centers, not to electronic gap opening. This interpretation is in full
agreement with the findings by infrared spectroscopy and with low energy
electron diffraction.",1903.04826v1
2019-03-29,Epitaxial TiOx Surface in Ferroelectric BaTiO3: Native Structure and Dynamic Patterning at the Atomic Scale,"Surfaces and interfaces of ferroelectric oxides exhibit enhanced
functionality, and therefore serve as a platform for novel nano and quantum
technologies. Experimental and theoretical challenges associated with examining
the subtle electro-chemo-mechanical balance at metal-oxide surfaces have
hindered the understanding and control of their structure and behavior. Here,
we combine advanced electron-microscopy and first-principles thermodynamics
methods to reveal the atomic-scale chemical and crystallographic structure of
the surface of the seminal ferroelectric BaTiO3. We show that the surface is
composed of a native < 2-nm thick TiOx rock-salt layer in epitaxial registry
with the BaTiO3. Using electron-beam irradiation, we successfully patterned
artificially TiOx sites with sub-nanometer resolution, by inducing Ba escape.
Therefore, our work offers electro-chemo-mechanical insights into ferroelectric
surface behavior in addition to a method for scalable high-resolution
beam-induced chemical lithography for selectively driving surface phase
transitions, and thereby functionalizing metal-oxide surfaces.",1903.12435v1
2019-03-29,Structural modification of thin Bi(1 1 1) films by passivation and native oxide model,"The structure of thin terminated Bi(1 1 1) films of approximately 1 nm
thickness is investigated from first principles. Our density functional theory
calculations show that covalent bonds to the surface can change the orientation
of the films completely. For thicker films, the effect is limited to the
surface only. Based on these observations, we further present a simple model
structure for the native oxide and chemically similar oxides, which form a
protective capping layer, leaving the orientation of the films unchanged. The
advantages of this energetically favorable layered termination are discussed in
the context of the films' technological exploitation in nanoelectronic devices.",1903.12654v2
2019-04-06,Constriction Percolation Model for Coupled Diffusion-Reaction Corrosion of Zirconium in PWR,"Percolation phenomena are pervasive in nature, ranging from capillary flow,
crack propagation, ionic transport, fluid permeation, etc. Modeling percolation
in highly-branched media requires the use of numerical solutions, as problems
can quickly become intractable due to the number of pathways available. This
becomes even more challenging in dynamic scenarios where the generation of
pathways can quickly become a combinatorial problem. In this work, we develop a
new constriction percolation paradigm, using cellular automata to predict the
transport of oxygen through a stochastically cracked Zr oxide layer within a
coupled diffusion-reaction framework. We simulate such branching trees by
generating a series porosity-controlled media. Additionally, we develop an
analytical criterion based on compressive yielding for bridging the transition
state in corrosion regime, where the percolation threshold has been achieved.
Our model extends Dijkstras shortest path method to constriction pathways and
predicts the arrival rate of oxygen ions at the oxide interface. This is a
critical parameter to predict oxide growth in the so-called post-transition
regime, when bulk diffusion is no longer the rate-limiting phenomenon.",1904.03344v1
2019-04-10,Influence of vacuum annealing on interface properties of SiC (0001) MOS structures,"We investigated the influence of vacuum annealing on interface properties of
silicon carbide (SiC) metal-oxide-semiconductor (MOS) structures. For
as-oxidized and nitric oxide (NO)-annealed samples, the interface state density
($D_{\rm it}$) near the conduction band edge ($E_{\rm C}$) of SiC did not
increase by subsequent vacuum annealing. For phosphoryl chloride
(POCl$_3$)-annealed samples, in contrast, $D_{\rm it}$ at $E_{\rm C}-0.2$ eV
increased from $1.3\times10^{10}$ to $2.2\times10^{12}$ cm$^{-2}$eV$^{-1}$ by
the vacuum annealing, and the channel mobility of MOS field effect transistors
(MOSFETs) decreased from 109 to 44 cm$^2$V$^{-1}$s$^{-1}$. Mechanism of the
observed increase in $D_{\rm it}$ was discussed based on the results of
secondary ion mass spectrometry measurement.",1904.05006v1
2019-04-12,Synthesis of anti-perovskite-type carbides and nitrides from metal oxides and melamine,"Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are
synthesised through reactions between ingredient metal oxides and organic
compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by
choosing different reaction temperatures and nominal oxide-to-melamine ratios.
SnNCo3 is synthesised for the first time by this melamine method. Resistivity,
magnetisation, and heat capacity measurements reveal that SnNCo3 is a
correlated metal with a high density of states at the Fermi level. Our results
demonstrate that this feasible synthetic route using melamine is useful in the
search for complex metal carbides and nitrides toward novel functional
materials.",1904.06103v1
2019-08-01,Liquid Marble Photosensor,"A liquid marble is a liquid droplet coated by a hydrophobic power. The liquid
marble does not wet adjacent surfaces and therefore can be manipulated as a dry
soft body. A Belousov-Zhabotinsky (BZ) reaction is an oscillatory chemical
reaction exhibiting waves of oxidation. We demonstrate how to make a
photo-sensor from BZ medium liquid marbles. We insert electrodes into a liquid
marble, prepared from BZ solution and coated with polyethylene powder. The
electrodes record a potential difference which oscillates due to oxidation
wave-fronts crossing the electrodes. When the BZ marble is illuminated by a
light source, the oxidation wave-fronts are hindered and, thus, the electrical
potential recorded ceases to oscillate. We characterise several types of
responses of BZ marble photosensors to various stimuli, and provide
explanations of the recorded activity. BZ liquid marble photosensors may find
applications in the fields of liquid electronics, soft robotics and
unconventional computing.",1908.00632v1
2019-08-02,Light scattering through the graphene oxide liquid crystal in a micro-channel,"In this paper, we examine the light scattering by the flow of levitated
flakes in a micro-channel to characterize the tunable functionality of the
graphene oxide liquid crystal in the nematic phase. Light interaction with the
mentioned material is decomposed to the scattered and transmitted parts and
they can determine the orientation of the flakes. Our results demonstrate that,
pumping the graphene oxide sample through the micro-channel leads to increase
the amplitude of scattered light. The time averaged of scattered light
intensity grows by increasing volume fraction. We also find that, the higher
volume fraction, the sooner reaching to saturated normalized scattered
intensity is. To get deep insight about our experimental results, we rely on
the general theoretical properties of the light scattering cross-section
incorporating the fluctuation of director vector and dielectric tensor. Our
proposal is a promising approach to carry out the mechanical-hydrodynamical
approach for controlling the orientation of a typical liquid crystal.",1908.00725v1
2019-08-05,Neutralization of slow helium ions scattered from single crystalline aluminum and tantalum surfaces and their oxides,"We investigated the impact of surface oxygen on the ion yield for He$^+$ ions
scattered from different single crystalline surfaces in low-energy ion
scattering. Initially clean Al(111) and Ta(111) were exposed to molecular
oxygen and ion spectra for different oxidation stages and different primary
energies were recorded. A comparison of ion yields normalized to the
differential scattering cross section as well as experimental factors allows
obtaining information about the influence of oxygen on charge exchange
processes. The decrease in the ion yield of both metals with exposure cannot be
explained by different surface coverages exclusively, but requires the
neutralization efficiency to be dependent on the chemical structure of the
surface. For Ta, additionally, a different energy dependency of the ion yield
obtained in the metal and oxide occurs. The ion yield for O shows in both
surfaces a significantly weaker energy dependency than the investigated metals.",1908.01629v1
2019-08-08,Descriptors for Electrolyte-Renormalized Oxidative Stability of Solvents in Lithium-ion Batteries,"Electrolyte stability against oxidation is one of the important factors
limiting the development of high energy density batteries. HOMO level of
solvent molecules has been successfully used for understanding trends in their
oxidative stability but assumes a non-interacting environment. However, solvent
HOMO levels are renormalized due to molecules in their solvation shells. In
this work, we first demonstrate an inexpensive and accurate method to determine
the HOMO level of solvent followed by simple descriptors for renormalization of
HOMO level due to different electrolyte components. The descriptors are based
on Gutmann Donor and Acceptor numbers of solvent and other components. The
method uses fast GGA-level DFT calculations compared to previously used
expensive, experimental data dependent methods. This method can be used to
screen for unexplored stable solvents among the large number of known organic
compounds to design novel high voltage stable electrolytes.",1908.03285v1
2019-08-21,Graphene Oxide Nanoparticles in the Interstellar Medium,"Dust particles play a major role in the formation, evolution and chemistry of
interstellar clouds, stars and planetary systems. Commonly identified forms
include amorphous and crystalline carbon-rich particles and silicates. Also
present in many astrophysical environments are polycyclic aromatic hydrocarbons
(PAHs), detected through their infrared emission, and which are essentially
small flakes of graphene. Astronomical observations over the past four decades
have revealed a widespread unassigned Extended Red Emission (ERE) feature which
is attributed to luminescence of dust grains. Numerous potential carriers for
ERE have been proposed but none has gained general acceptance. In this Letter
it is shown that there is a strong similarity between laboratory optical
emission spectra of graphene oxide and ERE, leading to this proposal that
emission from graphene oxide nanoparticles is the origin of ERE and that these
are a significant component of interstellar dust. The proposal is supported by
infrared emission features detected by the Infrared Space Observatory (ISO) and
the Spitzer Space Telescope.",1908.07787v1
2019-11-01,Mesoscopic theory of defect ordering-disordering transitions in thin oxide films,"Ordering of mobile defects in functional materials can give rise to
fundamentally new phases possessing ferroic and multiferroic functionalities.
Here we develop the Landau theory for strain induced ordering of defects (e.g.
oxygen vacancies) in thin oxide films, considering both the ordering and
wavelength of possible instabilities. Using derived analytical expressions for
the energies of various defect-ordered states, we calculated and analyzed phase
diagrams dependence on the film-substrate mismatch strain, concentration of
defects, and Vegard coefficients. Obtained results open possibilities to create
and control superstructures of ordered defects in thin oxide films by selecting
the appropriate substrate and defect concentration.",1911.00258v3
2019-11-07,"Thermodynamic stability of Borophene, $\mathrm{B_2O_3}$ and other $\mathrm{B_{1-x}O_x}$ sheets","The recent discovery of borophene, a two-dimensional allotrope of boron,
raises many questions about its structure and its chemical and physical
properties. Boron has a high chemical affinity to oxygen but little is known
about the oxidation behavior of borophene. Here we use first principles
calculations to study the phase diagram of free-standing, two-dimensional
$\mathrm{B_{1-x}O_x}$ for compositions ranging from $x=0$ to $x=0.6$, which
correspond to borophene and $\mathrm{B_2O_3}$ sheets, respectively. Our results
indicate that no stable compounds except borophene and $\mathrm{B_2O_3}$ sheets
exist. Intermediate compositions are heterogeneous mixtures of borophene and
$\mathrm{B_2O_3}$. Other hypothetical crystals such as $\mathrm{B_2O}$ are
unstable and some of them were found to undergo spontaneous disproportionation
into borophene and $\mathrm{B_2O_3}$. It is also shown that oxidizing borophene
inside the flakes is thermodynamically unfavorable over forming
$\mathrm{B_2O_3}$ at the edges. All findings can be rationalized by oxygen's
preference of two-fold coordination which is incompatible with higher in-plane
coordination numbers preferred by boron. These results agree well with recent
experiments and pave the way to understand the process of oxidation of
borophene and other two-dimensional materials.",1911.02950v1
2019-11-17,Pt Supported on Plasma-Chemical Titanium Nitride for Efficient Room-Temperature CO Oxidation,"Catalysts of carbon monoxide oxidation were synthesized by deposition of
platinum on titanium nitride (TiN). Two substrates with an average particle
size of 18 and 36 nm were obtained by hydrogen reduction of titanium
tetrachloride in a stream of microwave plasma of nitrogen. The surface of the
catalysts was studied by X-ray photoelectron spectroscopy (XPS). The CO
oxidation rate on the 9-15 wt.% Pt loaded TiN catalysts was found to be 120
times higher than that on platinum black with a specific surface of 30 m2/g.
Such catalysts are promising for use in catalytic air purification systems.",1911.07321v1
2019-11-27,Comparative Study of RF Sputtered Ba2(BiNb)O6 and Ba2Bi1.4Nb0.6 O6 thin films and Effect of Fluorine Doping in Their Photoelectrochemical (PEC) Performances,"Bismuth based ternary oxide photocatalysts are of considerable interest in
photoelectrochemical water splitting. Yet these oxides are highly stable in
different environment, their relative inertness limits the available synthesis
routes to obtain desired stoichiometry on the final product. This report
describes a method to prepare barium bismuth niobate (specifically, Ba2(BiNb)O6
and Ba2Bi1.4Nb0.6 O6) target by sintering a mixture of individual oxides and
successfully fabricate desired barium bismuth niobate thin film on TCO
substrate. The surface morphology, physical, and chemical properties of thin
film were systematically investigated. Compositional uniformity was obtained by
sputtering in oxygen argon plasma environment and higher photocatalytic
activities were observed after subsequent surface treatments. Sodium fluoride
surface treatment further enhanced the photocurrent density and improved
electrode stability against corrosion. This work further suggests a viable
approach to improve the PEC performance of sputtered barium bismuth niobate by
modulating their fundamental energy states.",1911.12188v1
2019-11-27,Study of RF Sputtered Antimony Alloyed Bismuth Vanadium Oxide (Sb:BiVO4) Thin Films for Enhanced Photoelectrochemical (PEC) performance from Bandgap Modulation to Thickness Optimization,"Monoclinic scheelite bismuth vanadate (BiVO4) is a promising photoanode for
water splitting yet the PEC performance is limited due to its relatively higher
(2.4 eV) band gap. Here, we successfully decreased its the band gap to 1.72 eV
by controlled antimony alloying. Low bandgap antimony alloyed bismuth vanadium
oxide (Sb:BiVO4) thin film was prepared by RF sputtering of high purity
homemade target, fabricated by solid-state reaction using a mixture of Sb2O3,
Bi2O3, and V2O5 powders with desired stoichiometric ratios. Several growth
parameters, powder crystallography, post-deposition effects, and surface
treatments, thickness dependence, effect of electrolytes on photocorrosion were
studied along with its optical and electrochemical characterization. We
discovered that Sb:BiVO4 is a direct band gap material in the visible light
range (1.72 eV) and a valence band position suitable for driving water
oxidation reaction under illumination. Furthermore, hole diffusion length is
increased with antimony alloying and achieved optimum thickness of 400 nm for
higher photocurrent. The controllably prepared Sb:BiVO4 particles are having
the sizes of 10-15 nm in room temperature deposition and can be grown up to 0.5
microns under air annealing.",1911.12191v1
2019-12-04,Optical phased arrays for LIDAR: beam steering via tunable plasmonic metasurfaces,"Controlling the phase and amplitude of light emitted by the elements (i.e.,
pixels) of an optical phased array is of paramount importance to realizing
dynamic beam steering for LIDAR applications. In this paper, we propose a
plasmonic pixel composed of a metallic nanoantenna covered by a thin oxide
layer, and a conductive oxide, e.g., ITO, for use in a reflectarray
metasurface. By considering voltage biasing of the nanoantenna via metallic
connectors, and exploiting the carrier refraction effect in the
metal-oxide-semiconductor capacitor in the accumulation and depletion regions,
our simulations predict control of the reflection coefficient phase over a
range $>330^{\circ}$ with a nearly constant magnitude. We discuss the physical
mechanism underlying the optical response, the effect of the connectors, and
propose strategies to maximize the magnitude of the reflection coefficient and
to achieve dual-band operation. The suitability of our plasmonic pixel design
for beam steering in LIDAR is demonstrated via 3D-FDTD simulations.",1912.02275v1
2019-12-17,Physical properties and device applications of graphene oxide,"Graphene oxide (GO), the functionalized graphene with oxygenated groups
(mainly epoxy and hydroxyl), has attracted resurgent interests in the past
decade owing to its large surface area, superior physical and chemical
properties, and easy composition with other materials via surface functional
groups. Usually, GO is used as an important raw material for mass production of
graphene via reduction. However, under different conditions, the coverage,
types, and arrangements of oxygen-containing groups in GO can be varied, which
give rise to excellent and controllable physical properties, such as tunable
electronic and mechanical properties depending closely on oxidation degree,
suppressed thermal conductivity, optical transparency and fluorescence, and
nonlinear optical properties. Based on these outstanding properties, many
electronic, optical, optoelectronic, and thermoelectric devices with high
performance can be achieved on the basis of GO. Here we present a comprehensive
review on recent progress of GO, focusing on the atomic structures, fundamental
physical properties, and related device applications, including transparent and
flexible conductors, field-effect transistors, electrical and optical sensors,
fluorescence quenchers, optical limiters and absorbers, surface enhanced Raman
scattering detectors, solar cells, light-emitting diodes, and thermal
rectifiers.",1912.07956v1
2019-12-18,Schottky barrier induced asymmetry in the negative differential resistance response of Nb/NbOx/Pt cross-point devices,"The negative differential resistance (NDR) response of Nb/NbOx/Pt cross-point
devices is shown to have a polarity dependence due to the effect of the
metal/oxide Schottky barriers on the contact resistance. Three distinct
responses are observed under opposite polarity testing: bipolar S-type NDR,
bipolar snap-back NDR, and combined S-type and snap-back NDR, depending on the
stoichiometry of the oxide film and device area. In-situ thermoreflectance
imaging is used to show that these NDR responses are associated with strong
current localisation, thereby justifying the use of a previously developed
two-zone, core shell thermal model of the device. The observed polarity
dependent NDR responses, and their dependence on stoichiometry and area are
then explained by extending this model to include the effect of the polarity
dependent contact resistance. This study provides an improved understanding of
the NDR response of metal/oxide/metal structures and informs the engineering of
devices for neuromorphic computing and non-volatile memory applications.",1912.08371v1
2019-12-20,Operando XANES from first-principles and its application to iridium oxide,"Efficient electro-catalytic water-splitting technologies require suitable
catalysts for the oxygen evolution reaction (OER). The development of novel
catalysts could benefit from the achievement of a complete understanding of the
reaction mechanism on iridium oxide (IrO$_2$), an active catalyst material that
is, however, too scarce for large-scale applications. Considerable insight has
already been provided by \emph{operando} X-ray absorption near-edge structure
(XANES) experiments, which paved the way towards an atomistic description of
the catalyst's evolution in a working environment. We combine here
first-principles simulations augmented with a continuum description of the
solvent and electrolyte to investigate the electrochemical stability of various
IrO$_2$ interfaces and to predict the XANES cross-section for selected
terminations under realistic conditions of applied potential. The comparison of
computed O K-edge XANES spectra to corresponding experiments supports the
formation of electron-deficient surface oxygen species in the OER-relevant
voltage regime. Furthermore, surface hydroxyl groups that are found to be
stable up to $\sim$1 V are suggested to be progressively oxidized at larger
potentials, giving rise to a shift in the Ir L$_3$-edge cross-section that
qualitatively agrees with measurements.",1912.09769v1
2020-05-04,On the origin of the premature breakdown of thermal oxide on 3C-SiC probed by electrical scanning probe microscopy,"The dielectric breakdown (BD) of thermal oxide (SiO2) grown on cubic silicon
carbide (3C-SiC) was investigated comparing the electrical behavior of
macroscopic metal-oxidesemiconductor (MOS) capacitors with nanoscale current
and capacitance mapping using conductive atomic force (C-AFM) and scanning
capacitance microscopy (SCM). Spatially resolved statistics of the oxide BD
events by C-AFM revealed that the extrinsic premature BD is correlated to the
presence of peculiar extended defects, the anti-phase boundaries (APBs), in the
3C-SiC layer. SCM analyses showed a larger carrier density at the stacking
faults (SFs) the 3C-SiC, that can be explained by a locally enhanced density of
states in the conduction band. On the other hand, a local increase of minority
carriers concentration was deduced for APBs, indicating that they behave as
conducting defects having also the possibility to trap positive charges. The
results were explained with the local electric field enhancement in
correspondence of positively charged defects.",2005.01290v1
2020-05-15,Moderate bandgap and high carrier mobility simultaneously realized in bilayer silicene by oxidation,"Semiconductors simultaneously possessing high carrier mobility, moderate
bandgap, and ambient environment stability are so important for the modern
industry, and Si-based semiconducting materials can match well with the
previous silicon based electronic components. Thus, searching for such Si-based
semiconductors has been one hot project due to the lack of them nowadays. Here,
with the help of density functional theory, we found that the oxidized bilayer
silicene exhibits high carrier mobility with a moderate direct bandgap of 1.02
eV. The high carrier mobility is caused by the remaining of big pi bond, and
the moderate bandgap is opened by the saturation of dangling Si 3p bonds.
Originated from the formation of strong Si-O and Si-Si bonds, the sample
exhibits strong thermodynamic and dynamical stabilities. Our work indicates
that the oxidized bilayer silicene has many potential applications in modern
electronic fields.",2005.07517v1
2020-05-19,Density fitting in periodic systems: application to TDHF in diamond and oxides,"A robust density fitting method for calculating Coulomb matrix elements over
Bloch functions based on calculation of two- and three-center matrix elements
of the Ewald potential is described and implemented in a Gaussian orbital basis
in the Exciton code. The method is tested by comparing Coulomb and exchange
energies from density fitting to corresponding energies from SCF HF
calculations for diamond, magnesium oxide and bulk Ne. Density fitting
coefficients from the robust method are compared to coefficients from a
variational method applied to wave function orbital products in bulk Ne. Four
center Coulomb matrix elements from density fitting are applied to time
dependent Hartree-Fock (TDHF) calculations in diamond, magnesium oxide and
anatase and rutile polytypes of titanium dioxide. Shifting virtual states
downwards uniformly relative to occupied states and scaling the electron-hole
attraction term in the TDHF Hamiltonian by 0.4 yields good agreement with
either experiment and/or Bethe-Salpeter equation calculations. This approach
mirrors similar 'scissors' adjustments of occupied and virtual states and
introduction of a scaled electron-hole attraction term in some time dependent
DFT calculations.",2005.09291v1
2020-06-17,On the microscopic origin of reversible and irreversible reactions of LiNixCoyMnx cathode materials: Ni-O hybrid bond formation vs. cationic and anionic redox,"Energy density limitations of layered oxides with different Ni contents,
i.e., of the conventional cathode materials in Li-ion batteries, are
investigated across the first discharge cycle using advanced spectroscopy and
state-of-the-art diffraction. For the first time unambiguous experimental
evidence is provided, that redox reactions in NCMs proceed via a reversible
oxidation of Ni and a hybridization with O, and not, as widely assumed, via
pure cationic or more recently discussed, pure anionic redox processes. Once
Ni-O hybrid states are formed, the sites cannot be further oxidized. Instead,
irreversible reactions set in which lead to a structural collapse and thus, the
lack of ionic Ni limits the reversible capacity. Moreover, the degree of
hybridization, which varies with the Ni content, triggers the electronic
structure and the operation potential of the cathodes. With an increasing
amount of Ni, the covalent character of the materials increases and the
potential decreases.",2006.09964v1
2020-08-27,Mapping nanoscale charge states and phase domains with quantitative hyperspectral coherent diffractive imaging spectroscopy,"The critical properties of functional materials and nanoscale devices often
originate from the coexistence of different thermodynamic phases and / or
oxidization states, but sample makeup is seldom completely known a priori.
Coherent diffractive imaging (CDI) provides the spatial resolution needed to
observe nanoscale coexistence while returning the full amplitude and phase
information of an object, but to date lacks the spectral information necessary
for composition identification. Here we demonstrate CDI spectroscopy (CDIS),
acquiring images of the prototypical quantum material vanadium oxide across the
vanadium L2,3 and oxygen K X-ray absorption edges with nanometer scale
resolution. Using the hyperspectral X-ray image we show coexistence of multiple
oxidization states and phases in a single sample and extract the full complex
refractive index of V2O5 and the monoclinic insulating and rutile conducting
phases of VO2. These results constrain the role of hidden phases in the
insulator-to-metal transition in VO2.",2008.11992v1
2020-09-09,An Experimentally Driven Automated Machine Learned lnter-Atomic Potential for a Refractory Oxide,"Understanding the structure and properties of refractory oxides are critical
for high temperature applications. In this work, a combined experimental and
simulation approach uses an automated closed loop via an active-learner, which
is initialized by X-ray and neutron diffraction measurements, and sequentially
improves a machine-learning model until the experimentally predetermined phase
space is covered. A multi-phase potential is generated for a canonical example
of the archetypal refractory oxide, HfO2, by drawing a minimum number of
training configurations from room temperature to the liquid state at ~2900oC.
The method significantly reduces model development time and human effort.",2009.04045v1
2020-09-24,Probing redox potential for Iron sulfur clusters in photosystem I,"Photosystem I is a light-driven electron transfer device. Available X-ray
crystal structure from Thermosynechococcus elongatus, showed that electron
transfer pathways consist of two nearly symmetric branches of cofactors
converging at the first iron sulfur cluster FX, which is followed by two
terminal iron sulfur clusters FA and FB. Experiments have shown that Fx has
lower oxidation potential than FA and FB, which facilitate the electron
transfer reaction. Here, we use Density Functional Theory and Multi-Conformer
Continuum Electrostatics to explain the differences in the midpoint Em
potentials of the Fx, FA and FB clusters. Our calculations show that Fx has the
lowest oxidation potential compared to FA and FB due strong pair-wise
electrostatic interactions with surrounding residues. These interactions are
shown to dominated by the bridging sulfurs and cysteine ligands, which may be
attributed to the shorter average bond distances between the oxidized Fe ion
and ligating sulfurs for FX compared to FA and FB. Moreover, the electrostatic
repulsion between the 4Fe-4S clusters and the positive potential of the
backbone atoms is least for FX compared to both of FA and FB. These results
agree with the experimental measurements from the redox titrations of
low-temperature EPR signals and of room temperature recombination kinetics.",2009.11681v1
2020-10-06,Identification of Li$_{\text{Ni}}$ and V$_{\text{Ni}}$ acceptor levels in doped nickel oxide,"Nickel oxide, in particular in its doped, semiconducting form, is an
important component of several optoelectronic devices. Doping NiO is commonly
achieved either by incorporation of lithium, which readily occupies Ni sites
substitutionally, producing the Li$_{\text{Ni}}$ acceptor, or by supplying
reactive oxygen species during NiO film deposition, which leads to the
formation of Ni vacancies (V$_{\mathrm{Ni}}$). However, the energetic position
of these acceptors in the NiO band gap has not been experimentally determined
until today. In this work, we close this knowledge gap by studying rectifying
n$^{++}$p heterojunctions of NiO on top of fluorine-doped tin oxide. These
structures show sufficient rectification to perform electric characterization
by defect spectroscopic techniques, specifically capacitance-voltage and
thermal admittance spectroscopy. Using these methods, the (0/-) charge
transition levels are determined to be 190meV and 409meV above the valence band
edge for the Li$_{\text{Ni}}$ and the V$_{\text{Ni}}$ acceptor, respectively.",2010.02694v1
2020-11-25,Effect of pseudo-cubic (111)-oriented orthorhombic substrate facets on perovskite oxide thin film synthesis,"Strain engineering with different substrate facets is promising for tuning
functional properties of thin film perovskite oxides. By choice of facet,
different surface symmetries and chemical bond directions for epitaxial
interfaces can be tailored. Here, preparation of well-defined pseudo-cubic
(111)-oriented orthorhombic substrates of DyScO3 , GdScO3 , and NdGaO3 is
reported. The choice of orthorhombic facet, (011)o or (101)o , both
corresponding to pseudo-cubic (111)pc , gives vicinal surfaces with single or
double (111pc layer terrace step heights, respectively, impacting subsequent
thin film growth. Orthorhombic LaFeO3 epitaxy on the (101)o facet reveals a
distinction between alternating (111)pc layers, both during and after growth.
The observed differences are explained based on the oxygen octahedral tilt
pattern relative to the two orthorhombic (111)pc surfaces. This robust
structural detail in the orthorhombic perovskite oxides enables utilisation of
different (111)pc facets for property engineering, through polyhedral
connectivity control and cation coordination at epitaxial interfaces.",2011.12874v1
2021-03-09,The Laser-Diode Heated Floating Zone Method for Automated Optimal Synthesis of Refractory Oxides and Alloys,"We perform an experimental investigation of the synthesis of complex
materials using the Laser-diode heated floating zone method (L-FZ). We will
briefly introduce the Infrared-heated floating zone method of bulk crystal
growth and then delve into recent advances in using a Laser-diode heated
floating zone method. We demonstrate L-FZ for the growth of large high-quality
single crystalline samples of of the n=2 Ruddlesden-Popper homologous series
$RE_2SrAl_2O_7$, RE = Nd, Sm, Eu, Gd, Tb, Dy with physically interesting
properties (e.g spin-ice) as well as the incongruently melting
stuffed-tridymite type oxide $BaCoSiO_4$. We conclude with a summary of the
results and future research directions in automating crystal growth, which will
open access into the synthesis and characterization of previously unstudied
class of materials such as refractory complex oxides and alloys.",2103.05587v1
2021-03-11,Highly confined phonon polaritons in monolayers of oxide perovskites,"Two-dimensional (2D) materials are able to strongly confine light hybridized
with collective excitations of atoms, enabling electric-field enhancements and
novel spectroscopic applications. Recently, freestanding monolayers of oxide
perovskites have been synthesized, which possess highly infrared-active phonon
modes and a complex interplay of competing interactions. In this study, we
evaluate central figures of merit for phonon polaritons in the tetragonal
phases of the 2D perovskites SrTiO$_3$, KTaO$_3$, and LiNbO$_3$, using density
functional theory calculations. Specifically, we compute the 2D
phonon-polariton dispersions, the propagation-quality, confinement, and
deceleration factors, and we show that they are comparable to those found in
the prototypical 2D dielectric hexagonal boron nitride. Our results suggest
that monolayers of oxide perovskites are promising candidates for polaritonic
platforms in the terahertz spectral range that enable possibilites to control
complex phases of matter through strongly enhanced electromagnetic fields.",2103.06949v1
2021-03-17,Raman Signal Reveals the Rhombohedral Crystallographic Structure in Ultra-thin Layers of Bismuth Thermally Evaporated on Amorphous Substrate,"Under the challenge of growing a single bilayer of Bi oriented in the (111)
crystallographic direction over amorphous substrates, we have studied different
thicknesses of Bi thermally evaporated onto silicon oxide in order to shed
light on the dominant atomic structures and their oxidation. We have employed
atomic force microscope, X-ray diffraction, and scanning electron microscope
approaches to demonstrate that Bi is crystalline and oriented in the (111)
direction for thicknesses over 20 nm. Surprisingly, Raman spectroscopy
indicates that the rhombohedral structure is preserved even for ultra-thin
layers of Bi, down to $\sim 5$ nm. Moreover, the signals also reveal that
bismuth films exposed to ambient conditions do not suffer major surface
oxidation.",2103.09400v1
2021-04-13,"Faraday law, oxidation numbers, and ionic conductivity: The role of topology","Faraday's experiment measures -- within a modern view -- the charge
adiabatically transported over a macroscopic distance by a given nuclear
species in insulating liquids: the reason why it is integer is deeply rooted in
topology. Whole numbers enter chemistry in a different form: atomic oxidation
states. They are not directly measurable, and are determined instead from an
agreed set of rules. Insulating liquids are a remarkable exception: Faraday's
experiment indeed measures the oxidation numbers of each dissociated component
in the liquid phase, whose topological values are unambiguous. Ionic
conductivity in insulating liquids is expressed in terms of the autocorrelation
function of the fluctuating charge current at a given temperature in zero
electric field; topology plays a major role in this important observable as
well. The existing literature deals with the above issues by adopting the
independent-electron framework; here I provide the many-body generalization of
all the above findings, which furthermore allows for compact and very
transparent notations and formulas.",2104.06026v2
2021-04-16,The Millimeter-Wave Spectrum of Doubly Deuterated Propylene Oxide CH$_3$CHCD$_2$O,"Spectra of doubly deuterated propylene oxide, CH$_3$CHCD$_2$O, were recorded
in the millimeter-wave spectral region up to 330 GHz utilizing a 2f frequency
modulated Terahertz spectrometer. Rotational and centrifugal distortion
constants and tunneling parameters for the description of the internal rotation
of the methyl group were retrieved. The software XIAM was used to describe the
A-E tunneling splitting with a frequency uncertainty of 82 kHz. Molecular
parameters derived from our measurements are complemented by quantum chemical
anharmonic frequency calculations on the B3LYP/augcc-pVTZ level of theory. In
addition, the barrier height to internal rotation of the methyl group,V3, was
derived experimentally and found to slightly differ from the value reported for
the main isotopologue. In view of astrophysical observations we provide
accurate line lists to search for doubly deuterated propylene oxide in space.
Furthermore, we deliver improved molecular parameters to further investigate
the properties of a simple chiral molecule possessing internal large amplitude
motions.",2104.08151v1
2021-04-27,Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces,"Mastery of order-disorder processes in highly non-equilibrium nanostructured
oxides has significant implications for the development of emerging energy
technologies. However, we are presently limited in our ability to quantify and
harness these processes at high spatial, chemical, and temporal resolution,
particularly in extreme environments. Here we describe the percolation of
disorder at the model oxide interface LaMnO$_3$ / SrTiO$_3$, which we visualize
during in situ ion irradiation in the transmission electron microscope. We
observe the formation of a network of disorder during the initial stages of ion
irradiation and track the global progression of the system to full disorder. We
couple these measurements with detailed structural and chemical probes,
examining possible underlying defect mechanisms responsible for this unique
percolative behavior.",2104.13272v1
2021-04-28,Effective reduction of PdCoO2 thin films via hydrogenation and sign tunable anomalous Hall effect,"PdCoO2 , belonging to a family of triangular oxides called delafossite, is
one of the most conducting oxides. Its in-plane conductivity is comparable to
those of the best metals, and exhibits hydrodynamic electronic transport with
extremely long mean free path at cryogenic temperatures. Nonetheless, it is
nonmagnetic despite the presence of the cobalt ion. Here, we show that a mild
hydrogenation process reduces PdCoO2 thin films to an atomically-mixed alloy of
PdCo with strong out-of-plane ferromagnetism and sign-tunable anomalous Hall
effect. Considering that many other compounds remain little affected under a
similar hydrogenation condition, this discovery may provide a route to creating
novel spintronic heterostructures combining strong ferromagnetism, involving
oxides and other functional materials.",2104.13536v1
2021-05-04,Electron-Phonon Coupling and Electron-Phonon Scattering in SrVO$_3$,"Understanding the physics of strongly correlated electronic systems has been
a central issue in condensed matter physics for decades. In transition metal
oxides, strong correlations characteristic of narrow $d$ bands is at the origin
of such remarkable properties as the Mott gap opening, enhanced effective mass,
and anomalous vibronic coupling, to mention a few. SrVO$_3$, with V$^{4+}$ in a
$3d^1$ electronic configuration is the simplest example of a 3D correlated
metallic electronic system. Here, we focus on the observation of a (roughly)
quadratic temperature dependence of the inverse electron mobility of this
seemingly simple system, which is an intriguing property shared by other
metallic oxides. The systematic analysis of electronic transport in SrVO$_3$
thin films discloses the limitations of the simplest picture of e-e
correlations in a Fermi liquid; instead, we show that the quasi-2D topology of
the Fermi surface and a strong electron-phonon coupling, contributing to dress
carriers with a phonon cloud, play a pivotal role on the reported electron
spectroscopic, optical, thermodynamic and transport data. The picture that
emerges is not restricted to SrVO$_3$ but can be shared with other $3d$ and
$4d$ metallic oxides.",2105.01579v1
2021-05-06,Balancing orbital effects and onsite Coulomb repulsion through Na modulations in NaxVO2,"Vanadium oxides have been highly attractive for over half a century since the
discovery of the metal insulator transition near room temperatures. Here NaxVO2
is studied through a systematic comparison with other layered sodium metal
oxides with early 3d transition metals, first disclosing a unified evolution
pattern of Na density waves through in situ XRD analysis. Combining ab-initio
simulations and theoretical modelings, a sodium-modulated Peierls-like
transition mechanism is then proposed for the bonding formation of metal ion
dimers. More importantly, the unique trimer structure in NaxVO2 is shown to be
very sensitive to the onsite Coulomb repulsion value, suggesting a delicate
balance between strong electronic correlations and orbital effects that can be
precisely modulated by both Na compositions and atomic stackings. This unveils
a unique opportunity to design strongly correlated materials with tailored
electronic transitions through electrochemical modulations and crystallographic
designs, to elegantly balance various competition effects. We think the
understanding will also help further elucidate complicated electronic behaviors
in other vanadium oxide systems.",2105.02416v1
2021-05-21,Novel ion-doped mesoporous glasses for bone tissue engineering: Study of their strctural characteristics influenced by the presence of phosphorous oxide,"Ion-doped binary SiO2-CaO and ternary SiO2-CaO-P2O5 mesoporous bioactive
glasses were synthesised and characterised to evaluate the influence of P2O5 in
the glass network structure. Strontium, copper and cobalt oxides in a
proportion of 0.8 mol% were selected as dopants because the osteogenic and
angiogenic properties reported for these elements. Although the four glass
compositions investigated presented analogous textural properties, TEM analysis
revealed that the structure of those containing P2O5 exhibited an increased
ordered mesoporosity. Furthermore, 29Si NMR revealed that the incorporation of
P2O5 increased the network connectivity and that this compound captured the
Sr2+, Cu2+ and Co2+ ions preventing them to behave as modifiers of the silica
network. In addition, 31P NMR results revealed that the nature of the cation
directly influences the characteristics of the phosphate clusters. In this
study, we have proven that phosphorous oxide entraps doping-metallic ions,
granting these glasses with a greater mesopores order.",2105.10222v1
2021-06-11,Redox Active Cerium Oxide Nanoparticles: Current Status and Burning Issues,"Research on cerium oxide nanoparticles (nanoceria) has captivated the
scientific community due to their unique physical and chemical properties, such
as redox activity and oxygen buffering capacity, which made them available for
many technical applications, including biomedical applications. The redox
mimetic antioxidant properties of nanoceria have been effective in the
treatment of many diseases caused by reactive oxygen species (ROS) and reactive
nitrogen species. The mechanism of ROS scavenging activity of nanoceria is
still elusive, and its redox activity is controversial due to mixed reports in
the literature showing pro-oxidant and antioxidant activity. In lieu of its
current research interest, it is critical to understand the behaviour of
nanoceria in the biological environment and provide answers to some of the
critical and open issues. This review critically analyses the status of
research on the application of nanoceria to treat diseases caused by ROS. It
reviews the proposed mechanism of action and shows the effect of surface
coatings on its redox activity. It also discusses some of the crucial issues in
deciphering the mechanism and redox activity of nanoceria and suggests areas of
future research.",2106.06473v1
2021-06-12,RF surface resistance tuning of superconducting niobium via thermal diffusion of native oxide,"Recently, Nb superconducting radio frequency cavities vacuum heat treated
between 300-400 C for a few hours have exhibited very high quality factors
(~5x10^10 at 2.0 K). New secondary ion mass spectrometry measurements of O, N
and C show this enhancement in RF surface conductivity is primarily associated
with interstitial O alloying via dissolution and diffusion of the native oxide.
We use a theory of oxide decomposition and O diffusion to quantify previously
unknown parameters crucial in modeling this process. RF measurements of a
vacuum heat treated Nb superconducting radio frequency cavity confirm the
minimized surface resistance (higher Q0) previously expected only from 800 C
diffusive alloying with N.",2106.06647v2
2021-06-14,Semi-Dirac and Weyl Fermions in Transition Metal Oxides,"We show that a class of compounds with $I$4/$mcm$ crystalline symmetry hosts
three-dimensional semi-Dirac fermions. Unlike the known two-dimensional
semi-Dirac points, the degeneracy of these three-dimensional semi-Dirac points
is not lifted by spin-orbit coupling due to the protection by a nonsymmorphic
symmetry -- screw rotation in the $a-b$ plane and a translation along the $c$
axis. This crystalline symmetry is found in tetragonal perovskite oxides,
realizable in thin films by epitaxial strain that results in
a$^0$a$^0$c$^-$-type octahedral rotation. Interestingly, with broken
time-reversal symmetry, two pairs of Weyl points emerge from the semi-Dirac
points within the Brillouin zone, and an additional lattice distortion leads to
enhanced intrinsic anomalous Hall effect. The ability to tune the Berry phase
by epitaxial strain can be useful in novel oxide-based electronic devices.",2106.07793v2
2021-06-23,Charged Oxygen Vacancy Induced Ferroelectric Structure Transition in Hafnium Oxide,"The discovery of ferroelectric HfO2 in thin films and more recently in bulk
is an important breakthrough because of its silicon-compatibility and
unexpectedly persistent polarization at low dimensions, but the origin of its
ferroelectricity is still under debate. The stabilization of the metastable
polar orthorhombic phase was often considered as the cumulative result of
various extrinsic factors such as stress, grain boundary, and oxygen vacancies
as well as phase transition kinetics during the annealing process. We propose a
novel mechanism to stabilize the polar orthorhombic phase over the nonpolar
monoclinic phase that is the bulk ground state. Our first-principles
calculations demonstrate that the doubly positively charged oxygen vacancy, an
overlooked defect but commonly presented in binary oxides, is critical for the
stabilization of ferroelectric phase. The charge state of oxygen vacancy serves
as a new degree of freedom to control the thermodynamic stability of competing
phases of wide-band-gap oxides.",2106.12159v1
2021-06-26,High Infrared Reflectance Modulation in VO2 Films Synthesized on Glass and ITO coated Glass substrates using Atmospheric Oxidation of Vanadium,"Vanadium Dioxide (VO2) is a strongly correlated material, which exhibits
insulator to metal transition at ~68 C along with large resistivity and
infrared optical reflectance modulation. In this work, we use atmospheric
pressure thermal oxidation of Vanadium to synthesize VO2 films on glass and ITO
coated glass substrates. With the optimized short oxidation durations of 2 min
and 4 min, the synthesized VO2 film shows high optical reflectance switching in
long-wavelength infrared on glass substrates and mid-wavelength infrared on ITO
coated glass substrates, respectively. Peak reflectance switching values of
~76% and ~79% are obtained on the respective substrates, which are among the
highest reported values. Using the reflectance data, we extract VO2 complex
refractive index in infrared wavelengths, in both the insulating and metallic
phases. The extracted refractive index shows good agreement with VO2
synthesized using other methods. This demonstration of high optical reflectance
switching in VO2 thin films, grown on low cost glass and ITO coated glass
substrates, using a simple low thermal budget process will aid in enhancing VO2
applications in the optical domain.",2106.14006v1
2021-07-04,Theoretical Prediction of Heterogeneous Integration of Dissimilar Semiconductor with Various Ultra-Thin Oxides and 2D Materials,"In this paper, we have built a numerical p-n Si/GaAs heterojunction model
using a quantum-mechanical tunneling theory with various quantum tunneling
interfacial materials including two-dimensional semiconductors such as
hexagonal boron nitride (h-BN) and graphene and ALD-enabled oxide materials
such as HfO2, Al2O3, and SiO2. Their tunneling efficiencies and tunneling
current with different thicknesses were systematically calculated and compared.
Multiphysics modeling was used with the aforementioned tunneling interfacial
materials to analyze changes in strain under different temperature conditions.
Considering the transport properties and thermal-induced strain analysis, Al2O3
among three oxide materials and graphene in 2D materials are favorable material
choices that offer the highest heterojunction quality. Overall, our results
offer the viable route to guide the selection of quantum tunneling materials
for myriad possible combinations of new heterostructures that can be obtained
via remote epitaxy and the UO method.",2107.01625v1
2021-08-26,Orbital Occupancy and Hybridization in Strained SrVO$_3$ Epitaxial Films,"Oxygen packaging in transition metal oxides determines the metal-oxygen
hybridization and electronic occupation at metal orbitals. Strontium vanadate
(SrVO$_3$), having a single electron in a $3d$ orbital, is thought to be the
simplest example of strongly correlated metallic oxides. Here, we determine the
effects of epitaxial strain on the electronic properties of SrVO$_3$ thin
films, where the metal-oxide sublattice is corner-connected. Using x-ray
absorption and x-ray linear dichroism at the V $L_{2,3}$ and O $K$-edges, it is
observed that tensile or compressive epitaxial strain change the hierarchy of
orbitals within the $t_{2g}$ and $e_g$ manifolds. Data show a remarkable
$2p-3d$ hybridization, as well as a strain-induced reordering of the V
$3d$($t_{2g}$, $e_g$) orbitals. The latter is itself accompanied by a
consequent change of hybridization that modulates the hybrid $\pi^*$ and
$\sigma^*$ orbitals and the carrier population at the metal ions, challenging a
rigid band picture.",2108.11718v1
2021-08-27,Low-temperature emergent neuromorphic networks with correlated oxide devices,"Neuromorphic computing which aims to mimic the collective and emergent
behavior of the brain's neurons, synapses, axons, dendrites offers an
intriguing, potentially disruptive solution to society's ever-growing
computational needs. Although much progress has been made in designing circuit
elements that mimic the behavior of neurons and synapses, challenges remain in
designing networks of elements that feature a collective response behavior. We
present simulations of networks of circuits and devices based on
superconducting and Mott-insulating oxides that display a multiplicity of
emergent states that depend on the spatial configuration of the network. Our
proposed network designs are based on experimentally known ways of tuning the
properties of these oxides using light ions. We show how neuronal and synaptic
behavior can be achieved with arrays of superconducting Josephson junction
loops, all within the same device. We also show how a multiplicity of synaptic
states could be achieved by designing arrays of devices based on hydrogenated
rare-earth nickelates. Together, our results demonstrate a new research
platform that utilizes the collective macroscopic properties of quantum
materials to mimic the emergent behavior found in biological systems.",2108.12454v1
2021-09-01,Disorder-induced ordering in gallium oxide polymorphs,"Polymorphs are common in nature and can be stabilized by applying external
pressure in materials. The pressure/strain can also be induced by the gradually
accumulated radiation disorder. However, in semiconductors, the radiation
disorder accumulation typically results in the amorphization instead of
engaging polymorphism. By studying these phenomena in gallium oxide we found
that the amorphization may be prominently suppressed by the monoclinic to
orthorhombic phase transition. Utilizing this discovery, a highly oriented
single-phase orthorhombic film on the top of the monoclinic gallium oxide
substrate was fabricated. Exploring this system, a novel mode of a lateral
polymorphic regrowth, not previously observed in solids, was detected. In
combination, these data envisage a new direction of research on polymorphs in
Ga2O3 and, potentially, for similar polymorphic families in other materials.",2109.00242v2
2021-08-30,Multi-charge Transfer from Photodoped ITO Nanocrystals,"Metal oxide nanocrystals are emerging as extremely versatile material for
addressing many of the current challenging demands of energy-conversion
technology. Being able to exploit their full potential is not only an advantage
but also a scientific and economic ambition for a more sustainable energy
technology. In this direction, photodoping of metal oxide nanocrystals is a
very notable process that allows accumulating multiple charge carriers per
nanocrystals after light absorption. The reactivity of the photodoped electrons
is currently the subject of an intense study. In this context, the possibility
to efficiently extract the stored electrons could be beneficial for numerous
processes, from photoconversion and sunlight energy storage, to photocatalysis
and photoelectrochemistry. In this work we provide, via oxidative titration and
optical spectroscopy, evidence for multi-electron transfer processes from
photodoped Sn:In2O3 nanocrystals to a widely employed organic electron acceptor
(F4TCNQ). The results of this study disclose the potential of photodoped
electrons to drive chemical reactions involving more than one electron at a
time.",2109.00499v1
2021-09-07,Luminescence of localized states in oxidized and fluorinated silica glass,"The photoluminescence of oxidized and fluorinated nominally pure silica
glasses, which have good optical transparency in the optical gap, has been
investigated under excitation by excimer lasers. The data are compared with the
data for chlorinated silica glass, as well as glass containing OH. The
excitation of localized states provides the release and capture of charge
carriers, despite the low absorption coefficient. Holes are self-trapped. The
recombination in the thermally activated or tunnel process creates luminescence
of oxygen-deficient centers. It is concluded that oxidation and fluorination do
not change the concentration of localized states, but they change the
electronic transitions of localized states to higher energies. In type III
glass with a high OH content, luminescence is suppressed by the presence of
hydrogen and appears after irradiation with photons of 7.9 eV of the F2 laser.
This can also be the evidence of existing of localized states even in such
glasses.",2109.03012v1
2021-09-11,Surface Van Hove Singularity Enabled Efficient Catalysis: The Cases of CO Oxidation and Hydrogen Evolution Reactions,"Surface Van Hove singularity (SVHS), defined as the surface states near the
Fermi level (EF) in low-dimensional systems, triggers exciting physical
phenomena distinct from bulk. We herein explore theoretically the potential
role of SVHS in catalysis taking CO oxidation reaction as prototype over
graphene/Ca2N (Gra/Ca2N) heterojunction and Pt2HgSe3 (001) surface. It is
demonstrated that both systems with SVHS could serve as an electron bath to
promote O2 adsorption and subsequent CO oxidation with low energy barriers of
0.2 ~ 0.6 eV for Gra/Ca2N and Pt2HgSe3 (001) surface. Importantly, the
catalytically active sites associated with SVHS are well-defined and uniformly
distributed over the whole surface plane, which is superior to the commonly
adopted defect or doping strategy, and further the chemical reactivity of SVHS
also can be tuned easily via adjusting its position with respect to EF. Our
study demonstrates the enabling power of SVHS, and provides novel physical
insights into the promising potential role of VHS in designing high-efficiency
catalysts.",2109.05209v1
2021-09-13,An Analytical 2-D Model of Triple Metal Double Gate Graded Channel Junctionless MOSFET with Hetero-dielectric Gate Oxide Stack,"In this paper, a two-dimensional analytical model of a laterally
graded-channel triple-metal double-gate Junctionless Field Effect Transistor
with hetero dielectric gate oxide stack consisting of SiO$_2$ and HfO$_2$ is
derived. The model illustrates higher drive current and better performance
against hazardous SCEs and HCEs in below 30 nm regime. Parabolic approximation
method is used here to construct channel potentials and electric fields by
solving 2-D Poisson's equation with applicable boundary conditions. The basic
central and surface potentials as well as central and surface electric fields
are being illustrated, Threshold voltage, DIBL, sub-threshold swing (SS) and a
compact current model have also been deduced. These parameters clearly show the
benefits of proposed graded-channel triple-metal double-gate structure with
hetero-dielectric gate oxide stack. The device has reliability in low power
applications because of its better Ion and Ioff control. Finally, the
analytical model is validated with self-consistent numerical calculations to
illustrate better performance of among available junctionless devices.",2109.09472v1
2021-10-07,A ruthenium oxide thermometer for dilution refrigerators operating down to 5 mK,"At the lowest temperatures achieved in dilution refrigerators, ruthenium
oxide resistance thermometers often saturate and therefore lose their
sensitivity. In an effort to extend the range of such temperature sensors, we
built a thermometer which maintains sensitivity to 5~mK. A key component of
this thermometer is an in situ radio frequency filter which is based on a
modern rf absorption material. We show that the use of such a filter is only
effective when it is encased in the same rf-tight enclosure as the ruthenium
oxide sensor. Our design delivers an attenuation level that is necessary to
mitigate the effects of parasitic heating of a fraction of pW present in our
circuit. Furthermore, we show that the likely origin of this parasitic heating
is the black body radiation present within the experimental space of the
refrigerator. We found that the equilibration time of the thermometer increases
rapidly as the temperature is lowered; below 5~mK this thermometer becomes
impractical because of the prohibitively long equilibration times.",2110.03788v1
2021-10-08,Emulating homoeostatic effects with metal-oxide memristors T-dependence,"Memristor technologies have been rapidly maturing for the past decade to
support the needs of emerging memory, artificial synapses, logic gates and
bio-signal processing applications. So far, however, most concepts are
developed by exploiting the tuneable resistive state of memristors with other
physical characteristics being ignored. Here, we report on the thermal
properties of metal-oxide memristors and demonstrate how these can be used to
emulate a fundamental function of biological neurons: homeostasis. We show that
thermal control mechanisms, frequently dismissed for their generally slow and
broad-brush granularity, may in fact be an appropriate approach to emulating
similarly slow and broad-brush biological mechanisms due to their extreme
simplicity of implementation. We further demonstrate that metal-oxide
memristors can be utilised as thermometers and exhibit a programmable
temperature sensitivity. This work paves the way towards future systems that
employ the rich physical properties of memristors, beyond their electrical
state-tuneability, to power a new generation of advanced electronic devices.",2110.04102v1
2021-10-11,Activity of Pd$_{\rm n}$ (n = 1-5) Clusters on Alumina Film on Ni$_3$Al(111) for CO Oxidation: A Molecular Beam Study,"Single atom catalyst (SAC) is a vivid new area of research in catalysis.
However, the activity in CO oxidation of isolated Pt or Pd atoms, generally
supported on an oxide powder, is still controversial. Furthermore, the steady
state activity of few atoms clusters is still not yet quantitatively known. In
this work we study, by molecular beam reactive scattering (MBRS), the activity
of Pd$_{\rm n}$ ($n$ = 1-5) clusters, grown on a nanostructured alumina films
on a Ni$_3$Al(111) surface. It is shown that the single atoms are not active at
473 K but they diffuse and coalesce at 533K forming larger clusters. The
activity of a cluster is proportional to the number of atoms it contains
(n=2-5). At 533 K, the activity per (surface-) atom, which is the turnover
frequency (TOF), is constant. Its value is close to those obtained for large
clusters of 181$\pm$13 atoms and Pd (111) extended surfaces, in the same
experimental conditions.",2110.05227v1
2021-10-10,Dynamic Control of Plasmonic Colors by Voltage Actuation MEMS Cantilevers for Optical Display Applications,"Conventional optical displays using ITO (indium tin oxide) and LC (liquid
crystal) materials present a lot of challenges in terms of long-term
sustainability. We show here how it is possible to generate a cost effective
and CMOS compatible fast and full range electrically controlled RGB color
display by combining transmission based plasmonic metasurfaces with MEMS
(Microelectromechanical systems) technology, using only two common materials:
Aluminum and silicon oxide. White light is filtered into red, green, and blue
components by plasmonic metasurfaces made of aluminum nanohole arrays, and the
transmission through each color filter is modulated by MEMS miniaturized
cantilevers fabricated with aluminum and silicon oxide on top of the color
filters. We show that the relative transmission of a color subpixel can be
freely modulated from 35% to 100%. Our pixels can also operate well above
800Hz, enabling future ultrafast displays. Our work provides a road to future
circular economic goals by exploiting advances in structural colors and MEMS
technologies to innovate optical displays.",2110.12836v2
2021-10-27,Emergent phenomena at oxide interfaces studied with standing-wave photoelectron spectroscopy,"Emergent phenomena at complex-oxide interfaces have become a vibrant field of
study in the past two decades due to the rich physics and a wide range of
possibilities for creating new states of matter and novel functionalities for
potential devices. Electronic-structural characterization of such phenomena
presents a unique challenge due to the lack of direct yet non-destructive
techniques for probing buried layers and interfaces with the required
Angstrom-level resolution, as well as element and orbital specificity. In this
review article, we survey several recent studies wherein soft x-ray
standing-wave photoelectron spectroscopy, a relatively newly developed
technique, is used to investigate buried oxide interfaces exhibiting emergent
phenomena such as metal-insulator transition, interfacial ferromagnetism, and
two-dimensional electron gas. Advantages, challenges, and future applications
of this methodology are also discussed.",2110.14458v1
2021-12-15,Discovery of a reversible redox-induced order-disorder transition in a 10-cation compositionally complex ceramic,"This study discovers a reversible order-disorder transition (ODT) in a
10-cation compositionally complex ceramic,
(Nd0.15Pr0.15Dy0.8Ho0.8Er0.8Ti0.2Yb0.1Hf0.1Zr0.1Nb0.8)O7-delta, induced via
annealing in oxidized vs. reduced environments at 1600C. Notably, the 10-cation
oxide remains a homogenous single-phase high-entropy solid solution before and
after the ODT in the pyrochlore vs. fluorite structure that can be quenched.
In-situ neutron diffraction reveals the oxygen vacancy formation and atomic
displacement during this ODT. The temperature dependence of thermal
conductivity is altered by the ODT. This study reveals a new pathway to induce
ODT via a redox transition to tailor the properties of compositionally complex
fluorite-based oxides.",2112.07979v1
2022-01-04,Two-dimensional superconductivity at the surfaces of KTaO3 gated with ionic liquid,"The recent observation of superconductivity at the interfaces between KTaO3
and EuO (or LaAlO3) offers a new example of emergent phenomena at oxide
interfaces. This superconductivity exhibits an unusual strong dependence on the
crystalline orientation of KTaO3 and its superconducting transition temperature
Tc is nearly one order of magnitude higher than that of the seminal
LaAlO3/SrTiO3 interface. To understand its mechanism, it is crucial to address
if the formation of oxide interfaces is indispensable for the presence of
superconductivity. Here, by exploiting ionic liquid (IL) gating, we obtain
superconductivity at KTaO3 (111) and (110) surfaces with Tc up to 2.0 K and 1.0
K, respectively. This oxide-interface-free superconductivity gives a clear
experimental evidence that the essential physics of KTaO3 interface
superconductivity lies in the KTaO3 surfaces doped with electrons. Moreover,
the ability to control superconductivity at surfaces with IL provides a simple
way to study the intrinsic superconductivity in KTaO3.",2201.00990v1
2022-01-13,Doping-Dependent Optical Response of a Hybrid Transparent Conductive Oxide/Plasmonic Medium,"Understanding the interaction between plasmonic nanoparticles and transparent
conductive oxides is instrumental to the development of next-generation
photovoltaic, opto-electronic and energy-efficient solid-state lighting
devices. We investigated the optical response of hybrid media composed of gold
nanoparticles deposited on aluminum-doped zinc oxide thin films with varying
doping concentration by spectroscopic ellipsometry. The dielectric functions of
bare AZO were addressed first, revealing doping-induced effects such as the
band-gap shift and the appearance of free carriers. In the hybrid media, a
blueshift of the localized surface plasmon resonance of Au NPs as a function of
increasing Al-doping of the substrate was observed, ascribed to the occurrence
of a charge transfer between the two materials and the doping-dependent
variation of the polarizability of the substrate.",2201.07002v1
2022-01-31,A Search for Alternative Solid Rocket Propellant Oxidizers,"Carbon-based caged and heterocyclic compounds tend to have strained molecular
structures leading to high heats of formation and energetic behavior. In the
current paper, molecular modelling calculations for 10 caged compounds of this
type along with 2 strained aliphatic compounds and 4 simple cyclic chains are
presented in view of their possible use as oxidizers in propulsion
applications. Density functional theory (B3LYP) was employed for the geometry
optimization of the proposed molecular structure using the 6-311++G(d,p) basis
set. Heats of formation of the compounds were calculated using the molecular
modeling results and their specific impulses were computed using the NASA CEA
[1] software package to evaluate their potentials as propellant oxidizers.",2202.02370v1
2022-02-03,Single nanosized graphene/TiOx multi-shells on TiO2 core via rapid-concomitant reaction pathway on metal oxide/polymer interface,"A novel design has been proposed for a facile and rapid build-up of highly
tailorable nanostructured multishells on metal oxide particles
(graphene/TiOx@TiO2) under a dry inert atmosphere to maximize the visible-light
photocatalytic performance. We also thoroughly and systematically investigated
the as-prepared nanostructured particle surface and the mechanisms of the
extraordinary in-situ graphene growth on the TiOx@TiO2 nanoparticles achieved
by a rapid-concomitant reaction in the metal oxide (TiO2)/polymer (polymethyl
methacrylate) interface under microwave irradiation. The as-prepared composite
materials are also found to perform a better photocatalytic activity in
comparison to the traditional synthesis pathway for degradation of organic
pollutants under visible light, associated with the synergetic effects of
homo-/hetero-junction on TiO2.",2202.06746v1
2022-02-05,New frontiers in characterising ZrB$_2$-MoSi$_2$ ultra-high temperature ceramics,"The structure-property(S-P) correlation,especially in the context of
high-temperature oxidation, in ZrB$_2$-MoSi$_2$ based Ultra High-Temperature
Ceramic Matrix Composites (UHTCMCs) have been extensively investigated for
quite some time since the last 25 years and a countless amount of published
data is presently available in this field.On the other hand,emergence of
correlative microscopy [1] has completely revolutionised the world of materials
research, in a number of ways.However,owing to the challenges of sample
preparation, there has hardly been a literature aimed at understanding the
aforesaid phenomenon of understanding S-P correlation,based on oxidation in
ZrB$_2$-MoSi$_2$ UHTCMCs,which,in future, may open up new frontiers of research
in UHTCMCs.The present review intends to discuss some of the most interesting
data published existing in this field and intends to provide a brief overview
of the challenges associated along with some of the currently unexplored
avenues in this field,especially in terms of fundamental research.However,in
view of the enormous amount of research already done in understanding
oxidation-based S-P correlation in these materials,the author does not claim to
address all the issues which may be associated with understanding the same.",2202.11162v1
2022-02-23,Metalated Porous-Organic-Polymer Renders Mustard-Gas Simulant Harmless: Core Planarity Matters,"The presence of open active metal sites in Metal-Organic Frameworks (MOFs)
exhibit higher catalytic activity. However, rational accomplishment of MOFs in
heterogeneous catalysis is limited due to coordination bonds. Recently balanced
characteristic feature with combination of both the covalent bonds (structural
stability) and open metal sites (single site catalysis) introduced an entirely
organic alternative architecture named as Metalated Porous-Organic-Polymers
(M-POPs). In this contribution, we demonstrate successful construction of two
Fe-POPs (Fe-Tt-POP & Fe-Rb-POP) by ternary copolymerization approach for
catalytic oxidative decontamination of different sulfur-based mustard gas
simulants. Fe-Tt-POP exhibited superior catalytic performance for oxidation of
the thioanisole (TA) studied in terms of conversion (99% after 13 h) in
comparison with Fe-Rb-POP (43% after 13h). The remarkable difference in the
mechanistic pathways towards catalytic performance for oxidation of TA was
investigated by in situ operando Diffuse Reflectance Infrared Fourier Transform
Spectroscopy (DRIFTS) analysis, complemented by Density Functional Theory (DFT)
computational study.",2202.11677v1
2022-02-26,Predicting the formation and stability of oxide perovskites by extracting underlying mechanisms using machine learning,"The optimization of properties of perovskite oxides has drawn interest on
account of their diverse areas of application. In this work, the hierarchical
clustering technique is used to reduce the multi-collinearity among selected
features from literature that are reported to have an effect on perovskite
formation and stability. Operating on the vast composition space of double
oxide perovskite compositions available in literature and online repositories,
in this manuscript, an attempt has been made to extract the relationship
between the composition and structure to predict their formability and
stability. Machine learning (ML) classifiers are trained on these datasets to
predict novel stable perovskite compositions. The study uses a vast feature
space to narrow down the most important factors affecting the formability and
stability in perovskite compounds. It also identifies stable compositions that
have band gaps suitable for photovoltaic and photocatalytic applications. The
developed random forest (RF)-based models may be extended to include the
implications beyond photosensitive applications by focusing on the
physico-chemical mechanisms driving the phenomena behind each application.",2202.13087v1
2022-02-28,Hybrid Molecular Beam Epitaxy of Ge-based Oxides,"Germanium-based oxides such as rutile GeO2 are garnering attention owing to
their wide band gaps and the prospects for ambipolar doping for application in
high-power devices. Here, we present the use of germanium tetraisopropoxide
(GTIP) (an organometallic chemical precursor) as a source of Ge for the
demonstration of hybrid molecular beam epitaxy (MBE) for Ge-containing
compounds. We use Sn1-xGexO2 and SrSn1-xGexO3 as model systems to demonstrate
this new synthesis method. A combination of high-resolution X-ray diffraction,
scanning transmission electron microscopy, and X-ray photoelectron spectroscopy
confirms the successful growth of epitaxial rutile Sn1-xGexO2 on TiO2(001)
substrates up to x = 0.54 and coherent perovskite SrSn1-xGexO3 on GdScO3(110)
substrates up to x = 0.16. Characterization and first-principles calculations
corroborate that Ge preferentially occupies the Sn site, as opposed to the Sr
site. These findings confirm the viability of the GTIP precursor for the growth
of germanium-containing oxides by hybrid MBE, and thus open the door to
high-quality perovskite germanate films.",2202.13494v1
2022-03-06,Scaled indium oxide transistors fabricated using atomic layer deposition,"In order to continue to improve integrated circuit performance and
functionality, scaled transistors with short channel lengths and low thickness
are needed. But the further scaling of silicon-based devices and the
development of alternative semiconductor channel materials that are compatible
with current fabrication processes is challenging. Here we report
atomic-layer-deposited indium oxide transistors with channel lengths down to 8
nm, channel thicknesses down to 0.5 nm and equivalent dielectric oxide
thickness down to 0.84 nm. Due to the scaled device dimensions and low contact
resistance, the devices exhibit high on-state currents of 3.1 A/mm at a drain
voltage of 0.5 V and a transconductance of 1.5 S/mm at a drain voltage 1 V. Our
devices are a promising alternative channel material for scaled transistors
with back-end-of-line processing compatibility.",2203.02869v1
2022-03-09,Modelling dielectric loss in superconducting resonators: Evidence for interacting atomic two-level systems at the Nb/oxide interface,"While several experiments claim that two-level system (TLS) defects in
amorphous surfaces/interfaces are responsible for energy relaxation in
superconducting resonators and qubits, none can provide quantitative
explanation of their data in terms of the conventional noninteracting TLS
model. Here a model that interpolates between the interacting and
noninteracting TLS loss tangent is proposed to perform numerical analysis of
experimental data and extract information about TLS parameters and their
distribution. As a proof of principle, the model is applied to TESLA cavities
that contain only a single lossy material in their interior, the
niobium/niobium oxide interface. The best fits show interacting TLSs with a
sharp modulus of electric dipole moment for both thin (5 nm) and thick (100 nm)
oxides, indicating that the TLSs are ""atomic"" instead of ""glassy"". The proposed
method can be applied to other devices with multiple material interfaces and
substrates, with the goal of elucidating the nature of TLSs causing energy loss
in resonators and qubits.",2203.05054v3
2022-03-14,In situ study of zinc peroxide decomposition to zinc oxide by X-ray absorption spectroscopy and reverse Monte-Carlo simulations,"The Zn K-edge X-ray absorption spectroscopy has been used to investigate in
situ the decomposition of zinc peroxide (ZnO$_2$) to zinc oxide (ZnO).
Principal component and linear combination analyses of the EXAFS spectra have
been employed to identify the phase composition of the oxide upon heating to
900$^\circ$C. Only the ZnO$_2$ phase has been found up to 180$^\circ$C, whereas
only the nanocrystalline ZnO phase has occurred above 250$^\circ$C. Detailed
structural information on the temperature dependence of the local environment
of zinc atoms has been obtained using the reverse Monte Carlo simulations. A
strong increase of disorder has been found upon approaching the decomposition
temperature, evidenced by the broadening of Zn-O and Zn-Zn pair distribution
functions and related mean-square relative displacements.",2203.07170v2
2022-03-14,Water Oxidation and Hydrogen Evolution with Organic Photooxidants: A Theoretical Perspective,"In this perspective, we discuss a novel water-splitting scenario, namely the
direct oxidation of water molecules by organic photooxidants in hydrogen-bonded
chromophore-water complexes. In comparison with the established scenario of
semiconductor-based water splitting, the distance of electron transfer
processes is thereby reduced from mesoscopic scales to the {\AA}ngstr{\o}m
scale and the time scale is reduced from milliseconds to femtoseconds, which
suppresses competing loss processes. The concept is illustrated by
computational studies for the heptazine-H2O complex. The excited-state
landscape of this complex has been characterized with ab initio
electronic-structure methods and the proton-coupled electron-transfer dynamics
has been explored with nonadiabatic dynamics simulations. A unique feature of
the heptazine chromophore is the existence of a low-lying and exceptionally
long-lived 1{\pi}{\pi}* state in which a substantial part of the photon energy
can be stored for hundreds of nanoseconds and is available for the oxidation of
water molecules. The calculations reveal that the absorption spectra and the
photochemical functionalities of heptazine chromophores can be systematically
tailored by chemical substitution. The options of harvesting hydrogen and the
problems posed by the high reactivity of OH radicals are discussed.",2203.07176v1
2022-03-18,Implications of phonon anisotropy on thermal conductivity of fluorite oxides,"Fluorite oxides are attractive ionic compounds for a range of applications
with critical thermal management requirements. In view of recent reports
alluding to anisotropic thermal conductivity in this face-centered cubic
crystalline systems, we perform a detailed analysis of the impact of
direction-dependent phonon group velocities and lifetimes on the thermal
transport of fluorite oxides. We demonstrate that the bulk thermal conductivity
of this class of materials remains isotropic despite notable anisotropy in
phonon lifetime and group velocity. However, breaking the symmetry of the
phonon lifetime under external stimuli including boundary scattering present in
nonequilibrium molecular dynamics simulations of finite size simulation cell
gives rise to apparent thermal conductivity anisotropy. We observe that for
accurate determination of thermal conductivity, it is important to consider
phonon properties not only along high symmetry directions commonly measured in
inelastic neutron or x-ray scattering experiments but also of those along lower
symmetry. Our results suggests that certain low symmetry directions have a
larger contribution to thermal conductivity compared to high symmetry ones.",2203.09923v2
2022-04-11,Nonlinear optical response of ferroelectric oxides: first-principles calculations within the time-domain and the frequency-domain,"The second and third order nonlinear susceptibilities of the ferroelectric
oxides LiNbO$_3$, LiTaO$_3$, and KNbO$_3$ are calculated from first principles.
Two distinct methodologies are compared, one approach is based on a
perturbative approach within the frequency-domain, another on the
time-evolution of the electric polarization. The frequency dependence of the
second harmonic coefficients of the ferroelectric phase of LiNbO$_3$ calculated
within the two approaches is in excellent agreement. This is further validated
by experimental data for LiNbO$_3$ and LiTaO$_3$, measured for an incident
range of photon energies between 0.78 eV and 1.6 eV. The real-time based
approach is furthermore employed to estimate the third order nonlinear
susceptibilities of all investigated ferroelectric oxides. We further show that
the quasiparticle effects, considered by means of a scissors-shift in
combination with the the computationally efficient independent particle
approximation, result in a shift all spectral features towards higher energies
and decrease the magnitude of the optical nonlinearities. The energy of the
main resonances in the hyperpolarizabilities suggests that the spectra can be
understood by multi-photon adsorption within the fundamental bandgap for all
investigated materials.",2204.04985v1
2022-05-10,Effect of substrate temperature on the optoelectronic properties of DC magnetron sputtered copper oxide films,"Copper oxide thin films are deposited on quartz substrates by DC magnetron
sputtering and the effect of deposition temperature on their optoelectronic
properties is examined in detail. Scanning Electron Microscopy (SEM), X-ray
diffraction (XRD) analysis, Raman spectroscopy, UV-Vis spectroscopy, and
four-probe sheet resistance measurements are used to characterize the surface
morphology, structural, optical, and electrical properties respectively.
Deposition is carried out at room temperature and between 200 and 300 {\deg}C.
XRD analysis indicates that the oxide formed is primarily Cu$_2$O and the
absorption spectra show the films have a critical absorption edge at around 300
nm. The sheet resistance gradually decreases with increase in deposition
temperature thereby increasing the conductivity of these thin films. Also
observed is the increase in band gap from 2.20 eV for room temperature
deposition to 2.35 eV at 300 {\deg}C. The optical band gap and the variation of
sheet resistance with temperature shows that the microstructure plays a vital
role in their behavior. These transformation characteristics are of huge
technological importance having variety of applications including transparent
solar cell fabrication.",2205.05615v1
2022-05-19,Ultrafast structural color change in indium tin oxide/titanium dioxide 1D photonic crystal,"Photonic crystals can integrate plasmonic materials such as indium tin oxide
(ITO) in their structure. Exploiting ITO plasmonic properties it is possible to
tune the photonic band gap of the photonic crystal upon the application of an
external stimuli. In this work, we have fabricated a one-dimensional multilayer
photonic crystal via radiofrequency sputtering and we have triggered its
optical response with ultrafast pump-probe spectroscopy. Upon photoexcitation
we observe a change in the refractive index of indium tin oxide. Such effect
has been used to create a photonic crystal that change its photonic bandgap in
an ultrafast time scale. All optical modulation in the visible region, that can
be tuned by designing the photonic crystal, has been demonstrated.",2205.09694v1
2022-06-09,Perspective: Molecular beam epitaxy of antiperovskite oxides,"Antiperovskites, or inverse perovskites, have recently emerged as a material
class with a plethora of promising electronic properties. This perspective
describes the molecular beam epitaxy (MBE) growth of oxide antiperovskites
Sr$_3$PbO and Sr$_3$SnO. We show that MBE offers great potential not only in
growing antiperovskites with high structural quality, but also in providing a
means to seamlessly connect with advanced characterization tools, including
x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED),
reflection high-energy electron diffraction (RHEED), and scanning tunneling
microscopy (STM), to facilitate the analyses of their intrinsic properties. The
initial results point toward the feasibility of atomically controlled
antiperovskite growth, which could open doors to study topological and
correlated electronic states in an electronic environment quite distinct from
what is available in conventional complex oxides.",2206.04768v1
2022-07-07,Oxygen vacancy dynamics in Pt/TiOx/TaOy/Pt memristors: exchange with the environment and internal electromigration,"Memristors are expected to be one of the key building blocks for the
development of new bio-inspired nanoelectronics. Memristive effects in
transition metal oxides are usually linked to the electromigration at the
nanoscale of charged oxygen vacancies (OV). In this paper we address, for
Pt/TiOx/TaOy/Pt devices, the exchange of OV between the device and the
environment upon the application of electrical stress. From a combination of
experiments and theoretical simulations we determine that both TiOx and TaOy
layers oxidize, via environmental oxygen uptake, during the electroforming
process. Once the memristive effect is stabilized (post-forming behavior) our
results suggest that oxygen exchange with the environment is suppressed and the
OV dynamics that drives the memristive behavior is restricted to an internal
electromigration between TiOx and TaOy layers. Our work provides relevant
information for the design of reliable binary oxide memristive devices.",2207.03538v1
2022-07-12,Digital Twins solve the mystery of Raman spectra of parental and reduced graphene oxides,"A still amazing identity of the D-G doublet Raman spectra of parental and
reduced graphene oxides is considered from the digital twins viewpoint. About
thirty DTs, presenting different aspects of the GO structure and properties,
were virtually synthesized using atomic spin-density algorithm, which allowed
reliably displaying reasons for this extraordinary spectral feature. In both
cases, it was established that the D-G doublets owe their origin to the sp3-sp2
C-C stretchings, respectively. This outwardly similar community of the doublets
origin of GO and rGO is thoroughly analyzed to reveal different grounds of the
feature in the two cases. Multilayer packing of individual rGO molecules in
stacks, in the first case, and spin-influenced prohibition of the 100%
oxidative reaction, the termination of which is accompanied with a particular
set of highly ordered by length sp3- and sp2 C-C bonds, protecting the carbon
carcass from destruction caused by the stress induced sp2-to-sp3
transformation, in the second, are the main reasons. The DT concept has been
realized on the basis of virtual vibrational spectrometer HF Spectrodyn.",2207.05744v1
2022-07-28,Electronic interaction $U_{pp}$ on oxygen $p$ orbitals in oxides: Role of correlated orbitals on the example of UO$_2$ and TiO$_2$,"We carry out a detailed study of the role of electronic interaction on $p$
oxygen orbitals in a Mott insulator oxide (UO$_2$) and a charge transfer oxide
(TiO$_2$). First, we calculate values of effective interactions \Uff, \Upp{}
and $U_{fp}$ in UO$_2$ and \Udd{}, \Upp{} and $U_{dp}$ in TiO$_2$. Second, we
analyze the role of electronic interactions \Upp{} on $p$ orbitals of oxygen in
spectral and structural properties. Finally, we show that this role depends
strongly on the definition of correlated orbitals and that using Wannier
functions leads to more physical results for spectral and structural
properties.",2207.14137v2
2022-08-11,Superconductivity in epitaxially grown LaVO3/KTaO3(111) heterostructures,"Complex oxide heterointerfaces can host a rich of emergent phenomena, and
epitaxial growth is usually at the heart of forming these interfaces. Recently,
a strong crystalline-orientation-dependent two-dimensional superconductivity
was discovered at interfaces between KTaO3 single-crystal substrates and films
of other oxides. Unexpectedly, rare of these oxide films was epitaxially grown.
Here, we report the existence of superconductivity in epitaxially grown
LaVO3/KTaO3(111) heterostructures, with a superconducting transition
temperature of ~0.5 K. Meanwhile, no superconductivity was detected in the
(001)- and (110)-orientated LaVO3/KTaO3 heterostructures down to 50 mK.
Moreover, we find that for the LaVO3/KTaO3(111) interfaces to be conducting, an
oxygen-deficient growth environment and a minimum LaVO3 thickness of ~0.8 nm (~
2 unit cells) are needed.",2208.05712v3
2022-08-16,Strain effect on the ground-state structure of Sr2SnO4 Ruddlesden-Popper oxides,"Ruddlesden-Popper (RP) oxides (A$_{n+1}$B$_n$O$_{3n+1}$) comprised of
perovskite (ABO$_3$)$_n$ slabs can host a wider variety of structural
distortions than their perovskite counterparts. This makes accurate structural
determination of RP oxides more challenging. In this study, we investigate the
structural phase diagram of $n=1$ RP Sr$_2$SnO$_4$, one of alkaline earth
stannates that are promising for opto-electronic applications by using group
theory-based symmetry analysis and first-principles calculations. We explore
the symmetry breaking effects of different dynamical instabilities, predict the
energies of phases they lead to, and take into account different (biaxial
strain and hydrostatic pressure) boundary conditions. We also address the
effect of structural changes on the electronic structure and find that
compressive biaxial strain drives Sr$_2$SnO$_4$ into a regime with wider
bandgap and lower electron effective mass.",2208.07481v2
2022-08-30,Optimizing nucleation layers for the integration of ferroelectric HZO on CVD-grown graphene,"Direct integration of ferroelectric Hf0.5Zr0.5O2 (HZO) on the inert surface
of graphene is challenging. Here, using nucleation layers to promote atomic
layer deposition of HZO was investigated. Different metals were deposited as
nucleation layers via dc sputtering. Ta, which oxidizes in air to form a
sub-stoichiometric oxide, was compared to Pt, which offers a more stable
electrode. For thicker interlayers, Ta leads to unstable switching behavior of
the HZO film. Conversely, at smaller thicknesses, a higher Pr can be achieved
with an oxidized Ta interlayer. In both cases, Pt offers higher endurance. The
choice of interlayer may strongly depend on the required application.",2208.14061v2
2022-09-09,CO oxidation by Pt2/Fe3O4: metastable dimer and support configurations facilitate lattice oxygen extraction,"Heterogeneous catalysts based on sub-nanometer metal clusters often exhibit
strongly size-dependent properties, and the addition or removal of a single
atom can make all the difference. Identifying the most active species and
deciphering the reaction mechanism is extremely difficult, however, because it
is often not clear how the catalyst evolves in operando. Here, we utilize a
combination of atomically resolved scanning probe microscopies, spectroscopic
techniques, and density functional theory (DFT)-based calculations to study CO
oxidation by a model Pt/Fe3O4(001) single-atom catalyst. We demonstrate that
(PtCO)2 dimers, formed dynamically through the agglomeration of mobile
Pt-carbonyl species, catalyse a reaction involving the oxide support to form
CO2. Pt2 dimers produce one CO2 molecule before falling apart into two adatoms,
releasing the second CO. Interestingly, Olattice extraction only becomes facile
when both the Pt-dimer and the Fe3O4 support can access metastable
configurations, suggesting that substantial, concerted rearrangements of both
cluster and support must be considered for reactions occurring at elevated
temperature.",2209.04222v1
2022-09-06,Study of uranium oxide milling in order to obtain nanostructured UCx target,"A R&D program is developed at the ALTO facility to provide new beams of
exotic neutron-rich nuclei, as intense as possible. In the framework of
European projects, it has been shown that the use of refractory targets with
nanometric structure allows us to obtain beams of nuclei unreachable until now.
The first parameter to be controlled in the processing to obtain targets with a
homogeneous nanostructure is the grinding of uranium dioxide, down to 100 nm
grain size. In this study, dry and wet grinding routes are studied and the
powders are analyzed in terms of phase stabilization, specific surface area and
grain morphology. It appears that the grinding, as well dry as wet, leads to
the decrease of the particle size. The oxidation of UO2 is observed whatever
the grinding. However, the dry grinding is the most efficient and leads to the
oxidation of UO2 into U4O9 and U3O7 whose quantities increase with the grinding
time while crystallite sizes decrease.",2209.05230v1
2022-09-13,Ab Initio Calculations of XUV Ground and Excited States for First-Row Transition Metal Oxides,"Transient X-ray spectroscopies have become ubiquitous in studying
photoexcited dynamics in solar energy materials due to their sensitivity to
carrier occupations and local chemical or structural dynamics. The
interpretation of solid-state photoexcited dynamics, however, is complicated by
the core-hole perturbation and the resulting many-body dynamics. Here, an ab
initio, Bethe-Salpeter equation (BSE) approach is developed that can
incorporate photoexcited state effects for solid-state materials. The extreme
ultraviolet (XUV) absorption spectra for the ground, photoexcited, and
thermally expanded states of first row transition metal oxides - $TiO_2,
\alpha-Cr_2O_3, \beta-MnO_2, \alpha-Fe_2O_3, Co_3O_4, NiO, CuO, and ZnO$ - are
calculated to demonstrate the accuracy of this approach. The theory is used to
decompose the core-valence excitons into the separate components of the X-ray
transition Hamiltonian for each of the transition metal oxides investigated.
The decomposition provides a physical intuition about the origins of XUV
spectral features as well as how the spectra will change following
photoexcitation. The method is easily generalized to other K, L, M, and N edges
to provide a general approach for analyzing transient X-ray absorption or
reflection data.",2209.06347v1
2022-09-16,Rashba-like spin-orbit interaction and spin texture at the KTaO$_\text{3}$ (001) surface from DFT calculations,"Rashba-like spin-orbit interaction at oxide heterostructures emerges as a
much sought-after feature in the context of oxide spintronics and
spin-orbitronics. KTaO$_3$ (KTO) is one of the best substrates available for
the purpose, owing to its strong spin-orbit interaction and alternating $+1|-1$
charged layers along the (001) direction. Employing first-principles
calculations within density functional theory (DFT) and proposing a possible
electrostatic model for charge transfer to the surfaces of KTO slabs, we
comprehensively analyze Rashba-like spin-orbit interaction with the help of
three-dimensional band dispersion, isoenergetic contours, and projected spin
textures $-$ all directly obtained from our DFT results $-$ in a thin
insulating slab and a conducting thick slab of KTO. Our results reveal
reasonably strong linear Rashba interaction with no signature of Dresselhaus or
higher order Rashba interactions in the systems considered here. The rigorous
analysis presented here may be crucial for future developments in oxide
spintronics.",2209.07723v1
2022-10-27,Zeolite-based photocatalysts immobilized on aluminum support by plasma electrolytic oxidation,"The preparation and properties of zeolite-containing oxide coatings obtained
by plasma electrolytic oxidation are investigated and discussed. Pure and
Ce-exchanged natural (clinoptilolite) and synthetic (13X) zeolites are
immobilized on aluminum support from silicate-based electrolyte. Obtained
coatings are characterized with respect to their morphology, phase and chemical
composition, photocatalytic activity and anti-corrosion properties. It is
observed that all mentioned properties of obtained coatings are dependent on
processing time and type of immobilized zeolite. Coatings with Ce-exchanged
zeolite show higher photocatalytic activity and more effective corrosion
protection than those with pure zeolite. The highest photocatalytic activity is
observed for coatings processed in pulsed a DC regime for 30 minutes containing
Ce-exchanged 13X zeolite, followed by those containing Ce-exchanged
clinoptilolite. Pronounced anti-corrosion properties feature almost all samples
containing Ce-exchanged 13X zeolite.",2210.15455v1
2022-11-01,Programmable Charge Trap for Junction-less selective extraction of holes in Solar Cells,"Selective extraction of photo-generated carriers is a fundamental challenge
in solar cells which is usually achieved through junctions with the associated
doping as well as band offset differences. In this context, here we propose a
new paradigm for selective extraction for majority carriers through novel usage
of the programmable charge trap which comprises of Oxide-Nitride-Oxide (ONO)
stack and has the primary function of holding electrically injected charge.
Through detailed numerical simulations, here we show that such a charge trap
with an additional metal contact can (i) compensate for efficiency loss due to
sub-optimal passivation and sub-optimal hole selectivity in homojunction as
well as transition metal oxide-based heterojunction solar cells and (ii) can
also function as a standalone hole selection scheme. The proposed scheme, with
its easy integration and the capability of programmable compensation of
performance loss, is of interest to the photovoltaic community.",2211.00540v1
2022-11-04,"Ferroelectric Switching Pathways and Domain Structure of SrBi$_2$(Ta,Nb)$_2$O$_9$ from First Principles","Several families of layered perovskite oxide ferroelectrics exhibit a
coupling between polarization and structural order parameters, such as
octahedral rotation distortions. This coupling provides opportunities for novel
electric field-based manipulation of material properties, and also stabilizes
complex domain patterns and domain wall vortices. Amongst layered perovskites
with such coupled orders, the Aurivillius-phase oxides SrBi$_2B_2$O$_9$
($B$=Ta, Nb) are well-known for their excellent room temperature ferroelectric
performance. This work combines group theoretic analysis with density
functional theory calculations to examine the ferroelectric switching processes
of SrBi$_2B_2$O$_9$. Low-energy two-step ferroelectric switching paths are
identified, with polarization reversal facilitated by structural order
parameter rotations. Analysis of the domain structure reveals how the relative
energetics of the coupled order parameters translates into a network of several
distinct domain wall types linked by domain wall vortex structures. Comparisons
are made between the ferroelectric switching and domain structure of
SrBi$_2B_2$O$_9$ and those of the layered $n$=2 Ruddlesden-Popper hybrid
improper ferroelectrics. The results provide new insight into how ferroelectric
properties may be optimized by engineering the complex crystal structures of
Aurivllius-phase oxides.",2211.02735v1
2022-11-12,Contact Angle Studies on Porous Silicon: Evidence for Heterogeneous Wetting and Implications of Oxidation,"A study of wetting was carried out on porous silicon films with pore
diameters spanning three orders of magnitude. Water contact angle measurements
on adjoining porous and nonporous regions yielded Wenzel roughness ratios that
were either unphysical (less than unity) or unrealistically low when compared
to those expected from specific surface area considerations. Moreover, results
obtained from a sample consisting of a microporous film on a macroporous layer
gave contact angles that were very similar to those found on films consisting
of only a single microporous layer, contrary to what would be expected for
complete filling of the pores by liquid. Values for wetted surface fractions
calculated from the Cassie-Baxter model are unreasonably high for micro- ,
meso- and oxidized macroporous films considering their porosities, while
relatively oxide-free macroporous films give wetted surface fractions in accord
with those expected based on film porosity. Collectively, these results show
that the predominant mode of wetting on these films is heterogeneous.",2211.06554v1
2022-11-15,Intergranular corrosion in evolving media: experiment and modeling by cellular automata,"We investigate the impact of the oxidizing character of the nitric medium on
the evolution of the intergranular corrosion of a stainless steel. In two
different oxidizing conditions (""severe"" and ""soft""), the corroded surface of
the steel reaches a different steady state: the oxide is thicker, the
intergranular grooves are thinner and the surface area is larger in the
""severe"" conditions than in the ""soft"" ones. Then we investigate the effect of
an alternative ""severe then soft"" corrosion sequence. We show that the system
re-adapts to the ""soft"" conditions without memory effect from the previous
""severe"" ones. bstra",2211.08276v1
2022-12-05,A study of PbF2 nanoparticles crystallization mechanism in mixed oxyde-fluoride glasses,"The heat-treated oxyfluoride glasses with different contents of thulium Tm3+
and holmium Ho3+ ions have been studied using small-angle X-ray scattering and
diffraction. With an increase in relative concentration of added Ho2O3 and
Tm2O3 oxides, the growing in the average size of both nanoparticles and local
density fluctuations in the glass matrix is observed. In addition, at high
relative concentrations of initial rare-earth oxides, the appearance of a
crystalline cubic phase PbF2:Tm-Ho is observed, which can provide a source of
up-conversion luminescence in the studied glass materials. A change in the
concentration of the initial Ho2O3 and Tm2O3 oxides does not effect on a
morphology and fractal dimension of the formed luminescence nanoparticles. The
structural aspects of nanoparticle formation with up-conversion luminescence
phenomenon are discussed.",2212.02189v1
2022-12-15,Quantitative 3D mapping of chemical defects at charged grain boundaries in a ferroelectric oxide,"Polar discontinuities and structural changes at oxide interfaces can give
rise to a large variety of electronic and ionic phenomena. Related effects have
been intensively studied in epitaxial systems, including ferroelectric domain
walls and interfaces in superlattices. Here, we investigate the relation
between polar discontinuities and the local chemistry at grain boundaries in
polycrystalline ferroelectric ErMnO3. Using orientation mapping and different
scanning probe microscopy techniques, we demonstrate that the polycrystalline
material develops charged grain boundaries with enhanced electronic
conductance. By performing atom probe tomography measurements, we find an
enrichment of erbium and a depletion of oxygen at all grain boundaries. The
observed compositional changes translate into a charge that exceeds possible
polarization-driven effects, demonstrating that structural phenomena rather
than electrostatics determine the local chemical composition and related
changes in the electronic transport behavior. The study shows that the charged
grain boundaries behave distinctly different from charged domain walls, giving
additional opportunities for property engineering at polar oxide interfaces.",2212.07924v2
2023-01-07,Defective high-entropy oxide photocatalyst with high activity for CO2 conversion,"High-entropy oxides (HEOs), as a new family of materials with five or more
principal cations, have shown promising properties for various applications. In
this work and inspired by inherent defective and strained structure of HEOs,
photocatalytic CO2 conversion is examined on a dual-phase TiZrNbHfTaO11
synthesized by a two-step high-pressure torsion mechanical alloying and
high-temperature oxidation. The HEO, which had various structural defects,
showed simultaneous photocatalytic activity for CO2 to CO and H2O to H2
conversion without the addition of a co-catalyst. The photocatalytic activity
of this HEO for CO2 conversion was better than conventional photocatalysts such
as anatase TiO2 and BiVO4 and similar to P25 TiO2. The high activity of HEO was
discussed in terms of lattice defects, lattice strain, light absorbance, band
structure, photocurrent generation and charge carrier mobility to activation
centers. The current study confirms the high potential of HEOs as a new family
of photocatalysts for CO2 conversion.",2301.05008v1
2023-02-06,B dopant evolution in Pd catalysts after H evolution/oxidation reaction in alkaline environment,"Introduction of interstitial dopants has opened a new pathway to optimize
nanoparticle catalytic activity for, e.g., hydrogen evolution/oxidation and
other reactions. Here, we discuss the stability of a property-enhancing dopant,
B, introduced through controlled synthesis of an electrocatalyst Pd aerogel. We
observe significant removal of B after the hydrogen evolution/oxidation
reaction. Ab-initio calculations show that the high stability of sub-surface B
in Pd is substantially reduced when H is ad/absorbed on the surface, favoring
its departure from the host nanostructure. The destabilization of sub-surface B
is more pronounced as more H occupies surface sites and empty interstitial
sites. We hence demonstrate that the H2 fuel/product itself favors the
microstructural degradation of the electrocatalyst and an associated drop in
activity.",2302.02588v1
2023-02-24,Operando analysis of a solid oxide fuel cell by environmental transmission electron microscopy,"Correlating the microstructure of an energy conversion device to its
performance is often a complex exercise, notably in solid oxide fuel cell
(SOFC) research. SOFCs combine multiple materials and interfaces that evolve in
time due to high operating temperatures and reactive atmospheres. We
demonstrate here that operando environmental transmission electron microscopy
can simplify the identification of structure-property links in such systems. By
contacting a cathode-electrolyte-anode cell to a heating and biasing
microelectromechanical system in a single-chamber configuration, a direct
correlation is found between the environmental conditions (O2 and H2 partial
pressures, temperature), the cell voltage, and the microstructural evolution of
the fuel cell, down to the atomic scale. The results shed new insights into the
impact of the anode oxidation state and its morphology on the cell electrical
properties.",2302.12514v1
2023-03-09,Graphene on quartz modified with rhenium oxide as a semitransparent electrode for organic electronic,"Our research shows that commercially available graphene on quartz modified
with rhenium oxide meets the requirements for its use as a conductive and
transparent anode in optoelectronic devices. The cluster growth of rhenium
oxide enables an increase in the work function of graphene by 1.3 eV up to 5.2
eV, which guarantees an appropriate adjustment to the energy levels of the
organic semiconductors used in OLED devices.",2303.05303v2
2023-03-21,Numerical simulation of self-oscillating catalytic reaction in a plug-flow reactor,"Self-oscillations in some oxidation reactions on metal catalysts are
associated with periodic oxidation/reduction of the catalyst surface. If the
reaction proceeds in a flow reactor at atmospheric pressure, then the reaction
dynamics is complicated by the mass transfer in the gas phase. In this paper,
the reaction in a flow reactor is described by an 1D system of
advection-diffusion-reaction equations with an abstract STM-type kinetic model
of the surface catalytic reaction. The dependencies of the solution of the
system on the reaction parameters, the intensity of diffusion in the adsorption
layer, and on the gas flow rate are studied numerically. Solutions such as
localized oscillations (""breathing"" structures) and mobile oxidation/reduction
fronts on the catalyst surface are constructed.",2303.12022v1
2023-03-25,Surface termination control of charge transfer and band alignment across a semiconductor-crystalline oxide heterojunction,"Charge redistribution across heterojunctions has long been utilized to induce
functional response in materials systems. Here we examine how the composition
of the terminating surface affects charge transfer across a heterojunction
consisting of Si and the crystalline complex oxide SrTiO3. Itinerant electrons
in Si migrate across the interface toward the surface of SrTiO3 due to surface
depletion. The electron transfer in turn creates an electric field across the
interface that modifies the interfacial dipole associated with bonding between
SrTiO3 and Si, leading to a change in the band alignment from type-II to
type-III. By capping the SrTiO3 surface with ultra-thin layers of BaO, SrO or
TiO2, charge transfer across the interface can be weakened or inhibited. Ab
initio modeling implicates the adsorption of oxygen as driving surface
depletion in SrTiO3. The electronic coupling between the surface and buried
interface expands the functionality of semiconductor-crystalline oxide
heterojunctions.",2303.14323v1
2023-04-11,Accessible Chemical Space for Metal Nitride Perovskites,"Building on the extensive exploration of metal oxide and metal halide
perovskites, metal nitride perovskites represent a largely unexplored class of
materials. We report a multi-tier computational screening of this chemical
space. From a pool of 3660 ABN$_3$ compositions covering I-VIII, II-VII, III-VI
and IV-V oxidation state combinations, 279 are predicted to be chemically
feasible. The ground-state structures of the 25 most promising candidate
compositions were explored through enumeration over octahedral tilt systems and
global optimisation. We predict 12 dynamically and thermodynamically stable
nitride perovskite materials, including YMoN$_3$, YWN$_3$, ZrTaN$_3$, and
LaMoN$_3$. These feature significant electric polarisation and low predicted
switching electric field, showing similarities with metal oxide perovskites and
making them attractive for ferroelectric memory devices",2304.05450v1
2023-05-07,Phase stability of entropy stabilized oxides with the $α$-PbO$_2$ structure,"The prediction of new high entropy oxides (HEOs) remains a profound challenge
due to their inherent chemical complexity. In this work, we combine
experimental and computational methods to search for new HEOs in the
tetravalent $A$O$_2$ family, using exclusively $d^0$ and $d^{10}$ cations, and
to explain the observed phase stability of the $\alpha$-PbO$_2$ structure, as
found for the medium entropy oxide (Ti, Zr, Hf, Sn)O$_2$. Using a pairwise
approach to approximate the mixing enthalpy, we confirm that $\alpha$-PbO$_2$
is the expected lowest energy structure for this material above other
candidates including rutile, baddeleyite, and fluorite structures. We also show
that no other five-component compound composed of the tetravalent cations
considered here is expected to form under solid state synthesis conditions,
which we verify experimentally. Ultimately, we conclude that the flexible
geometry of the $\alpha$-PbO$_2$ structure can be used to understand its
stability among tetravalent HEOs.",2305.04221v1
2023-05-09,Photo-Induced CO Desorption Dominates over Oxidation on Different O+CO Covered Ru(0001) Surfaces,"The photo-induced desorption and oxidation of CO on Ru(0001) is simulated
using ab initio molecular dynamics with electronic friction that accounts for
the non-equilibrated excited electrons and phonons. Different (O,CO) coverages
are considered, the experimental room temperature coverage consisting in
0.5ML-O+0.25ML- CO (low coverage), the saturation coverage achieved
experimentally at low temperatures (0.5ML-O+0.375ML-CO, intermediate coverage),
and the equally mixed monolayer that is stable according to our calculations
but not experimentally observed yet (0.5ML-O+0.5ML-CO, high coverage). The
results of our simulations for the three coverages are consistent with
femtosecond laser experiments showing that the CO photo-desorption largely
dominates over CO photo-oxidation. These results cannot be explained in terms
of the distinct activation energies calculated for the relaxed surfaces.
Different (dynamical) factors such as the coupling to the laser-excited
electrons and, more importantly, the interadsorbate energy exchange and the
strong surface distortions induced in the more crowded surfaces are fundamental
to understand the competition between these two processes under the extremely
non-equilibrated conditions created by the laser.",2305.05298v2
2023-05-11,Thermodynamic properties for metal oxides from first-principles,"In this study, an efficient first-principles approach for calculating the
thermodynamic properties of mixed metal oxides at high temperatures is
demonstrated. More precisely, this procedure combines density functional theory
and harmonic phonon calculations with tabulated thermochemical data to predict
the heat capacity, formation energy, and entropy of important metal oxides.
Alloy cluster expansions are, moreover, employed to represent phases that
display chemical ordering as well as to calculate the configurational
contribution to the specific heat capacity. The methodology can, therefore, be
applied to compounds with vacancies and variable site occupancies. Results are,
moreover, presented for a number of systems of high practical relevance:
Fe-K-Ti-O, K-Mn-O, and Ca-Mn-O. In the case of ilmenite (FeTiO3), the agreement
with experimental measurements is exceptionally good. When the generated data
is used in multi-phase thermodynamic calculations to represent materials for
which experimental data is not available, the predicted phase-diagrams for the
K-Mn-O and K-Ti-O systems change dramatically. The demonstrated methodology is
highly useful for obtaining approximate values on key thermodynamic properties
in cases where experimental data is hard to obtain, inaccurate or missing.",2305.06828v1
2023-05-31,Atom-by-atom design of metal oxide catalysts for the oxygen evolution reaction with machine learning,"Green hydrogen production is crucial for a sustainable future, but current
catalysts for the oxygen evolution reaction (OER) suffer from slow kinetics,
despite many efforts to produce optimal designs, particularly through the
calculation of descriptors for activity. In this study, we develop a dataset of
density functional theory calculations of bulk and surface perovskite oxides,
and adsorption energies of OER intermediates, which includes compositions up to
quaternary and facets up to (555). We demonstrate that per-site properties of
perovskite oxides such as Bader charge or band center can be tuned through
element substitution and faceting, and develop a machine learning model that
accurately predicts these properties directly from the local chemical
environment. We leverage these per-site properties to identify promising
perovskites with high theoretical OER activity. The identified design
principles and promising new materials provide a roadmap for closing the gap
between current artificial catalysts and biological enzymes.",2305.19930v1
2023-05-31,"Thermodynamic, Kinetic and Mechanical Modeling to Evaluate CO2-induced Corrosion via Oxidation and Carburization in Fe, Ni alloys","A computational framework integrating thermodynamics, kinetics, and
mechanical stress calculations is developed to study supercritical CO2 induced
corrosion in model Fe-based MA956 and Ni-based H214 alloys. Empirical models
parametrized using experimental data show surface oxidation and sub-surface
carburization for a wide range of thermodynamic conditions (800-1200 {\deg}C,
1-250 bar). CALPHAD simulations based on empirical models demonstrate higher
carburization resistance in H214 compared to MA956 below 900 {\deg}C and
through-thickness carburization in both alloys at higher temperatures. Finite
element modeling reveals enhanced volumetric misfit induced stresses at oxide
and carbide interfaces, and its critical dependence on the carbide chemistry
and concentration.",2306.00106v1
2023-06-01,Oxide perovskite BaSnO3: A promising high-temperature thermoelectric material for transparent conducting oxides,"The new technology of energy conversion must be developed to ensure energy
sustainability. Thermoelectric (TE) materials provide an effective means to
solve the energy crisis. As a potential TE candidate, the TE properties of
perovskite have received extensively attention. We here investigate the TE
transport properties of the transparent conducting oxide (TCO) BaSnO3 by
first-principles calculations. We find that the BaSnO3 perovskite exhibits
outstanding dynamic and thermal stabilities, which provide excellent electronic
and thermal transport properties simultaneously. These properties contribute to
the remarkable Seebeck coefficient and power factor, which gives rise to the ZT
of n-0.37 and p-1.52 at 900 K. Additionally, doping and nanostructure open
prospects for effectively improving the TE properties of BaSnO3. Our work
provides a basis for further optimizing the TE transport properties of cubic
BaSnO3 and may have worthwhile practical significance for applying cubic
perovskite to the high-temperature thermoelectric field.",2306.00320v2
2023-06-14,Metastable Cation-Disordered Niobium Tungsten Oxides as Li-ion Battery Anode Materials,"Metastable cation-disordered compounds have greatly expanded the
synthesizable compositions of solid-state materials and drawn sharp attention
among battery electrochemists. While such a strategy has been very successful
in a few well-known structures, such as rock salts, metastable
cation-disordered materials for other structural types, especially for
non-close packed structures, are peculiarly underexplored. In this work, we
develop a new series of fully cation-disordered metastable niobium tungsten
oxides with a simple structure, and name this new structural type anti-Li3N.
Furthermore, we find that metastable anti-Li3N NWOs transform to a
cation-disordered cubic structure when applied as a Li-ion battery anode,
highlighting an intriguing non-close packed to close packed conversion between
two cation-disordered phases, as evidenced in various physicochemical
characterizations, in terms of diffraction, electronic, and vibrational
structures. This work enriches the structural and compositional space of
niobium tungsten oxide families, cation-disordered solid-state materials, and
the working mechanisms of Li-ion battery anodes.",2306.08735v1
2023-06-19,"Oxidation, Reduction and Semi-Classical Limit for Quantum Matrix Geometries","Matrix configurations define noncommutative spaces endowed with extra
structure including a generalized Laplace operator, and hence a metric
structure. Made dynamical via matrix models, they describe rich physical
systems including noncommutative gauge theory and emergent gravity. Refining
the construction in [1], we construct a semi-classical limit through an
immersed submanifold of complex projective space based on quasi-coherent
states. We observe the phenomenon of oxidation, where the resulting
semi-classical space acquires spurious extra dimensions. We propose to remove
this artifact by passing to a leaf of a carefully chosen foliation, which
allows to extract the geometrical content of the noncommutative spaces. This is
demonstrated numerically via multiple examples.",2306.10771v2
2023-06-23,Quantifying Defects and Finite Size Effects in Graphene Oxide Models,"Oxidation of graphite and subsequent exfoliation leads to single layer
graphene oxide (GO). GO has found many applications across diverse fields
including medicinal chemistry, catalysis as well as a precursor for graphene.
One of the key structural features of GO is the presence of different kinds of
defects. Molecular dynamics simulations with ReaxFF force fields have been
widely used to model realistic representations of GO that include defects of
various types. In these simulations, one can vary the extent and distribution
of the defects by changing the initial O/C ratio. It is therefore very
important to employ a proper measure of the defect density. Traditionally, the
total number of non-graphitic carbon atoms have been employed to quantify the
amount of defects. Our simulations suggest that this parameter may not be a
good measure at low defect densities. Herein, we introduce a hitherto
unexplored metric, relative area of the defects, to gauge the defect density.
We show that this metric has desirable properties at both low and high defect
densities. Additionally, we investigate the changes in the defect distribution
and mechanical properties upon varying the size of the simulation cell.",2306.13457v1
2023-07-07,Mechanical Properties of Silicon Nanowires with Native Oxide Surface State,"Silicon nanowires have attracted considerable interest due to their
wide-ranging applications in nanoelectromechanical systems and nanoelectronics.
Molecular dynamics simulations are powerful tools for studying the mechanical
properties of nanowires. However, these simulations encounter challenges in
interpreting the mechanical behavior and brittle to ductile transition of
silicon nanowires, primarily due to surface effects such as the assumption of
an unreconstructed surface state. This study specifically focuses on the
tensile deformation of silicon nanowires with a native oxide layer, considering
critical parameters such as cross-sectional shape, length-to-critical dimension
ratio, temperature, the presence of nano-voids, and strain rate. By
incorporating the native oxide layer, the article aims to provide a more
realistic representation of the mechanical behavior for different critical
dimensions and crystallographic orientations of silicon nanowires. The findings
contribute to the advancement of knowledge regarding size-dependent elastic
properties and strength of silicon nanowires.",2307.03650v2
2023-08-12,Initial demonstration of AlGaAs-GaAsP-beta-Ga2O3 n-p-n double heterojunctions,"Beta phase gallium oxides, an ultrawide-bandgap semiconductor, has great
potential for future power and RF electronics applications but faces challenges
in bipolar device applications due to the lack of p-type dopants. In this work,
we demonstrate monocrystalline AlGaAs_GaAsP_beta phase gallium oxides n-p-n
double-heterojunctions, synthesized using semiconductor grafting technology. By
transfer printing an n-AlGaAs_p-GaAsP nanomembrane to the n-beta
phase-Ga$_2$O$_3$ epitaxial substrate, we simultaneously achieved AlGaAs_GaAsP
epitaxial n-p junction diode with an ideality factor of 1.29 and a
rectification ratio of 2.57E3 at +/- 2 V, and grafted GaAsP_beta_phase_gallium
oxides p-n junction diode exhibiting an ideality factor of 1.36 and a
rectification ratio of 4.85E2 at +/- 2 V.",2308.06575v2
2023-09-05,Controlling Spontaneous Orientation Polarization in Organic Semiconductors -- The Case of Phosphine Oxides,"Upon film growth by physical vapor deposition, the preferential orientation
of polar organic molecules can result in a non-zero permanent dipole moment
(PDM) alignment, causing a macroscopic film polarization. This effect, known as
spontaneous orientation polarization (SOP), was studied in the case of
different phosphine oxides. We investigate the control of SOP by molecular
design and film-growth conditions. Our results show that using less polar
phosphine oxides with just one phosphor-oxygen bond yields an exceptionally
high degree of SOP with the so-called giant surface potential (slope) reaching
more than 150mV/nm in a neat BCPO film grown at room temperature. Additionally,
by altering the evaporation rate and the substrate temperature, we are able to
control the SOP magnitude over a broad range from 0 to almost 300mV/nm.
Diluting BCPO in a non-polar host enhances the PDM alignment only marginally,
but combining temperature control together with dipolar doping can result in
almost perfectly aligned molecules with more than 80% of their PDMs standing
upright on the substrate on average.",2309.02261v2
2023-10-02,Thermoelectric properties of high-entropy wolframite oxide: (CoCuNiFeZn)$_{1-x}$Ga$_x$WO$_4$,"In this report, the synthesis of high-entropy wolframite oxide
(CoCuNiFeZn)$_{1-x}$Ga$_x$WO$_4$ through standard solid-state route followed by
spark plasma sintering (SPS) and their structural, microstructural, and
thermoelectric properties are investigated. X-ray diffraction pattern followed
by pattern matching refinement shows monoclinic structure with volume of the
unit cell decreasing with increasing Ga content. The optical band gap for these
oxides shows a cocktail effect in high entropy configuration. The Seebeck
coefficient indicates electrons as dominating charge carriers with a
non-degenerate behavior. The electrical resistivity decreases with increasing
temperature depicting a semiconducting nature. Thermal conductivity in
high-entropy samples ($\kappa\sim$2.1 W/mK @ 300\,K) is significantly lower as
compared to MgWO$_4$ ($\kappa\sim$11.5 W/mK @ 300\,K), which can be explained
by the strong phonon scattering due to large lattice disorder in high entropy
configuration. The thermoelectric figure of merit zT increases with Ga doping
via modifying all three thermoelectric parameters positively.",2310.00930v1
2023-10-05,Electrocatalytic removal of persistent organic contaminants at molybdenum doped manganese oxide coated TiO2 nanotube-based anode,"Electrooxidation is an attractive technique that can be effectively applied
for the treatment of persistent organic contaminants, but its implementation in
practice is limited by the lack of efficient and low cost anode material that
would not lead to the generation of chlorinated by products. Herein, we
developed a novel anode based on TiO2 nanotube array NTA coated with Mo-doped
MnxOy, and applied it for electrooxidation of persistent organic contaminants.
The Ti TiO2 NTA MnxOyMo anode outperformed the commercial Ti IrOxPt anode and
effectively oxidized organic contaminants, with a significantly reduced
electric energy per order, and avoiding chlorine evolution reaction. Mo doping
played a key role in the excellent performance of the synthesized anode as it
favored the formation of oxygen vacancies in the host lattice and Mn and Mo
species redox couples, which increased the oxidizing power of the anode and
ensured its complete stability.",2310.03390v1
2023-10-07,Numerical simulation of defect states and electron transport mechanisms in amorphous oxide thin film transistors,"Physics based numerical simulation has been carried out to probe the sub-gap
density of states (DOS) and underlying electron transport properties of
amorphous oxide based thin film transistors (TFTs). The DOS model of TFTs
consists of exponential band tails, Gaussian shallow donor levels and deep
acceptor states. Electrical transport and various TFT performance parameters
are found to be critically dependent on the sub-gap DOS. At low gate bias, when
Fermi level lies below the conduction band mobility edge, defect states
mediated trap limited conduction is found to be the dominant transport
mechanism. However, at relatively higher gate bias, percolation conduction
above the mobility edge becomes prevalent. Such possible crossover of electron
transport is well corroborated by gate bias dependent band bending and induced
free electron density in the channel layer. Such studies are important to
unravel the critical role of sub-gap DOS on the electrical performance and
charge transport processes of disordered amorphous oxide TFTs.",2310.04707v2
2023-09-01,Insight into the melt processed Polylimonene oxide/Polylactic acid blends,"In this work, the polymerization of limonene oxide (LO) has been optimized at
room temperature with two different aluminium-based catalysts
[AlMeX{2,6-(CHPh$_2$)$_2$-4-tBu-C$_6$H$_2$O}] (X = Me (1), Cl (2)). A fully
bio-based ether, polylimonene oxide (PLO), has been synthesized with low
molecular weight and good thermal stability, being a potential sustainable
polymeric additive for other bio-based and biodegradable polymers such as
polylactic acid (PLA). Hence, we have explored its ability to influence the
thermal, mechanical and morphological properties of PLA by preparing their
blends by melt processing. The addition of a low amount of PLO led to a nearly
10 $^\circ$C decrease in the PLA glass transition temperature. Moreover, a
decrease in the PLA melting temperature and the degree of crystallinity was
observed. Interestingly, a remarkable increase in the flexibility of PLA-based
films was noticed. All the results point to the existence of strong
interactions between the components, suggesting their partial miscibility.",2310.08590v1
2023-10-27,AFLOW-CCE for the thermodynamics of ionic materials,"Accurate thermodynamic stability predictions enable data-driven computational
materials design. Standard density functional theory (DFT) approximations have
limited accuracy with average errors of a few hundred meV/atom for ionic
materials such as oxides and nitrides. Thus, insightful correction schemes as
given by the coordination corrected enthalpies (CCE) method, based on an
intuitive parameterization of DFT errors with respect to coordination numbers
and cation oxidation states present a simple, yet accurate solution to enable
materials stability assessments. Here, we illustrate the computational
capabilities of our AFLOW-CCE software by utilizing our previous results for
oxides and introducing new results for nitrides. The implementation reduces the
deviations between theory and experiment to the order of the room temperature
thermal energy scale, i.e. ~25 meV/atom. The automated corrections for both
materials classes are freely available within the AFLOW ecosystem via the
AFLOW-CCE module, requiring only structural inputs.",2310.18187v1
2023-11-03,Schottky photodetectors with transparent conductive oxides for photonic integrated circuits,"Silicon photonics has many attractive features but faces a major issue:
inefficient and slow photodetection in the telecom range. New
metal-semiconductor Schottky photodetectors based on intraband absorption
address this problem, but their efficiency remains low. We suggest that by
creating a junction between silicon and a transparent oxide with appropriate
doping, which results in a real permittivity close to zero (known as the
epsilon near zero or ENZ regime), detection efficiency could increase by more
than tenfold. Using Aluminum Zinc Oxide (AZO) as an example, we design an
optimized AZO/Si slot photonic waveguide detector that could potentially reach
an efficiency of several tens of percent, in contrast to a few percent for a
metal/Si Schottky detector. This increase is primarily due to the lower density
of states in AZO compared to metal, along with superior coupling efficiency and
strong absorption within a 10 nm slot.",2311.01643v1
2023-12-04,In-situ tuning of optomechanical crystals with nano-oxidation,"Optomechanical crystals are a promising device platform for quantum
transduction and sensing. Precise targeting of the optical and acoustic
resonance frequencies of these devices is crucial for future advances on these
fronts. However, fabrication disorder in these wavelength-scale nanoscale
devices typically leads to inhomogeneous resonance frequencies. Here we achieve
in-situ, selective frequency tuning of optical and acoustic resonances in
silicon optomechanical crystals via electric field-induced nano-oxidation using
an atomic-force microscope. Our method can achieve a tuning range >2 nm (0.13%)
for the optical resonance wavelength in the telecom C-band, and >60 MHz (1.2%)
for the acoustic resonance frequency at 5 GHz. The tuning resolution of 1.1 nm
for the optical wavelength, and $150$ kHz for the acoustic frequency allows us
to spectrally align multiple optomechanical crystal resonators using optimal
oxidation patterns determined via an inverse design protocol. Our results
establish a method for precise post-fabrication tuning of optomechancical
crystals. This technique can enable coupled optomechanical resonator arrays,
scalable resonant optomechanical circuits, and frequency matching of
microwave-optical quantum transducers.",2312.02123v1
2024-01-10,Origin of discrete electrical switching in chemically heterogeneous vanadium oxide crystals,"Electrically driven insulator-metal transitions in prototypical quantum
materials such as VO2 offer a foundational platform for designing novel
solid-state devices. Tuning the V: O stoichiometry offers a vast electronic
phase space with non-trivial collective properties. Here, we report the
discovery of discrete threshold switching voltages with constant threshold
voltage difference between cycles in vanadium oxide crystals. The observed
threshold fields over 10000 cycles are ~100X lower than that noted for
stoichiometric VO2 and show unique discrete behaviour. We correlate the
observed discrete memristor behaviour with the valence change mechanism and
fluctuations in the chemical composition of spatially distributed VO2-VnO2n-1
complex oxide phases. Design of chemical heterogeneity in Mott insulators,
therefore, offers an intriguing path to realizing low-energy neuromorphic
devices.",2401.05222v1
2024-01-16,Formation of yttrium oxalate phase filled by carbon clusters on the surface of yttrium oxide films,"In the current paper, we report the results of surface modification of cubic
Y2O3 films employing carbon-ion implantation. The characterization results
demonstrate the formation of a stable yttrium oxalate-based structure with
cavities filled with carbon clusters. Theoretical simulations demonstrate that
the incorporation of eighteen-atom carbon clusters into the cavities of
Y2(C2O4)3 does not lead to valuable changes in the crystal structure of yttrium
oxalate. X-ray diffraction and optical measurements demonstrate that the
subsurface bulk area of cubic yttrium oxide remains unperturbed. The oxalate
""skin"" thickness with embedded carbon clusters is estimated to be approximately
10 nm. The prospective employing the method to manage optical properties and
increase the biocompatibility of yttria and lanthanide oxides are discussed.",2401.08459v1
2024-01-29,High-k gadolinium scandate on Si obtained by high pressure sputtering from metal targets and in-situ plasma oxidation,"This article studies the physical and electrical behavior of Gd2-xScxO3
layers grown by high pressure sputtering from metallic Gd and Sc targets. The
aim is to obtain a high permittivity dielectric for microelectronic
applications. The films were obtained by the deposition of a metallic
nanolaminate of Gd and Sc alternating layers, which is afterwards in-situ
oxidized by plasma. The oxide films obtained were close to stoichiometry,
amorphous and with minimal interfacial regrowth. By fabricating
metal-insulator-semiconductor capacitors we found that a moderate temperature
annealing is needed to enhance permittivity, which reaches a high value of 32
while keeping moderate leakage. Finally, the feasibility of interface
scavenging in this material with Ti gate electrodes is also demonstrated.",2401.17332v1
2024-02-06,Formation of a boron-oxide termination for the (100) diamond surface,"A boron-oxide termination of the diamond (100) surface has been formed by
depositing molecular boron oxide $\rm{B_2O_3}$ onto the hydrogen-terminated
(100) diamond surface under ultrahigh vacuum conditions and annealing to
$\rm{950^{\circ} C}$. The resulting termination was highly oriented and
chemically homogeneous, although further optimisation is required to increase
the surface coverage beyond the 0.4 ML achieved here. This work demonstrates
the possibility of using molecular deposition under ultrahigh vacuum conditions
for complex surface engineering of the diamond surface, and may be a first step
in an alternative approach to fabricating boron doped delta layers in diamond.",2402.03940v2
2024-02-13,Coexistence and interplay of two ferroelectric mechanisms in Zn1-xMgxO,"Ferroelectric materials promise exceptional attributes including low power
dissipation, fast operational speeds, enhanced endurance, and superior
retention to revolutionize information technology. However, the practical
application of ferroelectric-semiconductor memory devices has been
significantly challenged by the incompatibility of traditional perovskite oxide
ferroelectrics with metal-oxide-semiconductor technology. Recent discoveries of
ferroelectricity in binary oxides such as Zn1-xMgxO and Hf1-xZrxO have been a
focal point of research in ferroelectric information technology. This work
investigates the ferroelectric properties of Zn1-xMgxO utilizing automated band
excitation piezoresponse force microscopy. Our findings reveal the coexistence
of two ferroelectric subsystems within Zn1-xMgxO. We propose a ""fringing-ridge
mechanism"" of polarization switching that is characterized by initial lateral
expansion of nucleation without significant propagation in depth, contradicting
the conventional domain growth process observed in ferroelectrics. This unique
polarization dynamics in Zn1-xMgxO suggests a new understanding of
ferroelectric behavior, contributing to both the fundamental science of
ferroelectrics and their application in information technology.",2402.08852v1
2024-02-29,Variability mitigation in epitaxial-heterostructure-based spin qubit devices via gate layout optimization,"The scalability of spin qubit devices is conditioned by qubit-to-qubit
variability. Disorder in the host materials indeed affects the wave functions
of the confined carriers, which leads to variations in their charge and spin
properties. Charge disorder in the amorphous oxides is particularly detrimental
owing to its long-range influence. Here we analyze the effects of charge traps
at the semiconductor/oxide interface, which are generally believed to play a
dominant role in variability. We consider multiple random distributions of
these interface traps and numerically calculate their impact on the chemical
potentials, detuning and tunnel coupling of two adjacent quantum dots in SiGe
heterostructure. Our results highlight the beneficial screening effect of the
metal gates. The surface of the heterostructure shall, therefore, be covered as
much as possible by the gates in order to limit variability. We propose an
alternative layout with tip-shaped gates that maximizes the coverage of the
semiconductor/oxide interface and outperforms the usual planar layout in some
regimes. This highlights the importance of design in the management of
device-to-device variability.",2402.18991v1
2024-03-04,Spectroscopic investigations on trivalent ruthenium ions in ruthenium perovskite oxide thin films,"The $d^5$ electron configurations under the crystal field, spin-orbit
coupling, and Coulomb interaction give rise to a plethora of profound ground
states. Ruthenium perovskite oxides exhibit a number of unconventional
properties yet the Ru$^{4+}$ state ($4d^4$) is usually stable in these
materials. In this regard, Ru$^{3+}$ ions in perovskite materials are expected
to be a mesmerising playground of $4d^5$ electron configurations. Here, we
report measurements of x-ray photoemission spectroscopy on recently synthesized
perovskite ruthenium oxide thin films, LaRuO$_3$ and NdRuO$_3$, whose valence
state of the ruthenium ions is trivalent. We discuss correlation and spin-orbit
effects from the valence-band spectra, in particular an additional peak
structure around 3-5 eV, reminiscent of the so-called 3 eV peak observed in
Sr$_2$RuO$_4$. Moreover, we find that the core-level spectra of these materials
are quantitatively different from those in other ruthenates which possess
Ru$^{4+}$ ions, e.g., SrRuO$_3$. We therefore argue that the core level spectra
of LaRuO$_3$ and NdRuO$_3$ are peculiar to the Ru$^{3+}$ states.",2403.01853v1
2024-03-19,Large Rashba spin-orbit coupling in metallic SrTaO$_3$ thin films,"Epitaxial thin films of SrTaO$_3$ with thickness ($t$) smaller than 74 nm
were successfully fabricated on an insulator
(LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ substrate. Films with $t$ above
8.6 nm showed metallic conduction. Both conductivity and a mobility showed a
decrease with increasing $t$ above 42 nm, suggesting the instability of thick
SrTaO$_3$ films. This instability was also supported by TEM image and XRD
intensity. For the metallic films with $t$ below 25 nm, energy band splitting
due to spin-orbit coupling ($\Delta$$_{so}$) and Rashba parameter
($\alpha$$_R$) were deduced from an analysis of a magnetoresistance using
two-dimensional weak antilocalization theory. The values of $\Delta$$_{so}$
ranged from 26 to 120 meV, which were the largest among other metallic oxide
films, such as SrNbO$_3$, SrIrO$_3$, and La$_{2/3}$Sr$_{1/3}$MnO$_3$ thin
films, indicating that spin-orbit coupling in SrTaO$_3$ was the largest among
the metallic perovskite oxides reported so far. The values of $\alpha$$_R$ for
our SrTaO$_3$ films ranged from $8.8 \times$10$^{-13}$ to $1.7
\times$10$^{-12}$ eV m, which were much larger than those reported for other
metallic oxide thin films.",2403.12612v1
2024-04-07,Morphological stability of electrostrictive thin films,"A large electric field is typically present in anodic or passive oxide films.
Stresses induced by such a large electric field are critical in understanding
the breakdown mechanism of thin oxide films and improving their corrosion
resistance. In this work, we consider electromechanical coupling through the
electrostrictive effect. A continuum model incorporating lattice misfit and
electric field-induced stresses is developed. We perform a linear stability
analysis of the full coupled model and show that, for typical oxides,
neglecting electrostriction underestimates the film's instability, especially
in systems with a large electric field. Moreover, a region where
electrostriction can potentially provide a stabilizing effect is identified,
allowing electrostriction to enhance corrosion resistance. We identified an
equilibrium electric field intrinsic to the system and the corresponding
equilibrium film thickness. The film's stability is very sensitive to the
electric field: a 40 percent deviation from the equilibrium electric field can
change the maximum growth rate by nearly an order of magnitude. Moreover, our
model reduces to classical morphological instability models in the limit of
misfit-only, electrostatic-only, and no-electrostriction cases. Finally, the
effect of various parameters on the film's stability is studied.",2404.05093v1
2023-08-18,The SPARC Toroidal Field Model Coil Program,"The SPARC Toroidal Field Model Coil (TFMC) Program was a three-year effort
between 2018 and 2021 that developed novel Rare Earth Yttrium Barium Copper
Oxide (REBCO) superconductor technologies and then successfully utilized these
technologies to design, build, and test a first-in-class, high-field (~20 T),
representative-scale (~3 m) superconducting toroidal field coil. With the
principal objective of demonstrating mature, large-scale, REBCO magnets, the
project was executed jointly by the MIT Plasma Science and Fusion Center (PSFC)
and Commonwealth Fusion Systems (CFS). The TFMC achieved its programmatic goal
of experimentally demonstrating a large-scale high-field REBCO magnet,
achieving 20.1 T peak field-on-conductor with 40.5 kA of terminal current, 815
kN/m of Lorentz loading on the REBCO stacks, and almost 1 GPa of mechanical
stress accommodated by the structural case. Fifteen internal demountable
pancake-to-pancake joints operated in the 0.5 to 2.0 nOhm range at 20 K and in
magnetic fields up to 12 T. The DC and AC electromagnetic performance of the
magnet, predicted by new advances in high-fidelity computational models, was
confirmed in two test campaigns while the massively parallel, single-pass,
pressure-vessel style coolant scheme capable of large heat removal was
validated. The REBCO current lead and feeder system was experimentally
qualified up to 50 kA, and the crycooler based cryogenic system provided 600 W
of cooling power at 20 K with mass flow rates up to 70 g/s at a maximum design
pressure of 20 bar-a for the test campaigns. Finally, the feasibility of using
passive, self-protection against a quench in a fusion-scale NI TF coil was
experimentally assessed with an intentional open-circuit quench at 31.5 kA
terminal current.",2308.12301v1
2022-04-18,The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms,"This work reviews the long-term evolution of the atmosphere of Venus, and
modulation of its composition by interior-exterior cycling. The formation and
evolution of Venus's atmosphere, leading to contemporary surface conditions,
remain hotly debated topics, and involve questions that tie into many
disciplines. We explore these various inter-related mechanisms which shaped the
evolution of the atmosphere, starting with the volatile sources and sinks.
Going from the deep interior to the top of the atmosphere, we describe volcanic
outgassing, surface atmosphere interactions, and atmosphere escape.
Furthermore, we address more complex aspects of the history of Venus, including
the role of Late Accretion impacts, how magnetic field generation is tied into
long-term evolution, and the implications of geochemical and geodynamical
feedback cycles for atmospheric evolution. We highlight plausible end-member
evolutionary pathways that Venus could have followed, from accretion to its
present-day state, based on modeling and observations. In a first scenario, the
planet was desiccated by atmospheric escape during the magma ocean phase. In a
second scenario, Venus could have harbored surface liquid water for long
periods of time, until its temperate climate was destabilized and it entered a
runaway greenhouse phase. In a third scenario, Venus's inefficient outgassing
could have kept water inside the planet, where hydrogen was trapped in the core
and the mantle was oxidized. We discuss existing evidence and future
observations and missions required to refine our understanding of the planet's
history and of the complex feedback cycles between the interior, surface, and
atmosphere that have been operating in the past, present or future of Venus.",2204.08540v2
2008-04-17,"Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites","We report isotopic data for a total of 96 presolar oxide grains found in
residues of several unequilibrated ordinary chondrite meteorites. Identified
grain types include Al2O3, MgAl2O4, hibonite (CaAl12O19) and Ti oxide. This
work greatly increases the presolar hibonite database, and is the first report
of presolar Ti oxide. O-isotopic compositions of the grains span previously
observed ranges and indicate an origin in red giant and asymptotic giant branch
(AGB) stars of low mass (<2.5 MSun) for most grains. Cool bottom processing in
the parent AGB stars is required to explain isotopic compositions of many
grains. Potassium-41 enrichments in hibonite grains are attributable to in situ
decay of now-extinct 41Ca. Inferred initial 41Ca/40Ca ratios are in good
agreement with model predictions for low-mass AGB star envelopes, provided that
ionization suppresses 41Ca decay. Stable Mg and Ca isotopic ratios of most of
the hibonite grains reflect primarily the initial compositions of the parent
stars and are generally consistent with expectations for Galactic chemical
evolution, but require some local interstellar chemical inhomogeneity. Very
high 17O/16O or 25Mg/24Mg ratios suggest an origin for some grains in binary
star systems where mass transfer from an evolved companion has altered the
parent star compositions. A supernova origin for the hitherto enigmatic
18O-rich Group 4 grains is strongly supported by multi-element isotopic data
for two grains. The Group 4 data are consistent with an origin in a single
supernova in which variable amounts of material from the deep 16O-rich interior
mixed with a unique end-member mixture of the outer layers. The Ti oxide grains
primarily formed in low-mass AGB stars. They are smaller and rarer than
presolar Al2O3, reflecting the lower abundance of Ti than Al in AGB envelopes.",0804.2866v1
2009-07-08,Charge Distribution Near Oxygen Vacancies in Reduced Ceria,"Understanding the electronic charge distribution around oxygen vacancies in
transition metal and rare earth oxides is a scientific challenge of
considerable technological importance. We show how significant information
about the charge distribution around vacancies in cerium oxide can be gained
from a study of high resolution crystal structures of higher order oxides which
exhibit ordering of oxygen vacancies. Specifically, we consider the
implications of a bond valence sum analysis of Ce$_{7}$O$_{12}$ and
Ce$_{11}$O$_{20}$. To illuminate our analysis we show alternative
representations of the crystal structures in terms of orderly arrays of
co-ordination defects and in terms of flourite-type modules. We found that in
Ce$_{7}$O$_{12}$, the excess charge resulting from removal of an oxygen atom
delocalizes among all three triclinic Ce sites closest to the O vacancy. In
Ce$_{11}$O$_{20}$, the charge localizes on the next nearest neighbour Ce atoms.
Our main result is that the charge prefers to distribute itself so that it is
farthest away from the O vacancies. This contradicts \emph{the standard picture
of charge localisation} which assumes that each of the two excess electrons
localises on one of the cerium ions nearest to the vacancy. This standard
picture is assumed in most calculations based on density functional theory
(DFT). Based on the known crystal structure of Pr$_{6}$O$_{11}$, we also
predict that the charge in Ce$_{6}$O$_{11}$ will be found in the second
coordination shell of the O vacancy. Although this review focuses on bulk
cerium oxides our approach to characterising electronic properties of oxygen
vacancies and the physical insights gained should also be relevant to surface
defects and to other rare earth and transition metal oxides.",0907.1320v3
2012-10-01,Investigation of X-ray induced radiation damage at the Si-SiO2 interface of silicon sensors for the European XFEL,"Experiments at the European X-ray Free Electron Laser (XFEL) require silicon
pixel sensors which can withstand X-ray doses up to 1 GGy. For the
investigation of X-ray radiation damage up to these high doses, MOS capacitors
and gate-controlled diodes built on high resistivity n-doped silicon with
crystal orientations <100> and <111> produced by two vendors, CiS and
Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III
synchrotron light source. Using capacitance/conductance-voltage,
current-voltage and thermal dielectric relaxation current measurements, the
surface densities of oxide charges and interface traps at the Si-SiO2
interface, and the surface-current densities have been determined as function
of dose. Results indicate that the dose dependence of the surface density of
oxide charges and the surface-current density depend on the crystal orientation
and producer. In addition, the influence of the voltage applied to the gates of
the MOS capacitor and the gate-controlled diode during X-ray irradiation on the
surface density of oxide charges and the surface-current density has been
investigated at doses of 100 kGy and 100 MGy. It is found that both strongly
depend on the gate voltage if the electric field in the oxide points from the
surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have
been performed at 60 and 80 degree C on MOS capacitors and gate-controlled
diodes irradiated to 5 MGy and the annealing kinetics of oxide charges and
surface current determined.",1210.0427v3
2017-03-17,Effects of Dielectric Stoichiometry on the Photoluminescence Properties of Encapsulated WSe2 Monolayers,"Two-dimensional transition-metal-dichalcogenide semiconductors have emerged
as promising candidates for optoelectronic devices with unprecedented
properties and ultra-compact performances. However atomically thin materials
are highly sensitive to surrounding dielectric media, which imposes severe
limitations to their practical applicability. Hence for their suitable
integration into devices, the development of reliable encapsulation procedures
that preserve their physical properties are required. Here, the excitonic
photoluminescence of WSe2 monolayer flakes is assessed, at room temperature and
10 K, on mechanically exfoliated flakes encapsulated with SiOx and AlxOy layers
employing chemical and physical deposition techniques. Conformal flakes coating
on untreated - non-functionalized - flakes is successfully demonstrated by all
the techniques except for atomic layer deposition, where a cluster-like oxide
coating is observed. No significant compositional or strain state changes in
the flakes are detected upon encapsulation by any of the techniques.
Remarkably, our results evidence that the flakes' optical emission is strongly
influenced by the quality of the encapsulating oxide - stoichiometry -. When
the encapsulation is carried out with slightly sub-stoichiometric oxides two
remarkable phenomena are observed. First, there is a clear electrical doping of
the monolayers that is revealed through a dominant trion - charged exciton -
room-temperature photoluminescence. Second, a strong decrease of the monolayers
optical emission is measured attributed to non-radiative recombination
processes and/or carriers transfer from the flake to the oxide. Power- and
temperature-dependent photoluminescence measurements further confirm that
stoichiometric oxides obtained by physical deposition lead to a successful
encapsulation.",1703.06186v3
2020-07-01,Predicting Oxidation and Spin States by High-Dimensional Neural Networks: Applications to Lithium Manganese Oxide Spinels,"Lithium ion batteries often contain transition metal oxides like
Li$_{x}$Mn$_2$O$_4$ ($0\leq x\leq2$). Depending on the Li content different
ratios of Mn$^\text{III}$ to Mn$^\text{IV}$ ions are present. In combination
with electron hopping the Jahn-Teller distortions of the Mn$^\text{III}$O$_6$
octahedra can give rise to complex phenomena like structural transitions and
conductance. While for small model systems oxidation and spin states can be
determined using density functional theory (DFT), the investigation of
dynamical phenomena by DFT is too demanding. Previously, we have shown that a
high-dimensional neural network potential can extend molecular dynamics (MD)
simulations of Li$_{x}$Mn$_2$O$_4$ to nanosecond time scales, but these
simulations did not provide information about the electronic structure. Here we
extend the use of neural networks to the prediction of atomic oxidation and
spin states. The resulting high-dimensional neural network is able to predict
the spins of the Mn ions with an error of only 0.03 $\hbar$. We find that the
Mn e$_\text{g}$ electrons are correctly conserved and that the number of
Jahn-Teller distorted Mn$^\text{III}$O$_6$ octahedra is predicted precisely for
different Li loadings. A charge ordering transition is observed between 280 and
300 K, which matches resistivity measurements. Moreover, the activation energy
of the electron hopping conduction above the phase transition is predicted to
be 0.18 eV deviating only 0.02 eV from experiment. This work demonstrates that
machine learning is able to provide an accurate representation of both, the
geometric and the electronic structure dynamics of Li$_x$Mn$_2$O$_4$, on time
and length scales that are not accessible by ab initio MD.",2007.00335v2
2015-12-30,Computationally Designed Zirconium Organometallic Catalyst for Direct Epoxidation of Alkenes without Allylic H Atoms: Aromatic Linkage Eliminates Formation of Inert Octahedral Complexes,"We used density functional theory to computationally design a Zr
organometallic catalyst for selectively oxidizing substrates using molecular
oxygen as oxidant without coreductant. Each selective oxidation cycle involves
four general steps: (a) a peroxo or weakly adsorbed O2 group releases an O atom
to substrate to form substrate oxide and an oxo group, (b) an oxygen molecule
adds to the oxo group to generate an eta2-ozone group, (c) the eta2-ozone group
rearranges to form an eta3-ozone group, and (d) the eta3-ozone group releases
an O atom to substrate to form substrate oxide and regenerate the peroxo or
weakly adsorbed O2 group. This catalyst could potentially be synthesized via
the condensation reaction Zr(N(R)R')4 + 2
C6H4-1,6-(N(C6H3-2',6'-(CH(CH3)2)2)OH)2 -->
Zr(C6H4-1,6-(N(C6H3-2',6'-(CH(CH3)2)2)O)2)2 [aka Zr_Benzol catalyst] + 4
N(R)(R')H where R and R' are CH3, CH2CH3, or other alkyl groups. For direct
ethylene epoxidation, the computed enthalpic energetic span (i.e., effective
activation energy for the entire catalytic cycle) is 27.1 kcal/mol, which is
one of the lowest values for catalysts studied to date. We study reaction
mechanisms and the stability of different catalyst forms as a function of the
oxygen atom chemical potential. Notably, an aromatic linkage in each ligand
prevents this catalyst from deactivating to form an inactive octahedral-like
structure that contains the same atoms as the dioxo complex, Zr(Ligand)2(O)2.
Due to a side reaction that can transfer an allylic H atom from alkene to
catalyst, this catalyst is useful for directly epoxidizing alkenes such as
ethylene that do not contain allylic H atoms. To better understand the reaction
chemistry, we computed net atomic charges and bond orders for the two
catalytically relevant reaction cycles. These results quantify electron
transfer and bond forming and breaking during the catalytic process.",1512.09372v1
2016-08-04,Disentangling Vacancy Oxidation on Metallicity-Sorted Carbon Nanotubes,"Pristine single-walled carbon nanotubes (SWCNTs) are rather inert to O$_2$
and N$_2$, which for low doses chemisorb only on defect sites or vacancies of
the SWCNTs at the ppm level. However, very low doping has a major effect on the
electronic properties and conductivity of the SWCNTs. Already at low O$_2$
doses (80 L), the X-ray photoelectron spectroscopy (XPS) O 1s signal becomes
saturated, indicating nearly all the SWCNT's vacancies have been oxidized. As a
result, probing vacancy oxidation on SWCNTs via XPS yields spectra with rather
low signal-to-noise ratios, even for metallicity-sorted SWCNTs. We show that,
even under these conditions, the first principles density functional theory
calculated Kohn-Sham O 1s binding energies may be used to assign the XPS O 1s
spectra for oxidized vacancies on SWCNTs into its individual components. This
allows one to determine the specific functional groups or bonding environments
measured. We find the XPS O 1s signal is mostly due to three O-containing
functional groups on SWCNT vacancies: epoxy (C$_2$$>$O), carbonyl
(C$_2$$>$C$=$O), and ketene (C$=$C$=$O), as ordered by abundance. Upon
oxidation of nearly all the SWCNT's vacancies, the central peak's intensity for
the metallic SWCNT sample is 60\% greater than for the semiconducting SWCNT
sample. This suggests a greater abundance of O-containing defect structures on
the metallic SWCNT sample. For both metallic and semiconducting SWCNTs, we find
O$_2$ does not contribute to the measured XPS O~1s spectra.",1608.01424v1
2018-06-04,Predicting the thermodynamic stability of perovskite oxides using machine learning models,"Perovskite materials have become ubiquitous in many technologically relevant
applications, ranging from catalysts in solid oxide fuel cells to light
absorbing layers in solar photovoltaics. The thermodynamic phase stability is a
key parameter that broadly governs whether the material is expected to be
synthesizable, and whether it may degrade under certain operating conditions.
Phase stability can be calculated using Density Functional Theory (DFT), but
the significant computational cost makes such calculation potentially
prohibitive when screening large numbers of possible compounds. In this work,
we developed machine learning models to predict the thermodynamic phase
stability of perovskite oxides using a dataset of more than 1900 DFT-calculated
perovskite oxide energies. The phase stability was determined using convex hull
analysis, with the energy above the convex hull (Ehull) providing a direct
measure of the stability. We generated a set of 791 features based on elemental
property data to correlate with the Ehull value of each perovskite compound.
For classification, the extra trees algorithm achieved the best prediction
accuracy of 0.93 (+/- 0.02), with an F1 score of 0.88 (+/- 0.03). For
regression, leave-out 20% cross-validation tests with kernel ridge regression
achieved the minimal root mean square error (RMSE) of 28.5 (+/- 7.5) meV/atom
between cross-validation predicted Ehull values and DFT calculations, with the
mean absolute error (MAE) in cross-validation energies of 16.7 (+/- 2.3)
meV/atom. We further validated our model by predicting the stability of
compounds not present in the training set and demonstrated our machine learning
models are a fast and effective means of obtaining qualitatively useful
guidance for a wide-range of perovskite oxide stability, potentially impacting
materials design choices in a variety of technological applications.",1806.01038v1
2019-11-21,Oxidized-monolayer Tunneling Barrier for Strong Fermi-level Depinning in Layered InSe Transistors,"In 2D-semiconductor-based field-effect transistors and optoelectronic
devices, metal-semiconductor junctions are one of the crucial factors
determining device performance. The Fermi-level (FL) pinning effect, which
commonly caused by interfacial gap states, severely limits the tunability of
junction characteristics, including barrier height and contact resistance. A
tunneling contact scheme has been suggested to address the FL pinning issue in
metal-2D-semiconductor junctions, whereas the experimental realization is still
elusive. Here, we show that an oxidized-monolayer-enabled tunneling barrier can
realize a pronounced FL depinning in indium selenide (InSe) transistors,
exhibiting a large pinning factor of 0.5 and a highly modulated Schottky
barrier height. The FL depinning can be attributed to the suppression of metal-
and disorder-induced gap states as a result of the high-quality tunneling
contacts. Structural characterizations indicate uniform and atomically thin
surface oxidation layer inherent from nature of van der Waals materials and
atomically sharp oxide-2D-semiconductor interfaces. Moreover, by effectively
lowering the Schottky barrier height, we achieve an electron mobility of 2160
cm$^2$/Vs and a contact barrier of 65 meV in two-terminal InSe transistors. The
realization of strong FL depinning in high-mobility InSe transistors with the
oxidized monolayer presents a viable strategy to exploit layered semiconductors
in contact engineering for advanced electronics and optoelectronics.",1911.09327v1
2019-12-20,"Strong Performance Enhancement in Lead-Halide Perovskite Solar Cells through Rapid, Atmospheric Deposition of n-type Buffer Layer Oxides","Thin (approximately 10 nm) oxide buffer layers grown over lead-halide
perovskite device stacks are critical for protecting the perovskite against
mechanical and environmental damage. However, the limited perovskite stability
restricts the processing methods and temperatures (<=110 C) that can be used to
deposit the oxide overlayers, with the latter limiting the electronic
properties of the oxides achievable. In this work, we demonstrate an
alternative to existing methods that can grow pinhole-free TiOx (x =
2.00+/-0.05) films with the requisite thickness in <1 min without vacuum. This
technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid
but soft deposition enables growth temperatures of >=180 {\deg}C to be used to
coat the perovskite. This is >=70 {\deg}C higher than achievable by current
methods and results in more conductive TiOx films, boosting solar cell
efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on
perovskites, there is also minimal damage to the perovskite beneath. The SnOx
layer is pinhole-free and conformal, which reduces shunting in devices, and
increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx),
with fill factors reaching 84%. This work shows AP-CVD to be a versatile
technique for growing oxides on thermally-sensitive materials.",1912.09850v1
2020-03-07,"Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant Insights","The advent of nanotechnology has hurtled the discovery and development of
nanostructured materials with stellar chemical and physical functionalities in
a bid to address issues in energy, environment, telecommunications and
healthcare. In this quest, a class of two-dimensional layered materials
consisting of alkali or coinage metal atoms sandwiched between slabs
exclusively made of transition metal and chalcogen (or pnictogen) atoms
arranged in a honeycomb fashion have emerged as materials exhibiting
fascinatingly rich crystal chemistry, high-voltage electrochemistry, fast
cation diffusion besides playing host to varied exotic electromagnetic and
topological phenomena. Currently, with a niche application in energy storage as
high-voltage materials, this class of honeycomb layered oxides serves as ideal
pedagogical exemplars of the innumerable capabilities of nanomaterials drawing
immense interest in multiple fields ranging from materials science, solid-state
chemistry, electrochemistry and condensed matter physics. In this review, we
delineate the relevant chemistry and physics of honeycomb layered oxides, and
discuss their functionalities for tunable electrochemistry, superfast ionic
conduction, electromagnetism and topology. Moreover, we elucidate the
unexplored albeit vastly promising crystal chemistry space whilst outlining
effective ways to identify regions within this compositional space,
particularly where interesting electromagnetic and topological properties could
be lurking within the aforementioned alkali and coinage-metal honeycomb layered
oxide structures. We conclude by pointing towards possible future research
directions, particularly the prospective realisation of
Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and
Floquet theory in closely-related honeycomb layered oxide materials.",2003.03555v10
2020-03-23,Influence of Surface Hydrophilicity and Hydration on the Rotational Relaxation of Supercooled Water on Graphene Oxide Surfaces,"Hydration or interfacial water present in biomolecules and inorganic solids
have been shown to exhibit a dynamical transition upon supercooling. However,
an understanding of the extent of the underlying surface hydrophilicity as well
as the local distribution of hydrophilic/hydrophobic patches on the dynamical
transition is unexplored. Here, we use molecular dynamics simulations with a
TIP4P/2005 water model to study translational and rotational relaxation
dynamics of interfacial water on graphene surfaces. The purpose of this study
is to investigate the influence of both surface chemistry as well as the extent
of hydration on the rotational transitions of interfacial water on graphene
oxide (GO) surfaces in the deeply supercooled region. We have considered three
graphene-based surfaces; a GO surface with equal proportions of oxidized and
pristine graphene regions in a striped topology, a fully oxidized surface and a
pristine graphene surface. The dipole relaxation time of interfacial water
shows a strong-to-strong, strong, and a fragile-to-strong transition on these
surfaces, respectively, in the temperature range of 210-298 K. In contrast,
bulk water shows a fragile-to-strong transition upon supercooling. In all these
cases at high hydration, interfacial water co-exists with a thick water film
with bulk-like properties. To investigate the influence of bulk water on
dynamical transitions, we simulated a low hydration regime where only bound
water (surface water) is present on the GO surfaces and found that the
rotational relaxation of surface water on both the GO and fully oxidized
surfaces show a single Arrhenius behavior. Our results indicate that not only
does the local extent of surface hydrophilicity play a role in determining the
energy landscape explored by the water molecules upon supercooling, but the
presence of bulk water also modulates the dynamic transition.",2003.10515v1
2020-08-04,Vacuum ultraviolet photoabsorption spectroscopy of space-related ices: 1 keV electron irradiation of nitrogen- and oxygen-rich ices,"Molecular oxygen, nitrogen, and ozone have been detected in the Solar System.
They are also expected to be present in ice-grain mantles within star-forming
regions. Laboratory experiments that simulate energetic processing (ions,
photons, and electrons) of ices are essential for interpreting and directing
future astronomical observations. We provide VUV photoabsorption spectroscopic
data of energetically processed nitrogen- and oxygen-rich ices that will help
to identify absorption bands and/or spectral slopes observed on icy objects in
the Solar System and on ice-grain mantles of the interstellar medium. We
present VUV photoabsorption spectra of frozen O2 and N2, a 1:1 mixture of both,
and a new systematic set of pure and mixed nitrogen oxide ices. Spectra were
obtained at 22 K before and after 1 keV electron bombardment of the ice sample.
Ices were then annealed to higher temperatures to study their thermal
evolution. In addition, Fourier-transform infrared spectroscopy was used as a
secondary probe of molecular synthesis to better identify the physical and
chemical processes at play. Our VUV data show that ozone and the azide radical
(N3) are observed in our experiments after electron irradiation of pure O2 and
N2 ices, respectively. Energetic processing of an O2:N2 = 1:1 ice mixture leads
to the formation of ozone along with a series of nitrogen oxides. The electron
irradiation of solid nitrogen oxides, pure and in mixtures, induces the
formation of new species such as O2, N2 , and other nitrogen oxides not present
in the initial ice. Results are discussed here in light of their relevance to
various astrophysical environments. Finally, we show that VUV spectra of solid
NO2 and water can reproduce the observational VUV profile of the cold surface
of Enceladus, Dione, and Rhea, strongly suggesting the presence of nitrogen
oxides on the surface of the icy Saturn moons.",2008.01783v1
2020-09-15,Self-formed $LaAlO_3/SrTiO_3$ Micro-Membranes,"Oxide heterostructures represent a unique playground for triggering the
emergence of novel electronic states and for implementing new device concepts.
The discovery of 2D conductivity at the $LaAlO_3/SrTiO_3$ interface has been
linking for over a decade two of the major current research fields in Materials
Science: correlated transition-metal-oxide systems and low-dimensional systems.
A full merging of these two fields requires nevertheless the realization of
$LaAlO_3/SrTiO_3$ heterostructures in the form of freestanding membranes. Here
we show a completely new method for obtaining oxide hetero-membranes with
micrometer lateral dimensions. Unlike traditional thin-film-based techniques
developed for semiconductors and recently extended to oxides, the concept we
demonstrate does not rely on any sacrificial layer and is based instead on pure
strain engineering. We monitor through both real-time and post-deposition
analyses, performed at different stages of growth, the strain relaxation
mechanism leading to the spontaneous formation of curved hetero-membranes.
Detailed transmission electron microscopy investigations show that the
membranes are fully epitaxial and that their curvature results in a huge strain
gradient, each of the layers showing a mixed compressive/tensile strain state.
Electronic devices are fabricated by realizing ad hoc circuits for individual
micro-membranes transferred on silicon chips. Our samples exhibit metallic
conductivity and electrostatic field effect similar to 2D-electron systems in
bulk heterostructures. Our results open a new path for adding oxide
functionality into semiconductor electronics, potentially allowing for
ultra-low voltage gating of a superconducting transistors, micromechanical
control of the 2D electron gas mediated by ferroelectricity and
flexoelectricity, and on-chip straintronics.",2009.06900v2
2021-02-01,Data-driven Approach to Parameterize SCAN+U for an Accurate Description of 3d Transition Metal Oxide Thermochemistry,"Semi-local DFT methods exhibit significant errors for the phase diagrams of
transition-metal oxides that are caused by an incorrect description of
molecular oxygen and the large self-interaction error in materials with
strongly localized electronic orbitals. Empirical and semiempirical corrections
based on the DFT+U method can reduce these errors, but the parameterization and
validation of the correction terms remains an on-going challenge. We develop a
systematic methodology to determine the parameters and to statistically assess
the results by considering thermochemical data across a set of transition metal
compounds. We consider three interconnected levels of correction terms: (1) a
constant oxygen binding correction, (2) Hubbard-U correction, and (3) DFT/DFT+U
compatibility correction. The parameterization is expressed as a unified
optimization problem. We demonstrate this approach for 3d transition metal
oxides, considering a target set of binary and ternary oxides. With a total of
37 measured formation enthalpies taken from the literature, the dataset is
augmented by the reaction energies of 1,710 unique reactions that were derived
from the formation energies by systematic enumeration. To ensure a balanced
dataset across the available data, the reactions were grouped by their
similarity using clustering and suitably weighted. The parameterization is
validated using leave-one-out cross-validation (CV), a standard technique for
the validation of statistical models. We apply the methodology to the SCAN
density functional. Based on the CV score, the error of binary (ternary) oxide
formation energies is reduced by 40% (75%) to 0.10 (0.03) eV/atom. The method
and tools demonstrated here can be applied to other classes of materials or to
parameterize the corrections to optimize DFT+U performance for other target
physical properties.",2102.01131v2
2021-04-25,Electronic excitation spectra of cerium oxides: from ab initio dielectric response functions to Monte Carlo charge transport simulations,"Nanomaterials made of the cerium oxides CeO$_2$ and Ce$_2$O$_3$ have a broad
range of applications, from catalysts in automotive, industrial or energy
operations to promising materials to enhance hadrontherapy effectiveness in
oncological treatments. To elucidate the physico-chemical mechanisms involved
in these processes, it is of paramount importance to know the electronic
excitation spectra of these oxides, which are obtained here through
high-accuracy linear-response time-dependent density functional theory
calculations. In particular, the macroscopic dielectric response functions
$\bar\epsilon$ of both bulk CeO$_2$ and Ce$_2$O$_3$ are derived, which compare
remarkably well with the available experimental data. These results stress the
importance of appropriately accounting for local field effects to model the
dielectric function of metal oxides. Furthermore, we reckon the materials
energy loss functions $\mbox{Im} (-1/\bar{\epsilon})$, including the accurate
evaluation of the momentum transfer dispersion from first-principles. In this
respect, by using a Mermin-type parametrization we are able to model the
contribution of different electronic excitations to the dielectric loss
function. Finally, from the knowledge of the electron inelastic mean free path,
together with the elastic mean free path provided by the relativistic Mott
theory, we carry out statistical Monte Carlo (MC) charge transport simulations
to reproduce the major features of the reported experimental reflection
electron energy loss (REEL) spectra of cerium oxides. The good agreement with
REEL experimental data strongly supports our approach based on MC modelling
informed by ab initio calculated electronic excitation spectra in a broad range
of momentum and energy transfers.",2104.12242v1
2021-09-02,Drastically enhanced cation incorporation in the epitaxy of oxides due to formation and evaporation of suboxides from elemental sources,"In the molecular beam epitaxy of oxide films, the cation (Sn, Ga) or dopant
(Sn) incorporation does not follow the vapor pressure of the elemental metal
sources, but is enhanced by several orders of magnitude for low source
temperatures. Using line-of-sight quadrupole mass spectrometry, we identify the
dominant contribution to the total flux emanating from Sn and Ga sources at
these temperatures to be due to the unintentional formation and evaporation of
the respective suboxides SnO and Ga$_{2}$O. We quantitatively describe this
phenomenon by a rate-equation model that takes into account the O background
pressure, the resulting formation of the suboxides via oxidation of the metal
source, and their subsequent thermally activated evaporation. As a result, the
total flux composed of the metal and the suboxide fluxes exhibit an
\textsf{S}-shape temperature dependence instead of the expected linear one in
an Arrhenius plot, in excellent agreement with the available experimental data.
Our model reveals that the thermally activated regimes at low and high
temperatures are almost exclusively due to suboxide and metal evaporation,
respectively, joined by an intermediate plateau-like regime in which the flux
is limited by the available amount of O. An important suboxide contribution is
expected for all elemental sources whose suboxide exhibits a higher vapor
pressure than the element, such as B, Ga, In, La, Si, Ge, Sn, Sb, Mo, Nb, Ru,
Ta, V, and W. This contribution can play a decisive role in the molecular beam
epitaxy of oxides, including multicomponent or complex oxides, from elemental
sources. Finally, our model predicts suboxide-dominated growth in low-pressure
chemical vapor deposition of Ga$_{2}$O$_{3}$ and In$_{2}$O$_{3}$.",2109.01195v1
2022-06-22,Non-trivial topological phases in transition metal rich half-Heusler Oxides,"Topological Insulators with gapless surface states and insulating bulk in
non-centrosymmetric cubic systems have been extensively explored following the
discovery of two-dimensional quantum spin hall effect in zincblende HgTe. In
such systems the negative band inversion strength E$_{BIS}$ ($=$ E$_{\Gamma_6}
-$ E$_{\Gamma_8} <$ 0) governs the robustness of the non-trivial topological
states at ambient conditions. Hence, realizing large negative values of
E$_{BIS}$ has been a guiding motivation of several investigations reported in
literature. Here, we present a material design approach which can be employed
to realize large negative values of E$_{BIS}$ in cubic materials such as
half-Heusler (HH) oxides with 18 valence electron configurations. We explore 27
HH oxides of the form ABO (A = Li, K, Rb; B = Cu, Ag, Au) in $\alpha$-,
$\beta$-, and $\gamma$-phase (by placing transition metal atom at different
Wyckoff positions) for their non-trivial topological phase. Off these three
phases, we found that, the $\alpha$-phase of nine HH oxides (wherein the
transition metal atoms occupy 4a Wyckoff positions in the crystal structure) is
the most promising with non-trivial topological phase which is governed by the
mass-darwin relativistic effects enhancing E$_{BIS}$. Whereas the other phases
were found to be either trivial semiconductors or semimetals or metals and most
of them being dynamically unstable. We focus on RbAuO in $\alpha$-phase with
E$_{BIS}$ of $-$ 1.29 eV and the effect of strain fields on the topological
surface states of this compound. We conclude that the $\alpha$-phase of HH
oxide presented here can be synthesized experimentally for diverse room
temperature applications in spintronics and nanoelectronics.",2206.10976v2
2023-04-24,Development of an eReaxFF Force Field for BZY20 Solid Oxide Electrocatalysis,"Electrocatalysis is a catalytic process where the rate of an electrochemical
reaction occurring at the electrode-electrolyte interface can be controlled by
varying the electrical potential. Electrocatalysis can be applied to generate
hydrogen which can be stored for future use in fuel cells for clean
electricity. The use of solid oxide in electrocatalysis specially in hydrogen
evolution reaction is promising. However, further improvements are essential in
order to meet the ever-increasing global energy demand. Improvement of the
performance of these high energy chemical systems is directly linked to the
understanding and improving the complex physical and chemical phenomena and
exchanges that take place at their different interfaces. To enable large length
and time scale atomistic simulations of solid oxide electrocatalysis for
hydrogen generation, we developed an eReaxFF force field for barium zirconate
doped with 20 mol% of yttrium (BZY20). All parameters for the eReaxFF were
optimized to reproduce quantum mechanical (QM) calculations on relevant
condensed phase and cluster systems describing oxygen vacancies, vacancy
migrations, water adsorption, water splitting and hydrogen generation on the
surfaces of the BZY20 solid oxide. Using the developed force field, we
performed zero-voltage molecular dynamics simulations to observe water
adsorption and the eventual hydrogen production. Based on our simulation
results, we conclude that this force field sets a stage for the introduction of
explicit electron concept in order to simulate electron conductivity, electron
leakage and non-zero-voltage effects on hydrogen generation. Overall, we
demonstrate how atomistic-scale simulations can enhance our understanding of
processes at interfaces in solid oxide materials.",2304.14256v1
2023-09-12,Universal interatomic potential for perovskite oxides,"With their celebrated structural and chemical flexibility, perovskite oxides
have served as a highly adaptable material platform for exploring emergent
phenomena arising from the interplay between different degrees of freedom.
Molecular dynamics (MD) simulations leveraging classical force fields, commonly
depicted as parameterized analytical functions, have made significant
contributions in elucidating the atomistic dynamics and structural properties
of crystalline solids including perovskite oxides. However, the force fields
currently available for solids are rather specific and offer limited
transferability, making it time-consuming to use MD to study new materials
systems since a new force field must be parameterized and tested first. The
lack of a generalized force field applicable to a broad spectrum of solid
materials hinders the facile deployment of MD in computer-aided materials
discovery (CAMD). Here, by utilizing a deep-neural network with a
self-attention scheme, we have developed a unified force field that enables MD
simulations of perovskite oxides involving 14 metal elements and conceivably
their solid solutions with arbitrary compositions. Notably, isobaric-isothermal
ensemble MD simulations with this model potential accurately predict the
experimental phase transition sequences for several markedly different
ferroelectric oxides, including a 6-element ternary solid solution,
Pb(In$_{1/2}$Nb$_{1/2}$)O$_3$--Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$--PbTiO$_3$. We
believe the universal interatomic potential along with the training database,
proposed regression tests, and the auto-testing workflow, all released
publicly, will pave the way for a systematic improvement and extension of a
unified force field for solids, potentially heralding a new era in CAMD.",2309.06391v3
2023-10-19,Limits of dispersoid size and number density in oxide dispersion strengthened alloys fabricated with powder bed fusion-laser beam,"Previous work on additively-manufactured oxide dispersion strengthened alloys
focused on experimental approaches, resulting in larger dispersoid sizes and
lower number densities than can be achieved with conventional powder
metallurgy. To improve the as-fabricated microstructure, this work integrates
experiments with a thermodynamic and kinetic modeling framework to probe the
limits of the dispersoid sizes and number densities that can be achieved with
powder bed fusion-laser beam. Bulk samples of a Ni-20Cr $+$ 1 wt.% Y$_2$O$_3$
alloy are fabricated using a range of laser power and scanning velocity
combinations. Scanning transmission electron microscopy characterization is
performed to quantify the dispersoid size distributions across the processing
space. The smallest mean dispersoid diameter (29 nm) is observed at 300 W and
1200 mm/s, with a number density of 1.0$\times$10$^{20}$ m$^{-3}$. The largest
mean diameter (72 nm) is observed at 200 W and 200 mm/s, with a number density
of 1.5$\times$10$^{19}$ m$^{-3}$. Scanning electron microscopy suggests that a
considerable fraction of the oxide added to the feedstock is lost during
processing, due to oxide agglomeration and the ejection of oxide-rich spatter
from the melt pool. After accounting for these losses, the model predictions
for the dispersoid diameter and number density align with the experimental
trends. The results suggest that the mechanism that limits the final number
density is collision coarsening of dispersoids in the melt pool. The modeling
framework is leveraged to propose processing strategies to limit dispersoid
size and increase number density.",2310.12416v3
2024-03-26,"Utilizing (Al, Ga)2O3/Ga2O3 superlattices to measure cation vacancy diffusion and vacancy-concentration-dependent diffusion of Al, Sn, and Fe in \b{eta} -Ga2O3","Diffusion of native defects such as vacancies and their interactions with
impurities are fundamental in semiconductor crystal growth, device processing,
and long-term aging of equilibration and transient diffusion of vacancies are
rarely investigated. We used aluminum-gallium oxide/gallium oxide superlattices
(SLs) to detect and analyze transient diffusion of cation vacancies during
annealing in O2 at 1000-1100 C. Using a novel finite difference scheme for the
diffusion equation with time- and space-varying diffusion constant, we extract
diffusion constants for Al, Fe, and cation vacancies under the given
conditions, including the vacancy concentration dependence for Al. indicate
that vacancies present in the substrate transiently diffuse through the SLs,
interacting with Sn as it also diffuses. In the case of SLs grown on Sn-doped
beta-gallium oxide substrates, gradients observed in the extent of Al diffusion
indicate that vacancies present in the substrate transiently diffuse through
the SLs, interacting with Sn as it also diffuses. In the case of SLs grown on
(010) Fe-doped substrates, the Al diffusion is uniform through the SLs,
indicating a depth-uniform concentration of vacancies. We find no evidence in
either case for the introduction of gallium vacancies from the free surface at
rates sufficient to affect Al diffusion down to ppm concentrations, which has
important bearing on the validity of typically-made assumptions of vacancy
equilibration. Additionally, we show that unintentional impurities in Sn-doped
gallium oxide such as Fe, Ni, Mn, Cu, and Li also diffuse towards the surface
and accumulate. Many of these likely have fast interstitial diffusion modes
capable of destabilizing devices over time, thus highlighting the importance of
controlling unintentional impurities in beta-gallium oxide wafers.",2403.17298v1
2024-03-27,Classical dynamics and semiclassical analysis of excitons in cuprous oxide,"Excitons, as bound states of electrons and holes, embody the solid state
analogue of the hydrogen atom, whose quantum spectrum is explained within a
classical framework by the Bohr-Sommerfeld atomic model. In a first
hydrogenlike approximation the spectra of excitons are also well described by a
Rydberg series, however, due to the surrounding crystal environment deviations
from this series can be observed. A theoretical treatment of excitons in
cuprous oxide needs to include the band structure of the crystal, leading to a
prominent fine-structure splitting in the quantum spectra. This is achieved by
introducing additional spin degrees of freedom into the system, making the
existence and meaningfulness of classical exciton orbits in the physical system
a non-trivial question. Recently, we have uncovered the contributions of
periodic exciton orbits directly in the quantum mechanical recurrence spectra
of cuprous oxide [J. Ertl et al., Phys. Rev. Lett. 129, 067401 (2022)] by
application of a scaling technique and fixing the energy of the classical
dynamics to a value corresponding to a principle quantum number $n=5$ in the
hydrogenlike case. Here, we present a comprehensive derivation of the classical
and semiclassical theory of excitons in cuprous oxide. In particular, we
investigate the energy dependence of the exciton dynamics. Both the
semiclassical and quantum mechanical recurrence spectra exhibit stronger
deviations from the hydrogenlike behavior with decreasing energy, which is
related to a growing influence of the spin-orbit coupling and thus a higher
velocity of the secular motion of the exciton orbits. The excellent agreement
between semiclassical and quantum mechanical exciton recurrence spectra
demonstrates the validity of the classical and semiclassical approach to
excitons in cuprous oxide.",2403.18303v1
2023-04-26,Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation,"We present a novel transmon qubit fabrication technique that yields
systematic improvements in T$_1$ relaxation times. We fabricate devices using
an encapsulation strategy that involves passivating the surface of niobium and
thereby preventing the formation of its lossy surface oxide. By maintaining the
same superconducting metal and only varying the surface structure, this
comparative investigation examining different capping materials, such as
tantalum, aluminum, titanium nitride, and gold, and film substrates across
different qubit foundries definitively demonstrates the detrimental impact that
niobium oxides have on the coherence times of superconducting qubits, compared
to native oxides of tantalum, aluminum or titanium nitride. Our
surface-encapsulated niobium qubit devices exhibit T$_1$ relaxation times 2 to
5 times longer than baseline niobium qubit devices with native niobium oxides.
When capping niobium with tantalum, we obtain median qubit lifetimes above 300
microseconds, with maximum values up to 600 microseconds, that represent the
highest lifetimes to date for superconducting qubits prepared on both sapphire
and silicon. Our comparative structural and chemical analysis suggests why
amorphous niobium oxides may induce higher losses compared to other amorphous
oxides. These results are in line with high-accuracy measurements of the
niobium oxide loss tangent obtained with ultra-high Q superconducting
radiofrequency (SRF) cavities. This new surface encapsulation strategy enables
even further reduction of dielectric losses via passivation with ambient-stable
materials, while preserving fabrication and scalable manufacturability thanks
to the compatibility with silicon processes.",2304.13257v3
2022-09-09,Magnetically confined mountains on accreting neutron stars with multipole magnetic fields,"Magnetically confined mountains on accreting neutron stars are candidates for
producing continuous gravitational waves. We formulate a magnetically confined
mountain on a neutron star with strong multipole magnetic fields and obtain
some sequences of numerical solutions. We find that the mass ellipticity of the
mountain increases by one order of magnitude if the neutron star has strong
multipole magnetic fields. As matter accretes on to the magnetic pole, the size
of the mountain increases and the magnetic fields are buried. If the neutron
star has a dipole magnetic field, the dipole magnetic field is buried and
transformed into multipole components. By contrast, if the neutron star has
both dipole and strong multipole magnetic fields, the multipole magnetic fields
are buried and transformed into a negative dipole component. We also calculate
magnetically confined mountains with toroidal magnetic fields and find that the
ellipticity becomes slightly smaller when the mountain has toroidal magnetic
fields. If the multipole magnetic fields are buried, they sustain the intense
toroidal magnetic field near the stellar surface, and the ratio of the toroidal
magnetic field to the poloidal magnetic field is close to 100. The hidden
strong toroidal magnetic fields are sustained by the buried multipole magnetic
fields.",2209.04352v1
2022-10-31,Superconducting Magnet System Concept with a Mechanical Energy Transfer in the Magnetic Field,"There is an interest to design superconducting magnet systems working in a
persistent current mode. These systems continuously generate magnetic field
with disconnected power source working like permanent magnet devices. In this
paper proposed a magnet system concept based on the direct mechanical energy
transfer in the magnetic field. Short circuited superconducting coils do not
have current leads and power source. To pump the mechanical energy in the
superconducting coil used a magnetizer which magnetically coupled with the
coil. The mechanical removing the magnetizer from the magnet induces a
persistent current in the superconducting coil which generates the magnetic
field. Iron dominated magnet system concept was investigated using OPERA3d code
which confirmed a visibility of proposed approach.",2211.00102v1
2014-06-25,Transforming magnets,"Based on the form-invariant of Maxwell's equations under coordinate
transformations, we extend the theory of transformation optics to
transformation magneto-statics, which can design magnets through coordinate
transformations. Some novel DC magnetic field illusions created by magnets
(e.g. shirking magnets, cancelling magnets and overlapping magnets) are
designed and verified by numerical simulations. Our research will open a new
door to designing magnets and controlling DC magnetic fields.",1406.6512v1
2019-02-26,The Evidence of Cathodic Micro-discharges during Plasma Electrolytic Oxidation Process,"Plasma electrolytic oxidation (PEO) processing of EV 31 magnesium alloy has
been carried out in fluoride containing electrolyte under bipolar pulse current
regime. Unusual PEO cathodic micro-discharges have been observed and
investigated. It is shown that the cathodic micro-discharges exhibit a
collective intermittent behavior which is discussed in terms of charge
accumulations at the layer/electrolyte and layer/metal interfaces. Optical
emission spectroscopy is used to determine the electron density (typ. 10 15
cm-3) and the electron temperature (typ. 7500 K) while the role of F-anions on
the appearance of cathodic micro-discharges is pointed out. Plasma Electrolytic
Oxidation (PEO) is a promising plasma-assisted surface treatment of light
metallic alloys (e.g. Al, Mg, Ti). Although the PEO process makes it possible
to grow oxide coatings with interesting corrosion and wear resistant
properties, the physical mechanisms of coating growth are not yet completely
understood. Typically, the process consists in applying a high voltage
difference between a metallic piece and a counter-electrode which are both
immersed in an electrolyte bath. Compare to anodizing, the main differences
concern the electrolyte composition and the current and voltage ranges which
are at least one order of magnitude higher in PEO 1. These significant
differences in current and voltage imply the dielectric breakdown and
consequently the appearance of micro-discharges on the surface of the sample
under processing. Those micro-discharges are recognized as being the main
contributors to the formation of a dielectric porous crystalline oxide coating.
2 Nevertheless, the breakdown mechanism that governs the appearance of those
micro-discharges is still under investigation. Hussein et al. 3 proposed a
mechanism with three different plasma formation processes based on differences
in plasma chemical composition. The results of Jovovi{\'c} et al. 4,5
concerning physical properties of the plasma seem to corroborate this
mechanism, and also point out the importance of the substrate material in the
plasma composition. 6 Compared with DC conducted PEO process, using a bipolar
pulsed DC or AC current supply gives supplementary control latitude through the
current waveform parameters. The effect of these parameter on the
micro-discharges behavior has been investigated in several previous works.
2,3,7,8 One of the main results of these studies is the absence of
micro-discharge during the cathodic current half-period. 9-11 Even if the
cathodic half-period has an obvious effect on the efficiency of PEO as well as
on the coating growth and composition, the micro-plasmas appear only in anodic
half-period. Sah et al. 8 have observed the cathodic breakdown of an oxide
layer but at very high current density (10 kA.dm-${}^2$), and after several
steps of sample preparation. Several models of micro-discharges appearance in
AC current have already been proposed. 1,2,8,12,13 Though cathodic
micro-discharges have never been observed within usual process conditions, the
present study aims at defining suitable conditions to promote cathodic
micro-discharges and at studying the main characteristics of these
micro-plasmas.",1902.09828v1
2016-09-27,The magnetic properties of the hollow cylindrical ideal remanence magnet,"We consider the magnetic properties of the hollow cylindrical ideal remanence
magnet. This magnet is the cylindrical permanent magnet that generates a
uniform field in the cylinder bore, using the least amount of magnetic energy
to do so. The remanence distribution of this magnet is derived and the
generated field is compared to that of a Halbach cylinder of equal dimensions.
The ideal remanence magnet is shown in most cases to generate a significantly
lower field than the equivalent Halbach cylinder, although the field is
generated with higher efficiency. The most efficient Halbach cylinder is shown
to generate a field exactly twice as large as the equivalent ideal remanence
magnet.",1609.08548v1
2022-07-19,Magnetic Field of a Permanent Magnet,"For magnetic field calculations, cylindrical permanent magnets are often
approximated as ideal, azimuthally symmetric solenoids. Despite the frequent
usage of this approximation, research papers demonstrating the validity and
limitations of this approach are scarcely available. In this paper, the
experimentally derived magnetic field of a cylindrical permanent magnet is
compared with the analytically calculated magnetic field of an ideal solenoid.
An experimental setup for measuring the magnetic field distribution is
demonstrated and employed for gathering the data. The proposed setup allows to
measure the distributions of the axial and radial components of the magnetic
field surrounding the magnet. The experimental data is in a very good agreement
with the theoretical predictions, confirming the validity of using the model of
an ideal solenoid for predicting a magnetic field distribution of a permanent
magnet.",2207.09911v1
2022-09-09,Magnetization dynamics and reversal of two-dimensional magnets,"Micromagnetics simulation based on the classical Landau-Lifshitz-Gilbert
(LLG) equation has long been a powerful method for modeling magnetization
dynamics and reversal of three-dimensional (3D) magnets. For two-dimensional
(2D) magnets, the magnetization reversal always accompanies the collapse of the
magnetization even at low temperatures due to intrinsic strong spin
fluctuation. We propose a micromagnetic theory that explicitly takes into
account the rapid demagnetization and remagnetization dynamics of 2D magnets
during magnetization reversal. We apply the theory to a single-domain magnet to
illustrate fundamental differences in magnetization trajectories and reversal
times for 2D and 3D magnets.",2209.04483v1
2004-08-24,Reconsidering the origin of the 21 micron feature: Oxides in carbon-rich PPNe?,"The origin of the so-called ""21 micron"" feature which is especially prominent
in the spectra of some carbon-rich protoplanetary nebulae (PPNe}) is the matter
of a lively debate. A large number of potential band carriers have been
presented and discarded within the past decade. The present paper gives an
overview of the problems related to the hitherto proposed feature
identifications, including the recently suggested candidate carrier silicon
carbide. We also discuss the case for spectroscopically promising oxides.
  SiC is shown to produce a strong resonance band at 20-21 micron if coated by
a layer of silicon dioxide. At low temperatures, core-mantle particles composed
of SiC and amorphous SiO$_2$ indeed have their strongest spectral signature at
a position of 20.1 micron, which coincides with the position of the ""21 micron""
emission band.
  The optical constants of another candidate carrier that has been relatively
neglected so far -- iron monoxide -- are proven to permit a fairly accurate
reproduction of the ""21 micron"" feature profile as well, especially when
low-temperature measurements of the infrared properties of FeO are taken into
account. As candidate carrier of the ""21 micron"" emission band, FeO has the
advantage of being stable against further oxidation and reduction only in a
narrow range of chemical and physical conditions, coinciding with the fact that
the feature, too, is detected in a small group of objects only. However, it is
unclear how FeO should form or survive particularly in carbon-rich PPNe.",0408447v1
1999-07-22,Coupling strength of charge carriers to spin fluctuations in high-temperature superconductors,"In conventional superconductors, the most direct evidence of the mechanism
responsible for superconductivity comes from tunneling experiments in which a
clear image of the electron-phonon interaction is revealed. The observed
structure in the current voltage characteristics at the phonon energies can be
used to measure, through inversion of the Eliashberg equations, the electron
phonon spectral density \alpha^2F(\omega). The coherence length in conventional
materials is long and the tunneling process probes several atomic layers into
the bulk of the superconductor. On the contrary, in the high-T_c oxides,
particularly for c-axis tunneling, the coherence length can be quite short and
in an optical experiment or in neutron scattering experiments the bulk of the
sample is probed. Therefore, these spectroscopies become the methods of choice
for the investigation of mechanisms of high-T_c superconductivity. Accurate
reflectance measurements in the infrared range and precise polarized neutron
scattering data are available for a variety of oxides. In this paper we show
that conducting carriers studied by means of infrared spectroscopy reveal
strong coupling to a resonance structure in the spectrum of spin fluctuations
examined with neutron scattering. The coupling strength inferred from
experiment is sufficient to account for high values of T_c which signals the
prominent role of spin excitations in the superconductivity of oxides.",9907338v2
1999-08-17,Experiments on Ladders Reveal a Complex Interplay between a Spin-Gapped Normal State and Superconductivity,"In recent years, the study of ladder materials has developed into a
well-established area of research within the general context of Strongly
Correlated Electrons. This effort has been triggered by an unusual
cross-fertilization between theory and experiments. In this paper, the main
experimental results obtained in the context of ladders are reviewed from the
perspective of a theorist. Emphasis is given to the many similarities between
the two-dimensional high-$\rm T_c$ cuprates and the two-leg ladder compounds,
including Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (14-24-41) which has a
superconducting phase at high pressure and a small hole density. Examples of
these similarities include regimes of linear resistivity vs temperature in
metallic ladders and a normal state with spin-gap or pseudogap characteristics.
Some controversial results in this context are also discussed. It is remarked
that the ladder 14-24-41 is the first superconducting copper-oxide material
with a non-square-lattice layered arrangement, and certainly much can be
learned from a careful analysis of this compound. A short summary of the main
theoretical developments in this field is also included, as well as a brief
description of the properties of non-copper-oxide ladders. Suggestions by the
author on possible experiments are described in the text. Overall, it is
concluded that the enormous experimental effort carried out on ladders has
already unveiled quite challenging and interesting physics that adds to the
rich behavior of electrons in transition-metal-oxides, and in addition
contributes to the understanding of the two-dimensional cuprates. However,
still considerable work needs to be carried out to fully understand the
interplay between charge and spin degrees of freedom in these materials.",9908250v1
2004-04-13,Electron Phonon Interaction and Strong Correlations in High-Temperature Superconductors: One can not avoid unavoidable,"The important role of the electron-phonon interaction (EPI) in explaining the
properties of the normal state and pairing mechanism in high-T$_{c}$
superconductors (HTSC) is discussed. A number of experimental results are
analyzed such as: dynamical conductivity, Raman scattering, neutron scattering,
ARPES, tunnelling measurements, isotope effect and etc. They give convincing
evidence that the EPI is strong and dominantly contributes to pairing in HTSC
oxides. It is argued that strong electronic correlations in conjunction with
the pronounced (in relatively weakly screened materials) EPI are unavoidable
ingredients for the microscopic theory of pairing in HTSC oxides. I present the
well defined and controllable theory of strong correlations and the EPI. It is
shown that strong correlations give rise to the pronounced \textit{forward
scattering peak} in the EPI - the FSP theory. The FSP theory explains in a
consistent way several (crucial) puzzles such as much smaller transport
coupling constant than the pairing one ($\lambda_{tr}\ll \lambda$), which are
present if one interprets the results in HTSC oxides by the old
Migdal-Eliashberg theory for the EPI. The ARPES shift puzzle where the nodal
kink at 70 meV is unshifted in the superconducting state, while the anti-nodal
one at 40 meV is shifted can be explained at present only by the FSP theory. A
number of other interesting predictions of the FSP theory are also discussed.",0404287v1
2005-07-29,Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron-hole Bose liquid,"We develop a model approach to describe charge fluctuations and different
charge phases in strongly correlated 3d oxides. As a generic model system one
considers that of centers each with three possible valence states described in
frames of pseudo-spin (isospin) formalism by an effective anisotropic
non-Heisenberg Hamiltonian. Simple uniform mean-field phases include an
insulating monovalent phase, mixed-valence binary disproportionated phase, and
mixed-valence ternary under-disproportionated phase. We consider two first
phases in more details focusing on the problem of electron/hole states and
different types of excitons in monovalent phase and formation of electron-hole
Bose liquid in disproportionated phase. Pseudo-spin formalism provides a useful
framework for revealing and describing different topological charge
fluctuations, in particular, like domain walls or bubble domains in
antiferromagnets. All the insulating systems such as monovalent phase may be
subdivided to two classes: stable and unstable ones with regard to the
formation of self-trapped charge transfer (CT) excitons. The latter systems
appear to be unstable with regard to the formation of CT exciton clusters, or
droplets of the electron-hole Bose liquid. The model approach suggested is
believed to be applied to describe a physics of strongly correlated oxides with
charge transfer excitonic instability and a mixed valence. We shortly discuss
an unconventional scenario of the essential physics of cuprates and manganites
that implies their instability with regard to the self-trapping of charge
transfer excitons and the formation of electron-hole Bose liquid.",0507705v1
2008-03-20,Electronic charge and orbital reconstruction at cuprate-titanate interfaces,"In complex transition metal oxide heterostructures of physically dissimilar
perovskite compounds, interface phenomena can lead to novel physical properties
not observed in either of their constituents. This remarkable feature opens new
prospects for technological applications in oxide electronic devices based on
nm-thin oxide films. Here we report on a significant electronic charge and
orbital reconstruction at interfaces between YBa2Cu3O6 and SrTiO3 studied using
local spin density approximation (LSDA) with intra-atomic Coulomb repulsion
(LSDA+U). We show that the interface polarity results in the metallicity of
cuprate-titanate superlattices with the hole carriers concentrated
predominantly in the CuO2 and BaO layers and in the first interface TiO2 and
SrO planes. We also find that the interface structural relaxation causes a
strong change of orbital occupation of Cu 3d orbitals in the CuO2 layers. The
concomitant change of Cu valency from +2 to +3 is related to the partial
occupation of the Cu $3d_{3z^2-r^2}$ orbitals at the interface with SrO planes
terminating SrTiO3. Interface-induced predoping and orbital reconstruction in
CuO2 layers are key mechanisms which control the superconducting properties of
field-effect devices developed on the basis of cuprate-titanate
heterostructures.",0803.2988v1
2008-09-11,Experimental and modeling study of the low-temperature oxidation of large alkanes,"This paper presents an experimental and modeling study of the oxidation of
large linear akanes (from C10) representative from diesel fuel from low to
intermediate temperature (550-1100 K) including the negative temperature
coefficient (NTC) zone. The experimental study has been performed in a
jet-stirred reactor at atmospheric pressure for n-decane and a
n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed
using computer-aided generation (EXGAS) with improved rules for writing
reactions of primary products. These mechanisms have allowed a correct
simulation of the experimental results obtained. Data from the literature for
the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock
tubes, and of n-dodecane in a pressurized flow reactor have also been correctly
modeled. A considerable improvement of the prediction of the formation of
products is obtained compared to our previous models. Flow rates and
sensitivity analyses have been performed in order to better understand the
influence of reactions of primary products. A modeling comparison between
linear alkanes for C8 to C16 in terms of ignition delay times and the formation
of light products is also discussed.",0809.1921v1
2009-05-28,Mottness in High-Temperature Copper-Oxide Superconductors,"The standard theory of metals, Fermi liquid theory, hinges on the key
assumption that although the electrons interact, the low-energy excitation
spectrum stands in a one-to-one correspondence with that of a non-interacting
system. In the normal state of the copper-oxide high-temperature
superconductors, drastic deviations from the Fermi liquid picture obtain,
highlighted by a pseudogap, broad spectral features and $T-$ linear
resistivity. This article focuses on the series of experiments on the
copper-oxide superconductors which reveal that the number of low-energy
addition states per electron per spin exceeds unity, in direct violation of the
key Fermi liquid tenet. These experiments point to new degrees of freedom, not
made out of the elemental excitations, as the key mechanism by which Fermi
liquid theory breaks down in the cuprates. A recent theoretical advance which
permits an explicit integration of the high energy scale in the standard model
for the cuprates reveals the source of the new dynamical degrees of freedom at
low energies, a charge 2e bosonic field which has nothing to do with pairing
but rather represents the mixing with the high energy scales. We demonstrate
explicitly that at half-filling, this new degree of freedom provides a
dynamical mechanism for the generation of the charge gap, antiferromagnetism in
the insulating phase and explains many of the anomalies in the normal state of
the cuprates.",0905.4637v1
2009-06-19,Enhancement mode double top gated MOS nanostructures with tunable lateral geometry,"We present measurements of silicon (Si) metal-oxide-semiconductor (MOS)
nanostructures that are fabricated using a process that facilitates essentially
arbitrary gate geometries. Stable Coulomb blockade behavior free from the
effects of parasitic dot formation is exhibited in several MOS quantum dots
with an open lateral quantum dot geometry. Decreases in mobility and increases
in charge defect densities (i.e. interface traps and fixed oxide charge) are
measured for critical process steps, and we correlate low disorder behavior
with a quantitative defect density. This work provides quantitative guidance
that has not been previously established about defect densities for which Si
quantum dots do not exhibit parasitic dot formation. These devices make use of
a double-layer gate stack in which many regions, including the critical gate
oxide, were fabricated in a fully-qualified CMOS facility.",0906.3748v2
2010-03-03,Effects of Mismatch Strain and Substrate Surface Corrugation on Morphology of Supported Monolayer Graphene,"Graphene monolayers supported on oxide substrates have been demonstrated with
superior charge mobility and thermal transport for potential device
applications. Morphological corrugation can strongly influence the transport
properties of the supported graphene. In this paper, we theoretically analyze
the morphological stability of a graphene monolayer on an oxide substrate,
subject to van der Waals interactions and in-plane mismatch strains. First, we
define the equilibrium separation and the interfacial adhesion energy as the
two key parameters that characterize the van der Waals interaction between a
flat monolayer and a flat substrate surface. By a perturbation analysis, a
critical compressive mismatch strain is predicted, beyond which the graphene
monolayer undergoes strain-induced instability, forming corrugations with
increasing amplitude and decreasing wavelength on a perfectly flat surface.
When the substrate surface is not perfectly flat, the morphology of graphene
depends on both the amplitude and the wavelength of the surface corrugation. A
transition from conformal (corrugated) to non-conformal (flat) morphology is
predicted. The effects of substrate surface corrugation on the equilibrium mean
thickness of the supported graphene and the interfacial adhesion energy are
analyzed. Furthermore, by considering both the substrate surface corrugation
and the mismatch strain, it is found that, while a tensile mismatch strain
reduces the corrugation amplitude of graphene, a corrugated substrate surface
promotes strain-induced instability under a compressive strain. These
theoretical results suggest possible means to control the morphology of
graphene monolayer on oxide substrates by surface patterning and strain
engineering.",1003.0853v1
2010-09-17,Unveiling a two-dimensional electron gas with universal subbands at the surface of SrTiO3,"Similar to silicon that is the basis of conventional electronics, strontium
titanate (SrTiO3) is the bedrock of the emerging field of oxide electronics.
SrTiO3 is the preferred template to create exotic two-dimensional (2D) phases
of electron matter at oxide interfaces, exhibiting metal-insulator transitions,
superconductivity, or large negative magnetoresistance. However, the physical
nature of the electronic structure underlying these 2D electron gases (2DEGs)
remains elusive, although its determination is crucial to understand their
remarkable properties. Here we show, using angle-resolved photoemission
spectroscopy (ARPES), that there is a highly metallic universal 2DEG at the
vacuum-cleaved surface of SrTiO3, independent of bulk carrier densities over
more than seven decades, including the undoped insulating material. This 2DEG
is confined within a region of ~5 unit cells with a sheet carrier density of
~0.35 electrons per a^2 (a is the cubic lattice parameter). We unveil a
remarkable electronic structure consisting on multiple subbands of heavy and
light electrons. The similarity of this 2DEG with those reported in
SrTiO3-based heterostructures and field-effect transistors suggests that
different forms of electron confinement at the surface of SrTiO3 lead to
essentially the same 2DEG. Our discovery provides a model system for the study
of the electronic structure of 2DEGs in SrTiO3-based devices, and a novel route
to generate 2DEGs at surfaces of transition-metal oxides.",1009.3412v1
2010-10-05,Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface,"Many-body interactions in transition-metal oxides give rise to a wide range
of functional properties, such as high-temperature superconductivity, colossal
magnetoresistance, or multiferroicity. The seminal recent discovery of a
two-dimensional electron gas (2DEG) at the interface of the insulating oxides
LaAlO3 and SrTiO3 represents an important milestone towards exploiting such
properties in all-oxide devices. This conducting interface shows a number of
appealing properties, including a high electron mobility, superconductivity,
and large magnetoresistance and can be patterned on the few-nanometer length
scale. However, the microscopic origin of the interface 2DEG is poorly
understood. Here, we show that a similar 2DEG, with an electron density as
large as 8x10^13 cm^-2, can be formed at the bare SrTiO3 surface. Furthermore,
we find that the 2DEG density can be controlled through exposure of the surface
to intense ultraviolet (UV) light. Subsequent angle-resolved photoemission
spectroscopy (ARPES) measurements reveal an unusual coexistence of a light
quasiparticle mass and signatures of strong many-body interactions.",1010.0763v2
2010-11-07,Interactions between sub-10 nm iron and cerium oxide nanoparticles and 3T3 fibroblasts : the role of the coating and aggregation state,"Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the cerium and iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts.
Coating strategies include low-molecular weight ligands (citric acid) and
polymers (poly(acrylic acid), MW = 2000 g mol-1). Electrostatically adsorbed on
the surfaces, the organic moieties provide a negatively charged coating in
physiological conditions. We find that most particles were biocompatible, as
exposed cells remained 100% viable relative to controls. Only the bare and the
citrate-coated nanoceria exhibit a slight decrease of the mitochondrial
activity for cerium concentrations above 5 mM (equivalent to 0.8 g L-1). We
also observe that the citrate-coated particles are internalized by the cells in
large amounts, typically 250 pg per cell after a 24 h incubation for iron
oxide. In contrast, the polymer-coated particles are taken up at much lower
rates (< 30 pg per cell). The strong uptake shown by the citrate-coated
particles is related to the destabilization of the dispersions in the cell
culture medium and their sedimentation down to the cell membranes. In
conclusion, we show that the uptake of nanomaterials by living cells depends on
the coating of the particles and on its ability to preserve the colloidal
nature of the dispersions.",1011.1670v1
2010-12-29,Competing Exotic Topological Insulator Phases in Transition Metal Oxides on the Pyrochlore Lattice with Distortion,"In this work we investigate the phase diagram of heavy (4d and 5d) transition
metal oxides on the pyrochlore lattice, such as those of the form
$\mathrm{A_2M_2O_7}$, where A is a rare earth element and M is a transition
metal element. We focus on the competition between Coulomb interaction,
spin-orbit coupling, and lattice distortion when these energy scales are
comparable. Strong spin-orbit coupling entangles the spin and the $t_{2g}$
$d$-orbitals giving rise to doublet $j=1/2$ and quadruplet $j=3/2$ states. In
contrast to previous works which focused on the doublet manifold, we also
discuss the quadruplet manifold which is relevant for several pyrochlore
oxides. The Coulomb interaction is taken into account by use of the slave-rotor
mean field theory and different classes of lattice distortions which further
split the levels of the quadruplet $j=3/2$ manifold are studied. Various
topological phases are predicted, including exotic strong and weak topological
Mott insulating phases. We discuss the general structure of the phase diagram
for several values of $d$-shell filling and various symmetry classes of lattice
distortions. Our results are relevant to the search for exotic topological
insulators and quantum spin liquids in strongly correlated materials with
strong spin-orbit coupling.",1101.0007v2
2011-02-06,Enhanced Li capacity at high lithiation potentials in graphene oxide,"We have studied lithiation of graphene oxide (GO) as a function of oxygen
coverage using first principles calculations. Our results show that the
lithiation potentials and capacities in GO can be tuned by controlling the
oxygen coverage, or the degree of reduction. We find a range of coverages where
the lithiation potentials are above the solid electrolyte interface (SEI)
formation threshold, but with capacities comparable to, or larger than
graphite. We observe that in highly oxidized and mildly reduced sheets,
lithiation occurs through the formation of Li-O bonds, whereas at low coverages
that are typical of reduced-GO (rGO) (O:C - 12.5 %), both Li-O bonds and LiC6
configurations are observed. The covalent Li-O bond is much stronger than the
bonds formed in the LiC6 ring and the lithiation potentials for epoxides at
high and medium coverages are generally large (> 1 eV). For these
congifurations, as in the case of Li4Ti5O12 anodes, there will be no formation
of SEI, but with the additional advantage of having higher lithium storage
capacity than Li4Ti5O12. In reduced GO sheets, the presence of residual oxygen
atoms allows for formation of covalent Li-O bonds that lead to storage
capacities and lithiation potentials higher than that of graphite. Finally, our
calculations show high lithiation potentials for the edges of graphene
nanoribbons, which will impede the formation of SEI and hence lead to large
reversible capacity.",1102.1211v1
2011-06-06,An electron hole doping and soft x-ray spectroscopy study on La1-xSrxFe0.75Ni0.25O3-δ,"The conductivity of the electron hole and polaron conductor
La1-xSrxFe0.75Ni0.25O3-{\delta}, a potential cathode material for intermediate
temperature solid oxide fuel cells, was studied for 0 <x < 1 and for
temperatures 300 K <T < 1250 K. In LaSrFe-oxide, an ABO3 type perovskite,
A-site substitu-tion of the trivalent La3+ by the divalent Sr2+ causes
oxidation of Fe3+ towards Fe4+, which forms conducting electron holes. Here we
have in addition a B-site substitution by Ni. The compound for x = 0.5 is
identified as the one with the highest conductivity ({\sigma} ~ 678 S/cm) and
lowest activation energy for polaron conductivity (Ep = 39 meV). The evolution
of the electronic structure was monitored by soft x-ray Fe and oxygen K-edge
spectroscopy. Homogeneous trend for the oxida-tion state of the Fe was
observed. The variation of the ambient temperature conductivity and activation
energy with relative Sr content (x) shows a correlation with the ratio of
(eg/eg+t2g) in Fe L3 edge up to x=0.5. The hole doping process is reflected by
an almost linear trend by the variation of the pre-peaks of the oxygen K-edge
soft x-ray absorption spectra.",1106.1019v1
2011-07-30,"Synthesis, Structural, Electrical and Microchemistry Properties of Novel (LSCFM) LaxSr1-xCo1-y-zFeyMnzO3-δ (x=0.4, 0.6, 0.8, y=0.4, 0.8 and z=0.1, 0.2) Perovskites for SOFC Applications","Perovskites are mixed oxides with the general formula ABO3. Many different
compositions have been found to be possible and their number is growing rapidly
due to their characteristics that make them ideal for various applications,
such as fabrication of cathodes for solid oxide fuel cells (SOFCs). Oxide
powders of LaxSr1-xCo1-y-zFeyMnzO3-{\delta} (x=0.4, 0.6, 0.8, y=0.4, 0.8 and
z=0.1, 0.2), named LSCFM, were prepared by mixing commercial powders. The
powders have been investigated as a function of the stoichiometry and the
crystal structure parameters have been determined using Rietveld analysis. The
results of the structural analysis for each sintered sample, at low temperature
sintering (1100 {\omicron}C), have been obtained by considering two cubic
perovskite phases, for x=0.4 or one cubic and one orthorhombic phase for x=0.6,
0.8, respectively. Analysis of microstructure has shown a maximum grain size of
~0.63 {\mu}m. The annealed sample at 1100 {\omicron}C, an almost single phase
specimen, exhibited an electrical conductivity of 1.29\times103 ({\Omega} \cdot
cm)-1. The sintered sample at 1250 {\omicron}C has higher conductivity but
sharper curve close to the maximum. We suggest that low temperature sintering
reveal two phase system with broader curve maximum and high conductivity for
future applications in SOFCs.",1108.0104v1
2011-10-12,"Covalency, double-counting and the metal-insulator phase diagram in transition metal oxides","Dynamical mean field theory calculations are used to show that for late
transition-metal-oxides a critical variable for the Mott/charge-transfer
transition is the number of d-electrons, which is determined by charge transfer
from oxygen ions. Insulating behavior is found only for a narrow range of
d-occupancy, irrespective of the size of the intra-d Coulomb repulsion. The
result is useful in interpreting 'density functional +U' and 'density
functional plus dynamical mean field' methods in which additional correlations
are applied to a specific set of orbitals and an important role is played by
the 'double counting correction' which dictates the occupancy of these
correlated orbitals. General considerations are presented and are illustrated
by calculations for two representative transition metal oxide systems: layered
perovskite Cu-based ""high-Tc"" materials, an orbitally non-degenerate
electronically quasi-two dimensional systems, and pseudocubic rare earch
nickelates, an orbitally degenerate electronically three dimensional system.
Density functional calculations yield d-occupancies very far from the Mott
metal-insulator phase boundary in the nickelate materials, but closer to it in
the cuprates, indicating the sensitivity of theoretical models of the cuprates
to the choice of double counting correction and corroborating the critical role
of lattice distortions in attaining the experimentally observed insulating
phase in the nickelates.",1110.2782v2
2011-12-28,Behavior of Lithium Oxide at Superionic Transition: First Principles and Molecular Dynamics Studies,"We report studies on the vibrational and elastic behavior of lithium oxide,
Li2O around its superionic transition temperature. Phonon frequencies
calculated using the ab-initio and empirical potential model are in excellent
agreement with the reported experimental data. Further, volume dependence of
phonon dispersion relation has been calculated, which indicates softening of
zone boundary transverse acoustic phonon mode along [110] at volume
corresponding to the superionic transition in Li2O. The instability of phonon
mode could be a precursor leading to the dynamical disorder of the lithium sub
lattice. Empirical potential model calculations have been carried out to deduce
the probable direction of lithium diffusion by constructing a super cell
consisting of 12000 atoms. The barrier energy for lithium ion diffusion from
one lattice site to another at ambient and elevated temperature has been
computed. Barrier energy considerations along various symmetry directions
indicate that [001] is the most favourable direction for lithium diffusion in
the fast ion phase. This result corroborates our observation of dynamical
instability in the transverse mode along (110) wave vector. Using molecular
dynamics simulations we have studied the temperature variation of elastic
constants, which are important to the high-temperature stability of lithium
oxide.",1112.6100v1
2012-08-29,Molecule-Electrode Interface Energetics in Molecular Junction: a Transition Voltage Spectroscopy Study,"We assess the performances of the transition voltage spectroscopy (TVS)
method to determine the energies of the molecular orbitals involved in the
electronic transport though molecular junctions. A large number of various
molecular junctions made with alkyl chains but with different chemical
structure of the electrode-molecule interfaces are studied. In the case of
molecular junctions with clean, unoxidized electrode-molecule interfaces, i.e.
alkylthiols and alkenes directly grafted on Au and hydrogenated Si,
respectively, we measure transition voltages in the range 0.9 - 1.4 V. We
conclude that the TVS method allows estimating the onset of the tail of the
LUMO density of states, at energy located 1.0 - 1.2 eV above the electrode
Fermi energy. For oxidized interfaces (e.g. the same monolayer measured with Hg
or eGaIn drops, or monolayers formed on a slightly oxidized silicon substrate),
lower transition voltages (0.1 - 0.6 V) are systematically measured. These
values are explained by the presence of oxide-related density of states at
energies lower than the HOMO-LUMO of the molecules. As such, the TVS method is
a useful technique to assess the quality of the molecule-electrode interfaces
in molecular junctions.",1208.5901v1
2012-12-07,Binding of an oxide layer to a metal: the case of Ti(10-10)/TiO2(100),"We study the chemical nature of the bonding of an oxide layer to the parent
metal. In order to disentangle chemical effects from strain/misfit,
Ti(10$\bar{1}$0)/TiO$_{2}$(100) interface has been chosen. We use the density
functional pseudopotential method which gives good agreement with experiment
for known properties of bulk and surface Ti and TiO$_2$. Two geometries, a
film-like model (with free surface in the structure) and a bulk-like model
(with no free surface in the structure) are used to simulate the interface, in
each case with different terminations of Ti and TiO$_2$. For the single-oxygen
interfaces, the interface energy obtained using these two models agree with
each other; however for the double-oxygen ones, the relative stability is quite
different. The disturbance to the electronic structure is confined within a few
atomic layers of the interface. The interfacial bonding is mainly ionic, and
surprisingly there is more charge transfer from Ti to O in the interface than
in the bulk. In consequence the Ti/TiO$_2$ interface has stronger binding than
the bulk of either material. This helps to explain why the oxide forms a
stable, protective layer on Ti and Ti alloys.",1212.1659v1
2012-12-12,Correlated Electron Materials and Field Effect Transistors for Logic: A Review,"Correlated electron systems are among the centerpieces of modern condensed
matter sciences, where many interesting physical phenomena, such as
metal-insulator transition and high-Tc superconductivity appear. Recent efforts
have been focused on electrostatic doping of such materials to probe the
underlying physics without introducing disorder as well as to build
field-effect transistors that may complement conventional semiconductor
metal-oxide-semiconductor field effect transistor (MOSFET) technology. This
review focuses on metal-insulator transition mechanisms in correlated electron
materials and three-terminal field effect devices utilizing such correlated
oxides as the channel layer. We first describe how electron-disorder
interaction, electron-phonon interaction and/or electron correlation in solids
could modify the electronic properties of materials and lead to metal-insulator
transitions. Then we analyze experimental efforts toward utilizing these
transitions in field effect transistors and their underlying principles. It is
pointed out that correlated electron systems show promise among these various
materials displaying phase transitions for logic technologies. Furthermore,
novel phenomena emerging from electronic correlation could enable new
functionalities in field effect devices. We then briefly review unconventional
electrostatic gating techniques, such as ionic liquid gating and ferroelectric
gating, which enables ultra large carrier accumulation density in the
correlated materials which could in turn lead to phase transitions. The review
concludes with a brief discussion on the prospects and suggestions for future
research directions in correlated oxide electronics for information processing.",1212.2684v1
2012-12-27,Cs in high oxidation states and as a p-block element,"The major chemical feature of an element is the number of electrons available
for forming chemical bonds. A doctrine rooted in the atomic shell model states
that the atoms will maintain a complete inner shell while interacting with
other atoms. Therefore, group IA elements, for example, are invariably stable
in the +1 charge state because the p electrons of their inner shells do not
react with other chemical species. This general rule governs our understanding
of the structures and reactions of matter and has never been challenged. In
this work, we show for the first time that while mixing with fluorine under
pressure, Cs atoms will share their 5p electrons and become oxidized to a
higher charge state. The formal oxidation state can be as high as +5 within the
pressure range of our study (<200 GPa) and stable Cs2+ and Cs3+ compounds can
form at lower pressures. While sharing its 5p electrons, Cs behaves like a
p-block element forming compounds with molecular, covalent, ionic and metallic
features. Considering the pressure range required for the CsFn compounds, the
inner shell electrons in other group IA and IIA elements may also bond with F
or other chemical species under higher pressure.",1212.6290v1
2013-01-24,First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides,"We present a scheme to construct model potentials, with parameters computed
from first principles, for large-scale lattice-dynamical simulations of
materials. Our method mimics the traditional solid-state approach to the
investigation of vibrational spectra, i.e., we start from a suitably chosen
reference configuration of the material and describe its energy as a function
of arbitrary atomic distortions by means of a Taylor series. Such a form of the
potential-energy surface is completely general, trivial to formulate for any
compound, and physically transparent. Further, the approximations involved in
our effective models are clear-cut, and the precision can be improved in a
systematic and well-defined fashion. Moreover, such a simple definition allows
for a straightforward determination of the parameters in the low-order terms of
the series, as they are the direct result of
density-functional-perturbation-theory calculations, which greatly simplifies
the model construction. Here we present such a scheme, discuss a practical and
versatile methodology for the calculation of the model parameters from first
principles, and describe our results for two challenging cases in which the
model potential is strongly anharmonic, namely, ferroic perovskite oxides
PbTiO3 and SrTiO3. The choice of test materials was partly motivated by
historical reasons, since our scheme can be viewed as a natural extension of
(and was initially inspired by) the so-called first-principles effective
Hamiltonian approach to the investigation of temperature-driven effects in
ferroelectric perovskite oxides. Thus, the study of these compounds allows us
to better describe the connections between the effective-Hamiltonian method and
ours.",1301.5731v1
2013-07-08,5d transition metal oxide IrO2 as a material for spin current detection,"Devices based on a pure spin current (a flow of spin angular momentum) have
been attracting increasing attention as key ingredients for low-dissipation
electronics. To integrate such spintronics devices into charge-based
technologies, an electric detection of spin current is essential. Inverse spin
Hall effect converts a spin current into an electric voltage through spin-orbit
coupling. Noble metals such as Pt and Pd, and also Cu-based alloys, owing to
the large direct spin Hall effect, have been regarded as potential materials
for a spin-current injector. Those materials, however, are not promising as a
spin-current detector based on inverse spin Hall effect. Their spin Hall
resistivity rho_SH, representing the performance as a detector, is not large
enough mainly due to their low charge resistivity. Here we demonstrate that
heavy transition metal oxides can overcome such limitations inherent to
metal-based spintronics materials. A binary 5d transition metal oxide IrO2,
owing to its large resistivity as well as a large spin-orbit coupling
associated with 5d character of conduction electrons, was found to show a
gigantic rho_SH ~ 38 microohm cm at room temperature, one order of magnitude
larger than those of noble metals and Cu-based alloys and even comparable to
those of atomic layer thin film of W and Ta.",1307.2121v1
2013-10-02,Simulation of a hump structure in the optical scattering rate within a generalized Allen formalism and its application to copper oxide systems,"We propose a possible way to simulate a hump structure in the optical
scattering rate. The optical scattering rate of correlated charge carriers can
be defined within an extended Drude model formalism. When some electron and
hole doped copper oxide systems are in the spin density or charge density wave
phases they show hump structures in their optical scattering rates. The hump
structures have not yet been simulated and understood clearly. We are able to
simulate the hump structure by using a peak followed by a dip feature in the
normalized density of states within a generalized Allen formalism. We observe
that reversing the order of the dip and peak gives completely different
features in the optical scattering rate; a peak-dip (dip peak) results in a
hump (a valley) in the scattering rate. We also obtain the real part of the
optical conductivity and reflectance spectra from the simulated optical
scattering rate and compare them with published experimental spectra. From
these comparisons we conclude that the peak-dip order can give the hump
structure, which is observed experimentally in copper oxide systems. Finally we
fit two published optical spectra with our new model and discuss our results
and the possible origin of the dip or peak features in the normalized density
of states.",1310.0698v1
2013-11-06,Modulating charge density and inelastic optical response in graphene by atmospheric pressure localized intercalation through wrinkles,"The intercalation of an oxide barrier between graphene and its metallic
substrate for chem- ical vapor deposition is a contamination-free alternative
to the transfer of graphene to dielectric supports, usually needed for the
realization of electronic devices. Low-cost pro- cesses, especially at
atmospheric pressure, are desirable but whether they are achievable remains an
open question. Combining complementary microscopic analysis, providing
structural, electronic, vibrational, and chemical information, we demonstrate
the spontaneous reactive intercalation of 1.5 nm-thick oxide ribbons between
graphene and an iridium substrate, at atmospheric pressure and room
temperature. We discover that oxygen-containing molecules needed for forming
the ribbons are supplied through the graphene wrinkles, which act as tunnels
for the efficient diffusion of molecules entering their free end. The
intercalated oxide ribbons are found to modify the graphene-support
interaction, leading to the formation of quasi-free-standing high quality
graphene whose charge density is modulated in few 10-100 nm-wide ribbons by a
few 10^12 cm-2, where the inelastic optical response is changed, due to a
softening of vibrational modes - red-shifts of Raman G and 2D bands by 6 and 10
cm-1, respectively.",1311.1357v1
2013-12-11,Local Electrostatic Imaging of Striped Domain Order in LaAlO3/SrTiO3,"The emerging field of complex oxide interfaces is generically built on one of
the most celebrated substrates - strontium titanate (SrTiO3). This material
hosts a range of phenomena, including ferroelasticity, incipient
ferroelectricity, and most puzzlingly, contested giant piezoelectricity.
Although these properties may markedly influence the oxide interfaces,
especially on microscopic length scales, the lack of local probes capable of
studying such buried systems has left their effects largely unexplored. Here we
use a scanning charge detector - a nanotube single-electron transistor - to
noninvasively image the electrostatic landscape and local mechanical response
in the prototypical LaAlO3/SrTiO3 system with unprecedented sensitivity. Our
measurements reveal that on microscopic scales SrTiO3 exhibits large anomalous
piezoelectricity with curious spatial dependence. Through electrostatic imaging
we unravel the microscopic origin for this extrinsic piezoelectricity,
demonstrating its direct, quantitative connection to the motion of locally
ordered tetragonal domains under applied gate voltage. These domains create
striped potential modulations that can markedly influence the two-dimensional
electron system at the conducting interface. Our results have broad
implications to all complex oxide interfaces built on SrTiO3 and demonstrate
the importance of microscopic structure to the physics of electrons at the
LaAlO3/SrTiO3 interface.",1312.3343v1
2014-07-09,Role of charge transfer in catalytic hydrogen oxidation over platinum,"Charge transfer plays the central role in chemisorption and chemical
reactions at metal surfaces. The Somorjai group in Nano. Lett. {\bf 9}, 3930
(2009) has reported a chemicurrent, a flux of charge carriers in response to
$\mathrm{H_2}$ oxidation by $\mathrm{O_2}$ into $\mathrm{H_2O}$ over a platinum
surface. The nature of the chemicurrent has been debated in the literature;
explanations both extrinsic and intrinsic to the reaction mechanism have been
offered. This article suggests a picture behind the chemicurrent experiments,
which is intrinsic to the mechanism of hydrogen oxidation in a high temperature
regime. Surface reaction intermediates, $""\mathrm{O^-}""$, $""\mathrm{H^-}""$,
$""\mathrm{OH^-}""$, are negatively charged while the product, $\mathrm{H_2O}$,
and reactants, $\mathrm{H_2}$ and $\mathrm{O_2}$, are neutral. Hence, charge
transfers between the metal and reacting species are inevitable. After
electrons are transferred from the metal to the interface in dissociative
oxygen and hydrogen adsorption, translationally excited electrons in the metal
arise in part as a result of decay of negatively charged transition states in
reaction steps connecting surface species of different charges,
$""\mathrm{O^-+H^-}"" \rightleftarrows ""\mathrm{2 e+OH^-}""$ and
$""\mathrm{OH^-+H^-}""\rightleftarrows ""\mathrm{2 e+H_2O}""$. These transition
states are the lowest energy configurations possible for changing the charge of
the negatively charged surface intermediates. In particular, the transition
state for $""\mathrm{O^-+H^-}"" \rightleftarrows \mathrm{""2 e+OH^-""}$ limits the
reaction rate. These processes may contribute to the chemicurrent. This picture
should also apply to other catalytic chemical reactions on metal surfaces that
proceed through formation of charged surface intermediates and their consequent
discharge into the metal.",1407.2570v2
2014-07-24,Macro- and microscopic properties of strontium doped indium oxide,"Solid state synthesis and physical mechanisms of electrical conductivity
variation in polycrystalline, strontium doped indium oxide In2O3:(SrO)x were
investigated for materials with different doping levels at different
temperatures (T=20-300 C) and ambient atmosphere content including humidity and
low pressure. Gas sensing ability of these compounds as well as the sample
resistance appeared to increase by 4 and 8 orders of the magnitude,
respectively, with the doping level increase from zero up to x=10%. The
conductance variation due to doping is explained by two mechanisms:
acceptor-like electrical activity of Sr as a point defect and appearance of an
additional phase of SrIn2O4. An unusual property of high level (x=10%) doped
samples is a possibility of extraordinarily large and fast oxygen exchange with
ambient atmosphere at not very high temperatures (100-200 C). This peculiarity
is explained by friable structure of crystallite surface. Friable structure
provides relatively fast transition of samples from high to low resistive state
at the expense of high conductance of the near surface layer of the grains.
Microscopic study of the electro-diffusion process at the surface of oxygen
deficient samples allowed estimation of the diffusion coefficient of oxygen
vacancies in the friable surface layer at room temperature as 3x10^(-13)
cm^2/s, which is by one order of the magnitude smaller than that known for
amorphous indium oxide films.",1407.6471v1
2014-10-08,Epitaxial growth of Bi$_2$Pt$_2$O$_7$ pyrochlore,"Certain pyrochlore oxides are among the best oxygen catalysts in alkaline
media. Hence, exploring epitaxial films of these materials is of great
fundamental and technological interest. Unfortunately, direct film growth of
one of the most promising pyrochlores, Bi$_2$Pt$_2$O$_7$, has not yet been
achieved, owing to the difficulty of oxidizing platinum metal in the precursor
material to Pt$^{4+}$. In this work, in order to induce oxidation of the
platinum, we annealed pulsed laser deposited films consisting of epitaxial
$\delta$-Bi$_2$O$_3$ and co-deposited, comparatively disordered platinum. We
present synchrotron x-ray diffraction results that show the annealed films are
the first epitaxial crystals of Bi$_2$Pt$_2$O$_7$. We also visualized the
pyrochlore structure by scanning transmission electron microscopy, and observed
ordered cation vacancies in a bismuth-rich film but not in a platinum-rich
film. The similarity between the $\delta$-Bi$_2$O$_3$ and Bi$_2$Pt$_2$O$_7$
structures appears to facilitate the pyrochlore formation. These results
constitute a new approach for synthesis of novel pyrochlore thin film oxygen
catalysts.",1410.2307v1
2015-02-12,CO Oxidation Catalysed by Pd-based Bimetallic Nanoalloys,"Density functional theory based global geometry optimization has been used to
demonstrate the crucial influence of the geometry of the catalytic cluster on
the energy barriers for the CO oxidation reaction over Pd-based bimetallic
nanoalloys. We show that dramatic geometry change between the reaction
intermediates can lead to very high energy barriers and thus be prohibitive for
the whole process. This introduces challenges for both the design of new
catalysts, and theoretical methods employed. On the theory side, a careful
choice of geometric configurations of all reaction intermediates is crucial for
an adequate description of a possible reaction path. From the point of view of
the catalyst design, the cluster geometry can be controlled by adjusting the
level of interaction between the cluster and the dopant metal, as well as
between the adsorbate molecules and the catalyst cluster by mixing different
metals in a single nanoalloy particle. We show that substitution of a Pd atom
in the Pd$_{5}$ cluster with a single Ag atom to form Pd$_{4}$Ag$_{1}$ leads to
a potential improvement of the catalytic properties of the cluster for the CO
oxidation reaction. On the other hand, a single Au atom does not enhance the
properties of the catalyst, which is attributed to a weaker hybridization
between the cluster's constituent metals and the adsorbate molecules. Such
flexibility of properties of bimetallic nanoalloy clusters illustrates the
possibility of fine-tuning, which might be used for design of novel efficient
catalytic materials.",1502.03617v1
2015-03-03,Crossover of electron-electron interaction effect in Sn-doped indium oxide films,"We systematically study the structures and electrical transport properties of
a series of Sn-doped indium oxide (ITO) films with thickness $t$ ranging from
$\sim$5 to $\sim$53\,nm. Scanning electron microscopy and x-ray diffraction
results indicate that the $t\lesssim 16.8$\,nm films are polycrystalline, while
those $t\gtrsim 26.7$\,nm films are epitaxially grown along [100] direction.
For the epitaxial films, the Altshuler and Aronov electron-electron interaction
(EEI) effect governs the temperature behaviors of the sheet conductance
$\sigma_\square$ at low temperatures, and the ratios of relative change of Hall
coefficient $\Delta R_H/R_H$ to relative change of sheet resistance $\Delta
R_\square/R_\square$ are $\approx$2, which is quantitatively consistent with
Altshuler and Aronov EEI theory and seldom observed in other systems. For those
polycrystalline films, both the sheet conductance and Hall coefficient vary
linearly with logarithm of temperature below several tens Kelvin, which can be
well described by the current EEI theories in granular metals. We extract the
intergranular tunneling conductance of each film by comparing the
$\sigma_\square(T)$ data with the predication of EEI theories in granular
metals. It is found that when the tunneling conductance is less than the
conductance of a single indium tin oxide (ITO) grain, the ITO film reveals
granular metal characteristics in transport properties, conversely, the film
shows transport properties of homogeneous disordered conductors. Our results
indicate that electrical transport measurement can not only reveal the
underlying charge transport properties of the film but also be a powerful tool
to detect the subtle homogeneity of the film.",1503.00863v2
2015-03-25,Anisotropy of Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature,"We investigated thermal conductivity of free-standing reduced graphene oxide
films subjected to a high-temperature treatment of up to 1000 C. It was found
that the high-temperature annealing dramatically increased the in-plane thermal
conductivity, K, of the films from 3 W/mK to 61 W/mK at room temperature. The
cross-plane thermal conductivity, Kc, revealed an interesting opposite trend of
decreasing to a very small value of 0.09 W/mK in the reduced graphene oxide
films annealed at 1000 C. The obtained films demonstrated an exceptionally
strong anisotropy of the thermal conductivity, K/Kc ~ 675, which is
substantially larger even than in the high-quality graphite. The electrical
resistivity of the annealed films reduced to 1 - 19 Ohms/sq. The observed
modifications of the in-plane and cross-plane thermal conductivity components
resulting in an unusual K/Kc anisotropy were explained theoretically. The
theoretical analysis suggests that K can reach as high as ~500 W/mK with the
increase in the sp2 domain size and further reduction of the oxygen content.
The strongly anisotropic heat conduction properties of these films can be
useful for applications in thermal management.",1503.07239v1
2015-08-12,Mottness at finite doping and charge-instabilities in cuprates,"The intrinsic instability of underdoped copper oxides towards inhomogeneous
states is one of the central puzzles of the physics of correlated materials.
The influence of the Mott physics on the doping-temperature phase diagram of
copper oxides represents a major issue that is subject of intense theoretical
and experimental effort. Here, we investigate the ultrafast electron dynamics
in prototypical single-layer Bi-based cuprates at the energy scale of the
O-2p$\rightarrow$Cu-3d charge-transfer (CT) process. We demonstrate a clear
evolution of the CT excitations from incoherent and localized, as in a Mott
insulator, to coherent and delocalized, as in a conventional metal. This
reorganization of the high-energy degrees of freedom occurs at the critical
doping p$_{cr}\simeq$0.16 irrespective of the temperature, and it can be well
described by dynamical mean field theory calculations. We argue that the onset
of the low-temperature charge instabilities is the low-energy manifestation of
the underlying Mottness that characterizes the p<p$_{cr}$ region of the phase
diagram. This discovery sets a new framework for theories of charge order and
low-temperature phases in underdoped copper oxides.",1508.03075v3
2015-11-06,Experimental Demonstration of Single Electron Transistors Featuring SiO2 PEALD in Ni-SiO2-Ni Tunnel Junctions,"We report the use of plasma-enhanced atomic layer deposition (PEALD) to
fabricate single-electron transistors (SETs) featuring ultra-thin (~1 nm)
tunnel-transparent SiO2 in Ni-SiO2-Ni tunnel junctions. We show that as a
result of the O2 plasma steps in PEALD of SiO2, the top surface of the
underlying Ni electrode is oxidized. Additionally, the bottom surface of the
upper Ni layer is also oxidized where it is in contact with the deposited SiO2,
most likely as a result of oxygen-containing species on the surface of the
SiO2. Due to the presence of these surface parasitic layers of NiO, which
exhibit features typical of thermally activated transport, the resistance of
Ni-SiO2-Ni tunnel junctions is drastically increased. Moreover, the transport
mechanism is changed from quantum tunneling through the dielectric barrier to
one consistent with thermally activated resistors in series with tunnel
junctions. The reduction of NiO to Ni is therefore required to restore the
metal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealing
in a forming gas ambient at elevated temperatures is presented as a technique
to reduce both parasitic oxide layers. This method is of great interest for
devices that rely on MIM tunnel junctions with ultra-thin barriers. Using this
technique, we successfully fabricated MIM SETs with minimal trace of parasitic
NiO component. We demonstrate that the properties of the tunnel barrier in
nanoscale tunnel junctions can be evaluated by electrical characterization of
SETs.",1511.01980v1
2015-11-17,Accurate First-Principles Electrochemical Phase Diagrams for Ti Oxides from Density Functional Calculations,"Developing an accurate simulation method for the electrochemical stability of
solids, as well as understanding the physics related with its accuracy, is
critically important for improving the performance of compounds and predicting
the stability of new materials in aqueous environments. Herein we propose a
workflow for the accurate calculation of first-principles electrochemical phase
(Pourbaix) diagrams. With this scheme, we study the electrochemical stabilities
of Ti and Ti oxides using density-functional theory. First, we find the
accuracy of an exchange-correlation functional in predicting formation energies
and electrochemical stabilities is closely related with the electronic exchange
interaction therein. Second, the metaGGA and hybrid functionals with a more
precise description of the electronic exchange interaction lead to a systematic
improvement in the accuracy of the Pourbaix diagrams. Furthermore, we show that
accurate Ti Pourbaix diagrams also require that thermal effects are included
through vibrational contributions to the free energy. We then use these
diagrams to explain various experimental electrochemical phenomena for the
Ti--O system, and show that if experimental formation energies for Ti oxides,
which contain contributions from defects owing to their generation at high
(combustion) temperatures, are directly used to predict room temperature
Pourbaix diagrams then significant inaccuracies result. In contrast, the
formation energies from accurate first-principles calculations, e.g., using
metaGGA and hybrid functionals, are found to be more reliable. Finally to
facilitate the future application of our accurate electrochemical phase
equilibria diagrams, the variation of the Ti Pourbaix diagrams with aqueous ion
concentration is also provided.",1511.05549v1
2016-01-20,Strongly enhanced Rashba splittings in oxide heterostructure: a tantalite monolayer on BaHfO$_3$,"In the two-dimensional electron gas (2DEG) emerging at the transition metal
oxide surface and interface, it has been pointed out that the Rashba spin-orbit
interaction, the momentum-dependent spin splitting due to broken inversion
symmetry and atomic spin-orbit coupling, can have profound effects on
electronic ordering in the spin, orbit, and charge channels, and may help give
rise to exotic phenomena such as ferromagnetism-superconductivity coexistence
and topological superconductivity. Although a large Rashba splitting is
expected to improve experimental accessibility of such phenomena, it has not
been understood how we can maximally enhance this splitting. Here, we present a
promising route to realize significant Rashba-type band splitting using a thin
film heterostructure. Based on first-principles methods and analytic model
analyses, a tantalate monolayer on BaHfO$_3$ is shown to host two-dimensional
bands originating from Ta $t_{2g}$ states with strong Rashba spin splittings -
up to nearly 10% of the bandwidth - at both the band minima and saddle points
due to the maximal breaking of the inversion symmetry. Such 2DEG band structure
makes this oxide heterostructure a promising platform for realizing both a
topological superconductor which hosts Majorana fermions and the electron
correlation physics with strong spin-orbit coupling.",1601.05443v1
2016-02-22,"The effect of Ta oxygen scavenger layer on HfO$_2$-based resistive switching behavior: thermodynamic stability, electronic structure, and low-bias transport","Reversible resistive switching between high-resistance and low-resistance
states in metal-oxide-metal heterostructures makes them very interesting for
applications in random access memories. While recent experimental work has
shown that inserting a metallic ""oxygen scavenger layer"" between the positive
electrode and oxide improves device performance, the fundamental understanding
of how the scavenger layer modifies heterostructure properties is lacking. We
use density functional theory to calculate thermodynamic properties and
conductance of TiN/HfO$_2$/TiN heterostructures with and without Ta scavenger
layer. First, we show that Ta insertion lowers the formation energy of
low-resistance states. Second, while the Ta scavenger layer reduces the
Schottky barrier height in the high-resistance state by modifying the interface
charge at the oxide-electrode interface, the heterostructure maintains a high
resistance ratio between high- and low-resistance states. Finally, we show that
the low-bias conductance of device on-states becomes much less sensitive to the
spatial distribution of oxygen removed from the HfO$_2$ in the presence of the
Ta layer. By providing fundamental understanding of the observed improvements
with scavenger layers, we open a path to engineer interfaces with oxygen
scavenger layers to control and enhance device performance. In turn, this may
enable the realization of a non-volatile low-power memory technology with
concomitant reduction in energy consumption by consumer electronics and
significant benefits to society.",1602.06793v1
2016-03-08,Spatial conductivity mapping of unprotected and capped black phosphorus using microwave microscopy,"Thin layers of black phosphorus present an ideal combination of a 2D material
with a tunable direct bandgap and high carrier mobility. However the material
suffers from degradation in ambient conditions due to an oxidation reaction
which involves water, oxygen and light. We have measured the spatial profile of
the conductivity on flakes of black phosphorus as a function of time using
scanning microwave impedance microscopy. A microwave excitation (3 GHz) allows
to image a conducting sample even when covered with a dielectric layer. We
observe that on bare black phosphorus, the conductivity changes drastically
over the whole surface within a day. We demonstrate that the degradation
process is slowed down considerably by covering the material with a 10 nm layer
of hafnium oxide. It is stable for more than a week, opening up a route towards
stable black phosphorus devices in which the high dielectric constant of
hafnium oxide can be exploited. Covering black phosphorus with a 15 nm boron
nitride flake changes the degradation process qualitatively, it is dominated by
the edges of the flake indicating a diffusive process and happens on the scale
of days.",1603.02733v1
2016-06-04,Electrical characterization of chemical and dielectric passivation of InAs nanowires,"The native oxide at the surface of III-V nanowires, such as InAs, can be a
major source of charge noise and scattering in nanowire-based electronics,
particularly for quantum devices operated at low temperatures. Surface
passivation provides a means to remove the native oxide and prevent its
regrowth. Here, we study the effects of surface passivation and conformal
dielectric deposition by measuring electrical conductance through nanowire
field effect transistors treated with a variety of surface preparations. By
extracting field effect mobility, subthreshold swing, threshold shift with
temperature, and the gate hysteresis for each device, we infer the relative
effects of the different treatments on the factors influencing transport. It is
found that a combination of chemical passivation followed by deposition of an
aluminum oxide dielectric shell yields the best results compared to the other
treatments, and comparable to untreated nanowires. Finally, it is shown that an
entrenched, top-gated device using an optimally treated nanowire can
successfully form a stable double quantum dot at low temperatures. The device
has excellent electrostatic tunability owing to the conformal dielectric layer
and the combination of local top gates and a global back gate.",1606.01405v2
2016-07-25,Remarkable Hydrogen Storage on Beryllium Oxide Clusters: First Principles Calculations,"Since the current transportation sector is the largest consumer of oil, and
subsequently responsible for major air pollutants, it is inevitable to use
alternative renewable sources of energies for vehicular applications. The
hydrogen energy seems to be a promising candidate. To explore the possibility
of achieving a solid-state high-capacity storage of hydrogen for onboard
applications, we have performed first principles density functional theoretical
calculations of hydrogen storage properties of beryllium oxide clusters
(BeO)$_{n}$ (n=2 -- 8). We observed that polar BeO bond is responsible for
H$_{2}$ adsorption. The problem of cohesion of beryllium atoms does not arise,
as they are an integral part of BeO clusters. The (BeO)$_{n}$ (n=2 -- 8)
adsorbs 8--12 H$_{2}$ molecules with an adsorption energy in the desirable
range of reversible hydrogen storage. The gravimetric density of H$_{2}$
adsorbed on BeO clusters meets the ultimate 7.5 wt% limit, recommended for
onboard practical applications.
  In conclusion, beryllium oxide clusters exhibit a remarkable solid-state
hydrogen storage.",1607.07162v1
2016-09-04,Effect of thermal annealing on the heat transfer properties of reduced graphite oxide flakes: a nanoscale characterization via scanning thermal microscopy,"This paper reports on the thermal properties of reduced graphite oxide (RGO)
flakes, studied by means of scanning thermal microscopy (SThM). This technique
was demonstrated to allow thermal characterization of the flakes with a spatial
resolution of the order of a few tens of nanometers, while recording nanoscale
topography at the same time. Several individual RGO flakes were analyzed by
SThM, both as obtained after conventional thermal reduction and after a
subsequent annealing at 1700{\deg}C. Significant differences in the thermal
maps were observed between pristine and annealed flakes, reflecting higher heat
dissipation on annealed RGO flakes compared with pristine ones. This result was
correlated with the reduction of RGO structure defectiveness. In particular, a
substantial reduction of oxidized groups and sp3 carbons upon annealing was
proven by X-ray photoelectron and Raman spectroscopies, while the increase of
crystalline order was demonstrated by X-ray diffraction, in terms of higher
correlation lengths both along and perpendicular to the graphene planes.
Results presented in this paper provide experimental evidence for the
qualitative correlation between the defectiveness of graphene-related materials
and their thermal conductivity, which is clearly crucial for the exploitation
of these materials into thermally conductive nanocomposites.",1609.00998v2
2016-09-06,Size and density controlled metal nanocluster embedded metal-oxide-semiconductor structure for memory applications,"Metal-nanoclusters (NC), deposited by magnetron-based nanocluster source
coupled with quadrupole mass filter (QMF) assembly having independent control
over its size and density, are used in fabricating NC-based non-volatile memory
(NVM) devices. The effect of diameter and density on the NVM charge storage
characteristics are presented where Ag is used as the metal NC. The Ag-NC,
sandwiched between HfO$_2$ tunnel and control oxides, is deposited by using the
combination of the above two instruments. No annealing is performed at any
stage of the device fabrication. The largest hysteresis loop area in the
capacitance-voltage ($C-V$) characteristics of metal-oxide-semiconductor (MOS)
characteristics is observed for a cluster density of 1 $\times$ 10$^{11}$
cm$^{-2}$. Further, an NC size dependent hysteresis loop area is observed with
the MOS devices where the NC diameter is varied from 3 to 1.5 nm keeping the NC
density at 1 $\times$ 10$^{11}$ cm$^{-2}$. The device performance is found to
be improved with a reduction of the NC size and shows its best with the NC
diameter of 1.5 nm. The storage time of the NVM devices also increases with the
decrease in the NC diameter and exhibits their best performances for the NCs
with a diameter of 1.5 nm.",1609.01523v1
2016-09-20,Electron transport properties of sub-3-nm diameter copper nanowires,"Density functional theory and density functional tight-binding are applied to
model electron transport in copper nanowires of approximately 1 nm and 3 nm
diameters with varying crystal orientation and surface termination. The copper
nanowires studied are found to be metallic irrespective of diameter, crystal
orientation and/or surface termination. Electron transmission is highly
dependent on crystal orientation and surface termination. Nanowires oriented
along the [110] crystallographic axis consistently exhibit the highest electron
transmission while surface oxidized nanowires show significantly reduced
electron transmission compared to unterminated nanowires. Transmission per unit
area is calculated in each case, for a given crystal orientation we find that
this value decreases with diameter for unterminated nanowires but is largely
unaffected by diameter in surface oxidized nanowires for the size regime
considered. Transmission pathway plots show that transmission is larger at the
surface of unterminated nanowires than inside the nanowire and that
transmission at the nanowire surface is significantly reduced by surface
oxidation. Finally, we present a simple model which explains the transport per
unit area dependence on diameter based on transmission pathways results.",1609.06160v1
2016-09-21,Highly efficient and tuneable spin-to-charge conversion through Rashba coupling at oxide interfaces,"The spin-orbit interaction couples the electrons' motion to their spin.
Accordingly, passing a current in a material with strong spin-orbit coupling
generates a transverse spin current (spin Hall effect, SHE) and vice-versa
(inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as
charge-to-spin interconversion mechanisms offers a variety of novel spintronics
functionalities and devices, some of which do not require any ferromagnetic
material. However, the interconversion efficiency of SHE and ISHE (spin Hall
angle) is a bulk property that rarely exceeds ten percent, and does not take
advantage of interfacial and low-dimensional effects otherwise ubiquitous in
spintronics hetero- and mesostructures. Here, we make use of an
interface-driven spin-orbit coupling mechanism - the Rashba effect - in the
oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve
spin-to-charge conversion with unprecedented efficiency. Through spin-pumping,
we inject a spin current from a NiFe film into the oxide 2DES and detect the
resulting charge current, which can be strongly modulated by a gate voltage. We
discuss the amplitude of the effect and its gate dependence on the basis of the
electronic structure of the 2DES.",1609.06464v1
2016-10-06,Automated Phase Mapping with AgileFD and its Application to Light Absorber Discovery in the V-Mn-Nb Oxide System,"Rapid construction of phase diagrams is a central tenet of combinatorial
materials science with accelerated materials discovery efforts often hampered
by challenges in interpreting combinatorial x-ray diffraction datasets, which
we address by developing AgileFD, an artificial intelligence algorithm that
enables rapid phase mapping from a combinatorial library of x-ray diffraction
patterns. AgileFD models alloying-based peak shifting through a novel expansion
of convolutional nonnegative matrix factorization, which not only improves the
identification of constituent phases but also maps their concentration and
lattice parameter as a function of composition. By incorporating Gibbs phase
rule into the algorithm, physically meaningful phase maps are obtained with
unsupervised operation, and more refined solutions are attained by injecting
expert knowledge of the system. The algorithm is demonstrated through
investigation of the V-Mn-Nb oxide system where decomposition of eight oxide
phases, including two with substantial alloying, provides the first phase map
for this pseudo-ternary system. This phase map enables interpretation of
high-throughput band gap data, leading to the discovery of new solar light
absorbers and the alloying-based tuning of the direct-allowed band-gap energy
of MnV2O6. The open-source family of AgileFD algorithms can be implemented into
a broad range of high throughput workflows to accelerate materials discovery.",1610.02005v1
2016-10-26,Spatially Resolved Electronic Properties of Single-Layer WS$_2$ on Transition Metal Oxides,"There is a substantial interest in the heterostructures of semiconducting
transition metal dichalcogenides (TMDCs) amongst each other or with arbitrary
materials, through which the control of the chemical, structural, electronic,
spintronic, and optical properties can lead to a change in device paradigms. A
critical need is to understand the interface between TMDCs and insulating
substrates, for example high-$\kappa$ dielectrics, which can strongly impact
the electronic properties such as the optical gap. Here we show that the
chemical and electronic properties of the single-layer (SL) TMDC, WS$_2$, can
be transferred onto high-$\kappa$ transition metal oxide substrates TiO$_2$ and
SrTiO$_3$. The resulting samples are much more suitable for measuring their
electronic and chemical structures with angle-resolved photoemission than their
native-grown SiO$_2$ substrates. We probe the WS$_2$ on the micron scale across
100-micron flakes, and find that the occupied electronic structure is exactly
as predicted for freestanding SL WS$_2$ with a strong spin-orbit splitting of
420~meV and a direct band gap at the valence band maximum. Our results suggest
that TMDCs can be combined with arbitrary multi-functional oxides, which may
introduce alternative means of controlling the optoelectronic properties of
such materials.",1610.08480v1
2017-02-13,Design of $n$- and $p$-type oxide thermoelectrics in LaNiO$_3$/SrTiO$_3(001)$ superlattices exploiting interface polarity,"We investigate the structural, electronic, transport, and thermoelectric
properties of LaNiO$_3$/SrTiO$_3(001)$ superlattices containing either
exclusively $n$- or $p$-type interfaces or coupled interfaces of opposite
polarity by using density functional theory calculations with an on-site
Coulomb repulsion term. The results show that significant octahedral tilts are
induced in the SrTiO$_3$ part of the superlattice. Moreover, the La-Sr
distances and Ni-O out-of-plane bond lengths at the interfaces exhibit a
distinct variation by about $7\,\%$ with the sign of the electrostatic doping.
In contrast to the much studied LaAlO$_3$/SrTiO$_3$ system, the charge mismatch
at the interfaces is exclusively accommodated within the LaNiO$_3$ layers,
whereas the interface polarity leads to a band offset and to the formation of
an electric field within the coupled superlattice. Features of the electronic
structure indicate an orbital-selective quantization of quantum well states.
The potential- and confinement-induced multiband splitting results in complex
cylindrical Fermi surfaces with a tendency towards nesting that depends on the
interface polarity. The analysis of the thermoelectric response reveals a
particularly large positive Seebeck coefficient ($135~\mu$V/K) and a high
figure of merit ($0.35$) for room-temperature cross-plane transport in the
$p$-type superlattice that is attributed to the participation of the SrTiO$_3$
valence band. Superlattices with either $n$- or $p$-type interfaces show
cross-plane Seebeck coefficients of opposite sign and thus emerge as a platform
to construct an oxide-based thermoelectric generator with structurally and
electronically compatible $n$- and $p$-type oxide thermoelectrics.",1702.03898v1
2017-02-23,Optical Spectra of Open-Shell and Closed-Shell Graphene-Based Molecules,"We have computationally investigated absorption spectra of a specifically
configured set of graphene-based molecules involving (1) a sp2 bare graphene
sheet; (2) framed graphene sheets containing different chemical addends
terminating dangling bonds of edge atoms but keeping sp2 configured basal
plane; and (3) bulk sp3 graphene sheets resulted from the chemical modification
occurred at not only the bare sheet circumference but at its basal plane as
well. Framed molecules, open-shell by nature, present different kinds of
reduced graphene oxides and present the main building blocks of graphene
quantum dots. Closed-shell bulk molecules present models of nanosize graphene
oxide. UHF ground states and ZINDO/S excited states of the molecules were
analyzed. The UHF-ZINDO/S combination is well coherent in the case of bulk
molecules for which UHF and RHF ground state results are identical. In the case
of framed molecules, the incoherence of the UHF and close-shell ZINDO/S
approaches is revealed in a considerable decreasing of the HOMO-LUMO energy
gap, which provides unreal drastic red shift of absorption spectra of
open-shell molecules into IR region. The conclusion is justified by a
comparative analysis of calculated and experimental data on absorption and
fluorescence spectra of graphene quantum dots and graphene oxides.",1702.07197v1
2017-02-25,Serum protein resistant behavior of multisite-bound poly(ethylene glycol) chains onto iron oxide surfaces,"Recent surveys have shown that the number of nanoparticle-based formulations
actually used at the clinical level is significantly lower than expected a
decade ago. One reason for this is that the nanoparticle physicochemical
properties fall short for handling the complexity of biological environments
and for preventing nonspecific protein adsorption. In this study, we address
the issue of the interactions of plasma proteins with polymer coated surfaces.
To this aim, we use a non-covalent grafting-to method to functionalize iron
oxide sub-10 nm nanoparticles and iron oxide flat substrates, and compare their
protein responses. The functionalized copolymers consist in alternating
poly(ethylene glycol) (PEG) chains and phosphonic acid grafted on the same
backbone. Quartz Crystal Microbalance with dissipation was used to monitor the
polymer adsorption kinetics and to evaluate the resistance to protein
adsorption. On flat substrates, functionalized PEG copolymers adsorb and form a
brush in the moderate or in the highly stretched regimes, with density between
0.15 and 1.5 nm-2. PEG layers using phosphonic acid as linkers exhibit
excellent protein resistance. In contrast, layers prepared with carboxylic acid
as grafting agent exhibit mitigated protein responses and layer
destructuration. The present study establishes a correlation between the
long-term stability of PEG coated particles in biofluids and the protein
resistance of surfaces coated with the same polymers.",1702.07857v1
2017-02-25,Mott metal-insulator transition in the Doped Hubbard-Holstein model,"Motivated by the current interest in the understanding of the Mott insulators
away from half filling, observed in many perovskite oxides, we study the Mott
metal-insulator transition (MIT) in the doped Hubbard-Holstein model using the
Hatree-Fock mean field theory. The Hubbard-Holstein model is the simplest model
containing both the Coulomb and the electron-lattice interactions, which are
important ingredients in the physics of the perovskite oxides. In contrast to
the half-filled Hubbard model, which always results in a single phase (either
metallic or insulating), our results show that away from half-filling, a mixed
phase of metallic and insulating regions occur. As the dopant concentration is
increased, the metallic part progressively grows in volume, until it exceeds
the percolation threshold, leading to percolative conduction. This happens
above a critical dopant concentration $\delta_c$, which, depending on the
strength of the electron-lattice interaction, can be a significant fraction of
unity. This means that the material could be insulating even for a substantial
amount of doping, in contrast to the expectation that doped holes would destroy
the insulating behavior of the half-filled Hubbard model. Our theory provides a
framework for the understanding of the density-driven metal-insulator
transition observed in many complex oxides.",1703.02886v2
2017-03-21,Electro-Oxidation of Ni42 Steel: A highly Active Bifunctional Electrocatalyst,"Janus type Water-Splitting Catalysts have attracted highest attention as a
tool of choice for solar to fuel conversion. AISI Ni 42 steel was upon harsh
anodization converted in a bifunctional electrocatalyst. Oxygen evolution
reaction- (OER) and hydrogen evolution reaction (HER) are highly efficiently
and steadfast catalyzed at pH 7, 13, 14, 14.6 (OER) respectively at pH 0, 1,
13, 14, 14.6 (HER). The current density taken from long-term OER measurements
in pH 7 buffer solution upon the electro activated steel at 491 mV
overpotential was around 4 times higher (4 mA/cm2) in comparison with recently
developed OER electrocatalysts. The very strong voltage-current behavior of the
catalyst shown in OER polarization experiments at both pH 7 and at pH 13 were
even superior to those known for IrO2-RuO2. No degradation of the catalyst was
detected even when conditions close to standard industrial operations were
applied to the catalyst. A stable Ni-, Fe- oxide based passivating layer
sufficiently protected the bare metal for further oxidation. Quantitative
charge to oxygen- (OER) and charge to hydrogen (HER) conversion was confirmed.
High resolution XPS spectra showed that most likely gamma-NiO(OH) and FeO(OH)
are the catalytic active OER and NiO is the catalytic active HER species.",1703.07775v1
2017-03-29,Molecular dynamics simulations and in vitro analysis of the CRMP2 thiol switch,"Collapsin response mediator protein CRMP2 (gene: DPYSL2) is crucial for
neuronal development. The homotetrameric CRMP2 complex is regulated via two
mechanisms, first by phosphorylation at, and second by reduction and oxidation
of the Cys504 residues of two adjacent subunits. Here, we analyzed the effects
of this redox switch on the protein in vitro combined with force field
molecular dynamics (MD). Earlier X-ray data contain the structure of the rigid
body of the molecule but lack the flexible C-terminus with the important sites
for phosphorylation and redox regulation. An in silico model for this part was
established by replica exchange simulations and homology modelling, which is
consistent with results gained from CD spectroscopy with recombinant protein.
Thermofluor data indicated that the protein aggregates at bivalent ion
concentrations below 200 mM. In simulations the protein surface was covered at
these conditions by large amounts of ions, which most likely prevent
aggregation. A tryptophan residue (Trp295) in close proximity to the forming
disulfide allowed the measurement of the structural relaxation of the rigid
body upon reduction by fluorescent quenching. We were also able to determine
the second order rate constant of CRMP2 oxidation by H2O2. The simulated
solvent accessible surface of the hydroxyl group of Ser518 significantly
increased upon reduction of the disulfide bond. Our results give first detailed
insight in the profound structural changes of the tetrameric CRMP2 due to
oxidation and indicate a tightly connected regulation by phosphorylation and
redox modification.",1703.10124v1
2017-08-13,Maximal Rashba-like spin splitting via kinetic energy-driven inversion symmetry breaking,"Engineering and enhancing inversion symmetry breaking in solids is a major
goal in condensed matter physics and materials science, as a route to advancing
new physics and applications ranging from improved ferroelectrics for memory
devices to materials hosting Majorana zero modes for quantum computing. Here,
we uncover a new mechanism for realising a much larger energy scale of
inversion symmetry breaking at surfaces and interfaces than is typically
achieved. The key ingredient is a pronounced asymmetry of surface hopping
energies, i.e. a kinetic energy-driven inversion symmetry breaking, whose
energy scale is pinned at a significant fraction of the bandwidth. We show,
from spin- and angle-resolved photoemission, how this enables surface states of
3d and 4d-based transition-metal oxides to surprisingly develop some of the
largest Rashba-like spin splittings that are known. Our findings open new
possibilities to produce spin textured states in oxides which exploit the full
potential of the bare atomic spin-orbit coupling, raising exciting prospects
for oxide spintronics. More generally, the core structural building blocks
which enable this are common to numerous materials, providing the prospect of
enhanced inversion symmetry breaking at judiciously-chosen surfaces of a
plethora of compounds, and suggesting routes to interfacial control of
inversion symmetry breaking in designer heterostructures.",1708.03887v1
2017-08-18,Design of new Mott multiferroics via complete charge transfer: promising candidates for bulk photovoltaics,"Optimal materials to induce bulk photovoltaic effects should lack inversion
symmetry and have an optical gap matching the energies of visible radiation.
Ferroelectric perovskite oxides such as BaTiO$_3$ and PbTiO$_3$ exhibit
substantial polarization and stability, but have the disadvantage of
excessively large band gaps. We use both density functional theory and
dynamical mean field theory calculations to design a new class of Mott
multiferroics--double perovskite oxides $A_2$VFeO$_6$ ($A$=Ba, Pb, etc). While
neither perovskite $A$VO$_3$ nor $A$FeO$_3$ is ferroelectric, in the double
perovskite $A_2$VFeO$_6$ a `complete' charge transfer from V to Fe leads to a
non-bulk-like charge configuration--an empty V-$d$ shell and a half-filled
Fe-$d$ shell, giving rise to a polarization comparable to that of ferroelectric
$A$TiO$_3$. Different from nonmagnetic $A$TiO$_3$, the new double perovskite
oxides have an antiferromagnetic ground state and around room temperatures, are
paramagnetic Mott insulators. Most importantly, the V $d^0$ state significantly
reduces the band gap of $A_2$VFeO$_6$, making it smaller than that of
$A$TiO$_3$ and BiFeO$_3$ and rendering the new multiferroics a promising
candidate to induce bulk photovoltaic effects.",1708.05506v1
2017-08-30,Transport properties of the top and bottom surfaces in monolayer MoS2 grown by chemical vapor deposition,"The advantage of MoS2, compared with graphene, is the direct growth on
various oxide substrates by chemical vapor deposition (CVD) without utilizing
catalytic metal substrates, which facilitates practical applications for
electronics. The carrier mobility is, however, degraded from the intrinsic
limit mainly due to short-range scattering caused by S vacancies formed during
CVD growth. If the upper limit for the crystallinity of CVD-MoS2 on oxide
substrates is determined by the MoS2/substrate interaction during growth, it
will hinder the advantage. In this study, we investigated the interaction
between monolayer MoS2 and a SiO2/Si substrate and the difference in
crystallinity between the top and bottom S surfaces due to the MoS2/substrate
interaction. Raman and photoluminescence spectroscopy indicated that doping and
strain were induced in MoS2 from the substrate, but they could be removed by
transferring MoS2 to a new substrate using polymers. The newly developed
polymer-transfer technique enabled selective transfer of the bottom or top
surface of CVD-MoS2 onto a new SiO2/Si substrate. The metal-insulator
transition was clearly observed for both the normal and inverse transfers,
suggesting that the crystallinity of CVD-MoS2 is high and that the
crystallinity of the bottom surface interacting with the substrate was similar
to that of the top free surface. These results provide positive prospects for
the further improvement of the crystallinity of MoS2 on oxide substrates by
reconsidering the growth conditions.",1708.09240v1
2018-02-26,Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors,"Two dimensional materials such as Transition Metal Dichalcogenides (TMDC) and
their bi-layer/tri-layer heterostructures have become the focus of intense
research and investigation in recent years due to their promising applications
in electronics and optoelectronics. In this work, we have explored device level
performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M=Mo or, W and X=S
or, Se) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in the
quantum ballistic regime. Our simulation shows that device 'on' current can be
improved by inserting a WS2 monolayer between two MoS2 monolayers. Application
of biaxial tensile strain reveals a reduction in drain current which can be
attributed to the lowering of carrier effective mass with increased tensile
strain. In addition, it is found that gate underlap geometry improves
electrostatic device performance by improving sub-threshold swing. However,
increase in channel resistance reduces drain current. Besides exploring the
prospect of these materials in device performance, novel trilayer TMDC
heterostructure double gate Field Effect Transistors (FETs) are proposed for
sensing Nano biomolecules as well as for pH sensing. Bottom gate operation
ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation
results found in this work reveal that scaling of bottom gate oxide results in
better sensitivity while top oxide scaling exhibits an opposite trend. It is
also found that, for identical operating conditions, proposed TMDC FET pH
sensors show super-Nernst sensitivity indicating these materials as potential
candidates in implementing such sensor. Besides pH sensing, all these materials
show high sensitivity in the sub-threshold region as a channel material in
nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.",1802.09141v1
2018-11-06,An optical transmission spectrum of the ultra-hot Jupiter WASP-33b. First indication of AlO in an exoplanet,"There has been increasing progress toward detailed characterization of
exoplanetary atmospheres, in both observations and theoretical methods.
Improvements in observational facilities and data reduction and analysis
techniques are enabling increasingly higher quality spectra, especially from
ground-based facilities. The high data quality also necessitates concomitant
improvements in models required to interpret such data. In particular, the
detection of trace species such as metal oxides has been challenging. Extremely
irradiated exoplanets (~3000 K) are expected to show oxides with strong
absorption signals in the optical. However, there are only a few hot Jupiters
where such signatures have been reported. Here we aim to characterize the
atmosphere of the ultra-hot Jupiter WASP-33b using two primary transits taken
18 orbits apart. Our atmospheric retrieval, performed on the combined data
sets, provides initial constraints on the atmospheric composition of WASP-33b.
We report a possible indication of aluminum oxide (AlO) at 3.3-sigma
significance. The data were obtained with the long slit OSIRIS spectrograph
mounted at the 10-meter Gran Telescopio Canarias. We cleaned the brightness
variations from the light curves produced by stellar pulsations, and we
determined the wavelength-dependent variability of the planetary radius caused
by the atmospheric absorption of stellar light. A simultaneous fit to the two
transit light curves allowed us to refine the transit parameters, and the
common wavelength coverage between the two transits served to contrast our
results. Future observations with HST as well as other large ground-based
facilities will be able to further constrain the atmospheric chemical
composition of the planet.",1811.02573v1
2018-11-09,Oxygen Electromigration and Energy Band Reconstruction Induced by Electrolyte Field Effect at Oxide Interfaces,"Electrolyte gating is a powerful means for tuning the carrier density and
exploring the resultant modulation of novel properties on solid surfaces.
However, the mechanism, especially its effect on the oxygen migration and
electrostatic charging at the oxide heterostructures, is still unclear. Here we
explore the electrolyte gating on oxygen-deficient interfaces between SrTiO3
(STO) crystals and LaAlO3 (LAO) overlayer through the measurements of
electrical transport, X-ray absorption spectroscopy (XAS) and photoluminescence
(PL) spectra. We found that oxygen vacancies (Ovac) were filled selectively and
irreversibly after gating due to oxygen electromigration at the amorphous
LAO/STO interface, resulting in a reconstruction of its interfacial band
structure. Because of the filling of Ovac, the amorphous interface also showed
an enhanced electron mobility and quantum oscillation of the conductance.
Further, the filling effect could be controlled by the degree of the
crystallinity of the LAO overlayer by varying the growth temperatures. Our
results reveal the different effects induced by electrolyte gating, providing
further clues to understand the mechanism of electrolyte gating on buried
interfaces and also opening a new avenue for constructing high-mobility oxide
interfaces.",1811.03793v1
2018-11-12,Low Lattice Thermal Conductivity of a Two-Dimensional Phosphorene Oxide,"A fundamental understanding of the phonon transport mechanism is important
for optimizing the efficiency of thermoelectric devices. In this study, we
investigate the thermal transport properties of the oxidized form of
phosphorene called phosphorene oxide (PO) by solving phonon Boltzmann transport
equation based on first-principles density functional theory. We reveal that PO
exhibits a much lower thermal conductivity (2.42-7.08 W/mK, at 300 K) than its
pristine counterpart as well as other two-dimensional materials. To comprehend
the physical origin of such low thermal conductivity, we scrutinize the
contribution of each phonon branch to the thermal conductivity by evaluating
various mode-dependent quantities including Gruneisen parameters, anharmonic
threep-honon scattering rate, phase space of three-phonon scattering processes.
Our results show that its exible puckered structure of PO leads to smaller
sound velocities; its broken-mirror symmetry allows more ZA phonon scattering;
and the relatively-free vibration of dangling oxygen atoms in PO gives rise to
additional scattering resulting in further reduction in the phonon lifetime.
These results can be verified by the fact that PO has larger phase space for
three-phonon processes than phosphorene. Furthermore we show that the thermal
conductivity of PO can be optimized by controlling its size or its phonon mean
free path, indicating that PO can be a promising candidate for low-dimensional
thermoelectric devices.",1811.04612v2
2018-11-20,Towards integrated metatronics: a holistic approach on precise optical and electrical properties of Indium Tin Oxide,"The class of transparent conductive oxides includes the material indium tin
oxide (ITO) and has become a widely used material of modern every-day life such
as in touch screens of smart phones and watches, but also used as an optically
transparent low electrically-resistive contract in the photovoltaics industry.
More recently ITO has shown epsilon-near-zero (ENZ) behavior in the
telecommunication frequency band enabling both strong index modulation and
other optically-exotic applications such as metatronics. However the ability to
precisely obtain targeted electrical and optical material properties in ITO is
still challenging due to complex intrinsic effects in ITO and as such no
integrated metatronic platform has been demonstrated to-date. Here we deliver
an extensive and accurate description process parameters of RF-sputtering,
showing a holistic control of the quality of ITO thin films in the visible and
particularly near-infrared spectral region. We further are able to
custom-engineer the ENZ point across the telecommunication band by explicitly
controlling the sputtering process conditions. Exploiting this control we
design a functional sub-wavelength-scale filter based on lumped
circuit-elements, towards the realization of integrated metatronic devices and
circuits.",1811.08344v4
2019-04-30,Semitransparent Polymer-Based Solar Cells with Aluminum-Doped Zinc Oxide Electrodes,"With the usage of two transparent electrodes, organic solar cells are
semitransparent and may be combined to parallel-connected multi-junction
devices or used for innovative applications like power-generating windows. A
challenging issue is the optimization of the electrodes, in order to combine
high transparency with adequate electric properties. In the present work, we
study the potential of sputter-deposited aluminum-doped zinc oxide (AZO) as an
alternative to the widely used but relatively expensive indium tin oxide (ITO)
as cathode material in semitransparent polymer-fullerene solar cells.
Concerning the anode, we utilized an insulator/metal/insulator structure based
on ultra-thin Au films embedded between two evaporated MoO$_3$ layers, with the
outer MoO$_3$ film (capping layer) serving as a light coupling layer. The
performance of the ITO-free semitransparent solar cells is systematically
studied as dependent on the thickness of the capping layer and the active
layer, as well as the illumination direction. These variations are found to
have strong impact on the obtained photocurrent. We performed optical
simulations of the electric field distribution within the devices to analyze
the origin of the current variations and provide deep insight in the device
physics. With the conventional absorber materials studied herein, optimized
ITO-free and semitransparent devices reached 2.0% power conversion efficiency
and a maximum optical transmission of 60%, with the device concept being
potentially transferable to other absorber materials.",1905.00112v1
2019-05-11,Separating Electrons and Donors in BaSnO3 via Band Engineering,"Through a combination of thin film growth, hard X-ray photoelectron
spectroscopy (HAXPES), scanning transmission electron microscopy/electron
energy loss spectroscopy (STEM/EELS), magneto-transport measurements, and
transport modeling, we report on the demonstration of modulation-doping of
BaSnO3 (BSO) using a wider bandgap La-doped SrSnO3 (LSSO) layer. Hard X-ray
photoelectron spectroscopy (HAXPES) revealed a valence band offset of 0.71 +/-
0.02 eV between LSSO and BSO resulting in a favorable conduction band offset
for remote doping of BSO using LSSO. Nonlinear Hall effect of LSSO/BSO
heterostructure confirmed two-channel conduction owing to electron transfer
from LSSO to BSO and remained in good agreement with the results of
self-consistent solution to one-dimensional Poisson and Schr\""odinger
equations. Angle-dependent HAXPES measurements revealed a spatial distribution
of electrons over 2-3 unit cells in BSO. These results bring perovskite oxides
a step closer to room-temperature oxide electronics by establishing
modulation-doping approaches in non-SrTiO3-based oxide heterostructure.",1905.04563v1
2019-05-26,Plasmonic Light Illumination Creates a Channel to Achieve Fast Degradation of Ti3C2Tx Nanosheets,"Two-dimensional (2D) material-controllable degradation under light radiation
is crucial for their photonics and medical-related applications, which are yet
to be investigated. In this paper, we first report the laser illumination
method to regulate the degradation rate of Ti3C2Tx nanosheets in aqueous
solution. Comprehensive characterization of intermediates and final products
confirmed that plasmonic laser promoting the oxidation was strikingly different
from heating the aqueous solution homogeneously. Laser illumination would
nearly 10 times accelerate the degradation of Ti3C2Tx nanosheets in initial
stage and create many smaller-sized oxidized products in a short time.
Laser-induced fast degradation was principally ascribed to surface plasmonic
resonance effect of Ti3C2Tx nanosheets. The degradation ability of such
illumination could be controlled either by tuning the excitation wavelength or
changing the excitation power. Furthermore, the laser- or thermal-induced
degradation could be retarded by surface protection of Ti3C2Tx nanosheets. Our
results suggest that plasmonic electron excitation of Ti3C2Tx nanosheets could
build a new reaction channel and lead to the fast oxidation of nanosheets in
aqueous solution, potentially enabling a series of water-based applications.",1905.10839v2
2019-05-31,Coexistence of polar displacements and conduction in doped ferroelectrics: an ab initio comparative study,"Polar metals are rare because free carriers in metals screen electrostatic
potential and eliminate internal dipoles. Degenerate doped ferroelectrics may
create an approximate polar metallic phase. We use first-principles
calculations to investigate $n$-doped LiNbO$_3$-type oxides (LiNbO$_3$ as the
prototype) and compare to widely studied perovskite oxides (BaTiO$_3$ as the
prototype). In the rigid-band approximation, substantial polar displacements in
$n$-doped LiNbO$_3$ persist even at 0.3 $e$/f.u. ($\simeq$ 10$^{21}$
cm$^{-3}$), while polar displacements in $n$-doped BaTiO$_3$ quickly get
suppressed and completely vanish at 0.1 $e$/f.u. Furthermore, in $n$-doped
LiNbO$_3$, Li-O displacements decay more slowly than Nb-O displacements, while
in $n$-doped BaTiO$_3$, Ba-O and Ti-O displacements decay approximately at the
same rate. Supercell calculations that use oxygen vacancies as electron donors
support the main results from the rigid-band approximation and provide more
detailed charge distributions. Substantial cation displacements are observed
throughout LiNbO$_{3-\delta}$($\delta = 4.2\%$), while cation displacements in
BaTiO$_{3-\delta}$($\delta = 4.2\%$) are almost completely suppressed. We find
that conduction electrons in LiNbO$_{3-\delta}$ are not as uniformly
distributed as in BaTiO$_{3-\delta}$, implying that the rigid-band
approximation should be used with caution in simulating electron doped
LiNbO$_3$-type oxides. Our work shows that polar distortions and conduction can
coexist in a wide range of electron concentration in $n$-doped LiNbO$_3$, which
is a practical approach to generating an approximate polar metallic phase.
Combining doped ferroelectrics and doped semiconductors may create new
functions for devices.",1905.13384v1
2014-03-20,Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals,"Hexagonal boron nitride is the only substrate that has so far allowed
graphene devices exhibiting micron-scale ballistic transport. Can other
atomically flat crystals be used as substrates for making quality graphene
heterostructures? Here we report on our search for alternative substrates. The
devices fabricated by encapsulating graphene with molybdenum or tungsten
disulphides and hBN are found to exhibit consistently high carrier mobilities
of about 60,000 cm$^{2}$V$^{-1}$s$^{-1}$. In contrast, encapsulation with
atomically flat layered oxides such as mica, bismuth strontium calcium copper
oxide and vanadium pentoxide results in exceptionally low quality of graphene
devices with mobilities of ~ 1,000 cm$^{2}$ V$^{-1}$s$^{-1}$. We attribute the
difference mainly to self-cleansing that takes place at interfaces between
graphene, hBN and transition metal dichalcogenides. Surface contamination
assembles into large pockets allowing the rest of the interface to become
atomically clean. The cleansing process does not occur for graphene on
atomically flat oxide substrates.",1403.5225v2
2014-03-29,Tailored surfaces of perovskite oxide substrates for conducted growth of thin films,"Oxide electronics relies on the availability of epitaxial oxide thin films.
The extreme flexibility of the chemical composition of ABO3 perovskites and the
broad spectrum of properties they cover, inspire the creativity of scientists
and place perovskites in the lead of functional materials for advanced
technologies. Moreover, emerging properties are being discovered at interfaces
between distinct perovskites that could not be anticipated on the basis of
those of the adjacent epitaxial layers. All dreamed new prospects require the
use of suitable substrates for epitaxial growth. Perovskite single crystals are
the workhorses of this activity and understanding and controlling their surface
properties have become critical. In this tutorial review we will chiefly focus
on the impact of the morphology and composition of the surface of ABO3
perovskite substrates on the growth mechanisms and properties of thin films
epitaxially grown on them. As SrTiO3 is the most popular substrate, we will
mostly concentrate on describing the current understanding and achievements for
it. Illustrative examples of other perovskite substrates (LaAlO3, LSAT and
DyScO3) will be also included. We will show that distinct chemical terminations
can exist on the surfaces used for growth and we will review methods employed
either to select the most appropriate one for specific growth to allow, for
instance, tailoring the ultimate outmost epilayer, or to induce self-ordering
to engineer long-range nanoscale patterns of chemical terminations. We will
demonstrate the capacity of this knowledge by the growth of low-dimensional
organic and inorganic structures.",1403.7655v1
2016-11-09,Importance of strain reduction in improvement of optical transmission and conductance in Si4+ doped ZnO: a probable new moisture resistant Transparent Conductive Oxide,"Si doped ZnO has been reported to be a better conductor than pure ZnO. It is
reported that carrier density increases and hence conductivity increases.
However, the effect on optical transmission is yet not clear until our recent
report [1]. Zn1-xSixO for x= 0, 0.013, 0.020 and 0.027 have been synthesized
using sol-gel method (a citric acid-glycerol route) followed by solid state
sintering. We found that there is a decrease in defect states due to Si doping.
The correlation of strain to the decrement in vacancy sites is discussed in
this report. In modern electronics and solar cell fabrication, transparent
conductive oxides (TCOs) are important components which conduct electrically
without absorbing visible light. Known TCOs are extremely costly and are
composed of non-abundant elements. Search for new ecofriendly, cheap and
sustainable TCOs has been a recent research of attraction. Keeping in mind that
most solar cells are exposed to natural conditions, the humidity tolerance
becomes a determining factor. We report that sensitivity to moisture decreases
drastically while the conductivity and optical transparency increases with
doping. The reduction of strain and improvement of transport properties results
in increased conductivity of Si doped ZnO pellets, tempting us to envisage this
material as a probable alternate TCO.",1611.02837v1
2017-01-03,Conduction Channel Formation and Dissolution Due to Oxygen Thermophoresis/Diffusion in Hafnium Oxide Memristors,"Transition metal oxide memristors, or resistive random-access memory (RRAM)
switches, are under intense development for storage-class memory because of
their favorable operating power, endurance, speed, and density. Their
commercial deployment critically depends on predictive compact models based on
understanding nanoscale physico-chemical forces, which remains elusive and
controversial owing to the difficulties in directly observing atomic motions
during resistive switching, Here, using scanning transmission synchrotron x-ray
spectromicroscopy to study in-situ switching of hafnium oxide memristors, we
directly observed the formation of a localized oxygen-deficiency-derived
conductive channel surrounded by a low-conductivity ring of excess oxygen.
Subsequent thermal annealing homogenized the segregated oxygen, resetting the
cells towards their as-grown resistance state. We show that the formation and
dissolution of the conduction channel are successfully modeled by radial
thermophoresis and Fick diffusion of oxygen atoms driven by Joule heating. This
confirmation and quantification of two opposing nanoscale radial forces that
affect bipolar memristor switching are important components for any future
physics-based compact model for the electronic switching of these devices.",1701.00864v1
2017-01-19,Tuneable Sieving of Ions Using Graphene Oxide Membranes,"Graphene oxide membranes show exceptional molecular permeation properties,
with a promise for many applications. However, their use in ion sieving and
desalination technologies is limited by a permeation cutoff of ~9 Angstrom,
which is larger than hydrated ion diameters for common salts. The cutoff is
determined by the interlayer spacing d ~13.5 Angstrom, typical for graphene
oxide laminates that swell in water. Achieving smaller d for the laminates
immersed in water has proved to be a challenge.Here we describe how to control
d by physical confinement and achieve accurate and tuneable ion sieving.
Membranes with d from ~ 9.8 Angstrom to 6.4 Angstrom are demonstrated,
providing the sieve size smaller than typical ions' hydrated diameters.In this
regime, ion permeation is found to be thermally activated with energy barriers
of ~10-100 kJ/mol depending on d. Importantly, permeation rates decrease
exponentially with decreasing the sieve size but water transport is weakly
affected (by a factor of <2). The latter is attributed to a low barrier for
water molecules entry and large slip lengths inside graphene capillaries.
Building on these findings, we demonstrate a simple scalable method to obtain
graphene-based membranes with limited swelling, which exhibit 97% rejection for
NaCl.",1701.05519v1
2017-04-04,Review on Titania Nanopowder- Processing and Applications,"This review work focuses on the milling process of titania (TiO2) nanopowder.
TiO2 is a naturally available material. It is an inorganic semi-conducting
oxide of titanium metal. Titanium oxide, titanium dioxide, and titanium (IV)
oxide are the other names. TiO2 nanopowder is one of the well-known synthetic
materials in the modern nanotechnology field. It has many interesting,
lucrative and salient properties. These characters are attracting the
researchers towards to exploit this material in variety of applications from
energy to environmental. It is a highly sensitive and excellent photo-catalyst
material. So, it can be used in gas sensors, in water splitting to generate
hydrogen, and in waste water treatment to degrade the organic pollutants. It is
soluble in ethanol, ethylene glycol and chloroform. TiO2 nanopowder is prepared
by many methods such as sol-gel method, chemical vapour deposition,
hydro-thermal, micro-emulsion etc. However, low cost and large scale synthesis
of nanoparticles for commercial applications are the major challenges in the
present day scenario. Mechanical milling is a simple method to prepare
nanopowder where milling time plays very important role. The milling time may
vary from 0 to 60 hour. The crystallinity, phase, size, shape and surface
features are some of the factors affected by the milling process. For the
preparation of TiO2 nanomaterial, the mechanical milling is more advantageous
than other methods. It is a low cost, non toxic method which offers high
chemical stability. The finely grinded TiO2 nano powder offers shiny surface
and brilliant colours. Milling of TiO2 is done for size reduction. Doping of
TiO2 is done to improve the efficiencies and to minimize drawbacks.",1704.00981v1
2011-11-27,Evolution of structural properties of iron oxide nano particles during temperature treatment from 250°C - 900°C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study,"Iron oxide nano particles with nominal Fe2O3 stoichiometry were synthesized
by a wet, soft chemical method with the heat treatment temperatures from
250{\deg}C to 900{\deg}C in air. The variation in the structural properties of
the nano particles with the heat treatment temperature was studied by X-ray
diffraction and Fe K shell X-ray absorption study. X-ray diffractograms show
that at lower annealing temperatures nano particle comprises both maghemite and
hematite phases. With increasing temperature, the remainder of the maghemite
phase transformed completely to hematite. Profile analysis of the leading Bragg
reflections reveals that the average crystallite size increases from 50 nm to
150 nm with increasing temperature. The mean primary particle size decreased
from 105 nm to 90 nm with increasing heat treatment temperature. The X-ray
diffraction results are paralleled by systematic changes in the pre-edge
structure of the Fe K-edge X-ray absorption spectra, in particular by a gradual
decrease of the t2g/eg peak height ratio of the two leading pre-edge
resonances, confirming oxidation of the Fe from Fe2+ towards Fe3+. Transmission
electron microscopy (TEM) on the samples treated at temperatures as high as
900{\deg}C showed particles with prismatic morphology along with the formation
of stacking fault like defects. High resolution TEM with selected area electron
diffraction (SAED) of samples heat treated above 350{\deg}C showed that the
nano particles have well developed lattice fringes corresponding to that of
(110) plane of hematite.",1111.6204v1
2012-01-30,Electronic correlations and crystal structure distortions in BaBiO3,"BaBiO3 is a material where formally Bi4+ ions with the half-filled 6s-states
form the alternating set of Bi3+ and Bi5+ ions resulting in a charge ordered
insulator. The charge ordering is accompanied by the breathing distortion of
the BiO6 octahedra (extension and contraction of the Bi-O bond lengths).
Standard Density Functional Theory (DFT) calculations fail to obtain the
crystal structure instability caused by the pure breathing distortions.
Combining effects of the breathing distortions and tilting of the BiO6
octahedra allows DFT to reproduce qualitatively experimentally observed
insulator with monoclinic crystal structure but gives strongly underestimate
breathing distortion parameter and energy gap values. In the present work we
reexamine the BaBiO3 problem within the GGA+U method using a Wannier functions
basis set for the Bi 6s-band. Due to high oxidation state of bismuth in this
material the Bi 6s-symmetry Wannier function is predominantly extended
spatially on surrounding oxygen ions and hence differs strongly from a pure
atomic 6s-orbital. That is in sharp contrast to transition metal oxides (with
exclusion of high oxidation state compounds) where the major part a of d-band
Wannier function is concentrated on metal ion and a pure atomic d-orbital can
serve as a good approximation. The GGA+U calculation results agree well with
experimental data, in particular with experimental crystal structure parameters
and energy gap values. Moreover, the GGA+U method allows one to reproduce the
crystal structure instability due to the pure breathing distortions without
octahedra tilting.",1201.6154v3
2012-04-24,Structural modification in Au/Si(100) system: Role of surface oxide and vacuum level,"To understand surface structural modifications for Au/Si (100) system, a thin
gold film of ~2.0 nm was deposited under ultra high vacuum (UHV) condition on
reconstructed Si surfaces using molecular beam epitaxy (MBE). Post annealing
was done at 500{\deg}C in three different vacuum conditions: (1) low vacuum
(LV) furnace (10-2 mbar), (2) UHV (10-10 mbar) (MBE chamber), (3) high vacuum
(HV) chamber. The variation in the overall shape of the gold nanostructures and
finer changes at the edges, like rounding of corners has been reported in this
work. Although well aligned nano rectangles were formed in both HV and LV
cases, corner rounding is more prominent in LV case. Furthermore in UHV case,
random structures were formed having sharp corners. In all the above three
cases, samples were exposed to air (for half an hour) before annealing. To
study the effect of surface oxide, in-situ annealing inside UHV-MBE chamber was
done without exposing to air. Well aligned rectangles with sharp corners (no
corner rounding) were formed. The details about the role of surface oxides in
the corner rounding process are discussed.",1204.5370v1
2014-05-09,Impermeable Barrier Films and Protective Coatings Based on Reduced Graphene Oxide,"Barrier films preventing permeation of gases and moistures are important for
many industries ranging from food to medical and from chemical to electronic.
From this perspective, graphene has recently attracted particular interest
because its defect free monolayers are impermeable to all gases and liquids.
However, it has proved challenging to develop large-area defectless graphene
films suitable for industrial use. Here we report barrier properties of
multilayer graphitic films made by chemical reduction of easily and cheaply
produced graphene oxide laminates. They are found to provide a practically
perfect barrier that blocks all gases, liquids and aggressive chemicals
including, for example, hydrofluoric acid. In particular, if graphene oxide
laminates are reduced in hydroiodic acid, no permeation of hydrogen and water
could be detected for films as thin as 30 nm, which remain optically
transparent. The films thicker than 100 nm become completely impermeable. The
exceptional barrier properties are attributed to a high degree of
graphitization of the laminates and little structural damage during reduction.
This work indicates a close prospect of thin protective coatings with stability
and inertness similar to that of graphene and bulk graphite, which can be
interesting for numerous applications.",1405.2360v1
2015-12-14,Quantum interference in an interfacial superconductor,"The two-dimensional superconductor formed at the interface between the
complex oxides, lanthanum aluminate (LAO) and strontium titanate (STO) has
several intriguing properties that set it apart from conventional
superconductors. Most notably, an electric field can be used to tune its
critical temperature (T$_c$), revealing a dome-shaped phase diagram reminiscent
of high T$_c$ superconductors. So far, experiments with oxide interfaces have
measured quantities which probe only the magnitude of the superconducting order
parameter and are not sensitive to its phase. Here, we perform phase-sensitive
measurements by realizing the first superconducting quantum interference
devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new
paradigm for the creation of superconducting circuit elements, where local
gates enable in-situ creation and control of Josephson junctions. These
gate-defined SQUIDs are unique in that the entire device is made from a single
superconductor with purely electrostatic interfaces between the superconducting
reservoir and the weak link. We complement our experiments with numerical
simulations and show that the low superfluid density of this interfacial
superconductor results in a large, gate-controllable kinetic inductance of the
SQUID. Our observation of robust quantum interference opens up a new pathway to
understand the nature of superconductivity at oxide interfaces.",1512.04290v3
2016-05-02,Partial oxidation of Step-Bound Water Leads to Anomalous pH Effects on Metal Electrode Step-Edges,"The design of better heterogeneous catalysts for applications such as fuel
cells and electrolyzers requires a mechanistic understanding of
electrocatalytic reactions and the dependence of their activity on operating
conditions such as pH. A satisfactory explanation for the unexpected pH
dependence of electrochemical properties of platinum surfaces has so far
remained elusive, with previous explanations resorting to complex co-adsorption
of multiple species and resulting in limited predictive power. This knowledge
gap suggests that the fundamental properties of these catalysts are not yet
understood, limiting systematic improvement. Here, we analyze the change in
charge and free energies upon adsorption using density-functional theory (DFT)
to establish that water adsorbs on platinum step edges across a wide voltage
range, including the double-layer region, with a loss of approximately 0.2
electrons upon adsorption. We show how this as-yet unreported change in net
surface charge due to this water explains the anomalous pH variations of the
hydrogen underpotential deposition (Hupd) and the potentials of zero total
charge (PZTC) observed in published experimental data. This partial oxidation
of water is not limited to platinum metal step edges, and we report the charge
of the water on metal step edges of commonly used catalytic metals, including
copper, silver, iridium, and palladium, illustrating that this partial
oxidation of water broadly influences the reactivity of metal electrodes.",1605.00550v2
2016-05-19,Shear-Induced Nitric Oxide Production by Endothelial Cells,"We present a biochemical model of the wall shear stress (WSS)-induced
activation of endothelial nitric oxide synthase (eNOS) in an endothelial cell
(EC). The model includes three key mechanotransducers: mechanosensing ion
channels, integrins and G-protein-coupled receptors. The reaction cascade
consists of two interconnected parts. The first is rapid activation of calcium,
which results in formation of calcium-calmodulin complexes, followed by
recruitment of eNOS from caveolae. The second is phosphoryaltion of eNOS by
protein kinases PKC and AKT. The model also includes a negative feedback loop
due to inhibition of calcium influx into the cell by cyclic guanosine
monophosphate (cGMP). In this feedback, increased nitric oxide (NO) levels
cause an increase in cGMP levels, so that cGMP inhibition of calcium influx can
limit NO production. The model was used to predict the dynamics of NO
production by an EC subjected to a step increase of WSS from zero to a finite
physiologically relevant value. Among several experimentally observed features,
the model predicts a highly nonlinear, biphasic transient behavior of eNOS
activation and NO production: a rapid initial activation due to the very rapid
influx of calcium into the cytosol (occurring within 1 to 5 minutes) is
followed by a sustained period of activation due to protein kinases.",1605.05804v1
2016-05-28,"Hubbard interactions in iron-based pnictides and chalcogenides: Slater parametrization, screening channels and frequency dependence","We calculate the strength of the frequency-dependent on-site electronic
interactions in the iron pnictides LaFeAsO, BaFe2As2, BaRu2As2, and LiFeAs and
the chalcogenide FeSe from first principles within the constrained random phase
approximation. We discuss the accuracy of an atomic-like parametrization of the
two-index density-density interaction matrices based on the calculation of an
optimal set of three independent Slater integrals, assuming that the angular
part of the Fe-d localized orbitals can be described within spherical harmonics
as for isolated Fe atoms. We show that its quality depends on the ligand-metal
bonding character rather than on the dimensionality of the lattice: it is
excellent for ionic-like Fe-Se (FeSe) chalcogenides and a more severe
approximation for more covalent Fe-As (LaFeAsO, BaFe2As2) pnictides. We
furthermore analyze the relative importance of different screening channels,
with similar conclusions for the different pnictides but a somewhat different
picture for the benchmark oxide SrVO3: the ligand channel does not appear to be
dominant in the pnictides, while oxygen screening is the most important process
in the oxide. Finally, we analyze the frequency dependence of the interaction.
In contrast to simple oxides, in iron pnictides its functional form cannot be
simply modeled by a single plasmon, and the actual density of modes enters the
construction of an effective Hamiltonian determining the low-energy properties.",1605.08918v1
2016-12-11,Modeling Nucleation and Growth of Zinc Oxide During Discharge of Primary Zinc-Air Batteries,"Metal-air batteries are among the most promising next-generation energy
storage devices. Relying on abundant materials and offering high energy
densities, potential applications lie in the fields of electro-mobility,
portable electronics, and stationary grid applications. Now, research on
secondary zinc-air batteries is revived, which are commercialized as primary
hearing aid batteries. One of the main obstacles for making zinc-air batteries
rechargeable is their poor lifetime due to the degradation of alkaline
electrolyte in contact with atmospheric carbon dioxide. In this article, we
present a continuum theory of a commercial Varta PowerOne button cell. Our
model contains dissolution of zinc and nucleation and growth of zinc oxide in
the anode, thermodynamically consistent electrolyte transport in porous media,
and multi-phase coexistance in the gas diffusion electrode. We perform
electrochemical measurements and validate our model. Excellent agreement
between theory and experiment is found and novel insights into the role of zinc
oxide nucleation and growth and carbon dioxide dissolution for discharge and
lifetime is presented. We demonstrate the implications of our work for the
development of rechargeable zinc-air batteries.",1612.03464v2
2017-06-25,Assessing the performance of self-consistent hybrid functional for band gap calculation in oxide semiconductors,"In this paper we assess the predictive power of the self-consistent hybrid
functional scPBE0 in calculating the band gap of oxide semiconductors. The
computational procedure is based on the self-consistent evaluation of the
mixing parameter $\alpha$ by means of an iterative calculation of the static
dielectric constant using the perturbation expansion after discretization
(PEAD) method and making use of the relation $\alpha = 1/\epsilon_{\infty}$.
Our materials dataset is formed by 30 compounds covering a wide range of band
gaps and dielectric properties, and includes materials with a wide spectrum of
application as thermoelectrics, photocatalysis, photovoltaics, transparent
conducting oxides, and refractory materials. Our results show that the scPBE0
functional provides better band gaps than the non self-consistent hybrids PBE0
and HSE06, but scPBE0 does not show significant improvement on the description
of the static dielectric constants. Overall, the scPBE0 data exhibit a mean
absolute percentage error of 14 \% (band gaps) and 10 \% ($\epsilon_\infty$).
For materials with weak dielectric screening and large excitonic biding
energies scPBE0, unlike PBE0 and HSE06, overestimates the band gaps, but the
value of the gap become very close to the experimental value when excitonic
effects are included (e.g. for SiO$_2$). However, special caution must be given
to the compounds with small band gaps due to the tendency of scPBE0 to
overestimate the dielectric constant in proximity of the metallic limit.",1706.08159v2
2017-07-11,Self-Assembling Oxide Catalyst for Electrochemical Water Splitting,"Renewable energy conversion and storage, and greenhouse gas emission-free
technologies are within the primary tasks and challenges for the society.
Hydrogen fuel, produced by alkaline water electrolysis is fulfilling all these
demands, however the technology is economically feeble, limited by the slow
rate of oxygen evolution reaction. Complex metal oxides were suggested to
overcome this problem being low-cost efficient catalysts. However, the
insufficient long-term stability, degradation of structure and electrocatalytic
activity are restricting their utilization. Here we report on a new
perovskite-based self-assembling material BaCo0.98Ti0.02O3-$\delta$:Co3O4 with
superior performance, showing outstanding properties compared to current
state-of-the-art materials without degeneration of its properties even at 353
K. By chemical and structural analysis the degradation mechanism was identified
and modified by selective doping. Short-range order and chemical composition
rather than long-range order are factors determining the outstanding
performance. The derived general design rules can be used for further
development of oxide-based electrocatalytic materials.",1707.03346v1
2017-07-13,Deuteration of ammonia with D atoms on oxidized partly ASW covered graphite surface,"The deuteration of ammonia by D atoms has been investigated experimentally in
the sub-monolayer regime on realistic analogues of interstellar dust grain
surfaces. About 0.8 monolayer of solid NH3 was deposited on top of an oxidized
graphite surface held at 10 K, partly covered with ASW ice. Ammonia ice is
subsequently exposed to D atoms for different exposure times using a
differentially pumped beam-line. The deuteration experiments of ammonia were
carried out by mass spectroscopy and temperature programmed desorption (TPD)
technique. The experimental results showed the formation of three isotopologue
ammonia species by direct exothermic H-D substitution surface reactions:
NH3+D->NH2D+H, NH2D+D->NHD2+H, and NHD2+D->ND3+H. The formation of the
deuterated isotopologues NH2D, NHD2, and ND3 at low surface temperature (10 K)
is likely to occur through quantum tunneling process on the oxidized graphite
surface. A kinetic model taking into account the diffusion of D atoms on the
surface is developed to estimate the width and the hight of the activation
energy barriers for the successive deuteration reactions of ammonia species by
D atoms. Identical control experiments were performed using CH3OH and D atoms.
The deuteration process of solid methanol is ruled by H abstraction and D
addition mechanism, and is almost five orders of magnitude faster than ammonia
deuteration process.",1707.04063v2
2017-10-13,"Optical constants of DC sputtering derived ITO, TiO2 and TiO2:Nb thin films characterized by spectrophotometry and spectroscopic ellipsometry for optoelectronic devices","Thin films of inorganic materials as Tin-doped indium oxide, titanium oxide,
Niobium doped titanium oxide, were deposited for comparison on glass and
Polyethylene terephthalate (PET) substrates with a DC sputtering method. These
thin films have been characterized by different techniques: Dektak Surface
Profilometer, X-ray diffraction (XRD), SEM, (UV/Vis/NIR) spectrophotometer and
spectroscopic ellipsometry (SE). The optical parameters of these films such as
transmittance, reflectance, refractive index, extinction coefficient, energy
gap obtained with different electronic transitions, real and imaginary
({\epsilon}_r,{\epsilon}_i) dielectric constants, were determined in the
wavelengths range of (200 - 2200) nm. The results were compared with SE
measurements in the ranges of (0.56- 6.19) eV by a new amorphous model with
steps of 1 nm. SE measurements of optical constant have been examined and
confirm the accuracy of the (UV/Vis/NIR) results. The optical properties
indicate an excellent transmittance in the visible range of (400 - 800) nm. The
average transmittance of films on glass is about (86%, 91%, 85%) for (ITO,
TiO2, TiO2:Nb (NTO)) respectively and decreases to about (85%, 81%, 82%) for
PET substrates. For all these materials the optical band gap for direct
transition was (3.53, 3.3, 3.6) eV on glass substrates and on PET substrates
using two methods (UV and SE). A comparison between optical constants and
thickness of these ultrathin films observed gives an excellent agreement with
the UV results. The deposited films were also analyzed by XRD and showed an
amorphous structure. The structural morphology of these thin films has been
investigated and compared.",1710.04814v1
2017-10-27,"Doping Li-rich cathode material Li$_2$MnO$_3$: Interplay between lattice site preference, electronic structure, and delithiation mechanism","We report a detailed first-principles study of doping in Li$_2$MnO$_3$, in
both the dilute doping limit and heavy doping, using hybrid density-functional
calculations. We find that Al, Fe, Mo, and Ru impurities are energetically most
favorable when incorporated into Li$_2$MnO$_3$ at the Mn site, whereas Mg is
most favorable when doped at the Li sites. Ni, on the other hand, can be
incorporated at the Li site and/or the Mn site, and the distribution of Ni over
the lattice sites can be tuned by tuning the materials preparation conditions.
There is a strong interplay between the lattice site preference and charge and
spin states of the dopant, the electronic structure of the doped material, and
the delithiation mechanism. The calculated electronic structure and voltage
profile indicate that, in Ni-, Mo-, or Ru-doped Li$_2$MnO$_3$, oxidation occurs
on the electrochemically active transition-metal ion(s) before it does on
oxygen during the delithiation process. The role of the dopants is to provide
charge-compensation and bulk electronic conduction mechanisms in the initial
stages of delithiation, hence enabling the oxidation of the lattice oxygen in
the later stages. This work thus illustrates how the oxygen-oxidation mechanism
can be used in combination with the conventional mechanism involving
transition-metal cations in design of high-capacity battery cathode materials.",1710.10241v2
2017-12-05,Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits,"This work is concerned with Al/Al-oxide(AlO$_{x}$)/Al-layer systems which are
important for Josephson-junction-based superconducting devices such as quantum
bits. The device performance is limited by noise, which has been to a large
degree assigned to the presence and properties of two-level tunneling systems
in the amorphous AlO$_{x}$ tunnel barrier. The study is focused on the
correlation of the fabrication conditions, nanostructural and nanochemical
properties and the occurrence of two-level tunneling systems with particular
emphasis on the AlO$_{x}$-layer. Electron-beam evaporation with two different
processes and sputter deposition were used for structure fabrication, and the
effect of illumination by ultraviolet light during Al-oxide formation is
elucidated. Characterization was performed by analytical transmission electron
microscopy and low-temperature dielectric measurements. We show that the
fabrication conditions have a strong impact on the nanostructural and
nanochemical properties of the layer systems and the properties of two-level
tunneling systems. Based on the understanding of the observed structural
characteristics, routes are derived towards the fabrication of
Al/AlO$_{x}$/Al-layers systems with improved properties.",1712.01581v1
2018-01-18,"Material Discovery and Design Principles for Stable, High Activity Perovskite Cathodes for Solid Oxide Fuel Cells","Critical to the development of improved solid oxide fuel cell (SOFC)
technology are novel compounds with high oxygen reduction reaction (ORR)
catalytic activity and robust stability under cathode operating conditions.
Approximately 2145 distinct perovskite compositions are screened for potential
use as high activity, stable SOFC cathodes, and it is verified that the
screening methodology qualitatively reproduces the experimental activity,
stability, and conduction properties of well-studied cathode materials. The
calculated oxygen p-band center is used as a first principle-based descriptor
of the surface exchange coefficient (k*), which in turn correlates with cathode
ORR activity. Convex hull analysis is used under operating conditions in the
presence of oxygen, hydrogen, and water vapor to determine thermodynamic
stability. This search has yielded 52 potential cathode materials with good
predicted stability in typical SOFC operating conditions and predicted k* on
par with leading ORR perovskite catalysts. The established trends in predicted
k* and stability are used to suggest methods of improving the performance of
known promising compounds. The material design strategies and new materials
discovered in the computational search help enable the development of high
activity, stable compounds for use in future solid oxide fuel cells and related
applications.",1801.06109v2
2018-09-24,Origin of Improved Photoelectrochemical Water Splitting in Mixed Perovskite Oxides,"Owing to the versatility in their chemical and physical properties,
transition metal perovskite oxides have emerged as a new category of highly
efficient photocatalysts for photoelectrochemical water splitting. Here, to
understand the underlying mechanism for the enhanced photoelectrochemical water
splitting in mixed perovskites, we explore ideal epitaxial thin films of the
BiFeO3-SrTiO3 system. The electronic struture and carrier dynamics are
determined from both experiment and density-functional theory calculations. The
intrinsic phenomena are measured in this ideal sytem, contrasting to commonly
studied polycrstalline solid solutions where extrinsic structural features
obscure the intrinsic phenomena. We determined that when SrTiO3 is added to
BiFeO3 the conduction band minimum position is raised and an exponential tail
of trap states from hybridized Ti 3d and Fe 3d orbitals emerges near the
conduction band edge. The presence of these trap states strongly suppresses the
fast electron-hole recombination and improves the photocurrent density in the
visible-light region, up to 16 times at 0 VRHE compared to the pure end member
compositions. Our work provides a new design approach for optimising the
photoelectrochemical performance in mixed perovksite oxides.",1809.09209v1
2018-10-06,Two-dimensional honeycomb borophene oxide: Strong anisotropy and nodal loop transformation,"The search for topological semimetals is mainly focused on heavy-element
compounds as following the footsteps of previous research on topological
insulators, with less attention on light-element materials. However, the
negligible spin orbit coupling with light elements may turn out to be
beneficial for realizing topological band features.Here, using first-principles
calculations, we propose a new two-dimensional light-element material-the
honeycomb borophene oxide (h-B2O), which has nontrivial topological
properties.The proposed structure is based on the recently synthesized
honeycomb borophene on Al (111) substrate [Sci. Bull. 63, 282 (2018)]. The
h-B2O monolayer is completely flat, unlike the oxides of graphene or silicene.
We systematically investigate the structural properties of h-B2O, and find that
it has very good stability and exhibits significant mechanical anisotropy.
Interestingly, the electronic band structure of h-B2O hosts a nodal loop
centered around the Y point in the Brillouin zone, protected by the mirror
symmetry. Furthermore, under moderate lattice strain, the single nodal loop can
be transformed into two loops, each penetrating through the Brillouin zone. The
loops before and after the transition are characterized by different Z*Z
topological indices. Our work not only predicts a new two-dimensional material
with interesting physical properties, but also offers an alternative approach
to search for new topological phases in 2D light-element systems.",1810.03009v2
2018-10-10,Charge transfer and tunable built-in electric fields across semiconductor-crystalline oxide interfaces,"Built-in electric fields across heterojunctions between semiconducting
materials underpin the functionality of modern device technologies.
Heterojunctions between semiconductors and epitaxially grown crystalline oxides
provide a rich setting in which built-in fields can be explored. Here, we
present an electrical transport and hard X-ray photoelectron spectroscopy study
of epitaxial SrNbxTi1-xO3-{\delta} / Si heterojunctions. A non-monotonic
anomaly in the sheet resistance is observed near room temperature, which is
accompanied by a crossover in sign of the Hall resistance. The crossover is
consistent with the formation of a hole gas in the Si and the presence of a
built-in field. Hard X-ray photoelectron spectroscopy measurements reveal
pronounced asymmetric features in both the SrNbxTi1-xO3-{\delta} and Si
core-level spectra that we show arise from built-in fields. The extended probe
depth of hard X-ray photoelectron spectroscopy enables band bending across the
SrNbxTi1-xO3-{\delta} / Si heterojunction to be spatially mapped. Band
alignment at the interface and surface depletion in SrNbxTi1-xO3-{\delta} are
implicated in the formation of the hole gas and built-in fields. Control of
charge transfer and built-in electric fields across semiconductor-crystalline
oxide interfaces opens a pathway to novel functional heterojunctions.",1810.04648v1
2018-10-12,Berry phase engineering at oxide interfaces,"Geometric phases in condensed matter play a central role in topological
transport phenomena such as the quantum, spin and anomalous Hall effect (AHE).
In contrast to the quantum Hall effect - which is characterized by a
topological invariant and robust against perturbations - the AHE depends on the
Berry curvature of occupied bands at the Fermi level and is therefore highly
sensitive to subtle changes in the band structure. A unique platform for its
manipulation is provided by transition metal oxide heterostructures, where
engineering of emergent electrodynamics becomes possible at atomically sharp
interfaces. We demonstrate that the Berry curvature and its corresponding
vector potential can be manipulated by interface engineering of the correlated
itinerant ferromagnet SrRuO$_3$ (SRO). Measurements of the AHE reveal the
presence of two interface-tunable spin-polarized conduction channels. Using
theoretical calculations, we show that the tunability of the AHE at SRO
interfaces arises from the competition between two topologically non-trivial
bands. Our results demonstrate how reconstructions at oxide interfaces can be
used to control emergent electrodynamics on a nanometer-scale, opening new
routes towards spintronics and topological electronics.",1810.05619v1
2018-10-18,Gate-tunable superconductivity at SrTiO3 surface realized by Al layer evaporation,"Electronic properties of low dimensional superconductors are determined by
many-body-effects. This physics has been studied traditionally with
superconducting thin films, and in recent times with two-dimensional electron
gases (2DEGs) at oxide interfaces. In this work, we show that a superconducting
2DEG can be generated by simply evaporating a thin layer of metallic Al under
ultra-high vacuum on a SrTiO3 crystal, whereby Al oxidizes into amorphous
insulating alumina, doping the SrTiO3 surface with oxygen vacancies. The
superconducting critical temperature of the resulting 2DEG is found to be
tunable with a gate voltage with a maximum value of 360 mK. A gate-induced
switching between superconducting and resistive states is demonstrated.
Compared to conventionally-used pulsed-laser deposition (PLD), our work
simplifies to a large extent the process of fabricating oxide-based
superconducting 2DEGs. It will make such systems accessible to a broad range of
experimental techniques useful to understand low-dimensional phase transitions
and complex many-body-phenomena in electronic systems.",1810.08069v2
2018-10-19,"Monatomic Co, CoO$_2$, and CoO$_3$ Nanowires on Ir(100) and Pt(100) surfaces: Formation, Structure, and Energetics","In this study we investigate the structural and chemical changes of monatomic
CoO$_2$ chains grown self-organized on the Ir(100) surface [P. Ferstl et al.,
PRL 117, 2016, 046101] and on Pt(100) under reducing and oxidizing conditions.
By a combination of quantitative low-energy electron diffraction, scanning
tunnelling microscopy, and density functional theory we show that the cobalt
oxide wires are completely reduced by H$_2$ at temperatures above 320 K and a
3x1 ordered Ir$_2$Co or Pt$_2$Co surface alloy is formed. Depending on
temperature the surface alloy on Ir(100) is either hydrogen covered (T < 400 K)
or clean and eventually undergoes an irreversible order-disorder transition at
about 570 K. The Pt$_2$Co surface alloy disorders with the desorption of
hydrogen, whereby Co submerges into subsurface sites. Vice versa, applying
stronger oxidants than O$_2$ such as NO$_2$ leads to the formation of CoO3
chains on Ir(100) in a 3x1 superstructure. On Pt(100) such a CoO$_3$ phase
could not be prepared so far, which however, is due to the UHV conditions of
our experiments. As revealed by theory this phase will become stable in a
regime of higher pressure. In general, the structures can be reversibly
switched on both surfaces using the respective agents O$_2$, NO$_2$ and H$_2$.",1810.08574v1
2018-10-25,Doping induced site-selective Mott insulating phase in LaFeO$_3$,"Tailoring transport properties of strongly correlated electron systems in a
controlled fashion counts among the dreams of materials scientists. In copper
oxides, varying the carrier concentration is a tool to obtain high-temperature
superconducting phases. In manganites, doping results in exotic physics such as
insulator-metal transitions (IMT), colossal magnetoresistance (CMR), orbital-
or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides,
antiferromagnetic order and charge-disproportionation are asssociated with
insulating behavior. Here we report the realization of a unique physical state
that can be induced by Mo doping in LaFeO$_3$: the resulting metallic state is
a site-selective Mott insulator where itinerant electrons evolving in
low-energy Mo states coexist with localized carriers on the Fe sites. In
addition, a local breathing-type lattice distortion induces charge
disproportionation on the latter, without destroying the antiferromagnetic
order. A state, combining antiferromangetism, metallicity and CD phenomena is
rather rare in oxides and may be of utmost significance for future
antiferromagnetic memory devices.",1810.10978v1
2018-10-26,Mechanical stress dependence of the Fermi level pinning on an oxidized silicon surface,"A combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron
spectroscopy) mapping on statically deflected p-type silicon cantilevers is
used to study the mechanical stress dependence of the Fermi level pinning at an
oxidized silicon (001) surface. With uniaxial compressive and tensile stress
applied parallel to the $\langle$110$\rangle$ crystal direction, the
observations are relevant to the electronic properties of strain-silicon
nano-devices with large surface-to-volume ratios such as nanowires and
nanomembranes. The surface Fermi level pinning is found to be even in applied
stress, a fact that may be related to the symmetry of the Pb$_0$ silicon/oxide
interface defects. For stresses up to 160 MPa, an increase in the pinning
energy of 0.16 meV/MPa is observed for compressive stress, while for tensile
stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation
potentials the reduction in surface band bending in compression (0.09 meV/MPa)
and in tension (0.13 meV/MPa) can be estimated.",1810.11219v3
2019-06-13,Chemical and radiative transfer modeling of Propylene Oxide,"The recent identification of the first complex chiral molecule, propylene
oxide (PrO) in space opens up a new window to further study the origin of
homochirality on the Earth. There are some recent studies to explain the
formation of PrO however additional studies on the formation of this species
are needed for better understanding. We seek to prepare a complete reaction
network to study the formation of propylene oxide in the astrophysically
relevant conditions. Based on our results, a detailed radiative transfer
modeling has been carried out to propose some more transitions which would
potentially be targeted in the millimeter wave domain. Gas-grain chemical
network was used to explain the observed abundance of PrO in a cold shell
surrounding the high-mass star-forming region of Sgr B2. Quantum chemical
calculations were employed to study various reaction parameters and to compute
multiple vibrational frequencies of PrO. To model the formation of PrO in the
observed region, we considered a dark cloud model. Additionally, we used a
model to check the feasibility of forming PrO in the hot core region. Some
potential transitions in the millimeter wave domain are predicted which could
be useful for the future astronomical detection. Radiative transfer modeling
has been utilized to extract the physical condition which might be useful to
know the properties of the source in detail. Moreover, vibrational transitions
of PrO has been provided which could be very useful for the future detection of
PrO by the upcoming James Webb Space Telescope (JWST).",1906.05604v1
2019-06-22,Si-incorporated amorphous indium oxide thin-film transistors,"Amorphous oxide semiconductors, especially indium oxide-based (InOx)
thin-films, have been major candidates for high mobility with easy-to-use
device processability. As one of the dopants in InOx semiconductors, we
proposed Si to design a thin-film transistor (TFT) channel. Because the
suppression of unstable oxygen vacancies in InOx is crucial to maintaining the
semiconducting behavior, Si was selected as a strong oxygen binder that is
reasonably available for large production. In this review, we focus on the
overall properties observed in Si-incorporated amorphous InOx TFTs in terms of
bond-dissociation energy, Gibbs free energy, Si-concentration dependence of TFT
properties, carrier transport mechanism, and bias stress instability. In
comparing low and high doping densities, we found that the activation energy
and density of states decreased at a high Si concentration in InOx TFTs,
implying that the trap density was reduced. As a result, stable operation under
bias stresses could be realized. Furthermore, the inverse Meyer-Neldel rule was
observed in the highly Si-doped InOx TFT, indicating reasonable ohmic contact.
Based on our fundamental knowledge of the Si-doped InOx film, we developed a
high-mobility bilayer TFT with a homogeneous stacked channel that was different
from a TFT with an etch stop layer structure. The TFT showed remarkably stable
operation. With simple element components based on InOx, it is possible to
systematically discuss vacancy engineering in terms of conduction properties.",1906.09366v1
2019-07-30,Analysis of hydrogen distribution and migration in fired passivating contacts (FPC),"In this work, the hydrogenation mechanism of fired passivating contacts (FPC)
based on c-Si/SiO$_{x}$/nc-SiC$_{x}$(p) stacks was investigated, by correlating
the passivation and local re-distribution of hydrogen. Secondary ion mass
spectroscopy (SIMS) depth profiling was used to assess the hydrogen
(/deuterium) content. The SIMS profiles show that hydrogen almost completely
effuses out of the SiC$_{x}$(p) during firing, but can be re-introduced by
hydrogenation via forming gas anneal (FGA) or by release from a hydrogen
containing layer such as SiN$_{x}$:H. A pile-up of H at the c-Si/SiO$_{x}$
interface was observed and identified as a key element in the FPC's passivation
mechanism. Moreover, the samples hydrogenated with SiN$_{x}$:H exhibited higher
H content compared to those treated by FGA, resulting in higher iV$_{OC}$
values. Further investigations revealed that the doping of the SiC$_{x}$ layer
does not affect the amount of interfacial defects passivated by the
hydrogenation process presented in this work. Eventually, an effect of the
oxide's nature on passivation quality is evidenced. iV$_{OC}$ values of up to
706 mV and 720 mV were reached with FPC test structures using chemical and
UV-O$_{3}$ tunneling oxides, respectively, and up to 739 mV using a reference
passivation sample featuring a ~25 nm thick thermal oxide.",1907.13069v1
2019-09-13,Electric field and current induced electroforming modes in NbOx,"Electroforming is used to initiate the memristive response in
metal/oxide/metal devices by creating a filamentary conduction path in the
oxide film. Here we use a simple photoresist-based detection technique to map
the spatial distribution of conductive filaments formed in Nb/NbOx/Pt devices,
and correlate these with current-voltage characteristics and in-situ
thermoreflectance measurements to identify distinct modes of electroforming in
low and high conductivity NbOx films. In low conductivity films the filaments
are randomly distributed within the oxide film, consistent with a field-induced
weakest-link mechanism, while in high conductivity films they are concentrated
in the center of the film. In the latter case the current-voltage
characteristics and in-situ thermoreflectance imaging show that electroforming
is associated with current bifurcation into regions of low and high current
density. This is supported by finite element modelling of the current
distribution and shown to be consistent with predictions of a simple core-shell
model of the current distribution. These results clearly demonstrate two
distinct modes of electroforming in the same materials system and show that the
dominant mode depends on the conductivity of the film, with field-induced
electroforming dominant in low conductivity films and current-bifurcation
induced electroforming dominant in high conductivity films. Finally, we
demonstrate S-type and snap-back negative differential resistance in the high
conductivity films and explain this behavior in terms of two-zone model.",1909.06443v2
2019-09-16,Presolar Grains in Primitive Ungrouped Carbonaceous Chondrite Northwest Africa 5958,"We report a correlated NanoSIMS-transmission electron microscopy study of the
ungrouped carbonaceous chondrite Northwest Africa (NWA) 5958. We identified 10
presolar SiC grains, 2 likely presolar graphite grains, and 20 presolar
silicate and/or oxide grains in NWA 5958. We suggest a slight modification of
the commonly used classification system for presolar oxides and silicates that
better reflects the grains' likely stellar origins. The matrix-normalized
presolar SiC abundance in NWA 5958 is $18_{-10}^{+15}$ ppm (2$\sigma$), similar
to that seen in many classes of unmetamorphosed chondrites. In contrast, the
matrix-normalized abundance of presolar O-rich phases (silicates and oxides) is
$30.9_{-13.1}^{+17.8}$ ppm (2$\sigma$), much lower than seen in interplanetary
dust particles and the least altered CR, CO and ungrouped C chondrites, but
close to that reported for CM chondrites. NanoSIMS mapping also revealed an
unusual $^{13}$C-enriched ($\delta ^{13}$C$\sim$ 100--200 permil) carbonaceous
rim surrounding a 1.4 $\mu$m diameter phyllosilicate grain. TEM analysis of two
presolar grains with a likely origin in asymptotic giant branch stars
identified one as enstatite and one as Al-Mg spinel with minor Cr. The
enstatite grain amorphized rapidly under the electron beam, suggesting partial
hydration. TEM data of NWA 5958 matrix confirm that it has experienced aqueous
alteration and support the suggestion of Jacquet et al. (2016) that this
meteorite has affinities to CM2 chondrites.",1909.07225v1
2019-10-11,Impact of cation redox chemistry on continuous hydrothermal synthesis of 2D-Ni(Co/Fe) hydroxides,"Continuous hydrothermal flow synthesis (CHFS) is a facile, upscalable and
cost-efficient synthetic method enabling the nanostructuring of advanced
functional materials in steady conditions, i.e. not in batch synthesis. In this
paper, we use CHFS to crystallize NiCo- and NiFe-hydroxides in water solution
with 2D nanofeatures. By tuning the synthetic parameters, we disclose the key
role of the cation redox chemistry in the transition between two competitive
phases: from 2D-nanoplatelets of brucite to layered double hydroxides (LDH).
For controlling the precipitation of different Ni, Fe, Co-hydroxide phases, we
propose the combined use of an oxidizing (H2O2) and a complexing (NH3) agent.
At temperatures as low as 80 {\deg}C, the presence of H2O2 and a low
concentration of NH3 favour the Ni2+/Co3+ over Ni2+/Co2+ oxidation states,
shifting the product structure from brucite phase (temperatures > 80 {\deg}C)
to LDH. Conversely, for the NiFe-hydroxides the transition from LDH
(temperatures < 80 {\deg}C) to brucite phase (temperatures > 80 {\deg}C) is
controlled by the reaction temperature only. Due to the high stability of Fe3+,
the synthesis of NiFe products by CHFS does not require oxidizing and
complexing agents, resulting in a robust process for large-scale production.",1910.05047v1
2019-10-16,LIPSS on thin metallic films: New insights from multiplicity of laser-excited electromagnetic modes and efficiency of metal oxidation,"Thin Cr films 28-nm thick deposited on glass substrates were processed by
scanning low-intensity femtosecond laser pulses with energy well below
single-pulse damage threshold. Two types of laser-induced periodic surface
structures (LIPSS) were produced, depending on the scanning velocity, (1)
parallel to laser light polarization with periodicity somewhat smaller than
laser wavelength and (2) perpendicular to polarization with spatial period much
smaller than wavelength. All structures are formed as protrusions above the
initial film surface and exhibit a high degree of oxidation. To explain
formation of the LIPSS and their conversion from one to another type, a
rigorous numerical approach for modeling surface electromagnetic waves in
thin-film geometry has been developed, which takes into account the change of
optical properties of material due to laser-induced oxidation and porosity. The
approach addresses the multiplicity of electromagnetic modes allowed for thin
films. It has been found that the low spatial frequency LIPSS parallel to laser
polarization, which are formed at low scanning velocities, are well described
by the Sipe theory for surfaces of low roughness. The SEW mode responsible for
high spatial frequency LIPSS formation at high scanning velocities has been
identified. The mechanisms of optical feedback and transformation between types
of LIPSS with scanning velocity have been proposed.",1910.07280v2
2019-10-28,Structural and Nanochemical Properties of AlOx Layers in $Al/AlO_x/Al$-Layer Systems for Josephson Junctions,"The structural and nanochemical properties of thin $AlO_x$ layers are
decisive for the performance of advanced electronic devices. For example, they
are frequently used as tunnel barriers in Josephson junction-based
superconducting devices. However, systematic studies of the influence of
oxidation parameters on structural and nanochemical properties are rare up to
now, as most studies focus on the electrical properties of $AlO_x$ layers. This
study aims to close this gap by applying transmission electron microscopy in
combination with electron energy loss spectroscopy to analyze the structural
and nanochemical properties of differently fabricated $AlO_x$ layers and
correlate them with fabrication parameters. With respect to the application of
$AlO_x$ as tunnel barrier in superconducting Josephson junctions,
$Al/AlO_x/Al$-layer systems were deposited on Si substrates. We will show that
the oxygen content and structure of amorphous $AlO_x$ layers is strongly
dependent on the fabrication process and oxidation parameters. Dynamic and
static oxidation of Al yields oxygen-deficient amorphous $AlO_x$ layers, where
the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure
and substrate temperature. Thicker layers of stoichiometric crystalline
$\gamma-Al_2O_3$ layers were grown by electron-beam evaporation of $Al_2O_3$
and reactive sputter deposition.",1910.12963v1
2020-01-03,Scanning Transmission Electron Microscopy of Oxide Interfaces and Heterostructures,"Thin film oxides are a source of endless fascination for the materials
scientist. These materials are highly flexible, can be integrated into almost
limitless combinations, and exhibit many useful functionalities for device
applications. While precision synthesis techniques, such as molecular beam
epitaxy (MBE) and pulsed laser deposition (PLD), provide a high degree of
control over these systems, there remains a disconnect between ideal and
realized materials. Because thin films adopt structures and chemistries
distinct from their bulk counterparts, it is often difficult to predict what
properties will emerge. The complex energy landscape of the synthesis process
is also strongly influenced by non-equilibrium growth conditions imposed by the
substrate, as well as the kinetics of thin film crystallization and
fluctuations in process variables, all of which can lead to significant
deviations from targeted outcomes. High-resolution structural and chemical
characterization techniques, as described in this volume, are needed to verify
growth models, bound theoretical calculations, and guide materials design.
While many characterization options exist, most are spatially-averaged or
indirect, providing only partial insight into the complex behavior of these
systems. Over the past several decades, scanning transmission electron
microscopy (STEM) has become a cornerstone of oxide heterostructure
characterization owing to its ability to simultaneously resolve structure,
chemistry, and defects at the highest spatial resolution. STEM methods are an
essential complement to averaged scattering techniques, offering a direct
picture of resulting materials that can inform and refine the growth process to
achieve targeted properties. There is arguably no other technique that can
provide such a broad array of information at the atomic-scale, all within a
single experimental session.",2001.00947v2
2020-01-04,Dielectric/semiconductor interfacial doping to develop solution processed high performance 1 V ambipolar oxide-transistor and its application as CMOS inverter,"p-type doping from the dielectric/semiconductor interface of a SnO2 thin film
transistor (TFT) has been utilized to develop high carrier mobility balanced
ambipolar oxide-transistor. To introduce this interfacial-doping, bottom-gate
top-contact TFTs have been fabricated by using two different ion-conducting
oxide dielectrics which contain trivalent atoms. These ion-conducting
dielectrics are LilnO2 and LiGaO2 respectively, containing mobile Li+ ion.
During SnO2 thin film fabrication on top of the ionic dielectric, those
trivalent atoms allow p- doping to the interfacial SnO2 layer to introduce the
hole conduction in channel of TFT. To realize this interfacial doping
phenomena, a reference TFT has been fabricated with Li2ZnO2 dielectric under
the same condition that contains divalent zinc (Zn) atom. Our comparative
electrical data indicates that TFTs with LilnO2 and LiGaO2 dielectric are
ambipolar in nature whereas, TFT with Li2ZnO2 dielectric is a unipolar
n-channel transistor which reveals the interfacial doping of SnO2. Most
interestingly, by using LilnO2 dielectric, we are capable to fabricated 1.0 V
balanced ambipolar TFT with a high electron and hole mobility values of 7 cm2
V-1 s-1and 8 cm2 V-1 s-1 respectively with an on/off ratio >102 for both
operations which has been utilized for low-voltage CMOS inverter fabrication.",2001.01038v1
2020-01-14,Electron trapping at SiO2/4H-SiC interface probed by transient capacitance measurements and atomic resolution chemical analysis,"Studying the electrical and structural properties of the interface of the
gate oxide (SiO2) with silicon carbide (4H-SiC) is a fundamental topic, with
important implications for understanding and optimizing the performances of
metal-oxide-semiconductor field effect transistor (MOSFETs). In this paper,
near interface oxide traps (NIOTs) in lateral 4H-SiC MOSFETs were investigated
combining transient gate capacitance measurements (C-t) and state of the art
scanning transmission electron microscopy in electron energy loss spectroscopy
(STEM-EELS) with sub-nm resolution. The C-t measurements as a function of
temperature indicated that the effective NIOTs discharge time is temperature
independent and electrons from NIOTs are emitted toward the semiconductor
via-tunnelling. The NIOTs discharge time was modelled taking into account also
the interface state density in a tunnelling relaxation model and it allowed to
locate traps within a tunnelling distance up to 1.3nm from the SiO2/4H-SiC
interface. On the other hand, sub-nm resolution STEM-EELS revealed the presence
of a Non-Abrupt (NA) SiO2/4H-SiC interface. The NA interface shows the
re-arrangement of the carbon atoms in a sub-stoichiometric SiOx matrix. A mixed
sp2/sp3 carbon hybridization in the NA interface region suggests that the
interfacial carbon atoms have lost their tetrahedral SiC coordination.",2001.04712v1
2020-02-27,Structure and morphology of low mechanical loss TiO$_2$-doped Ta$_2$O$_5$,"Amorphous oxide thin films play a fundamental role in state-of-the art
interferometry experiments, such as gravitational wave detectors where these
films compose the high reflectance mirrors of end and input masses. The
sensitivity of these detectors is affected by thermal noise in the mirrors with
its main source being the mechanical loss of the high index layers. These
thermally driven fluctuations are a fundamental limit to optical interferometry
experiments and there is a pressing need to understand the underlying processes
that lead to mechanical dissipation in materials at room temperature. Two
strategies are known to lower the mechanical loss: employing a mixture of
Ta$_2$O$_5$ with $\approx$ 20\% of TiO$_2$ and post-deposition annealing, but
the reasons behind this are not completely understood. In this work, we present
a systematic study of the structural and optical properties of ion beam
sputtered TiO$_2$-doped Ta$_2$O$_5$ films as a function of the annealing
temperature. We show for the first time that low mechanical loss is associated
with a material morphology that consists of nanometer sized Ar-rich bubbles
embedded into an atomically homogeneous mixed titanium-tantalum oxide. When the
Ti cation ratio is high, however, phase separation occurs in the film which
leads to increased mechanical loss. These results indicate that for designing
low mechanical loss mixed oxide coatings for interferometry applications it
would be beneficial to identify materials with the ability to form ternary
compounds while the dopant ratio needs to be kept low to avoid phase
separation.",2002.11866v1
2020-12-03,Oxygen vacancies in SrTiO$_{3}$ thin films at finite temperatures: A first-principles study,"Epitaxially grown SrTiO$_{3}$ (STO) thin films are material enablers for a
number of critical energy-conversion and information-storage technologies like
electrochemical electrode coatings, solid oxide fuel cells and random access
memories. Oxygen vacancies (${\rm V_{O}}$), on the other hand, are key defects
to understand and tailor many of the unique functionalities realized in oxide
perovskite thin films. Here, we present a comprehensive and technically sound
ab initio description of ${\rm V_{O}}$ in epitaxially strained (001) STO thin
films. The novelty of our first-principles study lies in the incorporation of
lattice thermal excitations on the formation energy and diffusion properties of
${\rm V_{O}}$ over wide epitaxial strain conditions ($-4 \le \eta \le +4$%). We
found that thermal lattice excitations are necessary to obtain a satisfactory
agreement between first-principles calculations and the available experimental
data on the formation energy of ${\rm V_{O}}$ for STO thin films. Furthermore,
it is shown that thermal lattice excitations noticeably affect the energy
barriers for oxygen ion diffusion, which strongly depend on $\eta$ and are
significantly reduced (increased) under tensile (compressive) strain, also in
consistent agreement with the experimental observations. The present work
demonstrates that for a realistic theoretical description of oxygen vacancies
in oxide perovskite thin films is necessary to consider lattice thermal
excitations, thus going beyond standard zero-temperature ab initio approaches.",2012.01802v1
2020-12-29,Electronic structure of InAs and InSb surfaces: density functional theory and angle-resolved photoemission spectroscopy,"The electronic structure of surfaces plays a key role in the properties of
quantum devices. However, surfaces are also the most challenging to simulate
and engineer. Here, we study the electronic structure of InAs(001), InAs(111),
and InSb(110) surfaces using a combination of density functional theory (DFT)
and angle-resolved photoemission spectroscopy (ARPES). We were able to perform
large-scale first principles simulations and capture effects of different
surface reconstructions by using DFT calculations with a machine-learned
Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. To facilitate direct
comparison with ARPES results, we implemented a ""bulk unfolding"" scheme by
projecting the calculated band structure of a supercell surface slab model onto
the bulk primitive cell. For all three surfaces, we find a good agreement
between DFT calculations and ARPES. For InAs(001), the simulations clarify the
effect of the surface reconstruction. Different reconstructions are found to
produce distinctive surface states. For InAs(111) and InSb(110), the
simulations help elucidate the effect of oxidation. Owing to larger charge
transfer from As to O than from Sb to O, oxidation of InAs(111) leads to
significant band bending and produces an electron pocket, whereas oxidation of
InSb(110) does not. Our combined theoretical and experimental results may
inform the design of quantum devices based on InAs and InSb semiconductors,
e.g., topological qubits utilizing the Majorana zero modes.",2012.14935v1
2021-01-10,Ionic liquid gating induced two superconductor-insulator phase transitions in spinel oxide Li$_{1 \pm x}$Ti$_2$O$_{4-δ}$,"The associations between emergent physical phenomena (e.g.,
superconductivity) and orbital, charge, and spin degrees of freedom of $3d$
electrons are intriguing in transition metal compounds. Here, we successfully
manipulate the superconductivity of spinel oxide Li$_{1\pm
x}$Ti$_2$O$_{4-\delta}$ (LTO) by ionic liquid gating. A dome-shaped
superconducting phase diagram is established, where two insulating phases are
disclosed both in heavily electron-doping and hole-doping regions. The
superconductor-insulator transition (SIT) in the hole-doping region can be
attributed to the loss of Ti valence electrons. In the electron-doping region,
LTO exhibits an unexpected SIT instead of a metallic behavior despite an
increase in carrier density. Furthermore, a thermal hysteresis is observed in
the normal state resistance curve, suggesting a first-order phase transition.
We speculate that the SIT and the thermal hysteresis stem from the enhanced
$3d$ electron correlations and the formation of orbital ordering by comparing
the transport and structural results of LTO with the other spinel oxide
superconductor MgTi$_2$O$_4$, as well as analysing the electronic structure by
first-principles calculations. Further comprehension of the detailed interplay
between superconductivity and orbital ordering would contribute to the
revealing of unconventional superconducting pairing mechanism.",2101.03518v2
2017-05-10,Surface oxidation and thermoelectric properties of indium-doped tin telluride nanowires,"The recent discovery of excellent thermoelectric properties and topological
surface states in SnTe-based compounds has attracted extensive attention in
various research areas. Indium doped SnTe is of particular interest because,
depending on the doping level, it can either generate resonant states in the
bulk valence band leading to enhanced thermoelectric properties, or induce
superconductivity that coexists with topological states. Here we report on the
vapor deposition of In-doped SnTe nanowires and the study of their surface
oxidation and thermoelectric properties. The nanowire growth is assisted by Au
catalysts, and their morphologies vary as a function of substrate position and
temperature. Transmission electron microscopy characterization reveals the
formation of amorphous surface in single crystalline nanowires. X-ray
photoelectron spectroscopy studies suggest that the nanowire surface is
composed of In2O3, SnO2, Te and TeO2 which can be readily removed by argon ion
sputtering. Exposure of the cleaned nanowires to atmosphere yields rapid
oxidation of the surface within only one minute. Characterizations of
electrical conductivity {\sigma}, thermopower S, and thermal conductivity
\k{appa} were performed on the same In-doped nanowire which shows suppressed
{\sigma} and \k{appa} but enhanced S yielding an improved thermoelectric figure
of merit ZT than the undoped SnTe.",1705.03874v2
2017-09-07,Importance of elastic finite-size effects: neutral defects in ionic compounds,"Small system sizes are a well known source of error in DFT calculations, yet
computational constraints frequently dictate the use of small supercells, often
as small as 96 atoms in oxides and compound semiconductors. In ionic compounds,
electrostatic finite size effects have been well characterised, but
self-interaction of charge neutral defects is often discounted or assumed to
follow an asymptotic behaviour and thus easily corrected with linear elastic
theory. Here we show that elastic effects are also important in the description
of defects in ionic compounds and can lead to qualitatively incorrect
conclusions if inadequately small supercells are used; moreover, the spurious
self-interaction does not follow the behaviour predicted by linear elastic
theory. Considering the exemplar cases of metal oxides with fluorite structure,
we show that numerous previous studies, employing 96-atom supercells,
misidentify the ground state structure of (charge neutral) Schottky defects. We
show that the error is eliminated by employing larger cells (324, 768 and 1500
atoms), and careful analysis determines that elastic effects, not
electrostatic, are responsible. The spurious self-interaction was also observed
in non-oxide ionic compounds and irrespective of the computational method used,
thereby resolving long standing discrepancies between DFT and force-field
methods, previously attributed to the level of theory. The surprising magnitude
of the elastic effects are a cautionary tale for defect calculations in ionic
materials, particularly when employing computationally expensive methods or
when modelling large defect clusters. We propose two computationally
practicable methods to test the magnitude of the elastic self-interaction in
any ionic system.",1709.02037v1
2017-08-15,Oxidative species-induced excitonic transport in tubulin aromatic networks: Potential implications for neurodegenerative disease,"Oxidative stress is a pathological hallmark of neurodegenerative tauopathic
disorders such as Alzheimer's disease and Parkinson's disease-related dementia,
which are characterized by altered forms of the microtubule-associated protein
(MAP) tau. MAP tau is a key protein in stabilizing the microtubule architecture
that regulates neuron morphology and synaptic strength. The precise role of
reactive oxygen species (ROS) in the tauopathic disease process, however, is
poorly understood. It is known that the production of ROS by mitochondria can
result in ultraweak photon emission (UPE) within cells. One likely absorber of
these photons is the microtubule cytoskeleton, as it forms a vast network
spanning neurons, is highly co-localized with mitochondria, and shows a high
density of aromatic amino acids. Functional microtubule networks may traffic
this ROS-generated endogenous photon energy for cellular signaling, or they may
serve as dissipaters/conduits of such energy. Experimentally, after in vitro
exposure to exogenous photons, microtubules have been shown to reorient and
reorganize in a dose-dependent manner with the greatest effect being observed
around 280 nm, in the tryptophan and tyrosine absorption range. In this paper,
recent modeling efforts based on ambient temperature experiment are presented,
showing that tubulin polymers can feasibly absorb and channel these
photoexcitations via resonance energy transfer, on the order of dendritic
length scales. Since microtubule networks are compromised in tauopathic
diseases, patients with these illnesses would be unable to support effective
channeling of these photons for signaling or dissipation. Consequent emission
surplus due to increased UPE production or decreased ability to absorb and
transfer may lead to increased cellular oxidative damage, thus hastening the
neurodegenerative process.",1709.03828v1
2017-09-20,A computational study of hafnia-based ferroelectric memories: from ab initio via physical modeling to circuit models of ferroelectric device,"The discovery of ferroelectric properties of binary oxides revitalized the
interest in ferroelectrics and bridged the scaling gap between the
state-of-the-art semiconductor technology and ferroelectric memories. However,
before hitting the markets, the origin of ferroelectricity and in-depth studies
of device characteristics are needed. Establishing a correlation between the
performance of the device and underlying physical mechanisms is the first step
toward understanding the device and engineering guidelines for a novel,
superior device. Therefore, in this paper a holistic modeling approaches which
lead to a better understanding of ferroelectric memories based on hafnium and
zirconium oxide is addressed. Starting from describing the stabilization of the
ferroelectric phase within the binary oxides via physical modeling the physical
mechanisms of the ferroelectric devices are reviewed. Besides, limitations and
modeling of the multilevel operation and switching kinetics of ultimately
scaled devices as well as the necessity for Landau-Khalatnikov approach are
discussed. Furthermore, a device-level model of ferroelectric memory devices
that can be used to study the array implementation and their operational
schemes are addressed. Finally, a circuit model of the ferroelectric memory
device is presented and potential further applications of ferroelectric devices
are outlined.",1709.06983v1
2017-11-14,Roughness of oxide glass subcritical fracture surfaces,"An original setup combining a very stable loading stage, an atomic force
microscope and an environmental chamber, allows to obtain very stable
sub-critical fracture propagation in oxide glasses under controlled
environment, and subsequently to finely characterize the nanometric roughness
properties of the crack surfaces. The analysis of the surface roughness is
conducted both in terms of the classical root mean square roughness to compare
with the literature, and in terms of more physically adequate indicators
related to the self-affine nature of the fracture surfaces. Due to the
comparable nanometric scale of the surface roughness, the AFM tip size and the
instrumental noise, a special care is devoted to the statistical evaluation of
the metrologic properties. The 2 roughness amplitude of several oxide glasses
was shown to decrease as a function of the stress intensity factor, to be quite
insensitive to the relative humidity and to increase with the degree of
heterogeneity of the glass. The results are discussed in terms of several
modeling arguments concerning the coupling between crack propagation,
material's heterogeneity, crack tip plastic deformation and water diffusion at
the crack tip. A synthetic new model is presented combining the predictions of
a model by Wiederhorn et al. [1] on the effect of the material's heterogeneity
on the crack tip stresses with the self-affine nature of the fracture surfaces.",1711.05040v1
2018-03-05,Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds,"Newly emerged materials from the family of Heuslers and complex oxides
exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much
higher than even room temperature. In this work, using the semiclassical
top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that
utilizes such ferromagnetic semiconductors as channel materials, in addition to
ferromagnetic source/drain contacts. Such a device could retain the spin
polarization of injected electrons in the channel, the loss of which limits the
operation of traditional spin transistors with non-ferromagnetic channels. We
examine the operation of four material systems that are currently considered
some of the most prominent known ferromagnetic semiconductors, three
Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family
(NiFe2O4). We describe their bandstructures by using data from DFT
calculations. We investigate under which conditions high spin polarization and
significant ION/IOFF ratio, two essential requirements for the spin-MOSFET
operation, are both achieved. We show that these particular Heusler channels,
in their bulk form, do not have adequate bandgap to provide high ION/IOFF
ratios, and have small magnetoconductance compared to state-of-the-art devices.
However, with confinement into ultra-narrow sizes down to a few nanometers, and
by engineering their spin dependent contact resistances, they could prove
promising channel materials for the realization of spin-MOSFET transistor
devices that offer combined logic and memory functionalities. Although the main
compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4
alone, we expect that the insight we provide is relevant to other classes of
such materials as well.",1803.01789v1
2018-03-06,The enzyme-like catalytic activity of cerium oxide nanoparticles and its dependency on Ce3+ surface area concentration,"Cerium oxide nanoparticles are known to catalyze the decomposition of
reactive oxygen species such as superoxide radical and hydrogen peroxide.
Herein, we examine the superoxide dismutase (SOD) and catalase (CAT) mimetic
catalytic activities of nanoceria and demonstrate the existence of generic
behaviors. For particles of size 4.5, 7.8, 23 and 28 nm, the SOD and CAT
catalytic activities exhibit the characteristic shape of a Langmuir isotherm as
a function of cerium concentration. Results show that the catalytic effects are
enhanced for smaller particles and for the particles with the largest Ce3+
fraction. The SOD-like activity obtained from the different samples is found to
superimpose on a single master curve using the Ce3+ surface area concentration
as a new variable, indicating the existence of particle independent redox
mechanisms. For the CAT assays the adsorption of H2O2 molecules at the particle
surface modulates the efficacy of the decomposition process and must be taken
into account. We design an amperometry-based experiment to evaluate the H2O2
adsorption at nanoceria surfaces, leading to the renormalization of the
particle specific area. Depending on the particle type the amount of adsorbed
H2O2 molecules varies from 2 to 20 nm-2. The proposed scalings are predictive
and allow determining SOD and CAT catalytic properties of cerium oxide solely
from physico-chemical features.",1803.01973v1
2018-03-21,A First-Principles Study on the Adsorption of Small Molecules on Antimonene: Oxidation Tendency and Stability,"Antimonene, a new group-VA 2D semiconducting material beyond phosphorene, was
recently synthesized through various approaches and was shown to exhibit a good
structural integrity in ambient conditions and various interesting properties.
In this work, we perform systematical first-principles investigations on the
interactions of antimonene with the small molecules CO, NO, NO2, H2O, O2, NH3
and H2. It is found that NO, NO2, H2O, O2, and NH3 serve as charge acceptors,
while CO shows a negligible charge transfer. H2 acts as a charge donor to
antimonene with the amount of charge transfer being ten times that of H2 on
phosphorene. The interaction of the O2 molecule with antimonene is much
stronger than that with phosphorene. Surprisingly, the kinetic barrier for the
splitting of the O2 molecule on antimonene is low (~0.40 eV), suggesting that
pristine antimonene may undergo oxidation in ambient conditions, especially at
elevated temperatures. Fortunately, the acceptor role of H2O on antimonene,
opposite to a donor role in phosphorene, helps to suppress further structural
degradation of the oxidized antimonene by preventing the proton transfer
between water molecules and oxygen species to form acids.",1803.07824v1
2018-06-06,Unveiling ADP-binding sites and channels in respiratory complexes: Validation of Murburn concept as a holistic explanation for oxidative phosphorylation,"Mitochondrial oxidative phosphorylation (mOxPhos) makes ATP, the energy
currency of life. Chemiosmosis, a proton centric mechanism, advocates that
Complex V harnesses a transmembrane potential (TMP) for ATP synthesis. This
perception of cellular respiration requires oxygen to stay tethered at Complex
IV (an association inhibited by cyanide) and diffusible reactive oxygen species
(DROS) are considered wasteful and toxic products. With new mechanistic
insights on heme and flavin enzymes, an oxygen or DROS centric explanation
(called murburn concept) was recently proposed for mOxPhos. In the new
mechanism, TMP is not directly harnessed, protons are a rate limiting reactant
and DROS within matrix serve as the chemical coupling agents that directly link
NADH oxidation with ATP synthesis. Herein, we report multiple ADP binding sites
and solvent accessible DROS channels in respiratory proteins, which validate
the oxygen or DROS centric power generation (ATP synthesis) system in mOxPhos.
Since cyanide's heme binding Kd is high (mM), low doses (uM) of cyanide is
lethal because cyanide disrupts DROS dynamics in mOxPhos. The critical study
also provides comprehensive arguments against Mitchell's and Boyer's
explanations and extensive support for murburn concept based holistic
perspectives for mOxPhos.",1806.02310v1
2018-06-13,Harmonic Generation from Metal-Oxide and Metal-Metal Boundaries,"We explore the outcomes of detailed microscopic models by calculating second-
and third-harmonic generation from thin film surfaces with discontinuous
free-electron densities. These circumstances can occur in structures consisting
of a simple metal mirror, or arrangements composed of either different metals
or a metal and a free electron system like a conducting oxide. Using a
hydrodynamic approach we highlight the case of a gold mirror, and that of a
two-layer system containing indium tin oxide (ITO) and gold. We assume the gold
mirror surface is characterized by a free-electron cloud of varying density
that spills into the vacuum, which as a result of material dispersion exhibits
epsilon-near-zero conditions and local field enhancement at the surface. For a
bylayer consisting of a thin ITO and gold films, if the wave is incident from
the ITO side the electromagnetic field is presented with a free-electron
discontinuity at the ITO/gold interface, and wavelength-dependent,
epsilon-near-zero conditions that enhance local fields and conversion
efficiencies, and determine the surface's emission properties. We evaluate the
relative significance of additional nonlinear sources that arise when a
free-electron discontinuity is present, and show that harmonic generation can
be sensitive to the density of the screening free-electron cloud, and not its
thickness. Our findings also suggest the possibility to control surface
harmonic generation through surface charge engineering.",1806.05014v1
2018-06-14,Synthesis of copper and silver nanoparticles by molecular beam method,"The paper presents the results of investigation of the structure of porous
condensates of Ag-NaCl and Cu-NaCl composition; chemical and phase compositions
and dimensions of nanoparticles, produced from the vapour phase by EBPVD
method. Silver and copper nanoparticles in a porous matrix, when removed from
vacuum, oxidize in air to lower oxides, and have considerable sorption capacity
relative to oxygen and moisture. Heating in air is accompanied by lowering of
porous condensate mass, primarily, due to desorption of physically sorbed
moisture, as well as afteroxidation to higher oxides due to physically adsorbed
oxygen. At copper concentrations up to 10 at.%, sorption capacity of the
condensate is greatly enhanced, that is attributable to presence of very fine
nanoparticles. Increase of copper concentration in the condensate is
accompanied by lowering of sorption capacity of nanoparticles with respect to
oxygen, and, therefore, also change of phase composition. In addition to
concentration change, phase composition of nanoparticles can be also controlled
by heat treatment of the initial condensate produced at low condensation
temperatures. Silver and copper nanoparticles can be converted into stable
colloidal systems.",1806.05509v1
2018-06-14,Resolving interfacial charge transfer in titanate superlattices using resonant X-ray reflectometry,"Charge transfer in oxide heterostructures can be tuned to promote emergent
interfacial states, and accordingly, has been the subject of intense study in
recent years. However, accessing the physics at these interfaces, which are
often buried deep below the sample surface, remains difficult. Addressing this
challenge requires techniques capable of measuring the local electronic
structure with high-resolution depth dependence. Here, we have used
linearly-polarized resonant X-ray reflectometry (RXR) as a means to visualize
charge transfer in oxide superlattices with atomic layer precision. From our
RXR measurements, we extract valence depth profiles of SmTiO$_3$
(SmTO)/SrTiO$_3$ (STO) heterostructures with STO quantum wells varying in
thickness from 5 SrO planes down to a single, atomically thin SrO plane. At the
polar-nonpolar SmTO/STO interface, an electrostatic discontinuity leads to
approximately half an electron per areal unit cell transferred from the
interfacial SmO layer into the neighboring STO quantum well. We observe this
charge transfer as a suppression of the t$_{2g}$ absorption peaks that
minimizes contrast with the neighboring SmTO layers at those energies and leads
to a pronounced absence of superlattice peaks in the reflectivity data. Our
results demonstrate the sensitivity of RXR to electronic reconstruction at the
atomic scale, and establish RXR as a powerful means of characterizing charge
transfer at buried oxide interfaces.",1806.05733v1
2018-07-09,Thermal Stability Study of Transition Metal Perovskite Sulfides,"Transition metal perovskite chalcogenides, a class of materials with rich
tunability in functionalities, are gaining increased attention as candidate
materials for renewable energy applications. Perovskite oxides are considered
excellent n-type thermoelectric materials. Compared to oxide counterparts, we
expect the chalcogenides to possess more favorable thermoelectric properties
such as lower lattice thermal conductivity and smaller band gap, making them
promising material candidates for high temperature thermoelectrics. Thus, it is
necessary to study the thermal properties of these materials in detail,
especially thermal stability, to evaluate their potential. In this work, we
report the synthesis and thermal stability study of five compounds,
\alpha-SrZrS$_3$, \beta-SrZrS$_3$, BaZrS$_3$, Ba$_2$ZrS$_4$, and
Ba$_3$Zr$_2$S$_7$. These materials cover several structural types including
distorted perovskite, needle-like, and Ruddlesden-Popper phases. Differential
scanning calorimeter and thermo-gravimetric analysis measurements were
performed up to 1200{\deg}C in air. Structural and chemical characterizations
such as X-ray diffraction, Raman spectroscopy, and energy dispersive analytical
X-ray spectroscopy were performed on all the samples before and after the heat
treatment to understand the oxidation process. Our studies show that perovskite
chalcogenides possess excellent thermal stability in air at least up to
600{\deg}C.",1807.03355v1
2018-07-10,Optimizing hot electron harvesting at planar metal-semiconductor interfaces with titanium oxynitride thin films,"Understanding metal-semiconductor interfaces is critical to the advancement
of photocatalysis and sub-bandgap solar energy harvesting where sub-bandgap
photons can be excited and extracted into the semiconductor. In this work, we
compare the electron extraction efficiency across Au/TiO2 and titanium
oxynitride/TiO2-x interfaces, where in the latter case the spontaneously
forming oxide layer (TiO2-x) creates a metal-semiconductor contact.
Time-resolved pump-probe spectroscopy is used to study the electron
recombination rates in both cases. Unlike the nanosecond recombination
lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the
TiON system, which we explain using a trap-mediated recombination model. Using
this model, we investigate the tunability of the relaxation dynamics with
oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the
highest carrier extraction efficiency, slowest trapping and an appreciable hot
electron population reaching the surface oxide. Our results demonstrate the
productive role oxygen can play in enhancing electron harvesting and elongating
electron lifetimes providing an optimized metal-semiconductor interface using
only the native oxide of titanium oxynitride.",1807.03702v1
2018-07-10,Influence of particle size and agglomeration in solid oxide fuel cell cathodes using manganite nanoparticles,"In this work we studied the influence of particle size and agglomeration in
the performance of solid oxide fuel cell cathodes made with nanoparticles of
La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix
method. In both procedures we introduced additional reagents in order to
separated the manganite particles. We evaluated cathodic performance by
Electrochemical Impedance Spectroscopy in symmetrical
(CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature
used for cathode sintering. Our results show that deagglomeration of the
particles, serves to improve the cathodes performance. However, the dependence
of the performance with the size of the particles is not clear, as different
trends were obtained for each synthesis route. As a common feature, the
cathodes with the lowest area specific resistance are the ones sintered at the
largest temperature. This result indicates that an additional factor related
with the quality of the cathode/electrolyte sintering, is superimposed with the
influence of particle size, however further work is needed to clarify this
issue. The enhancement obtained by deagglomeration suggest that the use of this
kind of methods deserved to be considered to develop high performance
electrodes for solid oxide fuel cells.",1807.03816v1
2018-07-11,Insights into the use of polyethylene oxide in energy storage/conversion devices: A critical review,"In this review, latest updates in the poly (ethylene oxide) based
electrolytes are summarized. The ultimate goal of researchers globally is
towards the development of free standing solid polymeric separator for energy
storage devices. This single free standing solid polymeric separator may
replace the liquid and separator (organic/Inorganic) used in existing
efficient/smart energy technology. As an example polyethylene oxide (PEO)
consist of an electron donor rich group which provides coordinating sites to
the cation for migration. Owing to this exclusive structure PEO exhibits some
remarkable properties such as; low glass transition temperature, excellent
flexibility and ability to make complexation with various metal salts which are
unattainable by another polymer host. Hence, the PEO is the most emerging
candidate that have been examined or is currently under audition for
application in energy storage devices. So, this review article first provides
the detailed study of the PEO properties, characteristic of constituents of the
polymer electrolyte and suitable approaches for the modification of polymer
electrolytes. Then, the synthesization and characterizations techniques are
outlined. The structures, characteristics, and performance during
charge-discharge of four types of electrolyte/separators which are Liquid,
Plasticized, and dispersed/intercalated electrolyte are highlighted. The
suitable ion transport mechanism proposed by researchers in the different
renowned group have been discussed for better understanding of the ion dynamics
in such systems.",1808.03699v1
2018-08-15,Electron Localization Enhances Cation Diffusion in Transition Metal Oxides: An Electronic Trebuchet Effect,"Ion diffusion is a central part of materials physics of fabrication,
deformation, phase transformation, structure stability and electrochemical
devices. Conventional theory focuses on the defects that mediate diffusion and
explains how their populations influenced by oxidation, reduction, irradiation
and doping can enhance diffusion. However, we have found the same influences
can also elevate their mobility by orders of magnitude in several prototypical
transition-metal oxides. First-principles calculation fundamentally connects
the latter observation to migrating ion's local structure, which is inherently
soft and has a broken symmetry, making it susceptible to electron or hole
localization, thereby realizing a lower saddle-point energy. This finding
resolves an unanswered question in physical ceramics of the past 30 years: why
cation diffusion against the prediction of classical nonstoichiometric defect
physics is enhanced in reduced zirconia, ceria and structurally related
ceramics? It also suggests the saddle-point electron-phonon interaction that
enables a negative-U state is akin to the counterweight effect that enables a
trebuchet. This simple picture for the transitional state explains why enhanced
kinetics mediated by radical-like-ion migration occurs often, especially under
extreme conditions.",1808.05196v3
2018-08-23,"Buffer layer-less fabrication of high-mobility transparent oxide semiconductor, La-doped BaSnO3","Transparent oxide semiconductors (TOSs) showing both high visible
transparency and high electron mobility have attracted great attention towards
the realization of advanced optoelectronic devices. La-doped BaSnO3 (LBSO) is
one of the most promising TOSs because its single crystal exhibits a high
electron mobility. However, in the LBSO films, it is very hard to obtain high
mobility due to the threading dislocations, which are originated from the
lattice mismatch between the film and the substrate. Therefore, many
researchers have tried to improve the mobility by inserting a buffer layer.
While the buffer layers increased the electron mobilities, this approach leaves
much to be desired since it involves a two-step film fabrication process and
the enhanced mobility values are still significantly lower than single crystal
values. We show herein that the electron mobility of LBSO films can be improved
without inserting any buffer layers if the films are grown under highly
oxidative ozone (O3) atmospheres. The O3 environments relaxed the LBSO lattice
and reduced the formation of Sn2+ states, which are known to suppress the
electron mobility in LBSO. The resultant O3-LBSO films showed improved mobility
values up to 115 cm2 V-1 s-1, which is among the highest in LBSO films on
SrTiO3 substrates and comparable to LBSO films with buffer layers.",1808.07619v1
2018-12-22,Fingerprint oxygen redox reactions in batteries through high-efficiency mapping of resonant inelastic X-ray scattering (mRIXS),"Realizing reversible reduction-oxidation (Redox) reactions of lattice oxygen
in batteries is a promising way to improve the energy and power density.
However, conventional oxygen absorption spectroscopy fails to distinguish the
critical oxygen chemistry in oxide-based battery electrodes. Therefore,
high-efficiency full-range mapping of resonant inelastic X-ray scattering
(mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here,
based on mRIXS results collected from a series of Li1.17Ni0.21Co0.08Mn0.54O2
electrodes at different electrochemical states and its comparison with
peroxides, we provide a comprehensive analysis of five components observed in
the mRIXS results. While almost all the components change upon electrochemical
cycling, comparison with peroxide species show that only two evolving features
correspond to the critical oxidized oxygen states. One is a specific feature at
531.0eV excitation and 523.7eV emission energy, the other is a low-energy loss
feature. We show that both features evolve with electrochemical cycling of
Li1.17Ni0.21Co0.08Mn0.54O2 electrodes, and could be used for characterizing
oxygen redox states in battery electrodes. This work is the first benchmark for
a complete assignment of all the important mRIXS features collected from
battery materials, which provides guidelines for future studies in
characterization, analysis and theoretical calculation for probing and
understanding oxygen redox reactions.",1812.09591v1
2018-12-25,Smoothed particle hydrodynamics study of friction of the coarse-grained $α$-Al2O3/$α$-Al2O3 and $α$-Fe2O3/$α$-Fe2O3 contacts in behavior of the spring interfacial potential,"The paper uses the spring potential to present interaction between the
coarse-grained interfacial particles of the $\alpha$-Al2O3/$\alpha$-Al2O3 and
$\alpha$-Fe2O3/$\alpha$-Fe2O3 contacts in the sliding friction study of these
micron-scale oxides by smoothed particle hydrodynamics simulations. The spring
constants of the potential for the particle systems are converted from those of
the atomic oxide systems that are yielded by the second order polynomial fits
of the probed surface potentials in molecular dynamics simulations, and are
dependent on the particle coarse-graining. It is founded that at micron-scale
the friction properties of the oxides are almost independent of the
coarse-graining and are the same in the different sliding directions. Even the
hardness contacts friction coefficient shows a decrease with increasing
intensity of normal component of the interfacial interaction, originating from
stability of friction force and growth of normal force. This result is as an
implementation for the previous observations of sliding friction of various
materials that showed that a drop of friction coefficient with increasing
externally applied normal load has originated from deformation of interfaces or
occurrence of debris at contact, indicating an unsteady contact.",1812.10051v2
2018-12-26,Lattice-mismatched semiconductor heterostructures,"Semiconductor heterostructure is a critical building block for modern
semiconductor devices. However, forming semiconductor heterostructures of
lattice-mismatch has been a great challenge for several decades. Epitaxial
growth is infeasible to form abrupt heterostructures with large
lattice-mismatch while mechanical-thermal bonding results in a high density of
interface defects and therefore severely limits device applications. Here we
show an ultra-thin oxide-interfaced approach for the successful formation of
lattice-mismatched semiconductor heterostructures. Following the depiction of a
theory on the role of interface oxide in forming the heterostructures, we
describe experimental demonstrations of Ge/Si (diamond lattices), Si/GaAs (zinc
blende lattice), GaAs/GaN (hexagon lattice), and Si/GaN heterostructures.
Extraordinary electrical performances in terms of ideality factor, current
on/off ratio, and reverse breakdown voltage are measured from p-n diodes
fabricated from the four types of heterostructures, significantly outperforming
diodes derived from other methods. Our demonstrations indicate the versatility
of the ultra-thin-oxide-interface approach in forming lattice-mismatched
heterostructures, open up a much larger possibility for material combinations
for heterostructures, and pave the way toward broader applications in
electronic and optoelectronic realms.",1812.10225v1
2018-12-27,Critical current density of hole doped high-Tc cuprates and heavy fermion superconductors: relevance to the possible quantum critical behavior,"The superconducting critical current density, Jc, in hole doped cuprates show
strong dependence on the doped hole content, p, within the copper oxide
plane(s). The doping dependent Jc mainly exhibits the variation of the
intrinsic depairing critical current density as p is varied. Jc(p) tends to
peak at p ~ 0.185 in copper oxide superconductors. This particular value of the
hole content, often termed as the critical hole concentration, has several
features putative to a quantum critical point (QCP). Very recently, pressure
dependences of the superconducting transition temperature (Tc) and the critical
current (Ic) in pure CeRhIn5 and Sn doped CeRhIn5 heavy fermion compounds have
been reported (Nature Communications (2018) 9:44, DOI:
10.1038/s41467-018-02899-5). The critical pressure demarcates an
antiferromagnetic quantum critical point where both Tc and Ic are maximized. We
have compared and contrasted this behavior with those found for
Y1-xCaxBa2Cu3O7-d in this brief communication. The resemblance of the
systematic behavior of the critical current with pressure and hole content
between heavy fermion systems and hole doped cuprates is significant. This adds
to the circumstantial evidence that quantum critical physics probably plays a
notable role beyond the unconventional normal and superconducting state
properties of copper oxide superconductors.",1812.10632v1
2018-12-29,Electronic structure and transport in amorphous metal oxide and amorphous metal oxy-nitride semiconductors,"Recently amorphous oxide semiconductors (AOS) have gained commercial interest
due to their low-temperature processability, high mobility and areal uniformity
for display backplanes and other large area applications. A multi-cation
amorphous oxide (a-IGZO) has been researched extensively and is now being used
in commercial applications. It is proposed in the literature that overlapping
In-5s orbitals form the conduction path and the carrier mobility is limited due
to the presence of multiple cations which create a potential barrier for the
electronic transport in a-IGZO semiconductors. A multi-anion approach towards
amorphous semiconductors has been suggested to overcome this limitation and has
been shown to achieve hall mobilities up to an order of magnitude higher
compared to multi-cation amorphous semiconductors. In the present work, we
compare the electronic structure and electronic transport in a multi-cation
amorphous semiconductor, a-IGZO and a multi-anion amorphous semiconductor,
a-ZnON using computational methods. Our results show that in a-IGZO, the
carrier transport path is through the overlap of outer s-orbitals of mixed
cations and in a-ZnON, the transport path is formed by the overlap of Zn-4s
orbitals, which is the only type of metal cation present. We also show that for
multi-component ionic amorphous semiconductors, electron transport can be
explained in terms of orbital overlap integral which can be calculated from
structural information and has a direct correlation with the carrier effective
mass which is calculated using computationally expensive first principle DFT
methods.",1812.11333v3
2019-01-15,Diluted Oxide Interfaces with Tunable Ground States,"The metallic interface between two oxide insulators, such as LaAlO3/SrTiO3
(LAO/STO), provides new opportunities for electronics and spintronics. However,
due to the presence of multiple orbital populations, tailoring the interfacial
properties such as the ground state and metal-insulator transitions remains
challenging. Here, we report an unforeseen tunability of the phase diagram of
LAO/STO by alloying LAO with a ferromagnetic LaMnO3 insulator without forming
lattice disorder and at the same time without changing the polarity of the
system. By increasing the Mn-doping level, x, of LaAl1-xMnxO3/STO, the
interface undergoes a Lifshitz transition at x = 0.225 across a critical
carrier density of nc= 2.8E13 cm-2, where a peak TSC =255 mK of superconducting
transition temperature is observed. Moreover, the LaAl1-xMnxO3 turns
ferromagnetic at x >=0.25. Remarkably, at x = 0.3, where the metallic interface
is populated by only dxy electrons and just before it becomes insulating, we
achieve reproducibly a same device with both signatures of superconductivity
and clear anomalous Hall effect. This provides a unique and effective way to
tailor oxide interfaces for designing on-demand electronic and spintronic
devices.",1901.04776v1
2019-03-03,Oxide: The Essence of Rust,"Rust claims to advance industrial programming by bridging the gap between
low-level systems programming and high-level application programming. At the
heart of the argument that this enables programmers to build more reliable and
efficient software is the borrow checker - a novel approach to ownership that
aims to balance type system expressivity with usability. And yet, to date there
is no core type system that captures Rust's notion of ownership and borrowing,
and hence no foundation for research on Rust to build upon.
  In this work, we set out to capture the essence of this model of ownership by
developing a type systems account of Rust's borrow checker. We present Oxide, a
formalized programming language close to source-level Rust (but with
fully-annotated types). This presentation takes a new view of lifetimes as an
approximation of the provenances of references, and our type system is able to
automatically compute this information through a substructural typing judgment.
We provide the first syntactic proof of type safety for borrow checking using
progress and preservation. Oxide is a simpler formulation of borrow checking -
including recent features such as non-lexical lifetimes - that we hope
researchers will be able to use as the basis for work on Rust.",1903.00982v4
2019-03-13,Combined in situ microstructural study of the relationships between local grain boundary structure and passivation on microcrystalline copper,"In situ Electro-Chemical Scanning Tunneling Microscopy (ECSTM) and Electron
Back-Scatter Diffraction analysis of the same local microstructural region were
combined to study the relationships between grain boundary (GB) type and
structure and passivation on microcrystalline copper in 0.1 M NaOH aqueous
solution. The results show that, for high angle random boundaries, passivation
in the Cu(I) oxidation range is characterized by a decrease of the depth of GB
edge region due to the formation of a passive film locally thicker than on the
adjacent grains and thus to anodic oxidation being locally less efficient since
it consumes more copper at the grain boundaries. For sigma3 CSL boundaries, the
Cu(I) passivation efficiency was observed to be dependent on the local
structure of the boundaries. A transition from more to less efficient
passivation was observed for a deviation angle of 0.4-0.5{\deg} of the {111} GB
plane with respect to the perfect geometry of an ideal coherent twin boundary.
This transition would result from the effect on the local anodic oxidation
properties of an increased density of misfit dislocations accommodating the
increased deviation of the boundary plane from the exact CSL plane.",1903.05371v1
2019-04-16,The role of Ce$^{3+}$/Ce$^{4+}$ in the spectroscopic properties of cerium oxide doped zinc-tellurite glasses prepared under air,"Emerging technologies are demanding innovative properties of glasses. In this
work, Cerium Oxide is used as a dopant in Zinc-Tellurite samples and its
effects on the properties of the glass are investigated. Thermal analysis and
x-ray diffraction confirmed the amorphous nature of all samples. The bivalent
nature of Cerium is investigated spectroscopically and a strong redshift
induced by the dopant is attributed to charge transfers
O$^{2-}{\rightarrow}$Ce$^{4+}$, while the 4f-5d transition of Ce$^{3+}$ could
not be identified in absorption or luminescence measurements. Yellow/red
(570/650 nm) emission under 405/450 nm pumping were observed and are originated
from Te$^{4+}$ ions, which absorbs light in the UV/blue region of the spectrum.
The incorporation of some Cerium Oxide enhanced the visible luminescence,
though we found no evidence that Cerium ions play some role in the radiative
process. The luminescence is enhanced though due changes in the glass network
induced by the dopant.",1904.07622v6
2019-08-06,FeOOH instability at the lower mantle conditions,"Goethite, {\alpha}-FeOOH, is a major component among oxidized iron species,
called rust, which formed as a product of metabolism of anoxygenic prokaryotes
(1, 2) inhabiting the Earth from about 3.8 billion years (Gy) ago until the
Great Oxidation Event (GOE) of about 2.5 Gy ago. The rust was buried on the
ocean floor (1, 2) and had to submerge into the Earth mantle with subducting
slabs due to the plate tectonics started about 2.8 Gy ago (3). The fate and the
geological role of the rust at the lower mantle high-pressure and
high-temperature(HPHT) conditions is unknown. We studied the behavior of
goethite up to 82(2) GPa and 2300(100) K using in situ synchrotron
single-crystal X-ray diffraction. At these conditions, corresponding to the
coldest slabs at the depth of about 1000 km, {\alpha}-FeOOH decomposes to
various iron oxides (Fe2O3, Fe5O7, Fe7O10, Fe6.32O9) and an oxygen-rich fluid.
Our results suggest that recycling of the rust in the Earth mantle could
contribute to oxygen release to the atmosphere and explain the sporadic
increase of the oxygen level before the GOE linked to the formation of Large
Igneous Provinces(4).",1908.02114v1
2019-08-08,Atomically-Smooth Single-Crystalline VO$_2$ thin films with Bulk-like Metal-Insulator Transitions,"Atomically-abrupt interfaces in transition metal oxide (TMO) heterostructures
could host a variety of exotic condensed matter phases that may not be found in
the bulk materials at equilibrium. A critical step in the development of such
atomically-sharp interfaces is the deposition of atomically-smooth TMO thin
films. Optimized deposition conditions exist for the growth of perovskite
oxides. However, the deposition of rutile oxides, such as VO$_2$, with
atomic-layer precision has been challenging. In this work, we used pulsed laser
deposition (PLD) to grow atomically-smooth VO$_2$ thin films on rutile TiO$_2$
(101) substrates. We show that optimal substrate preparation procedure followed
by the deposition of VO$_2$ films at a temperature conducive for step-flow
growth mode is essential for achieving atomically-smooth VO$_2$ films. The
films deposited at optimal substrate temperatures show a step and terrace
structure of the underlying TiO$_2$ substrate. At lower deposition
temperatures, there is a transition to a mixed growth mode comprising of island
growth and layer-by-layer growth modes. VO$_2$ films deposited at optimal
substrate temperatures undergo a metal to insulator transition at a transition
temperature of $\sim$325 K with $\sim$10$^3$ times increase in resistance, akin
to MIT in bulk VO$_2$.",1908.02937v1
2019-08-20,Factors limiting ferroelectric field-effect doping in complex-oxide heterostructures,"Ferroelectric field-effect doping has emerged as a powerful approach to
manipulate the ground state of correlated oxides, opening the door to a new
class of field-effect devices. However, this potential is not fully exploited
so far, since the size of the field-effect doping is generally much smaller
than expected. Here we study the limiting factors through magneto-transport,
scanning transmission electron and piezo-response force microscopy in
ferroelectric/superconductor (YBa2Cu3O7-{\delta} /BiFeO3) heterostructures, a
model system showing very strong field-effects. Still, we find that they are
limited in the first place by an incomplete ferroelectric switching. This can
be explained by the existence of a preferential polarization direction set by
the atomic terminations at the interface. More importantly, we also find that
the field-effect carrier doping is accompanied by a strong modulation of the
carrier mobility. Besides making quantification of field-effects via Hall
measurements not straightforward, this finding suggests that ferroelectric
poling produces structural changes (e.g. charged defects or structural
distortions) in the correlated oxide channel. Those findings have important
consequences for the understanding of ferroelectric field-effects and for the
strategies to further enhance them.",1908.07365v1
2019-08-22,Photoexcited Small Polaron Formation in Goethite (α-FeOOH) Nanorods Probed by Transient Extreme Ultraviolet Spectroscopy,"Small polaron formation limits the mobility and lifetimes of photoexcited
carriers in metal oxides. As the ligand field strength increases, the carrier
mobility decreases, but the effect on the photoexcited small polaron formation
is still unknown. Extreme ultraviolet transient absorption spectroscopy is
employed to measure small polaron formation rates and probabilities in goethite
({\alpha}-FeOOH) crystalline nanorods at pump photon energies from 2.2 to 3.1
eV. The measured polaron formation time increases with excitation photon energy
from 70 {\pm} 10 fs at 2.2 eV to 350 {\pm} 30 fs at 2.6 eV, whereas the polaron
formation probability (85 {\pm} 10%) remains constant. By comparison to
hematite ({\alpha}-Fe2O3), an oxide analog, the role of ligand composition and
metal center density in small polaron formation time is discussed. This work
suggests that incorporating small changes in ligands and crystal structure
could enable the control of photoexcited small polaron formation in metal
oxides.",1908.08591v1
2019-08-23,On the emergence of conductivity at SrTiO3-based oxide interfaces -- an in-situ study,"Heterostructures and crystal interfaces play a major role in state-of-the-art
semiconductor devices and play a central role in the field of oxide
electronics. In oxides the link between the microscopic properties of the
interfaces and bulk properties of the resulting heterostructures challenge our
fundamental understanding. Insights on the early growth stage of interfaces and
its influence on resulting physical properties are scarce -- typically the
information is inferred from post growth characterization. Here, we report on
real time measurements of the transport properties of SrTiO3-based
heterostructures while the crystal heterostructure is forming. Surprisingly, we
detect a conducting interface already at the initial growth stage, much earlier
than the well-established critical thickness limit for observing conductivity
ex-situ after sample growth. We investigate how the conductivity depends on
various physical processes occurring during pulsed laser depositions, including
light illumination, particle bombardment by the plasma plume, interactions with
the atmosphere and oxygen migration from SrTiO3 to the thin films of varying
compositions. Using this approach, we propose a new design tool to control the
electrical properties of interfaces in real time during their formation.",1908.09011v1
2019-08-29,Gate-tunable Rashba spin-orbit coupling and spin polarization at diluted oxide interfaces,"Diluted oxide interface of LaAl1-xMnxO/SrTiO3 (LAMO/STO) provides a new way
of tuning the ground states of the interface between the two band insulators of
LAO and STO from metallic/superconducting to highly insulating. Increasing the
Mn doping level (x) leads to a delicate control of the carrier density as well
as a raise in the electron mobility and spin polarization. Herein, we
demonstrate a tunable Rashba spin-orbit coupling (SOC) and spin polarization of
LAMO/STO (0.2 <= x <= 0.3) by applying a back gate. The presence of SOC causes
the splitting of energy band into two branches by a spin splitting energy. The
maximum spin splitting energy depends on the Mn doping and decreases with the
increasing Mn content and then vanishes at x = 0.3. The carrier density
dependence of the spin splitting energy for different compositions shows a
dome-shaped behavior with a maximum at different normalized carrier density.
These findings have not yet been observed in LAO/STO interfaces. A fully
back-gate-tunable spin-polarized 2DEL is observed at the interface with x = 0.3
where only dxy orbits are populated (5.3E12 cm-2 <= ns <= 1.0E13 cm-2). The
present results shed light on unexplored territory in SOC at STO-base oxide
heterostructures and make LAMO/STO an intriguing platform for spin-related
phenomena in 3d-electron systems.",1908.11167v1
2019-11-08,Chloride-induced alterations of the passive film on 316L stainless steel and blocking effect of pre-passivation,"Electrochemical polarization measurements were combined with surface analysis
by Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-Ray
Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) to study the
alterations of the passive film on 316L austenitic stainless steel induced by
the presence of chlorides in sulfuric acid electrolyte. The work was performed
at a stage of initiation of localized corrosion preceding metastable pitting at
the micrometer scale as verified by current transient analysis and AFM. The
results show that Cl-ions enter the bilayer structure of the surface oxide
already formed in the native oxide-covered initial surface state at
concentrations below the detection limit of XPS (< 0.5 at%), mostly in the
hydroxide outer layer where Fe(III) and Mo(IV,VI) species are concentrated but
barely in the oxide inner layer enriched in Cr(III). Their main effect is to
produce a less resistive passive state by poisoning dehydroxylation and further
Cr(III) and Mo(IV,VI) enrichments obtained in the absence of chlorides. This
detrimental effect can be suppressed by pre-passivation in a Cl-free
electrolyte, which blocks the entry of chlorides in the passive film, including
in the outer exchange layer, and enables the beneficial aging-induced
variations of the composition to take place despite the presence of chlorides
in the environment.",1911.03244v1
2019-11-11,Mechanical properties of VMoNO as a function of oxygen concentration: toward development of hard and tough refractory oxynitrides,"Improved toughness is a central goal in the development of wear-resistant
refractory ceramic coatings. Extensive theoretical and experimental research
has revealed that NaCl structure VMoN alloys exhibit surprisingly high
ductility combined with high hardness and toughness. However, during operation,
protective coatings inevitably oxidize, a problem which may compromise material
properties and performance. Here, we explore the role of oxidation in altering
VMoN properties. Density functional theory and theoretical intrinsic hardness
models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx
solid solutions as a function of the oxygen concentration x. Elastic-constant
and intrinsic hardness calculations show that oxidation does not degrade the
mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate
that the presence of oxygen reduces the covalent bond character, which slightly
lowers the alloy strength and intrinsic hardness. Nevertheless, the character
of metallic d-d states, which are crucial for allowing plastic deformation and
enhancing toughness, remains unaffected. Overall, our results suggest that
VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high
intrinsic hardness, while still being ductile.",1911.04165v1
2019-11-13,A carbon-nanofiber glass composite with high electrical conductivity,"The use of oxide glasses is pervasive throughout everyday amenities and
commodities. Such glasses are typically electrical insulators, and endowing
them with electrical conductivity without changing their salutary mechanical
properties, weight, or thermoformability enables new applications in
multifunctional utensils, smart windows, and automotive parts. Previous
strategies to impart electrical conductivity include modifying the glass
composition or forming a solid-in-solid composite of the glass and a conductive
phase. Here we demonstrate using the latter strategy the highest reported
room-temperature electrical conductivity in a bulk oxide glass 1800 S/m
corresponding to the theoretical limit for the loading fraction of the
conductive phase. This is achieved through glass-sintering of a mixture of
carbon nanofibers and oxide flint F2 or soda lime glasses, with the bulk
conductivity further enhanced by a polyethylene-block-poly(ethylene glycol)
additive. A theoretical model provides predictions that are in excellent
agreement with the dependence of conductivity of these composites on the
carbon-loading fraction. Moreover, nanoscale electrical characterization of the
composite samples provides evidence for the existence of a connected network of
carbon nanofibers throughout the bulk. Our results establish a potentially
low-cost approach for producing large volumes of highly conductive glass
independently of the glass composition.",1911.05273v1
2019-11-20,High electrical conducting deep-ultraviolet-transparent oxide semiconductor La-doped SrSnO3 exceeding ~3000 S cm-1,"La-doped SrSnO3 (LSSO) is known as one of deep-ultraviolet (DUV)-transparent
conducting oxides with an energy bandgap of ~4.6 eV. Since LSSO can be grown
heteroepitaxially on more wide bandgap substrates such as MgO (Eg ~7.8 eV),
LSSO is considered to be a good candidate as a DUV-transparent electrode.
However, the electrical conductivity of LSSO films are below 1000 S cm^-1, most
likely due to the low solubility of La ion in the LSSO lattice. Here we report
that high electrically conducting (>3000 S cm^-1) LSSO thin films with an
energy bandgap of ~4.6 eV can be fabricated by pulsed laser deposition on MgO
substrate followed by a simple annealing in vacuum. From the X-ray diffraction
and the scanning transmission electron microscopy analyses, we found that
lateral grain growth occurred during the annealing, which improved the
activation rate of La ion, leading to a significant improvement of carrier
concentration (3.26 x 10^20 cm^-3) and Hall mobility (55.8 cm^2 V^-1 s^-1). The
present DUV-transparent oxide semiconductor would be useful as a transparent
electrode for developing optoelectronic devices, which transmit and/or emit
DUV-light.",1911.08818v1
2019-12-26,From High-Entropy Ceramics to Compositionally-Complex Ceramics: A Case Study of Fluorite Oxides,"Using fluorite oxides as an example, this study broadens high-entropy
ceramics (HECs) to compositionally-complex ceramics (CCCs) or multi-principal
cation ceramics (MPCCs) to include medium-entropy and/or non-equimolar
compositions. Nine compositions of compositionally-complex fluorite oxides
(CCFOs) with the general formula of (Hf1/3Zr1/3Ce1/3)1-x(Y1/2X1/2)xO2-delta (X
= Yb, Ca, and Gd; x = 0.4, 0.148, and 0.058) are fabricated. The phase
stability, mechanical properties, and thermal conductivities are measured.
Compared with yttria-stabilized zirconia, these CCFOs exhibit increased cubic
phase stability and reduced thermal conductivity, while retaining high Young's
modulus (~210 GPa) and nanohardness (~18 GPa). Moreover, the
temperature-dependent thermal conductivity in the non-equimolar CCFOs shows an
amorphous-like behavior. In comparison with their equimolar high-entropy
counterparts, the medium-entropy non-equimolar CCFOs exhibit even lower thermal
conductivity (k) while maintaining high modulus (E), thereby achieving higher
E/k ratios. These results suggest a new direction to achieve
thermally-insulative yet stiff CCCs (MPCCs) via exploring non-equimolar and/or
medium-entropy compositions.",1912.11742v2
2020-03-06,Direct evidence for low-energy electron emission following O LVV Auger transitions at oxide surfaces,"Oxygen, the third most abundant element in the universe, plays a key role in
the chemistry of condensed matter and biological systems. Here, we report
evidence for a hitherto unexplored Auger transition in oxides, where a valence
band electron fills a vacancy in the 2s state of oxygen, transferring
sufficient energy to allow electron emission. We used a beam of positrons with
kinetic energies of $\sim$1 eV to create O 2s holes via matter-antimatter
annihilation. This made possible the elimination of the large secondary
electron background that has precluded definitive measurements of the
low-energy electrons emitted through this process. Our experiments indicate
that low-energy electron emission following the Auger decay of O 2s holes from
adsorbed oxygen and oxide surfaces are very efficient. Specifically, our
results indicate that the low energy electron emission following the Auger
decay of O 2s hole is nearly as efficient as electron emission following the
relaxation of O 1s holes in TiO$_2$. This has important implications for the
understanding of Auger-stimulated ion desorption, Coulombic decay, photodynamic
cancer therapies, and may yield important insights into the radiation-induced
reactive sites for corrosion and catalysis.",2003.02975v2
2020-03-06,Dynamical Transitions of Supercooled Water in Graphene oxide Nanopores: Influence of Surface Hydrophobicity,"Molecular dynamics simulations are carried out to explore the dynamical
crossover phenomenon in strongly confined and mildly supercooled water in
graphene oxide nanopores. In contrast to studies where confinement is used to
study the properties of bulk water, we are interested in the dynamical
transitions for strongly confined water in the absence of any bulk-like water.
The influence of the physicochemical nature of the graphene oxide surface on
the dynamical transitions is investigated by varying the extent of
hydrophobicity on the confining surfaces placed at an inter-surface separation
of 10 \AA\,. All dynamical quantities show a typical slowing down as the
temperature is lowered from 298 to 200 K; however, the nature of the transition
is a distinct function of the surface type. Water confined between surfaces
consisting of alternating hydrophilic and hydrophobic regions exhibit a
strong-to-strong dynamical transition in the diffusion coefficients and
rotational relaxation times at a crossover temperature of 237 K and show a
fragile-to-strong transition in the $\alpha$-relaxation time at 238 K. The
observed crossover temperature is much higher than the freezing point of the
SPC/E water model used in this study, indicating that these dynamical
transitions can occur with mild supercooling under strong confinement in the
absence of bulk-like water. In contrast, water confined in hydrophilic pore
shows a single Arrhenius energy barrier over the entire temperature range. Our
results indicate that in addition to confinement, the nature of the surface can
play a critical role in determining the dynamical transitions for water upon
supercooling.",2003.03163v1
2020-03-11,The pseudoatomic orbital basis: electronic accuracy and soft-mode distortions in ABO$_3$ perovskites,"The perovskite oxides are known to be susceptible to structural distortions
over a long wavelength when compared to their parent cubic structures. From an
ab initio simulation perspective, this requires accurate calculations including
many thousands of atoms; a task well beyond the remit of traditional plane
wave-based density functional theory (DFT). We suggest that this void can be
filled using the methodology implemented in the large-scale DFT code, CONQUEST,
using a local pseudoatomic orbital (PAO) basis. Whilst this basis has been
tested before for some structural and energetic properties, none have treated
the most fundamental quantity to the theory, the charge density $n(\mathbf{r})$
itself. An accurate description of $n(\mathbf{r})$ is vital to the perovskite
oxides due to the crucial role played by short-range restoring forces
(characterised by bond covalency) and long range coulomb forces as suggested by
the soft-mode theory of Cochran and Anderson. We find that modestly sized basis
sets of PAOs can reproduce the plane-wave charge density to a total integrated
error of better than 0.5% and provide Bader partitioned ionic charges, volumes
and average charge densities to similar degree of accuracy. Further, the
multi-mode antiferroelectric distortion of PbZrO$_3$ and its associated
energetics are reproduced by better than 99% when compared to plane-waves. This
work suggests that electronic structure calculations using efficient and
compact basis sets of pseudoatomic orbitals can achieve the same accuracy as
high cutoff energy plane-wave calculations. When paired with the CONQUEST code,
calculations with high electronic and structural accuracy can now be performed
on many thousands of atoms, even on systems as delicate as the perovskite
oxides.",2003.05327v1
2020-03-31,Electrochromism in Electrolyte-Free and Solution Processed Bragg Stacks,"Achieving an active manipulation of colours has huge implications in
optoelectronics, as colours engineering can be exploited in a number of
applications, ranging from display to lightning. In the last decade, the
synergy of the highly pure colours of 1D photonic crystals, also known as Bragg
stacks, with electro-tunable materials have been proposed as an interesting
route to attain such a technologically relevant effect. However, recent works
rely on the use of liquid electrolytes, which can pose issues in terms of
chemical and environmental stability. Here, we report on the proof-of-concept
of an electrolyte free and solution-processed electrochromic Bragg stack. We
integrate an electro-responsive plasmonic metal oxide, namely indium tin oxide,
in a 1D photonic crystal structure made of alternating layers of ITO and TiO2
nanoparticles. In such a device we observed 15 nm blue-shift upon application
of an external bias (5 V), an effect that we attribute to the increase of ITO
charge density arising from the capacitive charging at the metal
oxide/dielectric interface and from the current flowing throughout the porous
structure. Our data suggest that electrochromism can be attained in all-solid
state systems by combining a judicious selection of the constituent materials
with device architecture optimisation.",2003.14050v1
2020-05-18,Inversion-symmetry engineering in sub-unit-cell-layered oxide thin films,"Inversion symmetry breaking is a ubiquitous concept in condensed-matter
science. On the one hand, it is a prerequisite for many technologically
relevant effects such as piezoelectricity, photovoltaic and nonlinear optical
properties and spin-transport phenomena. On the other hand, it may determine
abstract properties such as the electronic topology in quantum materials.
Therefore, the creation of materials where inversion symmetry can be turned on
or off by design may be the ultimate route towards controlling parity-related
phenomena and functionalities. Here, we engineer the symmetry of ultrathin
epitaxial oxide films by sub-unit-cell growth control. We reversibly activate
and deactivate inversion symmetry in the layered hexagonal manganites,
h-RMnO$_3$ with R = Y, Er, Tb. While an odd number of half-unit-cell layers
exhibits a breaking of inversion symmetry through its arrangement of MnO$_5$
bipyramids, an even number of such half-unit-cell layers takes on a
centrosymmetric structure. Here we control the resulting symmetry by tracking
the growth in situ via optical second-harmonic generation. We furthermore
demonstrate that our symmetry engineering works independent of the choice of R
and even in heterostructures mixing constituents with different R in a
two-dimensional growth mode. Symmetry engineering on the atomic level thus
suggests a new platform for the controlled activation and deactivation of
symmetry-governed functionalities in oxide-electronic epitaxial thin films.",2005.09083v1
2020-06-03,The oxygen partial pressure in solid oxide electrolysis cells with two layer electrolytes,"A number of degradation mechanisms have been observed during the long-term
operation of solid oxide electrolysis cells (SOEC). Using an electrolyte charge
carrier transport model, we quantify the oxygen potentials across the
electrolyte and thereby provide insights into these degradation mechanisms. Our
model describes the transport of charge carriers in the electrolyte when the
oxygen partial pressure is extremely low by accounting for the spatial
variation of the concentration of oxygen vacancies in the electrolyte.
Moreover, we identify four quantities that characterize the distribution of
oxygen partial pressure in the electrolyte, which are directly related to the
degradation mechanisms in the electrolyte as well: the two oxygen partial
pressures at the interfaces of the electrodes and the electrolyte, the oxygen
partial pressure at the interface of YSZ/GDC, and the position of the abrupt
change in oxygen potential near the p-n junction that develops in YSZ when one
side of the cell is exposed to fuel (low oxygen potential, n-type conduction)
and the other side is exposed to oxidant (high oxygen potential, p-type
conduction). We give analytical estimates for all of these quantities. These
analytical expressions provide guidance on the parameters that need to be
controlled to suppress the degradation observed in the electrolyte. In
addition, the effects of operating conditions, particularly current density and
operating temperature, on degradation are discussed.",2006.02523v1
2020-06-10,Chemical-Grafting of Graphene Oxide Quantum Dots for Enhanced Electrochemical Analysis of Aromatics,"Because of high surface area and combination of various functional groups,
graphene oxide (GO) is currently one of the most actively studying materials
for electroanalytical applications. Self-supported GO is not practical enough
to be utilized individually and thus is commonly integrated with different
supporting carriers. Having large lateral size GO can only wrap the particles
of the support and thus, can significantly reduce the surface area of porous
materials. To reach synergy form high surface area and polyfunctional nature of
GO, and a rigid structure of porous support, the lateral size of GO must be
essentially decreased. Recently reported graphene oxide quantum dots (GOQDs)
can fulfill this task. We report successful preparation of mesoporous silica
supported GOQDs exhibiting strong luminescent band with the maximum at 404 nm.
From N2 adsorption isotherms, it was demonstrated that the surface area of the
resulted hybrid material was augmented. Raman spectrum of SiO2-GOQDs shows two
distinct peaks at 1585 cm-1(G-peak) and 1372 cm-1 (D-peak) indicating presence
ordered basal plane of graphene with aromatic sp2 domains, and disordered
oxygen-containing structure. Covalent immobilization of GOQDs on aminosilica
via such oxygen-containing fragments was proved by FTIR, MAS 13C MNR, and XPS
spectroscopy. SiO2-GOQDs was used as a modifier of carbon paste electrode for
differential pulse voltammetry determination of four environmental:
sulfamethoxazole, trimethoprim, diethylstilbestrol (DES), and estriol (EST).
The modified electrodes demonstrated an essential decrease in LOD for EST
(220%) and DES (760%), which was explained by significant pi-pi stacking
interaction between GOQDs and aromatic system of the analytes.",2006.05634v1
2020-06-19,Earth and Mars -- distinct inner Solar System products,"Composition of terrestrial planets records planetary accretion, core-mantle
and crust-mantle differentiation, and surface processes. Here we compare the
compositional models of Earth and Mars to reveal their characteristics and
formation processes. Earth and Mars are equally enriched in refractory elements
(1.9 $\times$ CI), although Earth is more volatile-depleted and less oxidized
than Mars. Their chemical compositions were established by nebular
fractionation, with negligible contributions from post-accretionary losses of
moderately volatile elements. The degree of planetary volatile element
depletion might correlate with the abundances of chondrules in the accreted
materials, planetary size, and their accretion timescale, which provides
insights into composition and origin of Mercury, Venus, the Moon-forming giant
impactor, and the proto-Earth. During its formation before and after the
nebular disk's lifetime, the Earth likely accreted more chondrules and less
matrix-like materials than Mars and chondritic asteroids, establishing its
marked volatile depletion. A giant impact of an oxidized, differentiated
Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced
proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth's
mantle composition. Chalcophile and some siderophile elements in the silicate
Earth added by the Mars-like impactor were extracted into the core by a sulfide
melt. In contrast, the composition of Mars indicates its rapid accretion of
lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars'
rapid cooling and early loss of its dynamo likely led to the absence of plate
tectonics and surface water, and the present-day low surface heat flux. These
similarities and differences between the Earth and Mars made the former
habitable and the other inhospitable to uninhabitable.",2006.11051v2
2020-06-28,Effective Reduction of Oxygen Debris in Graphene Oxide,"Graphene oxide (GO) raised substantial interest in the last two decades
thanks to its unique properties beyond those of pristine graphene, including
electronic energy band-gap, hydrophilic behavior and numerous anchoring sites
required for functionalization. In addition, GO was found to be a cheap
mass-production source for the formation of the pristine graphene. However, the
presence of numerous clusters containing oxygen functional groups (called
debris) on the GO surface hinders the GO integration in electronic devices.
Here, we present a simple method aimed to reduce the density of oxygen debris
weakly bonded to the surface. The method consists of minimal treatments, like
sonication and/or water rinsing processes. Whereas this simple method removed
epoxy and hydroxyl oxygen groups weakly attached to the graphene matrix, the
double C=O bonds are almost not affected by the applied treatment, as
demonstrated by X-ray photoelectron spectroscopy and Fourier transform infrared
spectroscopy. Scanning tunneling microscopy and high-resolution transmission
electron microscopy measures designated non-uniform distribution of the
oxidation sites, appearing as clusters concentrated preferentially on GO
defected regions, albeit separated by pristine graphene areas. The results
should have an impact in the implementation of GO in electronic devices
deposited on different substrates.",2006.15668v2
2020-09-02,Understanding modes of negative differential resistance in amorphous and polycrystalline vanadium oxides,"Metal-oxide-metal devices based on amorphous VOx are shown to exhibit one of
two distinct negative differential resistance (NDR) characteristics depending
on the maximum current employed for electroforming. For low compliance currents
they exhibit a smooth S-type characteristic and have a temperature-dependent
device resistance characterised by an activation energy of 0.25 eV, consistent
with conduction in polycrystalline VO2, while for high-compliance currents they
exhibit an abrupt snap-back characteristic and a resistance characterised by an
activation energy of 0.025 eV, consistent with conduction in oxygen deficient
VOx. In both cases, the temperature dependence of the switching voltage implies
that the conductivity change is due to the insulator-metal transition in VO2.
From this analysis it is concluded that electroforming at low currents creates
a conductive filament comprised largely of polycrystalline VO2, while
electroforming at high currents creates a composite structure comprised of VO2
and a conductive halo of oxygen deficient VOx. The effect of electroforming on
the NDR mode is then explained with reference to a lumped element model of
filamentary conduction that includes the effect of a parallel resistance
created by the halo. These results provide new insight into the NDR response of
vanadium-oxide-based devices and a basis for designing devices with specific
characteristics.",2009.00810v1
2020-09-03,Doped graphene oxide functionalization strategy for synthesis of nanocomposite membranes: electrospun coatings in biomedical field application,"An electrospun membrane for vascular stent coating made of
2-methacryloyloxyethyl phosphorylcholine and butyl methacrylate copolymer
(MPC-co-BMA), also known as (PMB), reinforced with functionalized and nitrogen
doped reduced graphene oxide (f-NrGO) is presented. This membrane due to the
nitrogen doped reduced graphene oxide (NrGO) negative electric charge has the
capacity to repeal low density lipoproteins (LDL), which under specific
conditions are the main cause of atherosclerotic disease. The NrGO
functionalization process is detailed, as it creates strong bonds between NrGO
and PMB, avoiding NrGO sheets to detach from the membrane. The copolymer
synthesis was characterized by FTIR and chemical bonds between f-NrGO and PMB
were proved by XPS and HNMR. Additionally, a simplified test bank that
simulates blood flow conditions demonstrated the NrGO functionalization effect
over the membrane. For the electrospinning process, optimal parameters were a
voltage of 14.5 kV, and a flow rate of 0.3 mL/h, which lead to better
properties of the membrane for the application. DMA results confirmed that the
best reinforcement percentage of f-NrGO in terms of mechanical properties was
0.1 wt% and AFM images indicated the presence of the f-NrGO sheets over the
fibers. Finally, the contact angle revealed the repulsion response to LDL, such
behavior is promising to applications like cardiovascular coated stents.",2009.01820v1
2020-10-06,Conductance Model for Single-Crystalline/Compact Metal Oxide Gas Sensing Layers in the Non-Degenerate Limit: Example of Epitaxial SnO$_2$(101),"Semiconducting metal oxide (SMOX)-based gas sensors are indispensable for
safety and health applications, e.g. explosive, toxic gas alarms, controls for
intake into car cabins and monitor for industrial processes. In the past, the
sensor community has been studying polycrystalline materials as sensors where
the porous and random microstructure of the SMOX does not allow a separation of
the phenomena involved in the sensing process. This lead to conduction models
that can model and predict the behavior of the overall response, but they were
not capable of giving fundamental information regarding the basic mechanisms
taking place. The study of epitaxial layers is the definite prove to clarify
the different aspects and contributions of the sensing mechanisms that are not
possible to do by studying a polycrystalline sample. A detailed analytical
model for n and p-type single-crystalline/compact metal oxide gas sensors was
developed that directly relates the conductance of the sample with changes in
the surface electrostatic potential. Combined DC resistance and work function
measurements were used in a compact SnO2 (101) layer in operando conditions
that allowed us to check the validity of our model in the region where
Boltzmann approximation holds to determine surface and bulk properties of the
material.",2010.02962v1
2020-10-19,Nitric Oxide and other molecules: Molecular Modelling and Low FrequencyExploration using the Murchison Widefield Array,"We present new molecular modelling for 14NO and 15NO and a deep, blind
molecular line survey at low radio frequencies (99-129 MHz). This survey is the
third in a series completed with the Murchison Widefield Array (MWA), but in
comparison with the previous surveys, uses four times more data (17 hours vs. 4
hours) and is three times better in angular resolution (1' vs. 3'). The new
molecular modelling for nitric oxide and its main isotopologue has seven
transitions within the MWA frequency band (although we also present the higher
frequency transitions). Although we did not detect any new molecular lines at a
limit of 0.21 Jy beam^-1, this work is an important step in understanding the
data processing challenges for the future Square Kilometre Array (SKA) and
places solid limits on what is expected in the future of low-frequency surveys.
The modelling can be utilised for future searches of nitric oxide.",2010.09868v1
2020-10-28,"Single-Layer Di-titanium oxide Ti2O MOene: Multifunctional Promises for Electride, Anode Materials, and Superconductor","Using the first-principles calculations, we report the existence of the
single-layer (SL) di-titanium oxide Ti$_2$O (labeled as MOene) that constructs
a novel family of MXene based on transition metal oxides. This MOene material
strongly contrasts the conventional ones consisting of transition metal
carbides and/or nitrides. SL Ti$_2$O has high thermal and dynamical stabilities
due to the strong Ti$-$O ionic bonding interactions. Moreover, this material is
an intrinsic electride and exhibits extremely low diffusion barriers of
$\sim$12.0 and 6.3 meV for Li- and Na diffusion, respectively. When applied as
anode materials in lithium-ion batteries and sodium-ion batteries, it possesses
a high energy storage capacity (960.23 mAhg$^{-1}$), surpassing the traditional
MXenes-based anodes. The superb electrochemical performance stems from the
existed anionic electron on Ti$_2$O surface. Astonishingly, SL Ti$_{2}$O is
also determined to be a superconductor with a superconducting transition
temperature (\textit{T$_{c}$}) of $\sim$9.8 K, which originates from the
soft-mode of the first acoustic phonon branch and enhanced electron-phonon
coupling in the low-frequency region. Our finding broadens the family of MXenes
and would facilitate more experimental efforts toward future nanodevices.",2010.14879v1
2020-11-19,Marangoni Fingering Instabilities in Oxidizing Liquid Metals,"Eutectic gallium-indium (EGaIn), a room-temperature liquid metal alloy, has
the largest tension of any liquid at room temperature, and yet can nonetheless
undergo fingering instabilities. This effect arises because, under an applied
voltage, oxides deposit on the surface of the metal, which leads to a lowering
of the interfacial tension, allowing spreading under gravity. Understanding the
spreading dynamics of room temperature liquid metals is important for
developing soft electronics and understanding fluid dynamics of liquids with
extreme surface tensions. When the applied voltage or the oxidation rate
becomes too high, the EGaIn undergoes fingering instabilities, including
tip-splitting, which occur due to a Marangoni stress on the interface. Our
experiments are performed with EGaIn droplets placed in an electrolyte (sodium
hydroxide); by placing the EGaIn on copper electrodes, which EGaIn readily
wets, we are able to control the initial width of EGaIn fingers, setting the
initial conditions of the spreading. Two transitions are observed: (1) a
minimum current density at which all fingers become unstable to narrower
fingers; (2) a current density at which the wider fingers undergo a single
splitting event into two narrower fingers. We present a phase diagram as a
function of current density and initial finger width, and identify the minimum
width below which the single tip-splitting does not occur.",2011.10016v1
2020-11-23,Bottom Contact Metal Oxide Interface Modification Improving the Efficiency of Organic Light Emitting Diodes,"The performance of solution-processed organic light emitting diodes (OLEDs)
is often limited by non-uniform contacts. In this work, we introduce
Ni-containing solution-processed metal oxide (MO) interfacial layers inserted
between indium tin oxide (ITO) and
poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to improve
the bottom electrode contact for OLEDs using the poly(p-phenylene vinylene)
(PPV) derivative Super-Yellow (SY) as an emission layer. For ITO/Ni-containing
MO/PEDOT:PSS bottom electrode structures we show enhanced wetting properties
that result in an improved OLED device efficiency. Best performance is achieved
using a Cu-Li co-doped spinel nickel cobaltite [(Cu-Li):NiCo2O4], for which the
current efficiency and luminous efficacy of SY OLEDs increased, respectively,
by 12% and 11% from the values obtained for standard devices without a
Ni-containing MO interface modification between ITO and PEDOT:PSS. The enhanced
performance was attributed to the improved morphology of PEDOT:PSS, which
consequently increased the hole injection capability of the optimized
ITO/(Cu-Li):NiCo2O4/PEDOT:PSS electrode.",2011.11445v1
2021-02-04,Resolving the History of Life on Earth by Seeking Life As We Know It on Mars,"An origin of Earth life on Mars would resolve significant inconsistencies
between the inferred history of life and Earth's geologic history. Life as we
know it utilizes amino acids, nucleic acids, and lipids for the metabolic,
informational, and compartment-forming subsystems of a cell. Such building
blocks may have formed simultaneously from cyanosulfidic chemical precursors in
a planetary surface scenario involving ultraviolet light, wet-dry cycling, and
volcanism. However, early Earth was a water world, and the timing of the rise
of oxygen on Earth is inconsistent with final fixation of the genetic code in
response to oxidative stress. A cyanosulfidic origin of life could have taken
place on Mars via photoredox chemistry, facilitated by orders of magnitude more
sub-aerial crust than early Earth, and an earlier transition to oxidative
conditions. Meteoritic bombardment may have generated transient habitable
environments and ejected and transferred life to Earth. The Mars 2020
Perseverance Rover offers an unprecedented opportunity to confirm or refute
evidence consistent with a cyanosulfidic origin of life on Mars, search for
evidence of ancient life, and constrain the evolution of Mars' oxidation state
over time. We should seek to prove or refute a Martian origin for life on Earth
alongside other possibilities.",2102.02362v1
2021-02-04,Interfacial Tension Modulation of Liquid Metal via Electrochemical Oxidation,"This progress report summarizes recent studies of electrochemical oxidation
to modulate the interfacial tension of gallium-based alloys. These alloys,
which are liquid at ambient conditions, have the largest interfacial tension of
any liquid at room temperature. The ability to modulate the tension offers the
possibility to create forces that change the shape and position of the metal.
It has been known since the late 1800s that electrocapillarity-the use of
potential to modulate the electric double layer on the surface of metals in
electrolyte-lowers the interfacial tension of liquid metal. Yet, this
phenomenon can only achieve modest changes in interfacial tension since it is
limited to potential windows that avoid reactions. A recent discovery suggests
that reactions driven by the electrochemical oxidation of gallium alloys cause
the interfacial tension to decrease from ~500 mN/m at 0 V to ~0 mN/m at ~0.8 V,
a change in tension that goes well beyond what is possible via conventional
electrocapillarity or surfactants. The changes in tension are reversible;
reductive potentials return the metal back to a state of high interfacial
tension. This report aims to summarize key work and introduce beginners to this
field by including electrochemistry basics while addressing misconceptions. We
discuss applications that utilize modulations in interfacial tension of liquid
metal and conclude with remaining opportunities and challenges that need
further investigation.",2102.02383v1
2021-02-05,Metal/SrTiO$_3$ two-dimensional electron gases for spin-to-charge conversion,"SrTiO$_3$-based two-dimensional electron gases (2DEGs) can be formed through
the deposition of epitaxial oxides like LaAlO$_3$ or of reactive metals such as
Al. Such 2DEGs possess a finite Rashba spin-orbit coupling that has recently
been harnessed to interconvert charge and spin currents through the direct and
inverse Edelstein and spin Hall effects. Here we compare the formation and
properties of 2DEGs generated in SrTiO$_3$ by the growth of Al, Ta and Y
ultrathin films by magnetron sputtering. By combining in situ and ex situ X-ray
photoelectron spectroscopy (XPS) we gain insight into the reduction of the
SrTiO$_3$ and the appearance of Ti$^{3+}$ states associated with 2DEG
formation, its reoxidation by exposure to the air, and the transformation of
the metal into its binary oxides. We extract the carrier densities through
magnetotransport and compare them with the XPS data. Finally, working with
samples covered by an extra layer of NiFe, we perform spin-pumping
ferromagnetic resonance experiments and investigate spin-charge conversion as a
function of gate voltage. We identify trends in the data across the different
sample systems and discuss them as a function of the carrier density and the
transparency of the metal oxide tunnel barrier.",2102.03093v1
2021-02-09,Direct Observation and Control of Surface Termination in Perovskite Oxide Heterostructures,"The interfacial behavior of quantum materials leads to emergent phenomena
such as two dimensional electron gases, quantum phase transitions, and
metastable functional phases. Probes for in situ and real time surface
sensitive characterization are critical for active monitoring and control of
epitaxial synthesis, and hence the atomic-scale engineering of heterostructures
and superlattices. Termination switching, especially as an interfacial process
in ternary complex oxides, has been studied using a variety of probes, often ex
situ; however, direct observation of this phenomena is lacking. To address this
need, we establish in situ and real time reflection high energy electron
diffraction and Auger electron spectroscopy for pulsed laser deposition, which
provide structural and compositional information of the surface during film
deposition. Using this unique capability, we show, for the first time, the
direct observation and control of surface termination in complex oxide
heterostructures of SrTiO3 and SrRuO3. Density-functional-theory calculations
capture the energetics and stability of the observed structures and elucidate
their electronic behavior. This demonstration opens up a novel approach to
monitor and control the composition of materials at the atomic scale to enable
next-generation heterostructures for control over emergent phenomena, as well
as electronics, photonics, and energy applications.",2102.05022v1
2021-02-20,Thermal lensing-induced soliton molecules in beta-phase Gallium Oxide,"In recent years, beta gallium oxide (beta-\ce{Ga2O3}) has become the most
investigated isomorph of gallium oxide polymorphs, due to the great potential
it represents for applications in optoelectronics and photonics for solar
technology, particularly in blind ultraviolet photodetector solar cells (SBUV)
designs. To optimize its use in these applications, and to identify possible
new features, knowledge of its fundamental properties is relevant. In this
respect, optical, thermal and electronic properties of beta-\ce{Ga2O3} have
been studied expriementally, providing evidence of a wide-band inorganic and
transparent semiconductor with a Kerr nonlinearity. Thermo-optical properties
of the material, probed in SBUV sensing experiments, have highlighted a sizable
heat diffusion characterized by a temperature gradient along the path of
optical beams, quadratic in beam position and promoting a refractive-index
change with temperature. The experimentally observed Kerr nonlinearity together
with the thermally induced birefringence, point unambiguously to a possible
formation of soliton molecules during propagation of high-intensity fields in
beta-\ce{Ga2O3}. To put this conjecture on a firm ground we propose a
theoretical analysis, based on the cubic nonlinear Schroedinger equation in 1+1
spatial dimension, in which thermal lensing creates an effective potential
quadratic in the coordinate of beam position. Using the non-isospectral
inverse-scattering transform method, the exact one-soliton solution to the
propagation equation is obtained. This solution features a bound state of
entangled pulses forming a soliton molecule, in which pulses are more or less
entangled depending on characteristic parameters of the system.",2102.10418v2
2021-02-23,Insight into the structure-property relation of UO2 nanoparticles,"Highly crystalline UO2 nanoparticles (NPs) with sizes of 2-3 nm were produced
by fast chemical deposition of uranium(IV) under reducing conditions at pH
8-11. The particles were then characterized by microscopic and spectroscopic
techniques including high-resolution transmission electron microscopy (HRTEM),
X-ray diffraction (XRD), high-energy resolution fluorescence detection (HERFD)
X-ray absorption spectroscopy at the U M4 edge and extended X-ray absorption
fine structure (EXAFS) spectroscopy at the U L3 edge. The results of this
investigation show that despite U(IV) being the dominant oxidation state of the
freshly prepared UO2 NPs, they oxidize to U4O9 with time and under the X-ray
beam, indicating the high reactivity of U(IV) under these conditions. Moreover,
it was found that the oxidation process of NPs is accompanied by their growth
in size to 6 nm. We highlight here the major differences and similarities of
the UO2 NPs properties with PuO2, ThO2 and CeO2 NPs.",2102.11643v1
2021-02-25,Metal-Oxide Sensor Array for Selective Gas Detection in Mixtures,"We present a monolithic, microfabricated, metal-oxide semiconductor (MOS)
sensor array in conjunction with a machine learning algorithm to determine
unique fingerprints of individual gases within homogenous mixtures. The array
comprises four different metal oxides, and is engineered for independent
temperature control and readout from each individual pixel in a multiplexed
fashion. The sensor pixels are designed on a very thin membrane to minimize
heat dissipation, thereby significantly lowering the overall power consumption
($<$30 $\mu$W average power). The high dimensional data obtained by running the
pixels at different temperatures, is used to train our machine learning
algorithm with an average accuracy $\sim$ 88$\%$ for high resolution detection
and estimation of concentration of individual constituents in a homogenous
mixture. While the response of MOS sensors to various gases has been
demonstrated, very few studies have investigated the response of these sensors
to homogeneous mixtures of gases comprising several gases. We demonstrate this
principle for a binary homogeneous mixture of ozone and carbon monoxide, both
of which are criteria pollutant gases. Our findings indicate that a
multiplicity of MOS elements together with the ability to vary and measure at
various temperatures are essential in predicting concentration of individual
gases within mixtures, thereby overcoming a key limitation of MOS sensors -
poor selectivity. The small form-factor and microfabrication approach of our
sensor array also lends itself to CMOS integration paving the way for a
platform for wearable and portable applications.",2102.12990v1
2021-02-26,Ion implantation in \b{eta}-Ga2O3: physics and technology,"Gallium oxide and in particular its thermodynamically stable \b{eta}-Ga2O3
phase is within the most exciting materials in research and technology nowadays
due to its unique properties, such as an ultra-wide band gap and a very high
breakdown electric field, finding a number of applications in electronics and
optoelectronics. Ion implantation is a traditional technological method used in
these fields, and its well-known advantages can contribute greatly to the rapid
development of physics and technology of Ga2O3-based materials and devices.
Here, the current status of ion beam implantation in \b{eta}-Ga2O3 is reviewed.
The main attention is paid to the results of experimental study of damage under
ion irradiation and the properties of Ga2O3 layers doped by ion implantation.
The results of ab initio theoretical calculations of the impurities and defects
parameters are briefly presented, and the physical principles of a number of
analytical methods used to study implanted gallium oxide layers are
highlighted. The use of ion implantation in the development of such Ga2O3-based
devices as metal oxide field effect transistors, Schottky barrier diodes, and
solar-blind UV detectors, is described together with systematical analysis of
the achieved values of their characteristics. Finally, the most important
challenges to be overcome in this field of science and technology are
discussed.",2102.13439v1
2021-02-28,Tuning the Reactivity of Nanoenergetic Gas Generators Based on Bismuth and Iodine oxidizers,"There is a growing interest on novel energetic materials called Nanoenergetic
Gas-Generators (NGGs) which are potential alternatives to traditional energetic
materials including pyrotechnics, propellants, primers and solid rocket fuels.
NGGs are formulations that utilize metal powders as a fuel and oxides or
hydroxides as oxidizers that can rapidly release large amount of heat and
gaseous products to generate shock waves. The heat and pressure discharge,
impact sensitivity, long term stability and other critical properties depend on
the particle size and shape, as well as assembling procedure and intermixing
degree between the components. The extremely high energy density and the
ability to tune the dynamic properties of the energetic system makes NGGs ideal
candidates to dilute or replace traditional energetic materials for emerging
applications. In terms of energy density, performance and controllability of
dynamic properties, the energetic materials based on bismuth and iodine
compounds are exceptional among the NGGs. The thermodynamic calculations and
experimental study confirm that NGGs based on iodine and bismuth compounds
mixed with aluminum nanoparticles are the most powerful formulations to date
and can be used potentially in microthrusters technology with high
thrust-to-weight ratio with controlled combustion and exhaust velocity for
space applications. The resulting nano thermites generated significant value of
pressure discharge up to 14.8 kPa m3/g. They can also be integrated with carbon
nanotubes to form laminar composite yarns with high power actuation of up to
4700 W/kg, or be used in other emerging applications such as biocidal agents to
effectively destroy harmful bacteria in seconds, with 22 mg/m2 minimal content
over infected area.",2103.00614v1
2021-03-03,Dimensional Control of Octahedral Tilt in SrRuO3 via Infinite-layered Oxides,"Manipulation of octahedral distortion at atomic length scale is an effective
means to tune the physical ground states of functional oxides. Previous work
demonstrates that epitaxial strain and film thickness are variable parameters
to modify the octahedral rotation and tilt. However, selective control of
bonding geometry by structural propagation from adjacent layers is rarely
studied. Here we propose a new route to tune the ferromagnetic response in
SrRuO3 (SRO) ultrathin layers by oxygen coordination of adjacent SrCuO2 (SCO)
layers. The infinite-layered CuO2 in SCO exhibits a structural transformation
from ""planar-type"" to ""chain-type"" as reducing film thickness. These two
orientations dramatically modify the polyhedral connectivity at the interface,
thus altering the octahedral distortion of SRO. The local structural variation
changes the spin state of Ru and hybridization strength between Ru 4d and O 2p
orbitals, leading to a significant change in the magnetoresistance and
anomalous Hall resistivity of SRO layers. These findings could launch further
investigations into adaptive control of magnetoelectric properties in quantum
oxide heterostructures using oxygen coordination.",2103.02101v1
2021-04-01,Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost,"Rich functionalities of transition-metal oxides and their interfaces bear an
enormous technological potential. Its realization in practical devices
requires, however, a significant improvement of yet relatively low electron
mobility in oxide materials. Recently, a mobility boost of about two orders of
magnitude has been demonstrated at the spinel/perovskite {\gamma}-Al2O3/SrTiO3
interface compared to the paradigm perovskite/perovskite LaAlO3/SrTiO3. We
explore the fundamental physics behind this phenomenon from direct measurements
of the momentum-resolved electronic structure of this interface using resonant
soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering
of the mobile electrons in {\gamma}-Al2O3/SrTiO3 which depopulates electron
states in the top STO layer. This rearrangement of the mobile electron system
pushes the electron density away from the interface that reduces its overlap
with the interfacial defects and weakens the electron-phonon interaction, both
effects contributing to the mobility boost. A crystal-field analysis shows that
the band order alters owing to the symmetry breaking between the spinel
{\gamma}-Al2O3 and perovskite SrTiO3. The band-order engineering exploiting the
fundamental symmetry properties emerges as another route to boost the
performance of oxide devices.",2104.00498v1
2021-05-20,Competition of superconductivity and charge density wave in selective oxidized CsV3Sb5 thin flakes,"The recently discovered layered kagome metals AV$_3$Sb$_5$ (A = K, Rb, and
Cs) with vanadium kagome networks provide a novel platform to explore
correlated quantum states intertwined with topological band structures. Here we
report the prominent effect of hole doping on both superconductivity and charge
density wave (CDW) order, achieved by selective oxidation of exfoliated thin
flakes. A superconducting dome is revealed as a function of the effective
doping content. The superconducting transition temperature ($T_{\mathrm{c}}$)
and upper critical field in thin flakes are significantly enhanced compared
with the bulk, which is accompanied by the suppression of CDW. Our detailed
analyses establish the pivotal role of van Hove singularities (VHSs) in
promoting correlated quantum orders in these kagome metals. Our experiment not
only demonstrates the intriguing nature of superconducting and CDW orders, but
also provides a novel route to tune the carrier concentration through both
selective oxidation and electric gating. This establishes AV$_3$Sb$_5$ as a
tunable 2D platform for the further exploration of topology and correlation
among 3$d$ electrons in kagome lattices.",2105.09898v4
2021-05-27,Route to High-Performance Micro-solid Oxide Fuel Cells on Metallic Substrates,"Micro-solid oxide fuel cells based on thin films have strong potential for
use in portable power devices. However, devices based on silicon substrates
typically involve thin-film metallic electrodes which are unstable at high
temperatures. Devices based on bulk metal substrates overcome these
limitations, though performance is hindered by the challenge of growing
state-of-the-art epitaxial materials on metals. Here, we demonstrate for the
first time the growth of epitaxial cathode materials on metal substrates
(stainless steel) commercially supplied with epitaxial electrolyte layers (1.5
{um (Y2O3)0.15(ZrO2)0.85 (YSZ) + 50 nm CeO2). We create epitaxial mesoporous
cathodes of (La0.60Sr0.40)0.95Co0.20Fe0.80O3 (LSCF) on the substrate by growing
LSCF/MgO vertically aligned nanocomposite films by pulsed laser deposition,
followed by selectively etching out the MgO. To enable valid comparison with
the literature, the cathodes are also grown on single-crystal substrates,
confirming state-of-the-art performance with an area specific resistance of
100ohmegacm2 at 500dC and activation energy down to 0.97 eV. The work marks an
important step toward the commercialization of high-performance micro-solid
oxide fuel cells for portable power applications.",2105.13117v1
2021-08-10,The Ionization Energies of Dust-Forming Metal Oxide Clusters,"Stellar dust grains are predominantly composed of mineralic, anorganic
material forming in the circumstellar envelopes of oxygen-rich AGB stars.
However, the initial stage of the dust synthesis, or its nucleation, is not
well understood. In particular, the chemical nature of the nucleating species,
represented by molecular clusters, is uncertain. We investigated the vertical
and adiabatic ionization energies of four different metal-oxide clusters by
means of density functional theory. They included clusters of magnesia
(MgO)$_n$, silicon monoxide (SiO)$_n$, alumina (Al$_2$O$_3$)$_n$, and titania
(TiO$_2$)$_n$ with stoichiometric sizes of $n$=1$-$8. The magnesia, alumina,
and titania clusters showed relatively little variation in their ionization
energies with respect to the cluster size n: 7.1$-$8.2 eV for (MgO)$_n$,
8.9$-$10.0 eV for (Al$_2$O$_3$)$_n$, and 9.3$-$10.5 eV for (TiO$_2$)$_n$. In
contrast, the (SiO)$_n$ ionization energies decrease with size $n$, starting
from 11.5 eV for $n$=1, and decreasing to 6.6 eV for $n$=8. Therefore, we set
constraints on the stability limit for neutral metal-oxide clusters to persist
ionization through radiation or high temperatures and for the nucleation to
proceed via neutral-neutral reactions.",2108.04618v1
2021-08-19,Electrochromism of Ni-deficient nickel oxide -- Theoretical justification,"The development of new electrochromic materials and devices, like smart
windows, has an enormous impact on the energy efficiency of modern society. One
of the crucial materials in this technology is nickel-oxide. Ni-deficient NiO
shows anodic electrochromism whose mechanism is still under debate. Using DFT+U
calculations, we show that Ni vacancy generation results in the formation of
hole polarons localised at the two oxygens next to the vacancy. Upon Li
insertion or injection of an extra electron into Ni-deficient NiO, one hole
gets filled, and the hole bipolaron is converted into a hole polaron
well-localized at one O atom. Furthermore, the calculated absorption
coefficients demonstrate that Li insertion/extraction or rather the
addition/removal of an extra electron into Ni-deficient NiO can lead to
switching between the oxidized (colored) and the reduced (bleached) states.
Hence, our results suggest a new mechanism of Ni-deficient NiO electrochromism
not related to the Ni2+/Ni3+ transition but based on the formation and
annihilation of hole polarons in oxygen p-states.",2108.08578v1
2021-08-25,Synthesis of a High-Capacity α-Fe2O3@C Conversion Anode and a High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode and Their Combination in a Li-Ion Battery,"A Li-conversion alpha-Fe2O3@C nanocomposite anode and a high-voltage
LiNi0.5Mn1.5O4 cathode are synthesized in parallel, characterized, and combined
in a Li-ion battery. alpha-Fe2O3@C is prepared via annealing of maghemite iron
oxide and sucrose under an argon atmosphere and subsequent oxidation in air.
The nanocomposite exhibits a satisfactory electrochemical response in a lithium
half-cell, delivering almost 900 mA h g-1, as well as a significantly longer
cycle life and higher rate capability compared to the bare iron oxide
precursor. The LiNi0.5Mn1.5O4 cathode, achieved using a modified
co-precipitation approach, reveals a well-defined spinel structure without
impurities, a sub-micrometrical morphology, and a reversible capacity of ca.
120 mA h g-1 in a lithium half-cell with an operating voltage of 4.8 V. Hence,
a lithium-ion battery is assembled by coupling the alpha-Fe2O3@C anode with the
LiNi0.5Mn1.5O4 cathode. This cell operates at about 3.2 V, delivering a stable
capacity of 110 mA h g-1 (referred to the cathode mass) with a Coulombic
efficiency exceeding 97%. Therefore, this cell is suggested as a promising
energy storage system with expected low economic and environmental impacts.",2108.11314v1
2021-09-09,Self-sealing complex oxide resonators,"Although 2D materials hold great potential for next-generation pressure
sensors, recent studies revealed that gases permeate along the membrane-surface
interface that is only weakly bound by van der Waals interactions,
necessitating additional sealing procedures. In this work, we demonstrate the
use of free-standing complex oxides as self-sealing membranes that allow the
reference cavity of pressure sensors to be sealed by a simple anneal. To test
the hermeticity, we study the gas permeation time constants in nano-mechanical
resonators made from SrRuO3 and SrTiO3 membranes suspended over SiO2/Si
cavities which show an improvement up to 4 orders of magnitude in the
permeation time constant after annealing the devices for 15 minutes. Similar
devices fabricated on Si3N4/Si do not show such improvements, suggesting that
the adhesion increase over SiO2 is mediated by oxygen bonds that are formed at
the SiO2/complex oxide interface during the self-sealing anneal. We confirm the
enhancement of adhesion by picosecond ultrasonics measurements which show an
increase in the interfacial stiffness by 70% after annealing. Since it is
straigthforward to apply, the presented self-sealing method is thus a promising
route toward realizing ultrathin hermetic pressure sensors.",2109.03978v1
2021-09-28,Insights into lithium manganese oxide-water interfaces using machine learning potentials,"Unraveling the atomistic and the electronic structure of solid-liquid
interfaces is the key to the design of new materials for many important
applications, from heterogeneous catalysis to battery technology. Density
functional theory (DFT) calculations can in principle provide a reliable
description of such interfaces, but the high computational costs severely
restrict the accessible time and length scales. Here, we report machine
learning-driven simulations of various interfaces between water and lithium
manganese oxide (Li$_x$Mn$_2$O$_4$), an important electrode material in lithium
ion batteries and a catalyst for the oxygen evolution reaction. We employ a
high-dimensional neural network potential (HDNNP) to compute the energies and
forces several orders of magnitude faster than DFT without loss in accuracy. In
addition, a high-dimensional neural network for spin prediction (HDNNS) is
utilized to analyze the electronic structure of the manganese ions. Combining
these methods, a series of interfaces is investigated by large-scale molecular
dynamics. The simulations allow us to gain insights into a variety of
properties like the dissociation of water molecules, proton transfer processes,
and hydrogen bonds, as well as the geometric and electronic structure of the
solid surfaces including the manganese oxidation state distribution,
Jahn-Teller distortions, and electron hopping.",2109.14068v2
2021-10-05,Oxide two-dimensional electron gas with high mobility at room-temperature,"The prospect of 2-dimensional electron gases (2DEGs) possessing high mobility
at room temperature in wide-bandgap perovskite stannates is enticing for oxide
electronics, particularly to realize transparent and high-electron mobility
transistors. Nonetheless only a small number of studies to date report 2DEGs in
BaSnO3-based heterostructures. Here, we report 2DEG formation at the
LaScO3/BaSnO3 (LSO/BSO) interface with a room-temperature mobility of 60 cm2/V
s at a carrier concentration of 1.7x1013 cm-2. This is an order of magnitude
higher mobility at room temperature than achieved in SrTiO3-based 2DEGs. We
achieved this by combining a thick BSO buffer layer with an ex-situ
high-temperature treatment, which not only reduces the dislocation density but
also produces a SnO2-terminated atomically flat surface, followed by the growth
of an overlying BSO/LSO interface. Using weak-beam dark field imaging and
in-line electron holography technique, we reveal a reduction of the threading
dislocation density, and provide direct evidence for the spatial confinement of
a 2DEG at the BSO/LSO interface. Our work opens a new pathway to explore the
exciting physics of stannate-based 2DEGs at application-relevant temperatures
for oxide nanoelectronics.",2110.02305v1
2021-10-28,Surface Stability of SrNbO$_{3+δ}$ Grown by Hybrid Molecular Beam Epitaxy,"4d transition metal oxides have emerged as promising materials for numerous
applications including high mobility electronics. SrNbO$_{3}$ is one such
candidate material, serving as a good donor material in interfacial oxide
systems and exhibiting high electron mobility in ultrathin films. However, its
synthesis is challenging due to the metastable nature of the d$^{1}$ Nb$^{4+}$
cation and the limitations in the delivery of refractory Nb. To date, films
have been grown primarily by pulsed laser deposition (PLD), but development of
a means to grow and stabilize the material via molecular beam epitaxy (MBE)
would enable studies of interfacial phenomena and multilayer structures that
may be challenging by PLD. To that end, SrNbO$_{3}$ thin films were grown using
hybrid MBE for the first time using a tris(diethalamido)(tert-butylimido)
niobium precursor for Nb and an elemental Sr source on GdScO$_{3}$ substrates.
Varying thicknesses of insulating SrHfO$_{3}$ capping layers were deposited
using a hafnium tert-butoxide precursor for Hf on top of SrNbO$_{3}$ films to
preserve the metastable surface. Grown films were transferred in vacuo for
X-ray photoelectron spectroscopy to quantify elemental composition, density of
states at the Fermi energy, and Nb oxidation state. Ex situ studies by X-ray
absorption near edge spectra illustrates the SrHfO$_{3}$ capping plays an
important role in preserving the Nb 4d$^{1}$ metastable charge state in
atmospheric conditions.",2110.15341v1
2021-11-06,Where have all the interstellar silicon carbides gone?,"The detection of the 11.3-micron emission feature characteristic of the Si--C
stretch in carbon-rich evolved stars reveals that silicon carbide (SiC) dust
grains are condensed in the outflows of carbon stars. SiC dust could be a
significant constituent of interstellar dust since it is generally believed
that carbon stars inject a considerable amount of dust into the interstellar
medium (ISM). The presence of SiC dust in the ISM is also supported by the
identification of presolar SiC grains of stellar origin in primitive
meteorites. However, the 11.3-micron absorption feature of SiC has never been
seen in the ISM and oxidative destruction of SiC is often invoked. In this work
we quantitatively explore the destruction of interstellar SiC dust through
oxidation based on molecular dynamics simulations and density functional theory
calculations. We find that the reaction of an oxygen atom with SiC molecules
and clusters is exothermic and could cause CO-loss. Nevertheless, even if this
is extrapolable to bulk SiC dust, the destruction rate of SiC dust through
oxidation could still be considerably smaller than the (currently believed)
injection rate from carbon stars. Therefore, the lack of the 11.3-micron
absorption feature of SiC dust in the ISM remains a mystery. A possible
solution may lie in the currently believed stellar injection rate of SiC (which
may have been overestimated) and/or the size of SiC dust (which may actually be
considerably smaller than submicron in size).",2111.03920v1
2021-11-07,"Low-loss tunable infrared plasmons in the high-mobility perovskite (Ba,La)SnO$_3$","BaSnO$_3$ exhibits the highest carrier mobility among perovskite oxides,
making it ideal for oxide electronics. Collective charge carrier oscillations,
plasmons, are expected to arise in this material, thus providing a tool to
control the nanoscale optical field for optoelectronics applications. Here, we
demonstrate the existence of relatively long-lived plasmons supported by
high-mobility charge carriers in La-doped BaSnO$_3$ (BLSO). By exploiting the
high spatial and energy resolution of electron energy-loss spectroscopy with a
focused beam in a scanning transmission electron microscope, we systematically
investigate the dispersion, confinement ratio, and damping of infrared
localized surface plasmons (LSP) in BLSO nanoparticles. We find that the LSPs
in BLSO are highly spatially confined compared to those sustained by noble
metals and have relatively low loss and high quality factor compared to other
doped oxides. Further analysis clarifies the relation between plasmon damping
and carrier mobility in BLSO. Our results support the use of nanostructured
degenerate semiconductors for plasmonic applications in the infrared region and
establish a relevant alternative to more traditional plasmonic materials.",2111.04144v1
2021-11-28,Investigations on the improved cycling stability of Kazakhstanite phase Fe-V-O layered oxide by using superconcentrated electrolytes: Generalized solubility limit approach (Part I),"In this article, we address the issue of vanadium dissolution pertinent in
the layered Fe5V15O39(OH)9.9H2O using the solubility limit approach. This
layered oxide is prepared via a low-cost solution phase synthesis route and
crystallizes in the Kazakhstanite phase (Space Group: C2/m), confirmed using
selected area electron diffraction and x-ray diffraction.The layered oxide
exhibits the 2 electron redox reaction of vanadium (V5+ to V3+) along with the
1 electron redox reaction of iron within the voltage window of 1.5-3.8V. This
results in a high specific capacity of ~350mAhg-1 which can be extracted from
this material. However, the transition from V4+ to V3+ is identified to
initiate a dissolution process at ~2.5V, resulting in a loss of active material
and poor cycling stability. The vanadium dissolution is found to be arrested by
switching to a superconcentrated electrolyte, wherein the amount of 'free'
solvent is low. An electrolyte, consisting of seven molar lithium
bis(trifluoromethanesulfonyl)imide in 1,3-Dioxolane: 1,2-Dimethoxyethane = 1:1
(v:v), is found to be suitable in providing the best cycling stability amongst
the other compositions tested. The electrochemical characteristics of the
passivation layers formed over lithium foil are mathematically modeled to
indicate the preference of superconcentrated electrolytes over relatively
dilute ones.",2111.14198v1
2021-11-15,Resistive-nanoindentation on gold: Experiments and modeling of the electrical contact resistance,"This paper reports the experimental, analytical, and numerical study of
resistive-nanoindentation tests performed on gold samples (bulk and thin film).
First, the relevant contributions to electrical contact resistance are
discussed and analytically described. A brief comparison of tests performed on
gold and on natively oxidized metals highlights the high reproducibility and
the voltage-independence of experiments on gold(thanks to its oxide-free
surface). Then, the evolution of contact resistance during nanoindentation is
fully explained in terms of electronic transport regimes: starting from
tunneling, electronic transport is then driven by ballistic conduction before
ending with pure diffusive conduction. The corresponding analytical
expressions, as well as their validity domains, are determined and compared
with experimental data,showing excellent agreement. From there, focus is made
on the diffusive regime. Resistive-nanoindentation outputs are fully described
by analytical and finite-element modeling. The developed numerical framework
allows a better understanding of the main parameters: it first assesses the
technique capabilities (validity domains, sensitivity to tip defect,
sensitivity to rheology, effect of an oxide layer, and so on), butit also
validates the different assumptions made on current line distribution. Finally,
it is shown that a simple calibration procedure allows a well-resolved
monitoring of the contact area during resistive-nanoindentation performed on
samples with complex rheologies (ductile thin film on an elastic substrate).
Comparison to analytical and numerical approaches highlights the strength of
resistive-nanoindentation for continuous area monitoring.",2111.15474v1
2021-12-07,Air filtration from sarin/air mixture by porous graphene-oxide membranes: a molecular dynamics study,"Sarin is a very lethal synthetic organophosphorated compound that inhibits
the nervous system muscle control. Although not used as a chemical weapon
anymore, it still worries the authorities regarding possible use by terrorists.
Most of the studies about sarin are theoretical/computational due to its high
lethality and are concentrated in its detection and degradation. Few studies
are about air filtration from sarin gas. Here, the potential of graphene
oxide-based membranes to filter air from sarin/air mixtures is investigated by
classical molecular dynamics simulations. Membranes formed by one and two
nanosheets of porous reduced graphene oxide (rGO) were considered. The passage
of sarin and air molecules through these membranes from a highly concentrated
region to an empty one, is evaluated as a function of temperature and sarin/air
relative concentration. Sarin molecules are shown to be trapped by hydroxyl and
carboxyl chemical groups in the nanosheet, while a considerable passage of air
molecules (N$_2$, O$_2$ and Ar) through the membranes was verified. The results
show the capacity of the rGO membranes to retain sarin from passing through,
even at high temperatures, thus indicating their potential to be used as a
filter for sarin gas.",2112.03830v2
2021-12-09,AlCrO protected textured stainless steel surface for high temperature solar selective absorber applications,"The diffusion of substrate material into absorbing layer and oxidation of
metal substrate or cermet metal nanoparticles at high temperatures are known as
inevitable problems of the solar selective absorbers. In this study, we
consider the use of textured stainless steel (SS) surface coated with a
protective AlCr oxide layer as a high temperature solar selective absorber. The
textured SS surface was prepared by ion etching techniques and AlCr oxide
protective layer was deposited by RF magnetron sputtering. The absorptivity and
emissivity of the as-prepared absorbers were 0.86-0.92 and 0.151-0.168,
respectively. In order to evaluate the thermal stability, the absorbers were
annealed at 600-800 C for different time in ambient atmosphere. Absorbers
demonstrated a red shift of the onset of the reflectivity at all annealing
temperatures. The high activation energy of 315 kJ/mol was calculated. The
service lifetime of the absorbers at 500 C was estimated to be about 100 years
and at 700 and 800 C the absorbers were stable about 50 and 1 hours,
respectively. A detailed examination of the annealed absorber surface revealed
growth of surface Mn3O4 nanocrystals, which resulted in observed change of the
reflectance spectra, while the textured surface morphology had no significant
change. The results show that the protective textured surface has much higher
thermal stability in air than iron based cermet absorbers.",2112.04823v1
2021-12-09,Extending the kinetic and thermodynamic limits of molecular-beam epitaxy utilizing suboxide sources or metal-oxide catalyzed epitaxy,"We observe a catalytic mechanism during the growth of III-O and IV-O
materials by suboxide molecular-beam epitaxy ($S$-MBE). By supplying the
molecular catalysts In$_2$O and SnO we increase the growth rates of Ga$_2$O$_3$
and In$_2$O$_3$. This catalytic action is explained by a metastable adlayer
$A$, which increases the reaction probability of the reactants Ga$_2$O and
In$_2$O with active atomic oxygen, leading to an increase of the growth rates
of Ga$_2$O$_3$ and In$_2$O$_3$. We derive a model for the growth of binary
III-O and IV-O materials by $S$-MBE and apply these findings to a generalized
catalytic description for metal-oxide catalyzed epitaxy (MOCATAXY), applicable
to elemental and molecular catalysts. We derive a mathematical description of
$S$-MBE and MOCATAXY providing a computational framework to set growth
parameters in previously inaccessible kinetic and thermodynamic growth regimes
when using the aforementioned catalysis. Our results indicate MOCATAXY takes
place with a suboxide catalyst rather than with an elemental catalyst. As a
result of the growth regimes achieved, we demonstrate a Ga$_2$O$_3$/Al$_2$O$_3$
heterostructure with unrivaled crystalline quality, paving the way to the
preparation of oxide device structures with unprecedented perfection.",2112.05022v2
2021-12-15,Thermal analysis of metal organic precursors for functional Cu doped NiOx hole transporting layer in inverted perovskite solar cells the role of solution combustion chemistry in Cu doped NiOx thin films processing,"Low temperature solution combustion synthesis emerges as a facile method for
synthesis of functional metal oxides thin films for electronic applications. We
study the solution combustion synthesis process of Cu:NiOx using different
molar ratios (w/o, 0.1 and 1.5) of fuel acetylacetone (Acac) to oxidizer (Cu,
Ni Nitrates) as a function of thermal annealing tempera-tures 150, 200 and 300
oC. The solution combustion synthesis process, in both thin films and bulk
Cu:NiOx, is investigated. Thermal analysis studies using TGA and DTA reveal
that the Cu:NiOx thin films show a more gradual mass loss while the bulk
Cu:NiOx exhibits a distinct combustion process. The thin films can crystallize
to Cu:NiOx at annealing temperature of 300 oC irrespective to the Acac/Oxidizer
ratio whereas lower annealing temperatures (150 and 200 oC) produce amorphous
materials. A detail characterization study of solution combustion synthesized
Cu:NiOx including XPS, UV-Vis, AFM and Contact angle measurements is presented.
Finally, 50 nm Cu:NiOx thin films are introduced as HTLs within the inverted
perovskite solar cell device architecture. The Cu:NiOx HTL annealed at 150 and
200 oC provided PVSCs with limited functionality whereas efficient
triple-cation Cs0.04(MA0.17FA0.83)0.96 Pb(I0.83Br0.17)3 based PVSCs achieved
for Cu:NiOx HTLs annealed at temperature 300 oC.",2112.08067v1
2021-12-21,Room-Temperature Valence Transition in a Strain-Tuned Perovskite Oxide,"Cobalt oxides have long been understood to display intriguing phenomena known
as spin-state crossovers, where the cobalt ion spin changes vs. temperature,
pressure, etc. A very different situation was recently uncovered in
praseodymium-containing cobalt oxides, where a first-order coupled
spin-state/structural/metal-insulator transition occurs, driven by a remarkable
praseodymium valence transition. Such valence transitions, particularly when
triggering spin-state and metal-insulator transitions, offer highly appealing
functionality, but have thus far been confined to cryogenic temperatures in
bulk materials (e.g., 90 K in Pr1-xCaxCoO3). Here, we show that in thin films
of the complex perovskite (Pr1-yYy)1-xCaxCoO3-{\delta}, heteroepitaxial strain
tuning enables stabilization of valence-driven
spin-state/structural/metal-insulator transitions to at least 291 K, i.e.,
around room temperature. The technological implications of this result are
accompanied by fundamental prospects, as complete strain control of the
electronic ground state is demonstrated, from ferromagnetic metal under tension
to nonmagnetic insulator under compression, thereby exposing a potential novel
quantum critical point.",2112.10917v2
2022-01-28,Substitutional Doped GeSe: Tunable Oxidative States with Strain Engineering,"Layered chalcogenide materials have a wealth of nanoelectronics applications
like resistive switching and energy-harvesting such as photocatalyst owing to
rich electronic, orbital, and lattice excitations. In this work, we explore
monochalcogenide germanium selenide GeSe with respect to substitutional doping
with 13 metallic cations by using first-principles calculations. Typical
dopants including s-shell (alkali elements Li and Na), p-shell (Al, Pb and Bi),
3d (Fe, Cu, Co and Ni), 4d (Pd and Ag) and 5d (Au and Pt) elements are
systematically examined. Amongst all the cationic dopants, Al with the highest
oxidation states, implying a high mobility driven by electric field, and
Al-doped GeSe may be a promising candidate for novel resistive switching
devices. We show that there exist many localized induced states in the band gap
of GeSe upon doping Fe, Co, or Ni, while for Cu, Ag, and Au cases there is no
such states in the gap. The Ag and Cu are + 0.27 and + 0.35 charged
respectively and the positive charges are beneficial for field-driven motion in
GeSe. In contrast, Au is slightly negatively charged renders Au-doped GeSe a
promising photocatalyst and enhanced surface plasmon. Moreover, we explore the
coexistence of dopant and strain in GeSe and find dynamical adjustments of
localized states in GeSe with levels successive shifting upward/downward with
strain. This induces dynamic oxidative states of the dopants under strain which
should be quite popular in composites where motion of metal adatoms causes
significant deformation.",2201.11890v1
2022-03-09,Unusual phase formation in reactively sputtered La-Co-O perovskite thin films,"La-based perovskites are a versatile class of materials that are of interest
for solid oxide fuel cells and electrocatalytic water splitting. During
fabrication of composition spread materials libraries of La-Co-based oxide
systems for the discovery of new catalytic materials, an unusual phase
formation phenomenon was observed: instead of the expected continuous
composition gradient, regions with homogeneous composition and single-phase
structure (La2O3 or stoichiometric La-perovskite) form. This phenomenon occurs
during reactive co-sputtering and is dependent on O2-flux and substrate
temperature, investigated from room temperature up to 700 C and is independent
of the used substrate. It can be described as a self-organized growth, where
excess transition metal cannot be incorporated into the growing film and the
forming single-phase regions. It is hypothesized that due to the high
reactivity of La and the significantly low formation energies of La2O3 and
La-perovskites, the reactive sputter deposition of La-based oxide films can
turn, regarding film growth, into a partial CVD-like process which results in
the unusual self-organized growth of single-phase regions. This phenomenon can
be leveraged for the exploration of multinary perovskite thin film libraries,
where the B-site atoms of La-perovskites are systematically substituted.",2203.04631v1
2022-03-15,Confining Eutectic Gallium Indium (eGaIn) in Expired Artificial Kidneys to Unveil Nanoporous Conductive Wires,"Nanoporous membranes have gained considerable interest in drug delivery1, ion
transportation2, micro/nanofluidics3, molecular sensing4, and separation
science5. Artificial kidneys, also known as dialyzers, reject pathogens and
other unwanted substances from the blood, utilize hundreds of soft and
nanoporous polymeric microtubes, and slowly become a burden to the environment
with the growing number of dialysis patients worldwide. We demonstrate the
fabrication of nanoporous conductive wires utilizing empty polysulfone
microtubes collected from expired and unused artificial kidneys, also known as
medical wastes. Injecting a fluidic, highly conductive, and room temperature
liquid alloy (eutectic gallium indium-eGaIn$_6$, 75% Ga, 25% In) into
microtubes of a twenty years old dialyzer, here, we have revealed a new class
of nanoporous and conductive functional materials. These conductive fibers
upcycle a medical waste, do not require expensive and conventional fabrication
processes, and still provide the quintessential metal-oxide/metal framework due
to the presence of the native surface oxide (i.e., Gallium Oxide, Ga2O3) of
eGaIn at the nanoconfinement (i.e., nanopores) for nano/biosensing. We
harnessed these new materials to sense and differentiate microliter volumes of
deionized (DI) water, 1M hydrochloric acid (HCl), and 95% ethanol (EtOH),
leveraging their electrical signatures. This new class of soft nanomaterials
has the potential to become the paradigm-shift platforms for the
next-generation of biomedical, bioelectronics, nanoelectronics, and sensor
devices.",2203.07744v1
2022-03-22,Selectivity in Ligand Functionalization of Photocatalytic Metal Oxide Nanoparticles for Phase Transfer and Self-assembly Applications,"Functionalization of photocatalytic metal oxide nanoparticles of TiO2, ZnO,
WO3 and CuO with amine-terminated (oleylamine) and thiol-terminated
(1-dodecanethiol) alkyl chained ligands was studied under ambient conditions. A
high selectivity was observed in the binding specificity of a ligand towards
nanoparticles of these different oxides. It was observed that oleylamine binds
stably to only TiO2 and WO3, while 1-dodecanethiol binds stably only to ZnO and
CuO. Similarly, polar to non-polar solvent phase transfer of TiO2 and WO3
nanoparticles could be achieved by using oleylamine, but not by
1-dodecanethiol, while the contrary holds for ZnO and CuO. The surface
chemistry of ligand functionalized nanoparticles was probed by ATR-FTIR
spectroscopy, that enabled to elucidate the occupation of the ligands at the
active sites. The photo-stability of the ligands on the nanoparticle surface
was determined by the photocatalytic self-cleaning properties of the material.
While TiO2 and WO3 degrade the ligands within 24 hours under both UV and
visible light, ligands on ZnO and CuO remain unaffected. The gathered insights
are also highly relevant from an application point of view. As an example,
since the ligand functionalized nanoparticles are hydrophobic in nature, they
can thus be self-assembled at the air-water interface, for obtaining
nanoparticle films with demonstrated photocatalytic as well as anti-fogging
properties.",2203.11674v1
2022-03-27,"Cryopreservation of seeds of blue waterlily (Nymphaea caerulea) using glutathione adding plant vitrification solution, PVS+","Nymphaea caerulea is a valuable freshwater aquatic plant, not only because of
its ornamental value but also its extractions for chemical and medical uses. It
is necessary to store its seeds as backup resources. Cryopreservation is the
reliable, cost-effective method for long-term preservation of botanical genetic
banks, especially for recalcitrant plants. In this study, we demonstrated that
due to unable to tolerate desiccation and low-temperature, N. caerulea is
recalcitrant. Since viability was lost before 6 months storage, N. caerulea
seeds were not appropriate to long-term store by traditional storage method.
The only way to long-term store N. caerulea seeds is cryopreservation. However,
Plant Vitrification Solution 3 (PVS3; 50% w/v sucrose, 50% w/v glycerol), a
commonly used plant vitrification solution, was ineffective on N. caerulea
seeds cryopreservation. The maximum survival rate of cryopreserved seeds
treated by PVS3 was only 23%. Oxidative stress induced by reactive oxygen
species (ROS) accumulation within seeds was the reason to cause inefficiency of
PVS3 treated seeds cryopreservation. We developed a new plant vitrification
solution (PVS+), by adding glutathione (GSH) into PVS3. PVS+ rescued the
inefficiency by decreasing ROS accumulation and elevated survival rate of
cryopreserved seeds to 97%. Our results showed some inefficiencies of plant
tissue cryopreservation may be caused by ROS-induced oxidative stress.
Antioxidants can reduce ROS-induced oxidative stress and improve seeds survival
after cryopreservation. In conclusion, N. caerulea seeds were identified as
recalcitrant and successfully cryopreserved. Suppressing ROS accumulation
during cryopreservation may be a potential strategy to improve survival rate of
recalcitrant seeds after cryopreservation.",2203.14201v2
2022-03-28,In search of the ground state crystal structure of Ta$_2$O$_5$ from ab-initio and Monte Carlo simulations,"Tantalum oxides (Ta$_2$O$_5$) are characterised by attractive physical and
chemical properties, such as high dielectric constants and anti-reflection
behaviour. Recently, Ta$_2$O$_5$ nanoparticles have also been proposed as
possible enhancers of the relative biological effectiveness in hadrontherapy
for cancer treatment. In principle, their electronic properties can be
accurately investigated from first-principles simulations. However, the
existence of several stable polymorphs of these oxides represents a major
difficulty in order to calculate and disentangle their respective spectral
features. To assess this problem, we use linear-response time-dependent density
functional to investigate the energy loss function $\mbox{Im}
(-1/\bar{\epsilon})$, which is a unique fingerprint of the material, in the
optical limit for various polymorphs. We show that the experimental reflection
energy loss signals can be rationalized and interpreted by assuming that the
$\gamma$-phase of Ta$_2$O$_5$ represents the underlying structural model. We
notice that both the inclusion of local field effects and spin-orbit coupling
are crucial to compute the energy loss functions of this material. Finally, to
further validate the $\gamma$-Ta$_2$O$_5$ polymorph as a model for experimental
tantalum oxide, we compute the reflection energy loss spectra using a Monte
Carlo approach, finding an excellent agreement with the experimental data.",2203.15105v1
2022-04-12,Role of Oxygen Functionalities in Graphene Oxide Architectural Laminate Subnanometer Spacing and Water Transport,"Active research in nanotechnology contemplates the use of nanomaterials for
engineering applications. However, a primary challenge is understanding the
effects of nanomaterial properties on industrial device performance and
translating unique nanoscale properties to the macroscale. One emerging example
is graphene oxide (GO) membranes for separation processes. Thus, here we
investigate how individual GO properties can impact layered GO characteristics
and water permeability. GO chemistry and morphology were controlled with
easy-to-implement photo-reduction and sonication techniques and were
quantitatively correlated offering a valuable tool to speed up the
characterization process. For example, one could perform chemical analysis and
concurrently obtain morphology information or vice versa. Chemical GO
modification allows for fine control of GO oxidation state and GO laminate
nanoarchitecture enabling controlled synthesis of a GO architectural laminate
(GOAL). The GOAL can be considered as the selective layer of the membrane
created by interconnected sub-nanometer channels, characterized by a length and
a height (i.e., GO spacing), through which water molecules permeate. Water
permeability was measured for eight GOAL characterized by different GO
chemistry and morphology, and indicate that GO nanochannel height dictates
water transport. The simulations indicate a no-slip Darcy-like water transport
regime inside the GOAL due to the presence of basal oxygen functionalities. The
experimental and simulation evidence presented in this letter help create a
clearer picture of water transport in GO and can be used to rationally design
more effective and efficient GO membranes.",2204.06039v1
2022-04-14,"Role of Polarons in Single-Atom Catalysts: Case Study of Me1 [Au1, Pt1, and Rh1] on TiO2(110)","The local environment of metal-oxide supported single-atom catalysts plays a
decisive role in the surface reactivity and related catalytic properties. The
study of such systems is complicated by the presence of point defects on the
surface, which are often associated with the localization of excess charge in
the form of polarons. This can affect the stability, the electronic
configuration, and the local geometry of the adsorbed adatoms. In this work,
through the use of density functional theory and surface-sensitive experiments,
we study the adsorption of Rh1, Pt1, and Au1 metals on the reduced TiO2(110)
surface; a prototypical polaronic material. A systematic analysis of the
adsorption configurations and oxidation states of the adsorbed metals reveals
different types of couplings between adsorbates and polarons. As confirmed by
scanning tunneling microscopy measurements, the favored Pt1 and Au1 adsorption
at oxygen vacancy sites is associated with a strong electronic charge transfer
from polaronic states to adatom orbitals, which results in a reduction of the
adsorbed metal. In contrast, the Rh1 adatoms interact weakly with the excess
charge, which leaves the polarons largely unaffected. Our results show that an
accurate understanding of the properties of single-atom catalysts on oxide
surfaces requires a careful account of the interplay between adatoms, vacancy
sites, and polarons.",2204.06991v1
2022-04-19,Ternary Wide Band Gap Oxides for High-Power Electronics Identified Computationally,"As electricity grids become more renewable energy-compliant, there will be a
need for novel semiconductors that can withstand high power, high voltage, and
high temperatures. Wide band gap (WBG) semiconductors tend to exhibit large
breakdown field, allowing high operating voltages. Currently explored WBG
materials for power electronics are costly (GaN), difficult to synthesize as
high-quality single crystals (SiC) and at scale (diamond, BN), have low thermal
conductivity ($\beta$-Ga$_2$O$_3$), or cannot be suitably doped (AlN). We
conduct a computational search for novel semiconductors across 1,340 known
metal-oxides using first-principles calculations and existing transport models.
We calculate the Baliga figure of merit (BFOM) and lattice thermal conductivity
($\kappa_L$) to identify top candidates for n-type power electronics. We find
40 mostly ternary oxides that have higher $\kappa_L$ than $\beta$-Ga$_2$O$_3$
and higher n-type BFOM than SiC and GaN. Among these, several material classes
emerge, including 2-2-7 stoichiometry thortveitites and pyrochlores, II-IV
spinels, and calcite-type borates. Within these classes, we propose
In$_2$Ge$_2$O$_7$, Mg$_2$GeO$_4$, and InBO$_3$ as they are the most favorable
for n-type doping based on our preliminary evaluation and could be grown as
single crystals or thin film heterostructures. These materials could help
advance power electronic devices for the future grid.",2204.09158v1
2022-05-04,Direct observation of nodeless superconductivity and phonon modes in electron-doped copper oxide Sr$_{1-x}$Nd$_x$CuO$_2$,"The microscopic understanding of high-temperature superconductivity in
cuprates has been hindered by the apparent complexity of crystal structures in
these materials. We used scanning tunneling microscopy and spectroscopy to
study an electron-doped copper oxide compound Sr$_{1-x}$Nd$_x$CuO$_2$ that has
only bare cations separating the CuO$_2$ planes and thus the simplest
infinite-layer structure among all cuprate superconductors. Tunneling
conductance spectra of the major CuO$_2$ planes in the superconducting state
revealed direct evidence for a nodeless pairing gap, regardless of variation of
its magnitude with the local doping of trivalent neodymium. Furthermore, three
distinct bosonic modes are observed as multiple peak-dip-hump features outside
the superconducting gaps and their respective energies depend little on the
spatially varying gaps. Along with the bosonic modes with energies identical to
those of the external, bending and stretching phonons of copper oxides, our
findings indicate their origin from lattice vibrations rather than spin
excitations.",2205.01843v1
2022-05-06,The role of atomization in the coupling between doped droplets dynamics and their flames,"The droplet and flame chemiluminescence dynamics as well as their coupling
during atomization events of graphene oxide doped diesel are investigated
experimentally. The tested doping concentrations are 0, 0.001, 0.005, 0.01, and
0.02% by weight. To minimize heat transfer between the droplet and its
suspension mechanism, small diameter fibers are used for the droplet
suspension. Separate shadowgraphy and OH* chemiluminescence measurements are
performed at 4000 Hz to study the droplet and flame dynamics, respectively. The
results show that both the droplet diameter squared and the flame
chemiluminescence feature intermittent oscillations. The droplet diameter
squared oscillations RMS is positively related to the number and intensity of
the atomization events and the graphene oxide doping concentration. The
probability density function of the inverse of the time separation between two
consecutive atomization events and the power spectrum density of the droplet
diameter squared oscillations feature dominant large probabilities and powers
at about 25 Hz prior to the occurrence of the first intense atomization event.
After the occurrence of the first intense atomization event, this frequency
decreases to about 5 Hz for both. Although the intense atomization triggers the
large amplitude oscillations at 5 Hz, it was argued that the retracting motion
of the igniter induces the oscillations at 25 Hz. Our findings suggest that the
atomization events are the root cause of the smaller frequency coupling between
liquid fuel droplets doped with graphene oxide and their flames. This has
implications for spray combustion research.",2205.02966v1
2022-06-04,Metal Oxide-Vertical Graphene Nanosheets for 2.6 V Aqueous Electrochemical Hybrid Capacitor,"Aqueous asymmetric electrochemical capacitor, with their high power density
and superior cycle stability in comparison to conventional batteries, are
presently considered as the most promising contender for energy storage.
However, fabricating an electrode material and choosing a suitable aqueous
electrolyte are vital in developing an electrochemical capacitor device with
high charge storage capacity. Herein, we report a feasible method to synthesize
MnO2/Vertical graphene nanosheets (VGN) and Fe2O3/VGN as positive and negative
electrodes, respectively. The surface of VGN skeleton is independently
decorated with MnO2 having sponge gourd-like morphology and Fe2O3 having
nanorice like morphology. A schematic representation of the growth mechanism
for metal oxide on VGN network is established. Both the electrode have shown
around 250 times higher charge-storage capacity than the bare VGN (0.47 mF/cm2)
with the specific capacitance of 118 (MnO2/VGN) and 151 mF/cm2 (Fe2O3/VGN). In
addition to the double layer capacitance contribution, the porous
interconnected vertical graphene architecture serves as a mechanical backbone
for the metal oxide materials and provides multiple conducting channels for the
electron transport. The fabricated asymmetric device exhibited a specific
capacitance of 76 mF/cm2 and energy density of 71 microWh/cm2 with an excellent
electrochemical stability up to 12000 cycles, over a potential window of 2.6 V.
The commendable performance of asymmetric electrochemical capacitor device
authenticated its potential utilization for next-generation portable energy
storage device.",2206.01998v1
2022-06-16,Scalable Composites Benefiting from Transition-Metal Oxides as Cathode Materials for Efficient Lithium-Sulfur Batteries,"Composite materials achieved by including transition-metal oxides with
different structures and morphologies in sulfur are suggested as scalable
cathodes for high-energy lithium-sulfur (Li-S) batteries. The composites
contain 80 wt.% sulfur and 20 wt.% of either MnO2 or TiO2, leading to a sulfur
content in the electrode of 64 wt.% and revealing a reversible, fast, and lowly
polarized conversion process in the cell with limited interphase resistance.
The S-TiO2 composite exhibits an excellent rate capability between C/10 and 2C,
and a cycle life extended over 400 cycles at 2C, owing to the effects of the
nanometric TiO2 additive in boosting the reaction kinetics. Instead, the
micrometric sized particles of MnO2 partially limit the electrochemical
activity of S-MnO2 to the current rate of 1C. Nevertheless, both S-MnO2 and
S-TiO2 withstand a sulfur loading up to values approaching 6 mgcm-2, and
deliver an areal capacit ranging from about 4.5 to 5.5 mAhcm-2 at C/5. The
excellent performances of the metal oxide-sulfur electrodes, even at high
active material loading, and the possible scalability of the synthetic pathway
adopted in the work suggest that the composites are viable cathodes for
next-generation Li-S batteries with high energy density and efficient
electrochemical process.",2206.14569v1
2022-06-29,Optical properties of oxygen-containing yttrium hydride thin films during and after the deposition,"The synthesis of the photochromic YHO films is based on the oxidation of
deposited yttrium hydride in ambient conditions. The actual state of the films
during the deposition process, which is influenced by the deposition pressure
and the oxidation caused by the residual gases, is not completely known. We
report on the YHxOy thin films deposited by reactive pulsed-DC magnetron
sputtering. Since the visible light transmittance is closely related to the
phase and chemical composition of the films, in-situ transmittance measurements
during and after deposition are performed. Ex-situ spectroscopic ellipsometry
is used to determine the optical constants of YHxOy throughout the film
thickness. In order to obtain metallic YH2-x films, the densest possible
structure with a high deposition rate is required, otherwise the films could
already be partially transparent during the deposition. The transmittance is
higher if deposition pressure is increased. This is because of the oxidation
promoted by more porous growth of the microstructure that is observed at the
surface and cross-section images of the films. The films exhibit a refractive
index gradient perpendicular to the substrate surface, which is related to the
porosity and variation of the chemical composition.",2206.14644v1
2022-06-29,Tailoring of rhenium oxidation state in ReOx thin films during reactive HiPIMS deposition process and following annealing,"Bulk rhenium trioxide (ReO3) has an unusually high electrical conductivity
and, being nanosized, has promising catalytic properties. However, the
production of pure ReO3 thin films is challenging due to the difficulty to
stabilize rhenium in a 6+ oxidation state. Here we present a novel approach for
the deposition of ReOx (x = 1.6-2.9) thin films using reactive high power
impulse magnetron sputtering (r-HiPIMS) from a metallic rhenium target in a
mixed Ar/O2 atmosphere. The thin films were deposited in the gas-sustained
self-sputtering regime, observed during r-HiPIMS process according to current
waveforms. The influence of the substrate temperature, the oxygen-to-argon flow
ratio and post-annealing at 250 {\deg}C in the air for 3 h on the properties of
the films were studied. The as-deposited films have an X-ray amorphous
structure (a-ReOx) when deposited at room temperature while a nano-crystalline
\b{eta}-ReO2 phase when deposited at elevated temperatures (150 or 250
{\deg}C). The amorphous a-ReOx can be converted into the crystalline ReO3 with
a lattice parameter of 3.75 {\AA} upon annealing in the air. The surface
morphology of the films is dense without detectable voids when elevated
substrate temperatures are used. Various Re oxidation states are observed on
the surface of the films in different ratios depending on the deposition
parameters. All samples exhibit electrical resistivity on the order of 10-3
Ohmxcm and optical properties typical for thin metallic films.",2206.14665v1
2022-07-12,Amorphous p-Type Conducting Zn-x Ir Oxide (x > 0.13) Thin Films Deposited by Reactive Magnetron Cosputtering,"Zinc-iridium oxide (Zn-Ir-O) thin films have been demonstrated as a p-type
conducting material. However, the stability of p-type conductivity with respect
to chemical composition or temperature is still unclear. In this study we
discuss the local atomic structure and the electrical properties of Zn-Ir-O
films in the large Ir concentration range. The films are deposited by reactive
DC magnetron co-sputtering at two different substrate temperatures-without
intentional heating and at 300 {\deg}C. Extended X-ray absorption fine
structure (EXAFS) analysis reveals that strongly disordered ZnO4 tetrahedra are
the main Zn complexes in Zn-Ir-O films with up to 67.4 at% Ir. As the Ir
concentration increases, an effective increase of Ir oxidation state is
observed. Reverse Monte Carlo analysis of EXAFS at Zn K-edge shows that the
average Zn-O interatomic distance and disorder factor increase with the Ir
concentration. We observed that the nano-crystalline w-ZnO structure is
preserved in a wider Ir concentration range if the substrate is heated during
deposition. At low Ir concentration, the transition from n- to p-type
conductivity is observed regardless of the temperature of the substrates.
Electrical resistivity decreases exponentially with the Ir concentration in the
Zn-Ir-O films.",2207.05438v1
2022-07-18,Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO$_3$ interfaces,"Rashba interfaces have emerged as promising platforms for spin-charge
interconversion through the direct and inverse Edelstein effects. Notably,
oxide-based two-dimensional electron gases (2DEGs) display a large and
gate-tunable conversion efficiency, as determined by transport measurements.
However, a direct visualization of the Rashba-split bands in oxide 2DEGs is
lacking, which hampers an advanced understanding of their rich spin-orbit
physics. Here, we investigate KTaO$_3$-2DEGs and evidence their Rashba-split
bands using angle resolved photoemission spectroscopy. Fitting the bands with a
tight-binding Hamiltonian, we extract the effective Rashba coefficient and
bring insight into the complex multiorbital nature of the band structure. Our
calculations reveal unconventional spin and orbital textures, showing
compensation effects from quasi-degenerate band pairs which strongly depend on
in-plane anisotropy. We compute the band-resolved spin and orbital Edelstein
effects, and predict interconversion efficiencies exceeding those of other
oxide 2DEGs. Finally, we suggest design rules for Rashba systems to optimize
spin-charge interconversion performance.",2207.08698v1
2022-07-20,Adatom and nanoparticle dynamics on single-atom catalyst substrates,"Single-atom catalysts represent an essential and ever-growing family of
heterogeneous catalysts. Recent studies indicate that besides the valuable
catalytic properties provided by single-atom active sites, the presence of
single-atom sites on the catalyst substrates may significantly influence the
population of supported metal nanoparticles coexisting with metal single atoms.
Treatment of ceria-based single-atom catalysts in oxidizing or reducing
atmospheres was proven to provide precise experimental control of the size of
the supported Pt nanoparticles, and, correspondingly, control of catalyst
activity and stability. Based on dedicated surface science experiments,
ab-initio calculations and kinetic Monte-Carlo simulations we demonstrate that
the morphology of Pt nanoparticle population on ceria surface is a result of a
competition for Pt atoms between Pt single-atom sites and Pt nanoparticles. In
oxidizing atmosphere, Pt single-atom sites provide strong bonding to single Pt
atoms and Pt nanoparticles shrink. In reducing atmosphere, Pt single atom sites
are depopulated and Pt nanoparticles grow. We formulate a generic model of Pt
redispersion and coarsening on ceria substrates. Our model provides a unified
atomic-level explanation for a variety of metal nanoparticle dynamic processes
observed in single-atom catalysts under stationary or alternating
oxidizing/reducing atmospheres, and allows to classify the conditions when
nanoparticle ensembles on single-atom catalysts substrates can be stabilized
against Ostwald ripening.",2207.09749v1
2022-08-23,Theoretical Study of Electronic Transport in Two-Dimensional Transition Metal Dichalcogenides: Effects of the Dielectric Environment,"We discuss the effect of the dielectric environment (insulators and metal
gates) on electronic transport in two-dimensional (2D) transition metal
dichalcogenides (TMD) monolayers. We employ well-known ab initio methods to
calculate the low-field carrier mobility in free-standing layers and use the
dielectric continuum approximation to extend our study to layers in double-gate
structures, including the effects of dielectric screening of the
electron-phonon interaction caused by the bottom oxide and the gate insulator,
and of scattering with hybrid interface optical-phonon/plasmon excitations
(`remote phonon scattering'). We find that the presence of insulators with a
high dielectric constant may improve significantly the carrier mobility.
However, scattering with the interface hybrid excitations negates this gain and
degrades the mobility significantly below its free-standing value. In a
double-gate geometry with SiO$_{2}$ as bottom-oxide and various top-gate
insulators, we find that the mobility decreases as the top-insulator dielectric
constant increases, as expected. However, a high mobility is predicted in the
case of the weakly polar hBN, and a mobility much lower than expected is
calculated in the case of gate-insulator/TMD/bottom-oxide stacks in which two
or more polar materials have optical-phonon with similar resonating
frequencies. We also find that the effect of screening by metal gates is
noticeable but not particularly strong. Finally, we discuss the effect of the
TMD dielectric constant, of the free-carrier density, and of temperature on the
transport properties of TMD monolayers.",2208.11031v1
2022-09-28,Functional thin films as cathode/electrolyte interlayers: a strategy to enhance the performance and durability of solid oxide fuel cells,"Electrochemical devices such as solid oxide fuel cells (SOFC) may greatly
benefit from the implementation of nanoengineered thin-film multifunctional
layers providing, alongside enhanced electrochemical activity, improved
mechanical, and long-term stability. In this study, an ultrathin (400 nm)
bilayer of samarium-doped ceria and a self-assembled nanocomposite made of
Sm0.2Ce0.8O1.9-La0.8Sr0.2MnO3-$\delta$ was fabricated by pulsed laser
deposition and is employed as a functional oxygen electrode in an
anode-supported solid oxide fuel cell. Introducing the functional bilayer in
the cell architecture results in a simple processing technique for the
fabrication of high-performance fuel cells (power density 1.0 W.cm-2 at 0.7 V
and 750 $^\circ$C). Durability tests were carried out for up to 1500 h, showing
a small degradation under extreme operating conditions of 1 A.cm-2, while a
stable behaviour at 0.5 A.cm-2. Post-test analyses, including scanning and
transmission electron microscopy and electrochemical impedance spectroscopy,
demonstrate that the nanoengineered thin film layers remain mostly
morphologically stable after the operation.",2209.14374v1
2022-10-26,Two-Dimensional Charge Localization at the Perovskite Oxide Interface,"The effects of atomic-scale disorder and charge (de)localization holds
significant importance,and they provide essential insights in unravelling the
role that strong and weak correlations play in condensed matter systems.For
perovskite oxide heterostructures,while disorders introduced via various
external stimuli have strong influences on the (de)localization of the
interfacial two-dimensional (2D) electrons, these factors alone could not fully
account for the system's charge dynamics where interfacial hybridization holds
very strong influence.Here, we determine that the displaced 2D free electrons
are localized in the specific hybridized states at the LaAlO3/SrTiO3(LAO/STO)
interface.This experimental study combines both transport measurements and
temperature-dependent X-ray absorption spectroscopy and suggests the
localization of 2D electrons can be induced via temperature reduction or ionic
liquid gating and it applies to both amorphous and crystalline interfacial
systems.Specifically, we demonstrate that interfacial hybridization plays a
pivotal role in regulating the 2D electron localization effects.Our study
resolves the location where the 2D electrons are localized and highlights the
importance of interfacial hybridization and opens further scientific
investigation of its influence on 2D charge localization in oxide
heterointerfaces.",2210.14435v1
2022-10-26,Visualizing giant ferroelectric gating effects in large-scale WSe$_2$/BiFeO$_3$ heterostructures,"Multilayers based on quantum materials (complex oxides, topological
insulators, transition-metal dichalcogenides, etc) have enabled the design of
devices that could revolutionize microelectronics and optoelectronics. However,
heterostructures incorporating quantum materials from different families remain
scarce, while they would immensely broaden the range of possible applications.
Here we demonstrate the large-scale integration of compounds from two
highly-multifunctional families: perovskite oxides and transition-metal
dichalcogenides (TMDs). We couple BiFeO$_3$, a room-temperature multiferroic
oxide, and WSe$_2$, a semiconducting two-dimensional material with potential
for photovoltaics and photonics. WSe$_2$ is grown by molecular beam epitaxy and
transferred on a centimeter-scale onto BiFeO$_3$ films. Using angle-resolved
photoemission spectroscopy, we visualize the electronic structure of 1 to 3
monolayers of WSe$_2$ and evidence a giant energy shift as large as 0.75 eV
induced by the ferroelectric polarization direction in the underlying
BiFeO$_3$. Such a strong shift opens new perspectives in the efficient
manipulation of TMDs properties by proximity effects.",2210.14786v1
2022-11-02,Tunable Rapid Electron Transport in Titanium Oxide Thin Films,"Rapid electron transport in the quantum well triggers many novel physical
phenomena and becomes a critical point for the high-speed electronics. Here, we
found electrical properties of the titanium oxide changed from semiconducting
to metallic as the degree of oxidation decreased and Schottky quantum well was
formed at the interface. We take the asymmetry interface electron scattering
effect into consideration when studying the electrical transport properties of
the multilayer thin films. A novel physical conductivity model for the
multilayer thin films was developed. We found electron would be transferred
from the low-mobility semiconducting and metallic conductive channels to the
high-mobility Schottky quantum well conductive channel with an in-plane applied
electric field. Electron concentration and mobility of the forming 2DEG in the
Schottky quantum well could be tuned thus the nano-devices exhibited non-linear
voltage-current curves. The differential resistivity of the nano-devices could
decrease by two orders with increasing electric field at room temperature. Weak
electron localization of electrons has been experimentally observed in our
nano-devices at low temperature, which further demonstrated the existence of
2DEG in the Schottky quantum well. Our work will provide us new physics about
the rapid electron transport in the multilayer thin films, and bring novel
functional devices for the modern microelectronic industry.",2211.01162v1
2022-11-07,Room temperature charge-to-spin conversion from q-2DEG at SrTiO3-based interfaces,"Interfacial two-dimensional electron gas (2DEG), especially the SrTiO3-based
ones at the unexpected interface of insulators, have emerged to be a promising
candidate for efficient charge-spin current interconversion. In this article,
to gain insight into the mechanism of the charge-spin current interconversion
at the oxide-based 2DEG, we focused on conducting interfaces between insulating
SrTiO3 and two types of aluminium-based amorphous insulators, namely SrTiO3/AlN
and SrTiO3/Al2O3, and estimated their charge-spin conversion efficiency,
{\theta}_cs. The two types of amorphous insulators were selected to explicitly
probe the overlooked contribution of oxygen vacancy to the {\theta}_cs. We
proposed a mechanism to explain results of spin-torque ferromagnetic resonance
(ST-FMR) measurements and developed an analysis protocol to reliably estimate
the {\theta}_cs of the oxide based 2DEG. The resultant {\theta}_cs/t, where t
is the thickness of the 2DEG, were estimated to be 0.244 nm-1 and 0.101 nm-1
for the SrTiO3/AlN and SrTiO3/Al2O3, respectively, and they are strikingly
comparable to their crystalline counterparts. Furthermore, we also observe a
large direct current modulation of resonance linewidth in SrTiO3/AlN samples,
confirming its high {\theta}_cs and attesting an oxygen-vacancy-enabled
charge-spin conversion. Our findings emphasize the defects' contribution to the
charge-spin interconversion, especially in the oxide-based low dimensional
systems, and provide a way to create and enhance charge-spin interconversion
via defect engineering.",2211.03383v1
2022-12-01,Investigation of process history and phenomenology of plutonium oxides using vector quantizing variational autoencoder,"Accurate, high throughput, and unbiased analysis of plutonium oxide particles
is needed for analysis of the phenomenology associated with process parameters
in their synthesis. Compared to qualitative and taxonomic descriptors,
quantitative descriptors of particle morphology through scanning electron
microscopy (SEM) have shown success in analyzing process parameters of uranium
oxides. We utilize a VQ-VAE to quantitatively describe plutonium dioxide (PuO2)
particles created in a designed experiment and investigate their phenomenology
and prediction of their process parameters. PuO2 was calcined from Pu(III)
oxalates that were precipitated under varying synthetic conditions that related
to concentrations, temperature, addition and digestion times, precipitant feed,
and strike order; the surface morphology of the resulting PuO2 powders were
analyzed by SEM. A pipeline was developed to extract and quantify useful image
representations for individual particles with the VQ-VAE to perform multiple
classification tasks simultaneously. The reduced feature space could predict
process parameters with greater than 80% accuracies for some parameters with a
single particle. They also showed utility for grouping particles with similar
surface morphology characteristics together. Both the clustering and
classification results reveal valuable information regarding which chemical
process parameters chiefly influence the PuO2 particle morphologies: strike
order and oxalic acid feedstock. Doing the same analysis with multiple
particles was shown to improve the classification accuracy on each process
parameter over the use of a single particle, with statistically significant
results generally seen with as few as four particles in a sample.",2212.00887v2
2022-12-02,Dynamics of the Great Oxidation Event from a 3D photochemical-climate model,"From the Archean toward the Proterozoic, the Earth's atmosphere underwent a
major shift from anoxic to oxic conditions, around 2.4 to 2.1 Gyr, known as the
Great Oxidation Event (GOE). This rapid transition may be related to an
atmospheric instability caused by the formation of the ozone layer. Previous
works were all based on 1D photochemical models. Here, we revisit the GOE with
a 3D photochemical-climate model to investigate the possible impact of the
atmospheric circulation and the coupling between the climate and the dynamics
of the oxidation. We show that the diurnal, seasonal and transport variations
do not bring significant changes compared to 1D models. Nevertheless, we
highlight a temperature dependence for atmospheric photochemical losses. A
cooling during the late Archean could then have favored the triggering of the
oxygenation. In addition, we show that the Huronian glaciations, which took
place during the GOE, could have introduced a fluctuation in the evolution of
the oxygen level. Finally, we show that the oxygen overshoot which is expected
to have occurred just after the GOE, was likely accompanied by a methane
overshoot. Such high methane concentrations could have had climatic
consequences and could have played a role in the dynamics of the Huronian
glaciations.",2212.01389v1
2022-12-11,Strain induced variations in transport and optical properties of SrVO$_3$: a DFT+U study,"First-principles calculations based on density functional theory + Hubbard U
(DFT+U) approach have been carried out to study the strain induced variations
in the optical and transport properties of the correlated perovskite SrVO$_3$.
By virtue of its conductivity, high carrier mobility and optical transparency,
SrVO$_3$ can be used as a potential replacement of indium tin oxide (ITO) as a
transparent conductor. As strain tuning is an effective way to tune the
electron-electron correlations in correlated oxides, the epitaxial strain
induced variations in V-3d bandwidth, band center shift and band splitting at
high symmetry points (${\Gamma}$, R) in SrVO$_3$ are investigated. The
alterations in resistivity, carrier concentration, Hall coefficient and plasma
frequency with applied strain are also elucidated. Our calculations revealed
that under tensile strain, the lifting of the threefold degeneracy of
3d-t$_{2g}$ orbital and d-band narrowing reinforces a relatively less
conducting state thus limiting the $\omega_P$ to lower frequencies. On the
contrary, in case of compressive strain the d-band widening predominates
leading to an increase in carrier concentration and decrease in resistivity
enhancing the metallic state. As a result, $\omega_P$ is increased to higher
frequencies which decreases the optical transparency window. Hence, our results
and findings clearly demonstrate the interdependence between the optical and
transport properties, and provides a detailed mechanism to tune the
optoelectronic properties of SrVO$_3$ for its applications as a transparent
conducting oxide.",2212.05449v1
2022-12-13,Improving Josephson junction reproducibility for superconducting quantum circuits: shadow evaporation and oxidation,"The most commonly used physical realization of superconducting qubits for
quantum circuits is a transmon. There are a number of superconducting quantum
circuits applications, where Josephson junction critical current
reproducibility over a chip is crucial. Here, we report on a robust chip scale
$Al/AlO_x/Al$ junctions fabrication method due to comprehensive study of shadow
evaporation and oxidation steps. We experimentally demonstrate the evidence of
optimal Josephson junction electrodes thickness, deposition rate and deposition
angle, which ensure minimal electrode surface and line edge roughness. The
influence of oxidation method, pressure and time on critical current
reproducibility is determined. With the proposed method we demonstrate
$Al/AlO_x/Al$ junction fabrication with the critical current variation
($\sigma/I_c$) less than 3.9% (from $150\times200$ to $150\times600$ $nm^2$
area) and 7.7% (for $100\times100$ $nm^2$ area) over $20\times20$ $mm^2$ chip.
Finally, we fabricate separately three $5\times10$ $mm^2$ chips with 18
transmon qubits (near 4.3 GHz frequency) showing less than 1.9% frequency
variation between qubit on different chips. The proposed approach and
optimization criteria can be utilized for a robust wafer-scale superconducting
qubit circuits fabrication.",2212.06692v1
2022-12-20,Wafer-Scale Fabrication of Hierarchically Porous Silicon and Silica Glass by Active Nanoparticle-Assisted Chemical Etching and Pseudomorphic Thermal Oxidation,"Many biological materials exhibit a multiscale porosity with small, mostly
nanoscale pores as well as large, macroscopic capillaries to simultaneously
achieve optimized mass transport capabilities and lightweight structures with
large inner surfaces. Realizing such a hierarchical porosity in artificial
materials necessitates often sophisticated and expensive top-down processing
that limits scalability. Here we present an approach that combines
self-organized porosity based on metal-assisted chemical etching (MACE) with
photolithographically induced macroporosity for the synthesis of
single-crystalline silicon with a bimodal pore-size distribution, i.e.,
hexagonally arranged cylindrical macropores with 1 micrometer diameter
separated by walls that are traversed by mesopores 60 nm across. The MACE
process is mainly guided by a metal-catalyzed reduction-oxidation reaction,
where silver nanoparticles (AgNPs) serve as the catalyst. In this process, the
AgNPs act as self-propelled particles that are constantly removing silicon
along their trajectories. High-resolution X-ray imaging and electron tomography
reveal a resulting large open porosity and inner surface for potential
applications in high-performance energy storage, harvesting and conversion or
for on-chip sensorics and actuorics. Finally, the hierarchically porous silicon
membranes can be transformed structure-conserving by thermal oxidation into
hierarchically porous amorphous silica, a material that could be of particular
interest for opto-fluidic and (bio-)photonic applications due to its multiscale
artificial vascularization.",2212.10160v1
2022-12-21,Defeating depolarizing fields with artificial flux closure in ultrathin ferroelectrics,"Material surfaces encompass structural and chemical discontinuities that
often lead to the loss of the property of interest in the so-called dead
layers. It is notably problematic in nanoscale oxide electronics, where the
integration of strongly correlated materials into devices is obstructed by the
thickness threshold required for the emergence of their functionality. Here, we
report the stabilization of ultrathin out-of-plane ferroelectricity in oxide
heterostructures through the design of an artificial flux-closure architecture.
Inserting an in-plane polarized ferroelectric epitaxial buffer provides
continuity of polarization at the interface, and despite its insulating nature
we observe the emergence of polarization in our out-of-plane-polarized model
ferroelectric BaTiO$_{3}$ from the very first unit cell. In BiFeO$_{3}$, the
flux-closure approach stabilizes a conceptually novel 251$^{\circ}$ domain
wall. Its unusual chirality is likely associated with the ferroelectric analog
to the Dzyaloshinskii-Moriya interaction. We thus see that in an adaptively
engineered geometry, the depolarizing-field-screening properties of an
insulator can even surpass those of a metal and be a source of new
functionalities. This should be a useful insight on the road towards the next
generation of ferroelectric-based oxide electronics.",2212.11073v1
2022-12-27,Compositionally Complex Perovskite Oxides as a New Class of Li-Ion Solid Electrolytes,"Compositionally complex ceramics (CCCs), including high-entropy ceramics
(HECs) as a subclass, offer new opportunities of materials discovery beyond the
traditional methodology of searching new stoichiometric compounds. Herein, we
establish new strategies of tailoring CCCs via a seamless combination of (1)
non-equimolar compositional designs and (2) controlling microstructures and
interfaces. Using oxide solid electrolytes for all-solid-state batteries as an
exemplar, we validate these new strategies via discovering a new class of
compositionally complex perovskite oxides (CCPOs) to show the possibility of
improving ionic conductivities beyond the limit of conventional doping. As an
example (amongst the 28 CCPOs examined), we demonstrate that the ionic
conductivity can be improved by >60% in
(Li0.375Sr0.4375)(Ta0.375Nb0.375Zr0.125Hf0.125)O3-{\delta}, in comparison with
the state-of-art (Li0.375Sr0.4375)(Ta0.75Zr0.25)O3-{\delta} (LSTZ) baseline,
via maintaining comparable electrochemical stability. Furthermore, the ionic
conductivity can be improved by another >70% via grain boundary (GB)
engineering, achieving >270% of the LSTZ baseline. This work suggests
transformative new strategies for designing and tailoring HECs and CCCs,
thereby opening a new window for discovering materials for energy storage and
many other applications.",2212.13451v1
2023-01-03,"Extracting optical parameters of Cu-Mn-Fe spinel oxide nanoparticles for optimizing air-stable, high-efficiency solar selective coatings","High-temperature Cu-Mn-Fe spinel-oxide nanoparticle solar selective absorber
coatings are investigated experimentally and theoretically. A reliable, general
approach to evaluate absorption coefficient spectra from the optical
measurements of the nanoparticle-pigmented coatings is developed based on
solving the inverse problem using four-flux-radiative method. The derived
absorption properties of NP materials can be directly applied to predict the
solar absorptance, optimize the nanoparticle-pigmented coatings, and analyze
the thermal degradation, which agree well with the experimental results. The
analysis reveals that the Cu-Mn-Fe spinel oxides are fundamentally indirect
bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap
material with Eg=1.84 eV. With the same coating thickness and nanoparticle
load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 <
CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented
coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a
high optical-to-thermal energy conversion efficiency of ~93.5 % under 1000x
solar concentration at 750 degrees C, and long-term endurance upon thermal
cycling between 750{\deg}C and room temperature in air. The optical parameter
analysis approach can be easily extended to other material systems to
facilitate the searching and optimizing high-temperature pigmented-solar
selective coatings.",2301.01194v1
2023-01-03,Spinel Cu-Mn-Cr Oxide Nanoparticle-Pigmented Solar Selective Coatings Maintaining >94% Efficiency at 750 degrees C,"High-temperature concentrating solar power (CSP) system is capable of
harvesting and storing solar energy as heat towards cost-effective dispatchable
solar electricity. Solar selective coating is a critical component to boost its
efficiency by maximizing solar absorptance and minimizing thermal emittance
losses. However, maintaining a high solar-thermal conversion efficiency >90%
for long-term operation at >750 degrees C remains a significant challenge.
Herein, we report spray-coated spinel Cu-Mn-Cr oxide nanoparticle-pigmented
solar selective coatings on Inconel tube sections maintaining >94% efficiency
at 750 degrees C and >92.5% at 800 degrees C under 1000x solar concentration
after 60 simulated day-night thermal cycles in air, each cycle comprising 12h
at 750 degrees C/800 degrees C and 12h cooling to 25 degrees C. The solar
spectral selectivity is intrinsic to the band-to-band and d-d transitions of
non-stoichiometric spinel Cu-Mn-Cr oxide nanoparticles by balancing the lattice
site inversion of Cu2+ and Mn3+ on tetrahedral vs. octahedral sites. This
feature offers a large fabrication tolerance in nanoparticle volume fraction
and coating thickness, facilitating low-cost and scalable spray-coated
high-efficiency solar selective absorbers for high-temperature CSP systems.",2301.01265v1
2023-01-19,Illuminating trap density trends in amorphous oxide semiconductors with ultrabroadband photoconduction,"Under varying growth and device processing conditions, ultrabroadband
photoconduction (UBPC) reveals strongly evolving trends in the defect density
of states (DoS) for amorphous oxide semiconductor thin-film transistors (TFTs).
Spanning the wide bandgap of amorphous InGaZnO$_x$ (a-IGZO), UBPC identifies
seven oxygen-deep donor vacancy peaks that are independently confirmed by
energetically matching to photoluminescence emission peaks. The sub-gap DoS
from 15 different types of a-IGZO TFTs all yield similar DoS, except only
back-channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the
conduction band mobility edge. This deep acceptor is likely a zinc vacancy,
evidenced by trap density which becomes 5-6x larger when TFT wet-etch methods
are employed. Certain DoS peaks are strongly enhanced for TFTs with active
channel processing damage caused by plasma exposure. While Ar implantation and
He plasma processing damage are similar, Ar plasma yields more disorder showing
a 2x larger valence-band Urbach energy and two orders of magnitude increase in
the deep oxygen vacancy trap density. Changing the growth conditions of a-IGZO
also impacts the DoS, with zinc-rich TFTs showing much poorer electrical
performance compared to 1:1:1 molar ratio a-IGZO TFTs owing to the former
having a ~10xlarger oxygen vacancy trap density. Finally, hydrogen is found to
behave as a donor in amorphous indium tin gallium zinc oxide TFTs.",2301.08196v1
2023-03-13,Probing Interface of Perovskite Oxide Using Surface-specific Terahertz Spectroscopy,"The surface/interface species in perovskite oxides play an essential role in
many novel emergent physical phenomena and chemical processes. With low
eigen-energy in the terahertz region, such species at buried interfaces remain
poorly understood due to the lack of feasible experimental techniques. Here, we
show that vibrational resonances and two-dimensional electron gas at the
interface can be characterized using surface-specific nonlinear spectroscopy in
the terahertz range. This technique uses intra-pulse difference frequency
mixing (DFM) process, which is allowed only at surface/interface of a medium
with inversion symmetry. Sub-monolayer sensitivity can be achieved using the
state-of-the-art detection scheme for the terahertz emission from
surface/interface. As a demonstration, Drude-like nonlinear response from the
two-dimensional electron gas emerging at LaAlO3/SrTiO3 or Al2O3/ SrTiO3
interface was successfully observed. Meanwhile, the interfacial vibrational
spectrum of the ferroelectric soft mode of SrTiO3 at 2.8 THz was also obtained
that was polarized by the surface field in the interfacial region. The
corresponding surface/interface potential, which is a key parameter for
SrTiO3-based interface superconductivity and photocatalysis, can now be
determined optically via quantitative analysis on the polarized phonon
spectrum. The interfacial species with resonant frequencies in the THz region
revealed by our method provide more insights into the understanding of physical
properties of complex oxides.",2303.07871v1
2023-03-16,Chemical bonding in americium oxides: x-ray spectroscopic view,"The electronic structure and the chemical state in Am binary oxides and
Am-doped UO$_2$ were studied by means of x-ray absorption spectroscopy at
shallow Am core ($4d$ and $5d$) edges. In particular, the Am $5f$ states were
probed and the nature of their bonding to the oxygen states was analyzed. The
interpretation of the experimental data was supported by the Anderson impurity
model (AIM) calculations which took into account the full multiplet structure
due to the interaction between $5f$ electrons as well as the interaction with
the core hole. The sensitivity of the branching ratio of the Am $4d_{3/2}$ and
$4d_{5/2}$ x-ray absorption lines to the chemical state of Am was shown using
Am binary oxides as reference systems. The observed ratio for Am-doped UO$_2$
suggests that at least at low Am concentrations, americium is in the Am(III)
state in the UO$_2$ lattice. To confirm the validity of the applied AIM
approach, the analysis of the Am $4f$ x-ray photoelectron spectra of AmO$_2$
and Am$_2$O$_3$ was also performed which revealed a good agreement between
experiment and calculations. As a whole, AmO$_2$ can be classified as the
charge-transfer compound with the $5f$ occupancy ($n_f$) equal to 5.73
electrons, while Am$_2$O$_3$ is rather a Mott-Hubbard system with $n_f$=6.05.",2303.09247v1
2023-04-04,Ultrathin Stable Ohmic Contacts for High-Temperature Operation of $β$-Ga$_2$O$_3$ Devices,"Beta gallium oxide ($\beta$-Ga$_2$O$_3$) shows significant promise in the
high-temperature, high-power, and sensing electronics applications. However,
long-term stable metallization layers for Ohmic contacts at high temperature
present unique thermodynamic challenges. The current most common Ohmic contact
design based on 20 nm of Ti has been repeatedly demonstrated to fail at even
moderately elevated temperatures (300-400$^{\circ}$C) due to a combination of
non-stoichiometric Ti/Ga$_2$O$_3$ interfacial reactions and kinetically favored
Ti diffusion processes. Here we demonstrate stable Ohmic contacts for
Ga$_2$O$_3$ devices operating up to 500-600$^{\circ}$C using ultrathin Ti
layers with a self-limiting interfacial reaction. The ultrathin Ti layer in the
5nm Ti / 100nm Au contact stack is designed to fully oxidize while forming an
Ohmic contact, thereby limiting both thermodynamic and kinetic instability.
This novel contact design strategy results in an epitaxial conductive anatase
titanium oxide interface layer that enables low-resistance Ohmic contacts that
are stable both under long-term continuous operation (>500 hours) at
600$^{\circ}$C in vacuum ($\leq$ 10$^{-4}$ Torr), as well as after repeated
thermal cycling (15 times) between room temperature and 550$^{\circ}$C in
flowing N$_2$. This stable Ohmic contact design will accelerate the development
of high-temperature devices by enabling research focus to shift towards
rectifying contacts and other interfacial layers.",2304.02161v1
2023-04-16,Earth shaped by primordial H$_2$ atmospheres,"Earth's water, intrinsic oxidation state, and metal core density are
fundamental chemical features of our planet. Studies of exoplanets provide a
useful context for elucidating the source of these chemical traits. Planet
formation and evolution models demonstrate that rocky exoplanets commonly
formed with hydrogen-rich envelopes that were lost over time. These findings
suggest that Earth may also have formed from bodies with H$_2$-rich primary
atmospheres. Here we use a self-consistent thermodynamic model to show that
Earth's water, core density, and overall oxidation state can all be sourced to
equilibrium between H$_2$-rich primary atmospheres and underlying magma oceans
in its progenitor planetary embryos. Water is produced from dry starting
materials resembling enstatite chondrites as oxygen from magma oceans reacts
with hydrogen. Hydrogen derived from the atmosphere enters the magma ocean and
eventually the metal core at equilibrium, causing metal density deficits
matching that of Earth. Oxidation of the silicate rocks from solar-like to
Earth-like oxygen fugacities also ensues as Si, along with H and O, alloys with
Fe in the cores. Reaction with hydrogen atmospheres and metal-silicate
equilibrium thus provides a simple explanation for fundamental features of
Earth's geochemistry that is consistent with rocky planet formation across the
galaxy.",2304.07845v1
2023-04-18,Superconductivity up to 17 K in the high-pressure rhombohedral-I phase of ReO3: a potential oxide analogy of hydride superconductors,"As an A-site-vacant perovskite-type oxide, ReO3 undergoes sequential
pressure-driven structural transitions associated with the rotation of ReO6
octahedra. The rhombohedral-I phase stable in the pressure range of 12-38 GPa
is featured by a lattice of nearly close-packed oxygen layers intercalated with
Re cations, in reminiscent of the recently discovered superhydride
superconductors. A combined study of first-principles calculations and
transport measurements under high pressures enabled us to discover
superconductivity in the rhombohedral-I phase showing a dome-shaped Tc(P) with
a maximum Tc of 17 K at about 30 GPa. In addition to the enhanced density of
states at the Fermi level compared to that of the ambient phase, the
low-frequency vibrations of hexagonal-close-packed oxygen lattice significantly
strengthen the electron-phonon coupling, which is responsible for observed
superconductivity with a relatively high Tc. The present work thus establishes
a rare case among oxide superconductors that the light-element oxygen lattice
plays a crucial role in inducing superconductivity.",2304.09011v1
2023-04-25,Effects of Oxidation on the Tribological Properties of Diamond Sliding Against Silica. Insights from Ab initio Molecular Dynamics,"Tribological phenomena such as adhesion, friction, and wear can undermine the
functionality of devices and applications based on the diamond-silica
interface. Controlling these phenomena is highly desirable, but difficult since
extrinsic factors, such as the surface termination by adsorbed species, can
deeply affect the reactivity of diamond and its resistance to wear. In this
work, we investigate the effects of diamond oxidation by massive ab initio
molecular dynamics simulations of silica sliding against diamond surfaces
considering different surface orientations, O-coverages, and tribological
conditions. Our findings reveal a dual role of oxygen that depends on coverage.
At full coverage, the adsorbed oxygen is very effective in friction and wear
reduction because the repulsion with the silica counter-surface prevents the
formation of chemical bonds across the interface. At reduced coverage and high
pressure, Si-O-C bonds are anyway established. In this situation the presence
of oxygen results detrimental as it weakens the surface C-C bonds making the
surface more vulnerable to wear. Indeed we observed atomic wear on the C(110)
surface at 50% O-coverage under harsh tribological conditions. The mechanisms
of friction reduction and atomistic wear are explained through the analysis of
the electronic properties and surface-surface interactions. Overall, our
accurate in silico experiments shed light into the effects of adsorbed oxygen
on the tribological behavior of diamond and show how oxidized diamond can be
worn by silica.",2304.12511v1
2023-04-30,"Surface activation by electron scavenger metal nanorod adsorption on TiH2, TiC, TiN, and Ti2O3","Metal/oxide support perimeter sites are known to provide unique properties
because the nearby metal changes the local environment on the support surface.
In particular, the electron scavenger effect reduces the energy necessary for
surface anion desorption, thereby contributes to activation of the (reverse)
Mars-van Krevelen mechanism. This study investigated the possibility of such
activation in hydrides, carbides, nitrides, and sulfides. The work functions
(WFs) of known hydrides, carbides, nitrides, oxides, and sulfides with group 3,
4, or 5 cations (Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta) were calculated. The WFs
of most hydrides, carbides, and nitrides are smaller than the WF of Ag,
implying that the electron scavenger effect may occur when late transition
metal nanoparticles are adsorbed on the surface. The WF of oxides and sulfides
decrease when reduced. The surface anion vacancy formation energy correlates
well with the bulk formation energy in carbides and nitrides, while almost no
correlation is found in hydrides because of the small range of surface hydrogen
vacancy formation energy values. The electron scavenger effect is explicitly
observed in nanorods adsorbed on TiH2 and Ti2O3; the surface vacancy formation
energy decreases at anion sites near the nanorod, and charge transfer to the
nanorod happens when an anion is removed at such sites. Activation of hydrides,
carbides, and nitrides by nanorod adsorption and screening support materials
through WF calculation are expected to open up a new category of supported
catalysts.",2305.00390v1
2023-05-02,Gate-tunable spin Hall effect in an all-light-element heterostructure: graphene with copper oxide,"Graphene is a light material for long-distance spin transport due to its low
spin-orbit coupling, which at the same time is the main drawback to exhibit a
sizeable spin Hall effect. Decoration by light atoms has been predicted to
enhance the spin Hall angle in graphene while retaining a long spin diffusion
length. Here, we combine a light metal oxide (oxidized Cu) with graphene to
induce the spin Hall effect. Its efficiency, given by the product of the spin
Hall angle and the spin diffusion length, can be tuned with the Fermi level
position, exhibiting a maximum (1.8 $\pm$ 0.6 nm at 100 K) around the charge
neutrality point. This all-light-element heterostructure shows a larger
efficiency than conventional spin Hall materials. The gate-tunable spin Hall
effect is observed up to room temperature. Our experimental demonstration
provides an efficient spin-to-charge conversion system free from heavy metals
and compatible with large-scale fabrication.",2305.01787v2
2023-05-10,"Design, Modeling and Fabrication of Nanostructure Devices for Optoelectronic Applications","The current research work encompasses design modelling and fabrication of
vertically aligned nanowire metal oxide semiconductor based voltage tunable
quantum dot devices for optoelectronic applications. A novel device scheme is
proposed for developing such VTQDs by combining the effects of nanowire
geometry dependent structural confinement in transverse directions and the
voltage assisted surface quantization in longitudinal direction. The formation
of VTQDs near oxide/semiconductor interface at room temperature is predicted by
developing a self consistent quantum electrostatic simultaneous solver. The
photogeneration phenomenon and carrier transport in nanowire MOS based VTQD
devices is analytically modelled by adopting non equilibrium Greens formalism
based on second quantization field operators for incident photons and generated
photocarriers. Engineering the combined effects of structural and electrical
quantization has enabled a route for developing wavelength selective direct
colour sensors with high spectral resolution. The developed NEGF based
analytical model is further extended to obtain photocurrent which can be
utilized for harvesting solar energy. A design window is also proposed for
obtaining the desired values of solar cell performance parameters with the
optimized device parameters such as, the nanowire diameter and oxide thickness.
Finally, a patterned array of such nanowire MOS based VTQD devices is
fabricated by employing electron beam lithography. The step like behaviour in
capacitance voltage characteristics of such devices measured in situ within the
FESEM chamber confirms the formation of VTQDs at room temperature. Such
patterned nanowire MOS based VTQD devices can be utilized for the advanced
photosensing and solar energy harvesting applications.",2305.06277v1
2023-05-18,Indium-Tin-Oxide for High-performance Electro-optic Modulation,"Advances in opto-electronics are often led by discovery and development of
materials featuring unique properties. Recently the material class of
transparent conductive oxides (TCO) has attracted attention for active photonic
devices on-chip. In particular Indium Tin Oxide (ITO) is found to have
refractive index changes on the order of unity. This property makes it possible
to achieve electro-optic modulation of sub-wavelength device scales, when thin
ITO films are interfaced with optical light confinement techniques such as
found in plasmonics; optical modes are compressed to nanometer scale to create
strong light-matter-interactions. Here we review efforts towards utilizing this
novel material for high-performance and ultra-compact modulation. While high
performance metrics are achieved experimentally, there are open questions
pertaining the permittivity modulation mechanism of ITO. Furthermore, we show
that a footprint-saving waveguide inline cavity can enhance obtainable
extinction-ratio to insertion-loss ratios by about one order of magnitude over
non-cavity based version. Moreover, we offer a speed analysis that shows that
the device is resistance limited, but not capacitance or drift-carrier limited.
Interestingly, two bias options exist for ITO and we find that a
side-connection enables devices that should in principle enable several hundred
of GHz fast devices, using our routinely achievable ITO film resistivities.
Finally, we offer a brief discuss about footprint savings of compact ITO
modulators showing a 3-orders of magnitude smaller footprint over Silicon
photonic MZI-based modulators.",2305.10639v1
2023-05-21,A Critical Evaluation of a Self-Driving Laboratory for the Optimization of Electrodeposited Earth-Abundant Mixed-Metal Oxide Catalysts for the Oxygen Evolution Reaction (OER),"This work highlights the potential of earth-abundant mixed-metal oxide
catalysts for the acid-based oxygen evolution reaction. These catalysts offer
numerous combinations of metal-centre compositions, which can enhance catalytic
activity and stability compared to precious-metal-based catalysts commonly used
today. Despite substantial research in this field, there is a need for new
methods and approaches to accelerate the exploration of these materials. In
this study, we present a comprehensive approach to designing, developing, and
implementing a self-driving laboratory to optimize the electrodeposition
synthesis of amorphous mixed-metal oxide catalysts for the acidic oxygen
evolution reaction. We particularly emphasize the development of methodologies
to address experimental variability. We investigate crucial parameters and
considerations when transitioning from manual bench-top synthesis and
evaluation to automation and machine learning guided optimization. We address
both experimental and optimization algorithm considerations in the presence of
experimental variability. To illustrate our approach, we demonstrate the
optimization of CoFeMnPbOx electrodeposited catalyst materials through multiple
campaigns. Our results highlight considerations for optimizing overpotential
and stability based on the outcomes of our experiments.",2305.12541v2
2023-05-29,Spin current generation from an epitaxial tungsten dioxide WO$_{2}$,"We report on efficient spin current generation at room temperature in rutile
type WO$_{2}$ grown on Al$_{2}$O$_{3}$(0001) substrate. The optimal WO$_{2}$
film has (010)-oriented monoclinically distorted rutile structure with metallic
conductivity due to 5$\it{d}$$^2$ electrons, as characterized by x-ray
diffraction, electronic transport, and x-ray photoelectron spectroscopy. By
conducting harmonic Hall measurement in Ni$_{81}$Fe$_{19}$/WO$_{2}$ bilayer, we
estimate two symmetries of the spin-orbit torque (SOT), i.e., dampinglike (DL)
and fieldlike ones to find that the former is larger than the latter. By
comparison with the Ni$_{81}$Fe$_{19}$/W control sample, the observed DL SOT
efficiency $\xi$$_{DL}$ of WO$_{2}$ (+0.174) is about two thirds of that of W
(-0.281) in magnitude, with a striking difference in their signs. The magnitude
of the $\xi$$_{DL}$ of WO$_{2}$ exhibits comparable value to those of widely
reported Pt and Ta, and Ir oxide IrO$_{2}$. The positive sign of the
$\xi$$_{DL}$ of WO$_{2}$ can be explained by the preceding theoretical study
based on the 4$\it{d}$ oxides. These results highlight that the epitaxial
WO$_{2}$ offers a great opportunity of rutile oxides with spintronic
functionalities, leading to future spin-orbit torque-controlled devices.",2305.17887v3
2023-05-31,Near-Atomic Scale Perspective on the Oxidation of Ti$_3$C$_2$T$_x$ MXenes: Insights from Atom Probe Tomography,"MXenes are a family of 2D transition metal carbides and nitrides with
remarkable properties and great potential for energy storage and catalysis
applications. However, their oxidation behavior is not yet fully understood,
and there are still open questions regarding the spatial distribution and
precise quantification of surface terminations, intercalated ions, and possible
uncontrolled impurities incorporated during synthesis and processing. Here,
atom probe tomography analysis of as-synthesized Ti$_3$C$_2$T$_x$ MXenes
reveals the presence of alkali (Li, Na) and halogen (Cl, F) elements as well as
unetched Al. Following oxidation of the colloidal solution of MXenes, it is
observed that the alkalies enriched in TiO$_2$ nanowires. Although these
elements are tolerated through the incorporation by wet chemical synthesis,
they are often overlooked when the activity of these materials is considered,
particularly during catalytic testing. This work demonstrates how the
capability of atom probe tomography to image these elements in 3D at the
near-atomic scale can help to better understand the activity and degradation of
MXenes, in order to guide their synthesis for superior functional properties.",2305.19822v1
2023-06-09,Dangling bonds as possible contributors to charge noise in silicon and silicon-germanium quantum dot qubits,"Spin qubits based on Si and Si$_{1-x}$Ge$_{x}$ quantum dot architectures
exhibit among the best coherence times of competing quantum computing
technologies, yet they still suffer from charge noise that limit their qubit
gate fidelities. Identifying the origins of these charge fluctuations is
therefore a critical step toward improving Si quantum-dot-based qubits. Here we
use hybrid functional calculations to investigate possible atomistic sources of
charge noise, focusing on charge trapping at Si and Ge dangling bonds (DBs). We
evaluate the role of global and local environment in the defect levels
associated with DBs in Si, Ge, and \sige alloys, and consider their trapping
and excitation energies within the framework of configuration coordinate
diagrams. We additionally consider the influence of strain and oxidation in
charge-trapping energetics by analyzing Si and Ge$_{\rm Si}$ DBs in SiO$_2$ and
strained Si layers in typical \sige quantum dot heterostructures. Our results
identify that Ge dangling bonds are more problematic charge-trapping centers
both in typical \sige alloys and associated oxidation layers, and they may be
exacerbated by compositional inhomogeneities. These results suggest the
importance of alloy homogeneity and possible passivation schemes for DBs in
Si-based quantum dot qubits and are of general relevance to mitigating possible
trap levels in other Si, Ge, and Si$_{1-x}$Ge$_{x}$-based
metal-oxide-semiconductor stacks and related devices.",2306.06229v1
2023-06-14,Radiation-Induced Degradation Mechanism of X-ray SOI Pixel Sensors with Pinned Depleted Diode Structure,"The X-ray Silicon-On-Insulator (SOI) pixel sensor named XRPIX has been
developed for the future X-ray astronomical satellite FORCE. XRPIX is capable
of a wide-band X-ray imaging spectroscopy from below 1 keV to a few tens of keV
with a good timing resolution of a few tens of $\mu$s. However, it had a major
issue with its radiation tolerance to the total ionizing dose (TID) effect
because of its thick buried oxide layer due to the SOI structure. Although new
device structures introducing pinned depleted diodes dramatically improved
radiation tolerance, it remained unknown how radiation effects degrade the
sensor performance. Thus, this paper reports the results of a study of the
degradation mechanism of XRPIX due to radiation using device simulations. In
particular, mechanisms of increases in dark current and readout noise are
investigated by simulation, taking into account the positive charge
accumulation in the oxide layer and the increase in the surface recombination
velocity at the interface between the sensor layer and the oxide layer. As a
result, it is found that the depletion of the buried p-well at the interface
increases the dark current, and that the increase in the sense-node capacitance
increases the readout noise.",2306.08716v1
2023-06-15,Vibrational Anharmonicity Assisted Phase Transitions in Perovskite Oxides under Terahertz Irradiation,"Despite extensive research interests in perovskite oxides, low energy
consumption, non-destructive and maneuverable methods for phase transition in
perovskite oxides are still the under its exploration, and the underlying
mechanisms remain ambiguous. Here, optical susceptibility including electronic
and anharmonic phononic contributions is used to evaluate Gibbs free energy
variations of $\mathrm{PbTiO}_3$ and $\mathrm{BaTiO}_3$ under terahertz
irradiation. This corresponds to an off-resonant light-controlled phase
transition, rather than the resonant approaches that excites hot carriers over
electronic band or infrared-active vibrations in the phonon band. We show that
intermediate terahertz light can trigger polarization change between
ferroelectric orientation variants of $\mathrm{PbTiO}_3$ at room temperature
300 K. Furthermore, the phase transition from low symmetric ferroelectric phase
to high symmetric paraelectric structure in $\mathrm{PbTiO}_3$ can be driven by
changing the direction and intensity of the incident light under the same
conditions. Similar results are observed in $\mathrm{BaTiO}_3$. In detail,
phonon spectrum and optical susceptibility are obviously modified and show
temperature dependence, in which we show the significant effects of anharmonic
vibration. In order to show its nonlinear optical nature, we perform an
alternating electric field dressed ab initio molecular dynamics simulation,
which maps the Raman-active phonon excitation under off-resonant terahertz
irradiation.",2306.08825v1
2023-06-22,Out-of-equilibrium charge redistribution in a copper-oxide based superconductor by time-resolved X-ray photoelectron spectroscopy,"Charge-transfer excitations are of paramount importance for understanding the
electronic structure of copper-oxide based high-temperature superconductors. In
this study, we investigate the response of a
Bi$_2$Sr$_2$CaCu$_2$O$_{\mathrm{8}+ \delta}$ crystal to the charge
redistribution induced by an infrared ultrashort pulse. Element-selective
time-resolved core-level photoelectron spectroscopy with a high energy
resolution allows disentangling the dynamics of oxygen ions with different
coordination and bonds thanks to their different chemical shifts. Our
experiment shows that the O\,$1s$ component arising from the Cu-O planes is
significantly perturbed by the infrared light pulse. Conversely, the apical
oxygen, also coordinated with Sr ions in the Sr-O planes, remains unaffected.
This result highlights the peculiar behavior of the electronic structure of the
Cu-O planes. It also unlocks the way to study the out-of-equilibrium electronic
structure of copper-oxide-based high-temperature superconductors by identifying
the O\,$1s$ core-level emission originating from the oxygen ions in the Cu-O
planes. This ability could be critical to gain information about the
strongly-correlated electron ultrafast dynamical mechanisms in the Cu-O plane
in the normal and superconducting phases.",2306.12905v1
2023-06-26,Microscopic conductivity of passive films on ferritic stainless steel for hydrogen fuel cells,"Hydrogen fuel cells offer a clean and sustainable energy conversion solution.
The bipolar separator plate, a critical component in fuel cells, plays a vital
role in preventing reactant gas cross-contamination and facilitating efficient
ion transport in a fuel cell. High chromium ferritic stainless steel with an
artificially formed thin chromium oxide passive film has recently gained
attention due to its superior electrical conductivity and corrosion resistance,
making it a suitable material for separators. In this study, we investigate the
microscopic electrical conductivity of the intrinsic passive oxide film on such
ferritic stainless steel. Through advanced surface characterization techniques
such as current sensing atomic force microscopy and scanning tunneling
microscopy/spectroscopy, we discover highly conductive regions within the film
that vary depending on location. These findings provide valuable insights into
the behavior of the passive oxide film in fuel cells. By understanding the
microscopic electrical properties, we can enhance the design and performance of
separator materials in hydrogen fuel cells. Ultimately, this research
contributes to a broader understanding of separator materials and supports the
wider application of hydrogen fuel cells.",2306.14513v1
2023-07-04,Self-Supervised Deep Learning for Model Correction in the Computational Crystallography Toolbox,"The Computational Crystallography Toolbox (CCTBX) is open-source software
that allows for processing of crystallographic data, including from serial
femtosecond crystallography (SFX), for macromolecular structure determination.
We aim to use the modules in CCTBX to determine the oxidation state of
individual metal atoms in a macromolecule. Changes in oxidation state are
reflected in small shifts of the atom's X-ray absorption edge. These energy
shifts can be extracted from the diffraction images recorded in serial
femtosecond crystallography, given knowledge of a forward physics model.
However, as the diffraction changes only slightly due to the absorption edge
shift, inaccuracies in the forward physics model make it extremely challenging
to observe the oxidation state. In this work, we describe the potential impact
of using self-supervised deep learning to correct the scientific model in CCTBX
and provide uncertainty quantification. We provide code for forward model
simulation and data analysis, built from CCTBX modules, at
https://github.com/gigantocypris/SPREAD , which can be integrated with machine
learning. We describe open questions in algorithm development to help spur
advances through dialog between crystallographers and machine learning
researchers. New methods could help elucidate charge transfer processes in many
reactions, including key events in photosynthesis.",2307.01901v1
2023-07-13,Metal Oxide-based Gas Sensor Array for the VOCs Analysis in Complex Mixtures using Machine Learning,"Detection of Volatile Organic Compounds (VOCs) from the breath is becoming a
viable route for the early detection of diseases non-invasively. This paper
presents a sensor array with three metal oxide electrodes that can use machine
learning methods to identify four distinct VOCs in a mixture. The metal oxide
sensor array was subjected to various VOC concentrations, including ethanol,
acetone, toluene and chloroform. The dataset obtained from individual gases and
their mixtures were analyzed using multiple machine learning algorithms, such
as Random Forest (RF), K-Nearest Neighbor (KNN), Decision Tree, Linear
Regression, Logistic Regression, Naive Bayes, Linear Discriminant Analysis,
Artificial Neural Network, and Support Vector Machine. KNN and RF have shown
more than 99% accuracy in classifying different varying chemicals in the gas
mixtures. In regression analysis, KNN has delivered the best results with R2
value of more than 0.99 and LOD of 0.012, 0.015, 0.014 and 0.025 PPM for
predicting the concentrations of varying chemicals Acetone, Toluene, Ethanol,
and Chloroform, respectively in complex mixtures. Therefore, it is demonstrated
that the array utilizing the provided algorithms can classify and predict the
concentrations of the four gases simultaneously for disease diagnosis and
treatment monitoring.",2307.06556v2
2023-07-18,Oxidation kinetics and non-Marcusian charge transfer in dimensionally confined semiconductors,"Electrochemical reactions represent essential processes in fundamental
chemistry that foster a wide range of applications. Although most
electrochemical reactions in bulk substances can be well described by the
classical Marcus-Gerischer charge transfer theory, the realistic reaction
character and mechanism in dimensionally confined systems remain unknown. Here,
we report the multiparametric survey on the kinetics of lateral photooxidation
in structurally identical WS2 and MoS2 monolayers, where electrochemical
oxidation occurs at the atomically thin monolayer edges. The oxidation rate is
correlated quantitatively with various crystallographic and environmental
parameters, including the density of reactive sites, humidity, temperature, and
illumination fluence. In particular, we observe distinctive reaction barriers
of 1.4 and 0.9 eV for the two structurally identical semiconductors and uncover
an unusual non-Marcusian charge transfer mechanism in these dimensionally
confined monolayers due to the limit in reactant supplies. A scenario of band
bending is proposed to explain the discrepancy in reaction barriers. These
results add important knowledge into the fundamental electrochemical reaction
theory in low-dimensional systems.",2307.08957v1
2023-08-07,The cycling mechanism of manganese-oxide cathodes in zinc batteries: A theory-based approach,"Zinc-based batteries offer good volumetric energy densities and are
compatible with environmentally friendly aqueous electrolytes. Zinc-ion
batteries (ZIBs) rely on a lithium-ion-like Zn$^{2+}$-shuttle, which enables
higher roundtrip efficiencies and better cycle life than zinc-air batteries.
Manganese-oxide cathodes in near-neutral zinc sulfate electrolytes are the most
prominent candidates for ZIBs. Zn$^{2+}$-insertion, H$^+$-insertion, and
Mn$^{2+}$-dissolution are proposed to contribute to the charge-storage
mechanism. During discharge and charge, two distinct phases are observed.
Notably, the pH-driven precipitation of zinc-sulfate-hydroxide is detected
during the second discharge phase. However, a complete and consistent
understanding of the two-phase mechanism of these ZIBs is still missing. This
paper presents a continuum full cell model supported by DFT calculations to
investigate the implications of these observations. We integrate the
complex-formation reactions of near-neutral aqueous electrolytes into the
battery model and, in combination with the DFT calculations, draw a consistent
picture of the cycling mechanism. We investigate the interplay between
electrolyte pH and reaction mechanisms at the manganese-oxide cathodes and
identify the dominant charge-storage mechanism. Our model is validated with
electrochemical cycling data, cyclic voltammograms, and in-situ pH measurments.
This allows us to analyse the influence of cell design and electrolyte
composition on cycling and optimize the battery performance.",2308.03352v1
2023-08-22,The prototypical organic-oxide interface: intra-molecular resolution of sexiphenyl on In$_2$O$_3$(111),"The performance of an organic-semiconductor device is critically determined
by the geometric alignment, orientation, and ordering of the organic molecules.
While an organic multilayer eventually adopts the crystal structure of the
organic material, the alignment and configuration at the interface with the
substrate/electrode material is essential for charge injection into the organic
layer. This work focuses on the prototypical organic semiconductor
para-sexiphenyl (6P) adsorbed on In$_2$O$_3$(111), the thermodynamically most
stable surface of the material that the most common transparent conducting
oxide, indium tin oxide (ITO) is based on. The onset of nucleation and
formation of the first monolayer are followed with atomically-resolved scanning
tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM).
Annealing to 200$^\circ$C provides sufficient thermal energy for the molecules
to orient themselves along the high-symmetry directions of the surface, leading
to a single adsorption site. The AFM data suggests a twisted adsorption
geometry. With increasing coverage, the 6P molecules first form a loose network
with poor long-range order. Eventually the molecules re-orient and form an
ordered monolayer. This first monolayer has a densely packed, well-ordered
(2$\times$1) structure with one 6P per In$_2$O$_3$(111) substrate unit cell,
i.e., a molecular density of 5.64$\times$10$^{13}$ cm$^{-2}$.",2308.11550v1
2023-08-23,"A study of Pt, Rh, Ni and Ir dispersion on anatase TiO2(101) and the role of water","Understanding how metal atoms are stabilized on metal oxide supports is
important for predicting the stability of single-atom catalysts. In this study,
we use scanning tunnelling microscopy (STM) and x-ray photoelectron
spectroscopy (XPS) to investigate four catalytically active metals - Platinum,
Rhodium, Nickel and Iridium - on the anatase TiO2(101) surface. The metals were
vapor deposited at room temperature in ultrahigh vacuum (UHV) conditions, and
also with a background water pressure of 2x10-8 mbar. Pt and Ni exist as a
mixture of adatoms and nanoparticles in UHV at low coverage, with the adatoms
immobilized at defect sites. Water has no discernible effect on the Pt
dispersion, but significantly increases the amount of Ni single atoms. Ir is
highly dispersed, but sinters to nanoparticles in the water vapor background
leading to the formation of large clusters at step edges. Rh forms clusters on
the terrace of anatase TiO2(101) irrespective of the environment. We conclude
that introducing defect sites into metal oxide supports could be a strategy to
aid the dispersion of single atoms on metal-oxide surfaces, and that the
presence of water should be taken into account in the modelling of single-atom
catalysts.",2308.11973v1
2023-09-29,Is the Mg-related GaN blue luminescence deep-level an MgO surface state?,"Mg is currently the only p-type dopant in technological use in GaN. Its
incorporation into the GaN lattice is difficult. It requires a thermal
treatment that only partially activates the Mg. To achieve moderate p-type
doping requires high doses of Mg that mostly remain inactive. High p-type
doping is thus typically achieved at the cost of certain lattice distortion and
the creation of defects. Using low-temperature surface photovoltage
spectroscopy, we obtain a wide spectrum of optical transitions within the
bandgap of Mg-doped GaN. The results reveal an optical transition from the
valence band into a deep trap around 0.49 eV above the valence band, along with
what appears to be a complimentary transition from the same trap into the
conduction band observed at 2.84 eV (coinciding with the energy of the famous
Mg-related GaN blue luminescence). The similar shape of the spectra, their
complimentary energies within the GaN gap and their opposite nature (hole vs.
electron trap) appear to be more than a coincidence suggesting that this is an
Mg-related surface state. The density of charge we calculate for this surface
state is about 2x1012 cm-2. We suggest that these small amounts of
surface-segregated Mg partially oxidize during the growth and further oxidize
during the consecutive Mg-activation heat treatment. This minute quantity of
oxidized surface Mg should be about enough to form an Mg-related surface state.
Etching the GaN with H3PO4 is shown to affect the photovoltage at the
blue-luminescence-related energy. Finally, we show that pure MgO powder
produces the same blue luminescence even at the absolute absence of GaN.",2309.17212v2
2023-10-09,"Impact of interface traps on charge noise, mobility and percolation density in Ge/SiGe heterostructures","Hole spins in Ge/SiGe heterostructure quantum dots have emerged as promising
qubits for quantum computation. The strong spin-orbit coupling (SOC),
characteristic of heavy-hole states in Ge, enables fast and all-electrical
qubit control. However, SOC also increases the susceptibility of spin qubits to
charge noise. While qubit coherence can be significantly improved by operating
at sweet spots with reduced hyperfine or charge noise sensitivity, the latter
ultimately limits coherence, underlining the importance of understanding and
reducing charge noise at its source. In this work, we study the voltage-induced
hysteresis commonly observed in SiGe-based quantum devices and show that the
dominant charge fluctuators are localized at the semiconductor-oxide interface.
By applying increasingly negative gate voltages to Hall bar and quantum dot
devices, we investigate how the hysteretic filling of interface traps impacts
transport metrics and charge noise. We find that the gate-induced accumulation
and trapping of charge at the SiGe-oxide interface leads to an increased
electrostatic disorder, as probed by transport measurements, as well as the
activation of low-frequency relaxation dynamics, resulting in slow drifts and
increased charge noise levels. Our results highlight the importance of a
conservative device tuning strategy and reveal the critical role of the
semiconductor-oxide interface in SiGe heterostructures for spin qubit
applications.",2310.05902v1
2023-10-18,Simulating high-pressure surface reactions with molecular beams,"Using a reactive molecular beam with high kinetic energy ($E_{kin}$) it is
possible to speed gas-surface reactions involving high activation barriers
($E_{act}$), which would require elevated pressures ($P_0$) if a random gas
with a Maxwell-Boltzmann distribution is used. By simply computing the number
of molecules that overcome the activation barrier in a random gas at $P_0$ and
in a molecular beam at $E_{kin}$=$E_{act}$, we establish an $E_{kin}$-$P_0$
equivalence curve, through which we postulate that molecular beams are ideal
tools to investigate gas-surface reactions that involve high activation
energies. In particular, we foresee the use of molecular beams to simulate gas
surface reactions within the industrial-range ($>$ 10 bar) using
surface-sensitive Ultra-High Vacuum (UHV) techniques, such as X-ray
photoemission spectroscopy (XPS). To test this idea, we revisit the oxidation
of the Cu(111) surface combining O$_2$ molecular beams and XPS experiments. By
tuning the kinetic energy of the O$_2$ beam in the range 0.24-1 eV we achieve
the same sequence of surface oxides obtained in Ambient Pressure Photoemission
(AP-XPS) experiments, in which the Cu(111) surface was exposed to a random
O$_2$ gas up to 1 mbar. We observe the same surface oxidation kinetics as in
the random gas, but with a much lower dose, close to the expected value derived
from the equivalence curve.",2310.12041v1
2023-11-01,Rational design of acid stable oxide catalysts for OER with OC22,"The efficiency of $H_2$ production via water electrolysis is typically
limited to the sluggish oxygen evolution reaction (OER). As such, significant
emphasis has been placed upon improving the rate of OER through the anode
catalyst. More recently, the Open Catalyst 2022 (OC22) has provided a large
dataset of density functional theory (DFT) calculations for OER intermediates
on the surfaces of oxides. When coupled with state-of-the-art graph neural
network models, total energy predictions can be achieved with a mean absolute
error as low as of 0.22 eV. In this work, we interpolated a database of the
total energy predictions for all slabs and OER surface intermediates for 4,119
oxide materialas in the original OC22 dataset using pre-trained models from the
OC22 framework. This database includes all terminations of all facets up to a
maximum Miller index of 1 with adsorption configurations for $O^*$ and $OH^*$.
To demonstrate the full utility of this database, we constructed a flexible
screening framework to identify viable candidate anode catalysts under a bulk
and nanoscale regime for OER by assessing the price, thermodynamic stability,
and resistance to corrosion, surface stability, and overpotential. Finally we
verified the overpotentials and reaction energies of the final candidate
catalysts using DFT. From our assessment, we were able to identify 48 and 69
viable candidates for OER under the bulk and nanoscale regime respectively.",2311.00784v2
2023-11-27,The influence of pinholes and weak-points in aluminium-oxide Josephson junctions,"Josephson junctions are the key components used in superconducting qubits for
quantum computing. The advancement of quantum computing is limited by a lack of
stability and reproducibility of qubits which ultimately originates in the
amorphous tunnel barrier of the Josephson junctions and other material
imperfections. Pinholes in the junction have been suggested as one of the
possible contributors to these instabilities, but evidence of their existence
and the effect they might have on transport is unclear. We use molecular
dynamics to create three-dimensional atomistic models to describe Al-AlOx-Al
tunnel junctions, showing that pinholes form when oxidation of the barrier is
incomplete. Following this we use the atomistic model and simulate the
electronic transport properties for tunnel junctions with different barrier
thicknesses using the non-equilibrium Green's function formalism. We observe
that pinholes may contribute to excess quasiparticle current flow in Al-AlOx-Al
tunnel junctions with thinner barriers, and in thicker barriers we observe
weak-points which facilitate leakage currents even when the oxide is
continuous. We find that the disordered nature of the amorphous barrier results
in significant variations in the transport properties. Additionally, we
determine the current-phase relationship for our atomistic structures,
confirming that devices with pinholes and weak-points cause a deviation from
the ideal sinusoidal Josephson relationship.",2311.15560v2
2023-11-27,Evaluation of microscale crystallinity modification induced by laser writing on Mn3O4 thin films,"Defining microstructures and managing local crystallinity allow the
implementation of several functionalities in thin film technology. The use of
ultrashort Bessel beams for bulk crystallinity modification has garnered
considerable attention as a versatile technique for semiconductor materials,
dielectrics, or metal oxide substrates. The aim of this work is the
quantitative evaluation of the crystalline changes induced by ultrafast laser
micromachining on manganese oxide thin films using micro-Raman spectroscopy.
Pulsed Bessel beams featured by a 1 micrometer-sized central core are used to
define structures with high spatial precision. The dispersion relation of Mn3O4
optical phonons is determined by considering the conjunction between X-ray
diffraction characterization and the phonon localization model. The asymmetries
in Raman spectra indicate phonon localization and enable a quantitative tool to
determine the crystallite size at micrometer resolution. The results indicate
that laser-writing is effective in modifying the low-crystallinity films
locally, increasing crystallite sizes from ~8 nm up to 12 nm, and thus
highlighting an interesting approach to evaluate laser-induced structural
modifications on metal oxide thin films.",2311.16061v1
2023-12-22,FeMnNiAlCr High Entropy Alloys with High-Efficiency Surface Oxide Solar Absorbers for Concentrating Solar Power Systems,"High entropy alloys (HEAs) have attracted substantial interest in recent
years. Thus far, most investigations have focused on their applications as
structural materials rather than functional materials. In this paper, we show
that FeMnNiAlCr HEAs can potentially be applied as both a structural and
functional material for high-efficiency concentrated solar thermal power (CSP)
systems working at >700 degrees C. The HEA itself would be used in
high-temperature tubing to carry working fluids, while its surface oxide would
act as a high-efficiency solar thermal absorber. These HEAs have demonstrated
yield strengths 2-3x greater than that of stainless steel at 700 degrees C and
a creep lifetime >800 h at 700 degrees C under a typical CSP tubing mechanical
load of 35 MPa. Their Mn-rich surface oxides maintain a high optical-to-thermal
conversion efficiency of ~87% under 1000x solar concentration for 20 simulated
day-night thermal cycles between 750 degrees C and environmental temperature.
These HEAs have also sustained immersion in unpurified bromide molten salts for
14 days at 750{\deg}C with <2% weight loss, in contrast to 70% weight loss from
a 316 stainless steel reference. The simultaneous achievement of promising
mechanical, optical, and thermochemical properties in this FeMnNiAlCr system
opens the door to new applications of HEAs in solar energy harvesting.",2312.15076v1
2024-01-02,Operando Plasma-XPS for Process Monitoring: Hydrogenation of Copper Oxide Confined Under h-BN Case Study,"We demonstrate that ambient pressure x-ray photoelectron spectroscopy (APXPS)
can be used for in situ studies of dynamic changes in surface chemistry in a
plasma environment. Hexagonal boron nitride (h-BN) was used in this study as a
model system since it exhibits a wide array of unique chemical, optical, and
electrical properties that make it a prospective material for advanced
electronics. To better understand the stability and surface chemistry of h-BN
during plasma-assisted processing, we used polycrystalline Cu foils with
single-layer h-BN, grown via chemical vapor deposition (CVD), and tracked in
real-time the plasma-induced reduction of the underlying Cu oxide using APXPS
equipped with 22 kHz 75 W discharge plasma source operating at 13 Pa. Residual
gas analysis (RGA) mass-spectra were concurrently collected during plasma-XPS
to track reaction products formed during plasma exposure. A clear reduction of
CuxO is seen, while an h-BN layer remains intact, suggesting H radical species
can attack the exposed and h-BN-covered Cu oxide patches and partially reduce
the underlying substrate. In addition to the demonstration and discussion of
plasma-XPS capabilities, our results indicate the h-BN encapsulated metallic Cu
interface might be repaired without significantly damaging the overlaying h-BN,
which is of practical importance for the development of h-BN encapsulated
devices and interfaces",2401.01434v1
2024-01-26,Solvent-Free High-Temperature Capillary Stamping of Stimuli-Responsive Polymers: Wettability Management by Orthogonal Substrate Functionalization,"The wettability of surfaces determines their antifouling, antifogging,
anti-icing, and self-cleaning properties as well as their usability for
sensing, oil-water separation, water collection, and water purification.
Solvent-free high-temperature capillary stamping of stimuli-responsive polymers
yielding arrays of stimuli-responsive polymer microdots on differently modified
substrates enables the flexible generation of switchable surfaces with
different water contact angles (WCAs). Potential problems associated with the
deposition of polymer solutions, such as the handling of volatile organic
solvents, phase separation induced by solvent evaporation, and
capillarity-driven flow processes, are circumvented. We used composite stamps
with topographically patterned contact surfaces consisting of metallic nickel
cores and porous MnO2 coatings taking up the stimuli-responsive polymers. The
short transport paths from the MnO2 contact layers to the counterpart
substrates enabled the stamping of polymer melts containing components impeding
flow, such as carbon nanotubes (CNTs). Thus-obtained arrays of polymer-CNT
hybrid microdots prevent problems associated with continuous coatings including
delamination and crack propagation. Moreover, the range within which the
properties of the stamped stimuli-responsive polymer microdots are switchable
can be tuned by orthogonal substrate modification. As an example, we stamped
hybrid microdots consisting of poly(2-(methacryloyloxy)ethyl
ferrocenecarboxylate) (PFcMA) and CNTs onto indium tin oxide (ITO) substrates.
Coating the ITO substrates with a poly(ethylene oxide)-terminated silane
shifted the WCAs obtained by switching the PFcMA between its oxidized and
reduced states by nearly 50{\deg}.",2401.14974v1
2024-01-29,Scavenging effect on plasma oxidized Gd$_2$O$_3$ grown by high pressure sputtering on Si and InP substrates,"In this work, we analyze the scavenging effect of titanium gates on metal
insulator semiconductor capacitors composed of gadolinium oxide as dielectric
material deposited on Si and InP substrates. The Gd$_2$O$_3$ film was grown by
high pressure sputtering from a metallic target followed by an in situ plasma
oxidation. The thickness of the Ti film was varied between 2.5 and 17 nm and
was capped with a Pt layer. For the devices grown on Si, a layer of 5 nm of Ti
decreases the capacitance equivalent thickness from 2.3 to 1.9 nm without
compromising the leakage current (1e-4 A cm$^{-2}$ at Vgate equal to 1 V).
Thinner Ti has little impact on device performance, while 17 nm of Ti produces
excessive scavenging. For InP capacitors, the scavenging effect is also
observed with a decrease in the capacitance equivalent thickness from 2.5 to
1.9 nm (or an increase in the accumulation capacitance after the annealing from
1.4 to 1.7-1.8 uF cm$^{-2}$). The leakage current density remains under 1e-2 A
cm$^{-2}$ at Vgate equal to 1.5 V. For these devices, a severe flatband voltage
shift with frequency is observed. This can be explained by a very high
interface trap state density (in the order of 1e13-1e14 eV$^{-1}$ cm$^{-2}$).",2401.17333v1
2024-03-06,Systematic Improvement of Quantum Monte Carlo Calculations in Transition Metal Oxides: sCI-Driven Wavefunction Optimization for Reliable Band Gap prediction,"Accurate determination of electronic properties of correlated oxides remains
a significant challenge for computational theory. Traditional Hubbard-corrected
density functional theory (DFT+U) frequently encounters limitations in
precisely capturing electron correlation, particularly when predicting band
gaps. We introduce a systematic methodology to enhance the accuracy of
diffusion Monte Carlo (DMC) simulations for both ground and excited states,
focusing on LiCoO$_2$ as a case study. By employing a selected CI (sCI)
approach, we demonstrate the capability to optimize wavefunctions beyond the
constraints of single-reference DFT+U trial wavefunctions. We show that the sCI
framework enables accurate prediction of band gaps in LiCoO$_2$, closely
aligning with experimental values and substantially improving upon traditional
computational methods. The study uncovers a nuanced mixed state of $t_{2g}$ a
$e_g$ orbitals at the band edges that is not captured by conventional
single-reference methods, further elucidating the limitations of PBE+U in
describing $d$-$d$ excitations. Our findings advocate for the adoption of
beyond-DFT methodologies, such as sCI, to capture the essential physics of
excited state wavefunctions in strongly correlated materials. The improved
accuracy in band gap predictions and the ability to generate more reliable
trial wavefunctions for DMC calculations underscore the potential of this
approach for broader applications in the study of correlated oxides. This work
not only provides a pathway for more accurate simulations of electronic
structures in complex materials but also suggests a framework for future
investigations into the excited states of other challenging systems.",2403.03466v2
2024-03-25,One-step architecture of bifunctional petal-like oxygen-deficient NiAl-LDHs nanosheets for high-performance hybrid supercapacitors and urea oxidation,"Nickel-based layered double hydroxides (LDHs) are promising electrode
materials in the fields of energy storage (supercapacitors) and conversion
(urea oxidation). The rational construction of atomic and electronic structure
is crucial for nickel-based LDHs to realize their satisfactory electrochemical
performance. Herein, we report a facile, ecofriendly, one-step synthesis
process to construct petal-like oxygen-deficient NiAl-LDH nanosheets for hybrid
super-capacitors (HSCs) and urea oxidation reaction (UOR). The asprepared
NiAl-LDH nanosheets with rich oxygen vacancies possess a large specific surface
area of 216.6 m2 g-1 and a desirable electronic conductivity of 3.45 * 10-4 S
cm-1 to deliver an ultra-high specific capacitance of 2801 F g-1 (700 C g-1) at
1 A g-1. Furthermore, high specific energy of 50.0 W h kg-1 at 400 W kg-1 and
excellent cycle stability with 91% capacitance retention after 10,000 cycles
are achieved by the NiAl-LDHs/CFP (carbon fiber paper) (+)//YP-80F (a
commercial activated carbon) (-) HSC. Besides, NiAl-LDH nanosheets also work as
an efficient electrocatalyst for UOR, which only requires 1.42 V vs. reversible
hydrogen electrode to drive 10 mA cm-2 in 1 mol L-1 KOH with 0.33 mol L-1 urea.
This remarkable performance is superior to most reported values of previous
candidates owing to the thin structure of NiAl-LDH nanosheets for exposing more
active sites and abundant oxygen vacancies. In addition, various reaction
parameters are investigated to optimize the electrochemical performance. In
general, this work paves a new way for the architecture of multifunctional
nanostructured energy materials.",2403.17038v1
2024-04-05,Reliable operation in high-mobility indium oxide thin film transistors,"Transparent oxide semiconductors (TOSs) based thin-film transistors (TFTs)
that exhibit higher field effect mobility (uFE) are highly required toward the
realization of next-generation displays. Among numerous types of TOS-TFTs,
In2O3-based TFTs are the front-running candidate because they exhibit the
highest uFE ~100 cm2/Vs. However, the device operation of In2O3 TFTs is
unreliable; a large voltage shift occurs especially when negative gate bias is
applied due to adsorption/desorption of gas molecules. Although passivation of
the TFTs is used to overcome such instability, previously proposed passivation
materials did not improve the reliability. Here, we show that the In2O3 TFTs
passivated with Y2O3 and Er2O3 films are highly reliable and do not show
threshold voltage shifts when applying gate bias. We applied positive and
negative gate bias to the In2O3 TFTs passivated with various insulating oxides
and found that only the In2O3 TFTs passivated with Y2O3 and Er2O3 films did not
exhibit threshold voltage shifts. We observed that only the Y2O3 grew
heteroepitaxially on the In2O3 crystal. This would be the origin of the high
reliability of the In2O3 TFTs passivated with Y2O3 and Er2O3 films. This
finding accelerates the development of next-generation displays using
high-mobility In2O3 TFTs.",2404.03856v1
2024-04-08,Negative Photo Conductivity Triggered with Visible Light in Wide Bandgap Oxide-Based Optoelectronic Crossbar Memristive Array for Photograph Sensing and Neuromorphic Computing Applications,"Photoresponsivity studies of wide-bandgap oxide-based devices have emerged as
a vibrant and popular research area. Researchers have explored various material
systems in their quest to develop devices capable of responding to
illumination. In this study, we engineered a mature wide bandgap oxide-based
bilayer heterostructure synaptic memristor to emulate the human brain for
applications in neuromorphic computing and photograph sensing. The device
exhibits advanced electric and electro-photonic synaptic functions, such as
long-term potentiation (LTP), long-term depression (LTD), and paired pulse
facilitation (PPF), by applying successive electric and photonic pulses.
Moreover, the device exhibits exceptional electrical SET and photonic RESET
endurance, maintaining its stability for a minimum of 1200 cycles without any
degradation. Density functional theory calculations of the band structures
provide insights into the conduction mechanism of the device. Based on this
memristor array, we developed an autoencoder and convolutional neural network
for noise reduction and image recognition tasks, which achieves a peak
signal-to-noise ratio of 562 and high accuracy of 84.23%, while consuming lower
energy by four orders of magnitude compared with the Tesla P40 GPU. This
groundbreaking research not only opens doors for the integration of our device
into image processing but also represents a significant advancement in the
realm of in-memory computing and photograph sensing features in a single cell.",2404.05701v1
1993-09-09,Effective t-J Hamiltonian for the Copper Oxides,"Starting from the Emery model, which is assumed to describe the copper oxygen
planes, and including direct oxygen hopping matrix elements, we have been able
to derive the effective t-J Hamiltonian for the copper orbitals using the
Linked Cluster Expansion Method up to fourth order in the hybridization matrix
element.",9309008v2
1996-02-28,Static and Dynamic Spin Structure Factors of Frustrated Heisenberg Antiferromagnet,"Using the modified spin-wave theory we calculate static and dynamic spin
structure factors in spin-liquid state of the J1-J2 model. The spectrum of
excitations in the vector channel is discussed. The developed technique can
also be applied to the t-J model describing copper oxide superconductors.",9602150v1
1996-11-06,Integer filling metal insulator transitions in the degenerate Hubbard model,"We obtain exact numerical solutions of the degenerate Hubbard model in the
limit of large dimensions (or large lattice connectivity). Successive
Mott-Hubbard metal insulator transitions at integer fillings occur at
intermediate values of the interaction and low enough temperature in the
paramagnetic phase. The results are relevant for transition metal oxides with
partially filled narrow degenerate bands.",9611045v1
1997-01-31,Hole Photoproduction in Insulating Copper Oxide,"To explain the experimental spectra for angle resolved photoemission we
consider a modified t-J model. The modified model includes next nearest (t')
and next next nearest (t'') hopping as well as Hubbard model corrections to the
spectral weights. A Dyson equation which relates the single hole Green's
functions for a given pseudospin and given spin is derived and is compared to
experimental results.",9702002v1
1997-03-12,Only Fermi-Liquids are Metals,"Any singular deviation from Landau Fermi-liquid theory appears to lead, for
arbitrarily small concentration of impurities coupling to a non-conserved
quantity, to a vanishing density of states at the chemical potential and
infinite resistivity as temperature approaches zero. Applications to
copper-oxide metals including the temperature dependence of the anisotropy in
resistivity, and to other cases of non Fermi-liquids are discussed.",9703122v1
1998-02-21,Quantum Mott transition in a silicon quantum dot,"Considering a double-barrier structure formed by a silicon quantum dot
covered by natural oxide, we derive simple conditions for the conductance of
the dot to become a step-like function of the number of doping atoms inside the
dot, with negligible dependence on the actual position of the dopants. The
found conditions are feasible in experimentally available structures.",9802227v1
1998-04-29,Stability of Solid State Reaction Fronts,"We analyze the stability of a planar solid-solid interface at which a
chemical reaction occurs. Examples include oxidation, nitridation, or silicide
formation. Using a continuum model, including a general formula for the
stress-dependence of the reaction rate, we show that stress effects can render
a planar interface dynamically unstable with respect to perturbations of
intermediate wavelength.",9804321v1
1998-08-27,A Progress Report on the SO(5) Theory of High T_c Superconductivity,"In this talk I give a brief update on the recent progress in the SO(5) theory
of high T_c superconductivity (Science, 275: 1089,1997). Reviewed topics
include SO(5) ladders, the unification of BCS and SDW quasi-particles in the
SO(5) theory and the microscopic origin of the condensation energy.",9808309v1
1999-06-09,Stripe Structures and the Berry-Phase Connection: Concept of Geometric Energy,"Electronic states of an $e_g$ electron are calculated in the system composed
of two MnO$_6$ octahedra with the inclusion of the Berry phase acquired by
parallel transport. Based on this calculation, a comment is made on the
controversy between ``Wigner-crystal'' and ``paired-stripe'' models for the the
insulating charge-ordered manganese oxides.",9906128v1
2002-07-04,Inversion of ARPES measurements in high Tc cuprates,"Recent energy dispersion measurements in several families of the hole-doped
copper oxides have revealed a kink in the energy vs. momentum relation. These
have tentatively been identified as due to electron phonon coupling. We invert
this data directly to determine the bosonic spectral function; the kink gives
rise to a singular function in the phonon energy region.",0207145v2
2003-03-03,Nonlinear Effects in Site Blocking Induced Oscillations,"Higher order nonlinear effects of site blocking, which induces oscillations
in the Monte Carlo simulation of CO oxidation, are outlined here. It is shown
that the rate equations which include these effects exhibit a supercritical
Hopf bifurcation in parameter domains where Monte Carlo simulations lead to
oscillations.",0303019v1
2003-08-27,Intrinsic and extrinsic inhomogeneities in mixed-valence manganites,"It is suggested that extrinsic inhomogeneities in mixed-valence manganites
deserve more attention and they should be taking into account on equal footing
with hypothetical phase separation while examinating experimental data and
developing the theoretical models of influence of stoichiometric and other
types of inhomogeneities on properties of these and other transition-metal
oxides.",0308571v1
2003-12-03,Electron-phonon interaction in cuprate-oxide superconductors,"We propose a novel electron-phonon interaction arising from the modulation of
the superexchange interaction by phonons. It is enhanced by spin and
superconducting fluctuations, which are developed mainly because of the
superexchange interaction. It must be responsible for the softening of phonons
and kinks in the dispersion relation of quasi-particles. However, the
superexchange interaction must be mainly responsible for the formation of
Cooper pairs.",0312085v1
2004-10-27,Scaling of the superfluid density in high-temperature superconductors,"A scaling relation \rho_s \simeq 35\sigma_{dc}T_c has been observed in the
copper-oxide superconductors, where \rho_s is the strength of the
superconducting condensate, T_c is the critical temperature, and \sigma_{dc} is
the normal-state dc conductivity close to T_c. This scaling relation is
examined within the context of a clean and dirty-limit BCS superconductor.
These limits are well established for an isotropic BCS gap 2\Delta and a
normal-state scattering rate 1/\tau; in the clean limit 1/\tau \ll 2\Delta, and
in the dirty limit 1/\tau > 2\Delta. The dirty limit may also be defined
operationally as the regime where \rho_s varies with 1/\tau. It is shown that
the scaling relation \rho_s \propto \sigma_{dc}T_c is the hallmark of a BCS
system in the dirty-limit. While the gap in the copper-oxide superconductors is
considered to be d-wave with nodes and a gap maximum \Delta_0, if 1/\tau >
2\Delta_0 then the dirty-limit case is preserved. The scaling relation implies
that the copper-oxide superconductors are likely to be in the dirty limit, and
that as a result the energy scale associated with the formation of the
condensate is scaling linearly with T_c. The a-b planes and the c axis also
follow the same scaling relation. It is observed that the scaling behavior for
the dirty limit and the Josephson effect (assuming a BCS formalism) are
essentially identical, suggesting that in some regime these two effects may be
viewed as equivalent. This raises the possibility that electronic
inhomogeneities in the copper-oxygen planes may play an important role in the
nature of the superconductivity in the copper-oxide materials.",0410719v2
2006-04-23,"Comment on ""Performance of a spin based insulated gate field effect transistor"" [cond-mat/0603260] [cond-mat/0603260]","In a recent e-print [cond-mat/0603260] Hall and Flatte claim that a
particular spin based field effect transistor (SPINFET), which they have
analyzed, will have a lower threshold voltage, lower switching energy and lower
leakage current than a comparable metal oxide semiconductor field effect
transistor (MOSFET). Here, we show that all three claims of HF are invalid.",0604532v1
2006-05-09,Self-Organized Networks and Lattice Effects in High Temperature Superconductors,"The entirely orbital self-organized dopant percolative filamentary model
describes many counter-intuitive chemical trends in oxide superconductors
quantitatively, especially the high superconductive transition temperatures Tc.
According to rules previously used successfully for network glasees, the host
networks are marginally stable mechanically, and the high Tc's are caused by
network softening, which produces large electron-phonon interactions at
interlayer dopants for states near the Fermi energy.",0605217v1
2006-09-11,"Inhomogeneous superconductivity and the ""pseudogap state of novel superconductors","Novel superconducting compounds such as the high Tc oxides are intrinsically
inhomogeneous systems. An inhomogeneous structure is created by doping and the
statistical nature of the distribution of dopants. Consequently, the critical
temperature is spatially dependent: Tc = Tc (r).",0609260v1
2002-04-17,The Target Silicon Detector for the FOCUS Spectrometer,"We describe a silicon microstrip detector interleaved with segments of a
beryllium oxide target which was used in the FOCUS photoproduction experiment
at Fermilab. The detector was designed to improve the vertex resolution and to
enhance the reconstruction efficiency of short-lived charm particles.",0204023v1
1997-03-08,D=9 supergravity and p-brane solitons,"We construct the N=2, D=9 supergravity theory up to the quartic fermionic
terms and derive the supersymmetry transformation rules for the fields modulo
cubic fermions. We consider a class of p-brane solutions of this theory, the
stainless p-branes, which cannot be isotropically oxidized into higher
dimensions. The new stainless elementary membrane and elementary particle
solutions are found. It is explicitly verified that these solutions preserve
half of the supersymmetry.",9703063v1
2004-05-18,"Oxidizing SuperYang-Mills from (N=4,d=4) to (N=1,d=10)","We introduce superspace generalizations of the transverse derivatives to
rewrite the four-dimensional N=4 Yang-Mills theory into the fully
ten-dimensional N=1 Yang-Mills in light-cone form. The explicit SuperPoincare
algebra is constructed and invariance of the ten-dimensional action is proved.",0405150v2
2007-06-06,Raman Spectroscopy of Nanostructures and Nanosized Materials,"The interest of micro and tip-enhanced Raman spectroscopy to analyze
nanosized and nanostructured materials, chiefly semiconductors, oxides and
pristine or functionalized carbon nanotubes, is reviewed at the light of the
contributions to this special issue. Particular attention is paid to the fact
that chemical reactions, size or shape distribution, defects, strain and
couplings may add to nano-dimensionality in defining the Raman signature.",0706.0775v1
2007-10-18,Surface Enhanced Raman Scattering Investigation of Uranium Hydride and Uranium Oxide,"The present approach to SERS does not rely on a hihj electrical conductivity
substrate or admixture to enable the SERS process. The novelty of our method is
to create an artificial periodic electron distribution on a surface by
illumination with ultraviolet radiation whose photon energy is above the
photoelectric work function of the material.",0710.3596v1
2007-12-14,Carbon in the trigonal prismatic environment of rheniums complexes,"The electronic state of carbon in trigonal prismatic environment of rheniums
was studied with electron localization function and was shown to be
characterized by sp2 hybridisation and oxidation state minus 4.",0712.2278v1
2008-05-28,Changes in the electronic structure and properties of graphene induced by molecular charge-transfer,"Interaction with electron donor and acceptor molecules such as aniline and
nitrobenzene brings about marked changes in the Raman spectrum and the
electronic structure of graphene, prepared by the exfoliation of graphitic
oxide.",0805.4242v1
2008-05-28,Nernst effect of epitaxial YBCO films doped with Ca and Zn,"We report Nernst effect measurements for some crystalline films of Ca and
Zn-doped yttrium barium copper oxide grown by pulsed laser deposition. We argue
that our results and most of the published data for LSCO are consistent with
the theory of Gaussian superconducting fluctuations.",0805.4293v1
2009-03-13,Mechanisms for higher $T_C$ in copper oxide superconductors; Ideas from band calculations,"Band calculations for the hole doped La$_2$CuO$_4$ system show that
artificial periodicities of Ba dopants can give the material different
properties than from a uniform distribution of dopants. A periodicity within
the planes make static pseudogaps which could be tuned to raise the
density-of-states (DOS) at $E_F$ and the superconducting $T_C$.
  A periodic doping dependence perpendicular to the CuO planes can increase the
matrix element for spin fluctuations.",0903.2335v1
2009-03-22,An Experimental and Kinetic Modeling Study of the Oxidation of the Four Isomers of Butanol,"Butanol, and alcohol which can be produced from biomass sources",0903.3708v1
2009-03-22,A Tentative Modeling Study of the Effect of Wall Reactions on Oxidation Phenomena,"This paper gives details of a tentative modeling study that investigates the
inhibiting effect of internal reactor walls treated with acid...",0903.3750v1
2009-10-01,Photonic Crystal Cavities in Silicon Dioxide,"One dimensional nano-beam photonic crystal cavities fabricated in silicon
dioxide are considered in both simulation and experiment. Quality factors of
over 10^4 are found via simulation, while quality factors of over 5*10^3 are
found in experiment, for cavities with mode volumes of 2.0 cubic wavelengths
(in oxide) and in the visible wavelength range (600-716nm). The dependences of
the cavity quality factor and mode volume for different design parameters are
also considered.",0910.0222v1
2009-10-19,Effect of a polymer additive on heat transport in turbulent Rayleigh-Bénard convection,"Measurements of heat transport, as expressed by the Nusselt number $Nu$, are
reported for turbulent Rayleigh-B\'enard convection of water containing up to
120 ppm by weight of poly-[ethylene oxide] with a molecular weight of
$4\times10^6$ g/mole. Over the Rayleigh number range $ 5\times 10^9 \alt Ra
\alt 7 \times 10^{10}$ $Nu$ is smaller than it is for pure water by up to 10%.",0910.3678v1
2009-10-28,Test of scaling theory in two dimensions in the presence of valley splitting and intervalley scattering in Si-MOSFETs,"We show that once the effects of valley splitting and intervalley scattering
are incorporated, renormalization group theory consistently describes the
metallic phase in silicon metal-oxide-semiconductor field-effect transistors
down to the lowest accessible temperatures.",0910.5510v1
2010-03-14,Laser-assisted coloration of Ti: oxides or nanostructures?,"Coloration of a Ti target under its ablation with picosecond laser pulses in
liquids is ascribed to the formation of self-organized nanostructures. The
density of nanostructures increases in an avalanche-like way with the number of
laser pulses. The Raman peaks observed in the laser-exposed areas may be due to
the auto-SERS effect.",1003.2796v1
2010-06-22,Coordinated Analyses of Presolar Grains in the Allan Hills 77307 and Queen Elizabeth Range 99177 Meteorites,"We report the identification of presolar silicates (~177 ppm), presolar
oxides (~11 ppm), and one presolar SiO2 grain in the Allan Hills (ALHA) 77307
chondrite. Three grains having Si isotopic compositions similar to SiC X and Z
grains were also identified, though the mineral phases are unconfirmed. Similar
abundances of presolar silicates (~152 ppm) and oxides (~8 ppm) were also
uncovered in the primitive CR chondrite Queen Elizabeth Range (QUE) 99177,
along with 13 presolar SiC grains and one presolar silicon nitride. The O
isotopic compositions of the presolar silicates and oxides indicate that most
of the grains condensed in low-mass red giant and asymptotic giant branch
stars. Interestingly, unlike presolar oxides, few presolar silicate grains have
isotopic compositions pointing to low-metallicity, low-mass stars (Group 3).
The 18O-rich (Group 4) silicates, along with the few Group 3 silicates that
were identified, likely have origins in supernova outflows. This is supported
by their O and Si isotopic compositions. Elemental compositions for 74 presolar
silicate grains were determined by scanning Auger spectroscopy. Most of the
grains have non-stoichiometric elemental compositions inconsistent with
pyroxene or olivine, the phases commonly used to fit astronomical spectra, and
have comparable Mg and Fe contents. Non-equilibrium condensation and/or
secondary alteration could produce the high Fe contents. Transmission electron
microscopic analysis of three silicate grains also reveals non-stoichiometric
compositions, attributable to non-equilibrium or multistep condensation, and
very fine scale elemental heterogeneity, possibly due to subsequent annealing.
The mineralogies of presolar silicates identified in meteorites thus far seem
to differ from those in interplanetary dust particles.",1006.4389v2
2010-08-12,Anisotropy of DC Electric Field Influence on Acoustic Wave Propagation in Piezoelectric Plate,"Anisotropy of dc electric field influence on the different types of acoustic
waves in piezoelectric plate has been investigated by means of computer
simulation. Detail calculations have made for bismuth germanium oxide crystals.",1008.2058v1
2010-10-07,Cathodoluminescence and Selective Emission of Er3+ in Oxides,"The dependence of the Er3+ cathodoluminescence and selective emission on the
power of the YAG:Er3+ and Er2O3 excitation by an electron beam is
spectroscopically studied for applications in high-intensity radiation sources
of the visible and near-IR spectral ranges.",1010.1452v1
2010-11-24,LaAlO3/SrTiO3-Based Device Concepts,"This is a book chapter that covers several device concepts based on the
LaAlO3/SrTiO3 interface.",1011.5290v1
2011-01-15,On the hardness of boron (III) oxide,"Our findings show that the hardness of glass-like B2O3 is of about 1.5 GPa,
while the hardness of the high-pressure phase is higher by a factor of 10
(16(5) GPa) and comparable with the hardness (16 GPa) of the WC-10% Co hard
alloy.",1101.2965v1
2011-10-19,"Growth of narrow-neck, epitaxial and nearly spherical Ge nanoislands on air-exposed Si(111)-(7$\times$7) surfaces","Growth of narrow-neck, epitaxial as well as non-epitaxial and nearly
spherical Ge islands on air-exposed Si(111)-(7\times7) surfaces has been
investigated by in-situ scanning tunnelling microscopy (STM) and ex-situ high
resolution cross-sectional transmission electron microscopy (HRXTEM). A thin
oxide is formed on Si(111)-(7\times7) surfaces via air exposure. Ge islands are
grown on this oxide. STM measurements reveal the growth of very small (~2 nm
diameter) Ge islands with a high number density of about 1.8\times10^12 cm-2.
The island size has been found to depend on the amount of deposited Ge as well
as the substrate temperature during Ge deposition. HRXTEM micrographs reveal
that the islands are nearly spherical in shape, making narrow-neck contact with
the substrate surface. At 520{\deg}C growth temperature both epitaxial and
non-epitaxial islands grow. However, at 550{\deg}C, Ge islands predominantly
grow epitaxially by a narrow-contact with Si via voids in the oxide layer.
Growth of vertically elongated Ge islands is also observed in HRXTEM
measurements with a very small diameter-to-height aspect ratio (~0.5-1), a
hitherto unreported feature of epitaxial Ge growth on Si surfaces. In addition,
stacking fault and faceting are observed in islands as small as 5 nm diameter.
Ge islands, not even in contact with the Si substrate, appear to be in
epitaxial alignment with the Si substrate. The island size distribution is
essentially monomodal. As the contact area of Ge islands with Si through the
voids in the oxide layer can be controlled via growth temperature, the results
indicate that tunability of the potential barrier at the interface and
consequently the tunability of electronic levels and optical properties can be
achieved by the control of growth temperature.",1110.4242v1
2012-03-03,Suppression of inelastic electron-electron scattering in Anderson Insulators,"We report on measurements of absorption from applied ac fields in
Anderson-localized indium-oxide films. The absorption shows a roll-off at a
frequency that is much smaller than the electron-electron scattering rate
measured at the same temperature in diffusive samples of this material. These
results are interpreted as evidence for discreteness of the energy spectrum.",1203.0673v2
2012-03-30,Rethinking the Paleoproterozoic Great Oxidation Event: A Biological Perspective,"Competing geophysical/geochemical hypotheses for how Earth's surface became
oxygenated - organic carbon burial, hydrogen escape to space, and changes in
the redox state of volcanic gases - are examined and a more biologically-based
hypothesis is offered in response. It is argued that organic carbon burial is
of minor importance to the accumulation of oxygen in a mainly anoxic world
where aerobic respiration is not globally significant. Thus, for the Great
Oxidation Event (GOE) ~ 2.4 Gyr ago, an increasing flux of O2 due to its
production by an expanding population of cyanobacteria is parameterized as the
primary source of O2. Various factors would have constrained cyanobacterial
proliferation and O2 production during most of the Archean and therefore a long
delay between the appearance of cyanobacteria and oxygenation of the atmosphere
is to be expected. Destruction of O2 via CH4 oxidation in the atmosphere was a
major O2 sink during the Archean, and the GOE is explained to a significant
extent by a large decline in the methanogen population and corresponding CH4
flux which, in turn, was caused primarily by partial oxygenation of the surface
ocean. The partially oxygenated state of these waters also made it possible for
an aerobic methanotroph population to become established. This further
contributed to the large reduction in the CH4 flux to the atmosphere by
increasing the consumption of CH4 diffusing upwards from the deeper anoxic
depths of the water column as well as any CH4 still being produced in the upper
layer. The reduction in the CH4 flux lowered the CH4 oxidation sink for O2 at
about the same time the metamorphic and volcanic gas sinks for O2 also
declined. As the O2 source increased from an expanding population of
cyanobacteria - triggered by a burst of continent formation ~ 2.7-2.4 Gyr ago -
the atmosphere flipped and became permanently oxygenated.",1203.6701v1
2012-06-15,Hubbard U and Hund's Exchange J in Transition Metal Oxides: Screening vs. Localization Trends from Constrained Random Phase Approximation,"In this work, we address the question of calculating the local effective
Coulomb interaction matrix in materials with strong electronic Coulomb
interactions from first principles. To this purpose, we implement the
constrained random phase approximation (cRPA) into a density functional code
within the linearized augmented plane wave (LAPW) framework.
  We apply our approach to the 3d and 4d early transition metal oxides SrMO3
(M=V, Cr, Mn) and (M=Nb, Mo, Tc) in their paramagnetic phases. For these
systems, we explicitly assess the differences between two physically motivated
low-energy Hamiltonians: The first is the three-orbital model comprising the
t2g states only, that is often used for early transition metal oxides. The
second choice is a model where both, metal d- and oxygen p-states are retained
in the construction of Wannier functions, but the Hubbard interactions are
applied to the d-states only (""d-dp Hamiltonian""). Interestingly, since -- for
a given compound -- both U and J depend on the choice of the model, so do their
trends within a family of these compounds. In the 3d perovskite series SrMO3
the effective Coulomb interactions in the t2g Hamiltonian decrease along the
series, due to the more efficient screening. The inverse -- generally expected
-- trend, increasing interactions with increasing atomic number, is however
recovered within the more localized ""d-dp Hamiltonian"". Similar conclusions are
established in the layered 4d perovskites series Sr2MO4 (M=Mo, Tc, Ru, Rh).
Compared to their isoelectronic and isostructural 3d analogues, the 4d 113
perovskite oxides SrMO3 (M=Nb, Mo, Tc) exhibit weaker screening effects.
Interestingly, this leads to an effectively larger U on 4d shells than on 3d
when a t2g model is constructed.",1206.3533v2
2012-09-20,Compositional disorder and tranport peculiarities in the amorphous indium-oxides,"(abridged) We present results of the disorder-induced
metal-insulator-transition (MIT) in three-dimensional amorphous indium-oxide
films. The amorphous version studied here differs from the one reported earlier
[PRB 46, 10917 (1992)] in that it has a much lower carrier concentration. As a
measure of the static disorder we use the dimensionless parameter kFl. Thermal
annealing is employed as the experimental handle to tune the disorder. On the
metallic side of the transition, the low temperature transport exhibits
weak-localization and electron-electron correlation effects characteristic of
disordered electronic systems. The MIT occurs at a kFl~0.3 for both versions of
the amorphous material. However, in contrast with the results obtained on the
electron-rich version of this system, no sign of superconductivity is seen down
to ~0.3K even for the most metallic sample used in the current study. This
demonstrates that using kFl as a disorder parameter for the
superconductor-insulator-transition (SIT) is an ill defined procedure. A
microstructural study of the films, employing high resolution chemical
analysis, gives evidence for spatial fluctuations of the stoichiometry. This
brings to light that, while the films are amorphous and show excellent
uniformity in transport measurements of macroscopic samples, they contain
compositional fluctuations that extend over mesoscopic scales. It is argued
that this compositional disorder may be the reason for the apparent violation
of the Ioffe-Regel criterion in the two versions of the amorphous indium-oxide.
However, more dramatic effects due to this disorder are expected when
superconductivity sets in, which are in fact consistent with the prominent
transport anomalies observed in the electron-rich version of indium-oxide. The
relevance of compositional disorder to other systems near their SIT is
discussed.",1209.4417v1
2012-11-30,Functional robust regression for longitudinal data,"We present a robust regression estimator for longitudinal data, which is
especially suited for functional data that has been observed on sparse or
irregular time grids. We show by simulation that the proposed estimators
possess good outlier-resistance properties compared with the traditional
functional least-squares estimator. As an example of application, we study the
relationship between levels of oxides of nitrogen and ozone in the city of San
Francisco.",1211.7332v1
2013-02-06,Flexible transistors exploiting P3HT on paper substrates and graphene oxide films as gate dielectrics: proof of concept,"In this paper we report: the use of GO in aqueous solution as a gate
dielectric material, its application to a MOS transistor based on organic
semiconductor and the use of paper as substrate material.",1302.1291v1
2013-11-21,Miscibility of blends of poly(methyl methacrylate) and oligodiols based on a bisphenol A nucleus and ethylene oxide or propylene oxide branches,"Cloud-point curves of blends of poly(methyl methacrylate) (PMMA) with a
series of oligodiols based on a bisphenol A nucleus and short branches of
poly(ethylene oxide) or poly(propylene oxide) (BPA-EO or BPA-PO), and with PEO
and PPO oligomers, were obtained using a light transmission device.
Experimental results were fitted with the Flory- Huggins model using an
interaction parameter depending on both temperature and composition. For
PMMA/PEO and PMMA/PPO blends, the miscibility increased when increasing the
size of the diol, due to the significant decrease in the entropic and enthalpic
terms contributing to the interaction parameter. This reflected the decrease in
the selfassociation of solvent molecules and in the contribution of terminal OH
groups to the mismatching of solubility parameters. For PMMA/BPA-EO blends, a
decrease of the entropic contribution to the interaction parameter when
increasing the size of the oligodiol was also found. However, the effect was
counterbalanced by the opposite contribution of combinatorial terms leading to
cloud-point curves located in approximately the same temperature range. For
PMMA/BPA-PO blends, the interaction parameter exhibited a very low value. In
this case, the effect of solvent size was much more important on combinatorial
terms than on the interaction parameter, leading to an increase in miscibility
when decreasing the oligodiol size. For short BPA-PO oligodiols no phase
separation was observed. The entropic contribution of the interaction parameter
exhibited an inverse relationship with the size of the oligodiols, independent
of the nature of the chains bearing the hydroxyls and the type of OH groups
(primary or secondary). This indicates that the degree of self-association of
solvent molecules through their OH terminal groups, was mainly determined by
their relative sizes.",1311.5452v1
2014-09-23,Study Of Organic Monolayer Modified Metal Oxide Semiconductor Devices For High Temperature Applications,"We report fabrication and characteristics of an organic monolayer based Metal
Oxide Semiconductor (MOS) device. In place of SiO2 oxide layer in the MOS
configuration, we used 1H, 1H, 2H, 2H- perfluorooctyl trichlorosilane (FOTS)
self-assembled monolayer as a substitution. The MOS device was fabricated by
simple steps like sputter deposition and dip coating method. The device was
heat treated to different temperatures to understand its performance and
efficiency for high temperature application. The MOS device was heated to
150{\deg} C, 350{\deg}C and 550{\deg}C and the energy band gap was found to be
varied in the order 2.5 eV, 3.0 eV and 3.4eV respectively. For non-heated
sample, the energy band gap is 3.4 eV. The results shows that the parameters
like charge mobility ({\mu}), energy band gap, and resistance were found to be
decreased after the heat treatment. The change in the energy band gap due to
heat treatment has significantly influenced the I-V and the impedance
characteristics. We observed that the MOS device started to conduct between 1V
to 3V, further the device conduct till 20V. Impedance analysis show that device
heated to 350 {\deg}C shows the low impedance but the impedance starts to
increase for further heating up to 550{\deg}C. Using Multi Dielectric Energy
Band Diagram Program (MEBDP) we studied the MOS structure and C-V
characteristics and temperature dependent behavior of the devices from 100K to
600K. Our experimental work and simulation studies confirm that the FOTS SAM
substituted MOS device could be used for high temperature applications. The
experimental observations are well supported by the simulation results. This
study shows that the FOTS organic monolayer are promising substitute for SiO2
oxide layer in the MOS and MOSFET which could be used high temperature
applications.",1409.6401v1
2014-12-15,"Defect physics, delithiation mechanism, and electronic and ionic conduction in layered lithium manganese oxide cathode materials","Layered LiMnO$_2$ and Li$_2$MnO$_3$ are of great interest for lithium-ion
battery cathodes because of their high theoretical capacities. The practical
application of these materials is, however, limited due to poor electrochemical
performance. We herein report a comprehensive first-principles study of defect
physics in LiMnO$_2$ and Li$_2$MnO$_3$ using hybrid-density functional
calculations. We find that manganese antisites have low formation energies in
LiMnO$_2$ and may act as nucleation sites for the formation of impurity phases.
The antisites can also occur with high concentrations in Li$_2$MnO$_3$;
however, unlike in LiMnO$_2$, they can be eliminated by tuning the experimental
conditions during preparation. Other intrinsic point defects may also occur and
have an impact on the materials' properties and functioning. An analysis of the
formation of lithium vacancies indicates that lithium extraction from LiMnO$_2$
is associated with oxidation at the manganese site, resulting in the formation
of manganese small hole polarons; whereas in Li$_2$MnO$_3$ the intrinsic
delithiation mechanism involves oxidation at the oxygen site, leading to the
formation of bound oxygen hole polarons $\eta_{\rm O}^{+}$. The layered oxides
are found to have no or negligible bandlike carriers and they cannot be doped
n- or p-type. The electronic conduction proceeds through hopping of hole and/or
electron polarons; the ionic conduction occurs through lithium monovacancy
and/or divacancy migration mechanisms. Since $\eta_{\rm O}^{+}$ is not stable
in the absence of negatively charged lithium vacancies in bulk Li$_2$MnO$_3$,
the electronic conduction near the start of delithiation is likely to be poor.
We suggest that the electronic conduction associated with $\eta_{\rm O}^{+}$
and, hence, the electrochemical performance of Li$_2$MnO$_3$ can be improved
through nanostructuring and/or ion substitution.",1412.4688v2
2015-05-30,Superconducting interaction charge in thallium-based high-Tc cuprates: Roles of cation oxidation state and electronegativity,"Superconductivity in the Tl-based cuprates encompasses a notably broad range
of measured optimal transition temperatures Tc0, ranging from lowest in the
charge-depleted Tl-1201 compounds
(Tl$_{1-x}$(Ba/Sr)$_{1+y}$La$_{1-y}$CuO$_{5-{\delta}}$), such as
Tl$_{0.7}$LaSrCuO$_5$ (37 K) and TlBa$_{1.2}$La$_{0.8}$CuO$_5$ (45.4 K), to
highest in the Tl-1223 compound TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$ (133.5
K). Seven Tl-based cuprates are considered and compared using the model of
superconductive pairing via electronic interactions between two physically
separated charge reservoirs, where Tc0 $\propto$
({\sigma}{\eta}/A)$^{1/2}${\zeta}$^{-1}$ is determined by the superconducting
interaction charge fraction {\sigma} the number {\eta} of CuO$_2$ layers, and
the basal-plane area A, each per formula unit, and the transverse distance
{\zeta} between interacting layers. Herein it is demonstrated that {\sigma}
follows from the elemental electronegativity and the oxidation state of Tl, and
other structurally analogous cations. The comparatively lower elemental
electronegativity of Tl, in conjunction with its oxidation state, explains the
higher {\sigma} and Tc0 values in the Tl-based compounds relative to their
Bi-based cuprate homologues. A derivation of {\sigma} is introduced for the
optimal Tl$_2$Ba$_2$Ca$_{{\eta}-1}$Cu$_{\eta}$O$_{2{\eta}+4}$ (for {\eta} = 1,
2, 3) compounds, which exhibit a Tl oxidation state at or near +3, obtaining
the fundamental value {\sigma}$_0$ = 0.228 previously established for
YBa$_2$Cu$_3$O$_{6.92}$. Also reported is the marked enhancement in {\sigma}
associated with Tl$^{+1}$ and analogous inner-layer cations relative to
higher-valence cations. For a model proposition of {\sigma} = {\sigma}$_0$, the
fractional Tl$^{+1}$ content of the mixed-valence compound,
TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$, is predicted to be 1/3 at
optimization, in agreement ...",1506.00065v1
2015-10-17,In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors,"Memristors are receiving keen interest because of their potential varied
applications and promising large-scale information storage capabilities.
Tantalum oxide is a memristive material that has shown promise for
high-performance nonvolatile computer memory. The microphysics has been elusive
because of the small scale and subtle physical changes that accompany
conductance switching. In this study, we probed the atomic composition, local
chemistry and electronic structure of functioning tantalum oxide memristors
through spatially mapped O K-edge x-ray absorption. We developed a
time-multiplexed spectromicroscopy technique to enhance the weak and possibly
localized oxide modifications with spatial and spectral resolutions of <30 nm
and 70 meV, respectively. During the initial stages of conductance switching of
a micrometer sized crosspoint device, the spectral changes were uniform within
the spatial resolution of our technique. When the device was further driven
with millions of high voltage-pulse cycles, we observed lateral motion and
separation of ~100 nm-scale agglomerates of both oxygen interstitials and
vacancies. We also demonstrate a unique capability of this technique by
identifying the relaxation behavior in the material during electrical stimuli
by identifying electric field driven changes with varying pulse widths. In
addition, we show that changes to the material can be localized to a spatial
region by modifying its topography or uniformity, as against spatially uniform
changes observed here during memristive switching. The goal of this report is
to introduce the capability of time-multiplexed x-ray spectromicroscopy in
studying weak-signal transitions in inhomogeneous media through the example of
the operation and temporal evolution of a memristor.",1510.05066v1
2015-11-30,Plasmonic Induced Potential in Metal-Semiconductor Composits,"We utilize experimental tools such as conductive atomic force microscopy and
electrostatic force microscopy on photo-excited arrays of gold nanoparticles on
indium tin oxide substrate. The nanoparticles are partially covered by a thin
semiconductor polymer. The change in the current and potential profiles of the
composite metal-semiconductor sample after excitation at plasmonic resonance
frequency of metallic nanoparticles is analyzed.",1511.09162v1
2016-03-19,"Quantitative use of electron energy-loss spectroscopy Mo-M$_{2,3}$ edges for the study of molybdenum oxides","Because of the large energy separation between O-K and Mo-L$_{2,3}$ edges,
extracting precise and reliable chemical information from core-loss EELS
analyze of molybdenum oxides has always been a challenge. In this regard
Mo-M$_{2,3}$ edges represents an interesting alternative as they are situated
close to the O-K edges. They should allow thus the extraction of a wealth of
chemical information from the same spectra. However the main difficulty to
overcome in order to work properly with these edges is the delayed maxima of
the Mo-M$_{4,5}$ edges which hinders the automated background subtraction with
the usual inverse power low function. In this study we propose another
background subtraction method specifically designed to overcome this obstacle
and we apply it to the study of MoO3 and MoO2. We are able to show that
quantitative chemical information can be precisely and accurately determined
from the joined analyze of O-K and Mo-M$_{2,3}$ edges. In particular k-factors
are derived as a function of the integration window width and standard errors
close to 2% are reported. The possibility to discriminate the two oxides thanks
to chemical shifts and energy-loss near-edge structures is also investigated
and discussed. Furthermore the M$_3$/M$_2$ ratios are derived and are found to
be strongly dependent on the local chemical environment. This result is
confirmed by multiplet calculations for which the crystal field parameters have
been determined by ab initio calculations. The whole methodology as well as the
conclusions presented in this paper should be easily transposable to any
transitions metal oxides of the 4d family. This work should open a new and
easier way regarding the quantitative EELS analyses of these compounds.",1603.06070v1
2016-06-09,Can the structure of amorphous indium gallium zinc oxide be described in terms of a few polyhedral motifs?,"The coordination polyhedra around the cations are the building blocks of
ionic solids. In context of amorphous InGaZn oxide (a-IGZO), even though the
coordination polyhedra are irregularly arranged, it will be beneficial to
identify them. In this work, we address the questions, (a) is it possible to
classify all the polyhedra that occur in a-IGZO into only a few distinct
groups? and (b) are these the same polyhedral motifs as those observed in the
crystalline indium gallium zinc oxide (c-IGZO) or other related crystalline
oxides of indium, gallium and zinc? Therefore, in this first principles based
study, a large number (ten) of equivalent samples of a-IGZO were prepared by ab
initio melt-and-quench molecular dynamics, so that several distinct samples of
the amorphous landscape are obtained. The combination of all these structures
thus obtained is a better representation of a real a-IGZO sample. For the ten
samples containing 360 cations, we propose a simpler and more accurate method
for determining the coordination number of each polyhedron, which was verified
by charge density plots. Based on a method of comparing bond angles between
metal and oxygen atoms, the identified polyhedra were matched to the polyhedral
motifs present in the related crystalline systems, such as, InGaZnO4, In2O3,
Ga2O3 and ZnO. We find, the a-IGZO primarily consists of the following
polyhedra: a tetrahedron from space group 199 and an octahedron from space
group 206 of In2O3; a tetrahedron from space group 12 and an octahedron from
space group 167 of Ga2O3; a tetrahedron from space group 186 of ZnO; zinc and
gallium trigonal bipyramids from c-IGZO; and one zinc 4-fold, one zinc 5-fold
and one indium 5-fold coordination polyhedra that occur only in the amorphous
phase. We are able to reduce the description of structure from 360 to 10 groups
of polyhedra. The benefits of this identification could be enormous.",1606.02842v1
2016-06-27,Structural and electronic phase evolution of Tin dioxide,"We investigate the effect of controlled annealing on the structural and
electronic phase evolution of Tin dioxide from Tin (II) oxyhydroxide prepared
by simple precipitation method. Thermogravimetric analysis suggests a complex
weight loss-gain process involved, passing through an intermediate phase of tin
oxide nanoparticles. The probable structural and electronic phase evolution is
discussed using detailed X-ray diffraction and X-ray photoelectron spectroscopy
investigations.",1606.08137v1
2018-11-14,Complex symplectic structures on Lie algebras,"We investigate Lie algebras endowed with a complex symplectic structure and
develop a method, called \emph{complex symplectic oxidation}, to construct
certain complex symplectic Lie algebras of dimension $4n+4$ from those of
dimension $4n$. We specialize this construction to the nilpotent case and apply
complex symplectic oxidation to classify eight-dimensional nilpotent complex
symplectic Lie algebras.",1811.05969v1
2020-07-10,Quantum interference effects of out-of-plane confinement on two-dimensional electron systems in oxides,"It was recently discovered that a conductive, metallic state is formed on the
surface of some insulating oxides. Firstly observed on SrTiO$_3$(001), it was
then found in other compounds as diverse as anatase TiO$_2$, KTaO$_3$,
BaTiO$_3$, ZnO, and also on different surfaces of SrTiO$_3$ (or other oxides)
with different symmetries. The spatial extension of the wave function of this
electronic state is of only a few atomic layers. Experiments indicate its
existence is related to the presence of oxygen vacancies induced at or near the
surface of the oxide. In this article we present a simplified model aimed at
describing the effect of its small spatial extension on measurements of its 3D
electronic structure by angular resolved photoemission spectroscopy (ARPES).
For the sake of clarity, we base our discussion on a simple tight binding
scheme plus a confining potential that is assumed to be induced by the oxygen
vacancies. Our model parameters are, nevertheless, obtained from density
functional calculations. With this methodology we can explain from a very
simple concept of selective interference the ""wobbling"", i.e., the
photoemission intensity modulation and/or apparent dispersion of the Fermi
surface and spectra along the out-of-plane ($k_z$) direction, and the ""mixed
2D/3D"" characteristics observed in some experiments. We conclude that the
critical model parameters for such an effect are the relative strength of the
electronic hopping of each band and the height/width aspect ratio of the
surface confining potential. By considering recent photoemission measurements
under the light of our findings, we can get relevant information on the
electronic wave functions and of the nature of the confining potential.",2007.05605v1
2010-05-13,Photostimulated spin-flip and the photodynamic therapeutic effect of fullerene solutions,"A new mechanism of photodynamic therapeutic effect of fullerene solution is
suggested. Spin flip of electrons in oxygen molecule in the vicinity of
negative-positive ion pair of fullerene lays the foundation of high oxidative
activity of complexes C60(minus) -O2 and C60(plus)-O2.",1005.2383v1
2014-03-10,Order quantification of hexagonal periodic arrays fabricated by in situ solvent-assisted nanoimprint lithography of block copolymers,"Directed self-assembly of block copolymer polystyrene-b-polyethylene oxide
(PS-b-PEO) thin film was achieved by one-pot methodology of solvent vapour
assisted nanoimprint lithography (SAIL).",1403.2250v1
2016-11-28,Numerical Study of Pseudo-gap Anisotropy for a Tight Binding Band,"The Fermi surface anisotropy of a pseudo-gap in the spectral weight, caused
by superconducting fluctuations or anti-ferromagnetic fluctuations, is
calculated for a tight binding band. The importance of the Fermi surface saddle
point, or hot spot, is illustrated. A peak-dip-hump structure due to a finite
frequency mode, is briefly explored. The connection to high temperature
superconducting copper-oxides is discussed.",1611.09305v1
2018-05-09,Low-Noble-Metal-Loading Hybrid Catalytic System for Oxygen Reduction Utilizing Reduced-Graphene-Oxide-Supported-Platinum Aligned with Carbon-Nanotube-Supported Iridium,"Hybrid systems composed of the reduced graphene oxide-supported platinum and
multiwall carbon nanotubes-supported iridium (both noble metals utilized at low
loadings on the level of 15 and < 5 microg cm-2, respectively) have been
considered as catalytic materials for the reduction of oxygen in acid media
(0.5 mol dm-3 H2SO4). The electrocatalytic activity toward reduction of oxygen
and formation of hydrogen peroxide intermediate have been tested using rotating
ring-disk electrode voltammetric experiments. The efficiency of the proposed
catalytic systems has also been addressed by performing galvanodynamic
measurements with gas diffusion electrode half-cell at 80 {\deg}C. The role of
carbon nanotubes is to improve charge distribution at the electrocatalytic
interface and facilitate the transport of oxygen and electrolyte in the
catalytic systems by lowering the extent of reduced graphene oxide restacking
during solvent evaporation. The diagnostic electrochemical experiments reveal
that at iridium-containing systems not only higher disk currents, but also much
smaller ring currents have been produced (compared to reduced graphene
oxide-supported platinum and its composite with bare carbon nanotubes), clearly
implying formation of lower amounts of the undesirable hydrogen peroxide
intermediate. The enhancement effect coming from the addition of traces of
iridium (supported onto carbon nanotubes) to Pt, utilized at low loading, may
originate from the high ability of Ir to induce decomposition of the
undesirable hydrogen peroxide intermediate. There is a competition between
activation (due to the presence of small amounts of Ir) and dilution (by carbon
nanotubes) of Pt active centers in hybrid systems, therefore special attention
is paid to the adjustment of their composition.",1805.03390v1
2016-12-17,Electrons and polarons at oxide interfaces explored by soft-X-ray ARPES,"Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical
specificity allows access to fundamental electronic structure characteristics -
momentum-resolved spectral function, band structure, Fermi surface - of systems
difficult and even impossible for the conventional ARPES such as
three-dimensional materials, buried interfaces and impurities. After a recap of
the spectroscopic abilities of SX-ARPES, we review its applications to oxide
interfaces, focusing on the paradigm LaAlO3-SrTiO3 interface. Resonant SX-ARPES
at the Ti L-edge accentuates photoemission response of the mobile interface
electrons and exposes their dxy-, dyz- and dxz-derived subbands forming the
Fermi surface in the interface quantum well. After a recap of the
electron-phonon interaction physics, we demonstrate that peak-dip-hump
structure of the experimental spectral function manifests the Holstein-type
large polaron nature of the interface charge carriers, explaining their
fundamentally reduced mobility. Coupling of the charge carriers to polar soft
phonon modes defines dramatic drop of mobility with temperature. Oxygen
deficiency adds another dimension to the rich physics of LaAlO3-SrTiO3
resulting from co-existence of mobile and localized electrons introduced by
oxygen vacancies. Oxygen deficiency allows tuning of the polaronic coupling and
thus mobility of the charge carriers, as well as of interfacial ferromagnetism
connected with various atomic configurations of the vacancies. Finally, we
discuss spectroscopic evidence of phase separation at the LaAlO3-SrTiO3
interface. Concluding, we put prospects of SX-ARPES for complex
heterostructures, spin-resolving experiments opening the totally unexplored
field of interfacial spin structure, and in-operando field-effect experiments
paving the way towards device applications of the reach physics of oxide
interfaces.",1612.05791v2
2017-10-16,Is stripe incommensurability in La_{2-x}Sr_xCoO_4 proportional to doping?,"The longstanding notion of stripe incommensurability being proportional to
doping, \delta(x) ~ x, in lanthanum transition-metal oxides, La_{2-x}Sr_xTmO_4
(Tm = Cu, Ni, Co), is partly borne out by experiment but also plagued with
exceptions. Future neutron-scattering experiments on cobaltates could provide a
clear distinction whether a linear or square-root dependence, \delta(x) ~
sqrt(x - x_0), is valid.",1710.06773v1
2018-01-28,Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor,"Using ALMA, we observed the stellar wind of two oxygen-rich Asymptotic Giant
Branch (AGB) stars, IK Tau and R Dor, between 335 and 362 GHz. One aim was to
detect metal oxides and metal hydroxides (AlO, AlOH, FeO, MgO, MgOH), some of
which are thought to be direct precursors of dust nucleation and growth. We
report on the potential first detection of FeO (v=0, Omega=4, J=11-10) in RDor
(mass-loss rate, Mdot, ~1e-7 Msun/yr). The presence of FeO in IK Tau (Mdot~5e-6
Msun/yr) cannot be confirmed due to a blend with 29SiS, a molecule that is
absent in R Dor. The detection of AlO in R Dor and of AlOH in IK Tau was
reported earlier by Decin et al. (2017). All other metal oxides and hydroxides,
as well as MgS, remain undetected. We derive a column density N(FeO) of
1.1+/-0.9e15 cm^{-2} in R Dor, or a fractional abundance [FeO/H]~1.5e-8
accounting for non-LTE effects. The derived fractional abundance [FeO/H] is a
factor ~20 larger than conventional gas-phase chemical kinetic predictions.
This discrepancy may be partly accounted for by the role of vibrationally
excited OH in oxidizing Fe, or may be evidence for other currently unrecognised
chemical pathways producing FeO. Assuming a constant fractional abundance
w.r.t. H_2, the upper limits for the other metals are [MgO/H_2] <5.5e-10 (R
Dor) and <7e-11 (IK Tau), [MgOH/H_2] <9e-9 (R Dor) and <1e-9 (IK Tau),
[CaO/H_2] <2.5e-9 (R Dor) and <1e-10 (IK Tau), [CaOH/H_2] <6.5e-9 (R Dor) and
<9e-10 (IK Tau), and [MgS/H_$] <4.5e-10 (R Dor) and <6e-11 (IK Tau). The
retrieved upper limit abundances for these latter molecules are in accord with
the chemical model predictions.",1801.09302v1
2018-01-29,Band alignments of electronic energy structure in epitaxially grown \b{eta}-Ga2O3 layers,"Gallium oxide epitaxial layers grown on native substrates and basal plane
sapphire were characherized by X-ray phtotelectron and optical reflectance
spectroscopies. The XPS electronic structure mapping was coupled to Density
functional theory calculations.",1801.09451v1
2018-09-17,Indium Tin Oxide/Barium Strontium Titanate THz Sensor Antenna,"A Bow-Tie ITO/BST and Au/BST antennas were designed and analyzed using the
finite element, Multiphysics COMSOL program. The study shows that the outputs
peak at several modes and ITO antennas allow for the integration of the antenna
with optoelectronic devices.",1809.06449v1
2019-06-10,Cation Disorder and Lithium Insertion Mechanism of Wadsley--Roth Crystallographic Shear Phases,"Wadsley--Roth crystallographic shear phases form a family of compounds that
have attracted attention due to their excellent performance as lithium-ion
battery electrodes. The complex crystallographic structure of these materials
poses a challenge for first-principles computational modelling and hinders the
understanding of their structural, electronic and dynamic properties. In this
article, we study three different niobium-tungsten oxide crystallographic shear
phases (Nb$_{12}$WO$_{33}$, Nb$_{14}$W$_{3}$O$_{44}$, Nb$_{16}$W$_5$O$_{55}$)
using an enumeration-based approach and first-principles density-functional
theory calculations. We report common principles governing the cation disorder,
lithium insertion mechanism, and electronic structure of these materials.
Tungsten preferentially occupies tetrahedral and block-central sites within the
block-type crystal structures. The lithium insertion proceeds via a three-step
mechanism, associated with an anisotropic evolution of the host lattice. Our
calculations reveal an important connection between long-range and local
structural changes: in the second step of the mechanism, the removal of local
structural distortions leads to the contraction of the lattice along specific
crystallographic directions, buffering the volume expansion of the material.
Niobium-tungsten oxide shear structures host small amounts of localised
electrons during initial lithium insertion due to the confining effect of the
blocks, but quickly become metallic upon further lithiation. We argue that the
combination of local, long-range, and electronic structural evolution over the
course of lithiation is beneficial to the performance of these materials as
battery electrodes. The mechanistic principles we establish arise from the
compound-independent crystallographic shear structure, and are therefore likely
to apply to Ti/Nb oxide or pure Nb oxide shear phases.",1906.04192v3
2019-07-10,Environmental Stability of Bismuthene: Oxidation Mechanism and Structural Stability of 2D Pnictogens,"Recently a new group of two dimensional (2D) materials, originating from the
group V elements (pnictogens), has gained global attention owing to their
outstanding properties.",1907.04806v1
2020-12-16,Interfacial electrical and chemical properties of deposited SiO2 layers in lateral implanted 4H-SiC MOSFETs subjected to different nitridations,"In this paper, SiO2 layers deposited on 4H-SiC and subjected to different
post deposition annealing (PDA) in NO and N2O were studied to identify the key
factors influencing the channel mobility and threshold voltage stability in
4H-SiC MOSFETs. In particular, PDA in NO gave a higher channel mobility (55
cm2V-1s-1) than PDA in N2O (20 cm2V-1s-1), and the subthreshold behavior of the
devices confirmed a lower total amount of interface states for the NO case.
This latter could be also deduced from the behavior of the capacitance-voltage
characteristics of 4H-SiC MOSFETs measured in gate controlled diode
configuration. On the other hand, cyclic gate bias stress measurements allowed
to separate the contributions of interface states (Nit) both on the upper and
bottom parts of the 4H-SiC band gap and near interface oxide traps (NIOTs) in
the two oxides. In particular, it was found that NO annealing reduced the total
density of charges trapped at the interface states down to 3 x 1011 cm- 2 and
those trapped inside the oxide down to 1 x 1011 cm-2. Electron energy loss
spectroscopy demonstrated that the reduction of these traps in the NO annealed
sample is due to the lower amounts of sub-stoichiometric silicon oxide (~ 1nm)
and carbon-related defects (< 1nm) at the interface, respectively. This
correlation represents a further step in the comprehension of the physics of
the SiO2/4H-SiC interface explaining the mobility and threshold voltage
behavior of 4H-SiC MOSFETs.",2012.08829v3
2017-05-12,Accumulation-layer Surface Plasmons,"A rigorous analytical study of the eigenmodes supported by a charge
accumulation layer within a transparent conductive oxide (TCO) is presented.
The new class of surface plasmons termed Accumulation-Layer Surface Plasmon
(ASP) is introduced. Near resonance ASP are tightly bound and display a vast
effective index tunability that could be of great practical interest. The
suppression of ASP in the presence of epsilon-near zero regions is discussed.",1705.04552v1
2017-09-13,Detection of titanium oxide in the atmosphere of a hot Jupiter,"As an exoplanet transits its host star, some of the light from the star is
absorbed by the atoms and molecules in the planet's atmosphere, causing the
planet to seem bigger; plotting the planet's observed size as a function of the
wavelength of the light produces a transmission spectrum. Measuring the tiny
variations in the transmission spectrum, together with atmospheric modelling,
then gives clues to the properties of the exoplanet's atmosphere. Chemical
species composed of light elements$-$such as hydrogen, oxygen, carbon, sodium
and potassium$-$have in this way been detected in the atmospheres of several
hot giant exoplanets, but molecules composed of heavier elements have thus far
proved elusive. Nonetheless, it has been predicted that metal oxides such as
titanium oxide (TiO) and vanadium oxide occur in the observable regions of the
very hottest exoplanetary atmospheres, causing thermal inversions on the
dayside. Here we report the detection of TiO in the atmosphere of the
hot-Jupiter planet WASP-19b. Our combined spectrum, with its wide spectral
coverage, reveals the presence of TiO (to a confidence level of 7.7{\sigma}), a
strongly scattering haze (7.4{\sigma}) and sodium (3.4{\sigma}), and confirms
the presence of water (7.9{\sigma}) in the atmosphere.",1709.04118v1
2018-06-18,Effect of Dissolved Oxygen Content on Photocatalytic Performance of Graphene Oxide,"Graphene, a two-dimensional (2D) promising emergent photocatalyst consisting
of earth-abundant elements. This study evaluated the potential of graphene
oxide (GO) towards photocatalytic degradation of a novel organic dye, Methylene
Blue (MB). In this work, photocatalytic activity of graphene oxide (GO),
graphene oxide (GO) along with hydrogen peroxide (H2O2) were tested by
photodegrading Methylene Blue (MB) in aqueous solution. The resulted GO
nanoparticles were characterized by X-ray powder diffraction, Scanning Electron
Microscopy, Energy Dispersive Spectroscopy and Fourier Transform Infrared Ray
Spectroscopy. The XRD data confirms the sharp peak centered at 2Theta=10.44
degree corresponding to (002) reflection of GO. Based on our results, it was
found that the resulted GO nanoparticles along with H2O2 achieved ~92%
photodecolorization of MB compared to ~63% for H2O2 under natural sunlight
irradiation at pH~7 in 60 min. The influences of oxygen and hydrogen peroxide
(H2O2) on the degradation of MB during sunlight/GO process were investigated.
Experimental results indicated that oxygen was a determining parameter for
promoting the photocatalytic degradation. The rate constant of degradation (k1)
increased from 0.019 to 0.042 per minute for dissolved oxygen content (DOC) 3.5
mg/L when direct photocatalysis (MB/GO) and H2O2-assisted photocatalysis
(MB/H2O2/GO) were used. Owing to the fact that H2O2 acted as an electron and
hydroxyl radicals scavenger, the addition of H2O2 should in a proper dosage to
enhance the degradation of MB. Moreover, as the initial concentration of
dissolved oxygen (DO) was increased from 2.8 to 3.9 mg/L, the rate constant of
degradation (k1) increased from 0.035 to 0.062 per minute. The mechanism of
photodegradation and kinetics were also studied for both direct photocatalysis
and H2O2-assisted photocatalysis.",1806.06492v2
2018-12-16,Performance-Enhanced Non-Enzymatic Glucose Sensor Based on Graphene-Heterostructure,"This study proposes a novel design of glucose sensor with enhanced
selectivity and sensitivity by using graphene Schottky diodes, which is
composed of Graphene (G)/Platinum Oxide (PtO)/n-Silicon (Si) heterostructure.
The sensor was tested with different glucose concentrations and interfering
solutions to investigate its sensitivity and selectivity. Different structures
of the device were studied by adjusting the platinum oxide film thickness to
investigate its catalytic activity. It was found that the film thickness plays
a significant role in the efficiency of glucose oxidation and hence in overall
device sensitivity. 0.8-2 uA output current was obtained in the case of 4-10 mM
with a sensitivity of 0.2 uA/mM.cm2. Besides, results have shown that 0.8 uA
and 15 uA were obtained by testing 4 mM glucose on two different PtO
thicknesses, 30 nm, and 50 nm, respectively. The sensitivity of the device was
enhanced by 150% (i.e., up to 30 uA/mM.cm2) by increasing the PtO layer
thickness. This was attributed to both the increase of the number of active
sites for glucose oxidation as well as the increase in the graphene layer
thickness, which leads to enhanced charge carriers concentration and mobility.
Moreover, theoretical investigations were conducted using the Density Function
Theory (DFT) to understand the detection method and the origins of selectivity
better. The working principle of the sensors puts it in a competitive position
with other non-enzymatic glucose sensors. DFT calculations provided a
qualitative explanation of the charge distribution across the graphene sheet
within a system of a platinum substrate with D-glucose molecules above. The
proposed G/PtO/n-Si heterostructure has proven to satisfy these factors, which
opens the door for further developments of more reliable non-enzymatic
glucometers for continuous glucose monitoring systems.",1812.06466v4
2018-12-19,Compact grating coupler using asymmetric waveguide scatterers,"We demonstrate a novel grating coupler design based on double asymmetric and
vertically oriented waveguide scatterers to efficiently couple normally
incident light to a fundamental mode silicon waveguide laying on a buried oxide
layer.",1812.07757v2
2019-04-18,GHz Dielectric Measurement of Powdery TiO,"This study experimentally determines the dielectric properties of a powdery
titanium (II) oxide (TiO) material within the microwave range (0.1-13.5 GHz).
The properties were determined using a coaxial airline method using a
TiO/paraffin mixture at several loading fractions. A permittivity of 60 for
volume fraction below 30% and 100 for volume fraction above were measured.",1904.08765v1
2019-11-01,Advanced chemical state studies of oxide films by lab-based HAXPES combining soft and hard X-ray sources,"The greater information depth provided in Hard X-ray Photoelectron
Spectroscopy (HAXPES) enables non-destructive analyses of the chemistry and
electronic structure of buried interfaces. Moreover, for industrially relevant
elements like Al, Si and Ti, the combined access to the Al 1s, Si 1s or Ti 1s
photoelectron line and its associated Al KLL, Si KLL or Ti KLL Auger
transition, as required for local chemical state analysis on the basis of the
Auger parameter, is only possible with hard X-rays. Until now, such
photoemission studies were only possible at synchrotron facilities. Recently
however, the first commercial XPS/HAXPES systems, equipped with both soft and
hard X-ray sources, have entered the market, providing unique opportunities for
monitoring the local chemical state of all constituent ions in functional
oxides at different probing depths, in a routine laboratory environment.
Bulk-sensitive shallow core-levels can be excited using either the hard or soft
X-ray source, whereas more surface-sensitive deep core-level photoelectron
lines and associated Auger transitions can be measured using the hard X-ray
source. As demonstrated for thin Al2O3, SiO2 and TiO2 films, the local chemical
state of the constituting ions in the oxide may even be probed at near constant
probing depth by careful selection of sets of photoelectron and Auger lines, as
excited with the combined soft and hard X-ray sources. We highlight the
potential of lab-based HAXPES for the research on functional oxides and also
discuss relevant technical details regarding the calibration of the kinetic
binding energy scale.",1911.00428v1
2019-11-04,Threshold Voltage variation with respect to Gate geometry in Nano-scale MOSFETS,"The tremendous progress in Metal Oxide Semiconductor (MOS) technology has
been a direct consequence of device scaling for past several decades. But as we
have entered the nanometer era many problems related to leakage currents and
other issues related to variability impacting the yield are of concern. Herein
we have investigated how the change in the Fin Architecture and Gate Length of
the MOS device impacts the Threshold Voltage.",1911.03557v1
2019-12-25,Deep Learning Aided Rational Design of Oxide Glasses,"Despite the extensive usage of oxide glasses for a few millennia, the
composition-property relationships in these materials still remain poorly
understood. While empirical and physics-based models have been used to predict
properties, these remain limited to a few select compositions or a series of
glasses. Designing new glasses requires a priori knowledge of how the
composition of a glass dictates its properties such as stiffness, density, or
processability. Thus, accelerated design of glasses for targeted applications
remain impeded due to the lack of universal composition-property models.
Herein, using deep learning, we present a methodology for the rational design
of oxide glasses. Exploiting a large dataset of glasses comprising of up to 37
oxide components and more than 100,000 glass compositions, we develop
high-fidelity deep neural networks for the prediction of eight properties that
enable the design of glasses, namely, density, Young's modulus, shear modulus,
hardness, glass transition temperature, thermal expansion coefficient, liquidus
temperature, and refractive index. These models are by far the most extensive
models developed as they cover the entire range of human-made glass
compositions. We demonstrate that the models developed here exhibit excellent
predictability, ensuring close agreement with experimental observations. Using
these models, we develop a series of new design charts, termed as glass
selection charts. These charts enable the rational design of functional glasses
for targeted applications by identifying unique compositions that satisfy two
or more constraints, on both compositions and properties, simultaneously. The
generic design approach presented herein could catalyze machine-learning
assisted materials design and discovery for a large class of materials
including metals, ceramics, and proteins.",1912.11582v1
2020-02-29,Role of intermediate 4$f$ states in tuning the band structure of high entropy oxides,"High entropy oxides (HEOs) are single phase solid solutions consisting of 5
or more cations in approximately equiatomic proportions. In this study, we show
reversible control of optical properties in a rare-earth (RE) based
HEO-(Ce$_{0.2}$La$_{0.2}$Pr$_{0.2}$Sm$_{0.2}$Y$_{0.2}$)O$_{2-\delta}$ and
subsequently utilize a combination of spectroscopic techniques to derive the
features of the electronic band structure underpinning the observed optical
phenomena. Heat treatment of the HEO under vacuum atmosphere followed by
reheat-treatment in air results in a reversible change of the band gap energy,
from 1.9 eV to 2.5 eV. The finding is consistent with the reversible changes in
the oxidation state and related $f$-orbital occupancy of Pr. However, no
pertinent changes in the phase composition or crystal structure is observed
upon the vacuum heat treatment. Further annealing of this HEO under H$_2$
atmosphere, followed by reheat-treatment in air, results in even larger but
still reversible change of the band gap energy from 1.9 eV to 3.2 eV. This is
accompanied by a disorder-order type crystal structure transition and changes
in the O 2$p$-RE 5$d$ hybridization evidenced from X-ray absorption near edge
spectra (XANES). The O $K$ and RE ${M_{4,5}}$/$L_{3}$ XANES indicate that the
presence of Ce and Pr (in 3+/4+) state leads to the formation of intermediate
4$f$ energy levels between the O 2$p$ and RE 5$d$ gap in HEO. It is concluded
that heat treatment under reducing/oxidizing atmospheres affects these
intermediate levels, thus, offering the possibility to tune the band gap energy
in HEO.",2003.00268v1
2020-06-11,Tunable Photodetectors via in situ Thermal Conversion of TiS$_3$ to TiO$_2$,"In two-dimensional materials research, oxidation is usually considered as a
common source for the degradation of electronic and optoelectronic devices or
even device failure. However, in some cases a controlled oxidation can open the
possibility to widely tune the band structure of 2D materials. In particular,
we demonstrate the controlled oxidation of titanium trisulfide (TiS$_3$), a
layered semiconductor that has attracted much attention recently thanks to its
quasi-1D electronic and optoelectronic properties and its direct bandgap of 1.1
eV. Heating TiS$_3$ in air above 300 {\deg}C gradually converts it into
TiO$_2$, a semiconductor with a wide bandgap of 3.2 eV with ap-plications in
photo-electrochemistry and catalysis. In this work, we investigate the
controlled thermal oxidation of individual TiS$_3$ nanoribbons and its
influence on the optoelectronic properties of TiS$_3$-based photodetectors. We
observe a step-wise change in the cut-off wavelength from its pristine value
~1000 nm to 450 nm after subjecting the TiS$_3$ devices to subsequent thermal
treatment cycles. Ab-initio and many-body calculations confirm an increase in
the bandgap of titanium oxysulfide (TiO$_{2-x}$S$_x$) when increasing the
amount of oxygen and reducing the amount of sulfur.",2006.06842v1
2020-08-11,Analytical Approach to Phonon Calculations in the SCC-DFTB Framework,"Detailed derivation of the analytical, reciprocal-space approach of Hessian
calculation within the self-consistent-charge density functional based
tight-binding framework (SCC-DFTB) is presented. This approach provides an
accurate and efficient way for obtaining the SCC-DFTB Hessian of periodic
systems. Its superiority with respect to the traditional numerical force
differentiation method is demonstrated for doped graphene, graphene
nanoribbons, boron-nitride nanotubes, bulk zinc-oxide and other systems.",2008.04642v1
2020-09-29,The iron record of asteroidal processes in carbonaceous chondrites,"The valence of iron has been used in terrestrial studies to trace the
hydrolysis of primary silicate rocks. Here, we use a similar approach to
characterize the secondary processes, namely thermal metamorphism and aqueous
alteration, that have affected carbonaceous chondrites. X-ray absorption
near-edge structure spectroscopy at the Fe-K- edge was performed on a series of
36 CM, 9 CR, 10 CV, and 2 CI chondrites. Among the four carbonaceous chondrites
groups studied, a correlation between the iron oxidation index (IOI = [2
((Fe2+) + 3(Fe3+))/FeTOT) and the hydrogen content is observed. However, within
the CM group, for which a progressive alteration sequence has been defined, a
conversion of Fe3+ to Fe2+ is observed with increasing degree of aqueous
alteration. This reduction of iron can be explained by an evolution in the
mineralogy of the secondary phases. In the case of the few CM chondrites that
experienced some thermal metamorphism, in addition to aqueous alteration, a
redox memory of the aqueous alteration is present: a significant fraction of 3+
2+ 0 Fe is present, together with Fe and sometimes Fe. From our data set, the
CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR
chondrites, the three oxidation states of iron coexist. Even in the
least-altered CR chondrites, the fraction of Fe3+ can be high (30% for MET
00426). This observation confirms that oxidized iron has been integrated during
formation of fine-grained amorphous material in the matrix. Last, the IOI of CV
chondrites does not reflect the reduced/oxidized classification based on metal
and magnetite proportions, but is strongly correlated with petrographic types.
The valence of iron in CV chondrites therefore appears to be most closely
related to thermal history, rather than aqueous alteration, even if these
processes can occur together .",2009.13950v2
2020-10-09,Theoretical Modelling of High-Resolution X-Ray Absorption Spectra at Uranium M4 Edge,"We investigate the origin of satellite features that appear in the
high-resolution x-ray absorption spectra measured at the uranium M 4 edge in
compounds where the uranium atoms are in the U 6+ oxidation state. We employ a
material-specific Anderson impurity model derived from the electronic structure
obtained by the density-functional theory.",2010.04410v1
2020-10-14,Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction,"Manganese oxides have received much attention over the years among the wide
range of electrocatalysts for the oxygen evolution reaction (OER) due to their
low toxicity, high abundance and rich redox chemistry. While many previous
studies focused on the activity of these materials, a better understanding of
the material transformations relating to activation or degradation is highly
desirable, both from a scientific perspective and for applications. We
electrodeposited Na-containing MnOx without long-range order from an alkaline
solution to investigate these aspects by cyclic voltammetry, scanning electron
microscopy and x-ray absorption spectroscopy at the Mn-K and Mn-L edges. The
pristine film was assigned to a layered edge-sharing Mn3+/4+ oxide with Mn-O
bond lengths of mainly 1.87 {\AA} and some at 2.30 {\AA} as well as Mn-Mn bond
lengths of 2.87 {\AA} based on fits to the extended x-ray fine structure. The
decrease of the currents at voltages before the onset of the OER followed power
laws with three different exponents depending on the number of cycles and the
Tafel slope decreases from 186 \pm 48 to 114 \pm 18 mV dec-1 after 100 cycles,
which we interpret in the context of surface coverage with unreacted
intermediates. Post-mortem microscopy and bulk spectroscopy at the Mn-K edge
showed no change of the microstructure, bulk local structure or bulk Mn
valence. Yet, the surface region of MnOx oxidized toward Mn4+, which explains
the reduction of the currents in agreement with literature. Surprisingly, we
find that MnOx reactivates after 30 min at open-circuit (OC), where the
currents and also the Tafel slope increase. Reactivation processes during OC
are crucial because OC is unavoidable when coupling the electrocatalysts to
intermittent power sources such as solar energy for sustainable energy
production.",2010.06957v1
2021-02-06,Aluminum Oxide at the Monolayer Limit via Oxidant-free Plasma-Assisted Atomic Layer Deposition on GaN,"Atomic layer deposition (ALD) is an essential tool in semiconductor device
fabrication that allows the growth of ultrathin and conformal films to
precisely form heterostructures and tune interface properties. The
self-limiting nature of the chemical reactions during ALD provides excellent
control over the layer thickness. However, in contrast to idealized growth
models, it is experimentally challenging to create continuous monolayers by ALD
because surface inhomogeneities and precursor steric interactions result in
island growth during film nucleation. Thus, the ability to create pin-hole free
monolayers by ALD would offer new opportunities for controlling interfacial
charge and mass transport in semiconductor devices, as well as for tailoring
surface chemistry. Here, we report full encapsulation of c-plane gallium
nitride (GaN) with an ultimately thin (~3 {\AA}) aluminum oxide (AlOx)
monolayer, which is enabled by the partial conversion of the GaN surface oxide
into AlOx using a combination of trimethylaluminum deposition and hydrogen
plasma exposure. Introduction of monolayer AlOx significantly modifies the
physical and chemical properties of the surface, decreasing the work function
and introducing new chemical reactivity to the GaN surface. This tunable
interfacial chemistry is highlighted by the reactivity of the modified surface
with phosphonic acids under standard conditions, which results in
self-assembled monolayers with densities approaching the theoretical limit.
More broadly, the presented monolayer AlOx deposition scheme can be extended to
other dielectrics and III-V-based semiconductors, with significant relevance
for applications in optoelectronics, chemical sensing, and
(photo)electrocatalysis.",2102.03642v1
2021-03-10,Solid phase epitaxial growth of the correlated-electron transparent conducting oxide SrVO3,"SrVO3 thin films with a high figure of merit for applications as transparent
conductors were crystallized from amorphous layers using solid phase epitaxy
(SPE). Epitaxial SrVO3 films crystallized on SrTiO3 using SPE exhibit a room
temperature resistivity of 2.5 x 10-5 Ohms cm, a residual resistivity ratio of
3.8, and visible light transmission above 0.5 for a 60 nm-thick film. SrVO3
layers were deposited at room temperature using radio-frequency sputtering in
an amorphous form and subsequently crystallized by heating in controlled gas
environment. The lattice parameters and mosaic angular width of x-ray
reflections from the crystallized films are consistent with partial relaxation
of the strain resulting from the epitaxial mismatch between SrVO3 and SrTiO3. A
reflection high-energy electron diffraction study of the kinetics of SPE
indicates that crystallization occurs via the thermally activated propagation
of the crystalline/amorphous interface, similar to SPE phenomena in other
perovskite oxides. Thermodynamic calculations based on density functional
theory predict the temperature and oxygen partial pressure conditions required
to produce the SrVO3 phase and are consistent with the experiments. The
separate control of deposition and crystallization conditions in SPE presents
new possibilities for the crystallization of transparent conductors in complex
geometries and over large areas.",2103.05797v2
2021-05-20,Paring density waves as the origin of a ring-like RIXS profile in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$,"The coexistence of a homogeneous d-wave gap and short-ranged pairing density
waves (PDW) accounts for the apparent ""ring"" charge order in all directions of
the copper oxide plane, observed by recent RIXS measurements in
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$",2105.09692v1
2021-05-21,Laboratory blueprints for interstellar searches of aromatic chiral molecules: rotational signatures of styrene oxide,"The tracking of symmetry-breaking events in space is a longlasting goal of
astrochemists, aiming at an understanding of homochiral Earth chemistry. One
current effort at this frontier aims at the detection of small chiral molecules
in the interstellar medium. For that, high-resolution laboratory spectroscopy
data is required, providing blueprints for the search and assignment of these
molecules using radioastronomy. Here, we used chirped-pulse Fourier transform
microwave and millimeter-wave spectroscopy and frequency modulation absorption
spectroscopy to record and assign the rotational spectrum of the chiral
aromatic molecule styrene oxide, $\mathrm{C_{6}H_{5}C_{2}H_{3}O}$, a relevant
candidate for future radioastronomy searches. Using experimental data from the
2-12, 75-110, 170-220, and 260-330 GHz regions, we performed a global spectral
analysis, complemented by quantum chemistry calculations. A global fit of the
ground state rotational spectrum was obtained, including rotational transitions
from all four frequency regions. Primary rotational constants as well as
quartic and sextic centrifugal distortion constants were determined. We also
investigated vibrationally excited states of styrene oxide, and for the three
lowest vibrational states, we determined rotational constants including
centrifugal distortion corrections up to the sextic order. In addition,
spectroscopic parameters for the singly-substituted $^{13}$C and $^{18}$O
isotopologues were retrieved from the spectrum in natural abundance and used to
determine the effective ground state structure of styrene oxide in the gas
phase. The spectroscopic parameters and line lists of rotational transitions
obtained here will assist future astrochemical studies of this class of chiral
organic molecules.",2105.11337v1
2021-06-24,Time-resolved diffraction and photoelectron spectroscopy investigation of the reactive molecular beam epitaxy of $\mathrm{Fe_3O_4}$ ultrathin films,"We present time-resolved high energy x-ray diffraction (tr-HEXRD),
time-resolved hard x-ray photoelectron spectroscopy (tr-HAXPES) and
time-resolved grazing incidence small angle x-ray scattering (tr-GISAXS) data
of the reactive molecular beam epitaxy (RMBE) of $\mathrm{Fe_3O_4}$ ultrathin
films on various substrates. Reciprocal space maps are recorded during the
deposition of $\mathrm{Fe_3O_4}$ on $\mathrm{SrTiO_3(001)}$, MgO(001) and
NiO/MgO(001) in order to observe the temporal evolution of Bragg reflections
sensitive to the octahedral and tetrahedral sublattices of the inverse spinel
structure of $\mathrm{Fe_3O_4}$. A time delay between the appearance of rock
salt and spinel-exclusive reflections reveals that first, the iron oxide film
grows with $\mathrm{Fe_{1-\delta}O}$ rock salt structure with exclusive
occupation of octahedral lattice sites. When this film is 1.1$\,$nm thick, the
further growth of the iron oxide film proceeds in the inverse spinel structure,
with both octahedral and tetrahedral lattice sites being occupied. In addition,
iron oxide on $\mathrm{SrTiO_3(001)}$ initially grows with none of these
structures. Here, the formation of the rock salt structure starts when the film
is 1.5$\,$nm thick. This is confirmed by tr-HAXPES data obtained during growth
of iron oxide on $\mathrm{SrTiO_3(001)}$, which demonstrate an excess of
$\mathrm{Fe^{2+}}$ cations in growing films thinner than 3.2$\,$nm. This rock
salt phase only appears during growth and vanishes after the supply of the Fe
molecular beam is stopped. Thus, it can be concluded the rock salt structure of
the interlayer is a property of the dynamic growth process. The tr-GISAXS data
link these structural results to an island growth mode of the first 2-3$\,$nm
on both MgO(001) and $\mathrm{SrTiO_3(001)}$ substrates.",2106.13192v1
2021-09-27,Structure-Property-Performance Relationships of Cuprous Oxide Nanostructures for Dielectric Mie Resonance-Enhanced Photocatalysis,"Nanostructured metal oxides, such as Cu2O, CeO2, {\alpha}-Fe2O3, and TiO2 can
efficiently mediate photocatalysis for solar-to-chemical energy conversion and
pollution remediation. In this contribution, we report a novel approach,
dielectric Mie resonance-enhanced photocatalysis, to enhance the catalytic
activity of metal oxide photocatalysts. Specifically, we demonstrate that Cu2O
nanostructures exhibiting dielectric Mie resonances can exhibit up to an order
of magnitude higher photocatalytic rate as compared to Cu2O nanostructures not
exhibiting dielectric Mie resonances. Our finite-difference time-domain (FDTD)
simulation and experimental results predict a volcano-type relationship between
the photocatalytic rate and the size of Cu2O nanospheres and nanocubes. Using
transient absorption measurements, we reveal that a coherent electronic process
associated with dielectric Mie resonance-mediated charge carrier generation is
dominant in Cu2O nanostructures that exhibit higher photocatalytic rates.
Although we experimentally demonstrate dielectric Mie resonance-enhanced
photocatalysis using Cu2O particles here, based on our FDTD simulations, we
anticipate the same can be achieved with other metal oxide photocatalysts,
including CeO2, {\alpha}-Fe2O3, and TiO2.",2109.13332v2
2021-12-15,"Recent progress of fabrication, characterization, and applications of anodic aluminum oxide (AAO) membrane: A review","The progress of membrane technology with the development of membranes with
controlled parameters led to porous membranes. These membranes can be formed
using different methods and have numerous applications in science and
technology. Anodization of aluminum in this aspect is an electro-synthetic
process that changes the surface of the metal through oxidation to deliver an
anodic oxide layer. This process results in a self-coordinated, exceptional
cluster of round and hollow formed pores with controllable pore widths,
periodicity, and thickness. After the initial introduction, the paper proceeds
with a brief overview of anodizing process. That engages anodic aluminum oxide
(AAO) layers to be used as formats in various nanotechnology applications
without the necessity for expensive lithographical systems. This review article
surveys the current status of the investigation on AAO membranes. A
comprehensive analysis is performed on AAO membranes in applications;
filtration, sensors, drug delivery, template-assisted growth of various
nanostructures. Their multiple usages in nanotechnology have also been
discussed to gather nanomaterials and devices or unite them into specific
applications, such as nano-electronic gadgets, channel layers, and clinical
platforms tissue designing. From this review, the fact that the specified
enhancement of properties of AAO can be done by varying geometric parameters of
AAO has been highlighted. No review paper focused on a detailed discussion of
applications of AAO with prospects and challenges. This review paper represents
the formation, properties, applications with objective consideration of the
prospects and challenges of AAO applications. The prospects may appeal to
researchers to promote the development of unique membranes with
functionalization and controlled geometric parameters and check the feasibility
of the AAO membranes in nano-devices.",2112.08450v1
2022-02-10,Monte-Carlo Multiscale Simulation Study of Argon Adsorption/Desorption Hysteresis in Mesoporous Heterogeneous Tubular Pores like MCM-41 or Oxidized Porous Silicon,"In a recent paper [J. Chem. Phys. 127, 154701 (2007)], a multiscale approach
was introduced which allowed the calculation of adsorption/desorption
hysteresis for fluid confined in a single",2202.04900v1
2022-06-16,New hybrid organic-inorganic ferrophotovoltaic perovskites nanoparticles with high voltage for indoor and IoT applications,"The ideal band gap for a photovoltaic active layer for the solar spectrum is
around 1.3 eV. However oxides with such values are rare. One of the most
studied oxides to date as a photovoltaic active layer is the cuprous oxide
Cu2O. Its band gap is around 2.1 eV and is therefore not ideal for the solar
spectrum. Power Conversion Efficiency generally do not exceed 4%. In this paper
we propose to study an emerging type of solar cell that is based on
ferroelectricity. In this type of solar cell, a p-n junction is not necessarily
required, unlike conventional solar cells. Interesting conversion efficiencies
are beginning to be obtained with this type of cell, however the mechanisms are
still not well understood and several material and engineering challenges must
be addressed. The objective of this paper is to initiate an innovative
photovoltaic technology based on novel inorganic with suitable bandgap widths
and organic materials (biopolymer). These oxides are more stables. We
synthesized ferroelectric materials that absorb a large part of the solar
spectrum with reduced bandgap widths. PZN-4.5PT nanoparticles were dispersed in
a biopolymer matrix. Hybrid thin films with these inorganic nanoparticles
embedded in a biopolymer have been successfully fabricated by spin coating on
ITO substrate. Structural, morphological and electrical properties were
investigated. The best Power Conversion Efficiencies measure under a light LED
illumination of 3550 lux are respectively 21.83 % and 31.62 % for 15 and 30 min
light exposition with an open-circuit voltage of 5.17 and 5.86 V.",2207.03340v1
2022-06-25,Advances in honeycomb layered oxides: Part I -- Syntheses and Characterisations of Pnictogen- and Chalcogen-Based Honeycomb Layered Oxides,"Advancements in nanotechnology continue to unearth material vistas that
presage a new age of revolutionary functionalities replete with unparalleled
physical properties and avant-garde chemical capabilities that promise sweeping
paradigm shifts in energy, environment, telecommunications and potentially
healthcare. At the upper echelons of this realm, the pnictogen and chalcogen
class of honeycomb layered oxides have emerged with fascinating crystal
chemistry and exotic electromagnetic and topological phenomena that muster
multifaceted concepts spanning from materials science to condensed matter
physics and potential applications in electrochemistry, quantum mechanics and
electronics. In a bid to shed light on the mechanisms governing these
biomimetic nanostructures, this review highlights the significant milestones
and breakthroughs that have augmented their current fundamental theory,
properties, and utilities. Herein, we elucidate the vast promising crystal
chemistry space against the backdrop of known synthesis and characterisation
techniques employed in the development and optimisation of this class of
honeycomb layered oxides. Further, we highlight key theoretical models that
have reinvigorated the exploration and characterisation of within this class of
materials and are poised to redefine the frontiers of material research and
their applications. We conclude by envisaging future research directions where
fascinating physicochemical, topological and electromagnetic properties could
be lurking and where valiant efforts ought to be inclined, particularly in the
prospective realisation of exotic material compositional space as well as their
utility as testing grounds for emergent two-dimensional (2D) topological
quantum gravity and conformal field theories.",2207.06499v4
2022-07-20,Anatomy of rocky planets formed by rapid pebble accretion I. How icy pebbles determine the core fraction and FeO contents,"We present a series of papers dedicated to modelling the accretion and
differentiation of rocky planets that form by pebble accretion within the
lifetime of the protoplanetary disc. In this first paper, we focus on how the
accreted ice determines the distribution of iron between the mantle (oxidized
FeO and FeO$_{1.5}$) and the core (metallic Fe and FeS). We find that an
initial primitive composition of ice-rich material leads, upon heating by the
decay of $^{26}$Al, to extensive water flow and the formation of clay minerals
inside planetesimals. Metallic iron dissolves in liquid water and precipitates
as oxidized magnetite Fe$_3$O$_4$. Further heating by $^{26}$Al destabilizes
the clay at a temperature of around 900 K. The released supercritical water
ejects the entire water content from the planetesimal. Upon reaching the
silicate melting temperature of 1,700 K, planetesimals further differentiate
into a core (made mainly of iron sulfide FeS) and a mantle with a high fraction
of oxidized iron. We propose that the asteroid Vesta's significant FeO fraction
in the mantle is a testimony of its original ice content. We consider Vesta to
be a surviving member of the population of protoplanets from which Mars, Earth,
and Venus grew by pebble accretion. We show that the increase in the core mass
fraction and decrease in FeO contents with increasing planetary mass (in the
sequence Vesta -- Mars -- Earth) is naturally explained by the growth of
terrestrial planets outside of the water ice line through accretion of pebbles
containing iron that was dominantly in metallic form with an intrinsically low
oxidation degree.",2207.09795v2
2022-07-20,"Anatomy of rocky planets formed by rapid pebble accretion III. Partitioning of volatiles between planetary core, mantle, and atmosphere","Volatile molecules containing hydrogen, carbon, and nitrogen are key
components of planetary atmospheres. In the pebble accretion model for rocky
planet formation, these volatile species are accreted during the main planetary
formation phase. For this study, we modelled the partitioning of volatiles
within a growing planet and the outgassing to the surface. The core stores more
than 90\% of the hydrogen and carbon budgets of Earth for realistic values of
the partition coefficients of H and C between metal and silicate melts. The
magma oceans of Earth and Venus are sufficiently deep to undergo oxidation of
ferrous Fe$^{2+}$ to ferric Fe$^{3+}$. This increased oxidation state leads to
the outgassing of primarily CO$_2$ and H$_2$O from the magma ocean of Earth. In
contrast, the oxidation state of Mars' mantle remains low and the main
outgassed hydrogen carrier is H$_2$. This hydrogen easily escapes the
atmosphere due to the irradiation from the young Sun in XUV wavelengths,
dragging with it the majority of the CO, CO$_2$, H$_2$O, and N$_2$ contents of
the atmosphere. A small amount of surface water is maintained on Mars, in
agreement with proposed ancient ocean shorelines, for moderately low values of
the mantle oxidation. Nitrogen partitions relatively evenly between the core
and the atmosphere due to its extremely low solubility in magma; the burial of
large reservoirs of nitrogen in the core is thus not possible. The overall low
N contents of Earth disagree with the high abundance of N in all chondrite
classes and favours a volatile delivery by pebble snow. Our model of rapid
rocky planet formation by pebble accretion displays broad consistency with the
volatile contents of the Sun's terrestrial planets. The diversity of the
terrestrial planets can therefore be used as benchmark cases to calibrate
models of extrasolar rocky planets and their atmospheres.",2207.09807v2
2022-08-03,Electron spin transport in a metal-oxide-semiconductor Si two-dimensional inversion channel: Effect of hydrogen annealing on spin scattering mechanism and spin lifetime,"Department of Electrical Engineering and Information Systems, The University
of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan Center for Spintronics
Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-8656, Japan",2208.01798v1
2022-09-27,Understanding the growth mechanism of BaZrS$_3$ chalcogenide perovskite thin films from sulfurized oxide precursors,"Barium zirconium sulfide (BaZrS3) is an earth-abundant and environmentally
friendly chalcogenide perovskite with promising properties for various energy
conversion applications. Recently, sulfurization of oxide precursors has been
suggested as a viable solution for effective synthesis, especially from the
perspective of circumventing the difficulty of handling alkali earth metals. In
this work, we explore in detail the synthesis of BaZrS3 from Ba-Zr-O oxide
precursor films sulfurized at temperatures ranging from 700 {\deg}C to 1000
{\deg}C. We propose a formation mechanism of BaZrS3 based on a two-step
reaction involving an intermediate amorphization step of the BaZrO3 crystalline
phase. We show how the diffusion of sulfur (S) species in the film is the
rate-limiting step of this reaction. The processing temperature plays a key
role in determining the total fraction of conversion from oxide to sulfide
phase at a constant flow rate of the sulfur-containing H2S gas used as a
reactant. Finally, we observe the formation of stoichiometric BaZrS3 (1:1:3),
even under Zr-rich precursor conditions, with the formation of ZrO2 as a
secondary phase. This marks BaZrS3 quite unique among the other types of
chalcogenides, such as chalcopyrites and kesterites, which can instead
accommodate quite a large range of non-stoichiometric compositions. This work
opens up a pathway for further optimization of the BaZrS3 synthesis process,
straightening the route towards future applications of this material.",2209.13478v4
2022-10-05,Direct evidence of a charge depletion region at the interface of Van der Waals monolayers and dielectric oxides: The case of superconducting FeSe/STO,"The discovery of two dimensional Van der Waals materials has opened up
several possibilities for designing novel devices. Yet a more promising way of
designing exotic heterostutures with improved physical properties is to grow a
monolayer of these materials on a substrate. For example, in the field of
superconductivity it has been demonstrated that the superconducting transition
temperature of a monolayer of FeSe grown on some oxide substrates e.g.,
strontium titanate (STO) is by far higher than its bulk counterpart. Although
the system has been considered as a model system for understanding the
phenomenon of high-temperature superconductivity, the physical mechanism
responsible for this high transition temperature is still highly under debate.
Here using momentum and energy resolved high-resolution electron energy-loss
spectroscopy we probe the dynamic charge response of the FeSe/STO(001) system
and demonstrate that the frequency- and momentum-dependent dynamic charge
response is not compatible with a simple film/substrate model. Our analysis
reveals the existence of a depletion region at the interface between this Van
der Waals monolayer and the substrate. The presence of the depletion layer,
accompanied with a considerably large charge transfer from STO into the FeSe
monolayer, leads to a strong renormalization of the STO energy bands and a
substantial band bending at the interface. Our results shed light on the
electronic complexities of the FeSe/oxide interfaces and pave the way of
designing novel low-dimensional high-temperature superconductors through
interface engineering. We anticipate that the observed phenomenon is rather
general and can take place in many two dimensional Van der Waals monolayers
brought in contact with dielectric oxides or semiconducting substrates.",2210.02058v1
2022-10-21,"MnEdgeNet -- Accurate Decomposition of Mixed Oxidation States for Mn XAS and EELS L2,3 Edges without Reference and Calibration","Accurate decomposition of the mixed Mn oxidation states is highly important
for characterizing the electronic structures, charge transfer, and redox
centers for electronic, electrocatalytic, and energy storage materials that
contain Mn. Electron energy loss spectroscopy (EELS) and soft X-ray absorption
spectroscopy (XAS) measurements of the Mn L2,3 edges are widely used for this
purpose. To date, although the measurement of the Mn L2,3 edges is
straightforward given the sample is prepared properly, an accurate
decomposition of the mix valence states of Mn remains non-trivial. For both
EELS and XAS, 2+, 3+, 4+ reference spectra need to be taken on the same
instrument/beamline and preferably in the same experimental session because the
instrumental resolution and the energy axis offset could vary from one session
to another. To circumvent this hurdle, in this study, we adopted a deep
learning approach and developed a calibration-free and reference-free method to
decompose the oxidation state of Mn L2,3 edges for both EELS and XAS. To
synthesize physics-informed and ground-truth labeled training datasets, we
created a forward model that takes into account plural scattering,
instrumentation broadening, noise, and energy axis offset. With that, we
created a 1.2 million-spectrum database with a three-element oxidation state
composition label. The library includes a sufficient variety of data including
both EELS and XAS spectra. By training on this large database, our
convolutional neural network achieves 85% accuracy on the validation dataset.
We tested the model and found it is robust against noise (down to PSNR of 10)
and plural scattering (up to t/{\lambda} = 1). We further validated the model
against spectral data that were not used in training.",2210.11657v1
2022-11-18,Investigation of the SiO2-SiC interface using low energy muon spin rotation spectroscopy,"Using positive muons as local probes implanted at low energy enables
gathering information about the material of interest with nanometer depth
resolution (low energy muon spin rotation spectroscopy (LE-$\mu$SR). In this
work, we leverage the capabilities of LE-$\mu$SR to perform an investigation of
the SiO$_\text{2}$-SiC interface. Thermally oxidized samples are investigated
before and after annealing in nitric oxide (NO) and argon (Ar) ambience.
Thermal oxidation is found to result in structural changes both in the SiC
crystal close to the interface and at the interface itself. Annealing in NO
environment is known to passivate the defects leading to a reduction of the
density of interface traps (D$_{it}$); LE-$\mu$SR further reveals that the NO
annealing results in a thin layer of high carrier concentration in SiC,
extending to more than 50 nm depending on the annealing conditions. We also see
indications of Si vacancy (V$_{Si}$) formation in SiC after thermal oxidation.
Following NO annealing, nitrogen occupies the V$_{Si}$ sites, leading to the
reduction in D$_{it}$ and at the same time, creating a charge-carrier-rich
region near the interface. By comparing the LE-$\mu$SR data from a sample with
known doping density, we perform a high-resolution quantification of the free
carrier concentration near the interface after NO annealing and discuss the
origin of observed near-surface variations. Finally, the depletion of carriers
in a MOS capacitor in the region below the interface is shown using LE-$\mu$SR.
The NO annealed sample shows the narrowest depletion region, likely due to the
reduced D$_{it}$ and charge-carrier-rich region near the interface. Our
findings demonstrate the many benefits of utilizing LE-$\mu$SR to study
critical regions of semiconductor devices that have been inaccessible with
other techniques while retaining nanoscale depth resolution and a
non-destructive approach.",2211.10252v1
2022-11-28,Nitrous Oxide and Climate,"Higher concentrations of atmospheric nitrous oxide (N2O) are expected to
slightly warm Earth's surface because of increases in radiative forcing.
Radiative forcing is the difference in the net upward thermal radiation flux
from the Earth through a transparent atmosphere and radiation through an
otherwise identical atmosphere with greenhouse gases. Radiative forcing,
normally measured in W/m^2, depends on latitude, longitude and altitude, but it
is often quoted for the tropopause, about 11 km of altitude for temperate
latitudes, or for the top of the atmosphere at around 90 km. For current
concentrations of greenhouse gases, the radiative forcing per added N2O
molecule is about 230 times larger than the forcing per added carbon dioxide
(CO2) molecule. This is due to the heavy saturation of the absorption band of
the relatively abundant greenhouse gas, CO2, compared to the much smaller
saturation of the absorption bands of the trace greenhouse gas N2O. But the
rate of increase of CO2 molecules, about 2.5 ppm/year (ppm = part per million
by mole), is about 3000 times larger than the rate of increase of N2O
molecules, which has held steady at around 0.00085 ppm/year since 1985. So, the
contribution of nitrous oxide to the annual increase in forcing is 230/3000 or
about 1/13 that of CO2. If the main greenhouse gases, CO2, CH4 and N2O have
contributed about 0.1 C/decade of the warming observed over the past few
decades, this would correspond to about 0.00064 K per year or 0.064 K per
century of warming from N2O. Proposals to place harsh restrictions on nitrous
oxide emissions because of warming fears are not justified by these facts.
Restrictions would cause serious harm; for example, by jeopardizing world food
supplies.",2211.15780v1
2022-12-02,Deposition of Reduced Graphene Oxide Thin Film by Spray Pyrolysis Method for Perovskite Solar Cell,"The Perovskite absorber layer, the electron transport layer (ETL), the hole
transport layer (HTL), and the transparent conducting oxide layer (TCO) are the
major components that make up a Perovskite solar cell. Between ETL and HTL, the
absorber layer is sandwiched, on which electron-hole pairs are created after
absorption of solar radiation. Despite substantial progress toward efficiency,
long-term stability still remains a serious concern. Present work focuses
toward contributing on the later issue by adopting Titanium dioxide (TiO2) as
ETL and reduced graphene oxide (rGO) as HTL. Specifically, in the present work,
we report our efforts on the preparation of compact titanium dioxide (C-TiO2)
and mesoporous titanium dioxide (M-TiO2) layers as an ETL and a reduced
graphene oxide thin film as a HTL. The C-TiO2 film was spin casted on FTO glass
followed by casting of M-TiO2 film using Doctor Blading technique. Similarly,
the rGO film was produced by spray casting over the glass substrate. The
as-prepared ETL and HTL layers were characterized by measuring their optical
properties (transmittance and reflectance of thin films). Then, the bandgap, Eg
was extracted from reflectance and transmittance curves for ETL and HTL
respectively. In the case of rGO, we found the value of Eg to be 2.1 eV, which
varies between 2.7eV and 0.02eV depending upon its reduction level based on the
previously reported values. Similarly, the bandgap of the C-TiO2 was 4.51 eV
which was reduced to 4.12 eV after the addition of M-TiO2, which are 0.9 to 1.1
eV higher than previously reported values. However, bandgap shows decreasing
trend after employing M- TiO2 over C-TiO2. In a Perovskite solar cell, both ETL
and HTL will be investigated.",2212.01066v1
2023-01-11,Chemical profiles of the oxides on tantalum in state of the art superconducting circuits,"Over the past decades, superconducting qubits have emerged as one of the
leading hardware platforms for realizing a quantum processor. Consequently,
researchers have made significant effort to understand the loss channels that
limit the coherence times of superconducting qubits. A major source of loss has
been attributed to two level systems that are present at the material
interfaces. We recently showed that replacing the metal in the capacitor of a
transmon with tantalum yields record relaxation and coherence times for
superconducting qubits, motivating a detailed study of the tantalum surface. In
this work, we study the chemical profile of the surface of tantalum films grown
on c-plane sapphire using variable energy X-ray photoelectron spectroscopy
(VEXPS). We identify the different oxidation states of tantalum that are
present in the native oxide resulting from exposure to air, and we measure
their distribution through the depth of the film. Furthermore, we show how the
volume and depth distribution of these tantalum oxidation states can be altered
by various chemical treatments. By correlating these measurements with detailed
measurements of quantum devices, we can improve our understanding of the
microscopic device losses.",2301.04567v2
2023-02-08,Bioabsorbable WE43 Mg alloy wires modified by continuous plasma electrolytic oxidation for implant applications. Part II: degradation and biological performance,"The corrosion, mechanical degradation and biological performance of
cold-drawn WE43 Mg wires were analyzed as a function of thermo-mechanical
processing and the presence of a protective oxide layer created by continuous
plasma electrolytic oxidation (PEO). It was found that the corrosion properties
of the non-surface-treated wire could be optimized by means of thermal
treatment within certain limits, but the corrosion rate remained very high.
Hence, strength and ductility of these wires vanished after 24 h of immersion
in simulated body fluid at 37$^\circ$C and, as a result of that rather quick
degradation, direct tests did not show any MC3T3-E1 preosteoblast cell
attachment on the surface of the Mg wires. In contrast, surface modification of
the annealed WE43 Mg wires by a continuous PEO process led to the formation of
a homogeneous oxide layer of $\approx$ 8$\mu$m and significantly improved the
corrosion resistance and hence the biocompatibility of the WE43 Mg wires. It
was found that a dense layer of Ca/P was formed at the early stages of
degradation on top of the Mg(OH)2 layer and hindered the diffusion of the
Cl-ions which dissolve Mg(OH)2 and accelerate the corrosion of Mg alloys. As a
result, pitting corrosion was suppressed and the strength of the Mg wires was
above 100 MPa after 96 h of immersion in simulated body fluid at 37$^\circ$C.
Moreover, many cells were able to attach on the surface of the PEO
surface-modified wires during cell culture testing. These results demonstrate
the potential of thin Mg wires surface-modified by continuous PEO in terms of
mechanical, degradation and biological performance for bioabsorbable wire-based
devices.",2302.13778v1
2023-05-25,Structure and properties of the films based on ternary transition metal borides: theory and experiment,"The review presents the results of theoretical and experimental studies of
the structure, bonding between atoms, mechanical properties, thermal stability,
and oxidation and corrosion resistance of films based on ternary transition
metal borides.",2305.15854v1
2023-06-11,Imaging emergent exotic quasiparticle state in a frustrated transition metal oxide,"The existence of rich Fermiology in anomalous metal phase in exotic
superconductors has attracted considerable interests, as exemplified in copper,
iron-based, and intermetallic frustrated kagome-based compounds. A common
feature in these cases is pseudo-gap opening or long-range lattice/electronic
ordering above superconducting critical temperature Tc. As yet developed area
is the potential existence of exotic Fermiology in superconducting transition
metal oxides on a geometrically frustrated lattice. Here, we focus on the
spinel oxide superconductor LiTi2O4, which can be viewed as the hole-doped side
of the orbital ordered 3d1 Mott system on the Ti-derived pyrochlore frustrated
network. By the in-situ combination of angle-resolved photoemission
spectroscopy (ARPES) and epitaxial thin film growth, we discovered the abrupt
flattening of near Fermi energy dispersion below the characteristic temperature
T* ~ 150 K. While the emergent negative thermal expansion below T* strongly
supports a distinct phase at low-temperature, absence of energy gap opening,
splitting/folding of bands, nor long-range lattice distortion are seen across
T*. We propose that the competition between growing instability towards orbital
ordering and its inherent geometric frustration in the Ti-pyrochlore network
results in a new quantum state of matter with robust high entropic nature below
T*. Our findings collectively point to a unique Fermiology in frustrated
three-dimensional transition metal oxides, and its connection to
superconductivity below Tc is open as an interesting future challenge. Also, a
potential guideline is unexpectedly provided for designing zero thermal
expansion metal to develop future solid-state devices.",2306.06708v1
2023-06-26,The Strange Metal State of the high-Tc Cuprates,"This paper is dedicated to the memory of Professor K. Alex M\""uller. I
present a few remarks about my interactions with Alex over the years. Then I
present a very brief summary of recent transport studies of the strange metal
normal-state in the high-temperature copper oxide superconductors, a subject of
great interest to Alex.",2306.14794v1
2023-06-29,A multiphase-field model for simulating the hydrogen-induced multi-spot corrosion on the surface of polycrystalline metals: Application to uranium metal,"Hydrogen-induced multi-spot corrosion on the surface of polycrystalline rare
metals is a complex process, which involves the interactions between phases
(metal, hydride and oxide), grain orientations, grain boundaries, and corrosion
spots. To accurately simulate this process and comprehend the underlying
physics, a theoretical method is required that includes the following
mechanisms: i) hydrogen diffusion, ii) phase transformation, iii) elastic
interactions between phases, especially, the interactions between the oxide
film and the hydride, iv) elastic interactions between grains, and v)
interactions between hydrogen solutes and grain boundaries. In this study, we
report a multiphase-field model that incorporates all these requirements, and
conduct a comprehensive study of hydrogen-induced spot corrosion on the uranium
metal surface, including the investigation of the oxide film, multi-spot
corrosion, grain orientation, and grain boundary in the monocrystal, bicrystal,
and polycrystal systems. The results indicate that the oxide film can inhibit
the growth of hydrides and plays a crucial role in determining the correct
morphology of the hydride at the triple junction of phases. The elastic
interaction between multiple corrosion spots causes the merging of corrosion
spots and promotes the growth of hydrides. The introduction of grain
orientations and grain boundaries results in a variety of intriguing
intracrystalline and intergranular hydride morphologies. The model presented
here is generally applicable to the hydrogen-induced multi-spot corrosion on
any rare metal surface.",2306.16920v2
2023-08-18,A mineralogical reason why all exoplanets cannot be equally oxidising,"From core to atmosphere, the oxidation states of elements in a planet shape
its character. Oxygen fugacity (fO$_2$) is one parameter indicating these
likely oxidation states. The ongoing search for atmospheres on rocky exoplanets
benefits from understanding the plausible variety of their compositions, which
depends strongly on their oxidation states -- and if derived from interior
outgassing, on the fO$_2$ at the top of their silicate mantles. This fO$_2$
must vary across compositionally-diverse exoplanets, but for a given planet its
value is unconstrained insofar as it depends on how iron (the dominant
multivalent element) is partitioned between its 2+ and 3+ oxidation states.
Here we focus on another factor influencing how oxidising a mantle is -- a
factor modulating fO$_2$ even at fixed Fe$^{3+}$/Fe$^{2+}$ -- the planet's
mineralogy. Only certain minerals (e.g., pyroxenes) incorporate Fe$^{3+}$.
Having such minerals in smaller mantle proportions concentrates Fe$^{3+}$,
increasing fO$_2$. Mineral proportions change within planets according to
pressure, and between planets according to bulk composition. Constrained by
observed host star refractory abundances, we calculate a minimum fO$_2$
variability across exoplanet mantles, of at least two orders of magnitude, due
to mineralogy alone. This variability is enough to alter by a hundredfold the
mixing ratio of SO$_2$ directly outgassed from these mantles. We further
predict that planets orbiting high-Mg/Si stars are more likely to outgas
detectable amounts of SO$_2$ and H$_2$O; and for low-Mg/Si stars, detectable
CH$_4$, all else equal. Even absent predictions of Fe$^{3+}$ budgets, general
insights can be obtained into how oxidising an exoplanet's mantle is.",2308.09505v1
2023-08-30,Sub-Volt High-Speed Silicon MOSCAP Microring Modulator Driven by High Mobility Conductive Oxide,"Low driving voltage (Vpp), high-speed silicon microring modulator plays a
critical role in energy-efficient optical interconnect and optical computing
systems owing to its ultra-compact footprint and capability for on-chip
wavelength-division multiplexing. However, existing silicon microring
modulators usually require more than 2 V of Vpp, which is limited by the
relatively weak plasma dispersion effect of silicon and the small capacitance
density of the reversed PN-junction. Here we present a highly efficient
metal-oxide semiconductor capacitor (MOSCAP) microring modulator through
heterogeneous integration between silicon photonics and titanium-doped indium
oxide, which is a high-mobility transparent conductive oxide (TCO) material
with a strong plasma dispersion effect. The device is co-fabricated by Intel's
photonics fab and TCO patterning processes at Oregon State University, which
exhibits a high electro-optic modulation efficiency of 117 pm/V with a low VpiL
of 0.12 Vcm, and consequently can be driven by an extremely low Vpp of 0.8 V.
At a 11 GHz modulation bandwidth where the modulator is limited by the high
parasitic capacitance, we obtained 25 Gb/s clear eye diagrams with energy
efficiency of 53 fJ/bit and demonstrated 35 Gb/s open eyes with a higher
driving voltage. Further optimization of the device is expected to increase the
modulation bandwidth up to 52 GHz that can encode data at 100 Gb/s for
next-generation, energy-efficient optical communication and computation with
sub-volt driving voltage without using any high voltage swing amplifier.",2308.16255v1
2023-09-20,Variability and Reliability of Graphene Field-Effect Transistors with CaF2 Insulators,"Graphene is a promising material for applications as a channel in graphene
field-effect transistors (GFETs) which may be used as a building block for
optoelectronics, high-frequency devices and sensors. However, these devices
require gate insulators which ideally should form atomically flat interfaces
with graphene and at the same time contain small densities of traps to maintain
high device stability. Previously used amorphous oxides, such as SiO2 and
Al2O3, however, typically suffer from oxide dangling bonds at the interface,
high surface roughness and numerous border oxide traps. In order to address
these challenges, here we use for the first time 2nm thick epitaxial CaF2 as a
gate insulator in GFETs. By analyzing device-to-device variability for over 200
devices fabricated in two batches, we find that tens of them show similar gate
transfer characteristics. Our statistical analysis of the hysteresis up to 175C
has revealed that while an ambient-sensitive counterclockwise hysteresis can be
present in some devices, the dominant mechanism is thermally activated charge
trapping by border defects in CaF2 which results in the conventional clockwise
hysteresis. We demonstrate that both the hysteresis and bias-temperature
instabilities in our GFETs with CaF2 are comparable to similar devices with
SiO2 and Al2O3. In particular, we achieve a small hysteresis below 0.01 V for
equivalent oxide thickness (EOT) of about 1 nm at the electric fields up to 15
MV/cm and sweep times in the kilosecond range. Thus, our results demonstrate
that crystalline CaF2 is a promising insulator for highly-stable GFETs.",2309.11233v1
2023-09-21,Experimental and theoretical assessment of native oxide in the superconducting TaN,"In this manuscript, we show through an experimental-computational proof of
concept the native oxide formation into superconducting TaN films. First, TaN
was synthesized at an ultra-high vacuum system by reactive pulsed laser
deposition and characterized in situ by X-ray photoelectron spectroscopy. The
material was also characterized ex situ by X-ray diffraction, transmission
electron microscopy, and the four-point probe method. It was detected that TaN
contained considerable oxygen impurities (up to 26 %O) even though it was grown
in an ultra-high vacuum chamber. Furthermore, the impurified TaN evidence a
face-centered cubic crystalline structure only and exhibits superconductivity
at 2.99 K. To understand the feasibility of the native oxide in TaN, we study
the effect of incorporating different amounts of O atoms in TaN using ab-initio
calculations. A thermodynamic stability analysis shows that a TaOxN1-x model
increases its stability as oxygen is added, demonstrating that oxygen may
always be present in TaN, even when obtained at ultra-high vacuum conditions.
All analyzed models exhibit metallic behavior. Charge density difference maps
reveal that N and O atoms have a higher charge density redistribution than Ta
atoms. The electron localization function maps and line profiles indicate that
Ta-O and Ta-N bonds are mainly ionic. As expected, stronger ionic behavior is
observed in the Ta-O bonds due to the electronegativity difference between O
and N atoms. Recent evidence points to superconductivity in bulk TaO,
confirming the asseverations of superconductivity in our samples. The results
discussed here highlight the importance of considering native oxide when
reporting superconductivity in TaN films since the TaO regions formed in the
compound may be key to understanding the different critical temperatures
reported in the literature.",2309.12520v1
2023-11-27,Electron correlation mediated site-selective charge compensation in polar/non-polar heterointerface,"One of the boundary conditions of the classical electromagnetic theory
demands continuous electric potential across any boundary, which may not be
naturally satisfied in atomically engineered heterostructures. Such polarity
mismatch in oxide heterointerfaces is compensated through some
(electronic/chemical/structural) reconstructions, leading to a myriad of
emergent phenomena. The question we are posing is whether conventional
semiconductor band bending framework is sufficient to comprehend compensation
mechanisms in oxide heterostructures since, unlike semiconductors, complex
oxides host strong electron correlations whose effects are indispensable. To
address this, we investigate the interface between a prototypical insulating
double perovskite Nd$_2$NiMnO$_6$ and a wide-bandgap insulator SrTiO$_3$. This
polar/non-polar interface offers a similar scenario as the famous
LaAlO$_3$/SrTiO$_3$ system but with an exception - two transition metal sites
with two individual correlated energy scales. By combining several experimental
techniques and density functional theory, we establish a site-selective charge
compensation process that occurs explicitly at the Mn site of the film, leaving
the Ni sites inert. This surprising selectivity, which cannot be accounted by
existing polar compensation mechanisms, is directly attributed to the TM
cations' relative correlation energy scales. This discovery presents that
site-specific charge compensation can be a designers tool for tailoring
emergent phenomena in oxide heterostructures.",2311.15726v1
2024-01-10,Redox Poise during Rhodospirillum rubrum Phototrophic Growth Drives Large-scale Changes in Macromolecular Synthesis Pathways,"During photoheterotrophic growth on organic substrates, purple nonsulfur
photosynthetic bacteria like Rhodospirillum rubrum can acquire electrons by
multiple means, including oxidation of organic substrates, oxidation of
inorganic electron donors (e.g. H$_2$), and by reverse electron flow from the
photosynthetic electron transport chain. These electrons are stored in the form
of reduced electron-carrying cofactors (e.g. NAD(P)H and ferredoxin). The ratio
of oxidized to reduced redox cofactors (e.g. ratio of NAD(P)+:NAD(P)H), or
'redox poise` is difficult to understand or predict, as are the the cellular
processes for dissipating these reducing equivalents. Using physics-based
models that capture mass action kinetics consistent with the thermodynamics of
reactions and pathways, a range of redox conditions for heterophototrophic
growth are evaluated, from conditions in which the NADP+/NADPH levels
approached thermodynamic equilibrium to conditions in which the NADP+/NADPH
ratio is far above the typical physiological values. Modeling results together
with experimental measurements of macro molecule levels (DNA, RNA, proteins and
fatty acids) indicate that the redox poise of the cell results in large-scale
changes in the activity of biosynthetic pathways. Phototrophic growth is less
coupled than expected to producing reductant, NAD(P)H, by reverse electron flow
from the quinone pool. Instead, it primarily functions for ATP production
(photophosphorylation), which drives reduction even when NADPH levels are
relatively low compared to NADP+. The model, in agreement with experimental
measurements of macromolecule ratios of cells growing on different carbon
substrates, indicate that the dynamics of nucleotide versus lipid and protein
production is likely a significant mechanism of balancing oxidation and
reduction in the cell.",2401.04862v1
2024-01-10,Morphological evolution and surface/interface Fe-oxide formation in epitaxial Fe(001)/MgO(001) thin film,"Epitaxial Fe film has been grown on ion beam sputtered MgO(001) substrate by
electron beam evaporation. Reflection high energy electron diffraction (RHEED)
and transport measurements (TM) were performed simultaneously during the growth
of the film. While TM provided information about film morphology, RHEED
provided information about the structure of the film.",2401.05091v1
2024-01-18,Treatment and Aging Studies of GaAs(111)B Substrates for van der Waals Chalcogenide Film Growth,"GaAs(111)B is a semiconductor substrate widely used in research and
commercial fields due to its low cost, mature synthesis technology, and
excellent properties for manufacturing electronic devices. It is not only used
to grow three-dimensional (3D) strongly-bonded materials, but has also been
used as a substrate for layered, van der Waals (vdW)-bonded chalcogenide film
growth. However, GaAs(111)B wafers cannot be directly used for growing
epitaxial vdW chalcogenide films for two reasons: (1) the GaAs surface has a
substantial number of dangling bonds that need to be passivated for vdW layers
growth; (2) the substrate surface is covered with a thin epi-ready oxide layer
which must be removed before film growth. In this paper, we optimize the method
for deoxidizing GaAs(111)B substrates under a Se overpressure and successfully
create a smooth, deoxidized, and passivated substrate for subsequent growth of
vdW chalcogenide materials. We demonstrate the benefits of this method for the
growth of vdW chalcogenide thin films using GaSe as a representative of vdW
chalcogenides. In addition, we find that severely aged substrates have
difficulty maintaining a smooth surface during the deoxidation and passivation
process and cause GaSe crystals to nucleate in random shapes and orientations.
We describe a method using water droplet testing to determine the age of the
substrate. Finally, X-ray photoelectron spectroscopy (XPS) characterization
reveals that the natural aging of GaAs(111)B in the air results in an increase
in surface oxides, Ga2O3 and As2O3, while exposure to ultraviolet (UV)-ozone
not only enhances the contents of these two oxides but also generates a new
oxide, As2O5. Our research contributes to expanding the compatibility of
GaAs(111)B with diverse growth materials and the production of high-quality
heterostructure devices.",2401.10425v1
2024-03-23,Bilinear magnetoresistance in 2DEG with isotropic cubic Rashba spin-orbit interaction,"Bilinear magnetoresistance has been studied theoretically in 2D systems with
isotropic cubic form of Rashba spin-orbit interaction. We have derived the
effective spin-orbital field due to current-induced spin polarization and
discussed its contribution to the unidirectional system response. The analysed
model can be applied to the semiconductor quantum wells as well as 2DEG at the
surfaces and interfaces of perovskite oxides.",2403.15817v1
2009-08-10,Tunnel magnetoresistance of magnetic junctions with cubic symmetry of the layers,"A tunnel magnetic junction is considered with magnetic hard and magnetic soft
layers of cubic symmetry. The magnetic switching is analyzed of the layers by a
magnetic field perpendicular to the initial magnetizations. In such a
situation, an additional peak of the TMR ratio appears at the magnetic field
value lower substantially than the anisotropy energy of the soft layer.",0908.1278v1
2014-09-03,Photo-induced Magnetic Force Between Nanostructures,"Photo-induced magnetic force between nanostructures, at optical frequencies,
is investigated theoretically. Till now optical magnetic effects are not used
in scanning probe microscopy because of the vanishing natural magnetism with
increasing frequency. On the other hand, artificial magnetism in engineered
nanostructures led to the development of measurable optical magnetism. Here,
two examples of nanoprobes that are able to generate strong magnetic dipolar
fields at optical frequency are investigated: first an ideal magnetically
polarizable nanosphere and then a circular cluster of silver nanospheres that
has a loop-like collective plasmonic resonance equivalent to a magnetic dipole.
Magnetic forces are evaluated based on nanostructure polarizabilities, i.e.
induced magnetic dipoles, and magnetic-near field evaluations. As an initial
assessment on the possibility of a magnetic nanoprobe to detect magnetic
forces, we consider two identical magnetically polarizable nanoprobes and
observe magnetic forces in the order of piconewtons thereby bringing it within
detection limits of conventional atomic force microscopes at ambient pressure
and temperature. The detection of magnetic force is a promising method in
studying optical magnetic transitions that can be the basis of innovative
spectroscopy applications.",1409.1188v2
2021-03-10,Searching for Magnetic Monopoles with the Earth's Magnetic Field,"Magnetic monopoles have long been predicted in theory and could exist as a
stable object in our universe. As they move around in galaxies, magnetic
monopoles could be captured by astrophysical objects like stars and planets.
Here, we provide a novel method to search for magnetic monopoles by detecting
the monopole moment of the Earth's magnetic field. Using over six years of
public geomagnetic field data obtained by the Swarm satellites, we apply
Gauss's law to measure the total magnetic flux, which is proportional to the
total magnetic charge inside the Earth. To account for the secular variation of
satellite altitudes, we define an altitude-rescaled magnetic flux to reduce the
dominant magnetic dipole contribution. The measured magnetic flux is consistent
with the existing magnetic field model that does not contain a monopole moment
term. We therefore set an upper limit on the magnetic field strength at Earth's
surface from magnetic monopoles to be $|B_{\rm m}| < 0.13$ nT at 95% confidence
level, which is less than $2\times 10^{-6}$ of Earth's magnetic field strength.
This constrains the abundance of magnetically-charged objects, including
magnetic black holes with large magnetic charges.",2103.06286v1
2005-06-23,"Magnetic phase diagram copper metaborate CuB_2O_4 in magnetic field parallel c-axis: resonant, magnetic and magnetoelastic investigations","The magnetic phase diagram in a single crystal of copper metaborate CuB_2O_4
in a magnetic field parallel to a tetragonal axis $c$ has been investigated.
  From the resonant, magnetic and magnetostrictive data the phase diagram of
CuB_2O_4 on a plane ``temperature - magnetic field'' is constructed. The
magnetic incommensurate-commensurate phase transition is caused by the
saturation of weak subsystem of copper ions in the strong magnetic field
$H\|c$.",0506596v1
2007-05-31,Geometry-induced frustration of magnetization in a planar soft-hard magnetic system,"We computationally study the frustrated magnetic configurations of a thin
soft magnetic layer with the boundary condition fixed by underlying hard
magnets. Driven by geometrical constraints and external magnetic field,
transitions between frustrated energy minima result in magnetic hysteretic
behavior. The presence of soft-magnet introduces strong undulations in the
energy landscape in a length scale set by the magnetic property of the soft
magnet. We propose a possible use of the phenomena to locally control the
movement of magnetic nanoparticles.",0705.4490v1
2014-05-19,Scaling laws of free magnetic energy stored in a solar emerging flux region,"This Letter reports scaling laws of free magnetic energy stored in a solar
emerging flux region which is a key to understanding the energetics of solar
active phenomena such as solar flares and coronal mass ejections. By performing
3-dimensional magnetohydrodynamic simulations that reproduce several emerging
flux regions of different magnetic configurations, we derive power law
relationships among emerged magnetic flux, free magnetic energy and relative
magnetic helicity in these emerging flux regions. Since magnetic flux is an
observable quantity, the scaling law between magnetic flux and free magnetic
energy may give a way to estimate invisible free magnetic energy responsible
for solar active phenomena.",1405.4587v1
2020-09-24,Magnetic winding: what is it and what is it good for?,"Magnetic winding is a fundamental topological quantity that underpins
magnetic helicity and measures the entanglement of magnetic field lines. Like
magnetic helicity, magnetic winding is also an invariant of ideal
magnetohydrodynamics. In this article we give a detailed description of what
magnetic winding describes, how to calculate it and how to interpret it in
relation to helicity. We show how magnetic winding provides a clear topological
description of magnetic fields (open or closed) and we give examples to show
how magnetic winding and helicity can behave differently, thus revealing
different and imporant information about the underlying magnetic field.",2009.11708v1
2022-10-31,HTS Dipole Magnet with a Mechanical Energy Transfer in the Magnetic Field,"There were designed and successfully tested at Fermilab several high
temperature superconducting (HTS) model magnets for particle accelerators. Some
of them worked in a persistent current mode continuously generating magnetic
field in the iron dominated magnet gap. In the paper was investigated a novel
HT dipole magnet concept with a mechanical energy transfer in the magnetic
field. To pump the energy in the superconducting HTS dipole magnet used a
detachable magnetizer. The HTS dipole magnet was build and successfully tested
at a liquid nitrogen temperature. Discussed the magnet design, test results,
the proposed approach limits, and efficiency.",2211.00105v1
2023-08-03,Magnetic interactions in IV-VI diluted magnetic semiconductors,"Diluted magnetic semiconductors (DMS) are interesting because of the
interplay between the electronic and magnetic subsystems. We describe selected
magnetic properties of IV-VI diluted magnetic semiconductors, looking at the
similarities and differences between magnetic properties of II-VI, IV-VI, and
III-V DMS. We focus on the influence of the crystalline and electronic
structure of the material on its magnetic properties, especially on the
exchange interactions among magnetic ions. We describe methods of determination
of the exchange parameters by using different experimental techniques, such as
measurements of magnetic susceptibility, magnetization, and specific heat. We
follow the development in the material technology from bulk crystals to thin
films and nanostructures.",2308.01780v1
2006-05-18,Small-scale magnetic buoyancy and magnetic pumping effects in a turbulent convection,"We determine the nonlinear drift velocities of the mean magnetic field and
nonlinear turbulent magnetic diffusion in a turbulent convection. We show that
the nonlinear drift velocities are caused by the three kinds of the
inhomogeneities, i.e., inhomogeneous turbulence; the nonuniform fluid density
and the nonuniform turbulent heat flux. The inhomogeneous turbulence results in
the well-known turbulent diamagnetic and paramagnetic velocities. The nonlinear
drift velocities of the mean magnetic field cause the small-scale magnetic
buoyancy and magnetic pumping effects in the turbulent convection. These
phenomena are different from the large-scale magnetic buoyancy and magnetic
pumping effects which are due to the effect of the mean magnetic field on the
large-scale density stratified fluid flow. The small-scale magnetic buoyancy
and magnetic pumping can be stronger than these large-scale effects when the
mean magnetic field is smaller than the equipartition field. We discuss the
small-scale magnetic buoyancy and magnetic pumping effects in the context of
the solar and stellar turbulent convection. We demonstrate also that the
nonlinear turbulent magnetic diffusion in the turbulent convection is
anisotropic even for a weak mean magnetic field. In particular, it is enhanced
in the radial direction. The magnetic fluctuations due to the small-scale
dynamo increase the turbulent magnetic diffusion of the toroidal component of
the mean magnetic field, while they do not affect the turbulent magnetic
diffusion of the poloidal field.",0605444v1
2019-09-09,Photospheric magnetic structure of coronal holes,"In this study, we investigate in detail the photospheric magnetic structure
of 98 coronal holes using line-of-sight magnetograms of SDO/HMI, and for a
subset of 42 coronal holes using HINODE/SOT G-band filtergrams. We divided the
magnetic field maps into magnetic elements and quiet coronal hole regions by
applying a threshold at $\pm 25$ G. We find that the number of magnetic bright
points in magnetic elements is well correlated with the area of the magnetic
elements (cc=$0.83\pm 0.01$). Further, the magnetic flux of the individual
magnetic elements inside coronal holes is related to their area by a power law
with an exponent of $1.261\pm 0.004$ (cc=$0.984\pm 0.001$). Relating the
magnetic elements to the overall structure of coronal holes, we find that on
average ($69\pm 8$) % of the overall unbalanced magnetic flux of the coronal
holes arises from long-lived magnetic elements with lifetimes > 40 hours. About
($22\pm 4$) % of the unbalanced magnetic flux arises from a very weak
background magnetic field in the quiet coronal hole regions with a mean
magnetic field density of about 0.2 to 1.2 G. This background magnetic field is
correlated to the flux of the magnetic elements with lifetimes of > 40 h
(cc=$0.88\pm 0.02$). The remaining flux arises from magnetic elements with
lifetimes < 40 hours. By relating the properties of the magnetic elements to
the overall properties of the coronal holes, we find that the unbalanced
magnetic flux of the coronal holes is completely determined by the total area
that the long-lived magnetic elements cover (cc=$0.994\pm 0.001$).",1909.03806v1
1997-10-15,Near-infrared narrow-band photometry of M-giant and Mira stars: models meet observations,"From near-infrared, narrow-band photometry of 256 oxygen-rich Mira variables
we obtain evidence about the loops that these stars follow in colour-colour
diagrams. We also find a phase lag between indices related to molecular
band-strength of titanium oxide and vanadium oxide. We compute colours for
normal M-giants and Miras using hydrostatic and hydrodynamic model atmospheres
and very extensive up-to-date line lists. Normal M-giants colours are well
reproduced, reaching a high quantitative agreement with observations for
spectral types earlier than M7. The out-of-phase variations of the various
spectral features of Miras are also acceptably reproduced, despite limitations
in the modelling. This enables us to confirm that the phase lag phenomenon
results from the propagation of perturbations in the extended atmosphere. It
opens new perspectives in the spectral modelling of Miras.",9710157v1
2005-10-05,Pixie Dust: The Silicate Features in the Diffuse Interstellar Medium,"We have analyzed the 9.7 and ``18'' micron interstellar silicate absorption
features along the line of sight toward four heavily extincted galactic WC-type
Wolf-Rayet (WR) stars. We construct two interstellar extinction curves from
1.25 to 25 micron using near-IR extinction measurements from the literature
along with the silicate profiles of WR 98a (representing the local ISM) and GCS
3 (representing the Galactic Center). We have investigated the mineralogy of
the interstellar silicates by comparing extinction profiles for amorphous
silicates with olivine and pyroxene stochiometry to the 9.7 and ``18'' micron
absorption features in the WR 98a spectrum. In this analysis, we have
considered solid and porous spheres and a continuous distribution of
ellipsoids. While it is not possible to simultaneously provide a perfect match
to both profiles, we find the best match requires a mixture of these two types
of compounds. We also consider iron oxides, aluminosilicates and silicate
carbide (SiC) as grain components. Iron oxides cannot be accommodated in the
observed spectrum, while the amount of Si in SiC is limited to <4%. Finally, we
discuss the cosmic elemental abundance constraints on the silicate mineralogy,
grain shape and porosity.",0510156v1
2006-03-21,"On the Unusual Depletions toward Sk 155, or What Are the Small Magellanic Cloud Dust Grains Made of?","The dust in the Small Magellanic Cloud (SMC), an ideal analog of primordial
galaxies at high redshifts, differs markedly from that in the Milky Way by
exhibiting a steeply rising far-ultraviolet extinction curve, an absence of the
2175 Angstrom extinction feature, and a local minimum at ~12 micron in its
infrared emission spectrum, suggesting the lack of ultrasmall carbonaceous
grains (i.e. polycyclic aromatic hydrocarbon molecules) which are ubiquitously
seen in the Milky Way. While current models for the SMC dust all rely heavily
on silicates, recent observations of the SMC sightline toward Sk 155 indicated
that Si and Mg are essentially undepleted and the depletions of Fe range from
mild to severe, suggesting that metallic grains and/or iron oxides, instead of
silicates, may dominate the SMC dust. However, in this Letter we apply the
Kramers-Kronig relation to demonstrate that neither metallic grains nor iron
oxides are capable of accounting for the observed extinction; silicates remain
as an important contributor to the extinction, consistent with current models
for the SMC dust.",0603573v1
2006-06-06,Constraints on the mass of a habitable planet with water of nebular origin,"From an astrobiological point of view, special attention has been paid to the
probability of habitable planets in extrasolar systems. The purpose of this
study is to constrain a possible range of the mass of a terrestrial planet that
can get water. We focus on the process of water production through oxidation of
the atmospheric hydrogen--the nebular gas having been attracted
gravitationally--by oxide available at the planetary surface. For the water
production to work well on a planet, a sufficient amount of hydrogen and enough
high temperature to melt the planetary surface are needed. We have simulated
the structure of the atmosphere that connects with the protoplanetary nebula
for wide ranges of heat flux, opacity, and density of the nebular gas. We have
found both requirements are fulfilled for an Earth-mass planet for wide ranges
of the parameters. We have also found the surface temperature of planets of <=
0.3 Earth masses is lower than the melting temperature of silicate (~ 1500K).
On the other hand, a planet of more than several Earth masses becomes a gas
giant planet through runaway accretion of the nebular gas.",0606117v1
1996-02-13,Surface Structure and Catalytic $CO$ Oxidation Oscillations,"A cellular automaton model is used to describe the dynamics of the catalytic
oxidation of $CO$ on a $Pt(100)$ surface. The cellular automaton rules account
for the structural phase transformations of the $Pt$ substrate, the reaction
kinetics of the adsorbed phase and diffusion of adsorbed species. The model is
used to explore the spatial structure that underlies the global oscillations
observed in some parameter regimes. The spatiotemporal dynamics varies
significantly within the oscillatory regime and depends on the harmonic or
relaxational character of the global oscillations. Diffusion of adsorbed $CO$
plays an important role in the synchronization of the patterns on the substrate
and this effect is also studied.",9602015v1
1992-09-19,Electron-Phonon Driven Spin Frustration in Multi-Band Hubbard Models: MX Chains and Oxide Superconductors,"We discuss the consequences of both electron-phonon and electron-electron
couplings in 1D and 2D multi-band (Peierls-Hubbard) models. After briefly
discussing various analytic limits, we focus on (Hartree-Fock and exact)
numerical studies in the intermediate regime for both couplings, where unusual
spin-Peierls as well as long-period, frustrated ground states are found. Doping
into such phases or near the phase boundaries can lead to further interesting
phenomena such as separation of spin and charge, a dopant-induced phase
transition of the global (parent) phase, or real-space (``bipolaronic'')
pairing. We discuss possible experimentally observable consequences of this
rich phase diagram for halogen-bridged, transition metal, linear chain
complexes (MX chains) in 1D and the oxide superconductors in 2D.",9209027v1
1993-08-27,Reduction of three-band model for copper oxides to single-band generalized t~-~J model,"A three-band model for copper oxides in the region of parameters where the
second hole on the copper has energy close to the first hole on the oxygen is
considered. The exact solution for one hole on a ferromagnetic background of
the ordered copper spins is obtained. A general procedure for transformation of
the primary Hamiltonian to the Hamiltonian of singlet and triplet excitations
is proposed. Reduction of the singlet-triplet Hamiltonian to the single-band
Hamiltonian of the generalized t~-~J model is performed. A comparison of the
solution for the generalized t~-~J model on a ferromagnetic background with the
exact solution shows a very good agreement.",9308034v1
1995-07-27,Intercalation and Staging Behavior in Super-Oxygenated $La_2CuO_{4 + δ}$,"A high temperature electrochemical oxidation process has been used to produce
large single crystals of $La_2CuO_{4 + \delta}$ suitable for neutron scattering
experiments. Below room temperature the oxygen-rich phases have structural
superlattice scattering peaks which indicate new periodicities ranging from 2
to 6.6 layers perpendicular to the copper oxide planes. A model structure
originally proposed for $La_2NiO_{4 + \delta}$ can account for the superlattice
peaks as a result of anti-phase domain boundaries between different tilt
directions of the CuO$_6$ octahedra. Within this model, the changes in CuO$_6$
tilt directions are induced by segregated layers of interstitial oxygen which
order in a manner similar to intercalants in graphite. This structural model
thus clarifies previous work and establishes $La_2CuO_{4 + \delta}$ as a unique
lamellar superconducting system with annealed disorder.",9507124v1
1995-10-02,A new approach for perovskites in large dimensions,"Using the Hubbard Hamiltonian for transition metal-3d and oxygen-2p states
with perovskite geometry, we propose a new scaling procedure for a nontrivial
extension of these systems to large spatial dimensions $D$. The scaling
procedure is based on a selective treatment of different hopping processes for
large $D$ and can not be generated by a unique scaling of the hopping element.
The model is solved in the limit $D \rightarrow \infty$ by the iterated
perturbation theory and using an extended non-crossing approximation. We
discuss the evolution of quasi particles at the Fermi-level upon doping,
leading to interesting insight into the dynamical character of the charge
carriers near the metal insulator instability of transition metal oxide
systems, three dimensional perovskites and other strongly correlated transition
metal oxides.",9510003v1
1996-02-06,Renormalization Group Approach to the Normal State of Copper-Oxide Superconductors,"We study by means of renormalization group techniques the effect that on the
two-dimensional electron liquid may have the van Hove singularities observed
experimentally in the copper-oxide superconductors. We find significant
deviations from Fermi liquid behavior, that lead to the appearance of an
unstable fixed point in the renormalization group flow of the effective
coupling constant. Besides the attenuation of electron quasiparticles already
known on phenomenological grounds, our approach is able to explain the
reduction in the dispersion of the band as well as the pinning of the Fermi
level near the singularity, as observed in the photoemission experiments.",9602033v1
1996-04-17,Dynamical Mean Field Theory for Perovskites,"Using the Hubbard Hamiltonian for transition metal-3d and oxygen-2p states
with perovskite geometry, we present a dynamical mean field theory which
becomes exactin the limit of large coordination numbers or equivalently large
spatial dimensions $D$. The theory is based on a new description of these
systems for large $D$ using a selective treatment of different hopping
processes which can not be generated by a unique scaling of the hopping
element. The model is solved using a perturbational approach and an extended
non-crossing approximation. We discuss the breakdown of the perturbation theory
near half filling, the origin of the various 3d and 2p bands, the doping
dependence of its spectral weight, and the evolution of quasi particles at the
Fermi-level upon doping, leading to interesting insight into the dynamical
character of the charge carriers near the metal insulator instability of
transition metal oxide systems, three dimensional perovskites and other
strongly correlated transition metal oxides.",9604108v2
1996-05-31,d-wave superconductivity near charge instabilities,"We investigate the symmetry of the superconducting order parameter in the
proximity of a phase-separation or of an incommensurate charge-density-wave
instability. The attractive effective interaction at small or intermediate
transferred momenta is singular near the instability. This strongly
$q$-dependent interaction, together with a residual local repulsion between the
quasiparticles and an enhanced density of states for band structures
appropriate for the high temperature superconducting oxides, strongly favors
the formation of $d$-wave superconductivity. The relative stability with
respect to superconductivity in the $s$-wave channel is discussed in detail,
finding this latter hardly realized in the above conditions. The
superconducting temperature is mostly determined by the closeness to the
quantum critical point associated to the charge instability and displays a
stronger dependence on doping with respect to the simple proximity to a Van
Hove singularity. The relevance of this scenario and the generic agreement of
the resulting phase diagram with the properties displayed by high temperature
superconducting oxides is discussed.",9605193v1
1996-06-22,Orbital Liquid in Perovskite Transition-Metal Oxides,"We study the effects of the degeneracy of the $e_g$ orbitals as well as the
double exchange interaction with $t_{2g}$ spins in perovskite transition-metal
oxides. In addition to the spin field ${\vec S}_i$, the isospin field ${\vec
T}_i$ is introduced to describe the orbital degrees of freedom. The isospin is
the quantum dynamical variable, and is represented by the boson with a
constraint. The dispersion of this boson is flat along $(\pi/a,\pi/a,k_z)$
($a$: lattice constant) and the other two equivalent directions. This enables
the orbital disordered phase down to low temperatures. We interpret some of the
anomalous experiments, i.e., optical absorption and d.c. resistivity, in the
low temperature ferromagnetic phase of La$_{1-x}$Sr$_x$MnO$_3$ with $x > 0.2$
in terms of this orbital liquid picture.",9606160v1
1996-11-12,Estimates of electronic interaction parameters for La$M$O$_3$ compounds ($M$=Ti-Ni) from ab-initio approaches,"We have analyzed the ab-initio local density approximation band structure
calculations for the family of perovskite oxides, La$M$O$_3$ with $M$=Ti-Ni
within a parametrized nearest neighbor tight-binding model and extracted
various interaction strengths. We study the systematics in these interaction
parameters across the transition metal series and discuss the relevance of
these in a many-body description of these oxides. The results obtained here
compare well with estimates of these parameters obtained via analysis of
electron spectroscopic results in conjunction with the Anderson impurity model.
The dependence of the hopping interaction strength, t, is found to be
approximately $r^{-3}$.",9611098v1
1996-11-27,Study of CO Oxidation over Ru(0001) at High Gas Pressures,"Experiments performed at high gas partial pressures have demonstrated that
the kinetics of the CO oxidation reaction at Ru(0001) is different and somewhat
anomalous compared to that over other transition metal surfaces and, in
particular, the turnover rate is exceptionally high. In order to gain insight
into the underlying reasons for this behavior, we performed density functional
theory calculations using the generalized gradient approximation for the
exchange-correlation functional. We find that the high rate is due to a weakly,
but nevertheless well bound, (1x1) oxygen adsorbate layer which may form for
high O_2 pressures but not under usual ultra high vacuum conditions. The
calculations indicate that reaction to CO_2 occurs both via scattering of
gas-phase CO molecules as well as by CO molecules weakly adsorbed at vacancies
in the oxygen adlayer, where the latter mechanism dominates the rate.",9611217v1
1996-11-27,Mechanism of efficient carbon monoxide oxidation at Ru(0001),"We performed density-functional theory calculations using the generalized
gradient approximation for the exhange-correlation functional to investigate
the unusual catalytic behavior of Ru under elevated gas pressure conditions for
the carbon monoxide oxidation reaction, which includes a particularly high CO_2
turnover. Our calculations indicate that a full monolayer of adsorbed oxygen
actuates the high rate, enabling CO_2 formation via both scattering of
gas-phase CO molecules as well as by CO molecules adsorbed at oxygen vacancies
in the adlayer, where the latter mechanism is expected to be very efficient due
to the relatively weak adsorption energy of both CO and O, as well as the close
proximity of these reactants. In the present paper we analyse the bonding and
electronic properties associated with the reaction pathway for CO_2 production
via the scattering reaction. We find that the identified ``bent'' transition
state is due to electron transfer into the unoccupied 2 pi orbitals of the CO
molecule which reduces the Pauli repulsion between the impinging CO and the
O-covered surface. Bond formation to CO_2 then proceeds by electron transfer
back from the CO 2 pi orbitals into the bonding region between CO and the
adsorbed O atom.",9611220v1
1997-05-09,Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides,"We examine the effect on the DC resistivity of small-q electron-phonon
scattering, in a system with the electronic topology of the high-T_c oxides.
Despite the fact that the scattering is dominantly forward, its contribution to
the transport can be significant due to ``ondulations'' of the bands in the
flat region and to the umpklapp process. When the extended van-Hove
singularities are sufficiently close to $E_F$ the acoustic branch of the
phonons contribute significantly to the transport. In that case one can obtain
linear $T$ dependent resistivity down to temperatures as low as 10 K, even if
electrons are scattered also by optical phonons of about 500 K as reported by
Raman measurements.",9705085v1
1998-03-14,Striped phases in the two-dimensional Hubbard model with long-range Coulomb interaction,"We investigate the formation of partially filled domain walls in the
two-dimensional Hubbard model in the presence of long-range interaction. Using
an unrestricted Gutzwiller variational approach we show that: i) the strong
local interaction favors charge segregation in stripe domain walls; ii) The
long-range interaction favors the formation of half-filled vertical stripes
with a period doubling due to the charge and a period quadrupling due to the
spins along the wall. Our results show that, besides the underlying lattice
structure, also the electronic interactions can contribute to determine the
different domain wall textures in Nd doped copper oxides and nickel oxides.",9803184v1
1998-05-27,Charge ordering and long-range interactions in layered transition metal oxides,"We study the competition between long-range and short-range interactions
among holes within the spin density wave picture of layered transition metal
oxides. We focus on the problem of charge ordering and the charge phase
diagram. We show that the main interactions are the long-range Coulomb
interaction and a dipolar short-range interaction generated by the short-range
antiferromagnetic fluctuations. We find four different phases depending on the
strength of the dipolar interaction and the density of holes: Wigner crystal,
diagonal stripes, horizontal-vertical stripes (loops) and a glassy-clumped
phase. We discuss the effect of temperature, disorder and lattice effects on
these phases.",9805367v1
1998-09-23,Transport Properties of the One Dimensional Ferromagnetic Kondo Lattice Model : A Qualitative Approach to Oxide Manganites,"The transport properties of the ferromagnetic Kondo lattice model in one
dimension are studied via bosonization methods. The antiferromagnetic
fluctuations, which normally appear because of the RKKY interactions, are
explicitly taken into account as a direct exchange between the ``core'' spins.
It is shown that in the paramagnetic regime with the local antiferromagnetic
fluctuations, the resistivity decays exponentially as the temperature increases
while in the ferromagnetic regime the system is an almost perfect conductor. %A
non-perturbative description of localized spin polarons %in the paramagnetic
region is obtained.
  The effect of a weak applied field is discussed to be reduced to the case of
the ferromagnetic state leading to band splitting. The qualitative relevance of
the results for the problem of the Oxide Manganites is emphasized.",9809309v1
1998-10-21,Ferromagnetic ground state of an orbital degenerate electronic model for transition-metal oxides: exact solution and physical mechanism,"We present an exact ground state solution of a one-dimensional electronic
model for transition-metal oxides in the strong coupling limit. The model
contains doubly degenerated orbit for itinerant electrons and the Hund coupling
between the itinerant electrons and localized spins. The ground state is proven
to be a full ferromagnet for any density of electrons. Our model provides a
rigorous example for metallic ferromagnetism in narrow band systems. The
physical mechanism for ferromagnetism and its relevance to high-dimensional
systems, like R$_{1-x}$X$_x$MnO$_3$, are discussed. Due to the orbital
degeneracy of itinerant electrons, the superexchange coupling can be
ferromagnetic rather than antiferromagnetic in the one-band case.",9810268v1
1998-11-26,Kinetics of electric field induced oxygen ion migration in epitaxial metallic oxide films,"In this paper we report the observation of curent induced change of
resistance of thin metallic oxide films. The resistance changes at a very low
current (current density $J \geq 10^{3}$ A/cm$^{2}$). We find that the time
dependence associated with the processes (increase of resistance) show a
streched exponential type dependence at lower temperature, which crosses over
to a creep type behavior at $T \geq$ 350 K. The time scale associated shows a
drastic drop in the magnitude at $T \approx$ 350 K, where a long range
diffusion sets in increasing the conductivity noise. The phenomena is like a
""glass-transition"" in the random lattice of oxygen ions.",9811377v1
1999-01-08,The Phase Separation Scenario for Manganese Oxides,"Recent computational studies of models for manganese oxides have revealed a
rich phase diagram, not anticipated in early calculations in this context
performed in the 1950's and 60's. In particular, the transition between the
antiferromagnetic insulator state of the hole-undoped limit and the
ferromagnetic metal at finite hole-density was found to occur through a
mixed-phase process. When extended Coulomb interactions are included, a
microscopically charge inhomogeneous state should be stabilized. These phase
separation tendencies, also present at low electronic densities, influence the
properties of the ferromagnetic region by increasing charge fluctuations.
Experimental data reviewed here using several techniques for manganites and
other materials are consistent with this scenario. Similarities with results
previously discussed in the context of cuprates are clear from this analysis,
although the phase segregation tendencies in manganites seem stronger.",9901057v2
1999-02-10,Threshold electronic structure at the oxygen K edge of 3d transition metal oxides: a configuration interaction approach,"It has been generally accepted that the threshold structure observed in the
oxygen K edge X-ray absorption spectrum in 3d transition metal oxides
represents the electronic structure of the 3d transition metal. There is,
however, no consensus about the correct description. We present an
interpretation, which includes both ground state hybridization and electron
correlation. It is based on a configuration interaction cluster calculation
using a MO6 cluster. The oxygen K edge spectrum is calculated by annihilating a
ligand hole in the ground state and is compared to calculations representing
inverse photoemission experiments in which a 3d transition metal electron is
added. Clear differences are observed related to the amount of ligand hole
created in the ground state. Two ""rules"" connected to this are discussed.
Comparison with experimental data of some early transition metal compounds is
made and shows that this simple cluster approach explains the experimental
features quite well.",9902132v2
1999-03-29,Structure and energetics of the Si-SiO_2 interface,"Silicon has long been synonymous with semiconductor technology. This unique
role is due largely to the remarkable properties of the Si-SiO_2 interface,
especially the (001)-oriented interface used in most devices. Although Si is
crystalline and the oxide is amorphous, the interface is essentially perfect,
with an extremely low density of dangling bonds or other electrically active
defects. With the continual decrease of device size, the nanoscale structure of
the silicon/oxide interface becomes more and more important. Yet despite its
essential role, the atomic structure of this interface is still unclear. Using
a novel Monte Carlo approach, we identify low-energy structures for the
interface. The optimal structure found consists of Si-O-Si ""bridges"" ordered in
a stripe pattern, with very low energy. This structure explains several
puzzling experimental observations.",9903424v1
1999-05-19,Effects of Orbital Degeneracy and Electron Correlation on Charge Dynamics in Perovskite Manganese Oxides,"Taking the orbital degeneracy of $e_g$ conduction bands and the Coulomb
interaction into account in a double-exchange model, we investigate charge
dynamics of perovskite Mn oxides by the Lancz$\ddot{\rm o}$s diagonalization
method. In the metallic phase near the Mott insulator, it is found that the
optical conductivity for a spin-polarized two-dimensional system exhibits a
weight transfer to a broad and incoherent structure within the lower-Hubbard
band together with a suppressed Drude weight. It reproduces qualitative feature
of the experimental results. As an orbital effect, we find that an anomalous
charge correlation at quarter filling suppresses the coherent charge dynamics
and signals precursor to the charge ordering.",9905271v1
1999-06-17,Anomalous c-axis charge dynamics in copper oxide materials,"Within the t-J model, the c-axis charge dynamics of the copper oxide
materials in the underdoped and optimally doped regimes is studied by
considering the incoherent interlayer hopping. It is shown that the c-axis
charge dynamics is mainly governed by the scattering from the in-plane
fluctuation. In the optimally doped regime, the c-axis resistivity is a linear
in temperatures, and shows the metallic-like behavior for all temperatures,
while the c-axis resistivity in the underdoped regime is characterized by a
crossover from the high temperature metallic-like behavior to the low
temperature semiconducting-like behavior, which are consistent with experiments
and numerical simulations.",9906260v2
1999-09-23,In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography,"A single-electron transistor has been realized in a Ga[Al]As heterostructure
by oxidizing lines in the GaAs cap layer with an atomic force microscope. The
oxide lines define the boundaries of the quantum dot, the in-plane gate
electrodes, and the contacts of the dot to source and drain. Both the number of
electrons in the dot as well as its coupling to the leads can be tuned with an
additional, homogeneous top gate electrode. Pronounced Coulomb blockade
oscillations are observed as a function of voltages applied to different gates.
We find that, for positive top-gate voltages, the lithographic pattern is
transferred with high accuracy to the electron gas. Furthermore, the dot shape
does not change significantly when in-plane voltages are tuned.",9909340v1
1999-10-17,Shrinking limits of silicon MOSFET's: Numerical study of 10-nm-scale devices,"We have performed numerical modeling of dual-gate ballistic n-MOSFET's with
channel length of the order of 10 nm, including the effects of quantum
tunneling along the channel and through the gate oxide. Our analysis includes a
self-consistent solution of the full (two-dimensional) electrostatic problem,
with account of electric field penetration into the heavily-doped electrodes.
The results show that transistors with channel length as small as 8 nm can
exhibit either a transconductance up to 4,000 mS/mm or gate modulation of
current by more than 8 orders of magnitude, depending on the gate oxide
thickness. These characteristics make the devices satisfactory for logic and
memory applications, respectively, though their gate threshold voltage is
rather sensitive to nanometer-scale variations in the channel length.",9910258v1
1999-10-22,Pseudogap due to antiferromagnetic fluctuations and the phase diagram of the high temperature oxide superconductors,"A reduction of the density of states near the Fermi energy in the normal
state (pseudogap) of high-temperature oxide superconductors is examined on the
basis of the two-dimensional tight-binding model with effective interactions
due to antiferromagnetic fluctuations. By using antiferromagnetic correlation
lengths which are phenomenologically assumed, the doping dependence of the
pseudogap is obtained. The superconducting transition temperature decreases and
eventually vanishes due to the pseudogap as the hole concentration is reduced.",9910349v4
2000-03-16,EXAFS indication of double-well potential for oxygen vibration in Ba_{1-x}K_xBiO_3,"X-ray absorption spectra of oxide systems Ba_{1-x}K_xBiO_3 and BaPbO_3 above
Bi- and Pb-L3 absorption edges were investigated. It was shown that oxygen ions
move in double-well potential and their oscillations are correlated with charge
carrier movement. Observed breathing-like oxygen vibration in double-well
potential with large amplitude and low frequency causes the strong
electron-phonon coupling and high Tc values in doped BaBiO_3. Based on the
experimental data, the model of relationship of electronic and local crystal
structures is proposed that is in a good agreement with the results of
transport measurements, inelastic neutron and electron scattering, Raman
scattering, and photoemission spectroscopy. In the framework of the model the
possible reasons of superconductivity in perovskite-like oxides are discussed.",0003279v1
2000-04-14,Incoherent Charge Dynamics in Perovskite Manganese Oxides,"A minimal model is proposed for the perovskite manganese oxides showing the
strongly incoherent charge dynamics with a suppressed Drude weight in the
ferromagnetic and metallic phase near the insulator. We investigate a
generalized double-exchange model including three elements; the orbital
degeneracy of $e_g$ conduction bands, the Coulomb interaction and fluctuating
Jahn-Teller distortions. We demonstrate that Lancz$\ddot{\rm o}$s
diagonalization calculations combined with Monte Carlo sampling of the largely
fluctuating lattice distortions result in the optical conductivity which
quantitatively accounts for the experimental indications. It is found that all
the three elements are indispensable to understand the charge dynamics in these
compounds.",0004232v1
2000-04-17,Ferromagnetism and phase separation in one-dimensional d-p and periodic Anderson models,"Using the Density Matrix Renormalization Group, we study metallic
ferromagnetism in a one-dimensional copper-oxide model which contains one
oxygen p-orbital and one copper d-orbital. The parameters for the d-p model can
be chosen so that it is similar to the one-dimensional periodic Anderson model.
For these parameters, we compare the ground-state phase diagram with that of
the Anderson model and find a ferromagnetic region analogous to one found in
the Anderson model, but which is pushed to somewhat higher densities and
interaction strengths. In both models, we find a region within the
ferromagnetic phase in which phase separation between a localized ferromagnetic
domain and a weakly antiferromagnetic regime occurs. We then choose a set of
parameter values appropriate for copper-oxide materials and explore the
ground-state phase diagram as a function of the oxygen-oxygen hopping strength
and the electron density. We find three disconnected regions of metallic
ferromagnetism and give physical pictures of the three different mechanisms for
ferromagnetism in these phases.",0004265v1
2000-11-22,Surface melting of methane and methane film on magnesium oxide,"Experiments on surface melting of several organic materials have shown
contradictory results. We study the Van der Waals interactions between
interfaces in surface melting of the bulk CH_4 and interfacial melting of the
CH_4 film on the MgO substrate. This analysis is based on the theory of
Dzyaloshinskii, Lifshitz, and Pitaevskii for dispersion forces in materials
characterized by the frequency dependent dielectric functions. These functions
for magnesium oxide and methane are obtained from optical data using an
oscillator model of the dielectric response. The results show that a repulsive
interaction between the solid-liquid and liquid-vapor interfaces exists for the
bulk methane. We also found that the van der Waals forces between two
solid-liquid interfaces are attractive for the CH_4 film on the MgO substrate.
This implies that the van der Waals forces induce the presence of complete
surface melting for the bulk methane and the absence of interfacial melting for
CH_4 on the MgO substrate.",0011377v1
2000-11-25,Memory Effect in Silicon Nitride in Silicon Devices,"The dominant dielectric used currently in silicon devices is silicon oxide.
Its application for future devices will be impeded by several fundamental
limitations which lead to low reliability of semiconductor devices and to the
necessity of alternative dielectrics. Amorphous silicon nitride and oxynitride
are considered now as alternative to silicon oxide in future devices. One of
the unique property of amorphous silicon nitride is the electron and hole
capture by the deep traps with extremely long life time (10 years) in the
captured state (the memory effect). This property is employed in memory devices
and microprocessors in computers. Despite numerous efforts the nature of traps
responsible for the memory effect in this material is so far unclear. In this
paper we discuss the nature of such traps using the quantum-chemical
simulation. The calculations show that the defects responsible for the electron
and hole capture in amorphous silicon nitride can be the Si-Si defects created
by excess silicon atoms.",0011435v1
2000-11-25,Evidence for novel polaronic Fermi-liquid in doped oxides,"The modern multi-polaron theory predicts a polaronic Fermi-liquid state, but
such a state has not been unambigously confirmed by experiment so far. Here we
report theoretical and experimental studies of the isotope effects on the low
temperature kinetic properties of the doped ferromagnetic manganites. Our
results provide clear evidence for a novel polaronic Fermi-liquid state in
doped oxides.",0011436v2
2001-02-20,Spinwaves and large electron-phonon coupling near the metal-insulator transition in hole-doped high-T$_C$ oxides,"A theory for spin and lattice couplings to the electronic states in
high-T$_C$ oxides is presented, with HgBa$_2$CuO$_4$ as an example. A simple
analytical model suggests that the barrel band is sensitive to potential
perturbations with long-range Fourier components, and that gaps can be opened
at the Fermi energy. This is confirmed in self-consistent band calculations for
modulations in elongated supercells, where spin waves and phonon coupling
compete for equal q-vectors. It is argued that the wavelengths of spin-wave
modulations and of the phonon modes with large coupling, depend on the doping.
This mechanism supports the idea that pseudogaps are caused by stripe like
spin-modulations in underdoped systems, while superconductivity is attributed
to enhanced electron-phonon coupling for long wavelength phonons.",0102343v1
2001-03-08,Superconducting thin films of MgB2 on (001)-Si by pulsed laser deposition,"Superconducting thin films have been prepared on Si-substrates, using pulsed
laser deposition from a target composed of a mixture of Mg and MgB2 powders.
The films were deposited at room temperature and post-annealed at 600 degrees
C. The zero resistance transition temperatures were 12 K, with an onset
transition temperature of 27 K. Special care has been taken to avoid oxidation
of Mg in the laser plasma and deposited film, by optimizing the background
pressure of Ar gas in the deposition chamber. For this the optical emission in
the visible range from the plasma has been used as indicator. Preventing Mg
from oxidation was found to be essential to obtain superconducting films.",0103198v1
2001-03-28,Soft x-ray spectroscopy measurements of the p-like density of states of B in MgB2 and evidence for surface boron oxides on exposed surfaces,"Soft X-ray absorption and fluorescence measurements are reported for the
K-edge of B in MgB2. The measurements confirm a high density of B
pxy(sigma)-states at the Fermi edge and extending to approximately 0.9 eV above
the edge. A strong resonance is observed in elastic scattering through a
core-exciton derived from out-of-plane pz(pi*)-states. Another strong
resonance, observed in both elastic and inelastic spectra, is identified as a
product of surface boron oxides.",0103593v1
2001-04-09,A continuous compositional-spread technique based on pulsed-laser deposition and applied to the growth of epitaxial films,"A novel continuous-compositional spread technique based on the non-uniformity
of the deposition rate typically observed in Pulsed Laser Deposition (PLD) is
introduced. The approach uses the spatial variations in the deposition-rate
naturally occurring in PLD; therefore, there is no need for the masks typically
used in combinatorial techniques. Consequently, combinatorial materials
synthesis can be carried out under optimized film growth conditions (e.g. at
high temperature). Additionally, lifting the need for post-annealing renders
this method applicable to heat-sensitive materials and substrates (e.g. films
of transparent oxides on polymer substrates). Composition determination across
the sample and mapping of physical properties onto the ternary phase diagram is
achieved via a simple algorithm using the parameters that describe the
deposition-rate profiles. Results are shown for the high-temperature growth of
crystalline perovskites (including (Ba,Sr)TiO3 and the formation of a
metastable alloy between SrRuO3 and SrSnO3) and the room-temperature growth of
transparent conducting oxides.",0104157v1
2001-04-17,Surface Core-Level Shifts at an oxygen-rich Ru Surface: O/Ru(0001) vs. RuO_2(110),"We present density-functional theory calculations of Ru 3d and O 1s surface
core-level shifts (SCLSs) at an oxygen-rich Ru(0001) surface, namely for the
O(1x1)/Ru(0001) chemisorption phase and for two surface terminations of fully
oxidized RuO_2(110). Including final-state effects, the computed SCLSs can be
employed for the analysis of experimental X-ray photoelectron spectroscopy
(XPS) data enabling a detailed study of the oxidation behaviour of the Ru(0001)
surface. We show that certain peaks can be used as a fingerprint for the
existence of the various phases and propose that the long disputed satellite
peak in RuO_2(110) XPS data originates from a hitherto unaccounted surface
termination.",0104306v2
2001-06-29,Fermi Surface Nesting and Nanoscale Fluctuating Charge/Orbital Ordering in Colossal Magnetoresistive Oxides,"We used high resolution angle-resolved photoemission spectroscopy to reveal
the Fermi surface and key transport parameters of the metallic state of the
layered Colossal Magnetoresistive (CMR) oxide La1.2Sr1.8Mn2O7. With these
parameters the calculated in-plane conductivity is nearly one order of
magnitude larger than the measured DC conductivity. This discrepancy can be
accounted for by including the pseudogap which removes at least 90% of the
spectral weight at the Fermi energy. Key to the pseudogap and many other
properties are the parallel straight Fermi surface sections which are highly
susceptible to nesting instabilities. These nesting instabilities produce
nanoscale fluctuating charge/orbital modulations which cooperate with
Jahn-Teller distortions and compete with the electron itinerancy favored by
double exchange.",0106655v1
2001-07-11,"Composition, structure and stability of RuO_2(110) as a function of oxygen pressure","Using density-functional theory (DFT) we calculate the Gibbs free energy to
determine the lowest-energy structure of a RuO_2(110) surface in thermodynamic
equilibrium with an oxygen-rich environment. The traditionally assumed
stoichiometric termination is only found to be favorable at low oxygen chemical
potentials, i.e. low pressures and/or high temperatures. At realistic O
pressure, the surface is predicted to contain additional terminal O atoms.
Although this O excess defines a so-called polar surface, we show that the
prevalent ionic model, that dismisses such terminations on electrostatic
grounds, is of little validity for RuO_2(110). Together with analogous results
obtained previously at the (0001) surface of corundum-structured oxides, these
findings on (110) rutile indicate that the stability of non-stoichiometric
terminations is a more general phenomenon on transition metal oxide surfaces.",0107229v1
2001-10-22,A Novel Theory for High Temperature Superconductors considering Inhomogeneous Charge Distributions,"We present a percolation theory for the high-$T_c$ oxides pseudogap and $T_c$
dependence on the hole level. The doping dependent inhomogeneous charge
structure is modeled by a distribution which may represent the stripe
morphology and yield a spatial distribution of local $T_c(r)$. The temperature
onset of spatial dependent superconducting gap is identified with the vanishing
of the pseudogap temperature $T^*$. The transition to a superconducting state
corresponds to the percolation threshold among regions of different $T_c$. As a
paradigm we use a Hubbard Hamiltonian with a mean field approximation to yield
a doping and temperature dependent superconducting d-wave gap. We show here
that this new approach reproduces the phase diagram, explains and gives new
insights on several experimental features of high-$T_c$ oxides.",0110479v1
2001-11-20,High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7,"Superconducting and structural phase transitions in a pyrochlore oxide
Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical
resistivity measurements. A rich P-T phase diagram is obtained, which contains
at least two phases with the ideal and slightly distorted pyrochlore
structures. It is found that the transition between them is suppressed with
increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa.
Remarkable enhancements in the residual resistivity as well as the coefficient
A of the AT 2 term in the resistivity are found around the critical pressure.
Superconductivity is detected only for the phase with the structural
distortion. It is suggested that the charge fluctuations of Re ions play a
crucial role in determining the electronic properties of Cd2Re2O7.",0111388v2
2002-01-09,A Quantum-Dot Array as Model for Copper-Oxide Superconductors: A Dedicated Quantum Simulator for the Many-Fermion Problem,"Quantum systems with a large number of fermionic degrees of freedom are
intractable by quantum simulations. In this paper we introduce the concept of a
dedicated quantum simulator(DQS) which is an artificial system of quantum dots
whose Hamiltonian maps exactly to the original many fermion problem. While the
universal quantum simulator (UQS) introduced by Feynman in 1982 can simulate
any quantum mechanical many-body problem, a DQS can only solve a particular
many body problem. Our concept of the dedicated quantum simulator is not a
quantum computer but rather a quantum ""analog"" device, dedicated to a
particular quantum computation. As an example, we consider the system of the
$CuO$ plane in the copper-oxide superconductors and we propose an array of
electrostatically confined quantum dots to be used as its dedicated quantum
simulator. We show that this dedicated device can be used to image stripe
formation as a function of the electron doping using electric force microscopy.
We argue that such a dedicated quantum simulator may be easier to realize in
the future compared to a general purpose quantum computer.",0201142v1
2002-01-29,Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides,"We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of $t$ and
$\delta$. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.",0201524v1
2002-04-11,In-plane Anisotropy on Resistivity and Thermopower in The Misfit Layered Oxide Bi2-xPbxSr2Co2Oy,"We investigated the in-plane anisotropy on the resistivity and thermopower of
Bi2-xPbxSr2Co2Oy single crystals, which have a misfit structure between the
hexagonal CoO2 layer and the rock salt Bi2Sr2O4 layer. The resistivity and
thermopower show significantly large anisotropy, which exceeds two at maximum.
This anisotropy would come from the anisotropic pseudogap formation enhanced by
the misfit structure. The thermopower changes with Pb doping to take a maximum
at x=0.4. The misfit structure improves the thermoelectric properties through
chemical pressure. The power factor is as large as 9 muW/cmK2 at 100 K for
x=0.6, which is the highest value for thermoelectric oxides at 100 K.",0204245v1
2002-08-07,Size and Location Control of Si Nanocrystals at Ion Beam Synthesis in Thin SiO2 Films,"Binary collision simulations of high-fluence 1 keV Si ion implantation into 8
nm thick SiO2 films on (001)Si were combined with kinetic Monte Carlo
simulations of Si nanocrystal (NC) formation by phase separation during
annealing. For nonvolatile memory applications, these simulations help to
control size and location of NCs. For low concentrations of implanted Si, NCs
form via nucleation, growth and Ostwald ripening, whereas for high
concentrations Si separates by spinodal decomposition. In both regimes, NCs
form above a thin NC free oxide layer at the SiO2/Si interface. This,
self-adjusted layer has just a thickness appropriate for NC charging by direct
electron tunneling. Only in the nucleation regime the width of the tunneling
oxide and the mean NC diameter remain constant during a long annealing period.
This behavior originates from the competition of Ostwald ripening and Si loss
to the Si/SiO2 interface. The process simulations predict that, for nonvolatile
memories, the technological demands on NC synthesis are fulfilled best in the
nucleation regime.",0208137v1
2002-10-04,Steps on current-voltage characteristics of a silicon quantum dot covered by natural oxide,"Considering a double-barrier structure formed by a silicon quantum dot
covered by natural oxide with two metallic terminals, we derive simple
conditions for a step-like voltage-current curve. Due to standard chemical
properties, doping phosphorus atoms located in a certain domain of the dot form
geometrically parallel current channels. The height of the current step
typically equals to (1.2 pA)N, where N=0,1,2,3... is the number of doping atoms
inside the domain, and only negligibly depends on the actual position of the
dopants. The found conditions are feasible in experimentally available
structures.",0210104v2
2002-10-17,Phase evolution of layered cobalt oxides versus varying corrugation of the cobalt-oxygen basal plane,"A general spin-state model and a qualitative physical picture have been
proposed for a class of lately synthesized layered cobalt oxides (LCOs) by
means of density functional calculations. As the plane corrugation of the
cobalt-oxygen layer decreases, the LCOs evolve from a high-spin (HS)
superexchange-coupled antiferromagnetic (AFM) insulator to an almost-HS
AFM/ferromagnetic (FM) competing system where the FM coupling is mediated via
the p-d exchange by an increasing amount of delocalized pd\sigma holes having
mainly the planar O 2p character. It is tentatively suggested that the
delocalized holes more than 0.3 per CoO_{2} basal square are likely necessary
for the insulator-metal and/or AFM-FM transitions in the corrugation-weakened
LCOs. A phase control may be realized in LCOs by varying the plane corrugation
(thus modifying the hole concentration) through an ionic-size change of the
neighboring layers on both sides of the cobalt-oxygen layer. In addition, a few
experiments are suggested for a check of the present model and picture.",0210369v1
2002-10-30,"Oxygen Stoichiometry in Co-1212, Co-1222 and Co-1232 of Homologous Series Co-12s2 of Category-B Layered Copper Oxides","Here results of a systematic study on oxygen stoichiometry are reported for
the first three members of the novel CoSr2(Y,Ce)sCu2O5+2s or Co-12s2 homologous
series, i.e. Co-1212, Co-1222 and Co-1232 phases with a
SrO-CoO1-SrO-CuO2-(Y,Ce)-[O2-(Y,Ce)]s-1-CuO2 layered structure. The oxygen
content was precisely determined by two independent chemical techniques:
coulometric Cu+/Cu2+ titration and iodometric titration. Furthermore, oxygen
stability/tunability was investigated by means of oxygenative and reductive
an-nealings carried out in a thermobalance. It was revealed that all the three
phases are rather stoichiometric in oxygen content and stable against both
oxygenative and reductive an-nealings. The present results for the Co-12s2
homologous series suggest that not only the CoO1 charge reservoir but also the
nominally oxygen-stoichiometric B-[O2-B]s-1 fluo-rite block, that is the
characteristic structural element for the Co-12s2 (s > 1) phases and all other
layered copper oxides of category-B [H. Yamauchi and M. Karppinen, Superlatt.
Microstructr. 21A (1997) 128] is non-tunable in terms of the oxygen content.",0210660v1
2002-12-13,The effect of a nucleating agent on lamellar growth in melt-crystallizing polyethylene oxide,"The effects of a (non co-crystallizing) nucleating agent on secondary
nucleation rate and final lamellar thickness in isothermally melt-crystallizing
polyethylene oxide are considered. SAXS reveals that lamellae formed in
nucleated samples are thinner than in the pure samples crystallized at the same
undercoolings. These results are in quantitative agreement with growth rate
data obtained by calorimetry, and are interpreted as the effect of a local
decrease of the basal surface tension, determined mainly by the nucleant
molecules diffused out of the regions being about to crystallize. Quantitative
agreement with a simple lattice model allows for some interpretation of the
mechanism.",0212328v1
2003-02-10,Dinitrosyl formation as an intermediate stage of the reduction of NO in the presence of MoO_3,"We present first-principles calculations in the framework of
density-functional theory and the pseudopotential approach, aiming to model the
intermediate stages of the reduction of NO in the presence of MoO$_3$(010). In
particular, we study the formation of dinitrosyl, which proves to be an
important intermediate stage in the catalytic reduction. We find that the
replacement of an oxygen of MoO$_3$ by NO is energetically favorable, and that
the system lowers further its energy by the formation of (NO)$_2$. Moreover,
the geometry and charge distribution for the adsorbed dinitrosyl indicates a
metal-oxide mediated coupling between the two nitrogen and the two oxygen
atoms. We discuss the mechanisms for the dinitrosyl formation and the role of
the oxide in the reaction.",0302189v1
2003-02-20,Correlation and surface effects in Vanadium Oxides,"Recent photoemission experiments have shown strong surface modifications in
the spectra from vanadium oxides as (V,Cr)_2O_3 or
  (Sr,Ca)VO_3. The effective mass is enhanced at the surface and the coherent
part of the surface spectrum is narrowed as compared to the bulk. The
quasiparticle weight is more sensitive at the surface than in the bulk against
bandwidth variations. We investigate these effects theoretically considering
the single-band Hubbard model for a film geometry. A simplified dynamical
mean-field scheme is used to calculate the main features of the interacting
layer-dependent spectral function. It turns out that the experimentally
confirmed effects are inherent properties of a system of strongly correlated
electrons. The reduction of the weight and the variance of the coherent part of
the surface spectrum can be traced back to the reduced surface coordination
number. Surface correlation effects can be strongly amplified by changes of the
hopping integrals at the surface.",0302427v1
2003-03-19,Is the Superconductiong State for the Cuprates Reached Through a Percolation Transition?,"Several recent experiments have revealed that the charge density $\rho$ in a
given compound (mostly underdoped) is intrinsic inhomogeneous with large
nanoscale spatial variations. Therefore it is appropriate to define a local
charge density $\rho(r)$. These differences in the local charge concentration
yield insulator and metallic regions, either in an intrinsic granular or in a
stripe morphology. In the metallic region, the inhomogeneous charge density
produces spatial or local distributions of superconducting critical
temperatures $T_c(r)$ and zero temperature gap $\Delta_0(r)$. We propose that
the superconducting phase in high-$T_c$ oxides is reached when the temperature
reachs a value which superconduction regions with different critical
temperatures percolates. We show also that this novel approach is able to
reproduce the phase diagram for a family of cuprates and provides new insights
on several experimental features of high-$T_c$ oxides",0303398v1
2003-03-21,Curie temperature enhancement of electron doped Sr$_2$FeMoO$_6$ perovskites studied by photoemission spectroscopy,"We report here on the electronic structure of electron-doped half-metallic
ferromagnetic perovskites such Sr$_{2-x}$La$_x$FeMoO$_6$ ($x$=0-0.6) as
obtained from high-resolved valence-band photoemission spectroscopy (PES). By
comparing the PES spectra with band structure calculations, a distinctive peak
at the Fermi level (E$_F$) with predominantly (Fe+Mo) t$_{2g}^\downarrow$
character has been evidenced for all samples, irrespectively of the $x$ values
investigated. Moreover, we show that the electron doping due to the La
substitution provides selectively delocalized carriers to the
t$_{2g}^\downarrow$ metallic spin channel. Consequently, a gradual rising of
the density of states at the E$_F$ has been observed as a function of the La
doping. By changing the incoming photon energy we have shown that electron
doping mainly rises the density of states of Mo parentage. These findings
provide fundamental clues for understanding the origin of ferromagnetism in
these oxides and shall be of relevance for tailoring oxides having still higher
T$_C$.",0303464v1
2003-04-04,The Pd(100)-(SQRT(5) x SQRT(5) R27^o)-O surface oxide revisited,"Combining high-resolution core-level spectroscopy (HRCLS), scanning tunneling
microscopy (STM) and density-functional theory
  (DFT) calculations we reanalyze the Pd(100)-(SQRT(5) x SQRT(5) R27^o)-O
surface oxide phase. We find that the prevalent structural model, a rumpled
PdO(001) film suggested by previous low energy electron diffraction (LEED) work
(M. Saidy et al.,
  Surf. Sci. 494, L799 (2001)), is incompatible with all three employed
methods. Instead, we suggest the two-dimensional film to consist of a strained
PdO(101) layer on top of Pd(100). LEED intensity calculations show that this
model is compatible with the experimental data of Saidy et al.",0304107v1
2003-04-22,Sodium and oxygen nonstoichiometry and thermoelectric properties of NaxCoO2+d,"The sodium-cobalt oxide NaxCoO2+d is a promising candidate for thermoelectric
applications since it may possess simultaneously large thermoelectric power and
low resistivity. It is difficult to understand the simultaneous appearance of
the two properties within the framework of conventional one-electron models. It
has been suggested that the spin state of cobalt ions plays a crucially
important role in enhancing the thermoelectric power. In order to study the
relationship between the cobalt spin state and thermoelectric properties,
NaxCoO2+d samples with precisely controlled sodium and oxygen contents are
indispensable. Recently, we established an uncon-ventional sample-synthesis
method that enables us to precisely control the Na content in NaxCoO2+d
samples. In this article, we discuss the effects of sodium and oxygen
nonstoichiometry on the thermoelectric properties of NaxCoO2+d.",0304479v1
2003-04-24,Room Temperature Electrochemical Synthesis of Hg-1212 Superconducting Thin Films,"In the present investigation, the novel two-step electrochemical process of
room temperature synthesis of Hg-1212 superconducting films has been developed
and reported first time. Electrochemical parameters were optimized by studying
cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry
(CA) for the deposition of Hg-Ba-Ca-Cu alloy at room temperature. Current time
transient showed progressive growth with hemispheriodal granules, which were
then revealed by scanning electron microscopy (SEM). Stoichiometric
electrocrystallization to get Hg1Ba2Ca1Cu2O6+x (Hg-1212) was completed by
electrochemically intercalating oxygen species into Hg-Ba-Ca-Cu alloy at room
temperature. The oxygen content in the samples was varied by varying the
electrochemical oxidation period and the changes in the crystal structure,
microstructure, and superconducting transition temperature (Tc) and critical
current density (Jc) were recorded. The films oxidized for 28 min showed Tc =
104.7 K with Jc = 1.437 x 103 A/cm2. The dependence of superconducting
parameters on oxygen content is correlated with structure property relations
and reported in this paper.",0304566v1
2003-05-03,Synthesis of Single Phase Hg-1223 High Tc Superconducting Films With Multistep Electrolytic Process,"We report the multistep electrolytic process for the synthesis of high Tc
single phase HgBa2Ca2Cu3O8+&#61540; (Hg-1223) superconducting films. The
process includes : i) deposition of BaCaCu precursor alloy, ii) oxidation of
BaCaCu films, iii) electrolytic intercalation of Hg in precursor BaCaCuO films
and iv) electrochemical oxidation and annealing of Hg-intercalated BaCaCuO
films to convert into Hg1Ba2Ca2Cu3O8+&#61540; (Hg-1223). Films were
characterized by thermo-gravimetric analysis (TGA) and differential thermal
analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM).
The electrolytic intercalation of Hg in BaCaCuO precursor is proved to be a
novel alternative to high temperature-high pressure mercuration process. The
films are single phase Hg-1223 with Tc = 121.5 K and Jc = 4.3 x 104 A/cm2.",0305059v1
2003-05-23,Drain Voltage Scaling in Carbon Nanotube Transistors,"While decreasing the oxide thickness in carbon nanotube field-effect
transistors (CNFETs) improves the turn-on behavior, we demonstrate that this
also requires scaling the range of the drain voltage. This scaling is needed to
avoid an exponential increase in Off-current with drain voltage, due to
modulation of the Schottky barriers at both the source and drain contact. We
illustrate this with results for bottom-gated ambipolar CNFETs with oxides of 2
and 5 nm, and give an explicit scaling rule for the drain voltage. Above the
drain voltage limit, the Off-current becomes large and has equal electron and
hole contributions. This allows the recently reported light emission from
appropriately biased CNFETs.",0305570v1
2003-05-28,Structural Studies on Semiconducting Hydrogenated Amorphous Silicon Oxide Films,"In hydrogenated amorphous silicon oxide (a-SiO:H) films, incorporation of
oxygen enhances optical gap due to a large number of St-O-Si bond formation,
which lies deep into valence band states. An induction effect of this Si-O on
other bonds within the network also takes place. At higher oxygen content
micro-void forms and bonded hydrogen accumulates in di and/or polyhydride form.
At this stage a phase separation of Si-rich and O-rich region taking place. A
peak shift of absorption spectra within 1850 - 2250 cm-1, towards higher wave
number is continuous. A gradual increase and broadening of 850 cm-1 absorption
band on both sides of peak position indicate higher structural disorder in
network formation. It may be considered that the stretching vibration of-OH
bonded to Si gives rise to 780 cm-1 absorption band. This Si-OH formation is
beneficial which prevents deterioration in photosensitivity due to reduction in
bonded hydrogen content. Hydrogen content is found reducing as oxygen content
increases from zero to ~15 at.%. A systematic study is carried out to correlate
the optoelectronic property with local atomic arrangement.",0305636v1
2003-06-06,Non-linear electrical response in a charge/orbital ordered $\Pr_{0.63}$Ca$_{0.37}$MnO$_3$ crystal : the charge density wave analogy,"Non-linear conduction in a charge-ordered manganese oxide
Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ is reported. To interpret such a feature, it is
usually proposed that a breakdown of the charge or orbitally ordered state is
induced by the current. The system behaves in such a way that the bias current
may generate metallic paths giving rise to resistivity drop. One can describe
this feature by considering the coexistence of localized and delocalized
electron states with independent paths of conduction. This situation is
reminiscent of what occurs in charge density wave systems where a similar
non-linear conduction is also observed. In the light of recent experimental
results suggesting the development of charge density waves in charge and
orbitally ordered manganese oxides, a phenomenological model for charge density
waves motion is used to describe the non-linear conduction in
Pr$_{0.63}$Ca$_{0.37}$MnO$_3$. In such a framework, the non-linear conduction
arises from the motion of the charge density waves condensate which carries a
net electrical current.",0306161v1
2003-06-10,Vortex Core Excitations in Superconductors with Frustrated Antiferromagnetism,"Motivated by recent discovery of cobalt oxide and organic superconductors, we
apply an effective model with strong antiferromagnetic and superconducting
pairing interaction to a related lattice structure. It is found that the
antiferromagnetism is highly frustrated and a broken-time-reversal-symmetry
chiral $d+id^{\prime}$-wave pairing state prevails. In the mixed state, we have
solved the local electronic structure near the vortex core and found no local
induction of antiferromagnetism. This result is in striking contrast to the
case of copper oxide superconductors. The calculated local density of states
indicates the existence of low-lying quasiparticle bound states inside the
vortex core, due to a fully gapped chiral pairing state. The prediction can be
directly tested by scanning tunneling microscopy.",0306253v1
2003-06-26,Vibrational edge modes in intrinsically inhomogeneous doped transition metal oxides,"By applying an unrestriced Hartree-Fock approximation and a Random Phase
approximation to multiband Peierls-Hubbard Hamiltonians, we determine the
phonon mode structure in models of transition metal oxides in the presence of
intrinsic nanoscale inhomogeneities induced by hole doping. We identify low
frequency $local$ vibrational modes pinned to the interface between regions of
distinct electronic structure and separated in frequency from the band of
extended phonons. A major characteristic of these ``edge'' modes is that their
energy is essentially insensitive to the doping level, while their intensity
increases with the density of interfaces (and thus doping level). We argue that
the presence of such modes is a typical feature of systems with phase
separation, including cuprates, nickelates, manganites, and bismuthates. We
specifically address the experimental signatures of these modes in lattice
inelastic neutron scattering.",0306672v1
2003-07-02,Adsorption of Methanol on Aluminum Oxide: A Density Functional Study,"Theoretical calculations based on density functional theory have made
significant contributions to our understanding of metal oxides, their surfaces,
and the binding of molecules at these surfaces. In this paper we investigate
the binding of methanol at the alpha-Al2O3(0001) surface using first-principles
density functional theory. We calculate the molecular adsorption energy of
methanol to be E^g_ads=1.03 eV/molecule. Taking the methanol-methanol
interaction into account, we obtain the adsorption energy E_ads=1.01
eV/molecule. Our calculations indicate that methanol adsorbs chemically by
donating electron charge from the methanol oxygen to the surface aluminum. We
find that the surface atomic structure changes upon adsorption, most notably
the spacing between the outermost Al and O layers changes from 0.11 Angstrom to
0.33 Angstrom.",0307039v1
2003-07-23,Electronic States in Two-Dimensional Triangular Cobalt Oxides: Role of Electronic Correlation,"We obtain the electronic states and structures of two-dimensional cobalt
oxides, Na$_{x}$CoO$_{2}$ (x=0, 0.35, 0.5 and 0.75) by utilizing the
full-potential linear muffin-tin orbitals (FP-LMTO) methods, from which some
essential electronic interaction parameters are estimated: the bare on-site
Coulomb interaction of cobalt U$_{dd}$=7.5 eV renormalizes to 5 eV for x=0.35,
the $pd$ hybridizations t$_{pd\sigma}$ and t$_{pd\pi}$ are -1.40 and 0.70 eV,
respectively. The density of states at E$_{F}$ decreases from 6-7 states/eV in
the local density approximation (LDA) to about 1.0 states/eV in the LDA+U
scheme. The role of the intercalation of water molecules and the microscopic
mechanism of the superconductivity in Na$_{0.35}$CoO$_{2}$$\cdot$mH$_{2}$O is
discussed.",0307560v2
2003-08-06,On the break in the single-particle energy dispersions and the `universal' nodal Fermi velocity in the high-temperature copper-oxide superconductors,"Recent data from angle-resolved photoemission experiments published by Zhou
et al. [Nature, Vol. 423, 398 (2003)] concerning a number of hole-doped
copper-oxide-based high-temperature superconductors reveal that in the nodal
directions of the underlying square Brillouin zones (i.e. the directions along
which the d-wave superconducting gap is vanishing) the Fermi velocities for
some finite range of k inside the Fermi sea and away from the nodal Fermi
wavevector k_F are to within an experimental uncertainty of approximately 20%
the same both in all the compounds investigated and over a wide range of doping
concentrations and that, in line with earlier experimental observations, at
some characteristic wavevector k_* away from k_F the Fermi velocities undergo a
sudden change, with this change (roughly speaking, a finite discontinuity)
being the greatest (smallest) in the case of underdoped (overdoped) compounds.
In this paper we present a rigorous analysis concerning the implications of
these observations. [Short abstract]",0308090v2
2003-08-25,Quantum Transport in a Nanosize Silicon-on-Insulator Metal-Oxide-Semiconductor,"An approach is developed for the determination of the current flowing through
a nanosize silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect
transistors (MOSFET). The quantum mechanical features of the electron transport
are extracted from the numerical solution of the quantum Liouville equation in
the Wigner function representation. Accounting for electron scattering due to
ionized impurities, acoustic phonons and surface roughness at the Si/SiO2
interface, device characteristics are obtained as a function of a channel
length. From the Wigner function distributions, the coexistence of the
diffusive and the ballistic transport naturally emerges. It is shown that the
scattering mechanisms tend to reduce the ballistic component of the transport.
The ballistic component increases with decreasing the channel length.",0308485v1
2003-09-01,Predicted Performance Advantages of Carbon Nanotube Transistors with Doped Nanotubes as Source/Drain,"Most carbon nanotube field-effect transistors (CNTFETs) directly attach metal
source/drain contacts to an intrinsic nanotube channel. When the gate oxide
thickness is reduced, such transistors display strong ambipolar conduction,
even when the Schottky barrier for electrons (or for holes) is zero. The
resulting leakage current, which increases exponentially with the drain
voltage, constrains the potential applications of such devices. In this paper,
we use numerical simulations to show that if CNT based
metal-oxide-semiconductor (MOS) FETs can be achieved by using heavily doped CNT
sections as source and drain, ambipolar conduction will be suppressed, leakage
current will be reduced, and the scaling limit imposed by source-drain
tunneling will be extended. By eliminating the Schottky barrier between the
source and channel, the transistor will be capable of delivering more
on-current. The leakage current of such devices will be controlled by the full
bandgap of CNTs (instead of half of the bandgap for SB CNTFETs) and
band-to-band tunneling. These factors will depend on the diameter of nanotubes
and the power supply voltage.",0309039v1
2003-09-09,An explanation for a universality of transition temperatures in families of copper oxide superconductors,"A remarkable mystery of the copper oxide high-transition-temperature (Tc)
superconductors is the dependence of Tc on the number of CuO2 layers, n, in the
unit cell of a crystal. In a given family of these superconductors, Tc rises
with the number of layers, reaching a peak at n=3, and then declines: the
result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is
still poorly understood and attention has instead been mainly focused on the
properties of a single CuO2 plane. Here we show that the quantum tunnelling of
Cooper pairs between the layers simply and naturally explains the experimental
results, when combined with the recently quantified charge imbalance of the
layers and the latest notion of a competing order nucleated by this charge
imbalance that suppresses superconductivity. We calculate the bell-shaped curve
and show that, if materials can be engineered so as to minimize the charge
imbalance as n increases, Tc can be raised further.",0309209v3
2003-09-30,Hydrogen adsorption at RuO2(110),"The structural, vibrational, energetic and electronic properties of hydrogen
at the stoichiometric RuO2(110) termination are studied using density
functional theory. The oxide surface is found to stabilize both molecular and
dissociated H2. The most stable configuration in form of hydroxyl groups
(monohydrides) at the undercoordinated O^br surface anions is at low
temperatures accessed via a molecular state at the undercoordinated Ru^cus
atoms (dihydrogen) and a second precursor in form of a water-like species
(dihydride) at the O^br sites. This complex picture of the low-temperature
dissociation kinetics of H2 at RuO2(110) is in agreement with existing data
from high-resolution energy-loss spectroscopy and temperature programmed
desorption. Hydrogen adsorption at O^br sites increases the reactivity of the
neighboring Ru^cus sites, which are believed to be the active sites in
catalytic oxidation reactions.",0309714v1
2003-11-29,Surface plasmon resonances in the absorption spectra of nanocrystalline cupric oxide,"Optical absorption spectra of nanocrystalline cupric oxide CuO samples,
obtained using the converging spherical shock wave procedure, reveal
significant spectral weight red-shift as compared with spectra of single
crystalline CuO samples. In addition, some of these samples manifest the
remarkable temperature-dependent ""peak-dip-hump"" feature near 1.3-1.6 eV. The
minimal model suggested to explain both effects implies the nanoceramic CuO to
be a system of two species of identical metallic-like droplets with volume
fractions p1 >> p2 and damping parameters gamma1 >> gamma2, respectively,
dispersed in an effective insulating matrix. In other words, both effects are
assigned to the surface plasmon (Mie) resonances due to a small volume fraction
of metallic-like nanoscale droplets with Drude optical response embedded in the
bare insulating medium. Simple effective medium theory is shown to provide the
reasonable description of the experimental spectra.",0312009v1
2004-03-22,Vibrational edge modes in intrinsically heterogeneous doped transition metal oxides,"By applying an unrestricted Hartree-Fock and a Random Phase approximations to
a multiband Peierls-Hubbard Hamiltonian, we study the phonon mode structure in
models of transition metal oxides in the presence of intrinsic nanoscale
inhomogeneities induced by hole doping. We identify low frequency $local$
vibrational modes pinned to the sharp interfaces between regions of distinct
electronic structure (doped and undoped) and separated in frequency from the
band of extended phonons. A characteristic of these ``edge'' modes is that
their energy is essentially insensitive to the doping level. We discuss the
experimental manifestations of these modes in inelastic neutron scattering, and
also in spin and charge excitation spectra.",0403525v2
2004-03-24,Ab initio Study of Valley Line on a Total-Energy Surface for Zone-Center Distortions of Ferroelectric Perovskite Oxides BaTiO3 and PbTiO3,"An ab initio structure optimization technique is newly developed to determine
the valley line on a total-energy surface for zone-center distortions of
ferroelectric perovskite oxides and is applied to barium titanate BaTiO3 and
lead titanate PbTiO3. The proposed technique is an improvement over King-Smith
and Vanderbilt's scheme [Phys. Rev. B 49, p.5828 (1994)] of evaluating total
energy as a function of the amplitude of atomic displacements. The results of
numerical calculations show that total energy can be expressed as a
fourth-order function of the amplitude of atomic displacements in BaTiO3 but
not in PbTiO3.",0403603v1
2004-05-10,The chemistry of La on the Si(001) surface,"This paper reports state-of-the-art electronic structure calculations of La
adsorption on the Si(001) surface. We predict La chains in the low coverage
limit, which condense in a stable phase at a coverage of 1/5 monolayer. At 1/3
monolayer we predict a chemically rather inert, stable phase. La changes its
oxidation state from La(3+) at lower coverages to La(2+) at coverages beyond
1/3 monolayer. In the latter oxidation state, one electron resides in a state
with a considerable contribution from La-d and f states.",0405192v2
2004-06-04,Spin entropy as the likely source of enhanced thermopower in $\rm\bf Na_xCo_2O_4,"In an electric field, the flow of electrons in a solid produces an entropy
current in addition to the familiar charge current. This Peltier effect
underlies all thermoelectric refrigerators. The upsurge in thermoelectric
cooling applications has led to a search for more efficient Peltier materials
and to renewed theoretical interest in how electron-electron interaction may
enhance the thermopower $Q$ of materials such as the transition-metal oxides
\cite{Mahan,Beni,Kotliar,Chaikin}. An important factor in this enhancement is
the electronic spin entropy, which is predicted \cite{Chaikin,Kwak,KwakChaikin}
to dominate the entropy current. Here we report evidence for such suppression
in the layered oxide $\rm Na_xCo_2O_4$, and present evidence that it is a
strong-correlation effect.",0406125v1
2004-06-22,Electronic structure properties and BCS superconductivity in beta-pyrochlore oxides: KOs_2O_6,"We report a first-principles density-functional calculation of the electronic
structure and properties of the recently discovered superconducting
beta-pyrochlore oxide KOs_2O_6. We find that the electronic structure near the
Fermi energy E_F is dominated by strongly hybridized Os-5d and O-2p states. A
van Hove singularity very close to E_F leads to a relatively large density of
states at E_F, and the Fermi surface exhibits strong nesting along several
directions. These features could provide the scattering processes leading to
the observed anomalous temperature dependence of the resistivity and to the
rather large specific heat mass enhancement we obtain from the calculated
density of states and the observed specific heat coefficient. An estimate of
T_c within the framework of the BCS theory of superconductivity taking into
account the possible effects of spin fluctuations arising from nesting yields
the experimental value.",0406538v1
2004-07-28,Fractal Self-Assembled Nanostructures on Monocrystalline Silicon Surface,"We present ultra-shallow diffusion profiles performed by short-time diffusion
of boron from the gas phase using controlled surface injection of
self-interstitials and vacancies into the n-type Si(100) wafers. The diffusion
profiles of this art are found to consist of both longitudinal and lateral
silicon quantum wells of the p-type that are self-assembled between the alloys
of microdefects, which are produced by previous oxidation. These alloys appear
to be passivated during short-time diffusion of boron thereby forming neutral
del'ta barriers. The fractal type self-assembly of microdefects is found to be
created by varying the thickness of the oxide overlayer, which causes the
system of microcavities embedded in the quantum well plane.",0407722v1
2004-08-09,Resonant two-photon excitation of 1s paraexcitons in Cuprous Oxide,"We have created paraexcitons in Cuprous Oxide via resonant two-photon
generation, and examined their population dynamics by means of time-correlated
single photon detection. Confining the excitons to a constant volume in a
harmonic potential trap made with inhomogeneous applied stress along the [001]
axis, we find that paraexcitons are created directly, and orthoexcitons appear
primarily through the well-known excitonic Auger process. Hot excitons are also
created via a three-photon process when the IR laser is non-resonant. Also we
generate excitons with two colliding pulses, and the luminescence is weaker
than that from one beam excitation with same total laser power. These results
show that resonant one-beam two-photon generation of paraexcitons is a
promising way to pursue Bose-Einstein condensation of paraexcitons.",0408188v3
2004-09-01,Decoherence of a Josephson qubit due to coupling to two level systems,"Noise and decoherence are major obstacles to the implementation of Josephson
junction qubits in quantum computing. Recent experiments suggest that two level
systems (TLS) in the oxide tunnel barrier are a source of decoherence. We
explore two decoherence mechanisms in which these two level systems lead to the
decay of Rabi oscillations that result when Josephson junction qubits are
subjected to strong microwave driving. (A) We consider a Josephson qubit
coupled resonantly to a two level system, i.e., the qubit and TLS have equal
energy splittings. As a result of this resonant interaction, the occupation
probability of the excited state of the qubit exhibits beating. Decoherence of
the qubit results when the two level system decays from its excited state by
emitting a phonon. (B) Fluctuations of the two level systems in the oxide
barrier produce fluctuations and 1/f noise in the Josephson junction critical
current I_o. This in turn leads to fluctuations in the qubit energy splitting
that degrades the qubit coherence. We compare our results with experiments on
Josephson junction phase qubits.",0409006v1
2004-09-04,A `checkerboard' electronic crystal state in lightly hole-doped Ca_{2-x}Na_{x}CuO_{2}Cl_{2},"The phase diagram of hole-doped copper oxides shows four different electronic
phases existing at zero temperature. Familiar among these are the Mott
insulator, high-transition-temperature superconductor and metallic phases. A
fourth phase, ofunknown identity, occurs at light doping along the
zero-temperature bound of the `pseudogap' regime. This regime is rich in
peculiar electronic phenomena, prompting numerous proposals that it contains
some form of hidden electronic order. Here we present low-temperature
electronic structure imaging studies of a lightly hole-doped copper oxide:
Ca_{2-x}Na_{x}CuO_{2}Cl_{2}. Tunnelling spectroscopy (at energies |E|>100 meV)
reveals electron extraction probabilities greatly exceeding those for
injection, as anticipated for a doped Mott insulator. However, for |E|<100 meV,
the spectrum exhibits a V-shaped energy gap centred on E=0. States within this
gap undergo intense spatial modulations, with the spatial correlations of a
four CuO_{2}-unit-cell square checkerboard, independent of energy. Intricate
atomic-scale electronic structure variations also exist within the
checkerboard. These data are consistent with an unanticipated crystalline
electronic state, possibly the hidden electronic order, existing in the
zero-temperature pseudogap regime of Ca_{2-x}Na_{x}CuO_{2}Cl_{2}.",0409102v1
2004-09-23,A user-friendly approach to local anodic oxidation,"A home made DSP-controlled scanning probe microscope (SPM) system has been
developed and its utilization as a tool for lithography on nanometer scale is
reported. User-friendly graphic interface allows to directly perform
nanolithography importing a bitmap pattern on previously-imaged sample region,
otherwise moving in real time the probe using an ordinary mouse, acting as a
pantograph from macroscopic down to nanometer scale, taking advantage from an
absolute-positioning stage. Any measured property of the sample can be used by
the lithographic interface to realize interactive patterning of the sample.
Moreover, the 'contour-mode' permits to move tip at a fixed relative tip-sample
distance, exploiting at each step the previously-acquired topographic signal.
The instrument has been successfully employed in order to perform local anodic
oxidation (LAO) lithography on semiconducting substrates.",0409608v1
2004-10-05,Optical Properties of Excitons in ZnO-based Quantum Well Heterostructures,"Recently the developments in the field of II-VI-oxides have been spectacular.
Various epitaxial methods has been used to grow epitaxial ZnO layers. Not only
epilayers but also sufficiently good-quality multiple quantum wells (MQWs) have
also been grown by laser molecular-beam epitaxy (laser-MBE). We discuss mainly
the experimental aspect of the optical properties of excitons in ZnO-based MQW
heterostructures. Systematic temperature-dependent studies of optical
absorption and photoluminescence in these MQWs were used to evaluate the
well-width dependence and the composition dependence of the major excitonic
properties. Based on these data, the localization of excitons, the influence of
exciton-phonon interaction, and quantum-confined Stark effects are discussed.
  The optical spectra of dense excitonic systems are shown to be determined
mainly by the interaction process between excitons and biexcitons. The
high-density excitonic effects play a role for the observation of
room-temperature stimulated emission in the ZnO MQWs. The binding energies of
exciton and biexciton are enhanced from the bulk values, as a result of
quantum-confinement effects.",0410120v2
2004-10-18,Structural Behavior of Non-Oxide Perovskite Superconductor MgCNi$_{3}$ at Pressures up to 32 GPa,"We report the pressure dependence of the structural parameters of the
non-oxide perovskite superconductor MgCNi$_{3}$ up to 32 GPa using a diamond
anvil cell and synchrotron x-rays at room temperature. The structure of the
compound remains in the Pm-3m cubic symmetry throughout the pressure range. The
bulk modulus $B_{0}=156.9\pm0.2$GPa with $B_{0}^{\prime}=9.8$obtained by
fitting the pressure-volume data is in good agreement with theoretical
calculations reported earlier. An anomalous shift of the (111) and (200) lines
observed above 9 GPa indicates a possible local short range distortion that is
consistent with earlier studies.",0410430v1
2004-11-05,X-ray photoelectron spectroscopy studies of non-stoichiometric superconducting NbB2+x,"Polycrystalline samples of NbB2+x with nominal composition (B/Nb) = 2.0, 2.1,
2.2, 2.3, 2.4 and 2.5 were studied by X-ray photoelectron spectroscopy (XPS).
The spectra revealed Nb and B oxides on the surface of the samples, mainly B2O3
and Nb2O5. After Ar ion etching the intensity of Nb and B oxides decreased. The
Nb 3d5/2 and B 1s core levels associated with the chemical states (B/Nb) were
identified and they do not change with etching time. The Binding Energy of the
Nb 3d5/2 and B 1s core levels increase as boron content increases, suggesting a
positive chemical shift in the core levels. On the other hand, analysis of
Valence Band spectra showed that the contribution of the Nb 4d states slightly
decreased while the contribution of the B 2p(pi) states increased as the boron
content increased. As a consequence, the electronic and superconducting
properties were substantially modified, in good agreement with band-structure
calculations.",0411131v3
2004-12-07,Breakdown of One-Paramater Scaling in Quantum Critical Scenarios for the High-Temperature Copper-oxide Superconductors,"We show that if the excitations which become gapless at a quantum critical
point also carry the electrical current, then a resistivity linear in
temperature, as is observed in the copper-oxide high-temperature
superconductors, obtains only if the dynamical exponent, $z$, satisfies the
unphysical constraint, $z<0$. At fault here is the universal scaling hypothesis
that, at a continuous phase transition, the only relevant length scale is the
correlation length. Consequently, either the electrical current in the normal
state of the cuprates is carried by degrees of freedom which do not undergo a
quantum phase transition, or quantum critical scenarios must forgo this basic
scaling hypothesis and demand that more than a single correlation length scale
is necessary to model transport in the cuprates.",0412179v2
2005-01-10,Orbital Insulators and Orbital Order-disorder Induced Metal-Insulator Transition in Transition-Metal Oxides,"The role of orbital ordering on metal-insulator transition of
transition-metal oxides is investigated by the cluster self-consistent field
approach in the strong correlation regime. A clear dependence of the insulating
gap on the orbital order parameter is found in the single-particle excitation
spectra. The thermal fluctuation drives the orbital order-disorder transition,
diminishes the gap and leads to the metal-insulator transition. The interplay
between spins and orbits results in unusual temperature dependence of the
orbital polarization in the orbital insulator, which can be seen in the
resonant x-ray scattering intensity.",0501155v2
2005-02-21,High pressure effects on the superconductivity of beta-pyrochlore oxides AOs2O6,"High pressure effects on the superconducting transitions of beta-pyrochlore
superconductors AOs2O6 (A = Cs, Rb, K) are studied by measuring resistivity
under high pressures up to 10 GPa. The superconducting transition temperature
Tc first increases with increasing pressure in all the compounds and then
exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for
A = Cs, Rb and K, respectviely. Finally, the superconductivity is suppressed
completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and
probably above 10 GPa for A = Cs. Characteristic changes in the coefficinet A
of the T2 term in resistivity and residual resistivity are observed, both of
which are synchronized with the corresponding change in Tc. It is suggested
that electron correlations and certain quantum fluctuations play important
roles in the occurrence or suppression of superconductivity in the
beta-pyrochlore oxides.",0502490v1
2005-03-03,The Schottky defect formation energy in MgO calculated by diffusion Monte Carlo,"The energetics of point defects in oxide materials plays a major role in
determining their high-temperature properties, but experimental measurements
are difficult, and calculations based on density functional theory (DFT) are
not necessarily reliable. We report quantum Monte Carlo (QMC) calculations of
the formation energy $E_{\rm S}$ of Schottky defects in MgO, which demonstrate
the feasibility of using this approach to overcome the deficiencies of DFT. In
order to investigate system-size errors, we also report DFT calculations of
$E_{\rm S}$ on repeating cells of up to $\sim 1000$ atoms, which indicate that
QMC calculations on systems of only 54 atoms should yield high precision. The
DFT calculations also provide the relaxed structures used in the variational
and diffusion Monte Carlo calculations. For MgO, we find $E_{\rm S}$ to be in
close agreement with results from DFT and from model interaction potentials,
and consistent with the scattered experimental values. The prospects for
applying the same approach to transition metal oxides such as FeO are
indicated.",0503074v1
2005-03-15,Physics of thin-film ferroelectric oxides,"This review covers the important advances in recent years in the physics of
thin film ferroelectric oxides, the strongest emphasis being on those aspects
particular to ferroelectrics in thin film form. We introduce the current state
of development in the application of ferroelectric thin films for electronic
devices and discuss the physics relevant for the performance and failure of
these devices. Following this we cover the enormous progress that has been made
in the first principles computational approach to understanding ferroelectrics.
We then discuss in detail the important role that strain plays in determining
the properties of epitaxial thin ferroelectric films. Finally, we look at the
emerging possibilities for nanoscale ferroelectrics, with particular emphasis
on ferroelectrics in non conventional nanoscale geometries.",0503372v1
2005-03-26,Effect of molecular structure and oxidation potential on the device performance of single-carrier organic diodes,"The fabrication of single-carrier organic diodes from a series of sixteen
molecular materials is reported. We experimentally demonstrate how the
molecular structure affects the film morphology, and how the film morphology
influences the diode performance. The compounds, with moderate molecular size
and dendritic structures, are shown to be more favorable for good device
performance than those small molecules with symmetry structures. The device
turn-on voltage is found to be strongly dependent on the molecular first
oxidation potentials. Independent of different anode materials, no obvious
interfacial charge/dipole effects are observed in the devices. Our results may
suggest that singlecarrier organic diode might offer a simple way for screeing
appropriate molecular materials preferable for practical multilayer devices.",0503629v1
2005-03-29,First principles study of rare-earth oxides,"The self-interaction-corrected local-spin-density approximation is used to
describe the electronic structure of dioxides, REO$_2$, and sesquioxides,
RE$_2$O$_3$, for the rare earths, RE=Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy and Ho.
The valencies of the rare earth ions are determined from total energy
minimization. We find Ce, Pr, Tb in their dioxides to have the tetravalent
configuration, while for all the sesquioxides the trivalent groundstate
configuration is found to be the most favourable. The calculated lattice
constants for these valency configurations are in good agreement with
experiment. Total energy considerations are exploited to show the link between
oxidation and $f$-electron delocalization, and explain why, among the dioxides,
only the CeO$_2$, PrO$_2$, and TbO$_2$ exist in nature. Tetravalent NdO$_2$ is
predicted to exist as a metastable phase - unstable towards the formation of
hexagonal Nd$_2$O$_3$.",0503667v1
2005-04-04,Origin of dielectric relaxation observed in complex perovskite oxides Ba(1-x)La(x)Ti(1-x)Cr(x)O3,"Frequency dependence of the dielectric constant of complex perovskite oxide
Ba(1-x)La(x)Ti(1-x)Cr(x)O3 (BLTC) ceramics with the composition ratio 0.4<= x
<= 0.7 is precisely measured in the temperature range from 20 K to 300 K, and
the dielectric relaxation is found to be quite similar to that of CaCu3Ti4O12
(CCTO), which exhibits the Debye-like frequency dispersion around 100 K. In
BLTC, the ferroelectric phase transition temperature shifts to lower
temperature with increase of x, while a remarkable dielectric relaxation newly
appears at higher temperature region. The dielectric relaxation can be
explained by an equivalent model of a series of two R-C parallel circuits,
which corresponds to a heterogeneous structure in the sample with an internal
barrier layer capacitor. Temperature and frequency dependences of the measured
dielectric constant are explained well by the model with the
temperature-dependent electrical conductivity and temperature-independent
intrinsic dielectric constant. It is also found that the contribution of thin
layer to the dielectric relaxation in a high temperature region is affected by
the dc bias field on the sample.",0504064v1
2005-06-20,Electron correlations and bond-length fluctuations in copper oxides: from Zhang--Rice singlets to correlation bags,"We perform first principles, multiconfiguration calculations on clusters
including several CuO$_6$ octahedra and study the ground-state electron
distribution and electron--lattice couplings when holes are added to the
undoped $d^9 p^6$ configuration. We find that the so-called Zhang--Rice state
on a single CuO$_4$ plaquette is nearly degenerate with a state whose leading
configuration is of the form Cu $d^9$-- O $p^5$-- Cu $d^9$. A strong coupling
between the electronic and nuclear motion gives rise to large inter-site charge
transfer effects for half-breathing displacements of the oxygen ions. Under the
assumption of charge segregation into alternating hole-free and hole-rich
stripes of Goodenough \cite{jbg_02,jbg_03}, our results seem to support the
vibronic mechanism and the traveling charge-density wave model from
Refs.\cite{jbg_02,jbg_03} for the superconductivity in copper oxides.",0506511v1
2005-08-05,Large Second Harmonic Kerr rotation in GaFeO3 thin films on YSZ buffered Silicon,"Epitaxial thin films of gallium iron oxide (GaFeO3) are grown on (001)
silicon by pulsed laser deposition (PLD) using yttrium-stabilized zirconia
(YSZ) buffer layer. The crystalline template buffer layer is in-situ PLD grown
through the step of high temperature stripping of the intrinsic silicon surface
oxide. The X-ray diffraction pattern shows c-axis orientation of YSZ and b-axis
orientation of GaFeO3 on Si (100) substrate. The ferromagnetic transition
temperature (TC ~ 215 K) is in good agreement with the bulk data. The films
show a large nonlinear second harmonic Kerr rotation of ~15 degrees in the
ferromagnetic state.",0508159v1
2005-08-05,Ideally Glassy Hydrogen Bonded Networks,"The axiomatic theory of ideally glassy networks, which has proved effective
in describing phase diagrams and properties of chalcogenide and oxide glasses
and their foreign interfaces, is broadened here to include intermolecular
interactions in hydrogen-bonded polyalcohols such as glycerol, monosaccharides
(glucose), and the optimal bioprotective hydrogen-bonded disaccharide networks
formed from trehalose. The methods of Lagrangian mechanics and Maxwellian
scaffolds are useful at the molecular level when bonding hierarchies are
characterized by constraint counting similar to the chemical methods used by
Huckel and Pauling. Whereas Newtonian molecular dynamical methods are useful
for simulating large-scale interactions for times of order 10 ps, constraint
counting describes network properties on glassy (almost equilibrated) time
scales, which may be of cosmological order for oxide glasses, or years for
trehalose. The ideally glassy network of trehalose may consist of extensible
tandem sandwich arrays.",0508164v1
2005-09-01,Complexity in Strongly Correlated Electronic Systems,"A wide variety of experimental results and theoretical investigations in
recent years have convincingly demonstrated that several transition metal
oxides and other materials, have dominant states that are not spatially
homogeneous. This occurs in cases in which several physical interactions --
spin, charge, lattice, and/or orbital -- are simultaneously active. This
phenomenon causes interesting effects, such as colossal magnetoresistance, and
it also appears crucial to understand the high temperature superconductors. The
spontaneous emergence of electronic nanometer-scale structures in transition
metal oxides, and the existence of many competing states, are properties often
associated with complex matter where nonlinearities dominate, such as soft
materials and biological systems. This electronic complexity could have
potential consequences for applications of correlated electronic materials,
because not only charge (semiconducting electronic), or charge and spin
(spintronics) are of relevance, but in addition the lattice and orbital degrees
of freedom are active, leading to giant responses to small perturbations.
Moreover, several metallic and insulating phases compete, increasing the
potential for novel behavior.",0509041v1
2005-10-06,Evidence for multiple impurity bands in sodium-doped silicon MOSFETs,"We report measurements of the temperature-dependent conductivity in a silicon
metal-oxide-semiconductor field-effect transistor that contains sodium
impurities in the oxide layer. We explain the variation of conductivity in
terms of Coulomb interactions that are partially screened by the proximity of
the metal gate. The study of the conductivity exponential prefactor and the
localization length as a function of gate voltage have allowed us to determine
the electronic density of states and has provided arguments for the presence of
two distinct bands and a soft gap at low temperature.",0510145v3
2005-10-10,"First-principles kinetic Monte Carlo simulations for heterogeneous catalysis, applied to the CO oxidation at RuO2(110)","We describe a first-principles statistical mechanics approach enabling us to
simulate the steady-state situation of heterogeneous catalysis. In a first step
density-functional theory together with transition-state theory is employed to
obtain the energetics of all relevant elementary processes. Subsequently the
statistical mechanics problem is solved by the kinetic Monte Carlo method,
which fully accounts for the correlations, fluctuations, and spatial
distributions of the chemicals at the surface of the catalyst under
steady-state conditions. Applying this approach to the catalytic oxidation of
CO at RuO2(110), we determine the surface atomic structure and composition in
reactive environments ranging from ultra-high vacuum (UHV) to technologically
relevant conditions, i.e. up to pressures of several atmospheres and elevated
temperatures. We also compute the CO2 formation rates (turnover frequencies).
The results are in quantitative agreement with all existing experimental data.
We find that the high catalytic activity of this system is intimately connected
with a disordered, dynamic surface ``phase'' with significant compositional
fluctuations. In this active state the catalytic function results from a
self-regulating interplay of several elementary processes.",0510234v1
2005-10-10,Resonance Anomalous Surface X-ray Scattering,"Resonance anomalous surface x-ray scattering (RASXS) technique was applied to
electrochemical interface studies. It was used to determine the chemical states
of electrochemically formed anodic oxide monolayers on platinum surface. It is
shown that RASXS exhibits strong polarization dependence when the surface is
significantly modified. The polarization dependence is demonstrated for three
examples; anodic oxide formation, sulfate adsorption, and CO adsorption on
platinum surfaces. s- and p- polarization RASXS data were simulated with the
latest version of ab initio multiple scattering calculations (FEFF8.2).
Elementary theoretical considerations are also presented for the origin of the
polarization dependence in RASXS.",0510235v1
2005-10-19,Why Some Interfaces Cannot be Sharp,"A central goal of modern materials physics and nanoscience is control of
materials and their interfaces to atomic dimensions. For interfaces between
polar and non-polar layers, this goal is thwarted by a polar catastrophe that
forces an interfacial reconstruction. In traditional semiconductors this
reconstruction is achieved by an atomic disordering and stoichiometry change at
the interface, but in multivalent oxides a new option is available: if the
electrons can move, the atoms don`t have to. Using atomic-scale electron energy
loss spectroscopy we find that there is a fundamental asymmetry between
ionically and electronically compensated interfaces, both in interfacial
sharpness and carrier density. This suggests a general strategy to design sharp
interfaces, remove interfacial screening charges, control the band offset, and
hence dramatically improving the performance of oxide devices.",0510491v1
2005-10-31,Ab Initio Structural Energetics of Beta-Si3N4 Surfaces,"Motivated by recent electron microscopy studies on the Si3N4/rare-earth oxide
interfaces, the atomic and electronic structures of bare beta-Si3N4 surfaces
are investigated from first principles. The equilibrium shape of a Si3N4
crystal is found to have a hexagonal cross section and a faceted dome-like base
in agreement with experimental observations. The large atomic relaxations on
the prismatic planes are driven by the tendency of Si to saturate its dangling
bonds, which gives rise to resonant-bond configurations or planar sp^2-type
bonding. We predict three bare surfaces with lower energies than the open-ring
(10-10) surface observed at the interface, which indicate that
non-stoichiometry and the presence of the rare-earth oxide play crucial roles
in determining the termination of the Si3N4 matrix grains.",0510823v1
2005-11-05,"Charge ordering, stripes and phase separation in manganese perovskite oxides: an STM/STS study","A microscopic characterisation of the phase transitions associated with
colossal magnetoresistance (CMR) in manganese perovskite oxides is a very
important ingredient in the quest of understanding its underlying mechanism.
Scanning tunneling microscopy (STM) is most suitable to investigate some of
their reported hallmarks, including charge ordering, lattice distortions, and
electronic phase separation. Here we investigate Bi1-XCaXMnO3 (BCMO) with
x=0.76. At this composition, BCMO develops an insulating charge-ordered phase
upon cooling, whose study as a function of temperature will allow identifying
atomic scale characteristics of the metal-insulator phase transition (MIT). We
observe distinct atomic scale phases at temperatures above and below the MIT,
with very different electronic and structural characteristics. Combining STM
micrographs and current-voltage tunneling characteristics, we find that charge
ordering correlates both with the local conduction state (metallic or
insulating) and the local structural order. Furthermore, STM shows coexistence
of these phases as expected for a first order phase transition.",0511139v1
2005-11-10,"Thermoelectric properties of the layered Pd oxide R_2PdO_4 (R = La, Nd, Sm and Gd)","We prepared polycrystalline samples of R$_2$PdO$_4$ (R = La, Nd, Sm and Gd)
using a NaCl-flux technique. The measured resistivity is of the order of
10$^3-10^4$ $\Omega$cm at room temperature, which is two orders of magnitude
smaller than the values reported so far. We further studied the substitution
effects of Ce for Nd in Nd$_{1.9}$Ce$_{0.1}$PdO$_4$, where the substituted Ce
decreases the resistivity and the magnitude of the thermopower. The activation
energy gap of 70-80 meV and the effective mass of 15 evaluated from the
measured data are suitable for thermoelectric materials, but the mobility of
10$^{-6}$ cm$^2$/Vs is much lower than a typical value of 1-10 cm$^2$/Vs for
other thermoelectric oxides.",0511245v1
2005-11-11,"Elasticity and piezoelectricity of zinc oxide crystals, single layers, and possible single-walled nanotubes","The elasticity and piezoelectricity of zinc oxide (ZnO) crystals and single
layers are investigated from the first-principles calculations. It is found
that a ZnO thin film less than three Zn-O layers prefers a planar graphite-like
structure to the wurtzite structure. ZnO single layers are much more flexible
than graphite single layers in the elasticity and stronger than boron nitride
single layers in the piezoelectricity. Single-walled ZnO nanotubes (SWZONTs)
can exist in principle because of their negative binding energy. The
piezoelectricity of SWZONTs depends on their chirality. For most ZnO nanotubes
except the zigzag type, twists around the tube axis will induce axial
polarizations. A possible scheme is proposed to achieve the SWZONTs from the
solid-vapor phase process with carbon nanotubes as templates.",0511274v3
2005-11-18,The Parent of Misfit-Layered Cobalt Oxides: [Sr2O2]qCoO2,"Misfit-layered (ML) cobalt oxides of the general formula of [MmA2Om+2]qCoO2
have been proven to be efficient thermoelectric materials as the structure is
capable in accommodating the two seemingly contradictory characteristics of
high electrical conductivity and large thermo-electric power. They are also
potential hosts for other oxymoron-like functions. The known phases all contain
one or two square-planar MO (M = Co, Bi, Pb, Tl, etc.) layers sandwiched
together with AO (A = Ca, Sr, Ba, etc.) planes of square symmetry and CoO2
layers of hexagonal symmetry. Here we report realization of the simplest (m =
0) ML phase forming in the Sr-Co-O system with the cation ratio, Sr/Co = 1.
Atomic-resolution TEM imaging confirms for the new phase the parent three-layer
crystal structure, SrO-SrO-CoO2, which is compatible with the formula of
[Sr2O2]qCoO2. Electron diffraction reveals that the phase is rather
commensurate, i.e. the ""misfit parameter"" q is 0.5. Nevertheless, in terms of
the transport-property characteristics the new ML parent is comparable to its
earlier-established and more complex derivatives.",0511449v1
2005-11-29,Enhanced thermopower in an intergrowth cobalt oxide Li$_{0.48}$Na$_{0.35}$CoO$_{2}$,"We report the measurements of thermopower, electrical resistivity and thermal
conductivity in a complex cobalt oxide Li$_{0.48}$Na$_{0.35}$CoO$_{2}$, whose
crystal structure can be viewed as an intergrowth of the O3 phase of
Li$_{x}$CoO$_{2}$ and the P2 phase of Na$_{y}$CoO$_{2}$ along the c axis. The
compound shows large room-temperature thermopower of $\sim$180 $\mu$V/K, which
is substantially higher than those of Li$_{x}$CoO$_{2}$ and Na$_{y}$CoO$_{2}$.
The figure of merit for the polycrystalline sample increases rapidly with
increasing temperature, and it achieves nearly 10$^{-4}$ K$^{-1}$ at 300 K,
suggesting that Li$_{x}$Na$_{y}$CoO$_{2}$ system is a promising candidate for
thermoelectric applications.",0511691v1
2005-12-02,Activation mechanisms in sodium-doped Silicon MOSFETs,"We have studied the temperature dependence of the conductivity of a silicon
MOSFET containing sodium ions in the oxide above 20 K. We find the impurity
band resulting from the presence of charges at the silicon-oxide interface is
split into a lower and an upper band. We have observed activation of electrons
from the upper band to the conduction band edge as well as from the lower to
the upper band. A possible explanation implying the presence of Hubbard bands
is given.",0512039v7
2005-12-09,Comparison of the Electronic Structures of Two Non-cuprate Layered Transition Metal Oxide Superconductors,"Comparison is made of the electronic structure of the little-studied layered
transition metal oxide LiNbO$_2$ with that of Na$_x$CoO$_2$, which has
attracted tremendous interest since superconductivity was discovered in its
hydrate. Although the active transition metal $d$ states are quite different
due to different crystal fields and band filling, both systems show a strong
change of electronic structure with changes in the distance between the
transition metal ion layer and the oxygen layers. The niobate is unusual in
having a large second-neighbor hopping amplitude, and a nearest neighbor
hopping amplitude that is sensitive to the Nb-O separation. Li$_x$NbO$_2$ also
presents the attractive simplicity of a single band triangular lattice system
with variable carrier concentration that is superconducting.",0512211v2
2005-12-10,Electron correlations and bond-length fluctuations in layered copper oxides: electron versus hole doping,"We investigate the nature of the electronic ground state and electron-lattice
couplings for doped chains of CuO_4 plaquettes or CuO_6 octahedra. The undoped
configuration implies here Cu 3d^9 and O 2p^6 formal valence states. The
results of multiconfiguration calculations on 4-plaquette (or 4-octahedra)
linear clusters indicate strong electron-lattice interactions and polaronic
behavior of the doped particles, for both electron and hole doping. For certain
phases of the oxygen-ion half-breathing distortions a multi-well energy
landscape is predicted. Since each well is associated to carriers localized at
different sites, the half-breathing displacements induce charge transfer along
the chain. In the case of hole-doping, the trends found by ab initio
multiconfiguration calculations on 4-octahedra clusters are confirmed by
density-matrix renormalization-group calculations for a p-d, extended Hubbard
model with chains of few tens of CuO_4 plaquettes. Under the assumption of
charge separation and the formation of 1/3-doped stripes, our results seem to
support the vibronic mechanism and the traveling charge-density wave scenario
proposed in some recent contributions for superconductivity in copper oxides.",0512219v3
2005-12-21,Full oxide heterostructure combining a high-Tc diluted ferromagnet with a high-mobility conductor,"We report on the growth of heterostructures composed of layers of the
high-Curie temperature ferromagnet Co-doped (La,Sr)TiO3 (Co-LSTO) with
high-mobility SrTiO3 (STO) substrates processed at low oxygen pressure. While
perpendicular spin-dependent transport measurements in STO//Co-LSTO/LAO/Co
tunnel junctions demonstrate the existence of a large spin polarization in
Co-LSTO, planar magnetotransport experiments on STO//Co-LSTO samples evidence
electronic mobilities as high as 10000 cm2/Vs at T = 10 K. At high enough
applied fields and low enough temperatures (H < 60 kOe, T < 4 K) Shubnikov-de
Haas oscillations are also observed. We present an extensive analysis of these
quantum oscillations and relate them with the electronic properties of STO, for
which we find large scattering rates up to ~ 10 ps. Thus, this work opens up
the possibility to inject a spin-polarized current from a high-Curie
temperature diluted oxide into an isostructural system with high-mobility and a
large spin diffusion length.",0512533v1
2006-01-17,Surface Reactivity and Quantum-Size effects on the Electronic Density Decay Length of ultrathin Metal Films,"The origin of the correlation between surface reactivity and quantum-size
effects, observed in recent experiments on the oxidation of ultrathin magnesium
films, is addressed by means of ab-initio calculations and model predictions.
We show that the decay length in vacuum of the electronic local density of
states at the Fermi energy exhibits systematic oscillations with film
thickness, with local maxima induced when a quantum well state at k// = 0
crosses the Fermi energy. The predicted changes in the decay length are
expected to have a major impact on the electron transfer rate by tunneling,
which has been proposed to control the initial sticking of O2 in the oxidation
process.",0601364v1
2006-02-21,Evidance for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Oxides,"Electric pulse induced resistance (EPIR) switching hysteresis loops for
Pr0.7Ca0.7MnO3 (PCMO) perovskite oxide films were found to exhibit an
additional sharp ""shuttle peak"" around the negative pulse maximum for films
deposited in an oxygen deficient ambient. The device resistance hysteresis loop
consists of stable high resistance and low resistance states, and transition
regions between them. The resistance relaxation of the ""shuttle peak"" and its
temperature behavior as well as the resistance relaxation in the transition
regions were studied, and indicate that the resistance switching relates to
oxygen diffusion with activation energy about 0.4eV. An oxygen diffusion model
with the oxygen ions (vacancies) as the active agent is proposed for the
non-volatile resistance switching effect in PCMO.",0602507v2
2006-03-20,The role of oxygen vacancies in SrTiO3 at the LaAlO3/SrTiO3 interface,"Strontium titanate, SrTiO3, a widely used substrate material for electronic
oxide thin film devices, has provided many interesting features. In a
combination with a similar oxide material, LaAlO3, it has recently received
great interest. It was suggested that two-dimensional electron gas is formed at
the interface between SrTiO3 and LaAlO3, resulting in high electrical
conductivity and mobility. In this report we demonstrate that the transport
properties in those heterostructures are very sensitive to the deposition
parameters during thin film growth. Using cathode- and photoluminescence
studies in conjunction with measurements of electrical transport properties and
microstructure we show that the electronic properties observed at a
LaAlO3/SrTiO3 interface can be explained by oxygen reduced SrTiO3. In addition,
we demonstrate that oxygen can be pushed in and out of the sample, but that
re-oxygenation of an initially oxygen depleted LaAlO3/SrTiO3 heterostructure is
partly prevented by the presence of the film.",0603501v1
2006-03-24,Angle-resolved photoemission spectroscopy of perovskite-type transition-metal oxides and their analyses using tight-binding band structure,"Nowadays it has become feasible to perform angle-resolved photoemission
spectroscopy (ARPES) measurements of transition-metal oxides with
three-dimensional perovskite structures owing to the availability of
high-quality single crystals of bulk and epitaxial thin films. In this article,
we review recent experimental results and interpretation of ARPES data using
empirical tight-binding band-structure calculations. Results are presented for
SrVO$_3$ (SVO) bulk single crystals, and La$_{1-x}$Sr$_x$FeO$_3$ (LSFO) and
La$_{1-x}$Sr$_x$MnO$_3$ (LSMO) thin films. In the case of SVO, from comparison
of the experimental results with calculated surface electronic structure, we
concluded that the obtained band dispersions reflect the bulk electronic
structure. The experimental band structures of LSFO and LSMO were analyzed
assuming the G-type antiferromagnetic state and the ferromagnetic state,
respectively. We also demonstrated that the intrinsic uncertainty of the
electron momentum perpendicular to the crystal surface is important for the
interpretation of the ARPES results of three-dimensional materials.",0603642v1
2006-04-28,Carrier concentration dependence of optical Kerr nonlinearity in indium tin oxide films,"Optical Kerr nonlinearity (n2) in n-type indium tin oxide (ITO) films coated
on glass substrates has been measured using Z-scans with 200-fs laser pulses at
wavelengths ranging from 720 to 780 nm. The magnitudes of the measured
nonlinearity in the ITO films were found to be dependent on the carrier
concentration with a maximum n2-value of 4.1 x 10-5 cm2/GW at 720-nm wavelength
and an electron density of Nd = 5.8 x 1020 cm-3. The Kerr nonlinearity was also
observed to be varied with the laser wavelength. By employing a femtosecond
time-resolved optical Kerr effect (OKE) technique, the relaxation time of OKE
in the ITO films is determined to be ~1 ps. These findings suggest that the
Kerr nonlinearity in ITO can be tailored by controlling the carrier
concentration, which should be highly desirable in optoelectronic devices for
ultrafast all-optical switching.",0604652v1
2006-05-24,Morphological and Structural Characterization of Cro2/Cr2o3 Films Grown by Laser-CVD,"This work reports on the synthesis of chromium (III, IV) oxides films by KrF
laser-assisted CVD. Films were deposited onto sapphire substrates at room
temperature by photodissociation of Cr(CO)6 in dynamic atmospheres containing
oxygen and argon. A study of the processing parameters has shown that partial
pressure ratio of O2 to Cr(CO)6 and laser fluence are the prominent parameters
that have to be accurately controlled in order to co-deposit both crystalline
oxide phases. Films consistent with such a two-phase system were synthesised
for a laser fluence of 75 mJ cm-2 and a partial pressure ratio about 1.
  PACS: 81.15.Fg, 81.15.Kk, 81.05.Je",0605592v1
2006-06-15,Angle-resolved photoemission study of cobalt oxide superconductor NaxCoO2.yH2O : Observation of the Fermi surface,"Cobalt oxide superconductor NaxCoO2.yH2O is studied by angle-resolved
photoemission spectroscopy (ARPES). We report the Fermi surface (FS) topology
and electronic structure near the Fermi level (EF) of NaxCoO2.yH2O. Our result
indicates the presence of the hexagonal FS centered at G point, while the small
pocket FSs along G-K direction are absent similar to NaxCoO2. The top of the
eg' band, which is expected in band calculations to form the small pocket FSs,
extends to within 20 - 50 meV below EF, more closer to EF than in NaxCoO2. We
discuss its possible role in superconductivity, comparing with other
experimental and theoretical results.",0606424v1
2006-07-03,"Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)","We investigated the electronic structures of the two-dimensional layered
perovskite Sr$_{2}$\textit{M}O$_{4}$ (\textit{M}=4\textit{d} Ru, 4\textit{d}
Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O
1\textit{s} x-ray absorption spectroscopy. While the ground states of the
series of compounds are rather different, their optical conductivity spectra
$\sigma(\omega)$ exhibit similar interband transitions, indicative of the
common electronic structures of the 4\textit{d} and 5\textit{d} layered oxides.
The energy splittings between the two $e_{g}$ orbitals, $i.e.$,
$d_{3z^{2}-r^{2}}$ and $d_{x^{2}-y^{2}}$, are about 2 eV, which is much larger
than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The
electronic properties of the Sr$_{2}$\textit{M}O$_{4}$ compounds are discussed
in terms of the crystal structure and the extended character of the 4\textit{d}
and 5\textit{d} orbitals.",0607026v2
2006-07-07,Uniaxial to unidirectional transition of perpendicular interlayer coupling in IrMn/CoFe/NiFeO/CoFe quadrilayers,"We studied the interlayer coupling in the quadrilayer consisting of IrMn/CoFe
(bottom layer)/NiFeOx/ CoFe (top layer). The in-plane perpendicular interlayer
coupling is observed between CoFe layers at room temperature. An anisotropy
transition from uniaxial to unidirectional in the perpendicular direction is
observed around Tt = 55 K. The nano-oxide layer NiFeOx shows no distinguishable
ferromagnetic signal in the high-temperature (uniaxial) phase, while a strong
signal appeared in the low-temperature (unidirectional) phase. A possible
two-component scenario, that the nano-oxide layer may contain both amorphous
short-range antiferromagnetic domains and superparamagneitc clusters, is
proposed to explain the phase transition.",0607199v1
2006-08-08,Stable Oxide Nanoparticle Clusters Obtained by Complexation,"We report on the electrostatic complexation between polyelectrolyte-neutral
copolymers and oppositely charged 6 nm-crystalline nanoparticles. For two
different dispersions of oxide nanoparticles, the electrostatic complexation
gives rise to the formation of stable nanoparticle clusters in the range 20 -
100 nm. It is found that inside the clusters, the particles are pasted together
by the polyelectrolyte blocks adsorbed on their surface. Cryo-transmission
electronic microscopy allows to visualize the clusters and to determine the
probability distributions functions in size and in aggregation number. The
comparison between light scattering and cryo-microscopy results suggests the
existence of a polymer brush around the clusters.",0608189v1
2006-09-28,The Effect of Counterions on the Interactions of Charged Oligothiophenes,"The functionality of conjugated polymer systems often relies on oxidations or
reductions, in most cases mediated by the presence of counterions. The effect
that the common counterion hexafluorophosphate (PF6-) has on the intermolecular
interactions between charged oligothiophenes is investigated here using ab
initio quantum chemistry methods. Counterions are explicitly included in the
simulations of oxidized oligothiophenes and in the dimerization process. Our
calculations provide quantitative and qualitative insight into the
intermolecular interactions in oligothiophene-counterion systems and show that
the intermolecular pi-stacking of oligothiophenes is not adversely affected by
the presence of counterions, and that in fact oligothiophene dimerization is
further stabilized by their presence.",0609722v1
2006-10-06,Resistive hystersis effects in perovskite oxide-based heterostructure junctions,"In this paper, we report the electrical and structural properties of the
oxide-based metal/ferroelectric/metal (MFM) junctions. The heterostructures are
composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and,
BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the
dimensions of 400 x 200 micom2, have been fabricated upon LCMO/BTO/LCMO
heterostructures by photolithography and Ar-ion milling technique. The DC
current-voltage (I-V) characteristics of the MFM junctions were carried out. At
300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K,
(I-V) curves exhibited some reproducible switching behaviours with well-defined
remnant currents. The resulting resistance modulation is very different from
what was already reported in ultrathin ferroelectric layers displaying
resistive switching. A model is presented to explain the datas",0610172v1
2006-10-12,Effect of the Fe substitution in Ti-Ni shape memory alloys,"Shape memory Ti-Ni alloys attracted much attention in the recent years, since
they are shape memory, intelligent as well as functional materials. In the
present investigation Ti51Ni49 and Ti51Ni45Fe4 alloys were synthesized through
radio frequency (RF) induction melting. The alloy was characterized through
x-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer
spectroscopy (MS) and positron annihilation techniques (PAT).The Fe
substitution stabilized the TiNi type cubic (a=2.998 A) phase. The surface
microstructure and presence of the oxide layer in Ti51Ni45Fe4 alloy have been
investigated by SEM. The Positron annihilation measurements indicated a similar
bulk electron density in both the as-cast and annealed (1000 0 C for 30 hrs)
alloys, typically like that of bulk Ti. Mossbauer spectroscopy studies of
as-cast and annealed iron substituted samples showed regions in the samples
where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was
found to be present in as cast Ti51Ni45Fe4 alloy, while annealed sample
indicated the presence of bcc iron phase .",0610340v1
2007-03-09,Weak coupling Bardeen-Cooper-Schrieffer suerconductivity in the Electron-Doped Cuprate Superconductors,"We use in-plane tunneling spectroscopy to study the temperature dependence of
the local superconducting gap $\Delta(T)$ in electron-doped copper oxides with
various $T_c$'s and Ce-doping concentrations. We show that the temperature
dependence of $\Delta(T)$ follows the expectation of the
Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, where
$\Delta(0)/k_{B}T_{c}\approx1.72\pm 0.15$ and $\Delta(0)$ is the average
superconducting gap across the Fermi surface, for all the doping levels
investigated. These results suggest that the electron-doped superconducting
copper oxides are weak coupling BCS superconductors.",0703256v2
2007-03-19,Band-to-band tunneling in a carbon nanotube metal-oxide-semiconductor field-effect transistor is dominated by phonon assisted tunneling,"Band-to-band tunneling (BTBT) devices have recently gained a lot of interest
due to their potential for reducing power dissipation in integrated circuits.
We have performed extensive simulations for the BTBT operation of carbon
nanotube metal-oxide-semiconductor field-effect transistors (CNT-MOSFETs) using
the non-equilibrium Green's functions formalism for both ballistic and
dissipative quantum transport. In comparison with recently reported
experimental data (Y. Lu et al, J. Am. Chem. Soc., v. 128, p. 3518-3519, 2006),
we have obtained strong evidence that BTBT in CNT-MOSFETs is dominated by
optical phonon assisted inelastic transport, which can have important
implications on the transistor characteristics. It is shown that under large
biasing conditions two-phonon scattering may also become important.",0703493v1
1997-03-02,Towards a Field Theory of F-theory,"We make a proposal for a bosonic field theory in twelve dimensions that
admits the bosonic sector of eleven-dimensional supergravity as a consistent
truncation. It can also be consistently truncated to a ten-dimensional
Lagrangian that contains all the BPS p-brane solitons of the type IIB theory.
The mechanism allowing the consistent truncation in the latter case is unusual,
in that additional fields with an off-diagonal kinetic term are non-vanishing
and yet do not contribute to the dynamics of the ten-dimensional theory. They
do, however, influence the oxidation of solutions back to twelve dimensions. We
present a discussion of the oxidations of all the basic BPS solitons of
M-theory and the type IIB string to D=12. In particular, the NS-NS and R-R
strings of the type IIB theory arise as the wrappings of membranes in D=12
around one or other circle of the compactifying 2-torus.",9703012v2
1997-10-20,Interacting Intersections,"Intersecting p-branes can be viewed as higher-dimensional interpretations of
multi-charge extremal p-branes, where some of the individual p-branes undergo
diagonal dimensional oxidation, while the others oxidise vertically. Although
the naive vertical oxidation of a single p-brane gives a continuum of p-branes,
a more natural description arises if one considers a periodic array of p-branes
in the higher dimension, implying a dependence on the compactification
coordinates. This still reduces to the single lower-dimensional p-brane when
viewed at distances large compared with the period. Applying the same logic to
the multi-charge solutions, we are led to consider more general classes of
intersecting p-brane solutions, again depending on the compactification
coordinates, which turn out to be described by interacting functions rather
than independent harmonic functions. These new solutions also provide a more
satisfactory interpretation for the lower-dimensional multi-charge p-branes,
which otherwise appear to be nothing more than the improbable coincidence of
charge-centres of individual constituents with zero binding energy.",9710155v2
2002-06-21,"On d=4,5,6 Vacua with 8 Supercharges","We show how all known N=2, d=4,5,6 maximally supersymmetric vacua (Hpp-waves
and aDSxS solutions) are related through dimensional reduction/oxidation
preserving all the unbroken supersymmetries. In particular we show how the N=2,
d=5 family of vacua (which are the near-horizon geometry of supersymmetric
rotating black holes) interpolates between aDS_2xS^3 and aDS_3xS^2 in parameter
space and how it can be dimensionally reduced to an N=2, d=4 dyonic
Robinson-Bertotti solution with geometry aDS_2xS^2 and oxidized to an N=2, d=6
solution with aDS_3xS^3 geometry (which is the near-horizon of the self-dual
string).",0206200v3
2002-10-18,The group theory of oxidation,"Dimensional reduction of (super-)gravity theories to 3 dimensions results in
sigma models on coset spaces G/H, such as the E_8/SO(16) coset in the bosonic
sector of 3 dimensional maximal supergravity. The reverse process, oxidation,
is the reconstruction of a higher dimensional gravity theory from a coset sigma
model. Using the group G as starting point, the higher dimensional models
follow essentially from decomposition into subgroups. All equations of motion
and Bianchi identities can be directly reconstructed from the group lattice,
Kaluza-Klein modifications and Chern-Simons terms are encoded in the group
structure. Manipulations of extended Dynkin diagrams encode matter content, and
(string) dualities. The reflection symmetry of the ``magic triangle'' for E_n
gravities, and approximate reflection symmetry of the older ``magic triangle''
of supergravities in 4 dimensions, are easily understood in this framework.",0210178v3
2004-09-27,"Chemistry of Chern-Simons Supergravity: reduction to a BPS kink, oxidation to M-theory and thermodynamical aspects","We construct a supersymmetric extension of the two dimensional
Kaluza-Klein-reduced gravitational Chern-Simons term, and globally study its
solutions, labelled by mass and U(1) charge c. The kink solution is BPS, and in
an appropriate conformal frame all solutions asymptotically approach AdS. The
thermodynamics of the Hawking effect yields interesting behavior for the
specific heat and hints at a Hawking-Page-like transition at T_{critical} \sim
c^{3/2}. We address implications for higher dimensions (""oxidation""), in
particular D=3,4 and 11, and comment briefly on AdS/CFT aspects of the kink.",0409273v2
2002-01-14,Statistical Analysis of a Semilinear Hyperbolic System Advected by a White in Time Random Velocity Field,"We study a system of semilinear hyperbolic equations passively advected by
smooth white noise in time random velocity fields. Such a system arises in
modeling non-premixed isothermal turbulent flames under single-step kinetics of
fuel and oxidizer. We derive closed equations for one-point and multi-point
probability distribution functions (PDFs) and closed form analytical formulas
for the one point PDF function, as well as the two-point PDF function under
homogeneity and isotropy. Exact solution formulas allows us to analyze the
ensemble averaged fuel/oxidizer concentrations and the motion of their level
curves. We recover the empirical formulas of combustion in the thin reaction
zone limit and show that these approximate formulas can either underestimate or
overestimate average concentrations when reaction zone is not tending to zero.
We show that the averaged reaction rate slows down locally in space due to
random advection induced diffusion; and that the level curves of ensemble
averaged concentration undergo diffusion about mean locations.",0201024v1
2006-10-26,Front explosion in a periodically forced surface reaction,"Resonantly-forced oscillatory reaction-diffusion systems can exhibit fronts
with complicated interfacial structure separating phase-locked homogeneous
states. For values of the forcing amplitude below a critical value the front
""explodes"" and the width of the interfacial zone grows without bound. Such
front explosion phenomena are investigated for a realistic model of catalytic
CO oxidation on a Pt(110) surface in the 2:1 and 3:1 resonantly-forced regimes.
In the 2:1 regime, the fronts are stationary and the front explosion leads to a
defect-mediated turbulent state. In the 3:1 resonantly-forced system, the
fronts propagate. The front velocity tends to zero as the front explosion point
is reached and the final asymptotic state is a 2:1 resonantly-locked
labyrinthine pattern. The front dynamics described here should be observable in
experiment since the model has been shown to capture essential features of the
CO oxidation reaction.",0610064v1
2002-08-26,A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory,"As photodisintegration of deuterons mimics the disintegration of deuterons by
neutrinos, the accurate measurement of the radioactivity from thorium and
uranium decay chains in the heavy water in the Sudbury Neutrino Observatory
(SNO) is essential for the determination of the total solar neutrino flux. A
radium assay technique of the required sensitivity is described that uses
hydrous titanium oxide adsorbent on a filtration membrane together with a
beta-alpha delayed coincidence counting system. For a 200 tonne assay the
detection limit for 232Th is a concentration of 3 x 10^(-16) g Th/g water and
for 238U of 3 x 10^(-16) g U/g water. Results of assays of both the heavy and
light water carried out during the first two years of data collection of SNO
are presented.",0208015v1
2000-11-30,Modelling horizontal and vertical concentration profiles of ozone and oxides of nitrogen within high-latitude urban area,"A Lagrangian column model has been developed to simulate the mean (monthly
and annual) three-dimensional structure in ozone and nitrogen oxides
concentrations in the boundary layer within and immediately around an urban
area. Short time-scale photochemical processes of ozone, as well as emissions
and deposition to the ground are simulated. The results show that the average
surface ozone concentration in the urban area is lower than the surrounding
rural areas by typically 50%. Model results are compared with observations.",0011074v2
2003-11-24,Laser ablation synthesis of zinc oxide clusters: a new family of fullerenes?,"Positively charged zinc oxide clusters ZnnOm (up to n = 16, m <= n) of
various stoichiometry were synthesized in the gas phase by excimer ArF laser
ablation of a ZnO target and investigated using time-of-flight mass
spectrometry. Depending on ablation conditions, either metal rich or
stoichiometric clusters dominate in the mass spectrum. When the irradiated
target surface is fairly fresh, the most abundant clusters are metal rich with
Zn(n+1)On and Zn(n+3)On being the major series. The stoichiometric clusters are
observed with an etched ablated surface. The magic numbers at n = 9, 11 and 15
in mass spectra of (ZnO)n clusters indicate that the clusters have hollow
spheroid structures related to fullerenes. A local abundance minimum at n = 13
provides an additional evidence for the presence in the ablation plume of
fullerene-like (ZnO)n clusters.",0311117v1
2006-03-13,Experimental and modeling study of the oxidation of xylenes,"This paper describes an experimental and modeling study of the oxidation of
the three isomers of xylene (ortho-, meta- and para-xylenes). For each
compound, ignition delay times of hydrocarbon-oxygen-argon mixtures with fuel
equivalence ratios from 0.5 to 2 were measured behind reflected shock waves for
temperatures from 1330 to 1800 K and pressures from 6.7 to 9 bar. The results
show a similar reactivity for the three isomers. A detailed kinetic mechanism
has been proposed, which reproduces our experimental results, as well as some
literature data obtained in a plug flow reactor at 1155 K showing a clear
difference of reactivity between the three isomers of xylene. The main reaction
paths have been determined by sensitivity and flux analyses and have allowed
the differences of reactivity to be explained.",0603102v1
2006-04-24,Mathematical model for blood flow autoregulation by endothelium-derived relaxing factor,"The fluid shear stress is an important regulator of the cardiovascular system
via the endothelium-derived relaxing factor (EDRF) that is Nitric Oxide. This
mechanism involves biochemical reactions in an arterial wall. The
autoregulation process is managed by the vascular tonus and gives the negative
feedback for the shear stress changing. A new mathematical model for the
autoregulation of a blood flow through arteria under the constant transmural
pressure is presented. Endothelium-derived relaxing factor Nitric Oxide, the
multi-layer structure of an arterial wall, and kinetic-diffusion processes are
taken into consideration. The limit case of the thin-wall artery is
analytically studied. The stability condition for a stationary point of the
linearized system is given. The exact stationary solutions of the origin system
are found. The numerical simulation for the autoregulation system is presented.
It is shown the arteria adaptation to an initial radial perturbation and the
transition of the system to new equilibrium state in response on the blood flow
changing.",0604192v1
2005-03-17,Globally controlled artificial semiconducting molecules as quantum computers,"Quantum computers are expected to be considerably more efficient than
classical computers for the execution of some specific tasks. The difficulty in
the practical implementation of thoose computers is to build a microscopic
quantum system that can be controlled at a larger mesoscopic scale. Here I show
that vertical lines of donor atoms embedded in an appropriate Zinc Oxide
semiconductor structure can constitute artificial molecules that are as many
copy of the same quantum computer. In this scalable architecture, each unit of
information is encoded onto the electronic spin of a donor. Contrary to most
existing practical proposals, here the logical operations only require a global
control of the spins by electromagnetic pulses. Ensemble measurements simplify
the readout. With appropriate improvement of its growth and doping methods,
Zinc Oxide could be a good semiconductor for the next generation of computers.",0503161v1
2007-04-01,Aspects of Electron-Phonon Self-Energy Revealed from Angle-Resolved Photoemission Spectroscopy,"Lattice contribution to the electronic self-energy in complex correlated
oxides is a fascinating subject that has lately stimulated lively discussions.
Expectations of electron-phonon self-energy effects for simpler materials, such
as Pd and Al, have resulted in several misconceptions in strongly correlated
oxides. Here we analyze a number of arguments claiming that phonons cannot be
the origin of certain self-energy effects seen in high-$T_c$ cuprate
superconductors via angle resolved photoemission experiments (ARPES), including
the temperature dependence, doping dependence of the renormalization effects,
the inter-band scattering in the bilayer systems, and impurity substitution. We
show that in light of experimental evidences and detailed simulations, these
arguments are not well founded.",0704.0093v1
2007-04-12,Extremely strong-coupling superconductivity and anomalous lattice properties in the beta-pyrochlore oxide KOs2O6,"Superconducting and normal-state properties of the beta-pyrochlore oxide
KOs2O6 are studied by means of thermodynamic and transport measurements. It is
shown that the superconductivity is of conventional s-wave type and lies in the
extremely strong-coupling regime. Specific heat and resistivity measurements
reveal that there are characteristic low-energy phonons that give rise to
unusual scattering of carriers due to strong electron-phonon interactions. The
entity of the low-energy phonons is ascribed to the heavy rattling of the K ion
confined in an oversized cage made of OsO6 octahedra. It is suggested that this
electron-rattler coupling mediates the Cooper pairing, resulting in the
extremely strong-coupling superconductivity.",0704.1528v1
2007-04-19,"High Mobility in LaAlO3/SrTiO3 Heterostructures: Origin, Dimensionality and Perspectives","We have investigated the dimensionality and origin of the magnetotransport
properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001)
substrates. High mobility conduction is observed at low deposition oxygen
pressures (PO2 < 10^-5 mbar) and has a three-dimensional character. However, at
higher PO2 the conduction is dramatically suppressed and nonmetallic behavior
appears. Experimental data strongly support an interpretation of these
properties based on the creation of oxygen vacancies in the SrTiO3 substrates
during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low
PO2, other oxides generate the same high mobility as LaAlO3 films. This opens
interesting prospects for all-oxide electronics.",0704.2523v1
2007-05-31,Simple approach for high-contrast optical imaging and characterization of graphene-based sheets,"A simple optical method is presented for identifying and measuring the
effective optical properties of nanometer-thick, graphene-based materials,
based on the use of substrates consisting of a thin dielectric layer on
silicon. High contrast between the graphene-based materials and the substrate
is obtained by choosing appropriate optical properties and thickness of the
dielectric layer. The effective refractive index and optical absorption
coefficient of graphene oxide, thermally reduced graphene oxide, and graphene
are obtained by comparing the predicted and measured contrasts.",0706.0029v2
2007-06-14,Modelling of the gas-phase oxidation of cyclohexane,"This paper presents a modeling study of the oxidation of cyclohexane from low
to intermediate temperature (650-1050 K), including the negative temperature
coefficient (NTC) zone. A detailed kinetic mechanism has been developed using
computer-aided generation. This comprehensive low-temperature mechanism
involves 513 species and 2446 reactions and includes two additions of
cyclohexyl radicals to oxygen, as well as subsequent reactions. The rate
constants of the reactions involving the formation of bicyclic species
(isomerizations, formation of cyclic ethers) have been evaluated from
literature data. This mechanism is able to satisfactorily reproduce
experimental results obtained in a rapid-compression machine for temperatures
ranging from 650 to 900 K and in a jet-stirred reactor from 750 to 1050 K.
Flow-rate analyses have been performed at low and intermediate temperatures.",0706.2064v1
2007-07-16,Quantum critical behaviour in the superfluid density of strongly underdoped ultrathin cuprate films,"A central issue in the physics of high temperature superconductors is to
understand superconductivity within a single copper-oxide layer or bilayer, the
fundamental structural unit in the cuprates, and how it is lost with
underdoping. As mobile holes are removed from the CuO_2 planes, the transition
temperature T_C and superfluid density n_S decrease in a surprisingly
correlated fashion in crystals and thick films. We seek to elucidate the
intrinsic physics of bilayers in the strongly underdoped regime, near the
critical doping level where superconductivity disappears. We report
measurements of n_S(T) in films of Y_{1-x}Ca_xBa_2Cu_3O_{7-\delta} as thin as
two copper-oxide bilayers with T_C's as low as 3 K. In addition to seeing the
two-dimensional (2D) Kosterlitz-Thouless-Berezinski transition at T_C, we
observe a remarkable scaling of T_C with n_S(0) that demonstrates that the
disappearance of superconductivity with underdoping is due to quantum
fluctuations near a T = 0 2D quantum critical point.",0707.2397v1
2007-07-20,A canonical transformation theory from extended normal ordering,"The Canonical Transformation theory of Yanai and Chan [J. Chem. Phys. 124,
194106 (2006)] provides a rigorously size-extensive description of dynamical
correlation in multireference problems. Here we describe a new formulation of
the theory based on the extended normal ordering procedure of Mukherjee and
Kutzelnigg [J. Chem. Phys. 107, 432 (1997)].
  On studies of the water, nitrogen, and iron-oxide potential energy curves,
the Linearised Canonical Transformation Singles and Doubles theory is
competitive in accuracy with some of the best multireference methods, such as
the Multireference Averaged Coupled Pair Functional, while computational
timings (in the case of the iron-oxide molecule) are two-three orders of
magnitude faster and comparable to those of Complete Active Space Second-Order
Perturbation Theory. The results presented here are greatly improved both in
accuracy and in cost over our earlier study as the result of a new numerical
algorithm for solving the amplitude equations.",0707.3128v1
2007-09-12,Ferroelectricity in artificial bicolor oxide superlattices,"We report on the growth and properties of high quality bicolor oxide
superlattices, composed of two perovskites out of BaTiO3, CaTiO3, and SrTiO3.
The artificially grown superlattices are structurally unique and have a
macroscopically homogeneous phase, which is not feasible to recreate in bulk
form. By artificial structuring, it is found that the polarization of such
superlattices can be highly increased as compared to pseudo-binary ceramics
with the same overall composition. Such strong enhancement in superlattice is
attributed to newly-developed ionic motions of A-site cations at the
hetero-interfaces due to the interfacial coupling of electrostatic and elastic
interactions, which cannot be found in single phase materials.",0709.1791v1
2007-10-07,Mapping the Spatial Distribution of Charge Carriers in LaAlO3/SrTiO3 Heterostructures,"At the interface between complex insulating oxides, novel phases with
interesting properties may occur, such as the metallic state reported in the
LaAlO3/SrTiO3 system. While this state has been predicted and reported to be
confined at the interface, some works indicate a much broader spatial
extension, thereby questioning its origin. Here we provide for the first time a
direct determination of the carrier density profile of this system through
resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples
with a conducting-tip atomic force microscope (CT-AFM). We find that, depending
upon specific growth protocols, the spatial extension of the high-mobility
electron gas can be varied from hundreds of microns into SrTiO3 to a few
nanometers next to the LaAlO3/SrTiO3 interface. Our results emphasize the
potential of CT-AFM as a novel tool to characterize complex oxide interfaces
and provide us with a definitive and conclusive way to reconcile the body of
experimental data in this system.",0710.1395v2
2007-10-25,Circuit-Level Modeling for Concurrent Testing of Operational Defects due to Gate Oxide Breakdown,"As device sizes shrink and current densities increase, the probability of
device failures due to gate oxide breakdown (OBD) also increases. To provide
designs that are tolerant to such failures, we must investigate and understand
the manifestations of this physical phenomenon at the circuit and system level.
In this paper, we develop a model for operational OBD defects, and we explore
how to test for faults due to OBD. For a NAND gate, we derive the necessary
input conditions that excite and detect errors due to OBD defects at the gate
level. We show that traditional pattern generators fail to exercise all of
these defects. Finally, we show that these test patterns can be propagated and
justified for a combinational circuit in a manner similar to traditional ATPG.",0710.4715v1
2007-11-12,Hyper-Raman scattering analysis of the vibrations in vitreous boron oxide,"Hyper-Raman scattering has been measured on vitreous boron oxide,
$v-$B$_2$O$_3$. This spectroscopy, complemented with Raman scattering and
infrared absorption, reveals the full set of vibrations that can be observed
with light. A mode analysis is performed based on the local D$_{3h}$ symmetry
of BO$_3$ triangles and B$_3$O$_3$ boroxol rings. The results show that in
$v-$B$_2$O$_3$ the main spectral components can be succesfully assigned using
this relatively simple model. In particular, it can be shown that the
hyper-Raman boson peak arises from external modes that correspond mainly to
librational motions of rigid boroxol rings.",0711.1782v1
2007-12-11,Lattice instabilities in cubic pyrochlore Bi$_2$Ti$_2$O$_7$,"The oxide pyrochlore Bi$_2$Ti$_2$O$_7$ is in some ways analogous to
perovskite PbTiO$_3$, in that Bi$_2$Ti$_2$O$_7$ has two cations, Bi$^{3+}$ and
Ti$^{4+}$ in oxidation states that are normally associated with a propensity to
off-center. However, unlike PbTiO$_3$, Bi$_2$Ti$_2$O$_7$ is experimentally
observed to remain cubic down to 2 K, while the only observed ionic
displacements are local and incoherent. Here we report first-principles
calculations of the zone-center phonons of the ordered cubic pyrochlore which
reveal several lattice instabilities. An analysis of the structural energetics
suggest that the ordered cubic pyrochlore is unstable with respect to
distortion towards a ferroelectric ground state with a large polarization. Our
results suggest a key role of a frustrated soft polar mode in the dielectric
properties of bismuth pyrochlores.",0712.1846v1
2007-12-14,Optical conductivity and the correlation strength of high temperature copper-oxide superconductors,"High temperature copper-oxide-based superconductivity is obtained by adding
carriers to insulating ""parent compounds"". It is widely believed the parent
compounds are ""Mott"" insulators, in which the lack of conduction arises from
anomalously strong electron-electron repulsion, and that the unusual properties
of Mott insulators are responsible for high temperature superconductivity. This
paper presents a comparison of optical conductivity measurements and
theoretical calculations which challenges this belief. The analysis indicates
that the correlation strength in the cuprates is not as strong as previously
believed, that the materials are not properly regarded as Mott insulators, that
antiferromagnetism is essential to obtain the insulating state and, by
implication, that antiferromagnetism is essential to the properties of the
doped metallic and superconducting state as well.",0712.2392v1
2007-12-18,Effect of Edge Roughness on Electronic Transport in Graphene Nanoribbon Channel Metal Oxide Semiconductor Field-Effect Transistors,"Results of quantum mechanical simulations of the influence of edge disorder
on transport in graphene nanoribbon metal oxide semiconductor field-effect
transistors (MOSFETs) are reported. The addition of edge disorder significantly
reduces ON-state currents and increases OFF-state currents, and introduces wide
variability across devices. These effects decrease as ribbon widths increase
and as edges become smoother. However the bandgap decreases with increasing
width, thereby increasing the band-to-band tunneling mediated subthreshold
leakage current even with perfect nanoribbons. These results suggest that
without atomically precise edge control during fabrication, MOSFET performance
gains through use of graphene will be difficult to achieve.",0712.3068v1
2007-12-21,First-principles LDA+U and GGA+U study of plutonium oxides,"The electronic structure and properties of PuO$_{2}$ and Pu$_{2}$O$_{3}$ have
been studied from first principles by the all-electron projector-augmented-wave
(PAW) method. The local density approximation (LDA)+$U$ and the generalized
gradient approximation (GGA)+$U$ formalism have been used to account for the
strong on-site Coulomb repulsion among the localized Pu $5f$ electrons. We
discuss how the properties of PuO$_{2}$ and Pu$_{2}$O$_{3}$ are affected by the
choice of $U$ as well as the choice of exchange-correlation potential. Also,
oxidation reaction of Pu$_{2}$O$_{3}$, leading to formation of PuO$_{2}$, and
its dependence on $U$ and exchange-correlation potential have been studied. Our
results show that by choosing an appropriate $U$ it is promising to correctly
and consistently describe structural, electronic, and thermodynamic properties
of PuO$_{2}$ and Pu$_{2}$O$_{3}$, which enables it possible the modeling of
redox process involving Pu-based materials.",0712.3623v1
2008-02-21,Enhanced Sensing Characteristics in MEMS-based Formaldehyde Gas Sensor,"This study has successfully demonstrated a novel self-heating formaldehyde
gas sensor based on a thin film of NiO sensing layer. A new fabrication process
has been developed in which the Pt micro heater and electrodes are deposited
directly on the substrate and the NiO thin film is deposited above on the micro
heater to serve as sensing layer. Pt electrodes are formed below the sensing
layer to measure the electrical conductivity changes caused by formaldehyde
oxidation at the oxide surface. Furthermore, the upper sensing layer and
NiO/Al2O3 co-sputtering significantly increases the sensitivity of the gas
sensor, improves its detection limit capability. The microfabricated
formaldehyde gas sensor presented in this study is suitable not only for
industrial process monitoring, but also for the detection of formaldehyde
concentrations in buildings in order to safeguard human health.",0802.3072v1
2008-02-22,Recent advances in pulsed-laser deposition of complex-oxides,"Pulsed-laser deposition (PLD) is one of the most promising techniques for the
formation of complex-oxide heterostructures, superlattices, and well-controlled
interfaces. The first part of this paper presents a review of several useful
modifications of the process, including methods inspired by combinatorial
approaches. We then discuss detailed growth kinetics results, which illustrate
that 'true' layer-by-layer (LBL) growth can only be approached, but not fully
met, even though many characterization techniques reveal interfaces with
unexpected sharpness. Time-resolved surface x-ray diffraction measurements show
that crystallization and the majority of interlayer mass transport occur on
time scales that are comparable to those of the plume/substrate interaction,
providing direct experimental evidence that a growth regime exists in which
non-thermal processes dominate PLD. This understanding shows how kinetic growth
manipulation can bring PLD closer to ideal LBL than any other growth method
available today.",0802.3386v1
2008-03-12,A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface,"NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite
solution are studied by near edge X-ray absorption fine structure spectroscopy
(NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron
diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED
patterns and STM images show that no long range ordered structures are formed
after NO adsorption on a Pt(111) surface. Although the total NO coverage is
very low, spectroscopic features in N K-edge and O K-edge absorption spectra
have been singled out and related to the different species induced by this
preparation method. From these measurements it is concluded that the NO
molecule is adsorbed trough the N atom in an upright conformation. The maximum
saturation coverage is about 0.3 monolayers, and although nitric oxide is the
major component, nitrite and nitrogen species are slightly co-adsorbed on the
surface. The results obtained from this study are compared with those
previously reported in the literature for NO adsorbed on Pt(111) under UHV
conditions.",0803.1789v1
2008-03-19,Electrodynamics of the vanadium oxides VO2 and V2O3,"The optical/infrared properties of films of vanadium dioxide (VO2) and
vanadium sesquioxide (V2O3) have been investigated via ellipsometry and
near-normal incidence reflectance measurements from far infrared to ultraviolet
frequencies. Significant changes occur in the optical conductivity of both VO2
and V2O3 across the metal-insulator transitions at least up to (and possibly
beyond) 6 eV. We argue that such changes in optical conductivity and electronic
spectral weight over a broad frequency range is evidence of the important role
of electronic correlations to the metal-insulator transitions in both of these
vanadium oxides. We observe a sharp optical transition with possible final
state (exciton) effects in the insulating phase of VO2. This sharp optical
transition occurs between narrow a1g bands that arise from the
quasi-one-dimensional chains of vanadium dimers. Electronic correlations in the
metallic phases of both VO2 and V2O3 lead to reduction of the kinetic energy of
the charge carriers compared to band theory values, with paramagnetic metallic
V2O3 showing evidence of stronger correlations compared to rutile metallic VO2.",0803.2739v1
2008-03-29,Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs,"Since the discovery of copper oxide superconductor in 1986 [1], extensive
efforts have been devoted to the search of new high-Tc superconducting
materials, especially high-Tc systems other than cuprates. The recently
discovered quaternary superconductor La[O1-xFx]FeAs with the superconducting
critical transition Tc of 26 K [2], which has a much simple layered structure
compared with cuprates, has attracted quick enthusiasm and is going to become a
new high-Tc system [3-6]. Here we report the discovery of bulk
superconductivity in the praseodymium-arsenide oxides Pr[O1-xFx]FeAs with an
onset drop of resistivity as high as 52 K, and the unambiguous zero-resistivity
and Meissner transition at low temperature, which will place these quaternary
compounds to another high-Tc superconducting system explicitly.",0803.4283v1
2008-04-04,Cavity-enhanced radiative emission rate in a single-photon-emitting diode operating at 0.5 GHz,"We report the observation of a Purcell enhancement in the electroluminescence
decay rate of a single quantum dot, embedded in a microcavity
light-emitting-diode structure. Lateral confinement of the optical mode was
achieved using an annulus of low-refractive-index aluminium oxide, formed by
wet oxidation. The same layer acts as a current aperture, reducing the active
area of the device without impeding the electrical properties of the p-i-n
diode. This allowed single photon electroluminescence to be demonstrated at
repetition rates up to 0.5 GHz.",0804.0663v1
2008-04-04,Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation,"We report on the UV laser induced fluorescence of hexagonal boron nitride
(h-BN) following nanosecond laser irradiation of the surface under vacuum and
in different environments of nitrogen gas and ambient air. The observed
fluorescence bands are tentatively ascribed to impurity and mono (VN), or
multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence
band between 300 nm and 350 nm is assigned to impurity-band transition and its
complex lineshape is attributed to phonon replicas. An additional band at 340
nm, assigned to VN vacancies on surface, is observed under vacuum and quenched
by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a
broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further
irradiation breaks more B-N bonds enriching the surface with elemental boron.
However, no boron deposit appears under irradiation of samples in ambient
atmosphere. This effect is explained by oxygen healing of radiation-induced
surface defects. Formation of the oxide layer prevents B-N dissociation and
preserves the bulk sample stoichiometry.",0804.0764v1
2008-04-05,Doubly degenerate orbital system in honeycomb lattice: implication of orbital state in layered iron oxide,"We study a doubly-degenerate orbital model on a honeycomb attice. This is a
model for orbital states in multiferroic layered iron oxides. The classical and
quantum models are analyzed by spin-wave approximation, Monte-Carlo simulation
and Lanczos method. A macroscopic number of degeneracy exists in the classical
ground state. In the classical model, a peak in the specific heat appears at a
temperature which is much lower than the mean-field ordering one. Below this
temperature, angle of orbital pseudo-spin is fixed, but conventional orbital
orders are not suggested. The degeneracy in the ground state is partially
lifted by thermal fluctuation. We suggest a role of zero-dimensional
fluctuation in hexagons on a low-temperature orbital structure. Lifting of the
degeneracy also occurs at zero temperature due to the quantum zero-point
fluctuation. We show that the ground-state wave function is well represented by
a linear combination of the states where a honeycomb lattice is covered by
nearest-neighboring pairs of orbitals with the minimum bond energy.",0804.0843v1
2008-05-07,Fabrication of Nanostructured PLGA Scaffolds Using Anodic Aluminum Oxide Templates,"PLGA (poly(lactic-co-glycolic acid)) is one of the most used biodegradable
and biocompatible materials. Nanostructured PLGA even has great application
potentials in tissue engineering. In this research, a fabrication technique for
nanostructured PLGA membrane was investigated and developed. In this novel
fabrication approach, an anodic aluminum oxide (AAO) film was use as the
template ; the PLGA solution was then cast on it ; the vacuum air-extraction
process was applied to transfer the nano porous pattern from the AAO membrane
to the PLGA membrane and form nanostures on it. The cell culture experiments of
the bovine endothelial cells demonstrated that the nanostructured PLGA membrane
can double the cell growing rate. Compared to the conventional chemical-etching
process, the physical fabrication method proposed in this research not only is
simpler but also does not alter the characteristics of the PLGA. The
nanostructure of the PLGA membrane can be well controlled by the AAO temperate.",0805.0879v1
2008-05-09,Network rigidity and dynamics of oxides,"If a hierarchy of interatomic interactions exists in a solid, low-frequency
modes can be found from viewing this solid as a mechanical network. In this
case, the low-frequency modes are determined by the network rigidity. We study
the low-frequency modes (rigid unit modes, or RUMs) in several important oxide
materials and discuss how the RUMs affect their properties. In SiO$_2$ glass,
the ability to support RUMs governs its relaxation in the wide range of
pressures and temperatures, giving rise to the non-trivial pressure window. It
also affects other properties, including crystallization, slow relaxation and
compressibility. At ambient pressure and low temperature, RUM flexibility is
related to the large-scale localized atomic motions. Whether these motions are
interpreted as independent two-level systems or collective density excitations,
the RUM flexibility determines whether and to what extent low-energy
excitations can exist in a given glass structure. Finally, we discuss the RUM
in, perhaps unexpectedly, cuprate superconductors, and its relevance for
superconductivity, including the d-wave symmetry of the order parameter and
other properties.",0805.1392v1
2008-06-04,Nanolithography and manipulation of graphene using an atomic force microscope,"We use an atomic force microscope (AFM) to manipulate graphene films on a
nanoscopic length scale. By means of local anodic oxidation with an AFM we are
able to structure isolating trenches into single-layer and few-layer graphene
flakes, opening the possibility of tabletop graphene based device fabrication.
Trench sizes of less than 30 nm in width are attainable with this technique.
Besides oxidation we also show the influence of mechanical peeling and
scratching with an AFM of few layer graphene sheets placed on different
substrates.",0806.0716v2
2008-06-16,Band Jahn-Teller Instability and Formation of Valence Bond Solid in a Mixed-Valent Spinel Oxide LiRh2O4,"We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent
configuration of Rh3+ and Rh4+. At room temperature it is a paramagnetic metal,
but on cooling, a metal-insulator transition occurs and a valence bond solid
state is formed below 170 K. We argue that the formation of valence bond solid
is promoted by a band Jahn-Teller transition at 230 K and the resultant
confinement of t2g holes within the xy band. The band Jahn-Teller instability
is also responsible for the observed enhanced thermoelectric power in the
orbital disordered phase above 230 K.",0806.2504v2
2008-08-04,Highly Conducting Graphene Sheets and Langmuir-Blodgett Films,"Graphene is an intriguing material with properties that are distinct from
those of other graphitic systems. The first samples of pristine graphene were
obtained by peeling off and epitaxial growth. Recently, the chemical reduction
of graphite oxide was used to produce covalently functionalized single-layer
graphene oxide. However, chemical approaches for the large-scale production of
highly conducting graphene sheets remain elusive. Here, we report that the
exfoliation-reintercalation-expansion of graphite can produce high-quality
single-layer graphene sheets stably suspended in organic solvents. The graphene
sheets exhibit high electrical conductance at room and cryogenic temperatures.
Large amounts of graphene sheets in organic solvents are made into large
transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer
manner. The chemically derived high quality graphene sheets could lead to
future scalable graphene devices.",0808.0502v1
2008-09-21,Synthesis and characterization of chloride doped polyaniline by bulk oxidative chemical polymerization.Doping effect on electrical conductivity,"Conductive polymers or ""organic metals"" are highly engineered nanostructured
materials made from organic building blocks. They are candidates as molecular
wires for nanotechnology applications in molecular electronics. The conduction
in these polymers is due to the presence of delocalized molecular orbitals. In
this work, we present the synthesis of chloride doped polyaniline by bulk
oxidative chemical polymerization using a solid aniline salt as a monomer
instead of liquid aniline to diminish toxic hazards. The FTIR and UV-visible
spectra confirmed the expected structure of the polymer. The electrical
conductivity measured using a four-probe method was 1.7 S/cm. The dependence of
impedance modulus on frequency was measured using an HP impedance analyzer in
the range 10 kHz-13 MHz. The influence of doping and the preparation
temperature on the electrical conductivity were also investigated.",0809.3552v1
2008-09-26,Improved structural ordering in sexithiophene thick films grown on single crystal oxide substrates,"We report on sexithiophene films, about 150nm thick, grown by thermal
evaporation on single crystal oxides and, as comparison, on Si/SiO2. By heating
the entire deposition chamber at 100 C we obtain standing-up oriented molecules
all over the bulk thickness. Surface morphology shows step-like islands, each
step being only one monolayer height. The constant and uniform warming of the
molecules obtained by heating the entire deposition chamber allows a stable
diffusion-limited growth process. Therefore, the regular growth kinetic is
preserved when increasing the thickness of the film. Electrical measurements on
differently structured films evidence the impact of the inter island separation
region size on the main charge transport parameters.",0809.4683v2
2008-09-27,Tuning of metal-insulator transition of two-dimensional electrons at parylene/SrTiO$_3$ interface by electric field,"Electrostatic carrier doping using a field-effect-transistor structure is an
intriguing approach to explore electronic phases by critical control of carrier
concentration. We demonstrate the reversible control of the insulator-metal
transition (IMT) in a two dimensional (2D) electron gas at the interface of
insulating SrTiO$_3$ single crystals. Superconductivity was observed in a
limited number of devices doped far beyond the IMT, which may imply the
presence of 2D metal-superconductor transition. This realization of a
two-dimensional metallic state on the most widely-used perovskite oxide is the
best manifestation of the potential of oxide electronics.",0809.4774v1
2008-10-05,Quantum Wells in Polar-Nonpolar Oxide Heterojunction Systems,"We address the electronic structure of quantum wells in polar-nonpolar oxide
heterojunction systems focusing on the case of non-polar BaVO$_3$ wells
surrounded by polar LaTiO$_3$ barriers. Our discussion is based on a density
functional description using the local spin density approximation with local
correlation corrections (LSDA+U). We conclude that a variety of quite different
two-dimensional electron systems can occur at interfaces between insulating
materials depending on band line-ups and on the geometrical arrangement of
polarity discontinuities.",0810.0798v2
2008-10-16,PBG properties of three-component 2D photonic crystals,"In this paper we analyze theoretically how the introduction of the third
component into the two-dimensional photonic crystal influences the photonic
band structure and the density-of-states of the system. We consider the
periodic array of cylindrical air rods in a dielectric, and the third medium is
introduced as a ring-shaped intermediate layer between the air pores and the
dielectric background. Using the plane wave method, we have obtained the band
structures for the 2D triangular lattice photonic crystals. The dependencies of
TE and TM band gaps' widths and gaps' edges position on the interlayer
dielectric constant and interlayer thickness were analyzed. In the framework of
this approach, we have estimated the influence of the surface oxide layer on
the band structure of macroporous silicon. We observed the shift of the gaps'
edges to the higher or lower frequencies, depending on the interlayer thickness
and dielectric constant. We have shown that the existence of a native oxide
surface layer should be taken into consideration to understand the optical
properties of 2D photonic crystals, particularly in macroporous silicon
structures.",0810.2947v1
2008-10-27,Systematic tight-binding analysis of ARPES spectra of transition-metal oxides,"We have performed systematic tight-binding (TB) analyses of the
angle-resolved photoemission spectroscopy (ARPES) spectra of transition-metal
(TM) oxides A$M$O$_3$ ($M=$ Ti, V, Mn, and Fe) with the perovskite-type
structure and compared the obtained parameters with those obtained from
configuration-interaction (CI) cluster-model analyses of photoemission spectra.
The values of $\epsilon_d-\epsilon_p$ from ARPES are found to be similar to the
charge-transfer energy $\Delta$ from O $2p$ orbitals to empty TM 3d orbitals
and much larger than $\Delta-U/2$ ($U$: on-site Coulomb energy) expected for
Mott-Hubbard-type compounds including SrVO$_3$. $\epsilon_d-\epsilon_p$ values
from {\it ab initio} band-structure calculations show similar behaviors to
those from ARPES. The values of the $p-d$ transfer integrals to describe the
global electronic structure are found to be similar in all the estimates,
whereas additional narrowing beyond the TB description occurs in the ARPES
spectra of the $d$ band.",0810.4905v1
2008-11-05,Enhancement of ferroelectricity at metal/oxide interfaces,"By performing first-principles calculations on four capacitor structures
based on BaTiO3 and PbTiO3, we determine the intrinsic interfacial effects that
are responsible for the destabilization of the polar state in thin-film
ferroelectric devices. We show that, contrary to the established
interpretation, the interfacial capacitance depends crucially on the local
chemical environment of the interface through the force constants of the
metal-oxide bonds, and is not necessarily related to the bulk screening
properties of the electrode material. In particular, in the case of interfaces
between AO-terminated perovskites and simple metals, we demonstrate a novel
mechanism of ""interfacial ferroelectricity"" that produces an overall
enhancement of the ferroelectric instability of the film, rather than a
suppression as is usually assumed. The resulting ""negative dead layer"" suggests
a route to thin-film ferroelectric devices that are free of deleterious size
effects.",0811.0632v1
2008-11-06,Ag-Cu alloy surfaces in an oxidizing environment: a first-principles study,"Recent experiments on model catalysts have shown that Ag-Cu alloys have
improved selectivity with respect to pure silver for ethylene epoxidation. In
this paper we review our first-principles investigations on the (111) surface
of this alloy and present new findings on other low index surfaces. We find
that, for every surface orientation, the presence of oxygen leads to copper
segregation to the surface. Considering the alloy to be in equilibrium with an
oxygen atmosphere and accounting for the effect of temperature and pressure, we
compute the surface free energy and study the stability of several surface
structures. Investigating the dependence of the surface free energy on the
surface composition, we construct the phase diagram of the alloy for every
surface orientation. Around the temperature, pressure and composition of
interest for practical applications, we find that a limited number of
structures can be present, including a thin layer of copper oxide on top of the
silver surface and copper-free structures. Different surface orientations show
a very similar behavior and in particular a single layer with CuO
stoichiometry, significantly distorted when compared to a layer of bulk CuO,
has a wide range of stability for all orientations. Our results are consistent
with, and help explain, recent experimental measurements.",0811.0864v1
2008-11-09,Comparison of Resonant Inelastic X-Ray Scattering Spectra and Dielectric Loss Functions in Copper Oxides,"We report empirical comparisons of Cu K-edge indirect resonant inelastic
x-ray scattering (RIXS) spectra, taken at the Brillouin zone center, with
optical dielectric loss functions measured in a number of copper oxides. The
RIXS data are obtained for Bi$_2$CuO$_4$, CuGeO$_3$, Sr$_2$Cu$_3$O$_4$Cl$_2$,
La$_2$CuO$_4$, and Sr$_2$CuO$_2$Cl$_2$, and analyzed by considering both
incident and scattered photon resonances. An incident-energy-independent
response function is then extracted. The dielectric loss functions, measured
with spectroscopic ellipsometry, agree well with this RIXS response, especially
in Bi$_2$CuO$_4$ and CuGeO$_3$.",0811.1379v1
2008-11-15,Pentacene islands grown on ultra-thin SiO2,"Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at
room temperature and characterized by scanning tunneling microscopy. The
ultra-thin oxide films were then used as substrates for room temperature growth
of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm,
indicating standing up pentacene grains in the thin-film phase were formed.
Pentacene is molecularly resolved in the second and subsequent molecular
layers. The measured in-plane unit cell for the pentacene (001) plane (ab
plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The
films are unperturbed by the UTO's short-range spatial variation in tunneling
probability, and reduce its corresponding effective roughness and correlation
exponent with increasing thickness. The pentacene surface morphology follows
that of the UTO substrate, preserving step structure, the long range surface
rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.",0811.2515v1
2008-11-17,Thermal degradation of ligno-cellulosic fuels: DSC and TGA studies,"The scope of this work was to show the utility of thermal analysis and
calorimetric experiments to study the thermal oxidative degradation of
Mediterranean scrubs. We investigated the thermal degradation of four species;
DSC and TGA were used under air sweeping to record oxidative reactions in
dynamic conditions. Heat released and mass loss are important data to be
measured for wildland fires modelling purpose and fire hazard studies on
ligno-cellulosic fuels. Around 638 and 778 K, two dominating and overlapped
exothermic peaks were recorded in DSC and individualized using a experimental
and numerical separation. This stage allowed obtaining the enthalpy variation
of each exothermic phenomenon. As an application, we propose to classify the
fuels according to the heat released and the rate constant of each reaction.
TGA experiments showed under air two successive mass loss around 638 and 778 K.
Both techniques are useful in order to measure ignitability, combustibility and
sustainability of forest fuels.",0811.2742v1
2008-11-18,Controlling the efficiency of spin injection into graphene by carrier drift,"Electrical spin injection from ferromagnetic metals into graphene is hindered
by the impedance mismatch between the two materials. This problem can be
reduced by the introduction of a thin tunnel barrier at the interface. We
present room temperature non-local spin valve measurements in
cobalt/aluminum-oxide/graphene structures with an injection efficiency as high
as 25%, where electrical contact is achieved through relatively transparent
pinholes in the oxide. This value is further enhanced to 43% by applying a DC
current bias on the injector electrodes, that causes carrier drift away from
the contact. A reverse bias reduces the AC spin valve signal to zero or
negative values. We introduce a model that quantitatively predicts the behavior
of the spin accumulation in the graphene under such circumstances, showing a
good agreement with our measurements.",0811.2960v1
2008-11-27,Monolithic Pixel Sensors in Deep-Submicron SOI Technology with Analog and Digital Pixels,"This paper presents the design and test results of a prototype monolithic
pixel sensor manufactured in deep-submicron fully-depleted Silicon-On-Insulator
(SOI) CMOS technology. In the SOI technology, a thin layer of integrated
electronics is insulated from a (high-resistivity) silicon substrate by a
buried oxide. Vias etched through the oxide allow to contact the substrate from
the electronics layer, so that pixel implants can be created and a reverse bias
can be applied. The prototype chip, manufactured in OKI 0.15 micron SOI
process, features both analog and digital pixels on a 10 micron pitch. Results
of tests performed with infrared laser and 1.35 GeV electrons and a first
assessment of the effect of ionising and non-ionising doses are discussed.",0811.4540v1
2008-12-05,The role of static disorder in negative thermal expansion in ReO3,"Time-of-flight neutron powder diffraction and specific heat measurements were
used to study the nature of thermal expansion in rhenium trioxide, an
electrically conducting oxide with cubic symmetry. The temperature evolution of
the lattice parameters show that ReO3 can exhibit negative thermal expansion at
low temperatures and that the transition from negative to positive thermal
expansion depends on sample preparation; the single crystal sample demonstrated
the highest transition temperature, 300 K, and largest negative value for the
coefficient of thermal expansion, alpha = -1.1(1)x 10^-6 K^-1. For the oxygen
atoms, the atomic displacement parameters are strongly anisotropic even at 15
K, indicative of a large contribution of static disorder to the displacement
parameters. Further inspection of the temperature evolution of the oxygen
displacement parameters for different samples reveals that the static disorder
contribution is greater for the samples with diminished NTE behavior. In
addition, specific heat measurements show that ReO3 lacks the low energy
Einstein-type modes seen in other negative thermal expansion oxides such as
ZrW2O8.",0812.1187v1
2008-12-18,Reduced leakage current in Josephson tunnel junctions with codeposited barriers,"Josephson junctions were fabricated using two different methods of barrier
formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the
first two layers were epitaxial. The oxide barrier was formed either by
exposing the Al surface to O2 or by codepositing Al in an O2 background. The
codeposition process yielded junctions that showed the theoretically predicted
subgap current and no measurable shunt conductance. In contrast, devices with
barriers formed by thermal oxidation showed a small shunt conductance in
addition to the predicted subgap current.",0812.3636v3
2009-01-23,Fabrication of nanotubules of thermoelectric gamma-Na0.7CoO2 using porous aluminum oxide membrane as supporting template,"We report the successful synthesis of nanotubules of thermoelectric materials
gamma-NaxCoO2 using two different sol-gel routes aided by porous anodized
aluminium oxide (AAO) membrane as supporting templates. The gamma-NaxCoO2
nanotubule using urea-based route can be achieved at 650 degree C at a heating
rate of 1 degree C/min and held for 4h. The gamma-NaxCoO2 nanotubule using
citric acid-based route can be achieved at 500 degree C using a rapid-heat-up
procedure and held for 30 min. The products were investigated using various
techniques including XRD, SEM and TEM. Electron diffraction pattern taken along
[001] zone axis direction on the nanotubule shows that all the diffraction
spots can be indexed using a hexagonal unit cell with a = b = 0.56 nm, which
can be considered as a superstructure with cell doubling within the ab plane.",0901.3628v1
2009-02-07,Engineering graphene by oxidation: a first principles study,"Graphene epoxide, with oxygen atoms lining up on pristine graphene sheets, is
investigated theoretically in this Letter. Two distinct phases: metastable
clamped and unzipped structures are unveiled in consistence with experiments.
In the stable (unzipped) phase, epoxy group breaks underneath sp2 bond and
modifies the mechanical and electronic properties of graphene remarkably. The
foldable epoxy ring structure reduces its Young's modulus by 42.4%, while
leaves the tensile strength almost unchanged. Epoxidation also perturbs the pi
state and opens semiconducting gap for both phases, with dependence on the
density of epoxidation. In the unzipped structures, localized states revealed
near the Fermi level resembles the edge states in graphene nanoribbons. The
study reported here paves the way for oxidation-based functionalization of
graphene-related materials.",0902.1237v1
2009-02-21,The f-electron challenge: localized and itinerant states in lanthanide oxides united by GW@LDA+U,"Many-body perturbation theory in the GW approach is applied to lanthanide
oxides, using the local-density approximation plus a Hubbard U correction
(LDA+U) as the starting point. Good agreement between the G0W0 density of
states and experimental spectra is observed for CeO2 and Ce2O3. Unlike the
LDA+U method G0W0 exhibits only a weak dependence on U in a physically
meaningful range of U values. For the whole lanthanide sesquioxide (Ln2O3)
series G0W0@LDA+U reproduces the main features found for the optical
experimental band gaps. The relative positions of the occupied and unoccupied
f-states predicted by G0W0 confirm the experimental conjecture derived from
phenomenological arguments.",0902.3697v1
2009-03-13,Probing the interface of Fe3O4/GaAs thin films by hard x-ray photoelectron spectroscopy,"Magnetite (Fe3O4) thin films on GaAs have been studied with HArd X-ray
PhotoElectron Spectroscopy (HAXPES) and low-energy electron diffraction. Films
prepared under different growth conditions are compared with respect to
stoichiometry, oxidation, and chemical nature. Employing the considerably
enhanced probing depth of HAXPES as compared to conventional x-ray
photoelectron spectroscopy (XPS) allows us to investigate the chemical state of
the film-substrate interfaces. The degree of oxidation and intermixing at the
interface are dependent on the applied growth conditions; in particular, we
found that metallic Fe, As2O3, and Ga2O3 exist at the interface. These
interface phases might be detrimental for spin injection from magnetite into
GaAs.",0903.2377v1
2009-03-18,Monolithic Pixel Sensors in Deep-Submicron SOI Technology,"Monolithic pixel sensors for charged particle detection and imaging
applications have been designed and fabricated using commercially available,
deep-submicron Silicon-On-Insulator (SOI) processes, which insulate a thin
layer of integrated full CMOS electronics from a high-resistivity substrate by
means of a buried oxide. The substrate is contacted from the electronics layer
through vias etched in the buried oxide, allowing pixel implanting and reverse
biasing. This paper summarizes the performances achieved with a first prototype
manufactured in the OKI 0.15 micrometer FD-SOI process, featuring analog and
digital pixels on a 10 micrometer pitch. The design and preliminary results on
the analog section of a second prototype manufactured in the OKI 0.20
micrometer FD-SOI process are briefly discussed.",0903.3205v1
2009-03-30,Interface relaxation and electrostatic charge depletion in the oxide heterostructure LaAlO3/SrTiO3,"Performing an analysis within density functional theory, we develop insight
into the structural and electronic properties of the oxide heterostructure
LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal
lattice distortion in order to clarify their interplay. We first study the
interface relaxation by a multi-layer system without surface, and the surface
effects, separately, by a substrate-film system. While elongation of the TiO6
octahedra at the interface enhances the metallicity, reduction of the film
thickness has the opposite effect due to a growing charge depletion. The
interplay of these two effects, as reflected by the full lattice relaxation in
the substrate-film system, however, strongly depends on the film thickness. An
inversion of the TiO6 distortion pattern for films thinner than four LaAlO3
layers results in an insulating state.",0903.5196v1
2009-04-06,"New Series of Nickel-Based Pnictide Oxide Superconductors (Ni2Pn2)(Sr4Sc2O6) (Pn = P, As)","We have discovered new nickel-based pnictide oxide superconductors,
(Ni2Pn2)(Sr4Sc2O6) (Pn = P, As). These compounds have a tetragonal unit cell
with a space group of P4/nmm and they consist of alternate stacking of
anti-fluorite Ni2Pn2 layers and K2NiF4-type Sr4Sc2O6 blocking layers. Lattice
parameters were a = 4.044 A and c = 15.23 A for (Ni2P2)(Sr4Sc2O6) and a = 4.078
A and c = 15.41 A for (Ni2As2)(Sr4Sc2O6), indicating their thicker blocking
layers than that of LaNiPO (c ~ 8.1 A). Both (Ni2P2)(Sr4Sc2O6) and
(Ni2As2)(Sr4Sc2O6) exhibited superconductivity with zero resistivity at 3.3 K
and 2.7 K, respectively. The perfect diamagnetism observed in both compounds
guaranteed their bulk superconductivity.",0904.0825v4
2009-04-15,Some properties of a long lifetime strongly-coupled molecular plasma produced by high Rydberg excitation of nitric oxide in a supersonic free jet,"A long life-time (>0.3 ms) strongly-coupled molecular Rydberg plasma is
generated by the excitation of nitric oxide into the high-n Rydberg threshold
region in the high-density region of a supersonic jet expansion. After 310 \mus
the plasma has expanded to a size of ca. 3 cm. When subjected to very small DC
fields from 0.2 to 1.0 V/cm the plasma reveals a much smaller high-density core
structure of only 0.6 cm. The molecular Rydberg plasma is observed over a broad
range of excitation energies, from threshold down to Rydberg states as low as n
= 19.",0904.2280v3
2009-04-20,Theoretical kinetic study of the low temperature oxidation of ethanol,"In order to improve the understanding of the low temperature combustion of
ethanol, high-level ab initio calculations were performed for elementary
reactions involving hydroxyethylperoxy radicals. These radicals come from the
addition of hydroxethyl radicals (?CH3CHOH and ?CH2CH2OH) on oxygen molecule.
Unimolecular reactions involving hydroxyethylperoxy radicals and their radical
products were studied at the CBS-QB3 level of theory. The results allowed to
highlight the principal ways of decomposition of these radicals. Calculations
of potential energy surfaces showed that the principal channels lead to the
formation of HO2 radicals which can be considered, at low temperature, as
slightly reactive. However, in the case of CH3CH(OOH)O? radicals, a route of
decomposition yields H atom and formic peracid, which is a branching agent that
can strongly enhance the reactivity of ethanol in low temperature oxidation. In
addition to these analyses, high-pressure limit rate constants were derived in
the temperature range 400 to 1000 K.",0904.2974v1
2009-04-30,Fundamental asymmetry in interfacial electronic reconstruction between insulating oxides,"We present an ab initio study of the (001) interfaces between two insulating
perovskites, the polar LaAlO3 and the nonpolar SrTiO3. We observe an
insulating-to-metallic transition above a critical LaAlO3 thickness. We explain
that the high conductivity observed at the TiO2 /LaO interface and the lack of
similar conductivity at the SrO/AlO2 interface are inherent in the atomic
geometry of the system. A large interfacial hopping matrix element between
cations causes the formation of a bound electron state at the TiO2 /LaO
interface. This mechanism for the formation of interfacial bound states
suggests a robust means for tuning conductivities at various oxide
heterointerfaces.",0904.4734v1
2009-05-06,Oxide superlattices with alternating p and n interfaces,"The physics of oxide superlattices is considered for pristine (001)
multilayers of the band insulators LaAlO3 and SrTiO3 with alternating p and n
interfaces. First principles results and a model of capacitor plates offer a
simple paradigm to understand their dielectric properties and the insulator to
metal transition (IMT) at interfaces with increasing layer thickness. The
charge at insulating interfaces is found to be as predicted from the formal
ionic charges, not populations. Different relative layer thicknesses produce a
spontaneous polarization of the system, and allow manipulation of the
interfacial electron gas. Large piezoresistance effects can be obtained from
the sensitivity of the IMT to lateral strain. Carrier densities are found to be
ideal for exciton condensation.",0905.0881v3
2009-05-08,Double-gated graphene-based devices,"We discuss transport through double gated single and few layer graphene
devices. This kind of device configuration has been used to investigate the
modulation of the energy band structure through the application of an external
perpendicular electric field, a unique property of few layer graphene systems.
Here we discuss technological details that are important for the fabrication of
top gated structures, based on electron-gun evaporation of SiO$_2$. We perform
a statistical study that demonstrates how --contrary to expectations-- the
breakdown field of electron-gun evaporated thin SiO$_2$ films is comparable to
that of thermally grown oxide layers. We find that a high breakdown field can
be achieved in evaporated SiO$_2$ only if the oxide deposition is directly
followed by the metallization of the top electrodes, without exposure to air of
the SiO$_2$ layer.",0905.1221v2
2009-06-09,Initial stages of nickel oxide growth on Ag(001) by pulsed laser deposition,"Submonolayers of nickel oxide films were grown on an Ag(001) by pulsed laser
deposition, and characterized in-situ by both scanning tunneling microscopy and
X-ray photoelectron spectroscopy. We observed quasi-two-dimensional growth of
the film, and clearly identified several kinds of defects, such as embedded
metallic Ni clusters and, notably, oxygen atoms, even while looking deeply into
the substrate. These originated from Ni and O hyperthermal projectiles as well
as from NiO clusters that were formed during laser ablation of a NiO target.
Those defects played a role of nucleation sites in extending the nucleation
stage of thin film growth.",0906.1653v3
2009-06-25,Rattling-Induced Superconductiviy in the Beta-Pyrochlore Oxides AOs2O6,"The superconducting properties of two beta-pyrochlore oxides, CsOs2O6 and
RbOs2O6, are studied by thermodynamic and transport measurements using
high-quality single crystals. It is shown that the character of
superconductivity changes systematically from weak coupling for CsOs2O6 to
moderately strong coupling for RbOs2O6, and finally to extremely strong
coupling with BCS-type superconductivity for KOs2O6, with increasing Tc.
Strong-coupling correction analyses of the superconducting properties reveal
that a low-energy rattling mode of the alkali metal ions is responsible for the
mechanism of the superconductivity in each compound. The large enhancement of
Tc from Cs to K is attributed to the increase in the electron-rattler coupling
with decreasing characteristic energy of the rattling and with increasing
anharmonicity. The existence of weak anisotropy in the superconducting gap or
in the electron-rattler interactions is found for the Cs and Rb compounds.",0906.4656v1
2009-06-27,Resistive switching in nanogap systems on SiO2 substrates,"Voltage-controlled resistive switching is demonstrated in various gap systems
on SiO2 substrate. The nanosized gaps are made by different means using
different materials including metal, semiconductor, and metallic nonmetal. The
switching site is further reduced by using multi-walled carbon nanotubes and
single-walled carbon nanotubes. The switching in all the gap systems shares the
same characteristics. This independence of switching on the material
compositions of the electrodes, accompanied by observable damage to the SiO2
substrate at the gap region, bespeaks the intrinsic switching from
post-breakdown SiO2. It calls for caution when studying resistive switching in
nanosystems on oxide substrates, since oxide breakdown extrinsic to the
nanosystem can mimic resistive switching. Meanwhile, the high ON/OFF ratio
(10E5), fast switching time (2 us, test limit), durable cycles demonstrated
show promising memory properties. The intermediate states observed reveal the
filamentary conduction nature.",0906.5100v1
2009-06-29,Stratospheric Albedo Modification by Aerosol Injection,"This paper reviews and develops the proposal, widely discussed but not
examined in detail, to use stratospheric aerosols to increase the Earth's
albedo to Solar radiation in order to control climate change. The potential of
this method has been demonstrated by the ""natural experiments"" of volcanic
injection of sulfate aerosols into the stratosphere that led to subsequent
observed global cooling. I consider several hygroscopic oxides as possible
aerosol materials in addition to oxides of sulfur. Aerosol chemistry,
dispersion and transport have been the subject of little study and are not
understood, representing a significant scientific risk. Even the optimal
altitude of injection and aerosol size distribution are poorly known. Past
attention focused on guns and airplanes as means of lofting aerosols or their
chemical precursors, but large sounding rockets are cheap, energetically
efficient, can be designed to inject aerosols at any required altitude, and
involve little technical risk. Sophisticated, mass-optimized ""engineered""
particles have been proposed as possible aerosols, but the formidable problems
of their production in quantity, lofting and dispersion have not been
addressed.",0906.5307v1
2009-07-09,Cotunnite-structured titanium dioxide: the hardest known oxide,"Despite great technological importance and many investigations, a material
with measured hardness comparable to that of diamond or cubic boron nitride has
yet to be identified. Combined theoretical and experimental investigations led
to the discovery of a new polymorph of titanium dioxide with titanium
nine-coordinated to oxygen in the cotunnite (PbCl2) structure. Hardness
measurements on the cotunnite-structured TiO2 synthesized at pressures above 60
GPa and temperatures above 1000 K reveal that this material is the hardest
oxide yet discovered. Furthermore, it is one of the least compressible (with a
measured bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa)
polycrystalline materials studied thus far.",0907.1464v1
2009-07-16,Dependence of Band Renormalization Effect on the Number of Copper-oxide Layers in Tl-based Copper-oxide Superconductor using Angle-resolved Photoemission Spectroscopy,"Here we report the first angle-resolved photoemission measurement on nearly
optimally-doped multi-layer Tl-based superconducting cuprates (Tl-2212 and
Tl-1223) and a comparison study to single layer (Tl-2201) compound. A ""kink"" in
the band dispersion is found in all three compounds but exhibits different
momentum dependence for the single layer and multi-layer compounds, reminiscent
to that of Bi-based cuprates. This layer number dependent renormalization
effect strongly implies that the spin resonance mode is unlikely responsible
for the dramatic renormalization effect near the antinodal region.",0907.2747v1
2009-08-10,Nanometer-scale striped surface terminations on fractured SrTiO$_{3}$ surfaces,"Using cross-sectional scanning tunneling microscopy on in situ fractured
SrTiO$_{3}$, one of the most commonly used substrates for the growth of complex
oxide thin films and superlattices, atomically smooth terraces have been
observed on (001) surfaces. Furthermore, it was discovered that fracturing this
material at room temperature results in the formation of stripe patterned
domains having characteristic widths (~10 nm to ~20 nm) of alternating surface
terminations that extend over a long-range. Spatial characterization utilizing
spectroscopy techniques revealed a strong contrast in the electronic structure
of the two domains. Combining these results with topographic data, we are able
to assign both TiO$_{2}$ and SrO terminations to their respective domains. The
results of this proof-of-principle experiment reveal that fracturing this
material leads to reproducibly flat surfaces that can be characterized at the
atomic-scale and suggests that this technique can be utilized for the study of
technologically relevant complex oxide interfaces.",0908.1419v1
2009-08-13,Structure and morphology of hydroxylated nickel oxide (111) surfaces,"We report an experimental and theoretical analysis of the sqrt(3)x
sqrt(3)-R30 and 2x2 reconstructions on the NiO (111) surface combining
transmission electron microscopy, x-ray photoelectron spectroscopy, and
reasonably accurate density functional calculations using the meta-GGA hybrid
functional TPSSh. While the main focus here is on the surface structure, we
also observe an unusual step morphology with terraces containing only even
numbers of unit cells during annealing of the surfaces. The experimental data
clearly shows that the surfaces contain significant coverage of hydroxyl
terminations, and the surface structures are essentially the same as those
reported on the MgO (111) surface implying an identical kinetically-limited
water-driven structural transition pathway. The octapole structure can
therefore be all but ruled out for single crystals of NiO annealed in or
transported through humid air. . The theoretical analysis indicates, as
expected, that simple density functional theory methods for such
strongly-correlated oxide surfaces are marginal, while better consideration of
the metal d-electrons has a large effect although, it is still not perfect.",0908.1888v1
2009-08-18,Detection of a single-charge defect in a metal-oxide-semiconductor structure using vertically coupled Al and Si single-electron transistors,"An Al-AlO_x-Al single-electron transistor (SET) acting as the gate of a
narrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET)
can induce a vertically aligned Si SET at the Si/SiO_2 interface near the
MOSFET channel conductance threshold. By using such a vertically coupled Al and
Si SET system, we have detected a single-charge defect which is tunnel-coupled
to the Si SET. By solving a simple electrostatic model, the fractions of each
coupling capacitance associated with the defect are extracted. The results
reveal that the defect is not a large puddle or metal island, but its size is
rather small, corresponding to a sphere with a radius less than 1 nm. The small
size of the defect suggests it is most likely a single-charge trap at the
Si/SiO_2 interface. Based on the ratios of the coupling capacitances, the
interface trap is estimated to be about 20 nm away from the Si SET.",0908.2479v1
2009-08-25,Bipolar resistive switching in amorphous titanium oxide thin films,"Using isothermal and temperature-dependent electrical measurements, we
investigated the resistive switching mechanism of amorphous titanium oxide thin
films deposited by a plasma-enhanced atomic layer deposition method between two
aluminum electrodes. We found a bipolar resistive switching behavior in the
high temperature region (> 140 K), and two activation energies of shallow
traps, 0.055 eV and 0.126 eV in the ohmic current regime. We also proposed that
the bipolar resistive switching of amorphous TiO2 thin films is governed by the
transition of conduction mode from a bulk-limited SCLC model (Off state) to an
interface-limited Schottky emission (On state), generated by the ionic movement
of oxygen vacancies.",0908.3525v1
2009-09-13,Blue photoluminescence from chemically derived graphene oxide,"Fluorescent organic compounds are of significant importance to the
development of low-cost opto-electronic devices. Blue fluorescence from
aromatic or olefinic molecules and their derivatives is particularly important
for display and lighting applications. Thin film deposition of
low-molecular-weight fluorescent organic compounds typically requires costly
vacuum evaporation systems. On the other hand, solution-processable polymeric
counterparts generally luminesce at longer wavelengths due to larger
delocalization in the chain. Blue light emission from solution-processed
materials is therefore of unique technological significance. Here we report
near-UV to blue photoluminescence (PL) from solution-processed graphene oxide
(GO). The characteristics of the PL and its dependence on the reduction of GO
indicates that it originates from the recombination of electron-hole (e-h)
pairs localized within small sp2 carbon clusters embedded within an sp3 matrix.
These results suggest that a sheet of graphene provides a parent structure on
which fluorescent components can be chemically engineered without losing the
macroscopic structural integrity. Our findings offer a unique route towards
solution-processable opto-electronics devices with graphene.",0909.2456v1
2009-09-23,Intermediate-valence behavior of the transition-metal oxide CaCu$_3$Ru$_4$O$_{12}$,"The transition--metal oxide CaCu$_3$Ru$_4$O$_{12}$ with perovskite--type
structure shows characteristic properties of an intermediate--valence system.
The temperature--dependent susceptibility exhibits a broad maximum around $150
- 160$ K. At this temperature, neutron powder diffraction reveals a small but
significant volume change whereby the crystal structure is preserved. Moreover,
the temperature--dependent resistivity changes its slope. NMR Knight shift
measurements of Ru reveal a cross--over from high temperature paramagnetic
behavior of localized moments to itinerant band states at low temperatures.
Additional density--functional theory calculations can relate the structural
anomaly with the $d$--electron number. The different experimental and
calculational methods result in a mutually consistent description of
CaCu$_3$Ru$_4$O$_{12}$ as an intermediate--valent system in the classical sense
of having low--energy charge fluctuations.",0909.4208v1
2009-09-25,"Fluorescent Carbon Nanoparticle: Synthesis, Characterization and Bio-imaging Application","Fluorescent carbon nanoparticle (CNP) having 2-6 nm in size with quantum
yield of about ~3% were synthesized via nitric acid oxidation of carbon soot
and this approach can be used for milligram scale synthesis of these water
soluble particles. These CNPs are nano-crystalline with predominantly graphitic
structure and shows green fluorescence under UV exposure. While nitric acid
oxidation induces nitrogen and oxygen incorporation into soot particle that
afforded water solubility and light emitting property; the isolation of small
particles from a mixture of different size particles improved the fluorescence
quantum yield. These CNP shows encouraging cell imaging application. They enter
into cell without any further functionalization and fluorescence property of
these particles can be used for fluorescence based cell imaging application.",0909.4622v1
2009-10-22,Metal-insulator transition through a semi-Dirac point in oxide nanostructures: VO$_2$ (001) layers confined within TiO$_2$,"Multilayer (TiO$_2$)$_m$/(VO$_2$)$_n$ nanostructures ($d^1$ - $d^0$
interfaces with no polar discontinuity) show a metal-insulator transition with
respect to the VO$_2$ layer thickness in first principles calculations. For $n$
$\geq$ 5 layers, the system becomes metallic, while being insulating for $n$ =
1 and 2. The metal-insulator transition occurs through a semi-Dirac point phase
for $n$ = 3 and 4, in which the Fermi surface is point-like and the electrons
behave as massless along the zone diagonal in k-space and as massive fermions
along the perpendicular direction. We provide an analysis of the evolution of
the electronic structure through this unprecedented insulator-to-metal
transition, and identify it as resulting from quantum confinement producing a
non-intuitive orbital ordering on the V $d^1$ ions, rather than being a
specific oxide interface effect. Spin-orbit coupling does not destroy the
semi-Dirac point for the calculated ground state, where the spins are aligned
along the rutile c-axis, but it does open a substantial gap if the spins lie in
the basal plane.",0910.4411v1
2009-10-30,Charge and orbital ordering in Fe and Mn perovskite oxides far from half- doping by resonant x- ray scattering,"The emergence of superlattice periodicities at metal to insulator transitions
in hole doped perovskite oxides responds to a rearrangement of the local atomic
structure, and electron and spin density distribution. Originally, the ionic
model based on a checkerboard- type atomic distribution served to describe the
low temperature charge and orbital ordered (COO) phases arising in half- doped
manganites. In the last years, the exploitation of resonant x- ray scattering
(RXS) capabilities has shown the need to revisit these concepts and improve the
picture. Yet, we have realised that COO is a more common phenomenon than
expected that can be observed in a wide range of doping levels. Here we compare
the experimental data recently collected by RXS on La_0.4Sr_1.6MnO_4 (x=0.60)
and La(Pr)_1/3Sr_2/3FeO_3 (x=0.67). The first shows a COO phase similar to that
found in the x=0.5 sample but angular peak positions vs. T denotes the
incommensurability of superlattice reflections. Meanwhile, the analysis of the
commensurate CO phase in the studied ferrite underlines the role of the
structural changes also involving La(Sr) and O atoms.",0910.5788v1
2009-11-02,Non-monotonic Fermi surface evolution and its correlation with stripe ordering in bilayer manganites,"In correlated electron systems such as cuprate superconductors and colossal
magnetoresistive (CMR) oxides there is often a tendency for a nanoscale
self-organization of electrons that can give rise to exotic properties and to
extreme non-linear responses. The driving mechanisms for this self-organization
are highly debated, especially in the CMR oxides in which two types of
self-organized stripes of charge and orbital order coexist with each other. By
utilizing angle-resolved photoemission spectroscopy measurements over a wide
doping range, we show that one type of stripe is exclusively linked to long
flat portions of nested Fermi surface, while the other type prefers to be
commensurate with the real space lattice but also may be driven away from this
by the Fermi surface. Complementarily, the Fermi surface also appears to be
driven away from its non-interacting value at certain doping levels, giving
rise to a host of unusual electronic properties.",0911.0439v1
2010-01-08,Preparation of light-atom tips for Scanning Probe Microscopy by explosive delamination,"To obtain maximal resolution in STM and AFM, the size of the protruding tip
orbital has to be minimized. Beryllium as tip material is a promising candidate
for enhanced resolution because a beryllium atom has just four electrons,
leading to a small covalent radius of only 96 pm. Besides that, beryllium is
conductive and has a high elastic modulus, which is a necessity for a stable
tip apex. However beryllium tips that are prepared ex situ, are covered with a
robust oxide layer, which cannot be removed by just heating the tip. Here we
present a successful preparation method that combines the heating of the tip by
field emission and a mild collision with a clean metal plate. That method
yields a clean, oxide-free tip surface as proven by a work function of as
deduced from a current-distance curve. Additionally, a STM image of the
Si-(111)-(7x7) is presented to prove the single-atom termination of the
beryllium tip.",1001.1321v1
2010-01-11,Catalyst preparation for CMOS-compatible silicon nanowire synthesis,"Metallic contamination was key to the discovery of semiconductor nanowires,
but today it stands in the way of their adoption by the semiconductor industry.
This is because many of the metallic catalysts required for nanowire growth are
not compatible with standard CMOS (complementary metal oxide semiconductor)
fabrication processes. Nanowire synthesis with those metals which are CMOS
compatible, such as aluminium and copper, necessitate temperatures higher than
450 C, which is the maximum temperature allowed in CMOS processing. Here, we
demonstrate that the synthesis temperature of silicon nanowires using copper
based catalysts is limited by catalyst preparation. We show that the
appropriate catalyst can be produced by chemical means at temperatures as low
as 400 C. This is achieved by oxidizing the catalyst precursor, contradicting
the accepted wisdom that oxygen prevents metal-catalyzed nanowire growth. By
simultaneously solving material compatibility and temperature issues, this
catalyst synthesis could represent an important step towards real-world
applications of semiconductor nanowires.",1001.1725v1
2010-01-13,Compact and explicit physical model for lateral metal-oxide-semiconductor field-effect transistor with nanoelectromechanical system based resonant gate,"We propose a simple analytical model of a metal-oxide-semiconductor
field-effect transistor with a lateral resonant gate based on the coupled
electromechanical equations, which are self-consistently solved in time. All
charge densities according to the mechanical oscillations are evaluated. The
only input parameters are the physical characteristics of the device. No extra
mathematical parameters are used to fit the experimental results. Theoretical
results are in good agreement with the experimental data in static and dynamic
operation. Our model is comprehensive and may be suitable for any
electromechanical device based on the field-effect transduction.",1001.2148v1
2010-02-18,Logarithmic behavior of degradation dynamics in metal--oxide semiconductor devices,"In this paper the authors describe a theoretical simple statistical modelling
of relaxation process in metal-oxide semiconductor devices that governs its
degradation. Basically, starting from an initial state where a given number of
traps are occupied, the dynamics of the relaxation process is measured
calculating the density of occupied traps and its fluctuations (second moment)
as function of time. Our theoretical results show a universal logarithmic law
for the density of occupied traps $\bar{<n(t)>} \sim \phi (T,E_{F}) (A+B \ln
t)$, i.e., the degradation is logarithmic and its amplitude depends on the
temperature and Fermi Level of device. Our approach reduces the work to the
averages determined by simple binomial sums that are corroborated by our Monte
Carlo simulations and by experimental results from literature, which bear in
mind enlightening elucidations about the physics of degradation of
semiconductor devices of our modern life.",1002.3571v1
2010-02-18,Ferromagnetic transition in the double-exchange model on the pyrochlore lattice,"The double-exchange model, which has been extensively studied in the context
of colossal magneto-resistance in perovskite manganese oxides, is known to
exhibit a ferromagnetic metallic state at low temperatures because of the
interplay between localized moments and itinerant electrons through the
Hund's-rule coupling. Here we investigate numerically the ferromagnetic
transition in the double-exchange model defined on the frustrated pyrochlore
lattice as a simple model for ferromagnetic pyrochlore oxides. We demonstrate
that the finite-size corrections are largely reduced by implementing averages
over the twisted boundary conditions in the Monte Carlo simulation, which
enables to estimate the ferromagnetic transition temperature in relatively
small size clusters. The estimate is compared with that for the non-frustrated
cubic lattice system.",1002.3642v1
2010-02-26,Deep level transient spectroscopy study for the development of ion-implanted silicon field-effect transistors for spin-dependent transport,"A deep level transient spectroscopy (DLTS) study of defects created by
low-fluence, low-energy ion implantation for development of ion-implanted
silicon field-effect transistors for spin-dependent transport experiments is
presented. Standard annealing strategies are considered to activate the
implanted dopants and repair the implantation damage in test
metal-oxide-semiconductor (MOS) capacitors. Fixed oxide charge, interface
trapped charge and the role of minority carriers in DLTS are investigated. A
furnace anneal at 950 $\rm ^{o}$C was found to activate the dopants but did not
repair the implantation damage as efficiently as a 1000 $\rm ^{o}$C rapid
thermal anneal. No evidence of bulk traps was observed after either of these
anneals. The ion- implanted spin-dependent transport device is shown to have
expected characteristics using the processing strategy determined in this
study.",1002.4934v1
2010-03-09,Stability of exfoliated Bi$_2$Sr$_2$Dy$_x$Ca$_{1-x}$Cu$_2$O$_{8+δ}$ studied by Raman microscopy,"Nanometer thick cuprates are an appealing platform for devices as well as
exploring the roles of dimensionality, disorder, and free carrier density in
these compounds. To this end we have produced exfoliated crystals of
Bi2Sr2CaCu2O8 on oxidized silicon substrates. The exfoliated crystals were
characterized via Atomic Force and polarized Raman microscopies. Proper
procedures for production, handling and monitoring of these thin oxides are
described. Subtle differences between the exfoliated and bulk crystals are also
discussed.",1003.1979v2
2010-03-12,Exchange bias and interface electronic structure in Ni/Co3O4(011),"A detailed study of the exchange bias effect and the interfacial electronic
structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are
observed at low temperatures, and the exchange bias effect persists to
temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to
~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni
films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy
measurements as a function of Ni thickness show that Co reduction and Ni
oxidation occur over an extended interfacial region. We conclude that the
exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4
systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at
the interface.",1003.2478v1
2010-04-19,Cu_{2}O as nonmagnetic semiconductor for spin transport in crystalline oxide electronics,"We probe spin transport in Cu_{2}O by measuring spin valve effect in
La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/Co and
La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/La_{0.7}Sr_{0.3}MnO_{3} epitaxial
heterostructures. In La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/Co systems we find that a
fraction of out-of-equilibrium spin polarized carrier actually travel across
the Cu_{2}O layer up to distances of almost 100 nm at low temperature. The
corresponding spin diffusion length dspin is estimated around 40 nm.
Furthermore, we find that the insertion of a SrTiO_{3} tunneling barrier does
not improve spin injection, likely due to the matching of resistances at the
interfaces. Our result on dspin may be likely improved, both in terms of
Cu_{2}O crystalline quality and sub-micrometric morphology and in terms of
device geometry, indicating that Cu_{2}O is a potential material for efficient
spin transport in devices based on crystalline oxides.",1004.3201v1
2010-04-30,Scalability of Atomic-Thin-Body (ATB) Transistors Based on Graphene Nanoribbons,"A general solution for the electrostatic potential in an atomic-thin-body
(ATB) field-effect transistor geometry is presented. The effective
electrostatic scaling length, {\lambda}eff, is extracted from the analytical
model, which cannot be approximated by the lowest order eigenmode as
traditionally done in SOI-MOSFETs. An empirical equation for the scaling length
that depends on the geometry parameters is proposed. It is shown that even for
a thick SiO2 back oxide {\lambda}eff can be improved efficiently by thinner top
oxide thickness, and to some extent, with high-k dielectrics. The model is then
applied to self-consistent simulation of graphene nanoribbon (GNR)
Schottky-barrier field-effect transistors (SB-FETs) at the ballistic limit. In
the case of GNR SB-FETs, for large {\lambda}eff, the scaling is limited by the
conventional electrostatic short channel effects (SCEs). On the other hand, for
small {\lambda}eff, the scaling is limited by direct source-to-drain tunneling.
A subthreshold swing below 100mV/dec is still possible with a sub-10nm gate
length in GNR SB-FETs.",1004.5560v1
2010-06-02,Towards a first-principles chemical engineering: Transport limitations and bistability in in situ CO oxidation at RuO2(110),"We present a first-principles based multiscale modeling approach to
heterogeneous catalysis that integrates first-principles kinetic Monte Carlo
simulations of the surface reaction chemistry into a fluid dynamical treatment
of the macro-scale flow structures in the reactor. The approach is applied to a
stagnation flow field in front of a single-crystal model catalyst, using the CO
oxidation at RuO2(110) as representative example. Our simulations show how heat
and mass transfer effects can readily mask the intrinsic reactivity at
gas-phase conditions typical for modern in situ experiments. For a range of
gas-phase conditions we furthermore obtain multiple steady-states that arise
solely from the coupling of gas-phase transport and surface kinetics. This
additional complexity needs to be accounted for when aiming to use dedicated in
situ experiments to establish an atomic-scale understanding of the function of
heterogeneous catalysts at technologically relevant gas-phase conditions.",1006.0343v1
2010-06-11,"Superconductivity Above 40 K Observed in a New Iron Arsenide Oxide (Fe2As2)(Ca4(Mg,Ti)3Oy)","A new layered iron arsenide oxide (Fe2As2)(Ca4(Mg,Ti)3Oy) was discovered. Its
crystal structure is tetragonal with a space group of I4/mmm consisted of the
anti-fluorite type FeAs layer and blocking layer of triple perovskite cells and
is identical with (Fe2As2)(Sr4(Sc,Ti)3O8) discovered in our previous study. The
lattice constants of (Fe2As2)(Ca4(Mg,Ti)3Oy) are a = 3.877 A and c = 33.37 A.
This compound exhibited bulk superconductivity up to 43 K in susceptibility
measurement without intentional carrier doping. A resistivity drop was observed
at ~47 K and zero resistance was achieved at 42 K. These values correspond to
the second highest Tc among the layered iron-based superconductors after
REFeAsO system.",1006.2367v2
2010-06-12,Role of van der Waals bonding in layered oxide: Bulk vanadium pentoxide,"Sparse matter is characterized by regions with low electron density and its
understanding calls for methods to accurately calculate both the van der Waals
(vdW) interactions and other bonding. Here we present a first-principles
density functional theory (DFT) study of a layered oxide (V2O5) bulk structure
which shows charge voids in between the layers and we highlight the role of the
vdW forces in building up material cohesion. The result of previous
first-principles studies involving semilocal approximations to the
exchange-correlation functional in DFT gave results in good agreement with
experiments for the two in-plane lattice parameters of the unit cell but
overestimated the parameter for the stacking direction. To recover the third
parameter we include the nonlocal (dispersive) vdW interactions through the
vdW-DF method [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] testing also
various choices of exchange flavors. We find that the transferable
first-principle vdW-DF calculations stabilizes the bulk structure. The vdW-DF
method gives results in fairly good agreement with experiments for all three
lattice parameters.",1006.2494v1
2010-06-24,Visualizing nanoscale electronic band alignment at the La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/Nb:SrTiO$_{3}$ interface,"Cross-sectional scanning tunnelling microscopy and spectroscopy (XSTM/S) were
used to map out the band alignment across the complex oxide interface of
La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/Nb-doped SrTiO$_{3}$. By a controlled
cross-sectional fracturing procedure, unit-cell high steps persist near the
interface between the thin film and the substrate in the non-cleavable
perovskite materials. The abrupt changes of the mechanical and electronic
properties were visualized directly by XSTM/S. Using changes in the DOS as
probe by STM, the electronic band alignment across the heterointerface was
mapped out providing a new approach to directly measure the electronic
properties at complex oxide interfaces.",1006.4886v2
2010-06-28,Reversible carrier-type transition in gas-sensing oxides and nanostructures,"Despite many important applications of a-Fe2O3 and Fe doped SnO2 in
semiconductors, catalysis, sensors, clinical diagnosis and treatments, one
fundamental issue that is crucial to these applications remains theoretically
equivocal- the reversible carrier-type transition between n- and p-type
conductivities during gas-sensing operations. Here, we give unambiguous and
rigorous theoretical analysis in order to explain why and how the oxygen
vacancies affect the n-type semiconductors, a-Fe2O3 and Fe doped SnO2 in which
they are both electronically and chemically transformed into a p-type
semiconductor. Furthermore, this reversible transition also occurs on the oxide
surfaces during gas-sensing operation due to physisorbed gas molecules (without
any chemical reaction). We make use of the ionization energy theory and its
renormalized ionic displacement polarizability functional to reclassify,
generalize and to explain the concept of carrier-type transition in solids, and
during gas-sensing operation. The origin of such a transition is associated to
the change in ionic polarizability and the valence states of cations in the
presence of (a) oxygen vacancies and (b) physisorped gas molecules.",1006.5304v2
2010-07-29,Low-energy kink in the nodal dispersion of copper-oxide superconductors: Insights from Dynamical Mean Field Theory,"Motivated by the observation in copper-oxide high-temperature
superconductors, we investigate the appearance of kinks in the electronic
dispersion due to coupling to phonons for a system with strong electronic
repulsion. We study a Hubbard model supplemented by an electron-phonon coupling
of Holstein type within Dynamical Mean Field Theory (DMFT) utilizing Numerical
Renormalization Group as impurity solver. Paramagnetic DMFT solutions in the
presence of large repulsion show a kink only for large values of the
electron-phonon coupling $\lambda$ or large doping and, contrary to the
conventional electron-phonon theory, the position of such a kink can be shifted
to energies larger than the renormalized phonon frequency $\omega_0^r$. When
including antiferromagnetic correlations we find a stronger effect of the
electron-phonon interaction on the electronic dispersion due to a cooperative
effect and a visible kink at $\omega_0^r$, even for smaller $\lambda$. Our
results provide a scenario of a kink position increasing with doping, which
could be related to recent photoemission experiments on Bi-based cuprates.",1007.5268v3
2010-07-30,Thermal Activation and Quantum Field Emission in a Sketch-Based Oxide Nano Transistor,"We report direct measurements of the potential barriers and electronic
coupling between nanowire segments within a sketch-based oxide nanotransistor
(SketchFET) device. Near room temperature, switching is governed by thermally
activation across a potential barrier controlled by the nanowire gate. Below
T=150 K, a crossover to quantum field emission is observed that is sensitive to
structural phase transitions in the SrTiO3 layer. This direct measurement of
the source-drain and gate-drain energy barriers is crucial for the development
of room-temperature logic and memory elements and low-temperature quantum
devices.",1007.5468v2
2010-08-05,The structure of graphite oxide: Investigation of its surface chemical groups,"The structure of graphite oxide (GO) has been systematically studied using
various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy
(FT-IR), X-ray photoemission spectroscopy (XPS), 13C solid state NMR, and O
K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that
GO consists of amorphous and crystalline phases. The XPS data show that some
carbon atoms have sp3 orbitals and others have sp2 orbitals. The ratio of sp2
to sp3 bonded carbon atoms decreases as sample preparation times increase. The
13C solid-state NMR spectra of GO indicate the existence of -OH and -O- groups
for which peaks appear at 60 and 70 ppm, respectively. FT-IR results
corroborate these findings. The existence of ketone groups is also implied by
FT-IR, which is verified by O K-edge XANES and 13C solid-state NMR. We propose
a new model for GO based on the results; -O-, -OH, and -C=O groups are on the
surface.",1008.0937v1
2010-08-11,Scale-free structural organization of oxygen interstitials in La2CuO4+y,"It is well known that the microstructures of the transition-metal oxides
(refs 1-3), including the high-transition-temperature (high-Tc) copper oxide
superconductors (refs 4-7), are complex. This is particularly so when there are
oxygen interstitials or vacancies (ref.8), which influence the bulk properties.
For example, the oxygen interstitials in the spacer layers separating the
superconducting CuO2 planes undergo ordering phenomena in Sr(2)O(1+y)CuO(2)
(ref. 9), YBa(2)Cu(3)O(6+y) (ref. 10) and La(2)CuO(4+y) (refs 11-15) that
induce enhancements in the transition temperatures with no changes in hole
concentrations. It is also known that complex systems often have a
scale-invariant structural organization16, but hitherto none had been found in
high-Tc materials. Here we report that the ordering of oxygen interstitials in
the La(2)O(2+y) spacer layers of La(2)CuO(4+y) high-Tc superconductors is
characterized by a fractal distribution up to a maximum limiting size of 400
microns. Intriguingly, these fractal distributions of dopants seem to enhance
superconductivity at high temperature.",1008.2015v2
2010-08-27,Flow boiling of water on nanocoated surfaces in a microchannel,"Experiments were performed to study the effects of surface wettability on
flow boiling of water at atmospheric pressure. The test channel is a single
rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was
set at 100 kg/m2 s and the base heat flux varied from 30 to 80 kW/m2. Water
enters the test channel under subcooled conditions. The samples are silicone
oxide (SiOx), titanium (Ti), diamond-like carbon (DLC) and carbon-doped silicon
oxide (SiOC) surfaces with static contact angles of 26{\deg}, 49{\deg},
63{\deg} and 103{\deg}, respectively. The results show significant impacts of
surface wettability on heat transfer coefficient.",1008.4696v1
2010-08-31,"Size, oxidation, and strain in small Si/SiO2 nanocrystals","The structural, electronic and optical properties of Si nanocrystals of
different size and shape, passivated with hydrogens, OH groups, or embedded in
a SiO2 matrix are studied. The comparison between the embedded and free,
suspended nanocrystals shows that the silica matrix produces a strain on the
embedded NCs, that contributes to determine the band gap value. By including
the strain on the hydroxided nanocrystals we are able to reproduce the
electronic and optical properties of the full Si/SiO2 systems. Moreover we
found that, while the quantum confinement dominates in the hydrogenated
nanocrystals of all sizes, the behaviour of hydroxided and embedded
nanocrystals strongly depends on the interface oxidation degree, in particular
for diameters below 2 nm. Here, the proportion of NC atoms at the Si/SiO2
interface becomes relevant, producing surface-related states that may affect
the quantum confinement appearing as inner band gap states and then drastically
changing the optical response of the system.",1008.5272v1
2010-09-02,Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High Pressure,"Rattling-induced superconductivity in the {\beta}-pyrochlore oxide KOs2O6 is
investigated under high pressure up to 5 GPa. Resistivity measurements in a
high-quality single crystal reveal a gradual decrease in the superconducting
transition temperature Tc from 9.7 K at 1.0 GPa to 6.5 K at 3.5 GPa, followed
by a sudden drop to 3.3 K at 3.6 GPa. Powder X-ray diffraction experiments show
a structural transition from cubic to monoclinic or triclinic at a similar
pressure. The sudden drop in Tc is ascribed to this structural tran-sition, by
which an enhancement in Tc due to a strong electron-rattler interaction present
in the low-pressure cubic phase is abrogated as the rattling of the K ion is
completely suppressed or weakened in the high-pressure phase of reduced
symmetry. In addition, we find two anomalies in the temperature dependence of
resistivity in the low-pressure phase, which may be due to subtle changes in
rattling vibration.",1009.0355v1
2010-09-09,Thermal Activation and Quantum Field Emission in a Sketch-Based Oxide Nano Transistor,"The interface between polar LaAlO3 and non-polar SrTiO3 exhibits a remarkable
variety of electronic behavior associated with the formation of an interfacial
quasi-two-dimensional electron gas (q-2DEG). By ""sketching"" patterns of charge
on the top LaAlO3 surface, the LaAlO3/SrTiO3 interface conductance can be
controlled with near-atomic spatial resolution. Using this technique, a
sketch-based oxide nanotransistor (SketchFET) was demonstrated with a minimum
feature size of just two nanometers. Here we report direct measurements of the
potential barriers and electronic coupling between nanowire segments within a
SketchFET device. Near room temperature, switching is governed by thermally
activated field emission from the nanowire gate. Below T=150 K, a crossover to
quantum field emission is observed that is sensitive to structural phase
transitions in the SrTiO3 layer. This direct measurement of the source-drain
and gate-drain energy barriers is crucial for the development of
room-temperature logic and memory elements and low-temperature quantum devices.",1009.1893v1
2010-10-05,Interatomic potentials for mixed oxide (MOX) nuclear fuels,"We extend our recently developed interatomic potentials for UO_{2} to the
mixed oxide fuel system (U,Pu,Np)O_{2}. We do so by fitting against an
extensive database of ab initio results as well as to experimental
measurements. The applicability of these interactions to a variety of mixed
environments beyond the fitting domain is also assessed. The employed formalism
makes these potentials applicable across all interatomic distances without the
need for any ambiguous splining to the well-established short-range
Ziegler-Biersack-Littmark universal pair potential. We therefore expect these
to be reliable potentials for carrying out damage simulations (and Molecular
Dynamics simulations in general) in nuclear fuels of varying compositions for
all relevant atomic collision energies.",1010.0976v1
2010-10-11,Restoring the electrical conductivity of graphene oxide films by UV light induced oxygen desorption,"We report a chemical free method for the reduction of graphene oxide (GO)
thin films. It was observed how for GO films annealed in air the oxygen species
desorb from the GO surface upon exposure to UV light and how the surface
resistivity of such deoxygenated GO films decreases with increasing the
exposure to the UV light. The obtained results open a clean as well as easy
route for the integration of GO based materials into optoelectronic devices.",1010.2108v4
2010-10-23,Silicon Oxide is a Non-Innocent Surface for Molecular Electronics and Nanoelectronics Studies,"Silicon oxide (SiOx) has been widely used in many electronic systems as a
supportive and insulating medium. Here we demonstrate various electrical
phenomena such as negative differential resistance, resistive switching and
current hysteresis intrinsic to a thin layer of SiOx. These behaviors can
largely mimic numerous electrical phenomena observed in molecules and other
nanomaterials, suggesting that substantial caution should be paid when studying
conduction in electronic systems with SiOx as a component. The actual switching
can be the result of SiOx and not the presumed molecular or nanomaterial
component. These electrical properties and the underlying mechanisms are
discussed in detail.",1010.4853v1
2010-10-29,Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry,"We present transport measurements of a tunable silicon
metal-oxide-semiconductor double quantum dot device with lateral geometry.
Experimentally extracted gate-to-dot capacitances show that the device is
largely symmetric under the gate voltages applied. Intriguingly, these gate
voltages themselves are not symmetric. Comparison with numerical simulations
indicates that the applied gate voltages serve to offset an intrinsic asymmetry
in the physical device. We also show a transition from a large single dot to
two well isolated coupled dots, where the central gate of the device is used to
controllably tune the interdot coupling.",1011.0034v1
2010-11-12,Identification of the major cause of endemically poor mobilities in SiC/SiO2 structures,"Materials with good carrier mobilities are desired for device applications,
but in real devices the mobilities are usually limited by the presence of
interfaces and contacts. Mobility degradation at semiconductor-dielectric
interfaces is generally attributed to defects at the interface or inside the
dielectric, as is the case in Si/SiO2 structures, where processing does not
introduce detrimental defects in the semiconductor. In the case of SiC/SiO2
structures, a decade of research focused on reducing or passivating interface
and oxide defects, but the low mobilities have persisted. By invoking
theoretical results and available experimental evidence, we show that thermal
oxidation generates carbon di-interstitial defects inside the semiconductor
substrate and that they are a major cause of the poor mobility in SiC/SiO2
structures.",1011.2820v1
2010-11-23,Design of a low band gap oxide ferroelectric: Bi$_6$Ti$_4$O$_{17}$,"A strategy for obtaining low band gap oxide ferroelectrics based on charge
imbalance is described and illustrated by first principles studies of the
hypothetical compound Bi$_6$Ti$_4$O$_{17}$, which is an alternate stacking of
the ferroelectric Bi$_4$Ti$_3$O$_{12}$. We find that this compound is
ferroelectric, similar to Bi$_4$Ti$_3$O$_{12}$ although with a reduced
polarization. Importantly, calculations of the electronic structure with the
recently developed functional of Tran and Blaha yield a much reduced band gap
of 1.83 eV for this material compared to Bi$_4$Ti$_3$O$_{12}$. Therefore,
Bi$_6$Ti$_4$O$_{17}$ is predicted to be a low band gap ferroelectric material.",1011.5089v2
2010-11-24,A model for the degradation of polyimides due to oxidation,"Polyimides, due to their superior mechanical behavior at high temperatures,
are used in a variety of applications that include aerospace, automobile and
electronic packaging industries, as matrices for composites, as adhesives etc.
In this paper, we extend our previous model in [S. Karra, K. R. Rajagopal,
Modeling the non-linear viscoelastic response of high temperature polyimides,
Mechanics of Materials, In press, doi:10.1016/j.mechmat.2010.09.006], to
include oxidative degradation of these high temperature polyimides. Appropriate
forms for the Helmholtz potential and the rate of dissipation are chosen to
describe the degradation. The results for a specific boundary value problem,
using our model compares well with the experimental creep data for PMR-15 resin
that is aged in air.",1011.5451v1
2010-12-07,Intrinsic Reliability improvement in Biaxially Strained SiGe p-MOSFETs,"In this letter we not only show improvement in the performance but also in
the reliability of 30nm thick biaxially strained SiGe (20%Ge) channel on Si
p-MOSFETs. Compared to Si channel, strained SiGe channel allows larger hole
mobility ({\mu}h) in the transport direction and alleviates charge flow towards
the gate oxide. {\mu}h enhancement by 40% in SiGe and 100% in Si-cap SiGe is
observed compared to the Si hole universal mobility. A ~40% reduction in NBTI
degradation, gate leakage and flicker noise (1/f) is observed which is
attributed to a 4% increase in the hole-oxide barrier height ({\phi}) in SiGe.
Similar field acceleration factor ({\Gamma}) for threshold voltage shift
({\Delta}VT) and increase in noise ({\Delta}SVG) in Si and SiGe suggests
identical degradation mechanisms.",1012.1579v2
2010-12-16,Ab Initio determination of Cu 3d orbital energies in layered copper oxides,"It has long been argued that the minimal model to describe the low-energy
physics of the high-Tc superconducting cuprates must include copper states of
other symmetries besides the canonical x2-y2 one, in particular the z2 orbital.
Experimental and theoretical estimates of the energy splitting of these states
vary widely. With a novel ab initio quantum chemical computational scheme we
determine these energies for a range of copper-oxides and -oxyclorides,
determine trends with the apical Cu-ligand distances and find excellent
agreement with recent Resonant Inelastic X-ray Scattering measurements,
available for La2CuO4, Sr2CuO2Cl2, and CaCuO2.",1012.3603v2
2010-12-17,Halving the Casimir force with conductive oxides: experimental details,"This work is an extended version of a paper published last year in Physical
Review Letters [S. de Man et al., Phys. Rev. Lett. 103, 040402 (2009)], where
we presented measurements of the Casimir force between a gold coated sphere and
a plate coated with either gold or an indium-tin-oxide (ITO) layer. The
experiment, which was performed in air, showed that ITO is sufficiently
conducting to prevent charge accumulation, but still transparent enough to
halve the Casimir attraction when compared to gold. Here, we report all the
experimental details that, due to the limited space available, were omitted in
the previous article. We discuss the performance of our setup in terms of
stability of the calibration procedure and reproducibility of the Casimir force
measurement. We also introduce and demonstrate a new technique to obtain the
spring constant of our force sensor. Furthermore, we present a thorough
description of the experimental method, a comprehensive explanation of data
elaboration and error analysis, and a complete characterization of the
dielectric function and of the surface roughness of the samples used in the
actual experiment.",1012.3831v1
2010-12-17,First-principles study of phase stability of Gd-doped EuO and EuS,"Phase diagrams of isoelectronic Eu$_{1-x}$Gd$_x$O and Eu$_{1-x}$Gd$_{x}$S
quasi-binary alloy systems are constructed using first-principles calculations
combined with the standard cluster expansion approach and Monte-Carlo
simulations. The oxide system has a wide miscibility gap on the Gd-rich side
but forms ordered compounds on the Eu-rich side, exhibiting a deep asymmetric
convex hull in the formation enthalpy diagram. The sulfide system has no stable
compounds. The large difference in the formation enthalpies of the oxide and
sulfide compounds is due to the contribution of local lattice relaxation, which
is sensitive to the anion size. The solubility of Gd in both EuO and EuS is in
the range of 10-20% at room temperature and quickly increases at higher
temperatures, indicating that highly doped disordered solid solutions can be
produced without the precipitation of secondary phases. We also predict that
rocksalt GdO can be stabilized under appropriate experimental conditions.",1012.4026v1
2011-01-17,Reduction of a Single Layer Graphene Oxide Film on Pt(111),"Graphene oxide (GO) is one of chemically modified graphenes and has been
extensively studied worldwide. A monolayer sheet of GO which is chemically
produced in solution can be deposited on various substrates. We have proved
that use of graphite powder with a large grain size enables preparation of a
single layer GO film that is larger than 100 micrometers easily and
reproducibly. If it is possible to reduce the GO film completely, one can
obtain graphene without mechanical exfoliation. However, the reduction methods
employed so far have been insufficient to remove oxygen or to restore the long
range order in graphene lattice. In the present work we annealed the GO sheet
which was placed on Pt(111) in ultrahigh vacuum. The STM observation of the
annealed specimen reveals that a honeycomb lattice appears together with moire
structures of long range ordering. The XPS result indicated complete removal of
oxygen from the GO sheet. These results would open a new way to synthesize a
high quality graphene film, which replaces the conventional CVD method.",1101.3117v1
2011-02-08,Conductive Atomic Force Microscopy of Chemically Synthesized Graphene Oxide and Interlayer Conduction,"Graphene oxide (GO) is one of chemically modified graphenes and has been
extensively investigated worldwide. A monolayer sheet of GO can be chemically
produced in solution and it has been expected to be adaptable to a wide variety
of applications. Most of works have focused on fabrication and reduction
processes of GO, while its intrinsic property has not been explored in detail.
We have succeeded in fabricating large scale GO nanosheets reproducibly. In the
present work, we observed GO nanosheets by conductive atomic force microscopy.
The current image is useful to monitor the GO thickness as well as wrinkles and
folds in the nanosheet with high contrast. In addition to the current images,
local I-V characteristics of the GO sheet were measured with the conductive
cantilever. Based on the applied electric filed dependence, the conduction
normal to the GO sheet could be described in terms of Poole Frenkel emission
mechanism and the relative permittivity of GO is evaluated to be 4.8.",1102.1515v3
2011-02-15,Predicted Oxidation of CO Catalyzed by Au Nanoclusters on a Thin Defect-Free MgO Film Supported on a Mo(100) Surface,"Here we show results of first-principles investigations aiming at tuning and
controlling the catalytic activity of gold nanoclusters through the design of
the underlying support. We show that gold clusters adsorbed on a very thin (2
layers) defect-free MgO film which is itself supported on Mo(100), may serve as
model catalysts for the low-barrier oxidation of CO. The origin of the emergent
activity of the nanoclusters is a dimensionality crossover of the adsorbed gold
clusters, from inactive three-dimensional (3D) optimal structures on thick MgO
films, to catalytically active 2D ones for sufficiently thin MgO films (less
then 1nm in thickness) supported on Mo(100).",1102.3011v1
2011-03-03,Two-probe study of hot carriers in reduced graphene oxide,"The energy relaxation of carriers in reduced graphene oxide thin films is
studied using optical pump-probe spectroscopy with two probes of different
colors. We measure the time difference between peaks of the carrier density at
each probing energy by measuring a time-resolved differential transmission and
find that the carrier density at the lower probing energy peaks later than that
at the higher probing energy. Also, we find that the peak time for the lower
probing energy shifts from about 92 to 37 fs after the higher probing energy
peak as the carrier density is increased from 1.5E12 to 3E13 per square
centimeter, while no noticeable shift is observed in that for the higher
probing energy. Assuming the carriers rapidly thermalize after excitation, this
indicates that the optical phonon emission time decreases from about 50 to
about 20 fs and the energy relaxation rate increases from 4 to 10 meV/fs. The
observed density dependence is inconsistent with the phonon bottleneck effect.",1103.0728v1
2011-03-04,Voltage bias induced modification of all oxide Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 junctions,"In this paper we report what happens to a pristine oxide junction
Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 (PCMO/Nb:STO), when it is subjected to cycling
of voltage bias of moderate value ({\pm}4V). It is found that the initial
cycling leads to formation of a permanent state of lower resistance where the
lower resistance arises predominantly due to development of a shunt across the
device film (PCMO). On successive voltage cycling with increasing magnitude,
this state transforms into states of successive lower resistance that can be
transformed back to the initial stable state on cycling to below a certain
bias. A simple model based on p-n junction with shunt has been used to obtain
information on the change of the junction on voltage cycling. It has been shown
that the observation can be explained if the voltage cycling leads to lowering
of barrier at the interface and also reduction in series resistance. It is
suggested that this lowering can be related to the migration of oxygen ions and
vacancies at the junction region. Cross-sectional imaging of the junction shows
formation of permanent filamentary bridges across the thickness of the PCMO
after the pristine p-n junction is first taken through a voltage cycle, which
would explain appearance of a finite shunt across the p-n junction.",1103.0884v1
2011-03-19,Field emission from atomically thin edges of reduced graphene oxide,"Point sources exhibit low threshold electron emission due to local field
enhancement at the tip. The development and implementation of tip emitters have
been hampered by the need to position them sufficiently apart to achieve field
enhancement, limiting the number of emission sites and therefore the overall
current. Here we report low threshold field (< 0.1V/um) emission of multiple
electron beams from atomically thin edges of reduced graphene oxide (rGO).
Field emission microscopy (FEM) measurements show evidence for interference
from emission sites that are separated by a few nanometers, suggesting that the
emitted electron beams may be coherent. Based on our high-resolution
transmission electron microscopy, infrared spectroscopy and simulation results,
field emission from the rGO edge is attributed to a stable and unique
aggregation of oxygen groups in the form of cyclic edge ethers. Such closely
spaced electron beams from rGO offer prospects for novel applications and
understanding the physics of linear electron sources.",1103.3798v1
2011-04-04,Epitaxial growth of FeSe$_{0.5}$Te$_{0.5}$ thin films on CaF$_2$ substrates with high critical current density,"In-situ epitaxial growth of FeSe$_{0.5}$Te$_{0.5}$ thin films is demonstrated
on a non-oxide substrate CaF$_2$. Structural analysis reveals that compressive
stress is moderately added to 36-nm thick FeSe$_{0.5}$Te$_{0.5}$, which pushes
up the critical temperature above 15 K, showing higher values than that of bulk
crystals. Critical current density at $T$ = 4.5 K reaches 5.9 x 10$^4$
Acm$^{-2}$ at $\mu_0H$ = 10 T, and 4.2 x 10$^4$ Acm$^{-2}$ at $\mu_0H$ = 14 T.
These results indicate that fluoride substrates have high potential for the
growth of iron-based superconductors in comparison with popular oxide
substrates.",1104.0477v2
2011-04-18,"Electronic band structure and inter-atomic bonding in layered 1111-like Th-based pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO from first principles calculations","First-principles FLAPW-GGA band structure calculations were employed to
examine the structural, electronic properties and the chemical bonding picture
for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO,
ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be
viewed as ""intermediate"" systems between two main isostructural groups of
superconducting and semiconducting 1111 phases. The Th 5f states participate
actively in the formation of valence bands and the Th 5f states for ThMPnO
phases are itinerant and partially occupied. We found also that the bonding
picture in ThMPnO phases can be classified as a high-anisotropic mixture of
ionic and covalent contributions: inside [Th2O2] and [M2Pn2] blocks, mixed
covalent-ionic bonds take place, whereas between the adjacent [Th2O2]/[M2Pn2]
blocks, ionic bonds emerge owing to [Th2O2] \to [M2Pn2] charge transfer.",1104.3434v1
2011-05-19,Electron-Spin Excitation Coupling in an Electron Doped Copper Oxide Superconductor,"High-temperature (high-Tc) superconductivity in the copper oxides arises from
electron or hole doping of their antiferromagnetic (AF) insulating parent
compounds. The evolution of the AF phase with doping and its spatial
coexistence with superconductivity are governed by the nature of charge and
spin correlations and provide clues to the mechanism of high-Tc
superconductivity. Here we use a combined neutron scattering and scanning
tunneling spectroscopy (STS) to study the Tc evolution of electron-doped
superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing
process. We find that spin excitations detected by neutron scattering have two
distinct modes that evolve with Tc in a remarkably similar fashion to the
electron tunneling modes in STS. These results demonstrate that
antiferromagnetism and superconductivity compete locally and coexist spatially
on nanometer length scales, and the dominant electron-boson coupling at low
energies originates from the electron-spin excitations.",1105.3987v1
2011-06-04,Janus-faced influence of the Hund's rule coupling in strongly correlated materials,"We show that in multi-band metals the correlations are strongly affected by
the Hund's rule coupling, which depending on the filling promotes metallic,
insulating or bad-metallic behavior. The quasiparticle coherence and the
proximity to a Mott insulator are influenced distinctly and, away from single-
and half-filling, in opposite ways. A strongly correlated bad-metal far from a
Mott phase is found there. We propose a concise classification of 3d and 4d
transition-metal oxides within which the ubiquitous occurrence of strong
correlations in Ru- and Cr-based oxides, as well as the recently measured high
N\'eel temperatures in Tc-based perovskites are naturally explained.",1106.0815v1
2011-06-16,"Reverse Monte Carlo neutron scattering study of the ""ordered-ice"" oxide pyrochlore Pb2Ru2O6.5","We employ high-resolution total neutron scattering in conjunction with
reverse Monte Carlo simulations to examine, in a detailed and unbiased manner,
the crystal structure of the vacancy-ordered oxide pyrochlore Pb2Ru2O6.5 in
light of its structural analogy with proton-ordering in the structures of ice.
We find that the vacancy and the O' ion are completely ordered, and that the
average structure in the F43m space group describes the vacancy ordering
precisely. We complement these results with an examination of the Pb2+ lone
pair network using density functional electronic structure calculations, and a
comparison of the low-temperature lattice-only heat capacity of Pb2Ru2O6.5 with
that of other related pyrochlores.",1106.3257v1
2011-06-21,Process Optimization and Downscaling of a Single Electron Single Dot Memory,"This paper presents the process optimization of a single-electron nanoflash
electron memory. Self-aligned single dot memory structures have been fabricated
using a wet anisotropic oxidation of a silicon nanowire. One of the main issue
was to clarify the process conditions for the dot formation. Based on the
process modeling, the influence of various parameters (oxidation temperature,
nanowire shape) has been investigated. The necessity of a sharp compromise
between these different parameters to ensure the presence of the memory dot has
been established. In order to propose an aggressive memory cell, the
downscaling of the device has been carefully studied. Scaling rules show that
the size of the original device could be reduced by a factor of 2. This point
has been previously confirmed by the realization of single-electron memory
devices.",1106.4289v1
2011-06-21,Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures,"Topological insulators are characterized by a nontrivial band topology driven
by the spin-orbit coupling. To fully explore the fundamental science and
application of topological insulators, material realization is indispensable.
Here we predict, based on tight-binding modeling and first-principles
calculations, that bilayers of perovskite-type transition-metal oxides grown
along the [111] crystallographic axis are potential candidates for
two-dimensional topological insulators. The topological band structure of these
materials can be fine-tuned by changing dopant ions, substrates, and external
gate voltages. We predict that LaAuO$_3$ bilayers have a
topologically-nontrivial energy gap of about 0.15 eV, which is sufficiently
large to realize the quantum spin-Hall effect at room temperature. Intriguing
phenomena, such as fractional quantum Hall effect, associated with the
nearly-flat topologically-nontrivial bands found in $e_g$ systems are also
discussed.",1106.4296v4
2011-06-30,Controlled fabrication of single-walled carbon nanotube electrodes by electron-beam-induced oxidation,"The fabrication of metallic single-walled carbon nanotube electrodes
separated by gaps of typically 20nm width by electron-beam-induced oxidation is
studied within an active device configuration. The tube conductance is measured
continuously during the process. The experiment provides a statistical
evaluation of gap sizes as well as the electron dose needed for gap formation.
Also, the ability to precisely cut many carbon nanotubes in parallel is
demonstrated.",1106.6274v1
2011-07-01,Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium-Sulfur-Battery Cathode Material with High Capacity and Cycling Stability,"We report the synthesis of a graphene-sulfur composite material by wrapping
polyethyleneglycol (PEG) coated submicron sulfur particles with mildly oxidized
graphene oxide sheets decorated by carbon black nanoparticles. The PEG and
graphene coating layers are important to accommodating volume expansion of the
coated sulfur particles during discharge, trapping soluble polysulfide
intermediates and rendering the sulfur particles electrically conducting. The
resulting graphene-sulfur composite showed high and stable specific capacities
up to ~600mAh/g over more than 100 cycles, representing a promising cathode
material for rechargeable lithium batteries with high energy density.",1107.0109v1
2011-07-07,Reduced effective spin-orbital degeneracy and spin-orbital ordering in paramagnetic transition metal oxides: Sr2IrO4 vs. Sr2RhO4,"We discuss the notions of spin-orbital polarization and ordering in
paramagnetic materials, and address their consequences in transition metal
oxides. Extending the combined density functional and dynamical mean field
theory scheme to the case of materials with large spin-orbit interactions, we
investigate the electronic excitations of the paramagnetic phases of Sr2IrO4
and Sr2RhO4. We show that the interplay of spin-orbit interactions, structural
distortions and Coulomb interactions suppresses spin-orbital fluctuations. As a
result, the room temperature phase of Sr2IrO4 is a paramagnetic spin-orbitally
ordered Mott insulator. In Sr2RhO4, the effective spin-orbital degeneracy is
reduced, but the material remains metallic, due to both, smaller spin-orbit and
smaller Coulomb interactions. We find excellent agreement of our ab-initio
calculations for Sr2RhO4 with angle-resolved photoemission, and make
predictions for spectra of the paramagnetic phase of Sr2IrO4.",1107.1371v1
2011-07-11,New Indivisible Geoscience Paradigm,"Earth's interior, I posit, is like one of the rare, oxygen-starved ""enstatite
chondrite"" meteorites (and unlike a more-oxidized ""ordinary chondrite"" as has
been believed for seventy years). Laboratory-analyzed enstatite-chondrite
samples are comparable to having-in-hand impossibleto- gather deep-Earth
samples. Enstatite-chondrite formation in oxygen-starved conditions caused
oxygen-loving elements to occur, in part, as non-oxides in their iron-alloy.
Observations, consistent with solar abundance and behavior of chemical
elements, lead me to a new interpretation of: (1) Earth's early formation as a
Jupiter-like gas-giant, (2) its decompressionpowered surface geology, (3)
Earth's internal composition, and (4) a natural, planetocentric nuclear-fission
reactor as source of both the geomagnetic field and energy channeled to surface
""hot-spots"". I present a unified vision of Earth formation and concomitant
dynamics that explains in a logical and causally related way: (1) fluid
Earth-core formation without wholeplanet melting, and (2) the myriad
measurements and observations, previously attributed to ""plate tectonics"", but
without necessitating mantle convection.",1107.2149v1
2011-07-15,Orbital degeneracy and Mott transition in Mo pyrochlore oxides,"We present our theoretical results on an effective two-band double-exchange
model on a pyrochlore lattice for understanding intricate phase competition in
Mo pyrochlore oxides. The model includes the twofold degeneracy of $e_g'$
orbitals under trigonal field splitting, the interorbital Coulomb repulsion,
the Hund's-rule coupling between itinerant $e_g'$ electrons and localized
$a_{1g}$ spins, and the superexchange antiferromagnetic interaction between the
$a_{1g}$ spins. By Monte Carlo simulation with treating the Coulomb repulsion
at an unrestricted-type mean-field level, we obtain the low-temperature phase
diagram as functions of the Coulomb repulsion and the superexchange
interaction. The results include four dominant phases with characteristic spin
and orbital orders and the metal-insulator transitions among them. The
insulating region is characterized by a `ferro'-type orbital ordering of the
$e_g'$ orbitals along the local $<111>$ axis, irrespective of the spin
ordering.",1107.2986v1
2011-08-11,Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction,"Catalysts for oxygen reduction and evolution reactions are at the heart of
key renewable energy technologies including fuel cells and water splitting.
Despite tremendous efforts, developing oxygen electrode catalysts with high
activity at low costs remains a grand challenge. Here, we report a hybrid
material of Co3O4 nanocrystals grown on reduced graphene oxide (GO) as a
high-performance bi-functional catalyst for oxygen reduction reaction (ORR) and
oxygen evolution reaction (OER). While Co3O4 or graphene oxide alone has little
catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR
activity that is further enhanced by nitrogen-doping of graphene. The
Co3O4/N-doped graphene hybrid exhibits similar catalytic activity but superior
stability to Pt in alkaline solutions. The same hybrid is also highly active
for OER, making it a high performance non-precious metal based bi-catalyst for
both ORR and OER. The unusual catalytic activity arises from synergetic
chemical coupling effects between Co3O4 and graphene.",1108.2331v1
2011-08-10,The role of the coating and aggregation state in the interactions between iron oxide nanoparticles and 3T3 fibroblasts,"Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts. Coating
strategies include low-molecular weight ligands (citric acid) and polymers
(poly(acrylic acid), MW = 2000 g mol-1). We find that most particles were
biocompatible, as exposed cells remained 100% viable relative to controls. The
strong uptake shown by the citrate-coated particles is related to the
destabilization of the dispersions in the cell culture medium and their
sedimentation down to the cell membranes.",1108.2395v1
2011-08-16,Investigation of the Novel Attributes of a Dual Material Gate Nanoscale Tunnel Field Effect Transistor,"In this paper, we propose the application of a Dual Material Gate (DMG) in a
Tunnel Field Effect Transistor (TFET) to simultaneously optimize the
on-current, the off-current and the threshold voltage, and also improve the
average subthreshold slope, the nature of the output characteristics and the
immunity against the DIBL effects. We demonstrate that if appropriate
work-functions are chosen for the gate materials on the source side and the
drain side, the tunnel field effect transistor shows a significantly improved
performance. We apply the technique of DMG in a Strained Double Gate Tunnel
Field Effect Transistor with a high-k gate dielectric to show an overall
improvement in the characteristics of the device along with achieving a good
on-current and an excellent average subthreshold slope. The results show that
the DMG technique can be applied to TFETs with different channel materials,
channel lengths, gate-oxide materials, gate-oxide thicknesses and power supply
levels to achieve significant gains in the overall device characteristics.",1108.3148v1
2011-08-25,Dealloying of Platinum-Aluminum Thin Films Part II. Electrode Performance,"Highly porous Pt/Al thin film electrodes on yttria stabilized zirconia
electrolytes were prepared by dealloying of co-sputtered Pt/Al films. The
oxygen reduction capability of the resulting electrodes was analyzed in a solid
oxide fuel cell setup at elevated temperatures. During initial heating to 523 K
exceptionally high performances compared to conventional Pt thin film
electrodes were measured. This results from the high internal surface area and
large three phase boundary length obtained by the dealloying process. Exposure
to elevated temperatures of 673 K or 873 K gave rise to degradation of the
electrode performance, which was primarily attributed to the oxidation of
remaining Al in the thin films.",1108.5132v2
2011-09-06,Effects of inert species in the gas phase in a model for the catalytic oxidation of CO,"We study by kinetic Monte Carlo simulations the catalytic oxidation of carbon
monoxide on a surface in the presence of contaminants in the gas phase. The
process is simulated by a Ziff-Gulari-Barshad (ZGB) model that has been
modified to include the effect of the contaminants and to eliminate the
unphysical oxygen-poisoned phase. The impurities can adsorb and desorb on the
surface, but otherwise remain inert. We find that, if the impurities can not
desorb, no matter how small their proportion in the gas mixture, the first
order transition and the reactive window that characterize the ZGB model
disappear. The coverages become continuous, and once the surface has reached a
steady state there is no production of CO$_2$. This is quite different from the
behavior of a system in which the surface presents a fixed percentage of
impurities. When the contaminants are allowed to desorb, the reactive window
appears again, and disappears at a value that depends on the proportion of
contaminants in the gas and on their desorption rate.",1109.1315v2
2011-09-12,Electrical Properties of Atomic Layer Deposited Aluminum Oxide on Gallium Nitride,"We report on our investigation of the electrical properties of
metal/Al2O3/GaN metal-insulator-semiconductor (MIS) capacitors. We determined
the conduction band offset and interface charge density of the alumina/GaN
interface by analyzing capacitance-voltage characteristics of atomic layer
deposited Al2O3 films on GaN substrates. The conduction band offset at the
Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical
predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band
conditions in the GaN was inferred, which we attribute to a fixed net positive
charge density of magnitude 4.60x1012 cm-2 at the Al2O3/GaN interface. We
provide hypotheses to explain the origin of this charge by analyzing the energy
band line-up.",1109.2566v1
2011-09-16,"Verification, Validation and Testing of Kinetic Mechanisms of Hydrogen Combustion in Fluid Dynamic Computations","A one-step, a two-step, an abridged, a skeletal and four detailed kinetic
schemes of hydrogen oxidation have been tested. A new skeletal kinetic scheme
of hydrogen oxidation has been developed. The CFD calculations were carried out
using ANSYS CFX software. Ignition delay times and speeds of flames were
derived from the computational results. The computational data obtained using
ANSYS CFX and CHEMKIN, and experimental data were compared. The precision,
reliability, and range of validity of the kinetic schemes in CFD simulations
were estimated. The impact of kinetic scheme on the results of computations was
discussed. The relationship between grid spacing, timestep, accuracy, and
computational cost were analyzed.",1109.3563v2
2011-09-22,Microscopic model for the ferroelectric field effect in oxide heterostructures,"A microscopic model Hamiltonian for the ferroelectric field effect is
introduced for the study of oxide heterostructures with ferroelectric
components. The long-range Coulomb interaction is incorporated as an
electrostatic potential, solved self-consistently together with the charge
distribution. A generic double-exchange system is used as the conducting
channel, epitaxially attached to the ferroelectric gate. The observed
ferroelectric screening effect, namely the charge accumulation/depletion near
the interface, is shown to drive interfacial phase transitions that give rise
to robust magnetoelectric responses and bipolar resistive switching, in
qualitative agreement with previous density functional theory calculations. The
model can be easily adapted to other materials by modifying the Hamiltonian of
the conducting channel, and it is useful in simulating ferroelectric field
effect devices particularly those involving strongly correlated electronic
components where ab-initio techniques are difficult to apply.",1109.4791v1
2011-09-22,Universal exchange-driven phonon splitting in antiferromagnets,"We report a linear dependence of the phonon splitting \Delta\omega on the
non-dominant exchange coupling constant J_{nd} in the antiferromagnetic
transition-metal monoxides MnO, FeO, CoO, NiO, and in the frustrated
antiferromagnetic oxide spinels CdCr2O4, MgCr2O4, and ZnCr2O4. It directly
confirms the theoretical prediction of an exchange induced splitting of the
zone-centre optical phonon for the monoxides and explains the magnitude and the
change of sign of the phonon splitting on changing the sign of the non-dominant
exchange also in the frustrated oxide spinels. The experimentally found linear
relation \hbar\Delta\omega = \beta J_{nd} S^2 with slope \beta = 3.7 describes
the splitting for both systems and agrees with the observations in the
antiferromagnets KCoF3 and KNiF3 with perovskite structure and negligible
next-nearest neighbour coupling. The common behavior found for very different
classes of cubic antiferromagnets suggests a universal dependence of the
exchange-induced phonon splitting at the antiferromagnetic transition on the
non-dominant exchange coupling.",1109.4809v2
2011-09-26,Superconductivity and Rattling under High Pressure in the beta-Pyrochlore Oxide RbOs2O6,"Rattling-induced superconductivity in the beta-pyrochlore oxide RbOs2O6 is
investigated under high pressures up to 6 GPa. Resistivity measurements in a
high-quality single crystal show that the superconducting transition
temperature Tc increases gradually from 6.3 K at ambient pressure to 8.8 K at
3.5 GPa, surprisingly remains almost constant at 8.8 \pm 0.1 K in a wide
pressure range between 3.5 (Po) and 4.8 GPa, and suddenly drops to 6.3 K at Ps
= 4.9 GPa, followed by a gradual decrease with further pressure increase. Two
anomalies in the temperature dependence of the normal-state resistivity are
observed at Po < P < Ps and P > Ps, revealing the presence of two high-pressure
phases corresponding to the changes in Tc. The rattling of the Rb ion inside a
cage made of Os and O atoms may be slightly and seriously modified in these
high-pressure phases that probably have cages of reduced symmetry,
respectively, so that electron-rattler interactions that govern the
superconducting and transport properties of beta-RbOs2O6 are significantly
affected.",1109.5422v1
2011-10-04,Imaging Oxygen Defects and their Motion at a Manganite Surface,"Manganites are technologically important materials, used widely as solid
oxide fuel cell cathodes: they have also been shown to exhibit
electroresistance. Oxygen bulk diffusion and surface exchange processes are
critical for catalytic action, and numerous studies of manganites have linked
electroresistance to electrochemical oxygen migration. Direct imaging of
individual oxygen defects is needed to underpin understanding of these
important processes. It is not currently possible to collect the required
images in the bulk, but scanning tunnelling microscopy could provide such data
for surfaces. Here we show the first atomic resolution images of oxygen defects
at a manganite surface. Our experiments also reveal defect dynamics, including
oxygen adatom migration, vacancy-adatom recombination and adatom bistability.
Beyond providing an experimental basis for testing models describing the
microscopics of oxygen migration at transition metal oxide interfaces, our work
resolves the long-standing puzzle of why scanning tunnelling microscopy is more
challenging for layered manganites than for cuprates.",1110.0636v1
2011-10-07,Versatile sputtering technology for Al2O3 gate insulators on graphene,"We report a novel fabrication method of graphene Al2O3 gate insulators based
on sputtering. Electrical performance of dual-gated mono- and bilayer
exfoliated graphene devices is presented. Sputtered Al2O3 layers possess
comparable quality to oxides obtained by atomic layer deposition (ALD) with
respect to a high relative dielectric constant of about 8, as well as
low-hysteresis performance and high breakdown voltage. We observe a moderate
carrier mobility of about 1000 cm2/Vs in graphene and 350 cm2/Vs in its bilayer
due to increased resonant scattering on atomic scale defects. Most likely this
originated from the thin Al precursor layer evaporated prior to sputtering the
Al2O3 gate oxide.",1110.1535v1
2011-10-10,A Universal Critical Density Underlying the Physics of Electrons at the LaAlO3/SrTiO3 Interface,"The two-dimensional electron system formed at the interface between the
insulating oxides LaAlO3 and SrTiO3 exhibits ferromagnetism, superconductivity,
and a wide range of unique magnetotransport properties. A key challenge is to
find a unified microscopic mechanism that underlies these emergent phenomena.
Here we show that a universal Lifshitz transition between d-orbitals lies at
the core of the observed transport phenomena in this system. Our measurements
find a critical electronic density at which the transport switches from single
to multiple carriers. This density has a universal value, independent of the
LaAlO3 thickness and electron mobility. The characteristics of the transition,
its universality, and its compatibility with spectroscopic measurements
establish it as a transition between d-orbitals of different symmetries. A
simple band model, allowing for spin-orbit coupling at the atomic level,
connects the observed universal transition to a range of reported
magnetotransport properties. Interestingly, we also find that the maximum of
the superconducting transition temperature occurs at the same critical
transition, indicating a possible connection between the two phenomena. Our
observations demonstrate that orbital degeneracies play an important role in
the fascinating behavior observed so far in these oxides.",1110.2184v1
2011-10-14,Negative refraction in Al:ZnO/ZnO metamaterial in the near-infrared,"Noble metals such as gold and silver are the primary metallic building blocks
of metamaterial devices. Making subwavelength-sized structural elements from
these metals seriously limits the optical performance of a device, however, and
complicates the manufacturing process of nearly all metamaterial devices in the
optical wavelength range. As an alternative to noble metals, we propose to use
heavily-doped oxide semiconductors that offer both functional and fabrication
advantages in the near-infrared. In this letter, we report an experimental
demonstration of negative refraction in a near-infrared metamaterial device
that is designed and fabricated using aluminum-doped zinc oxide.",1110.3231v1
2011-10-18,Unintentional F doping of the surface of SrTiO3(001) etched in HF acid -- structure and electronic properties,"We show that the HF acid etch commonly used to prepare SrTiO3(001) for
heteroepitaxial growth of complex oxides results in a non-negligible level of F
doping within the terminal surface layer of TiO2. Using a combination of x-ray
photoelectron spectroscopy and scanned angle x-ray photoelectron diffraction,
we determine that on average ~13 % of the O anions in the surface layer are
replaced by F, but that F does not occupy O sites in deeper layers. Despite
this perturbation to the surface, the Fermi level remains unpinned, and the
surface-state density, which determines the amount of band bending, is driven
by factors other than F doping. The presence of F at the STO surface is
expected to result in lower electron mobilities at complex oxide
heterojunctions involving STO substrates because of impurity scattering.
Unintentional F doping can be substantially reduced by replacing the HF-etch
step with a boil in deionized water, which in conjunction with an oxygen tube
furnace anneal, leaves the surface flat and TiO2 terminated.",1110.4061v1
2011-10-25,Atomic-scale visualization of initial growth of homoepitaxial SrTiO3 thin film on an atomically ordered substrate,"The initial homoepitaxial growth of SrTiO3 on a (\surd13\times\surd13) -
R33.7{\deg}SrTiO3(001) substrate surface, which can be prepared under oxide
growth conditions, is atomically resolved by scanning tunneling microscopy. The
identical (\surd13\times\surd13) atomic structure is clearly visualized on the
deposited SrTiO3 film surface as well as on the substrate. This result
indicates the transfer of the topmost Ti-rich (\surd13\times\surd13) structure
to the film surface and atomic-scale coherent epitaxy at the film/substrate
interface. Such atomically ordered SrTiO3 substrates can be applied to the
fabrication of atom-by-atom controlled oxide epitaxial films and
heterostructures.",1110.5410v1
2011-12-06,Comparison between different oxygen adsorption mechanisms for the catalytic oxidation of CO on a surface,"We study by kinetic Monte Carlo simulations the dynamic behavior of a
Ziff-Gulari-Barshad (ZGB) model for the catalytic oxidation of CO on a surface.
It is well known that the ZGB model presents a continuous transition between an
oxygen poisoned state and a reactive state that it is not observed in nature.
Based on some experimental results that indicate that the oxygen atoms move
away from each other upon dissociation at the surface, we modify the standard
ZGB model by changing the entrance mechanism of the oxygen molecule. We study
three different ways in which the oxygen atoms can be adsorbed at the surface
such that the nonphysical continuous phase transition disappears. We calculate
the phase diagram for the three cases and study the effects of including a CO
desorption mechanism.",1112.1433v1
2011-12-12,Realization of the Switching Mechanism in Resistance Random Access Memory (RRAMTM) Devices: Structural and Electronic Properties Affecting Electron Conductivity in Halfnium Oxide-Electrode System through First Principles Calculations,"Resistance Random Access Memory (RRAMTM) device, with its electrically
induced nanoscale resistive switching capacity, has been gaining considerable
attention as future non-volatile memory device. Here, we propose a mechanism of
switching based on oxygen vacancy migration-driven change in electronic
properties of the transition metal oxide (TMO) film stimulated by set pulse
voltages. We used density functional theory (DFT)-based calculations to account
for the effect of oxygen vacancy and its migration on the electronic properties
of HfO2 and Ta/HfO2 systems, and thereby create the entire story on RRAMTM's
switching mechanism. Computational results on the activation energy barrier for
oxygen vacancy migration were found to be consistent with the results of set
and reset pulse voltage obtained from experiment. Understanding of this
mechanism would be beneficial to effectively realize materials design in these
devices.",1112.2500v1
2011-12-15,Intrinsic origin of the two-dimensional electron gas at polar oxide interfaces,"The predictions of the polar catastrophe scenario to explain the occurrence
of a metallic interface in heterostructures of the solid
solution(LaAlO$_3$)$_{x}$(SrTiO$_3$)$_{1-x}$ (LASTO:x) grown on (001) SrTiO$_3$
were investigated as a function of film thickness and $x$. The films are
insulating for the thinnest layers, but above a critical thickness, $t_c$, the
interface exhibits a constant finite conductivity which depends in a
predictable manner on $x$. It is shown that $t_c$ scales with the strength of
the built-in electric field of the polar material, and is immediately
understandable in terms of an electronic reconstruction at the nonpolar-polar
interface. These results thus conclusively identify the polar-catastrophe model
as the intrinsic origin of the doping at this polar oxide interface.",1112.3532v1
2011-12-20,Computational studies for reduced graphene oxide in hydrogen-rich environment,"We employ molecular dynamic simulations to study the reduction process of
graphene-oxide (GO) in a chemically active environment enriched with hydrogen.
We examine the concentration and pressure of hydrogen gas as a function of
temperature in which abstraction of oxygen is possible with minimum damage to
C-sp$^2$ bonds hence preserving the integrity of the graphene sheet. Through
these studies we find chemical pathways that demonstrate beneficiary mechanisms
for the quality of graphene including formation of water as well as suppression
of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by
hydrogen gas in the environment.",1112.4546v1
2011-12-20,"Comment on ""Uncovering the Complex Behavior of Hydrogen in Cu2O""","In a recent Letter Scanlon and Watson reported their first principles results
on hydrogen in Cu2O. Their main conclusions are: (1) an interstitial H in Cu2O
prefers to occupy the tetrahedral site, which is coordinated with four Cu
cations, in all three charge states (+1, neutral, and -1); (2) H will bind with
a Cu vacancy and form an electrically active H-VCu defect complex, which is
amphoteric with (+/0) and (0/-)transition levels at Ev + 0.1 and Ev + 1.1 eV,
respectively. However, these two conclusions contradict two generally observed
behaviors of H in oxides: (i) cationic H usually binds with an O atom, forming
a single O-H bond, while the anionic H usually binds with cations with
multi-coordination; (ii) H usually passivates cation vacancies in oxides. In
this Comment, we explicitly show that with charge state +1, H prefers to bind
with a single O anion rather than with four Cu cations and that H-VCu does not
induce any defect levels inside the band gap.",1112.4840v1
2011-12-23,Ionically-mediated electromechanical hysteresis in transition metal oxides,"Electromechanical activity, remanent polarization states, and hysteresis
loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the
ionic dynamics and incipient ferroelectricity in these materials is analyzed
using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of
electromechanical coupling including ionic dynamics, surface-charge induced
electrostriction, and ionically-induced ferroelectricity are identified. For
the latter, the ionic contribution can change the sign of first order GLD
expansion coefficient, rendering material effectively ferroelectric. These
studies provide possible explanation for ferroelectric-like behavior in
centrosymmetric transition metal oxides.",1112.5581v2
2012-02-08,Electron dephasing in homogeneous and inhomogeneous indium tin oxide thin films,"The electron dephasing processes in two-dimensional homogeneous and
inhomogeneous indium tin oxide thin films have been investigated in a wide
temperature range 0.3--90 K. We found that the small-energy-transfer
electron-electron ($e$-$e$) scattering process dominated the dephasing from a
few K to several tens K. At higher temperatures, a crossover to the
large-energy-transfer $e$-$e$ scattering process was observed. Below about 1--2
K, the dephasing time $\tau_\varphi$ revealed a very weak temperature
dependence, which intriguingly scaled approximately with the inverse of the
electron diffusion constant $D$, i.e., $\tau_\varphi (T \approx 0.3 \, {\rm K})
\propto 1/D$. Theoretical implications of our results are discussed. The reason
why the electron-phonon relaxation rate is negligibly weak in this
low-carrier-concentration material is presented.",1202.1627v1
2012-03-20,Optical and Luminescence Properties of Zinc Oxide,"We generalize and systematize basic experimental data on optical and
luminescence properties of ZnO single crystals, thin films, powders, ceramics,
and nanocrystals. We consider and study mechanisms by which two main emission
bands occur, a short-wavelength band near the fundamental absorption edge and a
broad long-wavelength band, the maximum of which usually lies in the green
spectral range. We determine a relationship between the two luminescence bands
and study in detail the possibility of controlling the characteristics of ZnO
by varying the maximum position of the short-wavelength band. We show that the
optical and luminescence characteristics of ZnO largely depend on the choice of
the corresponding impurity and the parameters of the synthesis and subsequent
treatment of the sample. Prospects for using zinc oxide as a scintillator
material are discussed. Additionally, we consider experimental results that are
of principal interest for practice.",1203.4366v1
2012-03-21,Reversible Superconductivity in Electrochromic Indium-Tin Oxide Films,"Transparent conductive indium tin oxide (ITO) thin films, electrochemically
intercalated with sodium or other cations, show tunable superconducting
transitions with a maximum $T_c$ at 5 K. The transition temperature and the
density of states, $D(E_F)$ (extracted from the measured Pauli susceptibility
$\chi_p$ exhibit the same dome shaped behavior as a function of electron
density. Optimally intercalated samples have an upper critical field $\approx
4$ T and $\Delta/{k_BT_c} \approx 2.0$. Accompanying the development of
superconductivity, the films show a reversible electrochromic change from
transparent to colored and are partially transparent (orange) at the peak of
the superconducting dome. This reversible intercalation of alkali and alkali
earth ions into thin ITO films opens diverse opportunities for tunable,
optically transparent superconductors.",1203.4644v2
2012-03-21,Few Electron Limit of n-type Metal Oxide Semiconductor Single Electron Transistors,"We report electronic transport on n-type silicon Single Electron Transistors
(SETs) fabricated in Complementary Metal Oxide Semiconductor (CMOS) technology.
The n-MOSSETs are built within a pre-industrial Fully Depleted Silicon On
Insulator (FDSOI) technology with a silicon thickness down to 10 nm on 200 mm
wafers. The nominal channel size of 20 $\times$ 20 nm$^{2}$ is obtained by
employing electron beam lithography for active and gate levels patterning. The
Coulomb blockade stability diagram is precisely resolved at 4.2 K and it
exhibits large addition energies of tens of meV. The confinement of the
electrons in the quantum dot has been modeled by using a Current Spin Density
Functional Theory (CS-DFT) method. CMOS technology enables massive production
of SETs for ultimate nanoelectronics and quantum variables based devices.",1203.4811v1
2012-03-30,Using of the natural radioactive elements for determining Ge-detector efficiencies,"A method is proposed to use of the mixture of Uran oxide and non-active
matrix (e.g., NaCl) and also potassium and lanthanum for determining
Ge-detector efficiencies. The preparations containing of known amouts of the U
or K, or La were measured by means of the Ge-detector, which a efficiency curve
has been obtained through the reference solutions of 241Am, 109Cd, 57Co, 139Ce,
137Cs, 60Co. Results the measurements were compared the activities of the
preparations calculated from mass of 235U, 238U, 138La, 40K in the samples, its
natural abundance, half lives and intensities of gamma lines. Discrepancy of
the activities in the energy range between 163 and 1461 keV does not exeed 7 %.
For correct comparison of the activities the coefficients {\omega} were
calculated, which took into consideration a varied sorption of gamma-rays in
water and in mixture of the Uran oxide and matrix.",1203.6772v1
2012-06-05,A pairing hypothesis based on resonating valence bond state for hole doped copper oxide high temperature superconductors,"To explain the high-temperature superconductivity of hole-doped copper-oxide
high-temperature superconductors (HDCO-HTSCs), Anderson proposed a theory: (A)
the pseudogap state is a resonating valence-bond (RVB) state below T* and (B)
the RVB state translates itself into high-temperature superconducting state
below Tc. In this paper we abandon Anderson theory B but still retain Anderson
theory A and add three new hypotheses. Jointed three hypotheses with Anderson
theory A, we construct an effective Hamiltonian of HDCO-HTSCs and explain why
Tc-line is a dome in phase diagram and why HDCO-HTSCs have a higher Tc than
that of conventional superconductors.",1206.0862v4
2012-06-13,High pressures make Hg a transition metal in a thermodynamically stable solid,"The appropriateness of including Hg among the transition metals has been
debated for a long time. Although the synthesis of HgF$_{4}$ molecules in gas
phase was reported before, the molecules show strong instabilities and
dissociate. Therefore, the transition metal propensity of Hg remains an open
question. Here, we propose that high pressure provides a controllable method
for preparing unusual oxidation states of matter. Using an advanced structure
search method based on first-principles electronic structure calculations, we
predict that under high pressures, Hg can transfer the electrons in its outmost
$d$ shell to F atoms, thereby acting as a transition metal. Oxidation of Hg to
the +4 state yielded thermodynamically stable molecular crystals consisting of
HgF$_{4}$ planar molecules, a typical geometry for $d^{8}$ metal centers.",1206.2874v1
2012-07-22,Strain-induced stabilization of Al functionalization in graphene oxide nanosheet for enhanced NH3 storage,"Strain effects on the stabilization of Al ad-atom on graphene
oxide(GO)nanosheet as well as its implications for NH3 storage have been
investigated using first-principles calculations.The binding energy of Al
ad-atom on GO is found to be a false indicator of its stability.Tensile strain
is found to be very effective in stabilizing the Al ad-atom on GO.It
strengthens the C-O bonds through an enhanced charge transfer from C to O
atoms. Interestingly,C-O bond strength is found to be the correct index for
Al's stability.Optimally strained Al-functionalized GO binds up to 6 NH3
molecules,while it binds no NH3 molecule in unstrained condition.",1207.5243v2
2012-08-06,A Variant of the Point Defect Model for Passivity of Metals,"A variant of the point defect model originally enunciated by Macdonald and
co-workers is advanced and its theoretical implications for the steady state
current density, barrier layer thickness and the concentration of metal vacancy
at the metal/film interface are deduced. The differences between the original
point defect model and the present variant are also highlighted. The empirical
parameters alpha and beta in the original point defect model are replaced with
two physical parameters Rcont and Rhof which represent respectively the
electronic contact resistance at the metal/film interface and the electronic
resistivity of the oxide film. The present variant correctly describes the
annihilation of the metal vacancies at the metal/film interface and also
enforces the conservation of particle and defect volumes during the solid-state
reactions leading to the natural inclusion of the famous Pilling-Bedsworth
ratio RPB into the model. Diagnostics which help to check the model predictions
with experiments are given. Use of this variant to describe stress-induced
failure of the barrier oxide leading to pitting is also discussed.",1208.1096v1
2012-08-09,The role of charge traps in inducing hysteresis: capacitance - voltage measurements on top gated bilayer graphene,"Understanding the origin of hysteresis in the channel resistance from top
gated graphene transistors is important for transistor applications.
Capacitance - voltage measurements across the gate oxide on top gated bilayer
graphene show hysteresis with a charging and discharging time constant of ~100
{\mu}s. However, the measured capacitance across the graphene channel does not
show any hysteresis, but shows an abrupt jump at a high channel voltage due to
the emergence of an order, indicating that the origin of hysteresis between
gate and source is due to charge traps present in the gate oxide and graphene
interface.",1208.1831v1
2012-08-17,Nanostructured Zinc Oxide as a Prospective Room Temperature Thermoelectric Material,"Nanostructured Zinc oxide (ZnO) was synthesized via a ball milling for 10
hours using high energy planetary ball mill. Phase purity and homogeneity of
all the samples have been investigated by X-ray diffraction (XRD) and Field
Emission Scanning Electron Microscopy (FE-SEM). All the diffraction peaks can
be indexed to the hexagonal phase ZnO with hexagonal symmetry (space group
P63mc). Average crystallite size was observed to be 20 nm. There was a
remarkable suppression in thermal conductivity ({\kappa}) compared to the bulk
values by a factor of ~50 at room temperature. This suggests to the possibility
of using nanostructured ZnO as a prospective room temperature thermoelectric
material.",1208.3519v1
2012-08-18,The environmental dependence of redox energetics of PuO2 and α-Pu2O3: A quantitative solution from DFT+U calculations,"We report a comprehensive density functional theory (DFT) + $U$ study of the
energetics of charged and neutral oxygen defects in both PuO$_{2}$ and
$\alpha$-Pu$_{2}$O$_{3}$, and present a quantitative determination of the
equilibrium compositions of reduced PuO$_{2}$ (PuO$_{2-x}$) as functions of
environmental temperature and partial pressure of oxygen, which shows fairly
agreement with corresponding high-temperature experiments. Under ambient
conditions, the endothermic reduction of PuO$_{2}$ to $\alpha$-Pu$_{2}$O$_{3} $
is found to be facilitated by accompanying volume expansion of PuO$_{2-x}$ and
the possible migration of O-vacancy, whereas further reduction of $\alpha
$-Pu$_{2}$O$_{3}$ is predicted to be much more difficult. In contrast to the
endothermic oxidation of PuO$_{2}$,\ the oxidation of $\alpha$-Pu$_{2} $O$_{3}$
is a stable exothermic process.",1208.3745v1
2012-08-22,Optical modes in oxide-apertured micropillar cavities,"We present a detailed experimental characterization of the spectral and
spatial structure of the confined optical modes for oxide-apertured micropillar
cavities, showing good-quality Hermite-Gaussian profiles, easily mode-matched
to external fields. We further derive a relation between the frequency
splitting of the transverse modes and the expected Purcell factor. Finally, we
describe a technique to retrieve the profile of the confining refractive index
distribution from the spatial profiles of the modes.",1208.4472v2
2012-09-06,High-temperature thermoelectric properties of the double-perovskite ruthenium oxide (Sr$_{1-x}$La$_x$)$_2$ErRuO$_6$,"We have prepared polycrystalline samples of (Sr$_{1-x}$La$_x$)$_2$ErRuO$_6$
and (Sr$_{1-x}$La$_x$)$_2$YRuO$_6$, and have measured the resistivity, Seebeck
coefficient, thermal conductivity, susceptibility and x-ray absorption in order
to evaluate the electronic states and thermoelectric properties of the doped
double-perovskite ruthenates. We have observed a large Seebeck coefficient of
-160 $\mu$V/K and a low thermal conductivity of 7 mW/cmK for $x$=0.1 at 800 K
in air. These two values are suitable for efficient oxide thermoelectrics,
although the resistivity is still as high as 1 $\Omega$cm. From the
susceptibility and x-ray absorption measurements, we find that the doped
electrons exist as Ru$^{4+}$ in the low spin state. On the basis of the
measured results, the electronic states and the conduction mechanism are
discussed.",1209.1250v1
2012-09-13,Origin of the Superior Conductivity of Perovskite Ba(Sr)SnO3,"ASnO3 (A=Ba, Sr) are unique perovskite oxides in that they have superior
electron conductivity despite their wide optical band gaps. Using
first-principles band structure calculations, we show that the small electron
effective masses, thus, good electron conductivity of ASnO3 can be attributed
to the large size of Sn in this system that gives the conduction band edge with
antibonding Sn and O s characters. Moreover, we show that ASnO3 can be easily
doped by La with shallow LaA(+/0) donor level. Our results, therefore,
explained why the perovskite BaSnO3, SrSnO3, and their alloys are promising
candidates for transparent conducting oxides.",1209.2845v3
2012-09-14,Trapped charge dynamics in InAs nanowires,"We study random telegraph noise in the conductance of InAs nanowire
field-effect transistors due to single electron trapping in defects. The
electron capture and emission times are measured as functions of temperature
and gate voltage for individual traps, and are consistent with traps residing
in the few-nanometer-thick native oxide, with a Coulomb barrier to trapping.
These results suggest that oxide removal from the nanowire surface, with proper
passivation to prevent regrowth, should lead to the reduction or elimination of
random telegraph noise, an important obstacle for sensitive experiments at the
single electron level.",1209.3237v2
2012-10-04,"Oxygen reduction activity on perovskite oxide surfaces: a comparative first-principle study of LaMnO$_3$, LaFeO$_3$ and LaCrO$_3$","The understanding of oxygen reduction reaction (ORR) activity on perovskite
oxide surfaces is essential for promising future fuel cell applications. We
report a comparative study of ORR mechanisms on La$B$O$_3$ ($B$=Mn, Fe, Cr)
surfaces by first-principles calculations based on density functional theory
(DFT). Results obtained from varied DFT methods such as generalized gradient
approximation(GGA), GGA+$U$ and the hybrid Hartree-Fock density functional
method are reported for comparative purposes. We find that the results
calculated from hybrid-functional method suggest that the order of ORR activity
is LaMnO$_3$ $>$ LaCrO$_3$ $>$ LaFeO$_3$, which is in better agreement with
recent experimental results (Suntivich \textit{et al.}, Nature Chemistry 3, 546
(2011)) than those using the GGA or GGA+$U$ method.",1210.1554v1
2012-10-05,Preparation of atomically-flat SrTiO3 surfaces using a deionized-water etching and thermal annealing procedure,"We report that a deionized water etching and thermal annealing technique can
be effective for preparing atomically-flat and singly-terminated surfaces of
single crystalline SrTiO3 substrates. After a two-step thermal-annealing and
deionized-water etching procedure, topography measured by atomic force
microscopy shows the evolution of substrates from a rough to step-terraced
surface structure. Lateral force microscopy confirms that the atomically-flat
surfaces are singly-terminated. Moreover, this technique can be used to remove
excessive strontium oxide or hydroxide composites segregated on the SrTiO3
surface. This acid-etchant-free technique facilitates the preparation of
atomically-aligned SrTiO3 substrates, which promotes studies on two-dimensional
physics of complex oxide interfaces.",1210.1860v1
2012-10-05,Efros-Shklovskii variable range hopping in reduced graphene oxide sheets of varying carbon sp2 fraction,"We investigate the low temperature electron transport properties of
chemically reduced graphene oxide (RGO) sheets with different carbon sp2
fractions of 55 to 80 %. We show that in the low bias (Ohmic) regime, the
temperature (T) dependent resistance (R) of all the devices follow
Efros-Shklovskii variable range hopping (ES-VRH) R ~ exp[(T(ES)/T)^1/2] with
T(ES) decreasing from 30976 to 4225 K and electron localization length
increasing from 0.46 to 3.21 nm with increasing sp2 fraction. From our data, we
predict that for the temperature range used in our study, Mott-VRH may not be
observed even at 100 % sp2 fraction samples due to residual topological defects
and structural disorders. From the localization length, we calculate a bandgap
variation of our RGO from 1.43 to 0.21 eV with increasing sp2 fraction from 55
to 80 % which agrees remarkably well with theoretical prediction. We also show
that, in the high bias regime, the hopping is field driven and the data follow
R ~ exp[(E(0)/E)^1/2] providing further evidence of ES-VRH.",1210.1876v1
2012-10-08,Doped Mott Insulators in (111) Bilayers of Perovskite Transition-Metal Oxides with a Strong Spin-Orbit Coupling,"The electronic properties of Mott insulators realized in (111) bilayers of
perovskite transition-metal oxides are studied. The low-energy effective
Hamiltonians for such Mott insulators are derived in the presence of a strong
spin-orbit coupling. These models are characterized by the antiferromagnetic
Heisenberg interaction and the anisotropic interaction whose form depends on
the $d$ orbital occupancy. From exact diagonalization analyses on finite
clusters, the ground state phase diagrams are derived, including a Kitaev spin
liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson
mean-field analyses indicate the possibility of novel superconducting states
induced by carrier doping into the Mott-insulating parent systems, suggesting
the present model systems as unique playgrounds for studying
correlation-induced novel phenomena. Possible experimental realizations are
also discussed.",1210.2290v3
2012-10-13,Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature,"We predict through our first-principles calculations that four double
perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs) are half-metallic
ferrimagnets. Our calculated results shows that the four optimized structures
have negative formation energy, from -0.42 to -0.26 eV per formula unit, which
implies that they could probably be realized. In the case of Bi2FeMoO6, the
half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and
650 K, respectively, which indicates that high spin polarization could be kept
at high temperatures far beyond room temperature. It is believed that some of
them could be synthesized soon and would prove useful for spintronic
applications.",1210.3706v2
2012-10-24,Combined GW and dynamical mean field theory: Dynamical screening effects in transition metal oxides,"We present the first dynamical implementation of the combined GW and
dynamical mean field scheme (""GW+DMFT"") for first principles calculations of
the electronic properties of correlated materials. The application to the
ternary transition metal oxide SrVO3 demonstrates that this schemes inherits
the virtues of its two parent theories: a good description of the local low
energy correlation physics encoded in a renormalized quasi-particle band
structure, spectral weight transfer to Hubbard bands, and the physics of
screening driven by long-range Coulomb interactions. Our data is in good
agreement with available photoemission and inverse photoemission spectra; our
analysis leads to a reinterpretation of the commonly accepted ""three-peak
structure"" as originating from orbital effects rather than from the electron
addition peak within the t2g manifold.",1210.6580v2
2012-10-30,High mobility conduction at (110) and (111) LaAlO3/SrTiO3 interfaces,"In recent years, striking discoveries have revealed that two-dimensional
electron liquids (2DEL) confined at the interface between oxide band-insulators
can be engineered to display a high mobility transport. The recognition that
only few interfaces appear to suit hosting 2DEL is intriguing and challenges
the understanding of these emerging properties not existing in bulk. Indeed,
only the neutral TiO2 surface of (001)SrTiO3 has been shown to sustain 2DEL. We
show that this restriction can be surpassed: (110) and (111) surfaces of SrTiO3
interfaced with epitaxial LaAlO3 layers, above a critical thickness, display
2DEL transport with mobilities similar to those of (001)SrTiO3. Moreover we
show that epitaxial interfaces are not a prerequisite: conducting (110)
interfaces with amorphous LaAlO3 and other oxides can also be prepared. These
findings open a new perspective both for materials research and for elucidating
the ultimate microscopic mechanism of carrier doping.",1210.7955v1
2012-11-16,Single-layer MoS2 as efficient photocatalyst,"The potential application of the single-layer MoS2 as photocatalyst was
revealed in this work based on first-principles calculations. It is found that
the pristine single-layer MoS2 is a good candidate for photocatalyst, and its
catalyzing ability can be tuned by the applied mechanical strain. Furthermore,
the p-type doping could improve the catalyzing ability more efficiently: first,
the p-type doping makes the direct transition of electron from valence band
maximum (VBM) to conduction band minimum (CBM) viable; second, it separates the
water splitting reaction sites by having reduction in Mo sites and oxidation in
P dopant sites; third, it improves the efficiency by equalizing the reducing
power {\Delta}1 and oxidizing power {\Delta}2, as well as by enhancing the
light absorption in long wavelength end of the visible light. Thus enables the
single-layer MoS2 to be a efficient visible-light photocatalyst.",1211.4052v2
2012-11-24,Ab initio simulations of oxygen interaction with surfaces and interfaces in uranium mononitride,"The results of DFT supercell calculations of oxygen behavior upon the UN
(001) and (110) surfaces as well as at the tilt grain boundary are presented.
Oxygen adsorption, migration, incorporation into the surface N vacancies on
(001) and (110) surfaces have been modeled using 2D slabs of different
thicknesses and supercell sizes. The temperature dependences of the N vacancy
formation energies and oxygen incorporation energies are calculated. We
demonstrate that O atoms easily penetrate into UN surfaces and grain boundaries
containing N vacancies, due to negative incorporation energies and a small
energy barrier. The Gibbs free energies of N vacancy formation and O atom
incorporation therein at the two densely-packed surfaces and tilt grain
boundaries are compared. It has been also shown that the adsorbed oxygen atoms
are highly mobile which, combined with easy incorporation into surface N
vacancies, explains efficient (but unwanted) oxidation of UN surfaces. The
atomistic mechanism of UN oxidation via possible formation of oxynitrides is
discussed.",1211.5695v1
2012-11-26,Complex Orbital State Stabilized by Strong Spin-Orbit Coupling in a Metallic Iridium Oxide IrO$_{2}$,"Resonant x-ray diffraction experiments were performed for the metallic
iridium oxide IrO$_{2}$. We observed anisotropic tensor of susceptibility (ATS)
scattering, the spectrum of which shows a sharp contrast between the $L_{3}$
and $L_{2}$ edges. At the $L_{3}$ edge, resonance excitations were clearly
observed from the core 2$p$ orbitals to both the 5$d$ $t_{2g}$ and $e_{g}$
orbitals. In contrast, the resonance mode associated with 5$d$ $t_{2g}$
orbitals was indiscernible at the $L_{2}$ edge. This contrasting behavior
indicates that Ir 5$d$ $t_{2g}$ orbitals are fairly close to the $J_{\rm eff}$
= 1/2 state due to the strong spin--orbit coupling in 5$d$ transition metal
ions, as in the Mott insulator Sr$_{2}$IrO$_{4}$. Our results clearly
demonstrate that ATS scattering is a useful probe for investigating complex
orbital states in a metallic state. Such states induce novel phenomena such as
the spin Hall effect.",1211.5855v1
2012-11-29,Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy,"We have investigated the growth of BaTiO3 thin films deposited on pure and 1%
Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular
beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to
30 nm were investigated for various layer compositions. We demonstrate 2D
growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before
additional 3D features appear; lattice parameter relaxation occurs during the
first few nanometers and is completed at {\guillemotright}10 nm. The presence
of a Ba oxide rich top layer that probably favors 2D growth is evidenced for
well crystallized layers. We show that the Ba oxide rich top layer can be
removed by chemical etching. The present work stresses the importance of
stoichiometry and surface composition of BaTiO3 layers, especially in view of
their integration in devices.",1211.6994v1
2012-12-04,Epitaxial growth of (111)-oriented LaAlO$_3$/LaNiO$_3$ ultra-thin superlattices,"The epitaxial stabilization of a single layer or superlattice structures
composed of complex oxide materials on polar (111) surfaces is severely
burdened by reconstructions at the interface, that commonly arise to neutralize
the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$
pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the
proposed complex oxide candidate for a topological insulating behavior.
Comprehensive X-Ray diffraction measurements, RHEED, and element specific
resonant X-ray absorption spectroscopy affirm their high structural and
chemical quality. The study offers an opportunity to fabricate interesting
interface and topology controlled (111) oriented superlattices based on
ortho-nickelates.",1212.0590v1
2012-12-07,Monte Carlo study of an unconventional superconducting phase in Ir-oxide J_{eff}=1/2 Mott insulators induced by carrier doping,"Based on a microscopic theoretical study, we show that novel
superconductivity is induced by carrier doping in layered perovskite Ir oxides
where a strong spin-orbit coupling causes an effective total angular momentum
J_{eff}=1/2 Mott insulator. Using a variational Monte Carlo method, we find an
unconventional superconducting state in the ground state phase diagram of a
t_{2g} three-orbital Hubbard model on the square lattice. This superconducting
state is characterized by a d_{x^2-y^2}-wave ""pseudospin singlet"" formed by the
J_{eff}=1/2 Kramers doublet, which thus contains inter-orbital as well as both
singlet and triplet components of t_{2g} electrons. The superconducting state
is found stable only by electron doping, but not by hole doping, for the case
of carrier doped Sr_2IrO_4. We also study an effective single-orbital Hubbard
model to discuss the similarities to high-T_c cuprate superconductors and the
multi-orbital effects.",1212.1546v1
2012-12-11,Characterization of nanostructured material images using fractal descriptors,"This work presents a methodology to the morphology analysis and
characterization of nanostructured material images acquired from FEG-SEM (Field
Emission Gun-Scanning Electron Microscopy) technique. The metrics were
extracted from the image texture (mathematical surface) by the volumetric
fractal descriptors, a methodology based on the Bouligand-Minkowski fractal
dimension, which considers the properties of the Minkowski dilation of the
surface points. An experiment with galvanostatic anodic titanium oxide samples
prepared in oxalyc acid solution using different conditions of applied current,
oxalyc acid concentration and solution temperature was performed. The results
demonstrate that the approach is capable of characterizing complex morphology
characteristics such as those present in the anodic titanium oxide.",1212.2677v1
2012-12-20,Electrostatic Tuning of the Properties of Disordered Indium Oxide Films near the Superconductor-Insulator Transition,"The evolution with carrier concentration of the electrical properties of
amorphous indium oxide (InO) thin films has been studied using electronic
double layer transistor configurations. Carrier variations of up to 7 X 10^(14)
carriers/cm^2 were achieved using an ionic liquid as a gate dielectric. The
superconductor-insulator transition was traversed and the magnitude and
position of the large magnetoresistance peak found in the insulating regime
were modified. The systematic variation of the magnetoresistance peak with
charge concentration was found to be qualitatively consistent with a simulation
based on a model involving granularity.",1212.5177v2
2012-12-26,Oxidation of self-duality to 12 dimensions and beyond,"Using (partial) curvature flows and the transitive action of subgroups of
O(d,Z) on the indices {1,...,d} of the components of the Yang-Mills curvature
in an orthonormal basis, we obtain a nested system of equations in successively
higher dimensions d, each implying the Yang-Mills equations on d-dimensional
Riemannian manifolds possessing special geometric structures. This `matryoshka'
of self-duality equations contains the familiar self-duality equations on
Riemannian 4-folds as well as their generalisations on complex K\""ahler 3-folds
and on 7- and 8-dimensional manifolds with G_2 and Spin(7) holonomy. The
matryoshka allows enlargement (`oxidation') to a remarkable system in 12
dimensions invariant under Sp(3). There are hints that the underlying geometry
is related to the sextonions, a six-dimensional algebra between the quaternions
and octonions.",1212.6270v3
2012-12-31,Metallic and insulating interfaces of amorphous SrTiO3-based oxide heterostructures,"The conductance confined at the interface of complex oxide heterostructures
provides new opportunities to explore nanoelectronic as well as nanoionic
devices. Herein we show that metallic interfaces can be realized in
SrTiO3-based heterostructures with various insulating overlayers of amorphous
LaAlO3, SrTiO3 and yttria-stabilized zirconia films. On the other hand, samples
of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The
interfacial conductivity results from the formation of oxygen vacancies near
the interface, suggesting that the redox reactions on the surface of SrTiO3
substrates play an important role.",1212.6901v1
2013-01-05,Potential thermoelectric performance of hole-doped Cu2O,"High thermoelectric performance in oxides requires stable conductive
materials that have suitable band structures. Here we show based on an analysis
of the thermopower and related properties using first-principles calculations
and Boltzmann transport theory that hole doped Cu2O may be such a material. We
find that hole-doped Cu2O has a high thermopower of above 200 microV/K even
with doping levels as high as 5.5x10 20 cm-3 at 500 K, mainly attributed to the
heavy valence bands of Cu2O. This is reminiscent of the cobaltate family of
high performance oxide thermoelectrics and implies that hole-doped Cu2O could
be an excellent thermoelectric material if suitably doped.",1301.0913v1
2013-01-07,Oxidizing Borcherds symmetries,"The tensor hierarchy of maximal supergravity in D dimensions is known to be
closely related to a Borcherds (super)algebra that is constructed from the
global symmetry group E(11-D). We here explain how the Borcherds algebras in
different dimensions are embedded into each other and can be constructed from a
unifying Borcherds algebra. The construction also has a natural physical
explanation in terms of oxidation. We then go on to show that the Hodge duality
that is present in the tensor hierarchy has an algebraic counterpart. For D>8
the Borcherds algebras we find differ from the ones existing in the literature
although they generate the same tensor hierarchy.",1301.1346v1
2013-01-14,ω/T scaling of the optical conductivity in strongly correlated layered cobalt oxide,"We report infrared spectroscopic properties of the strongly correlated
layered cobalt oxide [BiBa$_{0.66}$K$_{0.36}$O$_2$]CoO$_2$. These measurements
performed on single crystals allow us to determine the optical conductivity as
a function of temperature. In addition to a large temperature dependent
transfer of spectral weight, an unconventional low energy mode is found. We
show that both its frequency and damping scale as the temperature itself. In
fact, a basic analysis demonstrates that this mode fully scales onto a function
of $\omega$/T up to room temperature. This behavior suggests low energy
excitations of non-Fermi liquid type originating from quantum criticality.",1301.2970v1
2013-01-17,Dimer Mott Insulator in an Oxide Heterostructure,"We study the problem of designing an artificial Mott insulator in a
correlated oxide heterostructure. We consider the extreme limit of quantum
confinement based on ionic discontinuity doping, and argue that a unique dimer
Mott insulator can be achieved for the case of a single SrO layer in a
GdTiO$_3$ matrix. In the dimer Mott insulator, electrons are localized not to
individual atoms but to bonding orbitals on molecular dimers formed across a
bilayer of two TiO$_2$ planes, and is analogous to the Mott insulating state of
Hubbard ladders, studied in the 1990s. We verify the existence of the dimer
Mott insulator through both ab initio and model Hamiltonian studies, and find
for reasonable values of Hubbard $U$ that it is stable and ferromagnetic with a
clear bonding/anti-bonding splitting of order 0.65eV, and a significant smaller
Mott gap whose size depends upon $U$. The combined effects of polar
discontinuity, strong structural relaxation and electron correlations all
contribute to the realization of this unique ground state.",1301.4222v1
2013-01-18,Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris,"We report the first detection of pure rotational transitions of TiO and TiO_2
at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational
temperature, T_rot, of about 250 K was derived for TiO_2. Although T_rot was
not well constrained for TiO, it is likely somewhat higher than that of TiO_2.
The detection of the Ti oxides confirms that they are formed in the
circumstellar envelopes of cool oxygen-rich stars and may be the ""seeds"" of
inorganic-dust formation, but alternative explanations for our observation of
TiO and TiO_2 in the cooler regions of the envelope cannot be ruled out at this
time. The observations suggest that a significant fraction of the oxides is not
converted to dust, but instead remains in the gas phase throughout the outflow.",1301.4344v1
2013-01-22,Oxidation of D=3 cosets and Bonnor dualities in $D\leq 6$,"Bonnor's map in General Relativity is duality between (dimensionally reduced)
vacuum gravity and static truncation of electro-vacuum theory. It was used as a
tool to generate an exact solution of electro-vacuum from some vacuum solution.
It can be expected that similar dualities will be useful for solution
generation in higher-dimensional theories too. Here we study such maps within a
class of theories in dimensions $D\leq 6$ using oxidation of D=3 cosets and
consistent truncation of the corresponding theories. Our class includes those
theories whose D=3 symmetries are subgroups of $G=O(5,4)$. It contains
six-dimensional minimal supergravity, five-dimensional minimal and $U(1)^3$
supergravities and a number of four-dimensional theories which attracted
attention recently in the search of exact solutions. We give explicit
reduction/truncation formulas relating different theories in dimensions $D=4,
5, 6$ in terms of metrics and matter fields and discuss various alternative
duality chains between them.",1301.5084v2
2013-01-28,Tunneling through Al/AlOx/Al junction: analytical models and first principles simulations,"We study from first principles the transport properties of Al/AlOx/Al tunnel
junctions. On this basis, we analyze the reliability of two analytical models
for the conductance, namely the trapezoid potential barrier model and a
tight-binding model. Our findings show that (i) the interface width used in the
models is determined by the electronic density profile, and it is shorter than
the width one expects from the atomic arrangements; (ii) the effective mass},
found to be about on third of the free electron mass, can be determined from
the oxide band-structure calculations, and (iii) the barrier height is given by
one fourth of the bandgap in the oxide, which explains the apparently small
values found for these junctions experimentally.",1301.6536v1
2013-01-31,Nanoscale Surface Analysis on Second Generation Advanced High Strength Steel after Hot Dip Galvanizing,"Second Generation advanced high strength steel is the material of choice for
modern automotive structural parts because of its outstanding maximal
elongation and tensile strength. Nonetheless there is still a lack of corrosion
protection for this material due to the fact that cost efficient hot dip
galvanizing can not be applied. The reason for the insufficient coatability
with zinc is found in the segregation of manganese to the surface during
annealing and the formation of manganese oxides prior coating. This work
analyses the structure and chemical composition of the surface oxides on so
called nano-TWIP (twinning induced plasticity) steel on the nanoscopic scale
after hot dip galvanizing in a simulator with employed analytical methods
comprising scanning Auger electron spectroscopy (SAES), energy dispersive x-ray
spectroscopy (EDX), and focused ion beam (FIB) for cross section preparation.
By the combination of these methods it was possible to obtain detailed chemical
images serving a better understanding which processes exactly occur on the
surface of this novel kind of steel and how to promote in the future for this
material system galvanic protection.",1301.7733v1
2013-02-01,Electronic properties and Fermi surface for new Fe-free layered superconductor BaTi2Bi2O from first principles,"Very recently, as an important step in the development of layered Fe-free
pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which
has the highest TC (about 4.6 K) among all related non-doped systems. In this
Letter, we report for the first time the electronic bands, Fermi surface
topology, total and partial densities of electronic states for BaTi2Bi2O
obtained by means of the first-principles FLAPW-GGA calculations. The
inter-atomic bonding picture is described as a high-anisotropic mixture of
metallic, covalent, and ionic contributions. Besides, the structural and
electronic factors, which can be responsible for the increased transition
temperature for BaTi2Bi2O (as compared with related pnictide-oxides BaTi2As2O
and BaTi2Sb2O), are discussed.",1302.0108v1
2013-02-06,In situ X-ray photoelectron spectroscopy of model catalysts: At the edge of the gap,"We present a High-Pressure X-ray Photoelectron Spectroscopy (HP-XPS) and
first-principles kinetic Monte Carlo study addressing the nature of the active
surface in CO oxidation over Pd(100). Simultaneously measuring the chemical
composition at the surface and in the near-surface gas-phase, we reveal both
O-covered pristine Pd(100) and a surface oxide as stable, highly active phases
in the near-ambient regime accessible to HP-XPS. Surprisingly, no adsorbed CO
can be detected during high CO2 production rates, which can be explained by a
combination of a remarkably short residence time of the CO molecule on the
surface and mass-transfer limitations in the present set-up.",1302.1388v1
2013-02-08,Ultra-high-ohmic microstripline resistors for Coulomb blockade devices,"In this paper, we report on the fabrication and the low-temperature
characterization of extremely high-ohmic microstrip resistors made of a thin
film of weakly oxidized titanium. Nearly linear voltage-current characteristics
were measured at temperatures down to $T \sim \unit[20]{mK}$ for films with
sheet resistivity up to as high as $\sim \unit[7]{k\Omega}$, i.e. about an
order of magnitude higher than our previous findings for weakly oxidized Cr.
Our analysis indicates that such an improvement can help to create an
advantageous high-impedance environment for different Coulomb blockade devices.
Further properties of the Ti film addressed in this work show a promise of
low-noise behavior of the resistors when applied in different realizations of
the quantum standard of current.",1302.2086v1
2013-02-08,Metal nanoparticle field-effect transistor,"We demonstrate that by means of a local top-gate current oscillations can be
observed in extended, monolayered films assembled from monodisperse metal
nanocrystals -- realizing transistor function. The oscillations in this
metal-based system are due to the occurrence of a Coulomb energy gap in the
nanocrystals which is tunable via the nanocrystal size. The nanocrystal
assembly by the Langmuir-Blodgett method yields homogeneous monolayered films
over vast areas. The dielectric oxide layer protects the metal nanocrystal
field-effect transistors from oxidation and leads to stable function for
months. The transistor function can be reached due to the high monodispersity
of the nanocrystals and the high super-crystallinity of the assembled films.
Due to the fact that the film consists of only one monolayer of nanocrystals
and all nanocrystals are simultaneously in the state of Coulomb blockade the
energy levels can be influenced efficiently (limited screening).",1302.2110v2
2013-02-13,Electronic phase diagram of high temperature copper oxide superconductors,"In order to understand the origin of high-temperature superconductivity in
copper oxides, we must understand the normal state from which it emerges. Here,
we examine the evolution of the normal state electronic excitations with
temperature and carrier concentration in Bi2Sr2CaCu2O8 using angle-resolved
photoemission. In contrast to conventional superconductors, where there is a
single temperature scale Tc separating the normal from the superconducting
state, the high- temperature superconductors exhibit two additional temperature
scales. One is the pseudogap scale T*, below which electronic excitations
exhibit an energy gap. The second is the coherence scale Tcoh, below which
sharp spectral features appear due to increased lifetime of the excitations. We
find that T* and Tcoh are strongly doping dependent and cross each other near
optimal doping. Thus the highest superconducting Tc emerges from an unusual
normal state that is characterized by coherent excitations with an energy gap.",1302.3252v1
2013-02-26,Ultrafast plasmonics using transparent conductive oxide hybrids in the epsilon near-zero regime,"The dielectric response of transparent conductive oxides near the bulk
plasmon frequency is characterized by a refractive index less than vacuum. In
analogy with x-ray optics, it is shown that this regime results in total
external reflection and air-guiding of light. In addition, the strong reduction
of the wavevector in the ITO below that of free space enables a new surface
plasmon polariton mode which can be excited without requiring a prism or
grating coupler. Ultrafast control of the surface plasmon polariton mode is
achieved with a modulation amplitude reaching 20%.",1302.6604v1
2013-02-27,Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film,"We show that the third order optical nonlinearity of 15-atom gold clusters is
significantly enhanced when in contact with indium tin oxide (ITO) conducting
film. Open and close aperture z-scan experiments together with non-degenerate
pump-probe differential transmission experiments were done using 80 fs laser
pulses centered at 395 nm and 790 nm on gold clusters encased inside
cyclodextrin cavities. We show that two photon absorption coefficient is
enhanced by an order of magnitude as compared to that when the clusters are on
pristine glass plate. The enhancement for the nonlinear optical refraction
coefficient is ~3 times. The photo-induced excited state absorption using
pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also
show an enhancement by an order of magnitude. These results attributed to the
excited state energy transfer in the coupled gold cluster-ITO system are
different from the enhancement seen so far in charge donor-acceptor complexes
and nanoparticle-conjugate polymer composites.",1302.7001v1
2013-04-03,Octahedral Engineering of Orbital Polarizations in Charge Transfer Oxides,"Negative charge transfer $AB$O$_3$ oxides may undergo electronic
metal--insulator transitions (MIT) concomitant with a dilation and contraction
of nearly rigid octahedra. On both sides of the MIT are in-phase or
out-of-phase (or both) rotations of adjacent octahedra that buckle the
$B$--O--$B$ bond angle away from 180$^\circ$. Using density functional theory
with the PBEsol$+U$ approach, we describe a novel octahedral engineering avenue
to control the $B$ 3d and O $2p$ orbital polarization through enhancement of
the $B$O$_6$ rotation ""sense"" rather than solely through conventional changes
to the $B$--O bond lengths, \emph{i.e.} crystal field distortions. Using
CaFeO$_3$ as a prototypical material, we show the flavor of the octahedral
rotation pattern when combined with strain--rotation coupling and thin film
engineering strategies offers a promising avenue to fine tune orbital
polarizations near electronic phase boundaries.",1304.0982v1
2013-04-10,Multi-band superconductivity and nanoscale inhomogeneity at oxide interfaces,"The two-dimensional electron gas at the LaTiO3/SrTiO3 or LaAlO3/SrTiO3 oxide
interfaces becomes superconducting when the carrier density is tuned by gating.
The measured resistance and superfluid density reveal an inhomogeneous
superconductivity resulting from percolation of filamentary structures of
superconducting ""puddles"" with randomly distributed critical temperatures,
embedded in a non-superconducting matrix. Following the evidence that
superconductivity is related to the appearance of high-mobility carriers, we
model intra-puddle superconductivity by a multi-band system within a weak
coupling BCS scheme. The microscopic parameters, extracted by fitting the
transport data with a percolative model, yield a consistent description of the
dependence of the average intra-puddle critical temperature and superfluid
density on the carrier density.",1304.2970v1
2013-04-16,EUV induced defects on few-layer graphene,"We use Raman spectroscopy to show that exposing few-layer graphene to extreme
ultraviolet (EUV, 13.5 nm) radiation, i.e. relatively low photon energy,
results in an increasing density of defects. Furthermore, exposure to EUV
radiation in a H2 background increases the graphene dosage sensitivity, due to
reactions caused by the EUV induced hydrogen plasma. X-ray photoelectron
spectroscopy (XPS) results show that the sp2 bonded carbon fraction decreases
while the sp3 bonded carbon and oxide fraction increases with exposure dose.
Our experimental results confirm that even in reducing environment oxidation is
still one of the main source of inducing defects.",1304.4395v1
2013-04-22,Electronic Structure Modeling of Electrochemical Reactions at Electrode/Electrolyte Interfaces in Lithium Ion Batteries,"We review recent ab initio molecular dynamics studies of
electrode/electrolyte interfaces in lithium ion batteries. Our goals are to
introduce experimentalists to simulation techniques applicable to models which
are arguably most faithful to experimental conditions so far, and to emphasize
to theorists that the inherently interdisciplinary nature of this subject
requires bridging the gap between solid and liquid state perspectives. We
consider liquid ethylene carbonate (EC) decomposition on lithium intercalated
graphite, lithium metal, oxide-coated graphite, and spinel manganese oxide
surfaces. These calculations are put in the context of more widely studied
water-solid interfaces. Our main themes include kinetically controlled
two-electron-induced reactions, the breaking of a previously much neglected
chemical bond in EC, and electron tunneling. Future work on modeling batteries
at atomic lengthscales requires capabilities beyond state-of-the-art, which
emphasizes that applied battery research can and should drive fundamental
science development.",1304.5976v1
2013-04-26,Learning and Spatiotemporally Correlated Functions Mimicked in Oxide-Based Artificial Synaptic Transistors,"Learning and logic are fundamental brain functions that make the individual
to adapt to the environment, and such functions are established in human brain
by modulating ionic fluxes in synapses. Nanoscale ionic/electronic devices with
inherent synaptic functions are considered to be essential building blocks for
artificial neural networks. Here, Multi-terminal IZO-based artificial synaptic
transistors gated by fast proton-conducting phosphosilicate electrolytes are
fabricated on glass substrates. Proton in the SiO2 electrolyte and IZO channel
conductance are regarded as the neurotransmitter and synaptic weight,
respectively. Spike-timing dependent plasticity, short-term memory and
long-term memory were successfully mimicked in such protonic/electronic hybrid
artificial synapses. And most importantly, spatiotemporally correlated logic
functions are also mimicked in a simple artificial neural network without any
intentional hard-wire connections due to the naturally proton-related coupling
effect. The oxide-based protonic/electronic hybrid artificial synaptic
transistors reported here are potential building blocks for artificial neural
networks.",1304.7072v1
2013-05-02,Inductively Coupled Plasma etching of amorphous silicon nanostructures over nanotopography using C4F8/SF6 chemistry,"Inductively Coupled Plasma (ICP) etching of amorphous silicon (a-Si)
nanostructures using a continuous C4F8/SF6 plasma over nanotopography in
silicon dioxide (SiO2) is investigated. The coil power of the ICP system is
used to tune the a-Si etch rate from 20 to 125 nm/min. The etch rates of a-Si,
SiO2 and electroresist are measured depending on the SF6 ratio, platen power
and chamber pressure and used to optimize the a-Si:SiO2 etch selectivity. The
results on nanostructures show that the presence of an insulating etch-stop
layer affects the passivation ratio required to achieve vertical sidewalls. A
low pressure is also necessary in order to etch the silicon nanostructure
embedded into the oxide nanotrenches to form a highly conformable a-Si
nanowire. We argue that both of these behaviors could be explained by surface
charging effects. Finally, etching of 20 nm a-Si nanowires that cross 15 nm
trenches in oxide with vertical sidewalls and a 4.3:1 a-Si:SiO2 etch
selectivity is demonstrated. This etching process can be used in applications
where nanotopography is present such as single electron transistors or
multigate transistors.",1305.0589v1
2013-05-07,Enhanced and continuous electrostatic carrier doping on the SrTiO$_{3}$ surface,"Paraelectrical tuning of a charge carrier density as high as
10$^{13}$\,cm$^{-2}$ in the presence of a high electronic carrier mobility on
the delicate surfaces of correlated oxides, is a key to the technological
breakthrough of a field effect transistor (FET) utilising the metal-nonmetal
transition. Here we introduce the Parylene-C/Ta$_{2}$O$_{5}$ hybrid gate
insulator and fabricate FET devices on single-crystalline SrTiO$_{3}$, which
has been regarded as a bedrock material for oxide electronics. The gate
insulator accumulates up to $\sim10^{13}$cm$^{-2}$ carriers, while the
field-effect mobility is kept at 10\,cm$^2$/Vs even at room temperature.
Further to the exceptional performance of our devices, the enhanced
compatibility of high carrier density and high mobility revealed the mechanism
for the long standing puzzle of the distribution of electrostatically doped
carriers on the surface of SrTiO$_{3}$. Namely, the formation and continuous
evolution of field domains and current filaments.",1305.1440v1
2013-05-20,Hidden Structural Order in Orthorhombic Tantalum Pentoxide (Ta$_2$O$_5$),"We investigate using first-principles calculations the atomic structure of
the orthorhombic phase of Ta$_2$O$_5$. Although this structure has been studied
for decades, the correct structural model is controversial owing to the
complication of structural disorder. We identify a new low-energy high-symmetry
structural model where all Ta and O atoms have correct formal oxidation states
of +5 and -2, respectively, and the experimentally reported triangular lattice
symmetry of the Ta sublattice appears dynamically at finite temperatures. To
understand the complex atomic structure of the Ta$_2$O$_3$ plane, a triangular
graph-paper representation is devised and used alongside oxidation state
analysis to reveal infinite variations of the low-energy structural model. The
structural disorder of Ta$_2$O$_5$ observed in experiments is attributed to the
intrinsic structural variations, and oxygen vacancies that drive collective
relaxation of the O sublattice.",1305.4425v1
2013-05-30,Transport properties of p-type metal-oxide-semiconductor inversion layer in (110) and (111) silicon channel under uniaxial stress,"Valence subband and transport properties of p-type metal-oxide-semiconductor
(PMOS) inversion layer in uniaxially strained (110) and (111) Si channel have
been studied theoretically in this work. Equal energy lines, carrier
concentration effective mass, conductivity effective mass, and mobility are
calculated based on Luttinger-Kohn Hamiltonian [16]. Three compact expressions
of scattering rate are derived in this paper. The direction of applied uniaxial
stresses considered is in either parallel or perpendicular to channel. My
results show mobility is very sensitive to effective mass under different
stresses. The favorable mobility directions are found in (110) system with -3
GPa stress parallel to channel and +3 GPa stress perpendicular to channel.",1305.7037v2
2013-06-04,GaN / VO2 heteroepitaxial p-n junctions: Band offset and minority carrier dynamics,"We report on experimental realization of p-n heterojunctions based on p-type
GaN, and an n-type correlated oxide, VO2. The band offsets are evaluated by
current-voltage and capacitance voltage measurements at various temperatures. A
band diagram based on the conventional band bending picture is proposed to
explain the evolution of the apparent barier height from electrical
measurements and it suggests that the work function of VO2 decreases by ~0.2 eV
when it goes through the insulator to metal transtion, in qualitative agreement
with Kelvin force microscopy measurements reported in literature. The frequency
dependent capacitance measurements allows us to differentiate the miniority
carrier effect from the interface states and series resistance contributions,
and estimate the minority carrier lifetime in insulating phase of VO2 to be of
the order of few microseconds. The nitride-oxide based p-n heterojunctions
provide a new dimension",1306.0916v1
2013-06-04,Bipolar electrical switching in metal-metal contacts,"Electrical switching has been observed in carefully designed
metal-insulator-metal devices built at small geometries. These devices are also
commonly known as memristors and consist of specific materials such as
transition metal oxides, chalcogenides, perovskites, oxides with valence
defects, or a combination of an inert and an electrochemically active
electrode. No simple physical device has been reported to exhibit electrical
switching. We have discovered that a simple point-contact or a granular
arrangement formed of metal pieces exhibits bipolar switching. These devices,
referred to as coherers, were considered as one-way electrical fuses. We have
identified the state variable governing the resistance state and can program
the device to switch between multiple stable resistance states. Our
observations render previously postulated thermal mechanisms for their
resistance-change as inadequate. These devices constitute the missing canonical
physical implementations for memristor, often referred as the fourth passive
element. Apart from the theoretical advance in understanding metallic contacts,
the current discovery provides a simple memristor to physicists and engineers
for widespread experimentation, hitherto impossible.",1306.0942v2
2013-06-12,Dimensional Oxidation of Non-geometric Fluxes in Type II Orientifolds,"Some aspects of string compactifications with non-geometric fluxes are
revisited in the light of recent progress in double field theory. After
rederiving the general form of these fluxes, we consider the proposed flux
induced four-dimensional effective superpotential and oxidize its induced
scalar potential to terms in a ten-dimensional action. This analysis is
performed independently for an explicit toroidal type IIA and its T-dual type
IIB orientifold. We show in detail that the result of this bottom-up approach
is compatible with the gauged supergravity motivated flux formulation of the
double field theory action in both the NS-NS and the R-R sector.",1306.2761v3
2013-06-20,Limitations of the hybrid functional approach to electronic structure of transition metal oxides,"During the last decade, ab initio methods to calculate electronic structure
of materials based on hybrid functionals are increasingly becoming widely
popular. In this Letter, we show that, in the case of small gap transition
metal oxides, such as VO2, with rather subtle physics in the vicinity of the
Fermi-surface, such hybrid functional schemes without the inclusion of
""expensive"" fully self-consistent GW corrections fail to yield this physics and
incorrectly describe the features of the wave function of states near the
Fermi-surface. While a fully self-consistent GW on top of hybrid functional
approach does correct these wave functions as expected, and is found to be in
general agreement with the results of a fully self-consistent GW approach based
on semilocal functionals, it is much more computationally demanding as compared
to the latter approach for the benefit of essentially the same results.",1306.4948v1
2013-06-24,Electron-electron scatttering in Sn-doped indium oxide thick films,"We have measured the low-field magnetoresistances (MRs) of a series of
Sn-doped indium oxide thick films in the temperature $T$ range 4--35 K. The
electron dephasing rate $1/\tau_{\varphi}$ as a function of $T$ for each film
was extracted by comparing the MR data with the three-dimensional (3D)
weak-localization theoretical predictions. We found that the extracted
$1/\tau_{\varphi}$ varies linearly with $T^{3/2}$. Furthermore, at a given $T$,
$1/\tau_{\varphi}$ varies linearly with $k_F^{-5/2}l^{-3/2}$, where $k_{F}$ is
the Fermi wavenumber, and $l$ is the electron elastic mean free path. These
features are well explained in terms of the small-energy-transfer
electron-electron scattering time in 3D disordered conductors. This electron
dephasing mechanism dominates over the electron-phonon ($e$-ph) scattering
process because the carrier concentrations in our films are $\sim$ 3 orders of
magnitude lower than those in typical metals, which resulted in a greatly
suppressed $e$-ph relaxation rate.",1306.5610v1
2013-07-02,Energy ordering of grain boundaries in Cr2O3: Insights from theory,"The grain boundaries, GBs, of corundum Cr2O3 are known to play an important
role in the diffusion of ions within the oxide, which is an important
phenomenon for the corrosion of the stainless steels. The extent of the growth
of oxide layers in stainless steel depends upon which interfaces are preferred
within Cr2O3. Therefore, we have constructed four different grain boundary
planes (rhombohedral, basal, prismatic and pyramidal) and their various
associated interface symmetries known in literature for corundum Al2O3. Their
structural, electronic, and energetic properties are investigated theoretically
with periodic calculations using the DFT+U approach. We find that the prismatic
screw GB with a Cr-O plane interface is the energetically preferred GB with the
rhombohedral GB with screw symmetry and Cr vacancy termination being the second
energetically preferred GB. The increase of the number of in-plane Cr atoms at
the interface of prismatic GB enhances the stability which is also evident in
the electronic density of states.",1307.0691v1
2013-07-11,Lanthanide impurities in wide bandgap semiconductors: a possible roadmap for spintronic devices,"The electronic properties of lanthanide (from Eu to Tm) impurities in
wurtzite gallium nitride and zinc oxide were investigated by first principles
calculations, using an all electron methodology plus a Hubbard potential
correction. The results indicated that the 4f-related energy levels remain
outside the bandgap in both materials, in good agreement with a recent
phenomenological model, based on experimental data. Additionally, zinc oxide
doped with lanthanide impurities became an n-type material, showing a coupling
between the 4f-related spin polarized states and the carriers. This coupling
may generate spin polarized currents, which could lead to applications in
spintronic devices.",1307.3209v1
2013-07-15,Doping-Induced Spectral Shifts in Two Dimensional Metal Oxides,"Doping of strongly layered ionic oxides is an established paradigm for
creating novel electronic behavior. This is nowhere more apparent than in
superconductivity, where doping gives rise to high temperature
superconductivity in cuprates (hole-doped) and to surprisingly high Tc in HfNCl
(Tc=25.5K, electron-doped). First principles calculations of hole-doping of the
layered delafossite CuAlO2 reveal unexpectedly large doping-induced shifts in
spectral density, strongly in opposition to the rigid band picture that is
widely used as an accepted guideline. These spectral shifts, of similar origin
as the charge transfer used to produce negative electron affinity surfaces and
adjust Schottky barrier heights, drastically alter the character of the Fermi
level carriers, leading in this material to an O-Cu-O molecule-based carrier
(or polaron, at low doping) rather than a nearly pure-Cu hole as in a rigid
band picture. First principles linear response electron-phonon coupling (EPC)
calculations reveal, as a consequence, net weak EPC and no superconductivity
rather than the high Tc obtained previously using rigid band expectations.
These specifically two-dimensional dipole-layer driven spectral shifts provides
new insights into materials design in layered materials foe functionalities
besides superconductivity.",1307.4126v1
2013-07-16,First-principles thermodynamic screening approach to photo-catalytic water splitting with co-catalysts,"We adapt the computational hydrogen electrode approach to explicitly account
for photo-generated charges and use it to computationally screen for viable
catalyst/co-catalyst combinations for photo-catalytic water splitting. The hole
energy necessary to thermodynamically drive the reaction is employed as
descriptor for the screening process. Using this protocol and hybrid-level
density-functional theory we show that water oxidation on bare TiO2 surfaces is
thermodynamically more complex than previously thought. This motivates a
screening for suitable co-catalysts for this half-reaction, which we carry out
for Au particles down to the non-scalable size regime. We find that almost all
small Au clusters studied are better suited for water photo-oxidation than an
extended Au(111) surface or bare TiO2 facets.",1307.4199v1
2013-07-18,Structural position and oxidation state of nickel in SrTiO3,"The properties of Ni-doped strontium titanate are studied using X-ray
diffraction and XAFS spectroscopy. It is shown that regardless of the
preparation conditions, the SrTi1-xNixO3 solid solution and the NiTiO3 phase
are the most stable phases which can coexist. According to the EXAFS data, in
the single-phase sample of SrTi0.97Ni0.03O3, the Ni atoms substitute for the Ti
ones and are on-center. The distortion of the oxygen octahedra is not observed.
The XANES spectra analysis shows that the oxidation state of nickel in NiTiO3
is 2+, and in the SrTi1-xNixO3 solid solution it is close to 4+. It is shown
that the strongest light absorption in doped samples is associated with the
presence of tetravalent nickel in the SrTi1-xNixO3 solid solution. This doping
seems the most promising one for solar energy converters that exploit the bulk
photovoltaic effect.",1307.5082v2
2013-07-24,Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides,"High-k dielectric materials are important as gate oxides in microelectronics
and as potential dielectrics for capacitors. In order to enable computational
discovery of novel high-k dielectric materials, we propose a fitness model
(energy storage density) that includes the dielectric constant, bandgap, and
intrinsic breakdown field. This model, used as fitness function in conjunction
with first-principles calculations and global optimization evolutionary
algorithm USPEX, efficiently leads to practically important results. We found a
number of high-fitness structures of SiO2 and HfO2, some of which correspond to
known phases and some are new. The results allow us to propose characteristics
(genes) common to high-fitness structures - these are the coordination
polyhedra and their degree of distortion. Our variable-composition searches in
the HfO2-SiO2 system uncovered several high-fitness states. This hybrid
algorithm opens up a new avenue of discovering novel high-k dielectrics with
both fixed and variable compositions, and will speed up the process of
materials discovery.",1307.6358v2
2013-10-04,Designing a robustly metallic noncenstrosymmetric ruthenate oxide with large thermopower anisotropy,"The existence of approximately 30 noncentrosymmetric metals (NCSM) suggests a
contraindication between crystal structures without inversion symmetry and
metallic behavior. Those containing oxygen are especially scarce. Here we
propose and demonstrate a design framework to remedy this property disparity
and accelerate NCSM-oxide discovery: The primary ingredient relies on the
removal of inversion symmetry through displacements of atoms whose electronic
degrees of freedom are decoupled from the states at the Fermi level. Density
functional theory calculations validate this crystal--chemistry strategy, and
we predict a new polar ruthenate exhibiting robust metallicity. We demonstrate
that the electronic structure is unaffected by the inclusion of spin-orbit
interactions (SOI), and that cation ordered SrCaRu$_2$O$_6$ exhibits a large
thermopower anisotropy ($\left|\Delta\mathcal{S}_\perp\right|\sim6.3 \mu
\textrm{V K}^{-1}$ at 300 K) derived from its polar structure. Our findings
provide chemical and structural selection guidelines to aid in the search of
new NCS metals with enhanced thermopower anisotropy.",1310.1148v2
2013-10-04,Covalency in transition metal oxides within all-electron Dynamical Mean Field Theory,"A combination of dynamical mean field theory and density functional theory,
as implemented in Phys. Rev. B 81, 195107 (2010), is applied to both the early
and late transition metal oxides. For fixed value of the local Coulomb
repulsion, without fine tuning, we obtain the main features of these series,
such as the metallic character of SrVO$_3$ and the the insulating gaps of
LaVO$_3$, LaTiO$_3$ and La$_2$CO$_4$ which are in good agreement with
experiment. The study highlights the importance of local physics and high
energy hybridization in the screening of the Hubbard interaction and how
different low energy behaviors can emerge from the a unified treatment of the
transition metal series.",1310.1158v2
2013-10-09,Emergent topological and half semimetallic Dirac Fermions at oxide interfaces,"It is highly desirable to combine recent advances in the topological quantum
phases with technologically relevant materials. Chromium dioxide (CrO2) is a
half-metallic material, widely used in high-end data storage applications.
Using first principles calculations, we show via interfacial orbital design
that a novel class of half semi-metallic Dirac electronic phase emerges at the
interface CrO2 with TiO2 in both thin film and superlattice configurations,
with four spin-polarized Dirac points in momentum-space (k-space) band
structure. When the spin and orbital degrees of freedom are allowed to couple,
the CrO2/TiO2 superlattice becomes a Chern insulator without external fields or
additional doping. With topological gaps equivalent to 43 Kelvin and a Chern
number 2, the ensuing quantization of Hall conductance to 2e^2/h will enable
potential development of these highly industrialized oxides for applications in
topologically high fidelity data storage and energy-efficient electronic and
spintronic devices.",1310.2471v1
2013-10-14,Non-volatile multilevel resistive switching memory cell: A transition metal oxide-based circuit,"We study the resistive switching (RS) mechanism as way to obtain multi-level
memory cell (MLC) devices. In a MLC more than one bit of information can be
stored in each cell. Here we identify one of the main conceptual difficulties
that prevented the implementation of RS-based MLCs. We present a method to
overcome these difficulties and to implement a 6-bit MLC device with a
manganite-based RS device. This is done by precisely setting the remnant
resistance of the RS-device to an arbitrary value. Our MLC system demonstrates
that transition metal oxide non-volatile memories may compete with the
currently available MLCs.",1310.3613v1
2013-10-17,Designing heavy metal oxide glasses with threshold properties from network rigidity,"Here we show that a new class of glasses composed of heavy metal oxides
involving transition metals (V$_\text {2}$O$_\text{}$5-TeO$_\text{2}$), can
surprisingly be designed from very basic tools using topology and rigidity of
their underlying molecular networks. When investigated as a function of
composition, such glasses display abrupt changes in network packing and
enthalpy of relaxation at Tg, underscoring presence of flexible to rigid
elastic phase transitions. We find that these elastic phases are fully
consistent with polaronic nature of electronic conductivity at high
V$_\text{2}$O$_\text{5}$ content. Such observations have new implications for
designing electronic glasses which differ from the traditional amorphous
electrolytes having only mobile ions as charge carriers.",1310.4789v1
2013-10-22,Inhomogeneity of donor doping in SrTiO3 substrates studied by fluorescence-lifetime imaging microscopy,"Fluorescence-lifetime imaging microscopy (FLIM) was applied to investigate
the donor distribution in SrTiO3 single crystals. On the surfaces of Nb- and
La-doped SrTiO3, structures with different fluorescence intensities and
lifetimes were found that could be related to different concentrations of Ti3+.
Furthermore, the inhomogeneous distribution of donors caused a non-uniform
conductivity of the surface, which complicates the production of potential
electronic devices by the deposition of oxide thin films on top of doped single
crystals. Hence, we propose FLIM as a convenient technique (length scale: 1
$\mu$m) for characterizing the quality of doped oxide surfaces, which could
help to identify appropriate substrate materials.",1310.5813v1
2013-11-04,Artificial Synapse Network on Inorganic Proton Conductor for Neuromorphic Systems Applications,"The basic units in our brain are neurons and each neuron has more than 1000
synapse connections. Synapse is the basic structure for information transfer in
an ever-changing manner, and short-term plasticity allows synapses to perform
critical computational functions in neural circuits. Therefore the major
challenge for the hardware implementation of neuromorphic computation is to
develop artificial synapse. Here, in-plane oxide-based artificial synapse
network coupled by proton neurotransmitters are self-assembled on glass
substrates at room-temperature. A strong lateral modulation is observed due to
the proton migration in the nanogranular phosphorus-doped SiO2 electrolyte
films. Functional roles of short-term plasticity, including paired-pulse
facilitation, dynamic filtering and spatiotemporally correlated signal
processing are mimicked. Such in-plane oxide-based protonic/electronic hybrid
synapse network proposed here are interesting for building future neuromorphic
systems.",1311.0559v1
2013-11-05,Spin accumulation detection of FMR driven spin pumping in silicon-based metal-oxide-semiconductor heterostructures,"The use of the spin Hall effect and its inverse to electrically detect and
manipulate dynamic spin currents generated via ferromagnetic resonance (FMR)
driven spin pumping has enabled the investigation of these dynamically injected
currents across a wide variety of ferromagnetic materials. However, while this
approach has proven to be an invaluable diagnostic for exploring the spin
pumping process it requires strong spin-orbit coupling, thus substantially
limiting the materials basis available for the detector/channel material
(primarily Pt, W and Ta). Here, we report FMR driven spin pumping into a weak
spin-orbit channel through the measurement of a spin accumulation voltage in a
Si-based metal-oxide-semiconductor (MOS) heterostructure. This alternate
experimental approach enables the investigation of dynamic spin pumping in a
broad class of materials with weak spin-orbit coupling and long spin lifetime
while providing additional information regarding the phase evolution of the
injected spin ensemble via Hanle-based measurements of the effective spin
lifetime.",1311.0965v1
2013-11-10,A Nanoscale Shape Memory Oxide,"Stimulus-responsive shape memory materials have attracted tremendous research
interests recently, with much effort focused on improving their mechanical
actuation. Driven by the needs of nanoelectromechnical devices, materials with
large mechanical strain particularly at nanoscale are therefore desired. Here
we report on the discovery of a large shape memory effect in BiFeO3 at the
nanoscale. A maximum strain of up to ~14% and a large volumetric work density
can be achieved in association with a martensitic-like phase transformation.
With a single step, control of the phase transformation by thermal activation
or electric field has been reversibly achieved without the assistance of
external recovery stress. Although aspects such as hysteresis, micro-cracking
etc. have to be taken into consideration for real devices, the large shape
memory effect in this oxide surpasses most alloys and therefore demonstrates
itself as an extraordinary material for potential use in state-of-art
nano-systems.",1311.2243v1
2013-11-11,A first principles study of As doping at a disordered Si--SiO$_2$ interface,"Understanding the interaction between dopants and semiconductor-oxide
interfaces is an increasingly important concern in the drive to further
miniaturize modern transistors. To this end, using a combination of
first-principles density-functional theory and a continuous random network
Monte Carlo method, we investigate electrically active arsenic donors at the
interface between silicon and its oxide. Using a realistic model of the
disordered interface, we find that a small percentage (on the order of ~10%) of
the atomic sites in the first few monolayers on the silicon side of the
interface are energetically favourable for segregation, and that this is
controlled by the local bonding and local strain of the defect centre. We also
find that there is a long-range quantum confinement effect due to the
interface, which results in an energy barrier for dopant segregation, but that
this barrier is small in comparison to the effect of the local environment.
Finally, we consider the extent to which the energetics of segregation can be
controlled by the application of strain to the interface.",1311.2480v1
2013-11-12,Realizing Chemical Codoping in Oxide Semiconductors,"We demonstrate experimentally a chemical codoping approach that would
simultaneously narrow the band gap and control the band edge positions of oxide
semiconductors. Using TiO2 as an example, we show that a sequential doping
scheme with nitrogen (N) leading the way, followed by phosphorous (P), is
crucial for the incorporation of both N and P into the anion sites. Various
characterization techniques confirm the formation of the N-P bonds, and as a
consequence of the chemical codoping, the band gap of the TiO2 is reduced from
3.0 eV to 1.8 eV. The realization of chemical codoping could be an important
step forward in improving the general performance of electronic and
optoelectronic materials and devices.",1311.2779v1
2013-11-15,Transport properties of Ag5Pb2O6: a three-dimensional electron-gas-like system with low-carrier-density,"We report normal-state transport properties of the single-crystalline samples
of the silver-lead oxide superconductor Ag5Pb2O6, including the electrical
resistivity, magnetoresistance, and Hall coefficient. From the Hall coefficient
measurement, we confirmed that the carrier density of this oxide is as low as
5x10^{21} cm^{-3}, one order of magnitude smaller than those for ordinary
alkali metals and noble metals. The magnetoresistance behavior is well
characterized by the axial symmetry of the Fermi surface and by a single
relaxation time. The T^2 term of the resistivity is scaled with the specific
heat coefficient, based on the recent theory for the electron-electron
scattering. The present results provide evidence that Ag5Pb2O6 is a
low-carrier-density three-dimensional electron-gas-like system with enhanced
electron-electron scatterings.",1311.3860v1
2013-11-19,Charge transfer satellites in x-ray spectra of transition metal oxides,"Strongly correlated materials such as transition metal oxides (TMOs) often
exhibit large satellites in their x-ray photoemission (XPS) and x-ray
absorption spectra (XAS). These satellites arise from localized charge-transfer
(CT) excitations that accompany the sudden creation of a core hole. Here we use
a two-step approach to treat such excitations in a localized system embedded in
a condensed system and coupled to a photoelectron. The total XAS is then given
by a convolution of a spectral function representing the localized excitations
and the XAS of the extended system. The local system is modeled roughly in
terms of a simple three-level model, leading to a double-pole approximation for
the spectral function that represents dynamically weighted contributions from
the dominant neutral and charge-transfer excitations. This method is
implemented using a resolvent approach, with potentials, radial wave-functions
and matrix elements from the real-space Green's function code FEFF, and
parameters fitted to XPS experiments. Representative calculations for several
TMOs are found to be in reasonable agreement with experiment.",1311.4910v1
2013-12-10,Importance of d-p Coulomb interaction for high T$_C$ cuprates and other oxides,"Current theoretical studies of electronic correlations in transition metal
oxides typically only account for the local repulsion between d-electrons even
if oxygen ligand p-states are an explicit part of the effective Hamiltonian.
Interatomic interactions such as Upd between d- and (ligand) p-electrons, as
well as the local interaction between p-electrons, are neglected. Often, the
relative d-p orbital splitting has to be adjusted ""ad hoc"" on the basis of the
experimental evidence. By applying the merger of local density approximation
and dynamical mean field theory (LDA+DMFT) to the prototypical case of the
3-band Emery dp model for the cuprates, we demonstrate that, without any ""ad
hoc"" adjustment of the orbital splitting, the charge transfer insulating state
is stabilized by the interatomic interaction Upd. Our study hence shows how to
improve realistic material calculations that explicitly include the p-orbitals.",1312.2757v1
2014-01-10,Combined therapies of antithrombotics and antioxidants delay in silico brain tumor progression,"Glioblastoma multiforme, the most frequent type of primary brain tumor, is a
rapidly evolving and spatially heterogeneous high-grade astrocytoma that
presents areas of necrosis, hypercellularity and microvascular hyperplasia. The
aberrant vasculature leads to hypoxic areas and results in an increase of the
oxidative stress selecting for more invasive tumor cell phenotypes. In our
study we assay in silico different therapeutic approaches which combine
antithrombotics, antioxidants and standard radiotherapy. To do so, we have
developed a biocomputational model of glioblastoma multiforme that incorporates
the spatio-temporal interplay among two glioma cell phenotypes corresponding to
oxygenated and hypoxic cells, a necrotic core and the local vasculature whose
response evolves with tumor progression. Our numerical simulations predict that
suitable combinations of antithrombotics and antioxidants may diminish, in a
synergetic way, oxidative stress and the subsequent hypoxic response. This
novel therapeutical strategy, with potentially low or no toxicity, might reduce
tumor invasion and further sensitize glioblastoma multiforme to conventional
radiotherapy or other cytotoxic agents, hopefully increasing median patient
overall survival time.",1401.2397v1
2014-01-14,Precise and ultrafast molecular sieving through graphene oxide membranes,"There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries.",1401.3134v1
2014-01-31,Observation of strontium segregation in LaAlO$_{3}$/SrTiO$_{3}$ and NdGaO$_{3}$/SrTiO$_{3}$ oxide heterostructures by X-ray photoemission spectroscopy,"LaAlO$_{3}$ and NdGaO$_{3}$ thin films of different thickness have been grown
by pulsed laser deposition on TiO$_2$-terminated SrTiO$_{3}$ single crystals
and investigated by soft X-ray photoemission spectroscopy. The surface
sensitivity of the measurements has been tuned by varying photon energy $h\nu$
and emission angle $\Theta$. In contrast to the core levels of the other
elements, the Sr $3d$ line shows an unexpected splitting for higher surface
sensitivity, signaling the presence of a second strontium component. From our
quantitative analysis we conclude that during the growth process Sr atoms
diffuse away from the substrate and segregate at the surface of the
heterostructure, possibly forming strontium oxide.",1401.8165v1
2014-04-04,Atomically precise interfaces from non-stoichiometric deposition,"Complex oxide heterostructures display some of the most chemically abrupt,
atomically precise interfaces, which is advantageous when constructing new
interface phases with emergent properties by juxtaposing incompatible ground
states. One might assume that atomically precise interfaces result from
stoichiometric growth, but here we show that the most precise control is
obtained for non-stoichiometric growth where differing surface energies can be
compensated by surfactant-like effects. For the precise growth of
Sr$_{n+1}$Ti$_n$O$_{3n+1}$ Ruddlesden-Popper (RP) phases, stoichiometric
deposition leads to the loss of the first RP rock-salt double layer, but
growing with a strontium-rich surface layer restores the bulk stoichiometry and
ordering of the subsurface RP structure. Our results dramatically expand the
materials that can be prepared in epitaxial heterostructures with precise
interface control---from just the $n=\infty$ end members (perovskites) to the
entire RP family---enabling the exploration of novel quantum phenomena at a
richer variety of oxide interfaces.",1404.1374v1
2014-04-06,Piezoelectric properties of graphene oxide from the first-principles calculations,"Some highly ordered compounds of graphene oxide (GO), e.g., the so-called
clamped and unzipped GO, are shown to have piezoelectric responses via
first-principles density functional calculations. By applying an electric field
perpendicular to the GO basal plane, the largest value of in-plane strain and
strain piezoelectric coefficient, d31 are found to be 0.12% and 0.24 pm/V,
respectively, which are comparable with those of some advanced piezoelectric
materials. An in-depth molecular structural analysis reveals that deformation
of the oxygen doping regions in the clamped GO dominates its overall strain
output, whereas deformation of the regions without oxygen dopant in the
unzipped GO determines its overall piezoelectric strain. This understanding
explains the observed dependence of d31 on oxygen doping rate, i.e., higher
oxygen concentration giving rise to a larger d31 in the clamped GO whereas
leading to a reduced d31 in the unzipped GO. As the thinnest two-dimensional
piezoelectric materials, GO has a great potential for a wide range of MEMS/NEMS
actuators and sensors.",1404.1635v1
2014-04-08,Electron-beam patterning of polymer electrolyte films to make multiple nanoscale gates for nanowire transistors,"We report an electron-beam based method for the nanoscale patterning of the
poly(ethylene oxide)/LiClO$_{4}$ polymer electrolyte. We use the patterned
polymer electrolyte as a high capacitance gate dielectric in single nanowire
transistors and obtain subthreshold swings comparable to conventional
metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact
overlap which reduces parasitic effects and enables multiple, independently
controllable gates. The method's simplicity broadens the scope for using
polymer electrolyte gating in studies of nanowires and other nanoscale devices.",1404.1975v1
2014-04-13,Vector rectangular-shape laser based on reduced graphene oxide interacting with long fiber taper,"A vector dual-wavelength rectangular-shape laser (RSL) based on a long fiber
taper deposited with reduced graphene oxide is proposed, where the nonlinearity
is enhanced due to large evanescent-field-interacting length and strong field
confinement of a 8 mm fiber taper with a waist diameter of 4 micronmeters.
Graphene flakes are deposited uniformly on the taper waist with light pressure
effect, so this structure guarantees both excellent saturable absorption and
high nonlinearity. The RSL with a repetition rate of 7.9 MHz exhibits fast
polarization switching in two orthogonal polarization directions, and the
temporal and spectral characteristics are investigated. The results suggest
that the long taper-based graphene structure is an efficient choice for
nonlinear devices.",1404.3400v1
2014-04-15,Topological superconductivity and unconventional pairing in oxide interfaces,"To pinpoint the microscopic mechanism for superconductivity has proven to be
one of the most outstanding challenges in the physics of correlated quantum
matter. Thus far, the most direct evidence for an electronic pairing mechanism
is the observation of a new symmetry of the order-parameter, as done in the
cuprate high-temperature superconductors. Like distinctions based on the
symmetry of a locally defined order-parameter, global, topological invariants
allow for a sharp discrimination between states of matter that cannot be
transformed into each other adiabatically. Here we propose an unconventional
pairing state for the electron fluid in two-dimensional oxide interfaces and
establish a direct link to the emergence of nontrivial topological invariants.
Topological superconductivity and Majorana edge states can then be used to
detect the microscopic origin for superconductivity. In addition, we show that
also the density wave states that compete with superconductivity sensitively
depend on the nature of the pairing interaction. Our conclusion is based on the
special role played by the spin-orbit coupling and the shape of the Fermi
surface in SrTiO$_{3}$/LaAlO$_{3}$-interfaces and closely related systems.",1404.4039v1
2014-04-17,Pico- and nanosecond laser ablation of mixed tungsten / aluminium films,"In order to extend the investigation of laser-assisted cleaning of
ITER-relevant first mirror materials to the picosecond regime, a commercial
laser system delivering 10 picosecond pulses at 355 nm at a frequency of up to
1 MHz has been used to investigate the ablation of mixed aluminium (oxide) /
tungsten (oxide) layers deposited on poly- and nanocrystalline molybdenum as
well as nanocrystalline rhodium mirrors. Characterization before and after
cleaning using scanning electron microscopy (SEM) and spectrophotometry shows
heavy dust formation, resulting in a degradation of the reflectivity. Cleaning
using a 5 nanosecond pulses at 350 and 532 nm, on the other hand, proved very
promising. The structure of the film remnants suggests that in this case
buckling was the underlying removal mechanism rather than ablation. Repeated
coating and cleaning using nanosecond pulses is demonstrated.",1404.4494v1
2014-07-02,Effects of carbon nanotubes and graphene oxide absorbers on the noise of mode-locked fiber lasers,"Phase noise is very important for the ultrafast pulse application in
telecommunication, ultrafast diagnose, material science, and biology. In this
paper, two types of carbon nano-materials, single-wall carbon nanotube and
graphene oxide, are investigated for noise suppression in ultrafast photonics.
Various properties of the wall-paper SAs, such as saturable intensity, optical
absorption and degree of purity, are found to be key factors determining the
phase noise of the ultrafast pulses. A reduced-noise femtosecond fiber laser is
experimentally demonstrated by optimizing the above parameters of carbon
material based SAs. The phase noise reduction more than 10 dB at 10 kHz can be
obtained in the experiments. To our knowledge, this is the first time that the
relationship between different carbon material based SAs and the phase noise of
mode-locked lasers has been investigated. This work will pave the way to get a
high-quality ultrashort pulse in passively mode-locked fiber lasers.",1407.0507v1
2014-07-02,Giant Rydberg Excitons in Cuprous Oxide,"Highly excited atoms with an electron moved into a level with large principal
quantum number are fascinating hydrogen-like objects. The giant extension of
these Rydberg atoms leads to huge interaction effects. Monitoring these
interactions has provided novel insights into molecular and condensed matter
physics problems on a single quantum level. Excitons, the fundamental optical
excitations in semiconductors consisting of a negatively charged electron and a
positively charged hole, are the condensed matter analogues of hydrogen. Highly
excited excitons with extensions similar to Rydberg atoms are attractive
because they may be placed and moved in a crystal with high precision using
microscopic potential landscapes. Their interaction may allow formation of
ordered exciton phases or sensing of elementary excitations in the surrounding,
also on a quantum level. Here we demonstrate the existence of Rydberg excitons
in cuprous oxide, Cu2O, with principal quantum numbers as large as n=25 . These
states have giant wave function extensions of more than 2 micrometers, compared
to about a nanometer for the ground state. The strong dipole-dipole interaction
is evidenced by a blockade effect, where the presence of an exciton prevents
excitation of a further exciton in its vicinity.",1407.0691v1
2014-07-11,Microstructure-dependent oxidation-assisted dealloying of Cu0.7Al0.3 thin films,"In this paper, the oxidation-assisted dealloying (OAD) of Cu0.7Al0.3 films
with different microstructures which were obtained by high vacuum annealing at
different temperatures were studied using powder X-ray diffraction,
field-emission scanning electron microscopy and energy dispersive X-ray
analysis. It was observed that different microstructures such as eutectic
mixture or solid solution, the grain size of Cu or Al component in
eutectic-mixture Cu0.7Al0.3 films affected the corrosion morphology greatly. It
thus provided a practical route to fabricate flexible CuO porous
nanostructure-films (PNFs) with controllable pore size, porosity, block size
and shape. Further, the underlying OAD mechanisms for the structure-resultant
different corrosion morphologies of Cu0.7Al0.3 films were also explored. In
these senses, the study is suggestive and crucial to both the mechanism
understanding of OAD process and the technical controlling of PNF fabrication.",1407.3131v2
2014-07-14,Insights and challenges of applying the $GW$ method to transition metal oxides,"The ab initio $GW$ method is considered as the most accurate approach for
calculating the band gaps of semiconductors and insulators. Yet its application
to transition metal oxides (TMOs) has been hindered by the failure of
traditional approximations developed for conventional semiconductors. In this
work, we examine the effects of these approximations on the values of band gaps
for ZnO, Cu$_2$O, and TiO$_2$. In particular, we explore the origin of the
differences between the two widely used plasmon-pole models. Based on the
comparison of our results with the experimental data and previously published
calculations, we discuss which approximations are suitable for TMOs and why.",1407.3781v5
2014-07-24,Path of the current flow at the metal contacts of graphene field-effect transistors with distorted transfer characteristics,"Graphene field-effect transistors with source/drain contacts made of metals
that can be easily oxidized such as ferromagnetic metals often display a double
dip structure in the transfer characteristics because of charge density
depinning at the contacts. Generally, transfer characteristics of field-effect
transistors show no dependence on the length of the source/drain contacts
because charge carrier injection occurs mainly at the edges of the contact.
However, the shape of the transfer characteristics of devices fabricated using
Ni contacts is found to be dependent on the length of the contact. This
peculiar behavior was attributed to charge carrier injection from near the
center of the contacts. This is because of oxygen diffusion and the resultant
formation of an interfacial oxide layer of non-uniform thickness. The observed
contact length dependent transfer characteristics were reproduced using a model
calculation that includes charge carrier injection from the center of the
electrode and subsequent charge transport underneath the metal contact.",1407.6754v1
2014-08-01,Charge transfer across transition metal oxide interfaces: emergent conductance and new electronic structure,"We perform density functional theory plus dynamical mean field theory
calculations to investi- gate internal charge transfer in an artificial
superlattice composed of alternating layers of vanadate and manganite
perovskite and Ruddlesden-Popper structure materials. We show that the elec-
tronegativity difference between vanadium and manganese causes moderate charge
transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper based
superlattices, leading to hole doping of the VO2 layer and electron doping of
the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper based
heterostructures provides insights into the role of the apical oxy- gen. Our
first principles simulations demonstrate that the combination of internal
charge transfer and quantum confinement provided by heterostructuring is a
powerful approach to engineering electronic structure and tailoring correlation
effects in transition metal oxides.",1408.0217v2
2014-08-02,Exfoliating pristine black phosphorus down to the monolayer: photo-oxidation and electronic confinement effects,"Thin layers of black phosphorus have recently raised interest for their
two-dimensional (2D) semiconducting properties, such as tunable direct bandgap
and high carrier mobilities. This lamellar crystal of P atoms stacked together
by weak van der Waals forces can be exfoliated down to the stratophosphane
monolayer (also called phosphorene) using procedures similar to those used for
graphene. Properties of this 2D material are however challenging to probe due
to a fast and ubiquitous degradation upon exposure to ambient conditions.
Herein, we investigate the crystal degradation using in-situ Raman and
transmission electron spectroscopies and highlight a process involving a
photo-induced oxidation reaction with adsorbed oxygen in water. The
experimental conditions to prepare and preserve mono-, bi- and multilayers of
stratophosphane in their pristine states were determined. Study on these 2D
layers provides new insights on the effect of confinement on the chemical
reactivity and the vibrational modes of black phosphorus.",1408.0345v2
2014-08-11,Importance of tetrahedral coordination for high-valent transition metal oxides: YCrO$_4$ as a model system,"We have investigated the electronic structure of the high oxidation state
material YCrO$_4$ within the framework of the Zaanen-Sawatzky-Allen phase
diagram. While Cr$^{4+}$-based compounds like SrCrO$_3$/CaCrO$_3$ and CrO$_2$
can be classified as small-gap or metallic negative-charge-transfer systems, we
find using photoelectron spectroscopy that YCrO$_4$ is a robust insulator
despite the fact that its Cr ions have an even higher formal valence state of
5+. We reveal using band structure calculations that the tetrahedral
coordination of the Cr$^{5+}$ ions in YCrO$_4$ plays a decisive role, namely to
diminish the bonding of the Cr $3d$ states with the top of the O $2p$ valence
band. This finding not only explains why the charge-transfer energy remains
effectively positive and the material stable, but also opens up a new route to
create doped carriers with symmetries different from those of other
transition-metal ions.",1408.2396v1
2014-08-18,Breakdown voltage of metal-oxide resistors in liquid argon,"We characterized a sample of metal-oxide resistors and measured their
breakdown voltage in liquid argon by applying high voltage (HV) pulses over a 3
second period. This test mimics the situation in a HV-divider chain when a
breakdown occurs and the voltage across resistors rapidly rise from the static
value to much higher values. All resistors had higher breakdown voltages in
liquid argon than their vendor ratings in air at room temperature. Failure
modes range from full destruction to coating damage. In cases where breakdown
was not catastrophic, subsequent breakdown voltages were lower in subsequent
measuring runs. One resistor type withstands 131\,kV pulses, the limit of the
test setup.",1408.4013v4
2014-08-19,Aluminium-oxide wires for superconducting high kinetic inductance circuits,"We investigate thin films of conducting aluminium-oxide, also known as
granular aluminium, as a material for superconducting high quality, high
kinetic inductance circuits. The films are deposited by an optimised reactive
DC magnetron sputter process and characterised using microwave measurement
techniques at milli-Kelvin temperatures. We show that, by precise control of
the reactive sputter conditions, a high room temperature sheet resistance and
therefore high kinetic inductance at low temperatures can be obtained. For a
coplanar waveguide resonator with 1.5\,k$\Omega$ sheet resistance and a kinetic
inductance fraction close to unity, we measure a quality factor in the order of
700\,000 at 20\,mK. Furthermore, we observe a sheet resistance reduction by
gentle heat treatment in air. This behaviour is exploited to study the kinetic
inductance change using the microwave response of a coplanar wave guide
resonator. We find the correlation between the kinetic inductance and the sheet
resistance to be in good agreement with theoretical expectations.",1408.4347v3
2014-09-18,Electrical and optical properties of ITO thin films prepared by DC magnetron sputtering for low-emitting coatings,"Optimized DC magnetron sputtering system for the deposition of transparent
conductive oxides (TCOs), such indium tin oxide (ITO) on glass substrate has
been applied in order to achieve low-emitting (low-e) transparent coatings. To
obtain the concerned electrical resistance and high infrared reflection, first
the effect of applied sputtering power then oxygen flow on the properties of
films have been investigated. The other depositions parameters are kept
constant. Film deposition at at temperature 400 degree of Celsius in oxygen
flow of 3 Standard Cubic Centimeters per Minute results in transparent and
infrared reflecting coatings. Under this condition the highest attained average
reflectance in the infrared is ({\lambda}=3-25 micron) 89.5% (lowest emittance
equals to less than 11%), whereas transparency in the visible is 85%
approximately. Plasma wavelength and carrier concentration was measured.",1409.5293v1
2014-09-23,Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO,"Two families of high temperature superconductors whose critical temperatures
are higher than 50K are known. One is the copper oxides and the other is the
iron-based superconductors. Comparisons of mechanisms between these two in
terms of common ground as well as distinctions will greatly help in searching
for higher Tc superconductors. However, studies on mechanisms for the iron
family based on first principles calculations are few. Here we first show that
the superconductivity emerges in the state-of-the-art numerical calculations
for an ab initio multi-orbital model of an electron-doped iron-based
superconductor LaFeAsO, in accordance with experimental observations. Then the
mechanism of the superconductivity is identified as enhanced uniform density
fluctuations by one-to-one correspondence with the instability toward
inhomogeneity driven by first-order antiferromagnetic and nematic transitions.
Despite many differences, certain common features with the copper oxides are
also figured out in terms of the underlying orbital selective Mottness found in
the iron family.",1409.6536v1
2014-09-25,Topological Phases in Oxide Heterostructures with Light and Heavy Transition Metal Ions,"Using a combination of density functional theory, tight-binding models, and
Hartree-Fock theory, we predict topological phases with and without
time-reversal symmetry breaking in oxide heterostructures. We consider both
heterostructures containing light transition metal ions, and those containing
heavy transition metal ions. We find the (111) growth direction naturally leads
to favorable conditions for topological phases in both perovskite structures
and pyrochlore structures. For the case of light transition metal elements,
Hartree-Fock theory predicts the spin-orbit coupling is effectively enhanced by
on-site multiple-orbital interactions and may drive the system through a
topological phase transition, while heavy elements with intrinsically large
spin-orbit coupling require much weaker, or even vanishing electron
interactions to bring about a topological phase.",1409.7148v1
2014-09-25,"Wavelength Spacing Tunable, Multiwavelength Q-switched Fiber Laser Mode-locked by Graphene Oxide","We demonstrate a wavelength spacing tunable, multiwavelength Q-switched
mode-locked fiber laser (QML) based on a fiber taper deposited with graphene
oxide. The operation of the laser can be understood in terms of the formation
of bunches of QMLs which possess small temporal intervals, and multiwavelength
spectra are generated due to the Fourier transformation. We find that the
temporal spacing of the QMLs is highly sensitive to the pump power, and as a
result, the wavelength spacing can be easily tuned by varying the pump power.
Our experimental laser provides a wavelength spacing tuning range from ~0.001
nm to 0.145 nm with a pump power variation less than 10 mW. The laser could be
developed into a low lost wavelength spacing tunable optical source for a wide
range of applications, such as spectroscopy, microwave/terahertz signal
generation, optical metrology, optical communications and sensing.",1409.7417v1
2014-09-26,Structure Evolution of Graphene Oxide during Thermally Driven Phase Transformation: Is the Oxygen Content Really Preserved?,"A mild annealing procedure was recently proposed for the scalable enhancement
of graphene oxide (GO) properties with the oxygen content preserved, which was
demonstrated to be attributed to the thermally driven phase separation. In this
work, the structure evolution of GO with mild annealing is closely
investigated. It reveals that in addition to phase separation, the
transformation of oxygen functionalities also occurs, which leads to the slight
reduction of GO membranes and furthers the enhancement of GO properties. These
results are further supported by the density functional theory based
calculations. The results also show that the amount of chemically bonded oxygen
atoms on graphene decreases gradually and we propose that the strongly
physisorbed oxygen species constrained in the holes and vacancies on GO lattice
might be responsible for the preserved oxygen content during the mild annealing
procedure. The present experimental results and calculations indicate that both
the diffusion and transformation of oxygen functional groups might play
important roles in the scalable enhancement of GO properties.",1409.7739v2
2014-10-08,Resistive switching phenomena in TiOx nanoparticle layers for memory applications,"Electrical characteristics of a Co/TiO_x/Co resistive memory device,
fabricated by two different methods are reported. In addition to crystalline
TiO_2 layers fabricated via conventional atomic layer deposition (ALD), an
alternative method has been examined, where TiO_x nanoparticle layers were
fabricated via sol-gel. The different devices have shown different hysteresis
loops with a unique crossing point for the sol-gel devices. A simple
qualitative model is introduced to describe the different current-voltage
behaviours by suggesting only one active metal-oxide interface for the ALD
devices and two active metal-oxide interfaces for the sol-gel devices.
Furthermore, we show that the resistive switching behaviour could be easily
tuned by proper interface engineering and that despite having a similar active
material, different fabrication methods can lead to dissimilar resistive
switching properties.",1410.2019v1
2014-10-08,Nanoscale Electrostatic Control of Oxide Interfaces,"We develop a robust and versatile platform to define nanostructures at oxide
interfaces via patterned top gates. Using LaAlO$_3$/SrTiO$_3$ as a model
system, we demonstrate controllable electrostatic confinement of electrons to
nanoscale regions in the conducting interface. The excellent gate response,
ultra-low leakage currents, and long term stability of these gates allow us to
perform a variety of studies in different device geometries from room
temperature down to 50 mK. Using a split-gate device we demonstrate the
formation of a narrow conducting channel whose width can be controllably
reduced via the application of appropriate gate voltages. We also show that a
single narrow gate can be used to induce locally a superconducting to
insulating transition. Furthermore, in the superconducting regime we see
indications of a gate-voltage controlled Josephson effect.",1410.2237v2
2014-10-11,Manganese reduction/oxidation reaction on graphene composites as a reversible process for storing enormous energy at a fast rate,"Oxygen reduction/evolution reaction (ORR/OER) is a basic process for fuel
cells or metal air batteries. However, ORR/OER generally requires noble metal
catalysts and suffers from low solubility (10-3 molar per liter) of O2, low
kinetics rate (10-6 cm2/s) and low reversibility. We report a manganese
reduction/oxidation reaction (MRR/MOR) on graphene/MnO2 composites, delivering
a high capacity (4200 mAh/g), fast kinetics (0.0024 cm2/s, three orders higher
than ORR/OER), high solubility (three orders than O2), and high reversibility
(100%). We further use MRR/MOR to invent a rechargeable manganese ion battery
(MIB), which delivers an energy density of 1200 Wh/Kg (several times of lithium
ion battery), a fast charge ability (3 minutes), and a long cycle life (10,000
cycles). MRR/MOR renders a new class of energy conversion or storage systems
with a very high energy density enabling electric vehicles run much more miles
at one charge.",1410.4223v1
2014-10-16,Photocatalytic acetaldehyde oxidation in air using spacious TiO2 films prepared by atomic layer deposition on supported carbonaceous sacrificial templates,"Supported carbon nanosheets and carbon nanotubes served as sacrificial
templates for preparing spacious TiO2 photocatalytic thin films. Amorphous TiO2
was deposited conformally on the carbonaceous template material by atomic layer
deposition (ALD). Upon calcination at 550{\deg}C, the carbon template was
oxidatively removed and the as-deposited continuous amorphous TiO2 layers
transformed into interlinked anatase nanoparticles with an overall morphology
commensurate to the original template structure. The effect of type of
template, number of ALD cycles and gas residence time of pollutant on the
photocatalytic activity, as well as the stability of the photocatalytic
performance of these thin films was investigated. The TiO2 films exhibited
excellent photocatalytic activity towards photocatalytic degradation of
acetaldehyde in air as a model reaction for photocatalytic indoor air pollution
abatement. Optimized films outperformed a reference film of commercial PC500.",1410.4405v1
2014-11-01,Manipulating electronic states at oxide interfaces using focused micro X-rays from standard lab-sources,"Recently, x-ray illumination, using synchrotron radiation, has been used to
manipulate defects, stimulate self-organization and to probe their structure.
Here we explore a method of defect-engineering low-dimensional systems using
focused laboratory-scale X-ray sources. We demonstrate an irreversible change
in the conducting properties of the 2-dimensional electron gas at the interface
between the complex oxide materials LaAlO3 and SrTiO3 by X-ray irradiation. The
electrical resistance is monitored during exposure as the irradiated regions
are driven into a high resistance state. Our results suggest attention shall be
paid on electronic structure modification in X-ray spectroscopic studies and
highlight large-area defect manipulation and direct device patterning as
possible new fields of application for focused laboratory X-ray sources.",1411.0177v1
2014-11-21,Structural Modificationand Variation in the Kinetics of Isoconversional Phenomena: A Study on the Effect of Gamma Irradiation on Poly (Ethylene Oxide),"Interactions of Poly (Ethylene Oxide) [PEO] and gamma irradiation of variable
doses (1-30 kGy) on the thermal, crystalline and structural properties are
investigated using DSC and FTIR technique. Two states of PEO, viz. powder
(P-S-series) and solution (P-L-series) are subjected to irradiationand are
castinto uniform film.DSC results revealed steady increment of crystallinity
upto 20 kGy for P-S-series after which amorphous region increases till 30 kGy.
Conversely, P-L-series shows much enhanced crystallinity retained within low
regime of 7 kGy, followed by sharp declining trend till 30 kGy. DSC is also
used to determine the multiple kinetic processes in an isoconversional PEO
melting using Friedman differential analysis. Gamma irradiation is found to
generate newer functional groups established from FTIR study. FTIR spectra of
generated peaks viz. -C=O, -C=C- exhibit scission dominated irradiation induced
in presence of air. Contribution of cross-linkage which is higher in liquid
irradiation is also proved from FTIR. The studied observations of DSC and FTIR
are correlated with polymer microstructures. Hence, selective irradiation dose
could be determined with respect to the exposed state (solid or solution) of
polymer and utilized to tailor the properties of PEO.",1411.5809v1
2014-11-26,First Principles Prediction of Topological Phases in Thin Films of Pyrochlore Iridates,"Topological phases have attracted much interest in recent years. While there
are a number of three-dimensional materials exhibiting topological properties,
there are relatively few two-dimensional examples aside from the well-known
quantum Hall systems. Here we make materials-specific predictions for
topological phases using density functional theory combined with Hartree-Fock
theory that includes the full orbital structure of the relevant iridum
$d$-orbitals and the strong but finite spin-orbit coupling strength. We find
Y$_2$Ir$_2$O$_7$ bilayer and trilayer films grown along the [111] direction can
support topological metallic phases with a direct gap of up to 0.02 eV, which
could potentially bring transition metal oxides to the fore as a new class of
topological materials with potential applications in oxide electronics.",1411.7333v1
2014-11-30,Two-Dimensional Magnetotransport in a Black Phosphorus Naked Quantum Well,"Black phosphorus (bP) is the second known elemental allotrope with a layered
crystal structure that can be mechanically exfoliated down to atomic layer
thickness. We have fabricated bP naked quantum wells in a back-gated field
effect transistor geometry with bP thicknesses ranging from $6\pm1$ nm to
$47\pm1$ nm. Using an encapsulating polymer superstrate, we have suppressed bP
oxidation and have observed field effect mobilities up to 600 cm$^2$/Vs and
on/off current ratios exceeding $10^5$. Importantly, Shubnikov-de Haas (SdH)
oscillations observed in magnetotransport measurements up to 35 T reveal the
presence of a 2-D hole gas with Schr\""odinger fermion character in an
accumulation layer at the bP/oxide interface. Our work demonstrates that 2-D
electronic structure and 2-D atomic structure are independent. 2-D carrier
confinement can be achieved in layered semiconducting materials without
necessarily approaching atomic layer thickness, advantageous for materials that
become increasingly reactive in the few-layer limit such as bP.",1412.0259v1
2014-12-02,Coupling Thermal Integration of a Solid Oxide Fuel Cell with a Magnesium Metal Hydride Tank,"The dehydrogenation behaviour of a cylindrical Mg metal hydride tank is
simulated and examined in the case where the tank is thermally coupled with an
operating Solid Oxide Fuel Cell (SOFC) at 7000C. A three-dimensional validated
mathematical model is utilized to simulate the hydrogen desorption from a
cylindrical Mg hydride tank. Four scenarios are simulated: a base case where
the heat source for the desorption process is an external heater surrounding
the tank. The second case examines the effect of the radiation heat transfer
from the SOFC to the metal hydride as a possible heat source for the desorption
procedure. The third scenario uses the exhaust air from the SOFC cathode as the
heating source which is driven to the hydride and the fourth scenario is a
combination of both the exhaust air from the SOFC cathode and the external
heater as the heat source for the desorption. According to the results, the
exhaust air from the SOFC and the combination of external heater and the
exhaust heat have a uniform temperature distribution within the tank and
enhance the desorption capacity.",1412.0878v1
2014-12-09,Elliptically polarized terahertz radiation from a chiral oxide,"Polarization control of terahertz wave is a challenging subject in terahertz
science and technology. Here, we report a simple method to control polarization
state of the terahertz wave in terahertz generation process. At room
temperature, terahertz radiation from a noncentrosymmetric and chiral oxide,
sillenite Bi$_{12}$GeO$_{20}$, is observed by the irradiation of linearly
polarized femtosecond laser pulses at 800 nm. The polarization state of the
emitted terahertz wave is found to be elliptic with an ellipticity of
$\sim$0.37$\pm$0.10. Furthermore, the ellipticity was altered to a nearly zero
($\sim$0.01$\pm$0.01) by changing the polarization of the incident linearly
polarized femtosecond laser pulses. Such a terahertz radiation characteristic
is attributable to variation of the polarization state of the emitted terahertz
waves, which is induced by retardation due to the velocity mismatch between the
incident femtosecond laser pulse and generated terahertz wave and by the
polarization tilting due to the optical activity at 800 nm.",1412.2835v1
2014-12-10,Observation and Structural Control of Charge-Density-Waves resonating with Terahertz Frequencies in NdNiO3,"Formation of charge-density-waves in ordered electronic phases (such as
charge-order) is an emergent phenomenon in the perovskite class of correlated
oxides. This scenario is visualized to prevail in exotic RNiO3 (R=rare-earth)
nickelates in which the structure controls the incipient charge-order to form
in weak localization limit. However, any consequent effect demonstrating these
nickelates in rare category of charge-density-waves conductors with controlled
charge-lattice interactions has been a fundamental challenge so-far. Here, we
present first evidence of the charge-density-waves in a prototypical NdNiO3
system employing terahertz time-domain spectroscopy along selective crystal
axes. A finite peak structure at 5meV in the terahertz conductivity displays
all the characteristics of a charge-density-wave condensate. Contrasting
charge-dynamics of collective charge-density-waves mode and Drude conductivity
emerging, respectively, from orthorhombic and cubic symmetries disentangle
charge-ordering from the insulating state, establish a novel structure-property
cause-effect relationship, and present opportunities to harness these diverse
attributes in oxide electronics.",1412.3244v1
2014-12-14,X-ray and neutron reflectometry study of copper surface reconstruction caused by implantation of high-energy oxygen ions,"Combination of neutron and X-ray reflectometry was used to study the vertical
structure of 100 nm-thin copper films with implanted oxygen ions of energy E =
[10-30] keV and doses D=[0.2-5.4]x$10^{16}$ $cm^{-2}$. The study shows that
oxygen ion implantation with an energy of E = 30 keV leads to the formation of
a 3 nm thick layer on the surface. Density and copper/oxygen stoichiometry of
the observed surface layer are close to $Cu_2O$ oxide. We attribute the $Cu_2O$
oxide formation to highly mobilized copper atoms generated by stimulated ion
implantation.",1412.4356v1
2014-12-16,Defect chemistry in layered transition-metal oxides from screened hybrid density functional calculations,"We report a comprehensive first-principles study of the thermodynamics and
transport of intrinsic point defects in layered oxide cathode materials
LiMO$_2$ (M=Co, Ni), using density-functional theory and the
Heyd-Scuseria-Ernzerhof screened hybrid functional. We find that LiCoO$_2$ has
a complex defect chemistry; different electronic and ionic defects can exist
under different synthesis conditions, and LiCoO$_2$ samples free of cobalt
antisite defects can be made under Li-excess (Co-deficient) environments. A
defect model for lithium over-stoichiometric LiCoO$_2$ is also proposed, which
involves negatively charged lithium antisites and positively charged small
(hole) polarons. In LiNiO$_2$, a certain amount of Ni$^{3+}$ ions undergo
charge disproportionation and the concentration of nickel ions in the lithium
layers is high. Tuning the synthesis conditions may reduce the nickel antisites
but would not remove the charge disproportionation. In addition, we find that
LiMO$_2$ cannot be doped $n$- or $p$-type; the electronic conduction occurs via
hopping of small polarons and the ionic conduction occurs via migration of
lithium vacancies, either through a monovacancy or divacancy mechanism,
depending on the vacancy concentration.",1412.5064v1
2014-12-19,Hydrogen sensing by sol-gel grown NiO and NiO:Li thin films,"Hydrogen sensors have been prepared using nickel oxide (NiO) and
lithium-doped nickel oxide (NiO:Li) thin films, deposited on glass substrates
by the sol-gel spin coating technique. The surface morphology, structure,
optical and electrical properties of the obtained films were studied. Hydrogen
sensing results are presented for three operating temperatures (140, 160, and
180 {\deg}C) and for hydrogen concentrations ranging from 1000 to 15000 ppm in
synthetic air. The NiO and NiO:Li (2% and 8% doping concentrations) sensors
show maximum responses for the operating temperature of 180 {\deg}C. When
tested at different hydrogen concentrations in air, the lithium-doped NiO
sensors showed a higher response than the undoped NiO films.",1412.6554v1
2014-12-22,Large anisotropic thermal conductivity of intrinsically two-dimensional metallic oxide PdCoO$_2$,"The highly conductive layered metallic oxide \pdcoo{} is a near-perfect
analogue to an alkali metal in two dimensions. It is distinguished from other
two-dimensional electron systems where the Fermi surface does not reach the
Brillouin zone boundary by a high planar electron density exceeding $10^{15}$
cm$^{-2}$. The simple single-band quasi-2D electronic structure results in
strongly anisotropic transport properties and limits the effectiveness of
electron-phonon scattering. Measurements on single crystals in the temperature
range from 10-300K show that the thermal conductivity is much more weakly
anisotropic than the electrical resistivity, as a result of significant phonon
heat transport. The in-plane thermoelectric power is linear in temperature at
300\,K and displays a purity-dependent peak around 50K. Given the extreme
simplicity of the band-structure, it is possible to identify this peak with
phonon drag driven by normal electron-phonon scattering processes.",1412.6919v1
2014-12-22,Dimensionality Control of d-orbital Occupation in Oxide Superlattices,"Manipulating the orbital state in a strongly correlated electron system is of
fundamental and technological importance for exploring and developing novel
electronic phases. Here, we report an unambiguous demonstration of orbital
occupancy control between t2g and eg multiplets in quasi-twodimensional
transition metal oxide superlattices (SLs) composed of a Mott insulator LaCoO3
and a band insulator LaAlO3. As the LaCoO3 sublayer thickness approaches its
fundamental limit (i.e. one unit-cell-thick), the electronic state of the SLs
changed from a Mott insulator, in which both t2g and eg orbitals are partially
filled, to a band insulator by completely filling (emptying) the t2g (eg)
orbitals. We found the reduction of dimensionality has a profound effect on the
electronic structure evolution, which is, whereas, insensitive to the epitaxial
strain. The remarkable orbital controllability shown here offers a promising
pathway for novel applications such as catalysis and photovoltaics, where the
energy of d level is an essential parameter.",1412.7139v1
2014-12-25,Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to CaRuO$_3$,"Density functional plus dynamical mean field calculations are used to show
that in transition metal oxides, rotational and tilting (GdFeO$_3$-type)
distortions of the ideal cubic perovskite structure produce a multiplicity of
low-energy optical transitions which affect the conductivity down to
frequencies of the order of $1$ or $2$~mV (terahertz regime), mimicking
non-Fermi-liquid effects even in systems with a strictly Fermi-liquid
self-energy. For CaRuO$_3$, a material whose measured electromagnetic response
in the terahertz frequency regime has been interpreted as evidence for
non-Fermi-liquid physics, the combination of these band structure effects and a
renormalized Fermi-liquid self-energy accounts for the low frequency optical
response which had previously been regarded as a signature of exotic physics.
Signatures of deviations from Fermi-liquid behavior at higher frequencies
($\sim 100$~meV) are discussed.",1412.7803v2
2015-01-20,Formation of hydroxylamine on dust grains via ammonia oxidation,"The quest to detect prebiotic molecules in space, notably amino acids,
requires an understanding of the chemistry involving nitrogen atoms.
Hydroxylamine (NH$_2$OH) is considered a precursor to the amino acid glycine.
Although not yet detected, NH$_2$OH is considered a likely target of detection
with ALMA. We report on an experimental investigation of the formation of
hydroxylamine on an amorphous silicate surface via the oxidation of ammonia.
The experimental data are then fed into a simulation of the formation of
NH$_2$OH in dense cloud conditions. On ices at 14 K and with a modest
activation energy barrier, NH$_2$OH is found to be formed with an abundance
that never falls below a factor 10 with respect to NH$_3$. Suggestions of
conditions for future observations are provided.",1501.04701v1
2015-01-27,Realization of a reversible switching in TaO2 polymorphs via Peierls distortion for resistance random access memory,"Transition-metal-oxide based resistance random access memory is a promising
candidate for next-generation universal non-volatile memories. Searching and
designing appropriate new materials used in the memories becomes an urgent
task. Here, a new structure with the TaO2 formula was predicted using
evolutionary algorithms in combination with first-principles calculations. This
new structure having a triclinic symmetry (T-TaO2) is both energetically and
dynamically more favorable than the commonly believed rutile structure
(R-TaO2). Our hybrid functional calculations show that T-TaO2 is a
semiconductor with a band gap of 1.0 eV, while R-TaO2 is a metallic conductor.
This large difference in electrical property makes TaO2 a potential candidate
for resistance random access memory (RRAM). Furthermore, we have shown that
T-TaO2 is actually a Peierls distorted R-TaO2 phase and the transition between
these two structures is via a directional displacement of Ta atoms. The energy
barrier for the reversible phase transition from R-TaO2 to T-TaO2 is 0.19
eV/atom and the other way around is 0.23 eV/atom, suggesting low power
consumption for the resistance switch. The present findings provide a new
mechanism for the resistance switch and will also stimulate experimental work
to fabricate tantalum oxides based RRAM.",1501.06632v1
2015-01-29,"Link between local iron coordination, Fe 2p XPS core level line shape and Mg segregation into thin magnetite films grown on MgO(001)","A well ordered Fe(001) ultra thin film epitaxially grown on MgO(001) has been
oxidized by post deposition annealing in oxygen atmosphere. LEED patterns
indicate the formation of magnetite (Fe$_3$O$_4$) after one hour of oxygen
exposure. The LEED pattern remains stable despite annealing the sample for
further four hours. In contrast X-ray Photoelectron Spectroscopy (XPS) of the
Fe $2p$ core levels suggests the formation of an iron oxide comprising mostly
of merely trivalent iron. This discrepancy is analyzed and discussed employing
charge transfer multiplet calculations for the Fe $2p$ XPS spectra. We find
that Mg ion segregation from the substrate into the magnetite thin film
replacing octahedrally coordinated Fe$^{2+}$ ions and the excess occupation of
octahedral sites which are unoccupied in the ideal inverse spinel structure are
driving forces for the altered shape of the Fe $2p$ XPS spectra. Different
potential models which might explain the nature of the Mg ion segregation into
the magnetite films are discussed.",1501.07443v1
2015-02-03,Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001),"Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using
reactive molecular beam epitaxy to investigate their structural properties and
their morphology. The film thickness either of the Fe3O4 film or of the NiO
film has been varied to shed light on the relaxation of the bilayer system. The
surface properties as studied by x-ray photo electron spectroscopy and low
energy electron diffraction show clear evidence of stoichiometric well-ordered
film surfaces. Based on the kinematic approach x-ray diffraction experiments
were completely analyzed. As a result the NiO films grow pseudomorphic in the
investigated thickness range (up to 34nm) while the Fe3O4 films relax
continuously up to the thickness of 50nm. Although all diffraction data show
well developed Laue fringes pointing to oxide films of very homogeneous
thickness, the Fe3O4-NiO interface roughens continuously up to 1nm
root-mean-square roughness with increasing NiO film thickness while the Fe3O4
surface is very smooth independent on the Fe3O4 film thickness. Finally, the
Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide
films while the NiO-MgO interface is expanded.",1502.00866v1
2015-02-04,Persistent semi-metal-like nature of epitaxial perovskite CaIrO3 thin films,"Strong spin-orbit coupled 5d transition metal based ABO3 oxides, especially
iridates, allow tuning parameters in the phase diagram and may demonstrate
important functionalities, for example, by means of strain effects and
symmetry-breaking, because of the interplay between the Coulomb interactions
and strong spin-orbit coupling. Here, we have epitaxially stabilized high
quality thin films of perovskite (Pv) CaIrO3. Film on the best lattice-matched
substrate shows semi-metal-like characteristics. Intriguingly, imposing tensile
or compressive strain on the film by altering the underlying lattice-mismatched
substrates still maintains semi-metallicity with minute modification of the
effective correlation as tensile (compressive) strain results in tiny increases
(decreases) of the electronic bandwidth. In addition, magnetoresistance remains
positive with a quadratic field dependence. This persistent semi-metal-like
nature of Pv-CaIrO3 thin films with minute changes in the effective correlation
by strain may provide new wisdom into strong spin-orbit coupled 5d based oxide
physics.",1502.01261v3
2015-02-06,Crack Formation in Ceramic Films Used in Solid Oxide Fuel Cells,"The manufacture of solid oxide fuel cells (SOFCs) involves fabrication of a
multilayer ceramic structure, for which constrained sintering is a key
processing step in many cases. Defects are often observed in the sintered
structure, but their formation during sintering is not well understood. In this
work, various ceramic films were fabricated by screen printing and a variety of
defects observed. Some films showed mud-cracking defects, whereas others
presented distributed large pores. Mud cracking defects were found to originate
from a network of fine cracks present in the green film and formed during
drying and binder burn-out. Control of these early stages is essential for
producing crack-free films. In order to investigate how defects evolve during
sintering, artificial cracks were introduced in the green films using
indentation. It was observed that crack opening always increased during
constrained sintering. In contrast, similar initial cracks could be closed and
healed during co-sintering.",1502.01878v1
2015-02-10,Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires,"We explore ballistic regime quantum transport characteristics of
oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale
empirical pseudopotential electronic structure framework, coupled to the
Kubo-Greenwood transport analysis. A real-space wave function study is
undertaken and the outcomes are interpreted together with the findings of
ballistic transport calculations. This reveals that ballistic transport edge
lies tens to hundreds of millielectron volts above the lowest unoccupied
molecular orbital, with a substantial number of localized states appearing in
between, as well as above the former. We show that these localized states are
not due to the oxide interface, but rather core silicon-derived. They manifest
the wave nature of electrons brought to foreground by the reflections
originating from NW junctions and bends. Hence, we show that the crossings and
kinks of even ultraclean Si NWs possess a conduction band tail without a
recourse to atomistic disorder.",1502.03033v1
2015-02-11,Combined AES/Factor Analysis and RBS Investigation of a Thermally Treated Pt/Ti Metallisation on SiO2,"Pt/Ti metallisation bilayers are used as bottom electrodes for ferroelectric
thin films. During deposition of the ferroelectric films, these electrodes are
exposed to elevated temperatures causing modifications of the Pt/Ti bottom
electrode. Diffusion and oxidation of the Ti adhesion layer have been studied
by the application of factor analysis to AES depth profile data and by RBS.
Factor analysis was employed to extract the chemical information from the
measured AES spectra and to derive semiquantitative depth profiles of the
identified material compounds. RBS was used to obtain the quantitative depth
distribution of the elements. By the combination of both methods, diffusion and
oxidation processes were observed and could be precisely describe.",1502.03413v1
2015-02-12,"Electroluminescence from isolated defects in zinc oxide, towards electrically triggered single photon sources at room temperature","Single photon sources are required for a wide range of applications in
quantum information science, quantum cryptography and quantum communications.
However, so far majority of room temperature emitters are only excited
optically, which limits their proper integration into scalable devices. In this
work, we overcome this limitation and present room temperature electrically
triggered light emission from localized defects in zinc oxide (ZnO)
nanoparticles and thin films. The devices emit at the red spectral range and
show excellent rectifying behavior. The emission is stable over an extensive
period of time, providing an important prerequisite for practical devices. Our
results open up possibilities to build new ZnO based quantum integrated devices
that incorporate solid-state single photon sources for quantum information
technologies.",1502.03735v1
2015-02-16,Photostimulation activates restorable fragmentation of single mitochondrion by initiating oxide flashes,"Mitochondrial research is important to ageing, apoptosis, and mitochondrial
diseases. In previous works, mitochondria are usually stimulated indirectly by
proapoptotic drugs to study mitochondrial development, which is in lack of
controllability, or spatial and temporal resolution. These chemicals or even
gene techniques regulating mitochondrial dynamics may also activate other
inter- or intra-cellular processes simultaneously. Here we demonstrate a
photostimulation method on single-mitochondrion level by tightly-focused
femtosecond laser that can precisely activate restorable fragmentation of
mitochondria which soon recover their original tubular structure after tens of
seconds. In this process, series of mitochondrial reactive oxygen species
(mROS) flashes are observed and found very critical to mitochondrial
fragmentation. Meanwhile, transient openings of mitochondrial permeability
transition pores (mPTP), suggested by oscillations of mitochondrial membrane
potential, contribute to the scavenging of redundant mROS and recovery of
fragmented mitochondria. Those results demonstrate photostimulation as an
active, precise and controllable method for the study of mitochondrial
oxidative and morphological dynamics or related fields.",1502.04591v2
2015-02-20,Giant switchable Rashba effect in oxide heterostructures,"One of the most fundamental phenomena and a reminder of the electron's
relativistic nature is the Rashba spin splitting for broken inversion symmetry.
Usually this splitting is a tiny relativistic correction, hardly discernible in
experiment. Interfacing a ferroelectric, BaTiO$_3$, and a heavy 5$d$ metal with
a large spin-orbit coupling, Ba(Os,Ir)O$_3$, we show that giant Rashba spin
splittings are indeed possible and even fully controllable by an external
electric field. Based on density functional theory and a microscopic tight
binding understanding, we conclude that the electric field is amplified and
stored as a ferroelectric Ti-O distortion which, through the network of oxygen
octahedra, also induces a large Os-O distortion. The BaTiO$_3$/BaOsO$_3$
heterostructure is hence the ideal test station for studying the fundamentals
of the Rashba effect. It allows intriguing application such as the Datta-Das
transistor to operate at room temperature.",1502.05870v1
2015-02-23,Creation of high mobility two-dimensional electron gases via strain induced polarization at an otherwise nonpolar complex oxide interface,"The discovery of two-dimensional electron gases (2DEGs) in SrTiO3-based
heterostructures provides new opportunities for nanoelectronics. Herein, we
create a new type of oxide 2DEG by the epitaxial-strain-induced polarization at
an otherwise nonpolar perovskite-type interface of CaZrO3/SrTiO3. Remarkably,
this heterointerface is atomically sharp, and exhibits a high electron mobility
exceeding 60,000 cm2V-1s-1 at low temperatures. The 2DEG carrier density
exhibits a critical dependence on the film thickness, in good agreement with
the polarization induced 2DEG scheme.",1502.06364v1
2015-02-25,Prediction of new thermodynamically stable aluminum oxides,"Recently, it has been shown that under pressure, unexpected and
counterintuitive chemical compounds become stable. Laser shock experiments (A.
Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition
of alumina with the formation of free Al and a mysterious transparent phase.
Inspired by these observations, with have explored the possibility of the
formation of new chemical compounds in the system Al-O. Using the
variable-composition structure prediction algorithm USPEX, in addition to the
well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to
be thermodynamically stable in the pressure range 330-443 GPa and above 332
GPa, respectively. Both of these compounds at the same time contain oxide O2-
and peroxide O22- ions, and both are insulating. Peroxo-groups are responsible
for gap states, which significantly reduce the electronic band gap of both
Al4O7 and AlO2.",1502.07012v1
2015-02-25,"Biophotons, coherence and photocount statistics: a critical review","Biological samples continuously emit ultra-weak photon emission (UPE, or
""biophotons"") which stems from electronic excited states generated chemically
during oxidative metabolism and stress. Thus, UPE can potentially serve as a
method for non-invasive diagnostics of oxidative processes or, if discovered,
also of other processes capable of electron excitation. While the fundamental
generating mechanisms of UPE are fairly elucidated together with their
approximate ranges of intensities and spectra, statistical properties of UPE is
still a highly challenging topic. Here we review claims about nontrivial
statistical properties of UPE, such as coherence and squeezed states of light.
After introduction to the necessary theory, we categorize the experimental
works of all authors to those with solid, conventional interpretation and those
with unconventional and even speculative interpretation. The conclusion of our
review is twofold; while the phenomenon of UPE from biological systems can be
considered experimentally well established, no reliable evidence for the
coherence or nonclassicality of UPE was actually achieved up to now.
Furthermore, we propose perspective avenues in the research of statistical
properties of biological UPE.",1502.07316v1
2015-03-10,A Universal Channel Model for Molecular Communication Systems with Metal-Oxide Detectors,"In this paper, we propose an end-to-end channel model for molecular
communication systems with metal-oxide sensors. In particular, we focus on the
recently developed table top molecular communication platform. The system is
separated into two parts: the propagation and the sensor detection. There is
derived, based on this, a more realistic end-to-end channel model. However,
since some of the coefficients in the derived models are unknown, we collect a
great deal of experimental data to estimate these coefficients and evaluate how
they change with respect to the different system parameters. Finally, a noise
model is derived for the system to complete an end-to-end system model for the
tabletop platform.",1503.02809v1
2015-03-12,Indium Tin Oxide film characterization using the classical Hall effect,"We have used the classical Hall effect to electrically characterize Indium
Tin Oxide (ITO) films grown by two different techniques on silica substrates.
ITO films have the unique property that they can be both electrically
conducting (and to be used for a gate electrode for example) as well as
optically transparent (at least in the visible part of the spectrum). In the
near infrared (NIR) the transmission typically reduces. However, the light
absorption can in principle be compensated by growing thinner films.",1503.03679v1
2015-03-12,"Watt-level, all-fiber, ultrafast Er/Yb-codoped double-clad fiber laser mode-locked by reduced graphene oxide interacting with a weak evanescent field","We propose a Watt-level, all-fiber, ultrafast Er/Yb-codoped double-clad fiber
laser passively mode-locked by reduced graphene oxide (rGO) interacting with a
weak evanescent field of photonic crystal fiber (PCF). The rGO solution is
filled into the cladding holes of the PCF based on total reflection, and after
evaporation, the rGO flakes bear only 1/107 of the total energy in laser
system, which enhances the thermal damage threshold and decreases the
accumulated nonlinearity. By incorporating the saturable absorber into an
Er/Yb-codoped fiber ring cavity, stable conventional soliton with a duration of
573 fs is generated, and a average output power up to 1.14 W is obtained.",1503.03748v1
2015-03-18,Observation of high angular momentum excitons in cuprous oxide,"The recent observation of dipole-allowed $P$-excitons up to principal quantum
numbers of $n=25$ in cuprous oxide has given insight into exciton states with
unprecedented spectral resolution. While so far the exciton description as a
hydrogen-like complex has been sufficient for cubic crystals, we demonstrate
here distinct deviations: The breaking of rotational symmetry leads to mixing
of high angular momentum $F$- and $H$-excitons with the $P$-excitons so that
they can be observed in absorption. The $F$-excitons show a three-fold
splitting that depends systematically on $n$, in agreement with theoretical
considerations. From detailed comparison of experiment and theory we determine
the cubic anisotropy parameter of the Cu$_2$O valence band.",1503.05517v1
2015-03-27,Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory,"In an oxide apertured quantum dot (QD) micropillar cavity-QED system, we
found strong QD hysteresis effects and lineshape modifications even at very low
intensities corresponding to less than 0.001 intracavity photons. We attribute
this to the excitation of charges by the intracavity field; charges that get
trapped at the oxide aperture, where they screen the internal electric field
and blueshift the QD transition. This in turn strongly modulates light
absorption by cavity QED effects, eventually leading to the observed hysteresis
and lineshape modifications. The cavity also enables us to observe the QD
dynamics in real time, and all experimental data agrees well with a power-law
charging model. This effect can serve as a novel tuning mechanism for quantum
dots.",1503.08142v1
2015-04-08,Giant Oscillating Thermopower at Oxide Interfaces,"Understanding the nature of charge carriers at the LaAlO3/SrTiO3 interface is
one of the major open issues in the full comprehension of the charge
confinement phenomenon in oxide heterostructures. Here, we investigate
thermopower to study the electronic structure in LaAlO3/SrTiO3 at low
temperature as a function of gate field. In particular, under large negative
gate voltage, corresponding to the strongly depleted charge density regime,
thermopower displays record-high negative values of the order of 10^4 - 10^5
microV/K, oscillating at regular intervals as a function of the gate voltage.
The huge thermopower magnitude can be attributed to the phonon-drag
contribution, while the oscillations map the progressive depletion and the
Fermi level descent across a dense array of localized states lying at the
bottom of the Ti 3d conduction band. This study is the first direct evidence of
a localized Anderson tail in the two-dimensional (2D) electron liquid at the
LaAlO3/SrTiO3 interface.",1504.01901v1
2015-04-17,Temporal and Dose Kinetics of Tunnel Relaxation of Non-Equilibrium Near-Interfacial Charged Defects in Insulators,"This paper is devoted mainly to mathematical aspects of modeling and
simulation of tunnel relaxation of nonequilibrium charged oxide traps located
at/near the interface insulator - conductive channel, for instance in
irradiated MOS devices. The generic form of the tunnel annealing response
function was derived from the rate equation for the charged defect buildup and
annealing as a linear superposition of the responses of different defects with
different time constants. Using this linear response function, a number of
important practical problems are analyzed and discussed. Combined tunnel and
thermal or RICN annealing, power-like temporal relaxation after a single ion
strike into the gate oxide, are described in context of general approach.",1504.04525v1
2015-05-07,Suppression of excess oxygen for environmentally stable amorphous In-Si-O thin-film transistors,"We discuss the environmental instability of amorphous indium oxide
(InOx)-based thin-film transistors (TFTs) in terms of the excess oxygen in the
semiconductor films. A comparison between amorphous InOx doped with low and
high concentrations of oxygen binder (SiO2) showed that out-diffusion of oxygen
molecules causes drastic changes in the film conductivity and TFT turn-on
voltages. Incorporation of sufficient SiO2 could suppress fluctuations in
excess oxygen because of the high oxygen bond-dissociation energy and low Gibbs
free energy. Consequently, the TFT operation became rather stable. The results
would be useful for the design of reliable oxide TFTs with stable electrical
properties.",1505.01628v1
2015-05-19,Flexible Sensory Platform Based on an Electrolyte-Gated Oxide Neuron Transistor,"Inspired by the dendritic integration and spiking operation of a biological
neuron, flexible oxide-based neuron transistors gated by solid-state
electrolyte films are fabricated on flexible plastic substrates for biochemical
sensing applications. When a quasi-static dual-gate laterally synergic sensing
mode is adopted, the neuron transistor sensor shows a high pH sensitivity of
~105 mV/pH, which is higher than the Nernst limit. Our results demonstrate that
single-spike dynamic mode can remarkably improve the pH sensitivity, reduce
response/recover time and power consumption. We also find that appropriate
depression applied on the sensing gate electrode can further enhance the pH
sensitivity and reduce the power consumption. Our flexible neuron transistors
provide a new-concept sensory platform for biochemical detection with high
sensitivity, rapid response and ultralow power consumption.",1505.04964v1
2015-05-26,Functionalized graphene as a model system for the two-dimensional metal-insulator transition,"Reports of metallic behavior in two-dimensional (2D) systems such as high
mobility metal-oxide field effect transistors, insulating oxide interfaces,
graphene, and MoS2 have challenged the well-known prediction of Abrahams, et
al. that all 2D systems must be insulating. The existence of a metallic state
for such a wide range of 2D systems thus reveals a wide gap in our
understanding of 2D transport that has become more important as research in 2D
systems expands. A key to understanding the 2D metallic state is the
metal-insulator transition (MIT). In this report, we demonstrate the existence
of a disorder induced MIT in functionalized graphene, a model 2D system.
Magneto-transport measurements show that weak-localization overwhelmingly
drives the transition, in contradiction to theoretical assumptions that
enhanced electron-electron interactions dominate. These results provide the
first detailed picture of the nature of the transition from the metallic to
insulating states of a 2D system.",1505.07053v1
2015-05-29,An in- and ex-situ TEM study into the oxidisation of titanium (IV) sulphide,"The degradation of liquid dispersed titanium (IV) sulphide (TiS$_2$) is
studied from the point of view of oxidisation. TiS$_2$ is a layered
two-dimensional nanomaterial, with potential for energy storage applications.
However, flakes in dispersion were observed to degrade. We examined two
oxidisation routes: deionised water at room temperature and oxygen gas within
the temperature range 150-350{\deg}C. Water was seen to slowly oxidise flakes
inwards from the edge, forming an amorphous oxide, a result comparable to the
state of flakes which degraded within the original dispersion. Oxygen gas was
seen to rapidly oxidise entire flakes to a polycrystalline oxide, when heated
275 {\deg}C and above. Degradation was studied with scanning transmission
electron microscopy (STEM), energy dispersed x-ray spectroscopy (EDX) and
electron energy-loss spectroscopy (EELS). Density Functional Theory
calculations have shown oxidisation by both water and gas molecules to be
thermodynamically favourable.",1505.08074v1
2015-06-01,Lattice correlation of Hubbard excitons in a Mott insulator Sr2IrO4 and reconstruction of their hopping dynamics via time-dependent coherence analysis of the Bragg diffraction,"In correlated oxides the coupling of quasiparticles to other degrees of
freedom such as spin and lattice plays critical roles in the emergence of
symmetry-breaking quantum ordered states such as high temperature
superconductivity. We report a strong lattice coupling of photon induced
Hubbard excitonic quasiparticles in spin-orbital coupling Mott insulator
Sr2IrO4. Combining time-resolved optical spectroscopy techniques, we further
reconstructed spatiotemporal map of the diffusion of quasiparticles via
time-dependent coherence analysis of the x-ray Bragg diffraction peak. Due to
the unique electronic configuration of the exciton, the strong lattice
correlation is unexpected but extends the similarity between Sr2IrO4 and
cuprates under highly non-equilibrium conditions. The coherence analysis method
we developed may have important implications for characterizing the structure
and carrier dynamics in a wider group of oxide heterostructures.",1506.00630v1
2015-06-11,Surface diffusion control of the photocatalytic oxidation in air/TiO2 heterogeneous reactors,"The diffusion of superoxide radical anions on the surface of TiO2 catalysts
is theoretically considered as an important step in the kinetics of
photocatalytic oxidation of toxic pollutants. A detailed analysis is performed
to discriminate the effects of rotation, anion and adsorption bonds vibrations
on the diffusion coefficient. A resonant dependence of the diffusivity on the
lattice parameters of the TiO2 surface is discovered showing that the most
rapid diffusion takes place when the lattice parameters are twice larger than
the bond length of the superoxide radical anions. Whereas the rotation and
vibrations normal to the catalyst surface are important, the anion bond
vibrations do not affect the diffusivity due to their low amplitudes as
compared to the lattice parameters.",1506.03581v2
2015-06-15,Phase separation from electron confinement at oxide interfaces,"Oxide heterostructures are of great interest both for fundamental and
applicative reasons. In particular the two-dimensional electron gas at the
LaAlO$_3$/SrTiO$_3$ or LaTiO$_3$/SrTiO$_3$ interfaces displays many different
physical properties and functionalities. However there are clear indications
that the interface electronic state is strongly inhomogeneous and therefore it
is crucially relevant to investigate possible intrinsic electronic mechanisms
underlying this inhomogeneity. Here the electrostatic potential confining the
electron gas at the interface is calculated self-consistently, finding that the
electron confinement at the interface may induce phase separation, to avoid a
thermodynamically unstable state with a negative compressibility. This provides
a generic robust and intrinsic mechanism for the experimentally observed
inhomogeneous character of these interfaces.",1506.04777v1
2015-06-28,"Nitrogen oxides under pressure stability, ionization, polymerization, and superconductivity","Nitrogen oxides are textbook class of molecular compounds, with extensive
industrial applications. Nitrogen and oxygen are also among the most abundant
elements in the universe. We explore the N-O system at 0 K and up to 500 GPa
though ab initio evolutionary simulations. Results show that two phase
transformations of stable molecular NO2 exist at 7 and 64 GPa, and followed by
decomposition of NO2 at 91 GPa. All of the NO+NO3- structures are found to be
metastable at T=0 K, so experimentally reported ionic NO+NO3- is either
metastable or stabilized by temperature. Upon increasing pressure, N2O5
transforms from P-1 to C2/c structure at 51 GPa. NO becomes thermodynamically
stable at 198 GPa. This polymeric phase is superconducting (Tc = 2.0 K) and
contains a -N-N- backbone.",1506.08362v1
2015-06-29,New class of planar ferroelectric Mott insulators via first principles design,"Inorganic perovskite oxide ferroelectrics have recently generated substantial
interest for photovoltaic applications; however, existing materials suffer from
excessive electronic band gaps and insufficient electric polarization. The
recent resurgence of hybrid perovskite ferroelectrics addresses the
aforementioned deficiencies, but they are highly unstable against environmental
effects and an inorganic resolution may still be optimal. Here we use
first-principles calculations to design a low band gap, planar ferroelectric by
leveraging the complexity of layered double perovskite oxides AA$^\prime
$BB$^\prime$O$_6$. We exploit A$\ne$A$^\prime$ size mismatch, a nominally empty
$d$-shell on the B-site, and A cations bearing lone-pair electrons to achieve a
large ferroelectric polarization. Additionally, B$^\prime\ne$B is chosen to
achieve full charge transfer and a Mott susceptible filling on the
B$^\prime$-site, yielding a low band gap. These principles are illustrated in
BaBiCuVO$_6$, BaBiNiVO$_6$, BaLaCuVO$_6$, and PbLaCuVO$_6$, which could be
realized in layer-by-layer growth. This new class of materials could lead to
stable, high-efficiency photovoltaic.",1506.08855v1
2015-07-06,Implementing odd-axions in dimensional oxidation of non-geometric type IIB action,"In a setup of type IIB superstring compactification on an orientifold of a
${\mathbb T}^6/{\mathbb Z}_4$ sixfold, the presence of geometric flux
($\omega$) and non-geometric fluxes ($Q, R$) is implemented along with the
standard NS-NS and RR three-form fluxes ($H, F$). After computing the F/D-term
contributions to the ${\cal N}=1$ four dimensional effective scalar potential,
we rearrange the same into `suitable' pieces by using a set of new generalized
flux orbits. Subsequently, we dimensionally oxidize the various pieces of the
total four dimensional scalar potential to guess their ten-dimensional origin.",1507.01612v3
2015-07-18,Addressing the Challenges of Using Ferromagnetic Electrodes in the Molecular Spintronics Devices,"Ferromagnetic electrodes chemically bonded with thiol functionalized
molecules can produce novel molecular spintronics devices. However, major
challenges lie in developing Ferromagnetic electrodes based commercially viable
device fabrication scheme that consider the susceptibility of ferromagnetic
electrodes to oxidation, chemical etching, and stress induced deformations
during fabrication and usage. This paper studies NiFe, an alloy used in the
present day memory devices and high-temperature engineering applications, as a
candidate FM electrode for the fabrication of MSDs. Our spectroscopic
reflectance studies show that NiFe start oxidizing aggressively beyond 90 C.
The NiFe surfaces, aged for several months or heated for several minutes below
90 C, exhibited remarkable electrochemical activity and were suitable for
chemical bonding with the thiol functionalized molecular device elements. NiFe
also demonstrated excellent etching resistance and minimized the mechanical
stress induced deformities. This paper demonstrates the successful utilization
of NiFe electrodes in the tunnel junction based molecular device fabrication
approach. This paper is expected to fill the knowledge gap impeding the
experimental development of ferromagnetic electrode based molecular spintronics
devices for realizing novel logic and memory devices and observing a numerous
theoretically predicted phenomenon.",1507.05146v1
2015-07-21,Compensation for TID Damage in SOI Pixel Devices,"We are investigating adaption of SOI pixel devices for future high energy
physic(HEP) experiments. The pixel sensors are required to be operational in
very severe radiation environment. Most challenging issue in the adoption is
the TID (total ionizing dose) damage where holes trapped in oxide layers affect
the operation of nearby transistors. We have introduced a second SOI layer -
SOI2 beneath the BOX (Buried OXide) layer - in order to compensate for the TID
effect by applying a negative voltage to this electrode to cancel the effect
caused by accumulated positive holes. In this paper, the TID effects caused by
Co gamma-ray irradiation are presented based on the transistor characteristics
measurements. The irradiation was carried out in various biasing conditions to
investigate hole accumulation dependence on the potential configurations. We
also compare the data with samples irradiated with X-ray. Since we observed a
fair agreement between the two irradiation datasets, the TID effects have been
investigated in a wide dose range from 100~Gy to 2~MGy.",1507.05860v1
2015-07-25,Chemical Bondings Induced Rich Electronic Properties of Oxygen Absorbed Few-layer Graphenes,"Electronic properties of graphene oxides enriched by the strong chemical
bondings are investigated using first-principle calculations. They are very
sensitive to the changes in the number of graphene layer, stacking
configuration, and distribution of oxygen. The feature-rich electronic
structures exhibit the destruction or distortion of Dirac cone, opening of band
gap, anisotropic energy dispersions, O- and (C,O)-dominated energy dispersions,
and extra critical points. All the few-layer graphene oxides are semi-metals
except for the semiconducting monolayer ones. For the former, the distorted
Dirac-cone structures and the O-dominated energy bands near the Fermi level are
revealed simultaneously. The orbital-projected density of states (DOS) have
many special structures mainly coming from a composite energy band, the
parabolic and partially flat ones. The DOS and spatial charge distributions
clearly indicate the critical bondings in O-O, C-O and C-C bonds, being
responsible for the diversified properties.",1507.07057v1
2015-07-26,New ground states of fluorinated and oxidized phosphorene: structural and electronic properties,"We systematically explore chemical functionalization of monolayer black
phosphorene via chemisorption of oxygen and fluorine atoms. Using the cluster
expansion technique, with vary- ing concentration of the adsorbate, we
determine the ground states considering both single- as well as double- side
chemisorption, which have novel chemical and electronic properties. The nature
of the bandgap depends on the concentration of the adsorbate: for fluorination
the direct bandgap first decreases, and then increases while becoming indirect,
with increasing fluorination, while for oxidation the bandgap first increases
and then decreases, while mostly maintaining its direct nature. Further we find
that the unique anisotropic free-carrier effective mass for both the electrons
and holes, can be changed and even rotated by 90 degrees, with controlled
chemisorption, which can be useful for exploring unusual quantum Hall effect,
and novel electronic devices based on phosphorene.",1507.07230v3
2015-08-07,Interplay between O defects and SiC stacking at the SiC/SiO$_2$ interface,"We investigate the effect of SiC stacking on the 4H-SiC/SiO$_2$ interface,
both in the presence and absence of O defects, which appear during thermal
oxidation, via first principles calculations. It is known that 4H-SiC(0001) has
two different surface types, depending on which of the two lattice sites, $h$
or $k$, is at the surface [K. Arima \textit{et al}., Appl. Phys. Lett.
\textbf{90}, 202106 (2007)]. We find interlayer states along the conduction
band edge of SiC, whose location changes depending on the interface type, and
thus too the effect of defects. When $h$ sites are directly at the interface, O
defects remove interfacial conduction band edge states. On the other hand, when
$k$ sites are at the interface, the conduction band edge is insensitive to the
presence of O defects. These differences will impact on the operation of SiC
devices because the most commonly used SiC based metal-oxide-semiconductor
field-effect transistors rely on the electronic structure of the conduction
band.",1508.01590v1
2015-08-11,Multilayer Layer Graphene Nanoribbon Flash Memory: Analysis of Programming and Erasing Operation,"Flash memory based on floating gate transistor is the most widely used memory
technology in modern microelectronic applications. We recently proposed a new
concept of multilayer graphene nanoribbon (MLGNR) and carbon nanotube (CNT)
based floating gate transistor design for future nanoscale flash memory
technology. In this paper, we analyze the tunneling current mechanism in the
proposed graphene-CNT floating gate transistor. We anticipate that the proposed
floating gate transistor would adopt Fowler-Nordheim (FN) tunneling during its
programming and erase operations. In this paper, we have investigated the
mechanism of tunneling current and the factors that would influence this
current and the behavior of the proposed floating gate transistor. The analysis
reveals that FN tunneling is a strong function of the high field induced by the
control gate, and the thicknesses of the control oxide and the tunnel oxide.",1508.02590v1
2015-08-19,Electric field control of spin lifetimes in Nb-SrTiO$_3$ by spin-orbit fields,"We show electric field control of the spin accumulation at the interface of
the oxide semiconductor Nb-SrTiO$_{3}$ with Co/AlO$_{x}$ spin injection
contacts at room temperature. The in-plane spin lifetime $\tau_\parallel$ as
well as the ratio of the out-of-plane to in-plane spin lifetime
$\tau_\perp/\tau_\parallel$ is manipulated by the built-in electric field at
the semiconductor surface, without any additional gate contact. The origin of
this manipulation is attributed to Rashba Spin-Orbit Fields (SOFs) at the
Nb-SrTiO$_3$ surface and shown to be consistent with theoretical model
calculations based on SOF spin flip scattering. Additionally, the junction can
be set in a high or low resistance state, leading to a non-volatile control of
$\tau_\perp/\tau_\parallel$, consistent with the manipulation of the Rashba SOF
strength. Such room temperature electric field control over the spin state is
essential for developing energy-efficient spintronic devices and shows promise
for complex oxide based (spin)electronics",1508.04649v1
2015-08-29,Degradation of Phosphorene in Air: Understanding at Atomic Level,"Phosphorene is a promising two dimensional (2D) material with a direct band
gap, high carrier mobility, and anisotropic electronic properties.
Phosphorene-based electronic devices, however, are found to degrade upon
exposure to air. In this paper, we provide an atomic level understanding of
stability of phosphorene in terms of its interaction with O2 and H2O. The
results based on density functional theory together with first principles
molecular dynamics calculations show that O2 could spontaneously dissociate on
phosphorene at room temperature. H2O will not strongly interact with pristine
phosphorene, however, an exothermic reaction could occur if phosphorene is
first oxidized. The pathway of oxidation first followed by exothermic reaction
with water is the most likely route for the chemical degradation of the
phosphorene-based devices in air.",1508.07461v2
2015-09-15,Non-linear photochemical pathways in laser induced atmospheric aerosol formation,"We measured the chemical composition and the size distribution of aerosols
generated by femtosecond-Terawatt laser pulses in the atmosphere using an
aerosol mass spectrometer (AMS). We show that nitric acid condenses in the form
of ammonium nitrate, and that oxidized volatile organics also contribute to
particle growth. These two components account for two thirds and one third,
respectively, of the dry laser-condensed mass. They appear in two different
modes centred at 380 nm and 150 nm. The number concentration of particles
between 25 and 300 nm increases by a factor of 15. Pre-existing water droplets
strongly increase the oxidative properties of the laser-activated atmosphere,
substantially enhancing the condensation of organics under laser illumination.",1509.04600v1
2015-09-23,Ferroelectric thermal phase transition and polarization precursor dynamics in CaxBa1-xNb2O6(CBN) tungsten bronze type oxides,"Polycrystals of CaxBa1-xNb2O6(CBN) tungsten bronze type oxides have been
prepared and their structural, dielectric, and thermal properties have been
investigated. It was found that CBN alloys with ferroelectric tetragonal
tungsten bronze structure were only available in a composition range of 0.19 <=
x <= 0.32. It was also showed that CBN can be classified as a ferroelectric
with a first-order thermal phase transition showing polarization precursor
dynamics before transition into the ferroelectric phase, in sharp contrast to
an isostructural alloy SrxBa1-xNb2O6(SBN) that shows typical relaxor behaviors.
The local polarizations were found to grow exponentially within the
paraelectric mother phase in a large temperature range of Tc<T<Tc+ 88~140 K on
cooling. Furthermore, a phase diagram was established for CBN ferroelectric
alloys. These findings may get an insight into the true nature of ferroelectric
phase transition in this potential electro-optic material.",1509.06852v1
2015-09-24,First observation of temperature dependent lightinduced response of Ge25As10Se65 thin films,"Ge rich ternary chalcogenide glasses (ChG) exhibit photobleaching (PB) when
illuminated with bandgap light and such an effect is originating from the
combined effect of intrinsic structural changes and photo-oxidation. In a sharp
contradict to these previous observations, in this letter, we demonstrate for
the first time that Ge rich Ge25As10Se65 ChG thin films exhibit photodarkening
(PD) at 20 K and PB at 300 and 420 K for continuous illumination of ~ 3 hours.
Strikingly, the temporal evolution of PD/PB show distinct characteristics at
the temperatures of illumination and provide valuable information on the light
induced structural changes. Further, structure specific far infrared (FIR)
absorption measurements give direct evidence of different structural units
involved in PD/PB at the contrasting temperatures. By comparing the
lightinduced effects in vacuum and air, we conclude that intrinsic structural
changes dominate over photo-oxidation in the observed PB in Ge25As10Se65 ChG
thin films.",1509.07412v1
2015-10-07,Layer-by-Layer Dielectric Breakdown of Hexagonal Boron Nitride,"Hexagonal boron nitride (BN) is widely used as a substrate and gate insulator
for two-dimensional (2D) electronic devices. The studies on insulating
properties and electrical reliability of BN itself, however, are quite limited.
Here, we report a systematic investigation of the dielectric breakdown
characteristics of BN using conductive atomic force microscopy. The electric
field strength was found to be ~12 MV/cm, which is comparable to that of
conventional SiO2 oxides because of the covalent bonding nature of BN. After
the hard dielectric breakdown, the BN fractured like a flower into equilateral
triangle fragments. However, when the applied voltage was terminated precisely
in the middle of the dielectric breakdown, the formation of a hole that did not
penetrate to the bottom metal electrode was clearly observed. Subsequent I-V
measurements of the hole indicated that the BN layer remaining in the hole was
still electrically inactive. Based on these observations, layer-by-layer
breakdown was confirmed for BN with regard to both physical fracture and
electrical breakdown. Moreover, statistical analysis of the breakdown voltages
using a Weibull plot suggested the anisotropic formation of defects. These
results are unique to layered materials and unlike the behavior observed for
conventional 3D amorphous oxides.",1510.01930v1
2015-10-16,Thermodynamics of the Oxygen Evolution Electrocatalysis in Metal-Organic Frameworks,"Metal-organic frameworks (MOFs) provide a versatile and tailorable material
platform that embody many desirable attributes for photocatalytic
water-splitting. The approach taken in this study was to use Density Functional
Theory (DFT) to predict the thermodynamic energy barriers of the oxygen
evolution reaction (OER) for three MOF functionalizations. A Zr-MIL-125 MOF
design was selected for this study that incorporates three linker designs, a
1,4-benzenedicarboxylate (BDC), BDC functionalized with an amino group
(BDC+NH2), and BDC functionalized with nitro group (BDC+NO2). The study found
several key differences between homogeneous planar catalyst thermodynamics and
MOF based thermodynamics, the most significant being the non-unique or
heterogeneity of reaction sites. Additionally, the funcationalization of the
MOF was found to significantly influence the hydroperoxyl binding energy, which
proves to be the largest hurdle for both oxide and MOF based catalyst. Both of
these findings provide evidance that many of the limitations precluding planar
homogeneous catalysts can be surpassed with a MOF based catalyst. While none of
the MOF designs selected for this study out-performed state-of-the-art oxide
based catalysts, the BDC+NH2 proved to be the best with a predicted
over-potential for spontaneous OER evolution to be 3.03eV.",1510.04851v1
2015-10-30,Design of Mott and topological phases on buckled 3d-oxide honeycomb lattices,"Perovskite bilayers with (111)-orientation combine a honeycomb lattice as a
key feature with the strongly correlated, multiorbital nature of electrons in
transition metal oxides. In a systematic DFT+$U$ study of (111)-oriented
(La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$ superlattices, we establish trends in the
evolution of ground states versus band filling in (111)-oriented
(La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$ superlattices, with $X$ spanning the entire
$3d$ transition metal series. The competition between local quasi-cubic and
global triangular symmetry triggers unanticipated broken symmetry phases, with
mechanisms ranging from Jahn-Teller distortions, to charge-, spin-, and
orbital-ordering. LaMnO$_3$, where spin-orbit coupling opens a sizable gap in
the Dirac-point Fermi surface, emerges as a topological Chern insulator.",1510.09177v1
2015-11-01,Ab initio GW plus cumulant calculation for isolated band system: Application to organic conductor (TMTSF)2PF6 and transition-metal oxide SrVO3,"We present ab initio GW plus cumulant-expansion calculations for an organic
compound (TMTSF)2PF6 and a transition-metal oxide SrVO3. These materials
exhibit characteristic low-energy band structures around the Fermi level, which
bring about interesting low-energy properties; the low-energy bands near the
Fermi level are isolated from the other bands and, in the isolated bands,
unusually low-energy plasmon excitations occur. To study the effect of this
low-energy-plasmon fluctuation on the electronic structure, we calculate
spectral functions and photoemission spectra using the ab initio cumulant
expansion of the Green's function based on the GW self-energy. We found that
the low-energy plasmon fluctuation leads to an appreciable renormalization of
the low-energy bands and a transfer of the spectral weight into the incoherent
part, thus resulting in an agreement with experimental photoemission data.",1511.00218v1
2015-11-02,On the modeling and simulation of reaction-transfer dynamics in semiconductor-electrolyte solar cells,"The mathematical modeling and numerical simulation of
semiconductor-electrolyte systems play important roles in the design of
high-performance semiconductor-liquid junction solar cells. In this work, we
propose a macroscopic mathematical model, a system of nonlinear partial
differential equations, for the complete description of charge transfer
dynamics in such systems. The model consists of a
reaction-drift-diffusion-Poisson system that models the transport of electrons
and holes in the semiconductor region and an equivalent system that describes
the transport of reductants and oxidants, as well as other charged species, in
the electrolyte region. The coupling between the semiconductor and the
electrolyte is modeled through a set of interfacial reaction and current
balance conditions. We present some numerical simulations to illustrate the
quantitative behavior of the semiconductor-electrolyte system in both dark and
illuminated environments. We show numerically that one can replace the
electrolyte region in the system with a Schottky contact only when the bulk
reductant-oxidant pair density is extremely high. Otherwise, such replacement
gives significantly inaccurate description of the real dynamics of the
semiconductor-electrolyte system.",1511.00417v1
2015-11-16,Detection of the adsorption of water monolayers through the ion oscillation frequency in the magnesium oxide lattice by means of Low Energy Electron Diffraction,"We investigate the variation of the oscillation frequency of the Mg$^{2+}$
and O$^{2-}$ ions in the magnesium oxide lattice due to the interactions of the
surface with water monolayers by means of Low Energy Electron Diffraction. Our
key result is a new technique to determine the adsorbate vibrations produced by
the water monolayers on the surface lattice as a consequence of their change in
the surface Debye temperature and its chemical shift. The latter was
systematically investigated for different annealing times and for a constant
external thermal perturbation in the range of 110-300 K in order to accomplish
adsorption or desorption of water monolayers in the surface lattice.",1511.05074v1
2015-11-17,Deviations of the exciton level spectrum in cuprous oxide from the hydrogen series,"Recent high-resolution absorption spectroscopy on excited excitons in cuprous
oxide [Nature (London) 514, 343 (2014)] has revealed significant deviations of
their spectrum from that of the ideal hydrogen-like series. Here we show that
the complex band dispersion of the crystal, which determines the kinetic energy
of electrons and holes, strongly affects the exciton binding energy.
Specifically, we show that the nonparabolicity of the band dispersion is the
main cause of the deviation from the hydrogen series. Experimental data
collected from high-resolution absorption spectroscopy in electric fields
validate the assignment of the deviation to the nonparabolicity of the band
dispersion.",1511.05458v2
2015-11-19,Symmetry-driven atomic rearrangement at a brownmillerite-perovskite interface,"Many of the recent advancements in oxide heterostructures have been
attributed to modification of spin, charge, lattice, and orbital order
parameters at atomically well-defined interfaces. However, the details on the
structural, chemical, and electrostatic evolution of interfaces comprised of
materials with different crystallographic symmetries remain to be understood.
In this work, we have mapped out the interfacial connectivity of atoms of two
dissimilar materials, the perovskite SrTiO3 and the brownmillerite SrCoO2.5,
using high resolution scanning transmission electron microscopy and geometric
phase analysis. We observed unique symmetry-mismatch driven atomic
displacements restricted to only the first few atomic layers, which can
critically modify the properties of the system. Provided that SrCoO2.5 is a
promising energy material due to its open framework structure, the improved
understanding of the interfacial structure on the atomic level can lead to the
rational design of novel oxide heterostructures.",1511.06405v1
2015-11-24,Field Effect Transistors with Sub-Micrometer Gate Lengths Fabricated from LaAlO$_3$-SrTiO$_3$-Based Heterostructures,"The possible existence of short-channel effects in oxide field-effect
transistors is investigated by exploring field-effect transistors with various
gate lengths fabricated from LaAlO$_3$-SrTiO$_3$ heterostructures. The studies
reveal the existence of channel-length modulation and drain-induced barrier
lowering for gate lengths below 1 {\mu}m, with a characteristic behavior
comparable to semiconducting devices. With the fabrication of field-effect
transistors with gate lengths as small as 60 nm the results demonstrate the
possibility to fabricate by electron-beam lithography functional devices based
on complex oxides with characteristic lengths of several ten nanometers.",1511.07680v1
2016-01-20,In-vacuum scattered light reduction with cupric oxide surfaces for sensitive fluorescence detection,"We demonstrate a simple and easy method for producing low-reflectivity
surfaces that are ultra-high vacuum compatible, may be baked to high
temperatures, and are easily applied even on complex surface geometries. Black
cupric oxide (CuO) surfaces are chemically grown in minutes on any copper
surface, allowing for low-cost, rapid prototyping and production. The
reflective properties are measured to be comparable to commercially available
products for creating optically black surfaces. We describe a vacuum apparatus
which uses multiple blackened copper surfaces for sensitive, low-background
detection of molecules using laser-induced fluorescence.",1601.05308v1
2016-02-03,Direct Observation of Localized Radial Oxygen Migration in Functioning Tantalum Oxide Memristors,"Oxygen migration in tantalum oxide, a promising next-generation storage
material, is studied using in-operando x-ray absorption spectromicroscopy and
is used to microphysically describe accelerated evolution of conduction channel
and device failure. The resulting ring-like patterns of oxygen concentration
are modeled using thermophoretic forces and Fick diffusion, establishing the
critical role of temperature-activated oxygen migration that has been under
question lately.",1602.01204v2
2016-02-02,Linewidths in excitonic absorption spectra of cuprous oxide,"We present a theoretical calculation of the absorption spectrum of cuprous
oxide $\left(\mathrm{Cu_{2}O}\right)$ based on the general theory developed by
Y. Toyozawa. An inclusion not only of acoustic phonons but also of optical
phonons and of specific properties of the excitons in $\mathrm{Cu_{2}O}$ like
the central-cell corrections for the $1S$-exciton allows us to calculate the
experimentally observed line widths in experiments by T. Kazimierczuk et al
[Nature 514, 343, (2014)] within the same order of magnitude, which
demonstrates a clear improvement in comparison to earlier work on this topic.
We also discuss a variety of further effects, which explain the still
observable discrepancy between theory and experiment but can hardly be included
in theoretical calculations.",1602.01813v1
2016-02-11,Enhanced bifunctional oxygen catalysis in strained LaNiO3 perovskites,"Strain is known to greatly influence low temperature oxygen electrocatalysis
on noble metal films, leading to significant enhancements in bifunctional
activity essential for fuel cells and metal-air batteries. However, its
catalytic impact on transition metal oxide thin films, such as perovskites, is
not widely understood. Here, we epitaxially strain the conducting perovskite
LaNiO3 to systematically determine its influence on both the oxygen reduction
and oxygen evolution reaction. Uniquely, we found that compressive strain could
significantly enhance both reactions, yielding a bifunctional catalyst that
surpasses the performance of noble metals such as Pt. We attribute the improved
bifunctionality to strain-induced splitting of the eg orbitals, which can
customize orbital asymmetry at the surface. Analogous to strain-induced shifts
in the d-band center of noble metals relative to Fermi level, such splitting
can dramatically affect catalytic activity in this perovskite and other
potentially more active oxides.",1602.03858v1
2016-02-12,Nanopatterning process based on epitaxial masking for the fabrication of electronic and spintronic devices made of La0.67Sr0.33MnO3/LaAlO3/SrTiO3 heterostructures with in situ interfaces,"The fabrication of oxide electronics devices is presently hindered by the
lack of standardized and well established patterning procedures, applicable
down to the nanoscale. In this work, the authors propose a procedure to obtain
patterns with resolution around 100 nm on (La,Sr)MnO3/LaAlO3/SrTiO3
heterostructures. Our method is based on a multistep technique, which includes
wet and dry etching, epitaxial masking, and e-beam lithography. Our procedure
is devised to define independent patterns on the interfacial two dimensional
electron gas and on the metallic top electrode, while preserving an all-in situ
approach for the heterostructure growth. The authors show results on nano-scale
devices based on (La,Sr)MnO3/LaAlO3/SrTiO3, suitable for oxide spintronics
applications.",1602.04108v1
2016-02-18,"Uniting Superhydrophobic, Superoleophobic and Lubricating Fluid Infused Slippery Behavior on Copper Oxide Nano-structured Substrates","Copper oxide nanostructures with spherical (0D), needle (1D) and hierarchical
cauliflower (3D) morphologies are used to demonstrate superhydrophobic,
superoleophobic and slippery behavior. These nanostructures are synthesized on
galvanized steel substrates using a simple chemical bath deposition method by
tuning precursor concentration. Subsequent coating of low surface energy
polymer, polydimethylsiloxane, results in superhydrophobicity with water
contact angle ~160(2){\deg} and critical sliding angle ~2{\deg}. When
functionalized with low-surface energy perfluoroalkyl silane, these surfaces
display high repellency for low surface tension oils and hydrocarbons. Among
them, the hierarchical cauliflower morphology exhibits better re-entrant
structure thus show the best superoleophobicity with 149{\deg} contact angle
for dodecane having surface tension 25.3 mNm-1. If these nanostructured
substrates are infused with lubricant Silicone oil, they show excellent
slippery behavior for water drops. Due to the lubricating nature of Silicone
oil, the Silicone oil infused slippery surfaces (SOIS) show low contact angle
hysteresis (~2{\deg}) and critical tilt angle (~2{\deg}). The hierarchical
cauliflower nanostrcuture exhibit better slippery characteristics and stability
compared to the other nanostructured surfaces.",1602.05813v1
2016-02-24,"Mechanisms for p-type behavior of ZnO, Zn$_{1-x}$Mg$_x$O and related oxide semiconductors","Possibilities of turning intrinsically n-type oxide semiconductors like ZnO
and Zn$_{1-x}$Mg$_x$O into p-type materials are investigated. Motivated by
recent experiments on Zn$_{1-x}$Mg$_x$O doped with nitrogen we analyze the
electronic defect levels of point defects N$_{{\rm O}}$, v$_{{\rm Zn}}$, and
N$_{{\rm O}}$-v$_{{\rm Zn}}$ pairs in ZnO and Zn$_{1-x}$Mg$_x$O by means of
self-interaction-corrected density functional theory calculations. We show how
the interplay of defects can lead to shallow acceptor defect levels, although
the levels of individual point defects N$_{{\rm O}}$ are too deep in the band
gap for being responsible for p-type conduction. We relate our results to
p-type conduction paths at grain boundaries seen in polycrystalline ZnO and
develop an understanding of a p-type mechanism which is common to ZnO,
Zn$_{1-x}$Mg$_x$O, and related materials.",1602.07451v2
2016-02-24,Transport in strongly-coupled graphene-LaAlO3/SrTiO3 hybrid systems,"We report on the transport properties of hybrid devices obtained by
depositing graphene on a LaAlO3/SrTiO3 oxide junction hosting a 4 nm-deep
two-dimensional electron system. At low graphene-oxide inter-layer bias the two
electron systems are electrically isolated, despite their small spatial
separation, and very efficient reciprocal gating is shown. A pronounced
rectifying behavior is observed for larger bias values and ascribed to the
interplay between electrostatic depletion and tunneling across the LaAlO3
barrier. The relevance of these results in the context of strongly-coupled
bilayer systems is discussed.",1602.07506v1
2016-02-29,"Easily doped p-type, low hole effective mass, transparent oxides","Fulfillment of the promise of transparent electronics has been hindered until
now largely by the lack of semiconductors that can be doped p-type in a stable
way, and that at the same time present high hole mobility and are highly
transparent in the visible spectrum. Here, a high-throughput study based on
first-principles methods reveals four oxides, namely X2SeO2, with X = La, Pr,
Nd, and Gd, which are unique in that they exhibit excellent characteristics for
transparent electronic device applications-i.e., a direct band gap larger than
3.1 eV, an average hole effective mass below the electron rest mass, and good
p-type dopability. Furthermore, for La2SeO2 it is explicitly shown that Na
impurities substituting La are shallow acceptors in moderate to strong
anion-rich growth conditions, with low formation energy, and that they will not
be compensated by anion vacancies VO or VSe.",1602.08945v1
2016-03-02,Correlation effects on electron-phonon coupling in semiconductors: many-body theory along thermal lines,"A method is proposed for the inclusion of electron correlation in the
calculation of the temperature dependence of band structures arising from
electron-phonon coupling. It relies on an efficient exploration of the
vibrational phase space along the recently introduced thermal lines. Using the
$G_0W_0$ approximation, the temperature dependence of the direct gaps of
diamond, silicon, lithium fluoride, magnesium oxide, and titanium dioxide is
calculated. Within the proposed formalism, a single calculation at each
temperature of interest is sufficient to obtain results of the same accuracy as
in alternative, more expensive methods. It is shown that many-body
contributions beyond semi-local density functional theory modify the
electron-phonon coupling strength by almost $50$% in diamond, silicon, and
titanium dioxide, but by less than $5$% in lithium flouride and magnesium
oxide. The results reveal a complex picture regarding the validity of
semi-local functionals for the description of electron-phonon coupling.",1603.00551v1
2016-03-07,Prediction of a Two-dimensional Phosphorus Nitride Monolayer,"Today, 2D semiconductor materials have been extended into the nitrogen group:
phosphorene, arsenene, antimonene and even nitrogene. Motivated by them, based
upon first-principles density functional calculations, we propose a new
two-dimensional phosphorus nitride (PN) structure that is stable well above the
room temperature, due to its extremely high cohesive energy. Unlike
phosphorene, PN structure is resistant to high temperature oxidation. The
structure is predicted to be a semiconductor with a wide, indirect band gap of
2.64 eV. More interestingly, the phosphorus nitride monolayer experiences an
indirect-to-direct band-gap transition at a relatively small tensile strain.
Such dramatic transformation in the electronic structure combined with
structural stability and oxidation resistance at high temperature could pave
the way for exciting innovations in high-speed ultrathin transistors, power
electronic modules, ultra-high efficiency LEDs and semiconductor lasers.",1603.01957v2
2016-03-09,Oxygen vacancies: The origin of n-type conductivity in ZnO,"Oxygen vacancy (VO) is a common native point defects that plays crucial roles
in determining the physical and chemical properties of metal oxides such as
ZnO. However, fundamental understanding of VO is still very sparse.
Specifically, whether VO is mainly responsible for the n-type conductivity in
ZnO has been still unsettled in the past fifty years. Here we report on a study
of oxygen self-diffusion by conceiving and growing oxygen-isotope ZnO
heterostructures with delicately-controlled chemical potential and Fermi level.
The diffusion process is found to be predominantly mediated by VO. We further
demonstrate that, in contrast to the general belief of their neutral attribute,
the oxygen vacancies in ZnO are actually +2 charged and thus responsible for
the unintentional n-type conductivity as well as the non-stoichiometry of ZnO.
The methodology can be extended to study oxygen-related point defects and their
energetics in other technologically important oxide materials.",1603.02831v2
2016-03-09,Novel chemistry of lithium oxides and superconducting low-pressure LiO4,"We study the stability of Li-O compounds as a function of pressure, with Li
ion battery applications and fundamental chemical interest in mind. Using the
ab initio evolutionary algorithm, we predict stability of novel compounds LiO4,
Li5O3 and Li6O under pressure. LiO4, formed at the pressure of just 6 GPa, can
be seen as {\epsilon}-O8 accepting two electrons from two Li atoms. This phase
is superconducting, with Tc up to 12.2 K at 10 GPa. This is remarkable, because
elemental oxygen becomes superconducting at much higher pressure (96 GPa) and
has much lower Tc (<0.6 K), and suggests that chemical alloying with other
elements has the potential of not only decreasing metallization pressure, but
also of increasing Tc. Since {\epsilon}-O8 is called red oxygen, LiO4 can be
identified ""lithium red-oxid"", and is distinct from superoxide. Additionally,
Li5O3 is stable at pressures above 70 GPa and can be represented as a hybrid
structure 4Li2O {\cdot} Li2O2, and electride suboxide Li6O is stable above 62
GPa.",1603.02880v1
2016-03-13,A sub-1-volt analog metal oxide memristive-based synaptic device for energy-efficient spike-based computing systems,"Nanoscale metal oxide memristors have potential in the development of
brain-inspired computing systems that are scalable and efficient1-3. In such
systems, memristors represent the native electronic analogues of the biological
synapses. However, the characteristics of the existing memristors do not fully
support the key requirements of synaptic connections: high density, adjustable
weight, and low energy operation. Here we show a bilayer memristor that is
forming-free, low-voltage (~|0.8V|), energy-efficient (full On/Off switching at
~2pJ), and reliable. Furthermore, pulse measurements reveal the analog nature
of the memristive device, that is it can be directly programmed to intermediate
resistance states. Leveraging this finding, we demonstrate
spike-timing-dependent plasticity (STDP), a spike-based Hebbian learning rule4.
In those experiments, the memristor exhibits a marked change in the normalized
synaptic strength (>30 times) when the pre- and post-synaptic neural spikes
overlap. This demonstration is an important step towards the physical
construction of high density and high connectivity neural networks.",1603.03979v1
2016-03-14,Spin Hall Effect Induced Spin Transfer Through an Insulator,"When charge current passes through a normal metal that exhibits spin Hall
effect, spin accumulates at the edge of the sample in the transverse direction.
We predict that this spin accumulation, or spin voltage, enables quantum
tunneling of spin through an insulator or vacuum to reach a ferromagnet without
transferring charge. In a normal metal/insulator/ferromagnetic insulator
trilayer (such as Pt/oxide/YIG), the quantum tunneling explains the
spin-transfer torque and spin pumping that exponentially decay with the
thickness of the insulator. In a normal metal/insulator/ferromagnetic metal
trilayer (such as Pt/oxide/Co), the spin transfer in general does not decay
monotonically with the thickness of the insulator. Combining with the spin Hall
magnetoresistance, this tunneling mechanism points to the possibility of a new
type of tunneling spectroscopy that can probe the magnon density of states of a
ferromagnetic insulator in an all-electrical and noninvasive manner.",1603.04240v2
2016-03-28,Liquid-Gated High Mobility and Quantum Oscillation of the Two-Dimensional Electron Gas at an Oxide Interface,"Electric field effect in electronic double layer transistor (EDLT)
configuration with ionic liquids as the dielectric materials is a powerful
means of exploring various properties in different materials. Here we
demonstrate the modulation of electrical transport properties and extremely
high mobility of two-dimensional electron gas at LaAlO$_3$/SrTiO$_3$ (LAO/STO)
interface through ionic liquid-assisted electric field effect. By changing the
gate voltages, the depletion of charge carrier and the resultant enhancement of
electron mobility up to 19380 cm$^2$/Vs are realized, leading to quantum
oscillations of the conductivity at the LAO/STO interface. The present results
suggest that high-mobility oxide interfaces which exhibit quantum phenomena
could be obtained by ionic liquid-assisted field effect.",1603.08471v1
2016-04-14,Vacancies and oxidation of 2D group-IV monochalcogenides,"Point defects in the binary group-IV monochalcogenide monolayers of SnS,
SnSe, GeS, GeSe are investigated using density-functional-theory calculations.
Several stable configurations are found for oxygen defects, however we give
evidence that these materials are less prone to oxidation than phosphorene,
with which monochalcogenides are isoelectronic and share the same orthorhombic
structure. Concurrent oxygen defects are expected to be vacancies and
substitutional oxygen. We show that it is energetically favorable oxygen be
incorporated into the layers substituting for a chalcogen (O S/Se defects), and
different from most of the other defects investigated, this defect preserves
the electronic structure of the material. Thus, we suggest that annealing
treatments can be useful for the treatment of functional materials where loss
mechanisms due to the presence of defects are undesirable.",1604.04092v1
2016-04-22,Thermoelectric Properties of Antiperovskite Calcium Oxides Ca3PbO and Ca3SnO,"We report the thermoelectric properties of polycrystalline samples of
Ca3Pb1-xBixO (x = 0, 0.1, 0.2) and Ca3SnO, both crystallizing in a cubic
antiperovskite-type structure. The Ca3SnO sample shows metallic resistivity and
its thermoelectric power approaches 100 uV K-1 at room temperature, resulting
in the thermoelectric power factor of Ca3SnO being larger than that of
Ca3Pb1-xBixO. On the basis of Hall and Sommerfeld coefficients, the Ca3SnO
sample is found to be a p-type metal with a carrier density of ~1019 cm-3, a
mobility of ~80 cm2 V-1 s-1, both comparable to those in degenerated
semiconductors, and a moderately large hole carrier effective mass. The
coexistence of moderately high mobility and large effective mass observed in
Ca3SnO, as well as possible emergence of a mutivalley electronic structure with
a small band gap at low-symmetry points in k-space, suggests that the
antiperovskite Ca oxides have strong potential as a thermoelectric material.",1604.06541v2
2016-04-25,Quasiparticle interference on cubic perovskite oxide surfaces,"We report the first observation of coherent surface states on cubic
perovskite oxide SrVO3(001) thin films through spectroscopic imaging scanning
tunneling microscopy. A direct link between the observed atomic-scale
interference patterns and the formation of a dxy-derived surface state is
supported by first-principles calculations. Furthermore, we show that the
apical oxygens on the topmost VO2 plane play a critical role in controlling the
spectral weight of the observed coherent surface state.",1604.07334v2
2016-05-22,Hybrid Multi-Walled Carbon Nanotube TiO2 Electrode Material for Next Generation Energy Storage Devices,"Current supercapacitors present several distinct limitations that severely
inhibit the efficiency, power, and electrical capacitance of energy storage
devices. Supercapacitors present an exciting prospect that has countless
applications in renewable energy storage and modern day electronic devices. In
recent years the exciting development of carbon nanotubes (CNTs) has presented
an advantage in electrode development. CNTs, however beneficial for their
increased electrode surface area, have severe limitations regarding
conductivity and electrode density. Creating a nanocomposite hybrid out of a
transition metal-oxide and carbon nanotube array would help the current
limitations of the modern supercapacitor. TiO2 was chosen for its common
occurrence in everyday materials and promising capacitance levels. A
multi-walled carbon nanotube array was grown on a SiO2 precursor via CCVD. The
transition metal oxide was then deposited via RF Sputtering methods to a MWCNT
array. Recharge tests and characterization were conducted using scanning
capacitance microscopy (SCM). While these tests are preliminary, this novel
hybrid electrode represents an exciting prospect for the future of the
efficiency of electrochemical energy storage as well as an advance towards a
future of providing inexpensive energy storage solutions around the world.",1606.00820v1
2016-06-14,Drastic changes of electronic structure and crystal chemistry upon oxidation of SnII2TiO4E2 into SnIV2TiO6: an ab initio study,"From DFT based calculations establishing energy-volume equations of state and
electron localization mapping, the electronic structure and crystal chemistry
changes from Sn2TiO4 to Sn2TiO6 by oxidation are rationalized; the key effect
being the destabilization of divalent tin SnII towards tetravalent state SnIV
leading to rutile Sn2TiO6 as experimentally observed. The subsequent electronic
structure change is highlighted in the relative change of the electronic band
gap which increases from ~1eV up to 2.2 eV and the 1.5 times increase of the
bulk modulus assigned to the change from covalently SnII based compound to the
more ionic SnIV one. Such trends are also confronted with the relevant
properties of black SnIIO characterized by very small band gap.",1606.04201v1
2016-06-23,Rashba-Dresselhaus spin-splitting in the bulk ferroelectric oxide BiAlO$_3$,"It has been recently suggested that the coexistence of ferroelectricity and
Rashba-like spin-splitting effects due to spin-orbit coupling in a single
material may allow for a non-volatile electric control of spin degrees of
freedom. In the present work, we compared the structural and ferroelectric
properties of tetragonal and rhombohedral phases of ferroelectric BiAlO$_3$ by
means of density-functional calculations. In both phases, we carefully
investigated Rashba and Dresselhaus effects, giving rise to spin-splitting in
their bulk electronic structure, particularly near the conduction band minimum,
supplementing our first-principles results with an effective $ k\cdot p$ model
analysis. The full reversal of the spin texture with ferroelectric polarization
switching was also predicted. BiAlO$_3$ can therefore be considered as the
first known oxide to exhibit a coexistence of ferroelectricity and
Rashba-Dresselhaus effects.",1606.07400v2
2016-06-30,Dynamic defect correlations dominate activated electronic transport in SrTiO3,"Strontium titanate (SrTiO3, STO) is a critically important material for the
study of emergent electronic phases in complex oxides, as well as for the
development of applications based on their heterostructures. Despite the large
body of knowledge on STO, there are still many uncertainties regarding the role
of defects in the properties of STO, including their influence on
ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures.
We present a detailed analysis of the decay of persistent photoconductivity in
STO single crystals with defect concentrations that are relatively low but
significantly affect their electronic properties. The results show that
photo-activated electron transport cannot be described by a superposition of
the properties due to independent point defects as current models suggest but
is, instead, governed by defect complexes that interact through dynamic
correlations. These results emphasize the importance of defect correlations for
activated electronic transport properties of semiconducting and insulating
perovskite oxides.",1606.09475v1
2016-07-07,Understanding and controlling the work function of perovskite oxides using Density Functional Theory,"Perovskite oxides containing transition metals are promising materials in a
wide range of electronic and electrochemical applications. However, neither
their work function values nor an understanding of their work function physics
have been established. Here, we predict the work function trends of a series of
perovskite ($ABO_3$ formula) materials using Density Functional Theory, and
show that the work functions of (001)-terminated AO- and $BO_2$-oriented
surfaces can be described using concepts of electronic band filling, bond
hybridization, and surface dipoles. The calculated range of AO ($BO_2$) work
functions are 1.60-3.57 eV (2.99-6.87 eV). We find an approximately linear
correlation ($R^2$ between 0.77-0.86, depending on surface termination) between
work function and position of the oxygen 2p band center, which correlation
enables both understanding and rapid prediction of work function trends.
Furthermore, we identify $SrVO_3$ as a stable, low work function, highly
conductive material. Undoped (Ba-doped) $SrVO_3$ has an intrinsically low
AO-terminated work function of 1.86 eV (1.07 eV). These properties make
$SrVO_3$ a promising candidate material for a new electron emission cathode for
application in high power microwave devices, and as a potential electron
emissive material for thermionic energy conversion technologies.",1607.02121v1
2016-07-27,The humidity sensing properties and mechanism of strontium-hexaferrite ceramics,"The humidity sensitivity of n-type strontium-hexaferrite semiconductors,
X-type (Sr2Co2Fe28O46) and Z-type (Sr3Co2Fe24O41), are investigated at room
temperature. The contact and reactions between water and material surface are
demonstrated considering the formation of oxide ion vacancy, singly-ionized /
fully-ionized oxide ion vacancy, and the chemisorbed / physisorbed / condensed
water. An impedance spectra model is proposed considering the
material-electrode interface, interior material, grain boundary, absorbed water
and Warburg response. The mechanism of electronic coupled with protonic
conduction and humidity sensing mechanism are explained.",1607.07929v2
2016-09-06,From Filter Paper to Functional Actuator by Poly(ionic liquid)-Modified Graphene Oxide,"A commercially available membrane filter paper composed of mixed cellulose
esters bearing typically an interconnected pore structure was transformed into
a stimuli-responsive bilayer actuator by depositing a thin film of poly(ionic
liquid)-modified graphene oxide sheets (GO-PIL) onto the filter paper. In
acetone vapor, the as-synthesized bilayer actuator bent readily into multiple
loops at a fast speed with the GO-PIL top film inwards. Upon pulling back into
air the actuator recovered their original shape. The asymmetric swelling of the
top GO-PIL film and the bottom porous filter paper towards organic vapor offers
a favorably synergetic function to drive the actuation. The PIL polymer chains
in the hybrid film were proven crucial to enhance the adhesion strength between
the GO sheets and the adjacent filter paper to avoid interfacial delamination
and thus improve force transfer. The overall construction allows a prolonged
lifetime of the bilayer actuator under constant operation, especially when
compared to that of the GO/filter paper bilayer actuator without PIL.",1609.01390v1
2016-09-12,Sequential pulsed laser deposition of homoepitaxial SrTiO$_3$ thin films,"Control of thin film stoichiometry is of primary relevance to achieve desired
functionality. Pulsed laser deposition ablating from binary-oxide targets
(sequential deposition) can be applied to precisely control the film
composition, offsetting the importance of growth conditions on the film
stoichiometry. In this work, we demonstrate that the cation stoichiometry of
SrTiO$_3$ thin films can be finely tuned by sequential deposition from SrO and
TiO$_2$ targets. Homoepitaxial SrTiO$_3$ films were deposited at different
substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a
growth window for stoichiometric SrTiO$_3$. The growth kinetics and nucleation
processes were studied by reflection high-energy electron diffraction and
atomic force microscopy, providing information about the growth mode and the
degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions,
films exhibit atomically flat surfaces, whereas off-stoichiometry is
accommodated by crystal defects, 3D islands and/or surface precipitates
depending on the substrate temperature and the excess cation. This technique
opens the way to precisely control stoichiometry and doping of oxide thin
films.",1609.03318v1
2016-09-12,Orthorhombic boron oxide under pressure: in situ study by X-ray diffraction and Raman scattering,"High-pressure phase of boron oxide, orthorhombic \b{eta}-B2O3, has been
studied in situ by synchrotron X-ray diffraction to 22 GPa and Raman scattering
to 46 GPa at room temperature. The bulk modulus of \b{eta}-B2O3 has been found
to be 169(3) GPa that is in good agreement with our ab initio calculations.
Raman and IR spectra of \b{eta}-B2O3 have been measured at ambient pressure,
all experimentally observed bands have been attributed to the theoretically
calculated ones, and the mode assignment has been performed. Based on the data
on Raman shift as a function of pressure, combined with equation-of-state data,
the Gr\""uneisen parameters of all experimentally observed Raman bands have been
calculated. \b{eta}-B2O3 enriched by 10B isotope has been synthesized, and the
effect of boron isotopic substitution on Raman spectra has been studied.",1609.03422v1
2016-09-20,"Effect of strain, thickness, and local surface environment on electron transport properties of oxygen-terminated copper thin films","Electron transport is studied in surface oxidized single-crystal copper thin
films with a thickness of up to 5.6 nm by applying density functional theory
and density functional tight binding methods to determine electron transport
properties within the ballistic regime. The variation of the electron
transmission as a function of film thickness as well as the different
contributions to the overall electron transmission as a function of depth into
the the films is examined. Transmission at the oxidized copper film surfaces is
found to be universally low. Films with thickness greater than 2.7 nm exhibit a
similar behavior in local transmission per unit area with depth from the film
surface; transmission per unit area initially increases rapidly and then
plateaus at a depth of approximately 0.35-0.5 nm away from the surface,
dependent on surface facet. Unstrained films tend to exhibit a higher
transmission per unit area than corresponding films under tensile strain.",1609.06150v2
2016-09-23,The mechanism of spin-orbit coupling in a 2D oxide interface,"The presence of spin-orbit coupling drives the anomalous magnetotransport at
oxide interfaces and forms the basis for numerous intriguing properties of
these 2D electron systems, such as topologically protected phases or
anti-localization. For many of those systems, the identification of the
underlying coupling mechanism is obfuscated by multi-band effects. We therefore
analyze the transport of LaAlO$_3$/SrTiO$_3$ interfaces under high pressures, a
technique to single out the multi-band contributions. We argue that the
observed magnetoresistance is due to quantum interference and not related to
Coulomb interaction. Therefore, this system is an excellent candidate to
generate a metal-insulator transition of the long-sought symplectic 2D
universality class. It is shown that the spin-orbit coupling can be linked
unambiguously to the band structure with a cubic (Dresselhaus-like) rather than
a linear (Rashba-like) spin-orbit band splitting.",1609.07425v1
2016-10-01,"Ab initio model of amorphous zinc oxide (a-ZnO) and a-X_0.375 Z_0.625 O (X=Al, Ga and In)","Density functional theory (DFT) calculations are carried out to study the
structure and electronic structure of amorphous zinc oxide (a-ZnO). The models
were prepared by the ""melt-quench"" method. The models are chemically ordered
with some coordination defects. The effect of trivalent dopants in the
structure and electronic properties of a-ZnO is investigated. Models of
a-X_0.375 Z_0.625 O (X=Al, Ga and In) were also prepared by the ""melt- quench""
method. The trivalent dopants reduce the four-fold Zn and O, thereby
introducing some coordination defects in the network. The dopants prefer to
bond with O atom. The network topology is discussed in detail. Dopants reduce
the gap in EDOS by producing defect states minimum while maintaining the
extended nature of the conduction band edge.",1610.00156v1
2016-10-07,Spin-orbit coupling controlled $J=3/2$ electronic ground state in 5$d^{3}$ oxides,"Entanglement of spin and orbital degrees of freedom drives the formation of
novel quantum and topological physical states. Discovering new spin-orbit
entangled ground states and emergent phases of matter requires both
experimentally probing the relevant energy scales and applying suitable
theoretical models. Here we report resonant inelastic x-ray scattering
measurements of the transition metal oxides Ca$_3$LiOsO$_6$ and Ba$_2$YOsO$_6$.
We invoke an intermediate coupling approach that incorporates both spin-orbit
coupling and electron-electron interactions on an even footing and reveal the
ground state of $5d^3$ based compounds, which has remained elusive in
previously applied models, is a novel spin-orbit entangled J=3/2 electronic
ground state. This work reveals the hidden diversity of spin-orbit controlled
ground states in 5d systems and introduces a new arena in the search for
spin-orbit controlled phases of matter.",1610.02375v1
2016-10-13,Topological Phase Transition Coupled with Spin-Valley Physics in Ferroelectric Oxide Heterostructures,"The possibility to engineer the coupling of spin and valley physics is
explored in ferroelectric oxide heterostructures with eg electronic
configuration. We show that the polar structural distortion induces the
appearance of spin-valley coupled properties, at the same time being
responsible for a topological transition from a quantum spin-Hall insulating
phase to a trivial band insulator. The coupled spin-valley physics is affected
by the topological band inversion in a non-trivial way; while the
valley-dependent spin polarization of both conduction and valence bands is
preserved, a change of the Berry curvature and of spin-valley selection rules
is predicted, leading to different circular dichroic response as well as valley
and spin Hall effects.",1610.03982v1
2016-10-17,Photocatalytic H2 generation using dewetted Pt-decorated TiO2 nanotubes - Optimized dewetting and oxide crystallization by a multiple annealing process,"In the present work we use TiO2 nanotube arrays, carrying a Pt coating that
is optimally dewetted, as a photocatalyst to generate H2. In order to achieve a
maximum H2-generation efficiency, on the one hand an ideal thermal dewetting of
the Pt layer into nanoparticles is needed that requires an oxygen free heat
treatment, and on the other hand an optimal crystallization of the TiO2
nanotubes into anatase with reduced defect density is achieved only by
annealing in O2 containing environment. To overcome this issue, we combine
adequate reducing and oxidizing conditions in a multiple annealing treatment,
and obtain Pt-decorated anatase TiO2 nanotubes showing significantly enhanced
photocatalytic H2 generation ability.",1610.05208v1
2016-10-27,Metal Insulator transition in tin doped indium oxide (ITO) thin films Quantum Correction to the electrical Conductivity,"Tin doped indium oxide (ITO) thin films are being used extensively as
transparent conductors in several applications. In the present communication,
we report the electrical transport in DC magnetron sputtered ITO thin films in
low temperatures (25-300 K). The low temperature Hall effect and resistivity
measurements reveal that the ITO thin films are moderately dis-ordered (kfl~1)
and degenerate semiconductor. The transport of charge carriers in these
disordered ITO thin films takes place via the de-localized states. The disorder
effects lead to the well- known metal-insulator transition; this transition is
observed at 110 K in ITO thin films. The metal-insulator behaviour is explained
by the quantum correction to the conductivity (QCC); this approach is based on
the quantum-mechanical interference effects in the disordered systems. The
insulating behaviour is attributed to the combined effect of the weak
localization and the electron-electron interactions.",1610.08799v1
2016-10-27,"High efficiency, hybrid electrochromic device on polycarbonate substrates with neon sputtered WO3-x thin films","Electrochromic materials change color reversibly by applying an external DC
voltage. One among the many emerging application of electro-chromics is the
smart windows. The coloration efficiency, the optical colour modulation and the
cyclability are the factors that bench mark the device. Tungsten oxide (WO3-x)
is versatile material and reactive DC magnetron sputtering (with argon as
sputter gas) technique is common for electro-chromics. In the present
communication we have prepared tungsten oxide thin films by reactive DC
magnetron sputtering technique (at room temperature 300 K) using Neon as the
sputter gas. The thickness of the WO3 thin films are varied from 190 nm to 712
nm. These WO3 thin films are subjected for electrochemical measurements with
three electrode electrochemical cell in presence of 1M HCl, 1M Li2SO4 aqueous
electrolyte and we have prepared a solid state electrochromic device with
nafion thin film. The highest coloration efficiency of the neon sputtered WO3
is observed as 187.9 cm2/C by lithium intercalation.",1610.08825v2
2016-10-28,Experimental and theoretical study of metal combustion in oxygen flows,"The effects of oxygen flow speed and pressure on the iron and mild steel
combustion are investigated experimentally and theoretically. The studied
specimens are vertical cylindrical rods subjected to an axial oxygen flow and
ignited at the upper end by laser irradiation. Three main stages of the
combustion process have been identified experimentally: (1) Induction period,
during which the rod is heated until an intensive metal oxidation begins at its
upper end; (2) Static combustion, during which a laminar liquid ""cap"" slowly
grows on the upper rod end; and, after the liquid cap detachment from the
sample, (3) Dynamic combustion, which is characterized by a rapid metal
consumption and turbulent liquid motions. An analytical description of these
stages is given. In particular, a model of the dynamic combustion is
constructed based on the turbulent oxygen transport through the liquid
metal-oxide flow. This model yields a simple expression for the fraction of
metal burned in the process, and allows one to calculate the normal propagation
speed of the solid metal--liquid interface as a function of the oxygen flow
speed and pressure. A comparison of the theory with the experimental results is
made.",1610.09126v2
2017-02-13,Ultra-low Thermal Conductivity of Nanogranular Indium Tin Oxide Films Deposited by Spray Pyrolysis,"The authors have shown that nanogranular indium tin oxide (ITO) films,
deposited by spray pyrolysis on silicon substrate, demonstrate ultralow thermal
conductivity ~ 0.84 +/-0.12 Wm-1K-1 at room temperature. This value is
approximately by one order of magnitude lower than that in bulk ITO. The strong
drop of thermal conductivity is explained by nanogranular structure and
porosity of ITO films, resulting in enhanced phonon scattering on grain
boundaries. The experimental results were interpreted theoretically, employing
Boltzmann transport equation approach for phonon transport and filtering model
for electronic transport. The calculated values of thermal conductivity are in
a reasonable agreement with the experimental findings. The presented results
show that ITO films with optimal nanogranular structure may be prospective for
thermoelectric applications.",1702.03842v1
2017-02-14,Metal-Insulator Transition and Jeff = 1/2 Spin-Orbit Insulating State in Rutile-based IrO2/TiO2 Superlattices,"By combining 5d transition-metal oxides showing pronounced spin-orbit
interactions and oxide-based heterostructures, we propose rutile-based
IrO2/TiO2 superlattices as promising candidates for unconventional electronic
properties. By means of density-functional-theory simulations complemented with
Hubbard-like corrections, we focus on the evolution of the electronic structure
as a function of the IrO2 layer thickness and predict the heterostructures to
exhibit a thickness-controlled metal-to-insulator transition, crucially related
to the connectivity among IrO6 octahedra. The subtle interplay between electron
correlation and spin-orbit coupling leads to an almost pure Jeff = 1/2
spin-orbit insulating state at the level of atomically-thin IrO2 monolayer with
almost isolated IrO6 octahedra, leading to a predicted emerging state awaiting
for experimental confirmation.",1702.04408v1
2017-01-29,Built-in Homojunction Dominated Intrinsically Rectifying-Resistive Switching in NiO Nanodots for Selection Device-Free Memory Application,"The intrinsically rectifying-resistive switching (IR-RS) has been regarded as
an effective way to address the crosstalk issue, due to the Schottky diodes
formed at the metal/oxide interfaces in the ON states to suppress the sneak
current at reverse biases. In this letter, we report for the first time another
type of IR-RS that is related to the built-in homojunction. The IR-RS study was
usually limited to macroscopic samples with micron-order pad-type electrodes,
while this work is on NiO nanodots fabricated with ultrathin
anodic-aluminum-oxide templates and acting as nanoscaled analogs of real
devices. The NiO nanodots show high storage density and high uniformity, and
the IR-RS behaviors are of good device performances in terms of retention,
endurance, switching ratio and rectification ratio. The feasibility of the
IR-RS for selection device-free memory application has been demonstrated, by
calculating the maximum crossbar array size under the worst-case scenario to be
3 Mbit.",1702.05665v1
2017-01-26,Review of flexible and transparent thin-film transistors based on zinc oxide and related materials,"Flexible and transparent electronics presents a new era of electronic
technologies. Ubiquitous applications involve wearable electronics, biosensors,
flexible transparent displays, radio-frequency identifications (RFIDs),
etc.Zinc oxide (ZnO) and related materials are the most commonly used inorganic
semiconductors in flexible and transparent devices, owing to their high
electrical performance, together with low processing temperature and good
optical transparency.In this paper, we review recent advances in flexible and
transparent thin-film transistors (TFTs) based on ZnO and related
materials.After a brief introduction, the main progresses on the preparation of
each component (substrate, electrodes, channel and dielectrics) are summarized
and discussed. Then, the effect of mechanical bending on electrical performance
was highlighted. Finally, we suggest the challenges and opportunities in future
investigations.",1702.05669v1
2017-03-02,Thermal conduction across a boron nitride and silicon oxide interface,"The needs for efficient heat removal and superior thermal conduction in
nano/micro devices have triggered tremendous studies in low-dimensional
materials with high thermal conductivity. Hexagonal boron nitride (h-BN) is
believed to be one of the candidates for thermal management and heat
dissipation due to its novel physical properties, i.e. thermal conductor and
electrical insulator. Here we reported interfacial thermal resistance between
few-layer h-BN and its silicon oxide substrate using differential 3 omega
method. The measured interfacial thermal resistance is around ~1.6*10-8 m2K/W
for monolayer h-BN and ~3.4*10-8 m2K/W for 12.8nm-thick h-BN in metal/h-BN/SiO2
interfaces. Our results suggest that the voids and gaps between substrate and
thick h-BN flakes limit the interfacial thermal conduction. This work provides
a deeper understanding of utilizing h-BN flake as lateral heat spreader in
electronic and optoelectronic nano/micro devices with further miniaturization
and integration.",1703.00669v1
2017-03-06,Phonon linewidth due to electron-phonon interactions with strong forward scattering in FeSe thin films on oxide substrates,"The discovery of an enhanced superconducting transition temperature $T_c$ in
monolayers of FeSe grown on several oxide substrates has opened a new route to
high-$T_c$ superconductivity through interface engineering. One proposal for
the origin of the observed enhancement is an electron-phonon (e-ph) interaction
across the interface that peaked at small momentum transfers. In this paper, we
examine the implications of such a coupling on the phononic properties of the
system. We show that a strong forward scattering leads to a sizable broadening
of phonon lineshape, which may result in charge instabilities at
long-wavelengths. However, we further find that the inclusion of Coulombic
screening significantly reduces the phonon broadening. Our results show that
one might not expect anomalously broad phonon linewidths in the FeSe interface
systems, despite the fact that the e-ph interaction has a strong peak in the
forward scattering (small $q$) direction.",1703.02013v1
2017-03-09,Oxygen migration during resistance switching and failure of hafnium oxide memristors,"While the recent establishment of the role of thermophoresis/diffusion-driven
oxygen migration during resistance switching in metal oxide memristors provided
critical insights required for memristor modeling, extended investigations of
the role of oxygen migration during ageing and failure remain to be detailed.
Such detailing will enable failure-tolerant design, which can lead to enhanced
performance of memristor-based next-generation storage-class memory. Here we
directly observed lateral oxygen migration using in-situ synchrotron x-ray
absorption spectromicroscopy of HfOx memristors during initial resistance
switching, wear over millions of switching cycles, and eventual failure,
through which we determined potential physical causes of failure. Using this
information, we reengineered devices to mitigate three failure mechanisms, and
demonstrated an improvement in endurance of about three orders of magnitude.",1703.03106v1
2017-03-22,Intersubband polarons in oxides,"Intersubband (ISB) polarons result from the interaction of an ISB transition
and the longitudinal optical (LO) phonons in a semiconductor quantum well (QW).
Their observation requires a very dense two dimensional electron gas (2DEG) in
the QW and a polar or highly ionic semiconductor. Here we show that in
ZnO/MgZnO QWs the strength of such a coupling can be as high as 1.5 times the
LO-phonon frequency due to the very dense 2DEG achieved and the large
difference between the static and high-frequency dielectric constants in ZnO.
The ISB polaron is observed optically in multiple QW structures with 2DEG
densities ranging from $5\times 10^{12}$ to $5\times 10^{13}$ cm$^{-2}$, where
an unprecedented regime is reached in which the frequency of the upper ISB
polaron branch is three times larger than that of the bare ISB transition. This
study opens new prospects to the exploitation of oxides in phenomena happening
in the ultrastrong coupling regime.",1703.07743v1
2017-03-29,Superconducting qubits on silicon substrates for quantum device integration,"We present the fabrication and characterization of transmon qubits formed
from aluminum Josephson junctions on two different silicon-based substrates:
(i) high-resistivity silicon (Si) and (ii) silicon-on-insulator (SOI). Key to
the qubit fabrication process is the use of an anhydrous hydrofluoric vapor
process which removes silicon surface oxides without attacking aluminum, and in
the case of SOI substrates, selectively removes the lossy buried oxide
underneath the qubit region. For qubits with a transition frequency of
approximately $5$GHz we find qubit lifetimes and coherence times comparable to
those attainable on sapphire substrates ($T_{1,\text{Si}} = 27\mu$s,
$T_{2,\text{Si}} = 6.6\mu$s; $T_{1,\text{SOI}} = 3.5\mu$s, $T_{2,\text{SOI}} =
2.2\mu$s). This qubit fabrication process in principle permits co-fabrication
of silicon photonic and mechanical elements, providing a route towards
chip-scale integration of electro-opto-mechanical transducers for quantum
networking of superconducting microwave quantum circuits.",1703.10195v2
2017-08-22,Highly Confined Stacks of Graphene Oxide Sheets in Water,"Since the discovery of graphene oxide (GO), the most accessible of the
precursors of graphene, this material has been widely studied for applications
in science and technology. In this work, we describe a procedure to obtain GO
dispersions in water at high concentrations, these highly dehydrated
dispersions being in addition fully redispersible by dilution. With the
availability of such concentrated samples, it was possible to investigate the
structure of hydrated GO sheets in a previously unexplored range of
concentrations, and to evidence a structural phase transition. Tentatively
applying models designed for describing the small-angle scattering curve in the
Smectic A (or L$_{\alpha}$) phase of lyotropic systems, it was possible to
extract elastic parameters characterising the system on the dilute side of the
transition, thereby evidencing the relevance of both electrostatic and steric
(Helfrich) interactions in stabilising aqueous lamellar stacks of GO sheets",1708.06661v2
2017-08-23,One-step deposition and in-situ reduction of graphene oxide in glass microcapillaries and application to photonics,"Films of graphene oxide (GO) were produced on the inner walls of glass
microcapillaries via insertion of a GO water suspension followed by quick
drying with a hot finger (no previous surface functionalization required).
Individual capillaries from an array could also be selectively GO coated. Raman
hyperspectral images revealed the films to be continuous along tens of
centimeters. Furthermore, the films could be thermally reduced through an
annealing process, which also decreased the concentration of defects. As a
proof of principle application, the microcapillaries of photonic crystal fibers
were covered with a GO film, leading to the demonstration of fiber polarizers
and mode lockers for pulsed fiber lasers. A comparison between GO- and reduced
GO-coated fibers revealed that shorter pulses are obtained with the latter.",1708.06954v1
2017-08-29,Commensurate Stripes and Phase Coherence in Manganites Revealed with Cryogenic Scanning Transmission Electron Microscopy,"Incommensurate charge order in hole-doped oxides is intertwined with exotic
phenomena such as colossal magnetoresistance, high-temperature
superconductivity, and electronic nematicity. Here, we map at atomic resolution
the nature of incommensurate order in a manganite using scanning transmission
electron microscopy at room temperature and cryogenic temperature ($\sim$ 93K).
In diffraction, the ordering wavevector changes upon cooling, a behavior
typically associated with incommensurate order. However, using real space
measurements, we discover that the underlying ordered state is
lattice-commensurate at both temperatures. The cations undergo picometer-scale
($\sim $6-11 pm) transverse displacements, which suggests that charge-lattice
coupling is strong and hence favors lattice-locked modulations. We further
unearth phase inhomogeneity in the periodic lattice displacements at room
temperature, and emergent phase coherence at 93K. Such local phase variations
not only govern the long range correlations of the charge-ordered state, but
also results in apparent shifts in the ordering wavevector. These
atomically-resolved observations underscore the importance of lattice coupling
and provide a microscopic explanation for putative ""incommensurate"" order in
hole-doped oxides.",1708.08871v1
2017-08-30,Tuning up or down the critical thickness in LaAlO3/SrTiO3 through in situ deposition of metal overlayers,"The quasi 2D electron system (q2DES) that forms at the interface between
LaAlO3 and SrTiO3 has attracted much attention from the oxide electronics
community. One of its hallmark features is the existence of a critical LaAlO3
thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. In this
paper, the chemical, electronic, and transport properties of LaAlO3/SrTiO3
samples capped with different metals grown in a system combining pulsed laser
deposition, sputtering, and in situ X-ray photoemission spectroscopy are
investigated. The results show that for metals with low work function a q2DES
forms at 1-2 uc of LaAlO3 and is accompanied by a partial oxidation of the
metal, a phenomenon that affects the q2DES properties and triggers the
formation of defects. In contrast, for noble metals, the critical thickness is
increased above 4 uc. The results are discussed in terms of a hybrid mechanism
that incorporates electrostatic and chemical effects.",1708.09189v1
2018-02-02,Electrofluorochromism at the single molecule level,"The interplay between the oxidation state and the optical properties of
molecules plays a key role for applications in displays, sensors or
molecular-based memories. The fundamental mechanisms occurring at the level of
a single-molecule have been difficult to probe. We used a scanning tunneling
microscope (STM) to characterize and control the fluorescence of a single
Zn-phthalocyanine radical cation adsorbed on a NaCl-covered Au(111) sample. The
neutral and oxidized states of the molecule were identified on the basis of
their fluorescence spectra that revealed very different emission energies and
vibronic fingerprints. The emission of the charged molecule was controlled by
tuning the thickness of the insulator and the plasmons localized at the apex of
the STM tip. In addition, sub-nanometric variations of the tip position were
used to investigate the charging and electroluminescence mechanisms.",1802.00764v2
2017-12-25,Combined Oxy-fuel Magnetohydrodynamic Power Cycle,"Oxy-fuel carbon capture in power plants is a relatively new concept aiming at
reducing carbon dioxide emissions from the plants. This is achieved by burning
the fossil fuel using oxygen as oxidizer with no nitrogen, thereby rendering
the exhaust gases very rich in carbon dioxide (after condensing water vapor by
cooling), which facilitates its capture for environmental or commercial
purposes. Despite the worldwide interest in oxy-fuel carbon capture, its
progress is at risk given the large energy needed to separate oxygen from air
in order to provide the oxidizer, thereby hindering further progress of this
concept toward large-scale applications. This paper focuses on alleviating this
drawback of oxy-fuel combustion by making it more attractive through combining
it with another concept, namely magnetohydrodynamic (MHD) power generators. The
end product is a power plant operating on a combined cycle composed of a
topping MHD ultra-high-temperature cycle with direct electricity extraction
from plasma, followed by a bottoming steam cycle with conventional
turbo-generators. Different design aspects and simplified technical analysis
for the MHD generator are presented.",1802.02039v1
2018-02-04,Characterization of spin coated Zn doped cupric oxide thin films,"Thin films of Zn2+ doped cupric oxide (CuO) were synthesized using spin
coating technique starting from a solution with Cu and Zn. The speed of spin
coating and time duration were varied to fabricate a film with required uniform
thickness. Samples were subsequently annealed in air at different annealing
temperatures to crystallize the phase of CuO. Doping concentration of Zn2+ was
varied up to weight percentage of 10%. Structural properties of samples were
determined using X-ray diffraction technique. Particle size, dislocation
density and strain at different doping concentrations were determined using XRD
patterns. Optical properties were measured by means of UV/Vis spectrometer.
Optical band gap of CuO could be tailored by doping a trace amount of Zn2+. The
optical band gap decreases with increase of particle size. The particle size,
dislocation density, strain and optical band gap have a turning point close to
the doping concentration of 6%.",1802.02886v1
2018-02-22,Toward High Temperature Quasi-two-dimensional Superconductivity,"The demonstration of a quasi-two-dimensional electron gas (2DEG) and
superconducting properties in LaAlO$_3$/SrTiO$_3$ heterostructures has
stimulated intense research activity in recent ten years. The 2DEG has unique
properties that are promising for applications in all-oxide electronic devices.
The superconductivity in such heterostructures has been observed below 300 mK.
For superconductivity applications it is desirable to have more wide
temperature of the existence range and the ability to control superconductivity
properties by external stimulus. Based on first-principles calculations and
theoretical consideration we show that all-oxide heterostructures incorporating
ferroelectric constituent, such as BaTiO$_3$/La$_2$CuO$_4$, allow creating
2DEG. We predict a possibility of a high temperature guasi-two-dimensional
superconductivity state. This state could be switchable between superconducting
and conducting states by ferroelectric polarization reversal. We also discuss
that such structures must be more simple for preparation. The proposed concept
of ferroelectrically controlled interface superconductivity offers the
possibility to design novel electronic devices.",1802.08569v1
2018-03-30,Growth of Thin Oxidation-Resistive Crystalline Si Nanostructures on Graphene,"We report the growth of Si nanostructures, either as thin films or
nanoparticles, on graphene substrates. The Si nanostructures are shown to be
single crystalline, air stable and oxidation resistive, as indicated by the
observation of a single crystalline Si Raman mode at around 520 cm-1, a STM
image of an ordered surface structure under ambient condition, and a Schottky
junction with graphite. Ultra-thin silicon regions exhibit silicene-like
behavior, including a Raman mode at around 550 cm-1, a triangular lattice
structure in STM that has distinctly different lattice spacing from that of
either graphene or thicker Si, and metallic conductivity of up to 500 times
higher than that of graphite. This work suggests a bottom-up approach to
forming a Si nanostructure array on a large scale patterned graphene substrate
for fabricating nanoscale Si electronic devices.",1804.00072v1
2018-04-08,New optimization scheme to obtain interaction potentials for oxide glasses,"We propose a new scheme to parameterize effective potentials that can be used
to simulate atomic systems such as oxide glasses. As input data for the
optimization, we use the radial distribution functions of the liquid and the
vibrational density of state of the glass, both obtained from ab-initio
simulations, as well as experimental data on the pressure dependence of the
density of the glass. For the case of silica, we find that this new scheme
facilitates finding pair potentials that are significantly more accurate than
previous ones even if the functional form is the same, thus demonstrating that
even simple two-body potentials can be superior to more complex three-body
potentials. We have tested the new potential by calculating the pressure
dependence of the elastic moduli and find a good agreement with the
corresponding experimental data.",1804.02741v1
2018-04-13,Aggregation and Electronically-Induced Migration of Oxygen Vacancies in TiO2 Anatase,"The influence of the electric field and electric current on the behavior of
oxygen vacancies (VOs) in TiO2 anatase was investigated with Scanning Tunneling
Microscopy (STM). At the anatase (101) surface VOs are not stable; they migrate
into the bulk at temperatures above 200 K. Scanning a clean anatase (101)
surface at a sample bias greater than +4.3 V results in surface VOs in the
scanned area, suggesting that subsurface VOs migrate back to the surface. To
test this hypothesis, surface VOs were first created through bombardment with
energetic electrons. The sample was then mildly annealed, which caused the VOs
to move to the subsurface region, where they formed vacancy clusters. These VO
clusters have various, distinct shapes. Scanning VO clusters with a high STM
bias reproducibly converts them back into groupings of surface VO, with a
configuration that is characteristic for each type of cluster. The dependence
of the subsurface-to-surface VO migration on the applied STM bias voltage,
tunneling current, and sample temperature was investigated systematically. The
results point towards a key role of energetic, 'hot' electrons in this process.
The findings are closely related to the memristive behavior of oxides and
oxygen diffusion in solid-oxide membranes.",1804.04920v1
2018-04-22,Toward a topological scenario for high-temperature superconductivity of copper oxides,"The structure of the joint phase diagram demonstrating high-$T_c$
superconductivity of copper oxides is studied on the basis of the theory of
interaction-induced flat bands. Prerequisites of an associated topological
rearrangement of the Landau state are established, and related non-Fermi-liquid
(NFL) behavior of the normal states of cuprates is investigated. We focus on
manifestations of this behavior in the electrical resistivity $\rho(T)$,
especially the observed gradual crossover from normal-state $T$-linear behavior
$\rho(T,x)=A_1(x)T$ at doping $x$ below the critical value $x_c^h$ for
termination of superconductivity, to $T$-quadratic behavior at $x>x_c^h$, which
is incompatible with predictions of the conventional quantum-critical-point
scenario. It is demonstrated that at $x<x^h_c$, in agreement with available
experimental data, the coefficient $A_1( x)$ is decomposed into the product of
two factors, one of which changes linearly with doping $x$, while the second is
universal, being of the Planckian form.",1804.08177v2
2018-04-27,High-pressure Raman study on the superconducting pyrochlore oxide Cd2Re2O7,"The superconducting pyrochlore oxide Cd2Re2O7 (Tc = 1 K), which is now
considered as a candidate of the spin-orbit-coupled metal, shows an
inversion-symmetry-breaking structural transition at Ts1 = 200 K. Ts1 decreases
with increasing pressure and disappears at around Pc = 4:2GPa, where at least
four high-pressure phases with tiny structural distortions are suggested by
means of powder X-ray diffraction [Yamaura PRB 2017]. We have carried out Raman
scattering experiments to investigate changes in the crystal symmetry under
high pressures up to 4.8 GPa. A structural transition at 1.9-3.0 GPa and the
recovery of inversion symmetry above Pc are observed at 12 K.",1804.10487v1
2018-04-28,Effect of the reduction process on the field emission performance of reduced graphene oxide cathodes,"The electron field emission (FE) properties of reduced graphene oxide (rGO)
cathodes produced by three different reduction methods were assessed and
compared. In particular, chemical reduction techniques, using either NaOH or
KOH as reducing agents, were compared with thermal reduction (TR) methods. Xray
photoelectron spectroscopy (XPS) measurements revealed that different reduction
techniques led to different GO lattice parameters. Furthermore, the work
function measured with ultraviolet photoelectron spectroscopy (UPS) varied
among the samples giving rise to different electron emission characteristics.
In particular, the cathodes prepared by the TR method presented the best FE
performance, showing a turnon field of as low as ca. 1.8 V mm^-1 and a field
enhancement factor of ca. 1300, which was very close however to that shown by
the NaOH-reduced sheets. The worst FE properties were exhibited by the
KOH-reduced nanosheets. In light of the above results, the role of the
different reduction techniques as well as the final rGO lattice characteristics
with regards to the emission performance are evaluated and discussed.",1804.10813v1
2018-11-16,Ensemble versus Local Restructuring of Core-shell Nickel-Cobalt Nanoparticles upon Oxidation and Reduction Cycles,"Bimetallic nanoparticles are widely studied, for example in catalysis.
However, possible restructuring in the environment of use, such as segregation
or alloying, may occur. Taken individually, state-of-the-art analytical tools
fail to give an overall picture of these transformations. This study combines
an ensemble analysis (near-ambient-pressure X-ray photoelectron spectroscopy)
with a local analysis (environmental transmission electron microscopy) to
provide an in situ description of the restructuring of core--shell
nickel-cobalt nanoparticles exposed to cycles of reduction and oxidation. It
reveals a partial surface alloying accompanied by fragmentation of the shell
into smaller clusters, which is not reversible. Beyond this case study, the
methodology proposed here should be applicable in a broad range of studies
dealing with the reactivity of mono- or bi-metallic metal nanoparticles.",1811.06900v1
2018-11-21,Coordination corrected ab initio formation enthalpies,"The correct calculation of formation enthalpy is one of the enablers of
ab-initio computational materials design. For several classes of systems (e.g.
oxides) standard density functional theory produces incorrect values. Here we
propose the ""Coordination Corrected Enthalpies"" method (CCE), based on the
number of nearest neighbor cation-anion bonds, and also capable of correcting
relative stability of polymorphs. CCE uses calculations employing the Perdew,
Burke and Ernzerhof (PBE), Local Density Approximation (LDA) and Strongly
Constrained and Appropriately Normed (SCAN) exchange correlation functionals,
in conjunction with a quasiharmonic Debye model to treat zero-point vibrational
and thermal effects. The benchmark, performed on binary and ternary oxides
(halides), shows very accurate room temperature results for all functionals,
with the smallest mean absolute error of 27 (24) meV/atom obtained with SCAN.
The zero-point vibrational and thermal contributions to the formation
enthalpies are small and with different signs - largely cancelling each other.",1811.08952v2
2018-10-17,"Compact Modeling of I-V Characteristics, Temperature Dependency, Variations, and Noise of Integrated, Reproducible Metal-Oxide Memristors","We present a comprehensive phenomenological model for the crossbar integrated
metal-oxide continuous-state memristors. The model consists of static and
dynamic equations, which are obtained by fitting a large amount of experimental
data, collected on several hundred devices. The static equation describes the
device current, at non-disturbing voltages, as a sum of three components,
representing the average behavior and its device-to-device and temporal
variations. All three components are expressed as functions of the applied
voltage, ambient temperature, and the current memory state. The dynamic
equation models the change in the memory state as a function of the applied
voltage stress and the current memory state, and is also expressed as a sum of
the average and the device-to-device variation terms. Both equations are
explicit, computationally inexpensive, and suitable for SPICE modeling. At the
same time, the model has good predictive power, which is supported by the
validation results. The presented model is useful for realistic simulations of
various mixed-signal computing circuits, such as image compression and image
classification applications, discussed in this paper.",1811.10385v1
2018-11-27,Directional freezing of binary colloidal suspensions: A model for size fractionation of graphene oxide,"The performance of graphene oxide(GO)-based materials strongly depends on the
lateral size and size distribution of GO nanosheets. Various methods are
employed to prepare GO nanosheets with a narrow size distribution. One of the
promising method was proposed recently by directionally freezing of a GO
aqueous dispersion at a controlled growth rate of the freezing front. We
develop a theoretic model of binary colloids suspension, incorporating both the
moving freezing boundary and the preferential adsorption of colloidal particles
to the ice phase. We numerically solve the coupled diffusion equations and
present state diagrams of size fractionation. Selective trapping of colloids
according to their size can be achieved by a suitable choice of the
experimental parameters, such as the adsorption rates and the freezing speed.",1811.11070v1
2018-11-27,Second Neighbor Electron Hopping and Pressure Induced Topological Quantum Phase Transition in Insulating Cubic Perovskites,"Perovskite structure is one of the five symmetry families suitable for
exhibiting topological insulator phase. However, none of the halides and oxides
stabilizing in this structure exhibit the same. Through density functional
calculations on cubic perovskites (CsSnX$_3$ ; X = Cl, Br, and I), we predict a
band insulator -- Dirac semimetal -- topological insulator phase transition
with uniform compression. With the aid of a Slater-Koster tight binding
Hamiltonian, we show that, apart from the valence electron count, the band
topology of these perovksites is determined by five parameters involving
electron hopping among the Sn-{s, p} orbitals. These parameters monotonically
increase with pressure to gradually transform the positive band gap to a
negative one and thereby enable the quantum phase transition. The universality
of the mechanism of phase transition is established by examining the band
topology of Bi based oxide perovskites. Dynamical stability of the halides
against pressure strengthens the experimental relevance.",1811.11081v1
2018-11-30,Dichotomy of the Photo Induced 2-Dimensional Electron Gas on SrTiO$_3$ Surface Terminations,"Oxide materials are important candidates for the next generation of
electronics due to a wide array of desired properties which they can exhibit
alone or when combined with other materials. While SrTiO$_3$ (STO) is often
considered a prototypical oxide, it too hosts a wide array of unusual
properties including a two dimensional electron gas (2DEG) which can form at
the surface when exposed to UV light. Using layer-by-layer growth of high
quality STO films, we show that the 2DEG only forms with the SrO termination
and not with the TiO$_2$ termination, contrary to expectation. This behavior is
similarly seen in BaTiO$_3$ (BTO), in which the 2DEG is only observed for BaO
terminated films. These results will allow for a deeper understanding, and
better control, of the electronic structure of titanate films, substrates and
heterostructures.",1811.12652v1
2018-11-30,Engineering mass transport properties in oxide ionic and mixed ionic electronic thin film ceramic conductors for energy applications,"New emerging disciplines such as Nanoionics and Iontronics are dealing with
the exploitation of mesoscopic size effects in materials, which become visible
(if not predominant) when downsizing the system to the nanoscale. Driven by the
worldwide standardisation of thin film deposition techniques, the access to
radically different properties than those found in the bulk macroscopic systems
can be accomplished. This opens up promising approaches for the development of
advanced microdevices, by taking advantage of the nanostructural deviations
found in nanometre sized, interface dominated materials compared to the ideal
relaxed structure of the bulk. A completely new set of functionalities can be
explored, with implications in many different fields such as energy conversion
and storage, or information technologies. This manuscript reviews the
strategies, employed and foreseen, for engineering mass transport properties in
thin film ceramics, with the focus in oxide ionic and mixed ionic electronic
conductors and their application in micro power sources.",1811.12771v1
2019-05-02,The inequivalent substitution on Ca site of cubic CaTiO3 perovskite for transparent conductive oxides from USPEX and DFT,"Based on genetic evolution algorithm, universal structure predictor USPEX
assists to explore the most stable structure from Na+ substituting Ca2+ under
variable concentration, for p type transparent conductive oxide application.
The study finds 2 atoms of NaCa maintain the octahedral packing and cubic phase
without the presence of oxygen vacancy, but the electron loss causes in fermi
level entering into valence band, realizing p type TCOs character. While others
still remain insulator character due to the compensation of oxygen vacancy.
Applying Al3+ substituting Ca2+ achieve the fermi level into conduction band
with n-type TCOs, with the symmetry of tetragonal phase. And the transport
properties for p- type Ca0.75Na0.25TiO3 and n-type Ca0.75Al0.25TiO3 are
calculated, the mobility in p- type Ca0.75Na0.25TiO3 is more superior owing to
its curvature edge.",1905.00548v1
2019-05-05,Metal oxide nanomaterials for pseudocapacitors,"With the rapid development of economy, the consumption of fossil fuels, and
the increasing environment pollution, there is in urgent need of seeking clean
and renewable energy sources, as well as highly efficient and low-cost energy
storage technologies. Concerning electrochemically active materials, transition
metal oxides (TMOs) are regarded as the most promising candidates for the next
generation SCs and have been widely reported. Therefore, in this review, we
mainly pay attention to TMOs with excellent electrochemical performance. This
review is divided into four parts: (a) the background including energy storage
mechanisms and electrochemical characterizations of SCs; (b) various kinds of
TMOs for SCs are analyzed in detail involved in crystal structure,
conductivity, and energy storage mechanism; (c) hybridizations with other
materials to improve the electrochemical performance of TMOs are summarized and
discussed; (d) a perspective and short remarks about the development and design
of TMOs for superior performance SCs are shown.",1905.01766v2
2019-05-09,More than 3-mm-long carrier diffusion and strong absorption over the full solar spectrum in copper oxide and selenium composite film,"Usually, single-crystal material has a longer carrier diffusion length due to
fewer defects. Here, we report a nano/amorphous copper oxide and selenium (COS)
composite film prepared by radio frequency magnetron co-sputtering of CuO and
Se and post annealing. The photo-generated carriers in the COS film can diffuse
very far (3.147 mm). Additionally, the COS film can strongly absorb light over
the entire solar spectrum region (250-2500 nm) (average absorptance is ~80%).
These results indicate that the COS composite is an excellent material and can
be used in solar cells and other photo-electric devices.",1905.03432v1
2019-05-14,Revealing the complex nature of bonding in binary high-pressure compound FeO$_2$,"Extreme pressures and temperatures are known to drastically affect the
chemistry of iron oxides resulting in numerous compounds forming homologous
series $n$FeO$\cdot m$Fe$_2$O$_3$ and the appearance of FeO$_2$. Here, based on
the results of \emph{in situ} single-crystal X-ray diffraction, M\""ossbauer
spectroscopy, X-ray absorption spectroscopy, and DFT+dynamical mean-field
theory calculations we demonstrate that iron in high pressure cubic FeO$_2$ and
isostructural FeO$_2$H$_{0.5}$ is ferric (Fe$^{3+}$), and oxygen has a formal
valence less than two. Reduction of oxygen valence from 2, common for oxides,
down to 1.5 can be explained by a formation of a localized hole at oxygen
sites.",1905.05497v2
2019-05-15,Coupled Cluster Benchmark of New Density Functionals and Domain Pair Natural Orbital Methods: Mechanisms of Hydroarylation and Oxidative Coupling Catalyzed by Ru(II) Chloride Carbonyls,"In the present work, we tested the performance of several new functionals for
studying the mechanisms of concurrent reaction of hydroarylation and oxidative
coupling catalyzed by Ru(II) chloride carbonyls. We find that DLPNO-CCSD(T) is
an acceptable substitute for full canonical CCSD(T) calculations; that the
recent {\omega}B97X-V and {\omega}B97M-V functionals exhibit superior
performance to commonly used DFT functionals; and that the revised DSD-PBEP86
double hybrid represents an improvement over the original, even though
transition metals were not involved in its parametrization.",1905.06168v2
2019-05-16,Tuning the work function of graphene toward application as anode and cathode,"The rapid technological progress in the 21st century demands new
multi-functional materials applicable to a wide variety of industries.
Two-dimensional (2D) materials are predicted to have a revolutionary impact on
the cost, size, weight, and functions of future electronic and optoelectronic
devices. Graphene, which shows potential as an alternative to conventional
conductive transparent metal oxides, may play a central role. Since its work
function (WF) is tunable, graphene exhibits the interesting ability to serve
two different roles in electronic and optoelectronic devices, both as an anode
and a cathode. After introducing some basic concepts, this work reviews the
most important advances in controlling the tuned WF of graphene, highlighting
special features of graphene electronic band structure and recognizing
different methods for measuring WF. The impact of thickness, type of contact,
chemical doping, UV and plasma treatments, defects, and functional groups of
graphene oxide are considered and related with the applications of the
modulated material. The results of the review, organized in lookup tables, have
been used to identify the advantages and main challenges of the tuning methods.",1905.06594v1
2019-05-23,Laser machined ultrathin microscale platinum thermometers on transparent oxide substrates,"Ultrathin microscale resistive thermometers are of key value to many
applications. Here we have fabricated a laser machined 50 ${\mu}$m wide and 50
nm thick serpentine Pt thin film sensor capable of sensing temperatures up to
650 ${^\circ}$ C over multiple heating and cooling cycles. Various materials
and associated processing conditions were studied, including both sapphire and
silica as transparent substrates, alumina and TiO2 as adhesion layers, and
lastly alumina and silicon oxide as capping layer. In-situ resistance
monitoring helps to verify the multi-cycle stability of the sensor and guide
the optimization. 10 ${\mu}$m sized sensors can be laser machined but will not
survive multiple heating and cooling cycles. We demonstrate that the sensors
with amorphous Ge thin layers can also repeatably measure temperatures up to
650 ${^\circ}$ C. It is anticipated that this sensor can be used for fast and
high spatial resolution temperature probing for laser processing applications.",1905.09812v1
2019-05-25,Actively tunable terahertz electromagnetically induced transparency analogue based on vanadium-oxide-assisted metamaterials,"Recently, phase-change materials (PCMs) have drawn more attention due to the
dynamically tunable optical properties. Here, we investigate the active control
of electromagnetically induced transparency (EIT) analogue based on terahertz
(THz) metamaterials integrated with vanadium oxide (VO2). Utilizing the
insulator-to-metal transition of VO2, the amplitude of EIT peak can be actively
modulated with a significant modulation depth. Meanwhile the group delay within
the transparent window can also be dynamically tuned, achieving the active
control of slow light effect. Furthermore, we also introduce independently
tunable transparent peaks as well as group delay based on a double-peak EIT
with good tuning performance. Finally, based on broadband EIT, the active
tuning of quality factor of the EIT peak is also realized. This work introduces
active EIT control with more degree of freedom by employing VO2, and can find
potential applications in future wireless and ultrafast THz communication
systems as multi-channel filters, switches, spacers, logic gates and
modulators.",1905.10623v1
2019-05-30,Layer-Resolved Ultrafast XUV Measurement of Hole Transport in a Ni-TiO2-Si Photoanode,"Metal-oxide-semiconductor junctions are central to most electronic and
optoelectronic devices. Here, the element-specificity of broadband extreme
ultraviolet (XUV) ultrafast pulses is used to measure the charge transport and
recombination kinetics in each layer of a Ni-TiO2-Si junction. After
photoexcitation of silicon, holes are inferred to transport from Si to Ni
ballistically in ~100 fs, resulting in spectral shifts in the Ni M2,3 XUV edge
that are characteristic of holes and the absence of holes initially in TiO2.
Meanwhile, the electrons are observed to remain on Si. After picoseconds, the
transient hole population on Ni is observed to back-diffuse through the TiO2,
shifting the Ti spectrum to higher oxidation state, followed by electron-hole
recombination at the Si-TiO2 interface and in the Si bulk. Electrical
properties, such as the hole diffusion constant in TiO2 and the initial hole
mobility in Si, are fit from these transient spectra and match well with values
reported previously.",1905.13097v1
2020-07-07,Nanoelectrodes for intracellular measurements of reactive oxygen and nitrogen species in single living cells,"Reactive oxygen and nitrogen species (ROS and RNS) play important roles in
various physiological processes (e.g., phagocytosis) and pathological
conditions (e.g., cancer). The primary ROS/RNS, viz., hydrogen peroxide,
peroxynitrite ion, nitric oxide, and nitrite ion, can be oxidized at different
electrode potentials and therefore detected and quantified by electroanalytical
techniques. Nanometer-sized electrochemical probes are especially suitable for
measuring ROS/RNS in single cells and cellular organelles. In this article, we
survey recent advances in localized measurements of ROS/RNS inside single cells
and discuss several methodological issues, including optimization of
nanoelectrode geometry, precise positioning of an electrochemical probe inside
a cell, and interpretation of electroanalytical data.",2007.03245v1
2020-07-16,ENZ materials and Anisotropy: Enhancing Nonlinear Optical Interactions at the Nanoscale in Metal/Conducting-Oxide Multilayer Stacks,"Epsilon-near-zero materials are exceptional candidates for studying
electrodynamics and nonlinear optical processes at the nanoscale. We
demonstrate that by alternating a metal and a highly doped conducting-oxide,
the epsilon-near-zero regime may be accessed resulting in an anisotropic,
composite nanostructure that significantly enhances nonlinear interactions.
Using two independent and different computation techniques we show that the
structure can enhance the local field intensity by nearly two orders of
magnitudes, in large part due to the onset of the effective anisotropy. The
investigation of the multilayer nanostructure using a microscopic, hydrodynamic
approach also sheds light on the roles of two competing contributions that are
for the most part overlooked, but that can significantly modify linear and
nonlinear responses of the structure: nonlocal effects, which blueshift the
resulting resonance, and the hot electron nonlinearity, which redshifts the
plasma frequency as the effective mass of free electrons increases as a
function of incident power density. Finally, we show that, even in absence of
second order bulk nonlinearity, second order nonlinear processes are also
significantly enhanced by the layered structure.",2007.08312v1
2010-05-13,Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis,"We demonstrate top-gated field effect transistor made of reduced graphene
oxide (RGO) monolayer (graphene) by dielectrophoresis. Raman spectrum of RGO
flakes of typical size of 5{\mu}m x 5{\mu}m show a single 2D band at 2687 cm-1,
characteristic of a single layer graphene. The two probe current - voltage
measurements of RGO flakes, deposited in between the patterned electrodes with
a gap of 2.5 {\mu}m using a.c. dielectrophoresis show ohmic behavior with a
resistance of ~ 37k{\Omega}. The temperature dependence of the resistance (R)
of RGO measured between temperatures 305 K to 393 K yields temperature
coefficient of resistance [dR/dT]/R ~ -9.5x10-4 K-1, same as mechanically
exfoliated single layer graphene. The field effect transistor action was
obtained by electrochemical top-gating using solid polymer electrolyte (PEO +
LiClO4) and Pt wire. Ambipolar nature of graphene flakes is observed upto a
doping level of ~ 6x1012/cm2 and carrier mobility of ~ 50 cm2V-1sec-1. The
source - drain current characteristics shows a tendency of current saturation
at high source - drain voltage which is analyzed quantitatively by a diffusive
transport model.",1005.2258v1
2010-05-20,Hot carrier diffusion in graphene,"We report an optical study of charge transport in graphene. Diffusion of hot
carriers in epitaxial graphene and reduced graphene oxide samples are studied
using an ultrafast pump-probe technique with a high spatial resolution.
Spatiotemporal dynamics of hot carriers after a point-like excitation are
monitored. Carrier diffusion coefficients of 11,000 and 5,500 squared
centimeters per second are measured in epitaxial graphene and reduced graphene
oxide samples, respectively, with a carrier temperature on the order of 3,600
K. The demonstrated optical techniques can be used for non-contact and
non-invasive in-situ detection of transport properties of graphene.",1005.3850v2
2013-08-04,In vitro toxicity of nanoceria: effect of coating and stability in biofluids,"Due to the increasing use of nanometric cerium oxide in applications,
concerns about the toxicity of these particles have been raised and have
resulted in a large number of investigations. We report here on the
interactions between 7 nm anionically charged cerium oxide particles and living
mammalian cells. By a modification of the particle coating including
low-molecular weight ligands and polymers, two generic behaviors are compared:
particles coated with citrate ions that precipitate in biofluids and particles
coated with poly(acrylic acid) that are stable and remain nanometric. We find
that nanoceria covered with both coating agents are taken up by mouse
fibroblasts and localized into membrane-bound compartments. However, flow
cytometry and electron microscopy reveal that as a result of their
precipitation, citrate-coated particles interact more strongly with cells. At
cerium concentration above 1 mM, only citrate-coated nanoceria (and not
particles coated with poly(acrylic acid)) display toxicity and moderate
genotoxicity. The results demonstrate that the control of the surface chemistry
of the particles and its ability to prevent aggregation can affect the toxicity
of nanomaterials.",1308.0800v1
2013-08-08,Weak Coupling BCS-like Superconductivity in the Pnictide Oxide Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O (x=0 and 0.15),"We report the results of low-temperature heat capacity measurements of the
pnictide oxide superconductor BaTi$_2$Sb$_2$O doped with sodium. The
temperature and field dependent heat capacity data are well described by a
single-gap BCS theory. The estimated values for the normal state Sommerfeld
constant, the heat capacity jump at $T_c$, and the electron-phonon coupling
constant are in favor of a conventional weak coupling superconductivity
mediated by electron-phonon interaction. The results are discussed with regard
to and compared with recent first principle calculations.",1308.1880v1
2013-08-09,ALD grown zinc oxide with controllable electrical properties,"The paper presents results for zinc oxide films grown at low temperature
regime by Atomic Layer Deposition (ALD). We discuss electrical properties of
such films and show that low temperature deposition results in oxygen-rich ZnO
layers in which free carrier concentration is very low. For optimized ALD
process it can reach the level of 10^15 cm-3, while mobility of electrons is
between 20 and 50 cm2/Vs. Electrical parameters of ZnO films deposited by ALD
at low temperature regime are appropriate for constructing of the ZnO-based p-n
and Schottky junctions. We demonstrate that such junctions are characterized by
the rectification ratio high enough to fulfill requirements of 3D memories and
are deposited at temperature 100degC which makes them appropriate for
deposition on organic substrates.",1308.2064v1
2013-08-12,Quantum confinement in perovskite oxide heterostructures: tight binding instead of nearly free electron picture,"Most recently, orbital-selective quantum well states of $d$ electrons have
been experimentally observed in SrVO$_3$ ultrathin films [K. Yoshimatsu et.
al., Science 333, 319 (2011)] and SrTiO$_3$ surfaces [A. F. Santander-Syro et.
al., Nature 469, 189 (2011)]. Hitherto, one tries to explain these experiments
by a nearly free electron (NFE) model, an approach widely used for delocalized
electrons in semiconductor heterostructures and simple metal films. We show
that a tight binding (TB) model is more suitable for describing
heterostructures with more localized $d$ electrons. In this paper, we construct
from first principles simple TB models for perovskite oxide heterostructures
and surfaces. We show that the TB model provides a simple intuitive physical
picture and yields, already with only two parameters, quantitatively much more
reliable results, consistent with experiment.",1308.2615v1
2013-08-25,CO2/oxalate Cathodes as Safe and Efficient Alternatives in High Energy Density Metal-Air Type Rechargeable Batteries,"We present theoretical analysis on why and how rechargeable metal-air type
batteries can be made significantly safer and more practical by utilizing
CO2/oxalate conversions instead of O2/peroxide or O2/hydroxide ones, in the
positive electrode. Metal-air batteries, such as the Li-air one, may have very
large energy densities, comparable to that of gasoline, theoretically allowing
for long range all-electric vehicles. There are, however, still significant
challenges, especially related to the safety of their underlying chemistries,
the robustness of their recharging and the need of supplying high purity O2
from air to the battery. We point out that the CO2/oxalate reversible
electrochemical conversion is a viable alternative of the O2-based ones,
allowing for similarly high energy density and almost identical voltage, while
being much safer through the elimination of aggressive oxidant peroxides and
the use of thermally stable, non-oxidative and environmentally benign oxalates
instead.",1308.5457v2
2013-08-26,Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices,"Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker
of two structures formed in CaCuO2 at the interface with SrTiO3. For
non-superconducting superlattices, grown in low oxidizing atmosphere, the 425
cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films
with infinite layer structure (planar Cu-O coordination). For superconducting
superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift
to lower energy occurs. This is ascribed to a change from planar to pyramidal
Cu-O coordination because of oxygen incorporation at the interface. Raman
spectroscopy proves to be a powerful tool for interface structure
investigation.",1308.5616v2
2014-03-02,"Improper Ferroelectricity and Piezoelectric Responses in Rhombohedral ($A$,$A^{\prime}$)$B_2$O$_6$ Perovskite Oxides","High-temperature electronic materials are in constant demand as the required
operational range for various industries increases. Here we design
$(A,A^\prime)B_2$O$_6$ perovskite oxides with [111] ``rock salt"" $A$-site
cation order and predict them to be potential high-temperature piezoelectric
materials. By selecting bulk perovskites which have a tendency towards only
out-of-phase $B$O$_6$ rotations, we avoid possible staggered ferroelectric to
paraelectric phase transitions while also retaining non-centrosymmetric crystal
structures necessary for ferro- and piezoelectricity. Using density functional
theory calculations, we show that (La,Pr)Al$_2$O$_6$ and (Ce,Pr)Al$_2$O$_6$
display spontaneous polarizations in their polar ground state structures; we
also compute the dielectric and piezoelectric constants for each phase.
Additionally, we predict the critical phase transition temperatures for each
material from first-principles to demonstrate that the piezoelectric responses,
which are comparable to traditional lead-free piezoelectrics, should persist to
high temperature. These features make the rock salt $A$-site ordered aluminates
candidates for high-temperature sensors, actuators, or other electronic
devices.",1403.0151v1
2014-03-10,Solvent Induced Proton Hopping at a Water-Oxide Interface,"Despite widespread interest, a detailed understanding of the dynamics of
proton transfer at interfaces is lacking. Here we use ab initio molecular
dynamics to unravel the connection between interfacial water structure and
proton transfer for the widely studied and experimentally well-characterized
water-ZnO$(10\bar{1}0)$ interface. We find that upon going from a single layer
of adsorbed water to a liquid multilayer changes in the structure are
accompanied by a dramatic increase in the proton transfer rate at the surface.
We show how hydrogen bonding and rather specific hydrogen bond fluctuations at
the interface are responsible for the change in the structure and proton
transfer dynamics. The implications of this for the chemical reactivity and for
the modelling of complex wet oxide interfaces in general are also discussed.",1403.2416v1
2014-03-11,Electrical and thermal conductivities of reduced graphene oxide/polystyrene composites,"The author reports an experimental study of electrical and thermal transport
in reduced graphene oxide (RGO)/polystyrene (PS) composites. The electrical
conductivity ($\sigma$) of RGO/PS composites with different RGO concentrations
at room temperature shows a percolation behavior with the percolation threshold
of ~ 0.25 vol.%. Their temperature-dependent electrical conductivity follows
Efros-Shklovskii (ES) variable range hopping (VRH) conduction in the
temperature range of 30 to 300 K. The thermal conductivity ($\kappa$) of
composites is enhanced by ~ 90 % as the concentration is increased from 0 to 10
vol.%. The thermal conductivity of composites approximately linearly increases
with increasing temperature from 150 to 300 K. Composites with a higher
concentration show a stronger temperature dependence in the thermal
conductivity.",1403.2467v2
2016-11-04,Origin of multistate resistive switching in Ti/manganite/Si$O_x$/Si heterostructures,"We report on the growth and characterization of
Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/Si$O_x$/n-Si memristive devices. We demonstrate
that using current as electrical stimulus unveils an intermediate resistance
state, in addition to the usual high and low resistance states that are
observed in standard voltage controlled experiments. Based on thorough
electrical characterization (impedance spectroscopy, current-voltage curves
analysis), we disclose the contribution of three different microscopic regions
of the device to the transport properties: an ohmic incomplete metallic
filament, a thin manganite layer below the filament tip exhibiting
Poole-Frenkel like conduction, and the SiOx layer with an electrical response
well characterized by a Child-Langmuir law. Our results suggest that the
existence of the SiOx layer plays a key role in the stabilization of the
intermediate resistance level, indicating that the combination of two or more
active RS oxides adds functionalities in relation to single-oxide devices. We
understand that these multilevel devices are interesting and promising as their
fabrication procedure is rather simple and they are fully compatible with
standard Si-based electronics.",1611.01552v2
2016-11-17,Large bipolarons and oxide superconductivity,"Large-bipolaron superconductivity is plausible with carrier densities well
below those of conventional metals. Bipolarons form when carriers self-trap in
pairs. Coherently moving large-bipolarons require extremely large ratios of
static to optical dielectric-constants. The mutual Coulomb repulsion of a
planar large-bipolarons paired carriers drives it to a four-lobed shape. A
phonon-mediated attraction among large-bipolarons propels their condensation
into a liquid. This liquids excitations move slowly with a huge effective mass.
Excitations concomitant weak scattering by phonons produces a moderate
low-temperature dc resistivity that increases linearly with rising temperature.
With falling temperature an energy gap opens between large-bipolarons
excitations and those of their self-trapped electronic carriers.",1611.05813v2
2016-11-23,Detection of confined current paths on oxide surfaces by local-conductivity atomic force microscopy with atomic resolution,"The analysis of the electronic surface properties of transition metal oxides
being key materials for future nanoelectronics requires a direct
characterization of the conductivity with highest spatial resolution. Using
local conductivity atomic force microscopy (LC-AFM) we demonstrate the
possibility of recording current maps with true atomic resolution. The
application of this technique on surfaces of reduced TiO$_2$ and SrTiO$_3$
reveals that the distribution of surface conductivity has a significant
localized nature. Assisted by density functional theory (DFT) we propose that
the presence of oxygen vacancies in the surface layer of such materials can
introduce short range disturbances of electronic structure with confinement of
metallic states on the nanoscale.",1611.07773v1
2016-12-31,Room temperature single photon emission from oxidized tungsten disulphide multilayers,"Two dimensional systems offer a unique platform to study light matter
interaction at the nanoscale. In this work we report on robust quantum emitters
fabricated by thermal oxidation of tungsten disulphide multilayers. The
emitters show robust, optically stable, linearly polarized luminescence at room
temperature, can be modeled using a three level system, and exhibit moderate
bunching. Overall, our results provide important insights into understanding of
defect formation and quantum emitter activation in 2D materials.",1701.00041v1
2017-01-06,Fabrication and properties of luminescence polymer composites with erbium/ytterbium oxides and gold nanoparticles,"Rare-earth-doped optical materials are important for light sources in
optoelectronics, as well as for efficient optical amplification elements and
other elements of photonics. On the basis of the previously developed method of
anhydrous, low-temperature synthesis of Er/Yb oxides from their chlorides we
fabricated proper nanoparticles with defined parameters and used them for the
development of optically transparent, luminescent polymer nanocomposite with
low optical scattering, suitable for direct, light-induced formation of
photonic elements. Introduction of preformed gold nanoparticles in such a
nanocomposite was also performed and an enhancement of luminescence due to the
influence of plasmon effects was detected.",1701.01605v1
2017-01-09,Six-fold crystalline anisotropic magnetoresistance in the (111) LaAlO$_3$/SrTiO$_3$ oxide interface,"We measured the magnetoresistance of the 2D electron liquid formed at the
(111) LaAlO$_3$/SrTiO$_3$ interface. The hexagonal symmetry of the interface is
manifested in a six-fold crystalline component appearing in the anisotropic
magnetoresistance (AMR) and planar Hall data, which agree well with symmetry
analysis we performed. The six-fold component increases with carrier
concentration, reaching 15% of the total AMR signal. Our results suggest the
coupling between higher itinerant electronic bands and the crystal as the
origin of this effect and demonstrate that the (111) oxide interface is a
unique hexagonal system with tunable magnetocrystalline effects.",1701.02153v2
2017-01-10,High performance graphene oxide-based humidity sensor integrated on a photonic crystal cavity,"We report a high performance relative humidity (RH) microsensor by coating a
few-layer graphene oxide (GO) flake over a photonic crystal (PC) cavity. Since
the GO layer has a high water-activity and interacts with the evanescent cavity
mode strongly, the exposure of GO-PC cavity in varied humidity levels results
in significant resonant wavelength shifts, showing a slope of 0.68 nm/%RH in
the range of 60%-85% RH. By interrogating the power variation of the cavity
reflection, the microsensor presents an ultrahigh sensitivity exceeding 3.9
dB/%RH. Relying on the unimpeded permeation of water molecules through the GO
interlayers and microscale distribution of the cavity mode, the integrated
sensor has a response time less than 100 ms, which promises successful
measurements of human breathing. Combining with the ease of fabrication, this
high performance RH sensor has potential applications requiring optical access,
device compactness, and fast dynamic response.",1701.02499v1
2017-01-17,Conditions for $T^2$ resistivity from electron-electron scattering,"Many complex oxides (including titanates, nickelates and cuprates) show a
regime in which resistivity follows a power law in temperature ($\rho\propto
T^2$). By analogy to a similar phenomenon observed in some metals at low
temperature, this has often been attributed to electron-electron (Baber)
scattering. We show that Baber scattering results in a $T^2$ power law only
under several crucial assumptions which may not hold for complex oxides. We
illustrate this with sodium metal ($\rho_\text{el-el}\propto T^2$) and
strontium titanate ($\rho_\text{el-el}\not\propto T^2$). We conclude that an
observation of $\rho\propto T^2$ is not sufficient evidence for
electron-electron scattering.",1701.04744v1
2017-01-21,"Plasmonic Doped Semiconductor Nanocrystals: Properties, Fabrication, Applications and Perspectives","Degenerately doped semiconductor nanocrystals (NCs) are of recent interest to
the NC community due to their tunable localized surface plasmon resonances
(LSPRs) in the near infrared (NIR). The high level of doping in such materials
with carrier densities in the range of 1021 cm^-3 leads to degeneracy of the
doping levels and intense plasmonic absorption in the NIR. The lower carrier
density in degenerately doped semiconductor NCs compared to noble metals
enables LSPR tuning over a wide spectral range, since even a minor change of
the carrier density strongly affects the spectral position of the LSPR. We
focus on copper chalcogenide NCs and impurity doped metal oxide NCs as the most
investigated alternatives to noble metals. We shed light on the structural
changes upon LSPR tuning in vacancy doped copper chalcogenide NCs and deliver a
picture for the fundamentally different mechanism of LSPR modification of
impurity doped metal oxide NCs. We review on the peculiar optical properties of
plasmonic degenerately doped NCs by highlighting the variety of different
optical measurements and optical modeling approaches. These findings are merged
in an exhaustive section on new and exciting applications based on the special
characteristics that plasmonic semiconductor NCs bring along.",1701.05972v1
2017-01-23,Determination of Hund's coupling in 5d Oxides using Resonant Inelastic X-ray Scattering,"We report resonant inelastic X-ray scattering (RIXS) measurements on ordered
double perovskite samples containing Re$^{5+}$ and Ir$^{5+}$ with $5d^2$ and
$5d^4$ electronic configurations respectively. In particular, the observed RIXS
spectra of Ba$_2$YReO$_6$ and Sr$_2$MIrO$_6$ (M=Y, Gd) show sharp
intra-t$_{2g}$ transitions, which can be quantitatively understood using a
minimal `atomic' Hamiltonian incorporating spin-orbit coupling ($\lambda$) and
Hund's coupling ($J_H$). Our analysis yields $\lambda=0.38(2)$eV with
$J_H=0.26(2)$eV for Re$^{5+}$, and $\lambda=0.42(2)$eV with $J_H=0.25(4)$eV for
Ir$^{5+}$. Our results provide the first sharp estimates for the Hund's
coupling in $5d$ oxides, and suggest that it should be treated on equal footing
with spin-orbit interaction in multi-orbital $5d$ transition metal compounds.",1701.06584v3
2017-01-25,Non-conventional porous 12CaO7Al2O3 Transparent Oxide Semiconductor: A Journey from foams to cubes,"In the current study easy method to synthesize C12A7 particles with cubic
morphology was investigated for the application of Transparent Conducting Oxide
layer in thinfilm solar cell. By self-combustion method with proper amount of
urea addition, cubic and foamy structures of C12A7 were achieved at 950 {\deg}C
and at 510 {\deg}C respectively. Pure C12A7 formation confirmed by P-XRD and
growth mechanism of the cubes was also understood by SEM and FT-IR analysis.
Further the band gap was measured 3.07 eV in case of 510 {\deg}C and 3.32 eV in
case of 950 {\deg}C synthesized particles with the help of UV-Vis analysis.
During PL single sharp peaks at 399 nm noticed which indicates less defective
C12A7 at 950 {\deg}C, confirmed by XRD having more crystallinity and less
strain. No trap state or radiative recombination observed in case of C12A7
synthesized at 950 {\deg}C sample. Conductivity from conductometry titration
method was found to be 9.223 mS at 26.3 {\deg}C and 747.33 mS at 26.4 {\deg}C
for 510 {\deg}C and 950 {\deg}C synthesized samples respectively.",1701.07187v1
2017-01-31,Dirac nodal lines and induced spin Hall effect in metallic rutile oxides,"We have found Dirac nodal lines (DNLs) in the band structures of metallic
rutile oxides IrO$_2$, OsO$_2$, and RuO$_2$ and revealed a large spin Hall
conductivity contributed by these nodal lines, which explains a strong spin
Hall effect (SHE) of IrO$_2$ discovered recently. Two types of DNLs exist. The
first type forms DNL networks that extend in the whole Brillouin zone and
appears only in the absence of spin-orbit coupling (SOC), which induces surface
states on the boundary. Because of SOC-induced band anti-crossing, a large
intrinsic SHE can be realized in these compounds. The second type appears at
the Brillouin zone edges and is stable against SOC because of the protection of
nonsymmorphic symmetry. Besides reporting new DNL materials, our work reveals
the general relationship between DNLs and the SHE, indicating a way to apply
Dirac nodal materials for spintronics.",1701.09089v1
2017-04-06,Density inhomogeneities and Rashba spin-orbit coupling interplay in oxide interfaces,"There is steadily increasing evidence that the two-dimensional electron gas
(2DEG) formed at the interface of some insulating oxides like LaAlO3/SrTiO3 and
LaTiO3/SrTiO3 is strongly inhomogeneous. The inhomogeneous distribution of
electron density is accompanied by an inhomogeneous distribution of the
(self-consistent) electric field confining the electrons at the interface. In
turn this inhomogeneous transverse electric field induces an inhomogeneous
Rashba spin-orbit coupling (RSOC). After an introductory summary on two
mechanisms possibly giving rise to an electronic phase separation accounting
for the above inhomogeneity,we introduce a phenomenological model to describe
the density-dependent RSOC and its consequences. Besides being itself a
possible source of inhomogeneity or charge-density waves, the density-dependent
RSOC gives rise to interesting physical effects like the occurrence of
inhomogeneous spin-current distributions and inhomogeneous quantum-Hall states
with chiral ""edge"" states taking place in the bulk of the 2DEG. The
inhomogeneous RSOC can also be exploited for spintronic devices since it can be
used to produce a disorder-robust spin Hall effect.",1704.01852v1
2017-04-25,Perovskite Substrates Boost the Thermopower of Cobaltate Thin Films at High Temperatures,"Transition metal oxides are promising candidates for thermoelectric
applications, because they are stable at high temperature and because strong
electronic correlations can generate large Seebeck coefficients, but their
thermoelectric power factors are limited by the low electrical conductivity. We
report transport measurements on Ca3Co4O9 films on various perovskite
substrates and show that reversible incorporation of oxygen into SrTiO3 and
LaAlO3 substrates activates a parallel conduction channel for p-type carriers,
greatly enhancing the thermoelectric performance of the film-substrate system
at temperatures above 450 {\deg}C. Thin-film structures that take advantage of
both electronic correlations and the high oxygen mobility of transition metal
oxides thus open up new perspectives for thermopower generation at high
temperature.",1704.07660v1
2017-04-25,Observation of Caroli-de Gennes-Matricon Vortex States in YBa$_2$Cu$_3$O$_{7-δ}$,"The copper oxides present the highest superconducting temperature and
properties at odds with other compounds, suggestive of a fundamentally
different superconductivity. In particular, the Abrikosov vortices fail to
exhibit localized states expected and observed in all clean superconductors. We
have explored the possibility that the elusive vortex-core signatures are
actually present but weak. Combining local tunneling measurements with
large-scale theoretical modeling, we positively identify the vortex states in
YBa$_2$Cu$_3$O$_{7-\delta}$. We explain their spectrum and the observed
variations thereof from one vortex to the next by considering the effects of
nearby vortices and disorder in the vortex lattice. We argue that the
superconductivity of copper oxides is conventional, but the spectroscopic
signature does not look so because the superconducting carriers are a minority.",1704.07685v2
2018-05-03,Enhanced Electron Transport in Thin Copper Films via Atomic-Layer Materials Capping,"Using first-principles calculations based on density functional theory and
non-equilibrium Green's functions, we characterized the effect of surface
termination on the electronic transport properties of nanoscale Cu slabs. With
ideal, clean (111) surfaces and oxidized ones as baselines we explore the
effect of capping the slabs with graphene, hexagonal boron nitrate, molybdenum
disulfide and stanene. Surface oxide suppresses balistic conductance by a
factor of 10 compared to the ideal surface. Capping the ideal copper surface
with graphene slightly increase conductance but MoS$_2$ and stanene have the
opposite effect due to stronger interactions at the interface. Interestingly,
we find that capping atomistically roughed copper surfaces with graphene or
MoS$_2$ decreases the resistance per unit length by 20 and 13%, respectively,
due to reduced scattering. The results presented in this work suggest that
two-dimensional materials can be used as an ultra-thin liner in metallic
interconnect technology without increasing the interconnect line resistivity
significantly.",1805.01517v1
2018-05-07,Investigation of the Thermal Stability of the Carbon Framework of Graphene Oxide,"In this study, we use our recently prepared graphene oxide (GO) with an
almost intact {\sigma}-framework of C-atoms (ai-GO) to probe the thermal
stability of the carbon framework for the first time. Ai-GO exhibits few
defects only by preventing CO2 formation during synthesis. Ai-GO was thermally
treated before chemical reduction and subsequently the resulting defect density
in graphene was determined by statistical Raman microscopy. Surprisingly, the
carbon framework of ai-GO is stable in thin films up to 100 {\deg}C.
Furthermore, we find evidence for an increasing quality of ai-GO upon annealing
at 50 {\deg}C before reduction. The carbon framework of GO prepared according
to the popular Hummers method (GO-c)appears to be less stable and decomposition
starts at 50 {\deg}C what is qualitatively indicated by CO2-trapping
experiments in {\mu}m-thin films. Information about the stability of GO is
important for storing, processing and applying GO in applications.",1805.02654v1
2018-05-08,Surface Sensitive NMR Detection of the SEI Layer on Reduced Graphene Oxide,"The solid electrolyte interphase (SEI) is detrimental for rechargeable
batteries performance and lifetime. Understanding its formation requires
analytical techniques that provide molecular level insight. Here dynamic
nuclear polarization (DNP) is utilized for the first time for enhancing the
sensitivity of solid state NMR (ssNMR) spectroscopy to the SEI. The approach is
demonstrated on reduced-graphene oxide (rGO) cycled in Li-ion cells in natural
abundance and 13C-enriched electrolyte solvents. Our results indicate that DNP
enhances the signal of outer SEI layers, enabling detection of natural
abundance 13C spectra from this component of the SEI at reasonable timeframes.
Furthermore, 13C- enriched electrolytes measurements at 100K provide ample
sensitivity without DNP due to the vast amount of SEI filling the rGO pores,
thereby allowing differentiating the inner and outer SEI layers composition.
Developing this approach further will benefit the study of many electrode
materials, equipping ssNMR with the needed sensitivity to efficiently probe the
SEI.",1805.03068v1
2018-05-04,Highly Integrated Organic-Inorganic Hybrid Architectures by Non-Covalent Exfoliation of Graphite and Assembly with Zinc Oxide Nanoparticles,"Herein, we report an easy, straight forward, and versatile approach to build
0D/2D hybrid nanoparticle/graphene architectures by means of non-covalent
chemistry and a modified Layer-by-Layer assembly. Three water soluble perylene
diimides were employed to efficiently exfoliate pristine graphite into
positively charged few- and multilayer graphene flakes. Further combination of
these cationic building blocks with anionic zinc oxide nanoparticles led to the
formation of tailor-made hybrid films via electrostatic and van der Waals
interactions. These supramolecular hybrid nano-structures were thoroughly
characterized by UV/Vis and Raman spectroscopy, AFM as well as electron
microscopy, showing outstanding long-range homogeneity and high integrity in
the centimetre-scale, uniform nanometric thickness between 60-100 nm and a
close contact between the different building blocks. Due to their
straightforward assembly. These architectures can be considered as promising
candidates for numerous advanced applications especially in the field of energy
storage and conversion.",1805.09129v1
2008-07-02,Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping,"Patterned graphene shows substantial potential for applications in future
molecular-scale integrated electronics. Environmental effects are a critical
issue in a single layer material where every atom is on the surface. Especially
intriguing is the variety of rich chemical interactions shown by molecular
oxygen with aromatic molecules. We find that O2 etching kinetics vary strongly
with the number of graphene layers in the sample. Three-layer-thick samples
show etching similar to bulk natural graphite. Single-layer graphene reacts
faster and shows random etch pits in contrast to natural graphite where
nucleation occurs at point defects. In addition, basal plane oxygen species
strongly hole dope graphene, with a Fermi level shift of ~0.5 eV. These oxygen
species partially desorb in an Ar gas flow, or under irradiation by far UV
light, and readsorb again in an O2 atmosphere at room temperature. This
strongly doped graphene is very different than graphene oxide made by mineral
acid attack.",0807.0261v1
2008-07-23,Fluorescent oxide nanoparticles adapted to active tips for near-field optics,"We present a new kind of fluorescent oxide nanoparticles with properties well
suited to active-tip based near-field optics. These particles with an average
diameter in the range 5-10 nm are produced by Low Energy Cluster Beam
Deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission
electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), classical
photoluminescence, cathodoluminescence and near-field scanning optical
microscopy (NSOM). Particles of extreme photo-stability as small as 10 nm in
size are observed. These emitters are validated as building blocks of active
NSOM tips by coating a standard optical tip with a 10 nm thick layer of
YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing
NSOM imaging of test surfaces.",0807.3634v2
2008-07-30,PEGylated Nano-Graphene Oxide for Delivery of Water Insoluble Cancer Drugs,"It is known that many potent, often aromatic drugs are water insoluble, which
has hampered their use for disease treatment. In this work, we functionalized
nano-graphene oxide (NGO), a novel graphitic material, with branched
polyethylene glycol (PEG) to obtain a biocompatible NGO-PEG conjugate stable in
various biological solutions, and used them for attaching hydrophobic aromatic
molecules including a camptothecin (CPT) analog, SN38 non-covalently via pi-pi
stacking. The resulting NGO-PEG-SN38 complex exhibited excellent water
solubility while maintaining its high cancer cell killing potency similar to
that of the free SN38 molecules in organic solvents. The efficacy of
NGO-PEG-SN38 was far higher than that of irinotecan (CPT-11), a FDA approved
water soluble SN38 prodrug used for the treatment of colon cancer. Our results
showed that graphene is a novel class of material promising for biological
applications including future in vivo cancer treatment with various aromatic,
low-solubility drugs.",0807.4959v1
2009-12-03,Effects of polarization on the band-structure of delafossite transparent conductive oxides,"We use hybrid functionals and restricted self-consistent GW, state-of-the-art
theoretical approaches for quasiparticle band structures, to study the
electronic states of delafossite Cu(Al,In)O$_2$, the first p-type and bipolar
transparent conductive oxides. We show that self-consistent GW gives remarkably
wider band gaps than all the other approaches used so far. Accounting for
polaronic effects in the GW scheme we recover a very nice agreement with
experiments. Furthermore, the modifications with respect to the Kohn-Sham bands
are strongly k-dependent, which makes questionable the common practice of using
a scissor operator. Finally, our results support the view that the low energy
structures found in optical experiments, and initially attributed to an
indirect transition, are due to intrinsic defects in the samples.",0912.0618v2
2009-12-09,"Superconductivity in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6)","We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr, V), which were found in previous studies. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs layer and perovskite-type block layer. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). Bulk
superconductivity with Tc(onset) of ~26 K was observed for a partially Co
substituted sample. Moreover, Co-free and Ti-rich samples exhibited higher
Tc(onset)'s above 35 K, which were further enhanced by applying high pressures
up to ~43 K.",0912.1840v1
2009-12-10,Quasiparticle calculations of the electronic properties of ZrO$_2$ and HfO$_2$ polymorphs and their interface with Si,"Quasiparticle calculations are performed to investigate the electronic band
structures of various polymorphs of Hf and Zr oxides. The corrections with
respect to density-functional-theory results are found to depend only weakly on
the crystal structure. Based on these bulk calculations as well as those for
bulk Si, the effect of quasiparticle corrections is also investigated for the
band offsets at the interface between these oxides and Si assuming that the
lineup of the potential at the interface is reproduced correctly within
density-functional theory. On the one hand, the valence band offsets are
practically unchanged with a correction of a few tenths of eV. On the other
hand, conduction band offsets are raised by 1.3--1.5 eV. When applied to
existing calculations for the offsets at the density-functional-theory level,
our quasiparticle corrections provide results in good agreement with the
experiment.",0912.1977v1
2009-12-14,Visualizing Graphene Based Sheets by Fluorescence Quenching Microscopy,"Graphene based sheets have stimulated great interest due to their superior
mechanical, electrical and thermal properties. A general visualization method
that allows quick observation of these single atomic layers would be highly
desirable as it can greatly facilitate sample evaluation and manipulation, and
provide immediate feedback to improve synthesis and processing strategies. Here
we report that graphene based sheets can be made highly visible under a
fluorescence microscope by quenching the emission from a dye coating, which can
be conveniently removed afterwards by rinsing without disrupting the sheets.
Current imaging techniques for graphene based sheets rely on the use of special
substrates. In contrast, the fluorescence quenching mechanism is no longer
limited by the types of substrates. Graphene, reduced graphene oxide, or even
graphene oxide sheets deposited on arbitrary substrates can now be readily
visualized by eye with good contrast for layer counting. Direct observation of
suspended sheets in solution was also demonstrated. The fluorescence quenching
microscopy offers unprecedented imaging flexibility and could become a general
tool for characterizing graphene based materials.",0912.2675v1
2011-10-31,Direct Observation of an Interface Dipole between Two Metallic Oxides Caused by Localized Oxygen Vacancies,"Oxygen vacancies are increasingly recognized to play a role in phenomena
observed at transition-metal oxide interfaces. Here we report a study of
SrRuO3/La0.7Sr0.3MnO3 (SRO/LSMO) interfaces using a combination of quantitative
aberration-corrected scanning transmission electron microscopy, electron energy
loss spectroscopy, and density-functional calculations. Cation displacements
are observed at the interface, indicative of a dipole-like electric field even
though both materials are nominally metallic. The observed displacements are
reproduced by theory if O vacancies are present in the near-interface LSMO
layers. The results suggest that atomic-scale structural mapping can serve as a
quantitative indicator of the presence of O vacancies at interfaces.",1111.0023v1
2011-11-07,"Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies","Electronic structure of nickel nanoparticles encapsulated in carbon was
characterized by photoelectron, X-ray absorption, and X-ray emission
spectroscopies. Experimental spectra are compared with the density of states
calculated in the frame of the density functional theory. The carbon shell of
Ni nanoparticles has been found to be multilayer graphene with significant
(about 6%) amount of Stone--Wales defects. Results of the experiments evidence
protection of the metallic nanoparticles from the environmental degradation by
providing a barrier against oxidation at least for two years. Exposure in air
for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles
with coverage of functional groups.",1111.1470v1
2011-11-09,Ab initio calculation of d-d excitations in quasi-one-dimensional Cu d9 correlated materials,"With wavefunction-based electronic-structure calculations we determine the Cu
d-d excitation energies in quasi-one-dimensional spin-chain and ladder copper
oxides. A complete set of local excitations has been calculated for cuprates
with corner-sharing (Sr2CuO3 and SrCuO2) and edge-sharing (LiVCuO4, CuGeO3,
LiCu2O2 and Li2CuO2) CuO4 plaquettes, with corner-sharing CuF6 octahedra
(KCuF3), for the ladder system CaCu2O3, and for multiferroic cupric oxide CuO.
Our data compare well with available results of optical absorption measurements
on KCuF3 and the excitation energies found by resonant inelastic x-ray
scattering experiments for CuO. The ab initio results we report for the other
materials should be helpful for the interpretation of future resonant inelastic
x-ray scattering experiments on those highly anisotropic compounds.",1111.2231v1
2011-11-14,Ultrafast strain engineering in complex oxide heterostructures,"We report on ultrafast optical experiments in which femtosecond mid-infrared
radiation is used to excite the lattice of complex oxide heterostructures. By
tuning the excitation energy to a vibrational mode of the substrate, a
long-lived five-order-of-magnitude increase of the electrical conductivity of
NdNiO3 epitaxial thin films is observed as a structural distortion propagates
across the interface. Vibrational excitation, extended here to a wide class of
heterostructures and interfaces, may be conducive to new strategies for
electronic phase control at THz repetition rates.",1111.3155v1
2011-11-16,Dimensionality Control of Electronic Phase Transitions in Nickel-Oxide Superlattices,"The competition between collective quantum phases in materials with strongly
correlated electrons depends sensitively on the dimensionality of the electron
system, which is difficult to control by standard solid-state chemistry. We
have fabricated superlattices of the paramagnetic metal LaNiO3 and the wide-gap
insulator LaAlO3 with atomically precise layer sequences. Using optical
ellipsometry and low-energy muon spin rotation, superlattices with LaNiO3 as
thin as two unit cells are shown to undergo a sequence of collective
metalinsulator and antiferromagnetic transitions as a function of decreasing
temperature, whereas samples with thicker LaNiO3 layers remain metallic and
paramagnetic at all temperatures. Metal-oxide superlattices thus allow control
of the dimensionality and collective phase behavior of correlated-electron
systems.",1111.3819v1
2011-12-31,Modeling of biological doses and mechanical effects on bone transduction,"Shear stress, hormones like parathyroid and mineral elements like calcium
mediate the amplitude of stimulus signal which affects the rate of bone
remodeling. The current study investigates the theoretical effects of different
metabolic doses in stimulus signal level on bone. The model was built
considering the osteocyte as the sensing center mediated by coupled mechanical
shear stress and some biological factors. The proposed enhanced model was
developed based on previously published works dealing with different aspects of
bone transduction. It describes the effects of physiological doses variations
of Calcium, Parathyroid Hormone, Nitric Oxide and Prostaglandin E2 on the
stimulus level sensed by osteocytes in response to applied shear stress
generated by interstitial fluid flow. We retained the metabolic factors
(Parathyroid Hormone, Nitric Oxide, and Prostaglandin E2) as parameters of bone
cell mechanosensitivity because stimulation/inhibition of induced pathways
stimulates osteogenic response in vivo. We then tested the model response in
term of stimulus signal variation versus the biological factors doses to
external mechanical stimuli. Despite the limitations of the model, it is
consistent and has physiological bases. Biological inputs are histologically
measurable. This makes the model amenable to experimental verification.",1201.0239v1
2012-01-10,Adsorption and dissociation of H$_{2}$O monomer on ceria(111): Density functional theory calculations,"The adsorption properties of isolated H$_{2}$O molecule on stoichiometric and
reduced (with on-surface oxygen vacancy) ceria(1111) surfaces at low coverage
are theoretically investigated by using density-functional-theory+\emph{U}
calculations and \textit{ab initio} molecular dynamics simulations. We identify
the most stable adsorption configurations on these two kinds of surfaces, which
form two hydrogen bonds between the water molecule and the oxide surface. The
electronic structures indicate that the hybridization of the molecular orbitals
of water and surface-layer O-2\emph{p} states dominates the interactions
between adsorbate and substrate. The barrier of 0.51 eV for water diffusion on
the stoichiometric surface implies the inertia of water unless up to a high
temperature of 600 K, which is confirmed by the molecular dynamics simulations.
For the reduced surface, we find that the oxygen vacancy obviously enhances the
interaction. Moreover, it is facilitated for water to dissociate into H and OH
species with a hydroxyl surface formed, instead of oxidizing the reduced
surface with the production of hydrogen gas. In addition, the molecular
dynamics simulations at low temperature 100 K confirm the dissociation process.",1201.1974v2
2012-01-23,"Simulation study of a highly efficient, high resolution X-ry sensor based on self-organizing aluminum oxide","State of the art X-ray imaging sensors comprise a trade-off between the
achievable efficiency and the spatial resolution. To overcome such limitations,
the use of structured and scintillator filled aluminum oxide (AlOx) matrices
has been investigated. We used Monte-Carlo (MC) X-ray simulations to determine
the X-ray imaging quality of these AlOx matrices. Important factors which
influence the behavior of the matrices are: filling factor (surface ratio
between channels and 'closed' AlOx), channel diameter, aspect ratio, filling
material etc. Therefore we modeled the porous AlOx matrix in several different
ways with the MC X-ray simulation tool ROSI [1] and evaluated its properties to
investigate the achievable performance at different X-ray spectra, with
different filling materials (i.e. scintillators) and varying channel height and
pixel readout. In this paper we focus on the quantum efficiency, the spatial
resolution and image homogeneity.",1201.4660v1
2012-01-28,Topological Quantum Phase Transition in 5$d$ Transition Metal Oxide Na$_2$IrO$_3$,"We predict a quantum phase transition from normal to topological insulators
in the 5$d$ transition metal oxide Na$_2$IrO$_3$, where the transition can be
driven by the change of the long-range hopping and trigonal crystal field
terms. From the first-principles-derived tight-binding Hamiltonian we determine
the phase boundary through the parity analysis. In addition, our
first-principles calculations for Na$_2$IrO$_3$ model structures show that the
interlayer distance can be an important parameter for the existence of a
three-dimensional strong topological insulator phase. Na$_2$IrO$_3$ is
suggested to be a candidate material which can have both a nontrivial topology
of bands and strong electron correlations.",1201.5929v2
2012-04-27,Structural recovery of ion implanted ZnO nanowires,"Ion implantation is an interesting method to dope semiconducting materials
such as zinc oxide provided that the implantation-induced defects can be
subsequently removed. Nitrogen implantation followed by anneals under O2 were
carried out on zinc oxide nanowires in the same conditions as in a previous
study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct
comparison of the defect recovery mechanisms. Transmission electron microscopy
and cathodoluminescence were carried out to assess the effects of nitrogen
implantation and of subsequent anneals on the structural and optical properties
of ZnO nanowires. Defect recovery is shown to be more effective in nanowires
compared with bulk material due to the proximity of free surfaces.
Nevertheless, the optical emission of implanted and annealed nanowires
deteriorated compared to as-grown nanowires, as also observed for unimplanted
and annealed nanowires. This is tentatively attributed to the dissociation of
excitons in the space charge region induced by O2 adsorption on the nanowire
surface.",1204.6138v1
2012-04-29,Exponential decay of equal-time four-point correlation functions in the Hubbard model on the copper-oxide lattice,"For the Hubbard model on the two-dimensional copper-oxide lattice, equal-time
four-point correlation functions at positive temperature are proved to decay
exponentially in the thermodynamic limit if the magnitude of the on-site
interactions is smaller than some power of temperature. This result especially
implies that the equal-time correlation functions for singlet Cooper pairs of
various symmetries decay exponentially in the distance between the Cooper pairs
in high temperatures or in low-temperature weak-coupling regimes. The proof is
based on a multi-scale integration over the Matsubara frequency.",1204.6470v3
2013-09-18,Pseudosymmetric bias and correct estimation of Coulomb/confinement energy for unintentional quantum dot in channel of metal-oxide-semiconductor field-effect transistor,"We describe a measurement method that enables the correct estimation of the
charging energy of an unintentional quantum dot (QD) in the channel of a
metal-oxide-semiconductor field-effect transistor (MOSFET). If the channel has
a dominant QD with a large charging energy and an array of stray QDs with much
weaker charging, this method eliminates the additional voltage drops due to
stray QDs by regarding the stray QDs as series resistors. We apply this method
to a short-channel MOSFET and find that the charging energy of the dominant QD
can indeed be smaller than the size of the Coulomb diamond.",1309.4525v1
2013-09-19,Near-Field Optical Effect of a Core-Shell Nanostructure In Proximity to a Flat Surface,"We provide an analytical solution to study the near field optical effect of a
core-shell nanostructure in proximity to a flat surface, within quasi-static
approximation. The distribution of electrostatic potential and field
enhancement in this complex geometry are obtained by solving a set of linear
equations. This analytical result can be applied to a wide range of systems
associated with near field optics and surface plasmon polaritons. As an
illustration of the power of this technique, we study the field attenuation
effect of oxidized shell in a silver tip in near field scanning microscope. The
thickness of oxidized layer can be monitored by measuring the light intensity.
In addition, we propose a novel method to detect local temperature with spatial
resolution down to nm scale, based on a Ag-Au core-shell structure.",1309.5104v1
2013-09-20,CHx adsorption (x=1-4) and thermodynamic stability on CeO2(111) surface: A first-principles investigation,"We present an ab initio investigation of the interaction between methane, its
dehydrogenated forms and the cerium oxide surface. In particular, the
stoichiometric CeO2(111) surface and the one with oxygen vacancies are
considered. We study the geometries, energetics and electronic structures of
various configurations of these molecules adsorbed on the surface in vacuum,
and we extend the analysis to realistic environmental conditions. A phase
diagram of the adsorbate-surface system is constructed and relevant transition
phases are analyzed in detail, showing the conditions where partial oxidation
of methane can occur.",1309.5177v4
2014-05-05,"A model for the catalytic oxidation of CO that includes CO desorption and diffusion, O repulsion, and impurities in the gas phase","We present kinetic Monte Carlo simulations exploring the nonequilibrium phase
diagram of a modified Ziff-Gulari-Barshad (ZGB) dynamic lattice-gas model for
the catalytic oxidation of carbon monoxide (CO) on a surface. The modified
model includes the simultaneous presence of contaminants in the gas phase, CO
desorption, CO diffusion, and strong repulsion between adsorbed oxygen (O)
atoms; all of which have been observed in experimental systems. We find that
the strong O-O repulsion produces higher reaction rates, albeit in a reduced
reactive pressure window. In systems with impurities, the CO$_2$ production
rate is greatly reduced, but this effect is mitigated by CO desorption and
diffusion. CO desorption has the effect of widening the reactive pressure
window, while CO diffusion has the effect of increasing the reaction rate. In
some parameter regimes the presence of impurities destroys the discontinuous
transition between the reactive and high CO coverage phases.",1405.0948v2
2014-05-09,The role of random electric fields in relaxors,"PbZr_{1-x}Ti_xO_3 (PZT) and Pb(Mg_{1/3}Nb_{2/3})_{1-x}Ti_xO_3 (PMN-$x$PT) are
complex lead-oxide perovskites that display exceptional piezoelectric
properties for pseudorhombohedral compositions near a tetragonal phase
boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are
relaxors because the dielectric permittivity is frequency dependent and
exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to
PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and
correlates with a greater than 100% enhancement of the longitudinal
piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing
dielectric, structural, lattice dynamical, and piezoelectric measurements on
PZT and PMN-xPT, two nearly identical compounds that represent weak and strong
random electric field limits, we show that quenched (static) random fields
establish the relaxor phase and identify the order parameter.",1405.2306v1
2014-05-15,On the calculation of crystal field parameters using Wannier functions,"We discuss the calculation of crystal field splittings using Wannier
functions and show how the ligand field contributions can be separated from the
bare Coulomb contribution to the crystal field by constructing sets of Wannier
functions incorporating different levels of hybridization. We demonstrate this
method using SrVO$_3$ as a generic example of a transition metal oxide. We then
calculate trends in the crystal field splitting for two series of hypothetical
tetragonally distorted perovskite oxides and discuss the relation between the
calculated ""electro-static"" contribution to the crystal field and the simple
point charge model. Finally, we apply our method to the charge
disproportionated 5$d$ electron system CsAuCl$_3$. We show that the negative
charge transfer energy in this material leads to a reversal of the $p$-$d$
ligand contribution to the crystal field splitting such that the $e_g$ states
of the nominally Au$^{3+}$ cation are energetically lower than the
corresponding $t_{2g}$ states.",1405.3804v1
2014-05-17,High-performance bilayer metal-oxide thin film transistors using ultra-thin solution-processed ZrOx dielectric,"We reported here a high-performance In2O3/InZnO bilayer metal-oxide (BMO)
thin-film transistor (TFT) using ultra-thin solution-processed ZrOx dielectric.
A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing
the charge accumulation and yielding high carrier mobility. A thick layer of
InZnO controls the charge conductance resulting in low off-state current and
suitable threshold voltage. As a consequence, the BMO TFT showed higher
filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s).
More importantly, an on/off current ratio of 109, a subthreshold swing voltage
of 120 mV/decade, as well as a threshold voltage shift (less than 0.4 V) under
bias stress for 2.5 hours were obtained simultaneously. These promising
properties are obtained at a low operation voltage of 3 V. This work
demonstrates that the BMO TFT has great potential applications as switching
transistor and low-power devices.",1405.4373v2
2014-06-06,Probing the Electrical Properties of Overlapped Graphene Grain Boundaries by Raman spectroscopy,"The effect of grain boundaries and wrinkles on the electrical properties of
polycrystalline graphene is pronounced. Here we investigate the stitching
between grains of polycrystalline graphene, specifically, overlapping of layers
at the boundaries, grown by chemical vapor deposition (CVD) and subsequently
doped by the oxidized Cu substrate. We analyze overlapped regions between 60
and 220 nm wide via Raman spectroscopy, and find that some of these overlapped
boundaries contain AB stacked bilayers. The Raman spectra from the overlapped
grain boundaries are distinctly different from bilayer graphene and exhibit
splitting of the G band peak. The degree of splitting, peak widths, as well as
peak intensities depend on the width of the overlap. We attribute these
features to inhomogeneous doping by charge carriers (holes) across the
overlapped regions via the oxidized Cu substrate. As a result, the Fermi level
at the overlapped grain boundaries lies between 0.3 and 0.4 eV below the charge
neutrality point. Our results suggest an enhancement of electrical conductivity
across overlapped grain boundaries, similar to previously observed
measurements(1). The dependence of charge distribution on the width of
overlapping of grain boundaries may have strong implications for the growth of
large-area graphene with enhanced conductivity.",1406.1555v1
2014-06-18,Photoionization cross section of 1s orthoexcitons in cuprous oxide,"We report measurements of the attenuation of a beam of
orthoexciton-polaritons by a photoionizing optical probe. Excitons were
prepared in a narrow resonance by two photon absorption of a 1.016 eV, 54 ps
pulsed light source in cuprous oxide (Cu2O) at 1.4 K. A collinear, 1.165 eV, 54
ps probe delayed by 119 ps was used to measure the photoionization cross
section of the excitons. Two photon absorption is quadratic with respect to the
intensity of the pump and leads to polariton formation. Ionization is linear
with respect to the intensity of the probe. Subsequent carrier recombination is
quadratic with respect to the intenisty of the probe, and is distinguished
because it shifts the exciton momentum away from the polariton anticrossing;
the photoionizing probe leads to a rise in phonon-linked luminescence in
addition to the attenuation of polaritons. The evolution of the exciton density
was determined by variably delaying the probe pulse. Using the probe irradiance
and the reduction in the transmitted polariton light, a cross section of
3.9*10^(-22) m^2 was deduced for the probe frequency.",1406.4911v1
2014-06-25,Electron Glass in a three-dimensional system,"We report on non-equilibrium transport features observed in experiments using
three-dimensional amorphous indium-oxide films. It is demonstrated that all the
features that characterize intrinsic electron-glasses which heretofore were
seen in two-dimensional samples are also observed in field-effect measurements
of systems that exhibit three-dimensional variable-range-hopping. In
particular, a memory-dip is observed in samples configured with gate. The
memory-dip width and magnitude support models that associate the phenomenon
with the Coulomb-gap. The memory-dip and the glassy effects disappear once the
quenched disorder in the system is reduced and the system becomes diffusive.
This happens when the Ioffe-Regel dimensional parameter k_{F}l exceeds 0.3
which is the critical value for the metal-to-insulator transition in all
versions of the amorphous indium-oxides [Phys. Rev. B 86, 165101 (2012)]. This
confirms that being in the Anderson localized phase is a pre-requisite for
observing the memory-dip and the associated glassy effects. The results of the
gating experiments suggest that the out-of equilibrium effect caused by
inserted charge extend over spatial scales considerably larger than the
screening length.",1406.6455v2
2014-06-27,Competition between covalent bonding and charge transfer at complex-oxide interfaces,"Here we study the electronic properties of cuprate/manganite interfaces. By
means of atomic resolution electron microscopy and spectroscopy, we produce a
subnanometer scale map of the transition metal oxidation state profile across
the interface between the high $T_c$ superconductor YBa$_2$Cu$_3$O$_{7-\delta}$
and the colossal magnetoresistance compound (La,Ca)MnO$_3$. A net transfer of
electrons from manganite to cuprate with a peculiar non-monotonic charge
profile is observed. Model calculations rationalize the profile in terms of the
competition between standard charge transfer tendencies (due to band mismatch),
strong chemical bonding effects across the interface, and Cu substitution into
the Mn lattice, with different characteristic length scales.",1406.7323v1
2015-12-02,A machine learning-based selective sampling procedure for identifying the low energy region in a potential energy surface: a case study on proton conduction in oxides,"In this paper, we propose a selective sampling procedure to preferentially
evaluate a potential energy surface (PES) in a part of the configuration space
governing a physical property of interest. The proposed sampling procedure is
based on a machine learning method called the Gaussian process (GP), which is
used to construct a statistical model of the PES for identifying the region of
interest in the configuration space. We demonstrate the efficacy of the
proposed procedure for atomic diffusion and ionic conduction, specifically the
proton conduction in a well-studied proton-conducting oxide, barium zirconate
BaZrO3. The results of the demonstration study indicate that our procedure can
efficiently identify the low-energy region characterizing the proton conduction
in the host crystal lattice, and that the descriptors used for the statistical
PES model have a great influence on the performance.",1512.00623v2
2015-12-25,Photoluminescence from Silicon nanoparticles embedded in ammonium silicon hexafluoride,"Silicon (Si) nanoparticles (NPs) were synthesized by transforming Si wafer
surface to ammonium silicon hexafluoride (ASH) or (NH4)2SiF6 under acid vapor
treatment. Si-NPs are embedded within the polycrystalline (ASH) layer formed on
the Si surface exhibit a strong green-orange photoluminescence (PL). Difference
measurements revealed a major double component spectra consisting of a broad
band associated with the ASH-Si wafer interfacial porous oxide layer and a high
energy band attributable to Si-NPs embedded in the ASH. The origin of the
latter emission can be explained in terms of quantum/spatial confinement
effects probably mediated by oxygen related defects in or around Si-NPs.
Although Si-NPs are derived from the interface they are much smaller in size
than those embedded within the interfacial porous oxide layer (SiOx, 1 < x <
2). Transmission electron microscopy (TEM) combined with Raman scattering and
Fourier transformed infrared (FTIR) analysis confirmed the presence of Si-NPs
and Si-O bondings pointing to the role of oxygen related defects. The presence
of oxygen of up to 4.5 at.% in the (NH4)2SiF6 layer was confirmed by energy
dispersive spectroscopy (EDS) analysis.",1512.07991v1
2015-12-21,Modulation of diffusion rate of therapeutic peptide drugs using graphene oxide membranes,"We investigate diffusion of a peptide drug through Graphene Oxide (GO)
membranes that are modeled as a porous layered laminate constructed from
aligned flakes of GO. Our experiments using a peptide drug show a tunable
non-linear dependence of the peptide concentration upon time. This is confirmed
using numerical simulations with a diffusion equation accounting for the
photothermal degradation of fluorophores and an effective percolation model.
This modeling yields an interpretation of the control and delay of drug
diffusion through GO membranes. The ability to modulate the density of
hydrogel-like GO membranes to control drug release rates could be a step
forwards in tailoring drug release properties of the hydrogels for therapeutic
applications.",1512.08506v1
2015-12-29,$π$-bonding-dominated energy gaps in graphene oxides,"Chemical bondings of graphene oxides with oxygen concentration from 1\% to
50\% are investigated using first-principle calculations. Energy gaps are
mainly determined by the competition of orbital hybridizations in C-C, O-O, and
C-O bonds. They are very sensitive to the changes in oxygen concentration and
distributions. There exists five types of $\pi$ bondings during the variation
from the full to vanishing adsorptions, namely the complete termination, the
partial suppression, the 1D bonding, the deformed planar bonding, and the
well-behaved one. They can account for the finite and gapless characteristics,
corresponding to the O-concentrations of $>$25\% and $<$3\%, respectively. The
feature-rich chemical bondings dominate band structures and density of states,
leading to diverse electronic properties.",1512.08693v1
2016-05-04,Atomically Thin Boron Nitride: Unique Properties and Applications,"Atomically thin boron nitride (BN) is an important two-dimensional (2D)
nanomaterial, with many properties distinct from graphene. In this feature
article, these unique properties and associated applications often not possible
from graphene are outlined. The article starts with characterization and
identification of atomically thin BN. It is followed by demonstrating their
strong oxidation resistance at high temperatures and applications in protecting
metals from oxidation and corrosion. As flat insulators, BN nanosheets are
ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and
electronic devices based on 2D heterostructures. The light emission of BN
nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions are also
included for its scientific and technological importance. The last part is
dedicated to synthesis, characterization, and optical properties of BN
nanoribbons, a special form of nanosheets.",1605.01136v1
2016-05-08,Scanning tunneling spectroscopy of superconductivity on surfaces of LiTi2O4(111) thin films,"Unique superconductivity at surfaces/interfaces, as exemplified by
LaAlO3/SrTiO3 interfaces, and the high transition temperature in ultrathin FeSe
films, have triggered intense debates on how superconductivity is affected in
atomic and electronic reconstructions. The surface of superconducting cubic
spinel oxide LiTi2O4 is another interesting system because its inherent surface
electronic and atomic reconstructions add complexity to superconducting
properties. Investigations of such surfaces are hampered by the lack of single
crystals or high-quality thin films. Here, using low-temperature scanning
tunneling microscopy, we report an unexpected small superconducting energy gap
and a long coherence length on the surface of LiTi2O4 (111) epitaxial thin
films. Furthermore, we find that a pseudogap opening at the Fermi energy
modifies the surface superconductivity. Our results open an avenue, exploring
anomalous superconductivity on the surface of cubic transition-metal oxides
where the electronic states are spontaneously modulated with involving rich
many-body interactions.",1605.02327v2
2016-05-09,"Interplay between strain, defect charge state and functionality in complex oxides","We use first-principles calculations to investigate the interplay between
strain and the charge state of point defect impurities in complex oxides. Our
work is motivated by recent interest in using defects as active elements to
provide novel functionality in coherent epitaxial films. Using oxygen vacancies
as model point defects, and CaMnO$_3$ and MnO as model materials, we calculate
the changes in internal strain caused by changing the charge state of the
vacancies, and conversely the effect of strain on charge-state stability. Our
results show that the charge state is a degree of freedom that can be used to
control the interaction of defects with strain and hence the concentration and
location of defects in epitaxial films. We propose the use of field-effect
gating to reversibly change the charge state of defects and hence the internal
strain and corresponding strain-induced functionalities.",1605.02462v1
2016-08-01,Interferometric Motion Detection in Atomic Layer 2D Nanostructures: Visualizing Signal Transduction Efficiency and Optimization Pathways,"Atomic layer crystals are emerging building blocks for enabling new
two-dimensional (2D) nanomechanical systems, whose motions can be coupled to
other attractive physical properties in such 2D systems. Optical interferometry
has been very effective in reading out the infinitesimal motions of these 2D
structures and spatially resolving different modes. To quantitatively
understand the detection efficiency and its dependence on the device parameters
and interferometric conditions, here we present a systematic study of the
intrinsic motion responsivity in 2D nanomechanical systems using a
Fresnel-law-based model. We find that in monolayer to 14-layer structures, MoS2
offers the highest responsivity among graphene, h-BN, and MoS2 devices and for
the three commonly used visible laser wavelengths (633, 532, and 405nm). We
also find that the vacuum gap resulting from the widely used 300nm-oxide
substrate in making 2D devices, fortunately, leads to close-to-optimal
responsivity for a wide range of 2D flakes. Our results elucidate and
graphically visualize the dependence of motion transduction responsivity upon
2D material type and number of layers, vacuum gap, oxide thickness, and
detecting wavelength, thus providing design guidelines for constructing 2D
nanomechanical systems with optimal optical motion readout.",1608.00377v1
2016-08-03,Overall thermomechanical properties of layered materials for energy devices applications,"This paper is concerned with the analysis of effective thermomechanical
properties of multi- layered materials of interest for solid oxide fuel cells
(SOFC) and lithium ions batteries fabrication. The recently developed
asymptotic homogenization procedure is applied in order to express the overall
thermoelastic constants of the first order equivalent continuum in terms of
microfluctuations functions, and these functions are obtained by the solution
of the corresponding recursive cell problems. The effects of thermal stresses
on periodic multi-layered thermoelastic composite reproducing the
characteristics of solid oxide fuel cells (SOFC-like) are studied assuming
periodic body forces and heat sources, and the solution derived by means of the
asymptotic homogenization approach is compared with the results obtained by
finite elements analysis of the associate heterogeneous material.",1608.01078v1
2016-08-06,Extended friction elucidates the breakdown of fast water transport in graphene oxide membranes,"The understanding of water transport in graphene oxide (GO) membranes stands
out as a major theoretical problem in graphene research. Notwithstanding the
intense efforts devoted to the subject in the recent years, a consolidated
picture of water transport in GO membranes is yet to emerge. By performing
mesoscale simulations of water transport in ultrathin GO membranes, we show
that even small amounts of oxygen functionalities can lead to a dramatic drop
of the GO permeability, in line with experimental findings. The coexistence of
bulk viscous dissipation and spatially extended molecular friction results in a
major decrease of both slip and bulk flow, thereby suppressing the fast water
transport regime observed in pristine graphene nanochannels. Inspection of the
flow structure reveals an inverted curvature in the near-wall region, which
connects smoothly with a parabolic profile in the bulk region. Such inverted
curvature is a distinctive signature of the coexistence between single-particle
Langevin friction and collective hydrodynamics. The present mesoscopic model
with spatially extended friction may offer a computationally efficient tool for
future simulations of water transport in nanomaterials.",1608.02098v1
2016-08-11,Evolution of Insulator-Metal Phase Transitions in Epitaxial Tungsten Oxide Films during Electrolyte-Gating,"An interface between an oxide and an electrolyte gives rise to various
processes as exemplified by electrostatic charge accumulation/depletion and
electrochemical reactions such as intercalation/decalation under electric
field. Here we directly compare typical device operations of those in electric
double layer transistor geometry by adopting ${A}$-site vacant perovskite
WO$_3$ epitaxial thin films as a channel material and two different
electrolytes as gating agent. $\textit{In situ}$ measurements of x-ray
diffraction and channel resistance performed during the gating revealed that in
both the cases WO$_3$ thin film reaches a new metallic state through multiple
phase transitions, accompanied by the change in out-of-plane lattice constant.
Electrons are electrostatically accumulated from the interface side with an
ionic liquid, while alkaline metal ions are more uniformly intercalated into
the film with a polymer electrolyte. We systematically demonstrate this
difference in the electrostatic and electrochemical processes, by comparing
doped carrier density, lattice deformation behavior, and time constant of the
phase transitions.",1608.03357v1
2016-08-11,Orbital and spin order in oxide two-dimensional electron gases,"We describe a variational theory of multi-band two-dimensional electron gases
that captures the interplay between electrostatic confining potentials,
orbital-dependent interlayer electronic hopping and electron-electron
interactions, and apply it to the d-band two-dimensional electron gases that
form near perovskite oxide surfaces and heterojunctions. These multi-band
two-dimensional electron gases are prone to the formation of
Coulomb-interaction-driven orbitally-ordered nematic ground-states. We find
that as the electron density is lowered and interaction effects strengthen,
spontaneous orbital order occurs first, followed by spin order. We compare our
results with known properties of single-component two-dimensional electron gas
systems and comment on closely related physics in semiconductor quantum wells
and van der Waals heterostructures.",1608.03625v1
2016-08-18,A Simulation Study on the Feasibility of Radio Enhancement Therapy with Calcium Tungstate and Hafnium Oxide Nanoparticles,"Herein is a simulation study on the radio enhancement potential of calcium
tungstate (CaWO4) and hafnium oxide (HfO2) nanoparticles (NPs) relative to gold
(Au) NPs. The work utilizes the extensively studied Au NP as the ""gold
standard"" to which the novel materials can be compared. All three materials
were investigated in-silico with the software Penetration and Energy Loss of
Positrons and Electrons (PENELOPE) developed by Francesc Salvat and distributed
in the United States by the Radiation Safety Information Computational Center
(RSICC) at Oak Ridge National Laboratory. The aims are: (1) Do CaWO4 and HfO2
NPs function like Au?, and (2) if not, how else might they function to enhance
radio therapy? Our investigations have found that HfO2 likely functions as Au,
but not as effectively. CaWO4 likely does not function as Au, and we propose
that CaWO4 may exhibit cancer killing traits through its intrinsic UV
luminescence property.",1608.05302v1
2016-08-30,Doping-Induced Alterations in Electronic Structure of Copper Oxide Superconductors and a New Horizon for Higher Tc materials,"By paying special attention to the fact that the doped holes induce
deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors,
we develop a non-rigid band theory treating doping-induced alterations of
energy-band structures in copper oxide superconductors. Thanks to this theory,
we obtain a complete picture of the doping-induced alteration in the electronic
structure of La2CuO4, from the spin-disordered insulating phase to the metallic
phase. We conclude that the Fermi surface structure of this cuprate in the
underdoped region consists of Fermi pockets in the antinodal region and Fermi
arcs in the nodal region, and thus that the origin of a so-called pseudogap is
closely related to the existence of Fermi pockets. Moreover, we show that the
carriers on the Fermi pockets contribute to the phonon mechanism in d-wave
superconductivity. Finally, we discuss how one will be able to find higher Tc
materials, based on the conclusions mentioned above.",1608.08338v2
2016-12-04,Conducting interface in oxide homojunction: understanding of superior properties in black TiO2,"Black TiO2 nanoparticles with a crystalline-core and amorphous-shell
structure exhibit superior optoelectronic properties in comparison with
pristine TiO2. The fundamental mechanisms underlying these enhancements,
however, remain unclear, largely due to the inherent complexities and
limitations of powder materials. Here, we fabricate TiO2 homojunction films
consisting of an oxygen-deficient amorphous layer on top of a highly
crystalline layer, to simulate the structural/functional configuration of black
TiO2 nanoparticles. Metallic conduction is achieved at the
crystalline-amorphous homointerface via electronic interface reconstruction,
which we show to be the main reason for the superior properties of black TiO2.
This work not only achieves an unprecedented understanding of black TiO2, but
also provides a new perspective for investigating carrier generation and
transport behavior at oxide interfaces, which are of tremendous fundamental and
technological interest.",1612.01037v1
2016-12-05,"Phonon scattering limited mobility in the representative cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$ and SrTiO$_3$","Cubic perovskite oxides are emerging high-mobility transparent conducting
oxides (TCOs), but Ge-based TCOs had not been known until the discovery of
metastable cubic SrGeO$_3$. $0.5 \times 0.4 \times 0.2$-mm$^3$ large single
crystals of the cubic SrGeO$_3$ perovskite were successfully synthesized
employing the high-pressure flux method. The phonon spectrum is determined from
the IR optical reflectance and Raman-scattering analysis to evaluate the
electron transport governed by optical phonon scattering. A calculated
room-temperature mobility on the order of $3.9 \times 10^2$
cm$^2$V$^{-1}$s$^{-1}$ is obtained, identifying cubic SrGeO$_3$ as one of the
most promising TCOs. Employing classical phonon theory and a combined
experimental-theoretical approach, a comprehensive analysis of the intrinsic
electron mobility in the cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$,
and SrTiO$_3$ is provided based on the magnitude of polarization and
eigenfrequency of optically active phonons.",1612.01343v2
2016-12-09,Complex Quasi-Two-Dimensional Crystalline Order Embedded in VO$_2$ and Other Crystals,"Metal oxides such as VO$_2$ undergo structural transitions to low-symmetry
phases characterized by intricate crystalline order, accompanied by rich
electronic behavior. We derive a minimal ionic Hamiltonian based on symmetry
and local energetics which describes structural transitions involving all four
observed phases, in the correct order. An exact analysis shows that complexity
results from the symmetry-induced constraints of the parent phase which forces
ionic displacements to form multiple interpenetrating groups using
low-dimensional pathways and distant neighbors. Displacements within each group
exhibit independent, quasi two-dimensional order, which is frustrated and
fragile. This selective ordering mechanism is not restricted to VO$_2$: it
applies to other oxides which show similar complex order.",1612.03212v2
2016-12-12,Modeling the Effect of Blunt Impact on Mitochondrial Dysfunction in Cartilage,"Mounting evidence for the role of oxidative stress in the degeneration of
articular cartilage after an injurious impact requires our modeling &
simulation efforts to temporarily shift from just describing the effect of
mechanical stress and inflammation on osteoarthritis (OA). The hypothesis that
the injurious impact causes irreversible damage to chondrocyte mitochondria,
which in turn increase their production of free radicals, affecting their
energy production and their ability to rebuild the extracellular matrix, has to
be modeled and the processes quantified in order to further the understanding
of OA, its causes, and viable treatment options. The current article presents a
calibrated model that captures the damage oxidative stress incurs on the cell
viability, ATP production, and cartilage stability in a cartilage explant after
a drop-tower impact. The model validates the biological hypothesis and will be
used in further efforts to identify possibilities for treatment and be a part
of a bigger modeling & simulation framework for the development of OA.",1612.03859v1
2016-12-13,Electrical Double Layer Properties of Spherical Oxide Nanoparticles,"The accurate characterization of electrical double layer properties of
nanoparticles is of fundamental importance for optimizing their physicochemical
properties for specific biotechnological and biomedical applications. In this
article, we use classical solvation density functional theory and a surface
complexation model to investigate the effects of pH and nanoparticle size on
the structural and electrostatic properties of an electrolyte solution
surrounding a spherical silica oxide nanoparticle. The formulation has been
particularly useful for identifying dominant interactions governing the ionic
driving force under a variety of pH levels and nanoparticle sizes. As a result
of the energetic interplay displayed between electrostatic potential, ion-ion
correlation and particle crowding effects on the nanoparticle surface
titration, rich, non-trivial ion density profiles and mean electrostatic
potential behavior have been found.",1612.03984v1
2016-12-22,Nonlinear photoluminescence imaging of isotropic and liquid crystalline dispersions of graphene oxide,"We report a visible-range nonlinear photoluminescence (PL) from graphene
oxide (GO) flakes excited by near-infrared femtosecond laser light. PL
intensity has nonlinear dependence on the laser power, implying a multiphoton
excitation process, and also strongly depends on a linear polarization
orientation of excitation light, being at maximum when it is parallel to
flakes. We show that PL can be used for a fully three-dimensional label-free
imaging of isotropic, nematic, and lamellar liquid crystalline dispersions of
GO flakes in water. This nonlinear PL is of interest for applications in direct
label-free imaging of composite materials and study of orientational ordering
in mesomorphic phases formed by these flakes, as well as in biomedical and
sensing applications utilizing GO.",1612.07444v1
2017-06-07,Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure,"Layer-by-layer oxide molecular beam epitaxy has been used to synthesize
cuprate-nickelate multilayer structures of composition
(La$_2$CuO$_4$)$_m$/LaO/(LaNiO$_3$)$_n$. In a combined experimental and
theoretical study, we show that these structures allow a clean separation of
dopant and doped layers. Specifically, the LaO layer separating cuprate and
nickelate blocks provides an additional charge that, according to density
functional theory calculations, is predominantly accommodated in the
interfacial nickelate layers. This is reflected in an elongation of bond
distances and changes in valence state, as observed by scanning transmission
electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted
charge disproportionation in the nickelate interface layers leads to a
thickness-dependent metal-to-insulator transition for $n=2$, as observed in
electrical transport measurements. The results exemplify the perspectives of
charge transfer in metal-oxide multilayers to induce doping without introducing
chemical and structural disorder.",1706.02173v2
2017-06-25,"A review on the progress of polymer nanostructures with modulated morphologies and properties, using nonporous AAO templates","Polymers with the same chemical composition can provide different properties
by reducing the dimension or simply by altering their nanostructure. Recent
literature works report hundreds of examples of advances methods in the
fabrication of polymer nanostructures accomplished following different
approaches, soft lithography, self-assembly routes, template assisted methods,
etc. Polymer nanostructures with modulated morphologies and properties can be
easily achieved from anodized aluminum oxide (AAO) templates assisted methods.
In the last decade, fabrication of polymer nanostructures in the nanocavities
of AAO has raised a great interest since allows the control and tailoring of
dimension of a huge number of polymer and polymer-based composites materials.
The fact that polymer dimension can be adjusted allow the study of
size-dependency properties. Moreover, modulated polymer nanostructures can be
designed for specific applications from AAO templates methods. Taking into
account the last considerations, this review present an overview of recent and
new insights in the fabrication methods of polymer nanostructures from hard
porous Anodic Aluminum Oxide (AAO) templates with emphasis on the study of
polymer structure/property relationship at nanometric scale and stressing the
potential interest in particular applications.",1706.08069v1
2017-06-28,Unravelling Single Atom Catalysis: The Surface Science Approach,"Understanding the fundamental mechanisms of single-atom catalysis (SAC) is
important to design systems with improved performance and stability. This is
problematic, however, because single-atom active sites are extremely difficult
to characterize with existing experimental techniques. Over the last 40 years,
surface science has provided the fundamental insights to understand
heterogeneous catalysis, but model systems in which metal atoms are stable on
well-characterized metal-oxide substrates at reaction temperatures are scarce.
In this perspective, I discuss what is already known about isolated metal atoms
adsorbed on model metal-oxide surfaces, and how this information can be used to
understand SAC. A key issue is that, although the highly-idealised model
systems studied in surface science may not be representative of a real working
catalyst, they do very much resemble what can be calculated using
state-of-the-art theoretical modelling. Thus, surface science offers an
opportunity to rigorously benchmark the theoretical approach to modelling SAC
in future. Perhaps more excitingly, several groups have developed model systems
where metal adatoms remain stable at elevated temperatures. To date however,
there has been no clear demonstration of catalytic activity. The perspective
closes with a brief discussion of the prospect for STM experiments under
realistic reaction conditions.",1706.09473v1
2017-07-11,Hole spin resonance and spin-orbit coupling in a silicon metal-oxide-semiconductor field-effect transistor,"We study hole spin resonance in a p-channel silicon metal-oxide-semiconductor
field-effect transistor. In the sub-threshold region, the measured source-drain
current reveals a double dot in the channel. The observed spin resonance
spectra agree with a model of strongly coupled two-spin states in the presence
of a spin-orbit-induced anti-crossing. Detailed spectroscopy at the
anti-crossing shows a suppressed spin resonance signal due to
spin-orbit-induced quantum state mixing. This suppression is also observed for
multi-photon spin resonances. Our experimental observations agree with
theoretical calculations.",1707.03106v1
2017-07-11,Novel high-pressure calcium carbonates,"Calcium and magnesium carbonates are believed to be the host compounds for
most of the oxidized carbon in the Earth's mantle. Here, using evolutionary
crystal structure prediction method USPEX, we systematically explore the
MgO-CO2 and CaO-CO2 systems at pressures ranging from 0 to 160 GPa to search
for thermodynamically stable magnesium and calcium carbonates. While MgCO3 is
the only stable magnesium carbonate, three calcium carbonates are stable under
pressure: well-known CaCO3, and newly predicted Ca3CO5 and CaC2O5. Ca3CO5
polymorphs are found to contain isolated orthocarbonate (CO4)4- tetrahedra, and
are stable at relatively low pressures (>11 GPa), whereas CaC2O5 is stable
above 33 GPa and its polymorphs feature polymeric motifs made of CO4
tetrahedra. Detailed analysis of chemical stability of CaCO3, Ca3CO5 and CaC2O5
in the environment typical of the Earth's lower mantle reveals that none of
these compounds can exist in the Earth's lower mantle. We conclude that MgCO3
is the main host of oxidized carbon throughout the lower mantle.",1707.03226v2
2017-07-18,Insulator to Metal Transition in WO$_3$ Induced by Electrolyte Gating,"Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an
alkali metal) are well known for their interesting optical and electrical
characteristics. We have modified the transport properties of thin WO$_3$ films
by electrolyte gating using both ionic liquids and polymer electrolytes. We are
able to tune the resistivity of the gated film by more than five orders of
magnitude, and a clear insulator-to-metal transition is observed. To clarify
the doping mechanism, we have performed a series of incisive operando
experiments, ruling out both a purely electronic effect (charge accumulation
near the interface) and oxygen-related mechanisms. We propose instead that
hydrogen intercalation is responsible for doping WO$_3$ into a highly
conductive ground state and provide evidence that it can be described as a
dense polaronic gas.",1707.05748v1
2017-07-21,Generation of multiple plasmons in strontium niobates mediated by local field effects,"Recently, an anomalous generation of multiple plasmons with large spectral
weight transfer in the visible to ultraviolet range (energies below the band
gap) has been experimentally observed in the insulating-like phase of
oxygen-rich strontium niobium oxides (SrNbO$_{3+\delta}$). Here, we investigate
the ground state and dielectric properties of SrNbO$_{3+\delta}$ as a function
of $\delta$ by means of extensive first principle calculations. We find that in
the random phase approximation by taking into account the local field effects
(LFEs), our calculations are able to reproduce both the unconventional multiple
generations of plasmons and spectral weight transfers, consistent with
experimental data. Interestingly, these unconventional plasmons can be tuned by
oxygen stoichiometry as well as microscopic superstructure. This unusual
predominance of LFEs in this class of materials is ascribed to the strong
electronic inhomogeneity and high polarizability and paves a new path to induce
multiple plasmons in the untapped visible to ultraviolet ranges of
insulating-like oxides.",1707.06738v2
2017-07-26,Atomistic Mechanisms for the Nucleation of Aluminium Oxide Nanoparticles,"A predictive model for nanoparticle nucleation has not yet been successfully
achieved. Classical nucleation theory fails because the atomistic nature of the
seed has to be considered since geometrical structure as well as stoichiometry
do not always match the bulk values. We present a fully microscopic approach
based on a first-principle study of aluminium oxide clusters. We have
calculated stable structures of AlxOy} and their associated thermodynamic
properties. From these data, the chemical composition of a gas composed of
aluminium and oxygen atoms can be calculated as a function of temperature,
pressure, and aluminium to oxygen ratio. We demonstrate the accuracy of this
approach in reproducing experimental results obtained with time resolved
spectroscopy of a laser induced plasma from an Al2O3} target. We thus extended
the calculation to lower temperatures, i.e. longer time scales, to propose a
scenario of composition gas evolution leading to the first alumina seeds.",1707.08434v1
2017-07-28,Exciton mass and exciton spectrum in the cuprous oxide,"Excitons with a radius of a few lattice constants can be affected by strong
central-cell corrections, leading to significant deviations of the optical
spectrum from the hydrogen-like Rydberg series, and also to an enhancement of
the exciton mass. We present an approach to this situation based on a lattice
model that incorporates the effects of a non-parabolic band structure, short
distance corrections to the Coulomb interaction between electrons and holes,
spin-orbit and exchange coupling. The lattice model allows for observation of
the crossover from large radius Wannier to small radius Frenkel excitons
without invoking a continuum approximation. We apply the lattice model approach
especially to the yellow exciton series in the cuprous oxide, for which the
optical spectrum and exciton mass enhancement are obtained through adaptation
of only a few model parameters to material-specific values. Our results predict
a strongly anisotropic ortho-exciton mass.",1707.09224v2
2017-07-29,Extraordinary water adsorption characteristics of graphene oxide,"The laminated structure of graphene oxide (GO) confers unique interactions
with water molecules which may be utilised in a range of applications that
require materials with tuneable hygroscopic properties. Precise roles of the
expandable interlayer spacing and functional groups in GO laminates are not
fully understood till date. Herein, we report experimental and theoretical
study on the adsorption and desorption behaviour of water in GO laminates as a
function of relative pressure. We have observed that GO imparts excellent water
uptake capacity of up to 0.58 gram of water per gram of GO (g g-1), which is
much higher than silica gel a conventional desiccant material. More
interestingly, the adsorption and desorption kinetics of GO is one order of
magnitude higher than silica gel. The observed extraordinary
adsorption/desorption rate can be attributed to the high capillary pressure in
GO laminates as well as micro meter sized tunnel like wrinkles located at the
surface.",1707.09502v1
2017-10-03,The efficient photodesorption of nitric oxide (NO) ices A laboratory astrophysics study,"The study and quantification of UV photon-induced desorption of frozen
molecules furthers our understanding of the chemical evolution of cold
interstellar regions. Nitric oxide (NO) is an important intermediate species in
both gas-phase and solid-phase chemical networks. In this work, we present
quantitative measurements of the photodesorption of a pure NO ice.We used the
tunable monochromatic synchrotron light of the DESIRS beamline of the SOLEIL
facility near Paris to irradiate NO ices in the 6 - 13.6 eV range and measured
desorption by quadrupole mass spectrometry.We find that NO photodesorption is
very efficient, its yield being around 1e-2 molecule per incident photon for UV
fields relevant to the diffuse and dense interstellar medium. We discuss the
extrapolation of our results to an astrophysical context and we compare
photodesorption of NO to previously studied molecules.",1710.01028v1
2017-10-09,Asymmetrically Encapsulated vertical ITO/MoS2/Cu2O photodetector with ultra-high sensitivity,"Strong light absorption, coupled with moderate carrier transport properties,
makes two-dimensional (2-D) layered transition metal dichalcogenide (TMD)
semiconductors promising candidates for low intensity photodetection
applications. However, the performance of these devices is severely
bottlenecked by slow response with persistent photocurrent due to long lived
charge trapping, and nonreliable characteristics due to undesirable ambience
and substrate effects. Here we demonstrate ultra-high specific detectivity (D*)
of 3.2x10^14 Jones and responsivity (R) of 5.77x10^4 AW-1 at an optical power
density (P_op) of 0.26 Wm-2 and external bias (V_ext) of -0.5 V in an indium
tin oxide (ITO)/MoS2/copper oxide (Cu2O)/Au vertical multi-heterojunction
photodetector exhibiting small carrier transit time. The active MoS2 layer
being encapsulated by carrier collection layers allows us to achieve negligible
trap assisted persistent photocurrent and repeatable characteristics over large
number of cycles. We also achieved a large D*>10^14 Jones at zero external bias
due to the built-in field of the asymmetric photodetector. Benchmarking the
performance against existing reports in literature shows a pathway for
achieving reliable and highly sensitive photodetectors for ultra-low intensity
photodetection applications.",1710.02967v1
2017-10-10,Room Temperature deposition of ZnO and Al:ZnO ultrathin films on glass and PET substrates by DC sputtering Technique,"In the present work, ultrathin films of Zinc oxide (ZnO) and Aluminum doped
zinc oxide (AZO) with 20 nm thick were fabricated at 300 K on glass and
Polyethylene terephthalate (PET) substrates by means of directcurrent
sputtering method. The structural morphology of the films were analyzed by
(XRD) diffractometry. The average transmittance of films deposited on different
substrates showed high transparency (over 80%) in the visible spectrum. The
objective of the present work is to investigate the thicknesses and optical
constants of ZnO and AZO ultrathin films prepared by DC sputtering onto (glass
and PET) substrates using two methods (UV-vis-NIR spectrophotometer and
ellipsometer (SE) by new amorphous dispersion formula) with comparison to check
and confirm the results that obtained from UV with those obtained from SE
measurements. The optical constants of films were extracted and compared using
UV and SE techniques in the range of (200- 2200 nm) with increment of 1 nm in
order to confirm the accuracy of the UV and shown an excellent agreement.",1710.03493v1
2017-10-22,Electronic Stopping of Slow Protons in Oxides: Scaling Properties,"Electronic stopping of slow protons in ZnO, VO2 (metal and semiconductor
phases), HfO2, and Ta2O5 was investigated experimentally. As a comparison of
the resulting stopping cross sections (SCS) to data for Al2O3 and SiO2 reveals,
electronic stopping of slow protons does not correlate with electronic
properties of the specific material such as band gap energies. Instead, the
oxygen 2p states are decisive, as corroborated by density functional theory
calculations of the electronic densities of states. Hence, at low ion
velocities the SCS of an oxide primarily scales with its oxygen density.",1710.07994v1
2017-10-24,Atomic layer control of metal-insulator behavior in oxide quantum wells integrated directly on silicon,"We present electrical and structural characterization of epitaxial
LaTiO3/SrTiO3 quantum wells integrated directly on Si(100). The quantum wells
exhibit metallic transport described by Fermi-liquid behavior. Carriers arise
from both charge transfer from the LaTiO3 to SrTiO3 and oxygen vacancies in the
latter. By reducing the thickness of the quantum wells, an enhancement in
carrier-carrier scattering is observed, and insulating transport emerges.
Consistent with a Mott-driven transition in bulk rare-earth titanates, the
insulating behavior is described by activated transport, and the onset of
insulating transport occurs near 1 electron per Ti occupation within the SrTiO3
well. We also discuss the role that structure and gradients in strain may play
in enhancing the carrier density. The manipulation of metal-insulator behavior
in oxides grown directly on Si opens the pathway to harnessing strongly
correlated phenomena in device technologies.",1710.08597v1
2017-10-26,First-principles theory of doping in layered oxide electrode materials,"Doping lithium-ion battery electrode materials LiMO$_2$ (M = Co, Ni, Mn) with
impurities has been shown to be an effective way to optimize their
electrochemical properties. Here, we report a detailed first-principles study
of layered oxides LiCoO$_2$, LiNiO$_2$, and LiMnO$_2$ lightly doped with
transition-metal (Fe, Co, Ni, Mn) and non-transition-metal (Mg, Al) impurities
using hybrid-density-functional defect calculations. We find that the lattice
site preference is dependent on both the dopant's charge and spin states, which
are coupled strongly to the local lattice environment and can be affected by
the presence of co-dopant(s), and the relative abundance of the host compound's
constituting elements in the synthesis environment. On the basis of the
structure and energetics of the impurities and their complexes with intrinsic
point defects, we determine all possible low-energy impurity-related defect
complexes, thus providing defect models for further analyses of the materials.
From a materials modeling perspective, these lightly doped compounds also serve
as model systems for understanding the more complex, mixed-metal,
LiMO$_2$-based battery cathode materials.",1710.09895v1
2017-12-01,Titanium Contacts to Graphene: Process-Induced Variability in Electronic and Thermal Transport,"Contact Resistance (RC) is a major limiting factor in the performance of
graphene devices. RC is sensitive to the quality of the interface and the
composition of the contact, which are affected by the graphene transfer process
and contact deposition conditions. In this work, a linear correlation is
observed between the composition of Ti contacts, characterized by X-ray
photoelectron spectroscopy, and the Ti/graphene (Gr) contact resistance
measured by the transfer length method. We find that contact composition is
tunable via deposition rate and base pressure. Reactor base pressure is found
to effect the resultant contact resistance. The effect of contact deposition
conditions on thermal transport measured by time-domain thermoreflectance is
also reported and interfaces with higher oxide composition appear to result in
a lower thermal boundary conductance. Possible origins of this thermal boundary
conductance change with oxide composition are discussed.",1712.00331v1
2017-12-04,Characterizations of the Nonlinear Optical Properties for (010) and (-201) Beta-phase Gallium Oxide,"We report, for the first time, the characterizations on optical
nonlinearities of beta-phase gallium oxide (\b{eta}-Ga2O3), where both (010)
\b{eta}-Ga2O3 and (-201) \b{eta}-Ga2O3 were examined for two-photon absorption
(TPA) coefficient, Kerr refractive index, and their polarization dependence.
The wavelength dependence of the TPA coefficient and Kerr refractive index was
estimated using a widely used analytical model. \b{eta}-Ga2O3 exhibits a TPA
coefficient of 1.2 cm/GW for (010) \b{eta}-Ga2O3 and 0.58 cm/GW for (-201)
\b{eta}-Ga2O3. The Kerr refractive index is -2.14*10^(15) cm2/W for (010)
\b{eta}-Ga2O3 and -2.89*10^(15) cm2/W for (-201) \b{eta}-Ga2O3. In addition,
\b{eta}-Ga2O3 shows stronger nonlinear optical anisotropy on the (-201) plane
than on the (010) plane, possibly due to highly asymmetric crystal structure.
Compared with that of gallium nitride (GaN), the TPA coefficient of
\b{eta}-Ga2O3 is 20 times smaller, and the Kerr refractive index of
\b{eta}-Ga2O3 is also found to be 4 to 5 times smaller. These results indicate
that \b{eta}-Ga2O3 has the potential for use in ultra-low loss waveguides and
ultra-stable resonators and integrated photonics, especially in the UV and
visible wavelength spectral range.",1712.01390v1
2017-12-07,Nature of the growth of plasma electrolyte oxidation coating on Aluminum,"The localized dielectric breakdown had been considered as the driving force
for growth of plasma electrolytic oxide (PEO) coatings for several decades.
However, the TEM study here reveals the dielectric breakdown behavior has
little contribution for coating thickening. The presented evidences show the
nature of PEO coating growth in all three consecutive stages I-III is ionic
migration behavior inside the amorphous alumina layer (AAL) at the
coating/matrix interface. The evolution of morphological characterizations in
the PEO process is attributed to the interfacial reactions of AAL/alkaline
(stage I), AAL/discharge-on-surface (stage II) and AAL/discharge-in-pore (stage
III).",1712.02459v1
2017-12-12,Metal - TiO2 contacts: An electrical characterization study,"The electrical properties of thin TiO2 films have recently been extensively
exploited towards enabling a variety for metal-oxide electron devices:
unipolar/bipolar semiconductor devices and/or memristors. In such efforts,
investigations on the role of TiO2 as active material have been the main focus,
however, electrode materials are equally important. In this work, we address
this need by presenting a systematic quantitative electrical characterisation
study on the interface characteristics of Metal-TiO2-Metal structures. Our
study employs typical contact materials that are used both as top and bottom
electrodes in a Metal-TiO2-Metal setting. This allows investigating the effect
of Metal-TiO2 contacts as well as holistically studying an electrode's
influence to the opposite interface, referred to as top/bottom electrodes
coupling. Our methodology comprises the recording of current-voltage (I-V)
characteristics from a variety of solid-state prototypes in the temperature
range of 300-350 K and by analysing them through appropriate modelling. Clear
field and temperature dependent signature plots were also obtained towards
shinning more light on the role of each material as top/bottom electrodes in
Metal-TiO2-Metal structures. Our results provide a useful database for
selecting appropriate electrode materials in Metal-TiO2 devices, offering new
insights in metal-oxide electronics applications.",1712.04218v1
2017-12-21,Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber,"We report a novel optical waveguide design of a hollow step index fiber
modified with a thin layer of indium tin oxide (ITO). We show an excitation of
highly confined waveguide mode in the proposed fiber near the wavelength where
permittivity of ITO approaches zero. Due to the high field confinement within
thin ITO shell inside the fiber, the epsilon-near-zero (ENZ) mode can be
characterized by a peak in modal loss of the hybrid waveguide. Our results show
that such in-fiber excitation of ENZ mode is due to the coupling of the guided
core mode to the thin-film ENZ mode. We also show that the phase matching
wavelength, where the coupling takes place, varies depending on the refractive
index of the constituents inside the central bore of the fiber. These ENZ
nanostructured optical fibers have many potential applications, for example, in
ENZ nonlinear and magneto-optics, as in-fiber wavelength-dependent filters, and
as subwavelength fluid channel for optical and bio-photonic sensing.",1712.08202v1
2018-01-04,Reconstruction-Stabilized Epitaxy of LaCoO3/SrTiO3(111) Heterostructures by Pulsed Laser Deposition,"Unlike widely explored complex oxide heterostructures grown along [001], the
study of [111]-oriented heterointerfaces are very limited thus far. One of the
main challenges is to overcome the polar discontinuity that hinders the epitaxy
of atomically sharp interfaces. Here, by taking the LaCoO3/SrTiO3(111) as a
prototype, we show that the reconstruction, which effectively compensates the
surface polarity, can stabilize the epitaxy of the heterostructure with polar
discontinuity. Reconstructed substrate surface is prepared, while the growth is
controlled to form reconstruction on the film surface. To suppress the chemical
diffusion across the interface, the growth is interrupted between each unit
cell layer to allow the lattice relaxation at a lowered temperature. In this
way, high quality two-dimensional growth is realized and the heterointerfaces
exhibit sharpness at the atomic scale. Our work provides a path to precisely
control the growth of complex oxide heterostructures along polar orientations
that exhibit emergent quantum phenomena.",1801.01287v1
2018-01-15,Weighting graphene with QCM to monitor interfacial mass changes,"In this Letter, using quartz crystal microbalance (QCM), we experimentally
determined the mass density of graphene grown by chemical vapor deposition
method. We developed a transfer printing technique to integrate large area
single-layer graphene on QCM. By monitoring the resonant frequency of an
oscillating quartz crystal loaded with graphene, we were able to measure the
mass density of graphene as ~118 ng/cm2, which is significantly larger than the
ideal graphene (~76 ng/cm2) mainly due to the presence of wrinkles and
organic/inorganic residues on graphene sheets. High sensitivity of quartz
crystal resonator allowed us to determine the number of graphene layers in
samples. (The technique is very sensitive and able to determine the number of
graphene layers in a particular sample.) Besides, we extended our technique to
probe interfacial mass variation during adsorption of biomolecules on graphene
surface, and plasma-assisted oxidation of graphene. (Besides, we extended our
technique to probe interfacial mass variation during adsorption of biomolecules
on graphene surface, and plasma-assisted oxidation of graphene.)",1801.04755v1
2018-09-01,When supporting electrolyte matters - tuning capacitive response of graphene oxide via electrochemical reduction in alkali and alkaline earth metal chlorides,"The ability to tune charge storage properties of graphene oxide (GO) is of
utmost importance for energy conversion applications. Here we show that
electrochemical reduction of GO is highly sensitive to the cations present in
the solution. GO is reduced at lower potential in alkali metal chloride
solutions than in alkaline earth metal chlorides. During the reduction,
capacitance of GO increases from 10 to 70 times. Maximum capacitances of
reduced GO are between 65 and 130 F g-1, depending on the electrolyte and the
presence of conductive additive. We propose that different interactions of
cations with oxygen functional groups of GO during the reduction are
responsible for the observed effect.",1809.00265v1
2018-09-05,A combined approach of Lattice Boltzmann Method and Maxwell-Stefan equation for modeling multi-component diffusion in solid oxide fuel cell,"Lattice Boltzmann models provide better understanding with mesoscopic
eyesight on multi-component diffusion than macroscopic models. Based on the
kinetic theory and starting from the He-Luo model, the state-of-the-art
multi-component diffusion Lattice Boltzmann models have defects of the
compressible error and the limitations for velocity and viscosity settings in
lattice units. With these respects, a new Lattice Boltzmann model is presented
based on the advection-diffusion equation and is coupled with the
Maxwell-Stefan equation by relaxation time. Without introducing the pressure
term into the advection-diffusion equation, the model avoids the compressible
error. Furthermore, the velocities for components are calculated in the
Maxwell-Stefan equation and not contained in the equilibrium distribution
function, the limitations of the velocity and viscosity settings in lattice
units for under-relaxation iterations are reduced. Then a simulation for
H2-H2O-Ar ternary mass transport in the porous anode of the solid oxide fuel
cell is employed to validate the accuracy of the Lattice Boltzmann model. The
concentration overpotentials are calculated accordingly and compared to several
published continuum-scale and Lattice Boltzmann computations, among them, our
model offers a better consistency with the experimental measurments.",1809.01600v1
2018-09-07,"Space-filling, multi-fractal, localized thermal spikes in silicon, germanium and zinc oxide","The mechanism responsible for the emission of clusters from heavy ion
irradiated solids is proposed to be thermal spikes. Collision cascade-based
theories describe atomic sputtering but cannot explain the consistently
observed experimental evidence for significant cluster emission. Statistical
thermodynamic arguments for thermal spikes are employed here for qualitative
and quantitative estimation of the thermal spike-induced cluster emission from
silicon, germanium and zinc oxide. The evolving cascades and spikes in
elemental and molecular semiconducting solids are shown to have fractal
characteristics. Power law potential is used to calculate the fractal
dimension.The fractal dimension is shown to be dependent upon the exponent of
the power law interatomic potential. Each irradiating ion has the probability
of initiating a space-filling, multi-fractal thermal spike that may sublime a
localized region near the surface by emitting clusters in relative ratios that
depend upon the energies of formation of respective surface vacancies.",1809.02447v1
2018-09-20,"Synthesis, structural and photo physical properties of perovskite oxide (KNbO3)1-X+(La2NiMnO6)X for photovoltaic application","Solid solutions of perovskite oxides (KNbO3)1-x+(La2NiMnO6)x (x=0, 0.1, 0.2
and 0.3) with a variation of band gap (1.33-3.6 eV) have been introduced as a
promising photovoltaic absorber. The structural characterization of the
prepared samples was carried out using X-ray diffraction (followed by Rietveld
refinement) and Raman experiment. As the doping percentage of the monoclinic
La2NiMnO6 in the solid-solution increases, the crystal structure of host KNbO3
becomes more symmetric from orthorhombic to cubic. A large reduction in the
particle size has also been observed in the solid solutions in comparison to
the pure KNbO3. The band gap (~ 1.33 eV) of the synthesized solid solution
x=0.1 is found to be very close to the Shockley-Queisser band gap value of 1.34
eV, which suggests the promising photovoltaic possibility in this material.
Photoluminescence (PL) emission spectra reveal a strong PL quenching in the
solid-solutions in comparison to the KNbO3. The overall structural and optical
studies suggest the promising photovoltaic possibility in KNbO3/ La2NiMnO6
solid solution.",1809.07569v1
2018-09-25,Normal-state properties of the antiperovskite oxide Sr$_{3-x}$SnO revealed by $^{119}$Sn-NMR,"We have performed $^{119}$Sn-NMR measurements on the antiperovskite oxide
superconductor Sr$_{3-x}$SnO to investigate how its normal state changes with
the Sr deficiency. A two-peak structure was observed in the NMR spectra of all
the measured samples. This suggests that the phase separation tends to occur
between the nearly stoichiometric and heavily Sr-deficient Sr$_{3-x}$SnO
phases. The measurement of the nuclear spin-lattice relaxation rate $1/T_1$
indicates that the Sr-deficient phase shows a conventional metallic behavior
due to the heavy hole doping. In contrast, the nearly stoichiometric phase
exhibits unusual temperature dependence of $1/T_1$, attributable to the
presence of a Dirac-electron band.",1809.09275v1
2018-09-27,p-GaAs nanowire MESFETs with near-thermal limit gating,"Difficulties in obtaining high-performance p-type transistors and gate
insulator charge-trapping effects present two major challenges for III-V
complementary metal-oxide semiconductor (CMOS) electronics. We report a p-GaAs
nanowire metal-semiconductor field-effect transistor (MESFET) that eliminates
the need for a gate insulator by exploiting the Schottky barrier at the
metal-GaAs interface. Our device beats the best-performing p-GaSb nanowire
metal-oxide-semiconductor field effect transistor (MOSFET), giving a typical
sub-threshold swing of 62 mV/dec, within 4% of the thermal limit, on-off ratio
$\sim 10^{5}$, on-resistance ~700 k$\Omega$, contact resistance ~30 k$\Omega$,
peak transconductance 1.2 $\mu$S/$\mu$m and high-fidelity ac operation at
frequencies up to 10 kHz. The device consists of a GaAs nanowire with an
undoped core and heavily Be-doped shell. We carefully etch back the nanowire at
the gate locations to obtain Schottky-barrier insulated gates whilst leaving
the doped shell intact at the contacts to obtain low contact resistance. Our
device opens a path to all-GaAs nanowire MESFET complementary circuits with
simplified fabrication and improved performance.",1809.10479v1
2018-10-05,A Corkscrew Model for Highly Coupled Anisotropic Compliance in Ruddlesden-Popper Oxides with Frozen Octahedral Rotations,"A ""corkscrew"" mechanism, that couples changes in the in-plane rotation angle
to strains along the layering axis, has been proposed previously to explain
increased compliance in certain Ruddlesden-Popper phases that facilitates
uniaxial negative thermal expansion over a wide temperature range. Following
the procedure developed to study many simple, auxetic geometries, in the
present study we derive the elastic compliances predicted by this corkscrew
mechanism assuming that the four shortest metal-anion bonds remain stiff and
changes in bond angle are modelled by a harmonic angle potential. We
subsequently analyse the limitations of this model and show that it may be
extended to An+1BnO3n+1 Ruddlesden-Popper oxide phases of general layer
thickness n.",1810.02697v1
2018-10-10,Capturing the oxidation of silicon carbide in rocky exoplanetary interiors,"Theoretical models predict the condensation of silicon carbide around host
stars with C/O ratios higher than 0.65 (cf. C/O$_{\mathrm{Sun}}$ = 0.54), in
addition to its observations in meteorites, interstellar medium and
protoplanetary disks. Consequently, the interiors of rocky exoplanets born from
carbon-enriched refractory material are often assumed to contain large amounts
of silicon carbide. Here we aim to investigate the stability of silicon carbide
in the interior of carbon-enriched rocky exoplanets and to derive the reaction
leading to its transformation. We performed a high-pressure high-temperature
experiment to investigate the reaction between a silicon carbide layer and a
layer representative of the bulk composition of a carbon-enriched rocky
exoplanet. We report the reaction leading to oxidation of silicon carbide
producing quartz, graphite, and molten iron silicide. Combined with previous
studies, we show that in order to stabilize silicon carbide, carbon saturation
is not sufficient, and a complete reduction of Fe$^{2+}$ to Fe$^{0}$ in a
planetary mantle is required, suggesting that future spectroscopic detection of
Fe$^{2+}$ or Fe$^{3+}$ on the surface of rocky exoplanets would imply the
absence of silicon carbide in their interiors.",1810.04544v1
2018-10-11,Are Small Polarons Always Detrimental to Transparent Conducting Oxides ?,"Transparent conducting oxides (TCOs) are essential to many technologies
including solar cells and transparent electronics. The search for high
performance n- or p-type TCOs has mainly focused on materials offering
transport through band carriers instead of small polarons. In this work, we
break this paradigm and demonstrate using well-known physical models that, in
certain circumstances, TCOs exhibiting transport by small polarons offer a
better combination of transparency and conductivity than materials conducting
through band transport. We link this surprising finding to the fundamentally
different physics of optical absorption for band and polaronic carriers. Our
work rationalizes the good performances of recently emerging small-polaronic
Cr-based p-type TCOs such as Sr-doped LaCrO$_3$ and outlines design principles
for the development of high-performance TCOs based on transport by small
polarons. This opens new avenues for the discovery of high-performance TCOs
especially p-type.",1810.04919v1
2018-10-12,Superconductivity From Confinement of Singlets in Metal Oxides,"The Yang-Mills description of phonons and the consequent structure of
electron liquids in strongly anharmonic crystals such as metal oxides is shown
to yield an attractive electron-phonon interaction, and thus an instability
towards the formation of bound states, which can condense to form a
superconductor. This mechanism differs significantly from the pairing mechanism
of conventional superconductivity: the ground state from which
superconductivity emerges is a many-body state of paired electrons and holes
which is not amenable to a quasiparticle description, and whose properties are
similar to those seen in the Cuprate high temperature superconductors.
Confinement arises because the electron liquid structure acts as a source for
Yang-Mills bosons, and not the traditional longitudinal density waves of BCS
pairing.",1810.05339v2
2018-10-10,400%/W second harmonic conversion efficiency in $\mathrm{14 μ m}$-diameter gallium phosphide-on-oxide resonators,"Second harmonic conversion from 1550~nm to 775~nm with an efficiency of 400%
W$^{-1}$ is demonstrated in a gallium phosphide (GaP) on oxide integrated
photonic platform. The platform consists of doubly-resonant, phase-matched ring
resonators with quality factors $Q \sim 10^4$, low mode volumes $V \sim 30
(\lambda/n)^3$, and high nonlinear mode overlaps. Measurements and simulations
indicate that conversion efficiencies can be increased by a factor of 20 by
improving the waveguide-cavity coupling to achieve critical coupling in current
devices.",1810.06393v1
2018-10-18,Two-dimensional hybrid composites of SnS2 with graphene and graphene oxide for improving sodium storage: A first-principles study,"Among the recent achievements of sodium-ion battery (SIB) electrode
materials, hybridization of two-dimentional (2D) materials is one of the most
interesting appointments. In this work, we propose to use the 2D hybrid
composites of SnS2 with graphene or graphene oxide (GO) layers as SIB anode,
based on the first-principles calculations of their atomic structures, sodium
intercalation energetics and electronic properties. The calculations reveal
that graphene or GO film can effectively support not only the stable formation
of hetero-interface with the SnS2 layer but also the easy intercalation of
sodium atom with low migration energy and acceptable low volume change. The
electronic charge density differences and the local density of state indicate
that the electrons are transferred from the graphene or GO layer to the SnS2
layer, facilitating the formation of hetero-interface and improving the
electronic conductance of the semiconducting SnS2 layer. These 2D hybrid
composites of SnS2/G or GO are concluded to be more promising candidates for
SIB anodes compared with the individual monolayers.",1810.07864v1
2018-10-24,Charge transfer tuning in TiO2 hybrid nanostructures with acceptor-acceptor systems,"An interesting interplay between two different modifiers and the surface of
titanium dioxide leads to a significant change in photoelectrochemical
properties of the designed hybrid materials. The semiconductor is
photosensitized by one of the counterparts and exhibits the
photoelectrochemical photocurrent switching effect thanks to interactions with
graphene oxide - the second modifier mediates charge transfer processes in the
system, allowing us to design the materials response at the molecular level.
Based on the selection of molecular counterpart we may affect the behaviour of
hybrids upon light irradiation in a different manner, which may be useful for
the applications in photovoltaics, optoelectronics and photocatalysis. Here we
focus particularly on the nanocomposites made of titanium dioxide with graphene
oxide combined with either 2,3,5,6-tetrachlorobenzoquinone or
2,3-dichloro-5,6-dihydroxybenzoquinone - for these two materials we observed a
major change in the charge transfer processes occurring in the system.",1810.10522v1
2018-10-25,Raman Spectroscopy of Diesel and Gasoline Engine-Out Soot Using Different Laser Power,"We studied engine-out soot samples collected from a heavy-duty
direct-injection diesel engine and a port-fuel injection gasoline
spark-ignition engine. The two types of soot samples were characterized using
Raman spectroscopy with different laser power. A Matlab program using
least-square-method with trust-region-reflective algorithm was developed for
curve fitting. We used a DOE (design of experiments) method to avoid local
convergence. This method was used for two-band fitting and three-band fitting.
The fitting results were used to determine the intensity ratio of D and G Raman
bands. We find that high laser power may cause oxidation of soot samples, which
gives higher D/G intensity ratio. Diesel soot has consistently higher
amorphous/graphitic carbon ratio and thus higher oxidation reactivity, in
comparison to gasoline soot, which is revealed by the higher D/G intensity
ratio in Raman spectra measured under the same laser power.",1810.10701v1
2018-10-26,Lone-pair effect on carrier capture in Cu$_2$ZnSnS$_4$ solar cells,"The performance of kesterite thin-film solar cells is limited by a low
open-circuit voltage due to defect-mediated electron-hole recombination. We
calculate the non-radiative carrier-capture cross sections and
Shockley-Read-Hall recombination coefficients of deep-level point defects in
Cu$_2$ZnSnS$_4$ (CZTS) from first-principles. While the oxidation state of Sn
is +4 in stoichiometric CZTS, inert lone pair (5$s^2$) formation lowers the
oxidation state to +2. The stability of the lone pair suppresses the ionization
of certain point defects, inducing charge transition levels deep in the band
gap. We find large lattice distortions associated with the lone-pair defect
centers due to the difference in ionic radii between Sn(II) and Sn(IV). The
combination of a deep trap level and large lattice distortion facilitates
efficient non-radiative carrier capture, with capture cross-sections exceeding
$10^{-12}$ cm$^2$. The results highlight a connection between redox active
cations and `killer' defect centres that form giant carrier traps. This lone
pair effect will be relevant to other emerging photovoltaic materials
containing n$s^2$ cations.",1810.11259v1
2018-10-30,Direct coupling of first-principles calculations with replica exchange Monte Carlo sampling of ion disorder in solids,"We demonstrate the feasibility of performing sufficient configurational
sampling of disordered oxides directly from first principles without resorting
to the use of fitted models such as cluster expansion. This is achieved by
harnessing the power of modern-day cluster supercomputers using the replica
exchange Monte Carlo method coupled directly with structural relaxation and
energy calculation performed by density functional codes. The idea is applied
successfully to the calculation of the temperature-dependence of the degree of
inversion in the cation sublattice of MgAl$_2$O$_4$ spinel oxide. The
possibility of bypassing fitting models will lead to investigation of
disordered systems where cluster expansion is known to perform badly: for
example, systems with large lattice deformation due to defects, or systems
where long-range interactions dominate such as electrochemical interfaces.",1810.12517v1
2018-10-30,Substrate induced proximity effect in superconducting niobium nanofilms,"Structural and superconducting properties of high quality Niobium nanofilms
with different thicknesses are investigated on silicon oxide and sapphire
substrates. The role played by the different substrates and the superconducting
properties of the Nb films are discussed based on the defectivity of the films
and on the presence of an interfacial oxide layer between the Nb film and the
substrate. The X-ray absorption spectroscopy is employed to uncover the
structure of the interfacial layer. We show that this interfacial layer leads
to a strong proximity effect, specially in films deposited on a SiO$_2$
substrate, altering the superconducting properties of the Nb films. Our results
establish that the critical temperature is determined by an interplay between
quantum-size effects, due to the reduction of the Nb film thicknesses, and
proximity effects.",1810.12643v1
2019-06-06,Odd-Parity Superconductivity Driven by Octahedra Rotations in Iridium Oxides,"Iridium oxides have provided a playground to study novel phases originating
from spin-orbit coupling and electron-electron interactions. Among them, the
d-wave singlet superconductor was proposed for electron-doped Sr$_2$IrO$_4$,
containing two Ir atoms in a unit cell due to the staggered rotation of oxygen
octahedra about the c-axis. It was also noted that such oxygen octahedra
rotation affects electronic transports. Here we study the role of octahedra
tilting away from the c-axis, in determining superconducting pairing symmetry.
We show that the octahedra tilting changes the large Fermi surface to a Dirac
point, which strongly suppresses the conventional d-wave pairing. Furthermore,
it also promotes effective spin-triplet interactions in the strong Hubbard
interaction limit, leading to a transition from the even-parity to odd-parity
superconducting phase. Thus, tuning octahedra distortions can be used as a tool
to engineer a spin triplet superconductor in strongly correlated systems with
strong spin-orbit coupling.",1906.02749v1
2019-06-07,Self-limiting growth of two-dimensional palladium between graphene oxide layers,"The ability of different materials to display self-limiting growth has
recently attracted enormous attention due to the importance of nanoscale
materials in applications for catalysis, energy conversion, (opto)electronics,
etc. Here, we show that electrochemical deposition of palladium (Pd) between
graphene oxide (GO) sheets result in a self-limiting growth of 5 nm thin Pd
nanosheets. The self-limiting growth is found to be a consequence of strong
interaction of Pd with the confining GO sheets which results in bulk growth of
Pd being energetically unfavourable for larger thicknesses. Furthermore, we
have successfully carried out liquid exfoliation of the resulting Pd-GO
laminates to isolate Pd nanosheets and demonstrated their high efficiency in
continuous flow catalysis and electrocatalysis.",1906.03047v1
2019-06-03,"The Ratio Law of the Structure Evolution and Stability for Ti$_n$O$_m$ ($n=3$-$18$, $m=1$-$2n$) Clusters","Most theoretical investigations about titanium oxide clusters focus on
(TiO$_2$)$_n$. However, many Ti$_n$O$_m$ clusters with $m\neq 2n$ are produced
experimentally. In this work, first-principles calculations are performed to
probe the evolution of Ti$_n$O$_m$ clusters. Our investigations show that for
$n=3$-$11$, there exist one relatively stable specie; while for $n=12$-$18$,
there are two relatively stable species: Ti-rich and O-rich species. HOMO-LOMO
calculations show that the gap can be tuned by changing the size and
configurations of Ti$_n$O$_m$ clusters. Our investigation provides insights
into the evolution of cluster-to-bulk process in titanium oxide.",1906.05354v1
2019-06-24,Combination of informational storage and logical processing based on an all-oxide asymmetric multiferroic tunnel junction,"Multiferroic tunnel junctions (MFTJs) have already been proved to be
promising candidates for application in spintronics devices. The coupling
between tunnel magnetoresistance (TMR) and tunnel electroresistance (TER) in
MFTJs can provide four distinct resistive states in a single memory cell. Here
we show that in an all-oxide asymmetric MFTJ of La0.7Sr0.3MnO3 /PbZr0.2Ti0.8O3
/La0.7Te0.3MnO3 (LSMO/PZT/LTMO) with p-type and n-type electrodes, the
intrinsic rectification is observed and can be modified by the ferroelectric
polarization of PZT. Owing to the combined TMR, TER and diode effects, two
different groups of four resistive states under opposite reading biases are
performed. With two parallel asymmetric junctions and the appropriate series
resistance, the coexistence of logic units and quaternary memory cells can be
realized in the same array devices. The asymmetric MFTJ structure enables more
possibilities for designing next generation of multi-states memory and logical
devices with higher storage density, lower energy consumption and significantly
increased integration level.",1906.09993v1
2019-06-19,Origin of current-controlled negative differential resistance modes and the emergence of composite characteristics with high complexity,"Current-controlled negative differential resistance has significant potential
as a fundamental building block in brain-inspired neuromorphic computing.
However, achieving desired negative differential resistance characteristics,
which is crucial for practical implementation, remains challenging due to
little consensus on the underlying mechanism and unclear design criteria. Here,
we report a material-independent model of current-controlled negative
differential resistance to explain a broad range of characteristics, including
the origin of the discontinuous snap-back response observed in many transition
metal oxides. This is achieved by explicitly accounting for a non-uniform
current distribution in the oxide film and its impact on the effective circuit
of the device, rather than a material-specific phase transition. The
predictions of the model are then compared with experimental observations to
show that the continuous S-type and discontinuous snap-back characteristics
serve as fundamental building blocks for composite behaviour with higher
complexity. Finally, we demonstrate the potential of our approach for
predicting and engineering unconventional compound behaviour with novel
functionality for emerging electronic and neuromorphic computing applications.",1907.02651v1
2019-07-08,Role of Toll-Like Receptors in the interplay between pathogen and damage associated molecular patterns,"Various theoretical studies have been carried out to infer relevant
protein-protein interactions among pathogens and their hosts. Such studies are
generally based on preferential attachment of bacteria / virus to their human
receptor homologs. We have analyzed 17 pathogenic species mainly belonging to
bacterial and viral pathogenic classes, with the aim to identify the
interacting human proteins which are targeted by both bacteria and virus
specifically. Our study reveals that the TLRs play a crucial role between the
pathogen-associated molecular patterns (PAMPs) and the damage associated
molecular patterns (DAMPS). PAMPs include bacterial lipopolysaccharides (LPs),
endotoxins, bacterial flagellin, lipoteichoic acid, peptidoglycan in bacterial
organisms and nucleic acid variants associated with viral organisms, whereas
DAMPs are associated with host biomolecules that perpetuate non-infectious
inflammatory responses. We found out the presence of SOD1 and SOD2 (superoxide
dismutase) is crucial, as it acts as an anti-oxidant and helps in eliminating
oxidative stress by preventing damage from reactive oxygen species. Hence, such
strategies can be used as new therapies for anti-inflammatory diseases with
significant clinical outcomes.",1907.03512v1
2019-06-25,Work function tuning of graphene oxide by using cesium applied to low work function tethers,"Low Work Function Tethers (LWT) is long conductors with a segment coated with
a material that has loosely-bounded electrons. Unlike a standard bare tether
equipped with an active electron emitter, LWTs close the electrical circuit
(cathodic contact) with the ambient plasma in a passive manner thanks to the
thermionic and photoelectric effects. This work presents experimental results
on a novel procedure for manufacturing LWT samples. Conductive substrates
(aluminum and copper) have been coated with graphene oxide doped with Cesium by
using a scalable, simple and cost-effective coating method with an airbrush.
Both GO and Cs-doped GO (GO/Cs) samples were characterized utilizing X-ray
spectroscopy, field emission scanning electron microscopy, four-point probe,
and ultraviolet photoelectron spectroscopy (UPS). They showed that GO sheets
were successfully doped with Cs atoms, which do not agglomerate on the graphene
sheets and do not form particles. The UPS results indicated that by doping GO
sheets with Cs, the work function of GO decreases from 4.6 eV to 3.09 eV, thus
increasing the applicability of GO as an electron emitter material.",1907.03656v1
2019-07-15,Effects of Electron-Beam Irradiation on Graphene Oxide,"Graphene oxide (GO) is a nanofilm composed of graphene with various oxygen
functional groups attached. GO is of interest due to its unique
mechanical-enhancement properties, its tunable electronic properties, and its
potential use in the wide-scale production of graphene. Scanning electron
microscopes (SEMs) are frequently used to characterize and study GO films. The
purpose of this project was to study the effects of SEM-imaging on GO films.
Using an SEM, we irradiated GO samples at electron beam-energies of 10, 20, and
30 keV (at a constant emission current of ~40 micro-amps) for times ranging
from 15 minutes to one hour. Raman D- and G-band intensities were used to
examine structural modifications/damage to GO samples as a function of beam
energy and exposure time. The results suggest that imaging with a 30 keV
electron beam for 30 minutes may lead to the formation of amorphous carbon,
while imaging with 10 keV or 20 keV beams for 30 minutes does not have a
significant effect on GO samples.",1907.06311v1
2019-07-17,Low-frequency charge noise in Si/SiGe quantum dots,"Electron spins in silicon have long coherence times and are a promising qubit
platform. However, electric field noise in semiconductors poses a challenge for
most single- and multi-qubit operations in quantum-dot spin qubits. Here, we
investigate the dependence of low-frequency charge noise spectra on temperature
and aluminum-oxide gate dielectric thickness in Si/SiGe quantum dots with
overlapping gates. We find that charge noise increases with aluminum oxide
thickness. We also find strong dot-to-dot variations in the temperature
dependence of the noise magnitude and spectrum. These findings suggest that
each quantum dot experiences noise caused by a distinct ensemble of two-level
systems, each of which has a non-uniform distribution of thermal activation
energies. Taken together, our results suggest that charge noise in Si/SiGe
quantum dots originates at least in part from a non-uniform distribution of
two-level systems near the surface of the semiconductor.",1907.07549v3
2019-07-17,Novel Receiver for Superparamagnetic Iron Oxide Nanoparticles in a Molecular Communication Setting,"Superparamagnetic iron oxide nanoparticles (SPIONs) have recently been
introduced as information carriers in a testbed for molecular communication
(MC) in duct flow. Here, a new receiver for this testbed is presented, based on
the concept of a bridge circuit. The capability for a reliable transmission
using the testbed and detection of the proposed receiver was evaluated by
sending a text message and a 80 bit random sequence at a bit rate of 1/s, which
resulted in a bit error rate of 0 %. Furthermore, the sensitivity of the device
was assessed by a dilution series, which gave a limit for the detectability of
peaks between 0.1 to 0.5 mg/mL. Compared to the commercial susceptometer that
was previously used as receiver, the new detector provides an increased
sampling rate of 100 samples/s and flexibility in the dimensions of the
propagation channel. Furthermore, it allows to implement both single-ended and
differential signaling in SPION-bases MC testbeds.",1907.07805v1
2019-07-23,Interfacial phenomena in nanocapacitors with multifunctional oxides,"The analysis of the structure, chemical stability, electronic and
ferroelectric properties of the interfaces between Pt(001) and PbZrTiO$_3$(001)
(PZT) have been performed with $ab$ $initio$ methods. We show that the chemical
environment plays a critical role in determining the interfacial reconstruction
and charge redistribution at the metal/oxide interfaces. We demonstrate that
the difference in interfacial bonds formed at the Pt/PZT interfaces with
(TiZr)O$_2$ - and PbO- termination of PZT essentially defines the effectiveness
of the screening, and ease of polarisation switching in PZT-based capacitors.
The imperfect screening in Pt/PZT/Pt capacitors is caused by strong interfacial
bonds formed at the interface with (TiZr)O$_2$-terminated film, which is
accompanied by the suppressed polarisation of PZT film. In contrast, the
capacitors with PbO-terminated PZT show a negligible depolarising field and
high polarisation, which is the consequence of weak bonds formed at this type
of interfaces. The latter also causes a higher switching barrier than that in
the former system.",1907.09821v1
2019-07-24,Systematic beyond-DFT study of binary transition metal oxides,"Various methods going beyond density-functional theory (DFT), such as DFT+U,
hybrid functionals, meta-GGAs, GW, and DFT-embedded dynamical mean field theory
(eDMFT), have been developed to describe the electronic structure of correlated
materials, but it is unclear how accurate these methods can be expected to be
when applied to a given strongly correlated solid. It is thus of pressing
interest to compare their accuracy as they apply to different categories of
materials. Here, we introduce a novel paradigm in which a chosen set of
beyond-DFT methods is systematically and uniformly tested on a chosen class of
materials. For a first application, we choose the target materials to be the
binary transition-metal oxides FeO, CoO, MnO, and NiO in their
antiferromagnetic phase and present a head-to-head comparison of spectral
properties as computed using the various methods. We also compare with
available experimental angle-resolved photoemission spectroscopy (ARPES),
inverse-photoemission spectroscopy, and with optical absorption. We find both
B3LYP and eDMFT can reproduce the experiments quite well, with eDMFT doing best
in particular when comparing with the ARPES data.",1907.10498v1
2019-07-29,Air tightness of hBN encapsulation and its impact on Raman spectroscopy of van der Waals materials,"Raman spectroscopy is a precious tool for the characterization of van der
Waals materials, e.g. for the determination of the layer number in thin
exfoliated flakes. For sensitive materials, however, this method can be
dramatically invasive. In particular, the light intensity required to obtain a
significant Raman signal is sufficient to immediately photo-oxidize few-layer
thick metallic van der Waals materials. In this work we investigated the impact
of the environment on Raman characterization of thin NbSe$_2$ crystals. We show
that in ambient conditions the flake is locally oxidized even for very low
illumination intensity. On the other hand, we observe no degradation if the
Raman measurements are performed either in vacuum or on fully hBN-encapsulated
samples. Interestingly, we find that covering samples deposited on the usual
SiO$_2$ surface only from the top is not sufficient to prevent diffusion of
oxygen underneath the layers.",1907.12265v1
2019-07-30,Influence of Local Defects on the Dynamics of O-H Bond Breaking and Formation on a Magnetite Surface,"The transport of H adatoms across oxide supports plays an important role in
many catalytic reactions. We investigate the dynamics of H/Fe3O4(001) between
295 and 382 K. By scanning tunneling microscopy at frame rates of up to 19.6
fps, we observe the thermally activated switching of H between two O atoms on
neighboring Fe rows. This switching rate changes in proximity to a defect,
explained by density functional theory as a distortion in the Fe-O lattice
shortening the diffusion path. Quantitative analysis yields an apparent
activation barrier of 0.94 +/- 0.07 eV on a pristine surface. The present work
highlights the importance of local techniques in the study of atomic-scale
dynamics at defective surfaces such as oxide supports.",1907.12944v1
2019-07-30,Optical properties of mist CVD grown $α$-Ga$_2$O$_3$,"We report on the study of optical properties of mist CVD grown alpha Gallium
oxide with the observation of excitonic absorption in spectral responsivity
measurements. 163 nm of Gallium oxide was grown on sapphire using Gallium
acetylacetonate as the starting solution at a substrate temperature of 450 deg
C. The film was found to be crystalline and of alpha phase with an on axis full
width at half maximum of 92 arcsec as confirmed from X ray diffraction scans.
The Taucs plot extracted from absorption spectroscopy exhibited two transitions
in the UV regime at 5.3 eV and 5.6 eV, corresponding to excitonic absorption
and direct band to band transition respectively. The binding energy of exciton
was extracted to be 114 meV from spectral responsivity measurements. Further,
metal semiconductor metal photodetectors with lateral inter digitated geometry
were fabricated on the film. A sharp band edge was observed at 230 nm in the
spectral response with peak responsivity of around 1 Amperes per Watt at a bias
of 20 V. The UV to visible rejection ratio was found to be around 100 while the
dark current was measured to be around 0.1 nA.",1907.13072v1
2019-07-31,Limitations of In$_2$O$_3$ as a transparent conducting oxide,"Sn-doped In$_2$O$_3$ or ITO is the most widely used transparent conducting
oxide. We use first-principles calculations to investigate the limitations to
its transparency due to free-carrier absorption mediated by phonons or charged
defects. We find that the main contribution to the phonon-assisted indirect
absorption is due to emission (as opposed to absorption) of phonons, which
explains why the process is relatively insensitive to temperature. The
wavelength dependence of this indirect absorption process can be described by a
power law. Indirect absorption mediated by charged defects or impurities is
also unavoidable since doping is required to obtain conductivity. At high
carrier concentrations, screening by the free carriers becomes important. We
find that charged-impurity-assisted absorption becomes larger than
phonon-assisted absorption for impurity concentrations above 10$^{20}$
cm$^{-3}$. The differences in the photon-energy dependence of the two processes
can be explained by band-structure effects.",1907.13573v1
2019-09-04,"Effect of annealing on the structural, topographical and optical properties of sol gel derived ZnO and AZO thin films","A comparative study of the physical properties of undoped Zinc Oxide (ZnO)
and Al doped Zinc Oxide (AZO) thin films were performed as a function of
annealing temperature. The structural properties were analyzed using X-ray
diffraction and the recorded patterns indicated that the crystallinity of the
films always enhanced with increasing annealing temperature while it degrades
with Al doping. The topographical modification of the films due to heat
treatment was examined by atomic force microscopy which revealed that annealing
roughened the surface of all the films; however the AZO films always exhibited
smoother morphology than ZnO. Study of the optical properties by UV-Visible
spectrophotometer demonstrated that the transmittance was gradually diminished
with the rise in annealing temperature. In addition, a notable increase in the
optical band gap was also observed for the AZO films.",1909.01987v1
2019-09-23,Superstatistical approach to air pollution statistics,"Air pollution by Nitrogen Oxides (NOx) is a major concern in large cities as
it has severe adverse health effects. However, the statistical properties of
air pollutants are not fully understood. Here, we use methods borrowed from
nonequilibrium statistical mechanics to construct suitable superstatistical
models for air pollution statistics. In particular, we analyze time series of
Nitritic Oxide ($NO$) and Nitrogen Dioxide ($NO_2$) concentrations recorded at
several locations throughout Greater London. We find that the probability
distributions of concentrations have heavy tails and that the dynamics is
well-described by $\chi^2$ superstatistics for $NO$ and inverse $\chi^2$
superstatistics for $NO_2$. Our results can be used to give precise risk
estimates of high-pollution situations and pave the way to mitigation
strategies.",1909.10433v2
2019-09-23,Nanostructured La0.5Ba0.5CoO3 as cathode for solid oxide fuel cells,"A simple method has been used to synthesize nanostructured La0.5Ba0.5CoO3
(LBCO) powders, by confining chemical precursors into the pores of
polycarbonate filters. The proposed method allows us to obtain powders formed
by crystallites of different sizes, it is scalable and does not involve the use
of sophisticated deposition techniques. The area specific polarization
resistance of symmetrical cells was studied to analyze the electrochemical
behavior of the LBCO nanostructures as cathodes for Solid-Oxide Fuel Cells. We
show that the performance is improved by reducing the size of the crystallites,
obtaining area specific resistance values of 0.2 Wcm2 at 700C, comparable with
newly developed cathodes using novel deposition techniques.",1909.10611v1
2019-10-03,Temperature-programmed reduction and dispersive X-ray absorption spectroscopy studies of CeO2-based nanopowders for intermediate-temperature Solid-Oxide Fuel Cell anodes,"In this work, we study the influence of the average crystallite size and
dopant oxide on the reducibility of CeO2-based nanomaterials. Samples were
prepared from commercial Gd2O3-, Sm2O3- and Y2O3-doped CeO2 powders by
calcination at different temperatures ranging between 400 and 900C and
characterized by X-ray powder diffraction, transmission electron microscopy and
BET specific surface area. The reducibility of the samples was analyzed by
temperature-programmed reduction and in situ dispersive X-ray absorption
spectroscopy techniques. Our results clearly demonstrate that samples treated
at lower temperatures, of smallest average crystallite size and highest
specific surface areas, exhibit the best performance, while Gd2O3-doped ceria
materials display higher reducibility than Sm2O3- and Y2O3-doped CeO2.",1910.01715v1
2019-10-09,Antimony doped Tin Oxide/Polyethylenimine Electron Selective Contact for reliable and light soaking-free high Performance Inverted Organic Solar Cells,"We have demonstrated a high-performance low temperature solution processed
electron selective contact consisting of 10 at% antimony doped tin oxide (ATO)
and the neutral polymer polyethylenimine (PEI). Inverted organic photovoltaics
(OPVs) utilizing ATO/PEI as electron selective contact exhibited high power
conversion efficiencies for both the reference P3HT: PCBM and the non-fullerene
based P3HT- IDTBR active layer OPV material systems. Importantly it is shown
that the proposed ATO/PEI carrier selective contact provides light soaking-free
inverted OPVs. Furthermore, by increasing the thickness of ATO layer from 40 to
120 nm the power conversion efficiency of the corresponding inverted OPVs
remain unaffected a parameter which indicates the potential of the proposed
ATO/PEI carrier selective contact for high performance light-soaking-free and
reliable roll-to-roll printing solutions processed inverted OPVs.",1910.04017v1
2019-10-19,"Investigation of structural, electrical and electrochemical properties of La0.6Sr0.4Fe0.8Mn0.2O3-δ as an intermediate temperature solid oxide fuel cell cathode","La0.6Sr0.4Fe0.8Mn0.2O3 (LSFM) compound is synthesized by Sol-gel method and
evaluated as a cathode material for the intermediate temperature solid oxide
fuel cell (IT-SOFC). X-ray diffraction (XRD) indicates that the LSFM has a
Rhombohedral structure with R-3c space group symmetry. The XRD patterns reveal
very small amount of impurity phase in the LSFM and Y2O3-Stabilized ZrO2 (YSZ)
mixture powders sintered at 600, 700 and 800 C for a week. The maximum
electrical conductivity of LSFM is about 35.35 S.cm-1 at 783 C in the air. The
oxygen chemical diffusion coefficients, DChem, are increased from 1.39*10-6 up
to 7.66*10-6 .cm2. Besides, the oxygen surface exchange coefficients, kChem,
are obtained to lie between 2.9*10-3 and 8.7*10-3 cm.s-1 in a temperature range
of 600-800 C. The area-specific resistances (ASRs) of the LSFM symmetrical cell
are 7.53, 1.53, 1.13, 0.46 and 0.31 .cm2 at 600, 650, 700, 750 and 800 C
respectively, and related activation energy, Ea, is about 1.23 eV.",1910.08754v1
2019-10-22,Negative thermal expansion of nanoporous anodic aluminum oxide membranes,"We have measured the thermal expansion of Ni nanowires electrodeposited into
self-organized nanoporous amorphous aluminum oxide (AAO) membranes without Al
substrate using X-ray diffraction between 110K and 350K. The results indicate
an average thermal expansion of the Ni nanowires -- along the wire axis -- of
$\langle\alpha\rangle_{\rm NiNW}=-(1.6 \pm 1.5)\times 10^{-6}$/K. Assuming a
bulk-like thermal expansion of the isolated Ni nanowires, this result indicates
that AAO has also a negative thermal expansion. We estimate the thermal
expansion of nanoporous AAO to be $\langle\alpha\rangle_{\rm AAO}=-(5 \pm 1)
\times 10^{-6}$/K. We show that data obtained previously on the thermal
expansion of metallic nanowires grown in the nanoporous AAO may be interpreted
as originated in a negative thermal expansion of the matrix.",1910.11190v1
2019-10-30,Broadband and wide-temperature-range thermal emitter with super-hydrophobicity based on oxidized high-entropy film,"This paper demonstrates broadband and wide-temperature-range thermal emitter
with super-hydrophobicity based on an oxidized high-entropy film. The annealed
(NiCuCrFeSi)O high-entropy film can serve as a mid-infrared emitter due to its
three characteristics: i) High blackbody-like emission in a broadband
mid-infrared region from 2.5 um to 20 um; ii) High emittance (more than 90%) in
a wide temperature range from 300 K to 1000 K; iii) Super-hydrophobicity with
high contact angle (CA) of 151 degree and low title angle (TA) of 5 degree.
These characteristics originate from the recrystallization of as-deposited film
and formation of cavernous structure with a plethora of nanoscale polyhedrons
and holes after an annealing process, supported by the results of XRD and
SEM/EDX. This work may provide new ideas for applications of thermal emitters
operating at substantially wide temperature range.",1910.13629v1
2020-01-01,Mobile Small Polarons Explain Conductivity in Lithium Titanium Oxide Battery Electrodes,"Lithium titanium oxide Li$_4$Ti$_5$O$_{12}$ (LTO) is an intriguing anode
material promising particularly long lived batteries, due to its remarkable
phase stability during (dis)charging of the cell. However, its usage is limited
by its low intrinsic electronic conductivity. Introducing oxygen vacancies can
be one method to overcome this drawback, possibly by altering the charge
carrier transport mechanism. We use Hubbard corrected density-functional theory
(DFT+U) to show that polaronic states in combination with a possible hopping
mechanism can play a crucial role in the experimentally observed increase of
electronic conductivity. To gauge polaronic charge mobility, we compute
relative stabilities of different localization patterns and estimate polaron
hopping barrier heights. With this we finally show how defect engineering can
indeed raise the electronic conductivity of LTO up to the level of its ionic
conductivity, thereby explaining first experimental results for reduced LTO.",2001.00263v1
2020-01-02,Molecular Patterning and Directed Self-Assembly of Gold Nanoparticles on GaAs,"The ability to create micro/nano patterns of organic self-assembled
monolayers on semiconductor surfaces is crucial for fundamental studies and
applications in a number of emerging fields in nanoscience. Here, we
demonstrate the patterning of thiol molecular SAMs on oxide-free GaAs surface
by dip-pen nanolithography and micro-contact printing, facilitated by a process
of surface etching and passivation of the GaAs. A quantitative analysis on the
molecular diffusion on GaAs was conducted by examining the writing of nanoscale
dot and line patterns by DPN, which agrees well with surface diffusion models.
The functionality of the patterned thiol molecules was demonstrated by directed
self-assembly of gold nanoparticles onto a template of 4-Aminothiophenol SAM on
GaAs. The highly selective assembly of the Au NPs was evidenced with atomic
force microscopy and scanning electron microscopy. The ability to precisely
control the assembly of Au NPs on oxide-free semiconductor surfaces using
molecular templates may lead to an efficient bottom-up method for the
fabrication of nano-plasmonic structures.",2001.00592v1
2020-01-08,Influence of doping on the properties of vanadium oxide gel films,"Effect of doping with H and W on the properties of V2O5 and VO2 derived from
V2O5 gel has been studied. It is shown that the treatment of V2O5 in
low-temperature RF hydrogen plasma for 1 to 10 min. leads to either hydration
of vanadium pentoxide or its reduction (depending on the treatment conditions)
to lower vanadium oxides. For some samples, which are subject to plasma
treatment in the discharge active zone, a non-ordinary temperature dependence
of resistance, with a maxi-mum at T ~ 100 K, is observed. For W-doped VO2
films, it is shown that substitution of V4+ with W6+ results in a decrease of
the temperature of metal-insulator transition. Also, it has been shown that the
doping of the initial films with ~3 at.% of W reduces the statistical scatter
in the thresh-old parameters of the switching devices with S-shaped I-V
characteristics on the basis of V2O5 gel films.",2001.02402v1
2020-01-08,Effect of memory electrical switching in metal/vanadium oxide/silicon structures with VO2 films obtained by the sol-gel method,"Electrical switching and rectifying properties of the metal-VO2-Si
structures, on both p-type and n-type silicon, with vanadium dioxide films
obtained by an acetylacetonate sol-gel method, are studied. The switching
effect is shown to be due to the semiconductor-to-metal phase transition (SMPT)
in vanadium dioxide. The shift of the switching threshold voltage, accompanied
by the memory effect, in forward bias of the p-Si-VO2 anisotype heterojunction
is observed. To explain this effect, a model is proposed which suggests the
existence of an additional series resistance associated with a channel at the
VO2/Si interface, where a SiOx layer forms during the VO2 deposition process.
This resistance is responsible for both threshold switching characteristics,
and the memory effect, and the oxygen ion electromigration process is shown to
underlie this effect. Potential applications of the observed phenomena,
combining the effects of ReRAM and SMPT, in oxide electronics are discussed.",2001.03055v1
2020-01-25,"Prediction of perovskite-related structures in ACuO$_{3-x}$ (A $=$ Ca, Sr, Ba, Sc, Y, La) using density functional theory and Bayesian optimization","Oxygen vacancy ordering in perovskite-type transition-metal oxides plays an
important role in the emergence of exotic electronic properties, as typified by
superconducting cuprates. In this study, we predict the stability of
oxygen-deficient perovskite structures in ACuO$_{3-x}$ (A $=$ Ca, Sr, Ba, Sc,
Y, La) by density functional theory calculation. We introduce a combination of
the cluster expansion method, Gaussian process, and Bayesian optimization to
find stable oxygen-deficient structures among a considerable number of
candidates. Our calculations not only reproduce the reported structures but
suggest the presence of several unknown oxygen-deficient perovskite structures,
some of which are stabilized at high pressures. This work demonstrates the
great applicability of the present computational procedure for the elucidation
of the structural stability of strongly correlated oxides with a large
tolerance to oxygen deficiency.",2001.09312v1
2020-02-03,Actinide and Lanthanide Dioxide Lattice Dilatation Mechanisms with Defect Ingrowth,"{\alpha}-particle irradiated single-crystal isostructural oxide lattices
(CmO2, AmO2, CeO2, UO2, NpO2, PuO2, ThO2) were modeled by molecular dynamics
simulation method. Lattice parameter changes with IFP cation defects displayed
exponential increases. These data were compatible with the available lattice
parameter changes with {\alpha}-particle dose experiments. Pre- and post- peaks
emerged around principal peaks of irradiated oxide cation-cation radial
distribution functions, which indicate obstruction and distortion type defects,
respectively. Dependence of lattice dilatations on the number of obstruction
type cation defects was examined. In a previous study, obstruction type uranium
defects were found to be directly responsible for the UO2 lattice swelling and
there was a linear relationship between them. It was also determined that this
linear equation has two different slopes at low and high defect concentrations.
In this paper, it was found that these phenomena were not specific to UO2 and
applicable to all fluorite-structured actinide and lanthanide dioxides studied
here. These findings provide clues about the existence of more general law.",2002.00574v1
2020-02-06,Durability of solid oxide electrolysis stack under dynamic load cycling for syngas production,"A 6-cell solid oxide electrolysis stack was tested under H2O + CO2
co-electrolysis conditions. The cells used in the stack consisted of a
nickel-yttria stabilized zirconia (Ni-YSZ) fuel electrode, YSZ electrolyte and
lanthanum strontium cobaltite-gadolinium doped ceria (LSC-GDC) composite oxygen
electrode. The aim of this study was to investigate the stack durability when
operated under dynamic load conditions simulating a wind energy powered SOEC
stack for synthesis gas production. The degradation of the stack was observed
to be less than 1%/1000 h in terms of area specific resistance during the 1000
hours operation. Detailed electrochemical analysis revealed a constant ohmic
resistance, indicating intact contact in the stack. Only minor degradation was
observed, mainly due to the fuel electrode process. The overall stack voltage
degradation rate was 0.8%/1000 h.",2002.02169v1
2020-02-06,Quantized Auger Recombination of Polaronic Self-trapped Excitons in Bulk Iron Oxide,"The Auger recombination in bulk semiconductors can depopulate the charge
carriers in a non-radiative way, which, fortunately, only has detrimental
impact on optoelectronic device performance under the condition of high carrier
density because the restriction arising from concurrent momentum and energy
conservation limits the Auger rate. Here, we surprisingly found that the Auger
recombination in bulk Fe2O3 films was more efficient than narrow-bandgap
high-mobility semiconductors that were supposed to have much higher Auger rate
constants than metal oxides. The Auger process in Fe2O3 was ascribed to the
Coulombically coupled self-trapped excitons (STEs), which was enhanced by the
relaxation of momentum conservation because of the strong spatial localization
of these STEs. Furthermore, due to this localization effect the kinetic traces
of the STE annihilation for different STE densities exhibited characteristics
of quantized Auger recombination, and we demonstrated that these traces could
be simultaneously modeled by taking into account the quantized Auger rates.",2002.02389v1
2020-02-12,Green exciton series in cuprous oxide,"We numerically investigate the odd parity states of the green exciton series
in cuprous oxide. Taking into account the coupling to the yellow series and
especially to the yellow continuum, the green excitons are quasi-bound
resonances with a finite lifetime which cannot be described with Hermitian
operators. To calculate their positions and linewidths, we use the method of
complex-coordinate rotation, leading to a non-Hermitian complex eigenvalue
problem. We find that the behavior of the dominant P states is very well
approximated by a modified Rydberg formula using a negative quantum defect. The
corresponding linewidths induced by the coupling to the yellow continuum
decrease with the third power of the principal quantum number.",2002.04973v1
2020-02-17,Color Tuning by Spontaneous Propagation of Gap Surface Plasmons in Epsilon Near Zero Nano-Cavity,"This work presents numerical and experimental results of plasmonic
Metal-Insulator optical nano-cavities. The systems are composed of Silver as
metal, polyvinylpyrrolidone or indium tin oxide or zinc oxide as insulator. The
proposed nano-cavities exhibit extraordinary effects as colors changing in
function of the incident/view angles, enhancement of the experimental real and
imaginary parts of the pseudo dielectric constant, an extraordinary
transmission of 50$\%$ and zero reflection for both polarizations at the
resonant wavelengths. These results lead to the formation and propagation of
surface plasmon polaritons and their hybridization in gap surface plasmons. The
concurrence of these effects allow studying the Goos-H\""anchen shift by
exploiting the very narrow $\Delta$ and $\Psi$ ellipsometer parameters. Thank
to their optical properties, the proposed nano-cavities could be applied in
several fields such tunable color filters, optics, photonics and sensing.",2002.06972v1
2019-12-29,Bioinspired Nanocomposites: 2D Materials Within a 3D Lattice,"Advanced composites are used in a variety of industrial applications and
therefore attract much scientific interest. Here we describe the formation of
novel carbon-based nanocomposites via incorporation of graphene oxide into the
crystal lattice of single crystals of calcite. Incorporation of a 2D organic
material into single-crystal lattices has never before been reported. To
characterize the resulting nanocomposites we employed high-resolution
synchrotron powder X-ray diffraction, electron microscopy, transmission
electron microscopy, fluorescence microscopy, and nanoindentation tests.
Detailed analysis revealed a layered distribution of graphene oxide sheets
incorporated within the calcite host. Moreover, the optical and mechanical
properties of the calcite host were altered when a carbon-based nanomaterial
was introduced into its lattice. Compared to pure calcite, the composite
GO-calcite crystals exhibited lower elastic modulus and higher hardness. The
results of this study show that the incorporation of a 2D material within a 3D
crystal lattice is not only feasible but also can lead to the formation of
hybrid crystals exhibiting new properties.",2002.07059v1
2020-02-25,Antiferroelectricity in a family of pyroxene-like oxides with rich polymorphism,"Antiferroelectrics have potential applications in energy conversion and
storage, but are scarce, particularly among oxides that otherwise display rich
ferroic behaviours. Are we overlooking potential antiferroelectrics, simply
because we have not discovered their corresponding ferroelectric phase yet?
Here we report a first-principles study suggesting this is the case of a family
ABO$_3$ pyroxene-like materials, characterized by chains of corner-sharing
BO$_4$ tetrahedra, a well-known member being KVO$_3$. The irregular tetrahedra
have an electric dipole associated to them. In the most stable polymorph, the
dipoles display an antipolar pattern with zero net moment. However, upon
application of an electric field, half of the tetrahedra rotate, flipping the
corresponding dipoles and reaching a ferroelectric state. We discuss the unique
possibilities for tuning and optimization these antiferroelectrics offer. We
argue that the structural features enabling this antiferroelectric behaviour
are also present in other all-important mineral families.",2002.11120v1
2020-02-26,Stressor-Layer-Induced Elastic Strain Sharing in SrTiO3 Complex Oxide Sheets,"A precisely selected elastic strain can be introduced in submicron-thick
single-crystal SrTiO3 sheets using a silicon nitride stressor layer. A
conformal stressor layer deposited using plasma-enhanced chemical vapor
deposition produces an elastic strain in the sheet consistent with the
magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction
reveals that the strain introduced in the SrTiO3 sheets is on the order of 10
4, matching the predictions of an elastic model. This approach to elastic
strain sharing in complex oxides allows the strain to be selected within a wide
and continuous range of values, an effect not achievable in heteroepitaxy on
rigid substrates.",2002.11287v1
2020-02-26,Effect of lattice distortions on the electron and thermal transport properties of transparent oxide semiconductor Ba1-xSrxSnO3 solid solution films,"La-doped ASnO3 (A = Ba, Sr) have great potential as advanced transparent
oxide semiconductors due to their large optical bandgap and relatively high
electron mobility. The bandgap of Ba1-xSrxSnO3 solid solution increases from
3.2 eV (BaSnO3) to 4.6 eV (SrSnO3) with x. However, the increase in the bandgap
is accompanied by reductions in the electrical conductivity. The versatility in
the changes in the electrical properties are not trivial, and the property
optimization has been challenging. Here we propose a simple metric for
quantifying the transport properties of ASnO3. We investigated the
electron/thermal transport properties of Ba1-xSrxSnO3 solid solution films and
their relationship with the lattice distortion. The results suggest that the
all transport properties of Ba1-xSrxSnO3 are dominated by the lattice
distortion. This phenomenon is attributed to the distortions in the SnO6
octahedron, which consists the conduction band.",2002.11308v1
2020-04-02,Device-aware inference operations in SONOS nonvolatile memory arrays,"Non-volatile memory arrays can deploy pre-trained neural network models for
edge inference. However, these systems are affected by device-level noise and
retention issues. Here, we examine damage caused by these effects, introduce a
mitigation strategy, and demonstrate its use in fabricated array of SONOS
(Silicon-Oxide-Nitride-Oxide-Silicon) devices. On MNIST, fashion-MNIST, and
CIFAR-10 tasks, our approach increases resilience to synaptic noise and drift.
We also show strong performance can be realized with ADCs of 5-8 bits
precision.",2004.00802v1
2020-03-03,Tunable capacitance in all-inkjet-printed nanosheet heterostructures,"Heterostructures constructed from two-dimensional building blocks have shown
promise for field-effect transistors, memory devices, photosensors and other
electronic applications1,2. 2D nanosheet crystals can be constructed into
multilayer heterostructures using layer-by-layer methods3, but that method
cannot be used to fabricate large-scale and thick heterostructures, due to the
time-consuming nature and low efficiency of the process. An alternative
approach to deposit different two-dimensional materials is by inkjet
printing4-7. Here we show the fabrication of a nanosheet supercapacitor by
inkjet printing Ti3C2Tx MXene nanosheets as electrodes, and graphene oxide
nanosheets as solid-state electrolyte. The free water molecules trapped between
graphene oxide sheets facilitate proton movement through the layered solid
electrolyte8. The as-made supercapacitor shows high areal capacitance, good
cycling stability and high areal energy and power densities comparable with
existing printed supercapacitors. Moreover, the specific capacitance can be
increased further by addition of liquid electrolytes.",2004.03350v1
2020-04-09,Double photoionization of propylene oxide: a coincidence study of the ejection of a pair of valence-shell electrons,"Propylene oxide, a favorite target of experimental and theoretical studies of
circular dichroism, was recently discovered in interstellar space, further
amplifying the attention to its role in the current debate on protobiological
homochirality. In the present work, a photoelectron-photoion-photoion
coincidence technique, using an ion-imaging detector and tunable synchrotron
radiation in the 18.0-37.0 eV energy range, permits: (i)-to observe six
double-ionization fragmentation channels, their relative yields being accounted
for about two-thirds by the couple (C2H4+, CH2O+), one-fifth by (C2H3+, CH3O+);
(ii)-to measure thresholds for their openings as a function of photon energy;
(iii)-to unravel a pronounced bimodality for a kinetic-energy-released
distribution, fingerprint of competitive non-adiabatic mechanisms.",2004.04639v1
2020-04-30,Precision Spectroscopy of Nitrous Oxide Isotopocules with a Cross-Dispersed Spectrometer and Mid-Infrared Frequency Comb,"As a potent greenhouse gas and ozone depleting agent, nitrous oxide (N$_2$O)
plays a critical role in the global climate. Effective mitigation relies on
understanding global sources and sinks which can be supported through isotopic
analysis. We present a cross-dispersed spectrometer, coupled with a
mid-infrared frequency comb, capable of simultaneously monitoring all singly
substituted, stable isotopic variants of N$_2$O. Rigorous evaluation of the
instrument lineshape function and data treatment are discussed. Laboratory
characterization of the spectrometer demonstrates sub-GHz spectral resolution
and an average precision of $7.4\times10^{-6}$ for fractional isotopic
abundance retrievals in 1 s.",2004.14962v1
2020-12-02,High-temperature topological superconductivity in twisted double layer copper oxides,"A great variety of novel phenomena occur when two-dimensional materials, such
as graphene or transition metal dichalcogenides, are assembled into bilayers
with a twist between individual layers. As a new application of this paradigm,
we consider structures composed of two monolayer-thin $d$-wave superconductors
with a twist angle $\theta$ that can be realized by mechanically exfoliating
van der Waals-bonded high-$T_c$ copper oxide materials, such as
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. On the basis of symmetry arguments and
detailed microscopic modelling, we predict that for a range of twist angles in
the vicinity of $45^{\rm o}$, such bilayers form a robust, fully gapped
topological phase with spontaneously broken time-reversal symmetry and
protected chiral Majorana edge modes. When $\theta\approx 45^{\rm
  o}$, the topological phase sets in at temperatures close to the bulk
$T_c\simeq 90$ K, thus furnishing a long sought realization of a true
high-temperature topological superconductor.",2012.01412v1
2020-12-08,Empirical Analysis of the Photoelectrochemical Impedance Response of Hematite Photoanodes for Water Photo-Oxidation,"Photoelectrochemical impedance spectroscopy (PEIS) is a useful tool for the
characterization of photoelectrodes for solar water splitting. However, the
analysis of PEIS spectra often involves a priori assumptions that might bias
the results. This work puts forward an empirical method that analyzes the
distribution of relaxation times (DRT), obtained directly from the measured
PEIS spectra of a model hematite photoanode. By following how the DRT evolves
as a function of control parameters such as the applied potential and
composition of the electrolyte solution, we obtain unbiased insights into the
underlying mechanisms that shape the photocurrent. In a subsequent step, we fit
the data to a process-oriented equivalent circuit model (ECM) whose makeup is
derived from the DRT analysis in the first step. This yields consistent
quantitative trends of the dominant polarization processes observed. Our
observations reveal a common step for the photo-oxidation reactions of water
and H2O2 in alkaline solution",2012.05081v1
2020-12-17,High pressure computational search of trivalent lanthanide di-nitrides,"Transition metal nitrides have attracted much interest of the scientific
community for their intriguing properties and technological applications. Here
we focus on yttrium dinitride (YN$_{2}$) and its formation and structural
transition under pressure. We employed a fixed composition USPEX search to find
the most stable polymorphs. We choose yttrium as a proxy for the lanthanide
series because it has only $+3$ oxidation state, contrary to most transition
metals. We then computed thermodynamic and dynamical stability of these
structures compared to the decomposition reactions and we found that the
compound undergoes two structural transitions, the latter showing the formation
N$_{4}$ chains. A closer look into the nature of the nitrogen bonding showed
that in the first two structures, where nitrogen forms dimers, the bond length
is intermediate between that of a single bond and that of a double bond, making
it hard to rationalize the proper oxidation state configuration for YN$_{2}$.
In the latter structure where there is the formation of N$_{4}$ chains, the
bond lengths increase significantly, up to a value that can be justified as a
single bond. Finally, we also studied the electronic structure and the
dynamical stability of the structures we found.",2012.09576v1
2020-12-22,Perovskite oxide heterojunction for Rashba-Dresselhaus assisted antiferromagnetic spintronics,"A major impediment towards realizing technologies based on the emerging
principles of antiferromagnetic spintronics is the shortage of suitable
materials. In this paper, we propose a design of polar|nonpolar
heterostructures of perovskite oxides, where a single unit cell of SrIrO3 is
sandwiched between a thin film of LaAlO3 and a substrate of SrTiO3. Our
calculations within the framework of density-functional theory + Hubbard U +
spin-orbit coupling reveal a two-dimensional conducting layer with electron and
hole pockets at the interface, exhibiting a strong anisotropic
Rashba-Dresselhaus effect along with noncollinear antiferromagnetism,
indicating the possibility of realizing a spin-orbit torque. An insightful
physical model for the anisotropic Rashba-Dresselhaus effect nicely interprets
our results, providing an estimate for the Rashba-Dresselhaus coefficients and
illustrating pseudospin orientation.We also observe a proximity-induced
prominent Rashba-like effect for Ti 3d empty bands. Our results suggest that
the heterostructure may possess the essential ingredients for antiferromagnetic
spintronics, deserving experimental verification.",2012.11868v1
2020-12-22,Dynamical heterogeneities in non-entangled polystyrene and poly(ethylene oxide) star melts,"Star polymers can exhibit a heterogeneous dynamical behavior due to their
internal structure. In this work we employ atomistic molecular dynamics
simulations to study translational motion in non-entangled polystyrene and
poly(ethylene oxide) star-shaped melts. We focus on the local heterogeneous
dynamics originating from the multi-arm star-like architecture and quantify the
intramolecular dynamical gradient. By examining the translational motion at
length scales of the order of the Kuhn length, we aim to find common features
for both studied chemistries and to provide a critical and direct comparison
with theoretical models of polymer dynamics. We discuss the observed tendencies
with respect to the continuous Rouse model adjusted for the star-like
architectures. Two versions of the Rouse model are examined: one assuming
uniform friction on every Rouse bead and another one considering larger branch
point friction. Apart from chain connectivity between neighboring beads, both
versions disregard interactions between the chains. Despite the tolerable
description of the simulation data, neither model appears to reflect the
mobility gradient accurately. The detailed quantitative atomistic models
employed here bridge the gap between the theoretical and general,
coarse-granined models of star-like polymers which lack the indispensable
chemical details.",2012.12333v1
2020-12-30,Study of SiO2-PbO-CdO-Ga2O3 glass system for mid infrared optical elements,"Glasses based on SiO2-PbO-CdO-Ga2O3 system have been studied for the first
time for fabrication of mid-infrared optical elements. Gallium oxide
concentration was gradually increased, replacing silicon dioxide, for different
cadmium and lead oxide content. The thermal and optical properties were
investigated for different compositions. It was observed that the thermal
stability, refractive index, and the transmission in the infrared range
increased with increase of gallium and lead concentrations. The most thermally
stable glass composition was selected for fabrication of optical elements such
as optical fibers. We also successfully fabricated mid-infrared lenses by hot
embossing for potential application in compact gas detectors",2012.15096v1
2021-01-07,Optically Facet-Resolved Reaction Anisotropy in Two-Dimensional Transition Metal Dichalcogenides,"Quantifying anisotropy in the chemical reactions of mesoscopic crystals has
mostly resorted on the combination of electron microscopy and diffraction. In
this work, we established crystal-facet-resolved kinetic measurements of
oxidation reactions in 2D transition metal dichalcogenides (TMDs) using optical
second-harmonic generation spectroscopy and scanning probe microscopy. We show
the in-plane anisotropy of their bond-breaking reactions is governed by their
structure and strongly material-dependent among four TMDs. The facet-resolved
analysis directly revealed that the reactions proceed fastest (slowest) for
chalcogen (metal)-terminated zigzag edges with armchair edges in the middle.
The degree of the anisotropy inducing trigonal oxidation patterns was much
higher in MoS2 and MoSe2 than WS2 and WSe2. Kinetic Wulff construction based on
edge-specific reaction rates verified the material-dependent mesoscopic
reaction patterns. We also show that the reactions are initiated at
substrate-mediated defects located on the bottom and top surfaces of 2D TMDs.",2101.02376v2
2021-01-07,Automated coordination corrected enthalpies with AFLOW-CCE,"The computational design of materials with ionic bonds poses a critical
challenge to thermodynamic modeling since density functional theory yields
inaccurate predictions of their formation enthalpies. Progress requires
leveraging physically insightful correction methods. The recently introduced
coordination corrected enthalpies (CCE) method delivers accurate formation
enthalpies with mean absolute errors close to room temperature thermal energy,
i.e., 25meV/atom. The CCE scheme, depending on the number of cation-anion bonds
and oxidation state of the cation, requires an automated analysis of the system
to determine and apply the correction. Here, we present AFLOW-CCE -- our
implementation of CCE into the AFLOW framework for computational materials
design. It features a command line tool, a web interface and a Python
environment. The workflow includes a structural analysis, automatically
determines oxidation numbers, and accounts for temperature effects by
parametrizing vibrational contributions to the formation enthalpy per bond.",2101.02724v2
2021-01-09,Interface-Driven Thermo-Electric Switching Performance of VO$^+$ Diffused Soda-Lime Glass,"Strongly confined NaVO$^+$ segregation and its thermo-responsive
functionality at the interface between simple sputter-deposited amorphous
vanadium oxide thin films and soda-lime glass was substantiated in the present
study by in-situ temperature-controlled Time of Flight Secondary Ion Mass
Spectrometry (ToF-SIMS). The obtained ToF-SIMS depth profiles provided
unambiguous evidence for a reversible transformation that caused systematic
switching of the NaVO$^+$/ Na$^+$ and Na$^+$/ VO$^+$ intensities upon cycling
the temperature between 25 $^\circ$C and 340 $^\circ$C. Subsequently, NaVO
complexes were found to be reversibly formed (at 300 $^\circ$C) in vanadium
oxide diffused glass, leading to thermo-responsive electrical behaviour of the
thin film glass system. This new segregation -- and diffusion-dependent
multifunctionality of NaVO$^+$ -- points towards applications as an advanced
material for thermo-optical switches, in smart windows or in thermal sensors.",2101.03330v1
2021-01-12,Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates,"The enhanced superconductivity in monolayer FeSe on titanates opens a
fascinating pathway towards the rational design of high-temperature
superconductors. Utilizing the state-of-the-art oxide plus chalcogenide
molecular beam epitaxy systems in situ connected to a synchrotron
angle-resolved photoemission spectroscope, epitaxial LaTiO3 layers with varied
atomic thicknesses are inserted between monolayer FeSe and SrTiO3, for
systematic modulation of interfacial chemical potential.With the dramatic
increase of electron accumulation at the LaTiO3-SrTiO3 surface, providing a
substantial surge of work function mismatch across the FeSe-oxide interface,
the charge transfer and the superconducting gap in the monolayer FeSe are found
to remain markedly robust. This unexpected finding indicates the existence of
an intrinsically anchored magic doping within the monolayer FeSe systems.",2101.04787v1
2021-01-20,Highly sensitive silver decorated-graphene oxide-silicon nanowires hybrid SERS sensors for trace level detection of environmental pollutants,"In this study, we evaluated the sensing performance of silver
nanoprism/graphene oxide/silicon nanowires (AgNPr/GO/SiNWs) nanohybrid system
for effective detection of organic dye and herbicide residues in freshwater via
surface-enhanced Raman scattering (SERS). Homogenous and vertically aligned
SiNWs have been successfully synthesized using metal-assisted chemical etching
technique by varying the etching time from 10 to 30 min. AgNPr/GO/SiNW hybrids
were assembled by spin-coating of GO followed by drop-casting deposition of
AgNPr. The microstructures of AgNPr/GO/SiNWs are strongly affected by the
etching time of SiNWs, which in turn affected its SERS performance when
rhodamine 6G is used as an analyte molecule. Owing to the synergetic effects of
GO and AgNPr, SERS response of AgNPr/GO/SiNWs composites were found to be
superior compared to AgNPr/SiNWs. High efficiency of 6.1 x 1010 has been
achieved with AgNPr/GO/SiNWs based sensor fabricated with 30-min etched SiNWs
for rhodamine 6G. An effective way of rapid detection of drinking water
pollutants such as methylene blue and atrazine up to picomolar (10-12 M)
concentrations was demonstrated using these low-cost AgNPr/GO/SiNWs nanohybrids
SERS sensors.",2101.07955v1
2021-01-25,"A full configuration interaction quantum Monte Carlo study of ScO, TiO and VO molecules","Accurate ab initio calculations of 3d transition metal monoxide molecules
have attracted extensive attention because of its relevance in physical and
chemical science, as well as theoretical challenges in treating strong electron
correlation. Meanwhile, recent years have witnessed the rapid development of
full configuration interaction quantum Monte Carlo (FCIQMC) method to tackle
electron correlation. In this study, we carry out FCIQMC simulations to ScO,
TiO and VO molecules and obtain accurate descriptions of 13 low-lying
electronic states (ScO $^2\Sigma^+$, $^2\Delta$, $^2\Pi$; TiO $^3\Delta$,
$^1\Delta$, $^1\Sigma^+$, $^3\Pi$, $^3\Phi$; VO $^4\Sigma^-$, $^4\Phi$,
$^4\Pi$, $^2\Gamma$, $^2\Delta$), including states that have significant
multi-configurational character. The FCIQMC results are used to assess the
performance of several other wave function theory and density functional theory
methods. Our study highlights the challenging nature of electronic structure of
transition metal oxides and demonstrates FCIQMC as a promising technique going
forward to treat more complex transition metal oxide molecules and materials.",2101.09873v1
2012-02-13,Nanostructured antimony tin oxide synthesized via chemical precipitation method: its characterization and application in humidity sensing,"In present investigation we report the synthesis of antimony tin oxide
nanoparticles via chemical precipitation method. The synthesized material was
characterized using X-ray diffractometer, Scanning Electron Microscope,
UV-visible absorption spectroscopy. XRD shows the crystalline nature of the
synthesized material and the crystallite size was estimated by using
Debye-Scherer equation and its minimum value was 3 nm. Pelletization of
synthesized material was done using hydraulic press machine under uniform
pressure of 616 MPa. Then the pellets were annealed at 200, 400 and 600{\deg}C.
Further each pellet was put in humidity sensing chamber and corresponding
variations in resistance with relative humidity (%RH) were measured. The
average sensitivity was calculated by taking the average of all sensitivities
ranging from 10 to 90% RH. The average sensitivity of the pellet annealed at
600{\deg}C was best among all the sensing pellets and was 2.18 K{\Omega}/%RH.
Results were reproducible {\pm}84% after 2 months.",1205.2336v1
2012-02-13,Temperature Sensors based on Semiconducting Oxides: An Overview,"Earlier studies show that organic and inorganic semiconducting materials are
the most promising materials for use in temperature sensors. In this brief
review, attention will be focused on temperature sensors and its applications
in various fields. In addition, we have investigated the temperature sensing
characteristics of nanostructured ZnO and ZnO-CuO nanocomposite. For this
purpose, ZnO and ZnO-CuO nanocomposite were synthesized via chemical
precipitation method. Scanning electron microscopy and X-ray diffraction of
sensing materials have also performed. The average crystallite size was 45 and
68 nm for ZnO and ZnO-CuO respectively. The pelletization of the synthesized
powder was done using hydraulic pressing machine (MB Instrument, Delhi) under a
pressure of 616 MPa at room ambient. This pellet was put within the
Ag-Pellet-Ag electrode configuration for temperature sensing. Temperature
sensitivities of above semiconducting oxides were calculated. Electrical
properties of the materials establish the semiconducting nature of these
sensing pellets. In addition, the activation energies of ZnO and ZnO-CuO
nanocomposite were estimated.",1205.2712v1
2012-05-16,Ab-initio Low-Energy Model of Transition-Metal-Oxide Heterostructure LaAlO3/SrTiO3,"We develop the multi-scale ab-initio scheme for correlated electrons (MACE)
for transitionmetal-oxide heterostructures, and determine the parameters of the
low-energy effective model. By separating Ti t2g bands near the Fermi level
from the global Kohn-Sham (KS) bands of LaAlO3/SrTiO3 which are highly
entangled with each other, we are able to calculate the parameters of the
low-energy effective model of the interface with the help of constrained random
phase approximation (cRPA). The on-site energies of the Ti t2g orbitals in the
1stlayer is about 650 meV lower than those in the 2nd-layer. In the 1st-layer,
the transfer integral of the Ti t2g orbital is nearly the same as that of the
bulk SrTiO3, while the effective screened Coulomb interaction becomes about 10
percent larger than that of the bulk SrTiO3. The differences of the parameters
from the bulk SrTiO3 reduce rapidly with increasing distance from the
interface. Our present versatile method makes it possible to derive effective
ab-initio low-energy models and allows studying interfaces of strongly
correlated electron systems from first principles.",1205.3600v1
2012-05-31,Transfer-free Grown Bilayer Graphene Transistors for Digital Applications,"We invented a novel method to fabricate graphene transistors on oxidized
silicon wafers without the need to transfer graphene layers. By means of
catalytic chemical vapor deposition (CCVD) the in-situ grown bilayer graphene
transistors (BiLGFETs) are realized directly on oxidized silicon substrate,
whereby the number of stacked graphene layers is determined by the selected
CCVD process parameters, e.g. temperature and gas mixture. BiLGFETs exhibit
ultra-high on/off-current ratios of 107 at room temperature, exceeding
previously reported values by several orders of magnitude. This will allow a
simple and low-cost integration of graphene devices for digital nanoelectronic
applications in a hybrid silicon CMOS environment for the first time.",1205.6909v1
2017-05-05,Berezinskii-Kosterlitz-Thouless Type Scenario in Molecular Spin Liquid $A$Cr$_2$O$_4$,"The spin relaxation in chromium spinel oxides $A$Cr$_{2}$O$_{4}$ ($A=$ Mg,
Zn, Cd) is investigated in the paramagnetic regime by electron spin resonance
(ESR). The temperature dependence of the ESR linewidth indicates an
unconventional spin-relaxation behavior, similar to spin-spin relaxation in the
two-dimensional (2D) chromium-oxide triangular lattice antiferromagnets. The
data can be described in terms of a generalized Berezinskii-Kosterlitz-Thouless
(BKT) type scenario for 2D systems with additional internal symmetries. Based
on the characteristic exponents obtained from the evaluation of the ESR
linewidth, short-range order with a hidden internal symmetry is suggested.",1705.02234v1
2017-05-01,Non Volatile MoS$_{2}$ Field Effect Transistors Directly Gated By Single Crystalline Epitaxial Ferroelectric,"We demonstrate non-volatile, n-type, back-gated, MoS$_{2}$ transistors,
placed directly on an epitaxial grown, single crystalline,
PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$ (PZT) ferroelectric. The transistors show decent
ON current (19 ${\mu}A/{\mu}$m), high on-off ratio (10$^{7}$), and a
subthreshold swing of (SS ~ 92 mV/dec) with a 100 nm thick PZT layer as the
back gate oxide. Importantly, the ferroelectric polarization can directly
control the channel charge, showing a clear anti-clockwise hysteresis. We have
selfconsistently confirmed the switching of the ferroelectric and corresponding
change in channel current from a direct time-dependent measurement. Our results
demonstrate that it is possible to obtain transistor operation directly on
polar surfaces and therefore it should be possible to integrate 2D electronics
with single crystalline functional oxides.",1705.03746v2
2017-05-15,Theoretical insight into the interaction of O2 and H2O molecules with the perfect and the defective InSe monolayers,"By using first-principles calculation, the interaction of O2 and H2O
molecules with the pristine and the defective InSe monolayers is studied. It is
predicted that the single Se and In vacancies exhibit significantly enhanced
chemical activity toward the adsorbates compared with the perfect InSe lattice
site, and the Se vacancies have a much higher chemical activity than the In
vacancies. H2O molecule should be only physisorbed on the various InSe
monolayers at ambient conditions, according to the calculated energies. The
doping of the various InSe monolayers is discussed by the physisorbed H2O. The
vacancies show a much higher chemical activity toward O2 than H2O. Although O2
molecules are still physisorbed on the pristine InSe monolayer, they will be
chemisorbed on the defective InSe monolayers. Especially, our calculated
energies suggest that the surface oxidation of the 2D InSe semiconductor should
be dominated by the defects that expose under-coordinated host atoms,
especially In atoms. Our theoretical results can help better understanding the
doping and the oxidation of the 2D InSe semiconductor under ambient conditions.",1705.05140v1
2017-05-16,Raman study of electron-phonon coupling in thin films of LiTi$_2$O$_4$ spinel oxide superconductor,"We performed a Raman scattering study of thin films of LiTi$_2$O$_4$ spinel
oxide superconductor. We detected four out of five Raman active modes, with
frequencies in good accordance with our first-principles calculations. Three
T$_{2g}$ modes show a Fano lineshape from 5 K to 295 K, which suggests an
electron-phonon coupling in LiTi$_2$O$_4$. Interestingly, the electron-phonon
coupling shows an anomaly across the negative to positive magnetoresistance
transition at 50 K, which may be due to the unset of other competing orders.
The strength of the electron-phonon interaction estimated from the Allen's
formula and the observed lineshape parameters suggests that the three T$_{2g}$
modes contribute little to superconductivity.",1705.05568v1
2017-05-16,Quantum Conductance Probing of Oxygen Vacancies in SrTiO3 Epitaxial Thin Film Using Graphene,"The quantum Hall conductance in monolayer graphene on an epitaxial SrTiO3
(STO) thin film is studied to understand the role of oxygen vacancies in
determining the dielectric properties of STO. As the gate voltage sweep range
is gradually increased in our device, we observe systematic generation and
annihilation of oxygen vacancies evidenced from the hysteretic conductance
behavior in graphene. Furthermore, based on the experimentally observed linear
scaling relation between the effective capacitance and the voltage sweep range,
a simple model is constructed to manifest the relationship among the dielectric
properties of STO with oxygen vacancies. The inherent quantum Hall conductance
in graphene can be considered as a sensitive, robust, and non-invasive probe
for understanding the electronic and ionic phenomena in complex transition
metal oxides without impairing the oxide layer underneath.",1705.05672v1
2017-05-16,Transition-Metal Oxide (111) bilayers,"Correlated electron systems on a honeycomb lattice have emerged as a fertile
playground to explore exotic electronic phenomena. Theoretical and experimental
work has appeared to realize novel behavior, including quantum Hall effects and
valleytronics, mainly focusing on van der Waals compounds, such as graphene,
chalcogenides, and halides. In this article, we review our theoretical study on
perovskite transition-metal oxides (TMOs) as an alternative system to realize
such exotic phenomena. We demonstrate that novel quantum Hall effects and
related phenomena associated with the honeycomb structure could be artificially
designed by such TMOs by growing their heterostructures along the [111]
crystallographic axis. One of the important predictions is that such TMO
heterostructures could support two-dimensional topological insulating states.
The strong correlation effects inherent to TM $d$ electrons further enrich the
behavior.",1705.05683v2
2017-05-24,Multicomponent exciton gas in cuprous oxide: cooling behaviour and the role of Auger decay,"In this paper we present a hydrodynamic model to describe the dynamics of
para- and orthoexcitons in cuprous oxide at ultralow temperatures inside a
stress induced potential trap. We take into account the finite lifetime of the
excitons, the excitation process and exciton-phonon as well as exciton-exciton
interaction. Furthermore, we model the two-body loss mechanism assuming an
Auger-like effect and compare it to an alternative explanation which relies on
the formation of biexcitons. We discuss in detail the influence on the
numerical results and compare the predictions to experimental data.",1705.08769v1
2017-05-26,Observation of a two-dimensional electron gas at CaTiO$_3$ film surfaces,"The two-dimensional electron gas at the surface of titanates gathered
attention due to its potential to replace conventional silicon based
semiconductors in the future. In this study, we investigated films of the
parent perovskite CaTiO$_3$, grown by pulsed laser deposition, by means of
angular-resolved photoelectron spectroscopy. The films show a c(4x2) surface
reconstruction after the growth that is reduced to a p(2x2) reconstruction
under UV-light. At the CaTiO$_3$ film surface, a two-dimensional electron gas
(2DEG) is found with an occupied band width of 400 meV. With our findings
CaTiO$_3$ is added to the group of oxides with a 2DEG at their surface. Our
study widens the phase space to investigate strontium and barium doped
CaTiO$_3$ and the interplay of ferroelectric properties with the 2DEG at oxide
surfaces. This could open up new paths to tailor two-dimensional transport
properties of these systems towards possible applications.",1705.09495v1
2017-05-30,"Two-dimensional electron systems in ATiO3 perovskites (A = Ca, Ba, Sr): control of orbital hybridization and order","We report the existence of a two-dimensional electron system (2DES) at the
(001) surface of CaTiO3. Using angle-resolved photoemission spectroscopy, we
find a hybridization between the d_xz and d_yz orbitals, not observed in the
2DESs at the surfaces of other ATiO3 perovskites, e.g. SrTiO3 or BaTiO3. Based
on a comparison of the 2DES properties in these three materials, we show how
the electronic structure of the 2DES (bandwidth, orbital order and electron
density) is coupled to different typical lattice distortions in perovskites.
The orbital hybridization in orthorhombic CaTiO3 results from the rotation of
the oxygen octahedra, which can also occur at the interface of oxide
heterostructures to compensate strain. More generally, the control of the
orbital order in 2DES by choosing different A-site cations in perovskites
offers a new gateway towards 2DESs in oxide heterostructures beyond SrTiO3.",1705.10755v1
2017-09-05,3D Nanoporous Gold with Very Low Parting Limit Derived from Au-based Metallic Glass and Enhanced Methanol Electro-oxidation Catalytic Performance,"Nanoporous gold (NPG) with bi-continuous ligaments and pores structure has
promising potential in functional applications, among which one prominent
example is fuel cell electrocatalyst. However, current application of NPG is
mostly limited to methanol electro-oxidation due to its weak catalytic
performance. Here we report a simple chemical dealloying process, for
generating peculiar three-dimensional (3D) free-standing NPG with high specific
surface area associated with a novel porous cone shaped protrusion morphology.
This NPG structure possesses the highest specific activity of catalytic
performance reported NPG catalysts so far.",1709.01376v1
2017-09-14,Towards Universal Non-Volatile Resistance Switching in Non-metallic Monolayer Atomic Sheets,"Here, we report the intriguing observation of stable non-volatile resistance
switching (NVRS) in single-layer atomic sheets sandwiched between metal
electrodes. NVRS is observed in the prototypical semiconducting (MX2, M=Mo, W;
and X=S, Se) transitional metal dichalcogenides (TMDs), and insulating
hexagonal boron nitride (h-BN), which alludes to the universality of this
phenomenon in non-metallic 2D monolayers, and features forming-free switching.
This observation of NVRS phenomenon, widely attributed to ionic diffusion,
filament and interfacial redox in bulk oxides and electrolytes, inspires new
studies on defects, ion transport and energetics at the sharp interfaces
between atomically-thin sheets and conducting electrodes. From a contemporary
perspective, switching is all the more unexpected in monolayers since leakage
current is a fundamental limit in ultra-thin oxides. Emerging device concepts
in non-volatile flexible memory fabrics, and brain-inspired (neuromorphic)
computing could benefit substantially from the pervasive NVRS effect and the
associated wide materials and engineering co-design opportunity.
Experimentally, a 50 GHz radio-frequency (RF) monolayer switch is demonstrated,
which opens up a new application for electronic zero-static power RF switching
technology.",1709.04592v1
2017-09-21,Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity,"Oxygen vacancies, especially their distribution, are directly coupled to the
electromagnetic properties of oxides and related emergent functionalities that
have implication in device applications. Here using a homoepitaxial strontium
titanate thin film, we demonstrate a controlled manipulation of the oxygen
vacancy distribution using the mechanical force from a scanning probe
microscope tip. By combining Kelvin probe force microscopy imaging and
phase-field simulations, we show that oxygen vacancies can move under a
stress-gradient-induced depolarisation field. When tailored, this nanoscale
flexoelectric effect enables a controlled spatial modulation. In motion, the
scanning probe tip thereby deterministically reconfigures the spatial
distribution of vacancies. The ability to locally manipulate oxygen vacancies
on-demand provides a tool for the exploration of mesoscale quantum phenomena,
and engineering multifunctional oxide devices.",1709.07201v1
2017-09-26,Nanoscale Bandgap Tuning across an Inhomogeneous Ferroelectric Interface,"We report nanoscale bandgap engineering via a local strain across the
inhomogeneous ferroelectric interface, which is controlled by the
visible-light-excited probe voltage. Switchable photovolatic effects and the
spectral response of the photocurrent were explore to illustrate the reversible
bandgap variation (~0.3eV). This local-strain-engineered bandgap has been
further revealed by in situ probe-voltage-assisted valence electron energy-loss
spectroscopy (EELS). Phase-field simulations and first-principle calculations
were also employed for illustration of the large local strain and the bandgap
variation in ferroelectric perovskite oxides. This reversible bandgap tuning in
complex oxides demonstrates a framework for the understanding of the
opticallyrelated behaviors (photovoltaic, photoemission, and photocatalyst
effects) affected by order parameters such as charge, orbital, and lattice
parameters.",1709.08788v1
2017-09-26,First-Principles Many-Body Investigation of Correlated Oxide Heterostructures: Few-Layer-Doped SmTiO$_3$,"Correlated oxide heterostructures pose a challenging problem in condensed
matter research due to their structural complexity interweaved with demanding
electron states beyond the effective single-particle picture. By exploring the
correlated electronic structure of SmTiO$_3$ doped with few layers of SrO, we
provide an insight into the complexity of such systems. Furthermore, it is
shown how the advanced combination of band theory on the level of Kohn-Sham
density functional theory with explicit many-body theory on the level of
dynamical mean-field theory provides an adequate tool to cope with the problem.
Coexistence of band-insulating, metallic and Mott-critical electronic regions
is revealed in individual heterostructures with multi-orbital manifolds.
Intriguing orbital polarizations, that qualitatively vary between the metallic
and the Mott layers are also encountered.",1709.08875v1
2017-11-03,Towards Hardware Implementation of Double-Layer Perceptron Based on Metal-Oxide Memristive Nanostructures,"Construction and training principles have been proposed and tested for an
artificial neural network based on metal-oxide thin-film nanostructures
possessing bipolar resistive switching (memristive) effect. Experimental
electronic circuit of neural network is implemented as a double-layer
perceptron with a weight matrix composed of 32 memristive devices. The network
training algorithm takes into account technological variations of the
parameters of memristive nanostructures. Despite the limited size of weight
matrix the developed neural network model is well scalable and capable of
solving nonlinear classification problems.",1711.01041v1
2017-11-09,Room Temperature Giant Charge-to-Spin Conversion at SrTiO3/LaAlO3 Oxide Interface,"Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3
(STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba
spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge
conversion) in the 2DEG layer is reported. However, the direct effect of
charge-to-spin conversion, an essential ingredient for spintronic devices in a
current induced spin-orbit torque scheme, has not been demonstrated yet. Here
we show, for the first time, a highly efficient spin generation with the
efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using
spin torque ferromagnetic resonance. In addition, we suggest that the spin
transmission through the LAO layer at high temperature range is attributed to
the inelastic tunneling via localized states in the LAO band gap. Our findings
may lead to potential applications in the oxide insulator based spintronic
devices.",1711.03268v1
2017-11-17,Atom Probe Analysis of Ex Situ Gas-Charged Stable Hydrides,"In this work, we report on the atom probe tomography analysis of two metallic
hydrides formed by pressurized charging using an ex situ hydrogen charging
cell, in the pressure range of 200-500 kPa (2-5 bar). Specifically we report on
the deuterium charging of Pd/Rh and V systems. Using this ex situ system, we
demonstrate the successful loading and subsequent atom probe analysis of
deuterium within a Pd/Rh alloy, and demonstrate that deuterium is likely
present within the oxide-metal interface of a native oxide formed on vanadium.
Through these experiments, we demonstrate the feasibility of ex situ hydrogen
analysis for hydrides via atom probe tomography, and thus a practical route to
three-dimensional imaging of hydrogen in hydrides at the atomic scale.",1711.06667v1
2017-11-20,Unconventional aspects of electronic transport in delafossite oxides,"The electronic transport properties of the delafossite oxides ABO$_2$ are
usually understood in terms of two well separated entities, namely, the
triangular A$^+$ and (BO$_2$)$^-$ layers. Here we review several cases among
this extensive family of materials where the transport depends on the
interlayer coupling and displays unconventional properties. We review the doped
thermoelectrics based on CuRhO$_2$ and CuCrO$_2$, which show a high-temperature
recovery of Fermi-liquid transport exponents, as well as the highly anisotropic
metals PdCoO$_2$, PtCoO$_2$ and PdCrO$_2$ where the sheer simplicity of the
Fermi surface leads to unconventional transport. We present some of the
theoretical tools that have been used to investigate these transport properties
and review what can and cannot be learned from the extensive set of electronic
structure calculations that have been performed.",1711.07202v1
2017-11-20,CFD investigation of thermal performance of aluminum oxide nanofluid in channel,"This paper shows the CFD investigation of pressure drop and thermal
performance of aluminum oxide nano fluid inside square channel inserted a
cylinder with and without fin using two-phase method. The constant heat flux on
outer wall and laminar flow regime are applied in the considered domain using
finite volume method. The results depict that the enhance of nano-particles
volume concentration and Reynolds number have dramatic effects on heat transfer
coefficient enhancement. Moreover, the increase of nano-particle diameter has
opposite impact on heat transfer efficiency. The passive way leads to higher
pressure drops. For all fluids under consideration, pressure drop escalated
with Reynolds number. Injecting nano-particles into the water causes to
increase in pressure drop and this impact is more significant in high
nano-particle volume fraction.",1711.07407v2
2017-11-28,Dendritic Growth of a Polymer on a 2D Mesoscale Square Lattice,"Dendritic growth patterns exhibiting four-fold anisotropy are observed when
polyethylene oxide undergoes phase segregation from a solution phase to a solid
phase. When this phase transition occurs on a substrate that has patterns of
cross-linked polyethylene oxide resist pillars made using electron beam
lithography, the polymer grows in between the patterns giving rise to dendritic
growth structures exhibiting eight-fold anisotropy. This paper presents these
experimental observations and explains the dendritic growth using principles of
minimization of free energy associated with phase change. Numerical simulations
are carried out using phase-field modeling, and the results are shown to
qualitatively match experimental observations. The simulations reveal that the
polymer assumes the anisotropy of the patterned lattice.",1711.10141v3
2018-03-06,Atomic Visualization of Copper Oxide Structure in Infinite-Layer Cuprate SrCuO2,"We report on atomic-scale visualization of the structure of infinite-layer
cuprate SrCuO2 thin films grown on Nb-doped SrTiO3 substrates by molecular beam
epitaxy. In-situ scanning tunneling microscopy study reveals stoichiometric
copper oxide (CuO2) plane with a 2 x 2 surface reconstruction, prompted by
preferential clustering of four adjacent CuO2 plaquettes. By imaging the
subsurface Sr atoms, intra-unit-cell rotational symmetry breaking is observed,
which, together with the adjacent CuO2 clustering, can be well accounted for by
a periodic up-down buckling of oxygen ions on the CuO2 plane. Further
post-annealing leads to an incommensurate stripe structure of the surface
layer. Our findings provide important structural information for deeply
understanding the electronic structure of superconducting CuO2 plane as well as
high temperature superconductivity in cuprates.",1803.02033v2
2018-03-08,Design of a nickel-base superalloy using a neural network,"A new computational tool has been developed to model, discover, and optimize
new alloys that simultaneously satisfy up to eleven physical criteria. An
artificial neural network is trained from pre-existing materials data that
enables the prediction of individual material properties both as a function of
composition and heat treatment routine, which allows it to optimize the
material properties to search for the material with properties most likely to
exceed a target criteria. We design a new polycrystalline nickel-base
superalloy with the optimal combination of cost, density, gamma' phase content
and solvus, phase stability, fatigue life, yield stress, ultimate tensile
strength, stress rupture, oxidation resistance, and tensile elongation.
Experimental data demonstrates that the proposed alloy fulfills the
computational predictions, possessing multiple physical properties,
particularly oxidation resistance and yield stress, that exceed existing
commercially available alloys.",1803.03039v1
2018-03-10,Continuum Charge Excitations in High-Valence Transition-Metal Oxides Revealed by Resonant Inelastic X-ray Scattering,"We present a theoretical investigation of the origin of Raman-like and
fluorescencelike (FL) features of resonant inelastic x-ray scattering (RIXS)
spectra. Using a combination of local-density approximation + dynamical
mean-field theory and a configuration interaction solver for Anderson impurity
model, we calculate the $L$-edge RIXS and x-ray absorption spectra of
high-valence transition-metal oxides LaCuO$_3$ and NaCuO$_2$. We analyze in
detail the behavior of the FL feature and show how it is connected to the
details of electronic and crystal structure. On the studied compounds we
demonstrate how material details determine whether the electron-hole continuum
can be excited in the $L$-edge RIXS process.",1803.03820v4
2018-03-16,Evolution of superconductivity in ultrathin NbS2,"We report a systematic study of thickness-dependent superconductivity and
carrier transport properties in exfoliated layered 2H-NbS2. Hall-effect
measurements reveal 2H-NbS2 in its normal state to be a p-type metal with hole
mobility of 1-3 cm2/Vs. The superconducting transition temperature is found to
decrease with thickness. We find that the suppression of superconductivity is
due to disorder resulting from the incorporation of atmospheric oxygen and a
reduced hole density. Cross-section transmission electron microscope (TEM)
imaging reveals a chemical change of NbS2 in ambient conditions, resulting in
the formation of amorphous oxide layers sandwiching crystalline layered NbS2.
Though few-nm-thick 2H-NbS2 completely converts to amorphous oxide in ambient
conditions, PMMA encapsulation prevents further chemical change and preserves
superconductivity.",1803.06097v1
2018-02-19,Synthesis and Characterization of Copper Doped Zinc Oxide Thin Films for CO Gas Sensing,"Objective of this work was to synthesize Copper doped Zinc Oxide (CZO) films
and optimization of process parameters by varying molarity of zinc acetate
dehydrate from 0.5 M to 1.0 M, concentration of copper acetate monohydrate from
1% to 5 % and annealing temperature from 200 C to 300 C to measure the
sensitivity of CZO films for CO (Carbon Monoxide) gas. The concentration of CO
gas was maintained at 5 ppm and operating temperature of 250 oC was used for
sensing. Analysis for sensitivity showed highest grading for parametric
combination of 0.75 molarity, 3% copper concentration and 300 C annealing
temperature with surface roughness of 3.90 nm and grain size of 256 nm. TEM
image revealed the crystalline grain size was 5 nm. ANOVA showed that annealing
temperature influenced the sensitivity by 69.06 % .",1803.07144v1
2018-03-12,ALLEGRO Core Degradation Study using MELCOR 2.1,"ALLEGRO is an experimental high-temperature gas (He)-cooled fast reactor
(GFR) under development by the European Consortium V4G4 Centre of Excellence on
basis of the concept ALLEGRO presented by CEA in 2009. Its main purpose is to
demonstrate the viability of GFR in pilot scale and simultaneously serve as a
test bed for GFR-related technologies, above all the high-temperature resistant
refractory fuel in the conventional oxide fuel driver core. Severe accident
studies of the concept with the first core (oxide fuel in stainless steel
claddings) are an important part of safety analyses leading to improves in
reactor design and safety. This paper extends our previous study using the
MELCOR code. Major difference between the previous and this work is decrease of
thermal power and power density to 50 MWth and 66,6 MWth/m3 respectively.
Analyses are focused on protected scenarios based on total station blackout
individually aggravated by loss of primary coolant, water ingress into primary
coolant or malfunction of check valves in the decay heat removal system. The
results indicate the timing and extent of core degradation and provide valuable
data for design of the core catcher in ALLEGRO.",1803.07652v1
2018-03-28,Porous silicon carbide and aluminum oxide with unidirectional open porosity as model target materials for radioisotope beam production,"New silicon carbide (SiC) and aluminum oxide (Al2O3) of a tailor-made
microstructure were produced using the ice-templating technique, which permits
controlled pore formation conditions within the material. These prototypes will
serve to verify aging of the new advanced target materials under irradiation
with proton beams. Before this, the evaluation of their mechanical integrity
was made based on the energy deposition spectra produced by FLUKA codes.",1803.10527v1
2018-06-01,Hot-electron mediated ion diffusion in proton-irradiated magnesium oxide,"Highly energetic ions that impact materials have applications from
semiconductor industry to medicine, and are fundamentally interesting as they
trigger multi-length and time-scale processes. In particular, they excite
electrons into non-thermalized energy distributions with subsequent
non-equilibrium electron-electron and electron-ion dynamics. In order to
achieve a quantitative description of these, we propose a general
first-principles framework that bridges time scales from ultrafast electron
dynamics directly after impact, to ion diffusion over migration barriers in
semiconductors. We apply it to magnesium oxide under proton irradiation and
discover a diffusion mechanism that is mediated by hot electrons. Our
quantitative simulations show that this mechanism strongly depends on the
projectile-ion velocity. This indicates that it may occur only at a specific
penetration depth in the target and that it can be triggered by varying the
kinetic energy of the particle radiation. Either of these predictions should
facilitate direct experimental observation of this effect and significantly
advances current understanding of non-equilibrium electron-ion dynamics.",1806.00443v3
2018-06-05,Reaction front occurrence on imperfection profiles during oxygen chemical diffusion in oxides. I. Thermodynamic background,"We present a theoretical study of the impact of oxygen diffusion in oxide
crystals on metal dopants ionic state and the conduction type under thermal
equilibrium. Oxygen vacancy formation acting as a shallow, double-electronic
donor is assumed to result from the crystal exposure to a low ambient oxygen
pressure. It is shown, that critical transitions from n- to a p-type at an
oxygen partial pressure Pi, and in ionization state of the metal dopant at an
oxygen partial pressure PM, are usually not simultaneous, and depend on the
different reaction constants. Experimental study of the different species
concentrations at thermodynamic equilibrium as functions of pressure and
temperature should allow assessment of various reversible reaction constants
controlling the process. In the Part II companion paper, the kinetic
(diffusion) characteristics are considered in detail.",1806.01687v1
2018-06-05,Reaction front occurrence on imperfection profiles during oxygen chemical diffusion in oxides. II. Kinetic analysis,"We present a theoretical study of the impact of oxygen diffusion in oxide
crystals on metal dopants ionic state and the conduction type under dynamic
changes. The slow changes under thermal equilibrium are provided in a
companion, Part I paper. Oxygen vacancy formation acting as a shallow,
double-electronic donor, is assumed to result from the crystal exposure to a
low ambient oxygen pressure. Critical transitions from n- to a p-type at an
oxygen partial pressure Pi, and in ionization state of the metal dopant at an
oxygen partial pressure PM, are usually not simultaneous, and depend on the
different reaction constants. Invoking ambipolar diffusion for all
participating species, it is shown that oxygen vacancy diffusion exhibits well
defined characteristics in specific regions of the vacancy concentration
related to the said critical pressures. Particularly, the oxygen chemical
diffusivity is practically constant between Pi and PM, and increases sharply
for pressures P << Pi,PM and P >> P,PM. Prominent reaction fronts occur under
specific conditions in the two latter regions.",1806.01706v1
2018-06-06,Single-band to two-band superconductivity transition in two-dimensional oxide interfaces,"In multiorbital materials, superconductivity can exhibit new exotic forms
that include several coupled condensates. In this context, quantum confinement
in two-dimensional superconducting oxide interfaces offers new degrees of
freedom to engineer the band structure and selectively control 3d-orbitals
occupancy by electrostatic doping. However, the presence of multiple
superconducting condensates in these systems has not yet been demonstrated.
Here, we use resonant microwave transport to extract the superfluid stiffness
of the (110)-oriented LaAlO3/SrTiO3 interface in the entire phase diagram. We
evidence a transition from single-band to two-band superconductivity driven by
electrostatic doping, which we relate to the filling of the different
3d-orbitals based on numerical simulations of the quantum well. Interestingly,
the superconducting transition temperature decreases while the second band is
populated, which challenges the Bardeen-Cooper-Schrieffer theory. To explain
this behaviour, we propose that the superconducting order parameters associated
with the two bands have opposite signs with respect to each other.",1806.02212v1
2018-06-11,Evaluation of Porosity for Gamma Irradiated Poly(ethylene oxide): A New Approach Using Microscopic Image Aided with Computer Programming,"Porous polymer films of Poly(ethylene oxide)(PEO) are synthesized by solution
casting technique using gamma irradiated: (a) PEO powder (S-series) and (b) PEO
- methanol solution (L-series). Pore phase forms instantaneously during
preparation. Optimization of the pore content and distribution enables
tailoring of associated properties for multifaceted applications. This method
could be analyzed for mapping of porosity and average pore size. Practicability
and repeatability of the developed programme has been established for
monophasic system using backscattered imaging mode of SEM. This program is
underdevelopment, but PROGIMAGE-POR bears the novelty of using image from
either 2D-or 3D imaging system and could be applied for intricate
composite/layered system.",1806.03777v1
2018-06-11,Inverted structure perovskite solar cells: A theoretical study,"We analysed perovskite CH3NH3PbI3-xClx inverted planner structure solar cell
with nickel oxide (NiO) and spiro-MeOTAD as hole conductors. This structure is
free from electron transport layer. The thickness is optimized for NiO and
spiro-MeOTAD hole conducting materials and the devices do not exhibit any
significant variation for both hole transport materials. The back metal contact
work function is varied for NiO hole conductor and observed that Ni and Co
metals may be suitable back contacts for efficient carrier dynamics. The solar
photovoltaic performance showed a linear decrease in efficiency with increasing
temperature. The electron affinity and band gap of transparent conducting oxide
and NiO layers are varied to understand their impact on conduction and valence
band offsets. A range of suitable band gap and electron affinity values are
found essential for efficient device performance.",1806.03950v1
2018-06-28,Optoelectronic properties of zinc oxide: A first-principles investigation using the Tran-Blaha modified Becke-Johnson potentia,"In this work we use density functional theory (DFT) to investigate the
influence of semi-local exchange and correlation effects on the electronic and
optical properties of zinc oxide. We find that the inclusion of such effects
using the Tran-Blaha modified Becke-Johnson potential yields an excellent
description of the electronic structure of this material giving energy band gap
which is systematically larger than the one obtained with standard local
functionals such as the generalized gradient approximation. The discrepancy
between the experimental and theoretical band gaps is then significantly
reduced at a computational low cost. We also calculated the dielectric
functions of ZnO and find a violet shift to the absorption edge which is in
good agreement with experimental results.",1806.11016v1
2018-06-28,Single Crystal High Entropy Perovskite Oxide Epitaxial Films,"The first examples of single crystal epitaxial thin films of a high entropy
perovskite oxide are synthesized. Pulsed laser deposition is used to grow the
configurationally disordered ABO3 perovskite, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3,
epitaxially on SrTiO3 and MgO substrates. X-ray diffraction and scanning
transmission electron microscopy demonstrate that the films are single phase
with excellent crystallinity and atomically abrupt interfaces to the underlying
substrates. Atomically-resolved electron energy loss spectroscopy mapping shows
a uniform and random distribution of all B-site cations. The ability to
stabilize perovskites with this level of configurational disorder offers new
possibilities for designing materials from a much broader combinatorial cation
pallet while providing a fresh avenue for fundamental studies in strongly
correlated quantum materials where local disorder can play a critical role in
determining macroscopic properties.",1806.11209v1
2018-06-30,Stability of charges in titanium compounds and charge transfer to oxygen in titanium dioxide,"We investigate the charge density distribution in titanium dioxide, molecular
titanium complexes and a variety of periodic titanium compounds using
delocalization indices and Bader charge analysis. Our results are in agreement
with previous experimental and theoretical investigations on the charge
stability and deviation from formal oxidation states in transition metal
compounds. We present examples for practically relevant redox processes, using
molecular titanium dioxide model systems, that illustrate the failure of formal
oxidation states to account for some redox phenomena. We observe a pronounced
charge stability on titanium for trial systems which are expected to be mainly
ionic. No environment tested by us is capable to reduce the local titanium
charge remainder below one electron.",1807.00115v1
2018-06-30,"Theoretical specific heat, and thermal conductivity estimated by detailed phonon vibrations","We report the calculation results of specific heat ($c_v$), and thermal
conductivity ($\kappa$) by using Einstein, and Debye models about rock salt
(NaCl), oxides: Na$_x$CoO$_2$, SrTiO$_3$, and LiNbO$_3$. In calculation, the
longitudinal (L), and transverse (T) sound velocities ($v_T$, $v_L$) were
estimated from acoustic phonons' dispersion's (~$\omega$/$K$) in above
materials, and the average sound velocities ($v_a$) were input into Debye model
for $\kappa$ equation, and results were compared with that of Einstein model.
In some oxides, $v_a$ is relatively reduced at slight high $v_T$
($v_T$/$v_L$=0.3-0.5). The relation of $\kappa$, $v_a$ and $T$ were imaged as
the contour plots about realizing low $\kappa$ values to be application of
thermoelectric properties.",1807.00237v2
2018-07-03,Tuning oxygen vacancy diffusion through strain in SrTiO$_3$ thin films,"Understanding the diffusion of oxygen vacancies in oxides under different
external stimuli is crucial for the design of ion-based electronic devices,
improve catalytic performance, etc. In this manuscript, using an external
electric field produced by an AFM tip, we obtain the room-temperature diffusion
coefficient of oxygen-vacancies in thin-films of SrTiO$_3$ under
compressive/tensile epitaxial strain. Tensile strain produces a substantial
increase of the diffusion coefficient, facilitating the mobility of vacancies
through the film. Additionally, the effect of tip bias, pulse time, and
temperature on the local concentration of vacancies is investigated. These are
important parameters of control in the production and stabilization of
non-volatile states in ion-based memresistive devices. Our findings show the
key role played by strain for the control of oxygen vacancy migration in
thin-film oxides.",1807.01008v1
2018-07-12,Superior thermal conductivity of poly (ethylene oxide) for solid-state electrolytes: a molecular dynamics study,"Solid-state lithium-ion batteries (SSLIBs) are considered to be the new
generation of devices for energy storage due to better performance and safety.
Poly (ethylene oxide) (PEO) based material becomes one of the best candidate of
solid electrolytes, while its thermal conductivity is crucial to heat
dissipation inside batteries. In this work, we study the thermal conductivity
of PEO by molecular dynamics simulation. By enhancing the structure order,
thermal conductivity of aligned crystalline PEO is obtained as high as 60 W/m-K
at room temperature, which is two orders higher than the value (0.37 W/m-K) of
amorphous structure. Interestingly, thermal conductivity of ordered structure
shows a significant stepwise negative temperature dependence, which is
attributed to the temperature-induced morphology change. Our study offers
useful insights into the fundamental mechanisms that govern the thermal
conductivity of PEO but not hinder the ionic transport, which can be used for
the thermal management and further optimization of high-performance SSLIBs.",1807.04412v2
2018-07-19,Detailed analysis of transitions in the CO oxidation on Palladium(111) under noisy conditions,"It has been shown that CO oxidation on Pd(111) under ultra-high vacuum
conditions can suffer rare transitions between two stable states triggered by
weak intrinsic perturbations. Here we study the effects of adding controlled
noise by varying the concentrations of O2 and CO that feed the vacuum chamber,
while the total flux stays constant. In addition to the regime of rare
transitions between states of different CO2 reaction rate induced by intrinsic
fluctuations, we found three distinct effects of external noise depending on
its strength: small noise suppresses transitions and stabilizes the upper rate
state; medium noise induces bursting; and large noise gives rise to reversible
transitions in both directions. To explain some of the features present in the
dynamics, we propose an extended stochastic model that includes a global
coupling through the gas phase to account for the removal of CO gas caused by
the adsorption of the Pd surface. The numerical simulations based in the model
show a qualitative agreement with the noise-induced transitions found in
experiments, but suggest that more complex spatial phenomena are present in the
observed fluctuations.",1807.07219v1
2018-07-19,The Effect of Hole Transporting Layer in Charge Accumulation Properties of p-i-n Perovskite Solar Cells,"The charge accumulation properties of p-i-n perovskite solar cells were
investigated using three representative organic and inorganic hole transporting
layer (HTLs): a) Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)
(PEDOT:PSS, Al 4083), b) copper-doped nickel oxide (Cu:NiOx) and c) Copper
oxide (CuO). Through impedance spectroscopy analysis and modelling it is shown
that charge accumulation is decreased in the HTL/Perovskite interface, between
PEDOT:PSS to Cu:NiOx and CuO respectively. This was indicative from the
decrease in double layer capacitance (Cdl) and interfacial charge accumulation
capacitance (Cel), resulting in an increase to recombination resistance (Rrec),
thus decreased charge recombination events between the three HTLs. Through AFM
measurements it is also shown that the reduced recombination events (followed
by the increase in Rrec) is also a result of increased grain size between the
three HTLs, thus reduction in the grain boundaries area. These charge
accumulation properties of the three HTLs have resulted in an increase to the
power conversion efficiency between the PEDOT:PSS (8.44%), Cu:NiOx (11.45%) and
CuO (15.3%)-based devices.",1807.07308v1
2018-07-19,Dielectric Properties and Ion Transport in Layered MoS_{2} Grown by Vapor-Phase Sulfurization,"Electronic and dielectric properties of vapor-phase grown MoS_{2} have been
investigated in metal/MoS_{2}/silicon capacitor structures by
capacitance-voltage and conductancevoltage techniques. Analytical methods
confirm the MoS_{2} layered structure, the presence of interfacial silicon
oxide (SiO_{x}) and the composition of the films. Electrical characteristics in
combination with theoretical considerations quantify the concentration of
electron states at the interface between Si and a 2.5 - 3 nm thick silicon
oxide interlayer between Si and MoS_{2}. Measurements under electric field
stress indicate the existence of mobile ions in MoS_{2} that interact with
interface states. Based on time-offlight secondary ion mass spectrometry, we
propose OH^{-} ions as probable candidates responsible for the observations.
The dielectric constant of the vapor-phase grown MoS_{2} extracted from CV
measurements at 100 KHz is in the range of 2.6 to 2.9. The present study
advances the understanding of defects and interface states in MoS_{2}. It also
indicates opportunities for ion-based plasticity in 2D material devices for
neuromorphic computing applications.",1807.07592v1
2018-07-23,The role of metastability in enhancing water-oxidation activity,"While metastability enhanced water-oxidation activity was experimentally
reported, the reason behind this effect is still unclear. We determine here,
using density functional theory calculations, oxygen evolution reaction
overpotentials for a variety of defective (001) surfaces of three different
perovskite materials. For all three, we find a large range of overpotentials
for different reaction sites including also overpotentials at the top of the
activity volcano. Assuming that these sites dominate the apparent catalytic
activity, this implies that a large number of geometrically different reaction
sites, as they occur when a catalyst is operated at the border of its stability
conditions, can lead to a strong enhancement of the apparent activity. This
also implies that a pre-treatment of the catalyst creating a variety of
different reactive sites could lead to superior catalytic activities for
thermodynamically stable materials.",1807.08546v4
2018-07-29,Lifting of Spin Blockade by Charged Impurities in Si-MOS Double Quantum Dot Devices,"One obstacle that has slowed the development of electrically gated
metal-oxide-semiconductor (MOS) singlet-triplet qubits is the frequent lack of
observed spin blockade, even in samples with large singlet-triplet energy
splittings. We present theoretical and experimental evidence that the cause of
this problem in MOS double quantum dots is the stray positive charges in the
oxide inducing accidental levels near the device's active region that allow
spin blockade lifting. We also present evidence that these effects can be
mitigated by device design modifications, such as overlapping gates.",1807.11064v3
2018-08-01,Low-loss integrated photonics for the blue and ultraviolet regime,"We present a low-loss integrated photonics platform in the visible and near
ultraviolet regime. Fully-etched waveguides based on atomic layer deposition
(ALD) of aluminum oxide operate in a single transverse mode with $<$3 dB/cm
propagation loss at a wavelength of 371 nm. Ring resonators with intrinsic
quality factors exceeding 470,000 are demonstrated at 405 nm, and the thermo
optic coefficient of ALD aluminum oxide is estimated to be $2.75\times10^{-5}$
[RIU/$^\circ$C]. Absorption loss is sufficiently low to allow on-resonance
operation with intra-cavity powers up to at least 12.5 mW, limited by available
laser power. Experimental and simulated data indicates the propagation loss is
dominated by sidewall roughness, suggesting lower loss in the blue and UV is
achievable.",1808.00429v2
2018-08-06,Stress-sign-tunable Poisson's Ratio in Monolayer Blue Phosphorus Oxide,"Negative Poisson's ratio (NPR) materials have attracted tremendous interest
due to their unusual physical properties and potential applications. Certain
two-dimensional (2D) monolayer materials have also been found to exhibit NPR
and the corresponding deformation mechanism varies. In this study, we found,
based on first-principles calculations, that the Poisson's ratio (PR) sign of
monolayer Blue Phosphorus Oxide (BPO) can be tuned by strain: the PR is
positive under uniaxial strain <= -1% but becomes negative under > 0. The
deformation mechanism for BPO under strain depends on the mutual competition
between the P-P attraction and P-O repulsion effect, and these two factors
induce two different deformation pathways (one with positive PR, and the other
with NPR). Moreover, with increasing of strain, both the decreased strength of
P-P attraction and the increased strength of P-O repulsion effect modulate the
PR of BPO from positive to negative.",1808.01733v2
2018-08-08,An operando calorimeter for high temperature electrochemical cells,"Operando calorimetry has previously been utilized to study degradation, side
reactions, and other electrochemical effects in electrochemical cells such as
batteries at or near room temperature. Calorimetric data can provide important
information on the lifetime and thermal properties of electrochemical cells and
can be used in practical engineering applications such as thermal management.
High temperature electrochemical cells such as solid oxide fuel cells or
electrolyzers can also benefit from operando calorimetry, although to our
knowledge no such unit has been developed commercially. Herein, we report an
operando calorimeter capable of simultaneous calorimetry and electrochemistry
at temperatures up to 1,000 {\deg}C and in both oxidizing and reducing
atmospheres. The calorimeter is constructed by modifying a commercial apparatus
originally designed to study high temperature electrochemical cells in various
gas environments. We utilize a grey-box, nonlinear system identification model
to analyze calorimetric data and achieve an electrochemical cell power
sensitivity of 16.1 +/- 11.7 mW. This operando calorimeter provides the tools
needed to study both the thermal and kinetic behavior of electrochemical cells
at elevated temperatures.",1808.02596v1
2018-08-11,Polaritonic hybrid-epsilon-near-zero modes: engineering strong optoelectronic coupling and dispersion in doped cadmium oxide bilayers,"Polaritonic materials that support epsilon-near-zero (ENZ) modes offer the
opportunity to design light-matter interactions at the nanoscale through
phenomena like resonant perfect absorption and extreme sub-wavelength light
concentration. To date, the utility of ENZ modes is limited in propagating
polaritonic systems by a relatively flat spectral dispersion, which gives ENZ
modes small group velocities and short propagation lengths. Here we overcome
this constraint by coupling ENZ modes to surface plasmon polariton (SPP) modes
in doped cadmium oxide ENZ-on-SPP bilayers. What results is a strongly coupled
hybrid mode, characterized by strong anti-crossing and a large spectral
splitting on the order of 1/3 of the mode frequency. The resonant frequencies,
dispersion, and coupling of these polaritonic-hybrid-epsilon-near-zero (PH-ENZ)
modes are controlled by tailoring the modal oscillator strength and the ENZ-SPP
spectral overlap, which can potentially be utilized for actively tunable strong
coupling at the nanoscale. PH-ENZ modes ultimately leverage the most desirable
characteristics of both ENZ and SPP modes through simultaneous strong interior
field confinement and mode propagation.",1808.03847v1
2018-08-21,Cu:ZnO deposited on porous ceramic substrates by a simple thermal method for photocatalytic application,"Thin films of undoped zinc oxide (ZnO) and doped ZnO with copper were
deposited on ceramic pellets made from abundant local clay materials with an
addition of zirconia (ZrO2). The thin layers were prepared by a thermal method
using an autoclave. The resulting structural and morphological properties of
the products were studied in order to determine the effectiveness of their
photocatalytic activities. X-ray diffraction, Scanning Electron Microscopy,
energy-dispersive X-ray spectroscopy and UV-visible spectrophotometry were used
in this goal. An application test was carried out to quantify the
photocatalytic degradation of a toxic organic dye by these samples under UV
light. In similar conditions, the layers deposited on the ceramics with
addition of zirconia have shown better performances than those without
zirconia. This result can be related to the porosity created when the zirconium
oxide reacted with SiO2 of the clay. The open porosity observed on this type of
substrate allows a larger surface for the photocatalysis. The degradation rate
of the dye reached 90.5 % during a period of 7 hours with Cu doped ZnO thin
layers deposited on porous substrates modified with addition of ZrO2.",1808.06786v1
2018-08-23,Model Building of Metal Oxide Surfaces and Vibronic Coupling Density as a Reactivity Index: Regioselectivity of CO$_2$ Adsorption on Ag-loaded Ga$_2$O$_3$,"The step-by-step hydrogen-terminated (SSHT) model is proposed as a model for
the surfaces of metal oxides. Using this model, it is found that the vibronic
coupling density (VCD) can be employed as a reactivity index for surface
reactions. As an example, the regioselectivity of CO$_2$ adsorption on the
Ag-loaded Ga$_2$O$_3$ photocatalyst surface is investigated based on VCD
analysis. The cluster model constructed by the SSHT approach reasonably
reflects the electronic structures of the Ga$_2$O$_3$ surface. The geometry of
CO$_2$ adsorbed on the Ag-loaded Ga$_2$O$_3$ cluster has a bent structure,
which is favorable for its photocatalytic reduction to CO.",1808.07740v1
2018-08-28,Theory of charge-spin conversion at oxide interfaces: The inverse spin-galvanic effect,"We evaluate the non-equilibrium spin polarization induced by an applied
electric field for a tight-binding model of electron states at oxides
interfaces in LAO/STO heterostructures. By a combination of analytic and
numerical approaches we investigate how the spin texture of the electron
eigenstates due to the interplay of spin-orbit coupling and inversion asymmetry
determines the sign of the induced spin polarization as a function of the
chemical potential or band filling, both in the absence and presence of local
disorder. With the latter, we find that the induced spin polarization evolves
from a non monotonous behavior at zero temperature to a monotonous one at
higher temperature. Our results may provide a sound framework for the
interpretation of recent experiments.",1808.09157v1
2018-08-29,Synthesizing Cu-Sn nanowires alloy in highly-ordered Aluminum Oxide templates by using electrodeposition method,"In this research a novel and simple electrochemical method is developed in
order to facilitate the large-scale production of nanowires. The proposed
electrochemical technique shows versatile controllability over chemical
composition and crystalline structure of Cu-Sn nanowires. Another important
factor, which could be controlled by using this method, is the order structure
of nanowires more accurately in comparison to conventional synthesizing
procedures. As a result, the Cu-Sn nanowires as well as Aluminum Oxide
templates synthesized by using the proposed electrochemical method are examined
due to their morphology and chemical structure to find a relation between
electrodeposition's solution chemistry and materials properties of Cu-Sn
nanowires. The results show that the proposed electrochemical method maintains
a highly-ordered morphology as well as versatile controllability over chemical
composition of nanowires, which could be used to optimize the procedure for
industrial applications due to low cost and simple experimental setup.",1808.09838v1
2018-12-04,Absolute Reference Energy to Realign the Band-edges of Inorganic Semiconductors Using First-principles Calculations,"The challenge of finding an absolute reference energy from first-principles
simulations to realigning semiconductor's valence band-top and conduction
band-bottom, a theoretical methodology is proposed based on plane-wave
calculations as implemented within state-of-art density functional theory. We
have studied some of inorganic binary semiconductors, including both oxides and
non-oxides, as for example rutile- and anatase TiO2, wurtzite ZnO, rutile SnO2,
blende phase of GaP, GaAs, InP, ZnTe, CdS, CdSe, and SiC, those are well known
and qualitatively important for photoelectrochemical, optoelectronic device
applications in their standalone and/or heterostructure morphologies. The
calculated band-edges of these well known semiconductors are realigned with
respect to our proposed absolute vacuum reference energy, which is defined with
our proposed corrections and compared to their available experimental values
from flat-band measurement. The prediction is reasonably well agreed with known
experimental flat-band measured data. Our estimated mean absolute error bar for
these set of eleven compounds is ~ 0.17 eV, closer to the known experimental
limit 0.10-0.20 eV.",1812.01293v2
2018-12-07,An atomically thin oxide layer on the elemental superconductor Ta(001) surface,"Recently the oxygen-reconstructed tantalum surface Ta(001)-p(3$\times$3)-O
has experienced considerable attention due its use as a potential platform for
Majorana physics in adatom chains. Experimental studies using scanning
tunneling microscopy and spectroscopy found rich atomic and electronic
structures already for the clean Ta(001)-O surface, which we combine here with
$ab~initio$ methods. We discover two metastable superstructures at the root of
the different topographic patterns, discuss its emergence during annealing, and
identify the electronic properties. The latter is determined as the sole origin
for the contrast reversal seen at positive bias. The observed effects are
essentially connected to the two distinct oxygen states appearing on the
surface in different geometries. The second superstructure was found in
simulations by introducing oxygen vacancies, what was also observed in tantalum
pentoxide systems. Additionally we study the charge distribution on the
oxidized surface and underline its importance for the adsorption process of
polarizable atoms and molecules.",1812.03141v1
2018-12-12,The use of strain to tailor electronic thermoelectric transport properties: A first principles study of 2H-phase CuAlO2,"Using first principles calculations, the use of strain to adjust electronic
transport and the resultant thermoelectric (TE) properties is discussed using
2H phase CuAlO2 as a test case. Transparent oxide materials, such as CuAlO2, a
p-type transparent conducting oxide (TCO), have recently been studied for high
temperature thermoelectric power generators and coolers for waste heat. Given
TCO materials with relative ease of fabrication, low cost of materials, and
non-toxicity, the ability to tailor them to specific temperature ranges, power
needs, and size requirements, through the use of strain opens an interesting
avenue. We find that strain can have a significant effect on these properties,
in some cases detrimental and in others beneficial, including the potential for
n-type power factors larger than the highest p-type case. The physical reasons
for this behavior are explained in the terms of the thermoelectric transport
distribution and the Landauer distribution of modes.",1812.05085v1
2018-12-13,On the Ferroelectric Polarization Switching of Hafnium Zirconium Oxide in Ferroelectric/Dielectric Stack,"The ferroelectric polarization switching in ferroelectric hafnium zirconium
oxide (Hf0.5Zr0.5O2, HZO) in the HZO/Al2O3 ferroelectric/dielectric stack is
investigated systematically by capacitance-voltage and polarization-voltage
measurements. The thickness of dielectric layer is found to have a determinant
impact on the ferroelectric polarization switching of ferroelectric HZO. A
suppression of ferroelectricity is observed with thick dielectric layer. In the
gate stacks with thin dielectric layers, a full polarization switching of the
ferroelectric layer is found possible by the proposed leakage-current-assist
mechanism through the ultrathin dielectric layer. Theoretical simulation
results agree well with experimental data. This work clarifies some of the
critical parts of the long-standing confusions and debating related to negative
capacitance field-effect transistors (NC-FETs) concepts and experiments.",1812.05260v2
2018-12-28,Anti-doping in Insulators and Semiconductors having Intermediate Bands with Trapped Carriers,"Ordinary doping by electrons (holes) generally means that the Fermi level
shifts towards the conduction band (valence band) and that the conductivity of
free carriers increases. Recently, however, some peculiar doping
characteristics were sporadically recorded in different materials without
noting the mechanism: electron doping was observed to cause a portion of the
lowest unoccupied band to merge into the valance band, leading to a decrease in
conductivity. This behavior we dub as 'anti-doping' was seen in rare-earth
nickel oxides SmNiO3, cobalt oxides SrCoO2.5, Li-ion battery materials and even
MgO with metal vacancies. We describe the physical origin of anti-doping as
well as its inverse problem, the 'design principles' that would enable
intelligent search of materials. We find that electron anti-doping is expected
in materials having pre-existing trapped holes and is caused by annihilation of
such 'hole polarons' via electron doping. This may offer an unconventional way
of controlling conductivity.",1812.10894v2
2019-01-08,Enhanced Seebeck coefficient by a filling-induced Lifshitz transition in KxRhO2,"We have systematically measured the transport properties in the layered
rhodium oxide K$_{x}$RhO$_{2}$ single crystals ($0.5\lesssim x \lesssim 0.67$),
which is isostructural to the thermoelectric oxide Na$_{x}$CoO$_{2}$. We find
that below $x = 0.64$ the Seebeck coefficient is anomalously enhanced at low
temperatures with increasing $x$, while it is proportional to the temperature
like a conventional metal above $x=0.65$, suggesting an existence of a critical
content $x^{*} \simeq 0.65$. For the origin of this anomalous behavior, we
discuss a filling-induced Lifshitz transition, which is characterized by a
sudden topological change in the cylindrical hole Fermi surfaces at the
critical content $x^*$.",1901.02116v1
2019-01-15,Limitations of the DFT-1/2 method for covalent semiconductors and transition-metal oxides,"The DFT-1/2 method in density functional theory [L. G. Ferreira et al., Phys.
Rev. B 78, 125116 (2008)] aims to provide accurate band gaps at the
computational cost of semilocal calculations. The method has shown promise in a
large number of cases, however some of its limitations or ambiguities on how to
apply it to covalent semiconductors have been pointed out recently [K.-H. Xue
et al., Comput. Mater. Science 153, 493 (2018)]. In this work, we investigate
in detail some of the problems of the DFT-1/2 method with a focus on two
classes of materials: covalently bonded semiconductors and transition-metal
oxides. We argue for caution in the application of DFT-1/2 to these materials,
and the condition to get an improved band gap is a spatial separation of the
orbitals at the valence band maximum and conduction band minimum.",1901.04800v1
2019-01-16,Mathematical modelling of Solid Oxide Fuel Cells revisited -- a modified formulation of the problem,"In the paper a mathematical model of the PEN structure (positive electrode -
electrolyte - negative electrode) of the Solid Oxide Fuel Cell (SOFC) is
analyzed. It is proved that classical formulation of the problem leads
inevitably to locally unphysical effects related to negative values of the
activation overpotential. Moreover, the active layers' thicknesses are shown to
be components of solution and cannot be predefined in an arbitrary way. A
modified mathematical formulation of the problem is proposed which includes
this novelty alongside an amended definition of the activation overpotential. A
dedicated computational scheme is developed for the cathode sub-problem. The
accuracy of computations is investigated by means of a newly introduced
analytical benchmark example. The numerical results obtained for LSCF cathode
are used to discuss certain aspects of the modified formulation and the active
layer thickness. The new modelling approach is validated by comparison with
experimental data.",1901.05509v2
2019-01-23,"Structure and energetics of carbon-related defects in SiC (0001)/SiO$_{\rm 2}$ systems revealed by first-principles calculations: Defects in SiC, SiO$_{\rm 2}$, and just at their interface","We report first-principles calculations that reveal the atomic forms,
stability, and energy levels of carbon-related defects in SiC (0001)/SiO$_{\rm
2}$ systems. We clarify the stable position (SiC side, SiO$_{\rm 2}$ side, or
just at the SiC/SiO$_{\rm 2}$ interface) of defects depending on the oxidation
environment. Under an O-rich condition, the di-carbon antisite ((C$_{\rm
2}$)$_{\rm Si}$) in the SiC side is stable and critical for $n$-channel
MOSFETs, whereas the di-carbon defect (Si-C-C-Si) at the interface becomes
critical under an O-poor condition. Our results suggest that the oxidation of
SiC under a high-temperature O-poor condition is favorable in reducing the
defects, in consistent with recent experimental reports.",1901.07730v2
2019-01-25,Self-assembly of a binary mixture of iron oxide nanoparticles in Langmuir film: X-ray scattering study,"In present study we exploited Langmuir technique to produce self-assembled
arrays composed of monodisperse iron oxide nanoparticles 10 nm and 20 nm in
diameter and of their binary mixture. A combination of in-situ X-ray
reflectometry and Grazing-incident small-Angle X-ray scattering was used to
obtain in-plane and out-of-plane structure of the arrays directly on the water
surface. Surface pressure isotherms and X-ray reflectometry analysis showed
that monodisperse 10 nm nanoparticles form a highly ordered monolayer, while 20
nm particles pack in three-dimensional clusters with a short-range
(nearest-neighbor) correlations between the particles. In a binary mixture of
10 nm and 20 nm nanoparticles composed in proportion 3:1 the self-assembly
process results in a structure where the monolayer of 10 nm particles is
perturbed by the larger particles. Non-trivial mixing causes an enlargement of
interparticle distance but keeps the symmetry of two-dimensional lattice of
smaller nanoparticles. Estimation of the acting interactions and micromagnetic
simulation suggest the optimal formation for monodisperse and binary ensembles.",1901.08822v1
2019-02-01,Impact of Polarity on the Anisotropic Diffusion of Conjugated Organic Molecules on (10-10) Zinc Oxide Surface,"We study the influence of polarity on the binding and diffusion of single
conjugated organic molecules on the inorganic (10-10) zinc oxide surface by
means of all-atom molecular dynamics simulations at room temperature and above.
In particular, we consider the effects of partial fluorination of the
para-sexiphenyl (p-6P) molecule with chemical modifications of one head group
(p-6PF2) or both (symmetric) head and tail (p-6PF4). Quantum-mechanical and
classical simulations both result in consistent and highly distinct dipole
moments and densities of the fluorinated molecules, which interestingly lead to
a weaker adhesion to the surface than for p-6P. The diffusion for all molecules
is found to be normal and Arrhenius-like for long times. Strikingly, close to
room temperature the polar molecules diffuse 1-2 orders of magnitudes slower
compared to the p-6P reference in the apolar x-direction of the
electrostatically heterogeneous surface, while in the polar y-direction they
diffuse 1-2 orders of magnitude faster. We demonstrate that this rather
unexpected behavior is governed by a subtle electrostatic anisotropic mismatch
between the polar molecules and the chemically specific surface, as well as by
increased entropic contributions coming from orientational and internal degrees
of freedom.",1902.00276v1
2019-01-02,"Application of image processing in optical method, Moire deflectometry for investigating the optical properties of zinc oxide nanoparticle","Nowadays for measurement of refractive index of nanomaterials usually
spectro-photometric and mechanical methods are used which are expensive and
indirect. In this paper for measuring these parameters of zinc oxide
nanomaterial with two different stabilizers, a simple optical method, Moire
deflectometry, which is based on wave front analysis and geometric optics is
used. In the Moire deflectometry method, the beam of light from the laser diode
passes through the sample. As a result of that, a change in the sample
environment is observed as deflections of the fringes. By recording of these
deflections using CCD and image processing with MATLAB, the nanomaterials
refractive indices can be calculated. Due to the high accuracy of this method
and improved the image processing code in Matlab, the smallest changes of the
refractive index in the sample can be measured. Digital Image processing is
used for processing images in a way that features can be selected and being
shown. The results obtained in this method show a good improvement over the
other used methods.",1902.01196v1
2019-02-05,Cu$_2$O Microcrystals Grown on Silicon as Platform for Quantum-Degenerate Excitons and Rydberg States,"Cuprous oxide (Cu$_2$O) is a semiconductor with large exciton binding energy
and significant technological importance in applications such as photovoltaics
and solar water splitting. It is also a superior material system for quantum
optics that enabled the observation of two intriguing phenomena, i.e. Rydberg
excitons as solid-state analogue to highly-excited atomic states and dense
exciton gases showing quantum degeneracy when approaching the phase transition
to Bose-Einstein condensation. Previous experiments focused on natural bulk
crystals due to major difficulties in growing high-quality synthetic samples.
Here, we present Cu$_2$O microcrystals with excellent optical material quality
capable of hosting both quantum-degenerate excitons and excited Rydberg states.
Growth of Cu$_2$O with exceedingly low point defect levels was achieved on
silicon by a scalable thermal oxidation process compatible with lithographic
patterning. Using the latter, we demonstrate Rydberg excitons in
site-controlled Cu$_2$O microstructures, paving the way for a plethora of
applications in integrated quantum photonics.",1902.01853v1
2019-02-05,Supercontinuum Generation in Heavy-Metal Oxide Glass Based Suspended-Core Photonic Crystal Fibers,"We investigate supercontinuum generation in several suspended-core soft-glass
photonic crystal fibers pumped by an optical parametric oscillator tunable
around 1550 nm. The fibers were drawn from lead-bismuth-gallium-cadmium-oxide
glass (PBG-81) with a wide transmission window from 0.5-2.7 micron and a high
nonlinear refractive index up to 4.3.10^(-19) m^2/W. They have been
specifically designed with a microscale suspended hexagonal core for efficient
supercontinuum generation around 1550 nm. We experimentally demonstrate two
supercontinuum spectra spanning from 1.07-2.31 micron and 0.89-2.46 micron by
pumping two PCFs in both normal and anomalous dispersion regimes, respectively.
We also numerically model the group velocity dispersion curves for these fibers
from their scanning electron microscope images. Results are in good agreement
with numerical simulations based on the generalized nonlinear Schrodinger
equation including the pump frequency chirp.",1902.02385v1
2019-02-11,Improved oxidation resistance of high emissivity coatings on fibrous ceramic for reusable space system,"To develop high emissivity coatings on fibrous ceramic substrates with
improved thermal resistance for reusable space systems,
WSi2-MoSi2-Si-SiB6-borosilicate glass coatings were prepared on fibrous ZrO2 by
slurry dipping and subsequent high temperature rapid sintering. A coating with
50 wt% WSi2 and 50 wt% MoSi2 presents optimal thermal stability with only 10.06
mg/cm2 mass loss and 4.0 % emissivity decrease in the wavelength regime of 1.27
to 1.73 microns after 50 h oxidation at 1773 K. The advantages of double phase
metal silicide coatings combining WSi2 and MoSi2 include improved thermal
compatibility with the substrate and an enhanced glass mediated self healing
ability.",1902.03943v2
2019-02-11,Small Polarons in Transition Metal Oxides,"The formation of polarons is a pervasive phenomenon in transition metal oxide
compounds, with a strong impact on the physical properties and functionalities
of the hosting materials. In its original formulation the polaron problem
considers a single charge carrier in a polar crystal interacting with its
surrounding lattice. Depending on the spatial extension of the polaron
quasiparticle, originating from the coupling between the excess charge and the
phonon field, one speaks of small or large polarons. This chapter discusses the
modeling of small polarons in real materials, with a particular focus on the
archetypal polaron material TiO2. After an introductory part, surveying the
fundamental theoretical and experimental aspects of the physics of polarons,
the chapter examines how to model small polarons using first principles schemes
in order to predict, understand and interpret a variety of polaron properties
in bulk phases and surfaces. Following the spirit of this handbook, different
types of computational procedures and prescriptions are presented with specific
instructions on the setup required to model polaron effects.",1902.04183v2
2019-02-14,Indium tin oxide nanoparticle:TiO$_{2}$:air layers for one-dimensional multilayer photonic structures,"In this work we study the optical properties, by means of the transfer matrix
method, of one-dimensional photonic crystals in which layers of silica
nanoparticles are alternated with layers of indium tin oxide nanoparticle (ITO)
/ titania nanoparticle mixture. The dielectric function of the mixed
ITO/TiO$_{2}$ nanoparticle layer is carefully accounted for with a generalized
Rayleigh equation for the ternary mixture ITO:TiO$_{2}$:air. We have studied
the light transmission of the multilayer photonic crystal as a function of the
ITO/TiO$_{2}$ ratio. We observe that, by increasing the ITO content in the
three-phase mixture, the intensity of the plasmon resonance in the near
infrared (NIR) increases and the intensity of the photonic band gap (visible)
decreases. Thus, our study is of major importance for the realization of
electrochromic smart windows, in which separate and independent NIR and visible
light control is required.",1902.05353v1
2019-02-14,Epitaxial Integration on Si(001) of Ferroelectric Hf0.5Zr0.5O2 Capacitors with High Retention and Endurance,"Epitaxial ferroelectric Hf0.5Zr0.5O2 films have been successfully integrated
in a capacitor heterostructure on Si(001). The orthorhombic Hf0.5Zr0.5O2 phase,
[111] out-of-plane oriented, is stabilized in the films. The films present high
remnant polarization Pr close to 20 {\mu}C/cm2, rivaling with equivalent
epitaxial films on single crystalline oxide substrates. Retention time is
longer than 10 years for writing field of around 5 MV/cm, and the capacitors
show endurance up to 1E9 cycles for writing voltage of around 4 MV/cm. It is
found that the formation of the orthorhombic ferroelectric phase depends
critically on the bottom electrode, being achieved on La0.67Sr0.33MnO3 but not
on LaNiO3. The demonstration of excellent ferroelectric properties in epitaxial
films of Hf0.5Zr0.5O2 on Si(001) is relevant towards fabrication of devices
that require homogeneity in the nanometer scale, as well as for better
understanding of the intrinsic properties of this promising ferroelectric
oxide.",1902.05504v1
2019-03-19,Metal to insulator transition in Conducting Polyaniline/Graphene Oxide composites,"Broadband Dielectric Spectroscopy (BDS) measurements of
P{\omicron}lyaniline/Graphene oxide composites were conducted for an
as-prepared and a thermally annealed specimen, respectively, from 15K to room
temperature. Electrical conductivity values of the annealed composite display a
very modest rise denoting the important contributions of the GO component to
achieving electrical stability of the polymer. Patterns of the dc conductivity
as a function of temperature also reveal a metal to insulator transition around
75K. The transition is dominated by two key factors; temperature and annealing
process. Metal-like and insulating features are subsequently detected, as well,
and accordingly described to provide a qualitative inspection of the charge
transfer mechanisms involved",1903.07954v2
2019-03-26,"Oxygen atom reactions with C2H6, C2H4, and C2H2 in ices","Oxygen atom addition and insertion reactions may provide a pathway to
chemical complexity in ices that are too cold for radicals to diffuse and
react. We have studied the ice-phase reactions of photo-produced oxygen atoms
with C2 hydrocarbons under ISM-like conditions. The main products of oxygen
atom reactions with ethane are ethanol and acetaldehyde; with ethylene are
ethylene oxide and acetaldehyde; and with acetylene is ketene. The derived
branching ratio from ethane to ethanol is ~0.74 and from ethylene to ethylene
oxide is ~0.47. For all three hydrocarbons there is evidence of an effectively
barrierless reaction with O(^1D) to form oxygen-bearing organic products; in
the case of ethylene, there may be an additional barriered contribution of the
ground-state O(^3P) atom. Thus, oxygen atom reactions with saturated and
unsaturated hydrocarbons are a promising pathway to chemical complexity even at
very low temperatures where the diffusion of radical species is thermally
inaccessible.",1903.10981v1
2019-03-28,Atomistic manipulation of reversible oxidation and reduction in Ag by electron beam,"Employing electrons for direct control of nanoscale reaction is highly
desirable since it provides fabrication of nanostructures with different
properties at atomic resolution and with flexibility of dimension and location.
Here, applying in situ transmission electron microscopy, we show the reversible
oxidation and reduction kinetics in Ag, well controlled by changing the dose
rate of electron beam. Aberration-corrected high-resolution transmission
electron microscopy observation reveals that O atoms are preferably inserted
and extracted along the {111} close-packed planes of Ag, leading to the
nucleation and decomposition of nanoscale Ag2O islands on the Ag substrate. By
controlling electron beam size and dose rate, we demonstrated fabrication of an
array of 3 nm Ag2O nanodots in an Ag matrix. Our results open up a new pathway
to manipulate atomistic reaction with electron beam towards the precise
fabrication of nanostructures for device applications.",1903.12038v1
2019-03-28,Vertical Organic Thin-Film Transistor with Anodized Permeable Base for Very Low Leakage Current,"The Organic Permeable Base Transistor (OPBT) is currently the fastest organic
transistor with a transition frequency of 40 MHz. It relies on a thin aluminum
base electrode to control the transistor current. This electrode is surrounded
by a native oxide layer for passivation, currently created by oxidation in air.
However, this process is not reliable and leads to large performance variations
between samples, slow production and relatively high leakage currents. Here, we
demonstrate for the first time that electrochemical anodization can be
conveniently employed for the fabrication of high performance OPBTs with vastly
reduced leakage currents and more controlled process parameters. Very large
transmission factors of 99.9996% are achieved, while excellent on/off ratios of
5x10$^5$ and high on-currents greater than 300 mA/cm$^2$ show that the C$_{60}$
semiconductor layer can withstand the electrochemical anodization. These
results make anodization an intriguing option for innovative organic transistor
design.",1903.12047v2
2019-04-05,Water oxidation catalysis on reconstructed NaTaO$_3$ (001) surfaces,"Polar perovskite oxide surfaces are subject to structural reconstruction as a
possible stabilisation mechanisms, which changes the surface structure and
hence the surface chemistry. To investigate this effect, we study the oxygen
evolution reaction (OER) on the reconstructed (001) surface of NaTaO$_3$, by
means of density functional theory (DFT) calculations and compare it with the
non-polar (113) surface of the same material. For the clean surface the
reconstruction has a beneficial effect on the catalytic activity, lowering the
minimal overpotential from 0.88 V to 0.70 V while also changing the most active
reaction site from Na to Ta. Under photocatalytic conditions, the Ta sites are
covered by oxygen adsorbates, rendering a lattice oxygen site on the NaO
terrace the most active with a very low overpotential of 0.32 V. An alternative
surface reconstruction stable in contact with water leads to an oxygen coupling
mechanism with an overpotential of 0.52 V. Our results show that terraced
surface reconstructions enable novel reaction pathways with low overpotentials
that do not exist on other non-polar NaTaO$_3$ surfaces nor on non-polar
surfaces of chemically similar materials such as SrTaO$_2$N.",1904.03070v1
2019-03-23,Photon Management for Silicon Solar Cells featuring Hole-Selective Molybdenum Oxide Rear Contacts: An Optical Simulation Study,"Passivated, hole-selective contacts play important role in reducing surface
recombination by lowering the concentration of electrons in the rear side of a
solar cell. However, parasitic optical losses in these contacts can still limit
the performance of the cell. In this work, the long wavelength optical losses
of silicon solar cells featuring hole-selective molybdenum oxide (MoOx) rear
contacts are investigated using optical simulations. The potential of these
selective contacts for possible enhancement of photogenerated current density
was also investigated for their use with nanostructured dielectric layers.",1904.04210v2
2019-04-23,"Real-time observation of electronic, vibrational, and rotational dynamics in nitric oxide with attosecond soft X-ray pulses at 400 eV","Photoinduced quantum dynamics in molecules have hierarchical temporal
structures with different energy scales that are associated with electron and
nuclear motions. Femtosecond-to-attosecond transient absorption spectroscopy
(TAS) using high-harmonic generation (HHG) with a photon energy below 300 eV
has been a powerful tool to observe such electron and nuclear dynamics in a
table-top manner. However, comprehensive measurements of the electronic,
vibrational, and rotational molecular dynamics have not yet been achieved.
Here, we demonstrate HHG-based TAS at the nitrogen K-edge (400 eV) for the
first time, and observe all the electronic, vibrational, and rotational degrees
of freedom in a nitric oxide molecule at attosecond to sub-picosecond time
scales. This method of employing core-to-valence transitions offers an
all-optical approach to reveal complete molecular dynamics in photochemical
reactions with element and electronic state specificity.",1904.10456v2
2019-04-30,Two-dimensional honeycomb borophene oxide: A promising anode material offering super high capacity for Li/Na-ion batteries,"Rational design of novel two-dimensional (2D) electrode materials with high
capacity is crucial for the further development of Li-ion and Na-ion batteries.
Herein, based on first-principles calculations, we systemically investigate Li
and Na storage behaviors in the recently discovered 2D topological nodal-loop
metal - the honeycomb borophene oxide (h-B2O). We show that h-B2O is an almost
ideal anode material. It has good conductivity before and after Li/Na
adsorption, fast ion diffusion with diffusion barrier less than 0.5 eV, low
open-circuit voltage (less than 1 V), and small lattice change (less than 6.2%)
during intercalation. Most remarkably, its theoretical storage capacity is
extremely high, reaching up to 2137 mAh/g for Li and 1425 mAh/g for Na. Its Li
storage capacity is more than six times higher than graphite (372 mAh/g), and
is actually the highest among all 2D materials discovered to date. Our results
strongly suggest that 2D h-B2O is an exceedingly promising anode material for
both Li- and Na-ion batteries with super high capacity.",1904.13084v1
2019-08-01,Enhanced ambient stability of exfoliated black phosphorus by passivation with nickel nanoparticles,"Since its discovery, the environmental instability of exfoliated black
phosphorus (2D bP) has emerged as a challenge that hampers its wide application
in chemistry, physics, and materials science. Many studies have been carried
out to overcome this drawback. Here we show a relevant enhancement of ambient
stability in few-layer bP decorated with nickel nanoparticles as compared to
pristine bP. In detail, the behavior of the Ni-functionalized material exposed
to ambient conditions in the dark is accurately studied by TEM (Transmission
Electron Microscopy), Raman Spectroscopy, and high resolution X-ray
Photoemission and Absorption Spectroscopy. These techniques provide a
morphological and quantitative insight of the oxidation process taking place at
the surface of the bP flakes. In the presence of Ni NPs, the decay time of 2D
bP to phosphorus oxides is more than three time slower compared to pristine bP,
demonstrating an improved structural stability within twenty months of
observation.",1908.00237v1
2019-08-13,Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS,"The real-time dissolution of the single-phase compositionally complex alloy
(CCA), Al1.5TiVCr, was studied using an inline inductively coupled plasma
method. Compositionally complex alloys (CCAs), a term encompassing high entropy
alloys (HEAs) or multi-principal element alloys (MPEAs), are - in general -
noted for their inherently high corrosion resistance. In order to gain an
insight into the dissolution of Al1.5TiVCr alloy, atomic emission
spectroelectrochemistry was utilised in order to measure the ion dissolution of
the alloy during anodic polarisation. It was revealed that incongruent
dissolution occurred, with preferential dissolution of Al, and essentially no
dissolution of Ti, until the point of alloy breakdown. Results were correlated
with X-ray photoelectron spectroscopy, which revealed a complex surface oxide
inclusive of unoxidised metal, and metal oxides in disproportion to the bulk
alloying element ratio.",1908.04493v1
2019-08-14,Comparison of aluminum oxide empirical potentials from cluster to nanoparticle,"Aluminum oxide nanoparticles are increasingly sought in numerous
technological applications. However, as the nanoparticles grow during the
synthesis, two phase transitions occur. At the nanoscale, numerical simulation
of the stability of the alumina phases requires the use of empirical potentials
that are reliable over a large range of system sizes going from a few atoms to
several hundred thousand atoms. In this work, we confronted four different
empirical potentials that are currently employed for bulk alumina. We found
that only two of them are correct at the molecular level when compared to DFT
calculations. Furthermore, the two potentials remain the best at the nanoscale
as they reproduce one or two phase transitions that were observed
experimentally: from amorphous solid to cubic crystal ({\gamma}) and from cubic
to hexagonal ({\alpha}, i.e. corundum) crystal.",1908.05046v2
2019-08-16,"Influence of annealing temperature on the structural, topographical and optical properties of sol gel derived ZnO thin films","This investigation deals with the effect of annealing temperature on the
structural, topographical and optical properties of Zinc Oxide thin films
prepared by sol gel method. The structural properties were studied using X-ray
diffraction and the recorded patterns indicated that all the films had a
preferred orientation along (002) plane and the crystallinity along with the
grain size were augmented with annealing temperature. The topographical
modification of the films due to heat treatment was probed by atomic force
microscopy which revealed that annealing roughened the surface of the film. The
optical properties were examined by a UV visible spectrophotometer which
exhibited that maximum transmittance reached nearly 90% and it diminished with
increasing annealing temperature.",1908.05886v1
2019-08-16,"An sp-hybridized molecular carbon allotrope, cyclo[18]carbon","Carbon allotropes built from rings of two-coordinate atoms, known as
cyclo[n]carbons, have fascinated chemists for many years, but until now they
could not be isolated or structurally characterized, due to their high
reactivity. We generated cyclo[18]carbon (C18) using atom manipulation on
bilayer NaCl on Cu(111) at 5 Kelvin by eliminating carbon monoxide from a
cyclocarbon oxide molecule C24O6. Characterization of cyclo[18]carbon by
high-resolution atomic force microscopy revealed a polyynic structure with
defined positions of alternating triple and single bonds. The high reactivity
of cyclocarbon and cyclocarbon oxides allows covalent coupling between
molecules to be induced by atom manipulation, opening an avenue for the
synthesis of other carbon allotropes and carbon-rich materials from the
coalescence of cyclocarbon molecules.",1908.05904v1
2019-08-20,Dissipative dynamics of atomic and molecular Rydberg gases: Avalanche to ultracold plasma states of strong coupling,"Not long after metastable xenon was photoionized in a magneto-optical trap,
groups in Europe and North America found that similar states of ionized gas
evolved spontaneously from state-selected, high principal quantum number
Rydberg gases. Studies of atomic xenon and molecular nitric oxide entrained in
a supersonically cooled molecular beam subsequently showed much the same final
state evolved from a sequence of prompt Penning ionization and electron-impact
avalanche to plasma, well-described by coupled rate-equation simulations. But,
measured over longer times, the molecular ultracold plasma was found to exhibit
an anomalous combination of very long lifetime and very low apparent electron
temperature. This review summarizes early developments in the study of
ultracold plasmas formed by atomic and molecular Rydberg gases, and then
details observations as they combine to characterize properties of the nitric
oxide molecular ultracold plasma that appear to call for an explanation beyond
the realm of conventional plasma physics.",1908.07633v1
2019-11-08,Core-level x-ray photoemission and Raman spectroscopy studies on electronic structures in Mott-Hubbard type nickelate oxide NdNiO$_2$,"We perform core-level X-ray photoemission spectroscopy (XPS) and electronic
Raman scattering studies of electronic structures and spin fluctuations in the
bulk samples of the nickelate oxide NdNiO$_2$. According to Nd $3d$ and O $1s$
XPS spectra, we conclude that NdNiO$_2$ has a large transfer energy. From the
analysis of the main line of the Ni $2p_{3/2}$ XPS, we confirm the NiO$_2$
planes in NdNiO$_2$ are of Mott-Hubbard type in the Zaanen-Sawatzky-Allen
scheme. The two-magnon peak in the Raman scattering provides direct evidence
for the strong spin-fluctuation in NdNiO$_2$. The peak position determines the
antiferromagnetic exchange $J=25$~meV. Our experimental results agree well with
our previous theoretical results.",1911.03177v2
2019-11-10,Epitaxial stabilization of ultra thin films of high entropy perovskite,"High entropy oxides (HEOs) are a class of materials, containing equimolar
portions of five or more transition metal and/or rare-earth elements. We report
here about the layer-by-layer growth of HEO
[(La$_{0.2}$Pr$_{0.2}$Nd$_{0.2}$Sm$_{0.2}$Eu$_{0.2}$)NiO$_3$] thin films on
NdGaO$_3$ substrates by pulsed laser deposition. The combined characterizations
with in-situ reflection high energy electron diffraction, atomic force
microscopy, and X-ray diffraction affirm the single crystalline nature of the
film with smooth surface morphology. The desired +3 oxidation of Ni has been
confirmed by an element sensitive X-ray absorption spectroscopy measurement.
Temperature dependent electrical transport measurements revealed a first order
metal-insulator transition with the transition temperature very similar to the
undoped NdNiO$_3$. Since both of these systems have a comparable tolerance
factor, this work demonstrates that the electronic behaviors of $A$-site
disordered perovskite-HEOs are primarily controlled by the average tolerance
factor.",1911.03866v1
2019-11-16,Exploiting Oxide Based Resistive RAM Variability for Bayesian Neural Network Hardware Design,"Uncertainty plays a key role in real-time machine learning. As a significant
shift from standard deep networks, which does not consider any uncertainty
formulation during its training or inference, Bayesian deep networks are being
currently investigated where the network is envisaged as an ensemble of
plausible models learnt by the Bayes' formulation in response to uncertainties
in sensory data. Bayesian deep networks consider each synaptic weight as a
sample drawn from a probability distribution with learnt mean and variance.
This paper elaborates on a hardware design that exploits cycle-to-cycle
variability of oxide based Resistive Random Access Memories (RRAMs) as a means
to realize such a probabilistic sampling function, instead of viewing it as a
disadvantage.",1911.08555v5
2019-11-21,Crystallization of Cuprous Oxide Thin Films by Continuous-Wave Laser Diode with Micro-Chevron Laser Beam (μ-CLB),"Crystallization of thin film materials by exploiting laser induced
crystallization has been advancing for the past four decades. This unique thin
film technique has been predominantly used in processing thin film materials
made of a single chemical element; however, harnessing this technique to extend
its use for thin film materials containing multiple chemical elements (e.g.,
metal oxides) unlocks applications currently not accessible. In this study,
laser crystallization of a Cu2O strip was demonstrated. A continuous-wave laser
diode with a micrometer-scale chevron-shaped beam profile (micro chevron laser
beam) was used to crystallize CuO thin films covered with an amorphous carbon
(a-C) cap layer, deposited on fused silica substrates. Electron backscatter
diffraction, Raman spectroscopy, photoluminescence spectroscopy, and UV-Vis
spectroscopy were used to investigate the crystallinity and optical properties
of the Cu2O thin films revealing their unique characteristics associated with
the crystallization process.",1911.09778v1
2019-11-21,Is density functional theory accurate for lytic polysaccharide monooxygenase enzymes?,"The lytic polysaccharide monooxygenase (LPMO) enzymes boost polysaccharide
depolymerization through oxidative chemistry, which has fueled the hope for
more energy-efficient production of biofuel. We have recently proposed a
mechanism for the oxidation of the polysaccharide substrate (Hedeg{\aa}rd &
Ryde, Chem. Sci. 2018, 9, 3866). In this mechanism, complexes with superoxide,
oxyl, as well as hydroxyl (i.e. [CuO2]+, [CuO]+ and [CuOH]2+) cores were
involved. These complexes can have both singlet and triplet spin states, and
both spin-states may be important for how LPMOs function during catalytic
turnover. Previous calculations on LPMOs have exclusively been based on density
functional theory (DFT). However, different DFT functionals are known to
display large differences for spin-state splittings in transition-metal
complexes, and this has also been an issue for LPMOs. In this paper, we study
the accuracy of DFT for spin-state splittings in superoxide, oxyl, and hydroxyl
intermediates involved in LPMO turnover. As reference we employ
multiconfigurational perturbation theory (CASPT2).",1911.09780v2
2019-11-25,Externally driven local colloidal ordering induced by a point-like heat source,"We study here how phase transitions are induced in colloidal suspensions by a
point-like heat source, an optically trapped metal oxide particle absorbing
light. We find that thermophoresis increases the number density of colloids
around the oxide particle, leading to the appearance of solid clusters. Our
analysis based on thermophoresis reveals that the solid-fluid interface
position is purely determined by the relationship of the particle concentration
profile in the fluid state with the volume fraction of the phase transition,
and no other effect of thermodynamics is seen in the cluster sizes. In this
system, we observe the formation of face-centered cubic crystals, amorphous
states, and structures with icosahedral order. This shows a rich possibility of
non-trivial orderings under spatially controlled heterogeneous growth in
external ""semi-soft"" potentials that are softer than walls but with substantial
variations at the scale of a few particle diameters. Because of the tuneable
rate of addition of particles to the clusters, we propose this method could be
used to study the complex interplay of densification with local spatial
confinement effects, kinetics, and ordering.",1911.10759v1
2019-12-03,Enhancing the understanding of hydrogen evolution and oxidation reaction on Pt(111) through ab initio simulations on electrode/electrolyte kinetics,"The hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER)
play an important role in hydrogen based energy conversion. Recently, the
frustrating performance in alkaline media raised debates on the relevant
mechanism, especially on the role of surface hydroxyl (OH*). We present a full
pH range electrode/electrolyte kinetics simulation for HER/HOR on Pt(111), with
the potential-related rate constants been calculated with density functional
theory methods. The polarization curves agree well with the experimental
observations. The stability of OH* is found to be unlikely an effective
activity descriptor since it is irrelevant to the onset potential of HOR/HER.
Degree of rate control analyses reveal that the alkaline current is controlled
jointly by Tafel and Volmer steps, while the acidic current solely by Tafel
step, which explains the observed pH-dependent kinetics. Therefore, it is also
possible to reduce the overpotential of alkaline HER/HOR by accelerating the
Tafel step besides tuning the hydrogen binding energy.",1912.01152v1
2019-12-06,Vertically-Oriented Graphene Oxide Membranes for High-Performance Osmotic Energy Conversion,"Reverse electrodialysis is a promising method to harvest the osmotic energy
stored between seawater and freshwater, but it has been a long-standing
challenge to fabricate permselective membranes with the power density
surpassing the industry benchmark of 5.0 W $m^{-2}$ for half a century. Herein,
we report a vertically-oriented graphene oxide membranes (V-GOMs) with the
combination of high ion selectivity and ultrafast ion permeation, whose
permeation is three orders of magnitude higher than the extensively studied
horizontally stacked GOMs (H-GOMs). By mixing artificial seawater and river
water, we obtained an unprecedented high output power density of 10.6 W
$m^{-2}$, outperforming all existing materials. Molecular dynamics (MD)
simulations reveal the mechanism of the ultrafast transport in V-GOMs results
from the quick entering of ions and the large accessible area as well as the
apparent short diffusion paths in V-GOMs. These results will facilitate the
practical application of osmotic energy and bring innovative design strategy
for various systems involving ultrafast transport, such as filtration and
catalysis.",1912.03093v1
2019-12-12,A numerical ellipsometric analysis (NEA) of nanoscale layered systems,"A simple and robust method able to predict, with high accuracy, the optical
properties of single and multi-layer nanostructures is presented. The method
exploits a COMSOL Multiphysics simulation platform and it has been validated by
three case studies with increasing numerical complexity: i) a single thin layer
(20 nm) of Ag deposited on a glass substrate; ii) a metamaterial composed of
five bi-layers of Ag/ITO (Indium Tin Oxide), with a thickness of 20 nm each;
iii) a system based on a three-materials unit cell (AZO/ITO/Ag), but without
any thickness periodicity (AZO stands for Al$_2$O$_3$/Zinc Oxide). Numerical
results have been compared with experimental data provided by real
ellipsometric measurements performed on the above mentioned nanostructures
ad-hoc fabricated. The obtained agreement is excellent suggesting this research
as a valid approach to design materials able to work in a broad spectrum range.",1912.05717v1
2019-12-13,The use of strain and grain boundaries to tailor phonon transport properties: A first principles study of 2H-phase $CuAlO_{2}$ (Part II),"Transparent oxide materials, such as $CuAlO_{2}$, a p-type transparent
conducting oxide (TCO), have recently been studied for high temperature
thermoelectric power generators and coolers for waste heat. TCO materials are
generally low cost and non-toxic. The potential to engineer them through strain
and nano-structuring are two promising avenues toward continuously tuning the
electronic and thermal properties to achieve high zT values and low cost/kW-hr
devices. In this work, the strain-dependent lattice thermal conductivity of 2H
$CuAlO_{2}$ is computed by solving the phonon Boltzmann transport equation with
interatomic force constants extracted from first-principles calculations. While
the average bulk thermal conductivity is around 32 W/(K-m) at room temperature,
it drops to between 5-15 W/(K-m) for typical experimental grain sizes from 3nm
to 30nm at room temperature. We find that strain can offer both an increase as
well as a decrease in the thermal conductivity as expected, however the overall
inclusion of small grain sizes dictates the potential for low thermal
conductivity in this material.",1912.06595v1
2019-12-18,Metal-oxide interface reactions and their effect on integrated resistive/threshold switching in NbOx,"Reactive metal electrodes (Nb, Ti, Cr, Ta, and Hf) are shown to play an
important role in controlling the volatile switching characteristics of
metal/Nb2O5/Pt devices. In particular, devices are shown to exhibit stable
threshold switching under negative bias but to have a response under positive
bias that depends on the choice of metal. Three distinct responses are
highlighted: Devices with Nb and Ti top electrodes are shown to exhibit stable
threshold switching with symmetric characteristics for both positive and
negative polarities; devices with Cr top electrodes are shown to exhibit stable
threshold switching but with asymmetric hysteresis windows under positive and
negative polarities; and devices with Ta and Hf electrodes are shown to exhibit
an integrated threshold-memory (1S1M) response. Based on thermodynamic data and
lumped element modelling these effects are attributed to the formation of a
metal-oxide interlayer and its response to field-induced oxygen exchange. These
results provide important insight into the physical origin of the switching
response and pathways for engineering devices with reliable switching
characteristics.",1912.08373v1
2019-12-20,Mott and spin-Peierls physics in TiPO$_4$ under high pressure,"TiPO$_4$ is a Mott insulator and one of few inorganic compounds featuring a
spin-Peierls phase at low temperature. Recent experimental studies have
suggested the presence of spin-Peierls dimerization also at ambient temperature
though at high pressure. Here, we present a combined experimental and
theoretical study of the energetics of the high-pressure phase. We analyse
dimerization properties and their coupling to spin degrees of freedom. Most
importantly, we argue that TiPO$_4$ resents a direct analogue to the celebrated
binary transition metal oxide VO$_2$. TiPO$_4$ allows to assess spin-dimer
physics in the high-pressure regime in a controlled fashion, having the
potential to become an important model system representative of the class of
dimerized transition metal oxides.",1912.09692v1
2019-12-29,Epitaxial antiperovskite/perovskite heterostructures for materials design,"We demonstrate fabrication of atomically sharp interfaces between nitride
antiperovskite Mn$_{3}$GaN and oxide perovskites
(La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35}$)O$_{3}$ (LSAT) and SrTiO$_{3}$ as
paradigms of nitride-antiperovskite/oxide-perovskite heterostructures. Using a
combination of scanning transmission electron microscopy (STEM),
atomic-resolution spectroscopic techniques, and first-principle calculations,
we investigated the atomic-scale structure, composition, and boding at the
interface. We show that the epitaxial growth between the antiperovskite and
perovskite compounds is mediated by a coherent interfacial monolayer that
connects the two anti-structures. We anticipate our results to be a major step
for the development of functional antiperovskite/perovskite heterostructures
opening to harness a combination of their functional properties including
topological properties for ultra low power applications.",1912.12583v1
2020-03-01,Bi2W2O9: a potentially antiferroelectric Aurivillius phase,"Ferroelectric tungsten-based Aurivillius oxides are naturally stable
superlattice structures, in which A-site deficient perovskite blocks
[WnO3n+1]-2 (n = 1, 2, 3, ...) interleave with fluorite-like bismuth oxide
layers [Bi2O2]+2 along the c -axis. In the n = 2 Bi2W2O9 phase, an in-plane
antipolar distortion dominates but there has been controversy as to the ground
state symmetry. Here we show, using a combination of first-principles density
functional theory calculations and experiments, that the ground state is a
non-polar phase of Pnab symmetry. We explore the energetics of metastable
phases and the potential for antiferroelectricity in this n=2 Aurivillius
phase.",2003.00486v1
2020-03-06,Indium tin oxide films meet circular Rydberg atoms: prospects for novel quantum simulation schemes,"Long-lived circular Rydberg atoms are picking up increasing interest for
boosting coherence times in Rydberg-based quantum simulation. We elaborate a
novel approach to stabilize circular Rydberg states against spontaneous and
blackbody-induced decay using a suppression capacitor made from indium tin
oxide (ITO) thin films, which combine reflection of microwaves with
transparency in the visible spectral range. To this end, we perform detailed
characterization of such films using complementary spectroscopic methods at GHz
and THz frequencies and identify conditions that allow for reaching
circular-state lifetimes up to tens of milliseconds in a room-temperature
environment. We discuss prospects of our findings in view of the quest for
quantum simulations with high-$n$ circular Rydberg states at room temperature.",2003.03161v3
2020-03-16,Signature of band inversion in the perovskite thin-film alloys BaSn$_{1-x}$Pb$_x$O$_3$,"Perovskite oxides ABO$_3$ containing heavy B-site elements are a class of
candidate materials to host topological metals with a large spin-orbit
interaction. In contrast to the band insulator BaSnO$_3$, the semimetal
BaPbO$_3$ is proposed to be a typical example with an inverted band structure,
the conduction band of which is composed of mainly the O-2p orbital. In this
study, we exemplify a band-gap modification by systematic structural, optical,
and transport measurements in BaSn$_{1-x}$Pb$_x$O$_3$ films. A sudden
suppression of the conductivity and an enhancement of the weak antilocalization
effect at $x$ = 0.9 indicate the presence of a singular point in the electronic
structure as a signature of the band inversion. Our findings provide an
intriguing platform for combining topological aspects and electron correlation
in perovskite oxides based on band-gap engineering.",2003.07181v1
2020-03-17,Number Parity effect in the normal state of $SrTiO_3$,"We study the recently discovered even-odd effects in the normal state of
single-electron devices manufactured at strontium titanium oxide/lanthanum
aluminum oxide interfaces (STO/LAO). Within the framework of the number
parity-projected formalism and a phenomenological fermion-boson model we find
that, in sharp contrast to conventional superconductors, the crossover
temperature $T^*$ for the onset of number parity effect is considerably larger
than the superconducting transition temperature $T_c$ due to the existence of a
pairing gap above $T_c$. Furthermore, the finite lifetime of the preformed
pairs reduces by several orders of magnitude the effective number of states
$N_{\rm eff}$ available for the unpaired quasiparticle in the odd parity state
of the Coulomb blockaded STO/LAO island. Our findings are in qualitative
agreement with the experimental results reported by Levy and coworkers for
STO/LAO based single electron devices.",2003.07479v3
2020-03-17,The role of silanol nests in the activation of the [Fe=O]2+ group in the reaction of hydrogen atom transfer from methane,"Silanol nests can play the role of places into which positively charged
groups, such as, [FeO]2+, can invade. In the framework of this work, the
influence of such structures on the activity of the [FeO]2+ group in the
reaction of detachment of a hydrogen atom from methane was considered. Two ways
of the reaction of hydrogen atom transfer (HAT) from methane were found: the
so-called ferryl and oxyl routes. It was shown that the reaction of the
detachment of a hydrogen atom from methane, which is a limiting stage of the
oxidation of methane to methanol at the alpha center, proceeds through the
formation of the so-called oxidation state [Fe(III)-O(-)]2+, and fingerprint of
this state is negative spin density on oxo moiety.",2003.07565v1
2020-03-19,"Universal relationship between the energy scales of the pseudogap phase, the superconducting state and the charge density wave order in copper oxide superconductors","We report the hole doping dependencies of the pseudogap phase energy scale,
$2\Delta_{\rm PG}$, the anti-nodal (nodal) superconducting energy scales
$2\Delta^{AN}_{\rm SC}$ ($2\Delta^{N}_{\rm SC}$) and the charge density wave
energy scale, $2\Delta_{\rm CDW}$. They have been extracted from the electronic
Raman responses of distinct copper oxide families. For all the cuprates
studied, we reveal universal doping dependencies which suggest that
$2\Delta_{\rm PG}$, $2\Delta^{AN}_{\rm SC}$ and $2\Delta_{\rm CDW}$ are
governed by common microscopic interactions and that these interactions become
relevant well above the superconducting transition at $T_c$. In sharp contrast,
$2\Delta^N_{\rm SC}$ tracks the doping dependence of $T_c$, appearing to be
controlled by a different kind of interactions than the energy scales above.",2003.08957v2
2020-03-22,Light-driven permanent transition from insulator to conductor in Ga2O3,"The transition from insulator to conductor can be achieved in some materials
but requires modification of both the arrangement of atoms and their electronic
configurations. This is often achieved by doping. Here we reveal a mechanism
the lattice may adopt to induce such a transition. We show that limited
exposure to sub-bandgap light caused a permanent transition from an insulator
state to a conductor state in the insulating oxide Ga2O3 with 9-orders of
magnitude increase in electronic conduction. Photoexcitation modifies the
charge state of an O-vacancy and the redistribution of the localized electrons,
leading to a massive structural distortion in the lattice that is shown to be
the underlying mechanism. It modifies density of states and introduces new
stable states with shallower energy levels, leading to this intriguing
behavior. We suggest that this mechanism may occur in other wide bandgap metal
oxides leading to drastic modification in their electronic properties.",2003.09954v1
2020-03-25,Universal Gelation of Metal Oxide Nanocrystals via Depletion Attractions,"Nanocrystal gelation provides a powerful framework to translate nanoscale
properties into bulk materials and to engineer emergent properties through the
assembled microstructure. However, many established gelation strategies rely on
chemical reactions and specific interactions, e.g., stabilizing ligands or ions
on the surface of the nanocrystals, and are therefore not easily transferrable.
Here, we report a general gelation strategy via non-specific and purely
entropic depletion attractions applied to three types of metal oxide
nanocrystals. The gelation thresholds of two compositionally distinct spherical
nanocrystals agree quantitatively, demonstrating the adaptability of the
approach for different chemistries. Consistent with theoretical phase behavior
predictions, nanocrystal cubes form gels at a lower polymer concentration than
nanocrystal spheres, allowing shape to serve as a handle to control gelation.
These results suggest that the fundamental underpinnings of depletion-driven
assembly, traditionally associated with larger colloidal particles, are also
applicable at the nanoscale.",2003.11633v1
2020-03-30,"In situ atomic force microscopy depth-corrected 3-dimensional focused ion beam based time-of-flight secondary ion mass spectroscopy: spatial resolution, surface roughness, oxidation","Atomic force microscopy (AFM) is a well-known tool for studying surface
roughness and to collect depth information about features on the top atomic
layer of samples. By combining secondary ion mass spectroscopy (SIMS) with
focused ion beam (FIB) milling in a scanning electron microscope (SEM),
chemical information of sputtered structures can be visualized and located with
high lateral and depth resolution. In this paper, a high vacuum (HV) compatible
AFM has been installed in a TESCAN FIB-SEM instrument that was equipped with a
time-of-flight secondary ion mass spectroscopy (ToF-SIMS) detector. To
investigate the crater's depth caused by the ToF-SIMS sputtering, subsequent
AFM measurements were performed on a multilayer vertical cavity surface
emitting laser (VCSEL) sample. Surface roughness and milling depth were used to
aid accurate 3D reconstruction of the sputtered volume's chemical composition.
Achievable resolution, surface roughness during sputtering and surface
oxidation issues are analysed. Thus, the integration of complementary detectors
opens up the ability to determine the sample properties as well as to
understand the influence of the analysis method on the sample surface during
the analysis.",2003.13294v1
2020-04-30,Excitation and characterization of long-lived hydrogenic Rydberg states of nitric oxide,"High Rydberg states of nitric oxide (NO) with principal quantum numbers
between 40 and 100 and lifetimes in excess of 10 $\mu$s have been prepared by
resonance enhanced two-color two-photon laser excitation from the X
$^2\Pi_{1/2}$ ground state through the A $^2\Sigma^+$ intermediate state.
Molecules in these long-lived Rydberg states were detected and characterized
126 $\mu$s after laser photoexcitation by state-selective pulsed electric field
ionization. The laser excitation and electric field ionization data were
combined to construct two-dimensional spectral maps. These maps were used to
identify the rotational states of the NO$^+$ ion core to which the observed
series of long-lived hydrogenic Rydberg states converge. The results presented
pave the way for Rydberg-Stark deceleration and electrostatic trapping
experiments with NO, which are expected to shed further light on the decay
dynamics of these long-lived excited states, and are of interest for studies of
ion-molecule reactions at low temperatures.",2005.00090v1
2020-05-02,Mechanical properties of graphene oxide: the impact of functional groups,"In the current study, mechanical characteristics of graphene oxide (GO) as a
promising substitute of graphene are systematically studied through molecular
dynamics simulation. For this purpose, several GO samples having different
concentrations of epoxide and hydroxyl functional groups are considered. The
results reveal that increasing the epoxide coverage causes a noticeable
deterioration in the mechanical characteristics of GO systems. This change is
correlated with the increase of the formation of ripples in the structure upon
increasing the epoxide coverage. Moreover, investigating the bond lengths in
the system, it is concluded that the higher epoxide percentage leads to an
increase in the length of single and hybrid resonance bonds leading to an
overall deterioration of the mechanical properties of GO samples. Additionally,
our results demonstrate that high concentration of functional groups can lead
to a negative Poisson ratio. Increasing the amount of hydroxyl groups shows the
same declining effect on the Young modulus. In a graphene system containing
both epoxide and hydroxyl groups, it is deduced that a higher percentage of the
former can result in a higher residual strain because of the formation of more
ripples within the system.",2005.00712v1
2020-05-08,Surface electronic properties of diamond,"Surface electronic properties of undoped hydrogen terminated diamond covered
with adsorbates or in electrolyte solutions are summarized. The formation of a
conductive layer at the surface of diamond is discussed based on Hall effect,
conductivity, contact potential difference (CPM), scanning electron microscopy
(SEM), and cyclic voltammetry data applied on homoepitaxially grown CVD diamond
films with atomically smooth hydrogen terminated surfaces. Due to electron
transfer from valence band states into empty states of the electrolyte
(transfer doping), a highly conductive surface layer is generated. Holes
propagate in the layer with mobilities up to 350 cm2/Vs. The sheet hole density
is in the range 10^11 to 5x10^12 cm^-2, and dependents on pH of the
electrolyte. Numerical solutions of the Schrodinger and Poisson equations
reveal a 2D density of state (DOS) distribution. This has been utilized to
manufacture ion-sensitive field effect transistors (ISFET). The drain source
conductivity is pH dependent, with about 66 mV/pH. Application of potentials
larger than the oxidation threshold of +0.7 V (pH 13) to +1.6 V (pH 1) gives
rise to strong leakage currents and to partial surface oxidation.",2005.03893v1
2020-05-18,Spatially-resolved insulator-metal transition for rewritable optical gratings,"Doping is an effective way to tune the property of metal oxides1-5, for
achieving functional oxide electronics6-8. Previously we developed a
controllable hydrogen doping technology at ambient conditions by use of
electron-proton synergistic doping strategy, which enables one to get rid of
high-temperature/pressure treatments required by traditional technologies9.
Here, based on this facile doping route, we achieve a visual and reversible
insulator-metal transition (MIT) for tungsten trioxide (WO3) film. Its
outstanding spatial selection is comparable to standard UV lithography, which
shows the potential of becoming a viable way for rewritable WO3 grating device
fabrication. Furthermore, the period of the obtained WO3 structural grating can
also be easily changed for requirement by doping area selection. This advanced
doping technology opens up alternative approaches for developing not only
optical devices, but also rewritable ions devices and integrated circuits for
various oxide electronics.",2005.08819v2
2020-05-28,Studies of thorium and ytterbium ion trap loading from laser ablation for gravity monitoring with nuclear clocks,"Compact and robust ion traps for thorium are enabling technology for the next
generation of atomic clocks based on a low-energy isomeric transition in the
thorium-229 nucleus. We aim at a laser ablation loading of single triply
ionized thorium in a radio-frequency electromagnetic linear Paul trap.
Detection of ions is based on a modified mass spectrometer and a channeltron
with single-ion sensitivity. In this study, we successfully created and
detected 232Th+ and 232Th2+ ions from plasma plumes, studied their yield
evolution, and compared the loading to a quadrupole ion trap with Yb. We
explore the feasibility of laser ablation loading for future low-cost 229Th3+
trapping. The thorium ablation yield shows a strong depletion, suggesting that
we have ablated oxide layers from the surface and the ions were a result of the
plasma plume evolution and collisions. Our results are in good agreement with
similar experiments for other elements and their oxides.",2005.13918v3
2020-06-06,High-Entropy Oxides Based on Valence Combinations: Design and Practice,"High-entropy oxides (HEOs) are a new class of materials that are promising
for a wide range of applications. Designing HEOs needs to consider both
geometric compatibility and electrical equilibrium. However, there is currently
no available method to systematically consider these two factors when selecting
constituent materials for making HEOs. Here we propose a two-step strategy,
where a HEO system to be explored is first partitioned into multiple subsystems
based on the valence combinations of substituted cations; the geometric
compatibility is then considered in selecting suitable substituted cations. We
demonstrate this strategy by using A(5B0.2)O3 perovskite as a model system. We
show that the system can be partitioned into 12 subsystems. Ten of the
subsystems have formed a single-phase cubic perovskite, while two have
partially ordering structure. The formation of single phases is correlated to
Goldschmidt's tolerance factor, while the formation of the ordering structure
is mainly correlated to cation-valence difference. We anticipate that this
strategy is applicable to exploring HEOs in other systems.",2006.03834v1
2020-06-16,Classical and semiclassical description of Rydberg excitons in cuprous oxide,"Experimental and theoretical investigations of excitons in cuprous oxide have
revealed a significant fine-structure splitting of the excitonic Rydberg states
caused by a strong impact of the valence band structure. We provide a
semiclassical interpretation of that splitting by investigating the classical
dynamics of the excitonic electron-hole pair beyond the hydrogen-like model.
Considering the slow motion of Rydberg excitons in coordinate space compared to
the fast dynamics of quasispin and hole spin we use an adiabatic approach and
energy surfaces in momentum space for the computation of the exciton dynamics.
We observe quasi-periodic motion on near-integrable tori. Semiclassical torus
quantization yields the energy regions of the fine-structure splitting of
$n$-manifolds in agreement with quantum mechanical computations.",2006.08955v1
2020-06-29,Radio frequency field-induced electron mobility in an ultracold plasma state of arrested relaxation,"Penning ionization releases electrons in a state-selected Rydberg gas of
nitric oxide entrained in a supersonic molecular beam. Subsequent processes of
electron impact avalanche, bifurcation, and quench form a strongly coupled,
spatially correlated ultracold plasma of NO$^+$ ions and electrons that
exhibits characteristics of self-organized criticality. This plasma contains a
residue of nitric oxide Rydberg molecules. A conventional fluid dynamics of
ion-electron-Rydberg quasi-equilibrium predicts rapid decay to neutral atoms.
Instead, the NO plasma endures for a millisecond or more, suggesting that
quenched disorder creates a state of suppressed electron mobility. Supporting
this proposition, a 60 MHz radiofrequency field with a peak-to-peak amplitude
less than 1 V cm$^{-1}$ acts dramatically to mobilize electrons, causing the
plasma to dissipate by dissociative recombination and Rydberg predissociation.
An evident density dependence shows that this effect relies on collisions,
giving weight to the idea of arrested relaxation as a cooperative property of
the ensemble.",2006.16412v2
2020-08-06,Promising photovoltaic efficiency of a layered silicon oxide crystal Si$_{3}$O,"Computational searching and screening of new functional materials exploiting
earth abundant elements can accelerate developments of their energy
applications. Based on a state-of-the-art materials search algorithm and ab
initio calculations, we demonstrate a recently suggested stable silicon oxide
with a layered structure (Si$_{3}$O) as an ideal photovoltaic material. With
many-body first-principles approaches, the monolayer and layered bulk of
Si$_{3}$O show direct quasiparticle gaps of 1.85 eV and 1.25 eV, respectively,
while an optical gap of about 1.2 eV is nearly independent of the number of
layers. Spectroscopic limited maximum efficiency (SLME) is estimated to be 27%
for a thickness of 0.5 {\mu}m, making it a promising candidate for solar energy
applications.",2008.02654v1
2020-08-05,Part2: Ultra-short pulse laser patterning of very thin indium tin oxide on glass substrates,"We investigate selective patterning of ultra-thin 20 nm Indium Tin Oxide
(ITO) thin films on glass substrates, using 343, 515, and 1030 nm femtosecond
(fs), and 1030 nm picoseconds (ps) laser pulses. An ablative removal mechanism
is observed for all wavelengths at both femtosecond and picoseconds
time-scales. The absorbed threshold fluence values were determined to be 12.5
mJ/cm2 at 343 nm, 9.68 mJ/cm2 at 515 nm, and 7.50 mJ/cm2 at 1030 nm for
femtosecond and 9.14 mJ/cm2 at 1030 nm for picosecond laser exposure. Surface
analysis of ablated craters using atomic force microscopy confirms that the
selective removal of the film from the glass substrate is dependent on the
applied fluence. Film removal is shown to be primarily through ultrafast
lattice deformation generated by an electron blast force. The laser absorption
and heating process was simulated using a two temperature model (TTM). The
predicted surface temperatures confirm that film removal below 1 J/cm2 to be
predominately by a non-thermal mechanism.",2008.05294v1
2020-08-19,Deep-ultraviolet Layered Oxide B2S2O9 with Strong and Robust Second Harmonic Generation,"Two-dimensional (2D) layered semiconductors with both ultrawide bandgap and
strong second harmonic generation (SHG) are essential for expanding the
nonlinear optical (NLO) applications to deep-ultraviolet (DUV) region in
nanoscale. Unfortunately, these materials are rare in nature and have not been
discovered until now. In this Letter, we predict the B2S2O9 (BSO), an existing
layered oxide, can exhibit both DUV bandgap and strong SHG effects, comparable
to the best known DUV NLO bulks. The strong SHG intensities in BSO, originated
from the ordered arrangement of polar SO4 and BO4 tetrahedra forming planar
structure, are linearly tunable by the layer thickness. Surprisingly, the
spontaneous rotations of rigid tetrahedra under strains can induce the (nearly)
zero Poisson's ratios in BSO, which simultaneously result in the robust SHG
effects against large strains, fundamentally differing from other known 2D NLO
semiconductors. The discovery of BSO may provide an unprecedented opportunity
to explore DUV NLO physics and applications in 2D limit.",2008.08309v2
2020-08-24,One-Dimensional Twisted and Tubular Structures of Zinc Oxide by Semiconductor-Catalyzed Vapor-Liquid-Solid Synthesis,"The exploration of new catalysts for the vapor-liquid-solid (VLS) synthesis
of one-dimensional (1-D) materials promises to yield new morphologies and
functionality. Here, we show, for the model ZnO system, that this possible
using a semiconductor (Ge) catalyst. In particular, two unusual morphologies
are described: twisted nanowires and twisted nanotubes, in addition to the
usual straight nanowires. The twisted nanotubes show large hollow cores and
surprisingly high twisting rates (up to 9o/{\mu}m), which cannot be easily
explained through the Eshelby twist model. A combination of ex situ and in situ
transmission electron microscopy measurements suggest that the hollow core
results from a competition between growth and etching at the Ge-ZnO interface
during synthesis. The twisting rate is consistent with a softening of elastic
rigidity. These results indicate that the use of unconventional, nonmetallic
catalysts provide opportunities to synthesize unusual oxide structures with
potentially useful properties.",2008.10137v1
2020-08-26,Charge pumping under spin resonance in Si(100) metal-oxide-semiconductor transistors,"Gate-pulse-induced recombination, known as the charge pumping (CP), is a
fundamental carrier recombination process, and has been utilized as a method
for analyzing electrical properties of defects (or dangling bonds) at the
transistor interfaces, which is now recognized to be well-matured and
conventional. Nevertheless, neither the origin (the bonding configuration) of
the defects responsible for the CP, nor their detailed recombination sequence
has been clarified yet for Si metal-oxide-semiconductor (MOS) interfaces. In
order to address these problems, we investigated the CP under spin resonance
conditions at temperatures ranging from 27 to 300 K in Si(100) n-type MOS
transistors. We obtained evidence that Pb0 and E' centers, the two major
dangling bonds at (and near) the Si(100) interface, participate in the CP
recombination process. We also show that the spin-dependent CP process is
explained by the formation of electron-electron spin pairs, which in turn
reveals that the CP via Pb0 and E' centers is inherently a two-electron
process.",2008.11857v1
2020-08-28,Two-beam coupling by a hot electron nonlinearity,"Transparent conductive oxides such as indium tin oxide (ITO) bear the
potential to deliver efficient all-optical functionality due to their
record-breaking optical nonlinearity at epsilon near zero (ENZ) wavelengths.
All-optical applications generally involve more than one beam, but the coherent
interaction between beams has not previously been discussed in materials with a
hot electron nonlinearity. Here we study the optical nonlinearity at ENZ in ITO
and show that spatial and temporal interference has important consequences in a
two beam geometry. Our pump-probe results reveal a polarization-dependent
transient that is explained by momentary diffraction of pump light into the
probe direction by a temperature grating produced by pump-probe interference.
We further show that this effect allows tailoring the nonlinearity by tuning
frequency or chirp. Having fine control over the strong and ultrafast ENZ
nonlinearity may enable applications in all-optical neural networks,
nanophotonics, and spectroscopy.",2008.12824v1
2020-09-04,Effective Thermal Conductivity of SrBi$_4$Ti$_4$O$_{15}$-La$_{0.7}$Sr$_{0.3}$MnO$_3$ Oxide composite: Role of Particle Size and Interface Thermal Resistance,"We present a novel approach to reduce the thermal conductivity ($\kappa$) in
thermoelectric composite materials using acoustic impedance mismatch and the
Debye model. Also, the correlation between interface thermal resistance
(R$_{int}$) and the particle size of the dispersed phase on the k of the
composite is discussed. In particular, the $\kappa$ of an oxide composite which
consists of a natural superlattice Aurivillius phase (SrBi$_4$Ti$_4$O$_{15}$)
as a matrix and perovskite (La$_{0.7}$Sr$_{0.3}$MnO$_3$) as a dispersed phase
is investigated. A significant reduction in the $\kappa$ of composite, even
lower than the $\kappa$ of the matrix when the particle size of
La$_{0.7}$Sr$_{0.3}$MnO$_3$ is smaller than the Kapitza radius (a$_K$) is
observed, depicting that R$_{int}$ dominates for particle size lower than a$_K$
due to increased surface to volume ratio. The obtained results have the
potential to provide new directions for engineering composite thermoelectric
systems with desired thermal conductivity and promising in the field of energy
harvesting.",2009.02218v1
2020-09-07,Strain game revisited for complex oxide thin-films: Substrate-film thermal expansion mismatch in PbTiO$_3$,"The sensitivity of materials properties, particularly those of perovskite
oxides, to epitaxial strain has been exploited to great advantage to create
materials with new or enhanced properties. Although it has certainly been
recognized that mismatch in the thermal expansion coefficients of the bulk and
substrate material will contribute to the misfit strain, the significance of
this contribution for ferroelectric perovskite thin-films has not been
systematically explored. We use first-principles density functional theory and
the example of ferroelectric PbTiO$_3$ thin-films on various substrates to show
that ignoring the thermal expansion of the substrate (that is, assuming that
the in-plane lattice parameter of the film remains roughly constant as a
function of temperature) results in ferroelectric transition temperatures and
structural trends that are completely qualitatively different from calculations
in which thermal expansion mismatch is properly taken into account. Our work
suggests that the concept of a misfit strain defined as a single number is
particularly ill-defined for PbTiO$_3$ and invites further study of the
interplay between thermal expansion mismatch and structural and functional
properties in other thin-film materials.",2009.03396v1
2020-09-14,Investigation of the Impact of Cold Plasma Treatment on the Wettability of Medical Grade Polyvinylchloride,"The impact of the Corona, dielectric barrier discharge and low pressure
radiofrequency air plasmas on the wettability of the medical grade
polyvinylchloride was investigated. Corona plasma treatment exerted the most
pronounced increase in the hydrophilization of polyvinylchloride. The specific
energy of adhesion of the pristine and plasma treated PVC tubing is reported.
The kinetics of hydrophobic recovery following the plasma treatment was
explored. The time evolution of the apparent contact angle under the
hydrophobic recovery is satisfactorily described by the exponential fitting.
Energy-dispersive X-ray spectroscopy of the chemical composition of the
near-surface layers of the plasma treated catheters revealed their oxidation.
The effect of the hydrophobic recovery is hardly correlated with oxidation of
the polymer surface, which is irreversible.",2009.07102v1
2020-09-19,Coherent transfer matrix analysis of the transmission spectra of Rydberg excitons in Cuprous Oxide,"In this study we analyze the transmission spectrum of a thin plate of Cuprous
Oxide in the range of the absorption of the yellow exciton states with the
coherent transfer matrix method. We demonstrate that, in contrast to the usual
analysis using Beer's law, which turns out to be a rather good approximation
only in the spectral region of high principal quantum numbers, a consistent
quantitative description over the whole spectral range under consideration is
possible. This leads to new and more accurate parameters not only for the
Rydberg exciton states, but also for the strengths of indirect transitions.
Furthermore, the results have consequences on the determination of the density
of electron-hole pairs after optical excitation.",2009.09214v1
2020-09-25,Controlling the macroscopic electrical properties of reduced graphene oxide by nanoscale writing of electronic channels,"The allure of all carbon electronics stems from the spread in physical
properties, across all its allotropes. The scheme also harbours unique
challenges, like tunability of band-gap, variability of doping and defect
control. Here, we explore the technique of scanning probe tip induced nanoscale
reduction of graphene oxide (GO), which nucleates conducting, sp2 rich
graphitic regions on the insulating GO background. Flexibility of direct
writing is supplemented with control over degree of reduction and tunability of
bandgap, through macroscopic control parameters. The fabricated reduced - GO
channels and ensuing devices are investigated via spectroscopic, and
temperature and bias dependent electrical transport and correlated with
spatially resolved electronic properties, using surface potentiometry. Presence
of carrier localization effects, induced by the phase-separated sp2/sp3
domains, and large local electric field fluctuations are reflected in the
non-linear transport across the channels. Together the results indicate a
complex transport phenomena which may be variously dominated by tunnelling,
variable range hopping or activated depending on the electronic state of the
material.",2009.12366v1
2020-09-29,Nb Implanted BaO as a Support for Gold Single Atoms,"Using first-principles modelling based on density functional theory we show
that oxides implanted with transition metal can act as support for Au single
atoms, which are stable against agglomeration. In our previous work we have
shown that implanted transition metal, doped in BaO is stable as interstitial
in various charge states by transferring the excess charge to an acceptor level
close to VBM. Taking Nb as an example we show that single atom Au has its Fermi
level close to the VBM of BaO and hence is able to accept charge from the
dopant. This charge transfer process between Nb and Au helps Au atoms bind
strongly on the doped BaO support. We also show that these charged Au atoms
repel each other and prefer to remain atomically dispersed preventing cluster
formation. Substitutional doping of transition metals have earlier been
reported to bind Au atoms. However, if doped at interstitial sites, they can
bind more Au atoms; for example, 5 Au atoms can be anchored per Nb dopant
present in BaO interstitial, compared to 3 Au atoms when Nb is doped at
substitutional site. This work paves the way for an altogether new technique of
stabilizing noble metal single atoms on transition metal doped oxides.",2009.14256v1
2020-10-04,$Mg_xZn_{1-x}O$ contact to $CuGa_3Se_5$ absorber for photovoltaic and photoelectrochemical devices,"$CuGa_3Se_5$ is a promising candidate material with wide band gap for top
cells in tandem photovoltaic (PV) and photoelectrochemical (PEC) devices.
However, traditional CdS contact layers used with other chalcopyrite absorbers
are not suitable for $CuGa_3Se_5$ due to the higher position of its conduction
band minimum. $Mg_xZn_{1-x}O$ is a transparent oxide with adjustable band gap
and conduction band position as a function of magnesium composition, but its
direct application is hindered by $CuGa_3Se_5$ surface oxidation. Here,
$Mg_xZn_{1-x}O$ is investigated as a contact (n-type buffer or window) material
to $CuGa_3Se_5$ absorbers pretreated in $Cd^{2+}$ solution, and an onset
potential close to 1 V vs RHE in 10 mM hexaammineruthenium (III) chloride
electrolyte is demonstrated. The $Cd^{2+}$ surface treatment changes the
chemical composition and electronic structure of the $CuGa_3Se_5$ surface, as
demonstrated by photoelectron spectroscopy measurements. The performance of
$CuGa_3Se_5$ absorber with $Cd^{2+}$ treated surface in the solid-state test
structure depends on the Zn/Mg ratio in the $Mg_xZn_{1-x}O$ layer. The measured
open circuit voltage close to 1 V is promising for tandem PEC water splitting
with $CuGa_3Se_5$/$Mg_xZn_{1-x}O$ top cells.",2010.01635v1
2020-10-06,New insights into the mechanism of graphene oxide and radionuclide interaction through vacancy defects,"The sorption of radionuclides by graphene oxides synthesized by different
methods was studied through a combination of batch experiments with
characterization by microscopic and spectroscopic techniques such as X-ray
photoelectron spectroscopy (XPS), attenuated total reflection fourier-transform
infrared spectroscopy (ATR-FTIR), high-energy resolution fluorescence detected
X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorption fine
structure (EXAFS) and high resolution transmission electron microscopy (HRTEM).",2010.02965v1
2020-10-07,Modeling of Nuclear Waste Forms: State-of-the-Art and Perspectives,"Computational modeling is an important aspect of the research on nuclear
waste materials. In particular, atomistic simulations, when used complementary
to experimental efforts, contribute to the scientific basis of safety case for
nuclear waste repositories. Here we discuss the state-of-the-art and
perspectives of atomistic modeling for nuclear waste management on a few cases
of successful synergy of atomistic simulations and experiments. In particular,
we discuss here: (1) the potential of atomistic simulations to investigate the
uranium oxidation state in mixed valence uranium oxides and (2) the ability of
cementitious barrier materials to retain radionuclides such as 226Ra and 90Sr,
and of studtite/metastudtite secondary peroxide phases to incorporate actinides
such as Np and Am. The new contribution we make here is the computation of the
incorporation of Sr by C-S-H (calcium silicate hydrate) phases.",2010.03270v1
2020-10-08,Structural evolution of binary oxide nanolaminates with annealing and its impact on room-temperature internal friction,"Internal friction in oxide thin films imposes a critical limitation to the
sensitivity and stability of ultra-high finesse optical cavities for
gravitational wave detectors. Strategies like doping or creating nanolaminates
are sought to introduce structural modifications that reduce internal friction.
This work describes an investigation of the morphological changes SiO2/Ta2O5
and TiO2/Ta2O5 nanolaminates undergo with annealing and their impact on room
temperature internal friction. It is demonstrated that thermal treatment
results in a reduction of internal friction in both nanolaminates, but through
different pathways. In the SiO2/Ta2O5 nanolaminate, which layers remain intact
after annealing, the total reduction in internal friction follows the reduction
in the composing SiO2 and Ta2O5 layers. Instead, interdiffusion initiated by
annealing at the interface of the TiO2/Ta2O5 nanolaminate and the formation of
a mixed phase dictate a more significant reduction in internal friction to ~
2.6 * 10-4, a value lower than any other Ta2O5 mixture coating with similar
cation concentration.",2010.04272v1
2020-10-16,An upgraded ultra-high vacuum magnetron-sputtering system for high-versatility and software-controlled deposition,"Magnetron sputtering is a widely used physical vapor deposition technique.
Reactive sputtering is used for the deposition of, e.g, oxides, nitrides and
carbides. In fundamental research, versatility is essential when designing or
upgrading a deposition chamber. Furthermore, automated deposition systems are
the norm in industrial production, but relatively uncommon in laboratory-scale
systems used primarily for fundamental research. Combining automatization and
computerized control with the required versatility for fundamental research
constitutes a challenge in designing, developing, and upgrading laboratory
deposition systems. The present article provides a detailed description of the
design of a lab-scale deposition chamber for magnetron sputtering used for the
deposition of metallic, oxide, nitride and oxynitride films with automated
controls, dc or pulsed bias, and combined with a coil to enhance the plasma
density near the substrate. LabVIEW software (provided as Supplementary
Information) has been developed for a high degree of computerized or automated
control of hardware and processes control and logging of process details.",2010.08411v2
2020-10-22,Electrical and Thermal Transport Properties of the beta-Pyrochlore Oxide CsW2O6,"We report the electrical resistivity, thermoelectric power, and thermal
conductivity of single-crystalline and sintered samples of the 5d pyrochlore
oxide CsW2O6. The electrical resistivity of the single crystal is 3 mohm cm at
295 K and gradually increases with decreasing temperature above 215 K (Phase
I). The thermoelectric power of the single-crystalline and sintered samples
shows a constant value of approximately -60 uV K-1 in Phase I. These results
reflect that the electron conduction by W 5d electrons in Phase I is incoherent
and in the hopping regime, although a band gap does not open at the Fermi
level. The thermal conductivity in Phase I of both samples is considerably low,
which might be due to the rattling of Cs+ ions. In Phase II below 215 K, the
electrical resistivity and the absolute value of thermoelectric power of both
samples strongly increase with decreasing temperature, corresponding to a
transition to a semiconducting state with a band gap open at the Fermi level,
while the thermal conductivity in Phase II is smaller than that in Phase I.",2010.11404v1
2020-10-27,Particle size effect on the Langmuir-Hinshelwood barrier for CO oxidation on regular arrays of Pd clusters supported on ultrathin alumina films,"The Langmuir-Hinshelwood barrier (ELH) and the pre-exponential factor
($\nu$LH) for CO oxidation have been measured at high temperature on hexagonal
arrays of Pd clusters supported on an ultrathin alumina film on Ni3Al(111). The
Pd clusters have a sharp size distribution and the mean sizes are: 174$\pm$13,
360$\pm$19 and 768$\pm$28 atoms. ELH and $\nu$LH are determined from the
initial reaction rate of a CO molecular beam with a saturation layer of
adsorbed oxygen on the Pd clusters, measured at different temperatures
(493$\le$T (K) $\le$613). The largest particles (3.5 nm) give values of ELH and
$\nu$LH similar to those measured on Pd (111) [2]. However, smaller particles
(2.7 and 2.1 nm) show very different behavior. The origin of this size effect
is discussed in terms of variation of the electronic structure and of the
atomic structure of the Pd clusters.",2010.14147v1
2020-10-28,A periodic equation-of-motion coupled-cluster implementation applied to $F$-centers in alkaline earth oxides,"We present an implementation of equation of motion coupled-cluster singles
and doubles (EOM-CCSD) theory using periodic boundary conditions and a plane
wave basis set. Our implementation of EOM-CCSD theory is applied to study
$F$-centers in alkaline earth oxides employing a periodic supercell approach.
The convergence of calculated electronic excitation energies for neutral color
centers in MgO, CaO and SrO crystals with respect to orbital basis set and
system size is explored. We discuss extrapolation techniques that approximate
excitation energies in the complete basis set limit and reduce finite size
errors. Our findings demonstrate that EOM-CCSD theory can predict optical
absorption energies of $F$-centers in good agreement with experiment.
Furthermore, we discuss calculated emission energies corresponding to the decay
from triplet to singlet states, responsible for the photoluminescence
properties. Our findings are compared to experimental and theoretical results
available in literature.",2010.15071v1
2020-10-29,Asymmetric Rydberg blockade of giant excitons in Cuprous Oxide,"The ability to generate and control strong long-range interactions via highly
excited electronic states has been the foundation for recent breakthroughs in a
host of areas, from atomic and molecular physics [1, 2] to quantum optics [3,
4] and technology [5-7]. Rydberg excitons provide a promising solid-state
realization of such highly excited states, for which record-breaking orbital
sizes of up to a micrometer have indeed been observed in cuprous oxide
semiconductors [8]. Here, we demonstrate the generation and control of strong
exciton interactions in this material by optically producing two distinct
quantum states of Rydberg excitons. This makes two-color pump-probe experiments
possible that allow for a detailed probing of the interactions. Our experiments
reveal the emergence of strong spatial correlations and an inter-state Rydberg
blockade that extends over remarkably large distances of several micrometers.
The generated many-body states of semiconductor excitons exhibit universal
properties that only depend on the shape of the interaction potential and yield
clear evidence for its vastly extended-range and power-law character.",2010.15459v1
2020-11-01,Light induced resistive switching in copper oxide thin films,"Copper oxide thin film based metal-insulator-metal structures were subjected
to white light irradiation.The top electrodes included Al, Cr and Ni while the
bottom electrode was either Au or Pt. A white light pulse controls the set
process and this light induced set (LIS) can be performed at very low voltages
(tens of milli volts) which is not possible in the normal set process. The LIS
is initiated at the positive edge of the pulse and there is no effect of the
falling edge of the light. In most cases the high resistance state (HRS) to low
resistance state (LRS) transition is irreversible i.e.the devices continue to
remain in the LRS even after the light pulse is switched off. Light induced
reset (LIR) is achieved in only one device structure Al/CuxO/Au. By using LIS
and LIR, set and reset power of the device can be reduced to a great extent and
the set and reset parameters variation also reduces. The current work, thus,
points to the possibility of formation and compliance-free resistive random
access memory devices.",2011.00423v1
2020-11-08,Studies on optical signal due to oxygen effect on hydrogenated amorphous/crystalline silicon thin-films,"We have studied the effects of oxygen on hydrogenated amorphous/crystalline
silicon films in terms of their structural and optical properties. Different
hydrogenated silicon oxide (SiO:H) and silicon (Si:H) films are fabricated
between microcrystalline and amorphous transition region. X-ray diffraction,
Raman, FTIR and UV-Vis emission spectrometry have been used to characterize
different films. A comparison of the results with those of different types of
films like hydrogenated amorphous silicon oxide (a-SiO:H), hydrogenated
amorphous silicon (a-Si:H) and microcrystalline silicon ($\mu$c-Si:H) films
reveal their superiority as an excellent substance for solar cell. X-ray
diffraction, FTIR and Raman spectral analysis show that difference of the H
dilution effect has a major effect on the structure of the film and the optical
properties. Photoluminescence analysis of amorphous silicon-oxygen and
silicon-hydride alloy films has established their efficient application
appropriate as Si based light emitting devices. A large optical band gap of
1.83 eV and appearance of strong photo luminescence at 2.0 eV validates the
applicability of a-SiO:H film as a better alternative for the solar cells.",2011.03930v1
2020-11-08,Molecular dynamics simulations of sodium nanoparticle deposition on magnesium oxide,"The interaction of mass-selected atomic clusters and nanoparticles with
surfaces attracts strong interest in view of fundamental research and
technological applications. Understanding dynamics of the deposition process is
important for controlling structure and functioning of deposited nanoparticles
on a substrate, but experimental techniques can usually observe only the final
outcome of the deposition process. In this paper, the deposition of 4 nm-sized
sodium nanoparticles on an experimentally relevant magnesium oxide substrate is
studied by means of classical molecular dynamics simulations. An empirical
force field is derived which accounts for the interaction of highly polarizable
Na atoms with the surface, reproducing the results of previously reported
quantum mechanics/molecular mechanics simulations. Molecular dynamics
simulations permit exploring the dynamics of deposited nanoparticles on long
timescales on the order of hundreds of picoseconds, thus enabling the analysis
of energy relaxation mechanisms and the evolution of nanoparticle structure up
to its thermalization with the substrate. Several nanoparticle characteristics,
such as internal structure, contact angle, and aspect ratio are studied in a
broad deposition energy range from the soft landing to multi-fragmentation
regimes.",2011.04024v1
2020-11-17,Observation of two-dimensional superconductivity at the LaAlO3/KTaO3(110) heterointerface,"We report on the observation of a Tc ~0.9 K superconductivity at the
interface between LaAlO3 film and the 5d transition-metal oxide KTaO3(110)
single crystal. The interface shows a large anisotropy of the upper critical
field, and its superconducting transition is consistent with a
Berezinskii-Kosterlitz-Thouless transition. Both facts suggest that the
superconductivity is two-dimensional (2D) in nature. The carrier density
measured at 5 K is ~7 time 10^13 cm-2. The superconducting layer thickness and
coherence length are estimated to be ~8 and ~30 nm, respectively. Our result
provides a new platform for the study of 2D superconductivity at oxide
interfaces.",2011.08526v1
2020-11-18,Crystal structure built from a GeO$_6$-GeO$_5$ polyhedra network with high thermal stability: $β$-SrGe$_2$O$_5$,"By tackling the challenge of extending transparent oxide semiconductors to Ge
based oxides, we have found a not-yet-reported crystal structure, named
$\beta$-SrGe$_2$O$_5$, which is composed of edge-sharing GeO$_6$ octahedra
interconnected by GeO$_5$ bipyramids. Single crystals were successfully grown
by the high-pressure flux method. $\beta$-SrGe$_2$O$_5$ has a band gap of 5.2
eV and a dispersive conduction band with an effective mass as small as 0.34
times the electron rest mass, which originates from the edge-sharing GeO$_6$
octahedra network. Although known compounds with octahedral GeO$_6$
coordination are commonly unstable at atmospheric pressure and elevated
temperatures, $\beta$-SrGe$_2$O$_5$ exhibits thermal stability up to 700
$^\circ$C.",2011.09443v1
2021-02-01,Predicting nanocrystal morphology governed by interfacial strain,"The shape dependence for the technologically important nickel oxide (NiO)
nanocrystals on (001) strontium titanate substrates is investigated under the
generalized Wulff-Kaichew (GWK) theorem framework. It is found that the shape
of the NiO nanocrystals is primarily governed by the existence (or absence) of
interfacial strain. Nanocrystals that have a fully pseudomorphic interface with
the substrate (i.e. the epitaxial strain is not relaxed) form an embedded
smooth ball-crown morphology with {001}, {011}, {111} and high-index {113}
exposed facets with a negative Wulff point. On the other hand, when the
interfacial strain is relaxed by misfit dislocations, the nanocrystals take on
a truncated pyramidal shape, bounded by {111} faces and a {001} flat top, with
a positive Wulff point. Our quantitative model is able to predict both
experimentally observed shapes and sizes with good accuracy. Given the
increasing demand for hetero-epitaxial nanocrystals in various physio-chemical
and electro-chemical functional devices, these results lay the important
groundwork in exploiting the GWK theorem as a general analytical approach to
explain hetero-epitaxial nanocrystal growth on oxide substrates governed by
interface strain.",2102.01220v1
2021-02-03,Band structure of tungsten oxide W$_{20}$O$_{58}$ with ideal octahedra,"The band structure, density of states, and the Fermi surface of a tungsten
oxide WO$_{2.9}$ with idealized crystal structure (ideal octahedra WO$_6$
creating a ""square lattice"") is obtained within the density functional theory
in the generalized gradient approximation. Because of the oxygen vacancies
ordering this system is equivalent to the compound W$_{20}$O$_{58}$
(Magn\'{e}li phase), which has 78 atoms in unit cell. We show that
5$d$-orbitals of tungsten atoms located immediately around the voids in the
zigzag chains of edge-sharing octahedra give the dominant contribution near the
Fermi level. These particular tungsten atoms are responsible of a low-energy
properties of the system.",2102.01983v2
2021-02-09,The role of heat generation and fluid flow in plasmon-enhanced reduction-oxidation reactions,"Recently, we have shown that thermal effects play a crucial role in speeding
up the rate of bond-dissociation reactions. This was done by applying a simple
temperature-shifted Arrhenius Law to the experimental data, corroborated with
detailed account of the heat diffusion occurring within the relevant samples
and identification of errors in the temperature measurements. Here, we provide
three important extensions of our previous studies. First, we analyze thermal
effects in reduction-oxidation (redox) reactions, where charge transfer is an
integral part of the reaction. Second, we analyze not only the spatial
distribution of the temperature, but also its temporal dynamics. Third, we also
model the fluid convection and stirring. An analysis of two exemplary
experimental studies allows us to show that thermal effects can explain the
experimental data in one of experiments (Baumberg and coworkers), but not in
the other (Jain and coworkers), showing that redox reactions are not
necessarily driven by non-thermal charge carriers.",2102.04783v1
2021-02-14,Graphene oxide films for ultra-flat optics and linear and nonlinear integrated photonic circuits,"With superior optical properties, high flexibility in engineering its
material properties, and strong capability for large-scale on-chip integration,
graphene oxide (GO) is an attractive solution for on-chip integration of
two-dimensional (2D) materials to implement functional integrated photonic
devices capable of new features. Over the past decade, integrated GO photonics,
representing an innovative merging of integrated photonic devices and thin GO
films, has experienced significant development, leading to a surge in many
applications covering almost every field of optical sciences. This paper
reviews the recent advances in this emerging field, providing an overview of
the optical properties of GO as well as methods for the on-chip integration of
GO. The main achievements made in GO hybrid integrated photonic devices for
diverse applications are summarized. The open challenges as well as the
potential for future improvement are also discussed.",2102.07251v1
2021-02-15,Data-driven analysis of the electronic-structure factors controlling the work functions of perovskite oxides,"Tuning the work functions of materials is of practical interest for
maximizing the performance of microelectronic and (photo)electrochemical
devices, as the efficiency of these systems depends on the ability to control
electronic levels at surfaces and across interfaces. Perovskites are promising
compounds to achieve such control. In this work, we examine the work functions
of more than 1,000 perovskite oxide surfaces (ABO$_3$) by data-driven
(machine-learning) analysis and identify the factors that determine their
magnitude. While the work functions of BO$_2$-terminated surfaces are sensitive
to the energy of the hybridized oxygen p bands, the work functions of
AO-terminated surfaces exhibit a much less trivial dependence with respect to
the filling of the d bands of the B-site atom and of its electronic affinity.
This study shows the utility of interpretable data-driven models in analyzing
the work functions of cubic perovskites from a limited number of
electronic-structure descriptors.",2102.07320v1
2021-02-17,Exchange interaction in the yellow exciton series of cuprous oxide,"We experimentally and numerically investigate the exchange interaction of the
yellow excitons in cuprous oxide. By varying the material parameters in the
numerical calculations, we can interpret experimental findings and understand
their origin in the complex band structure and central-cell corrections. In
particular, we experimentally observe the reversal of the ortho- and
paraexciton for the $2S$ yellow exciton, and explain this phenomenon by an
avoided crossing with the green $1S$ orthoexciton in a detailed numerical
analysis. Furthermore, we discuss the exchange splitting as a function of the
principal quantum number $n$ and its deviation from the $n^{-3}$ behavior
expected from a hydrogenlike model. We also explain why the observed exchange
splitting of the green $1S$ exciton is more than twice the splitting of the
yellow $1S$ state.",2102.08900v1
2021-02-23,Predicting the pseudocapacitive windows for MXene electrodes with voltage-dependent cluster expansion models,"MXene transition-metal carbides and nitrides are of growing interest for
energy storage applications. These compounds are especially promising for use
as pseudocapacitive electrodes due to their ability to convert energy
electrochemically at fast rates. Using voltage-dependent cluster expansion
models, we predict the charge storage performance of MXene pseudocapacitors for
a range of electrode compositions. $M_3C_2O_2$ electrodes based on group-VI
transition metals have up to 80% larger areal energy densities than
prototypical titanium-based ( e.g. $Ti_3C_2O_2$) MXene electrodes. We attribute
this high pseudocapacitance to the Faradaic voltage windows of group-VI MXene
electrodes, which are predicted to be 1.2 to 1.8 times larger than those of
titanium-based MXenes. The size of the pseudocapacitive voltage window
increases with the range of oxidation states that is accessible to the MXene
transition metals. By similar mechanisms, the presence of multiple ions in the
solvent (Li$^+$ and H$^+$) leads to sharp changes in the transition-metal
oxidation states and can significantly increase the charge capacity of MXene
pseudocapacitors.",2102.11863v1
2021-02-26,Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$],"The layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], often expressed as
the approximate formula Ca$_3$Co$_4$O$_9$, is a promising candidate for
efficient oxide thermoelectrics but an origin of its unusual thermoelectric
transport is still in debate. Here we investigate \textit{in-plane} anisotropy
of the transport properties in a broad temperature range to examine the
detailed conduction mechanism. The in-plane anisotropy between $a$ and $b$ axes
is clearly observed both in the resistivity and the thermopower, which is
qualitatively understood with a simple band structure of the triangular lattice
of Co ions derived from the angle-resolved photoemission spectroscopy
experiments. On the other hand, at high temperatures, the anisotropy becomes
smaller and the resistivity shows a temperature-independent behavior, both of
which indicate a hopping conduction of localized carriers. Thus the present
observations reveal a crossover from low-temperature itinerant to
high-temperature localized states, signifying both characters for the enhanced
thermopower.",2102.13250v1
2021-02-26,Catalytic effect of plasma in lowering the reduction temperature of $Fe_{2}O_{3}$,"Atmospheric pressure plasma (APP) generates highly reactive species that are
useful for surface activations. We demonstrate a fast regeneration of iron
oxides, that are popular catalysts in various industrial processes, using
microwave-driven argon APP under ambient condition. The surface treatment of
hematite powder by the APP with a small portion of hydrogen (0.5%) lowers the
oxide's reduction temperature. A near-infrared laser is used for localized
heating to control the surface temperature. Controlled experiments without
plasma confirm the catalytic effect of the plasma. Raman, XRD, SEM, and XPS
analyses show that the plasma treatment changed the chemical state of the
hematite to that of magnetite without sintering.",2102.13369v1
2021-03-05,High thermoelectric power factor of poly(3-hexylthiophene) through in-plane alignment and doping with a molybdenum dithiolene complex,"Here we report a record thermoelectric power factor of up to 160 $\mu$ W m-1
K-2 for the conjugated polymer poly(3-hexylthiophene) (P3HT). This result is
achieved through the combination of high-temperature rubbing of thin films
together with the use of a large molybdenum dithiolene p-dopant with a high
electron affinity. Comparison of the UV-vis-NIR spectra of the chemically doped
samples to electrochemically oxidized material reveals an oxidation level of
10%, i.e. one polaron for every 10 repeat units. The high power factor arises
due to an increase in the charge-carrier mobility and hence electrical
conductivity along the rubbing direction. We conclude that P3HT, with its
facile synthesis and outstanding processability, should not be ruled out as a
potential thermoelectric material.",2103.03852v1
2021-03-09,Anisotropy of the In-Plane and Out-of-Plane Resistivity and the Hall Effect in the Normal State of Vicinal-Grown YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films,"The resistivity and the Hall effect in the copper-oxide high-temperature
superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO) are remarkably
anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO$_3$
substrate allows one to investigate these anisotropic transport properties in a
planar and well-defined sample geometry employing a homogeneous current
density. In the normal state, the Hall voltage probed parallel to the
copper-oxide layers is positive and strongly temperature dependent, whereas the
out-of-plane Hall voltage is negative and almost temperature independent. The
results confirm previous measurements on single crystals by an entirely
different measurement method and demonstrate that vicinal thin films might be
also useful for investigations of other layered nanomaterials.",2103.05511v1
2021-03-23,Searching for refractory plasmonic materials: the structural and optical properties of Au$_{3}$Zr intermetallic thin films,"Optical properties of refractory intermetallic thin films of Au$_{3}$Zr were
experimentally investigated for the first time, which show distinctive
plasmonic properties in the visible and near infrared region. The films were
fabricated through DC magnetron sputtering at various deposition temperature
ranging from room temperature to 427$^{o}$C and annealed at different vacuum
levels. Both the structural and optical properties are found to be critically
dependent on deposition temperature and anneal conditions. Films deposited
between 205-320$^{o}$C are shown to exhibit lower negative permittivity and
better thermal stability, which could be linked to specific crystalline
orientations. The films are stable when annealed at 10$^{-8}$ Torr, but are
partially oxidized when annealed at 10$^{-6}$ Torr, suggesting oxidization
could be a restricting issue for high-temperature applications in ambient
environment.",2103.12888v1
2021-03-24,beta-Ga2O3 Double Gate Junctionless FET with an Efficient Volume Depletion Region,"This paper presents a new \b{eta}-Ga2O3 junctionless double gate
Metal-Oxide-Field-Semiconductor-Effect-Transistor (\b{eta}DG-JL-FET) that a P+
packet embedded in the oxide layer (PO-\b{eta}DG-JL-FET) for high-voltage
applications. Our goal is to achieve an efficient volume depletion region by
placing a P+ layer of silicon. We show that the proposed structure has a
subthreshold swing ~ 64 mV/decade and it suppressed the band to band tunneling
(BTBT) phenomenon. Also, the PO-\b{eta}DG-JL-FET structure has a high Ion/Ioff
~ 1.3e15. The embedded layer reduces the off-current (IOFF) by ~ 10-4, while
the on-current (ION) reduces slightly. Besides, we show that the proposed
structure has acceptable Ioff value in a range of gate work functions which
help us to the optimization of designs in terms of area, power gain, and
leakage current. The leakage current of the proposed structure is ~ 7e-17 A in
400 K temperature. Furthermore, the fabrication process steps of the proposed
structure will be investigated.",2103.13022v1
2021-03-29,"Double-site Substitution of Ce into (Ba, Sr)MnO3 Perovskites for Solar Thermochemical Hydrogen Production","Solar thermochemical hydrogen production (STCH) is a renewable alternative to
hydrogen produced using fossil fuels. While serial bulk experimental methods
can accurately measure STCH performance, screening chemically complex materials
systems for new promising candidates is more challenging. Here we identify
double-site Ce-substituted (Ba,Sr)MnO3 oxide perovskites as promising STCH
candidates using a combination of bulk synthesis and high-throughput thin film
experiments. The Ce substitution on the B-site in 10H-BaMnO3 and on the A-site
in 4P-SrMnO3 lead to 2-3x higher hydrogen production compared to CeO2, but
these bulk single-site substituted perovskites suffer from incomplete
reoxidation. Double-site Ce substitution on both A- and B-site in (Ba,Sr)MnO3
thin films increases Ce solubility and extends the stability of 10H and 4P
structures, which is promising for their thermochemical reversibility. This
study demonstrates a high-throughput experimental method for screening complex
oxide materials for STCH applications.",2103.15805v2
2021-03-29,Photoluminescence of ion-synthesized 9R-Si inclusions in SiO2/Si structure: effect of irradiation dose and oxide film thickness,"The study of hexagonal silicon polytypes attracts special attention due to
their unique physical properties compared to the traditional cubic phase of Si.
Thus, for some hexagonal phases, a significant improvement in the emission
properties has been demonstrated. In this work, the luminescent properties of
SiO2/Si structures irradiated with Kr+ ions at different doses and annealed at
800 {\deg}C have been systematically investigated. For such structures, a
photoluminescence line at ~ 1240 nm is observed and associated with the
formation of hexagonal 9R-Si phase inclusions. It is found that the variation
in the thickness of oxide film and the relative position of ion distribution
profile and film / substrate interface leads to a regular change in the
luminescence intensity. The nature of the observed dependencies is discussed as
related to the interplay between the desirable 3C-Si -> 9R-Si structural
transition and generation of nonradiative defects. The revealed regularities
suggest optimal ion irradiation conditions for synthesis of optically active
9R-Si phase in diamond-like silicon.",2103.15867v1
2021-03-29,Fluorescence intensity correlation imaging with high resolution and elemental contrast using intense x-ray pulses,"We theoretically investigate the fluorescence intensity correlation (FIC) of
Ar clusters and Mo-doped iron oxide nanoparticles subjected to intense,
femtosecond and sub-femtosecond XFEL pulses for high-resolution and elemental
contrast imaging. We present the FIC of {\Ka} and {\Kah} emission in Ar
clusters and discuss the impact of sample damage on retrieving high-resolution
structural information and compare the obtained structural information with
those from the coherent difractive imaging (CDI) approach. We found that, while
sub-femtosecond pulses will substantially benefit the CDI approach,
few-femtosecond pulses may be sufficient for achieving high-resolution
information with FIC. Furthermore, we show that the fluorescence intensity
correlation computed from the fluorescence of Mo atoms in Mo-doped iron oxide
nanoparticles can be used to image dopant distributions.",2103.15872v1
2021-03-31,An Unexpected Role of H During SiC Corrosion in Water,"During aqueous corrosion, atoms in the solid react chemically with oxygen,
leading either to the formation of an oxide film or to the dissolution of the
host material. Commonly, the first step in corrosion involves an oxygen atom
from the dissociated water that reacts with the surface atoms and breaks near
surface bonds. In contrast, hydrogen on the surface often functions as a
passivating species. Here, we discovered that the roles of O and H are reversed
in the early corrosion stages on a Si terminated SiC surface. O forms stable
species on the surface, and chemical attack occurs by H that breaks the Si-C
bonds. This so-called hydrogen scission reaction is enabled by a newly
discovered metastable bridging hydroxyl group that can form during water
dissociation. The Si atom that is displaced from the surface during water
attack subsequently forms H2SiO3, which is a known precursor to the formation
of silica and silicic acid. This study suggests that the roles of H and O in
oxidation need to be reconsidered.",2103.16739v1
2021-04-02,Transparent Conductive Oxides-based Architectures for the Electrical Modulation of the Optical Response: A Spectroscopic Ellipsometry Study,"Transparent Conductive Oxides (TCOs) are a class of materials that combine
high optical transparency with high electrical conductivity. This property
makes them uniquely appealing as transparent-conductive electrodes in solar
cells and interesting for optoelectronics and infrared-plasmonics applications.
One of the new challenges that researchers and engineers are facing is merging
optical and electrical control in a single device for developing
next-generation photovoltaic, opto-electronic devices and energyefficient
solid-state lighting. In this work, we investigated the possible variations in
the dielectric properties of aluminum-doped ZnO (AZO) upon gating, by means of
Spectroscopic Ellipsometry (SE). We investigated the electrical-bias-dependent
optical response of thin AZO films fabricated by magnetron sputtering, within a
parallel-plane capacitor configuration. We address the possibility to control
their optical and electric performances by applying bias, monitoring the effect
of charge injection/depletion in the AZO layer by means of in-operando SE vs
applied gate voltage.",2104.01147v1
2021-04-04,Stretchable optical diffraction grating from poly(acrylic acid)/polyethylene oxide stereocomplex,"Optical gratings are a key component in many spectroscopy, communications,
and imaging systems. While initially static elements, advances in optical
materials have enabled dynamically tunable gratings to be designed. One common
tuning strategy is relying on mechanical deformation of the grating pitch to
modify the diffraction pattern. To date, most mechanically adaptive optical
gratings consist of a hybrid system where rigid moieties are patterned on an
elastomeric substrate. In the present work, we demonstrate an all-polymer
tunable grating that is fabricated using replica molding from the poly(acrylic
acid) (PAA)/polyethylene oxide (PEO) polymer stereocomplex. PAA/PEO pristine
films exhibit excellent optical transmittance at or above 80% from 500 nm to
1400 nm and stretchability over 800% strain. The experimental studies on the
changes of diffraction mode distances with respect to the applied strains agree
well with the finite-difference time-domain (FDTD) theoretical modeling.",2104.01660v2
2021-04-06,Active learning and element embedding approach in neural networks for infinite-layer versus perovskite oxides,"Combining density functional theory simulations and active learning of neural
networks, we explore formation energies of oxygen vacancy layers, lattice
parameters, and their correlations in infinite-layer versus perovskite oxides
across the periodic table, and place the superconducting nickelate and cuprate
families in a comprehensive statistical context. We show that neural networks
predict these observables with high precision, using only 30-50% of the data
for training. Element embedding autonomously identifies concepts of chemical
similarity between the individual elements in line with human knowledge. Based
on the fundamental concepts of entropy and information, active learning
composes the training set by an optimal strategy without a priori knowledge and
provides systematic control over the prediction accuracy. This offers key
ingredients to considerably accelerate scans of large parameter spaces and
exemplifies how artificial intelligence may assist on the quantum scale in
finding novel materials with optimized properties.",2104.02529v1
2021-04-12,Quasiparticle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid,"Exploiting inversion symmetry breaking (ISB) in systems with strong
spin-orbit coupling promises control of spin through electric fields - crucial
to achieve miniaturization in spintronic devices. Delivering on this promise
requires a two-dimensional electron gas with a spin precession length shorter
than the spin coherence length and a large spin splitting so that spin
manipulation can be achieved over length scales of nanometers. Recently, the
transition metal oxide terminations of delafossite oxides were found to exhibit
a large Rashba spin splitting dominated by ISB. In this limit, the Fermi
surface exhibits the same spin texture as for weak ISB, but the orbital texture
is completely different, raising questions about the effect on quasiparticle
scattering. We demonstrate that the spin-orbital selection rules relevant for
conventional Rashba system are obeyed as true spin selection rules in this
correlated electron liquid and determine its spin coherence length from
quasiparticle interference imaging.",2104.05718v1
2021-04-14,Detailed thermal reduction analyses of Graphene Oxide via in-situ TEM/EELS studies,"We report an in-depth study of the reduction of graphene oxide (GO) by
in-situ thermal transmission electron microscopy (TEM) analysis. In-situ
heating high-resolution TEM (HRTEM) imaging and electron energy-loss
spectroscopy (EELS) measurements have been combined to identify the
transformations of different oxygen functional groups, the desorption of
physisorbed and chemisorbed water and the graphitization as a function of the
temperature in the range from 70 up to 1200{\deg}C. A model for the general
removal of water and OFGs is proposed based on different chemical and physical
parameters that have been monitored. All this unique information provides a
detailed roadmap of the thermal behaviour of GO at an extended range of
temperature. This is not only of interest to understand the thermal reduction
process of GO but also of critical relevance to the response of GO in
applications when exposed to thermal effects.",2104.06840v1
2021-04-14,In-situ reduction by Joule heating and measurement of electrical conductivity of graphene oxide in a transmission electron microscope,"Graphene oxide (GO) is reduced by Joule heating using in-situ transmission
electron microscopy (TEM). The approach allows the simultaneous study of GO
conductivity by electrical measurements and of its composition and structural
properties throughout the reduction process by TEM, electron diffraction and
electron energy-loss spectroscopy. The small changes of GO properties observed
at low applied electric currents are attributed to the promotion of diffusion
processes. The actual reduction process starts from an applied power density of
about 2 1014 Wm-3 and occurs in a highly uniform and localized manner. The
conductivity increases more than 4 orders of magnitude reaching a value of 3
103 Sm-1 with a final O content of less than 1%. We discuss differences between
the reduction by thermal annealing and Joule heating.",2104.07088v1
2021-04-25,Improved Hopfield Network Optimization using Manufacturable Three-terminal Electronic Synapses,"We describe via simulation novel optimization algorithms for a Hopfield
neural network constructed using manufacturable three-terminal
Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) synaptic devices. We first present
a computationally-light, memristor-based, highly accurate compact model for the
SONOS. Using the compact model, we describe techniques of simulated annealing
in Hopfield networks by exploiting imperfect problem definitions, current
leakage, and the continuous tunability of the SONOS to enable transient chaotic
group dynamics. We project improvements in energy consumption and latency for
optimization relative to the best CPUs and GPUs by at least 4 orders of
magnitude, and also exceeding the best projected memristor-based hardware;
along with a 100-fold increase in error-resilient hardware size (i.e., problem
size).",2104.12288v1
2021-05-01,Complementary electrochemical ICP-MS flow cell and in-situ AFM study of the anodic desorption of molecular adhesion promotors,"Molecular adhesion promoters are a central component of modern coating
systems for the corrosion protection of structural materials. They are
interface active and form ultrathin corrosion inhibiting and adhesion-promoting
layers. Here we utilize thiol-based self-assembled monolayers (SAMs) as model
system for demonstrating a comprehensive combinatorial approach to understand
molecular level corrosion protection mechanisms under anodic polarization.
Specifically, we compare hydrophilic 11-Mercapto-1-undecanol and hydrophobic
1-Undecanethiol SAMs and their gold-dissolution inhibiting properties. We can
show that the intermolecular forces (hydrophobic vs hydrophilic effects)
control how SAM layers perform under oxidative conditions. Specifically, using
\textit{in situ} electrochemical AFM and a scanning-flow cell coupled to an
ICP-MS a complementary view on both corrosion resistance, as well as on changes
in surface morphology/adhesion of the SAM is possible. Protection from
oxidative dissolution is higher with hydrophobic SAMs, which detach under
micelle formation, while the hydrophilic SAM exhibits lower protective effects
on gold dissolution rates, although it stays intact as highly mobile layer
under anodic polarization. The developed multi-technique approach will prove
useful for studying the interfacial activity and corrosion suppression
mechanism of inhibiting molecules on other metals and alloys.",2105.00280v1
2021-05-04,Ostwald ripening in an oxide-on-metal system,"Ostwald ripening is a well-known physicochemical phenomenon in which smaller
particles, characterized by high surface energy, dissolve and feed the bigger
ones that are thermodynamically more stable. The effect is commonly observed in
solid and liquid solutions, as well as in systems consisting of supported metal
clusters or liquid droplets. Here, we provide the first evidence for the
occurrence of Ostwald ripening in an oxide-on-metal system which, in our case,
consists of ultrathin iron monoxide (FeO) islands grown on Ru(0001)
single-crystal support. The results reveal that the thermally-driven sintering
of islands allows altering their fine structural characteristics, including
size, perimeter length, defect density and stoichiometry, which are crucial,
e.g., from the point of view of heterogeneous catalysis.",2105.01229v2
2021-05-04,First Demonstration of Robust Tri-Gate \b{eta}-Ga2O3 Nano-membrane Field-Effect Transistors Operated Up to 400 °C,"Nano-membrane tri-gate beta-gallium oxide (\b{eta}-Ga2O3) field-effect
transistors (FETs) on SiO2/Si substrate fabricated via exfoliation have been
demonstrated for the first time. By employing electron beam lithography, the
minimum-sized features can be defined with a 50 nm fin structure. For
high-quality interface between \b{eta}-Ga2O3 and gate dielectric, atomic
layer-deposited 15-nm-thick aluminum oxide (Al2O3) was utilized with
Tri-methyl-aluminum (TMA) self-cleaning surface treatment. The fabricated
devices demonstrate extremely low subthreshold slope (SS) of 61 mV/dec, high
drain current (IDS) ON/OFF ratio of 1.5 X 109, and negligible transfer
characteristic hysteresis. We also experimentally demonstrated robustness of
these devices with current-voltage (I-V) characteristics measured at
temperatures up to 400 {\deg}C.",2105.01721v1
2021-05-06,Anticorrosion and biocompatibility of a functionalized layer formed on ZK60 Mg alloy via hydroxyl ion implantation,"Magnesium and its alloys have aroused tremendous interests because of their
promising mechanical properties and biocompatibility. However, their
excessively fast corrosion rate hinders the development of Mg alloys in the
biomedical fields. Inspired by conventional ion implantation, a less-toxic
functional group (hydroxyl) is used as the ion source to bombard the ZK60 Mg
alloy surface to form a functionalized oxide layer. This functionalized oxide
layer significantly facilitates the corrosion resistance of the ZK60 Mg alloy
substrate and the proliferation of MC3T3-E1 cells, which is confirmed by
electrochemical, immersion, and in vitro cytocompatibility tests. In comparison
with results of ZK60 alloy implanted with carboxyl ions in our previous work,
it is concluded that hydroxyl-treated alloys exhibit slightly higher corrosion
rate while better biocompatibility. In summary, less-toxic functional ion
implantation can be an effective strategy for inhibiting corrosion of Mg alloy
implants and promoting their biocompatibility.",2105.02558v1
2021-05-05,High Permittivity Dielectric Field-Plated Vertical (001) $β$-Ga$_2$O$_3$ Schottky Barrier Diode with Surface Breakdown Electric Field of 5.45 MV/cm and BFOM of $>$ 1 GW/cm$^{2}$,"This paper presents vertical (001) oriented $\beta$-Ga$_2$O$_3$ field plated
(FP) Schottky barrier diode (SBD) with a novel extreme permittivity dielectric
field oxide. A thin drift layer of 1.7 $\mu m$ was used to enable a
punch-through (PT) field profile and very low differential specific
on-resistance (R$_{on-sp}$) of 0.32 m$\Omega$-cm$^{2}$. The extreme
permittivity field plate oxide facilitated the lateral spread of the electric
field profile beyond the field plate edge and enabled a breakdown voltage
($V_{br}$) of 687 V. The edge termination efficiency increases from 13.5 $\%$
for non-field plated structure to 63 $\%$ for high permittivity field plate
structure. The surface breakdown electric field was extracted to be 5.45 MV/cm
at the center of the anode region using TCAD simulations. The high permittivity
field plated SBD demonstrated a record high Baliga figure of merit (BFOM) of
1.47 GW/cm$^{2}$ showing the potential of Ga$_2$O$_3$ power devices for
multi-kilovolt class applications.",2105.04413v1
2021-05-10,Understanding Carbon Contamination in Proton Conducting Oxides,"Carbon contamination is a significant concern for proton-conducting oxides in
the cerate and zirconate family, particularly for BaCeO$_3$. Here, we use
first-principles calculations to evaluate carbon stability in SrCeO$_3$,
BaCeO$_3$, SrZrO$_3$, and BaZrO$_3$. The cerates require more carbon-poor
environments to prevent carbonate formation, though this requirement can be
loosened through the use of more oxygen-poor growth conditions. Carbonate
formation is not the only concern, however. We find that interstitial carbon
has lower formation energies in the cerates relative to the zirconates, leading
to higher carbon concentrations that compete with the desired oxygen vacancy
formation. We also examine the mobility of carbon interstitials, finding that
both migration barriers and binding energies to acceptors are lower in the
cerates. As a result, the cerates are likely to degrade when exposed to carbon
at operating temperatures. Our results show definitively why the cerates are
less stable than the zirconates with respect to carbon and elucidate the
mechanisms contributing to their instability, thereby helping to explain why
alloying with zirconium will enhance their operational efficiency.",2105.04640v1
2021-05-10,Continuous wave laser thermal restoration of oxidized lead-based pigments in mural paintings,"Red lead and lead white are some of the most ancient and common pigments in
mural paintings. However, they tend to blacken with time due to their oxidation
to plattnerite (\b{eta}-PbO2). The possibility to induce the reconversion
reactions by CW laser heating is hereby discussed. A thermodynamic study by TGA
showed that direct cerussite or hydrocerussite formation from plattnerite are
not suitable reconversion routes, which was confirmed by laser irradiation
trials under CO2 and CO2/H2O fluxes. Minium (Pb3O4) and subsequent massicot
(\b{eta}-PbO) formation from plattnerite were achieved (confirmed by SEM-EDS,
XRD and micro-Raman) under Ar+, 810 nm diode and Nd:YAG lasers. The latter
appears to be the most suited for restauration purposes, given the broad minium
reconversion irradiance range. This is confirmed by successful trials on
macroscopic areas of naturally darkened red lead containing samples.",2105.04677v2
2021-05-18,Rashba dominated spin-splitting in the bulk ferroelectric oxide perovskite KIO3,"The momentum-dependent Rashba and Dresselhaus spin-splitting has gained much
attention for its highly promising applications in spintronics. In the present
work, ab initio density functional theory calculations are performed to study
the spin-splitting effect in ferroelectric oxide perovskite KIO3. Our
calculations are additionally supported by symmetry adapted two-band k.p
Hamiltonian. Non-negligible spin-splitting effect is observed at conduction
band minimum (CBm) and valence band maximum (VBM) for rhombohedral R3m and R3c
phases. Linear Rashba terms successfully explain the splitting at VBM. However,
cubic terms become important in realizing spin-orientation near CBm. Our
results show the enhancement in Rashba parameters on tuning the ferroelectric
order parameter. Further, we have observed reversal of spin-orientation on
switching the direction of polarization.",2105.08452v1
2021-05-19,Ferroelectricity promoted by cation/anion divacancies in SrMnO$_3$,"We investigate the effect of polar Sr-O vacancy pairs on the electric
polarization of SrMnO$_3$ (SMO) thin films using density functional theory
(DFT) calculations. This is motivated by indications that ferroelectricity in
complex oxides can be engineered by epitaxial strain but also \textit{via} the
defect chemistry. Our results suggest that intrinsic doping by cation and anion
divacancies can induce a local polarization in unstrained non-polar SMO thin
films and that a ferroelectric state can be stabilized below the critical
strain of the stoichiometric material. This polarity is promoted by the
electric dipole associated with the defect pair and its coupling to the atomic
relaxations upon defect formation that polarize a region around the defect.
This suggests that polar defect pairs affect the strain-dependent
ferroelectricity in semiconducting antiferromagnetic SMO. For metallic
ferromagnetic SMO we find a much weaker coupling between the defect dipole and
the polarization due to much stronger electronic screening. Coupling of
defect-pair dipoles at high enough concentrations along with their switchable
orientation thus makes them a promising route to affect the ferroelectric
transition in complex transition metal oxide thin films.",2105.09360v1
2021-05-20,In-situ X-ray analysis of misfit strain and curvature of bent polytypic GaAs-In(x)Ga(1-x)As core-shell nanowires,"Misfit strain in core-shell nanowires can be elastically released by nanowire
bending in case of asymmetric shell growth around the nanowire core. In this
work, we investigate the bending of GaAs nanowires during the asymmetric
overgrowth by an In(x)Ga(1-x)As shell caused by avoiding substrate rotation. We
observe that the nanowire bending direction depends on the nature of the
substrate's oxide layer, demonstrated by Si substrates covered by native and
thermal oxide layers. Further, we follow the bending evolution by time-resolved
in-situ X-ray diffraction measurements during the deposition of the asymmetric
shell. The XRD measurements give insight into the temporal development of the
strain as well as the bending evolution in the core-shell nanowire.",2105.09665v1
2021-05-25,A decatungstate-based Ionic liquid exhibiting very low dielectric constant suitable for acting as solvent and catalyst for oxidation of organic substrates,"In this contribution, a new POM-based ionic liquid, namely
(P6,6,6,14)4[W10O32], was fully characterized. Its viscosity and its very low
dielectric constant make this hybrid ionic liquid suitable to be used as
solvent for organic transformations. As proof of concept, this unique ionic
liquid combining solvant and catalyst properties was tested for catalytic
oxidation of various alcohols and alkenes in presence of H2O2",2105.11714v1
2021-05-27,Pushing the Study of Point Defects in Thin Film Ferrites to Low Temperatures Using In Situ Ellipsometry,"Unveiling point defects concentration in transition metal oxide thin films is
essential to understand and eventually control their functional properties,
employed in an increasing number of applications and devices. Despite this
unquestionable interest, there is a lack of available experimental techniques
able to estimate the defect chemistry and equilibrium constants in such oxides
at intermediate-to-low temperatures. In this study, the defect chemistry of a
relevant material such as La1-xSrxFeO3-d (LSF) with (x = 0.2, 0.4 and 0.5
(LSF20, LSF40 and LSF50 respectively) is obtained by using a novel in situ
spectroscopic ellipsometry approach applied to thin films. Through this
technique, the concentration of holes in LSF is correlated to measured optical
properties and its evolution with temperature and oxygen partial pressure is
determined. In this way, a systematic description of defect chemistry in LSF
thin films in the temperature range from 350dC to 500dC is obtained for the
first time, which represents a step forward in the understanding of LSF20,
LSF40 and LSF50 for emerging low temperature applications.",2105.13039v1
2021-05-28,Nafion-induced reduction of manganese and its impact on the electrocatalytic properties of a highly active MnFeNi oxide for bifunctional oxygen conversion,"Electrocatalysts for bifunctional oxygen reduction (ORR) and oxygen evolution
reaction (OER) are commonly studied under hydrodynamic conditions, rendering
the use of binders necessary to ensure the mechanical stability of the
electrode films. The presence of a binder, however, may influence the
properties of the materials under examination to an unknown extent. Herein, we
investigate the impact of Nafion on a highly active ORR/OER catalyst consisting
of MnFeNi oxide nanoparticles supported on multi-walled carbon nanotubes.
Electrochemical studies revealed that, in addition to enhancing the mechanical
stability and particle connectivity, Nafion poses a major impact on the ORR
selectivity, which correlates with a decrease in the valence state of Mn
according to X-ray absorption spectroscopy. These findings call for awareness
regarding the use of electrode additives, since in some cases the extent of
their impact on the properties of electrode films cannot be regarded as
negligible.",2105.13888v1
2021-05-31,Effect of Zr and Al Addition on Nanocluster Formation in Oxide Dispersion Strenghthened Steel-an ab initio Study,"Conventional Oxide dispersion strengthened steels are characterized by
thermally stable, high density of Y-Ti-O nanoclusters, which are responsible
for their high creep strength. Ti plays a major role in obtaining a high
density of ultrafine particles of optimum size range of 2-10 nm. In
Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters
formed are of size range 20 -100 nm, and Ti fails in making dispersions finer
in the presence of Al. Usage of similar alloying elements like Zr in place of
Ti is widely considered. In this study, binding energies of different stages of
Y-Zr-O-Vacancy and Y-Al-O-Vacancy complexes in the bcc Iron matrix are studied
by first-principle calculations. It is shown that in all the stages of
formation, Y-Zr-O-Vacancy clusters have higher binding energy than
Y-Al-O-Vacancy clusters and hence in ferritic steel containing both Zr and Al,
Y-Zr-O-Vacancy clusters are more stable and more favored to nucleate than
Y-Al-O-Vacancy clusters. The bonding nature in each stage is analyzed using
charge density difference plots for the plausible reason for higher stability
of Y-Zr-O-Vacancy clusters.",2105.15063v1
2021-06-02,Environmental Sensitivity of Fabry-Perot Microcavities Induced By Layered Graphene-Dielectric Hybrid Coatings,"We propose a fiber-based environmental sensor that exploits the reflection
phase shift tunability provided by the use of layered coatings composed of
dielectric slabs spaced by conducting membranes. A transfer matrix study is
done in a simplified theoretical model, for which an enhanced sensitivity of
the reflection interference pattern to the output medium is demonstrated, in
the typical refractive index range of liquid media. An experimental
configuration using a cascaded Fabry-Perot microcavity coated by a graphene
oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its
cost effective chemical production method makes graphene oxide-based hybrid
coatings excellent candidates for future real-life sensing devices.",2106.01287v2
2021-06-06,"Modeling Temperature, Frequency, and Strain Effects on the Linear Electro-Optic Coefficients of Ferroelectric Oxides","An electro-optic modulator offers the function of modulating the propagation
of light in a material with electric field and enables seamless connection
between electronics-based computing and photonics-based communication. The
search for materials with large electro-optic coefficients and low optical loss
is critical to increase the efficiency and minimize the size of electro-optic
devices. We present a semi-empirical method to compute the electro-optic
coefficients of ferroelectric materials by combining first-principles
density-functional theory calculations with Landau-Devonshire phenomenological
modeling. We apply the method to study the electro-optic constants, also called
Pockels coefficients, of three paradigmatic ferroelectric oxides: BaTiO3,
LiNbO3, and LiTaO3. We present their temperature-, frequency- and
strain-dependent electro-optic tensors calculated using our method. The
predicted electro-optic constants agree with the experimental results, where
available, and provide benchmarks for experimental verification.",2106.02998v3
2021-06-07,Efficiency limits of Perovskite Solar Cells with Transition Metal Oxides as Hole Transport Layers,"Transition metal oxides (TMOs) like MoOx are increasingly explored as hole
transport layers for perovskite-based solar cells. Due to their large work
function, the hole collection mechanism of such solar cells are fundamentally
different from other materials like PEDOT: PSS, and the associated device
optimizations are not well elucidated. In addition, the prospects of such
architectures against the challenges posed by ion migration are yet to be
explored - which we critically examine in this contribution through detailed
numerical simulations. Curiously, we find that, for similar ion densities and
interface recombination velocities, ion migration is more detrimental for
Perovskite solar cells with TMO contact layers with much lower achievable
efficiency limits (21%). The insights shared by this work should be of broad
interest to the community in terms of long-term stability, efficiency
degradation and hence could help critically evaluate the promises and prospects
of TMOs as hole contact layers for perovskite solar cells.",2106.03881v1
2021-06-08,Increased hole mobility in anti-ThCr$_2$Si$_2$-type La$_2$O$_2$Bi co-sintered with alkaline earth metal oxides for oxygen intercalation and hole carrier doping,"Metallic anti-ThCr$_2$Si$_2$-type $RE_2$O$_2$Bi ($RE$ = rare earth) with Bi
square nets show superconductivity while insulating La$_2$O$_2$Bi shows high
hole mobility, by expanding the c-axis length through oxygen intercalation. In
this study, alkaline earth metal oxides (CaO, SrO, and BaO) were co-sintered
with La$_2$O$_2$Bi. CaO and BaO served as oxygen intercalants without
incorporation of Ca and Ba in La$_2$O$_2$Bi. On the other hand, SrO served as
not only oxygen intercalant but also hole dopant via Sr substitution with La in
La$_2$O$_2$Bi. The oxygen intercalation and hole doping resulted in expansion
of the c-axis length, contributing to improved electrical conduction. In
addition, the hole mobility was enhanced up to 150 cm$^2$V$^{-1}$s$^{-1}$ in
La$_2$O$_2$Bi, which almost doubles the mobility in previous study.",2106.04717v1
2021-06-18,Electrical tuning of the spin-orbit interaction in nanowire by transparent ZnO gate grown by atomic layer deposition,"We develop an InAs nanowire gate-all-around field-effect transistor using a
transparent conductive zinc oxide (ZnO) gate electrode, which is in-situ atomic
layer deposited after growth of gate insulator of Al2O3. We perform
magneto-transport measurements and find a crossover from weak localization to
weak antilocalization effect with increasing gate voltage, which demonstrates
that the Rashba spin-orbit coupling is tuned by the gate electrode. The
efficiency of the gate tuning of the spin-orbit interaction is higher than
those obtained for two-dimensional electron gas, and as high as that for a
gate-all-around nanowire metal-oxide-semiconductor field-effect transistor that
was previously reported. The spin-orbit interaction is discussed in line with
not only conventionally used one-dimensional model but also recently proposed
model that considers effects of microscopic band structures of materials.",2106.10036v1
2021-06-21,Nanocrystalline superconducting $γ$-Mo$_2$N ultra-thin films for single-photon detectors,"We analyze the influence of the surface passivation produced by oxides on the
superconducting properties of $\gamma$-Mo$_2$N ultra-thin films. The
superconducting critical temperature of thin films grown directly on Si (100)
with those using a buffer and a capping layer of AlN are compared. The results
show that the cover layer avoids the presence of surface oxides, maximizing the
superconducting critical temperature for films with thicknesses of a few
nanometers. We characterize the flux-flow instability measuring current-voltage
curves in a 6.4 nm thick Mo$_2$N film with a superconducting critical
temperature of 6.4 K. The data is analyzed using the Larkin and Ovchinnikov
model. Considering self-heating effects due to finite heat removal from the
substrate, we determine a fast quasiparticle relaxation time $\approx$ 45 ps.
This value is promising for its applications in single-photon detectors.",2106.10781v1
2021-07-13,Spatiotemporal refraction of light in an epsilon-near-zero ITO layer,"When light travels through a medium in which the refractive index is rapidly
changing with time, the light will undergo a shift in its frequency. Large
frequency shifting effects have recently been reported for transparent
conductive oxides. These observations have been interpreted as emerging from
temporal changes to the propagation phase in a bulk medium resulting from
temporal variations in the refractive index, an effect referred to as temporal
refraction. Here, we show that the frequency shift in an epsilon-near-zero
(ENZ) layer made of indium tin oxide (ITO) originates not only from this bulk
response, but includes a significant effect resulting from temporal changes to
the spatial boundary conditions. This boundary effect can lead to a dominant
opposing shift to the bulk effect for certain angles. Hence, this process gives
rise to a frequency shift that can be tailored through the angle of incidence,
decoupling the amplitude and phase modulation.",2107.05970v1
2021-07-23,Controlled oxygen plasma treatment of single-walled carbon nanotube films improves osteoblast cells attachment and enhances their proliferation,"The effects of oxidative treatment of single-walled carbon nanotubes (SWCNTs)
on the adhesion and proliferation of human osteoblasts (SAOS-2) were
investigated. The surface properties of SWCNTs after oxygen plasma treatment
were characterised by contact angle measurement, scanning electron microscopy
and Raman spectroscopy. The immunofluorescent staining of vinculin, actin
filaments and nuclei was used to probe cell adhesion and growth on SWCNT films.
Our results show that adhesion and proliferation of human osteoblasts
cultivated on SWCNT films indeed depends on the degree of an oxidative
treatment. As an optimal procedure was found the treatment with oxygen plasma
for 5 min. In the latter case the osteoblasts form a confluent layer with
pronounced focal adhesions throughout the entire cell body. The optimal
conditions compromise the effect of hydrophilic character of SWCNT films and
the level of damage of SWCNT surface.",2107.11294v1
2021-07-25,Formation of Copper oxide II in polymer solution-blow-spun fibers and the successful non-woven ceramic production,"Copper oxide II is a p-type semiconductor that can be used in several
applications. Focusing on producing such material using an easy and low-cost
technique, we followed an acetate one-pot-like route for producing a polymer
precursor solution with different acetates:PVP (polyvinylpyrrolidone) weight
ratios. Then, composite nanofibers were produced using the solution blow
spinning (SBS) technique. The ceramic CuO samples were obtained after a
calcination process at 600 oC for two hours, applying a heating rate of 0.5
oC/min. Non-woven fabric-like ceramic samples with average diameters lower than
300 nm were successfully obtained. SEM images show relatively smooth fibers
with a granular morphology. XRD shows the formation of randomly oriented grains
of CuO. In addition, FTIR and XRD analyses show the CuO formation before the
heat treatment. Thus, a chemical reaction sequence was proposed to explain the
results.",2107.11704v1
2021-07-26,Fracture and Fatigue of Thin Crystalline SrTiO$_3$ Membranes,"The increasing availability of a variety of two-dimensional materials has
generated enormous growth in the field of nanoengineering and nanomechanics.
Recent developments in thin film synthesis have enabled the fabrication of
freestanding functional oxide membranes that can be readily incorporated in
nanomechanical devices. While many oxides are extremely brittle in bulk, recent
studies have shown that, in thin membrane form, they can be much more robust to
fracture as compared to their bulk counterparts. Here, we investigate the
ultimate tensile strength of SrTiO$_3$ membranes by probing freestanding
SrTiO$_3$ drumheads using an atomic force microscope. We demonstrate that
SrTiO$_3$ membranes can withstand an elastic deformation with an average strain
of ~6% in the sub-20 nm thickness regime, which is more than an order of
magnitude beyond the bulk limit. We also show that these membranes are highly
resilient upon a high cycle fatigue test, surviving up to a billion cycles of
force modulation at 85% of their fracture strain, demonstrating their high
potential for use in nanomechanical applications.",2107.12468v1
2021-08-20,Thickness Dependent OER Electrocatalysis of Epitaxial LaFeO$_{3}$ Thin Films,"Transition metal oxides have long been an area of interest for water
electrocatalysis through the oxygen evolution and oxygen reduction reactions.
Iron oxides, such as LaFeO$_{3}$, are particularly promising due to the
favorable energy alignment of the valence and conduction bands comprised of
Fe$^{3+}$ cations and the visible light band gap of such materials. In this
work, we examine the role of band alignment on the electrocatalytic oxygen
evolution reaction (OER) in the intrinsic semiconductor LaFeO$_{3}$ by growing
epitaxial films of varying thicknesses on Nb-doped SrTiO$_{3}$. Using cyclic
voltammetry and electrochemical impedance spectroscopy, we find that there is a
strong thickness dependence on the efficiency of electrocatalysis for OER.
These measurements are understood based on interfacial band alignment in the
system as confirmed by layer-resolved electron energy loss spectroscopy and
electrochemical Mott-Schottky measurements. Our results demonstrate the
importance of band engineering for the rational design of thin film
electrocatalysts for renewable energy sources.",2108.09360v1
2021-08-20,Nonreciprocal ENZ-Dielectric Bilayers: Enhancement of Nonreciprocity from a Nonlinear Transparent Conducting Oxide Thin Film at Epsilon-Near-Zero (ENZ) Frequency,"We envision the use of an indium tin oxide (ITO) thin film as part of a
bi-layered silicon-photonics subwavelength device to boost
nonlinearity-assisted all-passive nonreciprocal behavior. The asymmetric
p-polarized oblique excitation of a mode near the epsilon-near-zero (ENZ)
frequency, with highly-confined and enhanced normal electric field component
and large absorption, allows to harness ITO's strong ultrafast nonlinear
response for the generation of a notable nonreciprocal performance in the
two-port element. Though limited by loss, we find the device's optimal
operational point and the maximum nonreciprocal transmittance ratio attainable
vs. light intensity -- including an apparent upper bound slightly over 2 --,
and we perform exhaustive numerical simulations considering nonlinear processes
of both anharmonic and thermal nature that validate our predictions, including
steady-state and pulsed-laser excitations.",2108.09381v1
2021-08-23,Z$_2$ nontrivial topology of rare-earth binary oxide superconductor,"Recently, superconductivity has been discovered in rock-salt structured
binary lanthanum monoxide LaO through state-of-the-art oxide thin-film epitaxy.
In this work, we reveal that the normal state of superconducting LaO is a $Z_2$
nontrivial topological metal, where the Dirac point protected by the crystal
symmetry is located around the Fermi energy. By analysing the orbital
characteristics, we show that the nature of the topological band structure of
LaO originates from the intra-atomic transition from the outer shell La 5$d$ to
the inner shell 4$f$ orbitals driven by the strong octahedral crystal-field.
Furthermore, the appearance of novel surface states unambiguously demonstrates
the topological signature of LaO superconductor. Our theoretical findings not
only shed new light into the understanding of the exotic quantum behaviors in
LaO superconductor with intimate correlation between 4$f$ and 5$d$ orbitals in
La, but also provide an exciting platform to explore the interplay between
nontrivial topology and superconductivity.",2108.10063v2
2021-08-24,Non-classical nucleation of zinc oxide from a physically-motivated machine-learning approach,"Observing non-classical nucleation pathways remains challenging in
simulations of complex materials with technological interests. This is because
it requires very accurate force fields that can capture the whole complexity of
their underlying interatomic interactions and an advanced structural analysis.
Here, we first report the construction of a machine-learning force field for
zinc oxide interactions using the Physical LassoLars Interaction Potentials
approach which allows us to be predictive even for untrained structures. Then,
we carried out freezing simulations from a liquid and observed the crystal
formation with atomistic precision. Our results, which are analyzed using a
data-driven approach based on bond order parameters, demonstrate the presence
of both prenucleation clusters and two-step nucleation scenarios thus
retrieving seminal predictions of non-classical nucleation pathways made on
much simpler models.",2108.10601v2
2021-08-25,Variational quantum eigensolver techniques for simulating carbon monoxide oxidation,"A family of Variational Quantum Eigensolver (VQE) methods is designed to
maximize the resource of existing noisy intermediate-scale quantum (NISQ)
devices. However, VQE approaches encounter various difficulties in simulating
molecules of industrially relevant sizes, among which the choice of the ansatz
for the molecular wavefunction plays a crucial role. In this work, we push
forward the capabilities of adaptive variational algorithms (ADAPT-VQE) by
demonstrating that the measurement overhead can be significantly reduced via
adding multiple operators at each step while keeping the ansatz compact. Within
the proposed approach, we simulate a set of molecules, O$_2$, CO, and CO$_2$,
participating in the carbon monoxide oxidation processes using the statevector
simulator and compare our findings with the results obtained using VQE-UCCSD
and classical methods. Based on these results, we estimate the energy
characteristics of the chemical reaction. Our results pave the way to the use
of variational approaches for solving practically relevant chemical problems.",2108.11167v3
2021-09-01,"Recent Progress on Synthesis, Characterization, and Applications of Metal Halide Perovskites@Metal Oxide","Metal halide perovskites (MHPs) have become a promising candidate in a myriad
of applications, such as light-emitting diodes, solar cells, lasing,
photodetectors, photocatalysis, transistors, etc. This is related to the
synergy of their excellent features, including high photoluminescence quantum
yields, narrow and tunable emission, long charge carrier lifetimes, broad
absorption spectrum along with high extinction absorptions coefficients, among
others. However, the main bottleneck is the poor stability of the MHPs under
ambient conditions. This is imposing severe restrictions with respect to their
industrialized applications and commercialization. In this context, metal oxide
(MOx) coatings have recently emerged as an efficient strategy towards
overcoming the stabilities issues as well as retain the excellent properties of
the MHPs, and therefore facilitate the development of the related devices
stabilities and performances.This review provides a summary of the recent
progress on synthetic methods, enhanced features, the techniques to assess the
MHPs-MOxcomposites, and applications of the MHPs@MOx.Specially, novel
approaches to fabricate the composites and new applications of the composites
are also reported in this review for the first time. This is rounded by a
critical outlook about the current MHPs stability issues and the further
direction to ensure a bright future of MHPs@MOx",2109.00508v1
2021-09-04,Physical limits of ultra-high-finesse optical cavities: Taming two-level systems of glassy metal oxides,"The framework of tunnelling states in amorphous media provides the
dissipative mechanism that imposes fundamental limits on the performances of
ultra-high-Q optical and microwave resonators. In the optical domain, however,
the microscopic nature of the tunnelling states and their direct consequences
to the optical losses have not been characterized. In this work, we examine the
interplay between glassy physics and stoichiometric point defects of
ultra-low-loss dielectric mirrors, with a focus on two-level systems of oxygen
defects in metal oxide, Ta$_2$O$_5$. In the context of ultra-high-finesse
optical cavities, we characterize the Urbach tail of Ta$_2$O$_5$ under thermal
annealing and reactive oxygen plasma. For the first time, we microscopically
resolve the individual oxygen point defects on the mirror surfaces and
introduce laser-assisted annealing to selectively ""cure"" surface defects. By
exploiting these techniques, we report the realization of ultra-high-finesse
optical cavity with finesse $\mathcal{F}=450,000$ and the absorption-scatter
loss $ 0.1 \pm 0.2$ ppm at $852$ nm.",2109.01856v1
2021-09-05,Discovery and Engineering of Low Work Function Perovskite Materials,"Materials with low work functions are critical for an array of applications
requiring the facile removal or efficient transport of electrons through a
device. Perovskite oxides are a promising class of materials for finding low
work functions, and here we target applications in thermionic and field
electron emission. Perovskites have highly malleable compositions which enable
tunable work function values over a wide range, robust stability at high
temperatures, and high electronic conductivities. In this work, we screened
over 2900 perovskite oxides in search of stable, conductive, low-work-function
materials using Density Functional Theory (DFT) methods. Our work provides
insight into the materials chemistry governing the work function value of a
perovskite, where materials with barely filled d bands possess the lowest work
functions. Our screening has resulted in a total of seven promising compounds,
such as BaMoO3 and SrNb0.75Co0.25O3 with work functions of 1.1 eV and 1.5 eV,
respectively. These promising materials and others presented in this study may
find use as low work function electron emitters in high power vacuum electronic
and thermionic energy conversion devices. Moreover, the database of calculated
work functions and materials chemistry trends governing the value of the work
function may aid in the engineering of perovskite heterojunction devices.",2109.02005v1
2021-09-14,Sparse expansions of multicomponent oxide configuration energy using coherency & redundancy,"Compressed sensing has become a widely accepted paradigm to construct high
dimensional cluster expansion models used for statistical mechanical studies of
atomic configuration in complex multicomponent crystalline materials. However,
strict sampling requirements necessary to obtain minimal coherence measurements
for compressed sensing to guarantee accurate estimation of model parameters are
difficult and in some cases impossible to satisfy due to the inability of
physical systems to access certain configurations. Nevertheless, the dependence
of energy on atomic configuration can still be adequately learned without these
strict requirements by using compressed sensing by way of coherent measurements
using redundant function sets known as frames. We develop a particular frame
constructed from the union of all occupancy-based cluster expansion basis sets.
We illustrate how using this highly redundant frame yields sparse expansions of
the configuration energy of complex oxide materials that are competitive and
often surpass the prediction accuracy and sparsity of models obtained from
standard cluster expansions.",2109.06905v2
2021-09-17,Effect of Buffer Termination on Intermixing and Conductivity in LaTiO$_3$/SrTiO$_3$ Heterostructures Integrated on Si(100),"The control of chemical exchange across heterointerfaces formed between
ultra-thin functional transition-metal oxide layers provides an effective route
to manipulate the electronic properties of these systems. We show that cationic
exchange across the interface between the Mott insulator, LaTiO$_3$(LTO) grown
epitaxially on SrTiO$_3$(STO)-buffered Silicon by molecular beam epitaxy
depends strongly on the surface termination of the strained STO buffer. Using a
combination of temperature-dependent transport and synchrotron X-ray crystal
truncation rods and reciprocal space mapping, an enhanced conductivity in
STO/LTO/SrO- terminated STO buffers compared to heterostructures with
TiO$_2$-terminated STO buffers is correlated with La/Sr exchange and the
formation of metallic La$_{1-x}$Sr$_x$TiO$_3$. La/Sr exchange effectively
reduces the strain energy of the system due to the large lattice mismatch
between the nominal oxide layers and the Si substrate.",2109.08586v1
2021-09-27,"Layered, Tunable Graphene Oxide-Nylon Heterostructures for Wearable Electrocardiogram Sensors","Nanoscale engineered materials combined with wearable wireless technologies
can deliver a new level of health monitoring. A reduced graphene oxide-nylon
composite material is developed and tested, demonstrating its usefulness as a
material for sensors in wearable, long-term electrocardiogram (ECG) monitoring
via a comparison to one of the widely used ECG sensors. The structural analysis
by scanning electron (SEM) and atomic force microscopy (AFM) shows a limited
number of defects on a macroscopic scale. Fourier Transform Infrared (FTIR) and
Raman spectroscopy confirm the presence of rGOx, and the ratio of D- and
G-features as a function of thickness correlates with the resistivity analysis.
The negligible effect of the defects and the tunability of electrical and
optical properties, together with live ECG data, demonstrate its signal
transduction capability.",2109.12739v2
2021-09-27,Surface Reduction State Determines Stabilization and Incorporation of Rh on α-Fe2O3(1-102),"Iron oxides (FeOx) are among the most common support materials utilized in
single atom catalysis. The support is nominally Fe2O3, but strongly reductive
treatments are usually applied to activate the as-synthesized catalyst prior to
use. Here, we study Rh adsorption and incorporation on the (1-102) surface of
hematite ({\alpha}-Fe2O3), which switches from a stoichiometric (1x1)
termination to a reduced (2x1) reconstruction in reducing conditions. Rh atoms
form clusters at room temperature on both surface terminations, but Rh atoms
incorporate into the support lattice as isolated atoms upon annealing above 400
{\deg}C. Under mildly oxidizing conditions, the incorporation process is so
strongly favoured that even large Rh clusters containing hundreds of atoms
dissolve into the surface. Based on a combination of low energy ion scattering
and scanning tunnelling microscopy data, as well as density functional theory,
we conclude that the Rh atoms are stabilized in the immediate subsurface,
rather than the surface layer.",2109.13084v1
2021-09-29,"Nonreciprocal transport in a Rashba ferromagnet, delafossite PdCoO$_2$","Rashba interfaces yield efficient spin-charge interconversion and give rise
to nonreciprocal transport phenomena. Here, we report magnetotransport
experiments in few-nanometer-thick films of PdCoO$_2$, a delafossite oxide
known to display a large Rashba splitting and surface ferromagnetism. By
analyzing the angle dependence of the first- and second-harmonic longitudinal
and transverse resistivities, we identify a Rashba-driven unidirectional
magnetoresistance that competes with the anomalous Nernst effect below the
Curie point. We estimate a Rashba coefficient of 0.75 {\pm} 0.3 eV {\AA} and
argue that our results qualify delafossites as a new family of oxides for
nano-spintronics and spin-orbitronics, beyond perovskite materials.",2109.14503v1
2021-10-02,The role of surface spin polarization on ceria-supported Pt nanoparticles,"In this work, we employ first-principles simulations to investigate the spin
polarization of CeO$_2$-(111) surface and its impact on interactions between a
ceria support and Pt nanoparticles. For the first time, we report that the
CeO$_2$-(111) surface exhibits a robust surface spin polarization due to the
internal charge transfer between atomic Ce and O layers. In turn, it can lower
the surface oxygen vacancy formation energy and enhance the oxide reducibility.
We show that the inclusion of spin polarization can therefore significantly
reduce the major activation barrier in the proposed reaction pathway of CO
oxidation on ceria-supported Pt nanoparticles. For metal-support interactions,
surface spin polarization enhances the bonding between Pt nanoparticle and
ceria surface oxygen, while CO adsorption on Pt nanoparticles weakens the
interfacial interaction regardless of spin polarization.",2110.00710v1
2021-10-07,A Modern-day Alchemy: Double Glow Plasma Surface Metallurgy Technology,"In the long history of science and technology development, one goal is to
diffuse solid alloy elements into the surface of steel materials to form
surface alloys with excellent physical and chemical properties. On the basis of
plasma nitriding technology, double glow plasma surface metallurgy technology
has answered this challenge. This technology, which seems to be a modern-day
alchemy, can use any element in the periodic table of chemical elements,
including solid metal elements and their combinations, to form many types of
surface alloyed layers with high hardness, wear resistance, corrosion
resistance and high temperature oxidation resistance on various metal
materials. For examples, nickel base alloys, stainless steels and high speed
steels are formed on the surfaces of ordinary carbon steels; and high hardness,
wear resistance and high temperature oxidation resistance alloy are formed on
the surface of titanium alloy.This article briefly introduces the formation and
principle of double glow plasma surface metallurgy technology, and summarizes
the experimental results and industry application. The significance and
development prospect of this technology are discussed.",2110.03236v1
2021-10-08,Charge capacity characteristics of a Lithium Nickel-Cobalt-Aluminium Oxide battery show fractional-derivative behavior,"Batteries experience capacity offset where available charge depends on the
rate at which this charge is drawn. In this work we analyze the capacity offset
of a 4.8 A h lithium nickel-cobalt-aluminium oxide battery using an equivalent
circuit model of a fractional capacitor in series with a resistor. In this
case, the available charge, in theory, becomes infinite in the limit of
infinitesimal rate. We show that the fractional properties of the capacitor can
be extracted from the charge against rate plot. We then use a network of RC
elements to represent the fractional capacitor in order to simulate the data
with Matlab. We find that the fractional exponent alpha obtained in this way,
0.971, agrees with that obtained in a more traditional manner from an impedance
versus frequency plot, although the fractional capacity does not. Such an
approach demonstrates the importance of a fractional description for capacity
offset even when an element is nearly a pure capacitor and is valuable for
predictions of state-of-charge when low currents are drawn.",2110.03883v1
2021-10-12,High-mobility field-effect transistor using 2-dimensional electron gas at the LaScO3/BaSnO3 interface,"A novel 2-dimensional electron gas (2DEG) system with high-mobility was
discovered at the interface of two perovskite oxides, a polar orthorhombic
perovskite LaScO3 (LSO) and a nonpolar cubic perovskite BaSnO3 (BSO). Upon
depositing the LSO film on the BSO film, the conductance enhancement and the
resulting 2DEG density (n2D) was measured. Comparing the results with the
previously reported LaInO3/BaSnO3 (LIO/BSO) polar interface, we applied the
interface polarization model to the LSO/BSO system, in which the polarization
exists only over 4 pseudocubic unit cells in LSO from the interface and
vanishes afterward like the LIO/BSO interface. Based on the calculations of the
self-consistent Poisson-Schrodinger equations, the LSO thickness dependence of
n2D of LSO/BSO heterointerface is consistent with this model. Furthermore, a
single subband in the quantum well is predicted. Using the conductive interface
and the LSO as a gate dielectric, a 2DEG transistor composed of only perovskite
oxides with high field-effect mobility (uFE) close to 100 cm2 V-1 s-1 is
demonstrated.",2110.05738v1
2021-10-18,Ambipolar Property of Isolated Hydrogen in Oxide Materials Revealed by Muon,"The study on the electronic state of muon as pseudo-hydrogen (represented by
the elemental symbol Mu) has long been appreciated as one of the few methods to
experimentally access the electronic state of dilute hydrogen (H) in
semiconductors and dielectrics. Meanwhile, theoretical predictions on the
electronic state of H in these materials by first-principles calculations using
density functional theory (DFT) do not always agree with the observed states of
Mu, standing as an obstacle to integrating the findings of both Mu and H. In
this paper, we provide resolution to this problem by a semi-quantitative model
that enables systematic understanding of the electronic states of Mu in most
oxides.",2110.09024v2
2021-10-27,Understanding the nonlinear optical response of epsilon near zero materials in the time-domain,"The promise of active nanophotonics technology relies on the confinement and
control of light at the nanoscale. Confinement via plasmonics, dielectric
resonators, and waveguides can be complemented with materials whose optical
properties can be controlled using nonlinear effects. Transparent conducting
oxides (TCOs) exhibit strong optical nonlinearities in their near zero
permittivity spectral region, on the femtosecond time-scale. Harnessing full
control over the nonlinear response requires a deeper understanding of the
process. To achieve this, we develop a self-consistent time-domain model for
the nonlinear optical response of TCOs and implement it into a
three-dimensional finite-difference time-domain code. We compare and tune our
simulation tools against recently published experimental results for intense
laser irradiation of thin indium tin oxide (ITO) films. Finally, by simulating
intense laser irradiation of ITO-based plasmonic metasurfaces, we demonstrate
the full power of our approach. As expected, we find validating the significant
enhancement of the nonlinear response of an ITO-based metasurface over bare ITO
thin films. Our work thus enables quantitative nanophotonics design with
epsilon-near-zero materials.",2110.14806v1
2021-11-01,Induced Giant Piezoelectricity in Centrosymmetric Oxides,"Piezoelectrics are materials that linearly deform in response to an applied
electric field. As a fundamental prerequisite, piezoelectric material must
possess a non centrosymmetric crystal structure. For more than a century, this
remains the major obstacle for finding new piezoelectric materials. We
circumvent this limitation by breaking the crystallographic symmetry, and
inducing large and sustainable piezoelectric effects in centrosymmetric
materials by electric field induced rearrangement of oxygen vacancies
Surprisingly, the results show the generation of extraordinarily large
piezoelectric responses d33 ~200,000 pm/V), in cubic fluorite Gd-doped CeO2-x
films, which is two orders of magnitude larger than in the presently best known
lead based piezoelectric relaxor ferroelectric oxide. These findings open
opportunities to design new piezoelectric materials from environmentally
friendly centrosymmetric ones.",2111.00829v3
2021-11-02,Local laser oxidation of titanium film for post-fabrication trimming of photonic integrated circuits,"Local laser oxidation of a thin titanium film is considered as a means of a
precise adjustment of losses and effective refractive index of dielectric
optical waveguides. A fine phase control of an operating point and extinction
ratio enhancement up to 57 dB were demonstrated using an integrated optical
Ti:LiNbO3 Mach-Zehnder modulator. This technique only slightly affects the
dielectric waveguide material and is very promising for a high precision
permanent trimming of photonic devices based on dielectric waveguides of
different material platforms and fabrication technologies.",2111.02884v2
2021-11-04,Glass-like Electronics in Vanadium Dioxide,"Functional materials can offer new paradigms for miniaturized and
energy-efficient electronics, providing a complementary or even alternative
platform to metal-oxide-semiconductors. Here we report on electronically
accessible long-lived structural states in Vanadium Dioxide that can offer a
scheme for data storage and processing. We show that such states can be
electrically manipulated and tracked beyond 10,000 seconds after excitation,
exhibiting similar features of glasses, which are beyond the classic
metastability in Mott systems. Glass-like electronics can potentially overcome
some of the fundamental limitations in conventional metal-oxide-semiconductor
electronics, and open avenues for neuromorphic computation and multi-level
memories.",2111.03181v1
2021-10-07,Chlorine-free electrochemical disinfection using graphene sponge electrodes,"Graphene sponge electrodes were employed for chlorine-free inactivation of
Escherichia coli from low conductivity water. The nitrogen-doped reduced
graphene oxide (NRGO) sponge anode bearing more positive charge achieved
complete E. coli inactivation (i.e., 5 log removal) in the anode-cathode
configuration at 115 A m-2, versus 2.6 log removal using boron-doped reduced
graphene oxide sponge anode. The bacteria were mainly inactivated via
electrosorption and electroporation, as confirmed by the scanning electron
microscopy. Storage of the electrochemically treated samples revealed further
killing of the bacteria due to the damaged cell membranes. When using real tap
water, 5.5 log E. coli removal required 5.70 kWh m-3, which was drastically
lowered to 1.38 kWh m-3 using intermittent current and thus exploiting the
capacitive properties of graphene. The developed graphene sponge anode does not
form any chlorine, chlorate, or perchlorate, and holds great promise for
efficient electro-disinfection without forming toxic disinfection byproducts.",2111.05252v1
2021-11-11,Simulation of lateral ion migration during electroforming process,"Non-volatile memory devices have received a lot of interest in both industry
and academia in the last decade. Transition metal oxide-based memories offer
potential applications as universal memory and artificial synapses. Here we
focus on the one-time conditioning of metal / oxide / metal structures leading
to the formation of a conducting filament in TiN/TaxO1-x/TiN structures and
develop a finite element model of this process. Model solved coupled equations
for charge, heat, and mass transport with the last one including concentration,
temperature, and stress gradients as driving forces. The results closely
replicated available structural data such as diameter and composition of
Ta-enriched core of the filament, O-enriched ring around it, and the dynamics
of filament formation. The range of critical material parameters, namely heats
of transport for Ta and O, is discussed.",2111.06215v1
2021-11-20,Contact conductance governs metallicity in conducting metal oxide nanocrystal films,"In bulk semiconductor materials, the insulator-metal transition (IMT) is
governed by the concentration of conduction electrons. Meanwhile, even when
fabricated from metallic building blocks, nanocrystal films are often
insulating with inter-nanocrystal contacts acting as electron transport
bottlenecks. Using a library of transparent conducting tin-doped indium oxide
nanocrystal films with varied electron concentration, size, and contact area,
we test candidate criteria for the IMT and establish a phase diagram for
electron transport behavior. From variable temperature conductivity
measurements, we learn that both the IMT and a subsequent crossover to
conventional metallic behavior near room temperature are governed by the
conductance of the inter-nanocrystal contacts. To cross the IMT,
inter-nanocrystal coupling must be sufficient to overcome the charging energy
of a nanocrystal, while conventional metallic behavior requires contact
conductance to reach the conductance of a nanocrystal. This understanding can
enable the design and fabrication of metallic conducting materials from
nanocrystal building blocks.",2111.10576v2
2021-11-25,Tuning Coherent-Phonon Heat Transport in LaCoO$_3$/SrTiO$_3$ Superlattices,"Accessing the regime of coherent phonon propagation in nanostructures opens
enormous possibilities to control the thermal conductivity in energy harvesting
devices, phononic circuits, etc. In this paper we show that coherent phonons
contribute substantially to the thermal conductivity of LaCoO3/SrTiO3 oxide
superlattices, up to room temperature. We show that their contribution can be
tuned through small variations of the superlattice periodicity, without
changing the total superlattice thickness. Using this strategy, we tuned the
thermal conductivity by 20% at room temperature. We also discuss the role of
interface mixing and epitaxial relaxation as an extrinsic, material dependent
key parameter for understanding the thermal conductivity of oxide
superlattices.",2111.13035v1
2021-12-06,Cerium Oxides without $U$: The Role of Many-Electron Correlation,"Electron transfer with changing occupation in the 4f subshell poses a
considerable challenge for quantitative predictions in quantum chemistry. Using
the example of cerium oxide, we identify the main deficiencies of common
parameter-dependent one-electron approaches, such as density functional theory
(DFT) with a Hubbard correction, or hybrid functionals. As a response, we
present the first benchmark of ab initio many-electron theory for electron
transfer energies and lattice parameters under periodic boundary conditions. We
show that the direct random phase approximation clearly outperforms all DFT
variations. From this foundation, we, then, systematically improve even
further. Periodic second-order M{\o}ller-Plesset perturbation theory meanwhile
manages to recover standard hybrid functional values. Using these approaches to
eliminate parameter bias allows for highly accurate benchmarks of strongly
correlated materials, the reliable assessment of various density functionals,
and functional fitting via machine-learning.",2112.02850v1
2021-12-07,Pressure-Dependent Phase Transitions in Hybrid Improper Ferroelectric Ruddlesden-Popper Oxides,"The temperature-dependent phase transitions in Ruddlesden-Popper oxides with
perovskite bilayers have been under increased scrutiny in recent years due to
the so-called hybrid improper ferroelectricity that some chemical compositions
exhibit. However, little is currently understood about the hydrostatic pressure
dependence of these phase transitions. Herein we present the results of a
high-pressure powder synchrotron X-ray diffraction experiment and $ab~initio$
calculations on the bilayered Ruddlesden-Popper phases Ca$_{3}$Mn$_{2}$O$_{7}$
and Ca$_{3}$Ti$_{2}$O$_{7}$. In both compounds we observe a first-order phase
transition between polar $A2_{1}am$ and non-polar $Acaa$ structures.
Interestingly, we show that while the application of pressure ultimately
favours a non-polar phase -- as is commonly observed for proper ferroelectrics
-- regions of response exist where pressure actually acts to increase the polar
mode amplitudes. The reason for this can be untangled by considering the varied
response of octahedral tilts and rotations to hydrostatic pressure and their
trilinear coupling with the polar instability.",2112.03819v1
2021-12-09,Valley splitting in silicon from the interference pattern of quantum oscillations,"We determine the energy splitting of the conduction-band valleys in
two-dimensional (2D) electrons confined in silicon metal oxide semiconductor
(Si-MOS) Hall-bar transistors. These Si-MOS Hall bars are made by advanced
semiconductor manufacturing on 300 mm Si wafers and support a 2D electron gas
of high quality with a maximum mobility of 17.6$\times$10$^3$cm$^2$/Vs and
minimum percolation density of 3.45$\times$10$^{10}$cm$^{-2}$. Because of the
low disorder, we observe beatings in the Shubnikov-de Haas oscillations that
arise from the energy-split two low-lying conduction band valleys. From the
analysis of the oscillations beating patterns up to T = 1.7 K, we estimate a
maximum valley splitting of 8.2 meV at a density of
6.8$\times$10$^{12}$cm$^{-2}$. Furthermore, the valley splitting increases with
density at a rate consistent with theoretical predictions for a near-ideal
semiconductor/oxide interface.",2112.05032v3
2021-12-10,Extraordinary strain hardening from dislocation loops in defect-free Al nanocubes,"The interaction of crystalline defects leads to strain hardening in bulk
metals. Metals with high stacking fault energy (SFE), such as aluminum, tend to
have low strain hardening rates due to an inability to form stacking faults and
deformation twins. Here, we use in situ SEM mechanical compressions to find
that colloidally synthesized defect-free 114 nm Al nanocubes combine a high
linear strain hardening rate of 4.1 GPa with a high strength of 1.1 GPa. These
nanocubes have a 3 nm self-passivating oxide layer that has a large influence
on mechanical behavior and the accumulation of dislocation structures.
Post-compression TEM imaging reveals stable prismatic dislocation loops and the
absence of stacking faults. MD simulations relate the formation of dislocation
loops and strain hardening to the surface oxide. These results indicate that
slight modifications to surface and interfacial properties can induce enormous
changes to mechanical properties in high SFE metals.",2112.05723v1
2021-12-16,Dynamics of water and ethanol in graphene oxide,"We utilized the momentum transfer(Q)-dependence of Quasi-Elastic Neutron
Scattering (QENS) to reveal the dynamics of water and ethanol confined in
Graphene Oxide (GO) powder or membranes at different temperatures and in
different orientations. The dynamics was measured across different length and
time scales using several spectrometers. We found reduced diffusivities (up to
30\% in the case of water) and a depression of the transition temperatures.
While water showed near Arrhenius behavior with an almost bulk-like activation
barrier in a temperature range of 280-310 K, the diffusivity of ethanol showed
little temperature dependence. For both water and ethanol, we found evidence
for immobile and mobile fractions of the confined liquid. The mobile fraction
exhibited jump diffusion, with a jump length consistent with the expected
average spacing of hydroxide groups in the GO surfaces. From anisotropy
measurements, we found weak anisotropy in diffusion, with the surprising result
that diffusion was faster perpendicular to membrane than parallel to it.",2112.09235v1
2021-12-17,"A generalized 3D elastic model for nanoscale, self-assembled oxide-metal thin films with pillar-in-matrix configurations","In recent years, functional oxide-metal based vertically aligned
nanocomposite (VAN) thin films have gained interest due to their intriguing
physical properties and multifunctionalities stemming from the complex
interactions between the two phases in the film and the substrate. In this
work, we develop a model for studying the energetics of these thin film
systems, including the effects of both lattice mismatch and capillary forces
due to interface curvature. Each phase is incorporated into the model using a
phase indicator function, and we introduce the capillary forces as body forces
using a vector density representation of the interface. The model is
implemented using the finite element method to study the deformation of the
thin film which is composed of Au nanopillars embedded in a La0.7Sr0.3MnO3
(LSMO) matrix on an SrTiO3 (STO) substrate. The results suggest that the total
energy is lowest for random configurations of pillars compared to ordered
square and hexagonal lattice configurations, consistent with the random
distribution of pillars found in experiments. Furthermore, we find that the
interfacial energy dominates the total energy of each configuration, suggesting
that interfacial energy in the system is an important design parameter for
nanocomposite growth, along with the lattice mismatch.",2112.09281v1
2021-12-22,Understanding Hot Carrier Reliability in FinFET Technology from Trap-based Approach,"In this paper, the recent advances of our studies on hot carrier degradation
(HCD) are presented from trap-based approach. The microscopic speculation of
interface trap generation is carried out by time-dependent DFT (TDDFT)
simulation in ""real-time"". Two types of oxide traps contributing to HCD are
identified from experiments. Combining the contributions of interface and oxide
traps, a unified compact model has been proposed which can accurately predict
hot carrier degradation and variation in full Vgs/Vds bias. The trap locations,
degradation contributions and temperature dependence are studied in detail. In
addition, the mixed mode reliability of HCD-BTI coupling through self-heating
and under off-state stress are discussed.",2112.11753v1
2022-01-05,Nitrogen Plasma Passivated Niobium Resonators for Superconducting Quantum Circuits,"Microwave loss in niobium metallic structures used for superconducting
quantum circuits is limited by a native surface oxide layer formed over a
timescale of minutes when exposed to an ambient environment. In this work, we
show that nitrogen plasma treatment forms a niobium nitride layer at the
metal-air interface which prevents such oxidation. X-ray photoelectron
spectroscopy confirms the doping of nitrogen more than 5 nm into the surface
and a suppressed oxygen presence. This passivation remains stable after aging
for 15 days in an ambient environment. Cryogenic microwave characterization
shows an average filling factor adjusted two-level-system loss tangent
$\rm{F\delta_{TLS}}$ of $(2.9\pm0.5)\cdot10^{-7}$ for resonators with 3
$\rm{\mu}$m center strip and $(1.0\pm0.3)\cdot10^{-7}$ for 20 $\rm{\mu}$m
center strip, exceeding the performance of unpassivated samples by a factor of
four.",2201.01776v2
2022-01-17,Ternary Metal Oxide Substrates for Superconducting Circuits,"Substrate material imperfections and surface losses are one of the major
factors limiting superconducting quantum circuitry from reaching the scale and
complexity required to build a practicable quantum computer. One potential path
towards higher coherence of superconducting quantum devices is to explore new
substrate materials with a reduced density of imperfections due to inherently
different surface chemistries. Here, we examine two ternary metal oxide
materials, spinel (MgAl2O4) and lanthanum aluminate (LaAlO3), with a focus on
surface and interface characterization and preparation. Devices fabricated on
LaAlO3 have quality factors three times higher than earlier devices, which we
attribute to a reduction in interfacial disorder. MgAl2O4 is a new material in
the realm of superconducting quantum devices and, even in the presence of
significant surface disorder, consistently outperforms LaAlO3. Our results
highlight the importance of materials exploration, substrate preparation, and
characterization to identify materials suitable for high-performance
superconducting quantum circuitry.",2201.06228v1
2022-01-21,Tuning Catalytic Activity and Selectivity in Photocatalysis on Dielectric Cuprous Oxide Particles,"Dye degradation has been for more than forty years in the scientific
community. All these studies have primarily focused on breaking various dyes
using catalysts driven by either light or heat. Most studies started to focus
on metal-oxides after the discovery of water-splitting by TiO2. Among the many
catalysts used plasmonic metal nanostructures have been explored significantly
in recent times due to their special property called localized surface plasmon
resonances (LSPR). However, facing multiple problems of heat losses and
instability, people started to focus on dielectric medium-to-high refractive
indexed materials for photonic applications. Most of these dielectric materials
have been studied from a physics point of view and less from chemistry. In this
work, we have focused on how these materials can be used for tuning selectivity
through wavelength-dependent studies by performing methylene blue (MB) dye
degradation.",2201.08828v2
2022-01-24,Study of voltage cycling conditions on Pt oxidation and dissolution in polymer electrolyte fuel cells,"This paper is devoted to study the electrochemical behavior of Pt catalyst in
a polymer electrolyte fuel cell at various operating conditions and at
different electric potential difference (also known as voltage) cycling applied
in accelerated stress tests. The degradation of platinum is considered with
respect to the Pt ion dissolution and the Pt oxide coverage of catalyst
described by a one-dimensional model. In the model, degradation rate increases
with temperature and decreasing particle diameter of Pt nano-particles. The
theoretical study of the underlying diffusion system with the nonlinear
reactions is presented by analytical methods and gives explicit solutions
through a first integral of the ODE system. Numerical tests are obtained using
a second order implicit-explicit scheme. The computer simulation shows that the
lifetime of the catalyst depends on the voltage profile and the upper potential
level. By this Pt mass loss is more significant at the membrane surface than at
the gas diffusion layer.",2201.09768v1
2022-01-28,Mass transport via in-plane nanopores in graphene oxide membranes,"Angstrom confined solvents in two-dimensional laminates travel through
interlayer spacings, gaps between adjacent sheets, and via in plane pores.
Among these, experimental access to investigate the mass transport through in
plane pores is lacking. Here, we create these nanopores in graphene oxide
membranes via ion irradiation with precise control over functional groups, pore
size and pore density. Low ion induced pore densities result in mild reduction
and increased water permeation for the membranes. Higher pore densities lead to
pronounced reduction and complete blockage of pure water however allows
permeation of ethanol water mixture due to weakening of hydrogen network. We
confirm with simulations, that the attraction of the solvents towards the pores
with functional groups and disruption of the angstrom confined hydrogen network
is crucial to allow in plane pore transport.",2201.11886v1
2022-01-31,Towards Optimized Charge Transport in Multilayer Reduced Graphene Oxides,"In the context of graphene-based composite applications, a complete
understanding of charge conduction in multilayer reduced graphene oxides (rGO)
is highly desirable. However, these rGO compounds are characterized by multiple
and different sources of disorder depending on the chemical method used for
their synthesis. Most importantly the precise role of interlayer interaction in
promoting or jeopardizing electronic flow remains unclear. Here, thanks to the
development of a multiscale computational approach combining first-principles
calculations with large scale transport simulations, the transport scaling laws
in multilayer rGO are unraveled, explaining why diffusion worsens with
increasing film thickness. In contrast, contacted films are found to exhibit an
opposite trend when the mean free path becomes shorter than the channel length,
since conduction becomes predominantly driven by interlayer hopping. These
predictions are favourably compared with experimental data and open a road
towards the optimization of graphene-based composites with improved electrical
conduction.",2201.13437v1
2022-02-14,Role of lithium intercalation in fluorine-doped tin oxide thin films: Ab-initio calculations and experiment,"Using a combination of experimental techniques and density functional theory
(DFT) calculations, the influence of lithium insertion on the electronic and
electrochemical properties of fluourine-doped SnO$_2$ (FTO) is assessed. For
this purpose, we investigate the electrochromic behavior of commercial FTO
electrode embedded in a solution of lithium perclorate (LiClO$_4$). The
electrochromic properties are evaluated by UV-VIS spectroscopy, cyclic
voltammetry, and chronoamperometry. These tests show that FTO exhibits
electrochromism with a respectable coloration efficiency ($\eta=47.9$ cm$^2$/C
@ 637 nm). DFT study indicates that lithium remains ionized in the lattice,
raising the Fermi level about 0.7 eV deep into the conduction band. X-ray
photoelectron spectroscopy (XPS) is used to study chemical bonding and
oxidation states. XPS analysis of the Sn 3d core levels reveals that lithium
insertion in FTO induces a shift of 350 meV in the Sn 3d states suggesting that
lithium is incorporated into the SnO$_2$ lattice.",2202.07083v1
2022-02-18,Molecular dynamics study of the linear viscoelastic shear and bulk relaxation moduli of poly(tetramethylene oxide) (PTMO),"Here we report the linear viscoelastic properties of amorphous
poly(tetramethylene oxide) (PTMO), which is one of the key components in
synthesizing segmented polyurethane (PU) elastomers. The temperature and
molecular weight dependent viscoelastic behavior is investigated in detail by
computing the shear relaxation modulus G(t) and the bulk relaxation modulus
K(t), using the Green-Kubo relationship with correlation function. Our results
provide new data for PTMO melt from the united atom model and also extend the
existing knowledge of viscoelastic properties of polymers in general. The
predicted viscoelastic behavior range is shifted on a master curve using the
time-temperature superposition principle (TTSP) with horizontal and vertical
shift factors. The emerging shift factors agree with the Williams-Landel-Ferry
(WLF) equation. For the validation of the united-atom model of PTMO using the
TraPPE-UA force field we explored the transport properties and observed a
position-dependent diffusion dynamics throughout the polymer chain, which
subsequently influences the scaling laws for chain dynamics. These findings are
discussed in terms of emerging experimental evidence on position dependent
displacement for different chain portions along the chain length.",2202.08993v1
2022-03-03,Direct observation of local antiferroelectricity induced phonon softening at a SrTiO3 defect,"Defects in oxides usually exhibit exotic properties that may be associated
with the local lattice dynamics. Here, at atomic spatial resolution, we
directly measure phonon modes of an antiphase boundary (APB) in SrTiO3
freestanding membrane and correlate them with the picometer-level structural
distortion. We find that the SrTiO3 APB introduces new defect phonon modes that
are absent in bulk SrTiO3. These modes are highly sensitive to the subtle
structure distortion, i.e., the SrTiO3 APB generates the local electric dipoles
forming an antiferroelectric configuration, which significantly softens the
transverse optical (TO) and longitudinal optical (LO) modes at {\Gamma} point.
Correlating the local phonons with the subtle structural distortion, our
findings provide valuable insights into understanding the defect properties in
complex oxides and essential information for their applications such as
thermoelectric devices.",2203.01772v1
2022-03-15,High-Temperature Decomposition of Diisopropyl Methylphosphonate (DIMP) on Alumina: Mechanistic Predictions from Ab Initio Molecular Dynamics,"The enhanced degradation of organophosphorous-based chemical warfare agents
(CWAs) on metal-oxide surfaces holds immense promise for neutralization
efforts; however, the underlying mechanisms in this process remain poorly
understood. We utilize large-scale quantum calculations for the first time to
probe the high-temperature degradation of diisopropyl methylphosphonate (DIMP),
a nerve agent simulant. Our Born-Oppenheimer molecular dynamics (BOMD)
calculations show that the $\gamma$-Al$_2$O$_3$ surface shows immense promise
for quickly adsorbing and destroying CWAs. We find that the alumina surface
quickly adsorbs DIMP at all temperatures, and subsequent decomposition of DIMP
proceeds via a propene elimination. Our BOMD calculations are complemented with
metadynamics simulations to produce free energy paths, which show that the
activation barrier decreases with temperature and DIMP readily decomposes on
$\gamma$-Al$_2$O$_3$. Our first-principle BOMD and metadynamics simulations
provide crucial diagnostics for sarin decomposition models and mechanistic
information for examining CWA decomposition reactions on other candidate metal
oxide surfaces.",2203.08035v1
2022-03-23,"Low-energy electron microscopy intensity-voltage data -- factorization, sparse sampling, and classification","Low-energy electron microscopy (LEEM) taken as intensity-voltage (I-V) curves
provides hyperspectral images of surfaces, which can be used to identify the
surface type, but are difficult to analyze. Here, we demonstrate the use of an
algorithm for factorizing the data into spectra and concentrations of
characteristic components (FSC3) for identifying distinct physical surface
phases. Importantly, FSC3 is an unsupervised and fast algorithm. As example
data we use experiments on the growth of praseodymium oxide or ruthenium oxide
on ruthenium single crystal substrates, both featuring a complex distribution
of coexisting surface components, varying in both chemical composition and
crystallographic structure. With the factorization result a sparse sampling
method is demonstrated, reducing the measurement time by 1-2 orders of
magnitude, relevant for dynamic surface studies. The FSC3 concentrations are
providing the features for a support vector machine (SVM) based supervised
classification of the types. Here, specific surface regions which have been
identified structurally, via their diffraction pattern, as well as chemically
by complementary spectro-microscopic techniques, are used as training sets. A
reliable classification is demonstrated on both exemplary LEEM I-V datasets.",2203.12353v1
2022-03-25,On-Demand Activation of Photochromic Nanoheaters for High Color Purity 3D Printing,"The creation of white and multicoloured 3D-printed objects with high colour
fidelity via powder sintering processes is currently limited by discolouration
from thermal sensitizers used in the printing process. Here we circumvent this
problem by using switchable, photochromic tungsten oxide nanoparticles, which
are colourless even at high concentrations. Upon ultraviolet illumination, the
tungsten oxide nanoparticles can be reversibly activated making them highly
absorbing in the infrared. Their strong infrared absorption upon activation
renders them efficient photothermal sensitizers that can act as fusing agents
for polymer powders in sintering-based 3D printing. The WO3 nanoparticles show
fast activation times, and when mixed with polyamide powders they exhibit a
heating-to-colour-change ratio greatly exceeding other sensitizers in the
literature. Upon mixing with coloured inks, powders containing WO3 display
identical colouration to a pristine powder. This demonstrates the potential of
WO3, and photochromic nanoparticles in general as a new class of material for
advanced manufacturing.",2203.13584v1
2022-03-29,Thermal decomposition of hydrated graphite oxide: A computational study,"We study the behavior of hydrated graphite oxide (GO) at high temperatures
using thermally accelerated molecular dynamics simulations based on ab initio
density functional theory. Our results suggest that GO, a viable candidate for
water treatment and desalination membranes, is more heat resilient than
currently used organic materials. The system we consider to represent important
aspects of thermal processes in highly disordered GO is a hydrated GO bilayer
in vacuum. Our study provides microscopic insight into reactions involving
water and functional epoxy-O and OH-groups bonded to graphene layers, and also
describes the swelling of the structure by water vapor pressure at elevated
temperatures. We find the system to withstand simulation temperatures up to
${\approx}$2,500 K before the graphitic layers start decomposing, implying the
possibility of cleaning biofouling residue from a GO-based membrane by heating
in an inert gas atmosphere.",2203.15891v1
2022-04-05,Cr (VI) biosorption at different Na (I) concentrations after Zn(II) uptake during Arthrobacter species growth,"The biosorption of Cr(VI) Arthrobacter species (Arthrobacter globiformis 151B
and Arthrobacter oxides 61B) after growth in the presence of Zn (II) ions at
different Na (I) concentrations was studied application using dialysis and
atomic absorption analysis. It was shown that after absorption of Zn(II) during
growth of types of Arthrobacter the biosorption of Cr (VI) with types
Arthrobacter (Arthrobacter globiformis 151B, Arthrobacter oxidas 61B) increases
at various concentration of Na (I) comparative without Zn(II), at identical
concentration of Na (I). It is seen, that zinc(II) ions promote for Cr(VI) part
of the active centers of Arthrobacter species and Na(I) ions already has
relatively little effect on them. However, this change is more pronounced for
Cr (VI) _Arthrobacter globiformis 151B + Zn (II) than for Cr (VI) _Arthrobacter
oxides of 61B + Zn (II).",2204.02309v1
2022-04-17,A phase field model combined with genetic algorithm for polycrystalline hafnium zirconium oxide ferroelectrics,"Ferroelectric hafnium zirconium oxide (HZO) thin films show significant
promise for applications in ferroelectric random-access memory, ferroelectric
field-effect transistors, and ferroelectric tunneling junctions. However, there
are shortcomings in understanding ferroelectric switching, which is crucial in
the operation of these devices. Here a computational model based on phase field
method is developed to simulate the switching behavior of polycrystalline HZO
thin films. Furthermore, we introduce a novel approach to optimize the
effective Landau coefficients describing the free energy of HZO by combining
the phase field model with a genetic algorithm. We validate the model by
accurately simulating switching curves for HZO thin films with different
ferroelectric phase fractions. The simulated domain dynamics during switching
also shows amazing similarity to the available experimental observations. The
present work also provides fundamental insights into enhancing the
ferroelectricity in HZO thin films by controlling grain morphology and
crystalline texture. It can potentially be extended to improve the
ferroelectric properties of other hafnia based thin films.",2204.07960v2
2022-04-28,Interplay of the disorder and strain in gallium oxide,"Ion irradiation is a powerful tool to tune properties of semiconductors and,
in particular, of gallium oxide (Ga2O3) which is a promising ultra-wide bandgap
semiconductor exhibiting phase instability for high enough strain/disorder
levels. In the present paper we observed an interesting interplay between the
disorder and strain in monoclinic \b{eta}-Ga2O3 single crystals by comparing
atomic and cluster ion irradiations as well as atomic ions co-implants. The
results obtained by a combination of the channeling technique, x-ray
diffraction and theoretical calculations show that the disorder accumulation in
\b{eta}-Ga2O3 exhibits superlinear behavior as a function of the collision
cascade density. Moreover, the level of strain in the implanted region can be
engineered by changing the disorder conditions in the near surface layer. The
results can be used for better understanding of the radiation effects in
\b{eta}-Ga2O3 and imply that disorder/strain interplay provides an additional
degree of freedom to maintain desirable strain in Ga2O3, potentially applicable
to modify the rate of the polymorphic transitions in this material.",2204.13302v2
2022-04-30,A Gate-All-Around Single-Channel In2O3 Nanoribbon FET with Near 20 mA/μm Drain Current,"In this work, we demonstrate atomic-layer-deposited (ALD) single-channel
indium oxide (In2O3) gate-all-around (GAA) nanoribbon FETs in a
back-end-of-line (BEOL) compatible process. A maximum on-state current (ION) of
19.3 mA/{\mu}m (near 20 mA/{\mu}m) is achieved in an In2O3 GAA nanoribbon FET
with a channel thickness (TIO) of 3.1 nm, channel length (Lch) of 40 nm,
channel width (Wch) of 30 nm and dielectric HfO2 of 5 nm. The record high drain
current obtained from an In2O3 FET is about one order of magnitude higher than
any conventional single-channel semiconductor FETs. This extraordinary drain
current and its related on-state performance demonstrate ALD In2O3 is a
promising oxide semiconductor channel with great opportunities in BEOL
compatible monolithic 3D integration.",2205.00360v1
2022-05-02,Recent advances in inorganic oxides-based resistive random-access memory devices,"Memory has always been a building block element for information technology.
Emerging technologies such as artificial intelligence, big data, the internet
of things, etc., require a novel kind of memory technology that can be energy
efficient and have an exception data retention period. Among several existing
memory technologies, resistive random-access memory (RRAM) is an answer to the
above question as it is necessary to possess the combination of speed of RAM
and nonvolatility, thus proving to be one of the most promising candidates to
replace flash memory in next-generation non-volatile RAM applications. This
review discusses the existing challenges and technological advancements made
with RRAM, including switching mechanism, device structure, endurance, fatigue
resistance, data retention period, and mechanism of resistive switching in
inorganic oxides material used as a dielectric layer. Finally, a summary and a
perspective on future research are presented.",2205.05537v1
2022-05-29,Polarimetric characterization of segmented mirrors,"We study the impact of the loss of axial symmetry around the optical axis on
the polarimetric properties of a telescope with segmented primary mirror when
each segment is present in a different aging stage. The different oxidation
stage of each segment as they are substituted in time leads to non-negligible
crosstalk terms. This effect is wavelength dependent and it is mainly
determined by the properties of the reflecting material. For an aluminum
coating, the worst polarimetric behavior due to oxidation is found for the blue
part of the visible. Contrarily, dust -- as modeled in this work -- does not
significantly change the polarimetric behavior of the optical system .
Depending on the telescope, there might be segment substitution sequences that
strongly attenuate this instrumental polarization.",2205.14640v1
2022-06-07,The Origin of Deformation Induced Topological Anisotropy in Silica Glass,"Oxide glasses with a network structure are omnipresent in daily life. Often,
they are regarded as isotropic materials; however, structural anisotropy can be
induced through processing in mechanical fields and leads to unique materials
properties. Unfortunately, due to the lack of local, atomic-scale analysis
methods, the microscopic mechanisms leading to anisotropy remained elusive.
Using novel analysis methods on glasses generated by molecular dynamics
simulations, this paper provides a microscopic understanding of topological
anisotropy in silica (SiO$_2$) glass under mechanical loads. The anisotropy
observed in silica glass originates from a preferred orientation of SiO$_4$
tetrahedra at both short- and medium-range levels that can be controlled via
the mode of mechanical loading. The findings elucidate the relation between the
deformation protocol and the resulting anisotropic structure of the silica
network (involving both persistent and transient effects), and thus provide
important insight for the design of oxide glasses with tailored materials
properties.",2206.03039v2
2022-06-23,Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium,"Birnessite was synthetized through redox reaction by mixing MnO4-, Mn2+ and
OH- solutions. The Mn(VII): Mn(II) ratio of 0.33 was chosen and three methods
were used consisting in a quick mixing under vigorous stirring of two of the
three reagents and then on the dropwise addition of the third one. The obtained
solids were characterized by XRD, FTIR and XPS spectroscopies. Their average
oxidation states were determined from ICP and CEC measurements while their
surface properties were investigated by XPS. This study provides an increased
understanding of the importance of dissolved oxygen in the formation of
birnessite and hausmannite and shows the ways to obtain pure birnessite. The
role of counter-ion ie. Na+ or K+ was also examined.",2206.11550v1
2022-07-04,New insight into 3-picoline - deuterium oxide (D$_2$O) mixtures of limited miscibility with the lower critical consolute temperature,"Coexistence curves in mixtures of limited miscibility with the lower critical
consolute temperature (LCT), of 3-picoline with deuterium oxide (D$_2$O), and
D2O/H2O have been determined. They were tested with respect to the order
parameter, the diameter of the binodal, and coordinates of the critical
consolute point (critical temperature Tc and critical concentration fic)
Studies were carried out using the innovative method based on the analysis of
relative volumes occupied by coexisting phases, yielding high-resolution data.
The clear violation of the Cailletet-Mathew law of rectilinear diameter for the
LCT mixtures of limited miscibility is evidenced. For the order parameter, the
new distortion-sensitive analysis method yielded the evidence for the
model-value of the order parameter critical exponent beta = 0.326.up to ca. 1 K
from Tc. Finally, the simple & easy method for determining the critical
concentration by testing relative volumes of coexisting phases (or
alternatively fractional meniscus heights, h) is presented. The significance of
the invariant value hc(Tc, fic) = 1/2 is highlighted. The appearance of the
milky & bluish critical opalescence is also shown",2207.01670v1
2022-07-06,Co-operative Influence of O2 and H2O in the Degradation of Layered Black Arsenic,"Layered black arsenic (b-As) has recently emerged as a new anisotropic
two-dimensional (2D) semiconducting material with applications in electronic
devices. Understanding factors affecting the ambient stability of this material
remains crucial for its applications. Herein we use first-principles density
functional theory (DFT) calculations to examine the stability of the (010) and
(101) surfaces of b-As in the presence of oxygen (O2) and water (H2O). We show
that the (101) surface of b-As can easily oxidize in presence of O2. In the
presence of moisture contained in air, the oxidized b-As surfaces favorably
react with H2O molecules to volatilize As in the form of As(OH)3 and AsO(OH),
which results in the degradation of the b-As surface, predominantly across the
(101) surface. These predictions are in good agreement with experimental
electron microscopy observations, thus demonstrating the co-operative
reactivity of O2 and H2O in the degradation of layered b-As under ambient
conditions.",2207.02416v1
2022-07-08,Copper migration and surface oxidation of $\text{Cu}_{x}\text{Bi}_2\text{Se}_3$ in ambient pressure environments,"Chemical modifications such as intercalation can be used to modify surface
properties or to further functionalize the surface states of topological
insulators. Using ambient pressure X-ray photoelectron spectroscopy, we report
copper migration in $\text{Cu}_{x}\text{Bi}_2\text{Se}_3$, which occurs on a
timescale of hours to days after initial surface cleaving. The increase in
near-surface copper proceeds along with the oxidation of the sample surface and
large changes in the selenium content. These complex changes are further
modelled with core-level spectroscopy simulations, which suggest a composition
gradient near the surface which develops with oxygen exposure. Our results shed
light on a new phenomenon that must be considered for intercalated topological
insulators$\unicode{x2014}$and intercalated materials in
general$\unicode{x2014}$that surface chemical composition can change when
specimens are exposed to ambient conditions.",2207.04155v1
2022-07-13,$g-B_{3}C_{2}N_{3}$: A new potential two dimensional metal-free photocatalyst for overall water splitting,"In this work, using a hybrid density functional theory (DFT) based
calculation, we propose a new two-dimensional (2D) B-C-N material,
$g-B_{3}C_{2}N_{3}$, with the promising prospect of metal-free photocatalysis.
A comprehensive investigation demonstrates that it is a near ultraviolet (UV)
absorbing direct band gap (3.69 eV) semiconductor with robust dynamical and
mechanical stability. Estimating the band positions with respect to water
oxidation and hydrogen reduction potential levels, we observe that
$g-B_{3}C_{2}N_{3}$ monolayer shows the possibility to be used for hydrogen
fuel generation through spontaneous solar water splitting, over a broad pH
range. Upon biaxial strain application the band gap decreases with increase in
tensile strain, leading to a subsequent red shift in absorption spectra,
implying enhanced photon harvest under solar irradiation. Furthermore, due to a
combined effect of band gap and work function variation, biaxial strain
realigns the band positions, allowing one to control the reducing or oxidizing
ability as per requirement to attain environmental sustainability.",2207.06232v1
2022-07-14,Thermal stability and optoelectronic behavior of polyaniline/GNP (graphene nanoplatelets) nanocomposites,"Polyaniline and graphene nanoplatelets (PANI-GNP) nanocomposites are
synthesized by in situ oxidative polymerization of polyaniline using an
oxidizing agent, ammonium peroxy disulphate (APS). The mass of GNP in the
nanocomposites varied by 5, 10, and 15 wt% compared to PANI. The synthesized
polyaniline coated graphene nanoplatelets (PANI-GNP) nanocomposites are
chemically characterized and using Fourier Transform Infrared Spectroscopy
(FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), UV-Vis
spectroscopy, and X-ray diffraction analysis (XRD). FTIR and Raman spectroscopy
analysis confirmed the uniform coating of polyaniline on GNP. The SEM
micrograph and XRD pattern demonstrate the polymerization quality and
crystallization degree of samples. UV-Vis analysis showed a decrease in the
bandgap of polyaniline, which confirms that nanocomposites are more suitable
for optoelectronic application because of variation in the bandgap. TGA
analysis showed the thermal stability of PANI is increased with the increased
mass of GNP. This study suggests the potential of GNP as a filler for efficient
modification in the morphological, electrical, optical, and thermal properties
of PANI.",2207.07062v1
2022-07-26,Engineering Surface Oxygen Vacancies in $\mathrm{SrTiO_3}$ to Form a High Mobility and Transparent Quasi Two dimensional Electron System,"Quasi-two-dimensional electron systems (q-2DES) are formed in various
hetero-structures, including oxide interfaces. Oxygen vacancies (OVs) in oxides
like $\mathrm{SrTiO_3}$ are known to produce electronic carriers. A novel way
to produce $\mathrm{SrTiO_{3-\delta}}$ on the surface using a low-energy
$\mathrm{H_2}$ plasma is shown here. It results in a q-2DES with mobility as
high as $\mu \sim 20,000 \; cm^2V^{-1}s^{-1}$, displaying quantum oscillations
in magneto-resistance. We can achieve a sharper or weaker confinement potential
by adjusting the process pressure. The system with sharper confinement displays
clearer quantum oscillations and Kondo-like temperature dependence of
resistance. OVs close to the surface behaving like a correlated Anderson
impurity is responsible for the Kondo behaviour. Quantum oscillations are less
prominent in the weakly confined system. A cross-over from weak-localization to
anti-localization with temperature is seen, but no Kondo behavior. The process
also results in a transparent conductor amenable to lithographic patterning.
This conductor's standard figure of merit is comparable to poly-crystalline ITO
films in the visible regime and extends with similar performance into the
$\lambda$ $\sim 1.5$ $\mu m$ telecommunication wavelength.",2207.12933v1
2022-07-28,Polaronic Optical Transitions in Hematite ($α-Fe_{2}O_{3}$) Revealed by First-Principles Electron-Phonon Coupling,"Polaron formation following optical absorption is a key process that defines
the photophysical properties of many semiconducting transition metal oxides,
which comprise an important class of materials with potential optoelectronic
and photocatalytic applications. In this work, we use hematite
(${\alpha}-Fe_{2}O_{3}$) as a model transition metal oxide semiconductor to
demonstrate the feasibility of direct optical population of band-edge polaronic
states. We employ first-principles electron-phonon computations within the
framework of the DFT+U+J method to reveal the presence of these states within a
thermal distribution of phonon displacements and model their evolution with
temperature. Our computations reproduce the temperature dependence of the
optical dielectric function of hematite with remarkable accuracy and indicate
that the band-edge optical absorption and second-order resonance Raman spectra
arise from polaronic optical transitions involving coupling to longitudinal
optical phonons with energies greater than 50 meV. Additionally, we find that
the resulting polaron comprises an electron localized to two adjacent Fe atoms
with distortions that lie primarily along the coordinates of phonons with
energies of 31 and 81 meV.",2207.14184v1
2022-07-28,What X-ray absorption spectroscopy can tell us about the active state of earth-abundant electrocatalysts for the oxygen evolution reaction,"Chemical energy storage is an attractive solution to secure a sustainable
energy supply. It requires an electrocatalyst to be implemented efficiently. In
order to rationally improve the electrocatalyst materials and thereby the
reaction efficiency, one must reveal the nature of the electrocatalyst under
reaction conditions, i.e., its active state. For a better understanding of
earth-abundant metal oxides as electrocatalysts for the oxygen evolution
reaction (OER), the combination of electrochemical (EC) methods and X-ray
absorption spectroscopy (XAS) has been very insightful and still holds untapped
potential. Herein, we concisely introduce the basics of EC and XAS and provide
the necessary framework to discuss changes that electrocatalytic materials
undergo, presenting manganese oxides as examples. Such changes may occur during
preparation and storage, during immersion in an electrolyte, as well as during
application of potentials without or with catalytic reactions. We conclude with
a concise summary of how EC and XAS are currently combined to elucidate the
active state as well as an outlook on future opportunities to understand the
mechanisms of electrocatalysis using combined operando EC-XAS experiments.",2207.14360v1
2022-07-29,Low-frequency Phonon at Perovskite Oxide Interface Studied by Surface-specific Nonlinear Terahertz Spectroscopy,"The low-frequency collective excitations, which often occur in the terahertz
or multi-terahertz spectral region, play an essential role in many novel
emergent phenomena. Despite numerous studies in the bulk, detection of such
excitations at interfaces remains challenging owing to the lack of feasible
experimental techniques. Here, we show that interfacial low-frequency modes can
be characterized using surface-specific nonlinear terahertz spectroscopy. This
technique uses intra-pulse difference frequency mixing (DFM) process that can
extend the second-order optical spectroscopy to the terahertz range. As a
demonstration, the surface phonon of SrTiO3(001) at 2.8 THz was successfully
measured. This surface polarization originates from the excess of oxygen
vacancies or charge transfer at the interface. We have also developed an
analytical procedure for remote measurement of the interfacial potential of
complex oxides in a practical environment. Our method offers new opportunities
for in situ studies of the low-frequency excitations at interfaces in broad
disciplines.",2207.14610v1
2022-08-03,Detection of High Energy Ionizing Radiation using Deeply Depleted Graphene-Oxide-Semiconductor Junctions,"Graphene's linear bandstructure and two-dimensional density of states provide
an implicit advantage for sensing charge. Here, these advantages are leveraged
in a deeply depleted graphene-oxide-semiconductor (D2GOS) junction detector
architecture to sense carriers created by ionizing radiation. Specifically, the
room temperature response of the silicon-based D2GOS junction is analyzed
during irradiation with 20 MeV Si4+ ions. Detection was demonstrated for doses
ranging from 12-1200 ions with device functionality maintained with no
substantive degradation. To understand the device response, D2GOS pixels were
characterized post-irradiation via a combination of electrical
characterization, Raman spectroscopy, and photocurrent mapping. This combined
characterization methodology underscores the lack of discernible damage caused
by irradiation to the graphene while highlighting the nature of interactions
between the incident ions and the silicon absorber.",2208.02366v1
2022-08-06,Tunable two-dimensional superconductivity and spin-orbit coupling at the EuO/KTaO3(110) interface,"Unconventional quantum states, most notably the two-dimensional (2D)
superconductivity, have been realized at the interfaces of oxide
heterostructures where they can be effectively tuned by the gate voltage
($V_G$). Here we report that the interface between high-quality EuO (111) thin
film and KTaO3 (KTO) (110) substrate shows superconductivity with onset
transition temperature $T_c^{onset}$ = 1.35 K. The 2D nature of
superconductivity is verified by the large anisotropy of the upper critical
field and the characteristics of a Berezinskii-Kosterlitz-Thouless transition.
By applying $V_G$, $T_c^{onset}$ can be tuned from ~ 1 to 1.7 K; such an
enhancement can be possibly associated with a boosted spin-orbit energy
${\epsilon}_{so}$ = $\hbar$ / ${\tau}_{so}$, where ${\tau}_{so}$ is the
spin-orbit relaxation time. Further analysis of ${\tau}_{so}$ based on the
upper critical field ($H_{c2}$) and magnetoconductance reveals complex nature
of spin-orbit coupling (SOC) at the EuO/KTO(110) interface with different
mechanisms dominate the influence of SOC effects for the superconductivity and
the magnetotransport in the normal state. Our results demonstrate that the SOC
should be considered as an important factor determining the 2D
superconductivity at oxide interfaces.",2208.03507v1
2022-08-18,Thermally Oxidized MoS$_2$-Based Hybrids as Superior Electrodes for Supercapacitor and Photoelectrochemical Applications,"High electronic transport and reasonable chemical stability of molybdenum
disulfide (MoS$_2$) make it very suitable for electrochemical applications.
However, its energy storage capacity is still low compared with other
nanostructures. In this work, pristine and thermally oxidized MoS$_2$
(O@MoS$_2$) based hybrids are introduced by a simple method with enhanced
capacitive performance thanks to the contribution of synergistic effects.
Scanning electron microscopy (SEM), Transmission electron microscopy (TEM),
X-ray diffraction (XRD), elemental mapping, UV-Visible, and Raman analyses are
employed to investigate the morphological and crystalline structure of the
introduced hybrids. In detail, the highest gravimetric capacitance of ~205.1
Fg-1 is achieved for the MoS$_2$:O@MoS$_2$ hybrid with a mass ratio of 2:1
compared to pristine and other electrodes. This electrode is also accompanied
by the longest discharging time and excellent cyclic stability of ~%113 after
2000 continuous charge-discharge cycles. In addition, photoelectrochemical
testing of the introduced electrode leads to a ~63% increase in carrier
photogeneration compared to MoS$_2$ due to the effective charge separation
within the hybrid, which makes it suitable for water splitting and hydrogen
production applications.",2208.08799v1
2022-08-24,Numerical analysis of dilute methanol spray flames in vitiated coflow using extended Flamelet Generated Manifold model,"The present work focuses on the large eddy simulation (LES) and the study of
turbulent dilute methanol spray flames in vitiated coflow using the secondary
oxidizer Flamelet Generated Model (FGM). The modified FGM model uses an
additional secondary oxidizer parameter in addition to the three other
parameters previously used for spray flames progress variable, mixture
fraction, and enthalpy. The results for gas phase and droplet properties are
validated against the dilute methanol spray flame database for varying fuel
injection amounts. The droplet statistics and the lift-off flame heights are
accurately captured for all the cases. A proper orthogonal decomposition (POD)
of the scalar fluctuating hydroxyl radical (OH) field and velocity-temperature
field capture the flame structures in the downstream region of ignition
kernels. The detailed POD analysis reveals that the base frequency of the
dominant OH field equals that of the dominant vortical structure of 67.3 Hz.
The flame propagation happens around these dominant vortical structures because
of the less-strained fluid mixing.",2208.11554v1
2022-08-29,Structure and transport properties of poly(ethylene oxide) based cross-linked polymer electrolytes -- A Molecular Dynamics Simulations study,"We present an extensive molecular dynamics (MD) simulation study of
poly(ethylene oxide) (PEO) based densely cross-linked polymers, focussing on
structural properties as well as the systems dynamics in the presence of
lithium salt. Motivated by experimental findings for networks with short PEO
strands we employ a combination of LiTFSI (Lithium
bis(trifluoromethanesulfonyl)imide) and LiDFOB (Lithium
difluoro(oxalato)borate). Recently, it has been shown that such multi-salt
systems outperform classical single salt systems (Shaji et al., Energy Storage
Materials, 2022, 44, 263). To analyse the microscopic scenario we employ an
analytical model, originally developed for non-cross-linked polymer
electrolytes or blends (Maitra et al., Phys. Rev. Lett., 2007, 98, 227802 and
Diddens et al., J. Electrochem. Soc., 2017, 164, E3225-E3231). Excluding very
short PEO strands, the local dynamics is only slightly restricted compared to
linear PEO and is not significantly dependent on the network structure. The
transfer of lithium ions between PEO chains and the motion along the polymer
backbone may be controlled through the employed salt.",2208.13450v1
2022-08-29,Machine Learning guided high-throughput search of non-oxide garnets,"Garnets, known since the early stages of human civilization, have found
important applications in modern technologies including magnetorestriction,
spintronics, lithium batteries, etc. The overwhelming majority of
experimentally known garnets are oxides, while explorations (experimental or
theoretical) for the rest of the chemical space have been limited in scope. A
key issue is that the garnet structure has a large primitive unit cell,
requiring an enormous amount of computational resources. To perform a
comprehensive search of the complete chemical space for new garnets,we combine
recent progress in graph neural networks with high-throughput calculations. We
apply the machine learning model to identify the potential (meta-)stable garnet
systems before systematic density-functional calculations to validate the
predictions. In this way, we discover more than 600 ternary garnets with
distances to the convex hull below 100~meV/atom with a variety of physical and
chemical properties. This includes sulfide, nitride and halide garnets. For
these, we analyze the electronic structure and discuss the connection between
the value of the electronic band gap and charge balance.",2208.13742v1
2022-09-01,From High-Entropy Ceramics (HECs) to Compositionally Complex Ceramics (CCCs),"This invited talk will review a series of our recent studies on high-entropy
ceramics (HECs) and compositionally complex ceramics (CCCs) and discuss the
future perspective. Various single-phase equimolar quinary (five-component)
HECs, e.g., MB2, MB, M3B4, MB4, and MB6 borides, MSi2 and M3Si5 silicides,
perovskite, fluorite, and pyrochlore oxides, and (intermetallic) aluminides
have been fabricated. We further proposed to extend HECs to CCCs to include
non-equimolar compositions and further consider short- and long-range orders,
which reduce configurational entropies but offer additional dimensions and
opportunities to tailor and improve various properties. We also reported the
first dual-phase HECs/CCCs. Using compositionally complex fluorite-based oxides
(CCFBOs, which can possess fluorite or defect fluorite, pyrochlore, weberite,
fergusonite, and bixbyite phases) as the model systems, we have recently
discovered long- and short- range orders, composition- and redox-induced
order-disorder transitions (ODTs), and ultrahigh-entropy weberite and
fergusonite phases in several 10- to 21-component systems.",2209.00752v1
2022-09-09,Flexo-photovoltaic effect and above-bandgap photovoltage in halide perovskites,"Halide perovskites have outstanding photovoltaic properties which have been
optimized through interfacial engineering. However, as these materials approach
the limits imposed by the physics of semiconductor junctions, it is urgent to
explore alternatives, such as the bulk photovoltaic effect, whose physical
origin is different and not bound by the same limits. In this context, we focus
on the flexo-photovoltaic effect, a type of bulk photovoltaic effect that was
recently observed in oxides under strain gradients. We have measured the
flexo-photovoltaic effect of MAPbBr3 and MAPbI3 crystals under bending and
found it to be orders of magnitude larger than for SrTiO3, the benchmark
flexo-photovoltaic oxide. For sufficiently large strain gradients,
photovoltages bigger than the bandgap can be produced. Bulk photovoltaic
effects are additive and, for MAPbI3, the flexo-photovoltage exists on top of a
native bulk photovoltage that is hysteretic, consistent with the electrically
switchable macroscopic polarization of this material. The results suggest that
harnessing the flexo-photovoltaic effect through strain gradient engineering
can provide a functional leap forward for halide perovskites.",2209.04277v3
2022-09-13,Gaussian-Based Quasiparticle Self-Consistent $GW$ for Periodic Systems,"We present a quasiparticle self-consistent $GW$ (QSGW) implementation for
periodic systems based on crystalline Gaussian basis sets. Our QSGW approach is
based on a full-frequency analytic continuation GW scheme with Brillouin zone
sampling and employs the Gaussian density fitting technique. We benchmark our
QSGW implementation on a set of weakly-correlated semiconductors and insulators
as well as strongly correlated transition metal oxides including MnO, FeO, CoO,
and NiO. Band gap, band structure, and density of states are evaluated using
finite size corrected QSGW. We find that although QSGW systematically
overestimates band gaps of tested semiconductors and transition metal oxides,
it completely removes the dependence on the choice of density functionals and
provides more consistent prediction of spectral properties than $G_0W_0$ across
a wide range of solids. This work paves the way for utilizing QSGW in ab initio
quantum embedding for solids.",2209.06179v2
2022-09-19,Effect of Pore Formation on Redox-Driven Phase Transformation,"When solid-state redox-driven phase transformations are associated with mass
loss, vacancies are produced that develop into pores. These pores can influence
the kinetics of certain redox and phase transformation steps. We investigated
the structural and chemical mechanisms in and at pores in a combined
experimental-theoretical study, using the reduction of iron oxide by hydrogen
as a model system. The redox product (water) accumulates inside the pores and
shifts the local equilibrium at the already reduced material back towards
re-oxidation into cubic-Fe1-xO (where x refers to Fe deficiency, space group
Fm3-m). This effect helps to understand the sluggish reduction of cubic-Fe1-xO
by hydrogen, a key process for future sustainable steelmaking.",2209.09069v2
2022-09-20,Characteristics of a Nickel Vanadium redox flow battery Based on COMSOL,"The overpotential, dissociation rate, electrode potential distributions and
current density are suggested in this study to analyze the Nickel Vanadium
Redox Flow Battery (NVRFB). Due to its large capacity and ecofriendly
properties, NVRFB may be a viable option in the present state of energy
constraint and environmental pollution. Due to their low cost and high energy
density, nickel-based flow batteries have gained popularity. This study
demonstrates that the Ni2+/Ni+ and V5+/V4+ ions have a higher rate of
dissociation at the membrane and a lower rate at the inlet, where the
electrolyte flow velocity is greater; Because the membrane undergoes more
oxidation-reduction reactions, the electrolyte flow rate is critical in the
redox flow cell; Additionally, we see that when electrode thickness is reduced,
current density and electrode potential increase while overpotential decreases;
the model's equations are solved using the finite-element method in the COMSOL
Multiphysics program. An electrolyte-electrode interface connection is used to
simulate the reaction. The dissociation rate indicates that the
oxidation-reduction process happens at a lower membrane potential. Improving
the electrolyte flow rate enhances battery performance. Compression of the
electrodes enhances conductivity and battery performance.",2209.09872v1
2022-09-28,Evolution of electronic band reconstruction in thickness-controlled perovskite SrRuO$_3$ thin films,"Transition metal perovskite oxides display a variety of emergent phenomena
which are tunable by tailoring the oxygen octahedral rotation. SrRuO$_3$, a
ferromagnetic perovskite oxide, is well-known to have various atomic structures
and octahedral rotations when grown as thin films. However, how the electronic
structure changes with the film thickness has been hardly studied. Here, by
using angle-resolved photoemission spectroscopy and electron diffraction
techniques, we study the electronic structure of SrRuO$_3$ thin films as a
function of the film thickness. Different reconstructed electronic structures
and spectral weights are observed for films with various thicknesses. We
suggest that octahedral rotations on the surface can be qualitatively estimated
via comparison of intensities of different bands. Our observation and
methodology shed light on how structural variation and transition may be
understood in terms of photoemission spectroscopy data.",2209.13813v1
2022-10-02,Nonlinear optical birefringence in Li2SO4-MgO-P2O5 amorphous system-influence of Cu ions,"Li2SO4-MgO-P2O5 glasses doped with varied contents of CuO (from 0- 1.0 mol%)
were prepared. The optical birefringence induced by a High Q-2 femtosecond
pulsed laser is explored as a function of copper oxide concentration in these
glasses. The magnitude of the light-induced birefringence exhibited a gradual
decrease with the increase of copper oxide content. The observed behavior is
discussed in terms of polymerization of the glass network, the degree of which
rises with concentration of Cu+ ions occupying Td sites in the glass matrix.
However, the samples containing low content of CuO are dominated by Cu2+ ions
that act as modifiers and induce structural imperfections by breaking of P-O-S
bonds. Accordingly, the samples mixed with lower content of CuO are more
favorable for inducing higher magnitudes of the optical birefringence. This
conclusion is corroborated by results of electrical conductivity, positron
annihilation and ultrasonic measurements.",2210.00404v1
2022-10-04,Atomic Level Strain Induced by Static and Dynamic Oxygen Vacancies on Reducible Oxide Surfaces,"Surface strain often controls properties of the material including charge
transport and chemical reactivity. Localized surface strain is measured with
atomic resolution on (111) ceria nanoparticle surfaces using environmental
transmission electron microscopy under different redox conditions. Density
Functional Theory (DFT) coupled with TEM image simulations have been used for
aid in interpreting the experimental data. Oxygen vacancy creation/annihilation
introduces strain at surface and near surface regions on cation sublattice.
Static and fluxional strainmaps are generated from images at these different
conditions and compared. While fluxional strain is highest at locations
associated with unstable vacancies at active sites, highly inhomogeneous static
strain fields comprising of alternating tensile/compressing strain is seen at
surface and subsurfaces linked to the presence of stable oxygen vacancies.
Interestingly, both stable and unstable oxygen vacancies are found within a few
atomic spacing of each other on the same surface. The static strain pattern
depends on the ambient inside TEM. Oxidizing environments tend to lower vacancy
concentrations at the surface whereas a highly reducing environment created
using high electron dose creates oxygen vacancies everywhere (bulk and
surfaces) in the nanoparticle.",2210.01764v2
2022-10-05,A quantum spin liquid phase in the Kitaev-Hubbard model,"The quantum spin liquid (QSL) state has been searched intensively in
Kitaev-like materials, such as the Iridium oxides $A_2$IrO$_3$ and
$\alpha$-RuCl$_3$. The half-filled Kitaev-Hubbard model with bond dependent
hopping terms is used to describe the Kitaev-like materials, which is
calculated using the state-of-the-art fermionic projected entangled pair states
(fPEPS) method. We find a QSL phase near the Mott insulator transition, which
has a strong first-order transition to the semi-metal phase with the decrease
of Hubbard $U$. We suggest that a promising routine to find the QSL is to find
the Iridium oxides that are near the Mott insulator transitions.",2210.01996v1
2022-10-28,Highly-Excited Rydberg Excitons in Synthetic Thin-Film Cuprous Oxide,"Cuprous oxide (Cu${}_2$O) has recently been proposed as a promising
solid-state host for excitonic Rydberg states with large principal quantum
numbers ($n$), whose exaggerated wavefunction sizes ($\propto n^2)$ facilitate
gigantic dipole-dipole ($\propto n^4$) and van der Waals ($\propto n^{11}$)
interactions, making them an ideal basis for solid-state quantum technology.
Synthetic, thin-film Cu${}_2$O samples are of particular interest because they
can be made defect-free via carefully controlled fabrication and are, in
principle, suitable for the observation of extreme single-photon nonlinearities
caused by the Rydberg blockade. Here, we present spectroscopic absorption and
photoluminescence studies of Rydberg excitons in synthetic Cu${}_2$O grown on a
transparent substrate, reporting yellow exciton series up to $n = 7$. We
perform these studies at powers up to 2 mW and temperatures up to 150 K, the
highest temperature where Rydberg series can be observed. These results open a
new portal to scalable and integrable on-chip Rydberg-based quantum devices.",2210.16416v1
2022-11-05,Photo-thermal tuning of graphene oxide coated integrated optical waveguides,"We experimentally investigate power sensitive photothermal tuning (PTT) of
two dimensional (2D) graphene oxide (GO) films coated on integrated optical
waveguides. We measure the light power thresholds for reversible and permanent
GO reduction in silicon nitride (SiN) waveguides integrated with 1 and 2 layers
of GO. Raman spectra at different positions of a hybrid waveguide with
permanently reduced GO are characterized, verifying the inhomogeneous GO
reduction along the direction of light propagation through the waveguide. The
differences between the PTT induced by a continuous wave laser and a pulsed
laser are also compared, confirming that the PTT mainly depend on the average
input power. These results reveal interesting features for 2D GO films coated
on integrated optical waveguides, which are of fundamental importance for the
control and engineering of GO properties in hybrid integrated photonic devices.",2211.02983v1
2022-11-11,Reverse Doping Asymmetry in Semiconductor Thin Films Using External Voltage,"Doping asymmetry is a notable phenomenon with semiconductors and a
particularly longstanding challenge limiting the applications of most
wide-band-gap semiconductors, which are inherent of spontaneous heavy n- or
p-type doping because of their extreme band edges. This study theoretically
shows that by applying a proper external voltage on materials during their
growth or doping processes, we can largely tune the band edges and consequently
reverse the doping asymmetry in semiconductor thin films. We take zinc oxide as
a touchstone and computationally demonstrate that this voltage-assisted-doping
approach efficiently suppresses the spontaneous n-type defects by around four
orders under three distinct growth conditions and successfully generates p-type
zinc oxide up to the lowest acceptor levels. The proposed approach is
insensitive to materials, growth conditions, or defects origins, and thus
offers a general solution to the doping asymmetry in semiconductor thin films.",2211.05990v2
2022-11-14,"Insight into the effect of rare earth $RE=Ce,\; Nd,\; Gd$ elements on the physical properties of Pb-Based Pervoskite Oxides ($PbREO_3$)","The electronic, elastic, structural, thermoelectric and optical parameters of
the Pb-based cubic perovskites $PbREO_3\; (RE=Ce,\; Gd,\; Nd)$ were calculated
using the WIEN2k Package. The mechanical optimization and structural
stabilities were evaluated. The found results are in full agreement with the
experimental ones. The obtained elastic results show that these perovskites
behave as stable ductile materials, and their higher $Y$ value gives them a
rigid structures. The $PbCeO_3$ presents n-type semiconductor while $PbREO_3\;
(RE= Gd,\; Nd)$ exhibit p-type semi-conductor with gap energies of $2.60\;eV$,
$1.02\;eV$ and $1.55\;eV$, respectively. The optical properties show that
$PbREO_3\; (RE=Ce,\; Gd,\; Nd)$ have significant absorption in the visible
light region with low reflectivity. The thermoelectric properties present a
desired electrical performance at room temperature for all materials. For these
generation of materials the effect of RE on Pb-based cubic perovskite oxides
can be exploited in manufacturing of thermoelectric, mechanic and
optoelectronic devices.",2211.07221v1
2022-11-22,Semi-supervised generative approach to point-defect formation in chemically disordered compounds: application to uranium-plutonium mixed oxides,"Machine-learning methods are nowadays of common use in the field of material
science. For example, they can aid in optimizing the physicochemical properties
of new materials, or help in the characterization of highly complex chemical
compounds. An especially challenging problem arises in the modeling of
chemically disordered solid solutions, for which some properties depend on the
distribution of chemical species in the crystal lattice. This is the case of
defect properties of uranium-plutonium mixed oxides nuclear fuels. The number
of possible configurations is so high that the problem becomes intractable if
treated with direct sampling. We thus propose a machine learning approach,
based on generative modeling, to optimize the exploration of this large
configuration space. A probabilistic, semi-supervised approach using Mixture
Density Network is applied to estimate the concentration of thermal defects in
(U, Pu)O2. We show that this method, based on the prediction of the density of
states of formation energy of a defect, is computationally much more
cost-efficient compared to other approaches available in the literature.",2211.12086v2
2022-12-03,Microstructure Evolution of Solid Oxide Fuel Cell Anodes Characterized by Persistent Homology,"Uncovering microstructure evolution mechanisms that accompany the long-term
operation of solid oxide fuel cells is a fundamental challenge in designing a
more durable energy system for the future. To date, the study of fuel cell
stack degradation has focused mainly on electrochemical performance and, more
rarely, on averaged microstructural parameters. Here we show an alternative
approach in which an evolution of three-dimensional microstructural features is
studied using electron tomography coupled with topological data analysis. The
latter produces persistent images of microstructure before and after long-term
operation of electrodes. Those images unveil a new insight into the degradation
process of three involved phases: nickel, pores, and yttrium-stabilized
zirconium.",2212.01576v1
2022-12-05,Discovery of a metallic oxide with ultralow thermal conductivity,"A compound with metallic electrical conductivity usually has a considerable
total thermal conductivity because both electrons and photons contribute to
thermal transport. Here, we show an exceptional example of iridium oxide,
Bi3Ir3O11, that concurrently displays metallic electrical conductivity and
ultralow thermal conductivity approaching 0.61 W m-1 K-1 at 300 K. The compound
crystallizes into a cubic structural framework with space group Pn-3. The edge-
and corner-sharing IrO6 octahedra with a mixed Ir4.33+ charge state favor
metallic electrical transport. Bi3Ir3O11 exhibits an extremely low lattice
thermal conductivity close to the minimum limit in theory owing to its
tunnel-like structure with filled heavy atoms Bi rattling inside. Theoretical
calculations reveal the underlying mechanisms for the extraordinary
compatibility between metallic electrical conductivity and ultralow thermal
conductivity. This study may establish a new avenue for designing and
developing unprecedented heat-insulation metals.",2212.02040v1
2022-12-15,Nd:YAG single crystals grown by floating zone method in laser furnace,"We report on single crystal growth of laser material Nd:YAG widely used in
the applications by innovative crucible-free floating zone method implemented
in an advanced laser optical furnace. We have optimized the parameters for the
production of high-quality single crystals of the size typical for laser tubes.
To reduce the strain and improve machinability, we have developed an
afterheater to thermalize the grown part of a single crystal below the hot
zone, which is a technique unavailable in common mirror furnaces. The high
quality of the single crystals was verified by Laue diffraction and the
internal strain was documented by neutron diffraction. The absorption spectrum
corresponds with the parameters of the commercially used material produced by
Czochralski method. The presented methodology for the single crystal growth by
floating zone method with laser heating is applicable for the preparation of
other high-quality single crystals of oxide-based materials, particularly in an
oxidizing environment unattainable in commonly used crucible methods.",2212.07662v1
2022-12-16,Reduced ITO for Transparent Superconducting Electronics,"Absorption of light in superconducting electronics is a major limitation on
the quality of circuit architectures that integrate optical components with
superconducting components. A 10 nm thick film of a typical superconducting
material like niobium can absorb over half of any incident optical radiation.
We propose instead using superconductors which are transparent to the
wavelengths used elsewhere in the system. In this paper we investigated reduced
indium tin oxide (ITO) as a potential transparent superconductor for
electronics. We fabricated and characterized superconducting wires of reduced
indium tin oxide. We also showed that a $\SI{10}{nm}$ thick film of the
material would only absorb about 1 - 20\% of light between 500 - 1700 nm.",2212.08573v1
2023-01-02,Thermo-optic phase shifter based on hydrogen-doped indium oxide microheater,"Thermo-optic (TO) phase shifters are very fundamental units in large-scale
active silicon photonic integrated circuits (PICs). However, due to the
limitation of microheater materials with a trade-off between heating efficiency
and absorption loss, designs reported so far typically suffer from slow
response time, high power consumption, low yields, and so on. Here, we
demonstrate an energy-efficient, fast-response, and low-loss TO phase shifter
by introducing hydrogen-doped indium oxide (IHO) films as microheater, and the
optimized electron concentration with enhanced mobility endows the IHO high
conductivity as well as high near-infrared (NIR) transparency, which allow it
to directly contact the silicon waveguide without any insulating layer for
efficient tuning and fast response. The TO phase shifter achieves a
sub-microsecond response time (970 ns/980 ns) with a {\pi} phase shift power
consumption of 9.6 mW. And the insertion loss introduced by the IHO microheater
is ~ 0.5 dB. The proposed IHO-based microheaters with compatible processing
technology illustrate the great potential of such material in the application
of large-scale silicon PICs.",2301.00816v1
2023-01-05,Review: Graphene oxide 2D thin films for high performance nonlinear integrated photonics,"Integrated photonic devices operating via optical nonlinearities offer a
powerful solution for all optical information processing, yielding processing
speeds that are well beyond that of electronic processing as well as providing
the added benefits of compact footprint, high stability, high scalability, and
small power consumption. The increasing demand for high performance nonlinear
integrated photonic devices has facilitated the hybrid integration of novel
materials to address the limitations of existing integrated photonic platforms,
such as strong nonlinear optical absorption or an inadequate optical
nonlinearity. Recently, graphene oxide (GO), with its large optical
nonlinearity, high flexibility in altering its properties, and facile
fabrication processes, has attracted significant attention, enabling many
hybrid nonlinear integrated photonic devices with improved performance and
novel capabilities. This paper reviews the applications of GO to nonlinear
integrated photonics. First, an overview of GOs optical properties and the
fabrication technologies needed for its onchip integration is provided. Next,
the state of the art GO nonlinear integrated photonic devices are reviewed,
together with comparisons of the nonlinear optical performance of different
integrated platforms incorporating GO. Finally, the challenges and perspectives
of this field are discussed.",2301.01862v1
2023-01-09,How do Quantum Effects Influence the Capacitance and Carrier Density of Monolayer MoS$_2$ Transistors?,"When transistor gate insulators have nanometer-scale equivalent oxide
thickness (EOT), the gate capacitance ($C_\textrm{G}$) becomes smaller than the
oxide capacitance ($C_\textrm{ox}$) due to the quantum capacitance and charge
centroid capacitance of the channel. Here, we study the capacitance of
monolayer MoS$_\textrm{2}$ as a prototypical two-dimensional (2D) channel while
considering spatial variations in the potential, charge density, and density of
states. At 0.5 nm EOT, the monolayer MoS$_\textrm{2}$ capacitance is smaller
than its quantum capacitance, limiting the single-gated $C_\textrm{G}$ of an
n-type channel to between 63% and 78% of $C_\textrm{ox}$ for gate overdrive
voltages between 0.5 and 1 V. Despite these limitations, for dual-gated
devices, the on-state $C_\textrm{G}$ of monolayer MoS$_\textrm{2}$ is 50%
greater than that of silicon at 0.5 nm EOT and more than three times that of
InGaAs at 1 nm EOT, indicating that 2D semiconductors are promising for
nanoscale devices at future technology nodes.",2301.03453v2
2023-01-12,Diagnostics for plasmon satellites and Hubbard bands in transition metal oxides,"Coulomb correlations between the electrons imprint characteristic signatures
to the spectral properties of materials. Among others, they are at the origin
of a rich phenomenology of satellite features, either stemming from atomic-like
multiplets or from interactions with particle-hole excitations or plasmons.
While in many cases the latter lie at considerably higher energies than the
former, suggesting clear distinction criteria, this picture has recently become
blurred by indications that satellites of different types can coexist in the
same energy range. It is now generally accepted that the identification of the
nature of spectral features is a highly non-trivial task. In this article we
propose a general procedure for tracing the origin of satellites of different
types within modern ab initio calculations. As an illustration, we analyze the
ternary transition metal oxides SrVO$_3$ and SrMoO$_3$, which are drosophila
compounds for the coexistence of Hubbard and plasmonic satellites, reconciling
previous seemingly contradictory findings in an unexpected manner.",2301.04908v1
2023-01-07,Significant CO2 photoreduction on a high-entropy oxynitride,"CO$_2$ photoreduction on photocatalysts is a nature-friendly solution to
decrease the CO$_2$ amount, but the method still has low efficiency because of
difficult separation and easy recombination of charge carriers in available
catalysts. In this study, a high-entropy oxynitride was introduced as an active
photocatalyst for photoreduction. The material had a chemical composition of
TiZrNbHfTaO$_6$N$_3$ and was produced by a high-pressure torsion method
followed by oxidation and nitriding. It showed higher photocatalytic CO$_2$ to
CO conversion compared to corresponding high-entropy oxide, benchmark
photocatalyst P25 TiO$_2$, and almost all catalysts introduced in the
literature. The high activity of this oxynitride, which also showed good
chemical stability, was attributed to the large absorbance of light and easy
separation of electrons and holes, the low recombination of charge carriers,
and the high CO$_2$ adsorption on the surface. These findings introduce
high-entropy oxynitrides as promising photocatalysts for CO$_2$ photoreduction.",2301.05013v2
2023-01-12,Surface acoustic wave generation and detection in quantum paraelectric regime of SrTiO$_3$-based heterostructure,"Strontium titanate (STO), apart from being a ubiquitous substrate for
complex-oxide heterostructures, possesses a multitude of strongly-coupled
electronic and mechanical properties. Surface acoustic wave (SAW) generation
and detection offers insight into electromechanical couplings that are
sensitive to quantum paraelectricity and other structural phase transitions.
Propagating SAWs can interact with STO-based electronic nanostructures, in
particular LaAlO$_3$/SrTiO$_3$ (LAO/STO). Here we report generation and
detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures
($T\ge$~2 K) using superconducting interdigitated transducers (IDTs). The
temperature dependence shows an increase in the SAWs quality factor that
saturates at $T\approx 8 $ K. The effect of backgate tuning on the SAW
resonance frequency shows the possible acoustic coupling with the ferroelastic
domain wall evolution. This method of generating SAWs provides a pathway
towards dynamic tuning of ferroelastic domain structures, which are expected to
influence electronic properties of complex-oxide nanostructures. Devices which
incorporate SAWs may in turn help to elucidate the role of ferroelastic domain
structures in mediating electronic behavior.",2301.05324v1
2023-01-18,Evolution of orbital excitations from insulating to superconducting MgTi$_2$O$_4$ films,"Spinel oxides are well-known functional materials but rarely show
superconductivity. Recently, emergent superconductivity was discovered in
MgTi$_2$O$_4$, which is attributed to the increase of electron doping and the
suppression of orbital order. Here, we utilized Ti $L$-edge resonant inelastic
X-ray scattering to study the orbital excitations in superconducting (SC) and
insulating MgTi$_2$O$_4$ films. We find that the spectral weight of orbital
excitations is enhanced and the energy of $t_{2g}$ intra-band excitation is
softened in the SC film compared to the insulating one, suggesting higher
electron doping and suppressed orbital order gap in the SC sample. These
observations were further supported by our multiplet calculations using minimal
two-site model. Our results provide spectroscopic evidence for the competition
between orbital order and superconductivity in MgTi$_2$O$_4$ and shed light on
searching for novel superconductors in spinel oxides.",2301.07299v1
2023-01-24,Accurate Energy Barriers for Catalytic Reaction Pathways: An Automatic Training Protocol for Machine Learning Force Fields,"In this study, we introduce a training protocol for developing machine
learning force fields (MLFFs), capable of accurately determining energy
barriers in catalytic reaction pathways. The protocol is validated on the
extensively explored hydrogenation of carbon dioxide to methanol over indium
oxide. With the help of active learning, the final force field obtains energy
barriers within 0.05 eV of Density Functional Theory. Thanks to the
computational speedup, not only do we reduce the cost of routine in-silico
catalytic tasks, but also find a 40\% reduction in the previously established
rate-limiting step. Furthermore, we illustrate the importance of
finite-temperature effects and compute free energy barriers. The
transferability of the protocol is demonstrated on the experimentally relevant,
yet unexplored, top-layer reduced indium oxide surface. The ability of MLFFs to
enhance our understanding of extensively studied catalysts underscores the need
for fast and accurate alternatives to direct ab-intio simulations.",2301.09931v2
2023-01-29,Interaction of oxygen with pristine and defective MoS2 monolayers,"Atom controlled sub-nanometer MoS$_2$ pores have been recently fabricated.
Oxidative environments are of particular interest for MoS$_2$ applications in
electronics, sensing and energy storage. In this work we carried out
first-principles calculations of oxygen adsorption in plain and sub-nanometer
MoS$_2$ nanopores. The chemical stability of the layers and pores towards
oxygen was verified using density-functional theory. Dissociation and diffusion
barriers have been calculated in order to understand surface and pore oxidation
and its electronic properties at the atomic scale, which opens the path for
future investigations of MoS$_2$ pores in a realistic environment.",2301.12337v1
2023-01-30,Growth of $α-Ga_2O_3$ on $Al_2O_3$ by conventional molecular-beam epitaxy and metal-oxide-catalyzed epitaxy,"We report the growth of $\alpha-Ga_2O_3$ on $m$-plane $Al_2O_3$ by
conventional plasma-assisted molecular-beam epitaxy (MBE) and In-mediated
metal-oxide-catalyzed epitaxy (MOCATAXY). We report a growth-rate-diagram for
$\alpha-Ga_2O_3$ (10-10), and observe (i) a growth rate increase, (ii) an
expanded growth window, and (iii) reduced out-of-lane mosaic spread when
MOCATAXY is employed for the growth of $\alpha-Ga_2O_3$. Through the use of
In-mediated catalysis, growth rates over $0.2\,\mu\text{m}\,\text{hr}^{-1}$ and
rocking curves with full width at half maxima of $\Delta\omega \approx
0.45^{\circ}$ are achieved. Faceting is observed along the $\alpha-Ga_2O_3$
film surface and is explored through scanning transmission electron microscopy.",2301.13053v1
2023-01-31,Orientation-dependent electron-phonon coupling in interfacial superconductors LaAlO3/KTaO3,"The emergent superconductivity at the LaAlO3/KTaO3 interfaces exhibits a
mysterious dependence on the KTaO3 crystallographic orientations. Here we show,
by soft X-ray angle-resolved photoemission spectroscopy, that the interfacial
superconductivity is contributed by mobile electrons with unexpected
quasi-three-dimensional character, beyond the ""two-dimensional electron gas""
scenario in describing oxide interfaces. At differently-oriented interfaces,
the quasi-three-dimensional electron gas ubiquitously exists and spatially
overlaps with the small q Fuchs-Kliewer surface phonons. Intriguingly,
electrons and the Fuchs-Kliewer phonons couple with different strengths
depending on the interfacial orientations, and the stronger coupling correlates
with the higher superconducting transition temperature. Our results provide a
natural explanation for the orientation-dependent superconductivity, and the
first evidence that interfacial orientations can affect electron-phonon
coupling strength over several nanometers, which may have profound implications
for the applications of oxide interfaces in general.",2301.13488v1
2023-01-31,Enhancement in physical properties of Pb-Based Perovskite Oxides ($PbGeO_{3}$): Ab initio Calculation,"In the present paper, the electronic, structural, thermodynamic, and elastic
properties of cubic $PbGeO_{3}$ perovskite oxide are presented and computed
using the WIEN2K code. The structural properties have been evaluated and they
are in good agreement with the theoretical and experimental data. A phonon
dispersion is made and it reveals that the cubic $PbGeO_{3}$ perovskite is
dynamically stable. In addition, the electronic properties of $PbGeO_{3}$ shows
an opening gap energy, meaning a semiconductor behavior with an indirect band
gap equal to $1.67 eV$. Moreover, the obtained elastic constants of cubic
$PbGeO_{3}$ satisfy Born's mechanical stability criteria, and this indicates
that our compound behaves as a stable ductile material. The
temperature-pressure effects on thermodynamic parameters are investigated using
the Gibbs$2$ package. Finally, based on the obtained results about the cubic
$PbGeO_{3}$ perovskite properties, we assume that this compound will have
potential applications.",2301.13493v1
2023-02-04,A method to measure the quenching factor for recoil energy of oxygen in bismuth germanium oxide scintillators,"Bismuth germanium oxide ($\rm Bi_{4} Ge_{3} O_{12}$, BGO) scintillation
crystals are widely used as detectors in the fields of particle physics and
astrophysics due to their high density, and thus higher efficiency for
gamma-ray detection. Owing to their good chemical stability, they can be used
in any environment. For rare-event searches, such as dark matter and coherent
elastic neutrino-nucleus scattering, BGO crystals are essential to comprehend
the response of nuclear recoil. In this study, we have analyzed the events of
neutron elastic scattering with oxygen in BGO crystals. Then, we have measured
the quenching factor for oxygen recoil energy in the BGO crystal as a function
of recoil energy by using a monoenergetic neutron source.",2302.02111v3
2023-02-09,Understanding the role of entropy in high entropy oxides,"The field of high entropy oxides (HEOs) flips traditional materials science
paradigms on their head by seeking to understand what properties arise in the
presence of profound configurational disorder. This disorder, which originates
from multiple elements sharing a single lattice site, can take on a
kaleidoscopic character due to the vast numbers of possible elemental
combinations. High configurational disorder appears to imbue some HEOs with
functional properties that far surpass their non-disordered analogs. While
experimental discoveries abound, efforts to characterize the true magnitude of
the configurational entropy and understand its role in stabilizing new phases
and generating superior functional properties have lagged behind. Understanding
the role of configurational disorder in existing HEOs is the crucial link to
unlocking the rational design of new HEOs with targeted properties. In this
Perspective, we attempt to establish a framework for articulating and beginning
to address these questions in pursuit of a deeper understanding of the true
role of entropy in HEOs.",2302.04394v1
2023-02-13,Electric control of two-dimensional Van Hove singularity in oxide ultra-thin films,"Divergent density of states (DOS) can induce extraordinary phenomena such as
significant enhancement of superconductivity and unexpected phase transitions.
Moreover, van Hove singularities (VHSs) are known to lead to divergent DOS in
two-dimensional (2D) systems. Despite the recent interest in VHSs, only a few
controllable cases have been reported to date. In this work, we investigate the
electronic band structures of a 2D VHS with angle-resolved photoemission
spectroscopy and control transport properties by utilizing an atomically
ultrathin SrRuO$_3$ film. By applying electric fields with alkali metal
deposition and ionic-liquid gating methods, we precisely control the 2D VHS,
and the sign of the charge carrier. Use of a tunable 2D VHS in an atomically
flat oxide film could serve as a new strategy to realize infinite DOS near the
Fermi level, thereby allowing efficient tuning of electric properties.",2302.06222v2
2023-02-13,Atomic scale understanding of the role of hydrogen and oxygen segregation in the embrittlement of grain boundaries in a twinning induced plasticity steel,"Twinning induced plasticity (TWIP) steels are high strength metallic
materials with potential for structural components in e.g. automotive
applications. However, they are prone to hydrogen embrittlement (HE) and
galvanic corrosion. We investigated the susceptibility of a model Fe 27Mn 0.3C
(wt%) TWIP steel towards HE and oxidation at the sub-nanometer scale by atom
probe tomography. We measured segregation of hydrogen and oxygen at grain
boundaries, which appears to be associated to a strong manganese depletion. Our
study suggests a correlation between HE and oxidation mechanisms in TWIP
steels, which we argue can combine to favor the previously reported hydrogen
enhanced decohesion (HEDE) of grain boundaries.",2302.06317v2
2023-02-27,Novel supercell compounds of layered Bi-Rh-O with $p$-type metallic conduction materialized as a thin film form,"Layered oxides have been intensively studied due to their high degree of
freedom in designing various electromagnetic properties and functionalities.
While Bi-based layered supercell (LSC) compounds
[Bi$_n$O$_{n+\delta}$]-[$M$O$_2$] ($M$ = Mn, Mn/Al, Mn/Fe, or Mn/Ni; $n=2, 3$)
are a group of prospective candidates, all of the reported compounds are
insulators. Here, we report on the synthesis of two novel metallic LSC
compounds [Bi$_{n}$O$_{n+\delta}$]-[RhO$_2$] ($n=2, 3$) by pulsed laser
deposition and subsequent annealing. With tuning the thickness of the
sublattice from Bi$_2$O$_{2+\delta}$ to Bi$_3$O$_{3+\delta}$, a
dimensionality-dependent electrical transport is revealed from a conventional
metallic transport in $n=2$ to a localized transport in $n=3$. Our successful
growth will be an important step for further exploring novel layered oxide
compounds.",2302.13538v1
2023-02-28,Near-field localization of the boson peak on tantalum films for superconducting quantum devices,"Superconducting circuits are among the most advanced quantum computing
technologies, however their performance is currently limited by losses found in
surface oxides and disordered materials. Here, we identify and spatially
localize a near-field signature of loss centers on tantalum films using
terahertz scattering-type scanning near-field optical microscopy (s-SNOM).
Making use of terahertz nanospectroscopy, we observe a localized excess
vibrational mode around 0.5 THz and identify this resonance as the boson peak,
a signature of amorphous materials. Grazing-incidence wide-angle x-ray
scattering (GIWAXS) shows that oxides on freshly solvent-cleaned samples are
amorphous, whereas crystalline phases emerge after aging in air. By localizing
defect centers at the nanoscale, our characterization techniques and results
will inform the optimization of fabrication procedures for new low-loss
superconducting circuits.",2302.14316v1
2023-03-02,Stoichiometric growth of SrTiO3 films via Bayesian optimization with adaptive prior mean,"Perovskite insulator SrTiO3 is expected to be applied to the next generation
of electronic and photonic devices as high-k capacitors and photocatalysts.
However, reproducible growth of highly insulating stoichiometric SrTiO3 films
remains challenging due to the difficulty of the precise stoichiometry control
in perovskite oxide films. Here, to grow stoichiometric SrTiO3 thin films by
fine-tuning multiple growth conditions, we developed a new Bayesian
optimization (BO)-based machine learning method that encourages the exploration
of the search space by varying the prior mean to get out of suboptimal growth
condition parameters. Using simulated data, we demonstrate the efficacy of the
new BO method, which reproducibly reaches the global best conditions. With the
BO method implemented in machine-learning-assisted molecular beam epitaxy
(ML-MBE), highly insulating stoichiometric SrTiO3 film with no absorption in
the band gap was developed in only 44 MBE growth runs. The proposed algorithm
provides an efficient experimental design platform that is not as dependent on
the experience of individual researchers and will accelerate not only oxide
electronics but also various material syntheses.",2303.00929v1
2023-03-07,"Graphene oxide: new opportunities for optoelectronic, electronic and photonic chips","As a derivative of graphene, graphene oxide (GO) was initially developed by
chemists to emulate some of the key properties of graphene, but it was soon
recognized as a unique material in its own right, addressing an application
space that is not accessible to chemical vapor deposition based materials. Over
the past decade, GO has emerged as a new frontier material with tremendous
advances in its material fabrication and quality control over its properties.
These in turn have led to rapid progress in GO based photonics, electronics,
and optoelectronics concepts and devices, evoking new science and paving the
way for many technological breakthroughs with exceptional performance. Here, we
review the unique fundamental characteristics of GO, its thin film fabrication
methods, patterning techniques, and mechanisms for tuning its material
properties. This latter capability in particular has enabled novel advanced
functional photonic, electronic, and optoelectronic devices. Understanding
these insights is essential for designing and tailoring GO properties for
state-of-the-art applications including solar energy harvesting, energy
storage, medical diagnosis, image displays, and optical communications. We
conclude by discussing the open challenges and exciting opportunities of this
field, together with future prospects for major technological advancements and
breakthroughs.",2303.03604v1
2023-03-13,Linking stability with molecular geometries of perovskites and lanthanide richness using machine learning methods,"Oxide perovskite materials of type ABO3 have a wide range of technological
applications, such as catalysts in solid oxide fuel cells and as
light-absorbing materials in solar photovoltaics. These materials often exhibit
differential structural and electrostatic properties through lanthanide or
non-lanthanide derived A- and B- sites. Although, experimental and/or
computational verification of these differences are often difficult. In this
paper, we thus take a data-driven approach. Specifically, we run three analysis
using the dataset Li, Jacobs, and Morgan [2018a] applying advanced machine
learning tools to perform nonparametric regressions and also to produce data
visualizations using latent factor analysis (LFA) and principal component
analysis (PCA). We also implement a nonparametric feature screening step while
performing our high dimensional regression analysis, ensuring robustness in our
results",2303.07441v3
2023-03-30,Impact of iso-structural template layer on stabilizing pyrochlore Bi$_2$Rh$_2$O$_7$,"We present an epitaxial stabilization of pyrochlore Bi$_2$Rh$_2$O$_7$ on
Y-stabilized ZrO$_2$ (YSZ) (111) substrate by inserting a pyrochlore
Eu$_2$Ti$_2$O$_7$ template layer, otherwise Bi-based layered structures being
formed directly on YSZ (111) substrate. This result reveals that
""iso-structural crystal phase"" plays an important role in the interfacial phase
control. The Bi$_2$Rh$_2$O$_7$ film exhibits $p$-type electrical conduction
with the lowest longitudinal resistivity ($\rho_\mathrm{xx}$) among the
reported Rh pyrochlore oxides. Such parameters as $\rho_\mathrm{xx}$, carrier
density, and mobility show almost no temperature dependence in the measured
range of 2$-$300 K, indicating Bi$_2$Rh$_2$O$_7$ as one of the rare examples of
conducting pyrochlore oxides.",2303.17136v1
2023-03-31,Direct-write projection lithography of quantum dot micropillar single photon sources,"We have developed a process to mass-produce quantum dot micropillar cavities
using direct-write lithography. This technique allows us to achieve high volume
patterning of high aspect ratio pillars with vertical, smooth sidewalls
maintaining a high quality factor for diameters below 2.0 $\mu$m. Encapsulating
the cavities in a thin layer of oxide (Ta$_2$O$_5$) prevents oxidation in the
atmosphere, preserving the optical properties of the cavity over months of
ambient exposure. We confirm that single dots in the cavities can be
deterministically excited to create high purity indistinguishable single
photons with interference visibility $(96.2\pm0.7)\%$.",2304.00141v1
2023-04-03,Navigating phase diagram complexity to guide robotic inorganic materials synthesis,"Efficient synthesis recipes are needed both to streamline the manufacturing
of complex materials and to accelerate the realization of theoretically
predicted materials. Oftentimes the solid-state synthesis of multicomponent
oxides is impeded by undesired byproduct phases, which can kinetically trap
reactions in an incomplete non-equilibrium state. We present a thermodynamic
strategy to navigate high-dimensional phase diagrams in search of precursors
that circumvent low-energy competing byproducts, while maximizing the reaction
energy to drive fast phase transformation kinetics. Using a robotic inorganic
materials synthesis laboratory, we perform a large-scale experimental
validation of our precursor selection principles. For a set of 35 target
quaternary oxides with chemistries representative of intercalation battery
cathodes and solid-state electrolytes, we perform 224 reactions spanning 27
elements with 28 unique precursors. Our predicted precursors frequently yield
target materials with higher phase purity than when starting from traditional
precursors. Robotic laboratories offer an exciting new platform for data-driven
experimental science, from which we can develop new insights into materials
synthesis for both robot and human chemists.",2304.00743v2
2023-04-21,"Comparison of Matlantis and VASP bulk formation and surface energies in metal hydrides, carbides, nitrides, oxides, and sulfides","Generic neural network potentials without forcing users to train potentials
could result in significantly acceleration of total energy calculations.
Takamoto et al. [Nat. Commun. (2022), 13, 2991] developed such a deep neural
network potential (NNP) and made it available in their Matlantis package. We
compared the Matlantis bulk formation, surface, and surface O vacancy formation
energies of metal hydrides, carbides, nitrides, oxides, and sulfides with our
previously calculated VASP values obtained from first-principles with the
PBEsol(+U) functional. Matlantis bulk formation energies were consistently ~0.1
eV/atom larger and the surface energies were typically ~10 meV/{\AA}^2 smaller
than the VASP counterpart. Surface O vacancy formation energies were generally
underestimated within ~0.8 eV. These results suggest that Matlantis energies
could serve as a relatively good descriptor of the VASP bulk formation and
surface energies.",2304.10820v1
2023-04-06,A Framework for Combustion Chemistry Acceleration with DeepONets,"A combustion chemistry acceleration scheme is developed based on deep
operator networks (DeepONets). The scheme is based on the identification of
combustion reaction dynamics through a modified DeepOnet architecture such that
the solutions of thermochemical scalars are projected to new solutions in small
and flexible time increments. The approach is designed to efficiently implement
chemistry acceleration without the need for computationally expensive
integration of stiff chemistry. An additional framework of latent-space
dynamics identification with modified DeepOnet is also proposed which enhances
the computational efficiency and widens the applicability of the proposed
scheme. The scheme is demonstrated on simple chemical kinetics of hydrogen
oxidation to more complex chemical kinetics of n-dodecane high- and
low-temperature oxidations. The proposed framework accurately learns the
chemical kinetics and efficiently reproduces species and temperature temporal
profiles corresponding to each application. In addition, a very large speed-up
with a great extrapolation capability is also observed with the proposed
scheme.",2304.12188v1
2023-04-27,On the structure-to-property relationship of polyanilines. A modern quantum chemistry perspective,"We employ state-of-the-art quantum chemistry methods to study the
structure-to-property relationship in polyanilines (PANIs) of different lengths
and oxidation states. Specifically, we focus on leucoemeraldine, emeraldine,
and pernigraniline in their tetramer and octamer forms. We scrutinize their
structural properties, HOMO and LUMO energies, HOMO-LUMO gaps, and vibrational
and electronic spectroscopy using various Density Functional Approximations
(DFAs). Furthermore, the accuracy of DFAs is assessed by comparing them to
experimental and wavefunction-based reference data. For that purpose, we
performed large-scale orbital-optimized pair-Coupled Cluster Doubles (oo-pCCD)
calculations for ground and electronically excited states and conventional
Configuration Interaction Singles (CIS) calculations for electronically excited
states in all investigated systems. Furthermore, we augment our study with a
quantum informational analysis of orbital correlations in various forms of
PANIs. Our study highlights the growing multi-reference nature of PANIs with
the length of the polymer. While structural and vibrational features of the
investigated PANIs, regardless of their oxidation states, are adequately
modeled in the tetramer forms, the length of the PANI chain profoundly affects
electronic spectra. Specifically, polymer elongation changes the character of
the leading transitions in the lowest-lying excited states in all investigated
PANIs.",2304.14547v1
2023-04-28,Ab-initio study of short-range ordering in vanadium-based disordered rocksalt structures,"Disordered rocksalt Li-excess (DRX) compounds are attractive new cathode
materials for Li-ion batteries as they contain resource-abundant metals and do
not require the use of cobalt or nickel. Understanding the delithiation process
and cation short-range ordering (SRO) in DRX compounds is essential to
improving these promising cathode materials. Herein, we use first-principles
calculations along with the cluster-expansion approach to model the disorder in
DRX Li2-xVO3, 0 < x < 1. We discuss the SRO of Li in tetrahedral and octahedral
sites, and the order in which Li delithiates and V oxidizes with respect to
local environments. We reveal that the number of nearest-neighbor V dictates
the order of delithiation from octahedral sites and that V are oxidized in a
manner that minimizes the electrostatic interactions among V. Our results
provide valuable insight for tailoring the performance of V-based DRX cathode
materials in general by controlling the SRO features that reduce energy
density.",2304.14645v1
2023-04-27,Real-time spectroscopic monitoring of continuous synthesis of zinc oxide nanostructures in femtosecond laser fabricated 3D microfluidic microchannels with integrated on-chip fiber probe array,"Materials synthesis in a microfluidic environment enables the flexible and
controllable production of various types of nanostructures which are of great
potential in the fields of chemistry, environmental science, bioengineering,
and medicine. Here, we demonstrate on-chip simultaneous continuous-flow
synthesis and in-situ spectrum diagnosis of zinc oxide (ZnO) nanomaterials
using a femtosecond-fabricated three-dimensional microchannel reactor
integrated with an array of optical fiber probes. The microchannel reactor
including 3D concentration gradient generators followed by 3D micromixing units
provides high-efficiency manipulation of reactants with different
concentrations as well as parallel reaction dynamics in an autonomous manner.
The integrated optical fiber probe array allows precise and parallel spectropic
detection in different microchannels with high spatial and temporal resolutions
for screening the synthetic conditions. The synthesized ZnO nanostructures can
be tailored in size, shape, and morphology by tuning the flow rates and
reactant concentrations based on the spectroscopic signals detected with the
fiber probe array.",2305.00920v1
2023-05-04,Photostrictive actuators based on freestanding ferroelectric membranes,"Complex oxides offer a wide range of functional properties, and recent
advances in fabrication of freestanding membranes of these oxides are adding
new mechanical degrees of freedom to this already rich functional ecosystem.
Here, we demonstrate photoactuation in freestanding thin film resonators of
ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate
(SrTiO3). The free-standing films, transferred onto perforated supports, act as
nano-drums, oscillating at their natural resonance frequency when illuminated
by a frequency-modulated laser. The light-induced deflections in the
ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the
paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under
illumination and temperature-dependent and holographic interferometry provide
combined evidence for the photostrictive strain in BaTiO3 originating from
partial screening of ferroelectric polarization by photo-excited carriers,
which decreases the tetragonality of the unit cell. These findings showcase the
potential of photostrictive freestanding ferroelectric films as wireless
actuators operated by light.",2305.03193v2
2023-05-05,K. Alex Müller: Science between ferroelectricity and superconductivity,"K. Alex M\""uller started his scientific career in 1958 when he was about
thirty-one years old. After his wife passed away and being in his nineties, his
interest in physics gradually faded. In those years shortly before he passed
away, on January 9, 2023, he was no longer interested in superconductivity or
ferroelectricity, he had become essentially devoted to philosophy and
psychology. It is of note that altogether his research in physics comprised
sixty years of activity. Almost in the middle of this period, he was awarded
the Nobel Prize in Physics for the discovery of high-temperature
superconductivity in ceramic copper oxides in 1987. This discovery made him
truly famous. While most researchers are familiar with his Nobel Prize work,
many are not aware of the fact that K. Alex M\""uller was already an acclaimed
scientist before that and highly respected in the field of perovskite oxides,
ferroelectricity, structural phase transitions, Jahn-Teller physics, electron
paramagnetic resonance (EPR) and, especially so in the properties of SrTiO3.",2305.03705v1
2023-05-09,Thermodynamic route of Nb3Sn nucleation: Role of oxygen,"Intermetallic Nb3Sn alloys have long been believed to form through Sn
diffusion into Nb. However, our observations of significant oxygen content in
Nb3Sn prompted an investigation of alternative formation mechanisms. Through
experiments involving different oxide interfaces (clean HF-treated, native
oxidized, and anodized), we demonstrate a thermodynamic route that
fundamentally challenges the conventional Sn diffusion mechanism for Nb3Sn
nucleation. Our results highlight the critical involvement of a SnOx
intermediate phase. This new nucleation mechanism identifies the principles for
growth optimization and new synthesis of high-quality Nb3Sn superconductors.",2305.05114v2
2023-05-13,Characteristic time of transient response of solid oxide cells (SOCs) to changes in voltage/current: from theory to applications,"The intermittency of solar and wind power can be addressed by integrating
them with Solid Oxide Cells (SOCs). This study delves into the transient
characteristics of SOCs and their dependence on dynamic heat and mass transfer
processes. Non-dimensional analysis was used to identify influential
parameters, followed by a 3-D numerical simulation-based parametric analysis to
examine the dynamic gaseous and thermal responses of SOCs with varying
dimensions, material properties, and operating conditions. For the first time,
we proposed characteristic times to describe the relationship between SOC
transients and multiple parameters. These characteristic times represent the
overall heat and mass transfer rats in SOCs. Their effectiveness was validated
against literature and demonstrated potential in characterizing the transient
characteristics of other electrochemical cells. Besides, two examples are
provided to illustrate how the characteristic times facilitate SOC design and
control at minimal computational cost.",2305.07926v1
2023-05-18,Unfaulting mechanisms of Frank loops in fluorite oxides,"Unfaulting of Frank loops in irradiated fluoride oxides are of significance
to microstructural evolution. However, the mechanisms have not been directly
observed. To this end, we utilize molecular dynamics to reveal the atomistic
details related to the unfaulting process of interstitial Frank loop in
ThO$_2$, which involve nucleation of single or multiple Shockley partial pairs
at the loop circumference. The unfaulting is achieved via a synchronous shear
of the partial pairs to remove the extrinsic stacking fault in the cation
sublattice and the intrinsic stacking fault in the anion sublattice. The strong
oxygen motion at the dislocation core may reduce the activation barriers of
dislocation nucleation and migration. These findings provide a fundamental
understanding of the transformation of faulted loops in irradiated ThO$_2$, and
could be transferable to other fluorite systems.",2305.11127v1
2023-05-08,Role of Nano-fertilizer in Plants Nutrient Use Efficiency (NUE)- A mini-review,"Over the past half-century, the combination of technology and innovation has
been developed to manage the negative impact of synthetic fertilizer on land
ecosystems to identify the limitations of sustainability and optimize
agricultural systems. The application of nano-fertilizers has achieved
considerable interest due to their significant role as environmentally
sustainable resources and soil health. Moreover, the increasing global
population increased food insecurity, especially under climate change.
Nanotechnology has emerged as a promising alternative to help improving crop
growth and productivity. However, un-balanced presence and long-term use of
nano-particles alter photosynthesis, and induce cellular redox imbalances
resulting in lipid peroxidation, protein oxidation and DNA oxidative damage in
plants, so more studies are still needed on their safe application with minimum
side effects. In this paper, we reviewed nano-fertilizer mechanisms in plant,
as well as their effects on microbiome and interaction with soil colloids. This
study reviews the recent studies and findings about role of Nanotechnology in
plant nutrition use efficiency to summarize a better understanding of this
important issue. A comprehensive picture of ecological issues such as soil and
water contamination in response to nano-fertilizer application will also be
assessed.",2305.14357v1
2023-05-27,"Bond formation at polycarbonate | X interfaces (X = Al$_2$O$_3$, TiO$_2$, TiAlO$_2$) studied by theory and experiments","Interfacial bond formation during sputter deposition of metal oxide thin
films onto polycarbonate (PC) is investigated by ab initio molecular dynamics
simulations and X-ray photoelectron spectroscopy (XPS) analysis of PC | X
interfaces (X = Al$_2$O$_3$, TiO$_2$, TiAlO$_2$). Generally, the predicted bond
formation is consistent with the experimental data. For all three interfaces,
the majority of bonds identified by XPS are (C-O)-metal bonds, whereas C-metal
bonds are the minority. Compared to the PC | Al$_2$O$_3$ interface, the PC |
TiO$_2$ and PC | TiAlO$_2$ interfaces exhibit a reduction in the measured
interfacial bond density by ~ 75 and ~ 65%, respectively. Multiplying the
predicted bond strength with the corresponding experimentally determined
interfacial bond density shows that Al$_2$O$_3$ exhibits the strongest
interface with PC, while TiO$_2$ and TiAlO$_2$ exhibit ~ 70 and ~ 60% weaker
interfaces, respectively. This can be understood by considering the complex
interplay between the metal oxide composition, the bond strength as well as the
population of bonds that are formed across the interface.",2305.17430v1
2023-05-30,VO2 Phase Change Electrodes in Li-ion Batteries,"Use of electrode materials that show phase change behavior and hence drastic
changes in electrochemical activity during operation, have not been explored
for Li-ion batteries. Here we demonstrate the vanadium oxide (VO2) cathode that
undergoes metal-insulator transition due to first-order structural phase
transition at accessible temperature of 68{\deg}C for battery operation. Using
a suitable electrolyte operable across the phase transition range and
compatible with vanadium oxide cathodes, we studied the effect of electrode
structure change on lithium insertion followed by the electrochemical
characteristics above and below the phase transition temperature. The
high-temperature VO2 phase shows significantly improved capacitance, enhanced
current rate capabilities, improved electrical conductivity and lithium-ion
diffusivity compared to the insulating low temperature phase. This opens up new
avenues for electrode designs, allowing manipulation of electrochemical
reactions around phase transition temperatures, and in particular enhancing
electrochemical properties at elevated temperatures contrary to existing
classes of battery chemistries that lead to performance deterioration at
elevated temperatures.",2305.19002v1
2023-06-05,Extraordinary Tunneling Magnetoresistance in Antiferromagnetic Tunnel Junctions with Antiperovskite Electrodes,"Recent theoretical predictions and experimental demonstrations of a large
tunneling magnetoresistance (TMR) effect in antiferromagnetic (AFM) tunnel
junctions (AFMTJs) offer a new paradigm for information technologies where the
AFM N\`eel vector serves as a state variable. A large TMR is beneficial for the
applications. Here, we predict the emergence of an extraordinary TMR (ETMR)
effect in AFMTJs utilizing noncollinear AFM antiperovskite XNMn$_{3}$ (X = Ga,
Sn,...) electrodes and a perovskite oxide ATiO$_{3}$ (A = Sr, Ba,...) barrier
layer. The ETMR effect stems from the perfectly spin-polarized electronic
states in the AFM antiperovskites that can efficiently tunnel through the
low-decay-rate evanescent states of the perovskite oxide while preserving their
spin state. Using an GaNMn$_{3}$/SrTiO$_{3}$/GaNMn$_{3}$ (001) AFMTJ as a
representative example, we demonstrate a giant TMR ratio exceeding $10^{4}$%
and originating from the ETMR effect. These results are promising for the
efficient detection and control of the N\`eel vector in AFM spintronics.",2306.03026v1
2023-05-30,Self-regulated ligand-metal charge transfer upon lithium ion de-intercalation process from LiCoO2 to CoO2,"Understanding the role of metal and oxygen in the redox process of layered 3d
transition metal oxides is crucial to build high density and stable next
generation Li-ion batteries. We combine hard X-ray photoelectron spectroscopy
and ab-initio-based cluster model simulations to study the electronic structure
of prototypical end-members LiCoO2 and CoO2. The role of cobalt and oxygen in
the redox process is analyzed by optimizing the values of d-d electron
repulsion and ligand-metal p-d charge transfer to the Co 2p spectra. We clarify
the nature of oxidized cobalt ions by highlighting the transition from positive
to negative ligand-to-metal charge transfer upon Li+ de-intercalation.",2306.03096v2
2023-06-15,Characteristic THz-emissions induced by optically excited collective orbital modes,"We study the generation of collective orbital modes, their evolution, and the
characteristic non-linear optical response induced by them in a photoinduced
orbital-ordered correlated oxide using real-time simulations based on an
interacting multiband tight-binding (TB) model. The d-d optical transitions
under femtoseconds light-pulse in a orbital-ordered state excite collective
orbital modes, also known as ""orbitons"". The consistent inclusion of electronic
interactions and the coupling between charge, spin, and lattice degrees of
freedom in the TB-model provide a better understanding of the underlying
mechanisms of the collective orbital modes. The dynamics of Jahn-Teller
vibrational modes in the photoinduced state modify the intersite orbital
interaction, which further amplifies these orbital modes. In the presence of
weak ferroelectricity, the excitation of collective orbital modes induces a
strong THz oscillatory photocurrent which is long-lived. This suggests an
alternative way to experimentally detect quasiparticles describing such
collective modes through THz-emission studies in the photoinduced state. Our
study also elucidates that quasiparticle dynamics in improper ferroelectric
oxides can be exploited to achieve highly interesting and non-trivial
optoelectronic properties.",2306.09107v1
2023-06-27,Zinc dialkyldithiophosphates adsorption and dissociation on ferrous substrates: an ab initio study,"Zinc dialkyldithiophosphates (ZDDPs) have been commonly used as anti-wear
additives in the automotive industry for the past 80 years. The morphology,
composition and structure of the ZDDPs phosphate-based tribofilm, which is
essential for its lubricant functioning, have been widely studied
experimentally. However, despite their widespread use, a general agreement on
their primary functioning mechanism is still lacking. The morphology and
composition of the ZDDPs phosphate-based tribofilm have been widely studied
experimentally, but the formation process and the relevant driving forces are
still largely debated. In particular, it is unclear whether the stress-induced
molecular dissociation occurs in the bulk oil or on the substrate. In this
work, we employ ab initio density-functional theory simulations to compare ZDDP
fragmentation in vacuum and over a reactive substrate, considering the effects
of surface oxidation on the dissociation path. Our results show that the
molecular dissociation is highly endothermic in the absence of a supporting
substrate, while in the presence of an iron substrate it becomes highly
energetically favoured. Moreover, the presence of the substrate changes the
reaction path. At the same time, surface oxidation reduces the
molecule-substrate interaction. These findings provide valuable insights into
the early stages of the formation of phosphate-based tribofilms.",2306.15654v1
2023-07-01,"Unusual nanoscale coexistence of polar-nonpolar domains underlying oxygen storage properties in Ho(Mn, Ti)O$_{3+δ}$","Hexagonal manganese oxides RMnO$_3$ show intriguing topological
ferroelectric-domain walls with variable conductivity, leading to domain wall
engineering. Despite the numerous experimental studies on the polar nanoscale
structures, controlling ferroelectric domains has not been sufficiently
investigated. Here, we reveal the unprecedented coexistence of polar-nonpolar
nanoscale domains that can be formed by substituting Ti ions in HoMnO$_3$.
Unusual polar nanoscale domains are embedded in nonpolar domains with different
crystallographic symmetry. This polar-nonpolar coexisting structure is
naturally assembled by adjusting the lattice length during a solid-state
reaction process. Furthermore, the comprehensive study reveals that the
reversible microstructural change with a nonpolar-polar transition is strongly
correlated with the oxygen storage properties in Ho(Mn, Ti)O$_{3+\delta}$. The
present results provide important insight into the nanoscale polar-nonpolar
domain coexistence in functional rare-earth manganese oxides, RMnO$_3$.",2307.00248v1
2023-07-03,Toward an accurate equation of state and B1-B2 phase boundary for magnesium oxide to TPa pressures and eV temperatures,"By applying auxiliary-field quantum Monte Carlo, we calculate the equation of
state (EOS) and B1-B2 phase transition of magnesium oxide (MgO) up to 1 TPa.
The results agree with available experimental data at low pressures and are
used to benchmark the performance of various exchange-correlation functionals
in density functional theory calculations. We determine PBEsol is an optimal
choice for the exchange-correlation functional and perform extensive phonon and
quantum molecular-dynamics calculations to obtain the thermal EOS. Our results
provide a preliminary reference for the EOS and B1-B2 phase boundary of MgO
from zero up to 10,500 K.",2307.01359v1
2023-07-07,Enhancing the ultrafast third order nonlinear optical response by charge transfer in VSe2-reduced graphene oxide hybrid,"Nonlinear optical phenomena play a critical role in understanding microscopic
light-matter interactions and have far-reaching applications across various
fields, such as biosensing, quantum information, optical switching, and
all-optical data processing. Most of these applications require materials with
high third-order absorptive and refractive optical nonlinearities. However,
most materials show weak nonlinear optical responses due to their perturbative
nature and often need to be improved for practical applications. Here, we
demonstrate that the charge donor-acceptor hybrid of VSe2-reduced graphene
oxide (rGO) hybrid exhibits enhanced ultrafast third-order absorptive and
refractive nonlinearities compared to the pristine systems, at least by one
order of magnitude. Through density functional theory and Bader charge
analysis, we elucidate the strong electronic coupling in the VSe2-rGO hybrid,
involving the transfer of electrons from VSe2 to rGO. Steady-state and
time-resolved photoluminescence (PL) measurements confirm the electronic
coupling and charge transfer. Furthermore, we fabricate an ultrafast optical
limiter device with better performance parameters, such as an onset threshold
of 2.5 mJ cm-2 and differential transmittance of 0.42.",2307.03485v1
2023-07-11,Tunable ferroelectricity in oxygen-deficient perovskites,"Using first-principles calculations, we predict that tunable ferroelectricity
can be realized in oxide perovskites with the Grenier structure and ordered
oxygen vacancies. Specifically, we show that
$R_{1/3}A_{2/3}\mathrm{FeO}_{2.67}$ solids (where $R$ is a rare-earth ion and
$A$ an alkaline-earth cation) exhibit stable polar phases, with a spontaneous
polarization tunable by an appropriate choice of $R$ and $A$. We find that
larger cations combined with small $R$ elements lead to a maximum in the
polarization and to a minimum in the energy barriers required to switch the
sign of the polarization. Ferroelectricity arises from cooperative distortions
of octahedral and tetrahedral units, where a combination of rotational and
sliding modes controls the emergence of polarization within three-dimensional
connected layers. Our results indicate that polar Grenier phases of oxide
perovskites are promising materials for microelectronic applications and, in
general, for the study of phenomena emerging from breaking inversion symmetry
in solids.",2307.04972v1
2023-07-17,Titanium and titanium oxides at the K- and L-edges: validating theoretical calculations of X-ray absorption and X-ray emission spectra with measurements,"Using well-calibrated experimental data we validate theoretical X-ray
absorption spectroscopy (XAS) as well as X-ray emission spectroscopy (XES)
calculations for titanium (Ti), titanium oxide (TiO), and titanium dioxide
(TiO$_2$) at the Ti K- and L-edges as well as O K-edge. XAS and XES in
combination with a multi-edge approach offer a detailed insight into the
electronic structure of materials since both the occupied and unoccupied
states, are probed. The experimental results are compared with ab initio
calculations from the OCEAN package which uses the Bethe-Salpeter equation
(BSE) approach. Using the same set of input parameters for each compound for
calculations at different edges, the transferability of the OCEAN calculations
across different spectroscopy methods and energy ranges is validated. Thus, the
broad applicability for analysing and interpreting the electronic structure of
materials with the OCEAN package is shown.",2307.08255v1
2023-07-18,Large scale synthesis of 2D graphene oxide by mechanical milling of 3D carbon nanoparticles in air,"Graphene oxide (GO) is one of the important functional materials. Large-scale
synthesis of it is very challenging. Following a simple cost-effective route,
large-scale GO was produced by mechanical (ball) milling, in air, of carbon
nanoparticles (CNPs) present in carbon soot in the present study. The thickness
of the GO layer was seen to decrease with an increase in milling time. Ball
milling provided the required energy to acquire the in-plane graphitic order in
the CNPs reducing the disorders in it. As the surface area of the layered
structure became more and more with the increase in milling time, more and more
oxygen of air got attached to the carbon in graphene leading to the formation
of GO. An increase in the time of the ball mill up to 5 hours leads to a
significant increase in the content of GO. Thus ball milling can be useful to
produce large-scale two-dimensional GO for a short time.",2307.09011v1
2023-07-19,Transparent conductive oxides as a material platform for photonic neural networks,"Photonics integrated circuits have a huge potential to serve as a framework
for a new class of information processing machines and can enable ultrafast
artificial neural networks. They can overcome the existing speed and power
limits of the electronic processing elements and provide additional benefits of
photonics such as high-bandwidth, sub-nanosecond latencies and low-energy
interconnect credentials leading to a new paradigm called neuromorphic
photonics. The main obstacle to realize such a task is a lack of proper
material platform that imposes serious requirements on the architecture of the
network. Here we suggest and justify that transparent conductive oxides can be
an excellent candidate for such a task as they provide a nonlinearity and
bistability under both optical and electrical inputs.",2307.10419v1
2023-07-20,Morphology and dynamics of dense nanometric precursor lms of polymer melts,"Nanometer-thick supported lms of polymer melts spontaneously form and spread
around sessile droplets that are deposited on oxidized silicon wafers. At
steady state, the lms become dense and adopt a uniform thickness which is equal
to twice the gyration radius of the free polymer. Remarkably, this law applies
to a wide variety of melts and does not depend on the polymer chemistry nor on
the surface state (oxide layer thickness, temperature, presence of water
adsorbed, etc.). We show that existing theoretical descriptions cannot
reproduce this experimental result. Conversely, the evolution toward this
equilibrium state witnesses the specicity of the interactions at stake in these
conned polymer lms. The chains spreading dynamics can be modeled by taking into
account both the polymer/surface friction and the polymer/polymer friction.",2307.10681v1
2023-07-20,Reconfigurable cascaded thermal neuristors for neuromorphic computing,"While the complementary metal-oxide semiconductor (CMOS) technology is the
mainstream for the hardware implementation of neural networks, we explore an
alternative route based on a new class of spiking oscillators we call thermal
neuristors, which operate and interact solely via thermal processes. Utilizing
the insulator-to-metal transition in vanadium dioxide, we demonstrate a wide
variety of reconfigurable electrical dynamics mirroring biological neurons.
Notably, inhibitory functionality is achieved just in a single oxide device,
and cascaded information flow is realized exclusively through thermal
interactions. To elucidate the underlying mechanisms of the neuristors, a
detailed theoretical model is developed, which accurately reflects the
experimental results. This study establishes the foundation for scalable and
energy-efficient thermal neural networks, fostering progress in brain-inspired
computing.",2307.11256v2
2023-07-23,Unconventional spin polarization at Argon ion milled SrTiO3 Interfaces,"Interfacial two-dimensional electron gas (2DEG) formed at the perovskite-type
oxide, such as SrTiO3, has attracted significant attention due to its
properties of ferromagnetism, superconductivity, and its potential application
in oxide-based low-power consumption electronics. Recent studies have
investigated spin-to-charge conversion at the STO interface with different
materials, which could affect the efficiency of this 2DEG interface. In this
report, we presented an Ar^+ ion milling method to create a 2DEG at STO
directly by inducing oxygen vacancies. To quantify the spin-to-charge
conversion of this interface, we measured the angular-dependent spin-torque
ferromagnetic resonance (ST-FMR) spectra, revealing an unconventional spin
polarization at the interface of Argon ion-milled STO and NiFe. Furthermore, a
micromagnetic simulation for angular-dependent spin-torque ferromagnetic
resonance (ST-FMR) has been performed, confirming the large unconventional spin
polarization at the interface.",2307.12390v1
2023-06-16,Piezo-resistive pressure sensor based on CVD-grown ZnO nanowires on Polyethylene Tetrathalate substrate,"Recent developments in the domain of electronic materials and devices have
attracted the interest of researchers toward flexible and printable electronic
components like organic transistors, printable electrodes and sensors. Zinc
Oxide (ZnO) nanowires (NWs) possess a number of excellent properties like high
mobility, large exciton binding energy and the direct-band gap in addition to
large piezoelectric coefficients. Here, we report on flexible piezo-resistive
sensor based on Indium tin oxide (ITO)-coated Polyethylene tetrathalate (PET)
substrate. The device shows sensitivity in terms of change in resistance from
100 {\Omega} to 2.4 K{\Omega} at an applied potential of 5V upon bending from
flat to 95 degrees. The 1-D nanowire flexible device in its flat state shows
saturated output current. We observed ten folds enhanced variation as compared
to previous reports. Improved sensitivity was observed in our experiments due
to fewer defects in CVD-grown NWs as compared to others where hydrothermally
grown nanowires were used. The methodology of device fabrication reported here
requires less time and enables efficient devices for the realization of
flexible and wearable technology.",2307.13805v1
2023-08-01,CMOS on-chip thermometry at deep cryogenic temperatures,"Accurate on-chip temperature sensing is critical for the optimal performance
of modern CMOS integrated circuits (ICs), to understand and monitor localized
heating around the chip during operation. The development of quantum computers
has stimulated much interest in ICs operating a deep cryogenic temperatures
(typically 0.01 - 4 K), in which the reduced thermal conductivity of silicon
and silicon oxide, and the limited cooling power budgets make local on-chip
temperature sensing even more important. Here, we report four different methods
for on-chip temperature measurements native to complementary
metal-oxide-semiconductor (CMOS) industrial fabrication processes. These
include secondary and primary thermometry methods and cover conventional
thermometry structures used at room temperature as well as methods exploiting
phenomena which emerge at cryogenic temperatures, such as superconductivity and
Coulomb blockade. We benchmark the sensitivity of the methods as a function of
temperature and use them to measure local excess temperature produced by
on-chip heating elements. Our results demonstrate thermometry methods that may
be readily integrated in CMOS chips with operation from the milliKelivin range
to room temperature.",2308.00392v1
2023-08-07,Oxide layer formation prevents deteriorating ion migration in thermoelectric Cu$_2$Se during operation in air,"Cu$_2$Se is a mixed ionic-electronic conductor with outstanding
thermoelectric performance originally envisioned for space missions.
Applications were discontinued due to material instability, where elemental Cu
grows at the electrode interfaces during operation in vacuum. Here, we show
that when Cu$_2$Se is operating in air, formation of an oxide surface layer
suppresses Cu$^+$ migration along the current direction. In operando X-ray
scattering and electrical resistivity measurements quantify Cu$^+$ migration
through refinement of atomic occupancies and phase composition analysis. Cu
deposition can be prevented during operation in air, irrespective of a critical
voltage, if the thermal gradient is applied along the current direction.
Maximum entropy electron density analysis provides experimental evidence that
Cu$^+$ migration pathways under thermal and electrical gradients differ
substantially from equilibrium diffusion. The study establishes new promise for
inexpensive sustainable Cu$_2$Se in thermoelectric applications, and it
underscores the importance of atomistic insight into materials during
thermoelectric operating conditions.",2308.03559v1
2023-08-16,Investigation of Magnesium Silicate as an Effective Gate Dielectric for AlGaN/GaN Metal Oxide High Electron Mobility Transistors (MOSHEMT),"In this study, a 6 nm layer of Magnesium Silicate (Mg-Silicate) was deposited
on AlGaN/GaN heterostructure by sputtering of multiple stacks of MgO and
SiO$_{2}$, followed by rapid thermal annealing in a nitrogen (N$_{2}$)
environment. The X-ray photoelectron spectroscopy (XPS) analysis confirmed the
stoichiometric Mg-Silicate (MgSiO$_{3}$) after being annealed at a temperature
of 850 $^\circ$C for 70 seconds. Atomic force microscopy (AFM) was employed to
measure the root mean square (RMS) roughness (2.20 nm) of the Mg-Silicate. A
significant reduction in reverse leakage current, by a factor of three orders
of magnitude, was noted for the Mg-Silicate/AlGaN/GaN metal-oxide-semiconductor
(MOS) diode in comparison to the Schottky diode. The dielectric constant of
Mg-Silicate($\mathcal{E}_{Mg-Silicate}$) and the interface density of states
(D$_{it}$) with AlGaN were approximated at $\sim$ 6.6 and 2.0 $\times$
10$^{13}$ cm$^{-2}$eV$^{-1}$ respectively, utilizing capacitance-voltage (CV)
characteristics.",2308.08515v1
2023-08-21,Impact of geometry on chemical analysis exemplified for photoelectron spectroscopy of black silicon,"For a smooth surface, the chemical composition can be readily evaluated by a
variety of spectroscopy techniques; a prominent example is X-ray photoelectron
spectroscopy (XPS), where the relative proportions of the elements are mainly
determined by the intensity ratio of the element-specific photoelectrons. This
deduction, however, is more intricate for a nanorough surface, such as black
silicon, since the steep slopes of the geometry mimic local variations of the
local emission angle. Here, we explicitly quantify this effect via an integral
geometric analysis, by using so-called Minkowski tensors. Thus, we match the
chemical information from XPS with topographical information from atomic force
microscopy (AFM). Our method provides reliable estimates of layer thicknesses
for nanorough surfaces. For our black silicon samples, we found that the oxide
layer thickness is on average comparable to that of a native oxide layer. Our
study highlights the impact of complex geometries at the nanoscale on the
analysis of chemical properties with implications for a broad class of
spectroscopy techniques.",2308.10625v1
2023-08-16,In situ Fault Diagnosis of Indium Tin Oxide Electrodes by Processing S-Parameter Patterns,"In the field of optoelectronics, indium tin oxide (ITO) electrodes play a
crucial role in various applications, such as displays, sensors, and solar
cells. Effective fault detection and diagnosis of the ITO electrodes are
essential to ensure the performance and reliability of the devices. However,
traditional visual inspection is challenging with transparent ITO electrodes,
and existing fault detection methods have limitations in determining the root
causes of the defects, often requiring destructive evaluations. In this study,
an in situ fault diagnosis method is proposed using scattering parameter
(S-parameter) signal processing, offering early detection, high diagnostic
accuracy, noise robustness, and root cause analysis. A comprehensive
S-parameter pattern database is obtained according to defect states. Deep
learning (DL) approaches, including multilayer perceptron (MLP), convolutional
neural network (CNN), and transformer, are then used to simultaneously analyze
the cause and severity of defects. Notably, it is demonstrated that the
diagnostic performance under additive noise levels can be significantly
enhanced by combining different channels of the S-parameters as input to the
learning algorithms, as confirmed through the t-distributed stochastic neighbor
embedding (t-SNE) dimension reduction visualization.",2308.11639v1
2023-08-31,Manganese Dissolution in alkaline medium with and without concurrent oxygen evolution in LiMn$_2$O$_4$,"Manganese dissolution during the oxygen evolution reaction (OER) has been a
persistent challenge that impedes the practical implementation of Mn-based
electrocatalysts including the LiMn$_x$O$_4$ system in aqueous alkaline
electrolyte. The investigated LiMn$_2$O$_4$ particles exhibit two distinct Mn
dissolution processes; one independent of OER and the other associated to OER.
Combining the bulk sensitive X-ray absorption spectroscopy, surface sensitive
X-ray photoelectron spectroscopy and electrochemical detection of Mn
dissolution using rotating ring-disk electrode, we explore the less understood
Mn dissolution mechanism during OER. We correlate near-surface oxidation with
the charge attributed to dissolved Mn, which demonstrates increasing Mn
dissolution with the formation of surface Mn4+ species under anodic potential.
The observed stronger dissolution during the OER is attributed to the formation
of additional Mn$^{4+}$ from Mn$^{3+}$ during OER. We show that control over
the amount of Mn4+ in Li$_x$Mn2O$_4$ before the onset of the OER can partially
mitigate the OER-triggered dissolution. Overall, our atomistic insights into
the Mn dissolution processes are crucial for knowledge-guided mitigation of
electrocatalyst degradation, which can be broadly extended to manganese-based
oxide systems.",2309.00101v1
2023-08-07,Modeling of electrochemical oxide film growth -- a PDM refinement,"The Point Defect Model (PDM) is known for over 40 years and has brought
deeper insight to the understanding of passivity. During the last decades it
has seen several changes and refinements, and it has been widely used to
analyze growth kinetics of different alloys. Nevertheless, the model has been
based on still unconfirmed assumptions, as constant and potential independent
electric field strength. To overcome this limitation, we introduce a Refined
PDM (R-PDM) in which we replace those assumptions by using additional equations
for charge distribution including new physically valid boundary conditions
based on considering finite dimensions for the defects by introduction of two
defect layer at the film boundaries and by calculating the potential drop at
the surface of the film towards the solution over the compact double layer. The
calculations by the R-PDM show that the original PDM assumptions are only valid
for very specific parameter combinations of oxide film growth and vacancies
transport and cannot generally be taken for granted. We believe our findings of
electric field and potential drop dependency on the external potential to pave
the way for a more realistic description of passive layer formation.",2309.04480v1
2023-09-25,Cerium oxide catalyzed disproportionation of hydrogen peroxide: a closer look at the reaction intermediate,"Cerium oxide nanoparticles (CNPs) have recently gained increasing interest as
redox enzyme-mimetics to scavenge the intracellular excess of reactive oxygen
species, including hydrogen peroxide (H2O2). Despite the extensive exploration
of CNP scavenging activity, there remains a notable knowledge gap regarding the
fundamental mechanism underlying the CNP catalyzed disproportionation of H2O2.
In this Letter, we present evidence demonstrating that H2O2 adsorption at CNP
surface triggers the formation of stable intermediates known as ceriumperoxo
complexes (Ce-O2 2-). The cerium-peroxo complexes can be resolved by Raman
scattering and UV-Visible spectroscopy. We further demonstrate that the
catalytic reactivity of CNPs in the H2O2 disproportionation reaction increases
with the Ce(III) fraction. The developed approach using UV-Visible spectroscopy
for the characterization of Ce-O2 2-complexes can potentially serve as a
foundation for determining the catalytic reactivity of CNPs in the
disproportionation of H2O2.",2309.13981v1
2023-09-25,Integrated bolometric photodetectors based on transparent conductive oxides from near- to mid-infrared wavelengths,"On-chip photodetectors are essential components in optical communications as
they convert light into an electrical signal. Photobolometers are type of
photodetector that functions through a resistance change caused by electronic
temperature fluctuations upon light absorption. They are widely used in the
broad wavelength range from UV to MIR and can operate on a wide material
platform. In this work, I introduce a novel waveguide-integrated bolometer that
operates in a wide wavelength range from NIR to MIR on the standard material
platform with the transparent conductive oxides (TCOs) as the active material.
This material platform enables the construction of both modulators and
photodetectors using the same material, which is fully CMOS compatible and
easily integrated with passive on-chip components. The photobolometers proposed
here consist of a thin TCO layer placed inside the rib photonic waveguide to
enhance light absorption and then heat the electrons in the TCO to temperatures
above 1000 K. This rise in electron temperature leads to decreasing electron
mobility and consequential electrical resistance change. In consequence, a
responsivity exceeding 10 A/W can be attained with a mere few microwatts of
optical input power. Calculations suggest that further improvements can be
expected with lower doping of the TCO, thus opening new doors in on-chip
photodetectors.",2309.14454v1
2023-09-27,Model-based design of temporal analysis of products (TAP) reactors: A simulated case study in oxidative propane dehydrogenation,"Temporal analysis of products (TAP) reactors enable experiments that probe
numerous kinetic processes within a single set of experimental data through
variations in pulse intensity, delay, or temperature. Selecting additional TAP
experiments often involves arbitrary selection of reaction conditions or the
use of chemical intuition. To make experiment selection in TAP more robust, we
explore the efficacy of model-based design of experiments (MBDoE) for precision
in TAP reactor kinetic modeling. We successfully applied this approach to a
case study of synthetic oxidative propane dehydrogenation (OPDH) that involves
pulses of propane and oxygen. We found that experiments identified as optimal
through the MBDoE for precision generally reduce parameter uncertainties to a
higher degree than alternative experiments. The performance of MBDoE for model
divergence was also explored for OPDH, with the relevant active sites (catalyst
structure) being unknown. An experiment that maximized the divergence between
the three proposed mechanisms was identified and led to clear mechanism
discrimination. However, re-optimization of kinetic parameters eliminated the
ability to discriminate. The findings yield insight into the prospects and
limitations of MBDoE for TAP and transient kinetic experiments.",2309.15786v2
2023-10-02,Estimation of In-Vitro Free Radical Scavenging and Cytotoxic Activities of Thiocarbohydrazones Derivatives,"Objective: To investigate free radical scavenging potential of
thiocarbohydrazones derivatives for the discovery of antioxidant compounds of
synthetic origin. Method: Eighteen thiocarbohydrazones derivatives were
screened for antioxidant activities by using in vitro radical inhibition assay.
Cytotoxicity all derivatives were evaluated using invitro cytotoxicity assay on
mouse fibroblast cell line. Results: various compounds of the have shown
significant radical scavenging activities as compared with the standard drug
butylated hydroxytoluene. In addition in an in vitro cell cytotoxicity assay
selected analogues were found to be non-cytotoxic against fibroblast 3T3 cell
line. Conclusion: Taken together, these findings all compound this series could
be further evaluated in in vivo model of oxidative stress to develop as a
therapeutic agent against oxidative stress related disorders due to exhibiting
excellent free radical scavenging properties and having their non cytotoxic
nature against normal cells.",2310.00939v1
2023-10-05,Visualising emergent phenomena at oxide interfaces,"Knowledge of atomic-level details of structure, chemistry, and electronic
states is paramount for a comprehensive understanding of emergent properties at
oxide interfaces. We utilise a novel methodology based on atomic-scale electron
energy loss spectroscopy (EELS) to spatially map the electronic states tied to
the formation of a two-dimensional electron gas (2DEG) at the prototypical
non-polar/polar $TiO_2$/$LaAlO_3$ interface. Combined with differential phase
contrast analysis we directly visualise the microscopic locations of ions and
charge and find that 2DEG states and $Ti^{3+}$ defect states exhibit different
spatial distributions. Supported by density functional theory (DFT) and
inelastic scattering simulations we examine the role of oxygen vacancies in
2DEG formation. Our work presents a general pathway to directly image emergent
phenomena at interfaces using this unique combination of arising microscopy
techniques with machine learning assisted data analysis procedures.",2310.03863v1
2023-10-10,To what extent airborne particulate matters are influenced by ammonia and nitrogen oxides?,"Intensive farming is known to significantly impact air quality, particularly
fine particulate matter (PM$_{2.5}$). Understanding in detial their relation is
important for scientific reasons and policy making. Ammonia emissions convey
the impact of farming, but are not directly observed. They are computed through
emission inventories based on administrative data and provided on a regular
spatial grid at daily resolution. In this paper, we aim to validate
\textit{lato sensu} the approach mentioned above by considering ammonia
concentrations instead of emissions in the Lombardy Region, Italy. While the
former are available only in few monitoring stations around the region, they
are direct observations. Hence, we build a model explaining PM2.5 based on
precursors, ammonia (NH3) and nitrogen oxides (NOX), and meteorological
variables. To do this, we use a seasonal interaction regression model allowing
for temporal autocorrelation, correlation between stations, and
heteroskedasticity. It is found that the sensitivity of PM2.5 to NH3 and NOX
depends on season, area, and NOX level. It is recommended that an emission
reduction policy should focus on the entire manure cycle and not only on spread
practices.",2310.09302v2
2023-10-16,An analysis on improvement of x-ray diffractometer results by controlling and calibration of parameters,"The X-ray diffractometer in the laboratory is a crucial instrument for
analyzing materials in science. It can be used on almost any crystal material,
and if the machine parameters are appropriately controlled, it can offer a lot
of information about the samples characteristics. Nevertheless, the data
obtained from these machines are complicated by an aberration function that can
be resolved through calibration. In this study, a powder comprising of Barium
Sulfate (BaSO4), Zinc Oxide (ZnO) and Aluminum (Al) was used as the first
sample and a single crystal sample comprised of Gallium Nitride (GaN) and
Aluminum Oxide (Al2O3). The required calibration parameters of the X-ray
diffractometer namely: Straight Beam Alignment, Beam Cut Alignment and Sample
Tilt Alignment for two samples were analyzed and carried out. Using the results
of the X-ray spectrum, important parameters such as corresponding planes for
peak positions, d-spacing of planes, intensities, smallest crystallite sizes
and lattice parameters, and a comparison with the reference data were all
carried out. As another result, the out-of-plane alignment and Full-Width at
Half-Maximum (FWHM) value for GaN could be determined using the rocking curve.",2310.10786v1
2023-10-18,Structures and Electronic States of Nickel Rich Oxides for Lithium Ion Batteries,"A new superstructure of layered pristine LiNiO2 (LNO) was obtained optimizing
a large supercell of the 166 space group, the one observed experimentally by
XRD, and relaxing both cell parameters and internal positions. The crystal
structure shows size and charge disproportionation of the NiO6 octahedra
instead of the Jahn-Teller distortion. The decrease of the internal energy
obtained with the structural optimization of the supercell relative to the same
structure in its primitive unit cell is much larger than the one obtained by
relaxing similarly dimensioned supercells of monoclinic symmetry relative to
their primitive unit cells, although the monoclinic phase remains more stable.
The Ni-O bond length distribution of the new structure agree well with the
experiments. Our results show that the choice of the simulation cell is
important for determining the energetics of this class of oxide materials,
proposed for cathodes in lithium ion batteries (LIBs). We used this new
structure as a template for the study of the structural and electronic changes
induced by the delithiation and Mn for Ni cation substitution, originating the
solid solutions LiNiyMn(1-y)O2 (LNMO). Our results, surprisingly, agree well
with the existing experiments and explain observed trends better than previous
studies.",2310.11856v1
2023-10-22,The Oxygen Reduction Pathway for Spinel Metal Oxides in Alkaline Media: An Experimentally Supported Ab Initio Study,"Precious-metal-free spinel oxide electrocatalysts are promising candidates
for catalyzing the oxygen reduction reaction (ORR) in alkaline fuel cells. In
this theory-driven study, we use joint density-functional theory in tandem with
supporting electrochemical measurements to identify a novel theoretical pathway
for the ORR on cubic Co3O4 nanoparticle electrocatalysts. This pathway aligns
more closely with experimental results than previous models. The new pathway
employs the cracked adsorbates *(OH)(O) and *(OH)(OH), which, through hydrogen
bonding, induce spectator surface *H. This results in an onset potential
closely matching experimental values, in stark contrast to the traditional ORR
pathway, which keeps adsorbates intact and overestimates the onset potential by
0.7 V. Finally, we introduce electrochemical strain spectroscopy (ESS), a
groundbreaking strain analysis technique. ESS combines ab initio calculations
with experimental measurements to validate proposed reaction pathways and
pinpoint rate-limiting steps.",2310.14377v1
2023-10-24,Identifying bimodality in data using a proximity-based null model with an application to classifying cell cycle phases using oxidative stress,"Detecting communities in large complex networks has found a wide range of
applications in physical, biological, and social sciences by identifying
mesoscopic groups based on the links between individual units. Moreover,
community detection approaches have been generalized to various data analysis
tasks by constructing networks whose links depend on individual units'
measurements. However, identifying well-separated subpopulations in data sets,
e.g., multimodality, still presents challenges as both community detection with
existing null models and other partition methods give partitions that do not
necessarily correspond to multimodality. Here we introduce a new spatially
informed null model for this task that takes into account spatial structure but
does not explicitly depend on distances between measurements. We find that
community detection using this null model successfully identifies
subpopulations in multimodal data and accurately does not for unimodal data. We
apply this new null model to first distinguish interphase and mitotic cell
cycle phases and then S and G2 cell cycle phases in a group of Dictyostelium
discoideum cells using measurements of oxidative stress, which have been shown
to correlate strongly with cell-cycle behaviors.",2310.16078v2
2023-10-27,Practical application of quantum neural network to materials informatics: prediction of the melting points of metal oxides,"Quantum neural network (QNN) models have received increasing attention owing
to their strong expressibility and resistance to overfitting. It is
particularly useful when the size of the training data is small, making it a
good fit for materials informatics (MI) problems. However, there are only a few
examples of the application of QNN to multivariate regression models, and
little is known about how these models are constructed. This study aims to
construct a QNN model to predict the melting points of metal oxides as an
example of a multivariate regression task for the MI problem. Different
architectures (encoding methods and entangler arrangements) are explored to
create an effective QNN model. Shallow-depth ansatzs could achieve sufficient
expressibility using sufficiently entangled circuits. The ""linear"" entangler
was adequate for providing the necessary entanglement. The expressibility of
the QNN model could be further improved by increasing the circuit width. The
generalization performance could also be improved, outperforming the classical
NN model. No overfitting was observed in the QNN models with a well-designed
encoder. These findings suggest that QNN can be a useful tool for MI.",2310.17935v1
2023-10-27,Collisional shift and broadening of Rydberg states in nitric oxide at room temperature,"We report on the collisional shift and line broadening of Rydberg states in
nitric oxide (NO) with increasing density of a background gas at room
temperature. As a background gas we either use NO itself or nitrogen (N$_{2}$).
The precision spectroscopy is performed by a sub-Doppler three-photon
excitation scheme with a subsequent readout of the Rydberg states realized by
the amplification of a current generated by free charges due to collisions. The
shift shows a dependence on the rotational quantum state of the ionic core and
no dependence on the principle quantum number of the orbiting Rydberg electron.
The experiment was performed in the context of developing a trace-gas sensor
for breath-gas analysis in a medical application.",2310.18256v2
2023-11-02,Unravelling the atomic and electronic structure of nanocrystals on superconducting Nb(110): Impact of the oxygen monolayer,"The Niobium surface is almost always covered by a native oxide layer which
greatly influences the performance of superconducting devices. Here we
investigate the highly stable Niobium oxide overlayer of Nb(110), which is
characterised by its distinctive nanocrystal structure as observed by scanning
tunnelling microscopy (STM). Our ab-initio density functional theory (DFT)
calculations show that a subtle reconstruction in the surface Niobium atoms
gives rise to rows of 4-fold coordinated oxygen separated by regions of 3-fold
coordinated oxygen. The 4-fold oxygen rows are determined to be the source of
the nanocrystal pattern observed in STM, and the two chemical states of oxygen
observed in core-level X-ray photoelectron spectroscopy (XPS) are ascribed to
the 3-fold and 4-fold oxygens. Furthermore, we find excellent agreement between
the DFT calculated electronic structure with scanning tunnelling spectroscopy
and valence XPS measurements.",2311.01275v1
2023-11-02,Going for Gold(-Standard): Attaining Coupled Cluster Accuracy in Oxide-Supported Nanoclusters,"Metal nanoclusters supported on oxide surfaces are widely-used catalysts that
boasts sharply enhanced activity over their bulk, especially for the coinage
metals: Au, Ag and Cu. These properties depend sensitively on the nanocluster
structure, which are challenging to model with density functional theory (DFT)
-- the workhorse modelling technique. Leveraging the recently developed SKZCAM
protocol, we perform the first ever benchmark study of coinage metal structures
on the MgO surface with coupled cluster theory [CCSD(T)] -- the gold-standard
modelling technique. We investigate a comprehensive range of DFT models
(exchange-correlation functional and dispersion correction) and our benchmarks
reveal that none of the investigated models can accurately describe this
system. We demonstrate that this arises from inadequate account of metal-metal
interactions in the nanocluster and propose a high-level correction which
provides reference accuracy at low cost. This forges a path towards studying
larger systems, which we highlight by benchmarking Au$_{20}$ on MgO, a
challenging system where DFT models have disagreed on its ground state
structure.",2311.01426v1
2023-11-13,Photochemical Upcycling of Ultrastrong Polyethylene Nanomembranes into Fibrous Carbon at Ambient Conditions,"The escalating global issue of plastic waste accumulation, specifically
polyolefins, necessitates an urgent solution for upcycling these materials into
beneficial compounds. Yet, achieving such upcycling without introducing carbon
dioxide into the environment remains a formidable challenge. In this study, we
demonstrate an eco-friendly approach for the photochemical conversion of
ultrastrong, ultratransparent, and ultrathin polyethylene membrane into fibrous
carbon nanomembrane at ambient conditions. The membrane was sputter-coated with
platinum and cuprous oxide nanoparticles and exposed to simulated sunlight,
resulting in a porous carbon membrane decorated with Pt nanoparticles. The new
carbonized nanomembrane maintained the pristine membrane's morphology. The
membrane exhibited high activity (2.11 mA/cm2) for electrochemical ethanol
oxidation with stability over 1000 cycles. This work holds significance for
sustainable plastic waste management and the design of new polyolefin materials
in a circular economy.",2311.07023v2
2023-11-18,Busting the Myth of Spontaneous Formation of H2O2 at the Air-Water Interface: Contributions of the Liquid-Solid Interface and Dissolved Oxygen Exposed,"Recent reports on the spontaneous formation of H2O2(aq) at the air-water
interface and the solid-water interface have been sensational. The speculated
mechanism at the air-water interface is based on instantaneous ultrahigh
electric fields and the micro-scale of droplets, whereas the solid-water
interface is speculated to be the site for oxidation of water (or hydroxide
ions) and reduction of the solid surface. We utilized 1H-NMR spectroscopy to
investigate the effects of the nebulizing gas, the dissolved oxygen content,
and solid substrates on the H2O2(aq) formation (detection limit 50 nM).
Experiments revealed that contrary to the sensational claims, the air-water
interface is not the site for H2O2(aq) formation; instead, it is the
solid-water interface where H2O2(aq) is formed during the reduction of
dissolved oxygen and oxidation of the solid surface. Curiously, the tendencies
of solid substrates towards forming H2O2(aq) follow the classic Galvanic
series. This report advances the current understanding of aquatic chemistry and
should be relevant to corrosion science, surface science, and electrochemistry.",2311.11133v1
2023-11-22,Electron-phonon mediated superconductivity in R$_6$Ni$_5$O$_{12}$ nickel oxides,"Nickel oxide superconductors offer an alternative playground for
understanding the formation of Cooper pairs in correlated materials such as the
famous cuprates. By studying the La$_{n+1}$Ni$_n$O$_{2n+2}$ phase diagram on
the basis of hybrid and spin-polarized density functional theory simulations,
we reveal the existence of charge and bond ordered (CBO) insulating phases that
are quenched by doping effects, ultimately resulting in a metallic phase at the
$n=5$ member. Nevertheless, the phonons associated with the CBO identified in
the phase diagram remain sufficiently large to mediate Cooper pairs in
La$_6$Ni$_5$O$_{12}$, yielding a computed critical temperature between
$T_c=11-19$ K consistent with the 13 K observed experimentally in
Nd$_6$Ni$_5$O$_{12}$. Thus, in order to identify the superconducting mechanism,
extracting the relevant instabilities in the doping phase diagram of
superconductors appears critical.",2311.13674v1
2023-11-27,Evolution of the surface atomic structure of multielement oxide films: curse or blessing?,"Atomically resolved scanning tunneling microscopy (STM) and x-ray
photoelectron spectroscopy (XPS) are used to gain atomic-scale insights into
the heteroepitaxy of lanthanum-strontium manganite (LSMO,
La$_{1-x}$Sr$_x$MnO$_{3-{\delta}}$, $x$ $\approx$ 0.2) on SrTiO$_3$(110). LSMO
is a perovskite oxide characterized by several composition-dependent surface
reconstructions. The flexibility of the surface allows it to incorporate
nonstoichiometries during growth, which result in composition-dependent surface
atomic structures. This happens up to a critical point, where phase separation
occurs, clusters rich in the excess cations form at the surface, and films show
a rough morphology. To limit the nonstoichiometry introduced by non-optimal
growth conditions, it proves useful to monitor the changes in surface atomic
structures as a function of the PLD parameters and tune the latter accordingly.",2311.15700v1
2023-11-29,Ferroelectric domain nucleation and switching pathways in hafnium oxide,"Nanoscale ferroelectrics that can be integrated into microelectronic
fabrication processes are highly desirable for low-power computing and
non-volatile memory devices. However, scalable novel ferroelectric materials,
such as hafnium oxide (HfO2), remain in a state of development, and a clear
understanding of the effects of relevant compositional and processing
parameters to control their ferroelectric properties and the actual
polarization switching mechanisms are still under investigation. One key
fundamental knowledge gap is the polarization switching pathway in
ferroelectric hafnia. To further our fundamental understanding of domain
nucleation and switching, we have studied polarization switching pathways in
HfO2-x thin films in real-time at the atomic scale using transmission electron
microscopy. We employed differential phase contrast imaging that allows for the
acquisition of both hafnium and oxygen atomic column signals and facilitates
the observation of relative movement of atomic columns between both
sublattices. Our results demonstrate that the switching pathway involves a
transient tetragonal-like local structure, as oxygen ions shift in locations
and remain within their parent hafnium polyhedra.",2311.17290v1
2023-12-07,Confinement-Induced Isosymmetric Metal-Insulator Transition in Ultrathin Epitaxial V2O3 Films,"Dimensional confinement has shown to be an effective strategy to tune
competing degrees of freedom in complex oxides. Here, we achieved atomic
layered growth of trigonal vanadium sesquioxide (V2O3) by means of
oxygen-assisted molecular beam epitaxy. This led to a series of high-quality
epitaxial ultrathin V2O3 films down to unit cell thickness, enabling the study
of the intrinsic electron correlations upon confinement. By electrical and
optical measurements, we demonstrate a dimensional confinement-induced
metal-insulator transition in these ultrathin films. We shed light on the
Mott-Hubbard nature of this transition, revealing an abrupt vanishing of the
quasiparticle weight as demonstrated by photoemission spectroscopy.
Furthermore, we prove that dimensional confinement acts as an effective
out-of-plane stress. This highlights the structural component of correlated
oxides in a confined architecture, while opening an avenue to control both
in-plane and out-of-plane lattice components by epitaxial strain and
confinement, respectively.",2312.04425v1
2023-12-09,Can silica nanoparticles improve lithium transport in polymer electrolytes?,"The question of if silica nanoparticles can enhance the ionic conductivity of
a polymer electrolyte above its crystallization temperature has remained
unclear for the two decades following the first experiments on these systems.
We use Molecular Dynamics simulations to decipher the atomic scale mechanisms
affecting the properties of LiTFSI-poly(ethylene oxide) electrolytes upon the
addition of silica nanoparticles. At any ionic concentration, adding
nanoparticles significantly decreases the conductivity. Most of this reduction
can be simply accounted for by the diffusion equation, resulting from the fact
that the space occupied by the nanoparticles is made inactive and unable to
sustain ionic diffusion. We identify two distinct regimes, above and below a
concentration threshold, corresponding to very different ionic distributions
and coordination features of the various species. The lack of conductivity
enhancement observed in the simulations supports the conclusions of some recent
measurements, and disagrees with the earliest experimental reports on hybrid
silica/polyethylene-oxide electrolytes.",2312.05681v2
2023-12-14,Reducing strain fluctuations in quantum dot devices by gate-layer stacking,"Nanofabricated metal gate electrodes are commonly used to confine and control
electrons in electrostatically defined quantum dots. However, these same gates
impart a complicated strain geometry that affects the confinement potential and
potentially impairs device functionality. Here we investigate strain-induced
fluctuations of the potential energy in Si/SiGe heterostructures, caused by (i)
lattice mismatch, (ii) materials-dependent thermal contraction, and (iii)
deposition stress in the metal gates. By simulating different gate geometries,
ranging from simple to realistically complicated, and including features like
overlapping metal and oxide layers, we can explain most observed strain
features. In particular, we show that strain-induced potential fluctuations can
be suppressed by employing overlapping gates that cover the whole active
region, when the oxide layers are thin. These results suggest that strain
effects should not present a serious challenge to qubit uniformity when
following simple design rules.",2312.09235v2
2023-12-28,"Antiferroelectric Oxide Thin-Films: Fundamentals, Properties, and Applications","Antiferroelectrics have received blooming interests because of a wide range
of potential applications in energy storage, solid-state cooling, thermal
switch, transducer, actuation, and memory devices. Many of those applications
are the most prospective in thin film form. The antiferroelectric ordering in
thin films is highly sensitive to a rich set of factors, such as lattice
strain, film thickness, surface and interface effects as well as film
stoichiometry. To unlock the full potential of these materials and design
high-quality thin films for functional devices, a comprehensive and systematic
understanding of their behavior is essential. In conjunction with the necessary
fundamental background of antiferroelectrics, we review recent progress on
various antiferroelectric oxide thin films, the key parameters that trigger
their phase transition and the device applications that rely on the robust
responses to electric, thermal, and optical stimuli. Current challenges and
future perspectives highlight new and emerging research directions in this
field. It is hoped that this review can boost the development of
antiferroelectric thin-film materials and device design, stimulating more
researchers to explore the unknowns together.",2312.16806v1
2023-12-29,Utilizing the Janus MoSSe surface polarization property in complementary metal-oxide-semiconductor field effect transistor design,"Janus transition metal dichalcogenides (JTMDs) have attracted much attention
because of their outstanding electronic and optical properties. The additional
out-of-plane dipole in JTMDs can form n- and p-like Ohmic contacts, and this
may be used in device applications such as pin diodes and photovoltaic cells.
In this study, we exploit this property to design n- and p-type
metal-oxide-semiconductor field effect transistors (MOSFETs). First, we use
density-functional theory calculations to study the inherent dipole field
strength in the trilayer JTMD MoSSe. The intrinsic dipole of MoSSe causes band
bending at both the metal/MoSSe and MoSSe/metal interfaces, resulting in
electron and hole accumulation to form n- and p-type Ohmic contact regions. We
incorporate this property into a 2D finite-element-based
Poisson-drift-diffusion solver to perform simulations, on the basis of which we
design complementary MOSFETs. Our results demonstrate that JTMDs can be used to
make n- and p-MOSFETs in the same layer without the need for any extra doping.",2312.17594v2
2024-01-04,Site-Specific Plan-view (S)TEM Sample Preparation from Thin Films using a Dual-Beam FIB-SEM,"Plan-view transmission electron microscopy (TEM) samples are key to
understand the atomic structure and associated properties of materials along
their growth orientation, especially for thin films that are stain-engineered
onto different substrates for property tuning. In this work, we present a
method to prepare high-quality plan-view samples for analytical STEM study from
thin-films using a dual-beam focused ion beam scanning electron microscope
(FIB-SEM) system. The samples were prepared from thin films of perovskite
oxides and metal oxides ranging from 20-80 nm thicknesses, grown on different
substrates using molecular beam epitaxy. A site-specific sample preparation
from the area of interest is described, which includes sample attachment and
thinning techniques to minimize damage to the final TEM samples. While
optimized for the thin film-like geometry, this method can be extended to other
site-specific plan-view samples from bulk materials. Aberration-corrected
scanning (S)TEM was used to access the quality of the thin film in each sample.
This enabled direct visualization of line defects in perovskite BaSnO3 and Ir
particle formation and texturing in IrO2 films.",2401.02538v1
2024-01-10,First-principles predictions of HfO$_2$-based ferroelectric superlattices,"The metastable nature of the ferroelectric phase of HfO$_2$ is a significant
impediment to its industrial application as a functional ferroelectric
material. In fact, no polar phases exist in the bulk phase diagram of HfO$_2$,
which shows a dominant non-polar monoclinic ground state. As a consequence,
ferroelectric orthorhombic HfO$_2$ needs to be kinetically stabilized. Here, we
propose an alternative approach, demonstrating the feasibility of
thermodynamically stabilizing polar HfO$_2$ in superlattices with other simple
oxides. Using the composition and stacking direction of the superlattice as
design parameters, we obtain heterostructures that can be fully polar, fully
antipolar or mixed, with improved thermodynamic stability compared to the
orthorhombic polar HfO$_2$ in bulk form. Our results suggest that combining
HfO$_2$ with an oxide that does not have a monoclinic ground state generally
drives the superlattice away from this non-polar phase, favoring the stability
of the ferroelectric structures that minimize the elastic and electrostatic
penalties. As such, these diverse and tunable superlattices hold promise for
various applications in thin-film ferroelectric devices.",2401.05288v1
2024-01-22,Towards reliable synthesis of superconducting infinite layer nickelate thin films by topochemical reduction,"Infinite layer nickelates provide a new route beyond copper oxides to address
outstanding questions in the field of unconventional superconductivity.
However, their synthesis poses considerable challenges, largely hindering
experimental research on this new class of oxide superconductors. That
synthesis is achieved in a two-step process that yields the most
thermodynamically stable perovskite phase first, then the infinite-layer phase
by topotactic reduction, the quality of the starting phase playing a crucial
role. Here, we report on reliable synthesis of superconducting infinite-layer
nickelate films after successive topochemical reductions of a parent perovskite
phase with nearly optimal stoichiometry. Careful analysis of the transport
properties of the incompletely reduced films reveals an improvement of the
strange metal behaviour of their normal state resistivity over subsequent
topochemical reductions, offering insight into the reduction process.",2401.12307v2
2024-01-23,Understanding atom probe's analytical performance for iron oxides using correlation histograms and ab initio calculations,"Field evaporation from ionic or covalently bonded materials often leads to
the emission of molecular ions. The metastability of these molecular ions,
particularly under the influence of the intense electrostatic field (1010
Vm-1), makes them prone to dissociation with or without an exchange of energy
amongst them. These processes can affect the analytical performance of atom
probe tomography (APT). For instance, neutral species formed through
dissociation may not be detected at all or with a time of flight no longer
related to their mass, causing their loss from the analysis. Here, we evaluated
the changes in the measured composition of FeO, Fe2O3 and Fe3O4 across a wide
range of analysis conditions. Possible dissociation reactions are predicted by
density-functional theory (DFT) calculations considering the spin states of the
molecules. The energetically favoured reactions are traced on to the multi-hit
ion correlation histograms, to confirm their existence within experiments,
using an automated Python-based routine. The detected reactions are carefully
analysed to reflect upon the influence of these neutrals from dissociation
reactions on the performance of APT for analysing iron oxides.",2401.12784v1
2024-01-27,Corrosion resistance of a water-borne resin doped with graphene derivatives applied on galvanized steel,"The present work reports the effect of adding Graphene Oxide (GO) and reduced
Graphene Oxide (rGO) in the corrosion protection provided by a water-borne
resin applied on a galvanized steel substrate. Three concentrations, 0.05, 0.1
and 0.15 (all wt%) were tested. The results were markedly affected not only by
the concentration of particles but also by their nature. Although the zeta
potential values suggested good dispersibility of the particles in the resin,
certain aggregation was observed, mainly in rGO 0.1 wt% and rGO 0.15 wt%
formulations. The electrochemical impedance spectroscopy (EIS) technique
characterised the free films' transport properties. The results suggested that
the aggregation strongly influenced the film morphology. The rGO 0.1 wt% and
rGO 0.15 wt% formulations exhibited percolating pores that facilitated the
electrolyte uptake through the films. The EIS technique was also used to study
the protective performance of the films when applied to the metallic substrate.
The results confirmed the harmful effect of the particle's aggregation. The
results were interesting for the rGO 0.05 wt% system, which displayed
long-lasting protection properties. This performance was explained considering
its good barrier properties and the zinc surface passivation by the generation
of zincite, ZnO.",2401.15410v1
2024-01-29,Optimization of scandium oxide growth by high pressure sputtering on silicon,"This work demonstrates the viability of scandium oxide deposition on silicon
by means of high pressure sputtering. Deposition pressure and radio frequency
power are varied for optimization of the properties of the thin films and the
ScOx-Si interface. The physical characterization was performed by ellipsometry,
Fourier transform infrared spectroscopy, x-ray diffraction and transmission
electron microscopy. Aluminum gate electrodes were evaporated for
metal-insulator-semiconductor (MIS) fabrication. From the electrical
characterization of the MIS devices, the density of interfacial defects is
found to decrease with deposition pressure, showing a reduced plasma damage of
the substrate surface for higher pressures. This is also supported by lower
flatband voltage shifts in the capacitance versus voltage hysteresis curves.
Sputtering at high pressures (above 100 Pa) reduces the interfacial SiOx
formation, according to the infrared spectra. The growth rates decrease with
deposition pressure, so a very accurate control of the layer thicknesses could
be provided.",2401.16489v1
2024-01-29,Two-step conversion of metal and metal oxide precursor films to 2D transition metal dichalcogenides and heterostructures,"From the laboratory to real-world applications, synthesis of two dimensional
(2D) materials requires modular techniques to control morphology, structure,
chemistry, and the plethora of exciting properties arising from these nanoscale
materials. In this review, we explore one of the many available synthesis
techniques; the extremely versatile two-step conversion (2SC) method. The 2SC
technique relies on deposition of a metal or metal oxide film, followed by
reaction with a chalcogen vapor at an elevated temperature, converting the
precursor film to a crystalline transition metal dichalcogenide (TMD). Herein,
we consider the variables at each step of the 2SC process including the impact
of the precursor film material and deposition technique, the influence of gas
composition and temperature during conversion, as well as other factors
controlling high quality 2D TMD synthesis. We feature the specific advantages
to the 2SC approach including deposition on diverse substrates, low temperature
processing, orientation control, and heterostructure synthesis, among others.
Finally, emergent opportunities that take advantage of the 2SC approach are
discussed to include next generation electronics, sensing, and optoelectronic
devices as well as catalysis for energy-related applications; spotlighting the
great potential of the 2SC technique.",2401.16513v1
2024-01-29,High Pressure Sputtering For Kigh-k Dielectric Deposition. Is It Worth Trying?,"Our research group studies the deposition of high permittivity dielectrics by
a non-standard method: high-pressure sputtering. The dielectrics studied here
are gadolinium scandate deposited from dielectric targets, and gadolinium oxide
deposited from a metallic target, with an in situ plasma oxidation. The
stoichiometric gadolinium scandate presents a slight permittivity boost after
annealing, but with gadolinium-rich scandate (grown with an annealing of a
nanolaminate) the dielectric shows a high effective permittivity of 21 and no
noticeable SiO2 layer at the interface with Si. On the other hand, the stacks
fabricated with the metallic Gd target have a SiO2 interface less than 0.7 nm
thick that can be further reduced by scavenging with Ti gates. In fact, this
scavenging effect is also demonstrated for the first time with indium phosphide
substrates, obtaining a low capacitance equivalent thickness of only 2.1 nm.",2401.17331v1
2024-01-29,Gadolinium scandate by high-pressure sputtering for future generations of high-k dielectrics,"Gd-rich gadolinium scandate (Gd2-xScxO3) was deposited by high-pressure
sputtering on (100) silicon by alternating the deposition of lower than 0.5 nm
thick films of its binary components: Sc2O3 and Gd2O3. The formation of the
ternary oxide was observed after the thermal treatments, with a high increase
in the effective permittivity of the dielectric (up to 21). The silicon
diffuses into the Gd2-xScxO3 films, which show an amorphous character. After
the annealing no interfacial silicon oxide is present. CHF-VG curves indicated
low hysteresis (55 mV) and a density of interfacial defects of 6e11 eV-1 cm-2.",2402.00887v1
2024-02-02,"Methanation of carbon dioxide over ceria-praseodymia promoted Ni-alumina catalysts. Influence of metal loading, promoter composition and alumina modifier","Two series of ceria-praseodymia promoted Ni-alumina catalysts were prepared
from two different commercial modified alumina supports by the incipient
wetness impregnation method in two successive steps.The resulting materials
were characterized in terms of their physico-chemical properties. Furthermore,
the as-prepared catalysts were tested for the CO2 methanation reaction. The
influence of the nominal Ni loading, molar composition of the Ce-Pr mixed oxide
promoter and alumina modifier on the catalytic performance was carefully
analyzed. Among these three composition parameters, the alumina dopant and
especially the Ni content appear to have by far a much more pronounced effect
on both the CO2 conversion and CH4 selectivity as compared to the Ce-Pr mixed
oxide composition.",2402.01394v1
2024-02-12,Epsilon near zero metal oxide based spectrally selective reflectors,"Epsilon near zero (ENZ) materials can contribute significantly to the
advancement of spectrally selective coatings aimed at enhancing efficient use
of solar radiation and thermal energy management. Here, we demonstrate a
subwavelength thick, multilayer optical coating that imparts a spectrally ""step
function"" like reflectivity onto diverse surfaces, from stainless steel to
glass, employing indium tin oxide as the key ENZ material. The coating,
harnessing the ENZ and plasmonic properties of nominally nanostructured ITO
along with ultrathin layers of Cr and Cr2O3 show 15% reflectivity over the
visible to near-infrared and 80% reflectivity (and low emissivity) beyond a
cut-in wavelength around 1500 nm, which is tunable in the infrared. A
combination of simulations and experimental results are used to optimize the
coating architecture and gain insights into the relevance of the components.
The straightforward design with high thermal stability will find applications
requiring passive cooling.",2402.07414v1
2024-02-12,Resistive switching acceleration induced by thermal confinement,"Enhancing the switching speed of oxide-based memristive devices at a low
voltage level is crucial for their use as non-volatile memory and their
integration into emerging computing paradigms such as neuromorphic computing.
Efforts to accelerate the switching speed often result in an energy tradeoff,
leading to an increase of the minimum working voltage. In our study, we present
an innovative solution: the introduction of a low thermal conductivity layer
placed within the active electrode, which impedes the dissipation of heat
generated during the switching process. The result is a notable acceleration in
the switching speed of the memristive model system SrTiO$_{3}$ by a remarkable
factor of 10$^{3}$, while preserving the integrity of the switching layer and
the interfaces with the electrodes, rendering it adaptable to various
filamentary memristive systems. The incorporation of HfO$_{2}$ or TaO$_{x}$ as
heat-blocking layers not only streamlines the fabrication process, but also
ensures compatibility with complementary metal-oxide-semiconductor technology.",2402.07603v1
2024-02-12,Electrically tunable plasmonic metasurface as a matrix of nanoantennas,"We report the fabrication and characterization of a plasmonic metasurface
comprising electrically contacted sub-wavelength gold dipole nanoantennas,
conformally coated by a thin hafnia film, an indium tin oxide layer and a
backside mirror, forming metal-oxide-semiconductor (MOS) capacitors, for use as
an electrically-tunable reflectarray or metasurface. By voltage biasing the
nanoantennas through metallic connectors and leveraging the carrier refraction
effect in the MOS capacitors, our measurements demonstrate phase control in
reflection over a range of about 30 degrees, with a constant magnitude of
reflection coefficient of 0.5, and the absence of secondary lobes.
Comprehensive electromagnetic and quantum carrier models of the structure are
developed and are in excellent agreement with the measurements. The metasurface
holds promise for use as an optical phased array.",2402.07805v2
2024-02-15,Adaptive multi-spectral mimicking with 2D-material nanoresonator networks,"Active nanophotonic materials that can emulate and adapt between many
different spectral profiles -- with high fidelity and over a broad bandwidth --
could have a far-reaching impact, but are challenging to design due to a
high-dimensional and complex design space. Here, we show that a metamaterial
network of coupled 2D-material nanoresonators in graphene can adaptively match
multiple complex absorption spectra via a set of input voltages. To design such
networks, we develop a semi-analytical auto-differentiable dipole-coupled model
that allows scalable optimization of high-dimensional networks with many
elements and voltage signals. As a demonstration of multi-spectral capability,
we design a single network capable of mimicking four spectral targets
resembling select gases (nitric oxide, nitrogen dioxide, methane, nitrous
oxide) with very high fidelity (${>}\,90\%$). Our results are relevant for the
design of highly reconfigurable optical materials and platforms for
applications in sensing, communication and display technology, and signature
and thermal management.",2402.09681v1
2024-02-19,Epitaxial rare-earth doped complex oxide thin films for infrared applications,"Rare earth dopants are one of the most extensively studied optical emission
centers for a broad range of applications such as laser optoelectronics,
sensing, lighting, and quantum information technologies due to their narrow
optical linewidth and exceptional coherence properties. Epitaxial doped oxide
thin films can serve as a promising and controlled host to investigate
rare-earth dopants suitable for scalable quantum memories, on-chip lasers and
amplifiers. Here, we report high-quality epitaxial thin films of Tm-doped
CaZrO$_3$ grown by pulsed laser deposition for infrared optoelectronic and
quantum memory applications. We perform extensive structural and chemical
characterization to probe the crystallinity of the films and the doping
behavior. Low temperature photoluminescence measurements show sharp radiative
transitions in the short-wave infrared range of 1.75 - 2 \mu m.",2402.12358v1
2024-02-20,Black brookite rich in oxygen vacancies as an active photocatalyst for CO2 conversion: experiments and first-principles calculations,"Photocatalytic CO2 conversion is a clean technology to deal with CO2
emissions, and titanium oxide (TiO2) polymorphs are the most investigated
photocatalysts for such an application. In this study, black TiO2 brookite is
produced by a high-pressure torsion (HPT) method and employed as an active
photocatalyst for CO2 conversion. Black brookite with a large concentration of
lattice defects (vacancies, dislocations and grain boundaries) showed enhanced
light absorbance, narrowed optical bandgap and diminished recombination rate of
electrons and holes. The photocatalytic activity of the black oxide for CO2
conversion was higher compared to commercial brookite and benchmark P25
catalyst powders. First-principles calculations suggested that the presence of
oxygen vacancies in black brookite is effective not only for reducing optical
bandgap but also for providing active sites for the adsorption of CO2 on the
surface of TiO2.",2402.12731v1
2024-02-21,Enhanced Superconductivity in SrTiO$_3$-based Interfaces via Amorphous Al2O3 Capping,"Oxide interfaces feature unique two-dimensional (2D) electronic systems with
diverse electronic properties such as tunable spin-orbit interaction and
superconductivity. Conductivity emerges in these interfaces when the thickness
of an epitaxial polar layer surpasses a critical value, leading to charge
transfer to the interface. Here, we show that depositing amorphous alumina on
top of the polar oxide can reduce the critical thickness and enhance the
superconducting properties for the (111) and the (100) SrTiO$_3$-based
interfaces. A detailed transmission electron microscopy analysis reveals that
the enhancement of the superconducting properties is linked to the expansion of
the LaAlO$_3$ lattice in a direction perpendicular to the interface. We propose
that the increase in the superconducting critical temperature, Tc, is a result
of epitaxial strain",2402.14051v1
2024-03-01,Deciphering diffuse scattering with machine learning and the equivariant foundation model: The case of molten FeO,"Bridging the gap between diffuse x-ray or neutron scattering measurements and
predicted structures derived from atom-atom pair potentials in disordered
materials, has been a longstanding challenge in condensed matter physics. This
perspective gives a brief overview of the traditional approaches employed over
the past several decades. Namely, the use of approximate interatomic pair
potentials that relate 3-dimensional structural models to the measured
structure factor and its associated pair distribution function. The use of
machine learned interatomic potentials has grown in the past few years, and has
been particularly successful in the cases of ionic and oxide systems. Recent
advances in large scale sampling, along with a direct integration of scattering
measurements into the model development, has provided improved agreement
between experiments and large-scale models calculated with quantum mechanical
accuracy. However, details of local polyhedral bonding and connectivity in
meta-stable disordered systems still require improvement. Here we leverage
MACE-MP-0; a newly introduced equivariant foundation model and validate the
results against high-quality experimental scattering data for the case of
molten iron(II) oxide (FeO). These preliminary results suggest that the
emerging foundation model has the potential to surpass the traditional
limitations of classical interatomic potentials.",2403.00259v1
2024-03-01,First-principles Investigation of Thermodynamic Properties of CrNbO4 and CrTaO4,"In the present study, the DFT+U method was employed to predict the
thermodynamic properties of Cr2O3, Nb2O5, and Ta2O5. Results were benchmarked
with experimental data showing high accuracy, except for the negative thermal
expansion (NTE) of Nb2O5, which is attributed to its polymorphic complexity.
Additionally, we extended our analysis to rutile-type oxides CrNbO4 and CrTaO4,
examining their entropy and heat capacity at finite temperatures. CrNbO4
displayed slightly higher entropy and heat capacity at high temperatures. The
mean linear thermal expansion coefficients for CrNbO4 and CrTaO4 from 500 K to
2000 K were predicted to be 6.00*10-6/K and 13.49*10-6/K, respectively,
corroborating with DFT predictions and experimental evidence. Our research
highlights the precision of the DFT+U and phonon methods in predicting the
thermodynamic properties of oxide materials, offering insights into the design
of corrosion-resistant materials.",2403.00705v1
2024-03-11,Electrical Degradation in Dielectric and Piezoelectric Oxides: Review of Defect Chemistry and Associated Characterization Techniques,"The properties of dielectric and piezoelectric oxides are determined by their
processing history, crystal structure, chemical composition, microstructure,
dopants (or defect) distribution, and defect kinetics. These materials are
essential in a diverse range of applications including aerospace, medical,
military, transportation, power engineering, and communication, where they are
used as ceramic discs, thick and thin films, multilayer devices, etc.
Significant advances in understanding the materials, processing, properties,
and reliability of these materials have led to their widespread use in consumer
electronics, military, and aerospace applications. This review delves into
electrical degradation in dielectrics and piezoelectrics, focusing on defect
chemistry and key characterization techniques. It also provides a detailed
discussion of various spectroscopic, microscopic, and electronic
characterization techniques essential for analyzing defects and degradation
mechanisms.",2403.06359v1
2024-03-19,Unveiling the Reactivity of Oxygen and Ozone on C2N Monolayer: A First-Principles Study,"The process of environmental oxidation is pivotal in determining the physical
and chemical properties of two-dimensional (2D) materials. Its impact holds
great significance for the practical application of these materials in
nanoscale devices functioning under ambient conditions. This study delves into
the influence of O2 and O3 exposure on the structural and electronic
characteristics of the C2N monolayer, focusing on the kinetics of adsorption
and dissociation reactions. Employing first-principles density functional
theory calculations alongside climbing image nudged elastic band calculations,
we observe that the C2N monolayer exhibits resistance to oxidation and
ozonation, evidenced by energy barriers of 0.05 eV and 0.56 eV, respectively.
These processes are accompanied by the formation of epoxide (C-O-C) groups.
Furthermore, the dissociation mechanism involves charge transfers from the
monolayer to the molecules. Notably, the dissociated configurations demonstrate
higher bandgaps compared to the pristine C2N monolayer, attributed to robust
C-O hybridization. These findings suggest the robustness of C2N monolayers
against oxygen/ozone exposures, ensuring stability for devices incorporating
these materials.",2403.12454v1
2024-03-21,Selective advantage of aerobic glycolysis over oxidative phosphorylation,"The utilization of glycolysis in aerobic conditions have been a subject of
debate for more than a century. A hypothesis supported by previous data is that
glycolysis has a higher rate of ATP production per protein mass and per
occupied volume than oxidative phosphorylation (OxPhos). However, a recent work
by Shen et al14 challenges previous estimates, reporting that OxPhos has a
higher rate of ATP production per protein mass than glycolysis. Here I show
that Shen et al14 make a key assumption that is a subject of debate: that the
proteomic cost of OxPhos is limited to proteins in enzymes of OxPhos and the
TCA cycle. I argue that an intact mitochondria is required for functional
OxPhos and therefore the whole mitochondrial protein content should be included
for the cost estimate of OxPhos. After doing so, glycolysis is the most
efficient pathway per protein mass or per volume fraction.",2403.14741v1
2024-03-25,Highly dispersed Ru nanoparticles anchored on NiAl layered double oxides catalyst for selective hydrodeoxygenation of vanillin,"The hydrodeoxygenation (HDO) of lignin-derived feedstocks into value-added
chemicals with high efficiency and selectivity is desirable for the utilization
of biomass resource. The complex oxygen-containing groups of lignin-derived
substance result in the challenge of the low selectivity toward the required
product. In this work, highly dispersed Ru nanoparticles anchored on Ni3Al1
layered double oxides (LDOs) catalyst derived from NiAl layered double
hydroxides (LDHs) with flower-shaped morphology was constructed by a simple
deposition-reduction method. The introduction of LDHs-derived support can
significantly impact the catalytic activity for the HDO of lignin-derived
vanillin (VL) into 2-methoxy-4-methylphenol (MMP). The Ru/Ni3Al1-400 catalyst
obtained complete conversion of VL and 94.2% yield of MMP at 130 {\deg}C in
methanol solvent, much better than the catalysts without LDHs-derived support.
The methanol solvent is beneficial for the conversion of reaction intermediate
of vanillin alcohol (VA). Detailed characterization reveals that the existence
of the enhanced metal-support interaction over Ru/Ni3Al1-400 and the easily
accessible acid sites facilitate the production of MMP.",2403.16433v1
2024-03-25,Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion,"Transition-metal-based layered double hydroxides (TM-LDHs) nanosheets are
promising electrocatalysts in the renewable electrochemical energy conversion
system, which are regarded as alternatives to noble metal-based materials. In
this review, recent advances on effective and facile strategies to rationally
design TM-LDHs nanosheets as electrocatalysts, such as increasing the number of
active sties, improving the utilization of active sites (atomic-scale
catalysts), modulating the electron configurations, and controlling the lattice
facets, are summarized and compared. Then, the utilization of these fabricated
TM-LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction,
urea oxidation reaction, nitrogen reduction reaction, small molecule
oxidations, and biomass derivatives upgrading is articulated through
systematically discussing the corresponding fundamental design principles and
reaction mechanism. Finally, the existing challenges in increasing the density
of catalytically active sites and future prospects of TM-LDHs nanosheets-based
electrocatalysts in each application are also commented.",2403.16461v1
2024-03-29,Electrical double layer and capacitance of TiO2 electrolyte interfaces from first principles simulations,"The electrical double layer (EDL) at aqueous solution-metal oxide interfaces
critically affects many fundamental processes in electrochemistry, geology and
biology, yet understanding its microscopic structure is challenging for both
theory and experiments. Here we employ ab initio-based machine learning
potentials including long-range electrostatics in large-scale atomistic
simulations of the EDL at the TiO2-electrolyte interface. Our simulations
provide a molecular-scale picture of the EDL that demonstrates the limitations
of standard mean-field models. We further develop a method to accurately
calculate the electrostatic potential drop at the interface. The computed
capacitance originating from the adsorbed charges and the potential drop agrees
with experiments, supporting the reliability of our description of the EDL. The
larger interfacial capacitance of basic relative to acidic solutions originates
from the higher affinity of the cations for the oxide surface and gives rise to
distinct charging mechanisms on negative and positive surfaces.",2404.00167v1
2006-08-14,Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy,"The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.",0608307v3
2007-06-13,Nonlinear turbulent magnetic diffusion and effective drift velocity of large-scale magnetic field in a two-dimensional magnetohydrodynamic turbulence,"We study a nonlinear quenching of turbulent magnetic diffusion and effective
drift velocity of large-scale magnetic field in a developed two-dimensional MHD
turbulence at large magnetic Reynolds numbers. We show that transport of the
mean-square magnetic potential strongly changes quenching of turbulent magnetic
diffusion. In particularly, the catastrophic quenching of turbulent magnetic
diffusion does not occur for the large-scale magnetic fields $B \gg B_{\rm eq}
/ \sqrt{\rm Rm}$ when a divergence of the flux of the mean-square magnetic
potential is not zero, where $B_{\rm eq}$ is the equipartition mean magnetic
field determined by the turbulent kinetic energy and Rm is the magnetic
Reynolds number. In this case the quenching of turbulent magnetic diffusion is
independent of magnetic Reynolds number. The situation is similar to
three-dimensional MHD turbulence at large magnetic Reynolds numbers whereby the
catastrophic quenching of the alpha effect does not occur when a divergence of
the flux of the small-scale magnetic helicity is not zero.",0706.1846v1
2007-10-26,Magnetic fluctuations and formation of large-scale inhomogeneous magnetic structures in a turbulent convection,"Magnetic fluctuations generated by a tangling of the mean magnetic field by
velocity fluctuations are studied in a developed turbulent convection with
large magnetic Reynolds numbers. We show that the energy of magnetic
fluctuations depends on magnetic Reynolds number only when the mean magnetic
field is smaller than $B_{eq} / 4 Rm^{1/4}$, where $B_{eq}$ is the
equipartition mean magnetic field determined by the turbulent kinetic energy
and Rm is magnetic Reynolds number. Generation of magnetic fluctuations in a
turbulent convection with a nonzero mean magnetic field results in a decrease
of the total turbulent pressure and may cause formation of the large-scale
inhomogeneous magnetic structures even in an originally uniform mean magnetic
field. This effect is caused by a negative contribution of the turbulent
convection to the effective mean Lorentz force. The inhomogeneous large-scale
magnetic fields are formed due to the excitation of the large-scale
instability. The energy for this instability is supplied by the small-scale
turbulent convection. The discussed effects might be useful for understanding
the origin of the solar nonuniform magnetic fields, e.g., sunspots.",0710.5052v1
2013-11-18,"Fabrication, properties, and applications of flexible magnetic films","Flexible magnetic devices, i.e., magnetic devices fabricated on flexible
substrates, are very attractive in application of detecting magnetic field in
arbitrary surface, non-contact actuators, and microwave devices due to the
stretchable, biocompatible, light-weight, portable, and low cost properties.
Flexible magnetic films are essential for the realization of various
functionalities of flexible magnetic devices. To give a comprehensive
understanding for flexible magnetic films and related devices, we have reviewed
recent advances in the studies of flexible magnetic films including fabrication
methods, magnetic and transport properties of flexible magnetic films, and
their applications in magnetic sensors, actuators, and microwave devices. Three
typical methods were introduced to prepare the flexible magnetic films.
Stretching or bending the flexible magnetic films offers a good way to apply
mechanical strain on magnetic films, so that magnetic anisotropy, exchanged
bias, coercivity, and magnetoresistance can be effectively manipulated.
Finally, a series of examples were shown to demonstrate the great potential of
flexible magnetic films for future applications.",1311.4318v1
2021-10-31,Shape Programmable Magnetic Pixel Soft Robot,"Magnetic response soft robot realizes programmable shape regulation with the
help of magnetic field and produces various actions. The shape control of
magnetic soft robot is based on the magnetic anisotropy caused by the orderly
distribution of magnetic particles in the elastic matrix. In the previous
technologies, magnetic programming is coupled with the manufacturing process,
and the orientation of magnetic particles cannot be modified, which brings
restrictions to the design and use of magnetic soft robot. This paper presents
a magnetic pixel robot with shape programmable function. By encapsulating
NdFeB/gallium composites into silicone shell, a thermo-magnetic response
functional film with lattice structure are fabricated. Basing on
thermal-assisted magnetization technique, we realized the discrete
magnetization region distribution on the film. Therefore, we proposed a
magnetic coding technique to realize the mathematical response action design of
software robot. Using these methods, we prepared several magnetic soft robots
based on origami structure. The experiments show that the behavior mode of
robot can be flexibly and repeatedly regulated by magnetic encoding technique.
This work provides a basis for the programmed shape regulation and motion
design of soft robot.",2111.00422v2
2022-02-07,Magnetism of QCD matter and pion mass from tensor-type spin polarization and anomalous magnetic moment of quarks,"We investigate the magnetism of QCD matter and pion mass under magnetic field
considering the contribution from the tensor-type spin polarization and the
anomalous magnetic moment (AMM) of quarks. It is found that the tensor-type
spin polarization (TSP) induces the magnetic catalysis of chiral condensate and
diamagnetism (negative magnetic susceptibility) of quark matter at low
temperature, both neutral and charged pion masses increase quickly with
magnetic field in the case of TSP. The anomalous magnetic moment (AMM) of
quarks induces magnetic inhibition and a magnetic dependent AMM causes inverse
magnetic catalysis at finite temperature, and the neutral pion mass decreases
with magnetic field while the charged pion mass shows nonmonotonic behavior
with the magnetic field, which is qualitatively in agreement with lattice
result. However, the magnetic susceptibility is positive at low temperature
with AMM. In the current framework, our results show the irreconcilable
contradiction between the diamagnetism and inverse magnetic catalysis.",2202.03226v1
2022-10-06,Current-induced perpendicular effective magnetic field in magnetic heterostructures,"Generation of perpendicular effective magnetic field or perpendicular spins
({\sigma}z) is central for the development of energy-efficient, scalable, and
external-magnetic-field-free spintronic memory and computing technologies.
Here, we report the first identification and the profound impacts of a
significant effective perpendicular magnetic field that can arise from
asymmetric current spreading within magnetic microstrips and Hall bars. This
effective perpendicular magnetic field can exhibit all the three
characteristics that have been widely assumed in the literature to ""signify""
the presence of a flow of {\sigma}z, i.e., external-magnetic-field-free current
switching of uniform perpendicular magnetization, a sin2{\phi}-dependent
contribution in spin-torque ferromagnetic resonance signal of in-plane
magnetization ({\phi} is the angle of the external magnetic field with respect
to the current, and a {\phi}-independent but field-dependent contribution in
the second harmonic Hall voltage of in-plane magnetization. This finding
suggests that it is critical to include current spreading effects in the
analyses of various spin polarizations and spin-orbit torques in magnetic
heterostructure. Technologically, our results provide perpendicular effective
magnetic field induced by asymmetric current spreading as a novel, universally
accessible mechanism for efficient, scalable, and external-magnetic-field-free
magnetization switching in memory and computing technologies.",2210.02916v1
2010-03-09,MAGNETIC ANOMALY IN SUPERCONDUCTING FeSe,"Synthesis, electrical and magnetic characterization of superconducting
FeSe0.85 compound is reported. An anomaly in the magnetization against
temperature around 90K is observed. Magnetic characterization of a commercial
compound with nominal FeSe stoichiometry is also presented. The overall
magnetic behaviors as well as the magnetic anomaly in both compounds are
discussed in terms of magnetic impurities and secondary phases. Keyword: A.
Superconductors",1003.1966v1
2011-05-19,Ultra-fast spin avalanches in crystals of molecular magnets in terms of magnetic detonation,"Recent experiments (Decelle et al., Phys. Rev. Lett. 102, 027203 (2009))
discovered an ultra-fast regime of spin avalanches in crystals of magnetic
magnets, which was three orders of magnitude faster than the traditionally
studied magnetic deflagration. The new regime has been hypothetically
identified as magnetic detonation. Here we demonstrate the possibility of
magnetic detonation in the crystals, as a front consisting of a leading shock
and a zone of Zeeman energy release. We study the dependence of the magnetic
detonation parameters on the applied magnetic field. We find that the magnetic
detonation speed only slightly exceeds the sound speed in agreement with the
experimental observations.",1105.3962v1
2013-07-18,Interaction effect detected by compared of the irreversible and remanent initial magnetization curves in Ni-Cu-Zn ferrites,"A new technique for estimation of magnetic interaction effects of initial
magnetization curves has been proposed. It deals with remanence, and initial
irreversible magnetization, curves. The method is applied for single-phase
polycrystalline Ni0.85-xCu0.15ZnxFe2O4, (x = 0, 0.2, 0.4 and 0.6), which were
synthesized by a standard ceramic technology. A study of the initial reversible
and irreversible magnetization processes in ferrite materials was carried out.
The field dependence of the irreversible, and reversible, magnetizations was
determined by magnetic losses of minor hysteresis loops obtained from different
points of an initial magnetization curve. The influence of Zn-substitutions in
Ni-Cu ferrites over irreversible magnetization processes and interactions in
magnetic systems has been analyzed.",1307.4881v1
2013-10-15,Plasticity-Induced Magnetization in Amorphous Magnetic Solids,"Amorphous magnetic solids, like metallic glasses, exhibit a novel effect: the
growth of magnetic order as a function of mechanical strain under athermal
conditions in the presence of a magnetic field. The magnetic moment increases
in steps whenever there is a plastic event. Thus plasticity induces the
magnetic ordering, acting as the effective noise driving the system towards
equilibrium. We present results of atomistic simulations of this effect in a
model of a magnetic amorphous solid subjected to pure shear and a magnetic
field. To elucidate the dependence on external strain and magnetic field we
offer a mean-field theory that provides an adequate qualitative understanding
of the observed phenomenon.",1310.3979v1
2017-09-11,Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2,"The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour
and we report here a neutron diffraction investigation into the magnetic
ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the
anti-Sr2MnO2Sb2-type structure and orders antiferromagnetically below TN = 105
K. We consider both its long-range magnetic structure and its magnetic
microstructure, and the onset of magnetic order. It adopts the multi-k vector
""2k"" magnetic structure (k = (0.5 0 0.5) and k = (0 0.5 0.5) and has
similarities with related iron oxychalcogenides, illustrating the robust nature
of the ""2k"" magnetic structure.",1709.03323v1
2022-12-07,Quark condensate and magnetic moment in a strong magnetic field,"This paper studies the quark condensate, magnetic moment, magnetic
polarization, and magnetic susceptibility in a strong external magnetic field
by employing the Dyson-Schwinger equations (DSE). The results show that these
physical quantities as functions of the magnetic field. We note that the
quark's spin polarizations are approximately proportional to the magnetic field
magnitude. For comparison, we investigate the magnetic moments and
susceptibility of the nucleon in the constituent quark model framework and
demonstrate that both these quantities increase as the magnetic field rises.",2212.03508v2
2023-12-26,Magnetic vortex control with current-induced axial magnetization in centrosymmetric Weyl materials,"We consider magnetic Weyl metals as a platform to achieve current control of
magnetization textures with transport currents, utilizing their underlying band
geometry. We show that the transport current in a Weyl semimetal produces an
axial magnetization due to orbital magnetic moments of the Weyl electrons. The
associated axial magnetization can generate a torque acting on the localized
magnetic moments. For the case of a magnetic vortex in a nanodisk of Weyl
materials, this current-induced torque can be used to reverse its circulation
and polarity. We discuss the axial magnetization torques in Weyl metals on
general symmetry grounds, and compare their strength to current-induced torques
in more conventional materials.",2312.16122v1
2004-09-08,Magnetic and electronic phase transformations in (Sm0.65Sr0.35)MnO3 induced by temperature and magnetic field,"Temperature (4.2-260 K) and magnetic field (0-50 kOe) dependencies of the dc
electrical resistance, dc magnetization, and ac magnetic susceptibility of
(Sm0.65Sr0.35)MnO3 prepared from high purity components have been studied.",0409213v1
2008-02-20,Anomalous Magnetic Properties of Sr2YRuO6,"Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.",0802.2953v2
2014-09-05,"Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders","The Halbach cylinder is a construction of permanent magnets used in
applications such as nuclear magnetic resonance apparatus, accelerator magnets
and magnetic cooling devices. In this paper the analytical expression for the
magnetic vector potential, magnetic flux density and magnetic field for a two
dimensional Halbach cylinder are derived. The remanent flux density of a
Halbach magnet is characterized by the integer $p$. For a number of
applications the force and torque between two concentric Halbach cylinders are
important. These quantities are calculated and the force is shown to be zero
except for the case where $p$ for the inner magnet is one minus $p$ for the
outer magnet. Also the force is shown never to be balancing. The torque is
shown to be zero unless the inner magnet $p$ is equal to minus the outer magnet
$p$. Thus there can never be a force and a torque in the same system.",1409.1712v1
2018-12-18,(Self-)Magnetized Bose-Einstein Condensate stars,"We study magnetic field effects on the Equations of State (EoS) and the
structure of Bose-Einstein Condensate (BEC) stars, i.e. a compact object
composed by a gas of interacting spin one bosons formed up by the pairing of
two neutrons. To include the magnetic field in the thermodynamic description,
we suppose that particle-magnetic field and particle-particle interactions are
independent. We consider two configurations for the magnetic field: one where
it constant and externally fixed, and another where it is produced by the
bosons by self-magnetization. Since the magnetic field produces the splitting
of pressures in the directions along and perpendicular to the magnetic axis,
stable configurations of self-magnetized and magnetized BEC stars are studied
using the recently found $\gamma$-structure equations that describe axially
symmetric objects. The magnetized BEC stars are, in general spheroidal, less
massive and smaller than the non-magnetic ones, being these effects more
relevant at low densities. For the self-magnetized BEC stars their inner
profiles of magnetic field can be computed as a function of the equatorial
radii. The values obtained for the core and surface magnetic fields are in
agreement with those typical of compact objects.",1812.07657v1
2019-12-03,Internally-Balanced Magnetic Mechanisms Using Magnetic Spring for Producing Large Amplified Clamping Force,"To detach a permanent magnet with a controlled force much smaller than its
original attractive force, the Internally-Balanced Magnetic Unit (IB Magnet)
was invented and has been applied to magnetic devices such as wall-climbing
robots, ceil-dangling drones, and modular swarm robots. In contrast to its
drastic reduction rate on the control force, the IB Magnet has two major
problems on its nonlinear spring which cancels out the internal force on the
magnet: complicated design procedure and trade-off relationship between
balancing precision and mechanism volume. This paper proposes a principle of a
new balancing method for the IB Magnet which uses a like-pole pair of magnets
as a magnetic spring, whose repulsive force ideally equals the attractive force
of an unlike-pole pair exactly. To verify the proposed principle, the authors
realized a prototype model of the IB Magnet using magnetic spring and verified
through experiments its reduction rate is comparable to those of conventional
IB Magnets. Moreover, the authors discussed and realized a robotic clamp as an
application example containing proposed IB Magnets as its internal mechanism.",1912.01292v1
2020-09-14,Voltage-driven Magnetization Switching via Dirac Magnetic Anisotropy and Spin--orbit Torque in Topological-insulator-based Magnetic Heterostructures,"Electric-field control of magnetization dynamics is fundamentally and
technologically important for future spintronic devices. Here, based on
electric-field control of both magnetic anisotropy and spin--orbit torque, two
distinct methods are presented for switching the magnetization in topological
insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in
magnetic TIs is formulated analytically as a function of the Fermi energy, and
it is confirmed that the out-of-plane magnetization is always favored for the
partially occupied surface band. Also proposed is a transistor-like device with
the functionality of a nonvolatile magnetic memory that uses voltage-driven
writing and the (quantum) anomalous Hall effect for readout. For the
magnetization reversal, by using parameters of Cr-doped
Bi_{1-x}Sb_{x})_{2}Te_{3}, the estimated source-drain current density and gate
voltage are of the orders of $10^4$--$10^5$~A/cm$^2$ and 0.1~V, respectively,
below 20~K and the writing requires no external magnetic field. Also discussed
is the possibility of magnetization switching by the proposed method in
TI/ferromagnetic-insulator bilayers with the magnetic proximity effect.",2009.06187v1
2021-07-10,Photoinduced Magnetic Force Microscopy: Enabling Direct and Exclusive Detection of Optical Magnetism,"Modern optical nano-elements pursue ever-smaller sizes and individualized
functionalities. Those elements that can efficiently manipulate the magnetic
field of light boast promising future applications with a great challenge: the
magnetic near field is irretrievable from conventional optical far-field
characterization. Here we propose photoinduced magnetic force microscopy to
directly and exclusively sense the magnetic field of light at the nanoscale.
The proposed instrument exploits a magnetic nanoprobe with exclusive magnetic
excitation under structured light illumination. The magnetic nanoprobe detects
the photoinduced magnetic force, which is defined as the dipolar Lorentz force
exerted on the photoinduced magnetic dipole in the nanoprobe. Since the
resulting magnetic force is proportional to the incident magnetic field, the
measured force reveals the magnetic near-field distribution at the nanoscale.
The proposed instrument represents a fundamental step towards comprehensive
electric and magnetic near-field detection and/or manipulation in single
nano-element optical devices.",2107.04739v1
2022-08-31,Second-order phase transition of silicon from a band insulator to metal induced by strong magnetic fields,"We present the second-order phase transition from a band insulator to metal
that is induced by a strong magnetic field. The magnetic-field dependences of
the magnetization and energy band gap of a crystalline silicon immersed in a
magnetic field are investigated by means of the nonperturbative
magnetic-field-containing relativistic tight-binding approximation method
[Phys. Rev. B 97, 195135 (2018)]. It is shown that the energy band gap
disappears at the critical magnetic field of 2.22x$10^4$ (T). At the critical
magnetic field, the magnetic-field dependence of the magnetization exhibits a
kink behavior, which means that this phenomenon is the second-order phase
transition from a band insulator to metal. It is found that in strong magnetic
fields above the critical magnetic field, namely in the metallic phase, the
oscillation of the magnetization appears. It is shown that this magnetic
oscillation comes from the energy bands in the magnetic Brillouin zone that
change from the occupied states to unoccupied states or vice vasa.",2208.14690v1
2023-07-18,Yu-Shiba-Rusinov tips: imaging spins at the atomic scale with full magnetic sensitivity,"Measurements of magnetic properties at the atomic scale require probes
capable of combining high spatial resolution with spin sensitivity.
Spin-polarized scanning tunneling microscopy (SP-STM) fulfills these conditions
by using atomically sharp magnetic tips. The imaging of spin structures results
from the tunneling magneto-conductance that depends on the imbalance in the
local density of spin-up and spin-down electrons. Spin-sensitive tips are
generally formed from bulk materials or by coating non-magnetic tips with a
thin magnetic layer. However, ferromagnetic materials generate stray magnetic
fields which can influence the magnetic structure of the probed system, while
the magnetization of antiferromagnetic materials is difficult to set tip by
externally applied magnetic fields. Here, we use functionalized
Yu-Shiba-Rusinov (YSR) tips prepared by attaching magnetic adatoms at the apex
of a superconducting cluster to image magnetic interactions at the atomic
scale. We demonstrate that YSR tips are capable of sensing different
magnetization directions, conferring them full magnetic sensitivity. We
additionally show that the finite size of the tip superconducting cluster makes
it robust against relatively strong magnetic fields, making YSR tips capable of
visualizing magnetic field driven transitions of the spin texture.",2307.09534v1
2024-03-20,Molecular Dynamics Simulations of Microscopic Structural Transition and Macroscopic Mechanical Properties of Magnetic Gels,"Magnetic gels with embedded micro/nano-sized magnetic particles in
crosslinked polymer networks can be actuated by external magnetic fields, with
changes in their internal microscopic structures and macroscopic mechanical
properties. We investigate the responses of such magnetic gels to an external
magnetic field, by means of coarse-grained molecular dynamics simulations. We
find that the dynamics of magnetic particles are determined by the interplay of
between magnetic dipole-dipole interactions, polymer elasticity and thermal
fluctuations. The corresponding microscopic structures formed by the magnetic
particles such as elongated chains can be controlled by the external magnetic
field. Furthermore, the magnetic gels can exhibit reinforced macroscopic
mechanical properties, where the elastic modulus increases algebraically with
the magnetic moments of the particles in the form of
$\propto(m-m_{\mathrm{c}})^{2}$ when magnetic chains are formed. This
simulation work can not only serve as a tool for studying the microscopic and
the macroscopic responses of the magnetic gels, but also facilitate future
fabrications and practical controls of magnetic composites with desired
physical properties.",2403.13481v1
2017-02-07,Characteristics of Low-Latitude Coronal Holes near the Maximum of Solar cycle 24,"We investigate the statistics of 288 low-latitude coronal holes extracted
from SDO/AIA-193 filtergrams over the time range 2011/01/01 to 2013/12/31. We
analyse the distribution of characteristic coronal hole properties, such as the
areas, mean AIA-193 intensities, and mean magnetic field densities, the local
distribution of the SDO/AIA-193 intensity and the magnetic field within the
coronal holes, and the distribution of magnetic flux tubes in coronal holes. We
find that the mean magnetic field density of all coronal holes under study is
3.0 +- 1.6 G, and the percentage of unbalanced magnetic flux is 49 +- 16 %. The
mean magnetic field density, the mean unsigned magnetic field density, and the
percentage of unbalanced magnetic flux of coronal holes depend strongly
pairwise on each other, with correlation coefficients cc > 0.92. Furthermore,
we find that the unbalanced magnetic flux of the coronal holes is predominantly
concentrated in magnetic flux tubes: 38 % (81 %) of the unbalanced magnetic
flux of coronal holes arises from only 1 % (10 %) of the coronal hole area,
clustered in magnetic flux tubes with field strengths > 50 G (10 G). The
average magnetic field density and the unbalanced magnetic flux derived from
the magnetic flux tubes correlate with the mean magnetic field density and the
unbalanced magnetic flux of the overall coronal hole (cc > 0.93). These
findings give evidence that the overall magnetic characteristics of coronal
holes are governed by the characteristics of the magnetic flux tubes.",1702.02050v1
2019-12-09,Field Dependence of Magnetic Disorder in Nanoparticles,"The performance characteristics of magnetic nanoparticles towards
application, e.g. in medicine, imaging, or as sensors, is directly determined
by their magnetization relaxation and total magnetic moment. In the commonly
assumed picture, nanoparticles have a constant overall magnetic moment
originating from the magnetization of the single-domain particle core
surrounded by a surface region hosting spin disorder. In contrast, this work
demonstrates the significant increase of the magnetic moment of ferrite
nanoparticles with applied magnetic field. At low magnetic field, the
homogeneously magnetized particle core initially coincides in size with the
structurally coherent grain of 12.8(2) nm diameter, indicating a strong
coupling between magnetic and structural disorder. Applied magnetic fields
gradually polarize the uncorrelated, disordered surface spins, resulting in a
magnetic volume more than 20\% larger than the structurally coherent core. The
intraparticle magnetic disorder energy increases sharply towards the
defect-rich surface as established by the field-dependence of the magnetization
distribution. In consequence, these findings illustrate how the nanoparticle
magnetization overcomes structural surface disorder. This new concept of
intraparticle magnetization is deployable to other magnetic nanoparticle
systems, where the in-depth knowledge of spin disorder and associated magnetic
anisotropies will be decisive for a rational nanomaterials design.",1912.04081v2
2021-04-23,Interesting magnetic response of the nuclear fuel material UO2,"Magnetic response of uranium dioxide (UO2) has been investigated through
temperature and magnetic field dependent dc magnetization measurements. UO2 is
a paramagnet at room temperature. The magnetic susceptibility, however,
deviates from Curie-Weiss (CW) like paramagnetic behavior below T = 280 K.
Further down the temperature UO2 undergoes phase transition to an
antiferromagnetic state below TN = 30.6 K. The zero field cooled (ZFC) and
field cooled (FC) magnetizations exhibit some distinct thermomagnetic
irreversibility below TN. The temperature dependence of the FC magnetization is
more like a ferromagnet, whereas ZFC magnetization exhibits distinct structures
not usually observed in the antiferromagnets. In low applied magnetic field
this thermomagnetic irreversibility in magnetization exists in a subtle way
even in the paramagnetic regime above TN up to a fairly high temperature, but
vanishes in high applied magnetic fields. Deviation from CW law and
irreversibility between ZFC and FC magnetization indicate that the paramagnetic
state above TN is not a trivial one. Magnetic response below TN changes
significantly with the increase in the applied magnetic field. Thermomagnetic
irreversibility in magnetization initially increases with the increase in the
strength of applied magnetic field, but then gets reduced in the high applied
fields. A subtle signature of a magnetic field induced phase transition is also
observed in the isothermal magnetic field vartaion of magnetization. All these
experimetal results highlight the non-trivial nature of the antiferromagnetic
state in UO2",2104.11412v1
1998-01-12,Persistent Currents and Magnetization in two-dimensional Magnetic Quantum Systems,"Persistent currents and magnetization are considered for a two-dimensional
electron (or gas of electrons) coupled to various magnetic fields.
Thermodynamic formulae for the magnetization and the persistent current are
established and the ``classical'' relationship between current and
magnetization is shown to hold for systems invariant both by translation and
rotation. Applications are given, including the point vortex superposed to an
homogeneous magnetic field, the quantum Hall geometry (an electric field and an
homogeneous magnetic field) and the random magnetic impurity problem (a random
distribution of point vortices).",9801106v1
1999-03-20,Magnetism Controlled Vortex Matter,"We discuss a new class of phenomena based on strong interaction between
magnetic superstructures and vortices in superconductors in combined
heterogeneous structures. An inhomogeneous magnetization can pin vortices or
create them spontaneously changing drastically properties of the
superconductor. On the other hand, the interaction between magnetic moments
mediated by vortices can result in specific types of magnetic ordering. The
same interaction can create coupled magnetic-superconducting defects. We
discuss possible experimental observation of magnetism controlled vortex matter
in superconducting films with magnetic nanoscale dots or stripes and layered
systems with alternating superconducting and magnetic layers.",9903312v1
1999-04-07,Perpendicular transport and magnetization processes in magnetic multilayers with strongly and weakly coupled magnetic layers,"Within the framework of a two-band tight-binding model, we have performed
calculations of giant magnetoresistance, exchange coupling and thermoelectric
power (TEP) for a system consisting of three magnetic layers separated by two
non-magnetic spacers with the first two magnetic layers strongly
antiferromagnetically exchange-coupled. We have shown how does the GMR relate
with the corresponding regions of magnetic structure phase diagrams and
computed some relevant hysteresis loops, too. The GMR may take negative values
for specific layers thicknesses, and the TEP reveals quite pronounced
oscillations around a negative bias.",9904086v1
1999-11-23,Magnetization-plateau state of the S=3/2 spin chain with single ion anisotropy,"We reexamine the numerical study of the magnetized state of the S=3/2 spin
chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where
M_{S} is the saturation magnetization. We find at this magnetization that for
D<D_{c1}=0.387 the system is critical and the magnetization plateau does not
appear. For D > D_{c1}, the parameter region is divided into two parts D_{c1} <
D < D_{c2}=0.943 and D_{c2} < D. In each region, the system is gapful and the
M=M_{S}/3 magnetization plateau appears in the magnetization process. From our
numerical calculation, the intermediate region D_{c1} < D < D_{c2} should be
characterized by a magnetized valence-bond-solid state.",9911364v1
2003-07-16,Magnetic moment of an electron gas on the surface of constant negative curvature,"The magnetic moment of an electron gas on the surface of constant negative
curvature is investigated. It is shown that the surface curvature leads to the
appearance of the region of the monotonic dependence $M(B)$ at low magnetic
fields. At high magnetic fields, the dependence of the magnetic moment on a
magnetic field is the oscillating one. The effect of the surface curvature is
to increase the region of the monotonic dependence of the magnetic moment and
to break the periodicity of oscillations of the magnetic moment as a function
of an inverse magnetic field.",0307401v1
2003-09-11,Giant Keplerate molecule Fe30 - the first octopole magnet,"The multipole expansion technique is applied to one of the largest magnetic
molecules, Fe30. The molecule's dipole, toroid and quadrupole magnetic moments
are equal to zero (in the absence of magnetic field) so the multipole expansion
starts from the octopole moment. Probably the Fe30 molecule is the most
symmetrical magnetic body synthesized so far. The magnetization process is
considered theoretically in different geometries. Some components of the
octopole moment experience a jump while the magnetization rises linearly up to
its saturation value. An elementary octopole moment consisting of four magnetic
dipoles is proposed as a hint for designing of an experiment for measurement of
octopole magnetic moment components.",0309282v1
2004-12-27,Magnetization suppression of Type-II Superconductors by external alternating magnetic field,"The effect of suppression of static magnetization of an anisotropic hard
superconductor by alternating magnetic field is analyzed theoretically. The
magnetic moment suppression dynamics is described with respect to the
magnetization loop of the superconductor. It is found that in some cases the
magnetic moment varies nonmonotonically with the growth in amplitude
$\mathrm{h}$ of the alternating field. Effect of transition, induced by
$\mathrm{\mathbf{h}}(t)$, of superconductor form paramagnetic into the
diamagnetic state is considered. The amplitude of alternating magnetic field
$\mathrm{h}_{c}(\delta,\vartheta)$ for which the complete suppression of the
magnetization occurs is calculated as the function of anisotropy parameter
$\delta$ and it orientation angle $\vartheta$ with respect to the
crystallographic axes of the sample.",0412695v1
2009-09-25,Probing punctual magnetic singularities during magnetization process in FePd films,"We report the use of Lorentz microscopy to observe the domain wall structure
during the magnetization process in FePd thin foils. We have focused on the
magnetic structure of domain walls of bubble-shaped magnetic domains near
saturation. Regions are found along the domain walls where the magnetization
abruptly reverses. Multiscale magnetic simulations shown that these regions are
vertical Bloch lines (VBL) and the different bubble shapes observed are then
related to the inner structure of the VBLs. We were thus able to probe the
presence of magnetic singularities as small as Bloch points in the inner
magnetization of the domain walls.",0909.4645v1
2010-06-21,Dynamics of magnetic charges in artificial spin ice,"Artificial spin ice has been recently implemented in two-dimensional arrays
of mesoscopic magnetic wires. We propose a theoretical model of magnetization
dynamics in artificial spin ice under the action of an applied magnetic field.
Magnetization reversal is mediated by domain walls carrying two units of
magnetic charge. They are emitted by lattice junctions when the the local field
exceeds a critical value $H_c$ required to pull apart magnetic charges of
opposite sign. Positive feedback from Coulomb interactions between magnetic
charges induces avalanches in magnetization reversal.",1006.4075v2
2010-11-08,Neutrino magnetic moment in a magnetized plasma,"The contribution of a magnetized plasma to the neutrino magnetic moment is
calculated. It is shown that only part of the additional neutrino energy in
magnetized plasma connecting with its spin and magnetic field strength defines
the neutrino magnetic moment. It is found that the presence of magnetized
plasma does not lead to the considerable increase of the neutrino magnetic
moment in contrast to the results presented in literature previously.",1011.1779v1
2011-03-08,Permanent magnets including undulators and wigglers,"After a few historic remarks on magnetic materials we introduce the basic
definitions related to permanent magnets. The magnetic properties of the most
common materials are reviewed and the production processes are described.
Measurement techniques for the characterization of macroscopic and microscopic
properties of permanent magnets are presented. Field simulation techniques for
permanent magnet devices are discussed. Today, permanent magnets are used in
many fields. This article concentrates on the applications of permanent magnets
in accelerators starting from dipoles and quadrupoles on to wigglers and
undulators.",1103.1573v1
2013-02-20,Non-magnetic doping induced magnetism in Li doped SnO2 nanoparticles,"We address the possibility of non-magnetic doping induced magnetism, in Li
doped SnO2 nano-particles. The compounds have been prepared by solid state
route at equilibrium and were found to be crystallized in single rutile phase.
The magnetization measurements have shown that Li-doping induces magnetism in
SnO2 for a particular range of Li concentration. However, for other Li
concentrations, including pure SnO2, the samples exhibit diamagnetism. To
investigate the possible origin of the induced magnetism, we have studied the
variation of the magnetization as a function of the average nano-particle
radius. Possible scenarios for the appearance of magnetism in these compounds
are discussed.",1302.4869v1
2013-12-04,Titan Magnetic Tail: Does its Configuration correspond to the Induced Magnetosphere?,"Magnetic field structure observed in numerous Cassini flybys in the region of
Titan interaction with the corotating flow of Kronian magnetosheric plasma
contradicts the classical picture of the ideal induced magnetosphere produced
by the magnetic field line draping about the obstacle. Clear draping is
observed only upstream the Titan, but not in the Titan magnetic wake. We
consider the magnetic field tension downstream the Titan magnetic tail and show
that the magnetic field direction is not consistent with the induced
magnetosphere produced by magnetic field lines draping. We arrive at the
conclusion that the mechanisms alternative to the induced magnetosphere
formation should be considered for the Titan magnetic surrounding.",1401.3729v1
2015-06-05,On the magnetization process of ferromagnetic materials,"The present article concludes that a ferromagnetic sample could be considered
like a paramagnetic system where the role of magnetic moments plays magnetic
domains. Based on this conclusion and taking into account presence of an
anisotropic field the formula which describes magnetization dependence on the
external magnetic field is derived. Expressions for a remanent magnetization
and a coercive force are presented. The new parameter to characterize a
magnetic stiffness of a material is introduced. A physical expression for a
dynamic magnetic susceptibility as a function of material's characteristics,
external magnetic field, and a temperature is given.",1506.01805v3
2015-05-19,Electromagnetic acceleration of permanent magnets,"We consider the acceleration of the permanent magnets, consisting of
neodymium iron boron by means of the running magnetic field gradient. It is
shown that the specific magnetic moment per nucleon in neodymium iron boron is
determined by the remained magnetization of the substance. The maximum
accessable gradient of the magnetic field accelerating the permanent magnets is
determined by the coercive force thirty kilogauss. For the neodymium iron boron
magnets this gradient is equal to twenty kilogauss divided by one centimeter.
The finite velocity of the magnets six kilometers per second, the length of
acceleration is six hundred thirty-seven meters.",1508.04078v1
2016-04-03,Soliton collisions in soft magnetic nanotube with uniaxial anisotropy,"The structure of stable magnetic solitons of various orders in soft magnetic
nanotube with uniaxial magnetic anisotropy has been studied using numerical
simulation. Solitons of even order are immobile in axially applied magnetic
field. Odd solitons show decreased mobility with respect to that of head-to
head domain wall. Solitons of various orders can participate in nanotube
magnetization reversal process. Various coalescence and decomposition processes
in soliton assembly are considered. It is shown that the general magnetization
state of magnetic nanotube consists of chains of magnetic solitons of various
orders.",1604.00614v1
2017-01-15,Magnetic Catalysis in Antiferromagnetic Films,"We study the low-temperature behavior of antiferromagnets in two spatial
dimensions that are subjected to a magnetic field oriented perpendicular to the
staggered magnetization order parameter. The evaluation of the partition
function is carried to two-loop order within the systematic effective
Lagrangian technique. Low-temperature series that are valid in weak magnetic
and staggered fields are derived for the pressure, staggered magnetization, and
magnetization. Remarkably, at $T$=0, the staggered magnetization is enhanced by
the magnetic field, implying that the phenomenon of magnetic catalysis also
emerges in antiferromagnetic films.",1701.04085v1
2023-05-26,"Practical Concepts for Design, Construction and Application of Halbach Magnets in Magnetic Resonance","This review is a compilation of relevant concepts in designing Halbach
multipoles for magnetic resonance applications. The main focus is on providing
practical guidelines to plan, design and build such magnets. Therefore,
analytical equations are presented for estimating the magnetic field from ideal
to realistic systems. Various strategies of homogenizing magnetic fields are
discussed together with concepts of opening such magnets without force, or
combining them for variable fields. Temperature compensation and other
practical aspects are also reviewed. For magnetic resonance two polarities (di-
and quadrupole) are of main interest, but higher polarities are also included.",2305.17227v2
2023-08-24,Non-reciprocal coherent all-optical switching between magnetic multi-states,"We present experimental and computational findings of the laser-induced
non-reciprocal motion of magnetization during ultrafast photo-magnetic
switching in garnets. We found distinct coherent magnetization precession
trajectories and switching times between four magnetization states, depending
on both directions of the light linear polarization and initial magnetic state.
As a fingerprint of the topological symmetry, the choice of the switching
trajectory is governed by an interplay of the photo-magnetic torque and
magnetic anisotropy. Our results open a plethora of possibilities for designing
energy-efficient magnetization switching routes at arbitrary energy landscapes.",2308.12771v1
2023-08-28,Revisiting the Wu-Yang approach to magnetic charge,"The Wu-Yang fiber bundle approach to magnetic charge has an overlooked
feature -- a disk-like sheet current density and associated magnetic field at
the equator where the Northern hemisphere and Southern hemisphere Dirac string
vector potentials connect. This disk magnetic field plays a role similar to the
Dirac string in the Dirac approach to magnetic charge. Placing an electric
charge near the disk magnetic field gives rise to a non-zero field momentum.
This implies that the Wu-Yang construction is not a true magnetic charge -- it
is a Coulomb magnetic field plus a disk magnetic field and planar current
density.",2308.14706v1
2024-01-19,Modelling and dynamics of pendulum systems subjected to a nonstationary magnetic field,"The prepared doctoral dissertation focuses on studying dynamics of systems
composed of magnetic pendulums subjected to a non-stationary magnetic field. A
magnetic pendulum is a physical pendulum with a magnet attached to its end and
is placed in an external magnetic field. The non-stationary external magnetic
field is generated by an electric coil placed under the pendulum and powered by
a time-varying current signal. The presented research mainly concerns the
oscillations in one potential well of a single magnetic pendulum, as well as
the control of the energy flow between two torsionally coupled magnetic
pendulums.",2401.10594v1
2024-04-09,"One-Dimensional Model for Coupled Flexural, Torsional and Extensional Motions of Elastic Beams with Embedded Point Magnets under Magnetic Fields","This paper establishes a one-dimensional theoretical model for an elastic
beam with embedded point magnets in extensional, bending and torsional motions.
The beam has a circular cross-section. The point magnets may be in the interior
or at the ends of the beam. They are assumed to be small and rigid, and may be
ferromagnetic with spontaneous magnetic moments that can change their
directions with respect to the magnets. The model shows that the extensional,
flexural and torsional motions of the beam may be coupled by the point magnets
when an external magnetic field is applied. A few examples are given.
Piezoelectric beams with point magnets are also discussed.",2404.06232v1
1999-09-27,Topological Constraints on the Relaxation of Complex Magnetic Fields,"Newly emerging magnetic flux can show a complicated linked or interwoven
topology of the magnetic field. The complexity of this linkage or knottedness
of magnetic flux is related to the free energy stored in the magnetic field.
Magnetic reconnection provides a process to release this energy on the time
scale of the dynamics. At the same time it approximately conserves the total
magnetic helicity. Therefore the conservation of total magnetic helicity is a
crucial constraint for the relaxation of complex magnetic fields. However, the
total magnetic helicity is only the first, most elementary, quantity of an
infinite series of topological invariants of the magnetic field. All these
invariants are strictly conserved in ideal magnetohydrodynamics. As an example
a preliminary set of these invariants is derived. The relevance of these higher
order invariants for the final state of relaxation under magnetic reconnection
and their implications for the release of magnetic energy are discussed.",9909443v1
2007-10-22,Observation of magnetization reversal and negative magnetization in a double perovskite compound Sr2YbRuO6,"Detailed magnetic properties of the compound Sr2YbRuO6 are presented here.
The compound belongs to the family of double perovskites forming a monoclinic
structure. Magnetization meas-urements reveal clear evidence for two components
of magnetic ordering aligned opposite to each other, leading to a magnetization
reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at
low temperatures and low magnetic fields. Heat capacity measurements
corroborate the presence of two components in the magnetic ordering and a
noticeable third anomaly at low temperatures (~15 K) which cannot be attributed
the Schottky effect. The calcu-lated magnetic entropy is substantially lower
than that expected for the ground states of the or-dered moments of Ru5+ and
Yb3+, indicating the presence of large crystal field effects and/ or
in-complete magnetic ordering and/or magnetic frustrations well above the
magnetic ordering. An attempt is made to explain the magnetization reversal
within the frameworks of available models.",0710.4043v3
2008-05-21,Energetic Analysis of Magnetic Transitions in Ultra-small Nanoscopic Magnetic Rings,"In this article, we report on experimental and theoretical investigations of
magnetic transitions in cobalt rings of size (diameter, width and thickness)
comparable to the exchange length of cobalt. Magnetization measurements were
performed for two sets of magnetic ring arrays: ultra-small magnetic rings
(outer diameter 13 nm, inner diameter 5nm and thickness 5 nm) and small
thin-walled magnetic rings (outer diameter 150 nm, width 5 nm and thickness 5
nm). This is the first report on the fabrication and magnetic properties of
such small rings. Our calculations suggest that if the magnetic ring's sizes
are comparable to, or smaller than, the exchange length of the magnetic
material, then only two magnetic states are important - the pure single domain
state and the flux closure vortex state. The onion-shape magnetic state does
not arise. Theoretical calculations are based on an energetic analysis of pure
and slightly distorted single domain and flux closure vortex magnetic states.
Based on the analytical calculations, a phase diagram is also derived for
ultra-small ring structures exhibiting the region for vortex magnetic state
formations as a function of material parameter.",0805.3191v2
2010-01-29,Orbital magnetization of the electron gas on a two-dimensional kagome lattice under a perpendicular magnetic field,"The orbital magnetization of the electron gas on a two-dimensional kagome
lattice under a perpendicular magnetic field is theoretically investigated. The
interplay between the lattice geometry and magnetic field induce nontrivial
$k$-space Chern invariant in the magnetic Brillouin zone, which turns to result
in profound effects on the magnetization properties. We show that the
Berry-phase term in the magnetization gives a paramagnetic contribution, while
the conventional term brought about by the magnetic response of the magnetic
Bloch bands produces a diamagnetic contribution. As a result, the superposition
of these two components gives rise to a delicate oscillatory structure in the
magnetization curve when varying the electron filling factor. The relationship
between this oscillatory behavior and the Hofstadter energy spectrum is
revealed by selectively discussing the magnetization and its two components at
the commensurate fluxes of $f$=1/4, 1/3, and 1/6, respectively. In particular,
we reveal as a typical example the fractal structure in the magnetic
oscillations by tuning the commensurate flux around $f$=1/4. The
finite-temperature effect on the magnetization is also discussed.",1001.5330v1
2011-03-16,Magnetization Plateaus in the Spin-1/2 Kagome Antiferromagnets: Volborthite and Vesignieite,"The magnetization of two spin-1/2 kagome antiferromagnets, volborthite and
vesignieite, has been measured in pulsed magnetic fields up to 68 T. A
magnetization plateau is observed for each compound near the highest magnetic
field. Magnetizations at saturation are approximately equal to 0.40Ms for both
compounds, where Ms is the fully saturated magnetization, irrespective of a
difference in the distortion of the kagome lattice between the two compounds.
It should be noted that these values of magnetizations are significantly larger
than Ms/3 predicted theoretically for the one-third magnetization plateau in
the spin-1/2 kagome antiferromagnet. The excess magnetization over Ms/3 is
nearly equal to the sum of the magnetizations gained at the second and third
magnetization steps in volborthite, suggesting that there is a common origin
for the excess magnetization and the magnetization steps.",1103.3116v1
2014-10-08,An optimized magnet for magnetic refrigeration,"A magnet designed for use in a magnetic refrigeration device is presented.
The magnet is designed by applying two general schemes for improving a magnet
design to a concentric Halbach cylinder magnet design and dimensioning and
segmenting this design in an optimum way followed by the construction of the
actual magnet. The final design generates a peak value of 1.24 T, an average
flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an
average low flux density of 0.08 T also in a 2 L volume. The working point of
all the permanent magnet blocks in the design is very close to the maximum
energy density. The final design is characterized in terms of a performance
parameter, and it is shown that it is one of the best performing magnet designs
published for magnetic refrigeration.",1410.1987v1
2018-02-08,Nonspecific biological effects of weak magnetic fields depend on molecular rotations,"The radical pair mechanism is a leading hypothesis in animal magnetic
navigation. This mechanism associates the magnetic sense with the visual
system, the radical pairs in cryptochromes of the eye retina being specialized
magnetic receptors that modulate rhodopsin-mediated photoreception. There are
also nonspecific magnetic effects in biology, which occur mostly by chance and
originate from the interaction of weak magnetic fields with the magnetic
moments dispersed all over the organism at the microscopic level. The radical
pair mechanism cannot explain this type of response for many reasons. We have
previously shown that the above interaction has a finite probability of
resulting in an observable. Here, we develop our physical model of nonspecific
magnetic effects for the case of magnetic moments located in rotating
molecules. We generalize the results of recent experiments on gene expression
in plants in a constant magnetic field, and show that the precession of the
magnetic moments that reside on rotating molecules can be slowed relative to
the immediate biophysical structures. In quantum mechanical language, the
crossing of the quantum levels of magnetic moments conjointly with molecular
rotations explain nonspecific magnetic effects and leads to magnetic
field-dependences that are in good agreement with the experiment.",1802.02903v1
2019-05-22,"Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5","YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits
magnetic ordering and dielectric anomaly above 200 K. Partial substitution of
Fe with other magnetic and non-magnetic ion affects the magnetic and the
structural properties of the system. We report detailed investigation of
structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni
and Ga). We observed that the partial replacement of Ni and Co in place of Fe,
results in magnetic dilution and broadening of the magnetic transition and
shifting towards lower temperature. The replacement of Fe with non-magnetic Ga
also results in shifting of the magnetic transition to the lower temperature
side. The observed dielectric relaxation behavior in these compounds is due to
the charge carrier hoping. This study highlights the impacts of magnetic and
non-magnetic doping at the magnetic site on magnetic and dielectric properties
in layered perovskite compound YBaCuFeO5.",1905.08982v2
2020-07-17,Unraveling nanoscale magnetic ordering in Fe3O4 nanoparticle assemblies via x-rays,": Understanding the correlations between magnetic nanoparticles is important
for nanotechnologies, such as high-density magnetic recording and biomedical
applications, where functionalized magnetic particles are used as contrast
agents and for drug delivery. The ability to control the magnetic state of
individual particles depends on the good knowledge of magnetic correlations
between particles when assembled. Inaccessible via standard magnetometry
techniques, nanoscale magnetic ordering in self-assemblies of Fe3O4
nanoparticles is here unveiled via x-ray resonant magnetic scattering (XRMS).
Measured throughout the magnetization process, the XRMS signal reveals
size-dependent inter-particle magnetic correlations. Smaller (5 nm) particles
show little magnetic correlation, even when tightly close-packed, yielding to
mostly magnetic disorder in the absence of external field, which is
characteristic of superparamagnetic behavior. In contrast, larger (11 nm)
particles tend to be strongly correlated, yielding a mix of magnetic orders
including ferromagnetic and anti-ferromagnetic orders. These strong magnetic
correlations are present even when the particles are sparsely distributed.",2007.09226v1
2016-12-28,"Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study","We report on the thermodynamic, magnetic properties and the magnetic
structure of ludwigite-type Cu2MnBO5. The specific heat, the low-field
magnetization and the paramagnetic susceptibility were studied on a single
crystal and combined with powder neutron diffraction data. The temperature
dependence of the specific heat and the neutron diffraction pattern reveal a
single magnetic phase transition at T=92 K, which corresponds to the magnetic
ordering into a ferromagnetic phase. The cation distribution and the values and
directions of magnetic moments of ions in different crystallographic sites are
established. The magnetic moments of Cu2+ and Mn3+ ions occupying different
magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their
directions do not coincide with the directions of the principal
crystallographic axes.The small value of the magnetic moment of copper ions
occupying site 2a is indicative of partial disordering of the magnetic moments
on this site. The magnetization measurements show a strong temperature
hysteresis of magnetization, which evidences for field-dependent transitions
below the phase transition temperature.",1612.08805v1
2019-11-08,Magnetic glassy state at low spin state of Co3+ in EuBaCo2O5+δ (δ = 0.47) cobaltite,"The magnetic glassy state is a fascinating phenomenon, which results from the
kinetic arrest of the first order magnetic phase transition. Interesting
properties, such as metastable magnetization and nonequilibrium magnetic
phases, are naturally developed in the magnetic glassy state. Here, we report
magnetic glass property in the low spin state of Co3+ in EuBaCo2O5+{\delta}
({\delta} = 0.47) cobaltite at low temperature (T < 60 K). The measurements of
magnetization under the cooling and heating in unequal fields, magnetization
relaxation and thermal cycling of magnetization show the kinetic arrest of low
magnetization state below 60 K. The kinetically arrested low temperature
magnetic phase is further supported through the study of isothermal magnetic
entropy, which shows the significant entropy change. The present results will
open a new window to search the microscopic relation between the spin state
transitions and the kinetic arrest induced magnetic glassy phenomena in complex
materials.",1911.03258v1
2021-12-02,Magnetic correction to the Anomalous Magnetic Moment of Electron,"We investigate the leading order correction of anomalous magnetic moment
(AMM) to the electron in weak magnetic field and find that the magnetic
correction is negative and magnetic field dependent, indicating a magnetic
catalysis effect for the electron gas. In the laboratory to measure the $g-2$,
the magnitude of the magnetic field $B$ is several $\mathrm{T}$,
correspondingly the magnetic correction to the AMM of electron/muon is around
$10^{-34}$/$10^{-42}$, therefore the magnetic correction can be safely
neglected in current measurement. However, when the magnitude of the magnetic
field strength is comparable with the electron mass, the magnetic correction of
electron's AMM will become considerable. This general magnetic correction to
charged fermion's AMM can be extended to study QCD matter under strong magnetic
field.",2112.01051v1
2022-08-07,Mixels: Fabricating Interfaces using Programmable Magnetic Pixels,"In this paper, we present Mixels, programmable magnetic pixels that can be
rapidly fabricated using an electromagnetic printhead mounted on an
off-the-shelve 3-axis CNC machine. The ability to program magnetic material
pixel-wise with varying magnetic force enables Mixels to create new tangible,
tactile, and haptic interfaces. To facilitate the creation of interactive
objects with Mixels, we provide a user interface that lets users specify the
high-level magnetic behavior and that then computes the underlying magnetic
pixel assignments and fabrication instructions to program the magnetic surface.
Our custom hardware add-on based on an electromagnetic printhead and hall
effect sensor clips onto a standard 3-axis CNC machine and can both write and
read magnetic pixel values from magnetic material. Our evaluation shows that
our system can reliably program and read magnetic pixels of various strengths,
that we can predict the behavior of two interacting magnetic surfaces before
programming them, that our electromagnet is strong enough to create pixels that
utilize the maximum magnetic strength of the material being programmed, and
that this material remains magnetized when removed from the magnetic plotter.",2208.03804v1
2006-02-02,Evolution of Rotating Molecular Cloud Core with Oblique Magnetic Field,"We studied the collapse of rotating molecular cloud cores with inclined
magnetic fields, based on three-dimensional numerical simulations.The numerical
simulations start from a rotating Bonnor-Ebert isothermal cloud in a uniform
magnetic field. The magnetic field is initially taken to be inclined from the
rotation axis. As the cloud collapses, the magnetic field and rotation axis
change their directions. When the rotation is slow and the magnetic field is
relatively strong, the direction of the rotation axis changes to align with the
magnetic field, as shown earlier by Matsumoto & Tomisaka. When the magnetic
field is weak and the rotation is relatively fast, the magnetic field inclines
to become perpendicular to the rotation axis. In other words, the evolution of
the magnetic field and rotation axis depends on the relative strength of the
rotation and magnetic field. Magnetic braking acts to align the rotation axis
and magnetic field, while the rotation causes the magnetic field to incline
through dynamo action. The latter effect dominates the former when the ratio of
the angular velocity to the magnetic field is larger than a critical value
\Omega_0/ B_0 > 0.39 G^1/2 c_s^-1, where B_0, \Omega_0, G, and c_s^-1 denote
the initial magnetic field, initial angular velocity, gravitational constant,
and sound speed, respectively. When the rotation is relatively strong, the
collapsing cloud forms a disk perpendicular to the rotation axis and the
magnetic field becomes nearly parallel to the disk surface in the high density
region. A spiral structure appears due to the rotation and the wound-up
magnetic field in the disk.",0602034v1
2017-02-06,The formation of magnetic depletions and flux annihilation due to reconnection in the heliosheath,"The misalignment of the solar rotation axis and the magnetic axis of the Sun
produces a periodic reversal of the Parker spiral magnetic field and the
sectored solar wind. The compression of the sectors is expected to lead to
reconnection in the heliosheath (HS). We present particle-in-cell simulations
of the sectored HS that reflect the plasma environment along the Voyager 1 and
2 trajectories, specifically including unequal positive and negative azimuthal
magnetic flux as seen in the Voyager data \citep{Burlaga03}. Reconnection
proceeds on individual current sheets until islands on adjacent current layers
merge. At late time bands of the dominant flux survive, separated by bands of
deep magnetic field depletion. The ambient plasma pressure supports the strong
magnetic pressure variation so that pressure is anti-correlated with magnetic
field strength. There is little variation in the magnetic field direction
across the boundaries of the magnetic depressions. At irregular intervals
within the magnetic depressions are long-lived pairs of magnetic islands where
the magnetic field direction reverses so that spacecraft data would reveal
sharp magnetic field depressions with only occasional crossings with jumps in
magnetic field direction. This is typical of the magnetic field data from the
Voyager spacecraft \citep{Burlaga11,Burlaga16}. Voyager 2 data reveals that
fluctuations in the density and magnetic field strength are anti-correlated in
the sector zone as expected from reconnection but not in unipolar regions. The
consequence of the annihilation of subdominant flux is a sharp reduction in the
""number of sectors"" and a loss in magnetic flux as documented from the Voyager
1 magnetic field and flow data \citep{Richardson13}.",1702.01697v1
2020-07-23,Signal Enhancement for Magnetic Navigation Challenge Problem,"Harnessing the magnetic field of the Earth for navigation has shown promise
as a viable alternative to other navigation systems. A magnetic navigation
system collects its own magnetic field data using a magnetometer and uses
magnetic anomaly maps to determine the current location. The greatest challenge
with magnetic navigation arises when the magnetic field measurements from the
magnetometer encompass the magnetic field from not just the Earth, but also
from the vehicle on which it is mounted. It is difficult to separate the Earth
magnetic anomaly field, which is crucial for navigation, from the total
magnetic field reading from the sensor. The purpose of this challenge problem
is to decouple the Earth and aircraft magnetic signals in order to derive a
clean signal from which to perform magnetic navigation. Baseline testing on the
dataset has shown that the Earth magnetic field can be extracted from the total
magnetic field using machine learning (ML). The challenge is to remove the
aircraft magnetic field from the total magnetic field using a trained model.
This challenge offers an opportunity to construct an effective model for
removing the aircraft magnetic field from the dataset by using a scientific
machine learning (SciML) approach comprised of an ML algorithm integrated with
the physics of magnetic navigation.",2007.12158v2
2023-04-13,High-performance descriptor for magnetic materials: Accurate discrimination of magnetic structure,"The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP), providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest-order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher-order
partial spectrum is required in general to differentiate detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from the first-principles calculations performed without spin-orbit coupling.
We apply the present method to the symmetry-classified magnetic structures for
the crystals of Mn$_3$Ir and Mn$_3$Sn, which are known to exhibit anomalous
transport under the antiferromagnetic order, and examine the discrimination
performance of the descriptor for different magnetic structures on the same
crystal.",2304.06282v2
2023-08-25,Coexistence of non-trivial van der Waals magnetic orders enable field-free spin-orbit torque switching at room temperature,"The discovery of van der Waals (vdW) materials exhibiting non-trivial and
tunable magnetic interactions at room temperature can give rise to exotic
magnetic states, which are not readily attainable with conventional materials.
Such vdW magnets can provide a unique platform for studying new magnetic
phenomena and realising magnetization dynamics for energy-efficient and
non-volatile spintronic memory and logic technologies. Recent developments in
vdW magnets have revealed their potential to enable spin-orbit torque (SOT)
induced magnetization dynamics. However, the deterministic and field-free SOT
switching of vdW magnets at room temperature has been lacking, prohibiting
their potential applications. Here, we demonstrate magnetic field-free and
deterministic SOT switching of a vdW magnet (Co0.5Fe0.5)5GeTe2 (CFGT) at room
temperature, capitalizing on its non-trivial intrinsic magnetic ordering. We
discover a coexistence of ferromagnetic and antiferromagnetic orders in CFGT at
room temperature, inducing an intrinsic exchange bias and canted perpendicular
magnetism. The resulting canted perpendicular magnetization of CFGT introduces
symmetry breaking, facilitating successful magnetic field-free magnetization
switching in the CFGT/Pt heterostructure devices. Furthermore, the SOT-induced
magnetization dynamics and their efficiency are evaluated using 2nd harmonic
Hall measurements. This advancement opens new avenues for investigating tunable
magnetic phenomena in vdW material heterostructures and realizing field-free
SOT-based spintronic technologies.",2308.13408v1
2006-09-08,Potential of Ozone Formation by the Smog Mechanism to shield the surface of the Early Earth from UV radiation?,"We propose that the photochemical smog mechanism produced substantial ozone
(O3) in the troposphere during the Proterozoic, which contributed to
ultraviolet (UV) radiation shielding hence favoured the establishment of life.
The smog mechanism is well-established and is associated with pollution hazes
which sometimes cover modern cities. The mechanism proceeds via the oxidation
of volatile organic compounds (VOCs) such as methane (CH4) in the presence of
UV radiation and nitrogen oxides (NOx). It would have been particularly
favoured during the Proterozoic given the high levels of CH4 (up to 1000 ppm)
recently suggested. Proterozoic UV levels on the surface of the Earth were
generally higher compared with today, which would also have favoured the
mechanism. On the other hand, Proterozoic O2 required in the final step of the
smog mechanism to form O3 was less abundant compared with present times.
Further, results are sensitive to Proterozoic NOx concentrations, which are
challenging to predict, since they depend on uncertain quantities such as NOx
source emissions and OH concentrations. We review NOx sources during the
Proterozoic and apply a photochemical box model having methane oxidation with
NOx, HOx and Ox chemistry to estimate the O3 production from the smog
mechanism. Runs suggest the smog mechanism during the Proterozoic can produce
about double present day ozone columns for NOx levels of 1.53 10-9 by volume
mixing ratio, which was attainable according to our NOx source analysis, with 1
per-cent present atmospheric levels (PALs) of O2. Clearly, forming ozone in the
troposphere is a trade-off for survivability. On the one hand harmful UV is
blocked, but on the other hand ozone is a respiratory irratant, which becomes
fatal at concentrations exceeding about 1 ppmv.",0609219v1
2007-01-30,A Search for Propylene Oxide and Glycine in Sagittarius B2 (LMH) and Orion,"We have used the Mopra Telescope to search for glycine and the simple chiral
molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We
have not detected either species, but have been able to put sensitive upper
limits on the abundances of both molecules. The 3-sigma upper limits derived
for glycine conformer I are 3.7 x 10^{14} cm^{-2} in both Orion-KL and Sgr B2
(LMH), comparable to the reported detections of conformer I by Kuan et al.
However, as our values are 3-sigma upper limits rather than detections we
conclude that this weighs against confirming the detection of Kuan et al. We
find upper limits for the glycine II column density of 7.7 x 10^{12} cm^{-2} in
both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al.
The results presented here show that glycine conformer II is not present in the
extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA
results (Jones et al.) have ruled out the detection of glycine (both conformers
I and II) in the compact hot core of the LMH at the levels reported, so we
conclude that it is unlikely that Kuan et al. have detected glycine in either
Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x
10^{14} cm^{-2} in Orion-KL and 6.7 x 10^{14} cm^{-2} in Sgr B2 (LMH). We have
detected fourteen features in Sgr B2 and four features in Orion-KL which have
not previously been reported in the ISM, but have not be able to plausibly
assign these transitions to any carrier.",0701866v1
2002-01-28,"Fracton pairing mechanism for ""strange"" superconductors: Self-assembling organic polymers and copper-oxide compounds","Self-assembling organic polymers and copper-oxide compounds are two classes
of ""strange"" superconductors, whose challenging behavior does not comply with
the traditional picture of Bardeen, Cooper, and Schrieffer (BCS)
superconductivity in regular crystals. In this paper, we propose a theoretical
model that accounts for the strange superconducting properties of either class
of the materials. These properties are considered as interconnected
manifestations of the same phenomenon: We argue that superconductivity occurs
in the both cases because the charge carriers (i.e., electrons or holes)
exchange {\it fracton excitations}, quantum oscillations of fractal lattices
that mimic the complex microscopic organization of the strange superconductors.
For the copper oxides, the superconducting transition temperature $T_c$ as
predicted by the fracton mechanism is of the order of $\sim 150$ K. We suggest
that the marginal ingredient of the high-temperature superconducting phase is
provided by fracton coupled holes that condensate in the conducting
copper-oxygen planes owing to the intrinsic field-effect-transistor
configuration of the cuprate compounds. For the gate-induced superconducting
phase in the electron-doped polymers, we simultaneously find a rather modest
transition temperature of $\sim (2-3)$ K owing to the limitations imposed by
the electron tunneling processes on a fractal geometry. We speculate that
hole-type superconductivity observes larger onset temperatures when compared to
its electron-type counterpart. This promises an intriguing possibility of the
high-temperature superconducting states in hole-doped complex materials. A
specific prediction of the present study is universality of ac conduction for
$T\gtrsim T_c$.",0201504v3
2004-07-13,Multi-Dot Floating-Gates for Nonvolatile Semiconductor Memories - Their Ion Beam Synthesis and Morphology,"Scalability and performance of current flash memories can be improved
substantially by replacing the floating poly-Si gate by a layer of Si dots.
This multi-dot layer can be fabricated CMOS-compatibly in very thin gate oxide
by ion beam synthesis (IBS). Here, we present both experimental and theoretical
studies on IBS of multi-dot layers consisting of Si nanocrystals (NCs). The NCs
are produced by ultra low energy Si ion implantation, which causes a high Si
supersaturation in the shallow implantation region. During post-implantation
annealing, this supersaturation leads to phase separation of the excess Si from
the SiO2. Till now, the study of this phase separation process suffered from
the weak Z contrast between Si and SiO2 in Transmission Electron Microscopy
(TEM). Here, this imaging problem is resolved by mapping Si plasmon losses with
a Scanning Transmission Electron Microscopy equipped with a parallel Electron
Energy Loss Spectroscopy system (PEELS-STEM). Additionally, kinetic lattice
Monte Carlo simulations of Si phase separation have been performed and compared
with the experimental Si plasmon maps. It has been predicted theoretically that
the morphology of the multi-dot Si floating-gate changes with increasing ion
fluence from isolated, spherical NCs to percolated spinodal Si pattern. These
patterns agree remarkably with PEELS-STEM images. However, the predicted
fluence for spinodal patterns is lower than the experimental one. Because
oxidants of the ambient atmosphere penetrate into the as-implanted SiO2, a
substantial fraction of the implanted Si might be lost due to oxidation.",0407329v1
2004-08-26,Ultrathin Organic Transistors on Oxide Surfaces,"In recent years, thin-film organic field-effect transistors (OFETs) have
begun to be considered as a possible alternative to the hydrogenated amorphous
silicon thin-film transistors (a-Si:H TFT's) used in active matrix flat panel
displays and other large-area electronics applications. Low-temperature
processability, low-cost fabrication and compatibility with arbitrary
substrates are some of the promising advantages of OFETs, among others. Of the
many organic materials available, pentacene, in particular, is one of the
leading candidates for use in current thin-film OFET architectures - this
because of its excellent electrical characteristics and its resistance to
atmospheric oxygen. In the recent literature, pentacene's transport properties,
as well as transistor performance, have already been analyzed from the point of
view of substrate treatments, pentacene evaporation rate and substrate
temperature, electrode chemical nature and channel geometry. The results show
that the morphology, crystal structure and molecular ordering of the first
organic monolayer(s) at the pentacene/dielectric interface are essential
determinants of carrier transport phenomena. To further investigate these
interface effects, we have built a model organic field-effect transistor which
consists essentially of a single layer of pentacene on an oxide substrate.
Four-probe and two-probe transport measurements as a function of temperature
and fields will be presented in relation with structural near-field
observations. The experimental results suggest a simple two-dimensional model
where the equilibrium between free and trapped carriers at the oxide interface
determines the OFET characteristics and performance.",0408562v2
2006-11-24,High expression of antioxidant proteins in dendritic cells: possible implications in atherosclerosis,"Dendritic cells (DCs) display the unique ability to activate naive T cells
and to initiate primary T cell responses revealed in DC-T cell alloreactions.
DCs frequently operate under stress conditions. Oxidative stress enhances the
production of inflammatory cytokines by DCs. We performed a proteomic analysis
to see which major changes occur, at the protein expression level, during DC
differentiation and maturation. Comparative two-dimensional gel analysis of the
monocyte, immature DC, and mature DC stages was performed. Manganese superoxide
dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC
stage. This important amount of Mn-SOD is a primary antioxidant defense system
against superoxide radicals, but its product, H(2)O(2), is also deleterious for
cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such
peroxide. Prx1 expression level continuously increased during DC
differentiation and maturation, whereas Prx6 continuously decreased, and Prx2
peaked at the immature DC stage. As a consequence, DCs were more resistant than
monocytes to apoptosis induced by high amounts of oxidized low density
lipoproteins containing toxic organic peroxides and hydrogen peroxide.
Furthermore DC-stimulated T cells produced high levels of receptor activator of
nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes
and DCs. This study provides insights into the original ability of DCs to
express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to
detoxify oxidized low density lipoproteins, and to induce high levels of
receptor activator of nuclear factor kappaB ligand by the T cells they activate
and further emphasizes the role that DCs might play in atherosclerosis, a
pathology recognized as a chronic inflammatory disorder.",0611082v1
2008-05-06,Hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides,"Using a linear combination of atomic orbitals approach, we report a
systematic comparison of various Density Functional Theory (DFT) and hybrid
exchange-correlation functionals for the prediction of the electronic and
structural properties of prototypical ferroelectric oxides. It is found that
none of the available functionals is able to provide, at the same time,
accurate electronic and structural properties of the cubic and tetragonal
phases of BaTiO$_3$ and PbTiO$_3$. Some, although not all, usual DFT
functionals predict the structure with acceptable accuracy, but always
underestimate the electronic band gaps. Conversely, common hybrid functionals
yield an improved description of the band gaps, but overestimate the volume and
atomic distortions associated to ferroelectricity, giving rise to an
unacceptably large $c/a$ ratio for the tetragonal phases of both compounds.
This super-tetragonality is found to be induced mainly by the exchange energy
corresponding to the Generalized Gradient Approximation (GGA) and, to a lesser
extent, by the exact exchange term of the hybrid functional. We thus propose an
alternative functional that mixes exact exchange with the recently proposed GGA
of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] which, for solids, improves
over the treatment of exchange of the most usual GGA's. The new functional
renders an accurate description of both the structural and electronic
properties of typical ferroelectric oxides.",0805.0753v1
2010-03-11,"Tailoring electronic and optical properties of TiO2: nanostructuring, doping and molecular-oxide interactions","Titanium dioxide is one of the most widely investigated oxides. This is due
to its broad range of applications, from catalysis to photocatalysis to
photovoltaics. Despite this large interest, many of its bulk properties have
been sparsely investigated using either experimental techniques or ab initio
theory. Further, some of TiO2's most important properties, such as its
electronic band gap, the localized character of excitons, and the localized
nature of states induced by oxygen vacancies, are still under debate. We
present a unified description of the properties of rutile and anatase phases,
obtained from ab initio state of the art methods, ranging from density
functional theory (DFT) to many body perturbation theory (MBPT) derived
techniques. In so doing, we show how advanced computational techniques can be
used to quantitatively describe the structural, electronic, and optical
properties of TiO2 nanostructures, an area of fundamental importance in applied
research. Indeed, we address one of the main challenges to TiO2-photocatalysis,
namely band gap narrowing, by showing how to combine nanostructural changes
with doping. With this aim we compare TiO2's electronic properties for 0D
clusters, 1D nanorods, 2D layers, and 3D bulks using different approximations
within DFT and MBPT calculations. While quantum confinement effects lead to a
widening of the energy gap, it has been shown that substitutional doping with
boron or nitrogen gives rise to (meta-)stable structures and the introduction
of dopant and mid-gap states which effectively reduce the band gap. Finally, we
report how ab initio methods can be applied to understand the important role of
TiO2 as electron-acceptor in dye-sensitized solar cells. This task is made more
difficult by the hybrid organic-oxide structure of the involved systems.",1003.2341v1
2010-03-23,A mathematical model for breath gas analysis of volatile organic compounds with special emphasis on acetone,"Recommended standardized procedures for determining exhaled lower respiratory
nitric oxide and nasal nitric oxide have been developed by task forces of the
European Respiratory Society and the American Thoracic Society. These
recommendations have paved the way for the measurement of nitric oxide to
become a diagnostic tool for specific clinical applications. It would be
desirable to develop similar guidelines for the sampling of other trace gases
in exhaled breath, especially volatile organic compounds (VOCs) which reflect
ongoing metabolism. The concentrations of water-soluble, blood-borne substances
in exhaled breath are influenced by: (i) breathing patterns affecting gas
exchange in the conducting airways; (ii) the concentrations in the
tracheo-bronchial lining fluid; (iii) the alveolar and systemic concentrations
of the compound. The classical Farhi equation takes only the alveolar
concentrations into account. Real-time measurements of acetone in end-tidal
breath under an ergometer challenge show characteristics which cannot be
explained within the Farhi setting. Here we develop a compartment model that
reliably captures these profiles and is capable of relating breath to the
systemic concentrations of acetone. By comparison with experimental data it is
inferred that the major part of variability in breath acetone concentrations
(e.g., in response to moderate exercise or altered breathing patterns) can be
attributed to airway gas exchange, with minimal changes of the underlying blood
and tissue concentrations. Moreover, it is deduced that measured end-tidal
breath concentrations of acetone determined during resting conditions and free
breathing will be rather poor indicators for endogenous levels. Particularly,
the current formulation includes the classical Farhi and the Scheid series
inhomogeneity model as special limiting cases.",1003.4475v3
2010-06-22,Automated NanoSIMS Measurements of Spinel Stardust from the Murray Meteorite,"We report new O isotopic data on 41 presolar oxide grains, 38 MgAl2O4
(spinel) and 3 Al2O3 from the CM2 meteorite Murray, identified with a recently
developed automated measurement system for the NanoSIMS. We have also obtained
Mg-Al isotopic results on 29 of the same grains (26 spinel and 3 Al2O3). The
majority of the grains have O isotopic compositions typical of most presolar
oxides, fall well into the four previously defined groups, and are most likely
condensates from either red giant branch or asymptotic giant branch stars. We
have also discovered several grains with more unusual O and Mg compositions
suggesting formation in extreme astrophysical environments, such as novae and
supernovae. One of these grains has massive enrichments in 17O, 25Mg, and 26Mg,
which are isotopic signatures indicative of condensation from nova ejecta. Two
grains of supernova origin were also discovered: one has a large 18O/16O ratio
typical of Group 4 presolar oxides; another grain is substantially enriched in
16O, and also contains radiogenic 44Ca from the decay of 44Ti, a likely
condensate from material originating in the O-rich inner zones of a Type II
supernova. In addition, several Group 2 presolar spinel grains also have large
25Mg and 26Mg isotopic anomalies that are difficult to explain by standard
nucleosynthesis in low-mass stars. Auger elemental spectral analyses were
performed on the grains and qualitatively suggest that presolar spinel may not
have higher-than- stoichiometric Al/Mg ratios, in contrast to SIMS results
obtained here and reported previously.",1006.4355v1
2011-01-25,Extreme 54Cr-rich nano-oxides in the CI chondrite Orgueil -Implication for a late supernova injection into the Solar System,"Systematic variations in 54Cr/52Cr ratios between meteorite classes (Qin et
al., 2010a; Trinquier et al., 2007) point to large scale spatial and/or
temporal isotopic heterogeneity in the solar protoplanetary disk. Two
explanations for these variations have been proposed, with important
implications for the formation of the Solar System: heterogeneous seeding of
the disk with dust from a supernova, or energetic-particle irradiation of dust
in the disk. The key to differentiating between them is identification of the
carrier(s) of the 54Cr anomalies. Here we report the results of our recent
NanoSIMS imaging search for the 54Cr-rich carrier in the acid-resistant residue
of the CI chondrite Orgueil. A total of 10 regions with extreme 54Cr-excesses
({\delta}54Cr values up to 1500 %) were found. Comparison between SEM, Auger
and NanoSIMS analyses showed that these 54Cr-rich regions are associated with
one or more sub-micron (typically less than 200 nm) Cr oxide grains, most
likely spinels. Because the size of the NanoSIMS primary O- ion beam is larger
than the typical grain size on the sample mount, the measured anomalies are
lower limits, and we estimate that the actual 54Cr enrichments in three grains
are at least 11 times Solar and in one of these may be as high as 50 times
Solar. Such compositions strongly favor a Type II supernova origin. The
variability in bulk 54Cr/52Cr between meteorite classes argues for a
heterogeneous distribution of the 54Cr carrier in the solar protoplanetary disk
following a late supernova injection event. Such a scenario is also supported
by the O-isotopic distribution and variable abundances in different planetary
materials of other presolar oxide and silicate grains from supernovae.",1101.4949v1
2012-08-27,Ferroelectricity in ultrathin film capacitors,"Going down to the limit of ultrathin films holds promise for a new generation
of devices such as ferroelectric tunnel junctions or resistive memories.
However, these length scales also make the devices sensitive to parasitic
effects related to miniaturization, and a better understanding of what happens
as size is reduced is of practical importance for the future development of
these devices.
  As the experimental advances in materials preparation and characterization
have come together with great progress in theoretical modeling of
ferroelectrics, both theorists and experimentalists can finally probe the same
length and time scales. This allows realtime feedback between theory and
experiment, with new discoveries now routinely made both in the laboratory and
on the computer. Throughout this chapter, we will highlight the recent advances
in density functional theory based modeling and the role it played in our
understanding of ultrathin ferroelectrics. We will begin with a brief
introduction to ferroelectricity and ferroelectric oxides, followed by an
overview of the major theoretical developments. We will then discuss some of
the subtleties of ferroelectricity in perovskite oxides, before turning our
attention to the main subject of the chapter -- ferroelectricity in ultrathin
films. We will discuss in detail the influence of the mechanical, electrical
and chemical boundary conditions on the stability of the polar state in a
parallel plate capacitor geometry, introducing the notion of depolarization
fields that tend to destabilize ferroelectricity. We will look at other ways in
which a thin ferroelectric can preserve its polar state, focusing on
ferroelectric domains and domain walls. Finally, we will briefly discuss
artificially layered ferroelectrics and the potential they hold as tailor-made
materials for electronic applications.",1208.5309v1
2014-07-24,Density functional plus dynamical mean field theory of the metal-insulator transition in early transition metal oxides,"The combination of density functional theory and single-site dynamical
mean-field theory, using both Hartree and full continuous-time quantum Monte
Carlo impurity solvers, is used to study the metal-insulator phase diagram of
perovskite transition-metal oxides of the form $AB$O$_3$ with a rare-earth ion
$A$=Sr, La, Y and transition metal $B$=Ti, V, Cr. The correlated subspace is
constructed from atomiclike $d$ orbitals defined using maximally localized
Wannier functions derived from the full $p$-$d$ manifold; for comparison,
results obtained using a projector method are also given. Paramagnetic DFT+DMFT
computations using full charge self-consistency along with the standard ""fully
localized limit"" (FLL) double counting are shown to incorrectly predict that
LaTiO$_3$, YTiO$_3$, LaVO$_3$ and SrMnO$_3$ are metals. A more general
examination of the dependence of physical properties on the mean $p$-$d$ energy
splitting, the occupancy of the correlated $d$ states, the double-counting
correction, and the lattice structure demonstrates the importance of
charge-transfer physics even in the early transition-metal oxides and
elucidates the factors underlying the failure of the standard approximations.
If the double counting is chosen to produce a $p$-$d$ splitting consistent with
experimental spectra, single-site dynamical mean-field theory provides a
reasonable account of the materials properties. The relation of the results to
those obtained from ""$d$-only"" models in which the correlation problem is based
on the frontier orbital $p$-$d$ antibonding bands is determined. It is found
that if an effective interaction $U$ is properly chosen the $d$-only model
provides a good account of the physics of the $d^1$ and $d^2$ materials.",1407.6505v2
2014-08-19,Soft chemical control of superconductivity in lithium iron selenide hydroxides Li1-xFex(OH)Fe1-ySe,"Hydrothermal synthesis is described of layered lithium iron selenide
hydroxides Li1-xFex(OH)Fe1-ySe (x ~ 0.2; 0.02 < y < 0.15) with a wide range of
iron site vacancy concentrations in the iron selenide layers. This iron vacancy
concentration is revealed as the only significant compositional variable and as
the key parameter controlling the crystal structure and the electronic
properties. Single crystal X-ray diffraction, neutron powder diffraction and
X-ray absorption spectroscopy measurements are used to demonstrate that
superconductivity at temperatures as high as 40 K is observed in the
hydrothermally synthesised samples when the iron vacancy concentration is low
(y < 0.05) and when the iron oxidation state is reduced slightly below +2,
while samples with a higher vacancy concentration and a correspondingly higher
iron oxidation state are not superconducting. The importance of combining a low
iron oxidation state with a low vacancy concentration in the iron selenide
layers is emphasised by the demonstration that reductive post-synthetic
lithiation of the samples turns on superconductivity with critical temperatures
exceeding 40 K by displacing iron atoms from the Li1-xFex(OH) reservoir layer
to fill vacancies in the selenide layer",1408.4350v2
2014-12-01,Training and Operation of an Integrated Neuromorphic Network Based on Metal-Oxide Memristors,"Despite all the progress of semiconductor integrated circuit technology, the
extreme complexity of the human cerebral cortex makes the hardware
implementation of neuromorphic networks with a comparable number of devices
exceptionally challenging. One of the most prospective candidates to provide
comparable complexity, while operating much faster and with manageable power
dissipation, are so-called CrossNets based on hybrid CMOS/memristor circuits.
In these circuits, the usual CMOS stack is augmented with one or several
crossbar layers, with adjustable two-terminal memristors at each crosspoint.
Recently, there was a significant progress in improvement of technology of
fabrication of such memristive crossbars and their integration with CMOS
circuits, including first demonstrations of their vertical integration.
Separately, there have been several demonstrations of discrete memristors as
artificial synapses for neuromorphic networks. Very recently such experiments
were extended to crossbar arrays of phase-change memristive devices. The
adjustment of such devices, however, requires an additional transistor at each
crosspoint, and hence the prospects of their scaling are less impressive than
those of metal-oxide memristors, whose nonlinear I-V curves enable
transistor-free operation. Here we report the first experimental implementation
of a transistor-free metal-oxide memristor crossbar with device variability
lowered sufficiently to demonstrate a successful operation of a simple
integrated neural network, a single layer-perceptron. The network could be
taught in situ using a coarse-grain variety of the delta-rule algorithm to
perform the perfect classification of 3x3-pixel black/white images into 3
classes. We believe that this demonstration is an important step towards the
implementation of much larger and more complex memristive neuromorphic
networks.",1412.0611v1
2015-03-30,Electrochemical synthesis of highly ordered nanowires with a rectangular cross-section using an in-plane nanochannel array,"Rapid and reproducible assembly of aligned nanostructures on a wafer-scale is
a crucial, yet one of the most challenging tasks in the incorporation of
nanowires into integrated circuits. We present the synthesis of a periodic
nanochannel template designed for electrochemical growth of perfectly aligned,
rectangular nanowires over large areas. The nanowires can be electrically
contacted and characterized in situ using a pre-patterned multi-point
measurement platform. During the measurement the wires remain within a thick
oxide matrix providing protection against breaking and oxidation. We use laser
interference lithography, reactive ion etching and atomic layer deposition to
create cm-long parallel nanochannels with characteristic dimensions as small as
40 nm. In a showcase study pulsed electrodeposition of iron is carried out
creating rectangular shaped iron nanowires within the nanochannels. By design
of the device, the grown wires are in contact with an integrated electrode
system on both ends directly after the deposition. No further processing steps
are required for electrical characterization, minimizing the risk of damage and
oxidation. The developed nanowire measurement device allows for multi-probe
resistance measurements and can easily be adopted for transistor applications.
The guided, in-plane growth of electrodeposited nanowire arrays which are
tunable in size and density paves the way for the incorporation of nanowires
into a large variety of multifunctional devices.",1503.08597v1
2015-06-22,Response of Atmospheric Biomarkers to NOx-induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M-Dwarf Stars,"Understanding whether M-dwarf stars may host habitable planets with
Earth-like atmospheres and biospheres is a major goal in exoplanet research. If
such planets exist, the question remains as to whether they could be identified
via spectral signatures of biomarkers. Such planets may be exposed to extreme
intensities of cosmic rays that could perturb their atmospheric photochemistry.
Here, we consider stellar activity of M-dwarfs ranging from quiet up to strong
flaring conditions and investigate one particular effect upon biomarkers,
namely, the ability of secondary electrons caused by stellar cosmic rays to
break up atmospheric molecular nitrogen (N2), which leads to production of
nitrogen oxides in the planetary atmosphere, hence affecting biomarkers such as
ozone. We apply a stationary model, that is, without a time-dependence, hence
we are calculating the limiting case where the atmospheric chemistry response
time of the biomarkers is assumed to be slow and remains constant compared with
rapid forcing by the impinging stellar flares. This point should be further
explored in future work with time-dependent models. For the flaring case O3 is
mainly destroyed via direct titration with nitrogen oxides and not via the
familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios
with low O3, Rayleigh scattering by the main atmospheric gases became more
important for shielding the planetary surface from ultra-violet radiation. A
major result of this work is that the biomarker O3 survived all the
stellar-activity scenarios considered except for the strong case, whereas the
biomarker nitrous oxide could survive in the planetary atmosphere under all
conditions of stellar activity considered here, which clearly has important
implications for missions that aim to detect spectroscopic biomarkers.",1506.06508v1
2015-10-17,Evolution of the dust in V4332 Sagittarii,"An eruptive nova-like event took place in 1994 in the stellar-merger
candidate V4332 Sgr. Following the eruption, dust consisting of refractory
silicate rich dust grains containing a significant component of AlO bonding was
formed sometime between 1998 and 2003. Observations using Spitzer between 2005
and 2009 show significant changes in the 10 micron silicate stretch feature.
There is a deepening of the 10 micron silicate stretch as well as the
development of a feature between about 13 and 20 microns consistent with a
blend of the MgO and FeO stretching features and the O-Si-O bending mode of
increasingly ordered silicate dust. Near-infrared observations show the
presence of AlO and water vapor in the outflow in 2003, 2004 and 2005: the AlO
has significantly decreased in spectra obtained in 2014 while the water vapor
remains largely unchanged. An attempt is made to correlate these observations
and understand the significance of these changes using DUSTY modeling. The
observations appear consistent with the kinetically-controlled, condensation of
highly under-oxidized SiO/AlO/Fe/Mg dust grains in the outflow followed by the
continuous evolution of the initial condensate due to thermal annealing and
oxidation of the dust via reaction with ambient O, OH and H2O in the expanding,
cooling shell. Periodic monitoring of this dust shell over the mid-infrared
spectral range could yield useful information on the evolution of
under-oxidized silicate condensates exposed to hot water vapor in more
conventional circumstellar environments.",1510.05074v1
2016-02-03,Exploiting plume structure to decode gas source distance using metal-oxide gas sensors,"Estimating the distance of a gas source is important in many applications of
chemical sensing, like e.g. environmental monitoring, or chemically-guided
robot navigation. If an estimation of the gas concentration at the source is
available, source proximity can be estimated from the time-averaged gas
concentration at the sensing site. However, in turbulent environments, where
fast concentration fluctuations dominate, comparably long measurements are
required to obtain a reliable estimate. A lesser known feature that can be
exploited for distance estimation in a turbulent environment lies in the
relationship between source proximity and the temporal variance of the local
gas concentration - the farther the source, the more intermittent are gas
encounters. However, exploiting this feature requires measurement of changes in
gas concentration on a comparably fast time scale, that have up to now only
been achieved using photo-ionisation detectors. Here, we demonstrate that by
appropriate signal processing, off-the-shelf metal-oxide sensors are capable of
extracting rapidly fluctuating features of gas plumes that strongly correlate
with source distance. We show that with a straightforward analysis method it is
possible to decode events of large, consistent changes in the measured signal,
so-called 'bouts'. The frequency of these bouts predicts the distance of a gas
source in wind-tunnel experiments with good accuracy. In addition, we found
that the variance of bout counts indicates cross-wind offset to the centreline
of the gas plume. Our results offer an alternative approach to estimating gas
source proximity that is largely independent of gas concentration, using
off-the-shelf metal-oxide sensors. The analysis method we employ demands very
few computational resources and is suitable for low-power microcontrollers.",1602.01815v2
2016-10-04,An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures,"The formation of silicate dust in oxygen-rich envelopes of evolved stars is
thought to be initiated by formation of seed particles that can withstand the
high temperatures close to the stellar photosphere and act as condensation
cores farther away from the star. Candidate species considered as first
condensates are TiO and TiO$_2$. We aim to identify and characterize the
circumstellar gas-phase chemistry of titanium that leads to the formation of
solid titanium compounds in the envelope of $o$ Cet, the prototypical Mira, and
seek an observational verification of whether titanium oxides play a major role
in the onset of dust formation in M-type AGB stars. We present high
angular-resolution ALMA observations at submillimeter (submm) wavelengths
supplemented by APEX and Herschel spectra of the rotational features of TiO and
TiO$_2$. In addition, circumstellar features of TiO and TiI are identified in
optical spectra which cover multiple pulsation cycles of $o$ Cet. The submm
ALMA data reveal TiO and TiO$_2$ bearing gas within the extended atmosphere of
Mira. While TiO is traceable up to a radius (FWHM/2) of 4.0 R$_{\star}$,
TiO$_2$ extends as far as 5.5 R$_{\star}$ and unlike TiO appears to be
anisotropically distributed. Optical spectra display variable emission of TiI
and TiO from inner parts of the extended atmosphere (<3 R$_{\star}$). Chemical
models which include shocks are in general agreement with the observations of
gas-phase titanium-bearing molecules. It is unlikely that substantial amounts
of titanium is locked up in solids because the abundance of the gaseous
titanium species is very high. In particular, formation of hot titanium-rich
condensates is very improbable because we find no traces of their hot precursor
species in the gas phase. It therefore appears unlikely that the formation of
dust in Mira, and possibly other M-type AGB stars, is initiated by titanium
oxides.",1610.01141v1
2016-10-20,First-principles analysis of electron transport in BaSnO$_3$,"BaSnO$_3$ (BSO) is a promising transparent conducting oxide (TCO) with
reported room-temperature (RT) Hall mobility exceeding 320
cm$^{2}$V$^{-1}$s$^{-1}$. Among perovskite oxides, it has the highest RT
mobility, about 30 times higher than that of the prototypical SrTiO$_3$. Using
first-principles calculations based on hybrid density functional theory, we
elucidate the physical mechanisms that govern the mobility by studying the
details of LO-phonon and ionized impurity scattering. A careful numerical
analysis to obtain converged results within the relaxation-time approximation
of Boltzmann transport theory is presented. The ${\bf k}$ dependence of the
relaxation time is fully taken into account. We find that the high RT mobility
in BSO originates not only from a small effective mass, but also from a
significant reduction in the phonon scattering rate compared to other
perovskite oxides; the origins of this reduction are identified. Ionized
impurity scattering influences the total mobility even at RT for dopant
densities larger than $5\times10^{18}$ cm$^{-3}$, and becomes comparable to
LO-phonon scattering for $1\times10^{20}$ cm$^{-3}$ doping, reducing the drift
mobility from its intrinsic LO-phonon-limited value of $\sim$594
cm$^{2}$V$^{-1}$s$^{-1}$ to less than 310 cm$^{2}$V$^{-1}$s$^{-1}$. We suggest
pathways to avoid impurity scattering via modulation doping or polar
discontinuity doping. We also explicitly calculate the Hall factor and Hall
mobility, allowing a direct comparison to experimental reports for bulk and
thin films and providing insights into the nature of the dominant mechanisms
that limit mobility in state-of-the art samples.",1610.06253v1
2017-02-25,Electronic conduction properties of indium tin oxide: single-particle and many-body transport,"Indium tin oxide (Sn-doped In$_2$O$_{3-\delta}$ or ITO) is an interesting and
technologically important transparent conducting oxide. This class of material
has been extensively studied for decades, with research efforts focusing on the
application aspects. The fundamental issues of the electronic conduction
properties of ITO from 300 K down to low temperatures have rarely been
addressed. Studies of the electrical-transport properties over a wide range of
temperature are essential to unraveling the underlying electronic dynamics and
microscopic electronic parameters. We show that one can learn rich physics in
ITO material, including the semi-classical Boltzmann transport, the
quantum-interference electron transport, and the electron-electron interaction
effects in the presence of disorder and granularity. To reveal the
opportunities that the ITO material provides for fundamental research, we
demonstrate a variety of charge transport properties in different forms of ITO
structures, including homogeneous polycrystalline films, homogeneous
single-crystalline nanowires, and inhomogeneous ultrathin films. We not only
address new physics phenomena that arise in ITO but also illustrate the
versatility of the stable ITO material forms for potential applications. We
emphasize that, microscopically, the rich electronic conduction properties of
ITO originate from the inherited free-electron-like energy bandstructure and
low-carrier concentration (as compared with that in typical metals)
characteristics of this class of material. Furthermore, a low carrier
concentration leads to slow electron-phonon relaxation, which causes ($i$) a
small residual resistance ratio, ($ii$) a linear electron diffusion
thermoelectric power in a wide temperature range 1-300 K, and ($iii$) a weak
electron dephasing rate. We focus our discussion on the metallic-like ITO
material.",1702.07845v1
2018-04-12,Bulk and surface characterization of In$_2$O$_3$(001) single crystals,"A comprehensive bulk and surface investigation of high-quality
In$_2$O$_3$(001) single crystals is reported. The transparent-yellow,
cube-shaped single crystals were grown using the flux method. Inductively
coupled plasma mass spectrometry (ICP-MS) reveals small residues of Pb, Mg, and
Pt in the crystals. Four-point-probe measurements show a resistivity of 2.0
$\pm$ 0.5 $\times$ 10$^5$ {\Omega} cm, which translates into a carrier
concentration of $\approx$10$^{12}$ cm$^{-3}$. The results from x-ray
diffraction (XRD) measurements revise the lattice constant to 10.1150(5) {\AA}
from the previously accepted value of 10.117 {\AA}. Scanning tunneling
microscopy (STM) images of a reduced (sputtered/annealed) and oxidized
(exposure to atomic oxygen at 300 {\deg}C) surface show a step height of 5
{\AA}, which indicates a preference for one type of surface termination. The
surfaces stay flat without any evidence for macroscopic faceting under any of
these preparation conditions. A combination of low-energy ion scattering (LEIS)
and atomically resolved STM indicates an indium-terminated surface with small
islands of 2.5 {\AA} height under reducing conditions, with a surface structure
corresponding to a strongly distorted indium lattice. Scanning tunneling
spectroscopy (STS) reveals a pronounced surface state at the Fermi level
($E_F$). Photoelectron spectroscopy (PES) shows additional, deep-lying band gap
states, which can be removed by exposure of the surface to atomic oxygen.
Oxidation also results in a shoulder at the O 1s core level at a higher binding
energy, possibly indicative of a surface peroxide species. A downward band
bending of 0.4 eV is observed for the reduced surface, while the band bending
of the oxidized surface is of the order of 0.1 eV or less.",1804.04478v1
2018-11-22,Effect of PEG binder on gas sensitivity of ferric oxide films synthesized by spin coating and doctor blade methods,"Ferric oxide (Fe2O3) thin films were fabricated on amorphous nonconductive
and FTO conductive glass substrates starting from iron acetate nanoparticles by
the doctor blade and the spin coating techniques. Thin films of Fe2O3 with and
without the PEG binder were investigated. Films were subsequently annealed at
500 0C in air for 1 hour to crystallize the phase Fe2O3. The structural and
chemical properties of Fe2O3 thin films were determined using XRD and FTIR.
According to XRD, the single phase of Fe2O3 crystallized in the thin film after
annealing. The optical band gap of synthesized Fe2O3 thin films were determined
by UV-Visible spectrums. Gas sensitivity, respond time and recovery time of
Fe2O3 thin films were measured in 1000ppm of CO2 gas using AUTO LAB. Thin films
synthesized by the doctor blade method were thicker and more uniform than the
thin films prepared by the spin coating technique. Gas sensitivity of Fe2O3
films synthesized by the doctor blade method is slightly higher than that of
the films fabricated by the spin coating technique. Fe2O3 films with the PEG
binder posses a higher gas sensitivity, lower respond time and lower recovery
time compared to films without PEG binder. After adding the PEG binder, the
optical band gap of Fe2O3 thin films reduces. The reduction of the activation
energy is the reason for the improvement of the gas sensitivity after adding
the PEG. However, the peak positions of FTIR do not indicate any significant
change due to the adding of the PEG. Adding the binder increased the gas
sensitivity of iron oxide by 15.44%. Both FTIR and UV-Visible data confirm the
formation of Fe2O3 in the thin film.",1811.09614v1
2020-07-30,"Understanding the Synthetic Pathway to Large Area, High Quality [AgSePh] Nanocrystal Films","Silver benzeneselenolate [AgSePh] is a coordination polymer that hosts a
hybrid quantum well structure. The recent advancements in the study of its
tightly bound excitons (~300 meV) and photoconductive properties (recently
employed in UV photodetection) makes it an interesting representative of a
material platform that is an environmentally stable alternative to 2D metal
halide perovskites in terms of optoelectronic properties. To this aim, several
challenges are to be addressed, among which the lack of control over the
metal-organic reaction process in the reported synthesis of the [AgSePh]
nanocrystal film (NC). This issue contributed to cast doubts over the origin of
its intra-bandgap electronic states. In this article we study all the steps to
obtain phase pure [AgSePh] NC films, from thin silver films through its
oxidation and reaction via a chemical vapor-solid with benzeneselenol, by means
of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopy are also employed to
provide vibrational peaks assignment, for the first time on this polymer. Our
analysis supports an acid-base reaction scheme based on an acid attacking the
metal oxide precursor, generating water as byproduct of the polymeric
synthesis, speeding up the reaction by solvating the PhSeH. The reaction
readily goes to completion within 30 min in a supersaturated PhSeH / N2
atmosphere at 90 {\deg}C. Our analysis suggests the absence of precursor's
leftovers or oxidized species that could contribute to the intra-gap states. By
tuning the reaction parameters, we gained control on film morphology to obtain
substrate-parallel oriented micro-crystals showing different excitonic
absorption intensities. Finally, centimeters size high quality [AgSePh] NC
films could be obtained, enabling exploitation of their optoelectronic
properties, such as UV photodetection, in large-area applications.",2007.15354v2
2016-11-25,The effect of the thermal reduction on the kinetics of low temperature 4He sorption and the structural characteristics of graphene oxide,"The kinetics of the sorption and the subsequent desorption of 4He by the
starting graphite oxide (GtO) and the thermally reduced graphene oxide samples
(TRGO, Treduction = 200, 300, 500, 700 and 900 C) have been investigated in the
temperature interval 1.5 - 20 K. The effect of the annealing temperature on the
structural characteristics of the samples was examined by the X-ray diffraction
(XRD) technique. On lowering the temperature from 20 K to 11-12 K, the time of
4He sorption increased for all the samples, which is typically observed under
the condition of thermally activated diffusion. Below 5 K the characteristic
times of 4He sorption by the GtO and TRGO-200 samples were only weakly
dependent on temperature, suggesting the dominance of the tunnel mechanism. In
the same region (T<5 K) the characteristic times of the TRGOs reduced at higher
temperatures (300, 500, 700 and 900 C) were growing with lowering temperature,
presumably due to the defects generated in the carbon planes on removing the
oxygen functional groups (oFGs). The estimates of the activation energy (Ea) of
4He diffusion show that in the TRGO-200 sample the Ea value is 2.9 times lower
as compared to the parent GtO, which is accounted for by GtO exfoliation due to
evaporation of the water intercalated in the interlayer space of carbon. The
nonmonotonic dependences Ea vs T for the GtO samples treated above 200 C are
determined by a competition between two processes - the recovery of the
graphite carbon structure, which increases the activation energy, and the
generation of defects, which decreases the activation energy by opening
additional surface areas and ways for sorption. The dependence of the
activation energy on treatment temperature correlates well with the contents of
the crystalline phase in GtO varying with a rise of the annealing temperature.",1611.08375v1
2011-11-14,Nanostructuring of Ba8Ga16Ge30 clathrates,"First thermoelectric properties measurements on bulk nanostructured
Ba8Ga16Ge30 clathrate-I are presented. A sol-gel-calcination route was
developed for preparing amorphous nanosized precursor oxides. The further
reduction of the oxides led to quantitative yield of crystalline nanosized
Ba8Ga16Ge30 clathrate-I. TEM investigations show the clathrate nanoparticles
retain the size and morphology of the precursor oxides. The clathrate
nanoparticles contain mainly thin plates (approx. 300 nm x 300 nm x 50 nm) and
a small amount of nanospheres (diameter ~ 10 nm). SAED patterns confirm the
clathrate-I structure type for both morphologies. The powders were compacted
via Spark Plasma Sintering (SPS) to obtain a bulk nano-structured material. The
Seebeck coefficient S, measured on low-density samples (53% of {\delta}x-ray),
reaches -145 {\mu}V/k at 375 {\deg}C. The ZT values are quite low (0.02) due to
the high resistivity of the sample (two orders of magnitude larger than bulk
materials) and the low sample density. The trend of the temperature dependence
of S is in agreement with the values obtained from electronic structure
calculations and semi-classical Boltzmann transport theory within the constant
scattering approximation. The total thermal conductivity (1.61 W/mK), measured
on high density samples (93% of {\delta}x-ray), shows a reduction of 20-25% in
relation to the bulk materials (2.1 W/mK). A further shaping of the sample for
the Seebeck coefficient and electrical conductivity measurements was not
possible due to the presence of cracks. An improvement on the design of the
pressing tools, loading of the sample and profile of the applied pressure will
enhance the mechanical stability of the samples. These investigations are now
in progress.",1111.3233v1
2013-09-11,Accelerating moderately stiff chemical kinetics in reactive-flow simulations using GPUs,"The chemical kinetics ODEs arising from operator-split reactive-flow
simulations were solved on GPUs using explicit integration algorithms. Nonstiff
chemical kinetics of a hydrogen oxidation mechanism (9 species and 38
irreversible reactions) were computed using the explicit fifth-order
Runge-Kutta-Cash-Karp method, and the GPU-accelerated version performed faster
than single- and six-core CPU versions by factors of 126 and 25, respectively,
for 524,288 ODEs. Moderately stiff kinetics, represented with mechanisms for
hydrogen/carbon-monoxide (13 species and 54 irreversible reactions) and methane
(53 species and 634 irreversible reactions) oxidation, were computed using the
stabilized explicit second-order Runge-Kutta-Chebyshev (RKC) algorithm. The
GPU-based RKC implementation demonstrated an increase in performance of nearly
59 and 10 times, for problem sizes consisting of 262,144 ODEs and larger, than
the single- and six-core CPU-based RKC algorithms using the
hydrogen/carbon-monoxide mechanism. With the methane mechanism, RKC-GPU
performed more than 65 and 11 times faster, for problem sizes consisting of
131,072 ODEs and larger, than the single- and six-core RKC-CPU versions, and up
to 57 times faster than the six-core CPU-based implicit VODE algorithm on
65,536 ODEs. In the presence of more severe stiffness, such as ethylene
oxidation (111 species and 1566 irreversible reactions), RKC-GPU performed more
than 17 times faster than RKC-CPU on six cores for 32,768 ODEs and larger, and
at best 4.5 times faster than VODE on six CPU cores for 65,536 ODEs. With a
larger time step size, RKC-GPU performed at best 2.5 times slower than six-core
VODE for 8192 ODEs and larger. Therefore, the need for developing new
strategies for integrating stiff chemistry on GPUs was discussed.",1309.2710v2
2013-09-12,Persistent photoconductivity in 2-dimensional electron gases at different oxide interfaces,"We report on the transport characterization in dark and under light
irradiation of three different interfaces: LaAlO3/SrTiO3, LaGaO3/SrTiO3, and
the novel NdGaO3/SrTiO3 heterostructure. All of them share a perovskite
structure, an insulating nature of the single building blocks, a polar/non-
polar character and a critical thickness of four unit cells for the onset of
conductivity. The interface structure and charge confinement in NdGaO3/SrTiO3
are probed by atomic-scale- resolved electron energy loss spectroscopy showing
that, similarly to LaAlO3/SrTiO3, extra electronic charge confined in a sheet
of about 1.5 nm in thickness is present at the NdGaO3/SrTiO3 interface.
Electric transport measurements performed in dark and under radiation show
remarkable similarities and provide evidence that the persistent perturbation
induced by light is an intrinsic peculiar property of the three investigated
oxide-based polar/non-polar interfaces. Our work sets a framework for
understanding the previous contrasting results found in literature about
photoconductivity in LaAlO3/SrTiO3 and highlights the connection between the
origin of persistent photoconductivity and the origin of conductivity itself.
An improved understanding of the photo- induced metastable electron-hole pairs
might allow to shed a direct light on the complex physics of this system and on
the recently proposed perspectives of oxide interfaces for solar energy
conversion.",1309.3120v2
2017-06-13,Surface Restructuring of Nickel Sulfide Generates Optimally-Coordinated Active Sites for ORR Catalysis,"First-row transition metal oxides and chalcogenides have been found to rival
the performance of precious metal-based catalysts for the interconversion of
water and O$_2$. The high lability of the first-row transition metal ions leads
to surface dynamics under the conditions of catalysis and results in active
site structures distinct from those expected by surface termination of the bulk
lattice. While these surface transformations have been well-characterized on
many metal oxides, the surface dynamics of heavier chalcogenides under
electrocatalytic conditions are largely unknown. We recently reported that the
heazlewoodite Ni$_3$S$_2$ bulk phase supports efficient ORR catalysis under
benign aqueous conditions and exhibits excellent tolerance to electrolyte
anions such as phosphate which poison Pt. Herein, we combine electrochemistry,
surface spectroscopy and high resolution microscopy to characterize the surface
dynamics of Ni$_3$S$_2$ under ORR catalytic conditions. We show that
Ni$_3$S$_2$ undergoes self-limiting oxidative surface restructuring to form an
approximately 2 nm amorphous surface film conformally coating the Ni$_3$S$_2$
crystallites. The surface film has a nominal NiS stoichiometry and is highly
active for ORR catalysis. Using DFT calculations we show that, to a first
approximation, the catalytic activity of nickel sulfides is determined by the
Ni-S coordination numbers at surface exposed sites through a simple geometric
descriptor. In particular, we find that the surface sites formed dynamically on
the surface of amorphous NiS during surface restructuring provide an optimal
energetic landscape for ORR catalysis. This work provides a systematic
framework for characterizing the rich surface chemistry of metal-chalcogenides
and provides principles for developing a broader understanding of
electrocatalysis mediated by amorphous materials.",1706.04090v1
2017-10-25,NaSn2As2: An Exfoliatable Layered van der Waals Zintl Phase,"The discovery of new families of exfoliatable 2D crystals that have diverse
sets of electronic, optical, and spin-orbit coupling properties, enables the
realization of unique physical phenomena in these few-atom thick building
blocks and in proximity to other materials. Herein, using NaSn2As2 as a model
system, we demonstrate that layered Zintl phases having the stoichiometry
ATt2Pn2 (A = Group 1 or 2 element, Tt = Group 14 tetrel element and Pn = Group
15 pnictogen element) and feature networks separated by van der Waals gaps can
be readily exfoliated with both mechanical and liquid-phase methods. We
identified the symmetries of the Raman active modes of the bulk crystals via
polarized Raman spectroscopy. The bulk and mechanically exfoliated NaSn2As2
samples are resistant towards oxidation, with only the top surface oxidizing in
ambient conditions over a couple of days, while the liquid-exfoliated samples
oxidize much more quickly in ambient conditions. Employing angle-resolved
photoemission spectroscopy (ARPES), density functional theory (DFT), and
transport on bulk and exfoliated samples, we show that NaSn2As2 is a highly
conducting 2D semimetal, with resistivities on the order of 10-6 {\Omega} m.
Due to peculiarities in the band structure, the dominating p-type carriers at
low temperature are nearly compensated by the opening of n-type conduction
channels as temperature increases. This work further expands the family of
exfoliatable 2D materials to layered van der Waals Zintl phases, opening up
opportunities in electronics and spintronics.",1710.09059v1
2017-12-12,"Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory","The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the
combined analysis of several materials science techniques - X-ray diffraction
(XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy
(XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT)
based calculations for the samples under study were performed as well. The
cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation
method exhibits spheroidal-like nanoclusters with well-defined edges assembled
from primary nanoparticles with an average size of 50 nm, whereas the
monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive
pyrolysis has a denser structure compared with natural gadolinia. This phase
also has a structure composed of three-dimensional complex agglomerates without
clear-edged boundaries that are ~21 nm in size plus a cubic phase admixture of
only 2 at. % composed of primary edge-boundary nanoparticles ~15 nm in size.
These atomic features appear in the electronic structure as different defects
([Gd...O-OH] and [Gd...O-O]) and have dissimilar contributions to the
charge-transfer processes among the appropriate electronic states with
ambiguous contributions in the Gd 5p - O 2s core-like levels in the valence
band structures. The origin of [Gd...O-OH] defects found by XPS was
well-supported by PL analysis. The electronic and atomic structures of the
synthesized gadolinias calculated using DFT were compared and discussed on the
basis of the well-known joint OKT-van der Laan model, and good agreement was
established.",1712.04115v1
2018-01-19,Mechanical Properties of Ultralow Density Graphene Oxide/Polydimethylsiloxane Foams,"Low-density, highly porous graphene/graphene oxide (GO) based-foams have
shown high performance in energy absorption applications, even under high
compressive deformations. In general, foams are very effective as energy
dissipative materials and have been widely used in many areas such as
automotive, aerospace and biomedical industries. In the case of graphene-based
foams, the good mechanical properties are mainly attributed to the intrinsic
graphene and/or GO electronic and mechanical properties. Despite the attractive
physical properties of graphene/GO based-foams, their structural and thermal
stabilities are still a problem for some applications. For instance, they are
easily degraded when placed in flowing solutions, either by the collapsing of
their layers or just by structural disintegration into small pieces. Recently,
a new and scalable synthetic approach to produce low-density 3D macroscopic GO
structure interconnected with polydimethylsiloxane (PDMS) polymeric chains
(pGO) was proposed. A controlled amount of PDMS is infused into the
freeze-dried foam resulting into a very rigid structure with improved
mechanical properties, such as tensile plasticity and toughness. The PDMS wets
the graphene oxide sheets and acts like a glue bonding PDMS and GO sheets. In
order to obtain further insights on mechanisms behind the enhanced mechanical
pGO response we carried out fully atomistic molecular dynamics (MD)
simulations. Based on MD results, we build up a structural model that can
explain the experimentally observed mechanical behavior.",1801.06257v1
2018-10-19,Theoretical evidence of spin-orbital-entangled $J_{\mathbf{eff}}$=1/2 state in the 3$d$ transition metal oxide CuAl$_2$O$_4$,"Transition metal oxides exhibit various competing phases and exotic phenomena
depending on how their reaction to the rich degeneracy of the $d$-orbital.
Large spin-orbit coupling (SOC) reduces this degeneracy in a unique way by
providing a spin-orbital-entangled ground state for 4$d$ and 5$d$ transition
metal compounds. In particular, the spin-orbital-entangled Kramers doublet,
known as the $J_{\mathbf{eff}}$=1/2 pseudospin, appears in layered iridates and
$\alpha$-RuCl$_3$, manifesting a relativistic Mott insulating phase. Such
entanglement, however, seems barely attainable in 3$d$ transition metal oxides,
where the SOC is small and the orbital angular momentum is easily quenched.
From experimental and theoretical evidence, here we report on the CuAl$_2$O$_4$
spinel as the first example of a $J_{\mathbf{eff}}$=1/2 Mott insulator in 3$d$
transition metal compounds. Based on the experimental study, including
synthesis of the cubic CuAl$_2$O$_4$ single crystal, density functional theory
and dynamical mean field theory calculations reveal that the
$J_{\mathbf{eff}}$=1/2 state survives the competition with an
orbital-momentum-quenched $S$=1/2 state. The electron-addition spectra probing
unoccupied states are well described by the $j_{\mathbf{eff}}$=1/2 hole state,
whereas electron-removal spectra have a rich multiplet structure. The fully
relativistic entity found in CuAl$_2$O$_4$ provides new insight into the
untapped regime where the spin-orbital-entangled Kramers pair coexists with
strong electron correlation.",1810.08594v3
2019-06-27,On the quest of low temperature nitrogen infusion relevant for superconducting Nb based radio-frequency cavities,"A detailed study of the near-surface structure and composition of Nb, the
material of choice for Superconducting Radio Frequency accelerator (SRF)
cavities, is of great importance in order to understand the effects of
different treatments applied during cavity production. By means of
surface-sensitive techniques such as grazing incidence diffuse X-ray
scattering, X-ray reflectivity and X-ray photoelectron spectroscopy,
single-crystalline Nb(100) samples were investigated in and ex-situ during
annealing in UHV as well as in nitrogen atmospheres with temperatures and
pressures similar to the ones employed in real Nb cavity treatments. Annealing
of Nb specimens up to 800{\deg}C in vacuum promotes partial reduction of the
natural surface oxides (Nb2O5, NbO2, NbO) into NbO. Upon cooling to 120{\deg}C,
no evidence of nitrogen-rich layers was detected after nitrogen exposure times
of up to 48 hours. Oxygen enrichment below the Nb/oxide interface and posterior
diffusion of oxygen species towards the Nb matrix, along with a partial
reduction of the natural surface oxides was observed upon a stepwise annealing
up to 250{\deg}C. Nitrogen introduction to the system at 250{\deg}C neither
promotes N diffusion into the Nb matrix nor the formation of new surface
layers. Upon further heating to 500{\deg}C in a nitrogen atmosphere, the growth
of a new subsurface Nb$_x$N$_y$ layer was detected. These results shed light on
the composition of the near-surface region of Nb after low-temperature nitrogen
treatments, which are reported to lead to a performance enhancement of SRF
cavities.",1906.11530v1
2019-07-11,"The Composition and Mineralogy of Rocky Exoplanets: A Survey of >4,000 Stars from the Hypatia Catalog","We present a survey of >4,000 star compositions from the Hypatia Catalog to
examine whether rocky exoplanets (i.e., those with rocky surfaces, dominated by
silicates) might be geologically similar to Earth, at least with respect to
composition and mineralogy. To do so, we explore the variety of reported
stellar compositions to then determine a possible range of exoplanetary mantle
mineralogies. We find that exoplanetary mantles will likely be dominated by
olivine and/or orthopyroxene, depending upon Fe partitioning during core
formation. Some exoplanets may be magnesiowustite- or quartz-saturated, and we
present a new classification scheme based on the weight $\%$ ratio
(FeO+MgO)/SiO$_{2}$, to differentiate rock types. But wholly exotic
mineralogies should be rare to absent. We find that half or more of the range
of exoplanet mantle mineralogy is controlled by core formation, which we model
using $\alpha_{Fe}$ = $Fe^{BSP}$/$Fe^{BP}$, where $Fe^{BSP}$ is Fe in a Bulk
Silicate Planet (bulk planet, minus core), on a cation weight $\%$ basis
(elemental weight proportions, absent anions) and $Fe^{BP}$ is the cation
weight $\%$ of Fe for a Bulk Planet. In our solar system, $\alpha_{Fe}$ varies
from 0 (Mercury) to about 0.54 (Mars). Remaining variations in exoplanet mantle
mineralogy result from non-trivial variations in star compositions. Our major
oxide analysis also verifies earlier, isotopic studies indicating that Earth is
non-solar (non-chondritic). We also find that major oxide estimates for Earth's
mantle appear to preclude a hidden component in the deep mantle that would
allow for a bulk solar/chondritic Earth. If it did exist, such a hidden
component must comprise at least 28% of the mass of the total mantle (to avoid
negative concentrations of some oxides) and would not look anything like the
sources of ocean island or mid-ocean ridge basalts.",1907.05506v1
2019-09-06,Electronic structure of the parent compound of superconducting infinite-layer nickelates,"The search for oxide materials with physical properties similar to the
cuprate high Tc superconductors, but based on alternative transition metals
such as nickel, has grown and evolved over time. The recent discovery of
superconductivity in doped infinite-layer nickelates RNiO2 (R = rare-earth
element) further strengthens these efforts.With a crystal structure similar to
the infinite-layer cuprates - transition metal oxide layers separated by a
rare-earth spacer layer - formal valence counting suggests that these materials
have monovalent Ni1+ cations with the same 3d electron count as Cu2+ in the
cuprates. Here, we use x-ray spectroscopy in concert with density functional
theory to show that the electronic structure of RNiO2 (R = La, Nd), while
similar to the cuprates, includes significant distinctions. Unlike cuprates
with insulating spacer layers between the CuO2 planes, the rare-earth spacer
layer in the infinite-layer nickelate supports a weakly-interacting
three-dimensional 5d metallic state. This three-dimensional metallic state
hybridizes with a quasi-two-dimensional, strongly correlated state with 3dx2-y2
symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded
as a sibling of the rare earth intermetallics, well-known for heavy Fermion
behavior, where the NiO2 correlated layers play an analogous role to the 4f
states in rare-earth heavy Fermion compounds. This unique Kondo- or
Anderson-lattice-like ""oxide-intermetallic"" replaces the Mott insulator as the
reference state from which superconductivity emerges upon doping.",1909.02678v1
2019-09-06,Hydrogen isotopic evidence for early oxidation of silicate Earth,"The Moon-forming giant impact extensively melts and partially vaporizes the
silicate Earth and delivers a substantial mass of metal to Earth's core.
Subsequent evolution of the magma ocean and overlying atmosphere has been
described by theoretical models but observable constraints on this epoch have
proved elusive. Here, we report calculations of the primordial atmosphere
during the magma ocean and water ocean epochs and forge new links with
observations to gain insight into the behavior of volatiles on the early Earth.
As Earth's magma ocean crystallizes, it outgasses the bulk of the volatiles
into the primordial atmosphere. The redox state of the magma ocean controls
both the chemical composition of the outgassed volatiles and the hydrogen
isotopic composition of water oceans that remain after hydrogen loss from the
primordial atmosphere. Whereas water condenses and is retained, molecular
hydrogen does not condense and can escape, allowing large quantities (~10^2
bars) of hydrogen - if present - to be lost from Earth in this epoch. Because
the escaping inventory of H can be comparable to the hydrogen inventory in the
early oceans, the corresponding deuterium enrichment can be large with a
magnitude that depends on the initial H2 inventory. By contrast, the common
view that terrestrial water has a carbonaceous chondrite source requires the
oceans to preserve the isotopic composition of that source, undergoing minimal
D-enrichment via H2 loss. Such minimal enrichment places upper limits on the
amount of primordial H2 in contact with early water oceans (pH2<20 bars),
implies oxidizing conditions for outgassing from the magma ocean, and suggests
that Earth's mantle supplied the oxidant for the chemical resorption of metals
during late accretion.",1909.03001v2
2019-09-21,Integrating high-quality dielectrics with one-nanometer equivalent oxide thickness on two-dimensional electronic devices,"Two-dimensional (2D) semiconductors are widely recognized as attractive
channel materials for low-power electronics. However, an unresolved challenge
is the integration of high-quality, ultrathin high-\k{appa} dielectrics that
fully meet the roadmap requirements for low-power applications. With a
dangling-bond free surface, the deposition of dielectrics by atomic layer
deposition (ALD) on 2D materials is usually characterized with non-uniform
nucleation and island formation, producing a highly porous dielectric layer
with serious leakage particularly at the small equivalent oxide thickness (EOT)
limit. Here, we report the robust ALD of highly uniform high-\k{appa}
dielectric on 2D semiconductors by using ~0.3 nm-thick exclusively monolayer
molecular crystal as seeding layer. Ultrathin dielectrics down to 1 nm EOT is
realized on graphene, MoS2 and WSe2, with considerably reduced roughness,
density of interface states, leakage current and improved breakdown field
compared to prior methods. Taking advantage of the reduced EOT, we demonstrate
graphene RF transistors operating at 60 GHz, as well as MoS2 and WSe2
complementary metal-oxide-semiconductor (CMOS) transistors with Vdd =0.8 V and
ideal subthreshold swing (SS) of 60 mV/dec, 20 nm-channel-length MoS2
transistors with on/off ratio over 10^7. These studies highlight that our
dielectric integration method is generally applicable for different 2D
materials, and compatible with top-down fabrication process on large-area
chemical vapor deposited films.",1909.09753v1
2020-02-11,Efficient Training of ANN Potentials by Including Atomic Forces via Taylor Expansion and Application to Water and a Transition-Metal Oxide,"Artificial neural network (ANN) potentials enable the efficient large-scale
atomistic modeling of complex materials with near first-principles accuracy.
For molecular dynamics simulations, accurate energies and interatomic forces
are a prerequisite, but training ANN potentials simultaneously on energies and
forces from electronic structure calculations is computationally demanding.
Here, we introduce an efficient alternative method for the training of ANN
potentials on energy and force information based on an extrapolation of the
total energy via a Taylor expansion. By translating the force information to
approximate energies, the quadratic scaling with the number of atoms exhibited
by conventional force-training methods can be avoided, which enables the
training on reference data sets containing complex atomic structures. We
demonstrate for different materials systems, clusters of water molecules, bulk
liquid water, and a lithium transition-metal oxide, that the proposed
force-training approach provides substantial improvements over schemes that
train on energies only. Including force information for training reduces the
size of the reference data sets required for ANN potential construction,
increases the transferability of the potential, and generally improves the
force prediction accuracy. For a set of water clusters, the Taylor-expansion
approach achieves around 50% of the force error improvement compared to the
explicit training on all force components, at a much smaller computational
cost. The alternative force training approach thus simplifies the construction
of general ANN potentials for the prediction of accurate energies and
interatomic forces for diverse types of materials, as demonstrated here for
water and a transition-metal oxide.",2002.04172v2
2020-02-21,Low Thermal Budget High-k/Metal Surface Gate for Buried Donor-Based Devices,"Atomic precision advanced manufacturing (APAM) offers creation of donor
devices in an atomically thin layer doped beyond the solid solubility limit,
enabling unique device physics. This presents an opportunity to use APAM as a
pathfinding platform to investigate digital electronics at the atomic limit.
Scaling to smaller transistors is increasingly difficult and expensive,
necessitating the investigation of alternative fabrication paths that extend to
the atomic scale. APAM donor devices can be created using a scanning tunneling
microscope (STM). However, these devices are not currently compatible with
industry standard fabrication processes. There exists a tradeoff between low
thermal budget (LT) processes to limit dopant diffusion and high thermal budget
(HT) processes to grow defect-free layers of epitaxial Si and gate oxide. To
this end, we have developed an LT epitaxial Si cap and LT deposited Al2O3 gate
oxide integrated with an atomically precise single-electron transistor (SET)
that we use as an electrometer to characterize the quality of the gate stack.
The surface-gated SET exhibits the expected Coulomb blockade behavior. However,
the leverage of the gate over the SET is limited by defects in the layers above
the SET, including interfaces between the Si and oxide, and structural and
chemical defects in the Si cap. We propose a more sophisticated gate stack and
process flow that is predicted to improve performance in future atomic
precision devices.",2002.09075v2
2020-04-01,A Computational Model of Levodopa-Induced Toxicity in Substantia Nigra Pars Compacta in Parkinson's Disease,"Parkinson's disease (PD) is caused by the progressive loss of dopaminergic
cells in substantia nigra pars compacta (SNc). The root cause of this cell loss
in PD is still not decisively elucidated. A recent line of thinking traces the
cause of PD neurodegeneration to metabolic deficiency. Due to exceptionally
high energy demand, SNc neurons exhibit a higher basal metabolic rate and
higher oxygen consumption rate, which results in oxidative stress. Recently, we
have suggested that the excitotoxic loss of SNc cells might be due to energy
deficiency occurring at different levels of neural hierarchy. Levodopa (LDOPA),
a precursor of dopamine, which is used as a symptom-relieving treatment for PD,
leads to outcomes that are both positive and negative. Several researchers
suggested that LDOPA might be harmful to SNc cells due to oxidative stress. The
role of LDOPA in the course of PD pathogenesis is still debatable. We
hypothesize that energy deficiency can lead to LDOPA-induced toxicity (LIT) in
two ways: by promoting dopamine-induced oxidative stress and by exacerbating
excitotoxicity in SNc. We present a multiscale computational model of
SNc-striatum system, which will help us in understanding the mechanism behind
neurodegeneration postulated above and provides insights for developing
disease-modifying therapeutics. It was observed that SNc terminals are more
vulnerable to energy deficiency than SNc somas. During LDOPA therapy, it was
observed that higher LDOPA dosage results in increased loss of somas and
terminals in SNc. It was also observed that co-administration of LDOPA and
glutathione (antioxidant) evades LDOPA-induced toxicity in SNc neurons. We show
that our proposed model was able to capture LDOPA-induced toxicity in SNc,
caused by energy deficiency.",2004.08320v1
2017-11-09,Experimental studies of thorium ions implantation from pulse laser plasma into thin silicon oxide layers,"We report the results of experimental studies related to implantation of
thorium ions into thin silicon dioxide by pulsed plasma fluxes expansion.
Thorium ions were generated by laser ablation from a metal target, and the
ionic component of the laser plasma was accelerated in an electric field
created by the potential difference (5, 10 and 15 kV) between the ablated
target and SiO2/Si(001) sample. Laser ablation system installed inside the
vacuum chamber of the electron spectrometer was equipped with YAG:Nd3+ laser
having the pulse energy of 100 mJ and time duration of 15 ns in the Q-switched
regime. Depth profile of thorium atoms implanted into the 10 nm thick
subsurface areas together with their chemical state as well as the band gap of
the modified silicon oxide at different conditions of implantation processes
were studied by means of X-ray photoelectron spectroscopy (XPS) and Reflected
Electron Energy Loss Spectroscopy (REELS) methods. Analysis of chemical
composition showed that the modified silicon oxide film contains complex
thorium silicates. Depending on local concentration of thorium atoms, the
experimentally established band gaps were located in the range of 6.0 - 9.0 eV.
Theoretical studies of optical properties of the SiO2 and ThO2 crystalline
systems have been performed by ab initio calculations within hybrid functional.
Optical properties of the SiO2/ThO2 composite were interpreted on the basis of
Bruggeman effective medium approximation. A quantitative assessment of the
yield of isomeric nuclei in ""hot"" laser plasma at the early stages of expansion
has been performed. The estimates made with experimental results demonstrated
that the laser implantation of thorium ions into the SiO2 matrix can be useful
for further research of low-lying isomeric transitions in 229Th isotope with
energy of 7.8(0.5) eV.",1711.03378v1
2018-06-26,Updated Compositional Models of the TRAPPIST-1 Planets,"After publication of our initial mass-radius-composition models for the
TRAPPIST-1 system in Unterborn et al. (2018), the planet masses were updated in
Grimm et al. (2018). We had originally adopted the data set of Wang et al.,
2017 who reported different densities than the updated values. The differences
in observed density change the inferred volatile content of the planets. Grimm
et al. (2018) report TRAPPIST-1 b, d, f, g, and h as being consistent with <5
wt% water and TRAPPIST-1 c and e has having largely rocky interiors. Here, we
present updated results recalculating water fractions and potential alternative
compositions using the Grimm et al., 2018 masses. Overall, we can only
reproduce the results of Grimm et al., 2018 of planets b, d and g having small
water contents if the cores of these planets are small (<23 wt%). We show that,
if the cores for these planets are roughly Earth-sized (33 wt%), significant
water fractions up to 40 wt% are possible. We show planets c, e, f, and h can
have volatile envelopes between 0-35 wt% that are also consistent with being
totally oxidized and lacking an Fe-core entirely. We note here that a pure
MgSiO$_3$ planet (Fe/Mg = 0) is not the true lowest density end-member
mass-radius curve for determining the probability of a planet containing
volatiles. All planets that are rocky likely contain some Fe, either within the
core or oxidized in the mantle. We argue the true low density end-member for
oxidizing systems is instead a planet with the lowest reasonable Fe/Mg and
completely core-less. Using this logic, we assert that planets b, d and g
likely must have significant volatile layers because the end-member planet
models produce masses too high even when uncertainties in both mass and radius
are taken into account.",1806.10084v1
2018-07-18,Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model,"Understanding the evolution of Earth and potentially habitable Earth-like
worlds is essential to fathom our origin in the Universe. The search for
Earth-like planets in the habitable zone and investigation of their atmospheres
with climate and photochemical models is a central focus in exoplanetary
science. Taking the evolution of Earth as a reference for Earth-like planets, a
central scientific goal is to understand what the interactions were between
atmosphere, geology, and biology on early Earth. The Great Oxidation Event
(GOE) in Earth's history was certainly caused by their interplay, but the
origin and controlling processes of this occurrence are not well understood,
the study of which will require interdisciplinary, coupled models. In this
work, we present results from our newly developed Coupled Atmosphere
Biogeochemistry model in which atmospheric O$_2$ concentrations are fixed to
values inferred by geological evidence. Applying a unique tool, ours is the
first quantitative analysis of catalytic cycles that governed O$_2$ in early
Earth's atmosphere near the GOE. Complicated oxidation pathways play a key role
in destroying O$_2$, whereas in the upper atmosphere, most O$_2$ is formed
abiotically via CO$_2$ photolysis. The O$_2$ bistability found by Goldblatt et
al. (2006) is not observed in our calculations likely due to our detailed
CH$_4$ oxidation scheme. We calculate increased CH$_4$ with increasing O$_2$
during the GOE. For a given atmospheric surface flux, different atmospheric
states are possible; however, the net primary productivity (NPP) of the
biosphere that produces O$_2$ is unique. Mixing, CH$_4$ fluxes, ocean
solubility, and mantle/crust properties strongly affect NPP and surface O$_2$
fluxes. Regarding exoplanets, different ""states"" of O$_2$ could exist for
similar biomass output. Strong geological activity could lead to false
negatives for life.",1807.06844v1
2018-08-15,Retrieval of nitric oxide in the mesosphere from SCIAMACHY nominal limb spectra,"We present a retrieval algorithm for nitric oxide (NO) number densities from
measurements from the SCanning Imaging Absorption spectroMeter for Atmospheric
CHartographY (SCIAMACHY, on Envisat) nominal limb mode (0--91 km). The NO
number densities are derived from atmospheric emissions in the gamma bands in
the range 230--300 nm, measured by the SCIAMACHY ultra-violet (UV) channel 1.
The retrieval is adapted from the mesosphere and lower thermosphere mode (MLT,
50--150 km) NO retrieval (Bender et al., 2013, arXiv:1808.02388), including the
same 3-D ray tracing, 2-D retrieval grid, and regularisations with respect to
altitude and latitude.
  Since the nominal mode limb scans extend only to about 91 km, we use NO
densities in the lower thermosphere (above 92 km), derived from empirical
models, as a priori input. The priors are the Nitric Oxide Empirical Model
(NOEM; Marsh et al., 2004) and a regression model derived from the MLT NO data
comparison (Bender et al., 2015). Our algorithm yields plausible NO number
densities from 60 to 85 km from the SCIAMACHY nominal limb mode scans. Using a
priori input substantially reduces the incorrect attribution of NO from the
lower thermosphere, where no direct limb measurements are available. The
vertical resolution lies between 5 and 10 km in the altitude range 65--80 km.
  Analysing all SCIAMACHY nominal limb scans provides almost 10 years (from
August 2002 to April 2012) of daily NO measurements in this altitude range.
This provides a unique data record of NO in the upper atmosphere and is
invaluable for constraining NO in the mesosphere, in particular for testing and
validating chemistry climate models during this period.",1808.04993v1
2018-08-20,Anisotropic spin-orbit torque generation in epitaxial SrIrO3 by symmetry design,"Spin-orbit coupling (SOC), the interaction between the electron spin and the
orbital angular momentum, can unlock rich phenomena at interfaces, in
particular interconverting spin and charge currents. Conventional heavy metals
have been extensively explored due to their strong SOC of conduction electrons.
However, spin-orbit effects in classes of materials such as epitaxial
5d-electron transition metal complex oxides, which also host strong SOC, remain
largely unreported. In addition to strong SOC, these complex oxides can also
provide the additional tuning knob of epitaxy to control the electronic
structure and the engineering of spin-to-charge conversion by crystalline
symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque
on a ferromagnet with extremely high efficiency via the spin-Hall effect in
epitaxial metastable perovskite SrIrO3. We first predict a large intrinsic
spin-Hall conductivity in orthorhombic bulk SrIrO3 arising from the Berry
curvature in the electronic band structure. By manipulating the intricate
interplay between SOC and crystalline symmetry, we control the spin-Hall torque
ratio by engineering the tilt of the corner-sharing oxygen octahedra in
perovskite SrIrO3 through epitaxial strain. This allows the presence of an
anisotropic spin-Hall effect due to a characteristic structural anisotropy in
SrIrO3 with orthorhombic symmetry. Our experimental findings demonstrate the
heteroepitaxial symmetry design approach to engineer spin-orbit effects. We
therefore anticipate that these epitaxial 5d transition-metal oxide thin films
can be an ideal building block for low-power spintronics.",1808.06650v1
2018-12-10,"Graphene oxide membranes: on the absence of ""graphene capillaries"", ""ultrafast flow"" rate and ""ultraprecise sieving""","The data by Q.Yang et al suggest absence of ""ultrafast flow"" of solvent
across graphene oxide (GO) membranes. The ""ultrafast flow"" is result of using
unrealistic geometrical model with close packed hole-free micrometer sized GO
flakes providing only 0.1 % of area in each layer available for permeation. The
data by Q.Yang et all demonstrate that at least 3-5 % of total layer area are
available for permeation in real GO membranes due to holes between irregularly
shaped flakes. At least 2-3 percent of area also needs to be added to the
permeation cross section due to holes and cracks in GO flakes, especially
abundant due to prolonged sonication of dispersions. Permeation of solutions
mostly through pinholes penetrating tens of GO layers suggests that ""graphene
capillaries"" are not required to explain water flow across the membrane. Taking
into account realistic packing of GO flakes with holes between the flakes and
across the flakes, 2-3 orders of magnitude shorter permeation path should be
formed. Considering shorter zigzag permeation path between GO sheets and 5-10 %
of area in each layer available for permeation due to holes across and between
GO flakes, permeation rates across GO membranes can be explained by trivial
diffusion. In absence of ""graphene capillaries"", the ""ultra-precise sieving""
related to ""cutoff"" value of 4.5 \AA{} (hydration diameter) provided by
""graphene capillaries"" has little meaning. As it is well known from earlier
studies and now demonstrated by Q.Yang et al using their own samples the
swelling of GO membranes is different for different solutions, depends on
concentration of solutes and results in delamination in many solutions. Q.Yang
et al provide controversial data for stability of their GO membranes in water
citing use of surfactant to prevent dissolving. Oxidation state of GO membranes
remains to be unknown due to incorrect analysis of XPS spectra.",1812.03941v1
2019-01-15,"Dust-depletion sequences in damped Ly-α absorbers II. The composition of cosmic dust, from low-metallicity systems to the Galaxy","We aim at assessing what are the most dominant dust species or types,
including silicate and iron oxide grains present in the ISM, by using recent
observations of dust depletion of galaxies at various evolutionary stages. We
use the observed elemental abundances in dust of several metals (O, S, Si, Mg,
and Fe) in different environments, considering systems with different
metallicities and dust content, namely damped Lyman-{\alpha} absorbers (DLAs)
towards quasars and the Galaxy. We derive a possible dust composition by
computationally finding the statistically expected elemental abundances in dust
assuming a set of key dust species with the iron content as a free parameter.
Carbonaceous dust is not considered in the present study. Metallic iron (likely
in the form of inclusions in silicate grains) and iron oxides is an important
component of the mass composition of carbon-free dust. Iron oxides make up a
significant mass fraction (~1/4 in some cases) of the oxygen-bearing dust and
there are good reasons to believe that metallic iron constitutes a similar mass
fraction of dust. W\""ustite (FeO) could be a simple explanation for the
depletion of iron and oxygen because it is easily formed. There appears to be
no silicate species clearly dominating the silicate mass, but rather a mix of
iron-poor as well as iron-rich olivine and pyroxene. To what extent sulphur
depletion is due to sulfides remains unclear. In general, there seems to be
little evolution of the dust composition (not considering carbonaceous dust)
from low-metallicity systems to the Galaxy.",1901.04710v3
2019-02-05,Reduction and simultaneous doping of graphene oxide to repel LDL in treatment of atherosclerosis disease,"Atherosclerotic disease develops when there is endothelial dysfunction,
making low density lipoproteins (LDL) which are cholesterol carriers traveling
in the blood, very likely to penetrate the endothelium layer triggering the
formation of the atheromatous plaque and leading to the obstruction of blood
vessels. For some time now, devices called stents have been used to re-open the
light of the plugged artery, allowing the restoration of blood flow. However,
this treatment has disadvantages like developing intra-stent restenosis and
progression of the atherosclerosis, clogging the blood vessel again. For these
reasons it is necessary to develop new materials and strategies focused on the
prevention and correction of this pathology and its subsequent complications.
In the present work, a reduction and in situ nitrogen doping method in graphene
oxide (N-rGO) was studied. By means of XPS a 9.57% at of nitrogen doping was
demonstrated and was found that the pyrrole type nitrogen is predominant. Due
to nitrogen doping and pyrrolic sites, the N-rGO surface reached high levels of
negative electric charge, which was verified by Electrostatic Force Microscopy
(EFM) and wettability tests between the LDL at different oxidation levels and
the synthesized N-rGO; contact angles between 95.7{\deg} and 130.4{\deg} were
obtained which indicates repulsion between both materials. The N-rGO was also
characterized by SEM and TEM where a wrinkled morphology typical of this type
of material was observed and the hexagonal atomic arrangement of GO is
distinguished. Finally, cell viability tests using
3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay were
carried out on human umbilical cord endothelial cells (HUVEC) to analyze the
cellular response at different concentrations of N-rGO, obtaining favorable
behavior up to concentrations of 100 ({\mu}g/mL).",1902.01850v1
2019-03-03,Topological phases in pyrochlore thallium niobate Tl$_2$Nb$_2$O$_{6+x}$,"The discovery of new topological electronic materials brings a chance to
uncover novel physics and plays a key role in observing and controlling various
intriguing phenomena. Up to now, many materials have been theoretically
proposed and experimentally proved to host different kinds of topological
states. Unfortunately, there is little convincing experimental evidence for the
existence of topological oxides. The reason is that oxidation of oxygen leads
to ionic crystal in general and makes band inversion unlikely. In addition, the
realization of different topological states in a single material is quite
difficult, but strongly needed for exploring topological phase transitions. In
this work, using first-principles calculations and symmetry analysis, we
propose that the experimentally tunable continuous solid solution of oxygen in
pyrochlore Tl$_2$Nb$_2$O$_{6+x}$ ($ 0\leq x \leq 1.0$) leads to various
topological states. Topological insulator, Dirac semimetal and triply
degenerate nodal point semimetal can be realized in it via changing the oxygen
content and/or tuning the crystalline symmetries. When $x = 1$, it is a
semimetal with quadratic band touching point at Fermi level. It transits into a
Dirac semimetal or a topological insulator depending on the in-plane strain.
When $x = 0.5$, the inversion symmetry is spontaneously broken in
Tl$_2$Nb$_2$O$_{6.5}$, leading to triply degenerate nodal points. When $x = 0$,
Tl$_2$Nb$_2$O$_6$ becomes a trivial insulator with a narrow band gap. These
topological phase transitions driven by solid solution of oxygen are unique and
physically plausible due to the variation of valence state of $Tl^{1+}$ and
$Tl^{3+}$. This topological oxide will be promising for studying correlation
induced topological states and potential applications.",1903.00891v4
2019-03-14,Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films,"We have investigated by spectroscopic ellipsometry (SE, 190-1700 nm) the
optical properties of uniform, amorphous thin films of Ta2O5 and Nb2O5 as
deposited and after annealing, and after so-called ""doping"" with Ti atoms which
leads to mixed oxides. Ta2O5 and Ti:Ta2O5 are currently used as high-index
components in Bragg reflectors for Gravitational Wave Detectors. Parallel to
the optical investigation, we measured the mechanical energy dissipation of the
same coatings, through the so-called ""loss angle"" phi = Q^-1, which quantifies
the energy loss in materials. By applying the well-known Cody-Lorentz model in
the analysis of SE data we have been able to derive accurate information on the
fundamental absorption edge through important parameters related to the
electronic density of states, such as the optical gap (E_g) and the energy
width of the exponential Urbach tail (the Urbach energy E_U). We have found
that E_U is neatly reduced by suitable annealing as is also perceptible from
direct inspection of SE data. Ti-doping also points to a minor decrease of E_U.
The reduction of E_U parallels a lowering of the mechanical losses quantified
by the loss angle phi. The correlation highlights that both the electronic
states responsible of Urbach tail and the internal friction are sensitive to a
self-correlation of defects on a medium-range scale, which is promoted by
annealing and in our case, to a lesser extent, by doping. These observations
may contribute to a better understanding of the relationship between structural
and mechanical properties in amorphous oxides.",1903.06094v5
2019-11-01,Which oxidation state of uranium and thorium as point defects in xenotime is favorable?,"Relativistic study of xenotime, YPO$_4$, containing atoms thorium and uranium
as point defects is performed in the framework of cluster model with using the
compound-tunable embedding potential (CTEP) method proposed by us recently. The
Y-(PO$_4$)$_6$-Y'$_{22}$-O'$_{104}$ cluster for xenotime is considered, in
which central part, [Y-(PO$_4$)$_6$]$^{-15}$, is the main cluster, whereas
outermost 22 atoms of yttrium and 104 atoms of oxygen are treated as its
environment and compose electron-free CTEP with the total charge of $+15$. The
P and O atoms of the orthophosphate groups nearest to the central Y atom are
treated at all-electron level. The central Y, its substitutes, Th and U,
together with environmental Y atoms are described within different versions of
the generalized relativistic pseudopotential method. Correctness of our cluster
and CTEP models, constructed in the paper, is justified by comparing the Y-O
and P-O bond lengths with corresponding periodic structure values of the \ypo4
crystal, both experimental and theoretical. Using this cluster model, chemical
properties of solitary point defects, X = U, Th, in xenotime are analyzed. It
has been shown that the oxidation state ${+3}$ is energetically more profitable
than ${+4}$ not only for thorium but for uranium as well ($\Delta E \approx 5$
eV) despite the notably higher ionic radius of U$^{+3}$ compared to Y$^{+3}$,
whereas ionic radii of U$^{+4}$ and Y$^{+3}$ are close. This leads to notable
local deformation of crystal geometry around the U$^{+3}$ impurity in xenotime
and contradicts to widespread opinion about favorite oxidation state of uranium
in such kind of minerals.",1911.00365v3
2020-06-16,Electromagnetic Duality and D3-Brane Scattering Amplitudes Beyond Leading Order,"We use on-shell methods to study the non-supersymmetric and supersymmetric
low-energy S-matrix on a probe D3-brane, including both the 1-loop
contributions of massless states as well as the effects of higher-derivative
operators. Our results include: (1) A derivation of the duality invariance of
Born-Infeld electrodynamics as the dimensional oxidation of the group of
spatial rotations transverse to a probe M2-brane; this is done using a novel
implementation of subtracted on-shell recursion. (2) The first explicit
loop-level BCJ double-copy in a non-gravitational model, namely the calculation
of the 4-point self-dual amplitude of non-supersymmetric Born-Infeld. (3) From
previous results for $n$-point self-dual 1-loop BI amplitudes and the
conjectured dimension-shifting relations in Yang-Mills, we obtain an explicit
all-multiplicity, at all orders in $\epsilon$, expression for the 1-loop
integrand of the MHV sector of $\mathcal{N}=4$ DBI. (4) For all $n>4$, the
explicitly integrated duality-violating 1-loop amplitudes (self-dual and
next-to-self-dual in pure BI as well as MHV in $\mathcal{N}=4$ DBI) are shown
to be removable at $\mathcal{O}(\epsilon^0)$ by adding finite local
counterterms; we propose that this may be true more generally at 1-loop order.
(5) We find that in non-supersymmetric Born-Infeld, not all finite local
counterterms needed to restore electromagnetic duality can be constructed using
the double-copy with higher-derivative corrections, suggesting a fundamental
tension between electromagnetic duality and color-kinematics duality at
loop-level. Finally we comment on oxidation of duality symmetries in
supergravity and the parallels it has to the M2-brane to D3-brane oxidation
demonstrated in this paper.",2006.08928v3
2020-08-19,Role of Catalyst Support and Regioselectivity of Molecular Adsorption on a Metal Oxide Surface: NO Reduction on Cu/γ-alumina,"The role of catalyst support and regioselectivity of molecular adsorption on
a metal oxide surface is investigated for the NO reduction on a
Cu/{\gamma}-alumina heterogeneous catalyst. For the solid surface,
computational models of the {\gamma}-alumina surface are constructed based on
the Step-by-Step Hydrogen Termination (SSHT) approach. Dangling bonds, which
appear by cutting the crystal structure of a model, are terminated stepwise
with H atoms until the model has an appropriate energy gap. The obtained SSHT
models exhibit the realistic infrared (IR) and ultraviolet-visible (UV/Vis)
spectra. Vibronic coupling density (VCD), as a reactivity index, is employed to
elucidate the regioselectivity of the Cu adsorption on the {\gamma}-alumina and
that of the NO adsorption on the Cu/{\gamma}-alumina in place of the frontier
orbital theory that could not provide clear results. We discovered that the
highly dispersed Cu atoms are loaded on Lewis-basic O atoms, which is known as
anchoring effect, located in the tetrahedral sites of the {\gamma}-alumina
surface. The role of the {\gamma}-alumina support is to raise the frontier
orbital of the Cu catalyst, which in turn gives rise to the electron
back-donation from the Cu/{\gamma}-alumina to NO. In addition, the penetration
of the VCD distribution of the Cu/{\gamma}-alumina into the {\gamma}-alumina
support indicates that the excessive reaction energies dissipate into the
support after the NO adsorption and reduction. In other words, the support
plays the role of a heat bath. The NO reduction on the Cu/{\gamma}-alumina
proceeds even in an oxidative atmosphere because the Cu-NO bond is strongly
bounded compared to the Cu-O2 bond.",2008.08329v1
2020-09-07,Giant Polarization and Abnormal Flexural Deformation in Bent Freestanding Perovskite Oxides,"Recent realizations of ultrathin freestanding perovskite oxides offer a
unique platform to probe novel properties in two-dimensional oxides. Here, we
observed a giant flexoelectric response in freestanding BiFeO3 and SrTiO3 in
their bent state arising from strain gradients up to 4x10e7/m, suggesting a
promising approach for realizing extremely large polarizations. Additionally, a
substantial reversible change in thickness was discovered in bent freestanding
BiFeO3, which implies an unusual bending-expansion/shrinkage and
thickness-dependence Poisson's ratios in this ferroelectric membrane that has
never been seen before in crystalline materials. Our theoretical modeling
reveals that this unprecedented flexural deformation within the membrane is
attributable to a flexoelectricity-piezoelectricity interplay. The finding
unveils intriguing nanoscale electromechanical properties and provides guidance
for their practical applications in flexible nanoelectromechanical systems.",2009.03177v1
2020-09-30,Effect of mantle oxidation state and escape upon the evolution of Earth's magma ocean atmosphere,"The magma ocean period was a critical phase determining how Earth atmosphere
developed into habitability. However there are major uncertainties in the role
of key processes such as outgassing from the planetary interior and escape of
species to space that play a major role in determining the atmosphere of early
Earth. We investigate the influence of outgassing of various species and escape
of H$_2$ for different mantle redox states upon the composition and evolution
of the atmosphere for the magma ocean period. We include an important new
atmosphere-interior coupling mechanism namely the redox evolution of the mantle
which strongly affects the outgassing of species. We simulate the volatile
outgassing and chemical speciation at the surface for various redox states of
the mantle by employing a C-H-O based chemical speciation model combined with
an interior outgassing model. We then apply a line-by-line radiative transfer
model to study the remote appearance of the planet in terms of the infrared
emission and transmission. Finally, we use a parameterized diffusion-limited
and XUV energy-driven atmospheric escape model to calculate the loss of H$_2$
to space. We have simulated the thermal emission and transmission spectra for
reduced or oxidized atmospheres present during the magma ocean period of Earth.
Reduced or thin atmospheres consisting of H$_2$ in abundance emit more
radiation to space and have larger effective height as compared to oxidized or
thick atmospheres which are abundant in H$_2$O and CO$_2$. We obtain the
outgassing rates of H2 from the mantle into the atmosphere to be a factor of
ten times larger than the rates of diffusion-limited escape to space. Our work
presents useful insight into the development of Earth atmosphere during the
magma ocean period as well as input to guide future studies discussing
exoplanetary interior compositions.",2009.14599v2
2020-10-08,Prediction of crystallized phases of amorphous Ta$_2$O$_5$-based mixed oxide thin films using density functional theory calculations,"The genomics approach to materials, heralded by increasingly accurate density
functional theory (DFT) calculations conducted on thousands of crystalline
compounds, has led to accelerated material discovery and property predictions.
However, so far amorphous materials have been largely excluded from this as
these systems are notoriously difficult to simulate. Here we study amorphous
Ta$_2$O$_5$ thin films mixed with Al$_2$O$_3$, SiO$_2$, Sc$_2$O$_3$, TiO$_2$,
ZnO, ZrO$_2$, Nb$_2$O$_5$ and HfO$_2$ to identify their crystalline structure
upon post-deposition annealing in air both experimentally and with simulations.
Using the Materials Project open database, phase diagrams based on DFT
calculations are constructed for the mixed oxide systems and the annealing
process is evaluated via grand potential diagrams with varying oxygen chemical
potential. Despite employing calculations based on crystalline bulk materials,
the predictions agree well with the experimentally observed crystallized phases
of the amorphous films. Only in two cases the database leads to incorrect
predictions: in TiO$_2$-doped Ta$_2$O$_5$ because it does not contain a ternary
compound found experimentally, and in Sc$_2$O$_3$-doped Ta$_2$O$_5$ because DFT
overestimates the formation enthalpy difference between Sc$_2$O$_3$ and
Ta$_2$O$_5$ and thus does not reproduce observed oxygen competition effects. In
the absence of ternary phases, the dopant acts as an amorphizer agent
increasing the thermal stability of Ta$_2$O$_5$. These results show that DFT
calculations can be applied for the prediction of crystallized structures of
annealed amorphous materials. This could pave the way for accelerated
\textit{in silico} material discovery and property predictions using the
powerful genomic approach for amorphous oxide coatings employed in a wide range
of applications such as optical coatings, energy storage and electronic
devices.",2010.04036v1
2020-10-27,Predicting Gas-Particle Partitioning Coefficients of Atmospheric Molecules with Machine Learning,"The formation, properties and lifetime of secondary organic aerosols in the
atmosphere are largely determined by gas-particle partitioning coefficients of
the participating organic vapours. Since these coefficients are often difficult
to measure or compute, we developed a machine learning (ML) model to predict
them given molecular structure as input. Our data-driven approach is based on
the dataset by Wang et al. (Atmos. Chem. Phys., 17, 7529 (2017)), who computed
the partitioning coefficients and saturation vapour pressures of 3414
atmospheric oxidation products from the master chemical mechanism using the
COSMOtherm program. We train a kernel ridge regression (KRR) ML model on the
saturation vapour pressure ($P_{sat}$), and on two equilibrium partitioning
coefficients: between a water-insoluble organic matter phase and the gas phase
($K_{WIOM/G}$), and between an infinitely dilute solution with pure water and
the gas phase ($K_{W/G}$). For the input representation of the atomic structure
of each organic molecule to the machine, we test different descriptors. Our
best ML model predicts $P_{sat}$ and $K_{WIOM/G}$ to within 0.3 and $K_{W/G}$
to within 0.4 logarithmic units of the original COSMOtherm calculations. This
is equal or better than the typical accuracy of COSMOtherm predictions compared
to experimental data. We then apply our ML model to a dataset of 35,383
molecules that we generated based on a carbon 10 backbone and functionalized
with 0 to 6 carboxyl, carbonyl or hydroxyl groups to evaluate its performance
for polyfunctional compounds with potentially low $P_{sat}$. The resulting
$P_{sat}$ and partitioning coefficient distributions were physico-chemically
reasonable, and the volatility predictions for the most highly oxidized
compounds were in qualitative agreement with experimentally inferred
volatilities of atmospheric oxidation products with similar elemental
composition.",2010.14207v1
2021-03-25,Synthesis of metallic nanoparticles for heterogeneous catalysis: Application to the Direct Borohydride Fuel Cell,"Until now, the fabrication of electrocatalysts to guarantee long life of fuel
cells and low consumption of noble metals remains a major challenge. The
electrocatalysts based on metals or metal oxides which are used today are
limited by the complexity of their synthesis processes and require several
steps before depositing the catalysts on the substrate. Herein is described a
chemical synthesis process that consists of a single-step synthesis and direct
deposition of catalysts nanoparticles such as gold (Au), palladium (Pd) and
platinum (Pt) in the thickness of a carbon-fibers-based porous transport layer
(PTL). The synthesis process essentially consists of dissolving in the same
PGMEA (Propylene glycol methyl ether acetate) solvent a metal precursor (HAuCl4
or PdNO2 or PtCl4) and a homopolymer PMMA (Polymethylmetacrylate), then the
metal solution is deposited on the surface of the PTL after cleaning. Special
emphasis is made on Pt-based materials. The obtained PTL-supported
nanoparticles were firstly characterized by scanning electron microscopy (SEM)
to evaluate their morphology, and then X-Ray diffraction (XRD) to observe the
crystal phases. To validate the methodology, Pt-coated PTL materials have been
used as anode for the borohydride oxidation reaction (BOR) in a direct
borohydride fuel cell (DBFC) and compared to a state-of-the-art nickel
electrode. There is an optimum loading of platinum (below 0.16 mg Pt/cm2) which
constitutes the best compromise between power density and faradic efficiency
for the borohydride oxidation reaction (BOR). Thanks to this low Pt loading,
hydrogen evolved during the anodic reaction is completely valorized. These
electrodes combine the advantages of high-performance with a very low metal
loading, hence lowering materials cost.",2103.13640v1
2021-05-18,"Effect of In-vitro Heat Stress Challenge on the function of Blood Mononuclear Cells from Dairy Cattle ranked as High, Average and Low Immune Responders","The warming climate is causing livestock to experience heat stress at an
increasing frequency. Holstein cows are particularly susceptible to heat stress
because of their high metabolic rate. Heat stress negatively affects immune
function, particularly with respect to the cell-mediated immune response, which
leads to increased susceptibility to disease. Cattle identified as having
enhanced immune response have lower incidence of disease. Therefore, the
objective of this study was to evaluate the impact of in vitro heat challenge
on blood mononuclear cells from dairy cattle, that had previously been ranked
for immune response, in terms of heat shock protein 70 concentration, nitric
oxide production, and cell proliferation. Bovine blood mononuclear cells, from
Holstein dairy cattle previously ranked for immune response based on their
estimated breeding values, were subjected to three heat treatments:
thermoneutral, heat stress 1 and heat stress 2. Cells of each treatment were
evaluated for heat shock protein 70, cell proliferation and nitric oxide
production. Blood mononuclear cells from dairy cattle classified as high immune
responders, based on their estimated breeding values for antibody and
cell-mediated responses, produced a significantly greater concentration of heat
shock protein 70 under most heat stress treatments compared to average and low
responders, and greater cell-proliferation across all treatments. Similarly, a
trend was observed where high responders displayed greater nitric oxide
production compared to average and low responders across heat treatments.
Overall, these results suggest that blood mononuclear cells from high immune
responder dairy cows are more thermotolerant compared to average and low immune
responders",2105.08801v1
2021-06-21,Enhancing the third-order optical nonlinear performance in CMOS devices with integrated 2D graphene oxide films,"We report enhanced nonlinear optics in complementary metal oxide
semiconductor compatible photonic platforms through the use of layered two
dimensional (2D) graphene oxide (GO) films. We integrate GO films with silicon
on insulator nanowires (SOI), high index doped silica glass (Hydex) and silicon
nitride (SiN) waveguides and ring resonators, to demonstrate an enhanced
optical nonlinearity including Kerr nonlinearity and four wave mixing (FWM).
The GO films are integrated using a large area, transfer free, layer by layer
method while the film placement and size are controlled by photolithography. In
SOI nanowires we observe a dramatic enhancement in both the Kerr nonlinearity
and nonlinear figure of merit (FOM) due to the highly nonlinear GO films. Self
phase modulation (SPM) measurements show significant spectral broadening
enhancement for SOI nanowires coated with patterned films of GO. The dependence
of GO Kerr nonlinearity on layer number and pulse energy shows trends of the
layered GO films from 2D to quasi bulk like behavior. The nonlinear parameter
of GO coated SOI nanowires is increased 16 fold, with the nonlinear FOM
increasing over 20 times to a FOM greater than 5. We also observe an improved
FWM efficiency in SiN waveguides integrated with 2D layered GO films. FWM
measurements for samples with different numbers of GO layers and at different
pump powers are performed, achieving up to 7.3 dB conversion efficiency (CE)
enhancement for a uniformly coated device with 1 layer of GO and 9.1 dB for a
patterned device with 5 layers of GO. These results reveal the strong potential
of GO films to improve the nonlinear optics of silicon, Hydex and SiN photonic
devices.",2106.10779v1
2021-10-15,Retention of water in terrestrial magma oceans and carbon-rich early atmospheres,"Massive steam and CO$_2$ atmospheres have been proposed for magma ocean
outgassing of Earth and terrestrial planets. Yet formation of such atmospheres
depends on volatile exchange with the molten interior, governed by volatile
solubilities and redox reactions. We determine the evolution of magma
ocean--atmosphere systems for a range of oxygen fugacities, C/H ratios and
hydrogen budgets that include redox reactions for hydrogen (H$_2$--H$_2$O),
carbon (CO--CO$_2$), methane (CH$_4$), and solubility laws for H$_2$O and
CO$_2$. We find that small initial budgets of hydrogen, high C/H ratios, and
oxidizing conditions, suppress outgassing of hydrogen until the late stage of
magma ocean crystallization. Hence early atmospheres in equilibrium with magma
oceans are dominantly carbon-rich, and specifically CO-rich except at the most
oxidizing conditions. The high solubility of H$_2$O limits its outgassing to
melt fractions below $\sim$30\%, the fraction at which the mantle transitions
from vigorous to sluggish convection with melt percolation. Sluggish melt
percolation could enable a surface lid to form, trapping water in the interior
and thereby maintaining a carbon-rich atmosphere (equilibrium crystallization).
Alternatively, efficient crystal settling could maintain a molten surface,
promoting a transition to a water-rich atmosphere (fractional crystallization).
However, additional processes, including melt trapping and H dissolution in
crystallizing minerals, further conspire to limit the extent of H outgassing,
even for fractional crystallization. Hence, much of the water delivered to
planets during their accretion can be safely harbored in their interiors during
the magma ocean stage, particularly at oxidizing conditions.",2110.08029v2
2021-11-01,A New Class of Alumina-Forming Superalloy for 3D Printing,"A new class of crack-resistant nickel-based superalloy containing high
$\gamma^\prime$ fraction is studied for the laser-powder bed fusion (L-PBF)
process. The effects of the (Nb+Ta)/Al ratio is emphasised, a strategy that is
shown to confer excellent low-temperature strength whilst maintaining oxidation
resistance at high temperatures via stable alumina scale formation. The
processability of the new alloys is characterised with respect to defect
assessment by micro-focus x-ray computed tomography; use is made of a prototype
turbine blade geometry and the heritage alloy CM247LC as a benchmark. In all
cases, some processing-related porosity is present in thin wall sections such
as the trailing edge, but this can be avoided by judicious processing. The
cracking seen in CM247LC -- in solid-state, liquation and solidification forms
-- is avoided. A novel sub-solvus heat treatment strategy is proposed which
takes advantage of AM not requiring solutioning; super-solvus heat treatment is
inappropriate since it embrittles the material by deterioration of the texture
and coarsening of grain boundary carbides. The tensile strength of the new
superalloy is greatest when the Nb+Ta content is highest and exceeds that of
CM247LC up to $\sim$900$\,$$^\circ$C. The oxidation resistance is best when Al
content is highest, and oxidation-assisted cracking resistance maximized when
the (Nb+Ta)/Al ratio is balanced. In all cases these are equivalent or superior
to that of CM247LC. Nevertheless, the creep resistance of the new alloys is
somewhat inferior to that of CM247LC for which the $\gamma^\prime$, C, and B
contents are higher; this implies a processing/property trade-off which
requires further clarification.",2111.01049v1
2021-11-16,Hydrogen incorporation into amorphous indium gallium zinc oxide thin-film transistors,"Within the subgap of amorphous oxide semiconductors like amorphous indium
gallium zinc oxide (a-IGZO) are donor-like and acceptor-like states that
control the operational physics of optically transparent thin-film transistors
(TFTs). Hydrogen incorporation into the channel layer of a top-gate a-IGZO TFT
exists as an electron donor that causes an observed negative shift in the drain
current-gate voltage ($\mathrm{I_{D} - V_{G}}$) transfer curve turn-on voltage.
Normally, hydrogen is thought to create shallow electronic states just below
the conduction band mobility edge, with the donor ionization state controlled
by equilibrium thermodynamics involving the position of the Fermi level with
respect to the donor ionization energy. However, hydrogen does not behave as a
normal donor as revealed by the subgap density of states (DoS) measured by the
photoconduction response of top-gate a-IGZO TFTs to within 0.3 eV of the CBM
edge. Specifically, the DoS shows a subgap peak above the valence band mobility
edge growing at the same rate that $\mathrm{I_{D} - V_{G}}$ transfer curve
measurements suggest that hydrogen was incorporated into the channel layer.
Such hydrogen donor behavior in a-IGZO is anomalous and can be understood as
follows: Non-bonded hydrogen ionization precedes its incorporation into the
a-IGZO network as a bonded species. Ionized hydrogen bonds to a charged
oxygen-on-an-oxygen-site anion, resulting in the formation of a defect complex
denoted herein as, $\mathrm{{[{O_{O}^{2-}}{H^+}]}^{1-}}$. Formation of an
$\mathrm{{[{O_{O}^{2-}}{H^+}]}^{1-}}$ defect complex creates a spectrally-broad
($\sim$0.3 eV FWHM) distribution of electronic states observed in the bandgap
centered at 0.4 eV above the valence band mobility edge.",2111.08588v1
2021-11-19,Electrochemical reduction of thin graphene-oxide films in aqueous solutions: restoration of conductivity,"Graphene oxide finds applications in different fields of science, including
energy conversion. Electrochemical reduction of graphene oxide (GO)
significantly improves its conductivity. However, the kinetics of this process
depends on the solvent, supporting electrolyte, pH, and numerous other factors.
Most studies report the macroscopic views and ex-situ properties of reduced GO.
To expand the knowledge about GO reduction, in this study, we used cyclic
voltammetry (CV), simultaneous 2 points and 4 points resistance measurement
(s24), conductive atomic force microscopy (AFM), and theoretical calculations.
Using CV, we demonstrated that the choice of supporting electrolyte (KCl or
LiCl) influences the potential range in which electrochemical GO reduction
occurs. The activation energy of this process was estimated to be below 30 kJ
mol-1 in both electrolytes, being significantly lower than that required for
thermal reduction of GO. Simultaneous in situ s24 resistance measurements
suggest that GO films reach a highly conductive state at deep negative
potentials, with an abrupt, irreversible switch from non-conductive to the
conductive state. However, conductive AFM presents a more exact picture of this
process: the reduction of GO films starts locally while the formed conductive
islands grow during the reduction. This mechanism was confirmed by theoretical
calculations indicating that the reduction starts on isolated oxygen-functional
groups over the GO basal plane, while clustered OH groups are more difficult to
reduce. The presented results can help in tailoring reduced GO for a particular
electrochemical application by precisely controlling the reduction degree and
percentage of the conductive area of the reduced GO films.",2111.10081v1
2021-11-22,Chemo-Mechanical Phase-Field Modeling of Iron Oxide Reduction with Hydrogen,"The reduction of iron ore with carbon-carriers is one of the largest sources
of greenhouse gas emissions in the industry, motivating global activities to
replace the coke-based blast furnace reduction by hydrogen-based direct
reduction (HyDR). Iron oxide reduction with hydrogen has been widely
investigated both experimentally and theoretically. The process includes
multiple types of chemical reactions, solid state and defect-mediated diffusion
(by oxygen and hydrogen species), several phase transformations, as well as
massive volume shrinkage and mechanical stress buildup. In this work, a
chemo-mechanically coupled phase-field (PF) model has been developed to explore
the interplay between phase transformation, chemical reaction, species
diffusion, large elasto-plastic deformation and microstructure evolution.
Energetic constitutive relations of the model are based on the system free
energy which is calibrated with the help of a thermodynamic database. The model
has been first applied to the classical core-shell (w\""ustite-iron) structure.
Simulations show that the phase transformation from w\""ustite to alpha-iron can
result in high stress and rapidly decelerating reaction kinetics. Mechanical
stresses can contribute elastic energy to the system, making phase
transformation difficult. Thus slow reaction kinetics and low metallization are
observed. However, if the stress becomes comparatively high, it can shift the
shape of the free energy from a double-well to a single-well case and speed up
the transformation. The model has been further applied to simulate an actual
iron oxide specimen with its complex microstructure, characterized by electron
microscopy. The simulation results show that isolated pores in the
microstructure are filled with water vapor during reduction, an effect which
influences the local reaction atmosphere and dynamics.",2111.11538v1
2021-11-24,Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189b,"The temperature of an atmosphere decreases with increasing altitude, unless a
shortwave absorber exists that causes a temperature inversion. Ozone plays this
role in the Earth`s atmosphere. In the atmospheres of highly irradiated
exoplanets, shortwave absorbers are predicted to be titanium oxide (TiO) and
vanadium oxide (VO). Detections of TiO and VO have been claimed using both low
and high spectral resolution observations, but later observations have failed
to confirm these claims or overturned them. Here we report the unambiguous
detection of TiO in the ultra-hot Jupiter WASP-189b using high-resolution
transmission spectroscopy. This detection is based on applying the
cross-correlation technique to many spectral lines of TiO from 460 to 690 nm.
Moreover, we report detections of metals, including neutral and singly ionised
iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe,
Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species
differ, which we interpret as a consequence of spatial gradients in their
chemical abundances, such that they exist in different regions or dynamical
regimes. This is direct observational evidence for the three-dimensional
thermo-chemical stratification of an exoplanet atmosphere derived from
high-resolution ground-based spectroscopy.",2111.12732v2
2021-12-12,Honeycomb Layered Oxides With Silver Atom Bilayers and Emergence of Non-Abelian SU(2) Interactions,"Honeycomb layered oxides with monovalent or divalent, monolayered cationic
lattices generally exhibit myriad crystalline features encompassing rich
electrochemistry, geometries and disorders, which particularly places them as
attractive material candidates for next-generation energy storage applications.
Herein, we report global honeycomb layered oxide compositions, ${\rm
Ag_2}M_2{\rm TeO_6}$ ($M = \rm Ni, Mg, \textit{etc}.$) exhibiting $\rm Ag$ atom
bilayers with sub-valent states within Ag-rich crystalline domains of ${\rm
Ag_6}M_2{\rm TeO_6}$ and $\rm Ag$-deficient domains of ${\rm Ag}_{2 - x}\rm
Ni_2TeO_6$ ($0 < x < 2$). The $\rm Ag$-rich material characterised by
aberration-corrected transmission electron microscopy reveals local atomic
structural disorders characterised by aperiodic stacking and incoherency in the
bilayer arrangement of $\rm Ag$ atoms. Meanwhile, the global material not only
displays high ionic conductivity, but also manifests oxygen-hole
electrochemistry during silver-ion extraction. Within the $\rm Ag$-rich
domains, the bilayered structure, argentophilic interactions therein and the
expected $\rm Ag$ sub-valent states ($1/2+, 2/3+, \textit{etc}.$) are
theoretically understood via spontaneous symmetry breaking of
SU($2$)$\times$U($1$) gauge symmetry interactions amongst $3$ degenerate
mass-less chiral fermion states, justified by electron occupancy of silver
$4d_{z^2}$ and $5s$ orbitals on a bifurcated honeycomb lattice. This implies
that bilayered frameworks have research applications that go beyond the
confines of energy storage.",2112.07355v7
2021-12-23,"Covalent Organic Functionalization of Graphene Nanosheets and Reduced Graphene Oxide via 1,3-Dipolar Cycloaddition of Azomethine Ylide","Organic functionalization of graphene is successfully performed via
1,3-dipolar cycloaddition of azomethine ylide in the liquid phase. The
comparison between 1-methyl-2-pyrrolidinone and N,N-dimethylformamide as
dispersant solvents, and between sonication and homogenization as dispersion
techniques, proves N,N-dimethylformamide and homogenization as the most
effective choice. The functionalization of graphene nanosheets and reduced
graphene oxide is confirmed using different techniques. Among them,
energy-dispersive X-ray spectroscopy allows to map the pyrrolidine ring of the
azomethine ylide on the surface of functionalized graphene, while micro-Raman
spectroscopy detects new features arising from the functionalization, which are
described in agreement with the power spectrum obtained from ab initio
molecular dynamics simulation. Moreover, X-ray photoemission spectroscopy of
functionalized graphene allows the quantitative elemental analysis and the
estimation of the surface coverage, showing a higher degree of
functionalization for reduced graphene oxide. This more reactive behavior
originates from the localization of partial charges on its surface due to the
presence of oxygen defects, as shown by the simulation of the electrostatic
features. Functionalization of graphene using 1,3-dipolar cycloaddition is
shown to be a significant step towards the controlled synthesis of
graphene-based complex structures and devices at the nanoscale.",2112.12505v1
2022-01-21,Oldhamite: a new link in mantle for C-O-S-Ca cycles and an indicator for planetary habitability,"In the solar system, oldhamite (CaS) is generally considered to be formed by
the condensation of solar nebula gas. Enstatite chondrites, one of the most
important repositories of oldhamite, are believed to be the representative of
the material which formed Earth. Thus, the formation mechanism and the
evolution process of oldhamite are of great significance to the deeply
understanding about the solar nebula, meteorites, the origin of Earth, and the
C-O-S-Ca cycles of Earth. To date, no report about the oldhamite in the mantle
exists. However, here we show the formation of oldhamite through the reaction
between sulfide-bearing orthopyroxenite and molten calcite at 1.5 GPa/1510 K
and 0.5 GPa/1320 K. Surprisingly the oxygen fugacities in our experiments are
within the range of mantle conditions, which is 6 orders of magnitude higher
than that of the solar nebula mechanism. Oldhamite is easily oxidized to
calcium sulfate. Both low oxygen fugacity of magma and extreme low oxygen
content of atmosphere are necessary for existence of oldhamite on the surface
of a planet; otherwise, anhydrite or gypsum will exist in large quantities. The
widespread existence of oldhamite on the planet surface indicates the planet is
definitely not habitable because of the scarcity of oxygen. The formation and
oxidation of oldhamite are accompanied by the production of carbon dioxide and
the consumption of oxygen, which may have an impact on the Earth atmosphere
before the Great Oxidation Event and during the Permian-Triassic Boundary.",2201.08615v7
2022-02-09,General embedded cluster protocol for accurate modeling of oxygen vacancies in metal-oxides,"The O vacancy (Ov) formation energy, $E_\textrm{Ov}$, is an important
property of a metal-oxide, governing its performance in applications such as
fuel cells or heterogeneous catalysis. These defects are routinely studied with
density functional theory (DFT). However, it is well-recognized that standard
DFT formulations (e.g. the generalized gradient approximation) are insufficient
for modeling the Ov, requiring higher levels of theory. The embedded cluster
method offers a promising approach to compute $E_\textrm{Ov}$ accurately,
giving access to all electronic structure methods. Central to this approach is
the construction of quantum(-mechanically treated) clusters placed within
suitable embedding environments. Unfortunately, current approaches to
constructing the quantum clusters either require large system sizes, preventing
application of high-level methods, or require significant manual input,
preventing investigations of multiple systems simultaneously. In this work, we
present a systematic and general quantum cluster design protocol that can
determine small converged quantum clusters for studying the Ov in metal-oxides
with accurate methods such as local coupled cluster with single, double and
perturbative triple excitations [CCSD(T)]. We apply this protocol to study the
Ov in the bulk and surface planes of rutile TiO2 and rocksalt MgO, producing
the first accurate and well-converged determinations of $E_\textrm{Ov}$ with
this method. These reference values are used to benchmark exchange-correlation
functionals in DFT and we find that all studied functionals underestimate
$E_\textrm{Ov}$, with the average error decreasing along the rungs of Jacob's
ladder. This protocol is automatable for high-throughput calculations and can
be generalized to study other point defects or adsorbates.",2202.04633v2
2022-02-17,Advances in honeycomb layered oxides: Part II -- Theoretical advances in the characterisation of honeycomb layered oxides with optimised lattices of cations,"The quest for a successful condensed matter theory that incorporates
diffusion of cations, whose trajectories are restricted to a
honeycomb/hexagonal pattern prevalent in honeycomb layered materials is
ongoing, with the recent progress discussed herein focusing on symmetries,
topological aspects and phase transition descriptions of the theory. Such a
theory is expected to differ both qualitatively and quantitatively from 2D
electron theory on static carbon lattices, by virtue of the dynamical nature of
diffusing cations within lattices in honeycomb layered materials. Herein, we
have focused on recent theoretical progress in the characterisation of
pnictogen- and chalcogen-based honeycomb layered oxides with emphasis on
hexagonal/honeycomb lattices of cations. Particularly, we discuss the link
between Liouville conformal field theory to expected experimental results
characterising the optimal nature of the honeycomb/hexagonal lattices in
congruent sphere packing problems. The diffusion and topological aspects are
captured by an idealised model, which successfully incorporates the duality
between the theory of cations and their vacancies. Moreover, the rather
intriguing experimental result that a wide class of silver-based layered
materials form stable Ag bilayers, each comprising a pair of triangular
sub-lattices, suggests a bifurcation mechanism for the Ag triangular
sub-lattices, which ultimately requires conformal symmetry breaking within the
context of the idealised model, resulting in a cation monolayer-bilayer phase
transition. Other relevant experimental, theoretical and computational
techniques applicable to the characterisation of honeycomb layered materials
have been availed for completeness.",2202.10323v5
2022-03-16,Developing a Chemical and Structural Understanding of the Surface Oxide in a Niobium Superconducting Qubit,"Superconducting thin films of niobium have been extensively employed in
transmon qubit architectures. Although these architectures have demonstrated
remarkable improvements in recent years, further improvements in performance
through materials engineering will aid in large-scale deployment. Here, we use
information retrieved from secondary ion mass spectrometry and electron
microscopy to conduct a detailed assessment of the surface oxide that forms in
ambient conditions for transmon test qubit devices patterned from a niobium
film. We observe that this oxide exhibits a varying stoichiometry with NbO and
NbO$_2$ found closer to the niobium film and Nb$_2$O$_5$ found closer to the
surface. In terms of structural analysis, we find that the Nb$_2$O$_5$ region
is semicrystalline in nature and exhibits randomly oriented grains on the order
of 1-2 nm corresponding to monoclinic N-Nb$_2$O$_5$ that are dispersed
throughout an amorphous matrix. Using fluctuation electron microscopy, we are
able to map the relative crystallinity in the Nb$_2$O$_5$ region with nanometer
spatial resolution. Through this correlative method, we observe that amorphous
regions are more likely to contain oxygen vacancies and exhibit weaker bonds
between the niobium and oxygen atoms. Based on these findings, we expect that
oxygen vacancies likely serve as a decoherence mechanism in quantum systems.",2203.08710v3
2022-05-24,Laser-induced crystallization of copper oxide thin films: A comparison made between Gaussian and chevron-beam profiles provides a clue for the failure of Gaussian-beam profile,"The use of laser with a Gaussian-beam profile is frequently adopted in
attempts of crystallizing non-single-crystal thin films; however, it merely
results in the formation of poly-crystal thin films. In this paper, selective
area crystallization of non-single-crystal copper(II) oxide (CuO) is described.
The crystallization is induced by laser, laser-induced crystallization, with a
beam profile in the shape of chevron. The crystallization is verified by the
exhibition of a transition from a non-single-crystal phase consisting of small
100 nm x 100 nm grains of CuO to a single-crystal phase of copper(I) oxide
(Cu2O). The transition is identified by electron back scattering diffraction
and Raman spectroscopy, which clearly suggests that a single-crystal domain of
Cu2O with size as large as 5 {\mu}m x 1 mm develops. Provided these
experimental findings, a theoretical assessment based on a cellular automaton
model, with the behaviors of localized recrystallization and stochastic
nucleation, is developed. The theoretical assessment can qualitatively describe
the laser beam geometry-dependence of vital observable features (e.g., size and
gross geometry of grains) in the laser-induced crystallization. The theoretical
assessment predicts that differences in resulting crystallinity, either
single-crystal or poly-crystal, primarily depend on a geometrical profile with
which melting of non-single-crystal regions takes place along the laser scan
direction; concave-trailing profiles yield larger grains which lead to
single-crystal while convex-trailing profiles results in smaller grains which
lead to poly-crystal, casting light on the fundamental question Why does a
chevron-beam profile succeed in producing single-crystal while a Gaussian-beam
profile fails?",2206.02532v1
2022-06-27,Effect of cationic chemical disorder on defect formation energies in uranium-plutonium mixed oxides,"At the atomic scale, uranium-plutonium mixed oxides (U,Pu)O_2 are
characterized by cationic chemical disorder, which entails that U and Pu
cations are randomly distributed on the cation sublattice. In the present work,
we study the impact of disorder on point-defect formation energies in (U,Pu)O_2
using interatomic-potential and Density Functional Theory (DFT+U) calculations.
We focus on bound Schottky defects (BSD) that are among the most stable defects
in these oxides. As a first step, we estimate the distance R_D around the BSD
up to which the local chemical environment significantly affects their
formation energy. To this end, we propose an original procedure in which the
formation energy is computed for several supercells at varying levels of
disorder. We conclude that the first three cation shells around the BSD have a
non-negligible influence on their formation energy (R_{D} = 7.0 \{AA}). We
apply then a systematic approach to compute the BSD formation energies for all
the possible cation configurations on the first and second nearest neighbor
shells around the BSD. We show that the formation energy can range in an
interval of 0.97 eV, depending on the relative amount of U and Pu neighboring
cations. Based on these results, we propose an interaction model that describes
the effect of nominal and local composition on the BSD formation energy.
Finally, the DFT+U benchmark calculations show a satisfactory agreement for
configurations characterized by a U-rich local environment, and a larger
mismatch in the case of a Pu-rich one. In summary, this work provides valuable
insights on the properties of BSD defects in (U,Pu)O_2, and can represent a
valid strategy to study point defect properties in disordered compounds.",2206.13150v1
2022-06-20,An Investigation into the $HfO_2/Si$ Interface: Materials Science Challenges and their Effects on MOSFET Device Performance,"Since the 1960's when Gordon Moore proposed that the transistor density in
our electronic devices should double every two years while the cost is halved,
the semiconductor industry has taken this statement to heart. Over the last few
decades, no other industry has seen growth even comparably close to that
experienced by the semiconductors industry. This has all been made possible by
the unbroken string of ingenious breakthroughs by brilliant minds that have
been working tirelessly to shrink down transistors. The latest of which is the
use of high-k dielectrics and a return to metal gates combined with
3D-transistor architectures. This has been the enabling technology for the
transition from the 90 nm node to the 45 nm node, allowing us to shrink our
transistors further without losing additional gate control. The fundamental
reason for using a high-k gate dielectric compared to SiO2 is that shrinking
our gate oxide further, which is already at a few angstroms, is no longer a
feasible option to gain additional gate control. High-k dielectric overcome
this by exploiting the fundamental physics of capacitors and the materials
science of dielectrics to provide a viable option to increase gate control
without the need for successively thinner gate oxides. Hafnium Oxide is the
most studied and popular of such materials. Its high dielectric constant ~16-25
and interface stability with silicon at operating temperatures make it an ideal
candidate for use in current CMOS technology. Despite its deceivingly simple
appearance, the processes involved in the fabrication of such high-k HfO2/Si
interfaces are full of process subtleties and nuances. In this term paper we
hope to explore the physics and materials science of these high-k HfO2/Si
interfaces, discussing the challenges and ways to overcome them when it comes
to its actual fabrication, and how this ultimately affects our device
performance.",2207.13054v1
2022-08-01,"Sustainable steel through hydrogen plasma reduction of iron ore: process, kinetics, microstructure, chemistry","Fe- and steelmaking is the largest single industrial CO2 emitter, accounting
for 6.5% of all CO2 emissions on the planet. This fact challenges the current
technologies to achieve carbon-lean steel production and to align with the
requirement of a drastic reduction of 80% in all CO2 emissions by around 2050.
Thus, alternative reduction technologies have to be implemented for extracting
iron from its ores. The H-based direct reduction has been explored as a
sustainable route to mitigate CO2 emissions, where the reduction kinetics of
the intermediate oxide product FexO wustite into Fe is the rate-limiting step
of the process. The total reaction has an endothermic net energy balance.
Reduction based on a H plasma may offer an attractive alternative. Here, we
present a study about the reduction of hematite using H plasma. The evolution
of both, chemical composition and phase transformations was investigated in
several intermediate states. We found that hematite reduction kinetics depends
on the balance between the initial input mass and the arc power. For an
optimized input mass-arc power ratio, complete reduction was obtained within 15
min of exposure to the H plasma. The wustite reduction is also the
rate-limiting step towards complete reduction. Nonetheless, the reduction
reaction is exothermic, and its rates are comparable with those found in
H-based direct reduction. Chemical and microstructure analysis revealed that
the gangue elements partition to the remaining oxide regions, probed by energy
dispersive spectroscopy and atom probe tomography. Si-enrichment was observed
in the interdendritic fayalite domains, at the wustite/Fe hetero-interfaces and
in the primarily solidified oxide particles inside the Fe. With proceeding
reduction, however, such elements are gradually removed from the samples so
that the final iron product is nearly free of gangue-related impurities.",2208.00661v1
2022-09-16,A simple KPFM-based approach for electrostatic-free topographic measurements: the case of MoS$_2$ on SiO$_2$,"A simple implementation of Kelvin probe force microscopy is reported that
enables recording topographic images in the absence of any component of the
electrostatic force. Our approach is based on a close loop z-spectroscopy
operated in data cube mode. Curves of the tip-sample distance as a function of
time are recorded onto a 2D grid. A dedicated circuit holds the KPFM
compensation bias and subsequently cut off the modulation voltage during
well-defined time-windows within the spectroscopic acquisition. Topographic
images are recalculated from the matrix of spectroscopic curves. This approach
is applied to the case of transition metal dichalcogenides (TMD) monolayers
grown by chemical vapour deposition on silicon oxide substrates. In addition,
we check to what extent a proper stacking height estimation can also be
performed by recording series of images for decreasing values of the bias
modulation amplitude. The outputs of both approaches are shown to be fully
consistent. The results exemplify how in the operating conditions of
non-contact AFM under ultra-high vacuum, the stacking height values can
dramatically be overestimated due to variations in the tip-surface capacitive
gradient, even though the KPFM controller nullifies the potential difference.
We show that the number of atomic layers of a TMD can be safely assessed, only
if the KPFM measurement is performed with a modulated bias amplitude reduced at
its strict minimum or, even better, without any modulated bias. Last, the
spectroscopic data reveal that defects at the TMD/oxide interface can have a
counterintuitive impact on the electrostatic landscape, resulting in an
apparent decrease of the measured stacking height by conventional nc-AFM/KPFM
compared to non-defective sample areas. Hence, electrostatic free z-imaging
proves to be a promising tool to assess the existence of defects in atomically
thin TMD layers grown on oxides",2209.07925v1
2022-09-26,Lightning-induced chemistry on tidally-locked Earth-like exoplanets,"Determining the habitability and interpreting atmospheric spectra of
exoplanets requires understanding their atmospheric physics and chemistry. We
use a 3-D Coupled Climate-Chemistry Model, the Met Office Unified Model with
the UK Chemistry and Aerosols framework, to study the emergence of lightning
and its chemical impact on tidally-locked Earth-like exoplanets. We simulate
the atmosphere of Proxima Centauri b orbiting in the Habitable Zone of its
M-dwarf star, but the results apply to similar M-dwarf orbiting planets. Our
chemical network includes the Chapman ozone reactions and hydrogen oxide
(HO$_{\mathrm{x}}$=H+OH+HO$_2$) and nitrogen oxide
(NO$_{\mathrm{x}}$=NO+NO$_2$) catalytic cycles. We find that photochemistry
driven by stellar radiation (177-850 nm) supports a global ozone layer between
20-50 km. We parameterise lightning flashes as a function of cloud-top height
and the resulting production of nitric oxide (NO) from the thermal
decomposition of N$_2$ and O$_2$. Rapid dayside convection over and around the
substellar point results in lightning flash rates of up to 0.16 flashes
km$^{-2}$yr$^{-1}$, enriching the dayside atmosphere below altitudes of 20 km
in NO$_{\mathrm{x}}$. Changes in dayside ozone are determined mainly by UV
irradiance and the HO$_{\mathrm{x}}$ catalytic cycle. ~45% of the planetary
dayside surface remains at habitable temperatures (T$_{\mathrm{surf}}$>273.15
K) and the ozone layer reduces surface UV radiation levels to 15%.
Dayside-nightside thermal gradients result in strong winds that subsequently
advect NO$_{\mathrm{x}}$ towards the nightside, where the absence of
photochemistry allows NO$_{\mathrm{x}}$ chemistry to involve reservoir species.
Our study also emphasizes the need for accurate UV stellar spectra to
understand the atmospheric chemistry of exoplanets.",2209.12502v1
2022-09-27,Investigating the Electronic Structure of Prospective Water-splitting Oxide BaCe$_{0.25}$Mn$_{0.75}$O$_{3-δ}$ Before and After Thermal Reduction,"BaCe$_{0.25}$Mn$_{0.75}$O$_{3-\delta}$ (BCM), a non-stoichiometric oxide
closely resembling a perovskite crystal structure, has recently emerged as a
prospective contender for application in renewable energy harvesting by solar
thermochemical hydrogen generation. Using solar energy, oxygen-vacancies can be
created in BCM and the reduced crystal so obtained can, in turn, produce H2 by
stripping oxygen from H2O. Therefore, a first step toward understanding the
working mechanism and optimizing the performance of BCM, is a thorough and
comparative analysis of the electronic structure of the pristine and the
reduced material. In this paper, we probe the electronic structure of BCM using
the combined effort of first-principles calculations and experimental O K-edge
x-ray absorption spectroscopy (XAS). The computed projected density-of-states
(PDOS) and orbital-plots are used to propose a simplified model for
orbital-mixing between the oxygen and the ligand atoms. With the help of
state-of-the-art simulations, we are able to find the origins of the XAS peaks
and to categorize them on the basis of contribution from Ce and Mn. For the
reduced crystal, the calculations show that, as a consequence of dielectric
screening, the change in electron-density resulting from the reduction is
strongly localized around the oxygen vacancy. Our experimental studies reveal a
marked lowering of the first O K-edge peak in the reduced crystal which is
shown to result from a diminished O-2p contribution to the frontier unoccupied
orbitals, in accordance with the tight-binding scheme. Our study paves the way
for investigation of the working-mechanism of BCM and for computational and
experimental efforts aimed at design and discovery of efficient water-splitting
oxides.",2209.13267v1
2023-01-18,Redox evolution of the crystallizing terrestrial magma ocean and its influence on atmosphere outgassing,"Magma oceans are episodes of large-scale melting of the mantle of terrestrial
planets. The energy delivered by the Moon-forming impact induced a deep magma
ocean on the young Earth, corresponding to the last episode of core-mantle
equilibration. The crystallization of this magma ocean led to the outgassing of
volatiles initially present in the Earth's mantle, resulting in the formation
of a secondary atmosphere. During outgassing, the magma ocean acts as a
chemical buffer for the atmosphere via the oxygen fugacity, set by the
equilibrium between ferrous- and ferric-iron oxides in the silicate melts. By
tracking the evolution of the oxygen fugacity during magma ocean
solidification, we model the evolving composition of a C-O-H atmosphere. We use
the atmosphere composition to calculate its thermal structure and radiative
flux. This allows us to calculate the lifetime of the terrestrial magma ocean.
We find that, upon crystallizing, the magma ocean evolves from a mildly
reducing to a highly oxidized redox state, thereby transiting from a CO- and
H2-dominated atmosphere to a CO2- and H2O-dominated one. We find the overall
duration of the magma ocean crystallization to depend mostly on the bulk H
content of the mantle, and to remain below 1.5 millions years for up to 9
Earth's water oceans' worth of H. Our model also suggests that reduced
atmospheres emit lower infrared radiation than oxidized ones, despite of the
lower greenhouse effect of reduced species, resulting in a longer magma ocean
lifetime in the former case. Although developed for a deep magma ocean on
Earth, the framework applies to all terrestrial planet and exoplanet magma
oceans, depending on their volatile budgets.",2301.07505v1
2023-01-22,Demonstration of the etching cobalt oxide grown on the stainless steel as a base metal surface using F2/He dielectric barrier discharge plasma in atmospheric pressure,"Metal surface cleaning or etching techniques using reactive plasma are
emerging as one of the dry processing techniques for surface contaminants with
high bond energy, especially for cleaning and decontamination of nuclear
components and equipment. In this study, the plasma reaction due to the
discharge of a dielectric barrier of a mixture of 95% helium and 5% fluorine
with cobalt oxide film grown on the surface of stainless steel 304 was studied
experimentally. Experimental results show that cobalt oxide becomes a powder
after plasma irradiation and is easily separated from the surface of the base
metal. The optimal plasma generating conditions of the dielectric barrier
discharge (DBD) used in this experimental study were obtained at atmospheric
pressure, voltage 4.5 kV, and frequency 25 kHz with a etching rate of 10.875
{\mu}mol/min. The samples were analyzed before and after plasma irradiation,
using Scanning electron microscopy with energy dispersive X-ray spectroscopy
(SEM/EDX) and the purification rate was performed using a sequential weighting
of the samples with scales 10^(-4) grams accurately obtained. The results show
the ability of this method to effectively remove the surface contamination of
cobalt from the surface of stainless steel 304.",2301.09065v4
2023-02-23,X-ray projection imaging of metal oxide particles inside gingival tissues,"There is increasing recognition that oral health affects overall health and
systemic diseases. Nonetheless it remains challenging to rapidly screen patient
biopsies for signs of inflammation or the pathogens or foreign materials that
elicit the immune response. This is especially true in conditions such as
foreign body gingivitis (FBG), where the foreign particles are often difficult
to detect. Our long term goal is to establish a method to determine if the
inflammation of the gingival tissue is due to the presence of a metal oxide,
with emphasis on elements that were previously reported in FBG biopsies, such
as silicon dioxide, silica, and titanium dioxide whose persistent presence can
be carcinogenic. In this paper, we proposed to use multiple energy X-ray
projection imaging to detect and to differentiate different metal oxide
particles embedded inside gingival tissues. To simulate the performance of the
imaging system, we have used GATE simulation software to mimic the proposed
system and to obtain images with different systematic parameters. The simulated
parameters include the X-ray tube anode metal, the X-ray spectra bandwidth, the
X-ray focal spot size, the X-ray photon number, and the X-ray dector pixel. We
have also applied the de-noising algorithm to obtain better Contrast-to-noise
ratio (CNR). Our results indicate that it is feasible to detect metal particles
as small as 0.5 micrometer in diameter when we use a Chromium anode target with
an energy bandwidth of 5 keV, an X-ray photon number of 10^8, and an X-ray
detector with a pixel size of 0.5 micrometer and 100 by 100 pixels. We have
also found that different metal particles could be differentiated from the CNR
at four different X-ray anodes and spectra. These encouraging initial results
will guide our future imaging system design.",2302.12310v1
2023-04-24,New compound and hybrid binding energy sputter model for modeling purposes in agreement with experimental data,"Rocky planets and moons experiencing solar wind sputtering are continuously
supplying their enveloping exosphere with ejected neutral atoms. To understand
the quantity and properties of the ejecta, well established Binary Collision
Approximation Monte Carlo codes like TRIM with default settings are used
predominantly. Improved models such as SDTrimSP have come forward and together
with new experimental data the underlying assumptions have been challenged. We
introduce a hybrid model, combining the previous surface binding approach with
a new bulk binding model akin to Hofs\""ass & Stegmaier (2023). In addition, we
expand the model implementation by distinguishing between free and bound
components sourced from mineral compounds such as oxides or sulfides. The use
of oxides and sulfides also enables the correct setting of the mass densities
of minerals, which was previously limited to the manual setting of individual
atomic densities of elements. All of the energies and densities used are
thereby based on tabulated data, so that only minimal user input and no fitting
of parameters are required. We found unprecedented agreement between the newly
implemented hybrid model and previously published sputter yields for incidence
angles up to 45{\deg} from surface normal. Good agreement is found for the
angular distribution of mass sputtered from enstatite MgSiO$_3$ compared to
latest experimental data. Energy distributions recreate trends of experimental
data of oxidized metals. Similar trends are to be expected from future mineral
experimental data. The model thus serves its purpose of widespread
applicability and ease of use for modelers of rocky body exospheres.",2304.12048v1
2023-04-28,A comparison of mechanistic models for the combustion of iron microparticles and their application to polydisperse iron-air suspensions,"Metals can serve as carbon-free energy carriers, e. g. in innovative
metal-metal oxide cycles as proposed by Bergthorson (Prog. Energy Combust.
Sci., 2018). Iron powder is a suitable candidate since it can be oxidized with
air. Nevertheless, the combustion of iron powder in air is challenging
especially with respect to flame stabilization which depends on the particle
size distribution among other factors. Models for the prediction of reaction
front speed in iron-air suspensions can contribute to overcoming this
challenge. To this end, three different models for iron particle oxidation are
integrated into a laminar flame solver for simulating reaction fronts. The
scientific objective of this work is to elucidate the influence of
polydispersity on the reaction front speed, which is still not satisfactorily
understood. In a systematic approach, cases with successively increasing
complexity are considered: From single particle combustion to iron-air
suspensions prescribing binary particle size distributions (PSDs), generic
PSDs, and a PSD measured for a real iron powder sample. The simulations show
that, dependent on the PSD, particles undergo thermochemical conversion in a
sequential manner according to their size and every particle fraction exhibits
an individual combustion environment. The local environment can be leaner or
richer than the overall iron-to-air ratio would suggest and can be very
different from single particle experiments. The contribution of individual
particle fractions to the overall reaction front speed depends on its ranking
within the PSD. The study further demonstrates, that although the three
particle models show good agreement for single particle combustion, they lead
to very different reaction front speeds. This is due to the different ignition
behavior predicted by the particle models, which is shown to strongly influence
the reaction front characteristics.",2304.14927v2
2023-05-22,A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment,"Harvesting organic matter from wastewater is widely applied to maximize
energy recovery; however, it limits the applicability of secondary treatment
for acceptable effluent discharge into surface water bodies. To turn this
bottleneck issue into an opportunity, this study developed oxygen-induced
thiosulfatE production duRing sulfATe reductiOn (EARTO) to provide an efficient
electron donor for wastewater treatment. Typical pretreated wastewater was
synthesized with chemical oxygen demand of 110 mg/L, sulfate of 50 mg S/L, and
varying dissolved oxygen (DO) and was fed into a moving-bed biofilm reactor
(MBBR). The MBBR was operated continuously with a short hydraulic retention
time of 40 min for 349 days. The formation rate of thiosulfate reached
0.12-0.18 g S/(m2.d) with a high produced thiosulfate-S/TdS-S ratio of 38-73%
when influent DO was 2.7-3.6 mg/L. The sludge yield was 0.23-0.29 gVSS/gCOD,
much lower than it was in conventional activated sludge processes. Then, batch
tests and metabolism analysis were conducted to confirm the oxygen effect on
thiosulfate formation, characterize the roles of sulfate and microbial
activities, and explore the mechanism of oxygen-induced thiosulfate formation
in ERATO. Results examined that oxygen supply promoted the
thiosulfate-Sproduced/TdS-Sproduced ratio from 4% to 24-26%, demonstrated that
sulfate and microbial activities were critical for thiosulfate production, and
indicated that oxygen induces thiosulfate formation through two pathways: 1)
direct sulfide oxidation, and 2) indirect sulfide oxidation, sulfide is first
oxidized to S0 (dominant) which then reacts with sulfite derived from
oxygen-regulated biological sulfate reduction. The proposed compact ERATO
process, featuring high thiosulfate production and low sludge production,
supports space- and energy-efficient secondary wastewater treatment.",2305.13343v1
2023-05-30,Monocrystalline Si/$β$-Ga$_2$O$_3$ p-n heterojunction diodes fabricated via grafting,"The $\beta$-Ga$_2$O$_3$ has exceptional electronic properties with vast
potential in power and RF electronics. Despite the excellent demonstrations of
high-performance unipolar devices, the lack of p-type doping in
$\beta$-Ga$_2$O$_3$ has hindered the development of Ga$_2$O$_3$-based bipolar
devices. The approach of p-n diodes formed by polycrystalline p-type oxides
with n-type $\beta$-Ga$_2$O$_3$ can face severe challenges in further advancing
the $\beta$-Ga$_2$O$_3$ bipolar devices due to their unfavorable band alignment
and the poor p-type oxide crystal quality. In this work, we applied the
semiconductor grafting approach to fabricate monocrystalline
Si/$\beta$-Ga$_2$O$_3$ p-n diodes for the first time. With enhanced
concentration of oxygen atoms at the interface of Si/$\beta$-Ga$_2$O$_3$,
double side surface passivation was achieved for both Si and
$\beta$-Ga$_2$O$_3$ with an interface Dit value of 1-3 x 1012 /cm2 eV. A
Si/$\beta$-Ga$_2$O$_3$ p-n diode array with high fabrication yield was
demonstrated along with a diode rectification of 1.3 x 107 at +/- 2 V, a diode
ideality factor of 1.13 and avalanche reverse breakdown characteristics. The
diodes C-V shows frequency dispersion-free characteristics from 10 kHz to 2
MHz. Our work has set the foundation toward future development of
$\beta$-Ga$_2$O$_3$-based transistors.",2305.19138v1
2023-06-22,"Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites","The relative abundances and chemical compositions of the macroscopic
components or ""inclusions"" (chondrules and refractory inclusions) and
fine-grained mineral matrix in chondritic meteorites provide constraints on
astrophysical theories of inclusion formation and chondrite accretion. We
present new techniques for analysis of low count per pixel Si, Mg, Ca, Al, Ti
and Fe x-ray intensity maps of rock sections, and apply them to large areas of
CO and CV chondrites, and the ungrouped Acfer 094 chondrite. For many thousands
of manually segmented and type-identified inclusions, we are able to assess,
pixel-by-pixel, the major element content of each inclusion. We quantify the
total fraction of those elements accounted for by various types of inclusion
and matrix. Among CO chondrites, both matrix and inclusion Mg to Si ratios
approach the solar (and bulk CO) ratio with increasing petrologic grade, but Si
remains enriched in inclusions relative to matrix. The oxidized CV chondrites
with higher matrix-inclusion ratios exhibit more severe aqueous alteration
(oxidation), and their excess matrix accounts for their higher porosity
relative to reduced CV chondrites. Porosity could accommodate an original ice
component of matrix as the direct cause of local alteration of oxidized CV
chondrites. We confirm that major element abundances among inclusions differ
greatly, across a wide range of CO and CV chondrites. These abundances in all
cases add up to near-chondritic (solar) bulk abundance ratios in these
chondrites, despite wide variations in matrix-inclusion ratios and inclusion
sizes: chondrite components are complementary. This ""complementarity"" provides
a robust meteoritic constraint for astrophysical disk models.",2306.12650v2
2023-09-03,A Spin-dependent Machine Learning Framework for Transition Metal Oxide Battery Cathode Materials,"Owing to the trade-off between the accuracy and efficiency,
machine-learning-potentials (MLPs) have been widely applied in the battery
materials science, enabling atomic-level dynamics description for various
critical processes. However, the challenge arises when dealing with complex
transition metal (TM) oxide cathode materials, as multiple possibilities of
d-orbital electrons localization often lead to convergence to different spin
states (or equivalently local minimums with respect to the spin configurations)
after ab initio self-consistent-field calculations, which causes a significant
obstacle for training MLPs of cathode materials. In this work, we introduce a
solution by incorporating an additional feature - atomic spins - into the
descriptor, based on the pristine deep potential (DP) model, to address the
above issue by distinguishing different spin states of TM ions. We demonstrate
that our proposed scheme provides accurate descriptions for the potential
energies of a variety of representative cathode materials, including the
traditional Li$_x$TMO$_2$ (TM=Ni, Co, Mn, $x$=0.5 and 1.0), Li-Ni anti-sites in
Li$_x$NiO$_2$ ($x$=0.5 and 1.0), cobalt-free high-nickel
Li$_x$Ni$_{1.5}$Mn$_{0.5}$O$_4$ ($x$=1.5 and 0.5), and even a ternary cathode
material Li$_x$Ni$_{1/3}$Co$_{1/3}$Mn$_{1/3}$O$_2$ ($x$=1.0 and 0.67). We
highlight that our approach allows the utilization of all ab initio results as
a training dataset, regardless of the system being in a spin ground state or
not. Overall, our proposed approach paves the way for efficiently training MLPs
for complex TM oxide cathode materials.",2309.01146v1
2023-09-03,Oxygen Vacancy Formation Energy in Metal Oxides: High Throughput Computational Studies and Machine Learning Predictions,"The oxygen vacancy formation energy ($\Delta E_{vf}$) governs defect dynamics
and is a useful metric to perform materials selection for a variety of
applications. However, density functional theory (DFT) calculations of $\Delta
E_{vf}$ come at a greater computational cost than the typical bulk calculations
available in materials databases due to the involvement of multiple
vacancy-containing supercells. As a result, available repositories of direct
calculations of $\Delta E_{vf}$ remain relatively scarce, and the development
of machine learning models capable of delivering accurate predictions is of
interest. In the present, work we address both such points. We first report the
results of new high-throughput DFT calculations of oxygen vacancy formation
energies of the different unique oxygen sites in over 1000 different oxide
materials, which together form the largest dataset of directly computed oxygen
vacancy formation energies to date, to our knowledge. We then utilize the
resulting dataset of $\sim$2500 $\Delta E_{vf}$ values to train random forest
models with different sets of features, examining both novel features
introduced in this work and ones previously employed in the literature. We
demonstrate the benefits of including features that contain information
specific to the vacancy site and account for both cation identity and oxidation
state, and achieve a mean absolute error upon prediction of $\sim$0.3 eV/O,
which is comparable to the accuracy observed upon comparison of DFT
computations of oxygen vacancy formation energy and experimental results.
Finally, we demonstrate the predictive power of the developed models in the
search for new compounds for solar-thermochemical water-splitting applications,
finding over 250 new AA$^{\prime}$BB$^{\prime}$O$_6$ double perovskite
candidates.",2309.01160v1
2023-09-05,Non-volatile optical phase shift in ferroelectric hafnium zirconium oxide,"A non-volatile optical phase shifter is a critical component for enabling
large-scale, energy-efficient programmable photonic integrated circuits (PICs)
on a silicon (Si) photonics platform. While ferroelectric materials like BaTiO3
offer non-volatile optical phase shift capabilities, their compatibility with
complementary metal-oxide-semiconductor (CMOS) fabs is limited. Hence, the
search for a novel CMOS-compatible ferroelectric material for non-volatile
optical phase shifting in Si photonics is of utmost importance. Hafnium
zirconium oxide (HZO) is an emerging ferroelectric material discovered in 2011,
which exhibits CMOS compatibility due to the utilization of high-k dielectric
HfO2 in CMOS transistors. Although extensively studied for ferroelectric
transistors and memories, its application in photonics remains relatively
unexplored. Here, we show the optical phase shift induced by ferroelectric HZO
deposited on a SiN optical waveguide. We observed a negative change in
refractive index at a 1.55 um wavelength in the pristine device regardless of
the direction of an applied electric filed. We achieved approximately pi phase
shift in a 4.5-mm-long device with negligible optical loss. The non-volatile
multi-level optical phase shift was confirmed with a persistence of > 10000 s.
This phase shift can be attributed to the spontaneous polarization within the
HZO film along the external electric field. We anticipate that our results will
stimulate further research on optical nonlinear effects, such as the Pockels
effect, in ferroelectric HZO. This advancement will enable the development of
various devices, including high-speed optical modulators. Consequently,
HZO-based programmable PICs are poised to become indispensable in diverse
applications, ranging from optical fiber communication and artificial
intelligence to quantum computing and sensing.",2309.01967v1
2023-10-01,Atomic Insights into the Oxidative Degradation Mechanisms of Sulfide Solid Electrolytes,"Electrochemical degradation of solid electrolytes is a major roadblock in the
development of solid-state batteries, and the formed solid-solid interphase
(SSI) plays a key role in the performance of solid-state batteries. In this
study, by combining experimental X-ray absorption spectroscopy (XAS)
measurements, first-principles simulations, and unsupervised machine learning,
we have unraveled the atomic-scale oxidative degradation mechanisms of sulfide
electrolytes at the interface using the baseline Li3PS4 (LPS) electrolyte as a
model system. The degradation begins with a decrease of Li neighbor affinity to
S atoms upon initial delithiation, followed by the formation of S-S bonds as
the PS4 tetrahedron deforms. After the first delithiation cycle, the PS4 motifs
become strongly distorted and PS3 motifs start to form. Spectral fingerprints
of the local structural evolution are identified, which correspond to the main
peak broadening and the peak shifting to a higher energy by about 2.5 eV in P
K-edge XAS and a new peak emerging at 2473 eV in S K-edge XAS during
delithiation. The spectral fingerprints serve as a proxy for the
electrochemical stability of phosphorus sulfide solid electrolytes beyond LPS,
as demonstrated in argyrodite Li6PS5Cl. We observed that the strong distortion
and destruction of PS4 tetrahedra and the formation of S-S bonds are correlated
with an increased interfacial impedance. To the best of our knowledge, this
study showcases the first atomic-scale insights into the oxidative degradation
mechanism of the LPS electrolyte, which can provide guidance for controlling
macroscopic reactions through microstructural engineering and, more generally,
can advance the rational design of sulfide electrolytes.",2310.00794v1
2023-09-12,"Innovative NiAl Electrodes for Long-Term, Intermediate High-Temperature SAW Sensing Applications Using LiNbO$_3$ Substrates","Wireless SAW reflective delay line (R-DL) technology is very powerful to
carry out remote measurements of various parameters under harsh environments,
while enabling the identification of a given sensor among several of them.
However, R-DL technology is currently limited to 350$^\circ$C for long-term
applications, likely because of aluminium electrodes oxidation and/or congruent
lithium niobate segregation process. In this study, an innovative alloy, namely
NiAl, is investigated as an alternative to Al to make R-DLs able to withstand
high temperatures up to 500$^\circ$C on the long term. Indeed, NiAl gathers, in
the bulk state, all the necessary properties (fairly low electrical resistivity
and density, high melting temperature and resistance to oxidation). The study
also examines the extent of the congruent LiNbO$_3$ segregation process, to
determine its impact on the NiAl/LiNbO$_3$ R-DLs performances. The obtained
results are very promising. NiAl electrodes self-passivate during the first 50h
of annealing at 500$^\circ$C: 20 nm-thick Al$_2$O$_3$ layers form at the
surface and in between the electrodes and the substrate, protecting the
remaining NiAl layer from further oxidation. Besides, the segregation process
occurs mainly in the same time. It is located in the first 150-200 nm of the
substrate. Both phenomena have no significant impact on the performance of
NiAl/LiNbO$_3$ R-DLs working at 433 MHz. Continuous in-situ electrical
monitoring of such devices shows a standard deviation of the operating
frequency of only 1.04 ppm during an annealing process of 250h at 500$^\circ$C.
Moreover, the time-resolved S11 response of the device at the end of this
treatment is not degraded at all. Thus, 433 MHz NiAl/LiNbO$_3$ R-DL sensors can
operate with high fidelity for at least 10 days at 500$^\circ$C under air
atmosphere, and there are strong signs that their lifetime is actually much
longer.",2310.11456v1
2023-10-23,Photoemission study and band alignment of GaN passivation layers on GaInP heterointerface,"III-V semiconductor-based photoelectrochemical (PEC) devices show the highest
solar-to-electricity or solar-to-fuel conversion efficiencies. GaInP is a
relevant top photoabsorber layer or a charge-selective contact in PEC for
integrated and direct solar fuel production, due to its tunable lattice
constant, electronic band structure, and favorable optical properties. To
enhance the stability of its surface against chemical corrosion which leads to
decomposition, we deposit a GaN protection and passivation layer. The n-doped
GaInP(100) epitaxial layers were grown by metalorganic chemical vapor
deposition on top of GaAs(100) substrate. Subsequently, thin 1-20 nm GaN films
were grown on top of the oxidized GaInP surfaces by atomic layer deposition. We
studied the band alignment of these multi-junction heterostructures by X-ray
and ultraviolet photoelectron spectroscopy. Due to the limited emission depth
of photoelectrons, we determined the band alignment by a series of separate
measurements in which we either modified the GaInP(100) surface termination or
the film thickness of the grown GaN on GaInP(100) buffer layers. On
n-GaInP(100) surfaces prepared with the well-known phosphorus-rich (2x2)/c(4x2)
reconstruction we found up-ward surface band bending (BB) of 0.34 eV, and Fermi
level pinning due to the present surface states. Upon oxidation, the surface
states are partially passivated resulting in a reduction of BB to 0.12 eV and a
valence band offset (VBO) between GaInP and oxide bands of 2.0 eV. Between the
GaInP(100) buffer layer and the GaN passivation layer, we identified a VBO of
1.8 eV. The corresponding conduction band offset of -0.2 eV is found to be
rather small. Therefore, we evaluate the application of the GaN passivation
layer as a promising technological step not only to reduce surface states but
also to increase the stability of the surfaces of photoelectrochemical devices.",2310.15212v1
2023-11-17,Conformal TiO$_2$ aerogel-like films by plasma deposition: from omniphobic antireflective coatings to perovskite solar cells photoelectrodes,"The ability to control porosity in oxide thin films is one of the key factors
that determine their properties. Despite the abundance of dry processes for the
synthesis of oxide porous layers, the high porosity range is typically achieved
by spin-coating-based wet chemical methods. Besides, special techniques such as
supercritical drying are required to replace the pore liquid with air while
maintaining the porous network. In this study, we propose a new method for the
fabrication of ultra-porous titanium dioxide thin films at room or mild
temperatures (T lower or equal to 120 degrees Celsius) by the sequential
process involving plasma deposition and etching. These films are conformal to
the substrate topography even for high-aspect-ratio substrates and show
percolated porosity values above 85 percent that are comparable to advanced
aerogels. The films deposited at room temperature are amorphous. However, they
become partly crystalline at slightly higher temperatures presenting a
distribution of anatase clusters embedded in the sponge-like structure.
Surprisingly, the porous structure remains after annealing the films at 450
degrees Celsius in air, which increases the fraction of the embedded anatase
nanocrystals. The films are antireflective, omniphobic, and photoactive
becoming super-hydrophilic subjected to UV light irradiation The supported
percolated nanoporous structure can be used as an electron-conducting electrode
in perovskite solar cells. The properties of the cells depend on the aerogel
film thickness reaching efficiencies close to those of commercial mesoporous
anatase electrodes. This generic solvent-free synthesis is scalable and is
applicable to ultra-high porous conformal oxides of different compositions with
potential applications in photonics, optoelectronics, energy storage, and
controlled wetting.",2311.10839v1
2023-12-07,High-throughput study of the phase constitution of the thin film system Mg-Mn-Al-O in relation to Li recovery from slags,"The increasing importance of recycling makes the recovery of valuable
elements from slags interesting, e.g., by the concept of engineered artificial
minerals (EnAMs). In this concept, it is aimed for the formation of EnAMs,
meaning phase(s) with a high content of the to-be-recovered element(s) from
slags of pyrometallurgical recycling processes. For this, understanding the
phase constitution of the slag systems is of high importance. The system
Mg-Mn-Al-O is a metal oxide slag subsystem from Li-ion battery recycling, that
is critical for the formation of spinel phases, which are competing phases to
the possible Li-containing EnAM phase LiAlO2. Here, the phase constitution was
investigated using a thin film materials library that covers the composition
space (Mg14-69Mn11-38Al14-74)Ox. By means of high-throughput energy-dispersive
X-ray spectroscopy and X-ray diffraction, the formation of the spinel solid
solution phase was confirmed for a wide composition space. Increasing
preferential orientation of the spinel solid solution along (400) with
increasing Mg content was identified. X-ray photoelectron spectroscopy was used
to measure the near-surface composition of selected areas of the materials
library, and detailed peak fitting of the Mn 2p3/2 region revealed the Mn
oxidation state to be a mixture of Mn2+ and Mn3+. For one measurement area of
the materials library containing equal atomic amounts of Mg, Mn and Al,
transmission electron microscopy showed that the approximately 420 nm-thick
film consists of columnar spinel grains with Mg, Mn and Al being evenly
distributed. Based on these results, we suggest that the shown high likelihood
of spinel formation in slags might be influenced by controlling the Mn
oxidation state to enable the formation of desirable EnAM phases.",2312.04146v1
2023-12-29,Bilayer Vanadium Dioxide Thin Film with Elevated Transition Temperatures and High Resistance Switching,"Despite widespread interest in the phase-change applications of vanadium
dioxide (VO$_2$), the fabrication of high-quality VO$_2$ thin films with
elevated transition temperatures (TIMT) and high Insulator-Metal-Transition
resistance switching still remains a challenge. This study introduces a
two-step atmospheric oxidation approach to fabricate bilayer VO$_{2-x}$/VO$_2$
films on a c-plane sapphire substrate. To quantify the impact of the VO$_2$
buffer layer, a single-layer VO$_2$ film of the same thickness was also
fabricated. The bilayer VO$_{2-x}$/VO$_2$ films wherein the top VO$_{2-x}$ film
was under-oxidized demonstrated an elevation in TIMT reaching ~97 $^\circ$C,
one of the highest reported to date for VO$_2$ films and is achieved in a
doping-free manner. Our results also reveal a one-order increase in resistance
switching, with the optimum bilayer VO$_2$/VO$_2$ film exhibiting ~3.6 orders
of switching from 25 $^\circ$C to 110 $^\circ$C, compared to the optimum
single-layer VO$_2$ reference film. This is accompanied by a one-order decrease
in the on-state resistance in its metallic phase. The elevation in TIMT,
coupled with increased strain extracted from the XRD characterization of the
bilayer film, suggests the possibility of compressive strain along the c-axis.
These VO$_{2-x}$/VO$_2$ films also demonstrate a significant change in the
slope of their resistance vs temperature curves contrary to the conventional
smooth transition. This feature was ascribed to the rutile/monoclinic
quasi-heterostructure formed due to the top VO$_{2-x}$ film having a reduced
TIMT. Our findings carry significant implications for both the lucid
fabrication of VO$_2$ thin film devices as well as the study of phase
transitions in correlated oxides.",2312.17437v1
2024-01-05,Vanadium oxide clusters in substellar atmospheres: A quantum chemical study,"We aim to understand the formation of cloud condensation nuclei in
oxygen-rich substellar atmospheres by calculating fundamental properties of the
energetically most favorable vanadium oxide molecules and clusters. A
hierarchical optimization approach is applied in order to find the most
favorable structures for clusters of (VO)$_{N}$ and (VO$_2$)$_{N}$ for N=1-10,
and (V$_2$O$_5$)$_{N}$ for N=1-4 and to calculate their thermodynamical
potentials. The candidate geometries are initially optimized applying classical
interatomic potentials and then refined at the B3LYP/cc-pVTZ level of theory to
obtain accurate zero-point energies and thermochemical quantities. We present
previously unreported vanadium oxide cluster structures as lowest-energy
isomers. We report revised cluster energies and their thermochemical
properties. Chemical equilibrium calculations are used to asses the impact of
the updated and newly derived thermodynamic potentials on the gas-phase
abundances of vanadium-bearing species. In chemical equilibrium, larger
clusters from different stoichiometric families are found to be the most
abundant vanadium-bearing species for temperatures below ~1000 K, while
molecular VO is the most abundant between ~1000 K and ~2000 K. We determine the
nucleation rates of each stoichiometric family for a given (T$_{gas}$,
p$_{gas}$) profile of a brown dwarf using classical and non-classical
nucleation theory. Small differences in the revised Gibbs free energies of the
clusters have a large impact on the abundances of vanadium bearing species in
chemical equilibrium at temperatures below ~1000 K, which subsequently has an
impact on the nucleation rates of each stoichiometric family. We find that with
the revised and more accurate cluster data non-classical nucleation rates are
up to 15 orders of magnitude higher than classical nucleation rates.",2401.02784v1
2024-01-16,The rheology of ultra-high molecular weight poly(ethylene oxide) dispersed in a low molecular weight carrier,"Gel spinning is the industrial method of choice for combining hydrophilic
ultra-high molecular weight (UHMW) polymer resins with a hydrophobic support
polymer to produce composite filaments for cytapheresis. Cytapheresis is a
medical technique for removal of leukocytes from blood. Gel spinning is used to
avoid high melt viscosity and thermal sensitivity of UHMW resins and the high
melt temperature of the substrate resin but requires the recovery of toxic
solvents. The UHMW resin is used because it forms a stable gel phase in the
presence of water; a lower molecular weight resin (LMW) simply dissolves. UHMW
and LMW resins were both poly(ethylene oxide) (PEO) and the substrate was
polyarylsulfone (PAS). The literature indicated PEO undergoes non-oxidative
thermal degradation above 200 {\deg}C and PAS is processed up to 350 {\deg}C.
Dynamic oscillatory shear rheometry was used to study 0, 25, 40, 50, 60, and 75
wt. % UHMW PEO in LMW PEO to take advantage of the sensitivity of viscosity to
changes in molecular weight and material configuration, indicating degradation.
Samples were exposed to 220 {\deg}C, 230 {\deg}C, 240 {\deg}C, 250 {\deg}C, 275
{\deg}C, and 300 {\deg}C temperatures for 5 min to explore conditions that
could result in sample degradation. The viscosity decreased less with
increasing UHMW PEO content for samples exposed to the same temperature and the
viscosity decreased more with increasing exposure temperature for samples with
the same UHMW PEO content. Parameters were regressed from observed data to
predict the change in molecular weight via empiricisms relating the viscosity
to molecular weight, shear rate, temperature, and time.",2401.08816v1
2024-01-25,"An atomically efficient, highly stable and redox active Ce0.5Tb0.5Ox (3% mol.)/MgO catalyst for total oxidation of methane","Redox and catalytic performance in total methane oxidation of a
nonostructured ceria-terbia catalyst supported on magnesia is presented and
compared to that of a pure ceria catalyst supported on MgO. The investigated
material, Ce0.5Tb0.5Ox (3% mol.)/MgO, features several remarkable properties: a
quite low total molar loading of the two lanthanide elements, high
reducibility, as well as very high oxygen storage capacity al low temperatures
and higher activity than MgO-supported ceria. In terms of lanthanide atomic
content the catalytic performance of Ce0.5Tb0.5Ox (3% mol.)/MgO largely
improves compared to that of bulk type ceria and ceria-magnesia solid
solutions. Such a behavior implies proper optimization of the usage of
lanthanide elements. A second contribution to atomic economy in the catalyst
design relates to the fact that the new formulation demonstrate a stabilyty in
the redox and catalytic performance against very high temperature treatments.
An investigation on the structure of both the fresh and high-temperature-aged
catalyst at the atomic scale by means of complementary aberration corrected
microscopy techniques, reveals the ocuurrence of a variety of exotic,
lanthanide-containing nanostructures, which span fron isolated, atomically
dispersed Ln species to nonometer-sized CeTbO2-x patches, extended CeTbO2-x
bilayers and 2D CeTbO2-x nanoparticles. Nanoanalytical results evidence the
mixing of the two lanthanides at atomic levels in these nanostructures. The
combined effects of nanostructuring, mixing of the lanthanides at the atomic
level, and interaction with the MgO oxide are the roots of the improvement in
funtional, redox and catalytic properties of the novel Ce0.5Tb0.5Ox (3%
mol.)/MgO catalyst.",2401.14105v1
2024-01-30,Carrier-phase DNS of ignition and combustion of iron particles in a turbulent mixing layer,"Three-dimensional CP-DNS of reacting iron particle dust clouds in a turbulent
mixing layer are conducted. The simulation approach considers the Eulerian
transport equations for the reacting gas phase and resolves all scales of
turbulence, whereas the particle boundary layers are modelled employing the
Lagrangian point-particle framework for the dispersed phase. The CP-DNS employs
an existing sub-model for iron particle combustion that considers the oxidation
of iron to FeO and that accounts for both diffusion- and kinetically-limited
combustion. At first, the particle sub-model is validated against experimental
results for single iron particle combustion considering various particle
diameters and ambient oxygen concentrations. Subsequently, the CP-DNS approach
is employed to predict iron particle cloud ignition and combustion in a
turbulent mixing layer. The upper stream of the mixing layer is initialised
with cold particles in air, while the lower stream consists of hot air flowing
in the opposite direction. Simulation results show that turbulent mixing
induces heating, ignition and combustion of the iron particles. Significant
increases in gas temperature and oxygen consumption occur mainly in regions
where clusters of iron particles are formed. Over the course of the oxidation,
the particles are subjected to different rate-limiting processes. While
initially particle oxidation is kinetically-limited it becomes
diffusion-limited for higher particle temperatures and peak particle
temperatures are observed near the fully-oxidised particle state. Comparing the
present non-volatile iron dust flames to general trends in volatile-containing
solid fuel flames, non-vanishing particles at late simulation times and a
stronger limiting effect of the local oxygen concentration on particle
conversion is found for the present iron dust flames in shear-driven
turbulence.",2401.16944v1
2024-02-09,High-Resolution X-Ray Spectroscopy of Interstellar Iron Toward Cygnus X-1 and GX 339-4,"We present a high-resolution spectral study of Fe L-shell extinction by the
diffuse interstellar medium (ISM) in the direction of the X-ray binaries Cygnus
X-1 and GX 339-4, using the XMM-Newton reflection grating spectrometer. The
majority of interstellar Fe is suspected to condense into dust grains in the
diffuse ISM, but the compounds formed from this process are unknown. Here, we
use the laboratory cross sections from Kortright & Kim (2000) and Lee et al.
(2009) to model the absorption and scattering profiles of metallic Fe, and the
crystalline compounds fayalite (Fe$_2$SiO$_4$), ferrous sulfate (FeSO$_4$),
hematite ($\alpha$-Fe$_2$O$_3$), and lepidocrocite ($\gamma$-FeOOH), which have
oxidation states ranging from Fe$^{0}$ to Fe$^{3+}$. We find that the observed
Fe L-shell features are systematically offset in energy from the laboratory
measurements. An examination of over two dozen published measurements of Fe
L-shell absorption finds a 1-2 eV scatter in energy positions of the L-shell
features. Motivated by this, we fit for the best energy-scale shift
simultaneously with the fine structure of the Fe L-shell extinction cross
sections. Hematite and lepidocrocite provide the best fits ($\approx +1.1$ eV
shift), followed by fayalite ($\approx +1.8$ eV shift). However, fayalite is
disfavored, based on the implied abundances and knowledge of ISM silicates
gained by infrared astronomical observations and meteoritic studies. We
conclude that iron oxides in the Fe$^{3+}$ oxidation state are good candidates
for Fe-bearing dust. To verify this, new absolute photoabsorption measurements
are needed on an energy scale accurate to better than 0.2 eV.",2402.06726v1
2024-03-21,Investigation of Genomic Effect of Zirconium Oxide Nanoparticles in Escherichia coli Bacteria,"Due to the concerns of the society about the increase of antibiotic resistant
infections, many studies and research have been done on nanoparticles and
applications of nano-biotechnology. Zirconium Oxide ($\text{ZrO}_{2}$) in which
called zirconia, is a white oxide of zirconium metal that its diameter is 20
nm. The colloidal size of these particles is often smaller than bacterial and
eukaryotic cells. The main intention of this paper is to investigate the effect
of different doses of $\text{ZrO}_{2}$ NPs on the sequences changes for the
$\textit{Escherichia coli}$ ($\textit{E. coli}$) genome. At the first step,
$\textit{E. coli}$ was cultured in eosin methylene blue agar and brain heart
broth (BHB) mediums, respectively. Then, bacteria were treated with
$\text{ZrO}_{2}$ NPs at concentrations of 100, 250, and 350 $\mu$g/ml. After
treatment, the growth of bacteria was evaluated by utilizing spectrophotometry
at 600 nm after incubation times including 2, 4, 6, 8, and 24 hours at 37
$^{\circ}$C. At the second step, the extraction of DNA was performed by using
control and treated samples. Then, the changes in the sequence of bacterial
genome were investigated using RAPD markers. Finally, NTSYS-PC platform was
employed in order to analyze of the results extracted by electrophoresis of
products on agarose gel. In this paper, it was observed that $\text{ZrO}_{2}$
NPs can inhibit the growth of bacteria at concentrations of 250 and 350
$\mu$g/ml after 8 hours of treatment. It was also found that the
$\text{ZrO}_{2}$ NPs at different concentrations have not changed the genome
sequence of $\textit{E. coli}$. Furthermore, it was concluded that the
$\text{ZrO}_{2}$ NPs with the concentration of 350 $\mu$g/ml had the highest
inhibitory properties without significant changing in the genomic sequence of
$\textit{E. coli}$.",2403.14728v1
2002-11-03,Magnetically induced signatures in a thin film superconductor,"We study the interaction between a one dimensional magnetic nanostructure and
a thin film superconductor. It is shown that different magnetic distributions
produce characteristic magnetic field signatures. Moreover, the magnetic
structure can induce a weak link in the superconducting film, or be positioned
directly above a predefined nonsuperconducting weak link. We estimate the
magnetic flux associated with such a structure, and discuss a general
expression for the energy calculated within the London model.",0211043v1
2004-09-25,Nano-mechanical magnetization reversal,"The dynamics of the ferromagnetic order parameter in thin magnetic films is
strongly affected by the magnetomechanical coupling at certain resonance
frequencies. By solving the equation of motion of the coupled mechanical and
magnetic degrees of freedom we show that the magnetic-field induced
magnetization switching can be strongly accelerated by the lattice and
illustrate the possibility of magnetization reversal by mechanical actuation.",0409681v1
2005-10-26,Ferroelectricity in spiral magnets,"It was recently observed that materials showing most striking multiferroic
phenomena are frustrated spin-density-wave magnets. We present a simple
phenomenological theory, which describes the orientation of the induced
electric polarization for various incommensurate magnetic states, its
dependence on temperature and magnetic field, and anomalies of dielectric
susceptibility at magnetic transitions. We show that electric polarization can
be induced at domain walls and that magnetic vortices carry electric charge.",0510692v1
2007-07-13,Magnetic Flux Effects in Statistical Magnetism of Electron Gas,"The effects of magnetic flux in statistical magnetisms, including Pauli
paramagnetism, Landau diamagnetism, and De Hass-van Alphen oscillation, are
discussed. It is shown that the diamagnetism could be much increased by the
fractional magnetic flux, and the amplitude of the magnetic oscillation of De
Hass-van Alphen can be amplified by the quantum effect of the flux.",0707.1920v1
2008-05-18,Effect of spin diffusion on spin torque in magnetic nanopillars,"We present systematic magnetoelectronic measurements of magnetic nanopillars
with different structures of polarizing magnetic layers. The magnetic reversal
at small magnetic field, the onset of magnetic dynamics at larger field, and
the magnetoresistance exhibit a significant dependence on the type of the
polarizing layer. We performed detailed quantitative modeling showing that the
differences can be explained by the effects of spin-dependent electron
diffusion.",0805.2706v1
2012-06-05,Negative magnetic relaxation in superconductors,"It was observed that the trapped magnetic moment of HTS tablets or annuli
increases in time (negative relaxation) if they are not completely magnetized
by a pulsed magnetic field. It is shown, in the framework of the Bean
critical-state model, that the radial temperature gradient appearing in tablets
or annuli during a pulsed field magnetization can explain the negative magnetic
relaxation in the superconductor.",1206.0861v1
2016-08-19,Vesicles in magnetic fields,"Liposome vesicles tend to align with an applied magnetic field. This is due
to the directional magnetic susceptibility difference of the lipids which form
the membrane of these vesicles. In this work a model of liposome vesicles
exposed to magnetic field is presented. Starting from the base energy of a
lipid membrane in a magnetic field, the force applied to the surrounding fluids
is derived. This force is then used to investigate the dynamics of vesicle in
the presence of magnetic fields.",1608.05587v1
2012-11-20,Magnetic Cluster Excitations,"Magnetic clusters, i.e., assemblies of a finite number (between two or three
and several hundred) of interacting spin centers which are magnetically
decoupled from their environment, can be found in many materials ranging from
inorganic compounds, magnetic molecules, artificial metal structures formed on
surfaces to metalloproteins. The magnetic excitation spectra in them are
determined by the nature of the spin centers, the nature of the magnetic
interactions, and the particular arrangement of the mutual interaction paths
between the spin centers. Small clusters of up to four magnetic ions are ideal
model systems to examine the fundamental magnetic interactions which are
usually dominated by Heisenberg exchange, but often complemented by anisotropic
and/or higher-order interactions. In large magnetic clusters which may
potentially deal with a dozen or more spin centers, the possibility of novel
many-body quantum states and quantum phenomena are in focus. In this review the
necessary theoretical concepts and experimental techniques to study the
magnetic cluster excitations and the resulting characteristic magnetic
properties are introduced, followed by examples of small clusters demonstrating
the enormous amount of detailed physical information which can be retrieved.
The current understanding of the excitations and their physical interpretation
in the molecular nanomagnets which represent large magnetic clusters is then
presented, with an own section devoted to the subclass of the single-molecule
magnets which are distinguished by displaying quantum tunneling of the
magnetization. Finally, some quantum many-body states are summarized which
evolve in magnetic insulators characterized by built-in or field-induced
magnetic clusters. The review concludes addressing future perspectives in the
field of magnetic cluster excitations.",1211.4688v1
2014-01-08,Generating buoyant magnetic flux ropes in solar-like convective dynamos,"Our Sun exhibits strong convective dynamo action which results in magnetic
flux bundles emerging through the stellar surface as magnetic spots.
Global-scale dynamo action is believed to generate large-scale magnetic
structures in the deep solar interior through the interplay of convection,
rotation, and shear. Portions of these large-scale magnetic structures are then
believed to rise through the convective layer, forming magnetic loops which
then pierce the photosphere as sunspot pairs. Previous global simulations of 3D
MHD convection in rotating spherical shells have demonstrated mechanisms
whereby large-scale magnetic wreaths can be generated in the bulk of the
convection zone. Our recent simulations have achieved sufficiently high levels
of turbulence to permit portions of these wreaths to become magnetically
buoyant and rise through the simulated convective layer through a combination
of magnetic buoyancy and advection by convective giant cells. These buoyant
magnetic loops are created in the bulk of the convective layer as strong
Lorentz force feedback in the cores of the magnetic wreaths dampen small-scale
convective motions, permitting the amplification of local magnetic energies to
over 100 times the local kinetic energy. While the magnetic wreaths are largely
generated the shearing of axisymmetric poloidal magnetic fields by axisymmetric
rotational shear (the $\Omega$-effect), the loops are amplified to their peak
field strengths before beginning to rise by non-axisymmetric processes. This
further extends and enhances a new paradigm for the generation of emergent
magnetic flux bundles, which we term turbulence-enabled magnetic buoyancy.",1401.1826v1
2014-07-15,Magnetic nanoparticle traveling in external magnetic field,"A set of equations describing the motion of a free magnetic nanoparticle in
an external magnetic field in a vacuum, or in a medium with negligibly small
friction forces is postulated. The conservation of the total particle momentum,
i.e. the sum of the mechanical and the total spin momentum of the nanoparticle
is taken into account explicitly. It is shown that for the motion of a
nanoparticle in uniform magnetic field there are three different modes of
precession of the unit magnetization vector and the director that is parallel
the particle easy anisotropy axis. These modes differ significantly in the
precession frequency. For the high-frequency mode the director points
approximately along the external magnetic field, whereas the frequency and the
characteristic relaxation time of the precession of the unit magnetization
vector are close to the corresponding values for conventional ferromagnetic
resonance. On the other hand, for the low-frequency modes the unit
magnetization vector and the director are nearly parallel and rotate in unison
around the external magnetic field. The characteristic relaxation time for the
low-frequency modes is remarkably long. This means that in a rare assembly of
magnetic nanoparticles there is a possibility of additional resonant absorption
of the energy of alternating magnetic field at a frequency that is much smaller
compared to conventional ferromagnetic resonance frequency. The scattering of a
beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic
field is also considered taking into account the precession of the unit
magnetization vector and director.",1407.3964v1
2014-05-05,The magnetic shielding for the neutron decay spectrometer aSPECT,"Many experiments in nuclear and neutron physics are confronted with the
problem that they use a superconducting magnetic spectrometer which potentially
affects other experiments by their stray magnetic field. The retardation
spectrometer aSPECT consists, inter alia, of a superconducting magnet system
that produces a strong longitudinal magnetic field of up to 6.2T. In order not
to disturb other experiments in the vicinity of aSPECT, we had to develop a
magnetic field return yoke for the magnet system. While the return yoke must
reduce the stray magnetic field, the internal magnetic field and its
homogeneity should not be affected. As in many cases, the magnetic shielding
for aSPECT must manage with limited space. In addition, we must ensure that the
additional magnetic forces on the magnet coils are not destructive. In order to
determine the most suitable geometry for the magnetic shielding for aSPECT, we
simulated a variety of possible geometries and combinations of shielding
materials of non-linear permeability. The results of our simulations were
checked through magnetic field measurements both with Hall and nuclear magnetic
resonance probes. The experimental data are in good agreement with the
simulated values: The mean deviation from the simulated exterior magnetic field
is (-1.7+/-4.8)%. However, in the two critical regions, the internal magnetic
field deviates by 0.2% respectively <1E-4 from the simulated values.",1405.0957v1
2018-12-30,Magnetic properties of an antiferromagnetic spin-1/2 XYZ model in the presence of different magnetic fields: finite-size effects of inhomogeneity property,"Magnetic and thermodynamic properties of the anisotropic XYZ spin-1/2 finite
chain under both homogeneous and inhomogeneous magnetic fields are
theoretically studied at low temperature. Using exact diagonalization method
(ED), we study the magnetization, magnetic susceptibility and specific heat of
the model characterized in terms of the finite correlation length in the
presence of three different magnetic fields including longitudinal, transverse
and transverse staggered magnetic fields. The magnetization, susceptibility and
the specific heat of the model are investigated under two conditions
separately: I) when the model is putted in the presence of homogeneous magnetic
fields; II) when finite inhomogeneities are considered for all applied magnetic
fields in the Hamiltonian. We show that for the finite-size XYZ chains at low
temperature, the evident magnetization plateaus gradually convert to their
counterpart quasi-plateaus when the transverse magnetic field increases.
Moreover, the influence of the transverse and staggered transverse magnetic
fields, and their corresponding inhomogeneities on the magnetization process,
magnetic susceptibility, and specific heat are reported in detail. Our exact
results illustrate that by altering the inhomogeneity parameters, magnetization
plateaus gradually convert to their counterpart quasi-plateaus. The specific
heat manifests Schottky-type maximum, double-peak and triple-peak, as well as,
transformation between them by varying considered inhomogeneity parameters in
the Hamiltonian.",1812.11468v2
2019-04-18,Insight into the magnetic behavior of Sr$_2$IrO$_4$:A spontaneous magnetization study,"Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted
anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and
important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the
magnetization under zero applied field i.e. spontaneous magnetization would be
interesting to study and would give insight into the novel magnetic behavior of
Sr$_2$IrO$_4$. Sophisticated techniques like neutron diffraction, $\mu$
\textit{SR} etc has been used to understand the magnetic behavior of
Sr$_2$IrO$_4$ under zero applied field. To understand the magnetic behavior we
have performed detail field and temperature dependent magnetization study, the
measured field and temperature dependent magnetic data is analyzed rigorously.
We have attempted the understand the temperature dependance of spontaneous
magnetization, remanent magnetization and coercive force. We observe that the
spontaneous magnetization extracted from Arrott plot shows that the
Sr$_2$IrO$_4$ is not an ideal ferromagnet. The temperature dependent coercive
field is found to follows Guant's model of strong domain wall pinning. Our
investigation explicit the temperature dependence of various magnetic
properties shows the magnetic transitions from paramagnetic to ferromagnetic
phase with $T_c$ around 225 K and a low temperature evolution of magnetic
magnetic moment around $T_M$ $\sim$90 K.",1904.08792v1
2021-09-24,Fluidic Endogenous Magnetism and Magnetic Monopole Clues from Liquid Metal Droplet Machine,"Magnetism and magnetic monopole are classical issues in basic physics.
Conventional magnets are generally composed of rigid materials with shapes and
structures unchangeable which may face challenges sometimes to answer the above
questions. Here, from an alternative other than rigid magnet, we disclosed an
unconventional way to generate endogenous magnetism and then construct magnetic
monopole through tuning liquid metal machine. Through theoretical
interpretation and conceptual experiments, we illustrated that when gallium
base liquid metal in solution rotates under actuation of an external electric
field, it forms an endogenous magnetic field inside which well explains the
phenomenon that two such discrete metal droplets could easily fuse together,
indicating their reciprocal attraction via N and S poles. Further, we conceived
that the self-driving liquid metal motor was also an endogenous magnet owning
the electromagnetic homology. When liquid metal in solution swallowed aluminum
inside, it formed a spin motor and dynamically variable charge distribution
which produced an endogenous magnetic field. This finding explains the
phenomena that there often happened reflection collision and attraction fusion
between running liquid metal motors which were just caused by the dynamic
adjustment of their N and S polarities. Finally, we conceived that such
endogenous magnet could lead to magnetic monopole and four technical routes
were suggested as: 1. Matching the interior flow field of liquid metal
machines; 2. Superposition between external electric effect and magnetic field;
3. Composite construction between magnetic particles and liquid metal motor; 4.
Chemical ways such as via galvanic cell reaction. Overall, the fluidic
endogenous magnet and the promising magnetic monopole it enabled may lead to
unconventional magnetoelectric devices and applications in the near future.",2111.02867v1
2023-09-21,Integrable Magnetic Fluid Hyperthermia Systems for 3D Magnetic Particle Imaging,"Background: Combining magnetic particle imaging (MPI) and magnetic fluid
hyperthermia (MFH) offers the ability to perform localized hyperthermia and
magnetic particle imaging-assisted ther-mometry of hyperthermia treatment. This
allows precise regional selective heating inside the body without invasive
interventions. In current MPI-MFH platforms, separate systems are used, which
require object transfer from one system to another. Here, we present the
design, development and evaluation process for integrable MFH platforms, which
extends a commercial MPI scanner with the functionality of MFH. Methods: The
biggest issue of integrating magnetic fluid hyperthermia platforms into a
magnetic par-ticle imaging system is the magnetic coupling of the devices,
which induces high voltage in the imaging system, and is harming its
components. In this paper we use a self-compensation approach derived from
heuristic algorithms to protect the magnetic particle imaging scanner. The
integrable platforms are evaluated regarding electrical and magnetic
characteristics, cooling capability, field strength, the magnetic coupling to a
replica of the magnetic particle imaging system's main solenoid and particle
heating. Results: The MFH platforms generate suitable magnetic fields for
magnetic heating of particles and are compatible with a commercial magnetic
particle imaging scanner. In combination with the imaging system, selective
heating with a gradient field and steerable heating positioning using the MPI
focus fields are possible. Conclusion: The proposed MFH platforms serve as a
therapeutic tool to unlock MFH functionality of a commercial magnetic particle
imaging scanner, enabling its use in future preclinical trials of MPI-guided,
spatially selective magnetic hyperthermia therapy.",2309.12186v1
2002-05-15,Magnetic Fluctuations with a Zero Mean Field in a Random Fluid Flow with a Finite Correlation Time and a Small Magnetic Diffusion,"Magnetic fluctuations with a zero mean field in a random flow with a finite
correlation time and a small yet finite magnetic diffusion are studied.
Equation for the second-order correlation function of a magnetic field is
derived. This equation comprises spatial derivatives of high orders due to a
non-local nature of magnetic field transport in a random velocity field with a
finite correlation time. For a random Gaussian velocity field with a small
correlation time the equation for the second-order correlation function of the
magnetic field is a third-order partial differential equation. For this
velocity field and a small magnetic diffusion with large magnetic Prandtl
numbers the growth rate of the second moment of magnetic field is estimated.
The finite correlation time of a turbulent velocity field causes an increase of
the growth rate of magnetic fluctuations. It is demonstrated that the results
obtained for the cases of a small yet finite magnetic diffusion and a zero
magnetic diffusion are different. Astrophysical applications of the obtained
results are discussed.",0205233v1
2005-06-30,Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8,"A study of an impurity driven phase-transition into a magnetically ordered
state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both,
macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR)
measurements reveal that the spin nature of dopants has a crucial role in
determining the stability of the induced long-range magnetic order. In the case
of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition
is observed in relatively low magnetic fields. On the other hand, the magnetic
order in magnetically (Co2+) doped compounds survives at much higher magnetic
fields and temperatures, which is attributed to a significant anisotropic
impurity-host magnetic interaction. The NMR measurements confirm the predicted
staggered nature of impurity-liberated spin degrees of freedom, which are
responsible for the magnetic ordering. In addition, differences in the
broadening of the NMR spectra and the increase of nuclear spin-lattice
relaxation in doped samples, indicate a diverse nature of electron spin
correlations in magnetically and nonmagnetically doped samples, which begin
developing at rather high temperatures with respect to the antiferromagnetic
phase transition.",0506808v1
2006-09-15,Superconducting pipes and levitating magnets,"Motivated by a beautiful demonstration of the Faraday's and Lenz's law in
which a small neodymium magnet falls slowly through a conducting
non-ferromagnetic tube, we consider the dynamics of a magnet falling through a
superconducting pipe. Unlike the case of normal conducting pipes, in which the
magnet quickly reaches the terminal velocity, inside a superconducting tube the
magnet falls freely. On the other hand, to enter the pipe the magnet must
overcome a large electromagnetic energy barrier. For sufficiently strong
magnets, the barrier is so large that the magnet will not be able to penetrate
it and will be suspended over the front edge. We calculate the work that must
done to force the magnet to enter a superconducting tube. The calculations show
that superconducting pipes are very efficient at screening magnetic fields. For
example, the magnetic field of a dipole at the center of a short pipe of radius
$a$ and length $L \approx a$ decays, in the axial direction, with a
characteristic length $\xi \approx 0.26 a$. The efficient screening of the
magnetic field might be useful for shielding highly sensitive superconducting
quantum interference devices, SQUIDs. Finally, the motion of the magnet through
a superconducting pipe is compared and contrasted to the flow of ions through a
trans-membrane channel.",0609141v1
2007-02-18,Planar Atom Trap and Magnetic Resonance 'Lens' Designs,"We present various planar magnetic designs that create points above the plane
where the magnitude of the static magnetic field is a local minimum. Structures
with these properties are of interest in the disciplines of neutral atom
confinement, magnetic levitation, and magnetic resonance imaging. Each planar
permanent magnet design is accompanied by the equivalent planar single
non-crossing conductor design. Presented designs fall into three categories
producing: a) zero value magnetic field magnitude point minima, b) non-zero
magnetic field magnitude point minima requiring external bias magnetic field,
and c) self-biased non-zero magnetic field magnitude point minima. We also
introduce the Principle of Amperean Current Doubling in planar perpendicularly
magnetized thin films that can be used to improve the performance of each
permanent magnet design we present. Single conductor current-carrying designs
are suitable for single layer lithographic fabrication, as we experimentally
demonstrate. Finally, we present the case that nanometer scale recording of
perpendicular anisotropy thin magnetic films using presently available data
storage technology can provide the ultimate miniaturization of the presented
designs.",0702154v1
2008-05-26,Magnetic field induced incommensurate resonance in cuprate superconductors,"The influence of a uniform external magnetic field on the dynamical spin
response of cuprate superconductors in the superconducting state is studied
based on the kinetic energy driven superconducting mechanism. It is shown that
the magnetic scattering around low and intermediate energies is dramatically
changed with a modest external magnetic field. With increasing the external
magnetic field, although the incommensurate magnetic scattering from both low
and high energies is rather robust, the commensurate magnetic resonance
scattering peak is broadened. The part of the spin excitation dispersion seems
to be an hourglass-like dispersion, which breaks down at the heavily low energy
regime. The theory also predicts that the commensurate resonance scattering at
zero external magnetic field is induced into the incommensurate resonance
scattering by applying an external magnetic field large enough.",0805.3922v2
2010-10-22,Dissipation in dynamos at low and high magnetic Prandtl numbers,"Using simulations of helically driven turbulence, it is shown that the ratio
of kinetic to magnetic energy dissipation scales with the magnetic Prandtl
number in power law fashion with an exponent of approximately 0.6. Over six
orders of magnitude in the magnetic Prandtl number the magnetic field is found
to be sustained by large-scale dynamo action of alpha-squared type. This work
extends a similar finding for small magnetic Prandtl numbers to the regime of
large magnetic Prandtl numbers. At large magnetic Prandtl numbers, most of the
energy is dissipated viscously, lowering thus the amount of magnetic energy
dissipation, which means that simulations can be performed at magnetic Reynolds
numbers that are large compared to the usual limits imposed by a given
resolution. This is analogous to an earlier finding that at small magnetic
Prandtl numbers, most of the energy is dissipated resistively, lowering the
amount of kinetic energy dissipation, so simulations can then be performed at
much larger fluid Reynolds numbers than otherwise. The decrease in magnetic
energy dissipation at large magnetic Prandtl numbers is discussed in the
context of underluminous accretion found in some quasars.",1010.4805v2
2011-07-08,Antimagnets: Controlling magnetic fields with superconductor-metamaterial hybrids,"Magnetism is very important in science and technology, from magnetic
recording to energy generation to trapping cold atoms. Physicists have managed
to master magnetism - to create and manipulate magnetic fields- almost at will.
Surprisingly, there is at least one property which until now has been elusive:
how to 'switch off' the magnetic interaction of a magnetic material with
existing magnetic fields without modifying them. Here we introduce the
antimagnet, a design to conceal the magnetic response of a given volume from
its exterior, without altering the external magnetic fields, somehow analogous
to the recent theoretical proposals for cloaking electromagnetic waves with
metamaterials. However, different from these devices requiring extreme material
properties, our device is feasible and needs only two kinds of available
materials: superconductors and isotropic magnetic materials. Antimagnets may
have applications in magnetic-based medical techniques such as MRI or in
reducing the magnetic signature of vessels or planes.",1107.1647v1
2012-06-29,Enhancement of critical current density in superconducting/magnetic multi-layers with slow magnetic relaxation dynamics and large magnetic susceptibility,"We propose to use superconductor-magnet multi-layer structure to achieve high
critical current density by invoking polaronic mechanism of pinning. The
magnetic layers should have large magnetic susceptibility to enhance the
coupling between vortices and magnetization in magnetic layers. The relaxation
of the magnetization should be slow. When the velocity of vortices is low, they
are dressed by nonuniform magnetization and move as polarons. In this case, the
viscosity of vortices proportional to the magnetic relaxation time is enhanced
significantly. As velocity increases, the polarons dissociate and the viscosity
drops to the usual Bardeen-Stephen one, resulting in a jump in the I-V curve.
Experimentally the jump shows up as a depinning transition and the
corresponding current at the jump is the depinning current. For Nb and proper
magnet multi-layer structure, we estimate the critical current density $J_c\sim
10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.",1206.6929v2
2013-03-07,Complex Magnetic Phase Diagram of a Geometrically Frustrated Sm Lattice: SmPd2Al3 case,"Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry
and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm
magnetism exhibiting complex magnetic behavior at low temperatures with four
consecutive magnetic phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich
magnetic phase diagram of this compound reflects the specific features of the
Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and
the first excited multiplet J = 7/2 in conjunction with strong crystal field
influence. Consequently, a significantly reduced Sm magnetic moment in
comparison with the theoretical Sm3+ free-ion value is observed. Despite the
strong neutron absorption by natural samarium and the small Sm magnetic moment
(~ 0.2 {\mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3,
0) of the phase existing in the temperature interval 12.5 - 4.3 K. This
observation classifies the SmPd2Al3 compound as a magnetically frustrated
system. The complex magnetic behavior of this material is further illustrated
by kinetic effects of the magnetization inducing rather complicated magnetic
structure with various metastable states.",1303.1607v1
2013-05-20,Magnetization of neutron star matter,"The magnetization of neutron star matter in magnetic fields is studied by
employing the FSUGold interaction. It is found that the magnetic
susceptibilities of the charged particles (proton, electron and muon) can be
larger than that of neutron. The effects of the anomalous magnetic moments
(AMM) of each component on the magnetic susceptibility are examined in detail.
It is found that the proton and electron AMM affect their respective magnetic
susceptibility evidently in strong magnetic fields. In addition, they are the
protons instead of the electrons that contribute most significantly to the
magnetization of the neutron star matter in a relative weak magnetic field, and
the induced magnetic field due to the magnetization can be appear to be very
large. Finally, the effect of the density-dependent symmetry energy on the
magnetization is discussed.",1305.4533v1
2014-09-29,Review and comparison of magnet designs for magnetic refrigeration,"One of the key issues in magnetic refrigeration is generating the magnetic
field that the magnetocaloric material must be subjected to. The magnet
constitutes a major part of the expense of a complete magnetic refrigeration
system and a large effort should therefore be invested in improving the magnet
design. A detailed analysis of the efficiency of different published permanent
magnet designs used in magnetic refrigeration applications is presented in this
paper. Each design is analyzed based on the generated magnetic flux density,
the volume of the region where this flux is generated and the amount of magnet
material used. This is done by characterizing each design by a figure of merit
magnet design efficiency parameter, $\Lambda_\mathrm{cool}$. The designs are
then compared and the best design found. Finally recommendations for designing
the ideal magnet design are presented based on the analysis of the reviewed
designs.",1409.8046v1
2015-04-22,Magnetized stars with differential rotation and a differential toroidal field,"We have succeeded in obtaining magnetized equilibrium states with
differential rotation and differential toroidal magnetic fields. If an internal
toroidal field of a proto-neutron star is wound up from the initial poloidal
magnetic field by differential rotation, the distribution of the toroidal
magnetic field is determined by the profile of this differential rotation.
However, the distributions of the toroidal fields in all previous magnetized
equilibrium studies do not represent the magnetic winding by the differential
rotation of the star. In this paper, we investigate a formulation of a
differential toroidal magnetic field that represents the magnetic field wound
up by differential rotation. We have developed two functional forms of
differential toroidal fields which correspond to a v-constant and a j-constant
field in analogy to differential rotations. As the degree of the differential
becomes very high, the toroidal magnetic field becomes highly localized and
concentrated near the rotational axis. Such a differential toroidal magnetic
field would suppress the low-T/|W| instability more efficiently even if the
total magnetic field energy is much smaller than that of a non-differential
toroidal magnetic field.",1504.05961v2
2016-04-01,Photoinduced Magnetic Nanoprobe Excited by Azimuthally Polarized Vector Beam,"The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a
magnetic near-field enhancement and vanishing electric field is presented and
investigated, together with their excitation. It is established that a
particular type of cylindrical vector beams called azimuthally electric
polarized vector beams yield strong longitudinal magnetic field on the beam
axis where the electric field is ideally null. These beams with an electric
polarization vortex and cylindrical symmetry are important in generating high
magnetic to electric field contrast, i.e., large local field admittance, and in
allowing selective excitation of magnetic transitions in matter located on the
beam axis. We demonstrate that azimuthally polarized vector beam excitation of
a photoinduced magnetic nanoprobe made of a magnetically polarizable nano
cluster leads to enhanced magnetic near field with resolution beyond
diffraction limit. We introduce two figures of merit as magnetic field
enhancement and local field admittance normalized to that of a plane wave that
are useful to classify magnetic nanoprobes and their excitation. The
performance of magnetic nanoprobe and azimuthal polarized beams is quantified
in comparison to other illumination options and with several defect scenarios.",1604.00379v1
2016-09-23,Chirality-driven orbital magnetic moments as a new probe for topological magnetic structures,"When electrons are driven through unconventional magnetic structures, such as
skyrmions, they experience emergent electromagnetic fields that originate
several Hall effects. Independently, ground state emergent magnetic fields can
also lead to orbital magnetism, even without the spin-orbit interaction. The
close parallel between the geometric theories of the Hall effects and of the
orbital magnetization raises the question: does a skyrmion display topological
orbital magnetism? Here we first address the smallest systems with nonvanishing
emergent magnetic field, trimers, characterizing the orbital magnetic
properties from first-principles. Armed with this understanding, we study the
orbital magnetism of skyrmions, and demonstrate that the contribution driven by
the emergent magnetic field is topological. This means that the topological
contribution to the orbital moment does not change under continous deformations
of the magnetic structure. Furthermore, we use it to propose a new experimental
protocol for the identification of topological magnetic structures, by soft
x-ray spectroscopy.",1609.07529v1
2017-02-24,Angle-dependence and optimal design for magnetic bubblecade with maximum speed,"Unidirectional magnetic domain-wall motion is a key concept underlying
next-generation application devices. Such motion has been recently demonstrated
by applying an alternating magnetic field, resulting in the coherent
unidirectional motion of magnetic bubbles. Here we report the optimal
configuration of applied magnetic field for the magnetic bubblecade, the
coherent unidirectional motion of magnetic bubbles, driven by a tilted
alternating magnetic field. The tilted alternating magnetic field induces
asymmetric expansion and shrinkage of the magnetic bubbles under the influence
of the Dzyaloshinskii-Moriya interaction, resulting in continuous shift of the
bubbles in time. By realizing the magnetic bubblecade in PtCoPt films, we find
that the bubblecade speed is sensitive to the tilt angle with a maximum at an
angle, which can be explained well by a simple analytical form within the
context of the domain-wall creep theory. A simplified analytic formula for the
angle for maximum speed is then given as a function of the amplitude of the
alternating magnetic field. The present observation provides a practical design
rule for memory and logic devices based on the magnetic bubblecade.",1702.07439v1
2014-03-11,Piezo-Voltage Manipulation of the Magnetization and Magnetic Reversal in Thin Fe Film,"We carefully investigated the in-plane magnetic reversal and corresponding
magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using
longitudinal magneto-optical Kerr microscopy. The coexistence of the <100>
cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our
Fe thin film grown on GaAs. The induced deformation along [110] orientation can
effectively manipulate the magnetic reversal with magnetic field applied along
magnetic uniaxial hard [110] axes. The control of two-jump magnetization
switching to one-jump magnetization switching during the magnetic reversal was
achieved by piezo-voltages with magnetic field applied in [100] direction. The
additional uniaxial anisotropy induced by piezo-voltages at -75 /75V are
-1.400/1400 J/m3 .",1403.2469v1
2018-09-13,On the role of magnetic fields in star formation,"Magnetic fields are observed in star forming regions. However simulations of
the late stages of star formation that do not include magnetic fields provide a
good fit to the properties of young stars including the initial mass function
(IMF) and the multiplicity. We argue here that the simulations that do include
magnetic fields are unable to capture the correct physics, in particular the
high value of the magnetic Prandtl number, and the low value of the magnetic
diffusivity. The artificially high (numerical and uncontrolled) magnetic
diffusivity leads to a large magnetic flux pervading the star forming region.
We argue further that in reality the dynamics of high magnetic Prandtl number
turbulence may lead to local regions of magnetic energy dissipation through
reconnection, meaning that the regions of molecular clouds which are forming
stars might be essentially free of magnetic fields. Thus the simulations that
ignore magnetic fields on the scales on which the properties of stellar masses,
stellar multiplicities and planet-forming discs are determined, may be closer
to reality than those which include magnetic fields, but can only do so in an
unrealistic parameter regime.",1809.04921v1
2020-04-24,Observation of magnetic domains in uniaxial magnets via small-angle electron diffraction and Foucault imaging,"Observation of magnetic domains is important in understanding the magnetic
properties of magnetic materials and devices. In this study, we report that the
magnetic domains of M-type hexaferrites with uniaxial anisotropy can be
visualized via small-angle electron diffraction and Foucault imaging. The
position of the diffraction pattern spots has the same period as that of
magnetic domains in a Sc-substituted hexaferrite
(BaFe$_{12-x-\delta}$Sc$_x$Mg$_\delta$O$_{19}$). Conversely, the spots were
observed four times longer than the period of magnetic domains in hexaferrite
without substitution (BaFe$_{12}$O$_{19}$), demonstrating the long-range order
of the Bloch walls. When the specimen was tilted, the magnetic deflection
effect, as well as the periodic spots of magnetic domains, occurred. Thus, we
were able to visualize the magnetic domains with different magnetization
directions and domain orientations by selecting deflection spots. The results
indicate that the technique utilized in this study is useful in observing the
magnetic materials with uniaxial anisotropy.",2004.11589v1
2021-01-12,Modeling of Thermal Magnetic Fluctuations in Nanoparticle Enhanced Magnetic Resonance Detection,"We present a systematic numerical modeling investigation of magnetization
dynamics and thermal magnetic moment fluctuations of single magnetic domain
nanoparticles in a configuration applicable to enhancing inductive magnetic
resonance detection signal to noise ratio (SNR). Previous proposals for
oriented anisotropic single magnetic domain nanoparticle amplification of
magnetic flux in MRI coil focused only on the coil pick-up voltage signal
enhancement. Here we extend the analysis to the numerical evaluation of the SNR
by modeling the inherent thermal magnetic noise introduced into the detection
coil by the insertion of such anisotropic nanoparticle-filled coil core. We
utilize the Landau-Lifshitz-Gilbert equation under the Stoner-Wohlfarth single
magnetic domain (macrospin) assumption to simulate the magnetization dynamics
in such nanoparticles due to AC drive field as well as thermal noise. These
simulations are used to evaluate the nanoparticle configurations and shape
effects on enhancing SNR. Finally, we explore the effect of narrow band
filtering of the broadband magnetic moment thermal fluctuation noise on the
SNR. Our results provide the impetus for relatively simple modifications to
existing MRI systems for achieving enhanced detection SNR in scanners with
modest polarizing magnetic fields.",2101.04649v1
2019-03-28,Micromagnetics of rare-earth efficient permanent magnets,"The development of permanent magnets containing less or no rare-earth
elements is linked to profound knowledge of the coercivity mechanism.
Prerequisites for a promising permanent magnet material are a high spontaneous
magnetization and a sufficiently high magnetic anisotropy. In addition to the
intrinsic magnetic properties the microstructure of the magnet plays a
significant role in establishing coercivity. The influence of the
microstructure on coercivity, remanence, and energy density product can be
understood by {using} micromagnetic simulations. With advances in computer
hardware and numerical methods, hysteresis curves of magnets can be computed
quickly so that the simulations can readily provide guidance for the
development of permanent magnets. The potential of rare-earth reduced and free
permanent magnets is investigated using micromagnetic simulations. The results
show excellent hard magnetic properties can be achieved in grain boundary
engineered NdFeB, rare-earth magnets with a ThMn12 structure, Co-based
nano-wires, and L10-FeNi provided that the magnet's microstructure is
optimized.",1903.11922v1
2021-04-27,Mechanism of parametric pumping of magnetization precession in a nanomagnet. Parametric mechanism of current-induced magnetization reversal,"A mechanism of current-induced magnetization reversal based on the parametric
resonance is described. The source of the magnetization reversal is a
current-induced magnetic field, which is applied perpendicularly to the easy
axis of magnetic anisotropy of a ferromagnetic nanomagnet. The current-induced
magnetic field was measured in a FeCoB nanomagnet to be 60 Gauss at a current
density of 65 mA/um2. Two mechanisms of the magnetization reversal are
described and calculated. The first mechanism is the reversal by a RF
electrical current, which modulated at a frequency close to the precession
frequency of the nanomagnet. The second mechanism is the reversal by a DC
electrical current, in which the magneto-resistance and the current dependency
of the induced magnetic field create a positive feedback loop, which amplifies
a random tiny thermal fluctuation into a large magnetization precession leading
to the magnetization reversal. The combination of the proposed mechanism with
conventional magnetization-reversal mechanisms such as the Spin Torque and the
Spin-Orbit Torque can improve the performance of a Magnetic Random Access
Memory.",2104.13008v1
2021-05-02,Magnetic textures in a hexaferrite thin film and their response to magnetic fields revealed by phase microscopy,"We investigated magnetic textures in a Sc-doped hexaferrite film by means of
phase microscopy (PM) with a hole-free phase plate in a transmission electron
microscope. In a zero magnetic field, the stripe-shaped magnetic domains
coexist with magnetic bubbles. The magnetization in both magnetic domains was
oriented perpendicular to the film and the domain walls have an in-plane
magnetization. In the remnant state at 9.2 mT, several magnetic bubbles were
formed with the formation of stripe-shaped magnetic domains, and the
out-of-plane component in the stripe-shaped domains gradually appeared as the
film thickness increased. As the film thickness increases further, the magnetic
bubbles with clockwise or counter-clockwise spin helicities formed a triangular
lattice. These results in the remnant state suggest that the domain wall energy
in the magnetic bubble domains is lower in the thicker region.",2105.00396v1
2022-04-20,Control of magnetic susceptibility of probiotic strain Lactobacillus Rhamnosus GG,"The paper investigates the increase in the natural magnetically controlled
properties of probiotic microorganisms Lactobacillus rhamnosus GG (LGG) and
their ability to form magnetic sensitive inclusions (MsI). The magnetic
susceptibility of LGG was increased by modifying the nutrient medium
composition and by cultivating the probiotic culture in a constant magnetic
field. Therefore, this study can be useful for their further use as
magnetically controlled vectors, since it is being extensively researched for
the use in targeted drug delivery in cancer treatment, for the prevention of
chemotherapy complications, etc. The results of this study indicate that
growing microorganisms with natural magnetically-guided properties in a
modified medium with iron chelate and in an external magnetic field leads to an
increase in the magnetic susceptibility of LGG by 1,8 and 2,6 times,
respectively, compared with the control. The best magnetic susceptibility was
recorded for LGG suspensions, which were grown in a constant magnetic field and
cultured in modified medium with iron chelate. The LGG suspension, grown both
in a constant magnetic field and on a modified medium with iron chelate, had
the highest magnetic susceptibility and was 4.8 times larger than the control.",2204.09338v1
2022-09-22,Stacking and Layer dependence of magnetic properties in Ti\textsubscript{2}C and Fe\textsubscript{2}C,"Magnetic MXenes are turning out to be an important family of materials for
exploring 2D magnetism. However, investigations into the inter-dependence of
layer thickness, stacking patterns and magnetism in these materials, from a
microscopic point of view, is still lacking. In this work, we have used Density
Functional Theory (DFT) based calculations to understand the effects of layer
thickness and stacking on the magnetic properties in two magnetic MXenes,
Ti$_{2}$C and Fe$_{2}$C in their monolayer and bilayer forms. The ground state
magnetic structures, magnetic moments, magnetic exchange interactions, magnetic
transition temperatures and magnetic anisotropy energies are calculated and
analysed using their electronic structures and standardised models. We find
that in both systems increase in layer thickness (monolayer to bilayer) affects
the ground state magnetic configuration which is driven by the changes in the
magnetic exchange interactions. While the effects of stacking pattern is rather
weak in Ti$_{2}$C, they are substantial, both qualitatively and quantitatively
in Fe$_{2}$C. The computed results are analysed from their electronic
structures. The results suggest that fascinating physical effects can be
obtained in Fe$_{2}$C by tuning the layer thickness and stacking patterns,
making it more suitable for device applications.",2209.10765v1
2023-01-04,Magnetic light amplification by stimulated emission of radiation in subwavelength systems of a dielectric cavity and magnetic quantum emitters,"We propose a magnetic laser in a subwavelength system consisting of a
high-refractive-index dielectric cavity and an active medium formed by magnetic
quantum emitters. Stimulated emissions of magnetic quantum emitters induced by
their coherent interactions with quantized magnetic fields of a cavity are
theoretically considered. The condition to archive such a magnetic laser is
obtained. Numerical results show that magnetic lasers are feasible in some
realistic systems, for example, a silicon disk of high-quality whispering
gallery modes with embedded emitters. Furthermore, the competitions between the
electric interaction and magnetic one in terms of their Purcell factors are
also considered in some magnetic laser achievable systems. In a
wavelength-scale silicon block of a high-order magnetic mode, the ratio of
magnetic Purcell factor to the electric one can reach more than ~10^3 large.
Our results open up ways to enhanced magnetic light-matter interactions.",2301.01418v2
2023-04-23,Magnetism and Fermiology of Kagome Magnet YMn6Sn4Ge2,"Kagome lattice magnets are an interesting class of materials as they can host
topological properties in their magnetic and electronic structures. YMn6Sn6 is
one such compound in which a series of competing magnetic phases is stabilized
by an applied magnetic field, and both an enigmatic topological Hall effect and
a Dirac crossing close to the Fermi energy have been realized. This material
also shows a magnetization-induced Lifshitz transition and evidence of a unique
charge spin coupling in one of the magnetic phases, namely the fan-like phase.
Tuning the magnetism, and thus the interplay with the electronic states, opens
new avenues for precise control of these novel properties. Here, we demonstrate
the extreme sensitivity of the magnetic phases in YMn6Sn4Ge2 through the
investigation of structural, magnetic, and transport properties. The high
sensitivity to small doping provides great potential for engineering the
magnetic phases and associated electronic properties in this family of
rare-earth kagome magnets.",2304.11502v1
2023-06-02,Accelerating the electronic-structure calculation of magnetic systems by equivariant neural networks,"Complex spin-spin interactions in magnets can often lead to magnetic
superlattices with complex local magnetic arrangements, and many of the
magnetic superlattices have been found to possess non-trivial topological
electronic properties. Due to the huge size and complex magnetic moment
arrangement of the magnetic superlattices, it is a great challenge to perform a
direct DFT calculation on them. In this work, an equivariant deep learning
framework is designed to accelerate the electronic calculation of magnetic
systems by exploiting both the equivariant constraints of the magnetic
Hamiltonian matrix and the physical rules of spin-spin interactions. This
framework can bypass the costly self-consistent iterations and build a direct
mapping from a magnetic configuration to the ab initio Hamiltonian matrix.
After training on the magnets with random magnetic configurations, our model
achieved high accuracy on the test structures outside the training set, such as
spin spiral and non-collinear antiferromagnetic configurations. The trained
model is also used to predict the energy bands of a skyrmion configuration of
NiBrI containing thousands of atoms, showing the high efficiency of our model
on large magnetic superlattices.",2306.01558v1
2023-08-10,Change ratios of magnetic helicity and magnetic free energy during major solar flares,"Magnetic helicity is an important concept in solar physics, with a number of
theoretical statements pointing out the important role of magnetic helicity in
solar flares and coronal mass ejections (CMEs). Here we construct a sample of
47 solar flares, which contains 18 no-CME-associated confined flares and 29
CME-associated eruptive flares. We calculate the change ratios of magnetic
helicity and magnetic free energy before and after these 47 flares. Our
calculations show that the change ratios of magnetic helicity and magnetic free
energy show distinct different distributions in confined flares and eruptive
flares. The median value of the change ratios of magnetic helicity in confined
flares is $-0.8$%, while this number is $-14.5$% for eruptive flares. For the
magnetic free energy, the median value of the change ratios is $-4.3$% for
confined flares, whereas this number is $-14.6$% for eruptive flares. This
statistical result, using observational data, is well consistent with the
theoretical understandings that magnetic helicity is approximately conserved in
the magnetic reconnection, as shown by confined flares, and the CMEs take away
magnetic helicity from the corona, as shown by eruptive flares.",2308.05366v1
1997-01-30,Light Element Abundances From z=0 To z=5,"Plausible ratios of deuterium to hydrogen D/H as a function of metallicity,
time, and redshift are investigated. Guided by the heavy element abundance
patterns observed locally in Galactic dwarf stars and at large redshift in
quasi-stellar object absorption line systems, empirical evolution of the
relative abundance ratios Li/D, B/D, N/D, O/D, and F/D for QSO absorption line
systems are given for the possible evolutionary patterns in D/H. Shortened
abstract.",9701243v1
2005-03-04,Solid state components of varying compositions in the outflow of the Red Rectangle,"We present high resolution Spitzer spectroscopy of several pointings in the
outflow of the Red Rectangle. Besides the resonances due to the C-rich PAHs,
the spectra show a wealth of new emission bands, in particular in the 13-19.5
micron range. We argue that these bands are due to solid state components, and
show that simple oxides of a varying composition show a good match to the data.
The presence of these O-rich species in the supposedly C-rich outflow is
unexplained.",0503101v1
1995-11-22,Influence of surfactants on the structure of titanium oxide gels : experiments and simulations,"We report here on experimental and numerical studies of the influence of
surfactants on mineral gel synthesis. The modification of the gel structure
when the ratios water-precursor and water-surfactant vary is brought to the
fore by fractal dimension measures. A property of {\em polydispersity of the
initial hydrolysis} is proposed to explain these results, and is successfuly
tested through numerical experiments of three dimensional chemically limited
aggregation.",9511002v1
1994-02-10,Critical Properties of the Mott Transition in the Hubbard Model,"We introduce a systematic low-energy approach to strongly correlated electron
systems in infinite dimensions, and apply it to the problem of the
correlation-induced metal-insulator transition in the half-filled Hubbard
model. We determine the low-energy scaling functions of the metallic state,
including the single-particle Green function and dynamical spin susceptibility,
as well as thermodynamic properties and relate them to experimental data in
transition metal oxides.",9402047v1
1994-03-01,Berezinskii-Kosterlitz-Thouless Transition in Spin-Charge Separated Superconductor,"A model for spin-charge separated superconductivity in two dimensions is
introduced where the phases of the spinon and holon order parameters couple
gauge-invariantly to a statistical gauge-field representing chiral
spin-fluctuations. The model is analyzed in the continuum limit and in the
low-temperature limit. In both cases we find that physical electronic phase
correlations show a superconducting-normal phase transition of the
Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations
are found to be strictly gapless. The normal-to-superconductor phase boundary
for this model is also obtained as a function of carrier density, where we find
that its shape compares favorably with that of the experimentally observed
phase diagram for the oxide superconductors.",9403003v1
1994-07-01,Charge Transfer Excitons and the Metal-Insulator Transition in the High Temperature Superconductors,"The effects of the nearest neighbour Coulomb repulsion, V, are considered in
the one dimensional copper-oxide chain using the modified Lanczos method. Above
a critical value of V we find that charge transfer excitons are the lowest
lying energy exitations in the insulating phase. Close to the metal-insulator
transition and $V=0$ there is good `particle-hole' symmetry, showing that the
mapping from a two band model to a one band model is appropriate. The effect of
the nearest neighbour repulsion is to create states in the gap and to pin the
Fermi level upon hole doping.",9407004v1
1994-08-31,Observable Zero Sound in Strongly Correlated Metals,"The slow zero-sound mode expected near the Mott transition in strongly
interacting two-dimensional Fermi systems that are neutral is shown to persist
as the physical sound mode in the case that the fermion carries electronic
charge and is embedded in a positive ionic background. The latter sound
velocity softens completely precisely at the Mott transition, indicating that a
zone-center structural transition will occur in the system. We suggest that
this phonon-softening mechanism is related to the structural transitions
commonly observed in the oxide superconductors.",9408096v1
1994-08-31,Liberating Exotic Slaves,"The introduction of confined, ``slave'' fields is frequently useful as a
formal device in models of condensed matter physics; it becomes a conceptual
necessity for describing possible phases of matter where the slaves are
liberated. Here I discuss some aspects of the fractional quantum Hall effect
from this point of view, emphasizing analogies with phenomena in other areas of
physics, particularly to the Meissner and Higgs mechanisms, and to
confinement-deconfinement transitions. In this application, and in some recent
attempts to model the normal state of copper oxide superconductors, it is
important to employ slave anyon fields.",9408100v1
1994-11-11,Many-body and Covalence Effects in the Polarization of Ferroelectric Perovskites,"The ferroelectric polarization of perovskite oxides is much larger than
implied by displacement of static ionic charges. We use an explicitly
correlated scheme to investigate the phenomenon; charge transport is evaluated
as a geometric quantum phase. Both covalence and electron-electron interaction
enhance polarization in the weakly correlated regime. At higher values of the
electron-electron interaction, the system undergoes a transition from a band
insulator to a Mott insulator: the static ionic charge is continuous across the
transition, whereas the polarization is discontinuous. Above the transition,
oxygen transports a positive charge.",9411050v1
1995-05-16,Umklapp scattering from spin fluctuations in Copper-Oxides,"The $\mathbf k$-dependent electronic momentum relaxation rate due to Umklapp
scattering from antiferromagnetic spin fluctuations is studied within a
renormalized mean-field approach to an extended $t-J$ model appropriate to
YBa$_2$Cu$_3$O$_{7-x}$ and other cuprates. Transport coefficients are
calculated in a relaxation time approximation. We compare these results with
those obtained with the phenomenological assumption that all scattering
processes dissipate momentum. We show that the latter, which violates momentum
conservation, leads to quite different magnitudes and temperature dependences
of resistivities and Hall coefficients.",9505067v2
1995-08-11,Superfluid anisotropy in YBCO: Evidence for pair tunneling superconductivity,"Proximity effect and pair tunneling models are applied as alternative
scenarios to explain the recently measured $ab$-plane and $c$-axis components
of the superfluid tensor in Copper-Oxide superconductors which contain chains,
such as $YBa_2Cu_3O_{6.95}$. It is argued that conventional proximity effect
models, which couple chains and planes via single electron tunneling only, are
incompatible with the experimental observations. On the other hand several
surprising features of the experimental data are readily explained by the
presence of a microscopic pair tunneling process.",9508043v1
1995-08-14,Interlayer tunneling in a non-Fermi-liquid metal,"We study the effect of interlayer tunneling in the gauge theory describing a
quasi-two-dimensional paramagnetic metal close to a second-order or weakly
first-order antiferromagnetic phase boundary. In that theory, two species of
fermions have opposite (rather than equal) charges with respect to the gauge
field. We find that single-particle interlayer tunneling is suppressed at low
energies. The effect of pair tunneling is analyzed within the $(3-d)$
expansion. The resulting phase diagram has superconducting and non-Fermi-liquid
normal phases, and so is compatible with that of the copper-oxide
superconductors.",9508050v1
1996-05-03,Finite-temperature Fermi-edge singularity in tunneling studied using random telegraph signals,"We show that random telegraph signals in metal-oxide-silicon transistors at
millikelvin temperatures provide a powerful means of investigating tunneling
between a two-dimensional electron gas and a single defect state. The tunneling
rate shows a peak when the defect level lines up with the Fermi energy, in
excellent agreement with theory of the Fermi-edge singularity at finite
temperature. This theory also indicates that defect levels are the origin of
the dissipative two-state systems observed previously in similar devices.",9605020v1
1996-05-30,Coupling to optical phonons in the one-dimensional t-J model: Effects on superconducting fluctuations and phase separation,"The one-dimensional (1D) $t$-$J$ Holstein model is studied by exact
diagonalization of finite rings using a variational approximation for the
phonon states. Due to renormalization effects induced by the phonons, for
intermediate electron-phonon coupling, the phase separation (PS) boundary, and
with it the region of dominating superconducting fluctuations is shifted
substantially to smaller values of $J/t$ as compared to the pure $t$-$J$ model.
Superconducting correlations are weakened through charge density wave
interactions mediated by the phonons. Possible consequences for the high $T_c$
oxides are discussed.",9605190v1
1996-06-06,Aspects of the normal state phase of copper oxide planes in high Tc superconductors,"We examine various aspects of the normal state phase of ${\rm CuO_{2}}$
planes in the high Tc superconductors. In particular, within the context of the
three band Hubbard model, we study as a function of doping the competition
between a charge density wave phase induced by oxygen breathing modes,
antiferromagnetic order and paramagnetism. To account for the strong electronic
interactions, we use the finite $U$ slave boson method of Kotliar and
Ruckenstein.",9606032v1
1996-09-25,Spectral functions in doped transition metal oxides,"We present experimental photoemission and inverse photoemission spectra of
SrTiO$_{3- \delta}$ representing electron doped $d^0$ systems. Photoemission
spectra in presence of electron doping exhibit prominent features arising from
electron correlation effects, while the inverse photoemssion spectra are
dominated by spectral features explainable within single-particle approaches.
We show that such a spectral evolution in chemically doped correlated systems
is not compatible with expectations based on Hubbard or any other similar
model. We present a new theoretical approach taking into account the
inhomogeneity of the `real' system which gives qualitatively different results
compared to standard `homogeneous' models and is in quantitative agreement with
experiments.",9609259v1
1997-02-12,Charge stripes and spin correlations in copper-oxide superconductors,"Recent neutron diffraction studies have yielded evidence that, in a
particular cuprate family, holes doped into the CuO(2) planes segregate into
stripes that separate antiferromagnetic domains. Here it is shown that such a
picture provides a quantitatively consistent interpretation of the spin
fluctuations measured by neutron scattering in La(1.85)Sr(0.15)CuO(4) and
YBa(2)Cu(3)O(6+x).",9702117v1
1997-02-21,Local moment formation in zinc doped cuprates,"We suggest that when zinc is substituted for copper in the copper oxide
planes of high $T_{c}$ superconductors, it does not necessarily have a valency
of 2+. Rather, the valency of a zinc impurity should be determined by its
surrounding medium. In order to study this hypothesis, we examine the effect of
static impurities inducing diagonal disorder within a one band Hubbard model
coupled to a localised state. We use this model to discuss the physics of zinc
doping in the cuprates. Specifically, we discuss the formation of local moments
near impurity sites and the modification of the transverse spin susceptibility
in the antiferromagnetic state.",9702190v1
1997-03-14,Theory of colossal magnetoresistance,"The history and recent developments in studying (colossal) magnetoresistance
in perovskite manganese oxides is reviewed. We emphasize the growing evidence
for strongly coupled spin, charge and lattice degrees of freedom. Together with
disorder, these provide the microscopic driving forces for local and
inhomogeneous textures. The modeling and experimental probes for localized
charge-spin-lattice (polaron) structures, and their multiscale ordering, is
discussed in terms of a growing synergy of solid state physics and materials
science perspectives.",9703148v1
1997-06-03,Nanoscale Field-Effect Transistors: An Ultimate Size Analysis,"We have used a simple, analytically solvable model to analyze the
characteristic s of dual-gate metal-oxide-semiconductor field-effect
transistors (MOSFETs) with 10-nm-scale channel length L. The model assumes
ballistic dynamics of 2D electrons in an undoped channel between highly doped
source and drain. When applied to silicon n-MOSFETs, calculations show that the
voltage gain (necessary for logic applications) drops sharply at L ~ 10 nm,
while the conductance modulation remains sufficient for memory applications
until L ~ 4 nm.",9706026v2
1997-07-31,Fingering Instability in Combustion,"A thin solid (e.g., paper), burning against an oxidizing wind, develops a
fingering instability with two decoupled length scales. The spacing between
fingers is determined by the P\'eclet number (ratio between advection and
diffusion). The finger width is determined by the degree two dimensionality.
Dense fingers develop by recurrent tip splitting. The effect is observed when
vertical mass transport (due to gravity) is suppressed. The experimental
results quantitatively verify a model based on diffusion limited transport.",9707333v1
1997-09-29,Modulated spin and charge densities in cuprate superconductors,"Neutron scattering experiments have played a crucial role in characterizing
the spin and charge correlations in copper-oxide superconductors. While the
data are often interpreted with respect to specific theories of the cuprates,
an attempt is made here to distinguish those facts that can be extracted
empirically, and the connections that can be made with minimal assumptions.",9709325v1
1997-10-08,Spin and orbital excitation spectrum in the Kugel-Khomskii model,"We discuss spin and orbital ordering in the twofold orbital degenerate
superexchange model in three dimensions relevant to perovskite transition metal
oxides. We focus on the particular point on the classical phase diagram where
orbital degeneracy is lifted by quantum effects exclusively. Dispersion and
damping of the spin and orbital excitations are calculated at this point taking
into account their mutual interaction. Interaction corrections to the
mean-field order parameters are found to be small. We conclude that
quasi-one-dimensional Neel spin order accompanied by the uniform
d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.",9710070v1
1998-04-15,Phase Diagram of High-T_c Superconductors from a Field Theory Model,"The renormalization group approach to correlated fermions is used to
determine the phase diagram of the oxide cuprates modeled by the t-t' Hubbard
model at the Van Hove filling. Spin-dependent interactions give rise to
instabilities corresponding to ferromagnetic, antiferromagnetic and d-wave
superconducting phases. Antiferromagnetism and d-wave superconductivity arise
from the same interactions, and compete in the same region of parameter space.",9804153v1
1998-06-26,Quantitative Determination of a Microscopic Mechanism of High Tc Superconductivity,"Within the t-J model of copper-oxides, the condensation energy can be related
to the change in the dynamical spin structure factor between the
superconducting and the normal states. By analyzing previous experimental data,
we show that the change associated with the resonant neutron scattering peak
found in $YBa_2Cu_3O_7$ can quantitatively account for the condensation energy.
We argue that this analysis suggests a microscopic mechanism for high Tc
superconductivity.",9806336v2
1998-09-18,On the glass transition temperature in covalent glasses,"We give a simple demonstration of the formula relating the glass transition
temperature, $T_g$, to the molar concentration $x$ of a modifier in two types
of glasses: binary glasses, whose composition can be denoted by
$X_nY_m+xM_pY_q$, with ^$X$ an element of III-rd or IV-th group (e.g. B, or Si,
Ge), while $M_pY_q$ is an alkali oxide or chalcogenide; next, the network
glasses of the type $A_xB_{1-x}$, e.g. $Ge_xSe_{1-x}$, $Si_xTe_{1-x}$, etc.
After comparison, this formula gives an exact expression of the parameter
$\beta$ of the modified Gibbs-Di Marzio equation.",9809245v1
1998-11-19,The Singlet-Triplet Pseudo-Jahn-Teller Centers in Copper Oxides,"One of the most exciting features of the hole centers CuO_{4}^{5-} in doped
cuprates is an unusually complicated ground state which is the result of the
electronic quasi-degeneracy. An additional hole, doped to the basic
CuO_{4}^{6-} cluster with the b_{1g} hole can occupy both the same hybrid
Cu3d-O2p orbital state resulting in a Zhang-Rice singlet ^1A_{1g} and the
purely oxygen e_u molecular orbital resulting in a singlet or triplet ^{1,3}E_u
term with the close energies. We present detailed analysis of the
(pseudo)-Jahn-Teller effect driven by the near-degeneracy within the
(^1A_{1g},^{1,3}E_u)-manifold.",9811293v1
1999-01-03,"Comment on ""Theory of metal-insulator transitions in gated semiconductors"" (B. L. Altshuler and D. L. Maslov, Phys. Rev. Lett. 82, 145 (1999))","In a recent Letter, Altshuler and Maslov propose a model which attributes the
anomalous temperature and field dependence of the resistivity of
two-dimensional electron (or hole) systems to the charging and discharging of
traps in the oxide (spacer), rather than to intrinsic behavior of interacting
particles associated with a conductor-insulator transition in two dimensions.
We argue against this model based on existing experimental evidence.",9901005v1
1999-02-09,Andreev reflections in the pseudogap state of cuprate supercondcutors,"We propose that, if the pseudogap state in the cuprate superconductors can be
described in terms of the phase-incoherent preformed pairs, there should exist
Andreev reflection from these pairs even above the superconducting transition
temperature, $T_c$. After giving qualitative arguments for this effect, we
present more quantitative calculations based on the Bogoliubov--de Gennes
equation. Experimental observations of the effects of Andreev reflections above
$T_c$---such as an enhanced tunneling conductance below the gap along the
copper oxide plane---could provide unambiguous evidence for the preformed pairs
in the pseudogap state.",9902125v2
1999-02-12,Optical Conductivity in a Simple Model of Pseudogap State in Two-Dimensional System,"We present calculation of optical conductivity in a simple model of
electronic spectrum of two-dimensional system with ""hot patches"" on the Fermi
surface, leading to non Fermi-liquid renormalization of the spectral density
(pseudogap) on these patches. It is shown that this model qualitatively
reproduces basic anomalies of optical experiments in the pseudogap state of
copper oxides.",9902192v1
1999-06-01,"Interplay between orbital ordering and lattice distortions in LaMnO3, YVO3, and YTiO3","We have studied the interplay between orbital ordering, Jahn-Teller and
GdFeO3-type lattice distortions in perovskite-type transition-metal oxides
using model Hartree-Fock calculations. It has been found that the covalency
between A-site cations and oxygens causes interaction between the Jahn-Teller
and GdFeO3-type distortions. The present calculations explain why the d-type
Jahn-Teller distortion and orbital ordering compatible with it are realized in
LaMnO3, YVO3 and YTiO3",9906010v1
1999-06-15,Internal Spatiotemporal Stochastic Resonance in a Microscopic Surface Reaction Model,"We show the existence of internal stochastic resonance in a microscopic
stochastic model for the oscillating CO oxidation on single crystal surfaces.
This stochastic resonance arises directly from the elementary reaction steps of
the system without any external input. The lattice gas model is investigated by
means of Monte Carlo simulations. It shows oscillation phenomena and mesoscopic
pattern formation. Stochastic resonance arises once homogeneous nucleation in
the individual surface phases (reconstructed and non-reconstructed) is added.
This nucleation is modelled as a noise process. As a result, synchronization of
the kinetic oscillations is obtained. Internal stochastic resonance may thus be
an internal regulation mechanism of extreme adaptability.",9906215v1
1999-07-02,Quantum Phase Fluctuations in High Tc Superconductors,"If phase coherence determines the superconducting transition temperature Tc
in the cuprate oxides, it is of great interest to understand the role that
dynamics of the phase fluctuation plays in bringing about depletion of the
superconducting condensate. We will show that a phase correlation function can
be calculated that allows us to describe depletion of superconducting
condensate as a result of the quantum fluctuation. In two dimension, dynamic
phase fluctuation or pair fluctuation gives rise to a condensate depletion
linear with temperature as T$\to O$ in superconductors with nodes at the fermi
surface.",9907035v2
1999-07-15,Stripe phases in high-temperature superconductors,"Stripe phases are predicted and observed to occur in a class of
strongly-correlated materials describable as doped antiferromagnets, of which
the copper-oxide superconductors are the most prominent representative. The
existence of stripe correlations necessitates the development of new principles
for describing charge transport, and especially superconductivity, in these
materials.",9907228v1
1999-08-03,"Transport Properties in (Na,Ca)Co_2O_4 Ceramics","The resistivity and thermopower of polycrystalline (Na,Ca)Co_2O_4 were
measured and analyzed. Both the quantities increase with x, suggesting that the
carrier density is decreased by the substitutions of Ca^{2+} for Na^{+}.
Considering that the temperature dependence of the resistivity show a
characteristic change with x, the conduction mechanism is unlikely to come from
a simple electron-phonon scattering. As a reference for NaCo_2O_4, single
crystals of a two-dimensional Co oxide (Bi,Pb)_2M_3Co_2O_9 (M=Sr and Ba) were
studied. The Pb substitution decreases the resistivity, leaving the thermopower
nearly intact.",9908039v1
1999-08-18,Inelastic neutron scattering peak in Zn substituted YBa2Cu3O7,"The effects of nonmagnetic impurities on the neutron scattering intensity are
studied for a model of the copper oxide layers in the normal state. The
contribution to the Q=(pi,pi) neutron scattering intensity from processes
involving the scattering of the spin fluctuations from an impurity with large
momentum transfers are calculated within the random phase approximation. It is
shown that this type of scatterings could lead to a peak in the neutron
scattering intensity in the normal state.",9908266v1
1999-09-01,Normal Fermi Liquid Behavior of Quasiholes in the Spin-Polaron Model for Copper Oxides,"Based on the t-J model and the self-consistent Born approximation, the
damping of quasiparticle hole states near the Fermi surface is calculated in a
low doping regime. Renormalization of spin-wave excitations due to hole doping
is taken into account. The damping is shown to be described by a familiar form
$\text{Im}\Sigma({\bf k}^{\prime},\epsilon)\propto (\epsilon^{2}/
\epsilon_{F})\ln(\epsilon/ \epsilon_{F})$ characteristic of the 2-dimensional
Fermi liquid, in contrast with the earlier statement reported by Li and Gong
[Phys. Rev. B {\bf 51}, 6343 (1995)] on the marginal Fermi liquid behavior of
quasiholes.",9909020v1
1999-09-22,Dielectric Response Near the Density-Driven Mott Transition in infinite dimensions,"We study the dielectric response of correlated systems which undergo a Mott
transition as a function of band filling within the dynamical mean field
framework. We compute the dielectric figure of merit (DFOM), which is a measure
of dielectric efficiency and an important number for potential device
applications. It is suggested how the DFOM can be optimized in real transition
metal oxides. The structures seen in the computed Faraday rotation are
explained on the basis of the underlying local spectral density of the
$d=\infty$ Hubbard model.",9909326v1
1999-10-20,Proposal for an Experiment to Test a Theory of High Temperature Superconductors,"A theory for the phenomena observed in Copper-Oxide based high temperature
superconducting materials derives an elusive time-reversal and rotational
symmetry breaking order parameter for the observed pseudogap phase ending at a
quantum-critical point near the composition for the highest $T_c$. An
experiment is proposed to observe such a symmetry breaking. It is shown that
Angle-resolved Photoemission yields a current density which is different for
left and right circularly polarized photons. The magnitude of the effect and
its momentum dependence is estimated. Barring the presence of domains of the
predicted phase an asymmetry of about 0.1 is predicted at low temperatures in
moderately underdoped samples.",9910310v1
1999-11-09,The Mott transition in V_2 O_3 and Ni Se_x S_{2-x}: insights from dynamical mean field theory,"We discuss some aspects of the pressure (or interaction) driven Mott
transition, in three dimensional transition metal oxides by means of dynami cal
mean field theory. We isolate the universal properties of the transition from
the aspects which depend more on the detailed chemistry of the compounds. In
this light we can understand the main differences and the remarkable
similarities between these systems. Both theory and experiment converge on the
transfer of spectral weight from low energies to high energies as the universal
mechanism underlying the Mott transition, and we comment on the possible
relevance of these ideas to other metal to non metal transitions.",9911114v1
1999-11-15,Selection Rules for Resonant Inelastic X-Ray Scattering from Tetragonal Copper-Oxides,"We demonstrate the utility of point group representation theory for symmetry
analysis in resonant inelastic x-ray scattering. From its
polarization-dependence, we show that a 5 eV inelastic feature in Sr2CuO2Cl2
has pure B1g symmetry and assign it to a transition in the cell-perturbation
calculations of Simon, et. al. [Phys. Rev. B., 54, R3780 (1996)]. We discuss
how Raman selection rules are broken at nonzero momentum transfer and how this
can also act as a probe of wave function symmetry.",9911215v1
1999-11-16,Topological Scenario for Stripe Formation in Manganese Oxides,"The spin-charge-orbital complex structures of manganites are studied using
topological concepts. The key quantity is the ""winding number"" w associated
with the Berry-phase connection of an e_g electron parallel-transported through
Jahn-Teller centers, along zigzag one-dimensional paths in an antiferromagnetic
environment of t_{2g} spins. From these concepts, it is shown that the
""bi-stripe"" and ""Wigner-crystal"" states observed experimentally have different
w's. Predictions for the spin structure of the charge-ordered states for
heavily doped manganites are discussed.",9911248v1
1999-11-30,From antiferromagnetism to d-wave superconductivity in the 2D t-J model,"We have found that the two dimensional t-J model, for the physical parameter
range J/t = 0.4 reproduces the main experimental qualitative features of
High-Tc copper oxide superconductors: d-wave superconducting correlations are
strongly enhanced upon small doping and clear evidence of off diagonal long
range order is found at the optimal doping \delta ~ 0.15. On the other hand
antiferromagnetic long range order, clearly present at zero hole doping, is
suppressed at small hole density with clear absence of antiferromagnetism at
\delta >~ 0.1.",9911478v1
1999-12-20,A planar diagram approach to the correlation problem,"We transpose an idea of 't Hooft from its context of Yang and Mills' theory
of strongly interacting quarks to that of strongly correlated electrons in
transition metal oxides and show that a Hubbard model of N interacting electron
species reduces, to leading orders in N, to a sum of almost planar diagrams.
The resulting generating functional and integral equations are very similar to
those of the FLEX approximation of Bickers and Scalapino. This adds the Hubbard
model at large N to the list of solvable models of strongly correlated
electrons.
  PACS Numbers: 71.27.+a 71.10.-w 71.10.Fd",9912350v1
2000-01-04,Doppler shift on local density of states and local impurity scattering in the vortex state,"The vortex state thermal and transport properties of the high T_c copper
oxides can be understood in a d-wave gap model and are dominated by the
extended quasiparticle states that exist along the nodal directions in momentum
space. The Doppler shift on these states due to the circulating supercurrents
around the vortex core, introduces new van Hove ridges into the energy
dependent local density of states (LDOS) as a function of distance in the
region between cores. We emphasize the topology of these ridges and the effect
on them of local impurity scattering in Born and unitary limit. We treat
possible orthorhombicity. Effective local scttering rates are also obtaines.",0001029v1
2000-01-27,s+d pairing in orthorhombic phase of copper-oxides,"A microscopical theory of electronic spectrum and superconductivity is
formulated within the two-dimensional anisotropic t-J model with t_{x}\neq
t_{y} and J_{x}\neq J_{y}. Renormalization of electronic spectrum and
superconductivity mediated by spin-fluctuations are investigated within the
Eliashberg equation in the weak coupling approximation. The gap function has
d+s symmetry with the extended s-wave component being proportional to the
asymmetry t_{y} - t_{x}. Some experimental consequences of the obtained results
are discussed.",0001401v1
2000-01-31,Universal c-axis conductivity of high-$T_c$ oxides in the superconducting state,"The anisotropy in the temperature dependence of the in-plane and c-axis
conductivities of high-T_c cuprates in the superconducting state is shown to be
consistent with a strong in-plane momentum dependence of both the quasiparticle
scattering rate and the interlayer hopping integral. Applying the cold spot
scattering model recently proposed by Ioffe and Millis (Phys. Rev. B {\bf 58},
11631 (1998)) to the superconducting state, we find that the c-axis
conductivity varies approximately as T^3 in an intermediate temperature regime,
in good agreement with the experimental result for optimally doped
YBa_2Cu_3O_{7-x} and Bi_2Sr_2CaCu_2O_{8+x}.",0001443v2
2000-02-02,Charge and spin ordering in Nd{1/3}Sr{2/3}FeO{3},"We have investigated the charge and spin ordering in Nd{1/3}Sr{2/3}FeO{3}
with neutron diffraction technique. This sample undergoes a charge ordering
transition accompanying charge disproportionation of 2Fe4+ -> Fe3+ + Fe5+. We
measured the superlattice reflections due to the charge and spin ordering, and
confirmed that charges and spins order simultaneously at Tco = 185 K. The
ordering pattern of charges and spins in this sample can be viewed as three
dimensional stripe order, and is compared with two dimensional stripe order
observed in other transition metal oxides.",0002023v1
2000-02-06,Double-dot charge transport in Si single electron/hole transistors,"We studied transport through ultra-small Si quantum dot transistors
fabricated from silicon-on-insulator wafers. At high temperatures, 4K<T<100K,
the devices show single-electron or single-hole transport through the
lithographically defined dot. At T<4K, current through the devices is
characterized by multidot transport. From the analysis of the transport in
samples with double-dot characteristics, we conclude that extra dots are formed
inside the thermally grown gate oxide which surrounds the lithographically
defined dot.",0002080v1
2000-05-10,Quantum phase transition in a random-tiling model,"The analogue of a Mott-Hubbard transition is discussed, which appears at an
incommensurate filling in a model of a two-dimensional plane, randomly tiled
with CuO_4 `molecules', simulating the copper-oxide planes of high-T_c
superconductors. It is shown to be a quantum phase transition, which can be
crossed either in doping, at a fixed hopping overlap t, or in t, when the
doping is fixed in a certain range below half-filling. It is first-order,
closely analogous to a liquid-gas transition.",0005170v1
2000-05-24,Difference between microscopic and effective overlaps in the copper-oxide planes of high-Tc superconductors,"We investigate parametrizations required to reproduce observed Fermi surfaces
of overdoped and slightly underdoped LSCO in two different models. One is the
standard three-band saddle-point slave boson (SB). The other is a model of CuO4
`molecules' randomly tiled in the plane, emphasizing the distinction between
the local overlap, always the full (bare) one, and the effective overlap,
connected with the reduced bandwidth due to the random tiling (RT). We conclude
this distinction is physically significant for underdoped, but not for
overdoped LSCO. This is consistent with the observed open Fermi surfaces being
due to correlation effects.",0005409v1
2000-07-27,"Pairing, Stripes, Lattice Distortions and Superconductivity in Cuprate Oxides","We propose a model for a spatially modulated collective state of
superconducting cuprates in which the electronic properties vary locally in
space. In this model the regions of higher hole density (called stripes) are
described as Luttinger liquids and the regions of lower density
(antiferromagnetic ladders) as an interacting bosonic gas of d$_{x^2-y^2}$ hole
pairs. We show that the transition to the superconducting state is topological
and driven by decay processes among these elementary excitations in the
presence of vibrations.",0007434v1
2000-09-12,The Electrochemical Carbon Nanotube Field-Effect Transistor,"We explore the electric-field effect of carbon nanotubes (NTs) in
electrolytes. Due to the large gate capacitance, Fermi energy shifts of order
+/- 1 V can be induced, enabling to tune NTs from p to n-type. Consequently,
large resistance changes are measured. At zero gate voltage the NTs are hole
doped in air with E_F ? 0.3-0.5 eV, corresponding to a doping level of ?
10^{13} cm^{-2}. Hole-doping increases in the electrolyte. This hole doping
(oxidation) is most likely caused by the adsorption of oxygen in air and
cations in the electrolyte.",0009171v1
2000-09-21,Single hole transistor in a p-Si/SiGe quantum well,"A single hole transistor is patterned in a p-Si/SiGe quantum well by applying
voltages to nanostructured top gate electrodes. Gating is achieved by oxidizing
the etched semiconductor surface and the mesa walls before evaporation of the
top gates. Pronounced Coulomb blockade effects are observed at small coupling
of the transistor island to source and drain.",0009323v2
2000-10-13,Ab initio calculations of response properties including electron-hole interaction,"We discuss the current status of a computational approach which allows to
evaluate the dielectric matrix, and hence electronic excitations like optical
properties, including local field and excitonic effects. We introduce a recent
numerical development which greatly reduces the use of memory in such type of
calculations, and hence eliminates one of the bottlenecks for the application
to complex systems. We present recent applications of the method, focusing our
interest on insulating oxides.",0010194v1
2000-10-17,Metal insulator transition in TlSr2CoO5 from orbital degeneracy and spin disproportionation,"To describe the metal insulator transition in the new oxide TlSr2CoO5 we
investigate its electronic structure by LDA and model Hartree-Fock
calculations. Within LDA we find a homogeneous metallic and ferromagnetic
ground state, but when including the Coulomb interaction more explicitly within
the Hartree-Fock approximation, we find an insulating state of lower energy
with both spin and orbital order. We also interpret our results in terms of a
simple model.",0010239v1
2000-11-04,Orbital polarons and ferromagnetic insulators in manganites,"We argue that in lightly hole doped perovskite-type Mn oxides the holes
(Mn$^{4+}$ sites) are surrounded by nearest neighbor Mn$^{3+}$ sites in which
the occupied $3d$ orbitals have their lobes directed towards the central hole
(Mn$^{4+}$) site and with spins coupled ferromagnetically to the central spin.
This composite object, which can be viewed as a combined orbital-spin-lattice
polaron, is accompanied by the breathing type (Mn$^{4+}$) and Jahn-Teller type
(Mn$^{3+}$) local lattice distortions. We present calculations which indicate
that for certain doping levels these orbital polarons may crystallize into a
charge and orbitally ordered ferromagnetic insulating state.",0011070v1
2000-11-07,Soft Phonon Anomalies in Relaxor Ferroelectrics,"A review is given of the phonon anomalies, which have been termed
``waterfalls,'' that were recently discovered through a series of neutron
inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT,
PMN, and PZN. We discuss a simple coupled-mode model that has been used
successfully to describe the basic features of the waterfall, and which relates
this unusual feature to the presence of polar micro-regions.",0011122v1
2000-11-13,Theory of Adsorption on Metal Substrates,"Contents:
  5.1 Introduction
  5.2 Concepts and definitions
  5.3 The tight-binding picture of bonding
  5.4 Adsorption of isolated adatoms
  5.5 Alkali-metal adsorption: the traditional picture of on-surface adsorption
  5.6 Substitutional adsorption and formation of surface alloys
  5.7 Adsorption of CO on transition-metal surfaces - a model system for a
simple molecular adsorbate
  5.8 Co-adsorption [the example CO plus O on Ru(0001)]
  5.9 Chemical reactions at metal surfaces
  5.10 The catalytic oxidation of CO
  5.11 Summary outline of main points",0011217v1
2001-01-01,Characterization of halogen-bridged binuclear metal complexes as hybridized two-band materials,"We study the electronic structure of halogen-bridged binuclear metal (MMX)
complexes with a two-band Peierls-Hubbard model. Based on a symmetry argument,
various density-wave states are derived and characterized. The ground-state
phase diagram is drawn within the Hartree-Fock approximation, while the thermal
behavior is investigated using a quantum Monte Carlo method. All the
calculations conclude that a typical MMX compound Pt_2(CH_3CS_2)_4I should
indeed be regarded as a d-p-hybridized two-band material, where the oxidation
of the halogen ions must be observed even in the ground state, whereas another
MMX family (NH_4)_4[Pt_2(P_2O_5H_2)_4X] may be treated as single-band
materials.",0101007v1
2001-02-08,Heavy-Fermion Formation at the Metal-to-Insulator Transition in Gd$_{1-x}$Sr$_x$TiO$_3$,"The perovskite-like transition-metal oxide Gd$_{1-x}$Sr$_x$TiO$_3$ is
investigated by measurements of resistivity, specific-heat, and electron
paramagnetic resonance (EPR). Approaching the metal-to-insulator transition
from the metallic regime ($x \geq 0.2$), the Sommerfeld coefficient $\gamma$ of
the specific heat becomes strongly enhanced and the resistivity increases
quadratically at low temperatures, which both are fingerprints of strong
electronic correlations. The temperature dependence of the dynamic
susceptibility, as determined from the Gd$^{3+}$-EPR linewidth, signals the
importance of strong spin fluctuations, as observed in heavy-fermion compounds.",0102161v1
2001-02-28,Nearest-neighbour Attraction Stabilizes Staggered Currents in the 2D Hubbard Model,"Using a strong-coupling approach, we show that staggered current vorticity
does not obtain in the repulsive 2D Hubbard model for large on-site Coulomb
interactions, as in the case of the copper oxide superconductors. This trend
also persists even when nearest-neighbour repulsions are present. However,
staggered flux ordering emerges {\bf only} when attractive nearest-neighbour
Coulomb interactions are included. Such ordering opens a gap along the
$(\pi,0)-(0,\pi)$ direction and persists over a reasonable range of doping.",0102527v3
2001-03-08,Upper critical field in {Ba$_{1-x}$K$_x$BiO$_3$}: magnetotransport versus magnetotunneling,"Elastic tunneling is used as a powerful direct tool to determine the upper
critical field $H_{c2}(T)$ in the high-$T_c$ oxide Ba$_{1-x}$K$_x$BiO$_3$. The
temperature dependence of $H_{c2}$ inferred from the tunneling follows the
Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A
comparison will be made with resistively determined critical field data.",0103183v1
2001-04-24,Electrical current distribution across a metal-insulator-metal structure during bistable switching,"Combining scanning electron microscopy (SEM) and electron-beam-induced
current (EBIC) imaging with transport measurements, it is shown that the
current flowing across a two-terminal oxide-based capacitor-like structure is
preferentially confined in areas localized at defects. As the thin-film device
switches between two different resistance states, the distribution and
intensity of the current paths, appearing as bright spots, change. This implies
that switching and memory effects are mainly determined by the conducting
properties along such paths. A model based on the storage and release of charge
carriers within the insulator seems adequate to explain the observed memory
effect.",0104452v1
2001-08-01,Quantum dots in suspended single-wall carbon nanotubes,"We present a simple technique which uses a self-aligned oxide etch to suspend
individual single-wall carbon nanotubes between metallic electrodes. This
enables one to compare the properties of a particular nanotube before and after
suspension, as well as to study transport in suspended tubes. As an example of
the utility of the technique, we study quantum dots in suspended tubes, finding
that their capacitances are reduced owing to the removal of the dielectric
substrate.",0108020v1
2001-08-21,"Structural compliance, misfit strain and stripe nanostructures in cuprate superconductors","Structural compliance is the ability of a crystal structure to accommodate
variations in local atomic bond-lengths without incurring large strain
energies. We show that the structural compliance of cuprates is relatively
small, so that short, highly doped, Cu-O-Cu bonds in stripes are subject to a
tensile misfit strain. We develop a model to describe the effect of misfit
strain on charge ordering in the copper oxygen planes of oxide materials and
illustrate some of the low energy stripe nanostructures that can result.",0108338v2
2001-08-29,Anomalous Co-site substitution effects on the physical properties of the thermoelectric oxide NaCo2O4,"We prepared polycrystalline samples of NaCo2-xMxO4 substituted for the Co
site by other 3d or 4d elements (M=Mn,Cu, Zn, Ru, Rh, and Pd). While some of
the elements (M=Mn,Ru and Rh) act as a strong scatterer to give rise to a rapid
increase in resistivity, the others (M=Cu, Zn and Pd) do not deteriorate the
electric conduction of the host. Most unusually, the Cu substitution
significantly enhances the thermopower, which increases the figure of merit by
several times at 100 K.",0108485v1
2001-09-20,Developments in the negative-U modelling of the cuprate HTSC systems,"The paper deals with the many stands that go into creating the unique and
complex nature of the HTSC cuprates above Tc as below. Like its predecessors it
treats charge, not spin or lattice, as prime mover, but thus taken in the
context of the chemical bonding relevant to these copper oxides. The crucial
shell filling, negative-U, double-loading fluctuations possible there require
accessing at high valent local environment as prevails within the mixed valent,
inhomogeneous two sub-system circumstance of the HTSC materials. Close
attention is paid to the recent results from Corson, Demsar, Li, Johnson,
Norman, Varma, Gyorffy and colleagues.",0109369v1
2001-10-09,Evidence for three dimensional superconductivity in the cuprates oxides,"We review the empirical scenario emerging from the measured doping dependence
of the transition temperature and the anisotropy parameter $% \gamma $ $=\xi
_{ab}/\xi_{c}$, defined as the ratio of the correlation lengths parallel and
perpendicular to the ab-planes. It suggests that two dimensional models cannot
explain the occurrence of superconductivity in the cuprates. This conclusion is
confirmed and extended in terms of a novel scaling relation. It involves the
transition temperature, the aerial superfluid density in the ground state,
$\gamma $ and the dynamic critical exponent of the quantum superconductor to
insulator transition. The important implication there is that a non vanishing
superfluid density in the ground state of the cuprates is unalterably linked to
an anisotropic but 3D condensation mechanism.",0110173v1
2001-10-12,What High Pressure Studies Have Taught Us about High-Temperature Superconductivity,"Superconductivity is an important area of modern research which has benefited
enormously from experiments under high pressure conditions. The focus of this
paper will be on three classes of high-temperature superconductors: (1) the new
binary compound MgB2, (2) the alkali-doped fullerenes, and (3) the cuprate
oxides. We will discuss results from experiment and theory which illustrate the
kinds of vital information the high-pressure variable can give to help better
understand these fascinating materials.",0110267v1
2001-11-22,Theory for high spin systems with orbital degeneracy,"High-spin systems with orbital degeneracy are studied in the large spin
limit. In the absence of Hund's coupling, the classical spin model is mapped
onto disconnected orbital systems with spins up and down, respectively. The
ground state of the isotropic model is an orbital valence bond state where each
bond is an orbital singlet with parallel spins, and neighbouring bonds interact
antiferromagnetically. The possible relevance to the transition metal oxides
are discussed.",0111426v1
2001-12-13,Dimensional cross-over and charge order in half-doped Manganites and Cobaltites,"We introduce a general model for understanding the effect of quenched
disorder on charge ordering in half-doped Manganese- and Cobalt-Oxides with
different crystal structures. Current experimental results (Table-1) are
discussed in light of the global phase diagram of the model (Fig. 2).",0112240v6
2002-01-03,Detection and Implications of a Time-reversal breaking state in underdoped Cuprates,"We present general symmetry considerations on how a Time-reversal breaking
state may be detected by angle-resolved photoemission using circularly
polarized photons as has been proposed earlier. Results of recent experiments
utilizing the proposal in underdoped cuprates are analysed and found to be
consistent in their symmetry and magnitude with a theory of the Copper-Oxides.
These togather with evidence for a quantum critical point and marginal
Fermi-liquid properties near optimum doping suggest that a valid microscopic
theory of the phenomena in the cuprates has been found.",0201036v3
2002-01-11,New Phase Transition in Polymer Solutions with Multicomponent Solvent,"Considering the density-density correlation function of a concentrated
polymer solution with multicomponent solvent we find a phase transition due to
the heterogeneity of excluded volume constant. This new phase transition
implies a strong enhancement of the scattered light intensity in the critical
region, which can explain a recent experiment showing strong light scattering
from a ternary polymer system consisting of polyethylene oxide (PEO) dissolved
in nitroethane and 3methyl-pentane.",0201170v2
2002-02-08,Fermi Surface of 3d^1 Perovskite CaVO3 Near the Mott Transition,"We present a detailed de Haas van Alphen effect study of the perovskite
CaVO3, offering an unprecedented test of electronic structure calculations in a
3d transition metal oxide. Our experimental and calculated Fermi surfaces are
in good agreement -- but only if we ignore large orthorhombic distortions of
the cubic perovskite structure. Subtle discrepancies may shed light on an
apparent conflict between the low energy properties of CaVO3, which are those
of a simple metal, and high energy probes which reveal strong correlations that
place CaVO3 on the verge of a metal-insulator transition.",0202147v1
2002-02-22,Hierarchical Random Telegraph Signals in nano-junctions with Coulomb correlations,"We propose a microscopic hamiltonian together with a master equation
description to model stochastic hierarchical Random Telegraph Signal (RTS) or
Pop-corn noise in nano-junctions. The microscopic model incorporates the
crucial Coulomb correlations due to the trapped charges inside the junction or
at the metal-oxide interface. The exact solution of the microscopic model is
based on a generalization of the Nozieres-De Dominicis method devised to treat
the problem of the edge singularity in the X-ray absorption and emission
spectra of metals. In the master equation description, the experimentally
accessible transition rates are expressed in terms of the exact multi-channel
Scattering matrix of the microscopic hamiltonian.",0202395v2
2002-02-28,On the heavy-fermion behavior of the pyrochlore transition-metal oxide $LiV_{2}O_{4}$,"Motivated by the heavy fermion Fermi liquid (HFFL) features observed at
low-$T$ in the pyrochlore $LiV_{2}O_{4}$, we consider a material-specific model
that includes aspects of the local quantum chemistry, the geometrically
frustrated lattice structure, and strong correlations in a {\it single}
approach. In particular, we show how geometrical frustration (GF) gives rise to
a crossover scale, $T^{*}<<J$, the intersite (AF) exchange, below which the
metallic system shows HFFL features. Our scenario is a specific realization of
the importance of GF effects in driving HFFL behavior in $LiV_{2}O_{4}$, and
provides a natural understanding of various puzzling features observed
experimentally.",0202531v1
2002-04-16,Spatial and temporal probes in inhomogeneous systems: Theory and experiment,"The experimental and theoretical challenges posed by the study of dynamically
inhomogeneous systems are outlined in the context of cuprates and other oxides.
Considering the pitfalls in the single-component approach to the analysis of
inhomogeneous systems, the effect of either temporal or spatial averaging by
different experiments is discussed. A group-theoretical symmetry analysis of
the observed inhomogeneities in real space and k-space observed in the cuprates
is shown to lead to a quantitatively verifiable description of the
inhomogeneous state, comprising of bound singlet pairs in the ground state and
unbound fermions in the excited state. The predicted symmetry breaking
associated with pairing is shown to be verifiable experimentally.",0204339v1
2002-06-13,Single domain transport measurements of C60 films,"Thin films of potassium doped C60, an organic semiconductor, have been grown
on silicon. The films were grown in ultra-high vacuum by thermal evaporation of
C60 onto oxide-terminated silicon as well as reconstructed Si(111). The
substrate termination had a drastic influence on the C60 growth mode which is
directly reflected in the electrical properties of the films. Measured on the
single domain length scale, these films revealed resistivities comparable to
bulk single crystals. In situ electrical transport properties were correlated
to the morphology of the film determined by scanning tunneling microscopy. The
observed excess conductivity above the superconducting transition can be
attributed to two-dimensional fluctuations.",0206221v1
2002-07-10,Different routes to charge disproportionation in perovskites-type Fe oxides,"Iron perovskites CaFeO_3 and La_{0.33}Sr_{0.67}FeO_3 show charge
disproportionation, resulting in charge-ordered states with Fe^{3+}:Fe^{5+}
=1:1 and =2:1, respectively. We have made photoemission and unrestricted
Hartree-Fock band-structure calculation of CaFeO_3 and compared it with
La_{0.33}Sr_{0.67}FeO_3. With decreasing temperature, a gradual decrease of the
spectral weight near the Fermi level occurred in CaFeO_3 as in
La_{0.33}Sr_{0.67}FeO_3 although lattice distortion occurs only in CaFeO_3.
Hartree-Fock calculations have indicated that both the breathing and tilting
distortions are necessary to induce the charge disproportionation in CaFeO_3,
while no lattice distortion is necessary for the charge disproportionation in
La_{0.33}Sr_{0.67}FeO_3.",0207250v1
2002-07-27,High-resolution Photoemission Study of Cd2Re2O7,"High-resolution bulk-sensitive photoemission has been measured for pyrochlore
oxide Cd2Re2O7. Temperature variations of the spectral shapes between 20 and
250 K are obviously observed for the Re 4f inner core and the valence band
spectra. The Re 5d states are dominant for the DOS near the Fermi level.",0207659v1
2002-08-28,On the Normal State Electronic properties of Layered Sr_2 RuO_4,"Based on a comprehensive perusal of experimental results, we construct a
microscopic model describing the normal state of layered 4d oxide Sr_2 RuO_4
incorporating relevant quantum chemical features of the material. The high-T
anomalies are explained within a Luttinger liquid (LL) picture. Interlayer
one-particle hopping drives a dimensional crossover to a correlated Fermi
liquid below a scale E^{*} << t_{perp}. Using recently developed
chain-dynamical mean field theory, the low value of E^{*}, as well as various
puzzling features of the low-T normal state are explained as manifestations of
the crossover from the high-T Luttinger liquid state in a consistent way.",0208559v1
2002-08-29,Tunnel junctions on as-grown superconducting MgB2 thin films,"We demonstrate that good superconductor/insulator/normal-metal tunnel
junctions can be fabricated on as-grown superconducting MgB2 thin films. The
as-grown films were prepared by coevaporation at low growth temperatures of
around 280deg. The insulating barrier was formed by an Mg overlayer, which is
subsequently oxidized in air. The tunneling spectra for Au/MgOx/MgB2 junctions
showed a reproducible and well-defined superconducting gap (delta= ~ 2.5 meV).
The resultant 2delta/ kBTc was significantly smaller than the predicted BCS
value of 3.52.",0208571v2
2002-09-05,Orbital Kondo Effect in $CrO_{2}$: A LSDA+DMFT Study,"Motivated by a collection of experimental results indicating the strongly
correlated nature of the ferromagnetic metallic state of $CrO_{2}$, we present
results based on a combination of the actual bandstructure [3] with dynamical
mean-field theory (DMFT) for the multi-orbital case. In striking contrast with
LSDA(+U) [3] and model many-body approaches [14], much better semiquantitative
agreement with (i) recent photoemission results, (ii) domain of applicability
of the half-metal concept, and (iii) thermodynamic and dc transport data, is
obtained within a single picture. Our approach has broad applications for the
detailed first principles investigation of other transition metal oxide-based
half-metallic ferromagnets.",0209132v1
2002-09-12,Phase control of La2CuO4 in thin-film synthesis,"The lanthanum copper oxide, La2CuO4, which is an end member of the prototype
high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the
""K2NiF4"" structure in high-temperature bulk synthesis. The crystal chemistry,
however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and
that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures.
In this article we demonstrate that low-temperature thin-film synthesis
actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the
phase control of ""K2NiF4""-type La2CuO4 versus ""Nd2CuO4""-type La2CuO4 can be
achieved by varying the synthesis temperature and using different substrates.",0209281v1
2002-09-13,Coexistence of bulk antiferromagnetic order and superconductivity in the QED3 theory of copper oxides,"Within the framework of the QED3 theory of cuprates it is argued that bulk
antiferromagnetic (AF) order can coexist with d-wave superconductivity in the
underdoped region, in agreement with recent experiments. The AF order arises
from the phase fluctuating d-wave superconductor via the mechanism of
spontaneous chiral symmetry breaking, provided that fluctuations are
sufficiently strong. The phase diagram for this coexistence is mapped out by
means of analytical and numerical solutions of the underlying Dyson-Schwinger
equation in the large N limit.",0209301v2
2002-11-14,Spin Chirality Fluctuation and Anomalous Hall Effect in Itinerant Ferromagnets,"The anomalous Hall effect due to the spin chirality order and fluctuation is
studied theoretically in a Kondo lattice model without the relativistic
spin-orbit interaction. Even without the correlations of the localized spins,
$\sigma_{xy}$ can emerge depending on the lattice structure and the spin
anisotropy. We reveal the condition for this chirality-fluctuation driven
mechanism for $\sigma_{xy}$. Our semiquantitative estimates for a pyrochlore
oxide Nd$_2$Mo$_2$O$_7$ give a finite $\sigma_{xy} \sim 10 \Ohm^{-1} \cm^{-1}$
together with a high resistivity $\rho_{xx} \sim 10^{-4}-10^{-3} \Ohm \cm$, in
agreement with experiments.",0211267v1
2002-11-28,Small polarons and c-axis transport in highly anisotropic metals,"Motivated by the anomalous c-axis transport properties of the quasi
two-dimensional metal, $\rm Sr_2 Ru O_4$, and related compounds, we have
studied the interlayer hopping of single electrons that are coupled strongly to
c-axis bosons. We find a c-axis resistivity that reflects the in-plane
electronic scattering in the low and very high temperature limits (relative to
the characteristic temperature of the boson $T_{\rm boson}$). For temperatures
near the $T_{\rm boson}$, a broad maximum in the resistivity can appear for
sufficiently strong electron-boson coupling. This feature may account for the
observed ``metallic to non-metallic crossover'' seen in these layered oxides,
where the boson may be a phonon.",0211675v1
2002-12-10,Quantum Phase Transition in the SU(4) Spin-Orbital Model on the Triangular Lattice,"Motivated by the absence of cooperative Jahn-Teller effect in LiNiO2 and
BaVS3, two layered oxides with triangular planes, we study the SU(4) symmetric
spin-orbital model on the triangular lattice. Upon reducing the next-nearest
neighbour coupling, we show that the system undergoes a quantum phase
transition to a liquid phase. A variational approach to this liquid phase shows
that simple types of long-range correlations are suppressed, suggesting that it
is stable against lattice distortions.",0212211v1
2003-02-04,Effect of a humid environment on the surface structure of RuO2(110),"Combining density-functional theory and thermodynamics we compute the phase
diagram of surface structures of rutile RuO2 (110) in equilibrium with water
vapor in the complete range of experimentally accessible gas phase conditions.
Through the formation of hydroxyl or water-like groups, already lowest
concentrations of hydrogen in the gas phase are sufficient to stabilize an
oxygen-rich polar oxide termination even at very low oxygen pressure.",0302075v1
2003-02-10,Unexpected Scaling of the Performance of Carbon Nanotube Transistors,"We show that carbon nanotube transistors exhibit scaling that is
qualitatively different than conventional transistors. The performance depends
in an unexpected way on both the thickness and the dielectric constant of the
gate oxide. Experimental measurements and theoretical calculations provide a
consistent understanding of the scaling, which reflects the very different
device physics of a Schottky barrier transistor with a quasi-one-dimensional
channel contacting a sharp edge. A simple analytic model gives explicit scaling
expressions for key device parameters such as subthreshold slope, turn-on
voltage, and transconductance.",0302175v1
2003-03-20,About possible Phonon to Magnon alignment in 2 dimensions and theory of superconductivity in Copper-Oxide planes,"We suggest that the phonon dispersion in cuprates becomes strongly
anisotropic due to interaction with spin waves; moreover the phonon dispersion
becomes singular along $|k_x|=|k_y|$ directions. This would allow more
electrons to form Cooper pairs and increase temperature of the superconducting
transition. The interaction of phonons with spin waves is more important than
the interaction of phonons with free electrons, because spin waves do not have
the Fermi surface constrain.",0303402v5
2003-04-07,Comment on ``Conduction states in oxide perovskites: Three manifestations of Ti$^{3 +}$ Jahn-Teller polarons in barium titanate'',"In this comment to [S. Lenjer, O. F. Schirmer, H. Hesse, and Th. W. Kool,
Phys. Rev. B {\bf 66}, 165106 (2002)] we discuss the electronic structure of
oxygen vacancies in perovskites. First principles computations are in favour of
rather deep levels in these vacancies, and Lenjer et al suggest that the
electrons' interaction energy is negative, but data on electroconductivity are
against.",0304160v1
2003-04-17,Crossover between mean-field and Ising critical behavior in a lattice-gas reaction-diffusion model,"Lattice-gas models for CO oxidation can exhibit a discontinuous
nonequilibrium transition between reactive and inactive states, which
disappears above a critical CO-desorption rate. Using finite-size-scaling
analysis, we demonstrate a crossover from Ising to mean-field behavior at the
critical point, with increasing surface mobility of adsorbed CO or with
decreasing system size. This behavior is elucidated by analogy with that of
equilibrium Ising-type systems with long-range interactions.",0304386v1
2003-04-30,Electronic and Structural Properties of a 4d-Perovskite: Cubic Phase of SrZrO$_3$,"First-principles density functional calculations are performed within the
local density approximation to study the electronic properties of SrZrO$_3$, an
insulating 4d-perovskite, in its high-temperature cubic phase, above 1400 K, as
well as the generic 3d-perovskite SrTiO$_3$, which is also a d^0-insulator and
cubic above 105 K, for comparison reasons. The energy bands, density of states
and charge density distributions are obtained and a detailed comparison between
their band structures is presented. The results are discussed also in terms of
the existing data in the literature for both oxides.",0304703v1
2003-06-04,"Chiral Symmetry and Collective Excitations in p-wave, d-wave and f-wave Superconductors","We discuss the origin of charge density wave (CDW) and spin density wave
(SDW) in p-wave, d-wave and f-wave superconductors. To describe the low-energy
quasiparticle excitation of p-wave case, we introduce a two- (one for time and
one for space) dimensional massless Dirac model. After the non-Abelian
bosonization is performed, the charge and spin density waves emerge from the
model. By using this scheme, we try to explain the characteristic aspect of
phase diagrams of various compounds, oxides and organic superconductors. The
purpose of this paper is to make an argument that the dimensionality of the
nodal excitation in superconductors plays an important role in the
determination of the structure of the phase diagram.",0306095v1
2003-06-26,Variation of Superconducting Transition Temperature in Hole-Doped Copper-Oxides,"The experimentally observed difference of superconducting critical
temperature $T_{c}$ in hole-doped cuprates is studied by using an extended
interlayer coupling model for layered d-wave superconductors. We show that the
change of the maximum $T_{c}$ from series to series is determined by the next
nearest neighboring hopping $t^{\prime}$, while the difference of the maximum
$T_{c}$ among the compounds in a homogeneous series is controlled by the
interlayer pairing strength. Our results provide helpful guidelines in the
search for new high-$T_{c}$ superconductors.",0306680v1
2003-06-27,The checkerboard modulation and the inter-layer asymmetry of the hole density in cuprates,"The 2D pair-condensate is characterized by a charge ordered state with a
""checkerboard"" pattern in the planes and with an alternating superstructure
along the c-axis.We find that Coulomb energy gain occurs along the c-axis,
which is proportional to the measured condensation energy and is due to
inter-layer charge complementarity (charge asymmetry of the boson condensate.
The static c-axis dielectric constant and the in-plane coherence length are
also calculated for various cuprates and compared with the available
experimental data. We find excellent agreement .",0306698v2
2003-06-28,Low-Temperature Quantum Critical Behaviour of Systems with Transverse Ising-like Intrinsic Dynamics,"The low-temperature properties and crossover phenomena of $d$-dimensional
transverse Ising-like systems within the influence domain of the quantum
critical point are investigated solving the appropriate one-loop
renormalization group equations. The phase diagram is obtained near and at
$d=3$ and several sets of critical exponents are determined which describe
different responses of a system to quantum fluctuations according to the way of
approaching the quantum critical point. The results are in remarkable agreement
with experiments for a wide variety of compounds exhibiting a quantum phase
transition, as the ferroelectric oxides and other displacive systems.",0306713v1
2003-07-11,Enhanced thermoelectric properties of NaxCoO2 whisker crystals,"Single-crystalline whiskers of thermoelectric cobalt oxide, NaxCoO2, have
been grown by an unconventional method from potassium-containing compositions,
and their transport properties, and chemical compositions were determined. The
growth mechanism was analyzed and interpreted by means of thermogravimetric
analysis. At 300 K, electrical resistivity r and thermoelectric power S of the
whisker are 102 u ohm cm and 83 uV/K, respectively. The power-factor, S2/r,
thus is enhanced up to ~ 68 uW/K2 cm.",0307277v1
2003-07-30,Combined atomic force microscope and electron-beam lithography used for the fabrication of variable-coupling quantum dots,"We have combined direct nanofabrication by local anodic oxidation with
conventional electron-beam lithography to produce a parallel double quantum dot
based on a GaAs/AlGaAs heterostructure. The combination of both nanolithography
methods allows to fabricate robust in-plane gates and Cr/Au top gate electrodes
on the same device for optimal controllability. This is illustrated by the
tunability of the interdot coupling in our device. We describe our fabrication
and alignment scheme in detail and demonstrate the tunability in
low-temperature transport measurements.",0307743v1
2003-08-05,Stress-aging in the electron-glass,"A new protocol for an aging experiment is studied in the electron-glass phase
of indium-oxide films. In this protocol, the sample is exposed to a non-ohmic
electric field F for a waiting time t_{w} during which the system attempts to
reach a steady state (rather than relax towards equilibrium). The relaxation of
the excess conductance dG after ohmic conditions are restored exhibit simple
aging as long as F is not too large.",0308071v1
2003-08-29,First-principles calculations of strontium on Si(001),"This paper reports state-of-the-art electronic structure calculations on the
deposition of strontium on the technologically relevant, (001) orientated
silicon surface. We identified the surface reconstructions from zero to four
thirds monolayers and relate them to experimentally reported data. A phase
diagram is proposed. We predict phases at 1/6, 1/4, 1/2, 2/3 and 1 monolayers.
Our results are expected to provide valuable information in order to understand
heteroepitaxial growth of a prominent class of high-K oxides around SrTiO3. The
insight obtained for strontium is expected to be transferable to other alkaline
earth metals.",0308621v1
2003-09-01,Heteroepitaxial growth of high-K gate oxides on silicon: insights from first-principles calculations on Zr on Si(001),"Metal deposition of Zr an a Si(001) surface has been studied by
state-of-the-art electronic structure calculations. The energy per Zr adatom as
a function of the coverage shows, that Zr forms silicide islands even at low
coverages. Adsorbed Zr is thermodynamically unstable against the formation of
bulk silicide ZrSi2. The observation that the islands consist of structural
elements of the bulk silicide is an indication that silicide grains will form
spontaneously.",0309030v1
2003-09-04,Mott transition and suppression of orbital fluctuations in orthorhombic 3$d^{1}$ perovskites,"Using $t_{2g}$ Wannier-functions, a low-energy Hamiltonian is derived for
orthorhombic $3d^{1}$ transition-metal oxides. Electronic correlations are
treated with a new implementation of dynamical mean-field theory for non-cubic
systems. Good agreement with photoemission data is obtained. The interplay of
correlation effects and cation covalency (GdFeO$_{3}$-type distortions) is
found to suppress orbital fluctuations in LaTiO$_{3},$ and even more in
YTiO$_{3}$, and to favor the transition to the insulating state.",0309102v3
2003-09-08,Computer Modeling of Electronic Properties of Scroll-like V2O5-based Nanotubes,"Atomic models of quasi-one-dimensional 1D vanadium oxide nanostructures -
nanotubes of various morphology (cylinder or scroll-like) formed by rolling
(010) single layers of V2O5 are constructed and their electronic properties are
studied using the tight-binding band theory. Compared to the cylindrical zigzag
(n,0) and armchair (n,n)-like nanotubes, which are uniformly semi-conducting
with the bang gap of about 2.5-2.7 eV, the band gap of the scroll-like tubes
trends significantly to vanish (up to about 0.1 eV) depending on the atomic
configurations of the tubes and inter-wall distances.",0309179v1
2003-09-16,Insulator-Metal transition in the Doped 3d1 Transition Metal Oxide LaTiO3,"The doping induced insulator-metal transition in $La_{1-x}Sr_{x}TiO_{3}$ is
studied using the ab-initio LDA+DMFT method. Combining the LDA bandstructure
for the actual, distorted structure found recently with multi-orbital DMFT to
treat electronic correlations, we find: $(i)$ ferro-orbital order in the Mott
insulating state without orbital degeneracy, $(ii)$ a continuous filling
induced transition to the paramagnetic metal (PM) with $x$, and $(iii)$
excellent quantitative agreement with published photoemission data for the case
of 6% doping. Our results imply that this system can be described as a
Mott-Hubbard system without orbital (liquid) degeneracy.",0309370v1
2003-10-03,Nanowire Growth for Sensor Arrays,"A design concept for nanowire-based sensors and arrays is described. The
fabrication technique involves electrodeposition to directly grow nanowires
between patterned thin film contact electrodes. To prove our concept, we have
electrodeposited 1-mm diameter Pd single wires and small arrays. To demonstrate
nanowire sensors, we have electrochemically grown metal (Pd, Au, Pt), metal
oxide (Sb2O3), and conducting polymer (polyaniline) bundled nanowires. Using Pt
bundled nanowires surface modified with glucose oxidase, we have demonstrated
glucose detection as a demonstration of a biomolecular sensor.",0310075v1
2003-10-15,Commensurability Transition and Stripe Phases in the Ginzburg-Landau Theory,"We phenomenologically describe the thermodynamics of charge and spin density
waves in doped high-$T_{c}$ oxides. We have explicitly calculated stable
non-homogeneous solutions in the incompressible spin driven stripe phase, where
stripes are static soliton-like charge density waves (CDW), and in the vicinity
of their critical point, where CDW's become harmonic. Our phase diagram points
to a commensurability transition separating the low (LI) and high (HI)
incommensurable phases. Besides, we demonstrate by rigorous group symmetry
arguments that the stripe criticality is compatible with a second order phase
transition.",0310364v1
2003-10-28,Universal features of charge and spin order in a half-doped layered perovskite,"We have investigated the peculiar structure of charge and spin ordering in
the half-doped layered perovskite oxide La$_{1.5}$Sr$_{0.5}$CoO$_4$ by elastic
neutron scattering. Two samples with different preparation histories were
studied. We find that the generic features of the ordered states, such as their
short-range, glassy nature and the spin incommensurability, are
sample-independent. At the same time, some subtle features of the ordered
phases, such as the correlation lengths, differ.",0310662v2
2003-11-11,First-principles study of the electrooptic effect in ferroelectric oxides,"We present a method to compute the electrooptic tensor from first principles,
explicitly taking into account the electronic, ionic and piezoelectric
contributions. It allows us to study the non-linear optic behavior of three
ferroelectric ABO_3 compounds : LiNbO_3, BaTiO_3 and PbTiO_3. Our calculations
reveal the dominant contribution of the soft mode to the electrooptic
coefficients in LiNbO_3 and BaTiO_3 and identify the coupling between the
electric field and the polar atomic displacements along the B-O chains as the
origin of the large electrooptic response in these compounds.",0311240v2
2003-11-12,Superconductivity in Na_xCoO_2yH_2O by charge fluctuation,"A new mechanism for superconductivity in the newly discovered Co-based oxide
is proposed by using charge fluctuation. A single-band extended Hubbard model
on the triangular lattice is studied within random phase approximation.
$f$-wave triplet superconductivity is stabilized in the vicinity of
charge-density-wave instability, which is in sharp contrast with the
square-lattice case. The physical origin of the realization of the $f$-wave
triplet state as well as the relevance to experiments are discussed.",0311266v1
2003-12-15,Influence of the incommensurability in $Sr_{14-x}Ca_xCu_{24}O_{41}$ family compounds,"The present paper studies the influence of the structural modulation on the
low energy physics of the $Sr_{14-x}Ca_xCu_{24}O_{41}$ oxides, using ab-initio
determination of the on-site and nearest neighbor effective parameters. The
structural modulations appears to be the key degree of freedom, responsible for
the low energy properties, such as the electron localization, the formation of
dimers in the $x=0$ compound or the anti-ferromagnetic order in the $x=13.6$
compound.",0312369v2
2003-12-17,In-situ epitaxial growth of superconducting La-based bilayer cuprate thin films,"We investigate the epitaxial growth of bilayer cuprate La2CaCu2O6+\delta
using pure ozone as an oxidant, and find that even the crystal with parent
composition without cation substitution can show metallic behavior with the aid
of epitaxial strain effect. The hole concentration is controlled simply by
excess-oxygen doping, and the films grown under the optimum conditions exhibit
superconductivity below 30 K. This is the first result on the superconductivity
of bilayer La2CaCu2O6+\delta induced purely by the excess oxygen.",0312428v1
2003-12-18,Renormalization of resonant tunneling in MOSFETs,"We study tunneling between a localized defect state and a conduction band in
the presence of strong electron-electron and electron-phonons interactions. We
derive the tunneling rate as a function of the position of the defect energy
level relative to the Fermi energy of conduction electrons. We argue that our
results can explain the large tunneling timescales observed in experiments on
random telegraph signals in ${\rm Si}$ metal-oxide-semiconductor field effect
transistors.",0312503v1
2003-12-21,"XANES spectroscopy study of Pb(Ti, Zr)O3 ferroelectric thin films","Thin films of zirconium-rich perovskites Pb1-3x/2 Lax Zr0.65 Ti0.35O3 (PLZT;
x=0.095) were studied using X-ray absorption near-edge structure (XANES)
spectroscopy. Is shown, that slow crystallization of the system is accompanied
by partial reduction of lead oxides to a metal (Pb0) state. The same results
were found in the samples of the same composition with addition of 30% mol of
PbO. The evidence for stereo active 6s2 lone-pair is discussed.",0312559v1
2003-12-28,"XANES Pb LIII spectra of mixed-valence compound: Minium, Pb3O4","Mixed-valence compound Pb3O4 (minium) has been studied using X-ray absorption
near-edge structure (XANES) spectroscopy and DFT calculations. In spite of
presence of two valence states of lead [Pb(II) and Pb(IV)], the XANES spectrum
of studied system is corresponding to apparently unified, an intermediate
valence state of Pb. On the other hand, the 207Pb NMR spectra definitely show
two different spectral bands corresponding to different Pb2+ and Pb4+ ions in
Pb3O4 crystal structure. The explanation of this contradiction is related to
the basics of XANES and NMR spectroscopy.",0312663v1
2004-01-29,Review on Giant Magnetoelectric effects in Oxide ferromagnetic/ferroelectric Layered Structures,"The synthesis of layered ferrite-lead titanate zirconate (PZT) and lanthanum
nanganite-PZT and the observation of giant magneto-electric interactions are
discussed. The ferrites used in our studies included pure and Zn substituted
cobalt-, nickel- and lithium ferrites. Ferromagnetic manganites used included
both calcium and strontium substituted systems. The samples were prepared from
10-40 mm thick films obtained by tape-casting. Our studies showed strong ME
coupling in manganite-PZT and cobalt zinc ferrite-PZT, and a giant ME effect in
nickel zinc ferrite-PZT. We found evidence for Zn assisted enhancement in ME
coefficients that were attributed to low anisotropy and high permeability that
resulted in favorable magneto-mechanical coupling in the composites.",0401607v1
2004-02-04,Quasi-Stationary Distributions for Models of Heterogeneous Catalysis,"We construct the quasi-stationary (QS) distribution for two models of
heterogeneous catalysis having two absorbing states: the ZGB model for the
oxidation of CO, and a version with noninstantaneous reactions. Using a
mean-field-like approximation, we study the quasi-stationary surface coverages,
moment ratios and the lifetime of the QS state. We also derive an improved,
consistent one-site mean-field theory for the ZGB model.",0402132v1
2004-02-05,Theoretical Study on Resonant Inelastic X-Ray Scattering in Quasi-One-Dimensional Cuprates,"We study theoretically the resonant inelastic x-ray scattering in
quasi-one-dimensional insulating copper oxides, where the incident photon
energy is tuned to the Cu1s-4p absorption energy. Our attention is focused
particularly on the strong momentum-transfer dependence of the spectral shape
observed in recent experiments. We describe the antiferromagnetic ground state
within the Hartree-Fock theory, and consider charge excitations from the ground
state within the random phase approximation. By taking account of the electron
correlation effects perturbatively, we obtain detailed momentum-transfer
dependence of the spectra in a semiquantitative agreement with the experiments.",0402150v1
2004-02-19,Possible singlet to triplet pairing transition in NaxCoO2 H2O,"We present precise measurements of the upper critical field (Hc2) in the
recently discovered cobalt oxide superconductor. We have found that the
critical field has an unusual temperature dependence; namely, there is an
abrupt change of the slope of Hc2(T) in a weak field regime. In order to
explain this result we have derived and solved Gor'kov equations on a
triangular lattice. Our experimental results may be interpreted in terms of the
field-induced transition from singlet to triplet superconductivity.",0402503v2
2004-03-08,Sodium Ion Ordering in NaxCoO2,"The layered sodium cobalt oxide NaxCoO2 is studied by electron diffraction
for a wide range of sodium contents, 0.15<x<0.75. An extensive series of
ordered Na ion-Na vacancy superlattices is found beyond the simple hexagonal
average structure. The most strongly developed superlattice is found for the
composition Na0.5CoO2, which displays Co3+/Co4+ charge ordering at low
temperatures. The structural principle for some of the observed ordering
schemes, particularly near x=0.5, is, surprisingly, the presence of lines of Na
ions and vacancies rather than simply maximized Na-Na separations.",0403206v1
2004-05-14,Combining high conductivity with complete optical transparency: A band-structure approach,"A comparison of the structural, optical and electronic properties of the
recently discovered transparent conducting oxide (TCO), nanoporous Ca12Al14O33,
with those of the conventional TCO's (such as Sc-doped CdO) indicates that this
material belongs conceptually to a new class of transparent conductors. For
this class of materials, we formulate criteria for the successful combination
of high electrical conductivity with complete transparency in the visible
range. Our analysis suggests that this set of requirements can be met for a
group of novel materials called electrides.",0405317v1
2004-05-16,Structural and electronic properties of MgO nanotube clusters,"Finite magnesium oxide nanotubes are investigated. Stacks of four parallel
squares, hexagons, octagons, and decagons are constructed and studied by the
pseudopotential density functional theory within the local-density
approximation. Optimized structures are slightly distorted stacks of polygons.
These clusters are insulators and the band gap of 8.5 eV is constant over an
investigated range of the diameters of stacked polygonal rings. Using the
L""owdin population analysis a charge transfer towards the oxygen atoms is
estimated as 1.4, which indicates that the mixed ionocovalent bonding exists in
investigated MgO nanotubes.",0405347v1
2004-06-17,Superconductivity in three-layer Na0.3CoO2*1.3H2O,"The observation of superconductivity at 4.3 K in a new crystalline form of
Na0.3CoO2*1.3H2O is reported. The new superconductor has three layers of CoO6
octahedra per crystallographic unit cell, in contrast to the previously
reported two-layer superconductor. The three-layer cell occurs because the
relative orientations of neighboring CoO2 layers are distinctly different from
what is seen in the two-layer superconducting phase. This type of structural
difference in materials that are otherwise chemically and structurally
identical is not possible to attain on the layered copper oxide
superconductors. The synthesis and stability of the new phase are described.",0406409v1
2004-06-25,Strong electron correlation effects in non-volatile electronic memory devices,"We investigate hysteresis effects in a model for non-volatile memory devices.
Two mechanisms are found to produce hysteresis effects qualitatively similar to
those often experimentally observed in heterostructures of transition metal
oxides. One of them is a novel switching effect based on a metal-insulator
transition due to strong electron correlations at the dielectric/metal
interface. The observed resistance switching phenomenon could be the
experimental realisation of a novel type of strongly correlated electron
device.",0406646v1
2004-07-04,Correlation pseudogaps in HTSC,"The electronic correlations in oxide HTSC in the normal state are analyzed by
the generalized Hartree-Fock theory of Nambu and Gorkov. It yields two kinds of
pseudogaps, the small pseudogap (SPG) and the large pseudogap (LPG). The first
is obtained by the Fock integral, and the second by the Hartree integral. We
find real gaps for the undoped materials, and pseudogaps for the doped and
conducting ones. The latter result in the V- shaped experimental density of
states.",0407090v1
2004-07-12,Asymmetric Silver to Oxide Adhesion in Multilayers Deposited on Glass by Sputtering,"We have developed a wedge-loaded double-cantilever beam adhesion measurement
set-up for thin films deposited on glass by sputtering. The test is described
in details. Results on the Glass/sublayer/Ag/ZnO multilayer provide evidence
that \SnOd or \TiOd perform better than ZnO as a sublayer. Then however,
rupture within the multilayer shifts to the upper Ag/ZnO interface. The latter
is shown to be tougher than the lower ZnO/Ag interface, an asymmetry due to
non-equilibrium interfacial structures.",0407296v1
2004-07-18,Directional Ordering of Fluctuations in a Two-dimensional Compass Model,"In the Mott insulating phase of the transition metal oxides, the effective
orbital-orbital interaction is directional both in the orbital space and in the
real space. We discuss a classical realization of directional coupling in two
dimensions. Despite extensive degeneracy of the ground state, the model
exhibits partial orbital ordering in the form of directional ordering of
fluctuations at low temperatures stabilized by an entropy gap. Transition to
the disordered phase is shown to be in the Ising universality class through
exact mapping and multicanonical Monte Carlo simulations.",0407470v1
2004-09-13,Pi-stacking in charged thiophene oligomers,"The pi-stacking of oxidized thiophene oligomers is investigated using
ab-initio quantum chemistry methods. Dimers of singly-charged oligothiophenes
are found to be unstable in the gas phase, but can be stabilized as bound
dications in the singlet state by a polarizable solvent such as acetonitrile.
Our calculations provide a detailed description of the mechanisms and the
energetics involved in the dimerization phenomenon, and highlight the role and
importance of the environment in the stabilization of the stacks. The need for
accurate treatments of electronic correlations and of solvation effects for a
realistic description of these materials is underscored.",0409328v1
2004-10-05,Self-generated electronic heterogeneity and quantum glassiness in the high temperature superconductors,"We present a systematic study of the spin and charge dynamics of copper oxide
superconductors as a function of carrier concentration $x$. Our results portray
a coherent physical picture, which reveals a quantum critical point at optimum
doping ($x=x_{opt}$), and the formation of an inhomogeneous glassy state at $x
< x_{opt}$. This mechanism is argued to arise as an intrinsic property of doped
Mott insulators, and therefore to be largely independent of material quality
and level of disorder.",0410111v1
2004-10-29,Raman thresholds and rigid to floppy transitions in calcium silicate glasses,"Alkaline earth silicate glasses $xCaO-(1-x)SiO_2$ exhibit a well marked
threshold in Raman lineshapes which can be related to the onset of network
rigidity as the concentration of calcium oxide $x$ is decreased. The present
results are analyzed by constraint counting algorithms and more deeply
characterized by a size increasing cluster approximation that allows to perform
Maxwell mechanical constraint counting beyond the usual mean-field treatment.
This permits to discuss under which structural conditions an elastic
intermediate phase can be obtained.",0410770v1
2004-11-09,Quantum Mott Transition and Superconductivity,"The gas-liquid transition is a first-order transition terminating at a
finite-temperature critical point with diverging density fluctuations. Mott
transition, a metal-insulator transition driven by Coulomb repulsion between
electrons, has been identified with this textbook transition. However, the
critical temperature of the Mott transition can be suppressed, resulting in
unusual quantum criticality. It accounts for non-Fermi-liquid-like properties,
and strongly momentum dependent quasiparticles as in many materials near the
Mott insulator. Among all, the mode-coupling theory of the density fluctuations
supports d-wave superconductivity at the order of a hundred Kelvin for relevant
parameters of the copper oxide superconductors.",0411217v1
2004-11-15,Hydration phase diagram for sodium cobalt oxide Na0.3CoO2*yH2O,"The hydration phase diagram for sodium cobalt oxyhydrate, Na0.3CoO2*yH2O
(y=0, 0.6, 1.3), was determined as a function of relative humidity at 298K. It
is found that greater than 75% relative humidity is needed for complete
hydration of anhydrous Na0.3CoO2 to the superconducting phase Na0.3CoO2*1.3H2O.
Dehydration studies show that a minimum of 43% relative humidity is needed to
maintain the stability of the fully hydrated superconducting phase. The
intermediate hydrate, Na0.3CoO2*0.6H2O, is stable between 10% and 50% relative
humidity on hydration, and 35% to 0% relative humidity on dehydration.",0411387v1
2004-11-20,Device modeling of long-channel nanotube electro-optical emitter,"We present a simple analytic model of nanotube electro-optical emitters,
along with improved experimental measurements using PMMA-passivated devices
with reduced hysteresis. Both the ambipolar electrical characteristics and the
motion of the infrared-emission spot are well described. The model indicates
that the electric field is strongly enhanced at the emission spot, and that
device performance can be greatly improved by the use of thinner gate oxides.",0411537v2
2005-03-01,Carbon Nanotubes as Intracellular Protein Transporters: Generality and Biological Functionality,"Various proteins adsorb spontaneously on the sidewalls of acid-oxidized
single-walled carbon nanotubes. This simple non-specific binding scheme can be
used to afford non-covalent protein-nanotube conjugates. The proteins are found
to be readily transported inside various mammalian cells with nanotubes acting
as the transporter via the endocytosis pathway. Once released from the
endosomes, the internalized protein-nanotube conjugates can enter into the
cytoplasm of cells and perform biological functions, evidenced by apoptosis
induction by transported cytochrome c. Carbon nanotubes represent a new class
of molecular transporters potentially useful for future in-vitro and in-vivo
protein delivery applications.",0503005v1
2005-03-07,Synthesis and Structure of the Monolayer Hydrate K03CoO2 x 04H2O,"The monolayer hydrate (MLH) K03CoO2 x 04H2O was synthesized from K06CoO2 by
extracting K+ cations using K2S2O8 as an oxidant and the subsequent
intercalation of water between the layers of edge-sharing CoO6 octahedra. A
hexagonal structure (space group P63/mmc) with lattice parameters a = 2.8262(1)
Angstrom, c = 13.8269(6) Angstrom similar to the MLH Na036CoO2 x 07H2O was
established using high-resolution synchrotron X-ray powder diffraction data.
The K/H2O layer in the K-MLH is disordered, which is in contrast to the Na-MLH.
At low temperatures metallic and paramagnetic behavior was found.",0503165v1
2005-03-21,Two Dimensional Atomic Crystals,"We report free-standing atomic crystals that are strictly 2D and can be
viewed as individual atomic planes pulled out of bulk crystals or as unrolled
single-wall nanotubes. By using micromechanical cleavage, we have prepared and
studied a variety of 2D crystals, including single layers of boron nitride,
graphite, several dichalcogenides and complex oxides. These atomically-thin
sheets (essentially gigantic 2D molecules unprotected from the immediate
environment) are stable under ambient conditions, exhibit high crystal quality
and are continuous on a macroscopic scale.",0503533v1
2005-04-05,How to detect the fourth order cumulant of electrical noise,"It is proposed to measure the current noise generated in a mesoscopic
conductor by macroscopic quantum tunneling (MQT) in a current biased Josephson
junction placed in parallel to the conductor. The theoretical description of
this set-up takes into account the complete dynamics of detector and noise
source. Explicit results are given for the specific case of current
fluctuations in an oxide layer tunnel junction, and it is shown how the device
allows to extract the fourth order cumulant of the noise from the MQT data for
realistic experimental parameters.",0504120v1
2005-04-30,Structural and Electronic Properties of the Interface between the High-k oxide LaAlO3 and Si(001),"The structural and electronic properties of the LaAlO3/Si(001) interface are
determined using state-of-the-art electronic structure calculations. The atomic
structure differs from previous proposals, but is reminiscent of La adsorption
structures on silicon. A phase diagram of the interface stability is calculated
as a function of oxygen and Al chemical potentials. We find that an
electronically saturated interface is obtained only if dopant atoms segregate
to the interface. These findings raise serious doubts whether LaAlO3 can be
used as an epitaxial gate dielectric.",0505013v2
2005-05-02,Orbital order in vanadium spinels,"Motivated by recent theoretical and experimental controversy, we present a
theoretical study to clarify the orbital symmetry of the ground state of
vanadium spinel oxides AV$_2$O$_4$ (A=Zn, Mg, Cd). The study is based on an
effective Hamiltonian with spin-orbital superexchange interaction and a local
spin-orbit coupling term. We construct a classical phase-diagram and prove the
complex orbital nature of the ground state. Remarkably, with our new analysis
we predict correctly also the coherent tetragonal flattening of oxygen
octahedra. Finally, through analytical considerations as well as numerical
ab-initio simulations, we propose how to detect the predicted complex orbital
ordering through vanadium K edge resonant x-ray scattering.",0505031v1
2005-05-06,Comparison of multiple-gate MOSFET architectures using Monte Carlo simulation,"Multiple-gate SOI MOSFETs with gate length equal to 25 nm are compared using
device Monte Carlo simulation. In such architectures, the short channel effects
may be controlled with much less stringent body and oxide thickness
requirements than in single-gate MOSFET. Our results highlight that planar
double-gate MOSFET is a good candidate to obtain both high current drive per
unit-width and weak subthreshold leakage with large integration density and
aggressive delay time, compared to non planar devices such as triple-gate or
quadruple-gate structures.",0505168v1
2005-05-24,Non-ohmicity and energy relaxation in diffusive 2D metals,"We analyze current-voltage characteristics taken on Au-doped indium-oxide
films. By fitting a scaling function to the data, we extract the
electron-phonon scattering rate as function of temperature, which yields a
quadratic dependence of the electron-phonon scattering rate on temperature from
1K down to 0.28K. The origin of this enhanced electron-phonon scattering rate
is ascribed to the mechanism proposed by Sergeev and Mitin.",0505595v1
2005-06-20,A phenomenological model of the Resonance peak in High Tc Superconductors,"A notable aspect of high-temperature superconductivity in the copper oxides
is the unconventional nature of the underlying paired-electron states. The
appearance of a resonance peak, observed in inelastic neutron spectroscopy in
the superconducting state of the High Tc cuprates, its apparent linear
correlation with the critical superconducting temperature of each of the
compounds and its disappearance in the normal state are rather intriguing. It
may well be that this peak is the signature of the singlet to triplet
excitation, and is an unique characteristic of a d-wave superconductor. We
develop a simple criterion for the resonance peak which is based on the concept
of twist sti ness and its disappearance at T=Tc.",0506490v1
2005-07-09,Direct Observation of Hydrogen Adsorption Sites and Nano-Cage Formation in Metal-Organic Frameworks (MOF),"The hydrogen adsorption sites in MOF5 were determined using neutron powder
diffraction along with first-principles calculations. The metal-oxide cluster
is primarily responsible for the adsorption while the organic linker plays only
a secondary role. Equally important, at low temperatures and
high-concentration, H2 molecules form unique interlinked high-symmetry
nano-clusters with intermolecular distances as small as 3.0 Ang. and H2-uptake
as high as 10-wt%. These results hold the key to optimizing MOF materials for
hydrogen storage applications and also suggest that MOFs can be used as
templates to create artificial interlinked hydrogen nano-cages with novel
properties.",0507220v1
2005-08-23,Direct measurement of charge transfer phenomena at ferromagnetic/superconducting oxide interfaces,"YBa2Cu3O7-x/La0.67Ca0.33MnO3 ferromagnetic/superconducting interfaces are
analyzed by scanning transmission electron microscopy and electron energy loss
spectroscopy with monolayer resolution. We demonstrate that extensive charge
transfer occurs between the manganite and the superconductor, in a manner
similar to modulation-doped semiconductors, which explains the reduced critical
temperatures of heterostructures. This behavior is not seen with insulating
PrBa2Cu3O7 layers. Furthermore, we confirm directly that holes in the
YBa2Cu3O7-x are located on the CuO2 planes.",0508564v2
2005-08-26,Role of Orbitals in the Physics of Correlated Electron Systems,"Rich properties of systems with strongly correlated electrons, such as
transition metal oxides, is largely connected with an interplay of different
degrees of freedom in them: charge, spin, orbital ones, as well as crystal
lattice. Specific and often very important role is played by orbital degrees of
freedom. In this comment I will shortly summarize the main concepts and discuss
some of the well-known manifestations of orbital degrees of freedom, but will
mostly concentrate on a recent development in this field.",0508631v1
2005-09-26,Correlation between floppy to rigid transitions and non-Arrhenius conductivity in glasses,"Non-Arrhenius behaviour and fast increase of the ionic conductivity is
observed for a number of potassium silicate glasses $(1-x)SiO_2-xK_2O$ with
potassium oxide concentration larger than a certain value $x=x_c=0.14$.
Recovering of Arrhenius behaviour is provided by the annealing that enhances
densification. Conductivity furthermore obeys a percolation law with the same
critical concentration $x_c$. These various results are the manifestation of
the floppy or rigid nature of the network and can be analyzed with constraint
theory. They underscore the key role played by network rigidity for the
understanding of conduction and saturation effects in glassy electrolytes.",0509644v1
2005-10-05,Simulation of phonon-assisted band-to-band tunneling in carbon nanotube field-effect transistors,"Electronic transport in a carbon nanotube (CNT) metal-oxide-semiconductor
field effect transistor (MOSFET) is simulated using the non-equilibrium Green's
functions method with the account of electron-phonon scattering. For MOSFETs,
ambipolar conduction is explained via phonon-assisted band-to-band
(Landau-Zener) tunneling. In comparison to the ballistic case, we show that the
phonon scattering shifts the onset of ambipolar conduction to more positive
gate voltage (thereby increasing the off current). It is found that the
subthreshold swing in ambipolar conduction can be made as steep as 40mV/decade
despite the effect of phonon scattering.",0510122v1
2005-10-13,Electrodynamics of correlated electron matter,"Infrared spectroscopy has emerged as a premier experimental technique to
probe enigmatic effects arising from strong correlations in solids. Here we
report on recent advances in this area focusing on common patterns in
correlated electron systems including transition metal oxides, intermetallics
and organic conductors. All these materials are highly conducting substances
but their electrodynamic response is profoundly different from the canonical
Drude behavior observed in simple metals. These unconventional properties can
be attributed in several cases to the formation of spin and/or charge ordered
states, zero temperature phase transitions and strong coupling to bosonic
modes.",0510351v1
2005-10-31,Coexistence of double-Q spin density wave and multi-Q pair density wave in cuprate oxide superconductors,"Spatial 4a x 4a modulations, with a the lattice constant of CuO_2 planes, or
the so called checkerboards can arise from double-Q spin density wave (SDW)
with Q_1 = (pm pi/a, pm 3 pi/4a) and Q_2 = (pm 3 pi/4a, pm pi/a). When multi-Q
pair density wave, that is, the condensation of d gamma-wave Cooper pairs with
zero total momenta, pm 2Q_1, pm 2Q_2, pm 4Q_1, pm 4Q_2, and so on is induced by
the SDW, gaps can have fine structures similar to those of the so called
zero-temperature pseudogaps.",0510829v1
2005-11-02,Self-aligned carbon nanotube transistors with charge transfer doping,"This letter reports a charge transfer p-doping scheme which utilizes
one-electron oxidizing molecules to obtain stable, unipolar carbon nanotube
transistors with a self-aligned gate structure. This doping scheme allows one
to improve carrier injection, tune the threshold voltage Vth, and enhance the
device performance in both the ON- and OFF- transistor states. Specifically,
the nanotube transistor is converted from ambipolar to unipolar, the device
drive current is increased by 2-3 orders of magnitude, the device OFF current
is suppressed and an excellent Ion/Ioff ratio of six order of magnitude is
obtained. The important role played by metal-nanotube contacts modification
through charge transfer is demonstrated.",0511039v1
2005-11-22,Fabrication of high quality ferromagnetic Josephson junctions,"We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with
an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized
regarding junction insulation and homogeneity of current transport. Using
ion-beam-etching and anodic oxidation we defined and insulated the junction
mesas. The additional 2 nm thin Cu layer below the ferromagnetic NiCu (SINFS)
lowered interface roughness and ensured very homogeneous current transport. A
high yield of junctional devices with jc spreads less than 2% was obtained.",0511546v1
2005-12-15,Predicting polarization enhancement in multicomponent ferroelectric superlattices,"Ab initio calculations are utilized as an input to develop a simple model of
polarization in epitaxial short-period CaTiO3/SrTiO3/BaTiO3 superlattices grown
on a SrTiO3 substrate. The model is then combined with a genetic algorithm
technique to optimize the arrangement of individual CaTiO3, SrTiO3 and BaTiO3
layers in a superlattice, predicting structures with the highest possible
polarization and a low in-plane lattice constant mismatch with the substrate.
This modelling procedure can be applied to a wide range of layered
perovskite-oxide nanostructures providing guidance for experimental development
of nanoelectromechanical devices with substantially improved polar properties.",0512328v1
2006-01-31,Crosstalk between nanotube devices: contact and channel effects,"At reduced dimensionality, Coulomb interactions play a crucial role in
determining device properties. While such interactions within the same carbon
nanotube have been shown to have unexpected properties, device integration and
multi-nanotube devices require the consideration of inter-nanotube
interactions. We present calculations of the characteristics of planar carbon
nanotube transistors including interactions between semiconducting nanotubes
and between semiconducting and metallic nanotubes. The results indicate that
inter-tube interactions affect both the channel behavior and the contacts. For
long channel devices, a separation of the order of the gate oxide thickness is
necessary to eliminate inter-nanotube effects. Because of an exponential
dependence of this length scale on dielectric constant, very high device
densities are possible by using high-k dielectrics and embedded contacts.",0602006v1
2006-02-02,Lattice polarization effects on electron-gas charge densities in ionic superlattices,"The atomic-level control achievable in artificially-structured oxide
superlattices provides a unique opportunity to explore interface phases of
matter including high-density 2D electron gases. Electronic-structure
calculations show that the charge distribution of the 2D gas is strongly
modulated by electron-phonon interactions with significant ionic polarization.
Anharmonic finite-temperature effects must be included to reproduce experiment.
Density functional perturbation theory is used to parameterize a simple model
introduced to represent these effects and predict temperature dependencies.",0602045v2
2006-02-17,Excited state spectroscopy in carbon nanotube double quantum dots,"We report on low temperature measurements in a fully tunable carbon nanotube
double quantum dot. A new fabrication technique has been used for the top-gates
in order to avoid covering the whole nanotube with an oxide layer as in
previous experiments. The top-gates allow us to form single dots, control the
coupling between them and we observe four-fold shell filling. We perform
inelastic transport spectroscopy via the excited states in the double quantum
dot, a necessary step towards the implementation of new microwave-based
experiments.",0602424v1
2006-02-24,Crystal-field states in NaCoO2 and in wet cobalt superconductors (NaxCoO2),"We claim that for calculations of the electronic structure of 3d oxides very
strong electron correlations have to be taken into account similarly to those
assumed in many-electron crystal field approach. For Co3+ ions in NaxCoO2.yH2O
there are 15 low lying many-electron states within 0.1 eV as can be obtained in
the many-electron CEF approach with taking into account the spin-orbit
coupling. We claim, that the used by us Hamiltonian for the trigonal distortion
is correct.",0602592v1
2006-02-27,"Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd)","Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single
crystals have been studied upon continuous doping of CoO_2 planes with either
electrons or holes. The thermoelectric response and the resistivity behavior
reveal a hopping character of the transport in both compounds, providing the
basis for understanding the recently found remarkable divergence of the Seebeck
coefficient at x=0.5. The doping dependence of the thermoelectric power evinces
that the configurational entropy of charge carriers, enhanced by their spin and
orbital degeneracy, plays a key role in the origin of the large thermoelectric
response in these correlated oxides.",0602618v1
2006-03-03,Electrostatic Modulation of the Superfluid Density in a Ultrathin La2-xSrxCuO4 Film,"By capacitively charging an underdoped ultrathin La2-xSrxCuO4 film with an
electric field applied across a gate insulator with a high dielectric constant,
relative changes of the areal superfluid density n_{s\Box}$ of unprecedented
strength were observed in measurements of the film kinetic inductance. Although
$n_{s\Box}$ appears to be substantially reduced by disorder, the data provide,
for the first time on the same sample, direct compelling evidence for the
Uemura relation $T_{c} \propto n_{s\Box}(T=0)$ in the underdoped regime of
copper-oxide superconductors.",0603076v2
2006-03-13,Charge Transfer Induced Polarity Switching in Carbon Nanotube Transistors,"We probed the charge transfer interaction between the amine-containing
molecules: hydrazine, polyaniline and aminobutyl phosphonic acid, and carbon
nanotube field effect transistors (CNTFETs). We successfully converted p-type
CNTFETs to n-type and drastically improved the device performance in both the
ON- and OFF- transistor states utilizing hydrazine as dopant. We effectively
switched the transistor polarity between p- and n- type by accessing different
oxidation states of polyaniline. We also demonstrated the flexibility of
modulating the threshold voltage (Vth) of a CNTFET by engineering various
charge-accepting and -donating groups in the same molecule.",0603322v1
2006-04-05,Growth mode control of the free carrier density in SrTiO3-d films,"We have studied the growth dynamics and electronic properties of SrTiO3-d
homoepitaxial films by pulsed laser deposition. We find the two dominant
factors determining the growth mode are the kinetics of surface crystallization
and oxidation. When matched, persistent two-dimensional layer-by-layer growth
can be obtained for hundreds of unit cells. By tuning these kinetic factors,
oxygen vacancies can be frozen in the film, allowing controlled, systematic
doping across a metal-insulator transition. Metallic films can be grown,
exhibiting Hall mobilities as high as 25,000 cm2/Vs.",0604117v1
2006-04-24,Potential Profiling of the Nanometer-Scale Charge Depletion Layer in n-ZnO/p-NiO Junction Using Photoemission Spectroscopy,"We have performed a depth-profile analysis of an all-oxide p-n junction diode
n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering.
Systematic core-level shifts were observed during the gradual removal of the
ZnO overlayer, and were interpreted using a simple model based on charge
conservation. Spatial profile of the potential around the interface was
deduced, including the charge-depletion width of 2.3 nm extending on the ZnO
side and the built-in potential of 0.54 eV.",0604549v1
2006-05-12,Surfactant assisted synthesis of Co and Li doped ZnO nanocrystalline samples showing room temperature ferromagnetism,"We have developed a simple, surfactant assisted synthesis route for the
preparation, in gram quantities, of Co and Li doped ZnO nanocrystalline samples
showing robust room temperature ferromagnetism. Our studies show that RTF is
intrinsic to Zn0.85Co0.05Li0.10O and not due to any segregated secondary
phases. In addition, it has been shown that the defects play an important role
in activating RTF in these oxide systems. This also provide an explanation for
the widely varying results observed in the literature. The method can also be
extended for the synthesis of other transition metal doped ZnO.",0605332v1
2006-05-26,Role of Inelastic Tunneling through the Barrier in Scanning Tunneling Microscope Experiments on Cuprates,"The tunneling path between the CuO2-layers in cuprate superconductors and a
scanning tunneling microscope tip passes through a barrier made from other
oxide layers. This opens up the possibility that inelastic processes in the
barrier contribute to the tunneling spectra. Such processes cause one or
possibly more peaks in the second derivative current-voltage spectra displaced
by phonon energies from the density of states singularity associated with
superconductivity. Calculations of inelastic processes generated by apical
O-phonons show good qualitative agreement with recent experiments reported by
Lee et al.[1]. Further tests to discriminate between these inelastic processes
and coupling to planar phonons are proposed.",0605646v1
2006-06-09,Current spinon-holon description of the one-dimensional charge-transfer insulator SrCuO2: Angle-resolved photoemission measurements,"We have investigated the low-energy electronic structure of the strongly
correlated one-dimensional copper oxide chain compound SrCuO2 by angle resolved
photoemission as a function of excitation energy. In addition to the prominent
spinon-holon continuum we observe a peaklike and dispersive feature at the zone
boundary. By fine-tuning the experimental parameters we are able to monitor the
full holon branch and to directly measure the electronic hopping parameter with
unprecedented accuracy.",0606238v1
2006-06-15,"Microscopic Reversibility, Space-Filling, and Internal Stress in Strong Glasses","The axiomatic theory of ideally glassy networks, which has proved effective
in describing phase diagrams and many properties of chalcogenide, oxide, and
even molecular glasses, is here broadened to describe both geometrical
properties, such as the first sharp diffraction peak, and kinetic properties,
such as the nonreversible enthalpy of the glass transition, as measured by
modulated differential scanning calorimetry. The discussion shows why the
latter is such an effective tool for identifying strong glasses.",0606418v1
2006-06-23,Resonant X-ray diffraction studies on the charge ordering in magnetite,"Here we show that the low temperature phase of magnetite is associated with
an effective, although fractional, ordering of the charge. Evidence and a
quantitative evaluation of the atomic charges are achieved by using resonant
x-ray diffraction (RXD) experiments whose results are further analyzed with the
help of ab initio calculations of the scattering factors involved. By
confirming the results obtained from X-ray crystallography we have shown that
RXD is able to probe quantitatively the electronic structure in very complex
oxides, whose importance covers a wide domain of applications.",0606596v1
2006-08-04,Optical Sum Rule in Finite Bands,"In a single finite electronic band the total optical spectral weight or
optical sum carries information on the interactions involved between the charge
carriers as well as on their band structure. It varies with temperature as well
as with impurity scattering. The single band optical sum also bears some
relationship to the charge carrier kinetic energy and, thus, can potentially
provide useful information, particularly on its change as the charge carriers
go from normal to superconducting state. Here we review the considerable
advances that have recently been made in the context of high $T_c$ oxides, both
theoretical and experimental.",0608116v1
2006-08-24,The nature of ferroelectricity under pressure,"Advances in first-principles computational approaches have, over the past
fifteen years, made possible the investigation of physical properties of
ferroelectric systems. In particular, such approaches have led to a microscopic
understanding of the occurrence of ferroelectricity in perovskite oxides at
ambient pressure. In this paper, we report ab-initio studies on the effect of
hydrostatic pressure on the ferroelectricity in perovskites and related
materials. We found that, unlike commonly believed, these materials exhibit
ferroelectricity at high enough pressure. We also explained in details the
(unusual) nature of this ferroelectricity.",0608530v1
2006-10-13,Coexistence of polar order and local domain dynamics in ferroelectric SrTi18O3,"Perovskite oxide ferroelectrics show classical soft mode behaviour typical
for the onset of a homogeneous long-range polar state and a displacive phase
transition. Besides these long wave length properties, local effects are
observed by different probes which reveal that dynamical symmetry breaking
already takes place already far above the actual instability. It is shown here
that displacive mean-field type dynamics can indeed coexist with local
dynamical symmetry breaking.",0610362v1
2006-10-31,Temperature and field dependence of Dynamics in the Electron-Glass,"We describe several experimental methods to quantify dynamics in electron
glasses and illustrate their use in the glassy phase of crystalline
indium-oxide films. These methods are applied to study the dependence of
dynamics on temperature and on non-ohmic electric fields at liquid helium
temperatures. It is shown that over a certain range of temperature the dynamics
becomes slower with temperature or upon increasing an applied non-ohmic field,
a behavior suggestive of a quantum-glass. It is demonstrated that non-ohmic
fields produce qualitatively similar results as raising the system temperature.
Quantitatively however, their effect may differ marekdly. The experimental
advantages of using fields to mimic higher temperature are pointed out and
illustrated.",0610859v1
2006-11-02,Field-effect transistors assembled from functionalized carbon nanotubes,"We have fabricated field effect transistors from carbon nanotubes using a
novel selective placement scheme. We use carbon nanotubes that are covalently
bound to molecules containing hydroxamic acid functionality. The functionalized
nanotubes bind strongly to basic metal oxide surfaces, but not to silicon
dioxide. Upon annealing, the functionalization is removed, restoring the
electronic properties of the nanotubes. The devices we have fabricated show
excellent electrical characteristics.",0611051v1
2006-12-21,Photoinduced charge and spin dynamics in strongly correlated electron systems,"Motivated by photoinduced phase transition in manganese oxides, charge and
spin dynamics induced by photoirradiation are examined. We calculate the
transient optical absorption spectra of the extended double-exchange model by
the density matrix renormalization group (DMRG) method. A charge-ordered
insulating (COI) state becomes metallic just after photoirradiation, and the
system tends to recover the initial COI state. The recovery is accompanied with
remarkable suppression of an antiferromagnetic correlation in the COI state.
The DMRG results are consistent with recent pump-probe spectroscopy data.",0612540v1
2007-03-05,Orbital correlations in monolayer manganites - From spin t-J model to orbital t-J model,"On the example of monolayer manganites we show that the theoretical ideas
developed long ago along the derivation of the spin t-J model from the Hubbard
model are nowadays very helpful in strongly correlated oxides with partly
filled degenerate orbitals. We analyze a realistic orbital t-J model for e_g
electrons in La_{1-x}Sr_{1+x}MnO_4 monolayer manganites, and discuss the
evolution of spin and orbital correlations under increasing doping by
performing exact diagonalization of finite clusters, with electronic kinetic
energy determined self-consistently at finite temperature by classical Monte
Carlo for t_2g spins. Several experimental results are reproduced.",0703127v1
1999-03-14,Precision Crystal Calorimetry in High Energy Physics,"Crystal Calorimetry is widely used in high energy physics because of its
precision. Recent development in crystal technology identified two key issues
to reach and maintain crystal precision: light response uniformity and
calibration in situ. Crystal radiation damage is understood. While the damage
in alkali halides is found to be caused by the oxygen/hydroxyl contamination,
it is the structure defects, such as oxygen vacancies, cause damage in oxides.",9903023v1
1999-09-10,Supersensitive avalanche silicon drift photodetector,"Physical principles of performance and main characteristics of a novel
avalanche photodetector developed on the basis of MOS(metal-oxide-silicon)
technology is presented. The photodetector contains a semitransparent gate
electrode and a drain contact to provide a drift of multiplicated charge
carriers along the semiconductor surface. A high gain(more than 10^4) of
photocurrent was achived due to the local negative feedback effect realizied on
the Si-SiO_2 boundary. Special attention is paid to the possibilities of
development of a supersensitive avalanche CCD (charge coupled device) for
detection of individual photons in visible and ultraviolet spectral regions.
Experimental results obtained with a two-element CCD prototype are discussed.",9909017v1
1995-12-10,Rusty Scatter Branes,"We derive double dimensional reduction/oxidation in a framework where it is
applicable to describe general non-static (and anisotropic) $p$-brane
solutions. Given this procedure, we are able to relate the dynamical
interaction potential for parallel extremal $p$-branes in $D$ dimensions to
that for extremal black holes in $D-p$ dimensions. In particular, we find that
to leading order the potential vanishes for all $\kappa$-symmetric $p$-branes.",9512061v1
2002-03-01,Revisiting Supergravity and Super Yang-Mills Renormalization,"Standard superspace Feynman diagram rules give one estimate of the onset of
ultraviolet divergences in supergravity and super Yang-Mills theories. Newer
techniques motivated by string theory but which also make essential use of
unitarity cutting rules give another in certain cases. We trace the difference
to the treatment of higher-dimensional gauge invariance in supersymmetric
theories that can be dimensionally oxidized to pure supersymmetric gauge
theories.",0203015v1
2002-08-07,Domain Walls and Spaces of Special Holonomy,"We review the relations between a family of domain-wall solutions to M-theory
and gravitational instantons with special holonomy. When oxidized into the
maximal-dimension parent supergravity, the transverse spaces of these domain
walls become cohomogeneity-one spaces with generalized Heisenberg symmetries
and a homothetic conformal symmetry. These metrics may also be obtained as
scaling limits of generalized Eguchi-Hanson metrics, or, with appropriate
discrete identifications, from generalized Atiyah-Hitchin metrics, thus
providing field-theoretic realizations of string-theory orientifolds.",0208055v1
2003-09-10,The topology of U-duality (sub-)groups,"We discuss the topology of the symmetry groups appearing in compactified
(super-)gravity, and discuss two applications. First, we demonstrate that for 3
dimensional sigma models on a symmetric space G/H with G non-compact and H the
maximal compact subgroup of G, the possibility of oxidation to a higher
dimensional theory can immediately be deduced from the topology of H. Second,
by comparing the actual symmetry groups appearing in maximal supergravities
with the subgroups of SL(32,R) and Spin(32), we argue that these groups cannot
serve as a local symmetry group for M-theory in a formulation of de Wit-Nicolai
type.",0309106v1
2005-01-11,Eleven-Dimensional Supergravity in Light-Cone Superspace,"We show that Supergravity in eleven dimensions can be described in terms of a
constrained superfield on the light-cone, without the use of auxiliary fields.
We build its action to first order in the gravitational coupling constant
\kappa, by ""oxidizing"" (N=8,d=4) Supergravity. This is simply achieved, as for
N=4 Yang-Mills, by extending the transverse derivatives into superspace. The
eleven-dimensional SuperPoincare algebra is constructed and a fourth order
interaction is conjectured.",0501079v2
2004-10-21,Equation-free optimal switching policies for bistable reacting systems using coarse time-steppers,"We present a computer-assisted approach to locating approximate coarse
optimal switching policies between stationary states of chemically reacting
systems described by microscopic/stochastic evolution rules. The ``coarse
time-stepper"" constitutes a bridge between the underlying kinetic Monte Carlo
simulation and traditional, continuum numerical optimization techniques
formulated in discrete time. The approach is illustrated through two simple
catalytic surface reaction models, implemented through kinetic Monte Carlo: NO
reduction on Pt, and CO oxidation on Pt. The objective sought in both cases is
to switch between two coexisting stable stationary states by minimal
manipulation of a macroscopic system parameter.",0410467v1
2005-11-28,Geometry-induced pulse instability in microdesigned catalysts: the effect of boundary curvature,"We explore the effect of boundary curvature on the instability of reactive
pulses in the catalytic oxidation of CO on microdesigned Pt catalysts. Using
ring-shaped domains of various radii, we find that the pulses disappear
(decollate from the inert boundary) at a turning point bifurcation, and trace
this boundary in both physical and geometrical parameter space. These
computations corroborate experimental observations of pulse decollation.",0511063v1
2005-12-08,Guiding chemical pulses through geometry: Y-junctions,"We study computationally and experimentally the propagation of chemical
pulses in complex geometries.The reaction of interest, CO oxidation, takes
place on single crystal Pt(110) surfaces that are microlithographically
patterned; they are also addressable through a focused laser beam, manipulated
through galvanometer mirrors, capable of locally altering the crystal
temperature and thus affecting pulse propagation. We focus on sudden changes in
the domain shape (corners in a Y-junction geometry) that can affect the pulse
dynamics; we also show how brief, localized temperature perturbations can be
used to control reactive pulse propagation.The computational results are
corroborated through experimental studies in which the pulses are visualized
using Reflection Anisotropy Microscopy.",0512019v1
2000-10-04,Dynamics of Chemical Reactions: Open Equilibrium,"Dynamic properties of chemical reactions and appropriate relationships for
open chemical equilibrium are discussed in approach of the chemical dynamics.
New way to calculate composition of chemical systems in open equilibrium, based
on the amended equation for the change of Gibbs' free energy, was exemplified
using reactions of cobalt double oxides with sulfur. Evaluated this way
equilibrium reaction extents had a good match with values found by direct
thermodynamic simulation. The developed method allows us to perform analysis of
complex chemical systems without coefficients of thermodynamic activity. In
cases when the coefficients are in need or just desirable, the method offers a
simple way to calculate them. Possible systems to apply method of chemical
dynamics are discussed.",0010013v2
2001-04-23,Adsorption of CO on a Platinum (111) surface - a study within a four-component relativistic density functional approach,"We report on results of a theoretical study of the adsorption process of a
single carbon oxide molecule on a Platinum (111) surface. A four-component
relativistic density functional method was applied to account for a proper
description of the strong relativistic effects. A limited number of atoms in
the framework of a cluster approach is used to describe the surface. Different
adsorption sites are investigated. We found that CO is preferably adsorbed at
the top position.",0104071v1
2003-01-18,Fundamental building blocks of eumelanins: electronic properties of indolequinone-dimers,"We present results from the theoretical INDO calculations of the electronic
structure for stacked eumelanins' monomers. As basic indolic components of the
eumelanin structure 5,6-dihydroxyindole (DHI or HQ) and its oxidized forms (SQ
and IQ) were chosen. The results reveal dependency of electronic properties of
such aggregates on monomers' redox states. They point out also a tendency to
localize an extra charge on one of dimer's subunits that could be suggestive of
an electron hopping as a model mechanism forthe electron transfer in
eumelanins.",0301042v1
2004-06-01,Ultraviolet photonic crystal laser,"We fabricated two dimensional photonic crystal structures in zinc oxide films
with focused ion beam etching. Lasing is realized in the near ultraviolet
frequency at room temperature under optical pumping. From the measurement of
lasing frequency and spatial profile of the lasing modes, as well as the
photonic band structure calculation, we conclude that lasing occurs in the
strongly localized defect modes near the edges of photonic band gap. These
defect modes originate from the structure disorder unintentionally introduced
during the fabrication process.",0406005v1
2005-10-25,Equations for filling factor estimation in opal matrix,"We consider two equations for the filling factor estimation of infiltrated
zinc oxide (ZnO) in silica (SiO_2) opal and gallium nitride in ZnO opal. The
first equation is based on the effective medium approximation, while the second
one - on Maxwell-Garnett approximation. The comparison between two filling
factors shows that both equations can be equally used for the estimation of the
quantity of infiltrated nanocrystals inside opal matrix.",0510230v2
2006-08-10,Analysis of surface waves generated on subwavelength-structured silver films,"Using transmission electron microscopy (TEM) to analyse the physical-chemical
surface properties of subwavlength structured silver films and
finite-difference time-domain (FDTD) numerical simulations of the optical
response of these structures to plane-wave excitation, we report on the origin
and nature of the persistent surface waves generated by a single slit-groove
motif and recently measured by far-field optical interferometry. The surface
analysis shows that the silver films are free of detectable oxide or sulfide
contaminants, and the numerical simulations show very good agreement with the
results previously reported.",0608116v2
2006-12-19,N_2O weak lines observed between 3900 and 4050 cm^-1 from long path absorption spectra,"Previously unobserved nitrous oxide transitions around 2.5 $\mu$m are
measured by intracavity laser absorption spectroscopy (ICLAS) analyzed by
time-resolved Fourier transform (TRFT) spectrometer. With an accuracy of the
order of 10^-3 cm^-1, measured positions of 1637 assigned weak transitions are
provided. They belong to 42 vibrational transitions, among which 33 are
observed for the first time. These data are believed to be useful in particular
to monitoring atmosphere purposes.",0612181v1
1995-01-19,Phonon Assisted Multimagnon Optical Absorption and Long Lived Two-Magnon States in Undoped Lamellar Copper Oxides,"We calculate the effective charge for multimagnon infrared (IR) absorption
assisted by phonons in the parent insulating compounds of cuprate
superconductors and the spectra for two-magnon absorption using interacting
spin-wave theory. Recent measured bands in the mid IR [Perkins et al. Phys.
Rev. Lett. {\bf 71} 1621 (1993)] are interpreted as involving one phonon plus a
two-magnon virtual bound state, and one phonon plus higher multimagnon
absorption processes. The virtual bound state consists of a narrow resonance
occurring when the magnon pair has total momentum close to $(\pi,0)$.",9501001v1
2007-04-05,Evidence of Spatially Inhomogeous Pairing on the Insulating Side of a Disorder-Tuned Superconductor-Insulator Transition,"Measurements of transport properties of amorphous insulating indium oxide
thin films have been interpreted as evidence of the presence of superconducting
islands on the insulating side of a disorder-tuned superconductor-insulator
transition. Although the films are not granular, the behavior is similar to
that observed in granular films. The results support theoretical models in
which the destruction of superconductivity by disorder produces spatially
inhomogenous pairing with a spectral gap.",0704.0765v2
2007-04-09,Electrical transport properties of polar heterointerface between KTaO3 and SrTiO3,"Electrical transport of a polar heterointerface between two insulating
perovskites, KTaO3 and SrTiO3, is studied. It is formed between a thin KTaO3
film deposited on a top of TiO2- terminated (100) SrTiO3 substrate. The
resulting (KO)1-(TiO2)0 heterointerface is expected to be hole-doped according
to formal valences of K (1+) and Ti (4+). We observed electrical conductivity
and mobility in the KTaO3/SrTiO3 similar to values measured earlier in
electron-doped LaAlO3/SrTiO3 heterointerfaces. However, the sign of the charge
carriers in KTaO3/SrTiO3 obtained from the Hall measurements is negative. The
result is an important clue to the true origin of the doping at perovskite
oxide hetero-interfaces.",0704.1050v1
2007-04-11,Surface Structure Analysis of Atomically Smooth BaBiO$_3$ Films,"Using low energy Time-of-Flight Scattering and Recoil Spectroscopy (TOF-SARS)
and Mass Spectroscopy of Recoiled Ions (MSRI) we analyze the surface structure
of an atomically smooth BaBiO$_3$ film grown by molecular beam epitaxy. We
demonstrate high sensitivity of the TOF-SARS and MSRI spectra to slight changes
in the orientation of the ion scattering plane with respect to the
crystallographic axes. The observed angle dependence allows us to clearly
identify the termination layer as BiO$_2$. Our data also indicate that
angle-resolved MSRI data can be used for high resolution studies of surface
structure of complex oxide thin films.",0704.1501v1
2007-04-26,Quantum Hall Effect in a Graphene p-n Junction,"We report on the fabrication and transport studies of a single-layer graphene
p-n junction. Carrier type and density in two adjacent regions are individually
controlled by electrostatic gating using a local top gate and a global back
gate. A functionalized Al203 oxide that adheres to graphene and does not
significantly affect its electronic properties is described. Measurements in
the quantum Hall regime reveal new plateaus of two-terminal conductance across
the junction at 1 and 3/2 times the quantum of conductance, e2/h, consistent
with theory.",0704.3487v2
2007-05-01,Visibility of graphene flakes on a dielectric substrate,"We model the optical visibility of monolayer and bilayer graphene deposited
on a silicon/silicon oxide substrate or thermally annealed on the surface of
silicon carbide. We consider reflection and transmission setups, and find that
visibility is strongest in reflection reaching the optimum conditions when the
bare substrate transmits light resonantly. In the optical range of frequencies
a bilayer is approximately twice as visible as a monolayer thereby making the
two types of graphene distinguishable from each other.",0705.0091v2
2007-05-15,Growth control of GaAs nanowires using pulsed laser deposition with arsenic over pressure,"Using pulsed laser ablation with arsenic over pressure, the growth conditions
for GaAs nanowires have been systematically investigated and optimized. Arsenic
over pressure with As$_2$ molecules was introduced to the system by thermal
decomposition of polycrystalline GaAs to control the stoichiometry and shape of
the nanowires during growth. GaAs nanowires exhibit a variety of geometries
under varying arsenic over pressure, which can be understood by different
growth processes via vapor-liquid-solid mechanism. Single-crystal GaAs
nanowires with uniform diameter, lengths over 20 $\mu$m, and thin surface oxide
layer were obtained and can potentially be used for further electronic
characterization.",0705.2181v1
2007-06-14,Use of detailed kinetic mechanisms for the prediction of autoignitions,"This paper describes how automatically generated detailed kinetic mechanisms
are obtained for the oxidation of alkanes and how these models could lead to a
better understanding of autoignition and cool flame risks at elevated
conditions. Examples of prediction of the occurrence of different autoignition
phenomena, such as cool flames or two-stage ignitions are presented depending
on the condition of pressure, temperature and mixture composition. Three
compounds are treated, a light alkane, propane, and two heavier ones, n-heptane
and n-decane.",0706.2067v1
2007-06-22,Transition metal oxides using quantum Monte Carlo,"The transition metal-oxygen bond appears prominently throughout chemistry and
solid-state physics. Many materials, from biomolecules to ferroelectrics to the
components of supernova remnants contain this bond in some form. Many of these
materials' properties strongly depend on fine details of the TM-O bond and
intricate correlation effects, which make accurate calculations of their
properties very challenging. We present quantum Monte Carlo, an explicitly
correlated class of methods, to improve the accuracy of electronic structure
calculations over more traditional methods like density functional theory. We
find that unlike s-p type bonding, the amount of hybridization of the d-p bond
in TM-O materials is strongly dependant on electronic correlation.",0706.3380v1
2007-06-28,Effect of physical inactivity on the oxidation of saturated and monounsaturated dietary Fatty acids: results of a randomized trial,"OBJECTIVES: Changes in the way dietary fat is metabolized can be considered
causative in obesity. The role of sedentary behavior in this defect has not
been determined. We hypothesized that physical inactivity partitions dietary
fats toward storage and that a resistance exercise training program mitigates
storage.",0706.4219v1
2007-06-29,A simple model of Coulomb disorder and screening in graphene,"We suggest a simple model of disorder in graphene assuming that there are
randomly distributed positive and negative centers with equal concentration
$N/2$ in the bulk of silicon oxide substrate. We show that at zero gate voltage
such disorder creates two-dimensional concentration $n_0 \sim N^{2/3}$ of
electrons and holes in graphene. Electrons and holes reside in alternating in
space puddles of the size $R_0 \sim N^{-1/3}$. A typical puddle has only one or
two carriers in agreement with recent scanning single electron transistor
experiment.",0706.4425v3
2007-07-03,Surface Encapsulation for Low-Loss Silicon Photonics,"Encapsulation layers are explored for passivating the surfaces of silicon to
reduce optical absorption in the 1500-nm wavelength band. Surface-sensitive
test structures consisting of microdisk resonators are fabricated for this
purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and
SiO2 are applied under varying deposition and annealing conditions. A short dry
thermal oxidation followed by a long high-temperature N2 anneal is found to be
most effective at long-term encapsulation and reduction of interface
absorption. Minimization of the optical loss is attributed to simultaneous
reduction in sub-bandgap silicon surface states and hydrogen in the capping
material.",0707.0415v1
2007-07-04,Role of oxygen vacancies in Cr-doped SrTiO3 for resistance-change memory,"Transition-metal oxides exhibiting a bistable resistance state are attractive
for non-volatile memory applications. The relevance of oxygen vacancies (VO)
for the resistance-change memory was investigated with x-ray fluorescence,
infrared microscopy, and x-ray absorption spectroscopy using Cr-doped SrTiO3 as
example. We propose that the microscopic origin of resistance switching in this
class of materials is due to an oxygen-vacancy drift occurring in close
proximity to one of the electrodes.",0707.0563v1
2007-07-05,Observation of a uniform temperature dependence in the electrical resistance across the structural phase transition in thin film vanadium oxide ($VO_{2}$),"An electrical study of thin $VO_{2}$ films in the vicinity of the structural
phase transition at $68^{0}C$ shows (a) that the electrical resistance $R$
follows $log (R)$ $\propto$ $-T$ over the $T$-range, $20 < T < 80 ^{0}C$
covering both sides of the structural transition, and (b) a history dependent
hysteresis loop in $R$ upon thermal cycling. These features are attributed here
to transport through a granular network.",0707.0885v1
2007-07-31,Quantum phase transition in the two-band Hubbard model,"The interaction between itinerant and Mott localized electronic states in
strongly correlated materials is studied within dynamical mean field theory in
combination with the numerical renormalization group method. A novel
nonmagnetic zero temperature quantum phase transition is found in the
bad-metallic orbital-selective Mott phase of the two-band Hubbard model, for
values of the Hund's exchange which are relevant to typical transition metal
oxides.",0707.4535v2
2007-08-03,Spin polaron theory for the photoemission spectra of layered cobaltates,"Recently, strong reduction of the quasiparticle peaks and pronounced
incoherent structures have been observed in the photoemission spectra of
layered cobaltates. Surprisingly, these many-body effects are found to increase
near the band insulator regime. We explain these unexpected observations in
terms of a novel spin-polaron model for CoO_2 planes which is based on a fact
of the spin-state quasidegeneracy of Co^{3+} ions in oxides. Scattering of the
photoholes on spin-state fluctuations suppresses their coherent motion. The
observed ``peak-dip-hump'' type lineshapes are well reproduced by the theory.",0708.0543v1
2007-08-09,Antiferromagnetic fluctuations in the superconducting phase of low- and high-temperature superconductors,"Based on recent experimental results for electron-doped cuprate oxides and
ferromagnetic superconductors, it is shown that antiferromagnetic fluctuations
always develop in the superconducting phase of both low- and high-temperature
superconductors. The relation between the magnitude of the antiferromagnetic
pseudogap and the characteristic temperature of the antiferromagnetic pseudogap
opening is obtained. The characteristic temperature of the antiferromagnetic
pseudogap opening for metal superconductors is estimated.",0708.1230v3
2007-08-09,Electroluminescence from single nanowires by tunnel injection: an experimental study,"We present a hybrid light-emitting diode structure composed of an n-type
gallium nitride nanowire on a p-type silicon substrate in which current is
injected along the length of the nanowire. The device emits ultraviolet light
under both bias polarities. Tunnel-injection of holes from the p-type substrate
(under forward bias) and from the metal (under reverse bias) through thin
native oxide barriers consistently explains the observed electroluminescence
behaviour. This work shows that the standard p-n junction model is generally
not applicable to this kind of device structure.",0708.1266v1
2007-08-21,Scale dependent superconductor-insulator transition,"We study the disorder driven superconductor to insulator transition in
amorphous films of high carrier-concentration indium-oxide. Using thin films
with various sizes and aspect ratios we show that the `critical'
sheet-resistance $R_{{\small \square}}$ depends systematically on sample
geometry; superconductivity disappears when $R_{{\small \square}}$ exceeds
$\approx6 $k$\Omega$ in large samples. On the other hand, wide and sufficiently
short samples of the same batch exhibit superconductivity (judged by
conductivity versus temperature) up to $R_{{\small \square}}$ which is
considerably larger. These results support the inhomogeneous scenario for the
superconductor-insulator transition.",0708.2751v1
2007-08-24,"Ab-initio calculation of the vibrational modes of SiH4, H2SiO, Si10H16, and Si10H14O","We have studied the normal modes of hydrogenated and oxidized silicon
nanocrystals, namely SiH4 (silan), H2SiO (silanon), Si10H16 and Si10H14O. The
small clusters (SiH4 and H2SiO) have been used for convergence tests and their
bondlengths and frequencies have been compared with experimental and
theoretical reference data. For the large clusters (Si10H16 and Si10H14O) we
have investigated the vibrational density of states where we have identified
the oxygen-related spectral features. The vibrational modes have been also
analyzed with respect to the displacement patterns. The calculations have been
carried out within the density-functional and density-functional perturbation
theory using the local-density approximation.",0708.3312v1
2007-08-25,Does Simple Two-Dimensional Hubbard Model Account for High-Tc Superconductivity in Copper Oxides?,"We reexamine whether the essence of high-Tc superconductivity is contained in
doped Hubbard models on the square lattice by using recently developed
pre-projected Gaussian-basis Monte Carlo method. The superconducting
correlations of the dx2-y2 wave symmetry in the ground state at distance r
decays essentially as inverse cubic of r. The upper bound of the correlation at
long distances estimated by this unbiased method is 0.001, indicating that
recent extensions of dynamical mean-field theories and variational methods
yielded at least an order of magnitude overestimates of it. The correlations
are too weak for the realistic account of the cuprate high-Tc
superconductivity.",0708.3416v1
2007-09-11,Electronic transport in locally gated graphene nanoconstrictions,"We have developed the combination of an etching and deposition technique that
enables the fabrication of locally gated graphene nanostructures of arbitrary
design. Employing this method, we have fabricated graphene nanoconstrictions
with local tunable transmission and characterized their electronic properties.
An order of magnitude enhanced gate efficiency is achieved adopting the local
gate geometry with thin dielectric gate oxide. A complete turn off of the
device is demonstrated as a function of the local gate voltage. Such strong
suppression of device conductance was found to be due to both quantum
confinement and Coulomb blockade effects in the constricted graphene
nanostructures.",0709.1731v1
2007-09-13,Observation of the Purcell effect in high-index-contrast micropillar,"We have fabricated pillar microcavity samples with Bragg mirrors consisting
of alternate layers of GaAs and Aluminium Oxide. Compared to the more widely
studied GaAs/AlAs micropillars these mirrors can achieve higher reflectivities
with fewer layer repeats and reduce the mode volume. We have studied a number
of samples containing a low density of InGaAs/GaAs self assembled quantum dots
in a cavity and here report observation of a three fold enhancement in the
radiative lifetime of a quantum dot exciton state due to the Purcell effect.",0709.2101v1
2007-11-27,Integrating Superconductive and Optical Circuits,"We have integrated on oxidized silicon wafers superconductive films and
Josephson junctions along with sol-gel optical channel waveguides. The
fabrication process is carried out in two steps that result to be solid and
non-invasive. It is demonstrated that 660 nm light, coupled from an optical
fibre into the channel sol-gel waveguide, can be directed toward
superconducting tunnel junctions whose current-voltage characteristics are
affected by the presence of the radiation. The dependence of the change in the
superconducting energy gap under optical pumping is discussed in terms of a
non-equilibrium superconductivity model.",0711.4221v1
2007-12-19,Decomposition and Oxidation of the N-Extended Supersymmetric Quantum Mechanics Multiplets,"We furnish an algebraic understanding of the inequivalent connectivities
(computed up to $N\leq 10$) of the graphs associated to the irreducible
supermultiplets of the N-extended Supersymmetric Quantum Mechanics. We prove
that the inequivalent connectivities of the N=5 and N=9 irreducible
supermultiplets are due to inequivalent decompositions into two sets of N=4
(respectively, N=8) supermultiplets. ""Oxido-reduction"" diagrams linking the
irreducible supermultiplets of the N=5,6,7,8 supersymmetries are presented. We
briefly discuss these results and their possible applications.",0712.3176v1
2007-12-30,Characterization of ZnO:Si Nanocomposite Films Grown by Thermal Evaporation,"Nanocomposite thin films of Zinc Oxide and Silicon were grown by
co-evaporating powdered ZnO and Si. This resulted in nanocrystallites of ZnO
being embedded in Silicon. The mismatch in crystal structures of constituent
materials result in the ZnO nanocrystals to exist in a state of stress. This
along with oxygen vacancies in the samples result in good Photoluminescence
emission at 520nm. Also, Silicon background gave a photoluminescence emission
at 620nm. The structure was found quite stable over time since the homgenously
dispersed ZnO nanocrystals do not agglomerate. The nanocomposites promises to
be a useful candidate for future optoelectronic devices.",0801.0144v1
2008-01-25,Free-running InGaAs/InP Avalanche Photodiode with Active Quenching for Single Photon Counting at Telecom Wavelengths,"We present an InGaAs/InP avalanche photodiode with an active quenching
circuit on an ASIC (application specific integrated circuit) that is capable of
operating in both gated and free-running modes. The 1.6mm2 ASIC chip is
fabricated using CMOS (complementary metal oxide semiconductor) technology
guaranteeing long-term stability, reliability and compactness. In the
free-running mode we find a single photon detection efficiency of 10% with
<2kHz of noise.",0801.3899v1
2008-02-04,Logic Ciucuits Using Solution-processed Single-walled Carbon Nanotue Transistors,"This letter reports on the realization of logic circuits employing
solution-processed networks of single-walled carbon nanotubes. We constructed
basic logic gates (inverter, NAND and NOR) with n- and p-type field-effect
transistors fabricated by solution-based chemical doping. Complementary
metal-oxide-semiconductor inverters exhibited voltage gains of up to 20, which
illustrates the great potential of carbon nanotube networks for printable
flexible electronics.",0802.0334v1
2008-02-14,Absence of Hole Confinement in Transition Metal Oxides with Orbital Degeneracy,"We investigate the spectral properties of a hole moving in a two-dimensional
Hubbard model for strongly correlated t_2g electrons. Although superexchange
interactions are Ising-like, a quasi-one-dimensional coherent hole motion
arises due to effective three-site terms. This mechanism is fundamentally
different from the hole motion via quantum fluctuations in the conventional
spin model with SU(2) symmetry. The orbital model describes also propagation of
a hole in some e_g compounds, and we argue that orbital degeneracy alone does
not lead to hole self-localization.",0802.2012v1
2008-02-26,Wide-field Fourier transform spectral imaging,"We report experimental results of parallel measurement of spectral components
of the light. The temporal fluctuations of an optical field mixed with a
separate reference are recorded with a high throughput complementary metal
oxide semi-conductor camera (1 Megapixel at 2 kHz framerate). A numerical
Fourier transform of the time-domain recording enables wide-field coherent
spectral imaging. Qualitative comparisons with frequency-domain wide-field
laser Doppler imaging are provided.",0802.3773v1
2008-03-28,Abrupt boundaries of intermediate phases and space filling in oxide glasses,"Modulated DSC measurements on bulk (Na2O)x(GeO2)1-x glasses show a sharp
reversibility window in the 14% < x < 19% soda range, which correlates well
with a broad global minimum in molar volumes. Raman and IR reflectance TO and
LO mode frequencies exhibit anomalies between xc(1) = 14% (stress transition)
and xc(2) = 19% (rigidity transition), with optical elasticity power-laws
confirming the nature of the transitions . Birefringence measurements dramatize
the macroscopically stress-free nature of the Intermediate Phase in the
reversibility window.",0803.4109v1
2008-04-03,Understanding the Unique Structural and Electronic Properties of SrFeO2,"We report a first-principles study of SrFeO$_2$, an infinite-layer oxide with
Fe atoms in a perfect square-planar coordination down to essentially 0 K. Our
results reveal this striking behavior relies on the double occupation of the
3$d_{z^2}$ orbitals of high-spin Fe$^{2+}$. Such an electronic state results
from the hybridization of iron's 3$d_{z^2}$ and 4$s$ orbitals, which enables a
large reduction of the intra-atomic exchange splitting of the $z^2$ electrons.
The generality of the phenomenon is discussed.",0804.0495v1
2008-04-24,"Spin, Orbital and Charge Order at the Interface between Correlated Oxides","The collective behavior of correlated electrons in the VO$_2-$interface layer
of LaVO$_3$/SrTiO$_3$ heterostructure is studied within a quarter-filled
$t_{2g}$-orbital Hubbard model on a square lattice. We argue that the ground
state is ferromagnetic driven by the double exchange mechanism, and is
orbitally and charge ordered due to a confined geometry and electron
correlations. The orbital and charge density waves open gaps on the entire
Fermi surfaces of all orbitals. The theory explains the observed insulating
behavior of the $p$-type interface between LaVO$_3$ and SrTiO$_3$.",0804.3974v2
2008-05-28,Dielectric and polarization experiments in high loss dielectrics: a word of caution,"The recent quest for improved functional materials like high permittivity
dielectrics and/or multiferroics has triggered an intense wave of research.
Many materials have been checked for their dielectric permittivity or their
polarization state. In this report, we call for caution when samples are
simultaneously displaying insulating behavior and defect-related conductivity.
Many oxides containing mixed valent cations or oxygen vacancies fall in this
category. In such cases, most of standard experiments may result in effective
high dielectric permittivity which cannot be related to ferroelectric
polarization. Here we list few examples of possible discrepancies between
measured parameters and their expected microscopic origin.",0805.4335v1
2008-06-03,A gate-defined silicon quantum dot molecule,"We report electron transport measurements of a silicon double dot formed in
multi-gated metal-oxide-semiconductor structures with a 15-nm-thick
silicon-on-insulator layer. Tunable tunnel coupling enables us to observe an
excitation spectrum in weakly coupled dots and an energy level anticrossing in
strongly coupled ones. Such a quantum dot molecule with both charge and energy
quantization provides the essential prerequisite for future implementation of
silicon-based quantum computations.",0806.0422v1
2008-06-18,Diffusion based degradation mechanisms in giant magnetoresistive spin valves,"Spin valve systems based on the giant magnetoresistive (GMR) effect as used
for example in hard disks and automotive applications consist of several
functional metallic thin film layers. We have identified by secondary ion mass
spectrometry (SIMS) two main degradation mechanisms: One is related to oxygen
diffusion through a protective cap layer, and the other one is interdiffusion
directly at the functional layers of the GMR stack. By choosing a suitable
material as cap layer (TaN), the oxidation effect can be suppressed.",0806.2978v1
2008-06-25,Morphology and flexibility of graphene and few-layer graphene on various substrates,"We report on detailed microscopy studies of graphene and few-layer-graphene
produced by mechanical exfoliation on various semi-conducting substrates. We
demonstrate the possibility to prepare and analyze graphene on (001)-GaAs,
manganese p-doped (001)-GaAs and InGaAs substrates. The morphology of graphene
on these substrates was investigated by scanning electron and atomic force
microscopy and compared to layers on silicon oxide. It was found that graphene
sheets strongly follow the texture of the sustaining substrates independent on
doping, polarity or roughness. Furthermore resist residues exist on top of
graphene after a lithographic step. The obtained results provide the
opportunity to research the graphene-substrate interactions.",0806.4074v1
2008-06-30,The superconductivity at 18 K in LiFeAs system,"A new iron arsenide superconducting system LiFeAs was found that crystallizes
into a tetragonal structure with space group P4/nmm. The superconductivity with
Tc up to 18 K was observed in the compounds. This simple 111 type layered iron
arsenide superconductor can be viewed as an analogue of the infinite layer
structure of copper oxides.",0806.4688v3
2008-08-07,Ferromagnetism and spin polarized charge carriers in In$_{2}$O$_{3}$ thin films,"We present evidence for spin polarized charge carriers in In$_2$O$_3$ films.
Both In$_2$O$_3$ and Cr doped In$_2$O$_3$ films exhibit room temperature
ferromagnetism after vacuum annealing, with a saturation moment of
approximately 0.5 emu/cm$^3$. We used Point Contact Andreev Reflection
measurements to directly determine the spin polarization, which was found to be
approximately 50$\pm$5% for both compositions. These results are consistent
with suggestions that the ferromagnetism observed in certain oxide
semiconductors may be carrier mediated.",0808.1123v1
2008-09-08,Observation of excited states in a p-type GaAs quantum dot,"A quantum dot fabricated by scanning probe oxidation lithography on a p-type,
C-doped GaAs/AlGaAs heterostructure is investigated by low temperature
electrical conductance measurements. Clear Coulomb blockade oscillations are
observed and analyzed in terms of sequential tunneling through the
single-particle levels of the dot at T_hole = 185 mK. The charging energies as
large as 2 meV evaluated from Coulomb diamond measurements together with the
well resolved single-hole excited state lines in the charge stability diagram
indicate that the dot is operated with a small number of confined particles
close to the ultimate single-hole regime.",0809.1362v1
2008-09-17,Polaron Coherence as Origin of the Pseudogap Phase in High Temperature Superconducting Cuprates,"Within a two component approach to high Tc copper oxides including polaronic
couplings, we identify the pseudogap phase as the onset of polaron ordering.
This ordering persists in the superconducting phase. A huge isotope effect on
the pseudogap onset temperature is predicted and in agreement with experimental
data. The anomalous temperature dependence of the mean square copper oxygen ion
displacement observed above, at and below Tc stems from an s-wave
superconducting component of the order parameter, whereas a pure d-wave order
parameter alone can be excluded.",0809.2881v1
2008-09-22,Collision of a sphere onto a wall coated with a liquid film,"Particle-particle and particle-wall collisions occur in many natural and
industrial applications such as sedimentation, agglomeration, and granular
flows. To accurately predict the behavior of particulate flows, fundamental
knowledge of the mechanisms of a single collision is required. In this fluid
dynamics video, particle-wall collisions onto a wall coated with 1.5%
poly(ethylene-oxide) (PEO) (viscoelastic liquid) and 80% Glycerol and water
(Newtonian liquid) are shown.",0809.3770v1
2008-09-24,Optically induced electrokinetic patterning and manipulation of particles,"This fluid dynamics video showcases how optically induced electrokinetic
forces can be used to drive three-dimensional micro-vortices. The strong
microfluidic vortices are used constructively in conjunction with other
electrokinetic forces to dynamically and rapidly aggregate particle groups.
Particle manipulation is achieved on the surface of a parallel-plate
gold/indium tin oxide (ITO) electrode that is illuminated with near-infrared
(1064 nm) optical patterns and biased with a low frequency ($<$ 100 kHz)
alternating current (AC) signal. The fluid dynamics video shows how
electrokinetically driven flows in the microdomain can be used for non-invasive
particle manipulation.",0809.4083v2
2008-09-26,DNA adsorption at liquid/solid interfaces,"DNA adsorption on solid or liquid surfaces is a topic of broad fundamental
and applied interest. Here we study by x-ray reflectivity the adsorption of
monodisperse double-stranded DNA molecules a positively-charged surface,
obtained through chemical grafting of a homogeneous organicmonomolecular layer
of N-(2-aminoethyl) dodecanamide on an oxide-free monocrystalline Si(111)
wafer. The adsorbed dsDNA is found to embed into the soft monolayer which is
deformed in the process. The surface coverage is very high and this adsorbed
layer is expected to display 2D nematic ordering.",0809.4639v1
2008-10-14,Successive Phase Transitions in Na_{0.5}CoO_{2} based on the Triangular Lattice d-p Model,"We investigate the electronic states of the CoO_2 plane in the layered cobalt
oxides Na_{0.5}CoO_{2} using the realistic 11 band d-p model on a
two-dimensional triangular lattice. Effects of the Coulomb interaction on a Co
site: the intra- and inter-orbital direct terms U and U', the exchange coupling
J and the pair-transfer J', are treated within the Hartree-Fock approximation.
It is found that the metallic antiferromagnetism takes place below T_{c1} and,
in addition, the orbital order accompanied by the small charge order takes
place below T_{c2} (< T_{c1}) where the system becomes insulator. The obtained
results are consistent with the successive phase transitions observed in
Na_{0.5}CoO_{2}.",0810.2380v1
2008-10-19,Spin-triplet f-wave pairing due to three-site cyclic-exchange ferromagnetic interactions,"Ferromagnetiam and superconductivity in a two-dimensional triangular-lattice
Hubbard model are studied using the density-matrix renormalization group
method. We propose a mechanism of the {\it f}-wave spin-triplet pairing derived
from the three-site cyclic-exchange ferromagnetic interactions. We point out
that a triangular network of hopping integrals, which is required for the
three-site cyclic hopping processes, is contained in the (possibly)
spin-triplet superconducting systems, such as Bechgaard salts (TMTSF)$_2$X,
cobalt oxide Na$_{0.35}$CoO$_2$$\cdot$1.3H$_2$O, and layered perovskite
Sr$_2$RuO$_4$.",0810.3387v1
2008-10-20,Modulation Doping of a Mott Quantum Well by a Proximate Polar Discontinuity,"We present evidence for hole injection into LaAlO3/LaVO3/LaAlO3 quantum wells
near a polar surface of LaAlO3 (001). As the surface is brought in proximity to
the LaVO3 layer, an exponential drop in resistance and a decreasing positive
Seebeck coefficient is observed below a characteristic coupling length of 10-15
unit cells. We attribute this behavior to a crossover from an atomic
reconstruction of the AlO2-terminated LaAlO3 surface to an electronic
reconstruction of the vanadium valence. These results suggest a general
approach to tunable hole-doping in oxide thin film heterostructures.",0810.3469v1
2008-10-21,Generalizing the Cooper-Pair Instability to Doped Mott Insulators,"Copper oxides become superconductors rapidly upon doping with electron holes,
suggesting a fundamental pairing instability. The Cooper mechanism explains
normal superconductivity as an instability of a fermi-liquid state, but
high-temperature superconductors derive from a Mott-insulator normal state, not
a fermi liquid. We show that precocity to pair condensation with doping is a
natural property of competing antiferromagnetism and d-wave superconductivity
on a singly-occupied lattice, thus generalizing the Cooper instability to doped
Mott insulators, with significant implications for the high-temperature
superconducting mechanism.",0810.3862v1
2008-10-24,High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated on Epitaxial Ferroelectric Gate Oxides,"The carrier mobility \mu of few-layer graphene (FLG) field-effect transistors
increases ten-fold when the SiO_2 substrate is replaced by single-crystal
epitaxial Pb(Zr_0.2Ti_0.8)O_3 (PZT). In the electron-only regime of the FLG,
\mu reaches 7x10^4 cm^2/Vs at 300K for n = 2.4x10^12/cm^2, 70% of the intrinsic
limit set by longitudinal acoustic (LA) phonons; it increases to 1.4x10^5
cm^2/Vs at low temperature. The temperature-dependent resistivity \rho(T)
reveals a clear signature of LA phonon scattering, yielding a deformation
potential D = 7.8+/-0.5 eV.",0810.4466v1
2008-10-27,Emergence of Antiferromagnetic Correlation in LiTi2-xVxO4 via 7Li NMR,"We report 7Li NMR studies of V-substitution effects on spinel oxide
superconductor LiTi2O4 (Tc = 13.4 K). In LiTi2-xVxO4 (x = 0-0.4), the V
substitution for the Ti site suppressed the relative volume fraction of
superconductivity faster than Tc. From the observation of fairly homogeneous
enhancement in a 7Li nuclear spin-lattice relaxation rate, we conclude that the
V substitution changes electron correlation effects through electron carrier
doping from quarter electron filling 3d0.5 to 3d1.5 and then the
antiferromagnetic correlation emerges.",0810.4865v1
2008-10-29,High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated on Epitaxial Ferroelectric Gate Oxides (Supplementary Information),"Supplementary Information to arXiv:0810.4466: 1. Characterizations of
Pb(Zr_0.2Ti_0.8)O_3 (PZT) films. 2. Substrate preparation before the
exfoliation of graphene. 3. The band structure of FLG. 4. Dielectric constant
measurements of PZT. 5. rho(V_g) and R_H(V_g) fitting inside the band overlap
regime. 6. The deformation potential of longitudinal acoustic (LA) phonons in
graphene. 7. Resistivity and Hall measurements of a SiO_2-gated FLG.",0810.5339v1
2008-10-30,Removal of Pollutants by Atmospheric Non Thermal Plasmas,"Results on the application of non thermal plasmas in two environmentally
important fields: oxidative removal of VOC and NOx in excess of oxygen were
presented. The synergetic application of a plasma-catalytic treatment of NOx in
excess of oxygen is also described.",0810.5432v1
2008-11-05,Giant electro-thermal conductivity and spin-phonon coupling in an antiferromagnetic oxide,"The application of weak electric fields (<~ 100 V/cm) is found to
dramatically enhance the lattice thermal conductivity of the antiferromagnetic
(AF) insulator CaMnO(3) over a broad range of temperature about the Neel
ordering point (125 K). The effect is coincident with field-induced de-trapping
of bound electrons, suggesting that phonon scattering associated with short-
and long-ranged AF order is suppressed in the presence of the mobilized charge.
This interplay between bound charge and spin-phonon coupling might allow for
the reversible control of spin fluctuations using weak external fields.",0811.0744v1
2008-11-07,Strong Anomalous Optical Dispersion of Graphene: Complex Refractive Index Measured by Picometrology,"We apply spinning-disc picometrology to measure the complex refractive index
of graphene on thermal oxide on silicon. The refractive index varies from n =
2.4-1.0i at 532 nm to n = 3.0-1.4i at 633 nm at room temperature. The
dispersion is five times stronger than bulk graphite (2.67-1.34i to 2.73-1.42i
from 532 nm to 633 nm).",0811.1210v1
2008-11-10,"Low-dimensional NbO structures on the Nb(110) surface: scanning tunneling microscopy, electron spectroscopy and diffraction","X-ray photoelectron spectroscopy and diffraction (XPS, XPD) and scanning
tunneling microscopy (STM) have been used for study of NbOx-structures on the
Nb(110) surface. It is shown that niobium atoms are ordered to form a
two-dimensional superstructure with equidistant spacing between the chains of
niobium atoms. Chemical shifts of Nb3d- and O1s-levels demonstrate that the
oxide layer corresponds to niobium monoxide NbO and the most part of oxygen in
chemisorbed state is localized on the surface. A model of quasi-ordered
structure of NbO on the Nb(110) surface is proposed.",0811.1424v1
2008-11-25,Etching-dependent reproducible memory switching in vertical SiO2 structures,"Vertical structures of SiO$_{2}$ sandwiched between a top tungsten electrode
and conducting non-metal substrate were fabricated by dry and wet etching
methods. Both structures exhibit similar voltage-controlled memory behaviors,
in which short voltage pulses (1 $\mu$s) can switch the devices between high-
and low-impedance states. Through the comparison of current-voltage
characteristics in structures made by different methods, filamentary conduction
at the etched oxide edges is most consistent with the results, providing
insights into similar behaviors in metal/SiO/metal systems. High ON/OFF ratios
of over 10$^{4}$ were demonstrated.",0811.4099v1
2008-12-08,Metal-Insulator phase diagram and orbital selectivity in 3-orbital models with rotationally invariant Hund coupling,"A three band model containing the essential physics of transition metal
oxides with partially filled t_2g shells is solved in the single-site dynamical
mean field approximation, using the full rotationally invariant Slater-Kanamori
interactions. We compute the metal-Mott insulator phase diagram in the space of
chemical potential and interaction strength, determine the response of the
different phases to perturbations which break the orbital symmetry, and
establish the regimes in which an orbital selective Mott phase occurs. The
results are compared to data on titanates, ruthenates, vanadates and C_60.",0812.1520v1
2008-12-12,Autocatalytic MBE growth of GaAs nanowires on oxidized Si(100),"GaAs nanowires were grown by molecular beam epitaxy on Si(100) substrates
covered with 5 nm SiO2. The growth was performed with As4 at low, close to
stoichiometric, As4/Ga flux ratio, using Ga nanodroplets as catalyst. The
nanowires are found to be in epitaxial relation to the Si substrate due to
contact via pinholes through the SiO2 layer. The nanowires are up to 15
micrometers long and have diameters of about 100 nm, the catalyzing Ga
nanodroplets are observed at their tops.",0812.2453v1
2008-12-15,First-Principles Study on Leakage Current through Si/SiO$_2$ Interface,"The relationship between the presence of defects at the stacking structure of
the Si/SiO$_2$ interface and leakage current is theoretically studied by
first-principles calculation. I found that the leakage current through the
interface with dangling bonds is 530 times larger than that without any
defects, which is expected to lead to dielectric breakdown. The direction of
the dangling bonds is closely related to the performance of the oxide as an
insulator. In addition, it is proved that the termination of the dangling bonds
by hydrogen atoms is effective for reducing the leakage current.",0812.2773v2
2008-12-22,Green's function of fully anharmonic lattice vibration,"Motivated by the discovery of superconductivity in beta-pyrochlore oxides, we
study property of rattling motion coupled with conduction electrons. We derive
the general expression of the Green's function of fully anharmonic lattice
vibration within the accuracy of the second order perturbation of electron-ion
interaction by introducing self-energy, vertex-correction, and normalization
factor for each transition. Using the expression, we discuss the characteristic
properties of the spectral function in the entire range from weakly anharmonic
potential to double-well case, and calculate NMR relaxation rate due to the two
phonon Raman process.",0812.4100v1
2009-01-07,Phase-transition driven memristive system,"Memristors are passive circuit elements which behave as resistors with
memory. The recent experimental realization of a memristor has triggered
interest in this concept and its possible applications. Here, we demonstrate
memristive response in a thin film of Vanadium Dioxide. This behavior is driven
by the insulator-to-metal phase transition typical of this oxide. We discuss
several potential applications of our device, including high density
information storage. Most importantly, our results demonstrate the potential
for a new realization of memristive systems based on phase transition
phenomena.",0901.0899v2
2009-01-19,A new temperature scale T* in lead-based relaxor systems,"Via a combination of various experimental and theoretical techniques, a
peculiar, identical temperature scale T* is found to exist in all complex
lead-based relaxor ferroelectrics. T* corresponds to a nanoscale phase
transition due to random fields. Interestingly, T* also exists in other oxides
with extraordinary properties, such as giant magnetoresistivity or
superconductivity. By analogy with such latter systems, the giant
piezoelectricity related to relaxors might originate from proximity competing
states effect.",0901.2604v1
2009-02-11,Screening of electromagnetic field fluctuations by s--wave and d--wave superconductors,"We investigate theoretically the shielding of the electromagnetic field
fluctuations by s-wave and d-wave superconductors within the framework of
macroscopic quantum electrodynamics. The spin flip lifetime is evaluated above
a niobium and a bismuth strontium calcium copper oxide (BSCCO) surface, and the
screening effect is studied as a function of the thickness of the
superconducting layer. Further, we study the different temperature dependence
of the atomic spin relaxation above the two superconductors.",0902.1981v2
2009-03-13,Optical Trajectory of the Insulator-to-metal Transition of Ultra-thin Gold Films,"We apply interferometric picometrology to measure the complex refractive
index and dielectric properties of ultra-thin gold films as a continuous
function of thickness from 0.2 nm to 10 nm deposited on thermal oxide on
silicon. Three distinct regimes are found for the dielectric constant
trajectory in the complex plane. The first regime shows a circular trajectory
predicted by the Drude equation tracing the gold bulk-to-thin film transition.
The second and third regimes are manifested as metal clusters range from large
to small size and sparse coverage. The entire atom-to-bulk transition of gold
is revealed from the optical perspective.",0903.2492v1
2009-03-24,Band structure of new layered 17 K superconductor Sr4Sc2Fe2P2O6 in comparison with hypothetical Sr4Sc2Fe2As2O6,"The results of the ab initio FLAPW-GGA calculations of the band structure of
the newly synthesized tetragonal (space group P4/nmm) layered iron
phosphide-oxide: 17K superconductor Sr4Sc2Fe2P2O6 are presented. For
Sr4Sc2Fe2P2O6 the optimized structural data, the energy bands, total and
partial densities of states, Fermi surface topology, low-temperature electron
specific heat and molar Pauli paramagnetic susceptibility have been determined
and discussed in comparison with hypothetical isostructural iron arsenide-oxide
phase Sr4Sc2Fe2As2O6 and related layered FeAs and FeP superconductors.",0903.4038v1
2009-03-25,"Universal Non-Landau, Self-Organized, Lattice Disordering Percolative Dopant Network Sub-Tc Phase Transitions in Ceramic Superconductors","Ceramic superconductors (cuprates, pnictides, ...) exhibit universal features
in both Tcmax and in their planar lattice disordering measured by EXAFS, as
reflected by three phase transitions. The two highest temperature transitions
are known to be associated with formation of pseudogaps and superconductive
gaps, with corresponding Landau order parameters, but no new gap is associated
with the third transition below Tc. It is argued that the third transition is a
dopant glass transition, which is remarkably similar to transitions previously
observed in chalcogenide and oxide alloy network glasses (like window glass).",0903.4376v1
2009-04-01,Electronic structure of Ti-doped Sr4Sc2Fe2As2O6,"First principle FLAPW-GGA calculations have been performed with the purpose
to understand the electronic properties for the newly synthesized tetragonal
(space group P4/nmm) layered iron arsenide-oxide: Sr4Sc2Fe2As2O6 doped with
titanium. The total and partial densities of states, low-temperature electron
specific heat and molar Pauli paramagnetic susceptibility have been obtained
and discussed for Sr4ScTiFe2As2O6 in comparison with parent phase
Sr4Sc2Fe2As2O6.
  Our results show that the insertion of Ti into Sc sublattice of iron
arsenide-oxide phase Sr4Sc2Fe2As2O6 leads to principal change of its electronic
structure; in result the insulating so-called ""charge reservoirs', i.e.
perovskite-based [Sr4Sc2O6] blocks became conducting. This situation differs
essentially from the known picture for all others Fe-As superconductors where
the conducting [Fe2As2] blocks are separated by isolating blocks.",0904.0117v1
2009-04-21,Molecular modeling and simulation of thermophysical properties: Application to pure substances and mixtures,"At the Institute for Thermodynamics and Thermal Process Engineering (ITT)
about 100 molecular models for pure substances have been developed so far.
These models reproduce vapor pressure, saturated liquid density, and enthalpy
of vaporization with a technical accuracy of less than 5%, less than 1%, and
less than 5% deviation compared to experimental data, respectively.
  Simulation results are outlined for the pure substances ethylene oxide and
ammonia, demonstrating the outstanding predictive power of the applied methods.
Secondly, nucleation processes are discussed. Underlying effects on are studied
on the molecular level.",0904.3191v1
2009-04-27,Production d'hydrogène par oxydation catalytique partielle du méthane Etude du mécanisme réactionnel,"The partial oxidation of methane was investigated using a self-stirred
reactor under a wide range of operating conditions. The recation mechanism was
determined by comparing ecperimental results with the results of simulations
made using the Chemkin-Surface software. The proposed mechanism includes 444
homogeneous reactions and 33 surface reactions.",0904.4138v1
2009-05-02,Quantum fluctuation and geometrical frustration effects on electric polarization,"We examine theoretically a possibility of ferroelectricity caused by
electronic charge order without inversion symmetry, motivated by layered iron
oxides. Quantum electronic models in a paired-triangular lattice are analyzed
by utilizing the variational Monte Carlo simulation. Our calculation
demonstrates that combined effects of electron transfer between the layers,
corresponding to quantum fluctuation between the potential minima, and
geometrical frustration promote appearance of an electric polarization. Present
results are in contrast to the conventional manner of quantum fluctuation in
ferroelectricity.",0905.0182v1
2009-05-05,Spectroscopic studies on nanocomposites obtained by functionalization of carbon nanotubes with conducting polymers,"Vibrational properties of composites based on single-walled carbon nanotubes
(SWNTs) and conducting polymers of the type polyaniline (PANI) and poly
(3,4-ethylene dioxythiophene) (PEDOT) are reported. For PANI-functionalized
SWNTs, the intensity increase of the Raman band at 178 cm-1, associated with
radial breathing modes of SWNTs bundles, indicates an additional roping of
nanotubes due to the presence of the polymer. The interaction of this composite
with NH4OH solution involves an internal redox reaction between PANI and SWNTs.
Thus, the polymer chain undergoes a transition from the semi-oxidized state
into a reduced one. The functionalization of SWNT side walls with PEDOT is
invoked as well.",0905.0533v1
2009-05-05,"A new material for hydrogen storage, ScAl0.8Mg0.2","A novel aluminium rich alloy for hydrogen storage has been discovered,
ScAl0.8Mg0.2, which has superior properties regarding hydrogen storage
capacity, kinetics and stability towards air oxidation in comparison to
hydrogen absorption in state-of-the-art intermetallic compounds. Detailed
analysis of the hydrogen absorption in ScAl0.8Mg0.2 has been performed using in
situ synchrotron radiation powder X-ray diffraction, neutron powder diffraction
and quantum mechanical calculations. The results from calculations and
experiments are in good agreement with each other.",0905.0630v2
2009-05-18,NO2 and Humidity Sensing Characteristics of Few-layer Graphene,"Sensing characteristics of few-layer graphenes for NO2 and humidity have been
investigated with graphene samples prepared by the thermal exfoliation of
graphitic oxide (EG), conversion of nanodiamond (DG) and arc-discharge of
graphite in hydrogen (HG). The sensitivity for NO2 is found to be highest with
DG. Nitrogen-doped HG (n-type) shows increased sensitivity for NO2 compared to
pure HG. The highest sensitivity for humidity is observed with HG. The sensing
characteristics of graphene have been examined for different aliphatic alcohols
and the sensitivity is found to vary with the chain length and branching.",0905.2852v1
2009-06-30,Identification of vacancy defects in a thin film perovskite oxide,"Vacancy defects in thin film laser ablated SrTiO3 on SrTiO3 were identified
using variable energy positron annihilation lifetime measurements. Strontium
vacancy related defects were the dominant positron traps and, apart from in the
top ~ 50 nm, were found to be uniformly distributed. The surface layer showed
an increase in annihilation from larger open-volume defects, large vacancy
clusters or nanovoids.",0906.5558v1
2009-07-22,Partial order in a frustrated Potts model,"We investigate a 4-state ferromagnetic Potts model with a special type of
geometrical frustration on a three dimensional diamond lattice by means of
Wang-Landau Monte Carlo simulation motivated by a peculiar structural phase
transition found in $\beta$-pyrochlore oxide KOs$_2$O$_6$. We find that this
model undergoes unconventional first-order phase transition; half of the spins
in the system order in a two dimensional hexagonal-sheet-like structure, while
the remaining half stay disordered. The ordered sheets and the disordered
sheets stack one after another. We obtain a fairly large residual entropy at $T
= 0$ which originates from the disordered sheets.",0907.3812v1
2009-08-12,Edge-carboxylated Carbon Nanoflakes from Nitric Acid Oxidised Arc-discharge Material,"Carbon Nanoflakes (CNFs) with average diameters of about 30 nm have been
prepared and isolated in bulk quantities by a single-step oxidation procedure
using single-wall carbon nanotube arc-discharge material and nitric acid. The
CNFs are predominately single, graphenic sheets containing a small number of
internal defects. The edges are decorated with primarily carboxylic acid groups
which allow facile chemical functionalisation and cross-linking of the
fragments using multivalent cations.",0908.1740v1
2009-08-12,Hierarchy of Electronic Properties of Chemically Derived and Pristine Graphene Probed by Microwave Imaging,"Local electrical imaging using microwave impedance microscope is performed on
graphene in different modalities, yielding a rich hierarchy of the local
conductivity. The low-conductivity graphite oxide and its derivatives show
significant electronic inhomogeneity. For the conductive chemical graphene, the
residual defects lead to a systematic reduction of the microwave signals. In
contrast, the signals on pristine graphene agree well with a lumped-element
circuit model. The local impedance information can also be used to verify the
electrical contact between overlapped graphene pieces.",0908.1778v1
2009-09-23,First-Principles Approach to Heat and Mass Transfer Effects in Model Catalyst Studies,"We assess heat and mass transfer limitations in in situ studies of model
catalysts with a first-principles based multiscale modeling approach that
integrates a detailed description of the surface reaction chemistry and the
macro-scale flow structures. Using the CO oxidation at RuO2(110) as a
prototypical example we demonstrate that factors like a suppressed heat
conduction at the backside of the thin single-crystal, and the build-up of a
product boundary layer above the flat-faced surface play a significant role.",0909.4261v1
2009-10-16,Checkerboard superconducting order and antinodal Bogoliubov quasiparticle interference,"Numerical study of momentum-dependent gap function is presented to make clear
the origin of superconductivity in copper oxides. We claim that antinodal
region with pronounced nesting feature of the Fermi contour gives rise to
superconducting pairing with large momentum under screened Coulomb repulsion.
Such a pairing results in both spatial checkerboard pattern of the
superconducting state below Tc and a gapped state of incoherent pairs in a
broad temperature range above Tc. We explain the momentum dependence of the
coherent spectral weight detected in angle-resolved photoemission spectroscopy
and predict antinodal Bogoliubov quasiparticle interference other than observed
in the nodal region.",0910.3172v1
2009-11-07,Lifetime positron annihilation spectroscopy and photo-inactivated bacteria,"Combined positron and visible light irradiations in the photodynamical
therapy (PDT) applications are analyzed. Objectives and goals of PDT are
killing or irreversible oxidative damage of pathogenic cells, or rather their
cell walls, cell membranes, peptides, and nucleic acids by photo-activated
oxygen of photosentizer injected into the target cell during light irradiation.
In this paper, the arguments for involving of lifetime positron annihilation
spectroscopy to control of photodamaging cells in the course of the PDT
procedure are given on the examples of gram-positive and gram-negative bacteria
basing on a brief survey of the literature.",0911.1389v3
2009-11-09,Luminescent Ions in Silica-Based Optical Fibers,"We present some of our research activities dedicated to doped silica-based
optical fibers, aiming at understanding the spectral properties of luminescent
ions, such as rare-earth and transition metal elements. The influence of the
local environment on dopants is extensively studied: energy transfer mechanisms
between rare-earth ions, control of the valence state of chromium ions, effect
of the local phonon energy on thulium ions emission efficiency, and broadening
of erbium ions emission induced by oxide nanoparticles. Knowledge of these
effects is essential for photonics applications.",0911.1683v1
2009-11-27,Melting slope of MgO from molecular dynamics and density functional theory,"We combine density functional theory (DFT) with molecular dynamics
simulations based on an accurate atomistic force field to calculate the
pressure derivative of the melting temperature of magnesium oxide at ambient
pressure - a quantity for which a serious disagreement between theory and
experiment has existed for almost 15 years. We find reasonable agreement with
previous DFT results and with a very recent experimental determination of the
slope. We pay particular attention to areas of possible weakness in theoretical
calculations and conclude that the long-standing discrepancy with experiment
could only be explained by a dramatic failure of existing density functionals
or by flaws in the original experiment.",0911.5309v1
2010-01-01,Dipole trap model for the metallic state in gated silicon-inversion layers,"In order to investigate the metallic state in high-mobility Si-MOS
structures, we have further developed and precised the dipole trap model which
was originally proposed by B.L. Altshuler and D.L. Maslov [Phys. Rev. Lett.\
82, 145 (1999)]. Our additional numerical treatment enables us to drop several
approximations and to introduce a limited spatial depth of the trap states
inside the oxide as well as to include a distribution of trap energies. It
turns out that a pronounced metallic state can be caused by such trap states at
appropriate energies whose behavior is in good agreement with experimental
observations.",1001.0205v1
2010-02-01,The Novelty of Syntheses & Varied Applications of ZnO nano systems,"Controlled synthesis of nano materials is critical for the development of
nanotechnologies concerned with respect to shape and size. Especially, ZnO
nanosystems, such as wires, belts, needles and films can be easily formed by
either physical or chemical approaches such as, Chemical Vapour Deposition,
Metal Organic Chemical Vapour Deposition, Pulsed Laser Deposition, Molecular
Beam Epitaxy, Sol Gel process, Thermal Annealing method and Solvothermal
Oxidation. ZnO has polar surfaces that help in the formation of a wide range of
nanostructures such as needles,films rings, springs, bows and helices",1002.0199v1
2010-02-18,Hysteresis Switching Loops in Ag-manganite memristive interfaces,"Multilevel resistance states in silver-manganite interfaces are studied both
experimentally and through a realistic model that includes as a main ingredient
the oxygen vacancies diffusion under applied electric fields. The switching
threshold and amplitude studied through Hysteresis Switching Loops are found to
depend critically on the initial state. The associated vacancy profiles further
unveil the prominent role of the effective electric field acting at the
interfaces. While experimental results validate main assumptions of the model,
the simulations allow to disentangle the microscopic mechanisms behind the
resistive switching in metal-transition metal oxide interfaces.",1002.3593v1
2010-04-04,Simulation of ion track ranges in uranium oxide,"Direct comparisons between statistically sound simulations of ion-tracks and
published experimental measurements of range densities of iodine implants in
uranium dioxide have been made with implant energies in the range of 100-800
keV. Our simulations are conducted with REED-MD (Rare Event Enhanced
Domain-following Molecular Dynamics) in order to account for the materials
structure in both single crystalline and polycrystalline experimental samples.
We find near-perfect agreement between REED-MD results and experiments for
polycrystalline target materials.",1004.0490v1
2010-04-01,Lattice coupling and Franck-Condon effects in K-edge resonant inelastic X-ray scattering,"We discuss recent Cu K-edge resonant inelastic scattering (RIXS) results for
CuB2O4, a model system consisting of electronically-isolated CuO4 plaquettes,
which exhibits anomalies in the incident photon energy dependence that are not
captured by electron-only models. We show that these anomalous features can be
qualitatively described by extending the electron-only considerations to
include the lattice degrees of freedom. Our findings have important general
implications for the interpretation of K-edge RIXS results for electronically
higher-dimensional transition metal oxides.",1004.0859v1
2010-04-26,Andreev reflection in ferrimagnetic CoFe2O4/SrRuO3 spin filters,"We have performed point contact spectroscopy measurements on a sample
constituted by a metallic ferromagnetic oxide (SrRuO_3) bottom electrode and a
tunnel ferrimagnetic (CoFe_2O_4) barrier. Andreev reflection is observed across
the tunnel barrier. From the comparison of Andreev reflection in SrRuO3 and
across the CoFe_2O_4 barrier we infer that the ferrimagnetic barrier has a spin
filter efficiency not larger than +13%. The observation of a moderate and
positive spin filtering is discussed in the context of the microstructure of
the barriers and symmetry-related spin filtering effects.",1004.4631v1
2010-06-08,Dramatic Mobility Enhancements in Doped SrTiO3 Thin Films by Defect Management,"We report bulk-quality n-type SrTiO3 (n-SrTiO3) thin films fabricated by
pulsed laser deposition, with electron mobility as high as 6600 cm2 V-1 s-1 at
2 K and carrier density as low as 2.0 x 10^18cm-3 (~ 0.02 at. %), far exceeding
previous pulsed laser deposition films. This result stems from precise
strontium and oxygen vacancy defect chemistry management, providing a general
approach for defect control in complex oxide heteroepitaxy.",1006.1564v1
2010-06-25,Paramagnetic centers in graphene nanoribbons prepared from longitudinal unzipping of carbon nanotubes,"Electron spin resonance (ESR) investigation of graphene nanoribbons (GNRs)
prepared through longitudinal unzipping of multiwalled carbon nanotubes
(MWCNTs) indicates the presence of C-related dangling bond centers, exhibiting
paramagnetic features. ESR signal broadening from pristine or oxidized graphene
nanoribbons (OGNRs) is explained in terms of unresolved hyperfine structure,
and in the case of reduced GNRs (RGNRs), the broadening of ESR signal can be
due to enhancement in conductivity upon reduction. The spin dynamics observed
from ESR linewidth-temperature data reflect a variable range hopping (VRH)
mechanism through localized states, consistent with resistance-temperature
data.",1006.4942v1
2010-07-13,Size and Defect related Broadening of Photoluminescence Spectra in ZnO:Si Nanocomposite Films,"Nanocomposite films of Zinc Oxide and Silicon were grown by thermal
evaporation technique using varying ratios of ZnO:Si in the starting material.
Analysis reveal the role of ZnO and amorphous silicon interface in contributing
to relatively less common blue photoluminescence emissions (at $\sim$ 400 and
470nm). These blue peaks are observed along with the emissions resulting from
band edge transition (370nm) and those related to defects (522nm) of ZnO.
Careful analysis shows that along with the grain size of ZnO, a suitable
compositional ratio (of ZnO to silicon) is critical for the coexistence of all
the four peaks. Proper selection of conditions can give comparable
photoluminescence peak intensities leading to broad-band emission.",1007.2142v1
2010-08-18,Diminished Short Channel Effects in Nanoscale Double-Gate Silicon-On-Insulator Metal-Oxide- Semiconductor Field-Effect-Transistors due to Induced Back-Gate Step Potential,"In this letter we discuss how the short channel behavior in sub 100 nm
channel range can be improved by inducing a step surface potential profile at
the back gate of an asymmetrical double gate (DG) Silicon-On-Insulator (SOI)
Metal-Oxide-Semiconductor Field-Effect- Transistor (MOSFET) in which the front
gate consists of two materials with different work functions.",1008.3016v1
2010-08-28,Resonant Inelastic X-ray Scattering on Spin-Orbit Coupled Insulating Iridates,"We determine how the elementary excitations of iridium-oxide materials, which
are dominated by a strong relativistic spin-orbit coupling, appear in Resonant
Inelastic X-ray Scattering (RIXS). Whereas the RIXS spectral weight at the L2
x-ray edge vanishes, we find it to be strong at the L3-edge. Applying this to
Sr2IrO4, we observe that RIXS, besides being sensitive to local doublet to
quartet transitions, meticulously maps out the strongly dispersive delocalized
excitations of the low-lying spin-orbit doublets.",1008.4862v1
2010-08-31,Chemisorption of a molecular oxygen on the UN (001) surface: ab initio calculations,"The results of DFT GGA calculations on oxygen molecules adsorbed upon the
(001) surface of uranium mononitride (UN) are presented and discussed. We
demonstrate that O2 molecules oriented parallel to the substrate can dissociate
either (i) spontaneously when the molecular center lies above the surface
hollow site or atop N ion, (ii) with the activation barrier when a molecule
sits atop the surface U ion. This explains fast UN oxidation in air.",1008.5323v1
2010-09-03,Superconducting junctions from non-superconducting doped CuO$_2$ layers,"The theoretical approach proposed recently for description of redistribution
of electronic charge in multilayered selectively doped systems is modified for
a system with finite number of layers. A special attention is payed to the case
of a finite heterostructure made of copper-oxide layers which are all
non-superconducting (including non-conducting) because of doping levels being
beyond the well-known characteristic interval for superconductivity. Specific
finite structures and doping configurations are proposed to obtain atomically
thin superconducting heterojunctions of different compositions.",1009.0740v4
2010-09-07,"Composite-Fermion Theory for Pseudogap, Fermi Arc, Hole Pocket, and Non-Fermi-Liquid of Underdoped Cuprate Superconductors","We propose that an extension of the exciton concept to doped Mott insulators
offers a fruitful insight into challenging issues of the copper oxide
superconductors. In our extension, new fermionic excitations called cofermions
emerge in conjunction to generalized excitons. The cofermions hybridize with
conventional quasiparticles. Then a hybridization gap opens, and is identified
as the pseudogap observed in the underdoped cuprates. The resultant
Fermi-surface reconstruction naturally explains a number of unusual properties
of the underdoped cuprates, such as the Fermi arc and/or pocket formation.",1009.1197v1
2010-09-14,Highly Tunable Hybrid Quantum Dots with Charge Detection,"In order to employ solid state quantum dots as qubits, both a high degree of
control over the confinement potential as well as sensitive charge detection
are essential. We demonstrate that by combining local anodic oxidation with
local Schottky-gates, these criteria are nicely fulfilled in the resulting
hybrid device. To this end, a quantum dot with adjacent charge detector is
defined. After tuning the quantum dot to contain only a single electron, we are
able to observe the charge detector signal of the quantum dot state for a wide
range of tunnel couplings.",1009.2578v1
2010-10-27,Molecular dynamics simulations of oxide memory resistors (memristors),"Reversible bipolar nano-switches that can be set and read electronically in a
solid-state two-terminal device are very promising for applications. We have
performed molecular-dynamics simulations that mimic systems with oxygen
vacancies interacting via realistic potentials and driven by an external bias
voltage. The competing short- and long-range interactions among charged mobile
vacancies lead to density fluctuations and short-range ordering, while
illustrating some aspects of observed experimental behavior, such as memristor
polarity inversion.",1010.5656v1
2010-11-24,Electronic properties of new low-temperature superconductors: 3.3K (Ni2P2)(Sr4Sc2O6) and 2.7K (Ni2As2)(Sr4Sc2O6) from first principles,"Based on first-principle FLAPW-GGA calculations, we have investigated
structural and electronic properties of the recently synthesized tetragonal
(space group P4/nmm) nickel-based pnictide oxide superconductors: 3.3K
(Ni2P2)(Sr4Sc2O6) and 2.7K (Ni2As2)(Sr4Sc2O6). Optimized structural data,
electronic bands, total and partial densities of states, and Fermi surface
topology have been obtained and discussed in comparison with available
experiments and with their Fe-based (Fe2P2)(Sr4Sc2O6) and (Fe2As2)(Sr4Sc2O6)
analogs.",1011.5323v1
2010-11-26,Maximally Supersymmetric Yang-Mills in five dimensions in light-cone superspace,"We formulate maximally supersymmetric Yang-Mills theory in five dimensions in
light-cone superspace. The light-cone Hamiltonian is of the quadratic form and
the theory can be understood as an oxidation of the N=4 Super Yang-Mills Theory
in four dimensions. We specifically study three-point counterterms and show how
these counterterms vanish on-shell. This study is a preliminary to set up the
technique in order to study possible four-point counterterms.",1011.5817v2
2010-12-11,First-principles modeling of electrostatically doped perovskite systems,"Macroscopically, confined electron gases at polar oxide interfaces are
rationalized within the simple ""polar catastrophe"" model. At the microscopic
level, however, many other effects such as electric fields, structural
distortions and quantum-mechanical interactions enter into play. Here we show
how to bridge the gap between these two length scales, by combining the
accuracy of first-principles methods with the conceptual simplicity of model
Hamiltonian approaches. To demonstrate our strategy, we address the equilibrium
distribution of the compensating free carriers at polar LaAlO3/SrTiO3
interfaces. Remarkably, a model including only calculated bulk properties of
SrTiO3 and no adjustable parameters accurately reproduces our full
first-principles results. Our strategy provides a unified description of charge
compensation mechanisms in SrTiO3-based systems.",1012.2468v1
2010-12-26,Molecular dynamics simulations of oxide memristors: thermal effects,"We have extended our recent molecular-dynamic simulations of memristors to
include the effect of thermal inhomogeneities on mobile ionic species appearing
during operation of the device. Simulations show a competition between an
attractive short-ranged interaction between oxygen vacancies and an enhanced
local temperature in creating/destroying the conducting oxygen channels. Such a
competition would strongly affect the performance of the memristive devices.",1012.5514v1
2011-01-07,"High-pressure synthesis of rock salt LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions","Metastable LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions with rock salt
crystal structure have been synthesized by solid state reaction of ZnO with
LiMeO2 complex oxides at 7.7 GPa and 1350-1450 K. Structure, phase composition,
thermal stability and thermal expansion of the recovered samples have been
studied by X-ray diffraction with synchrotron radiation. At ambient pressure
rock salt LiMeO2-ZnO solid solutions are kinetically stable up to 670-800 K
depending on the composition.",1101.1386v1
2011-01-14,In-Situ Grown Erbium-Doped Dielectric Nanoparticles in Silica-Based Transparent Optical Fibers,"An efficient method to fabricate transparent glass ceramic fibers containing
in-situ grown Er3+-doped oxide nanoparticles is presented. Characterization of
the drawn fibers exhibits low loss (0.4 dB/m) and broadened Er3+ emission
spectrum. This attractive method offers new scopes for fiber amplifiers.",1101.2814v2
2011-02-03,Medium Energy Ion Scattering of Gr on SiC(0001) and Si(100),"Depth profiling of graphene with high-resolution ion beam analysis is a
practical method for analysis of monolayer thicknesses of graphene. Not only is
the energy resolution sufficient to resolve graphene from underlying SiC, but
by use of isotope labeling it is possible to tag graphene generated from
reacted ethylene. Furthermore, we are able to analyze graphene supported by
oxidized Si(100) substrates, allowing the study of graphene films grown by
chemical vapor deposition on metal and transfered to silicon. This introduces a
powerful method to explore the fundamentals of graphene formation.",1102.0675v1
2011-02-25,"Orbital ordering, ferroelasticity, and the large pressure induced volume collapse in PbCrO3","We report a new tetragonal ground-state for perovskite-structured PbCrO3 from
DFT+U calculations, and explain its anomalously large volume. The new structure
is stabilized due to orbital ordering of Cr-d in the presence of a large
tetragonal crystal field, mainly due to off-centering of the Pb atom. At higher
pressures (smaller volumes) there is a first-order transition to a cubic phase
where the Cr-d orbitals are orbitally liquid. This phase-transition is
accompanied by a ~11.5% volume collapse, one of the largest known for
transition-metal oxides. The large ferroelasticity and its strong coupling to
the orbital degrees of freedom could be exploited to form potentially useful
magnetostrictive materials",1102.5323v1
2011-04-05,Isotope effect in the pseudogap of high-temperature superconducting copper oxides,"We study cuprates within Dynamical Cluster Approximation and find the
pseudogap displays an isotope effect of the same sign as observed
experimentally. Notwithstanding the non-phononic origin of the pseudogap the
interplay between electronic repulsion and retarded phonon-mediated attraction
gives rise to an isotope dependence of the antinodal spectra. Due to the strong
momentum differentiation, such interplay is highly non-trivial and leads to the
simultaneous presence of heavier quasiparticles along the nodal direction. We
predict an isotope effect in electron-doped materials.",1104.0940v1
2011-04-05,Observation of asymmetric spectrum broadening induced by silver nanoparticles in a heavy-metal oxide glass,"We demonstrate experimentally and support by a theoretical analysis an effect
of asymmetric spectrum broadening, which results from doping of silver
nanoparticles into a heavy-glass matrix, 90(0.5WO3-0.3SbPO4-0.2PbO)-10AgCl. The
strong dispersion of the effective nonlinear coefficient of the composite
significantly influences the spectral broadening via the self-phase modulation,
and leads to a blue upshift of the spectrum. Further extension of the spectrum
towards shorter wavelengths is suppressed by a growing loss caused by the
plasmon resonance in the silver particles. The red-edge spectral broadening is
dominated by the stimulated Raman Scattering.",1104.0952v1
2011-04-07,Detection of melting by in-situ observation of spherical-drop formation in laser-heated diamond-anvil cells,"A simple method for detection of melting event in laser-heated diamond anvil
cells (DACs) is introduced. The melting is registered optically by the
formation of spherical drops of the investigated material as heated in an inert
pressure transmitting medium. Feasibility of the method is demonstrated on the
examples of metal (iron and gold) and iron oxide (Fe2O3), materials molten at
pressures over 40 GPa employing a portable laser heating system.",1104.1304v1
2011-04-11,Tunable 2-dimensional/3-dimensional electron gases by submonolayer La doping of SrTiO_{3},"First-principles calculation was used to study the structural and electronic
features of the low dimensional oxide structure,
SrTiO_{3}/Sr_{1-x}La_{x}TiO_{3} (x=0.25) superlattices, constructed by
submonolayer low dimensional La doping into SrTiO_{3}. We demonstrate a
dimensionality crossover from three-dimensional to two-dimensional (3D \to 2D)
electronic behavior in the system. Two types of carriers, one confined to 2D
and the other extended, exhibit distinct tunable (3D \to 2D) transport
characteristics that will enable the study of many properties (e.g.,
superconductivity) through this change in dimensionality.",1104.1921v1
2011-04-12,The Role of Intermediate States in Low-Velocity Friction between Amorphous Surfaces,"Simulated sliding between an oxidized silicon tip and surface over six
decades of velocity using accelerated molecular dynamics reproduces the
experimentally observed velocity dependence of the friction force. Unlike in
the crystalline case, as increasing force is applied to the amorphous tip
intermediate states arise. These intermediate states serve as critical
transition pathways. The emergence of such states leads to the emergence of a
plateau in sliding velocity at lower sliding speeds and higher temperatures. A
simple theory based on these observations successfully describes both the
experimental and the simulated data.",1104.2226v1
2011-04-13,Single-molecule interfacial electron transfer dynamics manipulated by external electric current,"Interfacial electron transfer (IET) dynamics in 1,1'-dioctadecyl-3, 3, 3',
3'-tetramethylindodicarbocyanine (DiD) dye molecules / indium tin oxide (ITO)
film system have been probed at the ensemble and single-molecule level by
recording the change of fluorescence emission intensity. By comparing the
difference of the external electric current (EEC) dependence of lifetime and
intensity for enambles and single molecules, it is shown that the
single-molecule probe can effcienly demonstrate the IET dynamics. The backward
electron transfer and electron transfer of ground state induce the single
molecules fluorescence quenching when an EEC is applied to ITO film.",1104.2361v1
2011-04-15,Laterally proximized aluminum tunnel junctions,"This letter presents experiments on junctions fabricated by a new technique
that enables the use of high quality aluminum oxide tunnel barriers with normal
metal electrodes at low temperatures. Inverse proximity effect is applied to
diminish the superconductivity of an aluminum dot through a clean lateral
connection to a normal metal electrode. To demonstrate the effectiveness of
this method, fully normal-state single electron transistors (SET) and normal
metal-insulator-superconductor (NIS) junctions applying proximized Al junctions
were fabricated. The transport characteristics of the junctions were similar to
those obtained from standard theoretical models of regular SETs and NIS
junctions.",1104.3052v1
2011-05-04,Strain-induced interface reconstruction in epitaxial heterostructures,"We investigate in the framework of Landau theory the distortion of the strain
fields at the interface of two dissimilar ferroelastic oxides that undergo a
structural cubic-to-tetragonal phase transition. Simple analytical solutions
are derived for the dilatational and the order parameter strains that are
globally valid over the whole of the heterostructure. The solutions reveal that
the dilatational strain exhibits compression close to the interface which may
in turn affect the electronic properties in that region.",1105.0860v2
2011-05-05,Determination of characteristic relaxation times and their significance in glassy disordered insulators,"We revisit the field effect procedure used to characterise the slow dynamics
of glassy Anderson insulators. It is shown that in the slowest systems the
procedure fails and the ""characteristic"" time values extracted are not
intrinsic but determined by the experimental procedure itself. In other cases
(like lightly doped indium oxide) qualitative indications about the dynamics
might be obtained, however the times extracted cannot be seen as characteristic
relaxation times of the system in any simple manner, and more complete
experiments are necessary. Implications regarding the effect of carrier
concentration on the emergence of glassiness are briefly outlined.",1105.0984v2
2011-05-23,Molecular dynamics simulations of oxide memristors: crystal field effects,"We present molecular-dynamic simulations of memory resistors (memristors)
including the crystal field effects on mobile ionic species such as oxygen
vacancies appearing during operation of the device. Vacancy distributions show
different patterns depending on the ratio of a spatial period of the crystal
field to a characteristic radius of the vacancy-vacancy interaction. There are
signatures of the orientational order and of spatial voids in the vacancy
distributions for some crystal field potentials. The crystal field stabilizes
the patterns after they are formed, resulting in a non-volatile switching of
the simulated devices.",1105.4445v1
2011-06-10,Electrostatic effects on contacts to carbon nanotube transistors,"We use numerical simulations to investigate the effect of electrostatics on
the source and drain contacts of carbon nanotube field-effect transistors. We
find that unscreened charge on the nanotube at the contact-channel interface
leads to a potential barrier that can significantly hamper transport through
the device. This effect is largest for intermediate gate voltages and for
contacts near the ohmic-Schottky crossover, but can be mitigated with a
reduction in the gate oxide thickness. These results help to elucidate the
important role that contact geometry plays in the performance of carbon
nanotube electronic devices.",1106.2186v1
2011-06-20,Giant Flexoelectric Effect in Ferroelectric Epitaxial Thin Films,"We report on nanoscale strain gradients in ferroelectric HoMnO3 epitaxial
thin films, resulting in a giant flexoelectric effect. Using grazing-incidence
in-plane X-ray diffraction, we measured strain gradients in the films, which
were 6 or 7 orders of magnitude larger than typical values reported for bulk
oxides. The combination of transmission electron microscopy, electrical
measurements, and electrostatic calculations showed that flexoelectricity
provides a means of tuning the physical properties of ferroelectric epitaxial
thin films, such as domain configurations and hysteresis curves.",1106.3792v1
2011-06-22,Voltage percolation thresholds evidenced in the electrical behaviour of different nanostructures,"Percolation phenomena are investigated and discussed in three kinds of
nanostructures: first two are nanocrystalline silicon-based systems, Si
nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an
oxidized nanowire network, and the third consisting of a multi-walled carbon
nanotube network embedded in amorphous SiN. The current-voltage characteristics
measured on first two systems present voltage percolation thresholds with the
same shape - a saturation plateau region of the current, followed by an abrupt
increase. The current-voltage and conductance-voltage curves measured on
multi-walled carbon nanotube network embedded in amorphous SiN present
non-periodic and temperature independent oscillations. These oscillations are
interpreted as voltage percolation thresholds.",1106.4419v1
2011-06-27,Graphene microwave transistors on sapphire substrates,"We have developed metal-oxide graphene field-effect transistors (MOGFETs) on
sapphire substrates working at microwave frequencies. For monolayers, we obtain
a transit frequency up to ~ 80 GHz for a gate length of 200 nm, and a power
gain maximum frequency of about ~ 3 GHz for this specific sample. Given the
strongly reduced charge noise for nanostructures on sapphire, the high
stability and high performance of this material at low temperature, our MOGFETs
on sapphire are well suited for a cryogenic broadband low-noise amplifier.",1106.5529v1
2011-07-08,Dynamically controlled charge sensing of a few-electron silicon quantum dot,"We report charge sensing measurements of a silicon metal-oxide-semiconductor
quantum dot using a single-electron transistor as a charge sensor with dynamic
feedback control. Using digitallycontrolled feedback, the sensor exhibits
sensitive and robust detection of the charge state of the quantum dot, even in
the presence of charge drifts and random charge rearrangements. The sensor
enables the occupancy of the quantum dot to be probed down to the single
electron level.",1107.1557v1
2011-07-27,High-frequency asymptotic behavior of self-energies in quantum impurity models,"We present explicit expressions for the high-frequency asymptotic behavior of
electron self-energy of general quantum impurity models, which may be useful
for improving the convergence of dynamical mean-field calculations and for the
analytic continuation of the electron self-energy. We also give results,
expressed in more physical terms, for the two-orbital and three-orbital
rotationally invariant Slater-Kanamori interactions, in order to facilitate
calculations of transition metal oxides.",1107.5536v1
2011-07-28,Phase transition close to room temperature in BiFeO3 thin films,"BiFeO3 (BFO) multiferroic oxide has a complex phase diagram that can be
mapped by appropriately substrate-induced strain in epitaxial films. By using
Raman spectroscopy, we conclusively show that films of the so-called
supertetragonal T-BFO phase, stabilized under compressive strain, displays a
reversible temperature-induced phase transition at about 100\circ, thus close
to room temperature.",1107.5801v1
2011-08-03,Switching magnetoresistance in vertically interfaced Pr0.5Ca0.5MnO3 grown on ZnO nanowires,"The synthesis, morphology and magneto-transport properties of
nanostructure-engineered charge-ordered Pr0.5Ca0.5MnO3 grown on ZnO nanowires
are reported. The stability of the charge-ordering can be tuned, but more
interestingly the sign of the magnetoresistance is inverted at low
temperatures. Coexistence of ferromagnetic clusters on the surface and
antiferromagnetic phase in the core of the grains were considered in order to
understand these features. This work suggests that such a process of growing on
nanowires network can be readily extended to other transition metal oxides and
open doors towards tailoring their functionalities.",1108.0765v1
2011-08-09,Interface-induced d-wave pairing,"We discuss a scenario for interface-induced superconductivity involving
pairing by dipolar excitations proximate to a two-dimensional electron system
controlled by a transverse electric field. If the interface consists of
transition metal oxide materials, the repulsive on-site Coulomb interaction is
typically strong and a superconducting state is formed via exchange of
non-local dipolar excitations in the d-wave channel. Perspectives to enhance
the superconducting transition temperature are discussed.",1108.1942v1
2011-08-12,Ferromagnetism in semiconductors and oxides: prospects from a ten years' perspective,"Over the last decade the search for compounds combining the resources of
semiconductors and ferromagnets has evolved into an important field of
materials science. This endeavour has been fuelled by continual demonstrations
of remarkable low-temperature functionalities found for ferromagnetic
structures of (Ga,Mn)As, p-(Cd,Mn)Te, and related compounds as well as by ample
observations of ferromagnetic signatures at high temperatures in a number of
non-metallic systems. In this paper, recent experimental and theoretical
developments are reviewed emphasising that, from the one hand, they disentangle
many controversies and puzzles accumulated over the last decade and, on the
other, offer new research prospects.",1108.2582v1
2011-09-13,Fabrication and Room-Temperature Single-Charging Behavior of Self-Aligned Single-Dot Memory Devices,"Self-aligned single-dot memory devices and arrays were fabricated based on
arsenic-assisted etching and oxidation effects. The resulting device has a
floating gate of about 5-10 nm, presenting single-electron memory operation at
room temperature. In order to realize the final single-electron memory circuit,
this paper investigates process repeatability, device uniformity in single-dot
memory arrays, device scalability, and process transferability to an industrial
application.",1109.2921v1
2011-09-13,Optimisation and Simulation of an Alternative nano-flash Memory: the SASEM device,"Process simulation are performed in order to simulate the full fabrication
process of an alternative nano-flash memory in order to optimise it and to
improve the understanding of the dot storage formation. The influence of
various parameters (oxidation temperature, nanowire shape) have been
investigated.",1109.2927v2
2011-09-20,Electric breakdown effect in the current-voltage characteristics of amorphous indium oxide thin films near the superconductor-insulator transition,"Current-voltage characteristics in the insulator bordering superconductivity
in disordered thin films exhibit current jumps of several orders of magnitude
due to the development of a thermally bistable electronic state at very low
temperatures. In this high-resolution study we find that the jumps can be
composed of many (up to 100) smaller jumps that appear to be random. This
indicates that inhomogeneity develops near the transition to the insulator and
that the current breakdown proceed via percolative paths spanning from one
electrode to the other.",1109.4406v1
2011-09-22,Intrinsic coupling of orbital excitations to spin fluctuations in Mott insulators,"We show how the general and basic asymmetry between two fundamental degrees
of freedom present in strongly correlated oxides, spin and orbital, has very
profound repercussions on the elementary spin and orbital excitations. Whereas
the magnons remain largely unaffected, orbitons become inherently coupled with
spin fluctuations in spin-orbital models with antiferromagnetic and
ferroorbital ordered ground states. The composite orbiton-magnon modes that
emerge fractionalize again in one dimension, giving rise to spin-orbital
separation in the peculiar regime where spinons are faster than orbitons.",1109.4745v1
2011-09-26,"Hidden symmetries in a gauge covariant approach, Hamiltonian reduction and oxidation","Hidden symmetries in a covariant Hamiltonian formulation are investigated
involving gauge covariant equations of motion. The special role of the
Stackel-Killing tensors is pointed out. A reduction procedure is used to reduce
the original phase space to another one in which the symmetries are divided
out. The reverse of the reduction procedure is done by stages performing the
unfolding of the gauge transformation followed by the Eisenhart lift in
connection with scalar potentials.",1109.5449v1
2011-10-07,Power comparison of CMOS and adiabatic full adder circuit,"Full adders are important components in applications such as digital signal
processors (DSP) architectures and microprocessors. Apart from the basic
addition adders also used in performing useful operations such as subtraction,
multiplication, division, address calculation, etc. In most of these systems
the adder lies in the critical path that determines the overall performance of
the system. In this paper conventional complementary metal oxide semiconductor
(CMOS) and adiabatic adder circuits are analyzed in terms of power and
transistor count using 0.18UM technology.",1110.1549v1
2011-10-10,Evidences of Superconductivity without Direct Relation to Valence Electron Density in Metal Doped Y123 Cuprates,"We investigated systemically YBa2Cu3-x(Fe, Co, Al, Zn)xO7-{\delta}
(x=0.0\sim0.5) cuprates through the XRD, the test of superconductivity, oxygen
contents,positron annihilation technology and simulated calculations. The
experimental results and theoretic calculations support such a conclusion that
the Tc does not depend directly on the density of valence electron in the
samples. Moreover, whether or not it may imply some correlations between
Fe-oxide superconductors and cuprates that Fe doped Y123 samples show some
unique characteristics.",1110.2499v1
2011-10-14,Quantification of correlations in quantum many-particle systems,"We introduce a well-defined and unbiased measure of the strength of
correlations in quantum many-particle systems which is based on the relative
von Neumann entropy computed from the density operator of correlated and
uncorrelated states. The usefulness of this general concept is demonstrated by
quantifying correlations of interacting electrons in the Hubbard model and in a
series of transition-metal oxides using dynamical mean-field theory.",1110.3214v3
2011-12-07,Modified Mott-Schottky Analysis of Nanocrystal Solar Cells,"Mott-Schottky analysis is adapted to determine the built-in bias (Vbi) and
doping density (N) of lead sulfide-zinc oxide colloidal quantum dot
heterojunction solar cells. We show that charge injection barriers at the solar
cell's electrodes create a constant capacitance that distorts the junction's
depletion capacitance and result in erroneous Vbi and N values when determined
through Mott-Schottky analysis. The injection barrier capacitance is taken into
account by incorporating a constant capacitance in parallel with the depletion
capacitance.",1112.1623v1
2011-12-12,Relaxor ferroelectric behavior and structural aspects of SrNaBi2Nb3O12 ceramics,"SrNaBi2Nb3O12 powder was prepared via the conventional solid-state reaction
method. X-ray structural studies confirmed the phase to be a three-layered
member of the Aurivillius family of oxides. SrNaBi2Nb3O12 (SNBN) ceramics
exhibited the typical characteristics of relaxor ferroelectrics, associated
with broad and dispersive dielectric maxima. The variation of temperature of
dielectric maxima (Tm) with frequency obeyed the Vogel-Fulcher relationship.
Relaxor behavior was believed to be arising from the cationic disorder at
A-site. Pinched ferroelectric hysteresis loops were observed well above Tm.",1112.2416v1
2011-12-21,Exploring spin-orbital models with dipolar fermions in zig-zag optical lattices,"Ultra-cold dipolar spinor fermions in zig-zag type optical lattices can mimic
spin-orbital models relevant in solid-state systems, as transition-metal oxides
with partially filled d-levels, with the interesting advantage of reviving the
quantum nature of orbital fluctuations. We discuss two different physical
systems in which these models may be simulated, showing that the interplay
between lattice geometry and spin-orbital quantum dynamics produces a wealth of
novel quantum phases.",1112.5082v2
2011-12-22,Electric field effect on superconductivity at complex oxide interfaces,"We examine the enhancement of the interfacial superconductivity between
LaAlO$_{3}$ and SrTiO$_{3}$ by an effective electric field. Through the
breaking of inversion symmetry at the interface, we show that a term coupling
the superfluid density and an electric field can augment the superconductivity
transition temperature. Microscopically, we show that an electric field can
also produce changes in the carrier density by relating the measured
capacitance to the density of states. Through the electron-phonon induced
interaction in bulk SrTiO$_{3}$, we estimate the transition temperature.",1112.5466v2
2012-02-07,Interplay between strain and oxygen vacancies in lanthanum aluminate,"We evaluate the interplay between epitaxial strain and oxygen vacancy
formation in the perovskite-structure oxide lanthanum aluminate, LaAlO$_3$.
Using density functional theory within the GGA$+U$ approximation we calculate
the dependence of the oxygen vacancy formation energy on the biaxial strain
conditions. We find that the change in formation energy with strain is
negligible over the range of strain values usually accessible through coherent
epitaxial growth. Our findings suggest that experimental reports of different
oxygen vacancy concentrations in strained films result from extrinsic factors,
or from other impurities such as defect complexes.",1202.1431v1
2012-02-20,Elastic properties of freely suspended MoS2 nanosheets,"We study the elastic deformation of few layers (5 to 25) thick freely
suspended MoS2 nanosheets by means of a nanoscopic version of a bending test
experiment, carried out with the tip of an atomic force microscope. The Young's
modulus of these nanosheets is extremely high (E = 0.33 TPa), comparable to
that of graphene oxide, and the deflections are reversible up to tens of
nanometers.",1202.4439v1
2012-02-21,Oxygen vacancy segregation and space-charge effects in grain boundaries of dry and hydrated BaZrO3,"A space-charge model is applied to describe the equilibrium effects of
segregation of double-donor oxygen vacancies to grain boundaries in dry and wet
acceptor-doped samples of the perovskite oxide BaZrO3. The grain boundary core
vacancy concentrations and electrostatic potential barriers resulting from
different vacancy segregation energies are evaluated. Density-functional
calculations on vacancy segregation to the mirror-symmetric \Sigma 3 (112)
[-110] tilt grain boundary are also presented. Our results indicate that oxygen
vacancy segregation can be responsible for the low grain boundary proton
conductivity in BaZrO3 reported in the literature.",1202.4570v1
2012-02-26,A unique metal-semiconductor interface and resultant electron transfer phenomenon,"An unusual electron transfer phenomenon has been identified from an n-type
semiconductor to Schottky metal particles, the result of a unique metal
semiconductor interface that results when the metal particles are grown from
the semiconductor substrate. The unique interface acts as a one-way
(rectifying) open gateway and was first identified in reduced rutile
polycrystalline titanium dioxide (an n-type semiconductor) to Group VIII
(noble) metal particles. The interface significantly affects the Schottky
barrier height resulting in electron transfer to the metal particles from the
reduced rutile titanium dioxide (TiO2) based on their respective work
functions. The result is a negative charge on the metal particles which is of
sufficient magnitude and duration to provide cathodic protection of the metal
particles from surface oxidation.",1202.5771v1
2012-03-24,4f and 5d levels of Ce3+ in D2 eightfold oxygen coordination,"The effects on the 4f and 5d levels of Ce3+ of its first coordination shell
geometry in Ce-doped oxides with a D2 8-fold site, like garnets, are studied
with embedded cluster, wave function based ab initio methods. The only
deformations of a CeO8 cube that are found to shift the lowest 4f-5d transition
to the red are the symmetric Ce-O bond compression and the tetragonal symmetric
bond bending. These results are analyzed in terms of centroid and ligand field
stabilization energy differences. The splittings of the upper 5d levels and of
the 4f levels are also discussed.",1203.5391v1
2012-06-21,Symmetrical field effect and slow electron relaxation in granular aluminium,"Conductivity and field effect measurements in thin insulating Al granular
films are reported. The occurrence of a symmetrical field effect and of very
slow conductance relaxations is demonstrated. They are identical to the
electron glassy behaviours already reported in insulating indium oxide thin
films. The results suggest that the phenomena are quite general. The study of
structurally discontinuous samples should help to understand the origin and
mechanism of the glassy behaviour.",1206.4978v1
2012-07-16,Optimal T$_c$ of cuprates: role of screening and reservoir layers,"We explore the role of charge reservoir layers (CRLs) on the superconducting
transition temperature of cuprate superconductors. Specifically, we study the
effect of CRLs with efficient short distance dielectric screening coupled
capacitively to copper oxide metallic layers. We argue that dielectric
screening at short distances and at frequencies of the order of the
superconducting gap, but small compared to the Fermi energy can significantly
enhance T$_c$, the transition temperature of an unconventional superconductor.
We discuss the relevance of our qualitative arguments to a broader class of
unconventional superconductors.",1207.3584v1
2012-06-29,On the algorithmic behaviour of complex physical systems,"Starting from the idea that the underlying mechanisms driving the observable
processes in nature are algorithmic, we exemplify this in two ways: nature
works as a computing machine and thus the processes running on it optimize
themselves in an intrinsic manner so as to save time. As a first example we
will place the empirical analysis of oxidation in the context of algorithm
complexity analysis. Second, we will show that deformations suffered by a
shape-memory alloy may be produced by nature showing a LIFO (Last In First Out)
behaviour.",1207.5398v1
2012-08-03,"Accurate screened exchange band structures for transition metal monoxides MnO, FeO, CoO and NiO","We report calculations of the band structures and density of states of the
four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density
functional sX-LDA. Late transition metal oxides are prototypical examples of
strongly correlated materials, which pose challenges for electronic structure
methods. We compare our results with available experimental data and show that
our calculations yield accurate predictions for the fundamental band gaps and
valence bands of FeO, CoO and NiO. For MnO, the band gaps are underestimated,
suggesting additional many-body effects that are not captured by our screened
hybrid functional approach.",1208.0786v2
2012-08-07,Superlattice Based on Graphene on a Strip Substrate,"A graphene-based superlattice formed due to the periodic modulation of the
band gap has been investigated. Such a modulation is possible in graphene
deposited on a strip substrate made of silicon oxide and hexagonal boron
nitride. The advantages and some possible problems in the superlattice under
consideration are discussed. A model describing such a superlattice is proposed
and the dispersion relation between the energy and momentum of carriers has
been obtained using the transfer matrix method within this model.",1208.1442v1
2012-08-09,Disorder-free sputtering method on graphene,"Deposition of various materials onto graphene without causing any disorder is
highly desirable for graphene applications. Especially, sputtering is a
versatile technique to deposit various metals and insulators for spintronics,
and indium tin oxide to make transparent devices. However, the sputtering
process causes damage to graphene because of high energy sputtered atoms. By
flipping the substrate and using a high Ar pressure, we demonstrate that the
level of damage to graphene can be reduced or eliminated in dc, rf, and
reactive sputtering processes.",1208.1835v1
2012-08-24,Car-Parrinello Simulation of the Reaction of Aluminium with Oxygen,"We present Car-Parrinello molecular dynamics simulations of the initial
reaction steps leading to an inert oxide layer on aluminium. The mechanism of
the reaction of the aluminium surface with single oxygen molecules is analysed.
After adsorption at the surface the oxygen molecules dissociate at a
femtosecond timescale and the atoms are chemisorbed at the surface at a
distance of several angstrom. When the aluminium surface is exposed to higher
oxygen pressure, a surface layer essentially consisting of threefold
coordinated oxygen atoms starts to form.",1208.4969v2
2012-10-10,Orientation dependent work function of in situ annealed strontium titanate,"We have used energy filtered x-ray photoelectron emission microscopy (XPEEM)
and synchrotron radiation to measure the grain orientation dependence of the
work function of a sintered niobium doped strontium titanate ceramic. A
significant spread in work function values is found. Grain orientation and
surface reducing/oxidizing conditions are the main factors in determining the
work function. Energy filtered XPEEM looks ideally suited for analysis of other
technologically interesting polycrystalline samples.",1210.3086v1
2012-10-22,New insights into the phase diagram of the copper oxide superconductors from electronic Raman scattering,"Mechanism of unconventional superconductivity is still unknown even if more
than 25 years have been passed since the discovery of high-Tc cuprate
superconductors by J.G. Bednorz and K. A. Muller. Here, we explore the cuprate
phase diagram by electronic Raman spectroscopy and shed light on the
superconducting state in hole doped cuprates. Namely, how superconductivity and
the critical temperature Tc are impacted by the pseudogap.",1210.5972v1
2013-02-15,An innovative approach of structural instabilities in tetragonal tungsten bronze crystals through the concept of rigid unit modes,"Tetragonal tungsten bronze (TTB) oxides are one of the most important classes
of ferroelectrics. Many of these framework structures undergo ferroelastic
transformations related to octahedron tilting deformations. Such tilting
deformations are closely related to the Rigid Unit Modes (RUMs). This paper
discusses the whole set of RUMs in an ideal TTB lattice and possible crystal
structures which can emerge owing to the condensation of some of them. Analysis
of available experimental data for the TTB-like niobates lends credence to the
obtained theoretical predictions.",1302.3692v2
2013-03-09,Low-temperature thermal expansion of rock-salt ZnO,"Lattice parameter of metastable high-pressure phase of zinc oxide, rock-salt
ZnO was measured in the 10-300 K temperature range using synchrotron X-ray
powder diffraction. No phase transition was observed down to 10 K. The lattice
parameter of rock-salt ZnO was found to increase from 4.266 {\AA} in the 10-80
K range up to 4.2752(3) {\AA} at 298 K, while the volume thermal expansion
coefficient increases from slight negative values below 40 K up to
4.77\times10^-5 K^-1 at 298 K.",1303.2216v1
2013-03-12,The chemistry of dust formation in red supergiants,"Massive stars in their late stages of evolution as Red Supergiants experience
mass loss. The resulting winds show various degrees of dynamical and chemical
complexity and produce molecules and dust grains. This review summarises our
knowledge of the molecular and dust components of the wind of Red Supergiants,
including VY CMa and Betelgeuse. We discuss the synthesis of dust as a
non-equilibrium process in stellar winds, and present the current knowledge of
the chemistry involved in the formation of oxygen-rich dust such as silicates
and metal oxides.",1303.2805v1
2013-03-15,Insulator-to-metal transition of SrTiO3:Nb single crystal surfaces induced by Ar+ bombardment,"In this paper, the effect of Ar+ bombardment of SrTiO3:Nb surface layers is
investigated on the macro- and nanoscale using surface-sensitive methods. After
bombardment, the stoichiometry and electronic structure are changed distinctly
leading to an insulator-to-metal transition related to the change of the Ti ""d""
electron from d0 to d1 and d2. During bombardment, conducting islands are
formed on the surface. The induced metallic state is not stable and can be
reversed due to a redox process by external oxidation and even by
self-reoxidation upon heating the sample to temperatures of 300{\deg}C.",1303.3760v1
2013-03-26,High performance fiber-coupled NbTiN superconducting nanowire single photon detectors with Gifford-McMahon cryocooler,"We present high performance fiber-coupled niobium titanium nitride
superconducting nanowire single photon detectors fabricated on thermally
oxidized silicon substrates. The best device showed a system detection
efficiency (DE) of 74%, dark count rate of 100 c/s, and full width at half
maximum timing jitter of 68 ps under a bias current of 18.0 uA with a practical
Gifford-McMahon cryocooler system. We also introduced six detectors into the
cryocooler and confirmed that the system DE of all detectors was higher than
67% at the dark count rate of 100 c/s.",1303.6381v2
2013-04-05,Fermi level density of states modulation without charge transfer in nickelate superlattices,"By using first-principles density functional theory calculations for
(LaNiO3)m/(SrTiO3)n superlattices, we report a systematic way of electronic
response to the interface geometry. It is found that Fermi level density of
states of metallic nickelate layers is significantly reduced without charge
transfer in the vicinity of interface to the insulating SrTiO3. This type of
electronic state redistribution is clearly distinctive from other interface
phenomena such as charge and orbital reconstruction. Our result sheds new light
towards understanding the nickelates and other transitionmetal oxide
heterostructures.",1304.1615v2
2013-04-23,Superconducting and Pseudogap effects on the interplane conductivity and Raman scattering cross section in the two dimensional Hubbard Model,"Cluster dynamical mean field methods are used to calculate the
superconductivity-induced changes in the interplane conductivity and Raman
scattering cross section of the two dimensional Hubbard model. When
superconductivity emerges from the pseudogap, the superconducting response is
found to be diminished in amplitude, broadened and, in the case of the
interplane conductivity, shifted to higher frequency. The results are in
agreement with data on high temperature copper-oxide superconductors indicating
that the Hubbard model contains the essential low energy physics of the
pseudogap and its interplay with superconductivity in the cuprates.",1304.6406v1
2013-04-30,Mechanism of Polarization Fatigue in BiFeO3: the Role of Schottky Barrier,"By using piezoelectric force microscopy and scanning Kelvin probe microscopy,
we have investigated the domain evolution and space charge distribution in
planar BiFeO3 capacitors with different electrodes. It is observed that charge
injection at the film/electrode interface leads to domain pinning and
polarization fatigue in BiFeO3. Furthermore, the Schottky barrier at the
interface is crucial for the charge injection process. Lowering the Schottky
barrier by using low work function metals as the electrodes can also improve
the fatigue property of the device, similar to what oxide electrodes can
achieve.",1304.7935v1
2013-05-20,Antiferromagnetic Ising model saturation field entropies: ladders and kagome lattice,"Saturation field entropies of antiferromagnetic Ising models on quasi
one-dimensional lattices (ladders) and the kagome lattice are calculated. The
former is evaluated exactly by constructing the corresponding transfer
matrices, while the latter calculation uses Binder's algorithm for efficiently
and exactly computing the partition function of over 1300 spins to give, in
Boltzmann's units, S = 0.393589(6). We comment on the relation of the kagome
lattice to the experimental situation in the spin-ice compound dysprosium
titanium oxide.",1305.4606v2
2013-05-24,Efficient Single Photon Absorption by Optimized Superconducting Nanowire Geometries,"We report on simulation results that shows optimum photon absorption by
superconducting nanowires can happen at a fill-factor that is much less than
100%. We also present experimental results on high performance of our
superconducting nanowire single photon detectors realized using NbTiN on
oxidized silicon.",1305.5832v1
2013-06-12,Optical absorption and emission of silicon nanocrystals: From single to collective response,"We report on the possibility of describing the absorption and emission
characteristics of an ensemble of silicon nanocrystals (NCs) with realistic
distributions in the NC size, by the sum of the reponses of the single NCs. The
individual NC responses are evaluated by means of ab-initio theoretical
calculations and the summation is performed by taking into account the trend of
the optical properties as a function of NC size and oxidation degree. The
comparison with experimental results shows a nice matching of the spectra, also
without any tuning of the parameters. Finally, the possibility of adapting the
model in order to reproduce the experimental data is explored and discussed.",1306.2785v1
2013-06-26,Layer-resolved study of Mg atom incorporation at MgO/Ag(001) buried interface,"By combining x-ray excited Auger electron diffraction experiments and
multiple scattering calculations we reveal a layer-resolved shift for the Mg
KL23L23 Auger transition in MgO ultrathin films (4-6 \AA) on Ag(001). This
resolution is exploited to demonstrate the possibility to control Mg atoms
incorporation at the MgO/Ag(001) interface by exposing the MgO films to a Mg
flux. A substantial reduction of the MgO/Ag(001) work function is observed
during the exposition phase and reflects, both band-offset variations at the
interface and band bending effects in the oxide film.",1306.6158v1
2013-07-23,Thermodynamic stability of new phase Bi12.5Sm1.5ReO24.5,"The Bi12.5Sm1.5ReO24.5 phase has been synthesized for the first time. The
preparation of Bi12.5Sm1.5ReO24.5 has been performed by solid-state reaction
from Bi2O3, Gd2O3, Re2O7. The X-ray measurements have showed that
Bi12.5Sm1.5ReO24.5 was cubic structure (space group Fm3m). The standard molar
enthalpy of formation of Bi12.5Sm1.5ReO24.5 has been determined by solution
calorimetry combining the enthalpies of dissolution of Bi12.5Sm1.5ReO24.5 and
6.25Bi2O3 + 0.75Sm2O3 + 0.5Re2O7 mixture in 2 M HCl and literature data. It has
been obtained that above-mentioned phase is thermodynamically stable with
respect to their decomposition into binary oxides at room temperatures.",1307.5938v1
2013-07-24,"Charge expulsion, charge inhomogeneity and phase separation in dynamic Hubbard models","Dynamic Hubbard models are extensions of the conventional Hubbard model that
take into account the fact that atomic orbitals expand upon double occupancy.
It is shown here that systems described by dynamic Hubbard models have a
tendency to expel negative charge from their interior to the surface, and to
develop charge inhomogeneity and even phase separation in the bulk. These
effects are associated with lowering of electronic kinetic energy. We propose
that these models may explain the charge inhomogeneity and negatively charged
grain boundaries observed in cuprate oxides and other materials.",1307.6526v1
2013-10-10,Dynamics of Coalescence-Induced Jumping Water Droplets,"This fluid dynamics video shows the different interaction mechanisms of
coalescence-induced droplet jumping during condensation on a nanostructured
superhydrophobic surface. High speed imaging was used to show jumping behavior
on superhydrophobic copper oxide and carbon nanotube surfaces. Videos
demonstrating multi-jumping droplets, jumping droplet return to the surface,
and droplet-droplet electrostatic repulsions were analyzed. Experiments using
external electric fields in conjunction with high speed imaging in a custom
built experimental chamber were used to show that all coalescence-induced
jumping droplets on superhydrophobic surfaces become positively charged upon
leaving the surface, which is detailed in the video.",1310.2975v1
2013-10-24,Temperature dependence of crystal field excitations in CuO,"We report a study on the temperature dependence of the charge-neutral crystal
field (dd) excitations in cupric oxide, using nonresonant inelastic x-ray
scattering (IXS) spectroscopy. Thanks to a very high energy resolution (60
meV), we observe thermal effects on the dd excitation spectrum fine structure
between temperatures of 10-320 K. With an increasing temperature, the spectra
broaden considerably. We assign the temperature dependence of the dd
excitations to the relatively large electron-phonon coupling.",1310.6730v1
2013-10-29,Thin Film Substrates from the Raman spectroscopy point of view,"We have investigated ten standard single crystal substrates of complex oxides
on the account of their applicability in the Raman spectroscopy based thin film
research. In this study we suggest a spectra normalization procedure that
utilizes a comparison of the substrate Raman spectra to those of
well-established Raman reference materials. We demonstrate that MgO, LaGaO3,
(LaAlO3)_0.3(Sr2AlTaO6)_0.7 (LSAT), DyScO3, YAlO3, and LaAlO3 can be of
potential use for a Raman based thin film research. At the same time TiO2
(rutile), NdGaO3, SrLaAlO4, and SrTiO3 single crystals exhibit multiple phonon
modes accompanied by strong Raman background that substantially hinder the
Raman based thin film experiments.",1310.7966v1
2013-11-06,The role of screened exact exchange in accurately describing properties of transition metal oxides: Modeling defects in LaAlO3,"The properties of many intrinsic defects in the wide band gap semiconductor
LaAlO3 are studied using the screened hybrid functional of Heyd, Scuseria, and
Ernzerhof (HSE). As in pristine structures, exact exchange included in the
screened hybrid functional alleviates the band gap underestimation problem,
which is common to semilocal functionals; this allows accurate prediction of
defect properties. We propose correction-free defect energy levels for bulk
LaAlO3 computed using HSE that might serve as guide in the interpretation of
photoluminescence experiments.",1311.1340v1
2013-11-09,A first principles investigated optical spectra of oxizided graphene,"The electronic and optical properties of mono, di, tri, and tetravacancies in
graphene are studied in comparison to each other, using density functional
theory. In addition, oxidized monovacancies are considered for different oxygen
concentrations. Pristine graphene is found to be more absorptive than any
defect configuration at low energy. We demonstrate characteristic differences
in the optical spectra of the various defects for energies up to 3 eV. This
makes it possible to quantify by optical spectroscopy the ratios of the defect
species present in a sample.",1311.2213v1
2013-12-10,Large thermal biasing of individual gated nanostructures,"We demonstrate a novel nanoheating scheme that yields very large and uniform
temperature gradients up to about 1K every 100nm, in an architecture which is
compatible with the field-effect control of the nanostructure under test. The
temperature gradients demonstrated largely exceed those typically obtainable
with standard resistive heaters fabricated on top of the oxide layer. The
nanoheating platform is demonstrated in the specific case of a short-nanowire
device.",1312.2845v3
2013-12-24,Possibility of obtaining atomic metallic hydrogen by electrochemical method,"In this work we show, that atomic metallic hydrogen (AMH) is formed inside of
sintered oxide-nickel electrodes of nickel-cadmium battery over a long period
of electrochemical hydrogenation (more than five years). It was established
that density AMH is 12 times higher, than the density of liquid molecular
hydrogen, the specific energy of hydrogen recombination is 20 times higher than
of liquid hydrogen-oxygen fuel. At the room temperature AMH is a good
conductor, but not a superconductor.",1312.6851v1
2014-01-29,Electrostatic theory of metal whiskers,"Needle shaped whiskers grow on various metal surfaces often across leads of a
package causing current leakage or short circuits and raising reliability
issues in electronic components. The nature of metal whiskers remains a mystery
after several decades of research. Here, the existence of metal whiskers is
attributed to the energy gain due to electrostatic polarization of needle
shaped metal filaments in the electric field. The field is induced by surface
imperfections: contaminations, oxide states, grain boundaries, etc. A proposed
theory provides closed form expressions and quantitative estimates for the
whisker nucleation and growth rates, explains the range of whisker parameters
and effects of external biasing, and predicts statistical distribution of their
lengths.",1401.7689v1
2014-02-07,Lithography-free sub-100nm nanocone array antireflection layer for low-cost silicon solar cell,"High density and uniformity sub-100nm surface oxidized silicon nanocone
forest structure is created and integrated onto the existing texturization
microstructures on photovoltaic device surface by a one-step high throughput
plasma enhanced texturization method. We suppressed the broadband optical
reflection on chemically textured grade-B silicon solar cells for up to 70.25%
through this nanomanufacturing method. The performance of the solar cell is
improved with the short circuit current increased by 7.1%, fill factor
increased by 7.0%, conversion efficiency increased by 14.66%. Our method
demonstrates the potential to improve the photovoltaic device performance with
low cost high and throughput nanomanufacturing technology.",1402.1737v1
2014-02-14,Carrier type modulation in current annealed graphene layers,"We report on the electrical properties of current annealed graphene and few
layer graphene devices. It is observed that current annealing for several hours
results the n-type doping in the graphene layers. After current annealing Dirac
point start to shift toward positive gate voltage and saturate at some fixed
gate voltage. N-type conduction in current annealed graphene layers is caused
by the charge trapping in oxide layer during current annealing and recovery of
charge neutrality point with time span is understood due to the de-trapping of
charge with time.",1402.3436v1
2014-04-04,3D Vertical Dual-Layer Oxide Memristive Devices for Neuromorphic Computing,"Dual-layer resistive switching devices with horizontal W electrodes, vertical
Pd electrodes and WOx switching layer formed at the sidewall of the horizontal
electrodes have been fabricated and characterized. The devices exhibit
well-characterized analog switching characteristics and small mismatch in
electrical characteristics for devices formed at the two layers. The
three-dimensional (3D) vertical device structure allows higher storage density
and larger connectivity for neuromorphic computing applications. We show the
vertical devices exhibit potentiation and depression characteristics similar to
planar devices, and can be programmed independently with no crosstalk between
the layers.",1404.1158v1
2014-04-07,Synthesis of Tungsten Oxide Nanoparticles using a Hydrothermal Method at Ambient Pressure,"Tungstite (WO3.H2O) nanoparticles were synthesized using a simple and
inexpensive low temperature and low pressure hydrothermal method by adding
hydrochloric acid to diluted sodium tungstate solutions (Na2WO4.2H2O) at
temperatures below 5oC. A heat treatment at temperatures at or above 300oC
resulted in a phase transformation to monoclinic WO3, while preserving the
nanoparticles morphology. The products were characterized using powder x-ray
diffraction, transmission electron microscopy (including electron energy-loss
spectroscopy and electron diffraction) and x-ray photoelectron spectroscopy.",1404.2612v1
2014-04-14,Theoretical study of charge exchange dynamics in He$^+$ + NO collisions,"We investigate the charge transfer mechanism in the collisions of helium ions
on nitric oxide using a molecular description framework with consideration of
the orientation of the projectile toward the target. The anisotropy of the
collision process has been analysed in detail in connection with the
non-adiabatic interactions around avoided crossings. Potential energy curves,
radial and rotational coupling matrix elements have been determined by means of
ab initio quantum chemical methods. The collision dynamics is performed in the
[1.-25.] keV collision energy range using a semiclassical approach, and the
total electron transfer cross sections are analysed with regard to available
experimental data.",1404.3635v1
2014-07-31,First-principles study of the multi-mode anti-ferroelectric transition of PbZrO3,"We have studied ab initio the phase transition in PbZrO3, a perovskite oxide
usually presented as the prototypic anti-ferroelectric material. Our work
reveals the crucial role that anti-ferrodistortive modes -- involving concerted
rotations of the oxygen octahedra in the structure -- play in the
transformation, as they select the observed anti-ferroelectric phase, among
competing structural variants, via a cooperative trilinear coupling.",1407.8405v1
2014-08-11,Single- and multi-domain ferroelectricity driven by interfaces,"The design of the interfacial bondings at metal-oxide interfaces yields
exciting new phenomena and can be a route to sustain, and even promote,
ferroelectricity at the nanoscale. We study the impact of these interfaces on
the nature of the spontaneous polarization (single- vs. multi-domain) of
ferroelectric capacitors. We show that interfacial properties intertwine with
both ferrolectric and electrode parameters to determine the actual ground state
of the system. We find analytically the criterion that specifies if
ferroelectricity appears in a single- or multi- domain fashion as a result of
this intertwining. The physics behind this criterion suggests new means for
tailoring ferroelectric functionalities.",1408.2373v1
2014-08-21,Simulation of Schottky-Barrier Phosphorene Transistors,"Schottky barrier field-effect transistors (SBFETs) based on few and mono
layer phosphorene are simulated by the non-equilibrium Green's function
formalism. It is shown that scaling down the gate oxide thickness results in
pronounced ambipolar I-V characteristics and significant increase of the
minimal leakage current. The problem of leakage is especially severe when the
gate insulator is thin and the number of layer is large, but can be effectively
suppressed by reducing phosphorene to mono or bilayer. Different from
two-dimensional graphene and layered dichalcogenide materials, both the
ON-current of the phosphorene SBFETs and the metal-semiconductor contact
resistance between metal and phosphorene strongly depend on the transport
crystalline direction.",1408.5013v1
2014-10-15,Colloidal Plasmonic Titanium Nitride Nanoparticles: Properties and Applications,"Optical properties of colloidal plasmonic titanium nitride nanoparticles are
examined with an eye on their photothermal via transmission electron microscopy
and optical transmittance measurements. Single crystal titanium nitride cubic
nanoparticles with an average size of 50 nm exhibit plasmon resonance in the
biological transparency window. With dimensions optimized for efficient
cellular uptake, the nanoparticles demonstrate a high photothermal conversion
efficiency. A self-passivating native oxide at the surface of the nanoparticles
provides an additional degree of freedom for surface functionalization.",1410.3920v1
2014-12-10,Lattice strain at c-Si surfaces: a density functional theory calculation,"The measurement of the Avogadro constant by counting Si atoms is based on the
assumption that Si balls of about 94 mm diameter have a perfect crystal
structure up to the outermost atom layers. This not the case because of the
surface relaxation and reconstruction, the possible presence of an amorphous
layer, and the oxidation process due to the interaction with the ambient. This
paper gives the results of density functional calculations of the strain
components orthogonal to crystal surface in a number of configurations likely
found in real samples.",1412.3301v1
2014-12-16,Gold Nanoparticles supported on MoS2 Nanoribbons matrix as a biocompatible and water dispersible platform for enhanced photothermal ablation of cancerous cells using harmless near infrared irradiation,"With photothermal efficiency higher than traditionally used reduced graphene
oxide, while simultaneously being water dispersible, we propose biocompatible
Molybdenum Nanoribbons - gold Nanoparticles (MoS2 NR-Au NPs) system for
synergistically enhanced photo-thermal ablation of cancerous cells (100%
fatality) using NIR radiation (808nm), owing to commendable temperature rise
above 70oC at a much faster rate.",1412.4943v1
2014-12-24,Seaborg's Plutonium?,"Passive x-ray and gamma-ray analysis was performed on UC Berkeley's EH&S
Sample S338. The object was found to contain Pu-239 and no other radioactive
isotopes. The mass of Pu-239 contained in this object was determined to be 2.0
+- 0.3 micrograms. These observations are consistent with the identification of
this object being the 2.77-microgram plutonium oxide sample described by Glenn
Seaborg and his collaborators as the first sample of Pu-239 that was large
enough to be weighed.",1412.7590v2
2014-12-26,Screened exchange dynamical mean field theory and its relation to density functional theory: SrVO3 and SrTiO3,"We present the first application of a recently proposed electronic-structure
scheme to transition metal oxides: screened exchange dynamical mean-field
theory includes non-local exchange beyond the local density approximation and
dynamical correlations beyond standard dynamical mean-field theory. Our results
for the spectral function of SrVO3 are in agreement with the available
experimental data, including photoemission spectroscopy and thermodynamics.
Finally, the 3d0 compound SrTiO3 serves as a test case to illustrate how the
theory reduces to the band structure of standard electronic-structure
techniques for weakly correlated compounds.",1412.7971v1
2014-12-29,Molecular theory of graphene chemical modification,"The chapter is devoted to chemical uniqueness of graphene. In view of
molecular theory, the latter is a consequence of benzenoid packing of carbon
atoms, based on three neighbors to each carbon atom leaving the atom fourth
valence electron (the odd one) on its own. Due to rather large C-C distances,
the odd electrons of graphene molecules are correlated whereupon the molecules
are radicalized and molecular chemistry of graphene is the chemistry of
dangling bonds. The chapter presents the description of the
molecular-theory-dangling-bond view on graphene molecule hydrogenation and
oxidation. Specific peculiarities of the graphene molecular chemistry related
to size-dependent topochemical features are discussed, as well",1412.8306v1
2015-01-13,Intense femtosecond photoexcitation of bulk and monolayer MoS2,"The effect of femtosecond laser irradiation on bulk and single-layer MoS2 on
silicon oxide is studied. Optical, Field Emission Scanning Electron Microscopy
(FESEM) and Raman microscopies were used to quantify the damage. The intensity
of A1g and E2g1 vibrational modes was recorded as a function of the number of
irradiation pulses. The observed behavior was attributed to laser-induced bond
breaking and subsequent atoms removal due to electronic excitations. The
single-pulse optical damage threshold was determined for the monolayer and bulk
under 800nm and 1030nm pulsed laser irradiation and the role of two-photon
versus one photon absorption effects is discussed.",1501.02929v1
2015-01-14,Exact double-counting in combining the Dynamical Mean Field Theory and the Density Functional Theory,"We propose a continuum representation of the Dynamical Mean Field Theory, in
which we were able to derive an exact overlap between the Dynamical Mean Field
Theory and band structure methods, such as the Density Functional Theory. The
implementation of this exact double-counting shows improved agreement between
theory and experiment in several correlated solids, such as the transition
metal oxides and lanthanides. Previously introduced nominal double-counting is
in much better agreement with the exact double-counting than most widely used
fully localized limit formula.",1501.03438v1
2015-01-21,Many-Body electronic structure calculations of Eu doped ZnO,"The formation energies and electronic structure of europium doped zinc oxide
has been determined using DFT and many-body $GW$ methods. In the absence of
intrisic defects we find that the europium-$f$ states are located in the ZnO
band gap with europium possessing a formal charge of 2+. On the other hand, the
presence of intrinsic defects in ZnO allows intraband $f-f$ transitions
otherwise forbidden in atomic europium. This result coorroborates with recently
observed photoluminescence in the visible red region [1].",1501.05090v2
2015-01-31,Tuning Optical Properties of Transparent Conducting Barium Stannate by Dimensional Reduction,"We report calculations of the electronic structure and optical properties of
doped $n$-type perovskite BaSnO3 and layered perovskites. While doped BaSnO$_3$
retains its transparency for energies below the valence to conduction band
onset, the doped layered compounds exhibit below band edge optical conductivity
due to transitions from the lowest conduction band. This gives absorption in
the visible for Ba2SnO4. Thus it is important to minimize this phase in
transparent conducting oxide (TCO) films. Ba3Sn2O7 and Ba4Sn3O10 have strong
transitions only in the red and infrared, respectively. Thus there may be
opportunities for using these as wavelength filtering TCO.",1502.00171v1
2015-02-02,Electromechanical properties of freestanding graphene functionalized with tin oxide (SnO2) nanoparticles,"Freestanding graphene membranes were functionalized with SnO2 nanoparticles.
A detailed procedure providing uniform coverage and chemical synthesis is
presented. Elemental composition was determined using scanning electron
microscopy combined with energy dispersive X-ray analysis. A technique called
electrostatic-manipulation scanning tunneling microscopy was used to probe the
electromechanical properties of functionalized freestanding graphene samples.
We found ten times larger movement perpendicular to the plane compared to
pristine freestanding graphene, and propose a nanoparticle encapsulation model.",1502.00613v1
2015-02-03,Persistent ion beam induced conductivity in zinc oxide nanowires,"We report persistently increased conduction in ZnO nanowires irradiated by
ion beam with various ion energies and species. This effect is shown to be
related to the already known persistent photo conduction in ZnO and dubbed
persistent ion beam induced conduction. Both effects show similar excitation
efficiency, decay rates, and chemical sensitivity. Persistent ion beam induced
conduction will potentially allow countable (i.e., single dopant) implantation
in ZnO nanostructures and other materials showing persistent photo conduction.",1502.00828v1
2015-02-12,Impact of Ferroelectric Distortion on Thermopower in BaTiO3,"We present a strategy for increasing thermoelectric performance by invoking
ferroelectric distortion in a transition-metal oxide. By using an ab initio
calculation approach with the Boltzmann transport equation, a large Seebeck
coefficient is calculated in n-type BaTiO3. The polar structural distortion
causes the peculiar dispersion of the lowest conduction band, which enhances
the Seebeck coefficient along the polar direction. A microscopic mechanism of
carrier concentration dependence of the Seebeck coefficient is discussed in
terms of the band velocity distribution in the Brillouin zone.",1502.03525v1
2015-03-07,Ricci-flat spacetimes admitting higher rank Killing tensors,"Ricci-flat spacetimes of signature (2,q) with q=2,3,4 are constructed which
admit irreducible Killing tensors of rank-3 or rank-4. The construction relies
upon the Eisenhart lift applied to Drach's two-dimensional integrable systems
which is followed by the oxidation with respect to free parameters. In four
dimensions, some of our solutions are anti-self-dual.",1503.02162v1
2015-03-07,Synthesis and characterization of vertically oriented hybrid Zn2GeO4-ZnO beaded nanowire arrays and Zn2GeO4 nanotubes,"Vertically aligned, beaded zinc germinate (Zn2GeO4)/ zinc oxide (ZnO) hybrid
nanowire arrays were successfully synthesized by a vapor-solid process via a
catalyst-free approach. The as-synthesized products were characterized using
X-ray diffraction, scanning electron microscopy and transmission electron
microscopy equipped with an energy-dispersive X-ray spectrometer. TEM studies
revealed the beaded microstructures of the Zn2GeO4/ZnO nanowire. Furthermore,
Zn2GeO4 nanotubes were synthesized after wet etching treatments on Zn2GeO4/ZnO
hybrid nanowires.",1503.02201v1
2015-03-09,Fluidic Integration of Nanophotonic Devices Using Decomposable Polymers,"Polynorbornene-based decomposable polymer which can be patterned with
ultraviolet or electron-beam radiation is used to create micrometer-scale
fluidic channels. Silicon nitride substrates are used to fabricate nanophotonic
wavegide and resonators operating in the visible range of the spectrum. Fluidic
channels generated by thermally decomposing the polymer through the oxide
cladding is used to deliver ultra-small amounts of florescent samples to the
optical sensors.",1503.02631v1
2015-03-26,Emergent Transition for Superconducting Fluctuations in Antiferromagnetic Ruthenocuprates,"The emergence of carrier-pairing from the electronically inhomogeneous phase
of lightly hole-doped copper oxides has been investigated through
magnetoresistance measurements on 1222-type ruthenocuprates
RuSr2(R,Ce)2Cu2O10-d, principally with R = Gd, Sm, Nd. A well-defined
transition at which superconducting fluctuations emerge is discovered at a
remarkably low critical doping, pc = 0.0084, deep within the antiferromagnetic
phase. Systematic variations of the low temperature fluctuation density with
doping and cell volume demonstrate the intrinsic nature of the electronic
inhomogeneity and provide new support for bosonic models of the superconducting
mechanism.",1503.07714v1
2015-04-16,Coupling ferroelectricity with spin-valley physics in oxide-based heterostructure,"The coupling of spin and valley physics is nowadays regarded as a promising
route toward next-generation spintronic and valleytronic devices. In the aim of
engineering functional properties for valleytronic applications, we focus on
the ferroelectric heterostructure BiAlO3/BiIrO3, where the complex interplay
among trigonal crystal field, layer degrees of freedom and spin-orbit coupling
mediates a strong spin-valley coupling. Furthermore, we show that
ferroelectricity provides a non-volatile handle to manipulate and switch the
emerging valley-contrasting spin polarization.",1504.04091v1
2015-04-17,Synthesis of titanium-oxide nanoparticles with size and stoichiometry control,"Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an
Ar-O2 atmosphere using high power pulsing. It is shown that the stoichiometry
and the size of the nanoparticles can be varied independently, the former
through controlling the O2 gas flow and the latter by the independent biasing
of two separate anodes in the growth zone. Nanoparticles with diameters in the
range of 25 to 75 nm, and with different Ti-O compositions and crystalline
phases, have been synthesized.",1504.04458v1
2015-05-16,An Updated Wing TiO Sensitive Index for Classification of M-Type Stars,"By careful searching of synthetic and observed spectra in a sample of cool
giant and supergiant stars, we have updated the continuum band-passes of
near-infrared Wing three filter system. This photometric system measures the
strength of Titanium Oxide (TiO) absorption in Near-Infrared (NIR) at 719 nm.
We show that new reference continuum band-passes are essentially free from
molecular absorptions and the updated TiO-index defines the temperature
variation in a sample of cool giants with less scatter. A TiO-index vs.
effective temperature calibration is derived based on new continuum
band-passes.",1505.04332v1
2015-05-28,Intrinsic spin Hall effect in systems with striped spin-orbit coupling,"The Rashba spin-orbit coupling arising from structure inversion asymmetry
couples spin and momentum degrees of freedom providing a suitable (and very
intensively investigated) environment for spintronic effects and devices. Here
we show that in the presence of strong disorder, non-homogeneity in the
spin-orbit coupling gives rise to a finite spin Hall conductivity in contrast
with the corresponding case of a homogeneous linear spin-orbit coupling. In
particular, we examine the inhomogeneity arising from a striped structure for a
two-dimensional electron gas, affecting both density and Rashba spin-orbit
coupling. We suggest that this situation can be realized at oxide interfaces
with periodic top gating.",1505.07667v1
2015-06-03,Calculation method of spin accumulations and spin signals in nanostructures using spin resistors,"The understanding and calculation of spin transport are essential elements
for the development of spintronics devices. Here, we propose a simple method to
calculate analytically the spin accumulations, spin currents and
magnetoresistances in complex systems. This can be used both for CPP
experiments in multilayers and for multiterminal nanostructures made of
semiconductors, oxides, metals and carbon allotropes.",1506.01347v2
2015-07-23,Field-effect induced tunability in planar hyperbolic metamaterials,"We demonstrate that use of the field effect to tune the effective optical
parameters of a layered hyperbolic metamaterial leads to topological
transitions in its dispersion characteristics in the optical regime. Field
effect gating electrically modulates the permittivity in transparent conductive
oxides via changes in the carrier density. These permittivity changes lead to
active extreme modulation of ~200% of the effective electromagnetic parameters
along with active control of the anisotropic dispersion surface of hyperbolic
metamaterials and enable the opening and closing of photonic band gaps.",1507.06645v1
2015-10-07,Atomic layer deposition of Y2O3 on h-BN for a gate stack in graphene FETs,"The combination of h-BN and high-k dielectrics is required for a top gate
insulator in miniaturized graphene field-effect transistors because of the low
dielectric constant of h-BN. We investigated the deposition of Y2O3 on h-BN
using atomic layer deposition. The deposition of Y2O3 on h-BN was confirmed
without any buffer layer. An increase in the deposition temperature reduced the
surface coverage. The deposition mechanism could be explained by the
competition between the desorption and adsorption of the Y precursor on h-BN
due to the polarization. Although a full surface coverage was difficult to
achieve, the use of an oxidized metal seeding layer on h-BN resulted in a full
surface coverage.",1510.01928v1
2015-11-12,Simulation of Enhancement Mode GaN HEMTs with Threshold > 5 V using P-type Buffer,"A high threshold voltage enhancement-mode GaN HEMT with p-type doped buffer
is discussed and simulated. Analytical expressions are derived to explain the
role of buffer capacitance in designing and enhancing threshold voltage.
Simulations of the proposed device with p-type buffer show threshold voltages
above 5 V, and a positive shift in threshold voltage as the oxide capacitance
is reduced, thus enabling threshold voltage tunability over an unprecedented
range for GaN-based HEMTs. The electric field profiles, breakdown performance,
on-resistance and delay tradeoffs in the proposed pGaN back HEMT device are
also discussed.",1511.04438v1
2015-11-23,Metallic interface in non-SrTiO3 based titanate superlattice,"We report on the fabrication of all perovskite Mott insulator/band insulator
YTiO3/CaTiO3 superlattices by pulsed laser deposition. The combination of in
situ reflection high energy electron diffraction, X-ray diffraction, and X-ray
reflectivity confirms the high quality of the films grown in a layer-by-layer
mode. Electrical transport measurements reveal that a non-SrTiO3 based two
dimensional electron gas system has formed at the YTiO3/CaTiO3 interface. These
studies offer another route in the pursuit of complex oxide two-dimensional
electron gas systems, which allows to obtain greater insights into the exotic
many-body phenomena at such interfaces.",1511.07484v1
2016-01-01,Reverse degradation of nickel graphene junction by hydrogen annealing,"Metal contacts are fundamental building components for graphene based
electronic devices and their properties are greatly influenced by interface
quality during device fabrication, leading to resistance variation. Here we
show that nickel graphene junction degrades after air exposure, due to
interfacial oxidation, thus creating a tunneling barrier. Most importantly, we
demonstrate that hydrogen annealing at moderate temperature (300 0C) is an
effective technique to reverse the degradation.",1601.00109v2
2016-01-08,Persistence weighted Gaussian kernel for topological data analysis,"Topological data analysis (TDA) is an emerging mathematical concept for
characterizing shapes in complex data. In TDA, persistence diagrams are widely
recognized as a useful descriptor of data, and can distinguish robust and noisy
topological properties. This paper proposes a kernel method on persistence
diagrams to develop a statistical framework in TDA. The proposed kernel
satisfies the stability property and provides explicit control on the effect of
persistence. Furthermore, the method allows a fast approximation technique. The
method is applied into practical data on proteins and oxide glasses, and the
results show the advantage of our method compared to other relevant methods on
persistence diagrams.",1601.01741v2
2016-01-15,Decoherence and Decay of Two-level Systems due to Non-equilibrium Quasiparticles,"It is frequently observed that even at very low temperatures the number of
quasiparticles in superconducting materials is higher than predicted by
standard BCS-theory. These quasiparticles can interact with two-level systems,
such as superconducting qubits or two-level systems (TLS) in the amorphous
oxide layer of a Josephson junction. This interaction leads to decay and
decoherence of the TLS, with specific results, such as the time dependence,
depending on the distribution of quasiparticles and the form of the
interaction. We study the resulting decay laws for different experimentally
relevant protocols.",1601.03861v1
2016-01-18,Investigation of ITO based liquid sensor for ammonia hydroxide detection,"We proposed an Indium Tin Oxide (ITO) sensor for detecting the NH4OH in
seawater and carried out a series of experiments to investigate the feasibility
of it as a hazardous and noxious substance (HNS) sensor. The ITO layer revealed
a distinct resistance change ({\delta}R) which is linearly correlated with the
NH4OH concentration. Sensing mechanism of the porous ITO layer has been
explained in terms of reduction and electrical double layer (EDL) formation.
Also, the chemical stability of ITO as a HNS sensor has verified.",1601.04446v1
2016-03-11,Reconfigurable quadruple quantum dots in a silicon nanowire transistor,"We present a novel reconfigurable metal-oxide-semiconductor multi-gate
transistor that can host a quadruple quantum dot in silicon. The device consist
of an industrial quadruple-gate silicon nanowire field-effect transistor.
Exploiting the corner effect, we study the versatility of the structure in the
single quantum dot and the serial double quantum dot regimes and extract the
relevant capacitance parameters. We address the fabrication variability of the
quadruple-gate approach which, paired with improved silicon fabrication
techniques, makes the corner state quantum dot approach a promising candidate
for a scalable quantum information architecture.",1603.03636v1
2016-03-20,Oxygen Channels and Fractal Wave-Particle Duality in the Evolution of Myoglobin and Neuroglobin,"The evolution of terrestrial and aquatic wild type (WT) globins is dominated
by changes in two proximate - distal Histidine ligand exit channels, here
monitored quantitatively by hydropathic waves. These waves reveal allometric
functional features inaccessible to single amino acid stereochemical contact
models, and even very large all-atom Newtonian simulations. The evolutionary
differences between these features between myoglobin and neuroglobin are
related to the two oxidation channels through hydropathic wave analysis, which
identifies subtle interspecies functional differences inaccessible to
traditional size and metabolic scaling studies. Our analysis involves dynamic
synchronization of allometric interactions across entire globins.",1603.06219v1
2016-03-21,Improved Optimization for the Cluster Jastrow Antisymmetric Geminal Power and Tests on Triple-Bond Dissociations,"We present a novel specialization of the variational Monte Carlo linear
method for the optimization of the recently introduced cluster Jastrow
antisymmetric geminal power ansatz, achieving a lower-order polynomial cost
scaling than would be possible with a naive application of the linear method
and greatly improving optimization performance relative to the previously
employed quasi-Newton approach. We test the methodology on highly
multi-reference triple-bond stretches, achieving accuracies superior to
traditional coupled cluster theory and multi-reference perturbation theory in
both the typical example of N$_2$ and the transition-metal-oxide example of
[ScO]$^+$.",1603.06605v1
2016-04-05,Global sensitivity analysis of battery equivalent circuit model parameters,"This paper considers one of the most commonly used equivalent circuit models
(ECMs) for lithium-ion batteries and investigates the sensitivity of the model
output to changes of model parameters using the Morris method. Experiments are
carried out on a lithium-ion cell with nickel manganese cobalt oxide (NMC)
electrode and parameters of the model are identified in the state of charge
(SOC) range [100%,10%]. Although all the model parameters do vary with SOC,
global sensitivity analysis reveals that the uncertainties of some of the
parameters generate very little uncertainty in the voltage output, implying
that those parameters can be taken as constants without compromising the
accuracy of the model. This is further confirmed by experimental validation.",1604.01293v1
2016-04-20,Positive electron affinity of interfacial region in Polyethylene-MgO nanocomposite dielectric,"Polymer-based nanocomposite dielectrics are expected to become essential in
future generations of high voltage electrical insulation. However, the physics
behind their performance is not yet understood. Here we investigate electronic
properties of the interfacial area in magnesium oxide-polyethylene
nanocomposite. We use density functional theory to calculate densities of
states for MgO (100) and hydroxylated MgO (111) interfaces with polyethylene.
We evaluate the role of silicon-based nanoparticle surface modification at the
electronic level and propose a new theory for charge trapping in
nanocomposites.",1604.05984v2
2016-06-21,Proposal for a spin MOSFET based on spin gapless semiconductors,"We propose a spintronic metal oxide semiconductor field effect transistor
(spin MOSFET) where a spin gapless semiconductor (SGS) constitutes the channel
and the drain is a ferromagnetic metal. SGS exhibit a non-zero band gap in only
one of the spin sub-bands and feature complete spin polarization at finite
temperature. We present an analytical model of the device and comment the
properties relevant for devices applications. Our results boost SGS as a new
paradigm for the spin MOSFET concept.",1606.06445v1
2016-07-09,"Variation of the physical properties of four transition metal oxides SrTMO3 (TM = Rh, Ti, Mo, Zr) under pressure: An ab initio study","Using first principles calculations, we have studied the structural and
elastic properties of SrTMO3 (TM = Rh, Ti, Mo, Zr) under pressure by the plane
wave pseudopotential method based on the density functional theory (DFT) within
the generalized gradient approximation (GGA). The optical properties have been
investigated under zero pressure. It is observed that the calculated lattice
parameters are in good agreement with the available experimental result and
previous theoretical results.",1607.02592v1
2016-07-27,Interference-based molecular transistors,"Molecular transistors have the potential for switching with lower gate
voltages than conventional field-effect transistors. We have calculated the
performance of a single-molecule device in which there is interference between
electron transport through the highest occupied molecular orbital and the
lowest unoccupied molecular orbital of a single molecule. Quantum interference
results in a subthreshold slope that is independent of temperature. For
realistic parameters the change in gate potential required for a change in
source-drain current of two decades is 20 mV, which is a factor of six smaller
than the theoretical limit for a metal-oxide-semiconductor field-effect
transistor.",1607.07998v1
2016-09-14,Graphical analysis of Current-Voltage Characteristics in Typical Memristive Interfaces,"A graphical representation based on the isothermal current-voltage (IV)
measurements of typical memristive interfaces is presented. This is the
starting point to extract relevant microscopic information of the parameters
that control the electrical properties of a device based on a particular
metal-oxide interface. The convenience of the method is illustrated presenting
some examples were the IV characteristics were simulated in order to gain
insight on the influence of the fitting parameters.",1609.04472v3
2016-10-14,A local Fock-exchange potential in Kohn-Sham equations,"We derive and employ a local potential to represent the Fock exchange
operator in electronic single-particle equations. This local Fock-exchange
(LFX) potential is very similar to the exact exchange (EXX) potential in
density functional theory (DFT). The practical software implementation of the
two potentials (LFX and EXX) yields robust and accurate results for a variety
of systems (semiconductors, transition metal oxides) where Hartree Fock and
popular approximations of DFT typically fail. This includes examples
traditionally considered qualitatively inaccessible to calculations that omit
correlation.",1610.04363v1
2016-10-17,Role of nonlinearity in resistive switching phenomena of lanthanum calcium manganate heterostructures,"The present paper examines the influence of a nonlinear relationship between
the local oxygen-vacancy concentration and the local resistivity on resistive
switching effects in complex oxides. The continuity equation has been used as a
model for the motion of oxygen vacancies when a periodic time-dependent
electrical current is applied. The question of endurance of the switching
cycles is discussed. It is found that nonlinearity of the
resistivity-concentration dependence enhances the endurance.",1610.05194v1
2016-10-25,"Interface structure, band alignment and built-in potentials at LaFeO$_3$/$\textit{n}$-SrTiO$_3$ heterojunctions","Interface structure at polar/non-polar interfaces has been shown to be a key
factor in controlling emergent behavior in oxide heterostructures, including
the LaFeO$_3$/$\textit{n}$-SrTiO$_3$ system. We demonstrate via high energy
resolution x-ray photoemission that epitaxial LaFeO$_3$/$\textit{n}$-SrTiO$_3$
(001) heterojunctions engineered to have opposite interface polarities exhibit
very similar band offsets and potential gradients within the LaFeO$_3$ films.
However, differences in the potential gradient within the SrTiO$_3$ layer
depending on polarity may promote hole diffusion into LaFeO$_3$ for
applications in photocatalysis.",1610.08113v1
2017-02-04,Single-photon source based on Rydberg exciton blockade,"We propose to implement a new kind of solid-state single-photon source based
on the recently observed Rydberg blockade effect for excitons in cuprous oxide.
The strong interaction between excitons in levels with high principal quantum
numbers prevents the creation of more than one exciton in a small crystal. The
resulting effective two-level system is a good single-photon source. Our
quantitative estimates suggest that GHz rates and values of the second-order
correlation function $g_2(0)$ below the percent level should be simultaneously
achievable.",1702.01213v1
2017-02-14,Hidden radical reactivity of the [FeO]2+ group of the (hydro)oxide species in the H-abstraction from methane: a DFT and CASPT2 study,"Reactivity of the [FeO]2+ group in the abstraction of hydrogen from methane
is determined by metastable oxyl state FeIII-O* causing the negative spin
polarization of the methyl moiety as was shown by quantum-chemical means with
the use of model iron hydroxide species FeO(OH)2, Fe2O(OH)5, and Fe4O5(OH)3 as
an example.",1702.04092v1
2017-02-23,Dynamics in poly(propylene glycol) and silica oxide nanoparticles composite glassforming system,"Results of broadband dielectric spectroscopy and rheological studies of
poly(propylene glycol) + SiO${_2}$ nanocomposites are presented. They show that
the dynamics in high-concentrated composite is determined by confinement and
adsorption effects, resulting from interactions of confined polymers correspond
with the host system at the interface between PPG and solid nanoparticles. The
evolution of relaxation times follows the clear Vogel-Fulcher-Tammann pattern,
what is proved by the supplementary activation energy temperature index
analysis. The strong influence of nanoparticles on the transitional dynamics
and the fragility in the ultraviscous domain was noted.",1702.07280v1
2017-02-28,Conductance oscillations in graphene/nanoclusters hybrid material: towards large area single electron devices,"Large assemblies of self-organized aluminum nanoclusters embedded in an oxide
layer are formed on graphene templates and used to build tunnel-junction
devices. Unexpectedly, single-electron-transport behavior with well-defined
Coulomb oscillations is observed for a record junction area containing millions
of metal islands. Such hybrid materials offer new prospects for single-electron
electronics.",1703.00067v1
2017-03-25,Real-space analysis of scanning tunneling microscopy topography datasets using sparse modeling approach,"A sparse modeling approach is proposed for analyzing scanning tunneling
microscopy topography data, which contains numerous peaks corresponding to
surface atoms. The method, based on the relevance vector machine with
$\mathrm{L}_1$ regularization and $k$-means clustering, enables separation of
the peaks and atomic center positioning with accuracy beyond the resolution of
the measurement grid. The validity and efficiency of the proposed method are
demonstrated using synthetic data in comparison to the conventional
least-square method. An application of the proposed method to experimental data
of a metallic oxide thin film clearly indicates the existence of defects and
corresponding local lattice deformations.",1703.08643v1
2017-08-23,Orbital Physics,"A tutorial introduction into the principles of Orbital Physics in strongly
correlated transition metal oxides.",1708.07183v1
2018-02-06,Exploring the energy landscape of resistive switching in antiferromagnetic Sr(3)Ir(2)O(7),"We study the resistive switching triggered by an applied electrical bias in
antiferromagnetic Mott insulator Sr(3)Ir(2)O(7). The switching was previously
associated with an electric-field driven structural transition. Here we use
time-resolved measurements of the switching to probe the energy barrier
associated with the transition. We quantify the changes in the energy barrier
height with respect to the applied bias and find a linear decrease of the
barrier with increasing bias. Our observations support the potential of
antiferromagnetic transition metal oxides for spintronic applications.",1802.01923v1
2018-02-25,Spatial-resolved X-ray photoelectron spectroscopy of Weyl semimetal NbAs,"We utilized X-ray photoemission electron microscopy (XPEEM) and X-ray
photoelectron spectroscopy (XPS) to investigate the crystal surface of Weyl
semimetal NbAs. XPEEM images present white and black contrast in both the Nb 3d
and As 3d core level spectra. Surface-sensitive XPS spectra indicate that the
entire surface of the sample contains both surface states of Nb 3d and As 3d,
in form of oxides, and bulk states of NbAs. Estimated atomic percentage values
nNb/nAs suggest that the surface is Nb-rich and asymmetric for white and black
areas.",1802.08978v1
2018-02-26,2D materials coated plasmonic structures for SERS applications,"Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride,
are new kind of materials that can serve as substrates for surface enhanced
Raman spectroscopy (SERS). When combined with traditional metallic plasmonic
structures, the hybrid 2D materials/metal SERS platform brings extra benefits,
including higher SERS enhancement factors, oxidation protection of metal
surface, and protection of molecules from photo-induced damage. This
perspective gives an overview of recent progress in 2D materials coated
plasmonic structure in SERS application. This paper focuses on the fabrication
of the hybrid 2D materials/metal SERS platform and their applications for Raman
enhancement.",1802.09939v1
2018-04-24,Novel Highly Active Pt/Graphene Catalyst for Cathodes of Cu(II/I)-Mediated Dye-Sensitized Solar Cells,"Novel highly active, optically-transparent electrode catalyst containing Pt,
PtOx, graphene oxide and stacked graphene platelet nanofibers is developed for
a cathode of Cu(II/I)-mediated dye-sensitized solar cells.",1804.09119v1
2018-11-19,Photovoltaic effect in multi-domain ferroelectric perovskite oxides,"We propose a device model that elucidates the role of domain walls in the
photovoltaic effect in multi-domain ferroelectric perovskites. The model
accounts for the intricate interplay between ferroelectric polarization, space
charges, photo-generation and electronic transport. When applied to bismuth
ferrite, results show a significant electric potential step across both
71-degree and 109-degree domain walls, which in turn contributes to the
photovoltaic (PV) effect. We also find a strong correlation between
polarization and oxygen octahedra tilts, which indicates the nontrivial role of
the latter in the PV effect. The domain wall-based PV effect is further shown
to be additive in nature, allowing for the possibility of generating
above-bandgap voltage",1811.07948v1
2019-05-01,Degenerately Doped Transition Metal Dichalcogenides as Ohmic Homojunction Contacts to Transition Metal Dichalcogenide Semiconductors,"In search of an improved strategy to form low resistance contacts to MoS2 and
related semiconducting transition metal dichalcogenides, we use ab initio
density functional electronic structure calculations in order to determine the
equilibrium geometry and electronic structure of MoO3/MoS2 and MoO2/MoS2
bilayers. Our results indicate that, besides a rigid band shift associated with
charge transfer, the presence of molybdenum oxide modifies the electronic
structure of MoS2 very little. We find that the charge transfer in the bilayer
provides a sufficient degree of hole doping to MoS2, resulting in a highly
transparent contact region.",1905.00285v1
2019-05-21,Interseries transitions between Rydberg excitons in Cu$_{\mathrm{2}}$O,"We investigate the infrared optical transitions between excitons of the
yellow, green and blue series in the cuprous oxide Cu$_{\mathrm{2}}$O. We show
that in many cases the dipole approximation is inadequate and, in particular,
that it breaks down in yellow-blue transitions even for moderate principal
quantum numbers of $n \approx 10$. The interband matrix elements of the
transition operator needed for the evaluation of the excitonic transition
strengths are derived from known as well as from fitted band parameters.",1905.08752v2
2020-07-06,Interface evolution in phase transformation ruled by nucleation and growth,"An analytical model for the evolution of the boundary of the new phase in
transformations ruled by nucleation and growth is presented. Both homogeneous
and heterogeneous nucleation have been considered: The former includes
transformations in 2D and 3D space and the latter nucleation and growth on flat
solid substrate. The theory is formulated for the general case of spatially
correlated nuclei, arbitrary nucleation rate and power growth law of nuclei. In
the case of heterogeneous nucleation, spheroidal nuclei have been assumed and
the dependence of the kinetics on contact angle investigated. The validity of
the present approach is deemed through comparison with experimental data from
literature which also comprise oxide growth by ALD (Atomic Layer Deposition)
metal electrodeposition at solid substrate and alloy recrystallization.",2007.02700v1
2020-07-12,Reconstruction of 3D Image of Nanorice Particle from Randomly Oriented Single-Shot Experimental Diffraction Patterns Using Angular Correlation Method,"We reconstructed intensities in Fourier space and electron densities in the
real space for an azimuthally symmetric object Nanorice particle (Iron Oxide
nanoparticle) exposed in the ultrashort, bright and coherent x-ray free
electron laser (XFEL) pulses with random unknown orientations through the
method of angular correlations among intensities appeared in ninety eight 2D
diffraction patterns collected at Linac Coherent Light Source (LCLS).",2007.06030v1
2020-07-16,Piezoelectric SPDT NEMS Switch for Complementary Logic,"Off-state current leakage and switching delay has become the main challenge
for continued complementary metal-oxide-semiconductor (CMOS) technology
scaling. Previous work proposes a ""see-saw"" relay structure to mimic the
operation of CMOS. This paper presents a novel single-pole double-throw (SPDT)
switch structure based on AlN piezoelectric cantilever beam to improve the
former ""see-saw"" relay structure. Geometry parameters are given and key switch
parameters such as actuation voltage, switching time and contact force have
been calculated and compared with previous ""see-saw"" relay structure. Analysis
and design process is shown and micro-fabrication process is described as well.",2007.08134v1
2010-05-06,Diodes with Breakdown Voltages Enhanced by the Metal-Insulator Transition of LaAlO$_3$-SrTiO$_3$ Interfaces,"Using the metal-insulator transition that takes place as a function of
carrier density at the LaAlO$_3$-SrTiO$_3$ interface, oxide diodes have been
fabricated with room-temperature breakdown voltages of up to 200 V. With
applied voltage, the capacitance of the diodes changes by a factor of 150. The
diodes are robust and operate at temperatures up to 270 C.",1005.0941v1
2010-05-09,Piezoelectricity in the dielectric component of nanoscale dielectric/ferroelectric superlattices,"The origin of the functional properties of complex oxide superlattices can be
resolved using time-resolved synchrotron x-ray diffraction into contributions
from the component layers making up the repeating unit. The CaTiO3 layers of a
CaTiO3/BaTiO3 superlattice have a piezoelectric response to an applied electric
field, consistent with a large continuous polarization throughout the
superlattice. The overall piezoelectric coefficient at large strains, 54 pm/V,
agrees with first-principles predictions in which a tetragonal symmetry is
imposed on the superlattice by the SrTiO3 substrate.",1005.1430v1
2010-05-10,Internal structure of nanoparticles of Al generated by laser ablation in liquid ethanol,"Al NPs are synthesized by laser ablation of a bulk Al target immersed into
liquid ethanol saturated with hydrogen at atmospheric pressure. The
nanoparticles possess a well-distinguished core-shell structure. High
Resolution Transmission Electron Microscopy shows several layers inside the Al
nanoparticle: oxide layer, amorphous Al, single crystal Al, and a cavity in the
center. Formation of the cavity is attributed to the sharp increase of hydrogen
dissolution in Al upon its melting and its eventual release after the
solidification.",1005.1461v1
2010-05-10,Orbital order and possible superconductivity in LaNiO3/LaMO3 superlattices,"A hypothetical layered oxide La_2NiMO_6 where NiO_2 and MO_2 planes alternate
along the c-axis of ABO_3 perovskite lattice is considered theoretically. Here,
M denotes a trivalent cation Al, Ga,... such that MO_2 planes are insulating
and suppress the c-axis charge transfer. We predict that correlated e_g
electrons in the NiO_2 planes develop a planar x^2-y^2 orbital order driven by
the reduced dimensionality and further supported by epitaxial strain from the
substrate. Low energy electronic states can be mapped to a single-band t-t'-J
model, suggesting favorable conditions for high-T_c superconductivity.",1005.1464v1
2010-05-31,S-shaped current-voltage characteristics of organic solar devices,"Measuring the current-voltage characteristic of organic bulk heterojunction
solar devices sometimes reveals an s-shaped deformation. We qualitatively
produce this behaviour by a numerical device simulation assuming a reduced
surface recombination. Furthermore we show how to experimentally create these
double diodes by applying an oxygen plasma etch on the indium tin oxide (ITO)
anode. Restricted charge transport over material interfaces accumulates space
charges and therefore creates s-shaped deformations. Finally we discuss the
consequences of our findings for the open circuit voltage $V_{oc}$",1005.5669v2
2013-08-07,Electrochemical Grafting of Naphthylmethyl Radicals to Epitaxial Graphene: A Versatile Platform to Reversibly Engineer the Band Structure and Transport Properties of Graphene,"The Kolbe electrochemical oxidation strategy has been utilized to achieve an
efficient quasireversible electrochemical grafting of the alpha-naphthylmethyl
functional group to graphene. The method facilitates reversible bandgap
engineering in graphene and preparation of electrochemically erasable organic
dielectric films. The picture shows Raman D-band maps of both systems.",1308.1645v1
2013-08-30,Graphene Nanotechnology for the Next Generation Nonvolatile Memory,"As conventional silicon technology is approaching its fundamental material
and physical limits with continuous scaling, there is a growing push to look
for new platform to design memory circuits for nanoelectronic applications. In
this paper we explore new design concept of nonvolatile memory based on
graphene nanotechnology. The investigation focuses on two forms of graphene
based field effect transistor (FET) carbon nanotube FET (CNTFET) and graphene
nanoribbon FET (GNRFET). The analysis reveals that GNRFET with a high trapping
capable oxide layer is suitable for ultra high ensity nonvolatile memory.",1308.6782v1
2014-03-06,Single photon emission from ZnO nanoparticles,"Room temperature single photon emitters are very important resources for
photonics and emerging quantum technologies. In this work we study single
photon emission from defect centers in 20 nm zinc oxide (ZnO) nanoparticles.
The emitters exhibit bright broadband fluorescence in the red spectral range
centered at 640 nm with polarized excitation and emission. The studied emitters
showed continuous blinking, however, bleaching can be suppressed using a
polymethyl methacrylate (PMMA) coating. Furthermore, hydrogen termination
increased the density of single photon emitters. Our results will contribute to
the identification of quantum systems in ZnO.",1403.1301v1
2016-11-22,"The ALMA-PILS survey: First detections of ethylene oxide, acetone and propanal toward the low-mass protostar IRAS 16293-2422","One of the open questions in astrochemistry is how complex organic and
prebiotic molecules are formed. Aims. Our aim is to start the process of
compiling an inventory of oxygen-bearing complex organic molecules toward the
solar-type Class 0 protostellar binary IRAS16293-2422 from an unbiased spectral
survey with ALMA (PILS). Here we focus on the new detections of ethylene oxide
(c-C$_2$H$_4$O), acetone (CH$_3$COCH$_3$), and propanal (C$_2$H$_5$CHO).
Methods. With ALMA, we surveyed the spectral range from 329 to 363 GHz at
0.5$""$ (60 AU diameter) resolution. Using a simple model for the molecular
emission in LTE, the excitation temperatures and column densities of each
species were constrained. Results. We successfully detect propanal (44 lines),
ethylene oxide (20 lines) and acetone (186 lines) toward one component of the
protostellar binary, IRAS16293B. The high resolution maps demonstrate that the
emission for all investigated species originates from the compact central
region close to the protostar. This, along with a derived common excitation
temperature of $\sim$ 125 K, is consistent with a coexistence of these
molecules in the same gas. Conclusions. The observations mark the first
detections of acetone, propanal and ethylene oxide toward a low-mass protostar.
The relative abundance ratios of the two sets of isomers
(CH$_3$COCH$_3$/C$_2$H$_5$CHO $\sim$ 8 and CH$_3$CHO/c-C$_2$H$_4$O $\sim$ 12)
are comparable to previous observations toward high-mass protostars. The
majority of observed abundance ratios from these results as well as those
measured toward high-mass protostars are up to an order of magnitude above the
predictions from chemical models. This may reflect either missing reactions or
uncertain rates in the chemical networks. The physical conditions, such as
temperatures or densities, used in the models, may not be applicable to
solar-type protostars either.",1611.07314v1
2017-01-09,Rupture index: a quantitative measurement of sub-micrometer cracks in graphene,"Per weight graphene is stronger than steel, but because graphene is so thin,
it breaks and evidently forms cracks during handling, particularly when
supporting polymers are not used for transfer. In this paper, the parameter
rupture index is introduced to quantify the density of the cracks and related
defects in graphene during processing. The approach takes the advantages of the
high contrast achievable in fluorescence quenching microscopy to distinguish
between graphene and the background substrate, visible through the cracks in
graphene. The rupture index can well compare the effectiveness of different
graphene transferring methods in minimizing the formation of the cracks, and
quantify the oxidation of metals protected with graphene.",1701.02378v1
2017-01-25,Rotational state-selection and alignment of chiral molecules by electrostatic hexapoles,"Electrostatic hexapoles are revealed as a powerful tool in the rotational
state-selection and alignment of molecules to be utilized in beam experiments
on collisional and photoinitiated processes. In the paper, we report results on
the application of the hexapolar technique on the recently studied chiral
molecules propylene oxide, 2-butanol and 2bromobutane, to be investigated in
selective photodissociation and enantiomeric discrimination.",1701.07315v1
2017-04-24,Physics-Based Modeling of TID Induced Global Static Leakage in Different CMOS Circuits,"Compact modeling of inter-device radiation-induced leakage underneath the
gateless thick STI oxide is presented and validated taking into account CMOS
technology and hardness parameters, dose-rate and annealing effects, and
dependence on electric modes under irradiation. It was shown that proposed
approach can be applied for description of dose dependent static leakage
currents in complex FPGA circuits.",1704.07265v2
2018-05-09,Electro-optic polarization tuning of microcavities with a single quantum dot,"We present an oxide aperture microcavity with embedded quantum dots that
utilizes a three contact design to independently tune the quantum dot
wavelength and birefringence of the cavity modes. A polarization splitting
tuning of $\sim$5 GHz is observed. For typical microcavity polarization
splittings, the method can be used to achieve perfect polarization degeneracy
that is required for many polarization-based implementations of photonic
quantum gates. The embedded quantum dot wavelength can be tuned into resonance
with the cavity, independent of the polarization tuning.",1805.03387v1
2018-05-18,Origin of magnetoresistance suppression in thin $γ$-MoTe$_2$,"We use both classical magnetotransport and quantum oscillation measurements
to study the thickness evolution of the extremely large magnetoresistance (XMR)
material and type-II Weyl semimetal candidate, $\gamma$-MoTe$_2$, protected
from oxidation. We find that the magnetoresistance is systematically suppressed
with reduced thickness. This occurs concomitantly with both a decrease in
carrier mobility and increase in electron-hole imbalance. We model the two
effects separately and conclude that the XMR effect is more sensitive to the
former.",1805.07332v1
2009-12-04,On the mechanism of negative compressibility in layered compounds,"A mechanism of negative compressibility occurring in compressed layered
compounds in the presence of a pressure transmitting fluid medium is discussed
within a simple model. It takes into account the excluded volume effects and
soft fluid-matrix repulsion. It is demonstrated that a non-monotonic behavior
of the interlayer spacing with the applied pressure results from a competition
between the applied pressure and the internal one induced by the adsorbed
fluid. Recent experimental data on the graphite oxide ""structure breathing""
under compression in the presence of water are analyzed in the light of these
theoretical results.",0912.0892v1
2011-11-10,High-Temperature Superconductivity Mechanism for Cuprates,"Egorov and March plotted the product of resistivity and the copper
spin-lattice relaxation time vs. temperature for yttrium barium copper oxide
finding a minimum at temperature T greater than the superconducting
temperature, heralding an electronic phase change which can be interpreted as
the formation of a ""preformed"" pair. In this context we propose a
superconducting mechanism based on the notion that the preformed pair is a
""soft"" boson (a localized, different type of Cooper pair) which dissociates
above the classical BKT transition temperature, resulting in two circular
charge density waves. The model suggests explanations for considerable
experimental work and offers a physical explanation for the basis of the
Uemura-Homes law.",1111.2560v1
2011-11-15,Integrated TiO2 resonators for visible photonics,"We demonstrate waveguide-coupled titanium dioxide (TiO2) racetrack resonators
with loaded quality factors of 2x10^4 for the visible wavelengths. The
structures were fabricated in sputtered TiO2 thin films on oxidized silicon
substrates using standard top-down nanofabrication techniques, and passively
probed in transmission measurements using a tunable red laser. Devices based on
this material could serve as integrated optical elements as well as passive
platforms for coupling to visible quantum emitters.",1111.3545v1
2012-01-17,Multiscale Fractal Descriptors Applied to Nanoscale Images,"This work proposes the application of fractal descriptors to the analysis of
nanoscale materials under different experimental conditions. We obtain
descriptors for images from the sample applying a multiscale transform to the
calculation of fractal dimension of a surface map of such image. Particularly,
we have used the}Bouligand-Minkowski fractal dimension. We applied these
descriptors to discriminate between two titanium oxide films prepared under
different experimental conditions. Results demonstrate the discrimination power
of proposed descriptors in such kind of application.",1201.3410v1
2012-01-24,Determining the Location and Cause of Unintentional Quantum Dots in a Nanowire,"We determine the locations of unintentional quantum dots (U-QDs) in a silicon
nanowire with a precision of a few nanometers by comparing the capacitances to
multiple gates with a capacitance simulation. Because we observe U-QDs in the
same location of the wire in multiple devices, their cause is likely to be an
unintended consequence of the fabrication, not random atomic-scale defects as
is typically assumed. The locations of the U-QDs appear consistent with
conduction band modulation from strain from the oxide and the gates. This
allows us to suggest methods to reduce the frequency of U-QDs.",1201.5144v1
2012-01-25,Internal loss of superconducting resonators induced by interacting two level systems,"In a number of recent experiments with microwave high quality superconducting
coplanar waveguide (CPW) resonators an anomalously weak power dependence of the
quality factor has been observed. We argue that this observation implies that
the monochromatic radiation does not saturate the Two Level Systems (TLS)
located at the interface oxide surfaces of the resonator and suggests the
importance of their interactions. We estimate the microwave loss due to
interacting TLS and show that the interactions between TLS lead to a drift of
their energies that result in a much slower, logarithmic dependence of their
absorption on the radiation power in agreement with the data.",1201.5299v2
2012-04-04,Intrinsic instability of electronic interfaces with strong Rashba coupling,"We consider a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures, which includes a Rashba spin-orbit
coupling proportional to the electric field perpendicular to the interface.
Based on the standard mechanism of polarity catastrophe, we assume that the
electric field is proportional to the electron density. Under these simple and
general assumptions, we show that a phase separation instability occurs for
realistic values of the spin-orbit coupling and of the band parameters. This
could provide an intrinsic mechanism for the recently observed inhomogeneous
phases at the LaAlO_3/SrTiO_3 or LaTiO_3/SrTiO_3 interfaces.",1204.0962v3
2012-04-09,Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles,"We investigated the reversible ferromagnetic (FM) behavior of pure and Co
doped CeO2 nanopowders. The as-sintered samples displayed an increasing
paramagnetic contribution upon Co doping. Room temperature FM is obtained
simply by performing thermal treatments in vacuum at temperatures as low as
500^{\circ}C and it can be switched off by performing thermal treatments in
oxidizing conditions. The FM contribution is enhanced as we increase the time
of the thermal treatment in vacuum. Those systematic experiments establish a
direct relation between ferromagnetism and oxygen vacancies and open a path for
developing materials with tailored properties.",1204.1959v1
2012-04-10,Losses in superconducting Niobium Films caused by Interface Tunnel Exchange,"Identifying the loss mechanisms of niobium film cavities enables an accurate
determination of applications for future accelerator projects and points to
research topics required to mitigate their limitations. Measurements on samples
show that the electric field is a dominant loss mechanism for niobium films,
acting through interface tunneling between localized states in surface oxides
and delocalized states in the superconducting niobium.",1204.2166v3
2012-04-11,Laser written junctionless dual in-plane-gate thin-film transistors with AND Logic function,"A simple laser scribing process has been developed to fabricate low-voltage
junctionless in-plane-gate thin-film transistors (TFTs) arrays without any mask
and photolithography. Such junctionless TFTs feature that the channel and the
source/drain electrodes are of the same indium-tin-oxide films without any
intentional source/drain junction deposition process. Effective field-effect
modulation of the drain current has been realized on such in-plane-gate device
with a field-effect mobility of ~12.6cm2/Vs. At last, AND gate logic function
was demonstrated on dual in-plane-gate device.",1204.2312v1
2012-04-16,Ab initio investigation of competing instabilities in ferroelectric perovskite PbTiO3,"We have developed first-principles models, based on a general parametrization
of the full potential-energy surface, to investigate the lattice-dynamical
properties of perovskite oxides. We discuss the application of our method to
prototypic ferroelectric PbTiO3, showing that its properties are drastically
affected by a competition between structural instabilities. Indeed, we confirm
previous indications that the destructive interaction between the ferroelectric
and antiferrodistortive (involving rotations of the O6 octahedra) soft modes
shifts PbTiO3's Curie temperature by hundreds of degrees. Our theory provides
unique insight into this gigantic effect and its dynamical character.",1204.3394v1
2012-04-20,High carrier mobility in transparent Ba1-xLaxSnO3 crystals with a wide band gap,"We discovered that perovskite (Ba,La)SnO3 can have excellent carrier mobility
even though its band gap is large. The Hall mobility of Ba0.98La0.02SnO3
crystals with the n-type carrier concentration of \sim 8-10\times10 19 cm-3 is
found to be \sim 103 cm2 V-1s-1 at room temperature, and the precise
measurement of the band gap \Delta of a BaSnO3 crystal shows \Delta=4.05 eV,
which is significantly larger than those of other transparent conductive
oxides. The high mobility with a wide band gap indicates that (Ba,La)SnO3 is a
promising candidate for transparent conductor applications and also epitaxial
all-perovskite multilayer devices.",1204.4657v1
2012-04-23,Ferroelectricity induced by cooperative orbital ordering and Peierls instability,"A general mechanism by which orbital ordering, coupled to Peierls-like
lattice distortions, can induce an electronic switchable polarization is
discussed within a model Hamiltonian approach in the context of the modern
theory of polarization. By using a Berry-phase approach, a clear picture
emerges in terms of Wannier-function centers and orbital occupancies. The
proposed mechanism may apply to oxide spinels whose electronic structure has
effective one-dimensional character, such as CdV$_2$O$_4$, recently proposed to
display multiferroic behaviour.",1204.5106v1
2012-04-24,A Silicon Optical Transistor,"A fundamental road block for all-optical information processing is the
difficulty in realizing a silicon optical transistor with the ability to
provide optical gain, input output isolation and buffer action. In this work,
we demonstrate an all-optical transistor using optical nonlinearity in
microrings. By using weak light to control strong light, we observed an On/Off
ratio up to 20 dB. It can compensate losses in other optical devices and
provide fan-out capability. The device is ultra compact and is compatible with
current complementary metal-oxide-semiconductor (CMOS) processing.",1204.5515v1
2012-04-27,On the effect of oxygen partial pressure on the chromium distribution coefficient in melt-grown ruby crystals,"Small ruby crystals were grown by the Czochralski technique in different
atmospheres and their actual chromium content was analysed by a wet chemical
method. The chromium distribution coefficient k was found to be strongly
dependent on oxygen partial pressure p(O2). It ranges from k=0.3 in a reducing
atmosphere to k=1.2 in a slightly oxidizing atmosphere and to a good
approximation k depends linearly on log(p(O2)). The experimental data are
discussed on the basis of thermodynamic equilibrium calculations.",1204.6225v1
2013-09-04,Unexpected colloid-like supernatant from liquid-phase ball-milling graphite using miscible solutions as solvents: a failure analysis,"Ball-milling graphite was conducted in miscible solutions with the purpose to
exfoliate graphene. Colloid-like stable supernatants were unexpectedly
obtained. Followed were the characterizations with Scanning electronic
microscopy, Thermogravimetric analysis, X-ray diffraction and Elemental
dispersive X-ray mapping to recognize them. As a result, strongly against the
initial judgments, the components of colloid were mainly impurities of mixture
of zirconia, silicate and yttrium oxide, other than nano-graphite.",1309.1056v2
2013-09-05,Persistent photoconductivity in oxygen deficient YBCO/LCMO superlattices grown by PLD,"We report a large persistent photoconductivity (PPC) in oxygen reduced PLD
grown YBa2Cu3O7-{\delta}/La2/3Ca1/3MnO3-y (YBCO/LCMO) superlattices scaling
with the oxygen deficiency and being similar to that observed in single layer
YBa2Cu3O7-{\delta} films. These results contradict previous observations where
in sputtered bilayer samples only a transient photoconductivity (TPC) was
found. We argue that the PPC effect in superlattices is caused by the PPC
effect due to the YBa2Cu3O7-x layers with limited charge transfer to
La2/3Ca1/3MnO3-y. The discrepancy arises from the different permeability of
charges across the interface and shed light on the sensitivity of oxide
interface properties on details of their preparation.",1309.1295v1
2013-09-07,TCO Nanostructures as building blocks for nanophotonic devices in the infrared,"Transparent conducting oxides (TCOs), in general, are degenerated
semiconductors with large electronic band-gap. They have been widely used for
display screens, optoelectronic, photonic, and photovoltaic devices due to
their unique dual transparent and conductive properties. In this study, we
report in detail a technique that we developed to fabricate single crystal TCO
nanorod arrays with controlled conductivity, height, and lattice spacing in a
simple one-zone tube furnace system. We demonstrate how novel
photonic/plasmonic properties can be obtained by selecting unique combinations
of these basic parameters of the nano-rod arrays.",1309.1819v1
2013-09-16,Nucleation and growth of metal whiskers,"The existence of metal whiskers is attributed to the energy gain due to
electrostatic polarization of needle shaped metal filaments in the electric
field induced by surface imperfections: contaminations, oxide states, etc. A
proposed theory provides closed form expressions for the whisker nucleation and
growth rates, explains the range of whisker parameters and effects of external
biasing. It predicts a well controlled whisker growth on any metal surface via
generating surface plasmon polariton excitations.",1309.3822v3
2013-09-24,Electrophysical properties of PMN-PT-PS-PFN:Li ceramics,"We present the technology of obtaining and the electrophysical properties of
a multicomponent material 0.61PMN-0.20PT-0.09PS-0.1PFN:Li (PMN-PT-PS-PFN:Li).
The addition of PFN into PMN-PT decreases the temperature of final sintering
which is very important during technological process (addition of Li decreases
electric conductivity of PFN). Addition of PS i.e., PbSnO_3 (which is unstable
in ceramic form) permits to shift the temperature of the maximum of dielectric
permittivity. One-step method of obtaining ceramic samples from oxides and
carbonates has been used. XRD, microstructure, scanning calorimetry
measurements and the main dielectric, ferroelectric and electromechanical
properties have been investigated for the obtained samples.",1309.6093v1
2014-04-19,Negative Capacitance Tunnel Field Effect Transistor: A Novel Device with Low Subthreshold Swing and High ON Current,"In this paper we propose a modified structure of TFET incorporating
ferroelectric oxide as the complementary gate dielectric operating in negative
capacitance zone, called the Negative Capacitance Tunnel FET (NCTFET). The
proposed device effectively combines two different mechanisms of lowering the
sub threshold swing (SS) for a transistor garnering a further lowered one
compared to conventional TFET. A simple yet accurate analytical tunnel current
model for the proposed device is also presented here. The developed analytical
model demonstrates high ON current at low $V_{GS}$ and exhibits lower SS.",1405.5169v1
2014-05-25,Complementary memristive device based on a thin film of MoS2 monolayers,"In this manuscript we demonstrate experimentally that a thin film of MoS2
monolayers formed by drop-casting on a gold interdigitated electrode on Si/SiO2
behaves like a complementary memristive device, which is a key device of future
crossbar memories. The hysteretic behavior of this device is modulated by light
in a spectral range expanding from UV up to IR. In contrast to previous
complementary memristive devices based on complicated oxides heterostructures,
this device has a simple fabrication procedure and can be controlled by light,
in addition to electrical signals.",1405.6406v1
2014-06-02,New Electrochemical Characterization Methods for Nanocomposite Supercapacitor Electrodes,"Supercapacitor electrodes fabricated from a nanocomposite consisting of
multiwall carbon nanotubes and titanium oxide nanoparticles were characterized
electrochemically. Conventional electrochemical characterizations cyclic
voltammetry and galvanostatic charge-discharge in a lithium-based electrolyte
gave a specific capacitance of 345 F/g at a current density of 0.1 A/g. New
electrochemical characterization techniques that allow one to obtain the peak
capacitance associated with intercalation and to distinguish between
electrostatic and faradaic charge storage are described and applied to the
electrode measurements. Finally, the maximum energy density obtained was 31
Wh/kg.",1406.0470v3
2016-05-01,Further results on degree based topological indices of certain chemical networks,"There are various topological indices such as degree based topological
indices, distance based topological indices and counting related topological
indices etc. These topological indices correlate certain physicochemical
properties such as boiling point, stability of chemical compounds. In this
paper, we compute the sum-connectivity index and multiplicative Zagreb indices
for certain networks of chemical importance like silicate networks, hexagonal
networks, oxide networks, and honeycomb networks. Moreover, a comparative study
using computer-based graphs has been made to clarify their nature for these
families of networks.",1605.00253v2
2016-05-02,First Principles Prediction of Amorphous Phases Using Evolutionary Algorithms,"We discuss the efficacy of evolutionary method for the purpose of structural
analysis of amorphous solids. At present ab initio molecular dynamics (MD)
based melt-quench technique is used and this deterministic approach has proven
to be successful to study amorphous materials. We show that a stochastic
approach motivated by Darwinian evolution can also be used to simulate
amorphous structures. Applying this method, in conjunction with density
functional theory (DFT) based electronic, ionic and cell relaxation, we
re-investigate two well known amorphous semiconductors, namely silicon and
indium gallium zinc oxide (IGZO). We find that characteristic structural
parameters like average bond length and bond angle are within $\sim$ 2% to
those reported by ab initio MD calculations and experimental studies.",1605.00516v1
2016-05-10,Analysis of 3D-printed metal for rapid-prototyped reflective terahertz optics,"We explore the potential of 3D metal printing to realize complex conductive
terahertz devices. Factors impacting performance such as printing resolution,
surface roughness, oxidation, and material loss are investigated via
analytical, numerical, and experimental approaches. The high degree of control
offered by a 3D-printed topology is exploited to realize a zone plate operating
at 530 GHz. Reflection efficiency at this frequency is found to be over 90%.
The high-performance of this preliminary device suggest that 3D metal printing
can play a strong role in guided-wave and general beam control devices in the
terahertz range.",1605.03246v1
2016-08-05,Density functional theory calculations of the stress of oxidised (110) silicon surfaces,"The measurement of the lattice-parameter of silicon by x-ray interferometry
assumes the use of strain-free crystals. This might not be the case because
surface relaxation, reconstruction, and oxidation cause strains without the
application of any external force. In a previous work, this intrinsic strain
was estimated by a finite element analysis, where the surface stress was
modeled by an elastic membrane having a 1 N/m tensile strength. The present
paper quantities the surface stress by a density functional theory calculation.
We found a value exceeding the nominal value used, which potentially affects
the measurement accuracy.",1608.01885v1
2016-08-29,Full elasticity tensor from thermal diffuse scattering,"We present a method for the precise determination of the full elasticity
tensor from a single crystal diffraction experiment using monochromatic X-rays.
For the two benchmark systems calcite and magnesium oxide we show that the
measurement of thermal diffuse scattering in the proximity of Bragg reflections
provides accurate values of the complete set of elastic constants. This
approach allows for a reliable and model free determination of the elastic
properties and can be performed together with crystal structure investigation
in the same experiment.",1608.08061v1
2016-12-02,"A preliminary DFT study of the adsorption and dissociation of $CH_{4}$,$SO_{2}$ and $O_{2}$ reactions on $Cr_{2}O_{3}(0001)$","In the present work, we study the structures and molecular geometries of
$CH_{4}$, $SO_{2}$ and $O_{2}$ adsorbed on $Cr_{2}O_{3}(0001)$. Using
computational calculations based on the density functional theory (DFT), we
analyze the most suitable sites to carry out the adsorption of each of the
molecules mentioned, and the influence of each species on the adsorption and
dissociation of the others. The results allow us to understand the activation
of the $Cr_{2}O_{3}(0001)$ surface, which leads to the presence of $SO_{2}$
during the oxidation of $CH_{4}$, as was experimentally verified.",1612.00672v1
2016-12-22,Coulomb Correlations in 4d and 5d Oxides from First Principles - or How Spin-Orbit Materials choose their Effective Orbital Degeneracies,"The interplay of spin-orbit interactions and Coulomb correlations has become
a hot topic in condensed matter theory. Here, we review recent advances in
dynamical mean-field theory-based electronic structure calculations for
iridates and rhodates. We stress the notion of the effective degeneracy of the
compounds, which introduces an additional axis into the conventional picture of
a phase diagram based on filling and on the ratio of interactions to bandwidth.",1612.07546v1
2017-06-01,FeSe(en)0.3 - Separated FeSe layers with stripe-type crystal structure by intercalation of neutral spacer molecules,"Solvothermal intercalation of ethylenediamine molecules into FeSe separates
the layers by 1078 pm and creates a different stacking. FeSe(en)0.3 is not
superconducting although each layer exhibits the stripe-type crystal structure
and the Fermi surface topology of superconducting FeSe. FeSe(en)0.3 requires
electron-doping for high-Tc similar to monolayers of FeSe@SrTiO3, whose much
higher Tc may arise from the proximity of the oxide surface.",1706.00314v1
2017-06-04,Electric field induced phase transition and electrocaloric effect in PMN-PT,"Ferroelectric perovskite oxides possess a large electrocaloric (EC) effect,
but usually at high temperatures near the ferroelectric/paraelectric phase
transition temperature, which limits their potential application as
next-generation solid-state cooling devices. We use classical molecular
dynamics to study the electric field induced phase transitions and EC effect in
PMN-PT (PbMg1/3Nb2/3O3-PbTiO3). We find that the maximum EC strength of PMN-PT
occurs within the morphotropic phase boundary (MPB) region at 300 K. The large
adiabatic temperature change is caused by easy rotation of polarization within
the MPB region.",1706.01034v2
2017-06-06,Autoignition of Butanol Isomers at Low to Intermediate Temperature and Elevated Pressure,"Autoignition delay experiments for the isomers of butanol, including n-,
sec-, tert-, and iso-butanol, have been performed using a heated rapid
compression machine. For a compressed pressure of 15 bar, the compressed
temperatures have been varied in the range of 725-855 K for all the
stoichiometric fuel/oxidizer mixtures. Over the conditions investigated in this
study, the ignition delay decreases monotonically as temperature increases and
exhibits single-stage characteristics. Experimental ignition delays are also
compared to simulations computed using three kinetic mechanisms available in
the literature. Reasonable agreement is found for three isomers (tert-, iso-,
and n-butanol).",1706.01837v1
2017-06-07,What can one learn about material structure given a single first-principles calculation?,"We extract a variable $X$ from electron orbitals $\Psi_{n\bf{k}}$ and
energies $E_{n\bf{k}}$ in the parent high-symmetry structure of a wide range of
complex oxides: perovskites, rutiles, pyrochlores, and cristobalites. Even
though calculation was done only in the parent structure, with no distortions,
we show that $X$ dictates material's true ground state structure. We propose
using Wannier functions to extract concealed variables such as $X$ both for
material structure prediction and for high-throughput approaches.",1706.02012v2
2017-06-15,Studies on thermal degradation behavior of nano silica loaded cotton and polyester fabrics,"In this work cotton and polyester fabric were coated with silica nano
particles using pad-dry-cure method. The prepared composite fabrics were
analyzed in terms of change in their thermal degradation properties. The
oxidative degradation characteristic of control and treated samples were
studied using Thermo Gravimetric technique. The mass loss profile of untreated
fabric compared with treated fabric. The results indicate that the thermal
degradation rate was lower in treated sample as compare to control fabrics.",1706.04777v1
2017-06-27,Self-Assembled Monolayer Piezoelectrics: Electric-Field Driven Conformational Changes,"We demonstrate that an applied electric field causes piezoelectric distortion
across single molecular monolayers of oligopeptides. We deposited
self-assembled monolayers ~1.5 nm high onto smooth gold surfaces. These
monolayers exhibit strong piezoelectric response that varies linearly with
applied bias (1-3V), measured using piezoresponse force microscopy (PFM). The
response is markedly greater than control experiments with rigid alkanethiols
and correlates with surface spectroscopy and theoretical predictions of
conformational change from applied electric fields. Unlike existing
piezoelectric oxides, our peptide monolayers are intrinsically flexible, easily
fabricated, aligned and patterned without poling.",1706.08993v2
2017-10-05,Electronic Transport Properties of Carrier Controlled SnSe Single Crystals,"We found that the electronic transport property of SnSe single crystals was
sensitive to oxygen content. Semiconducting SnSe single crystals were obtained
by using Sn of grain form as a starting material while powder Sn resulted in
metallic SnSe. X-ray photoelectron spectroscopy analysis revealed that the
surfaces of raw Sn were oxidized, where the volume fraction was relatively low
in grain Sn. This demonstrates that contamination of oxygen causes metallic
behavior in grown SnSe single crystals.",1710.01863v1
2017-12-28,Theoretical calculation of transport properties of oxide material using narrow band model,"We report about the results of theoretical calculations of temperature
dependence of resistivity ($\rho$) and Seebeck coefficient ($S$) for
thermoelectric (TE) and superconductivity (SC) phases by arithmetic equations
based on narrow band model with oxygen deficient structure, as the functions of
band-filling degree ($F$), and band width ratio of electron and spin states
($W$\sigma/$W$D). The phase diagrams of TE and SC states, and boundary were
imaged to the properties of $\rho$ and $S$ as a function of $F$ and
$W$\sigma/$W$D.",1712.09840v1
2018-01-03,Reduction of Nitrogen Oxides (NOx) by Superalkalis,"NOx are major air pollutants, having negative impact on environment and
consequently, human health. We propose here the single-electron reduction of
NOx (x = 1, 2) using superalkalis. We study the interaction of NOx with FLi2,
OLi3 and NLi4 superalkalis using density functional calculations, which lead to
stable superalkali-NOx ionic complexes with negatively charged NOx. This
clearly reveals that the NOx can successfully be reduced to NOx- anion due to
electron transfer from superalkalis. It has been also noticed that the size of
superalkalis plays a crucial in the single-electron reduction of NOx.",1801.00913v1
2018-09-11,Al-Cu-Fe quasicrystals as anode of lithium ion battery,"In this paper, Al-Cu-Fe quasicrystal alloy was used as anode material of
lithium-ion batteries. The first specific discharge capacity of quasicrystal
was 204mAh/g. Cyclic voltammetry showed that oxidation peak of Al-Cu-Fe
quasicrystal was at about 1.4V. The reduction peak was at 0.3V. Al-Cu-Fe
quasicrystal have higher Li-ion diffusion impedance and Warburg in the first
cycle. X-ray diffraction analysis demonstrate that Li atom enter into
quasicrystal structure can not fully leave quasicrytal during first
charge/discharge cycle which induce the irreversible capacity.",1809.03667v1
2018-10-18,Strengthening of copper by carbon nanotubes,"The influence of a modifier based on multi walled carbon nanotubes (MWCNT) is
investigated using C11000 copper alloy. The influence of the modifier addition
into the melt was investigated using tensile test, hardness measurements, X-ray
diffraction method and microstructural investigations. It was evaluated that
the yield and tensile strengths of the metal increased due to the
microstructural changes in the formed metal after addition of 0.01wt.% of the
MWCNTs. It was also evaluated that the addition of mentioned amount of MWCNT
into alloy has no influence to the phase composition of the formed metal.",1810.08019v1
2018-10-19,Lévy flights confinement in a parabolic potential and fractional quantum oscillator,"We study L\'evy flights confined in a parabolic potential. This has to do
with a fractional generalization of ordinary quantum-mechanical oscillator
problem. To solve the spectral problem for the fractional quantum oscillator,
we pass to the momentum space, where we apply the variational method. This
permits to obtain approximate analytical expressions for eigenvalues and
eigenfunctions with very good accuracy. Latter fact has been checked by
numerical solution of the problem. We point to the realistic physical systems
ranging from multiferroics and oxide heterostructures to quantum chaotic
excitons, where obtained results can be used.",1810.08422v1
2018-10-21,Inversion of oxygen potential transitions at grain boundaries of SOFC/SOEC electrolytes,"Solid oxide fuel/electrolyzer cell (SOFC/SOEC) converts energy between
chemical and electrical forms inversely. Yet electrolyte degradation takes
place much more severe for SOEC than SOFC during long-term operations. By
solving transport equations, we found very large oxygen potential gradients and
sharp oxygen potential transitions at grain boundaries of polycrystalline
SOFC/SOEC electrolyte. Surprisingly, an inversion of oxygen potential
transitions was identified, suggesting a fundamentally different transport
mechanism for minor electronic charge carriers. Such findings could be critical
to understand and eliminate SOFC/SOEC degradations in practical applications.",1810.09016v1
2019-06-09,Experimental Investigation of Crack Jumps during Initiation and Growth in IN718,"The following study investigates the statistical nature of crack jumps during
fatigue of Inconel 718. In-situ measurement in atmospheric air of the crack
length at several loading and temperature conditions was conducted using a
direct current potential drop (DCPD) method. Both annealed and heat-treated
Inconel 718 samples were investigated. For a single sample, the normalized
change of crack length was confirmed to not be a random process. This finding
is significant in highlighting the time history features, which could be used
in training machine learning models for the fundamental understanding of
oxidation and the prediction of crack initiation and growth.",1906.03681v3
2019-06-11,Defect-Moderated Oxidative Etching of MoS2,"We report a simple technique for the selective etching of bilayer and
monolayer MoS$_2$. In this work, chosen regions of MoS$_2$ were activated for
oxygen adsorption and reaction by the application of low doses of He$^+$ at 30
keV in a gas ion microscope. Raman spectroscopy, optical microscopy and
scanning electron microscopy were used to characterize both the etched features
and the remaining material. It has been found that by using a pre-treatment to
introduce defects, MoS$_2$ can be etched very efficiently and with high region
specificity by heating in air.",1906.04850v1
2019-06-07,274-GHz CMOS Signal Generator with an On-Chip Patch Antenna in a QFN Package,"A 274-GHz signal generator with an on-chip antenna in a quad-flat no-leads
(QFN) package is demonstrated. The circuit is fabricated in a 65-nm
Complementary Metal Oxide Semiconductor (CMOS) process. The effective isotropic
radiated power (EIRP) measured from the packaged signal generator is -12.8-dBm
at 274GHz with DC power consumption of 26.3mW. The packaging material can help
improve the antenna performance, and integrated circuits with on-chip antennas
operating at ~300GHz can be packaged using low-cost techniques.",1906.05117v1
2019-06-25,Impact of Extrinsic Interface Traps and Doping Atoms on Conductivity of Graphene Field Effect Devices,"Near-interfacial oxide traps and chemical impurities on the graphene surface
or at the graphene-dielectric interface can be a source of intentional or
unintentional doping of graphene sheet. The efficiency of such chemical doping
can vary in a wide range depending on parameters of graphene field effect
devices. Mechanisms of such sensitivity of doping efficiency to the device
characteristics need to be understood. The objective of this paper is to
theoretically derive the analytical relations, adapted to the explicit
calculation of graphene chemical doping.",1906.10476v1
2019-07-05,Enhancing electrical conductivity of room temperature deposited Sn-doped In$_2$O$_3$ thin films by hematite seed layers,"Hematite Fe$_2$O$_3$ seed layers are shown to constitute a pathway to prepare
highly conductive transparent tin-doped indium oxide (ITO) thin films by room
temperature magnetron sputtering. Conductivities of up to $\sigma = 3300\,{\rm
S/cm}$ are observed. The improved conductivity is not restricted to the
interface but related to an enhanced crystallization of the films, which
proceeds in the rhombohedral phase.",1907.02867v1
2019-07-10,In Praise and in Search of Highly-Polarizable Semiconductors,"The dielectric response of materials underpins electronics and photonics.
Established semiconductor materials have a narrow range of dielectric
susceptibility, with low-frequency values on the order of 10. Strong and
variable dielectric response in wide-band gap materials is associated with
complex crystal structures and heavier elements. Based on underlying chemical
trends, we hypothesize that chalcogenides in crystal structures common to
complex oxides may feature many highly-polarizable semiconductors. Research on
these materials is motivated by fundamental inquiry into electrons and phonons
in solids, and by potential applications in photonics, high-frequency
communications, and photovoltaics.",1907.04600v1
2019-07-13,High-performance super-capacity using activated glassy carbon foam,"An urgent demand for new sustainable and efficient energy conversion and
storage devices required the development of novel electrode materials with
increased specific capacitance. However, low mass loading, poor scalability,
and low working voltage always limited further practical application of most
reported high-performance supercapacitors electrode materials. In this work, we
demonstrated the preparation of activated glassy carbon foam as
high-performance electrode via oxidizing commercial glassy carbon foam in HNO3
solution.",1907.06031v2
2019-07-24,On Calibration of a Nominal Structure-Property Relationship Model for Chiral Sculptured Thin Films by Axial Transmittance Measurements,"A chiral sculptured thin film is fabricated from patinal titanium oxide using
the serial bideposition technique. Axial transmittance spectrums are measured
over a spectral region encompassing the Bragg regime for axial excitation. The
same spectrums are calculated using a nominal structure-property relationship
model and the parameter space of the model is explored for best fits of the
calculated and measured transmittances. Ambiguity arising on calibrating the
model against axial transmittance measurements is shown to be resolvable using
non--axial transmittance measurements.",1907.10740v1
2019-10-02,Transition to bound states for bacteria swimming near surfaces,"It is well known that flagellated bacteria swim in circles near surfaces.
However, recent experiments have shown that a sulfide-oxidizing bacterium named
Thiovulum majus can transition from swimming in circles to a surface bound
state where it stops swimming while remaining free to move laterally along the
surface. In this bound state, the cell rotates perpendicular to the surface
with its flagella pointing away from it. Using numerical simulations and
theoretical analysis, we demonstrate the existence of a fluid-structure
interaction instability that causes cells with relatively short flagella to
become surface bound.",1910.01502v1
2020-01-15,Intense Anti-Stokes Emission of Erbium Ions in Gallium Lanthanum Sulphide-Oxide Glass in Visible Spectral Range,"Photoluminescence spectra have been investigated in erbium doped GaLaS(O)
glasses. The samples demonstrate intense green emission bands centered at
around 525 and 550 nm due to up-conversion processes in erbium ions. The
theoretical description of up-conversion intensity as a function of excitation
intensity has been offered. It is based on a solution of a system of rate
equations taking into account three up-conversion transitions.",2001.05464v1
2020-01-28,A C/V$_2$O$_5$ core-sheath nanofibrous cathode with mixed-ion intercalation for aluminium-ion batteries,"A new nanofibrous material, consisting of a conductive carbon core and an
external layer made of vanadium oxide, has been studied as a cathode for
aluminium-ion batteries. The material enables a mixed-ion intercalation
mechanism, resulting in the alternating insertion of $\text{Al}^{3+}$ and
$\text{AlCl}_4^-$ in the $\text{V}_2\text{O}_5$ and carbon layers,
respectively. This is a highly desirable feature for cathode materials which
may increase the energy density of future batteries by optimising the
utilisation of the electrolyte.",2001.10153v2
2020-04-23,X-ray phase contrast topography to measure the surface stress and bulk strain in a silicon crystal,"The measurement of the Si lattice parameter by x-ray interferometry assumes
the use of strain-free crystals, which might not be true because of intrinsic
stresses due to surface relaxation, reconstruction, and oxidation. We used
x-ray phase-contrast topography to investigate the strain sensitivity to the
finishing, annealing, and coating of the interferometer crystals.We assessed
the topography capabilities by measuring the lattice strain due to films of
copper deposited on the interferometer mirror-crystal. A byproduct has been the
measurement of the surface stresses after complete relaxation of the coatings.",2004.11275v2
2020-12-18,A CMOS Compatible Aluminum Scandium Nitride-based Ferroelectric Tunnel Junction Memristor,"We report a complementary metal oxide semiconductor (CMOS) technology
compatible ferroelectric tunnel junction memristor grown directly on top of a
Silicon substrate using a scandium doped aluminum nitride as the ferroelectric
layer.",2012.10019v2
2012-05-01,Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3,"We report the electron doping in the surface vicinity of KTaO_3 by inducing
oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility
(> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas
oscillations with both two- and three-dimensional components. A disparity of
the extracted in-plane effective mass, compared to the bulk values, suggests
mixing of the orbital characters. Our observations demonstrate that Ar^+
-irradiation serves as a flexible tool to study low dimensional quantum
transport in 5d semiconducting oxides.",1205.0197v1
2012-05-07,Suppression of Multilayer Graphene Patches during CVD Graphene growth on Copper,"By limiting the carbon segregation at the copper surface defects, a pulsed
chemical vapor deposition method for single layer graphene growth is shown to
inhibit the formation of few-layer regions, leading to a fully single-layered
graphene homogeneous at the centimeter scale. Graphene field-effect devices
obtained after transfer of pulsed grown graphene on oxidized silicon exhibit
mobilities above 5000 cm^2.V^-1.s^-1.",1205.1337v1
2012-05-30,"Multiple Superconducting Gaps, Anisotropic Spin Fluctuations and Spin-Orbit Coupling in Iron-Pnictides","This article reviews the NMR and NQR studies on iron-based high-temperature
superconductors by the IOP/Okayama group. It was found that the electron pairs
in the superconducting state are in the spin-singlet state with multiple
fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal
state are found to be closely correlated with the superconductivity. Also the
antiferromagnetic spin fluctuations are anisotropic in the spin space, which is
different from the case in copper oxide superconductors. This anisotropy
originates from the spin-orbit coupling and is an important reflection of the
multiple-bands nature of this new class of superconductors.",1205.6589v1
2017-09-04,Interaction of Rydberg Excitons in Cuprous Oxide with Phonons and Photons: Optical Linewidth and Polariton Effect,"We demonstrate that the optical linewidth of Rydberg excitons in Cu2O can be
completely explained by scattering with acoustical and optical phonons, whereby
the dominant contributions stems from the non-polar optical modes. The
consequences for the observation of polariton effects are discussed. We find
that an anti-crossing of photon and exciton dispersions exists only for states
with main quantum numbers n>28, so polariton effects do not play any role in
the experiments reported up to now.",1709.00895v1
2017-09-25,Light-induced switching in pDTE - FICO 1D photonic structures,"We propose the design of 1D photonic crystals and microcavities in which
fluorine-indium codoped cadmium oxide (FICO) nanocrystal based layers and
layers of diarylethene-based polyester (pDTE) are alternated or embedded in a
microcavity. The irradiation with UV light results in two different behaviours:
i) it dopes the FICO nanocrystals inducing a blue shift of their plasmonic
resonances; ii) it changes the real part of the refractive index of the
photochromic pDTE polymer. These two behaviours are combined in the proposed
photonic structures and can be useful for switchable filters and cavities for
light emission.",1709.08741v2
2017-09-26,Photoferroelectric oxides,"Giant photovoltaic effect due to bulk photovoltaic effect observed in
multiferroic BiFeO3 thin films has triggered a renewed interest on
photoferroelectric materials for photovoltaic applications. Tremendous advance
has been done to improve power conversion efficiency (up to up to 8.1%) in
photoferroelectrics via absorption increase using narrow bandgap
ferroelectrics. Other strategies, as it is the more efficient use of
ferroelectric internal electric field, are ongoing. Moreover, as a by-product,
several progress have been also achieved on photostriction that is the
photo-induced deformation phenomenon. Here, we review ongoing and promising
routes to improve ferroelectrics photoresponse.",1709.09202v1
2017-11-03,Blowing Polar Skyrmion Bubbles in Oxide Superlattices,"Particle-like topological structures such as skyrmions and vortices have
garnered ever-increasing interests due to the rich physical insights and
potential broad applications. Here we discover the reversible switching between
polar skyrmion bubbles and ordered vortex arrays in ferroelectric superlattices
under an electric field, reminiscent of the Plateau-Raleigh instability in
fluid mechanics. Electric field phase diagram is constructed, showing wide
stability window for the observed polar skyrmions. This study is a
demonstration for the computational design of ferroelectric topological
structures and field-induced topological phase transitions.",1711.00995v1
2017-11-05,Selective Orientation of Chiral Molecules by Laser Fields with Twisted Polarization,"We explore a pure optical method for enantioselective orientation of chiral
molecules by means of laser fields with twisted polarization. Several field
implementations are considered, including a pair of delayed cross-polarized
laser pulses, an optical centrifuge, and polarization shaped pulses. The
underlying classical orientation mechanism common for all these fields is
discussed, and its operation is demonstrated for a range of chiral molecules of
various complexity: hydrogen thioperoxide (${\rm HSOH}$), propylene oxide
(${\rm CH_{3}CHCH_{2}O}$) and ethyl oxirane (${\rm CH_{3}CH_{2}CHCH_{2}O}$).
The presented results demonstrate generality, versatility and robustness of
this optical method for manipulating molecular enantiomers in the gas phase.",1711.01552v1
2017-11-24,E$_8$ in $\mathcal N=8$ supergravity in four dimensions,"We argue that $\mathcal N=8$ supergravity in four dimensions exhibits an
exceptional $E_{8(8)}$ symmetry, enhanced from the known $E_{7(7)}$ invariance.
Our procedure to demonstrate this involves dimensional reduction of the
$\mathcal N=8$ theory to $d=3$, a field redefinition to render the $E_{8(8)}$
invariance manifest, followed by dimensional oxidation back to $d=4$.",1711.09110v1
2018-03-21,Large anomalous Nernst coefficient in an oxide Skyrmion crystal Chern insulator,"A sizable transverse thermoelectric coefficient N , large to the extent that
it potentially serves applications, is predicted to arise, by means of
first-principles calculations, in a Skyrmion crystal assumed on EuO monolayer
where carrier electrons are introduced upon a quantum anomalous Hall insulating
phase of Chern number C = 2. This encourages future experiments to pursue such
an effect.",1803.08148v2
2018-03-28,Complementary metal-oxide semiconductor compatible source of single photons at near-visible wavelengths,"We demonstrate on chip generation of correlated pairs of photons in the
near-visible spectrum using a CMOS compatible PECVD Silicon Nitride photonic
device. Photons are generated via spontaneous four wave mixing enhanced by a
ring resonator with high quality Q-factor of 320,000 resulting in a generation
rate of 950,000 $\frac{pairs}{mW}$. The high brightness of this source offers
the opportunity to expand photonic quantum technologies over a broad wavelength
range and provides a path to develop fully integrated quantum chips working at
room temperature.",1803.10484v1
2018-06-27,Ultrananocrystalline Diamond Film: Tribological Studies Against Metal and Ceramic Balls,"In this present work, friction and wear behavior of UNCD thin film has been
studied against three different sliding counterbodies i.e. Al2O3, SiC and steel
balls. UNCD/steel sliding pair showed high friction coefficient in the
beginning of the sliding process which decreased to the lower value after
longer sliding passes. This behavior might be explained by oxidation mechanism.
However, high friction value was observed in the case of UNCD/SiC and this was
attributed to strong adhesive force acting across the sliding interfaces.
Stable and low friction value was measured in UNCD/Al2O3 sliding combination.
This was governed by chemically inert interfaces and graphite tribolayer
formation.",1806.10302v1
2018-07-16,Interactions between Rydberg excitons in Cu$_2$O,"Highly-excited states of excitons in cuprous oxide have recently been
observed at a record quantum number of up to $n=25$. Here, we evaluate the
long-range interactions between pairs of Rydberg excitons in Cu$_2$O, which are
due to direct Coulomb forces rather than short-range collisions typically
considered for ground state excitons. A full numerical analysis is supplemented
by the van der Waals asymptotics at large exciton separations, including the
angular dependence of the potential surfaces.",1807.05896v1
2018-07-20,Atmosphere Pressure Chemical Vapor Deposition of Graphene,"Recently, graphene is of highly interest owing to its outstanding
conductivity, mechanical strength, thermal stability, etc. Among various
graphene synthesis methods, atmosphere pressure chemical vapor deposition
(APCVD) is one of the best synthesis one due to very low diffusitivity
coefficient and a critical step for graphene-based device fabrication.
High-temperature APCVD processes for thin film productions are being recognized
in many diversity technologies such as solid-state electronic devices, in
particular, high quality epitaxial semiconductor films for silicon bipolar and
metal oxide semiconductor (MOS) transistors. Graphene-based devices exhibit
high potential for applications in flexible electronics, optoelectronics, and
energy harvesting. In this chapter, recent advances of APCVD-based graphene
synthesis and their related applications will be addressed.",1807.07774v1
2018-08-05,Role of Doping Ratio on The Sensing Properties of ZnO:SnO2 Thin Films,"Thin films of ZnO:SnO2 were deposited on different substrates like glass and
c-Si using spray pyrolysis method .The structures and morphology of the
prepared samples films were cheeked using X-ray diffraction and atomic force
microscope. Gas sensing measurements provided from resistance measurement in
the absent and exposure to NO2 gas . The results showed that good enhancement
of sensitivity take place after doping with tin oxide. Maximum sensitivity
obtained at 9% doping ratio and operating temperature 200oC.",1808.04235v1
2018-08-14,High-Pressure Elasticity Tensor from Thermal Diffuse Scattering,"We report on the determination of high-pressure elasticity from thermal
diffuse x-ray scattering of magnesium oxide at pressures up to 28 GPa. We find
that the full elasticity tensor as a function of pressure can be extracted from
x-ray scattering of single crystals. This enables the simultaneous measurement
of elasticity and crystal structure from a single experiment and thus marks a
decisive step towards establishing reliable calibration for extreme pressures.
Elastic constants can be extracted with this method from small crystals of
arbitrary symmetry, shape and optical properties and will allow for significant
progress in our understanding of the elastic behaviour of planets interior at
geophysically relevant conditions, structural phase transitions and fundamental
interactions of phonons with other quasi-particles.",1808.04595v1
2018-08-14,"Short commentary on comparing previous claim of RT superconductivity with the data of arXiv:1807.08572, ""Evidence for Superconductivity at Ambient Temperature and Pressure in Nanostructures""","I briefly mention a previous claim of room temperature superconductivity (
arXiv:0905.3524) in Ag-based oxide material and compare their results with the
most recent claim of ambient temperature superconductivity in arXiv:1807.08572.
In both cases, an electrical transition to low resistance state and
diamagnetism are observed. Silver is a common ingredient in both claims. Does
it mean that silver holds the key to RT superconductivity or, the missing field
cool data (in both reports) hint of some other physical phenomenon than
superconductivity.",1808.04912v1
2018-08-20,Production of Metal-free Diamond Nanoparticles,"In this paper, the controlled production of high quality metal-free diamond
nanoparticles is demonstrated. Milling with tempered steel is shown to leave
behind iron oxide contamination which is difficult to remove. Milling with SiN
alleviates this issue but generates more non diamond carbon. Thus the choice of
milling materials is critically determined by the acceptable contaminants in
the ultimate application. The removal of metal impurities, present in all
commercially available nanoparticles, will open new possibilities towards the
production of customised diamond nanoparticles, covering the most demanding
quantum applications.",1808.06425v1
2018-12-13,Measuring thickness in thin NbN films for superconducting devices,"We present the use of a commercially available fixed-angle multi-wavelength
ellipsometer for quickly measuring the thickness of NbN thin films for the
fabrication and performance improvement of superconducting nanowire single
photon detectors. The process can determine the optical constants of absorbing
thin films, removing the need for inaccurate approximations. The tool can be
used to observe oxidation growth and allows thickness measurements to be
integrated into the characterization of various fabrication processes.",1812.05559v3
2018-12-20,"Layer-by-layer resistive switching: multi-state functionality due to electric-field-induced healing of ""dead"" layers","Materials exhibiting reversible resistive switching in electrical fields are
highly demanded for functional elements in oxide electronics. In particular,
multilevel switching effects allow for advanced applications like neuromorphic
circuits. Here we report on a structurally driven switching mechanism involving
the so-called `dead layers' of perovskite manganite surfaces. Forming a tunnel
barrier whose thickness can be changed in monolayer steps by electrical fields,
the switching effect exhibits well-defined and robust resistive states.",1812.08563v1
2018-12-26,Spin-valve Effect in Nanoscale Si-based Devices,"The silicon (Si) based spin-MOSFET (metal-oxide semiconductor field-effect
transistor) is considered to be the building block of low-power-consumption
electronics, utilizing spin-degrees of freedom in semiconductor devices. In
this paper, we review the latest results on the spin transport in nanoscale
Si-based spin-valve devices, which is important to realize the nanoscale
spin-MOSFET. Our results demonstrate the importance of ballistic transport in
obtaining high spin-dependent output voltage in nanoscale Si spin-valve
devices.",1812.10210v1
2019-01-25,Translation-Rotation Coupling in the Dynamics of Linear Molecules in Water,"We study by computer simulations the coupled rotational and translational
dynamics of three important linear diatomic molecules, namely, carbon monoxide
(CO), nitric oxide (NO) and cyanide ion (CN-) in water. Translational diffusion
of these molecules is found to be strongly coupled to their own rotational
dynamics which in turn are coupled to similar motions of surrounding water. We
examined the validity of hydrodynamic predictions and found them to be largely
insufficient, particularly for rotational diffusion. A mode coupling theory
approach is developed and applied to understand the complexity of
translation-rotation coupling.",1901.08852v1
2019-02-19,Topological quantisation and gauge invariance of charge transport in liquid insulators,"According to the Green-Kubo theory of linear response, the conductivity of an
electronically gapped liquid can be expressed in terms of the time correlations
of the adiabatic charge flux, which is determined by the atomic velocities and
Born effective charges. We show that topological quantisation of adiabatic
charge transport and gauge invariance of transport coefficients allow one to
rigorously express the electrical conductivity of an insulating fluid in terms
of integer-valued, scalar, and time-independent atomic oxidation numbers,
instead of real-valued, tensor, and time-dependent Born charges.",1902.07256v3
2019-02-23,Optical Properties of Nanoporous Al2O3 Matrices with Ammonium Dihydrogen Phosphate Crystals in Nanopores,"In this paper, the technology of growing ammonium dihydrogen phosphate (ADP)
crystals in pores of nanoporous aluminum oxide (Al2O3) matrices was presented.
On the grown nanocomposites, the optical properties of such structures were
studied. In particular, the direct and diffuse optical transmission, as well as
specular reflection of Al2O3 matrices with ADP crystals grown in nanopores,
were analyzed. From the performed experimental studies, it can be concluded
that the transmission and scattering of pure Al2O3 porous matrices and with ADP
crystals in nanopores depends largely on the properties of the Al2O3 matrices
and the technology of their production.",1902.08829v1
2019-03-08,Ti surface modification for biomedical applications,"Micro Arc Oxidation (MAO) is an electrochemical approach for the surface
treatment usually applied on so called valve metals such as Al, Mg and Ti. MAO
is usually carried out an aqueous electrolyte, which involves a bath cooling
and leads to the creation of surface contained components originated in the
electrolyte. In current work, we applied a different approach of ceramic
surface formation on Ti alloy used in biomedical applications. Here, MAO
process conducted in molten nitrate salt at 280 deg C. The developed surface
morphology, chemical and phase composition, and corrosion resistance were
investigated and described in the work.",1903.03507v1
2019-04-09,MOSFET GIDL Current Variation with Impurity Doping Concentration A Novel Theoretical Approach,"This paper depicts the actual variation of gate induced drain leakage current
with impurity doping concentration by complete qualitative and quantitative
approach. De Casteljaus algorithm is applied to describe the band to band
tunneling in a thin gate oxide nMOSFET and the results are remarkably matched.
Moreover for the very first time, the dependency of the leakage current over
impurity density in the MOSFET drain region is explained in the context of pure
geometrical approach. Surprisingly one of the proportionality constant exactly
behaves like impurity gradient which results same characteristics as MOSFET
Drain impurity doping profile measured using 2D simulator.",1904.04827v1
2019-12-12,Anomalous thermal fluctuation distribution sustains proto-metabolic cycles and biomolecule synthesis,"An environment far from equilibrium is thought to be a necessary condition
for the origin and persistence of life. In this context we report open-flow
simulations of a non-enzymic proto-metabolic system, in which hydrogen peroxide
acts both as oxidant and driver of thermochemical cycling. We find that a
Gaussian perturbed input produces a non-Boltzmann output fluctuation
distribution around the mean oscillation maximum. Our main result is that net
biosynthesis can occur under fluctuating cyclical but not steady drive.
Consequently we may revise the necessary condition to ""dynamically far from
equilibrium"".",1912.05781v1
2020-05-04,Using local GND density to study SCC initiation,"In this work, strain and geometric necessary dislocations (GNDs) have been
mapped with nm-resolution around grain boundaries affected by stress corrosion
cracking (SCC) or intergranular oxidation with the aim of clarifying which
local conditions trigger SCC initiation.",2005.01769v2
2020-07-03,Complexity matters: highly-accurate numerical models of coupled radiative-conductive heat transfer in a laser flash experiment,"Thermal diffusivity measurements of samples transmitting thermal radiation
require adjustments to the data treatment procedures in laser flash analysis.
Conventionally, an unconstrained diathermic model is used. Current results show
that the alternative coupled radiative-conductive models produce substantially
different results -- for instance, at high temperatures in oxide ceramics.
However, care must be taken to ensure accurate implementations of each
constituent computational technique. The latter are presented in this work.",2008.04079v1
2020-09-18,Slow decay processes of electrostatically trapped Rydberg NO molecules,"Nitric oxide (NO) molecules initially traveling at 795 m/s in pulsed
supersonic beams have been photoexcited to long-lived hydrogenic Rydberg-Stark
states, decelerated and electrostatically trapped in a cryogenically cooled,
chip-based transmission-line Rydberg-Stark decelerator. The decelerated and
trapped molecules were detected $in$ $situ$ by pulsed electric field
ionization. The operation of the decelerator was validated by comparison of the
experimental data with the results of numerical calculations of particle
trajectories. Studies of the decay of the trapped molecules on timescales up to
1 ms provide new insights into the lifetimes of, and effects of blackbody
radiation on, Rydberg states of NO.",2009.08877v1
2020-09-26,Suppressing The Ferroelectric Switching Barrier in Hybrid Improper Ferroelectrics,"Integration of ferroelectric materials into novel technological applications
requires low coercive field materials, and consequently, design strategies to
reduce the ferroelectric switching barriers. In this first principles study, we
show that biaxial strain, which has a strong effect on the ferroelectric ground
states, can also be used to tune the switching barrier of hybrid improper
ferroelectric Ruddlesden-Popper oxides. We identify the region of the strain --
tolerance factor phase diagram where this intrinsic barrier is suppressed, and
show that it can be explained in relation to strain induced phase transitions
to nonpolar phases.",2009.12486v1
2020-10-11,2D Surface Phase Diagram of a Multicomponent Perovskite Oxide: La$_{0.8}$Sr$_{0.2}$MnO$_3$(110),"The many surface reconstructions of (110)-oriented lanthanum--strontium
manganite (La$_{0.8}$Sr$_{0.2}$MnO$_3$, LSMO) were followed as a function of
the oxygen chemical potential ($\mu_\text{O}$) and the surface cation
composition. Decreasing $\mu_\text{O}$ causes Mn to migrate across the surface,
enforcing phase separation into A-site-rich areas and a variety of
composition-related, structurally diverse B-site-rich reconstructions. The
composition of these phase-separated structures was quantified with scanning
tunneling microscopy (STM), and these results were used to build a 2D phase
diagram of the LSMO(110) equilibrium surface structures.",2010.05205v1
2020-10-12,Optical and electronic properties in amorphous BaSnO3 thin films,"Wide-bandgap perovskite stannates are of interest for the emergent all-oxide
transparent electronic devices due to their unparalleled room temperature
electron mobility. Considering the advantage of amorphous material in
integrating with non-semiconductor platforms, we herein reported the optical
and electronic properties in the prototypical stannate, amorphous barium
stannate (BaSnO3) thin films, which were deposited at room temperature and
annealed at various temperatures. Despite remaining amorphous status, with
increasing the annealing temperature, the defect level within amorphous BaSnO3
thin films could be suppressed.",2010.05580v1
2020-10-24,Large spin Hall effect in 5d-transition metal anti-perovskites,"The spin Hall effect (SHE) is highly promising for spintronic applications,
and the design of materials with large SHE can enable ultra-low power memory
technology. Recently, 5d-transition metal oxides have been shown to demonstrate
a large SHE. Here we report large values of SHE in four 5d-transition metal
anti-perovskites which makes these anti-perovskites promising spintronic
materials. We demonstrate that these effects originate in the mixing of dx2-y2
and dxy orbitals caused by spin orbit coupling.",2010.12942v1
2021-02-10,Electromechanical dopant defect interaction in acceptor doped ceria,"Oxygen defective cerium oxides exhibits a non classical giant
electromechanical response that is superior to lead based electrostrictors. In
this work, we report the key role of acceptor dopants, with different size and
valence Mg2+, Sc3+, Gd3+, and La3+, on polycrystalline bulk ceria. Different
dopants tune the electrostrictive properties by changing the electrosteric
dopant defect interactions. We find two distinct electromechanical behaviors
when the interaction is weak dopant vacancy binding energy 0.3 eV,
electrostriction displays high coefficient, up to 10-17 m2V-2, with strongly
time dependent effects. In contrast, we observe no time dependent effects when
the interaction becomes strong 0.6 eV.",2102.05635v1
2021-02-28,Observation of soft X-ray Cherenkov radiation in Be and Si foils,"Currently, most of the Cherenkov phenomenon researches for the X-ray region
are theoretical studies; there are only a few experiments in this area. Here
the new experimental results on observation of X-ray Cherenkov radiation
generated by 5.7 MeV electrons in the thin Be and Si foils are presented. The
Cherenkov effect from Be was observed for the first time. The experimental
results are compared with the calculations performed according to the
theoretical model of transition radiation taking into account the oxide layer
on the target output surface.",2103.00579v4
2021-03-09,Engineering the light coupling between metalens and photonic crystal resonators for robust on-chip microsystems,"We designed an on-chip transformative optic system of a metalens-photonic
crystal resonator metasystem on a foundry compatible silicon photonic platform.
By adjusting the on-chip metalens' focusing length and mode dimension, the
insertion loss between the metalens and the photonic crystal resonator and
waveguide structures are minimized through mode-matching. The micro-system does
not involve any single mode silicon nanowire waveguide, and thus mechanically
robust without any oxide claddings. The proposed microsystem is ideal for
miniaturized chemical and biosensors operating in air or solution environment.",2103.05580v1
2021-03-15,Canadian Contributions to the Manhattan Project and Early Nuclear Research,"During the second world war, Canada made several important contributions to
the wartime work of the Manhattan Project. The three main contributions were:
establishing a domestic nuclear research laboratory in Montreal to investigate
heavy water reactors, creating supply chains to provide uranium oxide, heavy
water and polonium to the Manhattan Project, and the direct contributions of
several Canadians living the United States. These wartime efforts helped
establish a legacy of nuclear research in Canada which has persisted to the
present day.",2103.08582v1
2021-03-25,Microsphere-coupled light emission control of van der Waals heterostructures,"Two-dimensional transition metal dichalcogenides (TMDCs) integrated to
photonic structures provide an intriguing playground for the development of
novel optoelectronic devices with improved performance. Here, we show the
enhanced light emission from TMDC based van der Waals heterostructures through
coupling with microsphere cavities. We observe cavity-induced emission
enhancement of TMDC materials which varies by an order of magnitude, depending
on the size of the microsphere and thickness of the supporting oxide substrate.
Furthermore, we demonstrate microsphere cavity-enhanced electroluminescence of
van der Waals light emitting transistor, showing the potential of 2D material
based hybrid optoelectronic structures.",2103.13635v1
2021-04-09,The rise of Single-Atom Catalysts,"In recent years, single-atom catalysts attracted lots of attention because of
their high catalytic activity, selectivity, stability, maximum atom
utilization, exceptional performance, and low cost. Single-atom catalyst
contains isolated individual atom which are coordinated with the surface atoms
of support such as a metal oxide or 2d - materials. In this review article, we
present the advancement in single-atom catalysis in recent years with a focus
on the various synthesis methods and their application in catalytic reactions.
We also demonstrate the reaction mechanism of a single-atom catalyst for
different catalytic reactions from theoretical aspects using density functional
theory.",2104.04370v3
2021-04-14,"Oxygen hole content, charge-transfer gap, covalency, and cuprate superconductivity","Experiments have shown that the families of cuprate superconductors that have
the largest transition temperature at optimal doping also have the largest
oxygen hole content at that doping. They have also shown that a large
charge-transfer gap, a quantity accessible in the normal state, is detrimental
to superconductivity. We solve the three-band Hubbard model with cellular
dynamical mean-field theory and show that both of these observations follow
from the model. Cuprates play a special role amongst doped charge-transfer
insulators of transition metal oxides because copper has the largest covalent
bonding with oxygen.",2104.07087v1
2021-06-10,Enhanced pairing mechanism in Cuprate-type crystals,"Using a BCS mean-field approach, we show how the interplay between
low-momentum optical phonons and Jahn-Teller-type lattice distortions can open
an attractive channel that allows the formation of pairs with the corresponding
density exhibiting characteristic features of a pair-density wave (PDW). We
demonstrate this numerically on a copper-oxide type lattice.",2106.05567v2
2021-06-16,Optical Direct Write of Dolan--Niemeyer-Bridge Junctions for Transmon Qubits,"We characterize highly coherent transmon qubits fabricated with a
direct-write photolithography system. Multi-layer evaporation and oxidation
allows us to change the critical current density by reducing the effective
tunneling area and increasing the barrier thickness. Surface treatments before
resist application and again before evaporation result in high coherence
devices. With optimized surface treatments we achieve energy relaxation $T_1$
times in excess of $80\ \mu$s for three dimensional transmon qubits with
Josephson junction lithographic areas of 2 $\mu\mathrm{m}^2$.",2106.09034v2
2021-07-05,Ferroelectric Tunneling Junctions for Edge Computing,"Ferroelectric tunneling junctions (FTJ) are considered to be the
intrinsically most energy efficient memristors. In this work, specific
electrical features of ferroelectric hafnium-zirconium oxide based FTJ devices
are investigated. Moreover, the impact on the design of FTJ-based circuits for
edge computing applications is discussed by means of two example circuits.",2107.01853v1
2021-08-08,Threshold switching in solar cells and a no-scribe photovoltaic technology,"We show that thin film CdTe solar cells exhibit the phenomenon of threshold
switching similar to that in phase change and resistive memory. It creates a
conductive filament (shunt) through the solar cell reaching the buried
electrode, such as the transparent conductive oxide (TCO) in CdTe based
photovoltaics (PV). While in the existing PV the buried electrode was routinely
contacted via laser scribe filled metals, our work paves a way to an
alternative technology of no-scribe PV.",2108.03756v3
2021-08-26,Ferroptosis as a Biological Phase Transition I: avascular and vascular tumor growth,"Herewith we discuss a network model of the ferroptosis avascular and vascular
tumor growth based on our previous proposed framework. Chiefly, ferroptosis
should be viewed as a first order phase transition characterized by a
supercritical Andronov Hopf bifurcation, with the emergence of limit cycle. The
increase of the population of the oxidized PUFA fragments, take as the control
parameter, involves an inverse Feigenbaum, (a cascade of saddle foci
Shilnikov's bifurcations) scenario, which results in the stabilization of the
dynamics and in a decrease of complexity.",2109.02476v1
2021-09-27,Orbital entanglement mechanism of superconductivity in cuprates,"We utilize a 1d Hubbard model to show that the superconductivity in cuprate
superconductors likely arises due to the orbital entanglement between holes in
the copper oxide plane mediated by orbitally-selective charge hopping. The main
role of doping required to achieve superconductivity in cuprates is to suppress
the Mott correlations and orbital ordering. The proposed mechanism explains
superconductivity in other unconventional superconductors, and provides
guidance in the search for new high-temperature superconductors.",2109.13019v3
2021-10-15,Fabrication of Fiber-Reinforced Polymer Ceramic Composites by Wet Electrospinning,"We propose a novel approach of wet electrospinning to yield fiber-reinforced
polymer ceramic composites, where a reactive ceramic precursor gel is used as a
collector. We illustrate our approach by generating polyethylene oxide (PEO)
fibers in a potassium silicate gel; the gel is later activated using metakaolin
to yield a ceramic-0.5 wt% PEO fiber composite. An increase of 29% and 22% is
recorded for the fabricated polymer ceramic composites in terms of indentation
modulus and indentation hardness respectively. Our initial findings demonstrate
the process viability and might lead to a potentially scalable manufacturing
approach for fiber-reinforced polymer ceramic composites.",2110.08204v1
2021-10-27,Ferroelectric control of spin-polarized two-dimensional electron gas,"Spin-polarized two-dimensional electron gas (2DEG) at oxide interfaces is an
emerging physical phenomenon, which is technologically important for potential
device applications. However, most previous relevant studies only focused on
the creation and characterization of the spin-polarized 2DEG. To push forward
the device applications, the control of spin-polarized 2DEG by electric field
is an important step. Here, a model system based on antiferromagnetic and
ferroelectric perovskites, i.e., YTiO3/PbTiO3 superlattice, is designed to
manipulate the spin-polarized 2DEG. By switching the direction of polarization,
the spin-polarized 2DEG can be effectively tuned for both symmetric interfaces
and asymmetric polar interfaces.",2110.14304v1
2021-11-16,A Machine Learning Model for Predicting Progressive Crack Extension based on DCPD Fatigue Data,"Time history data collected from a Direct Current Potential Drop (DCPD)
fatigue experiment at a range of temperatures was used to train a Bidirectional
Long-Short Term Memory Neural Network (BiLSTM) model. The model was trained on
high sampling rate experimental data from crack initiation up through the Paris
regime. The BiLSTM model was able to predict the progressive crack extension at
intermediate temperatures and stress intensities. The model was able to
reproduce crack jumps and overall crack progression. The BiLSTM model
demonstrated the potential to be used as a tool for future investigation into
fundamental mechanisms such as high-temperature oxidation and new damage
models.",2111.08841v1
2021-12-09,Projection population analysis for molecules with heavy and superheavy atoms,"A new iterative version of population projection analysis is formulated and
applied to determine relativistic effective atomic configurations of superheavy
elements Cn and Fl and their lighter homologues (Hg and Pb) in the molecules of
their fluorides and oxides. The dependence of the computed populations on the
initial reference atomic spinors is completely avoided. The difference in
population of atomic spinors with the same orbital angular momentum and
different total angular momenta is demonstrated to be essential for
understanding the peculiarities of chemical bonding in superheavy element
compounds.",2112.05187v1
2022-01-14,Two-dimensional electron gas at LaInO$_3$/BaSnO$_3$ interfaces controlled by a ferroelectric layer,"With the example of LaInO$_{3}$/BaSnO$_3$, we demonstrate how both density
and distribution of a two-dimensional electron gas (2DEG) formed at the
interface between these perovskite oxides, can be efficiently controlled by a
ferroelectric functional material. A polarization induced in a BaTiO$_3$ layer
pointing toward the interface enhances the polar discontinuity which, in turn,
significantly increases the 2DEG density and confinement, while, the opposite
polarization depletes the 2DEG. Our predictions and analysis, based on
first-principles calculations, can serve as a guide for designing such material
combinations to be used in electronic devices.",2201.05449v1
2022-02-24,Line-field Coherent Sensing with LED Illumination,"We describe a method of low-coherence interferometry based optical
profilometry using standard light-emitting diode (LED) illumination and
complementary metal-oxide-semiconductor (CMOS) image sensors. A line-field
illumination strategy allows for the simultaneous measurement of many points in
space. Micron scale accuracy and resolution are achieved and demonstrated using
a variety of targets.",2202.12161v1
2022-03-15,High Rate and High Precision Timing and Calorimeter Detectors,"High precision timing, high rate calorimeters, and radiation resistance are
becoming an important issue in particle physics especially in Energy and
Intensity Frontiers. We discuss doped Zinc Oxide (ZnO:Ga or GZO; ZnO:X where X
is Al, Cu or others) as a very fast scintillator and wavelength shifter (WLS),
Total internal reflection films, and PMT capable of counting at 300 MHz with 10
ps timing precision, with superior radiation resistance.",2203.09942v1
2022-06-13,Stability of subnanometer MoS wires under realistic environment,"We carried out first-principles density functional theory calculations of
hydrogen and oxygen adsorption and diffusion on subnanometer MoS nanowires. The
nanowires are robust against adsorption of hydrogen. On the other hand,
interaction with oxygen shows that the nanowires can oxidize with a small
barrier. Our results open the path for understanding the behavior of MoS
nanowires under realistic environment.",2206.06342v1
2022-06-23,Negatively Charged Muonium and Related Centers in Solids,"Muonium (Mu) centers formed upon implantation of $\mu^+$ in a solid have long
been investigated as an experimentally accessible model of isolated hydrogen
impurities. Recent discoveries of hydridic centers formed at oxygen vacancies
have stimulated a renewed interest in H$^-$ and corresponding Mu$^-$ centers in
oxides. However, the two diamagnetic centers, Mu$^+$ and Mu$^-$, are difficult
to separate spectroscopically. In this review article, we summarize established
and developing methodologies for identifying Mu$^-$ centers in solids, and
review recent Mu studies on said centers supposedly formed in mayenite,
oxygen-deficient SrTiO$_{3-x}$, and BaTiO$_{3-x}$H$_x$ oxyhydride.",2206.11478v1
2022-06-23,Metallic delafossite thin films for unique device applications,"Metallic delafossites (ABO2) are layered oxides with quasi-two dimensional
conduction layers. Metallic delafossites are among the most conducting
materials with the in-plane conductivity comparable with that of elemental
metals. In this perspective, we will discuss basic properties and future
research prospects of metallic delafossites, mainly focusing on thin films and
heterostructures. We exemplify the fascinating properties of these compounds
such as high conductivity and surface polarity and discuss how it can be
utilized in thin films and heterostructures.",2206.11482v1
2022-07-27,Deposition of the stoichiometric coatings by reactive magnetron sputtering,"The investigations of the reactive magnetron depositing of the stoichiometric
coatings metal-metalloid were done. The dependences between sputtering
parameters of a target and processes of plasmochemical formation on the surface
of sample metal-metalloid and formations of coatings of the appropriate
structure were investigated. Experimental data on stoichiometric coatings AlN,
Al2O3, TiN, TiO2 is given. Features of reactive magnetron deposition and
investigation results for obtaining of coatings with pregiven properties in
particular for providing stability and controllability of coating deposition
processes in time. Keywords: reactive magnetron sputtering, coatings, oxide,
nitride compositions.",2207.13323v1
2022-08-15,Copper plasmonics with excitons,"We investigate the propagation of surface plasmons (SPPs) in a thin layer of
copper surrounded by copper oxide Cu$_2$O. It is shown that particularly strong
excitons in Cu$_2$O can have considerable impact on plasmon propagation,
providing many opportunities for plasmon-exciton and plasmon-plasmon
interactions. It is demonstrated that by the use of sufficiently thin metal
layer, one can excite the so-called long range plasmons (LRSPPs) which can
overcome the inherently high ohmic losses of Cu as compared to usual plasmonic
metals such as silver. Analytical results are confirmed by numerical
calculations.",2208.07184v1
2022-12-27,Study on the hydrogen behavior in Y and Co doped barium-zirconate,"Hydrogen release behavior from mixed-perovskite oxide, yttrium and cobalt
doped barium-zirconate, BaZr$_{0.955}$Y$_{0.03}$Co$_{0.015}$O$_{3-a}$ (BZYC)
exposed to D$_2$ or D$_2$O atmosphere was studied by thermal desorption
spectroscopy (TDS) detecting deuterium gas (D$_2$) and heavy water vapor
(D$_2$O) separately. The release of hydrogen appeared at around 1000 K.
Hydrogen solubility was higher in the BZYC sample exposed to the D$_2$O.",2301.02522v1
2023-01-09,Edges fractal approach in graphene -- Defects density gain,"Edges fractal approach in graphene e Defects density gain a b s t r a c t To
optimize the technological development together with energy gain, the crucial
materials needs to be tailored in a smart way to benefit a maximum from the
property-structure relation. Herein we propose the way to increase a defect
density in graphene moving from 1D linear edges to fractal edges, also
highlight the fractal nature of graphene structures them-self. The tentative
oxidation and hydrogenation catalytic etching of few layer graphene results in
structures with edges fractals, jaggy edges at graphene periphery or in newly
formed etched holes.",2301.03449v1
2023-01-27,"DFT, L(S)DA, LDA+U, LDA+DMFT..., whether we do approach to a proper description of optical response for strongly correlated systems?","I present a critical overview of so-called ""{\it ab initio}"" DFT (density
fuctional theory) based calculation schemes for the description of the
electronic structure, energy spectrum, and optical response for strongly
correlated 3$d$ oxides, in particular, crystal-field and charge transfer
transitions as compared with an ""old""\, cluster model that does generalize
crystal-field and ligand-field theory. As a most instructive illustration of
validity of numerous calculation techniques I address the prototypical 3$d$
insulator NiO predicted to be a metal in frames of a standard LDA (local
density approximation) band theory.",2301.11979v1
2023-02-10,A short note on the SIMS characterisation of ZnO/Si(100) interface,"The ZnO films, 25 nm thick were deposited by e-beam evaporation of ZnO
(99.9%) pellets onto native oxide covered silicon (100) substrates. Details of
the interface chemical composition and the chemical depth profile have been
deduced as follows: Adsorbed OH surface/OH: ZnO Interface/Pure ZnO thin
film/ZnO:H: Si Interface/H:SiO2/SiO2/Si(100). The physical profile of the
crater formed by the SIMS depth profiling was measured with a Tencor P-2
profilometer as depth profiling showed uniform ion milling and good consistency
with film thickness (25 nm) measured by SIMS depth profile (25.4 nm).",2302.05306v1
2023-02-28,A Multimode Hybrid Memristor-CMOS Prototyping Platform Supporting Digital and Analog Projects,"We present an integrated circuit fabricated in a process co-integrating CMOS
and hafnium-oxide memristor technology, which provides a prototyping platform
for projects involving memristors. Our circuit includes the periphery circuitry
for using memristors within digital circuits, as well as an analog mode with
direct access to memristors. The platform allows optimizing the conditions for
reading and writing memristors, as well as developing and testing innovative
memristor-based neuromorphic concepts.",2302.14577v1
2023-04-17,"Atomistic Wear Mechanisms in Diamond: Effects of Surface Orientation, Stress, and Interaction with Adsorbed Molecules","Despite its unrivaled hardness, diamond can be severely worn during the
interaction with others, even softer materials. In this work, we calculate from
first-principles the energy and forces necessary to induce the atomistic wear
of diamond, and compare them for different surface orientations and passivation
by oxygen, hydrogen, and water fragments. The primary mechanism of wear is
identified as the detachment of carbon chains. This is particularly true for
oxidized diamond and diamond interacting with silica. A very interesting result
concerns the role of stress, which reveals that compressive stresses can highly
favor wear, making it even energetically favorable.",2304.08207v1
2023-04-28,Machine learning-assisted close-set X-ray diffraction phase identification of transition metals,"Machine learning has been applied to the problem of X-ray diffraction phase
prediction with promising results. In this paper, we describe a method for
using machine learning to predict crystal structure phases from X-ray
diffraction data of transition metals and their oxides. We evaluate the
performance of our method and compare the variety of its settings. Our results
demonstrate that the proposed machine learning framework achieves competitive
performance. This demonstrates the potential for machine learning to
significantly impact the field of X-ray diffraction and crystal structure
determination. Open-source implementation:
https://github.com/maxnygma/NeuralXRD.",2305.15410v1
2023-08-11,Two-dimensional dynamic beam steering by Tamm plasmon polariton,"The dynamic steering of a beam reflected from a photonic structure supporting
Tamm plasmon polariton is demonstrated. The phase and amplitude of the
reflected wave are adjusted by modulating the refractive index of a transparent
conductive oxide layer by applying a bias voltage. It is shown that the
proposed design allows for two-dimensional beam steering by deflecting the
light beam along the polar and azimuthal angles.",2308.05910v1
2023-09-19,Vortex-core spectroscopy of $d$-wave cuprate high-temperature superconductors,"The mechanism of high-temperature superconductivity remains one of the great
challenges of contemporary physics. Here, we review efforts to image the vortex
lattice in copper oxide-based high-temperature superconductors and to measure
the characteristic electronic structure of the vortex core of a $d$-wave
superconductor using scanning tunneling spectroscopy.",2309.10446v1
2023-10-16,"1,1-Diphenyl-2-picrylhydrazyl and superoxide anion radical scavenging 1 activities of heterocyclic 2-oxo-1,2,3,4-tetrahydropyrimidines","To investigate1,1-Diphenyl-2-picrylhydrazyl (DPPH) and superoxide radical
(SOR) 17 scavenging activities of 2-oxo-1,2,3,4-tetrahydropyrimidines
derivatives. Free radicals are 18 highly unstable and reactive molecules/atoms.
In the body, free radicals form during 19 normal and abnormal metabolism in the
body and cause serious damage to other 20 biomolecules through generating
oxidative stress (OS). If free radicals induced OS does 21 not neutralized
properly, host multiple pathologies including several types of cancers.",2310.10063v1
2023-11-10,Revisiting the metal-to-metal transition in $2H$-AgNiO$_2$,"The layered delafossite compound AgNiO$_2$ with $2H$ stacking symmetry
undergoes a structural metal-to-metal transition at $T_{\rm S}\sim 365$ K. It
has been described in the past as a charge-ordering transition, where local
$S=1$ spins are formed on part of the Ni sites. By means of first-principles
many body calculations, we show that the transition is in fact a site-selective
Mott transition on the Ni sublattice with only minor charge differentiation.
Key to this finding is the uncovering of ligand-hole physics, rendering a
Ni$^{2+}$ instead of a formal Ni$^{3+}$ oxidation state, in conjunction with
strong local Coulomb repulsions.",2311.06053v1
2023-12-10,Optimum Design of GaAs/AlGaAs Surface-Relief VCSELs with Single-Mode Operation at 808 nm,"This paper reports an opto-electro-thermal analysis of VCSEL structures with
a surface-relief filter and different aperture diameters. 808-nm GaAs/AlGaAs
VCSELs with different aperture diameters and different surface-relief filter
diameters are studied and the LI curves, the optical spectra, and the
temperature peaks of the devices are obtained. Also, the impact of utilizing
different oxide apertures on the temperature peak is shown. The effect of the
surface-relief filter diameter on VCSEL's performance is also investigated and
the optimal filter diameter is obtained for maintaining single-mode operation
while producing as much output power as possible.",2312.07569v1
2023-12-22,Nanoscale X-ray imaging with high spectral sensitivity using fluorescence intensity correlations,"This paper introduces Spectral Incoherent Diffractive Imaging (SIDI) as a
novel method for achieving dark-field imaging of nanostructures with
heterogeneous oxidation states. With SIDI, shifts in photoemission profiles can
be spatially resolved, enabling the independent imaging of the underlying
emitter distributions contributing to each spectral line. In the X-ray domain,
this approach offers unique insights beyond the conventional combination of
diffraction and X-ray Emission Spectroscopy (XES). When applied at X-ray
Free-Electron Lasers (XFELs), SIDI promises to be a versatile tool for
investigating a broad range of systems, offering unprecedented opportunities
for detailed characterization of heterogeneous nanostructures for catalysis and
energy storage, including of their ultrafast dynamics.",2312.14602v1
2023-12-30,Ultrafast X-ray Diffraction Probe of Coherent Spin-state Dynamics in Molecules,"We propose an approach to probe coherent spin-state dynamics of molecules
using circularly polarized hard x-ray pulses. For the dynamically aligned
nitric oxide molecules in a coherent superposition spin-orbit coupled
electronic state that can be prepared through stimulated Raman scattering, we
demonstrate the capability of ultrafast x-ray diffraction to not only reveal
the quantum beating of the coherent spin-state wave packet, but also image the
spatial spin density of the molecule. With circularly polarized ultrafast x-ray
diffraction signal, we show that the electronic density matrix can be
retrieved. The spatio-temporal resolving power of ultrafast x-ray diffraction
paves the way for tracking transient spatial wave function in molecular
dynamics involving spin degree of freedom.",2401.00259v1
2024-02-27,Strong Correlations at Oxide Interfaces: What is Hidden in a Plane View?,"A prime goal for this lecture is to provide a reader with a reasonably
self-sufficient answer to the question of what interesting effects can happen
if you join two dissimilar materials with correlated carriers to construct a
sandwich with the interface across those layers. Through the lens of physical
phenomena, we will delve into the design ideas that lead to the creation of new
synthetic quantum materials with properties primarily governed by the
interface.",2403.00015v1
2024-03-10,Self-heating effect in nanoscale SOI Junctionless FinFET with different geometries,"In this work we study the self-heating (1) effect (SHE) in nanoscale Silicon
on Insulator Junctionless (SOI JL) FinFET transistor with fi cross section in
rectangular, trapeze and triangle form. The lattice temperature dependence on
the channel length as well as on buried oxide thickness is considered. It is
shown that for considered transistor structure the lattice temperature in the
middle of the channel is lower than at lateral sides, near source and drain.
Also, we have found at the same conditions the lattice temperature depends on
shape of channel cross section too",2403.06271v1
2024-03-16,Enhanced electron transfer using NiCo2O4@C hollow nanocages with an electron-shuttle effect for efficient tetracycline degradation,"Spinel oxides are recognized as promising Fenton-like catalysts for the
degradation of antibiotics. However, the catalytic performance is restrained by
the poor electron transfer rate (ETR). Herein, hollow NiCo2O4@C nanocages are
rationally designed and prepared to accelerate ETR in peroxymonosulfate (PMS)
activation for tetracycline (TC) degradation.",2403.10835v1
2002-04-09,Local Circumstellar Magnetic Fields Around Evolved Stars,"I argue that the presence of magnetic fields around evolved stars, e.g.,
asymptotic giant branch stars, and in PNe, does not necessarily imply that the
magnetic field plays a global dynamical role in shaping the circumstellar
envelope. Instead, I favor magnetic fields with small coherence lengths, which
result from stellar magnetic spots or from jets blown by an accreting
companion. Although the magnetic field does not play a global role in shaping
the circumstellar envelope, it may enhance local motion (turbulent) via
magnetic tension and reconnection. The locally strong magnetic tension may
enforce coherence flow which may favor the masing process.",0204157v1
1995-10-06,Magnetic excitations and effects of magnetic fields on the spin-Peierls transition in CuGeO$_3$,"We analyze the magnetic excitations of a spin-1/2 antiferromagnetic
Heisenberg model with alternating nearest neighbor interactions and uniform
second neighbor interactions recently proposed to describe the spin-Peierls
transition in CuGeO$_3$. We show that there is good agreement between the
calculated excitation dispersion relation and the experimental one. We have
also shown that this model reproduces satisfactorily the experimental results
for the magnetization vs. magnetic field curve and its saturation value. The
model proposed also reproduces qualitatively some features of the magnetic
phase diagram of this compound and the overall behavior of the magnetic
specific heat in the presence of applied magnetic fields.",9509160v1
1998-02-25,Magnetization Controlled Superconductivity in a Film with Magnetic Dots,"We consider a superconducting film with Magnetic Dots Array (MDA) placed on
it. Magnetic moments of these dots are supposed to be normal to the film and
strong enough to create vortices in the superconducting film. Magnetic
interaction between dots is negligible. Below the superconducting transition
temperature of the film in zero magnetic field the MDA with randomly magnetized
dots produces resistive state of the film. Paradoxically, in a finite magnetic
field the film with MDA is superconductive.",9802276v1
1999-05-21,Magnetic Field Induced Ordering in Quasi-One-Dimensional Quantum Magnets,"Three-dimensional magnetic ordering transitions are studied theoretically in
strongly anisotropic quantum magnets. An external magnetic field can drive
quasi-one-dimensional subsystems with a spin gap into a gapless regime, thus
inducing long-range three-dimensional magnetic ordering due to weak residual
magnetic coupling between the subsystems. Compounds with higher spin degrees of
freedom, such as N-leg spin-1/2 ladders, are shown to have cascades of ordering
transitions. At high magnetic fields, zero-point fluctuations within the
quasi-1D subsystems are suppressed, causing quantum corrections to the ordering
temperature to be reduced.",9905331v1
2000-04-05,Spin 1/2 Magnetic Impurity in a 2D Magnetic System Close to Quantum Critical Point,"We consider a magnetic impurity in a spin liquid state of a magnetic system
which is close to the quantum phase transition to the magnetically ordered
state. There is similarity between this problem and the Kondo problem. We
derive the impurity Green's function, consider renormalizations of the magnetic
moments of the impurity, calculate critical indexes for the magnetic
susceptibilities and finally consider specific heat and magnetic interaction of
two impurities.",0004057v1
2000-04-14,Magnetic Field Effects on Neutron Diffraction in the Antiferromagnetic Phase of $UPt_3$,"We discuss possible magnetic structures in UPt$_3$ based on our analysis of
elastic neutron-scattering experiments in high magnetic fields at temperatures
$T<T_N$. The existing experimental data can be explained by a single-{\bf q}
antiferromagnetic structure with three independent domains. For modest in-plane
spin-orbit interactions, the Zeeman coupling between the antiferromagnetic
order parameter and the magnetic field induces a rotation of the magnetic
moments, but not an adjustment of the propagation vector of the magnetic order.
A triple-{\bf q} magnetic structure is also consistent with neutron
experiments, but in general leads to a non-uniform magnetization in the
crystal. New experiments could decide between these structures.",0004253v1
2001-01-06,Evidence for Adiabatic Magnetization of cold Dy_N Clusters,"Magnetic properties of Dy_N clusters in a molecular beam generated with a
liquid helium cooled nozzle are investigated by Stern-Gerlach experiments. The
cluster magnetizations \mu_z are measured as a function of magnetic field (B =
0 - 1.6T) and cluster size (16 < N < 56). The most important observation is the
saturation of the magnetization \mu_z(B) at large field strengths. The
magnetization approaches saturation following the power law |\mu_z-\mu_0|
proportional to 1/\sqrt{B}, where \mu_0 denotes the magnetic moment. This gives
evidence for adiabatic magnetization.",0101075v1
2003-07-08,Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals,"The lineshape of crystal-field transitions in single crystals of Mn12ac
molecular magnets is determined by the magnetic history. The absorption lines
are symmetric and Gaussian for the non-magnetized state obtained by zero-field
cooling (zfc). In the magnetized state which is reached when the sample is
cooled in a magnetic field (fc), however, they are asymmetric even in the
absence of an external magnetic field. These observations are quantitatively
explained by inhomogeneous symmetrical (Gaussian) broadening of the
crystal-field transitions combined with a contribution of off-diagonal
components of the magnetic susceptibility to the effective magnetic
permeability.",0307164v1
2005-01-17,Frustration effects in magnetic molecules,"By means of exact diagonalization we study the ground-state and the
low-temperature physics of the Heisenberg antiferromagnet on the cuboctahedron
and the icosidodecahedron. Both are frustrated magnetic polytopes and
correspond to the arrangement of magnetic atoms in the magnetic molecules
Cu12La8 and Mo72Fe30. The interplay of strong quantum fluctuations and
frustration influences the ground state spin correlations drastically and leads
to an interesting magnetization process at low temperatures. Furthermore the
frustration yields low-lying non-magnetic excitations resulting in an extra
low-temperature peak in the specific heat.",0501376v1
2005-09-28,About low field memory and negative magnetization in semiconductors and polymers,"Ginzburg-Landau bulk magnetization of itinerant electrons can provide a
negative effective field in the Weiss model by coupling to localized magnetic
moments. The coupling enforces remnant magnetization, which can be negative or
positive depending on the sample magnetic history. Stable magnetic
susceptibility of coupled nonequilibrium subsystems with magnetization reversal
is always positive. Gauss-scale fields could be expected for switching between
negative and positive remnant moments in semiconductors with coupling at
ambient temperatures. Negative magnetization in ultra-high conducting polymers
is also discussed within the developed framework.",0509712v1
2005-10-10,Magnetic dipole-vortex interaction in a bilayer superconductor/soft-magnet heterostructure,"We study the penetration of the nonuniform magnetic field, created by a
magnetic dipole with out-of-plane magnetization, into a film heterostructure
composed of a type-II superconductor layer and a soft-magnet layer. In the
framework of the London approach, the energy of the magnetic dipole-vortex
interaction is derived and the critical value of the dipole moment for the
first appearance of a vortex in the superconducting constituent is found for
two cases of the layer ordering, namely when the dipole is located near the
superconducting or, respectively, the magnetic constituent.",0510251v1
2005-10-18,Local field of magnetic islands: role of their shape,"I analyze in details distribution of local magnetic field induced by micro-
and nano-magnets. I consider three kinds of elongated magnetic islands:
ellipse-, diamond- and rectangular shaped islands which were magnetized
uniformly along long axis. This report concentrates on the role of their shape
upon distribution of the field. Calculations show that unlike
rectangular-shaped magnet, ellipse-shaped and diamond-shaped ones produce much
more localized field in proximity of its magnetic poles. Additionally in the
case of ellipse-shaped islands the magnitude of induced field is large. This
two facts favor arrays of ellipse-shaped magnetic islands to build
zero-dimensional spin traps in a hybrid based on Ferromagnet/Semiconductor
structure.",0510486v1
2005-11-23,Nonequilibrium Magnetization of a Two-Dimensional Electron Gas in a Static Magnetic Field,"Using a sensitive DC torque magnetometer we measure the orbital magnetization
by sweeping the density at fixed magnetic fields on GaAs-AlGaAs
heterostructures. At low temperatures strong nonequilibrium magnetization
signals dominate the data. In literature the observation of nonequilibrium
signals are often associated with eddy currents generated by sweeping the
magnetic field. The elimination of a changing magnetic field then poses a
question regarding the origin of these signals. Our data suggests another
source of nonequilibrium magnetization potentially due to the change of area
occupied by compressible and incompressible states as one sweeps the Fermi
energy from one Landau level to the next.",0511569v1
2006-04-01,Magnetization reversal through synchronization with a microwave,"Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.",0604013v1
2006-05-01,Possible magnetic-field-induced voltage and thermopower in diluted magnetic semiconductors,"In diluted magnetic semiconductors, the carrier concentration and the
magnetization of local moments are strongly coupled, since the magnetic
interaction is mediated by the carriers. It is predicted that this coupling
leads to an electric polarization due to an applied magnetic-field gradient and
to the appearance of a magnetic-field-dependent voltage. An expression for this
voltage is derived within Landau theory and its magnitude is estimated for
(Ga,Mn)As. Furthermore, a large contribution to the thermopower based on the
same mechanism is predicted. The role of fluctuations is also discussed. These
predictions hold both if the magnetization is uniform and if it shows
stripe-like modulations, which are possible at lower temperatures.",0605043v1
2006-05-22,Kondo-transport spectroscopy of single molecule magnets,"We demonstrate that in a single molecule magnet (SMM) strongly coupled to
electrodes the Kondo effect involves all magnetic excitations. This Kondo
effect is induced by the quantum tunneling of the magnetic moment (QTM).
Importantly, the Kondo temperature $T_K$ can be much larger than the magnetic
splittings. We find a strong modulation of the Kondo effect as function of the
transverse anisotropy parameter or a longitudinal magnetic field. For both
integer and half-integer spin this can be used for an accurate transport
spectroscopy of the magnetic states in low magnetic fields on the order of the
easy-axis anisotropy parameter. We set up a relationship between the Kondo
effects for successive integer and half-integer spins.",0605514v1
2006-07-19,Magnetic-Field Induced Gap in One-Dimensional Antiferromagnet KCuGaF$_6$,"Magnetic susceptibility and specific heat measurements in magnetic fields
were performed on an $S=1/2$ one-dimensional antiferromagnet KCuGaF$_6$.
Exchange interaction was evaluated as $J/k_{\rm B}\simeq 100$ K. However, no
magnetic ordering was observed down to 0.46 K. It was found that an applied
magnetic field induces a staggered magnetic susceptibility obeying the Curie
law and an excitation gap, both of which should be attributed to the
antisymmetric interaction of the Dzyaloshinsky-Moriya type and/or the staggered
$g$-tensor. With increasing magnetic field $H$, the gap increases almost in
proportion to $H^{2/3}$.",0607469v1
1998-11-18,Magnetic field profiling for selected-states magnetic-resonance spectroscopy (SSMRS) and Stern-Gerlach spectroscopy (MGRS) in condensed matter,"A method was presented of profiling the magnetic field, with a zero vector of
magnetic flux density $B_{r}$ and strong gradient G, enabling conditions for
the Stern-Gerlach spectroscopy to be accomplished in condensed matter (the
method has been called magnetic field gradient spectroscopy - MGRS), as well
the previously proposed magnetic resonance spectroscopy for selected energy
states (SSMRS). Magnetic field distribution in a model electromagnet were shown
when condition $B_{r}= 0$ for resultant magnetic field was satisfied within the
sample",9811034v1
2007-08-22,Neutron channelling in a magnetic tube trap,Neutron channelling in a magnetic tube trap is discussed,0708.3042v1
2007-11-13,Magnetic nanowires as permanent magnet materials,"We present the fabrication of metallic magnetic nanowires using a low
temperature chemical process. We show that pressed powders and magnetically
oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe
at 300 K). We discuss the magnetic properties of these metamaterials and show
that they have the suitable properties to realize ""high temperature magnets""
competitive with AlNiCo or SmCo permanent magnets. They could also be used as
recording media for high density magnetic recording.",0711.1978v1
2008-06-28,Effect of magnetization and magnetic field variation on stationary axisymmetric equilibrium,"The inclusion of plasma magnetization in the equations of stationary
equilibrium is derived, and its effect on the determination of axisymmetric
equilibrium calculated. A factor of 2 on the pressure gradient arises in the
equilibrium equation from the force felt by the dipole moment density. The
algebraic and differential equation formulations are compared both with and
without consideration of magnetization, revealing the effects of both
magnetization and magnetic field variation on the equilibrium, which become
more pronounced for high pressures in a weak external field. The equivalence of
the magnetized equilibrium equation with the standard equilibrium equation in
the limit of vanishing magnetization is demonstrated.",0806.4696v2
2008-10-07,Multiple magnetic barriers in graphene,"We study the behavior of charge carriers in graphene in inhomogeneous
perpendicular magnetic fields. We consider two types of one-dimensional
magnetic profiles, uniform in one direction: a sequence of N magnetic barriers,
and a sequence of alternating magnetic barriers and wells. In both cases, we
compute the transmission coefficient of the magnetic structure by means of the
transfer matrix formalism, and the associated conductance. In the first case
the structure becomes increasingly transparent upon increasing N at fixed total
magnetic flux. In the second case we find strong wave-vector filtering and
resonant effects. We also calculate the band structure of a periodic magnetic
superlattice, and find a wave-vector-dependent gap around zero-energy.",0810.1236v1
2008-12-10,Magnetic monopole and the nature of the static magnetic field,"We investigate the factuality of the hypothetical magnetic monopole and the
nature of the static magnetic field. It is shown from many aspects that the
concept of the massive magnetic monopoles clearly is physically untrue. We
argue that the static magnetic field of a bar magnet, in fact, is the static
electric field of the periodically quasi-one-dimensional electric-dipole
superlattice, which can be well established in some transition metals with the
localized d-electron. This research may shed light on the perfect unification
of magnetic and electrical phenomena.",0812.2048v1
2010-04-15,Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet,"The magnetization process of the isotropic Heisenberg antiferromagnet on the
kagome lattice is studied. Data obtained from the numerical-diagonalization
method are reexamined from the viewpoint of the derivative of the magnetization
with respect to the magnetic field. We find that the behavior of the derivative
at approximately one-third of the height of the magnetization saturation is
markedly different from that for the cases of typical magnetization plateaux.
The magnetization process of the kagome-lattice antiferromagnet reveals a new
phenomenon, which we call the ""magnetization ramp"".",1004.2528v1
2011-07-14,Magnetic instability induced by tunnel current in single Co nanoparticles,"Measurements of magnetic hysteresis loops in single Co nanoparticles at
dilution refrigerator temperatures are presented. The nanoparticles are in
electric contact with bulk Al leads via tunnel junctions. The tunnel current
versus magnetic field displays a magnetic hysteresis loop. The magnetic
switching field is reduced by current, and the magnetization of the
nanoparticle can be switched by applying a voltage pulse, demonstrating that
the magnetic stability of the nanoparticle is diminished by electron transport.
Additional transitions and random switches of magnetization can be driven by
large currents.",1107.2850v3
2011-08-09,"Magnetic phases of a highly frustrated magnet, ZnCr2O4, up to an ultra-high magnetic field of 600 T","The Faraday rotation and magneto-optical absorption spectral measurements
were conducted to reveal the full-magnetization process and map out a magnetic
phase diagram of a typical geometrical frustrated magnet, ZnCr2O4, by using the
electromagnetic flux compression method in ultra-magnetic fields up to 600 T. A
fully polarized ferromagnetic phase is observed in which the absorption spectra
associated with an exciton-magnon-phonon transition disappears. Furthermore,
prior to the fully polarized ferromagnetic phase above 410 T, we found a novel
magnetic phase above 350 T followed by a canted 3:1 phase.",1108.1932v1
2012-03-21,Percolation and orientational ordering in systems of magnetic nanorods,"Based on Monte Carlo (MC) computer simulations we study the structure
formation of a system of magnetic nanorods. Our model particles consist of
fused spheres with permanent magnetic dipole moments, as inspired by recent
experiments. The resulting system behaves significantly different from a system
of hard (non-magnetic) rods or magnetic rods with a single longitudinal dipole.
In particular, we observe for the magnetic nanorods a significant decrease of
the percolation threshold (as compared to non-magnetic rods) at low densities,
and a stabilization of the high-density nematic phase. Moreover, the
percolation threshold is tunable by an external magnetic field.",1203.4707v1
2012-07-10,Micromagnetic simulation of magnetic small-angle neutron scattering from two-phase nanocomposites,"The recent development of a micromagnetic simulation methodology - suitable
for multiphase magnetic nanocomposites - permits the computation of the
magnetic microstructure and of the associated magnetic small-angle neutron
scattering (SANS) cross section of these materials. In this review article we
summarize results on the micromagnetic simulation of magnetic SANS from
two-phase nanocomposites. The decisive advantage of this approach resides in
the possibility to srutinize the individual magnetization Fourier contributions
to the total magnetic SANS cross section, rather than their sum, which is
generally obtained from experiment. The procedure furnishes unique and
fundamental information regarding magnetic neutron scattering from nanomagnets.",1207.2331v1
2013-04-10,A proposed new route to d0 magnetism in semiconductors,"Here we propose to induce magnetism in semiconductor utilizing the unique
properties of the interstitial defect to act as the magnetic impurity within
the alpha-PbO crystal structure. The Pbi interstitial generates the p-localized
state with two on-site electrons to obey the Hund's rule for their ordering. It
is demonstrated that instead of Pb interstitial other non-magnetic impurities
of s^2p^{x} outer shell configuration can be applied to induce d0 magnetism
with possibility to tune the local magnetic moments mu_B by varying a number of
electrons 1< x< 3. The magnetic coupling between such defects is found to be
driven by the long-range order interactions that in combination with high
defect solubility promises the magnetic percolation to remain above the room
temperature.",1304.2945v1
2013-10-23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2013-11-21,A new Approach for Magnetic Curves in 3D Riemannian Manifolds,"A magnetic field is defined by the property that its divergence is zero in a
three dimensional oriented Riemannian manifold. Each magnetic field generates a
magnetic flow whose trajectories are curves called as magnetic curves. In this
paper, we give a new variational approach to studies the magnetic flow
asociated with the Killing magnetic field in a three dimensional oriented
Riemann manifold, And then, we investigate the trajectories of the magnetic
fields called as N-magnetic and B-magnetic curves.",1311.5348v3
2014-07-01,Explaining Mercury's Density through Magnetic Erosion,"In protoplanetary disks, dust grains rich in metallic iron can attract each
other magnetically. If they are magnetized to values near saturation, the
magnetically induced collision speeds are high enough to knock off the
non-magnetized, loosely bound silicates. This process enriches the surviving
portions of the dust grains in metallic iron, which further enhances the
magnetically mediated collisions. The magnetic enhancement to the collisional
cross-section between the iron rich dust results in rapid grain growth leading
to planetesimal formation. While this process of knocking off silicates, which
we term ""magnetic erosion"", occurs only in a very limited portion of a
protoplanetary disk, it is a possible explanation for Mercury's
disproportionately large iron core.",1407.0274v1
2014-09-25,Atomistic simulation of sub-nanosecond non-equilibrium field cooling processes for magnetic data storage applications,"Thermally assisted magnetic writing is an important technology utilizing
temperature dependent magnetic properties to enable orientation of a magnetic
data storage medium. Using an atomistic spin model we study non-equilibrium
field cooled magnetization processes on sub-nanosecond timescales required for
device applications. We encapsulate the essential physics of the process in a
TRM-T curve and show that for fast timescales heating to the Curie temperature
is necessary where the magnetic relaxation time is shortest. Furthermore we
demonstrate the requirement for large magnetic fields to achieve a high
thermoremanent magnetization necessary for fast recording or data rates.",1409.7377v1
2015-07-22,Magnetic Response Functions in Landau Levels,"We propose a new quantization rule which generates Landau levels consistent
with the zero-field magnetic response functions from the semiclassical theory.
It reproduces the Onsager's rule in the leading order, and re-formulates
corrections from the Berry phase and magnetic moment effect in terms of one
single magnetic response: the zero-field magnetization. It can yield higher
order corrections by including successively magnetic susceptibility and higher
order magnetic response functions. In application, it can be easily applied to
obtain Landau levels in lattice models. Moreover, it provides an experimental
method of measuring different magnetic response functions directly from the
measurement of Landau level fan diagram or Hofstadter spectrum.",1507.06342v2
2016-02-29,Gyrotropic skyrmion modes in ultrathin magnetic circular dots,"We calculate low-frequency gyrotropic spin excitation modes of the skyrmion
ground state ultrathin cylindrical magnetic dots. The skyrmion is assumed to be
stabilized at room temperature and zero external magnetic field due to an
interplay of the isotropic and Dzyaloshinskii-Moriya exchange interactions,
perpendicular magnetic anisotropy and magnetostatic interaction. We consider
Bloch- and Neel-type magnetic skyrmions and assume that the dot magnetization
does not depend on the thickness coordinate. The skyrmion gyrotropic
frequencies are calculated in GHz range as a function of the skyrmion
equilibrium radius, dot radius and the dot magnetic parameters. Recent
experiments on magnetic skyrmion gyrotropic dynamics in nanodots are discussed.",1603.00072v1
2016-04-05,Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2,"We performed magnetic susceptibility and neutron powder diffraction
experiments on the ternary compound Pr5Ru3Al2. It belongs to the
noncentrosymmetric and nonmirrorsymmetric cubic I213 space group. The
previously reported ferromagnetic transition at 24 K was not detected in our
improved quality samples. Instead, magnetic ordering was observed in the DC
magnetic susceptibility at 3.8 K. Neutron powder diffraction further indicates
that an incommensurate magnetic structure is established below 3.8 K, with the
magnetic modulation vector (0.066, 0.066, 0.066) (r.l.u.). Using the magnetic
representation analysis, we propose the block helical structure as a candidate
for the incommensurate magnetic structure.",1604.01149v1
2016-06-08,Magnetic energy of sc ferromagnetic films with three layers as described by third order perturbed Heisenberg Hamiltonian,"The solution of third order perturbed Heisenberg Hamiltonian of simple cubic
ferromagnetic ultra-thin films with three layers were found. All the magnetic
energy parameters such as spin exchange interaction, magnetic dipole
interaction, second order magnetic anisotropy, fourth order magnetic
anisotropy, applied magnetic field, demagnetization factor and stress induced
anisotropy were included in the third order perturbed Heisenberg Hamiltonian.
3-D plots of stress induced anisotropy, out of plane magnetic field,
demagnetization factor and spin exchange interaction are presented in this
manuscript. Magnetic easy and hard directions were determined using these 3-D
plots. MATLAB program was employed to solve the equation with seven parameters.",1606.02439v1
2016-07-19,MHD flow and heat transfer due to the axisymmetric stretching of a sheet with induced magnetic field,"The full MHD equations, governing the flow due to the axisymmetric stretching
of a sheet in the presence of a transverse magnetic field, can be cast in a
self similar form. This allows evaluation of the induced magnetic field and its
effect on the flow and heat transfer. The problem involves three parameters-
the magnetic Prandtl number, the magnetic interaction number, and the Prandtl
number. Numerical solutions are obtained for the velocity field, the magnetic
field, and the temperature, at different values of the magnetic Prandtl number
and the magnetic interaction number. The contributions of the viscous
dissipation, Joule heating, and streamwise diffusion to the heat flux toward
the sheet are assessed.",1607.05722v1
2017-02-27,Magnetization reversal by superconducting current in $\varphi_0$ Josephson junctions,"We study magnetization reversal in a $\varphi_0$ Josephson junction with
direct coupling between magnetic moment and Josephson current. Our simulations
of magnetic moment dynamics show that by applying an electric current pulse, we
can realize the full magnetization reversal. We propose different protocols of
full magnetization reversal based on the variation of the Josephson junction
and pulse parameters, particularly, electric current pulse amplitude, damping
of magnetization and spin-orbit interaction. We discuss experiments which can
probe the magnetization reversal in $\varphi_0$-junctions.",1702.08394v4
2014-03-13,Monte Carlo simulated dynamical magnetization of single-chain magnets,"Here, a dynamical Monte-Carlo (DMC) method is used to study
temperature-dependent dynamical magnetization of famous Mn2Ni system as typical
example of single-chain magnets with strong magnetic anisotropy. Simulated
magnetization curves are in good agreement with experimental results under
typical temperatures and sweeping rates, and simulated coercive fields as
functions of temperature are also consistent with experimental curves. Further
analysis indicates that the magnetization reversal is determined by both
thermal-activated effects and quantum spin tunnelings. These can help explore
basic properties and applications of such important magnetic systems.",1403.3188v2
2016-11-14,Magnetization process and magnetocaloric effect of the spin-1/2 XXZ Heisenberg cuboctahedron,"Magnetic properties of the spin-1/2 XXZ Heisenberg cuboctahedron are examined
using exact numerical diagonalization depending on a relative strength of the
exchange anisotropy. While the Ising cuboctahedron exhibits in a
low-temperature magnetization curve only one-third magnetization plateau, the
XXZ Heisenberg cuboctahedron displays another four intermediate plateaux at
zero, one-sixth, one-half and two-thirds of the saturation magnetization. The
novel magnetization plateaux generally extend over a wider range of magnetic
fields with increasing of a quantum ($xy$) part of the XXZ exchange
interaction. It is shown that the XXZ Heisenberg cuboctahedron exhibits in a
vicinity of all magnetization jumps anomalous thermodynamic behavior
accompanied with an enhanced magnetocaloric effect.",1611.04301v1
2018-05-24,Searching the weakest link: Demagnetizing fields and magnetization reversal in permanent magnets,"Magnetization reversal in permanent magnets occurs by the nucleation and
expansion of reversed domains. Micromagnetic theory offers the possibility to
localize the spots within the complex structure of the magnet where
magnetization reversal starts. We compute maps of the local nucleation field in
a Nd2Fe14B permanent magnet using a model order reduction approach. Considering
thermal fluctuations in numerical micromagnetics we can also quantify the
reduction of the coercive field due to thermal activation. However, the major
reduction of the coercive field is caused by the soft magnetic grain boundary
phases and misorientation if there is no surface damage.",1805.09798v1
2012-01-04,Origin of training effect of exchange bias in Co/CoO due to irreversible thermoremanent magnetization of the magnetically diluted antiferromagnet,"The irreversible thermoremanent magnetization of a sole, magnetically diluted
epitaxial antiferromagnetic Co$_{1-y}$O(100) layer is determined by the mean of
its thermoremanent magnetizations at positive and negative remanence. During
hysteresis-loop field cycling, thermoremanent magnetization exhibits successive
reductions, consistent with the training effect (TE) of the exchange bias
measured for the corresponding Co$_{1-y}$O(100)/Co bilayer. The TE of exchange
bias is shown to have its microscopic origin in the TE of the irreversible
thermoremanent magnetization of the magnetically diluted AFM.",1201.0831v1
2018-01-09,Magneto-electric effect in doped magnetic ferroelectrics,"We propose a model of magneto-electric effect in doped magnetic
ferroelectrics. This magneto-electric effect does not involve the spin-orbit
coupling and is based purely on the Coulomb interaction. We calculate magnetic
phase diagram of doped magnetic ferroelectrics. We show that magneto-electric
coupling is pronounced only for ferroelectrics with low dielectric constant. We
find that magneto-electric coupling leads to modification of magnetization
temperature dependence in the vicinity of ferroelectric phase transition. A
peak of magnetization appears. We find that magnetization of doped magnetic
ferroelectrics strongly depends on applied electric field.",1801.03114v1
2019-06-04,Deterministic magnetization switching by voltage-control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction under in-plane magnetic field,"Based on the micromagnetic simulations the magnetization switching in a
triangle magnetic element by voltage-control of magnetic anisotropy and
Dzyaloshinskii-Moriya interaction under in-plane magnetic field is proposed.
The proposed switching scheme is not the toggle switching but the deterministic
switching where the magnetic state is determined by the polarity of the applied
voltage pulse. The mechanism and conditions for the switching are clarified.
The results provide a fast and low-power writing method for magnetoresistive
random access memories.",1906.01254v1
2019-06-14,Friedel oscillations in 2D electron gas from spin-orbit interaction in a parallel magnetic field,"Effects associated with the interference of electron waves around a magnetic
point defect in two-dimensional electron gas with combined Rashba-Dresselhaus
spin-orbit interaction in the presence of a parallel magnetic field are
theoretically investigated. The effect of a magnetic field on the anisotropic
spatial distribution of the local density of states and the local density of
magnetization is analyzed. The existence of oscillations of the density of
magnetization with scattering by a non-magnetic defect and the contribution of
magnetic scattering (accompanied by spin-flip) in the local density of electron
states are predicted.",1906.06043v1
2019-06-21,Magnetic lattices for ultracold atoms,"This article reviews the development in our laboratory of magnetic lattices
comprising periodic arrays of magnetic microtraps created by patterned magnetic
films to trap periodic arrays of ultracold atoms. Recent achievements include
the realisation of multiple Bose-Einstein condensates in a 10 micron-period
one-dimensional magnetic lattice; the fabrication of sub-micron-period square
and triangular magnetic lattice structures suitable for quantum tunnelling
experiments; the trapping of ultracold atoms in a sub-micron-period triangular
magnetic lattice; and a proposal to use long-range interacting Rydberg atoms to
achieve spin-spin interactions between sites in a large-spacing magnetic
lattice.",1906.08918v1
2017-05-16,An approach to 1000 T using the Electro-Magnetic Flux Compression,"An ultra-high magnetic field was generated by the electro-magnetic flux
compression technique under a reduced seed magnetic field condition and
achieved maximum magnetic field intensity was investigated. An ordinal pickup
coil measurement fails due to the dielectric breakdown at around 500 T. On the
other hand, by utilizing the magneto-optical Faraday rotation method with a
small probe, the measureable maximum magnetic field increased significantly. It
was found that reduced seed field increases the maximum magnetic field, but
with a reduced size of the final bore. A highest magnetic field over 763 T and
possibly up to 985 T approaching 1000 T was detected.",1705.05520v1
2018-03-03,Long Range Magnetic order stabilized by acceptors,"Tuning magnetic order in magnetic semiconductors is a long sought goal. A
proper concentration of acceptors can dramatically suppress local magnetic
order in favor of the long one. Using Mn and an acceptor codoped LiZnAs as an
example, we demonstrate, by first-principles calculation, the emergence of a
long-range magnetic order. This intriguing phenomenon can be understood from an
interplay between an acceptor-free magnetism and a band coupling magnetism. Our
observation thus lays the ground for a precise control of the magnetic order in
future spintronic devices.",1803.01179v1
2020-08-26,A Magnetic Velocity Verlet Method,"We discuss an extension of the velocity Verlet method that accurately
approximates the kinetic-energy-conserving charged particle motion that comes
from magnetic forcing. For a uniform magnetic field, the method is shown to
conserve both particle kinetic energy and magnetic dipole moment better than
midpoint Runge-Kutta. We then use the magnetic velocity Verlet method to
generate trapped particle trajectories, both in a cylindrical magnetic mirror
machine setup, and for dipolar fields like the earth's magnetic field. Finally,
the method is used to compute an example of (single) mirror motion in the
presence of a magnetic monopole field, where the trajectory can be described in
closed form.",2008.11810v1
2021-02-26,Distinctive magnetic properties of CrI3 and CrBr3 monolayers caused by spin-orbit coupling,"After the discovery of magnetism in monolayer CrI3, the magnetic properties
of different 2D materials from the chromium-trihalide family are intuitively
assumed to be similar, yielding magnetic anisotropy from the spin-orbit
coupling on halide ligands. Here we reveal significant differences between the
CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting
Curie temperature, hysteresis in external magnetic field, and evolution of
magnetism with strain, all predominantly attributed to distinctly different
interplay of atomic contributions to spin-orbit coupling in two materials.",2102.13325v1
2021-06-01,Impact of magnetic domains on magnetic flux concentrators,"The impact of magnetic domains in magnetic flux concentrators is studied
using the simulation software MuMax3. First, the simulation parameters are
validated using experimental results from magnetic force microscopy; second the
simulation output is benchmarked with the one obtained using Comsol
Multiphysics. Finally, the impact of magnetic domain is assessed, showing how
micromagnetic effects can become relevant, if not dominant, when scaling the
gap between the MFC and the sensor.",2106.00370v2
2021-10-16,A stretched exponential-based approach for the magnetic properties of spin glasses,"The spin glasses show intriguing characteristic features that are not well
understood yet, as for instance its aging, rejuvenation and memory effects.
Here a model based on a stretched exponential decay of its magnetization is
proposed, which can describe the main magnetic features of spin glasses
observed in experiments as the time-decay of thermoremament magnetization, the
relaxation of zero field cooled magnetization, the ac and dc magnetization as a
function of temperature and others. In principle, the here proposed model could
be adapted to describe other glassy systems.",2110.08625v2
2021-12-06,Magnetism of two-dimensional magnets in the presence of random fields,"In low-dimensional magnets, thermal agitation and spatial disorders generate
strong spin fluctuations that suppress the long-range magnetic ordering. We
develop an analytical equation for the equilibrium magnetization of
two-dimensional magnets at finite temperatures in the presence of the random
magnetic field. We find that the random field induces a first-order phase
transition in addition to the reduced Curie temperature. The first-order phase
transition persists even in the presence of the moderate external magnetic
field.",2112.03343v1
2022-04-11,Deformation of a magnetic liquid drop and unsteady flow inside and outside it in a non-stationary magnetic field,"Small steady-state deformational oscillations of a drop of a viscous magnetic
liquid in a non-stationary uniform magnetic field are theoretically
investigated for low Reynolds numbers. The drop is suspended in another viscous
magnetic liquid immiscible with the former. The non-stationary magnetic field
causes flow inside and outside the drop. The inertia is taken into account by
regarding the flow as essentially unsteady. The variation of the magnetic field
is so slow that the approximation of quasi-stationary magnetic field may be
used.",2204.05387v2
2022-10-06,MagNet: machine learning enhanced three-dimensional magnetic reconstruction,"Three-dimensional (3D) magnetic reconstruction is vital to the study of novel
magnetic materials for 3D spintronics. Vector field electron tomography (VFET)
is a major in house tool to achieve that. However, conventional VFET
reconstruction exhibits significant artefacts due to the unavoidable presence
of missing wedges. In this article, we propose a deep-learning enhanced VFET
method to address this issue. A magnetic textures library is built by
micromagnetic simulations. MagNet, an U-shaped convolutional neural network, is
trained and tested with dataset generated from the library. We demonstrate that
MagNet outperforms conventional VFET under missing wedge. Quality of
reconstructed magnetic induction fields is significantly improved.",2210.03066v1
2022-10-30,Controlling magnetic anisotropy in amplitude expansion of phase field crystal model,"The amplitude expansion for a magnetic phase-field-crystal (magnetic APFC)
model enables a convenient coarse-grained description of crystalline structures
under the influence of magnetic fields. Considering higher-order magnetic
coupling terms, we demonstrate the possibility of tuning the magnetic
anisotropy in these models. This allows for reproducing the easy and hard
direction of magnetization. Such a result can be achieved without increasing
the computational cost, enabling simulations of the manipulation of dislocation
networks and microstructures in ferromagnetic materials. As a demonstration, we
report on the simulation of the shrinkage of a spherical grain with the
magnetic anisotropy of Fe.",2210.16855v1
2023-12-13,Enhanced Magnetic Field Amplification by Ion-Beam Weibel Instability in Weakly Magnetized Astrophysical Shocks,"We examine the evolution of ion-beam Weibel instability at strong
collisionless shocks in weakly magnetized media. We find that a finite
background magnetic field substantially affects both linear and nonlinear
phases of the instability, depending on whether the background electrons behave
magnetized or not. Particle-in-cell simulations for magnetized electrons
identify a dynamo-like mechanism of magnetic field amplification, which
eventually leads to spontaneous magnetic reconnection. We conclude that this
scenario is applicable to typical young supernova remnant shocks.",2312.07933v1
2019-11-14,Real time observation of a stationary magneton,"The magnetic dipole field geometry of subatomic elementary particles like the
electron differs from the classical macroscopic field imprint of a bar magnet.
It resembles more like an eight figure or else joint double quantum-dots
instead of the classical, spherical more uniform field of a bar magnet. This
actual subatomic quantum magnetic field of an electron at rest, is called
Quantum Magnet or else a Magneton. Normally, a macroscale bar magnet should
behave like a relative giant Quantum Magnet with identical magnetic dipole
field imprint since all of its individual magnetons collectively inside the
material, dipole moments are uniformly aligned forming the total net field of
the magnet. However due to Quantum Decoherence (QDE) phenomenon at the
macroscale and macroscopic magnetic field imaging sensors limitations which
cannot pickup these rapid quantum magnetization fluctuations, this field is
masked and not visible at the macroscale. By using the relative inexpensive
submicron resolution Ferrolens quantum magnetic optical sensor and method, we
can actually make this net magneton field visible on macroscale magnets. We
call this net total field herein, Quantum Field of Magnet (QFM) differentiating
it therefore from the field of the single subatomic magneton thus quantum
magnet. Additionally, the unique potential of the Ferrolens device to display
also the magnetic flux lines of this macroscopically projected giant Magenton
gives us the unique opportunity to study the individual magnetic flux lines
geometrical pattern that of a single subatomic magneton. We describe this
particular magnetic flux of the magneton observed, quantum magnetic flux.
Therefore a novel observation has been made that the QFM of the Magnet-Magneton
consists of a dipole vortex shaped magnetic flux geometrical pattern
responsible for creating the classical macroscopic N-S field of the magnet.",1911.05735v1
2000-02-23,ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296,"Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.",0002440v1
2004-08-09,Solar System Formation Deduced from Observations of Matter,"Aspects of our Solar System's formation are deduced from observations of the
chemical nature of matter. Massive cores are indicative of
terrestrial-planet-composition-similarity to enstatite chondrite meteorites,
whose highly-reduced state of oxidation may be thermodynamically stable in
solar matter only at elevated temperatures and pressures. Consistent with the
formation of Earth as envisioned by Arnold Eucken, thermodynamic considerations
lead to the deduction that the terrestrial planets formed by
liquid-condensation, raining out from the central regions of hot, gaseous
protoplanets. The mass of protoplanetary-Earth, estimated to be 275-305mE, is
similar to the mass of Jupiter, 318mE. Solar primordial gases and volatile
elements were separated from the terrestrial planets early after planet
formation, presumably during some super-luminous solar event, perhaps even
before Mercury had completely formed. The
pre-super-luminosity-terrestrial-planet mass distribution appears to be more
consistent with observations of the close-in gas-giants of other planetary
systems than the present-day-terrestrial-planet mass distribution. Although
primarily formed by raining out from the centers of hot, gaseous protoplanets,
evidence for the Earth and, by inference for the other terrestrial planets,
suggests some outer, minor, secondary accretion of oxidized matter in the
grain-growth accumulation way envisioned by George W. Wetherill. By contrast,
the so-called ""standard model"" for our Solar System's formation has flawed
conceptual underpinnings and would lead to the contradiction of terrestrial
planets having insufficiently massive cores.",0408151v1
2004-10-01,Mercury's Protoplanetary Mass,"Major element fractionation among chondrites has been discussed for decades
as ratios relative to Si or Mg. Recently, by expressing ratios relative to Fe,
I discovered a new relationship admitting the possibility that ordinary
chondrite meteorites are derived from two components, a relatively oxidized and
undifferentiated, primitive component and a somewhat differentiated, planetary
component, with oxidation state like the highly reduced enstatite chondrites,
which I suggested was identical to Mercury's complement of lost elements. Here,
on the basis of that relationship, I derive expressions, as a function of the
mass of planet Mercury and the mass of its core, to estimate the mass of
Mercury's lost elements, the mass of Mercury's alloy and rock protoplanetary
core, and the mass of Mercury's gaseous protoplanet. Although Mercury's mass is
well known, its core mass is not, being widely believed to be in the range of
70-80 percent of the planet mass. For a core mass of 75 percent, the mass of
Mercury's lost elements is about 1.32 times the mass of Mercury, the mass of
the alloy and rock protoplanetary core is about 2.32 times the mass of Mercury,
and the mass of the gaseous protoplanet of Mercury is about 700 times the mass
of Mercury. Circumstantial evidence is presented in support of the supposition
that Mercury's lost elements is identical to the planetary component of
ordinary chondrite formation.",0410009v1
2004-10-08,Total Mass of Ordinary Chondrite Matter Originally Present in the Solar System,"Recently, I reported the discovery of a new fundamental relationship of the
major elements (Fe, Mg, Si) of chondrites that admits the possibility that
ordinary chondrite meteorites are derived from two components, a relatively
oxidized and undifferentiated, primitive component and a somewhat
differentiated, planetary component, with oxidation state like the highly
reduced enstatite chondrites, which I suggested was identical to Mercury's
complement of lost elements. Subsequently, on the basis of that relationship, I
derived expressions, as a function of the mass of planet Mercury and the mass
of its core, to estimate the mass of Mercury's lost elements, the mass of
Mercury's alloy and rock protoplanetary core, and the mass of Mercury's gaseous
protoplanet. Here, on the basis of the supposition that Mercury's complement of
lost elements is in fact identical to the planetary component of ordinary
chondrite formation, I estimate, as a function of Mercury's core mass, the
total mass of ordinary chondrite matter originally present in the Solar System.
Although Mercury's mass is well known, its core mass is not, being widely
believed to be in the range of 70 to 80 percent of the planet mass. For a core
mass of 75 percent, the calculated total mass of ordinary chondrite matter
originally present in the Solar System amounts to 1.83E24 kg, about 5.5 times
the mass of Mercury. That amount of mass is insufficient in itself to form a
planet as massive as the Earth, but may have contributed significantly to the
formation of Mars, as well as adding to the veneer of other planets, including
the Earth. Presently, only about 0.1 percent of that mass remains in the
asteroid belt.",0410242v1
2007-02-23,Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star,"Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to
high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in
earthlike atmospheres. We investigate to what extent this NOx may modify
biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as
related compounds such as water (H2O) (essential for life) and methane (CH4)
(which has both abiotic and biotic sources) . Our model results suggest that
such signals are robust, changing in the M-star world atmospheric column by up
to 20% due to the GCR NOx effects compared to an M-star run without GCR effects
and can therefore survive at least the effects of galactic cosmic rays. We have
not however investigated stellar cosmic rays here. CH4 levels are about 10
times higher than on the Earth related to a lowering in hydroxyl (OH) in
response to changes in UV. The increase is less than reported in previous
studies. This difference arose partly because we used different biogenic input.
For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike
on the Earth, relatively modest changes in these fluxes can lead to larger
changes in the concentrations of biomarker and related species on the M-star
world. We calculate a CH4 greenhouse heating effect of up to 4K. O3
photochemistry in terms of the smog mechanism and the catalytic loss cycles on
the M-star world differs considerably compared with the Earth.",0702622v1
1999-03-11,Ordering and Fluctuation of Orbital and Lattice Distortion in Perovskite Manganese Oxides,"Roles of orbital and lattice degrees of freedom in strongly correlated
systems are investigated to understand electronic properties of perovskite Mn
oxides such as La_{1-x}Sr_{x}MnO_{3}. An extended double-exchange model
containing Coulomb interaction, doubly degenerate orbitals and Jahn-Teller
coupling is derived under full polarization of spins with two-dimensional
anisotropy. Quantum fluctuation effects of Coulomb interaction and orbital
degrees of freedom are investigated by using the quantum Monte Carlo method. In
undoped states, it is crucial to consider both the Coulomb interaction and the
Jahn-Teller coupling in reproducing characteristic hierarchy of energy scales
among charge, orbital-lattice and spin degrees of freedom in experiments. Our
numerical results quantitatively reproduce the charge gap amplitude as well as
the stabilization energy and the amplitude of the cooperative Jahn-Teller
distortion in undoped compounds. Upon doping of carriers, in the absence of the
Jahn-Teller distortion, critical enhancement of both charge compressibility and
orbital correlation length is found with decreasing doping concentration. These
are discussed as origins of strong incoherence in charge dynamics. With the
Jahn-Teller coupling in the doped region, collapse of the Jahn-Teller
distortion and instability to phase separation are obtained and favorably
compared with experiments. These provide a possible way to understand the
complicated properties of lightly doped manganites.",9903183v2
2000-02-17,Adsorbed and Grafted Polymers at Equilibrium,"This chapter deals with various aspects related to the adsorption of long
chain-like macromolecules (polymers) onto solid surfaces. Physical aspects of
the adsorption mechanism are elaborated mainly at thermodynamical equilibrium.
The basic features needed in modeling of this adsorption are discussed. We
first discuss the adsorption of a single and long polymer chain to the surface.
The surface interaction is modeled by a potential well with a long-ranged
attractive tail. A simple mean-field theory description is presented and the
concept of polymer ""blobs"" is used to describe the conformation of the chain at
the surface. The thickness of the adsorbed layer depends on several polymer and
surface parameters. Fluctuation corrections to mean-field theory are also
discussed. We then review adsorption as well as depletion processes in the
many-chain case. Profiles, changes in the surface tension and polymer surface
excess are calculated within mean-field theory. Corrections due to fluctuations
in good solvent are taken into account using scaling concepts. The proximal
exponent is introduced in analogy to surface critical phenomena. The
interaction between two surfaces with adsorbed polymer layers is discussed, and
various cases leading to attractive and repulsive interactions are mentioned.
Polyelectrolytes are of practical importance due to their water solubility; we
give a short summary of recent progress in this rapidly evolving field. The
behavior of grafted polymers, i.e., polymers which are anchored with one end to
a solid substrate is also reviewed.",0002266v1
2000-10-05,The Structure and a Bond-Valence-Sum Study of the 1-2-3 Superconductors CLBLCO and YBCO,"We present a study of the crystal structure of the 1-2-3 superconductor
[Ca(x)La(1-x)][Ba$(1.75-x)La(0.25+x)]Cu(3)O(y) (``CLBLCO''). Because of the
presence of both La and Ba ions in the ``Ba'' layer, the local symmetry of
YBa(2)Cu(3)O(y) (``YBCO'') is lost. One can no longer assume that an ``apical''
oxygen atom always lies strictly on the line joining CuI and CuII ions, and a
Pauling bond-valence calculation is very useful as an adjunct to the Rietveld
refinement of the positions of the La and Ba ions. When a Rietveld analysis is
performed allowing for the possibility that the apical oxygen atoms may be
slightly displaced along the a or b direction, the bond valence sums for both
La and Ba are close to the natural oxidation states of these ions.
  We have also used the bond-valence-sum method to study the mean oxidation
states of the CuI and CuII ions in both CLBLCO and YBCO. Our results for YBCO
differ from some previously published results. Our main conclusion is that,
while the method may be useful in finding the charge concentration on the CuII
plane, it definitely does not yield the concentration of mobile holes, nor the
concentration of superconducting charge carriers.",0010079v1
2000-10-28,High-Resolution X-Ray Reflectivity Study of Thin Layered Pt-Electrodes for Integrated Ferroelectric Devices,"The structural interface properties of layered Pt/Ti/SiO2/Si electrodes have
been investigated using high-resolution specular and diffuse x-ray reflectivity
under grazing angles. Currently this multilayer system represents a
technological standard as bottom electrodes for ferroelectric thin film
applications. For the electronic and ferroelectric properties of integrated
devices, the film-electrode interface is of crucial importance. We focused on
Pt-100nm/Ti-10nm/SiO2/Si electrodes prepared under annealing conditions as
employed in industrial processing, prior to the deposition of ferroelectric
films. The comparison between annealed and non-annealed electrodes clearly
revealed strong interfacial effects due to interdiffusion and oxidation of Ti,
especially at the Pt-Ti interface. Migration of Ti into the Pt-layer results in
a clear shift of the critical angle due to enclosure of TiO(2-x) within the
Pt-layer. The heterogeneous distribution of TiO(2-x) suggests a diffusion
mechanism mainly along the Pt-grain boundaries. At the SiO2 interface a
relatively weakly oxidized, remaining Ti-layer of 20 Angstroem could be found,
which is most probably correlated with the remaining adhesion to the substrate.",0010467v1
2001-09-17,Catalytic CO Oxidation on Nanoscale Pt Facets: Effect of Inter-Facet CO Diffusion on Bifurcation and Fluctuation Behavior,"We present lattice-gas modeling of the steady-state behavior in CO oxidation
on the facets of nanoscale metal clusters, with coupling via inter-facet CO
diffusion. The model incorporates the key aspects of reaction process, such as
rapid CO mobility within each facet, and strong nearest-neighbor repulsion
between adsorbed O. The former justifies our use a ""hybrid"" simulation approach
treating the CO coverage as a mean-field parameter. For an isolated facet,
there is one bistable region where the system can exist in either a reactive
state (with high oxygen coverage) or a (nearly CO-poisoned) inactive state.
Diffusion between two facets is shown to induce complex multistability in the
steady states of the system. The bifurcation diagram exhibits two regions with
bistabilities due to the difference between adsorption properties of the
facets. We explore the role of enhanced fluctuations in the proximity of a cusp
bifurcation point associated with one facet in producing transitions between
stable states on that facet, as well as their influence on fluctuations on the
other facet. The results are expected to shed more light on the reaction
kinetics for supported catalysts.",0109295v1
2001-10-24,A Theory for High-$T_c$ Superconductors Considering Inhomogeneous Charge Distribution,"We propose a general theory for the critical $T_c$ and pseudogap $T^*$
temperature dependence on the doping concentration for high-$T_c$ oxides,
taking into account the charge inhomogeneities in the $CuO_2$ planes. The well
measured experimental inhomogeneous charge density in a given compound is
assumed to produce a spatial distribution of local $\rho(r)$. These differences
in the local charge concentration is assumed to yield insulator and metallic
regions, possibly in a stripe morphology. In the metallic region, the
inhomogeneous charge density yields also spatial distributions of
superconducting critical temperatures $T_c(r)$ and zero temperature gap
$\Delta_0(r)$. For a given sample, the measured onset of vanishing gap
temperature is identified as the pseudogap temperature, that is, $T^*$, which
is the maximum of all $T_c(r)$. Below $T^*$, due to the distribution of
$T_c(r)$'s, there are some superconducting regions surrounded by insulator or
metallic medium. The transition to a superconducting state corresponds to the
percolation threshold among the superconducting regions with different
$T_c(r)$'s. To model the charge inhomogeneities we use a double branched
Poisson-Gaussian distribution. To make definite calculations and compare with
the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO
families, with a mean field theory for superconductivity using an extended
Hubbard Hamiltonian. We show also that this novel approach provides new
insights on several experimental features of high-$T_c$ oxides.",0110519v3
2001-12-05,The LDA+DMFT Approach to Materials with Strong Electronic Correlations,"LDA+DMFT is a novel computational technique for ab initio investigations of
real materials with strongly correlated electrons, such as transition metals
and their oxides. It combines the strength of conventional band structure
theory in the local density approximation (LDA) with a modern many-body
approach, the dynamical mean-field theory (DMFT). In the last few years
LDA+DMFT has proved to be a powerful tool for the realistic modeling of
strongly correlated electronic systems. In this paper the basic ideas and the
set-up of the LDA+DMFT(X) approach, where X is the method used to solve the
DMFT equations, are discussed. Results obtained with X=QMC (quantum Monte
Carlo) and X=NCA (non-crossing approximation) are presented and compared. By
means of the model system La$_{1-x}$Sr$_{x}$TiO$_{3}$ we show that the method X
matters qualitatively and quantitatively. Furthermore, we discuss recent
results on the Mott-Hubbard metal-insulator transition in the transition metal
oxide V$_2$O$_3$ and the $\alpha$-$\gamma$ transition in the 4f-electron system
Ce.",0112079v1
2002-08-30,On the Structural and Optical Properties of Sputtered Hydrogenated Amorphous Silicon Thin Films,"The present work is essentially focused on the study of optical and
structural properties of hydrogenated amorphous silicon thin films (a-Si:H)
prepared by radio-frequency cathodic sputtering. We examine separately the
influence of hydrogen partial pressure during film deposition, and the effect
of post-deposition thermal annealings on the main optical characteristics of
the layers such as refraction index, optical gap and Urbach energy. Using the
grazing X-rays reflectometry technique, thin film structural properties are
examined immediately after films deposition as well as after surface oxidation
or annealing. We show that low hydrogen pressures allow a saturation of
dangling bonds in the layers, while high doses lead to the creation of new
defects. We show also that thermal annealing under moderate temperatures
improves the structural quality of the deposited layers. For the films examined
just after deposition, the role of hydrogen appears in the increase of their
density. For those analysed after a short stay in the ambient, hydrogen plays a
protective role against the oxidation of their surfaces. This role disappears
for a long time stay in the ambient.
  Keywords
  Amorphous silicon, Grazing incidence X-rays, Hydrogen, Optical properties,
Penetration depth, Reflectometry, Thermal annealing, Thin films.
  PACS Numbers
  61.10.K - 61.43.D - 68.55.JK - 68.55.81.15.A",0208601v1
2003-01-08,The problem of a metal impurity in an oxide: ab-initio study of electronic and structural properties of Cd in Rutile TiO2,"In this work we undertake the problem of a transition metal impurity in an
oxide. We present an ab-initio study of the relaxations introduced in TiO2 when
a Cd impurity replaces substitutionally a Ti atom. Using the Full-Potential
Linearized-Augmented-Plane-Wave method we obtain relaxed structures for
different charge states of the impurity and computed the electric-field
gradients (EFGs) at the Cd site. We find that EFGs, and also relaxations, are
dependent on the charge state of the impurity. This dependence is very
remarkable in the case of the EFG and is explained analyzing the electronic
structure of the studied system. We predict fairly anisotropic relaxations for
the nearest oxygen neighbors of the Cd impurity. The experimental confirmation
of this prediction and a brief report of these calculations have recently been
presented [P.R.L. 89, 55503 (2002)]. Our results for relaxations and EFGs are
in clear contradiction with previous studies of this system that assumed
isotropic relaxations and point out that no simple model is viable to describe
relaxations and the EFG at Cd in TiO2 even approximately.",0301099v2
2003-08-04,Normal-state conductivity in underdoped La_{2-x}Sr_xCuO_4 thin films: Search for nonlinear effects related to collective stripe motion,"We report a detailed study of the electric-field dependence of the
normal-state conductivity in La_{2-x}Sr_xCuO_4 thin films for two
concentrations of doped holes, x=0.01 and 0.06, where formation of diagonal and
vertical charged stripes was recently suggested. In order to elucidate whether
high electric fields are capable of depinning the charged stripes and inducing
their collective motion, we have measured current-voltage characteristics for
various orientations of the electric field with respect to the crystallographic
axes. However, even for the highest possible fields (~1000 V/cm for x=0.01 and
\~300 V/cm for x=0.06) we observed no non-linear-conductivity features except
for those related to the conventional Joule heating of the films. Our analysis
indicates that Joule heating, rather than collective electron motion, may also
be responsible for the non-linear conductivity observed in some other 2D
transition-metal oxides as well. We discuss that a possible reason why moderate
electric fields fail to induce a collective stripe motion in layered oxides is
that fairly flexible and compressible charged stripes can adjust themselves to
the crystal lattice and individual impurities, which makes their pinning much
stronger than in the case of conventional rigid charge-density waves.",0308045v1
2004-03-01,"Non-ionic contributions to the electric-field gradient at $^{181}$Ta and $^{111}$Cd impurity sites in R$_2$O$_3$ (R= Sc, In, Lu, Yb, Tm, Er, Y, Ho, Dy, Gd, Eu, Sm) bixbyites","The time-differential perturbed-angular-correlation (TDPAC) technique was
applied to the study of the internal electric-field gradient (EFG) in Eu- and
Ho-sesquioxides in their cubic bixbyite phases. The results, as well as
previous characterizations of the EFG at $^{181}$Ta sites in oxides with the
bixbyite structure, were compared to those obtained in experiments using
$^{111}$Cd as probe, and to point-charge model and {\it ab initio} results
calculations for the EFG tensor at impurity sites in binary oxides. These
studies provide quantitative information about electronic processes and the
structural relaxations induced by the presence of impurity probes in the host
lattices, and confirm the existence of nonionic contributions to the EFG in
these systems. Our FP-LAPW calculations show that this nonionic contribution to
the EFG is the dominating one, and that it is originated in the population of
{\it p} states (5{\it p} in the case of Cd, 6{\it p} for Ta).",0403060v2
2004-03-22,"New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides","A new DTA (Differential Thermal Analysis) device was designed and installed
in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure
thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be
carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The
calibration of the DTA apparatus under pressure was successfully performed
using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard
calibration references. The thermal properties of these metals have been
studied under pressure. The values of DV (volume variation between liquid and
solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal
expansion coefficient at Tm) have been extracted. A very good agreement was
found with the existing literature and new data were added. This HP-DTA
apparatus is very useful for studying the thermodynamics of those systems where
one or more volatile elements are present, such as high TC superconducting
oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar
under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading
to the formation of the 2223 phase was found to occur at higher temperatures
when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared
to the reaction at 1 bar. This temperature shift is due to the higher stability
of the Pb-rich precursor phases under pressure, as the high isostatic pressure
prevents Pb from evaporating.",0403556v1
2004-10-04,The role of nitrogen related defects in high-k dielectric oxides: Density functional studies,"Using ab initio density functional total energy and molecular dynamics
simulations, we study the effects of various forms of nitrogen post deposition
anneal (PDA) on the electric properties of hafnia in the context of its
application as a gate dielectric in field effect transistors (FET). We consider
the atomic structure and energetics of nitrogen containing defects which can be
formed during the PDA in various N-based ambients: N2, N+2, N, NH3, NO, N2O. We
analyse the role of such defects in fixed charge accumulation, electron
trapping and in the growth of the interface SiOx layer. We find that nitrogen
anneal of the oxides leads to an effective immobilization of native defects
such as oxygen vacancies and interstitial oxygen ions, which may inhibit growth
of silica layer. Nitrogen in any form effectively incorporates into the
pre-existing oxygen vacancies and, therefore may decrease the concentration of
shallow electron traps. However, nitrogen in any form is unlikely to
significantly reduce the fixed charge in the dielectric.",0410088v1
2005-03-30,Phonon Knudsen flow in nanostructured semiconductor systems,"We determine the size effect on the lattice thermal conductivity of nanoscale
wire and multilayer structures formed in and by some typical semiconductor
materials, using the Boltzmann transport equation and focusing on the Knudsen
flow effect. For both types of nanostructured systems we find that the phonon
transport is reduced significantly below the bulk value by boundary scattering
off interface defects and/or interface modes. The Knudsen flow effects are
important for almost all types of semiconductor nanostructures but we find them
most pronounced in Si and SiC systems due to the very large phonon mean-free
paths. We apply and test our wire thermal-transport results to recent
measurements on Si nanowires. We further investigate and predict size effects
in typical multilayered SiC nanostructures, for example, a
doped-SiC/SiC/SiO$_2$ layered structure that could define the transport channel
in a nanosize transistor. Here the phonon-interface scattering produces a
heterostructure thermal conductivity smaller than what is predicted in a
traditional heat-transport calculation, suggesting a breakdown of the
traditional Fourier analysis even at room temperatures. Finally, we show that
the effective thermal transport in a SiC/SiO$_2$ heterostructure is sensitive
to the oxide depth and could thus be used as an in-situ probe of the SiC
oxidation progress.",0503701v1
2005-04-20,Covalent bonding and hybridization effects in the corundum-type transition-metal oxides V2O3 and Ti2O3,"The electronic structure of the corundum-type transition-metal oxides V2O3
and Ti2O3 is studied by means of the augmented spherical wave method, based on
density-functional theory and the local density approximation. Comparing the
results for the vanadate and the titanate allows us to understand the peculiar
shape of the metal 3d a_{1g} density of states, which is present in both
compounds. The a_{1g} states are subject to pronounced bonding-antibonding
splitting due to metal-metal overlap along the c-axis of the corundum
structure. However, the corresponding partial density of states is strongly
asymmetric with considerably more weight on the high energy branch. We argue
that this asymmetry is due to an unexpected broadening of the bonding a_{1g}
states, which is caused by hybridization with the e_g^{pi} bands. In contrast,
the antibonding a_{1g} states display no such hybridization and form a sharp
peak. Our results shed new light on the role of the a_{1g} orbitals for the
metal-insulator transitions of V2O3. In particular, due to a_{1g} - e_g^{pi}
hybridization, an interpretation in terms of molecular orbital singlet states
on the metal-metal pairs along the c-axis is not an adequate description.",0504524v1
2005-05-19,Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9,"We have performed both in-plane resistivity, Hall effect and specific heat
measurements on the thermoelectric cobalt oxide Ca$_{3}$Co$_{4}$O$_{9}$. Four
distinct transport regimes are found as a function of temperature,
corresponding to a low temperature insulating one up to $T_{min}\approx $63 K,
a strongly correlated Fermi liquid up to $T^*\approx $140 K, with
$\rho=\rho_0+AT^2$ and $A\approx 3.63$ $10^{-2} \mu \Omega cm/K^{2}$, followed
by an incoherent metal with $k_Fl\leq 1$ and a high temperature insulator above
T$^{**}\approx $510 K . Specific heat Sommerfeld coefficient $\gamma = 93$
mJ/(mol.K$^{2}$) confirms a rather large value of the electronic effective mass
and fulfils the Kadowaki-Woods ratio $A/\gamma^2 \approx 0.45$ 10$^{-5}$ $\mu
\Omega cm.K^2/(mJ^2mol^{-2})$. Resistivity measurements under pressure reveal a
decrease of the Fermi liquid transport coefficient A with an increase of $T^*$
as a function of pressure while the product $A(T^*)^2/a$ remains constant and
of order $h/e^2$. Both thermodynamic and transport properties suggest a strong
renormalization of the quasiparticles coherence scale of order $T^*$ that seems
to govern also thermopower.",0505464v1
2005-05-30,"Bose-Einstein Condensation Picture of Superconductivity in Ag2 (Ag3Pb2H2O6), Na0.05WO3 and Na0.041NH3 composites. (Dilute metals)","Traditionally, when one describes the crystallographic structure of oxides,
the oxygen ion radius r02 is assumed to be approximately equal to 1.4A. The
oxygen ions occupy in this case 80-90% of the crystal volume. Metal atoms are
considered then as ions playing a role of donors with rather small radius of
(0.5 - 0.8) A. However, the atomic packing picture and, therefore, physical
properties such as electric conductivity and superconductivity of oxides will
be essentially different, if we assume r02- ~ 0.56 A. Such magnitude of the
radius is known from the quantum mechanics calculations [2]. According to this
picture, 80-90 % of the crystal volume is occupied by the metal atom orbitals
with radius (1.3-1.9) A, while the oxygen ions play a role of acceptors, which
reduce occupancy of these orbitals (""indirect"" dilution of the metal). A
""direct"" dilution of metals takes place in stoichiometric matrices. When
r02-~0.56 A, channels with diameter 3.6 A present in the hexagonal matrix
Ag3Pb2H2O6 directed along the ""c"" axis.
  The channels are filled by chains of the Ag2 molecules with atomic diameter
of 2.6 A and the molecule concentration n_B = 25.6 10^20 cm^-3.
  The Bose-Einstein condensation (BEC) temperature T_cB ~ 400K is calculated
for the electron effective mass value m*=7.5m_e, where m_e is the isolated
electron mass. Three-dimensional networks of Na2 chains form in Na solutions in
NH3 and WO3 as well (respectively, with n_B=4.71 10^20 cm^-3;
  T_c sim 180K; m*=5.0m_e and n_B=4.74 10^20 cm^-3; T_c sim 91K; m*=10m_e).
Close magnitudes of the Ag2 and Na2 chains parameters respectively in NH3 and
WO3 favors the opinion that all these structures have a composite structure and
similar mechanisms of the high temperature superconductivity.",0505718v1
2005-06-01,Insulator-metal transition in a conservative system: An evidence for mobility coalescence in island silver films,"Aging, which manifests itself as an irreversible increase in electrical
resistance in island metal films is of considerable interest from both academic
as well as applications point of view. Aging is attributed to various causes,
oxidation of islands and mobility of islands followed by coalescence (mobility
coalescence) being the main contenders. The effect of parameters like substrate
temperature, substrate cleaning, residual gases in the vacuum chamber,
ultrasonic vibration of the substrate, suggest that the mobility coalescence is
responsible for the aging in island metal films. Electron microscopy studies
show evidence for mobility of islands at high substrate temperatures. The
comparison of aging data of island silver films deposited on glass substrates
in ultra high vacuum and high vacuum suggests that the oxidation of islands, as
being responsible for aging in these films, can be ruled out. Further, under
certain conditions of deposition, island silver films exhibit a dramatic and
drastic fall in electrical resistance, marking the insulator-metal transition.
This interesting transition observed in a conservative system - after the
stoppage of deposition of the film- is a clear evidence for mobility
coalescence of islands even at room temperature. The sudden fall in resistance
is preceded by fluctuations in resistance with time and fluctuations are
attributed to the making and breaking of the percolation path in the film.",0506022v2
2005-06-13,"Decay of Metastable Nonequilibrium Phases, Enhanced Reaction Rate, and Dynamic Phase Transition in a Model of CO Oxidation with CO Desorption","We present a computational study of the dynamic behavior of a
Ziff-Gulari-Barshad model of CO oxidation with CO desorption on a catalytic
surface. Our results provide further evidence that below a critical desorption
rate the model exhibits a non-equilibrium, first-order phase transition between
low and high CO coverage phases. Our kinetic Monte Carlo simulations indicate
that the transition process between these phases follows a decay mechanism very
similar to the one described by the classic Kolmogorov-Johnson-Mehl-Avrami
theory of phase transformation by nucleation and growth. We measure the
lifetimes of the metastable phases on each side of the transition line and find
that they are strongly dependent on the direction of the transformation, i.e.,
from low to high coverage or vice versa. Inspired by this asymmetry, we
introduce a square-wave periodic external forcing, whose two parameters can be
tuned to enhance the catalytic activity. At CO desorption rates below the
critical value, we find that this far-from-equilibrium system undergoes a
dynamic phase transition between a CO_2 productive phase and a nonproductive
one. In the space of the parameters of the periodic external forcing, this
nonequilibrium phase transition defines a line of critical points. The maximum
enhancement rate for the CO_2 production rate occurs near this critical line.",0506271v1
2005-10-03,A Study of Apparent Symmetry Breakdown in Perovskite Oxide-based Symmetric RRAM Devices,"A new model of a symmetric two-terminal non-volatile RRAM device based on
Perovskite oxide thin film materials, specifically Pr1-xCaxMnO3 (PCMO), is
proposed and analyzed. The model consists of two identical half-parts, which
are completely characterized by the same resistance verses pulse voltage
hysteresis loop, connected together in series. Even though the modeled device
is physically symmetric with respect to the direction of current, it is found
to exhibit switching of the resistance with the application of voltage pulses
of sufficient amplitude and of different polarities. The apparent breakdown of
parity conservation of the device is attributed to changes in resistance of the
active material layer near the electrodes during switching. Thus the switching
is history dependent, a feature that can be very useful for the construction of
real non-volatile memory devices. An actual symmetric device, not previously
reported in the literature and based on the proposed model, is fabricated in
the PCMO material system. Measurements of the resistance of this new device
generated an experimental hysteresis curve that matches well the calculated
hysteresis curve of the model, thus confirming the features predicated by the
new symmetric model.",0510059v1
2005-10-17,Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites,"A characteristic feature of the copper oxide high-temperature superconductors
is the dichotomy between the electronic excitations along the nodal (diagonal)
and antinodal (parallel to the Cu-O bonds) directions in momentum space,
generally assumed to be linked to the ""d-wave"" symmetry of the superconducting
state. Angle-resolved photoemission measurements in the superconducting state
have revealed a quasiparticle spectrum with a d-wave gap structure that
exhibits a maximum along the antinodal direction and vanishes along the nodal
direction. Subsequent measurements have shown that, at low doping levels, this
gap structure persists even in the high-temperature metallic state, although
the nodal points of the superconducting state spread out in finite ""Fermi
arcs"". This is the so-called pseudogap phase, and it has been assumed that it
is closely linked to the superconducting state, either by assigning it to
fluctuating superconductivity or by invoking orders which are natural
competitors of d-wave superconductors. Here we report experimental evidence
that a very similar pseudogap state with a nodal-antinodal dichotomous
character exists in a system that is markedly different from a superconductor:
the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer
manganite La1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption
that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy
are hallmarks of the superconductivity state.",0510423v1
2005-11-11,Electronic Structure Calculations using Dynamical Mean Field Theory,"The calculation of electronic properties of materials is an important task of
solid state theory, albeit particularly difficult if electronic correlations
are strong, for example in transition metals, their oxides and in f-electron
systems. The standard approach to material calculations, the density functional
theory in its local density approximation (LDA), incorporates electronic
correlations only very rudimentarily and fails if the correlations are strong.
Encouraged by the success of dynamical mean field theory (DMFT) in dealing with
strongly correlated model Hamiltonians, physicists from the bandstructure and
the many-body community have joined forces and developed a combined LDA+DMFT
method recently. Depending on the strength of electronic correlations, this new
approach yields a weakly correlated metal as in LDA, a strongly correlated
metal, or a Mott insulator. By now, this approach is widely regarded as a
breakthrough for electronic structure calculations of strongly correlated
materials.
  The author will review this LDA+DMFT method and also discuss alternative
approaches to employ DMFT in electronic structure calculations, for example, by
replacing the LDA part by the so-called GW approximation. Different methods to
solve the DMFT equations are introduced with a focus on those that are suitable
for realistic calculations with many orbitals. An overview of the successful
application of LDA+DMFT to a wide variety of materials, ranging from Pu and Ce,
to Fe and Ni, to numerous transition metal oxides, is given.",0511293v2
2006-03-03,Study of Correlation Effects in the High Formal Oxidation State Compound Sr$_2$CoO$_4$,"Two recent reports confirm that the newly synthesized Sr$_2$CoO$_4$ (formal
oxidation state Co$^{4+}$) shows a high Curie temperature (~ 250 K), but they
report different moments of 1.8 $\mu_B$ and 1 $\mu_B$ per Co. Using both
commonly used functionals in the correlated band approach (LDA+U) as well as
the local density approximation (LDA),the combined effects of correlation and
hybridization with O 2p states are calculated and analyzed. Sr$_2$CoO$_2$ is
already ferromagnetic within LDA (M=1.95 $\mu_B$). Increasing U from zero, the
two LDA+U schemes affect the moment oppositely out to a critical value
$U_c$=2.5 eV, at which point they transform discontinuously from different
states to the same large U state. Fixing U at $U_c$, fixed spin moment
calculations show similar behavior out to a minimum at 1$\mu_B$ (a half
metallic state), beyond which the fully-localized-limit scheme jumps to a state
with energy minimum very near 2$\mu_B$ very close to the LDA moment). Although
the energy minima occur very near integer values of the moment/Co (1$\mu_B,
2$\mu_B$), the strong 3d-2p mixing and resulting 3d orbital occupations seem to
preclude any meaningful S=1/2 or S=1 assignment to the Co ion.",0603075v1
2006-03-04,Electronically coupled complementary interfaces between perovskite band insulators,"Perovskite oxides exhibit a plethora of exceptional electronic properties,
providing the basis for novel concepts of oxide-electronic devices. The
interest in these materials is even extended by the remarkable characteristics
of their interfaces. Studies on single epitaxial connections between the two
wide-bandgap insulators LaAlO3 and SrTiO3 have revealed them to be either
high-mobility electron conductors or insulating, depending on the atomic
stacking sequences. In the latter case they are conceivably positively charged.
For device applications, as well as for basic understanding of the interface
conduction mechanism, it is important to investigate the electronic coupling of
closely-spaced complementary interfaces. Here we report the successful
realization of such electronically coupled complementary interfaces in SrTiO3 -
LaAlO3 thin film multilayer structures, in which the atomic stacking sequence
at the interfaces was confirmed by quantitative transmission electron
microscopy. We found a critical separation distance of 6 perovskite unit cell
layers, corresponding to approximately 2.3 nm, below which a decrease of the
interface conductivity and carrier density occurs. Interestingly, the high
carrier mobilities characterizing the separate electron doped interfaces are
found to be maintained in coupled structures down to sub-nanometer interface
spacing.",0603088v1
2006-04-21,"Metastable phases and ""metastable"" phase diagrams","The work discusses specifics of phase transitions for metastable states of
substances. The objects of condensed media physics are primarily equilibrium
states of substances with metastable phases viewed as an exception, while the
overwhelming majority of organic substances investigated in chemistry are
metastable. It turns out that at normal pressure many of simple molecular
compounds based on light elements (these include: most hydrocarbons; nitrogen
oxides, hydrates, and carbides; carbon oxide (CO); alcohols, glycerin etc) are
metastable substances too, i.e. they do not match the Gibbs' free energy
minimum for a given chemical composition. At moderate temperatures and
pressures, the phase transitions for given metastable phases throughout the
entire experimentally accessible time range are reversible with the equilibrium
thermodynamics laws obeyed. At sufficiently high pressures (1-10 GPa), most of
molecular phases irreversibly transform to more energy efficient polymerized
phases, both stable and metastable. These transformations are not consistent
with the equality of the Gibbs' free energies between the phases before and
after the transition, i.e. they are not phase transitions in ""classical""
meaning. The resulting polymeric phases at normal pressure can exist at
temperatures above the melting one for the initial metastable molecular phase.
Striking examples of such polymers are polyethylene and a polymerized
modification of CO. Many of energy-intermediate polymeric phases can apparently
be synthesized by the ""classical"" chemistry techniques at normal pressure.",0604512v1
2006-11-19,Ferroelectric switched all-metallic-oxide $p$-$n$ junctions,"We report the first formation of the metallic $p$-$n$ junctions, the
ferroelectric (Ba,Sr)TiO$_3$ (BST) switched optimally electron-doped ($n$-type)
metallic T'-phase superconductor, (La,Ce)$_2$CuO$_4$ (LCCO), and hole-doped
($p$-type) metallic CMR manganite (La,Sr)MnO$_3$ (LSMO) junctions. In contrast
with the previous semiconductor $p$-$n$ ($p$-$I$-$n$) junctions which are
switched by the built-in field $V_0$, the present metallic oxides $p$-$I$-$n$
junctions are switched by double barrier fields, the built-in field $V_0$, and
the ferroelectric reversed polarized field $V_{rp}$, both take together to lead
the junctions to possess definite parameters, such as definite negligible
reversed current ($10^{-9}$ A), large breakdown voltage ($>$7 V), and ultrahigh
rectification ($>2\times10^4$) in the bias voltage 1.2 V to 2.0 V and
temperature range from 5 to over 300 K. The related transport feature, barrier
size effect, and temperature effect are also observed and defined.",0611501v1
2007-01-05,Origin and roles of a strong electron-phonon interaction in cuprate oxide superconductors,"A strong electron-phonon interaction arises from the modulation of the
superexchange interaction by lattice vibrations. It is responsible for the
softening of the half-breathing modes around (pm pi/a,0) and (0, pm pi/a) in
the two-dimensional Brillouin zone, with a being the lattice constant of CuO_2
planes, as is studied in Phys. Rev. B70, 184514 (2004). Provided that
antiferromagnetic spin fluctuations are developed around Q=(pm 3 pi/4a, pm
pi/a) and (pm pi/a, pm 3 pi/4a), the electron-phonon interaction can also cause
the softening of Cu-O bond stretching modes around 2Q, or around (pm pi/2a,0)
and (0, pm pi/2a). The softening around 2Q is accompanied by the development of
charge fluctuations corresponding to the so called 4a-period stripe or
4a*4a-period checker-board state. However, an observation that the 4a-period
modulating part or the 2Q part of the density of states is almost symmetric
with respect to the chemical potential contradicts a scenario that the
stabilization of a single-2Q or double-2Q charge density wave following the
complete softening of the 2Q bond stretching modes is responsible for the
ordered stripe or checker-board state. It is proposed that the stripe or
checker-board state is simply a single-Q or double-Q spin density wave, whose
second-harmonic effects can explain the observed almost symmetric 2Q part of
the density of states. The strong electron-phonon interaction can play no or
only a minor role in the occurrence of d gamma-wave superconductivity in
cuprate oxides.",0701088v1
2007-01-17,Superlight small bipolarons: a route to room temperature superconductivity,"Extending the BCS theory towards the strong electron-phonon interaction
(EPI), a charged Bose liquid of small bipolarons has been predicted by us with
a further prediction that the highest superconducting critical temperature is
found in the crossover region of the EPI strength from the BCS-like to
bipolaronic superconductivity. Later on we have shown that the unscreened
(infinite-range) Froehlich EPI combined with the strong Coulomb repulsion
create \emph{superlight} small bipolarons, which are several orders of
magnitude lighter than small bipolarons in the Holstein-Hubbard model (HHM)
with a zero-range EPI. The analytical and numerical studies of this
Coulomb-Froehlich model (CFM) provide the following recipes for
room-temperature superconductivity: (a) The parent compound should be an ionic
insulator with light ions to form high-frequency optical phonons, (b) The
structure should be quasi two-dimensional to ensure poor screening of
high-frequency phonons polarized perpendicular to the conducting planes, (c) A
triangular lattice is required in combination with strong, on-site
  Coulomb repulsion to form the small superlight bipolaron, (d) Moderate
carrier densities are required to keep the system of small bipolarons close to
the Bose-Einstein condensation regime. Clearly most of these conditions are
already met in the cuprates.",0701412v2
2007-01-26,Stoichiometry of Electrostatic Complexes Determined by Light Scattering,"We report on the electrostatic complexation between oppositely charged
polymers and inorganic nanoparticles investigated by static and dynamical light
scattering. The nanoparticles put under scrutiny were citrate-coated
nanocrystals of cerium oxide (CeO2, nanoceria), of iron oxide (Fe2O3,
maghemite) and of europium-doped yttrium vanadate (Eu:YVO4) with sizes in the
10 nm range. For the polymers, we have used cationic-neutral diblock copolymers
(poly(trimethylammonium ethylacrylate)-b-poly(acrylamide), hereafter referred
to as PTEA-b-PAM) with different molecular weights. For the three colloidal
dispersions, we show that the electrostatic complexation gives rise to the
formation of stable nanoparticle clusters in the 100 nm range. The complexation
was monitored by systematic measurements of the scattering intensity versus X,
the mixing ratio between nanoparticles and polymers. For 5 nanoparticle/polymer
pairs, namely CeO2/PTEA5K-b-PAM30K, Fe2O3/PTEA5K-b-PAM30K,
Fe2O3/PTEA11K-b-PAM30K, Eu:YVO4/PTEA2K-b-PAM60K and Eu:YVO4/PTEA5K-b-PAM30K, we
found a unique behavior : the scattering intensity exhibits a sharp and
prominent peak in the intermediate X-range. To account for this behavior, we
have developed a model which assumes that regardless of X, the mixed aggregates
are formed at a fixed polymer-to-nanoparticle ratio. The agreement between the
results and the model is excellent on the 5 systems. Results at different
molecular weights suggest that the stoichiometry of the mixed aggregates is
controlled by the electrostatic interactions between the opposite charges. The
model allows to derive the molecular weight and the stoichiometry of the mixed
aggregates.",0701662v1
2007-03-02,A physics-based life prediction methodology for thermal barrier coating systems,"A novel mechanistic approach is proposed for the prediction of the life of
thermal barrier coating (TBC) systems. The life prediction methodology is based
on a criterion linked directly to the dominant failure mechanism. It relies on
a statistical treatment of the TBC's morphological characteristics,
non-destructive stress measurements and on a continuum mechanics framework to
quantify the stresses that promote the nucleation and growth of microcracks
within the TBC. The last of these accounts for the effects of TBC constituents'
elasto-visco-plastic properties, the stiffening of the ceramic due to sintering
and the oxidation at the interface between the thermally insulating yttria
stabilized zirconia (YSZ) layer and the metallic bond coat. The mechanistic
approach is used to investigate the effects on TBC life of the properties and
morphology of the top YSZ coating, metallic low-pressure plasma sprayed bond
coat and the thermally grown oxide. Its calibration is based on TBC damage
inferred from non-destructive fluorescence measurements using
piezo-spectroscopy and on the numerically predicted local TBC stresses
responsible for the initiation of such damage. The potential applicability of
the methodology to other types of TBC coatings and thermal loading conditions
is also discussed.",0703069v1
2007-03-10,Hybridized quadrupole-dipole exciton effects in $Cu_2O$ - Organic Heterostructure,"In the present work we discuss resonant hybridization of the $1S$ quadrupole
Wannier-Mott exciton (WE) in a $Cu_2O$ quantum well with the Frenkel (FE)
dipole exciton in an adjacent layer of organic DCM2:CA:PA. The coupling between
excitons is due to interaction between the gradient of electric field induced
by DCM2 Frenkel exciton and the quadrupole moment of the $1S$ transition in the
cuprous oxide. The specific choice of the organic allows us to use the
mechanism of 'solid state solvation' to dynamically tune the WE and FE into
resonance during time $\approx 3.3 \: ns$ (comparable with the big life time of
the WE) of the 'slow' phase of the solvation. The quadrupole-dipole hybrid
utilizes the big oscillator strength of the FE along with the big lifetime of
the quadrupole exciton, unlike dipole-dipole hybrid exciton which utilizes big
oscillator strength of the FE and big radius of the dipole allowed WE. Due to
strong spatial dispersion and big mass of the quadrupole WE the hybridization
is not masked by the kinetic energy or the radiative broadening. The lower
branch of the hybrid dispersion exhibits a pronounced minimum and may be used
in applications. Also we investigate and report noticeable change in the
coupling due to a induced 'Stark effect' from the strong local electric field
of the FE. We investigated the fine energy structure of the quantum well
confined ortho and para excitons in cuprous oxide.",0703268v1
2003-12-16,"Exact solutions for Bianchi type cosmological metrics, Weyl orbits of E_{8(8)} subalgebras and p--branes","In this paper we pursue further a programme initiated in a previous work and
aimed at the construction, classification and property investigation of time
dependent solutions of supergravity (superstring backgrounds) through a
systematic exploitation of U-duality hidden symmetries. This is done by first
reducing to D=3 where the bosonic part of the theory becomes a sigma model on
E_{8(8)}/SO(16), solving the equations through an algorithm that produces
general integrals for any chosen regular subalgebra G_r of E_{8(8)} and then
oxiding back to D=10. Different oxidations and hence different physical
interpretations of the same solutions are associated with different embeddings
of G_r. We show how such embeddings constitute orbits under the Weyl group and
we study the orbit space. This is relevant to associate candidate superstring
cosmological backgrounds to space Dp-brane configurations that admit
microscopic descriptions. In particular in this paper we show that there is
just one Weyl orbit of A_r subalgebras for r < 6$. The orbit of the previously
found A_2 solutions, together with space--brane representatives contains a pure
metric representative that corresponds to homogeneous Bianchi type 2A
cosmologies in D=4 based on the Heisenberg algebra. As a byproduct of our
methods we obtain new exact solutions for such cosmologies with and without
matter. We present a thorough investigation of their properties.",0312189v1
2006-08-23,Kac-Moody Algebras in M-theory,"In this thesis, we consider several aspects of over-extended and
very-extended Kac-Moody algebras in relation with theories of gravity coupled
to matter. In the first part, we focus on the occurrence of KM algebras in the
cosmological billiards. We analyse the billiards in the simplified situation of
spatially homogeneous cosmologies. The most generic cases lead to the same
algebras as those met in the general inhomogeneous case, but also sub-algebras
of the ""generic"" ones appear. Next, we consider particular gravitational
theories which, upon toroidal compactification to D=3 space-time dimensions,
reduce to a theory of gravity coupled to a symmetric space non-linear
sigma-model. We show that the billiard analysis gives direct information on
possible dimensional oxidations (or on their obstructions) and field content of
the oxidation endpoint. We also consider all hyperbolic Kac-Moody algebras and
completely answer the question of whether or not a specific theory exists
admitting a billiard characterised by the given hyperbolic algebra. In the
second part, we turn to the set up of such gravity-matter theories through the
building of an action explicitly invariant under a Kac-Moody group. As a first
step to include fermions, we check the compatibility of the presence of a Dirac
fermion with the (hidden duality) symmetries appearing in the toroidal
compactification down to 3 space-time dimensions. Next, we investigate how the
fermions (with spin 1/2 or 3/2) fit in the conjecture for hidden over-extended
symmetry G++. Finally, in the context of G+++ invariant actions, we derive all
the possible signatures for all the GB++ theories that can be obtained from the
conventional one (1,D-1) by ""dualities"" generated by Weyl reflections. This
generalizes the results obtained for E8++.",0608161v1
1998-08-26,Structures and Stabilities of Doubly-charged (MgO)nMg2+ (n=1-29) Cluster Ions,"Ab initio perturbed ion plus polarization calculations are reported for
doubly-charged nonstoichiometric (MgO)nMg2+ (n=1-29) cluster ions. We consider
a large number of isomers with full relaxations of the geometries, and add the
correlation correction to the Hartree-Fock energies for all cluster sizes. The
polarization contribution is included at a semiempirical level also for all
cluster sizes. Comparison is made with theoretical results for neutral (MgO)n
clusters and singly-charged alkali-halide cluster ions. Our method is also
compared to phenomenological pair potential models in order to asses their
reliability for calculations on small ionic systems. The large
coordination-dependent polarizabilities of oxide anions favor the formation of
surface sites, and thus bulklike structures begin to dominate only after n=24.
The relative stabilities of the cluster ions against evaporation of a MgO
molecule show variations that are in excellent agreement with the experimental
abundance spectra.",9808036v2
2005-12-06,Measuring the role of surface chemistry in silicon microphotonics,"The silicon/silicon dioxide (Si/SiO2) interface plays a crucial role in the
performance, cost, and reliability of most modern microelectronic devices, from
the basic transistor to flash memory, digital cameras, and solar cells. Today
the gate oxide thickness of modern transistors is roughly 5 atomic layers, with
8 metal wire layers required to transport all the signals within a
microprocessor. In addition to the increasing latency of such reduced-dimension
metal wires, further ""Moore's Law"" scaling of transistor cost and density is
predicted to saturate in the next decade. As a result, silicon-based
microphotonics is being explored for the routing and generation of
high-bandwidth signals. In comparison to the extensive knowledge of the
electronic properties of the Si/SiO2 interface, little is known about the
optical properties of Si surfaces used in microphotonics. In this Letter, we
explore the optical properties of the Si surface in the
telecommunication-relevant wavelength band of 1400-1600 nm. Utilizing a high
quality factor (Q ~ 1.5x10^6) optical microresonator to provide sensitivity
down to a fractional surface optical loss of 10^-7, we show that optical loss
within Si microphotonic components can be dramatically altered by Si surface
preparation, with fraction loss of 2 x 10^-5 measured for chemical oxide
surfaces as compared to <2 x 10^-6 for hydrogen-terminated Si surfaces. These
results indicate that the optical properties of Si surfaces can be
significantly and reversibly altered by standard microelectronics treatments,
and that stable, high optical quality surface passivation layers will be
critical in future Si micro- and nano-photonic systems.",0512040v1
2006-04-06,Ceramic Methyltrioxorhenium,"The metal oxide polymeric methyltrioxorhenium [(CH3)xReO3] is an unique
epresentative of a layered inherent conducting organometallic polymer which
adopts the structural motifs of classical perovskites in two dimensions (2D) in
form of methyl-deficient, corner-sharing ReO5(CH3) octahedra. In order to
improve the characteristics of polymeric methyltrioxorhenium with respect to
its physical properties and potential usage as an inherentconducting polymer we
tried to optimise the synthetic routes of polymeric modifications of 1 to
obtain a sintered ceramic material, denoted ceramic MTO. Ceramic MTO formed in
a solvent-free synthesis via auto-polymerisation and subsequent sintering
processing displays clearly different mechanical and physical properties from
polymeric MTO synthesised in aqueous solution. Ceramic MTO is shown to display
activated Re-C and Re=O bonds relative to MTO. These electronic and structural
characteristics of ceramic MTO are also reflected by a different chemical
reactivity compared with its monomeric parent compound. First examples of the
unprecedented reactivity of ceramic MTO in the field of amine oxidations are
shown - results which warrant further exploitation.",0604046v1
2005-06-20,Chemical and Structural Disorder in Eumelanins - A Possible Explanation for Broad Band Absorbance,"We report the results of an experimental and theoretical study of the
electronic and structural properties of a key eumelanin precursor -
5,6,-dihydroxyindole-2-carboxylic acid (DHICA) and its dimeric forms. We have
used optical spectroscopy to follow the oxidative polymerization of DHICA to
eumelanin, and observe red shifting and broadening of the absorption spectrum
as the reaction proceeds. First principles density functional theory
calculations indicate that DHICA oligomers (possible reaction products of
oxidative polymerization) have red shifted HOMO-LUMO gaps with respect to the
monomer. Furthermore, different bonding configurations (leading to oligomers
with different structures) produce a range of gaps. These experimental and
theoretical results lend support to the chemical disorder model where the broad
band monotonic absorption characteristic of all melanins is a consequence of
the superposition of a large number of inhomogeneously broadened Gaussian
transitions associated with each of the components of a melanin ensemble. These
results suggest that the traditional model of eumelanin as an amorphous organic
semiconductor is not required to explain its optical properties, and should be
thoroughly re-examined. These results have significant implications for our
understanding of the physics, chemistry and biological function of these
important biological macromolecules. Indeed, one may speculate that the robust
functionality of melanins in vitro is a direct consequence of its
heterogeneity, i.e. chemical disorder is a ""low cost"" natural resource in these
systems.",0506028v2
2007-06-04,Critical Behaviour of Irreversible Reaction Systems,"An introductory review on the critical behaviour of some irreversible
reaction systems is given. The study of these systems has attracted great
attention during the last decades due to, on the one hand, the rich and complex
underlying physics, and on the other hand, their relevance for numerous
technological applications in heterogeneous catalysis, corrosion and coating,
development of microelectronic devices, etc. The review is focuses on recent
advances in the understanding of irreversible phase transitions (IPT's)
providing a survey of the theoretical development of the field during the last
decade, as well as a detailed discussion of relevant numerical simulations. The
Langevin formulation for the treatment of second-order IPT's is discussed.
Different Monte Carlo approaches are also presented in detail and the
finite-size scaling analysis of second-order IPT's is described. Special
attention is devoted to the description of recent progress in the study of
first-order IPT's observed upon catalytic oxidation of carbon monoxide and the
reduction of nitrogen monoxide, using lattice gas reaction models. Only brief
comments are given on other reactions such as the oxidation of hydrogen,
ammonia synthesis, etc. Also, a discussion of relevant experiments is presented
and measurement are compared with the numerical results. Furthermore, promising
areas for further research and open questions are also addressed.",0706.0419v1
2007-07-04,Superconductivity in spinel oxide LiTi2O4 epitaxial thin films,"LiTi2O4 is a unique material in that it is the only known oxide spinel
superconductor. Although bulk studies have demonstrated that superconductivity
can be generally described by the Bardeen-Cooper-Schreiffer theory, the
microscopic mechanisms of superconductivity are not yet resolved fully. The
sensitivity of the superconducting properties to various defects of the spinel
crystal structure provides insight into such mechanisms. Epitaxial films of
LiTi2O4 on single crystalline substrates of MgAl2O4, MgO, and SrTiO3 provide
model systems to systematically explore the effects of lattice strain and
microstructural disorder. Lattice strain that affects bandwidth gives rise to
limited variations in the superconducting and normal state properties.
Microstructural disorder such as antiphase boundaries that give rise to Ti
network disorder can reduce the critical temperature, but Ti network disorder
combined with Mg interdiffusion can affect the superconducting state much more
dramatically. Thickness dependent transport studies indicate a
superconductor-insulator transition as a function of film thickness regardless
of lattice strain and microstructure. In addition, surface sensitive X-ray
absorption spectroscopy has identified Ti to retain site symmetry and average
valence of the bulk material regardless of film thickness.",0707.0522v2
2007-10-18,Phase behavior and dynamics of a micelle-forming triblock copolymer system,"Synperonic F-108 (generic name, 'pluronic') is a micelle forming triblock
copolymer of type ABA, where A is polyethylene oxide (PEO) and B is
polypropylene oxide (PPO). At high temperatures, the hydrophobicity of the PPO
chains increase, and the pluronic molecules, when dissolved in an aqueous
medium, self-associate into spherical micelles with dense PPO cores and
hydrated PEO coronas. At appropriately high concentrations, these micelles
arrange in a face centred cubic lattice to show inverse crystallization, with
the samples exhibiting high-temperature crystalline and low-temperature
fluidlike phases. By studying the evolution of the elastic and viscous moduli
as temperature is increased at a fixed rate, we construct the
concentration-temperature phase diagram of Synperonic F-108. For a certain
range of temperatures and at appropriate sample concentrations, we observe a
predominantly elastic response. Oscillatory strain amplitude sweep measurements
on these samples show pronounced peaks in the loss moduli, a typical feature of
soft solids. The soft solid-like nature of these materials is further
demonstrated by measuring their frequency dependent mechanical moduli. The
storage moduli are significantly larger than the loss moduli and are almost
independent of the applied angular frequency. Finally, we perform strain rate
frequency superposition (SRFS) experiments to measure the slow relaxation
dynamics of this soft solid.",0710.3433v2
2007-11-09,Study of the Electronic Structure in Oxides Using Absorption and Resonant X-Ray Scattering,"Resonant X-ray scattering (RXS) is a spectroscopy where both the power of
site selective diffraction and the power of local absorption spectroscopy
regarding atomic species are combined. By virtue of the dependence on the core
level state energy and the three dimensional electronic structure of the
intermediate state, this technique is specially suited to study charge, orbital
or spin orderings and associated crystal distortions. In the case of charge
ordering, we exploit the fact that atoms with closely related site symmetries
but with small charge differences exhibit resonances at slightly different
energies. The sensitivity of this effect allows for quantitative estimations of
the charge disproportion. Opposite to fluorescence or absorption measurements,
the power of diffraction relies on the capability of detecting differences that
are smaller than the inverse lifetime of the core hole level. To account for
the uncertainty of the crystallographic structure and the fact that the charge
ordering must be disentangled from the associated atomic displacements, a
complete methodology is proposed and applied to the low temperature phase of
magnetite. Relative sensitivity on spin, toroidal and orbital ordering is also
shown and compared in different transition metal oxide compounds, like V2O3 and
GaFeO3.",0711.1449v1
2007-12-04,Organic versus Hybrid Coacervate Complexes : Co-Assembly and Adsorption Properties,"We report the co-assembly and adsorption properties of coacervate complexes
made from polyelectrolyte-neutral block copolymers and oppositely charged
nanocolloids. The nanocolloids put under scrutiny were ionic surfactant
micelles and highly charged 7 nm cerium oxide (CeO2) nanoparticles. Static and
dynamic light scattering was used to investigate the microstructure and
stability of the organic and hybrid complexes. The microstructure of the
CeO2-based complexes was resolved using cryogenic transmission electronic
microscopy (Cryo-TEM), and it revealed that the cores were clusters made from
densely packed nanoparticles. In the concentration range of interest, c = 10-4
- 1 wt. %, the surfactant-based complexes were shown to exhibit a critical
association concentration (cac) whereas the nanoparticle-polymer hybrids did
not. The adsorption properties of the same complexes were investigated above
the cac by stagnation point adsorption reflectometry. The adsorbed amount was
measured as a function of time for polymers and complexes using anionically
charged silica and hydrophobic poly(styrene) substrates. It was found that all
complexes adsorbed readily on both types of substrates up to a level of 1 - 2
mg m-2 at stationary state. Upon rinsing however, the adsorbed layer was
removed for the surfactant-based systems, but not for the cerium oxide
clusters. As for the solution properties, these finding were interpreted in
terms of a critical association concentrations which are very different for
organic and hybrid complexes.",0712.0475v1
2008-01-08,"Without Spectroscopy at the Beginning, Catalysis Research Proceeded in the Wrong Direction for More Than 100 Years","A study by infrared spectroscopy of the physisorbed region of catalysis
demonstrated that the intermediates of catalysis exist on the surface as a two
dimensional gas. Data in the Atomic Energy Level tables show that of the
thousands of positive ions tabulated only approximately one hundred have the
low-lying excited states that produce surface electric fields with a fractional
charge. The specific catalyst for a reaction has the electric field with the
fractional charge which when imparted to the two reactants changes the
frequency of the fields at the sites of reaction on each so that they are
harmonically equal, that is their ratio is a power of two. When the two
reactants meet in the electric field of the catalyst resonance occurs. It is
during resonance that electrons are shared, paired and exchanged and bonds are
broken and made. This analysis of catalysis explains the most extraordinary
observation that a catalyst is Not consumed when used because the catalyst is
the electric fields. These discoveries are applied to explain such diverse
reactions as the oxidation and chlorination of carbon monoxide and the
destruction of nitric oxide in automobile exhaust. The use of electric fields
to produce reactions may have application not only in chemistry but in biology
and mechanics as well.",0801.1322v1
2008-02-21,Monotonic and fatigue testing of spring-bridged freestanding microbeams application for MEMS,"Microelectromechanical systems (MEMS) technologies are developing rapidly
with increasing study of the design, fabrication and commercialization of
microscale systems and devices. Accurate knowledge on the mechanical behaviors
of thin film materials used for MEMS is important for successful design and
development of MEMS. Here a novel electroplating spring-bridge micro-tensile
specimen integrates pin-pin align holes, misalignment compensate spring, load
sensor beam and freestanding thin film is demonstrated and fabricated. The
specimen is fit into a specially designed micro-mechanical apparatus to carry
out a series of monotonic tensile testing on sub-micron freestanding thin
films. Certain thin films applicable as structure or motion gears in MEMS were
tested including sputtered gold, copper and tantalum nitride thin films. Metal
specimens were fabricated by sputtering; for tantalum nitride film samples,
nitrogen gas was introduced into the chamber during sputtering tantalum films
on the silicon wafer. The sample fabrication method involves three steps of
lithography and two steps of electroplating copper to hold a dog bone
freestanding thin film. Using standard wet etching or lift off techniques, a
series of microtensile specimens were patterned in metal thin films, holes, and
seed layer for spring and frame structure on the underlying silicon oxide
coated silicon substrate. Two steps of electroplating processing to distinct
spring and frame portion of the test chip. Finally, chemical etched away the
silicon oxide to separated electroplated specimen and silicon substrate.",0802.3083v1
2008-03-28,High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory,"The existing hydrous titanium oxide (HTiO) technique for the measurement of
224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been
changed to make it faster and less sensitive to trace impurities in the HTiO
eluate. Using HTiO-loaded filters followed by cation exchange adsorption and
HTiO co-precipitation, Ra isotopes from 200-450 tonnes of heavy water can be
extracted and concentrated into a single sample of a few millilitres with a
total chemical efficiency of 50%. Combined with beta-alpha coincidence
counting, this method is capable of measuring 2.0x10^3 uBq/kg of 224Ra and
3.7x10^3 uBq/kg of 226Ra from the 232Th and 238U decay chains, respectively,
for a 275 tonne D2O assay, which are equivalent to 5x10^16 g Th/g and 3x10^16 g
U/g in heavy water.",0803.4162v2
2008-03-31,Superconductivity in iron-based F-doped layered quaternary compound Nd[O1-xFx]FeAs,"The recently discovered quaternary arsenide oxide superconductor
La[O1-xFx]FeAs with the superconducting critical transition temperature (Tc) of
26 K [1], has been quickly expanded to another high-Tc superconducting system
beyond copper oxides by the replacement of La with other rare earth elements,
such as Sm, Ce, and Pr etc. [2-4], and the Pr[O1-xFx]FeAs has become to be the
first non-cuprate superconductor that holding a Tc above 50 K. All these
arsenide (including phosphide) superconductors formed in a same tetragonal
layered structure with the space group P4/nmm which has an alternant stacked
Fe-As layer and RO (R = rare earth metals) layer. Here we report the discovery
of another superconductor in this system, the neodymium-arsenide Nd[O1-xFx]FeAs
with an resistivity onset Tc of 51.9 K, which is the second non-cuprate
compound that superconducts above 50 K.",0803.4234v2
2008-04-14,"Correlation Strength, Gaps and Particle-Hole Asymmetry in High-Tc Cuprates: a Dynamical Mean Field Study of the Three-Band Copper-Oxide Model","The three-band model relevant to high temperature copper-oxide
superconductors is solved using single-site dynamical mean field theory and a
tight-binding parametrization of the copper and oxygen bands. For a band
filling of one hole per unit cell the metal/charge-transfer-insulator phase
diagram is determined. The electron spectral function, optical conductivity and
quasiparticle mass enhancement are computed as functions of electron and hole
doping for parameters such that the corresponding to the paramagnetic metal and
charge-transfer insulator sides of the one hole per cell phase diagram. The
optical conductivity is computed using the Peierls phase approximation for the
optical matrix elements. The calculation includes the physics of ""Zhang-Rice
singlets"". The effects of antiferromagnetism on the magnitude of the gap and
the relation between correlation strength and doping-induced changes in state
density are determined. Three band and one band models are compared. The two
models are found to yield quantitatively consistent results for all energies
less than about 4eV, including energies in the vicinity of the charge-transfer
gap. Parameters on the insulating side of the metal/charge-transfer insulator
phase boundary lead to gaps which are too large and near-gap conductivities
which are too small relative to data. The results place the cuprates clearly in
the intermediate correlation regime, on the paramagnetic metal side of the
metal/charge-transfer insulator phase boundary.",0804.2250v2
2008-06-04,Evidence for Supercurrent Connectivity in Conglomerate Particles in NdFeAsO1-d,"Here we use global and local magnetometry and Hall probe imaging to
investigate the electromagnetic connectivity of the superconducting current
path in the oxygen-deficient fluorine-free Nd-based oxypnictides. High
resolution transmission electron microscopy and scanning electron microscopy
show strongly-layered crystallites, evidence for a ~ 5nm amorphous oxide around
individual particles, and second phase neodymium oxide which may be responsible
for the large paramagnetic background at high field and at high temperatures.
  From global magnetometry and electrical transport measurements it is clear
that there is a small supercurrent flowing on macroscopic sample dimensions
(mm), with a lower bound for the average (over this length scale) critical
current density of the order of 103 A/cm2. From magnetometry of powder samples
and local Hall probe imaging of a single large conglomerate particle ~120
microns it is clear that on smaller scales, there is better current
connectivity with a critical current density of the order of 5 x 104 A/cm2. We
find enhanced flux creep around the second peak anomaly in the magnetisation
curve and an irreversibility line significantly below Hc2(T) as determined by
ac calorimetry.",0806.0828v1
2008-06-14,Synthesis of nanocrystalline Spinel phase by Mechanical Milling of Al-Cu-Fe and Al-Cu-Cr-Fe Quasicrystalline alloys,"In the present study, low-temperature synthesis of (Cu Fe)Al2O4 and (Cu Cr
Fe)Al2O4 spinels from the quasicrystalline phases was investigated with the
variation of process parameters during milling and annealing. The milling of
the quasicrystalline materials was carried out in an attritor mill at 400 rpm
for 40 hours with ball to powder ratio of 40:1 in hexane medium. Subsequently,
annealing was performed in an air ambience for 10, 20, and 40 h at 400, 500,
600 and 700 C in side a furnace in order to oxidize the mechanically milled
quasicrystalline phase for the possible formation of the spinel phase. It was
found that after annealing at higher temperature (500 C), mechanically milled
quasicrystalline alloy transformed to spinel phase whereas annealing at lower
temperature (500 C) it led to the formation of B2 phase as a major one along
with minor amount of oxide phase. The X-ray diffraction and transmission
electron microscopy of the annealed samples confirmed the formation of spinel
phase with an average grain size of 20-40 nm. It is interesting to note that
the nanospinel phases showed the different colors during various annealing time
and temperature. The optical properties of nanospinel materials, investigated
employing UV visible spectrometer exhibited absorption characteristics.",0806.2381v1
2008-09-10,TiO and VO broad band absorption features in the optical spectrum of the atmosphere of the hot-Jupiter HD209458b,"The presence of titanium oxide (TiO) and vanadium oxide (VO) gas phase
species is searched for in the atmosphere of the hot Jupiter HD209458b. We
compared a model for the planets transmitted spectrum to multi-wavelength
eclipse-depth measurements (from 3000 to 10000 Angstrom), obtained by Sing et
al. (2008a) using archived HST-STIS time series spectra. We make use of these
observations to search for spectral signatures from extra absorbers in the
planet atmosphere between 6000 and 8000 Angstrom. Along with sodium depletion
and Rayleigh scattering recently published for this exoplanet atmosphere, an
extra absorber of uncertain origin, redward of the sodium lines, resides in the
atmosphere of the planet. Furthermore, this planet has a stratosphere
experiencing a thermal inversion caused by the capture of optical stellar flux
by absorbers that resides at altitude. Recent models have predicted that the
presence of TiO and VO in the atmosphere of HD209458b may be responsible for
this temperature inversion. Although no specific TiO and VO spectral band head
signatures have been identified unambiguously in the observed spectrum, we
suggest here that the opacities of those molecules are possible candidates to
explain the remaining continuous broad band absorption observed between 6200
and 8000 Angstrom. To match reasonably well the data, the abundances of TiO and
VO molecules are evaluated from ten to one thousand times below solar. This
upper limit result is in agreement with expected variations with altitude due
to depletion effects such as condensation.",0809.1865v1
2008-11-26,Bipolar charge-carrier injection in semiconductor/insulator/conductor heterostructures: self-consistent consideration,"A self-consistent model of bipolar charge-carrier injection and transport
processes in a semiconductor/insulator/conductor system is developed which
incorporates space-charge effects in the description of the injection process.
The amount of charge-carriers injected is strongly determined by the energy
barrier emerging at the contact, but at the same time the electrostatic
potential generated by the injected charge-carriers modifies the height of this
injection barrier itself. In our model, self-consistency is obtained by
assuming continuity of the electric displacement and of the electrochemical
potential all over the system. The constituents of the system are properly
taken into account by means of their respective density of state distributions.
The consequences resulting from our model are discussed on the basis of an
indium tin oxide/organic semiconductor/conductor structure. The distributions
of the charge carriers and the electric field through the electrodes and the
organic layer are calculated. The recombination- and current-voltage
characteristics are analyzed for different heights of injection barriers and
varying values of the recombination rate and compared with the measured
current-voltage dependences for an indium tin oxide/poly(phenylene vinylene)/Ca
structure. The voltage dependences of the recombination efficiency for the
different values of injection barriers and recombination rate reveal optimum
conditions for the device performance.",0811.4330v1
2009-02-23,Can TiO Explain Thermal Inversions in the Upper Atmospheres of Irradiated Giant Planets?,"Spitzer Space Telescope infrared observations indicate that several
transiting extrasolar giant planets have thermal inversions in their upper
atmospheres. Above a relative minimum, the temperature appears to increase with
altitude. Such an inversion probably requires a species at high altitude that
absorbs a significant amount of incident optical/UV radiation. Some authors
have suggested that the strong optical absorbers titanium oxide (TiO) and
vanadium oxide (VO) could provide the needed additional opacity. However, if
regions of the atmosphere are cold enough for Ti and V to be sequestered into
solids they might rain out and be severely depleted. With a model of the
vertical distribution of a refractory species in gaseous and condensed form, we
address the question of whether enough TiO (or VO) could survive aloft in an
irradiated planet's atmosphere to produce a thermal inversion. We find that,
without significant macroscopic mixing, a heavy species such as TiO --
especially one that can condense in a cold-trap region -- cannot persist in a
planet's upper atmosphere. In our model, the amount of macroscopic mixing that
would be required to loft TiO to millibar pressures ranges from ~10^7 to
~10^{11} cm^2/s on HD 209458b, HD 149026b, TrES-4, OGLE-TR-56b, and WASP-12b,
depending on the planet and on assumed condensate sizes. Such large values may
be problematic for the TiO hypothesis. [Abridged]",0902.3995v2
2009-04-21,Characterization of a naphthalene dioxygenase endowed with an exceptionally broad substrate specificity toward polycyclic aromatic hydrocarbons,"In Sphingomonas CHY-1, a single ring-hydroxylating dioxygenase is responsible
for the initial attack of a range of polycyclic aromatic hydrocarbons (PAHs)
composed of up to five rings. The components of this enzyme were separately
purified and characterized. The oxygenase component (ht-PhnI) was shown to
contain one Rieske-type [2Fe-2S] cluster and one mononuclear Fe center per
alpha subunit, based on EPR measurements and iron assay. Steady-state kinetic
measurements revealed that the enzyme had a relatively low apparent Michaelis
constant for naphthalene (Km= 0.92 $\pm$ 0.15 $\mu$M), and an apparent
specificity constant of 2.0 $\pm$ 0.3 $\mu$M-1 s-1. Naphthalene was converted
to the corresponding 1,2-dihydrodiol with stoichiometric oxidation of NADH. On
the other hand, the oxidation of eight other PAHs occurred at slower rates, and
with coupling efficiencies that decreased with the enzyme reaction rate.
Uncoupling was associated with hydrogen peroxide formation, which is
potentially deleterious to cells and might inhibit PAH degradation. In single
turnover reactions, ht-PhnI alone catalyzed PAH hydroxylation at a faster rate
in the presence of organic solvent, suggesting that the transfer of substrate
to the active site is a limiting factor. The four-ring PAHs chrysene and
benz[a]anthracene were subjected to a double ring-dihydroxylation, giving rise
to the formation of a significant proportion of bis-cis-dihydrodiols. In
addition, the dihydroxylation of benz[a]anthracene yielded three dihydrodiols,
the enzyme showing a preference for carbons in positions 1,2 and 10,11. This is
the first characterization of a dioxygenase able to dihydroxylate PAHs made up
of four and five rings.",0904.3254v1
2009-04-23,Experimental and theoretical study of oxygen adsorption structures on Ag(111),"The oxidized Ag(111) surface has been studied by a combination of
experimental and theoretical methods, scanning tunneling microscopy (STM),
x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). A
large variety of different surface structures is found, depending on the
detailed preparation conditions. The observed structures fall into four
classes: (a) individually chemisorbed atomic oxygen atoms, (b) three different
oxygen overlayer structures, including the well-known p(4 x 4) phase, formed
from the same Ag$_6$ and Ag$_{10}$ building blocks, (c) a c(4 x 8) structure
not previously observed, and (d) at higher oxygen coverages structures
characterized by stripes along the high-symmetry directions of the Ag(111)
substrate. Our analysis provides a detailed explanation of the atomic-scale
geometry of the Ag$_6$/Ag$_{10}$ building block structures, and the c(4 x 8)
and stripe structures are discussed in detail. The observation of many
different and co-existing structures implies that the O/Ag(111) system is
characterized by a significantly larger degree of complexity than previously
anticipated, and this will impact our understanding of oxidation catalysis
processes on Ag catalysts.",0904.3734v2
2009-06-15,Coexistence of Fermi arcs and Fermi pockets in a high Tc copper oxide superconductor,"In the pseudogap state of the high-Tc copper-oxide (cuprate) superconductors,
angle-resolved photoemission (ARPES) measurements have seen an Fermi arc, i.e.,
an open-ended gapless section in the large Fermi surface, rather than a closed
loop expected of an ordinary metal. This is all the more puzzling because Fermi
pockets (small closed Fermi surface features) have been suggested from recent
quantum oscillation measurements. The Fermi arcs have worried the high-Tc
community for many years because they cannot be understood in terms of existing
theories. Theorists came up with a way out in the form of conventional Fermi
surface pockets associated with competing order, with a back side that is for
detailed reasons invisible by photoemission. Here we report ARPES measurements
of La-Bi2201 that give direct evidence of the Fermi pocket. The charge carriers
in the pocket are holes and the pockets show an unusual dependence upon doping,
namely, they exist in underdoped but not overdoped samples. A big surprise is
that these Fermi pockets appear to coexist with the Fermi arcs. This
coexistence has not been expected theoretically and the understanding of the
mysterious pseudogap state in the high-Tc cuprate superconductors will rely
critically on understanding such a new finding.",0906.2682v2
2009-10-05,Simultaneous Nitrogen-Doping and Reduction of Graphene Oxide,"We develop a simple chemical method to obtain bulk quantities of N-doped,
reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia.
X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various
reaction temperatures reveals that N-doping occurs at a temperature as low as
300C, while the highest doping level of ~5% N is achieved at 500C. N-doping is
accompanied by the reduction of GO with decreases in oxygen levels from ~28% in
as-made GO down to ~2% in 1100C NH3 reacted GO. XPS analysis of the N binding
configurations of doped GO finds pyridinic N in the doped samples, with
increased quaternary N (N that replaced the carbon atoms in the graphene plane)
in GO annealed at higher temperatures (>900C). Oxygen groups in GO were found
responsible for reactions with NH3 and C-N bond formation. Pre-reduced GO with
fewer oxygen groups by thermal annealing in H2 exhibits greatly reduced
reactivity with NH3 and lower N-doping level. Electrical measurements of
individual GO sheet devices demonstrate that GO annealed in NH3 exhibits higher
conductivity than those annealed in H2, suggesting more effective reduction of
GO by annealing in NH3 than in H2, consistent with XPS data. The N-doped
reduced GO shows clearly n-type electron doping behavior with Dirac point (DP)
at negative gate voltages in three terminal devices. Our method could lead to
the synthesis of bulk amounts of N-doped, reduced GO sheets useful for various
practical applications.",0910.0862v1
2009-10-15,Graphene on Insulating Oxide Substrates: Role of Surface Dangling States,"We study the effect of insulating oxide substrates on the energy band
structure of monolayer and bilayer graphene using a first principles density
functional based electronic structure method and a local exchange correlation
approximation. We consider two crystalline substrates, SiO2 (or alpha-quartz)
and Al2O3 (alpha-alumina or sapphire), each with two surface terminations. We
focus on the role of substrate surface dangling states and their passivation in
perturbing the linear energy spectrum of graphene. On non-passivated surface
terminations, with the relaxation of top surface layers, only Si-terminated
quartz retains the linear band structure of graphene due to relatively large
equilibrium separation from the graphene layer whereas the other three surface
terminations considerably distort it. However, without relaxations of the top
surface layer atoms, linear bands appear in the electronic spectrum but with
the Dirac point shifted away from the Fermi level. Interestingly, with a second
carbon layer on non-passivated oxygen terminated Quartz, with top surface
layers relaxation, graphene features appear in the spectrum but sapphire with
both surface terminations shows perturbed features even with two carbon layers.
By passivating the surface dangling states with hydrogen atoms and without top
layer atomic relaxations, the electron-hole symmetry occurs exactly at the
Fermi level. This suggests that surface dangling states play a less important
role than the atomic relaxations of the top surface layers in distorting the
linear spectrum. In all cases we find that the first layer of graphene forms
ripples, much like in suspended graphene, but the strength of rippling is found
to be weaker probably due to the presence of the substrate.",0910.2999v2
2009-11-14,Nanostructured Europium Oxide thin films deposited by pulsed laser ablation of a metallic target in a He buffer atmosphere,"Nanostrucured Europium oxide and hydroxide films were obtained by pulsed
Nd:Yag (532 nm) laser ablation of an Europium metallic target, in the presence
of a 1 mbar Helium buffer atmosphere. Both the produced film and the ambient
plasma were characterized. The plasma was monitored by an electrostatic probe,
for plume expansion in vacuum or in the presence of the buffer atmosphere. The
time evolution of the ion saturation current was obtained for several probe to
substrate distances. The results show the splitting of the plume into two
velocity groups, being the lower velocity profile associated with metal cluster
formation within the plume. The films were obtained in the presence of helium
atmosphere, for several target to substrate distances. They were analyzed by
Rutherford backscattering spectrometry (RBS), X-Ray Diffraction (XRD) and
Atomic Force Microscopy, for samples as-deposited and treated at 600 degrees C
in air. The results show that the as-deposited samples are amorphous and have
chemical composition compatible with Europium hydroxide. The thermally treated
samples show X-Ray diffraction peaks of Eu_2O_3, with chemical composition
showing excess oxygen. Film nanostructuring was shown to be strongly correlated
to cluster formation, as shown by velocity splitting in probe current versus
time plots.",0911.2790v3
2010-03-26,Growth of solid conical structures during multistage drying of sessile poly(ethylene oxide) droplets,"Sessile droplets of aqueous poly(ethylene oxide) solution, with average
molecular weight of 100 kDa, are monitored during evaporative drying at ambient
conditions over a range of initial concentrations $c_0$. For all droplets with
$c_0 \geq 3%$, central conical structures, which can be hollow and nearly 50%
taller than the initial droplet, are formed during a growth stage. Although the
formation of superficially similar structures has been explained for
glass-forming polymers using a skin-buckling model which predicts the droplet
to have constant surface area during the growth stage (L. Pauchard and C.
Allain, Europhys. Lett., 2003, 62, 897-903), we demonstrate that this model is
not applicable here as the surface area is shown to increase during growth for
all $c_0$. We interpret our experimental data using a proposed drying and
deposition process comprising the four stages: pinned drying; receding contact
line; bootstrap growth, during which the liquid droplet is lifted upon
freshly-precipitated solid; and late drying. Additional predictions of our
model, including a criterion for predicting whether a conical structure will
form, compare favourably with observations. We discuss how the specific
chemical and physical properties of PEO, in particular its amphiphilic nature,
its tendency to form crystalline spherulites rather than an amorphous glass at
high concentrations and its anomalous surface tension values for MW = 100 kDa
may be critical to the observed drying process.",1003.5150v1
2010-03-29,In-situ quantitative measurement of electric fields in zinc oxide thin films using electrostatic force microscopy,"Zinc oxide (ZnO) is the most important material for the fabrication of modern
varistors (variable resistors). It is known that the highly nonlinear
current-voltage relationship of ZnO varistors is due to effects taking place at
the grain boundaries. For an accurate investigation of the mechanism of this
process, techniques are required that allow a direct observation of local
electric fields in varistor samples. The objective of this study is to show
that an atomic force microscope in a set-up as an electrostatic force
microscope is capable of the in-situ observation and measurement of an applied
electric field in samples of ZnO thin films. The technique of Surface Potential
Imaging was used to investigate laterally applied electric fields in this type
of sample for the first time. The local change of the electric field across the
samples was monitored and quantified. It was observed here that the morphology
of the surface is convoluted into the surface potential images and the
magnitude of this effect was quantified by taking surface potential images
without an applied electric field. For the given measurement conditions, a
height difference of 80 nm in the topography image resulted in a voltage
difference of roughly 66 mV in the surface potential image. A simple model was
provided that attributes this observation to the surroundings of the surface
atom closest to the imaging tip.",1003.5427v1
2010-08-13,Strain-voltage and current-voltage Scanning Probe Microscopy (SPM) response of ionic semiconductor thin films: probing of deformation potential,"We performed analytical calculations of the current-voltage and
strain-voltage response of the heterostructure like ""charged SPM tip electrode
/ gap / ionic-semiconductor film"" caused by the local changes of (a) ions
concentration (stoichiometry contribution); (b) acceptors (donors) charge state
(recharging contribution via ionic radius variation); (c) free electrons
(holes) concentration (electron-phonon coupling via the deformation potential).
The contribution (b) into the strain-voltage SPM was not calculated previously,
while the contribution (c) was not even predicted before, while our estimations
performed for correlated oxides show that strength of (c) appeared comparable
with (a,b). For the case of ion-blocking tip and substrate electrode mainly the
changes in holes (electrons) concentration contribute into the
voltage-dependent mechanical displacement of the film surface, directly
registered by strain SPM. Thus, we predict that the SPM measurements of the
ionic semiconductor surface displacement could provide important information
about the local changes of the acceptors (donors) charge state and electron
(hole)-phonon correlations via the deformation potential. We obtained the great
variety of the nonlinear static and dynamic current-voltage and strain-voltage
hysteresis loops in the ionic semiconductor thin film with mobile acceptors
(donors) and holes (electrons). Some types of the current-voltage hysteresis
with pronounced memory window and double loops are observed experimentally in
the correlated oxides and resistive switching materials like p-La1-xSrxMnO3-d
and La1-xSrxCoO3-d, while predicted strain-voltage hysteresis of
piezoelectric-like and butterfly-like shape requires experimental justification
by SPM.",1008.2389v1
2010-10-28,Long electron dephasing length and disorder-induced spin-orbit coupling in indium tin oxide nanowires,"We have measured the quantum-interference magnetoresistances in two single
indium tin oxide (ITO) nanowires between 0.25 and 40 K, by using the four-probe
configuration method. The magnetoresistances are compared with the
one-dimensional weak-(anti)localization theory to extract the electron
dephasing length $L_\phi$. We found, in a 60-nm diameter nanowire with a low
resistivity of $\rho$(10 K) = 185 $\mu \Omega$ cm, that $L_\phi$ is long,
increasing from 150 nm at 40 K to 520 nm at 0.25 K. Therefore, the nanowire
reveals strict one-dimensional weak-localization effect up to several tens of
degrees of Kelvin. In a second 72-nm diameter nanowire with a high resistivity
of $\rho$(10 K) = 1030 $\mu \Omega$ cm, the dephasing length is suppressed to
$L_\phi$(0.26 K) = 200 nm, and thus a crossover of the effective device
dimensionality from one to three occurs at about 12 K. In particular,
disorder-induced spin-orbit coupling is evident in the latter sample,
manifesting weak-antilocalization effect at temperatures below $\sim$ 4 K.
These observations demonstrate that versatile quantum-interference effects can
be realized in ITO nanowires by controlling differing levels of atomic defects
and impurities.",1010.5863v1
2011-01-03,"A Self-consistent DFT+DMFT scheme in the Projector Augmented Wave : Applications to Cerium, Ce2O3 and Pu2O3 with the Hubbard I solver and comparison to DFT+U","An implementation of full self-consistency over the electronic density in the
DFT+DMFT framework on the basis of a plane wave-projector augmented wave (PAW)
DFT code is presented. It allows for an accurate calculation of the total
energy in DFT+DMFT within a plane wave approach. In contrast to frameworks
based on the maximally localized Wannier function, the method is easily applied
to f electron systems, such as cerium, cerium oxide (Ce2O3) and plutonium oxide
(Pu2O3). In order to have a correct and physical calculation of the energy
terms, we find that the calculation of the self-consistent density is
mandatory. The formalism is general and does not depend on the method used to
solve the impurity model. Calculations are carried out within the Hubbard I
approximation, which is fast to solve, and gives a good description of strongly
correlated insulators. We compare the DFT+DMFT and DFT+U solutions, and
underline the qualitative differences of their converged densities. We
emphasize that in contrast to DFT+U, DFT+DMFT does not break the spin and
orbital symmetry. As a consequence, DFT+DMFT implies, on top of a better
physical description of correlated metals and insulators, a reduced occurrence
of unphysical metastable solutions in correlated insulators in comparison to
DFT+U.",1101.0539v2
2011-01-20,Novel Superconducting Phases in Copper Oxides and Iron-oxypnictides: NMR Studies,"We reexamine the novel phase diagrams of antiferromagnetism (AFM) and
high-Tc$ superconductivity (HTSC) for a disorder-free CuO$_2$ plane based on an
evaluation of local hole density ($p$) by site-selective Cu-NMR studies on
multilayered copper oxides. Multilayered systems provide us with the
opportunity to research the characteristics of the disorder-free CuO$_2$ plane.
The site-selective NMR is the best and the only tool used to extract
layer-dependent characteristics. Consequently, we have concluded that the
uniform mixing of AFM and SC is a general property inherent to a single CuO$_2$
plane in an underdoped regime of HTSC. The $T$=0 phase diagram of AFM
constructed here is in quantitative agreement with the theories in a strong
correlation regime which is unchanged even with mobile holes. This {\it Mott
physics} plays a vital role for mediating the Cooper pairs to make $T_c$ of
HTSC very high. By contrast, we address from extensive NMR studies on
electron-doped iron-oxypnictides La1111 compounds that the increase in $T_c$ is
not due to the development of AFM spin fluctuations, but because the structural
parameters, such as the bond angle $\alpha$ of the FeAs$_4$ tetrahedron and the
a-axis length, approach each optimum value. Based on these results, we propose
that a stronger correlation in HTSC than in FeAs-based superconductors may make
$T_c$ higher significantly.",1101.3928v2
2011-01-26,Multiple superconducting gap and anisotropic spin fluctuations in iron arsenides: Comparison with nickel analog,"We present extensive 75As NMR and NQR data on the superconducting arsenides
PrFeAs0.89F0.11 (Tc=45 K), LaFeAsO0.92F0.08 (Tc=27 K), LiFeAs (Tc = 17 K) and
Ba0.72K0.28Fe2As2 (Tc = 31.5 K) single crystal, and compare with the nickel
analog LaNiAsO0.9F0.1 (Tc=4.0 K) . In contrast to LaNiAsO0.9F0.1 where the
superconducting gap is shown to be isotropic, the spin lattice relaxation rate
1/T1 in the Fe-arsenides decreases below Tc with no coherence peak and shows a
step-wise variation at low temperatures. The Knight shift decreases below Tc
and shows a step-wise T variation as well. These results indicate spinsinglet
superconductivity with multiple gaps in the Fe-arsenides. The Fe
antiferromagnetic spin fluctuations are anisotropic and weaker compared to
underdoped copper-oxides or cobalt-oxide superconductors, while there is no
significant electron correlations in LaNiAsO0.9F0.1. We will discuss the
implications of these results and highlight the importance of the Fermi surface
topology.",1101.5014v1
2011-04-08,CO Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators,"Surface states refer to electronic states emerging as a solid material
terminates at a surface, and can be present in many systems. Despite their
spatial proximity to material surfaces, surface states have been largely
overlooked in fundamental understanding of surface catalysis and potential
real-world applications, because of their vulnerability to local impurities or
defects. In contrast, the recently discovered three-dimensional topological
insulators (3DTI) have exceptionally robust metallic surface states that are
topologically protected against surface contamination and imperfection. The
robust topological surface state(s) (TSS) provides a perfect platform for
exploiting novel physical phenomena and potential applications of surface
states in less stringent environments. Here we employ first-principles density
functional theory to demonstrate that the TSS can play a vital and elegant role
in facilitating surface reactions by serving as an effective electron bath. We
use CO oxidation on gold-covered Bi2Se3 as a prototype example, and first show
that the TSS is preserved when a stable ultrathin Au film is deposited onto a
Bi-terminated Bi2Se3 substrate. Furthermore, the TSS can significantly enhance
the adsorption energy of both CO and O2 molecules, by promoting different
directions of electron transfer. For CO, the TSS accepts electrons from the
CO-Au system, thereby decreasing the undesirable occupation of the CO
antibonding states. For O2, the TSS donates the needed electrons to promote the
molecule towards dissociative adsorption. The present study adds a new arena to
the technological potentials of 3DTI, and the central concept of TSS as an
electron bath as revealed here may lead to new design principles beyond the
conventional d-band theory of heterogeneous catalysis.",1104.1467v1
2011-04-13,Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system LixCoO2,"Thermoelectric properties of the layered cobalt oxide system LixCoO2 were
investigated in a wide range of Li composition, 0.98 >= x >= 0.35. Single-phase
bulk samples of LixCoO2 were successfully obtained through electrochemical
deintercalation of Li from the pristine LiCoO2 phase. While LixCoO2 with x >=
0.94 is semiconductive, the highly Li-deficient phase (0.75 >= x >= 0.35)
exhibits metallic conductivity. The magnitude of Seebeck coefficient at 293 K
(S293K) significantly depends on the Li content (x). The S293K value is as
large as +70 ~ +100 uV/K for x >= 0.94, and it rapidly decreases from +90 uV/K
to +10 uV/K as x is lowered within a Li composition range of 0.75 >= x >= 0.50.
This behavior is in sharp contrast to the results of x <= 0.40 for which the
S293K value is small and independent of x (+10 uV/K), indicating that a
discontinuous change in the thermoelectric characteristics takes place at x =
0.40 ~ 0.50. The unusually large Seebeck coefficient and metallic conductivity
are found to coexist in a narrow range of Li composition at about x = 0.75. The
coexistence, which leads to an enhanced thermoelectric power factor, may be
attributed to unusual electronic structure of the two-dimensional CoO2 block.",1104.2419v2
2011-04-28,Metal-insulator transition on SrTiO$_{3}$ surface induced by ionic-bombardment,"SrTiO$_{3}$ is one of the most popular insulating single-crystal substrates
for various complex-oxide thin film growths, because of its good lattice match
with many complex oxide films. Here, we show that a common thin film processing
technique, argon ion-milling, creates highly conducting layer on the surface of
STO, not only at room temperatures but also at cryogenic temperatures at which
thermal diffusion is completely suppressed. Systematic \emph{in situ}
four-point conductance measurements were taken on single-crystal STO substrates
inside vacuum environment. The evolution of metallicity out of insulating STO
follows simple models based on oxygen vacancy doping effect. At cryogenic
temperatures, ion milling created a thin - but much thicker than the
argon-penetration depth - steady-state oxygen-vacant layer, leading to a
highly-concentric metallic state. Near room temperatures, however, significant
thermal diffusion occurred and the metallic state continuously diffused into
the bulk, leaving only low concentraion of electron carriers on the surface.
Analysis of the discrepancy between the experiments and the models also
provided evidence for vacany clustering, which seems to occur during any
vacancy formation process and affects the observed conductance. These
observations suggest that the transport properties of films processed on STO
substrates using energetic methods such as ion milling need to be taken with
caution. On the other hand, if properly controlled, ionic bombardment could be
used as a way to create selective conducting layers on the surface of STO for
device applications.",1104.5522v3
2011-05-10,Drying and deposition of poly(ethylene oxide) droplets determined by Péclet number,"We report results of a detailed experimental investigation into the drying of
sessile droplets of aqueous poly(ethylene oxide) (PEO) polymer solutions under
various experimental conditions. Samples are prepared with a range of initial
concentrations c_0 and are filtered to remove traces of undissolved PEO
clusters. In typical experiments, droplets with initial volumes between 5\muL
and 50\muL are left to evaporate while temperature and relative humidity are
monitored. Droplets either form a disk-like solid ""puddle"" or a tall conical
""pillar"". The droplet mass is monitored using a microbalance and the droplet
profile is recorded regularly using a digital camera. Subsequent processing of
the data allows values of droplet volume V, surface area A, base radius R,
contact angle {\theta} and height h to be determined throughout drying. From
this data we identify four stages during pillar formation: pinned drying;
pseudo-dewetting; bootstrap building; solid contraction and propose physical
models to explain key aspects of each stage and to predict the transition from
each stage to the next. The experimental parameters of relative humidity,
temperature, pressure, droplet volume and initial contact angle are all
systematically varied and observed to influence the drying process and
consequently whether the droplet forms a pillar or a puddle. We combine these
parameters into a dimensionless P\'eclet number Pe, which compares the relative
effects of evaporation and diffusion, and show that the drying behaviour is
only dependent on c_0 and Pe.",1105.1927v1
2011-06-23,Noise and microresonance of critical current in Josephson junction induced by Kondo trap states,"We analyze the impact of trap states in the oxide layer of a superconducting
tunnel junctions, on the fluctuation of the Josephson critical current, thus on
coherence in superconducting qubits. Two mechanisms are usually considered: the
current blockage due to repulsion at the occupied trap states, and the noise
from electrons hopping across a trap. We extend previous studies of
noninteracting traps to the case where the traps have on-site electron
repulsion inside one ballistic channel. The repulsion not only allows the
appropriate temperature dependence of 1/f noise, but also is a control to the
coupling between the computational qubit and the spurious two-level systems
inside the oxide dielectric. We use second order perturbation theory which
allows to obtain analytical formulae for the interacting bound states and
spectral weights, limited to small and intermediate repulsions. Remarkably, it
still reproduces the main features of the model as identified from the
Numerical Renormalization Group. We present analytical formulations for the
subgap bound state energies, the singlet-doublet phase boundary, and the
spectral weights. We show that interactions can reverse the supercurrent across
the trap. We finally work out the spectrum of junction resonators for qubits in
the presence of on-site repulsive electrons and analyze its dependence on
microscopic parameters that may be controlled by fabrication.",1106.4794v3
2011-07-29,Study of radiation damage induced by 12 keV X-rays in MOS structures built on high resistivity n-type silicon,"Imaging experiments at the European X-ray Free Electron Laser (XFEL) require
silicon pixel sensors with extraordinary performance specifications: Doses of
up to 1 GGy of 12 keV photons, up to 10^5 12 keV photons per pixel of 200 \mum
\times 200 \mum arriving within less than 100 fs, and a time interval between
XFEL pulses of 220 ns. To address these challenges, in particular the question
of radiation damage, the properties of the SiO_2 layer and of the Si-SiO_2
interface using MOS capacitors manufactured on high resistivity n-type silicon
irradiated to X-ray doses between 10 kGy and 1 GGy, have been studied.
Measurements of Capacitance/Conductance-Voltage (C/G-V) at different
frequencies, as well as Thermal Dielectric Relaxation Current (TDRC) have been
performed. The data can be described by a radiation dependent oxide charge
density and three dominant radiation-induced interface states with
Gaussian-like energy distributions in the silicon band gap. It is found that
the densities of the fixed oxide charges and of the three interface states
increase up to dose values of approximately 10 MGy and then saturate or even
decrease. The shapes and the frequency dependences of the C/G-V measurements
can be quantitatively described by a simple model using the parameters
extracted from the TDRC measurements.",1107.5949v2
2011-09-24,Structure and electronic structure of Metal-Organic Frameworks within the Density-Functional based Tight-Binding method,"Density-functional based tight-binding is a powerful method to describe large
molecules and materials. Metal-Organic Frameworks (MOFs), materials with
interesting catalytic properties and with very large surface areas have been
developed and have become commercially available. Unit cells of MOFs typically
include hundreds of atoms, which make the application of standard
Density-Functional methods computationally very expensive, sometimes even
unfeasible. The aim of this paper is to prepare and to validate the
Self-Consistent Charge Density-Functional based Tight Binding (SCC-DFTB) method
for MOFs containing Cu, Zn and Al metal centers. The method has been validated
against full hybrid density-functional calculations for model clusters, against
gradient corrected density-functional calculations for supercells, and against
experiment. Moreover, the modular concept of MOF chemistry has been discussed
on the basis of their electronic properties. We concentrate on MOFs comprising
three common connector units: copper paddlewheels (HKUST-1), zinc oxide Zn4O
tetrahedron (MOF-5, MOF-177, DUT-6 (MOF-205)) and aluminium oxide AlO4(OH)2
octahedron (MIL-53). We show that SCC-DFTB predicts structural parameters with
a very good accuracy (with less than 5% deviation, even for adsorbed CO and H2O
on HKUST-1), while adsorption energies differ by 12 kJ mol-1 or less for CO and
water compared to DFT benchmark calculations.",1109.5312v1
2011-09-26,Radiation damage of polyethylene exposed in the stratosphere at an altitude of 40 km,"Low Density Polyethylene (LDPE) films were exposed at an altitude of 40 km
over a 3 day NASA stratospheric balloon mission from Alice Springs, Australia.
The radiation damage, oxidation and nitration in the LDPE films exposed in
stratosphere were measured using ESR, FTIR and XPS spectroscopy. The results
were compared with those from samples stored on the ground and exposed in a
laboratory plasma. The types of free radicals, unsaturated hydrocarbon groups,
oxygen-containing and nitrogen-containing groups in LDPE film exposed in the
stratosphere and at the Earth's surface are different. The radiation damage in
films exposed in the stratosphere are observed in the entire film due to the
penetration of high energy cosmic rays through their thickness, while the
radiation damage in films exposed on the ground is caused by sunlight
penetrating into only a thin surface layer. A similarly thin layer of the film
is damaged by exposure to plasma due to the low energy of the plasma particles.
The intensity of oxidation and nitration of LDPE films reflects the difference
of atmospheric pressure on the ground and in the stratosphere. The high-density
radiation damage of the LDPE films above the ozone layer in the stratosphere is
caused by primary cosmic rays as well as collision induced cosmic ray air
showers, and is consistent with the measured flux of cosmic radiation. The
results show, that stratospheric flights can be used to simulate the effects of
space environments during interplanet space flights for the purposes of
investigating the degradation of polymer materials.",1109.5457v1
2011-09-27,Affect of film thickness on the blue photoluminescence from ZnO,"Zinc oxide (ZnO) films having various thicknesses were synthesized on
sapphire substrates by thermal oxidation of Zn-metallic films in air ambient.
X-ray diffraction (XRD) spectra indicate that the resulting films possess a
polycrystalline hexagonal wurtzite structure without preferred orientation. For
films having a thickness of 200 nm, crystal grain size was observed to decrease
with increasing annealing temperature up to 600C, and then increase at higher
temperatures. Thicker films demonstrated a modest increase in grain size as
temperature increased from 300C to 1200C. The influence of film thickness on
the optical properties was investigated using room temperature
photoluminescence (PL). Specifically, PL spectra indicate four emission bands:
excitonic ultraviolet, blue, and deep-level green and yellow emission. The
strongest UV emission and narrowest full width at half maximum (0.09 eV) was
observed for films having a thickness of 200 nm and annealed at low temperature
(300C). The ratio of deep-level green emission to UV excitonic emission was
observed to decrease with decreasing annealing temperature, which is attributed
to the generation of fewer oxygen vacancies and interstitial oxygen ions in the
bulk. As film thickness decreased, we observed the emergence of blue emission
and a significant red shift (0.15 eV) in the bandgap. The emergence of blue
emission and the corresponding decrease in emission associated with bulk
defects when depletion width grows relative to the bulk suggests that the
origin of the blue emission is related to the negatively charged Zinc
interstitials found within the deletion region near the interface.",1109.5973v2
2012-03-14,Electron-phonon relaxation and excited electron distribution in zinc oxide and anatase,"We propose a first-principle method for evaluations of the time-dependent
electron distribution function of excited electrons in the conduction band of
semiconductors. The method takes into account the excitations of electrons by
external source and the relaxation to the bottom of conduction band via
electron-phonon coupling. The methods permits calculations of the
non-equilibrium electron distribution function, the quasi-stationary
distribution function with steady-in-time source of light, the time of setting
of the quasi-stationary distribution and the time of energy loss via relaxation
to the bottom of conduction band. The actual calculations have been performed
for titanium dioxide in the anatase structure and zinc oxide in the wurtzite
structure. We find that the quasi-stationary electron distribution function for
ZnO is a fermi-like curve that rises linearly with increasing excitation energy
whereas the analogous curve for anatase consists of a main peak and a shoulder.
The calculations demonstrate that the relaxation of excited electrons and the
setting of the quasi-stationary distribution occur within the time no more than
500 fsec for ZnO and 100 fsec for anatase.
  We also discuss the applicability of the effective phonon model with
energy-independent electron-phonon transition probability. We find that the
model only reproduces the trends in changing of the characteristic times
whereas the precision of such calculations is not high. The rate of energy
transfer to phonons at the quasi-stationary electron distribution also have
been evaluated and the effect of this transfer on the photocatalyses has been
discussed. We found that for ZnO this rate is about 5 times less than in
anatase.",1203.3033v1
2012-07-04,Prediction of under pickling defects on steel strip surface,"An extremely important part of the finishing line is the pickling process, in
which oxides formed during the hot rolling stage are removed from the surface
of the steel sheets. The efficiency of the pickling process is mainly dependent
on the nature of the oxide present at the surface of the steel, but, also, on
process parameters such as bath composition and time duration are relevant.
When acid concentration, solution temperatures and line speed are not properly
balanced, in fact, sheet defects like under pickling or over pickling may
happen and their occurrence does have a very serious effect on cold-reduction
performance and surface appearance of the finished product. Furthermore,
product damage from handling or improper equipment adjustment can render the
steel unsuitable for further processing. This is the reason why it is important
that process significant parameters are controlled and maintained as accurately
as possible in order to avoid these undesired phenomena. In the present work, a
control algorithm, composed by two different modules, i.e. decision tree and
rectangular Basis Function Network, has been implemented to aim of predicting
pickling defects and suggesting the optimal speed or the admissible speed range
of the steel strip in the process line. In this way the most suitable line
speed value can be set in an automatic way or by the technical personnel.",1207.0911v1
2012-07-11,Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores,"Context. The abundances of many observed compounds in interstellar molecular
clouds still lack an explanation, despite extensive research that includes both
gas and solid (dust-grain surface) phase reactions. Aims. We aim to
qualitatively prove the idea that a hydrogen-poor subsurface chemistry on
interstellar grains is responsible for at least some of these chemical
""anomalies"". This chemistry develops in the icy mantles when photodissociation
reactions in the mantle release free hydrogen, which escapes the mantle via
diffusion. This results in serious alterations of the chemical composition of
the mantle because pores in the mantle provide surfaces for reactions in the
new, hydrogen-poor environment. Methods. We present a simple kinetic model,
using existing astrochemical reaction databases. Gas phase, surface and
subsurface pore reactions are included, as are physical transformations of
molecules. Results. Our model produces significantly higher abundances for
various oxidized species than most other models. We also obtain quite good
results for some individual species that have adequate reaction network. Thus,
we consider that the hydrogen-poor mantle chemistry may indeed play a role in
the chemical evolution of molecular clouds. Conclusions. The significance of
outward hydrogen diffusion has to be proved by further research. A huge number
of solid phase reactions between many oxidized species is essential to obtain
good, quantitative modeling results for a comparison with observations. We
speculate that a variety of unobservable hydrogen-poor sulfur oxoacid
derivatives may be responsible for the ""disappearance"" of sulfur in dark cloud
cores.",1207.2689v1
2012-08-05,Flexible Organic Photovoltaic Cells with In-situ Non-thermal Photoreduction of Spin Coated Graphene Oxide Electrodes,"This article is withdrawn since it is published in a journal
  We report on the first reduction methodology, compatible with flexible,
temperature sensitive substrates, for the production of reduced spin coated
graphene oxide (GO) electrodes. It is based on the use of a laser beam for the
in-situ, non-thermal, reduction of spin coated GO films on flexible substrates
over a large area. The photoreduction process is one-step, facile and is
rapidly carried out at room temperature in air without affecting the integrity
of the graphene lattice as well as the flexibility of the underlying substrate.
Conductive graphene films with a sheet resistance of as low as 700 {\Omega}/sq
can be obtained, much higher than flexible layers reduced by chemical means. As
a proof of concept of our technique, the laser-reduced GO (LrGO) films were
utilized as the transparent electrode in flexible, bulk heterojunction, organic
photovoltaic (OPV) devices, replacing the traditional ITO. The devices
displayed a power-conversion efficiency of 1.1 %, which is the highest reported
so far for OPV device incorporating reduced GO as the transparent electrode.
The in-situ non-thermal photoreduction of spin-coated GO films creates a new
way to produce flexible functional graphene electrodes for a variety of
electronic applications in a process that carries substantial promise for
potential industrial implementation.",1208.0988v3
2012-11-12,"Cation nonstoichiometry and its impact on nucleation, structure and defect formation in complex oxide heteroepitaxy : LaCrO3 on SrTiO3(001)","Our ability to design and fabricate electronic devices with reproducible
properties using complex oxides is critically dependent on our ability to
controllably synthesize these materials in thin-film form. Structure-property
relationships are intimately tied to film and interface composition. Here we
report on the effects of cation stoichiometry in LaCrO3 heteroepitaxial films
prepared using molecular beam epitaxy. We show that LaCrO3 films grow
pseudomorphically on SrTiO3(001) over a wide range of La-to-Cr atom ratios.
However, the growth mode and structural quality are sensitive to the La-to-Cr
ratio, with La-rich films being of considerably lower structural quality than
Cr-rich films. Cation mixing occurs at the interface for all La-to-Cr ratios
investigated, and is not quenched by deposition at ambient temperature.
Indiffused La atoms occupy Sr sites in the substrate. The presence of defects
in the SrTiO3 substrate is implicated in promoting La indiffusion by comparing
the properties of LaCrO3/SrTiO3 with those of LaCrO3/Si, both prepared at
ambient temperature. Additionally, pulsed laser deposition is shown to result
in more extensive interfacial mixing than molecular beam epitaxy for deposition
at ambient temperature on Si.",1211.2850v1
2012-11-24,Ab initio modelling of UN grain boundary interfaces,"The uranium mononitride (UN) is a material considered as a promising
candidate for Generation-IV nuclear reactor fuels. Unfortunately, oxygen in air
affects UN fuel performance and stability. Therefore, it is necessary to
understand the mechanism of oxygen adsorption and further UN oxidation in the
bulk and at surface. Recently, we performed a detailed study on oxygen
interaction with UN surface using density functional theory (DFT) calculations.
We were able to identify an atomistic mechanism of UN surface oxidation
consisting of several important steps, starting with the oxygen molecule
dissociation and finishing with oxygen atom incorporation into vacancies on the
surface. However, in reality most of processes occur at the interfaces and on
UN grain boundaries. In this study, we present the results of first DFT
calculations on O behaviour inside UN grain boundaries performed using GGA
exchange-correlation functional PW91 as implemented into the VASP computer
code. We consider a simple interface (310)[001](36.8{\deg}) tilt grain
boundary. The N vacancy formation energies and energies of O incorporation into
pre-existing vacancies in the grain boundaries as well as O solution energies
were compared with those obtained for the UN (001) and (110) surfaces.",1211.5693v1
2012-11-26,Plasmonic resonances in nanostructured transparent conducting oxide films,"Transparent conducting oxides (TCO) are emerging as possible alternative
constituent materials to replace noble metals such as silver and gold for
low-loss plasmonic and metamaterial (MMs) applications in the near infrared
(NIR) regime. The optical characteristics of TCOs have been studied to evaluate
the functionalities and potential of these materials as metal substitutes in
plasmonic and MM devices, even apart from their usual use as electrode
materials. However, patterning TCOs at the nanoscale, which is necessary for
plasmonic and MM devices, is not well-studied. This paper investigates
nanopatterning processes for TCOs, especially the lift-off technique with
electron-beam lithography, and the realization of plasmonic nanostructures with
TCOs. By employing the developed nanopatterning process, we fabricate
2D-periodic arrays of TCO nanodisks and characterize the material's plasmonic
properties to evaluate the performance of TCOs as metal substitutes.
Light-induced collective oscillations of the free electrons in the TCOs (bulk
plasmons) and localized surface plasmon resonances are observed in the
wavelength range from 1.6 to 2.1 micron. Well-defined resonance peaks are
observed, which can be dramatically tuned by varying the amount of dopant and
by thermally annealing the TCO nanodisks in nitrogen gas ambient while
maintaining the low-loss properties.",1211.5988v1
2012-12-07,Poly(acrylic acid)-coated iron oxide nanoparticles : quantitative evaluation of the coating properties and applications for the removal of a pollutant dye,"In this work, 6 to 12 nm iron oxide nanoparticles were synthesized and coated
with poly(acrylic acid) chains of molecular weight 2100 g/mol. Based on a
quantitative evaluation of the dispersions, the bare and coated particles were
thoroughly characterized. The number densities of polymers adsorbed at the
particle surface and of available chargeable groups were found to be 1.9 +/-
0.3 nm-2 and 26 +/- 4 nm-2, respectively. Occurring via a multi-site binding
mechanism, the electrostatic coupling leads to a solid and resilient anchoring
of the chains. To assess the efficacy of the particles for pollutant
remediation, the adsorption isotherm of methylene blue molecules, a model of
pollutant, was determined. The excellent agreement between the predicted and
measured amounts of adsorbed dyes suggests that most carboxylates participate
to the complexation and adsorption mechanisms. An adsorption of 830 mg/g was
obtained. This quantity compares well with the highest values available for
this dye.",1212.1580v1
2012-12-11,Photoluminescence and High Temperature Persistent Photoconductivity Experiments in SnO2 Nanobelts,"The Persistent Photoconductivity (PPC) effect was studied in individual tin
oxide (SnO2) nanobelts as a function of temperature, in air, helium, and vacuum
atmospheres, and low temperature Photoluminescence measurements were carried
out to study the optical transitions and to determine of the acceptor/donors
levels and their best representation inside the band gap. Under ultraviolet
(UV) illumination and at temperatures in the range of 200 to 400K we observed a
fast and strong enhancement of the photoconductivity, and the maximum value of
the photocurrent induced increases as the temperature or the oxygen
concentration decreases. By turning off the UV illumination the induced
photocurrent decays with lifetimes up to several hours. The photoconductivity
and the PPC results were explained by adsorption and desorption of molecular
oxygen at the surface of the SnO2 nanobelts. Based on the temperature
dependence of the PPC decay an activation energy of 230 meV was found, which
corresponds to the energy necessary for thermal ionization of free holes from
acceptor levels to the valence band, in agreement with the photoluminescence
results presented. The molecular-oxygen recombination with holes is the origin
of the PPC effect in metal oxide semiconductors, so that, the PPC effect is not
related to the oxygen vacancies, as commonly presented in the literature.",1212.2550v1
2013-02-13,Disappearance of Nodal Gap across the Insulator-Superconductor Transition in a Copper-Oxide Superconductor,"The parent compound of the copper-oxide high temperature superconductors is a
Mott insulator. Superconductivity is realized by doping an appropriate amount
of charge carriers. How a Mott insulator transforms into a superconductor is
crucial in understanding the unusual physical properties of high temperature
superconductors and the superconductivity mechanism. Here we report high
resolution angle-resolved photoemission measurement on heavily underdoped
Bi2Sr2-xLaxCuO6+d system. The electronic structure of the lightly-doped samples
exhibit a number of characteristics: existence of an energy gap along the nodal
direction, d-wave-like anisotropic energy gap along the underlying Fermi
surface, and coexistence of a coherence peak and a broad hump in the
photoemission spectra. Our results reveal a clear insulator-superconductor
transition at a critical doping level of ~0.10 where the nodal energy gap
approaches zero, the three-dimensional antiferromagnetic order disappears, and
superconductivity starts to emerge. These observations clearly signal a close
connection between the nodal gap, antiferromagnetism and superconductivity.",1302.3017v2
2013-02-13,Probing electron transport across a LSMO/Nb:STO heterointerface at the nanoscale,"We investigate electron transport across a complex oxide heterointerface of
La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) on Nb:SrTiO$_3$ (Nb:STO) at different
temperatures. For this, we employ the conventional current-voltage method as
well as the technique of Ballistic Electron Emission Microscopy (BEEM), which
can probe lateral inhomogeneities in transport at the nanometer scale. From
current-voltage measurements, we find that the Schottky Barrier height (SBH) at
the LSMO/Nb:STO interface decreases at low temperatures accompanied by a larger
than unity ideality factor. This is ascribed to the tunneling dominated
transport caused by the narrowing of the depletion width at the interface.
However, BEEM studies of such unbiased interfaces, do not exhibit SBH lowering
at low temperatures, implying that this is triggered by the modification of the
interface due to an applied bias and is not an intrinsic property of the
interface. Interestingly, the SBH at the nanoscale, as extracted from BEEM
studies, at different locations in the device is found to be spatially
homogeneous and similar both at room temperature and at low temperatures. Our
results highlight the application of BEEM in characterizing electron transport
and their homogeneity at such unbiased complex oxide interfaces and yields new
insights into the origin of the temperature dependence of the SBH at biased
interfaces.",1302.3187v1
2013-03-23,Keck II Observations of Hemispherical Differences in H2O2 on Europa,"We present results from Keck II observations of Europa over four consecutive
nights using the near-infrared spectrograph (NIRSPEC). Spectra were collected
in the 3.14--4.0 micron range, allowing detection and monitoring of the 3.5
micron feature due to hydrogen peroxide. Galileo Near-Infrared Spectrometer
(NIMS) results first revealed hydrogen peroxide on Europa in the anti-jovian
region of the leading hemisphere at an abundance of 0.13+/-0.07% by number
abundance relative to water. We find comparable results for the two nights over
which we observed the leading hemisphere. Significantly, we observed a small
amount of hydrogen peroxide (~0.04%) during observations of Europa's anti- and
sub-Jovian hemispheres. Almost no hydrogen peroxide was detected during
observations of just the trailing hemisphere. We conclude that the Galileo
observations likely represent the maximum hydrogen peroxide concentration, the
exception potentially being the cold water ice regions of the poles, which are
not readily observable from the ground. Our mapping of the peroxide abundance
across Europa requires revisions to previous estimates for Europa's global
surface abundance of oxidants and leads to a reduction in the total oxidant
delivery expected for the sub-surface ocean, if exchange of surface material
with the ocean occurs.",1303.5895v1
2013-04-11,Intrinsic Spin Hall Effect at Oxide Interfaces: a Simple Model,"An asymmetric triangular potential well provides the simplest model for the
confinement of mobile electrons at the interface between two insulating oxides,
such as LaAlO_3 and SrTiO_3 (LAO/STO). These electrons have been recently shown
to exhibit a large spin-orbit coupling of the Rashba type, i.e., linear in the
in-plane momentum. In this paper we study the intrinsic spin Hall effect due to
Rashba coupling in an asymmetric triangular potential well. Besides splitting
each subband into two branches of opposite helicity, the spin-orbit interaction
causes the wave function in the direction perpendicular to the plane of the
quantum well (the z direction) to depend on the in-plane wave vector k. In
contrast to the extreme asymmetric case, i.e., the wedge-shaped quantum well,
for which the intrinsic spin Hall effect vanishes due to vertex corrections, we
find that the asymmetric well supports a non-vanishing intrinsic spin Hall
conductivity, which increases in magnitude as the well becomes more symmetric.
The spin Hall conductivity is found to be proportional to the square of the
spin-orbit coupling constant and, in the limit of low carrier density, depends
only on the effective mass renormalization associated with the k-dependence of
the wave functions in the z direction. Its origin lies in the non-vanishing
matrix elements of the spin current between subbands corresponding to different
states of quantized motion perpendicular to the plane of the well.",1304.3476v2
2013-05-04,Interfacial activity of phosphonated-polyethylene glycol functionalized cerium oxide nanoparticles,"In a recent publication, we have highlighted the potential of phosphonic acid
terminated PEG oligomers to functionalize strong UV absorption cerium oxide
nanoparticles[1], which yield suspensions that are stable in aqueous or organic
solvents and are redispersible in different solvent after freeze-drying. In the
present work, we highlight the interfacial activity of the functional ceria
nanoparticles and their potential to modify hydrophobic surfaces. We first
investigated Phosphonated-PEG amphiphilic oligomers behavior as strong surface
active species forming irreversibly adsorbed layers. We then show that the
oligomers interfacial properties translate to the functional nanoparticles. In
particular, the addition of a small fraction of phosphonated-PEG oligomers with
an extra C16 aliphatic chain (stickers) into the formulation enabled the tuning
of i) the nanoparticles adsorption at the air/water, polystyrene/water,
oil/water interfaces and ii) the particle/particle interaction in aqueous
solutions. We also found that dense and closely packed two dimensional
monolayers of nanoceria can be formed by spontaneous adsorption or surface
compression using a Langmuir trough. A hexagonal organization controlled by
reversible and repulsive repulsion has been characterized by GISAXS. Mono- or
multilayers can also be stably formed or transferred on solid surfaces. Our
results are key features in the field of polymer surface modification, solid
stabilized emulsions (Pickering) or supracolloidal assemblies.",1305.0898v1
2013-05-15,Nanoscale order in the frustrated mixed conductor La$_{5.4}WO$_{12-δ}$,"We report a comprehensive investigation of the average and local structure of
La$_{5.4}$WO$_{12-\delta}$, which has excellent mixed proton, electron and
oxide ion conduction suitable for device applications. Synchrotron X-ray and
neutron powder diffraction show that a cubic fluorite supercell describes the
average structure, with highly disordered lanthanum and oxide positions. On
average the tungsten sites are six-fold coordinated, and we detect a trace
(4.4(2) %) of anti-site disorder. In addition to sharp Bragg reflections,
strong diffuse neutron scattering is observed, which hints at short-range
order. We consider plausible local configurations, and show that the defect
chemistry implies a simple 'chemical exchange' interaction that favours ordered
WO6 octahedra. Our local model is confirmed by synchrotron x-ray pair
distribution function analysis and EXAFS experiments performed at the La K and
W L3-edges. We show that ordered domains of around ca. 3.5 nm are found,
implying that mixed conduction in La$_{5.4}$WO$_{12-\delta}$? is associated
with a defective glassy-like anion sublattice. The origins of this ground state
are proposed to lie in the non-bipartite nature of the fcc lattice and the
pairwise interactions which link the orientation of neighbouring octahedral WO6
sites. This 'function through frustration' could provide a means of designing
new mixed conductors.",1305.3385v1
2013-05-30,Kelvin Probe Microscopy and Electronic Transport Measurements in Reduced Graphene Oxide Chemical Sensors,"Reduced Graphene Oxide (RGO) is an electronically hybrid material that
displays remarkable chemical sensing properties. Here, we present a
quantitative analysis of the chemical gating effects in RGO-based chemical
sensors. The gas sensing devices are patterned in a field-effect transistor
geometry, by dielectrophoretic assembly of RGO platelets between gold
electrodes deposited on SiO2/Si substrates. We show that these sensors display
highly selective and reversible responses to the measured analytes, as well as
fast response and recovery times (tens of seconds). We use combined electronic
transport/Kelvin Probe Microscopy measurements to quantify the amount of charge
transferred to RGO due to chemical doping when the device is exposed to
electron-acceptor (acetone) and electron-donor (ammonia) analytes. We
demonstrate that this method allows us to obtain high-resolution maps of the
surface potential and local charge distribution both before and after chemical
doping, to identify local gate-susceptible areas on the RGO surface, and to
directly extract the contact resistance between the RGO and the metallic
electrodes. The method presented is general, suggesting that these results have
important implications for building graphene and other nanomaterial-based
chemical sensors.",1305.7222v1
2013-06-05,Method and Advantages of Genetic Algorithms in Parameterization of Interatomic Potentials: Metal-Oxides,"The method and the advantages of an evolutionary computing based approach
using a steady state genetic algorithm (GA) for the parameterization of
interatomic potentials for metal oxides within the shell model framework are
developed and described. We show that the GA based methodology for the
parameterization of interatomic force field functions is capable of (a)
simultaneous optimization of the multiple phases or properties of a material in
a single run, (b) facilitates the incremental re-optimization of the whole
system as more data is available for either additional phases or material
properties not included in previous runs, and (c) successful global
optimization in the presence of multiple local minima in the parameter space.
As an example, we apply the method towards simultaneous optimization of four
distinct crystalline phases of Barium Titanate (BaTiO3 or BTO) using an ab
initio density functional theory (DFT) based reference dataset. We find that
the optimized force field function is capable of the prediction of the two
phases not used in the optimization procedure, and that many derived physical
properties such as the equilibrium lattice constants, unit cell volume, elastic
properties, coefficient of thermal expansion, and average electronic
polarization are in good agreement with the experimental results available from
the literature.",1306.1196v1
2013-07-10,Seeding ice growth at ambient conditions using nano graphene oxide,"Water wetting on a hydrophobic surface at ambient conditions is disallowed by
the nonpolar nature of the surface and high vapor pressure of water. However,
the presence of sub-millimeter sized hydrophilic patches allows the waxy wings
of desert beetles to become wettable by morning mist. Here, we show that a
sprinkle of graphene oxide nanoflakes (nanoGOs) is effective in condensing
water nanodroplets and seeding ice epitaxy on graphite at ambient conditions.
By controlling relative humidity and nanoGO density, we are able to study the
formation of a complete ice wetting layer on a time scale of 20 hours. This
presents an unprecedented opportunity to visualize ice nucleation and growth in
real time using non-contact atomic force microscopy. The stages of
crystallization, as proposed by Ostwald in 1897, is fully unfolded at a
microscopic level for the first time. We obtain real-time imaging of sequential
phase transition from amorphous ice to a transient cubic ice Ic stage and
finally to the stable hexagonal ice Ih. Most interestingly, we discover that
ice nucleation and growth can be influenced by modifying the functional groups
of nanoGO, and by intermolecular hydrogen-bonding between nanoGOs. This affords
a strategy to control heterogenous ice nucleation and snow crystal formation.",1307.2673v1
2013-07-17,"Sorption of 4He, H2, Ne, N2, CH4 and Kr impurities in graphene oxide at low temperatures. Quantum effects","Sorption and the subsequent desorption of 4He, H2,Ne, N2, CH4 and Kr gas
impurities by graphene oxide (GO), glucose-reduced GO (RGO-Gl) and
hydrazine-reduced GO (RGO-Hz) powders have been investigated in the temperature
interval 2-290 K. It has been found that the sorptive capacity of the reduced
sample RGO-Hz is three to six times higher than that of GO. The reduction of GO
with glucose has only a slight effect on its sorptive properties. The
temperature dependences of the diffusion coefficients of the GO, RGO-Gl and
RGO-Hz samples have been obtained using the measured characteristic times of
sorption. It is assumed that the temperature dependences of the diffusion
coefficients are determined by the competition of the thermally activated and
tunneling mechanisms, the tunneling contribution being dominant at low
temperatures.",1307.4528v1
2013-07-29,Evidence for hydrogen two-level systems in atomic layer deposition oxides,"Two-level system (TLS) defects in dielectrics are known to limit the
performance of electronic devices. We study TLS using millikelvin microwave
loss measurements of three atomic layer deposited (ALD) oxide
films--crystalline BeO ($\rm{c-BeO}$), amorphous $\rm{Al_2O_3}$
($\rm{a-Al_2O_3}$), and amorphous $\rm{LaAlO_3}$ ($\rm{a-LaAlO_3}$)--and
interpret them with room temperature characterization measurements. We find
that the bulk loss tangent in the crystalline film is 6 times higher than in
the amorphous films. In addition, its power saturation agrees with an amorphous
distribution of TLS. Through a comparison of loss tangent data to secondary ion
mass spectrometry (SIMS) impurity analysis we find that the dominant loss in
all film types is consistent with hydrogen-based TLS. In the amorphous films
excess hydrogen is found at the ambient-exposed surface, and we extract the
associated hydrogen-based surface loss tangent. Data from films with a factor
of 40 difference in carbon impurities revealed that carbon is currently a
negligible contributor to TLS loss.",1307.7664v1
2013-10-15,Reduced graphene oxide thin films as ultrabarriers for organic electronics,"Encapsulation of electronic devices based on organic materials that are prone
to degradation even under normal atmospheric conditions with hermetic barriers
is crucial for increasing their lifetime. A challenge is to develop
'ultrabarriers' that are impermeable, flexible, and preferably transparent.
Another important requirement is that they must be compatible with organic
electronics fabrication schemes (i.e. must be solution processable, deposited
at room temperature and be chemically inert). Here, we report lifetime increase
of 1,300 hours for poly(3-hexylthiophene) (P3HT) films encapsulated by uniform
and continuous thin (~10 nm) films of reduced graphene oxide (rGO). This level
of protection against oxygen and water vapor diffusion is substantially better
than conventional polymeric barriers such as CytopTM, which degrades after only
350 hours despite being 400 nm thick. Analysis using atomic force microscopy,
x-ray photoelectron spectroscopy and high resolution transmission electron
microscopy suggest that the superior oxygen gas/moisture barrier property of
rGO is due to the close interlayer distance packing and absence of pinholes
within the impermeable sheets. These material properties can be correlated to
the enhanced lag time of 500 hours. Our results provide new insight for the
design of high performance and solution processable transparent 'ultrabarriers'
for a wide range of encapsulation applications.",1310.3915v1
2013-10-22,Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy,"Knowledge of the electron sampling depth and related saturation effects is
important for quantitative analysis of X-ray absorption spectroscopy data, yet
for oxides with the perovskite structure no quantitative values are so far
available. Here we study absorption saturation in films of two of the
most-studied perovskites, LCMO and YBCO, at the L2,3 edge of Mn and Cu,
respectively. By measuring the electron-yield intensity as a function of photon
incidence angle and film thickness, the sampling depth d, photon attenuation
length, lambda, and the ratio lambda/d have been independently determined
between 50 and 300 K. The extracted sampling depth dLCMO=3 nm for LCMO at high
temperatures in its polaronic insulator state (150-300K) is not much larger
than values reported for pure transition metals (d Co or Ni=2-2.5nm) at room
temperature, but it is smaller than dYBCO=3.9 nm for metallic YBCO that is in
turn smaller than the value reported for Fe3O4 (d=4.5 nm) The measured dLCMO
increases to 4.5 nm when LCMO is in the metallic state at low temperatures.
These results indicate that a universal rule of thumb for the sampling depth in
oxides cannot be assumed, and that it can be measurably influenced by
electronic phase transitions that derive from strong correlations.",1310.5998v1
2013-10-23,Neutron scattering measurements of $dd$ and spin-orbit excitations below the Mott-Hubbard gap in CoO,"Neutron scattering is used to investigate the single-ion spin and orbital
excitations below the Mott-Hubbard gap in CoO. Three excitations are reported
at 0.870 $\pm$ 0.009 eV, 1.84 $\pm$ 0.03, and 2.30 $\pm$ 0.15 eV. These were
parameterized within a weak crystal field scheme with an intra-orbital exchange
of $J(dd)$=1.3 $\pm$ 0.2 eV and a crystal field splitting 10Dq=0.94 $\pm$ 0.10
eV. A reduced spin-orbit coupling of \lambda=-0.016 $\pm$ 0.003 eV is derived
from dilute samples of Mg$_{0.97}$Co$_{0.03}$O, measured to remove
complications due to spin exchange and structural distortion parameters which
split the cubic phase degeneracy of the orbital excitations complicating the
inelastic spectrum. The 1.84 eV, while reported using resonant x-ray and
optical techniques, was absent or weak for non resonant x-ray experiments and
overlaps with the expected position of a $^{4}A_{2}$ level. This transition is
absent in the dipolar approximation but expected to have a finite quadrupolar
matrix element that can be observed with neutron scattering techniques at
larger momentum transfers. Our results agree with a crystal field analysis (in
terms of Racah parameters and Tanabe-Sugano diagrams) and with previous
calculations performed using local-density band theory for Mott insulating
transition metal oxides. The results also demonstrate the use of neutron
scattering for measuring dipole forbidden transitions in transition metal oxide
systems.",1310.6207v1
2013-11-09,Atomized Spraying of Liquid Metal Droplets on Desired Substrate Surfaces as a Generalized Way for Ubiquitous Printed Electronics,"A direct electronics printing technique through atomized spraying for
patterning room temperature liquid metal droplets on desired substrate surfaces
is proposed and experimentally demonstrated for the first time. This method has
generalized purpose and is highly flexible and capable of fabricating
electronic components on any desired target objects, with either flat or rough
surfaces, made of different materials, or different orientations from 1-D to
3-D geometrical configurations. With a pre-designed mask, the liquid metal ink
can be directly deposited on the substrate to form various specific patterns
which lead to the rapid prototyping of electronic devices. Further, extended
printing strategies were also suggested to illustrate the adaptability of the
method such that the natural porous structure can be adopted to offer an
alternative way of making transparent conductive film with an optical
transmittance of 47% and a sheet resistance of 5.167{\Omega}/O. Different from
the former direct writing technology where large surface tension and poor
adhesion between the liquid metal and the substrate often impede the flexible
printing process, the liquid metal here no longer needs to be pre-oxidized to
guarantee its applicability on target substrates. One critical mechanism was
found as that the atomized liquid metal microdroplets can be quickly oxidized
in the air due to its large specific surface area, resulting in a significant
increase of the adhesive capacity and thus firm deposition of the ink to the
substrate. This study established a generalized way for pervasively and
directly printing electronics on various substrates which are expected to be
significant in a wide spectrum of electrical engineering areas.",1311.2158v1
2013-12-17,A Network Biology Approach to Denitrification in Pseudomonas aeruginosa,"Pseudomonas aeruginosa is a metabolically flexible member of the
Gammaproteobacteria. Under anaerobic conditions and the presence of nitrate, P.
aeruginosa can perform (complete) denitrification, a respiratory process of
dissimilatory nitrate reduction to nitrogen gas via nitrite ($NO_{2}$), nitric
oxide ($NO$) and nitrous oxide ($N_{2}O$). This study focuses on understanding
the influence of environmental conditions on bacterial denitrification
performance, using a mathematical model of a metabolic network in P.
aeruginosa. To our knowledge, this is the first mathematical model of
denitrification for this bacterium. Analysis of the long-term behavior of the
network under changing concentration levels of oxygen ($O_{2}$), nitrate
($NO_{3}$), and phosphate ($PO_{4}$) suggests that $PO_{4}$ concentration
strongly affects denitrification performance. The model provides five
predictions on denitrification activity of P. aeruginosa under various
environmental conditions, and these predictions are either experimentally
validated or supported by pertinent biological literature. One motivation for
this study is to capture the effect of $PO_{4}$ on a denitrification metabolic
network of P. aeruginosa in order to shed light on mechanisms for greenhouse
gas $N_{2}O$ accumulation during seasonal oxygen depletion in aquatic
environments such as Lake Erie (Laurentian Great Lakes, USA).",1312.4616v3
2013-12-29,Asymmetric band widening by screened exchange competing with local correlations in SrVO3: new surprises on an old compound from combined GW and dynamical mean field theory GW+DMFT,"The very first dynamical implementation of the combined GW and dynamical mean
field scheme ""GW+DMFT"" for a real material was achieved recently [J.M. Tomczak
et al., Europhys. Lett. 100 67001 (2012)], and applied to the ternary
transition metal oxide SrVO3. Here, we review and extend that work, giving not
only a detailed account of full GW+DMFT calculations, but also discussing and
testing simplified approximate schemes. We give insights into the nature of
exchange and correlation effects: Dynamical renormalizations in the Fermi
liquid regime of SrVO3 are essentially local, and nonlocal correlations mainly
act to screen the Fock exchange term. The latter substantially widens the
quasi-particle band structure, while the band narrowing induced by the former
is accompanied by a spectral weight transfer to higher energies. Most
interestingly, the exchange broadening is much more pronounced in the
unoccupied part of spectrum. As a result, the GW+DMFT electronic structure of
SrVO3 resembles the conventional density functional based dynamical mean field
(DFT+DMFT) description for occupied states, but is profoundly modified in the
empty part. Our work leads to a reinterpretation of inverse photoemission
spectroscopy (IPES) data. Indeed, we assign a prominent peak at about 2.7 eV
dominantly to eg states, rather than to an upper Hubbard band of t2g character.
Similar surprises can be expected for other transition metal oxides, calling
for more detailed investigations of the conduction band states.",1312.7546v1
2014-01-06,Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La$_{2-x}$Sr$_x$CuO$_4$,"In superconducting copper oxides some Cu-O bond-stretching phonons around
70meV show anomalous giant softening and broadening of electronic origin and
electronic dispersions have large renormalization kinks near the same energy.
These observations suggest that phonon broadening originates from quasiparticle
excitations across the Fermi surface and the electronic dispersion kinks
originate from coupling to anomalous phonons. We measured the phonon anomaly in
underdoped (x=0.05) and overdoped (x=0.20,0.25) La$_{2-x}$Sr$_x$CuO$_4$ by
inelastic neutron and x-ray scattering with high resolution. Combining these
and previously published data, we found that doping-dependence of the magnitude
of the giant phonon anomaly is very different from that of the ARPES kink, i.e.
the two phenomena are not connected. We show that these results provide
indirect evidence that the phonon anomaly originates from novel collective
charge excitations as opposed to interactions with electron-hole pairs. Their
amplitude follows the superconducting dome so these charge modes may be
important for superconductivity.",1401.1111v2
2014-02-03,Efficacy of the DFT+U formalism for modeling hole polarons in perovskite oxides,"We investigate the formation of self-trapped holes (STH) in three
prototypical perovskites (SrTiO3, BaTiO3, PbTiO3) using a combination of
density functional theory (DFT) calculations with local potentials and hybrid
functionals. First we construct a local correction potential for polaronic
configurations in SrTiO3 that is applied via the DFT+U method and matches the
forces from hybrid calculations. We then use the DFT+U potential to search the
configuration space and locate the lowest energy STH configuration. It is
demonstrated that both the DFT+U potential and the hybrid functional yield a
piece-wise linear dependence of the total energy on the occupation of the STH
level suggesting that self-interaction effects have been properly removed. The
DFT+U model is found to be transferable to BaTiO3 and PbTiO3, and formation
energies from DFT+U and hybrid calculations are in close agreement for all
three materials. STH formation is found to be energetically favorable in SrTiO3
and BaTiO3 but not in PbTiO3, which can be rationalized by considering the
alignment of the valence band edges on an absolute energy scale. In the case of
PbTiO3 the strong coupling between Pb 6s and O 2p states lifts the valence band
minimum (VBM) compared to SrTiO3 and BaTiO3. This reduces the separation
between VBM and STH level and renders the STH configuration metastable with
respect to delocalization (band hole state). We expect that the present
approach can be adapted to study STH formation also oxides with different
crystal structures and chemical composition.",1402.0435v1
2014-02-13,Fractal and Multifractal Analysis of the Rise of Oxygen in Earth's Early Atmosphere,"The rise of oxygen in Earth's atmosphere that occurred 2.4 to 2.2 billion
years ago is known as the Earth's Great Oxidation, and its impact on the
development of life on Earth has been profound. Thereafter, the increase in
Earth's oxygen level persisted, though at a more gradual pace. The proposed
underlying mathematical models for these processes are based on physical
parameters whose values are currently not well-established owing to
uncertainties in geological and biological data. In this paper, a previously
developed model of Earth's atmosphere is modified by adding different strengths
of noise to account for the parameters' uncertainties. The effects of the noise
on the time variations of oxygen, carbon and methane for the early Earth are
investigated by using fractal and multifractal analysis. We show that the time
variations following the Great Oxidation cannot properly be described by a
single fractal dimension because they exhibit multifractal characteristics. The
obtained results demonstrate that the time series as obtained exhibit
multifractality caused by long-range time correlations.",1402.3243v4
2014-04-03,Short-Range Structure and Phonon Assignment of the Brownmillerite-Type Oxide Ba$_{2}$In$_{2}$O$_{5}$ and its Hydrated Proton-Conducting Form BaInO$_{3}$H,"The vibrational spectra and short-range structure of the brownmillerite-type
oxide Ba$_{2}$In$_{2}$O$_{5}$ and its hydrated form BaInO$_{3}$H, are
investigated by means of Raman, infrared, and inelastic neutron scattering
spectroscopies together with density functional theory calculations. For
Ba$_{2}$In$_{2}$O$_{5}$, which may be described as an oxygen deficient
perovskite structure with alternating layers of InO$_{6}$ octahedra and
InO$_{4}$ tetrahedra, the results affirm a short-range structure of $Icmm$
symmetry, which is characterized by random orientation of successive layers of
InO$_{4}$ tetrahedra. For the hydrated, proton conducting, form, BaInO$_{3}$H,
the results suggest that the short-range structure is more complicated than the
$P4/mbm$ symmetry that has been proposed previously on the basis of neutron
diffraction, but rather suggest a proton configuration close to the lowest
energy structure predicted by Martinez et al. [J.-R. Martinez, C. E. Moen, S.
Stoelen, N. L. Allan, J. of Solid State Chem. 180, 3388, (2007)]. An intense
Raman active vibration at 150 cm$^{-1}$ is identified as a unique fingerprint
of this proton configuration.",1404.1034v2
2014-04-08,Structure and dehydration mechanism of the proton conducting oxide Ba$_{2}$In$_{2}$O$_{5}$(H$_{2}$O)$_{x}$,"The structure and dehydration mechanism of the proton conducting oxide
Ba$_{2}$In$_{2}$O$_{5}$(H$_{2}$O)$_{x}$ are investigated by means of variable
temperature Raman spectroscopy together with inelastic neutron scattering. At
room temperature, Ba$_{2}$In$_{2}$O$_{5}$(H$_{2}$O)$_{x}$ is found to be fully
hydrated ($x=1$) and to have a perovskite-like structure, which dehydrates
gradually with increasing temperature and at around 600 $^{\circ}$C the
material is essentially completely dehydrated ($x=0$). The dehydrated material
exhibits a brownmillerite structure, which is featured by alternating layers of
InO$_{6}$ octahedra and InO$_{4}$ tetrahedra. The transition from a
perovskite-like to a brownmillerite-like structure is featured by a
hydrated-to-intermediate phase transition at $ca.$ 370 {\deg}C. The structure
of the intermediate phase is similar to the structure of the fully dehydrated
material, but with the difference that it exhibits a non-centrosymmetric
distortion of the InO$_{6}$ octahedra not present in the latter. For
temperatures below the hydrated-to-intermediate phase transition, dehydration
is featured by the release of protons confined to the layers of InO$_{4}$
tetrahedra, whereas above the transition also protons bound to oxygens of the
layers of InO$_{6}$ are released. Finally, we found that the O-H stretch region
of the vibrational spectra is not consistent with a single-phase spectrum, but
is in agreement with the superposition of spectra associated with two different
proton configurations. The relative contributions of the two proton
configurations depend on how the sample is hydrated.",1404.2260v2
2014-07-24,Preventing corona effects: multi-phosphonic acid poly(ethylene glycol) copolymers for stable stealth iron oxide nanoparticles,"When disperse in biological fluids, engineered nanoparticles are selectively
coated with proteins, resulting in the formation of a protein corona. It is
suggested that the protein corona is critical in regulating the conditions of
entry into the cytoplasm of living cells. Recent reports describe this
phenomenon as ubiquitous and independent of the nature of the particle. For
nanomedicine applications however, there is a need to design advanced and
cost-effective coatings that are resistant to protein adsorption and that
increase the biodistribution in vivo. In this study, phosphonic acid
poly(ethylene glycol) copolymers were synthesized and used to coat iron oxide
particles. The copolymer composition was optimized to provide simple and
scalable protocols as well as long-term stability in culture media. It is shown
that polymers with multiple phosphonic acid functionalities and PEG chains
outperform other types of coating, including ligands, polyelectrolytes and
carboxylic acid functionalized PEG. PEGylated particles exhibit moreover
exceptional low cellular uptake, of the order of 100 femtograms of iron per
cell. The present approach demonstrates that the surface chemistry of
engineered particles is a key parameter in the interactions with cells. It also
opens up new avenues for the efficient functionalization of inorganic surfaces.",1407.6411v1
2014-08-29,Oxygen diffusion pathways in brownmillerite SrCoO2.5: Influence of structure and chemical potential,"To design and discover new materials for next-generation energy materials
such as solid-oxide fuel cells (SOFCs), a fundamental understanding of their
ionic properties and behaviors is essential. The potential applicability of a
material for SOFCs is critically determined by the activation energy barrier of
oxygen along various diffusion pathways. In this work, we investigate
interstitial-oxygen (Oi) diffusion in brownmillerite oxide SrCoO2.5, employing
a first-principles approach. Our calculations indicate highly anisotropic ionic
diffusion pathways, which result from its anisotropic crystal structure. The
one-dimensional-ordered oxygen vacancy channels are found to provide the
easiest diffusion pathway with an activation energy barrier height of 0.62 eV.
The directions perpendicular to the vacancy channels have higher energy
barriers for Oint diffusion. In addition, we have studied migration barriers
for oxygen vacancies that could be present as point defects within the
material. This in turn could also facilitate the transport of oxygen.
Interestingly, for oxygen vacancies, the lowest barrier height was found to
occur within the octahedral layer with an energy of 0.82 eV. Our results imply
that interstitial migration would be highly one-dimensional in nature. Oxygen
vacancy transport, on the other hand, could preferentially occur in the
two-dimensional octahedral plane.",1408.7077v1
2014-09-01,Nitric Oxide as stress inducer and synchronizer of p53 dynamics,"We study how the temporal behaviours of p53 and MDM2 are affected by stress
inducing bioactive molecules NO (Nitric Oxide) in the p53-MDM2-NO regulatory
network. We also study synchronization among a group of identical stress
systems arranged in a three dimensional array with nearest neighbour diffusive
coupling. The role of NO and effect of noise are investigated. In the single
system study, we have found three distinct types of temporal behaviour of p53,
namely, oscillation death, damped oscillation and sustain oscillation,
depending on the amount of stress induced by the NO concentration, indicating
how p53 responds to the incoming stress. The correlation among the coupled
systems increases as the value of coupling constant (\epsilon) is increased
(\gamma increases) and becomes constant after certain value of \epsilon. The
permutation entropy spectra H(\epsilon) for p53 and MDM2 as a function of
\epsilon are found to be different due to direct and indirect interaction of NO
with the respective proteins. \gamma versus \epsilon for p53 and MDM2 are found
to be similar in deterministic approach, but different in stochastic approach
and the separation between \gamma of the respective proteins as a function of
\epsilon decreases as system size increases. The role of NO is found to be
twofold: stress induced by it is prominent at small and large values of
\epsilon but synchrony inducing by it dominates in moderate range of \epsilon.
Excess stress induce apoptosis to the system.",1409.0528v1
2014-09-03,Mobility enhancement and temperature dependence in top-gated single-layer MoS2,"The deposition of a high-$\kappa$ oxide overlayer is known to significantly
enhance the room-temperature electron mobility in single-layer MoS$_{2}$ (SLM)
but not in single-layer graphene (SLG). We give a quantitative account of how
this mobility enhancement is due to the non-degeneracy of the two-dimensional
electron gas system in SLM at accessible temperatures. Using our charged
impurity scattering model [Ong and Fischetti, Phys. Rev. B 86, 121409 (2012)]
and temperature-dependent polarizability, we calculate the charged
impurity-limited mobility ($\mu_{\textrm{imp}}$) in SLM with and without a
high-$\kappa$ (HfO$_{2}$) top gate oxide at different electron densities and
temperatures. We find that the mobility enhancement is larger at low electron
densities and high temperatures because of finite-temperature screening, thus
explaining the enhancement of the mobility observed at room temperature.
$\mu_{\textrm{imp}}$ is shown to decrease significantly with increasing
temperature, suggesting that the strong temperature dependence of measured
mobilities should not be interpreted as being solely due to inelastic
scattering with phonons. We also reproduce the recently seen experimental trend
in which the temperature scaling exponent ($\gamma$) of
$\mu_{\textrm{imp}}\propto T^{-\gamma}$ is smaller in top-gated SLM than in
bare SLM. Finally, we show that a $\sim37$ percent mobility enhancement can be
achieved by reducing the HfO$_{2}$ thickness from 20 to 2 nm.",1409.1084v1
2014-09-23,Macromechanical behavior of oxide nanopowders during compaction processes,"Two granular systems (I and II) corresponding oxide nanopowders having
different agglomeration tendency are simulated by the granular dynamics method.
The particle size is 10 nanometer. The interaction of particles involves the
elastic forces of repulsion, the tangential forces of ""friction"", the
dispersion forces of attraction, and in the case of II system the opportunity
of creation/destruction of hard bonds of chemical nature. The processes of the
uniaxial compaction, the biaxial (radial) one, the isotropic one, the
compaction combined with shear deformation as well as the simple shear
deformation are studied. The effect of the positive dilatancy is found out in
the processes of shear deformation. The loading surfaces of nanopowders are
constructed in the space of stress tensor invariants, i.e., the hydrostatic
pressure and the deviator intensity. It is revealed that the form of the
loading surfaces is similar to an ellipse, which is shifted along the
hydrostatic axis to compressive pressures. The associated flow rule is
analyzed. The nonorthogonality of the deformation vectors to the loading
surface is established in the both systems modeled.",1409.6393v1
2014-10-06,Graphene-protected copper and silver plasmonics,"Plasmonics has established itself as a branch of physics which promises to
revolutionize data processing, improve photovoltaics, increase sensitivity of
bio-detection. A widespread use of plasmonic devices is notably hindered (in
addition to high losses) by the absence of stable and inexpensive metal films
suitable for plasmonic applications. This may seem surprising given the number
of metal compounds to choose from. Unfortunately, most of them either exhibit a
strong damping of surface plasmons or easily oxidize and corrode. To this end,
there has been continuous search for alternative plasmonic materials that are,
unlike gold, the current metal of choice in plasmonics, compatible with
complementary metal oxide semiconductor technology. Here we show that copper
and silver protected by graphene are viable candidates. Copper films covered
with one to a few graphene layers show excellent plasmonics characteristics
surpassing those of gold films. They can be used to fabricate plasmonic devices
and survive for at least a year, even in wet and corroding conditions. As a
proof of concept, we use the graphene-protected copper to demonstrate
dielectric loaded plasmonic waveguides and test sensitivity of surface plasmon
resonances. Our results are likely to initiate a wide use of graphene-protected
plasmonics.",1410.1459v1
2014-11-12,Quantum effects in proton-conducting oxides: an exhaustive study in barium stannate,"Density-functional theory calculations are performed to investigate hydrogen
transport in the proton conductor BaSnO$_3$. Structural optimizations in the
stable and saddle point configurations for transfer and reorientation allow
description of the high-temperature classical and semi-classical regimes, in
which diffusion occurs by over-barrier motion. At lower temperature (typically
below 300 K), we describe a thermally-assisted quantum regime. In this regime,
transfer and reorientation occur when the surrounding matrix adopts particular
""coincidence"" configurations in which quantum tunneling is favored. Both the
non-adiabatic and the adiabatic cases are examined. In the adiabatic case, the
energy landscape of hydrogen in the coincidence configuration is very flat,
with very low coincidence energy barriers. Path-integral molecular dynamics
simulations of the H atom in the coincidence potential reveal, in the transfer
case, highly quantum behavior up to T=300 K (the density of probability of H in
the coincidence configuration, has its maximum at the saddle point, due to the
fact that the zero-point energy exceeds the coincidence energy barrier).
Arguments are given that support the adiabatic picture for the transfer
mechanism. This suggests existence of this state of hydrogen during the very
short lifetime of the coincidence configurations ($\sim$ 10$^{-13}$ s), as a
transition state for the transfer mechanism. Remarkably, such state is
identical to that of ice X, a highly quantum phase of ice observed at high
pressures $\approx$ 100 GPa. In the case of reorientation, typical times for
existence of the coincidence configuration and for protonic motion are roughly
equal, suggesting that the adiabatic picture is not valid. Protonic transfer
and reorientation in oxides are therefore governed by radically different
mechanisms below room temperature.",1411.3207v1
2014-11-15,Shock-waves and commutation speed of memristors,"Progress of silicon based technology is nearing its physical limit, as
minimum feature size of components is reaching a mere 10 nm. The resistive
switching behaviour of transition metal oxides and the associated memristor
device is emerging as a competitive technology for next generation electronics.
Significant progress has already been made in the past decade and devices are
beginning to hit the market; however, it has been mainly the result of
empirical trial and error. Hence, gaining theoretical insight is of essence. In
the present work we report the striking result of a connection between the
resistive switching and {\em shock wave} formation, a classic topic of
non-linear dynamics. We argue that the profile of oxygen vacancies that migrate
during the commutation forms a shock wave that propagates through a highly
resistive region of the device. We validate the scenario by means of model
simulations and experiments in a manganese-oxide based memristor device. The
shock wave scenario brings unprecedented physical insight and enables to
rationalize the process of oxygen-vacancy-driven resistive change with direct
implications for a key technological aspect -- the commutation speed.",1411.4198v3
2014-11-21,Water Reaction Mechanism in Metal Organic Frameworks with Coordinatively Unsaturated Metal Ions: MOF-74,"Water dissociation represents one of the most important reactions in
catalysis, essential to the surface and nano sciences [e.g., Hass et al.,
Science, 1998, 282, 265-268; Brown et al., Science 2001, 294, 67-69; Bikondoa
et al., Nature 2005, 5, 189-192]. However, the dissociation mechanism on most
oxide surfaces is not well understood due to the experimental challenges of
preparing surface structures and characterizing reaction pathways. To remedy
this problem, we propose the metal organic framework MOF-74 as an ideal model
system to study water reactions. Its crystalline structure is well
characterized; the metal oxide node mimics surfaces with exposed cations; and
it degrades in water. Combining in situ IR spectroscopy and first-principles
calculations, we explored the MOF-74/water interaction as a function of vapor
pressure and temperature. Here, we show that, while adsorption is reversible
below the water condensation pressure (~19.7 Torr) at room temperature, a
reaction takes place at ~150 centigrades even at low water vapor pressures.
This important finding is unambiguously demonstrated by a clear spectroscopic
signature for the direct reaction using D2O, which is not present using H2O due
to strong phonon coupling. Specifically, a sharp absorption band appears at 970
cm-1 when D2O is introduced at above 150 centigrades, which we attribute to an
O-D bending vibration on the phenolate linker. Although H2O undergoes a similar
dissociation reaction, the corresponding O-H mode is too strongly coupled to
MOF vibrations to detect. In contrast, the O-D mode falls in the phonon gap of
the MOF and remains localized.",1411.5736v1
2014-11-21,Impact of Tailored Gamma Irradiation on Pore Size and Particle Size of Poly[Ethylene Oxide]Films: Correlation with Molecular Weight Distribution andMicrostructural Study,"The structure and morphology of polymers are significantly altered upon
exposure to high energy gamma irradiation. The present investigation reports
the influence of such irradiation of doses in the range of 1 - 30 kGy on the
particle size of Poly (Ethylene Oxide) [PEO] powder along with its correlation
with molecular weight distribution. Pore-size distribution and overall porosity
of the synthesized films prepared with irradiated and unirradiated PEO powder
is also reported. The particle size of both unirradiated and irradiated PEO
powders is found be in the range of 0.01 - 1000 micrometer. It is known that,
variation in irradiation dose either generates particles of lower dimension
through bond breakage i.e scission or higher dimension through cross-linkage.
PEO films exhibit strong dependence of irradiation effect on pore size
distribution and porosity. PEO films synthesized using both unirradiated and
irradiated powders exhibit pore dimension in the range of 20 - 500 nm. The
overall porosity of PEO films studied through BET adsorption technique
initially increases with dose upto 3 kGy followed by linear decrease upto 30
kGy. Films cast with unirradiated PEO powder show multimodal pore size
distribution, but perturbation with irradiation changes the modality to uni-or
bimodal nature. The mentioned outcome of irradiation viz. particle and pore
size variation is also correlated with PEO microstructures.The article
demonstrates that, selective irradiation is capable of tailoring the pore-size
within a definite regime thereby reducing the multimodal trait. The reported
study may be relevant towards applications such as catalysis, sensing and
filtration, where pore size distribution plays a crucial role.",1411.5816v1
2014-11-20,Concentration dependence of the fluorescence decay profile in transition metal doped chalcogenide glass,"In this paper we present the fluorescence decay profiles of vanadium and
titanium doped gallium lanthanum sulphide (GLS) glass at various doping
concentrations between 0.01 and 1% (molar). We demonstrate that below a
critical doping concentration the fluorescence decay profile can be fitted with
the stretched exponential function: exp[-(t/{\tau})\b{eta}], where {\tau} is
the fluorescence lifetime and \b{eta} is the stretch factor. At low
concentrations the lifetime for vanadium and titanium doped GLS was 30 {\mu}s
and 67 {\mu}s respectively. We validate the use of the stretched exponential
model and discuss the possible microscopic phenomenon it arises from. We also
demonstrate that above a critical doping concentration of around 0.1% (molar)
the fluorescence decay profile can be fitted with the double exponential
function: a*exp-(t/{\tau}1)+ b*exp-(t/{\tau}2), where {\tau}1and {\tau}2 are
characteristic fast and slow components of the fluorescence decay profile, for
vanadium the fast and slow components are 5 {\mu}s and 30 {\mu}s respectively
and for titanium they are 15 {\mu}s and 67 {\mu}s respectively. We also show
that the fluorescence lifetime of vanadium and titanium at low concentrations
in the oxide rich host gallium lanthanum oxy-sulphide (GLSO) is 43 {\mu}s and
97 {\mu}s respectively, which is longer than that in GLS. From this we deduce
that vanadium and titanium fluorescing ions preferentially substitute into high
efficiency oxide sites until at a critical concentration they become saturated
and low efficiency sulphide sites start to be filled.",1411.7045v1
2014-12-04,Heterogeneous electrocatalysis in porous cathodes of solid oxide fuel cells,"A general physics-based model is developed for heterogeneous electrocatalysis
in porous electrodes and used to predict and interpret the impedance of solid
oxide fuel cells. This model describes the coupled processes of oxygen gas
dissociative adsorption and surface diffusion of the oxygen intermediate to the
triple phase boundary, where charge transfer occurs. The model accurately
captures the Gerischer-like frequency dependence and the oxygen partial
pressure dependence of the impedance of symmetric cathode cells. Digital image
analysis of the microstructure of the cathode functional layer in four
different cells directly confirms the predicted connection between geometrical
properties and the impedance response. As in classical catalysis, the
electrocatalytic activity is controlled by an effective Thiele modulus, which
is the ratio of the surface diffusion length (mean distance from an adsorption
site to the triple phase boundary) to the surface boundary layer length (square
root of surface diffusivity divided by the adsorption rate constant). The
Thiele modulus must be larger than one in order to maintain high surface
coverage of reaction intermediates, but care must be taken in order to
guarantee a sufficient triple phase boundary density. The model also predicts
the Sabatier volcano plot with the maximum catalytic activity corresponding to
the proper equilibrium surface fraction of adsorbed oxygen adatoms. These
results provide basic principles and simple analytical tools to optimize porous
microstructures for efficient electrocatalysis.",1412.1548v1
2014-12-05,Resistance switching devices based on amorphous insulator-metal thin films,"Nanometallic devices based on amorphous insulator-metal thin films are
developed to provide a novel non-volatile resistance-switching random-access
memory (RRAM). In these devices, data recording is controlled by a bipolar
voltage, which tunes electron localization length, thus resistivity, through
electron trapping/detrapping. The low-resistance state is a metallic state
while the high-resistance state is an insulating state, as established by
conductivity studies from 2K to 300K. The material is exemplified by a Si3N4
thin film with randomly dispersed Pt or Cr. It has been extended to other
materials, spanning a large library of oxide and nitride insulator films,
dispersed with transition and main-group metal atoms. Nanometallic RRAMs have
superior properties that set them apart from other RRAMs. The critical
switching voltage is independent of the film thickness/device
area/temperature/switching speed. Trapped electrons are relaxed by
electron-phonon interaction, adding stability which enables long-term memory
retention. As electron-phonon interaction is mechanically altered, trapped
electron can be destabilized, and sub-picosecond switching has been
demonstrated using an electromagnetically generated stress pulse. AC impedance
spectroscopy confirms the resistance state is spatially uniform, providing a
capacitance that linearly scales with area and inversely scales with thickness.
The spatial uniformity is also manifested in outstanding uniformity of
switching properties. Device degradation, due to moisture, electrode oxidation
and dielectrophoresis, is minimal when dense thin films are used or when a
hermetic seal is provided. The potential for low power operation, multi-bit
storage and complementary stacking have been demonstrated in various RRAM
configurations.",1412.2083v1
2014-12-16,Reaction of the desulfoferrodoxin from Desulfoarculus baarsii with superoxide anion. Evidence for a superoxide reductase activity,"Desulfoferrodoxin is a small protein found in sulfate-reducing bacteria that
contains two independent mononuclear iron centers, one ferric and one ferrous.
Expression of desulfoferrodoxin from Desulfoarculus baarsii has been reported
to functionally complement a superoxide dismutase deficient Escherichia coli
strain. To elucidate by which mechanism desulfoferrodoxin could substitute for
superoxide dismutase in E. coli, we have purified the recombinant protein and
studied its reactivity toward O-(2). Desulfoferrodoxin exhibited only a weak
superoxide dismutase activity (20 units mg(-1)) that could hardly account for
its antioxidant properties. UV-visible and electron paramagnetic resonance
spectroscopy studies revealed that the ferrous center of desulfoferrodoxin
could specifically and efficiently reduce O-(2), with a rate constant of 6-7 x
10(8) M(-1) s(-1). In addition, we showed that membrane and cytoplasmic E. coli
protein extracts, using NADH and NADPH as electron donors, could reduce the
O-(2) oxidized form of desulfoferrodoxin. Taken together, these results
strongly suggest that desulfoferrodoxin behaves as a superoxide reductase
enzyme and thus provide new insights into the biological mechanisms designed
for protection from oxidative stresses.",1412.5038v1
2014-12-24,Impact of dopant species on the interfacial trap density and mobility in amorphous In-X-Zn-O solution-processed thin-film transistors,"Alloying of In/Zn oxides with various X atoms stabilizes the IXZO structures
but generates electron traps in the compounds, degrading the electron mobility.
To assess whether the latter is linked to the oxygen affinity or the ionic
radius, of the X element, several IXZO samples are synthesized by the sol-gel
process, with a large number (14) of X elements. The IXZOs are characterized by
XPS, SIMS, DRX, and UV-spectroscopy and used for fabricating thin film
transistors. Channel mobility and the interface defect density NST, extracted
from the TFT electrical characteristics and low frequency noise, followed an
increasing trend and the values of mobility and NST are linked by an
exponential relation. The highest mobility (8.5 cm2/Vs) is obtained in
In-Ga-Zn-O, and slightly lower value for Sb and Sn-doped IXZOs, with NST is
about 2E12 cm2/eV, close to that of the In-Zn-O reference TFT. This is
explained by a higher electronegativity of Ga, Sb, and Sn than Zn and In, their
ionic radius values being close to that of In and Zn. Consequently, Ga, Sb, and
Sn induce weaker perturbations of In-O and Zn-O sequences in the sol-gel
process, than the X elements having lower electronegativity and different ionic
radius. The TFTs with X = Ca, Al, Ni and Cu exhibited the lowest mobility and
NST > 1E13 cm2/eV, most likely because of metallic or oxide clusters formation.",1412.7710v1
2015-01-15,Flux growth utilizing the reaction between flux and crucible,"Flux growth involves dissolving the components of the target compound in an
appropriate flux at high temperatures and then crystallizing under
supersaturation controlled by cooling or evaporating the flux. A refractory
crucible is generally used to contain the high temperature melt. The reaction
between the melt and crucible materials can modify the composition of the melt,
which typically results in growth failure, or contaminates the crystals. Thus
one principle in designing a flux growth is to select suitable flux and
crucible materials thus to avoid any reaction between them. In this paper, we
review two cases of flux growth in which the reaction between flux and
Al$_2$O$_3$ crucible tunes the oxygen content in the melt and helps the
crystallization of desired compositions. For the case of La$_5$Pb$_3$O,
Al$_2$O$_3$ crucible oxidizes La to form a passivating La$_2$O$_3$ layer which
not only prevents further oxidization of La in the melt but also provides [O]
to the melt. For the case of La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$, it is believed
that the Al$_2$O$_3$ crucible reacts with NaAsO$_2$ and the reaction consumes
oxygen in the melt thus maintaining an oxygen-free environment.",1501.03770v1
2015-01-25,Out-of-plane Ionicity versus In-plane Covalency Interplay in High-Tc Superconducting Oxides,"It seems that the remarkable properties of the high temperature
superconducting oxides, especially the Insulator-Metal Transition (IMT) and the
Metal-Superconductor Transition (MST) both originate from the competition
(interplay) between ionic versus in-plane covalence nature of bonds in these
materials. As a result of this competition, the microscopic order parameter,
that is firmly identified to be the local field estimated from the ionic
polarization at the sub-unit level (one half of the unit cell), shows a strong
temperature as well as chemical doping dependence. While the out-of-plane
ionicity is responsible for the interlayer charge transfer (electrons) that
reduces it leading to IMT, the in-plane covalency is responsible for the
in-plane intersite transfer of charge (holes) that increases the ionicity and
leads to MST. This interplay of charge transfer, driven by the out-of-plane
ionicity and the in-plane covalency, leads at the critical temperature Tc to a
local field avalanche (ionic polarization catastrophe at the sub-unit cell
level) that triggers an out-of-plane correlation between the local polarization
fields at the unit cell and drives the compound into the superconducting state.
The asymmetry of the free charge carrier density breaks locally the inversion
symmetry of the order parameter leading to an unconventional pairing mechanism
characterized by the CPT transformation where C is the charge conjugation
symmetry, P is the parity symmetry and T is the time reversal symmetry. It is
established that the out-of-plane ionicity versus in-plane covalency is a
necessary condition for the occurrence of both IMT and MST. The underlined
microscopic mechanism provides a route to a possible unified description of
high-Tc superconductivity.",1501.06134v2
2015-02-05,Intrinsic electron mobility exceeding 1000 cm$^2$/Vs in multilayer InSe FETs,"Graphene-like two-dimensional (2D) materials, not only are interesting for
their exotic electronic structure and fundamental electronic transport or
optical properties but also, hold promises for device miniaturization down to
atomic thickness. As one material belonging to this category, InSe is not only
a promising candidate for optoelectronic devices but also has potential for
ultrathin field effect transistor (FET) with high mobility transport. In this
work, various substrates such as PMMA, bare silicon oxide, passivated silicon
oxide, and silicon nitride were used to fabricate multi-layer InSe FET devices.
Through back gating and Hall measurement in four-probe configuration, the
devices' field effect mobility and intrinsic Hall mobility were extracted at
various temperatures to study the material's intrinsic transport behavior and
the effect of dielectric substrate. The sample's field effect and Hall
mobilities over the range of 77-300K fall in the range of 0.1-2.0$\times$10$^3$
cm$^2$/Vs, which are comparable or better than the state of the art FETs made
of 2D transition metal-dichalcogenides.",1502.01615v3
2015-02-06,Identification of annealing temperature for high-$κ$-based gate oxides using differential scanning calorimetry,"This article identifies the process of crystallization of thin high-$\kappa$
dielectric films and an optimal range of annealing temperature in the field of
high-$\kappa$ dielectric-based metal-oxide-semiconductor (MOS) technology for
its improved electrical performances. Differential Scanning Calorimetry (DSC)
technique is employed to understand the thermal behaviour of thin high-$\kappa$
dielectric films of HfO$_2$, deposited by rf sputtering, on Si. The exothermic
trends of the DSC signal and Grazing Incidence X-ray diffraction (GIXRD) data
indicate an amorphous to crystalline transition in the high-$\kappa$ film at
higher temperature. The enthalpy-temperature variation shows a glass
temperature (T$_g$) at $\sim$ 590 $^o$C beyond which an amorphous to m-HfO$_2$
crystalline transition takes place. Further, the Hf-Silicate formation,
observed in DSC measurement and corroborated by Fourier transformed Infrared
Spectroscopy (FT-IR) studies, indicates that the process of formation of
Hf-Silicate begins at $\sim$ 717 $^oC$. High-frequency (HF) capacitance-voltage
$(C-V)$ and current density - voltage $(J-V)$ characteristics establish that
the crystallization of the film is not the root cause of degradation of the
electrical properties of the high-$\kappa$-based MOS devices, rather the device
degrades due to formation of interfacial Hf-Silicate.",1502.01889v2
2015-02-26,"Structural and Dielectric Properties of (La, Nd) (Mg1/2Ti1/2)O3 Perovskites","Using the high-resolution x-ray diffraction (XRD) analysis, scanning electron
microscopy (SEM), and the temperature-dependent microwave resonator
characterization, structural properties, phase assemblage and dielectric
properties of La(Mg1/2Ti1/2)O3 (LMT) and Nd(Mg1/2Ti1/2)O3 (NMT) ceramics
prepared via the mixed oxide route were investigated in this study.
Single-phase ceramics were synthesized for both LMT and NMT at sintering
temperatures from 1250 degree C to 1675 degree C. On the basis of the XRD
analysis we have found that the LMT and NMT compounds have cubic and monoclinic
crystal structures, respectively. We have also observed that the relative
densities of LMT and NMT vary between about 93 and 99% of the theoretical
density, depending on the sintering temperature. Finally, concerning the
dielectric properties of the microwave resonators made of LMT and NMT compounds
we have measured their temperature coefficient of the resonant frequency
({\tau}f) and the quality factor (Q). It is interesting to notice that
({\tau}f) in the case of the NMT compound (-16 ppm 1/K) is essentially smaller
than in the case of the LMT compound (-72 ppm 1/K), therefore proving a better
stability against temperature variations in the NMT based resonators. On the
other hand, the Q values are very similar, being 34000 at the resonance
frequency of 8.07 GHz and 38000 at the resonance frequency of 9.76 GHz in the
LMT and NMT cases, respectively.
  Keywords: dielectric properties; microstructure-final: grain growth; single
phase Ln(Mg0.5Ti0.5)O3 (Ln=Nd,La); Lanthanum magnesium titanium oxide.",1502.07547v1
2015-03-01,Generalized spectral method for near-field optical microscopy,"Electromagnetic interaction between a sub-wavelength particle (the `probe')
and a material surface (the `sample') is studied theoretically. The interaction
is shown to be governed by a series of resonances corresponding to surface
polariton modes localized near the probe. The resonance parameters depend on
the dielectric function and geometry of the probe, as well as the surface
reflectivity of the material. Calculation of such resonances is carried out for
several types of axisymmetric probes: spherical, spheroidal, and pear-shaped.
For spheroids an efficient numerical method is developed, capable of handling
cases of large or strongly momentum-dependent surface reflectivity. Application
of the method to highly resonant materials such as aluminum oxide (by itself or
covered with graphene) reveals a rich structure of multi-peak spectra and
nonmonotonic approach curves, i.e., the probe-sample distance dependence. These
features also strongly depend on the probe shape and optical constants of the
model. For less resonant materials such as silicon oxide, the dependence is
weak, so that the spheroidal model is reliable. The calculations are done
within the quasistatic approximation with the radiative damping included
perturbatively.",1503.00221v2
2015-03-10,Defect and Temperature Dependence of Tunneling in InAs/GaSb Heterojunctions,"Tunnel field effect transistors (TFETs) utilizing semiconductor
heterojunctions have shown promise for low energy logic but presently do not
display subthreshold swings steeper than the room-temperature thermal limit of
60 mV/decade. These devices also show a pronounced temperature dependence that
is not characteristic of a tunneling process. Herein, we explore these aspects
by studying the temperature dependence of two-terminal InAs/GaSb
heterojunctions, allowing for the true nature of tunneling at the interface to
be seen without convolution from other three-terminal parasitic effects such as
gate oxide traps. We compare the temperature dependence of peak current, excess
current, and conductance slope for InAs/GaSb interfaces with and without
interface defects. We identify that the tunnel and excess currents depend on
temperature and defect density and propose that the ultimate leakage current in
TFETs based on these materials will be affected by defects and inhomogeneity at
the interface. We determine that the conductance slope, a two-terminal analog
to subthreshold slope, does not depend on temperature, contrasting sharply with
the heavy temperature dependence seen in three terminal devices in literature.
We propose that TFETs based on this and similar materials systems are dominated
by parasitic effects such as tunneling into oxide trap states, or other
parasitics that are not intrinsic to the heterojunction itself, and that in the
absence of these effects, the true steepness from band-to-band tunneling is
limited by defects and inhomogeneity at the interface.",1503.02763v1
2015-03-12,Evaluation of Radiation Dose Reduction during CT Scans Using Oxide Bismuth and Nano-Barium Sulfate Shields,"The purpose of the present study was to evaluate radiation dose reduction and
image quality during CT scanning by using a new dose reduction fiber sheet
(DRFS) with commercially available bismuth shields. These DRFS were composed of
nano-barium sulfate (BaSO4), filling the gaps left by the large oxide bismuth
(Bi2O3) particle sizes. The radiation dose was measured five times at
directionss of 12 o'clock from the center of the polymethyl methacrylate (PMMA)
head phantom to calculate an average value using a CT ionization chamber. The
image quality measured CT transverse images of the PMMA head phantom depending
on X-ray tube voltages and the type of shielding. Two regions of interest in CT
transverse images were chosen from the right and left areas under the surface
of the PMMA head phantom and from ion chamber holes located at directions of 12
o'clock from the center of the PMMA head phantom. The results of this study
showed that the new DRFS shields could reduce dosages to 15.61%, 23.05%, and
22.71% more in 90 kVp, 120 kVp, and 140 kVp, respectively, than with a
conventional bismuth shield of the same thickness, while maintaining image
quality. In addition, the DRFS were produced to about 25% more thinness than
conventional bismuth. We concluded, therefore, that DRFS can replace the
conventional bismuth and may be utilized as a new shield.",1503.03702v1
2015-03-26,Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off,"Transparent conducting oxides have recently gained great attention as
CMOS-compatible materials for applications in nanophotonics due to their low
optical loss, metal-like behavior, versatile/tailorable optical properties, and
established fabrication procedures. In particular, aluminum doped zinc oxide
(AZO) is very attractive because its dielectric permittivity can be engineered
over a broad range in the near infrared and infrared. However, despite all
these beneficial features, the slow (> 100 ps) electron-hole recombination time
typical of these compounds still represents a fundamental limitation impeding
ultrafast optical modulation. Here we report the first epsilon-near-zero AZO
thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation
and recombination time below 1 ps) and an outstanding reflectance modulation up
to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength
of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the
result of a low temperature fabrication procedure promoting oxygen vacancies
and an ultra-high carrier concentration. As a proof-of-concept, an all-optical
AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and
operating at THz frequencies is numerically demonstrated. Our results overcome
the traditional ""modulation depth vs. speed"" trade-off by at least an order of
magnitude, placing AZO among the most promising compounds for
tunable/switchable nanophotonics.",1503.07832v1
2015-03-28,Epitaxial Phases of BiMnO$_3$ from First Principles,"Bulk BiMnO$_3$ is the only transition-metal perovskite oxide that is
insulating and shows strong ferromagnetism. This distinctive behavior would
make it a promising candidate as a magnetoelectric multiferroic if it was also
a polar material, but experiments have shown that bulk BiMnO$_3$ has either a
very small polarization (below 0.1~$\mu$C/cm$^2$) or, most likely, that it is a
paraelectric. There is also experimental evidence that the polarization in
BiMnO$_3$ {\em films} grown on SrTiO$_3$ can be as high as 20~$\mu$C/cm$^2$.
Despite of the interest of these behaviors, the diagram of BiMnO$_3$ as a
function of epitaxial strain has remained largely unexplored. In this article,
we use first-principles to predict that both under enough compressive and
tensile epitaxial strain BiMnO$_3$ films are ferroelectric with a giant
polarization around 100~$\mu$C/cm$^2$. The phases displayed by the films are
similar to those experimentally found for BiFeO$_3$ in similar conditions---at
compressive strains, the film is supertetragonal with a large component of the
polarization pointing out of plane, while at tensile strains the polarization
points mostly in plane. Like in BiFeO$_3$ films, these phases are
antiferromagnetic---the orbital ordering responsible for ferromagnetism in
BiMnO$_3$ is absent in the polar phases. Our calculations also show that the
band gap of some of these BiMnO$_3$ films is substantially smaller than gaps
typically found in ferroelectric oxides, suggesting it may be a suitable
material for photovoltaic applications.",1503.08293v1
2015-04-01,Chemical modifications and stability of phosphorene with impurities: A first principles study,"We perform a systematic first-principles study of phosphorene in the presence
of typical monovalent (hydrogen, fluorine) and divalent (oxygen) impurities.
The results of our modeling suggest a decomposition of phosphorene into weakly
bonded one-dimensional (1D) chains upon single- and double-side hydrogenation
and fluorination. In spite of a sizable quasiparticle band gap (2.29 eV), fully
hydrogenated phosphorene found to be dynamically unstable. In contrast, full
fluorination of phosphorene gives rise to a stable structure, being an indirect
gap semiconductor with the band gap of 2.27 eV. We also show that fluorination
of phosphorene from the gas phase is significantly more likely than
hydrogenation due to the relatively low energy barrier for the dissociative
adsorption of F2 (0.19 eV) compared to H2 (2.54 eV). At low concentrations,
monovalent impurities tend to form regular atomic rows phosphorene, though such
patterns do not seem to be easily achievable due to high migration barriers
(1.09 and 2.81 eV for H2 and F2, respectively). Oxidation of phosphorene is
shown to be a qualitatively different process. Particularly, we observe
instability of phosphorene upon oxidation, leading to the formation of
disordered amorphous-like structures at high concentrations of impurities.",1504.00124v2
2015-04-21,Mechanisms and Geochemical Models of Core Formation,"The formation of the Earth's core is a consequence of planetary accretion and
processes in the Earth's interior. The mechanical process of planetary
differentiation is likely to occur in large, if not global, magma oceans
created by the collisions of planetary embryos. Metal-silicate segregation in
magma oceans occurs rapidly and efficiently unlike grain scale percolation
according to laboratory experiments and calculations. Geochemical models of the
core formation process as planetary accretion proceeds are becoming
increasingly realistic. Single stage and continuous core formation models have
evolved into multi-stage models that are couple to the output of dynamical
models of the giant impact phase of planet formation. The models that are most
successful in matching the chemical composition of the Earth's mantle, based on
experimentally-derived element partition coefficients, show that the
temperature and pressure of metal-silicate equilibration must increase as a
function of time and mass accreted and so must the oxygen fugacity of the
equilibrating material. The latter can occur if silicon partitions into the
core and through the late delivery of oxidized material. Coupled dynamical
accretion and multi-stage core formation models predict the evolving mantle and
core compositions of all the terrestrial planets simultaneously and also place
strong constraints on the bulk compositions and oxidation states of primitive
bodies in the protoplanetary disk.",1504.05417v1
2015-04-28,Transboundary Secondary Organic Aerosol in Western Japan: An Observed Limitation of the f44 Oxidation Indicator,"To obtain evidence for secondary organic aerosol formation during the long
range transport of air masses over the East China Sea, we conducted field
measurements in March 2012 at the Fukue atmospheric monitoring station,
Nagasaki, in western Japan. The relative abundance of m/z 44 in fine organic
aerosol mass spectra (f44) was measured by an Aerodyne aerosol chemical
speciation monitor. The stable carbon isotope ratio (d13C) of low volatile
water soluble organic carbon (LV-WSOC) in the daily filter samples of total
suspended particulate matter was also analyzed using an elemental analyzer
coupled with an isotope ratio mass spectrometer. Additionally, in situ
measurements of NOx and NOy were performed using NOx and NOy analyzers. The
measurements showed that, unlike the systematic trends observed in a previous
field study, a scatter plot for d13C of LV-WSOC versus f44 indicated a random
variation. Comparison of f44 with the photochemical age estimated by the NOx to
NOy ratio revealed that the f44 values distributing around 0.2 likely reached a
saturation level already and the f44 values were significantly lower than the
observed f44, approximately 0.3, at Hedo in the previous study. These findings
imply that the saturation point of f44, and the use of f44 as an oxidation
indicator, is case dependent.",1504.07400v1
2015-05-02,Electronic Structure of Oxide Interfaces: A Comparative Analysis of GdTiO$_3$/SrTiO$_3$ and LaAlO$_3$/SrTiO$_3$ Interfaces,"Emergent phases in the two-dimensional electron gas (2DEG) formed at the
interface between two insulating oxides have attracted great attention in the
past decade. We present ab-initio electronic structure calculations for the
interface between a Mott insulator GdTiO$_3$ (GTO) and a band insulator
SrTiO$_3$ (STO) and compare our results with those for the widely studied
LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface between two band insulators. Our
GTO/STO results are in excellent agreement with experiments, but qualitatively
different from LAO/STO. We find an interface carrier density of 0.5$e^{-}$/Ti,
independent of GTO thickness in both superlattice and thin film geometries, in
contrast to LAO/STO. The superlattice geometry in LAO/STO offers qualitatively
the same result as in GTO/STO. On the other hand, for a thin film geometry, the
interface carrier density builds up only beyond a threshold thickness of LAO.
The positive charge at the vacuum surface that compensates the 2DEG at the
interface also exhibits distinct behaviors in the two systems. The top GTO
layer is found to be insulating due to correlation-driven charge
disproportionation, while the top LAO layer is metallic within band theory and
may become insulating due to surface disorder or surface reconstruction.",1505.00339v2
2015-05-16,Non-Arrhenius conduction due to the interface-trap-induced disorder in X-doped amorphous InXZnO thin-film transistors,"Thin film transistors, with channels composed of In-X-Zn oxides, IXZO, with X
dopants: Ga, Sb, Be, Mg, Ag, Ca, Al, Ni, and Cu, were fabricated and their I-V
characteristics were taken at selected temperatures in the 77K<T<300K range.
The low field mobility, mu, and the interface defect density, Nst were
extracted from the characteristics for each of the studied IXZOs. At higher T
the mobility follows the Arrhenius law with an upward distortion, increasing as
T was lowered, gradually transforming into the exp [-(T0/T)1/4] variation. We
showed that mu(T, Nst) follows mu0exp[-Eaeff(T,Nst)/kT], with T-dependent
effective activation energy Eaeff(T, Nst) accounts for the data, revealing a
linear correlation between Eaeff and Nst at higher T. Temperature variation of
Eaeff(T, Nst) was evaluated using a model assuming a random distribution of
conduction mobility edge Ec values in the oxides, stemming from spatial
fluctuations induced by disorder in the interface traps distribution. For a
Gaussian distribution of Ec, the activation energy Eaeff(T, Nst) varies
linearly with 1/T, which accounts satisfactorily for the data obtained on all
the studied IXZOs. The model also shows that Eaeff(T, Nst) is a linear function
of Nst at a fixed T, which explains the exponential decrease of mu with NST.",1505.04291v1
2015-05-20,Self-Adaptive Spike-Time-Dependent Plasticity of Metal-Oxide Memristors,"Metal-oxide memristors have emerged as promising candidates for hardware
implementation of artificial synapses - the key components of high-performance,
analog neuromorphic networks - due to their excellent scaling prospects. Since
some advanced cognitive tasks require spiking neuromorphic networks, which
explicitly model individual neural pulses (spikes) in biological neural
systems, it is crucial for memristive synapses to support the
spike-time-dependent plasticity (STDP), which is believed to be the primary
mechanism of Hebbian adaptation. A major challenge for the STDP implementation
is that, in contrast to some simplistic models of the plasticity, the
elementary change of a synaptic weight in an artificial hardware synapse
depends not only on the pre-synaptic and post-synaptic signals, but also on the
initial weight (memristor's conductance) value. Here we experimentally
demonstrate, for the first time, STDP protocols that ensure self-adaptation of
the average memristor conductance, making the plasticity stable, i.e.
insensitive to the initial state of the devices. The experiments have been
carried out with 200-nm Al2O3/TiO2-x memristors integrated into 12x12
crossbars. The experimentally observed self-adaptive STDP behavior has been
complemented with numerical modeling of weight dynamics in a simple system with
a leaky-integrate-and-fire neuron with a random spike-train input, using a
compact model of memristor plasticity, fitted for quantitatively correct
description of our memristors.",1505.05549v1
2015-06-11,Direct Imaging of Nanoscale Conductance Evolution in Ion-Gel-Gated Oxide Transistors,"Electrostatic modification of functional materials by electrolytic gating has
demonstrated a remarkably wide range of density modulation, a condition crucial
for developing novel electronic phases in systems ranging from complex oxides
to layered chalcogenides. Yet little is known microscopically when carriers are
modulated in electrolyte-gated electric double-layer transistors (EDLTs) due to
the technical challenge of imaging the buried electrolyte-semiconductor
interface. Here, we demonstrate the real-space mapping of the channel
conductance in ZnO EDLTs using a cryogenic microwave impedance microscope. A
spin-coated ionic gel layer with typical thicknesses below 50 nm allows us to
perform high resolution (on the order of 100 nm) sub-surface imaging, while
maintaining the capability of inducing the metal-insulator transition under a
gate bias. The microwave images vividly show the spatial evolution of channel
conductance and its local fluctuations through the transition, as well as the
uneven conductance distribution established by a large source-drain bias. The
unique combination of ultra-thin ion-gel gating and microwave imaging offers a
new opportunity to study the local transport and mesoscopic electronic
properties in EDLTs.",1506.03785v1
2015-07-17,4f fine-structure levels as the dominant error in the electronic structures of binary lanthanide oxides,"The ground-state 4f fine-structure levels in the intrinsic optical transition
gaps between the 2p and 5d orbitals of lanthanide sesquioxides (Ln2O3,
Ln=La...Lu) were calculated by a two-way crossover search for the U parameters
for DFT+U calculations. The original 4f-shell potential perturbation in the
linear response method were reformulated within the constraint volume of
thegiven solids. The band structures were also calculated. This method yields
nearly constant optical transition gaps between Ln-5d and O-2p orbitals, with
magnitudes of 5.3~5.5 eV. This result verifies that the error in the band
structure calculations for Ln2O3 is dominated by the inaccuracies in the
predicted 4f levels in the 2p-5d transition gaps, which strongly and
nonlinearly depend on the on-site Hubbard U. The relationship between the 4f
occupancies and Hubbard U is non-monotonic and is entirely different from that
for materials with 3d or 4d orbitals, such as transition metal oxides. This new
linear response DFT+U method can provide a simpler understanding of the
electronic structure of Ln2O3 and enables a quick examination of the electronic
structures of lanthanide solids prior to hybrid functional or GW calculations.",1507.05088v3
2015-07-23,Spatially resolved TiOx phases in RRAM conductive nanofilaments using soft X-ray spectromicroscopy,"Reduction in metal-oxide thin films has been suggested as the key mechanism
responsible for forming conductive nanofilaments within solid-state memory
devices, enabling their resistive switching capacity. The quantitative spatial
identification of such filaments is a daunting task, particularly for
metal-oxides capable of exhibiting multiple phases as in the case of TiOx.
Here, we spatially resolve and chemically characterize distinct TiOx phases in
localized regions of a TiOx-based memristive device by combining full-field
transmission X-ray microscopy with soft X-ray spectroscopic analysis that is
performed on lamella samples. We particularly show that electrically
pre-switched devices in low-resistive states comprise reduced disordered phases
with O/Ti ratios close to Ti2O3 stoichiometry that aggregate in a ~ 100 nm
filamentary region electrically conducting the top and bottom electrodes of the
devices. We have also identified crystalline rutile and orthorhombic-like TiO2
phases in the region adjacent to the filament, suggesting that the temperature
increases locally up to 1000 K, validating the role of Joule heating in
resistive switching. Contrary to previous studies, our approach enables to
simultaneously investigate morphological and chemical changes in a quantitative
manner without incurring difficulties imposed by interpretation of electron
diffraction patterns acquired via conventional electron microscopy techniques.",1507.06588v1
2015-08-12,Electrical Control of Broadband Terahertz Wave Transmission with Two-Terminal Graphene Oxide Devices,"Carbon nanomaterials such as carbon nanotubes and graphene have proved to be
efficient building blocks for active optoelectronic devices. Especially, the
exotic properties of crystalline graphene, such as a linear/gapless energy
dispersion, offer a generic route to the development of active photonic
modulator at the infrared (IR) and terahertz (THz) regime with large modulation
depth. Here, we show that graphene oxide (GO), an oxygenated derivative of
graphene with randomly distributed molecular defects (e.g., adsorbed water
molecules and punched holes), can provide a different way to effectively
control broadband THz transmission amplitude, when incorporated into
two-terminal electrode devices. Electrically trapped charge carriers within
localized impurity states (LIS) of GO, which originate from fully randomized
defective structure of GO, results in a large modulation of transmission
amplitude (~30%) for broadband THz waves (0.3 ~ 2.0 THz) even at room
temperature. Interesting hysteretic behavior observed in the control of
broadband THz transmission further confirms the key role of trapped charge
carriers in switching of broadband THz waves. The device architecture
constructed by simple solution printing of GO onto the two-terminal electrode
enables easy-to-implement active photonic devices.",1508.02813v1
2015-08-26,Tuning the electronic properties at the surface of BaBiO3 thin films,"The presence of 2D electron gases at surfaces or interfaces in oxide thin
films remains a hot topic in condensed matter physics. In particular, BaBiO3
appears as a very interesting system as it was theoretically proposed that its
(001) surface should become metallic if a Bi-termination is achieved (Vildosola
et al., PRL 110, 206805 (2013)). Here we report on the preparation by pulsed
laser deposition and characterization of BaBiO3 thin films on silicon. We show
that the texture of the films can be tuned by controlling the growth
conditions, being possible to stabilize strongly (100)-textured films. We find
significant differences on the spectroscopic and transport properties between
(100)-textured and non-textured films. We rationalize these experimental
results by performing first principles calculations, which indicate the
existence of electron doping at the (100) surface. This stabilizes Bi ions in a
3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing
the surface conductivity. Our results emphasize the importance of surface
effects on the electronic properties of perovskites, and provide strategies to
design novel oxide heterostructures with potential interface-related 2D
electron gases.",1508.06480v4
2015-08-28,Quantifying electronic correlation strength in a complex oxide: a combined DMFT and ARPES study of LaNiO$_3$,"The electronic correlation strength is a basic quantity that characterizes
the physical properties of materials such as transition metal oxides.
Determining correlation strengths requires both precise definitions and a
careful comparison between experiment and theory. In this paper we define the
correlation strength via the magnitude of the electron self-energy near the
Fermi level. For the case of LaNiO$_3$, we obtain both the experimental and
theoretical mass enhancements $m^\star/m$ by considering high resolution
angle-resolved photoemission spectroscopy (ARPES) measurements and density
functional + dynamical mean field theory (DFT + DMFT) calculations. We use
valence-band photoemission data to constrain the free parameters in the theory,
and demonstrate a quantitative agreement between the experiment and theory when
both the realistic crystal structure and strong electronic correlations are
taken into account. These results provide a benchmark for the accuracy of the
DFT+DMFT theoretical approach, and can serve as a test case when considering
other complex materials. By establishing the level of accuracy of the theory,
this work also will enable better quantitative predictions when engineering new
emergent properties in nickelate heterostructures.",1508.07247v2
2015-09-08,Two-dimensional TiOx nanostructures on Au(111): a Scanning Tunneling Microscopy and Spectroscopy investigation,"We investigated the growth of titanium oxide two-dimensional (2D)
nanostructures on Au(111), produced by Ti evaporation and post-deposition
oxidation. Scanning tunneling microscopy and spectroscopy (STM and STS) and
low-energy electron diffraction (LEED) measurements characterized the
morphological, structural and electronic properties of the observed structures.
Five distinct TiO\sub{x} phases were identified: the \emph{honeycomb} and
\emph{pinwheel} phases appear as monolayer films wetting the gold surface,
while nanocrystallites of the \emph{triangular}, \emph{row} and \emph{needle}
phases grow mainly over the honeycomb or pinwheel layers. Density Functional
Theory (DFT) investigation of the honeycomb structure supports a $(2\times 2)$
structural model based on a Ti-O bilayer having $\text{Ti}_2\text{O}_3$
stoichiometry. The pinwheel phase was observed to evolve, for increasing
coverage, from single triangular crystallites to a well-ordered film forming a
$(4\sqrt{7}\times 4\sqrt{7})R19.1^\circ$ superstructure, which can be
interpreted within a moir\~A\c{opyright}-like model. Structural characteristics
of the other three phases were disclosed from the analysis of high-resolution
STM measurements. STS measurements revealed a partial metallization of
honeycomb and pinwheel and a semiconducting character of row and triangular
phases.",1509.02363v1
2015-09-05,Towards rational design of catalysts supported on a topological insulator substrate,"Exotic and robust metallic surface states of topological insulators (TIs)
have been expected to provide a promising platform for novel surface chemistry
and catalysis. However, it is still an unprecedented field how TIs affect the
activity of catalysts. In this work, we study the effects of topological
surface states (TSSs) on the activity of transition metal clusters (Au, Ag, Cu,
Pt, and Pd), which are supported on a TI Bi2Se3 substrate. It was found the
adsorption energy of oxygen on the supported catalysts can be always enhanced
due to the TSSs. However, it does not necessarily mean an increase of the
activity in catalytic oxidation reaction. Rather, the enhanced adsorption
behavior in the presence of TSSs exhibits dual effects, determined by the
intrinsic reactivity of these catalysts with oxygen. For the Au case, the
activity of catalytic oxidation can be improved because the intrinsic binding
between Au and O is relatively weak. In contrast, a negative effect is found
for the Pt and Pd clusters since the intrinsic binding of Pt and Pd with oxygen
is too strong. We also found that the effect of TSSs on the activity of
hydrogen evolution reaction (HER) is quite similar, i.e. the metals with
original weak reactivity can gain a positive effect from TSSs. The present work
can pave a way for more rational design and selection of catalysts when using
TIs as substrates.",1509.02484v1
2015-09-09,Crystal Structure and Electronic Properties of Bulk and Thin Film Brownmillerite Oxides,"The equilibrium structure and functional properties exhibited by
brownmillerite oxides, a family of perovskite-derived structures with
alternating layers of $B$O$_6$ octahedra and $B$O$_4$ tetrahedra, viz., ordered
arrangements of oxygen vacancies, is dependent on a variety of competing
crystal-chemistry factors. We use electronic structure calculations to
disentangle the complex interactions in two ferrates, Sr$_2$Fe$_2$O$_5$ and
Ca$_2$Fe$_2$O$_5$, relating the stability of the equilibrium (strain-free) and
thin film structures to both previously identified and newly herein proposed
descriptors. We show that cation size and intralayer separation of the
tetrahedral chains provide key contributions to the preferred ground state. We
show the bulk ground state structure is retained in the ferrates over a range
of strain values; however, a change in the orientation of the tetrahedral
chains, i.e., a perpendicular orientation of the vacancies relative to the
substrate, is stabilized in the compressive region. The structure stability
under strain is largely governed by maximizing the intraplane separation of the
`dipoles' generated from rotations of the FeO$_4$ tetrahedra. Lastly, we find
that the electronic band gap is strongly influenced by strain, manifesting as
an unanticipated asymmetric-vacancy alignment dependent response. This
atomistic understanding establishes a practical route for the design of novel
functional electronic materials in thin film geometries.",1509.02593v1
2015-09-10,Resonant x-ray scattering studies of charge order in cuprates,"X-ray techniques have been used for more than a century to study the atomic
and electronic structure in virtually any type of material. The advent of
correlated electron systems, in particular complex oxides, brought about new
scientific challenges and opportunities for the advancement of conventional
x-ray methods. In this context, the need for new approaches capable of
selectively sensing new forms of orders involving all degrees of freedom --
charge, orbital, spin, and lattice -- paved the way for the emergence and
success of resonant x-ray scattering, which has become an increasingly popular
and powerful tool for the study of electronic ordering phenomena in solids.
Here we review the recent resonant x-ray scattering breakthroughs in the copper
oxide high-temperature superconductors, in particular regarding the phenomenon
of charge order -- a broken-symmetry state occurring when valence electrons
self-organize into periodic structures. After a brief historical perspective on
charge order, we outline the milestones in the development of resonant x-ray
scattering, as well as the basic theoretical formalism underlying its unique
capabilities. The rest of the review will focus on the recent contributions of
resonant scattering to the tremendous advancements in our description and
understanding of charge order. To conclude, we propose a series of present and
upcoming challenges, and discuss the future outlook for this technique.",1509.03313v1
2015-09-15,Characterization and Dielectric Properties of Microwave Rare Earth Ceramics Materials for Telecommunications,"The rare-earth-metal-oxide based electronic materials were produced via a
conventional mixed-oxide route. Thermal analysis, XRD and SEM were used to
follow phase evolution and demonstrate the phase purity. Analytical TEM were
used to analyze crystal structural defects and to track the presence of
secondary phases, especially at grain boundaries. A crystal structure
determination was also performed. Phonon modes were analyzed with FTIR and
Raman spectroscopies and correlated with the origin of dielectric permittivity
({\epsilon}r) and radiation losses (tan {\delta}) characteristics. In some
compound and mixed compound Raman band mode exist, but this band is absent in
simple perovskite indicating that this band is associated with distribution of
B-site cations ordering. Some of compound shows long range order in B-site,
while it does not present in other material. A photo-acoustic sampling
technique in conjunction with the FTIR spectroscopy was employed, allowing the
analysis of neat materials with minimal sample preparation. Measurements of the
quality factor (Qf), {\epsilon}r and the temperature coefficient of the
resonant frequency ({\tau}f) characteristics were made at the microwave
resonant frequency using a vector or network analyzer.
  These perovskite have low tolerance factor because of considerable size
misfit of constituting atoms. For determination of atomic size and
characterization of constitution atoms, the test of samples and Rietveld
refinement using GSAS programs were used to do this examination. These
materials have attractive dielectric properties are being evaluated extensively
for substrates for multi-chip-module (MCM) devices and microwave
telecommunications.",1509.04445v2
2015-09-18,Effect of Strain on Ferroelectric Field Effect in Strongly Correlated Oxide Sm$_{0.5}$Nd$_{0.5}$NiO$_3$,"We report the effect of epitaxial strain on the magnitude and retention of
the ferroelectric field effect in high quality PbZr$_{0.3}$Ti$_{0.7}$O$_3$
(PZT)/3.8-4.3 nm Sm$_{0.5}$Nd$_{0.5}$NiO$_3$ (SNNO) heterostructures grown on
(001) LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) substrates. For SNNO on LAO, which
exhibits a first-order metal-insulator transition (MIT), switching the
polarization of PZT induces a 10 K shift in the transition temperature
$T_{MI}$, with a maximum resistance change between the on and off states of
$\Delta$$R$/$R_{on}$ ~75%. In sharp contrast, only up to 5% resistance change
has been induced in SNNO on STO, where the MIT is second-order, with the
modulation of $T_{MI}$ negligibly small. We also observe thermally activated
retention of the off state resistance $R_{off}$ in both systems, with the
activation energy of 22 meV (28 meV) for devices on LAO (STO). The time
dynamics and thermal response of the field effect instability points to
phonon-assisted interfacical trapping of charged mobile defects, which are
attributed to strain induced oxygen vacancies. At room temperature, $R_{off}$
stabilizes at ~55% and ~19% of the initial switching levels for SNNO on LAO and
STO, respectively, reflecting the significantly different oxygen vacancy
densities in these two systems. Our results reveal the critical role of strain
in engineering and modeling the complex oxide composite structures for
nanoelectronic and spintronic applications.",1509.05493v2
2015-09-28,Nitride Multilayers as a Platform for Parallel Two-Dimensional Electron-Hole Gases: MgO/ScN(111),"At interfaces between insulating oxides LaAlO$_3$ and SrTiO$_3$, a two
dimensional electron gas (2DEG) has been observed and well studied, while the
predicted hole gas (2DHG) has not been realized due to the strong tendency of
holes in oxygen $2p$ orbitals to localize. Here we propose, via ab initio
calculations, an unexplored class of materials for the realization of parallel
two dimensional (2D), two carrier (electron+hole) gases: nitride-oxide
heterostructures, with (111)-oriented ScN and MgO as the specific example.
Beyond a critical thickness of five ScN layers, this interface hosts spatially
separated conducting Sc-$3d$ electrons and N-$2p$ holes, each confined to
$\sim$two atomic layers -- the transition metal nitride provides both gases. A
guiding concept is that the N$^{3-}$ anion should promote robust two carrier 2D
hole conduction compared to that of O$^{2-}$; metal mononitrides are mostly
metallic and even superconducting while most metal monoxides are insulating. A
second positive factor is that the density of transition metal ions, hence of a
resulting 2DG, is about three times larger for a rocksalt (111) interface than
for a perovskite(001) interface. Our results, including calculation of Hall
coefficient and thermopower for each conducting layer separately, provide
guidance for new exploration, both experimental and theoretical, on
nitride-based conducting gases that should promote study of long sought exotic
states viz. new excitonic phases and distinct, nanoscale parallel
superconducting nanolayers.",1509.08518v2
2015-10-11,Prediction of novel stable compounds in the Mg-Si-O system under exoplanet pressures,"The Mg-Si-O system is the major Earth and rocky planet-forming system. Here,
through quantum variable-composition evolutionary structure explorations, we
have discovered several unexpected stable binary and ternary compounds in the
Mg-Si-O system. Besides the well-known SiO2 phases, we have found two
extraordinary silicon oxides, SiO3 and SiO, which become stable at pressures
above 0.51 TPa and 1.89 TPa, respectively. In the Mg-O system, we have found
one new compound, MgO3, which becomes stable at 0.89 TPa. We find that not only
the (MgO)x(SiO2)y compounds, but also two (MgO3)x(SiO3)y compounds, MgSi3O12
and MgSiO6, have stability fields above 2.41 TPa and 2.95 TPa, respectively.
The highly oxidized MgSi3O12 can form in deep mantles of mega-Earths with
masses above 20 M+ (M+:Earth's mass). Furthermore, the dissociation pathways of
pPv-MgSiO3 are also clarified, and found to be different at low and high
temperatures. The low-temperature pathway is MgSiO3 -> Mg2SiO4 + MgSi2O5 ->
SiO2 + Mg2SiO4 -> MgO + SiO2, while the high-temperature pathway is MgSiO3 ->
Mg2SiO4 + MgSi2O5 -> MgO + MgSi2O5 -> MgO + SiO2. Present results are relevant
for models of the internal structure of giant exoplanets, and for understanding
the high-pressure behavior of materials.",1510.03061v1
2015-10-13,Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO3 Surfaces,"The (001)SrTiO3 crystal surface can be engineered to display a self-organized
pattern of well-separated and nearly pure single-terminated SrO and TiO2
regions by high temperature annealing in oxidizing atmosphere. By using surface
sensitive techniques we have obtained evidence of such surface chemical
self-structuration in as-prepared crystals and unambiguously identified the
local composition. The contact surface potential at regions initially
consisting of majority single terminations (SrO and TiO2) is determined to be
smaller for SrO than for TiO2, in agreement with theoretical predictions,
although the measured difference below 100 meV is definitely smaller than
theoretical predictions for ideally pure single-terminated SrO and TiO2
surfaces. These relative values are maintained if samples are annealed in UHV
up to 200 degrees Celsius. Annealing in UHV at higher temperature (400 degrees
Celsius) preserves the surface morphology of self-assembled TiO2 and SrO rich
regions, although a non-negligible chemical intermixing is observed. The most
dramatic consequence is that the surface potential is reversed. It thus follows
that electronic and chemical properties of (001)SrTiO3, widely used in oxide
thin films growth, can largely vary before growth starts in a manner strongly
dependent on temperature and pressure conditions.",1510.03631v1
2015-10-28,Systematics in the metal-insulator transition temperatures in vanadium oxides,"Nine of the known vanadium oxides, VO$_{2-1/n}$ (n - a positive or negative
integer) with n=2 - 6, 8, 9, $\infty$ and -6, undergo metal-insulator
transitions accompanied by structural transitions, at various temperatures
T$_{MIT}$ (V$_7$O$_{13}$ is metallic above T=0). Among the persistent efforts
to determine the driving force(s) of these transitions, electron-electron
(Mott-like) and electron-phonon (Peierls-like) interactions, there were several
attempts to find systematics in T$_{MIT}$ as function of n. Here we present an
unexpectedly simple and illuminating systematics that holds for positive n: if
T$_{MIT}$ is the absolute value of the difference between T$_M$(n) and
T$_P$(n), which represent the contributions of electron-electron and
electron-phonon interactions, respectively, all data points of T$_M$-T$_P$
versus 1/n lie on, or close to, two simple straight lines; one is T$_M$-T$_P$=
T$_{\infty}$(7/n-1) for V$_3$O$_5$, V$_4$O$_7$, V$_5$O$_9$, V$_7$O$_{13}$,
V$_8$O$_{15}$, V$_9$O$_{17}$ and VO$_2$ and the other is T$_M$-T$_P$=
T$_{\infty}$(3/n-1) for V$_2$O$_3$, V$_6$O$_{11}$ and VO$_2$.",1510.08286v1
2015-10-30,Ab initio study of the ferroelectric strain dependence and 180$^\circ$ domain walls in the barium metal fluorides BaMgF$_4$ and BaZnF$_4$,"We investigate the strain dependence of the ferroelectric polarization and
the structure of the ferroelectric domain walls in the layered
perovskite-related barium fluorides, BaMF$_4$ (M=Mg, Zn). The unusual
""geometric ferroelectricity"" in these materials is driven by the softening of a
single polar phonon mode consisting of rotations of the MF$_6$ octahedra
accompanied by polar displacements of the Ba cations, and in contrast to
conventional ferroelectrics involves minimal electronic rehybridization. We
therefore anticipate a different strain dependence of the polarization, and
alternative domain wall structures compared with those found in conventional
ferroelectric materials. Using first-principles calculations based on density
functional theory (DFT) within the general gradient approximation (GGA), we
calculate the variation of the crystal structure and the ferroelectric
polarization under both compressive and tensile strain. We perform structural
relaxations of neutral domain walls between oppositely oriented directions of
the ferroelectric polarization and calculate their corresponding energies to
determine which are most likely to form. We compare our results to literature
values for conventional perovskite oxides to provide a source of comparison for
understanding the ferroelectric properties of alternative non-oxide materials
such as the barium fluorides.",1510.09181v2
2015-11-27,Effect of interface geometry on electron tunnelling in Al/Al$_2$O$_3$/Al junctions,"We investigate how different interface geometries of an Al/Al$_2$O$_3$
junction, a common component of modern tunnel devices, affect electron
transport through the tunnel barrier. We study six distinct Al/Al$_2$O$_3$
interfaces which differ in stacking sequences of the metal and the oxide
surface atoms and the oxide termination. To construct model potential barrier
profiles for each examined geometry, we rely on first-principles
density-functional theory (DFT) calculations for the barrier heights and the
shapes of the interface regions as well as on experimental data for the barrier
widths. We show that even tiny variations in the atomic arrangement at the
interface cause significant changes in the tunnel barrier parameters and,
consequently, in electron transport properties. Especially, we obtain that
variations in the crucial barrier heights and widths can be as large as 2 eV
and 5 \AA, respectively. Finally, to gain information about the average
properties of the measured junction, we fit the conductance calculated within
the WKB approximation to the experimental data and interpret the fit parameters
with the help of the DFT results.",1511.08636v1
2015-11-30,Degradation of Black Phosphorus (BP): The Role of Oxygen and Water,"Black phosphorus (BP) has attracted significant interest as a monolayer or
few-layer material with extraordinary electrical and optoelectronic properties.
However, degradation in air and other environments is an unresolved issue that
may limit future applications. In particular the role of different ambient
species has remained controversial. Here, we report systematic experiments
combined with ab-initio calculations that address the effects of oxygen and
water in the degradation of BP. Our results show that BP rapidly degrades
whenever oxygen is present, but is unaffected by deaerated (i.e., O2 depleted)
water. This behavior is rationalized by oxidation involving a facile
dissociative chemisorption of O2, whereas H2O molecules are weakly physisorbed
and do not dissociate on the BP surface. Oxidation (by O2) turns the
hydrophobic pristine BP surface progressively hydrophilic. Our results have
implications on the development of encapsulation strategies for BP, and open
new avenues for exploration of phenomena in aqueous solutions including
solution-gating, electrochemistry, and solution-phase approaches for
exfoliation, dispersion, and delivery of BP.",1511.09201v2
2015-11-30,Simultaneous observation of small- and large-energy-transfer electron-electron scattering in three dimensional indium oxide thick films,"In three dimensional (3D) disordered metals, the electron-phonon
(\emph{e}-ph) scattering is the sole significant inelastic process. Thus the
theoretical predication concerning the electron-electron (\emph{e}-\emph{e})
scattering rate $1/\tau_\varphi$ as a function of temperature $T$ in 3D
disordered metal has not been fully tested thus far, though it was proposed 40
years ago [A. Schmid, Z. Phys. \textbf{271}, 251 (1974)]. We report here the
simultaneous observation of small- and large-energy-transfer \emph{e}-\emph{e}
scattering in 3D indium oxide thick films. In temperature region of
$T\gtrsim100$\,K, the temperature dependence of resistivities curves of the
films obey Bloch-Gr\""{u}neisen law, indicating the films possess degenerate
semiconductor characteristics in electrical transport property. In the low
temperature regime, $1/\tau_\varphi$ as a function of $T$ for each film can not
be ascribed to \emph{e}-ph scattering. To quantitatively describe the
temperature behavior of $1/\tau_\varphi$, both the 3D small- and
large-energy-transfer \emph{e}-\emph{e} scattering processes should be
considered (The small- and large-energy-transfer \emph{e}-\emph{e} scattering
rates are proportional to $T^{3/2}$ and $T^2$, respectively). In addition, the
experimental prefactors of $T^{3/2}$ and $T^{2}$ are proportional to
$k_F^{-5/2}\ell^{-3/2}$ and $E_F^{-1}$ ($k_F$ is the Fermi wave number, $\ell$
is the electron elastic mean free path, and $E_F$ is the Fermi energy),
respectively, which are completely consistent with the theoretical
predications. Our experimental results fully demonstrate the validity of
theoretical predications concerning both small- and large-energy-transfer
\emph{e}-\emph{e} scattering rates.",1511.09269v1
2015-11-26,Gate-tunable conducting oxide metasurfaces,"Metasurfaces composed of planar arrays of sub-wavelength artificial
structures show promise for extraordinary light manipulation; they have yielded
novel ultrathin optical components such as flat lenses, wave plates,
holographic surfaces and orbital angular momentum manipulation and detection
over a broad range of electromagnetic spectrum. However the optical properties
of metasurfaces developed to date do not allow for versatile tunability of
reflected or transmitted wave amplitude and phase after fabrication, thus
limiting their use in a wide range of applications. Here, we experimentally
demonstrate a gate-tunable metasurface that enables dynamic electrical control
of the phase and amplitude of the plane wave reflected from the metasurface.
Tunability arises from field-effect modulation of the complex refractive index
of conducting oxide layers incorporated into metasurface antenna elements which
are configured in a reflectarray geometry. We measure a phase shift of {\pi}
and ~ 30% change in the reflectance by applying 2.5 V gate bias. Additionally,
we demonstrate modulation at frequencies exceeding 10 MHz, and electrical
switching of +/-1 order diffracted beams by electrical control over subgroups
of metasurface elements, a basic requirement for electrically tunable
beam-steering phased array metasurfaces. The proposed tunable metasurface
design with high optical quality and high speed dynamic phase modulation
suggests applications in next generation ultrathin optical components for
imaging and sensing technologies, such as reconfigurable beam steering devices,
dynamic holograms, tunable ultrathin lens, nano-projectors, and nanoscale
spatial light modulators. Importantly, our design allows complete integration
with electronics and hence electrical addressability of individual metasurface
elements.",1511.09380v1
2016-01-06,Observation of quantum Hall plateau-plateau transition and scaling behavior of the zeroth Landau level in graphene p-n-p junctions,"We report distinctive magnetotransport properties of a graphene p-n-p
junction prepared by controlled diffusion of metallic contacts. In most cases,
materials deposited on a graphene surface introduce substantial carrier
scattering, which greatly reduces the high mobility of intrinsic graphene.
However, we show that an oxide layer only weakly perturbs the carrier
transport, which enables fabrication of a high-quality graphene p-n-p junction
through a one-step and resist-free method. The measured conductance-gate
voltage $(G-V_G)$ curves can be well described by a metal contact model, which
confirms the charge density depinning due to the oxide layer. The graphene
p-n-p junction samples exhibit pronounced quantum Hall effect, a well-defined
transition point of the zeroth Landau level (LL), and scaling behavior. The
scaling exponent obtained from the evolution of the zeroth LL width as a
function of temperature exhibits a relatively low value of
$\kappa=0.21\pm0.01$. Moreover, we calculate the energy level for the LLs based
on the distribution of plateau-plateau transition points, further validating
the assignment of the LL index of the QH plateau-plateau transition.",1601.01155v1
2016-01-11,Compositions in YBa2Cu3Oy for 3-D bond order superconductors,"Self-doping in YBa2Cu3Oy starts to switch from a charge balancing of chain
metal reduction and plane oxidation to one of chain ligand oxidation (O-) and
plane reduction on quenching from >600K. Amongst the responses are plane
expansions and types of unusually strong superconductivity such as elevated
temperature superconductivity (ETS), observed through laser pulsing (Tc=552K*)
and upon shot quenching (Tc=200K*). We ascribe ETS to limited 3-D
superconductivity due to a correlated system of bond ordering within
chain-plane sandwiches and propose how to stabilize it. Accordingly, plane
expanding n-doping arises from self-doping charge equilibration with local
chain Cu of two-fold O coordination (2). The dumbbell type bonds of both apical
O- are a result of high-energy environment and comparable in their metric with
electron pairs on the plane. Following empirical Tc=%(2)x11 we suggest
increasing %(2) to cause the observed retrograde rise in Tc (photo-induced
reflectivity edge) to a theoretical limit of Tc=1100K* at 100%(2). We propose
compositions and heat treatments based on charge-lattice commensurability.
Paired charge concentrations on planes, determined by bond ordering based on
magic number counts, suggest several promising candidates such as
c=0.22=2/3a0x3b0, c=0.17=2/3x4 or c=0.080=2/5x5. The latter could be achieved
with 32%(2) and display Tc=352K* not only in laser pulsed but in shot quenched
materials.",1601.02668v1
2016-01-19,Partial Oxidation of Methane on a Nickel Catalyst: Kinetic Monte-Carlo Simulation Study,"Kinetic Monte-Carlo simulation is applied to study the partial oxidation of
methane over a nickel catalyst. Based on the Langmuir-Hinshelwood mechanism,
the kinetic behavior of this reaction is analyzed and the results are compared
with previous experiments. This system exhibits kinetic phase transitions
between reactive regions with sustained reaction and poisoned regions without
reaction. The fractional coverages of the adsorbed species and the production
rates of H2, CO, H2O, and CO2 are evaluated at steady state as functions of
feed concentration of the methane and oxygen, and reaction temperature. The
influence of lattice coordination number, diffusion, and impurities on the
surface is investigated. The simulation results are in good agreement with the
experimental studies where such results are available. It is observed that when
the lattice coordination number is increased to eight, the width of the
reactive region increases significantly. Moreover, the phase transition becomes
continuous. The diffusion of adsorbed O and H on the surface plays a measurable
role in the reaction, increasing the maximum production rates as the diffusion
rate increases. In systems with impurities, the production rates are greatly
reduced and the phase transition is also changed from being abrupt to
continuous.",1601.05064v1
2016-02-08,Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations,"Recent studies have unequivocally proven the existence of clouds in
super-Earth atmospheres (Kreidberg et al. 2014). Here we provide a theoretical
context for the formation of super-Earth clouds by determining which
condensates are likely to form under the assumption of chemical equilibrium. We
study super-Earth atmospheres of diverse bulk composition, which are assumed to
form by outgassing from a solid core of chondritic material, following Schaefer
& Fegley (2010). The super-Earth atmospheres that we study arise from planetary
cores made up of individual types of chondritic meteorites. They range from
highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are
both subsolar and super-solar, thereby spanning a range of atmospheric
composition that is appropriate for low-mass exoplanets. Given the atomic
makeup of these atmospheres, we minimize the global Gibbs free energy of
formation for over 550 gases and condensates to obtain the molecular
composition of the atmospheres over a temperature range of 350-3,000 K. Clouds
should form along the temperature-pressure boundaries where the condensed
species appear in our calculation. We find that the composition of condensate
clouds depends strongly on both the H:O and C:O ratios. For the super-Earth
archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at
solar composition, in agreement with previous work (Morley et al. 2013;
Miller-Ricci Kempton et al. 2012). However, for oxidizing atmospheres, K2SO4
and ZnO condensates are favored instead, and for carbon-rich atmospheres with
super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds
form from a wide variety of rock-forming and metallic species.",1602.02759v2
2016-02-09,Quantum states entanglement in hemoglobin molecule active center,"An ab initio study of the electronic and spin configuration for the iron ion
in the active center of the human hemoglobin molecule is presented. It is well
known that the iron ion, being surrounded by the porphyrin ring and the
ligands, plays the key role in the realization of the basic oxygen-transport
functions of the molecule. This work is focused on the investigation the
features of the 3$d$-shell electronic states of the iron ion located inside the
active center of the hemoglobin molecule. Also in this paper we study in detail
the changes in these states occurring during the oxidation process. We use a
combination of the Density Functional Theory (DFT) method and the Dynamical
Mean Field Theory (DMFT) approach. This method allows to consider dynamic
correlation effects that are important in the description of systems containing
transition metal ions. It was found that the state of the valence electrons of
the iron ion of the active center of hemoglobin molecule is the entangled
quantum state. This state is a mixture of several electronic states with
comparable statistical probability. Furthermore, it was found that the process
of the bond formation between the iron-porphyrin complex and the oxygen
molecule is more complex than a simple high-spin to low-spin state of the Fe
ion transition. The transition metal ion oxidation is accompanied by
substantial redistribution of the states probabilities and the increasing of
the entanglement degree. This process also leads to the reduction of the total
spin moment from $s\approx$2.1 for the FeP(Im) to $s\approx$1.7 for the
FeP(Im)(O$_2$).",1602.02963v2
2016-02-09,Room-temperature quantum transport signatures in graphene/LaAlO3/SrTiO3 heterostructures,"The pseudospin quantum degree of freedom is one of the most remarkable
properties of graphene that distinguishes it from ordinary two-dimensional
metals and semiconductors. Pseudospin quantum interference leads to weak
antilocalization (WAL) and is influenced strongly by point defects and thermal
perturbations that break chirality and destroy phase coherence. Preserving and
manipulating quantum transport properties up to room temperature is key to
realizing practical pseudospin-based graphene devices. Here we report
fabrication and transport characterization of graphene field-effect devices on
a complex-oxide heterostructure, LaAlO3/SrTiO3. Signatures of WAL, a
consequence of pseudospin quantum interference, persist up to room temperature.
The LaAlO3/SrTiO3 substrate plays a critical role in suppressing short-range
impurity scattering and electron-phonon coupling. The observation of quantum
transport signatures at room temperature is unique to this system and presents
new opportunities for the development of pseudospin-based devices and novel
multifunctional devices that couple to the complex-oxide interface.",1602.03128v3
2016-03-08,Ligand-Surface Interactions and Surface Oxidation of Colloidal PbSe Quantum Dots Revealed by Thin-film Positron Annihilation Methods,"Positron Two Dimensional Angular Correlation of Annihilation Radiation
(2D-ACAR) measurements reveal modifications of the electronic structure and
composition at the surfaces of PbSe quantum dots (QDs), deposited as thin
films, produced by various ligands containing either oxygen or nitrogen atoms.
In particular, the 2D-ACAR measurements on thin films of colloidal PbSe QDs
capped with oleic acid ligands yield an increased intensity in the electron
momentum density (EMD) at high momenta compared to PbSe quantum dots capped
with oleylamine. Moreover, the EMD of PbSe QDs is strongly affected by the
small ethylediamine ligands, since these molecules lead to small distances
between QDs and favor neck formation between near neighbor QDs, inducing
electronic coupling between neighboring QDs. The high sensitivity to the
presence of oxygen atoms at the surface can be also exploited to monitor the
surface oxidation of PbSe QDs upon exposure to air. Our study clearly
demonstrates that positron annihilation spectroscopy applied to thin films can
probe surface transformations of colloidal semiconductor QDs embedded in
functional layers.",1603.02547v1
2016-04-12,Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal,"In most of the realistic ab initio and model calculations which have appeared
on the emission of light from Si nanocrystals, the role of surface oxygen has
been usually ignored, underestimated or completely ruled out. We investigate
theoretically, by density functional theory (DFT/B3LYP) possible modes of
oxygen bonding in hydrogen terminated silicon quantum dots using as a
representative case of the Si29 nanocrystal. We have considered Bridge-bonded
oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these
oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased
with respect to composition whereas spatial distribution of oxygen species
pointed out drastic change in electronic and cohesive characteristics of
nanocrytals. From an overall perspective of this study, it is shown that bridge
bonded oxygenated nanocrystals accompanied by Mix have higher binding energies
and large electronic gap compared to nanocrystals with doubly bonded oxygen
atoms. In addition, it is observed that the presence of OH along with BBO, DBO
and mixed configurations further lowers electronic gaps and binding energies
and trends. It is also demonstrated that oxidizing constituent besides their
spatial distribution significantly alters binding energy and highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap
(HOMO-LUMO gap up to 1.48 eV) within same composition.",1604.03528v1
2016-04-15,Single crystal growth from separated educts and its application to lithium transition-metal oxides,"Thorough mixing of the starting materials is the first step of a crystal
growth procedure. This holds true for almost any standard technique, whereas
the intentional separation of educts is considered to be restricted to a very
limited number of cases. A noticeable exception is the crystal growth in gels
that allows for a better control of the nucleation by limiting the diffusion.
The successful application of this principle to open systems, however, has
remained elusive. Here we show that single crystals of {\alpha}-Li2IrO3 can be
grown from separated educts in an open crucible in air. Elemental lithium and
iridium are oxidized and transported over a distance of typically one
centimeter in an isothermal process. Single crystals grow from an exposed
condensation point placed in between the educts. The method has also been
applied to the growth of Li2RuO3, Li2PtO3 and {\beta}-Li2IrO3 and a successful
use for various other materials is anticipated.",1604.04551v4
2016-04-27,Polyelectrolyte assisted charge titration spectrometry: applications to latex and oxide nanoparticles,"The electrostatic charge density of particles is of paramount importance for
the control of the dispersion stability. Conventional methods use
potentiometric, conductometric or turbidity titration but require large amount
of samples. Here we report a simple and cost-effective method called
polyelectrolyte assisted charge titration spectrometry or PACTS. The technique
takes advantage of the propensity of oppositely charged polymers and particles
to assemble upon mixing, leading to aggregation or phase separation. The mixed
dispersions exhibit a maximum in light scattering as a function of the
volumetric ratio X, and the peak position XMax is linked to the particle charge
density according to {\sigma} ~ D0 XMax where D0 is the particle diameter. The
PACTS is successfully applied to organic latex, aluminum and silicon oxide
particles of positive or negative charge using poly(diallyldimethylammonium
chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized
with respect to important parameters such as pH and concentration, and to the
polyelectrolyte molecular weight. The advantages of the PACTS technique are
that it requires minute amounts of sample and that it is suitable to a broad
variety of charged nano-objects.",1604.08033v1
2016-06-20,Anisotropic electron-phonon coupling in the spinel oxide superconductor,"Among hundreds of spinel oxides, LiTi2O4 (LTO) is the only one that exhibits
superconductivity (Tc ~13 K). Although the general electron-phonon coupling is
still the main mechanism for electron pairing in LTO, unconventional behaviors
such as the anomalous magnetoresistance, anisotropic orbital/spin
susceptibilities, etc. reveal that both the spin and the orbital interactions
should also be considered for understanding the superconductivity. Here, we
investigate tunneling spectra of [111]-, [110]- and [001]-oriented high quality
LTO thin films. Several bosonic modes in tunneling spectra are observed in the
[111]- and [110]-oriented films but not in [001]-oriented ones, and these modes
still exist at T = 2Tc and beyond the upper critical field, which are confirmed
as stemming from electron-phonon interaction by DFT calculations. These modes
only appear in special surface orientations, indicating that the
electron-phonon coupling in LTO system is highly anisotropic and may be
enhanced by orbital-related state. The anisotropic electron-phonon coupling
should be taken seriously in understanding the nature of LTO superconductivity.",1606.06109v3
2016-06-24,Π Band Dispersion along Conjugated Organic Nanowires Synthesized on a Metal Oxide Semiconductor,"Surface confined dehalogenation reactions are versatile bottom-up approaches
for the synthesis of carbon-based nanostructures with predefined chemical
properties. However, for devices generally requiring low conductivity
substrates, potential applications are so far severely hampered by the
necessity of a metallic surface to catalyze the reactions. In this work we
report the synthesis of ordered arrays of poly(p-phenylene) chains on the
surface of semiconducting TiO2(110) via a dehalogenative homocoupling of
4,4""-dibromoterphenyl precursors. The supramolecular phase is clearly
distinguished from the polymeric one using low energy electron diffraction and
scanning tunneling microscopy as the substrate temperature used for deposition
is varied. X ray photoelectron spectroscopy of C 1s and Br 3d core levels
traces the temperature of the onset of dehalogenation to around 475 K.
Moreover, angle-resolved photoemission spectroscopy and tight-binding
calculations identify a highly dispersive band characteristic of a substantial
overlap between the precursor's {\pi} states along the polymer, considered as
the fingerprint of a successful polymerization. Thus, these results establish
the first spectroscopic evidence that atomically precise carbon based
nanostructures can readily be synthesized on top of a transition-metal oxide
surface, opening the prospect for the bottom-up production of novel
molecule-semiconductor devices.",1606.07638v1
2016-06-30,Metal-Insulator Transition and the Role of Electron Correlation in FeO2,"Iron oxide is a key compound to understand the state of the deep Earth. It
has been believed that previously known oxides such as FeO and Fe2O3 will be
dominant at the mantle conditions. However, recent observation of FeO2 shed
another light to the composition of the deep lower mantle (DLM) and thus
understanding of the physical properties of FeO2 will be critical to model DLM.
Here, we report the electronic structure and structural properties of FeO2 by
using density functional theory (DFT) and dynamic mean field theory (DMFT). The
crystal structure of FeO2 is composed of Fe2+ and O2 2- dimers, where the Fe
ions are surround by the octahedral O atoms. We found that the bond length of
O2 dimer, which is very sensitive to the change of the Coulomb interaction U of
Fe 3d orbital, plays an important role in determining the electronic
structures. The band structures of DFT+DMFT show that the metal-insulator
transition is driven by the change of U and pressure. We suggest that the
correlation effect should be considered to correctly describe the physical
properties of FeO2 compound.",1606.09582v2
2016-07-07,An internal disulfide locks a misfolded aggregation-prone intermediate in cataract-linked mutants of human γD-crystallin,"Considerable mechanistic insight has been gained into amyloid aggregation;
however, a large class of non-amyloid protein aggregates are considered
'amorphous,' and in most cases little is known about their mechanisms.
Amorphous aggregation of {\gamma}-crystallins in the eye lens causes a
widespread disease of aging, cataract. We combined simulations and experiments
to study the mechanism of aggregation of two {\gamma}D-crystallin mutants, W42R
and W42Q - the former a congenital cataract mutation, and the latter a mimic of
age-related oxidative damage. We found that formation of an internal disulfide
was necessary and sufficient for aggregation under physiological conditions.
Two-chain all-atom simulations predicted that one non-native disulfide in
particular, between Cys32 and Cys41, was likely to stabilize an unfolding
intermediate prone to intermolecular interactions. Mass spectrometry and
mutagenesis experiments confirmed the presence of this bond in the aggregates
and its necessity for oxidative aggregation under physiological conditions in
vitro. Mining the simulation data linked formation of this disulfide to
extrusion of the N-terminal \b{eta}-hairpin and rearrangement of the native
\b{eta}-sheet topology. Specific binding between the extruded hairpin and a
distal \b{eta}-sheet, in an intermolecular chain reaction similar to domain
swapping, is the most probable mechanism of aggregate propagation.",1607.02110v1
2016-07-11,Dynamic Modulation of the Transport Properties of the LaAlO3/SrTiO3 Interface Using Uniaxial Strain,"Among the interfacial transport modulations to the LaAlO3/SrTiO3 (LAO/STO)
heterostructure, mechanical strain has been proven to be an effective approach
by growing the LAO/STO films on different substrates with varying lattice
mismatches to STO. However, this lattice-mismatch-induced strain effect is
static and biaxial, hindering the study of the strain effect in a dynamic way.
In this work we realize dynamic and uniaxial strain to the LAO/STO oxide
heterostructure at low temperature, through mechanical coupling from a
magnetostrictive template. This anisotropic strain results in symmetry breaking
at the interface and induces further splitting of the electronic band structure
and therefore produces different conductivities along the x and y in-plane
directions. In particular, we observe that along the strained direction the
interface conductivity decreases by up to 70% under a tensile strain, while it
increases by 6.8% under a compressive strain at 2 K. Also, it is revealed that
the modulation on the interfacial transport property can be anisotropic, i.e.,
the resistance changes differently when an excitation current is parallel or
perpendicular to the strain direction. This approach of strain engineering
provides another degree of freedom for control of transport properties of oxide
heterostructures and opens an additional way to investigate strain effects in
materials science.",1607.02808v1
2016-07-24,Evidence for percolation diffusion of cations and material recovery in disordered pyrochlore from accelerated molecular dynamics simulations,"We used classical and accelerated molecular dynamics simulations to
characterize vacancy-mediated diffusion of cations in Gd$_2$Ti$_2$O$_7$
pyrochlore as a function of the disorder on the microsecond timescale. We find
that cation vacancy diffusion is slow in materials with low levels of disorder.
However, higher levels of disorder allow for fast cation diffusion, which is
then also accompanied by fast antisite annihilation and ordering of the
cations. The cation diffusivity is therefore not constant, but decreases as the
material reorders. The results suggest that fast cation diffusion is triggered
by the existence of a percolation network of antisites. This is in marked
contrast with oxygen diffusion, which showed a smooth increase of the ionic
diffusivity with increasing disorder in the same compound. The increase of the
cation diffusivity with disorder is also contrary to observations from other
complex oxides and disordered media models, suggesting a fundamentally
different relation between disorder and mass transport. These results highlight
the dynamic interplay between fast cation diffusion and the recovery of
disorder and have important implications for understanding radiation damage
evolution, sintering and aging, as well as diffusion in disorder oxides more
generally.",1607.07101v1
2016-09-02,"Ab-initio study of structural, vibrational and optical properties of solid oxidizers","We report the structural, elastic and vibrational properties of five
ionic-molecular solid oxidizers MNO$_3$ (M = Li, Na, K) and MClO$_3$ (M = Na,
K). By treating long range electron-correlation effects, dispersion corrected
method leads to more accurate predictions of structural properties and phase
stability of KNO$_3$ polymorphs. The obtained elastic moduli show soft nature
of these materials and are consistent with Ultrasonic Pulse Echo measurements.
We made a complete assignment of vibrational modes which are in good accord
with available experimental results. From calculated IR and Raman spectra, it
is found that the vibrational frequencies show a red-shift from Li -> Na -> K
(Na -> K) and N -> Cl for nitrates (chlorates) due to increase in mass of metal
and non-metal atoms, respectively. The calculated electronic structure using
recently developed Tran-Blaha modified Becke-Johnson potential show that the
materials are wide band gap insulators with predominant ionic bonding between
M$^+$ (metal) and NO$_3^-$ /ClO$_3^-$ ions and covalent bonding (N-O and Cl-O)
within nitrate and chlorate anionic group. From the calculated optical spectra,
we observe that electric-dipole transitions are due to nitrate/chlorate group
below 20 eV and cationic transitions occur above 20 eV. The calculated
reflectivity spectra are consistent with the available experimental spectra.",1609.00473v1
2016-09-20,Compaction and flow rule of oxide nanopowders,"Transparent Al2O3 ceramics have attracted considerable interest for use in a
wide range of optical, electronic and structural applications. The fabrication
of these ceramics using powder metallurgy processes requires the development of
theoretical approaches to the compaction of nanopowders. In this work, we
investigate the compaction processes of two model granular systems imitating
Al2O3 nanosized powders. System I is a loosely aggregated powder, and system II
is a powder strongly inclined to agglomeration (for instance, calcined powder).
The processes of isostatical (uniform), biaxial, and uniaxial compaction as
well as uniaxial compaction with simultaneous shear deformation are studied.
The energy parameters of compaction such as the energy change of elastic
interparticle interactions and dispersion interactions, dissipative energy
losses related to the processes of interparticle friction, and the total work
of compaction are calculated for all the processes. The nonapplicability of the
associated flow rule to the description of deformation processes of oxide
nanopowders is shown and an alternative plastic flow rule is suggested. A
complete system of determining the relationship of the flow including
analytical approximations of yield surfaces is obtained.",1609.06099v1
2016-09-24,First principles modeling of defects in the Al_2O_3/In_0.53Ga_0.47As system,"Density functional theory paired with a first order many-body perturbation
theory correction is applied to determine formation energies and charge
transition energies for point defects in bulk In_0.53Ga_0.47As and for models
of the In_0.53Ga_0.47As/Al_2O_3 interface. The results are consistent with
previous computational studies that As_Ga antisites are candidates for defects
observed in capacitance voltage measurements on metal-oxide-semiconductor
capacitors, as the As_Ga antisite introduces energy states near the valence
band maximum and near the middle of the energy band gap. However, substantial
broadening in the distribution of the Ga_As charge transition levels due to the
variation in the local chemical environment resulting from alloying on the
cation (In/Ga) sublattice is found, whereas this effect is absent for As_Ga
antisites. Also, charge transition energy levels are found to vary based on
proximity to the semiconductor/oxide interface. The combined effects of alloy-
and proximity-shift on the Ga_As antisite charge transition energies are
consistent with the distribution of interface defect levels between the valence
band edge and midgap as extracted from electrical characterization data. Hence,
kinetic growth conditions leading to a high density of either Ga_As or As_Ga
antisites near the In_0.53Ga_0.47As/Al_2O_3 interface are both consistent with
defect energy levels at or below midgap.",1609.07624v1
2016-10-06,Diminish Electrostatic in Piezoresponse Force Microscopy through longer ultra-stiff tips,"Piezoresponse Force Microscopy is a powerful but delicate nanoscale technique
that measures the mechanical response resulting from the application of a
highly localized electric field. Though mechanical response is normally due to
piezoelectricity, other physical phenomena, especially electrostatic
interaction, can contribute to the signal read. We address this problematic
through the use of longer ultra-stiff probes providing state of the art
sensitivity, with the lowest electrostatic interaction and avoiding working in
high frequency regime. In order to find this solution we develop a theoretical
description addressing the effects of electrostatic contributions in the total
cantilever vibration and its quantification for different setups. The theory is
subsequently tested in a Periodically Poled Lithium Niobate (PPLN) crystal, a
sample with well-defined 0deg and 180deg domains, using different commercial
available conductive tips. We employ the theoretical description to compare the
electrostatic contribution effects into the total phase recorded. Through
experimental data our description is corroborated for each of the tested
commercially available probes. We propose that a larger probe length can be a
solution to avoid electrostatic forces, so the cantilever-sample electrostatic
interaction is reduced. For hard oxide samples we propose an ultra-stiff
cantilever which avoids the use of high frequency voltage but still diminishing
electrostatic forces. Our proposed commercially available solution have great
implications into avoiding artifacts while studying soft biological samples,
multiferroic oxides, and thin film ferroelectric materials and it opens a new
window into tip engineering.",1610.01809v1
2016-10-11,Valley splitting of single-electron Si MOS quantum dots,"Silicon-based metal-oxide-semiconductor quantum dots are prominent candidates
for high-fidelity, manufacturable qubits. Due to silicon's band structure,
additional low-energy states persist in these devices, presenting both
challenges and opportunities. Although the physics governing these valley
states has been the subject of intense study, quantitative agreement between
experiment and theory remains elusive. Here, we present data from a new
experiment probing the valley states of quantum dot devices and develop a
theory that is in quantitative agreement with both the new experiment and a
recently reported one. Through sampling millions of realistic cases of
interface roughness, our method provides evidence that, despite radically
different processing, the valley physics between the two samples is essentially
the same. This work provides the first evidence that valley splitting can be
deterministically predicted and controlled in metal oxide semiconductor quantum
dots, a critical requirement for such systems to realize a reliable qubit
platform.",1610.03388v1
2016-10-11,Measurement Error in Atomic-Scale STEM-EDS Mapping of a Model Oxide Interface,"With the development of affordable aberration-correctors, analytical scanning
transmission electron microscopy (STEM) studies of complex interfaces can now
be conducted at high spatial resolution at laboratories worldwide.
Energy-dispersive X-ray spectroscopy (STEM-EDS) in particular has grown in
popularity, since it enables elemental mapping over a wide range of ionization
energies. However, the interpretation of atomically-resolved data is greatly
complicated by beam-sample interactions that are often overlooked by novice
users. Here we describe the practical factors---namely, sample thickness and
the choice of ionization edge---that affect the quantification of a model
perovskite oxide interface. Our measurements of the same sample in regions of
different thickness indicate that interface profiles can vary by as much as 2-5
unit cells, depending on the spectral feature. This finding is supported by
multislice simulations, which reveal that on-axis maps of even perfectly abrupt
interfaces exhibit significant delocalization. Quantification of thicker
samples is further complicated by channeling to heavier sites across the
interface, as well as an increased signal background. We show that extreme care
must be taken to prepare samples to minimize channeling effects and argue that
it may not be possible to extract atomically-resolved information from many
chemical maps.",1610.03432v2
2016-10-18,Blue Phosphorene Oxide: Strain-tunable Quantum Phase Transitions and Novel 2D Emergent Fermions,"Tunable quantum phase transitions and novel emergent fermions in solid state
materials are fascinating subjects of research. Here, we propose a new stable
two-dimensional (2D) material, the blue phosphorene oxide (BPO), which exhibits
both. Based on first-principles calculations, we show that its equilibrium
state is a narrow-bandgap semiconductor with three bands at low energy.
Remarkably, a moderate strain can drive a semiconductor-to-semimetal quantum
phase transition in BPO. At the critical transition point, the three bands
cross at a single point at Fermi level, around which the quasiparticles are a
novel type of 2D pseudospin-1 fermions. Going beyond the transition, the system
becomes a symmetry-protected semimetal, for which the conduction and valence
bands touch quadratically at a single Fermi point that is protected by
symmetry, and the low-energy quasiparticles become another novel type of 2D
double Weyl fermions. We construct effective models characterizing the phase
transition and these novel emergent fermions, and we point out several exotic
effects, including super Klein tunneling, supercollimation, and universal
optical absorbance. Our result reveals BPO as an intriguing platform for the
exploration of fundamental properties of quantum phase transitions and novel
emergent fermions, and also suggests its great potential in nanoscale device
applications.",1610.05399v2
2016-10-24,The Role of H2O and O2 Molecules and Phosphorus Vacancies in the Structure Instability of Phosphorene,"The poor structural stability of phosphorene in air was commonly ascribed to
humidity and oxygen molecules. Recent exfoliation of phosphorene in
deoxygenated water promotes the need to re-examine the role of H2O and O2
molecules. Considering the presence of high population of vacancies in
phosphorene, we investigate the interaction of H2O and O2 molecules with
vacancy-contained phosphorene using first-principles calculations. In contrast
to the common notion that physisorbed molecules tend to have a stronger
adsorption at vacancy sites, we show that H2O has nearly the same adsorption
energy at the vacancy site as that at the perfect one. Charge transfer analysis
shows that O2 is a strong electron scavenger, which transfers the lone-pair
electrons of the phosphorus atoms to the 2{\pi}* antibonding orbital of O2. As
a result, the barrier for the O-O bond splitting to form O-P bonds is reduced
from 0.81 eV at the perfect site to 0.59 eV at the defect site, leading to an
about 5000 faster oxidizing rate at the defect site than at the perfect site at
room temperature. Hence, our work reveals that the vacancy in phosphorene shows
a stronger oxygen affinity than the perfect phosphorene lattice site.
Structural degradation of phosphorene due to oxidization may occur rapidly at
edges and grain boundaries where vacancies tend to agglomerate.",1610.07512v1
2017-02-17,Effect of Sr-doping of LaMnO3 spacer on modulation-doped two-dimensional electron gases at oxide interfaces,"Modulation-doped oxide two-dimensional electron gas (2DEG) formed at the
LaMnO3 (LMO) buffered disorderd-LaAlO3/SrTiO3 (d-LAO/LMO/STO) heterointerface,
provides new opportunities for electronics as well as quantum physics. Herein,
we studied the dependence of Sr-doping of La1-xSrxMnO3 (LSMO, x=0, 1/8, 1/3,
1/2, and 1) thus the filling of the Mn eg subbands as well as the LSMO polarity
on the transport properties of d-LAO/LSMO/STO. Upon increasing the LSMO film
thickness from 1 unit cell (uc) to 2 uc, a sharp metal to insulator transition
of interface conduction was observed, independent of x. The resultant electron
mobility is often higher than 1900 cm2V-1s-1 at 2 K, which increases upon
decreasing x. The sheet carrier density, on the other hand, is in the range of
6.9E1012~1.8E1013 cm-2 (0.01~0.03 e/uc) and is largely independent on x for all
the metallic d-LAO/LSMO (1 uc)/STO interfaces. These results are consistent
with the charge transfer induced modulation doping scheme and clarify that the
polarity of the buffer layer plays a trivial role on the modulation doping. The
negligible tunability of the carrier density could result from the reduction of
LSMO during the deposition of disordered LAO or that the energy levels of Mn 3d
electrons at the interface of LSMO/STO are hardly varied even when changing the
LSMO composition from LMO to SrMnO3.",1702.05256v1
2017-02-18,Soft-proton exchange on Magnesium-oxide-doped substrates a route toward efficient and power-resistant nonlinear converters,"Despite its attractive features, Congruent-melted Lithium Niobate (CLN)
suffers from Photo-Refractive Damage (PRD). This light-induced refractive-index
change hampers the use of CLN when high-power densities are in play, a typical
regime in integrated optics. The resistance to PRD can be largely improved by
doping the lithium-niobate substrates with magnesium oxide. However, the
fabrication of waveguides on MgO-doped substrates is not as effective as for
CLN: either the resistance to PRD is strongly reduced by the waveguide
fabrication process (as it happens in Ti-indiffused waveguides) or the
nonlinear conversion efficiency is lowered (as it occurs in annealed-proton
exchange). Here we fabricate, for the first time, waveguides starting from
MgO-doped substrates using the Soft-Proton Exchange (SPE) technique and we show
that this third way represents a promising alternative. We demonstrate that SPE
allows to produce refractive-index profiles almost identical to those produced
on CLN without reducing the nonlinearity in the substrate. We also prove that
the SPE does not affect substantially the resistance to PRD. Since the
fabrication recipe is identical between CLN and MgO-doped substrates, we
believe that SPE might outperform standard techniques to fabricate robust and
efficient waveguides for high-intensity-beam confinement.",1702.05590v1
2017-03-01,Atomically precise lateral modulation of a two-dimensional electron liquid in anatase TiO2 thin films,"Engineering the electronic band structure of two-dimensional electron liquids
(2DELs) confined at the surface or interface of transition metal oxides is key
to unlocking their full potential. Here we describe a new approach to tailoring
the electronic structure of an oxide surface 2DEL demonstrating the lateral
modulation of electronic states with atomic scale precision on an unprecedented
length scale comparable to the Fermi wavelength. To this end, we use pulsed
laser deposition to grow anatase TiO2 films terminated by a (1 x 4) in-plane
surface reconstruction. Employing photo-stimulated chemical surface doping we
induce 2DELs with tunable carrier densities that are confined within a few TiO2
layers below the surface. Subsequent in-situ angle resolved photoemission
experiments demonstrate that the (1 x 4) surface reconstruction provides a
periodic lateral perturbation of the electron liquid. This causes strong
backfolding of the electronic bands, opening of unidirectional gaps and a
saddle point singularity in the density of states near the chemical potential.",1703.00157v1
2017-08-10,Oxygen Partial Pressure during Pulsed Laser Deposition: Deterministic Role on Thermodynamic Stability of Atomic Termination Sequence at SrRuO3/BaTiO3 Interface,"With recent trends on miniaturizing oxide-based devices, the need for
atomic-scale control of surface/interface structures by pulsed laser deposition
(PLD) has increased. In particular, realizing uniform atomic termination at the
surface/interface is highly desirable. However, a lack of understanding on the
surface formation mechanism in PLD has limited a deliberate control of
surface/interface atomic stacking sequences. Here, taking the prototypical
SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we
investigated the formation of different interfacial termination sequences
(BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found
that a uniform SrO-TiO2 termination sequence at the SRO/BTO interface can be
achieved by lowering the PO2 to 5 mTorr, regardless of the total background gas
pressure (Ptotal), growth mode, or growth rate. Our results indicate that the
thermodynamic stability of the BTO surface at the low-energy kinetics stage of
PLD can play an important role in surface/interface termination formation. This
work paves the way for realizing termination engineering in functional oxide
heterostructures.",1708.03089v1
2017-08-10,A Design Based on Stair-case Band Alignment of Electron Transport Layer for Improving Performance and Stability in Planar Perovskite Solar Cells,"Among the n-type metal oxide materials used in the planar perovskite solar
cells, zinc oxide (ZnO) is a promising candidate to replace titanium dioxide
(TiO2) due to its relatively high electron mobility, high transparency, and
versatile nanostructures. Here, we present the application of low temperature
solution processed ZnO/Al-doped ZnO (AZO) bilayer thin film as electron
transport layers (ETLs) in the inverted perovskite solar cells, which provide a
stair-case band profile. Experimental results revealed that the power
conversion efficiency (PCE) of perovskite solar cells were significantly
increased from 12.25 to 16.07% by employing the AZO thin film as the buffer
layer. Meanwhile, the short-circuit current density (Jsc), open-circuit voltage
(Voc), and fill factor (FF) were improved to 20.58 mA/cm2, 1.09V, and 71.6%,
respectively. The enhancement in performance is attributed to the modified
interface in ETL with stair-case band alignment of ZnO/AZO/CH3NH3PbI3, which
allows more efficient extraction of photogenerated electrons in the CH3NH3PbI3
active layer. Thus, it is demonstrated that the ZnO/AZO bilayer ETLs would
benefit the electron extraction and contribute in enhancing the performance of
perovskite solar cells.",1708.03153v1
2017-08-24,Influence of inversion on Mg mobility and electrochemistry in spinels,"Magnesium oxide and sulfide spinels have recently attracted interest as
cathode and electrolyte materials for energy-dense Mg batteries, but their
observed electrochemical performance depends strongly on synthesis conditions.
Using first principles calculations and percolation theory, we explore the
extent to which spinel inversion influences Mg$^{2+}$ ionic mobility in
MgMn$_2$O$_4$ as a prototypical cathode, and MgIn$_2$S$_4$ as a potential solid
electrolyte. We find that spinel inversion and the resulting changes of the
local cation ordering give rise to both increased and decreased Mg$^{2+}$
migration barriers, along specific migration pathways, in the oxide as well as
the sulfide.
  To quantify the impact of spinel inversion on macroscopic Mg$^{2+}$
transport, we determine the percolation thresholds in both MgMn$_2$O$_4$ and
MgIn$_2$S$_4$. Furthermore, we analyze the impact of inversion on the
electrochemical properties of the MgMn$_2$O$_4$ cathode via changes in the
phase behavior, average Mg insertion voltages and extractable capacities, at
varying degrees of inversion. Our results confirm that inversion is a major
performance limiting factor of Mg spinels and that synthesis techniques or
compositions that stabilize the well-ordered spinel structure are crucial for
the success of Mg spinels in multivalent batteries.",1708.07458v1
2017-08-28,Limits in point to point resolution of MOS (Metal-Oxide-Semiconductor) based pixels detector arrays,"In high energy physics point to point resolution is a key prerequisite for
particle detector pixel arrays. Current and future experiments require the
development of inner-detectors able to resolve the tracks of particles down to
the micron range. Present-day technologies, although not fully implemented in
actual detectors can reach a 5 micometer limit, based on statistical
measurements, with a pixel-pitch in the 10 micrometer range. Attempts to design
small pixels based on SOI (Silicon On Insulator) technology will be briefly
recalled here. This paper is devoted to the evaluation of the building blocks
with regard to their use in pixel arrays for the accurate tracking of the
charged particles. We will make here a simulations based quantitative
evaluation of the physical limits in the pixel size. A design based on CMOS
(Complementary Metal-Oxide-Semiconductor) compatible technologies that allows a
reduction of the pixel size down to the sub-micronmeter range is introduced.
Its physical principle relies on a buried carrier-localizing collecting gate.
The fabrication process needed by this pixel design can be based on existing
process steps used in silicon microelectronics. The pixel characteristics will
be discussed as well as the design of pixel arrays. The existing bottlenecks
and how to overcome them will be discussed in the light of recent ion
implantation and material characterization.",1708.08330v4
2018-02-08,Limitation of atmospheric composition by combustion-explosion in exoplanetary atmospheres,"This work presents theoretical studies which combine aspects of combustion
and explosion theory with exoplanetary atmospheric science. Super Earths could
possess a large amount of molecular hydrogen depending on disk, planetary and
stellar properties. Super Earths orbiting pre-main sequence-M-dwarf stars have
been suggested to possess large amounts of O2 produced abiotically via water
photolysis followed by hydrogen escape . If these two constituents were present
simultaneously, such large amounts of H2 and O2 can react via photochemistry to
form up to about 10 Earth oceans. In cases where photochemical removal is slow
so that O2 can indeed build up abiotically, the atmosphere could reach the
combustion explosion limit. Then, H2 and O2 react extremely quickly to form
water together with modest amounts of hydrogen peroxide. These processes set
constraints for H2 O2 atmospheric compositions in Super Earth atmospheres. Our
initial study of the gas-phase oxidation pathways for modest conditions with
Earth insolation and about a tenth of a percent of H2 suggests that H2 is
oxidized by O2 into H2O mostly via HOx and mixed HOx NOx catalyzed cycles.
Regarding other atmospheric species-pairs we find that CO,O2 mixtures could
attain explosive combustive levels on mini gas planets for mid range for the C
to O ratio in the equilibrium chemistry regime for p more than about 1bar.
Regarding CH4,O2 mixtures, a small number of modeled rocky planets assuming
Earth like atmospheres orbiting cooler stars could have compositions at or near
the explosive combustive level although more work is required to investigate
this issue.",1802.02923v1
2018-02-13,Effect of support on the vanadyl oxygen abstraction in supported vanadia,"Supported vanadia catalysts are modeled within the cluster DFT approach to
get an insight into the mechanism in which the support affects the activity of
vanadia in the oxidation processes. The energy of the V=O group dissociation
chosen as a descriptor of the oxidation activity is estimated using two aligned
divanadate V2O3(OH)4 particles at various distances. Separation between
particles allows to imitate (i) the various supporting materials (e.g. TiO2,
SiO2, etc.), and (ii) the coverage of vanadia on a particular support. A
substantial compensation of the energy loss upon the vanadyl oxygen abstraction
via bonding to the vanadyl oxygen of neighboring vanadate particle has been
predicted. On account of such compensation the overall energy of the V=O
dissociation reaches its minimal value of 36 kcal/mol (dropping from maximum of
142 kcal/mol) at small separation of 3 {\AA} between dimers when the nearest
vanadyl oxygen occupies a bridge V-O-V position. For dimers separated by about
4 {\AA}, the dissociation energy achieves its maximal value for isolated dimers
of about 143 kcal/mol. Thus, these findings allows one to conclude that the
oxygen mobility is a result of a compensation effect in a chain-like bonding
between neighboring vanadyl groups on the surface of support.",1802.04496v2
2018-04-03,"Thermal theory of aluminum particle ignition in continuum, free-molecular, and transition heat transfer regimes","Most studies on nano- and micro- sized aluminum particle ignition have been
focused on the processes occuring inside particles. In the current paper,
thermal ignition of an aluminum particle in the air is simulated with different
heat transfer models: continuum, free-molecular and Fuchs model. A single
parabolic oxidation law is assumed in the particle size range from nano- to
millimeter diameters. A particle is considered ignited when it reaches the
oxide melting point. The criterion defining the limits of validity for each
model is the ratio of continuum and free-molecular heat transfer rates. The
dependence of ignition temperature $T_i$ on particle size is in a qualitative
agreement with the experimental trends: $T_i$ can have values in the range
700--1500 K for nanoparticles due to the dominating contribution of a
free-molecular heat transfer, and sharp growth of $T_i$ with the particle size
in the range of 1-100 $\mu$m diameter is due to the transitional character of
heat transfer. For small values of accommodation coefficient, ignition may
occur in the critical ignition mode with the thermal runaway. The results
suggest the importance of heat transfer and, in particular, energy
accommodation in ignition of nano- and micro- sized particles.",1804.01192v2
2018-04-08,Quantifying Confidence in DFT Predicted Surface Pourbaix Diagrams and Associated Reaction Pathways for Chlorine Evolution,"Density functional theory calculations can be used to identify dominant
reaction mechanisms. However, the dominant reaction mechanism is sensitive to
choice of the exchange correlation functional. Here, we demonstrate using the
example case of chlorine evolution reaction on rutile oxides, which can occur
through at least three reaction mechanisms each mediated by different surface
intermediates and active sites. We utilize Bayesian error estimation
capabilities within the BEEF-vdW exchange correlation (XC) functional to
quantify the uncertainty associated with predictions of the operative reaction
mechanism by systematically propagating the uncertainty originating from
DFT-computed adsorption free energies. We construct surface Pourbaix diagrams
based on the calculated adsorption free energies for rutile oxides of Ru, Ir,
Ti, Pt, V, Sn and Rh. We utilize confidence-value (c-value) to determine the
degree of confidence in the predicted surface phase diagrams. Using the scaling
relations between the adsorption energies of intermediates we construct a
generalized Pourbaix diagram showing the stable surface composition as a
function of potential and the oxygen binding energy on the cus site. This is
used to consistently determine activity volcano relationships. We incorporate
the uncertainty in linear scaling relations to quantify the confidence in
generalized Pourbaix diagram and the associated activity. This allows us to
compute the expectation limiting potential as a function of $\Delta E_{O^c}$,
which provides a more appropriate activity measure incorporating DFT
uncertainty. We show that the confidence in the classification problem of
identifying the active reaction mechanism is much better than the prediction
problem of determining catalytic activity.",1804.02766v1
2018-04-09,Inversion Charge-boost and Transient Steep-slope induced by Free charge-polarization Mismatch in a Ferroelectric-metal-oxide-semiconductor Capacitor,"In this letter, the transient behavior of a ferroelectric (FE)
metal-oxide-semiconductor (MOS) capacitor is theoretically investigated with a
series resistor. It is shown that compared to a conventional high-k dielectric
MOS capacitor, a significant inversion charge-boost can be achieved by a FE MOS
capacitor due to a steep transient subthreshold swing (SS) driven by the free
charge-polarization mismatch. It is also shown that the observation of steep
transient SS significantly depends on the viscosity coefficient under Landau's
mean field theory, in general representing the average FE time response
associated with domain nucleation and propagation. Therefore, this letter not
only establishes a theoretical framework that describes the physical origin
behind the inversion charge-boost in a FE MOS capacitor, but also shows that
the key feature of depolarization effect on a FE MOS capacitor should be the
inversion-charge boost, rather than the steep SS (e.g., sub-60mV/dec at room
temperature), which cannot be experimentally observed as the measurement time
is much longer than the FE response. Finally, we outlines the required material
targets for the FE response in field-effect transistors to be applicable for
next-generation high-speed and low-power digital switches.",1804.03125v1
2018-04-18,High order synaptic learning in neuro-mimicking resistive memories,"Memristors have demonstrated immense potential as building blocks in future
adaptive neuromorphic architectures. Recently, there has been focus on
emulating specific synaptic functions of the mammalian nervous system by either
tailoring the functional oxides or engineering the external programming
hardware. However, high device-to-device variability in memristors induced by
the electroforming process and complicated programming hardware are among the
key challenges that hinder achieving biomimetic neuromorphic networks. Here, an
electroforming-free and complementary metal oxide semiconductor
(CMOS)-compatible memristor based on oxygen-deficient SrTiO$_{3-x}$ (STO$_x$)
is reported to imitate synaptic learning rules. Through spectroscopic and
cross-sectional transmission electron microscopic analyses, electroforming-free
characteristics are attributed to the bandgap reduction of STO$_x$ by the
formation of oxygen vacancies. The potential of such memristors to behave as
artificial synapses is demonstrated by successfully implementing high order
time- and rate-dependent synaptic learning rules. Also, a simple hybrid
CMOS-memristor approach is presented to implement a variety of synaptic
learning rules. Results are benchmarked against biological measurements form
hippocampal and visual cortices with good agreement. This demonstration is a
step towards the realization of large scale adaptive neuromorphic computation
and networks.",1804.06688v1
2018-04-19,Confinement- and strain-induced enhancement of thermoelectric properties in LaNiO$_3$/LaAlO$_3(001)$ superlattices,"By combining ab initio simulations including an on-site Coulomb repulsion
term and Boltzmann theory, we explore the thermoelectric properties of
(LaNiO$_3$)$_n$/(LaAlO$_3$)$_n$(001) superlattices ($n=1,3$) and identify a
strong dependence on confinement, spacer thickness, and epitaxial strain. While
the system with $n=3$ shows modest values of the Seebeck coefficient and power
factor, the simultaneous reduction of the LaNiO$_3$ region and the LaAlO$_3$
spacer thickness to single layers results in a strong enhancement, in
particular of the in-plane values. This effect can be further tuned by using
epitaxial strain as control parameter: Under tensile strain corresponding to
the lateral lattice constant of SrTiO$_3$ we predict in- and cross-plane
Seebeck coefficients of $\pm 600$ $\mu$V/K and an in-plane power factor of $11$
$\mu$W/K$^2$cm for an estimated relaxation time of $\tau = 4$ fs around room
temperature. These values are comparable to some of the best performing oxide
systems such as La-doped SrTiO$_3$ or layered cobaltates and are associated
with the opening of a small gap ($0.29$ eV) induced by the concomitant effect
of octahedral tilting and Ni-site disproportionation. This establishes oxide
superlattices at the verge of a metal-to-insulator transition driven by
confinement and strain as promising candidates for thermoelectric materials.",1804.07070v2
2018-04-24,Gelation of Plasmonic Metal Oxide Nanocrystals by Polymer-Induced Depletion-Attractions,"Gelation of colloidal nanocrystals (NCs) emerged as a strategy to preserve
inherent nanoscale properties in multiscale architectures. Yet available
gelation methods still struggle to reliably control nanoscale optical phenomena
such as photoluminescence and localized surface plasmon resonance (LSPR) across
NC systems due to processing variability. Here, we report on an alternative
gelation method based on physical inter-NC interactions: short-range
depletion-attractions balanced by long-range electrostatic repulsions. The
latter are established by removing the native organic ligands that passivate
tin-doped indium oxide (ITO) NCs while the former are introduced by mixing with
small polyethylene glycol (PEG) chains. As we incorporate increasing
concentrations of PEG, we observe a reentrant phase behavior featuring two
favorable gelation windows; the first arises from bridging effects while the
second is attributed to depletion-attractions according to phase behavior
predicted by our unified theoretical model. The NCs remain discrete within the
gel network, based on X-ray scattering and high-resolution transmission
electron microscopy. The infrared optical response of the gel is reflective of
both the NC building blocks and the network architecture, being characteristic
of ITO NC LSPR with coupling interactions between neighboring NCs.",1804.09106v1
2018-04-25,"Testing the influence of the temperature, RH and filler type and content on the Universal Power Law for new reduced graphene oxide TPU composites","In this paper, 6 different reduced graphene oxide (rGO) were prepared by a
modified Hummers method and reduced by thermochemical methods. rGO materials
were intentionally prepared to obtain different BET and thickness and oxygen
content maintaining constant the lateral size to compare its performance on
thermoplastic polyurethane (TPU) matrix. Microstructure and the effect of the
incorporation of rGO on the hardness and electrical properties of TPU were
investigated. It has been studied the temperature and humidity dependence of
the electrical conductivity and the sensitivity and the response time to
humidity changes have been determined. Influence of the filler content,
temperature and humidity on the Jonschers universal power law (UPL) for ac
conductivity vs frequency and its fitting parameters A and n were determined.
It has been observed an anomalous behaviour (according to UPL) and a linear
correlation between log A and n independently of the filler content, humidity
and temperature, however there is an influence of the rGO used for the
preparation of the composite. To study the transport mechanisms the
experimental results were adjusted to the equation and the maximum adjustment
for like other carbon nanocomposites however there is not an unequivocal
behaviour.",1804.09361v1
2018-04-13,Influence of post-deposition annealing on the chemical states of crystalline tantalum pentoxide films,"We investigate the effect of post-deposition annealing (for temperatures from
848 K to 1273 K) on the chemical properties of crystalline Ta$_2$O$_5$ films
grown on Si(100) substrates by radio frequency magnetron sputtering. The atomic
arrangement, as determined by X-ray diffraction, is predominately hexagonal
($\delta$-Ta$_2$O$_5$) for the films exposed to heat treatments at 948 K and
1048 K; orthorhombic ($\beta$-Ta$_2$O$_5$) for samples annealed at 1148 K and
1273 K; and amorphous for samples annealed at temperatures below 948 K. X-ray
photoelectron spectroscopy for Ta $4f$ and O $1s$ core-levels were performed to
evaluate the chemical properties of all films as a function of annealing
temperature. Upon analysis, it is observed the Ta $4f$ spectrum characteristic
of Ta in Ta$^{5+}$ and the formation of Ta-oxide phases with oxidation states
Ta$^{1+}$, Ta$^{2+}$, Ta$^{3+}$, and Ta$^{4+}$. The study reveals that the
increase in annealing temperature increases the percentage of the state
Ta$^{5+}$ and the reduction of the others indicating that higher temperatures
are more desirable to produce Ta$_2$O$_5$, however, there seems to be an
optimal annealing temperature that maximizes the O\% to Ta\% ratio. We found
that at 1273 K the ratio slightly reduces suggesting oxygen depletion.",1804.09538v2
2018-11-01,The origin of negative charging in amorphous Al$_2$O$_3$ films: The role of native defects,"Amorphous aluminum oxide Al$_2$O$_3$ (a-Al$_2$O$_3$) layers grown by various
deposition techniques contain a significant density of negative charges. In
spite of several experimental and theoretical studies, the origin of these
charges still remains unclear. We report the results of extensive Density
Functional Theory (DFT) calculations of native defects - O and Al vacancies and
interstitials, as well as H interstitial centers - in different charge states
in both crystalline $\alpha$-Al$_2$O$_3$ and in a-Al$_2$O$_3$. The results
demonstrate that both the charging process and the energy distribution of traps
responsible for negative charging of a-Al$_2$O$_3$ films [M. B. Zahid et al.,
IEEE Trans. Electron Devices 57, 2907 (2010)] can be understood assuming that
the negatively charged O$_{\textrm{i}}$ and V$_{\textrm{Al}}$ defects are
nearly compensated by the positively charged H$_{\textrm{i}}$, V$_{\textrm{O}}$
and Al$_{\textrm{i}}$ defects in as prepared samples. Following electron
injection, the states of Al$_{\textrm{i}}$, V$_{\textrm{O}}$ or
H$_{\textrm{i}}$ in the band gap become occupied by electrons and sample
becomes negatively charged. The optical excitation energies from these states
into the oxide conduction band agree with the results of exhaustive
photo-depopulation spectroscopy (EPDS) measurements [M. B. Zahid et al., IEEE
Trans. Electron Devices 57, 2907 (2010)]. This new understanding of the origin
of negative charging of a-Al$_2$O$_3$ films is important for further
development of nanoelectronic devices and solar cells.",1811.00610v2
2018-11-14,Multifrequency Nanoscale Impedance Microscopy (m-NIM): A novel approach towards detection of selective and subtle modifications on the surface of polycrystalline boron-doped diamond electrodes,"In this paper, we describe the modification of Nanoscale Impedance Microscopy
(NIM), namely, a combination of contact-mode atomic force microscopy with local
impedance measurements. The postulated approach is based on the application of
multifrequency voltage perturbation instead of standard frequency-by-frequency
analysis, which among others offers more time-efficient and accurate
determination of the resultant impedance spectra with high spatial resolution.
Based on the impedance spectra analysis with an appropriate electric equivalent
circuit, it was possible to map surface resistance and contact capacitance.
Polycrystalline heavy boron-doped diamond (BDD) electrodes were the research
object. Recent studies have shown that the exposure of such electrodes to
oxidizing environment may result in the modification of termination type, and
thus it is a key factor in describing the electric and electrochemical
properties of BDD. We have successfully applied multifrequency NIM, which
allowed us to prove that the modification of termination type is selective and
occurs with different propensity on the grains having specific crystallographic
orientation. Furthermore, our approach enabled the detection of even subtle
submicroscopic surface heterogeneities, created as a result of various
oxidation treatments and to distinguish them from the surface heterogeneity
related to the local distribution of boron at the grain boundaries.",1811.05709v1
2018-11-30,Dynamically switching the surface electronic and electrostatic properties of indium tin oxide electrodes with photochromic monolayers,"The chemical modification of electrodes with organic materials is a common
approach to tune the electronic and electrostatic landscape between interlayers
in optoelectronic devices, thus facilitating charge injection at the
electrode/semiconductor interfaces and improving their performance. The use of
photochromic molecules for the surface modification allows dynamic control of
the electronic and electrostatic properties of the electrode and thereby
enables additional functionalities in such devices. Here, we show that the
electronic properties of a transparent indium tin oxide (ITO) electrode are
reversibly and dynamically modified by depositing organic photochromic switches
(diarylethenes) in the form of self-assembled monolayers (SAMs). By combining a
range of surface characterization and density functional theory calculations,
we present a detailed picture of the SAM binding onto ITO, the packing density
of molecules, their orientation, as well as the work function modification of
the ITO surface due to the SAM deposition. Upon illumination with ultraviolet
and green light, we observe a reversible shift of the frontier occupied levels
by 0.7 eV, and concomitantly a reversible work function change of ca. 60 meV.
Our results prove the viability of dynamic switching of the electronic
properties of the electrode with external light stimuli, which could be used to
fabricate ITO-based photo-switchable optoelectronic devices.",1811.12741v1
2019-05-02,Demonstration of Sputtering Atomic Layer Augmented Deposition (SALAD): Aluminum Oxide-Copper Dielectric-Metal Nanocomposite,"Designing a thin film structure often begins with choosing a film deposition
method that employs a specific primary process by which chemical species are
formed and transported. In other words, a film deposition system in which two
complementary deposition methods are hybridized should lead to new ways of
designing thin film structures with structural complexity tailored at a level
that has never been envisioned.This premise inspired us to uniquely combine
atomic layer deposition (ALD) and magnetron sputtering (SPU) within a single
deposition chamber; the combined film deposition system is referred to as
sputtering atomic layer augmented deposition (SALAD). SALAD allows us to take
full advantages of both ALDs precise and accurate precursor delivery and SPUs
versatility in choices of chemical elements. A SALAD system was designed based
on knowledge obtained by computational fluid dynamics with the goal of
conceiving a film deposition system that satisfied deposition conditions
distinctive for both ALD and SPU, and a prototype SALAD system was assembled by
employing off-the-shelf vacuum components.A s a demonstration, the SALAD system
was utilized to deposit a unique nanocomposite made of a stack of aluminum
oxide thin films by ALD and copper thin films by SPU, AlOx-Cu dielectric-metal
(ACDM) nanocomposite thin films, on Si and glass substrates. Spectroscopic
reflectivity collected on ACDM nanocomposite thin films shows unique dispersion
features to which conventional effective medium theories used for describing
optical properties of composites made of a dielectric host that contains
metallic inclusions do not seem to simply apply.",1905.00584v2
2019-05-02,All Inkjet-Printed Graphene-Silver Composite Inks for Highly Conductive Wearable E-Textiles Applications,"Inkjet-printed wearable electronic textiles (e-textiles) are considered to be
very promising due to excellent processing and environmental benefits offered
by digital fabrication technique. Inkjet-printing of conductive metallic inks
such as silver (Ag) nanoparticles (NPs) are well-established and that of
graphene-based inks is of great interest due to multi-functional properties of
graphene-based materials. However, poor ink stability at higher graphene
concentration and the cost associated with the higher Ag loading in metal inks
have limited their wider use. Moreover, graphene-based e-textiles reported so
far are mainly based on graphene derivatives such as graphene oxide (GO) or
reduced graphene oxide (rGO), which suffers from poor electrical conductivity.
Here we report inkjet printing of highly conductive and cost-effective
graphene/Ag composite inks for wearable e-textiles applications. The composite
inks were formulated, characterised and inkjet-printed onto PEL paper first and
then sintered at 150 C for 1 hr. The sheet resistance of the printed patterns
is found to be in the range of ~0.08 - 4.74 ohm/sq depending on the number of
print layers and the graphene/Ag ratio in the formulation. The optimised
composite ink was then successfully printed onto surface pre-treated (by inkjet
printing) cotton fabrics in order to produce all-inkjet-printed highly
conductive and cost-effective electronic textiles.",1905.00839v1
2019-05-03,Anisotropic Proton and Oxygen Ion Conductivity in Epitaxial Ba2In2O5 Thin Films,"Solid oxide oxygen ion and proton conductors are a highly important class of
materials for renewable energy conversion devices like solid oxide fuel cells.
Ba2In2O5 (BIO) exhibits both oxygen ion and proton conduction, in dry and humid
environment, respectively. In dry environment, the brownmillerite crystal
structure of BIO exhibits an ordered oxygen ion sublattice, which has been
speculated to result in anisotropic oxygen ion conduction. The hydrated
structure of BIO, however, resembles a perovskite and the protons in it were
predicted to be ordered in layers. To complement the significant theoretical
and experimental efforts recently reported on the potentially anisotropic
conductive properties in BIO, we measure here the proton and oxygen ion
conductivity along different crystallographic directions. Using epitaxial thin
films with different crystallographic orientations the charge transport for
both charge carriers is shown to be anisotropic. The anisotropy of the oxygen
ion conduction can indeed be explained through the layered structure of the
oxygen sublattice in brownmillerite BIO. The anisotropic proton conduction
however, further supports the suggested ordering of the protonic defects in the
material. The differences in proton conduction along different crystallographic
directions attributed to proton ordering in BIO are of a similar extent as
those observed along different crystallographic directions in materials where
proton ordering is not present but where protons find preferential conduction
pathways through chain-like or layered structures.",1905.01113v1
2019-05-05,Improving mobility of silicon metal-oxide-semiconductor devices for quantum dots by high vacuum activation annealing,"To improve mobility of fabricated silicon metal-oxide-semiconductor (MOS)
quantum devices, forming gas annealing is a common method used to mitigate the
effects of disorder at the Si/SiO2 interface. However, the importance of
activation annealing is usually ignored. Here, we show that a high vacuum
environment for implantation activation is beneficial for improving mobility
compared to nitrogen atmosphere. Low-temperature transport measurements of Hall
bars show that peak mobility can be improved by a factor of two, reaching 1.5
m^2/(Vs) using high vacuum annealing during implantation activation. Moreover,
the charge stability diagram of a single quantum dot is mapped, with no visible
disturbance caused by disorder, suggesting possibility of fabricating
high-quality quantum dots on commercial wafers. Our results may provide
valuable insights into device optimization in silicon-based quantum computing.",1905.01581v2
2019-05-11,ExoMol Molecular linelists -- XXXIII. The spectrum of Titanium Oxide,"Accurate line lists are crucial for correctly modelling a variety of
astrophysical phenomena, including stellar photospheres and the atmospheres of
extra-solar planets. This paper presents a new line database Toto for the main
isotopologues of titanium oxide (TiO): $^{46}$Ti$^{16}$O, $^{47}$Ti$^{16}$O,
$^{48}$Ti$^{16}$O, $^{49}$Ti$^{16}$O and $^{50}$Ti$^{16}$O. The TiO line list
contains transitions with wave-numbers up to 30,000 cm$^{-1}$ ie long-wards of
0.33 $\mu$m. The Toto line list includes all dipole-allowed transitions between
13 low-lying electronic states (X $^3\Delta$, a $^1\Delta$, d $^1\Sigma^+$, E
$^3\Pi$, A $^3\Phi$ B $^3\Pi$, C $^3\Delta$, b $^1\Pi$, c $^1\Phi$, f
$^1\Delta$, e $^1\Sigma^+$). Ab initio potential energy curves (PECs) are
computed at the icMRCI level and combined with spin-orbit and other coupling
curves. These PECs and couplings are iteratively refined to match known
empirical energy levels. Accurate line intensities are generated using ab
initio dipole moment curves. The Toto line lists are appropriate for
temperatures below 5000 K and contain 30 million transitions for TiO; it is
made available in electronic form via the CDS data centre and via
www.exomol.com. Tests of the line lists show greatly improved agreement with
observed spectra for objects such as M-dwarfs GJ876 and GL581.",1905.04587v2
2019-05-13,Velocity Saturation in La-doped BaSnO3 Thin Films,"BaSnO_{3}, a high mobility perovskite oxide, is an attractive material for
oxide-based electronic devices. However, in addition to low-field mobility,
high-field transport properties such as the saturation velocity of carriers
play a major role in determining device performance. We report on the
experimental measurement of electron saturation velocity in La-doped BaSnO_{3}
thin films for a range of doping densities. Predicted saturation velocities
based on a simple LO-phonon emission model using an effective LO phonon energy
of 120 meV show good agreement with measurements of velocity saturation in
La-doped BaSnO_{3} films.. Density-dependent saturation velocity in the range
of 1.6x10^{7} cm/s reducing to 2x10^{6} cm/s is predicted for {\delta}-doped
BaSnO3 channels with carrier densities ranging from 10^{13} cm^{-2} to
2x10^{14} cm^{-2} respectively. These results are expected to aid the informed
design of BaSnO3 as the active material for high-charge density electronic
transistors.",1905.05112v2
2019-05-16,"Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings","Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by
pulsed DC reactive sputter deposition on Si(100) at a temperature of 550
{\deg}C. XRD showed three different crystal structures depending on V-metal
fraction in the coating: {\alpha}-V2O3 rhombohedral structure for 100 at.% V, a
defect spinel structure for the intermediate region, 63 - 42 at.% V. At lower
V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed,
shifted to larger d-spacing compared to pure {\gamma}-Al2O3. The microstructure
changes from large columnar faceted grains for {\alpha}-V2O3 to smaller
equiaxed grains when lowering the vanadium content toward pure {\gamma}-Al2O3.
Annealing in air resulted in formation of V2O5 crystals on the surface of the
coating after annealing to 500 {\deg}C for 42 at.% V and 700 {\deg}C for 18
at.% V metal fraction respectively. The highest thermal stability was shown for
pure {\gamma}-Al2O3-coating, which transformed to {\alpha}-Al2O3 after
annealing to 1100{\deg} C. Highest hardness was observed for the Al-rich
oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7
at.% V metal fraction. The measured hardness after annealing in air decreased
in conjunction with the onset of further oxidation of the coatings.",1905.06714v2
2019-05-22,The polymorphous nature of cubic halide perovskites,"It has been long known that numerous halide and oxide perovskites can have
non-ideal octahedra, showing tilting, rotation, and metal atom displacements.
It has also been known that compounds that have at low temperatures a single
structural motif (""monomorphous structures"") could become disordered at higher
temperatures, resulting in non-ideal octahedra as an entropy effect. What is
shown here is that in many cubic halide perovskites and some oxides compounds a
distribution of different low-symmetry octahedra (""polymorphous networks"")
emerge already from the minimization of the systems internal energy, i.e., they
represent the intrinsic, preferred low temperature pattern of chemical bonding.
Thermal disorder effects build up at elevated temperatures on top of such low
temperature polymorphous networks. Compared with the monomorphous counterparts,
the polymorphous networks have lower predicted total energies (enhanced
stability), larger band gaps and dielectric constants now dominated by the
ionic part, and agrees much more closely with the observed pair distribution
functions. The nominal cubic perovskites (Pm-3m) structure deduced from X-Ray
diffraction is actually a macroscopically averaged, high symmetry
configuration, which should not be used to model electronic properties, given
that the latter reflect a low symmetry local configuration.",1905.09141v3
2019-05-24,"Quasiparticle band structure and optical properties of rutile GeO$_2$, an ultra-wide-band-gap semiconductor","Rutile GeO$_2$ is a visible and near-ultraviolet-transparent oxide that has
not been explored for semiconducting applications in electronic and
optoelectronic devices. We investigate the electronic and optical properties of
rutile GeO$_2$ with first-principles calculations based on density functional
theory and many-body perturbation theory. Our band-structure calculations
indicate a dipole-forbidden direct band gap at $\Gamma$ with an energy of 4.44
eV and effective masses equal to $m^*_{e\perp}$ =0.43$m_0$ , $m^*_{e||}$
=0.23$m_0$ , $m^*_{h\perp}$ =1.28$m_0$ , and $m^*_{h||}$=1.74$m_0$ . In
contrast to the self-trapped hole polarons by lattice distortions in other
wide-band-gap oxides that reduce the hole mobility, holes in rutile GeO$_2$ are
delocalized due to their small effective mass. The first allowed optical
transitions at $\Gamma$ occur at 5.04 eV ($\vec{E} \perp \vec{c}$) and 6.65 eV
($\vec{E} ||\vec{c} $). We also evaluate the optical absorption coefficient and
refractive index along both crystallographic directions. Our estimates for the
exciton binding energies using the Bohr model are close to the reported
experimental value. The ultra-wide-band-gap and light carrier effective masses
of rutile GeO$_2$, coupled with its optical transparency in the visible and
near UV are promising for applications in UV-transparent conductors and
solar-blind photodetectors.",1905.10301v2
2019-05-30,Sr-induced dipole scatter in BST: Insights from MD simulations using a transferable bond valence-based interatomic potential,"In order to design next-generation ferroelectrics, a microscopic
understanding of their macroscopic properties is critical. One means to
achieving an atomistic description of ferroelectric and dielectric phenomena is
classical molecular dynamics simulations. Previously, we have shown that
interatomic potentials based on the bond valence molecular dynamics (BVMD)
method can be used to study structural phase transitions, ferroelectric domain
nucleation, and domain wall migration in several perovskite oxides and
fixed-composition binary and ternary alloys. Most modern devices, however, use
variable-composition perovskite oxide alloys such as Ba$_x$Sr$_{1-x}$TiO$_3$
(BST). In this paper, we extend our bond valence approach to BST solid
solutions and, in so doing, show that the potential parameters for each element
are transferable between materials with different $x$. Using this potential, we
perform BVMD simulations investigating the temperature and composition
dependence of the lattice constants, Ti displacements, and ferroelectric
polarization of BST and find that our predictions match experiments and
first-principles theory. Additionally, based on a detailed analysis of local
dipole distributions, we demonstrate that substitution of Sr for Ba scrambles
dipoles, reduces global polarization, and enhances the order-disorder character
of the ferroelectric-paraelectric phase transition.",1905.13201v1
2020-06-30,"COTS MOS Dosimetry on the MeMOSat Board, Results After 2.5 Years in Orbit","We present the results after 2.5 years in or-bit of Total Ionizing Dose (TID)
measurements done using Metal Oxide Semiconductor (MOS) dosimeters on the
MeMOSat board. The MeMOSat board was launched on July 19th 2014 at the BugSat-1
""Tita"" microsatellite developed by Satellogic to stay at LEO. We used as
dosimeters p-channel Commercial Off The Shelf (COTS) MOS transistors with gate
oxides of 250~nm. Before launch, a subset of transistors with similar drain
current to voltage (I-V)curves where selected from a group of 100 devices. The
temperature dependence of the (I-V) curves was studied to find the minimum
temperature coefficient biasing point. Then, a calibration subgroup of sensors
was irradiated using a $^{60}$Co gamma source to study their response to TID,
showing responsivities of $\sim$75~mV/krad when the sensors are irradiated
without gate bias. Also, the post irradiation response of the sensors was
monitored, in order to include a correction for low dose rate irradiations,
yielding 30~mV/krad. A biasing and reading circuit was developed in order to
allow the reading of up to 4 sensors.The threshold voltage was monitored during
different periods of the mission. After 2.5 years in orbit,the threshold
voltage of the sensor mounted on the MeMOSat Board had a V$_\mathrm{T}$ shift
of approximately 35~mV corresponds to a dose of 1.2~krads.",2007.00143v1
2020-07-02,Enhanced graphitic domains of unreduced graphene oxide and the interplay of hydration behaviour and catalytic activity,"Previous studies indicate that the properties of graphene oxide (GO) can be
significantly improved by enhancing its graphitic domain size through thermal
diffusion and clustering of functional groups. Remarkably, this transition
takes place below the decomposition temperature of the functional groups and
thus allows fine-tuning of graphitic domains without compromising with the
functionality of GO. By studying the transformation of GO under mild thermal
treatment, we directly observe this size enhancement of graphitic domains from
originally 40 nm2 to 200 nm2 through an extensive transmission electron
microscopy (TEM) study. Additionally, we confirm the integrity of the
functional groups during this process by comprehensive chemical analysis. A
closer look into the process confirms the theoretically predicted relevance for
the room temperature stability of GO. We further investigate the influence of
enlarged graphitic domains on the hydration behaviour of GO and catalytic
performance of single-atom catalysts supported by GO.",2007.00860v5
2020-07-07,A switchable two-dimensional electron gas based on ferroelectric Ca:SrTiO$_3$,"Two-dimensional electron gases (2DEGs) can form at the surface of oxides and
semiconductors or in carefully designed quantum wells and interfaces. Depending
on the shape of the confining potential, 2DEGs may experience a finite electric
field, which gives rise to relativistic effects such as the Rashba spin-orbit
coupling. Although the amplitude of this electric field can be modulated by an
external gate voltage, which in turn tunes the 2DEG carrier density, sheet
resistance and other related properties, this modulation is volatile. Here, we
report the design of a ''ferroelectric'' 2DEG whose transport properties can be
electrostatically switched in a non-volatile way. We generate a 2DEG by
depositing a thin Al layer onto a SrTiO$_3$ single crystal in which 1 percent
of Sr is substituted by Ca to make it ferroelectric. Signatures of the
ferroelectric phase transition at 25 K are visible in the Raman response and in
the temperature dependences of the carrier density and sheet resistance that
shows a hysteretic dependence on electric field as a consequence of
ferroelectricity. We suggest that this behavior may be extended to other oxide
2DEGs, leading to novel types of ferromagnet-free spintronic architectures.",2007.03344v1
2020-07-08,Structure motif centric learning framework for inorganic crystalline systems,"Incorporation of physical principles in a network-based machine learning (ML)
architecture is a fundamental step toward the continued development of
artificial intelligence for materials science and condensed matter physics. In
this work, as inspired by the Pauling rule, we propose that structure motifs
(polyhedral formed by cations and surrounding anions) in inorganic crystals can
serve as a central input to a machine learning framework for crystalline
inorganic materials. Taking metal oxides as examples, we demonstrated that, an
unsupervised learning algorithm Motif2Vec is able to convert the presence of
structure motifs and their connections in a large set of crystalline compounds
into unique vector representations. The connections among complex materials can
be largely determined by the presence of different structure motifs and their
clustering information are identified by our Motif2Vec algorithm. To
demonstrate the novel use of structure motif information, we show that a
motif-centric learning framework can be effectively created by combining motif
information with the recently developed atom-based graph neural networks to
form an atom-motif dual graph network (AMDNet). Taking advantage of node and
edge information on both atomic and motif level, the AMDNet is more accurate
than an atom graph network in predicting electronic structure related material
properties of metal oxides such as band gaps. The work illustrates the route
toward fundamental design of graph neural network learning architecture for
complex material properties by incorporating beyond-atom physical principles.",2007.04145v1
2020-07-12,Fabrication of Germanium-on-insulator in a Ge wafer with a crystalline Ge top layer and buried GeO2 layer by Oxygen ion implantation,"The paper reports fabrication of Germanium-on-Insulator (GeOI) wafer by
Oxygen ion implantation of an undoped single crystalline Ge wafer of
orientation (100). Oxygen ions of energy 200 keV were implanted. The implanted
wafer was subjected to Rapid Thermal Annealing to 650 C. The resulting wafer
has a top crystalline Ge layer of 220 nm thickness and Buried Oxide layer (BOX)
layer of good quality crystalline Germanium oxide with thickness around 0.62
micron. The crystalline BOX layer has hexagonal crystal structure with lattice
constants close to the standard values. Raman Spectroscopy, cross-sectional
HRTEM with SAED and EDS established that the top Ge layer was recrystallized
during annealing with faceted crystallites. The top layer has a small tensile
strain of around +0.4\% and has estimated dislocation density of 2.7 x
10^{7}cm^{-2}. The thickness, crystallinity and electrical characteristics of
the top layer and the quality of the BOX layer of GeO_{2} are such that it can
be utilized for device fabrication.",2007.05897v1
2020-07-12,Artificial two-dimensional polar metal by charge transfer to a ferroelectric insulator,"Integrating multiple properties in a single system is crucial for the
continuous developments in electronic devices. However, some physical
properties are mutually exclusive in nature. Here, we report the coexistence of
two seemingly mutually exclusive properties-polarity and two-dimensional
conductivity-in ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin films at the
LaAlO$_3$/Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ interface at room temperature. The
polarity of a ~3.2 nm Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin film is preserved with a
two-dimensional mobile carrier density of ~0.05 electron per unit cell. We show
that the electronic reconstruction resulting from the competition between the
built-in electric field of LaAlO$_3$ and the polarization of
Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ is responsible for this unusual two-dimensional
conducting polar phase. The general concept of exploiting mutually exclusive
properties at oxide interfaces via electronic reconstruction may be applicable
to other strongly-correlated oxide interfaces, thus opening windows to new
functional nanoscale materials for applications in novel nanoelectronics.",2007.05903v1
2020-07-14,Mass Production of Two-Dimensional Materials by Intermediate-Assisted Grinding Exfoliation,"The scalable and high-efficiency production of two-dimensional (2D) materials
is a prerequisite to their commercial use. Currently, only graphene and
graphene oxide can be produced on a ton scale, and the inability to produce
other 2D materials on such a large scale hinders their technological
applications. Here we report a grinding exfoliation method that uses
micro-particles as force intermediates to resolve applied compressive forces
into a multitude of small shear forces, inducing the highly-efficient
exfoliation of layer materials. The method, referred to as
intermediate-assisted grinding exfoliation (iMAGE), can be used for the
large-scale production of many 2D materials. As an example, we have exfoliated
bulk h-BN into 2D h-BN with large flake sizes, high quality and structural
integrity, with a high exfoliation yield of 67%, a high production rate of 0.3
g h-1 and a low energy consumption of 3.01x10^6 J g-1. The production rate and
energy consumption are one to two orders of magnitude better than previous
results. Besides h-BN, this iMAGE technology has been used to exfoliate various
layer materials such as graphite, black phosphorus, transition metal
dichalcogenides, and metal oxides, proving its universality. Molybdenite
concentrate, a natural low-cost and abundant mineral, was used as a demo for
the large-scale exfoliation production of 2D MoS2 flakes. Our work indicates
the huge potential of the iMAGE method to produce large amounts of various 2D
materials, which paves the way for their commercial application.",2007.06921v1
2020-07-24,Integration of multi-layer black phosphorus into photoconductive antennas for THz emission,"We report the fabrication, characterization, and modeling of photoconductive
antennas using 40 nm thin-film flakes of black phosphorus (BP) as the
photoconductor and hexagonal boron nitride (hBN) as a capping layer to prevent
oxidation of BP. Dipole antennas were fabricated on oxidized high-resistivity
Si substrates, and BP and hBN flakes were picked up and transferred onto the
antenna inside a nitrogen glovebox. The transfer matrix technique was used to
optimize the thickness of BP and hBN for maximum absorption. BP flakes were
aligned with the armchair axis along the anode-cathode gap of the antenna, with
crystal orientation measured using reflection anisotropy. Photocurrent imaging
under illumination with 100 fs pulses at 780 and 1560 nm showed a
bias-dependent maximum photocurrent localized to the antenna gap with a peak
photoconductivity of 1 (2) S/cm in the linear regime of bias for excitation at
780 (1560) nm. Photocurrent saturation in bias (pump fluence) occurred at
approximately 1 V (0.25 mJ/cm$^2$). Device performance was modeled numerically
by solving Maxwell's equations and the drift-diffusion equation to obtain the
photocurrent density in response to pulsed laser excitation, which was largely
in qualitative agreement with the experimental observations. THz output
computed from surface current density suggests that BP THz PCA performance is
at least comparable to more traditional devices based on low-temperature-grown
GaAs. These devices represent a step toward high-performance THz
photoconductive antennas using BP.",2007.12775v1
2020-07-25,Industrial manufacturing and characterization of multiscale CFRP laminates made from prepregs containing graphene-related materials,"The introduction of graphene-related materials (GRMs) in carbon
fibre-reinforced polymers (CFRP) has been proved to enhance their mechanical
and electrical properties. However, methodologies to produce the 3-phase
materials (multiscale composites) at an industrial scale and in an efficient
manner are still lacking. In this paper, multiscale CFRP composites containing
different GRMs have been manufactured following standard procedures currently
used in the aerospace industry with the aim to evaluate its potential
application. Graphite nanoplateletelets (GNPs), in situ exfoliated graphene
oxide (GO) and reduced graphene oxide (rGO) have been dispersed into an epoxy
resin to subsequently impregnate aeronautical grade carbon fibre tape. The
resulting prepregs have been used for manufacturing laminates by hand lay-up
and autoclave curing at 180 {\deg}C. Abroad characterization campaign has been
carried out to understand the behaviour of the different multiscale laminates
manufactured. The degree of cure, glass transition temperature and degradation
temperature have been evaluated by thermal evolution techniques. Similarly,
their mechanical properties (tensile, flexural, in-plane shear, interlaminar
shear and mode I interlaminar fracture toughness) have been analysed together
with their electrical conductivity. The manufacturing process resulted
appropriated for producing three-phase laminates and their quality was as good
as in conventional CFRPs. The addition ofGOand rGO resulted in an enhancement
of the in-plane shear properties and delamination resistance while the addition
ofGNPimproved the electrical conductivity.",2007.12902v1
2020-07-28,Aluminum oxide nucleation in the early stages of atomic layer deposition on epitaxial graphene,"In this work, the nucleation and growth mechanism of aluminum oxide (Al2O3)
in the early stages of the direct atomic layer deposition (ALD) on monolayer
epitaxial graphene (EG) on silicon carbide (4H-SiC) has been investigated by
atomic force microscopy (AFM) and Raman spectroscopy. Contrary to what is
typically observed for other types of graphene, a large and uniform density of
nucleation sites was observed in the case of EG and ascribed to the presence of
the buffer layer at EG/SiC interface. The deposition process was characterized
by Al2O3 island growth in the very early stages, followed by the formation of a
continuous Al2O3 film (2.4 nm thick) after only 40 ALD cycles due to the
islands coalescence, and subsequent layer-by-layer growth. Raman spectroscopy
analyses showed low impact of the ALD process on the defects density and doping
of EG. The EG strain was also almost unaffected by the deposition in the regime
of island growth and coalescence, whereas a significant increase was observed
after the formation of a compact Al2O3 film. The obtained results can have
important implications for device applications of epitaxial graphene requiring
the integration of ultra-thin high-k insulators.",2007.14427v1
2020-07-29,High temperature mechanical properties and microstructure of hard TaSiN coatings,"Room and high temperature mechanical properties of reactive magnetron
sputtered TaSiN coatings were measured using nanoindentation (between 25C and
500C). Fracture toughness was also evaluated at a similar temperature range
using the micropillar splitting method. The influence of the nitrogen
concentration on the evolving phases and microstructure of the TaSiN coatings,
before and after the high temperature testing, were examined by X-ray
diffraction (XRD) and transmission electron microscopy (TEM) analysis. XRD
spectra showed broad peaks with hexagonal $\gamma$-Ta2N as the main phase, with
the cubic $\delta$-TaN phase emerging for higher N contents. Phase composition
remained unchanged before and after the 500C tests. However, after the high
temperature tests, TEM analysis showed the presence of an oxide surface layer,
with a thickness that decreased (from 42 to 15 nm) with N content, due to
residual oxygen diffusion, which replaces nitrogen to form amorphous SiOx.
Beneath the oxide-rich surface layer, coatings exhibited a stable
nanocrystalline columnar microstructure. Hardness and fracture toughness
increased with N content, initially due to the formation of an amorphous Si-N
tissue at grain boundaries, and for even higher N contents, due to the
appearance of the hard cubic $\delta$-TaN phase. Hardness at 500C decreased
only by 15%, while fracture toughness followed the opposite trend, due to
increased plasticity with temperature. The optimum composition turned out to be
Ta55Si10N35, which retained a hardness of 30 GPa at 500C, being also the
toughest. These observations make this system very interesting for high
temperature applications.",2007.14693v1
2013-08-07,Intrinsic electron-glass effects in strongly-localized thallium-oxide films,"Transport measurements made on films of thallium-oxide (n-type semiconductor)
are presented and discussed. The focus in this work is on the
strongly-localized regime where charge transport is by variable-range-hopping.
It is demonstrated that, at liquid-helium temperatures, these films exhibit all
the characteristic features of intrinsic electron-glasses. These include a slow
(logarithmic in time) conductance-relaxation that may be induced by any of the
following protocols: Quench-cooling from high temperatures, sudden change of
gate-voltage, exposure to infrared radiation, and stressing the system with a
non-Ohmic field. The microstructure of the films are characterized by electron
microscopy and their carrier-concentration are measured by Hall effect.
Field-effect experiments reveal a memory-dip that has a width compatible with
the carrier-concentration of the system as compared with previously studied
electron-glasses. It is observed that the common ingredient in all the systems
that exhibit electron-glass effects is high carrier-concentration suggesting
that their localized sites may be multi-occupied even when deep into the
insulating regime. That lightly-doped semiconductors do not show intrinsic
electron-glass effects is consistent with this empirical observation. The
connection between the memory-dip and the Coulomb-gap is discussed in light of
these findings.",1308.1601v1
2013-08-15,How Channel Segregates Originates: The Flow of Accumulated Impurity Clusters in Solidifying Steels,"The phenomenon, channel segregates (CS) as a result of gravity-driven flow
due to density contrast occurred in the solid-liquid mushy zones1during
solidification, often causes the severe destruction of homogeneity and even
some fatal damages. Investigation on its mechanism sheds light on the
understanding and controlling of the formation of solidifying metals,earth's
core, igneous rock and sea ice. Until now, it still remains controversial what
composes the density contrasts and, to what extent, how it affects channel
segregates. Here, we show that in experimental 500kg and 100 ton commercial
cast steel ingots CS originates from oxide Al2O3/MnS impurity clusters (OICs)
initially nucleated from the oxide (Al2O3) particles, which induce an extra
flow due to sharp density contrast between clusters and melt. The results
uncover that, as OICs enrich and grow, their driven flow becomes stronger than
the traditionally recognized inter-dendritic thermo-solutal convection,
dominating the subsequent opening of the channels. This study extends the
classical macrosegregation theory, highlights a significant technological
breakthrough to control CS, and could quickly yield practical benefits to the
worldwide manufacture of over 50 million tons of ingots, super-thick slab and
heavy castings annually, as well as has general implications for the
elaboration of other related natural phenomena.",1308.3344v1
2013-08-16,"Towards time-dependent, non-equilibrium charge-transfer force fields: Contact electrification and history-dependent dissociation limits","Force fields uniquely assign interatomic forces for a given set of atomic
coordinates. The underlying assumption is that electrons are in their
quantum-mechanical ground state or in thermal equilibrium. However, there is an
abundance of cases where this is unjustified because the system is only locally
in equilibrium. In particular, the fractional charges of atoms, clusters, or
solids tend to not only depend on atomic positions but also on how the system
reached its state. For example, the charge of an isolated solid -- and thus the
forces between atoms in that solid -- usually depends on the counterbody with
which it has last formed contact. Similarly, the charge of an atom, resulting
from the dissociation of a molecule, can differ for different solvents in which
the dissociation took place. In this paper we demonstrate that such
charge-transfer history effects can be accounted for by assigning discrete
oxidation states to atoms. With our method, an atom can donate an integer
charge to another, nearby atom to change its oxidation state as in a redox
reaction. In addition to integer charges, atoms can exchange ""partial charges""
which are determined with the split charge equilibration method.",1308.3573v1
2014-03-03,Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas,"Two-dimensional electron gases (2DEGs) in SrTiO$_3$ have become model systems
for engineering emergent behaviour in complex transition metal oxides.
Understanding the collective interactions that enable this, however, has thus
far proved elusive. Here we demonstrate that angle-resolved photoemission can
directly image the quasiparticle dynamics of the $d$-electron subband ladder of
this complex-oxide 2DEG. Combined with realistic tight-binding supercell
calculations, we uncover how quantum confinement and inversion symmetry
breaking collectively tune the delicate interplay of charge, spin, orbital, and
lattice degrees of freedom in this system. We reveal how they lead to
pronounced orbital ordering, mediate an orbitally-enhanced Rashba splitting
with complex subband-dependent spin-orbital textures and markedly change the
character of electron-phonon coupling, co-operatively shaping the low-energy
electronic structure of the 2DEG. Our results allow for a unified understanding
of spectroscopic and transport measurements across different classes of
SrTiO$_3$-based 2DEGs, and yield new microscopic insights on their functional
properties.",1403.0520v2
2016-11-17,Hydrogen plasma exposure of In/ITO bilayers as an effective way for dispersing In nanoparticles,"We address the production of indium nanoparticles (In NPs) from In thin films
thermally evaporated on both c-Si substrates and sputtered indium tin oxide
(ITO) as well as from sputtered ITO thin films, exposed to a hydrogen (H2)
plasma. On the one hand, we show that evaporated In thin films grow in
Volmer-Weber (VW) mode; H2 plasma reduces their surface oxide and substrate
annealing reshapes them from flat islands into spheres, without any remarkable
surface migration or coalescence. On the other hand, we studied the In NPs
formation on the ITO thin films and on In/ITO bilayer structures, by varying
the H2 plasma exposure time and the substrate temperature. This led us to
postulate that the main role of H2 plasma is to release In atoms from ITO
surface. At low substrate temperature (100{\deg}C), In NPs grow on ITO surface
via a solid phase VW mode, similar to evaporated In thin films, while at
300{\deg}C, small In droplets preferentially nucleate along the ITO grain
boundaries where ITO reduction rate and atomic diffusion coefficient are higher
compared with the ITO grain surface. As the droplets grow larger and connect
with each other, larger ones (1-2 um microns) are suddenly formed based on a
liquid phase growth-connection-coalescence process. This phenomenon is even
stronger in the case of In/ITO bilayer where the large In drops resulting from
the evaporated In connect with the smaller NPs resulting from ITO reduction and
rapidly merge into very large NPs (15 um)",1611.05606v2
2017-01-15,Programmable Molecular Composites of Tandem Proteins with Graphene-Oxide for Efficient Bimoprh Actuators,"The rapid expansion in the spectrum of two-dimensional (2D) materials has
driven the efforts of research on the fabrication of 2D composites and
heterostructures. Highly ordered structure of 2D materials provides an
excellent platform for controlling the ultimate structure and properties of the
composite material with precision. However, limited control over the structure
of the adherent material and its interactions with highly ordered 2D materials
results in defective composites with inferior performance. Here, we demonstrate
the successful synthesis, integration, and characterization of hybrid 2D
material systems consisting of tandem repeat (TR) proteins inspired by squid
ring teeth and graphene oxide (GO). The TR protein layer acts as a unique
programmable molecular spacer between GO layers. As an application, we further
demonstrate thermal actuation using bimorph molecular composite films. Bimorph
actuators made of molecular composite films (GO/TR) can lead to energy
efficiencies 18 times higher than regular bimorph actuators consisting of a GO
layer and a TR protein layer (i.e., conventional bulk composite of GO and TR).
Additionally, molecular composite bimorph actuators can reach curvature values
as high as 1.2 cm-1 by using TR proteins with higher molecular weight, which is
3 times higher than conventional GO and TR composites.",1701.04019v1
2017-01-19,Ultrafast Electron-Lattice Coupling Dynamics in VO2 and V2O3 Thin Films,"Ultrafast optical pump - optical probe and optical pump - terahertz probe
spectroscopy were performed on vanadium dioxide (VO2) and vanadium sesquioxide
(V2O3) thin films over a wide temperature range. A comparison of the
experimental data from these two different techniques and two different
vanadium oxides, in particular a comparison of the electronic oscillations
generated by the photoinduced longitudinal acoustic modulation, reveals the
strong electron-phonon coupling that exists in the metallic state of both
materials. The low energy Drude response of V2O3 appears more susceptible than
VO2 to ultrafast strain control. Additionally, our results provide a
measurement of the temperature dependence of the sound velocity in both
systems, revealing a four- to fivefold increase in VO2 and a three- to fivefold
increase in V2O3 across the phase transition. Our data also confirm
observations of strong damping and phonon anharmonicity in the metallic phase
of VO2, and suggest that a similar phenomenon might be at play in the metallic
phase of V2O3. More generally, our simple table-top approach provides relevant
and detailed information about dynamical lattice properties of vanadium oxides,
opening the way to similar studies in other complex materials.",1701.05531v1
2017-04-23,Steep-slope Hysteresis-free Negative Capacitance MoS2 Transistors,"The so-called Boltzmann Tyranny defines the fundamental thermionic limit of
the subthreshold slope (SS) of a metal-oxide-semiconductor field-effect
transistor (MOSFET) at 60 mV/dec at room temperature and, therefore, precludes
the lowering of the supply voltage and the overall power consumption. Adding a
ferroelectric negative capacitor to the gate stack of a MOSFET may offer a
promising solution to bypassing this fundamental barrier. Meanwhile,
two-dimensional (2D) semiconductors, such as atomically thin transition metal
dichalcogenides (TMDs) due to their low dielectric constant, and ease of
integration in a junctionless transistor topology, offer enhanced electrostatic
control of the channel. Here, we combine these two advantages and demonstrate
for the first time a molybdenum disulfide (MoS2) 2D steep slope transistor with
a ferroelectric hafnium zirconium oxide layer (HZO) in the gate dielectric
stack. This device exhibits excellent performance in both on- and off-states,
with maximum drain current of 510 {\mu}A/{\mu}m, sub-thermionic subthreshold
slope and is essentially hysteresis-free. Negative differential resistance
(NDR) was observed at room temperature in the MoS2 negative capacitance
field-effect-transistors (NC-FETs) as the result of negative capacitance due to
the negative drain-induced-barrier-lowering (DIBL). High on-current induced
self-heating effect was also observed and studied.",1704.06865v2
2018-05-14,Structural Dependence of Chemical Durability in Modified Aluminoborate Glasses,"Alkali and alkaline earth aluminoborate glasses feature high resistance to
cracking under sharp contact loading compared to other oxide glasses. However,
due to the high content of hygroscopic B2O3, it is expected that applications
of these glasses could be hindered by poor chemical durability in aqueous
solutions. Indeed, the compositional and structural dependence of their
dissolution kinetics remains unexplored. In this work, we correlate the
dissolution rates of aluminoborate glasses in acidic, neutral, and basic
solutions with the structural changes induced by varying the aluminum-to-boron
ratio. In detail, we investigate a total of seventeen magnesium, lithium, and
sodium aluminoborate glasses with fixed modifier content of 25 mol%. We show
that the structural changes induced by alumina depend on the network modifier.
We also demonstrate a correlation between the chemical durability at various pH
values and the structural changes in Mg-, Li- and Na- aluminoborate glasses.
The substitution of alumina by boron oxide leads to a general decrease of
chemical corrosion in neutral and acidic solutions. The lowest dissolution rate
value is observed in Mg-aluminoborate glasses, as a consequence of the
intermediate character of magnesium which can increase the network
cross-linking. For basic solutions, the chemical durability is almost constant
for the different amount of alumina in the three series, likely because B2O3 is
susceptible to nucleophilic attack, which is favored in high-OH- solutions.",1805.05191v1
2018-05-10,Reduced-Graphene-Oxide with Dispersed Au-Ir Nanoparticles as Active Support for Pt at low Loadding for Electrocatalytic Oxygen Electroreduction,"We report here on a novel and facile techniques for the synthesis
nanocomposite based on stable bimetallic catalyst containing iridium and gold
nanoparticles electrodeposited on chemically reduced graphene oxide (rGO) sheet
admixed with platinum nanoparticles as an efficient electrocatalyst to
facilitate the oxygen reduction reaction (ORR) in acidic medium. Raman
spectroscopy, infrared spectroscopy (IR), scanning electron microscope (SEM),
transmission electron microscope (TEM) methods were employed to characterize
the rGO, Au-NPS-rGO, Ir-NPS-rGO, Au-Ir-rGO nanocomposites formed on the
electrode surface. Here we present a comparative study into the relative
effects of each hybrid nanocomposites: Au-NPS-rGO, Ir-NPS-rGO, Au-Ir-rGO
nanocomposites on the performance of platinum nanoparticles towards the oxygen
reduction reaction (ORR) in acidic media. For the purposes of comparing the
supports, a simple platinum black catalyst is used and the performance
isevaluated via direct measurement of peroxide by rotating ring-disk electrode
(RRDE) to determine the number of electrons (n) transferred in the ORR. It was
found that platinum nanoparticles dispersed within Au-Ir-rGO support follows a
quasi 4-electron mechanism (3.99-4 electrons involved) due to that the ORR
takes place mainly on the active Pt particles, and produced hydrogen peroxide
is reduced at Au-Ir-rGO support.",1805.05458v1
2018-05-10,Prussian Blue Modified Reduced Graphene Oxide as Support for Pt Nanoparticles: Development of Efficient Catalysts for Oxygen Electroreduction in Acid Medium,"Pt electrocatalytic nanoparticles were deposited onto hybrid carriers
composed of reduced graphene oxide (rGO)-transition metal hexacyanoferrate
(Prussian Blue-PB) and the resulting system's electrochemical activity was
investigated during oxygen reduction reaction in acidic solution. The Prussian
Blue -utilizing and Pt nanoparticle-containing materials were characterized
using transmission electron microscopy, X-ray diffraction and electrochemical
diagnostic techniques such as cyclic voltammetry and rotating ring-disk
voltammetry. Application of rGO carriers modified with Prussian Blue as
matrices (supports) for Pt catalytic centers does not change practically the
potential of electroreduction of oxygen in 0.5 mol dm-3 H2SO4 (under rotating
disk voltammetric conditions) relative to the behavior of the analogous PB-free
system. What is even more important that, due to the presence of the
polynuclear cyanoferrate modifier, the amounts of the undesirable hydrogen
peroxide intermediate are significantly decreased (at ring in the rotating
ring-disk voltammetry). The results are consistent with the bifunctional
mechanism in which oxygen reduction is initiated at Pt centers and the hydrogen
peroxide intermediate is reductively decomposed at reactive PB-modified rGO
supports.",1805.05459v1
2018-05-16,Electrically controlled water permeation through graphene oxide membranes,"Developing 'smart' membranes that allow precise and reversible control of
molecular permeation using external stimuli would be of intense interest for
many areas of science: from physics and chemistry to life-sciences. In
particular, electrical control of water permeation through membranes is a
long-sought objective and is of crucial importance for healthcare and related
areas. Currently, such adjustable membranes are limited to the modulation of
wetting of the membranes and controlled ion transport, but not the controlled
mass flow of water. Despite intensive theoretical work yielding conflicting
results, the experimental realisation of electrically controlled water
permeation has not yet been achieved. Here we report electrically controlled
water permeation through micrometre-thick graphene oxide (GO) membranes. By
controllable electric breakdown, conductive filaments are created in the GO
membrane. The electric field concentrated around such current carrying
filaments leads to controllable ionisation of water molecules in graphene
capillaries, allowing precise control of water permeation: from ultrafast
permeation to complete blocking. Our work opens up an avenue for developing
smart membrane technologies and can revolutionize the field of artificial
biological systems, tissue engineering and filtration.",1805.06390v1
2008-07-16,Emergence of Particle-Hole Symmetry near Optimal Doping in High-Temperature Copper Oxide Superconductors,"High-temperature copper oxide superconductors (cuprates) display
unconventional physics when they are lightly doped whereas the standard theory
of metals prevails in the opposite regime. For example, the thermoelectric
power, that is the voltage that develops across a sample in response to a
temperature gradient, changes sign abruptly near optimal doping in a wide class
of cuprates, a stark departure from the standard theory of metals in which the
thermopower vanishes only when one electron exists per site. We show that this
effect arises from proximity to a state in which particle-hole symmetry is
dynamically generated. The operative mechanism is dynamical spectral weight
transfer from states that lie at least 2eV away from the chemical potential. We
show that the sign change is reproduced quantitatively within the Hubbard model
for moderate values of the on-site repulsion, $U$. For sufficiently large
values of on-site repulsion, for example, $U=20t$, ($t$ the hopping matrix
element), dynamical spectral weight transfer attenuates and our calculated
results for the thermopower are in prefect agreement with exact atomic limit.
The emergent particle-hole symmetry close to optimal doping points to pairing
in the cuprates being driven by high-energy electronic states.",0807.2854v3
2009-12-08,Effect of the nature of alkali and alkaline-earth oxides on the structure and crystallization of an aluminoborosilicate glass developed to immobilize highly concentrated nuclear waste solutions,"A complex rare-earth rich aluminoborosilicate glass has been proved to be a
good candidate for the immobilization of new high level radioactive wastes. A
simplified seven-oxides composition of this glass was selected for this study.
In this system, sodium and calcium cations were supposed in other works to
simulate respectively all the other alkali (R+=Li+, Rb+, Cs+) and
alkaline-earth (R'2+=Sr2+, Ba2+) cations present in the complex glass
composition. Moreover, neodymium or lanthanum are used here to simulate all the
rare-earths and actinides occurring in waste solutions. In order to study the
impact of the nature of R+ and R'2+ cations on both glass structure and melt
crystallization tendency during cooling, two glass series were prepared by
replacing either Na+ or Ca2+ cations in the simplified glass by respectively
(Li+, K+, Rb+, Cs+) or (Mg2+, Sr2+, Ba2+) cations. From these substitutions, it
was established that alkali ions are preferentially involved in the charge
compensation of (AlO4)- entities in the glass network comparatively to
alkaline-earth ions. The glass compositions containing calcium give way to the
crystallization of an apatite silicate phase bearing calcium and rare-earth
ions. The melt crystallization tendency during cooling strongly varies with the
nature of the alkaline-earth.",0912.1576v1
2011-11-04,Study of X-ray Radiation Damage in Silicon Sensors,"The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single complex
molecules and the study of ultra-fast processes. Silicon pixel sensors will be
used to record the diffraction images. In 3 years of operation the sensors will
be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no
bulk damage in silicon is expected. However fixed oxide charges in the
insulating layer covering the silicon and interface traps at the Si-SiO2
interface will be introduced by the irradiation and build up over time.
  We have investigated the microscopic defects in test structures and the
macroscopic electrical properties of segmented detectors as a function of the
X-ray dose. From the test structures we determine the oxide charge density and
the densities of interface traps as a function of dose. We find that both
saturate (and even decrease) for doses between 10 and 100 MGy. For segmented
sensors the defects introduced by the X-rays increase the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. We
observe that an electron accumulation layer forms at the Si-SiO2 interface. Its
width increases with dose and decreases with applied bias voltage. Using TCAD
simulations with the dose dependent parameters obtained from the test
structures, we are able to reproduce the observed results. This allows us to
optimize the sensor design for the XFEL requirements.",1111.1180v1
2012-01-07,Ni coarsening in the three-phase solid oxide fuel cell anode - a phase-field simulation study,"Ni coarsening in Ni-yttria stabilized zirconia (YSZ) solid oxide fuel cell
anodes is considered a major reason for anode degradation. We present a
predictive, quantative modeling framework based on the phase-field approach to
systematically examine coarsening kinetics in such anodes. The initial
structures for simulations are experimentally acquired functional layers of
anodes. Sample size effects and error analysis of contact angles are examined.
Three phase boundary (TPB) lengths and Ni surface areas are quantatively
identified on the basis of the active, dead-end, and isolated phase clusters
throughout coarsening. Tortuosity evolution of the pores is also investigated.
We find that phase clusters with larger characteristic length evolve slower
than those with smaller length scales. As a result, coarsening has small
positive effects on transport, and impacts less on the active Ni surface area
than the total counter part. TPBs, however, are found to be sensitive to local
morphological features and are only indirectly correlated to the evolution
kinetics of the Ni phase.",1201.1567v1
2013-08-31,An electrical conductivity relaxation study of oxygen transport in samarium doped ceria,"The efficacy of the electrical conductivity relaxation (ECR) technique for
investigating the oxygen transport properties of mixed conducting oxides has
been evaluated. Fifteen mol% samarium doped ceria (SDC15), for which
approximate values of the two principal transport properties, bulk oxygen
diffusivity, $D_{Chem}$, and surface reaction rate constant, $k_S$, can be
found in the literature, was chosen as the benchmark material against which to
validate the methodology. Measurements were carried out at temperatures between
750 $^\circ$C and 850 $^\circ$C and over a wide range of oxygen partial
pressures. An unexpectedly high p-type electronic transference number enabled
ECR measurements under oxidizing conditions. A systematic data analysis
procedure was developed to permit reliable extraction of the kinetic parameters
even in the general case of simultaneous bulk and surface limitation. The
$D_{Chem}$ from this study showed excellent qualitative and quantitative
agreement with expected values, falling in the range from $\sim 2\times10^{-5}$
to $2\times10^{-4}$ cm$^2$/s. The surface reaction constant under H$_2$/H$_2$O
mixtures also showed good agreement with literature results. Remarkably, this
value increased by a factor of 40 under mixtures of CO/CO$_2$ or O$_2$/Ar. This
observation suggests kinetic advantages for production of CO rather than H$_2$
in a two-step solar-driven thermochemical process based on samarium doped
ceria.",1309.0064v2
2013-09-01,Xe anions in stable Mg-Xe compounds: the mechanism of missing Xe in earth atmosphere,"The reactivity of noble gas elements is important for both fundamental
chemistry and geological science. The discovery of the oxidation of Xe extended
the doctrinal boundary of chemistry that a complete shell is inert to reaction.
The oxidations of Xe by various geological substances have been researched in
order to explain the missing Xe in earth atmosphere. Among many proposals, the
chemistry mechanisms are straightforward as they identify chemical processes
that can capture Xe in earth interior. However, all the mechanisms based on
current noble gas chemistry face the same difficulty: the earth lower mantle
and core are rich in metals and therefore their chemical environment is
reductive. On the other hand, up till now, the opposite chemical inclination,
the reductive propensity, i.e. gaining electrons and forming anions, has not
been proposed and examined for noble gas elements. In this work, we
demonstrate, using first principles calculations and an efficient structure
prediction method, that Xe and Kr can form stable MgXe and MgKr compounds under
high pressure. These compounds are intermetallic and Xe or Kr is negatively
charged. We also find that elevated temperature has large effect in stabilizing
MgXe and MgKr compounds. Our results show that the earth has the capability of
capturing Xe but not Kr, which is consistent to the depletion of Xe in earth
atmosphere. The stability of these compounds suggests that chemical species
with completely filled shell may still gain more electrons filling their outer
shell in chemical reactions.",1309.0696v2
2013-09-04,Splashing phenomena of room temperature liquid metal droplet striking on the pool of the same liquid under ambient air environment,"In this article, the fluid dynamics of room temperature liquid metal (RTLM)
droplet impacting onto a pool of the same liquid in ambient air was
investigated. A series of experiments were conducted in order to disclose the
influence of the oxidation effect on the impact dynamics. The droplet shape and
impact phenomenology were recorded with the aid of a high-speed digital camera.
The impact energy stored in the splash structures was estimated via a
theoretical model and several morphological parameters obtained from
instantaneous images of the splash. It was observed that the droplet shape and
the splashing morphology of RTLM were drastically different from those of
water, so was the impact dynamics between room temperature LM pool and high
temperature LM pool. The energy analysis disclosed that the height of the jet
is highly sensitive to the viscosity of the fluid, which is subjected to the
oxidation effect and temperature effect simultaneously, and thus perfectly
explained the phenomena. These basic findings are important for the application
of RTLM in a series of newly emerging technologies such as liquid metal based
spray cooling, ink-jet printed electronics, interface material painting and
coating, metallurgy, and 3D packages, etc.",1309.1075v1
2013-09-23,Polaron dynamics and decoherence in an interacting two-spin system coupled to optical phonon environment,"We study two anisotropically interacting spins coupled to optical phonons; we
restrict our analysis to the regime of strong coupling to the environment, to
the antiadiabatic region, and to the subspace with zero value for $S^z_T$ (the
z-component of the total spin). In the case where each spin is coupled to a
different phonon bath, we assume that the system and the environment are
initially uncorrelated (and form a simply separable state) in the polaronic
frame of reference. By analyzing the {polaron} dynamics through non-Markovian
quantum master equation, we find that the system manifests a small amount of
decoherence that decreases both with increasing non-adiabaticity and with
enhancing strength of coupling; whereas, under the Markovian approximation, the
polaronic system exhibits a decoherence free behavior. For the situation where
both spins are coupled to the same phonon bath, we also show that the system is
decoherence free in the subspace where $S^z_T$ is fixed. To suppress
decoherence through quantum control, we employ a train of pi pulses and
demonstrate that unitary evolution of the system can be retained. We propose
realization of a weakly decohering charge qubit from an electron in an
oxide-based (tunnel-coupled) double quantum dot system.",1309.5824v3
2014-05-13,"Energetics, structure, and composition of nanoclusters in Oxide Dispersion Strengthened Fe-Cr alloys","Extensive first-principle calculations on embedded clusters containing few O,
Y, Ti, and Cr atoms as well as vacancies are performed to obtain interaction
parameters to be applied in Metropolis Monte Carlo simulations, within the
framework of a rigid lattice model. A novel description using both pair and
triple parameters is shown to be more precise than the commonly used pair
parameterization. Simulated annealing provides comprehensive data on the
energetics, structure and stoichiometry of nm-size clusters at T=0. The results
are fully consistent with the experimental finding of negligible coarsening and
a high dispersion of the clusters, with the observation that the presence of Ti
reduces the cluster size, and with the reported radiation tolerance of the
clusters. In alloys without vacancies clusters show a planar structure, whereas
the presence of vacancies leads to three-dimensional configurations.
Additionally, Metropolis Monte Carlo simulations are carried out at high
temperature in order to investigate the dependence of nanocluster composition
on temperature. A good agreement between the existing experimental data on the
ratios (Y+Ti):O, Y:Ti, (Y+Cr):O, and Y:Cr, and the simulation results is found.
In some cases it is even possible to draw the conclusion that the respective
alloys contained a certain amount of vacancies, and that the clusters analyzed
were frozen-in high-temperature configurations. The comparison of experimental
data with those obtained by simulations demonstrates that the assumption of
nanoclusters consisting of nonstoichiometric oxides which are essentially
coherent with the bcc lattice of the Fe-Cr matrix leads to reasonable results.",1405.3041v1
2014-05-19,On the roles of graphene oxide doping for enhanced supercurrent in MgB2 based superconductors,"Due to their graphene-like properties after oxygen reduction, incorporation
of graphene oxide (GO) sheets into correlated-electron materials offers a new
pathway for tailoring their properties. Fabricating GO nanocomposites with
polycrystalline MgB2 superconductors leads to an order of magnitude enhancement
of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel
experimental approach to overcome the formidable challenge of performing
quantitative microscopy and microanalysis of such composites, so as to unveil
how GO doping influences the structure and hence the material properties. Atom
probe microscopy and electron microscopy were used to directly image the GO
within the MgB2, and we combined these data with computational simulations to
derive the property-enhancing mechanisms. Our results reveal synergetic effects
of GO, namely, via localized atomic (carbon and oxygen) doping as well as
texturing of the crystals, which provide both inter and intra granular flux
pinning. This study opens up new insights into how low-dimensional
nanostructures can be integrated into composites to modify the overall
properties, using a methodology amenable to a wide range of applications.",1405.4619v1
2016-05-03,Valence band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics,"We report valence band electronic structure evolution of graphene oxide (GO)
upon its thermal reduction. Degree of oxygen functionalization was controlled
by annealing temperatures, and an electronic structure evolution was monitored
using real-time ultraviolet photoelectron spectroscopy. We observed a drastic
increase in density of states around the Fermi level upon thermal annealing at
~600 oC. The result indicates that while there is an apparent band gap for GO
prior to a thermal reduction, the gap closes after an annealing around that
temperature. This trend of band gap closure was correlated with electrical,
chemical, and structural properties to determine a set of GO material
properties that is optimal for optoelectronics. The results revealed that
annealing at a temperature of ~500 oC leads to the desired properties,
demonstrated by a uniform and an order of magnitude enhanced photocurrent map
of an individual GO sheet compared to as-synthesized counterpart.",1605.01048v1
2016-08-02,Correlation of Fe-based Superconductivity and Electron-Phonon Coupling in an FeAs/Oxide Heterostructure,"Interfacial phonons between iron-based superconductors (FeSCs) and perovskite
substrates have received considerable attention due to the possibility of
enhancing preexisting superconductivity. Using scanning tunneling spectroscopy,
we studied the correlation between superconductivity and e-ph interaction with
interfacial-phonons in an iron-based superconductor Sr$_2$VO$_3$FeAs ($T_c
\approx$ 33 K) made of alternating FeSC and oxide layers. The quasiparticle
interference measurement over regions with systematically different average
superconducting gaps due to the e-ph coupling locally modulated by O vacancies
in VO$_2$ layer, and supporting self-consistent momentum-dependent Eliashberg
calculations provide a unique real-space evidence of the forward-scattering
interfacial phonon contribution to the total superconducting pairing.",1608.00886v4
2016-08-08,"On the Multi-Reference Nature of Plutonium Oxides: PuO$_2^{2+}$, PuO$_2$, PuO$_3$ and PuO$_2$(OH)$_2$","Actinide-containing complexes present formidable challenges for electronic
structure methods due to the large number of degenerate or quasi-degenerate
electronic states arising from partially occupied 5f and 6d shells.
Conventional multi-reference methods can treat active spaces that are often at
the upper limit of what is required for a proper treatment of species with
complex electronic structures, leaving no room for verifying their suitability.
In this work we address the issue of properly defining the active spaces in
such calculations, and introduce a protocol to determine optimal active spaces
based on the use of the Density Matrix Renormalization Group algorithm and
concepts of quantum information theory. We apply the protocol to elucidate the
electronic structure and bonding mechanism of volatile plutonium oxides
(PuO$_3$ and PuO$_2$(OH)$_2$), species associated with nuclear safety issues
for which little is known about the electronic structure and energetics. We
show how, within a scalar relativistic framework, orbital-pair correlations can
be used to guide the definition of optimal active spaces which provide an
accurate description of static/non-dynamic electron correlation, as well as to
analyse the chemical bonding beyond a simple orbital model. From this bonding
analysis we are able to show that the addition of oxo- or hydroxo-groups to the
plutonium dioxide species considerably changes the pi-bonding mechanism with
respect to the bare triatomics, resulting in bent structures with considerable
multi-reference character.",1608.02353v1
2016-08-12,Enhanced charge ordering transition in doped CaFeO3 through steric templating,"We report density functional theory (DFT) investigation of $B$-site doped
CaFeO$_3$, a prototypical charge-ordered perovskite. At 290 K, CaFeO$_3$
undergoes a metal-insulator transition and a charge disproportionation reaction
2Fe$^{4+}$$\rightarrow$Fe$^{5+}$+Fe$^{3+}$. We observe that when Zr dopants
occupy a (001) layer, the band gap of the resulting solid solution increases to
0.93 eV due to a 2D Jahn-Teller type distortion, where FeO$_6$ cages on the
$xy$ plane elongate along $x$ and $y$ alternatively between neighboring Fe
sites. Furthermore, we show that the rock-salt ordering of the Fe$^{5+}$ and
Fe$^{3+}$ cations can be enhanced when the $B$-site dopants are arranged in a
(111) plane due to a collective steric effect that facilitates the size
discrepancy between the Fe$^{5+}$O$_6$ and Fe$^{3+}$O$_6$ octahedra and
therefore gives rise to a larger band gap. The enhanced charge
disproportionation in these solid solutions is verified by rigorously
calculating the oxidation states of the Fe cations with different octahedral
cage sizes. We therefore predict that the corresponding transition temperature
will increase due to the enhanced charge ordering and larger band gap. The
compositional, structural and electrical relationships exploited in this paper
can be extended to a variety of perovskites and non-perovskite oxides providing
guidance in structurally manipulating electrical properties of functional
materials.",1608.03761v1
2016-08-21,A study on the growth mechanism and the process parameters controlling aluminum oxide thin films deposition by pulsed pressure MOCVD,"Aluminum oxide thin films were deposited on silicon substrates under
different deposition conditions using pulse pressure metal organic chemical
vapour deposition (PP-MOCVD). The current study investigates into the growth
mechanism of the deposited film and the control of the film morphology by
varying the processing parameters of PP-MOCVD - choice of solvent,
concentration, and presence of a shield. Aluminum sec-butoxide (ASB) was used
as the aluminum source while hexane and toluene were used as the solvents. The
films were deposited at 475oC at different precursor concentrations. It was
observed that the choice of solvent has no effect on the surface morphology,
but it influenced the deposition rate. The improved deposition rate, relatively
close enthalpy of vaporisation ({\Delta}H) values and uniformity of the film,
irrespective of the growth conditions, showed that hexane was a better solvent
for ASB than toluene. A hybrid mode of vapour deposition and vapour
condensation model for thin film growth is proposed where five different
mechanisms lead to a solid film formation. These include vapour phase
deposition under low arrival rate, vapour phase deposition under high arrival
rate, Leidenfrost aerosol formation, heterogeneous particle formation and
liquid droplet impingement. The important parameter that needs to be controlled
is the precursor flux arrival rate which can be controlled by varying the
precursor concentration, use of a solvent with a low {\Delta}H and the presence
of a shield over the substrate, which influences the surface morphology and the
growth rate of the films.",1608.05892v1
2016-12-02,Reactors as a source of antineutrinos: the effect of fuel loading and burnup for mixed oxide fuels,"In a conventional light water reactor loaded with a range of uranium and
plutonium-based fuel mixtures, the variation in antineutrino production over
the cycle reflects both the initial core fissile inventory and its evolution.
Under the assumption of constant thermal power, we calculate the rate at which
antineutrinos are emitted from variously fueled cores, and the evolution of
that rate as measured by a representative ton-scale antineutrino detector. We
find that antineutrino flux decreases with burnup for Low Enriched Uranium
cores, increases for full mixed-oxide (MOX) cores, and does not appreciably
change for cores with a MOX fraction of approximately 75%. Accounting for
uncertainties in the fission yields, in the emitted antineutrino spectra, and
the detector response function, we show that the difference in core-wide MOX
fractions at least as small as 8% can be distinguished using a hypothesis test.
The test compares the evolution of the antineutrino rate relative to an initial
value over part or all of the cycle. The use of relative rates reduces the
sensitivity of the test to an independent thermal power measurement, making the
result more robust against possible countermeasures. This rate-only approach
also offers the potential advantage of reducing the cost and complexity of the
antineutrino detectors used to verify the diversion, compared to methods that
depend on the use of the antineutrino spectrum. A possible application is the
verification of the disposition of surplus plutonium in nuclear reactors.",1612.00540v2
2016-12-27,Annealing shallow Si/SiO$_2$ interface traps in electron-beam irradiated high-mobility metal-oxide-silicon transistors,"Electron-beam (e-beam) lithography is commonly used in fabricating
metal-oxide-silicon (MOS) quantum devices but creates defects at the Si/SiO$_2$
interface. Here we show that a forming gas anneal is effective at removing
shallow defects ($\leq$ 4 meV below the conduction band edge) created by an
e-beam exposure by measuring the density of shallow electron traps in two sets
of high-mobility MOS field-effect transistors (MOSFETs). One set was irradiated
with an electron-beam (10 keV, 40 $\mu$C/cm$^2$) and was subsequently annealed
in forming gas while the other set remained unexposed. Low temperature (335 mK)
transport measurements indicate that the forming gas anneal recovers the e-beam
exposed sample's peak mobility (14,000 cm$^2$/Vs) to within a factor of two of
the unexposed sample's mobility (23,000 cm$^2$/Vs). Using electron spin
resonance (ESR) to measure the density of shallow traps, we find that the two
sets of devices are nearly identical, indicating the forming gas anneal is
sufficient to anneal out shallow defects generated by the e-beam exposure.
Fitting the two sets of devices' transport data to a percolation transition
model, we extract a T=0 percolation threshold density in quantitative agreement
with our lowest temperature ESR-measured trap densities.",1612.08729v2
2017-06-13,Tribopolymer Formation Mechanism on the RuO$_2$(110) Surface,"Tribopolymer formed on the contacts of microelectromechanical and
nanoelectromechanical system (MEMS/NEMS) devices is a major concern hampering
their practical use in information technology. Conductive metal oxides, such as
RuO$_2$ and ReO$_3$, have been regarded as promising candidate materials for
MEMS/NEMS contacts due to their conductivity, hardness, and relatively
chemically inert surfaces. However, recent experimental works demonstrate that
trace amounts of polymer could still form on RuO$_2$ surfaces. In this study,
we demonstrate the mechanism of this class of unexpected tribopolymer formation
by conducting density functional theory based computational compression
experiments with benzene as the contamination gas. First, mechanical force
during compression changes the benzene molecules from slightly physisorbed to
strongly chemisorbed. Further compression causes deformation and chemical
linkage of the benzene molecules. Finally, the two contacts detach, with one
having a complex organic molecule attached and the other with a more reactive
surface. The complex organic molecule, which has an oxabicyclic segment, can be
viewed as the rudiment of tribopolymer, and the more reactive surface can
trigger the next adsorption--reaction--tribopolymer formation cycle. Based on
these results, we also predict tribopolymer formation rates by using
transition--state theory and the second--order rate law. This study deepens our
understanding of tribopolymer formation (especially on metal oxides) and
provides strategies for suppressing tribopolymerization.",1706.04096v1
2017-06-19,Insights on the mechanism of water-alcohol separation in multilayer graphene oxide membranes: entropic versus enthalpic factors,"Experimental evidences have shown that graphene oxide (GO) can be impermeable
to liquids, vapors and gases, while it allows a fast permeation of water
molecules. The understanding of filtration mechanisms came mostly from studies
dedicated to water desalination, while very few works have been dedicated to
distilling alcohols. In this work, we have investigated the molecular level
mechanism underlying the alcohol/water separation inside GO membranes. A series
of molecular dynamics and Grand-Canonical Monte Carlo simulations were carried
out to probe the ethanol/water and methanol/water separation through GO
membranes composed of multiple layered graphene-based sheets with different
interlayer distance values and number of oxygen-containing functional groups.
Our results show that the size exclusion and membrane affinities are not
sufficient to explain the selectivity. Besides that, the favorable water
molecular arrangement inside GO 2D-channels forming a robust H-bond network and
the fast water diffusion are crucial for an effective separation mechanism. In
other words, the separation phenomenon is not only governed by affinities with
the membrane (enthalpic mechanisms) but mainly by the geometry and size factors
(entropic mechanisms). We verified that the 2D geometry channel with optimal
interlayer distance are key factors for designing more efficient alcohol-water
separation membranes. Our findings are consistent with the available
experimental data and contribute to clarify important aspects of the separation
behavior of confined alcohol/water in GO membranes.",1706.06213v1
2017-06-26,Oxide-mediated self-limiting recovery of field effect mobility in plasma-treated MoS$_2$,"Precise tunability of electronic properties of 2D nanomaterials is a key goal
of current research in this field of materials science. Chemical modification
of layered transition metal dichalcogenides leads to the creation of
heterostructures of low-dimensional variants of these materials. In particular,
the effect of oxygen-containing plasma treatment on molybdenum disulfide
(MoS$_2$) has long been thought to be detrimental to the electrical performance
of the material. Here we show that the mobility and conductivity of MoS$_2$ can
be precisely controlled and improved by systematic exposure to oxygen:argon
plasma, and characterise the material utilising advanced spectroscopy and
microscopy. Through complementary theoretical modelling which confirms
conductivity enhancement, we uncover the role of a two-dimensional phase of
molybdenum trioxide (2D-MoO$_3$) in improving the electronic behaviour of the
material. Deduction of the beneficial role of MoO$_3$ will serve to open the
field to new approaches with regard to the tunability of 2D semiconductors by
their low-dimensional oxides in nano-modified heterostructures.",1706.08573v1
2017-06-27,Towards Substrate Engineering of Graphene-Silicon Schottky Diode Photodetectors,"Graphene-Silicon Schottky diode photodetectors possess beneficial properties
such as high responsivities and detectivities, broad spectral wavelength
operation and high operating speeds. Various routes and architectures have been
employed in the past to fabricate devices. Devices are commonly based on the
removal of the silicon-oxide layer on the surface of silicon by wet-etching
before deposition of graphene on top of silicon to form the graphene-silicon
Schottky junction. In this work, we systematically investigate the influence of
the interfacial oxide layer, the fabrication technique employed and the silicon
substrate on the light detection capabilities of graphene-silicon Schottky
diode photodetectors. The properties of devices are investigated over a broad
wavelength range from near-UV to short-/mid-infrared radiation, radiation
intensities covering over five orders of magnitude as well as the suitability
of devices for high speed operation. Results show that the interfacial layer,
depending on the required application, is in fact beneficial to enhance the
photodetection properties of such devices. Further, we demonstrate the
influence of the silicon substrate on the spectral response and operating
speed. Fabricated devices operate over a broad spectral wavelength range from
the near-UV to the short-/mid-infrared (thermal) wavelength regime, exhibit
high photovoltage responses approaching 10$^6$ V/W and short rise- and
fall-times of tens of nanoseconds.",1706.09042v1
2017-06-28,Suppressed carrier density for the patterned high mobility two-dimensional electron gas at gamma-Al2O3/SrTiO3 heterointerfaces,"The two-dimensional electron gas (2DEG) at the non-isostructural interface
between spinel gamma-Al2O3 and perovskite SrTiO3 is featured by a record
electron mobility among complex oxide interfaces in addition to a high carrier
density up to the order of 1E15 cm-2. Herein, we report on the patterning of
2DEG at the gamma-Al2O3/SrTiO3 interface grown at 650 {\deg}C by pulsed laser
deposition using a hard mask of LaMnO3. The patterned 2DEG exhibits a critical
thickness of 2 unit cells of gamma-Al2O3 for the occurrence of interface
conductivity, similar to the unpatterned sample. However, its maximum carrier
density is found to be approximately 3E13 cm-2, much lower than that of the
unpatterned sample (1E15 cm-2). Remarkably, a high electron mobility of
approximately 3,600 cm2V-1s-1 was obtained at low temperatures for the
patterned 2DEG at a carrier density of 7E12 cm-2, which exhibits clear
Shubnikov-de Hass quantum oscillations. The patterned high-mobility 2DEG at the
gamma-Al2O3/SrTiO3 interface paves the way for the design and application of
spinel/perovskite interfaces for high-mobility all-oxide electronic devices.",1706.09235v1
2017-06-29,"Electrical Properties and Subband Occupancy at the (La,Sr)(Al,Ta)O$_3$/SrTiO$_3$ Interface","The quasi two-dimensional electron gas (q-2DEG) at oxide interfaces provides
a platform for investigating quantum phenomena in strongly correlated
electronic systems. Here, we study the transport properties at the
high-mobility
(La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35}$)O$_{0.3}$/SrTiO$_{0.3}$
(LSAT/STO) interface. Before oxygen annealing, the as-grown interface exhibits
a high electron density and electron occupancy of two subbands: higher-mobility
electrons ($\mu_1\approx{10^4}$ cm$^2$V$^{-1}$s$^{-1}$ at 2 K) occupy the
lower-energy $3d_{xy}$ subband, while lower-mobility electrons
($\mu_1\approx{10^3}$ cm$^{2}$V$^{-1}$s$^{-1}$ at 2 K) propagate in the
higher-energy $3d_{xz/yz}$-dominated subband. After removing oxygen vacancies
by annealing in oxygen, only a single type of 3dxy electrons remain at the
annealed interface, showing tunable Shubnikov-de Haas (SdH) oscillations below
9 T at 2 K and an effective mass of $0.7m_e$. By contrast, no oscillation is
observed at the as-grown interface even when electron mobility is increased to
$50,000$ cm$^{2}$V$^{-1}$s$^{-1}$ by gating voltage. Our results reveal the
important roles of both carrier mobility and subband occupancy in tuning the
quantum transport at oxide interfaces.",1706.09592v1
2017-07-20,Superconductivity proximate to antiferromagnetism in a copper-oxide monolayer grown on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$,"A nodeless superconducting (SC) gap was reported in a recent scanning
tunneling spectroscopy experiment of a copper-oxide monolayer grown on the
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) substrate [Y. Zhong {\it et al.},
Sci. Bull. {\bf 61}, 1239 (2016)], which is in stark contrast to the nodal
d-wave pairing gap in the bulk cuprates. Motivated by this experiment, we first
show with first-principles calculations that the tetragonal CuO (T-CuO)
monolayer on the Bi2212 substrate is more stable than the commonly postulated
CuO$_{2}$ structure. The T-CuO monolayer is composed of two CuO$_2$ layers
sharing the same O atoms. The band structure is obtained by first-principles
calculations, and its strong electron correlation is treated with the
renormalized mean-field theory. We argue that one CuO$_2$ sublattice is hole
doped while the other sublattice remains half filled and may have
antiferromagnetic (AF) order. The doped Cu sublattice can show d-wave SC;
however, its proximity to the AF Cu sublattice induces a spin-dependent
hopping, which splits the Fermi surface and may lead to a full SC gap.
Therefore, the nodeless SC gap observed in the experiment could be accounted
for by the d-wave SC proximity to an AF order, thus it is extrinsic rather than
intrinsic to the CuO$_2$ layers.",1707.06346v2
2017-10-04,Effects of porosity in a model of corrosion and passive layer growth,"We introduce a stochastic lattice model to investigate the effects of pore
formation in a passive layer grown with products of metal corrosion. It
considers that an anionic species diffuses across that layer and reacts at the
corrosion front (metal-oxide interface), producing a random distribution of
compact regions and large pores, respectively represented by O (oxide) and P
(pore) sites. O sites are assumed to have very small pores, so that the
fraction $\Phi$ of P sites is an estimate of the porosity, and the ratio
between anion diffusion coefficients in those regions is $D_{\text r}<1$.
Simulation results without the large pores ($\Phi =0$) are similar to those of
a formerly studied model of corrosion and passivation and are explained by a
scaling approach. If $\Phi >0$ and $D_{\text r}\ll 1$, significant changes are
observed in passive layer growth and corrosion front roughness. For small
$\Phi$, a slowdown of the growth rate is observed, which is interpreted as a
consequence of the confinement of anions in isolated pores for long times.
However, the presence of large pores near the corrosion front increases the
frequency of reactions at those regions, which leads to an increase in the
roughness of that front. This model may be a first step to represent defects in
a passive layer which favor pitting corrosion.",1710.01548v1
2017-10-06,A new role for exhaled nitric oxide as a functional marker of peripheral airway caliber changes: a theoretical study,"Though considered as an inflammation marker, exhaled nitric oxide (FENO) was
shown to be sensitive to airway caliber changes to such an extent that it might
be considered as a marker of them. It is thus important to understand how these
changes and their localization mechanically affect the total NO flux
penetrating the airway lumen (JawNO), hence FENO, independently from any
inflammatory status change. A new model was used which simulates NO production,
consumption and diffusion inside the airway epithelium wall, then, NO excretion
through the epithelial wall into the airway lumen and, finally, its axial
transport by diffusion and convection in the airway lumen. This model may also
consider the presence of a mucus layer coating the epithelial wall. Simulations
were performed that showed the great sensitivity of JawNO to peripheral airways
caliber changes. Moreover, FENO showed distinct behaviors depending on the
location of the caliber change. Considering a bronchodilation, absence of FENO
change was associated with dilation of central airways, FENO increase with
dilation up to pre-acinar small airways, and FENO decrease with intra-acinar
dilation due to amplification of the back-diffusion flux. The presence of a
mucus layer was also shown to play a significant role in FENO changes.
Altogether, the present work provides theoretical evidences that specific FENO
changes in acute situations are linked to specifically located airway caliber
changes in the lung periphery. This opens the way for a new role for FENO as a
functional marker of peripheral airway caliber change.",1710.02362v1
2017-10-16,Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopy,"The spinel/perovskite heterointerface $\gamma$-Al$_2$O$_3$/SrTiO$_3$ hosts a
two-dimensional electron system (2DES) with electron mobilities exceeding those
in its all-perovskite counterpart LaAlO$_3$/SrTiO$_3$ by more than an order of
magnitude despite the abundance of oxygen vacancies which act as electron
donors as well as scattering sites. By means of resonant soft x-ray
photoemission spectroscopy and \textit{ab initio} calculations we reveal the
presence of a sharply localized type of oxygen vacancies at the very interface
due to the local breaking of the perovskite symmetry. We explain the
extraordinarily high mobilities by reduced scattering resulting from the
preferential formation of interfacial oxygen vacancies and spatial separation
of the resulting 2DES in deeper SrTiO$_3$ layers. Our findings comply with
transport studies and pave the way towards defect engineering at interfaces of
oxides with different crystal structures.",1710.05574v1
2017-10-23,Realization of a hole-doped Mott insulator on a triangular silicon lattice,"The physics of doped Mott insulators is at the heart of some of the most
exotic physical phenomena in materials research including insulator-metal
transitions, colossal magneto-resistance, and high-temperature
superconductivity in layered perovskite compounds. Advances in this field would
greatly benefit from the availability of new material systems with similar
richness of physical phenomena, but with fewer chemical and structural
complications in comparison to oxides. Using scanning tunneling microscopy and
spectroscopy, we show that such a system can be realized on a silicon platform.
Adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a
triangular surface lattice with half-filled dangling bond orbitals. Modulation
hole-doping of these dangling bonds unveils clear hallmarks of Mott physics,
such as spectral weight transfer and the formation of quasi-particle states at
the Fermi level, well-defined Fermi contour segments, and a sharp singularity
in the density of states. These observations are remarkably similar to those
made in complex oxide materials, including high-temperature superconductors,
but highly extraordinary within the realm of conventional sp-bonded
semiconductor materials. It suggests that exotic quantum matter phases can be
realized and engineered on silicon-based materials platforms.",1710.08065v1
2017-10-30,Evidence for thermal activation in the glassy dynamics of insulating granular aluminum conductance,"Insulating granular aluminum is one of the proto-typical disordered
insulators whose low temperature electrical conductance exhibits ubiquitous
non-equilibrium phenomena. These include slow responses to temperature or gate
voltage changes, characteristic field effect anomalies and ageing phenomena
typical of a glass. In this system the influence of temperature on the glassy
dynamics has remained elusive, leading to the belief that the slow relaxations
essentially proceed via elastic quantum tunneling. A similar situation was met
in insulating indium oxide and it was concluded that in high carrier density
Anderson insulators, electrons form a quantum glass phase. In this work we
experimentally demonstrate that thermal effects do play a role and that the
slow dynamics in granular aluminum is subject to thermal activation. We show
how its signatures can be revealed and activation energy distributions can be
extracted, providing a promising grasp on the nature of the microscopic
mechanism at work in glassy Anderson insulators. We explain why some of the
experimental protocols previously used in the literature fail to reveal thermal
activation in these systems. Our results and analyses call for a reassessment
of the emblematic case of indium oxide, and question the existence of a quantum
glass in any of the systems studied so far.",1710.10939v1
2017-10-30,Rayleigh-Brillouin light scattering spectroscopy of nitrous oxide (N$_2$O),"High signal-to-noise and high-resolution light scattering spectra are
measured for nitrous oxide (N$_2$O) gas at an incident wavelength of 403.00 nm,
at 90$^\circ$ scattering, at room temperature and at gas pressures in the range
$0.5-4$ bar. The resulting Rayleigh-Brillouin light scattering spectra are
compared to a number of models describing in an approximate manner the
collisional dynamics and energy transfer in this gaseous medium of this
polyatomic molecular species. The Tenti-S6 model, based on macroscopic gas
transport coefficients, reproduces the scattering profiles in the entire
pressure range at less than 2\% deviation at a similar level as does the
alternative kinetic Grad's 6-moment model, which is based on the internal
collisional relaxation as a decisive parameter. A hydrodynamic model fails to
reproduce experimental spectra for the low pressures of 0.5-1 bar, but yields
very good agreement ($< 1$\%) in the pressure range $2-4$ bar. While these
three models have a different physical basis the internal molecular relaxation
derived can for all three be described in terms of a bulk viscosity of $\eta_b
\sim (6 \pm 2) \times 10^{-5}$ Pa$\cdot$s. A 'rough-sphere' model, previously
shown to be effective to describe light scattering in SF$_6$ gas, is not found
to be suitable, likely in view of the non-sphericity and asymmetry of the N-N-O
structured linear polyatomic molecule.",1710.11193v1
2017-10-31,Switching between normal and anomalous Laser Induced Periodic Surface Structures,"We report on the studies of switching mechanism between normal and anomalous
laser induced periodic surface structures. We have shown that for high loss
metals the switching mechanism between normal and anomalous modes relays on an
interplay between two different feedbacks inherent into the structure formation
process: long range, low intensity dipole-like scattering of light along the
surface, which governs anomalous ripples parallel to the laser polarization,
and short range, high intensity plasmon-polariton wave, which is initiated by
near field dipole radiation and responsible for creation of ripples
perpendicular to the polarization, i. e. normal structure. By managing these
two feedbacks, we demonstrated creation of both normal and anomalous laser
induced periodic surface structures on the same surface. In contrast to the
previous studies, we have shown that the thermal oxidation mechanism can form
both normal and anomalous types of the structure, while the ablation mechanism
is involved only during the normal structure formation. Unlike the formation of
oxidation type anomalous structure, the formation of ablation type normal
structure does not have inherent negative feedback, which is self-regulating
nano-ripples formation. This feedback needs to be applied artificially, by
regulating scanning speed and pulse energy at a given repetition rate of the
laser. With implementation of nonlinear laser lithography technique for
ablation type of normal laser induced periodic surface structures we
demonstrated large area high regular nano-grating formation on different
surfaces with extremely high industrially acceptable speed.",1710.11405v1
2017-11-28,Electrooxidation of a cobalt based steel in LiOH: a non-noble metal based electro-catalyst suitable for durable water-splitting in an acidic milieu,"The use of proton exchange membrane (PEM) electrolyzers is the method of
choice for the conversion of solar energy when frequently occurring changes of
the current load are an issue. However, this technique requires electrolytes
with low pH. All oxygen evolving electrodes working durably and actively in
acids contain IrOx. Due to their scarcity and high acquisition costs, noble
elements like Pt, Ru and Ir need to be replaced by earth abundant elements. We
have evaluated a cobalt containing steel for use as an oxygen-forming electrode
in H2SO4. We found that the dissolving of ingredients out of the steel
electrode at oxidative potential in sulfuric acid, which is a well-known,
serious issue, can be substantially reduced when the steel is electro-oxidized
in LiOH prior to electrocatalysis. Under optimized synthesis conditions a
cobalt-containing tool steel was rendered into a durable oxygen evolution
reaction (OER) electrocatalyst (weight loss: 39 mug mm-2 after 50 000 s of
chronopotentiometry at pH 1) that exhibits overpotentials down to 574 mV at 10
mA cm-2 current density at pH 1. Focused ion beam SEM FIB-SEM) was successfully
used to create a structure-stability relationship.",1712.01100v1
2017-12-05,Micro solid oxide fuel cells: a new generation of micro-power sources for portable applications,"Portable electronic devices are already an indispensable part of our daily
life; and their increasing number and demand for higher performance is becoming
a challenge for the research community. In particular, a major concern is the
way to efficiently power these energy-demanding devices, assuring long grid
independency with high efficiency, sustainability and cheap production. In this
context, technologies beyond Li-ion are receiving increasing attention, among
which the development of micro solid oxide fuel cells ({\mu}SOFC) stands out.
In particular, {\mu}SOFC provides a high energy density, high efficiency and
opens the possibility to the use of different fuels, such as hydrocarbons. Yet,
its high operating temperature has typically hindered its application as
miniaturized portable device. Recent advances have however set a completely new
range of lower operating temperatures, i.e. 350-450C, as compared to the
typical >900C needed for classical bulk SOFC systems. In this work, a
comprehensive review of the status of the technology is presented. The main
achievements, as well as the most important challenges still pending are
discussed, regarding (i.) the cell design and microfabrication, and (ii.) the
integration of functional electrolyte and electrode materials. To conclude, the
different strategies foreseen for a wide deployment of the technology as new
portable power source are underlined.",1712.01589v1
2017-12-21,A Review and Outlook for the Removal of Radon-Generated Po-210 Surface Contamination,"The next generation low-background detectors operating deep underground aim
for unprecedented low levels of radioactive backgrounds. The deposition and
presence of radon progeny on detector surfaces is an added source of energetic
background events. In addition to limiting the detector material's radon
exposure in order to reduce potential surface backgrounds, it is just as
important to clean surfaces to remove inevitable contamination. Such studies of
radon progeny removal have generally found that a form of etching is effective
at removing some of the progeny (Bi and Pb), however more aggressive
techniques, including electropolishing, have been shown to effectively remove
the Po atoms. In the absence of an aggressive etch, a significant fraction of
the Po atoms are believed to either remain behind within the surface or
redeposit from the etching solution back onto the surface. We explore the
chemical nature of the aqueous Po ions and the effect of the oxidation state of
Po to maximize the Po ions remaining in the etching solution of contaminated Cu
surfaces. We present a review of the previous studies of surface radon progeny
removal and our findings on the role of oxidizing agents and a cell potential
in the preparation of a clean etching technique.",1712.08167v1
2017-12-27,Stable Self-Assembled Atomic-Switch Networks for Neuromorphic Applications,"Nature inspired neuromorphic architectures are being explored as an
alternative to imminent limitations of conventional complementary metal-oxide
semiconductor (CMOS) architectures. Utilization of such architectures for
practical applications like advanced pattern recognition tasks will require
synaptic connections that are both reconfigurable and stable. Here, we report
realization of stable atomic-switch networks (ASN), with inherent complex
connectivity, self-assembled from percolating metal nanoparticles (NPs). The
device conductance reflects the configuration of synapses which can be
modulated via voltage stimulus. By controlling Relative Humidity (RH) and
oxygen partial-pressure during NP deposition we obtain stochastic conductance
switching that is stable over several months. Detailed characterization reveals
signatures of electric-field induced atomic-wire formation within the
tunnel-gaps of the oxidized percolating network. Finally we show that the
synaptic structure can be reconfigured by stimulating at different repetition
rates, which can be utilized as short-term to long-term memory conversion. This
demonstration of stable stochastic switching in ASNs provides a promising route
to hardware implementation of biological neuronal models and, as an example, we
highlight possible applications in Reservoir Computing (RC).",1712.09497v1
2018-01-02,Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity,"Electron conduction through bare metal oxide nanocrystal (NC) films is
hindered by surface depletion regions resulting from the presence of surface
states. We control the radial dopant distribution in tin-doped indium oxide
(ITO) NCs as a means to manipulate the NC depletion width. We find in films of
ITO NCs of equal overall dopant concentration that those with dopant-enriched
surfaces show decreased depletion width and increased conductivity. Variable
temperature conductivity data shows electron localization length increases and
associated depletion width decreases monotonically with increased density of
dopants near the NC surface. We calculate band profiles for NCs of differing
radial dopant distributions and, in agreement with variable temperature
conductivity fits, find NCs with dopant-enriched surfaces have narrower
depletion widths and longer localization lengths than those with
dopant-enriched cores. Following amelioration of NC surface depletion by atomic
layer deposition of alumina, all films of equal overall dopant concentration
have similar conductivity. Variable temperature conductivity measurements on
alumina-capped films indicate all films behave as granular metals. Herein, we
conclude that dopant-enriched surfaces decrease the near-surface depletion
region, which directly increases the electron localization length and
conductivity of NC films.",1801.00731v1
2018-01-15,Role of Water Molecule in Enhancing the Proton Conductivity on Graphene Oxide at Humidity Condition,"Recent experimental reports on in-plane proton conduction in reduced graphene
oxide (rGO) films open a new way for the design of proton exchange membrane
essential in fuel cells and chemical filters. At high humidity condition, water
molecules attached on the rGO sheet are expected to play a critical role, but
theoretical works for such phenomena have been scarcely found in the
literature. In this study, we investigate the proton migration on
water-adsorbed monolayer and bilayer rGO sheets using first-principles
calculations in order to reveal the mechanism. We devise a series of models for
the water-adsorbed rGO films as systematically varying the reduction degree and
water content, and optimize their atomic structures in reasonable agreement
with the experiment, using a density functional that accounts for van der Waals
correction. Upon suggesting two different transport mechanisms, epoxy-mediated
and water-mediated hoppings, we determine the kinetic activation barriers for
these in-plane proton transports on the rGO sheets. Our calculations indicate
that the water-mediated transport is more likely to occur due to its much lower
activation energy than the epoxy-mediated one and reveal new prospects for
developing efficient solid proton conductors.",1801.04648v2
2018-01-24,Ultrafast orbital manipulation and Mott physics in multi-band correlated materials,"Multiorbital correlated materials are often on the verge of multiple
electronic phases (metallic, insulating, super- conducting, charge and
orbitally ordered), which can be explored and controlled by small changes of
the external parameters. The use of ultrashort light pulses as a mean to
transiently modify the band population is leading to fundamentally new results.
In this paper we will review recent advances in the field and we will discuss
the pos- sibility of manipulating the orbital polarization in correlated
multi-band solid state systems. This technique can provide new understanding of
the ground state properties of many interesting classes of quantum materials
and offers a new tool to induce transient emergent properties with no
counterpart at equilibrium. We will address: the discovery of high-energy
Mottness in superconducting copper oxides and its impact on our understanding
of the cuprate phase diagram; the instability of the Mott insulating phase in
photoexcited vanadium oxides; the manipulation of orbital-selective
correlations in iron-based superconductors; the pumping of local electronic
excitons and the consequent transient effective quasiparticle cooling in
alkali-doped fullerides. Finally, we will discuss a novel route to manipulate
the orbital polarization in a a k-resolved fashion.",1801.07957v1
2018-09-05,Radial and vertical dust transport inhibit refractory carbon depletion in protoplanetary disks,"The Earth is strongly depleted in carbon compared to the dust in the ISM,
implying efficient removal of refractory carbon before parent body formation.
It has been argued that grains get rid of their carbon through oxidation and
photolysis in the exposed upper disk layers. We assess the efficacy of these
C-removal mechanisms accounting for the vertical and radial transport of
grains. We obtain the carbon and carbon free mass budget of solids by solving
two 1D advection-diffusion equations, accounting for the dust grain size
distribution and radial transport. The carbon removal acts on the fraction of
the grains that are in the exposed layer and requires efficient vertical
transport. In models without radial transport, oxidation and photolysis can
destroy most of the refractory carbon in terrestrial planet formation region.
But it only reaches the observed depletion levels for extreme parameter
combinations and requires that parent body formation was delayed by 1 Myr.
Adding radial transport of solids prevents the depletion entirely, leaving
refractory carbon equally distributed throughout the disk. It is unlikely that
the observed carbon depletion can ultimately be attributed to mechanisms
operating on small grains in the disk surface layers. Other mechanisms need to
be studied, for example flash heating events or FU Ori outbursts in order to
remove carbon quickly and deeply. However, a sustained drift barrier or
strongly reduced radial grain mobility are necessary to prevent replenishment
of carbon from the outer disk.",1809.01648v1
2018-09-06,Limits of surface analysis of thin film compounds using LEIS,"Low Energy Ion Scattering (LEIS) was employed to study the surface
composition of thin films of Ru on B, C and B4C films at different stages of
growth. Effects of surface segregation of C were observed. Previously unknown
matrix effects were observed in these samples, expressed in the decrease of
LEIS signals of Ru, B and C at low Ru concentrations. The effect disappears for
Ru-rich surfaces. Measurements with different He+ ion energies prove that the
characteristic velocities of the elements involved change with surface
composition. We suggest that these matrix effects appear due to the changes in
neutralization efficiency in quasiresonant neutralization from the valence band
(VB-qRN). This neutralization channel is present in elemental C and B due to a
wide valence band with energy states as low as -20 eV, which are in a
(quasi-)resonance with the He 1s level. This mechanism was earlier reported for
graphitic carbon. We suggest that it can be applied to a much wider range of
materials, leading to potential matrix effects in LEIS from a variety of
surfaces, containing B, C and potentially O and N atoms, e.g. borides,
carbides, oxides and nitrides, as well as alloys with B and C. This hypothesis
is supported by additional LEIS measurements on oxidized Ru which show matrix
effect in Ru-O LEIS signals as well. We argue that it is possible to avoid the
matrix effects from compounded surfaces within certain ranges of composition by
a proper choice of reference samples, while for other compositions knowledge of
characteristic velocities is required for reliable quantification.",1809.01918v1
2018-09-19,"Effects of the number of layers on the vibrational, electronic and optical properties of alpha lead oxide","We have investigated the effects of number of layers on the structural,
vibrational, electronic and optical properties of $\alpha$-PbO using first
principles calculations. Our theoretical calculations have shown that four
Raman active modes of $\alpha$-PbO tend to red-shift from bulk to monolayer due
to decreasing of force constants and increasing of bond lengths. It has been
shown that while bulk and multilayer $\alpha$-PbO have an indirect band gap,
monolayer form has a direct band gap value of 2.59 eV. Although lead atoms have
5d states, spin-orbit coupling does not significantly affect the band structure
of $\alpha$-PbO. The computed cleavage energy value (0.67 J/m$^2$) confirms
that monolayer PbO can be easily obtained from its bulk counterpart by
exfoliation methods. In addition to the band structure, we also calculated the
optical properties and absorbed photon flux $J_{abs}$ of $\alpha$-PbO
structures to investigate the possibility of solar absorption. Our calculations
reveal that while monolayer and bilayer PbO have relatively larger band gaps
and lower absorption coefficients, their $J_{abs}$ values are not ideal for
solar absorption devices. In contrast, the multilayer and bulk phases of the
$\alpha$-PbOs show good overlap with the solar spectrum and yield high
electrical current values. Our calculations have indicated that ultrathin films
of $\alpha$-PbO (such as 3nm thickness) could be excellent candidates for solar
cells. We believe that our work can be utilized to improve electronic and
optical devices based on lead oxide structures.",1809.07263v1
2018-09-27,Using ultra-thin parylene films as an organic gate insulator in nanowire field-effect transistors,"We report the development of nanowire field-effect transistors featuring an
ultra-thin parylene film as a polymer gate insulator. The room temperature,
gas-phase deposition of parylene is an attractive alternative to oxide
insulators prepared at high temperatures using atomic layer deposition. We
discuss our custom-built parylene deposition system, which is designed for
reliable and controlled deposition of <100 nm thick parylene films on III-V
nanowires standing vertically on a growth substrate or horizontally on a device
substrate. The former case gives conformally-coated nanowires, which we used to
produce functional $\Omega$-gate and gate-all-around structures. These give
sub-threshold swings as low as 140 mV/dec and on/off ratios exceeding $10^3$ at
room temperature. For the gate-all-around structure, we developed a novel
fabrication strategy that overcomes some of the limitations with previous
lateral wrap-gate nanowire transistors. Finally, we show that parylene can be
deposited over chemically-treated nanowire surfaces; a feature generally not
possible with oxides produced by atomic layer deposition due to the surface
`self-cleaning' effect. Our results highlight the potential for parylene as an
alternative ultra-thin insulator in nanoscale electronic devices more broadly,
with potential applications extending into nanobioelectronics due to parylene's
well-established biocompatible properties.",1809.10471v1
2018-10-02,Analysis of chemical pathways for n-dodecane/air turbulent premixed flames,"This paper analyzes turbulence-chemistry interactions for an n-dodecane-air
flame, focusing on the degree to which fuel oxidation pathways change in
turbulent flames relative to their corresponding laminar flames. This work is
based on a lean n-dodecane-air flame DNS database from Aspden et al. (Proc.
Combust. Institute, 36 (2017) 2005-2016). The relative roles of dominant
reactions that release heat and produce/consume radicals are examined at
various turbulence intensities and compared with stretched flame calculations
from counterflow flames and perfectly stirred reactors. These results show that
spatially integrated (i.e. integrated heat release or radical production rate
metrics averaged over the entire flame) chemical pathways are relatively
insensitive to turbulence intensity and mimic the behavior of stretched flames.
In other words, the contribution of a given reaction to heat release or radical
production, integrated over the entire flame, is nearly independent to
turbulence. Localized analysis conditioned on topological feature of the flame
and on temperature is also performed. The former analysis reveals that much
larger alteration of pathways occurs in the positively-curved regions of the
flame. The latter localized analysis shows that peak activity in the low
temperature (i.e. below 1200K) region shift towards higher temperatures with
increases in Karlovitz number. This result is particularly interesting given
that prior work with lighter fuels showed the opposite behavior suggesting a
disparate response of the reactions involved in the fuel oxidation process to
increased turbulence.",1810.01450v1
2018-10-08,Metasurface reconfiguration through lithium ion intercalation in a transition metal oxide,"In the latest years the optical engineer's toolbox has welcomed a new
concept, the metasurface. In a metasurface, properly tailored material
inclusions are able to reshape the electromagnetic field of an incident beam.
Change of amplitude, phase and polarization can be addressed within a thickness
of only a fraction of a wavelength. By means of this concept, a radical gain in
compactness of optical components is foreseen, even of the most complex ones;
other unique features like that of analog computing have also been identified.
With this huge potential ready to be disclosed, lack of tunability is still a
main barrier to be broken. Metasurfaces must now be made reconfigurable, i.e.
able to modify and memorize their state, possibly with a small amount of
energy. In this Communication we report low-energy, self-holding metasurface
reconfiguration through lithium intercalation in a vanadium pentoxide layer
integrated within the photonic device. By a proper meta-atom design, operation
on amplitude and phase of linearly polarized light has been demonstrated. In
addition, manipulation of circularly polarized light in the form of tunable
chirality and tunable handedness-preserving reflection has been implemented.
These operations are accomplished using as low as 50 pJ/{\mu}m^{2}, raising
lithium intercalation in transition metal oxides as one of the most energy
efficient self-holding tuning mechanisms known so far for metasurfaces, with
significant perspectives in the whole field of nanophotonics.",1810.03351v1
2018-10-15,A low-disorder Metal-Oxide-Silicon double quantum dot,"One of the biggest challenges impeding the progress of Metal-Oxide-Silicon
(MOS) quantum dot devices is the presence of disorder at the Si/SiO$_2$
interface which interferes with controllably confining single and few
electrons. In this work we have engineered a low-disorder MOS quantum
double-dot device with critical electron densities, i.e. the lowest electron
density required to support a conducting pathway, approaching critical electron
densities reported in high quality Si/SiGe devices and commensurate with the
lowest critical densities reported in any MOS device. Utilizing a nearby charge
sensor, we show that the device can be tuned to the single-electron regime
where charging energies of $\approx$8 meV are measured in both dots, consistent
with the lithographic size of the dot. Probing a wide voltage range with our
quantum dots and charge sensor, we detect three distinct electron traps,
corresponding to a defect density consistent with the ensemble measured
critical density. Low frequency charge noise measurements at 300 mK indicate a
1/$f$ noise spectrum of 3.4 $\mu$eV/Hz$^{1/2}$ at 1 Hz and magnetospectroscopy
measurements yield a valley splitting of 110$\pm$26 $\mu$eV. This work
demonstrates that reproducible MOS spin qubits are feasible and represents a
platform for scaling to larger qubit systems in MOS.",1810.06516v1
2018-10-16,Graphene oxide for enhanced nonlinear optics in low and high index contrast waveguides and nanowires,"We demonstrate enhanced four-wave mixing (FWM) in doped silica waveguides
integrated with graphene oxide (GO) layers. Owing to strong mode overlap
between the integrated waveguides and GO films that have a high Kerr
nonlinearity and low loss, the FWM efficiency of the hybrid integrated
waveguides is significantly improved. We perform FWM measurements for different
pump powers, wavelength detuning, GO coating lengths, and number of GO layers.
Our experimental results show good agreement with theory, achieving up to
~9.5-dB enhancement in the FWM conversion efficiency for a 1.5-cm-long
waveguide integrated with 2 layers of GO. We show theoretically that for
different waveguide geometries an enhancement in FWM efficiency of ~ 20 dB can
be obtained in the doped silica waveguides, and more than 30 dB in silicon
nanowires and slot waveguides. This demonstrates the effectiveness of
introducing GO films into integrated photonic devices in order to enhance the
performance of nonlinear optical processes.",1810.06756v3
2018-10-24,Graphene oxide upregulates the homeostatic functions of primary astrocytes and modulates astrocyte-to-neuron communication,"Graphene-based materials are the focus of intense research efforts to devise
novel theranostic strategies for targeting the central nervous system. In this
work, we have investigated the consequences of long-term exposure of primary
rat astrocytes to pristine graphene (GR) and graphene oxide (GO) flakes. We
demonstrate that GR/GO interfere with a variety of intracellular processes as a
result of their internalization through the endo-lysosomal pathway.
Graphene-exposed astrocytes acquire a more differentiated morphological
phenotype associated with extensive cytoskeletal rearrangements. Profound
functional alterations are induced by GO internalization, including the
upregulation of inward-rectifying K+ channels and of Na+-dependent glutamate
uptake, which are linked to the astrocyte capacity to control the extracellular
homeostasis. Interestingly, GO-pretreated astrocytes promote the functional
maturation of co-cultured primary neurons by inducing an increase in intrinsic
excitability and in the density of GABAergic synapses. The results indicate
that graphene nanomaterials profoundly affect astrocyte physiology in vitro,
with consequences for neuronal network activity. This work supports the view
that GO-based materials could be of great interest to address pathologies of
the central nervous system associated to astrocyte dysfunctions.",1810.10440v1
2018-10-22,Experimental Investigation of Programmed State Stability in OxRAM Resistive Memories,"Oxide-based Random Access Memory (OxRAM), is part of the larger family of
Resistive RAM (RRAM) memories. Generally OxRAM cells consist of a transition
metal oxide (typically HfO2, Ta2O5, TiO2) sandwiched between two metal
electrodes (typically TiN, TaN, W but also Pt, Ir). This thesis describes the
experimental investigation performed on OxRAM memories during a 6-months
internship project at imec research institute (Leuven, Belgium). From previous
studies, HfO-based OxRAM memories showed good endurance properties (with more
than 10e9 write cycles), low operating current (as low as 10 uA), and very fast
switching (programming pulses of 100 ns). However, it has been observed that,
under low programming current condition, data stability becomes challenging.
Therefore, this programming state stability needed further investigation. This
thesis addresses the problem of state stability, first, by presenting the
equipment and algorithms used to study OxRAM state loss over short time
intervals. Secondly, various experiments and tests are performed searching for
a key parameter in order to control memory retention. Finally, this work
demonstrates that resistance evolution over time is affected by both a
determinist drift (logarithmically dependent on time) and a random stochastic
fluctuation component. It also demonstrates that this behavior is intrinsic in
the nature of the device itself and does not depend on processing issues or
variation in the programming conditions. This experimental study proved the
intrinsic nature of the program instability phenomena in OxRAM devices, which
in turns leads to the ineffectiveness of verify algorithm for low current
operation.",1810.10528v1
2018-10-28,A mesoscopic model for the effective electrical conductivity of composite polymeric electrolytes,"The effective quasistatic conductivity of composite polymeric electrolytes is
studied in terms of a hard-core--penetrable-layer model. Used to incorporate
the interface phenomena (such as amorphization of the polymer matrix around
filler particles, stiffening effect by those on the amorphous phase,
irregularities of the filler grains' surfaces, etc.), the layers are assumed to
be electrically inhomogeneous, consisting of a finite or infinite number of
concentric uniform shells. The rules of dominance, imposed on the overlapping
regions, are equivalent to the requirement that the local electric properties
in the system be determined by the distance from the point of interest to the
nearest particle's center. The desired conductivity is calculated using our
original many-particle (compact-group) approach which, however, avoids an
in-depth elaboration of polarization and correlation processes. The result is
expressed through the electrical and geometrical parameters of the
constituents. Contrasting it with experiment reveals that the theory adequately
describes the effective conductivity as a function of the filler concentration
and temperature for a number of polymeric composites based on poly(ethylene
oxide) or oxymethylene-linked poly(ethylene oxide) and is more flexible in
comparison with other theories.",1810.11892v2
2019-06-01,"Caesium fallout in Tokyo on 15th March, 2011 is dominated by highly radioactive, caesium-rich microparticles","In order to understand the chemical properties and environmental impacts of
low-solubility Cs-rich microparticles (CsMPs) derived from the FDNPP, the CsMPs
collected from Tokyo were investigated at the atomic scale using
high-resolution transmission electron microscopy (HRTEM) and dissolution
experiments were performed on the air filters. Remarkably, CsMPs 0.58-2.0
micrometer in size constituted 80%-89% of the total Cs radioactivity during the
initial fallout events on 15th March, 2011. The CsMPs from Tokyo and Fukushima
exhibit the same texture at the nanoscale: aggregates of Zn-Fe-oxide
nanoparticles embedded in amorphous SiO2 glass. The Cs is associated with
Zn-Fe-oxide nanoparticles or in the form of nanoscale inclusions of intrinsic
Cs species,rather than dissolved in the SiO2 matrix. The Cs concentration in
CsMPs from Tokyo (0.55-10.9 wt%) is generally less than that in particles from
Fukushima (8.5-12.9 wt%).The radioactivity per unit mass of CsMPs from Tokyo is
still as high as 1E11 Bq/g, which is extremely high for particles originating
from nuclear accidents. Thus, inhalation of the low-solubility CsMPs would
result in a high localized energy deposition by beta (0.51-12)*1E-3 Gy/h within
the 100-micrometer-thick water layer on the CsMP surface) and may have
longer-term effects compared with those predicted for soluble Cs-species.",1906.00212v2
2019-06-16,First-Principles Study of Hydrogen Behaviors in $α$-Pu$_{2}$O$_{3}$,"The in-depth understanding of hydrogen permeation through plutonium-oxide
overlayers is the prerequisite to evaluate the complex hydriding induction
period of Pu. In this work, the incorporation, diffusion and dissolution of
hydrogen in $\alpha$-Pu$_{2}$O$_{3}$ are investigated by the first-principles
calculations and $\textit{ab initio}$ thermodynamic method based on DFT+U and
DFT-D3 schemes. Our study reveals that the hydrogen incorporation is
endothermic and the separated H atoms prefer to recombine as H$_{2}$ molecules
rather than reacting with $\alpha$-Pu$_{2}$O$_{3}$. The H and H$_{2}$ diffusion
are both feasible, generally, H will recombine first as H$_{2}$ and then
migrate. Both pressure P$_{H2}$ and temperature can promote the hydrogen
dissolution in $\alpha$-Pu$_{2}$O$_{3}$. The single H$_{2}$ molecule
incorporation and (H+H$_{2}$) mixed dissolution will successively appear when
increasing P$_{H2}$. Compared to PuO$_{2}$, this work indicates that Pu
sesquioxide is hardly reduced by hydrogen, but the porous
$\alpha$-Pu$_{2}$O$_{3}$ facilitates hydrogen transport in Pu oxide layers. We
presents the microscopic picture of hydrogen behaviors in the defect-free
$\alpha$-Pu$_{2}$O$_{3}$, which could shed some light on the study of the
hydriding induction period of Pu.",1906.06712v2
2019-06-24,Characterization of Surface and Structure of in-situ Doped Sol-Gel-Derived Silicon Carbide,"Silicon carbide (SiC), is an artificial semiconductor used for high-power
transistors and blue LEDs, for its extraordinary properties. SiC would be
attractive for more applications, but large-scale or large-surface area
fabrication, with control over defects and surface is challenging. Sol-gel
based techniques are an affordable alternative towards such requirements. This
report describes two types of microcrystalline SiC derived after carbothermal
reduction from sol-gel-based precursors, one with nitrogen added, the other
aluminum. Characterization of their bulk, structure and surface shows that
incorporation of dopants affects the formation of polytypes and surface
chemistry. Nitrogen leads exclusively to cubic SiC, exhibiting a native oxide
surface. Presence of aluminum instead promotes growth of hexagonal polytypes
and induces self-passivation of the crystallites surface during growth. This is
established by hydrogenation of silicon bonds and formation of a protecting
aluminum carbonate species. XPS provides support for the suggested mechanism.
This passivation is achieved in only one step, solely by aluminium in the
precursor. Hence, it is shown that growth, doping and passivation of SiC can be
performed as one-pot synthesis. Material without insulating oxide and a limited
number of defects is highly valuable for applications involving
surface-sensitive charge-transfer reactions, therefore the potential of this
method is significant.",1906.09875v1
2019-06-25,Graphene/Polyelectrolyte Layer-by-Layer Coatings for Electromagnetic Interference Shielding,"Electromagnetic interference (EMI) shielding coating materials with
thicknesses in the microscale are required in many sectors, including
communications, medical, aerospace and electronics, to isolate the
electromagnetic radiation emitted from electronic equipment. We report a spray,
layer-by-layer (LbL) coating approach to fabricate micron thick, highly-ordered
and electrically-conductive coatings with exceptional EMI shielding
effectiveness (EMI SE >4830 dB/mm), through the alternating self-assembly of
negatively-charged reduced graphene oxide (RGO) and a positively-charged
polyelectrolyte (PEI). The microstructure and resulting electrical properties
of the (PEI/RGO)n LbL structures are studied as function of increasing mass of
graphene deposited per cycle (keeping the PEI content constant), number of
deposited layers (n), flake diameter and type of RGO. A strong effect of the
lateral flake dimensions on the electrical properties is observed, which also
influences the EMI SE. A maximum EMI SE of 29 dB is obtained for a 6 um thick
(PEI/RGO)10 coating with 19 vol.% loading of reduced
electrochemically-exfoliated graphene oxide flakes with diameters ~3um. This SE
performance exceeds those previously reported for thicker graphene papers and
bulk graphene/polymer composite films with higher RGO or graphene nanoplatelets
contents, which represents an important step towards the fabrication of thin
and light-weight high-performance EMI shielding structures.",1906.10394v1
2019-07-01,Control of dopant crystallinity in electrochemically treated cuprate thin films,"We present a methodology based on \textit{ex-situ} (post-growth)
electrochemistry to control the oxygen concentration in thin films of the
superconducting oxide La$_2$CuO$_{4+y}$ grown epitaxially on substrates of
isostructural LaSrAlO$_4$. The superconducting transition temperature, which
depends on the oxygen concentration, can be tuned by adjusting the pH level of
the base solution used for the electrochemical reaction. As our main finding,
we demonstrate that the dopant oxygens can either occupy the interstitial layer
in an orientationally disordered state or organize into a crystalline phase via
a mechanism in which dopant oxygens are inserted into the substrate, changing
the lattice symmetry of both the substrate and the epitaxial film. We discuss
this mechanism, and describe the resulting methodology as a platform to be
explored in thin films of other transition metal oxides.",1907.01079v1
2019-07-03,Effect of Oxygen Defects Blocking Barriers on Gadolinium Doped Ceria (GDC) Electro-Chemo-Mechanical Properties,"Some oxygen defective metal oxides, such as cerium and bismuth oxides, have
recently shown exceptional electrostrictive properties that are even superior
to the best performing lead-based electrostrictors, e.g.
lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics,
electromechanical mechanisms of such materials do not depend on crystalline
symmetry, but on the concentration of oxygen vacancy in the lattice. In this
work, we investigate for the first time the role of oxygen defect configuration
on the electro-chemo-mechanical properties. This is achieved by tuning the
oxygen defects blocking barrier density in polycrystalline gadolinium doped
ceria with known oxygen vacancy concentration, Ce0.9Gd0.1O2-x,x= 0.05.
Nanometric starting powders of ca. 12 nm are sintered in different conditions,
including field assisted spark plasma sintering (SPS), fast firing and
conventional method at high temperatures. These approaches allow controlling
grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag
mechanism. By correlating the electro-chemo-mechanical properties, we show that
oxygen vacancy distribution in the materials play a key role in ceria
electrostriction, overcoming the expected contributions from grain size and
dopant concentration.",1907.01906v1
2019-07-09,Topological superconductivity from transverse optical phonons in oxide heterostructures,"A topological superconductor features at its boundaries and vortices Majorana
fermions, which are potentially applicable for topological quantum
computations. The scarcity of the known experimentally verified physical
systems with topological superconductivity, time-reversal invariant ones in
particular, is giving rise to a strong demand for identifying new candidate
materials. In this research, we study a heterostructure consisting of a
transition metal oxide two-dimensional electron gas (2DEG) sandwiched by
insulators near the paraelectric (PE) / ferroelectric (FE) phase transition.
Its relevant characteristics is the combination of the transition metal
spin-orbit coupling and the soft odd-parity phonons arising from the
ferroelectric fluctuation; it gives rise to the fluctuating Rashba effect,
which can mediate the pairing interaction for time-reversal invariant
topological superconductivity. As the PE / FE phase transition can be driven by
applying strain on the heterostructure, this system provides a tunable
electron-phonon coupling. Through the first-principle calculations on the (001)
[BaOsO3][BaTiO3]4, we find such electron-phonon coupling to be strong over a
wide range of applied tensile bi-axial strain in the monolayer BaOsO3
sandwiched between the (001) BaTiO3, hence qualifying it as a good candidate
material. Furthermore, the stability of topological superconductivity in this
material is enhanced by its orbital physics that gives rise to the anisotropic
dispersion.",1907.04304v2
2019-07-16,Integrated polarizers based on graphene oxide in waveguides and ring resonators,"Integrated waveguide polarizers and polarization-selective micro-ring
resonators (MRRs) incorporated with graphene oxide (GO) films are
experimentally demonstrated. CMOS-compatible doped silica waveguides and MRRs
with both uniformly coated and patterned GO films are fabricated based on a
large-area, transfer-free, layer-by-layer GO coating method that yields precise
control of the film thickness. Photolithography and lift-off processes are used
to achieve photolithographic patterning of GO films with precise control of the
placement and coating length. Detailed measurements are performed to
characterize the performance of the devices versus GO film thickness and
coating length as a function of polarization, wavelength and power. A high
polarization dependent loss of ~53.8 dB is achieved for the waveguide coated
with 2-mm-long patterned GO films. It is found that intrinsic film material
loss anisotropy dominates the performance for less than 20 layers whereas
polarization dependent mode overlap dominates for thicker layers. For the MRRs,
the GO coating length is reduced to 50 microns, yielding a ~ 8.3-dB
polarization extinction ratio between TE and TM resonances. These results offer
interesting physical insights and trends of the layered GO films and
demonstrate the effectiveness of introducing GO films into photonic integrated
devices to realize high-performance polarization selective components.",1907.06861v1
2019-07-17,Drag Reduction Performance of Mechanically Degraded Dilute Polyethylene Oxide Solutions,"Mechanical degradation of dilute solutions of polyethylene oxide (PEO) via
chain scission was investigated within a turbulent pipe flow. Comparisons of
the drag reduction performance with and without degradation were made by
matching the onset of drag reduction conditions, which has been shown for PEO
to be related to the mean molecular weight. The bulk flow behavior of both the
degraded and non-degraded samples were generally consistent with trends
observed in the literature, but a subset of conditions showed significant
deviation in the slope increment (drag reduction performance) between the
degraded and non-degraded samples. When they deviated, the degraded samples
were consistently more efficient than the non-degraded samples even though they
had the same mean molecular weight. The deviations were shown to scale with the
normalized difference between the initial and final molecular weights. The
current data and analysis as well as the literature suggests that the
deviations in the polymer performance (slope increment) are related to changes
in the molecular weight distribution. More specifically, the improved
performance of the degraded samples relative to the non-degraded ones at the
mean molecular weight of the degraded sample indicates an excess of longer
polymer chains since the higher chain fractions in a degraded solution more
effectively control the flow properties when within a certain degree of
degradation and Reynolds number.",1907.07614v1
2019-07-26,Moiré Engineering of Electronic Phenomena in Correlated Oxides,"Moir\'e engineering has recently emerged as a capable approach to control
quantum phenomena in condensed matter systems. In van der Waals
heterostructures, moir\'e patterns can be formed by lattice misorientation
between adjacent atomic layers, creating long range electronic order. To date,
moir\'e engineering has been executed solely in stacked van der Waals
multilayers. Herein, we describe our discovery of electronic moir\'e patterns
in films of a prototypical magnetoresistive oxide La0.67Sr0.33MnO3 (LSMO)
epitaxially grown on LaAlO3 (LAO) substrates. Using scanning probe
nano-imaging, we observe microscopic moir\'e profiles attributed to the
coexistence and interaction of two distinct incommensurate patterns of strain
modulation within these films. The net effect is that both electronic
conductivity and ferromagnetism of LSMO are modulated by periodic moir\'e
textures extending over mesoscopic scales. Our work provides an entirely new
route with potential to achieve spatially patterned electronic textures on
demand in strained epitaxial materials.",1907.11566v1
2019-07-29,Does the boson peak survive in an ultrathin oxide glass?,"Bulk glasses exhibit extra vibrational modes at low energies, known as the
boson peak. The microscopic dynamics in nanoscale alumina impact the
performance of qubits and other superconducting devices, however the existence
of the boson peak in these glasses has not been previously measured. Here we
report neutron spectroscopy on Al/Al$_2$O$_{3-x}$ nanoparticles consisting of
spherical metallic cores from 20 to 1000 nm surrounded by a 3.5 nm thick
alumina glass. An intense low-energy peak is observed at $\omega_{BP}$ = 2.8
$\pm$ 0.6 meV for highly oxidised particles, concurrent with an excess in the
density of states. The intensity of the peak scales inversely with particle
size and oxide fraction indicating a surface origin, and is red-shifted by 3
meV with respect to the van-Hove singularity of $\gamma$-phase Al$_2$O$_{3-x}$
nanocrystals. Molecular dynamics simulations of $\alpha$-Al$_2$O$_{3-x}$,
$\gamma$-Al$_2$O$_{3-x}$ and a-Al$_2$O$_{3-x}$ show that the observed boson
peak is a signature of the ultrathin glass surface, and the frequency is
softened compared to that of the hypothetical bulk glass.",1907.12200v1
2019-09-03,Strain engineering of oxide thin films for photocatalytic applications,"Photocatalytic materials are pivotal for the implementation of disruptive
clean energy applications such as conversion of H$_{2}$O and CO$_{2}$ into
fuels and chemicals driven by solar energy. However, efficient and
cost-effective materials able to catalyze the chemical reactions of interest
when exposed to visible light are scarce due to the stringent electronic
conditions that they must satisfy. Chemical and nanostructuring approaches are
capable of improving the catalytic performance of known photoactive compounds
however the complexity of the synthesized nanomaterials and sophistication of
the employed methods make systematic design of photocatalysts difficult. Here,
we show by means of first-principles simulation methods that application of
biaxial stress, $\eta$, on semiconductor oxide thin films can modify their
optoelectronic and catalytic properties in a significant and predictable
manner. In particular, we show that upon moderate tensile strains CeO$_{2}$ and
TiO$_{2}$ thin films become suitable materials for photocatalytic conversion of
H$_{2}$O into H$_{2}$ and CO$_{2}$ into CH$_{4}$ under sunlight. The band gap
shifts induced by $\eta$ are reproduced qualitatively by a simple analytical
model that depends only on structural and dielectric susceptibility changes.
Thus, epitaxial strain represents a promising route for methodical screening
and rational design of photocatalytic materials.",1909.00979v1
2019-09-05,Surface Reconstruction Limited Conductivity in Block-Copolymer Li Battery Electrolytes,"Solid polymer electrolytes for lithium batteries promise improvements in
safety and energy density if their conductivity can be increased.
Nanostructured block copolymer electrolytes specifically have the potential to
provide both good ionic conductivity and good mechanical properties. This study
shows that the previously neglected nanoscale composition of the polymer
electrolyte close to the electrode surface has an important effect on impedance
measurements, despite its negligible extent compared to the bulk electrolyte.
Using standard stainless steel blocking electrodes, the impedance of lithium
salt-doped poly(isoprene-b-styrene-b-ethylene oxide) (ISO) exhibited a marked
decrease upon thermal processing of the electrolyte. In contrast, covering the
electrode surface with a low molecular weight poly(ethylene oxide) (PEO) brush
resulted in higher and more reproducible conductivity values, which were
insensitive to the thermal history of the device. A qualitative model of this
effect is based on the hypothesis that ISO surface reconstruction at the
different electrode surfaces leads to a change in the electrostatic double
layer, affecting electrochemical impedance spectroscopy measurements. As a main
result, PEO-brush modification of electrode surfaces is beneficial for the
robust electrolyte performance of PEO-containing block-copolymers and may be
crucial for their accurate characterization and use in Li-ion batteries.",1909.02327v1
2019-09-26,Large-area implementation and critical evaluation of the material and fabrication aspects of a thin-film thermoelectric generator based on aluminum-doped zinc oxide,"A large-area thermoelectric generator (TEG) utilizing a folded thin-film
concept is implemented and the performance evaluated for near room temperature
applications having modest temperature gradients (< 50 K). The TEGs with the
area of ~0.33 m^2 are shown capable of powering a wireless sensor node of
multiple sensors suitable e.g. for monitoring environmental variables in
buildings. The TEGs are based on a transparent, non-toxic and abundant
thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on
flexible substrates. After folding, both the electrical current and heat flux
are in the plane of the thermoelectric thin-film. Heat leakage in the folded
TEG is shown to be minimal (close to that of air), enabling sufficient
temperature gradients without efficient heat sinks, contrary to the
conventional TEGs having the thermal flux and electrical current perpendicular
to the plane of the thermoelectric films. The long-term stability studies
reveal that there are no significant changes in the electrical or
thermoelectric properties of AZO over several months, while the contact
resistance between AZO and silver ink is an issue exhibiting a continuous
increase over time. The performance of the TEGs and technological implications
in relation to a state-of-the-art thermoelectric material are further assessed
via a computational study.",1909.12042v2
2019-10-02,Reversible Thermal Strain Control of Oxygen Vacancy Ordering in an Epitaxial La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$ Film,"Reversible topotactic transitions between oxygen-vacancy-ordered structures
in transition metal oxides provide a promising strategy for active manipulation
of material properties. While transformations between various oxygen-deficient
phases have been attained in bulk ABO$_{3-\delta}$ perovskites, substrate
clamping restricts the formation of distinct ordering patterns in epitaxial
films. Using in-situ scanning transmission electron microscopy (STEM), we image
a thermally driven reversible transition in
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$ films on SrTiO$_3$ from a multidomain
brownmillerite (BM) structure to a uniform phase wherein oxygen vacancies order
in every third CoO$_x$ plane. Because temperature cycling is performed over a
limited temperature range (25 {\deg}C - 385 {\deg}C), the oxygen deficiency
parameter $\delta$ does not vary measurably. Under constant $\delta$, the
topotactic transition proceeds via local reordering of oxygen vacancies driven
by thermal strain. Atomic-resolution imaging reveals a two-step process whereby
alternating vertically and horizontally oriented BM domains first scale in size
to accommodate the strain induced by different thermal expansions of
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$ and SrTiO$_3$, before the new phase
nucleates and quickly grows above 360 {\deg}C. Upon cooling, the film transform
back to the mixed BM phase. As the structural transition is fully reversible
and $\delta$ does not change upon temperature cycling, we rule out
electron-beam irradiation during STEM as the driving mechanism. Instead, our
findings demonstrate that thermal strain can solely drive topotactic phase
transitions in perovskite oxide films, presenting opportunities for switchable
ionic devices.",1910.00953v2
2019-10-05,Electronic structure of bulk manganese oxide and nickel oxide from coupled cluster theory,"We describe the ground- and excited-state electronic structure of bulk MnO
and NiO, two prototypical correlated electron materials, using coupled cluster
theory with single and double excitations (CCSD). As a corollary, this work
also reports the first implementation of unrestricted periodic ab initio
equation-of motion CCSD. Starting from a Hartree-Fock reference, we find
fundamental gaps of 3.46 eV and 4.83 eV for MnO and NiO respectively for the 16
unit supercell, slightly overestimated compared to experiment, although
finite-size scaling suggests that the gap is more severely overestimated in the
thermodynamic limit. From the character of the correlated electronic bands we
find both MnO and NiO to lie in the intermediate Mott/charge-transfer insulator
regime, although NiO appears as a charge transfer insulator when only the
fundamental gap is considered. While the lowest quasiparticle excitations are
of metal 3d and O 2p character in most of the Brillouin zone, near the {\Gamma}
point, the lowest conduction band quasiparticles are of s character. Our study
supports the potential of coupled cluster theory to provide high level
many-body insights into correlated solids.",1910.02191v2
2019-10-07,Epitaxial Growth of Perovskite SrBiO$_3$ Film on SrTiO$_3$ by Oxide Molecular Beam Epitaxy,"Hole-doped perovskite bismuthates such as Ba$_{1-x}$K$_x$BiO$_3$ and
Sr$_{1-x}$K$_x$BiO$_3$ are well-known bismuth-based oxide
high-transition-temperature superconductors. Reported thin bismuthate films
show relatively low quality, likely due to their large lattice mismatch with
the substrate and a low sticking coefficient of Bi at high temperatures. Here,
we report the successful epitaxial thin film growth of the parent compound
strontium bismuthate SrBiO$_3$ on SrO-terminated SrTiO$_3$ (001) substrates by
molecular beam epitaxy. Two different growth methods, high-temperature
co-deposition or recrystallization cycles of low-temperature deposition plus
high-temperature annealing, are developed to improve the epitaxial growth.
SrBiO$_3$ has a pseudocubic lattice constant $\sim$4.25 \AA, an $\sim$8.8\%
lattice mismatch on SrTiO$_3$ substrate, leading to a large strain in the first
few unit cells. Films thicker than 6 unit cells prepared by both methods are
fully relaxed to bulk lattice constant and have similar quality. Compared to
high-temperature co-deposition, the recrystallization method can produce higher
quality 1-6 unit cell films that are coherently or partially strained.
Photoemission experiments reveal the bonding and antibonding states close to
the Fermi level due to Bi and O hybridization, in good agreement with density
functional theory calculations. This work provides general guidance to the
synthesis of high-quality perovskite bismuthate films.",1910.02619v1
2019-10-09,Stability of Nitrogen in Planetary Atmospheres in Contact with Liquid Water,"Molecular nitrogen is the most commonly assumed background gas that supports
habitability on rocky planets. Despite its chemical inertness, nitrogen
molecule is broken by lightning, hot volcanic vents, and bolide impacts, and
can be converted into soluble nitrogen compounds and then sequestered in the
ocean. The very stability of nitrogen, and that of nitrogen-based habitability,
is thus called into question. Here we determine the lifetime of molecular
nitrogen vis-a-vis aqueous sequestration, by developing a novel model that
couples atmospheric photochemistry and oceanic chemistry. We find that HNO, the
dominant nitrogen compounds produced in anoxic atmospheres, is converted to N2O
in the ocean, rather than oxidized to nitrites or nitrates as previously
assumed. This N2O is then released back into the atmosphere and quickly
converted to N2. We also find that the deposition rate of NO is severely
limited by the kinetics of the aqueous-phase reaction that converts NO to
nitrites in the ocean. Putting these insights together, we conclude that the
atmosphere must produce nitrogen species at least as oxidized as NO2 and HNO2
to enable aqueous sequestration. The lifetime of molecular nitrogen in anoxic
atmospheres is determined to be >1 billion years on temperate planets of both
Sun-like and M dwarf stars. This result upholds the validity of molecular
nitrogen as a universal background gas on rocky planets.",1910.04111v1
2019-10-14,A Reversible Structural Phase Transition by Electrochemical Ion Injection into a Conjugated Polymer,"We find that conjugated polymers can undergo reversible structural phase
transitions during electrochemical oxidation and ion injection. We study
poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene]
(PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing
incidence wide angle X-ray scattering (GIWAXS), we show that, in contrast to
previously known polymers, this polymer switches between two structurally
distinct crystalline phases associated with electrochemical oxidation/reduction
in an aqueous electrolyte. Importantly, we show that this unique phase change
behavior has important physical consequences for ion transport. Notably, using
moving front experiments visualized by both optical microscopy and
super-resolution photoinduced force microscopy (PiFM), we show that a
propagating ion front in PB2T-TEG exhibits non-Fickian transport, retaining a
sharp step-edge profile, in stark contrast to the Fickian diffusion more
commonly observed. This structural phase transition is reminiscent of those
accompanying ion uptake in inorganic materials like LiFePO$_{4}$. We propose
that engineering similar properties in future conjugated polymers may enable
the realization of new materials with superior performance in electrochemical
energy storage or neuromorphic memory applications.",1910.06440v1
2019-10-18,Atomically Controlled Tunable Doping in High Performance WSe2 Devices,"Two-dimensional transitional metal dichalcogenide (TMD) field-effect
transistors (FETs) are promising candidates for future electronic applications,
owing to their excellent transport properties and potential for ultimate device
scaling. However, it is widely acknowledged that substantial contact resistance
associated with the contact-TMD interface has impeded device performance to a
large extent. It has been discovered that O2 plasma treatment can convert WSe2
into WO3-x and substantially improve contact resistances of p-type WSe2 devices
by strong doping induced thinner depletion width. In this paper, we carefully
study the temperature dependence of this conversion, demonstrating an oxidation
process with a precise monolayer control at room temperature and multilayer
conversion at elevated temperatures. Furthermore, the lateral oxidation of WSe2
under the contact revealed by HR-STEM leads to potential unpinning of the metal
Fermi level and Schottky barrier lowering, resulting in lower contact
resistances. The p-doping effect is attributed to the high electron affinity of
the formed WO3-x layer on top of the remaining WSe2 channel, and the doping
level is found to be dependent on the WO3-x thickness that is controlled by the
temperature. Comprehensive materials and electrical characterizations are
presented, with a low contact resistance of ~528 ohm-um and record high
on-state current of 320 uA/um at -1V bias being reported.",1910.08619v1
2019-10-21,Overlooked transportation anisotropies in d-band correlated rare-earth perovskite nickelates,"Anisotropies in electronic transportations conventionally originate from the
nature of low symmetries in crystal structures, and were not anticipated for
perovskite oxides, the crystal asymmetricity of which is far below, e.g. van
der Waals or topological crystal. Beyond conventional expectations, herein we
demonstrate pronounced anisotropies in the inter-band coulomb repulsion
dominated electronic transportation behaviors under low-dimensional confinement
for the perovskite family of rare-earth nickelates (ReNiO3). From one aspect,
imparting bi-axial interfacial strains upon various lattice planes results in
extrinsic anisotropies in the abrupt orbital transitions of ReNiO3, and their
metal to insulator transition behaviors that elevates the transition
temperature beyond the existing merit. From the other aspect, the in-plane
orbital entropy associated to the in-plane symmetry of the NiO6 octahedron
within ReNiO3 causes intrinsic anisotropies for the gradually orbital
transition with temperature to further improve their thermistor transportation
properties. The present work unveils the overlooked role of the electronic
orbital directionality within low dimensional correlated perovskites that can
trigger anisotropic transportation behaviors, in spite of their relatively
symmetric crystal structures. Establishing anisotropic transportations
integrating the electron correlation and quantum confinement effects will bring
in a new freedom for achieving further improvement in transportation properties
of multi-functional perovskite oxides.",1910.09160v1
2019-10-25,Interdiffusion between gadolinia doped ceria and yttria stabilized zirconia in solid oxide fuel cells: experimental investigation and kinetic modeling,"Interdiffusion between the yttria stabilized zirconia (YSZ) electrolyte and
the gadolinia doped ceria (CGO) barrier layer is one of the major causes to the
degradation of solid oxide fuel cells (SOFCs). We present in this work
experimental investigations on CGO-YSZ bi-layer electrolyte sintered at 1250 C
or 1315 C and element transport as a function of sintering temperature and
dwelling time. In order to quantitatively simulate the experimental
observations, the CALPHAD-type thermodynamic assessment of the CGO-YSZ system
is performed by simplifying the system to a CeO2-ZrO2 quasi-binary system, and
the kinetic descriptions (atomic mobilities) are constructed based on critical
review of literature data. The CGO-YSZ interdiffusion is then modeled with the
DICTRA software and the simulation results are compared with the experimental
data under different sintering or long-term operating conditions. The
corresponding ohmic resistance of the bi-layer electrolyte is predicted based
on the simulated concentration profile. The results implies that the
interdiffusion across the CGO-YSZ interface happens mainly during sintering at
high temperature, while during long-term operation at relatively lower
temperature the impact of interdiffusion on cell degradation is negligible.",1910.11947v2
2019-10-31,Early stages of GaAs nanowires VLS self-catalyzed growth on silica-terminated silicon substrate: A photoemission study,"In this paper the early stages of the self-catalyzed Vapor-Liquid-Solid (VLS)
growth of GaAs nanowires on epi-ready Si substrates by Molecular Beam Epitaxy
(MBE) are studied. The interaction of Ga nano-droplets (NDs) with the silica
overlayer is investigated by X-ray Photoemission Spectroscopy (XPS) and Atomic
Force Microscopy (AFM). We show how Ga NDs drill the silica overlayer and make
contact with bulk Si to allow GaAs nanowires (NWs) epitaxial growth by studying
each of the three steps of the NW growth process sequentially: Ga NDs
pre-deposition, post-deposition annealing to reach the NW growth temperature,
and finally NW growth itself. The pre-deposition temperature allows to control
the density and morphology of the NDs. A high enough annealing temperature
enhances the reduction of SiOx by Ga oxidation and leads to the formation of
holes which is seen by a new component in XPS spectra, assumed to be the
consequence of the Ga-Si interaction. Finally, these nano-holes act as
nucleation sites for the epitaxial GaAs VLS growth. During the GaAs growth,
three different chemical environments of Ga are identified in Ga2p core level:
metallic Ga due to the droplets at the top of the NWs, Ga oxide in contact with
the SiOx overlayer and Ga arsenide from NWs.",1910.14570v1
2020-01-14,Magnesium Oxide at Extreme Temperatures and Pressures Studied with First-Principles Simulations,"We combine two first-principles computer simulation techniques, path integral
Monte-Carlo and density functional theory molecular dynamics, to determine the
equation of state of magnesium oxide in the regime of warm dense matter, with
densities ranging from 0.35 to 71~g$\,$cm$^{-3}$ and temperatures from 10,000 K
to $5\times10^8$~K. These conditions are relevant for the interiors of giant
planets and stars as well as for shock wave compression measurements and
inertial confinement fusion experiments. We study the electronic structure of
MgO and the ionization mechanisms as a function of density and temperature. We
show that the L-shell orbitals of magnesium and oxygen hybridize at high
density. This results into a gradual ionization of the L-shell with increasing
density and temperature. In this regard, MgO behaves differently from pure
oxygen, which is reflected in the shape of the MgO principal shock Hugoniot
curve. The curve of oxygen shows two compression maxima, while that of MgO
shows only one. We predict a maximum compression ratio of 4.66 to occur for a
temperature of 6.73 $\times 10^7$ K. Finally we study how multiple shocks and
ramp waves can be used to cover a large range of densities and temperatures.",2001.05300v1
2020-01-21,Theoretical Investigation of Optical Intersubband Transitions and Infrared Photodetection in $β$-(AlxGa1-x)2O3/Ga2O3 Quantum Well Structures,"We provide theoretical consideration of intersubband transitions designed in
the ultrawide bandgap Aluminum Gallium Oxide ((AlxGa1-x)2O3)/Gallium Oxide
(Ga2O3)) quantum well system. Conventional material systems have matured into
successful intersubband device applications such as large area quantum well
infrared photodetector(QWIP) focal plane arrays for reproducible imaging
systems but are fundamentally limited via maximum conduction band offsets to
mid and long wavelength infrared applications. Short and near infrared devices
are technologically important to optical communications systems and biomedical
imaging applications, but are difficult to realize in intersubband designs for
this reason. In this work, we use a first principles approach to estimate the
expansive design space of monoclinic ${\beta}$(AlxGa1x)2O3/Ga2O3 material
system, which reaches from short wavelength infrared (1 to 3{\mu}m) to far
infrared (greater than 30{\mu}m) transition wavelengths. We estimate the
performance metrics of two QWIPs operating in the long and short wavelength
regimes, including an estimation of high room temperature detectivity (about
10^11 Jones) at the optical communication wavelength {\lambda}p 1.55{\mu}m. Our
findings demonstrate the potential of the rapidly maturing (AlxGa1-x)2O3/Ga2O3
material system to open the door for intersubband device applications.",2001.07299v2
2020-02-18,Proton Transport Entropy Increase In Amorphous SiO$_2$,"This paper presents a classical thermodynamic calculation of a Greens
function that describes the declining rate of entropy growth as protons move
under an applied electric field, through an amorphous SiO$_2$ layer in a MOS
field-effect device gate oxide. The analysis builds on work by McLean and
Ausman (1977) and Brown and Saks (1991). Polynomial models of fitting
parameters dB/d$\alpha$, y$_0$, and A/y$_0$ based on interpolation TABLE I of
McLean and Ausman are presented. Infinite boundary conditions are introduced
for the parameter dB/d$\alpha$. Polynomial representations are shown of
dB/d$\alpha$, y$_0$, A/y$_0$ and the Greens function as a function of the
dispersion parameter $\alpha$. The paper shows that parameters y$_0$ and
A/y$_0$ are nearly conic sections with small residuals of a few percent. This
work is intended as a first step toward a near-equilibrium thermodynamic
continuous-time random walk (CTRW) model (anomalous diffusion) of damage
introduced into thick-oxide silicon-based powerMOS parts by space radiation
effects such as those found in the Jovian radiation belts. Charge transport in
amorphous silica electrical insulators is by thermally activated tunneling, not
Brownian motion.",2002.07547v2
2020-03-31,Design and Simulation of Memristor-Based Artificial Neural Network for Bidirectional Adaptive Neural Interface,"This article proposes a general approach to the simulation and design of a
multilayer perceptron (MLP) network on the basis of cross-bar arrays of
metal-oxide memristive devices. The proposed approach uses the ANNM theory,
tolerance theory, simulation methodology and experiment design. The tolerances
analysis and synthesis process is performed for the ANNM hardware
implementation on the basis of two arrays of memristive microdevices in the
original 16x16 cross-bar topology being a component of bidirectional adaptive
neural interface for automatic registration and stimulation of bioelectrical
activity of a living neuronal culture used in robotics control system. The ANNM
is trained for solving a nonlinear classification problem of stable information
characteristics registered in the culture grown on a multi-electrode array.
Memristive devices are fabricated on the basis of a newly engineered
Au/Ta/ZrO2(Y)/Ta2O5/TiN/Ti multilayer structure, which contains self-organized
interface oxide layers, nanocrystals and is specially developed to obtain
robust resistive switching with low variation of parameters. An array of
memristive devices is mounted into a standard metal-ceramic package and can be
easily integrated into the neurointerface circuit. Memristive devices
demonstrate bipolar switching of anionic type between the high-resistance state
and low-resistance state and can be programmed to set the intermediate
resistive states with a desired accuracy. The ANNM tuning, testing and control
are implemented by the FPGA-based control subsystem. All developed models and
algorithms are implemented as Python-based software.",2004.00154v1
2020-04-01,Phase transitions and spin-state of iron in FeO at the conditions of Earth's deep interior,"Iron-bearing oxides undergo a series of pressure-induced electronic, spin and
structural transitions that can cause seismic anomalies and dynamic
instabilities in Earth's mantle and outer core. We employ x-ray diffraction and
x-ray emission spectroscopy along with state-of-the-art density functional plus
dynamical mean-field theory (DFT+DMFT) to characterize the electronic structure
and spin states, and crystal-structural properties of w\""ustite (Fe$_{1-x}$O)
-- a basic oxide component of Earth's interior -- at high pressure-temperature
conditions up to 140 GPa and 2100 K. We find that FeO exhibits complex
polymorphism under pressure, with abnormal compression behavior associated with
electron-spin and crystallographic phase transitions, and resulting in a
substantial change of bulk modulus. Our results reveal the existence of a
high-pressure phase characterized by a metallic high-spin state of iron at
about the pressure-temperature conditions of Earth's core-mantle boundary. The
presence of high-spin metallic iron near the base of the mantle can
significantly influence the geophysical and geochemical properties of Earth's
deep interior.",2004.00652v2
2020-04-03,Differential coloration efficiency of electrochromic amorphous tungsten oxide as a function of intercalation level: Comparison between theory and experiment,"Optical absorption in amorphous tungsten oxide ($\textit{a}\mathrm{WO}_{3}$),
for photon energies below that of the band gap, can be rationalized in terms of
electronic transitions between localized states. For the study of this
phenomenon, we employed the differential coloration efficiency concept, defined
as the derivative of the optical density with respect to the inserted charge.
We also made use of its extension to a complex quantity in the context of
frequency-resolved studies. Combined $\textit{in situ}$ electrochemical and
optical experiments were performed on electrochromic
$\textit{a}\mathrm{WO}_{3}$ thin films for a wide lithium intercalation range
using an optical wavelength of $810~\mathrm{nm}$ ($1.53~\mathrm{eV}$).
Quasi-equilibrium measurements were made by chronopotentiometry (CP). Dynamic
frequency-dependent measurements were carried out by simultaneous
electrochemical and color impedance spectroscopy (SECIS). The differential
coloration efficiency obtained from CP changes sign at a critical intercalation
level. Its response exhibits an excellent agreement with a theoretical model
that considers electronic transitions between $\mathrm{W}^{4+}$,
$\mathrm{W}^{5+}$, and $\mathrm{W}^{6+}$ sites. For the SECIS experiment, the
low-frequency limit of the differential coloration efficiency shows a general
trend similar to that from CP. However, it does not change sign at a critical
ion insertion level. This discrepancy could be due to degradation effects
occurring in the films at high $\mathrm{Li}^+$ insertion levels. The
methodology and results presented in this work can be of great interest both
for the study of optical absorption in disordered materials and for
applications in electrochromism.",2004.01516v1
2020-04-06,Electron-polaron dichotomy of charge carriers in perovskite oxides,"Many transition metal oxides (TMOs) are Mott insulators due to strong Coulomb
repulsion between electrons, and exhibit metal-insulator transitions (MITs)
whose mechanisms are not always fully understood. Unlike most TMOs, minute
doping in CaMnO3 induces a metallic state without any structural
transformations. This material is thus an ideal platform to explore band
formation through the MIT. Here, we use angle-resolved photoemission
spectroscopy to visualize how electrons delocalize and couple to phonons in
CaMnO3. We show the development of a Fermi surface where mobile electrons
coexist with heavier carriers, strongly coupled polarons. The latter originate
from a boost of the electron-phonon interaction (EPI). This finding brings to
light the role that the EPI can play in MITs even caused by purely electronic
mechanisms. Our discovery of the EPI-induced dichotomy of the charge carriers
explains the transport response of Ce-doped CaMnO3 and suggests strategies to
engineer quantum matter from TMOs.",2004.02953v2
2020-04-11,Boron phosphide as a \emph{p}-type transparent conductor: optical absorption and transport through electron-phonon coupling,"Boron phosphide has recently been identified as a potential high hole
mobility transparent conducting material. This promise arises from its low hole
effective masses. However, BP has a relatively small 2 eV indirect band gap
which will affect its transparency. In this work, we computationally study both
optical absorption across the indirect gap and phonon-limited electronic
transport to quantify the potential of boron phosphide as a \emph{p}-type
transparent conductor. We find that phonon-mediated indirect optical absorption
is weak in the visible spectrum and that the phonon-limited hole mobility is
very high (around 900 cm$^2$/Vs) at room temperature. This exceptional mobility
comes from a combination of low hole effective mass and very weak scattering by
polar phonon modes. We rationalize the weak scattering by the less ionic
bonding in boron phosphide compared to oxides. We suggest this could be a
general advantage of non-oxides for \emph{p}-type transparent conducting
applications. Using our computed properties, we assess the transparent
conductor figure of merit of boron phosphide and shows that it exceeds by one
order of magnitude that of established \emph{p}-type transparent conductors,
confirming the potential of this material.",2004.05390v1
2020-04-12,Fabrication process and failure analysis for robust quantum dots in silicon,"We present an improved fabrication process for overlapping aluminum gate
quantum dot devices on Si/SiGe heterostructures that incorporates
low-temperature inter-gate oxidation, thermal annealing of gate oxide, on-chip
electrostatic discharge (ESD) protection, and an optimized interconnect process
for thermal budget considerations. This process reduces gate-to-gate leakage,
damage from ESD, dewetting of aluminum, and formation of undesired alloys in
device interconnects. Additionally, cross-sectional scanning transmission
electron microscopy (STEM) images elucidate gate electrode morphology in the
active region as device geometry is varied. We show that overlapping aluminum
gate layers homogeneously conform to the topology beneath them, independent of
gate geometry, and identify critical dimensions in the gate geometry where
pattern transfer becomes non-ideal, causing device failure.",2004.05683v3
2020-04-14,"Forming a highly active, homogeneously alloyed AuPt co-catalyst decoration on O2 nanotubes directly during anodic growth","Au and Pt do not form homogeneous bulk alloys as they are thermodynamically
not miscible. However, we show that anodic TiO$_2$ nanotubes (NTs) can in-situ
be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during
their anodic growth. For this, a metallic Ti substrate containing low amounts
of dissolved Au (0.1 at%) and Pt (0.1 at%) is used for anodizing. The matrix
metal (Ti) is converted to oxide while at the oxide/metal interface direct
noble metal particle formation and alloying of Au and Pt takes place;
continuously these particles are then picked up by the growing nanotube wall.
In our experiments the AuPt alloy NPs have an average size of 4.2 nm and, at
the end of the anodic process, are regularly dispersed over the TiO$_2$
nanotubes. These alloyed AuPt particles act as excellent co-catalyst in
photocatalytic H2 generation - with a H2 production of 12.04 {\mu}L h-1 under
solar light. This represents a strongly enhanced activity as compared with
TiO$_2$ NTs decorated with monometallic particles of Au (7 {\mu}L h-1) or Pt
(9.96 {\mu}L h-1).",2004.06566v1
2020-04-15,Penetration depth and gap structure in the antiperovskite oxide superconductor Sr$_{3-x}$SnO revealed by $μ$SR,"We report a $\mu$SR study on the antiperovskite oxide superconductor
Sr$_{3-x}$SnO. With transverse-field $\mu$SR, we observed the increase of the
muon relaxation rate upon cooling below the superconducting transition
temperature $T_{\mathrm{c}}=5.4$ K, evidencing bulk superconductivity. The
exponential temperature dependence of the relaxation rate $\sigma$ at low
temperatures suggests a fully gapped superconducting state. We evaluated the
zero-temperature penetration depth $\lambda(0)\propto1/\sqrt{\sigma(0)}$ to be
around 320-1020 nm. Such a large value is consistent with the picture of a
doped Dirac semimetal. Moreover, we revealed that the ratio
$T_{\mathrm{c}}/\lambda(0)^{-2}$ is larger than those of ordinary
superconductors and is comparable to those of unconventional superconductors.
The relatively high $T_{\mathrm{c}}$ for small carrier density may hint at an
unconventional pairing mechanism beyond the ordinary phonon-mediated pairing.
In addition, zero-field $\mu$SR did not provide evidence of broken
time-reversal symmetry in the superconducting state. These features are
consistent with the theoretically proposed topological superconducting state in
Sr$_{3-x}$SnO, as well as with $s$-wave superconductivity.",2004.06993v1
2020-04-21,Solution-processed GaSe nanoflake-based films for photoelectrochemical water splitting and photoelectrochemical-type photodetectors,"Gallium selenide (GaSe) is a layered compound, which has been exploited in
nonlinear optical applications and photodetectors due to its anisotropic
structure and pseudo-direct optical gap. Theoretical studies predicted that its
two-dimensional (2D) form is a potential photocatalyst for water splitting
reactions. Herein, we first report the photoelectrochemical (PEC)
characterization of GaSe nanoflakes (single-/few-layer flakes), produced via
liquid phase exfoliation, for hydrogen evolution reaction (HER) and oxygen
evolution reaction (OER) in both acidic and alkaline media. In 0.5 M H2SO4, the
GaSe photoelectrodes display the best PEC performance, i.e. a ratiometric
power-saved metric for HER ({\Phi}saved,HER) of 0.09% and a ratiometric
power-saved metric for OER ({\Phi}saved,OER) of 0.25%. When used as PEC-type
photodetectors, GaSe photoelectrodes show a responsivity of ~0.16 A W-1 upon
455 nm illumination at light intensity of 63.5 uW cm-2 and applied potential of
-0.3 V vs. reversible hydrogen electrode (RHE). The stability analysis of the
GaSe photodetectors evidences a durable operation over tens of cathodic linear
sweep voltammetry scans in 0.5 M H2SO4 for HER. Viceversa, degradation effects
have been observed in both alkaline and anodic operation due to highly
oxidizing environment and O2-induced (photo-)oxidation effects. Our results
provide new insight into PEC properties of GaSe nanoflakes for their
exploitation in photoelectrocatalysis, PEC-type photodetectors and
(bio)sensors.",2004.10034v1
2020-04-23,Topological Hall effect in single thick SrRuO3 layers induced by defect engineering,"The topological Hall effect (THE) has been discovered in ultrathin SrRuO3
(SRO) films, where the interface between the SRO layer and another oxide layer
breaks the inversion symmetry resulting in the appearance of THE. Thus, THE
only occurs in ultra-thin SRO films of several unit cells. In addition to
employing a heterostructure, the inversion symmetry can be broken intrinsically
in bulk SRO by introducing defects. In this study THE is observed in 60 nm
thick SRO films, in which defects and lattice distortions are introduced by
helium ion irradiation. The irradiated SRO films exhibit a pronounced THE in a
wide temperature range from 5 K to 80 K. These observations can be attributed
to the emergence of Dzyaloshinskii-Moriya interaction as a result of artificial
inversion symmetry breaking associated to the lattice defect engineering. The
creation and control of the THE in oxide single layers can be realized by ex
situ film processing. Therefore, this work provides new insights into the THE
and illustrates a promising strategy to design novel spintronics devices.",2004.11301v1
2020-04-24,Robust and Bright Photoluminescence from Colloidal Nanocrystal / Al$_2$O$_3$ Composite Films fabricated by Atomic Layer Deposition,"Colloidal nanocrystals are a promising fluorescent class of materials, whose
spontaneous emission features can be tuned over a broad spectral range via
their composition, geometry and size. However, towards embedding nanocrystals
films in elaborated device geometries, one significant drawback is the
sensitivity of their emission properties on further fabrication processes like
lithography, metal or oxide deposition, etc. In this work, we demonstrate how
bright emitting and robust thin films can be obtained by combining nanocrystal
deposition from solutions via spin2 coating with subsequent atomic layer
deposition of alumina. For the resulting composite films, the layer thickness
can be controlled on the nanoscale, and their refractive index can be finely
tuned by the amount of deposited alumina. Ellipsometry is used to measure the
real and imaginary part of the dielectric permittivity, which gives direct
access to the wavelength dependent refractive index absorbance of the film.
Detailed analysis of the photophysics of thin films of core-shell nanocrystal
with different shape and different shell thickness allow to correlate the
behavior of the photoluminescence and of the decay life time to the changes in
the non-radiative rate that are induced by the alumina deposition. We show that
the photoemission properties of such composite films are stable in wavelength
and intensity over several months, and that the photoluminescence completely
recovers from heating processes up to 240$^\circ$C. The latter is particularly
interesting, since it demonstrates robustness to the typical heat treatment
that is needed in several process steps like resist-based lithography and
deposition by thermal or electron beam evaporation of metals or oxides.",2004.11634v1
2020-04-14,Photoanodes Based on TiO$_2$ and $α$-Fe$_2$O$_3$ for Solar Water Splitting Superior Role of 1D Nanoarchitectures and of Combined Heterostructures,"Solar driven photoelectrochemical water splitting (PEC-WS) using
semiconductor photoelectrodes represents a promising approach for a sustainable
and environmentally friendly production of renewable energy vectors and fuel
sources, such as dihydrogen (H2). In this context, titanium dioxide (TiO$_2$)
and iron oxide (hematite, $\alpha$-Fe$_2$O$_3$) are among the most investigated
candidates as photoanode materials, mainly owing to their resistance to
photocorrosion, non-toxicity, natural abundance, and low production cost. Major
drawbacks are, however, an inherently low electrical conductivity and a limited
hole diffusion length that significantly affect the performance of TiO$_2$ and
$\alpha$-Fe$_2$O$_3$ in PEC devices. To this regard, one-dimensional (1D)
nanostructuring is typically applied as it provides several superior features
such as a significant enlargement of the material surface area, extended
contact between the semiconductor and the electrolyte and, most remarkably,
preferential electrical transport that overall suppress charge carrier
recombination and improve TiO$_2$ and $\alpha$-Fe$_2$O$_3$
photo-electrocatalytic properties. The present review describes various
synthetic methods, properties and PEC applications of 1D-photoanodes
(nanotubes, nanorods, nanofibers, nanowires) based on titania, hematite, and on
$\alpha$-Fe$_2$O$_3$/TiO$_2$ heterostructures. Various routes towards
modification and enhancement of PEC activity of 1D photoanodes are also
discussed including doping, decoration with co-catalysts and heterojunction
engineering. Finally, the challenges related to the optimization of charge
transfer kinetics in both oxides are highlighted.",2004.12844v1
2020-04-27,Exploring Nanoscale Ferroelectricity in Doped Hafnium Oxide by Interferometric Piezoresponse Force Microscopy,"Hafnium oxide (HfO2)-based ferroelectrics offer remarkable promise for memory
and logic devices in view of their compatibility with traditional silicon CMOS
technology, high switchable polarization, good endurance and thickness
scalability. These factors have led to steep rise in research on this class of
materials over the past number of years. At the same time, only a few reports
on the direct sensing of nanoscale ferroelectric properties exist, with many
questions remaining regarding the emergence of ferroelectricity in these
materials. While piezoresponse force microscopy (PFM) is ideally suited to
probe piezo- and ferro-electricity on the nanoscale, it is known to suffer
artifacts which complicate quantitative interpretation of results and can even
lead to claims of ferroelectricity in materials which are not ferroelectric. In
this paper we explore the possibility of using an improved PFM method based on
interferometric displacement sensing (IDS) to study nanoscale ferroelectricity
in bare Si doped HfO2. Our results indicate a clear difference in the local
remnant state of various HfO2 crystallites with reported values for the
piezoelectric coupling in range 0.6-1.5 pm/V. In addition, we report unusual
ferroelectric polarization switching including possible contributions from
electrostriction and Vegard effect, which may indicate oxygen vacancies or
interfacial effects influence the emergence of nanoscale ferroelectricity in
HfO2.",2004.12903v2
2020-04-28,The Prominent Charge-Transfer Effects of Trinuclear Complexes with Nominally High Nickel Valences,"Recently synthesized Rh-Ni trinuclear complexes hexacoordinated with sulfur
ions, 3-aminopropanethiolate (apt) metalloligand
[Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ ($n$ = 2, 3, 4), are found to be
chemically interconvertible between the nominal Ni$^{2+}$ and Ni$^{4+}$ states.
In order to clarify the origins of their interconvertible nature and the
stability of such a high oxidation state as the tetravalency from the physical
point of view, we have systematically investigated the local 3$d$ electronic
structures of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ by means of soft X-ray
core-level absorption spectroscopy (XAS). The experimental data have been
reproduced by the single-site configuration-interaction cluster-model
simulations, which indicate that the charge-transferred configurations are more
stable than the nominal $d$-electron-number configuration for $n=3,4$ leading
to the prominent charge-transfer effects. These are also supported by S
$K$-edge XAS of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$. Our results imply
that the found charge-transfer effects have a key role to realize the
interconvertible nature as well as the stability of the high oxidization state
of the Ni ions.",2004.13686v1
2020-12-06,Economically viable CO2 electroreduction embedded within ethylene oxide manufacturing,"Electrochemical conversion of CO2 (CO2R) into fuels and chemicals can both
reduce CO2 emissions and allow for clean manufacturing in the scenario of
significant expansion of renewable power generation. However, large-scale
process deployment is currently limited by unfavourable process economics
resulting from significant up- and down-stream costs for obtaining pure CO2,
separation of reaction products and increased logistical effort. We have
discovered a method for economically viable recycling of waste CO2 that
addresses these challenges. Our approach is based on integration of a CO2R unit
into an existing manufacturing process: ethylene oxide (EO) production, which
emits CO2 as a by-product. The standard EO process separates waste CO2 from gas
stream, hence the substrate for electroreduction is available at an EO plant at
no additional cost. CO2 can be converted into an ethylene-rich stream and
recycled on-site back to the EO reactor, which uses ethylene as a raw material,
and also the anode product (oxygen) can be simultaneously valorized for the EO
production reaction. If powered by a renewable electricity source, the process
will significantly (ca. 80%) reduce the CO2 emissions of an EO manufacturing
plant. A sensitivity analysis shows that the recycling approach can be
economically viable in the short term and that its payback time could be as low
as 1-2 years in the regions with higher carbon taxes and/or with access to
low-cost electricity sources.",2012.03198v1
2020-12-11,"Polyvinyl Alcohol-Few Layer Graphene Composite Films Prepared from Aqueous Colloids. Investigations of Mechanical, Conductive and Gas Barrier Properties","Quasi all water soluble composites use graphene oxide (GO) or reduced
graphene oxide (rGO) as graphene based additives despite the long and harsh
conditions required for their preparation. Herein, polyvinyl alcohol (PVA)
films containing few layer graphene (FLG) are prepared by the co-mixing of
aqueous colloids and casting, where the FLG colloid is first obtained via an
effcient, rapid, simple, and bio-compatible exfoliation method providing access
to relatively large FLG flakes. The enhanced mechanical, electrical
conductivity, and O2 barrier properties of the films are investigated and
discussed together with the structure of the films. In four different series of
the composites, the best Young modulus is measured for the films containing
around 1% of FLG. The most significant enhancement is obtained for the series
with the largest FLG sheets contrary to the elongation at break which is well
improved for the series with the lowest FLG sheets. Relatively high one-side
electrical conductivity and low percolation threshold are achieved when
compared to GO(rGO) composites (almost 10-3 S.cm-1 for 3% of FLG and transport
at 0.5% FLG), while the conductivity is affected by the formation of a
macroscopic branched FLG network. The composites demonstrate a reduction of O2
transmission rate up to 60%.",2012.06239v1
2020-12-19,Parallelising Electrocatalytic Nitrogen Fixation Beyond Heterointerfacial Boundary,"The nitrogen (N2) reduction reaction (NRR) is an eco-friendly alternative to
the Haber-Bosch process to produce ammonia (NH3) with high sustainability.
However, the significant magnitude of uphill energies in the multi-step NRR
pathways is a bottleneck of its serial reactions. Herein, the concept of a
parallelized reaction is proposed to actively promote NH3 production via the
NRR using a multi-phase vanadium oxide-nitride (V2O3/VN) hybrid system. Density
functional theory calculations revealed that the V2O3/VN junction parallelizes
NRR pathways by exchanging intermediate N2H4* and NH2* products to avoid
massive uphill energies towards final NH3 generation. Such an exchange is
driven by the difference in coverage of the two species. The impact of the
reaction parallelization strategy for multi-step nitrogen reduction is
demonstrated with the V2O3/VN junction by an increased ammonia yield rate of
18.36 micro mol h^-1 cm^-2 and a Faraday efficiency (FE) of 26.62% at -0.3 V
versus a reversible hydrogen electrode in a 0.1 M aqueous KOH electrolyte, of
which FE value exhibits 16.95 times and 6.22 times higher than that of
single-phase V2O3 and VN, respectively. The introduction of multi-phase
oxides/nitrides into a transition metal-based electrocatalyst can thus be a
promising approach to realizing an alternative method for N2 fixation.",2012.10625v2
2020-12-21,Ionic-strength and pH dependent reactivities of ascorbic acid toward ozone in aqueous micro-droplets studied by aerosol optical tweezers,"The heterogeneous oxidation reaction of single aqueous ascorbic acid (AH$_2$)
aerosol particles with gas-phase ozone was investigated in this study utilizing
aerosol optical tweezers with Raman spectroscopy. The measured liquid-phase
bimolecular rate coefficients of the AH$_2$ + O$_3$ reaction exhibit a
significant pH dependence, and the corresponding values at ionic strength 0.2 M
are $(3.1 \pm 2.0) \times 10^5$ M$^{-1}$s$^{-1}$ and $(1.2 \pm 0.6) \times
10^7$ M$^{-1}$s$^{-1}$ for pH $\approx$ 2 and 6, respectively. These results
measured in micron-sized droplets agree with those from previous bulk
measurements, indicating that the observed aerosol reaction kinetics can be
solely explained by liquid phase diffusion and AH$_2$ + O$_3$ reaction.
Furthermore, the results indicate that high ionic strengths could enhance the
liquid-phase rate coefficients of the AH$_2$ + O$_3$ reaction. The results also
exhibit a negative ozone pressure dependence that can be rationalized in terms
of a Langmuir-Hinshelwood type mechanism for the heterogeneous oxidation of
AH$_2$ aerosol particles by gas-phase ozone. The results of the present work
imply that in acidified airway-lining fluids the antioxidant ability of AH$_2$
against atmospheric ozone will be significantly suppressed.",2012.11112v2
2020-12-22,Degradation of Nonylphenol Ethoxylate-10 (NPE-10) by Mediated Electrochemical Oxidation (MEO) Technology,"Nonylphenol ethoxylate (NPE 10) is a non ionic surfactant which is
synthesized from alkylphenol ethoxylate. The accumulation of NPE-10 in
wastewater will endanger the ecosystem as well as human being. At present, by
an advancement of technology NPE 10 can be degraded indirectly by using an
electrochemically treatment. Thus, this study aimed to evaluate the potential
electrodegradation of NPE 10 by mediated electrochemical oxidation (MEO) using
Ce(IV) ionic mediator. In addition, the influence of Ag(I) ionic catalyst in
the performance of MEO for degradation of NPE 10 was also observed. The potency
of MEO technology in degradation NPE 10 was evaluated by voltammetry technique
and confirmed by titrimetry and LC-MS analyses. The results showed that in the
absence of Ag(I) ionic catalyst, the degradation of NPE 10 by MEO was 85.93 %.
Furthermore, when the Ag(I) ionic catalyst was applied, the performance of MEO
in degradation of NPE 10 was improved to 95.12 %. The back titration using
Ba(OH)2 confirmed the formation of CO2 by 46.79 %. Whereas the redox titration
shows the total of degradation organic compounds by 42.50 %, which was
emphasized by formation of two new peaks in LC-MS chromatogram. In summary, our
results confirm the potential of MEO technology for NPE-10 degradation.",2012.11838v1
2021-01-08,The Impact of Bacteria Exposure on the Plasmonic Response of Silver Nanostructured Surfaces,"Silver, especially in the form of nanostructures, is widely employed as an
antimicrobial agent in a large range of commercial products. The origin of the
biocidal mechanism has been elucidated in the last decades, and most likely
originates from silver cation release due to oxidative dissolution followed by
cellular uptake of silver ions, a process that causes a severe disruption of
bacterial metabolism and eventually leads to eradication. Despite the large
number of works dealing with the effects of nanosilver shape/size on the
antibacterial mechanism and on the (bio)physical chemistry pathways that drive
bacterial eradication, little effort has been devoted to the investigation of
the silver NPs plasmon response upon interaction with bacteria. Here we present
a detailed investigation of the bacteria-induced changes of the plasmon
spectral and dynamical features after exposure to one of the most studied
bacterial models, Escherichia Coli. Ultrafast pump-probe measurements indicate
that the dramatic changes on particle size/shape and crystallinity, which stem
from a bacteria-induced oxidative dissolution process, translate into a clear
modification of the plasmon spectral and dynamical features. This study may
open innovative new avenues in the field of biophysics of bio-responsive
materials, with the aim of providing new and reliable biophysical signatures of
the interaction of these materials with complex biological environments.",2101.02926v1
2021-01-14,Superconducting dome with $extended$ $s$-$wave$ pairing symmetry in the heavily hole-overdoped copper-oxide planes,"We analyze the two-orbital (with $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals)
analogue of the $t$-$J$-$U$ model as applied to the description of the
copper-oxide monolayer deposited on the Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$
substrate (CuO$_2$/BSCCO). We show, that an $extended$ $s$-$wave$
superconducting dome appears in the heavily hole overdoped regime of the model,
with dominant contribution to the pairing coming from the $d_{3z^2-r^2}$
orbitals. Also, the lower critical doping for the appearance of the SC state
concurs with the Lifshitz Transition after which the hole-like Fermi pockets
are created around the $M$ points in the Brillouin zone. The obtained results
are in accord with the recent experimental result [cf. Y. Zhong et al., Sci.
Bull. 61, 1239 (2016)]. An analogous two-band description is also analyzed in
the context of the Ba$_2$CuO$_{4-y}$ bulk compound, where the heavily
hole-overdoped situation is believed to be reached [cf. W. M. Li et al. PNAS
116, 12156 (2019)]. As we show, a two dome structure can be realized in such
system with the $d$- and $s$-$wave$ symmetries of the gap corresponding to the
low hole-doping and heavily hole overdoped cases, respectively.",2101.05503v1
2021-01-25,Homogeneous superconducting gap in DBCO synthesized by oxide molecular beam epitaxy,"Much of what is known about high-temperature cuprate superconductors stems
from studies based on two surface analytical tools, angle-resolved
photoemission spectroscopy (ARPES) and spectroscopic imaging scanning tunneling
microscopy (SI-STM). A question of general interest is whether and when the
surface properties probed by ARPES and SI-STM are representative of the
intrinsic properties of bulk materials. We find this question is prominent in
thin films of a rarely studied cuprate DBCO. We synthesize DBCO films by oxide
molecular beam epitaxy and study them by in situ ARPES and SI-STM. Both ARPES
and SI-STM show that the surface DBCO layer is different from the bulk of the
film. It is heavily underdoped, while the doping level in the bulk is close to
optimal doping evidenced by bulk-sensitive mutual inductance measurements.
ARPES shows the typical electronic structure of a heavily underdoped CuO2 plane
and two sets of one-dimensional bands originating from the CuO chains with one
of them gapped. SI-STM reveals two different energy scales in the local density
of states, with one corresponding to the superconductivity and the other one to
the pseudogap. While the pseudogap shows large variations over the length scale
of a few nanometers, the superconducting gap is very homogeneous. This
indicates that the pseudogap and superconductivity are of different origins.",2101.10303v1
2021-01-28,"Oxidation stability of confined linear carbon chains, carbon nanotubes, and graphene nanoribbons as 1D nanocarbons","Three typical one-dimensional (1D)/quasi-1D nanocarbons, linear carbon
chains, carbon nanotubes, and graphene nanoribbons have been proven to grow
inside single-wall carbon nanotubes. This gives rise to three types of hybrid
materials whose behaviour and properties compared among each other are far from
understood. After proving successful the synthesis of these nanostructured
materials in recently published work, we have now been able to study their
oxidation stability systematically by using resonance Raman spectroscopy.
Surprisingly, the linear carbon chains, which have been theoretically predicted
to be very unstable, are actually thermally stable up to 500 {\deg}C assisted
by the protection of the carbon nanotube hosts. Besides, longer linear carbon
chains inside narrower CNTs are more stable than the shorter ones inside larger
tubes, suggesting that the thermal stability not only depends on the length of
linear carbon chains alone, but it is correlated with the confinement of the
host tubes in a more complicated manner. In addition, graphene nanoribbons come
overall in view as the most stable confined structures. On the other hand,
peculiarities like the higher stability of the (6,5) CNT over its (6,4)
counterpart allow this study to provide a solid platform for further studies on
the application of these 1D nanocarbons (including true 1D linear carbon
chains) at ambient conditions.",2101.11752v1
2021-01-29,Electrochemical tuning of alcohol oxidase and dehydrogenase catalysis via biosensing towards butanol-1 detection in fermentation media,"A novel approach for electrochemical tuning of alcohol oxidase (AOx) and
alcohol dehydrogenase (ADH) biocatalysis towards butanol-1 oxidation by
incorporating enzymes in various designs of amperometric biosensors is
presented. The biosensors were developed by using commercial graphene
oxide-based screen-printed electrodes and varying enzyme producing strains,
encapsulation approaches (layer-by-layer (LbL) or one-step electrodeposition
(EcD)), layers composition and structure, operating conditions (applied
potential values) and introducing mediators (Meldola Blue and Prussian Blue) or
Pd-nanoparticles (Pd-NPs). Simultaneous analysis/screening of multiple crucial
system parameters during the enzyme engineering process allowed to identify
within a period of one month that four out of twelve proposed designs
demonstrated a good signal reproducibility and linear response (up to 14.6 mM
of butanol) under very low applied potentials (from -0.02 to -0.32 V). Their
mechanical stability was thoroughly investigated by multi-analytical techniques
prior to butanol determination in cell-free samples from an anaerobic butanol
fermentation. The EcD-based biosensor that incorporates ADH, NAD+, Pd-NPs and
Nafion showed no loss of enzyme activity after preparation and demonstrated
capabilities towards low potential (-0.12 V) detection of butanol-1 in
fermentation medium (4 mM) containing multiple electroactive species with
almost 15 times enhanced sensitivity (0.2282 $\mu$A/mM $\pm$ 0.05) when
compared to the LbL design. Furthermore, the ADH-Nafion bonding for the S.
cerevisiae strain was confirmed to be 3 times higher than for E. coli.",2101.12350v1
2017-05-16,Modelling the descent of nitric oxide during the elevated stratopause event of January 2013,"Using simulations with a whole-atmosphere chemistry-climate model nudged by
meteorological analyses, global satellite observations of nitrogen oxide (NO)
and water vapour by the Sub-Millimetre Radiometer instrument (SMR), of
temperature by the Microwave Limb Sounder (MLS), as well as local radar
observations, this study examines the recent major stratospheric sudden warming
accompanied by an elevated stratopause event (ESE) that occurred in January
2013. We examine dynamical processes during the ESE, including the role of
planetary wave, gravity wave and tidal forcing on the initiation of the descent
in the mesosphere-lower thermosphere (MLT) and its continuation throughout the
mesosphere and stratosphere, as well as the impact of model eddy diffusion. We
analyse the transport of NO and find the model underestimates the large descent
of NO compared to SMR observations. We demonstrate that the discrepancy arises
abruptly in the MLT region at a time when the resolved wave forcing and the
planetary wave activity increase, just before the elevated stratopause reforms.
The discrepancy persists despite doubling the model eddy diffusion. While the
simulations reproduce an enhancement of the semi-diurnal tide following the
onset of the 2013 SSW, corroborating new meteor radar observations at high
northern latitudes over Trondheim (63.4$^{\circ}$N), the modelled tidal
contribution to the forcing of the mean meridional circulation and to the
descent is a small portion of the resolved wave forcing, and lags it by about
ten days.",1705.05706v1
2017-05-21,Post trimming of silicon photonics microresonators by nanoscale flash memory technology,"Flash memory technology is widely common in modern microelectronics, and is
essentially affecting our daily life. Considering the recent progress in
photonic circuitry, and in particular silicon photonics circuitry, there is now
an opportunity to embed the flash memory technology in photonic applications. A
particularly promising candidate that can benefit from such integration is the
photonic resonator. As of today, chip scale resonators are essential building
blocks in modern silicon photonic platform. However, their properties, and in
particular their resonance frequencies deviate from their designed values due
to unavoidable fabrication imperfections, imposing a stringent limitation on
the applicability of such devices. Here we present a solution for this major
obstacle and demonstrate electrical approach for post trimming of such
resonators. This is achieved by integrating the well-established flash memory
technology into the photonic circuitry. More specifically, we use the nanoscale
Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) structure in order to trap charges
in the thin silicon nitride layer, which is located in close proximity to the
silicon device layer. This enables the accumulation of charges in the silicon,
modifying the effective index of the optical mode and consequently the
resonance frequency. By doing so, we provide a robust and elegant CMOS
compatible memory solution, which can be easily manufactured and
commercialized. We expect such an approach to pave the way for even more
efficient utilization of resonators and interferometers in chip scale photonic
and electro optic systems, with wide range of applications such as filters,
modulators, sensors, and lasers, to name a few.",1705.08290v1
2017-05-30,"Synthesis, characterization and computational simulation of graphene nanoplatelets stabilized in poly(styrene sulfonate) sodium salt","The production of large area interfaces and the use of scalable methods to
build-up designed nanostructures generating advanced functional properties are
of high interest for many materials science applications. Nevertheless, large
area coverage remains a major problem for pristine graphene and here we present
a hybrid, composite graphene-like material soluble in water, which can be
exploited in many areas, such as energy storage, electrodes fabrication,
selective membranes and biosensing. Graphene oxide (GO) was produced by the
traditional Hummers method being further reduced in the presence of
poly(styrene sulfonate) sodium salt (PSS), thus creating stable reduced
graphene oxide (rGO) nanoplateles wrapped by PSS (GPSS). Molecular dynamics
simulations were carried out of further clarify the interactions between PSS
molecules and rGO nanoplatelets, with calculations supported by FTIR analysis.
The intermolecular forces between rGO nanoplatelets and PSS lead to the
formation of a hybrid material (GPSS) stabilized by van der Waals forces,
allowing the fabrication of high quality layer-by-layer (LbL) films with
polyalillamine hydrochloride (PAH). Raman and electrical characterizations
corroborated the successful modifications in the electronic structures from GO
to GPSS after the chemical treatment, resulting in (PAH/GPSS) LbL films four
orders of magnitude more conductive than (PAH/GO).",1705.10673v1
2017-09-14,Water nanoelectrolysis: A simple model,"A simple model of water nanoelectrolysis-defined as the nanolocalization at a
single point of any electrolysis phenomenon-is presented. It is based on the
electron tunneling assisted by the electric field through the thin film of
water molecules ($\sim$0.3 nm thick) at the surface of a tip-shaped
nanoelectrode (micrometric to nanometric curvature radius at the apex). By
applying, e.g., an electric potential V 1 during a finite time t 1 , and then
the potential --V 1 during the same time t 1 , we show that there are three
distinct regions in the plane (t 1 , V 1): one for the nanolocalization (at the
apex of the nanoelectrode) of the electrolysis oxidation reaction, the second
one for the nanolocalization of the reduction reaction, and the third one for
the nanolocalization of the production of bubbles. These parameters t 1 and V 1
completely control the time at which the electrolysis reaction (of oxidation or
reduction) begins, the duration of this reaction, the electrolysis current
intensity (i.e., the tunneling current), the number of produced O 2 or H 2
molecules, and the radius of the nanolocalized bubbles. The model is in good
agreement with our experiments.",1709.04827v2
2017-07-29,Optimizing Thermochromism of Solution-Processed VO$_2$ Nanocomposite Films for Chromogenic Fenestration,"Vanadium (IV) oxide is one of the most promising materials for thermochromic
films due to its unique, reversible crystal phase transition from monoclinic
(M1) to rutile (R) at its critical temperature (T$_c$) which corresponds to a
change in optical properties: above T$_c$, VO$_2$ films exhibit a decreased
transmittance for wavelengths of light in the near-infrared region. However, a
high transmittance modulation often sacrifices luminous transmittance which is
necessary for commercial and residential applications of this technology. In
this study, we explore the potential for synthesis of VO$_2$ films in a matrix
of metal oxide nanocrystals, using In$_2$O$_3$, TiO$_2$, and ZnO as diluents.
We seek to optimize the annealing conditions to yield desirable optical
properties. Although the films diluted with TiO$_2$ and ZnO failed to show
transmittance modulation, those diluted with In$_2$O$_3$ exhibited strong
thermochromism. Our investigation introduces a novel window film consisting of
a 0.93 metal ionic molar ratio VO$_2$-In$_2$O$_3$ nanocrystalline matrix,
demonstrating a significant increase in luminous transmittance without any
measurable impact on thermochromic character. Furthermore, solution-processing
mitigates costs, allowing this film to be synthesized 4x-7x cheaper than
industry standards. This study represents a crucial development in film
chemistry and paves the way for further application of VO$_2$ nanocomposite
films in chromogenic fenestration.",1709.06944v1
2017-09-21,Impacts of Surface Depletion on the Plasmonic Properties of Doped Semiconductor Nanocrystals,"Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized
surface plasmon resonance (LSPR) in the infrared range of the electromagnetic
spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics
enabled by doping, or via electrochemical or photochemical charging. Tuning
plasmonic properties through carrier density modulation suggests potential
applications in smart optoelectronics, catalysis, and sensing. Here, we
elucidate fundamental aspects of LSPR modulation through dynamic carrier
density tuning in Sn-doped Indium Oxide NCs. Monodisperse Sn-doped Indium Oxide
NCs with various doping level and sizes were synthesized and assembled in
uniform films. NC films were then charged in an in situ electrochemical cell
and the LSPR modulation spectra were monitored. Based on spectral shifts and
intensity modulation of the LSPR, combined with optical modeling, it was found
that often-neglected semiconductor properties, specifically band structure
modification due to doping and surface states, strongly affect LSPR modulation.
Fermi level pinning by surface defect states creates a surface depletion layer
that alters the LSPR properties; it determines the extent of LSPR frequency
modulation, diminishes the expected near field enhancement, and strongly
reduces sensitivity of the LSPR to the surroundings.",1709.07136v2
2017-09-21,Effect of nanostructure on thermoelectric properties of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in 300-600 K range,"In oxide materials, nanostructuring effect has been found very promising
approach for the enhancement of \textit{figure-of-merit}, \textit{ZT}. In the
present work, we have synthesized La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) compound
using sol-gel method and samples of crystallite size of 34, 41, and 49 nm were
obtained by giving different heat treatment. Seebeck coefficient ($\alpha$),
electrical resistivity ($\rho$), and thermal conductivity ($\kappa$)
measurements were carried out in 300-600 K temperature range. The systematic
change in the values of $\alpha$ from $\sim$ -19 $\mu$V/K to $\sim$ -24
$\mu$V/K and drastic reduction in the values of $\kappa$ from $\sim$0.88 W/mK
to $\sim$0.23 W/mK are observed as crystallite size is reduced from 49 nm to 34
nm at $\sim$600 K. Also, fall in the values of $\rho$ in the paramagnetic (PM)
insulator phase (400-600 K) are effectively responsible for the increasing
trend in the values of \textit{ZT} at high temperature. For the crystallite
size of 41 nm, value of \textit{ZT} at 600 K was found to be $\sim$0.017, which
can be further increased up to $\sim$0.045 around 650 K temperature. The
predicted value of \textit{ZT} suggests that LSMO can be suitable oxide
material for thermoelectric applications at high temperature.",1709.07205v2
2017-07-19,Pharmacokinetics and Molecular Docking studies of Plant-Derived Natural Compounds to Exploring Potential Anti-Alzheimer Activity,"Alzheimer disease (AD) is the leading cause of dementia, accounts for 60 to
80 percent cases. Two main factors called beta amyloid plaques and tangles are
prime suspects in damaging and killing nerve cells. However, oxidative stress,
the process which produces free radicals in cells, is believed to promote its
progression to the extent that it may responsible for the cognitive and
functional decline observed in AD. As of today there are few FDA approved drugs
in the market for treatment, but their cholinergic adverse effect, potentially
distressing toxicity and limited targets in AD pathology limits their use.
Therefore, it is crucial to find an effective compounds to combat AD. We choose
45 plant derived natural compounds that have antioxidant properties to slow
down disease progression by quenching free redicals or promoting endogenous
antioxidant capacity. However, we performed molecular docking studies to
investigate the binding interactions between natural compounds and 13 various
anti Alzheimer drug targets. Three known Cholinesterase inhibitors (Donepezil,
Galantamine and Rivastigmine) were taken as reference drugs over natural
compounds for comparison and drug likeness studies. Few of these compounds
showed good inhibitory activity besides anti oxidant activity. Most of these
compounds followed pharmacokinetics properties that make them potentially
promising drug candidates for the treatment of Alzheimer disease.",1709.10374v1
2017-11-02,Theory of Large Intrinsic Spin Hall Effect in Iridate Semimetals,"We theoretically investigate the mechanism to generate large intrinsic spin
Hall effect in iridates or more broadly in 5d transition metal oxides with
strong spin-orbit coupling. We demonstrate such a possibility by taking the
example of orthorhombic perovskite iridate with nonsymmorphic lattice symmetry,
SrIrO$_3$, which is a three-dimensional semimetal with nodal line spectrum. It
is shown that large intrinsic spin Hall effect arises in this system via the
spin-Berry curvature originating from the nearly degenerate electronic spectra
surrounding the nodal line. This effect exists even when the nodal line is
gently gapped out, due to the persistent nearly degenerate electronic
structure, suggesting a distinct robustness. The magnitude of the spin Hall
conductivity is shown to be comparable to the best known example such as doped
topological insulators and the biggest in any transition metal oxides. To gain
further insight, we compute the intrinsic spin Hall conductivity in both of the
bulk and thin film systems. We find that the geometric confinement in thin
films leads to significant modifications of the electronic states, leading to
even bigger spin Hall conductivity in certain cases. We compare our findings
with the recent experimental report on the discovery of large spin Hall effect
in SrIrO$_3$ thin films.",1711.00861v1
2017-11-08,Low-loss Tunable 1-D ITO-slot Photonic Crystal Nanobeam Cavity,"Tunable optical material properties enable novel applications in both
versatile metamaterials and photonic components including optical sources and
modulators. Transparent conductive oxides (TCOs) are able to highly tune their
optical properties with applied bias via altering their free carrier
concentration and hence plasma dispersion. The TCO material indium tin oxide
(ITO) exhibits unity-strong index changes, and epsilon-near-zero behavior.
However, with such tuning the corresponding high optical losses, originating
from the fundamental Kramers-Kronig relations, result in low cavity finesse.
However, achieving efficient tuning in ITO-cavities without using light matter
interaction enhancement techniques such as polaritonic modes, which are
inherently lossy, is a challenge. Here we discuss a novel one-dimensional
photonic crystal nanobeam cavity to deliver a cavity system offering a wide
range of resonance tuning range, while preserving physical compact footprints.
We show that a vertical Silicon-slot waveguide incorporating an actively
gated-ITO layer delivers ~3.4 nm of tuning. By deploying distributed feedback,
we are able to keep the Q-factor moderately high with tuning. Combining this
with the sub-diffraction limited mode volume (0.1 ({\lambda}/2n)3) from the
photonic (non-plasmonic) slot waveguide, facilitates a high Purcell factor
exceeding one thousand. This strong light-matter-interaction shows that
reducing the mode volume of a cavity outweighs reducing the losses in
diffraction limited modal cavities such as those from bulk Si3N4. These tunable
cavities enable future modulators and optical sources such as tunable lasers.",1711.02945v1
2017-11-08,Solution processable and optically switchable 1D photonic structures,"In this work, we report the first demonstration of a solution processable,
optically switchable 1D photonic crystal by implementing phototunable doped
metal oxide nanocrystals. The resulting device structure shows bi-photonic
response with the photonic bandgap covering the visible spectral range and the
plasmon resonance of the doped metal oxide the near infrared. By means of a
facile photodoping process, we tuned the plasmonic response and switched
effectively the optical properties of the photonic crystal, translating the
effect from the near infrared to the visible. The ultrafast bandgap pumping
induces a signal change in the region of the photonic stopband, with recovery
times of several picoseconds, providing a step toward the ultrafast optical
switching. Optical modeling uncovers the importance to understand largely the
variations of the dielectric function of the photodoped material, and
variations in the high frequency region of the Drude response are responsible
for the strong switching in the visible after photodoping. Our device
configuration offers unprecedented tunablility due to flexibility in device
design, cover wavelength ranges from the visible to the near infrared. Our
findings indicate a new protocol to modify the optical response of photonic
devices by optical triggers only.",1711.03192v1
2017-11-09,Gas-Phase Spectra of MgO Molecules: A Possible Connection from Gas-Phase Molecules to Planet Formation,"A more fine-tuned method for probing planet-forming regions, such as
protoplanetary discs, could be rovibrational molecular spectroscopy observation
of particular premineral molecules instead of more common but ultimately less
related volatile organic compounds. Planets are created when grains aggregate,
but how molecules form grains is an ongoing topic of discussion in astrophysics
and planetary science. Using the spectroscopic data of molecules specifically
involved in mineral formation could help to map regions where planet formation
is believed to be occurring in order to examine the interplay between gas and
dust. Four atoms are frequently associated with planetary formation: Fe, Si,
Mg, and O. Magnesium, in particular, has been shown to be in higher relative
abundance in planet-hosting stars. Magnesium oxide crystals comprise the
mineral periclase making it the chemically simplest magnesium-bearing mineral
and a natural choice for analysis. The monomer, dimer, and trimer forms of
(MgO)_n with n = 1 - 3 are analyzed in this work using high-level quantum
chemical computations known to produce accurate results. Strong vibrational
transitions at 12.5 {\mu}m, 15.0 {\mu}m, and 16.5 {\mu}m are indicative of
magnesium oxide monomer, dimer, and trimer making these wavelengths of
particular interest for the observation of protoplanetary discs and even
potentially planet-forming regions around stars. If such transitions are
observed in emission from the accretion discs or absorptions from stellar
spectra, the beginning stages of mineral and, subsequently, rocky body
formation could be indicated.",1711.03544v1
2017-11-12,Layer-by-Layer Assembly of Efficient Flame Retardant Coatings Based On High Aspect Ratio Graphene Oxide and Chitosan Capable of Preventing Ignition of PU Foam,"The layer-by-layer (LbL) technique is adopted for the construction of
multilayers encompassing chitosan and graphene oxide (GO) platelets capable of
improving the flame retardant properties open cell PU foams. The LbL assembly
follows a linear growth regime as evaluated by infrared spectroscopy and yields
a multilayer structure where GO platelets are embedded within a chitosan
continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D
structure of the foam and substantially improve its flame retardant properties.
3BL only add 10% to the original mass and can suppress the melt dripping during
flammability and reduce both the peak of heat release rate by 54% and the total
smoke released by 59% in forced combustion tests. Unprecedented among other LbL
assemblies employed for FR purposes, the deposition 6BL is capable of slowing
down the release of combustible volatile to the limits of non-ignitability thus
preventing ignition in half of the specimens during cone calorimetry tests.
This has been ascribed to the formation of a protective coating where the
thermally stable char produced by chitosan serves as a continuous matrix
embedding GO platelets, which control volatile release while mechanically
sustaining the PU foam structure.",1711.04318v2
2017-11-27,"A ferroelectric liquid crystal confined in cylindrical nanopores: Reversible smectic layer buckling, enhanced light rotation and extremely fast electro-optically active Goldstone excitations","The orientational and translational order of a thermotropic ferroelectric
liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores
with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are
explored by high-resolution linear and circular optical birefringence as well
as neutron diffraction texture analysis. The results are compared to
experiments on the bulk system. The native oxidic pore walls do not provide a
stable smectogen wall anchoring. By contrast, a polymeric wall grafting
enforcing planar molecular anchoring results in a thermal-history independent
formation of smectic C* helices and a reversible chevron-like layer buckling.
An enhancement of the optical rotatory power by up to one order of magnitude of
the confined compared to the bulk liquid crystal is traced to the
pretransitional formation of helical structures at the smectic-A*-to-smectic-C*
transformation. A linear electro-optical birefringence effect evidences
collective fluctuations in the molecular tilt vector direction along the
confined helical superstructures, i.e. the Goldstone phason excitations typical
of the para-to-ferroelectric transition. Their relaxation frequencies increase
with the square of the inverse pore radii as characteristic of plane-wave
excitations and are two orders of magnitude larger than in the bulk, evidencing
an exceptionally fast electro-optical functionality of the
liquid-crystalline-AAO nanohybrids.",1711.09673v1
2017-11-29,Electron-Hole Separation in Ferroelectric Oxides for Efficient Photovoltaic Responses,"Despite their potential to exceed the theoretical Shockley-Queisser limit,
ferroelectric photovoltaics (FPVs) have performed inefficiently due to their
extremely low photocurrents. Incorporating Bi2FeCrO6 (BFCO) as the light
absorber in FPVs has recently led to impressively high and record photocurrents
[Nechache et al. Nature Photon. 2015, 9, 61], reviving the FPV field. However,
our understanding of this remarkable phenomenon is far from satisfactory. Here,
we use first-principles calculations to determine that such excellent
performance mainly lies in the efficient separation of electron-hole (e-h)
pairs. We show that photoexcited electrons and holes in BFCO are spatially
separated on the Fe and Cr sites, respectively. This separation is much more
pronounced in disordered BFCO phases, which show exceptional PV responses. We
further set out to design a strategy for next-generation FPVs, not limited to
BFCO, by exploring 44 additional Bi-based double-perovskite oxides. We suggest
9 novel active-layer materials that can offer strong e-h separations and a
desired band gap energy for application in FPVs. Our work indicates that charge
separation is the most important issue to be addressed for FPVs to compete with
conventional devices.",1711.10979v1
2018-05-31,Electrochemical tuning of capacitive response of graphene oxide,"Increasing energy demands of modern society requires deep understanding of
the properties of energy storage materials as well as their performance tuning.
We show that the capacitance of graphene oxide (GO) can be precisely tuned
using a simple electrochemical reduction route. In situ resistance
measurements, combined with cyclic voltammetry measurement and Raman
spectroscopy, have shown that upon the reduction GO is irreversibly
deoxygenated which is further accompanied with structural ordering and
increasing of electrical conductivity. The capacitance is maximized when the
concentration of oxygen functional groups is properly balanced with the
conductivity. Any further reduction and de-oxygenation leads to the gradual
loss of the capacitance. The observed trend is independent on the preparation
route and on the exact chemical and structural properties of GO. It is proposed
that an improvement of capacitive properties of any GO can be achieved by
optimization of its reduction conditions.",1806.00130v2
2018-06-30,Study and characterization of SrTiO3 surface,"The two-dimensional electron gas (2DEG) at oxides interfaces and surfaces has
attracted large attention in physics and research due to its unique electronic
properties and possible application in optoelectronics and nanoelectronics. The
origin of 2DEGes at oxide interfaces has been attributed to the well known
""polar catastrophe"" mechanism. On the other hand, recently a 2DEG was also
found on a clean SrTiO3(001) surface where it is formed due to oxygen
vacancies. However, these 2DEG systems have been until now found mostly on
atomically perfect crystalline samples usually grown by pulsed laser deposition
or molecular beam epitaxy i.e. samples which are difficult to be prepared and
require specific experimental conditions. Here, we report on the fabrication of
SrTiO3 thin films deposited by magnetron sputtering which is suitable for
mass-production of samples adapted for nanoelectronic applications. The
characterization of their structural and electronic properties was done and
compared to those of SrTiO3 single crystals. XRD patterns and SEM micrography
show that the deposited films are amorphous and their structure changes to
polycrystalline by heating them at 900 {\deg}C. Photoemission spectroscopy (XPS
and UPS) was used to study the electronic properties of the films and the
crystal. In both, we observe the 2DEG system at Fermi level and the formation
of Ti3+ states after heating the surface at 900 {\deg}C.",1807.00150v1
2018-07-03,Comparison of the Thermospheric Nitric Oxide Emission Observations and the Global Ionosphere-Thermosphere Model (GITM) Simulations: Sensitivity to Solar and Geomagnetic Activities,"An accurate estimate of the energy budget (heating and cooling) of the
ionosphere and thermosphere, especially during space weather events, has been a
challenge. The abundance of Nitric Oxide (NO), a minor species in the
thermosphere, is an important component of energy balance here because its
production comes from energy sources able to break the strong bond of molecular
nitrogen, and infrared emissions from NO play an important role in
thermospheric cooling. Recent studies have significantly improved our
understanding of NO chemistry and its relationship to energy deposition in the
thermospheric photochemical reactions. In this study, the chemical scheme in
the Global Ionosphere Thermosphere Model (GITM) is updated to better predict
the lower thermospheric NO responses to solar and geomagnetic activity. We
investigate the sensitivity of the 5.3-micron NO emission to F10.7 and Ap
indices by comparing the global integrated emission from GITM with an empirical
proxy derived from the Sounding of the Atmosphere using Broadband Emission
Radiometry measurements. GITM's total emission agrees well within 20% of the
empirical values. The updated chemistry scheme significantly elevates the level
of integrated emission compared to the previous scheme. The inclusion of
N2(A)-related production of NO contributes an additional 5-25% to the emission.
Localized enhancement of ~70% in column density and a factor of three in column
emission are simulated at a moderate geomagnetic level.",1807.01380v1
2018-07-06,Fabrication of Hollow AlAu2 Nanoparticles by Solid State Dewetting and Oxidation of Al on Sapphire Substrate,"The Al-Au binary diffusion couple is a classic example of the system
exhibiting Kirkendall voiding during interdiffusion. We demonstrate that this
effect, which is a major reason for failures of the wire bonds in
microelectronics, can be utilized for producing hollow AlAu2 nanoparticles
attached to sapphire substrate. To this end, we produced the core-shell Al-Au
nanoparticles by performing a solid state dewetting treatment of Al thin film
deposited on sapphire substrate, followed by the deposition of thin Au layer on
the top of dewetted sample. Annealing of the core-shell nanoparticles in air
resulted in outdiffusion of Al from the particles, formation of pores, and
growth of the AlAu2 intermetallic phase in the particles. We demonstrated that
the driving force for hollowing is the oxidation reaction of the Al atoms at
the Au-sapphire interface, leading to the homoepitaxial growth of newly formed
alumina at the interface. We developed a kinetic model of hollowing controlled
by diffusion of oxygen through the Au thin film, and estimated the solubility
of oxygen in solid Au. Our work demonstrates that the core-shell nanoparticles
attached to the substrate can be hollowed by the Kirkendall effect in the thin
film spatially separated from the particles.",1807.02279v2
2018-07-06,Nitric Oxide in Climatological Global Energy Budget During 1982-2013,"Over the past decades, temperature and density of the upper atmosphere show
negative trends and decrease of the upper atmospheric temperature is attributed
to the declining neutral density. Specifically, nitric oxide (NO) and carbon
dioxide (CO2) govern thermospheric cooling at 5.3 and 15 micron, respectively.
While a lot of efforts have focused on the CO2 effects on the long-term trends,
relatively less attention has been paid to the impacts by NO, which responds to
solar and geomagnetic activities dynamically. In this study, we investigate the
role of NO in climatological global energy budget for the recent three solar
cycles using the Global Ionosphere Thermosphere Model. From 1982 to 2013, the
F10.7 and Ap indices showed a decadal decrease of ~8% and ~20%, respectively.
By imposing temporal-varying F10.7 and Ap values in the simulations, we find a
decadal change of -0.28x1011 W or -17.3% in total NO cooling power, which
agrees well with that (-0.34x1011 W or -17.2%) from the empirical Thermosphere
Climate Index derived from the TIMED/SABER data. Neutral density decreases by
10-20% at 200-450km and Tex decreases by 25.3 K per decade. The deduced-decadal
change of NO cooling reaches ~25% of the sum of total heating at ~130 km and
its significance decreases with altitude.",1807.02495v1
2018-07-23,Effect of Fluoropolymer Composition on Topochemical Synthesis of SrMnO$_{3-δ}$F$_{γ}$ Oxyfluoride Films,"We report the synthesis of SrMnO$_{3-{\delta}}$F$_{{\gamma}}$ perovskite
oxyfluoride thin films using a vapor transport method to fluorinate as-grown
SrMnO$_{2.5}$ epitaxial thin films. The influence of the fluoropolymer, which
acts as a fluorine vapor source, was investigated by utilizing polyvinyl
fluoride (PVF), polyvinylidene difluoride (PVDF) and polytetrafluoroethylene
(PTFE) in the reaction. The same process was carried out with polyethylene (PE)
to isolate the role of carbon in the vapor transport process. The F
distribution was probed by X-ray photoemission spectroscopy, which confirmed
the incorporation of F into the films and revealed higher F concentrations in
films exposed to PVF and PVDF compared to PTFE. The c-axis parameter expands
after fluorination, a result consistent with density functional theory
calculations that attribute the volume expansion to elongated Mn-F bonds
compared to shorter Mn-O bonds. Using X-ray absorption spectroscopy, we show
that the fluorination process reduces the nominal Mn oxidation state suggesting
that F substitutes on O sites in the lattice as opposed to filling anion
vacancy sites, a finding further supported by calculated formation energies of
different F site occupancies. These results provide new insights into
topochemical fluorination of perovskite oxides, which should enable future
synthesis and design efforts focused on oxyfluoride heterostructures.",1807.08815v1
2018-07-26,Expediting hydrogen evolution through topological surface states on Bi2Te3,"Recently, the development of efficient and non-noble metal electrocatalysts
with excellent durability for the hydrogen evolution reaction (HER) has
attracted increasing attention. The exotic and robust metallic surface states
of topological insulators (TIs) are theoretically predicted to enhance surface
catalytic activity of overlaying catalysts, but no experimental evidence for
TIs directly used as electrocatalysts has ever been reported. In this work, we
fabricated the TI thin films of Bi2Te3 with different thicknesses using the
molecular beam epitaxy method, and found that these thin films exhibit high
electrocatalytic activity in HER. The 48 nm Bi2Te3 thin film has the best
performance, which is attributed to its largest active area arising from the
spiral growth mode of triangular domains as revealed by atomic force microscopy
imaging. Importantly, our theoretical calculations reveal that while pure
Bi2Te3 is not a good electrocatalyst, the Bi2Te3 thin films with partially
oxidized surfaces or Te vacancies have high HER activity. The existence of the
corresponding surface oxides on the Bi2Te3 thin films is supported by our X-ray
photoelectron spectroscopy data. Particularly, we demonstrate that the
topological surface states play a key role in enhancing the HER performance.
Our study offers a new direction to design cost-effective electrocatalysts.",1807.09957v2
2018-08-07,Retrieval of nitric oxide in the mesosphere and lower thermosphere from SCIAMACHY limb spectra,"We use the ultra-violet (UV) spectra in the range 230--300 nm from the
SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY
(SCIAMACHY) to retrieve the nitric oxide (NO) number densities from atmospheric
emissions in the gamma-bands in the mesosphere and lower thermosphere. Using
3-D ray tracing, a 2-D retrieval grid, and regularisation with respect to
altitude and latitude, we retrieve a whole semi-orbit simultaneously for the
altitude range from 60 to 160 km.
  We present details of the retrieval algorithm, first results, and initial
comparisons to data from the Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS). Our results agree on average well with MIPAS data and are in
line with previously published measurements from other instruments. For the
time of available measurements in 2008--2011, we achieve a vertical resolution
of 5--10 km in the altitude range 70--140 km and a horizontal resolution of
about 9{\deg} from 60{\deg}S--60{\deg}N. With this we have independent
measurements of the NO densities in the mesosphere and lower thermosphere with
approximately global coverage. This data can be further used to validate
climate models or as input for them.",1808.02388v1
2018-08-15,"Electron Localization Enhances Cation Diffusion in Reduced ZrO2, CeO2 and BaTiO3","According to defect chemistry, the experimental observations of enhanced
cation diffusion in a reducing atmosphere in zirconia, ceria and barium
titanate are in support of an interstitial mechanism. Yet previous
computational studies always found a much higher formation energy for cation
interstitials than for cation vacancies, which would rule out the interstitial
mechanism. The conundrum has been resolved via first-principles calculations
comparing migration of reduced cations and oxidized ones, in cubic ZrO2, CeO2
and BaTiO3. In nearly all cases, reduction alone lowers the migration barrier,
and pronounced lowering results if cation's electrostatic energy at the saddle
point decreases. The latter is most effectively realized when a Ti cation is
allowed to migrate via an empty Ba site thus being fully screened all the way
by neighboring anions. Since reduction creates oxygen vacancies as well, which
are highly mobile, we also studied their effect on cation migration, and found
it only marginally lowers the migration barrier. In several cases, however, a
large synergistic effect between cation reduction and oxygen vacancy is
revealed, causing an electron to localize in the saddle-point state at a much
lower energy than normal, signaling that the saddle point is a negative-U state
in which the soft environment enables a large electron-phonon interaction that
can over-compensate the on-site Coulomb repulsion. These general findings are
expected to be applicable to defect-mediated ion migration in most transitional
metal oxides.",1808.05198v1
2018-08-16,A disclosure of the role of frequency on the plasma electrolytic oxidation of AZ31 magnesium alloy in aluminate-tungstate electrolyte,"Plasma electrolytic oxidation (PEO) was carried out to form black ceramic
coatings on AZ31 magnesium alloy in aluminate-tungstate electrolyte. Influences
of current frequency (such as 100, 1000 and 2000 Hz) on properties of the PEO
coatings have been explored. It was found that increment of frequency led to
coatings with higher thickness, higher roughness and darker appearance. In
order to explore the coating formation mechanism at different frequencies, the
micro-discharges at different frequencies were investigated by real-time
imaging method. Microstructure of coatings was characterized by scanning
electron microscopy (SEM) assisted with energy dispersive X-ray spectroscopy
(EDS). Coatings formed at 100 Hz show the most compact microstructure while
porosity of the coatings, both in the pore number and pore size, is greatly
increased at higher frequencies. The coatings formed at higher frequencies show
an increased atomic ratio of W/Al. The cancel of the negative pulse from the
pulsed waveform can also lead to a higher W/Al ratio, and hence a darker
coating. The higher porosity of the coatings was attributed to the stronger
plasma discharges and gas evolution at higher frequencies. The stronger plasma
discharge is induced by the fact that there is not sufficient time for the
cooling down of discharge channels at higher frequencies.",1808.06587v1
2018-10-31,Challenges in materials and devices for Resistive-Switching-based Neuromorphic Computing,"This tutorial describes challenges and possible avenues for the
implementation of the components of a solid-state system, which emulates a
biological brain. The tutorial is devoted mostly to a charge-based (i.e.
electric controlled) implementation using transition metal oxides materials,
which exhibit unique properties that emulate key functionalities needed for
this application. In the Introduction, we compare the main differences between
a conventional computational machine, based on the Turing-von Neumann paradigm,
to a Neuromorphic machine, which tries to emulate important functionalities of
a biological brain. We also describe the main electrical properties of
biological systems, which would be useful to implement in a charge-based
system. In Chapter II, we describe the main components of a possible
solid-state implementation. In Chapter III, we describe a variety of Resistive
Switching phenomena, which may serve as the functional basis for the
implementation of key devices for Neuromorphic computing. In Chapter IV we
describe why transition metal oxides, are promising materials for future
Neuromorphic machines. Theoretical models describing different resistive
switching mechanisms are discussed in Chapter V while existing implementations
are described in Chapter VI. Chapter VII presents applications to practical
problems. We list in Chapter VIII important basic research challenges and open
issues. We discuss issues related to specific implementations, novel materials,
devices and phenomena. The development of reliable, fault tolerant, energy
efficient devices, their scaling and integration into a Neuromorphic computer
may bring us closer to the development of a machine that rivals the brain.",1812.01120v1
2018-12-07,A Ferroelectric Semiconductor Field-Effect Transistor,"Ferroelectric field-effect transistors employ a ferroelectric material as a
gate insulator, the polarization state of which can be detected using the
channel conductance of the device. As a result, the devices are of potential to
use in non-volatile memory technology, but suffer from short retention times,
which limits their wider application. Here we report a ferroelectric
semiconductor field-effect transistor in which a two-dimensional ferroelectric
semiconductor, indium selenide ({\alpha}-In2Se3), is used as the channel
material in the device. {\alpha}-In2Se3 was chosen due to its appropriate
bandgap, room temperature ferroelectricity, ability to maintain
ferroelectricity down to a few atomic layers, and potential for large-area
growth. A passivation method based on the atomic-layer deposition of aluminum
oxide (Al2O3) was developed to protect and enhance the performance of the
transistors. With 15-nm-thick hafnium oxide (HfO2) as a scaled gate dielectric,
the resulting devices offer high performance with a large memory window, a high
on/off ratio of over 108, a maximum on-current of 862 {\mu}A {\mu}m-1, and a
low supply voltage.",1812.02933v2
2018-12-12,Potential jumps at transport bottlenecks cause instability of nominally ionic solid electrolytes in electrochemical cells,"Normal operations of electrochemical devices such as solid oxide fuel cells
(SOFC), solid oxide electrolyzer cells (SOEC) and lithium ion batteries (LIB)
sometimes fail because of unexpected formation of internal phases. These phases
include oxygen bubbles at grain boundaries inside the zirconia electrolyte of
SOEC, isolated Li metal islands inside the (garnet type) Li7La3Zr2O12
electrolyte of all-solid-state LIB, and similar Na metal islands inside the
Na-beta-alumina and NASICON electrolytes of Na-S batteries. Remarkably,
although the devices can operate in both polarities, the propensity for failure
depends on the polarity. Here we explain these and other phenomena in nominally
ionic solid electrolytes and mixed-conducting electrodes in simple
thermodynamic and kinetic terms: the unexpected internal phases are caused by a
large potential jump that is needed to push a constant ion or electron flow
through its internal transport bottleneck. Definite rules for internal phase
formation including its polarity dependence are formulated to help predict and
mitigate it, which leads to microstructural instability, efficiency
deterioration and breakdown.",1812.05187v5
2018-12-18,A hybrid silicon-sapphire cryogenic Fabry-Perot cavity using hydroxide catalysis bonding,"The third-generation gravitational wave detectors are under development by
operating the detector in cryogenic temperature to reduce the thermal noise.
Silicon and sapphire are promising candidate materials for the test masses and
suspension elements due to their remarkable mechanical and thermal properties
at cryogenic temperature. Here we present the performances of the cryogenic
thermal cycling and strength testing on hydroxide catalysis bonding between
sapphire and silicon. Our results suggest that although these two materials
have very different coefficients of thermal expansion, but if the flatness and
the thermally grown $\mathrm{SiO_2}$ oxidation layer on the silicon surface are
controlled well, the bonded samples can still survive thermal cycling from room
temperature to 5.5 K. A breaking strength of 3.6$\pm 0.6$ MPa is measured for
the bonds between sapphire and silicon with a 190 nm silicon oxidation
thickness after cooling cycle. We construct a hybrid sapphire-silicon
Fabry-Perot cavity with the developing bonding technique in our lab. The
measurement results reveal that the cavity can survive repeated thermal cycling
while maintaining a good finesse.",1812.07347v1
2018-12-27,Molecular dynamics analysis of adsorption process of anti-copper-corrosion additives to the copper surface,"As a model system of the adsorption process of anti-corrosion additives on a
metal surface, molecular dynamics simulations of benzotriazole (BTA) molecules
with copper slabs were completed. As a force field, ReaxFF was used to simulate
both adsorption dynamics and the charge transfer on the solid surface. Two
simulations are presented. In order to investigate the physical adsorption on
the surface, the simulation was done for the adsorption process of BTA
molecules on the copper (II) oxide slab. BTA molecules formed on adsorbed layer
in parallel to the surface, and aggregation of the molecules due to the surface
diffusion was found. In order to investigate the selective and chemical
adsorption on the surface, a hybrid slab, which has both a copper (Cu) area and
a copper (I) oxide (Cu2O) area, was used. A selective adsorption phenomenon was
found. The number of BTA molecules adsorbed on the Cu area is 5 times greater
than that on the Cu2O area. Detailed dynamics focused on charge transfer showed
a surface diffusion and enhancement of polarization due to charge transfer from
the metal surface caused the selective adsorption. In a real phenomenon, the
reason why a few anti-corrosion additives are able to protect a metal surface
is postulated to be due to this selective nature of adsorption onto a newly
formed metal surface.",1812.10647v1
2018-12-29,A microscopic perspective on heterogeneous catalysis,"A general formalism is presented to describe the turnover frequency (TOF)
during heterogeneous catalysis beyond a mean field treatment. For every
elementary reaction we define its multiplicity as the number of times the
reaction can be performed in the current configuration of the catalyst surface,
divided by the number of active sites. It is shown that any change in the
multiplicity with temperature can be directly understood as a modification in
configurational entropy. Based on this, we determine the probability of
observing any particular elementary reaction, leading to a procedure for
identifying any Rate Controlling Step (RCS) as well as the Rate Determining
Step (RDS), if it exists. Furthermore, it is shown that such probabilities
provide a thorough description of the overall catalytic activity, enabling a
deep understanding of the relative importance of every elementary reaction.
Most importantly, we formulate a simple expression to describe accurately the
apparent activation energy of the TOF, valid even when adsorbate-adsorbate
interactions are included, and compare it to previous, approximate expressions,
including the traditional Temkin formula for typical reaction mechanisms
(Langmuir-Hinshelwood, Eley-Rideal, etc...). To illustrate the validity of our
formalism beyond the mean field domain we present Kinetic Monte Carlo
simulations for two widely-studied and industrially-relevant catalytic
reactions, namely, the oxidation of CO on RuO$_2$(110) and the selective
oxidation of NH$_{3}$ on the same catalyst.",1812.11398v1
2019-01-02,Mott gapping in 3d ABO3 perovskites without Mott-Hubbard interelectronic U,"The existence of band gaps in Mott insulators such as perovskite oxides with
partially filled 3d shells has been traditionally explained in terms of strong,
dynamic inter-electronic repulsion codified by the on-site repulsion energy U
in the Hubbard Hamiltonian. The success of the ""DFT+U approach"" where an
empirical on-site potential term U is added to the exchange-and correlation
Density Functional Theory (DFT) raised questions on whether U in DFT+U
represents interelectronic correlation in the same way as it does in the
Hubbard Hamiltonian, and if empiricism in selecting U can be avoided. Here we
illustrate that ab-initio DFT without any U is able to predict gapping trends
and structural symmetry breaking (octahedra rotations, Jahn-Teller modes, bond
disproportionation) for all ABO3 3d perovskites from titanates to nickelates in
both spin-ordered and spin disordered paramagnetic phases. We describe the
paramagnetic phases as a supercell where individual sites can have different
local environments thereby allowing DFT to develop finite moments on different
sites as long as the total cell has zero moment. We use a recently developed
exchange and correlation functional (""SCAN"") that is sanctioned by the usual
single-determinant, mean-field DFT paradigm with static correlations, but has a
more precise rendering of self-interaction cancelation. Our results suggest
that strong dynamic electronic correlations are not playing a universal role in
gapping of 3d ABO3 Mott insulators, and opens the way for future applications
of DFT for studying a plethora of complexity effects that depend on the
existence of gaps, such as doping, defects, and band alignment in ABO3 oxides.",1901.00425v2
2019-01-03,Classification of Local Chemical Environments from X-ray Absorption Spectra using Supervised Machine Learning,"X-ray absorption spectroscopy is a premier element-specific technique for
materials characterization. Specifically, the x-ray absorption near-edge
structure (XANES) encodes important information about the local chemical
environment of an absorbing atom, including coordination number, symmetry, and
oxidation state. Interpreting XANES spectra is a key step towards understanding
the structural and electronic properties of materials, and as such, extracting
structural and electronic descriptors from XANES spectra is akin to solving a
challenging inverse problem. Existing methods rely on empirical fingerprints,
which are often qualitative or semiquantitative and not transferable. In this
paper, we present a machine learning-based approach, which is capable of
classifying the local coordination environments of the absorbing atom from
simulated K-edge XANES spectra. The machine learning classifiers can learn
important spectral features in a broad energy range without human bias and once
trained, can make predictions on the fly. The robustness and fidelity of the
machine learning method are demonstrated by an average 86% accuracy across the
wide chemical space of oxides in eight 3d transition-metal families. We found
that spectral features beyond the preedge region play an important role in the
local structure classification problem especially for the late 3d
transition-metal elements.",1901.00788v2
2019-01-07,Unexplored reactivity of (Sn)2- Oligomers with transition metals in low-temperature solid-state reactions,"Chalcogenides (Q = S, Se, Te), one of the most important family of materials
in solid-state chemistry, differ from oxides by their ability to form
covalently-bonded (Qn)2- oligomers. Each chalcogen atom within such entity
fulfills the octet rule by sharing electrons with other chalcogen atoms but
some antibonding levels are vacant. This makes these oligomers particularly
suited for redox reactions in solid state, namely towards elemental metals with
a low redox potential that may be oxidized. We recently used this strategy to
design, at low temperature and in an orientated manner, materials with 2D
infinite layers through the topochemical insertion of copper into preformed
precursors containing (S2)2- and/or (Se2)2- dimers (i.e. La2O2S2, Ba2F2S2 and
LaSe2). Herein we extend the validity of the concept to the redox activity of
(S2)2- and (S3)2- oligomers towards 3d transition metal elements (Cu, Ni, Fe)
and highlight the strong relationship between the structures of the precursors,
BaS2 and BaS3, and the products, BaCu2S2, BaCu4S3, BaNiS2 and BaFe2S3. Clearly,
beyond the natural interest for the chemical reactivity of oligomers to
generate compounds, this soft chemistry route may conduct to the rational
conception of materials with a predicted crystal structure.",1901.01907v1
2019-01-14,Transferable MARTINI Model of Poly(ethylene Oxide),"Motivated by the deficiencies of the previous MARTINI models of poly(ethylene
oxide) (PEO), we present a new model featuring a high degree of
transferability. The model is parametrized on (a) a set of 8 free energies of
transfer of dimethoxyethane (PEO dimer) from water to solvents of varying
polarity; (b) the radius of gyration in water at high dilution; and (c)
matching angle and dihedral distributions from atomistic simulations. We
demonstrate that our model behaves well in five different areas of application:
(1) it produces accurate densities and phase behavior or small PEO oligomers
and water mixtures; (2) it yields chain dimensions in good agreement with the
experiment in three different solvents (water, diglyme, and benzene) over a
broad range of molecular weights (1.2 kg/mol to 21 kg/mol); (3) it reproduces
qualitatively the structural features of lipid bilayers containing PEGylated
lipids in the brush and mushroom regime; (4) it is able to reproduce the phase
behavior of several PEO-based nonionic surfactants in water; and (5) it can be
combined with the existing MARTINI PS to model PS/PEO block copolymers.
Overall, the new PEO model outperforms previous models and features a high
degree of transferability.",1901.04413v1
2019-01-17,Stability of Implanted Transition Metal Dopants in Rock-salt Oxides,"Transition metals (TMs) implanted in oxides with rock-salt crystal structures
(for example MgO and BaO) are assumed to substitute cations (Mg in case of MgO)
from the lattice sites. We show that not all implanted TMs substitute cations
but can be stable in interstitial sites as well. Stability of TM (Sc--Zn)
dopants in various charge states in MgO and BaO has been investigated in the
framework of density functional theory. We propose an effective way to
calculate stability of implanted metals that let us predict site preference
(interstitial or substitution) of the dopant in the host. We find that two
factors govern the preference for an interstitial site: i) relative ionic
radius and ii) relative oxygen affinity of cation and the TM dopants. If the
radius of the cation is much larger than TM dopant, as in BaO, TM atoms always
sit at interstitial sites. On the other hand, if the radius of the cation is
comparable to that of the dopant TM, as in case of MgO, the transition of the
preferred defect site, from substituting lattice Mg atom (Sc to Mn) to
occupying interstitial site (Fe to Zn) is observed. This transition can be
attributed to the change in the oxygen affinity of the TM atoms from Sc to Zn.
Our results also explain experiments on Ni and Fe atoms implanted in MgO. This
is the first-time we have shown that TM dopants can be stable at interstitial
sites in stable compounds, which could potentially give rise to exotic
properties.",1901.05607v2
2019-01-25,"Tailoring Vanadium Dioxide Film Orientation using Nanosheets: A Combined Microscopy, Diffraction, Transport and Soft X-ray in Transmission Study","VO2 is a much-discussed material for oxide electronics and neuromorphic
computing applications. Here, heteroepitaxy of vanadium dioxide (VO2) was
realized on top of oxide nanosheets that cover either the amorphous silicon
dioxide surfaces of Si substrates or X-ray transparent silicon nitride
membranes. The out-of-plane orientation of the VO2 thin films was controlled at
will between (011)M1/(110)R and (-402)M1/(002)R by coating the bulk substrates
with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth.
Temperature dependent X-ray diffraction and automated crystal orientation
mapping in microprobe TEM mode (ACOM-TEM) characterized the high phase purity,
the crystallographic and orientational properties of the VO2 films. Transport
measurements and soft X-ray absorption in transmission are used to probe the
VO2 metal-insulator transition, showing results of a quality equal to those
from epitaxial films on bulk single-crystal substrates. Successful local
manipulation of two different VO2 orientations on a single substrate is
demonstrated using VO2 grown on lithographically-patterned lines of Ti0.87O2
and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally,
the excellent suitability of these nanosheet-templated VO2 films for advanced
lensless imaging of the metal-insulator transition using coherent soft X-rays
is discussed.",1901.08823v1
2019-01-30,Meeting the Scaling Challenge for Post-Silicon Nanoelectronics using CaF2 Insulators,"Two-dimensional (2D) semiconductors have been suggested both for
ultimately-scaled field-effect transistors (FETs) and More-than-Moore
nanoelectronics. However, these targets can not be reached without accompanying
gate insulators which are scalable into the nanometer regime. Despite the
considerable progress in the search for channel materials with high mobilities
and decent bandgaps, finding high-quality insulators compatible with 2D
technologies has remained a challenge. Typically used oxides (e.g. SiO2, Al2O3
and HfO2) are amorphous when scaled, while two-dimensional hBN exhibits
excessive gate leakages. To overcome this bottleneck, we extend the natural
stacking properties of 2D heterostructures to epitaxial fluorite (CaF2), which
forms a quasi van der Waals interface with 2D semiconductors. We report
scalable single-layer MoS2 FETs with a crystalline CaF2 insulator of about 2 nm
thickness, which corresponds to an equivalent oxide thickness of less than 1
nm. While meeting the stringent requirements of low leakage currents, our
devices exhibit highly competitive performance and record-small hysteresis. As
such, our results present a breakthrough for very large scale integration
towards commercially competitive nano-electronic devices.",1901.10980v1
2019-02-07,Theoretical insights into the hydrophobicity of low index CeO2 surfaces,"The hydrophobicity of CeO2 surfaces is examined here. Since wettability
measurements are extremely sensitive to experimental conditions, we propose a
general approach to obtain contact angles between water and ceria surfaces of
specified orientations based on density functional calculations. In particular,
we analysed the low index surfaces of this oxide to establish their
interactions with water. According to our calculations, the CeO2 (111) surface
was the most hydrophobic with a contact angle of {\Theta} = 112.53{\deg}
followed by (100) with {\Theta} = 93.91{\deg}. The CeO2 (110) surface was, on
the other hand, mildly hydrophilic with {\Theta} = 64.09{\deg}. By combining
our calculations with an atomistic thermodynamic approach, we found that the O
terminated (100) surface was unstable unless fully covered by molecularly
adsorbed water. We also identified a strong attractive interaction between the
hydrogen atoms in water molecules and surface oxygen, which gives rise to the
hydrophilic behaviour of (110) surfaces. Interestingly, the adsorption of water
molecules on the lower-energy (111) surface stabilises oxygen vacancies, which
are expected to enhance the catalytic activity of this plane. The findings here
shed light on the origin of the intrinsic wettability of rare earth oxides in
general and CeO2 surfaces in particular and also explain why CeO2 (100) surface
properties are so critically dependant on applied synthesis methods.",1902.02662v1
2019-02-13,Amphoteric behavior of hydrogen (H+1and H-1) in complex hydrides from van der Waals interaction included ab-initio calculation,"In order to identify potential hydrogen storage materials, worldwide
attention has been focused on hydrides with high gravimetric and volumetric
capacity. Hydrogen is a unique element that possess positive, negative or
neutral oxidation state in solids depending upon the chemical environment. If
one can find hydrogen storage materials where hydrogen is present in both
negative and positive oxidation state within the same structural framework then
one can accommodate hydrogen with high volume density. So, it is fundamentally
as well as technologically important to identify compounds in which hydrogen is
in amphoteric nature and understand the necessary criteria for its origin. The
experimental structural analysis of Cyclotriborazane and Diammonium dodeca
hydro-closo-dodecaborate insinuate the presence of hydrogen with anionic and
cationic behavior within the same structure. In order to understand the role of
van der Waals (vdW) interactions on structural parameters, we have considered
12 different vdW corrected functionals and found that the optPBE-vdW functional
predicts the equilibrium structural parameters reliably with less than 0.009 %
accuracy. So, the optPBE-vdW functional is used to calculate charge density,
electron localization function, total as well as the partial density of state,
Bader and Born effective charge etc. We have observed that hydrogen is
exhibiting amphoteric behavior with H closer to B in the negatively charged
state and that neighboring to N is in a positively charged state.",1902.04748v1
2019-02-15,Assessing correlations of perovskite catalytic performance with electronic structure descriptors,"Electronic structure descriptors are computationally efficient quantities
used to construct qualitative correlations for a variety of properties. In
particular, the oxygen p-band center has been used to guide material discovery
and fundamental understanding of an array of perovskite compounds for use in
catalyzing the oxygen reduction and evolution reactions. However, an assessment
of the effectiveness of the oxygen p-band center at predicting key measures of
perovskite catalytic activity has not been made, and would be highly beneficial
to guide future predictions and codify best practices. Here, we have used
Density Functional Theory at the PBE, PBEsol, PBE+U, SCAN and HSE06 levels to
assess the correlations of numerous measures of catalytic performance for a
series of technologically relevant perovskite oxides, using the bulk oxygen
p-band center as an electronic structure descriptor. We have analyzed
correlations of the calculated oxygen p-band center for all considered
functionals with the experimentally measured X-ray emission spectroscopy oxygen
p-band center and multiple measures of catalytic activity, including high
temperature oxygen reduction surface exchange rates, aqueous oxygen evolution
current densities, and binding energies of oxygen evolution intermediate
species. Our results show that the best correlations for all measures of
catalytic activity considered here are made with PBE-level calculations, with
strong observed linear correlations with the bulk oxygen p-band center (R2 =
0.81-0.87). This study shows that strong linear correlations between numerous
important measures of catalytic activity and the oxygen p-band bulk descriptor
can be obtained under a consistent computational framework, and these
correlations can serve as a guide for future experiments and simulations for
development of perovskite and related oxide catalysts.",1902.05867v1
2019-03-04,Rashba spin-splitting in ferroelectric oxides: from rationalizing to engineering,"Ferroelectric Rashba semiconductors (FERSC), in which Rashba spin-splitting
can be controlled and reversed by an electric field, have recently emerged as a
new class of functional materials useful for spintronic applications. The
development of concrete devices based on such materials is, however, still
hampered by the lack of robust FERSC compounds. Here, we show that the
coexistence of large spontaneous polarisation and sizeable spin-orbit coupling
is not sufficient to have strong Rashba effects and clarify why simple
ferroelectric oxide perovskites with transition metal at the B-site are
typically not suitable FERSC candidates. By rationalizing how this limitation
can be by-passed through band engineering of the electronic structure in
layered perovskites, we identify the Bi$_2$WO$_6$ Aurivillius crystal as the
first robust ferroelectric with large and reversible Rashba spin-splitting,
that can even be substantially doped without losing its ferroelectric
properties. Importantly, we highlight that a unidirectional spin-orbit field
arises in layered Bi$_2$WO$_6$, resulting in a protection against
spin-decoherence.We highlight moreover that a unidirectional spin-orbit field
arises in Bi$_2$WO$_6$, in which the spin-texture is so protected against
spin-decoherence.",1903.01241v3
2019-03-05,Polar Coupling Enabled Nonlinear Optical Filtering at MoS$_2$/Ferroelectric Heterointerfaces,"Complex oxide heterointerfaces and van der Waals heterostructures present two
versatile but intrinsically different platforms for exploring emergent quantum
phenomena and designing new functionalities. The rich opportunity offered by
the synergy between these two classes of materials, however, is yet to be
charted. Here, we report an unconventional nonlinear optical filtering effect
resulting from the interfacial polar alignment between monolayer MoS$_2$ and a
neighboring ferroelectric oxide thin film. The second harmonic generation
response at the heterointerface is either substantially enhanced or almost
entirely quenched by an underlying ferroelectric domain wall depending on its
chirality, and can be further tailored by the polar domains. Unlike the
extensively studied coupling mechanisms driven by charge, spin, and lattice,
the interfacial tailoring effect is solely mediated by the polar symmetry, as
well explained via our density functional theory calculations, pointing to a
new material strategy for the functional design of nanoscale reconfigurable
optical applications.",1903.01664v2
2019-03-06,Effective interaction for vanadium oxyhydrides Sr$_{n+1}$V$_n$O$_{2n+1}$H$_n$ ($n=1$ and $n\to\infty$): A constrained-RPA study,"Transition metal oxides have been one of the central objects in the studies
of electron correlation effects because of their rich variety of physical
properties mainly depending on the transition metal element. On the other hand,
exploiting the anion degrees of freedom is less popular but can be another
promising way to control properties of strongly correlated materials. In
particular, oxyhydrides offer a unique playground of strongly correlated
low-dimensional electronic structure, where the $s$ orbitals of hydrogen breaks
a chemical bond between the cation $t_{2g}$ orbitals. In this study, we
evaluate the effective interaction, i.e., the screened Coulomb interaction
parameters in low-energy effective models, for vanadium oxyhydrides
Sr$_{n+1}$V$_n$O$_{2n+1}$H$_n$ ($n=1,\infty$) using the constrained
random-phase approximation (cRPA). We find that the effective interaction in
the $t_{2g}$ model, where only the $t_{2g}$ orbitals are explicitly considered,
is strongly screened by the $e_g$ bands compared with that for oxides, because
the $e_g$ bands are much entangled with the $t_{2g}$ bands in the oxyhydrides.
On the other hand, the effective interaction is rather strong in the $d$ model,
where all the vanadium $d$ orbitals are explicitly considered, owing to a large
energy separation between the V-$d$ bands and the anion bands (O-$p$ and
H-$s$), because the O-$p$ states are stabilized by the existence of the
hydrogen atoms. These findings suggest that non-trivial and unique correlation
effects can take place in vanadium oxyhydrides.",1903.02222v2
2019-03-12,Few layer 2D pnictogens catalyze the alkylation of soft nucleophiles with esters,"Group 15 elements in zero oxidation state (P, As, Sb and Bi), also called
pnictogens, are rarely used in catalysis due to the difficulties associated in
preparing well-structured and stable materials. Here, we report on the
synthesis of highly exfoliated, few layer 2D phosphorene and antimonene in zero
oxidation state, suspended in an ionic liquid, with the native atoms ready to
interact with external reagents while avoiding aerobic or aqueous decomposition
pathways, and on their use as efficient catalysts for the alkylation of
nucleophiles with esters. The few layer pnictogen material circumvents the
extremely harsh reaction conditions associated to previous superacid-catalyzed
alkylations, by enabling an alternative mechanism on surface, protected from
the water and air by the ionic liquid. These 2D catalysts allow the alkylation
of a variety of acid-sensitive organic molecules and giving synthetic relevancy
to the use of simple esters as alkylating agents.",1903.04776v1
2019-03-20,An increase in membrane cholesterol by graphene oxide disrupts calcium homeostasis in primary astrocytes,"The use of graphene nanomaterials (GNMs) for biomedical applications targeted
to the central nervous system is exponentially increasing, although precise
information on their effects on brain cells is lacking. In this work, we
addressed the molecular changes induced in cortical astrocytes by few-layer
graphene (FLG) and graphene oxide (GO) flakes. Our results show that exposure
to FLG/GO does not affect cell viability or proliferation. However, proteomic
and lipidomic analyses unveiled alterations in several cellular processes,
including intracellular Ca2+ ([Ca2+]i) homeostasis and cholesterol metabolism,
which were particularly intense in cells exposed to GO. Indeed, GO exposure
impaired spontaneous and evoked astrocyte [Ca2+]i signals and induced a marked
increase in membrane cholesterol levels. Importantly, cholesterol depletion
fully rescued [Ca2+]i dynamics in GO-treated cells, indicating a causal
relationship between these GO-mediated effects. Our results indicate that
exposure to GNMs alters intracellular signaling in astrocytes and may impact on
astrocyte-neuron interactions.",1903.08447v1
2018-11-30,Tailoring ink-substrate interactions via thin polymeric layers for high-resolution printing,"The surface properties of a substrate are among the most important parameters
in the printing technology of functional materials, determining not only the
printing resolution but also the stability of the printed features. This paper
addresses the wetting difficulties encountered during inkjet printing on
homogeneous substrates as a result of improper surface properties. We show that
the wetting of a substrate and, consequently, the quality of the printed
pattern, can be mediated through the deposition of polymeric layers that are a
few nanometers thick. The chemical nature of the polymers determines the
surface energy and polarity of the thin layer. Some applications, however,
require a rigorous adjustment of the surface properties. We propose a simple
and precise method of surface-energy tailoring based on the thermal
decomposition of poly(methyl methacrylate) (PMMA) layers. A smooth transition
in the wetting occurs when the thickness of the PMMA layer approaches zero,
probably due to percolating the underlying surface of the substrate, which
enables the inkjet printing of complex structures with a high resolution. In
particular, the wetting of three substrate-ink systems was successfully
adjusted using the thin polymeric layer: (i) a tantalum-oxide-based ink on
indium-tin-oxide-coated glass, (ii) a ferroelectric lead zirconate titanate ink
on a platinized silicon substrate, and (iii) a silver nanoparticle ink on an
alumina substrate.",1903.10283v1
2019-01-02,Transport and Phototransport in ITO Nanocrystals with Short to Long-Wave Infrared Absorption,"Nanocrystals are often described as an interesting strategy for the design of
low-cost optoelectronic devices especially in the infrared range. However the
driving materials reaching infrared absorption are generally heavy
metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to
achieve infrared transition is the use of doped semiconductors presenting
intraband or plasmonic transition in the short, mid and long-wave infrared.
This strategy may offer more flexibility regarding the range of possible
candidate materials. In particular, significant progresses have been achieved
for the synthesis of doped oxides and for the control of their doping
magnitude. Among them, tin doped indium oxide (ITO) is the one providing the
broadest spectral tunability. Here we test the potential of such ITO
nanoparticles for photoconduction in the infrared. We demonstrate that In2O3
nanoparticles presents an intraband absorption in the mid infrared range which
is transformed into a plasmonic feature as doping is introduced. We have
determined the cross section associated with the plasmonic transition to be in
the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made
conductive and photoconductive due to a ligand exchange using a short
carboxylic acid, leading to a dark conduction with n-type character. We bring
further evidence that the observed photoresponse in the infrared is the result
of a bolometric effect.",1903.10295v1
2019-04-03,Possible superconductivity induced by a large spin-orbit coupling in carrier doped iridium oxide insulators: A weak coupling approach,"We study possible superconductivity in a carrier-doped iridium oxide
insulator Sr$_{2}$IrO$_{4}$ based on an effective $t_{2g}$ three-orbital
Hubbard model on the square lattice with a large spin-orbit coupling (SOC).
Numerically solving the linearized Eliashberg equation for the superconducting
(SC) gap function with the random phase approximation, we systematically
examine both singlet and triplet SC gap functions with possible pairing
symmetries and the parameter dependence of the superconductivity. For the
realistic SOC $\lambda$ and Hund's coupling $J/U$ relevant to
Sr$_{2}$IrO$_{4}$, namely, for a large $\lambda$ and small $J/U$ region, we
find that the intra-band antiferromagnetic (AF) pseudospin $\bm{j}_{\text{eff}}
= -\bm{l}+\bm{s}$ fluctuations favor a $d_{x^{2}-y^{2}}$-wave pseudospin
$j_{\text{eff}}=1/2$ singlet pairing in the electron-doping. We also find that
the $d_{x^{2}-y^{2}}$-wave pairing is more stabilized with increasing the SOC
and decreasing the Hund's coupling. Furthermore, we show for a small $\lambda$
and large $J/U$ region that an $s_{\pm}$-wave singlet pairing is favored in the
hole-doped region. The origin of the $s_{\pm}$-wave pairing is due to the
inter-band pair scattering arising from the intra-orbital AF spin $\bm s$
fluctuations. Although the possibility of a pseudospin triplet pairing is
considered, we find it always unfavorable for all parameters studied here. The
experimental consequences for other strongly correlated materials with a large
SOC are also discussed.",1904.01812v1
2019-04-14,Tuning the metal-insulator transition in epitaxial SrVO3 films by uniaxial strain,"Understanding of the metal-insulator transition (MIT) in correlated
transition-metal oxides is a fascinating topic in condensed matter physics and
a precise control of such transitions plays a key role in developing novel
electronic devices. Here we report an effective tuning of the MIT in epitaxial
SrVO3 (SVO) films by expanding the out-of-plane lattice constant without
changing in-plane lattice parameters, through helium ion irradiation. Upon
increase of the ion fluence, we observe a MIT with a crossover from metallic to
insulating state in SVO films. A combination of transport and magnetoresistance
measurements in SVO at low temperatures reveals that the observed MIT is mainly
ascribed to electron-electron interactions rather than disorder-induced
localization. Moreover, these results are well supported by the combination of
density functional theory and dynamical mean field theory (DFT+DMFT)
calculations, further confirming the decrease of the bandwidth and the enhanced
electron-electron interactions resulting from the expansion of out-of-plane
lattice constant. These findings provide new insights into the understanding of
MIT in correlated oxides and perspectives for the design of unexpected
functional devices based on strongly correlated electrons.",1904.06629v1
2019-08-08,Electric selective activation of memristive interfaces in TaO$_x$-based devices,"The development of novel devices for neuromorphic computing and
non-traditional logic operations largely relies on the fabrication of well
controlled memristive systems with functionalities beyond standard bipolar
behavior and digital ON-OFF states. In the present work we demonstrate for
Ta$_2$O$_5$-based devices that it is possible to selectively
activate/deactivate two series memristive interfaces in order to obtain
clockwise or counter-clockwise multilevel squared remanent resistance loops,
just by controlling the (a)symmetry of the applied stimuli and independently of
the nature of the used metallic electrodes. Based on our thorough
characterization, analysis and modeling, we show that the physical origin of
this electrical behavior relies on controlled oxygen vacancies electromigration
between three different zones of the active Ta$_2$O$_{5-x}$ layer: a central --
bulk -- one and two quasi-symmetric interfaces with reduced TaO$_{2-h(y)}$
layers. Our devices fabrication process is rather simple as it implies the room
temperature deposition of only one CMOS compatible oxide -- Ta-oxide -- and one
metal, suggesting that it might be possible to take advantage of these
properties at low cost and with easy scability. The tunable opposite remanent
resistance loops circulations with multiple -- analogic -- intermediate stable
states allows mimicking the adaptable synaptic weight of biological systems and
presents potential for non-standard logic devices.",1908.03056v1
2019-08-19,Exploring the role of electronic structure on photo-catalytic behavior of carbon-nitride polymorphs,"A fully self-consistent density-functional theory (DFT) with improved
functionals is used to provide a comprehensive account of structural,
electronic, and optical properties of C$_{3}$N$_{4}$ polymorphs. Using our
recently developed van Leeuwen-Baerends (vLB) corrected local-density
approximation (LDA), we implemented LDA+vLB within full-potential
N$^{th}$-order muffin-tin orbital (FP-NMTO) method and show that it improves
structural properties and band gaps compared to semi-local functionals
(LDA/GGA). We demonstrate that the LDA+vLB predicts band-structure and
work-function for well-studied 2D-graphene and bulk-Si in very good agreement
with experiments, and more exact hybrid functional (HSE) calculations as
implemented in the Quantum-Espresso (QE) package. The structural and
electronic-structure (band gap) properties of C$_{3}$N$_{4}$ polymorphs
calculated using FP-NMTO-LDA+vLB is compared with more sophisticated
hybrid-functional calculations. We also perform detailed investigation of
photocatalytic behavior using QE-HSE method of C$_{3}$N$_{4}$ polymorphs
through work-function, band (valence and conduction) position with respect to
water reduction and oxidation potential. Our results show
$\gamma$-C$_{3}$N$_{4}$ as the best candidate for photocatalysis among all the
C$_{3}$N$_{4}$~polymorphs but it is dynamically unstable at `zero' pressure. We
show that $\gamma$-C$_{3}$N$_{4}$ can be stabilized under hydrostatic-pressure,
which improves its photocatalytic behavior relative to water reduction and
oxidation potentials.",1908.06596v2
2019-08-22,High-throughput fabrication and semi-automated characterization of oxide thin film transistors,"High throughput experimental methods are known to accelerate the rate of
research, development, and deployment of electronic materials. For example,
thin films with lateral gradients in composition, thickness, or other
parameters have been used alongside spatially-resolved characterization to
assess how various physical factors affect material properties under varying
measurement conditions. Similarly, multi-layer electronic devices that contain
such graded thin films as one or more of their layers can also be characterized
spatially in order to optimize the performance. In this work, we apply these
high throughput experimental methods to thin film transistors (TFTs),
demonstrating combinatorial device fabrication and semi-automated
characterization using sputtered Indium-Gallium-Zinc-Oxide (IGZO) TFTs as a
case study. We show that both extrinsic and intrinsic types of device gradients
can be generated in a TFT library, such as channel thickness and length,
channel cation compositions, and oxygen atmosphere during deposition. We also
present a semi-automated method to measure the 44 devices fabricated on a
50x50mm substrate that can help to identify properly functioning TFTs in the
library and finish the measurement in a short time. Finally, we propose a fully
automated characterization system for similar TFT libraries, which can be
coupled with high throughput data analysis. These results demonstrate that high
throughput methods can accelerate the investigation of TFTs and other
electronic devices.",1908.08287v1
2019-11-09,Pulsed laser deposition of single phase n- and p-type Cu2O thin films with low resistivity,"Low resistivity (~3-24 mOhm.cm) with tunable n- and p-type phase pure Cu2O
thin films have been grown by pulsed laser deposition at 25-200 0C by varying
the background oxygen partial pressure (O2pp). Capacitance data obtained by
electrochemical impedance spectroscopy was used to determine the conductivity
(n- or p-type), carrier density, and flat band potentials for samples grown on
indium tin oxide (ITO) at 25 0C. The Hall mobility of the n- and p-type Cu2O
was estimated to be ~ 0.85 cm2.V-1s-1 and ~ 4.78 cm2.V-1s-1 respectively for
samples grown on quartz substrate at 25 0C. An elevated substrate temperature ~
200 0C with O2pp = 2 - 3 mTorr yielded p-type Cu2O films with six orders of
magnitude higher resistivities in the range ~ 9 - 49 kOhm.cm and mobilities in
the range ~ 13.5 - 22.2 cm2.V-1s-1. UV-Vis-NIR diffuse reflectance spectroscopy
showed optical bandgaps of Cu2O films in the range of 1.76 to 2.15 eV depending
on O2pp. Thin films grown at oxygen-rich conditions O2pp > 7 mTorr yielded
mixed-phase copper oxide irrespective of the substrate temperatures and upon
air annealing at 550 0C for 1 hour completely converted to CuO phase with
n-type semiconducting properties (~12 Ohm.cm, ~1.50 cm2.V-1s-1). The as-grown
p- and n-type Cu2O showed rectification and a photovoltaic (PV) response in
solid junctions with n-ZnO and p-Si electrodes respectively. Our findings may
create new opportunities for devising Cu2O based junctions requiring low
process temperatures.",1911.03727v2
2019-11-17,Interfacial-Redox-Induced Tuning of Superconductivity in YBa$_{2}$Cu$_{3}$O$_{7-δ}$,"Solid state ionic approaches for modifying ion distributions in getter/oxide
heterostructures offer exciting potentials to control material properties. Here
we report a simple, scalable approach allowing for total control of the
superconducting transition in optimally doped YBa$_{2}$Cu$_{3}$O$_{7-{\delta}}$
(YBCO) films via a chemically-driven ionic migration mechanism. Using a thin Gd
capping layer of up to 20 nm deposited onto 100 nm thick epitaxial YBCO films,
oxygen is found to leach from deep within the YBCO. Progressive reduction of
the superconducting transition is observed, with complete suppression possible
for a sufficiently thick Gd layer. These effects arise from the combined impact
of redox-driven electron doping and modification of the YBCO microstructure due
to oxygen migration and depletion. This work demonstrates an effective ionic
control of superconductivity in oxides, an interface induced effect that goes
well into the quasi-bulk regime, opening up possibilities for electric field
manipulation.",1911.07275v1
2019-12-04,X-rays induced atomic dynamics in a lithium-borate glass,"The continuous development of synchrotron-based experimental techniques in
the X-ray range provides new possibilities to probe the structure and the
dynamics of bulk materials down to inter-atomic distances. However, the
interaction of intense X-ray beams with matter can also induce changes in the
structure and dynamics of materials. A reversible and non-destructive beam
induced dynamics has recently been observed in X-ray photon correlation
spectroscopy experiments in some oxide glasses at sufficiently low absorbed
doses, and is here investigated in a (Li$_2$O)$_{0.5}$(B$_2$O$_3$)$_{0.5}$
glass. The characteristic time of this induced dynamics is inversely
proportional to the intensity of the X-ray beam, with a coefficient that
depends on the chemical composition and local structure of the probed glass,
making it a potentially new tool to investigate fundamental properties of a
large class of disordered systems. While the exact mechanisms behind this
phenomenon are yet to be elucidated, we report here on the measurement of the
exchanged wave-vector (and thus length-scale) dependence of the characteristic
time of this induced dynamics, and show that it follows the same power-law
observed in vitreous silica. This supports the idea that a unique explanation
for this effect in different oxide glasses should be looked for.",1912.01943v1
2019-12-05,Effect of Proton Irradiation Temperature on Zinc Oxide Metal-Semiconductor-Metal Ultraviolet Photodetectors,"The electrical and structural characteristics of 50 nm zinc oxide (ZnO)
metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors subjected to
proton irradiation at different temperatures are reported and compared. We
irradiated the devices with 200 keV protons to a fluence of 1016 cm-2.
Examination of the X-ray diffraction (XRD) rocking curves indicates a strongly
preferred (100) orientation for the grains of the as-deposited film, with
decreases in crystal quality for all irradiated samples. In addition, peak
shifts in XRD and Raman spectra of the control sample relative to well-known
theoretical positions are indicative of tensile strain in the as-deposited ZnO
films. We observed shifts of these peaks towards theoretical unstrained
positions in the irradiated films relative to the as-deposited film indicate
partial relaxation of this strain. Raman spectra also indicate increases of
oxygen vacancies (V_O ) and zinc interstitials (Zn_i ) relative to the control
sample. Additionally, photocurrent versus time measurements showed up to 2x
increases in time constants for samples irradiated at lower temperatures months
after irradiation, indicating that the defects introduced by suppression of
thermally-activated dynamic annealing process has a long-term deleterious
effect on device performance.",1912.02321v1
2019-12-09,Biochemically altered human erythrocytes as a carrier for targeted delivery of primaquine: an in vitro study,"The aim of this study was to investigate human erythrocytes as a carrier for
targeted drug delivery of primaquine (PQ). The process of PQ loading in human
erythrocytes, as well as the effect of PQ loading on the oxidative status of
erythrocytes, was also studied. At PQ concentrations of 2, 4, 6, and 8 mg/mL
and an incubation time of 2 h, the ratios of the concentrations of PQ entrapped
in erythrocytes to that in the incubation medium were 0.515, 0.688, 0.697 and
0.788, respectively. The maximal decline of erythrocyte reduced glutathione
content was observed at 8 mg/mL of PQ compared with native erythrocytes p <
0.001. In contrast, malondialdehyde and protein carbonyl were significantly
increased in cells loaded with PQ (p < 0.001). Furthermore, osmotic fragility
of PQ carrier erythrocytes was increased in comparison with unloaded cells.
Electron microscopy revealed spherocyte formation with PQ carrier erythrocytes.
PQ-loaded cells showed sustained drug release over a 48 h period. Erythrocytes
were loaded with PQ successfully, but there were some biochemical as well as
physiological changes that resulted from the effect of PQ on the oxidative
status of drug-loaded erythrocytes. These changes may result in favorable
targeting of PQ-loaded cells to reticulo-endothelial organs. The relative
impact of these changes remains to be explored in ongoing animal studies.",1912.04359v1
2019-12-10,A first-principles investigation of the structural and electrochemical properties of biredox ionic species in acetonitrile,"Biredox ionic liquids are a new class of functionalized electrolytes that may
play an important role in future capacitive energy storage devices. By allowing
additional storage of electrons inside the liquids, they can improve device
performance significantly. However current devices employ nanoporous carbons in
which the diffusion of the liquid and the adsorption of the ions could be
affected by the occurrence of electron-transfer reactions. It is therefore
necessary to understand better the thermodynamics and the kinetics of such
reactions in biredox ionic liquids. Here we perform ab initio molecular
dynamics simulations of both the oxidized and reduced species of several
redox-active ionic molecules (used in biredox ionic liquids) dissolved in
acetonitrile solvent and compare them with the bare redox molecules. We show
that in all the cases, it is necessary to introduce a two Gaussian state model
to calculate the reaction free energies accurately. These reaction free
energies are only slightly affected by the presence of the IL group on the
molecule. We characterize the structure of the solvation shell around the redox
active part of the molecules and show that in the case of TEMPO-based molecules
strong reorientation effects occur during the oxidation reaction.",1912.04879v1
2019-12-11,Molybdenum Trioxide Gates for Suppression of Leakage Current in InAlN/GaN HEMTs at 300°C,"Because high electron mobility transistors (HEMTs) often exhibit significant
gate leakage during high-temperature operation, the choice of Schottky metal is
critical. Increased gate leakage and reduced ON/OFF ratio are unsuitable for
the design of high-temperature electronics and integrated circuits. This paper
presents high-temperature characteristics of depletion-mode molybdenum trioxide
(MoO${_3}$)-gated InAlN/GaN-on-silicon HEMTs in air. After a room temperature
oxidation of the Mo for 10 weeks, the leakage of the HEMT is reduced over 60
times compared to the as-deposited Mo. The use of MoO${_3}$ as the Schottky
gate material enables low gate leakage, resulting in a high ON/OFF current
ratio of 1.2 x 10${^8}$ at 25{\deg}C and 1.2 x 10${^5}$ at 300{\deg}C in air.
At 400{\deg}C, gate control of the InAlN/GaN two-dimensional electron gas
(2DEG) channel is lost and unrecoverable. Here, this permanent device failure
is attributed to volatilization of the MoO${_3}$ gate due to the presence of
water vapor in air. Passivation of the device with SiN enables operation up to
500{\deg}C, but also increases the leakage current. The suppression of gate
leakage via Mo oxidation and resulting high ON/OFF ratio paves the way for
viable high-temperature GaN-based electronics that can function beyond the
thermal limit of silicon once proper passivation is achieved.",1912.05667v1
2019-12-13,Artifcial-intelligence-driven discovery of catalyst \textit{genes} with application to CO2 activation on semiconductor oxides,"Catalytic-materials design requires predictive modeling of the interaction
between catalyst and reactants. This is challenging due to the complexity and
diversity of structure-property relationships across the chemical space. Here,
we report a strategy for a rational design of catalytic materials using the
artifcial intelligence approach (AI) subgroup discovery. We identify catalyst
\textit{genes} (features) that correlate with mechanisms that trigger,
facilitate, or hinder the activation of carbon dioxide (CO$_2$) towards a
chemical conversion. The AI model is trained on frst-principles data for a
broad family of oxides. We demonstrate that surfaces of experimentally
identifed good catalysts consistently exhibit combinations of \textit{genes}
resulting in a strong elongation of a C-O bond. The same combinations of
\textit{genes} also minimize the OCO-angle, the previously proposed indicator
of activation, albeit under the constraint that the Sabatier principle is
satisfed. Based on these fndings, we propose a set of new promising catalyst
materials for CO$_2$ conversion.",1912.06515v3
2019-12-19,Prospects for laser cooling of polyatomic molecules with increasing complexity,"Optical cycling transitions and direct laser cooling have recently been
demonstrated for a number of alkaline-earth dimers and trimer molecules. This
is made possible by diagonal Franck-Condon factors between the vibrational
modes of the optical transition. Achieving a similar degree of cooling to
micro-Kelvin equivalent kinetic energy for larger polyatomic molecules,
however, remains challenging. Since polyatomic molecules are characterized by
multiple degrees of freedom and have a correspondingly more complex structure,
it is far from obvious whether there exist polyatomic molecules that can
repeatedly scatter photons. Here, we propose chemical substitution approaches
to engineer large polyatomic molecules with optical cycling centers (OCCs)
containing alkaline-earth oxide dimers or acetylenic alkaline-earth trimers
(i.e. M--C$\equiv$C) connected to CH$_n$ chains or fullerenes. To validate the
OCC-character of the selected molecules we performed electronic structure
calculations of the equilibrium configuration of both ground and excited
potential energy surfaces, evaluated their vibrational and bending modes, and
corresponding Franck-Condon factors for all but the most complex molecules. For
fullerenes, we have shown that OCCs based on M--C$\equiv$C can perform better
than those based on alkaline-earth oxide dimers.
  In addition, for heavier polyatomic molecules it might be advantageous to
attach two OCCs, thereby potentially doubling the photon scattering rate and
thus speeding up cooling rates.",1912.09364v3
2019-12-27,Attosecond time-domain measurement of core-excitonic decay in magnesium oxide,"Excitation of ionic solids with extreme ultraviolet pulses creates localized
core-excitons, which in some cases couple strongly to the lattice. Here,
core-excitonic states of magnesium oxide are studied in the time domain at the
Mg $\text{L}_{2,3}$ edge with attosecond transient reflectivity spectroscopy.
Attosecond pulses trigger the excitation of these short-lived quasiparticles,
whose decay is perturbed by time-delayed near infrared optical pulses. Combined
with a few-state theoretical model, this reveals that the optical pulse shifts
the energy of bright core-exciton states as well as induces features arising
from dark core-excitons. We report coherence lifetimes for the first two
core-excitons of $2.3 \pm 0.2$ and $1.6 \pm 0.5$ femtoseconds and show that
these short lifetimes are primarily a consequence of strong exciton-phonon
coupling, disclosing the drastic influence of structural effects in this
ultrafast relaxation process.",1912.12266v1
2019-12-29,Strain-Driven Disproportionation at a Correlated Oxide Metal-Insulator Transition,"Metal-to-insulator phase transitions in complex oxide thin films are exciting
phenomena which may be useful for device applications, but in many cases the
physical mechanism responsible for the transition is not fully understood. Here
we demonstrate that epitaxial strain generates local disproportionation of the
NiO6 octahedra, driven through changes in the oxygen stoichiometry, and that
this directly modifies the metal-to-insulator phase transition in epitaxial
(001) NdNiO3 thin films. Theoretically, we predict that the Ni-O-Ni bond angle
decreases, while octahedral tilt and local disproportionation of the NiO6
octahedra increases resulting in a small band gap in otherwise metallic system.
This is driven by an increase in oxygen vacancy concentration in the rare-earth
nickelates with increasing in-plane biaxial tensile strain. Experimentally, we
find an increase in pseudocubic unit-cell volume and resistivity with
increasing biaxial tensile strain, corroborating our theoretical predictions.
With electron energy loss spectroscopy and x-ray absorption, we find a
reduction of the Ni valence with increasing tensile strain. These results
indicate that epitaxial strain modifies the oxygen stoichiometry of rare-earth
perovskite thin films and through this mechanism affect the metal-to-insulator
phase transition in these compounds.",1912.12710v1
2019-12-31,Production of nitric oxide by a fragmenting bolide: An exploratory numerical study,"A meteoroid's hypersonic passage through the Earth's atmosphere results in
ablational and fragmentational mass loss. Potential shock waves associated with
a parent object as well as its fragments can modify the surrounding atmosphere
and produce a range of physico-chemical effects. Some of the thermally driven
chemical and physical processes induced by meteoroid-fragment generated shock
waves, such as nitric oxide (NO) production, are less understood. Any estimates
of meteoric NO production depend not only on a quantifiable meteoroid
population and a rate of fragmentation, with a size capable of producing high
temperature flows, but also on understanding the physical properties of the
meteor flows along with their thermal history. We performed an exploratory
pilot numerical study using ANSYS Fluent, the CFD code, to investigate the
production of NO in the upper atmosphere by small meteoroids (or fragments of
meteoroids after they undergo a disruption episode) in the size range from 1 cm
m to 1 m. Our model uses the simulation of a spherical body in the continuum
flow at 70 and 80 km altitude to approximate the behaviour of a small meteoroid
capable of producing NO. The results presented in this exploratory study are in
good agreement with previous studies.",1912.13130v2
2020-03-02,"Electrodynamics of Conductive Oxides: Intensity-dependent anisotropy, reconstruction of the effective dielectric constant, and harmonic generation","We study electromagnetic pulse propagation in an indium tin oxide nanolayer
in the linear and nonlinear regimes. We use the constitutive relations to
reconstruct the effective dielectric constant of the medium, and show that
nonlocal effects induce additional absorption resonances and anisotropic
dielectric response: longitudinal and transverse effective dielectric functions
are modulated differently along the propagation direction, and display
different epsilon-near-zero crossing points with a discrepancy that increases
with increasing intensity. We predict that hot carriers induce a dynamic
redshift of the plasma frequency and a corresponding translation of the
effective nonlinear dispersion curves that can be used to predict and quantify
nonlinear refractive index changes as a function of incident laser peak power
density. Our results suggest that large, nonlinear refractive index changes can
occur without the need for epsilon-near-zero modes to couple with plasmonic
resonators. At sufficiently large laser pulse intensities, we predict the onset
of optical bistability, while the presence of additional pump absorption
resonances that arise from longitudinal oscillations of the free electron gas
give way to corresponding resonances in the second and third harmonic spectra.
A realistic propagation model is key to unraveling the basic physical
mechanisms that play a fundamental role in the dynamics.",2003.01059v1
2020-03-24,Characteristic Lengths of Interlayer Charge-Transfer in Correlated Oxide Heterostructures,"Using interlayer interaction to control functional heterostructures with
atomic-scale designs has become one of the most effective interface-engineering
strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3
buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures. The
LaFeO3 buffer layer acts as an energetically favored electron acceptor in both
LaAlO3/SrTiO3 systems, resulting in modulation of interfacial carrier density
and hence metal-to-insulator transition. For amorphous and crystalline
LaAlO3/SrTiO3 heterostructures, the metal-to-insulator transition is found when
the LaFeO3 layer thickness crosses 3 and 6 unit cells, respectively. Such
different critical LaFeO3 thicknesses are explained in terms of distinct
characteristic lengths of the redox-reaction-mediated and
polar-catastrophe-dominated charge transfer, controlled by the interfacial
atomic contact and Thomas-Fermi screening effect, respectively. Our results not
only shed light on the complex interlayer charge transfer across oxide
heterostructures but also provides a new route to precisely tailor the
charge-transfer process at a functional interface.",2003.10677v1
2020-03-29,Domain evolution in bended freestanding BaTiO3 ultrathin films: a phase-field simulation,"Perovskite ferroelectric oxides are usually considered to be brittle
materials, however, recent work [Dong et al., Science 366, 475 (2019)]
demonstrated the super-elasticity in the freestanding BaTiO3 thin films. This
property may originate from the ferroelectric domain evolution during the
bending, which is difficult to observe in experiments. Therefore, understanding
the relation among the bending deformation, thickness of the films, and the
domain dynamics is critical for their potential applications in flexible
ferroelectric devices. Here, we reported the dynamics of ferroelectric
polarization in the freestanding BaTiO3 ultrathin films in the presence of
large bending deformation up to 40{\deg} using phase-field simulation. The
ferroelectric domain evolution reveals the transition from the flux-closure to
a/c domains with ""vortex-like"" structures, which caused by the increase of
out-of-plane ferroelectric polarization. Additionally, by varying the film
thickness in the identical bending situation, we found the a/c phase with
""vortex-like"" structure emerges only as the film thickness reached 12 nm or
higher. Results from our investigations provide instructive information for the
microstructure evolution of bending ferroelectric perovskite oxide films, which
could serve as guide for the future application of ferroelectric films on
flexible electronic devices.",2003.13020v1
2020-03-30,Vibrational coherent control of localized d-d electronic excitation,"Addressing the role of quantum coherence in the interplay between the
different matter constituents (electrons, phonons and spin) is a critical step
towards understanding transition metal oxides and design complex materials with
new functionalities. Here we use coherent vibrational control of onsite d-d
electronic transitions in a model edge-sharing insulating transition metal
oxide (CuGeO3) to single-out the effects of vibrational coherence in
electron-phonon coupling. By comparing time domain experiments based on high
and low frequency ultrashort pumps with a fully quantum description of phonon
assisted absorption, we could distinguish the processes associated to
incoherent thermal lattice fluctuations from those driven by the coherent
motion of the atoms. In particular, while thermal fluctuation of the phonon
bath uniformly increases the electronic absorption, the resonant excitation of
phonon modes results also in light-induced transparency which is coherently
controlled by the vibrational motion.",2003.13447v2
2020-04-14,Enhanced Solar Water Splitting by Swift Charge Separation in Au/FeOOH Sandwiched Single Crystalline Fe$_2$O$_3$ Nanoflake Photoelectrodes,"In this work, single crystalline $\alpha$-Fe$_2$O$_3$ nanoflakes (NFs) are
formed in a highly dense array by Au seeding of a Fe substrate by a thermal
oxidation technique. The NFs are conformally decorated with a thin FeOOH
cocatalyst layer. Photoelectrochemical (PEC) measurements show that this
photoanode with the $\alpha$-Fe$_2$O$_3$/FeOOH NFs rooted on the Au/Fe
structure exhibits a significantly enhanced PEC water oxidation performance
compared to the plain $\alpha$-Fe$_2$O$_3$ nanostructure on the Fe substrate.
The $\alpha$-Fe$_2$O$_3$/FeOOH NFs on Au/Fe photoanode yields a photocurrent
density of 3.1 mA cm-2 at 1.5 VRHE, and a remarkably low onset potential of
0.5-0.6 VRHE in 1 M KOH under AM 1.5G (100 mW cm-2) simulated sunlight
illumination. The enhancement in PEC performance can be attributed to a
synergistic effect of the FeOOH top decoration and Au under-layer. While FeOOH
facilitates hole transfer at the interface of electrode/electrolyte, the Au
layer provides a sink for the electron transport to the back contact: this
leads overall to a drastically improved charge-separation efficiency in the
single crystalline $\alpha$-Fe$_2$O$_3$ NF photoanode.",2005.01604v1
2020-05-06,Oxidation of the Interiors of Carbide Exoplanets,"Astrophysical measurements have shown that some stars have sufficiently high
carbon-to-oxygen ratios such that the planets they host would be mainly
composed of carbides instead of silicates. We studied the behavior of silicon
carbide in the presence of water under the high pressure-temperature conditions
relevant to planetary interiors in the laser-heated diamond-anvil cell (LHDAC).
When reacting with water, silicon carbide converts to silica (stishovite) and
diamond at pressures up to 50 GPa and temperatures up to 2500 K: SiC + 2H$_2$O
-> SiO$_2$ + C + 2H$_2$. Therefore, if water can be incorporated into carbide
planets during their formation or through later delivery, they could be
oxidized and have mineralogy dominated by silicates and diamond in their
interiors. The reaction could produce CH$_4$ at shallower depths and H$_2$ at
greater depths which could be degassed from the interior, causing the
atmospheres of the converted carbon planets to be rich in reducing gases.
Excess water after the reaction can be stored in dense silica polymorphs in the
interiors of the converted carbon planets. Such conversion of mineralogy to
diamond and silicates would decrease the density of carbon-rich planet, making
the converted planets distinct from silicate planets in mass-radius relations
for the 2-8 Earth mass range.",2005.03175v4
2020-05-22,Temperature dependence of the optical properties of silicon nanocrystals,"Silicon nanocrystals (SiNCs) have been under active investigation in the last
decades and have been considered as a promising candidate for many
optoelectronic applications including highly-efficient solar cells. Some of the
fundamental properties of interest in these nanostructures is the temperature
dependence of their optical absorption onset, and how this is controlled by
different passivation regimes. In the present work we employ first-principles
calculations in conjunction with the special displacement method to study the
temperature dependence of the band gap renormalization of free-standing
hydrogen-terminated, and oxidized SiNCs, as well as matrix-embedded SiNCs in
amorphous silica, and we obtain good agreement with experimental
photoluminescence data. We also provide strong evidence that the
electron-phonon interplay at the surface of the nanocrystal is suppressed by
oxidation and the surrounding amorphous matrix. For the matrix-embedded SiNCs,
we show a high correlation between the temperature dependence of the band gap
and the Si-Si strained bonds. This result emphasizes the immanent relationship
of electron-phonon coupling and thermal structural distortions. We also
demonstrate that, apart from quantum confinement, Si- Si strained bonds are the
major cause of zero-phonon quasidirect transitions in matrix-embedded SiNCs. As
a final point, we clarify that, unlike optical absorption in bulk Si,
phonon-assisted electronic transitions play a secondary role in SiNCs.",2005.11174v1
2020-05-24,Applying configurational complexity to the 2D Ruddlesden-Popper crystal structure,"The 2D layered Ruddlesden-Popper crystal structure can host a broad range of
functionally important behaviors. Here we establish extraordinary
configurational disorder in a two dimensional layered Ruddlesden-Popper (RP)
structure using entropy stabilization assisted synthesis. A protype A2CuO4 RP
cuprate oxide with five components (La, Pr, Nd, Sm, Eu) on the A-site
sublattice is designed and fabricated into epitaxial single crystal films using
pulsed laser deposition. By comparing (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 crystals
grown under identical conditions but different substrates, it is found that
heteroepitaxial strain plays an important role in crystal phase formation. When
grown on a near lattice matched substrate, the high entropy oxide film features
a T'-type RP structure with uniform A-site cation mixing and square-planar CuO4
units, however, growing under strong compressive strain results in a single
crystal non-RP cubic phase consistent with a CuX2O4 spinel structure. These
observations are made with a range of combined characterizations using X-ray
diffraction, atomic-resolution scanning transmission electron microscopy,
energy-dispersive X-ray spectroscopy, and X-ray absorption spectroscopy
measurements. Designing configurational complexity and moving between 2D
layered RP and 3D cubic crystal structures in this class of cuprate materials
opens many opportunities for new design strategies related to
magnetoresistance, unconventional superconductivity, ferroelectricity,
catalysis, and ion transport.",2005.11801v1
2020-06-03,Making Graphene Nano Inductor Using Table Top Laser Engraver,"There is great interest in so-called nano-electronic devices due to the
furious rate of device miniaturization. Fabrication of micro and nano scale
resistors and capacitors have already been achieved steadily, but so far, there
has been little development in the way of nano-scale coil inductors. This is
because of the physical limitations in miniaturization of the design of a
solenoid with wires coiled around a metallic core. So, while transistors get
steadily smaller, basic inductors in electronics remained relatively bulky. Few
methods exist for creating conductive polymer coils and graphene-based kinetic
nano-inductors, but their large-scale fabrication process is complex and mostly
beyond the current commercial technology available. So, a simpler, scalable,
and robust fabrication technique is needed to overcome this bottleneck. In this
work we demonstrate a new technique consisting of the laser lithography using a
laser engraver of a (poly)vinyl alcohol (PVA)/graphene oxide film composite
which results in a large inductive effect. We attribute this behavior to the
formation of high curvature twisted screw dislocation type conductive pathways
composed of polyacetylene chains linked by pi-pi interactions to reduced
graphene oxide flakes resulting in inductive effect.",2006.02331v1
2020-06-09,The effect of varying atmospheric pressure upon habitability and biosignatures of Earth-like planets,"Understanding the possible climatic conditions on rocky extrasolar planets,
and thereby their potential habitability, is one of the major subjects of
exoplanet research. Determining how the climate, as well as potential
atmospheric biosignatures, change under different conditions is a key aspect
when studying Earth-like exoplanets. One important property is the atmospheric
mass hence pressure and its influence on the climatic conditions. Therefore,
the aim of the present study is to understand the influence of atmospheric mass
on climate, hence habitability, and the spectral appearance of planets with
Earth-like, that is, N2-O2 dominated, atmospheres orbiting the Sun at 1
Astronomical Unit. This work utilizes a 1D coupled, cloud-free,
climate-photochemical atmospheric column model; varies atmospheric surface
pressure from 0.5 bar to 30 bar; and investigates temperature and key species
profiles, as well as emission and brightness temperature spectra in a range
between 2{\mu}m - 20{\mu}m. Increasing the surface pressure up to 4 bar leads
to an increase in the surface temperature due to increased greenhouse warming.
Above this point, Rayleigh scattering dominates and the surface temperature
decreases, reaching surface temperatures below 273K (approximately at ~34 bar
surface pressure). For ozone, nitrous oxide, water, methane, and carbon
dioxide, the spectral response either increases with surface temperature or
pressure depending on the species. Masking effects occur, for example, for the
bands of the biosignatures ozone and nitrous oxide by carbon dioxide, which
could be visible in low carbon dioxide atmospheres.",2006.05207v1
2020-06-19,Regular-Triangle Trimer and Charge Order Preserving the Anderson Condition in the Pyrochlore Structure of CsW$_2$O$_6$,"Since the discovery of the Verwey transition in magnetite, transition metal
compounds with pyrochlore structures have been intensively studied as a
platform for realizing remarkable electronic phase transitions. We report the
discovery of a unique phase transition that preserves the cubic symmetry of the
beta-pyrochlore oxide CsW$_2$O$_6$, where each of W 5d electrons are confined
in regular-triangle W3 trimers. This trimer formation is an unprecedented
self-organization of d electrons, which can be resolved into a charge order
satisfying the Anderson condition in a nontrivial way, orbital order caused by
the distortion of WO6 octahedra, and the formation of a spin-singlet pair in a
regular-triangle trimer. Electronic instability due to the unusual
three-dimensional nesting of Fermi surfaces and the localized nature of the 5d
electrons characteristic of the pyrochlore oxides were found to play important
roles in this unique charge-orbital-spin coupled phenomenon.",2006.11053v1
2020-06-23,Proton polarons in HxWO3 by synchrotron photoemission and DFT modelling,"The measurement of hydrogen induced changes on the electronic structure of
transition metal oxides by X-ray photoelectron spectroscopy is a challenging
endeavor, since the origin of the photoelectron cannot be unambiguously
assigned to hydrogen. The H-induced electronic structure changes in tungsten
trioxide have been known for more than 100 years, but are still being
controversially debated. The controversy stems from the difficulty in
disentangling effects due to hydrogenation from the effects of oxygen
deficiencies. Using a membrane approach to X-ray photoelectron spectroscopy, in
combination with tuneable synchrotron radiation we measure simultaneously core
levels and valence band up to a hydrogen pressure of 1000 mbar. Upon
hydrogenation, the intensities of the W$^{5+}$ core level and a state close to
the Fermi level increase following the pressure-composition isotherm curve of
bulk H$_x$WO$_3$. Combining experimental data and density-functional theory the
description of the hydrogen induced coloration by a proton polaron model is
corroborated. Although hydrogen is the origin of the electronic structure
changes near the Fermi edge, the valence band edge is now dominated by tungsten
orbitals instead of oxygen as is the case for the pristine oxide having wider
implication for its use as (photo-electrochemical) catalyst.",2006.13113v2
2020-06-23,Oxide Fermi liquid universality revealed by electron spectroscopy,"We present a combined soft x-ray and high-resolution vacuum-ultraviolet
angle-resolved photoemission spectroscopy study of the electron-overdoped
cuprate Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_4$ (PLCCO). Demonstration of its
highly two-dimensional band structure enabled precise determination of the
in-plane self-energy dominated by electron-electron scattering. Through
analysis of this self-energy and the Fermi-liquid cut-off energy scale, we find
-- in contrast to hole-doped cuprates -- a momentum isotropic and comparatively
weak electron correlation in PLCCO. Yet, the self-energies extracted from
multiple oxide systems combine to demonstrate a logarithmic divergent relation
between the quasiparticle scattering rate and mass. This constitutes a
spectroscopic version of the Kadowaki-Woods relation with an important merit --
the demonstration of Fermi liquid quasiparticle lifetime and mass being set by
a single energy scale.",2006.13119v2
2020-06-30,"Oxidation states, Thouless' pumps, and non-trivial ionic transport in non-stoichiometric electrolytes","Thouless' quantization of adiabatic particle transport permits to associate
an integer topological charge with each atom of an electronically gapped
material. If these charges are additive and independent of atomic positions,
they provide a rigorous definition of atomic oxidation states and atoms can be
identified as integer-charge carriers in ionic conductors. Whenever these
conditions are met, charge transport is necessarily convective, i.e. it cannot
occur without substantial ionic flow, a transport regime that we dub trivial.
We show that the topological requirements that allow these conditions to be
broken are the same that would determine a Thouless' pump mechanism if the
system were subject to a suitably defined time-periodic Hamiltonian. The
occurrence of these requirements determines a non-trivial transport regime
whereby charge can flow without any ionic convection, even in electronic
insulators. These results are first demonstrated with a couple of simple
molecular models that display a quantum pump mechanism upon introduction of a
fictitious time dependence of the atomic positions along a closed loop in
configuration space. We finally examine the impact of our findings on the
transport properties of non-stoichiometric alkali-halide melts, where the same
topological conditions that would induce a quantum pump mechanism along certain
closed loops in configuration space also determine a non-trivial transport
regime such that most of the total charge current results to be uncorrelated
from the ionic ones.",2006.16749v2
2020-08-10,On the suitability of hBN as an insulator for 2D material-based ultrascaled CMOS devices,"Complementary metal oxide semiconductor (CMOS) logic circuits at the ultimate
scaling limit place the utmost demands on the properties of all materials
involved. The requirements for semiconductors are well explored and could
possibly be satisfied by a number of layered two-dimensional (2D) materials,
like for example transition-metal dichalcogenides or black phosphorus. The
requirements for the gate insulator are arguably even more challenging and
difficult to meet. In particular the combination of insulator to semiconductor
which forms the central element of the metal oxide semiconductor field effect
transistor (MOSFET) has to be of superior quality in order to build competitive
devices. At the moment, hexagonal boron nitride (hBN) is the most common
two-dimensional insulator and widely considered to be the most promising gate
insulator in nanoscaled 2D material-based transistors. Here, we critically
assess the material parameters of hBN and conclude that while its properties
render hBN an ideal candidate for many applications in 2D nanoelectronics, hBN
is most likely not suitable as a gate insulator for ultrascaled CMOS devices.",2008.04144v1
2020-08-12,Controlled electrochemical functionalization of CNT fibers: structure-chemistry relations and application in current collector-free all-solid supercapacitors,"Chemical functionalization of nanocarbons is an important strategy to produce
electrochemical systems with higher energy/power density by generating surface
functional groups with additional faradaic contribution, by increasing their
surface area and correspondent capacitive contribution and by improving
compatibility with aqueous electrolytes and other active materials, such as
pseudocapacitive metal-oxides. Here we present an electrochemical method to
simultaneously swell and functionalize large electrodes consisting of fabrics
of macroscopic fibers of carbon nanotubes that renders the material hydrophilic
and produces a substantial increase of specific capacitance and energy density
in aqueous electrolytes. Through in-depth characterization of the carbon
nanotube fibres (CNTF) by Raman spectroscopy, transmission electron microscopy,
X-ray photoelectrocn spectroscopy (XPS) and small-angle X-ray scattering (SAXS)
we identify various contributions to such improvements, including surface
oxidation, tubular unzipping, debundling and inter-bundle swelling. Changes in
hydrophilicity of functionalized CNTF are determined by analyzing the dynamics
of spreading of polar and nonpolar liquids in the electrode. The extracted
contact angles and polar and dispersive surface energy components for different
treatment conditions are in agreement with changes in dipole-moment obtained by
XPS. Finally, functionalized CNTF electrodes were employed in current
collector-free solid flexible supercapacitors, which show enhanced
electrochemical properties compared to as-produced hydrophobic ones.",2008.05340v1
2020-08-14,Optical Identification of Materials Transformations in Oxide Thin Films,"Recent advances in high-throughput experimentation for combinatorial studies
have accelerated the discovery and analysis of materials across a wide range of
compositions and synthesis conditions. However, many of the more powerful
characterization methods are limited by speed, cost, availability, and/or
resolution. To make efficient use of these methods, there is value in
developing approaches for identifying critical compositions and conditions to
be used as a-priori knowledge for follow-up characterization with
high-precision techniques, such as micron-scale synchrotron based X-ray
diffraction (XRD). Here we demonstrate the use of optical microscopy and
reflectance spectroscopy to identify likely phase-change boundaries in thin
film libraries. These methods are used to delineate possible metastable phase
boundaries following lateral-gradient Laser Spike Annealing (lg-LSA) of oxide
materials. The set of boundaries are then compared with definitive
determinations of structural transformations obtained using high-resolution
XRD. We demonstrate that the optical methods detect more than 95% of the
structural transformations in a composition-gradient La-Mn-O library and a
Ga$_2$O$_3$ sample, both subject to an extensive set of lg-LSA anneals. Our
results provide quantitative support for the value of optically-detected
transformations as a priori data to guide subsequent structural
characterization, ultimately accelerating and enhancing the efficient
implementation of $\mu$m-resolution XRD experiments.",2008.06419v1
2020-08-22,Indium-Tin-Oxide Transistors with One Nanometer Thick Channel and Ferroelectric Gating,"In this work, we demonstrate high performance indium-tin-oxide (ITO)
transistors with the channel thickness down to 1 nm and ferroelectric
Hf0.5Zr0.5O2 as gate dielectric. On-current of 0.243 A/mm is achieved on
sub-micron gate-length ITO transistors with a channel thickness of 1 nm, while
it increases to as high as 1.06 A/mm when the channel thickness increases to 2
nm. A raised source/drain structure with a thickness of 10 nm is employed,
contributing to a low contact resistance of 0.15 {\Omega}mm and a low contact
resistivity of 1.1{\times}10-7 {\Omega}cm2. The ITO transistor with a recessed
channel and ferroelectric gating demonstrates several advantages over 2D
semiconductor transistors and other thin film transistors, including large-area
wafer-size nanometer thin film formation, low contact resistance and contact
resistivity, atomic thin channel being immunity to short channel effects, large
gate modulation of high carrier density by ferroelectric gating, high-quality
gate dielectric and passivation formation, and a large bandgap for the
low-power back-end-of-line (BEOL) CMOS application.",2008.09881v1
2020-08-27,Predicting band gaps and band-edge positions of oxide perovskites using DFT and machine learning,"Density functional theory within the local or semilocal density
approximations (DFT-LDA/GGA) has become a workhorse in electronic structure
theory of solids, being extremely fast and reliable for energetics and
structural properties, yet remaining highly inaccurate for predicting band gaps
of semiconductors and insulators. Accurate prediction of band gaps using
firstprinciples methods is time consuming, requiring hybrid functionals,
quasi-particle GW, or quantum Monte Carlo methods. Efficiently correcting
DFT-LDA/GGA band gaps and unveiling the main chemical and structural factors
involved in this correction is desirable for discovering novel materials in
high-throughput calculations. In this direction, we use DFT and machine
learning techniques to correct band gaps and band-edge positions of a
representative subset of ABO3 perovskite oxides. Relying on results of HSE06
hybrid functional calculations as target values of band gaps, we find a
systematic band gap correction of ~1.5 eV for this class of materials, where ~1
eV comes from downward shifting the valence band and ~0.5 eV from uplifting the
conduction band. The main chemical and structural factors determining the band
gap correction are determined through a feature selection procedure.",2008.12412v2
2020-09-06,$In$ $situ$ and $operando$ characterisation techniques for solid oxide electrochemical cells: Recent advances,"Oxygen activity and surface stability are two key parameters in the search
for advanced materials for intermediate temperature solid oxide electrochemical
cells, as overall device performance depends critically on them. In particular
$in$ $situ$ and $operando$ characterisation techniques have accelerated the
understanding of degradation processes and the identification of active sites,
motivating the design and synthesis of improved, nanoengineered materials. In
this short topical review we report on the latest developments of various
sophisticated $in$ $situ$ and $operando$ characterization techniques, including
Transmission and Scanning Electron Microscopy (TEM and SEM), surface-enhanced
Raman spectroscopy (SERS), Electrochemical Impedance Spectroscopy (EIS), X-ray
Diffraction (XRD) and synchrotron based X-ray photoelectron spectroscopy (XPS)
and X-ray absorption spectroscopy (XAS), among others. We focus on their use in
three emerging topics, namely: (i) the analysis of general electrochemical
reactions and the surface defect chemistry of electrode materials; (ii) the
evolution of electrode surfaces achieved by nanoparticle exsolution for
enhanced oxygen activity and (iii) the study of surface degradation caused by
Sr segregation, leading to reduced durability. For each of these topics we
highlight the most remarkable examples recently published. We anticipate that
ongoing improvements in the characterisation techniques and especially a
complementary use of them by multimodal approaches will lead to improved
knowledge of $operando$ processes, hence allowing a significant advancement in
cell performance in the near future.",2009.02693v1
2020-09-07,Resolving Few-Layer Antimonene/Graphene Heterostructures,"Two-dimensional (2D) antimony (Sb, antimonene) recently attracted interest
due to its peculiar electronic properties and its suitability as anode material
in next generation batteries. Sb however exhibits a large
polymorphic/allotropic structural diversity, which is also influenced by the
Sb's support. Thus understanding Sb heterostructure formation is key in 2D Sb
integration. Particularly 2D Sb/graphene interfaces are of prime importance as
contacts in electronics and electrodes in batteries. We thus study here
few-layered 2D Sb/graphene heterostructures by atomic-resolution (scanning)
transmission electron microscopy. We find the co-existence of two Sb
morphologies: First is a 2D growth morphology of layered beta-Sb with
beta-Sb(001)||graphene(001) texture. Second are one-dimensional (1D) Sb
nanowires which can be matched to beta-Sb with beta-Sb[2-21] perpendicular to
graphene(001) texture and are structurally also closely related to
thermodynamically non-preferred cubic Sb(001)||graphene(001). Importantly, both
Sb morphologies show rotational van-der-Waals epitaxy with the graphene
support. Both Sb morphologies are well resilient against environmental bulk
oxidation, although superficial Sb-oxide layer formation merits consideration,
including formation of novel epitaxial Sb2O3(111)/beta-Sb(001)
heterostructures. Exact Sb growth behavior is sensitive on employed processing
and substrate properties including, notably, the nature of the support
underneath the direct graphene support. This introduces the substrate
underneath a direct 2D support as a key parameter in 2D Sb heterostructure
formation. Our work provides insights into the rich phase and epitaxy landscape
in 2D Sb and 2D Sb/graphene heterostructures.",2009.03097v1
2020-09-08,Unveiling the role of carbon defects in the exceptional narrowing of m-ZrO2 bandgap for enhanced photoelectrochemical water splitting performance,"The development of efficient photoelectrodes via defect engineering of
wide-band gap metal oxides has been the prime focus for many years.
Specifically, the effect of carbon defects in wide-band gap metal oxides on
their performance in photoelectrochemical (PEC) applications raised numerous
controversies and still elusive. Herein, the effect of various carbon defects
in m-ZrO2 was investigated using the density functional theory to probe the
thermodynamic, electronic, and optical properties of the defective structures
against pristine m-ZrO2. The defect formation energies revealed that elevating
the temperature promotes and facilitates the formation of carbon defects.
Moreover, the binding energies confirmed the stability of all studied complex
carbon defects. Furthermore, the band edge positions against the redox
potentials of water species revealed that all the studied defective structures
can serve as photoanodes for water splitting. Additionally, CO3c (carbon atom
substituted O3c site) was the only defective structure that exhibited slight
straddling of the redox potentials of water. Importantly, all investigated
defective structures enhanced light absorption with different optical
activities. Finally, CO3cVO3c (carbon atom substituted O3c associated with O3c
vacancy) defective m-ZrO2 enjoyed low direct band gap (1.9 eV), low defect
formation energy, low exciton binding energy, high mobility of charge carriers,
fast charge transfer, and low recombination rate. Concurrently, its optical
properties were exceptional in terms of high absorption, low reflectivity and
improved static dielectric constant. Hence, the study recommends CO3cVO3c
defective m-ZrO2 as the leading candidate to serve as a photoanode for PEC
applications.",2009.03674v1
2020-09-18,Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition,"The integration of graphene (Gr) with nitride semiconductors is highly
interesting for applications in high-power/high-frequency electronics and
optoelectronics. In this work, we demonstrated the direct growth of Gr on
Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition
(CVD) at temperature of 1350{\deg}C. After optimization of the C3H8 flow rate,
a uniform and conformal Gr coverage was achieved, which proved beneficial to
prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy (XPS)
revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region.
Such chemical modification of a 2 nm thick AlGaN surface region was confirmed
by cross-sectional scanning transmission electron microscopy (STEM) combined
with electron energy loss spectroscopy (EELS), which also showed the presence
of a bilayer of Gr with partial sp2/sp3 hybridization. Raman spectra indicated
that the deposited Gr is nanocrystalline (with domain size 7 nm) and
compressively strained. A Gr sheet resistance of 15.8 kOhm/sq was evaluated by
four-point-probe measurements, consistently with the nanocrystalline nature of
these films. Furthermore, nanoscale resolution current mapping by conductive
atomic force microscopy (C-AFM) indicated local variations of the Gr carrier
density at a mesoscopic scale, which can be ascribed to changes in the charge
transfer from the substrate due to local oxidation of AlGaN or to the presence
of Gr wrinkles.",2009.08673v1
2020-09-18,Tail-states induced semiconductor-toconductor like transition under sub-bandgap light excitation in the zinc-tin-oxide photothinfilm transistors,"We report on a giant persistent photoconductivity (PPC) induced
semiconductor-to-conductor like transition in zinc-tin-oxide (ZTO)
photo-thinfilm transistors (TFT). The active ZTO channel layer was prepared by
remote-plasma reactive sputtering and possesses an amorphous structure. Under
subbandgap excitation of ZTO with UV light, the photocurrent reaches as high as
~10 -4 A (a photo-to-dark current ratio of ~10 7) and remains close to this
high value after switching off the light. During this time, the ZTO TFT
exhibits gigantic PPC with long-lasting recovery time, which leads the ZTO
compound to undergo a semiconductor-to-conductor like transition. In the
present case, the conductivity changes over six orders of magnitude, from ~10-7
to 0.92 {\Omega} -1cm-1. After UV exposure, the ZTO compound can potentially
remain in the conducting state for up to a month. The underlying physics of the
observed PPC effect is investigated by studying defects (deep-states and
tail-states) by employing a discharge current analysis (DCA) technique.
Findings from the DCA study reveal direct evidence for the involvement of
sub-gap tail-states of the ZTO in the giant PPC, while deep-states contribute
to mild PPC.",2009.08714v1
2020-09-20,Remarkable antibacterial activity of reduced graphene oxide functionalized by copper ions,"Despite long-term efforts for exploring antibacterial agents or drugs, it
remains challenging how to potentiate antibacterial activity and meanwhile
minimize toxicity hazards to the environment. Here, we experimentally show that
the functionality of reduced graphene oxide (rGO) through copper ions displays
selective antibacterial activity significantly stronger than that of rGO itself
and no toxicity to mammalian cells. Remarkably, this antibacterial activity is
two orders of magnitude greater than the activity of its surrounding copper
ions. We demonstrate that the rGO is functionalized through the cation-${\pi}$
interaction to massively adsorb copper ions to form a rGO-copper composite in
solution and result in an extremely low concentration level of surrounding
copper ions (less than ~0.5 ${\mu}M$). These copper ions on rGO are positively
charged and strongly interact with negatively charged bacterial cells to
selectively achieve antibacterial activity, while rGO exhibits the
functionality to not only actuate rapid delivery of copper ions and massive
assembly onto bacterial cells but also result in the valence shift in the
copper ions from Cu$^{2+}$ into Cu$^{+}$ which greatly enhances the
antibacterial activity. Notably, this functionality of rGO through
cation-${\pi}$ interaction with copper ions can similarly achieve algaecidal
activity but does not exert cytotoxicity against neutrally charged mammalian
cells. The remarkable selective antibacterial activity from the rGO
functionality as well as the inherent broad-spectrum-antibacterial physical
mechanism represents a significant step toward the development of a novel
antibacterial material and reagent without environmental hazards for practical
application.",2009.09365v1
2020-09-30,Domain Control by Adjusting Anisotropic Stress in Pyrochlore Oxide Cd2Re2O7,"The 5d pyrochlore oxide Cd2Re2O7 exhibits successive phase transitions from a
cubic pyrochlore structure (phase I) to a tetragonal structure without
inversion symmetry below Ts1 of ~200 K (phase II) and further to another
noncentrosymmetric tetragonal structure below Ts2 of ~120 K (phase III). The
two low-temperature phases may be characterized by odd-parity multipolar orders
induced by the Fermi liquid instability of the spin-orbit-coupled metal. To
control the tetragonal domains generated by the transitions and to obtain a
single-domain crystal for the measurements of anisotropic properties, we
prepared single crystals with the (0 0 1) surface and applied biaxial and
uniaxial stresses along the plane. Polarizing optical microscopy observations
revealed that inducing a small strain of approximately 0.05% could flip the
twin domains ferroelastically in a reversible fashion at low temperatures,
which evidences that the tetragonal deformation switches at Ts2 between c > a
for phase II and c < a for phase III. Resistivity measurements using
single-domain crystals under uniaxial stress showed that the anisotropy was
maximum at around Ts2 and turned over across Ts2: resistivity along the c axis
is larger (smaller) than that along the a axis by ~25% for phase II (III) at
around Ts2. These large anisotropies probably originate from spin-dependent
scattering in the spin-split Fermi surfaces of the cluster electric toroidal
quadrupolar phases of Cd2Re2O7.",2009.14443v1
2020-10-05,Proof-of-concept thermoelectric oxygen sensor exploiting oxygen mobility of GdBaCo2O5+δ,"In this paper, we demonstrate a proof-of-concept oxygen sensor based on the
thermoelectric principle using polycrystalline $GdBaCo_2O_{5+\delta}$ where
0.45<${\delta}$<0.55 (GDCO). The lattice oxygen in layered double perovskite
oxides is highly susceptible to the ambient oxygen partial pressure. The
as-synthesized GDCO sample processed in ambient conditions shows pure
orthorhombic ($P_{mmm}$ space group) phase and a ${\delta}$-value close to 0.5
as confirmed from X-ray diffraction reitveld refinement. The X-ray
photoelectron spectroscopy shows significant $Co^{3+}$ oxidation state in
non-octahedral sites in addition to $Co^{3+}$ and $Co^{4+}$ in octahedral
sites. The insulator-to-metal transition (MIT) is observed at nearly 340 K as
seen in electrical resistivity and seebeck coefficient measurements. The
seebeck coefficient shows a large change of about 10-13 $\mu$V/K with time
constant of ~20 sec, at room temperature (300 K) when the gas ambience changes
from 100% oxygen to 100% nitrogen and vice versa, under a constant temperature
gradient of 1 K. The response in seebeck is found to be particularly large
below MIT. The diffusion of oxygen into the lattice leading to hole doping
shows a large change in carrier concentration resulting in a large change in
the seebeck coefficient in insulating state. On the other hand, due to
insignificant increase in already large carrier concentration in metallic state
the change in seebeck is minimal. Nevertheless, below MIT the response is
fairly reproducible within stoichiometry ${\delta}$ = 0.5 $\pm$ 0.05. This
principle shall be of significant utility to design the oxygen sensors which
work at room temperature or even cryogenic temperatures.",2010.01783v1
2020-10-06,Li4-xGe1-xPxO4 a potential solid-state electrolyte for all-oxide microbatteries,"Solid-state electrolytes for Li-ion batteries are attracting growing interest
as they allow building safer batteries, also using lithium metal anodes. Here
we studied a compound in the lithium superionic conductor (LISICON) family,
i.e. Li4-xGe1-xPxO4 (LGPO). Thin films were deposited via pulsed laser
deposition and their electrical properties were compared with ceramic pellets.
A detailed characterization of the micro structure shows that thin films can be
deposited fully crystalline at higher temperatures but also partially amorphous
at room temperature. The conductivity is not strongly influenced by the
presence of grain boundaries, exposure to air or lithium deficiencies.
First-principles molecular dynamics simulations were employed to calculate the
lithium ion diffusion profile and the conductivity at various temperatures of
the ideal LGPO crystal. Simulations gives the upper limit of conductivity for a
defect free crystal, which is in the range of 10-2 S cm-1 at 300 deg. The ease
of thin film fabrication, the room-temperature Li-ion conductivity in the range
of a few microS cm-1 make LGPO a very appealing electrolyte material for thin
film all-solid-state all-oxide microbatteries.",2010.02608v1
2020-10-15,Electrolytes for Li-ion all-solid-state batteries: a first-principles comparative study of Li10GeP2O12 and Li10GeP2S12 in the LISICON and LGPS phases,"In this work we address Li-ion diffusion in thio-LISICON materials and in
their oxide counterparts, exploring both the orthorhombic and tetragonal phases
of Li10GeP2S12(LGPS) and Li10GeP2O12(LGPO) through extended Car-Parrinello
molecular dynamics in the canonical and isobaric-isothermal ensemble. The
(quasi-)orthorhombic and tetragonal phases are studied both for the oxide and
for the sulfide, with the aim of comparing their conductivity with the same
approach; out of these four case studies, tetragonal LGPO has not been reported
and, while dynamically stable, it sits (0.04 Ha/formula unit) above
orthorhombic LGPO. We calculate activation energies for diffusion of 0.18 eV
and 0.23 eV for tetragonal and orthorhombic LGPS, and of 0.22 eV and 0.34eV for
tetragonal and orthorhombic LGPO. In line with experiments, we find
orthorhombic LGPO orders of magnitude less conductive, at room temperature,
than the two sulfide systems. However, this is not the case for tetragonal
LGPO, which, although less stable than its orthorhombic allotrope, shows at
room temperature a conductivity comparable to orthorhombic and tetragonal LGPS,
and, if synthesized, could make a very attractive Li-ion conductor.",2010.08068v1
2020-10-21,Rydberg Excitons in Synthetic Cuprous Oxide (Cu$_2$O),"High-lying Rydberg states of Mott-Wannier excitons are receiving considerable
interest due to the possibility of adding long-range interactions to the
physics of exciton-polaritons. Here, we study Rydberg excitation in bulk
synthetic cuprous oxide grown by the optical float zone technique and compare
the result with natural samples. X-ray characterization confirms both materials
are mostly single crystal, and mid-infrared transmission spectroscopy revealed
little difference between synthetic and natural material. The synthetic samples
show principal quantum numbers up to $n=10$, exhibit additional absorption
lines, plus enhanced spatial broadening and spatial inhomogeneity. Room
temperature and cryogenic photoluminescence measurements reveal a significant
excess of copper vacancies in the synthetic material. These measurements
provide a route towards achieving \mbox{high-$n$} excitons in synthetic
crystals, opening a route to scalable quantum devices.",2010.11117v1
2020-10-23,"Air-stable, earth-abundant molten chlorides and corrosion-resistant containment for chemically-robust, high-temperature thermal energy storage for concentrated solar power","A dramatic reduction in man-made CO2 emissions could be achieved if the cost
of electricity generated from concentrated solar power (CSP) plants could
become competitive with fossil-fuel-derived electricity. The solar
heat-to-electricity conversion efficiency of CSP plants may be significantly
increased (and the associated electricity cost decreased) by operating CSP
turbines with inlet temperatures >750 C instead of <550 C, and by using thermal
energy storage (TES) at >750 C to allow for rapidly dispatchable and/or
continuous electricity production. Unfortunately, earth-abundant
MgCl2-KCl-based liquids currently being considered as low-cost media for
large-scale, high-temperature TES are susceptible to oxidation in air, with
associated undesired changes in liquid composition and enhanced corrosion of
metal alloys in pipes and tanks containing such liquids. In this paper,
alternative high-temperature, earth-abundant molten chlorides that are stable
in air are identified via thermodynamic calculations. The oxidation resistance,
and corrosion-resistant containment, of such molten chlorides at 750 C are then
demonstrated. Such chemically-robust, low-cost TES media and effective
containment provide critical advances towards the higher-temperature operation
of, and lower-cost electricity generation from, CSP plants.",2010.12476v1
2020-11-11,Voltage tunable quantum dot array by patterned Ge-nanowire based metal-oxide-semiconductor (MOS) devices,"Semiconductor quantum dots (QDs) are being regarded as the primary unit for a
wide range of advanced and emerging technologies including electronics,
optoelectronics, photovoltaics and biosensing applications as well as the
domain of q-bits based quantum information processing. Such QDs are suitable
for several novel device applications for their unique property of confining
carriers 3-dimensionally creating discrete quantum states. However, the
realization of such QDs in practice exhibits serious challenge regarding their
fabrication in array with desired scalability and repeatability as well as
control over the quantum states at room temperature. In this context, the
current work reports the fabrication of an array of highly scaled Ge-nanowire
(radius ~25 nm) based vertical metal-oxide-semiconductor devices that can
operate as voltage tunable quantum dots at room temperature. The electrons in
such nanowire experience a geometrical confinement in the radial direction,
whereas, they can be confined axially by tuning the applied bias in order to
manipulate the quantum states. Such quantum confinement of electrons has been
confirmed from the step-like responses in the room temperature
capacitance-voltage (C-V) characteristics at relatively low frequency (200
kHz). Each of such steps has observed to encompass convolution of the quantized
states occupying ~6 electronic charges. The details of such carrier confinement
are analyzed in the current work by theoretically modeling the device transport
properties based on non-equilibrium Green's function (NEGF) formalism.",2011.06580v1
2020-11-26,Oxidising and carburising catalyst conditioning for the controlled growth and transfer of large crystal monolayer hexagonal boron nitride,"Hexagonal boron nitride (h-BN) is well-established as a requisite support,
encapsulant and barrier for 2D material technologies, but also recently as an
active material for applications ranging from hyperbolic metasurfaces to room
temperature single-photon sources. Cost-effective, scalable and high quality
growth techniques for h-BN layers are critically required. We utilise
widely-available iron foils for the catalytic chemical vapour deposition (CVD)
of h BN and report on the significant role of bulk dissolved species in h-BN
CVD, and specifically, the balance between dissolved oxygen and carbon. A
simple pre-growth conditioning step of the iron foils enables us to tailor an
error-tolerant scalable CVD process to give exceptionally large h-BN monolayer
domains. We also develop a facile method for the improved transfer of as-grown
h-BN away from the iron surface by means of the controlled humidity oxidation
and subsequent rapid etching of a thin interfacial iron oxide; thus, avoiding
the impurities from the bulk of the foil. We demonstrate wafer-scale (2 inch)
production and utilise this h-BN as a protective layer for graphene towards
integrated (opto) electronic device fabrication.",2011.13176v1
2020-11-29,Dispersing and semi-flat bands in the wide band gap two-dimensional semiconductor bilayer silicon oxide,"Epitaxial bilayer silicon oxide is a transferable two-dimensional material
predicted to be a wide band gap semiconductor, with potential applications for
deep UV optoelectronics, or as a building block of van der Waals
heterostructures. The prerequisite to any sort of such applications is the
knowledge of the electronic band structure, which we unveil using
angle-resolved photoemission spectroscopy and rationalise with the help of
density functional theory calculations. We discover dispersing bands related to
electronic delocalisation within the top and bottom planes of the material,
with two linear crossings reminiscent of those predicted in bilayer AA-stacked
graphene, and semi-flat bands stemming from the chemical bridges between the
two planes. This band structure is robust against exposure to air, and can be
controled by exposure to oxygen. We provide an experimental lower-estimate of
the band gap size of 5 eV and predict a full gap of 7.36 eV using density
functional theory calculations.",2011.14376v2
2021-02-01,Atomistic calculations of charged point defects at grain boundaries in SrTiO$_3$,"Oxygen vacancies have been identified to play an important role in
accelerating grain growth in polycrystalline perovskite-oxide ceramics. In
order to advance the fundamental understanding of growth mechanisms at the
atomic scale, classical atomistic simulations were carried out to investigate
the atomistic structures and oxygen vacancy formation energies at grain
boundaries in the prototypical perovskite-oxide material SrTiO$_3$. In this
work, we focus on two symmetric tilt grain boundaries, namely
$\Sigma$5(310)[001] and $\Sigma$5(210)[001]. A one-dimensional continuum model
is adapted to determine the electrostatic potential induced by charged lattice
planes in atomistic structure models containing grain boundaries and point
defects. By means of this model, electrostatic artifacts, which are inherent to
supercell models with periodic or open boundary conditions, can be taken into
account and corrected properly. We report calculated formation energies of
oxygen vacancies on all the oxygen sites across boundaries between two
misoriented grains, and we analyze and discuss the formation-energy values with
respect to local charge densities at the vacant sites.",2102.01016v2
2021-02-03,Selective Enhancement in Phonon Scattering leads to High Thermoelectric Figure of Merit in ZnO -- Graphene Oxide Core-shell Nanohybrids,"ZnO is a promising candidate as an environment friendly thermoelectric (TE)
material. However, the poor TE figure of merit (zT) needs to be addressed to
achieve significant TE efficiency for commercial applications. Here we
demonstrate that selective enhancement in phonon scattering leads to increase
in zT of RGO encapsulated Al-doped ZnO core shell nanohybrids, synthesized via
a facile and scalable method. The incorporation of 1 at% Al with 1.5 wt% RGO
into ZnO (AGZO) has been found to show significant enhancement in zT (=0.52 at
1100 K) which is an order of magnitude larger compared to that of bare undoped
ZnO. Photoluminescence and X-ray photoelectron spectroscopy measurements
confirm that RGO encapsulation significantly quenches surface oxygen vacancies
in ZnO along with nucleation of new interstitial Zn donor states. Tunneling
spectroscopy reveals that the band gap of ~ 3.4 eV for bare ZnO reduces
effectively to ~ 0.5 eV upon RGO encapsulation, facilitating charge transport.
The electrical conductivity enhancement also benefits from the more than 95%
densification achieved, using the spark plasma sintering method, which aids
reduction of GO into RGO. The same Al doping and RGO capping synergistically
brings about drastic reduction of thermal conductivity, through enhanced
phonon-phonon and point defect-phonon scatterings. These opposing effects on
electrical and thermal conductivities enhances the power factors as well as the
zT value. Overall, a practically viable route for synthesis of oxide - RGO TE
material which could find its practical applications for the high-temperature
TE power generation.",2102.01896v1
2021-02-04,Structural phase transition and its consequences on optical behavior of LaV$_{1-x}$Nb$_x$O$_4$,"We present the structural, electronic, vibrational, and photoluminescence
properties of polycrystalline LaV$_{1-x}$Nb$_x$O$_4$ ($x =$ 0--0.2) samples at
room temperature. The substitution of Nb at the V site shows the fascinating
structural and optical behavior due to their isoelectronic character and larger
ionic radii of Nb$^{5+}$ as compared to the V$^{5+}$. The Rietveld refinement
of x-ray diffraction patterns demonstrate that the $x=$ 0 sample exist in a
monoclinic (P2$_1$/n) phase, whereas for the $x >$ 0, both monoclinic and
scheelite-tetragonal (I4$_1$/a) phases co-exist in a certain proportion.
Interestingly, a monotonous enhancement in the Raman spectral intensity with Nb
substitution is correlated with the substitution induced increase in the
scheelite-tetragonal phase. The x-ray absorption measurements reveal that the
La ions exist in a trivalent oxidation state, while V and Nb cations possess 5+
oxidation state in tetrahedral coordination. Moreover, the Fourier-transform
infrared (FTIR) spectra indicate that the Nb substitution give origin to some
additional IR modes owing to the deformation of the VO$_4$$^{3-}$ tetrahedra
and mixing of monoclinic and tetragonal phases. The photoluminescence
measurements on these samples exhibit broadband spectra and their deconvolution
designate the availability of more than one electron-hole pairs recombination
center.",2102.02442v2
2021-02-07,Quantum Conductors Formation and Resistive Switching Memory Effects in Zirconia Nanotubes,"The development prospects of memristive elements for non-volatile memory with
use of the metal-dielectric-metal sandwich structures with a thin oxide layer
are due to the possibility of reliable forming the sustained functional states
with quantized resistance. In the paper we study the properties of fabricated
memristors based on the non-stoichiometric $ZrO_2$ nanotubes in different
resistive switching modes. Anodic oxidation of the $Zr$ foil has been used to
synthesize a zirconia layer of $1.7$ $\mu$$m$ thickness, consisting of an
ordered array of vertically oriented nanotubes with outer diameter of 75 nm.
$Zr/ZrO_2/Au$ sandwich structures have been fabricated by mask magnetron
deposition. The effects of resistive switching in the $Zr/ZrO_2/Au$ memristors
in unipolar and bipolar modes have been investigated. The resistance ratios
$\geq3\cdot10^4$ between high-resistance (HRS) and low-resistance (LRS) states
have been evaluated. It has been founded the conductivity of LRS is quantized
in a wide range with minimum value of $0.5G_0=38.74$ $\mu$$S$ due to the
formation of quantum conductors based on oxygen vacancies ($V_O$). Resistive
switching mechanisms of $Zr/ZrO_2/Au$ memristors with allowing for migration of
$V_O$ in an applied electric field have been proposed. It has been shown that
the ohmic type and space charge limited conductivities are realized in the LRS
and HRS, correspondingly. We present the results which can be used for
development of effective memristors based on functional $Zr/ZrO_2/Au$
nanolayered structure with multiple resistive states and high resistance ratio.",2102.03764v1
2021-02-10,Control of the metal-insulator transition in NdNiO$_3$ thin films through the interplay between structural and electronic properties,"Heteroepitaxy offers a new type of control mechanism for the crystal
structure, the electronic correlations, and thus the functional properties of
transition-metal oxides. Here, we combine electrical transport measurements,
high-resolution scanning transmission electron microscopy (STEM), and density
functional theory (DFT) to investigate the evolution of the metal-to-insulator
transition (MIT) in NdNiO$_3$ films as a function of film thickness and
NdGaO$_3$ substrate crystallographic orientation. We find that for two
different substrate facets, orthorhombic (101) and (011), modifications of the
NiO$_6$ octahedral network are key for tuning the transition temperature
$T_{\text{MIT}}$ over a wide temperature range. A comparison of films of
identical thickness reveals that growth on [101]-oriented substrates generally
results in a higher $T_{\text{MIT}}$, which can be attributed to an enhanced
bond-disproportionation as revealed by the DFT+$U$ calculations, and a tendency
of [011]-oriented films to formation of structural defects and stabilization of
non-equilibrium phases. Our results provide insights into the
structure-property relationship of a correlated electron system and its
evolution at microscopic length scales and give new perspectives for the
epitaxial control of macroscopic phases in metal-oxide heterostructures.",2102.05415v2
2021-02-10,Atomic-scale insights into electro-steric substitutional chemistry of cerium oxide,"Cerium oxide (ceria, CeO2) is one of the most promising mixed ionic and
electronic conducting materials. Previous atomistic analysis has covered widely
the effects of substitution on oxygen vacancy migration. However, an in-depth
analysis of the role of cation substitution beyond trivalent cations has rarely
been explored. Here, we investigate soluble monovalent, divalent, trivalent and
tetravalent cation substituents. By combining classical simulations and quantum
mechanical calculations, we provide an insight into defect association energies
between substituent cations and oxygen vacancies as well as their effects on
the diffusion mechanisms. Our simulations indicate that oxygen ionic
diffusivity of subvalent cation-substituted systems follows the order Gd>Ca>Na.
With the same charge, a larger size mismatch with Ce cation yields a lower
oxygen ionic diffusivity, i.e., Na>K, Ca>Ni, Gd>Al. Based on these trends, we
identify species that could tune the oxygen ionic diffusivity: we estimate that
the optimum oxygen vacancy concentration for achieving fast oxygen ionic
transport is 2.5% for GdxCe1-xO2-x/2, CaxCe1-xO2-x and NaxCe1-xO2-3x/2 at 800
K. Remarkably, such a concentration is not constant and shifts gradually to
higher values as the temperature is increased. We find that co-substitutions
can enhance the impact of the single substitutions beyond that expected by
their simple addition. Furthermore, we identify preferential oxygen ion
migration pathways, which illustrate the electro-steric effects of substituent
cations in determining the energy barrier of oxygen ion migration. Such
fundamental insights into the factors that govern the oxygen diffusion
coefficient and migration energy would enable design criteria to be defined for
tuning the ionic properties of the material, e.g., by co-doping.",2102.05702v1
2021-02-10,cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM,"Atomic layer deposition (ALD) provides uniform and conformal thin films that
are of interest for a range of applications. To better understand the
properties of amorphous ALD films, we need improved understanding of their
local atomic structure. Previous work demonstrated measurement of how the local
atomic structure of ALD-grown aluminum oxide (AlOx) evolves in operando during
growth by employing synchrotron high energy X-ray diffraction (HE-XRD). In this
work, we report on efforts to employ electron diffraction pair distribution
function (ePDF) measurements using more broadly available transmission electron
microscope (TEM) instrumentation to study the atomic structure of amorphous
ALD-AlOx. We observe electron beam damage in the ALD-coated samples during ePDF
at ambient temperature and successfully mitigate this beam damage using ePDF at
cryogenic temperatures (cryo-ePDF). We employ cryo-ePDF and Reverse Monte Carlo
(RMC) modeling to obtain structural models of ALD-AlOx coatings formed at a
range of deposition temperatures from 150-332{\deg}C. From these model
structures, we derive structural metrics including stoichiometry, pair
distances, and coordination environments in the ALD-AlOx films as a function of
deposition temperature. The structural variations we observe with growth
temperature are consistent with temperature-dependent changes in the surface
hydroxyl density on the growth surface. The sample preparation and cryo-ePDF
procedures we report here can be used for routine measurement of ALD-grown
amorphous thin films to improve our understanding of the atomic structure of
these materials, establish structure-property relationships, and help
accelerate the timescale for the application of ALD to address technological
needs.",2102.05726v1
2021-02-14,Theoretical design study of FWM in silicon nitride waveguides with integrated graphene oxide films,"We theoretically investigate and optimize four-wave mixing (FWM) in silicon
nitride (SiN) waveguides integrated with two-dimensional (2D) layered graphene
oxide (GO) films. Based on extensive previous measurements of the material
parameters of the GO films, we perform detailed analysis for the influence of
device parameters including waveguide geometry, GO film thickness, length, and
coating position on the FWM conversion efficiency (CE) and conversion bandwidth
(CB). The influence of dispersion and photo-thermal changes in the GO films is
also discussed. Owing to the strong mode overlap between the SiN waveguides and
the highly nonlinear GO films, FWM in the hybrid waveguides can be
significantly enhanced. We obtain good agreement with previous experimental
results and show that by optimizing the device parameters to balance the
trade-off between Kerr nonlinearity and loss, the FWM CE can be improved by as
much as ~20.7 dB and the FWM CB can be increased by ~4.4 folds, relative to the
uncoated waveguides. These results highlight the significantly enhanced FWM
performance that can be achieved in SiN waveguides by integrating 2D layered GO
films.",2102.07118v1
2021-03-12,Numerical study of laser micro- and nano-processing of nanocomposite porous materials,"This thesis is focused on numerical simulations of the laser interaction with
porous materials. A possibility of well-controlled processing is particularly
important for the laser based micro-structuring of porous glass and
nano-machining of semiconducting porous materials in the presence of metallic
nanoparticles. To understand the periodic micro-void structures produced inside
porous glass by femtosecond laser pulses, a detailed numerical thermodynamic
analysis was performed. The calculation results show the possibility to control
laser micro-machining in volume of SiO2. The obtained characteristic dimensions
of the structures correlate with the experimental results. Comparing to the
porous glass, the mesoporous TiO2 films loaded by Ag ions and nanoparticles
support localized plasmon resonances. To identify the optimum parameters of the
continuous-wave laser, a multi-physical model considering Ag nanoparticle
growth, photo-oxidation, reduction was developed. The performed simulations
show that the laser writing speed controls the Ag nanoparticles size. The
thermally activated fast growth followed by the photo-oxidation was found to be
the main reason for the writing speed-dependent size-change and temperature
rises. Writing of mesoporous TiO2 films loaded with Ag nanoparticles by a
pulsed laser is, furthermore, promising to provide additional possibilities in
the generation of two kinds of nanostructures: laser-induced periodic surface
grooves and Ag nanogratingsinside the TiO2 film. To better understand the
effects of a pulsed laser, two multi-pulses models are developed to simulate
the Ag nanoparticle growth. The obtained results provided new insights into
laser micro-processing of porous material and better laser controlling over
nanostructuring in porous semiconducting films loaded with metallic
nanoparticles.",2103.07334v1
2021-03-13,Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate,"Improving the coherence of superconducting qubits is a fundamental step
towards the realization of fault-tolerant quantum computation. However,
coherence times of quantum circuits made from conventional aluminium-based
Josephson junctions are limited by the presence of microscopic two-level
systems in the amorphous aluminum oxide tunnel barriers. Here, we have
developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson
junctions on silicon substrates which promise to overcome the drawbacks of
qubits based on Al/AlO$_{x}$/Al junctions. The all-nitride qubits have great
advantages such as chemical stability against oxidation, resulting in fewer
two-level fluctuators, feasibility for epitaxial tunnel barriers that reduce
energy relaxation and dephasing, and a larger superconducting gap of $\sim$5.2
meV for NbN, compared to $\sim$0.3 meV for aluminium, which suppresses the
excitation of quasiparticles. By replacing conventional MgO by a silicon
substrate with a TiN buffer layer for epitaxial growth of nitride junctions, we
demonstrate a qubit energy relaxation time $T$$_{1}$=16.3 $\mu$s and a
spin-echo dephasing time $T$$_{2}$=21.5 $\mu$s. These significant improvements
in quantum coherence are explained by the reduced dielectric loss compared to
previously reported NbN-based qubits with MgO substrates
($T$$_{1}$$\approx$$T$$_{2}$$\approx$0.5 $\mu$s). These results are an
important step towards constructing a new platform for superconducting quantum
hardware.",2103.07711v3
2021-03-13,Water on Hot Rocky Exoplanets,"Data suggest that most rocky exoplanets with orbital period $p$ $<$ 100 d
(""hot"" rocky exoplanets) formed as gas-rich sub-Neptunes that subsequently lost
most of their envelopes, but whether these rocky exoplanets still have
atmospheres is unknown. We identify a pathway by which 1-1.7 $R_{Earth}$ (1-10
$M_{Earth}$) rocky exoplanets with orbital periods of 10-100 days can acquire
long-lived 10-2000 bar atmospheres that are H$_2$O-dominated, with mean
molecular weight $>$10. These atmospheres form during the planets' evolution
from sub-Neptunes into rocky exoplanets. H$_2$O that is made by reduction of
iron oxides in the silicate magma is highly soluble in the magma, forming a
dissolved reservoir that is protected from loss so long as the H$_2$-dominated
atmosphere persists. The large size of the dissolved reservoir buffers the
H$_2$O atmosphere against loss after the H$_2$ has dispersed. Within our model,
a long-lived, water-dominated atmosphere is a common outcome for efficient
interaction between a nebula-derived atmosphere (peak atmosphere mass fraction
0.1-0.6 wt%) and oxidized magma ($>$5 wt% FeO), followed by atmospheric loss.
This idea predicts that most rocky planets that have orbital periods of 10-100
days and that have radii within 0.1-0.2 $R_{Earth}$ of the lower edge of the
radius valley still retain H$_2$O atmospheres. This prediction is imminently
testable with JWST and has implications for the interpretation of data for
transiting super-Earths.",2103.07753v1
2021-03-15,"Good Solid-State Electrolytes Have Low, Glass-like Thermal Conductivity","Management of heat during charging and discharging of Li-ion batteries is
critical for their safety, reliability, and performance. Understanding the
thermal conductivity of the materials comprising batteries is crucial for
controlling the temperature and temperature distribution in batteries. This
work provides systemic quantitative measurements of the thermal conductivity of
three important classes of solid electrolytes (oxides, sulfides, and halides)
over the temperature range 150-350 K. Studies include the oxides
Li1.5Al0.5Ge1.5(PO4)3 and Li6.4La3Zr1.4Ta0.6O12, sulfides Li2S-P2S5, Li6PS5Cl,
and Na3PS4, and halides Li3InCl6 and Li3YCl6. Thermal conductivities of sulfide
and halide solid electrolytes are in the range 0.45-0.70 W m-1 K-1; thermal
conductivities of Li6.4La3Zr1.4Ta0.6O12 and Li1.5Al0.5Ge1.5(PO4)3 are 1.4 W m-1
K-1 and 2.2 W m-1 K-1, respectively. For most of the solid electrolytes studied
in this work, the thermal conductivity increases with increasing temperature;
i.e., the thermal conductivity has a glass-like temperature dependence. The
measured room-temperature thermal conductivities agree well with the calculated
minimum thermal conductivities indicating the phonon mean-free-paths in these
solid electrolytes are close to an atomic spacing. We attribute the low,
glass-like thermal conductivity of the solid electrolytes investigated to the
combination of their complex crystal structures and the atomic-scale disorder
induced by the materials processing methods that are typically needed to
produce high ionic conductivities.",2103.08718v1
2021-03-22,Time-frequency analysis assisted reconstruction of ruthenium optical constants in the sub-EUV spectral range 8nm-23.75nm,"The optical constants of ruthenium in the spectral range 8 nm to 23.75 nm
with their corresponding uncertainties are derived from the reflectance of a
sputtered ruthenium thin film in the Extreme Ultraviolet (EUV) spectral range
measured using monochromatized synchrotron radiation. This work emphasizes the
correlation between structure modelling and the reconstructed optical
parameters in a detailed inverse-problem optimization strategy. Complementary
X-ray Reflectivity (XRR) measurements are coupled with Markov chain Monte Carlo
(MCMC) based Bayesian inferences and quasi-model-independent methods to create
a model factoring the sample's oxidation, contamination, and surface roughness.
The sensitivity of the modelling scheme is tested and verified against
contamination and oxidation. A notable approach mitigating the high
dimensionality of the reconstruction problem is elaborated with the results of
this work compared to two previously published datasets. The presented dataset
is of high interest for the continuing development of Extreme Ultraviolet
Lithography (EUVL) and EUV astronomy optical systems.",2103.11868v1
2021-03-24,Metabolomic response of osteosarcoma cells to nanographene oxide-mediated hyperthermia,"Nanographene oxide (nGO)-mediated hyperthermia has been increasingly
investigated as a localised, minimally invasive anticancer therapeutic
approach. Near InfraRed (NIR) light irradiation for inducing hyperthermia is
particularly attractive, because biological systems mostly lack chromophores
that absorb in this spectral window, facilitating the selective heating and
destruction of cells which have internalized the NIR absorbing-nanomaterials.
However, little is known about biological effects accompanying nGO-mediated
hyperthermiaat cellular and molecular levels.In this work, well-characterised
pegylatednGOsheets with an hydrodynamic size of 300 nm were incubated with
human Saos-2 osteosarcoma cells for 24h and their incorporation verified by
flow cytometry and confocal microscopy. No effect on cell viability was
observed after nGO incorporation by Saos-2 cells. However, a proliferation
delay was observed due to the presence of nGO sheets in the cytoplasm.1H NMR
metabolomicswas employed to screen for changes in the metabolic profile of
cells, as this could help to improve understanding of celular responses to
nanomaterials and provide new endpoint markers of effect.Cells incorporating
nGO sheets showed noticeable changes in 10 metabolites compared to control
cells, including decreased levels of several amino acids, taurine and creatine
and increased levels of phosphocholine and uridine/adenosine nucleotides. After
NIR irradiation, cells showed decreases in glutamate and uridine nulceotides,
together with increases in glycerophosphocholine and adenosine monophosphate.
Overall, this study has shown that the celular metabolome sensitively responded
to nGO exposure and nGO-mediated hyperthermia and that NMR metabolomics is a
powerful tool toinvestigate treatment responses.",2103.13122v1
2021-04-07,Bulk photovoltaic effect in BaTiO$_3$-based ferroelectric oxides: An experimental and theoretical study,"The bulk photovoltaic effect exhibited by the non-centrosymmetric system
gains research interest due to the observed large open-circuit voltage. The
ferroelectric systems exhibiting anomalous photovoltaic effect are mostly
crystallized with multiphase coexistence. Hence, the computational difficulty
in building a multi-phase system restricts the detailed photovoltaic studies
through phenomenological and shift current theory. In this work, ferroelectric
Ba$_{1- x}$(Bi$_{0.5}$K$_{0.5}$)$_x$TiO$_3$ (BBKT) oxide is designed to
crystallize in single-phase tetragonal symmetry with improved polarization
characteristics, and it is found to exhibits large PV response. Both
experimental and theoretical studies on BBKT samples reveal ~18% reduction in
bandgap compared to the parent BaTiO$_3$. Short-circuit current measured as a
function of light intensity and light polarization angle reveal linear and
sinusoidal response, respectively. The observed features are in accordance with
phenomenological theory. Remarkably, x = 0.125 sample displays ~8 times higher
open-circuit voltage (7.39 V) than the parent compound. The enhanced PV effect
is attributed to the large shift current along z-direction as evidenced from
the additional charge-center shift of valence band occupied by O-2p orbital and
conduction band occupied by Bi-6p orbital. Notably, the degenerate Bi-p$_z$
state at conduction band minimum in BBKT favours the large shift current
response in the z-direction.",2104.03134v1
2021-04-12,Design of silicon waveguides for Kerr nonlinear optical performance with graphene oxide films,"The Kerr nonlinear optical performance of silicon nanowire waveguides
integrated with 2D layered graphene oxide (GO) films is theoretically studied
and optimized based on experimentally measured linear and nonlinear optical
parameters of the GO films. The strong mode overlap between the silicon
nanowires and highly nonlinear GO films yields a significantly enhanced Kerr
nonlinearity for the hybrid waveguides. A detailed analysis for the influence
of waveguide geometry and GO film thickness on the propagation loss, nonlinear
parameter, and nonlinear figure of merit (FOM) is performed. The results show
that the effective nonlinear parameter and nonlinear FOM can be increased by up
to 52 and 79 times relative to bare silicon nanowires, respectively. Self-phase
modulation (SPM)-induced spectral broadening of optical pulses is used as a
benchmark to evaluate the nonlinear performance, examining the tradeoff between
enhancing Kerr nonlinearity and minimizing loss. By optimizing the device
parameters to balance this, a high spectral broadening factor of 27.8 can be
achieved, more than 6 times that achieved in previous experiments. Finally, the
influence of pulse chirp, material anisotropy, and the interplay between
saturable absorption and SPM is also discussed, together with the comparison
between the spectral broadening after going through GO-coated and
graphene-coated silicon waveguides. These results provide useful guidance for
optimizing the Kerr nonlinear optical performance of silicon waveguides
integrated with 2D layered GO films.",2104.05836v1
2021-04-16,Machine Learning Approaches to Learn HyChem Models,"The HyChem approach has recently been proposed for modeling high-temperature
combustion of real, multi-component fuels. The approach combines lumped
reaction steps for fuel thermal and oxidative pyrolysis with detailed chemistry
for the oxidation of the resulting pyrolysis products. However, the approach
usually shows substantial discrepancies with experimental data within the
Negative Temperature Coefficient (NTC) regime, as the low-temperature chemistry
is more fuel-specific than high-temperature chemistry. This paper proposes a
machine learning approach to learn the HyChem models that can cover both
high-temperature and low-temperature regimes. Specifically, we develop a HyChem
model using the experimental datasets of ignition delay times covering a wide
range of temperatures and equivalence ratios. The chemical kinetic model is
treated as a neural network model, and we then employ stochastic gradient
descent (SGD), a technique that was developed for deep learning, for the
training. We demonstrate the approach in learning the HyChem model for F-24,
which is a Jet-A derived fuel, and compare the results with previous work
employing genetic algorithms. The results show that the SGD approach can
achieve comparable model performance with genetic algorithms but the
computational cost is reduced by 1000 times. In addition, with regularization
in SGD, the SGD approach changes the kinetic parameters from their original
values much less than genetic algorithm and is thus more likely to retrain
mechanistic meanings. Finally, our approach is built upon open-source packages
and can be applied to the development and optimization of chemical kinetic
models for internal combustion engine simulations.",2104.07875v1
2021-04-16,Near ambient pressure photoelectron spectro-microscopy: from gas-solid interface to operando devices,"Near Ambient Pressure Scanning Photoelectron Microscopy adds to the widely
used photoemission spectroscopy and its chemically selective capability two key
features: (i) the possibility to chemically analyse samples in a more realistic
environmental, gas pressure condition, and (ii) the capability to investigate a
system at the relevant spatial scale. To achieve these goals the approach
developed at the ESCA Microscopy beamline at the Elettra Synchrotron facility
combines the submicron lateral resolution of a Scanning Photoelectron
Microscope with a custom designed Near Ambient Pressure Cell where a gas
pressure up to 0.1 mbar is confined inside it around the sample. In this
manuscript a review of experiments performed with this unique setup will be
presented to illustrate its potentiality in both fundamental and applicative
research such as the oxidation reactivity and gas sensitivity of metal oxides
and semiconductors. In particular the capability to do operando experiment with
this setup opens the possibility to perform investigations with active devices
to properly address the real nature of the studied systems, because it can
yield to more conclusive results when microscopy and spectroscopy are
simultaneously combined in a single technique.",2104.08090v1
2021-04-30,Thermal transport evolution due to nanostructural transformations in Ga-doped indium-tin-oxide thin films,"We report on a comprehensive theoretical and experimental investigation of
thermal conductivity in indium-tin-oxide (ITO) thin films with various Ga
concentrations (0-30 at. %) deposited by spray pyrolysis technique. X-Ray
diffraction (XRD) and scanning electron microscopy have shown a structural
transformation in the range 15-20 at. % Ga from the nanocrystalline to the
amorphous phase. Room temperature femtosecond time domain thermoreflectance
measurements showed nonlinear decrease of thermal conductivity in the range
2.0-0.5 W/(m K) depending on Ga doping level. Comparing density functional
theory calculations with XRD data it was found that Ga atoms substitute In
atoms in the ITO nanocrystals retaining Ia-3 space group symmetry. The
calculated phonon dispersion relations revealed that Ga doping leads to the
appearance of hybridized metal atom vibrations with avoided-crossing behavior.
These hybridized vibrations possess shortened mean free paths and are the main
reason behind the thermal conductivity drop in nanocrystalline phase. An
evolution from propagative to diffusive phonon thermal transport in ITO:Ga with
15-20 at. % of Ga was established. The suppressed thermal conductivity of
ITO:Ga thin films deposited by spray pyrolysis may be crucial for their
thermoelectric applications.",2105.00062v1
2021-05-23,InAs nanocrystals with robust p-type doping,"Robust control over the carrier type is fundamental for the fabrication of
nanocrystal-based optoelectronic devices, such as the p-n homojunction, but
effective incorporation of impurities in semiconductor nanocrystals and its
characterization is highly challenging due to their small size. Herein, InAs
nanocrystals, post-synthetically doped with Cd, serve as a model system for
successful p-type doping of originally n-type InAs nanocrystals, as
demonstrated in field-effect transistors (FETs). Advanced structural analysis,
using atomic resolution electron microscopy and synchrotron X-ray absorption
fine structure spectroscopy reveal that Cd impurities reside near and on the
nanocrystal surface acting as substitutional p-dopants replacing Indium.
Commensurately, Cd-doped InAs FETs exhibited remarkable stability of their hole
conduction, mobility, and hysteretic behavior over time when exposed to air,
while intrinsic InAs NCs FETs were easily oxidized and their performance
quickly declined. Therefore, Cd plays a dual role acting as a p-type dopant,
and also protects the nanocrystals from oxidation, as evidenced directly by
Xray photoelectron spectroscopy measurements of air-exposed samples of
intrinsic and Cd doped InAs NCs films. This study demonstrates robust p-type
doping of InAs nanocrystals, setting the stage for implementation of such doped
nanocrystal systems in printed electronic devices.",2105.10881v1
2021-06-04,Materials Representation and Transfer Learning for Multi-Property Prediction,"The adoption of machine learning in materials science has rapidly transformed
materials property prediction. Hurdles limiting full capitalization of recent
advancements in machine learning include the limited development of methods to
learn the underlying interactions of multiple elements, as well as the
relationships among multiple properties, to facilitate property prediction in
new composition spaces. To address these issues, we introduce the Hierarchical
Correlation Learning for Multi-property Prediction (H-CLMP) framework that
seamlessly integrates (i) prediction using only a material's composition, (ii)
learning and exploitation of correlations among target properties in
multi-target regression, and (iii) leveraging training data from tangential
domains via generative transfer learning. The model is demonstrated for
prediction of spectral optical absorption of complex metal oxides spanning 69
3-cation metal oxide composition spaces. H-CLMP accurately predicts non-linear
composition-property relationships in composition spaces for which no training
data is available, which broadens the purview of machine learning to the
discovery of materials with exceptional properties. This achievement results
from the principled integration of latent embedding learning, property
correlation learning, generative transfer learning, and attention models. The
best performance is obtained using H-CLMP with Transfer learning (H-CLMP(T))
wherein a generative adversarial network is trained on computational density of
states data and deployed in the target domain to augment prediction of optical
absorption from composition. H-CLMP(T) aggregates multiple knowledge sources
with a framework that is well-suited for multi-target regression across the
physical sciences.",2106.02225v3
2021-06-04,Requirements for beneficial electrochemical restructuring: A model study on a cobalt oxide in selected electrolytes,"The requirements for beneficial materials restructuring into a higher
performance OER electrocatalyst are still a largely open question. Here we use
Erythrite (Co$_3$(AsO$_4$)$_2\cdot$8H$_2$O) as a Co-based OER electrocatalyst
to evaluate its catalytic properties during in-situ restructuring into an
amorphous Co-based catalyst in four different electrolytes at pH 7. Using
diffraction, microscopy and spectroscopy, we observed a strong effect in the
restructuring kinetics depending of the anions in the electrolyte. Only
carbonate electrolyte could activate the catalyst electrode, which we relate to
its slow restructuring kinetics. While its turnover frequency (TOF) reduced
from 2.84 O$_2$ Co$^{-1}$ s$^{-1}$ to a constant value of 0.10 O$_2$ Co$^{-1}$
s$^{-1}$ after 300 cycles, the number of redox active sites continuously
increased, which explained the current increase of around 100%. The final
activated material owns an adequate local order, a high Co oxidation state and
a high number of redox-active Co ions, which we identify as the trinity for
enhancing the OER activity. Thus, this work provides new insights into for the
rational design of high-performance OER catalysts by electrochemical
restructuring.",2106.02362v1
2021-06-18,Complementary junction field-effect transistor logic gate operational at 300$^\circ$C with 1.4 V supply voltage,"Integrated circuits (ICs) that can operate at high temperature have a wide
variety of applications in the fields of automotive, aerospace, space
exploration, and deep-well drilling. Conventional silicon-based complementary
metal-oxide-semiconductor (CMOS) circuits cannot work at higher than 200
$^\circ$C, leading to the use of wide bandgap semiconductor, especially silicon
carbide (SiC). However, high-density defects at an oxide-SiC interface make it
impossible to predict electrical characteristics of SiC CMOS logic gates in a
wide temperature range and high supply voltage (typically ${\geqq 15}$ V) is
required to compensate their large logic threshold voltage shift. Here, we show
that SiC complementary logic gates composed of p- and n-channel junction
field-effect transistors (JFETs) operate at 300 $^\circ$C with a supply voltage
as low as 1.4 V. The logic threshold voltage shift of the complementary JFET
(CJFET) inverter is 0.2 V from room temperature to 300 $^\circ$C. Furthermore,
temperature dependencies of the static and dynamic characteristics of the CJFET
inverter are well explained by a simple analytical model of SiC JFETs. This
allows us to perform electronic circuit simulation, leading to superior
designability of complex circuits or memories based on SiC CJFET technology,
which operate within a wide temperature range.",2106.09902v1
2021-07-02,Model of the Weak Reset Process in HfOx Resistive Memory for Deep Learning Frameworks,"The implementation of current deep learning training algorithms is
power-hungry, owing to data transfer between memory and logic units.
Oxide-based RRAMs are outstanding candidates to implement in-memory computing,
which is less power-intensive. Their weak RESET regime, is particularly
attractive for learning, as it allows tuning the resistance of the devices with
remarkable endurance. However, the resistive change behavior in this regime
suffers many fluctuations and is particularly challenging to model, especially
in a way compatible with tools used for simulating deep learning. In this work,
we present a model of the weak RESET process in hafnium oxide RRAM and
integrate this model within the PyTorch deep learning framework. Validated on
experiments on a hybrid CMOS/RRAM technology, our model reproduces both the
noisy progressive behavior and the device-to-device (D2D) variability. We use
this tool to train Binarized Neural Networks for the MNIST handwritten digit
recognition task and the CIFAR-10 object classification task. We simulate our
model with and without various aspects of device imperfections to understand
their impact on the training process and identify that the D2D variability is
the most detrimental aspect. The framework can be used in the same manner for
other types of memories to identify the device imperfections that cause the
most degradation, which can, in turn, be used to optimize the devices to reduce
the impact of these imperfections.",2107.06064v2
2021-07-19,"Low-energy consumption, free-form capacitive deionisation through nanostructured networks","Capacitive Deionization (CDI) is a non-energy intensive water treatment
technology. To harness the enormous potential of CDI requires improving
performance, while offering industrially feasible solutions. Following this
idea, the replacement of costly metallic components has been proposed as a mean
of limiting corrosion problems. This work explores the use of nanostructured
hybrid networks to enable free-form and metal-free CDI devices. The strategy
consists of producing interpenetrated networks of highly conductive flexible
carbon nanotube (CNT) fibre fabrics and nanostructured metal oxides,
{\gamma}Al2O3 and TiO2, through ultrasound-assisted nanoparticle infiltration
and sintering. In the resulting hybrids, a uniform distribution of porous metal
oxide is firmly attached to the nanocarbon network while the flexibility, high
conductivity and low-dimensional properties of the CNTs are preserved. These
electrodes present a high porosity ($105 - 118 m^{2} g^{1}$), notably low
electrical ($< 0,1 k \Omega cm^{2}$) and low charge transfer resistance (4
{\Omega}), thus enabling the infiltration of aqueous electrolytes and serving
as current collector. In this work we built a large asymmetrical cylindrical
CDI device solely made of these electrodes and conventional plastics. The cell
provides, high average salt adsorption rates of $1.16 mg /g_{AM} min$ ($0.23
mg/g_{CDIunit} min$, low energy consumption ($0.18 Wh/g_{salt}$) and stable
electrochemical performance above 50 cycles for brackish water desalination.",2107.08867v1
2021-07-30,Design of microring resonators integrated with 2D graphene oxide films for four-wave mixing,"We theoretically investigate and optimize the performance of four-wave mixing
(FWM) in microring resonators (MRRs) integrated with two-dimensional (2D)
layered graphene oxide (GO) films. Owing to the interaction between the MRRs
and the highly nonlinear GO films as well as to the resonant enhancement
effect, the FWM efficiency in GO-coated MRRs can be significantly improved.
Based on previous experiments, we perform detailed analysis for the influence
of the GO film parameters and MRR coupling strength on the FWM conversion
efficiency (CE) of the hybrid MRRs. By optimizing the device parameters to
balance the trade-off between the Kerr nonlinearity and loss, we achieve a high
CE enhancement of ~18.6 dB relative to the uncoated MRR, which is ~8.3 dB
higher than previous experimental results. The influence of photo-thermal
changes in the GO films as well as variations in the MRR parameters such as the
ring radius and waveguide dispersion on the FWM performance is also discussed.
These results highlight the significantly improved FWM performance that can be
achieved in MRRs incorporating GO films and provide a guide for optimizing
their FWM performance.",2108.00110v1
2021-08-12,Structure-selective operando x-ray spectroscopy,"The relationship between charge and structure dictates the properties of
electrochemical systems. For example, reversible Na-ion intercalation - a
low-cost alternative to Li-ion technology - often induces detrimental
structural phase transformations coupled with charge compensation reactions.
However, little is known about the underpinning charge-structure mechanisms
because the reduction-oxidation (redox) reactions within coexisting structural
phases have so far eluded direct operando investigation. Here, we distinguish
x-ray spectra of individual crystalline phases operando during a redox-induced
phase transformation in P2-Na2/3Ni1/3Mn2/3O2 - an archetypal layered oxide for
sodium-ion batteries. We measure the resonant elastic scattering on the Bragg
reflection corresponding to the P2-phase lattice spacing. These resonant
spectra become static midway through the sodium extraction in an operando coin
cell, while the overall sodium extraction proceeds as evidenced by the X-ray
absorption averaging over all electrochemically active Ni atoms. The stop of
redox activity in the P2-structure signifies its inability to host Ni4+ ions.
The coincident emergence of the O2- structure reveals the rigid link between
the local redox and the long-range order during the phase transformation. The
structure-selective x-ray spectroscopy thus opens a powerful avenue for
resolving the dynamic chemistry of different structural phases in multi-phase
electrochemical systems.",2108.05913v1
2021-08-18,High Entropy Alloy CrFeNiCoCu sputtered films,"High entropy alloy(HEA) films of CrFeCoNiCu were prepared by sputtering,
their structure was characterized, and their electric properties measured by
temperature dependent Hall and Seebeck measurement. The HEA films show a solid
solution with fcc structure, and a 111 texture with columnar grains of widths
15-30 nm extending through film thickness with very many twins. The residual
electrical resistivity of the films is around 140 {\mu}{\Omega}cm and the
temperature dependence of the resistivity is metal-like. The temperature
coefficient of resistivity (TCR) is small (2 ppm/K). The Hall coefficient is
positive while the Seebeck coefficients is negative. This is interpreted as
arising from an electronic structure where the Fermi level passes through band
states having both holes and electrons as indicated by band structure
calculations. The HEA structure appears stable for annealing in vacuum, while
annealing in an oxygen containing atmosphere causes the surface to oxidize and
grow a Cr-rich oxide on the surface. This is then accompanied by demixing of
the HEA solid solution and a decrease in residual resistance of the film.",2108.08373v2
2021-08-18,Correlated Oxide Dirac Semimetal in the Extreme Quantum Limit,"Quantum materials (QMs) with strong correlation and non-trivial topology are
indispensable to next-generation information and computing technologies.
Exploitation of topological band structure is an ideal starting point to
realize correlated topological QMs. Herein, we report that strain-induced
symmetry modification in correlated oxide SrNbO3 thin films creates an emerging
topological band structure. Dirac electrons in strained SrNbO3 films reveal
ultra-high mobility (100,000 cm2/Vs), exceptionally small effective mass
(0.04me), and non-zero Berry phase. More importantly, strained SrNbO3 films
reach the extreme quantum limit, exhibiting a sign of fractional occupation of
Landau levels and giant mass enhancement. Our results suggest that
symmetry-modified SrNbO3 is a rare example of a correlated topological QM, in
which strong correlation of Dirac electrons leads to the realization of
fractional occupation of Landau levels.",2108.08408v1
2021-08-19,Drift in a Popular Metal Oxide Sensor Dataset Reveals Limitations for Gas Classification Benchmarks,"Metal oxide (MOx) electro-chemical gas sensors are a sensible choice for many
applications, due to their tunable sensitivity, their space-efficiency and
their low price. Publicly available sensor datasets streamline the development
and evaluation of novel algorithm and circuit designs, making them particularly
valuable for the Artificial Olfaction / Mobile Robot Olfaction community. In
2013, Vergara et al. published a dataset comprising 16 months of recordings
from a large MOx gas sensor array in a wind tunnel, which has since become a
standard benchmark in the field. Here we report a previously undetected
property of the dataset that limits its suitability for gas classification
studies. The analysis of individual measurement timestamps reveals that gases
were recorded in temporally clustered batches. The consequential correlation
between the sensor response before gas exposure and the time of recording is
often sufficient to predict the gas used in a given trial. Even if compensated
by zero-offset-subtraction, residual short-term drift contains enough
information for gas classification. We have identified a minimally
drift-affected subset of the data, which is suitable for gas classification
benchmarking after zero-offset-subtraction, although gas classification
performance was substantially lower than for the full dataset. We conclude that
previous studies conducted with this dataset very likely overestimate the
accuracy of gas classification results. For the 17 potentially affected
publications, we urge the authors to re-evaluate the results in light of our
findings. Our observations emphasize the need to thoroughly document gas
sensing datasets, and proper validation before using them for the development
of algorithms.",2108.08793v1
2021-08-24,Dynamic Properties of Water inside Graphene Oxide Membranes,"Separation of salt ions from seawater using graphene oxide (GO) membrane is
an emerging desalination method. Here, we investigate the dynamic behavior of
water, sodium, and chloride ions inside GO membrane using a computational
approach. First, we developed four different models of GO membrane with
different distances between GO sheets (0.7, 0.9, 1.1, and 1.3 nm), and
performed molecular dynamics (MD) simulations of water inside each membrane for
20 ns. With the analysis of the mean squared displacement of water and the
Einstein relation equation for diffusion, we measured the diffusion coefficient
of water in each membrane. We found that the diffusion coefficient of water
inside the GO membrane decreased as the distance between sheets (d) decreased.
The measured diffusion coefficients (in unit of 0.00001 (cm*cm)/sec) of water
are 0.03 (d = 0.7 nm), 0.91 (d = 0.9 nm), 1.18 (d = 1.1 nm), and 1.49 (d = 1.3
nm), whereas it is 2.49 for bulk water. Second, for analyzing the desalination
performance of each membrane, we also calculated the free energy profile of
penetration of water, sodium, and chloride ions via the interlayer of the
membrane. The free energy profile of penetration revealed that the optimum
interlayer distance between GO sheets for desalination is 0.9 ~ 1.1 nm. With
0.9 and 1.1 nm interlayer distance between GO sheets, the free energy barrier
of membrane penetration of water is negligible, where it is 2 ~ 4 kcal/mol for
sodium or chloride ions. We believe that our simulation results would be a
significant contribution to designing a new GO-based membrane for desalination.",2108.10836v1
2021-08-25,Measurement of Hybrid Rocket Solid Fuel Regression Rate for a Slab Burner using Deep Learning,"This study presents an imaging-based deep learning tool to measure the fuel
regression rate in a 2D slab burner experiment for hybrid rocket fuels. The
slab burner experiment is designed to verify mechanistic models of reacting
boundary layer combustion in hybrid rockets by the measurement of fuel
regression rates. A DSLR camera with a high intensity flash is used to capture
images throughout the burn and the images are then used to find the fuel
boundary to calculate the regression rate. A U-net convolutional neural network
architecture is explored to segment the fuel from the experimental images. A
Monte-Carlo Dropout process is used to quantify the regression rate uncertainty
produced from the network. The U-net computed regression rates are compared
with values from other techniques from literature and show error less than 10%.
An oxidizer flux dependency study is performed and shows the U-net predictions
of regression rates are accurate and independent of the oxidizer flux, when the
images in the training set are not over-saturated. Training with monochrome
images is explored and is not successful at predicting the fuel regression rate
from images with high noise. The network is superior at filtering out noise
introduced by soot, pitting, and wax deposition on the chamber glass as well as
the flame when compared to traditional image processing techniques, such as
threshold binary conversion and spatial filtering. U-net consistently provides
low error image segmentations to allow accurate computation of the regression
rate of the fuel.",2108.11276v1
2021-08-25,A Stable High-Capacity Lithium-Ion Battery Using a Biomass-Derived Sulfur-Carbon Cathode and Lithiated Silicon Anode,"A full lithium-ion-sulfur cell with a remarkable cycle life was achieved by
combining an environmentally sustainable biomass-derived sulfur-carbon cathode
and a pre-lithiated silicon oxide anode. X-ray diffraction, Raman spectroscopy,
energy dispersive spectroscopy, and thermogravimetry of the cathode evidenced
the disordered nature of the carbon matrix in which sulfur was uniformly
distributed with a weight content as high as 75%, while scanning and
transmission electron microscopy revealed the micrometric morphology of the
composite. The sulfur-carbon electrode in the lithium half-cell exhibited a
maximum capacity higher than 1200 mAhgS-1, reversible electrochemical process,
limited electrode/electrolyte interphase resistance, and a rate capability up
to C/2. The material showed a capacity decay of about 40% with respect to the
steady-state value over 100 cycles, likely due to the reaction with the lithium
metal of dissolved polysulfides or impurities including P detected in the
carbon precursor. Therefore, the replacement of the lithium metal with a less
challenging anode was suggested, and the sulfur-carbon composite was
subsequently investigated in the full lithium-ion-sulfur battery employing a
Li-alloying silicon oxide anode. The full-cell revealed an initial capacity as
high as 1200 mAhgS-1, a retention increased to more than 79% for 100
galvanostatic cycles, and 56% over 500 cycles. The data reported herein well
indicated the reliability of energy storage devices with extended cycle life
employing high-energy, green, and safe electrode materials.",2108.11284v1
2021-08-25,Degradation of Layered Oxide Cathode in a Sodium Battery: A Detailed Investigation by X-Ray Tomography at the Nanoscale,"The degradation mechanism in a sodium cell of a layered
Na0.48Al0.03Co0.18Ni0.18Mn0.47O2 (NCAM) cathode with P3/P2 structure is
investigated by revealing the changes in microstructure and composition upon
cycling. The work aims to rationalize the gradual performance decay and the
alteration of the electrochemical response in terms of polarization, voltage
signature, and capacity loss. Spatial reconstructions of the electrode by X-ray
computed tomography at the nanoscale supported by quantitative and qualitative
analyses show fractures and deformations in the cycled layered metal-oxide
particles, as well as inorganic side compounds deposited on the material. These
irreversible morphological modifications reflect structural heterogeneities
across the cathode particles due to formation of various domains with different
Na+ intercalation degrees. Besides, X-ray photoelectron spectroscopy data
suggest that the latter inorganic species in the cycled electrode are mainly
composed of NaF, Na2O, and NaCO3 formed by parasitic electrolyte decomposition.
The precipitation of these insulating compounds at the electrode/electrolyte
interphase and the related structural stresses induced in the material lead to
a decrease in cathode particle size and partial loss of electrochemical
activity. The retention of the NCAM phase after cycling suggests that
electrolyte upgrade may improve the performance of the cathode to achieve
practical application for sustainable energy storage.",2108.11442v1
2021-09-14,Photo-memristive sensing with charge storing 2D carbon nitrides,"We report the charge storing 2D carbon nitride potassium poly(heptazine
imide), K-PHI, as a direct memristive (bio)sensing platform. Memristive devices
have the potential to innovate current (bio)electronic systems such as
photo-electrochemical sensors by incorporating new sensing capabilities
including non-invasive, wireless remote and time-delayed (memory) readout. We
demonstrate a direct photomemristive sensing platform that capitalizes on K
PHI's visible light bandgap, large oxidation potential and intrinsic optoionic
light energy storage properties. Our system simultaneously enables analyte
concentration information storage as well as potentiometric, impedimetric and
coulo-metric readouts on the same material, with no additional reagents
required. Utilizing the light-induced charge storage function of K-PHI, we
demonstrate analyte sensing via charge accumulation and present various methods
to write/erase this information from the material. Additionally, fully wireless
colorimetric and fluorometric detection of the charged state of K-PHI is
demonstrated and could facilitate its use as particle-based in-situ sensing
probe. The various readout options of the K PHI's response enable us to adapt
the sensitivities and dynamic ranges without modifying the sensor. We
demonstrate these features using glucose as an example analyte over a wide
range of concentrations (50 $\mu$M to 50 mM). Moreover, due to the strong
oxidative power of K-PHI, this sensing platform is able to detect a large
variety of organic or biologically relevant analytes. Since PHI is easily
synthesized, based on earth abundant precursors, biocompatible, chemically
robust and responsive to visible light, we anticipate that the sensing platform
presented herein opens up novel memristive and neuromorphic functions.",2109.06964v1
2021-09-11,Design and characterization of effective solar cells,"We propose a two-stage multi-objective optimization framework for full scheme
solar cell structure design and characterization, cost minimization and quantum
efficiency maximization. We evaluated structures of 15 different cell designs
simulated by varying material types and photodiode doping strategies. At first,
non-dominated sorting genetic algorithm~II (NSGA-II) produced
Pareto-optimal-solutions sets for respective cell designs. Then, on
investigating quantum efficiencies of all cell designs produced by NSGA-II, we
applied a new multi-objective optimization algorithm~II (OptIA-II) to discover
the Pareto fronts of select (three) best cell designs. Our designed OptIA-II
algorithm improved the quantum efficiencies of all select cell designs and
reduced their fabrication costs. We observed that the cell design comprising an
optimally doped zinc-oxide-based transparent conductive oxide (TCO) layer and
rough silver back reflector (BR) offered a quantum efficiency ($Q_e$) of
$0.6031.$ Overall, this paper provides a full characterization of cell
structure designs. It derives a relationship between quantum efficiency, $Q_e$
of a cell with its TCO layer's doping methods and TCO and BR layer's material
types. Our solar cells design characterization enables us to perform a
cost-benefit analysis of solar cells usage in real-world applications",2109.07279v1
2021-09-20,Microwave-optical coupling via Rydberg excitons in cuprous oxide,"We report exciton-mediated coupling between microwave and optical fields in
cuprous oxide (Cu$_2$O) at low temperatures. Rydberg excitonic states with
principal quantum number up to $n=12$ were observed at 4~K using both
one-photon (absorption) and two-photon (second harmonic generation)
spectroscopy. Near resonance with an excitonic state, the addition of a
microwave field significantly changed the absorption lineshape, and added
sidebands at the microwave frequency to the coherent second harmonic. Both
effects showed a complex dependence on $n$ and angular momentum, $l$. All of
these features are in semi-quantitative agreement with a model based on
intraband electric dipole transitions between Rydberg exciton states. With a
simple microwave antenna we already reach a regime where the microwave coupling
(Rabi frequency) is comparable to the nonradiatively broadened linewidth of the
Rydberg excitons. The results provide a new way to manipulate excitonic states,
and open up the possibility of a cryogenic microwave to optical transducer
based on Rydberg excitons.",2109.09614v2
2021-09-28,Remarkably Enhanced Dynamic Oxygen Migration on Graphene Oxide Supported by Copper Substrate,"The dynamic covalent properties of graphene oxide (GO) are of fundamental
interest to a broad range of scientific areas and technological applications.
It remains a challenge to access the feasible dynamic reactions for reversibly
breaking/reforming covalent bonds of oxygen functional groups on GO, although
these reactions can be induced by photonic or mechanical routes, or mediated by
adsorbed water. Here, using the density functional theory calculations, we
demonstrate the remarkably enhanced dynamic oxygen migration along the basal
plane of GO supported by copper substrate (GO@copper), with the C-O bond
breaking reaction and proton transfer between the neighboring epoxy and
hydroxyl groups. Compared to that on GO, the energy barrier of oxygen migration
on GO@copper is sharply reduced to be less than or comparable to thermal
fluctuations, and meanwhile the crystallographic match between GO and copper
substrate induces new oxygen migration paths on GO@copper. This work sheds
light on the understanding of metal substrate-enhanced dynamic properties of
GO, and evidences the strategy to tune the activity of
two-dimension-interfacial oxygen groups for various potential applications.",2109.13575v3
2021-10-15,Effective reduction of biofilm through photothermal therapy by gold core@shell based mesoporous silica nanoparticles,"Bacterial biofilms can initiate chronic infections that become difficult to
eradicate. There is an unmet need for effective therapeutic strategies that
control and inhibit the growth of these biofilms. Herein, light sensitive
mesoporous silica nanoparticles (MSNs) with photothermal (PTT) and
antimicrobial combined capabilities have been developed. These nanosystems have
high therapeutic potential to affect the bacterial biofilm architecture and
subsequently inhibit its growth. Nucleation of gold nanorods followed by the
growth of a silica shell leads to a core@shell design (AuNR@MSN) with PTT
properties. Incorporation of nitrosothiol groups (-SNO) with a heat liable
linker, enables an enhanced nitric oxide release upon photothermal stimulation
with near infrared radiation. Further loading of an antimicrobial molecule such
as the levofloxacin (LEVO) antibiotic creates a unique nanoassembly with
potential therapeutic efficacy against Staphylococcus aureus bacterial
biofilms. A dispersion rate of the bacterial biofilm was evident when light
stimuli is applied because impregnation of the nitrosothiol functionalized
nanosystem with the antibiotic LEVO led to ca. 30% reduction but its
illumination with near infrared (NIR) irradiation showed a biofilm reduction of
ca. 90%, indicating that localized antimicrobial exposure and PTT improves the
therapeutic efficacy. These findings envision the conception of
near-infraredactivated nanoparticle carriers capable of combined therapy upon
NIR irradiation, which enables photothermal therapy, together with the release
of levofloxacin and nitric oxide to disrupt the integrity of bacterial biofilms
and achieve a potent antimicrobial therapy.",2110.07924v1
2021-10-23,Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion,"Earth's surface environment is largely influenced by its budget of major
volatile elements: carbon (C), nitrogen (N), and hydrogen (H). Although the
volatiles on Earth are thought to have been delivered by chondritic materials,
the elemental composition of the bulk silicate Earth (BSE) shows depletion in
the order of N, C, and H. Previous studies have concluded that non-chondritic
materials are needed for this depletion pattern. Here, we model the evolution
of the volatile abundances in the atmosphere, oceans, crust, mantle, and core
through the accretion history by considering elemental partitioning and impact
erosion. We show that the BSE depletion pattern can be reproduced from
continuous accretion of chondritic bodies by the partitioning of C into the
core and H storage in the magma ocean in the main accretion stage and
atmospheric erosion of N in the late accretion stage. This scenario requires a
relatively oxidized magma ocean ($\log_{10} f_{\rm O_2}$ $\gtrsim$
$\rm{IW}$$-2$, where $f_{\rm O_2}$ is the oxygen fugacity, ${\rm IW}$ is
$\log_{10} f_{\rm O_2}^{\rm IW}$, and $f_{\rm O_2}^{\rm IW}$ is $f_{\rm O_2}$
at the iron-w\""{u}stite buffer), the dominance of small impactors in the late
accretion, and the storage of H and C in oceanic water and carbonates in the
late accretion stage, all of which are naturally expected from the formation of
an Earth-sized planet in the habitable zone.",2110.12195v1
2021-10-23,Zinc Oxide-Based Piezoelectric Pressure Sensor,"This paper reports the application of zinc oxide (ZnO) in the pressure
sensors that can be integrated with a microelectromechanical system (MEMS). ZnO
is one of the materials that has received a great deal of attention due to its
unique properties of being a semiconductor with wide bandgap and piezoelectric
effects. The simpler crystal growth mechanisms of ZnO have resulted in a lower
cost of ZnO-based sensors. Different types of pressure sensors based on ZnO
sensing elements have also been explored. A thin circular ZnO film was
simulated as a piezoelectric sensor employing the finite element method in
COMSOL. The pressure applied on the thin film surface was varied and a boundary
point probe was used to study the displacement field and voltage at the center
of the membrane. The displacement field and voltage induced by pressure vary
linearly with increasing pressure on the ZnO layer. Also. the method used in
this paper was applied to different piezoelectric materials, such as barium
titanate (BaTiO3), polyvinylidene fluoride (PVDF), and gallium arsenide (GaAs)
that were studied by other groups, and similar conclusions were made. These
simulations can be used in the design of piezoelectric sensors and the
optimization of the sensitivity and performance of the materials used in
pressure sensor applications.",2110.13643v1
2021-11-01,Pressure-induced metal-insulator transition in oxygen-deficient LiNbO$_3$-type ferroelectrics,"Hydrostatic pressure and oxygen vacancies usually have deleterious effects on
ferroelectric materials because both tend to reduce their polarization. In this
work we use first-principles calculations to study an important class of
ferroelectric materials - LiNbO$_3$-type ferroelectrics (LiNbO$_3$ as the
prototype), and find that in oxygen-deficient LiNbO$_{3-\delta}$, hydrostatic
pressure induces an unexpected metal-insulator transition between 8 and 9 GPa.
Our calculations also find that strong polar displacements persist in both
metallic and insulating oxygen-deficient LiNbO$_{3-\delta}$ and the size of
polar displacements is comparable to pristine LiNbO$_3$ under the same
pressure. These properties are distinct from widely used perovskite
ferroelectric oxide BaTiO$_3$, whose polarization is quickly suppressed by
hydrostatic pressure and/or oxygen vacancies. The anomalous pressure-driven
metal-insulator transition in oxygen-deficient LiNbO$_{3-\delta}$ arises from
the change of an oxygen vacancy defect state. Hydrostatic pressure increases
the polar displacements of oxygen-deficient LiNbO$_{3-\delta}$, which reduces
the band width of the defect state and eventually turns it into an in-gap
state. In the insulating phase, the in-gap state is further pushed away from
the conduction band edge under hydrostatic pressure, which increases the
fundamental gap. Our work shows that for LiNbO$_3$-type strong ferroelectrics,
oxygen vacancies and hydrostatic pressure combined can lead to new phenomena
and potential functions, in contrast to the harmful effects occurring to
perovskite ferroelectric oxides such as BaTiO$_3$.",2111.00911v1
2021-11-05,Surface plasmons on a Au waveguide electrode open new redox channels associated with the transfer of energetic carriers,"Plasmonic catalysis holds significant promise for opening new reaction
pathways inaccessible thermally, or for improving the efficiency of chemical
processes. However, challenges persist in distinguishing photothermal effects
from effects due to energetic electrons and/or holes excited in the metal
comprising a plasmonic structure. Here we use a Au stripe waveguide along which
surface plasmon polaritons (SPPs) propagate, operating simultaneously as a
working electrode in a 3-electrode electrochemical cell. Cyclic voltammograms
were obtained under SPP excitation as a function of incident optical power and
wavelength ~ 1350 nm, enabling processes involving energetic holes to be
separated from processes involving energetic electrons by investigating
oxidation and reduction reactions separately. Redox current densities increase
by 10x under SPP excitation. The oxidation, reduction and equilibrium
potentials drop by as much as 2x and split beyond a clear threshold with SPP
power in correlation with the photon energy. The temperature of the working
electrode under SPP excitation is monitored in situ and independent control
experiments isolate thermal effects. Chronoamperometry measurements with on-off
modulated SPPs at 600 Hz, yield a diffusion-limited rapid current response
modulated at the same frequency, ruling out thermally-enhanced mass transport.
Our observations are attributed to the opening of optically controlled
non-equilibrium redox channels associated with energetic carrier transfer to
the redox species.",2111.03681v1
2021-10-25,Modeling of Graphene Oxide Memory based on Hybridization State Modulation,"Graphene oxide (GO)-based resistive random access memory (RRAM) is one of the
most promising emerging non-volatile memories for flexible electronics because
of its simple structure and low fabrication cost. The reported switching
mechanism can be classified into either localized or bulk effect. The localized
effect is commonly observed in GO-RRAM with active electrode e.g. Cu and Al.
The switching mechanism includes metallic conduction filament evolution or
modification of interfacial resistance between GO layer and electrodes. On the
other hand, the bulk effect involves hybridization state change of the entire
GO layer and is typically observed in devices with inert electrode e.g. Pt and
Au. Numerous compact models have been proposed for RRAM that are based on
localized switching mechanism. However, compact modeling of GO-RRAM based on
bulk mechanism is still lacking. Thus, this paper presents a compact model for
GO-RRAM that relies on hybridization state modulation. The proposed model
associates the resistance switching mechanism with the electricaldriven
modification of sp2 clusters density in the switching layer. A SPICE model
incorporating the proposed compact model is developed for parameter
calibration. The simulated I-V characteristic exhibits strong correlation with
the experimental data. Hereby, we regard the proposed compact model as an
acceptable and close description of GO-RRAM operation that depends on the bulk
switching mechanism.",2111.04440v1
2021-11-18,Searching for Superconductivity in High Entropy Oxide Ruddlesden-Popper Cuprate Films,"In this work, the high entropy oxide A2CuO4 Ruddlesden-Popper
(La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 is explored by charge doping with Ce+4 and
Sr+2 at concentrations known to induce superconductivity in the simple parent
compounds, Nd2CuO4 and La2CuO4. Electron doped
(La0.185Pr0.185Nd0.185Sm0.185Eu0.185Ce0.075)2CuO4 and hole doped
(La0.18Pr0.18Nd0.18Sm0.18Eu0.18Sr0.1)2CuO4 are synthesized and shown to be
single crystal, epitaxially strained, and highly uniform. Transport
measurements demonstrate that all as-grown films are insulating regardless of
doping. Annealing studies show that resistivity can be tuned by modifying
oxygen stoichiometry and inducing metallicity but without superconductivity.
These results in turn are connected to extended x-ray absorption fine structure
(EXAFS) results indicating that the lack of superconductivity in the high
entropy cuprates likely originates from a large distortion within the Cu-O
plane ({\sigma}2>0.015 {\AA}2) due to A-site cation size variance, which drives
localization of charge carriers. These findings describe new opportunities for
controlling charge- and orbital-mediated functional responses in
Ruddlesden-Popper crystal structures, driven by balancing of cation size and
charge variances that may be exploited for functionally important behaviors
such as superconductivity, antiferromagnetism, and metal-insulator transitions,
while opening less understood phase spaces hosting doped Mott insulators,
strange metals, quantum criticality, pseudogaps, and ordered charge density
waves.",2111.09767v1
2021-12-03,Mid-infrared Fourier-transform spectrometer based on metamaterial lateral cladding suspended silicon waveguides,"Integrated mid-infrared micro-spectrometers have a great potential for
applications in environmental monitoring and space exploration.
Silicon-on-insulator (SOI) is a promising platform to tackle this integration
challenge, due to its unique capability for large volume and low-cost
production of ultra-compact photonic circuits. However, the use of SOI in the
mid-infrared is restricted by the strong absorption of the buried oxide layer
for wavelengths beyond 4 {\mu}m. Here, we overcome this limitation by utilizing
metamaterial-cladded suspended silicon waveguides to implement a spatial
heterodyne Fourier-transform (SHFT) spectrometer operating near 5.5{\mu}m
wavelength. The metamaterial-cladded geometry allows removal of the buried
oxide layer, yielding measured propagation loss below 2 dB/cm between 5.3{\mu}m
and 5.7{\mu}m wavelengths. The SHFT spectrometer comprises 19 Mach-Zehnder
interferometers with a maximum arm length imbalance of 200 {\mu}m, achieving a
measured spectral resolution of 13cm-1 and a free-spectral range of 100 cm-1
near 5.5{\mu}m wavelength.",2112.01961v1
2021-12-06,X-ray characterization of BUSARD chip: A HV-SOI monolithic particle detector with pixel sensors under the buried oxide,"This work presents the design of BUSARD, an application specific integrated
circuit (ASIC) for the detection of ionizing particles. The ASIC is a
monolithic active pixel sensor which has been fabricated in a High-Voltage
Silicon-On-Insulator (HV-SOI) process that allows the fabrication of a buried
N+ diffusion below the Buried OXide (BOX) as a standard processing step. The
first version of the chip, BUSARD-A, takes advantage of this buried diffusion
as an ionizing particle sensor. It includes a small array of 13$\times$13
pixels, with a pitch of $80\,\mu$m, and each pixel has one buried diffusion
with a charge amplifier, discriminator with offset tuning and digital
processing. The detector has several operation modes including particle
counting and Time-over-Threshold (ToT). An initial X-ray characterization of
the detector was carried out, obtaining several pulse height and ToT spectra,
which then were used to perform the energy calibration of the device. The
Molybdenum $\mathbf{K_{\alpha}}$ emission was measured with a standard
deviation of $127\,e^{-}$ of ENC by using the analog pulse output, and with
$276\,e^{-}$ of ENC by using the ToT digital output. The resolution in ToT mode
is dominated by the pixel-to-pixel variation.",2112.03166v1
2021-12-11,Hydrogen related defects in titanium dioxide at the interface to palladium,"A metal oxide support and a catalytically active metal are the two main
ingredients for complex catalysts used in heterogeneous catalysis. The gas
environment can change the catalyst during the reaction, modifying its
structural and electronic properties. Here, we use monochromated electron
energy loss spectroscopy (EELS) to reveal hydrogen-pressure-dependent changes
of the electronic structure at the Pd/rutile-TiO$_2$ interface in an
environmental transmission electron microscope (ETEM). Hydrogen-induced changes
are observed in rutile-TiO$_2$ within $2$~nm from the interface at $10$~Pa of
hydrogen pressure, in the Ti $L_{3,2}$ EEL spectra. Lower pressures such as
$1$~Pa show no changes in the EEL spectra. We attribute the observed changes in
the EEL spectra to hydrogen-induced defects accumulating in the vicinity of the
interface. Based on DFT calculations, we developed a thermodynamic multistate
defect (TMD) model of the interface and the bulk of the rutile-TiO$_2$. This
TMD model predicts high concentrations of positively charged defects
accumulating at the interface. The presence of the Schottky barrier stabilizes
these defects by significantly lowering their formation energy. Our findings
provide important new insights into catalytic processes taking place at
metal/metal oxide interfaces in hydrogen gas environments.",2112.05953v1
2021-12-15,All Inorganic p_n Heterojunction Solar Cells by Solution Combustion Synthesis using n_type FeMnO3 Perovskite Photoactive Layer,"This study outlines the synthesis and physicochemical characteristics of a
solution-processable iron manganite (FeMnO3) nanoparticles via a chemical
combustion method using tartartic acid as a fuel and demonstrates the
performance of this material as a n-type photoactive layer in all-oxide solar
cells. It is shown that the solution combustion synthesis (SCS) method enables
the formation of pure crystal phase FeMnO3 with controllable particle size. XRD
pattern and morphology images from TEM confirm the purity of FeMnO3 phase and
the relative small crystallite size (~13 nm), firstly reported in the
literature. Moreover, to assemble a network of connected FeMnO3 nanoparticles,
\b{eta}-alanine was used as a capping agent and dimethylformamide (DMF) as a
polar aprotic solvent for the colloidal dispersion of FeMnO3 NPs. This
procedure yields a ~500 nm thick photoactive layer. The proposed method is
crucial to obtain functional solution processed NiO/FeMnO3 heterojunction
inorganic photovoltaics. The optoelectronic properties of the heterojunction
were established. These solar cells demonstrate a high open circuit voltage of
1.31 V with sufficient fill factor of 54.3% and low short circuit current of
0.07 mA cm-2 delivering a power conversion efficiency of 0.05% under 100 mW
cm-2 illumination. This work expands on the burgeoning of environmentally
friendly, low-cost, sustainable solar cell material that derive from metal
oxides.",2112.08057v1
2021-12-16,Correct and accurate polymorphic energy ordering of transition-metal monoxides obtained from semilocal and onsite-hybrid exchange-correlation approximations,"The relative energetic stability of the structural phases of common
antiferromagnetic transition-metal oxides (MnO, FeO, CoO, and NiO) within the
semilocal and hybrid density functionals are fraught with difficulties. In
particular, MnO is known to be the most difficult case for almost all common
semilocal and hybrid density approximations. Here, we show that the
meta-generalized gradient approximation (meta-GGA) constructed from the
cuspless hydrogen model and Pauli kinetic energy density (MGGAC) can lead to
the correct ground state of MnO. The relative energy differences of zinc-blende
(zb) and rock-salt (rs) structures as computed using MGGAC are found to be in
nice agreement with those obtained from high-level correlation methods like the
random phase approximation or quantum Monte Carlo techniques. Besides, we have
also applied the onsite hybrid functionals (closely related to DFT+U ) based on
GGA and meta-GGA functionals, and it is shown that a relatively high amount of
Hartree-Fock exchange is necessary to obtain the correct ground-state
structure. Our present investigation suggests that the semilocal MGGAC and
onsite hybrids, both being computationally cheap, as methods of choice for the
calculation of the relative stability of antiferromagnetic transition-metal
oxides having potential applications in solid-state physics and structural
chemistry.",2112.09022v1
2021-12-22,Self-repairing high entropy oxides,"All biological organisms, from plants to living creatures, can heal minor
wounds and damage. The realization of a similar self-healing capacity in
inorganic materials has been a design target for many decades. This would
represent a breakthrough in materials engineering, enabling many novel
technological applications, since such materials would be able to resist damage
caused by electromagnetic irradiation and/or mechanical impact. Here we
demonstrate that a high-entropy oxide is intrinsically capable of undergoing an
autonomous self-repairing process. Transmission electron microscopy revealed
that the spinel structure of (AlCoCrCu0.5FeNi)3O4 can regrow and repair itself
at the atomic level when damaged. Density functional theory calculations reveal
that the extra enthalpy stored in the high entropy material during fabrication
can be released to effectively heal macroscopic defects by regrowing into a
partially ordered state. This extraordinary self-repairing phenomenon makes
this new material highly desirable as a coating, enabling structures used in
harsh environments to better withstand damage, such as cosmic irradiation in
space, nuclear irradiation in nuclear power facilities, or tribological damage.
Most importantly, our results set the general design principles for the
synthesis of self-repairing materials.",2112.11747v1
2021-12-28,A $d^8$ anti-Hund's Singlet Insulator in an Infinite-layer Nickelate,"The status of nickelate superconductors in relation to cuprate high
temperature superconductors is one of the concepts being discussed in high
temperature superconductivity in correlated transition metal oxides. New
additions to the class of infinite layer nickelates can provide essential input
relating to connections or distinctions. A recently synthesized compound
\bnoas, which contains isolated `infinite layer' NiO$_2$ planes, may lead to
new insights. Our investigations have discovered that, at density functional
theory mean field level, the ground state consists of an unusual $e_g$ singlet
on the Ni$^{2+}$ ion arising from large but separate Mott insulating gaps in
both $e_g$ orbitals, but with different, anti-Hund's, spin directions of their
moments. This textured singlet incorporates at the least new physics, and
potentially a new platform for nickelate superconductivity, which might be of
an unconventional form for transition metal oxides due to the unconventional
undoped state. We include in this paper a comparison of electronic structure
parameters of Ba$_2$NiO$_2$(AgSe)$_2$ with a better characterized infinite
layer nickelate LaNiO$_2$. We provide more analysis of the $d^8$ anti-Hund's
singlet that emerges in this compound, and consider a minimally correlated
wavefunction for this singlet in an itinerant background, and begin discussion
of excitations -- real or virtual -- that may figure into new electronic
phases.",2112.14010v2
2021-12-31,21-Component Compositionally Complex Ceramics: Discovery of Ultrahigh-Entropy Weberite and Fergusonite Phases and a Pyrochlore-Weberite Transition,"Two new high-entropy ceramics (HECs) in the weberite and fergusonite
structures, along with unexpected formation of ordered pyrochlore phases with
ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition,
are discovered in a 21-component oxide system. While the Gibbs phase rule
allows 21 equilibrium phases, nine out of the 13 compositions examined possess
single HEC phases (with ultrahigh ideal configurational entropies: ~2.7kB per
cation or higher on one sublattice in most cases). Notably,
(15RE1/15)(Nb1/2Ta1/2)O4 possess a single monoclinic fergusonite (C2/c) phase
and (15RE1/15)3(Nb1/2Ta1/2)1O7 form a single orthorhombic (C2221) weberite
phase, where 15RE1/15 represents
Sc1/15Y1/15La1/15Pr1/15Nd1/15Sm1/15Eu1/15Gd1/15Tb1/15Dy1/15Ho1/15Er1/15Tm1/15Yb1/15Lu1/15.
Moreover, a series of eight
(15RE1/15)2+x(Ti1/4Zr1/4Ce1/4Hf1/4)2-2x(Nb1/2Ta1/2)xO7 specimens all exhibit
single phases, where a pyrochlore-weberite transition occurs within 0.75 < x <
0.8125. This cubic-to-orthorhombic transition does not change the
temperature-dependent thermal conductivity appreciably, as the amorphous limit
may have already been achieved in the ultrahigh-entropy 21-component oxides.
These discoveries expand the diversity and complexity of HECs, towards
many-component compositionally complex ceramics (CCCs) and ultrahigh-entropy
ceramics.",2112.15381v2
2021-12-31,Predicting the Oxidation States of Mn ions in the Oxygen Evolving Complex of Photosystem II Using Supervised and Unsupervised Machine Learning,"Serial Femtosecond Crystallography at the X-ray Free Electron Laser (XFEL)
sources enabled the imaging of the catalytic intermediates of the oxygen
evolution reaction of Photosystem II. However, due to the incoherent transition
of the S-states, the resolved structures are a convolution from different
catalytic states. Here, we train Decision Tree Classifier and K-mean clustering
models on Mn compounds obtained from the Cambridge Crystallographic Database to
predict the S-state of the X-ray, XFEL, and CryoEm structures by predicting the
Mn's oxidation states in the oxygen evolving complex (OEC). The model agrees
mostly with the XFEL structures in the dark S1 state. However, significant
discrepancies are observed for the excited XFEL states (S2, S3, and S0) and the
dark states of the X-ray and CryoEm structures. Furthermore, there is a
mismatch between the predicted S-states within the two monomers of the same
dimer, mainly in the excited states. The model suggests that improving the
resolution is crucial to precisely resolve the geometry of the illuminated
S-states to overcome the noncoherent S-state transition. In addition,
significant radiation damage is observed in X-ray and CryoEM structures,
particularly at the dangler Mn center (Mn4). Our model represents a valuable
tool for investigating the electronic structure of the catalytic metal cluster
of PSII to understand the water splitting mechanism.",2112.15460v2
2022-01-02,Electrochemically-driven insulator-metal transition in ionic-liquid-gated antiferromagnetic Mott-insulating NiS$_2$ single crystals,"Motivated by the existence of superconductivity in pyrite-structure CuS$_2$,
we explore the possibility of ionic-liquid-gating-induced superconductivity in
the proximal antiferromagnetic Mott insulator NiS$_2$. A clear gating-induced
transition from a two-dimensional insulating state to a three-dimensional
metallic state is observed at positive gate bias on single crystal surfaces. No
evidence for superconductivity is observed down to the lowest measured
temperature of 0.45 K, however. Based on transport, energy-dispersive X-ray
spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and
other techniques, we deduce an electrochemical gating mechanism involving a
substantial decrease in the S:Ni ratio (over hundreds of nm), which is both
non-volatile and irreversible. This is in striking contrast to the reversible,
volatile, surface-limited, electrostatic gate effect in pyrite FeS$_2$. We
attribute this stark difference in electrochemical vs. electrostatic gating
response in NiS$_2$ and FeS$_2$ to the much larger S diffusion coefficient in
NiS$_2$, analogous to the different behaviors observed among electrolyte-gated
oxides with differing O-vacancy diffusivities. The gating irreversibility, on
the other hand, is associated with the lack of atmospheric S; this is in
contrast to the better understood oxide case, where electrolysis of atmospheric
H$_2$O provides an O reservoir. This study of NiS$_2$ thus provides new insight
into electrolyte gating mechanisms in functional materials, in a previously
unexplored limit.",2201.00340v1
2021-12-28,Template-assisted growth of silver nanowires by electrodeposition,"Template-assisted synthesis is a facile way of growing various
one-dimensional nanostructures. Among various nanoporous templates, anodic
aluminium oxide (AAO) is most commonly used. In this work, the kinetics of
silver nanowire growth by electrodeposition in AAO templates was investigated.
The AAO templates were fabricated using the standard two-step anodisation
process. The geometrical features of the fabricated templates, such as pore
diameter (55 nm), interpore distance (115 nm), wall thickness (27 nm), porosity
(19.87 %), and pore density were obtained using scanning electron microscopy.
The oxide layer at the bottom of the pores was modified by the barrier layer
thinning process and chemical etching in order to facilitate uniform metal
deposition. This was followed by pore widening to increase the diameter of the
pores to 65 nm to enhance deposition. Interpore distance increased to 119.8 nm
and wall thickness remained almost constant at 27.7 nm. Silver was deposited
using conventional electrodeposition in constant current mode. Deposition
parameters such as time, current, solution concentration, and temperature were
systematically investigated. For each deposition, the efficiency of the process
was calculated by considering the filling fraction of the pores and the average
length of the wires, all of which were measured from the SEM images. A linear
growth versus time was observed within the parameter range. From the
experiments, it was observed that decreasing the current, increasing the
deposition temperature, and depositing for longer duration increased the
average length of the nanowires. The use of electrodeposition to grow metallic
nanowires can be extended to other pure metal and alloy systems.",2201.04947v2
2022-01-12,Insights into cation ordering of double perovskite oxides from machine learning and causal relations,"This work investigates the origins of cation ordering of double perovskites
using first-principles theory computations combined with machine learning (ML)
and causal relations. We have considered various oxidation states of A, A', B,
and B' from the family of transition metal ions to construct a diverse
compositional space. A conventional framework employing traditional ML
classification algorithms such as Random Forest (RF) coupled with appropriate
features including geometry-driven and key structural modes leads to highly
accurate prediction (~98%) of A-site cation ordering. We have evaluated the
accuracy of ML models by entailing analyses of decision paths, assignments of
probabilistic confidence bound, and finally introducing a direct non-Gaussian
acyclic structural equation model to investigate causality. Our study suggests
that the structural modes are the most important features for classifying
layered, columnar and rock-salt ordering. For clear layered ordering, the
charge difference between the A and A' is the most important feature which in
turn depends on the B, B' charge separation. Based on the outputs from ML
models, we have designed functional forms with these features to derive energy
differences forming clear layered ordering. The trilinear coupling between
tilt, rotation, and A-site antiferroelectric displacement in Landau free-energy
expansion becomes the necessary condition behind the formation of A-site cation
ordering.",2201.04970v2
2022-01-17,Epitaxial stabilization of an orthorhombic Mg-Ti-O superconductor,"The family of titanium oxide superconductors exhibits many intriguing
phenomena comparable to cuprates and iron pnictides/chalcogenides, and thus
provides an ideal platform to contrastively study the unconventional pairing
mechanism of high-temperature superconductors. Here, we successfully deposit
superconducting Mg-Ti-O films on MgAl$_2$O$_4$ substrates with three principal
orientations by ablating a MgTi$_2$O$_4$ target. Particularly, it is striking
to observed that a single-crystalline film of an unintended structure has been
grown on the (011)-oriented substrate, with the highest zero resistance
transition temperature ($T_{\mathrm{c}0}$) of 5.0 K among them. The film has a
highly reduced Mg/Ti ratio and an orthorhombic Ti$_9$O$_{10}$-like structure
(denoted as Mg: Ti$_9$O$_{10}$), demonstrated by further characterizations of
chemical composition and structure. Such a structure is unstable in bulk but
favorable to be epitaxially stabilized on the (011)-surface of MgAl$_2$O$_4$
due to a relatively small strain at the formed interface. An isotropic upper
critical field ($B_{\mathrm{c}2}$) up to 13.7 T that breaks the Pauli limit is
observed in the Mg: Ti$_9$O$_{10}$ film, analogous to other superconducting
titanium oxides. The similarity points to a common origin for the
superconductivity in the family, which will provide valuable opinions for the
mechanism of unconventional superconductivity in transition metal compounds.",2201.06400v2
2022-01-18,Zoology of spin and orbital fluctuations in ultrathin oxide films,"Many metallic transition-metal oxides turn insulating when grown as films
that are only a few unit-cells thick. The microscopic origins of these
thickness induced metal-to-insulator transitions however remain under dispute.
Here, we simulate the extreme case of a monolayer of an inconspicuous
correlated metal -- the strontium vanadate SrVO$_3$ -- deposited on a SrTiO$_3$
substrate. Crucially, our system can have a termination to vacuum consisting of
either a SrO or a VO$_2$ top layer. While we find that both lead to Mott
insulating behavior at nominal stoichiometry, the phase diagram emerging upon
doping -- chemically or through an applied gate voltage -- is qualitatively
different. Indeed, our many-body calculations reveal a cornucopia of nonlocal
fluctuations associated with (in)commensurate antiferromagnetic, ferromagnetic,
as well as stripe and checkerboard orbital ordering instabilities. Identifying
that the two geometries yield crystal-field splittings of opposite signs, we
elucidate the ensuing phases through the lens of the orbital degrees of
freedom. Quite generally, our work highlights that interface and surface
reconstruction and the deformation or severing of coordination polyhedra in
ultra-thin films drive rich properties that are radically different from the
material's bulk physics.",2201.07058v1
2022-01-20,Evaluation of the Thermal Stability of TiW/Cu Heterojunctions Using a Combined SXPS and HAXPES Approach,"Power semiconductor device architectures require the inclusion of a diffusion
barrier to suppress, or at best prevent the interdiffusion between the copper
metallisation interconnects and the surrounding silicon substructure. The
binary pseudo-alloy of titanium-tungsten (TiW), with $>$70~at.\% W, is a well
established copper diffusion barrier but is prone to degradation via the
out-diffusion of titanium when exposed to high temperatures
($\geq$400$^\circ$C). Here, the thermal stability of physical vapour deposited
(PVD) TiW/Cu bilayer thin films in
Si/SiO\textsubscript{2}(50~nm)/TiW(300~nm)/Cu(25~nm) stacks were characterised
in response to annealing at 400$^\circ$C for 0.5~h and 5~h, using a combination
of soft and hard X-ray photoelectron spectroscopy (SXPS and HAXPES) and
transmission electron microscopy (TEM). Results show that annealing promoted
the segregation of titanium out of the TiW and interdiffusion into the copper
metallisation. Titanium was shown be driven toward the free copper surface,
accumulating there and forming a titanium oxide overlayer upon exposure to air.
Annealing for longer timescales promoted a greater out-diffusion of titanium
and a thicker oxide layer to grow on the copper surface. However, interface
measurements suggest that the diffusion is not significant enough to compromise
the barrier integrity and the TiW/Cu interface remains stable even after 5~h of
annealing.",2201.08074v1
2022-01-24,Stability of Oxygenated Groups on Pristine and Defective Diamond Surfaces,"The surface functionalization of diamond has been extensively studied through
a variety of techniques, such as oxidation. Several oxygen groups have been
correspondingly detected on the oxidized diamond, such as COC (ester), CO
(ketonic), and COH (hydroxyl). However, the composition and relative
concentration of these groups on diamond surfaces can be affected by the type
of oxygenation treatment and the diamond surface quality. To investigate the
stability of the oxygenated groups at specific diamond surfaces, we evaluated
through fully atomistic reactive molecular mechanics (FARMM) simulations, using
the ReaxFF force field, the formation energies of CO, COC, and COH groups on
pristine and defective diamond surfaces (110), (111), and (311). According to
our findings, the COH group has the lowest formation energy on a perfect (110)
surface, while the COC is favored on a defective surface. As for the (111)
surface, the COC group is the most stable for both pristine and defective
surfaces. Similarly, COC group is also the most stable one on the
defective/perfect (311) surface. In this way, our results suggest that if in a
diamond film the (110) surface is the major exposed facet, the most adsorbed
oxygen group could be either COH or COC, in which the COC would depend on the
level of surface defects.",2201.09690v1
2022-01-28,Oxygen Deficient α-MoO3 with Promoted Adsorption and State-Quenching of H2O for Gas Sensor: A DFT Study,"Semiconducting oxides with reducible cations are ideal platforms for various
functional applications in nanoelectronics and catalysts. Here we report an
ultrathin monolayer alpha-MoO3 where tunable electronic properties and
different gas adsorbing behaviors upon introducing the oxygen vacancies (VO).
The unique property of alpha-MoO3 is that it contains three different types of
oxygen atoms occupying three Wyckoff sites that are absent in other
low-dimensional oxides and provides rich electronic hybridized states. The
presence of VO triggers intermediate state in the gap at ~0.59 eV below the
conduction band minimum and reduces the work function dramatically, together
with new excitations at near infrared. The realigned Fermi level associated
with the dangling state of VO reduces the neighboring Mo atoms and affects the
gas adsorption thereafter. The binding energy of H2O molecules above VO is 2.5
times up to -0.75 eV compared with that of perfect lattice site and trends of
transfer of electrons also reverse. The latter is related with the shallow
localized state in the band gap due to H2O adsorbed above perfect MoO3 which
becomes quenched upon adsorbing at the VO site. Those rich in-gap defective
states in oxygen deficient MoO3, broadening the light absorption and promoting
the uptake of water, are conductive to the application of alpha-MoO3 for
optoelectronics, photothermal therapy, and sensor of moisture.",2201.11900v1
2022-02-06,Unexpectedly Spontaneous Water Dissociation on Graphene Oxide Supported by Copper Substrate,"Water dissociation is of fundamental importance in scientific fields and has
drawn considerable interest in diverse technological applications. However, the
high activation barrier of breaking the O-H bond within the water molecule has
been identified as the bottleneck, even for the water adsorbed on the graphene
oxide (GO). Herein, using the density functional theory calculations, we
demonstrate that the water molecule can be spontaneously dissociated on GO
supported by the (111) surface of the copper substrate (Copper-GO). This
process involves a proton transferring from water to the interfacial oxygen
group, and a hydroxide covalently bonding to GO. Compared to that on GO, the
water dissociation barrier on Copper-GO is significantly decreased to be less
than or comparable to thermal fluctuations. This is ascribed to the
orbital-hybridizing interaction between copper substrate and GO, which enhances
the reaction activity of interfacial oxygen groups along the basal plane of GO
for water dissociation. Our work provides a novel strategy to access water
dissociation via the substrate-enhanced reaction activity of interfacial oxygen
groups on GO and indicates that the substrate can serve as an essential key to
tuning the catalytic performance of various two-dimensional material devices.",2202.02746v2
2022-02-16,Solution-processed van der Waals heterojunction as the damage-free gate contact for high performance GaN HEMTs,"The junctions formed between gate contact and III-nitride are crucial
components of GaN-based electronics and optoelectronics. In this work,
solution-processed inorganic Ti3C2Tx MXene films were spray coated on the
AlGaN/GaN epitaxial wafer as the gate contact. The workfounction of MXene films
was effectively enhanced by partial oxidization process, and accordingly, the
gate leakage current and off-state drain current were significantly suppressed.
The van der Waals heterojunction between MXene films and III-nitride without
direct chemical bonding retained the pristine atomically flat native oxides of
III-nitride, record high Ion/Ioff current ratio of 1013, and near ideal
subthreshold swing of 61 mV/dec was achieved in the Schottky-Type gate GaN
HEMTs. In addition, the MXene gate GaN HEMTs display superior electron mobility
and transcoductance, high uniformity with 20 measured transistors. The
unprecedented performance can be correlated to the damage-free interface
between MXene and III-nitride, negligible atomic diffusion of MXene into the
semiconductor layer, and excellent adhesion between MXene and III-nitride. This
work provides an alternative method to create contact not only in GaN HEMTs but
also in other electronic and optoelectronic devices which uniquely features
cost-effective, non-vacuum, high deposition rate, and damage-free properties.",2202.08243v2
2022-03-04,"Character of the ""normal state"" of the nickelate superconductors","The occurrence of superconductivity in proximity to various strongly
correlated phases of matter has drawn extensive focus on their normal state
properties, to develop an understanding of the state from which
superconductivity emerges. The recent finding of superconductivity in layered
nickelates raises similar interests. However, transport measurements of doped
infinite-layer nickelate thin films have been hampered by materials limitations
of these metastable compounds - in particular, a relatively high density of
extended defects. Here, by moving to a substrate
(LaAlO$_{3}$)$_{0.3}$(Sr$_{2}$TaAlO$_{6}$)$_{0.7}$ which better stabilizes the
growth and reduction conditions, we can synthesize the doping series of
Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ essentially free from extended defects. This
enables the first examination of the 'intrinsic' temperature and doping
dependent evolution of the transport properties. The normal state resistivity
exhibits a low-temperature upturn in the underdoped regime, linear behavior
near optimal doping, and quadratic temperature dependence for overdoping. This
is strikingly similar to the copper oxides, despite key distinctions - namely
the absence of an insulating parent compound, multiband electronic structure,
and a Mott-Hubbard orbital alignment rather than the charge-transfer insulator
of the copper oxides. These results suggest an underlying universality in the
emergent electronic properties of both superconducting families.",2203.02580v1
2022-03-08,"Heteroepitaxial control of Fermi liquid, Hund metal, and Mott insulator phases in the single-atomic-layer limit","Interfaces between dissimilar correlated oxides can offer devices with
versatile functionalities. In that respect, manipulating and measuring novel
physical properties of oxide heterointerfaces are highly desired. Yet, despite
extensive studies, obtaining direct information on their momentum-resolved
electronic structure remains a great challenge. This is because most correlated
interfacial phenomena appear within a few atomic layers from the interface,
thus limiting the application of available experimental probes. Here, we
utilize atomic-scale epitaxy and photoemission spectroscopy to demonstrate the
interface control of correlated electronic phases in atomic-scale
ruthenate--titanate heterostructures. While bulk SrRuO$_3$ is a ferromagnetic
metal, the heterointerfaces exclusively realize three distinct correlated
phases in the single-atomic-layer limit. Our theory reveals that atomic-scale
structural proximity effects lead to the emergence of Fermi liquid, Hund metal,
and Mott insulator phases in the quantum-confined SrRuO$_3$. These results
highlight the extensive interfacial tunability of electronic phases, hitherto
hidden in the atomically thin correlated heterostructure.",2203.04244v1
2022-03-11,Tunable superconductivity at the oxide-insulator/KTaO$_3$ interface and its origin,"Superconductivity forms out of the condensation of Cooper pairs of electrons.
The mechanism by which Cooper pairs are created in non-conventional
superconductors is often elusive because experimental signatures that connect a
specific pairing mechanism to the properties of superconducting state are rare.
The recently discovered superconducting oxide-insulator/KTaO$_3$ interface may
offer clues about its origins. Here we observe distinct dependences of the
superconducting transition temperature Tc on carrier density n$_{2D}$ for
electron gases formed at KTaO$_3$ (111), (001) and (110) interfaces. For the
KTaO$_3$ (111) interface, a remarkable linear dependence of Tc on n$_{2D}$ is
observed over a range of nearly one order of magnitude. Further, our study of
the dependence of superconductivity on gate electric fields reveals the role of
the interface in mediating superconductivity, which also allows for a
reversible electric switching of superconductivity at T = 2 K. We found that
the extreme sensitivity of superconductivity to crystallographic orientation
can be explained by Cooper pairing via inter-orbital interactions induced by
the inversion-breaking transverse optical (TO1) phonons and quantum
confinement. This mechanism is also consistent with the dependence of Tc on
n$_{2D}$ at the KTaO$_3$ (111) interface. Our study may shed light on the
pairing mechanism in other superconducting quantum-paraelectrics.",2203.05867v1
2022-03-18,X-ray Nano-imaging of Defects in Thin Film Catalysts via Cluster Analysis,"Functional properties of transition-metal oxides strongly depend on
crystallographic defects. In transition-metal-oxide electrocatalysts such as
SrIrO3 (SIO), crystallographic lattice deviations can affect ionic diffusion
and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging
of local structural distortions across an extended spatial region of thin
samples. Line defects remain challenging to detect and localize using
nanodiffraction, due to their weak diffuse scattering. Here we apply an
unsupervised machine learning clustering algorithm to isolate the low-intensity
diffuse scattering in as-grown and alkaline-treated thin epitaxially strained
SIO films. We pinpoint the defect locations, find additional strain variation
in the morphology of electrochemically cycled SIO, and interpret the defect
type by analyzing the diffraction profile through clustering. Our findings
demonstrate the use of a machine learning clustering algorithm for identifying
and characterizing hard-to-find crystallographic defects in thin films of
electrocatalysts and highlight the potential to study electrochemical reactions
at defect sites in operando experiments.",2203.09980v2
2022-04-05,Exploring Mechanisms of Hydration and Carbonation of MgO and Mg(OH)2 in Reactive Magnesium Oxide-based Cements,"Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in
carbon capture processes. However, knowledge on the driving forces that control
the degree of carbonation and hydration and rate of reactions in this system
remains limited. In this work, density functional theory-based simulations are
used to investigate the physical nature of the reactions taking place during
the fabrication of RMCs under ambient conditions. Parametric indicators such as
adsorption energies, charge transfer, electron localization function,
adsorption/dissociation energy barriers and the mechanisms of interaction of
H2O and CO2 molecules with MgO and brucite (Mg(OH)2) clusters are considered.
The following hydration and carbonation interactions relevant to RMCs are
evaluated i) carbonation of MgO, ii) hydration of MgO, carbonation of hydrated
MgO, iii) carbonation of Mg(OH)2, iv) hydration of Mg(OH)2 and v) hydration of
carbonated Mg(OH)2. A comparison of the energy barriers and reaction pathways
of these mechanisms shows that the carbonation of MgO is hindered by presence
of H2O molecules, while the carbonation of Mg(OH)2 is hindered by the formation
of initial carbonate and hydrate layers as well as presence of excessed H2O
molecules. To compare these finding to bulk mineral surfaces, the interactions
of the CO2 and H2O molecules with the MgO(001) and Mg(OH)2 (001) surfaces are
studied. Therefore, this work presents deep insights into the physical nature
of the reactions and the mechanisms involved in hydrated magnesium carbonates
production that can be beneficial for its development.",2204.01993v1
2022-04-05,Unraveling the stable cathode electrolyte interface in all solid-state thin-film battery operating at 5V,"Spinel-type LiNi0.5Mn1.5O4 (LNMO) is one of the most promising 5 V-class
cathode materials for Li-ion batteries that can achieve high energy density and
low production costs. However, in liquid electrolyte cells, the high voltage
causes continuous cell degradation through the oxidative decomposition of
carbonate-based liquid electrolytes. In contrast, some solid-state electrolytes
have a wide electrochemical stability range and can withstand the required
oxidative potential. In this work, a thin-film battery consisting of a LNMO
cathode with a solid lithium phosphorus oxynitride (LiPON) electrolyte is
tested and their interface before and after cycling is characterized. With Li
metal as the anode, this system can deliver stable performance for 600 cycles
with an average Coulombic efficiency > 99%. Neutron depth profiling indicates a
slight overlithiated layer at the interface prior to cycling; a result that is
consistent with the excess charge capacity measured during the first cycle.
Cryogenic electron microscopy further reveals intimate contact between LNMO and
LiPON without noticeable structure and chemical composition evolution after
extended cycling, demonstrating the superior stability of LiPON against a high
voltage cathode. Consequently, we propose design guidelines for interface
engineering that could accelerate the commercialization of a high voltage cell
with solid or liquid electrolytes.",2204.02510v1
2022-05-02,Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$,"Some of the materials are more affected by oxidation than others. To
elucidate the oxidation-induced degradation mechanisms in transition metal
chalcogenides, the chemical effects in single layer MoS$_2$ and MoTe$_2$ were
studied in situ in an electron microscope under controlled low-pressure oxygen
environments at room temperature.Oxidation is the main cause of degradation of
many two-dimensional materials, including transition metal dichalcogenides,
under ambient conditions. MoTe$_2$ is found to be reactive to oxygen, leading
to significant degradation above a pressure of 1$\times 10^{-7}$ torr.
Curiously, the common hydrocarbon contamination found on practically all
surfaces accelerates the damage rate significantly, by up to a factor of forty.
In contrast to MoTe$_2$, MoS$_2$ is found to be inert under oxygen environment,
with all observed structural changes being caused by electron irradiation only,
leading to well-defined pores with high proportion of molybdenum
nanowire-terminated edges. Using density functional theory calculations, a
further atomic-scale mechanism leading to the observed oxygen-related
degradation in MoTe$_2$ is proposed and the role of the carbon in the etching
is explored. Together, the results provide an important insight into the
oxygen-related deterioration of two-dimensional materials under ambient
conditions relevant in many fields.",2205.00855v1
2022-05-10,Fine and hyperfine excitation of nitric oxide by collision with para-H2,"Nitric oxide is an open-shell molecule abundantly detected in the
interstellar medium. A precise modeling of its radiative and collisional
processes opens the path to a precise estimate of its abundance. We present
here the first rate coefficients for fine and hyperfine (de-)excitation of NO
by collisions with the most ubiquitous collision partner in the interstellar
medium, $para$-H$_2$ hydrogen molecules, using a recently developed accurate
interaction potential. We report quantum scattering calculations for
transitions involving the first 74 fine levels and the corresponding 442
hyperfine levels belonging to both $F_1$ and $F_2$ spin-orbit manifolds. To do
so, we have calculated cross sections by means of the quantum mechanical
close-coupling approach up to 1000 cm$^{-1}$ of total energy and rate
coefficients from 5 to 100 K. Propensity rules are discussed and the new
NO-H$_2$ rates are compared to those available in the literature, based on
scaled NO-He rates. Large differences are observed between the two sets of rate
coefficients, and this comparison shows that the new collision rates must be
used in interpreting NO emission lines. We also examined the effect of these
new rates on the NO excitation in cold clouds by performing radiative transfer
calculations of the excitation and brightness temperatures for the two NO lines
at 150.176 and 250.4368 GHz. This shows that the local thermodynamic
equilibrium is not fulfilled for this species for typical conditions. We expect
the use of the rates presented in this study to improve the constraints on the
abundance of NO.",2205.04863v1
2022-05-11,Reversible Tuning of Superconductivity in Ion-Gated NbN Ultrathin Films by Self-Encapsulation with a High-$κ$ Dielectric Layer,"Ionic gating is a powerful technique for tuning the physical properties of a
material via electric field-induced charge doping, but is prone to introduce
extrinsic disorder and undesired electrochemical modifications in the gated
material beyond pure electrostatics. Conversely, reversible, volatile and
electrostatic modulation is pivotal in the reliable design and operation of
novel device concepts enabled by the ultrahigh induced charge densities
attainable via ionic gating. Here we demonstrate a simple and effective method
to achieve reversible and volatile gating of surface-sensitive ultrathin
niobium nitride films via controlled oxidation of their surface. The resulting
niobium oxide encapsulation layer exhibits a capacitance comparable to that of
non-encapsulated ionic transistors, withstands gate voltages beyond the
electrochemical stability window of the gate electrolyte, and enables a
fully-reversible tunability of both the normal-state resistivity and the
superconducting transition temperature of the encapsulated films. Our approach
should be transferable to other materials and device geometries where more
standard encapsulation techniques are not readily applicable.",2205.05491v3
2022-05-13,Tuning cryogenic Jahn-Teller transition temperatures in magnetoelectric rare earth vanadates,"Few materials undergo cooperative Jahn-Teller (JT) transitions at low
temperatures, but zircon-type oxides are one class that includes DyVO$_4$,
which transforms from a tetragonal to an orthorhombic structure at around 13.6
K, with a narrow transition temperature range within 0.5 K. Since many
rare-earth ions can be accommodated in the structure, there should be ample
routes to vary the transition temperature and structural effects of the
transition. We have synthesized pure DyVO$_4$ and solid solutions
Dy$_{1-x}$Tm$_x$VO$_4$ ($x$ = 0.05, 0.1, 0.15, 0.2, and 0.5) and
Dy$_{1-y}$Pr$_y$VO$_4$ ($y$ = 0.03, 0.05, 0.1, 0.2, and 0.5), all by solution
precipitation. X-ray diffraction shows a systematic peak shift and a linear
change of lattice parameters with increasing substitution. We demonstrate
through heat capacity measurements that both Tm$^{3+}$ and Pr$^{3+}$
substitutions cause a depression of the cooperative JT transition temperature.
When the substitution level increases, the JT transition is eventually
suppressed. We examine a mean-field approximation model that can explain the
both the JT transition temperature shift and its eventual disappearance. The
cooperative JT effect in these zircon-type oxides is known to exhibit a large
magnetoelectric response, which should follow from the mean-field behavior. The
structural transformation can be easily detected via diffraction and can be
used as a temperature calibration in low temperature experiments.",2205.06856v1
2022-05-14,Enhanced spectral broadening via self-phase modulation with femtosecond optical pulses in silicon nanowires integrated with 2D graphene oxide films,"We experimentally demonstrate enhanced spectral broadening of femtosecond
optical pulses af-ter propagation through silicon-on-insulator (SOI) nanowire
waveguides integrated with two-dimensional (2D) graphene oxide (GO) films.
Owing to the strong mode overlap between the SOI nanowires and the GO films
with a high Kerr nonlinearity, the self-phase modulation (SPM) process in the
hybrid waveguides is significantly enhanced, resulting in greatly improved
spectral broadening of the femtosecond optical pulses. A solution-based,
transfer-free coating method is used to integrate GO films onto the SOI
nanowires with precise control of the film thickness. Detailed SPM measurements
using femtosecond optical pulses are carried out, achieving a broadening factor
of up to ~4.3 for a device with 0.4-mm-long, 2 layers of GO. By fit-ting the
experimental results with theory, we obtain an improvement in the waveguide
nonlin-ear parameter by a factor of ~3.5 and the effective nonlinear figure of
merit (FOM) by a factor of ~3.8, relative to the uncoated waveguide. Finally,
we discuss the influence of GO film length on the spectral broadening and
compare the nonlinear optical performance of different integrated waveguides
coated with GO films. These results confirm the improved nonlinear optical
per-formance for silicon devices integrated with 2D GO films.",2205.06942v1
2022-05-26,Ultrahigh ion diffusion in oxide crystal by engineering the interfacial transporter channels,"The mass storage and removal in solid conductors always played vital role on
the technological applications such as modern batteries, permeation membranes
and neuronal computations, which were seriously lying on the ion diffusion and
kinetics in bulk lattice. However, the ions transport was kinetically limited
by the low diffusional process, which made it a challenge to fabricate
applicable conductors with high electronic and ionic conductivities at room
temperature. It was known that at essentially all interfaces, the existed space
charge layers could modify the charge transport, storage and transfer
properties. Thus, in the current study, we proposed an acid solution/WO3/ITO
structure and achieved an ultrafast hydrogen transport in WO3 layer by
interfacial job-sharing diffusion. In this sandwich structure, the transport
pathways of the protons and electrons were spatially separated in acid solution
and ITO layer respectively, resulting the pronounced increasing of effective
hydrogen diffusion coefficient (Deff) up to 106 times. The experiment and
theory simulations also revealed that this accelerated hydrogen transport based
on the interfacial job-sharing diffusion was universal and could be extended to
other ions and oxide materials as well, which would potentially stimulate
systematic studies on ultrafast mixed conductors or faster solid-state
electrochemical switching devices in the future.",2205.13414v1
2022-05-31,Enhanced self-phase modulation in silicon nitride waveguides integrated with 2D graphene oxide films,"We experimentally demonstrate enhanced self-phase modulation (SPM) in silicon
nitride (Si3N4) waveguides integrated with 2D graphene oxide (GO) films. GO
films are integrated onto Si3N4 waveguides using a solution-based,
transfer-free coating method that enables precise control of the film
thickness. Detailed SPM measurements are carried out using both picosecond and
femtosecond optical pulses. Owing to the high Kerr nonlinearity of GO, the
hybrid waveguides show significantly improved spectral broadening compared to
the uncoated waveguide, achieving a broadening factor of up to ~3.4 for a
device with 2 layers of GO. By fitting the experimental results with theory, we
obtain an improvement in the waveguide nonlinear parameter by a factor of up to
18.4 and a Kerr coefficient (n2) of GO that is about 5 orders of magnitude
higher than Si3N4. Finally, we provide a theoretical analysis for the influence
of GO film length, coating position, and its saturable absorption on the SPM
performance. These results verify the effectiveness of on-chip integrating 2D
GO films to enhance the nonlinear optical performance of Si3N4 devices.",2205.15817v1
2022-05-31,Functionalization of graphene sponge electrodes with two-dimensional materials for tailored electrocatalytic activity towards specific contaminants of emerging concern,"Low-cost graphene sponge electrodes were functionalized with two-dimensional
(2D) materials, i.e., borophene and hexagonal boron nitride (hBN), using a
one-step, hydrothermal self-assembly method. Borophene and hBN-modified
graphene sponge anode and N-doped graphene sponge cathode were employed for
electrochemical degradation of model persistent contaminants of emerging
concern in one-pass, flow through mode, and using low-conductivity supporting
electrolyte. Functionalization of the reduced graphene oxide (RGO) coating with
2D materials led to specific modifications in the electrode electrocatalytic
performance and interactions with the target contaminants. For instance,
addition of hBN promoted the adsorption of more hydrophobic organic
contaminants via van der Waals and {\pi}-{\pi} interactions. Functionalization
of the graphene sponge anode with borophene enhanced the generation of oxidant
species such as H2O2 and O3 and yielded an order of magnitude higher
concentration of hydroxyl radicals (HO) compared with the non-functionalized
graphene sponge anode, thus enhancing the removal of target contaminants.
Experiments conducted with the selective radical scavengers indicated the key
role of surface-bound hydroxyl radicals (HOads) and singlet oxygen (1O2) in
electrochemical degradation. The study demonstrates that functionalization of
graphene sponge electrodes with 2D materials can enhance their electrocatalytic
activity and modulate the interaction with specific organic contaminants, thus
opening new possibilities for designing electrodes tailored to remove specific
groups of pollutants.",2206.04111v1
2022-06-09,Dynamics of H atoms surface recombination in low-temperature plasma,"The dynamics of H atom recombination on materials of interest for a EUV
lithographer was studied under a longterm low-pressure H2 plasma exposure. The
similarity of the experimental plasma with the typical EUV-induced plasma over
the multi-layer mirrors (MLMs) surface of the EUV lithographic machine is
demonstrated by means of 2D PIC MC simulation. The measurement of the temporal
dynamics of the H atom surface loss probability is chosen for testing the
surface modification during the treatment. Time-resolved actinometry of H atoms
with Kr as the actinometer gas was used to detect the dynamics of the H-atom
loss probability on the surface of Al, Ru, RVS and SiO2. It is demonstrated
that significant changes of the materials surface occur only at the very
beginning of the treatment and ist due to the surface heating and cleaning
effects. After that no changes of the H recombination rate are found,
indicating that the surface stays absolutely stable. A special test of the
sensitivity of the used method to the state of surface was carried out.
Dynamics of the H recombination rate changes with the small O2 addition clearly
demonstrated modification of the Al surface due to oxidation with the next
removal of the oxygen by the H2 plasma treatment. The rate of oxide removal is
shown to be determined by plasma parameters such as the ion energy and flux to
the surface.",2206.04391v1
2022-06-23,Modulation doping of the FeSe monolayer on SrTiO$_3$,"The discovery of higher-temperature superconductivity in FeSe monolayers on
SrTiO$_3$ (STO) substrates has sparked a surge of interest in the interface
superconductivity. One point of the agreement reached to date is that
modulation doping by impurities in the substrate is critical for the enhanced
superconductivity. Remarkably, the universal doping of about 0.1 electrons per
Fe, \textit{i.e.}, so-called ``magic'' doping, has been observed on a range of
Ti oxide substrates, which concludes that there likely is some important
interaction limiting the FeSe doping. Our study discovers that the polarization
change at the interface Se because of the close proximity to the substrate from
that in the free-standing FeSe film significantly amplifies the total potential
difference at the interface above and beyond the work function difference for
charge transfer. Additionally, the titanate substrate with a large number of
free electrons basically serves as an ``infinite'' charge reservoir, which
leads to the saturated FeSe doping with the complete removal of interface
potential gradient. Our work has developed the theory for modulation doping in
the Van der Waals materials/oxides heterostructure, providing a solution to the
puzzle of ``magic'' doping in FeSe monolayers on titanates. The information
also presents experimental pathways to accommodate a variable carrier density
of FeSe monolayers via modulation doping.",2206.11945v1
2022-06-26,Atomically imprinted graphene plasmonic cavities,"Plasmon polaritons in van der Waals (vdW) materials hold promise for
next-generation photonics. The ability to deterministically imprint spatial
patterns of high carrier density in cavities and circuitry with nanoscale
features underlies future progress in nonlinear nanophotonics and strong
light-matter interactions. Here, we demonstrate a general strategy to
atomically imprint low-loss graphene plasmonic structures using
oxidation-activated charge transfer (OCT). We cover graphene with a monolayer
of WSe$_2$, which is subsequently oxidized into high work-function WOx to
activate charge transfer. Nano-infrared imaging reveals low-loss plasmon
polaritons at the WOx/graphene interface. We insert WSe$_2$ spacers to
precisely control the OCT-induced carrier density and achieve a near-intrinsic
quality factor of plasmons. Finally, we imprint canonical plasmonic cavities
exhibiting laterally abrupt doping profiles with single-digit nanoscale
precision via programmable OCT. Specifically, we demonstrate technologically
appealing but elusive plasmonic whispering-gallery resonators based on
free-standing graphene encapsulated in WOx. Our results open avenues for novel
quantum photonic architectures incorporating two-dimensional materials.",2206.12754v1
2022-06-27,From Si Nanowires to Ge Nanocrystals for VIS-NIR-SWIR Sensors and Non-volatile Memories: A Review,"Nanocrystalline Si and Ge are of high interest for integrated Si photonics
related to light emission, optical sensors, photodetectors, solar energy
harvesting and conversion devices, and also for floating gate non-volatile
memories (NVMs). In this review, we have focused on nanocrystalline porous Si
(nc-PS) with extension to Si nanodots, and Ge nanocrystals (NCs)/quantum dots
(QDs)/nanoparticles (NPs) embedded in oxides (SiO$_2$, TiO$_2$, HfO$_2$,
Al$_2$O$_3$). The great asset of nc-PS is its intense photoluminescence in VIS
at room temperature (RT), while Ge NCs/NPs embedded in oxides show high
photosensitivity in VIS-NIR-SWIR in the spectral photocurrent up to 1325 nm at
RT. Ge NCs/NPs/QDs floating gate NVMs present high memory performance, the
retention characteristics corresponding to the state of the art for NCs
floating gate NVMs. We prove the relevance of controlling the preparation
parameters for obtaining films with targeted photoluminescence,
photosensitivity and charge storage properties for applications, e.g.
VIS-NIR-SWIR optical sensors and photodetectors, and electronic and
photoelectric NVMs. We evidence the correlation of preparation conditions,
morphology, composition and crystalline structure with optical, electrical,
photoelectrical and charge storage properties and also evidence the
contribution of quantum confinement effect, localized states and trapping
centers.",2206.13260v1
2022-07-01,"Trends in Bandgap of Epitaxial $\textit{A}$$_2$$\textit{B}$$_2$O$_7$ ($\textit{A}$ = Sn, Pb; $\textit{B}$ = Nb, Ta) Films Fabricated by Pulsed Laser Deposition","Pyrochlore oxides $A_2B_2$O$_7$ have been a fruitful playground for condensed
matter physics because of the unique geometry in the crystal structure.
Especially focusing on the $A$-site tetrahedral sub-lattice, in particular,
pyrochlore oxides $A_2B_2$O$_7$ ($A$ = Sn, Pb and $B$ = Nb, Ta), recent
theoretical studies predict the emergence of the ""quasi-flat band"" structure as
a result of the strong hybridization between filled $A$-n$s$ and O-2$p$
orbitals. In this work, we have established the growth conditions of
Sn$_2$Nb$_2$O$_7$, Sn$_2$Ta$_2$O$_7$, Pb$_2$Nb$_2$O$_7$, and Pb$_2$Ta$_2$O$_7$
films by pulsed laser deposition on Y-stabilized ZrO$_2$ (111) substrates to
elucidate their optical properties. Absorption-edge energies, both for direct
and indirect bandgaps, increase in the order of Sn$_2$Nb$_2$O$_7$,
Sn$_2$Ta$_2$O$_7$, Pb$_2$Nb$_2$O$_7$, and Pb$_2$Ta$_2$O$_7$. This tendency can
be well explained by considering the energy level of the constituent elements.
A comparison of the difference between direct and indirect bandgaps reveals
that Pb$_2B_2$O$_7$ tends to have a less dispersive valence band than
Sn$_2B_2$O$_7$. Our findings are consistent with the theoretical predictions
and are suggestive of the common existence of the hybridized states in this
class of compounds.",2207.00434v1
2022-06-10,"Fabrication of Periodic, Flexible and Porous Silicon Microwire Arrays with Controlled Diameter and Spacing: Effects on Optical properties","A new method of introducing nanopores with spongy morphology during
fabrication of size and pitch controlled flexible silicon microwires (SiMWs) in
wafer scale is presented using nanosphere lithography technique in addition to
metal catalyzed electroless etching technique by varying concentration of
oxidant and introducing surfactant or co-solvents to the etching solution. For
achieving self-assembled monolayer closed-pack pattern of SiO2 microparticles
in wafer-scale simple spin coating process was used. The effect of variation of
the etchant, oxidant and surfactant on the morphology and optical properties of
SiMWs were studied. By simply controlling the diameter of SiO2 microparticles
and concentration of H2O2 the size of the MWs as well as the introduction of
pores could be controlled in wafer-scale. Average reflectance suppressed to
below 8% in the broad spectral range of 400-800 nm for these porous, spongy and
flexible SiMW arrays in wafer scale. The mechanism behind this formation of
spongy, porous and flexible nature of the SiMWs is also demonstrated for a
better understanding of the etching process.",2207.06487v1
2022-07-15,Band-Engineered LaFeO$_{3}$-LaNiO$_{3}$ Thin Film Interfaces for Electrocatalysis of Water,"Transition metal oxides have generated significant interest for their
potential as catalysts for the oxygen evolution reaction (OER) in alkaline
environments. Iron and nickel-based perovskite oxides have proven particularly
promising, with catalytic over-potentials rivaling precious metal catalysts
when the alignment of the valence band relative to the OER reaction potential
is tuned through substitutional doping or alloying. Here we report that
engineering of band alignment in LaFeO$_{3}$/LaNiO$_{3}$ (LFO/LNO)
heterostructures via interfacial doping yields greatly enhanced catalytic
performance. Using density functional theory modeling, we predict a 0.2 eV
valence band offset (VBO) between metallic LNO and semiconducting LFO that
significantly lowers the barrier for hole transport through LFO compared to the
intrinsic material and make LFO a p-type semiconductor. Experimental band
alignment measurements using in situ X-ray photoelectron spectroscopy of
epitaxial LFO/LNO heterostructures agree quite well with these predictions,
producing a measured VBO of 0.3(1) eV. OER catalytic measurements on the same
samples in alkaline solution show an increase in catalytic current density by a
factor of ~275 compared to LFO grown on n-type Nb-doped SrTiO$_{3}$. These
results demonstrate the power of tuning band alignments through interfacial
band engineering for improved catalytic",2207.07264v1
2022-07-15,Tunable intervalence charge transfer in ruthenium Prussian blue analogue enables stable and efficient biocompatible artificial synapses,"Emerging concepts for neuromorphic computing, bioelectronics, and
brain-computer interfacing inspire new research avenues aimed at understanding
the relationship between oxidation state and conductivity in unexplored
materials. Here, we present ruthenium Prussian blue analogue (RuPBA), a mixed
valence coordination compound with an open framework structure and ability to
conduct both ionic and electronic charge, for flexible artificial synapses that
reversibly switch conductance by more than four orders of magnitude based on
electrochemically tunable oxidation state. Retention of programmed states is
improved by nearly two orders of magnitude compared to the extensively studied
organic polymers, thus reducing the frequency, complexity and energy costs
associated with error correction schemes. We demonstrate dopamine detection
using RuPBA synapses and biocompatibility with neuronal cells, evoking
prospective application for brain-computer interfacing. By application of
electron transfer theory to in-situ spectroscopic probing of intervalence
charge transfer, we elucidate a switching mechanism whereby the degree of mixed
valency between N-coordinated Ru sites controls the carrier concentration and
mobility, as supported by DFT.",2207.07756v1
2022-07-29,The electronic and thermal response of low electron density Drude materials to ultrafast optical illumination,"Many low electron density Drude (LEDD) materials such as transparent
conductive oxide or nitrides have recently attracted interest as alternative
plasmonic materials and future nonlinear optical materials. However, the
rapidly growing number of experimental studies has so far not been supported by
a systematic theory of the electronic, thermal and optical response of these
materials. Here, we use the techniques previously derived in the context of
noble metals to go beyond a simple electromagnetic modelling of low electron
density Drude materials and provide an electron dynamics model for their
electronic and thermal response. We find that the low electron density makes
momentum conservation in electron-phonon interactions more important, more
complex and more sensitive to the temperatures compared with noble metals;
moreover, we find that electron-electron interactions are becoming more
effective due to the weaker screening. Most importantly, we show that the low
electron density makes the electron heat capacity much smaller than in noble
metals, such that the electrons in LEDD materials tend to heat up much more and
cool down faster compared to noble metals. While here we focus on indium tin
oxide (ITO), our analytic results can be easily applied to any LEDD materials.",2207.14528v1
2022-08-01,Preferred corrosion pathways for oxygen in Al2Ca-twin boundaries and dislocations,"With an ongoing discussion on the oxygen diffusion along crystal defects
remaining, it is difficult to study this phenomenon in Al containing
intermetallic materials due to its rapid and passivating oxide formation. We
report here the observation of enhanced oxygen diffusion along crystal defects,
i.e. dislocations and twin boundaries, in the C15 Al 2 Ca Laves phase and how
the presence of oxygen induces structural changes at these defects. Three main
phases were identified and characterized structurally by aberration-corrected,
atomic resolution scanning transmission electron microscopy, analytically by
energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.
Unlike the C15 bulk phase, the twin boundary and dislocation transformed into a
few nanometer wide amorphous phase, which depletes in Al and Ca but is highly
enriched in oxygen. The dislocation even shows coexistence of the amorphous
phase with a simple Al-rich A1 fcc phase. This A1 phase only depletes in Ca,
not in Al (Al remains at bulk concentration), and is also enriched in oxygen.
The Al-rich A1 phase is coherent with the C15 matrix. Electron energy loss
spectroscopy revealed the amorphous phase to be Al 2 O 3 . We thereby show as
one of the first studies that oxygen diffusion along crystal defects,
especially also at the twin boundary can induce the formation of an amorphous
oxide along themselves. The identification of oxygen-induced transformation at
strained defects has to be considered when the material is exposed to air
during plastic deformation at elevated temperatures.",2208.01116v2
2022-08-16,Towards the simulation of transition-metal oxides of the cathode battery materials using VQE methods,"Variational quantum eigensolver (VQE) is a hybrid quantum-classical technique
that leverages noisy intermediate scale quantum (NISQ) hardware to obtain the
minimum eigenvalue of a model Hamiltonian. VQE has so far been used to simulate
condensed matter systems as well as quantum chemistry of small molecules. In
this work, we employ VQE methods to obtain the ground-state energy of
LiCoO$_2$, a candidate transition metal oxide used for battery cathodes. We
simulate Li$_2$Co$_2$O$_4$ and Co$_2$O$_4$ gas-phase models, which represent
the lithiated and delithiated states during the discharge and the charge of the
Li-ion battery, respectively. Computations are performed using a statevector
simulator with a single reference state for three different trial
wavefunctions: unitary coupled-cluster singles and doubles (UCCSD), unitary
coupled-cluster generalized singles and doubles (UCCGSD) and k-unitary pair
coupled-cluster generalized singles and doubles (k-UpCCGSD). The resources in
terms of circuit depth, two-qubit entangling gates and wavefunction parameters
are analyzed. We find that the k-UpCCGSD with k=5 produces results similar to
UCCSD but at a lower cost. Finally, the performance of VQE methods is
benchmarked against the classical wavefunction-based methods, such as
coupled-cluster singles and doubles (CCSD) and complete active space
configuration interaction (CASCI). Our results show that VQE methods
quantitatively agree with the results obtained from CCSD. However, the
comparison against the CASCI results clearly suggests that advanced trial
wavefunctions are likely necessary to capture the multi-reference
characteristics as well as the correlations emerging from high-level electronic
excitations.",2208.07977v1
2022-08-18,"Nanoscale mapping of sub-gap electroluminescence from step-bunched, oxidized 4H-SiC surfaces","Scanning tunneling luminescence microscopy (STLM) along with scanning
tunneling spectroscopy (STS) is applied to a step-bunched, oxidized 4H-SiC
surface prepared on the silicon face of a commercial, n-type SiC wafer using a
silicon melt process. The step-bunched surface consists of atomically smooth
terraces parallel to the [0001] crystal planes, and rougher risers consisting
of nanoscale steps formed by the termination of these planes. The rather
striking topography of this surface is well resolved with large tip biases of
the order of -8 V and set currents of magnitude less than 1 nA. Hysteresis in
the STS spectra is preferentially observed on the risers suggesting that they
contain a higher density of surface charge traps than the terraces where
hysteresis is more frequently absent. Similarly, at 50 K intense sub-gap light
emission centered around 2.4 eV is observed mainly on the risers albeit only
with larger tunneling currents of magnitude equal to or greater than 10 nA.
These results demonstrate that STLM holds great promise for the observation of
impurities and defects responsible for sub-gap light emission with spatial
resolutions approaching the length scale of the defects themselves.",2208.08775v1
2022-08-14,Energy-Exergy Analysis and Optimal Design of a Hydrogen Turbofan Engine,"In this study, the effect of inlet air cooling and fuel type on the
performance parameters of thrust-specific fuel consumption (TSFC), thermal and
exergetic efficiencies, entropy generation rate, and Nitrogen oxide emission
intensity index (SNOx) of the GENX 1B70 engine is analyzed in two states of
take-off and on design. The results show that with a 20-degree delicious
reduction in inlet air temperature on design conditions and JP10 fuel usage,
the thermal efficiency and entropy generation rate, thrust and fuel mass flow
rate, and TSFC of the engine increase by 1.85 percent, 16.51 percent, 11.76
percent, 10.53 percent, and 2.15 percent and SNOx and exergetic efficiency
decrease by 2.11 percent and 26.60 percent, respectively. Also, optimization of
the GENX 1B70 engine cycle as hydrogen fuel usage with three separate objective
functions: thrust maximization, thermal efficiency maximization, and propulsive
efficiency maximization on design point condition was performed based on the
Genetic algorithm. Based on the economic approach and exero-environmental, the
best cycles from the optimal states were selected using the TOPSIS algorithm.
In on design conditions, entropy generation rate, nitrogen oxide production
rate, and TSFC for the chosen cycle based on the economic approach +18.89
percent, +10.01 percent, and -0.21percent, respectively, and based on the
exero-environmental approach -54.03percent, -42.02percent, and +21.44percent
change compared to the base engine, respectively.",2208.08890v1
2022-08-19,Anomalous electrochemical capacitance in Mott insulator titanium sesquioxide,"Electrochemical capacitors with pure electric double layer capacitance are so
far largely been limited to carbon materials only. Conventional metal oxides
with Faradaic pseudocapacitance substantially suffer from material instability
at high temperatures and thus there is a demand for novel metal oxides
exhibiting thermally improved high electric double layer capacitance with
material stability. In this study, titanium sesquioxide, Ti$_2$O$_3$, a Mott
insulator in its metallic state at 300$^o$ C showed an anomalous increase of
$\approx$ 560% in the solid-state electrochemical capacitance as compared to
its pristine response at room temperature (RT). In aqueous electrolyte, the
maximum capacitance was obtained up to 1053 $\mu$F/cm$^2$, which is 307% higher
than with solid-state electrolyte. Moreover, the semiconducting state of
Ti$_2$O$_3$ demonstrated $\approx$ 3500% enhancement in its electrochemical
capacitance upon infrared illumination at RT. The observed electrochemical
responses in Ti$_2$O$_3$ are attributed to the transition of semiconducting to
the metallic state by redistribution of the localized electrons. Our
experimental results find a good agreement with the first-principles
density-functional theory calculations that revealed an increase in the charge
density with the rise in temperature, which is mainly attributed to the surface
Ti atoms. The study open has wide avenues to engineer the electrochemical
double layer capacitance of theory calculations that revealed an increase in
the charge density with the rise in temperature, which is mainly attributed to
the surface Ti atoms. The study opens wide avenues to engineer the
electrochemical double layer capacitance of Ti$_2$O$_3$ with high chemical
stability.",2208.09436v1
2022-08-23,"Hydrogen in Disordered Titania: Connecting Local Chemistry, Structure, and Stoichiometry through Accelerated Exploration","Hydrogen incorporation in native surface oxides of metal alloys often
controls the onset of metal hydriding, with implications for materials
corrosion and hydrogen storage. A key representative example is titania, which
forms as a passivating layer on a variety of titanium alloys for structural and
functional applications. These oxides tend to be structurally diverse,
featuring polymorphic phases, grain boundaries, and amorphous regions that
generate a disparate set of unique local environments for hydrogen. Here, we
introduce a workflow that can efficiently and accurately navigate this
complexity. First, a machine learning force field, trained on ab initio
molecular dynamics simulations, was used to generate amorphous configurations.
Density functional theory calculations were then performed on these structures
to identify local oxygen environments, which were compared against experimental
observations. Second, to classify subtle differences across the disordered
configuration space, we employ a graph-based sampling procedure. Finally, local
hydrogen binding energies are computed using exhaustive density functional
theory calculations on representative configurations. We leverage this
methodology to show that hydrogen binding energetics are described by local
oxygen coordination, which in turn is affected by stoichiometry. Together these
results imply that hydrogen incorporation and transport in TiO$_x$ can be
tailored through compositional engineering, with implications for improving
performance and durability of titanium-derived alloys in hydrogen environments.",2208.10956v1
2022-08-23,Direction-Dependent Lateral Domain Walls in Ferroelectric Hafnium Zirconium Oxide and their Gradient Energy Coefficients: A First Principles Study,"To understand and harness the physical mechanisms of ferroelectric Hafnium
Zirconium Oxide (HZO)-based devices, there is a need for clear understanding of
domain interactions, their dynamics, negative capacitance effects, and other
multi-domain characteristics. These crucial attributes depend on the coupling
between neighboring domains quantified by the gradient energy coefficient (g).
Furthermore, HZO has unique orientation-dependent lateral multidomain
configurations. To develop an in-depth understanding of multi-domain effects,
there is a need for thorough analysis of g. In this work, the energetics of
multidomain configurations and domain growth mechanism corresponding to lateral
domain walls of HZO are analyzed and gradient energy coefficients are
quantified using first-principles Density Functional Theory calculations. These
results indicate that one lateral direction exhibits the following
characteristics: i) DW is ultra-sharp and domain growth occurs
unit-cell-by-unit-cell, ii) the value of g is negative and in the order of
$10^{-12} Vm^{3}C^{-1}$, and iii) g reduces (increases) with compressive
(tensile) strain. In contrast, in the other lateral direction, the following
attributes are observed: i) DW is gradual and domain growth occurs in quanta of
half-unit-cell, ii) g is positive and in the order of $10^{-10} Vm^{3}C^{-1}$,
and iii) g increases (reduces) with compressive (tensile) strain.",2208.11029v4
2022-08-28,"Homologous self-assembled superlattices: What causes their periodic polarity switching? Review, model, and experimental test","Quantum semiconductor structures are commonly achieved by bandgap engineering
that relies on the ability to switch from one semiconductor to another during
their growth. Growth of a superlattice is typically demanding technologically.
In contrast, accumulated evidence points to a tendency among a certain class of
multiple-cation binary oxides to self-assemble spontaneously as superlattice
structures. This class has been dubbed the homologous superlattices. For a
famous example, when a mixture of indium and zinc is oxidized, the phases of
In-O and ZnO separate in an orderly periodic manner, along the ZnO polar axis,
with polarity inversion taking place between consecutive ZnO sections. As we
review here, the same structure has been observed when the indium was replaced
with other metals, and perhaps even in ZnO alone. This peculiar self-assembled
structure has been attracting research over the past decade. The purpose of
this study is to gain understanding of the physics underlying the formation of
this unique structure. Here, we first provide an extensive review of the
accumulated literature on these spontaneously-formed structures and then
propose an explanation for the long-standing mystery of this intriguing
self-assembly in the form of an electrostatic growth phenomenon and test the
proposed model on experimental data.",2208.13155v1
2022-09-09,Rapid oxygen exchange between hematite and water vapor,"Oxygen exchange at oxide/liquid and oxide/gas interfaces is important in
technology and environmental studies, as it is closely linked to both catalytic
activity and material degradation. The atomic-scale details are mostly unknown,
however, and are often ascribed to poorly defined defects in the crystal
lattice. Here we show that even thermodynamically stable, well-ordered surfaces
can be surprisingly reactive. Specifically, we show that all the 3-fold
coordinated lattice oxygen atoms on a defect-free single-crystalline r-cut
(1-102) surface of hematite ({\alpha}-Fe2O3) are exchanged with oxygen from
surrounding water vapor within minutes at temperatures below 70 {\deg}C, while
the atomic-scale surface structure is unperturbed by the process. A similar
behavior is observed after liquid water exposure, but the experimental data
clearly show most of the exchange happens during desorption of the final
monolayer, not during immersion. Density functional theory computations show
that the exchange can happen during on-surface diffusion, where the cost of the
lattice oxygen extraction is compensated by the stability of an HO-HOH-OH
complex. Such insights into lattice oxygen stability are highly relevant for
many research fields ranging from catalysis and hydrogen production to
geochemistry and paleoclimatology.",2209.04205v1
2022-09-14,Structural peculiarities of $\varepsilon$-Fe$_2$O$_3$ / GaN epitaxial layers unveiled by high-resolution transmission electron microscopy and neutron reflectometry,"The present paper is dedicated to the structural study of crystallographic
peculiarities appearing in epitaxial films of metastable epsilon iron oxide
($\varepsilon$-Fe$_2$O$_3$) grown by pulsed laser deposition onto a
semiconductor GaN (0001) substrate. The columnar structure of the nanoscale
$\varepsilon$-Fe$_2$O$_3$ films has been for the first time investigated using
high resolution electron microscopy (HRTEM) direct space technique complemented
by reciprocal space methods of high-energy electron diffraction and
color-enhanced HRTEM image Fourier filtering. The study of
$\varepsilon$-Fe$_2$O$_3$ / GaN interface formation has been further expanded
by carrying out a depth resolved analysis of density and chemical composition
by neutron reflectometry and energy-dispersive X-ray spectroscopy. The obtained
results shed light onto the properties and the origin of the enigmatic
few-nanometer thick low density transition layer residing at the
$\varepsilon$-Fe$_2$O$_3$ / GaN interface. A detailed knowledge of the
properties of this layer is believed to be highly important for the development
of $\varepsilon$-Fe$_2$O$_3$ / GaN heterostructures that can potentially become
part of the iron-oxide based ferroic-on-semiconductor devices with room
temperature magneto-electric coupling.",2209.06460v1
2022-09-15,Spin-charge coupling and decoupling in perovskite-type iron oxides (Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$,"The perovskite-type iron oxide Sr$_{2/3}$La$_{1/3}$FeO$_3$ is known to show
characteristic spin-charge ordering (SCO), where sixfold collinear spin
ordering and threefold charge ordering are coupled with each other. Here, we
report the discovery of a spin-charge decoupling and an antiferromagnetic (AFM)
state competing with the SCO phase in perovskites
(Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$. By comprehensive measurements
including neutron diffraction, M$\""{o}$ssbauer spectroscopy, and x-ray
absorption spectroscopy, we found that the isovalent Ba$^{2+}$ substitution
systematically reduces the critical temperature of the SCO phase and
additionally yields the spin-charge decoupling in $x$ > 0.75. Whereas the
ground state remains in the SCO phase in the whole $x$ region, an unexpected
G-type AFM phase with incoherent charge ordering or charge fluctuation appears
as the high-temperature phase in the range of $x$ > 0.75. Reflecting the
competing nature between them, the G-type AFM phase partially exists as a
metastable state in the SCO phase at low temperatures. We discuss the origin of
the spin-charge decoupling and the emergence of the G-type AFM phase with
charge fluctuation in terms of the bandwidth reduction by the Ba substitution.",2209.07310v1
2022-09-18,A facile top-down synthesis of phase pure CuBi2O4 photocathode materials by low-energy sequential ball milling,"Kusachiite (copper bismuth oxide) is one of the most promising photocathode
materials for high solar-to-hydrogen production efficiency. Here we attempt to
synthesize phase pure copper bismuth oxide (CuBi2O4) nanopowders using a facile
solid-state reaction technique, subsequently sintered at 750 0C for 4 h in air.
These CuBi2O4 (CBO) powders have been further sequentially ball-milled (SBM) up
to 25 h to elucidate the milling duration effect on the optical bandgap of the
ball-milled CuBi2O4 (SBM-CBO). The X-ray diffractometry (XRD), Raman, X-ray
Photoelectron spectroscopy (XPS), and UV-VIS-NIR Diffuse reflection studies
suggest that phase pure tetragonal CBO could be grown from raw CuO and Bi2O3
powders. The variations in morphology and chemical composition of CBO with
increasing milling hours were examined using field emission scanning electron
microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) microanalysis,
respectively. The optical bandgap of SBM-CBO powders was measured in the range
of approx. 1.70 - 1.85 eV. Photoelectrochemical studies of SBM-CBO slurry atop
the screen-printed electrode with aqueous Na2SO4 electrolyte suggest its
suitability as photocathode materials for sunlight-driven hydrogen production.",2209.08530v2
2022-09-23,Excitonic effects in X-ray absorption spectra of fluoride salts and their surfaces,"Operando X-ray absorption spectroscopy (XAS) can probe the
electrode-electrolyte interface with single-digit nanometer depth resolution
and offers a wealth of insight into the evolution and Coulombic efficiency or
degradation of prototype cells, provided that the spectra can be reliably
interpreted in terms of local oxidation state, atomic coordination, and
electronic structure aboutthe excited atoms. To this end, we explore fluorine
K-edge XAS of mono- (Li, Na, K) and di-valent (Mg, Ca, Zn) fluoride salts from
a theoretical standpoint and discover a surprising level of detailed electronic
structure information about these materials, despite the relatively predictable
oxidation state and ionicity of the fluoride anion and the metal cation.
Utilizing a recently developed many-body approach based on the delta-SCF
method, we calculate the XAS using density functional theory and experimental
spectral profiles are well reproduced, despite some experimental discrepancies
in energy alignment within the literature, which we can correct for in our
simulations. We outline a general methodology to explain shifts in the main XAS
peak energies in terms of a simple exciton model and explain line-shape
differences resulting from mixing of core-excited states with metal d character
(for K and Ca specifically). Given ultimate applications to evolving
interfaces, some understanding of the role of surfaces and their terminations
in defining new spectral features is provided to indicate the sensitivity of
such measurements to changes in interfacial chemistry.",2209.11845v1
2022-09-24,Energy-Environment evaluation and Forecast of a Novel Regenerative turboshaft engine combine cycle with DNN application,"In this integrated study, a turboshaft engine was evaluated by adding inlet
air cooling and regenerative cooling based on energy-environment analysis.
First, impacts of flight-Mach number, flight altitude, the compression ratio of
compressor-1 in the main cycle, the turbine inlet temperature of turbine-1 in
the main cycle, temperature fraction of turbine-2, the compression ratio of the
accessory cycle, and inlet air temperature variation in inlet air cooling
system on some functional performance parameters of Regenerative turboshaft
engine cycle equipped with inlet air cooling system such as power-specific fuel
consumption, Power output, thermal efficiency, and mass flow rate of Nitride
oxides (NOx) including NO and NO2 has been investigated via using hydrogen as
fuel working. Consequently, based on the analysis, a model was developed to
predict the energy-environment performance of the Regenerative turboshaft
engine cycle equipped with a cooling air cooling system based on a deep neural
network (DNN) with 2 hidden layers with 625 neurons for each hidden layer. The
model proposed to predict the amount of thermal efficiency and the mass flow
rate of nitride oxide (NOx) containing NO and NO2. The results demonstrated the
accuracy of the integrated DNN model with the proper amount of the MSE, MAE,
and RMSD cost function for both predicted outputs to validate both testing and
training data. Also, R and R^2 are noticeably calculated very close to 1 for
both thermal Efficiency and NOx emission mass flow rate for both validations of
thermal efficiency and NOx emission mass flow rate prediction values with its
training and its testing data.",2209.12020v1
2022-09-26,Quality Control (QC) of FBK Preproduction 3D Si Sensors for ATLAS HL-LHC Upgrades,"The challenging demands of the ATLAS High Luminosity (HL-LHC) Upgrade aim for
a complete swap of new generation sensors that should cope with the ultimate
radiation hardness. FBK has been one of the prime foundries to develop and
fabricate such radiation-hard 3D silicon (Si) sensors. These sensors are chosen
to be deployed into the innermost layer of the ATLAS Inner Tracker (ITk).
Recently, a pre-production batch of 3D Si sensors of 50x50 um2 pixel geometry,
compatible with the full-size ITKPix (RD53B) readout chip, was fabricated. Two
wafers holding temporary metal were diced at IZM, Germany, and a systematic QC
test campaign was carried out at the University of Trento electronics
laboratory. The paper briefly describes the 3D Si sensor design for ATLAS ITk
and the required QC characterization setups. It comprises electrical tests
(i.e., I-V, C-V, and I-T) of non-irradiated RD53B sensors. In addition, the
study of several parametric analyses, i.e., oxide charge density, oxide
thickness, inter-pixel resistance, inter-pixel capacitance, etc., are reported
with the aid of Process Control Monitor (PCM) structures.",2209.12991v2
2022-09-27,Evaluation and comparison of NiO/CuO nanocomposite and NiO nanofibers as non-enzymatic electrochemical cholesterol biosensor,"Fabrication of a highly sensitive non-enzymatic electrochemical sensor for
the detection of cholesterol is a challenging issue due to its low redox
activity. In the present study, the electrochemical response of a novel
combination of metal oxides has been explored. NiO/CuO nanocomposite was
fabricated by electrospinning method and its morphology and structural
characteristics were studied using scanning electron microscopy, EDX and X-ray
diffraction techniques. Electrochemical studies revealed that the NiO/CuO/GC
electrode poses a linear detection range between 0.8 to 6.5 mM, low detection
limit of 5.9 microM and a sensitivity of 10.27 microA.mM-1 .cm-2 in the neutral
buffer solution. The fabricated electrode has a response time of 3 seconds and
a good ability to discriminate interfering species. Moreover, the nanocomposite
electrode exhibited high stability as well as the other favorable factors,
makes it an effective sensor for the detection of cholesterol. In addition,
cyclic voltammetry experiments showed that the current response of NiO/GCE is
approximately 30 % of the NiO/CuO/GCE response, suggesting that the
nanocomposite has a greater electrocatalytic activity towards cholesterol
oxidation than NiO nanofibers. NiO/GCE results showed the sensitivity of 2.5
microA.mM-1 .cm-2 , response time of 2 seconds and a limited stability over
three-week time span.",2209.13144v1
2022-10-01,Stochastic Paleoclimatology: Modeling the EPICA Ice Core Climate Records,"We analyze and model the stochastic behavior of paleoclimate time series and
assess the implications for the coupling of climate variables during the
Pleistocene glacial cycles. We examine 800 kyr of carbon dioxide, methane,
nitrous oxide, and temperature proxy data from the EPICA Dome-C ice core, which
are characterized by 100~kyr glacial cycles overlain by fluctuations across a
wide range of time scales. We quantify this behavior through multifractal
time-weighted detrended fluctuation analysis, which distinguishes near
red-noise and white-noise behavior below and above the 100~kyr glacial cycle
respectively in all records. This allows us to model each time series as a
one-dimensional periodic non-autonomous stochastic dynamical system, and assess
the stability of physical processes and the fidelity of model-simulated time
series. We extend this approach to a four-variable model with linear coupling
terms, which we interpret in terms of the interrelationships between the time
series. Methane and nitrous oxide are found to have significant destabilizing
influences, while carbon dioxide and temperature have smaller stabilizing
influences. We draw conclusions about causal relationships in glacial
transitions and the climate processes that may have facilitated these
couplings, and highlight opportunities to further develop stochastic modeling
approaches.",2210.00308v2
2022-10-19,Predicting Oxide Glass Properties with Low Complexity Neural Network and Physical and Chemical Descriptors,"Due to their disordered structure, glasses present a unique challenge in
predicting the composition-property relationships. Recently, several attempts
have been made to predict the glass properties using machine learning
techniques. However, these techniques have the limitations, namely, (i)
predictions are limited to the components that are present in the original
dataset, and (ii) predictions towards the extreme values of the properties,
important regions for new materials discovery, are not very reliable due to the
sparse datapoints in this region. To address these challenges, here we present
a low complexity neural network (LCNN) that provides improved performance in
predicting the properties of oxide glasses. In addition, we combine the LCNN
with physical and chemical descriptors that allow the development of universal
models that can provide predictions for components beyond the training set. By
training on a large dataset (~50000) of glass components, we show the LCNN
outperforms state-of-the-art algorithms such as XGBoost. In addition, we
interpret the LCNN models using Shapely additive explanations to gain insights
into the role played by the descriptors in governing the property. Finally, we
demonstrate the universality of the LCNN models by predicting the properties
for glasses with new components that were not present in the original training
set. Altogether, the present approach provides a promising direction towards
accelerated discovery of novel glass compositions.",2210.10507v1
2022-10-25,Ultrafast ion sieving in two dimensional graphene oxide membranes,"Ultrahigh water permeance, together with a high rejection rate through
nanofiltration and separation membranes1,2, is crucial but still challenging
for multivalent ion sieving in water treatment processes of desalination,
separation, and purification3,4. To date, no theory or equation has ever been
quantitatively clarified the mechanism of water permeance in two-dimensional
(2D) membranes, despite intensive and prolonged searches. Here, we established
a new general equation of permeation through 2D membranes, and experimentally
achieved unprecedented advances in water permeance one to two orders of
magnitude higher than state-of-the-art membranes while simultaneously
maintaining high ion rejection rates for multivalent metal ions, by staking
nano-sized reduced graphene oxide (nano-rGO) flakes into nanofiltration
membranes. The equation is simply based on a fundamental steady-state flow
assumption and provides an essential description of water permeance through 2D
membranes, demonstrating that the ultrahigh water permeance is attributed to
the high effective channel area and shortened channel length elicited from the
nano-sized-flake stacking effects in nano-rGO membranes, consistent with our
theoretical simulations and previous experiments. These results pave the way
for fabrication of advanced 2D nanofiltration membranes to realize a
breakthrough in water permeance with exceptional ion sieving performance.",2210.13707v1
2022-10-26,Direct observation of two-dimensional small polarons at correlated oxide interface,"Two-dimensional (2D) perovskite oxide interfaces are ideal systems where
diverse emergent properties can be uncovered.The formation and modification of
polaronic properties due to short-range strong charge-lattice interactions of
2D interfaces remains hugely intriguing.Here, we report the direct observation
of small-polarons at the LaAlO3/SrTiO3 (LAO/STO) conducting interface using
high-resolution spectroscopic ellipsometry.First-principles investigations
further reveals that strong coupling between the interfacial electrons and the
Ti-lattice result in the formation of localized 2D small polarons.These
findings resolve the longstanding issue where the excess experimentally
measured interfacial carrier density is significantly lower than theoretically
predicted values.The charge-phonon induced lattice distortion further provides
an analogue to the superconductive states in magic-angle twisted bilayer
graphene attributed to the many-body correlations induced by broken periodic
lattice symmetry.Our study sheds light on the multifaceted complexity of broken
periodic lattice induced quasi-particle effects and its relationship with
superconductivity.",2210.14440v2
2022-11-02,One-Step Formation of Plasmonic Cu Nanodomains in p-Type Cu$_2$O Matrix Films for Enhanced Photoconversion of n-ZnO/p-Cu$_2$O Heterojunctions,"Plasmonic Cu nanoparticles were in-situ grown into a Cu$_2$O semiconductor
matrix by using reactive magnetron sputtering and adjusting the amount of
oxygen available during the synthesis in order to prevent the oxidation of part
of copper atoms landed on the film surface. Varying only the oxygen flowrate
(OFR) and using a single Cu target it was possible to observe the evolution in
the simultaneous formation of metallic Cu and Cu$_2$O phases for oxygen-poor
conditions. Suchformation is accompanied by the development of the surface
plasmon band (SPB) corresponding to Cu, as evidenced by UV-Vis
spectrophotometry and spectroscopic ellipsometry. The bandgap values of the
elaborated composites containing embedded Cu plasmonic nanodomains were lower
than the bandgap of single-phased Cu$_2$O films, likely due to the higher
defect density associated to the nanocrystalline nature of films, promoted by
the presence of metallic Cu. The resistivity of the thin films increased with
more oxidative deposition conditions and was associated to an increase in
Cu$_2$O/Cu ratio and smaller and more isolated Cu particles, as evidenced by
high resolution transmission electron microscopy and X-ray diffraction.
Photoconversion devices based on the studied nanocomposites were characterized
by I-V and spectral photocurrent measurements, showing an increase in the
photocurrent density under light illumination as consequence of the plasmonic
particles excitation leading to hot carrier's injection in the nearby ZnO and
Cu$_2$O semiconductors.",2211.01010v1
2022-11-09,Ultra-clean isotope engineered double-walled carbon nanotubes as tailored hosts to trace the growth of carbyne,"Increasing attention is currently given to carbyne, the sp1 hybridized
one-dimensional carbon allotrope, because of its predicted outstanding
mechanical, optical, and electrical properties. Although recently substantial
progress has been reported on confined carbyne synthesized inside double-walled
carbon nanotubes (DWCNTs), its formation mechanism and precursors for growth
remain elusive. Here, we show a rational design of isotope engineered
ultra-clean DWCNTs as tailored hosts to trace the growth of carbyne, which
allows to identify the precursor and unravel the formation mechanism of carbyne
during high-vacuum annealing at high-temperatures. Using this approach,
ultra-clean DWCNTs with 80.4% 13C-enriched inner walls and outer tubes of
naturally abundant served to unambiguously prove that only the carbonaceous
materials inside the DWCNTs can act as precursors. The exchange of C atoms
between inner and outer tubes happens without any growth of carbyne. After
applying a secondary oxidation step, it is possible to produce the carbonaceous
precursors from the partially oxidized DWCNTs. In this manner, not only carbyne
with a record of ~28.8% 13C enrichment is grown, but concomitant healing,
reorganization and regrowth of the DWCNTs occurs. This work enables to identify
the precursor and trace the growth mechanism of confined carbyne with
engineered properties. This is a crucial step, towards accessing the full
application potential of confined carbyne hybrids by tailoring not only the
isotopic fillers, but also the inner and outer tubes of the DWCNT hosts.",2211.04852v1
2022-11-11,The Impact of Inter-grain Phases on the Ionic Conductivity of LAGP Solid Electrolyte Prepared by Spark Plasma Sintering,"Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising oxide solid electrolyte for
all-solid-state batteries due to its excellent air stability, wide
electrochemical stability window and cost-effective precursor materials.
However, further improvement in their ionic conductivity performance is
hindered by the presence of inter-grain phases leading to a major obstacle to
the advanced design of oxide based solid-state electrolytes. This study
establishes and quantifies the influence of inter-grain phases, their 3D
morphology, and formed compositions on the overall ion conductivity properties
of LAGP pellets fabricated under different Spark plasma sintering conditions.
Based on complementary techniques, such as PEIS, XRD, 3D FIB-SEM tomography and
solid-state MAS NMR coupled with DFT modelling, a deep insight into the
inter-grain phase microstructures is obtained revealing that the inter-grain
region is comprised of Li4P2O7 and a disordered Li9Al3(P2O7)3(PO4)2 phase. We
demonstrate that optimal ionic conductivity for the LAGP system is achieved for
the 680 {\deg}C SPS preparation when the disordered Li9Al3(P2O7)3(PO4)2 phase
dominates the inter-grain region composition with reduced contributions from
the highly ordered Li4P2O7 phases.",2211.06129v1
2022-11-12,"Theoretical investigation of the physical properties of cubic perovskite oxides $SrXO_3 \;(X =Sc,\; Ge,\; Si)$","Various physical properties (electronic, optical and thermoelectric) of cubic
perovskite oxides $SrXO_3\; (X=Sc,\; Ge,\; Si)$ are investigated by using the
density functional theory (DFT) within Wien2k code. This code is based on
different approximations such as generalized gradient approximation GGA,
PBEsol, LDA, WC and the modified Becke-Johnson exchange potentials (mBJ, nmBJ
and unmBJ). Structural properties and the optimization have been calculated
using PBEsol functional which showed a significant results that are in good
agreement with the experimental ones. The results for physical properties such
as electronic, thermoelectric and optical are analyzed in detail by using the
nmBJ approximation. The obtained results present an opening gap for $SrSiO_3$,
$SrGeO_3$ and a metallic behavior for $SrScO_3$. An average of transmittance
which is about $94\%$ to $97\%$ was observed in the range of visible light. The
increase of electrical conductivity with temperature confirms the effect of
thermal agitation on the concentration of charges carriers using BolzTrap
Package. Lastly a phonon dispersion was made and show that for $X=\; Ge$ and
$Si$, the structure is relatively stable while $SrScO_3$ is dynamically
unstable. These results prove the ability that these materials can be exploited
in many applications and manufacturing of optoelectronics for Sensors.",2211.06622v1
2022-11-15,Data-driven design of new catalytic materials in methane oxidation based on a site isolation concept,"The conversion of natural gas (methane) to ethane and ethylene (OCM:
oxidative coupling of methane) facilitates its transportation and provides a
way to synthesize higher value chemicals. The search for high-performance
catalysts to achieve this conversion is the main scope of most corresponding
studies in the field of OCM. Here, we present a general data-driven strategy
for the search of novel catalytic materials, focusing particularly on materials
useful for the OCM reaction. Our strategy is based on consistent experimental
measurements and includes ab initio thermodynamics calculations and active
screening. Based on our experiments, which showed unique volcano-type
dependence of the performance on the stability of formed carbonates attributed
to the site isolation concept, we developed a method for efficient and
inexpensive DFT calculations of the formation energies of carbonates with
prediction accuracy 0.2 eV. This method was implemented into a high-throughput
screening scheme, which includes both general requirements for catalyst
candidates and an actively done artificial intelligence part. Experimental
validation of some of the candidates obtained during the screening showed
successful reproduction of the initial volcano dependence. Moreover, several
new materials were found to outperform standard OCM catalysts, specifically at
lower temperatures.",2211.08014v1
2022-11-15,Exploring the nanoscale origin of performance enhancement in Li$_{1.1}$Ni$_{0.35}$Mn$_{0.55}$O$_2$ batteries due to chemical doping,"Despite significant potential as energy storage materials for electric
vehicles due to their combination of high energy density per unit cost and
reduced environmental and ethical concerns, Co-free lithium ion batteries based
off layered Mn oxides presently lack the longevity and stability of their
Co-containing counterparts. Here, we demonstrate a reduction in this
performance gap via chemical doping, with Li$_{1.1}$Ni$_{0.35}$Mn$_{0.55}$O$_2$
achieving an initial discharge capacity of 159 mAhg$^{-1}$ at C/3 rate and a
corresponding capacity retention of 94.3% after 150 cycles. We subsequently
explore the nanoscale origins of this improvement through a combination of
advanced diffraction, spectroscopy, and electron microscopy techniques, finding
that optimized doping profiles lead to an improved structural and chemical
compatibility between the two constituent sub-phases that characterize the
layered Mn oxide system, resulting in the formation of unobstructed lithium ion
pathways between them. We also directly observe a structural stabilization
effect of the host compound near the surface using aberration corrected
scanning transmission electron microscopy and integrated differential phase
contrast imaging.",2211.08060v1
2022-11-23,Mesoscopic modeling and experimental validation of thermal and mechanical properties of polypropylene nanocomposites reinforced by graphene-based fillers,"The development of nanocomposites relies on structure-property relations,
which necessitate multiscale modeling approaches. This study presents a
modelling framework that exploits mesoscopic models to predict the thermal and
mechanical properties of nanocomposites starting from their molecular
structure. In detail, mesoscopic models of polypropylene (PP) and graphene
based nanofillers (Graphene (Gr), Graphene Oxide (GO), and reduced Graphene
Oxide (rGO)) are considered. The newly developed mesoscopic model for the PP/Gr
nanocomposite provides mechanistic information on the thermal and mechanical
properties at the filler-matrix interface, which can be then exploited to
enhance the prediction accuracy of traditional continuum simulations by
calibrating the thermal and mechanical properties of the filler-matrix
interface. Once validated through a dedicated experimental campaign, this
multiscale model demonstrates that with the modest addition of nanofillers (up
to 2 wt.%), the Young's modulus and thermal conductivity show up to 35% and 25%
enhancement, respectively, while the Poisson's ratio slightly decreases. Among
the different combinations tested, PP/Gr nanocomposite shows the best
mechanical properties, whereas PP/rGO demonstrates the best thermal
conductivity. This validated mesoscopic model can contribute to the development
of smart materials with enhanced mechanical and thermal properties based on
polypropylene, especially for mechanical, energy storage, and sensing
applications.",2211.13148v2
2022-11-28,Amorphous ultra-wide bandgap ZnOx thin films deposited at cryogenic temperatures,"Crystalline wurtzite zinc oxide (w-ZnO) can be used as a wide band gap
semiconductor for light emitting devices and for transparent or high
temperature electronics. The use of amorphous zinc oxide (a-ZnO) can be an
advantage in these applications. In this paper we report on X-ray amorphous
a-ZnOx thin films (~500 nm) deposited at cryogenic temperatures by reactive
magnetron sputtering. The substrates were cooled by a nitrogen flow through the
copper substrate holder during the deposition. The films were characterized by
X-ray diffraction (XRD), Raman, infrared, UV-Vis-NIR spectroscopies, and
ellipsometry. The a-ZnOx films on glass and Ti substrates were obtained at the
substrate holder temperature of approximately -100 oC. New vibration bands at
201, 372, and 473 cm-1 as well as O-H stretch and bend absorption bands in the
a-ZnOx films were detected by FTIR spectroscopy. Raman spectra showed
characteristic ZnO2 peaks at 386 and 858 cm-1 attributed to the peroxide ion
O22- stretching and libration modes, respectively. In addition, the films
contain neutral and ionized O2 and O2- species. The a-ZnOx films are highly
transparent in the visible light range (approx. 87%) and exhibit a refractive
index of 1.68 at 2.25 eV (550 nm). An optical band gaps is 4.65 eV with an
additional band edge absorption feature at 3.50 eV. It has been shown that the
deposition on actively cooled substrates can be a suitable technique to obtain
low temperature phases that cannot be deposited at room temperature.",2211.15219v1
2022-11-29,Tripling energy storage density through order-disorder transition induced polar nanoregions in PbZrO3 thin films by ion implantation,"Dielectric capacitors are widely used in pulsed power electronic devices due
to their ultrahigh power densities and extremely fast charge/discharge speed.
To achieve enhanced energy storage density, both maximum polarization (Pmax)
and breakdown strength (Eb) need to be improved simultaneously. However, these
two key parameters are inversely correlated. In this study, order-disorder
transition induced polar nanoregions (PNRs) have been achieved in PbZrO3 thin
films by making use of the low-energy ion implantation, enabling us overcome
the trade-off between high polarizability and breakdown strength, which leads
to the tripling of the energy storage density from 20.5 J/cm3 to 62.3 J/cm3 as
well as the great enhancement of breakdown strength. This approach could be
extended to other dielectric oxides to improve the energy storage performance,
providing a new pathway for tailoring the oxide functionalities.",2211.15896v1
2022-11-29,Manufacturing high-Q superconducting α-tantalum resonators on silicon wafers,"The performance of state-of-the-art superconducting quantum devices is
currently limited by microwave dielectric losses at different surfaces and
interfaces. {\alpha}-tantalum is a superconductor that has proven effective in
reducing dielectric loss and improving device performance due to its thin
low-loss oxide. However, without the use of a seed layer, this tantalum phase
has so far only been realised on sapphire substrates, which is incompatible
with advanced processing in industry-scale fabrication facilities. Here, we
demonstrate the fabrication of high-quality factor {\alpha}-tantalum resonators
directly on silicon wafers over a variety of metal deposition conditions and
perform a comprehensive material and electrical characterization study. By
comparing experiments with simulated resonator loss, we demonstrate that
two-level-system loss is dominated by surface oxide contributions and not the
substrate-metal interface. Our study paves the way to large scale manufacturing
of low-loss superconducting circuits and to materials-driven advancements in
superconducting circuit performance.",2211.16437v2
2022-12-09,Non-stationary thermophysical characterization of exfoliated graphite with carbon nanotubes composites,"The sheet samples of thermally exfoliated graphite (TEG) carbon nanotubes
(CNT) composites (TEG CNT cs) were obtained by persulphate oxidation using
chemical (CO) and electrochemical (anode) oxidation (ECAO). Electron microscopy
reveals multi layered structures of few layer graphene nanosheets with folded
and tubular like fragments.Electron microscopy reveals multilayered structures
of few layer graphene nanosheets with folded and tubular like fragments. The
effective thermal diffusivity values were estimated by nonstationary
photo-pyroelectric thermophysical characterization using the heat pulse and
thermo-wave modulation methods. Comparison with other carbon (C) based thermal
management materials shows that TEG CNTcs exhibit thermal diffusivity,
effusivity and conductivity comparable with those of actual C polymer and C C
composites. For TEG CNT cs, evaluated values of phonon mean free path (MFP) and
relaxation time (RT) are in the ranges estimated for defective graphene. The
values of diffusivity and effusivity, MFP and RT are lower for denser TEG CNT
cs obtained by ECAO and are higher for less dense TEG CNT cs obtained by CO.
The obtained diffusivity and effusivity values designate TEG CNT cs as suitable
thermal management materials.",2212.05036v1
2022-12-13,Acceptor and compensating donor doping of single crystalline SnO (001) films grown by molecular beam epitaxy and its perspectives for optoelectronics and gas-sensing,"(La and Ga)-doped tin monoxide (stannous oxide, tin (II) oxide, SnO) thin
films were grown by plasma-assisted and suboxide molecular beam epitaxy with
dopant concentrations ranging from $\approx5\times10^{18}$cm$^{-3}$ to
$2\times10^{21}$cm$^{-3}$. In this concentration range, the incorporation of Ga
into SnO was limited by the formation of secondary phases observed at
$1.2\times10^{21}$cm$^{-3}$ Ga, while the incorporation of La showed a lower
solubility limit. Transport measurements on the doped samples reveal that Ga
acts as an acceptor and La as a compensating donor. While Ga doping led to an
increase of the hole concentration from
$1\times10^{18}$cm$^{-3}-1\times10^{19}$cm$^{-3}$ for unintentionally (UID) SnO
up to $5\times10^{19}$cm$^{-3}$, La-concentrations well in excess of the UID
acceptor concentration resulted in semi-insulating films without detectable
$n$-type conductivity. Ab-initio calculations qualitatively agree with our
dopant assignment of Ga and La, and further predict In$_\text{Sn}$ to act as an
acceptor as well as Al$_\text{Sn}$ and B$_\text{Sn}$ as donor. These results
show the possibilities of controlling the hole concentration in $p$-type SnO,
which can be useful for a range of optoelectronic and gas-sensing applications.",2212.06350v1
2022-12-15,Lasing in a ZnO waveguide: clear evidence of polaritonic gain obtained by monitoring the continuous exciton screening,"The stimulated emission of exciton-polaritons was proposed as a means of
lowering the lasing threshold because it does not require the dissociation of
excitons to obtain an electron-hole plasma, as in a classical semiconductor
laser based on population inversion. In this work we propose a method to prove
unambiguously the polaritonic nature of lasing by combining experimental
measurements with a model accounting for the permittivity change as a function
of the carrier density. To do so we use angle resolved photoluminescence to
observe the lasing at cryogenic temperature from a polariton mode in a zinc
oxide waveguide structure, and to monitor the continuous shift of the
polaritonic dispersion towards a photonic dispersion as the optical intensity
of the pump is increased (up to 20 times the one at threshold). This shift is
reproduced thanks to a model taking into account the reduction of the
oscillator strength and the renormalization of the bandgap due to the screening
of the electrostatic interaction between electrons and holes. Furthermore, the
measurement of the carriers lifetime at optical intensities in the order of
those at which the polariton lasing occurs enables us to estimate the carrier
density, confirming it is lower than the corresponding Mott density for zinc
oxide reported in the literature.",2212.07842v2
2022-12-30,Transition metal ion ensembles in crystals as solid-state coherent spin-photon interfaces: The case of nickel in magnesium oxide,"We present general guidelines for finding solid-state systems that could
serve as coherent electron spin-photon interfaces even at relatively high
temperatures, where phonons are abundant but cooling is easier, and show that
transition metal ions in various crystals could comply with these guidelines.
As an illustrative example, we focus on divalent nickel ions in magnesium
oxide. We perform electron spin resonance spectroscopy and
polarization-sensitive magneto-optical fluorescence spectroscopy of a dense
ensemble of these ions and find that (i) the ground-state electron spin stays
coherent at liquid-helium temperatures for several microseconds, and (ii) there
exists energetically well-isolated excited states which can couple to two
ground state spin sub-levels via optical transitions of orthogonal
polarizations. The latter implies that fast, coherent optical control over the
electron spin is possible. We then propose schemes for optical initialization
and control of the ground-state electron spin using polarized optical pulses,
as well as two schemes for implementing a noise-free, broadband quantum-optical
memory at near-telecom wavelengths in this material system.",2212.14827v2
2023-01-09,High pressure bulk synthesis of InN by solid state reaction of binary oxide in a multi-anvil apparatus,"We present a new method to synthesize bulk indium nitride by means of a
simple solid-state chemical reaction carried out under hydrostatic high
pressure/high temperature conditions in a multi-anvil apparatus, not involving
gases or solvents during the process. The reaction occurs between the binary
oxide $In_2O_3$ and the highly reactive $Li_3N$ as nitrogen source, in powder
form. The formation of the hexagonal phase of InN, occurring at 350 {\deg}C and
P $\geq$ 3 GPa, was successfully confirmed by powder X-ray diffraction, with
the presence of $Li_2O$ as unique byproduct. A simple washing process in weak
acidic solution followed by centrifugation, allowed to obtain pure InN
polycrystalline powders as precipitate. With an analogous procedure it was
possible to obtain pure bulk GaN, from $Ga_2O_3$ and $Li_3N$ at T $\geq$
600{\deg}C and P $\geq$ 2.5 GPa. These results point out, particularly for InN,
a clean, and innovative way to produce significant quantities of one of the
most promising nitrides in the field of electronics and energy technologies.",2301.03460v2
2023-01-24,Design and Fabrication of PERC-Like CdTe Solar Cells Using Micropatterned Al2O3 Layer,"Recent studies have investigated novel strategies to further improve the
limited Voc of CdTe solar cells via increased carrier lifetime and doping
density of CdTe thin films. Among various metal oxides, aluminum oxide (Al2O3)
is a promising passivation candidate, where the negatively charged Al2O3 layer
repels the minority carrier in CdTe and Al2O3 provides a chemically passivating
interface, increasing the carrier lifetime. Despite the continuing efforts, an
optimized back-contact architecture to improve the Voc while maintaining high
Jsc and FF is still under development. In this work, we report the design,
fabrication, and characterization of PERC-like CdTe solar cells, where an Al2O3
passivation layer is patterned using laser-beam lithography. Our process
enables reproducible patterning on a rough surface CdTe while maintaining the
size of the array in the design. Analysis of CdTe PERC devices (As-doped) shows
a notably different Voc trend compared to FF and Jsc, independent of the
patterned array structures used in this study. The subsurface electronic
structure of CdTe and the interplay between carrier selectivity and collection
of the patterned Al2O3 could be responsible for the observed PV
characteristics.",2301.09787v1
2023-01-24,The importance of tight $f$ basis functions for heavy p-block oxides and halides: a parallel with tight $d$ functions in the second row,"It is well-known that both wavefunction ab initio and DFT calculations on
second-row compounds exhibit anomalously slow basis set convergence unless the
basis sets are augmented with additional `tight' (high-exponent) $d$ functions,
as in the cc-pV($n+d$)Z and aug-cc-pV($n+d$)Z basis sets. This has been
rationalized as being necessary for a better description of the low-lying $3d$
orbital, which as the oxidation state increases sinks low enough to act as a
back-donation acceptor from chalcogen and halogen lone pairs. This prompts the
question whether a similar phenomenon exists for the isovalent compounds of the
heavy p-block. We show that for the fourth and fifth row, this is the case, but
this time for tight $f$ functions enhancing the description of the low-lying
$4f$ and $5f$ Rydberg orbitals, respectively. In the third-row heavy $p$ block,
the $4f$ orbitals are too far up, while the $4d$ orbitals are adequately
covered by the basis functions already present to describe the $3d$ subvalence
orbitals.",2301.10098v2
2023-01-30,Graphene Oxide Photoreduction Recovers Graphene Hot Electron Cooling Dynamics,"Reduced graphene oxide (rGO) is a bulk-processable quasi-amorphous 2D
material with broad spectral coverage and fast electronic response. rGO sheets
are suspended in a polymer matrix and sequentially photoreduced while measuring
the evolving optical spectra and ultrafast electron relaxation dynamics.
Photoreduced rGO yields optical absorption spectra that fit with the same Fano
lineshape parameters as monolayer graphene. With increasing photoreduction
time, rGO transient absorption kinetics accelerate monotonically, reaching an
optimal point that matches the hot electron cooling in graphene. All stages of
rGO ultrafast kinetics are simulated with a hot-electron cooling model mediated
by disorder-assisted supercollisions. While the rGO room temperature 0.31
ps$^{-1}$ electronic cooling rate matches monolayer graphene, subsequent
photoreduction can rapidly increase the rate by ~10-12$\times$. Such
accelerated supercollision rates imply a reduced mean-free scattering length
caused by photoionized point-defects on the rGO sp$^2$ sub-lattice. For visible
range excitations of rGO, photoreduction shows three increasing spectral peaks
that match graphene quantum dot (GQD) transitions, while a broad peak from
oxygenated defect edge states shrinks. These three confined GQD states donate
their hot carriers to the graphene sub-lattice with a 0.17 ps rise-time that
accelerates with photoreduction. Collectively, many desirable photophysical
properties of 2D graphene are replicated through selectively reducing rGO
scaffolded within a 3D bulk polymeric network.",2301.13176v1
2023-02-03,Interface-tuning of ferroelectricity and quadruple-well state in CuInP$_2$S$_6$ via ferroelectric oxide,"Ferroelectric van der Waals CuInP$_2$S$_6$ possesses intriguing
quadruple-well states and negative piezoelectricity. Its technological
implementation has been impeded by the relatively low Curie temperature (bulk
$T_C$ ~42 {\deg}C) and the lack of precise domain control. Here we show that
CuInP$_2$S$_6$ can be immune to the finite size effect and exhibits enhanced
ferroelectricity, piezoelectricity, and polar alignment in the ultrathin limit
when interfaced with ferroelectric oxide PbZr$_{0.2}$Ti$_{0.8}$O$_3$ films.
Piezoresponse force microscopy studies reveal that the polar domains in thin
CuInP$_2$S$_6$ fully conform to those of underlying
PbZr$_{0.2}$Ti$_{0.8}$O$_3$, where the piezoelectric coefficient changes sign
and increases sharply with reducing thickness. High temperature $in$ $situ$
domain imaging points to a significantly enhanced $T_C$ exceeding 200 {\deg}C
for 13 nm CuInP$_2$S$_6$ on PbZr$_{0.2}$Ti$_{0.8}$O$_3$. Density functional
theory modeling and Monte Carlo simulations show that the enhanced polar
alignment and $T_C$ can be attributed to interface-mediated structure
distortion in CuInP$_2$S$_6$. Our study provides an effective material strategy
to engineer the polar properties of CuInP$_2$S$_6$ for flexible nanoelectronic,
optoelectronic, and mechanical applications.",2302.01504v2
2023-02-04,Single-shot polarization-resolved ultrafast mapping photography,"Single-shot ultrafast optical imaging plays a very important role in the
detection of transient scenes, especially in capturing irreversible or
stochastic dynamic scenes. To break the limit of time response speed of
electronic devices, such as charge-coupled device (CCD) or complementary
metal-oxide-semiconductor (CMOS) detectors, ultrafast optical imaging
techniques usually convert the time information of a transient scene into the
wavelength, angle, space or spatial frequency of the illumination light in
previous studies. In this work, we propose a novel polarization-resolved
ultrafast mapping photography (PUMP) technique by converting the time
information into the polarization. Here, the spatiotemporal information of a
dynamic scene is loaded into a rotationally polarized illumination laser pulse,
and a polarization filtering in imaging detection and a deconvolution algorithm
in image reconstruction are used to extract the original dynamic scene. In our
PUMP system, the temporal resolution is 850 fs, the spatial resolution is 28.5
lp/mm at 700 micrometer by 700 micrometer field of view, and the number of
frames is 16. By using PUMP, a spatiotemporal dynamics of femtosecond laser
ablation in an indium tin oxide film on glass substrate is successfully
captured. PUMP provides a new solution for measuring the transient scenes in a
snapshot, which will bring a very wide range of applications in the field of
ultrafast science.",2302.02100v1
2022-12-17,The role of plasma-activated water on the growth of freshwater algae Chlorella Pyrenoidosa and Chlorella Sorokiniana,"In the present work we have conducted two studies. In the first study, we
investigated the role of plasma-activated water (PAW) in algae growth
inhibition and in the second study, efforts are made to understand the role of
PAW as a nitrogen source for algae growth enhancement. Two freshwater algae
species are selected for the present study named Chlorella Pyrenoidosa and
Chlorella Sorokiniana. The PAW is prepared using a pencil plasma jet and air as
a plasma forming gas. The plasma is characterized electrically and
identification of generated species in plasma is carried out using optical
emission spectroscopy. The study clearly indicated that more oxidizing PAW
exhibits algicidal effect. The PAW treatment with both the algae species
substantially decreased their growth compared to control. Moreover, the
morphology of algae cells showed damage and cells structure get ruptured after
PAW treatment. In the second study, a less reactive PAW (low oxidizing
potential) used as a nitrogen replacement in Bolds Basal Medium. The PAW-grown
Chlorella Pyrenoidosa and Chlorella Sorokiniana showed higher growth compared
to control. Also, a higher concentration of chlorophyll a and b, sugar, and
protein observed compared to control. Further, we observed lower antioxidant
enzymatic activities in PAW-grown algae compared to control. In conclusion, the
PAW has algicidal efficacy as well as can be used as nitrogen source in
aquaculture to enhance algae growth.",2302.07102v1
2023-02-20,Combination effect of growth enhancers and carbon sources on synthesis of single-walled carbon nanotubes from solid carbon growth seeds,"In the synthesis of highly crystalline single-walled carbon nanotubes
(SWCNTs), high growth temperatures are preferred, while the formation of
impurity amorphous carbon (a-C) causes the termination of SWCNT growth and
degrades its properties. To remove this by-product, H2O and CO2 have been
employed in metal-catalyzed SWCNT growth systems because of their oxidizing
ability. Recently, nonmetallic nanoparticles have become one of the growth seed
candidates because of their high melting points and fewer metal impurities. In
this study, by using nanodiamond-derived carbon nanoparticles as the solid
growth seeds, we investigated the effect of CO2 and H2O on high-temperature
SWCNT growth with two types of carbon-source supplies: C2H2 and C2H4. In this
growth system, H2O showed oxidizing ability to etch a-C with either carbon
sources. CO2 exhibited a similar a-C formation-preventing role in C2H4-supplied
growth and achieved higher-purity SWCNTs with higher concentration of C2H4 than
the case of H2O. However, in contrast to the other combinations, CO2 injection
in the C2H2-supplied growth significantly enhanced the formation of a-C rather
than the removal of it while the yield of SWCNTs was also increased, indicating
the occurrence of the dehydration reaction between CO2 and C2H2. The present
findings will lead to efficient growth of high-quality SWCNTs from nonmetallic
growth seeds with the use of growth enhancers.",2302.09950v2
2023-02-23,Employing High-temperature-grown SrZrO$_3$ Buffer to Enhance the Electron Mobility in La:BaSnO$_3$-based Heterostructures,"We report a synthetic route to achieve high electron mobility at room
temperature in epitaxial La:BaSnO$_3$/SrZrO$_3$ heterostructures prepared on
several oxide substrates. Room-temperature mobilities of 157, 145, and 143
cm$^2$V$^{-1}$s$^{-1}$ are achieved for heterostructures grown on DyScO$_3$
(110), MgO (001), and TbScO$_3$ (110) crystalline substrates, respectively.
This is realized by first employing pulsed laser deposition to grow at very
high temperature the SrZrO$_3$ buffer layer to reduce dislocation density in
the active layer, then followed by the epitaxial growth of an overlaying
La:BaSnO$_3$ active layer by molecular-beam epitaxy. Structural properties of
these heterostructures are investigated, and the extracted upper limit of
threading dislocations is well below $1.0\times 10^{10}$cm$^{-2}$ for buffered
films on DyScO$_3$, MgO, and TbScO$_3$ substrates. The present results provide
a promising route towards achieving high mobility in buffered La:BaSnO$_3$
films prepared on most, if not all, oxide substrates with large compressive or
tensile lattice mismatches to the film.",2302.12323v3
2023-02-22,Oxidized organic molecules in the tropical free troposphere over Amazonia,"New particle formation (NPF) in the tropical free troposphere (FT) is a
globally important source of cloud condensation nuclei, affecting cloud
properties and climate. Oxidized organic molecules (OOMs) produced from
biogenic volatile organic compounds are believed to contribute to aerosol
formation in the tropical FT, but without direct chemical observations. We
performed in-situ molecular-level OOMs measurements at the Bolivian station
Chacaltaya at 5240 meters above sea level, on the western edge of Amazonia. For
the first time, we demonstrate the presence of OOMs, mainly with 4-5 carbon
atoms, simultaneously in both gas and particulate phases in tropical FT air
from Amazonia. These observations, combined with air mass history analyses,
indicate that the observed OOMs are linked to isoprene emitted from the
rainforests hundreds of kilometers away. Based on particle-phase measurements,
we find that these compounds can contribute to the growth of newly formed
particles, and are potentially crucial for new particle formation in the
tropical free troposphere on a continental scale. Our study will thus improve
the understanding of aerosol formation process in the tropics.",2302.14054v1
2023-02-28,New chondritic bodies identified in eight oxygen-bearing white dwarfs,"We present observations and analyses of eight white dwarf stars that have
accreted rocky material from their surrounding planetary systems. The spectra
of these helium-atmosphere white dwarfs contain detectable optical lines of all
four major rock-forming elements (O, Mg, Si, Fe). This work increases the
sample of oxygen-bearing white dwarfs with parent body composition analyses by
roughly thirty-three percent. To first order, the parent bodies that have been
accreted by the eight white dwarfs are similar to those of chondritic
meteorites in relative elemental abundances and oxidation states. Seventy-five
percent of the white dwarfs in this study have observed oxygen excesses
implying volatiles in the parent bodies with abundances similar to those of
chondritic meteorites. Three white dwarfs have oxidation states that imply more
reduced material than found in CI chondrites, indicating the possible detection
of Mercury-like parent bodies, but are less constrained. These results
contribute to the recurring conclusion that extrasolar rocky bodies closely
resemble those in our solar system, and do not, as a whole, yield unusual or
unique compositions.",2303.00063v1
2023-03-02,Subgap spectroscopy along hybrid nanowires by nm-thick tunnel barriers,"Tunneling spectroscopy is widely used to examine the subgap spectra in
semiconductor-superconductor nanostructures when searching for Majorana zero
modes (MZMs). Typically, semiconductor sections controlled by local gates at
the ends of hybrids serve as tunnel barriers. Besides detecting states only at
the hybrid ends, such gate-defined tunnel probes can cause the formation of
non-topological subgap states that mimic MZMs. Here, we develop an alternative
type of tunnel probes to overcome these limitations. After the growth of an
InSb-Al hybrid nanowire, a precisely controlled in-situ oxidation of the Al
shell is performed to yield a nm-thick Al oxide layer. In such thin isolating
layer, tunnel probes can be arbitrarily defined at any position along the
hybrid nanowire by shadow-wall angle-deposition of metallic leads. This allows
us to make multiple tunnel probes along single nanowire hybrids and to
successfully identify Andreev bound states (ABSs) of various spatial extension
residing along the hybrids.",2303.00903v1
2023-03-07,The potential of retrofitting existing coal power plants: a case study for operation with green iron,"Storing electrical energy for long periods and transporting it over long
distances is an essential task of the necessary transition to a CO$_2$-free
energy economy. An oxidation-reduction cycle based on iron and its oxides
represents a very promising technology in this regard. The present work
assesses the potential of converting an existing modern coal-fired power plant
to operation with iron. For this purpose, a systematic retrofit study is
carried out, employing a model that balances all material and energy fluxes in
a state-of-the-art coal-fired power plant. Particular attention is given to
components of the burner system and the system$'$s heat exchanger. The analysis
provides evidence that main components such as the steam generator and steam
cycle can be reused with moderate modifications. Major modifications are
related to the larger amounts of solids produced during iron combustion, for
instance in the particle feeding and removal systems. Since the high particle
densities and lower demand for auxiliary systems improve the heat transfer, the
net efficiencies of iron operation can be one to two percentage points better
than coal operation, depending on operating conditions. This new insight can
significantly accelerate the introduction of this innovative technology by
guiding future research and the development of the retrofit option.",2303.04000v2
2023-03-15,Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin Probe Force Microscopy,"Amorphous oxide semiconductors are receiving significant attention due to
their relevance for large area electronics. Their disordered microscopic
structure causes the formation of band tails in the density of states (DOS)
that strongly affect charge transport properties. Bandtail properties are
crucial to understand for optimizing thin film device performance. Among the
available techniques to measure the DOS, KPFM is exceptional as it enables
precise local electronic investigations combined with microscopic imaging.
However, a model to interpret KPFM spectroscopy data on amorphous
semiconductors of finite thickness is lacking. To address this issue, we
provide an analytical solution to the Poisson's equation for a
metal-insulator-semiconductor (MIS) junction interacting with the AFM tip. The
solution enables us to fit experimental data for semiconductors with finite
thickness and obtain the DOS parameters, such as band tail width (E_t), doping
density (N_D), and flat band potential. To demonstrate our method, we perform
KPFM experiments on Indium-Gallium-Zinc Oxide (IGZO) thin film transistors
(IGZO-TFTs). DOS parameters compare well to values obtained with photocurrent
spectroscopy. We demonstrate the potentials of the developed method by
investigating the impact of ionizing radiation on DOS parameters and TFT
performance. Our results provide clear evidence that the observed shift in
threshold voltage is caused by static charge in the gate dielectric leading to
a shift in flat band potential. Band-tails and doping density are not affected
by the radiation. The developed methodology can be easily translated to
different semiconductor materials and paves the way towards quantitative
microscopic mapping of local DOS parameters in thin film devices.",2303.08442v1
2023-03-27,PiNNwall: Heterogeneous Electrode Models from Integrating Machine Learning and Atomistic Simulation,"Electrochemical energy storage always involves the capacitive process. The
prevailing electrode model used in the molecular simulation of polarizable
electrode-electrolyte systems is the Siepmann-Sprik model developed for perfect
metal electrodes. This model has been recently extended to study the
metallicity in the electrode by including the Thomas-Fermi screening length.
Nevertheless, a further extension to heterogeneous electrode models requires
introducing chemical specificity, which does not have any analytical recipes.
Here, we address this challenge by integrating the atomistic machine learning
code (PiNN) for generating the base charge and response kernel and the
classical molecular dynamics code (MetalWalls) dedicated to the modeling of
electrochemical systems, and this leads to the development of the PiNNwall
interface. Apart from the cases of chemically doped graphene and graphene oxide
electrodes as shown in this study, the PiNNwall interface also allows us to
probe polarized oxide surfaces in which both the proton charge and the
electronic charge can coexist. Therefore, this work opens the door for modeling
heterogeneous and complex electrode materials often found in energy storage
systems.",2303.15307v4
2023-04-03,Supercontinuum generation in dispersion engineered highly doped silica glass waveguides,"We investigate the effect of a lower index oxide layer inclusion within a
highly doped silica glass slot waveguide for optimized supercontinuum
generation at telecom wavelengths. By controlling the thickness of the oxide
slot, we demonstrate that one can engineer the waveguide dispersion profile so
that to obtain supercontinua with vastly different spectral broadening dynamics
and bandwidths. Using this approach, we designed and fabricated a waveguide
with a low and flat dispersion profile of less than 43 ps/km/nm across a
wavelength range spanning over 1000 nm. We show that, when pumped at the
telecom C-band, we can generate a supercontinuum that spans over 1.5 octave,
from approximately 817 nm to 2183 nm. The numerical simulations, whose
parameters are derived from the measured waveguide dimension and material
indices, exhibit good agreement with experimental measurements, where one can
observe both a qualitative and quantitative match in the supercontinuum overall
spectrum and specific features (e.g. soliton and dispersive wave locations).
This study represents an important step forward in the control and manipulation
of dispersive and nonlinear dynamics in highly doped silica glass waveguides,
paving the way towards advanced on-chip broadband light manipulation.",2304.00800v1
2023-04-05,Identification of high-reliability regions of machine learning predictions in materials science using transparent conducting oxides and perovskites as examples,"Progress in the application of machine learning (ML) methods to materials
design is hindered by the lack of understanding of the reliability of ML
predictions, in particular for the application of ML to small data sets often
found in materials science. Using ML prediction for transparent conductor oxide
formation energy and band gap, dilute solute diffusion, and perovskite
formation energy, band gap and lattice parameter as examples, we demonstrate
that 1) analysis of ML results by construction of a convex hull in feature
space that encloses accurately predicted systems can be used to identify
regions in feature space for which ML predictions are highly reliable 2)
analysis of the systems enclosed by the convex hull can be used to extract
physical understanding and 3) materials that satisfy all well-known chemical
and physical principles that make a material physically reasonable are likely
to be similar and show strong relationships between the properties of interest
and the standard features used in ML. We also show that similar to the
composition-structure-property relationships, inclusion in the ML training data
set of materials from classes with different chemical properties will not be
beneficial and will slightly decrease the accuracy of ML prediction and that
reliable results likely will be obtained by ML model for narrow classes of
similar materials even in the case where the ML model will show large errors on
the dataset consisting of several classes of materials. Our work suggests that
analysis of the error distributions of ML predictions will be beneficial for
the further development of the application of ML methods in material science.",2304.02218v1
2023-04-07,Comparative analysis of five NH$_3$/air oxidation mechanisms,"Five recently developed chemical kinetics mechanisms for ammonia oxidation
are analysed and compared, in the context of homogeneous adiabatic
autoignition. The analysis focuses on the ignition delay and is based on the
explosive mode that is shown to drive the process. Using algorithmic tools
based on the Computational Singular Perturbation algorithm, the reactions
responsible for the generation of the explosive mode are identified, along with
the variables (species mass fractions and temperature) that associate the most
to this mode. Comparison of these sets of reactions and variables, obtained for
each mechanism, allows to correlate the differences in the predictive outcomes
from the mechanisms with specific reactions. The major differences identified,
which lead to different ignition delay times, relate to (i) the relative
duration of chemical and thermal runaways (a sizeable chemical runaway develops
only in some mechanisms) and (ii) the dominant chemistry during the chemical
runaway (chemistry involving species with two nitrogen atoms is active only in
some mechanisms). The major similarities identified refer to the thermal
runaway and in particular to (i) the chemical activity, which is supported
mainly by OH-producing reactions and by reactions producing their reactants and
(ii) the thermal activity, which is dominated by strongly exothermic
OH-consuming reactions.",2304.03549v1
2023-04-13,Importance of the catalytic effect of the substrate in the functionality of lubricant additives: the case of MoDTC,"Molybdenum dithiocarbamates (MoDTCs) are lubricant additives very efficient
in reducing the friction of steel and they are employed in a number of
industrial applications. The functionality of these additives is ruled by the
chemical interactions occurring at the buried sliding interface, which are of
key importance for the improvement of the lubrication performance. Yet, these
tribochemical processes are very difficult to monitor in real time. Ab initio
molecular dynamics simulations are the ideal tool to shed light into such a
complicated reactivity. In this work we perform ab initio simulations, both in
static and tribological conditions, to understand the effect of surface
oxidation on the tribochemical reactivity of MoDTC and we find that when the
surfaces are covered by oxygen, the first dissociative steps of the additives
are significantly hindered. Our preliminary tribological tests on oxidized
steel discs support these results. Bare metallic surfaces are necessary for a
stable adsorption of the additives, their quick decomposition, and the
formation of a durable MoS$_2$ tribolayer. This work demonstrates the
importance of the catalytic role of the substrate and confirms the full
capability of the computational protocol in the pursuit of materials and
compounds more efficient in reducing friction.",2304.06462v2
2023-04-15,Thermal Reconversion of Oxidised Lead White in Mural Paintings via a Massicot Intermediate,"Lead white is the most ancient and common white pigment used in mural
paintings. However, it tends to blacken with time due to its oxidation to
plattnerite (\b{eta}-PbO2). Chemical treatments were used but they can put the
pictorial layers supports at risks. Hereby we address the possibility of
thermally reconverting black plattnerite to white lead carbonates via a
massicot (\b{eta}-PbO) intermediate, with a view to developing a restoration
procedure using continuous wave laser heating. We first investigated the
conditions (temperature, time, and environment) in which pure powders react,
before studying mural painting samples. Experiments were made in ovens and TGA
and XRD and SEM characterization were achieved. Litharge ({\alpha}-PbO) and
massicot were obtained from plattnerite respectively between 564 and 567
{\deg}C and at 650 {\deg}C. Lead carbonates (cerussite, hydrocerussite and
plumbonacrite) formed from massicot in wet CO2 below 100 {\deg}C in a few
hours. Lastly, when heating plattnerite based mural painting samples, lead
species reacted with binders and mortar, yielding massicot, plumbonacrite but
also lead silicate and calcium lead oxides. This demonstrates the viability of
thermal reconversion of darkened lead in mural, while raising concerns about
the formation of several lead species by reaction with mural painting
constituents.",2304.07541v1
2023-04-27,Graphene-Based Transparent Flexible Strain Gauges with Tunable Sensitivity and Strain Range,"Flexible strain gauges with 88% optical transmittance, of reduced graphene
oxide (rGO) on poly dimethylsiloxne membranes, are produced form monolayers of
graphene oxide assembled into densely packed sheets at an immiscible
hexane/water interface and subsequently reduced in HI vapor to increase
electrical conductivity. Pre-straining and relaxing the membranes introduces a
population of cracks into the rGO film. Subsequent straining opens these
cracks, inducing piezoresistivity. Reduction for 30 s forms an array of
parallel cracks that do not individually span the membrane and results in a
strain gauge with a usable strain range > 0.2 and gauge factor of 20 - 100 at
low strain levels that increases with increasing pre-strain. In all cases the
gauge facto decreases with increasing applied strain and asymptotes to a value
of about 3, as it approaches the pre-strain value. If the rGO is reduced for 60
s, the cracks fully span the width of the membrane, leading to an increased
gauge resistance but a much more sensitive strain gauge with GF ranging from
1000 - 16000. However, the usable strain range reduces to < 0.01. A simple
equivalent resistor model is proposed to describe the behaviour of both gauge
types. The gauges show a repeatable and stable response with loading
frequencies up to 1 kHz and have been used to detect human body motion in a
simple e-skin demonstration.",2304.14297v2
2023-04-28,Anisotropic Electronic Structure of the Two-Dimensional Electron Gas at the AlOx/KTaO3(110) interface,"Oxide-based two-dimensional electron gases (2DEGs) have generated significant
interest due to their potential for discovering novel physical properties.
Among these, 2DEGs formed in KTaO3 stand out due to the recently discovered
crystal face-dependent superconductivity and large Rashba splitting, both of
which hold potential for future oxide electronics devices. In this work,
angle-resolved photoemission spectroscopy is used to study the electronic
structure of the 2DEG formed at the (110) surface of KTaO3 after deposition of
a thin Al layer. Our experiments revealed a remarkable anisotropy in the
orbital character of the electron-like dispersive bands, which form a Fermi
surface consisting of two elliptical contours with their major axes
perpendicular to each other. The measured electronic structure is used to
constrain the modeling parameters of self-consistent tight-binding slab
calculations of the band structure. In these calculations, an anisotropic
Rashba splitting is found with a value as large as 4 meV at the Fermi level
along the [-110] crystallographic direction. This large unconventional and
anisotropic Rashba splitting is rationalized based on the orbital angular
momentum formulation. These findings provide insights into the interpretation
of spin-orbitronics experiments and help to constrain models for
superconductivity in the KTO(110)-2DEG system.",2304.14805v1
2023-05-04,Accelerated Screening of Ternary Chalcogenides for High-Performance Optoelectronic Materials,"Chalcogenides, which refer to chalcogen anions, have attracted considerable
attention in multiple fields of applications, such as optoelectronics,
thermoelectrics, transparent contacts, and thin film transistors. In comparison
to oxide counterparts, chalcogenides have demonstrated higher mobility and
\textit{p}-type dopability, owing to larger orbital overlaps between metal-X
covalent chemical bondings and higher-energy valence bands derived by
p-orbitals. Despite the potential of chalcogenides, the number of successfully
synthesized compounds remains relatively low compared to oxides, suggesting the
presence of numerous unexplored chalcogenides with fascinating physical
characteristics. In this study, we implemented a systematic high-throughput
screening process combined with first-principles calculations on ternary
chalcogenides using 34 crystal structure prototypes. We generated a
computational material database containing over 400,000 compounds by exploiting
the ion-substitution approach at different atomic sites with elements in the
periodic table. The thermodynamic stabilities of the candidates were validated
using the chalcogenides included in the Open Quantum Materials Database.
Moreover, we trained a model based on Crystal Graph Convolutional Neural
Networks to predict the thermodynamic stability of novel materials.
Furthermore, we theoretically evaluated the electronic structures of the stable
candidates using accurate hybrid functionals. A series of in-depth
characteristics, including the carrier effective masses, electronic
configuration, and photovoltaic conversion efficiency, was also investigated.
Our work provides useful guidance for further experimental research in the
synthesis and characterization of such chalcogenides as promising candidates,
as well as charting the stability and optoelectronic performance of ternary
chalcogenides.",2305.02634v1
2023-05-09,Atomic Layer Deposited Protective Coating of Aluminum Oxide on Silver-based Telescope Mirror A Comparison Between a Pure Ozone and H2O Precursor,"Although silver-based telescope mirrors excel over other materials such as
gold and aluminum in the visible-infrared spectral range, they require robust
protective coatings to overcome their inherent low durability. Our research
shows that a single-layer of aluminum oxide (AlOx) deposited through thermal
atomic layer deposition (ALD) using trimethylaluminum (TMA) and water (H2O) at
low temperatures (~60{\deg}C) serves as an acceptable protective coating
without adversely impacting the optical performance of the mirrors. While
silver-based mirrors protected with a single-layer of AlOx perform decently in
the field, in environmental tests under high-humidity at high-temperature
conditions that accelerate underlying failure mechanisms, they degrade quickly,
suggesting that there is room for improvement. This paper describes a study
that compares the performance and endurance of two sets of silver-based mirrors
protected by a single-layer of AlOx prepared by thermal ALD with two types of
oxygen precursors: H2O and pure ozone (PO). The study shows that while the two
types of samples, regardless of their oxygen precursors, initially have
comparable spectral reflectance, the reflectance of the samples with AlOx
protective coatings prepared with PO remain nearly constant 1.6 times longer
than those with AlOx protective coatings prepared with H2O in the environmental
test, suggesting promising characteristics of AlOx protective coatings prepared
with PO.",2305.05109v1
2023-05-21,Head-to-Head and Tail-to-Tail Domain Wall in Hafnium Zirconium Oxide: A First Principles Analysis of Domain Wall Formation and Energetics,"180{\deg} domains walls (DWs) of Head-to-Head/Tail-to-Tail (H-H/T-T) type in
ferroelectric (FE) materials are of immense interest for a comprehensive
understanding of the FE attributes as well as harnessing them for new
applications. Our first principles calculation suggests that such DW formation
in Hafnium Zirconium Oxide (HZO) based FEs depends on the unique attributes of
the HZO unit cell, such as polar-spacer segmentation. Cross pattern of the
polar and spacer segments in two neighboring domains along the polarization
direction (where polar segment of one domain aligns with the spacer segment of
another) boosts the stability of such DWs. We further show that low density of
oxygen vacancies at the metal-HZO interface and high work function of metal
electrodes are conducive for T-T DW formation. On the other hand, high density
of oxygen vacancy and low work function of metal electrode favor H-H DW
formation. Polarization bound charges at the DW get screened when band bending
from depolarization field accumulates holes (electrons) in T-T (H-H) DW. For a
comprehensive understanding, we also investigate their FE nature and domain
growth mechanism. Our analysis suggests that a minimum thickness criterion of
domains has to be satisfied for the stability of H-H/T-T DW and switching of
the domains through such DW formation.",2305.12350v2
2023-05-31,Monofluorinated Ether Electrolyte with Acetal Backbone for High-Performance Lithium Metal Batteries,"High degree of fluorination for ether electrolytes has resulted in improved
cycling stability of lithium metal batteries (LMBs) due to stable SEI formation
and good oxidative stability. However, the sluggish ion transport and
environmental concerns of high fluorination degree drives the need to develop
less fluorinated structures. Here, we introduce bis(2-fluoroethoxy)methane
(F2DEM) which features monofluorination of the acetal backbone. High coulombic
efficiency (CE) and stable long-term cycling in Li||Cu half cells can be
achieved with F2DEM even under fast Li metal plating conditions. The
performance of F2DEM is further compared with diethoxymethane (DEM) and
2-[2-(2,2-Difluoroethoxy)ethoxy]-1,1,1-Trifluoroethane (F5DEE). The structural
similarity of DEM allows us to better probe the effects of monofluorination,
while F5DEE is chosen as the one of the best performing LMB electrolytes for
reference. The monofluorine substitution provides improved oxidation stability
compared to non-fluorinated DEM, as demonstrated in the linear sweep
voltammetry (LSV) and voltage holding experiments in Li||Pt and Li||Al cells.
Higher ionic conductivity compared to F5DEE is also observed due to the
decreased degree of fluorination. Furthermore, 1.75 M lithium
bis(fluorosulfonyl)imide (LiFSI) / F2DEM displays significantly lower
overpotential compared with the two reference electrolytes, which improves
energy efficiency and enables its application in high-rate conditions.
Comparative studies of F2DEM with DEM and F5DEE in anode-free (LiFePO4) LFP
pouch cells and high-loading LFP coin cells with 20 {\mu}m excess Li further
show improved capacity retention of F2DEM electrolyte.",2305.19580v1
2023-06-19,Ion Intercalation in Lanthanum Strontium Ferrite for Aqueous Electrochemical Energy Storage Devices,"Ion intercalation of perovskite oxides in liquid electrolytes is a very
promising method for controlling their functional properties while storing
charge, which opens the potential application in different energy and
information technologies. Although the role of defect chemistry in the oxygen
intercalation in a gaseous environment is well established, the mechanism of
ion intercalation in liquid electrolytes at room temperature is poorly
understood. In this study, the defect chemistry during ion intercalation of
La0.5Sr0.5FeO3-{\delta} thin films in alkaline electrolytes is studied. Oxygen
and proton intercalation into the LSF perovskite structure is observed at
moderate electrochemical potentials (0.5 V to -0.4 V), giving rise to a change
in the oxidation state of Fe (as a charge compensation mechanism). The
variation of the concentration of holes as a function of the intercalation
potential was characterized by in-situ ellipsometry and the concentration of
electron holes was indirectly quantified for different electrochemical
potentials. Finally, a dilute defect chemistry model that describes the
variation of defect species during ionic intercalation was developed.",2306.10887v1
2023-06-22,Dynamic Versus Static Oxidation of Nb/Al-AlO$_x$/Nb Trilayer,"High quality Nb-based superconductor-insulator-superconductor (SIS) junctions
with Al oxide (AlO$_x$) tunnel barriers grown from Al overlayers are widely
reported in the literature. However, the thin barriers required for high
critical current density (J$_c$) junctions exhibit defects that result in
significant subgap leakage current that is detrimental for many applications.
High quality, high-J$_c$ junctions can be realized with AlN$_x$ barriers, but
control of J$_c$ is more difficult than with AlO$_x$. It is therefore of
interest to study the growth of thin AlO$_x$ barriers with the ultimate goal of
achieving high quality, high-J$_c$ AlO$_x$ junctions. In this work, 100\%\
O$_2$ and 2\%\ O$_2$ in Ar gas mixtures are used both statically and
dynamically to grow AlO$_x$ tunnel barriers over a large range of oxygen
exposures. In situ ellipsometry is used for the first time to extensively
measure AlO$_x$ tunnel barrier growth in real time, revealing a number of
unexpected patterns. Finally, a set of test junction wafers was fabricated that
exhibited the well-known dependence of J$_c$ on oxygen exposure (E) in order to
further validate the experimental setup.",2306.12684v1
2023-06-23,Correlating activity and defects in (photo)electrocatalysts using in-situ transient optical microscopy,"(Photo)electrocatalysts capture sunlight and use it to drive chemical
reactions such as water splitting to produce H2. A major factor limiting
photocatalyst development is their large heterogeneity which spatially
modulates reactivity and precludes establishing robust structure-function
relationships. To make such links requires simultaneously probing of the
electrochemical environment at microscopic length scales (nm to um) and broad
timescales (ns to s). Here, we address this challenge by developing and
applying in-situ steady-state and transient optical microscopies to directly
map and correlate local electrochemical activity with hole lifetimes, oxygen
vacancy concentration and the photoelectrodes crystal structure. Using this
combined approach alongside spatially resolved X-Ray absorption measurements,
we study microstructural and point defects in prototypical hematite (Fe2O3)
photoanodes. We demonstrate that regions of Fe2O3, adjacent to microstructural
cracks have a better photoelectrochemical response and reduced back electron
recombination due to an optimal oxide vacancy concentration, with the film
thickness and carbon impurities also dramatically influencing activity in a
complex manner. Our work highlights the importance of microscopic mapping to
understand activity and the impact of defects in even, seemingly, homogeneous
solid-state metal oxide photoelectrodes.",2306.13401v1
2023-06-26,Atomic-Scale Tailoring of Chemisorbed Atomic Oxygen on Epitaxial Graphene for Graphene-Based Electronic Devices,"Graphene, with its unique band structure, mechanical stability, and high
charge mobility, holds great promise for next-generation electronics.
Nevertheless, its zero band gap challenges the control of current flow through
electrical gating, consequently limiting its practical applications. Recent
research indicates that atomic oxygen can oxidize epitaxial graphene in a
vacuum without causing unwanted damage. In this study, we have investigated the
effects of chemisorbed atomic oxygen on the electronic properties of epitaxial
graphene, using scanning tunneling microscopy (STM). Our findings reveal that
oxygen atoms effectively modify the electronic states of graphene, resulting in
a band gap at its Dirac point. Furthermore, we demonstrate that it is possible
to selectively induce desorption or hopping of oxygen atoms with atomic
precision by applying appropriate bias sweeps with an STM tip. These results
suggest the potential for atomic-scale tailoring of graphene oxide, enabling
the development of graphene-based atomic-scale electronic devices.",2306.14501v1
2023-06-27,Numerical study of nitrogen oxides chemistry during plasma assisted combustion in a sequential combustor,"Plasma Assisted Combustion (PAC) is a promising technology to enhance the
combustion of lean mixtures prone to instabilities and flame blow-off. Although
many PAC experiments demonstrated combustion enhancement, several studies
report an increase in NOx emissions. The aim of this study is to determine the
kinetic pathways leading to NOx formation in the second stage of a sequential
combustor assisted by Nanosecond Repetitively Pulsed Discharges (NRPDs). For
this purpose, Large Eddy Simulation (LES) associated with an accurate
description of the combustion/NOx chemistry and a phenomenological model of the
plasma kinetics is used. Detailed kinetics 0-Dimensional reactors complement
the study. First, the LES setup is validated by comparison with experiments.
Then, the NOx chemistry is analyzed. For the conditions of operation studied,
it is shown that the production of atomic nitrogen in the plasma by direct
electron impact on nitrogen molecules increases the formation of NO. Then, the
NO molecules are transported through the turbulent flame without being strongly
affected. This study illustrates the need to limit the diatomic nitrogen
dissociation process in order to mitigate harmful emissions. More generally,
the very good agreement with experimental measurements demonstrates the
capability of LES combined with accurate models to predict the NRPD effects on
both turbulent combustion and NOx emissions.",2306.15539v1
2023-06-29,Ion-beam sputtering of NiO hole transporting layers for p-i-n halide perovskite solar cells,"Ion-beam sputtering offers significant benefits in terms of deposition
uniformity and pinhole-free thin-films without limiting the scalability of the
process. In this work, the reactive ion-beam sputtering of nickel oxide has
been developed for the hole transporting layer of a p-i-n perovskite solar
cells (PCSs). The process is carried out by oxidation of the scattered Ni
particles with additional post-treatment annealing regimes. Using deposition
rate of 1.2 nm/min allowed growth of very uniform NiO coating with the
roughness below 0.5 nm on polished Si wafer (15x15 cm2). We performed a complex
investigation of structural, optical, surface and electrical properties of the
NiO thin-films. The post-treatment annealing (150-300C) was considered as an
essential process for improvement of the optical transparency, decrease of
defects concentration and gain of the charge carrier mobility. As result, the
annealed ion-beam sputtered NiO films delivered a power conversion efficiency
(PCE) up to 20.14%, while device without post-treatment reached the value of
11.84%. The improvement of the output performance originated from an increase
of the short-circuit current density (Jsc), open circuit voltage (Voc), shunt
and contact properties in the devices. We also demonstrate that the ion-beam
sputtering of NiO can be successfully implemented for the fabrication of large
area modules (54.5 cm2) and PSCs on a flexible plastic substrate (125 microns).",2306.16949v1
2023-07-14,Interpretable machine learning to understand the performance of semi local density functionals for materials thermochemistry,"This study investigates the use of machine learning (ML) to correct the
enthalpy of formation (Hf) from two separate DFT functionals, PBE and SCAN, to
the experimental Hf across 1011 solid-state compounds. The ML model uses a set
of 25 properties that characterize the electronic structure as calculated using
PBE and SCAN. The ML model significantly decreases the error in PBE-calculated
Hf values from an mean absolute error (MAE) of 195 meV/atom to an MAE = 80
meV/atom when compared to the experiment. For PBE, the PDP+GAM analysis shows
compounds with a high ionicity (I), i.e., I>0.22, have errors in Hf that are
twice as large as compounds having I < 0.22 (246 meV/atom compared to 113
meV/atom). Conversely, no analogous trend is observed for SCAN-calculated Hfs,
which explains why the ML model for PBE can more easily correct the systematic
error in calculated Hfs for PBE but not for SCAN. Although the literature
suggests PBE is reliable for intermetallics but less so for oxides and halides,
our analysis reveals intermetallics pose a challenge for PBE only when the
charge transfer is significant (I >0.22). Meanwhile, oxides and halides may be
described accurately by PBE for systems in which charge transfer is relatively
low (I < 0.22).",2307.07609v1
2023-07-19,Origin of Life Molecules in the Atmosphere After Big Impacts on the Early Earth,"The origin of life on Earth would benefit from a prebiotic atmosphere that
produced nitriles, like HCN, which enable ribonucleotide synthesis. However,
geochemical evidence suggests that Hadean air was relatively oxidizing with
negligible photochemical production of prebiotic molecules. These paradoxes are
resolved by iron-rich asteroid impacts that transiently reduced the entire
atmosphere, allowing nitriles to form in subsequent photochemistry. Here, we
investigate impact-generated reducing atmospheres using new time-dependent,
coupled atmospheric chemistry and climate models, which account for gas-phase
reactions and surface-catalysis. The resulting H$_2$-, CH$_4$- and NH$_3$-rich
atmospheres persist for millions of years, until hydrogen escapes to space. HCN
and HCCCN production and rainout to the surface can reach $10^9$ molecules
cm$^{-2}$ s$^{-1}$ in hazy atmospheres with a mole ratio of $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$. Smaller $\mathrm{CH_4} / \mathrm{CO_2}$ ratios produce
HCN rainout rates $< 10^5$ molecules cm$^{-2}$ s$^{-1}$, and negligible HCCCN.
The minimum impactor mass that creates atmospheric $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$ is $4 \times 10^{20}$ to $5 \times 10^{21}$ kg (570 to
1330 km diameter), depending on how efficiently iron reacts with a steam
atmosphere, the extent of atmospheric equilibration with an impact-induced melt
pond, and the surface area of nickel that catalyzes CH$_4$ production.
Alternatively, if steam permeates and deeply oxidizes crust, impactors $\sim
10^{20}$ kg could be effective. Atmospheres with copious nitriles have $> 360$
K surface temperatures, perhaps posing a challenge for RNA longevity, although
cloud albedo can produce cooler climates. Regardless, post-impact cyanide can
be stockpiled and used in prebiotic schemes after hydrogen has escaped to
space.",2307.09761v1
2023-07-31,Enhanced Nonlinearity of Epsilon-Near-Zero Indium Tin Oxide Nanolayers with Tamm Plasmon-Polariton States,"Recently, materials with vanishingly small permittivity, known as
epsilon-near-zero (ENZ) media, emerged as promising candidates to achieve
nonlinear optical effects of unprecedented magnitude on a solid-state platform.
In particular, the ENZ behavior of Indium Tin Oxide (ITO) thin films resulted
in Kerr-type nonlinearity with non-perturbative refractive index variations
that are key to developing more efficient Si-compatible devices with
sub-wavelength dimensions such as all-optical switchers, modulators, and novel
photon detectors. In this contribution, we propose and demonstrate enhancement
of the nonlinear index variation of 30 nm-thick ITO nanolayers by silicon
dioxide/silicon nitride (SiO2/SiN) Tamm plasmon-polariton structures fabricated
by radio-frequency magnetron sputtering on transparent substrates under
different annealing conditions. In particular, we investigate the linear and
nonlinear optical properties of ITO thin films and resonant photonic structures
using broadband spectroscopic ellipsometry and intensity dependent Z-scan
nonlinear characterization demonstrating enhancement of optical nonlinearity
with refractive index variations as large as in the non-perturbative regime.
Our study reveals that the efficient excitation of strongly confined
plasmon-polariton Tamm states substantially boost the nonlinear optical
response of ITO nanolayers providing a stepping stone for the engineering of
more efficient infrared devices and nanostructures for a broad range of
applications including all-optical data processing, nonlinear spectroscopy,
sensing, and novel photodetection modalities.",2308.00168v3
2023-08-02,Permissible domain walls in monoclinic MAB ferroelectric phases,"The concept of monoclinic ferroelectric phases has been extensively used over
recent decades for the understanding of ferroelectric materials. Monoclinic
phases have been actively invoked to describe the phase boundaries such as
Morphotropic Phase Boundary in functional perovskite oxides. These phases are
believed to play the major role in the enhancement of functional properties
such as dielectricity and electromechanical coupling through rotation of
spontaneous polarization and modification of the rich domain microstructures.
Unfortunately, such microstructures remain poorly understood due to the
complexity of the subject. The goal of this work is to formulate the
geometrical laws behind the monoclinic domain microstructures. Specifically, we
implement the result of our previous work (Gorfman et al, 2022) to catalogue
and outline some properties of permissible domain walls that connect strain
domains with monoclinic (MAB type) symmetry, occurring in ferroelectric
perovskite oxides. The term permissible (Fousek & Janovec, 1969) pertains to
the domain walls, connecting a pair of strain domains without a lattice
mismatch. We found that 12 monoclinic domains may form pairs connected along 84
types of permissible domain walls. These contain 48 domain walls with fixed
Miller indices (known as W-walls) and 36 domain walls whose Miller indices may
change when free lattice parameters change as well (known as S-walls). We
provide simple analytical expressions for the orientation of these domain
walls, the matrices of transformation between crystallographic basis vectors
and for the separation between Bragg peaks, diffracted from each of the pairs
of domains, connected along 84 permissible domain walls. The resultscan
contribute to the understanding and facilitate investigation of complex
monoclinic domain microstructures.",2308.01324v3
2023-08-08,ExoMol line lists -- LIII: Empirical Rovibronic spectra of Yttrium Oxide (YO),"Empirical line lists for the open shell molecule $^{89}$Y$^{16}$O (yttrium
oxide) and its isotopologues are presented. The line lists cover the 6 lowest
electronic states: $X {}^{2}\Sigma^{+}$, $A {}^{2}\Pi$, $A' {}^{2}\Delta$, $B
{}^{2}\Sigma^{+}$, $C {}^{2}\Pi$ and $D {}^{2}\Sigma^{+}$ up to 60000 cm$^{-1}$
($<0.167$ $\mu$m) for rotational excitation up to $J = 400.5$. An \textit{ab
initio} spectroscopic model consisting of potential energy curves (PECs),
spin-orbit and electronic angular momentum couplings is refined by fitting to
experimentally determined energies of YO, derived from published YO
experimental transition frequency data. The model is complemented by empirical
spin-rotation and $\Lambda$-doubling curves and \textit{ab initio} dipole
moment and transition dipole moment curves computed using MRCI. The \textit{ab
initio} PECs computed using the complete basis set limit extrapolation and the
CCSD(T) method with its higher quality provide an excellent initial
approximation for the refinement. Non-adiabatic coupling curves for two pairs
of states of the same symmetry $A$/$C$ and $B$/$D$ are computed using a
state-averaged CASSCF and used to built diabatic representations for the $A
{}^{2}\Pi$, $C {}^{2}\Pi$, $B {}^{2}\Sigma^{+}$ and $D {}^{2}\Sigma^{+}$
curves. Calculated lifetimes of YO are tuned to agree well with the experiment,
where available. The BRYTS YO line lists for are included into the ExoMol data
base (www.exomol.com).",2308.04173v3
2023-08-12,Polar discontinuities and interfacial electronic properties of Bi$_2$O$_2$Se on SrTiO$_3$,"The layered oxychalcogenide semiconductor Bi$_2$O$_2$Se (BOS) hosts a
multitude of unusual properties including high electron mobility. Owing to
similar crystal symmetry and lattice constants, the perovskite oxide SrTiO$_3$
(STO) has been demonstrated to be an excellent substrate for wafer-scale growth
of atomically thin BOS films. However, the structural and electronic properties
of the BOS/STO interface remain poorly understood. Here, through
first-principles study, we reveal that polar discontinuities and interfacial
contact configurations have a strong impact on the electronic properties of
ideal BOS/STO interfaces. The lowest-energy [Bi-TiO$_2$] contact type, which
features the contact between a Bi$_2$O$_2$ layer of BOS with the
TiO$_2$-terminated surface of STO, incurs significant interfacial charge
transfer from BOS to STO, producing a BOS/STO-mixed, $n$-type metallic state at
the interface. By contrast, the [Se-SrO] contact type, which is the most stable
contact configuration between BOS and SrO-terminated STO substrate, has a much
smaller interfacial charge transfer from STO to BOS and exhibits $p$-type
electronic structure with much weaker interfacial hybridization between BOS and
STO. These results indicate that BOS grown on TiO$_2$-terminated STO substrates
could be a fruitful system for exploring emergent phenomena at the interface
between an oxychalcogenide and an oxide, whereas BOS grown on SrO-terminated
substrates may be more advantageous for preserving the excellent intrinsic
transport properties of BOS.",2308.06486v1
2023-08-14,Physics-Informed Deep Learning to Reduce the Bias in Joint Prediction of Nitrogen Oxides,"Atmospheric nitrogen oxides (NOx) primarily from fuel combustion have
recognized acute and chronic health and environmental effects. Machine learning
(ML) methods have significantly enhanced our capacity to predict NOx
concentrations at ground-level with high spatiotemporal resolution but may
suffer from high estimation bias since they lack physical and chemical
knowledge about air pollution dynamics. Chemical transport models (CTMs)
leverage this knowledge; however, accurate predictions of ground-level
concentrations typically necessitate extensive post-calibration. Here, we
present a physics-informed deep learning framework that encodes
advection-diffusion mechanisms and fluid dynamics constraints to jointly
predict NO2 and NOx and reduce ML model bias by 21-42%. Our approach captures
fine-scale transport of NO2 and NOx, generates robust spatial extrapolation,
and provides explicit uncertainty estimation. The framework fuses
knowledge-driven physicochemical principles of CTMs with the predictive power
of ML for air quality exposure, health, and policy applications. Our approach
offers significant improvements over purely data-driven ML methods and has
unprecedented bias reduction in joint NO2 and NOx prediction.",2308.07441v1
2023-08-18,Predicting Properties of Oxide Glasses Using Informed Neural Networks,"Many modern-day applications require the development of new materials with
specific properties. In particular, the design of new glass compositions is of
great industrial interest. Current machine learning methods for learning the
composition-property relationship of glasses promise to save on expensive
trial-and-error approaches. Even though quite large datasets on the composition
of glasses and their properties already exist (i.e., with more than 350,000
samples), they cover only a very small fraction of the space of all possible
glass compositions. This limits the applicability of purely data-driven models
for property prediction purposes and necessitates the development of models
with high extrapolation power. In this paper, we propose a neural network model
which incorporates prior scientific and expert knowledge in its learning
pipeline. This informed learning approach leads to an improved extrapolation
power compared to blind (uninformed) neural network models. To demonstrate
this, we train our models to predict three different material properties, that
is, the glass transition temperature, the Young's modulus (at room
temperature), and the shear modulus of binary oxide glasses which do not
contain sodium. As representatives for conventional blind neural network
approaches we use five different feed-forward neural networks of varying widths
and depths. For each property, we set up model ensembles of multiple trained
models and show that, on average, our proposed informed model performs better
in extrapolating the three properties of previously unseen sodium borate glass
samples than all five conventional blind models.",2308.09492v3
2023-08-20,MgH2 nanoparticles confined in reduced graphene oxide pillared with organosilica: a novel type of hydrogen storage material,"Hydrogen is a promising energy carrier that can push forward the energy
transition because of its high energy density (142 MJ kg-1), variety of
potential sources, low weight and low environmental impact, but its storage for
automotive applications remains a formidable challenge. MgH2, with its high
gravimetric and volumetric density, presents a compelling platform for hydrogen
storage; however, its utilization is hindered by the sluggish kinetics of
hydrogen uptake/release and high temperature operation. Herein we show that a
novel layered heterostructure of reduced graphene oxide and organosilica with
high specific surface area and narrow pore size distribution can serve as a
scaffold to host MgH2 nanoparticles with a narrow diameter distribution around
~2.5 nm and superior hydrogen storage properties to bulk MgH2. Desorption
studies showed that hydrogen release starts at 50 {\deg}C, with a maximum at
348 {\deg}C and kinetics dependent on particle size. Reversibility tests
demonstrated that the dehydrogenation kinetics and re-hydrogenation capacity of
the system remains stable at 1.62 wt.% over four cycles at 200 {\deg}C. Our
results prove that MgH2 confinement in a nanoporous scaffold is an efficient
way to constrain the size of the hydride particles, avoid aggregation and
improve kinetics for hydrogen release and recharging.",2308.10137v1
2023-08-22,Direct assessment of the proton affinity of individual surface hydroxyls with non-contact atomic force microscopy,"The state of protonation/deprotonation of surfaces has far-ranging
implications in all areas of chemistry: from acid-base catalysis$^1$ and the
electro- and photocatalytic splitting of water$^2$, to the behavior of
minerals$^3$ and biochemistry$^4$. The acidity of a molecule or a surface site
is described by its proton affinity (PA) and pK$_\mathrm{a}$ value (the
negative logarithm of the equilibrium constant of the proton transfer reaction
in solution). For solids, in contrast to molecules, the acidity of individual
sites is difficult to assess. For mineral surfaces such as oxides they are
estimated by semi-empirical concepts such as bond-order valence sums$^5$, and
also increasingly modeled with first-principles molecular dynamics
simulations$^{6,7}$. Currently such predictions cannot be tested - the
experimental measures used for comparison are typically average quantities
integrated over the whole surface or, in some cases, individual crystal
facets$^8$, such as the point of zero charge (pzc)$^9$. Here we assess
individual hydroxyls on In$_2$O$_3$(111), a model oxide with four different
types of surface oxygen atoms, and probe the strength of their hydrogen bond
with the tip of a non-contact atomic force microscope (AFM). The force curves
are in quantitative agreement with density-functional theory (DFT)
calculations. By relating the results to known proton affinities and
pK$_\mathrm{a}$ values of gas-phase molecules, we provide a direct measure of
proton affinity distributions at the atomic scale.",2308.11437v1
2023-08-25,Interacting Two-Level Systems as a Source of 1/f Charge Noise in Quantum Dot Qubits,"Charge noise in semiconducting quantum dots has been observed to have a 1/f
spectrum. We propose a model in which a pair of quantum dots are coupled to a
2D bath of fluctuating two level systems (TLS) that have electric dipole
moments and that interact with each other, i.e., with the other fluctuators.
These interactions are primarily via the elastic strain field. We use a 2D
nearest-neighbor Ising spin glass to represent these elastic interactions and
to simulate the dynamics of the bath of electric dipole fluctuators in the
presence of a ground plane representing metal gates above the oxide layer
containing the fluctuators. The interactions between the TLS cause the energy
splitting of individual fluctuators to change with time. We calculate the
resulting fluctuations in the electric potential at the two quantum dots that
lie below the oxide layer. We find that 1/f electric potential noise spectra at
the quantum dots and cross correlation in the noise between the two quantum
dots are in qualitative agreement with experiment. Our simulations find that
the cross correlations decrease exponentially with increasing quantum dot
separation.",2308.13674v2
2023-08-28,Crystal-Chemical Origins of the Ultrahigh Conductivity of Metallic Delafossites,"Despite their highly anisotropic complex-oxidic nature, certain delafossite
compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for
reasons that remain poorly understood. Their room-temperature conductivity can
exceed that of Au, while their low-temperature electronic mean-free-paths reach
an astonishing 20 microns. It is widely accepted that these materials must be
ultrapure to achieve this, although the methods for their growth (which produce
only small crystals) are not typically capable of such. Here, we first report a
new approach to PdCoO2 crystal growth, using chemical vapor transport methods
to achieve order-of-magnitude gains in size, the highest structural qualities
yet reported, and record residual resistivity ratios (>440). Nevertheless, the
first detailed mass spectrometry measurements on these materials reveal that
they are not ultrapure, typically harboring 100s-of-parts-per-million impurity
levels. Through quantitative crystal-chemical analyses, we resolve this
apparent dichotomy, showing that the vast majority of impurities are forced to
reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly
pure (~1 ppm impurity concentrations). These purities are shown to be in
quantitative agreement with measured residual resistivities. We thus conclude
that a previously unconsidered ""sublattice purification"" mechanism is essential
to the ultrahigh low-temperature conductivity and mean-free-path of metallic
delafossites.",2308.14257v2
2023-08-29,In-situ Plasma Studies using a Direct Current Microplasma in a Scanning Electron Microscope,"Microplasmas can be used for a wide range of technological applications and
to improve our understanding of fundamental physics. Scanning electron
microscopy, on the other hand, provides insights into the sample morphology and
chemistry of materials from the mm-down to the nm-scale. Combining both would
provide direct insight into plasma-sample interactions in real-time and at high
spatial resolution. Up till now, very few attempts in this direction have been
made, and significant challenges remain. This work presents a stable direct
current glow discharge microplasma setup built inside a scanning electron
microscope. The experimental setup is capable of real-time in-situ imaging of
the sample evolution during plasma operation and it demonstrates localized
sputtering and sample oxidation. Further, the experimental parameters such as
varying gas mixtures, electrode polarity, and field strength are explored and
experimental $V$-$I$ curves under various conditions are provided. These
results demonstrate the capabilities of this setup in potential investigations
of plasma physics, plasma-surface interactions, and materials science and its
practical applications. The presented setup shows the potential to have several
technological applications, e.g., to locally modify the sample surface (e.g.,
local oxidation and ion implantation for nanotechnology applications) on the
$\mu$m-scale.",2308.15123v1
2023-09-05,Optical absorption spectra of metal oxides from time-dependent density functional theory and many-body perturbation theory based on optimally-tuned hybrid functionals,"Using both time-dependent density functional theory (TDDFT) and the
``single-shot"" $GW$ plus Bethe-Salpeter equation ($GW$-BSE) approach, we
compute optical band gaps and optical absorption spectra from first principles
for eight common binary and ternary closed-shell metal oxides (MgO,
Al$_2$O$_3$, CaO, TiO$_2$, Cu$_2$O, ZnO, BaSnO$_3$, and BiVO$_4$), based on the
non-empirical Wannier-localized optimally-tuned screened range-separated hybrid
functional. Overall, we find excellent agreement between our TDDFT and $GW$-BSE
results and experiment, with a mean absolute error less than 0.4 eV, including
for Cu$_2$O and ZnO, traditionally considered to be challenging for both
methods.",2309.02117v1
2023-08-29,Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Synaptic Devices,"Solid-state devices made from correlated oxides such as perovskite nickelates
are promising for neuromorphic computing by mimicking biological synaptic
function. However, comprehending dopant action at the nanoscale poses a
formidable challenge to understanding the elementary mechanisms involved. Here,
we perform operando infrared nanoimaging of hydrogen-doped correlated
perovskite, neodymium nickel oxide (H-NdNiO3) devices and reveal how an applied
field perturbs dopant distribution at the nanoscale. This perturbation leads to
stripe phases of varying conductivity perpendicular to the applied field, which
define the macroscale electrical characteristics of the devices. Hyperspectral
nano-FTIR imaging in conjunction with density functional theory calculations
unveil a real-space map of multiple vibrational states of H-NNO associated with
OH stretching modes and their dependence on the dopant concentration. Moreover,
the localization of excess charges induces an out-of-plane lattice expansion in
NNO which was confirmed by in-situ - x-ray diffraction and creates a strain
that acts as a barrier against further diffusion. Our results and the
techniques presented here hold great potential to the rapidly growing field of
memristors and neuromorphic devices wherein nanoscale ion motion is
fundamentally responsible for function.",2309.04486v1
2023-09-23,LES of a non-premixed hydrogen flame stabilized by bluff-bodies of various shapes,"Dynamics of flames stabilized downstream of different shape bluff-bodies
(cylindrical, square, star) with different wall topologies (flat, wavy) is
investigated using large-eddy simulations (LES). A two-stage computational
procedure involving the ANSYS software and an in-house academic high-order code
is combined to model a flow in the vicinity of the bluff-bodies and a flame
formed downstream. The fuel is nitrogen-diluted hydrogen and the oxidizer is
hot air in which the fuel auto-ignites. After the ignition, the flame
propagates towards the bluff-body surfaces and stabilizes in their vicinity. It
is shown that the flames reflect the bluff-body shape due to large-scale strong
vortices induced in the shear layer formed between the main recirculation zone
and the oxidizer stream. The influence of the acute corners of the bluff-bodies
on the flame dynamics is quantified by analysing instantaneous and
time-averaged results. Compared to the classical conical bluff-body the largest
differences in the temperature and velocity distributions are observed in the
configuration with the square bluff-body. The main recirculation zone is
shortened by approximately 15% and at its end temperature in the axis of the
flame is almost 200 K larger. Simultaneously, their fluctuations are slightly
larger than in the remaining cases. The influence of the wall topology (flat
vs. wavy) in the configuration with the classical conical bluff-body turned out
to be very small and it resulted in modifications of the flow and flame
structures only in the direct vicinity of the bluff-body surface.",2309.13344v1
2023-09-26,Fast emitting nanocomposites for high-resolution ToF-PET imaging based on multicomponent scintillators,"Time-of-Flight Positron Emission Tomography is a medical imaging technique,
based on the detection of two back-to-back {\gamma}-photons generated from
radiotracers injected in the body. Its limit is the ability of employed
scintillation detectors to discriminate in time the arrival of {\gamma}-pairs,
i.e. the coincidence time resolution (CTR). A CTR < 50 ps that would enable
fast imaging with ultralow radiotracer dose. Monolithic materials do not have
simultaneously the required high light output and fast emission
characteristics, thus the concept of scintillating heterostructure is proposed,
where the device is made of a dense scintillator coupled to a fast-emitting
light material. Here we present a composite polymeric scintillator, whose
density has been increased upon addition of hafnium oxide nanoparticles. This
enhanced by +300% its scintillation yield, surpassing commercial plastic
scintillators. The nanocomposite is coupled to bismuth germanate oxide (BGO)
realizing a multilayer scintillator. We observed the energy sharing between its
components, which activate the nanocomposite fast emission enabling a net CTR
improvement of 25% with respect to monolithic BGO. These results demonstrate
that a controlled loading with dense nanomaterials is an excellent strategy to
enhance the performance of polymeric scintillators for their use in advanced
radiation detection and imaging technologies.",2309.14968v1
2023-09-26,SuperGaN: Synthesis of NbTiN/GaN/NbTiN Tunnel Junctions,"Nb-based circuits have broad applications in quantum-limited photon
detectors, low-noise parametric amplifiers, superconducting digital logic
circuits, and low-loss circuits for quantum computing. The current
state-of-the-art approach for superconductor-insulator-superconductor (SIS)
junction material is the Gurvitch trilayer process based on magnetron
sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al
overlayer. However, a current limitation of elemental Nb-based circuits is the
low-loss operation of THz circuits operating above the 670 GHz gap frequency of
Nb and operation at higher temperatures for projects with a strict power
budget, such as space-based applications.
  NbTiN is an alternative higher energy gap material and we have previously
reported on the first NbTiN/AlN/NbTiN
superconducting-insulating-superconducting (SIS) junctions with an epitaxially
grown AlN tunnel barrier. One drawback of a directly grown tunnel barrier
compared to thermal oxidation or plasma nitridation is control of the barrier
thickness and uniformity across a substrate, leading to variations in current
density (Jc). Semiconductor barriers with smaller barrier heights enable
thicker tunnel barriers for a given Jc. GaN is an alternative semiconductor
material with a closed-packed Wurtzite crystal structure similar to AlN and it
can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion
Beam Deposition (RBTIBD) technique. This work presents the preliminary results
of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with
underdamped SIS I(V) characteristics.",2309.15100v1
2023-10-02,Breaking Through the Plasma Wavelength Barrier to Extend the Transparency Range of Ultrathin Indium Tin Oxide Films into the Far Infrared,"Indium tin oxide (ITO) film, which is the most commonly used transparent
conductive film (TCF), has traditionally been believed to be transparent in the
visible spectrum but to reflect infrared (IR) light beyond the plasma
wavelength (${\lambda}_p$). However, our theoretical analysis challenges this
notion by demonstrating that an ultrathin ITO TCF that is thinner than the
light's penetration depth, can overcome the transmission barrier at
${\lambda}_p$. To validate the theoretical modeling, we have successfully
fabricated ITO films that, despite having ${\lambda}_p \approx$ 1 ${\mu}$m,
remain transparent from 400 nm to 20 ${\mu}$m. This represents the broadest
transparency range ever reported for any In$_2$O$_3$-based TCF. The 10-nm-thick
ITO TCFs have high visible transmittance (91.0% at 550 nm), low resistivity (5
$\times$ 10$^{-4}$ ${\Omega}\cdot$ cm), and good IR transmittance (averaging
60% over 1.35 $\unicode{x2013}$ 18.35 ${\mu}$m). Their IR transparency
facilitates radiative cooling of the underlying circuitry. When an operational
resistor is enclosed by commercial ITO TCFs that are 140 nm thick, its
temperature increases. However, using 10-nm-thick ITO TCFs instead of the
commercial ones can completely avoid this temperature rise. Moreover, attaching
a silver grid to a 10-nm-thick ITO TCF can reduce the effective sheet
resistance to ~10 ${\Omega}/\square$ at the expense of only ~3% transmittance.
This development paves the way for large-scale applications that require low
sheet resistance and far-IR transparency.",2310.00984v1
2023-10-02,"A review and outlook on anionic and cationic redox in Ni-, Li- and Mn-rich layered oxides LiMeO2 (Me = Li, Ni, Co, Mn)","The present work reviews the charge compensation in Ni based layered oxides
(LiNi1-xMexO2 with x <= 0.2, Me = Co, Mn, space group R-3m) relating
performance parameters to changes in the electronic and crystallographic
structure of the cathode materials. Upon charge and discharge two fundamentally
different redox mechanisms are observed: At low and medium states of charge
(SOCs) charge compensation takes mainly place at oxygen sites while electron
density is shifted from the oxygen lattice to nickel (formation of sigma
bonds). At high SOCs the shift of electron density from the transition metals
to oxygen (formation of pi bonds) enables an additional redox process but also
oxygen release from the transition metal host structure and subsequent
detrimental reactions. Depending on the Ni:Co:Mn content, both processes lead
to characteristic features in the voltage profile of the cathode materials and
performance parameters like the capacity, the cycling stability and the open
cell voltage become a function of the composition.",2310.01295v2
2023-10-03,Simulation Guided Molecular Design of Hydrofluoroether Solvent for High Energy Batteries,"Electrolyte design is critical for enabling next-generation batteries with
higher energy densities. Hydrofluoroether (HFE) solvents have drawn a lot of
attention as the electrolytes based on HFEs showed great promise to deliver
highly desired properties, including high oxidative stability, ionic
conductivity, as well as enhanced lithium metal compatibility. However, the
structure-dynamics-properties relationships and design principles for
high-performance HFE solvents are still poorly understood. Herein, we proposed
four novel asymmetric HFE designs by systematically varying polyether and
fluorocarbon structural building blocks. By leveraging molecular dynamics (MD)
modeling to analyze the solvation structures and predict the properties of the
corresponding 1 M lithium bis(fluorosulfonyl)imide (LiTFSI) solutions, we
downselected the most promising candidate based on high conductivity, solvation
species distribution, and oxidative stability for extensive electrochemical
characterizations. The formulated electrolyte demonstrated properties
consistent with the predictions from the simulations and showed much-improved
capacity retention as well as Coulombic efficiency compared to the baseline
electrolytes when cycled in lithium metal cells. This work exemplifies the
construction of candidate electrolytes from building block functional moieties
to engineer fundamental solvation structures for desired electrolyte properties
and guide the discovery and rational design of new solvent materials.",2310.02188v1
2023-10-10,Mitigation of interfacial dielectric loss in aluminum-on-silicon superconducting qubits,"We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged
${T_1}$ energy relaxation times of up to ${270\,\mu s}$, corresponding to Q = 5
million, and a highest observed value of ${501\,\mu s}$. We use materials
analysis techniques and numerical simulations to investigate the dominant
sources of energy loss, and devise and demonstrate a strategy towards
mitigating them. The mitigation of loss is achieved by reducing the presence of
oxide, a known host of defects, near the substrate-metal interface, by growing
aluminum films thicker than 300 nm. A loss analysis of coplanar-waveguide
resonators shows that the improvement is owing to a reduction of dielectric
loss due to two-level system defects. We perform time-of-flight secondary ion
mass spectrometry and observe a reduced presence of oxygen at the
substrate-metal interface for the thicker films. The correlation between the
enhanced performance and the film thickness is due to the tendency of aluminum
to grow in columnar structures of parallel grain boundaries, where the size of
the grain depends on the film thickness: transmission electron microscopy
imaging shows that the thicker film has larger grains and consequently fewer
grain boundaries containing oxide near this interface. These conclusions are
supported by numerical simulations of the different loss contributions in the
device.",2310.06797v1
2023-10-25,Proton and molecular permeation through the basal plane of monolayer graphene oxide,"Two-dimensional (2D) materials offer a prospect of membranes that combine
negligible gas permeability with high proton conductivity and could outperform
the existing proton exchange membranes used in various applications including
fuel cells. Graphene oxide (GO), a well-known 2D material, facilitates rapid
proton transport along its basal plane but proton conductivity across it
remains unknown. It is also often presumed that individual GO monolayers
contain a large density of nanoscale pinholes that lead to considerable gas
leakage across the GO basal plane. Here we show that relatively large,
micrometer-scale areas of monolayer GO are impermeable to gases, including
helium, while exhibiting proton conductivity through the basal plane which is
nearly two orders of magnitude higher than that of graphene. These findings
provide insights into the key properties of GO and demonstrate that chemical
functionalization of 2D crystals can be utilized to enhance their proton
transparency without compromising gas impermeability.",2310.16495v1
2023-10-30,Interfacial Tension Hysteresis of Eutectic Gallium-Indium,"When in a pristine state, gallium and its alloys have the largest interfacial
tensions of any liquid at room temperature. Nonetheless, applying as little as
0.8 V of electric potential across eutectic gallium indium (EGaIn) placed
within aqueous NaOH (or other electrolyte) solution will cause the metal to
behave as if its interfacial tension is near zero. The mechanism behind this
phenomenon has remained poorly understood because NaOH dissolves the oxide
species, making it difficult to directly measure the concentration, thickness,
or chemical composition of the film that forms at the interface. In addition,
the oxide layers formed are atomically-thin. Here, we present a suite of
techniques which allow us to simultaneously measure both electrical and
interfacial properties as a function of applied electric potential, allowing
for new insights into the mechanisms which cause the dramatic decrease in
interfacial tension. A key discovery from this work is that the interfacial
tension displays hysteresis while lowering the applied potential. We combine
these observations with electrochemical impedance spectroscopy to evaluate how
these changes in interfacial tension arise from chemical, electrical, and
mechanical changes on the interface, and close with ideas for how to build a
free energy model to predict these changes from first principles.",2310.19298v1
2023-11-03,Generalization of Graph-Based Active Learning Relaxation Strategies Across Materials,"Although density functional theory (DFT) has aided in accelerating the
discovery of new materials, such calculations are computationally expensive,
especially for high-throughput efforts. This has prompted an explosion in
exploration of machine learning assisted techniques to improve the
computational efficiency of DFT. In this study, we present a comprehensive
investigation of the broader application of Finetuna, an active learning
framework to accelerate structural relaxation in DFT with prior information
from Open Catalyst Project pretrained graph neural networks. We explore the
challenges associated with out-of-domain systems: alcohol ($C_{>2}$) on metal
surfaces as larger adsorbates, metal-oxides with spin polarization, and
three-dimensional (3D) structures like zeolites and metal-organic-frameworks.
By pre-training machine learning models on large datasets and fine-tuning the
model along the simulation, we demonstrate the framework's ability to conduct
relaxations with fewer DFT calculations. Depending on the similarity of the
test systems to the training systems, a more conservative querying strategy is
applied. Our best-performing Finetuna strategy reduces the number of DFT
single-point calculations by 80% for alcohols and 3D structures, and 42% for
oxide systems.",2311.01987v1
2023-11-06,Sub-5-nm Ultra-thin In$_2$O$_3$ Transistors for High-Performance and Low-Power Electronic Applications,"Ultra-thin (UT) oxide semiconductors are promising candidates for
back-end-of-line (BEOL) compatible transistors and monolithic three-dimensional
integration. Experimentally, UT indium oxide (In$_2$O$_3$) field-effect
transistors (FETs) with thicknesses down to 0.4 nm exhibits extremely high
drain current (10000 $\mu$A/$\mu$m) and transconductance (4000 $\mu$S/$\mu$m).
Here, we employ the ab initio quantum transport simulation to investigate the
performance limit of sub-5-nm gate length (Lg) UT In$_2$O$_3$ FET. Based on the
International Technology Roadmap for Semiconductors (ITRS) criteria for
high-performance (HP) devices, the scaling limit of UT In$_2$O$_3$ FETs can
reach 2 nm in terms of on-state current, delay time, and power dissipation. The
wide bandgap nature of UT In$_2$O$_3$ (3.15 eV) renders it a suitable candidate
for ITRS low-power (LP) electronics with Lg down to 3 nm. Both the HP and LP UT
In$_2$O$_3$ FETs exhibit superior energy-delay products as compared to other
common 2D semiconductors such as monolayer MoS2 and MoTe2. Our study unveils
the immense promise of UT In$_2$O$_3$ for both HP and LP device applications.",2311.02943v1
2023-11-08,"Interaction of monoclinic ZrO$_2$ grain boundaries with oxygen vacancies, Sn and Nb -- implications for the corrosion of Zr alloy fuel cladding","We used density-functional-theory simulations to examine the structural and
electronic properties of the $\Sigma 180{\deg}(100)[001] $ grain boundary in
monoclinic ZrO$_2$, which is a very low-energy (0.06Jm$^{-2}$) twin boundary
present in experimental oxide texture maps, with suggested special properties.
This equilibrium structure was compared with a metastable structure (with a
boundary energy of 0.32Jm$^{-2}$), which was considered to be representative of
a more general oxide boundary. The interaction of oxygen vacancies,
substitutional Sn and Nb defects (substituting host Zr sites) with both
structures - and their effect on the boundary properties - were examined. We
found that the equilibrium structure energetically favours V$_\textrm{O}^{2+}$
and Nb$_\textrm{Zr}^{2-}$, whereas the metastable structure favours
V$_\textrm{O}^{2+}$ and Sn$_\textrm{Zr}^{2-}$. Tin was further found to bind
strongly with oxygen vacancies in both structures, and introduce gap states in
the band gap of their electronic structure. Sn$_\textrm{Zr}^{2-}$ was, however,
found to increase the segregation preference of V$_\textrm{O}^{2+}$ for the
metastable structure, which might contribute to increased oxygen and electron
transport down this interface, and therefore other more general boundaries,
compared to the equilibrium structure of the studied monoclinic twin boundary.",2311.04667v1
2023-11-27,Initial Characterization of the First Speedster-EXD550 Event-Driven X-Ray Hybrid Complementary Metal-Oxide Semiconductor Detectors,"Future x-ray observatories will require imaging detectors with fast readout
speeds that simultaneously achieve or exceed the other high performance
parameters of x-ray charge-coupled devices (CCDs) used in many missions over
the past three decades. Fast readout will reduce the impact of pile-up in
missions with large collecting areas while also improving performance in other
respects like timing resolution. Event-driven readout, in which only pixels
with charge from x-ray events are read out, can be used to achieve these faster
operating speeds. Speedster-EXD550 detectors are hybrid complementary
metal-oxide semiconductor (CMOS) detectors capable of event-driven readout,
developed by Teledyne Imaging Sensors and Penn State University. We present
initial results from measurements of the first of these detectors,
demonstrating their capabilities and performance in both full-frame and
event-driven readout modes. These include dark current, read noise, gain
variation, and energy resolution measurements from the first two
engineering-grade devices.",2311.16270v2
2023-11-30,Design Space and Variability Analysis of SOI MOSFET for Ultra-Low Power Band-to-Band Tunneling Neurons,"Large spiking neural networks (SNNs) require ultra-low power and low
variability hardware for neuromorphic computing applications. Recently, a
band-to-band tunneling-based (BTBT) integrator, enabling sub-kHz operation of
neurons with area and energy efficiency, was proposed. For an ultra-low power
implementation of such neurons, a very low BTBT current is needed, so
minimizing current without degrading neuronal properties is essential. Low
variability is needed in the ultra-low current integrator to avoid network
performance degradation in a large BTBT neuron-based SNN. To address this, we
conducted design space and variability analysis in TCAD, utilizing a
well-calibrated TCAD deck with experimental data from GlobalFoundries 32nm
PD-SOI MOSFET. First, we discuss the physics-based explanation of the tunneling
mechanism. Second, we explore the impact of device design parameters on SOI
MOSFET performance, highlighting parameter sensitivities to tunneling current.
With device parameters' optimization, we demonstrate a ~20x reduction in BTBT
current compared to the experimental data. Finally, a variability analysis that
includes the effects of random dopant fluctuations (RDF), oxide thickness
variability (OTV), and channel-oxide interface traps DIT in the BTBT, SS, and
ON regimes of operation is shown. The BTBT regime shows high sensitivity to the
RDF and OTV as any variation in them directly modulates the tunnel length or
the electric field at the drain-channel junction, whereas minimal sensitivity
to DIT is observed.",2311.18577v1
2023-11-13,Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO3/SrTiO3 heterostructures,"Phonon polaritons are promising for infrared applications due to a strong
light-matter coupling and subwavelength energy confinement they offer. Yet, the
spectral narrowness of the phonon bands and difficulty to tune the phonon
polariton properties hinder further progress in this field. SrTiO3 - a
prototype perovskite oxide - has recently attracted attention due to two
prominent far-infrared phonon polaritons bands, albeit without any tuning
reported so far. Here we show, using cryogenic infrared near-field microscopy,
that long-propagating surface phonon polaritons are present both in bare SrTiO3
and in LaAlO3/SrTiO3 heterostructures hosting a two-dimensional electron gas.
The presence of the two-dimensional electron gas increases dramatically the
thermal variation of the upper limit of the surface phonon polariton band due
to temperature dependent polaronic screening of the surface charge carriers.
Furthermore, we demonstrate a tunability of the upper surface phonon polariton
frequency in LaAlO3/SrTiO3 via electrostatic gating. Our results suggest that
oxide interfaces are a new platform bridging unconventional electronics and
long-wavelength nanophotonics.",2312.03711v1
2023-12-08,A novel control strategy to neutralize heat source within solid oxide electrolysis cell (SOEC) under variable solar power conditions,"The integration of a solid oxide electrolysis cell (SOEC) with a photovoltaic
(PV) system presents a viable method for storing variable solar energy through
the production of green hydrogen. To ensure the SOEC's safety and longevity
amidst dramatic fluctuations in solar power, control strategies are needed to
limit the temperature gradients and rates of temperature change within the
SOEC. Recognizing that the reactant supply influences the current, a novel
control strategy is developed to modulate heat generation in the SOEC by
adjusting the fuel flow rate. The effectiveness of this strategy is assessed
through numerical simulations conducted on a coupled PV-SOEC system using
actual solar irradiance data, recorded at two-second intervals, to account for
rapid changes in solar exposure. The results indicate that conventional control
strategies, which increase airflow rates, are inadequate in effectively
suppressing the rate of temperature variation in scenarios of drastic solar
power changes. In contrast, our proposed strategy demonstrates successful
management of the SOEC's heat generation, thereby reducing the temperature
gradient and rate of variation within the SOEC to below 5 K/cm and 1 K/min,
respectively.",2312.04923v3
2024-01-10,Wafer-scale CMOS-compatible graphene Josephson field-effect transistors,"Electrostatically tunable Josephson field-effect transistors (JoFETs) are one
of the most desired building blocks of quantum electronics. JoFET applications
range from parametric amplifiers and superconducting qubits to a variety of
integrated superconducting circuits. Here, we report on graphene JoFET devices
fabricated with wafer-scale complementary metal-oxide-semiconductor (CMOS)
compatible processing based on wet transfer of chemical vapour deposited
graphene, atomic-layer-deposited Al$_{2}$O$_{3}$ gate oxide, and evaporated
superconducting Ti/Al source, drain, and gate contacts. By optimizing the
contact resistance down to $\sim$ 170 $\Omega \mu m$, we observe
proximity-induced superconductivity in the JoFET channels with different gate
lengths of 150 - 350 nm. The Josephson junction devices show reproducible
critical current $I_{\text{C}}$ tunablity with the local top gate. Our JoFETs
are in short diffusive limit with the $I_{\text{C}}$ reaching up to $\sim\,$3
$\mu A$ for a 50 $\mu m$ channel width. Overall, our successful demonstration
of CMOS-compatible 2D-material-based JoFET fabrication process is an important
step toward graphene-based integrated quantum circuits.",2401.05089v2
2024-01-14,Waveguide optical parametric amplifiers in silicon nitride with 2D graphene oxide films,"Optical parametric amplification (OPA) represents a powerful solution to
achieve broadband amplification in wavelength ranges beyond the scope of
conventional gain media, for generating high-power optical pulses, optical
microcombs, entangled photon pairs and a wide range of other applications.
Here, we demonstrate optical parametric amplifiers based on silicon nitride
(Si3N4) waveguides integrated with two-dimensional (2D) layered graphene oxide
(GO) films. We achieve precise control over the thickness, length, and position
of the GO films using a transfer-free, layer-by-layer coating method combined
with accurate window opening in the chip cladding using photolithography.
Detailed OPA measurements with a pulsed pump for the fabricated devices with
different GO film thicknesses and lengths show a maximum parametric gain of
~24.0 dB, representing a ~12.2 dB improvement relative to the device without
GO. We perform a theoretical analysis of the device performance, achieving good
agreement with experiment and showing that there is substantial room for
further improvement. This work represents the first demonstration of
integrating 2D materials on chips to enhance the OPA performance, providing a
new way of achieving high performance photonic integrated OPA by incorporating
2D materials.",2401.07198v1
2024-01-15,Crystallization Instead of Amorphization in Collision Cascades in Gallium Oxide,"Disordering of solids typically leads to amorphization, but polymorph
transitions, facilitated by favorable atomic rearrangements, may temporarily
help to maintain long-range periodicity in the solid state. In
far-from-equilibrium situations, such as atomic collision cascades, these
rearrangements may not necessarily follow a thermodynamically gainful path, but
may be kinetically limited. In this Letter, we focused on such crystallization
instead of amorphization in collision cascades in gallium oxide (\ce{Ga2O3}).
We determined the disorder threshold for irreversible $\beta$-to-$\gamma$
polymorph transition and explained why it results in elevating energy to that
of the $\gamma$-polymorph, which exhibits the highest polymorph energy in the
system below the amorphous state. Specifically, we demonstrate that upon
reaching the disorder transition threshold, the \ce{Ga}-sublattice kinetically
favors transitioning to the $\gamma$-like configuration, requiring
significantly less migration for \ce{Ga} atoms to reach the lattice sites
during post-cascade processes. As such, our data provide a consistent
explanation of this remarkable phenomenon and can serve as a toolbox for
predictive multi-polymorph fabrication.",2401.07675v3
2024-01-18,Iodine and Bromine Radical Reactions in Atmospheric Mercury Oxidation,"We investigate the atmospheric oxidation of mercury Hg(0) by halogens,
initiated by Br and I to yield Hg(I), and continued by I, Br, BrO, ClO, IO, NO2
and HO2 to yield Hg(II) or Hg(0) using computational methods with focus on
determining the impact of rising iodine levels. We calculate reaction
enthalpies and Gibbs free energies using the Coupled Cluster singlets,
doublets, and perturbative triplets method (CCSD(T)) with the ma-def2-TZVP
basis set and effective core potential to account for relativistic effects.
Additionally, we investigate the reaction kinetics using variational transition
state theory based on geometric scans of bond dissociations at the
CASPT2/ma-def2-TZVP level. We compare the results obtained from the CASPT2 and
CCSD(T) methods to help define the uncertainty. Our results provide insights
into the mechanisms of these reactions and their implications for mercury
depletion events and for the atmosphere as a whole. The reaction HgBr + Br ->
HgBr2 was found to be twice as fast as HgI + I -> HgI2, with reaction rate
coefficients of 8.8x10^-13 and 4.2x10^-13 cm^3 molecule^-1 s^-1 respectively.
The BrHg + BrO -> BrHgOBr reaction was about 7.2 times faster than the HgI + IO
-> IHgOI reaction with their rates being 3.3x10^-14 and 4.6x10^-15 cm^3
molecule^-1 s^-1 respectively. We investigate the HgXOY (X and Y=halogen)
complexes. We find that rising iodine levels will lead to shortened mercury
lifetime due to the impact of the HgI + I -> HgI2 reaction.",2401.10053v1
2024-01-25,Atomic multiplet and charge-transfer screening effects in 1$s$ and 2$p$ core-level X-ray photoelectron spectra of early 3$d$ transition-metal oxides,"We present a comparative analysis of 1$s$ and 2$p$ core-level hard X-ray
photoelectron spectroscopy (HAXPES) spectra in metallic VO$_2$ and CrO$_2$.
Even though the V 1$s$ and 2$p$ spectra in VO$_2$ display similar line shapes
except the absence or presence of a spin-orbit coupling splitting, the Cr 1$s$
and 2$p$ spectra exhibit distinct main-line shapes. The experimental HAXPES
spectra are analyzed by the Anderson impurity model based on the density
functional theory + dynamical mean-field theory and a conventional MO$_6$
cluster model. We elucidate the complex interplay between formation of the
intra-atomic multiplet and charge transfer effect on the chemical bonding
followed by the 1$s$ and 2$p$ core electron excitations. We demonstrate the
advantage of the 1$s$ excitations to the routinely-employed 2$p$ excitations
for distinguishing between metal-ligand and metal-metal charge transfer
contributions in early 3$d$ transition-metal oxides.",2401.13951v2
2024-01-25,A facile one-pot hydrothermal synthesis as an efficient method to modulate the potassium content of cryptomelane and its effects on the redox and catalytic properties,"Cryptomelane has been widely applied as catalyst in oxidation reactions due
to its excellent redox properties and low cost. Here, a novel one-pot
hydrothermal synthesis using a potassium permanganate aqueous solution as
precursor and ethanol as reducing agent has successfully been developed to
obtain cryptomelane nano-oxides. This synthetic route makes it possible to
control the amount of potassium incorporated into the structure of the
cryptomelane by selecting the appropriate synthesis temperature and ethanol
initial concentration. Taking advantage of this approach, the effect of
potassium concentration on the structural stability and reducibility of the
cryptomelane, which are poorly discussed in the literature, has been studied.
We have observed that samples with low content of potassium (~11%) show high
conversions of CO to CO2 especially at low temperatures. The lower activity of
the samples with high K contents (~16%) can be ascribed to the beneficial
effect of K on the structural stability of cryptomelane in detriment of labile
oxygen on cryptomelane surface.",2401.14144v1
2024-02-05,Scanning tunnelling microscopy and X-ray photoemission studies of NdNiO2 infinite-layer nickelates films,"We report scanning tunnelling microscopy (STM) and x-ray photoemission
spectroscopy (XPS) measurements on uncapped and SrTiO3 (STO) capped NdNiO2
realized by pulsed-laser deposition and topotactic reduction process. We find
that untreated NdNiO2 surfaces are insulating and contain Ni mostly in a
nominal Ni2+ oxidation state. Room temperature STM shows signatures of a
striped-like topographic pattern, possibly compatible with recent reports of
ordered oxygen vacancies in uncapped nickelates due to incomplete oxygen
de-intercalation of the upper layers. A metallic surface and a full Ni1+
oxidation state is recovered by ultra high vacuum annealing at 250 C, as shown
by STM and XPS. STO-capped NdNiO2 films, on the other hand, show Ni mostly in
Ni1+ configuration, but Nd 3d5/2 core level spectra have a relevant
contribution from ligand 4f 4L states, suggesting the formation of a NdTiNiOx
layer at the interface with the STO. By in situ unit-cell by unit-cell Ar-ion
sputtering removal of the STO capping and of the non stoichiometric interface
layer, we were able to address the surface electronic properties of these
samples, as shown by high resolution valence band photoemission spectroscopy.
The results provide insights in the properties of infinite-layer NdNiO2 thin
films prepared by the CaH2 topotactic reduction of perovskite NdNiO3 and
suggest methods to improve their surface quality.",2402.03143v1
2024-02-06,Reducing two-level system dissipations in 3D superconducting Niobium resonators by atomic layer deposition and high temperature heat treatment,"Superconducting qubits have arisen as a leading technology platform for
quantum computing which is on the verge of revolutionizing the world's
calculation capacities. Nonetheless, the fabrication of computationally
reliable qubit circuits requires increasing the quantum coherence lifetimes,
which are predominantly limited by the dissipations of two-level system (TLS)
defects present in the thin superconducting film and the adjacent dielectric
regions. In this paper, we demonstrate the reduction of two-level system losses
in three-dimensional superconducting radio frequency (SRF) niobium resonators
by atomic layer deposition (ALD) of a 10 nm aluminum oxide Al2O3 thin films
followed by a high vacuum (HV) heat treatment at 650 {\deg}C for few hours. By
probing the effect of several heat treatments on Al2O3-coated niobium samples
by X-ray photoelectron spectroscopy (XPS) plus scanning and conventional high
resolution transmission electron microscopy (STEM/HRTEM) coupled with electron
energy loss spectroscopy (EELS) and (EDX) , we witness a dissolution of niobium
native oxides and the modification of the Al2O3-Nb interface, which correlates
with the enhancement of the quality factor at low fields of two 1.3 GHz niobium
cavities coated with 10 nm of Al2O3.",2402.04137v1
2024-02-07,Large Eddy Simulation of the evolution of the soot size distribution in turbulent nonpremixed bluff body flames,"Large Eddy Simulation (LES) was used to investigate the evolution of the soot
size distribution in a series of turbulent nonpremixed bluff body flames, with
different bluff body diameters. The new Bivariate Multi-Moment Sectional Method
(BMMSM) is employed to characterize the size distribution. BMMSM combines
elements of sectional methods and methods of moments and is capable of
reproducing fractal aggregate morphology, thanks to its joint volume-surface
formulation, all at relatively low computational costs with fewer transported
soot scalars compared to traditional sectional methods. LES results show soot
volume fraction profiles agreeing correctly with the experimental measurements,
exhibiting significant improvement compared to previous work using the HMOM.
The evolution of the particle size distribution function (PSDF) was examined
across the flame series and show that the size distribution is less sensitive
to the bluff body diameter than the overall soot volume fraction, which
increases with increasing bluff body diameter. The PSDF across the flame
exhibit different features compared to turbulent nonpremixed jet flames. The
long residence times in the recirculation zone leads to a nearly bimodal size
distribution, which eventually becomes bimodal in the downstream jet-like
region. Further analysis indicates that a size distribution model is needed to
correctly predict the soot evolution. Remarkably, due to improved descriptions
of oxidation with BMMSM compared to HMOM, significant nucleation and
condensation rates in both the recirculation zone and jet-like region were
found using BMMSM, on the same order of magnitude as surface growth and
oxidation, leading to the improved prediction of mean soot volume fraction
compared to HMOM. This work reveals that the need of size distribution is
crucial to both predict global soot quantities accurately and reproduce
fundamental mechanisms.",2402.04560v1
2024-02-07,Millimeter-scale freestanding superconducting infinite-layer nickelate membranes,"Progress in the study of infinite-layer nickelates has always been highly
linked to materials advances. In particular, the recent development of
superconductivity via hole-doping was predicated on the controlled synthesis of
Ni in a very high oxidation state, and subsequent topotactic reduction to a
very low oxidation state, currently limited to epitaxial thin films. Here we
demonstrate a process to combine these steps with a heterostructure which
includes an epitaxial soluble buffer layer, enabling the release of
freestanding membranes of (Nd,Sr)NiO2 encapsulated in SrTiO3, which serves as a
protective layer. The membranes have comparable structural and electronic
properties to that of optimized thin films, and range in lateral dimensions
from millimeters to ~100 micron fragments, depending on the degree of strain
released with respect to the initial substrate. The changes in the
superconducting transition temperature associated with membrane release are
quite similar to those reported for substrate and pressure variations,
suggestive of a common underlying mechanism. These membranes structures should
provide a versatile platform for a range of experimental studies and devices
free from substrate constraints.",2402.05104v1
2024-02-08,"Photo-Activated, Solid-State Introduction of Luminescent Oxygen Defects into Semiconducting Single-Walled Carbon Nanotubes","Oxygen defects in semiconducting single-walled carbon nanotubes (SWCNTs) are
localized disruptions in the carbon lattice caused by the formation of epoxy or
ether groups, commonly through wet-chemical reactions. The associated
modifications of the electronic structure can result in luminescent states with
emission energies below those of pristine SWCNTs in the near-infrared range,
which makes them promising candidates for applications in biosensing and as
single-photon emitters. Here, we demonstrate the controlled introduction of
luminescent oxygen defects into networks of monochiral (6,5) SWCNTs using a
solid-state photocatalytic approach. UV irradiation of SWCNTs on the
photoreactive surfaces of the transition metal oxides TiOx and ZnOx in the
presence of trace amounts of water and oxygen results in the creation of
reactive oxygen species that initiate radical reactions with the carbon lattice
and the formation of oxygen defects. The created ether-d and epoxide-l defect
configurations give rise to two distinct red-shifted emissive features. The
chemical and dielectric properties of the photoactive oxides influence the
final defect emission properties, with oxygen-functionalized SWCNTs on TiOx
substrates being brighter than those on ZnOx or pristine SWCNTs on glass. The
photoinduced functionalization of nanotubes is further employed to create
lateral patterns of oxygen defects in (6,5) SWCNT networks with micrometer
resolution and thus spatially controlled defect emission.",2402.05572v1
2024-02-12,Graphene Oxide and Polymer Humidity Micro-Sensors Prepared by Carbon Beam Writing,"In this study, novel flexible micro-scale humidity sensors were directly
fabricated in graphene oxide (GO) and polyimide (PI) using ion beam writing
without any further modifications, and then successfully tested in an
atmospheric chamber. Two low fluences of carbon ions with an energy of 5 MeV
were used, and structural changes in the irradiated materials were expected.
The shape and structure of prepared micro-sensors were studied using scanning
electron microscopy (SEM). The structural and compositional changes in the
irradiated area were characterized using micro-Raman spectroscopy, X-ray
photoelectron spectroscopy (XPS), Rutherford back-scattering spectroscopy
(RBS), energy-dispersive X-ray spectroscopy (EDS), and elastic recoil detection
analysis (ERDA) spectroscopy. The sensing performance was tested at a relative
humidity (RH) ranging from 5 % to 60 %, where the electrical conductivity of PI
varied by three orders of magnitude, and the electrical capacitance of GO
varied in the order of pico-farads. In addition, the PI sensor has proven
long-term sensing stability in air. We demonstrated a novel method of ion
micro-beam writing to prepare flexible micro-sensors that function over a wide
range of humidity and have good sensitivity and great potential for widespread
applications.",2402.07651v1
2024-02-20,Are boron-nitride nanobelts capable to capture greenhouse gases?,"Why is the question in the title pertinent? Toxic gases, which are
detrimental to both human health and the environment, have been released in
greater quantities as a result of industrial development. These gases
necessitate capture, immobilization, and measurement. Consequently, the present
study investigates the interactions between boron-nitride nanobelt and
M\""obius-type boron-nitride nanobelt and nine greenhouse gases, namely ammonia,
carbon dioxide, carbon monoxide, hydrogen sulfide, methane, methanol, nitric
dioxide, nitric oxide, and phosgene. The adsorption energies calculated for the
structures with optimized geometry are all negative, suggesting that all gases
are adsorbed favorably in both nanobelts. Furthermore, we discovered that the
recovery time of the sensors ranges from two hours to a few nanoseconds, and
that the nanobelts exhibit distinct responses to each gas. According to
electronic and topological investigations, covalent bonds were exclusively
formed by nitric oxide; the remaining gases formed non-covalent bonds.
Molecular dynamics ultimately demonstrate that the interaction between a single
gas molecule and the nanobelt remains consistent across the vast majority of
gases, whereas the interaction between 500 gas molecules and the nanobelts
functions as an attraction, notwithstanding the impact of volumetric effects
characteristic of high volume gases on the interaction. For the completion of
each calculation, semiempirical tight-binding methods were implemented
utilizing the xTB software. The outcomes of our study generated a favorable
response to the inquiry posed in the title.",2402.13102v1
2024-02-23,Effect of temperature and copper doping on the heterogeneous Fenton-like activity of Cu$_x$Fe$_{3-x}$O$_4$ nanoparticles,"Ferrite nanoparticles serve as potent heterogeneous Fenton-like catalysts,
producing reactive oxygen species (ROS) for decomposing organic pollutants. We
investigated the impact of temperature and copper content on the catalytic
activity of nanoparticles with different oxidation states of iron. Via
solvothermal synthesis, we fabricated copper-doped magnetite
(Cu$_x$Fe$_{3-x}$O$_4$) with a Fe$^{2+}$/Fe ratio ~0.33 for the undoped system.
Using a microwave-assisted method, we produced copper-doped oxidized ferrites,
yielding a Fe$^{2+}$/Fe ratio of ~0.11 for the undoped nanoparticles. The ROS
generated by the catalyst were identified and quantified by electron
paramagnetic resonance, while optical spectroscopy allowed us to evaluate its
effectiveness for the degradation of a model organic dye. At room temperature,
the magnetite nanoparticles exhibited the most $\cdot$OH radical production and
achieved almost 90% dye discoloration in 2 hours. This efficiency decreased
with increasing Cu concentration, concurrently with a decrease in $\cdot$OH
generation. Conversely, above room temperature, Cu-doped nanoparticles
significantly enhance the dye degradation, reaching 100% discoloration at
90$^\circ$C. This enhancement is accompanied by a systematic increase in the
kinetic constants, obtained from reaction equations, with Cu doping. This study
highlights the superior stability and high-temperature catalytic advantages of
copper ferrite holding promise for enhancing the performance of nanocatalysts
for decomposing organic contaminants.",2402.15338v1
2024-02-23,Two-dimensional photonic crystal cavities in ZnSe quantum well structures,"ZnSe and related materials like ZnMgSe and ZnCdSe are promising II-VI host
materials for optically mediated quantum information technology such as single
photon sources or spin qubits. Integrating these heterostructures into photonic
crystal (PC) cavities enables further improvements, for example realizing
Purcell-enhanced single photon sources with increased quantum efficiency. Here
we report on the successful implementation of two-dimensional (2D) PC cavities
in strained ZnSe quantum wells (QW) on top of a novel AlAs supporting layer.
This approach overcomes typical obstacles associated with PC membrane
fabrication in strained materials, such as cracks and strain relaxation in the
corresponding devices. We demonstrate the attainment of the required mechanical
stability in our PC devices, complete strain retainment and effective vertical
optical confinement. Structural analysis of our PC cavities reveals excellent
etching anisotropy. Additionally, elemental mapping in a scanning transmission
electron microscope confirms the transformation of AlAs into AlOx by
post-growth wet oxidation and reveals partial oxidation of ZnMgSe at the etched
sidewalls in the PC. This knowledge is utilized to tailor FDTD simulations and
to extract the ZnMgSe dispersion relation with small oxygen content. Optical
characterization of the PC cavities with cross-polarized resonance scattering
spectroscopy verifies the presence of cavity modes. The excellent agreement
between simulation and measured cavity mode energies demonstrates wide
tunability of the PC cavity and proves the pertinence of our model. This
implementation of 2D PC cavities in the ZnSe material system establishes a
solid foundation for future developments of ZnSe quantum devices.",2402.15349v1
2024-03-01,"Characterization of process-related interfacial dielectric loss in aluminum-on-silicon by resonator microwave measurements, materials analysis, and imaging","We systematically investigate the influence of the fabrication process on
dielectric loss in aluminum-on-silicon superconducting coplanar waveguide
resonators with internal quality factors ($Q_i$) of about one million at the
single-photon level. These devices are essential components in superconducting
quantum processors; they also serve as proxies for understanding the energy
loss of superconducting qubits. By systematically varying several fabrication
steps, we identify the relative importance of reducing loss at the
substrate-metal and the substrate-air interfaces. We find that it is essential
to clean the silicon substrate in hydrogen fluoride (HF) prior to aluminum
deposition. A post-fabrication removal of the oxides on the surface of the
silicon substrate and the aluminum film by immersion in HF further improves the
$Q_i$. We observe a small, but noticeable, adverse effect on the loss by
omitting either standard cleaning (SC1), pre-deposition heating of the
substrate to 300$\deg$C, or in-situ post-deposition oxidation of the film's top
surface. We find no improvement due to excessive pumping meant to reach a
background pressure below $6{\times} 10^{-8}$ mbar. We correlate the measured
loss with microscopic properties of the substrate-metal interface through
characterization with X-ray photoelectron spectroscopy (XPS), time-of-flight
secondary ion mass spectroscopy (ToF-SIMS), transmission electron microscopy
(TEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy
(AFM).",2403.00723v1
2024-03-06,The Geochemical Potential for Metabolic Processes on the Sub-Neptune Exoplanet K2-18b,"Quantifying disequilibria is important to understand whether an environment
could be habitable. It has been proposed that the exoplanet K2-18b has a
hydrogen-rich atmosphere and a water ocean, making it a ""hycean world"". The
James Webb Space Telescope recently made measurements of methane, CO$_2$, and
possibly dimethyl sulfide (DMS) in the atmosphere of this planet. The initial
interpretation of these data is that they may support the occurrence of hycean
conditions. Here, I attempt to take a next step in exploring the prospects for
habitability. I use constraints on the abundances of atmospheric gases to
calculate how much chemical disequilibrium there could be, assuming K2-18b is a
hycean world. I find that the presence of oxidized carbon species coexisting
with abundant H$_2$ (1-1000 bar) at cool to warm (25-120{\deg}C) conditions
creates a strong thermodynamic drive for methanogenesis. More than ~75 kJ (mol
C)$^{-1}$ of free energy can be released from CO$_2$ hydrogenation. Partially
oxidized carbon compounds such as DMS (if present) also have potential to
provide metabolic energy, albeit in smaller quantities. Because of the
thermodynamic instability of CO$_2$ under hycean conditions, other reductive
reactions of CO$_2$ are likely to be favored, including the synthesis of amino
acids. Glycine and alanine synthesis can be energy-releasing or at least much
less costly on K2-18b than in Earth's ocean, even when NH$_3$ is scarce but not
totally absent. These first bioenergetic calculations for a proposed
ocean-bearing exoplanet lay new groundwork for assessing exoplanetary
habitability.",2403.03918v1
2024-03-13,Highly confined epsilon-near-zero- and surface-phonon polaritons in SrTiO3 membranes,"Recent theoretical studies have suggested that transition metal perovskite
oxide membranes can enable surface phonon polaritons in the infrared range with
low loss and much stronger subwavelength confinement than bulk crystals. Such
modes, however, have not been experimentally observed so far. Here, using a
combination of far-field Fourier-transform infrared (FTIR) spectroscopy and
near-field synchrotron infrared nanospectroscopy (SINS) imaging, we study the
phonon-polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3
transferred on metallic and dielectric substrates. We observe a
symmetric-antisymmetric mode splitting giving rise to epsilon-near-zero and
Berreman modes as well as highly confined (by a factor of 10) propagating
phonon polaritons, both of which result from the deep-subwavelength thickness
of the membranes. Theoretical modeling based on the analytical finite-dipole
model and numerical finite-difference methods fully corroborate the
experimental results. Our work reveals the potential of oxide membranes as a
promising platform for infrared photonics and polaritonics.",2403.08500v1
2024-03-25,Recent advances on CO2-assisted synthesis of metal nanoparticles for the upgrading of biomass-derived compounds,"Nanostructured catalysts have attracted the increased attention for biomass
conversion into high-valued chemicals due to the rapid depletion of fossil
resources and increasingly severe environmental issues. Supercritical carbon
dioxide (scCO2) fluid is an attractive medium for synthesizing nanostructured
materials due to its favorable properties. In this review, the properties of
scCO2 and the roles of scCO2 in the fabrication of metal nanoparticles were
assessed in detailed. A general overview of the synthesis of different types of
metal nanoparticles (including metal oxide nanoparticles) using scCO2 and the
relationship between the structure of the obtained metal nanoparticles and the
preparation conditions such as reaction temperature and pressure, types of
metal precursors, and deposition time are system summarized and compared in
tables. Besides, compared to the meatal catalysts using the conventional
methods, the catalysts obtained using scCO2 exhibited excellent catalytic
performance on biomass conversion reactions, mainly focused on oxidation,
hydrogenation reactions. Finally, opportunities and challenges of metal
nanoparticle preparation using scCO2 for biomass valorization to chemicals and
liquid fuels are highlighted. This review could be helpful for the rational
design of more efficient metal catalysts for the selective synthesis of fine
chemicals and fuels from biomass-derived chemicals.",2403.16751v1
2024-03-26,Recent advances on the spherical metal oxides for sustainable degradation of antibiotics,"Due to the permanent harm to human health and ecosystem balance, antibiotic
pollution in water has become an important direction of current environmental
governance. Spherical metal oxides (SMOs) have been frequently utilized as
effective heterogeneous photocatalysts for the efficient degradation of
antibiotics due to the unique properties (e.g., strong light absorption
ability, high separation efficiency of photo-generated electron hole pairs, and
good catalytic activity). This review will firstly focus on summarizing the
rational design and synthesis of SMOs with various tuned microstructures such
as hollow, porous shell, yolk shell, core shell, and nanoflowers. These
structures can expose more active sites, achieve a higher utilization rate of
light, enhance the mass transfer efficiency and improve the effective diffusion
of reactive oxygen species (ROS). Secondly, this review will mainly analyze the
intrinsic relationship between the structure of SMOs and its photocatalytic
property, the ability to generate ROS, and the degradation pathway for
antibiotics. Moreover, the photocatalytic mechanisms and recent progress of
different SMOs catalysts for degrading typical antibiotics are compared in
detail. Finally, challenges and prospects of future direction in the
development of SMOs for antibiotic degradation are reviewed. It is expected to
provide a rational design of SMOs catalysts for efficient photocatalytic
degradation of environmental pollutants.",2403.17316v1
2002-05-12,The Role of Magnetic Helicity Transport in Nonlinear Galactic Dynamos,"We consider the magnetic helicity balance for the galactic dynamo in the
framework of the local dynamo problem, as well as in the no-z model (which
includes explicitly the radial distribution of the magnetic fields). When
calculating the magnetic helicity balance we take into account the
redistribution of the small-scale and large-scale magnetic fields between the
magnetic helicities, as well as magnetic helicity transport and diffusion due
to small-scale turbulence. We demonstrate that the magnetic helicity flux
through the galactic disc boundaries leads to a steady-state magnetic field
with magnetic energy comparable to the equipartition energy of the turbulent
motions of the interstellar medium. If such flux is ignored, the steady-state
magnetic field is found to be much smaller than the equipartition field. The
total magnetic helicity flux through the boundaries consists of both an
advective flux and a diffusive flux. The exact ratio of these contributions
seems not to be crucial for determining the strength of the steady-state
magnetic field and its structure. However at least some diffusive contribution
is needed to smooth the magnetic helicity profile near to the disc boundaries.
The roles of various transport coefficients for magnetic helicity are
investigated, and the values which lead to magnetic field configurations
comparable with those observed are determined.",0205165v1
2004-01-22,The magnetic field of pulsars and the gravito-magnetic theory,"Many authors have considered a gravitational origin of the magnetic field of
celestial bodies. Especially, the so-called Wilson-Blackett formula has been
investigated, both theoretically and observationally. It appeared possible to
deduce this formula from general relativity, e. g., by application of a special
interpretation of gravito-magnetic theory. More consequences of the latter
theory for pulsars will be considered in this work. As an example, the standard
quadrupolar charge density for pulsars can be deduced from the gravito-magnetic
theory. Moreover, a new magnetic dipole moment from electromagnetic origin is
found, generated in the basic magnetic field from gravito-magnetic origin. In
general, for thirteen accreting, slowly rotating, binary pulsars the agreement
between the observed magnetic field and the gravito-magnetic prediction is
better than between the observed value and the value from the standard magnetic
dipole radiation model. At present, an analogous comparison for five isolated
pulsars appears to be difficult. For a sample of 100 pulsars the averaged
(gravito-)magnetic field, extracted from the magnetic dipole spin-down model,
is in fair agreement with the gravito-magnetic prediction. Unfortunately, the
(gravito-)magnetic field has not yet directly been measured. Finally, it is
found that the first and second order braking indices only depend on the
magnetic field from electromagnetic origin.",0401468v1
2001-08-29,The Finite Energy Constant Magnetization of the Two - Dimensional Ising Model,"We suggest the new definition of the magnetization. For the two - dimensional
Ising model with the free boundary conditions we calculate any derivative of
this magnetization for zero magnetic field.",0108489v1
2002-07-08,The Magnetization by the Finite Energy Constant Magnetic Field in the Two - Dimentional Ising Model,"We suggest the new definition of the magnetization. For the two - dimensional
Ising model with the free boundary conditions we calculate this magnetization.",0207200v1
2009-11-12,Coherent states in the presence of a variable magnetic field,"We introduce magnetic coherent states for a particle in a variable magnetic
field. They provide a pure state quantization of the phase space R^{2N} endowed
with a magnetic symplectic form.",0911.2451v1
2010-06-07,Solitary Magnetic Bubbles,"Stability and attractor property of free-floating axisymmetric magnetic
bubbles in high-conductivity plasmas is (tentatively, numerically)
demonstrated. The existence of compact non-singular axisymmetric magnetic
equilibria is proved. Being attractors, the solitary magnetic bubbles should
exist in nature.",1006.1368v1
2011-06-18,Magnetic curves corresponding to Killing magnetic fields in $E^3$,"We explicitly determine all magnetic curves corresponding to the Killing
magnetic fields on the 3-dimensional Euclidean space.",1106.3673v1
2012-09-27,Growth of a localized seed magnetic field in a turbulent medium,"Turbulence dynamo deals with amplification of a seed magnetic field in a
turbulent medium and has been studied mostly for uniform or spatially
homogeneous seed magnetic fields. However, some astrophysical processes (e.g.
jets from active galaxies, galactic winds, or ram-pressure stripping in galaxy
clusters) can provide localized seed magnetic fields. In this paper, we
numerically study amplification of localized seed magnetic fields in a
turbulent medium. Throughout the paper, we assume that driving scale of
turbulence is comparable to the size of the system. Our findings are as
follows. First, turbulence can amplify a localized seed magnetic field very
efficiently. The growth rate of magnetic energy density is as high as that for
a uniform seed magnetic field. This result implies that a magnetic field
ejected from an astrophysical object can be a viable source of magnetic field
in a cluster. Second, the localized seed magnetic field disperses and fills the
whole system very fast. If turbulence in a system (e.g. a galaxy cluster or a
filament) is driven at large scales, we expect that it takes a few large-eddy
turnover times for magnetic field to fill the whole system. Third, growth and
turbulence diffusion of a localized seed magnetic field are also fast in high
magnetic Prandtl number turbulence. Fourth, even in decaying turbulence, a
localized seed magnetic field can ultimately fill the whole system. Although
the dispersal rate of magnetic field is not fast in purely decaying turbulence,
it can be enhanced by an additional forcing.",1209.6130v1
2013-01-28,Two-dimensional Ising model in a finite magnetic field for the square lattice of infinite sites-Partition function and Magnetization,"The partition function and magnetization equations are derived for the
two-dimensional nearest neighbour Ising models in a magnetic field.",1302.1084v1
2014-07-08,Competing magnetic phases and field-induced dynamics in DyRuAsO,"Analysis of neutron diffraction, dc magnetization, ac magnetic
susceptibility, heat capacity, and electrical resistivity for DyRuAsO in an
applied magnetic field are presented at temperatures near and below those at
which the structural distortion (T_S = 25 K) and subsequent magnetic ordering
(T_N = 10.5 K) take place. Powder neutron diffraction is used to determine the
antiferromagnetic order of Dy moments of magnitude 7.6(1) mu_B in the absence
of a magnetic field, and demonstrate the reorientation of the moments into a
ferromagnetic configuration upon application of a magnetic field. Dy magnetism
is identified as the driving force for the structural distortion. The magnetic
structure of analogous TbRuAsO is also reported. Competition between the two
magnetically ordered states in DyRuAsO is found to produce unusual physical
properties in applied magnetic fields at low temperature. An additional phase
transition near T* = 3 K is observed in heat capacity and other properties in
fields greater than about 3 T. Magnetic fields of this magnitude also induce
spin-glass-like behavior including thermal and magnetic hysteresis, divergence
of zero-field-cooled and field-cooled magnetization, frequency dependent
anomalies in ac magnetic susceptibility, and slow relaxation of the
magnetization. This is remarkable since DyRuAsO is a stoichiometric material
with no disorder detected by neutron diffraction, and suggests analogies with
spin-ice compounds and related materials with strong geometric frustration.",1407.2184v1
2017-03-30,Relative magnetic helicity as a diagnostic of solar eruptivity,"The discovery of clear criteria that can deterministically describe the
eruptive state of a solar active region would lead to major improvements on
space weather predictions. Using series of numerical simulations of the
emergence of a magnetic flux rope in a magnetized coronal, leading either to
eruptions or to stable configurations, we test several global scalar quantities
for the ability to discriminate between the eruptive and the non-eruptive
simulations. From the magnetic field generated by the three-dimensional
magnetohydrodynamical simulations, we compute and analyse the evolution of the
magnetic flux, of the magnetic energy and its decomposition into potential and
free energies, and of the relative magnetic helicity and its decomposition.
Unlike the magnetic flux and magnetic energies, magnetic helicities are able to
markedly distinguish the eruptive from the non-eruptive simulations. We find
that the ratio of the magnetic helicity of the current-carrying magnetic field
to the total relative helicity presents the highest values for the eruptive
simulations, in the pre-eruptive phase only. We observe that the eruptive
simulations do not possess the highest value of total magnetic helicity. In the
framework of our numerical study, the magnetic energies and the total relative
helicity do not correspond to good eruptivity proxies. Our study highlights
that the ratio of magnetic helicities diagnoses very clearly the eruptive
potential of our parametric simulations. Our study shows that
magnetic-helicity-based quantities may be very efficient for the prediction of
solar eruptions.",1703.10562v1
2018-11-30,Double bit in-plane magnetic skyrmions on a track,"A magnetic skyrmion isusually refers to a twisted spin texture surrounded by
uniformly aligned out-of-plane spinsin the background of a uniformly magnetized
state. The invariance of the magnetic skyrmion conserves its topological charge
under any continuous transformations of the spin textures, leads to which
represents the robustness of a magnetic skyrmion their texture against external
perturbations, making it ideal to use skyrmions as . Such a behaviour is
required for an ideal information carriers. To date, most magnetic skyrmion
studies have been performedfocused on in perpendicularly magnetized systems,
where the skyrmion topological number is determined by the relative orientation
between the core and /outer perpendicular magnetization directions of the
skyrmion is either up/down or down/up. Here we show that there also exists a
new type of magnetic skyrmion with surrounding spins to be uniformly aligned to
the in-plane direction. By continuous transformation and relaxation of the spin
textures of out-of-plane skyrmions, we showed that an in-plane skyrmion, where
the background magnetization is in the in-plane direction, is also possible.
Different from the conventional perpendicular magnetic skyrmionsContrary to the
skyrmions in a perpendicularly magnetized state, the in-plane magnetic
skyrmions with opposite signs of topological charges can inherentlycharges can
inherently coexist in the in-plane magnetization system coexist. Moreover, the
iIn-plane skyrmions of opposite charge can move together by an electric current
and exhibit with an opposite spin Hall effect. These findings showdemonstrate
the inherent possibility of a double-bit transfer in a single magnetic wire
that is not possible in a perpendicularly magnetized system.",1811.12552v1
2020-07-26,Effect of the anomalous magnetic moment of quarks on magnetized QCD matter and meson spectra,"We systematically investigate the effect of the anomalous magnetic
moment(AMM) of quarks on the magnetized QCD matter, including the magnetic
susceptibility, the inverse magnetic catalysis around the critical temperature
and the neutral/charged pion and rho meson spectra under magnetic fields. The
dynamical AMM of quarks, its coupling with magnetic field causes Zeeman
splitting of the dispersion relation of quarks thus changes the magnetism
properties and meson mass spectra under magnetic fields. It is found that
including the AMM of quarks cannot fully understand lattice results of the
magnetized matter: The AMM of quarks reduces the dynamical quark mass thus
causes the inverse magnetic catalysis around $T_c$. The neutral pion mass is
very sensitive to the AMM, it decreases with magnetic field quickly, and the
charged pion mass shows a nonlinear behavior, i.e., firstly linearly increases
with the magnetic field and then saturates at strong magnetic field. For rho
meson, it is observed that AMM reduces the mass of neutral rho meson mass with
different $s_z$, and reduces the mass of $s_z=+1,0$ component charged rho meson
mass but enhances the $s_z=-1$ component charged rho meson mass. The magnetic
susceptibility at low temperature can be either positive or negative with
different AMM.",2007.13122v3
2012-01-13,Development for Hardware for Programming of Spatial Magnetic Field Distributions in Nuclear Magnetic Resonance and Magnetic Resonance Imaging,"The proposal of a project aimed on a design of hardware for programming 3D
Magnetic Field shapes over sample volume in NMR and MRI is described.",1201.2764v1
2016-08-16,Magnetic Dirichlet Laplacian with radially symmetric magnetic field,"The aim of the paper is to derive spectral estimates on the eigenvalue
moments of the magnetic Dirichlet Laplacian defined on the two-dimensional disk
with a radially symmetric magnetic field.",1608.04555v1
2017-12-26,Evolution of Relative Magnetic Helicity: New Boundary Conditions for the Vector Potential,"We recently proposed a method to calculate the relative magnetic helicity in
a finite volume for a given magnetic field which however required the flux to
be balanced separately on all the sides of the considered volume. In order to
allow finite magnetic fluxes through the boundaries, a Coulomb gauge is
constructed that allows for global magnetic flux balance. We tested and
verified our method in a theoretical fore-free magnetic field model. We apply
the new method to the former calculation data and found a difference of less
than 1.2\%. We also applied our method to the magnetic field above active
region NOAA 11429 obtained by a new photospheric-data-driven MHD model code
GOEMHD3. We analyzed the magnetic helicity evolution in the solar corona using
our new method. It was found that the normalized magnetic helicityis equal to
-0.038 when fast magnetic reconnection is triggered. This value is comparable
to the previous value (-0.029) in the MHD simulations when magnetic
reconnection happened and the observed normalized magnetic helicity (-0.036)
from the eruption of newly emerging active regions. We found that only 8\% of
the accumulated magnetic helicity is dissipated after it is injected through
the bottom boundary. This is in accordance with the Woltjer conjecture. Only
2\% of magnetic helicity injected from the bottom boundary escapes through the
corona. This is consistent with the observation of magnetic clouds, which could
take away magnetic helicity into the interplanetary space, in the case
considered here, several halo CMEs and two X-class solar flares origin from
this active region.",1712.09219v1
2019-10-13,A systematically study of thermal width of heavy quarkonia in a finite temperature magnetized background from holography,"By simulating the finite temperatures magnetized background in the RHIC and
LHC energies, we systematically study the characteristics of thermal widths and
potentials of heavy quarkonia. It is found that the magnetic field has less
influence on the real potential, but has a significant influence on the
imaginary potential, especially in the low deconfined temperature. Extracted
from the effect of thermal worldsheet fluctuations about the classical
configuration, the thermal width of $\Upsilon(1s)$ in the finite temperature
magnetized background is investigated. It is found that at the low deconfined
temperature the magnetic field can generate a significant thermal fluctuation
of the thermal width of $\Upsilon(1s)$, but with the increase of temperature,
the effect of magnetic field on the thermal width becomes less important, which
means the effect of high temperature completely exceeds that of magnetic field
and magnetic field become less important at high temperature. The thermal width
decreases with the increasing rapidity at the finite temperature magnetized
background. It is also observed that the effect of the magnetic field on the
thermal width when dipole moving parallel to the magnetic field direction are
larger than that moving perpendicular to the magnetic field direction, which
implies that the magnetic field tends to enhance thermal fluctuation when
dipole moving parallel to the direction of magnetic field. The thermal width of
$\Upsilon(1S)$ hardly changes with the increasing temperature when dipole
moving perpendicular to the magnetic field. But when dipole moving parallel to
the magnetic field, the thermal width at low temperature is obviously larger
than that at high temperature.",1910.05668v1
2017-05-17,Magnetic Transport in Spin Antiferromagnets for Spintronics Applications,"Had magnetic monopoles been ubiquitous as electrons are, we would probably
have had a different form of matter, and power plants based on currents of
these magnetic charges would have been a familiar scene of modern technology.
Magnetic dipoles do exist, however, and in principle one could wonder if we can
use them to generate magnetic currents. In the present work, we address the
issue of generating magnetic currents and magnetic thermal currents in
electrically-insulating low-dimensional Heisenberg antiferromagnets by invoking
the (broken) electricity-magnetism duality symmetry. The ground state of these
materials is a spin-liquid state that can be described well via~the
Jordan--Wigner fermions, which permit an easy definition of the magnetic
particle and thermal currents. The magnetic and magnetic thermal conductivities
are calculated in the present work using the bond--mean field theory. The
spin-liquid states in these antiferromagnets are either gapless or gapped
liquids of spinless fermions whose flow defines a current just as the one
defined for electrons in a Fermi liquid. The driving force for the magnetic
current is a magnetic field with a gradient along the magnetic conductor. We
predict the generation of a magneto-motive force and realization of magnetic
circuits using low-dimensional Heisenberg antiferromagnets. The present work is
also about claiming that what the experiments in spintronics attempt to do is
trying to treat the magnetic degrees of freedoms on the same footing as the
electronic ones.",1705.06318v2
2020-03-18,On the saturation mechanism of the fluctuation dynamo at ${\text{Pr}_\mathrm{M}} \ge 1$,"The presence of magnetic fields in many astrophysical objects is due to
dynamo action, whereby a part of the kinetic energy is converted into magnetic
energy. A turbulent dynamo that produces magnetic field structures on the same
scale as the turbulent flow is known as the fluctuation dynamo. We use
numerical simulations to explore the nonlinear, statistically steady state of
the fluctuation dynamo in driven turbulence. We demonstrate that as the
magnetic field growth saturates, its amplification and diffusion are both
affected by the back-reaction of the Lorentz force upon the flow. The
amplification of the magnetic field is reduced due to stronger alignment
between the velocity field, magnetic field, and electric current density.
Furthermore, we confirm that the amplification decreases due to a weaker
stretching of the magnetic field lines. The enhancement in diffusion relative
to the field line stretching is quantified by a decrease in the computed local
value of the magnetic Reynolds number. Using the Minkowski functionals, we
quantify the shape of the magnetic structures produced by the dynamo as
magnetic filaments and ribbons in both kinematic and saturated dynamos and
derive the scalings of the typical length, width, and thickness of the magnetic
structures with the magnetic Reynolds number. We show that all three of these
magnetic length scales increase as the dynamo saturates. The magnetic
intermittency, strong in the kinematic dynamo (where the magnetic field
strength grows exponentially) persists in the statistically steady state, but
intense magnetic filaments and ribbons are more volume-filling.",2003.07997v1
2021-09-03,"Investigating the Magnetic Field outside small Accelerator Magnet Analogs via Experiment, Simulation, and Theory","Particle accelerators use powerful and complex magnetic fields to turn,
shape, and eventually collide beams of near-light-speed particles, yet the
fundamental magnetic principles behind the accelerator magnets can be
understood by undergraduate students. In this paper we use small-scale
accelerator magnet analogs in a multi-faceted, low-cost exploration of the
magnetic field exterior to accelerator magnets. These fields are best
understood using the multipole expansion of the field. If we assume that the
magnetic field is created by ideal magnetic dipoles, we can derive a
theoretical model that shows that each accelerator magnet configuration is
dominated by a single multipole moment and obeys $B \propto 1/r^{l+2}$, where
$l$ is the multipole order (with $l = 1, 2, 3, 4$ for the dipole, quadrupole,
octopole, and hexadecapole moments, respectively). Using commercially available
NdFeB magnets and the magnetic field sensor inside a smartphone, we
experimentally verify the power-law dependence of the accelerator magnet
configurations. Finally, we use the open-source Python library Magpylib to
simulate the magnetic field of the permanent magnet configurations, showing
good agreement between theory, experiment, and simulation.",2109.03057v4
2021-12-02,Heisenberg representation of nonthermal ultrafast laser excitation of magnetic precessions,"We derive the Heisenberg representation of the ultrafast inverse Faraday
effect that provides the time evolution of magnetic vectors of a magnetic
system during its interaction with a laser pulse. We obtain a time-dependent
effective magnetic operator acting in the Hilbert space of the total angular
momentum that describes a process of nonthermal excitation of magnetic
precessions in an electronic system by a circularly polarized laser pulse. The
magnetic operator separates the effect of the laser pulse on the magnetic
system from other magnetic interactions. The effective magnetic operator
provides the equations of motion of magnetic vectors during the excitation by
the laser. We show that magnetization dynamics calculated with these equations
is equivalent to magnetization dynamics calculated with the time-dependent
Schr\""odinger equation, which takes into account the interaction of an
electronic system with the electric field of light. We model and compare
laser-induced precessions of magnetic sublattices of an easy-plane and an
easy-axis antiferromagnetic systems. Using these models, we show how the
ultrafast inverse Faraday effect induces a net magnetic moment in
antiferromagnets and demonstrate that a crystal field environment and the
exchange interaction play essential roles for laser-induced magnetization
dynamics even during the action of a pump pulse. Using our approach, we show
that light-induced precessions can start even during the action of the pump
pulse with a duration several tens times shorter than the period of induced
precessions and affect the position of magnetic vectors after the action of the
pump pulse.",2112.01350v1
2022-07-20,Hot magnetic halo of NGC628 (M74),"In several spiral galaxies that are observed face-on, large-scale ordered
magnetic fields (the so-called magnetic arms) were found. One of the
explanations was the action of the magnetic reconnection, which leads to a
higher ordering of the magnetic fields. Because it simultaneously converts the
energy of the magnetic fields into thermal energy of the surroundings, magnetic
reconnection has been considered as a heating mechanism of the interstellar
medium for many years. Until recently, no clear observational evidence for this
phenomenon was found. We search for possible signatures of gas heating by
magnetic reconnection effects in the radio and X-ray data for the face-on
spiral galaxy NGC628 (M74), which presents pronounced magnetic arms and
evidence for vertical magnetic fields. The strengths and energy densities of
the magnetic field in the spiral and magnetic arms were derived, as were the
temperatures and thermal energy densities of the hot gas, for the disk and halo
emission. In the regions of magnetic arms, higher order and lower energy
density of the magnetic field is found than in the stellar spiral arms. The
global temperature of the hot gas is roughly constant throughout the disk. The
comparison of the findings with those obtained for the starburst galaxy M83
suggests that magnetic reconnection heating may be present in the halo of
NGC628. The joint analysis of the properties of the magnetic fields and the hot
gas in NGC628 also provided clues for possible tidal interaction with the
companion galaxy.",2207.09917v1
2022-09-07,Atypical magnetic behavior in the incommensurate $[CH_3NH_3][Ni(HCOO)_3]$ hybrid perovskite,"A plethora of temperature induced phase transitions have been observed in
$[CH_3NH_3][M(HCOO)_3]$ compounds, where M is Co(II) or Ni(II). Among them, the
nickel compound exhibits a combination of magnetic and nuclear
incommensurabil-ity below N\'eel temperature. Despite the fact that the
zero-field behavior has been previously addressed, here we study in depth the
macroscopic magnetic behavior of this compound to unveil the origin of the
atypical magnetic response found in it and in its parent family of formate
perovskites. In particular, they show a puzzling magnetization reversal in the
curves measured starting from low temperatures, after cooling under zero field.
The first atypical phenomena is the im-possibility of reaching zero
magnetization, even by nullifying the applied external field and even
compensating it for the influence earth's magnetic field. Relatively large
magnetic fields are needed to switch the magnetization from negative to
positive values or vice versa, which is compatible with a soft-ferromagnetic
system. The atypical path found in its first magnetization curve and hysteresis
loop at low temperatures is the most noticeable feature. The magnetization
curve switches from more than 1200 Oe from the first magnetization loop to the
subsequent magnetization loops. A feature that cannot be explained using a
model based on unbalanced pair of domains. As a result, we decipher this
behavior in light of the incommensurate structure of this material. We propose,
in particular, that the applied magnetic field induces a mag-netic phase
transition from a magnetically incommensurate structure to a magnetically
commensurate structure.",2209.03093v1
2022-12-02,A promising formation channel for symbiotic X-ray binaries: cases of IGR J17329-2731 and 4U 1700+24,"Recent observations demonstrate that the symbiotic X-ray binary (SyXB) IGR
J17329-2731 contains a highly magnetized neutron star (NS) which accretes
matter through the wind from its giant star companion, and suggest that 4U
1700+24 may also have a highly magnetized NS. Accretion-induced collapse (AIC)
from oxygen-neon-magnesium white dwarf (ONeMg WD) + red giant (RG) star
binaries is one promising channel to form these SyXBs, while other long
standing formation channels have difficulties to produce these SyXBs. By
considering non-magnetic and magnetic ONeMg WDs, I investigate the evolution of
ONeMg WD + RG binaries with the MESA stellar evolution code for producing SyXBs
with non-magnetic or magnetized NSs. In the pre-AIC evolution with magnetic
confinement, the mass accumulation efficiency of the accreting WD is increased
at low mass transfer rate compared to the non-magnetic case. The newborn NSs
formed via AIC of highly magnetized WDs could inherit the large magnetic field
through conservation of magnetic flux, and the systems could have a long age
compatible with that of the red giant companions. These young and highly
magnetized NSs could accrete matters from the stellar wind of the giant
companions to that shine as those observed SyXBs, and could preserve their high
magnetic field during this time. The MESA calculation results show that the
initial parameter (initial RG mass and orbital period) space for the AIC with
magnetic confinement to form SyXBs with highly magnetized NSs shifts to be
lower and narrower compared to that of the no magnetic confinement case.",2212.00997v2
2023-07-28,Reversible magnetic domain reorientation induced by magnetic field pulses with fixed direction,"Nanoscale magnetic domains with controllable configurations could be used for
classical and quantum applications, where the switching of magnetization
configurations is an essential operation for information processing. Here, we
report that the magnetic domain reorientation in a notched ferromagnetic
nanotrack can be realized and effectively controlled by applying uniform
magnetic field pulses in a fixed in-plane direction perpendicular to the
nanotrack. Our micromagnetic simulation results show that the configurations of
magnetic domains in the notched nanotrack can be switched between a
head-to-head state and a tail-to-tail state in a reversible manner driven by
magnetic field pulses, while it is unnecessary to reverse the direction of the
magnetic field. Such a unique magnetic domain reorientation dynamics is found
to depend on magnetic parameters and nanotrack geometries. The reorientation
dynamics of magnetic domains also depends on the strength and length of the
applied magnetic field pulse. In addition, we point out that the notches at the
center of the nanotrack play an important role for the stabilization of the
head-to-head and tail-to-tail states during the magnetic domain reorientation.
We also qualitatively explain the field-induced reorientation phenomenon with a
simplified two-dimensional macrospin model. Our results may make it possible to
build spintronic devices driven by a fixed magnetic field. Our findings may
also motivate future studies to investigate the classical and quantum
applications based on nanoscale magnetic domains.",2307.15263v1
2023-09-14,Disentangling the Entangled Linkages of Relative Magnetic Helicity,"Magnetic helicity, $H$, measures magnetic linkages in a volume. The early
theoretical development of helicity focused on magnetically closed systems in
$\mathcal{V}$ bounded by $\mathcal{S}$. For magnetically closed systems,
$\mathcal{V}\in\mathbb{R}^3=\mathcal{V}+\mathcal{V}^*$, no magnetic flux
threads the boundary, $\hat{\boldsymbol{n}}\cdot\boldsymbol{B}|_\mathcal{S}=0$.
Berger and Field (1984) and Finn and Antonsen (1985) extended the definition of
helicity to relative helicity, $\mathcal{H}$, for magnetically open systems
where magnetic flux may thread the boundary. Berger (1999,2003) expressed this
relative helicity as two gauge invariant terms that describe the self helicity
of magnetic field that closes inside $\mathcal{V}$ and the mutual helicity
between the magnetic field that threads the boundary $\mathcal{S}$ and the
magnetic field that closes inside $\mathcal{V}$. The total magnetic field that
permeates $\mathcal{V}$ entangles magnetic fields that are produced by current
sources $\boldsymbol{J}$ in $\mathcal{V}$ with magnetic fields that are
produced by current sources $\boldsymbol{J}^*$ in $\mathcal{V}^*$. Building on
this fact, we extend Berger's expressions for relative magnetic helicity to
eight gauge invariant quantities that simultaneously characterize both of these
self and mutual helicities and attribute their origins to currents
$\boldsymbol{J}$ in $\mathcal{V}$ and/or $\boldsymbol{J}^*$ in $\mathcal{V}^*$,
thereby disentangling the domain of origin for these entangled linkages. We
arrange these eight terms into novel expressions for internal and external
helicity (self) and internal-external helicity (mutual) based on their domain
of origin. The implications of these linkages for interpreting magnetic energy
is discussed and new boundary observables are proposed for tracking the
evolution of the field that threads the boundary.",2309.07776v1
2024-03-23,Engineering the electronic and magnetic properties of monolayer TiS$_2$ through systematic transition-metal doping,"Layered materials that exhibit magnetic ordering in their pristine form are
very rare. Several standard approaches, such as adsorption of atoms,
introduction of point defects, and edge engineering, have been developed to
induce magnetism in two-dimensional materials. In this way, we investigate the
electronic and magnetic properties of monolayer TiS$_2$ doped with 3$d$
transition metals (TMs) atoms in both octahedral 1T and trigonal prismatic 1H
structures using first-principles calculations. In its pristine form, TiS$_2$
is a non-magnetic semiconductor. The bands near the Fermi energy primarily
exhibit $d$ orbital characters, and due to the presence of ideal octahedral and
trigonal arrangements, they are well separated from other bands with $p$
character. Upon substituting 3$d$-TM atoms in both structures, a variety of
electronic and magnetic phases emerge, including magnetic semiconductor,
magnetic half-metal, non-magnetic metal, and magnetic metal. Chromium exhibits
the largest magnetic moment in both the 1T and 1H structures. The 1T structure
shows a slightly higher magnetic moment of 3.419 $\mu_B$ compared to the 1H
structure 3.138 $\mu_B$, attributed to the distorted octahedral structure of
the 1T structure. Unlike pristine TiS$_2$, the deficiency in saturation of
neighboring S atoms in the presence of impurities leads to the proximity of
energy levels of $d$ and $p$ states, resulting in unexpectedly sizable magnetic
moments. Another interesting case is Cobalt, which leads to a magnetic moment
of approximately 0.805 $\mu_B$ in the 1H structure, while the Co exhibits a
non-magnetic state in the 1H structure. These materials demonstrate a high
degree of tunability and can be optimized for various magnetic applications.",2403.15850v1
2003-05-06,How Spectral Shapes of Magnetic Energy and Magnetic Helicity Influence their Respective Decay Time Scales,"It is shown that in magnetohydrodynamics, the shapes of the magnetic energy
and magnetic helicity spectra can influence whether the magnetic helicity
resistive dissipation time scale is longer, equal to, or shorter than that of
magnetic energy. The calculations highlight that magnetic helicity need not
always dissipate significantly more slowly than magnetic energy. While this may
be implicitly understood in detailed studies of magnetic helicity in plasma
devices, it is not sufficiently emphasized in elementary discussions comparing
magnetic helicity vs. magnetic energy evolution. Measuring magnetic energy and
helicity decay times may provide a posteriori insight into the initial spectra.",0305069v2
1999-11-03,Magnetic properties of submicron Co islands and their use as artificial pinning centers,"We report on the magnetic properties of elongated submicron magnetic islands
and their influence on a superconducting film. The magnetic properties were
studied by magnetization hysteresis loop measurements and scanning-force
microscopy. In the as-grown state, the islands have a magnetic structure
consisting of two antiparallel domains. This stable domain configuration has
been directly visualized as a 2x2-checkerboard pattern by magnetic-force
microscopy. In the remanent state, after magnetic saturation along the easy
axis, all islands have a single-domain structure with the magnetic moment
oriented along the magnetizing field direction. Periodic lattices of these Co
islands act as efficient artificial pinning arrays for the flux lines in a
superconducting Pb film deposited on top of the Co islands. The influence of
the magnetic state of the dots on their pinning efficiency is investigated in
these films, before and after the Co dots are magnetized.",9911034v1
2000-04-26,Magnetic relaxation and magnetization field dependence measurements in La0.5Ca0.5MnO3,"We reported a systematic change in the average magnetic relaxation rate,
after the application and removal of a 5 T magnetic field, in a polycrystalline
sample of La0.5Ca0.5MnO3. Magnetic relaxation measurements and magnetization
versus field curves were taken from 10 K to 160 K. The long time behavior of
the relaxation curves was approximately logarithmic in all cases. Keywords:
Charge Ordering, Relaxation, Magnetic measurements",0004460v2
2004-08-30,Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots,"We show that through the resonant optical excitation of spin-polarized
excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic
magnetization of the Mn impurities. We observe very broad (4 meV linewidth)
emission lines of single dots, which are consistent with the formation of
strongly confined exciton magnetic polarons. Therefore we attribute the
optically induced magnetization of the magnetic dots results to the formation
of spin-polarized exciton magnetic polarons. We find that the photo-induced
magnetization of magnetic polarons is weaker for larger dots which emit at
lower energies within the QD distribution. We also show that the photo-induced
magnetization is stronger for quantum dots with lower Mn concentration, which
we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the
dots. Due to particular stability of the exciton magnetic polarons in QDs,
where the localization of the electrons and holes is comparable to the magnetic
exchange interaction, this optically induced spin alignment persists to
temperatures as high as 160 K.",0408658v1
2005-04-23,New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data,"The connection of strength of magnetic interactions and type ordering the
magnetic moments with crystal chemical characteristics in low-dimensional
magnets is investigated. The new method to calculate the sign and relative
strength of magnetic interactions in low-dimensional systems on the basis of
the structural data is proposed. This method allows to estimate magnetic
interactions not only inside low-dimensional fragments but also between them,
and also to predict the possibility of the occurrence of magnetic phase
transitions and anomalies of the magnetic interactions. Moreover, it can be
used for search of low-dimensional magnets among the compounds whose crystal
structures are known. The possibilities of the method are illustrated in an
example of research of magnetic interactions in familiar low-dimensional
magnets SrCu2(BO3)2, CaCuGe2O6, CaV4O9, Cu2Te2O5Cl2, Cu2Te2O5Br2, BaCu2Si2O7,
BaCu2Ge2O7, BaCuSi2O6, LiCu2O2, and NaCu2O2.",0504599v3
2005-10-21,Magnetostrictive hysteresis of TbCo/CoFe multilayers and magnetic domains,"Magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under
field applied along the hard magnetization axis are studied using vectorial
magnetization measurements, optical deflectometry and magneto optical Kerr
microscopy. Even a very small angle misalignment between hard axis and magnetic
field direction is shown to drastically change the shape of magnetization and
magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are
revealed during the magnetization: big regions with opposite rotation of
spontaneous magnetization vector and spontaneous magnetic domains which appear
in a narrow field interval and provide an inversion of this rotation.
  We show that the details of the hysteresis loops of our exchange-coupled
films can be described using the classical model of homogeneous magnetization
rotation of single uniaxial films and the configuration of observed domains.
The understanding of these features is crucial for applications (for MEMS or
microactuators) which benefit from the greatly enhanced sensitivity near the
point of magnetic saturation at the transverse applied field.",0510568v1
2006-02-14,Semiclassical pseudodifferential calculus and the reconstruction of a magnetic field,"We give a procedure for reconstructing a magnetic field and electric
potential from boundary measurements related to the magnetic Schroedinger
operator in three and higher dimensions.",0602290v1
1999-01-29,Gravimetric Measurement of Magnetic Field Gradient Spatial Distribution,"Magnetic interaction between a weighing sample and an external magnetic field
allows to measure characteristics of magnetic field (a sample with known
magnetic characteristics), as well as the magnetic properties of a sample (a
known magnetic field). Measurement of materials magnetic permeability is a well
known application of this method. In this paper we restrict ourselves to the
measurement of magnetic field spatial distribution, which was achieved by
scanning of samples from known materials along the vertical axis. Field
measurements by Hall detector were done to calibrate obtained data. Such
measurements are of great interest in some branches of physics, in particular,
in accelerator physics, where the quality of magnetic system parts eventually
determine the quality of accelerated bunches. Development of a simple and cheep
device for measurement of magnetic field spatial distribution is an urgent
problem. The developed system for gravimetric measurement of magnetic field
gradients partially solves this problem.",9901058v1
1999-05-06,A Brief Note on Jupiter's Magnetism,"A recent model which gives the contribution of the earth's solid core to geo
magnetism is seen to explain Jupiter's magnetism also.",9905014v1
2008-01-30,How to use magnetic field information for coronal loop identification?,"The structure of the solar corona is dominated by the magnetic field because
the magnetic pressure is about four orders of magnitude higher than the plasma
pressure. Due to the high conductivity the emitting coronal plasma (visible
e.g. in SOHO/EIT) outlines the magnetic field lines. The gradient of the
emitting plasma structures is significantly lower parallel to the magnetic
field lines than in the perpendicular direction. Consequently information
regarding the coronal magnetic field can be used for the interpretation of
coronal plasma structures. We extrapolate the coronal magnetic field from
photospheric magnetic field measurements into the corona. The extrapolation
method depends on assumptions regarding coronal currents, e.g. potential fields
(current free) or force-free fields (current parallel to magnetic field). As a
next step we project the reconstructed 3D magnetic field lines on an EIT-image
and compare with the emitting plasma structures. Coronal loops are identified
as closed magnetic field lines with a high emissivity in EIT and a small
gradient of the emissivity along the magnetic field.",0801.4573v1
2011-02-23,Possibility of conversion of neutron star to quark star in presence of high magnetic field,"Recent results and data suggests that high magnetic field in neutron stars
(NS) strongly affects the characteristic (radius, mass) of the star. They are
even separated as a class known as magnetars, for whom the surface magnetic
field are greater than $10^{14}$ G. In this work we discuss the effect of such
high magnetic field on the phase transition of NS to quark star (QS). We study
the effect of magnetic field on the transition from NS to QS including the
magnetic field effect in equation of state (EoS). The inclusion of the magnetic
field increases the range of baryon number density, for which the flow
velocities of the matter in the respective phase are finite. The magnetic field
helps in initiation of the conversion process. The velocity of the conversion
front however decreases due to the presence of magnetic field, as the presence
of magnetic field reduces the effective pressure (P). The magnetic field of the
star gets decreased by the conversion process, and the resultant QS has lower
magnetic field than that of the initial NS.",1102.4660v2
2011-03-06,"The Influence of Magnetic Anisotropy on the Kondo Effect and Spin-Polarized Transport through Magnetic Molecules, Adatoms and Quantum Dots","Transport properties in the Kondo regime of a nanosystem displaying uniaxial
magnetic anisotropy (such as a magnetic molecule, magnetic adatom or quantum
dot coupled to a localized magnetic moment) are analyzed theoretically. In
particular, the influence of spin-polarized transport through a local orbital
of the system and exchange coupling of conduction electrons to the system's
magnetic core on the Kondo effect is discussed. The numerical renormalization
group method is applied to calculate the spectral functions and linear
conductance in the case of the parallel and antiparallel configurations of the
electrodes' magnetic moments. It is shown that both the magnetic anisotropy as
well as the exchange coupling between electrons tunneling through the
conducting orbital and magnetic core play an important role in formation of the
Kondo resonance, leading generally to its suppression. Specific transport
properties of such a system appear also as a nontrivial behavior of tunnel
magnetoresistance. It is also shown that the Kondo effect can be restored by an
external magnetic field in both the parallel and antiparallel magnetic
configurations.",1103.1128v2
2011-03-18,Study of the interplay between magnetic shear and resonances using Hamiltonian models for the magnetic field lines,"The issue of magnetic confinement in magnetic fusion devices is addressed
within a purely magnetic approach. Using some Hamiltonian models for the
magnetic field lines, the dual impact of low magnetic shear is shown in a
unified way. Away from resonances, it induces a drastic enhancement of magnetic
confinement that favors robust internal transport barriers (ITBs) and
stochastic transport reduction. When low-shear occurs for values of the winding
of the magnetic field lines close to low-order rationals, the amplitude
thresholds of the resonant modes that break internal transport barriers by
allowing a radial stochastic transport of the magnetic field lines may be quite
low. The approach can be applied to assess the robustness versus magnetic
perturbations of general (almost) integrable magnetic steady states, including
non-axisymmetric ones such as the important single helicity steady states. This
analysis puts a constraint on the tolerable mode amplitudes compatible with
ITBs and may be proposed as a possible explanation of diverse experimental and
numerical signatures of their collapses.",1103.3595v1
2014-08-05,Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films,"We investigate the magnetization dynamics through the magnetoimpedance effect
in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance
response is dependent on the thickness of the non-magnetic Cu spacer material,
a fact associated to the kind of the magnetic interaction between the
ferromagnetic layers. Thus, we present an experimental study on asymmetric
magnetoimpedance in ferromagnetic films with biphase magnetic behavior and
explore the possibility of tuning the linear region of the magnetoimpedance
curves around zero magnetic field by varying the thickness of the non-magnetic
spacer material, and probe current frequency. We discuss the experimental
magnetoimpedance results in terms of the different mechanisms governing the
magnetization dynamics at distinct frequency ranges, quasi-static magnetic
properties, thickness of the non-magnetic spacer material, and the kind of the
magnetic interaction between the ferromagnetic layers. The results place
ferromagnetic films with biphase magnetic behavior exhibiting asymmetric
magnetoimpedance effect as a very attractive candidate for application as probe
element in the development of auto-biased linear magnetic field sensors.",1408.0992v1
2014-10-10,Comparison of adjustable permanent magnetic field sources,"A permanent magnet assembly in which the flux density can be altered by a
mechanical operation is often significantly smaller than comparable
electromagnets and also requires no electrical power to operate. In this paper
five permanent magnet designs in which the magnetic flux density can be altered
are analyzed using numerical simulations, and compared based on the generated
magnetic flux density in a sample volume and the amount of magnet material
used. The designs are the concentric Halbach cylinder, the two half Halbach
cylinders, the two linear Halbach arrays and the four and six rod mangle. The
concentric Halbach cylinder design is found to be the best performing design,
i.e. the design that provides the most magnetic flux density using the least
amount of magnet material. A concentric Halbach cylinder has been constructed
and the magnetic flux density, the homogeneity and the direction of the
magnetic field are measured and compared with numerical simulation and a good
agreement is found.",1410.2681v1
2014-11-25,Computing with spins and magnets,"The possible use of spin and magnets in place of charge and capacitors to
store and process information is well known. Magnetic tunnel junctions are
being widely investigated and developed for magnetic random access memories.
These are two terminal devices that change their resistance based on switchable
magnetization of magnetic materials. They utilize the interaction between
electron spin and magnets to read information from the magnets and write onto
them. Such advances in memory devices could also translate into a new class of
logic devices that offer the advantage of nonvolatile and reconfigurable
information processing over transistors. Logic devices having a transistor-like
gain and directionality could be used to build integrated circuits without the
need for transistor-based amplifiers and clocks at every stage. We review
device characteristics and basic logic gates that compute with spins and
magnets from the mesoscopic to the atomic scale, as well as materials,
integration, and fabrication challenges and methods.",1411.6960v1
2015-02-27,RC-circuit-like dynamic characteristic of the magnetic domain wall in ferromagnetic nanowires,"We have investigated dynamic behaviors of the magnetic domain wall under
perpendicular magnetic field pulses in ferromagnetic nanowires using
micromagnetic simulations. It has been found that the perpendicular magnetic
field pulse can trigger the magnetic domain wall motion, where all the field
torques are kept to be on the plane of nanowire strip. The magnetic domain wall
speed faster than several hundreds meters per second is predicted without the
Walker breakdown for the perpendicular magnetic driving field stronger than
$200~\mathrm{mT}$. Interestingly, the dynamic behavior of the moving magnetic
domain wall driven by perpendicular magnetic field pulses is explained by
charging- and discharging-like behaviors of an electrical RC-circuit model,
where the charging and the discharging of ""magnetic charges"" on the nanowire
planes are considered. The concept of the RC-model-like dynamic characteristic
of the magnetic domain wall might be promising for spintronic functional device
applications based on the magnetic domain wall motion.",1502.07807v1
2015-03-30,Effects of non-radial magnetic field on measuring magnetic helicity transport across solar photosphere,"It is generally believed that the evolution of magnetic helicity has a close
relationship with solar activity. Before the launch of SDO, earlier studies
have mostly used MDI/SOHO line of sight magnetograms and assumed that magnetic
fields are radial when calculating magnetic helicity injection rate from
photospheric magnetograms. However, this assumption is not necessarily true.
Here we use the vector magnetograms and line of sight magnetograms, both taken
by HMI/SDO, to estimate the effects of non-radial magnetic field on measuring
magnetic helicity injection rate. We find that: 1) The effect of non-radial
magnetic field on estimating tangential velocity is relatively small; 2) On
estimating magnetic helicity injection rate, the effect of non-radial magnetic
field is strong when active regions are observed near the limb and is
relatively small when active regions are close to disk center; 3) The effect of
non-radial magnetic field becomes minor if the amount of accumulated magnetic
helicity is the only concern.",1503.08563v1
2015-08-18,A self-consistent study of magnetic field effects on hybrid stars,"In this work we study the effects of strong magnetic fields on hybrid stars
by using a full general-relativity approach, solving the coupled
Maxwell-Einstein equation in a self-consistent way. The magnetic field is
assumed to be axi-symmetric and poloidal. We take into consideration the
anisotropy of the energy-momentum tensor due to the magnetic field, magnetic
field effects on equation of state, the interaction between matter and the
magnetic field (magnetization), and the anomalous magnetic moment of the
hadrons. The equation of state used is an extended hadronic and quark SU(3)
non-linear realization of the sigma model that describes magnetized hybrid
stars containing nucleons, hyperons and quarks. According to our results, the
effects of the magnetization and the magnetic field on the EoS do not play an
important role on global properties of these stars. On the other hand, the
magnetic field causes the central density in these objects to be reduced,
inducing major changes in the populated degrees of freedom and, potentially,
converting a hybrid star into a hadronic star.",1508.04431v1
2015-09-05,Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$,"We have investigated the magnetic and magnetocaloric properties of
antiferromagnetic Ising spin chain CoV$_{2}$O$_{6}$ by magnetization and heat
capacity measurements. Both monoclinic $\alpha$-CoV$_{2}$O$_{6}$ and triclinic
$\gamma$-CoV$_{2}$O$_{6}$ exhibit field-induced metamagnetic transition from
antiferromagnetic to ferromagnetic state via an intermediate ferrimagnetic
state with 1/3 magnetization plateau. Due to this field-induced metamagnetic
transition, these systems show large conventional as well as inverse
magnetocaloric effects. In $\alpha$-CoV$_{2}$O$_{6}$, we observe field-induced
complex magnetic phases and multiple magnetization plateaux at low temperature
when the field is applied along $c$ axis. Several critical temperatures and
fields have been identified from the temperature and field dependence of
magnetization, magnetic entropy change and heat capacity to construct the
$H$-$T$ phase diagram. As compared to $\alpha$-CoV$_{2}$O$_{6}$,
$\gamma$-CoV$_{2}$O$_{6}$ displays a relatively simple magnetic phase diagram.
Due to the large magnetic entropy change and adiabatic temperature change at
low or moderate applied magnetic field, $\gamma$-CoV$_{2}$O$_{6}$ may be
considered as a magnetic refrigerant in the low-temperature region.",1509.01690v2
2015-11-16,Observation of Magnetic Superviscosity in Metglas 2605SA1,"A quasi time constant for magnetic domain relaxation of Metglas 20605SA1 has
been measured to be 2.6 hours. The effective relative magnetic permeability has
been measured to be 57,000 after relaxation.",1511.05127v1
2017-02-28,Chemical Responsive Single Crystal Organic Magnet,"Materials that change their magnetic properties in response to the external
stimuli have long been of interest for their potential applicability in
magnetic storage device, spintronics and smart magnetic materials. Organic
materials are suitable candidates for such materials due to their chemical
diversity, flexibility and designablity. However, most methods used for
changing magnetism are inefficient or destructive to the magnetic material.
Hence there is a need for innovation in this field. Here we report
high-performance magnetic control of a gas-responsive single-molecule magnet
(SMM). The results exhibit that the magnetic properties of the SMM can be
significantly changed according to the gas environment it is in and some of the
magnetic states can be reversibly transformed or coexistent in the SMM through
artificial control. More importantly, the monocrystalline structure of the SMM
remains unchanged during the transformation process except for slight change of
the lattice constant. Thus, this work opens up new insights into the
stimuli-responsive magnetic materials which have great prospects for
application in artificial design magnetic network and also highlight their
potential as smart materials.",1703.00006v2
2018-02-14,Axisymmetric magnetic modes of neutron stars having mixed poloidal and toroidal magnetic fields,"We calculate axisymmetric magnetic modes of a neutron star possessing a mixed
poloidal and toroidal magnetic field, where the toroidal field is assumed to be
proportional to a dimensionless parameter $\zeta_0$. Here, we assume an
isentropic structure for the neutron star and consider no effects of rotation.
Ignoring the equilibrium deformation due to the magnetic field, we employ a
polytrope of the index $n=1$ as the background model for our modal analyses.
For the mixed poloidal and toroidal magnetic field with $\zeta_0\not=0$,
axisymmetric spheroidal and toroidal modes are coupled. We compute axisymmetric
spheroidal and toroidal magnetic modes as a function of the parameter $\zeta_0$
from $0$ to $\sim 1$ for the surface field strengths $B_S=10^{14}$G and
$10^{15}$G. We find that the frequency $\omega$ of the magnetic modes decreases
with increasing $\zeta_0$. We also find that the frequency of the spheroidal
magnetic modes is almost exactly proportional to $B_S$ for $\zeta_0\lesssim 1$
but that this proportionality holds only when $\zeta_0\ll 1$ for the toroidal
magnetic modes. The wave patterns of the spheroidal magnetic modes and toroidal
magnetic modes are not strongly affected by the coupling so long as
$\zeta_0\lesssim 1$. We find no unstable modes having $\omega^2<0$.",1802.04957v1
2017-01-12,Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field,"The magnetic properties of iron pnictide superconductors with magnetic
rare-earth ions under strong magnetic field are investigated based on the
cluster self-consistent field method. Starting from an effective Heisenberg
model, we present the evolution of magnetic structures on magnetic field in
RFeAsO (R=Ce, Pr, Nd, Sm, Gd and Tb) and RFe2As2 (R=Eu) compounds. It is found
that spin-flop transition occurs in both rare-earth and iron layers under
magnetic field, in good agreement with the experimental results. The interplay
between rare-earth and iron spins plays a key role in the magnetic-field-driven
magnetic phase transition, which suggests that the rare-earth layers can
modulate the magnetic behaviors of iron layers. In addition, the factors that
affect the critical magnetic field for spin-flop transition are also discussed.",1701.03258v1
2017-01-19,Linear Stability Analysis of a Levitated Nanomagnet in a Static Magnetic Field: Quantum Spin Stabilized Magnetic Levitation,"We theoretically study the levitation of a single magnetic domain nanosphere
in an external static magnetic field. We show that apart from the stability
provided by the mechanical rotation of the nanomagnet (as in the classical
Levitron), the quantum spin origin of its magnetization provides two additional
mechanisms to stably levitate the system. Despite of the Earnshaw theorem, such
stable phases are present even in the absence of mechanical rotation. For large
magnetic fields, the Larmor precession of the quantum magnetic moment
stabilizes the system in full analogy with magnetic trapping of a neutral atom.
For low magnetic fields, the magnetic anisotropy stabilizes the system via the
Einstein-de Haas effect. These results are obtained with a linear stability
analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy
in a Ioffe-Pritchard magnetic field.",1701.05410v3
2018-05-07,Single-shot multi-level all-optical magnetization switching mediated by spin-polarized hot electron transport,"All-optical ultrafast magnetization switching in magnetic material thin film
without the assistance of an applied external magnetic field is being explored
for future ultrafast and energy-efficient magnetic storage and memories. It has
been shown that femto-second light pulses induce magnetization reversal in a
large variety of magnetic materials. However, so far, only GdFeCo-based
ferrimagnetic thin films exhibit magnetization switching via a single optical
pulse. Here we demonstrate the single-pulse switching of Co/Pt multilayers
within a magnetic spin-valve structure ([Co/Pt] / Cu / GdFeCo) and further show
that the four possible magnetic configurations of the spin valve can be
accessed using a sequence of single femto-second light pulses. Our experimental
study reveals that the magnetization final state of the ferromagnetic [Co/Pt]
layer is determined by spin-polarized hot electrons generated by the light
pulse interactions with the GdFeCo layer. This work provides a new approach to
deterministically switch ferromagnetic layers and a pathway to engineering
materials for opto-magnetic multi-bit recording.",1805.02432v1
2012-04-26,Axisymmetric and stationary structures of magnetized barotropic stars with extremely strong magnetic fields deep inside,"We have succeeded in obtaining magnetized star models that have extremely
strong magnetic fields in the interior of the star. In our formulation,
arbitrary functions of the magnetic flux function appear in the expression for
the current density. By appropriately choosing the functional form for one of
the arbitrary functions that corresponds to the distribution of the toroidal
current density, we have obtained configurations with magnetic field
distributions that are highly localized within the central part and near the
magnetic axis region. The absolute values of the central magnetic fields are
stronger than those of the surface region by two orders of magnitude. By
applying our results to magnetars, the internal magnetic poloidal fields could
be 10^17 G, although the surface magnetic fields are about 10^15 G in the case
of magnetars. For white dwarfs, the internal magnetic poloidal fields could be
10^12 G, when the surface magnetic fields are 10^9-10^10 G .",1204.5830v2
2018-09-19,Effect of external magnetic field on nucleon mass in hot and dense medium : Inverse Magnetic Catalysis in Walecka Model,"Vacuum to nuclear matter phase transition has been studied in presence of
constant external background magnetic field with the mean field approximation
in Walecka model. The anomalous nucleon magnetic moment has been taken into
account using the modified ""weak"" field expansion of the fermion propagator
having non-trivial correction terms for charged as well as for neutral
particles. The effect of nucleon magnetic moment is found to favour the
magnetic catalysis effect at zero temperature and zero baryon density. However,
extending the study to finite temperatures, it is observed that the anomalous
nuclear magnetic moment plays a crucial role in characterizing the qualitative
behaviour of vacuum to nuclear matter phase transition even in case of the weak
external magnetic fields . The critical temperature corresponding to the vacuum
to nuclear medium phase transition is observed to decrease with the external
magnetic field which can be identified as the inverse magnetic catalysis in
Walecka model whereas the opposite behaviour is obtained in case of vanishing
magnetic moment indicating magnetic catalysis.",1809.07028v1
2019-10-17,Magnetic textures and dynamics in magnetic Weyl semimetals,"Recent theoretical and experimental attemps have been successful in finding
magnetic Weyl semimetal phases, which show both nodal-point structure in the
electronic bands and magnetic orders. Beyond uniform ferromagnetic or
antiferromagnetic orders, nonuniform magnetic textures, such as domain walls
and skyrmions, may even more enrich the properties of the Weyl electrons in
such materials. This article gives a topical review on interplay between Weyl
electrons and magnetic textures in those magnetic Weyl semimetals. The basics
of magnetic textures in non-topological magnetic metals are reviewed first, and
then the effect of magnetic textures in Weyl semimetals is discussed, regarding
the recent theoretical and experimental progress therein. The idea of the
fictitious ""axial gauge fields"" is pointed out, which effectively describes the
effect of magnetic textures on the Weyl electrons and can well account for the
properties of the electrons localized around magnetic domain walls.",1910.07774v1
2020-04-25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2020-12-09,Optimization of a NdFeB permanent magnet configuration for in-vivo drug delivery experiments,"We propose a new concept of magnetic focusing for targeting and accumulation
of functionalized superparamagnetic nanoparticles in living organs through
composite configurations of different permanent magnets. The proposed setups
fulfill two fundamental requirements for in vivo experiments: 1) reduced size
of the magnets to best focusing on small areas representing the targeted organs
of mice and rats and 2) maximization of the magnetic driving force acting on
the magnetic nanoparticles dispersed in blood. To this aim, several
configurations of permanent magnets organized with different degrees of
symmetry have been tested. The product B*grad(B) proportional to the magnetic
force has been experimentally measured, over a wide area (20x20 mm^2), at a
distance corresponding to the hypothetical distance of the mouse organ from the
magnets. A non-symmetric configuration of mixed shape permanent magnets
resulted in particularly promising to achieve the best performances for further
in vivo experiments.",2012.05059v1
2021-01-15,Magnetized Rutherford scattering angle for electron-ion collision in plasma,"Rutherford scattering formula plays an important role in plasma classical
transport. It is urgent to need a magnetized Rutherford scattering formula
since the magnetic field increases significantly in different fusion areas
(e.g. tokamak magnetic field, self-generated magnetic field, and compressed
magnetic field). The electron-ion Coulomb collisions perpendicular to the
external magnetic field are studied in this paper. The scattering angle is
defined according to the electron trajectory and asymptotic line (without
magnetic field). A magnetized Rutherford scattering formula is obtained
analytically under the weak magnetic field approximation. It is found that the
scattering angle decreases as external magnetic field increases. It is easy to
find the scattering angle decreasing significantly as incident distance, and
incident velocity increasing. It is shown that the theoretical results agree
well with numerical calculation by checking the dependence of scattering angle
on external magnetic field.",2101.05943v1
2017-09-13,Contactless and absolute linear displacement detection based upon 3D printed magnets combined with passive radio-frequency identification,"Within this work a passive and wireless magnetic sensor, to monitor linear
displacements is proposed. We exploit recent advances in 3D printing and
fabricate a polymer bonded magnet with a spatially linear magnetic field
component corresponding to the length of the magnet. Regulating the magnetic
compound fraction during printing allows specific shaping of the magnetic field
distribution. A giant magnetoresistance magnetic field sensor is combined with
a radio-frequency identification tag in order to passively monitor the exerted
magnetic field of the printed magnet. Due to the tailored magnetic field, a
displacement of the magnet with respect to the sensor can be detected within
the sub-mm regime. The sensor design provides good flexibility by controlling
the 3D printing process according to application needs. Absolute displacement
detection using low cost components and providing passive operation, long term
stability and longevity renders the proposed sensor system ideal for structural
health monitoring applications.",1709.04220v1
2018-12-13,Measuring Earth's Magnetic Field Using a Smartphone Magnetometer,"I use the magnetometers of a smartphone to measure the magnitude of the
earth's magnetic field. A method for eliminating bias due to internal magnetic
fields in the phone is proposed.",1901.00857v1
2019-12-03,Magnetic Force Microscopy Revealing Molecule Impact on Magnetic Tunnel Junction Based Molecular Devices at Room Temperature,"Commercially successful magnetic tunnel junction can harness the unmatched
capabilities of molecular device elements by solving decade-old fabrication
issues. Utilization of magnetic tunnel junction as a testbed for molecules also
enables unprecedented magnetic studies of molecular spintronics devices. This
paper utilizes magnetic force microscopy (MFM) to vividly show that
organometallic molecules when bridged between two ferromagnetic electrodes
along the magnetic tunnel junction edges, transformed the magnetic electrodes
itself. Molecules impacted several hundred-micron areas of ferromagnetic
electrodes at room temperature. Complementary, magnetic resonance and
magnetometer studies supported the dramatic MFM results. Molecule induced
changes in the magnetic electrodes impacted the transport of the magnetic
tunnel junction and stabilized as much as six orders smaller current at room
temperature. Magnetic tunnel junction based molecular devices can be a gateway
to a vast range of commercially viable futuristic logic and memory devices that
are controlled by the molecular quantum states near room temperature.",1912.01316v1
2019-12-12,Potential analysis of holographic Schwinger effect in the magnetized background,"We study the holographic Schwinger effect with magnetic field at RHIC and LHC
energies by using the AdS/CFT correspondence. We consider both weak and strong
magnetic field cases with $B\ll T^2$ and $B\gg T^2$ solutions respectively.
Firstly, we calculate separating length of the particle pairs at finite
magnetic field. It is found that for both weak and strong magnetic field
solutions the maximum value of separating length decreases with the increase of
magnetic field , which can be inferred that the virtual electron-positron pairs
become real particles more easily. We also find that the magnetic field reduces
the potential barrier and the critical field for the weak magnetic field
solution, thus favors the Schwinger effect. With strong magnetic field
solution, the magnetic field enhances the Schwinger effect when the pairs are
in perpendicular to the magnetic field although the magnetic field increases
the critical electric field.",1912.05806v2
2019-12-24,The origin and effect of hemispheric helicity imbalance in solar dynamo,"In this paper we study the effects of hemispheric imbalance of magnetic
helicity density on breaking the equatorial reflection symmetry of the dynamo
generated large-scale magnetic field. Our study employs the axisymmetric dynamo
model which takes into account the nonlinear effect of magnetic helicity
conservation. We find that the evolution of the net magnetic helicity density,
in other words, the magnetic helicity imbalance, on the surface follows the
evolution of the parity of the large-scale magnetic field. Random fluctuations
of the $\alpha$-effect and the helicity fluxes can inverse the causal
relationship, i.e., the magnetic helicity imbalance or the imbalance of
magnetic helicity fluxes can drive the magnetic parity breaking. We also found
that evolution of the net magnetic helicity of the small-scale fields follows
the evolution of the net magnetic helicity of the large-scale fields with some
time lag. We interpret this as an effect of the difference of the magnetic
helicity fluxes out of the Sun from the large and small scales.",1912.11285v2
2020-03-09,Magnetic Noise Enabled Biocompass,"The discovery of magnetic protein provides a new understanding of a
biocompass at the molecular level. However, the mechanism by which magnetic
protein enables a biocompass is still under debate, mainly because of the
absence of permanent magnetism in the magnetic protein at room temperature.
Here, based on a widely accepted radical pair model of a biocompass, we propose
a microscopic mechanism that allows the biocompass to operate without a finite
magnetization of the magnetic protein in a biological environment. With the
structure of the magnetic protein, we show that the magnetic fluctuation,
rather than the permanent magnetism, of the magnetic protein can enable
geomagnetic field sensing. An analysis of the quantum dynamics of our
microscopic model reveals the necessary conditions for optimal sensitivity. Our
work clarifies the mechanism by which magnetic protein enables a biocompass.",2003.13816v2
2020-05-02,Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnets,"Laser-induced switching and manipulation of the spins in magnetic materials
are of great interest to revolutionize future magnetic storage technology and
spintronics with fastest speed and least power dissipative. Inspired by the
recent discovery of intrinsic two-dimensional (2D) magnets, which provide
unique platform to explore the new phenomenon for light-control magnetism in
the 2D limit, we propose to realize light can efficiently tune magnetic
properties of 2D ferrimagnets in early time. Here, using the 2D ferrimagnetic
MXenes as prototype systems, our real-time density functional theory (TDDFT)
simulation show that laser pulses can directly induce ultrafast spin-selective
charge transfer between two magnetic sublattices on a few femtoseconds, and
further generate dramatic changes in the magnetic structure of these MXenes,
including a magnetic order transition from ferrimagnetic (FiM) to transient
ferromagnetic (FM). The microscopic mechanism underpinning this ultrafast
switching of magnetic order in MXenes is governed by optically induced
inter-site spin transfer (OISTR) effect, which theoretically enables the
ultrafast direct optical manipulation of the magnetic state in MXenes-based
materials. Our results open new opportunities to optically manipulate the spin
in 2D magnets.",2005.00871v1
2020-06-03,Structural and magnetic properties of small symmetrical and asymmetrical sized fullerene dimers,"Magnetism in carbon nanostructures is of high scientific interest, which
could lead to novel magnetic materials. The magnetic properties of symmetrical
and asymmetrical sized small fullerene dimers have been investigated using spin
polarized density functional theory. The interaction energies depict that small
fullerene cages form stable dimer structures and symmetrical sized fullerene
dimers are found more stable than asymmetrical sized dimers. The dimerization
of fullerene cages in different modes leads to change in their magnetic
properties. The non-magnetic fullerene cages become magnetic after formation of
dimer (C20-C20, C24-C24, C32-C32, C40-C40, C20-C24, C40-C44 and
C44-C50),whereas the magnetism of magnetic fullerenes is enhanced or lowered
after dimerization (C28-C28 C36-C36, C24-C28, C28-C32, C32-C36 and C36-C40).
The individual cages of dimer structures show ferromagnetic interactions
amongst them and resultant magnetic moment strongly depends on the type of
inter-connecting bonds. The magnetism may also be explained based on distortion
of carbon cages and change in the density of states (DOS) in dimer
configuration. The calculations presented show strong possibility of
experimental synthesis of small fullerene based magnetic dimers.",2006.02233v1
2020-09-03,Coincidence inelastic neutron scattering for detection of two-spin magnetic correlations,"Inelastic neutron scattering (INS) is one powerful technique to study the
low-energy single-spin dynamics of magnetic materials. A variety of quantum
magnets show novel magnetic correlations such as quantum spin liquids. These
novel magnetic correlations are beyond the direct detection of INS. In this
paper we propose a coincidence technique, coincidence inelastic neutron
scattering (cINS), which can detect the two-spin magnetic correlations of the
magnetic materials. In cINS there are two neutron sources and two neutron
detectors with an additional coincidence detector. Two neutrons from the two
neutron sources are incident on the target magnetic material, and they are
scattered by the electron spins of the magnetic material. The two scattered
neutrons are detected by the two neutron detectors in coincidence with the
coincidence probability described by a two-spin Bethe-Salpeter wave function.
Since the two-spin Bethe-Salpeter wave function defines the momentum-resolved
dynamical wave function with two spins excited, cINS can explicitly detect the
two-spin magnetic correlations of the magnetic material. Thus, it can be
introduced to study the various spin valence bond states of the quantum
magnets.",2009.01680v2
2020-10-19,Magnetic texture based magnonics,"The spontaneous magnetic orders arising in ferro-, ferri- and
antiferromagnets stem from various magnetic interactions. Depending on the
interplay and competition among the Heisenberg exchange interaction,
Dzyaloshinskii-Moriya exchange interaction, magnetic dipolar interaction and
crystal anisotropies, a great variety of magnetic textures may be stabilized,
such as magnetic domain walls, vortices, Skyrmions and spiral helical
structures. While each of these spin textures responds to external forces in a
specific manner with characteristic resonance frequencies, they also interact
with magnons, the fundamental collective excitation of the magnetic order,
which can propagate in magnetic materials free of charge transport and
therefore with low energy dissipation. Recent theories and experiments found
that the interplay between spin waves and magnetic textures is particularly
interesting and rich in physics. In this review, we introduce and discuss the
theoretical framework of magnons living on a magnetic texture background, as
well as recent experimental progress in the manipulation of magnons via
magnetic textures. The flexibility and reconfigurability of magnetic textures
are discussed regarding the potential for applications in information
processing schemes based on magnons.",2010.09180v1
2021-04-02,Highly Complex Magnetic Structures Resulting From Hierarchical Phase Separation in AlCo(Cr)FeNi High Entropy Alloys,"Magnetic high entropy alloys (HEAs) are a new category of high-performance
magnetic materials, with multi-component concentrated compositions and complex
multi-phase structures. Although there have been numerous reports of their
interesting magnetic properties, there is very limited understanding about the
interplay between their hierarchical multi-phase structures and their local
magnetic structures. By employing high spatial resolution correlative magnetic,
structural and chemical studies, we reveal the influence of a hierarchically
decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of
magnetic vortex states within individual A2 (disordered BCC) precipitates,
which are distributed in an ordered B2 matrix that is weakly ferromagnetic.
Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains
of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are
also observed. These results provide important insight into the origin of
coercivity in this HEA, which can be attributed to a complex magnetization
process that includes the successive reversal of magnetic vortices.",2104.00943v1
2021-06-28,Stability of a Magnetically Levitated Nanomagnet in Vacuum: Effects of Gas and Magnetization Damping,"In the absence of dissipation a non-rotating magnetic nanoparticle can be
stably levitated in a static magnetic field as a consequence of the spin origin
of its magnetization. Here we study the effects of dissipation on the stability
of the system, considering the interaction with the background gas and the
intrinsic Gilbert damping of magnetization dynamics. At large applied magnetic
fields we identify magnetization switching induced by Gilbert damping as the
key limiting factor for stable levitation. At low applied magnetic fields and
for small particle dimensions magnetization switching is prevented due to the
strong coupling of rotation and magnetization dynamics, and the stability is
mainly limited by the gas-induced dissipation. In the latter case, high vacuum
should be sufficient to extend stable levitation over experimentally relevant
timescales. Our results demonstrate the possibility to experimentally observe
the phenomenon of quantum spin stabilized magnetic levitation.",2106.14858v3
2021-08-26,Magnetic design study of coil-dominated superconducting quadrupole magnets based on racetrack coils,"Several coil structures have been used in accelerator superconducting
quadrupole magnets, and cos2{\theta} quadrupole magnets are the most mature in
theoretical research and engineering applications. However, the cos2{\theta}
quadrupole magnet has a complicated coil structure, especially at the end of
the coil, which makes it difficult to apply strain-sensitive high-temperature
superconductors. Racetrack quadrupole magnets are friendly to high-temperature
superconductors. Field strength of iron-dominated racetrack magnets is limited
by the magnetic saturation of the iron poles. Therefore, coil-dominated
racetrack quadrupole magnets with simple geometry have become the focus of our
research. In this paper, analytical expressions of the magnetic field harmonics
related to racetrack quadrupole coil parameters are obtained. These expressions
are used to find the solution of coil geometry parameters with field harmonics
on the order of 10-4. Then, examples are given to build ideal quadrupole model
and verify the theoretical formulas. Next, the design and optimization of
example racetrack quadrupole magnets are completed in ROXIE. Finally, the
advantages and disadvantages of the racetrack coils and the cos2{\theta} coils
are compared and discussed.",2108.11643v1
2021-12-21,Tunable room temperature magnetic skyrmions in centrosymmetric kagome magnet Mn$_4$Ga$_2$Sn,"The successful realization of skyrmion-based spintronic devices depends on
the easy manipulation of underlying magnetic interactions in the
skyrmion-hosting materials. Although the mechanism of skyrmion formation in
non-centrosymmetric magnets is comprehensively established, the stabilization
process of different skyrmion-like magnetic textures in centrosymmetric magnets
needs further investigation. Here, we utilize Lorentz transmission electron
microscopy study to report the finding of a tunable skyrmion lattice up to room
temperature in a centrosymmetric kagome ferromagnet Mn$_4$Ga$_2$Sn. We
demonstrate that a controlled switching between the topological skyrmions and
non-topological type-II magnetic bubbles can be realized at the optimal
magnetic anisotropy. We find that the topological skyrmions are the
energetically most stable magnetic objects in the centrosymmetric hexagonal
magnets, whereas application of in-plane magnetic field stabilizes type-II
magnetic bubbles as an excited state. The present study is a significant step
towards understanding of the skyrmion stabilization mechanism in
centrosymmetric materials for their future applications.",2112.11259v2
2022-02-25,Magnetic-Field-Dependent Thermodynamic Properties of Square and Quadrupolar Artificial Spin Ice,"Applied magnetic fields are an important tuning parameter for artificial spin
ice (ASI) systems, as they can drive phase transitions between different
magnetic ground states, or tune through regimes with high populations of
emergent magnetic excitations (e.g., monopole-like quasiparticles). Here, using
simulations supported by experiments, we investigate the thermodynamic
properties and magnetic phases of square and quadrupolar ASI as a function of
applied in-plane magnetic fields. Monte Carlo simulations are used to generate
field-dependent maps of the magnetization, the magnetic specific heat, the
thermodynamic magnetization fluctuations, and the magnetic order parameters,
all under equilibrium conditions. These maps reveal the diversity of magnetic
orderings and the phase transitions that occur in different regions of the
phase diagrams of these ASIs, and are experimentally supported by
magneto-optical measurements of the equilibrium ""magnetization noise"" in
thermally-active ASIs.",2202.12486v1
2022-03-23,R&D works for Superconducting Magnet for Future Accelerator Applications in Japan,"KEK cryogenics science center is developing superconducting magnet technology
for future accelerator science. Three major technological categories are
focused; 1) high precision 3D magnetic field technology based on the g-2/EDM
magnet developments, 2) rad-hard superconducting magnet technology based on the
COMET magnet developments, and 3) high magnetic field superconducting magnet
technology for future colliders based on the LHC MQXA and HL-LHC D1 magnet
developments. Extensive studies including Nb3Sn conductor and magnet
developments for high field magnets and HTS for rad-hard superconducting
magnets are ongoing with various collaboration programs such as the US-Japan
research collaboration.",2203.12118v1
2022-04-26,Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO$_3$,"We present a comprehensive study of static and dynamic magnetic properties in
the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC
magnetization measurements supported by classical Monte-Carlo calculations. Our
AC-susceptibility data show that the magnetic dynamics exhibit a clear
crossover from an Arrhenius-like regime to quantum tunneling of magnetization
(QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an
antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics
slow down to the minute timescale. The low-temperature magnetization curves
exhibit complex hysteretic behavior, which depends strongly on the magnetic
field sweep rate. We demonstrate that the low-field anomalies on the
magnetization curve are related to the metamagnetic transition, while the
hysteresis at higher fields is induced by a strong magnetocaloric effect. Our
theoretical calculations, which take into account dipolar interaction between
Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of
DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic
compound, which exhibits QTM at a single-ion level and magnetic order due to
classical dipolar interaction.",2204.12398v1
2022-05-08,Two-dimensional characterization of three-dimensional magnetic bubbles in Fe$_3$Sn$_2$ nanostructures,"We report differential phase contrast scanning transmission electron
microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet
Fe$_3$Sn$_2$ nanostructures. This technique can directly detect the deflection
angle of a focused electron beam, thus allowing clear identification of the
real magnetic structures of two magnetic objects including three-ring and
complex arch-shaped vortices in Fe$_3$Sn$_2$ by Lorentz transmission electron
microscopy imaging. Numerical calculations based on real material-specific
parameters well reproduced the experimental results, showing that the magnetic
objects can be attributed to integral magnetizations of two types of complex
three-dimensional (3D) magnetic skyrmion bubbles with depth-modulated spin
twisting. Magnetic configurations obtained using the high-resolution TEM are
generally considered as two-dimensional (2D) magnetic objects previously. Our
results imply the importance of the integral magnetizations of underestimated
3D magnetic structures in 2D TEM magnetic characterizations.",2205.03751v2
2022-05-09,"Controlling magnetic exchange and anisotropy by non-magnetic ligand substitution in layered MPX3 (M = Ni, Mn; X = S, Se)","Recent discoveries in two-dimensional (2D) magnetism have intensified the
investigation of van der Waals (vdW) magnetic materials and further improved
our ability to tune their magnetic properties. Tunable magnetism has been
widely studied in antiferromagnetic metal thiophosphates MPX3. Substitution of
metal ions M has been adopted as an important technique to engineer the
magnetism in MPX3. In this work, we have studied the previously unexplored
chalcogen X substitutions in MPX3 (M = Mn/Ni; X = S/Se). We synthesized the
single crystals of MnPS3-xSex (0 < x < 3) and NiPS3-xSex (0 < x < 1.3) and
investigated the systematic evolution of the magnetism with varying x. Our
study reveals the effective tuning of magnetic interactions and anisotropies in
both MnPS3 and NiPS3 upon Se substitution. Such efficient engineering of the
magnetism provides a suitable platform to understand the low-dimensional
magnetism and develop future magnetic devices.",2205.04585v1
2022-05-28,Finite element simulation for validation of multi-dipole line cusp magnetic field configuration for MPD,"A Multi-dipole line cusp configured Plasma Device (MPD) having six
electromagnets with embedded Vacoflux-50 as a core material has been operated
with a capability to experimentally control the field-free region, the radial
profile of magnetic field, and pole magnetic field by changing magnet current.
For the validation of multi-dipole line cusp magnetic field (MMF) configuration
in a 3-D geometry, a finite element simulation has been performed using COMSOL
software. This paper presents 3-D magnetic field simulation results of
multi-pole line cusp magnetic field configuration performed over the 1.2m
length and 40cm diameter chamber in the vacuum condition. The simulation
results show good agreement with the experimentally measured magnetic field
profile. The performed magnetic field simulation results clearly capture that
this configuration has full control over a null region (nearly field-free
region) as well is capable to change the magnetic field values and radial
variation of the magnetic field. Moreover, the magnetic field profiles over the
end cross-section of the device have been discussed.",2205.14381v1
2022-05-20,A Sacrificial Magnet Concept for Field Dependent Surface Science Studies,"We demonstrate a straightforward approach to integrating a magnetic field
into a low-temperature scanning tunneling microscope (STM) by adhering an NdFeB
permanent magnet to a magnetizable sample plate. To render our magnet concept
compatible with high-temperature sample cleaning procedures, we make the
irreversible demagnetization of the magnet a central part of our preparation
cycle. After sacrificing the magnet by heating it above its Curie temperature,
we use a transfer tool to attach a new magnet in-situ prior to transferring the
sample into the STM. We characterize the magnetic field created by the magnet
using the Abrikosov vortex lattice of superconducting NbSe2. Excellent
agreement between the distance dependent magnetic fields from experiments and
simulations allows us to predict the magnitude and orientation of magnetic flux
at any location with respect to the magnet and the sample plate. Our concept is
an accessible solution for field-dependent surface science studies that require
fields in the range of up to 400 mT and otherwise detrimental heating
procedures.",2206.02529v1
2022-07-14,Formation of Quiescent Prominence Magnetic Field by Supergranulations,"To understand the formation of quiescent solar prominences, the origin of
their magnetic field structures, i.e., magnetic flux ropes (MFRs), must be
revealed. We use three-dimensional magnetofriction simulations in a spherical
subdomain to investigate the role of typical supergranular motions in the
long-term formation of a prominence magnetic field. Time-dependant horizontal
supergranular motions with and without the effect of Coriolis force are
simulated on the solar surface via Voronoi tessellation. The vortical motions
by the Coriolis effect at boundaries of supergranules inject magnetic helicity
into the corona. The helicity is transferred and accumulated along the polarity
inversion line (PIL) as strongly sheared magnetic field via helicity
condensation. The diverging motions of supergranules converge opposite magnetic
polarities at the PIL and drive the magnetic reconnection between footpoints of
the sheared magnetic arcades to form an MFR. The magnetic network,
negative-helicity MFR in the northern hemisphere, and fragmented-to-continuous
formation process of magnetic dip regions are in agreement with observations.
Although diverging supergranulations, differential rotation, and meridional
flows are included, the simulation without the Coriolis effect can not produce
an MFR or sheared arcades to host a prominence. Therefore Coriolis force is a
key factor for helicity injection and the formation of magnetic structures of
quiescent solar prominences.",2207.06598v1
2022-11-28,Algorithms for magnetic symmetry operation search and identification of magnetic space group from magnetic crystal structure,"A crystal symmetry search is crucial for computational crystallography and
materials science. Although algorithms and implementations for the crystal
symmetry search have been developed, their extension to magnetic space groups
(MSGs) remains limited. In this paper, algorithms for determining magnetic
symmetry operations of magnetic crystal structures, identifying magnetic
space-group types of given MSGs, searching for transformations to a BNS
setting, and symmetrizing the magnetic crystal structures using the MSGs are
presented. The determination of magnetic symmetry operations is numerically
stable and is implemented with minimal modifications from the existing crystal
symmetry search. Magnetic space-group types and transformations to the BNS
setting are identified by a two-step approach combining space-group type
identification and the use of affine normalizers. Point coordinates and
magnetic moments of the magnetic crystal structures are symmetrized by
projection operators for the MSGs. An implementation is distributed with a
permissive free software license in spglib v2.0.2:
https://github.com/spglib/spglib.",2211.15008v2
2023-02-22,Controllable CVD-Growth of 2D Cr5Te8 Nanosheets with Thickness-Dependent Magnetic Domains,"As a typical 2D magnetic material with self-intercalated structure, Cr5Te8
exhibits many fascinating magnetic properties. Although the ferromagnetism of
2D Cr5Te8 has been reported, the study of its magnetic domain is still blank.
Herein, we successfully fabricated 2D Cr5Te8 nanosheets with controlled
thickness and lateral size by chemical vapor deposition (CVD). Then magnetic
property measurement system suggested Cr5Te8 nanosheets possessing intense
out-of-plane ferromagnetism with the Curie temperature of 179 K. Most
importantly, we found magnetic bubbles and thickness-dependent maze-like
magnetic domains by cryogenic magnetic force microscopy (MFM) for the first
time. The domain width of the maze-like magnetic domains increases rapidly with
decreasing sample thickness, while domain contrast decreases. This indicates
dipolar interaction is the dominant role over exchange interaction and magnetic
anisotropy. Our work not only paves a way for the controllable growth of 2D
magnetic materials, but also suggests new directions for controlling magnetic
phases and systematically adjusting domain properties.",2302.11422v2
2023-03-11,Magnetic field imaging by cosmic-ray muons (Magic-$μ$) -- First feasibility simulation for strong magnetic fields,"We have proposed a novel application for cosmic-ray muography, called
Magic-$\mu$, which is short for Magnetic field Imaging by Cosmic-ray Muons. The
general goal of Magic-$\mu$ is to detect the presence of a magnetic field or
magnetic flux density whose three-dimensional distribution is unknown.
Depending on the application, Magic-$\mu$ can have three detection modes. The
first is ""magnetic field imaging,"" which is detecting the presence of a
magnetic field in specific voxels within a region of space. The other two
modes, transmission and deflection, aim not only to detect the presence but
also to measure the flux density of the magnetic field. We have performed a
feasibility study using the PHITS Monte Carlo simulation code, for strong and
weak magnetic fields. In this paper, we first give an overview of the concept
and basic principles of magnetic field muography. Then, the results of the
feasibility study on magnetic field imaging for a strong magnetic field (more
than 500 mT) are presented.",2303.06290v3
2023-05-30,Magnetic field regression using artificial neural networks for cold atom experiments,"Accurately measuring magnetic fields is essential for magnetic-field
sensitive experiments in fields like atomic, molecular, and optical physics,
condensed matter experiments, and other areas. However, since many experiments
are conducted in an isolated vacuum environment that is inaccessible to
experimentalists, it can be challenging to accurately determine the magnetic
field. Here, we propose an efficient method for detecting magnetic fields with
the assistance of an artificial neural network (NN). Instead of measuring the
magnetic field directly at the desired location, we detect magnetic fields at
several surrounding positions, and a trained NN can accurately predict the
magnetic field at the target location. After training, we achieve a relative
error of magnetic field magnitude (magnitude of error over the magnitude of
magnetic field) below 0.3$\%$, and we successfully apply this method to our
erbium quantum gas apparatus. This approach significantly simplifies the
process of determining magnetic fields in isolated vacuum environments and can
be applied to various research fields across a wide range of magnetic field
magnitudes.",2305.18822v1
2023-07-06,Plasmon-enhanced optical control of magnetism at the nanoscale via the inverse Faraday effect,"The relationship between magnetization and light has been the subject of
intensive research for the past century, focusing on the impact of magnetic
moments on light polarization. Conversely, the manipulation of magnetism
through polarized light is being investigated to achieve all-optical control of
magnetism in spintronics. While remarkable discoveries such as single pulse
all-optical switching of the magnetization in thin films and sub-micrometer
structures have been reported, the demonstration of local optical control of
magnetism at the nanoscale has remained elusive. Here, we show that exciting
gold nanodiscs with circularly polarized femtosecond laser pulses leads to the
generation of sizeable local magnetic fields that enable ultrafast local
control of the magnetization of an adjacent magnetic film. In addition, we find
that the highest magnetic fields are generated when exciting the sample at a
wavelength larger than that of the actual plasmonic resonance of the gold
nanodiscs, so avoiding undesired heating effects due to absorption. Our study
paves the way for light-driven control in nanoscale spintronic devices and
provides important insights into the generation of magnetic fields in plasmonic
nanostructures.",2307.03326v1
2023-07-14,Parker Bounds on Monopoles with Arbitrary Charge from Galactic and Primordial Magnetic Fields,"We present a comprehensive study of Parker-type bounds on magnetic monopoles
with arbitrary magnetic charge, including minicharged monopoles and magnetic
black holes. We derive the bounds based on the survival of galactic magnetic
fields, seed magnetic fields, as well as primordial magnetic fields. We find
that monopoles with different magnetic charges are best constrained by
different astrophysical systems: while monopoles with a Dirac charge are
tightly constrained by seed galactic magnetic fields, minicharged monopoles are
strongly constrained by primordial magnetic fields, and magnetic black holes by
the density of dark matter. We also assess the viability of the various types
of monopoles as dark matter, by studying whether they can cluster with galaxies
hosting magnetic fields.",2307.07553v2
2023-10-10,Skyrmions and magnetic bubbles in spin-orbit coupled metallic magnets,"Motivated by the observation of Skyrmion-like magnetic textures in 2D
itinerant ferromagnets Fe$_n$GeTe$_2$ ($n \geq3$), we develop a microscopic
model combining itinerant magnetism and spin-orbit coupling on a triangular
lattice. The ground state of the model in the absence of magnetic field
consists of filamentary magnetic domain walls revealing a striking similarity
with our magnetic force microscopy experiments on Fe$_3$GeTe$_2$. In the
presence of magnetic field, these filaments were found to break into large size
magnetic bubbles in our experiments. We identify uniaxial magnetic anisotropy
as an important parameter in the model that interpolates between magnetic
Skyrmions and ferromagnetic bubbles. Consequently, our work uncovers new
topological magnetic textures that merge properties of Skyrmions and
ferromagnetic bubbles.",2310.06521v1
2023-11-10,Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu,"The exchange stiffness of magnetic materials is one of the essential
parameters governing magnetic texture and its dynamics in magnetic devices. The
effect of single-element doping on exchange stiffness has been investigated for
several doping elements for permalloy (NiFe alloy), a soft magnetic material
whose soft magnetic properties can be controlled by doping. However, the impact
of more practical multi-element doping on the exchange stiffness of permalloy
is unknown. This study investigates the typical magnetic properties, including
exchange stiffness, of permalloy systematically co-doped with Mo and Cu using
broadband ferromagnetic resonance spectroscopy. We find that the exchange
stiffness, which decreases with increasing doping levels, is proportional to a
power of magnetization, which also decreases with increasing doping levels. The
magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$,
of all the investigated samples, irrespective of the doping levels of each
element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with
exponent $n$ close to 2. This empirical power-law relationship provides a
guideline for predicting unknown exchange stiffness in non-magnetic
element-doped permalloy systems.",2311.05852v2
2024-02-18,Deep learning methods for Hamiltonian parameter estimation and magnetic domain image generation in twisted van der Waals magnets,"The application of twist engineering in van der Waals magnets has opened new
frontiers in the field of two-dimensional magnetism, yielding distinctive
magnetic domain structures. Despite the introduction of numerous theoretical
methods, limitations persist in terms of accuracy or efficiency due to the
complex nature of the magnetic Hamiltonians pertinent to these systems. In this
study, we introduce a deep-learning approach to tackle these challenges.
Utilizing customized, fully connected networks, we develop two
deep-neural-network kernels that facilitate efficient and reliable analysis of
twisted van der Waals magnets. Our regression model is adept at estimating the
magnetic Hamiltonian parameters of twisted bilayer CrI3 from its magnetic
domain images generated through atomistic spin simulations. The generative
model excels in producing precise magnetic domain images from the provided
magnetic parameters. The trained networks for these models undergo thorough
validation, including statistical error analysis and assessment of robustness
against noisy injections. These advancements not only extend the applicability
of deep-learning methods to twisted van der Waals magnets but also streamline
future investigations into these captivating yet poorly understood systems.",2402.11434v1
2001-08-29,Jet Collimation by Small-Scale Magnetic Fields,"A popular model for jet collimation is associated with the presence of a
large-scale and predominantly toroidal magnetic field originating from the
central engine (a star, a black hole, or an accretion disk). Besides the
problem of how such a large-scale magnetic field is generated, in this model
the jet suffers from the fatal long-wave mode kink magnetohydrodynamic
instability. In this paper we explore an alternative model: jet collimation by
small-scale magnetic fields. These magnetic fields are assumed to be local,
chaotic, tangled, but are dominated by toroidal components. Just as in the case
of a large-scale toroidal magnetic field, we show that the ``hoop stress'' of
the tangled toroidal magnetic fields exerts an inward force which confines and
collimates the jet. The magnetic ``hoop stress'' is balanced either by the gas
pressure of the jet, or by the centrifugal force if the jet is spinning. Since
the length-scale of the magnetic field is small (< the cross-sectional radius
of the jet << the length of the jet), in this model the jet does not suffer
from the long-wave mode kink instability. Many other problems associated with
the large-scale magnetic field are also eliminated or alleviated for
small-scale magnetic fields. Though it remains an open question how to generate
and maintain the required small-scale magnetic fields in a jet, the scenario of
jet collimation by small-scale magnetic fields is favored by the current study
on disk dynamo which indicates that small-scale magnetic fields are much easier
to generate than large-scale magnetic fields.",0108469v1
2003-10-20,Cyclic evolution and reversal of the solar magnetic field. I. The large-scale magnetic fields,"On the base of the solar magnetic field measurements obtained in Stanford in
1976--2003 the properties of the cyclic evolution of the large-scale magnetic
field are investigated. Some regularities are found in longitudinal and
latitudinal evolution of the magnetic field in cycles 21, 22 and 23. The cyclic
development of the large-scale magnetic field can be divided into two main
phases. The phase I, which includes a period approximately from two years
before and until three years after the maximum of the solar cycle, is studied
in detail. It is found that before the reversal of the large-scale magnetic
field the neutral line of the magnetic field in antipodal longitudinal
intervals shifts from the equator to opposite directions in cycles 21 and 22,
but not in cycle 23. During the sign reversal of the large-scale magnetic field
in cycles 21 and 22 in the antipodal longitudinal intervals the magnetic field
of opposite polarity is observed in all latitudes, thereby forming an
equatorial dipole. After the magnetic field reversal a longitudinal oscillation
of the magnetic neutral line with regard to the equator takes place, which has
a period about 2 years and damps to the minimum of the 11-year cycle. The
intervening longitudinal intervals of the large-scale magnetic field correspond
to positions of the active longitudes of sunspot activity, thus indicating a
close connection of the large-scale and the local magnetic fields. In evolution
of the large-scale magnetic field a periodicity with period $1.23\pm0.16$ year
is revealed, which is close to the period found by helioseismological methods
in variations of the solar rotation near the tachocline.",0310539v1
2009-03-16,Relationship between photospheric currents and coronal magnetic helicity for force-free bipolar fields,"The origin and evolution of the magnetic helicity in the solar corona are not
well understood. For instance, the magnetic helicity of an active region is
often about $10^{42}$ Mx$^2$ ($10^{26}$ Wb$^{2}$), but the observed processes
whereby it is thought to be injected into the corona do not yet provide an
accurate estimate of the resulting magnetic helicity budget or time evolution.
The variation in magnetic helicity is important for understanding the physics
of flares, coronal mass ejections, and their associated magnetic clouds. To
shed light on this topic, we investigate here the changes in magnetic helicity
due to electric currents in the corona for a single twisted flux tube that may
model characteristic coronal structures such as active region filaments,
sigmoids, or coronal loops. For a bipolar photospheric magnetic field and
several distributions of current, we extrapolated the coronal field as a
nonlinear force-free field. We then computed the relative magnetic helicity, as
well as the self and mutual helicities. Starting from a magnetic configuration
with a moderate amount of current, the amount of magnetic helicity can increase
by 2 orders of magnitude when the maximum current strength is increased by a
factor of 2. The high sensitivity of magnetic helicity to the current density
can partially explain discrepancies between measured values on the photosphere,
in the corona, and in magnetic clouds. Our conclusion is that the magnetic
helicity strongly depends on both the strength of the current density and also
on its distribution. Only improved measurements of current density at the
photospheric level will advance our knowledge of the magnetic helicity content
in the solar atmosphere.",0903.2697v1
2011-03-29,Relationship between vertical and horizontal magnetic fields in the quiet Sun,"Vertical magnetic fields have been known to exist in the internetwork region
for decades, while the properties of horizontal magnetic fields have recently
been extensively investigated with \textit{Hinode}. Vertical and horizontal
magnetic fields in the internetwork region are considered to be separate
entities and have thus far not been investigated in a unified way. We discover
clear positional association between the vertical and horizontal magnetic
fields in the internetwork region with \textit{Hinode}. Essentially all of the
horizontal magnetic patches are associated with the vertical magnetic patches.
Alternatively, half of the vertical magnetic patches accommodate the horizontal
magnetic patches. These horizontal patches are located around the borders of
the vertical patches. The intrinsic magnetic field strength as obtained with
the Stokes $V$ line ratio inside the horizontal patches is weak, and is in
sub-equipartition field regime ($B<700$ G), while the field strength outside
the horizontal patches ranges from weak to strong (kG) fields. Vertical
magnetic patches are known to be concentrated on mesogranular and supergranular
boundaries, while the horizontal magnetic patches are found only on the
mesogranular boundaries. These observations provide us with new information on
the origin of the vertical and horizontal internetwork magnetic fields, in a
unified way. We conjecture that internetwork magnetic fields are provided by
emergence of small-scale flux tubes with bipolar footpoints, and the vertical
magnetic fields of the footpoints are intensified to kG fields due to
convective collapse. Resultant strong vertical fields are advected by the
supergranular flow, and eventually form the network fields.",1103.5556v1
2011-11-30,Relation of Astrophysical Turbulence and Magnetic Reconnection,"Astrophysical fluids are generically turbulent and this must be taken into
account for most transport processes. We discuss how the preexisting turbulence
modifies magnetic reconnection and how magnetic reconnection affects the MHD
turbulent cascade. We show the intrinsic interdependence and interrelation of
magnetic turbulence and magnetic reconnection, in particular, that strong
magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence
entails fast reconnection. We follow the approach in Eyink, Lazarian & Vishniac
2011 to show that the expressions of fast magnetic reconnection in Lazarian &
Vishniac 1999 can be recovered if Richardson diffusion of turbulent flows is
used instead of ordinary Ohmic diffusion. This does not revive, however, the
concept of magnetic turbulent diffusion which assumes that magnetic fields can
be mixed up in a passive way down to a very small dissipation scales. On the
contrary, we are dealing the reconnection of dynamically important magnetic
field bundles which strongly resist bending and have well defined mean
direction weakly perturbed by turbulence. We argue that in the presence of
turbulence the very concept of flux-freezing requires modification. The
diffusion that arises from magnetic turbulence can be called reconnection
diffusion as it based on reconnection of magnetic field lines. The reconnection
diffusion has important implications for the continuous transport processes in
magnetized plasmas and for star formation. In addition, fast magnetic
reconnection in turbulent media induces the First order Fermi acceleration of
energetic particles, can explain solar flares and gamma ray bursts. However,
the most dramatic consequence of these developments is the fact that the
standard flux freezing concept must be radically modified in the presence of
turbulence.",1112.0022v1
2012-10-13,Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms,"Extrapolation codes in Cartesian geometry for modelling the magnetic field in
the corona do not take the curvature of the Sun's surface into account and can
only be applied to relatively small areas, e.g., a single active region. We
compare the analysis of the photospheric magnetic field and subsequent
force-free modeling based on full-disk vector maps from Helioseismic and
Magnetic Imager (HMI) on board solar dynamics observatory (SDO) and Vector
Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of
the Sun (SOLIS). We use Helioseismic and Magnetic Imager and Vector
Spectromagnetograph photospheric magnetic field measurements to model the
force-free coronal field above multiple solar active regions, assuming magnetic
forces to dominate. We solve the nonlinear force-free field equations by
minimizing a functional in spherical coordinates over a full disk excluding the
poles. After searching for the optimum modeling parameters for the particular
data sets, we compare the resulting nonlinear force-free model fields. We
compare quantities like the total magnetic energy content and free magnetic
energy, the longitudinal distribution of the magnetic pressure and surface
electric current density using our spherical geometry extrapolation code. The
magnetic field lines obtained from nonlinear force-free extrapolation based on
Helioseismic and Magnetic Imager and Vector Spectromagnetograph data have good
agreement. However, the nonlinear force-free extrapolation based on
Helioseismic and Magnetic Imager data have more contents of total magnetic
energy, free magnetic energy, the longitudinal distribution of the magnetic
pressure and surface electric current density compared to the one from Vector
Spectromagnetograph data.",1210.3668v1
2012-12-04,Evolution of Primordial Magnetic Fields from Phase Transitions,"We consider the evolution of primordial magnetic fields generated during
cosmological, electroweak or QCD, phase transitions. We assume that the
magnetic field generation can be described as an injection of magnetic energy
to cosmological plasma at a given scale determined by the moment of magnetic
field generation. A high Reynolds number ensures strong coupling between
magnetic field and fluid motions. The subsequent evolution of the magnetic
field is governed by decaying hydromagnetic turbulence. Both our numerical
simulations and a phenomenological description allow us to recover ""universal""
laws for the decay of magnetic energy and the growth of magnetic correlation
length in the turbulent (low viscosity) regime. In particular, we show that
during the radiation dominated epoch, energy and correlation length of
non-helical magnetic fields scale as conformal time to the powers -1/2 and
+1/2, respectively. For helical magnetic fields, energy and correlation length
scale as conformal time to the powers -1/3 and +2/3, respectively. The
universal decay law of the magnetic field implies that the strength of magnetic
field generated during the QCD phase transition could reach $\sim 10^{-9}$\,G
with the present day correlation length $\sim 50$ kpc. The fields generated at
the electroweak phase transition could be as strong as $\sim 10^{-10}$ G with
correlation lengths reaching $\sim 0.3$\,kpc. These values of the magnetic
fields are consistent with the lower bounds of the extragalactic magnetic
fields.",1212.0596v2
2014-12-10,Joint inverse cascade of magnetic energy and magnetic helicity in MHD turbulence,"We show that oppositely directed fluxes of energy and magnetic helicity
coexist in the inertial range in fully developed magnetohydrodynamic (MHD)
turbulence with small-scale sources of magnetic helicity. Using a helical shell
model of MHD turbulence, we study the high Reynolds number magnetohydrodynamic
turbulence for helicity injection at a scale that is much smaller than the
scale of energy injection. In a short range of scales larger than the forcing
scale of magnetic helicity, a bottleneck-like effect appears, which results in
a local reduction of the spectral slope. The slope changes in a domain with a
high level of relative magnetic helicity, which determines that part of the
magnetic energy related to the helical modes at a given scale. If the relative
helicity approaches unity, the spectral slope tends to $-3/2$. We show that
this energy pileup is caused by an inverse cascade of magnetic energy
associated with the magnetic helicity. This negative energy flux is the
contribution of the pure magnetic-to-magnetic energy transfer, which vanishes
in the non-helical limit. In the context of astrophysical dynamos, our results
indicate that a large-scale dynamo can be affected by the magnetic helicity
generated at small scales. The kinetic helicity, in particular, is not involved
in the process at all. An interesting finding is that an inverse cascade of
magnetic energy can be provided by a small-scale source of magnetic helicity
fluctuations without a mean injection of magnetic helicity.",1412.3225v1
2015-04-29,The formation of regular interarm magnetic fields in spiral galaxies,"Observations of regular magnetic fields in several nearby galaxies reveal
magnetic arms situated between the material arms. The nature of these magnetic
arms is a topic of active debate. Previously we found a hint that taking into
account the effects of injections of small-scale magnetic fields generated,
e.g., by turbulent dynamo action, into the large-scale galactic dynamo can
result in magnetic arm formation. We now investigate the joint roles of an
arm/interarm turbulent diffusivity contrast and injections of small-scale
magnetic field on the formation of large-scale magnetic field (""magnetic arms"")
in the interarm region. We use the relatively simple ""no-$z$"" model for the
galactic dynamo. This involves projection on to the galactic equatorial plane
of the azimuthal and radial magnetic field components; the field component
orthogonal to the galactic plane is estimated from the solenoidality condition.
We find that addition of diffusivity gradients to the effect of magnetic field
injections makes the magnetic arms much more pronounced. In particular, the
regular magnetic field component becomes larger in the interarm space compared
to that within the material arms.The joint action of the turbulent diffusivity
contrast and small-scale magnetic field injections (with the possible
participation of other effects previously suggested) appears to be a plausible
explanation for the phenomenon of magnetic arms.",1504.07824v3
2016-06-08,Simulation and experiments of Stacks of High Temperature Superconducting Coated Conductors Magnetized by Pulsed Field Magnetization with Multi-Pulse Technique,"High temperature superconducting (HTS) bulks or stacks of coated conductors
(CCs) can be magnetized to become trapped field magnets (TFMs). The magnetic
fields of such TFMs can break the limitation of conventional magnets (<2 T), so
they show potential for improving the performance of many electrical
applications that use permanent magnets like rotating machines. Towards
practical or commercial use of TFMs, effective in situ magnetization is one of
the key issues. The pulsed field magnetization (PFM) is among the most
promising magnetization methods in virtue of its compactness, mobility and low
cost. However, due to the heat generation during the magnetization, the trapped
field and flux acquired by PFM usually cannot achieve the full potential of a
sample (acquired by the field cooling or zero field cooling method). The
multi-pulse technique was found to effectively improve the trapped field by PFM
in practice. In this work, a systematic study on the PFM with successive pulses
is presented. A 2D electromagnetic-thermal coupled model with comprehensive
temperature dependent parameters is used to simulate a stack of CCs magnetized
by successive magnetic pulses. An overall picture is built to show how the
trapped field and flux evolve with different pulse sequences and the evolution
patterns are analyzed. Based on the discussion, an operable magnetization
strategy of PFM with successive pulses is suggested to provide more trapped
field and flux. Finally, experimental results of a stack of CCs magnetized by
typical pulse sequences are presented for demonstration.",1606.07732v1
2017-08-25,Statistics of magnetic field measurements and evolution of magnetic field of OBA stars,"We review the measurements of magnetic fields of OBA stars. Based on these
data we confirm that magnetic fields are distributed according to a lognormal
law with a mean log(B)=-0.5 (B in kG) with a standard deviation sigma=0.5. The
shape of the magnetic field distribution is similar to that for neutron stars.
This finding is in favor of the hypothesis that the magnetic field of a neutron
star is determined mainly by the magnetic field of its predecessor, the massive
OB star. Further, we model the evolution of an ensemble of magnetic massive
stars in the Galaxy. We use our own population synthesis code to obtain the
distribution of stellar radii, ages, masses, temperatures, effective magnetic
fields and magnetic fluxes from the pre-main sequence (PMS) via zero age main
sequence (ZAMS) up to the terminal age main sequence (TAMS) stages. A
comparison of the obtained in our model magnetic field distribution (MFD) with
that obtained from the recent measurements of the stellar magnetic field allows
us to conclude that the evolution of magnetic fields of massive stars is slow
if not absent. The shape of the real MFD shows no indications of the magnetic
desert proposed previously. Based on this finding we argue that the observed
fraction of magnetic stars is determined by physical conditions at the PMS
stage of stellar evolution.",1708.07816v2
2018-05-09,The Effects of Magnetic Field Strength on Properties of Wind Generated from Hot Accretion Flow,"Observations indicate that wind can be generated in hot accretion flow. By
performing numerical simulations, Yuan et al. studied the detailed properties
of wind generated from weakly magnetized accretion flow. However, properties of
wind generated from strongly magnetized hot accretion flow have not been
studied. In this paper, we study the properties of wind generated from both
weakly and strongly magnetized accretion flow. We focus on how the magnetic
field strength affects the wind properties. We solve time-steady
two-dimensional magnetohydrodynamic (MHD) equations of black hole accretion in
the presence of large-scale magnetic field. We assume self-similarity in radial
direction. The magnetic field is assumed to be evenly symmetric with the
equatorial plane. We find that wind exists in both weakly and strongly
magnetized accretion flow. When magnetic field is weak (magnetic pressure is
more than 2 orders of magnitude smaller than gas pressure), wind is driven by
gas pressure gradient and centrifugal forces. When magnetic field is strong
(magnetic pressure is slightly smaller than gas pressure), wind is driven by
gas pressure gradient and magnetic pressure gradient forces. The power of wind
in strongly magnetized case is just slightly larger than that in weakly
magnetized case. The power of wind lies in a range $ P_W \sim 10^{-4}-10^{-3}
\dot M_{\rm in} c^2 $, with $ \dot M_{\rm in} $ and $ c $ being mass inflow
rate and speed of light, respectively. The possible role of wind in active
galactic nuclei feedback is briefly discussed.",1805.03378v1
2011-11-15,Spin waves in nanosized magnetic films,"We have studied spin excitations in nanosized magnetic films in the
Heisenberg model with magnetic dipole and exchange interactions by the spin
operator diagram technique. Dispersion relations of spin waves in thin magnetic
films (in two-dimensional magnetic monolayers and in two-layer magnetic films)
and the spin-wave resonance spectrum in N-layer structures are found. For thick
magnetic films generalized Landau-Lifshitz equations are derived from first
principles. Landau-Lifshitz equations have the integral (pseudodifferential)
form, but not differential one. Spin excitations are determined by simultaneous
solution of the Landau-Lifshitz equations and the equation for the
magnetostatic potential. For normal magnetized ferromagnetic films the spin
wave damping has been calculated in the one-loop approximation for a diagram
expansion of the Green functions at low temperature. In thick magnetic films
the magnetic dipole interaction makes a major contribution to the relaxation of
long-wavelength spin waves. Thin films have a region of low relaxation of
long-wavelength spin waves. In thin magnetic films four-spin-wave processes
take place and the exchange interaction makes a major contribution to the
damping. It is found that the damping of spin waves propagating in magnetic
monolayer is proportional to the quadratic dependence on the temperature and is
very low for spin waves with small wavevectors. Spin-wave devices on the base
of nanosized magnetic films are proposed -- tunable narrow-band spin-wave
filters with high quality at the microwave frequency range and field-effect
transistor (FET) structures contained nanosized magnetic films under the gate
electrode. Spin-wave resonances in nanosized magnetic films can be used to
construct FET structures operating in Gigahertz and Terahertz frequency bands.",1111.3532v1
2014-06-21,Quark stars under strong magnetic fields,"Within the confined isospin- and density-dependent mass model, we study the
properties of strange quark matter (SQM) and quark stars (QSs) under strong
magnetic fields. The equation of state of SQM under a constant magnetic field
is obtained self-consistently and the pressure perpendicular to the magnetic
field is shown to be larger than that parallel to the magnetic field, implying
that the properties of magnetized QSs generally depend on both the strength and
the orientation of the magnetic fields distributed inside the stars. Using a
density-dependent magnetic field profile which is introduced to mimic the
magnetic field strength distribution in a star, we study the properties of
static spherical QSs by assuming two extreme cases for the magnetic field
orientation in the stars, i.e., the radial orientation in which the local
magnetic fields are along the radial direction and the transverse orientation
in which the local magnetic fields are randomly oriented but perpendicular to
the radial direction. Our results indicate that including the magnetic fields
with radial (transverse) orientation can significantly decrease (increase) the
maximum mass of QSs, demonstrating the importance of the magnetic field
orientation inside the magnetized compact stars.",1406.5610v2
2017-12-13,Studying the transfer of magnetic helicity in solar active regions with the connectivity-based helicity flux density method,"In the solar corona, magnetic helicity slowly and continuously accumulates in
response to plasma flows tangential to the photosphere and magnetic flux
emergence through it. Analyzing this transfer of magnetic helicity is key for
identifying its role in the dynamics of active regions (ARs). The
connectivity-based helicity flux density method was recently developed for
studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes
into account the 3D nature of magnetic helicity by explicitly using knowledge
of the magnetic field connectivity, which allows it to faithfully track the
photospheric flux of magnetic helicity. Because the magnetic field is not
measured in the solar corona, modeled 3D solutions obtained from force-free
magnetic field extrapolations must be used to derive the magnetic connectivity.
Different extrapolation methods can lead to markedly different 3D magnetic
field connectivities, thus questioning the reliability of the
connectivity-based approach in observational applications. We address these
concerns by applying this method to the isolated and internally complex AR
11158 with different magnetic field extrapolation models. We show that the
connectivity-based calculations are robust to different extrapolation methods,
in particular with regards to identifying regions of opposite magnetic helicity
flux. We conclude that the connectivity-based approach can be reliably used in
observational analyses and is a promising tool for studying the transfer of
magnetic helicity in ARs and relate it to their flaring activity.",1712.04691v1
2019-09-05,"The Magnetic Early B-type Stars III: A main sequence magnetic, rotational, and magnetospheric biography","Magnetic confinement of stellar winds leads to the formation of
magnetospheres, which can be sculpted into Centrifugal Magnetospheres (CMs) by
rotational support of the corotating plasma. The conditions required for the
CMs of magnetic early B-type stars to yield detectable emission in H$\alpha$ --
the principal diagnostic of these structures -- are poorly constrained. A key
reason is that no detailed study of the magnetic and rotational evolution of
this population has yet been performed. Using newly determined rotational
periods, modern magnetic measurements, and atmospheric parameters determined
via spectroscopic modelling, we have derived fundamental parameters, dipolar
oblique rotator models, and magnetospheric parameters for 56 early B-type
stars. Comparison to magnetic A- and O-type stars shows that the range of
surface magnetic field strength is essentially constant with stellar mass, but
that the unsigned surface magnetic flux increases with mass. Both the surface
magnetic dipole strength and the total magnetic flux decrease with stellar age,
with the rate of flux decay apparently increasing with stellar mass. We find
tentative evidence that multipolar magnetic fields may decay more rapidly than
dipoles. Rotational periods increase with stellar age, as expected for a
magnetic braking scenario. Without exception, all stars with H$\alpha$ emission
originating in a CM are 1) rapid rotators, 2) strongly magnetic, and 3) young,
with the latter property consistent with the observation that magnetic fields
and rotation both decrease over time.",1909.02530v1
2020-04-24,Observation of magnetic domain and bubble structures in magnetoelectric Sr$_3$Co$_2$Fe$_{24}$O$_{41}$,"The magnetic domain and bubble structures in the Z-type hexaferrite
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were investigated using Lorentz microscopy. This
hexaferrite exhibits a room-temperature magnetoelectric effect that is
attributed to its transverse conical spin structure (TC phase). Upon heating,
the TC phase transforms into a ferrimagnetic phase with magnetic moments in the
hexagonal $ab$ plane between 410 and 480 K (FM2 phase) and into another
ferrimagnetic phase with moments parallel to the $c$ axis between 490 and 680 K
(FM1 phase). Accordingly, in this study, the magnetic domain structures in
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were observed to change dramatically with
temperature. In the TC phase, irregular fine magnetic domains were observed
after cooling the specimen from the FM2 to TC phase. In the FM1 phase, striped
magnetic domain walls with pairs of bright and dark contrast were formed
parallel to the $c$ axis. Upon applying an external magnetic field, the striped
magnetic domain walls transformed into magnetic bubbles. The topology of the
magnetic bubbles was dependent on the angle between the external magnetic field
($H$) direction and the easy $c$ axis. Namely, magnetic bubbles with the
topological number $N$ = 1 (type I) were created for $H//c$, whereas magnetic
bubbles with $N$ = 0 (type II) were created when the magnetic field was tilted
from the c axis by 5{\deg}. We attribute the high magnetocrystalline anisotropy
of Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ to the emergence of magnetic bubbles in the
FM1 phase.",2004.11591v1
2017-08-22,A pico-Tesla magnetic sensor with PZT bimorph and permanent magnet proof mass,"Ferromagnetic-ferroelectric composites have attracted interests in recent
years for use as magnetic field sensors. The sensing is based on
magneto-electric (ME) coupling between the electric and magnetic subsystems and
is mediated by mechanical strain. Such sensors for AC magnetic fields require a
bias magnetic field to achieve pT-sensitivity. Here we discuss measurements and
theory for a novel passive, AC magnetic sensor that does not require a bias
magnetic field and is based on a PZT bimorph with a permanent magnet proof
mass. Mechanical strain on the PZT bimorph in this case is produced by
interaction between the applied AC magnetic field and remnant magnetization of
the permanent magnet, resulting in an induced voltage across PZT. Our studies
have been performed on sensors with a bimorph of oppositely poled PZT platelets
and a NdFeB permanent magnet proof mass. Magnetic floor noise N on the order of
100 pT per sqrHz and 10 nT per sqrHz are measured at 1 Hz and 10 Hz,
respectively. When the AC magnetic field is applied at the bending resonance of
40 Hz for the bimorph, the measured N 700 pT per sqrHz. We also discuss a
theory for the magneto-electro-mechanical coupling at low frequency and bending
resonance in the sensor and theoretical estimates of ME voltage coefficients
are in very good agreement with the data.",1709.01794v1
2018-08-08,Magnetic Gradiometer for Detection of Zero- and Ultralow-Field Nuclear Magnetic Resonance,"Magnetic sensors are important for detecting nuclear magnetization signals in
nuclear magnetic resonance (NMR). As a complementary analysis tool to
conventional high-field NMR, zero- and ultralow-field (ZULF) NMR detects
nuclear magnetization signals in the sub-microtesla regime. Current ZULF NMR
systems are always equipped with high-quality magnetic shieldings to ensure
that ambient magnetic field noise does not dwarf the magnetization signal. An
alternative approach is to separate the magnetization signal from the noise
based on their differing spatial profiles, as can be achieved using a magnetic
gradiometer. Here, we present a gradiometric ZULF NMR spectrometer with a
magnetic gradient noise of 17 fT_{rms}{cm}^{-1}{Hz}^{-1/2} in the frequency
range of 100-400 Hz, based on a single vapor cell (0.7x0.7x1.0{cm}^3). With
applied white magnetic-field noise, we show that the gradiometric spectrometer
achieves 13-fold enhancement in the signal-to-noise ratio (SNR) compared to the
single-channel configuration. By reducing the influence of common-mode magnetic
noise, this work enables the use of compact and low-cost magnetic shields.
Gradiometric detection may also prove to be beneficial for eliminating
systematic errors in ZULF-NMR experiments searching for exotic spin-dependent
interactions and molecular parity violation.",1808.02743v1
2019-01-30,Comparative Study of the Surface Potential of Magnetic and Non-magnetic Spherical Objects in a Magnetized RF Discharge Plasma,"We report measurements of the time-averaged surface floating potential of
magnetic and non-magnetic spherical probes (or large dust particles) immersed
in a magnetized capacitively coupled discharge. In this study, the size of the
spherical probes is taken greater than the Debye length. The surface potential
of a spherical probe first increases, i.e. becomes more negative at low
magnetic field (B $<$ 0.05 T), attains a maximum value and decreases with
further increase of the magnetic field strength (B $>$ 0.05 T). The rate of
change of the surface potential in the presence of a B-field mainly depends on
the background plasma and types of material of the objects. The results show
that the surface potential of the magnetic sphere is higher (more negative)
compared to the non-magnetic spherical probe. Hence, the smaller magnetic
sphere collects more negative charges on its surface than a bigger non-magnetic
sphere in a magnetized plasma. The different sized spherical probes have nearly
the same surface potential above a threshold magnetic field (B $>$ 0.03 T),
implicating a smaller role of size dependence on the surface potential of
spherical objects. The variation of the surface potential of the spherical
probes is understood on the basis of a modification of the collection currents
to their surface due to charge confinement and cross-field diffusion in the
presence of an external magnetic field.",1901.10955v4
2019-02-27,Relative magnetic field line helicity,"Context. Magnetic helicity is an important quantity in studies of magnetized
plasmas as it provides a measure of the geometrical complexity of the magnetic
field in a given volume. A more detailed description of the spatial
distribution of magnetic helicity is given by the field line helicity that
expresses the amount of helicity associated to individual field lines, rather
than in the full analysed volume. Aims. Magnetic helicity is not a
gauge-invariant quantity in general, unless it is computed with respect to a
reference field, yielding the so called relative magnetic helicity. The field
line helicity corresponding to the relative magnetic helicity has only been
examined under specific conditions so far. This work aims to define the field
line helicity corresponding to relative magnetic helicity in the most general
way. In addition to its general form, we provide the expression for the
relative magnetic field line helicity in a few commonly used gauges, and
reproduce known results as a limit of our general formulation. Methods. By
starting from the definition of relative magnetic helicity, we derive the
corresponding field line helicity, and we note the assumptions it is based on.
Results. We check that the developed quantity reproduces relative magnetic
helicity by using three different numerical simulations. For these cases we
also show the morphology of field line helicity in the volume, and on the
photospheric plane. As an application to solar situations, we compare the
morphology of field line helicity on the photosphere with that of the
connectivity-based helicity flux density in two reconstructions of an active
region's magnetic field. We discuss how the derived relative magnetic field
line helicity has a wide range of applications, notably in solar physics and
magnetic reconnection studies.",1902.10410v1
2020-06-12,Odd-even layer-number effect and layer-dependent magnetic phase diagrams in MnBi2Te4,"The intrinsic magnetic layered topological insulator MnBi2Te4 with nontrivial
topological properties and magnetic order has become a promising system for
exploring exotic quantum phenomena such as quantum anomalous Hall effect.
However, the layer-dependent magnetism of MnBi2Te4, which is fundamental and
crucial for further exploration of quantum phenomena in this system, remains
elusive. Here, we use polar reflective magnetic circular dichroism
spectroscopy, combined with theoretical calculations, to obtain an in-depth
understanding of the layer-dependent magnetic properties in MnBi2Te4. The
magnetic behavior of MnBi2Te4 exhibits evident odd-even layer-number effect,
i.e. the oscillations of the coercivity of the hysteresis loop (at {\mu}0Hc)
and the spin-flop transition (at {\mu}0H1), concerning the Zeeman energy and
magnetic anisotropy energy. In the even-number septuple layers, an anomalous
magnetic hysteresis loop is observed, which is attributed to the
thickness-independent surface-related magnetization. Through the linear-chain
model, we can clarify the odd-even effect of the spin-flop field and determine
the evolution of magnetic states under the external magnetic field. The
mean-field method also allows us to trace the experimentally observed magnetic
phase diagrams to the magnetic fields, layer numbers and especially,
temperature. Overall, by harnessing the unusual layer-dependent magnetic
properties, our work paves the way for further study of quantum properties of
MnBi2Te4.",2006.07216v1
2021-05-31,Theoretical development in the viscosity of ferrofluid,"The viscosity of ferrofluid has an important role in liquid sealing of the
hard disk drives, biomedical applications as drug delivery, hyperthermia, and
magnetic resonance imaging. In the absence of a magnetic field, the viscosity
of ferrofluid depends on the volume concentration of magnetic nanoparticles
including surfactant layers. However, under the influence of a stationary
magnetic field, the viscosity of ferrofluid depends on the angle between the
applied magnetic field and vorticity in the flow. If this angle is 90o, then
there is a maximum increase in the viscosity. If the magnetic field and the
vorticity in the flow are parallel to each other, then there is no change in
the viscosity since the applied magnetic field does not change the speed of the
rotation of magnetic nanoparticles in the fluid. The viscosity of ferrofluid in
the presence of an alternating magnetic field demonstrates interesting
behavior. When field frequency matches with the relaxation time, known as
resonance condition, then there is no impact of an alternating magnetic field
in the viscosity of ferrofluid. If the frequency of an alternating magnetic
field is less than resonance frequency, then an alternating magnetic field
increases the viscosity of ferrofluid. Using higher frequency than resonance
condition reduces the viscosity of ferrofluid and researchers reported this
incident as the negative viscosity effect. If the frequency of an alternating
magnetic field tends to infinite, then ferrofluid ceases to feel a magnetic
field. In this case, there is no impact of an alternating magnetic field on the
viscosity of ferrofluid.",2105.14721v1
2021-08-19,Quantized edge magnetizations and their symmetry protection in one-dimensional quantum spin systems,"The bulk electric polarization works as a nonlocal order parameter that
characterizes topological quantum matters. Motivated by a recent paper [H.
Watanabe \textit{et al.}, Phys. Rev. B {\bf 103}, 134430 (2021)], we discuss
magnetic analogs of the bulk polarization in one-dimensional quantum spin
systems, that is, quantized magnetizations on the edges of one-dimensional
quantum spin systems.The edge magnetization shares the topological origin with
the fractional edge state of the topological odd-spin Haldane phases. Despite
this topological origin, the edge magnetization can also appear in
topologically trivial quantum phases. We develop straightforward field
theoretical arguments that explain the characteristic properties of the edge
magnetization. The field theory shows that a U(1) spin-rotation symmetry and a
site-centered or bond-centered inversion symmetry protect the quantization of
the edge magnetization. We proceed to discussions that quantum phases on
nonzero magnetization plateaus can also have the quantized edge magnetization
that deviates from the magnetization density in bulk. We demonstrate that the
quantized edge magnetization distinguishes two quantum phases on a
magnetization plateau separated by a quantum critical point. The edge
magnetization exhibits an abrupt stepwise change from zero to $1/2$ at the
quantum critical point because the quantum phase transition occurs in the
presence of the symmetries protecting the quantization of the edge
magnetization. We also show that the quantized edge magnetization can result
from the spontaneous ferrimagnetic order.",2108.08458v2
2021-08-27,Effects of anisotropy on strongly magnetized neutron and strange quark stars in general relativity,"We investigate the properties of anisotropic, spherically symmetric compact
stars, especially neutron stars and strange quark stars, made of strongly
magnetized matter. The neutron stars are described by SLy equation of state,
the strange quark stars by an equation of state based on the MIT Bag model. The
stellar models are based on an a priori assumed density dependence of the
magnetic field and thus anisotropy. Our study shows that not only the presence
of a strong magnetic field and anisotropy, but also the orientation of the
magnetic field itself, have an important influence on the physical properties
of stars. Two possible magnetic field orientations are considered, a radial
orientation, where the local magnetic fields point in the radial direction, and
a transverse orientation, where the local magnetic fields are perpendicular to
the radial direction. Interestingly, we find that for a transverse orientation
of the magnetic field, the stars become more massive with increasing anisotropy
and magnetic field strength and increase in size, since the repulsive,
effective anisotropic force increases in this case. In the case of a radially
orientated magnetic field, however, the masses and radii of the stars decrease
with increasing magnetic field strength, because of the decreasing effective
anisotropic force. Importantly, we also show that in order to achieve
hydrostatic equilibrium configurations of magnetized matter, it is essential to
account for both the local anisotropy effects as well as the anisotropy effects
caused by a strong magnetic field. Otherwise, hydrostatic equilibrium is not
achieved for magnetized stellar models.",2108.12436v1
2021-11-03,Anisotropic magnetocaloric effect of CrI$_{3}$: A theoretical study,"CrI$_{3}$ is considered to be a promising candidate for spintronic devices
and data storage. We derived the Heisenberg Hamiltonian for CrI$_{3}$ from
density functional calculations using the Liechtenstein formula. Moreover, the
Monte--Carlo simulations with the Sucksmith--Thompson method were performed to
analyze the effect of magnetic anisotropy energy on the thermodynamic
properties. Our method successfully reproduced the negative sign of isothermal
magnetic entropy changes when a magnetic field was applied along the hard
plane. We found that the temperature dependence of the magnetocrystalline
anisotropy energy is not negligible at temperatures slightly above the Curie
temperature. We clarified that the origin of this phenomenon is attributed to
anisotropic magnetic susceptibility and magnetization anisotropy. The
difference between the entropy change of the easy axis and the hard plane is
proportional to the temperature dependence of the magnetic anisotropy energy,
implying that the anisotropic entropy term is the main source of the
temperature dependence of the free energy difference when magnetizing in a
specific direction other than the easy axis. We also investigated the magnetic
susceptibility that can be used for the characterization of the negative sign
of the entropy change in the case of a hard plane. The competition of
magnetocrystalline anisotropy energy and external magnetic field at low
temperature and low magnetic field region causes a high magnetic susceptibility
as the fluctuation of magnetization. Meanwhile, the anisotropy energy is
suppressed at a sufficient magnetic field applied along the hard axis, the
magnetization is fully rotated to the direction of the external magnetic field.",2111.02063v1
2022-06-28,Turbulent magnetic helicity fluxes in solar convective zone,"Combined action of helical motions of plasma (the $\alpha$ effect) and
non-uniform (differential) rotation is a key dynamo mechanism of solar and
galactic large-scale magnetic fields. Dynamics of magnetic helicity of
small-scale fields is a crucial mechanism in a nonlinear dynamo saturation
where turbulent magnetic helicity fluxes allow to avoid catastrophic quenching
of the $\alpha$ effect. The convective zone of the Sun and solar-like stars as
well as galactic discs are the source for production of turbulent magnetic
helicity fluxes. In the framework of the mean-field approach and the spectral
$\tau$ approximation, we derive turbulent magnetic helicity fluxes using the
Coulomb gauge in a density-stratified turbulence. The turbulent magnetic
helicity fluxes include non-gradient and gradient contributions. The
non-gradient magnetic helicity flux is proportional to a nonlinear effective
velocity (which vanishes in the absence of the density stratification)
multiplied by small-scale magnetic helicity, while the gradient contributions
describe turbulent magnetic diffusion of the small-scale magnetic helicity. In
addition, the turbulent magnetic helicity fluxes contain source terms
proportional to the kinetic $\alpha$ effect or its gradients, and also
contributions caused by the large-scale shear (solar differential rotation). We
have demonstrated that the turbulent magnetic helicity fluxes due to the
kinetic $\alpha$ effect and its radial derivative in combination with the
nonlinear magnetic diffusion of the small-scale magnetic helicity are dominant
in the solar convective zone.",2206.14152v2